Patent Publication Number: US-2011049779-A1

Title: Substrate carrier design for improved photoluminescence  uniformity

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims benefit of U.S. Provisional Patent Application Ser. No. 61/237,948 (Attorney Docket No. 14197L), filed Aug. 28, 2009, which is incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     Embodiments of the present invention generally relate to methods and apparatus for semiconductor processing. More particularly, embodiments of the present invention relate to methods and apparatus for supporting substrates during processing. 
     2. Description of the Related Art 
     During semiconductor processing, substrate carriers are sometimes used to transfer and support a plurality of substrates, and hold the substrates in place during batch processing. For example, sapphire substrates used in manufacturing of light emitting diodes (LED) are usually processed in a batch with a batch of sapphire substrates disposed and transferred in a substrate carrier during processing. The substrates may deform because of heating, cooling and other factors during processing. Deformation of the substrates can cause the substrates to lose a solid contact with the substrate carrier. The deformed substrates may move relative to the substrate carrier during processing. As a result of non-solid contact and relative motion, thermal conduction between substrates and the substrate carrier becomes non-uniform from area to area within a substrates and from substrate to substrate. Non-uniform thermal conduction between substrates and substrate carrier reduces process uniformity within a substrate and from substrate to substrate. 
       FIG. 1  schematically illustrates a substrate  102  disposed on a substrate carrier  101  having a planar supporting surface  103 . A back side of the substrate  102  is configured to contact the planar supporting surface  103  on the substrate carrier  101 . When the substrate  102  deforms during processing, in this case, the substrate  102  bows up, the planar supporting surface  103  only contacts a portion of a bottom surface  102   a  of the substrate  102 . The substrate  102  may wobble when the substrate carrier  101  moves during processing. When the substrate  102  is heated through the substrate carrier  101 , the substrate  102  cannot be heated uniformly because only a portion of the substrate  102  is in direct contact with the substrate carrier  101 . The wobbling and non-uniform heating usually result in non-uniform processing, such as non-uniform deposition, which may lead to defects in the final products. For example, in fabrication of LEDs, the process non-uniformity may cause the films deposited on the substrates to be non-uniform in thickness and quality within each substrate and among substrates. The thickness and quality of the film in a LED device directly affect the photoluminescence uniformity of the LED device. 
     Embodiments of the present invention provide methods and apparatus for supporting substrates during processing to overcome substrate deformation and improve process uniformity. 
     SUMMARY OF THE INVENTION 
     Embodiments of the present invention generally relate to methods and apparatus for semiconductor processing. More particularly, embodiments of the present invention relate to methods and apparatus for supporting substrates during processing. 
     One embodiment provides a substrate carrier comprising a body configured to provide structure support to one or more substrates. One or more pockets are formed in the body from a top surface. Each pocket is configured to retain one substrate by contacting only a portion of a back side of the substrate. Each pocket has a bottom surface and sidewalls surrounding the bottom surface. The sidewalls define an opening larger than a surface area of the substrate so that at least a majority portion of a bevel edge of the substrate is not in contact with the sidewalls. 
     Another embodiment provides a substrate carrier comprising a substantially disk shaped body configured to support a plurality of substrates thereon, wherein the disk shaped body has a top surface and a plurality of pockets formed from the top surface, wherein each pocket is configured to retain and support one substrate. Each pocket has a bottom surface, sidewalls surrounding the bottom surface, wherein the bottom and sidewalls defining a recess, the recess has an opening larger than a surface area of the substrate so that at least a majority portion of a bevel edge of the substrate is not in contact with the disk shaped body, and a supporting surface extending from the bottom surface and configured to support a portion of a back side of the substrate. 
     Yet another embodiment provides a method comprising disposing a substrate in a pocket formed in a substrate carrier, wherein the substrate carrier is configured to support the substrate on a back side of the substrate, at least a portion of the back side of the substrate is not in contact with the substrate carrier, and the pocket has sidewalls defining an opening larger than a surface area of the substrate so that at least a major portion of an edge of the substrate is not in contact with the substrate carrier. The method further comprises transferring the substrate carrier and the substrate to a processing chamber, and heating the substrate disposed in the substrate carrier to an elevated temperature in the processing chamber. 
    
    
     
       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. 
         FIG. 1  is a sectional view showing a portion of a substrate carrier of prior art. 
         FIG. 2  is a sectional side view of a metal organic chemical vapor deposition (MOCVD) chamber having a substrate carrier according to one embodiment of the present invention. 
         FIG. 3A  is a top view of a substrate carrier according to one embodiment of the present invention. 
         FIG. 3B  is a partial sectional view of the substrate carrier of  FIG. 3A . 
         FIG. 4A  is a partial top view of a substrate carrier according to one embodiment of the present invention. 
         FIG. 4B  is a partial sectional view of the substrate carrier of  FIG. 4A . 
         FIG. 5A  is a partial top view of a substrate carrier according to one embodiment of the present invention. 
         FIG. 5B  is a partial sectional view of the substrate carrier of  FIG. 5A . 
         FIG. 6A  is a partial top view of a substrate carrier according to one embodiment of the present invention. 
         FIG. 6B  is a partial sectional view of the substrate carrier of  FIG. 6A . 
         FIG. 7A  is a partial top view of a substrate carrier according to one embodiment of the present invention. 
         FIG. 7B  is a partial sectional view of the substrate carrier of  FIG. 7A . 
         FIG. 8A  is a partial top view of a substrate carrier according to one embodiment of the present invention. 
         FIG. 8B  is a partial sectional view of the substrate carrier of  FIG. 8A . 
         FIG. 9A  is a partial top view of a substrate carrier according to one embodiment of the present invention. 
         FIG. 9B  is a partial sectional view of the substrate carrier of  FIG. 9A . 
         FIG. 10A  is a partial top view of a substrate carrier according to one embodiment of the present invention. 
         FIG. 10B  is a partial sectional view of the substrate carrier of  FIG. 10A . 
         FIG. 11  is a perspective view of a substrate carrier having various supporting pockets according to one embodiment of the present invention. 
         FIG. 12  is a top view of a substrate carrier for supporting substrates with a flat according to one embodiment of the present invention. 
     
    
    
     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 provide methods and apparatus for supporting and transferring substrates during processing. One embodiment of the present invention provides a substrate carrier that overcome substrate deformation and improves process uniformity. In one embodiment, the substrate carrier has one or more pockets for supporting substrates. Each pocket has a supporting surface for supporting a bottom surface of a substrate. The supporting surface is configured to contact a small portion of the bottom surface of the substrate, therefore, providing steady support in case of deformation of the substrate and avoid non-uniform heat conduction between the substrate and the substrate carrier. In one embodiment, each pocket is shaped to accommodate a substrate with a flat. 
       FIG. 2  is a sectional side view of a metal organic chemical vapor deposition (MOCVD) chamber  200  having a substrate carrier  201  according to one embodiment of the present invention. The MOCVD chamber  200  is configured to perform a thermal based vapor deposition process on a plurality of substrates  202 , which are disposed on the substrate carrier  201  during processing. The substrates  202  may be heated up to about 450° C. to about 1100° C. 
     The MOCVD chamber  200  has a processing volume  214  defined by a showerhead assembly  210 , sidewalls  211 , an exhaust ring assembly  222 , and a lower dome  221 . The showerhead assembly  210  is connected to precursor sources  212 ,  213  and provides passages between the precursor sources  212 ,  213  and the processing volume  214 . The showerhead assembly  210  is also connected to a cooling fluid source  226  configured to provide cooling to the showerhead assembly  210 . The exhaust ring assembly  222  has a circular exhaust volume  223  which is coupled to a vacuum system  216 . The circular exhaust volume  223  is in fluid communication with the processing volume  214  via a plurality of holes  215 . The holes  215  are evenly distributed around the processing volume  214 . During processing, precursors and processing gases flow into the processing volume  214  through the showerhead assembly  210  and exit the processing volume  214  under vacuum force from the vacuum system  216  via the plurality of holes  215  and the circular exhaust volume  223 . 
     The MOCVD chamber  200  further comprises a substrate susceptor  217  configured to receive and support the substrate carrier  201  thereon. The susceptor  217  is disposed on a supporting shaft  218  which is configured to support and rotate the susceptor  217  and the substrate carrier  201  during processing. Three or more lifting pins  219  are movably disposed on the susceptor  217 . A carrier lift shaft  220  is configured to move the lifting pins  219  up and down relative to the susceptor  217 . When lifted, the lifting pins  219  can receive the substrate carrier  201  for a transfer mechanism or lift the substrate carrier  201  from the susceptor  219 . 
     The MOCVD chamber  200  further comprises a heating assembly  224  configured to provide heat energy to the processing volume  214  via the lower dome  221 , which is usually made from infrared transparent material, such as quartz. The substrates  202  are heated by the heating assembly  224  through the susceptor  219  and the substrate carrier  201 . In one embodiment, the susceptor  219  only contacts the substrate carrier  201  near an edge region of the substrate carrier  201 . A uniform spacing  225  may be formed between the substrate carrier  201  and the susceptor  219  to assure uniform heat transferring between the susceptor  219  and the substrate carrier  201 . In one embodiment, the substrate carrier  201  has a surface roughness of about 32 micron. 
     The substrate carrier  201  is designed to provide uniform heat transfer between the substrate carrier  201  and each substrate  202 . The substrate carrier  201  is also designed to provide a steady support to each substrate  202  during processing. 
       FIG. 3A  is a top view of a substrate carrier  300  according to one embodiment of the present invention.  FIG. 3B  is partial side view the substrate carrier  300  of  FIG. 3A . The substrate carrier  300  may be used in the MOCVD chamber  200  of  FIG. 2 . 
     The substrate carrier  300  generally comprises a body  301  configured to provide structural support to one or more substrates  202  thereon. In one embodiment, the body  301  may have a substantially disk shape. The body  301  may comprise a material which has similar thermal properties, such as similar thermal expansion, with as the substrates  202  to avoid unnecessary relative motion between the body  301  and the substrates  202  during heating and/or cooling. The body  301  may comprise silicon carbide. In one embodiment, the body  301  is formed from solid silicon carbide. In another embodiment, the body  301  comprises a core and a coating over the core formed by a chemical vapor deposition process. The body  301  may have a core comprising graphite and a silicon carbide coating formed by CVD. 
     The body  301  may be a circular disk having a planar back surface  308  and a top surface  307  with a plurality of pockets  302  formed thereon. Each pocket  302  is configured to retain one substrate  202  therein. The plurality of pockets  302  may be distributed on the body  301  to effectively use surface areas of the body  301 . In one embodiment, the plurality of pockets  302  are distributed in a circular manner. For example, one of the plurality of pockets  302  is positioned in the centered of the disk shaped body  301 , and seven pockets  302  forms a circle surrounding the pocket  302  in the center as shown in  FIG. 3A . The plurality of pockets  302  may form two or more concentric circles on the disk shaped body  301  depending on sizes of the substrate carrier  300  and the substrate  202 . 
     The pockets  302  are generally recesses formed in the body  301 . Each pocket  302  has sidewalls  304  and a bottom surface  306  defining a recess. The sidewalls  304  define an area slightly larger than the substrate  202  so that an edge  202   a  of the substrate  202  is not in contact with the sidewalls  304 . In one embodiment, the inner diameter of each pocket  302  may be lager than a diameter of the substrate being supported for up to about 0.05 inch (1.27 mm). 
     In one embodiment, a raised ring  303  extending from the bottom surface  306  provides a supporting surface  303   a  for supporting the substrate  202  on a bottom surface  202   b  of the substrate  202 . The supporting surface  303   a  only contacts a small portion of the bottom surface  202   b  and a majority of the bottom surface  202   b  is not in direct contact with the body  301 . By reducing contact areas between the substrate  202  and the substrate carrier  300 , deformation of the substrate  202 , for example bowing, will less likely to cause the substrate  202  to become unstable on the substrate carrier  300 . In one embodiment, the supporting surface  303   a  has a surface roughness of about 0.2 micron to about 1.6 micron. 
     In one embodiment, a plurality of stops  305  extend inward from the sidewalls  304  into the pocket  302 . The stops  305  are configured to constrain the substrate  202  from moving laterally. In one embodiment, the tip of the stops  305  form a circle with a diameter between about 3.94 inch (100.01 mm) to about 3.99 inch (101.35 mm) for supporting substrate with a diameter of about 3.93 inch (100 mm). 
     In one embodiment, an elevation difference  309  between the supporting surface  303   a  and the top surface  307  of the body is substantially similar to the thickness of the substrate  202  held therein. As a result, a top surface  202   c  of the substrate  202  levels with the top surface  307  of the body  301 . Leveling the top surface  202   c  of the substrate  202  and the top surface  307  of the substrate carrier  300  reduces interruptions to fluid flow over the substrate carrier  300  during process. 
     In one embodiment, the body  300  has a thickness about 0.06 inch (1.5 mm) to about 0.12 inch (3.0 mm). In one embodiment, the height difference between the bottom surface  306  and the supporting surface  303   a  is about 0.005 inch (0.13 mm) to about 0.02 inch (0.5 mm). The substrate carrier  300  may be formed by hot press. 
     Substrate carrier of the present invention may have alternative substrate supporting pockets.  FIGS. 4-10  describe substrate carriers with alternative substrate supporting pockets. 
       FIG. 4A  is a partial top view of a substrate carrier  310  in according to one embodiment of the present invention.  FIG. 4B  is a partial sectional view the substrate carrier  310  of  FIG. 4A . The substrate carrier  310  is similar to the substrate carrier  300  of  FIG. 3A  with a plurality of pockets  312  with a different design. Each pocket  312  is configured to retain one substrate  202 . The pocket  312  has a supporting surface  313   a  defined by top surfaces of a plurality of mesas  313  formed on a bottom surface  316  of the pocket  312 . In one embodiment, the plurality of mesas  313  are evenly distributed on the bottom surface  316 . Each mesa  313  may be circular and has a diameter of about 0.02 inch (0.5 mm) to about 0.06 inch (1.5 mm) and a height of about 0.005 inch (0.12 mm) to about 0.015 inch (0.38 mm). The distance  318  between neighboring mesas  313  may be between about 0.25 inch (6.35 mm) to about 0.75 inch (19.0 mm). The top surface of each mesa  313  may have a surface roughness of about 0.2 micron to about 1.6 micron. The plurality of mesas  313  may be formed by bead blasting. 
       FIG. 5A  is a partial top view of a substrate carrier  320  according to one embodiment of the present invention.  FIG. 5B  is a partial sectional view of the substrate carrier  320  of  FIG. 5A . 
     The substrate carrier  320  is similar to the substrate carrier  300  of  FIG. 3A  with a plurality of pockets  322  with a different design. Each pocket  322  is configured to retain one substrate  202 . The pocket  322  has a supporting surface  323   a  defined by a top surface of an island  323  formed on a bottom surface  326  of the pocket  322 . In one embodiment, the raised island  323  is circular. A radius difference  328  between sidewall  324  and the raised island  323  is between about 0.1 inch (2.54 mm) to about 0.25 inch (6.35 mm). In one embodiment, the raised island  323  has a height of about 0.005 inch (0.13 mm) to about 0.015 inch (0.38 mm). The top surface of the raised island  323  may have a surface roughness of about 0.2 micron to about 1.6 micron. 
       FIG. 6A  is a partial top view of a substrate carrier  330  according to one embodiment of the present invention.  FIG. 6B  is a partial sectional view of the substrate carrier  330  of  FIG. 6A . The substrate carrier  330  is similar to the substrate carrier  300  of  FIG. 3A  with a plurality of pockets  332  having a different design. Each pocket  332  is configured to retain one substrate  202 . The pocket  332  has a three or more raised islands  333  extending from a bottom surface  336 . A supporting surface  333   a  is defined by top surfaces of the three or more raised islands  333 . In one embodiment, each pocket  332  has three raised islands  333  located to contact the substrate  202  near the edge of the pocket  332 . The three raised islands  333  may be 120 degrees apart from one another. Each raised island  333  may be circular and have a diameter of about 0.02 inch (0.5 mm) to about 0.06 inch (1.5 mm) and a height of about 0.005 inch (0.12 mm) to about 0.015 inch (0.38 mm). The top surface of each raised island  333  may have a surface roughness of about 0.2 micron to about 1.6 micron. 
       FIG. 7A  is a partial top view of a substrate carrier  340  according to one embodiment of the present invention.  FIG. 7B  is a partial sectional view the substrate carrier  340  of  FIG. 7A . The substrate carrier  340  is similar to the substrate carrier  300  of  FIG. 3A  with a plurality of pockets  342  with a different design. Each pocket  342  is configured to retain one substrate  202 . The pocket  342  is similar to the pocket  302  of the substrate carrier  300  of  FIG. 3A , except that the pocket  342  has a supporting surface  343   a  defined by a step  343  directly extended inwardly from sidewalls  344 . Each pocket  342  has three or more stops  345  inwardly extending from sidewalls  344 . The stops  345  are configured to limit motions of the substrate  202  retained in the pocket  342 . In one embodiment, the step  343  has a width  348  of about 0.5 inch (12.7 mm) to about 1.0 inch (25.4 mm). The height of the step  343  may be between about 0.005 inch (0.12 mm) to about 0.015 inch (0.38 mm). The surface roughness of the step  343  may be about 0.2 micron to about 1.6 micron. 
       FIG. 8A  is a partial top view of a substrate carrier  350  according to one embodiment of the present invention.  FIG. 8B  is a sectional side view the substrate carrier  350  of  FIG. 8A . The substrate carrier  350  is similar to the substrate carrier  300  of  FIG. 3A  with a plurality of pockets  352  with a different design. Each pocket  352  is configured to retain one substrate  202 . Similar to the pocket  302  of  FIG. 3A , the pocket  352  has a raised ring  353  with a supporting surface  353   a  for supporting the substrate  202  on a bottom surface  202   b  of the substrate  202 . Unlike the pocket  302  of the substrate carrier  300  of  FIG. 3A , the pocket  352  does not have stops  305  extending from sidewalls. 
       FIG. 9A  is a partial top view of a substrate carrier  360  according to one embodiment of the present invention.  FIG. 9B  is a sectional view of the substrate carrier  360  of  FIG. 9A . The substrate carrier  360  is similar to the substrate carrier  300  of  FIG. 3A  with a plurality of pockets  362  with a different design. The pocket  362  is defined by a sidewall  364  and a bottom surface  366 . In one embodiment, the bottom surface  366  shapes like a reversed dome and the depth of the pocket  362  increases from the sidewall  364  to the center. The reversed dome bottom surface  366  provides tolerance to substrate bowing and other deformation. Additionally, the reserved dome bottom surface  366  also enables the pocket  362  to support substrates of different sizes. The radius  368  of the reversed dome bottom surface  366  may be between about 195 inch (4,953 mm) to about 985 inch (25,019 mm). The surface roughness of the bottom surface  366  is about 0.2 micron to about 1.6 micron. 
       FIG. 10A  is a partial top view of a substrate carrier  370  according to one embodiment of the present invention.  FIG. 10B  is a sectional view of the substrate carrier  370  of  FIG. 10A . The substrate carrier  370  is similar to the substrate carrier  300  of  FIG. 3A  with a plurality of pockets  372  with a different design. The pocket  372  is similar to the pocket  362  of  FIG. 9A  except that the pocket  372  has a flat supporting ring  373  extending inwardly from sidewalls  374 . A bottom surface  376  extends inwardly from the flat supporting ring  373 . The bottom surface  376  has a shape of reversed dome. The flat supporting ring  373  provides a supporting surface for contacting the substrate  202  during processing and the reversed dome shaped bottom surface  376  provides room to tolerant deformation of the substrate  202 . In one embodiment, the flat supporting ring  373  has a width of about 0.02 inch (0.5 mm) to about 0.08 inch (2 mm). In one embodiment, the radius  378  of the reversed dome bottom surface  376  is about 195 inch (4,953 mm) to about 985 inch (25,019 mm). In one embodiment, the surface roughness of the bottom surface  376  is about 0.2 micron to about 1.6 micron. 
     It should be noted that elements in the pockets  302 ,  312 ,  322 ,  332 ,  342 ,  352 ,  362 ,  372  may be combined or re-grouped to achieve desired effect according to a particular process. 
     Substrate carriers of the present invention may also include plurality of pockets with different designs.  FIG. 11  is a schematic view of a substrate carrier  400  according to one embodiment of the present invention. The substrate carrier  400  has a plurality of pockets  402 . Each pocket  402  is configured to support one substrate therein. Each pocket  402  has a different design. The pockets  402  may be similar to any one of the pockets  302 ,  312 ,  322 ,  332 ,  342 ,  352 ,  362 ,  372 , and any combination of elements in the pockets  302 ,  312 ,  322 ,  332 ,  342 ,  352 ,  362 ,  372 . The substrate carrier  400  may be used as a test substrate carrier used to efficiently determine which pocket design suits a particular process the best. 
       FIG. 12  is a schematic view of a substrate carrier  500  for supporting substrates with flats. The substrate carrier  500  is similar to the substrate carrier  300  or  400  except the substrate carrier  500  has a plurality of pockets  502  shaped with a flat  503 . The flat  503  in each pocket  502  corresponds to the flat in a substrate being processed to prevent the substrate from rotating within the each pocket  502 . In one embodiment, the flats  503  of the plurality of pockets  502  may be located in a symmetrical manner. As shown in  FIG. 12 , each flat  503  faces away from a center of the substrate carrier  500 . It should be noted that a flat can be incorporated in all other embodiments of the present invention, such as substrate carriers  300 ,  310 ,  320 ,  330 ,  340 ,  350 ,  360 ,  370  and  400 . 
     Even though, a MOCVD chamber is described in the description above, the substrate carrier and methods for supporting substrates in accordance with embodiment of the present invention can be used in any suitable processing chambers, or during transferring between processing, or during storage. For example, the substrate carrier in accordance with embodiments of the present invention can be used in hydride vapor phase epitaxy (HVPE) chamber, chemical vapor deposition chamber, and rapid thermal processing chamber. 
     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.