Patent Publication Number: US-2012037068-A1

Title: Composite substrates for direct heating and increased temperature uniformity

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims benefit of U.S. Provisional Patent Application Ser. No. 61/372,771, filed Aug. 11, 2010, which is herein incorporated by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     Embodiments of the present invention generally relate to methods and apparatus for uniformly heating substrates during epitaxial growth processes. 
     2. Description of the Related Art 
     The advantage of compound semiconductors (e.g., gallium nitride or gallium arsenide) holds much promise for a wide range of applications in electronics (high frequency, high power devices and circuits) and optoelectronics (lasers, light-emitting diodes and solid state lighting). Generally, compound semiconductors are formed by heteroepitaxial growth on a substrate material. The lattice mismatch and difference in thermal expansion between the compound semiconductor and the substrate causes the substrate to deform or bow during processing. The bowing of the substrate places a portion of the substrate closer to a heating source used during the epitaxial layer formation process which causes a non-uniform temperature profile across the surface of the substrate. Thermal uniformity of the substrate is important since the epitaxial layer composition, and thus LED emission wavelength, is a strong function of the surface temperature of the substrate. Additionally, since the surface of the substrate may have a non-uniform temperature profile, the formation rate of the epitaxial layer may be non-uniform across the substrate surface. In extreme cases, the substrate can bow enough to crack or break, damaging or ruining the epitaxial layer grown thereon. 
     Typically, substrates are positioned on a substrate carrier during processing. The substrate carrier is designed to transfer heat to the substrates during an epitaxial growth process. The substrate carrier may be flat, or may have pockets formed therein which attempt to mimic the bowed-shape of the substrate during processing. However, due to the unrepeatability of the shape of the substrate during processing, different portions and varying amounts of surface area of the substrates will be in contact with the substrate carrier during a deposition process. Since the surface area of the substrates in contact with the substrate carrier is inconsistent, varying amounts of heat will be transferred to each substrate. The variance in thermal profiles between substrates results in differing deposited film properties and the non-uniform growth of the epitaxial films, thereby decreasing process repeatability, and ultimately, device performance. Furthermore, the non-uniform thermal profile of the substrate may induce additional bowing of the substrate, which may lead to cracking or breaking of the substrate. 
     Therefore, there is a need for more uniformly applying heat and for reducing the amount of bow of substrates when forming compound semiconductors. 
     SUMMARY OF THE INVENTION 
     Embodiments of the present invention generally relate to apparatus and methods for uniformly heating substrates. The apparatus include a transferable puck having at least one electrode and a dielectric coating. The transferable puck can be biased with a biasing assembly relative to a substrate, and transferred independently of the biasing assembly during a fabrication process while maintaining the bias relative to the substrate. The puck absorbs radiant heat from a heat source and uniformly conducts the heat to a substrate coupled to the puck. The puck has high emissivity and high thermal conductivity for absorbing and transferring the radiant heat to the substrate. The high thermal conductivity allows for a uniform temperature profile across the substrate, thereby increasing deposition uniformity. The method includes disposing a light-absorbing material on an optically transparent substrate, and radiating the light-absorbing material with a radiant heat source to heat the optically transparent substrate. 
     In one embodiment, a transferable puck for supporting a substrate comprises at least one electrode having a dielectric coating thereon. A portion of the at least one electrode is exposed through the dielectric coating and is adapted to be contacted by a biasing assembly. 
     In another embodiment, a transferable puck for supporting a substrate comprises at least one electrode and a dielectric coating disposed over the at least one electrode. A portion of the at least one electrode is exposed through the dielectric coating and is adapted to be contacted by a biasing assembly. The at least one electrode is adapted to maintain a bias relative to the substrate while being transferred independent of the biasing assembly during a fabrication process. 
     In another embodiment, a method of forming an epitaxial film comprises disposing a light-absorbing material having an emissivity within a range from about 0.3 to about 0.95 on a first surface of an optically transparent substrate. The optically transparent substrate is positioned within a processing chamber. The optically transparent substrate is supported by a substrate support disposed in the processing chamber. Energy is then delivered to the light-absorbing material from one or more lamps. The one or more lamps are positioned to deliver energy to the light-absorbing material through an opening formed in the substrate support. An epitaxial layer is then formed on a second surface of the optically transparent substrate that is opposite to the first surface of the optically transparent substrate. 
     In another embodiment, a substrate used to support at least a portion of a light emitting diode or laser diode device during processing comprises an optically transparent substrate. The optically transparent substrate has a first side and a second side. The second side is on a side opposite to the first side. A light-absorbing material is disposed on the first side of the optically transparent substrate, and the second side is configured to receive one or more layers used to form a light emitting diode or laser diode device. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       So that the manner in which the above recited features of the present invention can be understood in detail, a more particular description of the invention, briefly summarized above, may be had by reference to embodiments, some of which are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only typical embodiments of this invention and are therefore not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments. 
         FIGS. 1A and 1B  are schematic illustrations of a composite substrate positioned on an annular substrate carrier. 
         FIGS. 2A-2F  are schematic illustrations of composite substrates according to other embodiments of the invention. 
         FIGS. 3A and 3B  are schematic illustrations of a flexible puck according to another embodiment of the invention. 
         FIGS. 4A-4E  are schematic illustrations of a composite substrate according to another embodiment of the invention. 
         FIGS. 5A-5D  are schematic illustrations of a substrate carrier according to embodiments of the invention. 
         FIGS. 6A-6C  are schematic illustrations of a puck having a bonding layer thereon. 
     
    
    
     To facilitate understanding, identical reference numerals have been used, where possible, to designate identical elements that are common to the figures. It is contemplated that elements disclosed in one embodiment may be beneficially utilized on other embodiments without specific recitation. 
     DETAILED DESCRIPTION 
     Embodiments of the present invention generally relate to apparatus and methods for uniformly heating substrates. The apparatus include a transferable puck having at least one electrode and a dielectric coating. The transferable puck can be biased with a biasing assembly relative to a substrate, and transferred independently of the biasing assembly during a fabrication process while maintaining the bias relative to the substrate. The puck absorbs radiant heat from a heat source and uniformly conducts the heat to a substrate coupled to the puck. The puck has high emissivity and high thermal conductivity for absorbing and transferring the radiant heat to the substrate. The high thermal conductivity allows for a uniform temperature profile across the substrate, thereby increasing deposition uniformity. The method includes disposing a light-absorbing material on an optically transparent substrate, and radiating the light-absorbing material with a radiant heat source to heat the optically transparent substrate. 
     Due to extrinsic and intrinsic stress created in a substrate during various heating and deposition processes, a processed substrate will tend to deform into a shape (e.g., convex or concave) that has an undesirable, unrepeatable and possibly variable curvature. In general, the curvature (K) of a substrate is equal to the inverse radius (r) of the bow curve (e.g., K=1/r). The bow (B) of the substrate is equal to one-half the curvature (K) of the substrate multiplied by the radius (R) of the substrate squared (e.g., B=(K/2*R 2 )). Thus, the bow of the substrate is proportional to the square of the radius (R) of the substrate. The bow is typically defined as the distance from the edge of the substrate to the maximum deflection of the substrate, or, for example, in a simple concave shaped substrate it is the distance from the deflected center of the substrate to the edge of the substrate in a direction passing through the center point of the substrate and the center of the curvature. 
     An increase in substrate size can cause an increase in substrate bow, due to the substrate curvature (the inverse radius of the arc formed by the substrate). This effect becomes especially pronounced in substrates having a diameter of six inches or greater. The substrate bow causes non-uniform heating and non-uniform epitaxial formation during epitaxial growth processes, which further induces stress and bowing on the substrate because of the increasing non-uniformity of the epitaxial layer. For curvatures of 50 millimeters and 100 millimeters, a two inch substrate has a theoretical bow of about 16 to about 32 micrometers. A four inch substrate has a theoretical bow of about 64 to about 129 micrometers. A six inch substrate has a theoretical bow of about 145 to about 290 micrometers. An eight inch substrate has a theoretical bow of about 258 to about 516 micrometers. Thus, as substrate size increases, the amount and proportionate variation in the bow of the substrate also increases. 
       FIGS. 1A and 1B  are schematic illustrations of a composite substrate positioned on an annular substrate carrier.  FIG. 1A  illustrates a composite substrate  110  positioned on an annular substrate carrier  104 . The annular substrate carrier  104  is formed from silicon carbide and has an opening  106  disposed therethrough. The composite substrate  110  includes a substrate  102  and a thermally-conducting layer  112  disposed on a back surface of the substrate  102 . In one configuration, the substrate may further comprise a plurality of surface features, such as random texture, formed geometric features (e.g., micron sized pyramids), holes or other useful surface topography, formed on the front surface of the substrate to promote the growth of an epitaxial layer that has desirable properties (e.g., reduced number of defects, improve stress). The substrate  102  is made of a material compatible for growing an epitaxial layer thereon; for example, a single crystal substrate made of sapphire or silicon. However, single crystal substrates are just one type of substrate which may benefit from embodiments disclosed herein. In one example, the substrate  102  is a sapphire substrate, which generally has an optical transmittance of at least 80% for wavelengths of light between about 0.3 and about 4.5 μm. In one example, the substrate  102  is a patterned sapphire substrate (PSS). In another example, the substrate  102  is a silicon substrate, which generally has an optical transmittance of about 50% or greater for wavelengths of light between about 1.5 and about 9 μm, such as between 3 and about 5 μm. It is contemplated that other substrates as known in the industry may also benefit from embodiments disclosed herein. For example, the substrate  102  may be gallium arsenide or silicon carbide, among others. 
     The thermally-conducting layer  112  is a layer or coating with high emissivity and high thermal conductivity, and is capable of absorbing heat from a radiant heat source, such as lamp  108 . In one configuration, tungsten-halogen lamps are used, which emit a large portion of the optical energy (e.g., up to 85 percent) in the infrared region, and primarily in the wavelengths between about 0.2 μm and about 3.0 μm (e.g., near-infrared region). Therefore, in conventional lamp heating applications, one will note that a large portion of the emitted energy from a lamp (e.g., tungsten-halogen lamp) will not be effectively or efficiently absorbed by a bare optically transparent substrate (e.g., sapphire and/or silicon substrates), thus there is need for the various embodiments of the invention described herein. 
     It is desirable that the thermally-conducting layer  112  has a high affinity for absorbing all or most of the wavelengths of radiant heat provided by a radiant heating source, such as lamp  108 . It is also desirable that the thermally-conducting layer  112  has a high thermal conductivity to evenly deliver absorbed radiant heat to the substrate  102 . The emissivity of the thermally-conducting layer  112  may be within a range of about 0.3-0.95, such as about 0.8 to about 0.95. However, it is contemplated that materials with other emissivities may be used, as long as the emissivity is sufficient to absorb the radiant energy at the emitted wavelengths supplied by the lamp  108 . The thermal conductivity of the thermally-conducting layer  112  is generally about 100 W/m·K or greater, such as about 120 W/m·K or greater, or within a range from about 200 W/m·K to about 500 W/m·K. If the thermal conductivity of the thermally-conducting layer  112  is too low, then uneven heating of the substrate  102  may occur since the heat absorbed by the thermally-conducting layer  112  will not be evenly distributed. 
     To further assist in the even distribution of absorbed heat, the thermally-conducting layer  112  should have a sufficient thickness to allow for lateral transfer of absorbed heat during an epitaxial growth process. Generally, the thermally-conducting layer  112  has a thickness within a range from about 0.1 micrometer to about 300 micrometers. For example, the thermally-conducting layer  112  may have a thickness of about 100 micrometers to about 200 micrometers. Depending on the type of substrate being processed and the material used for the thermally-conducting layer, the ratio of the thickness of the substrate  102  to the thermally-conducting layer may be about 1000:1 to about 3:1. For example, the ratio of the thickness of the substrate  102  to the thickness of the thermally-conducting layer  112  may be about 20:1 to about 5:1. 
     The thermally-conducting layer  112  is a metal-containing material. It is contemplated that the thermally-conducting layer  112  may be formed from other materials, including refractory metals, refractory metal alloys, or dielectrics. For example, the thermally-conducting layer may be formed from sintered polysilicon carbide, titanium, titanium nitride, tungsten, tungsten nitride, cobalt, boron nitride and silicon nitride. Silicon carbide generally has an emissivity within a range from about 0.83 to about 0.96 and thermal conductivity of about 120 W/m·K. The thermally-conducting layer  112  is deposited or coated on the substrate  102  by chemical vapor deposition. However, other deposition processes, such as physical vapor deposition, evaporation, or the like may also be used to form the thermally-conducting layer  112  on the substrate  102 . 
     Preferably, the thermally-conducting layer  112  is capable of withstanding the elevated temperatures used in an epitaxial growth process without contaminating the epitaxial growth chamber, such as about 1200 degrees Celsius or less. In the embodiment of  FIG. 1A , the composite substrate  110  is illustrated prior to an epitaxial growth process. 
     In the typical processing of substrates, heat is provided to a substrate by first heating the substrate carrier, and then conducting the heat to the substrate which is in physical contact with the substrate carrier. Substrate carriers which conduct heat to the substrate are often solid (lacking a central opening), and may be planar or have pockets formed therein. A solid substrate carrier is often used to conduct heat to the substrate because it is believed that this will allow more area to be in thermal contact between the substrate and the substrate carrier. Substrates generally are heated by thermal conduction since substrates are often optically transparent and therefore poorly absorb heat radiated from lamps. However, heating substrates by conducting heat through the substrate carrier to the substrates often results in non-uniform heating of the substrate due to the bowing of the substrate during processing. The bowed-shape of the substrate results in non-uniform thermal contact and conduction of heat to the substrate, which undesirably affects deposition uniformity. Therefore, it is desirable to more uniformly apply heat to a substrate during processing. 
     The composite substrate  110  need not rely upon the conduction of heat from the substrate carrier  104 , since the thermally-conducting layer  112  has been applied to the substrate  102 . The thermally-conducting layer  112 , which is part of the composite substrate  110 , is capable of absorbing heat from the lamp  108  and conducting the absorbed heat to the substrate  102  during epitaxial processing. Since the composite substrate  110  is not primarily heated during processing by heat conducted through the substrate carrier  104 , an opening  106  can be formed in the substrate carrier  104 . The opening  106  provides a path for heat to directly irradiate the composite substrate  110 , and also reduces the surface area of the composite substrate in contact with the substrate carrier  104  during processing. Therefore, even if the composite substrate  110  bows during processing, uneven thermal conduction of heat from the substrate carrier  104  to the composite substrate  110  is minimized, since less surface area of the composite substrate  110  is in contact with the substrate carrier  104 . 
       FIG. 1B  illustrates the composite substrate  110  positioned on the annular substrate carrier  104  while receiving light from the lamp  108  during an epitaxial growth process. The lamp  108  is positioned beneath the composite substrate  110 , and may be located outside of a process chamber or disposed within a process chamber wall. The radiant heat emitted by the lamp  108  is absorbed by the thermally-conducting layer  112  during the epitaxial growth process, and transferred to the substrate  102  via conduction. Thus, composite substrate  110  is able to directly absorb radiant heat using thermally-conducting layer  112 , which is not optically transparent. The high thermal conductivity of the thermally-conducting layer  112  allows for a uniform temperature profile within the thermally-conducting layer  112 . Consequently, a uniform temperature profile is created within the substrate  102 . Furthermore, unlike the substrates and solid substrate carrier combinations used in typical substrate processes, a central portion of the composite substrate  110  does not contact the substrate carrier  104  due to the opening  106  formed therein. Thus, non-uniform conduction of heat to the substrate  102  is reduced. 
     The thermally-conducting layer  112  is not only beneficial for absorbing radiant energy, but also serves to increase the rigidity of the substrate  102  due to increased thickness imparted by the thermally-conducting layer  112 . Thus, the potential for the substrate  102  to crack or break due to bowing is reduced. Since extra support is provided by the thermally-conducting layer  112 , a thinner and therefore cheaper substrate  102  may be used. For example, a substrate may require a thickness of 1300 micrometers for sufficient rigidity when performing epitaxial growth processes in the absence of the thermally-conducting layer  112 . However, when the thermally-conducting layer  112  is applied to the substrate  102 , the thickness of the substrate  102  can be reduced to about 900 micrometers. Generally, the material from which the substrate  102  is formed is significantly more expensive than the material from which the thermally-conducting layer  112  is formed. Therefore, the reduction in the thickness of the substrate  102  provides a cost savings when performing epitaxial growth processes. 
     Subsequent to an epitaxial growth process, the composite substrate  110  can optionally be removed from the epitaxial layer  114  by chemical or mechanical means. For example, the composite substrate  110  can be removed by grinding, polishing or etching. Alternatively, the composite substrate  110  may remain coupled to the epitaxial layer  114 , or only the thermally-conducting layer  112  may be removed while the substrate  102  remains coupled to the epitaxial layer  114 . 
       FIGS. 2A-2F  are schematic views of composite substrates according to other embodiments of the invention. The composite substrates of  FIGS. 2A-2F  include a substrate  102  coupled to one of pucks  220   a - 220   e.  The pucks generally include a dielectric layer  224  and one or more electrodes  222   a - 222   b.  The pucks  220   a - 220   e  serve a similar purpose to the thermally-conducting layer  112 , as discussed above. However, the pucks  220   a - 220   e  can be attached and detached from the substrate, and thus are reusable in subsequent epitaxial growth processes. The pucks  220   a - 220   e  can be temporarily attached to the substrate  102  on the side opposite of which epitaxial growth is to occur. After the epitaxial growth process, the pucks  220   a - 220   e  may be removed and reused on a different substrate in another epitaxial growth process. The pucks  220   a - 220   e  are adapted to be positioned on a substrate support or substrate carrier, such as a quartz support located within a processing chamber. 
     The pucks  220   a - 220   e  are sufficiently thin to enable transfer amongst a plurality of different process chambers or locations during a fabrication process. During the transfer, the pucks  220   a - 220   e  can remain coupled to the substrate  102 , for example, by electrostatic forces, since the pucks  220   a - 220   e  are able to maintain an electrical bias relative to the substrate  102  until the bias is dissipated. Because of the size of the pucks  220   a - 220   e,  the pucks  220   a - 220   e  can be coupled to a substrate  102  outside of an epitaxial growth chamber, and then transferred into the epitaxial growth chamber for processing, thus increasing ease of handling, or replacement when necessary. It is not necessary for the pucks to be fixed or secured to a pedestal within the epitaxial process chamber during an epitaxial growth process. Furthermore, due to the size of the pucks  220   a - 220   e,  a plurality of pucks  220   a - 220   e  can be supported and transferred on a substrate carrier  104  simultaneously. It is desirable that the pucks  220   a - 220   e  are sufficiently thin in order to be supported by the substrate carrier  104 , which is generally formed from silicon carbide, and has a thickness within a range of about 2.0 millimeters to about 2.7 millimeters. 
     The electrodes  222   a - 222   b  of pucks  220   a - 220   e  are formed from a conductive material, such as tungsten. It is contemplated that other conductive materials, such as titanium, molybdenum, tantalum, or cobalt may also be used. It is desirable that the material of the electrodes  222   a - 222   b  has a thermal conductivity of at least about 120 W/m·K and be non-reactive with process gases used to grow an epitaxial layer. Additionally, it is desirable that the electrodes  222   a - 222   b  can withstand the process temperatures reached during an epitaxial growth process; for example, up to about 1200 degrees Celsius. The dielectric coating  224  is formed from a ceramic such as alumina. However, it is contemplated that the dielectric coating  224  may be formed from other materials as well. For example, the dielectric coating may be silicon nitride, aluminum nitride, boron nitride, or pyrolytic boron nitride. Desirably, the dielectric coating has an emissivity greater than about 0.3, such as about 0.8-0.95. Additionally or alternatively, it is contemplated that the surface of the dielectric coating can be altered to increase the emissivity of the dielectric coating. 
       FIG. 2A  illustrates a puck  220   a  coupled to a substrate  102 . The puck  220   a  includes an electrode  222   a  and a dielectric coating  224  disposed over the electrode  222   a.  The electrode  222   a  is partially exposed on the bottom side of the puck  220   a  to allow an electrical bias to be applied to the electrode  222   a.  The thickness of electrode  222   a  is within a range from about 100 micrometers to about 1 millimeter or greater, such as about 500 micrometers to about 1 millimeter. The thickness of the electrode  222   a  accounts for about 5 percent to about 30 percent of the overall thickness of the puck  220   a.  The dielectric coating  224  is a ceramic which is generally less flexible than the electrode  222   a.  Thus, since a greater amount of the puck  220   a  is formed from the dielectric coating  224  as compared the electrode  222   a,  the puck  220   a  will be relatively rigid. The relative rigidity of the puck  220   a  reduces the bowing of the substrate  102  during processing. Since the substrate is chucked to the puck  220   a  during processing, the substrate  102  is forced to remain substantially planar as dictated by the puck  220   a.    
       FIG. 2B  illustrates a puck  220   b  coupled to a substrate  102 . The puck  220   b  has two electrodes  222   a,    222   b  covered with a dielectric coating  224 . The two electrodes are almost completely covered with the dielectric coating  224  except for two exposed electrical contacts  218 . The two electrical contacts allow the electrodes  222   a,    222   b  to be contacted with a power source and biased relative to one another, thereby chucking substrate  102  to the puck  220   b.  By covering substantially all of the electrodes  222   a,    222   b  with the dielectric coating  224 , the potential for the material of the electrodes  222   a,    222   b  to react with a processing gas during an epitaxial growth process is reduced. Thus, a material which would normally be reactive with the processing gas may be used for the electrodes  222   a,    222   b.  Additionally, the dielectric coating  224  is generally less reflective (higher emissivity) than the material from which the electrodes  222   a,    222   b  are formed. Therefore, the puck  220   b  more efficiently absorbs radiant energy compared to a puck having an exposed electrode on the underside. The electrical contacts  218  are formed from the same material as the electrodes  222   a,    222   b;  however, it is contemplated that other conductive materials may be used to form the electrical contacts  218 . 
     The electrodes  222   a,    222   b  are shaped as half-circles and have a thickness of about 1 millimeter; however, other electrode shapes are contemplated. The electrodes  222   a,    222   b  account for about 40 percent to about 60 percent of the thickness of the puck  220   b.  Since the dielectric coating  224  of the puck  220   b  accounts for less of the thickness of the puck  220   b  as compared to puck  220   a,  puck  220   b  is more flexible than puck  220   a.  However, it is contemplated that relative thicknesses of electrodes  222   a,    222   b,  and dielectric coating  224  can be adjusted to obtain the desired flexibility of puck  220   b.  Additionally, the material from which electrodes  222   a,    222   b  are formed, such as a metal, generally has a higher thermal conductivity than the material from which the dielectric coating  224  is formed (e.g., a ceramic). Therefore, pucks which are composed of a greater amount of electrode material generally have a more uniform temperature distribution due to the increased thermal conductivity of the electrode material compared to the dielectric coating material. 
       FIG. 2C  illustrates a puck  220   c  coupled to a substrate  102 . The puck  220   c  includes an electrode  222   a  and a dielectric coating  224 . The dielectric coating  224  completely surrounds the electrode  222   a  except for two electrical contacts  218  which are used to apply an electrical bias to the electrode  222   a.  The thickness of the electrode  222   a  is about 500 micrometers. The dielectric coating  224  is preferably alumina deposited by physical vapor deposition to a thickness within a range from about 10 nanometers to about 1000 nanometers. For example, the dielectric coating  224  may be physical vapor deposited to a thickness within a range from about 300 nanometers to about 500 nanometers. Alternatively, the dielectric coating may be a plasma-sprayed coating deposited to a thickness of about 100 micrometers or greater. 
     The composition of the puck  220   c  includes a greater amount of electrode  222   a  as compared to the puck  220   a.  Thus, puck  220   c  is slightly more flexible than puck  220   a,  since the electrode  222   a  is generally more flexible than the dielectric coating  224 . Additionally, the material from which the electrode  222   a  is formed generally has a higher thermal conductivity than the material from which the dielectric coating  224  is formed. Therefore, pucks which have a relatively larger electrode  222   a,  such as puck  220   c,  will generally have a more uniform temperature distribution during processing. The higher thermal conductivity and uniform temperature of puck  220   c  results in more uniform heating of the substrate  102  coupled thereto, thus resulting in more uniform epitaxial growth thereon. 
       FIG. 2D  illustrates a puck  220   d  coupled to a substrate  102 . The puck  220   d  includes an electrode  222   a  and a dielectric coating  224 . The bottom portion of the electrode  222   a  is exposed through the dielectric coating  224  so that the electrode  222   a  may be contacted with a power source to bias the electrode  222   a  and to chuck the substrate  102  to the puck  220   d.  Similar to puck  220   c,  the electrode  222   a  of puck  220   d  is relatively larger than the dielectric coating  224 . Thus, the puck  220   d  is relatively flexible (allowing substrate  102  to bow slightly during processing) and has increased thermal conductivity. 
       FIG. 2E  illustrates a puck  220   e  coupled to a substrate  102 . The puck  220   e  includes an electrode  222   e  and a dielectric coating  224 . The electrode  222   e  has a comb-like cross section. The electrode  222   e  has a circular-shaped disk  242  having perpendicular extensions  240  extending therefrom. The extensions  240  occupy space which would otherwise be occupied by the less-flexible dielectric coating  224 , thereby increasing flexibility. Additionally, the disk  242 , having a thickness less than the extensions  240 , provide points of increased flexibility between the extensions  240  to allow the puck  220   e  to have a greater range of flexible motion. Although the electrode  222   e  is shown as having a comb-like shape, other shapes which may allow for increased flexibility are contemplated. For example, it is contemplated that the electrode  222   e  may also have a waffle shape, a grid shape, or may be formed from flexible wiring. 
     The dielectric coating  224  surrounds the electrode  222   e  except for exposed portions where electrical contacts  218  may be positioned. The electrical contacts  218  allow a power source to be electrically coupled to the electrode  222   e  to bias the electrode  222   e  and to chuck the substrate  102  to the puck  220   e.  The electrode  222   e  is formed from the same materials as the electrodes  222   a,    222   b;  however, the electrode  222   e  is shaped to allow the puck  220   e  to have a greater range of flexibility. Thus, during processing, as the substrate  102  bows due to epitaxial growth thereon, the puck  220   e  will also bow with the substrate  102 . Therefore, since the puck  220   e  can bow with the substrate  102 , resistive stresses which would otherwise be imparted to the substrate  102  by a non-flexible puck are reduced. The reduction in resistive stress can help to reduce the damage to the substrate  102  during processing. 
       FIG. 2F  illustrates a composite substrate having both a thermally-conducting layer  112  and a puck  220   b  coupled to a substrate  102 .  FIG. 2F  illustrates the puck  220   b  coupled to a substrate  102  and positioned on a substrate carrier  104 . The substrate  102  has a thermally-conducting layer  112  disposed on a lower surface of the substrate  102  and positioned between the substrate  102  and the puck  220   b.  The thermally-conducting layer  112  is titanium; however, other materials are contemplated for the thermally-conducting layer  112 , such as titanium nitride, tungsten, or cobalt. It is desirable that the thermally-conducting layer is at least partially electrically conductive, thereby reducing the voltage required to chuck the puck  220   b  to the substrate  102  and decreasing the potential for unintentional dechucking at elevated processing temperatures. 
     The electrical contacts  218  of the puck  220   b  are covered by the substrate carrier  104 , thus, the potential for the contacts  218  reacting with deposition processes gases is reduced. Alternatively, it is contemplated that the electrical contacts  218  may remain exposed while the puck  220   b  is positioned on the substrate carrier  104 . When the electrical contacts  218  are exposed, the substrate  102  can be chucked and dechucked while the puck  220   b  remains positioned on the substrate carrier  104 . 
       FIGS. 3A and 3B  are schematic illustrations of pucks according to another embodiment of the invention. In the embodiment shown in  FIG. 3A , a puck  320  is formed from multiple concentric rings  326  which are movable relative to one another. The concentric rings  326  may be coupled together by tabs, springs, interlocking parts, or any other satisfactory method. The puck  320  may be glued to the lower surface of the substrate  102 ; however, it is contemplated that the puck  320  may be coupled to the substrate  102  in any suitable manner. For example, any of the concentric rings  326  may include electrodes having a dielectric coating formed thereon. Alternatively, any of the concentric rings  326  may contain a matrix of conductive particles allowing the puck  320  to be electrostatically coupled to a substrate. 
       FIG. 3B  illustrates the concentric rings  326  of the puck  320  formed into a concave shape and coupled to the substrate  102 . The concentric rings  326  include tabs  327  which are bonded together with a flexible adhesive. Since the concentric rings  326  are sufficiently flexible, the concentric rings  326  are free to assume the shape of an object coupled thereto. For example, if the substrate  102  has a tendency to form a curved shape during processing, the puck  320  will also form a curved shape as induced by the substrate  102 . Thus, the shape of the puck  320  is dictated by the shape assumed by the substrate  102  during processing. The flexibility of the puck  320  reduces the amount of resistive stress which would otherwise be applied by a more rigid material or puck attempting to hold substrate  102  in a planar shape. 
       FIGS. 4A-4E  are schematic illustrations of a composite substrate according to another embodiment of the invention.  FIG. 4A  illustrates a substrate  102  that may be used for growing an epitaxial layer thereon and a puck  420 . The puck  420  is similar to puck  220   b;  however, a relatively larger surface of the electrodes  222   a  and  222   b  are exposed through the dielectric coating  224 . Thus, the electrodes  222   a  and  222   b  can be contacted directly by a power source. 
     The electrodes  222   a,    222   b  can be separately biased to electrostatically couple the substrate  102  to a surface of the puck  420 . The one or more electrodes  222   a,    222   b  are covered with a dielectric coating  224 . The dielectric coating  224  allows the puck  420  to be electrostatically chucked to the substrate  102  via the one more electrodes  222   a,    222   b.  The emissivity and thermal conductivity of the dielectric coating  224  are preferably sufficient to absorb a large percentage of the transmitted heat from a radiant heat source and readily transmit the adsorbed heat to the substrate  102  during an epitaxial growth processes. The dielectric coating should also be corrosion-resistant to plasma and plasma processes, and be able to withstand process temperatures of about 1200 degrees Celsius or less. 
       FIG. 4B  illustrates the puck  420  electrostatically coupled to the substrate  102 . The backside of the substrate  102  is placed in contact with the upper surface of the puck  420 . The puck  420  is positioned on substrate carrier  104 , and positioned in a processing chamber  460  on a support  462 . A bias is applied across the electrodes  222   a  and  222   b  by a biasing assembly  430 . During the biasing process, charges migrate to the interface between the substrate  102  and the dielectric coating  224  disposed over the one or more electrodes  222   a,    222   b.  The bias is effected by the biasing assembly  430 , which includes power supply  432  and contact pins  431 . In one configuration, the contact pins  431  are titanium, but it is contemplated that the contact pins  431  may be any conductive material sufficient to reliably electrically couple the one or more electrodes  222   a,    222   b  to the power supply  432 . 
     The power supply  432  is a direct current power supply adapted to provide a bias of about 1000 volts. The charge provided by the power supply  432  is sufficient to chuck the substrate  102  to the puck  420 . The voltage need not be continuously applied, since the charge at the interface will remain until it is dissipated. This allows for the coupled substrate  102  and the puck  420  to be transferred independent of the biasing assembly  430  during processing. Generally, the puck  420  and the substrate  102  are electrostatically coupled together outside of the epitaxial process chamber  466  and then transferred via a robot into the epitaxial process chamber  466 , since the power supply need not remain coupled to the electrodes  222   a,    222   b.  Thus, puck  420  is adapted to be transferred during a fabrication process (e.g., a process for epitaxial growth on substrate  102 ) while remaining chucked to the substrate, due to the separated charge remaining in the substrate  102  and puck  420 . In  FIG. 4B , the puck  420  and the substrate  102  are chucked in the processing chamber  460 ; however, it is contemplated that the puck  420  and the substrate  102  may be chucked in other locations, including a transfer chamber  464  or a loadlock chamber. It is also contemplated that the puck  420  and the substrate  102  may also be coupled together in the same chamber as is used for epitaxial deposition. 
       FIG. 4C  illustrates an epitaxial process chamber  466  that may be used to form an epitaxial layer  414 , such as gallium nitride, on a substrate  102 . The epitaxial process chamber  466  includes a lower dome  480 , a showerhead  472 , and a quartz support shaft  468  disposed therebetween. The support shaft  468  is rotatable about an axis “CA”, and includes support legs  482  extending upwardly therefrom and coupling to an annular support ring  473 . The support shaft  468 , the support legs  482 , and the annular support ring  473  are formed from quartz. The annular support ring  473  has a central opening which allows light radiated from lamps  108  to be absorbed by the pucks  420 . The pucks  420  are disposed on a substrate carrier  404 , which is similar to substrate carrier  104 , except substrate carrier  404  is adapted to carry a plurality of substrates  102 . The substrate carrier  404  is disposed upon the annular support ring  473  during an epitaxial growth process. It should be noted that while  FIG. 4C  illustrates a processing chamber configuration that has a plurality of substrates  102  and pucks  420  disposed on a substrate carrier  404 , this configuration is not intended to be limiting as to the scope of the invention described herein, since other embodiments of the invention described herein could also be used. 
     In one configuration, the showerhead  472  includes multiple gas delivery channels that are each configured to uniformly deliver one or more processing gases to the substrates disposed in the processing volume  448 A. The multiple gas delivery channels are coupled with the chemical delivery module  470  for delivering one or more precursor gases normal, or perpendicular, to a surface of the substrates  102  (e.g., reference label “A”) that is adjacent to the processing volume  448 A. A temperature control channel may be formed in the showerhead  472  and coupled with a heat exchanging system  471  for flowing a heat exchanging fluid to the showerhead  472  to help regulate the temperature of the showerhead  472 . In one example, it is desirable to regulate the temperature of the surface  446  of the showerhead and surfaces exposed to the processing volume to temperatures less than about 200° C. at substrate processing temperatures between about 800° C. and about 1300° C. During processing, a first precursor or a first process gas mixture may be delivered to the processing volume  448 A and substrate surface via the multiple gas delivery channels formed in the showerhead  472  and coupled with the chemical delivery module  470 . A remote plasma source  490  is adapted to deliver gas ions or gas radicals to the processing volume  448 A via a conduit formed in the showerhead  472 . It should be noted that the process gas mixtures or precursors may comprise one or more precursor gases or process gases as well as carrier gases and dopant gases which may be mixed with the precursor gases. Exemplary showerheads that may be adapted to practice embodiments described herein are described in U.S. patent application Ser. No. 12/870,465 [Atty. Dkt. No. APPM 12242.02 US], filed Sep. 29, 2010, which is herein incorporated by reference in its entirety. 
     A catch pan  492  is disposed beneath the substrate carrier  404 . The catch pan  492  is formed from quartz or another optically transparent material to allow light to pass therethrough to permit heating of the substrates  102 , and in some cases the pucks  420  as shown. The catch pan  492  is positioned to catch particulate matter which may fall through openings disposed within the substrate carrier  404 , or particulates which may fall over the edge of the substrate carrier  404 . Thus, the catch pan, which is a circular-shaped piece of quartz or sapphire (which may include slots to accommodate support legs  482 ), has a diameter that is about 5 percent to about 10 percent greater than that of the substrate carrier  404 . Particulate matter (such as material which flakes off of the showerhead  472 , the pucks  420 , or the substrate carrier  404 ), which is generated during deposition processes, would fall onto the lower dome  480  in the absence of the catch pan  492 . Not only is it difficult and time consuming to remove the material from the lower dome  480  (which may require disassembly of the chamber  466 ), but particulate matter present on the lower dome  480  also affects the amount of energy delivered from the lamps  108  to the pucks  420 . The particulate matter which is present on the lower dome  480  may block some of the radiant heat emitted by the lamps  108 , causing non-uniform heating of the pucks  420  and substrates  102 . The non-uniform heating negatively affects the quality of the epitaxially-grown films, as discussed above. 
     The catch pan  492  is coupled to the support legs  482  and is located beneath the substrate carrier  404 . The catch pan  492  is positioned to catch particulate matter or debris which is generated during processing due to undesired deposition and/or flaking caused by rotation of chamber components. Between deposition processes, the catch pan  492  may be removed, for example by a robot, and then cleaned and replaced. Thus, cleaning downtown is greatly reduced through utilization of the catch pan  492 . 
     It is contemplated that the catch pan  492  may be disposed upon and supported by the annular support ring  473 . The substrate carrier  404  may then be disposed upon the upper surface of the catch pan  492 . In such an arrangement, the catch pan  492  may also include at least three protrusions on the upper surface thereof to position the substrate carrier  404  in a spaced apart relation from most of the catch pan  492 . The protrusions generally have a height of about 0.5 millimeters to about 5 millimeters, and function to minimize the contact, and thereby thermal conduction, between the catch pan  492  and the substrate carrier  404 . The reduced thermal conduction from the catch pan  492  to the substrate carrier  404  promotes uniform heating of the substrate  102  during processing. When the substrate carrier  404  is supported by the catch pan  492 , both the catch pan  492  and the substrate carrier supported thereon may be removed from the chamber simultaneously by a robot. Removal of the catch pan  492  and the substrate carrier  404  simultaneously further decreases chamber down time, as well as provides additional support to the substrate carrier  404  during transportation. 
     During an epitaxial growth process within the epitaxial process chamber  466 , a process gas is provided from a chemical delivery module  470  through the showerhead  472  into the epitaxial process chamber  466  to contact the substrates  102 . The process gas may optionally be ionized in the remote plasma source  490  prior to passing through the showerhead  472 . The process gas is removed from the epitaxial process chamber  466  by a vacuum system  484  via an exhaust channel  486  within the chamber wall  488 . As noted above, during processing, the pucks  420  remain electrostatically chucked to the substrates  102 , and need not have a power supply  432  coupled thereto. The pucks are adapted to be transferred through the transfer chamber  464  and into the epitaxial process chamber  466  while remaining electrostatically chucked to the substrates  102 . 
       FIG. 4D  is a close up view of the section of  FIG. 4C  denoted  FIG. 4D . As shown in  FIG. 4D , the puck  420  and the substrate  102  have a substantially planar shape. The planar shape of the puck  420  and the substrate  102  is accomplished by using a rigid material to form the one or more electrodes  222   a,    222   b  and/or the dielectric coating  224 . Alternatively, it is contemplated that rigidity can be maintained by using a sufficient amount of material to form the puck  420 . Due to the planar shape and mechanical properties of the puck  420 , the substrate  102  will maintain a planar shape when the substrate  102  is heated during the epitaxial layer  414  formation process. The rigid nature of the puck  420  will prevent the substrate  102  from bowing, thereby minimizing the allowable bow of the substrate  102 . 
       FIG. 4E  illustrates the substrate  102  subsequent to an epitaxial growth process. After an epitaxial layer  414  is formed on the substrate  102 , the puck  420  is transferred out of the epitaxial process chamber  466  via a robot. The puck  420  is then unchucked from the substrate  102  by dissipating the charge maintained by electrodes  222   a,    222   b.  The puck  420  is generally unchucked from the substrate  102  in the same location as the chucking occurred prior to the epitaxial growth process. The bias maintained by electrodes  222   a,    222   b  is dissipated by electrically coupling the biasing assembly  430  to the electrodes  222   a,    222   b.  The substrate  102  and epitaxial layer  414  can then be further processed, while puck  420  can be coupled to another substrate upon which an epitaxial layer is to be grown. 
     Although  FIGS. 4A-4E  are described with reference to the puck  420 , it is contemplated that any puck, including pucks  220   a - 220   e,  may be coupled to the substrate  102 . For example, the puck  220   a,  which has a single electrode, can be coupled to the substrate  102 . To couple the puck  220   a  to the substrate  102 , a reference electrode is disposed on a side of the substrate  102  opposite to the electrode  222   a  to chuck the substrate  102  to the puck  220   a.  In the single electrode configuration, the reference electrode can remain with the biasing assembly components (e.g., power supply and leads) and need not be transferred with the substrate  102 . Alternatively, a plasma may be used to chuck the substrate  102  to the puck  220   a  inside of the epitaxial deposition process chamber. 
       FIGS. 5A-5D  are schematic illustrations of substrate carriers according to embodiments of the invention.  FIG. 5A  illustrates a substrate carrier  504  having openings  506  therethrough over which a composite substrate is to be positioned during processing. The substrate carrier  504  shown in  FIG. 5A  is similar to the substrate carrier  104 . The substrate carrier  504  has four openings  506  disposed therethrough over which substrates may be positioned. Although the substrate carrier  504  is adapted to support four substrates, it is contemplated that the substrate carrier  504  may be adapted to support more or less substrates, depending on the substrate diameter and the desired throughput. 
     The substrate carriers  104  (as shown in  FIGS. 1) and 504  are formed from silicon carbide, however, it is contemplated that substrate carriers  104  and  504  may be formed from other materials as well. For example, the substrate carriers  104  and  504  may be formed from silicon nitride or boron nitride. Alternatively, the substrate carriers  104  and  504  could be formed from a plurality of materials, including graphite coated with silicon carbide. Furthermore, the substrate carriers  104  and  504  could be formed from a metal coated with a dielectric material. In such an embodiment, the substrate carriers  104  and  504  are generally formed from metal, and all surfaces are coated with the dielectric material. It is also contemplated that only the lower light-receiving surface may be coated with a high emissivity dielectric material, including boron nitride, silicon nitride, silicon carbide, or alumina. When the dielectric material is coated only on the lower surface of the substrate carriers  104  and  504 , the upper metal surface of the substrate carriers  104  and  504  may be polished to reduce heat transmittance from the upper portion of a processing chamber, such as light reflected from a showerhead. Furthermore, it is contemplated that the lower light-receiving surface may not be coated with a high emissivity dielectric material, and rather, the surface may be altered to increase the emissivity of the substrate carrier. 
     Suitable metals for forming the substrate carrier  504  include tungsten, titanium, titanium nitride, and other metals which are stable above epitaxial growth processing temperatures. Suitable dielectric materials include yttrium or alumina. It is desirable that the metal and the dielectric material have similar coefficients of thermal expansion to reduce the potential for delamination caused by repeated heating and cooling during processing. Generally, forming the substrate carrier  504  from a metal having a dielectric coating is cheaper and faster than forming the substrate carrier  504  from silicon carbide. 
       FIG. 5B  illustrates an enlarged view of the openings  506  of the substrate carrier  504  according to one embodiment of the invention. A composite substrate  110  is positioned within the opening  506 . The opening  506  has a vertical edge  546  perpendicular to the upper surface of the substrate carrier  504 . The composite substrate  110  is positioned on a lip  548  which has a smaller diameter than the composite substrate  110 . The upper surface of the lip  548  is parallel to and disposed below the upper surface of the substrate carrier  504 . Desirably, there are substantially no gaps between the lip  548  and the composite substrate  110  when the substrate  110  is positioned on the lip  548  to allow radiant energy to pass therebetween. Thus, when light is irradiated from beneath the substrate carrier  504 , the light is absorbed by the composite substrate  110  or the substrate carrier  504  and does not undesirably heat components within the processing chamber. It is undesirable to heat chamber components during processing because the heated chamber components may radiate heat to the composite substrate  110  thereby inducing thermal non-uniformity during epitaxial growth on the composite substrate  110 . 
       FIG. 5C  illustrates an enlarged view of the opening  506  of the substrate carrier  504  according to another embodiment of the invention. A composite substrate  110  is positioned within the opening  506 . The opening  506  has a vertical edge  546  perpendicular to the upper surface of the substrate carrier  504 . The composite substrate  110  is positioned on three triangular tabs  550  extending towards the center of the opening  506 . It is contemplated that three or more tabs  550  may be used and that the tabs  550  may also have other shapes. The tabs  550  are generally formed form the same material as the substrate carrier  504 . Since there is less physical contact between the composite substrate  110  and the tabs  550  (as compared to the composite substrate  110  and the lip  548  as shown in  FIG. 5B ), less heat is conducted from the substrate carrier  504  to the composite substrate  110 . Therefore, since less heat is conducted form the substrate carrier  504  to the edge of the composite substrate  110 , a more uniform temperature profile across the composite substrate  110  is maintained. 
       FIG. 5D  is a sectional view of the substrate carrier  504  illustrated in  FIG. 5B .  FIG. 5D  illustrates a composite substrate  110  positioned on the lip  548  within the opening  506  of the substrate carrier  504 . The composite substrate  110  is laterally supported by the vertical surfaces of the lip  548 . Sufficient space is provided between the vertical surface of the lip  548  and the composite substrate  110  to allow for thermal expansion of the composite substrate  110  during processing. 
     Although the above embodiments are described with reference to electrostatically chucking a substrate to a puck, the following description is directed to a substrate which is coupled to a puck via a bonding layer.  FIGS. 6A-6C  schematically illustrate a puck  620  having a bonding layer  670  thereon. The puck  620  is formed from silicon carbide; however, the puck  620  may also be formed from graphite coated with silicon carbide or other useful material(s). The puck  620  has a thickness within a range from about 2 millimeters to about 3 millimeters, and a diameter about equal to that of the substrate  102 . For example, the puck  620  may have a diameter of about 200 millimeters to about 300 millimeters, or greater. 
     The bonding layer  670  is a low melting point material such as gallium; however, other materials having low melting points are also contemplated. For example, the bonding layer may be indium, non-stoichiometric combinations of gallium nitride or indium gallium nitride, or low melting point ceramics, dielectrics, or metals which will not introduce contaminants into the subsequently formed epitaxial layer(s). In one example, the bonding layer comprises one or more materials or elements found in the subsequently deposited device layers that are formed on an opposing surface of the substrate  102 , so as not to dope or contaminate these subsequently formed layers during their formation or in later thermal processing steps. In one example, the bonding layer  670  has a melting point less than about 130 degrees Celsius. It is desirable that the bonding layer  670  have a sufficiently high thermal conductivity to transfer radiant energy absorbed by the puck  620  to the substrate  102  when the substrate  102  is in contact with the bonding layer  670  during processing. It is also desirable that the bonding layer  670  have a melting point that is lower than the melting point or decomposition temperature of the device layers (e.g., gallium nitride, indium gallium nitride) deposited on the substrate  102 . A low melting point bonding layer  670  can allow the puck  620  and substrate  102  to be easily separated from each other after processing, thereby minimizing any thermal budget issues that may arise due to the application of the additional amount of heat required to separate these parts. Further, although the bonding layer  670  is shown as having vertical edges near the perimeter of the puck  620 , it is to be understood that the bonding layer  670  will likely not have vertical edges due to the surface tension of the bonding layer  670  when in a liquid state. The edge shape of the bonding layer  670  will depend upon the contact angle of the bonding layer  670  with the substrate  102  and the puck  620 . However, to assist in explanation of the embodiment, the bonding layer  670  is shown as having vertical edges. 
     The bonding layer  670  generally has a thickness within a range from about 2 nanometers to about 10 nanometers. The bonding layer  670  may be deposited on the puck  620  in the same chamber in which epitaxial formation is to occur. This is especially convenient in applications where the bonding layer  670  and the epitaxial layer to be formed on the substrate  102  both include the same material, for example, gallium. In such an application, the same precursor material may be used in the formation of both the epitaxial layer and bonding layer  670 . When the bonding layer  670  contains gallium, relatively pure metallic gallium can be deposited on the surface of the puck  620  via a thermal process in a hydrogen containing atmosphere. Metallic gallium has a melting point of about 30 degrees Celsius. A gallium layer with a higher melting point can be deposited by incorporating small amounts of nitrogen into the bonding layer  670  through the addition of small amounts of ammonia gas in the processing atmosphere. In addition to in situ depositions, it is also contemplated that the bonding layer  670  may be deposited on the puck  620  in a chamber other than the one in which epitaxial formation is to occur. For example, the bonding layer  670  may be formed from a metal having a low melting point which is deposited by a physical vapor deposition process. 
     After formation of the bonding layer  670  on the puck  620 , a substrate  102  is positioned on top of the bonding layer  670  and is coupled to the puck  620  by the surface tension of the bonding layer  670  while the bonding layer  670  is in a liquid state. It is to be noted that the bonding layer  670  is generally in a liquid state during an epitaxial growth process, which may occur at temperatures within a range from about 700 degrees Celsius to about 1200 degrees Celsius. In configurations where the bonding layer is formed in the epitaxial growth chamber (e.g., in situ), the substrate  102  may be transferred into the epitaxial growth chamber and positioned on a surface of a puck  620  after the bonding layer  670  is formed thereon. The substrate  102  may be positioned on the bonding layer  670  while the bonding layer  670  is at a temperature above the melting point of the bonding layer  670 , or while the bonding layer  670  is solid and then subsequently heated. 
       FIG. 6B  illustrates a substrate  102  coupled to a puck  620  via a bonding layer  670  disposed therebetween. The puck  620  is positioned on an annular substrate support  673  located within an epitaxial growth chamber. Thus, the puck  620  performs a similar function as a substrate carrier, since the puck  620  supports the substrate  102  upon the annular substrate support  673  within the epitaxial growth chamber. In the embodiment shown in  FIG. 6B , a substrate carrier is not required in addition to the puck  620 , since the annular substrate support  673  allows light to contact the puck  620  from lamps disposed beneath the puck  620 . The puck  620  is formed from silicon carbide having a high emissivity, and therefore, can absorb radiant energy and conduct the energy to the substrate  102  through the bonding layer  670 . 
     Alternatively, the puck  620  may be used to support a plurality of substrates  102 , similar to a solid substrate carrier. When supporting a plurality of substrates  102  on the puck  620 , the puck  620  may include pockets having bottoms to support each of the substrates  102  therein. Desirably, a bonding layer  670  is positioned within each of the pockets to couple the substrates  102  to the portion of the puck  620  found within the pockets. Even though the substrates  102  may bow during processing, the bonding layer  670  (which will be fluid above the melting point of the material from which it is formed) will still remain in contact with the puck  620  and the substrate  102  due to the surface tension of the bonding layer  670  created between the puck  620  and the substrates  102 . Thus, the thickness of the bonding layer  670  may not be uniform when the substrate bows during processing. Instead, the fluidity and surface tension of the bonding layer  670  will fill the space formed between the puck  620  and the substrates  102 , therefore providing uniform thermal contact and heating of the substrate  102  during processing. 
       FIG. 6C  illustrates a substrate  102  having an epitaxial layer  114  formed thereon being removed from the puck  620  after processing. Due to the adhesive forces created between the puck  620  and the substrate  102  due to the bonding layer  670 , it can be difficult to separate the puck  620  from the substrate  102  by lifting the substrate  102  in a direction normal to the surface of the puck  620 . The substrate  102  can more easily be removed from the puck  620  by sliding the substrate  102  parallel to the surface of the puck  620 . The sliding action may be done manually or by an automated robotic device that is configured to cause the substrate  102  to be moved relative to the surface of the puck  620 . Since the substrate  102  is removed while the bonding layer is in a liquid phase, portions of the bonding layer  670  may adhere to the lower surface of the substrate  102 , and may need to be removed. Undesirably adhered portions of the bonding layer  670  can be removed using a wet etch process or a polishing process. Likewise, it may be necessary to occasionally remove and reapply a bonding layer  670  to the puck  620 . The bonding layer  670  present on the puck  620  may also be removed using a wet etch process. After removal of the substrate  102  and optional cleaning of the puck  620 , another substrate  102  may be processed using the bonding layer  670 . 
     Benefits of the present invention include apparatus for allowing transparent substrates to absorb radiant heat by coupling a transferable puck thereto. The puck allows the substrate to be directly heated instead of indirectly heated via conduction through a substrate carrier. Additionally, the puck allows a substrate to be processed using a substrate carrier having an opening therethrough, which prevents the bottom surface of the substrate from contacting the substrate carrier when the substrate assumes a concave shape. The use the puck also provides for a more uniform temperature distribution during epitaxial growth processes compared to methods employing indirect heating. 
     Additionally, pucks can be reused on multiple substrates thereby reducing the costs which would otherwise be required to coat each substrate individually. Furthermore, the additional rigidity and support provided by the pucks allows a thinner substrate to be used for epitaxial growth process, which reduces production costs. Also, the extra support and rigidity reduces the occurrence of cracking or breaking of substrates, which increases production yield. The pucks also increase deposition uniformity in conventional substrate carriers having pockets or dished-shapes due to the high thermal conductance of the pucks. Even when the substrate bows and places the puck in contact with the substrate carrier pocket, the high thermal conductance of the puck allows the substrate to maintain a uniform temperature profile. 
     While the foregoing is directed to embodiments of the present invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow.