Ultra high speed uniform plasma processing system

An apparatus for processing a substrate with a plasma. The apparatus includes first and second electrodes positioned with a spaced apart relationship. A separating ring has a vacuum-tight engagement with confronting surfaces of the first electrode and the second electrode to define an evacuatable processing region therebetween. Communicating with the processing region is a process gas port for introducing a process gas to the processing region. The processing region may be evacuated through a vacuum port defined in one of the first and second electrodes to a pressure suitable for exciting a plasma from the process gas in the processing region when the first and second electrodes are powered.

FIELD OF THE INVENTION

The invention generally relates to processing apparatus for processing substrates with a plasma.

BACKGROUND OF THE INVENTION

Plasma processing systems are commonly used for modifying the surface properties of substrates in various industrial applications. For example, plasma processing systems are routinely used to plasma treat the surfaces of integrated circuits, electronic packages, and printed circuit boards in semiconductor applications, solar panels, hydrogen fuel cell components, automotive components, and rectangular glass substrates used in flat panel displays. Plasma processing systems are also used in medical applications to modify the surface properties of devices, such as stents and implants, inserted into the human body. Plasma processing systems that rely on conventional parallel-plate type electrodes may experience process non-uniformities across the surface of relatively large substrates positioned in a processing region defined between the electrodes for processing.

When radio frequency power is supplied to the electrodes, equipotential field lines are induced across the surface of the substrate. During plasma processing, positive ions from the plasma in the processing region accelerate across the equipotential field lines to impinge on the surface of the substrate. The plasma is typically distributed over the entire evacuated volume of a processing chamber enclosing the electrodes with the highest plasma density observed between the electrodes. The uniformity of the plasma density in the processing region between the electrodes is influenced by external field effects factors, such as grounded chamber sidewalls, that alter the equipotential electric field lines between the electrodes and thereby modify the distribution of the constituent charged components of the plasma. The non-uniformity may be particularly significant at the peripheral edges of the processing region.

One conventional method of reducing external field effects is to make the processing chamber larger so that the grounded sidewalls are more distant from the electrodes. Among other disadvantages, this increases the chamber volume and the footprint of the processing system. The increase in chamber volume increases the time to evacuate the processing chamber and the time to bleed or vent the processing chamber to atmospheric pressure to insert unprocessed substrates or remove processed substrates. In particular, these are especially undesirable effects that significantly reduce throughput in in-line plasma processing systems intended to serially plasma process large quantities of substrates, which requires periodic evacuation and venting to exchange substrates after each processing cycle.

Another disadvantage of conventional plasma processing systems is that plasma is inadvertently generated in evacuated regions inside the processing chamber peripheral to the processing region between the electrodes. The generation of plasma in these regions renders the plasma process difficult to control and may damage components positioned within these regions. This unconfined plasma may also change the location of power absorbed by the plasma within the plasma processing chamber, thereby making it difficult to control the delivery of power to the electrodes to achieve consistent and reproducible processing.

Conventional approaches for confining the plasma generally include the use of repulsive fields, either electric or magnetic in nature. One specific conventional approach is to position confinement rings about the outer periphery of the parallel-plate type electrodes. The confinement rings, which are formed from an electrical insulator, charge to a potential comparable to that of the plasma, which generates a repulsive electric field that laterally confines the plasma. Nonetheless, the electrodes and confinement rings are still positioned inside of, and surrounded by, a considerably larger vacuum chamber that must be evacuated and in which a plasma discharge may still exist. The confinement rings are arranged with gaps so that the processing region defined between the electrodes is adequately evacuated.

It would therefore be desirable to provide a plasma processing system that overcomes these and other deficiencies of conventional plasma processing systems, as described herein.

SUMMARY OF INVENTION

In an embodiment of the invention, an apparatus for plasma processing a substrate includes first and second electrodes positioned with a spaced apart relationship and a separating ring having a vacuum-tight engagement with confronting surfaces of the first electrode and the second electrode to define an evacuatable vacuum processing region between the first electrode and the second electrode. Either the first electrode or the second electrode is adapted to support the substrate in the processing region for plasma processing. The separating ring electrically isolates the first electrode from the second electrode. The apparatus further includes a process gas port for introducing a process gas to the processing region and a vacuum port for evacuating the processing region to a pressure suitable for generating a plasma from the process gas in the processing region when the first and/or second electrodes are powered.

These and other objects and advantages of the present invention shall become more apparent from the accompanying drawings and description thereof.

DETAILED DESCRIPTION

With reference toFIGS. 1 and 2, a plasma processing system10generally includes an enclosure12having a lid14and a base16upon which the lid14rests, a pair of support arms18,20depending from the lid14, an upper electrode22, and a lower electrode24. The processing system10further includes a separating member or ring26positioned between the upper and lower electrodes22,24and contacting confronting faces about the perimeter of the upper and lower electrodes22,24. The confronting faces of the electrodes22,24are generally planar and parallel plates and have approximately identical surface areas. A shroud25extends downwardly from the base16toward the surface supporting system10.

Mechanically coupled with the support arms18,20is a lifting device28, illustrated as a pneumatic cylinder, that vertically lifts and lowers the lid14relative to the base16between a raised position (FIG. 3A) and a lowered position (FIG. 3B). In the raised position, a processing region40(FIG. 3B), as defined below, is accessible for inserting unprocessed substrates55and removing processed substrates55. In the lowered position (FIG. 3B), an environment may be established in the processing region40that is suitable for plasma processing a substrate55positioned in the processing region40. The invention contemplates that the processing region40may be accessed in any alternative manner understood by persons of ordinary skill in the art, such as a hinged connection that pivots the lid14relative to base16.

For in-line applications, the processing system10may be provided with an input carrier that provides unprocessed substrates55, an output carrier that receives processed substrates55, and a transfer arm or the like for transferring substrates55from the input carrier to the process chamber and from the process chamber to the output carrier. In addition, a plurality of discrete substrates55may be introduced in such a way that each substrate55within the plurality is independently introduced into the processing system10or in such a way that one or more substrates55within the plurality are jointly introduced into the processing system10. Discrete substrates55may also be positioned on a support or carrier and transported thereon into the processing system. The processing system10may comprise a single process station among multiple process stations that cooperate to sequentially process multiple substrates55moving in an assembly line fashion among the multiple process stations.

A power supply30, which is coupled with the electrodes22,24by shielded coaxial cables or transmission lines32,34, respectively, controls the power level and frequency of operation of the electrodes22,24. The power supply30may be an alternating current power supply operating at an extremely low frequency, such as 50 Hz and 60 Hz, at a high radio frequency, such as 40 kHz and 13.56 MHz, at a medium radio frequency, such as 1 kHz, or at a microwave frequency, such as 2.4 GHz. The power supply30may also operate at dual frequencies superimposed upon one another. Alternatively, the power supply30may be a direct current (DC) power supply in which the plasma is non-oscillating. In other alternative embodiments, power supply30may supply a radio frequency (RF) power component that provides a dense plasma and a DC power component that independently increases ion energy without effecting the plasma density.

In certain embodiments of the invention, the power supply30may operated at one or more radio frequencies and include an impedance matching network (not shown) that measures reflected power from the load represented by the electrodes22,24and plasma confined therebetween back to the power supply30. The impendence matching network adjusts the frequency of operation of power supply30to minimize the reflected power. The construction of such matching networks is understood by a person of ordinary skill in the art. For example, the impedance matching network may tune the matching network by changing the capacitance of variable capacitors within the matching network to match the impedance of the power supply30to the impedance of the load as the load changes. The power and voltage levels and operating frequency(ies) may vary of course, depending upon the particular application.

A vacuum pump36continuously pumps byproduct generated by the plasma process and non-reacted process gas from the processing region40, when the plasma processing system10is operating, through a vacuum manifold38. The vacuum pump36is operative to maintain the total pressure in the processing region40at a subatmospheric level low enough to facilitate creation of a plasma. Typically pressures suitable for plasma formation range from about twenty (20) millitorr to greater than about fifty (50) torr. The pressure within the processing region40is controlled in accordance with a particular desired plasma process and primarily consists of partial pressure contributions from the process gas, which may comprise one or more individual gas species, supplied to the evacuated processing region40.

The plasma processing system10includes a microprocessor-based controller that is programmed to control the operation of, among other components, the power supply30, the vacuum pump36, and the process gas supply114. For example, the controller regulates the power levels, voltages, currents and frequencies of the power supply30and orchestrates the provision of process gas from process gas supply114and the pumping rate of vacuum pump36to define a suitable pressure in processing region40in accordance with the particular plasma process and application.

During processing of substrate55, the power applied between the electrodes22,24by power supply30produces an electromagnetic field in a processing region40(FIGS. 3B and 4) defined between the two electrodes22,24, as described below, when the lid14and base16are contacting and an environment suitable for plasma processing is provided. The electromagnetic field excites the process gas present in the processing region to a plasma state, which is sustained by the application of power from power supply30for the duration of the plasma treatment.

Constituent components of the plasma interact with exposed material on the substrate55to perform the desired surface modification. The plasma is configured to perform the desired surface modification of the substrate55by selecting parameters such as the chemistry of the process gas, the pressure inside the processing region40, and the amount of power and/or frequency applied to the electrodes22,24. The processing system10may include an end point recognition system (not shown) that automatically recognizes when a plasma process (e.g., an etching process) has reached a predetermined end point or, alternatively, plasma processes may be timed based upon an empirically-determined process time.

With reference toFIGS. 3A and 3B, the upper electrode22is suspended from the upper housing by a plurality of electrically insulating spacers, of which spacers42and44are visible inFIG. 3Aand spacer46is visible inFIG. 4. In one embodiment of the invention in which the upper electrode22is rectangular, insulating spacers similar to spacers42,44and46are positioned between each corner of upper electrode22and each corner of the lid14. Secured by conventional fasteners to the perimeter of the lid14is a retaining ring48that operates to secure the separating ring26to the lid14. As a result, the upper electrode22and the retaining ring48move along with the lid14when the lid14is moved by the lifting device28between the raised and lowered positions relative to the base16.

A sealing member50is compressed between separating26and the upper electrode22by a vertical force applied by the retaining ring48when fastened to the lid14. When the lid14is lowered into contact with the base16as shown inFIG. 3B, a sealing member52is compressed between the separating ring26and a perimeter of the lower electrode24. The sealing members50,52are illustrated as conventional elastomeric O-rings, although the invention is not so limited.

Mounted to the lower electrode24is a substrate holder54configured to support either one or more substrates or one or more carriers each bearing one or more substrates55at locations inside the processing region40suitable for plasma treatment. The substrate holder54has a good electrical contact with the lower electrode24so that the substrate holder54and substrates55are at the same potential as the lower electrode24. However, the invention is not so limited as, in an alternative embodiment, the substrate holder54may be at a floating potential and electrically insulated from the lower electrode24. The invention also contemplates that the substrate55may be supported from the upper electrode22or by the separating ring26. When the lid14and base16are contacting, the processing region40is defined as the space bounded vertically between the inwardly-facing horizontal surfaces of the electrodes22,24and bounded laterally inside the inwardly-facing vertical surface of the sidewall defined by the separating ring26.

The base16includes an opening61over which is positioned a base thin-walled metallic closure62, which constitutes a component of the enclosure12. An unpumped atmospheric-pressure cavity or air gap58is defined between the lower electrode24and the assembly of the base16and the closure62, respectively. Another unpumped atmospheric-pressure cavity or air gap56is defined between the lid14, a lid cover60removable from lid14, and the upper electrode22. Typically, the air gaps56,58are dimensioned to minimize energy loss from the electrodes22,24to the lid14, base16and closure62and are coupled together as a single, continuous air-filled space by portions of gaps56,58encircling the perimeter of the electrodes22,24and separating ring26, as best depicted inFIG. 3B.

When the lid14is in its lowered position, a conducting member64captured between the respective perimeters of the lid14and base16, which are metallic, supplies a good electrical contact between the lid14and base16. The lid14, base16, cover60, and closure62collectively define a substantially closed electrically conducting shell, which acts as a shield to confine power supplied to the electrodes22,24within the interior of the enclosure12.

Transmission line34, which is electrically coupled in a known manner with the lower electrode24, is routed through opening61to lower electrode24. Transmission line32enters the lid14at a location between the removable lid cover60and the upper electrode22, and is electrically coupled in a known manner with the upper electrode22. If both electrodes22,24are coupled with the power supply30and the power supply30is an alternating current power supply, one of the electrodes22,24may be driven 180° out of phase from the other of the electrodes22,24so that both electrodes22,24are powered. Alternatively, one of the electrodes22,24may be grounded and the other of the electrodes22,24may be powered.

In certain embodiments of the invention, an appropriate cooling fluid may be circulated through these air gaps56,58for cooling the processing system10and, in particular, for cooling the electrodes22,24. To that end, a fitting57(FIG. 2) may be provided in the lid14to define a coolant port for coupling a coolant supply59(FIG. 2) with air gap56. A forced flow of a coolant, such as air, may be introduced from the coolant supply59to air gap56via fitting57to establish a continuous coolant flow about the electrodes22,24through air gaps56,58. Air gap58is structured to provide an exhaust path for the flowing coolant to the open environment about the processing system10.

The volume bounded by the electrodes22,24and the separating ring26constitutes the processing region40and represents the only volume, aside from the vacuum manifold38, in the processing system10that is evacuated by the vacuum pump36and, hence, represents the vacuum envelope of the plasma processing system10. This is in marked contrast to conventional plasma processing systems in which electrodes are positioned inside a vacuum chamber with a significant evacuated volume surrounding the electrodes in which the process gas may be excited to provide an unconfined plasma that uses available power but is otherwise not available for processing workpieces55positioned between the electrodes22,24. As a result, the effective evacuated volume of system10is significantly smaller than the evacuated volume of conventional processing chambers. This provides multiple benefits including, but not limited to, an increased plasma density, a significant reduction in the time required to evacuate the processing chamber to a pressure suitable for exciting the plasma, and a significant reduction in the time required to bleed or vent the processing chamber to atmospheric pressure. These benefits contribute to an increased throughput with decreased cost of operation and a reduced processing time required to provide a targeted plasma treatment as compared with conventional plasma processing systems.

The electrodes22,24are formed from an electrically-conductive material, such as aluminum. The separating ring26is formed from a non-conducting dielectric material that is able to withstand the plasma environment inside the processing region40without unduly contaminating the processed substrate55. Generally, this implies that the material forming the separating ring26should be substantially resistant to etching by the plasma present in the processing region40. The separating ring26defines a vertical sidewall of non-conductive material, in addition to providing the vacuum seal between the electrodes22,24.

The absence of a conventional vacuum chamber eliminates or, at the least, significant reduces external field effects. More specifically, the electrodes22,24of plasma processing system10are not surrounded by grounded metallic walls characterizing a conventional vacuum chamber. Instead, the non-conducting separating ring26effectively operates as the vertical sidewall boundary of the processing region40. Therefore, external field effects are minimized or absent and the equipotential electric field lines are uniform across the entire surface of the substrate55without fringing at the electrode edges, which allows plasma processing to proceed in a uniform manner across the substrate55.

In one embodiment, jade glass (i.e., calcium magnesium iron silicate or sodium aluminum iron silicate) is employed as the dielectric material for separating ring26but another ceramic material, such as alumina, float glass, silica or quartz, may also be used. In alternative embodiments of the invention, the dielectric material constituting separating ring26may any of a number of polymeric fluorocarbon materials including but not limited to polytetrafluoroethylene (PTFE), the homopolymer of tetrafluoroethylene sold under the trademark TEFLON by DuPont; perfluorinated ethylene-propylene (FEP), the copolymer of tetrafluoroethylene and hexafluoropropylene sold under the trademark TEFLON FEP by DuPont; perfluoroalkoxy fluorocarbon resin (PFA), the copolymer of tetrafluoroethylene-perfluorovinyl ether sold under the trademark TEFLON PFA by DuPont; or ethylene tetrafluoroethylene (ETFE), the copolymer of ethylene and tetrafluoroethylene sold under the trademark TEFZEL by DuPont. Use of such polymers to construct separating ring26may be appropriate, for example, in etching applications with plasma species capable of chemically attacking ceramics. Because the separating ring26constitutes a portion of the vacuum envelope of the processing region40, the separating ring26should be engineered with a strength sufficient to withstand the external forces arising from the pressure differential between the evacuated processing region40and the atmospheric pressure in air gaps56,58.

With reference toFIGS. 3A and 5, the lower electrode24includes a laterally-spaced pair of vacuum ports66,68each of which is positioned to coincide spatially with one of flanged ports70,72at the ends of opposed arms74,76, respectively, of the vacuum manifold38. The flanged ports70,72are fastened to the lower electrode24by bolts (not shown) to compress respective sealing members78,80and thereby form vacuum seals. The arms74,76converge at a vertical tubing section82that leads to the vacuum pump36. Received partially in the opening in flanged port70and partially inside of a mounting plate84surrounding port70is an insert88. Similarly, received partially in the opening in flanged port72and partially inside of a mounting plate86surrounding port72is an insert90. A centering ring92,94is also positioned inside a corresponding one of the flanged ports70,72. Disposed between the base16and the lower electrode24are manifold mounting spacers96,98each of which has a central opening that coincides with one of the vacuum ports66,68.

The identical manifold mounting spacers96,98are each formed from an electrically insulating material, such as a thermoplastic elastomer (TPE), and their presence contributes to isolating the lower electrode24from the base16of the enclosure12. The identical inserts88,90, which are each formed from an electrically insulating material such as a ceramic with a relatively high dielectric constant, serve to electrically isolate the lower electrode24from the base16of the enclosure12and the flanged ports70,72of the vacuum manifold38.

The inserts88,90and, to a minor extent, the centering rings92,94fill otherwise empty spaces at the juncture between the lower electrode24and the vacuum manifold38. The lower electrode24and the vacuum manifold38are spaced apart due to the electrical isolation needed between the lower electrode24and the base16of enclosure12. The presence of the inserts88,90and centering rings92,94prevents plasma excitation in these otherwise unfilled spaces between the vacuum manifold38and the lower electrode24. The inserts88,90effectively operate as a charged particle filter that confines the plasma to the processing region40.

With reference toFIGS. 3A,5, and7, each of the vacuum ports66,68in the lower electrode24includes an array of passages100, respectively, which are registered with a corresponding array of passages102, respectively, formed in a corresponding one of the inserts88,90and a corresponding array of passages104, respectively, formed in a corresponding one of the centering rings92,94. The vacuum pump36exhausts byproduct generated by the plasma process and non-reacted gas from the processing region40into the vacuum manifold38through the registered passages100,102,104. The arrangement and dimensions of the passages100,102,104, which typically have substantially identical arrangement and dimensions, are selected to maximize pumping conductance while simultaneously preventing plasma excitation based on the hollow cathode effect. As a result, the plasma is confined to the processing region40, which makes efficient use of the input excitation power.

With reference toFIGS. 7A and 7B, the pattern and configuration of the passages100,102,104is not limited to the illustrated embodiment inFIG. 7but, instead, is contemplated to include any pattern and configuration that provides suitable pumping conductance without plasma excitation. Generally, the passages100,102,104are spaced apart in a direction normal to that of the flow of the exhausting gases. In one specific alternative embodiment and with specific reference toFIG. 7A, the passages102ain a representative insert88aand the passages100ain a representative vacuum port66aof a lower electrode24aare configured as a set of parallel slots. The passages in a centering ring (not shown) are configured to coincide with the passages100a,102a. In one specific alternative embodiment of the invention and with specific reference toFIG. 7B, the passages102bin a representative insert88band the passages100bin a representative vacuum port66bof a lower electrode24bare configured as a set of concentric curved slots. The passages in a centering ring (not shown) are configured to coincide with the passages100b,102b.

With reference toFIGS. 4 and 6, fastened to an upper horizontal surface of the upper electrode22is a gas inlet plate106. Extending through the gas inlet plate106is a gas port108(FIG. 4) coupled by a conduit110with a fitting112. Fitting112is further coupled by a delivery line113with a process gas supply114(FIG. 2). The delivery line113and process gas supply114may include a mass flow controller and a flow measurement device (not shown) that cooperate for regulating the flow rate of each individual process gas to the processing region40. A planar surface106aof the gas inlet plate106facing the upper electrode22includes a plurality of recessed radial channels116that intersect at and diverge away from the location of the gas port108. Extending through the upper electrode22is a plurality of perforations or gas openings118arranged in a pattern such that each gas opening118is registered with one of the radial channels116in the gas inlet plate106when the gas inlet plate106is fastened to the upper electrode22. A conventional sealing member120, illustrated as an elastomeric o-ring, provides a seal about the adjacent perimeters of the gas inlet plate106and the upper electrode22.

Process gas supplied to the gas port108is distributed among the radial channels116to the gas openings118. The process gas is admitted to the processing region40through gas openings118positioned with spaced-apart locations above the lower electrode24and across the substrate55supported on the substrate holder54. The gas distribution may be tailored for a specific processing application by inserting a plug122into one or more of the gas openings118that is effective to block process gas flow. In one embodiment of the invention, the gas openings118may be threaded and the plug122may be an appropriately-sized set screw. The adjustment of the gas distribution may be empirically determined by examining the process uniformity on processed substrates55. The flow of process gas into the processing region40and the pumping rate of vacuum pump36are coordinated to maintain the total gas pressure in the processing region40at a level low enough to facilitate plasma creation from the partial pressure of process gas.

The gas distribution system of the invention promotes uniform distribution of the process gas across the substrate55and has the flexibility to permit adjustments to the pattern of gas distribution. In alternative embodiments of the invention, the process gas may be supplied to the processing region40by a different type of gas distribution system, such as a gas distribution ring, gas injectors, a single gas port, etc.

The invention contemplates that electrode22may be configured to produce an ion-free or downstream plasma in the processing region30. A suitable configuration for electrode22is disclosed in commonly-owned and currently pending application Ser. No. 10/324,436, filed Dec. 20, 2002 in the name of James Scott Tyler et al. and entitled “Plasma Treatment System”, which is hereby incorporated by reference herein in its entirety.

References herein to terms such as “vertical”, “horizontal”, etc. are made by way of example, and not by way of limitation, to establish a frame of reference. The term “horizontal” as used herein is defined as a plane substantially parallel to a plane containing one of the confronting surfaces of the electrodes22,24, regardless of orientation. The term “vertical” refers to a direction perpendicular to the horizontal, as just defined. Terms, such as “upper”, “lower”, “on”, “above”, “below”, “side” (as in “sidewall”), “higher”, “lower”, “over”, “beneath” and “under”, are defined with respect to the horizontal plane. It is understood various other frames of reference may be employed without departing from the spirit and scope of the invention as a person of ordinary skill will appreciate that the defined frame of reference is relative as opposed to absolute.

With reference toFIGS. 8 and 9in which like reference numerals refer to like features inFIGS. 1-7and in accordance with an alternative embodiment of the invention, a plasma processing system10afeatures a second processing level stacked vertically in relationship with the first processing level. This increases the workpiece capacity of system10afor a single processing operation and expands the system throughput as compared with system10(FIGS. 1-7). The second level is provided by inserting an intermediate electrode130between upper and lower electrodes22,24and adding an additional separating member or ring132that is substantially identical to separating ring26. Electrode130and separating ring132are carried by a frame134and electrically insulated from the frame134by electrically insulating member136(FIG. 8).

A lifting device (not shown) similar to lifting device28(FIGS. 1 and 2) vertically lifts and lowers the frame134relative to the base16after the lid14is moved to a raised position (FIG. 3A). This provides access to a processing space consisting of, when the lid14and frame134are in a lowered position (FIGS. 8 and 9), a first portion40abounded by the upper electrode22, the separating ring26, and the intermediate electrode130and a second portion40bbounded by the lower electrode24, the intermediate electrode130and the separating ring132.

The frame134constitutes a portion of the enclosure12in this alternative embodiment and is separated from the electrode130and separating ring132by an air gap133that is continuous with air gaps56,58. When the lid14is in its lowered position, a conducting member138, which is similar or identical to conducting member64, is captured between the respective perimeters of the frame134and lid14. Conducting member64now is captured between the respective perimeters of frame134and base16. The lid14, base16, closure62and frame134collectively define a substantially closed electrically conducting shell, which acts as a shield to confine power supplied to the electrodes22,24within the interior of the enclosure12.

The two portions40a,bof the processing space communicate by an array of passages135(FIG. 9) arranged about the periphery of the intermediate electrode130. Processing space40bis evacuated directly through vacuum ports66,68and processing space40ais pumped through passages135. In analogy to processing space40(FIGS. 3-7), processing space40a,brepresents the only evacuated volume of system10and provides various advantages and benefits identical to those described above for system10. The invention is not limited to two processing levels as additional levels may be introduced in a consistent manner.

A sealing member50a, which is similar or identical to sealing member50, is compressed between separating ring132and a perimeter of the lower section130aof the intermediate electrode130by a vertical force applied by a retaining ring137. A sealing member52a, which is similar or identical to sealing member52, is compressed between the separating ring26and a perimeter of the upper section130bof the intermediate electrode130. Sealing member52is now compressed between separating ring132and the lower electrode24.

The frame134is mounted to a lifting device (not shown) that lifts an assembly including electrode130and separating ring132relative to base14. After the lid14of enclosure12is lifted relative to electrode130, the assembly including electrode130and separating ring132may be moved relative to base16for accessing a substrate holder138mounted to electrode130. The substrate holder140, which is identical to substrate holder54, is configured to support either one or more substrates55or one or more carriers each bearing one or more substrates55at locations suitable for plasma treatment inside the processing region40a. Similarly, substrate holder54now holds substrates55supports either one or more substrates55or one or more carriers each bearing one or more substrates55at locations suitable for plasma treatment inside the processing region40b.

The intermediate electrode130includes a lower section130aconfigured similar to upper electrode22with a gas distribution system that evenly and uniformly distributes process gas into processing space40band an upper section130carrying substrate holder140. The lower section130aof the intermediate electrode130includes a gas inlet plate142, which is similar or identical to gas inlet plate106, having a gas port144coupled by a conduit146with a fitting148, which is further coupled with process gas supply114(FIG. 2). A planar surface of the gas inlet plate142facing the lower section130aof intermediate electrode130includes a plurality of recessed radial channels150, which are similar or identical to channels116, that intersect at and diverge away from the location of the gas port144. Extending through the lower section130ais a plurality of perforations or gas openings152, which are similar or identical to gas openings118, arranged in a pattern such that each gas opening152is registered with one of the radial channels150in the gas inlet plate142. A conventional sealing member154, illustrated as an elastomeric o-ring, provides a seal about the adjacent perimeters of the gas inlet plate142and the lower section130aof intermediate electrode130. In this embodiment of the invention, gas openings118now uniformly distribute process gas across the confronting surface of workpiece55in processing region40aand, in a similar manner, gas openings152distribute process gas across the confronting surface of workpiece55in processing region40b.

A transmission line156is electrically coupled in a known manner with the intermediate electrode130. Typically, all three electrodes22,24, and130are coupled with the power supply30and, if the power supply30is an alternating current power supply, the middle electrode130is driven 180° out of phase from the other electrodes22,24.

While the present invention has been illustrated by a description of various embodiments and while these embodiments have been described in considerable detail, it is not the intention of the applicants to restrict or in any way limit the scope of the appended claims to such detail. Additional advantages and modifications will readily appear to those skilled in the art. The invention in its broader aspects is therefore not limited to the specific details, representative apparatus and methods, and illustrative examples shown and described. Accordingly, departures may be made from such details without departing from the spirit or scope of applicants” general inventive concept. The scope of the invention itself should only be defined by the appended claims, wherein we claim: