BACKGROUND

Field

[0001] Embodiments of the disclosure generally relate to a gas confiner assembly for improving profile uniformity and method for distributing gas in a processing chamber.

Description of the Related Art

[0002] Liquid crystal displays or flat panels are commonly used for active matrix displays such as computer and television monitors. Plasma enhanced chemical vapor deposition (PECVD) is generally employed to deposit thin films on a substrate such as a transparent substrate for flat panel display or semiconductor wafer. PECVD is generally accomplished by introducing a precursor gas or gas mixture, e.g., silane (SiH ₄ ) and nitrogen (N ₂ ), into a vacuum chamber that contains a substrate. The precursor gas or gas mixture is typically directed downwardly through a distribution plate situated near the top of the chamber. The precursor gas or gas mixture in the chamber is energized (e.g., excited) into a plasma by applying radio frequency (RF) power to the chamber from one or more RF sources coupled to the chamber. The excited gas or gas mixture reacts to form a layer of material, e.g., silicon nitride (SiN _x ), on a surface of the substrate that is positioned on a temperature controlled substrate support. The silicon nitride layer forms passivation layers, gate insulators, buffer layers, and/or etch stop layers for a low temperature poly silicon (LTPS) film stack in the next generation thin film transistors (TFT) and active matrix organic light emitting diodes (AMOLED). TFT and AMOLED are but two types of devices for forming flat panel displays.

[0003] Flat panels processed by PECVD techniques are typically large, often exceeding 4 square meters. As the size of substrates continues to grow in the flat panel display industry, film thickness and film uniformity control for large area PECVD becomes an issue. Shadow frames are typically used in PECVD to protect the substrate support from plasma. However, because shadow frames cover the outer most edge of the substrate, they: (1 ) increase the edge exclusion (EE) by 3 mm to 5 mm; and (2) negatively affect the film deposition near the perimeter/edge regions of the substrate. One way to improve the edge uniformity is to eliminate the shadow frame. However, eliminating the shadow frame still leaves a perimeter region of the substrate support surface exposed to the plasma, which may result in higher deposition rates at the edge region of the substrate due to the offset between the substrate and the uncovered substrate support surface. Additionally, if the substrate support surface is exposed to the plasma, it may lead to plasma arcing and non-uniform deposition.

[0004] Therefore, there is a need for improving the deposition rate and film profile uniformity in substrates.

SUMMARY

[0005] In one embodiment, a gas confiner assembly for a processing chamber includes a gas confiner configured to decrease gas flow and compensate for high deposition rates on edge regions of substrates. The gas confiner assembly also includes a cover disposed below the gas confiner. The cover is configured to prevent a substrate support from being exposed to plasma. The cover includes one or more ceramic plates, wherein the one or more ceramic plates include slotted locating pins and fixed screws to join the one or more ceramic plates to each other. The one or more ceramic plates overlap each other at corners of the gas confiner assembly such that an end of one of the one or more ceramic plates extends beyond an adjacent overlapping ceramic plate's ends' width.

[0006] In another embodiment, a processing chamber includes a gas distribution plate and a substrate support configured to support a substrate. The substrate support is disposed below the gas distribution plate to define a plasma processing volume. The processing chamber also includes a gas confiner assembly disposed around a periphery of the substrate support. The gas confiner assembly includes a gas confiner configured to decrease gas flow and compensate for high deposition rates on edge regions of the substrate, and a cover disposed below the gas confiner. The cover is configured to prevent the substrate support from being exposed to the plasma processing volume.

[0007] In yet another embodiment, a method for distributing gas in a processing chamber includes using a gas confiner to confine a gas flow at edges of a substrate in the processing chamber. The method also includes reducing deposition rates on the edges of the substrate.

BRIEF DESCRIPTION OF THE DRAWINGS

[0008] So that the manner in which the above recited features of the present disclosure can be understood in detail, a more particular description of the disclosure, briefly summarized above, may be had by reference to embodiments, some of which are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only typical embodiments of this disclosure and are therefore not to be considered limiting of its scope, for the disclosure may admit to other equally effective embodiments.

[0009] Figure 1 is a schematic cross-section view of one embodiment of a PECVD chamber having a gas confiner assembly.

[0010] Figure 2 is a plan view of the gas confiner assembly surrounding the substrate support of Figure 1 .

[0011] To facilitate understanding, identical reference numerals have been used, where possible, to designate identical elements that are common to the figures. It is contemplated that elements and features of one embodiment may be beneficially incorporated in other embodiments without further recitation. DETAILED DESCRIPTION

[0012] The present disclosure generally relates to a gas confiner assembly designed to decrease high deposition rates on edge regions of substrates by re-distributing gas flow. According to embodiments described herein, the gas confiner reduces the non-uniform deposition rates by confining the gas flow and changing the local gas flow distribution near the edge regions of the substrate. The material, size, shape and other features of the gas confiner assembly can be varied based on the processing requirements and associated deposition rates.

[0013] Embodiments herein are illustratively described below in reference to a PECVD system configured to process large area substrates, such as a PECVD system, available from AKT, a division of Applied Materials, Inc., Santa Clara, California. However, it should be understood that the invention has utility in other system configurations such as etch systems, other chemical vapor deposition systems and any other system in which distributing gas within a process chamber is desired, including those systems configured to process round substrates. Additionally, it is contemplated that the embodiments discussed herein are applicable to systems sold by other manufacturers.

[0014] Figure 1 is a schematic cross-section view of one embodiment of a PECVD chamber 100 for forming electronic devices, such as TFT and AMOLED. It is noted that Figure 1 is just an exemplary apparatus that may be used to electronic devices on a substrate. One suitable PECVD chamber is available from Applied Materials, Inc., located in Santa Clara, CA. It is contemplated that other deposition chambers, including those from other manufacturers, may be utilized to practice the present invention.

[0015] The chamber 100 generally includes walls 102, a bottom 104, and a gas distribution plate or diffuser 1 10, and a substrate support 130 which define a process volume 106. In one embodiment, the substrate support 130 is fabricated from aluminum. The process volume 106 is accessed through a sealable slit valve 108 formed through the walls 102 such that a substrate 140, may be transferred in and out of the chamber 100. In one embodiment, the substrate 140 is 1850 mm x 1500 mm, 700 mm x 920 mm, or 2500 mm x 2200 mm. The substrate support 130 includes a substrate receiving surface 132 for supporting the substrate 140 and a stem 134 coupled to a lift system 136 to raise and lower the substrate support 130.

[0016] A gas confiner assembly 129 is disposed around the periphery of the substrate support 130. The gas confiner assembly 129 is configured to decrease high deposition rates on edge regions of the substrate 140. In one embodiment, the gas confiner assembly 129 includes a base 131 , a cover 133, and a gas confiner 135. The base 131 is configured to support the gas confiner 135, and the cover 133 is configured to cover the substrate support 130 when the substrate 140 is disposed thereon during processing, i.e., prevent the substrate support 130 from being exposed to plasma. In one embodiment, the cover 133 overlaps the substrate 140 by 10 mm, or by 5 mm during processing temperatures, e.g., 400 degrees Celsius. Even if the substrate 140 is misaligned with the substrate support 130, the cover 133 advantageously protects the substrate support 130 from plasma. In one embodiment, the gas confiner 135 is configured to act as a barrier to gas flow to change the local gas flow distribution near the edge of the substrate 140. In one embodiment, the gas confiner 135 has a bar shape and surrounds the substrate support 130. Details of the gas confiner assembly 129 will be discussed below.

[0017] Lift pins 138 are moveably disposed through the substrate support 130 to move the substrate 140 to and from the substrate receiving surface 132 to facilitate substrate transfer. The substrate support 130 may also include heating and/or cooling elements 139 to maintain the substrate support 130 and substrate 140 positioned thereon at a desired temperature. The substrate support 130 may also include grounding straps 141 to provide RF grounding at the periphery of the substrate support 130. [0018] The diffuser 1 10 is coupled to a backing plate 1 12 at its periphery by a suspension 1 14. The diffuser 1 10 may also be coupled to the backing plate 1 12 by one or more center supports 1 16 to help prevent sag and/or control the straightness/curvature of the diffuser 1 10. A gas source 120 is coupled to the backing plate 1 12 to provide one or more gases through the backing plate 1 12 to a plurality of gas passages 1 1 1 formed in the diffuser 1 10 and to the substrate receiving surface 132. Suitable gasses may include, but are not limited to, a silicon containing gas, e.g., silane (SiH ), a nitrogen containing gas, e.g., nitrogen (N ₂ ), nitrous oxide (N ₂ O) and/or ammonia (NH ₃ ), an oxygen containing gas, e.g., oxygen (O ₂ ), and argon (Ar). A vacuum pump

109 is coupled to the chamber 100 to control the pressure within the process volume 106. An RF power source 122 is coupled to the backing plate 1 12 and/or to the diffuser 1 10 to provide RF power to the diffuser 1 10 to generate an electric field between the diffuser 1 10 and the substrate support 130 so that a plasma may be formed from the gases present between the diffuser

1 10 and the substrate support 130. Various RF frequencies may be used, such as a frequency between about 0.3 MHz and about 200 MHz. In one embodiment, the RF power source 122 provides power to the diffuser 1 10 at a frequency of 13.56 MHz.

[0019] A remote plasma source 124, such as an inductively coupled remote plasma source, may also be coupled between the gas source 120 and the backing plate 1 12. Between processing substrates, a cleaning gas may be provided to the remote plasma source 124 and excited to form a remote plasma from which dissociated cleaning gas species are generated and provided to clean chamber components. The cleaning gas may be further excited by the RF power source 122 provided to flow through the diffuser 1 10 to reduce recombination of the dissociated cleaning gas species. Suitable cleaning gases include but are not limited to NF ₃ , F ₂ , and SF ₆ .

[0020] In one embodiment, the heating and/or cooling elements 139 may be utilized to maintain the temperature of the substrate support 130 and substrate 140 thereon during deposition less than about 400 degrees Celsius or less. In one embodiment, the heating and/or cooling elements 139 may used to control the substrate temperature to less than 100 degrees Celsius, such as between 20 degrees Celsius and about 90 degrees Celsius.

[0021] The spacing during deposition between a top surface of the substrate 140 disposed on the substrate receiving surface 132 and a bottom surface 150 of the diffuser 1 10 may be between about 400 mil and about 1 ,200 mil, for example between about 400 mil and about 800 mil, for example between about 400 mil to about 600 mil, for example about 500 mil.

[0022] The chamber 100 may be used to deposit amorphous silicon (aSi), a nitride, e.g., silicon nitride (SiN _x ), and/or an oxide, e.g., silicon oxide (SiO _x ) by a PECVD process which is widely used as a passivation layer, a gate insulator film, a buffer layer or an etch stop layer in TFT and AMOLED. The uniformity (i.e., thickness) of the deposited amorphous silicon, nitride or oxide layer has a significant impact on the final device performance, such as threshold voltage and drain current uniformity. In one embodiment, a film uniformity of about 5%, or less, across the surface of the substrate and at a 10 mm EE (instead of the conventional 15 mm EE) is desired. While many strides have been made toward this goal, there are regions of the substrate 140 where this uniformity is not achieved. For example, edges of the substrate experience a higher or lower deposition rate which results in film thicknesses at these regions that is greater or less than other regions. Although not wishing to be bound by theory, the cause of higher deposition rates in the edge regions is attributed to gas flow driven processes, as opposed to plasma-driven processes. An inventive gas confiner assembly has been developed and tested to overcome these effects and minimize non- uniformities in films on the edge regions of the substrate 140.

[0023] Figure 2 is a plan view of the cover 133 of the gas confiner assembly 129 surrounding the substrate support 130 (the gas confiner base 131 and the gas confiner 135 are removed for clarity). Referring to Figures 1 and 2, the gas confiner assembly is 129 is configured to confine the gas flow and change the local distribution of the gas flow being deposited on the edge regions of the substrate 140. In one embodiment, the gas confiner assembly 129 reduces high deposition rates at the edges of the substrate 140, without affecting the large range uniformity profile of the substrate 140.

[0024] The gas confiner assembly 129 is fabricated from a non-metal or glass. For example, the gas confiner assembly 129 may be fabricated from a ceramic, such as aluminum oxide (AI ₂ O ₃ ). The base 131 is disposed on the substrate support 130, and in one embodiment, the base 131 includes one or more ceramic buttons (not shown) disposed on a side of the base 131 configured to face the top surface 132 of the substrate support 130. The ceramic buttons may reduce the thermal and mechanical contact with the substrate support 130. The gas confiner 135 is coupled to the substrate support 130 through the base 131 disposed on the substrate support 130. In one embodiment, the base 131 includes one or more locating pins for aligning with the gas confiner 135.

[0025] The cover 133 is coupled to the substrate support 130 between the base 131 and the gas confiner 135. The cover 133 is configured such that the substrate support 130 is not exposed to plasma during processing, even if the substrate 140 is misaligned on the substrate support 130. In one embodiment, the cover 133 includes one or more ceramic plates 200 joined at intersections or seams 206. The ceramic plates 200 are located on the top outer perimeter of the substrate support 130, and disposed under the outer perimeter of the substrate 140 (as shown in Figure 1 ). One or more slotted locating pins 202 and fixed screws 204 are used to join the ceramic plates 200 to each other at ends 210 of the ceramic plates 200 to form the cover 133. In one embodiment, the ends 210 of the ceramic plates 200 overlap with each other at corners of the gas confiner assembly 129, such that one end 210 of the ceramic plate 200 extends lengthwise greater than or beyond an adjacent overlapping ends' 210 width. Due to the difference in the thermal expansion of the substrate support 130 material, e.g., aluminum, and the thermal expansion of the ceramic plates 200, the slotted locating pins 202 and fixed screws 204 prevent the cover ceramic plates 200 from opening at the seams 206. A distance between the center of the locating pins 202 in the ceramic plates 200, and the center of the fixed screws 204 in the ceramic plates 200 is defined as "X". The distance X may be selected to allow the substrate support 130 to thermally expand more than the ceramic plates 200, while still preventing the ceramic plates 200 from forming substantial gaps at the seams 206. This advantageously prevents the substrate support 130 from being exposed to plasma even while thermally expanding at processing temperatures, e.g., 400 degrees Celsius.

[0026] Referring back to Figure 1 , the gas confiner 135 has a thickness between about 1 mm to about 9 mm, for example, about 3 mm or about 6 mm, and has a width between about 25 mm to about 75 mm, for example about 50 mm. A gap 137 may be formed between the edge of the substrate 140 and the gas confiner 135. In one embodiment, the gap 137 is between about 1 mm to about 5 mm, for example about 2 mm (or about 5 mm to about 6 mm at 400 degrees Celsius). As one skilled in the art would appreciate, the above recited materials and measurements of the gas confiner assembly 129, and more specifically, the gas confiner 135 and the gap 137 measurements may be selected based on the gasses being flowed and the desired compensated gas flow rates.

[0027] Advantageously, embodiments of the gas confiner assembly 129 as described herein decrease the gas flow and compensate for high deposition rates on edge regions of substrates. The gas confiner assembly 129 changes the local gas flow below the gas confiner 135 by pushing the gas back below a height of the gas confiner 135 and moving the gas upwards. Therefore, the local gas distribution is decreased and consecutively, the local plasma density and deposition rates are also decreased. Thereby, overall film thickness uniformity, and in particular at the edge regions of 50 mm or less EE, is improved. [0028] While the present disclosure is described in relation to a gas confiner assembly, it is contemplated that other barrier configurations are extendable to processing chamber hardware. For example, increasing or decreasing the thickness of shadow frames or introducing a thickness gradient to an existing shadow frame to compensate for the effects from using a shadow frame may be employed.

[0029] The overall uniformity of substrates similar to the substrate 140 were tested and the inventive gas confiner assembly showed the following beneficial results: (1 ) for amorphous silicon deposition, a gas confiner having a thickness of about 6 mm improved the normalized deposition rate (DR) range from 6.8% to 4.5%, in the range of 10 mm to 50 mm at the edge, with a potential uniformity of 2.3% and overall uniformity was improved from 6.0% to 3.8% at 10 mm EE; (2) for high DR silicon nitride, a gas confiner having a thickness of about 6 mm improved the normalized DR range from 9.5% to 4.1 %, with a potential uniformity of 2.1 % and overall uniformity was improved from 4.3% to 3.6% at 10 mm EE; (3) for high DR silicon oxide, a gas confiner having a thickness of about 6 mm improved the normalized DR range from 8.5% to 2.5%, with a potential uniformity of 1 .3% and overall uniformity was improved from 6.2% to 4.8%; (4) for low DR silicon nitride, a gas confiner having a thickness of about 3 mm improved the normalized DR range from 14.4% to 9.7%, with a potential uniformity of 4.8% and overall uniformity was improved from 12.9% to 7.7%; and (5) for low DR silicon oxide, a gas confiner having a thickness of about 6 mm improved the normalized DR range from 6.3% to 1 .1 %, with a potential uniformity of 0.6% and overall uniformity was improved from 7.4% to 6.8%;

[0030] While the foregoing is directed to embodiments of the present disclosure, other and further embodiments of the disclosure may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow.