Abstract:
Methods and apparatus of substrate supports having temperature profile control are provided herein. In some embodiments, a substrate support includes: a plate having a substrate receiving surface and an opposite bottom surface; and a shaft having a first end comprising a shaft heater and a second end, wherein the first end is coupled to the bottom surface. Methods of making a substrate support having temperature profile control are also provided.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims benefit of U.S. provisional patent application Ser. No. 61/878,370, filed Sep. 16, 2014, which is herein incorporated by reference in its entirety. 
     
    
     FIELD 
       [0002]    Embodiments of the present invention generally relate to semiconductor processing equipment. 
       BACKGROUND 
       [0003]    In semiconductor substrate processing, the temperature of the substrate is often a critical process parameter. Changes in temperature, and temperature gradients across the substrate surface during processing are often detrimental to material deposition, etch rate, feature taper angles, step coverage, and the like. It is often desirable to have control over a substrate temperature profile before, during, and after substrate processing to enhance processing and minimize undesirable characteristics and/or defects. 
         [0004]    The substrate is often supported upon a substrate support or pedestal having a centrally located support shaft to support the substrate support. The substrate support often includes one or more embedded heaters adapted to heat a substrate disposed thereon. However, the inventors have observed that conventional heated substrate supports with embedded heaters often display a temperature non-uniformity at the central region of the substrate support resulting in non-uniform of process results in the substrate. The inventors have observed that, in some cases, the temperature non-uniformity of the substrate support can be attributed to the support shaft drawing heat away from the substrate support. 
         [0005]    Therefore, the inventors have provided embodiments of a heated substrate support having improved temperature uniformity. 
       SUMMARY 
       [0006]    Methods and apparatus of substrate supports having temperature profile control are provided herein. In some embodiments, a substrate support includes: a plate having a substrate receiving surface and an opposite bottom surface; and a shaft having a first end comprising a shaft heater and a second end, wherein the first end is coupled to the bottom surface. 
         [0007]    In some embodiments, a substrate support includes: a plate having a substrate receiving surface and an opposite bottom surface; a plate heater disposed in the plate; a plate temperature sensor disposed in the plate, wherein the plate heater and the plate temperature sensor are coupled to a controller; a shaft having a first end comprising a shaft heater and a second end, wherein the first end is coupled to the bottom surface; and a shaft temperature sensor disposed at the first end wherein the shaft temperature sensor and the shaft heater are coupled to a controller. 
         [0008]    In some embodiments, a method of making a substrate support is provided and includes: forming a plate having a substrate receiving surface and an opposite bottom surface; forming a first layer of ceramic material, the first layer comprising a first end and an opposite second end; disposing a heater on the first layer at the first end; disposing a conduit on the first layer such that one end of the conduit is coupled to the heater and a second end of the conduit extends beyond the second end of the ceramic material; forming a second layer of ceramic material atop the first layer such the second layer at least partially covers the heater; processing the first layer and the second layer to form a shaft; and coupling the first end to the bottom surface of the plate. 
         [0009]    Other and further embodiments of the present invention are described below. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]    Embodiments of the present invention, briefly summarized above and discussed in greater detail below, can be understood by reference to the illustrative embodiments of the invention depicted 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. 
           [0011]      FIG. 1  depicts a schematic side sectional view of a substrate support in accordance with some embodiments of the present invention. 
           [0012]      FIG. 2  depicts a schematic side sectional view of a substrate support in accordance with some embodiments of the present invention. 
           [0013]      FIG. 3  depicts a flow chart for fabricating a substrate support in accordance with some embodiments of the present invention. 
       
    
    
       [0014]    To facilitate understanding, identical reference numerals have been used, where possible, to designate identical elements that are common to the figures. The figures are not drawn to scale and may be simplified for clarity. It is contemplated that elements and features of one embodiment may be beneficially incorporated in other embodiments without further recitation. 
       DETAILED DESCRIPTION 
       [0015]    Embodiments of the present invention provide heated substrate supports having improved temperature uniformity control. Embodiments of the present invention may be used to support and heat a substrate for any process using a heated substrate support with enhanced control over a temperature profile created on the substrate. Non-limiting examples of processes that may benefit from the discloses substrate support include chemical vapor deposition (CVD), atomic layer deposition (ALD), or laser annealing processes. 
         [0016]      FIG. 1  is a schematic side sectional view of a substrate support  100  in accordance with some embodiments of the present invention. The substrate support  100  comprises a heater plate, plate  102  comprising a substrate receiving surface  104  and a bottom surface  106 . The plate  102  may be formed from one or more process compatible materials including ceramic materials such as silicon nitride (Si 3 N 4 ), alumina (Al 2 O 3 ), aluminum nitride (AlN), or silicon carbide (SiC) and metallic materials such as aluminum and stainless steel (SST) or alloys like silicon-aluminum alloys (Si—Al). 
         [0017]    Embedded or disposed within the plate  102  are one or more plate heaters  108  (two plate heaters  108  shown). The plate heaters  108  may be in the form of rings, as illustrated. Alternately, the plate heaters  108  may be separate heater elements embedded within the plate  102 . The plate heaters  108  are coupled to a power supply such as DC source  110  via conductors  111  to provide power to the plate heaters  108  to facilitate heating of the plate  102 . 
         [0018]    A plate temperature sensor  112 , such as a resistive temperature device(RTD), is embedded in or coupled to the plate  102  to sense a temperature at an area of interest in the plate  102 . The plate temperature sensor  112  is coupled to the controller  114  via conductor  116  to provide data regarding the plate  102  temperature to the controller  114 . 
         [0019]    The DC source  110  is also coupled to the controller  114  via conductor  118 . The controller  114  regulates the amount of power provided to the plate heaters  108  based on the temperature data from the plate temperature sensor  112  to provide a preselected plate temperature. As such, the plate heaters  108 , the DC source  110 , the plate temperature sensor  112 , and the controller  114  are linked and operate as a first closed loop control circuit to maintain a preselected temperature of the plate  102 . 
         [0020]    The controller  114  may be any general purpose computer adapted to read and monitor the temperature of the plate  102  from the data provided by the plate temperature sensor  112  and to regulate the amount of power provided to the plate heaters  108 . 
         [0021]    The plate  102  may rest on, and be supported by, a first end  126  of a shaft  120 . The shaft  120  may be formed from process compatible materials as discussed above. 
         [0022]    The first end  126  is mounted to the bottom surface  106  to support the plate  102 , and a substrate  122  when disposed on the substrate receiving surface  104 , in a position within a chamber  124  for example, for substrate processing or transfer. In some embodiments, the shaft  120  may provide one or more of vertical positioning and rotational positioning of the plate  102  and substrate  122  within the chamber  124  by a suitable lift actuator, a rotational actuator, or a combination lift and rotation actuator coupled to the shaft  120  (not shown). 
         [0023]    In some embodiments, the first end  126  comprises a flange  128  to facilitate mounting of the shaft  120  to the bottom surface  106 . The flange  128  may be mounted to the bottom surface  106  using any suitable mechanical fasteners, adhesives, welding, brazing, or the like. The flange  128  may be an integral component of the shaft  120  or a separate component coupled to the shaft  120 , for example, by welding. In some embodiments, the first end  126  of the shaft  120  may be mounted to the bottom surface  106  without a flange. For example, adhesives, welding, brazing, or the like may be used to mount the first end  126  of the shaft  120  to the bottom surface  106 . The shaft  120  may be directly coupled to the bottom surface  106  to minimize thermal resistance between the shaft  120  and the bottom surface  106  of the plate  102 . 
         [0024]    At least one shaft heater  130  is coupled to the flange  128 . In some embodiments, the at least one shaft heater  130  is at least partially embedded in the flange  128 . In some embodiments, the at least one shaft heater  130  is a resistive heater. A first end  133  of conductor  134  is coupled to the shaft heater  130 . A second end  135  of conductor  134  extends beyond the second end  127  of the shaft  120  and is coupled to a power supply, such as DC source  140 , to facilitate providing power to the at least one shaft heater  130  to heat the first end  126  of the shaft  120 . 
         [0025]    A shaft temperature sensor  132 , such as a resistive temperature device , is also embedded in or coupled to the flange  128 . A first end  137  of conductor  138  is coupled to the shaft temperature sensor  132 . A second end  139  of the conductor  138  extends beyond the second end  127  of the shaft  120  and is coupled to a controller, for example controller  114 . The DC source  140  may also be coupled to the controller  114 , for example via conductor  136 . A control circuit similar to the first closed loop control circuit described above comprises the shaft heater  130 , the DC source  140 , the shaft temperature sensor  132 , and the controller  114  linked to operate as a second closed loop control circuit. In the second closed loop circuit, the controller  114  regulates the power to the shaft heater  130  in response to temperature data provided by the shaft temperature sensor  132  to facilitate temperature control of the first end  126  of the shaft  120 . The first closed loop circuit and the second closed loop circuit may have a common controller  114  as shown, or the closed loop circuits may have separate controllers that may be in communication with each other. 
         [0026]    In some embodiments, the first closed loop control circuit (the plate heaters  108 , the DC source  110 , the plate temperature sensor  112 , and the controller  114 ) and the second closed loop circuit (the shaft heater  130 , the DC source  140 , the shaft temperature sensor  132 , and the controller  114 ) are linked together, for example through the controller  114 . The controller  114  may be configured to independently control the first and second closed loop control circuits to maintain the plate  102  and the shaft  120  at first and second temperatures, respectively. The first and second temperatures may be the same temperature. 
         [0027]      FIG. 2  depicts a simplified schematic side sectional view of a substrate support  200  in accordance with an embodiment of the present invention. The plate  102  may be constructed as described above and is illustrated with some details (for example, the components of the first closed loop circuit described above) omitted for clarity. A ceramic support shaft, shaft  220 , is provided to support the plate  102  which rests upon a first end  226  of the shaft  220 . In some embodiments, the first end  226  includes a flange  228  adapted to be mounted to the bottom surface  106  of the plate  102  as described above. In some embodiments, the first end  226  may be mounted to the bottom surface  106  of the plate  102  without a flange, as described above. 
         [0028]    The shaft  220  as illustrated comprises two layers of ceramic material, a first layer  202  and a second layer  204  (although additional layers may be used). The shaft  220  may be formed from, in non-limiting examples, the ceramic materials discussed above. One or more electrical components may be disposed at the interface  212  between the first layer  202  and the second layer  204 . 
         [0029]    For example a shaft heater  230  may be disposed in a portion of the flange  228  at the interface  212 . Similar to the shaft heater  130  in the embodiment of  FIG. 1 , a first end  233  of a conductor  234  is coupled to the shaft heater  230 . A second end  235  of the conductor  234  extends beyond the second end  227  of the shaft  220  and is coupled to a power source, for example DC source  240 , to provide power to the shaft heater  230  and facilitate heating the first end  226  of the shaft  220 . The conductor  234  may be completely or partially disposed along the interface  212  between the first layer  202  and the second layer  204 . 
         [0030]    One or more of the shaft heater  230  and the conductor  234  may be printed on a surface  213  of the first layer  202  or the second layer  204 . For example, at least one of the shaft heater  230  and the conductor  234  may be formed by a solution of tungsten, molybdenum, or other metal with a suitable electrical resistivity that is screen printed on a portion of the first layer  202 . In some embodiments, the shaft heater  230  and the conductor  234  may be printed on an outer surface  203  of the first layer  202  of ceramic material. For example, the first layer  202  of ceramic material may be formed and the shaft heater  230  and conductor  234  printed on the outer surface  203 . A second layer  204  of ceramic material may be formed over the first layer  202  at least partially covering the shaft heater  230  and the conductor  234 . The combined first and second layers  202  and  204  may be further processed, for example by sintering, to form a finished shaft  220  with the shaft heater  230  and the conductor  234  disposed at the interface  212 . 
         [0031]    Prior to further processing, and in a similar fashion, a shaft temperature sensor  232 , such as a resistive temperature device (RTD), may also be disposed at the interface  212 . The shaft temperature sensor  232  may be printed on the outer surface  203  of the first layer  202 . A first end  237  of a conductor  238  may be coupled to the shaft temperature sensor  232 . A second end  239  of the conductor  238  extends beyond the second end  227  of the first layer  202  and is coupled to the controller  214 . The DC source  240  may also be coupled to the controller  214 , for example via conductor  236 . 
         [0032]    The shaft heater  230 , the DC source  240 , the shaft temperature sensor  232 , and the controller  214  comprise a closed loop circuit similar in construction and function to the second closed loop circuit described above. 
         [0033]    In some substrate processes, the temperature profile of the substrate receiving surface predicts the temperature profile of the substrate supported thereon. The temperature non-uniformities across the substrate receiving surface are manifest by non-uniform process performance on the substrate supported thereon. The inventors have observed that in some cases, heat is lost at the central area of the plate, opposite the mounting location of the shaft. The inventors have noted the shaft appears to create a heat sink, removing some of the heat from the plate at the interface of the shaft and the plate. The mounting of the shaft to the plate causes a temperature discontinuity at the substrate mounting surface. 
         [0034]    The inventive substrate support may include a heater and temperature sensor at the first end (mounting end) of the shaft to reduce heat loss from the plate. The heater at the first end of the shaft generates additional heat with closed loop control to compensate for heat lost to the shaft. It has been observed that the closed loop control of the shaft heaters advantageously allows accurate control of the temperature of the first end of the shaft. When used in conjunction with the closed loop control of the temperature of the plate, the temperature difference between the plate and the first end of the shaft can be minimized. In cases where the temperature of the first end of the shaft is the same, or substantially the same, as the plate temperature, the inventors have noted an adiabatic interface can be established in which heat neither transfers to nor from the plate. Under such conditions, the inventors have observed no thermal imprint of the shaft on the substrate support surface or on the substrate supported thereon. Accordingly, processing of the substrate can be advantageously effected by maintaining a more uniform temperature across the substrate. In addition, the substrate support may be operated to develop a purposeful non-uniform thermal gradient across the surface of the substrate support (e.g., central region hotter or central region colder) in order to compensate for other sources of heat transfer to or from the substrate during processing (e.g., to maintain a more uniform thermal gradient on the substrate during processing) or to compensate for other sources of processing non- uniformities or non-uniform incoming substrates (e.g., to maintain a purposefully non-uniform thermal gradient on the substrate during processing). 
         [0035]    The inventors have also observed that the temperature differential between the heated plate and the unheated shaft in conventional substrate supports can also cause thermal stresses at the interface between the shaft and the bottom of the plate. Thermal stresses can make the attachment between the shaft and the plate problematic, for example as the plate and the shaft expand or contract differently because of the different temperatures. 
         [0036]    In the present invention, as discussed above, the shaft heater can advantageously minimize or substantially eliminate the temperature differential between the shaft and the plate at the interface. Accordingly, the thermal stresses and the associated disadvantages can also be minimized or substantially eliminated. 
         [0037]    The inventors have developed a novel way of forming the inventive heated substrate support disclosed above. The method is outlined beginning at  300  in  FIG. 3 , with reference made to the plate  102  ( FIG. 1 ) and the shaft  220  ( FIG. 2 ). At  302 , a plate  102  having a substrate receiving surface  104  and an opposite bottom surface  106  is formed. The plate  102  may include one or more plate heaters  108 , and a plate temperature sensor  112 , such as a resistive temperature device (RTD), embedded in the plate  102 . As described above, the plate heaters  108  and the plate temperature sensor  112  may be coupled to the DC source  110  and the controller  114  to form a first closed loop control circuit. 
         [0038]    The plate  102  may be formed form ceramic materials as listed above. Forming the plate  102  may include sintering to densify the ceramic materials. Other fabrication processes suitable to the particular material (ceramics or metallic) may be used as appropriate. Forming the plate  102  may occur separately from forming the shaft  220 . 
         [0039]    At  304 , a first layer  202  of ceramic material is formed, the first layer  202  comprising a first end  226  and an opposite second end  227 . The first layer  202  may include an area corresponding to the flange  228 . In some embodiments, the first layer  202  is formed as a sheet of ceramic material having an upper edge  242  (corresponding to the first end  226  of the shaft, including the flange  228 ), an opposite bottom edge  244  (corresponding to the second end  227 ) and lengthwise edges (not shown). 
         [0040]    At  306 , a shaft heater  230  is disposed on the first layer  202  at the upper edge  242 . In some embodiments, the shaft heater  230  is printed on a surface  213  of the first layer  202  using a solution comprising tungsten, molybdenum, or another metal with a suitable electrical resistivity using screen printing techniques as discussed above. The shaft heater  230  may be formed by printing a plurality of layers of the same or different configuration at the upper edge  242 . 
         [0041]    A conductor  234  may be disposed on a surface  213  of the first layer  202  as at  308 . A first end  233  of the conductor  234  may be coupled to the shaft heater  230 . A second end  235  extends to the bottom edge  244  of the first layer  202 . In some embodiments, the second end  235  extends beyond the bottom edge  244 . In some embodiments, the conductor  234  may be printed, for example screen printed, as above using similar materials. An additional conductor (not shown), may be coupled to the conductor  234  at the bottom edge  244  when the conductor  234  is printed on the surface  213 , to extend the conductor  234  beyond the bottom edge  244 . 
         [0042]    Optionally, at  310 , the shaft temperature sensor  232 , such as a resistive temperature device (RTD), may be disposed on the first layer  202  at the upper edge  242  of the first layer. The shaft temperature sensor  232  may be coupled to a conductor  238  which may be integrally formed with the shaft temperature sensor  232  or separately formed. In some embodiments at least one of the shaft temperature sensor  232  or the conductor  238  may be printed on the surface  213 , such as by screen printing. 
         [0043]    At  312 , a second layer  204  of ceramic material is formed atop the first layer  202  such that the second layer  204  at least partially covers the shaft heater  230 . If the conductor  234  is printed on the surface  213 , the second layer  204  may at least partially cover the conductor  234 . In embodiments in which the first layer  202  is formed as a sheet of ceramic material, the second layer  204  may also be formed as sheet of ceramic material having an upper edge  246  aligned with upper edge  242 , an opposite bottom edge  248  aligned with bottom edge  244 , and lengthwise edges (not shown). 
         [0044]    At  314 , the first layer  202  with the heater disposed on surface  213 , and with the second layer  204  formed atop the first layer and at least partially covering the heater, are processed together to form a shaft  220 . The processing may include a procedure to densify the first and second layers  202 ,  204  of ceramic materials. For example, the first and second layers  202 ,  204  may be sintered under elevated temperature and high pressure to form a shaft  220 . 
         [0045]    In the embodiments in which the first and second layers  202  and  204  are formed sheets of ceramic materials, the sheets may be formed into an open ended tube such that the upper edge  246  is aligned with upper edge  242 , and the bottom edge  248  is aligned with bottom edge  244 . For example, the first and second layers  202  and  204  may be rolled into a tubular form such that the lengthwise edges of the first layer  202  are joined and the lengthwise edges of the second layer  204  are joined. The tubular form may be a cylinder or other convenient shape. 
         [0046]    At  316 , the first end  226  of the shaft  220  is coupled to the bottom surface  106  of the plate  102  to form a substrate support in accordance with the present invention. The coupling may be achieved using any suitable mechanical fasteners, such as threaded fasteners or mechanical clamping devices, or adhesives as appropriate. 
         [0047]    Thus, embodiments of heated substrate supports having improved temperature uniformity control have been provided. Embodiments of the present invention may be used to support and heat a substrate for any process using a heated substrate support with enhanced control over a temperature profile created on the substrate. Non-limiting examples of processes that may benefit from the discloses substrate support include chemical vapor deposition (CVD), atomic layer deposition (ALD), or laser annealing processes. 
         [0048]    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.