JP2009065153A - Cathode liner adapted for injecting gas at wafer edge in plasma reactor chamber - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a plasma reactor chamber adapted to enable an uniform distribution of etching rate over an entire wafer in the plasma reactor chamber. <P>SOLUTION: The plasma reactor chamber is provided with: a chamber housing including a sidewall 108 and a ceiling 110; a workpiece support 125; a cathode liner 200 which surrounds the workpiece support 125 having a top surface and a base with a plurality of internal gas-flow channels extending from the base to the top surface; a gas supply plenum of the base joined to each of the internal gas-flow channels; a process ring 205 laid on the top surface of the cathode liner 200 having an inner edge end adjoining the outer edge of the wafer support surface; a gas injection device in the process ring 205 having a gas injection path, routed through the inner edge end facing the workpiece supporting face, and joined to the plurality of internal gas-flow channels; and a gas supplying system joined to the gas supply plenum. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

Cross-reference of related applications

  This application is filed by Dan Katz et al., US patent application Ser. No. 11 / 899,614 filed on Sep. 5, 2007 under the name “Cathodeliner injecting gas at wafer edge in plasma reactor chamber”. And U.S. patent application Ser. No. 11/1993, filed by Dan Katz et al. On September 5, 2007 under the title "Method of processing workpieces by independently injecting process gas at wafer edge in plasma reactor". Claim priority based on No. 899613.

  The present disclosure relates to a plasma reactor chamber for processing a workpiece such as a semiconductor wafer to produce an integrated circuit. Specifically, the present disclosure relates to injecting process gases independently at the ceiling and wafer edge in such a reactor chamber.

background

  In a plasma reactor chamber for etching silicon or polysilicon thin films on a semiconductor wafer, a uniform distribution of etching rate across the wafer is required. The lack of uniformity in the etch rate distribution across the wafer is indicated by CD (Critical dimension) non-uniformity. CD can be a typical line width in a thin film circuit pattern. CD is small in the wafer surface region where the etching rate is high and large in the region where the etching rate is slow.

  In silicon etch chambers where process gas is injected from the ceiling, it has been found that the CD at the wafer edge is very small compared to other areas of the wafer surface. The effect of reducing the CD typically remains in the range of 1% outside or the outer periphery of the wafer surface. This problem could not be solved by conventional techniques. Specifically, the etching uniformity is to divide the gas distribution into independent inner and outer gas injection areas at the ceiling, and adjust the gas flow rate to the inner and outer areas to maximize the uniformity. Can be improved. However, even if the flow rates in the inner and outer gas injection zones are adjusted, the problem that the CD is reduced by 1% outside the wafer surface cannot be solved. Specifically, the CD is fairly uniform across the wafer by adjusting the flow rates of the inner and outer gas injection zones at the ceiling, with the exception of the wafer edge region that is about 1% wide of the wafer diameter. .

  Therefore, it is necessary to independently control the CD at the wafer edge, which is the outer 1%, without compromising the uniformity of etch rate distribution achieved in other areas of the wafer.

Overview

  A workpiece support is installed to support a workpiece such as a semiconductor wafer during processing in the plasma reactor. The workpiece support includes a pedestal having a workpiece support surface. A processing ring lies on the outer periphery of the pedestal. The processing ring is adjacent to the outer peripheral boundary of the workpiece support surface. The wafer edge gas injection section is formed by a processing ring and typically has a gas injection opening facing the workpiece position on the workpiece support surface. The processing gas supply source is connected to the wafer edge gas injection section.

  In one embodiment, the wafer edge gas inlet comprises an annular slit opening. In another embodiment, the liner has a top surface that wraps around the sides of the pedestal and lies under the processing ring. A plurality of axial channels within the liner extend through the liner to its top surface. An annular feed channel is defined between the processing ring and the liner. Each of the plurality of axial channels is connected to an annular supply channel, and the wafer edge gas inlet is connected to the annular supply channel.

  In yet another embodiment, the liner further comprises a bottom surface and a base portion lying below the bottom surface, the base portion containing an annular plenum. The plurality of axial channels are connected to the annular plenum.

Detailed description

  Referring to FIG. 1, the plasma reactor includes a cylindrical side wall portion 108 and a vacuum chamber 100 surrounded by a ceiling portion 110 and a floor portion 115. Wafer support 125 supports semiconductor wafer 130 during wafer processing. Wafer support 125 includes a cathode electrode 135 that also functions as an electrostatic chuck (ESC) electrode. The support 125 includes an insulating layer 137 that separates the electrode 135 from the wafer 130, and an insulating layer 139 that separates the electrode 135 from the underlying components of the wafer support 125. The upper insulating layer 137 has an upper wafer support surface 137a. The reactor further includes an inductively coupled source power applicator or coil antenna 140 lying on the ceiling 110. The RF plasma source power generator 145 is connected to the coil antenna 140 via the RF impedance matching device 150. The RF plasma bias power generator 155 is connected to the cathode electrode 135 through the RF impedance matching device 160. A DC chuck voltage supply source 161 is connected to the ESC electrode 135 via the control switch 162. The insulating capacitor 163 blocks the DC current from the supply source 161 from the RF bias power generator 155.

The processing gas is sent into the chamber by the gas distribution injection unit 165 of the ceiling part 110. The injection part 165 includes an inner area injection part 170 and an outer area injection part 175. Each of the inner region injection part 170 and the outer region injection part 175 may be implemented by a plurality of injection holes or slits. The inner zone injector 170 is oriented to direct the process gas toward the central region of the chamber. The outer region injection part 175 is oriented to direct the process gas towards the peripheral region of the chamber. The inner zone injection part 170 is connected to the gas distribution panel 185 via a valve 180. The outer zone injection part 175 is connected to the gas distribution panel 185 via a valve 190. Different process gas supply sources 101, 102, 103, 104, 105 supply different process gases to the gas distribution panel 185. As illustrated in FIG. 1, in one embodiment, each gas supply may be connected separately to each of the inner and outer valves 180, 190 via independent valves 195. In the embodiment of FIG. 1, the gas supply source 101 contains a fluorinated hydrocarbon gas such as CH ₂ F ₂ or CHF ₃ , the gas supply source 102 contains a hydrogen bromide gas, and the gas supply source 103 Contains chlorine gas, the gas supply source 104 contains argon gas, and the gas supply source 105 contains oxygen gas. The gases referred to in this application are examples and any suitable process gas may be used.

  The wafer support 125 is surrounded by a ring-shaped cathode liner 200. The cathode liner 200 can be formed from a material suitable for processing, such as quartz. A processing ring 205 covers the upper portion of the cathode liner 200 and covers the outer periphery of the wafer support surface 137a. The processing ring 205 is made of a material suitable for processing such as quartz. Although wafer support 125 may contain materials such as metals that are not compatible with plasma processing, liner 200 and ring 205 isolate wafer support 125 from the plasma. A radially inner edge 205a of the processing ring 205 is adjacent to the wafer 130 edge. In one embodiment, the processing ring improves the RF field distribution.

In the silicon or polysilicon etching process, a silicon material is etched using a silicon etching gas such as HBr or Cl ₂ , and an etching profile is improved using a polymerized species such as CH ₂ F ₂ or CHF ₃ . The polymer is deposited on the sidewalls of the deep aspect ratio opening during the polymer deposition reaction that competes with the etching reaction.

  The reactor of FIG. 1 may suffer from inferior CD control at the wafer edge. Typically, CD is the width of the selected line in the circuit pattern. The CD tends to be smaller at the edge than at other locations on the wafer 130. The problem of decreasing CD tends to occur in the annular region at the edge of the wafer 130 that is about 1% wide (extending inwardly from the wafer edge) of the wafer diameter (this narrow annulus). The area is hereinafter referred to as the wafer edge area 130 shown in FIG. 5 and will be described later in this specification). In the remainder of the wafer 130, such problems are minimized by adjusting the valves 180 and 190 to optimize the ratio of process gas flow to the inner and outer area ceiling gas inlets 170,175. Suppressed or prevented. However, the problem that the CD control in the wafer edge region 130a is poor is not solved even by optimal adjustment in this way. A small CD at the wafer edge region 130a indicates a higher etch rate at the wafer edge region than at other sites.

The inventor has discovered that the gas flow rate at the wafer edge region 130a is extremely slower than the gas flow rate at most other locations on the wafer. For example, in certain applications, the gas flow rate at the majority of the wafer surface is about 10 to 20 m / sec, while the gas flow at the wafer edge region is close to zero. If the gas flow in the wafer edge region is thus stagnant, the gas residence time in the wafer edge region becomes extremely long, and the dissociation rate of the processing gas species correspondingly increases. Such a high dissociation rate can increase the number of highly reactive species in the wafer edge region. Such highly reactive species may include radicals or neutral species that (a) etch extremely fast or (b) inhibit polymer deposition. The highly reactive etching species generated by such dissociation may include, for example, atomic HBr and / or atomic Cl ₂ . As a result, the etching rate is increased and the CD is correspondingly reduced.

  In one embodiment, a new gas is injected at the wafer edge to address non-uniform etch rates at the wafer edge. This new gas is an inert gas such as argon. In one embodiment, the new gas injection increases the gas flow rate at the wafer edge region and reduces the process gas residence time at the wafer edge region. Shortening the residence time reduces the number of highly reactive species such as radicals or neutral species in the wafer edge region. The flow rate or flow rate when injecting a new gas at the wafer edge is low enough to avoid affecting the etch rate at sites other than the narrow wafer edge area. Typically, the wafer edge area is about 3 mm wide.

In one embodiment, polymerization gas is injected at the wafer edge to address non-uniform etch rates at the wafer edge. The polymerization gas is, for example, CH ₂ F ₂ or CHF ₃ . The addition of polymerized species increases the polymer deposition rate in the wafer edge region and decreases the etch rate. The rate or flow rate at which the polymerization seed gas is injected at the wafer edge is low enough to avoid affecting the etch rate at sites other than the narrow wafer edge region. Typically, the wafer edge area is about 3 mm wide.

  In one embodiment, the processing ring 205 is divided into an upper processing ring 210 and a lower processing ring 212 with a narrow circular slit 220 facing (substantially contacting) the edge of the wafer 130 between the upper and lower rings. Is forming. The circular slit 220 is separated from the wafer edge by a very short distance in the range of 0.6 mm to 3 mm, for example about 1% of the wafer diameter. A desired gas (such as an inert gas or a polymerization seed gas) is supplied and ejected directly from the circular slit 220 inward in the radial direction and to the edge of the wafer. This new gas or polymerized seed gas can be supplied from the gas distribution panel 185.

  In one embodiment, an annular gas plenum 225 is provided at the bottom of the cathode liner 200. Cathode gas flow control valve 227 controls gas flow from gas distribution panel 185 to plenum 225 through conduit 229. Gas is fed from the plenum 225 to the circular slit 220 at the wafer edge by a vertical channel 240 inside the cathode liner 200.

  FIG. 2 illustrates an exemplary internal structure of the cathode liner 200. The cathode liner 200 is described as being formed of an insulator such as quartz when referring to FIG. In the embodiment of FIG. 2, the cathode liner 200 is formed from metal, and a quartz liner 126 separates the metal cathode liner 200 from the wafer support 125 as illustrated in FIG. The cathode liner 200 includes a cylindrical wall 201 having an annular upper surface 201a. An annular base portion 215 supports the cylindrical wall portion 201. A stepped portion 235 extends radially outward from the base 215 and accommodates the gas supply port 230 therein. The plenum 225 shown in FIG. 1 is formed in the cathode ring annular base 215 of FIG. 2 as depicted in the cross-sectional view of FIG. The internal channel 232 extends radially through the step 235 and has one end connected to the gas supply port 230 and the opposite end connected to the plenum 225 as depicted in the cross-sectional view of FIG. Yes. As shown in FIG. 2, the vertical flow paths 240 extend in the axial direction in the cylindrical wall portion 201 and are arranged at intervals on an azimuth angle along the periphery of the cylindrical wall portion 201. The bottom end of each vertical channel 240 is connected to the plenum 225, and the upper end of each vertical channel 240 is opened at the annular upper surface 201 a of the cylindrical wall 201. In one embodiment, the thickness of the cylindrical wall 201 is about 0.25 inches, and each vertical channel 240 is a 0.05 inch hole extending axially through the cylindrical wall 201.

  In the embodiment of FIG. 1, the cylindrical wall 201 supports the lower processing ring 212 and the upper processing ring 210 is supported on the lower processing ring 215.

  As shown in FIG. 5, an internal quartz liner 126 surrounds a workpiece support 125 and is surrounded by a cylindrical wall 201 of the cathode liner. As illustrated in FIG. 5, the inner liner 126 supports the lower processing ring 212, and the cylindrical wall 201 of the cathode liner supports the upper processing ring 210. The annular gas supply chamber 260 is bounded by the upper surface 201 a of the cylindrical wall portion, the upper processing ring, and the lower processing ring 212. The annular supply path 262 is formed as a gap between the upper and lower processing rings 210, 212. The outer annular protrusion 210 a on the bottom surface of the upper processing ring 210 faces the outer annular recess 212 a on the upper surface of the lower processing ring 212. An inner annular recess 210 b is provided on the bottom surface of the upper processing ring 210. The inner annular recess 210 b faces the raised stepped portion 212 b of the lower processing ring 212 and forms a gas injection slit 220. The meandering supply path 262 is formed by the protrusion 210a, the recess 212a, the recess 212b, and the step 212b as shown in FIG. The gas supplied through valve 227 of FIG. 1 flows to the cathode or wafer support 125, enters the supply port 230 shown in FIG. 4, and then flows through the internal channel 232 to the plenum 225. From the plenum 225, gas flows up the vertical channel 240 into the supply chamber 260 of FIG. 5 and then flows through the supply path 262 into the injection slit 220.

  As shown in the side view of FIG. 6, the end of the injection slit 220, that is, the discharge port, is at a very short distance D from the edge of the wafer 130, and D is about 0.6 mm to 3 mm. The short distance makes the gas flow effect from the injection slit 220 very localized and does not affect the process beyond the 3 mm wide wafer edge region 130a. Such localization can be achieved by establishing a very low gas flow rate in the injection slit 220. For example, the gas flow rate through valve 227 (to wafer edge injection slit 220) is 1% to 10% of the gas flow rate through valves 180, 190. In this manner, the gas flowing out from the injection slit 220 affects the processing (for example, the etching rate) only in the narrow wafer edge region 130a, and does not affect the processing in the remaining portion of the wafer 130.

In FIG. 7, a polymerization gas such as CH ₂ F ₂ or CHF ₃ is introduced through the wafer edge injection slit 220 in FIGS. 1 to 6, and an etching gas such as HBr and Cl _{2 is applied} to the ceiling injection parts 170 and 175. FIG. 6 is a graph showing the density of SiCl ₂ at the wafer surface as a function of radial position in a process introduced through FIG. The density of SiCl ₂ is an indicator of the degree of polymerization in such treatment. The graph of FIG. 7 shows that in the absence of gas flow from the injection slit 220, polymerization is relatively suppressed at the wafer edge (curve A). When the polymerization gas is supplied through the injection slit 220, the degree of polymerization at the edge of the wafer significantly increases (curve B). The polymerization gas flow through the wafer edge injection slit 220 is limited to a low flow rate. This limitation of the flow rate through the injection slit keeps the increase in the degree of polymerization within the wafer edge area, which is 1% outside the wafer diameter. In one embodiment, the etch process gas flow through the ceiling injection nozzles 170, 175 was about 150 sccm and the polymerization gas flow through the wafer edge injection slot 220 was about 5 sccm.

FIG. 8 illustrates an exemplary method of operating the plasma reactor of FIGS. 1-6 to raise the CD at the wafer edge region. Silicon etchant gases such as HBr and Cl ₂ are injected through the inner zone ceiling injection section 170 at a first gas flow rate (block 400 of FIG. 8) and through the outer zone ceiling injection section 175 at a second flow rate (FIG. 8 block 405). The gas flow through the inner zone and outer zone ceiling implants 170, 175 is sufficient to obtain the desired average etch rate across the wafer surface. By independently adjusting the flow rate of the gas flowing through the inner region and outer region ceiling injection portions 170 and 175 until the etching rate distribution uniformity is optimized, the etching rate distribution is adjusted to 1% of the outer periphery of the wafer surface. Except for the overall adjustment (block 410 in FIG. 8). This adjustment generally results in an etch rate that is too high (ie, the CD is too low) in the wafer edge area, ie 1% outside the wafer surface. By shortening the gas residence time in the wafer edge region and reducing dissociation in the wafer edge region, the etching rate in the wafer edge region (only) is corrected downward (that is, the CD is corrected upward). In one embodiment, shortening the gas residence time in the wafer edge region may cause a suitable gas, such as an inert gas or oxygen, to flow through the wafer edge injection slit 220 to disturb the gas flow at the wafer edge. (Block 415 in FIG. 8). Increasing the gas flow or shortening the gas residence time stays in the wafer edge region by limiting the gas flow rate through the wafer edge injection slit low. This low flow rate is selected to provide the most uniform CD distribution, and the flow rate may be affected by the choice of process gas species, for example, in the range of 1-20 sccm.

FIG. 9 illustrates another exemplary method for operating the plasma reactor of FIGS. 1-6 to raise the CD at the wafer edge region. Silicon etchant gases such as HBr and Cl ₂ are injected through the inner ceiling injection section 170 at a first gas flow rate (block 420 in FIG. 9) and through the outer ceiling injection section 175 at a second flow rate (FIG. 9 block 425). The gas flow through the inner and outer area ceiling implants 170, 175 is sufficient to obtain the desired average etch rate across the wafer surface. By independently adjusting the flow rate of the gas passing through the inner zone and the outer zone ceiling injection portions 170 and 175 until the etching rate distribution uniformity is optimized, the etching rate distribution is adjusted to 1% on the outer periphery of the wafer surface. All the adjustments are made except for (block 430 in FIG. 9). This adjustment generally results in an etch rate that is too high (ie, the CD is too low) in the wafer edge area, ie 1% outside the wafer surface. By increasing the degree of polymerization in the wafer edge region (only) and decreasing the etching rate in the wafer edge region, the etching rate in the wafer edge region is corrected downward (that is, the CD is corrected upward). In one embodiment, increasing the degree of polymerization in the wafer edge region is performed by flowing a polymerization gas, such as CH ₂ F ₂ or CHF ₃ , through the wafer edge injection slit 220 (block 435 in FIG. 9). As a result, CD increases with increasing polymer deposition rate. This increase in the degree of polymerization remains in the wafer edge region by limiting the gas flow rate through the wafer edge injection slit to be low. This low flow rate is selected to provide the most uniform CD distribution, and the flow rate may be affected by the choice of process gas species, for example in the range of 1-20 sccm.

  8 or 9, further optimization is achieved by adjusting the gas flow rate through the ceiling implants 170, 175 and / or adjusting the gas flow rate through the wafer edge slit 220. Is possible. For example, the etchant gas flow through the ceiling injection portions 170 and 175 is reduced, and the amount of inert gas or polymerization gas flow through the wafer edge slit 220 is increased to further increase the CD at the wafer edge region. Let However, the flow rate through the wafer edge slit is low enough to keep the effect within the wafer edge area. The flow rate of the etchant gas flowing through the ceiling injection portions 170 and 175 may be lowered as desired (for example, to zero). Conversely, even if the etchant gas flow flowing through the ceiling injection portions 170 and 175 is raised and the inert or polymerization gas flow flowing through the wafer edge slit 220 is lowered, the CD in the wafer edge region can be lowered. Good.

  Although the present invention has been described with reference to an embodiment in which a selected gas is injected in contact with the wafer edge through a continuous slit-like implant, the wafer edge implant has multiple gas inlets on the wafer. Other forms arranged or connected around the edge may be used.

  While the above is directed to embodiments of the invention, other and further embodiments of the invention may be made without departing from the basic scope thereof, which scope is defined by the claims. It is done.

In order that the foregoing embodiments of the present invention may be obtained and become more fully understood, a more particular description of the invention summarized above will be made with reference to the embodiments, which are set forth in the accompanying drawings. . It should be noted, however, that the accompanying drawings are merely illustrative of exemplary embodiments of the invention and are not to be construed as limiting the scope of the invention as the invention may include other equally effective embodiments. Should.
It is a figure which shows the plasma reactor by one Embodiment. It is a figure which shows the internal structural element of the cathode liner of the reactor of FIG. FIG. 3 is a cross-sectional view taken along line 3-3 in FIG. FIG. 4 is a cross-sectional view taken along line 4-4 of FIG. 2 is a detailed view of a portion of a treatment ring and cathode liner according to one embodiment. FIG. 6 is a side view corresponding to FIG. 5. ₂ is a graph showing the radial distribution of SiCl ₂ in the reactor of FIG. 1 with and without gas flow through the wafer edge injection slot. FIG. 3 illustrates a method according to one embodiment. FIG. 6 illustrates a method according to another embodiment.

  For the sake of smooth understanding, the same reference numerals are used for the same elements in the drawings as much as possible. The drawing of the drawing is a schematic and is not true to scale.

Claims (15)

A plasma reactor for processing a workpiece,
A chamber housing including a side wall portion and a ceiling portion;
A workpiece support in the chamber having a workpiece support surface facing the ceiling; and
A cathode liner surrounding the workpiece support, having a top surface and a base portion, and having a plurality of internal gas flow channels extending from the base portion to the top surface;
A gas supply plenum of the base connected to each of the internal gas flow channels;
A processing ring lying on the top surface of the cathode liner and having an inner edge adjacent to an outer edge of the wafer support surface;
A gas injection section in the processing ring having a gas injection path passing through the inner edge and facing the workpiece support surface and connected to the plurality of internal gas flow channels;
A reactor including a gas supply system coupled to the gas supply plenum.   The reactor of claim 1, wherein the gas injection path through the inner edge includes a continuous slit opening facing the workpiece support surface.   The reactor according to claim 1, wherein the gas injection path passing through the inner edge includes a plurality of gas injection ports.   The reactor according to claim 1, wherein the gas injection part includes a gap in the processing ring that divides the processing ring into an upper processing ring and a lower processing ring.   And further comprising an internal supply channel bounded by the processing ring and the cathode liner, wherein the plurality of internal gas flow channels are connected to the supply channel at the top surface, and the supply channel is connected to the gap of the processing ring. The reactor according to claim 4.   The reactor of claim 1, wherein the inner edge is spaced from the outer periphery of the workpiece support surface by a distance less than about 1% of the diameter of the workpiece support surface.   A processing gas diffusion unit connected to the gas supply system is further included in the ceiling, and the processing gas diffusion unit includes inner and outer gas injection regions and independent gas flow channels connecting the inner and outer gas injection regions. The reactor according to claim 1.   The gas flow rate to the gas injection part in the processing ring, (b) the inner gas injection area of the gas diffusion part, and (c) the gas flow rate to the outer gas injection area of the gas diffusion part is independently controlled. The reactor according to claim 7, which is possible.   The reactor according to claim 8, wherein the gas supply system includes a supply source of a first process gas connected to the gas diffusion part and a supply source of a second process gas connected to the gas injection part in the processing ring. .   The reactor of claim 1 wherein the wafer support has a generally cylindrical axis of symmetry, the liner includes a cylindrical wall that is coaxial with the wafer support, and the gas inlet includes an annular slit.   The wafer support surface has an outer edge corresponding to the outer edge of the wafer supported by the wafer support surface, and the annular slit is at a distance of less than about 1% of the diameter of the workpiece support surface from the outer edge. 11. A reactor according to claim 10, which is spaced apart. A method of processing a workpiece in a plasma reactor,
Placing the workpiece on a workpiece support in a chamber of a plasma reactor;
Introducing a first process gas through a workpiece support process gas inlet adjacent to and surrounding the outer edge of the workpiece;
Plasma RF source power is coupled to the plasma reactor to generate plasma in the plasma reactor chamber;
Introducing a second process gas into the chamber through a ceiling process gas diffusion located at the ceiling of the chamber lying on the workpiece support;
Controlling the flow rate of gas flowing through the workpiece support process gas injection section independently of the flow rate of gas flowing through the ceiling process gas diffusion section. The ceiling processing gas diffusion portion includes an outer gas diffusion portion and an inner processing gas diffusion portion,
The method
Adjusting the gas flow rate through the inner and outer process gas diffusions to optimize process uniformity across the majority of the workpiece;
The method of claim 12, further comprising adjusting a process gas flow rate through the workpiece support process gas inlet to optimize processing at an outer peripheral area of the workpiece. Introducing the first process gas through the workpiece support process gas inlet,
Supplying the first process gas through a gas flow channel within a portion of the workpiece support;
The method of claim 12, comprising sending processing gas received from the gas flow channel through a processing ring surrounding the workpiece.   The method of claim 13, further comprising restricting a gas flow rate through the workpiece support gas inlet to keep the effect of the first process gas within the outer peripheral area of the workpiece.

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