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Title:
METHOD OF PATTERNING A SUBSTRATE USING DUAL TONE DEVELOPMENT
Document Type and Number:
WIPO Patent Application WO/2010/025198
Kind Code:
A1
Abstract:
A method for patterning a substrate is described. In particular, the invention relates to a method for double patterning a substrate using dual tone development. Further, the invention relates to optimizing a dual tone development process.

Inventors:
GRONHEID, Roel (Zesdagmaalstraat 6, Huldeberg, Huldeberg, BE)
BERNARD, Sophie (Frederik Lintsstraat 99, Leuven, Leuven, BE)
FONSECA, Carlos, A. (811 Huntington Drive, Fishkill, NY, 12524, US)
SOMERVELL, Mark (101 Chancery Court, Austin, TX, 78737, US)
SCHEER, Steven (7621 Seneca Falls Loop, Austin, TX, 78739, US)
Application Number:
US2009/055084
Publication Date:
March 04, 2010
Filing Date:
August 26, 2009
Export Citation:
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Assignee:
TOKYO ELECTRON LIMITED (Akasaka Biz Tower, 3-1 Akasaka 5-chomeMinato-k, Tokyo ., 107-6325, JP)
GRONHEID, Roel (Zesdagmaalstraat 6, Huldeberg, Huldeberg, BE)
BERNARD, Sophie (Frederik Lintsstraat 99, Leuven, Leuven, BE)
FONSECA, Carlos, A. (811 Huntington Drive, Fishkill, NY, 12524, US)
SOMERVELL, Mark (101 Chancery Court, Austin, TX, 78737, US)
SCHEER, Steven (7621 Seneca Falls Loop, Austin, TX, 78739, US)
INTERUNIVERSITAIR MICROELEKTRONICA CENTRUM (IMEC) VZW (Kapeldreef 75, Leuven, Leuven, BE)
KATHOLIEKE UNVERSITEIT LEUVEN, K.U. LEUVEN R&D (Minderbroedersstraat 8a, bus 5105, Leuven, Leuven, BE)
International Classes:
G03C5/00; G03F9/00
Foreign References:
US5906910A
US6348301B1
US6242344B1
US20060194154A1
Attorney, Agent or Firm:
STRANG, Eric (4350 W. Chandler Blvd, Suite 10Chandler, AZ, 85226, US)
Download PDF:
Claims:
1. A method of patterning a substrate, comprising: forming a layer of radiation-sensitive material on a substrate; exposing said layer of radiation-sensitive material to a pattern of radiation using a mask having a mask critical dimension to form one or more first radiation-sensitive material portions, one or more second radiation-sensitive material portions, and one or more third radiation- sensitive material portions; removing said one or more first radiation-sensitive material portions from said substrate using a first chemistry, wherein said removed one or more first radiation-sensitive material portions is characterized by a first critical dimension; elevating a temperature of said substrate to a first post-exposure temperature following said exposing and preceding said removing said one or more first radiation-sensitive material portions; removing said one or more second radiation-sensitive material portions from said substrate using a second chemistry, wherein said removed one or more second radiation-sensitive material portions is characterized by a second critical dimension; elevating a temperature of said substrate to a second postexposure temperature following said exposing and preceding said removing said one or more second radiation-sensitive material portions; and adjusting said first critical dimension, or said second critical dimension, or both said first critical dimension and said second critical dimension, wherein said adjusting comprises adjusting one or more process parameters selected from the group consisting of: said first post-exposure temperature, a time said substrate is elevated to said first post-exposure temperature, a heating rate for achieving said first post-exposure temperature, a cooling rate for reducing said first post-exposure temperature, a pressure of a gaseous environment surrounding said substrate during said elevation of said substrate to said first post-exposure temperature, a composition of a gaseous environment surrounding said substrate during said elevation of said substrate to said first post-exposure temperature, said second post-exposure temperature, a time said substrate is elevated to said second post-exposure temperature, a heating rate for achieving said second post-exposure temperature, a cooling rate for reducing said second post-exposure temperature, a pressure of a gaseous environment surrounding said substrate during said elevation of said substrate to said second post-exposure temperature, a composition of a gaseous environment surrounding said substrate during said elevation of said substrate to said second post-exposure temperature, a composition of said first chemistry, a time duration for applying said first chemistry, a temperature of said first chemistry, a composition of said second chemistry, a time duration for applying said second chemistry, or a temperature of said second chemistry.

2. The method of claim 1 , wherein said adjusting further comprises performing one or more of the following: adjusting an exposure dose for said exposing of said layer of radiation-sensitive material; adjusting said mask critical dimension for said exposing of said layer of radiation-sensitive material; or a combination of two or more thereof.

3. The method of claim 1 , wherein said layer of radiation-sensitive material comprises a 248 nm photo-resist, a 193 nm photo-resist, a 157 nm photo-resist, or an extreme ultraviolet photo-resist, or a combination of two or more thereof.

4. The method of claim 1 , wherein said layer of radiation-sensitive material comprises a positive-tone photo-resist.

5. The method of claim 1 , wherein said layer of radiation-sensitive material comprises a dual-tone photo-resist.

6. The method of claim 1 , wherein said layer of radiation-sensitive material comprises a photo-resist that switches solubility due to a change in polarity upon said exposing to said pattern of radiation and said optionally elevating said temperature of said substrate to said first postexposure temperature, or said second post-exposure temperature, or both following said exposure.

7. The method of claim 1 , wherein said layer of radiation-sensitive material comprises a photo-resist that provides acid-catalyzed deprotection upon said exposing to said pattern of radiation and said optionally elevating said temperature of said substrate to said first postexposure temperature, or said second post-exposure temperature, or both following said exposure.

8. The method of claim 1 , wherein said first chemistry comprises an organic solvent, and said second chemistry comprises a base solution.

9. The method of claim 1 , wherein said first chemistry comprises a base solution, and said second chemistry comprises an organic solvent.

10. The method of claim 1 , further comprising: exposing said layer of radiation-sensitive material to a second pattern of radiation.

1 1 . A method of double patterning a substrate, comprising: forming a layer of radiation-sensitive material on a substrate; exposing said layer of radiation-sensitive material only once to a pattern of radiation using a mask having a mask critical dimension to form first radiation-sensitive material portions having a high radiation exposure, second radiation-sensitive material portions having a low radiation exposure, and third radiation-sensitive material portions having an intermediate radiation exposure; removing said first radiation-sensitive material portions from said substrate using a first chemistry; elevating a temperature of said substrate to a first post-exposure temperature following said exposing and preceding said removing said first radiation-sensitive material portions; removing said second radiation-sensitive material portions from said substrate using a second chemistry; elevating a temperature of said substrate to a second postexposure temperature following said exposing and preceding said removing said second radiation-sensitive material portions; and adjusting a critical dimension of said third radiation-sensitive material portions having said intermediate radiation exposure, wherein said adjusting said critical dimension comprises adjusting one or more process parameters selected from the group consisting of: said first post-exposure temperature, a time said substrate is elevated to said first post-exposure temperature, a heating rate for achieving said first post-exposure temperature, a cooling rate for reducing said first postexposure temperature, a pressure of a gaseous environment surrounding said substrate during said elevation of said substrate to said first postexposure temperature, a composition of a gaseous environment surrounding said substrate during said elevation of said substrate to said first post-exposure temperature, said second post-exposure temperature, a time said substrate is elevated to said second post-exposure temperature, a heating rate for achieving said second post-exposure temperature, a cooling rate for reducing said second post-exposure temperature, a pressure of a gaseous environment surrounding said substrate during said elevation of said substrate to said second postexposure temperature, a composition of a gaseous environment surrounding said substrate during said elevation of said substrate to said second post-exposure temperature, a composition of said first chemistry, a time duration for applying said first chemistry, a temperature of said first chemistry, a composition of said second chemistry, a time duration for applying said second chemistry, or a temperature of said second chemistry.

12. The method of claim 1 1 , wherein said removing said first radiation-sensitive material portions precedes said removing said second radiation-sensitive material portions.

13. The method of claim 1 1 , wherein said removing said second radiation-sensitive material portions precedes said removing said first radiation-sensitive material portions.

14. The method of claim 1 1 , wherein said adjusting said critical dimension further comprises performing one or more of the following: adjusting an exposure dose for said exposing of said layer of radiation-sensitive material; adjusting said mask critical dimension for said exposing of said layer of radiation-sensitive material; or a combination of two or more thereof.

15. The method of claim 1 1 , wherein said layer of radiation- sensitive material comprises a photo-resist that switches solubility due to a change in polarity upon said exposing to said pattern of radiation and said optionally elevating said temperature of said substrate to said first postexposure temperature, or said second post-exposure temperature, or both following said exposure.

16. The method of claim 1 1 , wherein said layer of radiation- sensitive material comprises a photo-resist that provides acid-catalyzed deprotection upon said exposing to said pattern of radiation and said optionally elevating said temperature of said substrate to said first postexposure temperature, or said second post-exposure temperature, or both following said exposure.

17. A method of double patterning a substrate, comprising: forming a layer of radiation-sensitive material on a substrate; exposing said layer of radiation-sensitive material to a pattern of radiation using a mask having a mask critical dimension to form first radiation-sensitive material portions having a high radiation exposure, second radiation-sensitive material portions having a low radiation exposure, and third radiation-sensitive material portions having an intermediate radiation exposure; performing positive-tone developing of said layer of radiation- sensitive material to remove said first radiation-sensitive material portions from said substrate using a first chemistry comprising a base solution; performing a first post-exposure bake of said substrate following said exposing and preceding said positive-tone developing; performing negative-tone developing of said layer of radiation- sensitive material to remove said second radiation-sensitive material portions from said substrate using a second chemistry comprising an organic solvent; performing a second post-exposure bake of said substrate following said positive-tone developing and preceding said negative-tone developing; and adjusting a critical dimension of said third radiation-sensitive material portions having said intermediate radiation exposure by adjusting a second post-exposure temperature for said second post-exposure bake, a time said substrate is elevated to said second post-exposure temperature, a heating rate for achieving said second post-exposure temperature, a cooling rate for reducing said second post-exposure temperature, a pressure of a gaseous environment surrounding said substrate during said elevation of said substrate to said second post- exposure temperature, or a composition of a gaseous environment surrounding said substrate during said elevation of said substrate to said second post-exposure temperature, or a combination of two or more thereof.

18. The method of claim 17, further comprising: exposing said layer of radiation-sensitive material to a second pattern of radiation.

19. A method of double patterning a substrate, comprising: forming a layer of radiation-sensitive material on a substrate; exposing said layer of radiation-sensitive material to a pattern of radiation using a mask having a mask critical dimension to form first radiation-sensitive material portions having a high radiation exposure, second radiation-sensitive material portions having a low radiation exposure, and third radiation-sensitive material portions having an intermediate radiation exposure; performing positive-tone developing of said layer of radiation- sensitive material to remove said first radiation-sensitive material portions from said substrate using a first chemistry comprising a base solution; performing negative-tone developing of said layer of radiation- sensitive material, following said positive-tone developing, to remove said second radiation-sensitive material portions from said substrate using a second chemistry comprising an organic solvent; and adjusting a critical dimension of said third radiation-sensitive material portions having said intermediate radiation exposure by adjusting a composition of said base solution.

20. The method of claim 19, further comprising: performing a first post-exposure bake of said substrate following said exposing and preceding said positive-tone developing; and performing a second post-exposure bake of said substrate following said positive-tone developing and preceding said negative-tone developing.

21 . The method of claim 19, wherein said base solution comprises tetramethylammonium hydroxide, water and an optional surfactant, and wherein said adjusting said composition comprises adjusting an amount of said tetramethylammonium hydroxide relative to said water and said optional surfactant.

22. The method of claim 19, further comprising: exposing said layer of radiation-sensitive material to a second pattern of radiation.

23. A method of optimizing a double patterning process, comprising: performing a dual-tone development process that includes: exposing a layer of radiation-sensitive material to a pattern of radiation, performing a positive-tone development process to remove a first radiation-sensitive material portion characterized by a positive- tone critical dimension, and performing a negative-tone development process to remove a second radiation-sensitive material portion characterized by a negative-tone critical dimension; and optimizing said dual-tone development process to achieve a target difference between a target positive-tone critical dimension and a target negative-tone critical dimension by: acquiring one or more positive-tone characteristics, said one or more positive-tone characteristics relate said positive-tone critical dimension to a control parameter for a first set of process parameters; acquiring one or more negative-tone characteristics, said one or more negative-tone characteristics relate said negative-tone critical dimension to said control parameter for a second set of process parameters; selecting a target positive-tone characteristic from the one or more positive-tone characteristics that approximately intersects the target positive-tone critical dimension at a target control parameter to within a first deviation; selecting a target negative-tone characteristic from the one or more negative-tone characteristics that approximately intersects the target negative-tone critical dimension at the target control parameter to within a second deviation; and establishing a process recipe for said performing said dual- tone development process using said target positive-tone characteristic, said target negative-tone characteristic, and said target control parameter.

24. The method of claim 23, wherein said layer of radiation- sensitive material comprises a photo-resist.

25. The method of claim 23, wherein said layer of radiation- sensitive material comprises a 248 nm photo-resist, a 193 nm photo-resist, a 157 nm photo-resist, or an extreme ultraviolet photo-resist, or a combination of two or more thereof.

26. The method of claim 23, wherein said layer of radiation- sensitive material comprises a positive-tone photo-resist.

27. The method of claim 23, wherein said layer of radiation- sensitive material comprises a dual-tone photo-resist.

28. The method of claim 23, wherein said layer of radiation- sensitive material comprises a photo-resist that switches solubility due to a change in polarity upon said exposing to said pattern of radiation and said optionally elevating said temperature of said substrate following said exposure.

29. The method of claim 23, wherein said layer of radiation- sensitive material comprises a photo-resist that provides acid-catalyzed deprotection upon said exposing to said pattern of radiation and said optionally elevating said temperature of said substrate following said exposure.

30. The method of claim 23, wherein said positive-tone development process is performed prior to said negative-tone development process.

31 . The method of claim 23, wherein said negative-tone development process is performed prior to said positive-tone development process.

32. The method of claim 23, wherein said positive-tone development process comprises utilizing a base solution, and said negative-tone development process comprises utilizing an organic solvent.

33. The method of claim 23, further comprising: performing a first post-exposure bake by elevating a temperature of said substrate to a first post-exposure temperature following said exposing and preceding said performing said positive-tone development process.

34. The method of claim 33, further comprising: performing a second post-exposure bake by elevating a temperature of said substrate to a second post-exposure temperature following said exposing and preceding said performing said negative-tone development process.

35. The method of claim 23, further comprising: performing a first post-exposure bake by elevating a temperature of said substrate to a first post-exposure temperature following said exposing and preceding said performing said positive-tone development process; and performing a second post-exposure bake by elevating a temperature of said substrate to a second post-exposure temperature following said exposing and preceding said performing said negative-tone development process.

36. The method of claim 35, wherein said control parameter comprises an exposure dose.

37. The method of claim 36, wherein said first set of process parameters comprises a first post-exposure temperature for said first postexposure bake, a time said substrate is elevated to said first postexposure temperature, a heating rate for achieving said first post-exposure temperature, a cooling rate for reducing said first post-exposure temperature, a pressure of a gaseous environment surrounding said substrate during said elevation of said substrate to said first post-exposure temperature, a composition of a gaseous environment surrounding said substrate during said elevation of said substrate to said first post-exposure temperature, a composition of a first chemistry used during said positive- tone development process, a time duration for applying said first chemistry, or a temperature of said first chemistry, or a combination of two or more thereof.

38. The method of claim 37, wherein said acquiring said one or more positive-tone characteristics comprises varying one or more process parameters in said first set of process parameters.

39. The method of claim 37, wherein said acquiring said one or more positive-tone characteristics comprises varying said composition of said first chemistry used during said positive-tone development process.

40. The method of claim 36, wherein said second set of process parameters comprises a second post-exposure temperature for said second post-exposure bake, a time said substrate is elevated to said second post-exposure temperature, a heating rate for achieving said second post-exposure temperature, a cooling rate for reducing said second post-exposure temperature, a pressure of a gaseous environment surrounding said substrate during said elevation of said substrate to said second post-exposure temperature, a composition of a gaseous environment surrounding said substrate during said elevation of said substrate to said second post-exposure temperature, a composition of a second chemistry used during said negative-tone development process, a time duration for applying said second chemistry, or a temperature of said second chemistry, or a combination of two or more thereof.

41 . The method of claim 37, wherein said acquiring said one or more negative-tone characteristics comprises varying one or more process parameters in said second set of process parameters.

42. The method of claim 37, wherein said acquiring said one or more negative-tone characteristics comprises varying said second postexposure temperature for said second post-exposure bake, or said time said substrate is elevated to said second post-exposure temperature, or both.

Description:
METHOD OF PATTERNING A SUBSTRATE USING DUAL TONE

DEVELOPMENT

CROSS-REFERENCE TO RELATED APPLICATIONS [0001] This application is related to co-pending U.S. Patent Application No. 12/198,853, entitled "METHOD OF PROCESS OPTIMIZATION FOR DUAL TONE DEVELOPMENT" (TEE-007), filed on even date herewith. The entire content of this application is herein incorporated by reference in its entirety.

BACKGROUND OF THE INVENTION

FIELD OF THE INVENTION

[0002] The invention relates to a method for patterning a substrate. In particular, the invention relates to a method for double patterning a substrate using dual-tone development.

DESCRIPTION OF RELATED ART

[0003] In material processing methodologies, such as those used in the fabrication of micro-electronic devices, pattern etching is often utilized to define the intricate patterns associated with various integrated circuit elements. Pattern etching comprises applying a patterned layer of radiation-sensitive material, such as photo-resist, to a thin film on an upper surface of a substrate, and transferring the pattern formed in the layer of radiation-sensitive material to the underlying thin film by etching. [0004] The patterning of the radiation-sensitive material generally involves coating an upper surface of the substrate with a thin film of radiation-sensitive material and then exposing the thin film of radiation- sensitive material to a pattern of radiation by projecting radiation from a radiation source through a mask using, for example, a photolithography system. Thereafter, a developing process is performed, during which the removal of the irradiated regions of the radiation-sensitive material occurs (as in the case of positive-tone photo-resist), or the removal of non- irradiated regions occurs (as in the case of negative-tone photo-resist). The remaining radiation-sensitive material exposes the underlying substrate surface in a pattern that is ready to be etched into the surface. [0005] As an example, for positive-tone pattern development, a typical lithographic patterning technique is shown in FIGs. 1A and 1 B. As shown in FIG. 1A, a layer of positive-tone photo-resist 102 is formed on a substrate 101. The layer of photo-resist 102 is exposed to electromagnetic (EM) radiation 107 through a mask 103. Mask 103 includes transparent portions 104 and opaque features 108 that form a pattern, as shown in FIG. 1A. A distance (or pitch) 109 between opaque features 108 is shown in FIG. 1A. The transparent portions 104 transmit EM radiation 107 to the layer of positive-tone photo-resist 102, and the opaque features 108 prevent EM radiation 107 from being transmitted to the layer positive-tone photo-resist 102. FIG. 1A shows the layer of positive-tone photo-resist 102 having exposed portions 105 that are exposed to EM radiation 107 and unexposed portions 106 that are not exposed to EM radiation 107. As shown in FIG. 1A, mask features 108 are imaged onto the layer of positive-tone photo-resist 102 to produce corresponding photo-resist features aligned with unexposed portions 106. [0006] As shown in FIG. 1 B, after removing exposed portions 105 of the layer of positive-tone photo-resist 102, unexposed portions 106 remain on substrate 101 and form the pattern transferred from mask 103 to substrate 101 . As shown in FIGs. 1A and 1 B, mask features 108 are imaged onto the layer of positive-tone photo-resist 102 to produce corresponding photo-resist features (i.e., unexposed portions 106). As shown in FIGS. 1A and 1 B, pitch 1 10 between unexposed portions 106 is determined by pitch 109 between features 108 of mask 103. [0007] As another example, for negative-tone pattern development, a typical lithographic patterning technique is shown in FIGs. 2A and 2B. As shown in FIG. 2A, a layer of negative-tone photo-resist 202 is formed on a substrate 201. The layer of negative-tone photo-resist 202 is exposed to the EM radiation 207 through a mask 203. The mask 203 includes transparent features 204 that form a pattern and opaque portions 208, as shown in FIG. 2A. A distance (pitch) 209 between transparent features 204 is shown in FIG. 2A. Transparent features 204 transmit EM radiation

207 to the layer of negative-tone photo-resist 202, and opaque portions

208 prevent EM radiation 207 from being transmitted to the layer of negative-tone photo-resist 202. FIG. 2A shows the layer of negative-tone photo-resist 202 having exposed portions 205 that are exposed to EM radiation 207 and unexposed portions 206 that are not exposed to EM radiation 207. As shown in FIG. 1 A, mask features 204 are imaged onto the layer of negative-tone photo-resist 202 to produce corresponding photo-resist features aligned with exposed portions 205.

[0008] As shown in FIG. 2B, after removing unexposed portions 206 of the layer of negative-tone photo-resist 202, exposed portions 205 remain on substrate 201 and form a pattern transferred from mask 203 to substrate 201. As shown in FIGS. 2A and 2B, mask features 204 are imaged onto the layer of negative-tone photo-resist 202 to produce corresponding photo-resist features (i.e., exposed portions 205). Pitch 210 between exposed portions 205 is determined by pitch 209 between features 204 of mask 203, as shown in FIGS. 2A and 2B. [0009] Photolithographic systems for performing the above-described material processing methodologies have become a mainstay of semiconductor device patterning for the last three decades, and are expected to continue in that role down to 32 nm resolution, and less. Typically, in both positive-tone and negative-tone pattern development, the minimum distance (i.e., pitch) between the center of features of patterns transferred from the mask to the substrate by a lithography system defines the patterning resolution.

[0010] As indicated above, the patterning resolution (r 0 ) of a photolithographic system determines the minimum size of devices that can be made using the system. Having a given lithographic constant k-i, the resolution is given by the equation

[0011] r o = k x λlNA , (1 )

[0012] where λ is the operational wavelength of the EM radiation, and

NA is the numerical aperture given by the equation

[0013] NA = n - ήn θ o . (2)

[0014] Angle θ 0 is the angular semi-aperture of the photo-lithography system, and n is the index of refraction of the material filling the space between the system and the substrate to be patterned. [0015] Following equation (1 ), conventional methods of resolution improvement have lead to three trends in photolithographic technology: (1 ) reduction in wavelength λ from mercury g-line (436 nm) to the 193 nm excimer laser, and further to 157 nm and the still developing extreme- ultraviolet (EUV) wavelengths; (2) implementation of resolution enhancement techniques (RETs) such as phase-shifting masks, and off- axis illumination that have lead to a reduction in the lithographic constant k-i from approximately a value of 0.6 to values approaching 0.25; and (3) increases in the numerical aperture (NA) via improvements in optical designs, manufacturing techniques, and metrology. These latter improvements have created increases in NA from approximately 0.35 to values greater than 1 .35.

[0016] Immersion lithography provides another possibility for increasing the NA of an optical system, such as a lithographic system. In immersion lithography, a substrate is immersed in a high-index of refraction fluid (also referred to as an immersion medium), such that the space between a final optical element and the substrate is filled with a high-index fluid (i.e., n>1 ). Accordingly, immersion provides the possibility of increasing resolution by increasing the NA (see equations (1 ), and (2)).

[0017] However, many of these approaches, including EUV lithography, RET lithography, and immersion lithography, have added considerable cost and complexity to lithography equipment. Furthermore, many of these approaches continue to face challenges in integration and challenges in extending their resolution limits to finer design nodes. [0018] Therefore, another trend in photolithographic technology is to utilize a double patterning approach, which has been introduced to allow the patterning of smaller features at a smaller pitch than what is currently possible with standard lithographic techniques. One approach to reduce the feature size is to use standard lithographic pattern and etch techniques on the same substrate twice, thereby forming larger patterns spaced closely together to achieve a smaller feature size than would be possible by single exposure. During double patterning, a layer of radiation- sensitive material on the substrate is exposed to a first pattern, the first pattern is developed in the radiation-sensitive material, the first pattern formed in the radiation-sensitive material is transferred to an underlying layer using an etching process, and then this series of steps is repeated for a second pattern, while shifting the second pattern relative to the first pattern. Herein, the double patterning approach may require an excessive number of steps, including exiting the coating/developing tool and re- application of a second layer of radiation-sensitive material. [0019] Another approach to double the resolution of a lithographic pattern is to utilize a dual-tone development approach, wherein a layer of radiation-sensitive material on the substrate is exposed to a pattern of radiation, and then a double pattern is developed into the layer of radiation-sensitive material by performing a positive-tone development and a negative-tone development. However, current dual-tone development approaches lack the ability to adjust, control and/or optimize the double pattern formed on the substrate.

SUMMARY OF THE INVENTION

[0020] The invention relates to a method for patterning a substrate. In particular, the invention relates to a method for double patterning a substrate using dual tone development. Further, the invention relates to optimizing a dual tone development process. [0021] According to an embodiment, a method of patterning a substrate to double the resolution of a lithographic pattern is described. The patterning process utilizes a dual-tone development approach, wherein a layer of radiation-sensitive material applied to the substrate is exposed to a pattern of radiation, and then a double pattern is developed into the layer of radiation-sensitive material by performing a positive-tone development followed by a negative-tone development. Furthermore, a critical dimension of the features formed in the double pattern is adjusted, controlled and/or optimized to meet pre-specified pattern requirements that may include a pre-specified critical dimension. This adjusting, controlling and/or optimizing include altering any process step, or altering a combination of steps in the double patterning process. For example, the altering of any step or a combination of steps may include adding, subtracting, and/or re-ordering the combination of steps. [0022] According to another embodiment, a method of patterning a substrate is described, comprising: forming a layer of radiation-sensitive material on a substrate; exposing the layer of radiation-sensitive material to a pattern of radiation using a mask having a mask critical dimension to form one or more first radiation-sensitive material portions, one or more second radiation-sensitive material portions, and one or more third radiation-sensitive material portions; removing the one or more first radiation-sensitive material portions from the substrate using a first chemistry, wherein the removed one or more first radiation-sensitive material portions is characterized by a first critical dimension; elevating a temperature of the substrate to a first post-exposure temperature following the exposing and preceding the removing the one or more first radiation- sensitive material portions; removing the one or more second radiation- sensitive material portions from the substrate using a second chemistry, wherein the removed one or more second radiation-sensitive material portions is characterized by a second critical dimension; elevating a temperature of the substrate to a second post-exposure temperature following the exposing and preceding the removing the one or more second radiation-sensitive material portions; and adjusting the first critical dimension, or the second critical dimension, or both the first critical dimension and the second critical dimension. The adjusting comprises adjusting one or more process parameters selected from the group consisting of: the first post-exposure temperature, a time the substrate is elevated to the first post-exposure temperature, a heating rate for achieving the first post-exposure temperature, a cooling rate for reducing the first post-exposure temperature, a pressure of a gaseous environment surrounding the substrate during the elevation of the substrate to the first post-exposure temperature, a composition of a gaseous environment surrounding the substrate during the elevation of the substrate to the first post-exposure temperature, the second post-exposure temperature, a time the substrate is elevated to the second post-exposure temperature, a heating rate for achieving the second post-exposure temperature, a cooling rate for reducing the second post-exposure temperature, a pressure of a gaseous environment surrounding the substrate during the elevation of the substrate to the second post-exposure temperature, a composition of a gaseous environment surrounding the substrate during the elevation of the substrate to the second post-exposure temperature, a composition of the first chemistry, a time duration for applying the first chemistry, a temperature of the first chemistry, a composition of the second chemistry, a time duration for applying the second chemistry, or a temperature of the second chemistry.

[0023] According to another embodiment, a method of double patterning a substrate is described, comprising: forming a layer of radiation-sensitive material on a substrate; exposing the layer of radiation- sensitive material only once to a pattern of radiation using a mask having a mask critical dimension to form first radiation-sensitive material portions having a high radiation exposure, second radiation-sensitive material portions having a low radiation exposure, and third radiation-sensitive material portions having an intermediate radiation exposure; removing the first radiation-sensitive material portions from the substrate using a first chemistry; elevating a temperature of the substrate to a first post-exposure temperature following the exposing and preceding the removing the first radiation-sensitive material portions; removing the second radiation- sensitive material portions from the substrate using a second chemistry; elevating a temperature of the substrate to a second post-exposure temperature following the exposing and preceding the removing the second radiation-sensitive material portions; and adjusting a critical dimension of the third radiation-sensitive material portions having the intermediate radiation exposure. The adjusting the critical dimension comprises adjusting one or more process parameters selected from the group consisting of: the first post-exposure temperature, a time the substrate is elevated to the first post-exposure temperature, a heating rate for achieving the first post-exposure temperature, a cooling rate for reducing the first post-exposure temperature, a pressure of a gaseous environment surrounding the substrate during the elevation of the substrate to the first post-exposure temperature, a composition of a gaseous environment surrounding the substrate during the elevation of the substrate to the first post-exposure temperature, the second postexposure temperature, a time the substrate is elevated to the second postexposure temperature, a heating rate for achieving the second postexposure temperature, a cooling rate for reducing the second postexposure temperature, a pressure of a gaseous environment surrounding the substrate during the elevation of the substrate to the second postexposure temperature, a composition of a gaseous environment surrounding the substrate during the elevation of the substrate to the second post-exposure temperature, a composition of the first chemistry, a time duration for applying the first chemistry, a temperature of the first chemistry, a composition of the second chemistry, a time duration for applying the second chemistry, or a temperature of the second chemistry. [0024] According to another embodiment, a method of double patterning a substrate is described, comprising: forming a layer of radiation-sensitive material on a substrate; exposing the layer of radiation- sensitive material to a pattern of radiation using a mask having a mask critical dimension to form first radiation-sensitive material portions having a high radiation exposure, second radiation-sensitive material portions having a low radiation exposure, and third radiation-sensitive material portions having an intermediate radiation exposure; performing positive- tone developing of the layer of radiation-sensitive material to remove the first radiation-sensitive material portions from the substrate using a first chemistry comprising a base solution; performing a first post-exposure bake of the substrate following the exposing and preceding the positive- tone developing; performing negative-tone developing of the layer of radiation-sensitive material to remove the second radiation-sensitive material portions from the substrate using a second chemistry comprising an organic solvent; performing a second post-exposure bake of the substrate following the positive-tone developing and preceding the negative-tone developing; and adjusting a critical dimension of the third radiation-sensitive material portions having the intermediate radiation exposure by adjusting a second post-exposure temperature for the second post-exposure bake, a time the substrate is elevated to the second postexposure temperature, a heating rate for achieving the second postexposure temperature, a cooling rate for reducing the second postexposure temperature, a pressure of a gaseous environment surrounding the substrate during the elevation of the substrate to the second postexposure temperature, or a composition of a gaseous environment surrounding the substrate during the elevation of the substrate to the second post-exposure temperature, or a combination of two or more thereof.

[0025] According to yet another embodiment, a method of double patterning a substrate is described, comprising: forming a layer of radiation-sensitive material on a substrate; exposing the layer of radiation- sensitive material to a pattern of radiation using a mask having a mask critical dimension to form first radiation-sensitive material portions having a high radiation exposure, second radiation-sensitive material portions having a low radiation exposure, and third radiation-sensitive material portions having an intermediate radiation exposure; performing positive- tone developing of the layer of radiation-sensitive material to remove the first radiation-sensitive material portions from the substrate using a first chemistry comprising a base solution; performing negative-tone developing of the layer of radiation-sensitive material, following the positive-tone developing, to remove the second radiation-sensitive material portions from the substrate using a second chemistry comprising an organic solvent; and adjusting a critical dimension of the third radiation- sensitive material portions having the intermediate radiation exposure by adjusting a composition of the base solution.

BRIEF DESCRIPTION OF THE DRAWINGS [0026] In the accompanying drawings:

[0027] FIGs. 1 A and 1 B illustrate a lithographic patterning technique utilizing a positive-tone photo-resist according to the prior art; [0028] FIGs. 2A and 2B illustrate a lithographic patterning technique utilizing a negative-tone photo-resist according to the prior art; [0029] FIG. 3 illustrates a method of patterning a substrate according to an embodiment;

[0030] FIGs. 4A through 4D illustrate a method of patterning a substrate according to another embodiment;

[0031] FIG. 5 illustrates a method of patterning a substrate according to another embodiment;

[0032] FIG. 6 illustrates a method of patterning a substrate according to another embodiment;

[0033] FIG. 7 illustrates a method of patterning a substrate according to another embodiment;

[0034] FIG. 8 presents exemplary data for patterning a substrate; [0035] FIG. 9 presents exemplary data for patterning a substrate; [0036] FIG. 10 presents additional exemplary data for patterning a substrate; [0037] FIG. 1 1 presents additional exemplary data for patterning a substrate; and

[0038] FIG. 12 illustrates a method of patterning a substrate according to yet another embodiment.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS [0039] A method for patterning a substrate is disclosed in various embodiments. However, one skilled in the relevant art will recognize that the various embodiments may be practiced without one or more of the specific details, or with other replacement and/or additional methods, materials, or components. In other instances, well-known structures, materials, or operations are not shown or described in detail to avoid obscuring aspects of various embodiments of the invention. [0040] Similarly, for purposes of explanation, specific numbers, materials, and configurations are set forth in order to provide a thorough understanding of the invention. Nevertheless, the invention may be practiced without specific details. Furthermore, it is understood that the various embodiments shown in the figures are illustrative representations and are not necessarily drawn to scale.

[0041] Reference throughout this specification to "one embodiment" or "an embodiment" or variation thereof means that a particular feature, structure, material, or characteristic described in connection with the embodiment is included in at least one embodiment of the invention, but do not denote that they are present in every embodiment. Thus, the appearances of the phrases such as "in one embodiment" or "in an embodiment" in various places throughout this specification are not necessarily referring to the same embodiment of the invention. Furthermore, the particular features, structures, materials, or characteristics may be combined in any suitable manner in one or more embodiments. Various additional layers and/or structures may be included and/or described features may be omitted in other embodiments. [0042] Various operations will be described as multiple discrete operations in turn, in a manner that is most helpful in understanding the invention. However, the order of description should not be construed as to imply that these operations are necessarily order dependent. In particular, these operations need not be performed in the order of presentation. Operations described may be performed in a different order than the described embodiment. Various additional operations may be performed and/or described operations may be omitted in additional embodiments. [0043] Methods for patterning a substrate, including methods to reduce the minimum pitch of a pattern that can be transferred onto a substrate for a given lithographic tool and mask, are described herein. Multiple chemical treatments on exposed radiation-sensitive materials, such as photo-resist, are used to achieve a reduction in a lithographic pitch of about a factor of two.

[0044] According to an embodiment, a method of patterning a substrate to double the resolution of a lithographic pattern is described. The patterning process utilizes a dual-tone development approach, wherein a layer of radiation-sensitive material applied to the substrate is exposed to a pattern of radiation, and then a double pattern is developed into the layer of radiation-sensitive material by performing a positive-tone development followed by a negative-tone development. Furthermore, a critical dimension of the features formed in the double pattern is adjusted, controlled and/or optimized to meet pre-specified pattern requirements that may include a pre-specified critical dimension. This adjusting, controlling and/or optimizing include altering any process step, or altering a combination of steps in the double patterning process. For example, the altering of any step or a combination of steps may include adding, subtracting, and/or re-ordering the combination of steps. [0045] FIG. 3 illustrates a method of transferring a pattern from a mask onto a substrate according to one embodiment. A layer of radiation- sensitive material 302, such as photo-resist, is formed on a substrate 301 , and then it is exposed to radiation 320 from a radiation source of a lithography system (not shown) using a mask 303. Mask 303 has opaque features 310 that are periodically spaced at a mask pitch 31 1 and transparent portions 304, as shown in FIG. 3.

[0046] According to one embodiment, the radiation-sensitive material 302 comprises photo-resist. According to another embodiment, the radiation-sensitive material 302 comprises a 248 nm photo-resist, a 193 nm photo-resist, a 157 nm photo-resist, or an extreme ultraviolet photoresist, or a combination of two or more thereof. According to another embodiment, the radiation-sensitive material 302 comprises a positive- tone photo-resist, or a negative-tone photo-resist. According to another embodiment, the radiation-sensitive material 302 comprises a dual-tone photo-resist. A dual-tone photo-resist may be characterized as a photoresist that behaves as a positive-tone photo-resist or a negative-tone photo-resist depending upon the developing chemistry that is utilized. According to another embodiment, the radiation-sensitive material 302 comprises a photo-resist that switches solubility due to a change in polarity upon exposure to the pattern of radiation and an optionally elevation of the temperature of the substrate following the exposure. According to another embodiment, the radiation-sensitive material 302 comprises a photo-resist that provides acid-catalyzed deprotection upon exposure to the pattern of radiation and an optional elevation of the temperature of the substrate following the exposure.

[0047] FIG. 3 shows a radiation exposure profile 305 and a resist response profile 306 of a response produced in the layer of radiation- sensitive material 302 by a pattern of radiation resulting from the projection of radiation 320 through mask 303 using the lithography system. As shown in FIG. 3, first radiation-sensitive material portions 312 that correspond to transparent portions 304 receive a high radiation exposure from radiation 320, second radiation-sensitive material portions 313 that correspond to opaque features 310 receive a low radiation exposure from radiation 320, and third radiation-sensitive material portions 314 that approximately correspond to edges of opaque features 310 receive an intermediate radiation exposure from radiation 320. As shown in FIG. 3, the resist response profile 306 corresponding to the first radiation-sensitive material portions 312 of radiation-sensitive material 302 is higher than an upper threshold 308, while the resist response profile 306 corresponding to the second radiation-sensitive material portions 313 is lower than a lower threshold 309. Further, the resist response profile 306 corresponding to the third radiation-sensitive material portions 314 lies between the lower threshold 309 and the upper threshold 308. [0048] In one embodiment, when the layer of radiation-sensitive material 302 includes a positive-tone photo-resist, resist response profile 306 may represent a chemical concentration of deprotected polymers in the layer of radiation-sensitive material 302 that is approximately proportional to radiation exposure profile 305, as shown in FIG. 3. In another embodiment, when the layer of radiation-sensitive material 302 includes a positive-tone photo-resist, resist response profile 306 may be an acid concentration in the layer of radiation-sensitive material 302 that is proportional to radiation exposure profile 305. In another embodiment, when the layer of radiation-sensitive material 302 includes a negative-tone photo-resist, resist response profile 306 is an average polymer molecular weight in the layer of radiation-sensitive material 302 that is proportional to radiation exposure profile 305.

[0049] In one embodiment, upper threshold 308 corresponds to a first threshold of solubility of the layer of radiation-sensitive material 302 when a first chemistry is applied. In one embodiment, lower threshold 309 corresponds to a second threshold of solubility of the layer of radiation- sensitive material 302 when a second chemistry is applied. In one embodiment, first radiation-sensitive material portions 312 of the layer of radiation-sensitive material 302 that correspond to transparent portions 304 that have high radiation exposure in radiation exposure profile 305 are selectively removed from substrate 301 using a first chemistry. Second radiation-sensitive material portions 313 of the layer of radiation-sensitive material 302 that have low radiation exposure in the radiation exposure profile 305 are selectively removed from substrate 301 using a second chemistry. The third radiation-sensitive material portions 314 that correspond to approximately the edges of opaque features 310 that have intermediate exposure in the radiation exposure profile 305 (i.e., radiation exposure between the upper threshold 308 and the lower threshold 309) remain on substrate 301 intact, as shown in FIG. 3. Selectively removing first radiation-sensitive material portions 312 and second radiation- sensitive material portions 313 using different chemistries while leaving third radiation-sensitive material portions 314 on substrate 301 intact. [0050] In one embodiment, for first radiation-sensitive material portions 312, resist response profile 306 includes a concentration of acid in the layer of radiation-sensitive material 302 that is higher than an upper threshold 308 of acid concentration. In one embodiment, upper threshold

308 represents an acid level solubility threshold of the layer of radiation- sensitive material 302. For example, if an acid concentration in the layer of radiation-sensitive material 302 is higher than the upper threshold 308 of acid concentration, the layer of radiation-sensitive material 302 becomes soluble when a first chemistry is applied.

[0051] In one embodiment, for second radiation-sensitive material portions 313, resist response profile 306 includes a concentration of acid in the layer of radiation-sensitive material that is lower than lower threshold

309 of acid concentration. In one embodiment, lower threshold 309 represents another acid level solubility threshold of the layer of radiation- sensitive material 302. For example, if acid concentration in the layer of radiation-sensitive material 302 is lower than lower threshold 309 of acid concentration, the layer of radiation-sensitive material 302 becomes soluble when a second chemistry is applied.

[0052] In one embodiment, the layer of radiation-sensitive material 302 includes an upper acid concentration threshold in ranging from about 30% to about 60% of the clear field acid level and a lower acid concentration threshold ranging from about 10% to about 25% of the clear field acid concentration. In one embodiment, the clear field acid concentration is defined as the acid level of the photo-resist completely exposed to radiation. In another embodiment, the clear field acid concentration is defined as the acid concentration when all the PAG (PhotoAcid Generation) material has reacted with radiation to produce acid species. [0053] Due to diffraction of radiation 320, the third radiation-sensitive material portions 314 corresponding to intermediate radiation exposure are created. In one embodiment, third radiation-sensitive material portions 314 comprise an acid concentration between the upper acid concentration threshold and the lower acid concentration threshold. The first radiation- sensitive material portions 312 corresponding to high radiation exposure are selectively removed from the substrate using a first chemistry. The second radiation-sensitive material portions 313 corresponding to low radiation exposure are selectively removed from the substrate using a second chemistry. The third radiation-sensitive material portions 314 corresponding to intermediate radiation exposure remain on substrate 301 to form a pattern transferred by mask 303 and the lithography system. [0054] As shown in FIG. 3, two photo-resist features (i.e., third radiation-sensitive material portions 314) are produced for every one mask feature 310, thereby doubling the amount of the pattern features on substrate 301 . As a result, feature pitch 319 between the center of photoresist features (i.e., third radiation-sensitive material portions 314) becomes twice as small as the mask pitch 31 1 of the mask 303, as shown in FIG. 3.

[0055] Referring now to FIGs. 4A through 4D, a method of patterning a substrate is illustrated according to another embodiment. As illustrated in FIG. 4A, a lithographic structure 400 is prepared by forming a layer of radiation-sensitive material 402 on a substrate 401. [0056] The substrate 401 may comprise a semiconductor, e.g., a mono-crystalline silicon, germanium, and any other semiconductor. In alternate embodiments, substrate 401 may comprise any material used to fabricate integrated circuits, passive microelectronic devices (e.g., capacitors, inductors) and active microelectronic devices (e.g., transistors, photo-detectors, lasers, diodes). Substrate 401 may include insulating materials that separate such active and passive microelectronic devices from a conductive layer or layers that are formed on top of them. In one embodiment, substrate 401 comprises a p-type mono-crystalline silicon substrate that includes one or more insulating layers e.g., silicon dioxide, silicon nitride, sapphire, and other insulating materials. [0057] As described above, the substrate 401 may comprise a film stack having one or more thin films disposed between the substrate 401 and the layer of radiation-sensitive material 402. Each thin film may comprise a conductive layer, a non-conductive layer, or a semi-conductive layer. For instance, the thin film may include a material layer comprising a metal, metal oxide, metal nitride, metal oxynithde, metal silicate, metal suicide, silicon, poly-crystalline silicon (poly-silicon), doped silicon, silicon dioxide, silicon nitride, silicon carbide, silicon oxynithde, etc. Additionally, for instance, the thin film may comprise a low dielectric constant (i.e., low- k) or ultra-low dielectric constant (i.e., ultra-low-k) dielectric layer having a nominal dielectric constant value less than the dielectric constant of SiO 2 , which is approximately 4 (e.g., the dielectric constant for thermal silicon dioxide can range from 3.8 to 3.9). More specifically, the thin film may have a dielectric constant of less than 3.7, or a dielectric constant ranging from 1 .6 to 3.7.

[0058] According to one embodiment, the radiation-sensitive material 402 comprises photo-resist. According to another embodiment, the radiation-sensitive material 402 comprises a 248 nm photo-resist, a 193 nm photo-resist, a 157 nm photo-resist, or an extreme ultraviolet photoresist, or a combination of two or more thereof. According to another embodiment, the radiation-sensitive material 402 comprises a positive- tone photo-resist, or a negative-tone photo-resist. According to another embodiment, the radiation-sensitive material 402 comprises a dual-tone photo-resist. According to another embodiment, the radiation-sensitive material 402 comprises poly(hydroxystyrene)-based resist or a (meth)acrylate-based resist. According to another embodiment, the radiation-sensitive material 402 comprises a photo-resist that switches solubility due to a change in polarity upon exposure to the pattern of radiation and an optionally elevation of the temperature of the substrate following the exposure. According to another embodiment, the radiation- sensitive material 402 comprises a photo-resist that provides acid- catalyzed deprotection upon exposure to the pattern of radiation and an optional elevation of the temperature of the substrate following the exposure.

[0059] The layer of radiation-sensitive material 402 may be formed using a track system. For example, the track system can comprise a Clean Track ACT 8, ACT 12, or Lithius resist coating and developing system commercially available from Tokyo Electron Limited (TEL). Other systems and methods for forming a photo-resist film on a substrate are well known to those skilled in the art of spin-on resist technology. [0060] Following the application of the layer of radiation-sensitive material 402 to substrate 401 , the layer of radiation-sensitive material may be thermally treated in a post-application bake (PAB). For example, a temperature of the substrate may be elevated to about 50 degrees C to about 200 degrees C for a time duration of about 30 seconds to about 180 seconds. A track system having post-application substrate heating and cooling equipment may be used to perform the PAB. For example, the track system can comprise a Clean Track ACT 8, ACT 12, or Lithius resist coating and developing system commercially available from Tokyo Electron Limited (TEL). Other systems and methods for thermally treating an exposed photo-resist film on a substrate are well known to those skilled in the art of spin-on resist technology.

[0061] As shown in FIG. 4B, the layer of radiation-sensitive material 402 is exposed to radiation 407 through a mask 403. The mask 403 comprises opaque features 410 that prevent radiation 407 from being transmitted to the layer of radiation-sensitive material 402 and transparent portions 404 that transmit the radiation 407 to the layer of radiation- sensitive material 402. Mask 403 may include any mask suitable for use in wet or dry lithography, including wavelengths ranging from about 365 nm to about 13 nm. Mask 403 may include a binary mask or chrome on glass mask. Alternatively, mask 403 may include an alternating phase shift mask, or an embedded phase shift mask.

[0062] The exposure of the layer of radiation-sensitive material 402 to the pattern of EM radiation may be performed in a dry or wet photolithography system. The lithography system may be capable of providing a pattern of EM radiation at wavelengths of 365 nm, 248 nm, 193 nm, 157 nm, and 13 nm. The image pattern can be formed using any suitable conventional stepping lithographic system, or scanning lithographic system. For example, the photo-lithographic system may be commercially available from ASML Netherlands B.V. (De Run 6501 , 5504 DR Veldhoven, The Netherlands), or Canon USA, Inc., Semiconductor Equipment Division (3300 North First Street, San Jose, CA 95134). Mask 403 can be illuminated, for example, with normal incident light and off-axis illumination light, such as annular illumination, quadrupole illumination, and dipole illumination. These methods of illumination and exposing the layer of radiation-sensitive material 402 to radiation using the mask 403 are known to one of ordinary skill in the art of microelectronic device manufacturing.

[0063] As shown in FIG. 4B, radiation 407 is projected through mask 403 to the layer of radiation-sensitive material 402. The radiation exposure forms one or more first radiation-sensitive material portions 405, one or more second radiation-sensitive material portions 406, and one or more third radiation-sensitive material portions 408 in the layer of radiation-sensitive material 402. As shown in FIG. 4B, the one or more second radiation-sensitive material portions 406 that correspond to opaque features 410 of mask 403 have low exposure to radiation 407, the one or more first radiation-sensitive material portions 405 that correspond to transparent portions 404 of mask 403 have high exposure to radiation 407, and the one or more third radiation-sensitive material portions 408 that correspond approximately to the edges of opaque features 410 of mask 403 have an intermediate exposure to radiation 407. The one or more third radiation-sensitive material portions 408 of intermediate radiation exposure are created because of diffraction of radiation 407 from the edges of opaque features 410.

[0064] In one embodiment, the one or more first radiation-sensitive material portions 405 corresponding to high radiation exposure receive about 50% or more of radiation 407 incident on substrate 401 , the one or more second radiation-sensitive material portions 406 corresponding to low radiation exposure receive less than 15% of the radiation 407 incident on substrate 401 , and the one or more third radiation-sensitive material portions 408 corresponding to intermediate radiation exposure receive between about 15% and about 50% of the radiation 407 incident on substrate 401.

[0065] In one embodiment, high exposure to radiation 407 increases the concentration of an acid in the one or more first radiation-sensitive material portions 405 to a level higher than an upper acid concentration threshold. The upper acid concentration threshold is a first solubility threshold of the layer of radiation-sensitive material 402. In one embodiment, when the concentration of the acid in the one or more first radiation-sensitive material portions 405 increases to a level higher than the first threshold of solubility of the layer of radiation-sensitive material 402 (e.g., acid concentration threshold), the one or more first radiation- sensitive material portions 405 become soluble when a first chemistry is applied.

[0066] In another embodiment, when the chemical concentration of deprotected polymers in the one or more first radiation-sensitive material portions 405 increases to a level higher than the first threshold of solubility of the layer of radiation-sensitive material 402 (e.g., acid concentration threshold), the one or more first radiation-sensitive material portions 405 become soluble when a first chemistry is applied. [0067] In yet another embodiment, when the average polymer molecular weight in the one or more first radiation-sensitive material portions 405 increases to a level higher than the first threshold of solubility of the layer of radiation-sensitive material 402, the one or more first radiation-sensitive material portions 405 become soluble when the first chemistry is applied.

[0068] In the one or more second radiation-sensitive material portions 406 corresponding to low radiation exposure, a concentration of an acid and/or chemical concentration of deprotected polymers is less than a lower threshold of solubility of the layer of radiation-sensitive material 402 (e.g., acid concentration threshold). The one or more second radiation- sensitive material portions 406 become soluble when a second chemistry is applied.

[0069] In another embodiment, when the concentration of average polymer molecular weight in one or more second radiation-sensitive material portions 406 is lower than the second threshold of solubility of the layer of radiation-sensitive material 402, the one or more second radiation- sensitive material portions 406 become soluble when the second chemistry is applied.

[0070] Typically, the first solubility threshold and the second solubility threshold are determined by a material property of the layer of radiation- sensitive material 402. The one or more third radiation-sensitive material portions 408 corresponding to an intermediate radiation exposure have an acid concentration between about the first solubility threshold and the second solubility threshold. That is, the one or more third radiation- sensitive material portions 408 are not soluble when each of the first chemistry and the second chemistry is applied to layer of radiation- sensitive material 402.

[0071] Following the exposure of the layer of radiation-sensitive material 402 to EM radiation, the exposed layer of radiation-sensitive material may be thermally treated in a post-exposure bake (PEB). For example, a temperature of the substrate may be elevated to about 50 degrees C to about 200 degrees C for a time duration of about 30 seconds to about 180 seconds. A track system having post-exposure substrate heating and cooling equipment may be used to perform the PEB. For example, the track system can comprise a Clean Track ACT 8, ACT 12, or Lithius resist coating and developing system commercially available from Tokyo Electron Limited (TEL). Other systems and methods for thermally treating an exposed photo-resist film on a substrate are well known to those skilled in the art of spin-on resist technology. [0072] Referring still to FIG. 4B, the one or more first radiation-sensitive material portions 405 may be characterized by a first critical dimension 420. For example, the first critical dimension may be related to a positive- tone critical dimension following positive-tone developing. Additionally, the one or more second radiation-sensitive material portions 406 may be characterized by a second critical dimension 422. As shown in FIG. 4B, the second critical dimension 422 represents an inner dimension of the one or more second radiation-sensitive material portions 406 (beyond which these portions exist). For example, the second critical dimension 422 may be related to a negative-tone critical dimension following negative-tone developing. Furthermore, the one or more third radiation- sensitive material portions 408 may be characterized by a third critical dimension 424. For example, the third critical dimension 424 may be related to a feature critical dimension for the features 430 (see FIG. 4D) remaining on substrate 401.

[0073] Referring now to FIG. 4C, the one or more first radiation- sensitive material portions 405 corresponding to high radiation exposure are selectively removed using a first developing process comprising a first chemistry. In one embodiment, the first chemistry to selectively remove the one or more first radiation-sensitive material portions 405 includes a base, e.g., alkali, amines, etc. In one embodiment, the first chemistry to selectively remove the one or more first radiation-sensitive material portions 405 includes tetramethylammonium hydroxide (TMAH). In another embodiment, the first chemistry to selectively remove the one or more first radiation-sensitive material portions 405 includes a base, water, and an optional surfactant. [0074] In one embodiment, substrate 401 having the exposed layer of radiation-sensitive material 402 is immersed into a development solution containing the first chemistry to remove soluble one or more first radiation- sensitive material portions 405. Thereafter, the substrate 401 is dried. The developing process may be performed for a pre-specified time duration (e.g., about 30 seconds to about 180 seconds), a pre-specified temperature (e.g., room temperature), and a pre-specified pressure (atmospheric pressure). The developing process can include exposing the substrate to a developing solution in a developing system, such as a track system. For example, the track system can comprise a Clean Track ACT 8, ACT 12, or Lithius resist coating and developing system commercially available from Tokyo Electron Limited (TEL). [0075] As shown in FIG. 4C, a first critical dimension 420' (corresponding to the one or more first radiation-sensitive material portions 405), a second critical dimension 422' (corresponding to the one or more second radiation-sensitive material portions 406), or a third critical dimension 424' (corresponding to the one or more third radiation-sensitive material portions 408) may be adjusted, controlled, and/or optimized, as will be discussed below.

[0076] As illustrated in FIG. 4C, the one or more second radiation- sensitive material portions 406 and the one or more third radiation sensitive material portions 408 remain on substrate 401. [0077] Referring now to FIG. 4D, the one or more second radiation- sensitive material portions 406 corresponding to low radiation exposure are selectively removed using a second developing process comprising a second chemistry. In one embodiment, the second chemistry to selectively remove the one or more second radiation-sensitive material portions 406 includes an organic solvent. In one embodiment, the second chemistry to selectively remove the one or more second radiation-sensitive material portions 406 includes an organic solvent, optionally water, and an optional surfactant. In one embodiment, the second chemistry to selectively remove the one or more second radiation-sensitive material portions 406 includes an alcohol or acetone.

[0078] In one embodiment, substrate 401 having the exposed layer of radiation-sensitive material 402 is immersed into a development solution containing the second chemistry to remove soluble one or more second radiation-sensitive material portions 406. Thereafter, the substrate 401 is dried. The developing process may be performed for a pre-specified time duration (e.g., about 30 seconds to about 180 seconds), a pre-specified temperature (e.g., room temperature), and a pre-specified pressure (atmospheric pressure). The developing process can include exposing the substrate to a developing solution in a developing system, such as a track system. For example, the track system can comprise a Clean Track ACT 8, ACT 12, or Lithius resist coating and developing system commercially available from Tokyo Electron Limited (TEL). [0079] As shown in FIG. 4D, a first critical dimension 420" (corresponding to the one or more first radiation-sensitive material portions 405), a second critical dimension 422" (corresponding to the one or more second radiation-sensitive material portions 406), or a third critical dimension 424" (corresponding to the one or more third radiation-sensitive material portions 408) may be adjusted, controlled, and/or optimized, as will be discussed below.

[0080] As illustrated in FIG. 4D, the one or more second radiation- sensitive material portions 406 are removed, so that the one or more third radiation sensitive material portions 408 remain on substrate 401 . Since an image corresponding to each mask feature (e.g., transparent portions 404) has two regions of intermediate radiation exposure (or transitions regions ranging from low radiation intensity to high radiation intensity), the resulting resist pattern comprises twice the number of features 430 than the mask pattern on mask 403. As illustrated in FIG. 4D, for every one transparent portion 404 of mask 403, two features 430 are produced and a reduced feature pitch 432 between features 430 is achieved. [0081] Pitch 432 between features 430 is less than or equal to about half of mask pitch 409 between opaque features 410 of mask 403, as shown in FIG. 4D. In one embodiment, feature pitch 432 between features 430 may range from about 5 nm to about 30 nm. [0082] The order of the positive-tone development (i.e., development using first chemistry) and the negative-tone development (i.e., development using second chemistry) of the layer of radiation-sensitive material 402, as described above with respect to FIGs. 4C and 4D, may be performed in any order without changing the resulting pattern. In one embodiment, the one or more first radiation-sensitive material portions 405 corresponding to high radiation exposure are selectively removed from substrate 401 before removing the one or more second radiation-sensitive material portions 406 corresponding to low radiation exposure from substrate 401. In another embodiment, the one or more first radiation- sensitive material portions 405 corresponding to high radiation exposure are selectively removed from substrate 401 after removing the one or more second radiation-sensitive material portions 406 corresponding to low radiation exposure from substrate 401.

[0083] Referring now to FIG. 5, a flow chart 500 of a method for patterning a substrate is presented according to an embodiment. Flow chart 500 begins in 510 when a layer of radiation-sensitive material is formed on a substrate and, in 520, the layer of radiation-sensitive material is exposed to a pattern of radiation using a mask having a mask critical dimension to form one or more first radiation-sensitive material portions, one or more second radiation-sensitive material portions, and one or more third radiation-sensitive material portions. The one or more first radiation- sensitive material portions may comprise first radiation-sensitive material portions subjected to high radiation exposure. The one or more second radiation-sensitive material portions may comprise second radiation- sensitive material portions subjected to low radiation exposure. The one or more third radiation-sensitive material portions may comprise third radiation-sensitive material portions subjected to intermediate radiation exposure characterized by a third critical dimension. [0084] In 530, a temperature of the substrate is optionally elevated to a first post-exposure temperature. The thermal treatment process may comprise a first post-exposure bake (PEB), as described above. The first PEB may comprise setting the first post-exposure temperature, a time the substrate is elevated to the first post-exposure temperature, a heating rate for achieving the first post-exposure temperature, a cooling rate for reducing the first post-exposure temperature, a pressure of a gaseous environment surrounding the substrate during the elevation of the substrate to the first post-exposure temperature, or a composition of a gaseous environment surrounding the substrate during the elevation of the substrate to the first post-exposure temperature, or a combination of two or more thereof. The first post-exposure temperature may be ramped, or stepped.

[0085] In 540, the one or more first radiation-sensitive material portions are removed from the substrate using a first chemistry. The removal of the one or more first radiation-sensitive material portions may be characterized by a first critical dimension. The removal of the one or more first radiation-sensitive material portions may be performed using a first development process, such as a positive-tone development process or a negative-tone development process. The first development process may comprise setting a composition of the first chemistry, a time duration for the first development process, or a temperature for the first development process, or any combination of two or more thereof. The first chemistry may comprise a base solution. The first chemistry may further comprise a base solution, water, and an optional surfactant.

[0086] In 550, a temperature of the substrate is optionally elevated to a second post-exposure temperature. The thermal treatment process may comprise a second post-exposure bake (PEB). The second PEB may comprise setting the second post-exposure temperature, a time the substrate is elevated to the second post-exposure temperature, a heating rate for achieving the second post-exposure temperature, a cooling rate for reducing the second post-exposure temperature, a pressure of a gaseous environment surrounding the substrate during the elevation of the substrate to the second post-exposure temperature, or a composition of a gaseous environment surrounding the substrate during the elevation of the substrate to the second post-exposure temperature, or a combination of two or more thereof. The first post-exposure temperature may be ramped, or stepped.

[0087] In 560, the one or more second radiation-sensitive material portions are removed from the substrate using a second chemistry. The removal of the one or more second radiation-sensitive material portions may be characterized by a second critical dimension. The removal of the one or more second radiation-sensitive material portions may be performed using a second development process, such as a positive-tone development process or a negative-tone development process. The second development process may comprise setting a composition of the first chemistry, a time duration for the second development process, or a temperature for the second development process, or any combination of two or more thereof. The second chemistry may comprise an organic solvent. The second chemistry may further comprise an organic solvent, optionally water, and an optional surfactant.

[0088] In 570, the first critical dimension, the second critical dimension, and/or third critical dimension (corresponding to the critical dimension of the third radiation-sensitive material portions) are adjusted, controlled and/or optimized to meet pre-specified pattern requirements that may include a pre-specified first critical dimension, second critical dimension, and/or third critical dimension (corresponding to the critical dimension of the third radiation-sensitive material portions). This adjusting, controlling and/or optimizing include altering the patterning process. The adjusting, controlling, and/or optimizing is discussed in greater detail below. [0089] The adjusting of the patterning process to achieve a target first critical dimension and/or second critical dimension, and/or a target critical dimension for the critical dimension of third radiation-sensitive material portions comprises performing one or more of the following: (1 ) adjusting an exposure dose for the exposing of the layer of radiation-sensitive material; (2) adjusting the mask critical dimension for the exposing of the layer of radiation-sensitive material; (3) adjusting the first post-exposure temperature, the time the substrate is elevated to the first post-exposure temperature, the heating rate for achieving the first post-exposure temperature, the cooling rate for reducing the first post-exposure temperature, the pressure of a gaseous environment surrounding the substrate during the elevation of the substrate to the first post-exposure temperature, or a composition of the gaseous environment surrounding the substrate during the elevation of the substrate to the first postexposure temperature, or a combination of two or more thereof; (4) adjusting the second post-exposure temperature, the time the substrate is elevated to the second post-exposure temperature, the heating rate for achieving the second post-exposure temperature, the cooling rate for reducing the second post-exposure temperature, the pressure of a gaseous environment surrounding the substrate during the elevation of the substrate to the second post-exposure temperature, or a composition of the gaseous environment surrounding the substrate during the elevation of the substrate to the second post-exposure temperature, or a combination of two or more thereof; (5) adjusting the composition of the first chemistry, the time duration for applying the first chemistry, or a temperature of the first chemistry, or a combination of two or more thereof; or (6) adjusting the composition of the second chemistry, the time duration for applying the second chemistry, or a temperature for the second chemistry, or a combination of two or more thereof; or (7) performing a combination of two or more thereof.

[0090] Referring now to FIG. 6, a flow chart 600 of a method for double patterning a substrate is presented according to an embodiment. Flow chart 600 begins in 610 when a layer of radiation-sensitive material is formed on a substrate and, in 620, the layer of radiation-sensitive material is exposed to a pattern of radiation using a mask having a mask critical dimension to form first radiation-sensitive material portions having a high radiation exposure, second radiation-sensitive material portions having a low radiation exposure, and third radiation-sensitive material portions having an intermediate radiation exposure.

[0091] In 630, the first radiation-sensitive material portions are removed from the substrate by performing positive-tone developing of the layer of radiation-sensitive material from the substrate using a first chemistry. The removal of the first radiation-sensitive material portions may be characterized by a first critical dimension, or positive-tone critical dimension. The positive-tone development process may comprise setting a composition of the first chemistry, a time duration for the first development process, or a temperature for the first development process, or any combination of two or more thereof. The first chemistry may comprise a base solution. The first chemistry may further comprise a base solution, water, and an optional surfactant.

[0092] In 640, a temperature of the substrate is elevated to a first postexposure temperature. The thermal treatment process may comprise a first post-exposure bake (PEB). The first PEB proceeds after the exposing and before the positive-tone developing of the layer of radiation-sensitive material. The first PEB may comprise setting the first post-exposure temperature, a time the substrate is elevated to the first post-exposure temperature, a heating rate for achieving the first post-exposure temperature, a cooling rate for reducing the first post-exposure temperature, a pressure of a gaseous environment surrounding the substrate during the elevation of the substrate to the first post-exposure temperature, or a composition of a gaseous environment surrounding the substrate during the elevation of the substrate to the first post-exposure temperature, or a combination of two or more thereof. [0093] In 650, the second radiation-sensitive material portions are removed from the substrate by performing negative-tone developing of the layer of radiation-sensitive material from the substrate using a second chemistry. The removal of the second radiation-sensitive material portions may be characterized by a second critical dimension, or negative-tone critical dimension. The negative-tone development process may comprise setting a composition of the second chemistry, a time duration for the negative-tone development process, or a temperature for the negative- tone development process, or any combination of two or more thereof. The second chemistry may comprise an organic solvent. The second chemistry may further comprise an organic solvent, water, and an optional surfactant.

[0094] In 660, a temperature of the substrate is elevated to a second post-exposure temperature. The thermal treatment process may comprise a second post-exposure bake (PEB). The second PEB proceeds after the positive-tone developing of the layer of radiation-sensitive material and before the negative-tone developing of the layer of radiation-sensitive material. The second PEB may comprise setting the second postexposure temperature, a time the substrate is elevated to the second postexposure temperature, a heating rate for achieving the second postexposure temperature, a cooling rate for reducing the second postexposure temperature, a pressure of a gaseous environment surrounding the substrate during the elevation of the substrate to the second postexposure temperature, or a composition of a gaseous environment surrounding the substrate during the elevation of the substrate to the second post-exposure temperature, or a combination of two or more thereof.

[0095] The features remaining on the substrate occupy regions related to the third radiation-sensitive material regions (subject to intermediate radiation exposure) may be characterized by a third critical dimension. [0096] In 670, the third critical dimension is adjusted, controlled and/or optimized to meet pre-specified pattern requirements that may include a pre-specified third critical dimension. This adjusting, controlling and/or optimizing include altering the patterning process. [0097] The adjusting of the patterning process to achieve a target third critical dimension comprises: the use of and the adjustment, control and/or optimization of the second post-exposure bake. The second PEB may be adjusted by: adjusting the second post-exposure temperature, the time the substrate is elevated to the second post-exposure temperature, the heating rate for achieving the second post-exposure temperature, the cooling rate for reducing the second post-exposure temperature, the pressure of a gaseous environment surrounding the substrate during the elevation of the substrate to the second post-exposure temperature, or a composition of the gaseous environment surrounding the substrate during the elevation of the substrate to the second post-exposure temperature, or a combination of two or more thereof.

[0098] According to one example, as will be illustrated below, the second critical dimension, or negative-tone critical dimension (associated with negative-tone developing) may be increased by the mere addition of the second thermal treatment step and the elevation of the substrate to the second post-exposure temperature for a period of time. In this example, following the exposure to the pattern of radiation, the substrate is elevated to the first post-exposure temperature, followed by positive-tone developing, followed by elevating the substrate to the second postexposure temperature, followed by negative-tone developing. The second post-exposure temperature should be sufficiently high to cause chemical modification of the layer of radiation-sensitive material remaining on the substrate prior to negative-tone developing. Additionally, an increase in the second post-exposure temperature may cause a further increase in the second critical dimension. When holding the first critical dimension or positive-tone critical dimension approximately constant, the third critical dimension may also be increased with the second PEB and an increase in the second post-exposure temperature.

[0099] According to another example, the first critical dimension, or positive-tone critical dimension (associated with positive-tone developing) may be increased by the addition of the second thermal treatment step and the elevation of the substrate to the second post-exposure temperature for a period of time. In this example, following the exposure to the pattern of radiation, the substrate is elevated to the first postexposure temperature, followed by negative-tone developing, followed by elevating the substrate to the second post-exposure temperature, followed by positive-tone developing. The second post-exposure temperature should be sufficiently high to cause chemical modification of the layer of radiation-sensitive material remaining on the substrate prior to positive- tone developing. Additionally, an increase in the second post-exposure temperature may cause a further increase in the first critical dimension. When holding the second critical dimension or negative-tone critical dimension approximately constant, the third critical dimension may also be decreased with the second PEB and an increase in the second postexposure temperature.

[00100] Referring now to FIG. 7, a flow chart 700 of a method for double patterning a substrate is presented according to an embodiment. Flow chart 700 begins in 710 when a layer of radiation-sensitive material is formed on a substrate and, in 720, the layer of radiation-sensitive material is exposed to a pattern of radiation using a mask having a mask critical dimension to form first radiation-sensitive material portions having a high radiation exposure, second radiation-sensitive material portions having a low radiation exposure, and third radiation-sensitive material portions having an intermediate radiation exposure.

[00101] In 730, the first radiation-sensitive material portions are removed from the substrate by performing positive-tone developing of the layer of radiation-sensitive material from the substrate using a first chemistry. The removal of the first radiation-sensitive material portions may be characterized by a first critical dimension, or positive-tone critical dimension. The positive-tone development process may comprise setting a composition of the first chemistry, a time duration for the first development process, or a temperature for the first development process, or any combination of two or more thereof. The first chemistry may comprise a base solution. The first chemistry may further comprise a base solution, water, and an optional surfactant.

[00102] Optionally, a temperature of the substrate is elevated to a first post-exposure temperature. The thermal treatment process may comprise a first post-exposure bake (PEB). The first PEB proceeds after the exposing and before the positive-tone developing of the layer of radiation- sensitive material. The first PEB may comprise setting the first postexposure temperature, a time the substrate is elevated to the first postexposure temperature, a heating rate for achieving the first post-exposure temperature, a cooling rate for reducing the first post-exposure temperature, a pressure of a gaseous environment surrounding the substrate during the elevation of the substrate to the first post-exposure temperature, or a composition of a gaseous environment surrounding the substrate during the elevation of the substrate to the first post-exposure temperature, or a combination of two or more thereof. [00103] In 740, the second radiation-sensitive material portions are removed from the substrate by performing negative-tone developing of the layer of radiation-sensitive material from the substrate using a second chemistry. The removal of the second radiation-sensitive material portions may be characterized by a second critical dimension, or negative-tone critical dimension. The negative-tone development process may comprise setting a composition of the second chemistry, a time duration for the negative-tone development process, or a temperature for the negative- tone development process, or any combination of two or more thereof. The second chemistry may comprise an organic solvent. The second chemistry may further comprise an organic solvent, water, and an optional surfactant.

[00104] Optionally, a temperature of the substrate is elevated to a second post-exposure temperature. The thermal treatment process may comprise a second post-exposure bake (PEB). The second PEB proceeds after the positive-tone developing of the layer of radiation- sensitive material and before the negative-tone developing of the layer of radiation-sensitive material. The second PEB may comprise setting the second post-exposure temperature, a time the substrate is elevated to the second post-exposure temperature, a heating rate for achieving the second post-exposure temperature, a cooling rate for reducing the second post-exposure temperature, a pressure of a gaseous environment surrounding the substrate during the elevation of the substrate to the second post-exposure temperature, or a composition of a gaseous environment surrounding the substrate during the elevation of the substrate to the second post-exposure temperature, or a combination of two or more thereof.

[00105] The features remaining on the substrate occupy regions related to the third radiation-sensitive material regions (subject to intermediate radiation exposure) may be characterized by a third critical dimension. [00106] In 750, the third critical dimension is adjusted, controlled and/or optimized to meet pre-specified pattern requirements that may include a pre-specified third critical dimension. This adjusting, controlling and/or optimizing include altering the patterning process. [00107] The adjusting of the patterning process to achieve a target third critical dimension comprises: the adjustment, control and/or optimization of the positive-tone developing. The positive-tone developing may be adjusted by: adjusting the composition of the first chemistry, the time duration for applying the first chemistry, or a temperature of the first chemistry, or a combination of two or more thereof. [00108] According to one example, as will be illustrated below, the first critical dimension, or positive-tone critical dimension (associated with positive-tone developing) may be decreased by an adjustment of the composition of the first chemistry. When the first chemistry comprises a base with water and an optional surfactant, the dilution of the base in the solution may cause a decrease in the first critical dimension. When holding the second critical dimension or negative-tone critical dimension approximately constant, the third critical dimension may also be increased with the dilution of the positive-tone developing solution. [00109] Referring now to FIG. 8, exemplary data 800 is provided for a dual-tone double patterning process. As illustrated in FIG. 8, the printed critical dimension (nm, nanometers) is provided as a function of exposure dose (mJ/cm 2 , milli-Joules per square centimeters) for a set of negative- tone development characteristics 810 and a set of positive-tone development characteristics 820. The set of negative-tone development characteristics 810 and the set of positive-tone development characteristics 820 may be acquired using numerical simulation, experiment, or a combination thereof.

[00110] A characteristic defines a relationship between a critical dimension and a control parameter, such as an exposure dose; however, other control parameters may be used. The characteristic is determined by setting a set of process parameters for performing the dual-tone patterning process, such as the processes described in FIGs. 3, 4A-4D, 5, 6, and 7, wherein the set of process parameters includes any one or more of the process parameters described above with respect to these processes. While holding these process parameters constant, a critical dimension is measured and/or computed as the control parameter is varied. This procedure for preparing a characteristic may be used to determine one or more negative-tone characteristics and/or one or more positive-tone characteristics. The characteristics may be prepared using a negative-tone pattern development process, a positive-tone pattern development process, or a dual-tone pattern development process. [00111 ] The set of negative-tone development characteristics 810 exhibit a variation in one or more parameters useful in adjusting or controlling the negative-tone critical dimension. For example, the one or more parameters may include any parameter, as described above, for performing a second post-exposure bake following the positive-tone development. Additionally, for example, the one or more parameters may include any parameter for performing the negative-tone development. [00112] As shown in FIG. 9, a film thickness (nm) (or normalized film thickness) for a layer of radiation-sensitive material following negative-tone development is shown as a function of exposure dose (mJ/cm 2 ). A first contrast curve 910 in the exemplary data 900 is presented wherein the second post-exposure bake following positive-tone development is not performed. A second set of curves 920 are also presented wherein the second post-exposure bake following positive-tone development is performed. As depicted in FIG. 9, the contrast curves shift to lower exposure dose (indicated by arrow 930) indicating a decrease in the lower solubility threshold or a resulting increase in the negative-tone critical dimension. The shift to lower exposure dose of the negative contrast curves may be achieved by increasing the second post-exposure temperature and/or the time duration for elevation at the second postexposure temperature (see trend 814 in FIG. 8). [00113] In FIG. 8, the set of positive-tone development characteristics 820 exhibit a variation in one or more parameters useful in adjusting or controlling the positive-tone critical dimension. For example, the one or more parameters may include any parameter, as described above, for performing a second post-exposure bake following the positive-tone development. Additionally, for example, the one or more parameters may include any parameter for performing the positive-tone development. [00114] As shown in FIG. 10, a film thickness (nm) (or normalized film thickness) for a layer of radiation-sensitive material following positive-tone development is shown as a function of exposure dose (mJ/cm 2 ). A first set of positive contrast curves 1010 in exemplary data 1000 is provided having a first contrast curve 1012 and a second contrast curve 1014. The first contrast curve 1012 is acquired when the second post-exposure bake following positive-tone development is not performed. The second contrast curve 1014 is acquired when the second post-exposure bake following positive-tone development is not performed and the positive-tone development solution (e.g., first chemistry having a base, water, and optional surfactant) is diluted relative to the first contrast curve 1012. As depicted in FIG. 10, the contrast curves shift to higher exposure dose (indicated by arrow 1030) indicating an increase in the upper solubility threshold or a resulting decrease in the positive-tone critical dimension. The shift to higher exposure dose of the positive contrast curves may be achieved by increasing the dilution of the positive-tone development chemistry (see trend 824 in FIG. 8).

[00115] A second set of curves 1020 is provided having a third contrast curve 1022 and a fourth contrast curve 1024. The third contrast curve 1022 is acquired when the second post-exposure bake following positive- tone development is performed and the positive-tone development solution is the same for the first contrast curve 1012. As depicted in FIG. 10, the contrast curves shift to lower exposure dose (indicated by arrow 1040) indicating a decrease in the upper solubility threshold or a resulting increase in the positive-tone critical dimension. The shift to lower exposure dose of the positive contrast curves may be achieved by increasing the second post-exposure temperature and/or the time duration for elevation at the second post-exposure temperature. [00116] The fourth contrast curve 1024 is acquired when the second post-exposure bake following positive-tone development is performed and the positive-tone development solution is diluted relative to the first contrast curve 1012. As depicted in FIG. 10, the contrast curves shift to higher exposure dose (indicated by arrow 1030) indicating an increase in the upper solubility threshold or a resulting decrease in the positive-tone critical dimension.

[00117] As shown in FIG. 1 1 , a film thickness (nm) (or normalized film thickness) for a layer of radiation-sensitive material following negative-tone development is shown as a function of exposure dose (mJ/cm 2 ). Following the exposure of the layer of radiation-sensitive material to a pattern of radiation, the layer of radiation-sensitive material undergoes a first postexposure bake for a first time duration followed by positive-tone development, and then undergoes a second post-exposure bake for a second time duration followed by negative-tone development. A family of contrast curves 1 1 10 in the exemplary data 1 100 is presented, wherein the first time duration for the first post-exposure bake (e.g., the first time duration is indicated in the legend by the time preceding "POS") and the second time duration for the second post-exposure bake (e.g., the second time duration is indicated in the legend by the time preceding "NEG") are varied.

[00118] As illustrated in FIG. 1 1 , when the first time duration for the first post-exposure bake (preceding the positive-tone development) is held constant (i.e., at 25 sec (seconds), 35 sec, and 45 sec) while the second time duration for the second post-exposure bake (preceding the negative- tone development) is increased (i.e., 35 sec to 95 sec, 25 sec to 85 sec, and 15 sec to 75 sec), the lower exposure threshold shifts to the left (i.e., the lower exposure threshold decreases) (trend indicated by arrow 1 140). The decrease in the lower exposure threshold manifests as an increase in the second critical dimension or negative-tone critical dimension. Furthermore, while the lower exposure threshold is decreased by increasing the second time duration during the second post-exposure bake, the upper exposure threshold remains substantially constant when the first time duration is held constant.

[00119] Additionally, as illustrated in FIG. 1 1 , when the second time duration for the second post-exposure bake (preceding the negative-tone development) is held approximately constant with a slight variation (i.e., at 35 sec, 25 sec, and 15 sec; and at 95 sec, 85 sec, and 75 sec) while the first time duration for the first post-exposure bake (preceding the positive- tone development) is increased (i.e., 35 sec to 35 sec to 45 sec), the upper exposure threshold shifts to the left (i.e., the upper exposure threshold decreases) (trend indicated by arrow 1 130). The decrease in the upper exposure threshold manifests as an increase in the first critical dimension or positive-tone critical dimension. Furthermore, while the upper exposure threshold is decreased by increasing the first time duration during the first post-exposure bake, the lower exposure threshold remains approximately constant when the second time duration is held approximately constant. [00120] Referring again to FIG. 8, when printing a pattern of features on a substrate, a target positive-tone critical dimension (CD PO s) and a target negative-tone critical dimension (CD NEG ) may be selected or specified. Thereafter, a target difference (T DD ) between the target positive-tone critical dimension and the target negative-tone critical dimension may be computed for the double development metric. Alternatively, two or more of the target difference, the target positive-tone critical dimension and the target negative-tone critical dimension may be specified, while the third is computed.

[00121] Through inspection of the set of negative-tone development characteristics 810 and the set of positive-tone development characteristics 820, a target negative-tone characteristic 812 may be selected and a target positive-tone characteristic 822 may be selected that possesses a ΔCDN P comparable to T DD - Desirably, the selected characteristics possess a ΔCD N p that is greater than T DD - [00122] The dual-tone double patterning process may be optimized by selecting the target negative-tone characteristic and the target positive- tone characteristic such that the target positive-tone characteristic intersects the target positive-tone critical dimension at a given exposure dose and the target negative-tone characteristic intersects the target negative-tone critical dimension at the same given exposure dose. [00123] Alternatively, the dual-tone double patterning process may be optimized by selecting the target positive-tone characteristic such that the target positive-tone characteristic intersects the target positive-tone critical dimension at a given exposure dose. Then, the target negative-tone characteristic may be selected when ΔCD N p is approximately comparable to T DD for the given exposure dose. Alternatively yet, the target negative- tone characteristic may be selected when DDM is approximately unity, where:

[00124] DDM = 1 -([|ΔCD NP | - T DD ]/T D D). (3)

[00125] Referring now to FIG. 12, a flow chart 1200 of a method for optimizing a double patterning process is presented according to an embodiment. Flow chart 1200 begins in 1210 with performing a dual-tone development process. The dual-tone development process comprises: exposing a layer of radiation-sensitive material to a pattern of radiation, performing a positive-tone development process to remove a first radiation-sensitive material portion characterized by a positive-tone critical dimension, and performing a negative-tone development process to remove a second radiation-sensitive material portion characterized by a negative-tone critical dimension.

[00126] In 1220, the dual-tone development process is optimized to achieve a target difference between a target positive-tone critical dimension and a target negative-tone critical dimension. The optimization of the dual-tone development process comprises: acquiring one or more positive-tone characteristics, wherein the one or more positive-tone characteristics relate the positive-tone critical dimension to a control parameter for a first set of process parameters; acquiring one or more negative-tone characteristics, wherein the one or more negative-tone characteristics relate the negative-tone critical dimension to the control parameter for a second set of process parameters; selecting a target positive-tone characteristic from the one or more positive-tone characteristics that approximately intersects the target positive-tone critical dimension at a target control parameter to within a first deviation; selecting a target negative-tone characteristic from the one or more negative-tone characteristics that approximately intersects the target negative-tone critical dimension at the target control parameter to within a second deviation; and establishing a process recipe for the performing the dual- tone development process using the target positive-tone characteristic, the target negative-tone characteristic, and the target control parameter. [00127] The first deviation and the second deviation may be selected to be an absolute value, such as plus or minus 5 nm, plus or minus 2 nm. Alternatively, first deviation and the second deviation may be selected to be an relative value, such as plus or minus 10% of T DD , plus or minus 5% [00128] Although only certain embodiments of this invention have been described in detail above, those skilled in the art will readily appreciate that many modifications are possible in the embodiments without materially departing from the novel teachings and advantages of this invention. For example, several embodiments are described herein that use a single exposure of a layer of radiation-sensitive material to a pattern of radiation. However, a plurality of exposures may be utilized. Accordingly, all such modifications are intended to be included within the scope of this invention.