Abstract:
A gas distribution system is disclosed in order to obtain better film uniformity on a wafer. The better film uniformity may be achieved by utilizing an expansion plenum and a plurality of, for example, proportioning valves to ensure an equalized pressure or flow along each gas line disposed above the wafer.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
       [0001]    The present application claims priority to U.S. Provisional Patent Application No. 62/305,886, entitled “Gas Distribution Apparatus for Improved Film Uniformity in an Epitaxial System,” and filed on Mar. 9, 2016. 
     
    
     FIELD OF INVENTION 
       [0002]    The invention relates to an epitaxial system for processing semiconductor substrates. Specifically, the invention relates to a gas distribution apparatus that results in improved film uniformity for the epitaxial system. 
       BACKGROUND OF THE DISCLOSURE 
       [0003]    Obtaining film uniformity in substrate processing can be difficult when there is an uneven distribution of gas applied to substrates. The uneven distribution of gas may cause uneven growth of film or crystalline instability, among other issues. This may cause defects in the finished products, and thus, may render them unusable. 
         [0004]    The uneven distribution of gas may be attributable to the way flows occur in a reaction system. A single source of gas may provide a required precursor along many points of a substrate&#39;s surface. But a distance traveled by gas at one point of the substrate&#39;s surface may differ than that of another location on the substrate&#39;s surface. This may be due to the unequal length lines of a gas distribution system. 
         [0005]      FIG. 1  shows a prior art gas distribution system  100  for depositing an epitaxial film on a substrate. The gas distribution system  100  may include a base gas source (not pictured) that provides a base gas to a base gas feed  102 . The base gas feed  102  may include a gas line and fittings. An example of the gas line in the gas distribution system  100  may be a high purity gas line (316L SST, electro-polished inside) manufactured by Swagelok®. 
         [0006]    The base gas may then pass through base gas feed  102  to a base gas distribution rail  104 , which extends across the substrate&#39;s surface. From the base gas distribution rail  104 , the base gas then passes downward through an upper base gas feed line  106  to a metering or proportioning valve  108 , of which seven of both the upper base gas feed line  106  and the metering or proportioning valve  108  are shown in  FIG. 1 . The metering or proportioning valve  108  may control a flow rate of the base gas to a lower base gas feed line  110 . The metering or proportioning valve  108  may comprise a Swagelok® BM-series High-purity metering valve. 
         [0007]    From the lower base gas feed line  110 , the base gas may reach a gas injection port  112 . The gas injection port  112  may be coupled an injection flange  114 , which is installed onto a chamber  116 . The base gas may then enter into the chamber  116  and encounter a substrate to be processed. 
         [0008]    The gas distribution system  100  may also include a dopant gas source that provides a dopant gas to a dopant gas feed  118 . Similar to the base gas feed  102 , the dopant gas feed  118  may also include a gas line and fittings. The dopant gas may then pass through to a dopant gas distribution rail  120  and then an upper dopant gas feed line  122 . 
         [0009]    The dopant gas then proceeds from the upper dopant gas feed line  122  to a metering or proportioning valve  124 , of which three are shown in  FIG. 1 . The metering or proportioning valve  124  may control a flow rate of the dopant gas to a lower dopant gas feed line  126 . 
         [0010]    From the lower dopant gas feed line  126 , the dopant gas may reach a dopant injection port  128 . The dopant injection port  128  may be coupled an injection flange  114 , which is installed onto a chamber  116 . The dopant gas may then enter into the chamber  116  and encounter a substrate to be processed. 
         [0011]    As shown in  FIG. 1 , a distance traveled by a gas may differ based on which injection port the gas travels through. For example, a gas that enters an injection port centered in the middle of the substrate may travel much less than a gas that enters an injection port on the ends of the substrate. Such may be reflected in the lengths of the lower base gas feed line  110  and the lower dopant gas feed line  126 . 
         [0012]    The difference in distance traveled may reflect themselves in the flow rates of gas, and the pressures within the gas lines.  FIG. 2  illustrates a pressure diagram of a prior art gas distribution system. The pressure diagram reflects a greater pressure difference for gas lines  130  located in the middle of the substrate compared to gas lines  132  located on the ends of the substrate. With a greater pressure difference, a higher flow rate is possible for the gas lines  130  in comparison to gas lines  132 . Such may result in more deposition occurring in the middle of the substrate compared to the edges. 
         [0013]    As a result, a need exists for a system that distributes gas in a manner that improves film uniformity. 
       SUMMARY OF THE DISCLOSURE 
       [0014]    A reaction system is disclosed for obtaining a better film uniformity across a wafer to be processed. The reaction system may include: a reaction chamber, the reaction chamber holding a wafer to be processed; a gas source; an inlet gas feed line configured to receive a gas from the gas source; a plurality (e.g., a pair) of symmetrical feeds, the symmetrical feeds configured to split a flow of the gas from the inlet gas feed line; an expansion plenum with a plurality of outlet ports, wherein the expansion plenum receives gas from the pair of symmetrical feeds at opposite ends of the expansion plenum; and a plurality of valves (e.g., proportioning, such as needle valves) configured to control flow of the gas from the outlet ports of the expansion plenum into the reaction chamber; wherein the plurality of valves maintains a substantially equalized pressure across the plurality of outlet ports; and wherein a substantially equal flow of gas across the wafer is achieved. 
         [0015]    For purposes of summarizing the invention and the advantages achieved over the prior art, certain objects and advantages of the invention have been described herein above. Of course, it is to be understood that not necessarily all such objects or advantages may be achieved in accordance with any particular embodiment of the invention. Thus, for example, those skilled in the art will recognize that the invention may be embodied or carried out in a manner that achieves or optimizes one advantage or group of advantages as taught or suggested herein without necessarily achieving other objects or advantages as may be taught or suggested herein. 
         [0016]    All of these embodiments are intended to be within the scope of the invention herein disclosed. These and other embodiments will become readily apparent to those skilled in the art from the following detailed description of certain embodiments having reference to the attached figures, the invention not being limited to any particular embodiment(s) disclosed. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWING FIGURES 
         [0017]    The patent or application file contains at least one drawing executed in color. Copies of this patent or patent application publication with color drawing(s) will be provided by the Office upon request and payment of the necessary fee. 
           [0018]    These and other features, aspects, and advantages of the invention disclosed herein are described below with reference to the drawings of certain embodiments, which are intended to illustrate and not to limit the invention. 
           [0019]      FIG. 1  illustrates a prior art gas distribution system. 
           [0020]      FIG. 2  illustrates a pressure diagram of a prior art gas distribution system. 
           [0021]      FIG. 3  illustrates a view of a gas distribution system component according to at least one embodiment of the invention. 
           [0022]      FIG. 4  illustrates a gas distribution system according to at least one embodiment of the invention. 
           [0023]      FIG. 5  illustrates a pressure diagram of a gas distribution system according to at least one embodiment of the invention. 
           [0024]      FIG. 6  illustrates a component of a gas distribution system according to at least one embodiment of the invention. 
       
    
    
       [0025]    It will be appreciated that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help improve understanding of illustrated embodiments of the present disclosure. 
       DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS 
       [0026]    Although certain embodiments and examples are disclosed below, it will be understood by those in the art that the invention extends beyond the specifically disclosed embodiments and/or uses of the invention and obvious modifications and equivalents thereof. Thus, it is intended that the scope of the invention disclosed should not be limited by the particular disclosed embodiments described below. 
         [0027]    Embodiments of the invention are directed to creating a more uniform flow of gas onto the substrate. Such may be achieved by equalizing a pressure of the gas flow across the substrate. 
         [0028]      FIG. 3  illustrates a gas distribution system  200  in accordance with at least one embodiment of the invention. The gas distribution system  200  includes a base gas source that provides base gas to a base gas feed  202 . The base gas feed  202  may include a gas line, bends, and fittings. An example of the gas line in the gas distribution system  200  may be a high purity gas line (316L SST, electro-polished inside) manufactured by Swagelok®. 
         [0029]    The base gas feed  202  may provide gas into a gas manifold  204 . The gas manifold  204  may be configured to equalize a pressure of the base gas across the substrate and then pass along the base gas to a set of proportioning or metering valves  206 . The proportioning or metering valves  206  (e.g., needle valves) may control a flow rate of the base gas to a lower base gas feed line  208 . The proportioning or metering valves  206  may comprise a Swagelok® BM-series High-purity metering valve, for example. 
         [0030]    From the lower base gas feed line  208 , the base gas may reach a gas injection port as previously described. The gas injection port may be coupled an injection flange, which is installed onto a chamber. The base gas may then enter into the chamber and encounter a substrate to be processed. 
         [0031]    In at least one embodiment of the invention, it may be possible that a plurality of lower base gas feed lines  208  may provide gas into a second lower gas manifold, separate from the gas manifold  204 . From the second lower gas manifold, the base gas may enter into the chamber through a set of injection flanges. 
         [0032]    The gas distribution system  200  may also include a dopant gas source that provides a dopant gas to a dopant gas feed  210 . Similar to the base gas feed  202 , the dopant gas feed  210  may also include a gas line and fittings. The dopant gas may then pass through to a dopant gas distribution rail  212  and then an upper dopant gas feed line  214 . 
         [0033]    The dopant gas then proceeds from the upper dopant gas feed line  214  to a metering or proportioning valve  216  (e.g., a needle valve), of which three are shown in  FIG. 1 . The metering or proportioning valve  216  may control a flow rate of the dopant gas to a lower dopant gas feed line  218 . 
         [0034]    From the lower dopant gas feed line  218 , the dopant gas may reach a dopant injection port. The dopant injection port may be coupled an injection flange, which is installed onto a chamber. The dopant gas may then enter into the chamber and encounter a substrate to be processed. 
         [0035]      FIG. 4  provides a zoomed view of the gas manifold  204  in accordance with at least one embodiment of the invention. The gas manifold  204  may include a single base gas feed  250 . The single base gas feed  250  may be located at a centerline of the gas manifold  204 . By locating the single base gas feed  250  accordingly, an equal split of the gas flow into a set of symmetrical feeds  252  may occur. 
         [0036]    The symmetrical feeds  252  pass the base gas into an expansion plenum  254 . The symmetrical feeds  252  may be configured to maintain an equalized pressure and flow into opposite ends of the expansion plenum  254 . Once flowed inside the expansion plenum  254 , the base gas may reside inside the expansion plenum  254  and attain an equalized pressure. 
         [0037]    The base gas may then flow from the expansion plenum  254  to an upper base gas feed line  256 . Flow of the base gas from the expansion plenum may be controlled with a set of needle proportioning valves (not shown in  FIG. 4 ). The needle proportioning valves may be of a metering stem tip or regulating stem tip design manufactured by Swagelok®, for example. The needle proportioning valves may be configured to create restrictions to counteract a cascading flow of the gas across openings in the expansion plenum. A result of the restrictions imposed by the needle proportioning valves is a matched pressure/flow at each feed port to the upper base gas feed lines  256 . 
         [0038]    Pressure differentials may exist in the current state of the art delivery systems due to influences from the Bernoulli effects of base gas flow.  FIG. 5  illustrates the extent to which the pressure differentials may be reduced. With the design of the manifold and the base gas feed line  202 , the Bernoulli effect may be reduced after the tee as the gas flows along the symmetrical feeds  252  toward the expansion plenum  254 . The expansion plenum  254  volume may be designed to reduce the gas velocity as it expands to fill the volume to continue its flow path to the wafer. The base gas may flow from the plenum becomes equalized across the lower base gas feed lines  208  as a result of the expansion plenum and velocity reduction. The base feed lines  208  may then be finely regulated for individual flow by using the metering or proportioning valve  206  to equalize the gas distribution across the wafer (substrate) surface via the lower base gas feed lines  208 . 
         [0039]    In accordance with at least one embodiment of the invention, a gas distribution block  300  may be used to replace lower base gas feed lines.  FIG. 6  illustrates the gas distribution block  300 . The gas distribution block  300  may comprise a plurality of base gas metering (e.g., needle) valves  302  and a plurality of dopant gas metering (e.g., needle) valves  304  installed onto a monoblock  306 . 
         [0040]    The monoblock  306  may make unnecessary the need for lower base gas feed lines, which may be unequal in length. By eliminating the unequal length lower base gas feed lines, the base gas metering valves  302  and the dopant gas metering valves  304  may be surface-mounted, and may be used to provide higher resolution control of base gas distribution. Thus, a conductance path between the valves and the injection flange may be reduced. 
         [0041]    The particular implementations shown and described are illustrative of the invention and its best mode and are not intended to otherwise limit the scope of the aspects and implementations in any way. Indeed, for the sake of brevity, conventional manufacturing, connection, preparation, and other functional aspects of the system may not be described in detail. Furthermore, the connecting lines shown in the various figures are intended to represent exemplary functional relationships and/or physical couplings between the various elements. Many alternative or additional functional relationship or physical connections may be present in the practical system, and/or may be absent in some embodiments. 
         [0042]    It is to be understood that the configurations and/or approaches described herein are exemplary in nature, and that these specific embodiments or examples are not to be considered in a limiting sense, because numerous variations are possible. The specific routines or methods described herein may represent one or more of any number of processing strategies. Thus, the various acts illustrated may be performed in the sequence illustrated, in other sequences, or omitted in some cases. 
         [0043]    The subject matter of the present disclosure includes all novel and nonobvious combinations and subcombinations of the various processes, systems, and configurations, and other features, functions, acts, and/or properties disclosed herein, as well as any and all equivalents thereof.