Ceramic top plate with an annular projection to protect a seal ring and a bonding layer of a substrate support from ion erosion

Abstract

A substrate support for a plasma processing system includes a baseplate and a ceramic top plate including a cylindrical body and an annular projection extending from a bottom surface of the cylindrical body at a radially outer edge of the cylindrical body. A bonding layer bonds the ceramic top plate to the baseplate. A seal ring includes an annular body arranged around the baseplate and a radially outer edge of the bonding layer and between the bottom surface of the ceramic top plate and the baseplate. An edge ring is arranged around and spaced from the ceramic top plate and the seal ring. The annular projection of the ceramic top plate is configured to prevent a direct line of sight between ions generated by plasma and the seal ring.

Description

CERAMIC TOP PLATE WITH AN ANNULAR PROJECTION TO PROTECT A SEAL RING AND A BONDING LAYER OF A SUBSTRATE SUPPORT FROM ION EROSIONCROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of U.S. Provisional Application No. 63 / 606,040 filed on December 4, 2023. The entire disclosure of the above application is incorporated herein by reference.FIELD

[0002] The present disclosure relates to substrate processing systems, and more particularly to a ceramic top plate including an annular projection for protecting a seal ring and a bonding layer of a substrate support.BACKGROUND

[0003] The background description provided here is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.

[0004] Substrate processing systems may be used to treat substrates such as semiconductor wafers. The substrate treatments may include deposition, etching, cleaning, and other treatments. A substrate is arranged on a substrate support in a processing chamber. During processing, gas mixtures may be introduced into the processing chamber using a showerhead or other gas delivery device and plasma may be used to initiate chemical reactions.

[0005] The substrate support may include an electrostatic chuck (ESC) including a baseplate, a bonding layer, and a ceramic top plate. Substrates are supported on the top plate during plasma processing such as etching. The top plate is typically made of ceramic and is attached by the bonding layer to the baseplate. Since the substrate support is arranged in the processing chamber, it is exposed to plasma. Over time, plasma or ions from the plasma erode a radially outer edge of the bonding layer and eventually require the bonding layer to be repaired. Typically, the bonding layer fails prior to the lifetime of the ESC and requires downtime for repair / replacement.SUMMARY

[0006] A substrate support for a plasma processing system includes a baseplate and a ceramic top plate including a cylindrical body and an annular projection extending from a bottom surface of the cylindrical body at a radially outer edge of the cylindrical body. A bonding layer bonds the ceramic top plate to the baseplate. A seal ring includes an annular body arranged around the baseplate and a radially outer edge of the bonding layer and between the bottom surface of the ceramic top plate and the baseplate. An edge ring is arranged around and spaced from the ceramic top plate and the seal ring. The annular projection of the ceramic top plate is configured to prevent a direct line of sight between ions generated by plasma and the seal ring.

[0007] In other features, the annular body of the seal ring is made of elastomer. The ceramic top plate is made of alumina. A bottom and radially outer edge of the annular projection of the ceramic top plate is chamfered. A bottom and radially inner edge of the annular projection of the ceramic top plate is chamfered. A corner between the annular projection of the ceramic top plate is chamfered.

[0008] In other features, the bonding layer extends radially outwardly relative to the baseplate and between the seal ring and the ceramic top plate radially inwardly from the annular projection. The seal ring includes a notch to provide a seal against at least one of a bottom surface and a radially inner surface of the annular projection.

[0009] A ceramic top plate for a substrate support of a plasma processing system includes a cylindrical body made of ceramic and configured for attachment to a baseplate. An annular projection is made of ceramic and extends from a bottom surface of the cylindrical body at a radially outer edge of the cylindrical body. The annular projection is configured to extend between a seal ring and an edge ring. The annular projection of the ceramic top plate is configured to prevent a direct line of sight between ions generated by plasma and the seal ring.

[0010] In other features, the ceramic top plate is made of alumina. A bottom and radially outer edge of the annular projection of the ceramic top plate is chamfered. A bottom and radially inner edge of the annular projection of the ceramic top plate is chamfered. A corner between the annular projection of the ceramic top plate is chamfered.

[0011] Further areas of applicability of the present disclosure will become apparent from the detailed description, the claims, and the drawings. The detailed description andspecific examples are intended for purposes of illustration only and are not intended to limit the scope of the disclosure.BRIEF DESCRIPTION OF THE DRAWINGS

[0012] The present disclosure will become more fully understood from the detailed description and the accompanying drawings, wherein:

[0013] FIG. 1 is a functional block diagram of an example of a substrate processing system comprising a substrate support including a baseplate, a ceramic top plate, a bonding layer, and a seal ring;

[0014] FIG. 2 is an enlarged cross sectional view showing an example of the baseplate, the ceramic top plate, the bonding layer, and the seal ring;

[0015] FIGS. 3A to 3C are cross sectional views illustrating an example of exposure of the seal ring to ion bombardment from plasma;

[0016] FIG. 4 is an enlarged cross sectional view showing an example of the baseplate, a ceramic top plate including a downwardly-directed annular projection at a radially outer edge of thereof, the bonding layer, and the seal ring according to the present disclosure;

[0017] FIGS. 5A to 5C are cross sectional views illustrating an example of protection of the seal ring from ion bombardment from plasma using the ceramic top plate including the downwardly-directed annular projection at the radially outer edge thereof according to the present disclosure;

[0018] FIG. 6 is an enlarged cross sectional view showing another example of the baseplate, a ceramic top plate including the downwardly-directed annular projection at a radially outer edge of thereof, the bonding layer, and the seal ring according to the present disclosure; and

[0019] FIG. 7 is an enlarged cross sectional view showing another example of the baseplate, a ceramic top plate including the downwardly-directed annular projection at a radially outer edge of thereof, the bonding layer, and the seal ring according to the present disclosure.

[0020] In the drawings, reference numbers may be reused to identify similar and / or identical elements.DETAILED DESCRIPTION

[0021] A substrate support such as an electrostatic chuck (ESC) includes a baseplate and a ceramic top plate arranged on the baseplate. A bonding layer bonds the ceramic top plate to an upper surface of the baseplate. In addition to mechanically connecting the ceramic top plate to the baseplate, the bonding layer also provides a vacuum seal and a temperature break between the ceramic top plate and the baseplate. Unless the bonding layer is protected, a radially outer edge of the bonding layer is exposed to plasma and is prone to ion and / or plasma erosion. Failure of the bonding layer may occur in less than 100 RF hours. However, some processes have a target mean time between clean (MTBC) of 1000 hours.

[0022] Seal rings have been used to protect the radially outer edge of the bonding layer from ion / plasma attack. The seal rings are made of plasma-resistant materials and are arranged below the ceramic top plate and around the radially outer edge of the bonding layer. In some examples, the seal rings are made from an elastomer such as fluoroelastomer polymer (e.g., elastomer seals or E-seals). Examples of elastomers include fluoroelastomer polymers such as perfluoroelastomer (FFKM) or fluorocarbon- based fluoroelastomer (FKM), although other plasma resistant materials can be used.

[0023] While the lifetime of the seal ring is shorter than the lifetime of the ESC, the seal ring is field replaceable at a relatively low cost. The seal ring provides a seal against the ceramic top plate and the baseplate to protect the radially outer edge of the bonding layer during plasma processing. Trade-offs are made when the seal rings are designed. For example, seal rings with larger radial thicknesses provide improved protection of the bonding layer but have a higher risk of cracking. Seal rings with a smaller radial thickness have a shorter lifetime and require more frequent replacement. This tradeoff will become more difficult with increased RF power levels that are used in next generation substrate processing tools.

[0024] In some processes, the ESC / edge ring / substrate geometry is optimized to improve thermal uniformity at the edge of the substrate as well as to reduce arcing from the substrate to the edge ring. Some combinations of the geometry changes create a larger field of view (or line of sight) for ions generated by the plasma to the seal ring and / or the bonding layer. Ions generated by the plasma travel along the line of sight and increase erosion of bond protection materials (e.g., the seal ring and / or the bonding layer).

[0025] The erosion caused by the ions is typically the main prohibiting factor for meeting the target MTBC of the processing chamber. For example, the ion exposure erodes the seal ring within 1 / 3 of the MTBC (e.g., ~ 300 RF hours for a 1000 RF hour MBTC). After erosion, protection provided by the seal ring is weakened or lost and erosion of the bonding layer begins. Erosion of the seal ring may cause arcing at edges of the ceramic top plate, thermal uniformity changes at the radially outer edge of the substrate, and / or leakage of gas such as helium from backside gas delivery holes.

[0026] Some processes have attempted to use a cover band arranged around the seal ring to protect the seal ring. In some examples, the cover band is made of polytetrafluoroethylene (PTFE). The cover band increases the lifetime of the seal ring to around 1 / 2 of the MTBC before failing and exposing the seal band to ion bombardment and / or plasma.

[0027] To withstand the higher MTBC specification, the thickness of cover band would need to increase by 4 to 5 times. However, there is typically insufficient room for a thicker cover band. Installation of the cover band is challenging due to tight spacing. The seal ring and the cover band are positioned accurately around the substrate support with vertical clearance of less than 1.5 mm. Incorrect placement of the seal ring and / or the cover band can cause misplacement of the edge ring (and a corresponding shift in process uniformity and / or arcing at edge ring). At higher temperatures, expansion of the cover band can cause the cover band to contact the edge ring.

[0028] A ceramic top plate according to the present disclosure includes a cylindrical body and a downwardly-directed annular projection arranged at a radially outer edge of the cylindrical body. The downwardly-directed annular projection prevents a line of sight between ions generated by the plasma and the seal ring to reduce wear on the seal ring due to ion bombardment. The downwardly-directed annular projection increases the life of the seal ring beyond the MTBC.

[0029] Erosion of the ceramic top plate due to ion exposure is much slower than erosion of the seal ring or cover band. In some examples, the ceramic top plate with the downwardly-directed annular projection may last the lifetime of the ESC. The downwardly-directed annular projection protects the seal ring from ion exposure, and the seal ring protects the bonding layer from the plasma / radical erosion. The ceramic top plate with the downwardly-directed annular projection provides improved protectionwithout impacting other ESC / edge ring / substrate geometry developed for thermal uniformity at the edge and reduced arcing from substrate to edge ring.

[0030] Referring now to FIG. 1 , an example of a substrate processing system 100 for performing treatment such as etching using RF plasma is shown. While etching is shown, the ceramic top plate with the downwardly-directed annular projection can be used on substrate supports for other types of plasma-assisted substrate treatments. The substrate processing system 100 includes a processing chamber 102 that encloses other components of the substrate processing system 100 and contains the RF plasma. The substrate processing system 100 includes an upper electrode 104 and a substrate support 106, such as an electrostatic chuck (ESC). During operation, a substrate 108 is arranged on the substrate support 106.

[0031] For example only, the upper electrode 104 may include a showerhead 109 that introduces and distributes process gases within the processing chamber 102. The showerhead 109 may include a stem portion including one end connected to the top surface of the processing chamber. A base portion is generally cylindrical and extends radially outwardly from an opposite end of the stem portion at a location that is spaced from the top surface of the processing chamber. A substrate-facing surface or faceplate of the base portion of the showerhead includes a plurality of holes through which process gas or purge gas flows. Alternately, the upper electrode 104 may include a conducting plate and the process gases may be introduced in another manner.

[0032] The substrate support 106 may comprise an electrostatic chuck (ESC) that includes a baseplate 110 that is conductive and acts as a lower electrode. A ceramic top plate 1 12 is arranged on the baseplate 1 10. A bonding layer 114 attaches the ceramic top plate 1 12 to the baseplate 1 10 to provide a mechanical connection, a vacuum seal, and / or a thermal break. The baseplate 1 10 may include one or more channels 1 16 for flowing fluid such as coolant.

[0033] As will be described further below, a seal ring 1 17 is arranged around the baseplate 1 10 between the ceramic top plate 1 12 and a radially projecting lower portion of the baseplate 1 10. The seal ring 1 17 protects the bonding layer 114. An edge ring 1 18 is arranged radially outside of the ceramic top plate 1 12. A gap is formed between the edge ring 1 18 and the ceramic top plate 112. During plasma processing, plasma and / or ions generated by plasma 1 19 pass through the gap, erode the seal ring 117, and attack the bonding layer 114.

[0034] An RF generating system 120 generates and outputs an RF voltage to one of the upper electrode 104 and the lower electrode (e.g., the baseplate 1 10 of the substrate support 106). The other one of the upper electrode 104 and the baseplate 1 10 may be DC grounded, AC grounded, or floating. For example only, the RF generating system 120 may include an RF voltage generator 122 that generates the RF voltage that is fed by a matching and distribution network 124 to the upper electrode 104 or the baseplate 1 10. In other examples, the plasma may be generated inductively or remotely. While the RF generating system 120 corresponds to a capacitively coupled plasma (CCP) system, other plasma processing systems may be used such as an inductively coupled plasma (ICP) system or other types of plasma processing systems.

[0035] A gas delivery system 130 includes one or more gas sources 132-1 , 132-2, ..., and 132-N (collectively gas sources 132), where N is an integer greater than zero. The gas sources 132 supply one or more precursors, etching gases, carrier gases, purge gases, and mixtures thereof to the processing chamber 102. Vaporized precursors may also be used. The gas sources 132 are connected by valves 134-1 , 134-2, ..., and 134- N (collectively valves 134) and mass flow controllers 136-1 , 136-2, ..., and 136-N (collectively mass flow controllers 136) to a manifold 140. An output of the manifold 140 is connected to the gas delivery device in the processing chamber 102.

[0036] A temperature controller 142 may be connected to a plurality of heating elements 144 (e.g., thermal control elements, or TCEs) arranged in the ceramic top plate 1 12. For example, the heating elements 144 may include, but are not limited to, macro heating elements corresponding to respective zones in a multi-zone heating plate and / or an array of micro heating elements disposed across multiple zones of a multi-zone heating plate. The ceramic top plate 1 12 may also include one or more conductors (not shown) to engage and release the substrate 108 using electrostatic force. The temperature controller 142 may be used to adjust output of the plurality of heating elements 144 to control a temperature of the substrate support 106 and the substrate 108. The temperature controller 142 may also communicate with a coolant assembly 146 to control coolant flow through the channels 116. For example, the coolant assembly 146 may include a coolant pump and reservoir. The temperature controller 142 operates the coolant assembly 146 to selectively flow the coolant through the channels 1 16 to cool the substrate support 106.

[0037] A valve 148 and pump 149 may be used to control pressure and / or to evacuate reactants from the processing chamber 102. A system controller 150 may be used to control components of the substrate processing system 100. Although shown as separate controllers, the temperature controller 142 may be implemented by the system controller 150.

[0038] Referring now to FIG. 2, an example configuration of a baseplate, a ceramic top plate, a bonding layer, and a seal ring is shown. A substrate 210 is arranged on the top surface of a ceramic top plate 214. The bottom surface of the ceramic top plate 214 is attached to the top surface of a baseplate 222 by a bonding layer 218. A cavity 220 is formed below the ceramic top plate 214, a radially outer side 223 of the baseplate 222, and a radially inner side 231 of an edge ring 230. A seal ring 226 is arranged in the cavity 220 adjacent to and / or in contact with the radially outer side of the baseplate 222 and a radially inner edge of the bonding layer 218 to protect the bonding layer 218.

[0039] The seal ring 226 includes an annular body 227, a radially inner surface 229, and a radially outer surface 228. In some examples, the radially outer surface of the seal ring 226 is concave (shown), convex (not shown), parallel to a vertical direction, and / or another suitable shape. The top surface of the seal ring 226 contacts the bottom surface of the ceramic top plate 214. The bottom surface of the seal ring 226 contacts the upper surface of a radially outer portion 224 of the baseplate 222.

[0040] The edge ring 230 includes an annular body 234. The annular body 234 includes a radially inner side 231 and a sloped surface 246 between the radially inner side 231 and the bottom surface of the edge ring 230. In some examples, a conductive gel 250 may be arranged between the edge ring 230 and the radially outer portion 224 of the baseplate 222. A surface 240 of the edge ring 230 extends radially outwardly from the radially inner side 231 in a plane below and parallel to a plane including the substrate. A top surface of the edge ring 230 transitions to a sloped surface 238 extending outwardly and upwardly from the surface 240.

[0041] Critical dimensions that may be controlled to provide different processing effects include a distance d1 from a radially outer edge of the ceramic top plate to a radially inner surface of the edge ring, a substrate overhang distance d2, a pocket depth distance d3, and a ceramic to top of edge ring distance d4. Varying the critical dimensions may be performed to adjust etching of the substrate, substrate temperature uniformity, or other processing effects. However, some changes to the critical dimensions may increaseexposure of the seal ring 226 and / or the bonding layer 218 to ion bombardment from the plasma.

[0042] For example, the distance d4 from the bottom surface of the ceramic top plate to top of the edge ring 230 ensures edge ring placement in view of manufacturing / thermal / placement tolerances. Increasing the distance d1 may allow the edge ring 230 to move or walk in one direction or another which may cause increased ion exposure and erosion.

[0043] For example, some applications may require a relatively high pocket depth d3 (e.g., greater than 15, 20, 25, or 30 mil) to ensure that polymer buildup at the back of the substrate does not cause arcing from the substrate 210 to the edge ring 230. However, increasing the pocket depth d3 opens up the field of view and may cause the seal ring 226 to experience direct ion exposure. Some processes may require decreased substrate overhang d2 to improve edge thermal uniformity. Usually, the inner diameter of the substrate support is increased to decrease substrate overhang. Decreasing the substrate overhang d2 also opens up the field of view and may cause the seal ring 226 to experience direct ion exposure.

[0044] In some processes, the RF power is increased to provide improved performance. Higher energy and flux increases the rate of erosion. In some processes, the MTBC is increased (e.g., from 350 RF hours to 1000 RF hours) to reduce cost which increases ion exposure duration and erosion.

[0045] Referring now to FIGS. 3A to 3C, ion bombardment is shown for various substrate positions. In FIG. 3A, the substrate 210 is arranged on the ceramic top plate 214 during etching. In FIG. 3B, a substrate 210’ such as a dummy substrate is raised above the ceramic top plate 214 during plasma treatment. In FIG. 3C, the substrate 210 is removed from the processing chamber for processing chamber cleaning. Excessive wear of the seal ring 226 occurs when one or more of the substrate positions allow exposure of the seal ring 226 to ion bombardment. In the example in FIGS. 3A to 3C, all of the substrate positions allow ions to have a direct line of sight path to the seal ring 226.

[0046] Referring now to FIG. 4, a ceramic top plate 300 according to the present disclosure includes a cylindrical body 304, a top surface 306, a bottom surface 308, and a downwardly-directed annular projection 318. The downwardly-directed annular projection 318 extends from the bottom surface 308 of the ceramic top plate 300 at a radially outer edge 314 thereof. In some examples, the downwardly-directed annularprojection 318 includes chamfered surfaces on a lower, radially outer edge 322 and a lower radially inner edge 324 to avoid chipping of the ceramic top plate 300. An additional chamfered surface may be arranged at a corner 328 between the bottom surface 308 of the ceramic top plate 300 and a radially inner surface 320 of the downwardly-directed annular projection 318. As can be appreciated, the downwardly-directed annular projection 318 prevents direct line of sight for ions generated by the plasma when the substrate is on the ceramic top plate, above the ceramic top plate, and / or removed from the processing chamber.

[0047] The downwardly-directed annular projection 318 maintains the pocket depth to avoid arcing of wafer to edge ring. In some examples, the ceramic top plate 300 is made of alumina (AI2O3) or another suitable ceramic material that has low sputtering yield and higher resistance to ion exposure / bombardment as compared to PTFE. The significantly increased resistance of this arrangement to ion exposure / bombardment allows the seal ring 226 to last significantly longer. For example, the downwardly-directed annular projection 318 allows the seal ring 226 and the bonding layer 218 to last longer than the MTBC and / or the lifetime of the substrate support (e.g., 10k RF hours).

[0048] The downwardly-directed annular projection 318 also prevents the seal ring 226 from walking out and exposing the bonding layer 218. The downwardly-directed annular projection 318 creates a more torturous path for radicals and may improve the radical immunity of the seal ring 226.

[0049] In some examples, the ceramic top plate 300 with the downwardly-directed annular projection 318 is made using a stack of green sheets that are patterned for a given layer, stacked, and sintered. In other words, a plurality of circular green sheets are stacked with a plurality of annular green sheets (located at a radially outer edge of the circular green sheets). Ceramic paste may be used between the green sheets. Then the green sheets are sintered and finishing (e.g., machining, grinding, etc.) of the ceramic top plate is performed. In other examples, the ceramic top plate 300 is initially sintered with a thickness greater than or equal to the final ceramic top plate at the radially outer edge (e.g., wider at the downwardly-directed annular projection 318) and machining of the ceramic top plate 300 forms an inner cavity to define the downwardly-directed annular projection 318.

[0050] Referring now to FIGS. 5A to 5C, ion bombardment of the arrangement including the ceramic top plate with the downwardly-directed annular projection 318 is shown forvarious substrate positions. In FIG. 5A, the substrate 210 is arranged on the ceramic top plate 214. In FIG. 5B, the substrate 210’ is raised above the ceramic top plate 214. In FIG. 5C, the substrate 210 is removed from the processing chamber for cleaning of the processing chamber. The downwardly-directed annular projection 318 prevents a line of sight between ions generated by the plasma when the substrate is on the ceramic top plate, above the ceramic top plate, and / or removed from the processing chamber. As a result, excessive wear of the seal ring 226 does not occur.

[0051] Referring now to FIGS. 6 and 7, other arrangements of the ceramic top plate and the seal ring can be used. In FIG. 6, a ceramic top plate 400 includes a cylindrical body 404, a top surface 406, a bottom surface 408, and a downwardly-directed annular projection 418. The downwardly-directed annular projection 418 extends from the bottom surface 408 of the ceramic top plate 400 at a radially outer edge 414 thereof. The downwardly-directed annular projection 418 includes a chamfered surface on a lower, radially outer edge 422 to avoid chipping of the ceramic top plate 400. As can be appreciated, the downwardly-directed annular projection 418 prevents line of sight for ions generated by the plasma when the substrate 210 is arranged on the ceramic top plate 400, above the ceramic top plate 400, and / or removed from the processing chamber. In this example, the bonding layer 218 extends radially outwardly relative to a radially outer edge of the baseplate 222 beyond the ceramic top plate 400 and above the seal ring 226. A radially outer edge of a top surface 430 of seal ring 226 is in contact with a bottom surface of the downwardly-directed annular projection 418.

[0052] In FIG. 7, a seal ring 526 includes an annular body 527 with a radially inner side 530 and a radially outer side 528. An upper and radially outer edge 536 of the seal ring 526 (e.g., between the top surface and the radially outer side 528) includes a notch 540 having a profile that conforms to and forms a seal with a lower and radially inner portion of the downwardly-directed annular projection 318.

[0053] The foregoing description is merely illustrative in nature and is in no way intended to limit the disclosure, its application, or uses. The broad teachings of the disclosure can be implemented in a variety of forms. Therefore, while this disclosure includes particular examples, the true scope of the disclosure should not be so limited since other modifications will become apparent upon a study of the drawings, the specification, and the following claims. It should be understood that one or more steps within a method may be executed in different order (or concurrently) without altering the principles of thepresent disclosure. Further, although each of the embodiments is described above as having certain features, any one or more of those features described with respect to any embodiment of the disclosure can be implemented in and / or combined with features of any of the other embodiments, even if that combination is not explicitly described. In other words, the described embodiments are not mutually exclusive, and permutations of one or more embodiments with one another remain within the scope of this disclosure.

[0054] Spatial and functional relationships between elements (for example, between modules, circuit elements, semiconductor layers, etc.) are described using various terms, including “connected,” “engaged,” “coupled,” “adjacent,” “next to,” “on top of,” “above,” “below,” and “disposed.” Unless explicitly described as being “direct,” when a relationship between first and second elements is described in the above disclosure, that relationship can be a direct relationship where no other intervening elements are present between the first and second elements, but can also be an indirect relationship where one or more intervening elements are present (either spatially or functionally) between the first and second elements. As used herein, the phrase at least one of A, B, and C should be construed to mean a logical (A OR B OR C), using a non-exclusive logical OR, and should not be construed to mean “at least one of A, at least one of B, and at least one of C.”

Claims

CLAIMSWhat is claimed is:1 . A substrate support for a plasma processing system, comprising: a baseplate; a ceramic top plate including a cylindrical body and an annular projection extending from a bottom surface of the cylindrical body at a radially outer edge of the cylindrical body; a bonding layer to bond the ceramic top plate to the baseplate; a seal ring including an annular body arranged around the baseplate and a radially outer edge of the bonding layer and between the bottom surface of the ceramic top plate and the baseplate; and an edge ring around and spaced from the ceramic top plate and the seal ring, wherein the annular projection of the ceramic top plate is configured to prevent a direct line of sight between ions generated by plasma and the seal ring.

2. The substrate support of claim 1 , wherein the annular body of the seal ring is made of elastomer.

3. The substrate support of claim 1 , wherein the ceramic top plate is made of alumina.

4. The substrate support of claim 1 , wherein a bottom and radially outer edge of the annular projection of the ceramic top plate is chamfered.

5. The substrate support of claim 1 , wherein a bottom and radially inner edge of the annular projection of the ceramic top plate is chamfered.

6. The substrate support of claim 1 , wherein a corner between the annular projection of the ceramic top plate is chamfered.

7. The substrate support of claim 1 , wherein the bonding layer extends radially outwardly relative to the baseplate and between the seal ring and the ceramic top plate radially inwardly from the annular projection.

8. The substrate support of claim 1 , wherein the seal ring includes a notch to provide a seal against at least one of a bottom surface and a radially inner surface of the annular projection.

9. A ceramic top plate for a substrate support of a plasma processing system, comprising: a cylindrical body made of ceramic and configured for attachment to a baseplate; and an annular projection made of ceramic and extending from a bottom surface of the cylindrical body at a radially outer edge of the cylindrical body and configured to extend between a seal ring and an edge ring, wherein the annular projection of the ceramic top plate is configured to prevent a direct line of sight between ions generated by plasma and the seal ring.

10. The ceramic top plate of claim 9, wherein the ceramic top plate is made of alumina.1 1 . The ceramic top plate of claim 9, wherein a bottom and radially outer edge of the annular projection of the ceramic top plate is chamfered.

12. The ceramic top plate of claim 11 , wherein a bottom and radially inner edge of the annular projection of the ceramic top plate is chamfered.

13. The ceramic top plate of claim 1 1 , wherein a corner between the annular projection of the ceramic top plate is chamfered.

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