Patent Publication Number: US-2023139249-A1

Title: Thermal diffuser for a semiconductor wafer holder

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a continuation of U.S. patent application Ser. No. 16/552,790 filed Aug. 27, 2019. The disclosure of the above application is incorporated herein by reference. 
    
    
     FIELD 
     The present disclosure relates to electrostatic chucks, and more generally to ceramic chucks with a plurality of heating zones. 
     BACKGROUND 
     The statements in this section merely provide background information related to the present disclosure and may not constitute prior art. 
     A wafer support assembly, such as an electrostatic chuck (also referred to herein as an “E-chuck”), may be used in semiconductor processing to support and hold a wafer thereon. For example, the E-chuck may include an electrostatic puck (also referred to herein as an “E-puck”) that applies an electrostatic clamping force on the wafer. The E-chuck is generally exposed to high heat in a plasma processing chamber that performs various wafer processing/treatment steps, such as chemical vapor deposition (CVD), etching, sputtering, and ion implantation, among others. The E-chuck may be heated by a heater integrated in the E-chuck and a cooling device is generally disposed below the E-chuck to adjust or lower the temperature of the E-chuck during wafer processing or after wafer processing is completed. Throughout processing of the wafer, the E-chuck is subjected to wide and rapid temperature changes while the temperature of the wafer must be controlled to extremely tight tolerance such as less than about 0.5° C. during etching processes (e.g., processing temperatures up to about 120° C.) and less than about 5° C. during deposition processes (e.g., processing temperatures in the range of about 400-700° C.). 
     These issues of controlling the temperature of a wafer during semiconductor processing, among other issues related to the semiconductor processing, are addressed by the present disclosure. 
     SUMMARY 
     This section provides a general summary of the disclosure and is not a comprehensive disclosure of its full scope or all of its features. 
     In one form of the present disclosure, a heating assembly is provided, which includes a support member for supporting a target thereon, a diffuser layer attached to the support member, and a heater attached to the diffuser layer. The diffuser layer includes discrete diffuser segments separated by gaps. The discrete diffuser segments are made of the same material and are configured to allow a desired thermal gradient to be maintained between the discrete diffuser segments during heating of the target. 
     In other features, the diffuser layer is disposed between the support member and the heater. The discrete diffuser segments define continuous concentric rings, discontinuous concentric rings, or a combination thereof. The discrete diffuser segments are separated by at least one trench in the diffuser layer. The at least one trench extends partially through the diffuser layer or completely through the diffuser layer to the support member. The at least one trench defines a variable depth or a variable width. The support member is a ceramic material. The heater comprises at least two heating zones and the diffuser rings are axially aligned with the at least two heating zones such that the at least two heating zones are thermally decoupled from each other. The heater comprises an outer heating zone and an inner heating zone, and the diffuser rings are axially aligned with the outer heating zone and the inner heating zone to thermally decouple the outer heater zone from the inner heating zone such that a desired thermal gradient is maintained between the outer heater zone and the inner heating zone during heating of the target. The diffuser layer is formed from a material selected from the group consisting of aluminum, molybdenum, tungsten, nickel, zinc, silicon, and alloys thereof. The heater is selected from the group consisting of a foil heater, a layered heater, a damascene heater, and a polyimide heater. The heating assembly further includes a cooling plate attached to the heater. The diffuser layer is an aluminum diffuser layer with a thickness of less than 0.040 inches (1.02 mm). The support member is an E-puck including a substrate and at least one electrode embedded within the substrate. 
     In another form of the present disclosure, a heating assembly is provided, which includes a support member for supporting a target thereon, a diffuser layer disposed on the support member, a polyimide heater bonded to the diffuser layer, and a base plate bonded to the polyimide heater. The diffuser layer defines at least two diffuser rings arranged concentrically on the support member and defines predetermined intervals with spacing in a radial direction. The polyimide heater includes at least two heating zones. The at least two diffuser rings are disposed between the support member and the polyimide heater, are made of the same material, and are axially aligned with the at least two heating zones to thermally decouple the at least two heating zones such that a desired thermal gradient is maintained between the at least two diffuser rings during heating of the target. 
     In other features, the at least two heating zones include an outer heating zone and an inner heating zone, and a desired thermal gradient is maintained between the outer heater zone and the inner heating zone during heating of the target on the support member. The support member is bonded to the polyimide heater with a first elastomer layer and the polyimide heater is bonded to the base plate with a second elastomer layer. 
     Further areas of applicability will become apparent from the description provided herein. It should be understood that the description and specific examples are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure. 
    
    
     
       DRAWINGS 
       In order that the disclosure may be well understood, there will now be described various forms thereof, given by way of example, reference being made to the accompanying drawings, in which: 
         FIG.  1 A  is a cross-sectional view of an E-chuck constructed in accordance with one form of the present disclosure; 
         FIG.  1 B  is a cross-sectional view of an E-chuck constructed in accordance with another form of the present disclosure; 
         FIG.  2 A  to  FIG.  2 G  depict a series of steps for a method of manufacturing an E-chuck in accordance with the teachings of the present disclosure where:  FIG.  2 A  is a cross-sectional view of an E-puck;  FIG.  2 B  is a cross-sectional view of the E-puck in  FIG.  2 A  with a diffuser layer being formed thereon;  FIG.  2 C  is a cross-sectional view of the E-puck in  FIG.  2 B  with trenches being formed in the diffuser layer;  FIG.  2 D  is a cross-sectional view of the E-puck in  FIG.  2 C  with discrete diffuser segments formed in the diffuser layer;  FIG.  2 E  is a cross-sectional view of the E-puck in  FIG.  2 D  with the diffuser layer machined to a reduced thickness;  FIG.  2 F  is a top view of the E-puck in  FIG.  2 E  with discrete diffuser segments formed in the diffuser layer;  FIG.  2 G  is a cross-sectional view of an assembly of the E-puck in  FIG.  2 F  with a heater and a cooling plate; 
         FIG.  3 A  to  FIG.  3 D  depict a series of diffuser layers with trenches forming discrete diffuser segments where:  FIG.  3 A  is a cross-sectional view of a rectangular shaped trench extending into and through a diffuser layer;  FIG.  3 B  is a cross-sectional view of a rectangular shaped trench extending into a diffuser layer;  FIG.  3 C  is a cross-sectional view of a hemispherical-shaped trench extending into a diffuser layer; and  FIG.  3 D  is a cross-sectional view a v-shaped trench extending into a diffuser layer; 
         FIG.  4    is a plan view of a diffuser layer with discrete diffuser segments in accordance with one form of the present disclosure; 
         FIG.  5    is a plan view of a diffuser layer with discrete diffuser segments in accordance with another form of the present disclosure; 
         FIG.  6    is a plan view of a diffuser layer with discrete diffuser segments in accordance with yet another form of the present disclosure; and 
         FIG.  7    is a graph showing E-puck ceramic surface temperature and E-puck ceramic surface temperature range as a function of diffuser layer thickness in accordance with the teachings of the present disclosure. 
     
    
    
     The drawings described herein are for illustration purposes only and are not intended to limit the scope of the present disclosure in any way. 
     DETAILED DESCRIPTION 
     The following description is merely exemplary in nature and is not intended to limit the present disclosure, application, or uses. It should be understood that throughout the drawings, corresponding reference numerals indicate like or corresponding parts and features. Examples are provided to fully convey the scope of the disclosure to those who are skilled in the art. Numerous specific details are set forth such as types of specific components, devices, and methods, to provide a thorough understanding of variations of the present disclosure. It will be apparent to those skilled in the art that specific details need not be employed and that the examples provided herein, may include alternative embodiments and are not intended to limit the scope of the disclosure. In some examples, well-known processes, well-known device structures, and well-known technologies are not described in detail. 
     Referring to  FIG.  1 A , an E-chuck  2  constructed in accordance with one form of the present disclosure is shown. The E-chuck  2  comprises an E-puck  10 , a diffuser layer  20 , an upper bond layer  30 , a heater  40  for generating heat, a lower bond layer  42 , and a cooling plate  60 . In this form, the heater  40  is an etched foil heater that includes a polyimide layer  35  (or an “inter-layer dielectric”) and an etched foil heater circuit  44  on the polyimide layer  35 . It should be understood, however, that other heater constructions may be employed while remaining within the scope of the present disclosure. Further, both the upper and lower bond layers  30 / 42  may be optional if an appropriate dielectric is provided around the heater circuit  44  and that can be secured directly to the diffuser layer  20  and the cooling plate  60 . 
     Generally, the E-chuck  2  is used as a part of a support member in a semiconductor processing pedestal assembly. However, it should be understood that the teachings of the present disclosure may be employed in other applications besides semiconductor processing equipment, such as by way of example, industrial manufacturing equipment, cooktops, and medical devices, among others, while remaining within the scope of the present disclosure. 
     The E-puck  10  includes a substrate  12  and an electrode  4  embedded within the substrate  12 . The substrate  12  defines a first surface  6  and a second surface  8 , the latter of which is for heating a target (i.e., wafer) thereon. In at least one form of the present disclosure, the substrate  12  is formed from a ceramic material such as an aluminum oxide (Al 2 O 3 ) or aluminum nitride (AlN). However, it should be understood that other ceramic materials, or materials other than ceramic may be employed while remaining within the scope of the present disclosure. 
     The diffuser layer  20  is disposed between the E-puck  10  and the heater  40 . The diffuser layer  20  defines a first surface  22  and a second surface  24 . The first surface  22  is disposed directly on the first surface  6  of the E-puck  10 , and the second surface  24  is disposed on the heater  40 . In one variation, the second surface  24  of the diffuser layer  20  is disposed directly on the inter-layer dielectric  35  of the heater  40 , such that the heater  40  is directly secured to the diffuser layer  20 . In another variation, a bonding layer  30  is disposed between the diffuser layer  20  and the heater  40  to secure the heater  40  to the diffuser layer  20 . 
     As further shown, the diffuser layer  20  includes at least one trench or gap  26 . The trench  26  results in or forms discrete diffuser segments  28  within the diffuser layer  20 , which are described in greater detail below. Generally, the diffuser layer  20  enhances temperature uniformity across the second surface  8  of the E-puck  10 , while the discrete diffuser segments  28  allow a desired thermal gradient to be maintained between the segments during heating of a target on the E-puck  10 , the operation of which is described in greater detail below. 
     Referring to  FIG.  1 B , an E-chuck  10  constructed in accordance with another form of the present disclosure, which generally includes a routing layer, is shown. The E-chuck  10  generally comprises an E-puck  100 , a diffuser layer  120 , a dielectric layer  135 , a heater  140  for generating heat, a routing layer  146 , and a cooling plate  160 . 
     The E-puck  100  includes a substrate  102  and an electrode  104  embedded within the substrate  102 . The substrate  102  defines a first surface  106  and a second surface  108  for heating a target thereon. In at least one form of the present disclosure, the substrate  102  is formed from a ceramic material such as an aluminum oxide (Al 2 O 3 ) or aluminum nitride (AlN). 
     The diffuser layer  120  is disposed between the E-puck  100  and the dielectric layer  135 . The diffuser layer  120  defines a first surface  122  and a second surface  124 . The first surface  122  is disposed directly on the E-puck  100  and the second surface  124  is disposed on the dielectric layer  135 . 
     As further shown, the diffuser layer  120  includes at least one trench or gap  126 . The trench  126  results in or forms discrete diffuser segments  128  within the diffuser layer  120 , which are also shown in more detail in  FIGS.  3 - 6   . As discussed in greater detail below, the diffuser layer  120  enhances temperature uniformity across the second surface  108  of the E-puck  100  while the discrete diffuser segments  128  allow a desired thermal gradient to be maintained between the segments during heating of a target on the E-puck  100 . 
     The dielectric layer  135  is disposed between the diffuser layer  120  and the heater  140 . In at least one variation of the present disclosure, a bonding layer  130  is disposed between the diffuser layer  120  and the dielectric layer  135 . It should be understood that the bonding layer  130  bonds or attaches the E-puck  100  with the diffuser layer  120  to the dielectric layer  135 . It should be understood, however, that the diffuser layer  120  may be directly disposed on the E-puck  100  without a bonding layer  130  while remaining within the scope of the present disclosure. In such a form, the diffuser layer  120  may be thermally sprayed, by way of example, directly to the E-puck  100 . 
     The heater  140  is disposed between the dielectric layer  135  and the cooling plate  160 . In at least one form of the present disclosure, the heater  140  includes a heating layer  142 , an inter-layer dielectric  145 , and a routing layer  146 , and the inter-layer dielectric  145  is disposed between the heating layer  142  and the routing layer  146 . The heating layer  142  includes a heating layer substrate  143 , which is a thin layer of elastomer in one form of the present disclosure (approximately 0.001 in.-0.002 in.) and functions to affix at least one heating element  144  to the dielectric layer  135 . The routing layer  146  includes a routing layer substrate  147 , which is a dual function material that provides dielectric strength while bonding the routing layer  146  to the cooling plate  160 . As shown, the routing layer  146  includes at least one routing element  148 . At least one via interconnect  149  is disposed between the heating layer  142  and the routing layer  146  such that the at least one heating element  144  is in electrical connection with the at least one routing element  148 , thus enabling multiple heating zones as shown and described in greater detail below. While  FIG.  1 B  shows the heater  140  with an upper (+z direction) heating layer  142  and a lower (−z direction) routing layer  146 , it should be understood that the heating layer  142  and routing layer  146  can be in any order provided the diffuser layer  120  is disposed directly on the E-puck  100 . For example, the heating layer  142  can be positioned below (−z direction) the inter-layer dielectric  145  and the routing layer  146  can be positioned above (+z direction) the inter-layer dielectric  145 . It should also be understood that other functional layers, by way of example, a sensor layer, may be provided in addition to those shown and described. 
     In one form, the cooling plate  160  comprises cooling channels  162 , through which a cooling fluid flows, such that heat from the heater  140 , and other components or targets associated with the E-chuck  10 , can be dissipated away from the E-puck  100  during semiconductor processing of one or more wafers. 
     While  FIG.  1 B  shows only one bonding layer, i.e., bonding layer  130 , it should be understood that more than one bonding layer can be included and disposed between the various layers of the E-puck  10 . For example, a bonding layer (not shown) can be disposed between heater  140  and the cooling plate  160 . 
     Referring now to  FIGS.  2 A- 2 G , a method of manufacturing E-chuck  10  according to the teachings of the present disclosure is provided. The method includes providing the E-puck  100  with the at least one electrode  104  embedded within the substrate  102  as shown in  FIG.  2 A  and forming a diffuser layer  120  on the first surface  106  as shown in  FIG.  2 B . The diffuser layer  120  includes a first surface  122 , a second surface  124 , and a thickness (z-direction, not labeled) between the first surface  122  and the second surface  124 . In at least one variation of the present disclosure, the first surface  122  of the diffuser layer  120  is disposed directly on the first surface  106  of the E-puck  100 , while in other variations the first surface  122  of the diffuser layer  120  is not disposed directly on the first surface  106  of the E-puck  100 . For example, one or more additional layers (not shown) are disposed between the first surface  122  of the diffuser layer  120  and the first surface  106  of the E-puck  100 . It should be understood that the diffuser layer  120  can be deposited using any known or yet to be developed material layer deposition technique(s). Non-limiting examples of material layer deposition techniques include cathodic arc discharge, cold spray, chemical vapor deposition (CVD) techniques, physical vapor deposition (PVD) techniques, sol-gel techniques, sputtering, and vacuum plasma spray, among others. In one form of the present disclosure, a cold spray apparatus ‘S’ is used to deposit aluminum onto the first surface  106  of the E-puck  100 . 
     The diffuser layer  120  is formed from a material with a high thermal conductivity. As used herein the phrase “high thermal conductivity” refers to a thermal conductivity greater than 10 W/m·K, for example, greater than 50 W/m·K or greater than 100 W/m·K. Non-limiting examples of materials used to form the diffuser layer  120  include aluminum, copper, silver, gold, nickel and alloys thereof, among others. Other non-limiting examples of materials used to form the diffuser layer  120  include diamond-like carbon (DLC) and AlN, among others. Also, the diffuser layer  120  has a thickness between about 0.005 inches (0.13 mm) and about 0.100 inches (2.54 mm). For example, in one variation the diffuser layer  120  has a thickness between about 0.010 (0.25 mm) inches and about 0.020 (0.51 mm) inches. In another variation, the diffuser layer  120  has a thickness between about 0.020 inches (0.51 mm) and about 0.030 inches (0.76 mm). In still another variation, the diffuser layer  120  has a thickness between about 0.030 inches (0.76 mm) and about 0.040 inches (1.02 mm). 
     The diffuser layer  120  may have a monolithic composition along its thickness (z direction), or in the alternative, a graded composition (or a varying coefficient of thermal expansion (CTE)) through its thickness (z direction) such that the thermal expansion mismatch between the first surface  122  of the diffuser layer  120  and the first surface  106  of the E-puck  100  is reduced. In one variation, the diffuser layer  120  has a first thickness (not labeled) adjacent to the first surface  106  of the substrate  102  and a second thickness (not labeled) distal from (further away) the first surface  106  compared to the first thickness. The first thickness has a first composition and the second thickness has a second composition different than the first composition. Also, the first composition has a first coefficient of the thermal expansion (CTE) and the second composition has a second CTE different than the first CTE. One non-limiting example includes a substrate  102  formed from alumina and a diffuser layer  120  with a first thickness (not labeled) having a first composition extending from the first surface  106  towards the second surface  108  and a second thickness (not labeled) having a second composition extending from the first thickness towards the second surface  108 . The first thickness is about 10-15 μm and the first composition has a CTE of about 1.1 times the CTE for alumina. The second thickness is about 25-50 μm and the second composition has a CTE of about 1.2 times the CTE for alumina. It should be understood that additional thicknesses with different compositions (and different CTEs) can be included in the diffuser layer  120  such that the diffuser layer has a gradient of CTE values. It should also be understood that the entire diffuser layer  120  can have a continuously changing composition from the first surface  122  to the second surface  124  such that the diffuser layer  120  has a gradient CTE from the first surface  122  to the second surface  124 . 
     Referring now to  FIG.  2 C , at least one trench  126  (also referred to herein as a “gap”) is formed in the diffuser layer  120 . The trench  126  extends from the second surface  124  of the diffuser layer  120  towards the first surface  106  of the E-puck  100 . In some variations of the present disclosure, one or more trenches  126  extend completely through the diffuser layer  120 , i.e., from the second surface  126  of the diffuser layer  120  to the first surface  106  of the E-puck  100 , while in other variations one or more trenches  126  extend only partially through the diffuser layer  120 . In still other variations, one or more trenches  126  have at least one portion (not shown) where the trench  126  extends completely through the diffuser layer  120  and at least one other portion where the trench  126  extends only partially through the diffuser layer  120 . In one form of the present disclosure, the at least one trench is formed with a laser ‘L’, e.g., by laser machining. 
     It should be understood that the at least one trench  126 , and other trenches disclosed herein, can be formed using any known or yet to be developed material removal technique. Non-limiting examples of material removal techniques include grinding, laser cutting, etching, machining, photolithography, and sand or grit blasting, among others. It should also be understood that while  FIGS.  2 B and  2 C  depict the diffuser layer with at least one trench  126  being formed by depositing the diffuser layer  120  and then removing material to form the trench  126 , other techniques or methods can be used to form the diffuser layer  120  and trenches  126 . For example, in one variation, the first surface  106  is masked (not shown) to cover the locations or positions of the trenches  126 , the diffuser layer  120  is deposited onto the first surface  106 , and then the mask is removed to reveal the trenches  126  in the diffuser layer  120 . In the alternative, or in addition to, the diffuser layer  120  with the trenches  126  is formed with an additive manufacturing technique (e.g., 3D printing) without any masking or subsequent removal process as described herein. 
     Referring now to  FIGS.  2 D and  2 E , the method includes forming a plurality of trenches  126  such that discrete diffuser segments  128  are formed and separated by the trenches  126 , and machining the diffuser layer  120  ( FIG.  2 E ) such that a generally flat second surface  124  that is generally parallel to the second surface  108  of the E-puck  100  is provided. That is, the second surface  126  is machined such that a flat diffuser layer  120  is provided at an interface where the heater  140  is to be secured. Non-limiting examples of machining techniques or processes for machining the diffuser layer include lapping, polishing, and chemical mechanical polishing (CMP), among others. While  FIG.  2 E  depicts machining of the diffuser layer  120  after the at least one trench  126  is formed, it should be understood that the diffuser layer  120  can be machined before the at least one trench  126  is formed or during the same process as forming the trenches. 
       FIG.  2 F  shows a completed diffuser layer  120  with a central or first discrete diffuser segment  128   a  separated from a second discrete diffuser segment  128   b  by a trench  126   a , a third discrete diffuser segment  128   c  separated from the second discrete diffuser segment  128   b  by a trench  126   b , and a fourth discrete diffuser segment  128   d  separated from the third discrete diffuser segment  128   c  by a trench  126   c.    
     Referring now to  FIG.  2 G , the method includes assembling E-puck  100  with the diffuser layer  120 , the dielectric layer  135 , the heater  140  and the cooling plate  160  to provide the E-chuck  10  shown in  FIG.  1 B . Particularly, the E-puck  100  with the diffuser layer  120  is bonded to the dielectric layer  135 , the dielectric layer is bonded to the heater  140 , and the heater  140  is bonded to the cooling plate  160 . In at least one variation of the present discloser, the bonding layer  130  is disposed between the diffuser layer  120  and the heater  140 . Also, additional bonding layers can be disposed between the various layers of the E-chuck  10 . It should be understood that the at least one trench  126  may be filled with air, an elastomer material, a dielectric material, and/or a bonding material such that a low thermal conductivity gap is between adjacent discrete diffuser segments  128 . 
     The dielectric layer  135  electrically isolates the heater  140  from the diffuser layer  120 . Non-limiting examples of materials used to form the dielectric layer  135  include elastomers, polyimide, thermally sprayed dielectrics (e.g., Al 2 O 3 , yttria), thick film dielectrics, liquid polyimide, and other dielectric polymers, among others. The heater  140  can be any heater known or yet to be developed to provide heat to and for use with an E-chuck. Non-limiting examples of the heater  140  include a polyimide foil heater, a layered heater, or a damascene heater, among others. In at least one form of the present disclosure, the heater  140  includes the inter-layer dielectric  145  disposed between an elastomer heating layer substrate  143  and an elastomer routing layer substrate  147 . 
     Referring now to  FIGS.  3 A- 3 D , non-limiting examples of trenches  126  formed in the diffuser layer  120  are shown. For example,  FIG.  3 A  shows a rectangular-shaped trench  126  extending from the second surface  124  of the diffuser layer  120  to the first surface  106  of the E-puck  100 , i.e., the rectangular-shaped trench  126  in  FIG.  3 A  extends completely through the diffuser layer  120  such that discrete diffuser segments  128 L and  128 R are separated by a trench. In the alternative,  FIG.  3 B  shows a rectangular-shaped trench  126  extending from the second surface  124  of the diffuser layer  120  towards but not completely to the first surface  106  of the E-puck  100 , i.e., the rectangular-shaped trench  126  in  FIG.  3 A  extends only partially through the diffuser layer  120  such that discrete diffuser segments  128 L and  128 R are separated by a trench.  FIG.  3 C  shows a hemispherical-shaped trench  126  extending into the diffuser layer  120  and  FIG.  3 D  shows a v-shaped trench  126  extending into the diffuser layer  120  such that discrete diffuser segments  128 L and  128 R are separated by a trench. It should be understood that the trench  126  can have other shapes that extend completely or partially through the diffuser layer  120  such that discrete diffuser segments are separated by a trench. 
     While  FIG.  2 E  shows the diffuser layer  120  with radially disposed discrete diffuser segments  128   a - 128   d , it should be understood that the diffuser layer  120  can include azimuthal disposed discrete diffuser segments. For example, and with reference to  FIG.  4   , the diffuser layer  120  includes a central discrete diffuser segment  128   a  separated from a first radial discrete diffuser segment  128   b  by a trench  126   a  and a plurality of second radial discrete diffuser segments  128   c  separated from the first radial discrete diffuser segment  128   b  by a trench  126   b , and azimuthally separated from each other by trenches  127   a . As shown in  FIG.  4   , in one variation the plurality of second radial discrete diffuser segments  128   c  includes four (4) second radial discrete diffuser segments  128   c , however, it should be understood that the number of second radial discrete diffuser segments  128   c  can be less than four or more than four. Also, a plurality of third radial discrete diffuser segments  128   d  are separated from the second radial discrete diffuser segments  128   c  by a trench  126   c , and azimuthally separated from each other by trenches  127   b . As shown in  FIG.  4   , in one variation the plurality of third radial discrete diffuser segments  128   d  includes four (4) third radial discrete diffuser segments  128   d , however, it should be understood that the number of third radial discrete diffuser segments  128   d  can be less than four or more than four. In addition, it should also be understood that the diffuser layer  120  can include any number of radial discrete diffuser segments and any number of azimuthal discrete diffuser segments. For example, the diffuser layer  120  shown in  FIG.  5    includes a central discrete diffuser segment  128  and nine (9) radial discrete diffuser segments  128  separated by trenches  126 , and up to twenty-four (24) azimuthal discrete diffuser segments  128  within a given radial discrete diffuser segment separated by trenches  127 . In addition, adjacent radial discrete diffuser segments can be aligned as shown in  FIG.  4    or be offset from each other as shown in  FIG.  5   . 
     While  FIGS.  2 E,  4  and  5    show the diffuser layer  120  with regular shaped discrete diffuser segments  128  comprising a generally constant radial width and/or azimuthal length, it should be understood that in some variations of the present disclosure the diffuser layer  120  includes irregular shaped discrete diffuser segments. For example,  FIG.  6    shows a diffuser layer  120  with a plurality of irregular-shaped discrete diffuser segments  128 ′ separated by trenches or trenches  126 ′. 
     Referring now to  FIG.  7   , results from a Finite Element Analysis (FEA) of temperature of an outer surface (e.g., second surface  108 ) of a substrate and temperature range of the outer surface as a function of diffuser layer thickness (+z direction in  FIG.  1   ) are shown. Particularly, FEA of an alumina substrate heated to an average temperature of about 79° C. was performed for no diffuser layer, a 0.010 inch thick diffuser layer, a 0.020 inch thick diffuser layer, and a 0.030 inch thick diffuser layer. From the FEA, the maximum temperature, the minimum temperature and the range of temperature (i.e., maximum temperature−minimum temperature) was determined and is plotted in  FIG.  7   . As shown in  FIG.  7   , a diffuser layer 0.030 inches thick reduced the range of temperature of the outer surface from about 7.6° C. to about to about 4.8° C., i.e. almost 40%. 
     Accordingly, each discrete diffuser segment enhances temperature uniformity of a particular region or area of an E-puck outer surface while the trenches provide at least a partial thermal decoupling of the discrete diffuser segments from each other such that a desired thermal gradient (e.g., 20° C. from center to edge of a discrete diffuser segment  128 ) is maintained between the segments during heating of a target on the E-puck. The term “at least a partial thermal decoupling” (and variations thereof) should be construed to mean that a thermal conductivity of the trenches/gaps  26 / 126  between diffuser segments  28 / 128  is less than, or independent from, a thermal conductivity of the adjacent diffuser segments  128 . For example, the trenches/gaps  26 / 126  may have approximately 50% or less of the thermal conductivity of the diffuser segments  28 / 128  while remaining within the scope of the present disclosure. 
     Further, while the diffuser segments  28 / 128  are illustrated herein as taking on an arcuate geometry, it should be understood that any shape or combination of shapes, whether the same or different in a given diffuser layer  20 / 120 , may be employed in order to provide a desired thermal gradient across the E-puck  10 / 100  while remaining within the scope of the present disclosure. 
     It should be understood from the figures and the discussion above that an E-chuck with a diffuser layer that enhances temperature uniformity across the surface of an E-puck, thereby enhancing temperature uniformity of a target on the E-puck, is provided. Also, the diffuser layer includes discrete diffuser segments that are thermally decoupled from each other, e.g., via trenches or gaps between the discrete diffuser segments, such that a desired thermal gradient between the segments is maintained during heating of the target on the E-puck. The combination of the enhanced E-puck surface temperature uniformity and thermal gradient control between or across areas or portions of the E-puck surface provides enhanced process control during semiconductor wafer processing. 
     When an element or layer is referred to as being “on,” “engaged to,” or “disposed on” another element or layer, it may be directly on, engaged, connected or disposed on the other element or layer, or intervening elements or layers may be present. In contrast, when an element is referred to as being “directly on,” “directly engaged to,” “directly connected to,” or “directly disposed on” another element or layer, there may be no intervening elements or layers present. Other words used to describe the relationship between elements should be interpreted in like fashion (e.g., “between” versus “directly between,” “adjacent” versus “directly adjacent,” etc.). As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items. 
     Although the terms first, second, third, etc. may be used to describe various elements, components, regions, layers and/or sections, these elements, components, regions, layers and/or sections, should not be limited by these terms. These terms may be only used to distinguish one element, component, region, layer and/or section, from another element, component, region, layer and/or section. Terms such as “first,” “second,” and other numerical terms when used herein do not imply a sequence or order unless clearly indicated by the context. Thus, a first element, component, region, layer or section, could be termed a second element, component, region, layer or section without departing from the teachings of the example forms. Furthermore, an element, component, region, layer or section may be termed a “second” element, component, region, layer or section, without the need for an element, component, region, layer or section termed a “first” element, component, region, layer or section. 
     Spatially relative terms, such as “inner,” “outer,” “beneath,” “below,” “lower,” “above,” “upper,” and the like, may be used herein for ease of description to describe one element or feature&#39;s relationship to another element(s) or feature(s) as illustrated in the figures. Spatially relative terms may be intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. For example, if the device in the figures is turned over, elements described as “below” or “beneath” other elements or features would then be oriented “above” the other elements or features. Thus, the example term “below” can encompass both an orientation of above or below. The device may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein interpreted accordingly. 
     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. 
     Unless otherwise expressly indicated, all numerical values indicating mechanical/thermal properties, compositional percentages, dimensions and/or tolerances, or other characteristics are to be understood as modified by the word “about” or “approximately” in describing the scope of the present disclosure. This modification is desired for various reasons including industrial practice, manufacturing technology, and testing capability. 
     The terminology used herein is for the purpose of describing particular example forms only and is not intended to be limiting. The singular forms “a,” “an,” and “the” may be intended to include the plural forms as well, unless the context clearly indicates otherwise. The terms “including,” and “having,” are inclusive and therefore specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. The method steps, processes, and operations described herein are not to be construed as necessarily requiring their performance in the particular order discussed or illustrated, unless specifically identified as an order of performance. It is also to be understood that additional or alternative steps may be employed. 
     The description of the disclosure is merely exemplary in nature and, thus, examples that do not depart from the substance of the disclosure are intended to be within the scope of the disclosure. Such examples are not to be regarded as a departure from the spirit and scope of the disclosure. 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.