Corner spoiler for improving profile uniformity

The present disclosure relates to a corner spoiler designed to decrease high deposition rates on corner regions of substrates by changing the gas flow. In one embodiment, a corner spoiler for a processing chamber includes an L-shaped body fabricated from a dielectric material, wherein the L-shaped body is configured to change plasma distribution at a corner of a substrate in the processing chamber. The L-shaped body includes a first and second leg, wherein the first and second legs meet at an inside corner of the L-shaped body. The length of the first or second leg is twice the distance defined between the first or second leg and the inside corner. In another embodiment, a shadow frame for a depositing chamber includes a rectangular shaped body having a rectangular opening therethrough, and one or more corner spoilers coupled to the rectangular shaped body at corners of the rectangular shaped body.

BACKGROUND OF THE DISCLOSURE

Field

Embodiments of the disclosure generally relate to a corner spoiler for improving profile uniformity and method for distributing gas in a processing chamber.

Description of the Background Art

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 (SiH4) and nitrogen (N2), 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 (SiNx), on a surface of the substrate that is positioned on a temperature controlled substrate support. The silicon nitride layer forms passivation layers, gate insulators, and/or buffer 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.

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. Further, as the substrates are rectangular, edges of the substrate, such as sides and corners thereof, experience conditions that may be different than the conditions experienced at other portions of the substrate. For example, centrally located plasma increases the deposition rate at the corners of the substrate, resulting in “corner peaks”. The corner peaks adversely affect processing parameters, such as film thickness, and increase the edge exclusion range. Overall film thickness affects the drain current and the threshold voltage of the flat panel.

Conventional techniques for controlling the deposition rate include modulating the flow of the gas through the gas distribution plate and changing the material of chamber components to affect the impedance of the plasma distribution. However, conventional techniques are often costly and only capable of changing the film uniformity profile at a larger range, e.g., greater than 300 mm from the corner of the substrate.

Therefore, there is a need for improving the deposition rate and film thickness uniformity in substrates, particularly at the corner regions of the substrate.

SUMMARY

The present disclosure generally relates to a corner spoiler designed to decrease high deposition rates on corner regions and/or edge regions of substrates by changing the gas flow.

In one embodiment, a corner spoiler for a processing chamber is provided. The corner spoiler includes an L-shaped body fabricated from a dielectric material. The L-shaped body is configured to change plasma distribution at a corner of a substrate in the processing chamber. The L-shaped body includes a first and second leg, wherein the first and second legs meet an inside corner of the L-shaped body. The length of the first or second leg is twice the distance defined between the first or second leg and the inside corner.

In another embodiment, a shadow frame for a processing chamber is provided. The shadow frame includes a rectangular shaped body having a rectangular opening therethrough. The shadow frame also includes one or more corner spoilers coupled to the rectangular shaped body at corners of the rectangular shaped body. The one or more corner spoilers include an L-shaped body fabricated from a dielectric material. The L-shaped body is configured to change plasma distribution at a corner of a substrate in the processing chamber.

In yet another embodiment, a method for distributing gas in a processing chamber is provided. The method includes using a spoiler to reduce plasma distribution at a corner of a substrate in the processing chamber. The method also includes reducing an electric field disposed below the spoiler.

DETAILED DESCRIPTION

The present disclosure generally relates to a corner spoiler designed to decrease high deposition rates on corner regions and/or edge regions of substrates by changing the gas flow. According to embodiments described herein, the corner spoiler reduces the non-uniform depositing rates by adjusting gas flow and reducing the electric field formed below the corner spoiler. The material, size, shape and other features of the corner spoiler can be varied based on the processing requirements and associated deposition rates.

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, Calif. However, it should be understood that the disclosure 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.

FIG. 1is a schematic cross-section view of one embodiment of a PECVD chamber100for forming electronic devices, such as TFT and AMOLED. It is noted thatFIG. 1is 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, Calif. It is contemplated that other deposition chambers, including those from other manufacturers, may be utilized to practice the present disclosure.

The chamber100generally includes walls102, a bottom104, and a gas distribution plate or diffuser110, and substrate support130which define a process volume106. The process volume106is accessed through a sealable slit valve108formed through the walls102such that a substrate105, may be transferred in and out of the chamber100. In one embodiment, the substrate105is 1850 mm×1500 mm. The substrate support130includes a substrate receiving surface132for supporting the substrate105and a stem134coupled to a lift system136to raise and lower the substrate support130. A shadow frame133may be placed over periphery of the substrate105during processing. The shadow frame133is configured to prevent or reduce unwanted deposition from occurring on surfaces of the substrate support130that are not covered by the substrate105during processing. In one embodiment, the shadow frame133is generally rectangular and has rectangular opening therethrough for circumscribing the substrate105. Lift pins138are moveably disposed through the substrate support130to move the substrate105to and from the substrate receiving surface132to facilitate substrate transfer. The substrate support130may also include heating and/or cooling elements139to maintain the substrate support130and substrate105positioned thereon at a desired temperature. The substrate support130may also include grounding straps131to provide RF grounding at the periphery of the substrate support130.

The diffuser110is coupled to a backing plate112at its periphery by a suspension114. The diffuser110may also be coupled to the backing plate112by one or more center supports116to help prevent sag and/or control the straightness/curvature of the diffuser110. A gas source120is coupled to the backing plate112to provide one or more gases through the backing plate112to a plurality of gas passages111formed in the diffuser110and to the substrate receiving surface132. Suitable gases may include, but are not limited to, a silicon containing gas, e.g., silane (SiH4), and a nitrogen containing gas, e.g., nitrogen (N2) and/or ammonia (NH3). A vacuum pump109is coupled to the chamber100to control the pressure within the process volume106. An RF power source122is coupled to the backing plate112and/or to the diffuser110to provide RF power to the diffuser110to generate an electric field between the diffuser110and the substrate support130so that a plasma may be formed from the gases present between the diffuser110and the substrate support130. 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 source122provides power to the diffuser110at a frequency of 13.56 MHz.

A remote plasma source124, such as an inductively coupled remote plasma source, may also be coupled between the gas source120and the backing plate112. Between processing substrates, a cleaning gas may be provided to the remote plasma source124and 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 source122provided to flow through the diffuser110to reduce recombination of the dissociated cleaning gas species. Suitable cleaning gases include but are not limited to NF3, F2, and SF6.

In one embodiment, the heating and/or cooling elements139may be utilized to maintain the temperature of the substrate support130and substrate105thereon during deposition less than about 400 degrees Celsius or less. In one embodiment, the heating and/or cooling elements139may used to control the substrate temperature to less than 100 degrees Celsius, such as between 20 degrees Celsius and about 90 degrees Celsius.

The spacing during deposition between a top surface of the substrate105disposed on the substrate receiving surface132and a bottom surface140of the diffuser110may be between about 400 mm and about 1,200 mm, for example between about 400 mm and about 800 mm, for example between about 400 mm to about 600 mm, for example about 500 mm. In one embodiment, the spacing between a top surface of the shadow frame133and the diffuser110is between about 275 mm and about 475 mm, for example about 375 mm. In one embodiment, the bottom surface140of the diffuser110may include a concave curvature wherein the center region is thinner than a peripheral region thereof, as shown in the cross-sectional view ofFIG. 1.

The chamber100may be used to deposit a nitride, such as silicon nitride (SiNx), using silane (SiH4) gas and one or more nitrogen containing gases, e.g., nitrogen (N2) and ammonia (NH3), by a PECVD process which is widely used as a passivation layer, a gate insulator film, or a buffer layer in TFT and AMOLED. The uniformity (i.e., thickness) of the silicon nitride film 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, as well as minimal edge exclusion, is desired. While many strides have been made toward this goal, there are regions of the substrate105where this uniformity is not achieved. For example, edges of the substrate, such as corner regions and sides of the substrate, experience a higher deposition rate which results in film thicknesses at these regions that is greater than other regions. Although not wishing to be bound by theory, the cause of the higher deposition rate in the edge regions is attributed to electromagnetic field variations and/or gas distribution adjacent these areas. An inventive spoiler has been developed and tested to overcome these effects and minimize non-uniformities in films formed on the substrate105.

FIG. 2is a plan view of one embodiment of one or more corner spoilers200coupled to the top surface of the shadow frame133. The corner spoiler200is configured to locally change the gas flow being deposited on the substrate105and “spoil” the non-uniform plasma distribution at the corner regions of the substrate105. The corner spoiler200reduces high deposition rates, i.e., corner peaks, at the corner of the substrate105, without affecting the large range uniformity profile of the substrate105.

In the embodiment shown inFIG. 2, the substrate105and the shadow frame133have a rectangular shape, and the corner spoiler200has an L-shaped body. It is contemplated, however, that the corner spoiler200may have alternative shapes to account for different shaped substrates and different processing requirements. In one embodiment, the corner spoiler200is fabricated from a non-metal or glass material. For example, the corner spoiler200is fabricated from a dielectric material, such as aluminum oxide (Al2O3) or Teflon® (polytetrafluoroethylene). In another embodiment, the corner spoiler200is fabricated from the same material as the shadow frame133, e.g., aluminum oxide. As one skilled in the art would appreciate, the material for the corner spoiler200may be selected based on the processing requirements.

FIG. 3is an exploded view of one embodiment of one or more corner spoilers200coupled to the top surface of the shadow frame133. The corner spoilers200may be coupled to the shadow frame133. The shadow frame is coupled to a peripheral edge of the substrate105. The substrate105is disposed on a substrate receiving surface132, which is disposed on a substrate support130. The substrate support130is supported by a stem134which may be coupled to a lift system136.

In one embodiment, the corner spoiler200may be coupled to the surface of the shadow frame133between an outside corner203and an inside corner202of the shadow frame133by one or more screws, Teflon® tape, or any other suitable means for coupling the corner spoiler200. Advantageously, the corner spoiler200may be retrofitted to existing PECVD hardware, and removed with ease for maintenance or replacement. In another embodiment, the shadow frame133is die-casted or molded to include the corner spoilers200as a unitary structure, integrated with the shadow frame133body.

FIG. 4is a close-up view of one embodiment of a corner spoiler200. The L-shaped corner spoiler200includes a first leg204and a second leg206. The first and second legs204,206meet at an inside corner208to form an angle, which may be a 90 degree angle. In one embodiment, a horizontal or vertical distance (i.e., width) between a first end209of the legs204,206and the inside corner208is defined as “A”. A length or height of the legs204,206is defined as “B”, which is about two times the distance A. In one embodiment, A is between about 35 mm to about 55 mm, for example 45 mm, and B is between about 70 mm to about 110 mm, for example 90 mm. In one embodiment, the uniform thickness of the corner spoiler200is between about 3 mm to about 9 mm, for example about 6 mm. As one skilled in the art would appreciate, the above recited measurements of the corner spoiler200may also be selected based on the distance between the shadow frame133having the corner spoiler200thereon, and the diffuser110. In one embodiment, the corner spoiler200is between about 0 mm and about 12 mm above the substrate support130, for example about 3 mm or less, or about 6 mm, or about 9 mm.

In one embodiment, a distance between an inside210of the first and second legs204,206and an inside edge212of the shadow frame133is defined as “X”. As one skilled in the art would appreciate, the distance X governs: (1) how much the local gas flow changes before it is deposited on the substrate105; and (2) how much the plasma distribution is “spoiled” at the corner regions of the substrate105. In one embodiment, the distance X is selected based on the material of the film being formed on the substrate105. For example, where nitrides are being formed on the substrate105, X is between about 2 mm to about 15 mm, for example 10 mm. As such, the corner spoiler200is not limited to having an L-shaped body, rather, the corner spoiler200may have any suitable shape for forming the distance X between the shadow frame133and the inside surface of the corner spoiler200.

Advantageously, embodiments of the corner spoiler200as described herein decrease the gas flow and compensate for high deposition rates on corner regions and/or edge regions of substrates. The corner spoiler200changes the local impedance of the plasma simultaneously brings down the strength of the plasma generated electric field by pushing it below a top surface (i.e., the height) of the corner spoiler200disposed on the shadow frame133. Thereby, overall film thickness uniformity, and in particular at the corner regions of 30 mm or less edge exclusion, is improved.

Corner regions of a substrate similar to the substrate105were tested and the inventive corner spoiler200showed about a 3% (absolute value) reduction in the deposition rate, while maintaining the integrity of the film at the corner of the substrate. In addition, as a result, the diagonal uniformity over the whole substrate was improved from 5.6% at 15 mm edge exclusion to 3.5% at 15 mm edge exclusion, and from 4.7% at 20 mm edge exclusion to 3.4% at 20 mm edge exclusion. Furthermore, the average electric field in the space below the height of the corner spoiler decreased by about 50% in the range of 50 mm to the corner spoiler.