Biasable Platen and Methods to Bias a Platen

Abstract

A deflectable platen and a method for deflecting the platen are provided. The deflectable platen comprises an annular sidewall, a first layer coupled to the annular sidewall, wherein the first layer has a first temperature control element associated with the first layer, a second layer connected to the annular sidewall and spaced apart from the first layer to define a gap between them, wherein the second layer has a second temperature control element associated with the second layer, and a controller coupled to the first and second temperature control elements and configured to operate the first and second temperature control elements to change the temperatures of the first and second layers relative to each other in order to deflect the deflectable platen so as to match more closely to the contour of a wafer.

Description

Technology Field

[0001] The embodiments of the present invention generally relate to the field of semiconductor device manufacturing, and more specifically, to a deflectable platen for facilitating effective clamping of semiconductor wafers. Background Technology

[0002] Semiconductor wafers are typically placed on planar platens during ion implantation and certain other processes performed during the manufacture of semiconductor devices. Generally, semiconductor wafers are secured to the platens via electrostatic clamping, where a voltage is applied between electrodes embedded in the platens and the resulting electric field holds the semiconductor wafer to the platens. Electrostatic clamping is preferred over mechanical clamping because mechanical clamping can damage and / or contaminate the semiconductor wafer.

[0003] The ability of a platen to firmly clamp a semiconductor wafer to the platen via electrostatic clamping depends heavily on the proximity of the bottom surface of the semiconductor wafer to the top surface of the platen. Ideally, these surfaces are planar and positioned to be in flat and continuous contact with each other. In some cases, the semiconductor wafer may be warped (e.g., deflected by 1 / 20,000ths of an inch), which causes a relatively large gap between the top surface of the platen and the bottom surface of the semiconductor wafer. This can result in weak or inefficient electrostatic clamping. This problem can be exacerbated when the semiconductor wafer and platen are exposed to high or cryogenic processes (e.g., during high or cryogenic ion implantation), where incoherent deflection of the semiconductor wafer and platen can lead to an increase in the size of the gap between them.

[0004] Therefore, minimizing surface-to-surface proximity between the semiconductor wafer and the platen is desirable to facilitate secure electrostatic clamping between them. Improvements may be required regarding these and other considerations. means of solving the problem

[0005] This summary is provided to introduce a selection of concepts in a simplified form. This summary is not intended to identify the core or essential features of the claimed subject matter, nor is it intended to assist in determining the scope of the claimed subject matter.

[0006] An exemplary embodiment of a deflectable platen according to the present disclosure may include an annular sidewall, a first layer coupled to the annular sidewall, wherein the first layer has a first temperature control element associated with the first layer, and a second layer connected to the annular sidewall and spaced apart from the first layer to define a gap between them, wherein the second layer has a second temperature control element associated with the second layer.

[0007] Another exemplary embodiment of a deflectable platen according to the present invention may include an annular sidewall, a first layer coupled to the annular sidewall, wherein the first layer has a first temperature control element associated with the first layer, a second layer connected to the annular sidewall and spaced apart from the first layer to define a gap between them, wherein the second layer has a second temperature control element associated with the second layer, and a controller coupled to the first and second temperature control elements and configured to operate the first and second temperature control elements to change the temperatures of the first and second layers relative to each other in order to deflect the deflectable platen to match more closely with the contour of a wafer.

[0008] An exemplary embodiment of a method for deflecting a platen according to the present disclosure may include the steps of: providing an annular sidewall; providing a first layer coupled to the annular sidewall, wherein the first layer has a first temperature control element associated with the first layer; providing a second layer connected to the annular sidewall and spaced apart from the first layer to define a gap therebetween, wherein the second layer has a second temperature control element associated with the second layer; and changing the temperature of at least one of the first and second layers using the first and second temperature control elements. Brief explanation of the drawing

[0009] As an example, various embodiments of the disclosed device will now be described with reference to the accompanying drawings. FIG. 1a is a top view illustrating an exemplary embodiment of a deflectable platen according to the present disclosure. FIG. 1b is a side cross-sectional view illustrating a deflectable platen taken along line AA of FIG. 1a. FIG. 2a is a side cross-sectional view illustrating the deflectable platen of FIG. 1a and FIG. 1b having a convexly deflected semiconductor wafer placed thereon. FIG. 2b is a side cross-sectional view illustrating the deflectable platen of FIG. 2a in a convexly deflected state. FIG. 2c is a side cross-sectional view illustrating the deflectable platen of FIG. 1a and FIG. 1b in a concavely deflected state having a concavely deflected semiconductor wafer placed thereon. FIG. 3 is a flowchart illustrating an exemplary method for deflecting a platen according to the present disclosure. Specific details for implementing the invention

[0010] The embodiments described below will now be explained more fully with reference to the accompanying drawings, some of which are illustrated. The subject matter of this disclosure may be embodied in a number of different forms and should not be interpreted as being limited to the embodiments described herein. These embodiments are provided to ensure that this disclosure is complete and thorough and will fully convey the scope of this application to those skilled in the art. In the drawings, similar reference numerals refer to similar elements throughout.

[0011] Referring to FIGS. 1a and 1b, a top view and a side cross-sectional view illustrating a deflectable platen (10) (hereinafter referred to as "platen (10)") according to an exemplary embodiment of the present disclosure are respectively shown. The platen (10) may be elastically deformable (as further described below) to provide a close clearance relationship between the bottom surface of a bent or curved semiconductor wafer placed on the platen (10) and the top surface of the platen (10) in order to facilitate effective clamping between them.

[0012] The platen (10) may include a first layer (12) and a second layer (14) that are generally planar and arranged in a parallel, vertically spaced relationship (i.e., spaced from each other in a direction perpendicular to the X-axis or parallel to the Y-axis as shown in FIG. 1b) to define a gap (15) between them. The perimeter edges of the first and second layers (12, 14) may be connected to an annular sidewall (16) surrounding the first and second layers (12, 14) as further described below. In various examples, the first and second layers (12, 14) are 6.0 x 10 -6 / ℃ to 8.0 x 10 -6It may be formed from a material having a coefficient of thermal expansion (CTE) within the range of / °C. In certain examples, the first and second layers (12, 14) may be formed from ceramics including aluminum oxide, zirconia, or aluminum nitride, but not limited thereto. The present disclosure is not limited thereto. Alternatively, the first and / or second layers (12, 14) may be formed from other relatively high or low CTE materials, including aluminum, silver, copper, and alloys thereof, or quartz, but not limited thereto.

[0013] The sidewall (16) of the platen (10) may be formed of a dielectric material having a CTE similar to or relatively lower than the CTE of the material of the first and second layers (12, 14). In various examples, the sidewall (16) is 6.0 x 10 -6 Less than / ℃ (e.g., 2.0 x 10⁻⁶ -6 / ℃ to 4.0 x 10 -6 It may be formed from a material having a CTE (between / °C). In certain examples, the sidewall (16) may be formed from a ceramic such as aluminum nitride or aluminum oxide. The present disclosure is not limited thereto. Alternatively, the sidewall (16) may be formed from other dielectric materials, including other ceramics and various composite materials. The sidewall (16) may be connected to the edges of the first and second layers (12, 14) by soldering, welding, heat-resistant adhesives, various mechanical fasteners, glass bonding, and / or other techniques suitable for joining or fastening the material of the sidewall (16) to the materials of the first and second layers (12, 14). As will be described in more detail below, the sidewall (16) may mechanically translate the expansion and contraction of the first and second layers (12, 14) to each other.

[0014] The first and second layers (12, 14) may include individual first and second heating elements (20, 22) associated therewith. For example, in the embodiment of the platen shown in FIG. 1b, the first and second heating elements (20, 22) may be embedded within the first and second layers (12, 14). The first and second heating elements (20, 22) may include one or more wires, cables, plates, tapes, etc., connected to one or more power sources (not shown). The first and second heating elements (20, 22) may be independently operable to selectively and independently heat the first and second layers (12, 14). In various examples, the first and second heating elements (20, 22) may heat the first and second layers (12, 14) to a temperature exceeding 800 degrees Celsius (e.g., a temperature within the range of 800 to 1200 degrees Celsius). The present disclosure is not limited thereto. A gap (15) separating the first and second layers (12, 14) may be held in a vacuum or near vacuum, thereby providing thermal separation between the first and second layers (12, 14). Specifically, the gap (15) may prevent all or most of the heat generated by the first heating element (20) from communicating with the second layer (14), and may prevent all or most of the heat generated by the second heating element (22) from communicating with the first layer (12). In various embodiments, the platen (10) may additionally or alternatively include one or more layers of thermal insulating material disposed between the first and second layers (12, 14).

[0015] The second layer (14) of the platen (10) may have a plurality of associated electrodes (23). For example, in the embodiment of the platen shown in FIG. 1b, the electrodes (23) may be embedded within the second layer (14). In various alternative embodiments of the platen (10), the electrodes (23) may be embedded within a separate layer of dielectric material placed at the top of the second layer (14). The present disclosure is not limited thereto. The electrodes (23) may be connected to a source of power (not shown) and may be arranged and configured to operate in a manner of conventional electrostatic clamping familiar to those skilled in the art. In particular, by applying a voltage across the electrodes (23), an electric field may be generated and the semiconductor wafer may be held to the platen (10) through electrostatic force. The strength of the electrostatic force acting on the wafer will partially depend on the proximity of the wafer to the electrodes (23). Ideally, (e.g., if these surfaces are flat or nearly flat) the contour of the bottom surface of the wafer will match or nearly match the contour of the top surface of the platen (10), thus establishing the shortest possible distance between the electrodes (23) and the wafer to provide a strong electrostatic coupling between them. In some cases, a wafer such as the semiconductor wafer (24) shown in FIG. 2a (hereinafter referred to as the "wafer (24)") may be bent or curved (e.g., deflected by 1 / 20,000 of an inch and possibly more than this) and may exhibit a concave bottom surface relative to the generally flat top surface of the platen (10) (the deflection of the wafer (24) as shown in FIG. 2a is exaggerated for illustrative purposes). The resulting gap (25) between the wafer (24) and the platen (10) can attenuate the electrostatic force acting on the wafer (24), and thus cause poor electrostatic clamping between the platen (10) and the wafer (24).

[0016] In various alternative embodiments of the platen (10), the electrodes (23) may be omitted, and the wafer (24) may be secured to the top surface of the platen (10) using various mechanical clamps (27) (shown by dashed lines in FIG. 1b) familiar to those skilled in the art. As in the case of electrostatic coupling, (e.g., if these surfaces are flat or nearly flat), the contour of the bottom surface of the wafer (24) will be matched or nearly matched to the contour of the top surface of the platen (10) to facilitate optimal contact and secure mechanical coupling between them, as well as optimal thermal coupling between the platen (10) and the wafer (24). Good thermal coupling would be desirable if the platen (10) is configured to heat or cool the wafers placed thereon (e.g., heat transfer through an inert gas introduced between the platen (10) and the wafer (24). If the wafer (24) is bent or warped, the resulting gap (25) between the wafer (24) and the platen (10) may be detrimental to establishing an effective thermal bond between the wafer (24) and the platen (10) and / or secure mechanical clamping.

[0017] Referring to FIG. 2b, the platen (10) is shown in a convexly deflected state. In particular, the second heating element (22) is activated and the first heating element (20) is not activated or is activated at a lower power to cause heating of the second layer (14), while the first layer (12) is not heated or is heated to a lower temperature than the second layer (14). When heated, the second layer (14) may exhibit thermal expansion according to its CTE. Because the second layer (14) is connected to the first layer (12) by the side wall (16), and because the unheated first layer (12) does not expand (or expands at a slower rate and / or to a lesser degree than the heated second layer (14), the expansion of the second layer (14) in the radial direction can cause the upper portion of the side wall (16) to be deflected outward, which consequently causes the edges of the first and second layers (12, 14) to be pulled downward or deflected, thereby causing a convex deflection of the platen (10) as shown in FIG. 2b. Thus, the contour of the top surface of the platen (10) can be made to match more closely with the contour of the bottom surface of the wafer (24) to reduce the size of the gap (25) between them compared to the undeflected state of the platen (10) shown in FIG. 2a. In the case of electrostatic clamping, the closer proximity of the electrodes (23) to the wafer (24) and the smaller gap (25) facilitated by the deflected platen (10) provide a stronger electrostatic force acting on the wafer (24) compared to the electrostatic force applied by the undeflected platen (10) shown in FIG. 2a, thus causing better electrostatic coupling between the wafer (24) and the platen (10). In the case of mechanical clamping, the smaller gap (25) achieved by the deflected platen (10) facilitates more secure clamping of the wafer (24) to the platen (10) and better thermal coupling between the platen (10) and the wafer (24) compared to the undeflected platen (10) shown in FIG. 2a.

[0018] The platen (10) may also be deflected in a concave direction to accommodate curved or bent semiconductor wafers that have a convex surface relative to the top surface of the platen (10). For example, referring to FIG. 2c, the platen (10) is shown in a concavely deflected state with a concavely deflected semiconductor wafer (28) (hereinafter "wafer (28)") placed thereon. In particular, the first heating element (20) is activated and the second heating element (22) is not activated (or is activated at a lower power), which causes the heating of the first layer (12) relative to the second layer (14). When heated, the first layer (12) may exhibit thermal expansion according to its CTE. Because the first layer (12) is connected to the second layer (14) by the sidewall (16), and because the unheated second layer (14) does not expand (or expands at a slower rate and / or to a lesser degree than the heated first layer (12), the expansion of the first layer (12) in the radial direction may cause the lower portion of the sidewall (16) to be deflected outward, which consequently the first The edges of the second layers (12, 14) can be pulled upward or deflected to cause a concave deflection of the platen (10) as shown in FIG. 2c. Thus, the contour of the top surface of the platen (10) can be made to match more closely with the contour of the bottom surface of the wafer (28), thereby causing better electrostatic or mechanical clamping between the platen (10) and the wafer (28) as described above.

[0019] In various examples, the first and second layers (12, 14) may be heated to a temperature between 300 and 800 degrees Celsius to achieve a target amount of deflection. In certain non-limiting examples, the platen (10) may exhibit a convex deflection of 1 / 18,000 of an inch when the second layer is heated to a temperature of 500 degrees Celsius, and may exhibit a convex deflection of 1 / 18,000 of an inch when the first layer is heated to 500 degrees Celsius. The present disclosure is not limited thereto. The degree of deflection in the platen (10) will depend, without limitation, on a number of factors including the CTEs of the first and second layers (12, 14), the amount of heat applied to the first and second layers (12, 14), the diameters of the first and second layers (12, 14), and the thicknesses of the first and second layers (12, 14).

[0020] In various embodiments, the deflection stress on the first and second layers (12, 14) during heating of either layer may be smaller than the yield strength of the materials of the first and second layers (12, 14). Thus, when the first and second layers (12, 14) are allowed to cool to room temperature, the platen (10) may return to its original, generally flat state as shown in FIG. 1b. Thus, by varying the amount of heat applied to the first and second layers (12, 14), the platen (10) may be controllably deflected to varying degrees (e.g., from 0 to 1 / 20,000 inch) in either direction (i.e., concavely or convexly) to match or approach the contours of wafers having varying degrees of deflection placed thereon to provide effective electrostatic or mechanical clamping between them. Accordingly, the deflection of the incoming wafer can be analyzed (e.g., through contact sensors, image analysis, etc.), and a controller (29) operably coupled to the platen (10) can direct the operation of the first and second heating elements (20, 22) to deflect the platen (10) to match or approach the contour of the incoming wafer upon receiving data indicating the measured deflection of the wafer.

[0021] Although the platen (10) has been described above as comprising first and second heating elements (20, 22) built in to controllably and selectively heat the first and second layers (12, 14), various alternative embodiments of the platen (10) are considered in which the first and second heating elements (20, 22) shown in the drawings and described above may instead be cooling elements for controllably and selectively cooling the first and second layers (12, 14). Accordingly, the first and second heating elements (20, 22) may alternatively be referred to herein as "cooling elements (20, 22)" or more generally as "temperature control elements (20, 22)". Cooling elements may be or include various channels, conduits, tubes, pipes, ducts, etc., embedded within or placed on top of the first and second layers (12, 14) to circulate a cooling fluid (e.g., water, liquid nitrogen, etc.) through them. Cooling elements (20, 22) may be used to cool the first and / or second layers (12, 14) to a temperature within the range of, for example, 0 degrees Celsius to -150 degrees Celsius. By cooling one of the first and second layers (12, 14) and not cooling the other of the first and second layers (12, 14), the cooled layer may exhibit thermal shrinkage according to its CTE.Because the first and second layers (12, 14) are connected to each other by the sidewall (16), and because the uncooled layer does not shrink (or shrinks at a slower rate and / or to a lesser extent than the cooled layer), the shrinkage of the cooled layer in the radial direction may cause the sidewall to be deflected, which consequently causes the edges of the first and second layers (12, 14) to be pulled upward or downward or deflected depending on the layer being cooled, thereby causing a concave or convex deflection of the platen (10) as illustrated in FIG. 2b and FIG. 2c. In various other embodiments, the first and second layers (12, 14) may include heating elements and cooling elements such as those described above.

[0022] Referring to FIG. 3, a flowchart illustrating an exemplary method for deflecting a platen according to the present disclosure is shown. Now, the method will be described together with examples of platens (10) shown in FIG. 1a through 2c.

[0023] In the block (100) of the exemplary method, a first layer (12) and a second layer (14) may be provided, and they may be joined to the annular sidewall (16) by, for example, soldering, welding, heat-resistant adhesive, various mechanical fasteners, glass bonding, and / or other techniques suitable for joining or fastening the material of the sidewall (16) to the materials of the first and second layers (12, 14). The first layer (12) and the second layer (14) may be arranged in a parallel spaced relationship that defines a gap (15) between them, and the gap (15) may be held in a vacuum or near vacuum to provide thermal insulation between the first and second layers (12, 14). The first and second layers (12, 14) may include individual first and second temperature control elements (20, 22) associated with them (e.g., embedded therein). In the block (110) of the exemplary method, the second layer (14) may be provided with associated electrodes (23) (e.g., embedded therein) to facilitate electrostatic clamping of wafers to the platen (10). In various alternative embodiments, the electrodes (23) may be omitted and a mechanical clamp (27) may be implemented.

[0024] In block (120) of the exemplary method, the deflection of the incoming wafer may be analyzed (e.g., through contact sensors, imaging analysis, etc.), and a controller (29) operably coupled to the platen (10) may direct the operation of the first and second temperature control elements (20, 22) to deflect the platen (10) to match or approach the contour of the incoming wafer upon receiving data indicating the measured deflection of the wafer. In one example where the first and second temperature control elements (20, 22) are heating elements, the second temperature control element (22) may be activated to heat the second layer (14) relative to the first layer (12) in block (130a) of the exemplary method. When heated, the second layer (14) may exhibit thermal expansion according to its CTE. Because the second layer (14) is connected to the first layer (12) by the side wall (16), and because the unheated first layer (12) does not expand (or expands at a slower rate and / or less than the heated second layer (14)), the expansion of the second layer (14) in the radial direction can cause the upper portion of the side wall (16) to be deflected outward, which consequently causes the edges of the first and second layers (12, 14) to be pulled downward or deflected, thereby causing a convex deflection of the platen (10) as shown in FIG. 2B. Thus, the contour of the top surface of the platen (10) can be made to match more closely with the contour of the bottom surface of the incoming wafer.

[0025] In another example where the first and second temperature control elements (20, 22) are heating elements, the first temperature control element (20) can be activated to heat the first layer (12) relative to the second layer (14) in block (130b) of the exemplary method. When heated, the first layer (12) may exhibit thermal expansion according to its CTE. Because the first layer (12) is connected to the second layer (14) by the side wall (16), and because the unheated second layer (14) does not expand (or expands at a slower rate and / or to a lesser degree than the first layer (12)), the expansion of the first layer (12) in the radial direction can cause the lower portion of the side wall (16) to be deflected outward, which consequently causes the edges of the first and second layers (12, 14) to be pulled upward or deflected, thereby causing a concave deflection of the platen (10) as shown in FIG. 2C. Thus, the contour of the top surface of the platen (10) can be made to match more closely with the contour of the incoming wafer.

[0026] In another example where the first and second temperature control elements (20, 22) are cooling elements, the first temperature control element (20) can be activated to cool the first layer (12) relative to the second layer (14) in block (130c) of the exemplary method. When cooled, the first layer (12) may exhibit thermal shrinkage according to its CTE. Because the first layer (12) is connected to the second layer (14) by the side wall (16), and because the uncooled second layer (14) does not shrink (or shrinks at a slower rate and / or to a lesser degree than the first layer (12)), the shrinkage of the first layer (12) in the radial direction can cause the lower portion of the side wall (16) to be deflected inward, which consequently causes the edges of the first and second layers (12, 14) to be pulled downward or deflected, thereby causing a convex deflection of the platen (10) as shown in FIG. 2B. Thus, the contour of the top surface of the platen (10) can be made to match more closely with the contour of the incoming wafer.

[0027] In one example where the first and second temperature control elements (20, 22) are cooling elements, the second temperature control element (22) can be activated to cool the second layer (14) relative to the first layer (12) in block (130d) of the exemplary method. When cooled, the second layer (14) may exhibit thermal shrinkage according to its CTE. Because the second layer (14) is connected to the first layer (12) by the side wall (16), and because the uncooled first layer (12) does not shrink (or shrinks at a slower rate and / or to a lesser degree than the cooled second layer (14)), the shrinkage of the second layer (14) in the radial direction can cause the upper portion of the side wall (16) to be deflected inward, which consequently causes the edges of the first and second layers (12, 14) to be pulled upward or deflected, thereby causing a concave deflection of the platen (10) as shown in FIG. 2C. Thus, the contour of the top surface of the platen (10) can be made to match more closely with the contour of the bottom surface of the incoming wafer.

[0028] As will be understood by those skilled in the art, the deflectable platen (10) described above offers distinct advantages over conventional platens. For example, the platen (10) can be selectively and dynamically deflected through the controlled application of heat (or cooling) to the first and second layers (12, 14) to facilitate quick and convenient effective clamping with wafers having varying degrees of concave or convex deflection. Additionally, the ability of the platen (10) to conform to the contour of the wafer placed thereon facilitates effective thermal communication between the platen (10) and the wafer (e.g., for heating and / or cooling the wafer).

[0029] The scope of this disclosure is not limited by the specific embodiments described herein. Rather, in addition to the embodiments described herein, various other embodiments of this disclosure and modifications thereof will become apparent to those skilled in the art from the foregoing description and the accompanying drawings. Accordingly, such other embodiments and modifications are intended to fall within the scope of this disclosure. Additionally, although this disclosure has been described herein in the context of specific embodiments in specific environments for specific purposes, those skilled in the art will recognize that its usefulness is not limited thereto. Embodiments of this disclosure may be advantageously implemented in any number of environments for any number of purposes. Accordingly, the claims described below should be interpreted in the full breadth and spirit of this disclosure as described herein.

Claims

Claim 1 A deflectable platen comprising: an annular sidewall; a first layer coupled to the annular sidewall, wherein the first layer has a first temperature control element associated with the first layer; and a second layer connected to the annular sidewall and spaced apart from the first layer to define a gap providing thermal insulation between them, wherein the second layer has a second temperature control element associated with the second layer. Claim 2 The deflectable platen of claim 1, wherein the deflectable platen further comprises a plurality of electrodes associated with the second layer to facilitate electrostatic clamping of wafers with respect to the deflectable platen. Claim 3 In claim 1, the first and second temperature control elements are first and second heating elements, a deflectionable platen. Claim 4 In claim 3, the first and second heating elements comprise one or more of wires, cables, plates, and tapes coupled to one or more power sources, a deflectable platen. Claim 5 In claim 3, the first and second heating elements are independently controllable to independently heat the first and second layers to a temperature exceeding 800 degrees Celsius, a deflectable platen. Claim 6 In claim 1, the first and second temperature control elements are first and second cooling elements, a deflectable platen. Claim 7 In claim 6, the first and second cooling elements comprise one or more of channels, conduits, tubes, pipes, and ducts for circulating a cooling fluid, a deflectable platen. Claim 8 In claim 6, the first and second cooling elements are independently controllable to independently cool the first and second layers to a temperature within the range of 0 degrees Celsius to -150 degrees Celsius, a deflectable platen. Claim 9 In claim 1, the first and second layers are 6.0 x 10 -6 / ℃ to 8.0 x 10 -6 A deflectionable platen formed of a material having a coefficient of thermal expansion within the range of / ℃. Claim 10 In claim 1, the annular sidewall is 6.0 x 10 -6 A deflectionable platen formed of a material having a coefficient of thermal expansion smaller than / ℃. Claim 11 A deflectionable platen according to claim 1, wherein the gap is a vacuum. Claim 12 A deflectable platen comprising: an annular sidewall; a first layer coupled to the annular sidewall, wherein the first layer has a first temperature control element associated with the first layer; a second layer connected to the annular sidewall and spaced apart from the first layer to define a gap providing thermal insulation between them, wherein the second layer has a second temperature control element associated with the second layer; and a controller coupled to the first and second temperature control elements and configured to operate the first and second temperature control elements to change the temperatures of the first and second layers relative to each other in order to deflect the deflectable platen so as to match more closely to the contour of a wafer. Claim 13 A method for deflecting a platen, comprising: providing an annular sidewall; providing a first layer coupled to the annular sidewall, wherein the first layer has a first temperature control element associated with the first layer; providing a second layer connected to the annular sidewall and spaced apart from the first layer to define a gap providing thermal insulation between them, wherein the second layer has a second temperature control element associated with the second layer; and changing the temperature of at least one of the first and second layers using the first and second temperature control elements. Claim 14 The method of claim 13 further comprises the step of providing electrodes associated with the second layer to the second layer to facilitate electrostatic clamping of wafers to the platen. Claim 15 The method of claim 13, wherein the first and second temperature control elements are first and second heating elements, and the method further comprises the step of activating the second heating element to heat the second layer relative to the first layer to cause thermal expansion of the second layer and convex deflection of the platen. Claim 16 The method of claim 13, wherein the first and second temperature control elements are first and second heating elements, and the method further comprises the step of activating the first heating element to heat the first layer relative to the second layer to cause thermal expansion of the first layer and concave deflection of the platen. Claim 17 The method of claim 13, wherein the first and second temperature control elements are first and second cooling elements, and the method further comprises the step of activating the second cooling element to cool the second layer relative to the first layer, thereby causing thermal shrinkage of the second layer and concave deflection of the platen. Claim 18 The method of claim 13, wherein the first and second temperature control elements are first and second cooling elements, and the method further comprises the step of activating the first cooling element to cool the first layer relative to the second layer to cause thermal shrinkage of the first layer and convex deflection of the platen. Claim 19 The method of claim 13 further comprises: measuring the deflection of a wafer to be placed on the platen; communicating data representing the measured deflection of the wafer to a controller operably connected to the first and second temperature control elements; and activating at least one of the first and second temperature control elements through the controller to change the temperature of the first and second layers to deflect the platen to match more closely to the contour of the wafer. Claim 20 A method according to claim 19, wherein the deflection of the wafer is measured using one of contact sensors and image analysis.

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