METHOD OF SELECTIVE DEPOSITION FOR BEOL DIELECTRIC ETCH

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application is related to and claims priority to United States Provisional Patent Application serial no. 62/435,580 filed on December 16, 2016, the entire contents of which are herein incorporated by reference.

FIELD OF INVENTION

[0002] The present invention relates to the field of dry etching of low-k materials and their treatment for integration in the back-end-of-line (BEOL) part of the integrated circuit (IC) fabrication process where the interconnects are made.

BACKGROUND OF THE INVENTION

[0003] The advancement of the technology for the chip design is calling for the integration of low-k value dielectric materials in the various BEOL levels. As a result, the search for low-k materials has resulted in incorporation of more carbon (C) and some porosity in the dielectric materials. Consequently, the low-k materials are getting more prone to damage during dry etch plasma processes, including during the via etch, the trench etch, the strip of an organic planarizing layer (OPL), and post etch treatment (PET). The critical dimensions (CD) of the Cu interconnects are also directly influenced by the amount of damage of the low-k materials. The CD and profile control of the via, the trench, and the spacing between the via and the trench, are getting more critical at smaller dimensions in order to achieve good reliability.

SUMMARY OF THE INVENTION

[0004] Embodiments of the invention describe processing of substrates containing dielectric materials. According to one embodiment, the method includes providing a patterned substrate containing a dielectric material, exposing the substrate to a gas phase plasma to functionalize a surface of the dielectric material, exposing the substrate to a silanizing reagent that reacts with the functionalized surface of the dielectric material to form a dielectric film on the dielectric material, and sequentially repeating the exposing steps at least once to increase a thickness of the dielectric film. [0005] According to another embodiment, the method includes providing a patterned substrate containing a SiCOH layer, exposing the substrate to an 02-based or C02-based gas phase plasma to functionalize a surface of the SiCOH layer, exposing the substrate to a silanizing reagent that reacts with the functionalized surface of the SiCOH layer to form a SiOx film on the SiCOH layer, and sequentially repeating the exposing steps at least once to increase a thickness of the SiOx film.

[0006] According to another embodiment, the method includes providing a patterned substrate containing a porous low-k material, exposing the substrate to an 02-based or CO2- based gas phase plasma to functionalize a surface of the porous low-k material, exposing the substrate to a silanizing reagent that reacts with the functionalized surface of the porous low- k material to form a dielectric film on the dielectric material, and sequentially repeating the exposing steps at least once to increase a thickness of the dielectric film.

BRIEF DESCRIPTION OF THE DRAWINGS

[0007] A more complete appreciation of the invention and many of the attendant advantages thereof will be readily obtained as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings, wherein:

[0008] FIG. 1 schematically shows a method of functionalizing a surface of a dielectric material and silanizing the functionalized surface according to an embodiment of the invention;

[0009] FIG. 2 shows a dielectric film thickness as a function of number of process cycles according to an embodiment of the invention;

[0010] FIGS. 3A - 3F schematically shows through cross-sectional views a method of processing a patterned substrate according to an embodiment of the invention;

[0011] FIG. 4 schematically shows a cross-sectional view a patterned substrate;

[0012] FIGS. 5A - 5F schematically show through cross-sectional views a method of processing a patterned substrate according to an embodiment of the invention;

[0013] FIGS. 6A - 6E schematically shows through cross-sectional views a method of processing a patterned substrate according to an embodiment of the invention;

[0014] FIGS. 7 A - 7D schematically shows through cross-sectional views a method of processing a patterned substrate according to an embodiment of the invention; [0015] FIGS. 8A and 8B show cross-sectional transmission electron microscopy (TEM) images of the effect of thin a SiO _x film on metal bleaching of a porous low-k material according to an embodiment of the invention; and

[0016] FIGS. 9A and 9B schematically shows through cross-sectional views a method of processing a patterned substrate according to an embodiment of the invention.

DETAILED DESCRIPTION OF SEVERAL EMBODIMENTS

[0017] Embodiments of the invention address several issues and problems associated with etching of dielectric materials for BEOL applications, including a) how to mitigate low-k material damage, b) how to achieve a high via chamfer angle, c) how to seal the pores of porous low-k materials, d) how to better maintain the via and trench CDs after etching, wet cleaning, and Cu metallization, e) how to obtain a straighter pattern profile (trench and via) of a stack containing multiple layers of low-k materials, and f) how to suppress the interaction between a low-k material and a planarizing material.

[0018] Embodiments of the invention relate to a method of processing a dielectric material. According to one embodiment, the method provides selective deposition of a thin dielectric film onto a dielectric material. According to some embodiments, the dielectric film can include SiO _x , SiN _x , SiO _x N _y , or a combination thereof, and the dielectric material can include S1O2, SiN, SiCN and SiC, a low-k material (for example SiCOH), an Organo Silicate Glass (OSG), or a Carbon Doped Oxide (CDO).

[0019] The method includes a step of surface functionalization of a dielectric material by means of plasma processing, and a step of exposing the functionalized surface to a silanizing reagent. The two step process results in deposition of a thin dielectric film on the dielectric material, where the two step process may be repeated at least once to increase a thickness of the dielectric film on the dielectric material. One process cycle includes a surface functionalization step and a silanizing step, and a thickness of the deposited dielectric film is proportional to the number of process cycles. Chemical composition of the dielectric film may be selected and adjusted by varying the chemical environment of the surface

functionalization and the silanizing reagent. In some examples, the chemical environment for the surface functionalization can be selected from N2-based, N2/H2-based, 02-based, CO2- based, COS-based, Nfh-based, fh-based, and FhO-based. The surface functionalization can, for example, include -OH species, -NH species, and -SH species.

[0020] According to one embodiment, the surface functionalization step can include plasma oxidation of a surface of the dielectric material to form surface species with reactive bonds (for example silanol with Si-OH bonds). The plasma oxidation is followed by a step of exposing the dielectric material to a silanizing reagent, for example trimethylsilane dimethylamine (TMSDMA). The process cycle may be repeated at least once to deposit a thin SiOx (x<2) film on the dielectric material. Experimental data showed that a thickness of the deposited SiO _x film is directly proportional to the number of process cycles.

[0021] FIG. 1 schematically shows a method of functionalizing a surface of a dielectric material and silanizing the functionalized surface according to an embodiment of the invention. In general, the basic silanizing reactions depicted in FIG. 1 apply to any silanizing reagent. According to some embodiments of the invention, silanizing reagent may be selected from dimethylsilane dimethylamine (DMSDMA), trimethylsilane dimethylamine (TMSDMA), bis(dimethylamino) dimethylsilane (BDMADMS), tetramethyldisilazane (TMDS), and other alkyl amine silanes. The silanizing reaction includes thermally reacting in step (1) the silanizing reagent (B) with a hydrophilic site (e.g., -OH) on a surface of a dielectric material (A) at a substrate temperature below approximately 200°C. In the case of TMSDMA, the silanizing reaction bonds a SiMe3 group to the hydrophilic site to form a silanized dielectric material (C) and HNMe2 reaction by-products (D) that are removed from the silanized dielectric material (C). The silanized dielectric material (C) can be referred to as a SiOx film. The TMSDMA silanizing reaction may be performed in a process chamber where a wafer (substrate) is placed on a substrate holder heated to 180°C and exposed to a gas mixture containing TMSDMA and N2 at a gas pressure of 5 Torr.

[0022] The silanizing reagent may have the chemical formula R _n SiX ₄ -n, where R is an alkyl group or a functional chain, X is OR, NH2, or NR2, and n=0-4. In one example, the silanizing reagent can be an organo alkoxysilane reagent such as tetraethoxysilane (Si(OEt) ₄ , TEOS). In another example, the silanizing reagent can include dimethyldimethoxysilane (DMDMOS) or dimethyldiethoxysilane (DMDEOS).

[0023] Still referring to FIG. 1, according to an embodiment of the invention, a process cycle includes a step (2) of surface functionalization of a dielectric material (C ) (e.g., a silylated surface) by means of plasma processing (E) (e.g., plasma oxidation containing O2 gas or CO2 gas). The surface functionalization further forms reaction by-products (G) that are removed. A subsequent step (3) includes exposing the functionalized surface (F) to a silanizing reagent (H) to form the SiO _x film (I) and HNMe2 reaction by-products (J) that are removed. The step of surface functionalization forms a dielectric material surface (F) that is reactive towards the silanizing reagent (I). The process cycle of steps (2) and (3) may be repeated at least once to increase a thickness of the SiO _x film on the dielectric material. The process cycle provides selective growth of a thin SiOx film that may contain carbon and hydrogen. In the example shown in FIG. 1, the methyl groups (Me) contain carbon and hydrogen.

[0024] FIG. 2 shows a dielectric film thickness as a function of number of process cycles according to an embodiment of the invention. SiOx films were deposited on wafers having a blanket SiCOH films thereon using process cycles containing alternating steps of O2 plasma oxidation and TMSDMA gas exposure. The O2 plasma oxidation was performed for 5 seconds without applying radio frequency (RF) bias power to the wafers. This plasma processing conditions resulted in relatively low energy of ions impacting the surface of the wafer. The ions were accelerated through the plasma sheath with a potential equal to the plasma potential. The SiO _x film thickness was measured by ellipsometry. FIG. 2 shows that the SiOx film thickness was linear with the number of process cycles up to at least 20 process cycles, and that about 1 Angstrom (A) of SiO _x was deposited per process cycle. Thus, the SiOx film thickness may be directly controlled by the number of process cycles.

[0025] The effect of different plasma oxidation times on SiO _x film deposition rates was studied using O2 gas and CO2 gas. Two different plasma oxidation times, 5 seconds and 10 seconds of O2 and CO2 gas plasma exposures, were investigated for 10 process cycles. The thickness of all the deposited SiO _x films was about 1 nm, thereby showing that the functionalization of the dielectric material surface is readily achieved within several seconds of the plasma treatment.

[0026] Examples of Selective Deposition of Dielectric Films for BEOL Dielectric Etch

[0027] FIGS. 3A - 3F schematically shows through cross-sectional views a method of processing a patterned substrate according to an embodiment of the invention. In this embodiment, the method helps mitigate low-k material damage by forming a dielectric film on the low-k material, where the dielectric film acts as a barrier against carbon depletion as an organic film is stripped from the patterned substrate. In FIG. 3A, the patterned substrate 30 contains vias 303 etched through layers of an organic planarization layer (OPL) 312, a patterning hardmask (HM) 310, a metal hardmask 308, a dielectric hardmask 306, a SiCOH layer 304, and stopping on the etch stop layer 302. The SiCOH layer 304 is a low-k layer with a dielectric constant (k) that is lower than that of S1O2 (k~3.9). According to one embodiment, the etch stop layer 302 can contain or consist of Si, C, H, and N. The etch stop layer may consist of a single material, or alternatively, may contain multiple materials with different compositions.

[0028] Following formation of the vias 303 by gas phase etching, an oxygen-based ashing process may be performed to remove CHF _X etch products from the patterned substrate 30 and to functionalize surfaces of the dielectric materials. The surface functionalization creates Si- OH surface termination 305 on the surfaces of the dielectric hardmask 306, the SiCOH layer 304, and the etch stop layer 302. As depicted in FIG. 3B, the oxygen-based ashing process also removes a portion of the thickness of the OPL 312.

[0029] Thereafter, the Si-OH surface termination 305 is silylated by an exposure to a silanizing reagent (e.g., TMSDMA) to form a SiOx film 307 (e.g., Si-O-SilVfes) on the dielectric hardmask 306, the SiCOH layer 304, and the etch stop layer 302 in the vias 303. This is schematically shown in FIG. 3C.

[0030] An oxygen-based plasma ashing process may be performed on the SiO _x film 307 to regenerate the Si-OH surface termination. Multiple process cycles of an oxygen-based ashing and silanizing may be formed to increase a thickness of the SiO _x film 307 in the vias 303 and form a SiOx film 309 (FIG. 3D. Each ashing step removes a portion of the OPL 312 but the SiOx film 309 protects the surfaces of the dielectric hardmask 306 and the SiCOH layer 304 in the vias 303 from carbon depletion. In FIG. 3E, the OPL 312 has been fully removed.

[0031] According to one embodiment, the patterned substrate 30 in FIG. 3E may be etched to form a trench 311 and extend the vias 303 through the etch stop layer 302 to the metal line 301. This is schematically shown in FIG. 3F. The presence of the SiOx film 309 helps to better preserve the corner 313 between the vias 303 and the trench 311, thereby resulting in a high chamfer angle. The SiOx film 309 is denser than the SiCOH layer 304 and this results in a lower etch rate of the SiOx film 309 than the SiCOH layer 304 during the etch process. For comparison, as schematically shown for the patterned substrate 40 in FIG. 4, the absence of the a SiOx film 309 results in a sloped chamfer and a low chamfer angle at the corner 315 between the vias 303 and the trench 311. Further, the SiO _x film 309 protects the dielectric surfaces in the vias 303 from carbon depletion during the trench etch.

[0032] FIGS. 9A and 9B schematically shows through cross-sectional views a method of processing a patterned substrate according to an embodiment of the invention. The patterned substrate 90 is similar to the patterned substrate 30 in FIG. 3A but the SiCOH layer 304 has been replaced by a plurality of dielectric layers. The plurality of dielectric layers may be low-k layers. In this example, the SiCOH layer 304 has been replaced by a first dielectric layer 316, an etch stop layer 318, and a second dielectric layer 320. The first dielectric layer 316 and the second dielectric layer 320 may have different chemical composition and density, thus displaying different etch behavior. The formation of the SiO _x film 309 can be used to improve the profile of the pattern (e.g., via, trench) etched into the patterned substrate 90, including minimizing bowing or undercutting between a softer (lower density) and a harder (higher density) dielectric layers.

[0033] FIGS. 5A - 5F schematically show through cross-sectional views a method of processing a patterned substrate according to an embodiment of the invention. The method includes forming vias 303 in the patterned substrate 50 by gas phase etching, removing the OPL 312 (FIG. 5B), exposing the patterned substrate 50 to an oxygen-based ashing process to creates Si-OH surface termination 305 on the surfaces of the dielectric hardmask 306, the SiCOH layer 304, and the etch stop layer 302 (FIG. 5C). The Si-OH surface termination 305 is silylated by an exposure to a silanizing reagent to form a SiOx film 307 on the dielectric hardmask 306, the SiCOH layer 304, and the etch stop layer 302 in the vias 303 (FIG. 5D). The processing may be repeated to form a SiOx film 309 (FIG. 5E). Thereafter, a trench etching process may be carried out to form trench 311 and extend the vias 303 through the etch stop layer 302 to the metal line 301 (FIG. 5F).

[0034] FIGS. 6A - 6E schematically shows through cross-sectional views a method of processing a patterned substrate according to an embodiment of the invention. The method includes performing trench hard mask patterning of patterned substrate 60 (FIG. 6A), performing a trench etch process to form a trench 311 and exposing the patterned substrate 60 to an oxygen-based ashing process to create Si-OH surface termination 305 on the surfaces of the dielectric hardmask 306 and the SiCOH layer 304 (FIG. 6B). The Si-OH surface termination 305 is silylated by an exposure to a silanizing reagent to form a SiOx film 307 on the dielectric hardmask 306 and the SiCOH layer 304 (FIG. 6C). The processing may be repeated to form a SiOx film 309 (FIG. 6D). The patterned substrate 60 in FIG. 6D may be further processed by forming a planarization layer 314 that fills the trench 311 (FIG. 6E). The SiOx film 309 functions as a barrier layer and suppresses the interaction between the SiCOH layer 304 and the planarization layer 314. The planarization layer 314 can be an organic material or can contain amount of Si.

[0035] FIGS. 7 A - 7D schematically shows through cross-sectional views a method of processing a patterned substrate according to an embodiment of the invention. The method includes performing trench hard mask patterning of patterned substrate 70 (FIG. 7A), performing a via etch process to forms vias 303, performing a trench etch process to form a trench 311, and exposing the patterned substrate 70 to an oxygen-based ashing process to create Si-OH surface termination 305 on the surfaces of the dielectric hardmask 306 and the SiCOH layer 304 (FIG. 7B). The Si-OH surface termination 305 is silylated by an exposure to a silanizing reagent to form a SiOx film 307 on the dielectric hardmask 306 and SiCOH layer 304 (FIG. 7C). The processing may be repeated to form a SiOx film 309 (FIG. 7D).

[0036] Examples of pore sealing of porous low-k material.

[0037] In addition to enabling deposition of a thin dielectric film (e.g., SiOx) on low-k materials by alternating surface functionalization and silanizing, some embodiments of the inventions may be used to seal the pores of porous low-k materials.

[0038] FIGS. 8A and 8B show cross-sectional TEM images of the effect of a thin SiOx film on metal bleaching of a porous low-k material according to an embodiment of the invention. FIG. 8A shows Cu line bleaching through a metal-containing barrier layer into a porous spin- on low-k material. A barrier layer and a Cu line were deposited into recessed features in the low- material. The Cu metallization process causes the Cu line bleeding due to the weakness of the low-k material and the pores' interconnect! vity. In FIG. 8B, a thin SiO _x film was selectively deposited on the low-k material using 10 process cycles of CO2 plasma treatment and TMSDMA exposure. This image shows that the presence of the thin SiO _x film was able to seal the pores at the surface and create a dense surface film. This thin SiOx film eventually was able to withstand the barrier metal deposition and the Cu filling process and provide a well-defined metal and low-k material interface with no Cu line bleeding. Further, another difference between FIGS. 8 A and 8B is the large via bottom CD in FIG. 8 A compared to the smaller target via bottom CD on FIG. 8B. This shows the benefit of the thin SiO _x film to mitigate the low-k material damage according to an embodiment of the invention.

[0039] According to one embodiment, the process cycles described above may be performed in two different process chambers, where one process chamber includes an etch chamber configured for etching the dielectric material (via and trench patterns). The step of surface functionalization of the dielectric material by means of plasma processing (e.g., plasma oxidation containing O2 gas or CO2 gas) may also be performed in the etch chamber. The silanizing step may be performed in another process chamber that may be at an elevated temperature to thermally activate the silanizing reaction.

[0040] According to another embodiment, the process cycles may be performed in a single process chamber configured for performing etching, surface functionalization, and silanizing.

[0041] A plurality of embodiments for a method of processing a dielectric material have been described. The foregoing description of the embodiments of the invention has been presented for the purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise forms disclosed. This description and the claims following include terms that are used for descriptive purposes only and are not to be construed as limiting. Persons skilled in the relevant art can appreciate that many modifications and variations are possible in light of the above teaching. It is therefore intended that the scope of the invention be limited not by this detailed description, but rather by the claims appended hereto.