Cooling shield for icp source

Abstract

The present disclosure provides a plasma processing apparatus comprising: a plasma chamber comprising a dielectric wall having an outer surface; an inductively coupled plasma source configured to generate a plasma in the plasma chamber; a shielding device disposed between an outer surface of the dielectric wall and the inductively coupled plasma source, the shielding device comprising: a top annular portion; a bottom annular portion; an induction coil assembly comprising one or more conductive coils wound around at least a portion of an outer surface of the dielectric wall of the plasma chamber; and a plurality of thermal pads joined to the top annular portion and / or the bottom annular portion by one or more retention members, where the one or more retention members provide a compressive force to secure one or more of the plurality of thermal pads against an outer surface of the dielectric wall, where the plurality of thermal pads are configured to regulate heat flux from the dielectric wall to the respective thermal pads.

Description

[0001] This application is a divisional application of the Chinese application entitled “Cooling shield for ICP source”, filed on December 21, 2021, and with application number 202111571118.6. Technical Field

[0002] The present disclosure generally relates to apparatus, systems, and methods for plasma processing of workpieces. Background Art

[0003] Plasma processing is widely used in the semiconductor industry for deposition, etching, resist removal, and related processing of semiconductor wafers and other substrates. Plasma sources (e.g., microwave, ECR, inductively coupled, etc.) are typically used in plasma processing to generate high-density plasma and reactive species for processing substrates. In a plasma dry stripping process, neutral species (e.g., free radicals) from a plasma generated in a remote plasma chamber pass through a barrier into a processing chamber to process a workpiece, such as a semiconductor wafer. In a plasma etching process, free radicals, ions, and other species generated in the plasma that is directly exposed to the workpiece can be used to etch and / or remove material from the workpiece. Summary of the Invention

[0004] Aspects and advantages of embodiments of the present disclosure will be set forth in part in the description which follows, or may be learned from the description, or may be learned through practice of the embodiments.

[0005] Aspects of the present disclosure relate to a plasma processing apparatus comprising: a plasma chamber including a dielectric wall having an outer surface; an inductively coupled plasma source configured to generate plasma in the plasma chamber; a shield disposed between the outer surface of the dielectric wall and the inductively coupled plasma source, the shield comprising: a top annular portion; a bottom annular portion; an inductive coil assembly including one or more conductive coils wrapped around at least a portion of the outer surface of the dielectric wall of the plasma chamber; and a plurality of thermal pads coupled to the top annular portion and / or the bottom annular portion by one or more retaining members, wherein the one or more retaining members provide a compressive force to secure one or more of the plurality of thermal pads against the outer surface of the dielectric wall, wherein the plurality of thermal pads are configured to regulate heat flux from the dielectric wall to the respective thermal pads.

[0006] These and other features, aspects and advantages of various embodiments will be better understood with reference to the following description and appended claims.The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the present disclosure and, together with the description, serve to explain the relevant principles. BRIEF DESCRIPTION OF THE DRAWINGS

[0007] A detailed discussion of the embodiments for those skilled in the art is set forth in the specification with reference to the accompanying drawings, in which:

[0008] Figure 1 depicts an exemplary plasma processing apparatus according to an exemplary embodiment of the present disclosure;

[0009] Figure 2 depicts a side view of an exemplary shield according to an exemplary embodiment of the present disclosure;

[0010] Figure 3 depicts a top view of an exemplary shield according to an exemplary embodiment of the present disclosure;

[0011] Figure 4 depicts a bottom view of an exemplary shield according to an exemplary embodiment of the present disclosure;

[0012] Figure 5 depicts certain components of a shield connected by a plurality of exemplary mounting brackets and having thermal pads disposed therebetween according to an exemplary embodiment of the present disclosure;

[0013] Figure 6 depicts certain components of a shield connected by a plurality of exemplary mounting brackets according to an exemplary embodiment of the present disclosure;

[0014] Figure 7 depicts an enlarged view of one end of a mounting bracket according to an exemplary embodiment of the present disclosure;

[0015] Figure 8 depicts certain components of a shield connected by a plurality of exemplary mounting brackets according to an exemplary embodiment of the present disclosure;

[0016] Figure 9 depicts a plurality of retaining members attached to a thermal pad according to an exemplary embodiment of the present disclosure;

[0017] Figure 10 depicts an enlarged view of a retaining member according to an exemplary embodiment of the present disclosure;

[0018] Figure 11 depicts a plurality of exemplary thermal pads arranged in a circular formation according to an exemplary embodiment of the present disclosure;

[0019] Figure 12 depicts an exemplary thermal pad according to an exemplary embodiment of the present disclosure, wherein a plug is selectively inserted into a cooling channel;

[0020] Figure 13 Depicts an exemplary embodiment of the present disclosure Figure 12 A perspective view of an exemplary thermal pad;

[0021] Figure 14 depicts an exemplary thermal pad having an inlet tube and an outlet tube connected thereto according to an exemplary embodiment of the present disclosure;

[0022] Figure 15 depicts a shield surrounded by an exemplary induction coil according to an exemplary embodiment of the present disclosure;

[0023] Figure 16 depicts a shield surrounded by an exemplary induction coil according to an exemplary embodiment of the present disclosure;

[0024] Figure 17 depicts a detailed view of an aperture in a mounting bracket according to an exemplary embodiment of the present disclosure; and

[0025] Figure 18 A flowchart of an exemplary method of processing a workpiece according to an exemplary embodiment of the present disclosure is depicted. DETAILED DESCRIPTION

[0026] Exemplary aspects of the present disclosure relate to electromagnetic shields (e.g., Faraday shields) for plasma sources that additionally provide for heat removal from the plasma source. Some existing designs of plasma sources have issues related to overheating. For example, a plasma source may include a dielectric chamber or tube containing the plasma. In high-power applications, the energy transmitted through the dielectric material to excite the plasma heats the dielectric material and causes degradation, in some cases leading to failure or breakage (e.g., cracking of the ceramic dielectric chamber). This problem is compounded for inductively coupled plasma sources, which typically include a high-power induction coil surrounding a dielectric tube. In such configurations, the areas typically exposed to the highest heat are those located near the induction coil. Therefore, it is desirable to shield the dielectric chamber from the coil using, for example, a Faraday shield to limit capacitive coupling between the induction coil and the plasma within the dielectric chamber. Providing for dielectric chamber cooling while also shielding the dielectric chamber from the coil presents particular challenges. One solution involves increasing the coil diameter to accommodate both the cooling jacket and the shield. However, such changes can reduce RF power efficiency, reduce collisions and process windows, generate higher RF voltages, and increase the risk of coil arcing.

[0027] In some embodiments, a shield according to aspects of the present disclosure may include a plurality of thermal pads that partially or completely surround and contact the dielectric wall of the plasma chamber. By connecting the thermal pads to each other and to a desired reference potential (e.g., ground, floating reference, etc.), a conductive "cage" can be formed around the dielectric chamber to provide the desired shielding effect.

[0028] In some exemplary embodiments, the heat pads may also be connected to a heat sink (e.g., a conductive heat sink, a convection heat sink, a radiant heat sink, and / or a combination thereof). In some embodiments, each heat pad is individually connected to a heat sink. For example, each heat pad may include a cooling channel into which a heat exchange fluid (e.g., a coolant) flows. In this way, each heat pad may be individually provided with a heat exchange fluid, so that the amount of heat extracted from each heat pad may be monitored and / or controlled by controlling the flow rate of the heat exchange fluid flowing through each heat pad. In some embodiments, the tubes that provide the heat exchange fluid to the heat pads may be formed of a dielectric material that is transparent to the RF field emitted from the ICP source coil. In this way, flexible tubing can be used to reduce the possibility of coolant leakage due to thermal expansion and contraction.

[0029] In some exemplary embodiments, the thermal pad can be elastically suspended from the housing of the plasma source to maintain a desired contact pressure on the dielectric chamber to provide sufficient heat transfer. The elastic mounting of the thermal pad can be configured to have a sufficient range of motion to accommodate thermal expansion and contraction of the dielectric wall. In addition, the elastic mounting can be configured so that the expected operating position of the thermal pad (e.g., after the dielectric chamber has expanded to its operating size at its operating temperature) is within the linear range of the elastic mounting, so that the contact pressure between the thermal pad and the dielectric wall is substantially constant as the dielectric wall expands and contracts during the operating cycle. In this way, the pressure applied to the dielectric wall can be managed to remain less than any critical threshold (e.g., associated with damage to any part of the plasma source and / or its housing) while maintaining sufficient pressure to provide sufficient heat transfer from the dielectric wall.

[0030] In some embodiments, the resilient mounting member can form part of the conductive shield. For example, the thermal pad can be suspended from a grounded housing or frame of the plasma source by a conductive retaining member (e.g., an elastic band). For example, one or more copper bands (e.g., beryllium copper, optionally silver-plated) can be preformed so that once the thermal pad is suspended against the side of the dielectric wall, the retaining member elastically deforms to clamp the thermal pad against the side of the dielectric chamber.

[0031] Thus, aspects of the present disclosure provide numerous technical effects and benefits. Advantageously, devices and systems according to exemplary aspects of the present disclosure provide a shield for a plasma source that additionally provides for removing heat from a dielectric chamber containing the generated plasma. A further advantage is that embodiments of the shield according to certain aspects of the present disclosure can accommodate the thermal "breathing" of the dielectric chamber as the dielectric chamber expands and contracts due to temperature changes, while maintaining good thermal conductivity between the shield and the dielectric chamber. In addition to accommodating thermal expansion and contraction, embodiments of the shield according to aspects of the present disclosure can provide a more uniform temperature distribution around the circumference of the dielectric chamber, helping to alleviate excessive thermally induced material stresses within the dielectric chamber walls. Furthermore, embodiments of the present disclosure can reduce production costs by reducing manufacturing complexity. For example, moving coolant flow into each thermal pad can be less expensive than moving into a standard Faraday cage.

[0032] Reference will now be made in detail to the embodiments, one or more examples of which are shown in the accompanying drawings. Each example is provided to explain the embodiments and is not intended to limit the present invention. In fact, it will be apparent to those skilled in the art that various modifications and variations may be made to the embodiments without departing from the scope or spirit of the present disclosure. For example, a feature shown or described as part of one embodiment may be used together with another embodiment to produce yet another embodiment. Therefore, aspects of the present disclosure are intended to encompass such modifications and variations.

[0033] For purposes of illustration and discussion, aspects of the present disclosure are discussed with reference to a "workpiece," a "wafer," or a semiconductor wafer. One of ordinary skill in the art, using the disclosure provided herein, will understand that the exemplary aspects of the present disclosure may be used in connection with any semiconductor workpiece or other suitable workpiece. Additionally, the term "about" used in conjunction with a numerical value shall be intended to mean within ten percent (10%) of the stated value. "Pedestal" refers to any structure that can be used to support a workpiece. "Remote plasma" refers to a plasma generated away from a workpiece, such as a plasma generated in a plasma chamber that is separated from the workpiece by a barrier. "Direct plasma" refers to a plasma that is directly exposed to a workpiece, such as a plasma generated in a processing chamber having a pedestal operable to support the workpiece.

[0034] Figure 1An exemplary plasma processing apparatus 500 is depicted that can be used to implement processes according to exemplary embodiments of the present disclosure. The plasma processing apparatus includes a processing chamber 110 and a plasma chamber 120 separate from the processing chamber 110. The processing chamber 110 includes a workpiece support 112 or susceptor operable to hold a workpiece 114 to be processed, such as a semiconductor wafer. In this exemplary illustration, a plasma 502 is generated in the plasma chamber 120 (i.e., the plasma generation region) by an inductively coupled plasma source 135, and a desired species is transported from the plasma chamber 120 through a channel to a surface of the workpiece 114 via a barrier assembly 200.

[0035] The plasma chamber 120 includes dielectric sidewalls 122 and a top plate 124. The dielectric sidewalls 122, top plate 124, and barrier 200 define a plasma chamber interior 125. The dielectric sidewalls 122 can be formed of a dielectric material, such as quartz and / or alumina. The dielectric sidewalls 122 can be formed of a ceramic material. The dielectric walls 122 can include an outer surface that does not face the plasma chamber interior 125. An inductively coupled plasma source 135 can include a source coil assembly, such as an induction coil 130, disposed proximate the dielectric sidewalls 122 around the plasma chamber 120. The induction coil 130 is coupled to an RF power generator 134 via a suitable matching network 132. The plasma processing apparatus 500 can include a shielding arrangement 128 (e.g., a grounded Faraday shield) surrounding the plasma chamber 120 (e.g., to reduce capacitive coupling of the induction coil 130 to the plasma 502).

[0036] The process gas can be provided to the interior of the chamber from a gas supply 150 and an annular gas distribution channel 151 or other suitable gas introduction mechanism. According to an exemplary aspect of the present disclosure, the apparatus 100 may include a gas delivery system 155 configured to deliver the process gas to the plasma chamber 120, for example, via the gas distribution channel 151 or other distribution system (e.g., a showerhead). The gas delivery system 155 may include a plurality of feed gas lines 159. The feed gas lines 159 may be controlled using valves 158 and / or gas flow controllers 185 to deliver a desired amount of gas into the processing chamber 109 as a process gas. The gas delivery system 155 may be used to deliver any suitable process gas (e.g., process gas 1, process gas 2, process gas 3, process gas 4, etc.). Exemplary process gases include oxygen-containing gases (e.g., O2, O3, N2O, H2O), hydrogen-containing gases (e.g., H2, D2), nitrogen-containing gases (e.g., N2, NH3, N2O), fluorine-containing gases (e.g., CF4, C2F4, CHF3, CH2F2, CH3F, SF6, NF3), hydrocarbon-containing gases (e.g., CH4), or combinations thereof. Additional feed gas lines containing other gases may be added as needed. In some embodiments, the process gas may be mixed with an inert gas, which may be referred to as a "carrier" gas, such as He, Ar, Ne, Xe, or N2. Control valves 158 may be used to control the flow rate of each feed gas line to flow the process gas into the plasma chamber 120. In embodiments, the gas delivery system 155 may be controlled by a gas flow controller 185.

[0037] Further, if Figure 1 As shown, a barrier 200 separates the plasma chamber 120 from the processing chamber 110. The barrier 200 can be used to perform ion filtration from a mixture generated by the plasma in the plasma chamber 120 to produce a filtered mixture. The filtered mixture can be exposed to the workpiece 114 in the processing chamber. In some embodiments, the barrier 200 can be a multi-plate barrier. For example, the barrier 200 can include a first grid plate 210 and a second grid plate 220 spaced apart in parallel relation to each other. The first grid plate 210 and the second grid plate 220 can be separated by a distance.

[0038] The first grid plate 210 may have a first grid pattern with a plurality of holes. The second grid plate 220 may have a second grid pattern with a plurality of holes. The first grid pattern may be the same as or different from the second grid pattern. Charged particles may recombine on the walls of the holes in each grid plate 210, 220 as they pass through the grid. Neutral species (e.g., free radicals) may flow relatively freely through the holes in the first grid plate 210 and the second grid plate 220. The size of the holes and the thickness of each grid plate 210, 220 may affect the transmittance of charged and neutral particles.

[0039] In some embodiments, the first grid plate 210 may be made of metal (e.g., aluminum) or other conductive materials, and / or the second grid plate 220 may be made of conductive or dielectric materials (e.g., quartz, ceramic, etc.). In some embodiments, the first grid plate 210 and / or the second grid plate 220 may be made of other materials, such as silicon or silicon carbide. In the case where the grid plates are made of metal or other conductive materials, the grid plates may be grounded.

[0040] For example, the barrier assembly 200 can be used to filter ions generated by the plasma. The barrier assembly 200 can have a plurality of holes. Charged particles (e.g., ions) can recombine on the walls of the plurality of holes as they pass through them. Neutral species (e.g., free radicals) can pass through the holes.

[0041] In some embodiments, the barrier 200 can be configured to filter ions with an efficiency greater than or equal to about 90%, such as greater than or equal to about 95%. The percentage efficiency of ion filtration refers to the number of ions removed from a mixture relative to the total number of ions in the mixture. For example, an efficiency of about 90% means that about 90% of the ions are removed during the filtration process. An efficiency of about 95% means that about 95% of the ions are removed during the filtration process.

[0042] In some embodiments, the grid 200 can be a multi-plate grid. The multi-plate grid can have multiple parallel grid plates. The arrangement and alignment of the holes in the grid plates can be selected to provide a desired ion filtration efficiency, such as greater than or equal to about 95%.

[0043] For example, the barrier 200 may include a first grid plate 210 and a second grid plate 220 arranged in parallel relation to each other. The first grid plate 210 may have a first grid pattern with a plurality of holes. The second grid plate 220 may have a second grid pattern with a plurality of holes. The first grid pattern may be the same as or different from the second grid pattern. Charged particles (e.g., ions) may recombine on the walls of the holes in each grid plate 210, 220 in the barrier 200. Neutral species (e.g., free radicals) may flow relatively freely through the holes in the first grid plate 210 and the second grid plate 220.

[0044] In embodiments, the apparatus 500 may include a controller 175. The controller 175 controls various components of the apparatus 500 to direct the processing of the workpiece 114. For example, the controller 175 may be used to control a power source (e.g., a DC power source, an AC power source, and / or an RF power source) connected to the induction coil 130. Additionally or alternatively, the controller 175 may communicate (e.g., wirelessly) with a temperature measurement system 180 configured to measure the temperature of the plasma chamber 120 and / or the dielectric wall 122. Based on the dielectric wall 122 temperature, the controller 175 may adjust the flow of a heat exchange fluid through one or more heat pads disposed on the shield 128, as discussed further below. The controller 175 may be configured to maintain a certain dielectric wall temperature 122 for the plasma chamber 120. The controller 175 may also implement one or more process parameters, such as controlling a gas flow controller 185 and / or changing conditions in the plasma chamber 120 and / or the processing chamber 110 during processing of the workpiece 114. The controller 175 may include, for example, one or more processors and / or one or more memory devices. The one or more memory devices may store computer-readable instructions that, when executed by the one or more processors, cause the one or more processors to perform operations, such as any of the control operations described herein.

[0045] In some embodiments, the workpiece support 112 can be movable in a vertical direction V. For example, the workpiece support 112 can include a vertical lift that can be configured to adjust the distance between the workpiece support 112 and the grid assembly 200. As an example, the workpiece support 112 can be positioned in a first vertical position for processing using a remote plasma 502. The workpiece support 112 can be positioned in a second vertical position for processing using a direct plasma 504. The first vertical position can be closer to the grid assembly 200 than the second vertical position.

[0046] Figure 1 The exemplary plasma processing apparatus 500 is operable to generate a first plasma 502 (eg, remote plasma) in the plasma chamber 120 and a second plasma 504 (eg, direct plasma) in the processing chamber 110. More specifically, Figure 1 The plasma processing apparatus 500 includes a bias source having a bias electrode 510 in a workpiece support 112. The bias electrode 510 can be coupled to an RF power generator 514 via a suitable matching network 512. When the bias electrode 510 is energized by RF energy, a second plasma 504 can be generated from the mixture in the processing chamber 110 to be directly exposed to the workpiece 114. The processing chamber 110 can include an exhaust port 516 for exhausting gas from the processing chamber 110. Using the first plasma 502 and / or the second plasma 504, radicals or species used during workpiece processing according to exemplary aspects of the present disclosure can be generated.

[0047] RF generators 134 and 514 can operate at various frequencies. In some embodiments, for example, RF generator 134 can energize induction coil 130 (and additionally or alternatively, RF generator 514 can energize bias electrode 510) with RF power at a frequency of approximately 13.56 MHz. In certain exemplary embodiments, the RF generator can be operable to provide RF power at a frequency within a range between approximately 400 KHz and approximately 60 KHz.

[0048] Now refer to Figure 2-Figure 17 Discuss exemplary embodiments of the shield 128 and features of the shield 128. For example, reference is now made to Figure 2 , shows an exemplary embodiment of a shield 128 capable of transferring heat away from the plasma chamber 120 via the dielectric wall 122. For example, the shield 128 includes one or more thermal pads 300. In one embodiment, as shown, the shield 128 is constructed around a top annular portion 302 and a bottom annular portion 304. Each of the top annular portion 302 and the bottom annular portion 304 terminates and surrounds the plasma chamber 120. The top annular portion 302 and the bottom annular portion 304 can be configured with various mounting features (e.g., mounting flanges) thereon for mounting a bracket 310 and / or a retaining member 312, as will be discussed further below. The thermal pads 300 are configured to be attached to the top annular portion 302 and the bottom annular portion 304 via one or more retaining members 312, as will be discussed further herein. The thermal pads 300 are generally configured to regulate heat flux from the plasma chamber 120 (e.g., the dielectric wall 122) to the respective thermal pads 300. One or more fluid inlets 306 and fluid outlets 308 can be coupled to the thermal pad 300 to circulate a heat exchange fluid through the thermal pad 300, as will be discussed further below. A mounting bracket 310 is also disposed between the top annular portion 302 and the bottom annular portion 304 for supporting an induction coil assembly (e.g., the induction coil 130). The induction coil 130 can be supported by the combination of the mounting bracket 310 and the mounting bracket panel 360. In addition, one or more apertures 366 are disposed in the mounting bracket 310. Figure 3 and Figure 4 They are shown as Figure 2 Top and bottom views of shield 128 are shown.

[0049] The materials used to form portions of the shield 128 may include any suitable metal material or combination of metal materials. For example, the top annular portion 302 and the bottom annular portion 304 may be formed from a copper material, an aluminum material, or a combination thereof. In an embodiment, the material used to form the top annular portion 302 and the bottom annular portion 304 is electrically conductive. Similarly, the thermal pad 300 may also be formed from any suitable metal material or combination of metal materials. For example, the thermal pad 300 may be formed from a copper material, an aluminum material, or a combination thereof. In addition, the retaining member 312 may be formed from a conductive material (e.g., a metal material). In certain embodiments, the retaining member 312 is formed from a copper material, such as beryllium copper and / or an optional silver-plated copper material. In addition, the mounting bracket 310 and the mounting bracket panel 360 may also be formed from a conductive material, such as a metal material. Connecting the top annular portion 302 to the bottom annular portion 304 using one or more conductive mounting brackets 310, retaining members 312, and / or thermal pads 300 facilitates forming a shield 128 that is electrically conductive and / or in which certain components of the shield 128 are electrically conductive and therefore electrically connected.

[0050] Also in Figure 5 More specifically, Figure 6-Figure 8 As shown in FIG, one or more mounting brackets 310 can be disposed between the top annular portion 302 and the bottom annular portion 304. The mounting brackets 310 can be configured to support the induction coil 130, as will be discussed further. The mounting brackets 310 can be used to electrically connect the top annular portion 302 to the bottom annular portion 304, so that multiple elements of the shield 128 are electrically connected. In addition, the mounting brackets 310 can be evenly spaced around the periphery of the dielectric wall 122. In some examples, the mounting brackets 310 can be machined, printed and / or molded (e.g., injection molded). As shown, the thermal pad 300 can be arranged in the space between the mounting brackets 310. In addition, the assembly of the top annular portion 302, the bottom annular portion 304 and the mounting brackets 310 can be placed around the dielectric wall of the plasma chamber 120.

[0051] The top annular portion 302 and / or the bottom annular portion 304 may be configured with additional mounting flanges 350 for mounting a plurality of mounting brackets 310 as shown. In addition, each of the mounting brackets 310 may be configured with one or more struts 352 configured to engage the mounting flanges 350 to secure the mounting bracket 310 to the top annular portion 302 and / or the bottom annular portion 304. For example, Figure 7An exemplary embodiment of one end of a mounting bracket 310 is shown having a post 352 disposed thereon. The post 352 can be fabricated so that each of the top annular portion 302 and the bottom annular portion 304 rests on an opposing shoulder of the post 352, thereby providing a consistent space between the top annular portion 302 and the bottom annular portion 304, and for ease of assembly. In some examples, the post 352 can be machined, printed, and / or molded (e.g., injection molded). Figure 5 As shown, the top annular portion 302 , the bottom annular portion 304 , and the mounting bracket 310 may be positioned around the dielectric wall 122 of the plasma chamber 120 .

[0052] Now refer to Figure 2 、 Figure 5 and Figure 9 , the thermal pad 300 can be coupled to the top annular portion 302 or the bottom annular portion 304 using one or more retaining members 312. The thermal pad 300 can be configured to include a top portion 314 and a bottom portion 316. The top portion 314 can be configured to engage a first end 318 of the retaining member 312, while the second end 319 of the retaining member 312 is coupled to the top annular portion 302 or the bottom annular portion 304. For example, Figure 10 As shown, the top 314 of the thermal pad 300 includes a small notch that substantially corresponds to the size and shape of the first end 318 of the retaining member 312. The first end 318 of the retaining member 312 can be secured to the top 314 of the thermal pad 300 and the second end 319 of the retaining member 312 can be secured to a portion of the top annular portion 302. The retaining member 312 can be secured to both the thermal pad 300 and the annular portion 304 via any suitable fasteners. Examples of suitable fasteners include screws. Similarly, one or more retaining members 312 can be engaged to the bottom 316 of the thermal pad 300 and the bottom annular portion 304 to secure the bottom 316 of the thermal pad 300.

[0053] The retaining members 312 can be positioned around the top annular portion 302 or the bottom annular portion 304 to provide consistent spacing between the top annular portion 302 and the bottom annular portion 304. Furthermore, the retaining members 312 can be positioned around the top annular portion 302 and / or the bottom annular portion 304 such that the thermal pads 300 are evenly distributed and / or positioned at even intervals around the perimeter and / or circumference of the dielectric wall 122 of the plasma chamber 120.

[0054] The retaining members 312 can be configured such that they provide resilience with respect to the placement of the thermal pad 300 on the shield 128. For example, the retaining members 312 can be formed of any suitable material, such as a metallic material (e.g., copper or beryllium copper or optionally silver-plated beryllium copper), such that the thermal pad 300 is retained against the outer surface of the dielectric wall 122 of the plasma chamber 120 by a compressive force. In an embodiment, the retaining members 312 can include one or more resilient bands (e.g., copper bands) that can be positioned and secured to the top annular portion 302, the bottom annular portion 304, and the thermal pad 300 to hold the thermal pad 300 in place.

[0055] In some embodiments, the retaining member 312 and the corresponding thermal pad 300 are configured so that the retaining member 312 is fully fixed in place and an internal torque is generated in the retaining member 312, causing the retaining member 312 to compress the thermal pad 300 against the side wall 122. For example, the ends of the retaining member 312 can be positioned radially offset relative to their placement on the top annular portion 302 or the bottom annular portion 304, and the thermal pad 300 can be radially offset so that tightening the retaining member 312 causes the retaining member 312 to elastically deform. In other embodiments, the retaining member 312 can be pre-formed so that placement into substantially any fixed configuration will produce a desired compression response. The thickness of the retaining member 312 can also be adjusted to adjust the clamping force. In some embodiments, thermal paste and / or other thermally conductive materials (e.g., adhesive pads) can be used at the interface between the thermal pad 300 and the side wall 122 (not shown). For example, in an embodiment, additional material (eg, thermal paste or conductive material) may be used between the inner surface 322 of the thermal pad 300 and the dielectric wall 122 to facilitate heat transfer from the dielectric wall 122 to the thermal pad 300 .

[0056] Additionally and / or alternatively, the retaining member 312 can be used to flexibly suspend the thermal pad 300, thereby allowing greater elastic deflection in the radial direction of the thermal pad 300. Thus, during operation of the device 500, the thermal pad 300 can expand and compress along with the dielectric wall 122. In such an embodiment, the thermal pad 300 can expand and contract without applying additional compressive forces to the dielectric wall 122 through the thermal pad 300, which could cause further stress and crack the dielectric wall 122.

[0057] like Figure 11As shown, when the thermal pad 300 is secured with one or more retaining members 312, the thermal pad 300 can include an outer surface 320 that faces generally away from the dielectric wall 122 and an inner surface 322 that faces and presses against the dielectric wall 122. Furthermore, in some examples, the thermal pad 300 can be formed to conform to a desired radius on one face (e.g., the inner surface 322) to provide a more uniform contact pressure distribution when clamped against the dielectric sidewall 122. For example, the thermal pad 300 can be formed to have a desired radius or curvature, indicated by arrow R, to provide more uniform contact throughout the face (e.g., the inner surface 322) of the thermal pad 300 that bears against the dielectric wall 122.

[0058] In addition to securely holding the thermal pad 300 against the dielectric wall 122, the retaining member 312 can also be used to electrically connect each thermal pad 300. For example, since each thermal pad 300 is connected to the top annular portion 302 and the bottom annular portion 304 via one or more retaining members 312, the retaining member 312 can provide an electrical connection between the top annular portion 302 and the bottom annular portion 304 via the retaining member 312 and the thermal pad 300. For example, in an embodiment, each thermal pad 300 is electrically conductive and in electrical communication with each other. Furthermore, the thermal pad 300 can be in electrical communication with the top annular portion 302 and / or the bottom annular portion 304. Furthermore, the one or more retaining members 312 can be configured to electrically connect the thermal pad 300 to a reference potential, such as ground potential. In certain embodiments, the reference potential can include a floating reference potential referenced to each of the plurality of thermal pads 300. For example, in certain embodiments, the top annular portion 302 and / or the bottom annular portion 304 can be electrically connected to a reference potential (e.g., ground potential) such that each thermal pad 300 is also electrically connected to the reference potential. Thus, in certain embodiments, the retaining member 312 can electrically connect the corresponding thermal pad 300 to a reference potential.

[0059] The thermal pad 300 can be operably connected to one or more heat sinks to remove heat from the one or more thermal pads 300. For example, Figure 12-14 An exemplary embodiment of a heat pad 300 that can be used in accordance with the present disclosure is shown. As shown, the heat pad 300 includes a top portion 314 and a bottom portion 316, as previously discussed. Additionally, one or more cooling channels 340 can be provided on or within the heat pad 300 for removing heat from the heat pad. The cooling channels 340 provided within the heat pad 300 can circulate a heat exchange fluid or other heat exchange medium to absorb and remove heat from the heat pad 300. Figure 13-14 As shown, the cooling channels 340 can be arranged in any of a variety of patterns within the thermal pad 300. In one example, the thermal pad 300 having the internal cooling channels 340 can be manufactured using additive manufacturing techniques (e.g., laser sintering techniques). In certain other embodiments, the thermal pad 300 can also be manufactured using subtractive machining techniques. For example, Figure 13-14 As shown, one arrangement of cooling channels can be formed in a series of drilling operations (e.g., three drilling operations). Alternatively, portions of the cooling channels 340 can be strategically plugged (e.g., with press-fit or threaded plugs, or with an injectable and / or curable compound) to provide U-shaped cooling channels. When arranged around the circumference of the plasma chamber 120, the thermal pads 300 can provide uniform coverage of the cooling channels 340 overall around at least a portion of the dielectric wall 122 of the plasma chamber 120. Thus, if a hot spot is detected, the flow of heat exchange fluid through any one (or any group of) thermal pads 300 can be adjusted to increase heat removal from the detected point.

[0060] Each thermal pad 300 may include a cooling channel 340 having one or more ends, such as a first end 342 and a second end 344. Figure 14 As shown, the first end 342 and the second end 344 can be connected to a port, such as a port for introducing and / or removing a heat exchange fluid. For example, the first end 342 can be joined to the fluid inlet 306 so that a heat exchange fluid (e.g., a fresh heat exchange fluid) can be provided to the cooling channel 340. The fluid outlet 308 is joined to the second end 344 so that a heat exchange fluid (e.g., a used heat exchange fluid) can be removed from the cooling channel 340. Additional inlet and outlet pipes can be used to connect the cooling channel 340 to ports (e.g., inlet 306 and / or outlet 308). For example, the inlet and outlet pipes can be attached via any suitable method, such as by brazing. The inlet 306 and outlet 308 can be connected to a manifold, such as a coolant, for distributing a heat exchange fluid (e.g., a coolant) by any necessary pipe. In one example, a flexible tube (e.g., a PTFE tube) is used to connect the inlet 306 and / or outlet 308 to a manifold (e.g., an 8-to-1 manifold). If desired, any plug (if used) can also be sealed and / or brazed. The heat exchange fluid utilized can be any known heat exchange fluid, including but not limited to water (e.g., deionized water), a mixture of ethylene glycol and an aqueous solution, a dielectric fluid (e.g., a fluorocarbon fluid and / or a poly-α-olefin), and / or mixtures thereof.

[0061] In embodiments, heat generated during operation of the induction coil 130 may generate a heat flux that is exposed to the plasma chamber 120 and / or the dielectric wall 122. Thus, in embodiments, the use of the thermal pad 300 allows for the regulation (e.g., reduction) of the heat flux from the dielectric wall 122 via one or more of the plurality of thermal pads 300. In such embodiments, the thermal pad 300 may be used to regulate the heat flux such that a substantially uniform temperature gradient may be maintained within the dielectric wall 122 about the circumferential direction (C) and / or the longitudinal direction (L).

[0062] Now refer to Figure 15In some embodiments, the induction coil 130 may be wound around the plasma chamber 120. For example, Figure 15-16 As shown, the induction coil 130 may include an induction coil assembly that is wrapped around at least a portion of the periphery of the dielectric wall 122 and held in place by one or more mounting brackets 310. In addition, a mounting bracket panel 360 may be positioned to adequately support and / or hold the induction coil 130 in place. Although only one induction coil assembly containing one induction coil is shown, the present disclosure is not limited in this regard. In fact, any number of induction coils may be combined and used with the shield 128 provided herein. For example, certain embodiments may include at least two induction coils, such as at least three induction coils, such as at least four induction coils, etc. In addition, as shown, the induction coil 130 completes one or more complete turns (e.g., multiple turns) around the circumference and / or periphery of the dielectric wall 122 of the plasma chamber 120 as shown. In addition, when the induction coil 130 is mounted to the mounting bracket 310 and the mounting bracket panel 360 is positioned to securely hold the induction coil 130 in place, one or more apertures 366 may be provided in the mounting bracket configuration, more specifically as shown. Figure 17 The aperture 366 is configured to reduce the risk of coil arcing during operation of the induction coil 130 .

[0063] Furthermore, in embodiments, the plurality of thermal pads 300 may be collectively characterized as having a total width in a circumferential direction relative to the outer surface of the dielectric wall 122, the total width spanning at least approximately 60% of the total circumference of the dielectric wall 122. In other words, the total width of the plurality of thermal pads 300 disposed on the dielectric wall 122 covers at least approximately 60% of the circumferential length of the dielectric wall 122, such as at least approximately 70%, such as at least approximately 80%, such as at least approximately 90%, or more. Furthermore, each thermal pad 300 may include a height in the longitudinal direction (L) that is generally greater than the height in the longitudinal direction (L) of the inductively coupled plasma source's inductive coil 130. For example, in embodiments, the thermal pads 300 may extend further in the longitudinal direction than the inductive coil 130 of the inductive coil assembly.

[0064] Figure 18 A flow chart of an exemplary method (700) according to an exemplary aspect of the present disclosure is depicted. The method (700) will be described with reference to the example Figure 1 The method (700) may be implemented in any suitable plasma processing apparatus. For purposes of illustration and discussion, Figure 18The steps are depicted as being performed in a particular order. One of ordinary skill in the art, using the disclosure provided herein, will appreciate that the individual steps of any method described herein may be omitted, expanded, performed simultaneously, rearranged, and / or modified in various ways without departing from the scope of the present disclosure. Furthermore, individual steps (not shown) may be performed without departing from the scope of the present disclosure.

[0065] At (702), the method may include placing a workpiece 114 in a processing chamber 110 of a plasma processing apparatus 500. For example, the workpiece 114 may be placed on a workpiece support 112 disposed in the processing chamber 110. The processing chamber 110 may be separated from the plasma chamber 120 (e.g., by a barrier assembly).

[0066] At (704), the method may include generating a plasma in the plasma chamber 120 of the plasma processing apparatus 500 using an inductively coupled plasma source. For example, a process gas may be admitted from a gas source 150 via an annular gas distribution channel 151 or other suitable gas introduction mechanism into the plasma chamber interior 125. The process gas is excited via the inductively coupled plasma source 135 to generate a plasma in the plasma chamber 120. For example, the inductive coil 130 may be excited by RF energy from an RF power generator 134 to generate a plasma in the plasma chamber interior 125. In some embodiments, the inductively coupled plasma source may be excited with pulsed power to obtain desired free radicals with reduced plasma energy. The plasma may be used to generate one or more free radicals from the process gas.

[0067] Optionally, the method may include filtering one or more species (e.g., ions) generated by the plasma to produce a filtered mixture. In some embodiments, the one or more species may be filtered using a barrier assembly 200 that separates the plasma chamber 120 from the processing chamber 110 where the workpiece 114 resides. For example, the barrier assembly 200 may be used to filter ions generated by the plasma. The barrier 200 may have a plurality of apertures. Charged particles (e.g., ions) may recombine on the walls of the barrier 200 as they pass through the apertures. Neutral species (e.g., free radicals) may pass through the apertures.

[0068] At (706), the method may include exposing the workpiece 114 to one or more substances in the plasma and / or filtered mixture to provide a treatment process to the workpiece 114. For example, the one or more substances generated by exposing the workpiece 114 to the plasma may cause material, chemical, and / or physical changes to certain layers or features present on the workpiece 114. For example, in some embodiments, the treatment process includes a plasma etching process. The plasma etching process may selectively remove one or more material layers from the workpiece 114. In other embodiments, the treatment process includes a plasma deposition process. For example, the plasma deposition process may selectively deposit one or more material layers on the workpiece 114. Other plasma processes may be used to modify material layers present on the workpiece. For example, a plasma-based surface treatment process may be utilized to modify the surface morphology of the workpiece or to modify the chemical composition of a layer on the workpiece. Any other known suitable plasma-based treatment for a workpiece may be performed on the workpiece 114.

[0069] At 708, the method may include shielding the plasma chamber 120 from the inductively coupled plasma source 135 with a shield 128. For example, the shield 128, including the thermal pad 300, the retaining member 312, the mounting bracket 310, the top annular portion 302, and the bottom annular portion 304, may be disposed around the dielectric wall 122 of the plasma chamber 120. Portions or the entire shield 128 may be electrically connected and coupled to a reference potential (e.g., ground potential) to reduce capacitive coupling of the inductive coil 130 to the generated plasma.

[0070] At 710, the method includes cooling the dielectric wall 122 of the plasma chamber 120 with the shield 128. For example, the shield 128 can be operable to regulate heat flux out of the dielectric wall 122 and / or the plasma chamber 120 before, during, or after processing of the workpiece 114. For example, in certain embodiments, a specific dielectric wall temperature or parameter associated with a desired temperature difference between the dielectric wall 122, the plasma chamber 120, and / or the induction coil 130 can be provided to the controller 175. The controller 175 can then operate one or more components of the shield 128 (e.g., controlling the flow of a heat exchange fluid through the thermal pad 300) to maintain the desired processing temperature parameters for the plasma chamber 12 and / or the dielectric wall 122. Furthermore, the controller 175 can operate a closed-loop system to maintain a desired temperature input to the dielectric wall 122, the plasma chamber 120, and / or the induction coil 130 during processing. Thus, the controller 175 can adjust the flow of heat exchange fluid to one or more of the plurality of thermal pads 300 to adjust the thermal gradient within the dielectric wall 122. The thermal gradient can decrease circumferentially, longitudinally, or both relative to the plasma chamber 120.

[0071] At (712), the method may include removing the workpiece from the processing chamber 109. For example, the workpiece 106 may be removed from the workpiece support 112 in the processing chamber 110. The plasma processing apparatus may then be conditioned for future processing of additional workpieces.

[0072] An exemplary embodiment of the present disclosure is directed to a plasma processing apparatus, comprising: a plasma chamber including a dielectric wall having an outer surface; an inductively coupled plasma source configured to generate plasma in the plasma chamber; a shield disposed between the outer surface of the dielectric wall and the inductively coupled plasma source, the shield comprising: a top annular portion, a bottom annular portion, and a plurality of thermal pads, the plurality of thermal pads being coupled to the top annular portion and / or the bottom annular portion by one or more retaining members, wherein the one or more retaining members provide a compressive force to secure one or more of the plurality of thermal pads against the outer surface of the dielectric wall, wherein the plurality of thermal pads are configured to regulate heat flux from the dielectric wall to the respective thermal pads.

[0073] In some embodiments, the top annular portion, the bottom annular portion, and / or the plurality of thermal pads comprise a metallic material.

[0074] In some embodiments, one or more retaining members comprise a metallic material. For example, in some embodiments, one or more retaining members comprise copper, aluminum, or a combination thereof.

[0075] In some embodiments, the apparatus includes one or more mounting brackets extending from the top annular portion to the bottom annular portion, the mounting brackets configured to support the inductively coupled plasma source. For example, the one or more mounting brackets include one or more apertures disposed therein to reduce arcing of the coil of the inductively coupled plasma source.

[0076] In some embodiments, an inductively coupled plasma source includes a source coil assembly configured to make one or more 360° turns around a circumference of a dielectric wall. In some embodiments, one or more thermal pads are disposed between one or more turns of the source coil assembly and the dielectric wall.

[0077] In some embodiments, the dielectric wall comprises quartz or a ceramic material.

[0078] In some embodiments, the thermal pad is operably coupled to one or more heat sinks to remove heat from the one or more thermal pads.

[0079] In some embodiments, the plurality of thermal pads include one or more cooling channels disposed therein, the cooling channels configured to circulate a heat exchange fluid to remove heat from the thermal pads. For example, the one or more cooling channels may include a first end coupled to a fluid inlet for providing fresh heat exchange fluid to the one or more cooling channels, and a second end coupled to a fluid outlet for removing spent heat exchange fluid from the one or more cooling channels.

[0080] In some embodiments, one or more thermal pads include an outer surface comprising a top and a bottom configured to engage one or more retaining members, wherein a first end of a first retaining member is engaged to the top of the thermal pad and a second end of the first retaining member is engaged to a top annular portion of the shield arrangement, wherein a first end of a second retaining member is engaged to the bottom of the thermal pad and a second end of the second retaining member is engaged to the bottom of the shield body to couple the thermal pad to the shield arrangement.

[0081] In some embodiments, each thermal pad is electrically conductive and in electrical communication with each other.

[0082] In some embodiments, heat flux from the dielectric wall is regulated via one or more of the plurality of thermal pads to maintain a substantially uniform temperature gradient around the circumference within the dielectric wall.

[0083] In some embodiments, heat flux from the dielectric wall is regulated via one or more of the plurality of thermal pads to maintain a substantially uniform temperature gradient about a longitudinal direction within the dielectric wall.

[0084] In some embodiments, one or more retaining members are electrically conductive.

[0085] In some embodiments, the one or more retention members comprise one or more copper strips.

[0086] In some embodiments, one or more retaining members flexibly suspend the corresponding thermal pad to allow greater elastic deflection of the thermal pad in the radial direction.

[0087] In some embodiments, one or more retaining members electrically connect the respective thermal pads to a reference potential. For example, in some embodiments, the reference potential is ground potential. In some embodiments, the reference potential is a floating potential referenced to each of the plurality of thermal pads.

[0088] In some embodiments, the plurality of thermal pads are collectively characterized by a total width in a circumferential direction relative to one or more surfaces of the plasma source that spans at least about 60% of the total circumference of the dielectric wall.

[0089] In some embodiments, a height of the plurality of thermal pads in a longitudinal direction is greater than a height of the coil assembly of the inductively coupled plasma source in a longitudinal direction.

[0090] Another exemplary embodiment of the present disclosure is directed to a plasma processing system comprising: a plasma chamber including a dielectric wall having an outer surface; an inductively coupled plasma source configured to generate plasma in the plasma chamber; a shield disposed between the outer surface of the dielectric wall and the inductively coupled plasma source, the shield comprising: a top annular portion, a bottom annular portion, and a plurality of heat pads, the plurality of heat pads being coupled to the top annular portion and / or the bottom annular portion by one or more retaining members, wherein the one or more retaining members provide a compressive force to secure one or more of the plurality of heat pads against the outer surface of the dielectric wall, wherein the plurality of heat pads are configured to regulate heat flux from the dielectric wall to the respective heat pads, wherein the heat pads include one or more cooling channels disposed therein, the cooling channels configured to circulate a heat exchange fluid to remove heat from the heat pads; a temperature measurement system configured to monitor a temperature of the dielectric wall; and a controller configured to perform one or more operations, the one or more operations comprising (i) regulating a fluid flow rate of the heat exchange fluid to one or more of the plurality of heat pads, and / or (ii) regulating power input to the inductively coupled plasma source.

[0091] Another exemplary embodiment relates to a method for processing a workpiece, comprising: placing the workpiece on a workpiece support disposed in a processing chamber of a plasma processing apparatus; generating plasma in a plasma chamber of the plasma processing apparatus using an inductively coupled plasma source, the plasma chamber including a dielectric wall; exposing the workpiece to one or more species in the plasma to provide a treatment process for the workpiece; and shielding the plasma chamber from the inductively coupled plasma source using a shielding apparatus, the shielding apparatus comprising: a top annular portion, a bottom annular portion, and a plurality of thermal pads coupled to the top annular portion and / or the bottom annular portion by one or more retaining members, wherein the one or more retaining members provide a compressive force to secure the one or more thermal pads against an outer surface of the dielectric wall, wherein the plurality of thermal pads are configured to regulate heat flux from the dielectric wall to the respective thermal pads.

[0092] In some embodiments, a method includes cooling a dielectric wall of a plasma chamber with a shield.

[0093] In some embodiments, the method includes adjusting a heat exchange fluid flow to one or more of the plurality of thermal pads to adjust a thermal gradient within the dielectric wall. In some embodiments, the thermal gradient decreases circumferentially, longitudinally, or both relative to the plasma chamber.

[0094] Although the subject matter has been described in detail with respect to specific exemplary embodiments thereof, it should be understood that modifications, variations, and equivalents of such embodiments may readily occur to those skilled in the art upon gaining an understanding of the foregoing. Accordingly, the scope of the present disclosure is intended to be exemplary rather than limiting, and the present disclosure does not exclude the inclusion of such modifications, variations, and / or additions to the subject matter, which would be apparent to one of ordinary skill in the art.

Claims

1. A plasma processing apparatus comprising: a plasma chamber comprising a dielectric wall having an outer surface; an inductively coupled plasma source configured to generate plasma in the plasma chamber; a shielding device disposed between the outer surface of the dielectric wall and the inductively coupled plasma source, the shielding device comprising: top annular portion; bottom annular portion; an induction coil assembly comprising one or more conductive coils wrapped around at least a portion of the outer surface of the dielectric wall of the plasma chamber; and a plurality of thermal pads coupled to the top annular portion and / or the bottom annular portion via one or more retaining members, wherein the one or more retaining members provide a compressive force to secure one or more of the plurality of thermal pads against the outer surface of the dielectric wall, wherein the plurality of thermal pads are configured to regulate heat flux from the dielectric wall to the respective thermal pads.

2. The plasma processing apparatus according to claim 1, wherein The induction coil assembly is held in place by one or more mounting brackets.

3. The plasma processing apparatus according to claim 2, wherein: The one or more mounting brackets include a mounting bracket panel to support the one or more induction coils.

4. The plasma processing apparatus according to claim 1, wherein The one or more induction coils are configured to complete one or more complete turns around the outer surface of the dielectric wall of the plasma chamber.

5. The plasma processing apparatus according to claim 1, wherein The top annular portion, the bottom annular portion, and / or the plurality of thermal pads comprise a metal material.

6. The plasma processing apparatus according to claim 1, wherein The one or more retaining members comprise a metallic material.

7. The plasma processing apparatus of claim 1 , further comprising one or more mounting brackets extending from the top annular portion to the bottom annular portion, the mounting brackets being configured to support the inductively coupled plasma source, wherein: The one or more mounting brackets include one or more apertures disposed therein to reduce coil arcing of the inductively coupled plasma source.

8. The plasma processing apparatus according to claim 1, wherein The thermal pad is operably coupled to one or more heat sinks to remove heat from the one or more thermal pads.

9. The plasma processing apparatus according to claim 1, wherein: The plurality of thermal pads include one or more cooling channels disposed therein, the one or more cooling channels configured to circulate a heat exchange fluid to remove heat from the thermal pads.

10. The plasma processing apparatus according to claim 9, wherein The one or more cooling channels include a first end coupled to a fluid inlet for providing fresh heat exchange fluid to the one or more cooling channels and a second end coupled to a fluid outlet for removing spent heat exchange fluid from the one or more cooling channels.

11. The plasma processing apparatus according to claim 1, wherein The one or more thermal pads include an outer surface including a top and a bottom configured to engage the one or more retaining members, wherein a first end of a first retaining member is engaged to the top of the thermal pad and a second end of the first retaining member is engaged to the top annular portion of the shield arrangement, wherein a first end of a second retaining member is engaged to the bottom of the thermal pad and a second end of the second retaining member is engaged to the bottom of the shield body to join the thermal pad to the shield arrangement.

12. The plasma processing apparatus according to claim 1, wherein Each of the thermal pads is electrically conductive and in electrical communication with each other.

13. The plasma processing apparatus according to claim 1, wherein The one or more retaining members are electrically conductive.

14. The plasma processing apparatus according to claim 1, wherein The one or more retaining members flexibly suspend the corresponding thermal pad to allow greater elastic deflection of the thermal pad in the radial direction.

15. The plasma processing apparatus according to claim 1, wherein The one or more retaining members electrically connect the respective thermal pad to a reference potential.

16. The plasma processing apparatus according to claim 15, wherein: The reference potential is ground potential.

17. The plasma processing apparatus according to claim 15, wherein: The reference potential is a floating potential referenced to each of the plurality of thermal pads.

18. The plasma processing apparatus according to claim 1, wherein The plurality of thermal pads are collectively characterized by a total width in a circumferential direction relative to one or more surfaces of the plasma source that spans at least 60% of a total circumference of the dielectric wall.

19. The plasma processing apparatus according to claim 1, wherein A height of the plurality of thermal pads in a longitudinal direction is greater than a height of the coil assembly of the inductively coupled plasma source in the longitudinal direction.

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