Abstract:
An apparatus which includes a laminated ceramic body with multilayer electrodes and a method of fabricating this apparatus are disclosed. The laminated ceramic body is formed by layers of ceramic material, with portions of certain layers being silk screened with an intermediate layer of electrically conductive material. Subsequent sintering results in the formation of a solid ceramic body with multilayer electrodes made up of the electrically conductive material layers. The apparatus further comprises an electrical connector extending partially into the ceramic body and intersecting at least one of these electrodes.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation-in-part application of commonly assigned patent application Ser. No. 08/834,702 entitled CONDUCTIVE FEEDTHROUGH FOR A CERAMIC BODY AND METHOD OF FABRICATING SAME, filed Apr. 1, 1997 and incorporated herein by reference. 
    
    
     BACKGROUND OF THE DISCLOSURE 
     1. Field of the Invention 
     The present invention relates to semiconductor wafer processing equipment and, more particularly, to a conductive feedthrough extending from a volume containing atmospheric pressure through a ceramic body into a vacuum chamber, and further relates to a laminated ceramic body with multiple internal electrodes. 
     2. Description of the Background Art 
     A semiconductor wafer processing system generally contains a vacuum chamber within which is mounted a wafer support pedestal or susceptor. The pedestal is used to support the wafer within the chamber during processing. The pedestal contains various components which provide heating and/or cooling of the wafer as well as clamping (chucking) of the wafer to retain the wafer in a stationary position upon the pedestal surface. Such clamping is provided by either a mechanical clamp or an electrostatic chuck. Within the vacuum chamber, the space above the pedestal where the wafer is processed is generally maintained at a high vacuum. However, the space below or inside the pedestal is maintained at atmospheric pressure. 
     For high-temperature processes, such as high temperature physical vapor deposition, the pedestal may sometime be fabricated of ceramic. Heretofore, there has not been a convenient nor practical solution for providing an electrically conductive, yet vacuum sealed, connection through a ceramic pedestal such that electrical current can be passed from the atmosphere side of the pedestal to the vacuum side of the pedestal without violating the integrity of the vacuum. 
     Therefore, there is a need in the art for apparatus that provides a conductive feedthrough connection through a ceramic body, such as a ceramic pedestal, and a method of fabricating the feedthrough. 
     Additionally, electrostatic chucks are used to electrostatically attract and retain a semiconductor wafer during processing. In some plasma-based wafer processing operation, radiofrequency (RF) power may be coupled to the electrostatic chuck to bias the chuck in order to provide and/or enhance movement of ions in the plasma in the direction of the wafer during processing. The electrostatic chuck typically includes a ceramic body in which a pair of electrodes resides and upon application of DC voltage to the electrodes, the chuck electrostatically attracts a semiconductor wafer to the chuck according to the Johnsen-Rahbek effect. An electrostatic chuck utilizing the Johnsen-Rahbek effect is disclosed in U.S. Pat. No. 5,656,093 entitled WAFER SPACING MASK FOR A SUBSTRATE SUPPORT CHUCK AND METHOD OF FABRICATING SAME, Burkhart et al. inventors, patented Aug. 12, 1997; this patent is incorporated herein by reference. Further, when the electrostatic chuck is used in high temperature physical vapor deposition of the type noted above, the chuck may be biased by coupling RF power to the chuck. If the electrostatic chuck is RF biased by applying the RF power to electrodes embedded and residing in the semiconductor body, the electrodes and metal feedthroughs to the electrodes must be relatively large and thick to carry the RF power. The metal electrodes and metal feedthroughs carrying the RF power have a different coefficient of expansion than the body of ceramic in which they reside and since the metal electrodes and metal feedthroughs are heated during RF biasing, cracking of the body of ceramic can result, causing destruction of the electrostatic chuck, ruination of a partially processed semiconductor wafer residing on the chuck during breakage, and the need to open the chamber and replace the chuck. 
     Accordingly, there is a need in the art for an electrostatic chuck comprising a ceramic body having electrodes residing or embedded therein which do not cause ceramic breakage upon the application of RF bias to the chuck and heating of the electrodes. 
     SUMMARY OF THE INVENTION 
     The disadvantages heretofore associated with the prior art are overcome by the present invention of a conductive feedthrough connector for facilitating the flow of electrical current through a ceramic body. Specifically, ceramic bodies such as ceramic support pedestals are generally fabricated by stacking a plurality of layers of ceramic material (e.g., aluminum-nitride, alumina, and the like) and then sintering the stack of layers to cure the layers into a unitary, solid ceramic body. In accordance with the present invention, as each layer is positioned upon the stack, a portion of a select number of layers is silk screened with a conductive material (tungsten alloy) prior to the next layer being positioned atop the silk screened layer. Each silk screened region is coaxially aligned along a vertical axis through the ceramic body within another conductive region of another layer. The stack of silk screened layers are then sintered to form a solid ceramic body containing a plurality of stacked conductive electrodes. 
     Conductive vias are then formed vertically into one surface of the ceramic body to intersect the embedded electrodes. These vias are formed by drilling, bead blasting, etching, or some other process used to generate bores in the ceramic body. Using a physical vapor deposition (PVD), chemical vapor deposition (CVD), brazing or other means of metal deposition, the vias are filled with a conductive material such that the embedded electrodes are interconnected by one or more vertical conductive vias. Depending on the specific procedure used for this via-filling step, the surface may or may not be masked. Suffice to say that the exact procedure employed is not critical to practicing the present invention. A top end of the vias are exposed by lapping the surface of the ceramic body. As such, electrodes and other conductors can be sputtered onto the surface of the ceramic body and connect to the exposed ends of the vias. 
     Alternatively, conductive vias may also be formed by vertically boring through the layers, prior to sintering (i.e., while the ceramic is in a green state), and filling the vias with a conductive paste containing titanium (Ti), titanium nitride (TiN) or tungsten (W). These vias may be formed by inserting a solid cylindrical probe into the stack of green state ceramic, then packing the conductive paste into the bore. Subsequent sintering will allow both the ceramic layers and paste to harden, with the electrodes being interconnected by vertical conductive vias. 
     From the opposite side of the ceramic body (i.e., the side not containing the conductive vias), a bore is formed into the surface of the ceramic body passing through (intersecting) one or more of the layers of electrodes. An electrical connector member, or pin, is then brazed into this bore such that the pin conductively connects to the intersected layers of electrode. As such, a conductive path is formed between the conductive vias on one side of the ceramic body (e.g., the vacuum side) and the electrical connector on the other side of the ceramic body (e.g., the atmosphere side). This feedthrough is completely vacuum-sealed and permits a variety of electrical connections to be made to the feedthrough on the vacuum side of the ceramic body. 
     Alternatively, two or more conductive electrode stacks can be fashioned in various, laterally disparate, locations in the ceramic body. These electrode stacks are laterally interconnected with one another through conductive traces deposited (silk screened) between the ceramic layers. 
     In one illustrative application for the invention, the inventive feedthrough is used in a PVD system where the ceramic body is a Johnsen-Rahbek electrostatic chuck, and the feedthrough connector of the present invention provides current to a surface electrode located on the vacuum side of the chuck. 
     A laminated ceramic body having multiple spaced-apart electrodes formed therein, and an electrical connecting pin for the electrodes, is provided which permits the application of RF power with increased current capacity without the above-noted ceramic breakage due to electrode heating upon the application of the RF power. This structure is particularly useful as an RF biasable electrostatic chuck for semiconductor wafer processing such as high temperature physical vapor deposition. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The teachings of the present invention can be readily understood by considering the following detailed description in conjunction with the accompanying drawings, in which: 
     FIG. 1 is a top view of a ceramic wafer support pedestal containing the present invention; 
     FIG. 2 is a cross-section of a portion of the ceramic wafer support pedestal taken along lines  2 — 2  of FIG. 1; 
     FIG. 3 is a top view of a ceramic wafer support pedestal containing an alternative embodiment of the present invention; 
     FIG. 4 is a cross-section of a portion of the ceramic wafer support pedestal taken along lines  4 — 4  of FIG. 3; 
     FIG. 5 a  is a cross-section of a portion of a further embodiment of a ceramic wafer support pedestal; 
     FIG. 5 b  is a cross-section of an embodiment of a bipolar electrostatic chuck using the present invention; and 
     FIG. 6 is a cross-section of another embodiment of an electrostatic chuck having multiple conductive vias between electrodes. 
    
    
     To facilitate understanding, identical reference numerals have been used, where possible, to designate identical elements that are common to the figures. 
     DETAILED DESCRIPTION 
     FIG. 1 depicts a top plan view of an illustrative ceramic body containing the feedthrough of the present invention. In this illustrative example, the ceramic body is a ceramic wafer support pedestal, e.g., a Johnsen-Rahbek electrostatic chuck, for a semiconductor wafer processing system such as a physical vapor deposition system. However, those skilled in the art will realize from the following disclosure that the inventive feedthrough finds use in any application of a ceramic body where a conductive feedthrough is necessary. 
     Pedestal  100  contains a circumferential mounting flange  102  having a plurality of mounting bores  106 . The support surface  104  of the pedestal  100  has illustratively affixed thereto an electrode  108 . Although a single, centrally-located electrode is shown to illustrate one application of the invention, a multitude of electrodes may be affixed to the surface, or no electrode at all may be used and a feedthrough  110  may be positioned to supply electrical current to diagnostic equipment within a vacuum chamber. In the example shown, the feedthrough  110  of the present invention connects the vacuum side of the pedestal, e.g., the side that supports the wafer, to the atmosphere side of the pedestal. 
     FIG. 2 depicts a cross-sectional view of a portion of the pedestal  100  taken along  2 — 2  of FIG.  1 . This first embodiment of the invention is a single, vertical feedthrough  110  that conductively connects the vacuum side  50  of the pedestal  100  to the atmosphere side  52  of the pedestal  100 . Illustratively, this feedthrough is supplying power to a conductive electrode positioned on the vacuum side of the pedestal, i.e., the electrode  108  affixed to surface  104 . The atmosphere side  52  of the pedestal is located below surface  202  of the pedestal  100 . 
     The feedthrough  110  contains a plurality of conductive layers  206  (e.g.,  206   1 ,  206   2 ,  206   3 ,  206   4 , and  206   5 ) arranged vertically within the ceramic body and interconnected by a plurality of vias  208  (e.g.,  208   1 ,  208   2 ,  208   3  and  208   4 ). The atmosphere side  52  is connected to the electrodes  206  by a bore  210  and a conductive pin  214  having a pin head  218  coupled to a shaft  216 , whereby the shaft  216  is braised into the bore  210  such that the pin  214  electrically connects to one or more of the electrode layers  206 . 
     More specifically, the ceramic body, represented by the pedestal  100 , is fabricated of a plurality of stacked layers of ceramic material  204   1 ,  204   2 ,  204   3  . . .  204   8  . During the layering process, the layers of ceramic material are “dough-like” and are easily cut and shaped into a desired form. This state is commonly referred to as the “green state”. During fabrication, as each layer of ceramic material (e.g., aluminum nitride (AlN)) is positioned atop the next, the electrodes  206  are silk screened upon selected layers. The silk screened regions are formed in a vertical stack as each of the ceramic layers are positioned. The silk screened regions are generally coaxially aligned along a vertical axis through the stack of ceramic layers. Generally, the electrodes are fabricated of a tungsten alloy that, when sintered, solidifies into a tungsten electrode. Once the stack of silk screened ceramic layers is complete, the stack is dewaxed to bake out any hydrocarbons in the ceramic material. Then, the stack is cured by sintering the ceramic layers at approximately 2000 deg. C. within a nitrogen atmosphere. 
     Once cured, one or more conductive vias (e.g., four vias) are vertically formed into the vacuum side  50  of the ceramic body  100 . These vias  208  (specifically  208   1 ,  208   2 ,  208   3 , and  208   4 ) are generally created by boring a hole in the ceramic body such that the hole passes through the plurality of ceramic layers  204  and through a plurality of electrodes  206 . These bores are formed in the ceramic using conventional boring techniques such as bead blasting, drilling, etching and the like. Once the holes are formed, the vias are completed by depositing a conductive material e.g., a tungsten alloy) into the holes to interconnect the electrodes  206 . Such deposition is accomplished using conventional techniques such as physical vapor deposition (PVD), chemical vapor deposition (CVD), or other means of depositing metals. After depositing the conductive material, the surface  104  of the ceramic body  100  is lapped to expose the top end of the vias. Once exposed, a conductive layer  108  can be sputtered on the surface  104 . The exposed vias bond with the conductive layer  108 . Alternatively, wires, current probes, and other electrical circuitry can be connected to the exposed vias. 
     Alternatively, these conductive vias may be formed by boring through the ceramic layers in their pre-cured, green state (prior to sintering), and then filling the bores with a conductive paste containing metals such as titanium, titanium nitride or tungsten. Subsequent sintering will allow the ceramic layers and paste to harden, with the electrodes being interconnected by vertical conductive vias. The bores may be formed in each layer and the layers aligned to produce a contiguous bore through the stack of layers, or a bore may be formed by pushing a cylindrical probe through the stacked layers. In either instance, once the bore is formed in the stack, the conductive paste is packed into the bore. Then, the assembly is sintered. 
     To complete the feedthrough  110 , a bore  210  is formed into the surface  202  on the atmosphere side  52  of the ceramic body  100 . The shaft  216  of the conductive pin  214  is then brazed  212  into the bore  210  such that the pin is in conductive contact with one or more of the electrodes  206 . As such, the conductive via  208  is electrically connected to the pin  214  and provides a conductive path through the ceramic body. 
     The vias  208  are then be connected to, for example, an electrode  108  that is affixed to the surface  104  of the pedestal  100 . As such, electric power can be applied to the atmosphere side of the ceramic body, and the power is carried through the feedthrough to the electrode  108 . 
     Although the first illustrative embodiment of the invention depicts a pin connector on the atmosphere side of the ceramic body and the via connector on the vacuum side of the ceramic body, obviously the pin connector could be used on the vacuum side and the via connector used on the atmosphere side. Furthermore, a feedthrough may also be constructed having pin connectors on both sides of the ceramic body or a via connector on both sides of the ceramic body. 
     FIG. 3 depicts a top plan view of an alternative embodiment of the present invention. This embodiment contains a ceramic body  300  (e.g., a ceramic wafer support pedestal) with a feedthrough  302  electrically connecting a vacuum side  400  to an atmosphere side  402  of the ceramic body  300 . Rather than a linear (vertical) connection from a pin to an electrode, this embodiment of the invention has the location of the pin connector  306  laterally offset from the location of the via connector  304 . Specifically, a centrally located electrode  108  affixed to the support surface of the pedestal  100  is connected through an offset feedthrough  302  to the atmosphere side  402  of the pedestal. 
     FIG. 4 depicts a cross-sectional view of the alternative embodiment taken along line  4 — 4  of FIG.  3 . In this embodiment, the offset feedthrough  302  contains a pair of partial feedthroughs  304  and  306 . These partial feedthroughs are laterally distant from one another and interconnected by a bus electrode  308 . In the manner described above, a plurality of coaxially aligned electrode layers  316   1 ,  316   2 ,  316   3  are formed within the ceramic body  300 . Similarly, a plurality of coaxially aligned electrodes  310   1 ,  310   2 , and  310   3  are formed in the ceramic body  300 . The electrodes  316  are laterally displaced from the electrodes  310 . The two sets of electrodes are interconnected by bus  308 . The bus is formed by silk screening a conductive trace upon one of the ceramic layers that forms the ceramic body such that one end of the trace forms an electrode in one set of electrodes and the other end of the trace forms an electrode in the other set of electrodes. As such, the bus  308  interconnects the two sets of electrodes  316  and  310 . Once the layers of ceramic and conductive trace/regions are assembled, the body is baked and sintered to cure the ceramic into a unitary ceramic body. 
     Once cured, a plurality of conductive vias  312   1 ,  312   2 ,  312   3  and  312   4  are formed vertically into the ceramic body to interconnect the electrodes  310 . Similarly, the electrodes  316  are interconnected by vias  314   1 ,  314   2 ,  314   3  and  314   4 . The surfaces  318  and  320  of the ceramic body  100  are lapped to remove any residual conductive materials and to expose the vias  314  and  312 . Alternatively, these conductive vias may be formed by boring through the ceramic layers in their pre-cured, green state (prior to sintering), and then filling the bores with a conductive paste containing a metal such as Ti, TiN or W. Subsequent sintering will allow the ceramic layers and paste to harden, with the electrodes being interconnected by vertical conductive vias. 
     Once the conductive vias are formed using one of the foregoing processes, electrodes  108  and  322  are deposited upon the surfaces of the ceramic body  100  using conventional metalization techniques. Then, an electrical contact pin  324  is brazed or soldered to the conductive pad  322 . As such, when electrical current is applied to pin  324 , that current flows to the electrode  108  through the offset feedthrough  302 . 
     Of course, rather than utilize a surface mounted pin  324 , a conductive pin  214  of FIG. 2 could be substituted for the surface mounted pin  324 . Furthermore, a pin, surface mount or not, could be used on the vacuum side of the ceramic body. 
     By fabricating and using the invention as described, the integrity of a vacuum on one side of a ceramic body is maintained although electrical currents can be supplied through the ceramic body. This technique for creating a feedthrough extending through a ceramic body is applicable to any ceramic body, however, it has particular importance to ceramic wafer support pedestals including those that contain electrostatic chucks and/or ceramic heaters. 
     FIG. 5 a  is a partial transverse vertical cross-sectional view of an illustrative laminated ceramic body containing multilayer electrodes in accordance with the present invention. In this illustrative example, the ceramic body may be, for example, a ceramic wafer support pedestal, i.e., a Johnsen-Rahbek electrostatic chuck for a semiconductor wafer processing system such as a physical vapor deposition system. However, those skilled in the art will recognize from the following disclosure that this invention can find use in any application requiring a ceramic body and an internal electrode. 
     FIG. 5 a  depicts apparatus  502  includes a body  504  of ceramic, an electrode  506  embedded in the body of ceramic and an electrical connector  508  or connecting pin. 
     The body  504  of ceramic may be fabricated of a plurality of stacked layers of ceramic material  504   1 ,  504   2  . . .  504   7  in the same manner and of the same ceramic material that the stacked layers of ceramic material  204   1 ,  204   2  . . .  204   8  are fabricated as described hereinabove to form the pedestal  100  shown in FIGS. 1 and 2. 
     The electrode  506  includes a plurality of axially aligned (aligned along the axis  509  in FIG. 5 a ), parallel spaced-apart electrodes  506   1 ,  506   2  . . .  506   4  and may be fabricated in the same manner and of the same electrically conductive material that the plurality of electrodes or conductive layers  206   1 ,  206   2  . . .  206   5  are fabricated as described hereinabove to form the plurality of conductive layers or electrodes  206   1 ,  206   2  . . .  206   5  shown in FIG.  2 . In this manner, the electrode  506  is “distributed” such that each layer will handle a portion of the RF current. As such, the RF current is carried by a large cumulative surface area of the layers  506   1 ,  506   2  . . .  506   5 . 
     After fabrication of the ceramic body  504  and the electrode  506 , a bore  512  is suitably formed extending partially into the body of ceramic  504  and the forward end of the electrical connector member or pin  508  is inserted into the bore to intersect and to be mechanically and electrically connected to, such as by brazing or soldering, the electrodes  506   3  and  506   4 . The pin  508  needs only contact a subset of all the layers, e.g., two of seven, or even just one, because the RF energy supplied to directly connected electrodes will capacitively couple to the remaining (floating) electrode layers. 
     Apparatus  502  is particularly useful as a ceramic pedestal for supporting a semiconductor wafer during processing and is particularly useful for coupling RF power to the electrode  506  and electrical connector  508  as may be required for wafer processing in high temperature physical vapor deposition. It will be understood that this is to provide RF on or beneath the wafer to attract ions from the plasma towards the substrate. Since the electrode  506  is comprised of a plurality of relatively thin electrodes  506   1 ,  506   2  . . .  506   4 , less heating, and/or less concentration of thermal stress in localized portions of the chuck, is produced on coupling of RF power to the electrical connector  508  and electrode  506 . Hence any tendency toward cracking or breakage of the body of ceramic  504  is reduced even if the body of ceramic  504  and electrode  506  have different coefficients of expansion. Upon the apparatus  502  being embodied as a ceramic pedestal, it will be understood that the apparatus  502  will include the mounting flange  102  provided with mounting bores  106  (or other mounting hardware) shown in FIG.  1 . 
     It will be further understood that apparatus  502  may include two sets of electrodes  506   a  and  506   b , and electrical connecting pins  508   a  and  508   b , spaced laterally from each other, as shown in FIG. 5 b . Two conductive vias  514   a  and  514   b  are used to directly connect the bottom layer electrodes ( 506   a   4 ,  506   b   4 ) to the top layer electrodes ( 506   a   1 ,  506   b   1 ) within each set of electrodes,  506   a  and  506   b . In this particular cross-sectional view, the intermediate layer electrodes ( 506   a   2 ,  506   a   3 ,  506   b   2 ,  506   b   3 ) are illustrated as “broken” around the vias  514   a  and  514   b  to emphasize that there is no direct connection between these electrodes  506   a   2 ,  506   a   3 ,  506   b   2  and  506   b   3 ) and the conductive vias  514   a  and  514   b . In this embodiment, the apparatus  502  is particularly useful as a RF biased electrostatic chuck for both electrostatically retaining a semiconductor wafer and biasing the wafer. Both RF and DC voltages are supplied to the two electrical connecting pins  508   a  and  508   b . In this bipolar ESC configuration, the DC voltage applied to the two pins ( 508   a ,  508   b ) and to the top electrodes ( 506   a   1 ,  506   b   1 ) is used to attract a semiconductor wafer to the apparatus  502  in accordance with the Johnsen Rahbek effect. The RF power applied or coupled to the pair of connecting pins ( 508   a ,  508   b ) provides the RF bias necessary for wafer processing. As shown in FIG. 5 b , pins  508   a  and  508   b  are electrically connected to the two bottom electrodes  506   a   4  and  506   b   4 . In this configuration, the RF power from the bottom electrodes  506   a   4  and  506   b   4  is coupled to the top of the chuck by a direct connection to the top electrodes ( 506   a   1 ,  506   b   1 ) through the two conductive vias ( 514   a ,  514   b ), and capacitive coupling via the other floating electrodes ( 506   a   2 ,  506   b   2 ,  506   a   3 ,  506   b   3 ). This RF bias is then coupled to the entire wafer through the top electrodes  506   a   1 , and  506   b   1 . Again, such distributed RF coupling through multiple-layered electrodes can minimize local thermal stress that may otherwise arise from excessive heating when only a single electrode is used. It is understood that the embodiment shown in FIG. 5 b  may be fabricated using different combinations of the same process steps (stacking material layers, drilling and filling conductive vias and sintering) previously described. For example, this embodiment may be fabricated by stacking the respective ceramic layers  504   i  (i =2 to 7) and the electrode layers  506   a   i  and  506   b   i  (i=2 to 4) in proper sequence, forming the conductive vias  514   a ,  514   b , followed by the silk-screening of electrodes  506   a   1 ,  506   b   1 , stacking the ceramic layer  504   1  on top of the electrodes  506   a   1 ,  506   b   1  and sintering the entire structure. 
     Another alternative embodiment is shown in FIG. 6, where a pin  608  is shown to intersect a bottom layer electrode  606   4  within the chuck body  504 . Multiple direct connections are formed between this bottom electrode  606   4  and the top electrode  606   1 , as illustrated by the conductive vias  614   a ,  614   b ,  614   c , and  614   d . Again, intermediate electrodes  606   3  and  606   2  are shown as “broken” around these conductive vias  614   a ,  614   b ,  614   c , and  614   d  to emphasize that there is no direct connection between these electrodes ( 606   3  and  606   2 ) and the conductive vias ( 614   a ,  614   b ,  614   c , and  614   d ). Similar to the embodiment in FIG. 5 b , both RF and DC powers may be supplied to the pin  608 . As previously discussed, capacitive coupling of RF power takes place via the intermediate electrodes  606   3  and  606   2 . The DC and RF powers are both coupled to the top electrode  606   1  through multiple direct connections provided by the vias  614   a ,  614   b ,  614   c  and  614   d . Again, such a configuration minimizes the potential of breakage of the chuck due to local thermal stress that may otherwise arise if the power were concentrated on a single connection alone. 
     There has thus been shown and described a novel apparatus for providing a feedthrough connection through a ceramic body and a laminated ceramic body containing a multilayer electrode. Many changes, modifications, variations and other uses and applications of the subject invention will, however, become apparent to those skilled in the art after considering the specification and the accompanying drawings which disclose the embodiments thereof. For example, such a multilayer electrode arrangement is also applicable to plasma etching or deposition processes employing electrostatic chucks. All such changes, modifications, variations and other uses and applications which do not depart from the spirit and the scope of the invention are deemed to be covered by the invention, which is to be limited only by the claims which follow.