Patent Publication Number: US-2021175115-A1

Title: Thermal processing susceptor

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 16/109,945, filed Aug. 23, 2018, which is a divisional of U.S. patent application Ser. No. 14/698,793, filed Apr. 28, 2015, which claims benefit of U.S. Provisional Patent Application Ser. No. 62/001,562, filed on May 21, 2014, which are each herein incorporated by reference. 
    
    
     FIELD 
     Embodiments of the present disclosure generally relate to a susceptor for thermal processing of semiconductor substrates, and more particularly to a susceptor having features to improve thermal uniformity across a substrate during processing. 
     BACKGROUND 
     Semiconductor substrates are processed for a wide variety of applications, including the fabrication of integrated devices and microdevices. One method of processing substrates includes depositing a material, such as a dielectric material or a conductive metal, on an upper surface of the substrate. Epitaxy is one deposition process that is used to grow a thin, ultra-pure layer, usually of silicon or germanium on a surface of a substrate in a processing chamber. Epitaxy processes are able to produce such quality layers by maintaining highly uniform process conditions, such as temperature, pressures, and flow rates, within the processing chambers. Maintaining highly uniform process condition in areas around the upper surface of the substrate is necessary for producing the high-quality layers. 
     Susceptors are often used in epitaxy processes to support the substrate as well as heat the substrate to a highly uniform temperature. Susceptors often have platter or dish-shaped upper surfaces that are used to support a substrate from below around the edges of the substrate while leaving a small gap between the remaining lower surface of the substrate and the upper surface of the susceptor. Precise control over a heating source, such as a plurality of heating lamps disposed below the susceptor, allows a susceptor to be heated within very strict tolerances. The heated susceptor can then transfer heat to the substrate, primarily by radiation emitted by the susceptor. 
     Despite the precise control of heating the susceptor in epitaxy, temperature non-uniformities persist across the upper surface of the substrate often reducing the quality of the layers deposited on the substrate. Undesirable temperature profiles have been observed near the edges of the substrate as well as over areas closer to the center of the substrate. Therefore, a need exists for an improved susceptor for supporting and heating substrates in semiconductor processing. 
     SUMMARY 
     In one embodiment, a susceptor for thermal processing is provided. The susceptor includes an outer rim surrounding and coupled to an inner dish, the outer rim having an inner edge and an outer edge. The susceptor further includes one or more structures for reducing a contacting surface area between a substrate and the susceptor when the substrate is supported by the susceptor, wherein at least one of the one or more structures is coupled to the inner dish proximate the inner edge of the outer rim. 
     In another embodiment, a susceptor for a thermal processing chamber is provided. The susceptor includes an outer rim surrounding and coupled to an inner dish, the outer rim having an inner edge and an outer edge. The susceptor further includes one or more elevated structures relative to an upper surface of the inner dish, the one or more elevated structures to reduce a contacting surface area between the susceptor and a substrate to be supported by the susceptor, wherein at least one of the elevated structures is coupled to the inner dish at a location proximate the inner edge of the outer rim. 
     In another embodiment, a susceptor for a thermal processing chamber is provided. The susceptor includes an outer rim surrounding and coupled to an inner dish, the outer rim having an inner edge and an outer edge. The susceptor further includes six wedges extending radially inward from the inner edge of the outer rim above the inner dish, wherein each wedge is separated from two other wedges by a gap. The susceptor further includes a quartz insulating separator disposed between each of the wedges. Each quartz insulating separator contacting two wedges and the inner edge of the outer rim. The susceptor further includes three bumps extending from an upper surface of the inner dish. Each bump is located closer than each wedge to a center of the inner dish, wherein no bisection of the inner dish comprises all three bumps. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       So that the manner in which the above recited features of the embodiments disclosed above can be understood in detail, a more particular description, briefly summarized above, may be had by reference to the following embodiments, some of which are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only typical embodiments and are therefore not to be considered limiting of its scope to exclude other equally effective embodiments. 
         FIG. 1A  is a top sectional view of a susceptor, according to one embodiment. 
         FIG. 1B  is a top sectional view of a susceptor, according to another embodiment. 
         FIG. 1C  is a top sectional view of a susceptor, according to another embodiment. 
         FIG. 1D  is a top sectional view of a susceptor, according to another embodiment. 
         FIG. 1E  is a partial cross sectional view of a susceptor, according to the embodiment shown in  FIG. 1D . 
         FIG. 2A  is a top sectional view of a susceptor, according to another embodiment. 
         FIG. 2B  is a partial cross sectional view of a susceptor, according to the embodiment shown in  FIG. 2A . 
         FIG. 2C  is a top sectional view of a susceptor, according to another embodiment. 
         FIG. 3A  is a top sectional view of a susceptor, according to another embodiment. 
         FIG. 3B  is a partial cross sectional view of a susceptor, according to the embodiment shown in  FIG. 3A . 
         FIG. 4  is a partial cross sectional view of a susceptor, according another embodiment. 
         FIG. 5  is a partial cross sectional view of a susceptor, according another embodiment. 
     
    
    
     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 
     The embodiments disclosed generally relate to a susceptor for thermal processing of semiconductor substrates. The embodiments disclosed can improve thermal uniformity across the surface of a substrate during processing by reducing a contacting surface area between the susceptor and the substrate. Reducing the contacting surface area between the susceptor and the substrate reduces the amount of heat that is transferred from the susceptor to the substrate by conduction during processing. Embodiments of some structures that can reduce the contacting surface area between the substrate and the susceptor are described below. 
       FIG. 1A  is a top sectional view of a susceptor  120 , according to one embodiment. The susceptor  120  includes an outer rim  110  surrounding and coupled to an inner dish  102 . The inner dish  102  could be concave with the center of the inner dish being slightly lower than the edges of the inner dish  102 . The outer rim  110  includes an inner edge  112  and an outer edge  114 . Susceptors, such as susceptor  120 , are generally sized so that the substrate to be processed on the susceptor fits just inside the outer rim, such as the outer rim  110 . The susceptor  120  further includes lift pins  104  to aid in transferring substrates into and out of a thermal processing chamber (not shown) housing the susceptor  120 . 
     The susceptor  120  further includes six wedges  122  for reducing a contacting surface area between a substrate (not shown) and the susceptor  120  when the substrate is supported by the susceptor  120 , wherein the wedges  122  contact the inner dish  102  proximate the inner edge  112  of the outer rim  110 . The wedges  122  may be formed as an integral part of the susceptor  120 , or may be attached to the susceptor, for example by welding. Each wedge  122  extends radially inward from the inner edge  112  of the outer rim  110  and each wedge is separated from two other wedges by a gap  124 . The gaps  124  correspond to areas of the underside of the substrate that will not contact the susceptor  120  allowing for more heat to be radiated from the susceptor  120  to the substrate during processing while reducing conductive heating at the substrate edge. Each wedge  122  is an elevated structure relative to an upper surface of the inner dish  102 . The wedges  122  can be symmetrically arranged around the center of the inner dish  102 . Each wedge  122  could contact the inner edge  112  of the outer rim  110  and each wedge  122  could have an upper surface higher than the upper surface of the inner dish  102 . The inner dish, outer rim as well as the wedges could be fabricated from silicon carbide, silicon carbide coated graphite, graphite coated with glassy carbon, or other materials with high thermal conductivity. 
     Although six wedges  122  are shown in  FIG. 1A , two or more wedges can be used in different embodiments.  FIG. 1B  shows a top sectional view of a susceptor  140  with eight wedges  142  separated by gaps  144 .  FIG. 1C  shows a top sectional view of a susceptor  160  with nine wedges  162  separated by gaps  164 . In some embodiments, additional wedges can improve thermal uniformity during processing by reducing the size of the individual surface areas on the susceptor (i.e., the top surface of each wedge) transferring heat to the substrate by conduction. Additional wedges can improve thermal uniformity at the edges of the substrate because there are more gaps where the substrate is not contacting another surface. This improved thermal uniformity helps prevent hotspots from forming along the edges. 
     Susceptors  140  and  160  further include three rounded bumps  118  extending from the upper of the inner dish  102 . Each bump  118  is located closer than each wedge  142 ,  162  to a center of the inner dish  102 . The bumps  118  could be fastened to inner dish  102  through a threaded connection or other common fastening means. The bumps  118  may be made of the same material as the susceptor, or a different material, and may be made from silicon carbide, or graphite coated with silicon carbide or glassy carbon. When substrates are supported around the edges, such as when a susceptor is used during processing, the center of the substrate can sag below the edges of the substrate. Susceptor dishes, such as the inner dish  102 , are often slightly concave to prevent portions of an underside of a sagging substrate from contacting the susceptor dish during processing. On the other hand, to create the highly uniform process conditions in epitaxy, the distance between the upper surface of the inner dish and the lower surface of the substrate is kept quite low, for example less than 0.25 mm. If the substrate contacts the dish, heat is transferred from the inner dish to the substrate by conduction and thermal uniformity may be reduced. 
     The bumps  118  can be used to support a sagging substrate preventing contact between the inner dish  102  and the substrate. The bumps  118  provide a contact surface area between the sagging substrate and the susceptor that is smaller than the surface area of the substrate that would contact the inner dish  102  absent the bumps  118 . The bumps  118  can be evenly distributed around the center of the inner dish  102  as shown in  FIGS. 1B and 1C . In some embodiments, to ensure adequate support of a sagging substrate there could always be at least one bump  118  on a side of the inner dish  102 . 
       FIG. 1D  is a top sectional view of a susceptor  180 , according to another embodiment. The susceptor  180  further includes six wedges  182  for reducing a contacting surface area between a substrate (not shown) and the susceptor  180  when the substrate is supported by the susceptor  180 , wherein the wedges  182  contact the inner dish  102  proximate the inner edge  112  of the outer rim  110 . Each wedge  182  extends radially inward from the inner edge  112  of the outer rim  110  and each wedge is separated from two other wedges by a gap  184 . The gap  184  is larger than the gap  124  shown in  FIG. 1A  to further reduce the contacting surface area between the substrate and the susceptor. Susceptor  180  further includes an insulating separator  188  disposed between each of the wedges  182 . 
       FIG. 1E  is a partial cross sectional view of the susceptor  180 , according to the embodiment shown in  FIG. 1D . The cross sectional view shows the top of the wedge  182  at the same height as the top of the insulating separator  188 . A substrate  50  is shown resting on the top of the wedge  182  and the insulating separator  188 . The insulating separator  188  may be disposed in a groove  189  formed around the susceptor surface near the inner edge  112  of the outer rim  110 , or at the specified radial location of the insulating separator  188 . The groove  189  maintains the insulating separator  188  in a specified location. The insulating separator  188  typically has a thickness that is greater than a depth of the groove  189  so an upper surface of the insulating separator  188  rises above the surrounding surface of the susceptor  220 , thus reducing contact between a substrate edge and the susceptor surface. 
     The insulating separators  188  are typically made from a thermally insulating material, such as silicon oxide, quartz of any type (i.e. amorphous, crystalline, optical, bubble, etc.), glass, or the like. The insulating separators  188  provide thermal breaks, or areas of reduced thermal conductivity, around the inner dish during processing. This thermal break reduces thermal conduction into the edge of the substrate from the susceptor, which is typically made from a high thermal conductivity material. Reduced contact between the substrate edge and the highly conductive susceptor material reduces conductive heating of the substrate edge during processing. The insulating separators  188  may contact the inner edge  112  of the outer rim  110 , but could also be disposed at other locations on a susceptor. For example the insulating separators  188  may be spaced apart from the inner edge  112  of the outer rim  110 . 
       FIG. 2A  is a top sectional view of a susceptor  220 , according to another embodiment.  FIG. 2B  is a partial cross sectional view of the susceptor  220 . Referring to  FIGS. 2A and 2B , the susceptor  220  is similar to the susceptor  120  including an outer rim  210  surrounding an inner dish  202 , the outer rim  210  having an inner edge  212  and an outer edge  214 . Three lift pins  204  can extend above the inner dish  202 . 
     The susceptor  220  includes concentric annular ridges  222  surrounding the center of the inner dish  202 . Each annular ridge  222  has a different diameter. At least some of the annular ridges  222  can be located proximate the inner edge  212  of the outer rim  210 . In some embodiments, some of the annular ridges  222  may be located within about 1 mm of the inner edge  212 , for example within about 0.5 mm of the inner edge  212 . The susceptor  220  may further include six spokes  228  extending from the center of the inner dish  202  to the inner edge  212  of the outer rim  210 . More or fewer spokes  228  may be included in different embodiments. Each spoke  228  extends to a different angular location around the inner edge  212  of the outer rim  210 . In some embodiments, the upper surface of each spoke  228  is above the tops of the annular ridges  222 . In other embodiments, the upper surface of each spoke could be at substantially the same height as the tops of the annular ridges  222 . In some embodiments, the annular ridges  222  continue under or through the spokes  228  making a complete ring around the center of the inner dish  202 . In other embodiments, the spokes  228  separate portions of the annular ridges  222 . 
     The spokes  228  and annular ridges  222  can reduce a contacting surface area between a substrate  50  and the susceptor  220  when the substrate  50  is supported by the susceptor  220 . In some embodiments, the substrate  50  may only contact the spokes  228  during processing without contacting the annular ridges  222 . In other embodiments, the substrate  50  may contact both the spokes  228  and at least some of the annular ridges  222  during processing. In some embodiments, the one or both of the annular ridges  222  and the spokes  228  or their respective upper surfaces are elevated structures relative to the upper surface of the inner dish  202 . The ridges  222  may also improve thermal uniformity when processing a substrate by increasing radiative surface area of the upper surface of the susceptor  220 . 
     The spokes  228  and annular ridges  222  may be made of the same material or a different material, which may be any of the same materials from which the susceptor  220  is made. The spokes  228  and annular ridges  222  may be made, in one embodiment, by sculpting the annular ridges  222  from an unpatterned susceptor dish surface. In another embodiment, recesses may be formed in an unpatterned susceptor dish surface to define the spokes, and then a pattern of ridged pieces attached to the susceptor surface within the recesses to form the annular ridges  222 , for example by welding. 
     In some embodiments, the susceptor  220  can include an angled surface  216  connecting the inner dish  202  as well as the spokes  228  and annular ridges  222  to the inner edge  212  of the outer rim  210 . The angled surface  216  can be used as part of a supporting surface for the substrate  50 . Varying the slope or dimensions of the angled surface  216  can control the height of the substrate  50  relative to the spokes  228  and the annular ridges  222 . 
       FIG. 2C  is a top sectional view of a susceptor  240 , according to another embodiment. Susceptor  220  is similar to susceptor  240  except that susceptor  240  does not include any spokes  228 . Susceptor  240  includes annular ridges  242  that are similar to annular ridges  222 . When a substrate is placed on susceptor  240 , the underside of the substrate could contact at least some of the annular ridges  242  in some embodiments. In other embodiments, there could be a small gap between the underside of the substrate and the tops of the annular ridges  242  as the substrate is supported by a separate surface, such as angled surface  216  of  FIG. 2B . 
       FIG. 3A  is a top sectional view of a susceptor  320 , according to another embodiment.  FIG. 3B  is a partial cross sectional view of the susceptor  320 . Referring to  FIGS. 3A and 3B , the susceptor  320  is similar to the susceptor  120  including an outer rim  310  surrounding an inner dish  302 , the outer rim  310  having an inner edge  312  and an outer edge  314 . Three lift pins  304  can extend above the inner dish  302 . 
     The susceptor  320  includes a series of bumps  322  extending from an upper surface of the inner dish  302 , so at least part of each bump is elevated above the inner dish  302 . At least some of the bumps  322  can be located proximate the inner edge  312  of the outer rim  310 . In some embodiments, some of the bumps  322  may be located within about 1 mm of the inner edge  312 , for example within about 0.5 mm of the inner edge  312 . Bumps  322  are arranged in a ringed pattern on the inner dish  302 , but other arrangements could be used, such as multiple rings, a triangular, square, or rectangular pattern, or a gridded pattern. In some embodiments, each quadrant of the inner dish  302  could include at least one bump  322 . The bumps  322  could be fastened to inner dish  302  through a threaded connection or other common fastening means. 
     The bumps  322  can reduce a contacting surface area between a substrate  50  and the susceptor  320  when the substrate  50  is supported by the susceptor  320 . In some embodiments, the substrate  50  may only contact the bumps  322  during processing without contacting the inner dish  302  or any other surface. When the substrate  50  is supported using bumps  322 , hot spots around the edges of the substrates are greatly reduced. In other embodiments, additional bumps, such as bumps  118  shown in  FIGS. 1B and 1C  could extend up from inner dish  302  at locations closer to the center of the inner dish  302  to prevent a sagging substrate from contacting the inner dish  302 . 
     The bumps  322  are typically made from a low thermal conductivity material, such as silicon oxide, quartz of any type, glass, etc. The bumps provide a raised contact for the edge of a substrate disposed on the susceptor  320  to reduce conductive heating of the substrate edge. The bumps  322  may be inserted into recesses formed in the surface of the susceptor  320 . Features may be added to the bumps  322  and the recesses to allow the bumps  322  to be secured in the susceptor surface. Such features may include threads or other rotational engagement structures. 
       FIG. 4  is a partial cross sectional view of a susceptor  420 , according another embodiment. The susceptor  420  is similar to the susceptor  120  including an outer rim  410  surrounding an inner dish  402 , the outer rim  410  having an inner edge  412  and an outer edge  414 . Three lift pins (not shown) could extend above the inner dish  402 . 
     The susceptor  420  includes an annular ridge  422  extending from an upper surface of the inner dish  402 , so at least part of the annular ridge is elevated above the inner dish  402 . The annular ridge can surround the center of the inner dish  402  at a a radial distance  424  from the center of the inner dish  402  that is less than the radius of a substrate  50  to be supported by the susceptor  420 . The annular ridge  422  may be made of a high thermal conductivity material, such as silicon carbide or graphite coated with silicon carbide or glassy carbon. A height  426  of the annular ridge  422  can be designed to control the gap between the substrate  50  and the inner dish  402 . In some embodiments, two or more annular ridges  422  could extend from the upper surface of the inner dish  402 . The additional annular ridges (not shown) could have different diameters as well as different heights from the other annular ridges. Annular ridge  422  is arranged in a ringed pattern on the inner dish  402 , but other arrangements could be used, such as multiple rings, a triangular, square, or rectangular pattern, or a gridded pattern. The annular ridge  422  can be located proximate the inner edge  412  of the outer rim  410 . In some embodiments, some of the annular ridges  422  may be located within about 1 mm of the inner edge  412 , for example within about 0.5 mm of the inner edge  412 . 
     The annular ridge  422  can reduce a contacting surface area between a substrate  50  and the susceptor  420  when the substrate  50  is supported by the susceptor  420 . In some embodiments, the substrate  50  may only contact the annular ridge  422  during processing without contacting the inner dish  402  or any other surface. The radial location  424  as well as the height  426  of the annular ridge  422  could be modified to achieve different thermal profiles during processing. In other embodiments, bumps, such as bumps  118  shown in  FIGS. 1B and 1C  could extend from inner dish  402  at locations closer to the center of the inner dish  402  to prevent a sagging substrate from contacting the inner dish  402 . 
       FIG. 5  is a partial cross sectional view of a susceptor  520 , according another embodiment. The susceptor  520  is similar to the susceptor  120  including an outer rim  510  surrounding an inner dish  502 , the outer rim  510  having an inner edge  512  and an outer edge  514 . Three lift pins (not shown) could extend above the inner dish  502 . 
     The susceptor  520  includes an angled surface  522  extending radially inward from the inner edge  512  of the outer rim  510  to a depression  526 . At least part of angled surface  522  is an elevated structure relative to the upper surface of the inner dish  502 . The upper surface of the depression  526  is located below the upper surface of the inner dish  502 . The upper surface of the depression  526  couples the angled surface  522  to the upper surface of the inner dish  502 . The angled surface  522  could be angled between about three degrees and about twenty degrees from the upper surface of the inner dish  502 , such as between about four degrees and about twelve degrees, for example about seven degrees. The angle and location of the angled surface  522  can be used to control a radial location  524  corresponding to where the substrate  50  can contact the angled surface  522  during processing. The angle and location of the angled surface  522  can also be used to control the size of a gap  528  between the bottom of the substrate  50  and the upper surface of the depression  526 . The size of the gap  528  could be between 0.1 mm and 1 mm, for example about 0.3 mm. 
     The angled surface  522  can reduce a contacting surface area between a substrate  50  and the susceptor  520  when the substrate  50  is supported by the susceptor  520 . In some embodiments, the substrate  50  may only contact the angled surface  522  during processing without contacting the inner dish  502  or any other surface. By using a relatively steep angle, such as between about three degrees and about twenty degrees from the upper surface of the inner dish  502 , such as between about four degrees and about twelve degrees, for example about seven degrees, a smaller surface area of the substrate edge contacts the susceptor during processing, which reduces the amount of conductive heat that can be transferred from the susceptor  520  to the substrate  50 . The angle and location of the angled surface  522  could be modified to achieve different thermal profiles during processing. In some embodiments, bumps, such as bumps  118 , shown in  FIGS. 1B and 1C  could extend from inner dish  502  at locations closer to the center of the inner dish  502  to prevent a sagging substrate from contacting the inner dish  502 . 
     The susceptor embodiments described herein allow for more uniform temperature control of substrates during thermal processes, such as epitaxy. The temperature control is improved by reducing the surface area of the substrate contacting the susceptor, which reduces the amount of conductive heat transferred from the susceptor and the substrate. Conductive heat transfer between the susceptor and the substrate is more difficult to control than radiant heat transfer, the primary source of heat transfer between the susceptor and the substrate. Reducing the surface area of the substrate contacting the susceptor allows for a higher percentage of the heat transfer to be radiant heat resulting in improved temperature control and improved depositions on the substrate. The embodiments disclosed reduce the conductive heat transfer near the edge of the substrate by adding a structure, such as a annular ridge around the center of the inner dish proximate the outer rim, to reduce the contacting surface area between the susceptor and the substrate. The embodiments disclosed also prevent the possibility of substantial amounts of conductive heat transfer near the center of the substrate by including three bumps to support a substrate above the inner dish if the substrate sags. 
     Although the foregoing embodiments have been described using circular geometries (e.g., inner dish, outer rim, annular ridge, etc.) to be used on semiconductor “wafers,” the embodiments disclosed can be adapted to conform to different geometries. 
     While the foregoing is directed to typical embodiments, other and further embodiments may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow.