Abstract:
Substrate support assemblies and deposition chambers employing such support assemblies to improve temperature uniformity during film depositions, such as epitaxial growths of group-V material stacks for LEDs. In one embodiment, the support assembly includes a first component having a first thermal resistance and a top surface upon which the substrate is to be disposed at a first location. The support assembly further includes a second component to be disposed over the first component and cover a second location of the susceptor while the substrate is disposed over the first location and having a second thermal resistance to insulate regions of the susceptor adjacent to the substrate by an amount approximating that of the substrate during a deposition process. In embodiments, the second component is removable from the first component and supports the substrate in absence of the first component during transfer of the substrate between multiple deposition systems.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of U.S. Provisional Application No. 61/453,392 (Attorney Docket No. 015724LAEPNEONESONG) filed on Mar. 16, 2011, entitled SUBSTRATE SUPPORT ASSEMBLY FOR THIN FILM DEPOSITION SYSTEMS, the entire contents of which are hereby incorporated by reference in its entirety for all purposes. 
     
    
     TECHNICAL FIELD 
       [0002]    Embodiments of the invention are in the field of thin film deposition and more particularly relate to a substrate support assembly for thin film deposition systems. 
       BACKGROUND 
       [0003]    Substrate heating during thin film deposition processes, particularly epitaxial growth processes which are performed at high temperatures ranging from 700° C. to 1300° C., can suffer temperature induced substrate deformation. Depending on mismatch of thermal expansion coefficients between a substrate and various materials disposed on the substrate, a substrate may bow in a convex manner (i.e., substrate center disposed a greater distance from an underlying flat support than substrate edges to have a positive radius of curvature) or concave manner (i.e., substrate edges disposed a greater distance from an underlying flat support than substrate center to have a negative radius of curvature) during film deposition. Such bowing can lead to uneven heating of the substrate as thermal coupling between the substrate backside and underlying support varies with substrate bow. Uneven heating may, in turn, induce nonuniformity in film material properties across the substrate. For certain applications (e.g., light-emitting diodes (LED), power transistors, etc.) in which a plurality of group III-V films are grown on a substrate to form a stack, substrate bow may vary by degree or even alternate between concave and convex as different films of the film stack are grown at different process temperatures. 
         [0004]    Many deposition systems employed to perform epitaxial thin film growths utilize a carrier to support one or more substrates during transfer to a deposition chamber as well as during the film growth. It is therefore difficult to compensate for a substrate bow which varies in degree or varies in sign (concave vs. convex) during successive processing operations which are conducted at different process temperatures. 
         [0005]    Additionally, as the carrier dimensions can be quite large (e.g., 300 mm or more), depending on the diameter of the substrate and number of substrates supported at any given time, a heated carrier may further radiate heat to other portions of a deposition chamber, for example a gas showerhead, which is often maintained at a temperature below that of the substrate and/or carrier. Such radiation can induce cool spots across the carrier and also cause the carrier to reach different average temperatures as different films of a stack are grown a particular substrate or set of substrates. Carrier cool spots and variation in the average carrier temperature also effect substrate temperature during film growth and are additional sources of variation in grown film properties. 
         [0006]    As such, depending on the substrates and processes performed by a deposition chamber, a significant variation in properties of the films formed on each substrate, between multiple substrates, within a process run (i.e., single growth), and/or across multiple growths (i.e., run-to-run) may adversely affect device yield. A carrier assembly, as well as a deposition system and growth method employing such a carrier assembly, which can reduce these growth temperature non-uniformities is advantageous. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0007]    Embodiments of the present invention are illustrated by way of example, and not limitation, in the figures of the accompanying drawings in which: 
           [0008]      FIG. 1A  illustrates an isometric view of a substrate support assembly for supporting a substrate during a deposition process, in accordance with an embodiment; 
           [0009]      FIG. 1B  illustrates isometric views of a first and second component of the substrate assembly depicted in  FIG. 1A ; 
           [0010]      FIGS. 2A ,  2 B, and  2 C illustrate cross-sectional views of a first component of the substrate support assembly, the first component assembled with the second component, and a substrate disposed on the substrate support assembly, in accordance with embodiments; 
           [0011]      FIG. 3A  illustrates an expanded view of a carrier component of a substrate support assembly, in accordance with and embodiment; 
           [0012]      FIG. 3B  illustrates an expanded view of a carrier component depicted in  FIG. 3A  when supporting a substrate, in accordance with an embodiment; 
           [0013]      FIG. 3C  illustrates an isometric view of a robotic handler positioning the carrier component illustrated in  FIG. 3B  on a susceptor component, in accordance with an embodiment; 
           [0014]      FIG. 3D  illustrates a plan view of a substrate disposed on a pedestal surface with a carrier component surrounding the pedestal, in accordance with an embodiment; 
           [0015]      FIG. 4  illustrates a multi-chambered deposition system, in accordance with an embodiment; and 
           [0016]      FIG. 5  illustrates a method of epitaxially growing a stack of films, in accordance with an embodiment. 
       
    
    
     DETAILED DESCRIPTION 
       [0017]    In the following description, numerous details are set forth. It will be apparent, however, to one skilled in the art, that the present invention may be practiced without these specific details. In some instances, well-known methods and devices are shown in block diagram form, rather than in detail, to avoid obscuring the present invention. Reference throughout this specification to “an embodiment” means that a particular feature, structure, function, or characteristic described in connection with the embodiment is included in at least one embodiment of the invention. Thus, the appearances of the phrase “in an embodiment” in various places throughout this specification are not necessarily referring to the same embodiment of the invention. Furthermore, the particular features, structures, functions, or characteristics may be combined in any suitable manner in one or more embodiments. For example, a first embodiment may be combined with a second embodiment anywhere the two embodiments are not mutually exclusive. 
         [0018]    Substrate carriers made of silicon carbide (SiC) have high emissivity coefficient c and high thermal conductivity k (i.e., low thermal resistivity, Km/W). In comparison with SiC, a substrate, often sapphire, typically has low emissivity coefficient and low thermal conductivity. For such a carrier/substrate material combination, most of the heat and radiant energy from the carrier will transfer to nearby chamber components, such as a gas showerhead disposed above the carrier, via the regions of a carrier not covered by a substrate. While high carrier emissivity and thermal conductivity is beneficial in regions disposed below a substrate for heating of the substrate  103  by the carrier, in certain circumstances it is advantageous to reduce energy transferred from the carrier to the chamber. For example, where a gas showerhead is cooled to a temperature of about 30° C.-300° C., well below that of the substrate (heated to 700° C.-1300° C., or more, by the carrier which is heated, for example via lamps, resistive elements, or induction coils disposed below the carrier,), carrier temperature uniformity and showerhead performance may be improved by reducing heat loss from the carrier to the showerhead. 
         [0019]      FIG. 1A  illustrates an isometric view of a substrate support assembly  100  for supporting a substrate during a deposition process, in accordance with an embodiment. The support assembly  100  includes at least two components,  105  and  110 . Component  105  has low thermal resistance and may further have a high emissivity to transfer heat to a substrate which is to be disposed on a support  114  of the component  105  during a deposition process. Second, component  110  having a higher thermal resistance is disposed over, and may further be disposed directly on, the component  105  to surround the support  114 . 
         [0020]    Generally, the thermal resistance provided by component  110  is to better approximate the thermal resistance of the substrate than does the component  105  to thermally insulate peripheral regions of the component  105  by an amount approximately equal to the amount by which a substrate disposed on the support  114  thermally insulates the component  105 . In the exemplary embodiment, the thermal resistance of component  110  is approximately equal to the thermal resistance of the substrate. The thermal resistance may be matched to that of a particular substrate, be it sapphire, silicon or otherwise, by forming the component  110  of a material having a particular thermal conductivity and particular thickness. In further embodiments, component  110  has a lower emissivity than component  105 . In certain such embodiments, component  110  has an emissivity approximately equal to that of the substrate to match the thermal transmission through the support  114  with that occurring through peripheral regions of the substrate support assembly  100 . As such, material composition of the components  105  and  110  is a matter of design choice with only a few exemplary materials and thicknesses describe for the sake of illustration herein. 
         [0021]      FIG. 1B  illustrates exploded isometric views of the separate components  105  and  110  of the substrate assembly  100  depicted in  FIG. 1A . As shown, the component  105  has a top side  109  and a bottom side  104 . In an embodiment, the bottom side  104  is to be disposed over a heat source, such as one or more lamps. Depending on the size of the substrates, one or more of the supports  114  are present on the top side  109  (e.g., seven substrate locations are depicted in  FIG. 1 ). In the exemplary embodiment, the first component  105  further comprises a pedestal  106  raised a distance above the surrounding surface of top side  109 . The pedestal  106  has a diameter D 1  which is sized depending on the embodiment to be approximately equal to, slightly smaller than, or slightly larger than the substrate. In exemplary embodiments, component  105  is of silicon carbide or aluminum, with other embodiments employing materials known in art to be suitable for a susceptor in thin film deposition chambers. 
         [0022]    The component  110  includes a top side  112  and a bottom side  113  with the component  110  configured to mate to the component  105  so that the bottom side  113  is facing the top side  109 . The component  110  is generally a disk having one or more through openings  111  of a diameter D 2  sized to clear the support(s)  114  (i.e., D 2  is at least equal to D 1 ). The component  110  is to be disposed over the component  105 , as shown in  FIG. 1A , during a deposition process. The top side  112  is to remain uncovered by any substrate during processing. In exemplary embodiments, the component  110  is of quartz or sapphire, with other embodiments employing materials known in art to have similarly high temperature stability, high thermal resistance (e.g., low thermal conductivity) and low particulates. 
         [0023]      FIGS. 2A ,  2 B, and  2 C illustrate cross-sectional views of the component  105 , the component  105  assembled with the component  110 , and a substrate  103  disposed on the substrate support assembly  100 , in accordance with embodiments. As shown in  FIG. 2A , in various embodiments, the pedestal  106  has a planar or flat top surface  108 A, a concave top surface  108 B, or convex top surface  108 C to accommodate a predetermined bow that will occur in the substrate to be disposed on the pedestal  106  (e.g., at deposition process temperature). The vertical displacement, B, of a concave top surface may be 200 μm or more, depending on the deposition process performed, substrate properties, and various film stack stresses. 
         [0024]    As shown in  FIG. 2B , with the component  110  disposed over the component  105  the pedestal  106  has a thermal resistance, TR 1 , while at an adjacent region the component  105  has a thermal resistance, TR 2  which is supplemented by the component  110  having a thermal resistance, TR 3 . In an embodiment, the serial sum of TR 3  and TR 2  is greater than TR 1  by approximately the thermal resistance of the substrate. For example, as further shown in  FIG. 2C , with a substrate  103  disposed on the pedestal the thermal resistance of the substrate, TR 2  adds to TR 1  for a total thermal resistance at a substrate center of TR C . In the periphery, TR 1  adds to TR 3  (along with any interface and gap resistance components) for a resistance at the periphery of TR P . In the exemplary embodiment TR P  is approximately equal to TR C  (i.e., within 10%) to reduce any center to edge thermal gradient. As such, when heat is applied to a subsurface (e.g., bottom side  104 ) during a bottom-up heating process, a substrate topside surface temperature T S  is approximately equal to a peripheral support assembly top surface temperature T P  (i.e., within 10%). 
         [0025]    Heights of the pedestal  106 , and thickness of the second component  110  may be predetermined based on the thermal conductivity of the component  110  to have the top side  112  disposed at predetermined height relative to the substrate, for example to contain/position the substrate  103  during process and/or to reduce particulates resulting from sidewall deposition mechanisms). In an embodiment, the component  110  has a thermal conductivity which is lower than the thermal conductivity of the component  105 . The component  110  may be selected to have a thermal conductivity which is sufficiently low that TR P  is approximately equal to TR C  while the top side  112  is substantially flush, slightly below, or slightly above the top surface the substrate  103  when seated upon the pedestal  106  with the exemplary embodiments having the pedestal height at least equal to the thickness of the component  110 . 
         [0026]    In an embodiment, the component  110  is removably disposable upon the component  105  and the component  110  is configured to support a substrate in absence of the first component. As such, the component  110  may serve as a substrate carrier  310  (illustrated in  FIG. 3A ) and the component  105  may serve as a susceptor  305  (illustrated in  FIG. 3D ) which interlocks with the carrier  310  while maintaining all the thermo-mechanical properties described elsewhere herein for benefit of thermal uniformity during film deposition. In one such embodiment, the susceptor  305  is to remain in a particular deposition chamber while the carrier  310  is to transfer to and from one or more deposition chambers along with substrates being processed. The susceptor  305  is to be rigidly affixed to the deposition chamber using any mechanical means while the carrier  310  is removably disposed on the susceptor  305  to remain in chamber during a deposition process. For such embodiments, in addition to the physical properties previously described for the component  110 , the carrier  310  is to be of a material, and with sufficient thickness, to provide support and toughness suitable for substrate transfer. Exemplary carrier materials include any previously described for component  110 , such as quartz or sapphire. 
         [0027]      FIG. 3A  illustrates an expanded view of a carrier  310  in a substrate support assembly  300 , in accordance with and embodiment. As shown within the opening  311  are a plurality of tabs  320 A,  320 B, and  320 C projecting radially toward the center of the opening  311 . The plurality of tabs is to provide a means of interference to support a substrate within the opening  311 . As illustrated in  FIG. 3B , a substrate  303  is disposed on the plurality of tabs to span the opening  311 . 
         [0028]      FIG. 3C  illustrates an isometric view of a robotic handler  330  positioning the carrier  310  on a susceptor  305 , in accordance with an embodiment. As shown, the carrier  310  includes the substrate  303  in one opening  311  while a second opening  311  is vacant for illustrating the tabs  320 A,  320 B, and  320 C. The handler  330  is to align the carrier  310  relative to the susceptor  305  with the openings  311  disposed over the pedestals  306 . During a chamber load sequence, the carrier  310  is lowered onto pins  309  and the handler  330  removed from the chamber. Pins  309  then lower the carrier  310  onto the susceptor  305  to contact the substrate  103  with a top surface of the pedestal  306 . Depending on the embodiment, the pedestal  306  has a diameter dimensioned to allow the carrier surfaces supporting the substrate  303  to be recessed below the top surface of the pedestal  306  such that support of the substrate  303  is alternated from the carrier  310  to the pedestal  306 . 
         [0029]    With the carrier  310  separable from the susceptor  305 , the pedestal  306  to specific for a particular process and/or deposition chamber. For example, as described further elsewhere herein, a first deposition chamber may include a first susceptor  305  having a pedestal  306  with a concave top surface to accommodate a first substrate bow while a second deposition chamber may include a second susceptor  305  having a pedestal  306  with a flat or even convex top surface to accommodate a second degree, or direction, of substrate bow. Furthermore, because the susceptor  305  remains disposed in the chamber, the thermal mass of susceptor  305  is unconstrained and may be increased as there is no weight constraint imposed by the robotic handler  450 . Greater thermal mass improves temperature uniformity and may also reduce warping of the support surface relative to a single-component carrier. These benefits are achieved while the opening  311  maintains a high heat transfer because, as shown in  FIG. 2C , the thermal resistance between the substrate and a subsurface heat source is that of the susceptor only. 
         [0030]      FIG. 3D  illustrates a plan view of a substrate disposed on a pedestal surface with a carrier surrounding the pedestal, in accordance with an embodiment. In the exemplary embodiment illustrated in  FIG. 3D , the pedestal  306  further comprises a plurality of pedestal slots  321 A,  321 B and  321 C, each pedestal slot providing clearance to each tab  320 A,  320 B, and  320 C, respectively. Following a deposition process, the load sequence described for the interlocking susceptor  305  and carrier  310  may be reversed to pick the substrate off the pedestal  306  with the carrier  310  and then remove the carrier  310  with the robotic handler  330 . 
         [0031]      FIG. 4  illustrates a multi-chambered deposition system  400 , in accordance with an embodiment. As shown in  FIG. 4 , two or more epitaxy chambers, such as two or more MOCVD chamber or HVPE chambers, or a combination of MOCVD and HVPE chambers, are coupled to a platform to form a multi-chambered deposition system  400 . Embodiments described herein which utilize an intra-film stack transfer of the substrate between two deposition chambers may be performed using the multi-chambered deposition system  400 . Referring to  FIG. 4 , the multi-chambered deposition system  400  may be any platform known in the art that is capable of adaptively controlling a plurality of process modules simultaneously. Exemplary embodiments include an Opus™ AdvantEdge™ system or a Centura™ system, both commercially available from Applied Materials, Inc. of Santa Clara, Calif. 
         [0032]    The first, second, and third deposition chambers  405 ,  415 , and  420  perform particular growth operations on a substrate  103 . In the exemplary embodiment, the deposition chambers  405 ,  415 , and  420  are separately dedicated to growth of p-doped layers (e.g., Mg-doped GaN layers) in the first deposition chamber  405 , and growth of Mg-free films in the other chambers (e.g., MQW and undoped barrier layers in the second deposition chamber  415  and/or n-type doped GaN films in the third deposition chamber  420 ). Substrate  103  are transferred between the chambers  405 ,  415  and  420  as supported on the carrier  310  which is transferred by a robotic handler  450 . As further depicted in  FIG. 4 , the multi-chambered deposition system  400  includes an optional substrate integrated metrology (IM) chamber  425 , as well as load lock chambers  430  holding cassettes  435  and  445 , coupled to the transfer chamber  401 . 
         [0033]    In an embodiment, each the deposition chambers  405 ,  415 , and  420  includes a susceptor  305 A,  305 B, and  305 C, respectively, with each susceptor having at least one pedestal,  306 A,  306 B, and  306 C. In a further embodiment, a top surface of the pedestals  306 A,  306 B,  306 C differ. For example, in a specific embodiment where the multi-chambered deposition system  400  is to grow a GaN-based LED stack and the first deposition chamber  405  is dedicated to growth of p-doped GaN layers, the pedestal  306 A has a concave top surface to accommodate a concave substrate bow to improve temperature uniformity across the substrate during the p-doped GaN layer growth (a higher temperature operation often performed at 700° C. or more). In a further embodiment where the multi-chambered deposition system  400  is to grow a GaN-based LED stack and the second deposition chamber  415  is dedicated to growing a MQW (which is typically a lower temperature operation), the pedestal  306 B has a flat or planar surface to accommodate a substrate with no significant bow. In a further embodiment, where the multi-chambered deposition system  400  is to grow a GaN-based LED stack and the third deposition chamber  420  is dedicated to growing an n-type doped GaN film, the pedestal  306 C is has a concave top surface to accommodate a concave substrate bow to improve temperature uniformity across the substrate during the n-doped GaN layer growth (which is again typically a higher temperature operation). For these embodiments, with the carrier  310  serving as a transfer medium between chambers  405 ,  415  and  420  and the susceptors  305 A,  305 B, and  305 C serving as the heat transfer medium in each chamber, different pedestals or “pocket” types are possible without changing carrier dimensions. 
         [0034]    In one embodiment of the present invention, control of the multi-chambered deposition system  400 , including the robotic handler  450 , is provided by a controller  470 . The controller  470  may be a system level controller, in which case it is in control of events in the transfer chamber  401  and may also be in communication with chamber-level controllers associated with each of the deposition chambers  405 ,  406  and  416 . In other embodiments the controller  470  is a chamber level controller, in which case it is in control of events occurring only in a particular deposition chamber (e.g., the first deposition chamber  405 ). The controller  470  may be one of any form of general-purpose data processing system that can be used in an industrial setting for controlling the various subprocessors and subcontrollers. Generally, the system controller  470  or deposition chamber controller includes a central processing unit (CPU)  472  in communication with a memory  473  and an input/output (I/O) circuitry  474 , among other common components. Software commands executed by the CPU  472 , cause the multi-chambered deposition system  400  to, for example, load a substrate into the first deposition chamber  405 , execute a first growth process, transfer the substrate to the second deposition chamber  415  and execute a second growth process. 
         [0035]      FIG. 5  illustrates a method  500  for epitaxially growing a stack of films, in accordance with an embodiment. At operation  505 , the substrate  103  is dispensed on the carrier  310 . In one implementation, the substrate  103  is single crystalline sapphire (e.g., (0001)) and may be patterned or unpatterned. Other embodiments contemplated include the use of substrates other than sapphire substrates, such as, Silicon (Si), germanium (Ge), silicon carbide (SiC), gallium arsenide (GaAs), zinc oxide (ZnO), lithium aluminum oxide (γ-LiAlO 2 ). 
         [0036]    At operation  510 , the carrier  310  is loaded in to a first process chamber, such as the deposition chamber  405 , and aligned over a pedestal, such as the pedestal  306 A. The carrier  310  is then lowered onto susceptor  305  to contact a backside of the substrate  103  to a top surface of the first pedestal. At operation  520 , a film is then deposited on the substrate  103 . In one exemplary LED embodiment, one or more bottom n-type epitaxial layers is formed over a buffer and/or undoped layer at operation  520  as part of an LED or power transistor film stack. In the exemplary group III-nitride material system, a bottom n-type epitaxial layer may be any n-type group III-nitride based material, such as, but not limited to, GaN, InGaN, AlGaN. For this exemplary embodiment, the top surface of the pedestal  306 A is concave to accommodate high growth temperature substrate bow. 
         [0037]    At operation  525 , the carrier  310  is lifted off the susceptor  305 A, for example with lift pins  309  ( FIG. 3C ) to pick the substrate off the pedestal  306 A. A robotic handler, such as the handler  330  ( FIG. 3C ), then transfers the carrier  310  to a second process chamber, such as deposition chamber  415 , at which point method  500  returns to operation  510  for a second iteration. For the exemplary LED film stack, the deposition chamber  415  forms a single quantum wells (SQW), a double hetereostructures, or a multiple quantum well (MQW) structure on the substrate  103 . Such structures may be any known in the art to provide a particular emission wavelength. In a certain embodiments, an MQW structure may have a wide range of indium (In) content within GaN. For example, depending on the desired wavelength(s), the MQW structure may have between about a 10% to over 40% of mole fraction indium as a function of growth temperature, ratio of indium to gallium precursor, etc. For this exemplary embodiment, the top surface of the pedestal  306 B is flat to accommodate low growth temperature substrate bow. 
         [0038]    To complete an LED stack, a third iteration of the method  500  is performed, for example with the carrier  310  transferred with the substrate  103  into the deposition chamber  420  where one or more p-type epitaxial layers are disposed over the MQW structure on substrate  103 . The p-type epitaxial layers may include one or more layers of differing material composition. For example, in one embodiment the p-type epitaxial layers include both p-type GaN and p-type AlGaN layers doped with Mg. In other embodiments only one of these, such as p-type GaN are utilized. For this exemplary embodiment, the top surface of the pedestal  306 C is concave to accommodate high growth temperature substrate bow. 
         [0039]    It is to be understood that the above description is intended to be illustrative, and not restrictive. Many other embodiments will be apparent to those of skill in the art upon reading and understanding the above description. Although the present invention has been described with reference to specific exemplary embodiments, it will be recognized that the invention is not limited to the embodiments described, but can be practiced with modification and alteration. Accordingly, the specification and drawings are to be regarded in an illustrative sense rather than a restrictive sense.