Abstract:
Embodiments described herein relate to a lower side wall for use in a processing chamber. In one embodiment, the lower side wall includes an annular body. The annular body as an inner circumference, an outer circumference, a plurality of flanges projecting from the inner circumference, and a first concave portion formed in the outer circumference. The outer circumference has a plurality of grooves arranged in a circumferential direction of the lower side wall. In another embodiment, the annular body further includes a top surface having a mounting surface formed thereon and a second concave portion formed opposite the first concave portion. The second concave portion has a plurality of purge holes. In another embodiment, each groove of the plurality of grooves formed in the first concave portion has an arc shape.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a continuation of U.S. application Ser. No. 13/934,708 filed on Jul. 3, 2013, which claims priority to Japanese Patent Application Number 2013-052479 filed on Mar. 14, 2013, both of which are hereby incorporated by reference in its entirety. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to a film forming method using epitaxial growth and an epitaxial growth apparatus. 
         [0004]    2. Background Art 
         [0005]    At present, as an epitaxial growth apparatus for causing an epitaxial film to grow on a substrate using epitaxial growth, an apparatus including a process chamber and a rotatable substrate support disposed in the process chamber and configured to rotate a substrate about a rotation axis is known in which a reactant gas is introduced to the substrate in a direction parallel to the substrate to form a film on the substrate on the substrate support. 
         [0006]    In such an epitaxial growth apparatus, there is currently a need for an increase in growth rate. However, it is not preferable that a large amount of source gas is included in the reactant gas so as to further increase the growth rate, for example, because an increase in the film formation cost or an increase in the number of particles is caused. 
         [0007]    In epitaxial growth, when the thickness of a boundary layer (at a position at which the flow rate is 99% of the flow rate of the main stream of the reactant gas flow) on the surface of a substrate decreases, it is known that an increase in growth rate is expected. On the other hand, when the thickness of the boundary layer simply decreases, a flow in which the reactant gas escapes toward the circumferential edge of the substrate on the surface of the substrate is formed and it is thus difficult to adjust a film thickness distribution or a resistivity distribution. 
       SUMMARY OF THE INVENTION 
       [0008]    In one embodiment, a lower side wall for use in a processing chamber is disclosed herein. The lower side wall includes an annular body. The annular body includes an inner circumference, an outer circumference, a plurality of flanges, and a first concave portion. The outer circumference is concentric with the inner circumference. The first concave portion is formed in the outer circumference. The first concave portion includes a plurality of grooves arranged along a circumferential direction of the lower side wall. 
         [0009]    In another embodiment, a lower side wall for use in a processing chamber is disclosed herein. The lower side wall includes an annular body. The annular body includes an inner circumference, an outer circumference, a plurality of flanges, a top surface, a first concave portion, and a second concave portion. The outer circumference is concentric with the inner circumference. The plurality of flanges project from the inner circumference. The top surface has a mounting surface formed thereon. The first concave portion is formed in the outer circumference. The first concave portion includes a plurality of grooves arranged along a circumferential direction of the lower side wall. The second concave portion is formed opposite the first concave portion. The second concave portion includes a plurality of purge holes formed therethrough. 
         [0010]    In another embodiment a lower side wall for use in a processing chamber is disclosed herein. The lower side wall includes an inner circumference, an outer circumference, a top surface, a plurality of flanges, and a first concave portion. The outer circumference is concentric with the inner circumference. The plurality of flanges project from the inner circumference. The first concave portion includes a plurality of grooves arranged along a circumferential direction of the lower side wall. Each groove has an arc shape such that the plurality of grooves concentrate a gas when the gas contacts the plurality of grooves. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]      FIG. 1  is a cross-sectional view illustrating the entire configuration of an epitaxial growth apparatus according to an embodiment of the present invention. 
           [0012]      FIG. 2  is an exploded perspective view illustrating the configuration of a reaction chamber according to the embodiment of the present invention. 
           [0013]      FIG. 3  is an exploded perspective view illustrating the outer configuration of the reaction chamber according to the embodiment of the present invention. 
           [0014]      FIG. 4  is a perspective cross-sectional view illustrating the configuration of a ceiling portion according to the embodiment of the present invention. 
           [0015]      FIG. 5  is a diagram schematically illustrating the inner configuration of a side wall according to the embodiment of the present invention. 
           [0016]      FIG. 6  is a cross-sectional view illustrating a reactant gas supply path according to the embodiment of the present invention. 
           [0017]      FIGS. 7A and 7B  are diagrams schematically illustrating the reactant gas supply path according to the embodiment of the present invention. 
           [0018]      FIGS. 8A and 8B  are perspective views illustrating an example of a rectification plate according to the embodiment of the present invention. 
           [0019]      FIG. 9  is a partial cross-sectional view illustrating an example of a susceptor ring according to the embodiment of the present invention. 
           [0020]      FIG. 10  is a partial cross-sectional view illustrating another example of the susceptor ring according to the embodiment of the present invention. 
           [0021]      FIG. 11  is a plan view illustrating an example of a susceptor according to the embodiment of the present invention. 
           [0022]      FIG. 12  is a plan view illustrating another example of the susceptor according to the embodiment of the present invention. 
           [0023]      FIG. 13  is a diagram schematically illustrating the configuration of a susceptor support according to the embodiment of the present invention. 
           [0024]      FIG. 14  is a perspective view illustrating a susceptor shaft according to the embodiment of the present invention. 
           [0025]      FIG. 15  is a perspective view illustrating an example of a substrate lift according to the embodiment of the present invention. 
           [0026]      FIG. 16  is a perspective cross-sectional view illustrating an example of a gas discharge tube according to the embodiment of the present invention. 
           [0027]      FIG. 17  is a perspective view illustrating an example of an upper reflector according to the embodiment of the present invention. 
           [0028]      FIG. 18  is a plan view illustrating an example of a lower reflector according to the embodiment of the present invention. 
           [0029]      FIG. 19  is a graph illustrating results of examples and comparative examples. 
           [0030]      FIG. 20  is a perspective cross-sectional view illustrating the configuration of a ceiling portion of an epitaxial growth apparatus according to the related art. 
           [0031]      FIG. 21  is an exploded perspective view illustrating the outer configuration of a reaction chamber of the epitaxial growth apparatus according to the related art. 
           [0032]      FIG. 22  is a plan view illustrating an example of an upper reflector of the epitaxial growth apparatus according to the related art. 
           [0033]      FIG. 23  is a plan view illustrating an example of a lower reflector of the epitaxial growth apparatus according to the related art. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0034]    Hereinafter, an epitaxial growth apparatus according to an embodiment of the present invention and a film forming method using epitaxial growth which is performed using the epitaxial growth apparatus will be described. 
       Configuration of Epitaxial Growth Apparatus 
       [0035]    First, the configuration of an epitaxial growth apparatus  1  according to the embodiment of the present invention will be schematically described.  FIG. 1  is a cross-sectional view illustrating the entire configuration of the epitaxial growth apparatus  1 .  FIG. 2  is an exploded perspective view illustrating the configuration of a reaction chamber  2  of the epitaxial growth apparatus  1 .  FIG. 3  is an exploded perspective view illustrating the outer configuration of the reaction chamber  2  of the epitaxial growth apparatus  1 . 
         [0036]    The epitaxial growth apparatus  1  is a film forming apparatus that enables, for example, a film of silicon to epitaxially grow on a substrate W. 
         [0037]    The epitaxial growth apparatus  1  includes a reaction chamber  2 . The reaction chamber  2  includes a susceptor  3  on which the substrate W. is mounted, a side wall  4 , and a ceiling  5 . 
         [0038]    The susceptor  3  is a plate-like member having a circular shape when seen from the upper side and has a size slightly larger than the substrate W. The susceptor  3  is provided with a substrate concave portion  3   a  on which the substrate W is mounted. The susceptor  3  is supported by a susceptor support  6  having plural arms. 
         [0039]    The susceptor support  6  lifts up and down the susceptor  3  while supporting the susceptor  3 . The lifting range of the surface of the susceptor  3  on which the substrate W is mounted ranges from a film-forming position P 1  at which a film is formed on the substrate W on the susceptor  3  to a substrate-carrying position P 2  at which the substrate W is put in and out of the epitaxial growth apparatus  1 . The susceptor support  6  is configured to enable the susceptor  3  and the substrate W to rotate by rotating about the axis of the susceptor support  6  at the film-forming position P 1 . 
         [0040]    An annular susceptor ring  7  is disposed around the susceptor  3  at the film-forming position P 1 . Although details will be described later, the susceptor ring  7  includes a first ring  11  and a second ring  12  placed on the first ring  11 . The susceptor ring  7  is supported by a flange portion  13  disposed in the side wall  4  of the reaction chamber  2 . 
         [0041]    The ceiling portion  5  includes a ceiling plate  21  and a support  22  supporting the ceiling plate  21 . The ceiling plate  21  has permeability and is configured to heat the inside of the reaction chamber  2  by transmitting heat from heating means  23  (for example, a halogen lamp) disposed above the outside of the ceiling plate  21  and an upper reflector  26 . That is, the epitaxial growth apparatus  1  according to this embodiment is a cold wall type epitaxial growth apparatus. In this embodiment, the ceiling plate  21  is formed of quartz. 
         [0042]    The support  22  supporting the ceiling plate  21  has an annular shape. The ceiling plate  21  is fixed to an end, which is close to the substrate W, of an opening  24  inside the inner edge of the support  22 . An example of the fixing method is a welding method. 
         [0043]    The side wall  4  includes an annular upper side wall  31  and an annular lower side wall  32 . The flange portion  13  is disposed on the inner circumference of the lower side wall  32 . A substrate carrying port  30  is disposed below the flange portion  13 . The upper side wall  31  has a slope portion corresponding to a slope portion outside of a protrusion  25  of the support  22  on the top surface thereof. The support  22  is disposed on the slope of the upper side wall  31 . 
         [0044]    In the top surface of the lower side wall  32 , a part of the outer circumference thereof is cut out an a region in which the cutout is not formed serves as a mounting surface  33  on which the upper side wall  31  is mounted. A first concave portion  34  is formed in the lower side wall  32  by the cutout of the lower side wall  32 . That is, the first concave portion  34  is a concave portion formed in a part, in which the mounting surface  33  is not formed, of the top surface of the lower side wall  32 . In the upper side wall  31 , a first convex portion  36  is formed at the position corresponding to the first concave portion  34  at the time of mounting the upper side wall on the lower side wall  32  so as to correspond to the shape of the first concave portion  34  and to form a gap  35  between the first concave portion  34  and the first convex portion. The gap  35  between the first convex portion  36  and the first concave portion  34  serves as a reactant gas supply path  41  (supply path). Details of the reactant gas supply path  41  will be described later. 
         [0045]    In the region opposed to the first concave portion  34  of the lower side wall  32 , a part of the outer circumferential portion of the top surface of the lower side wall  32  is cut out to form a second concave portion  37 . In the upper side wall  31 , a second convex portion  39  is formed at the position corresponding to the second concave portion  37  at the time of mounting the upper side wall on the lower side wall  32  so as to correspond to the shape of the second concave portion  37  and to form a gap  38  between the second concave portion  37  and the second convex portion. A gas discharge path  42  is formed by the second concave portion  37  and the second convex portion  39  of the upper side wall  31 . 
         [0046]    In this way, the reactant gas supply path  41  and the gas discharge path  42  face each other in the reaction chamber  2  and the reactant gas in the reaction chamber  2  flows over the substrate W in the horizontal direction. 
         [0047]    A purge hole  44  through which a purge gas is discharged is formed in a wall surface  43  constituting the second concave portion  37  of the lower side wall  32 . The purge hole  44  is formed below the flange portion  13 . In that the purge hole  44  is formed in the wall surface  43  constituting the second concave portion  37 , the purge hole  44  communicates with the gas discharge path  42 . Therefore, both the reactant gas and the purge gas are discharged through the gas discharge path  42 . 
         [0048]    An annular platform  45  is disposed on the bottom surface side of the lower side wall  32  of the side wall  4  and the side wall  4  is placed on the platform  45 . 
         [0049]    An annular clamping portion  51  is disposed on the outer circumference sides of the ceiling portion  5 , the side wall  4 , and the platform  45 , and the annular clamping portion  51  clamps and supports the ceiling portion  5 , the side wall  4 , and the platform  45 . The clamping portion  51  is provided with a supply-side communication path  52  communicating with the reactant gas supply path  41  and a discharge-side communication path  53  communicating with the gas discharge path  42 . A gas introduction tube  55  is inserted into the supply-side communication path  52 . A gas discharge tube  58  is inserted into the discharge-side communication path  53 . 
         [0050]    A reactant gas introducing portion  54  is disposed outside the clamping portion  51 , and the reactant gas introducing portion  54  and the supply-side communication path  52  communicate with each other. In this embodiment, a first source gas and a second source gas are introduced from the reactant gas introducing portion  54 . The second source gas also serves as a carrier gas. A mixture of three or more types of gases may be used as the reactant gas. A rectifying plate  56  is disposed in the joint of the supply-side communication path  52  and the reactant gas introducing portion  54  so as to be perpendicular to the gas flow channel. The rectifying plate  56  is provided with plural holes  56   a  in a line along the circumferential direction, and the first source gas and the second source gas are mixed and rectified by causing the reactant gas to pass through the holes  56   a . A gas discharge portion  57  is disposed outside the clamping portion  51 . The gas discharge portion  57  is disposed at a position facing the reactant gas introducing portion  54  with the center of the reaction chamber  2  interposed therebetween. 
         [0051]    An apparatus bottom portion  61  is disposed in the lower part of the inner circumference side of the platform  45 . Another heating means  62  and a lower reflector  65  are disposed outside the apparatus bottom portion  61  and the substrate W can be heated from the lower side. 
         [0052]    The center of the apparatus bottom portion  61  is provided with a purge gas introducing portion (not shown) through which the axis portion  63  of the susceptor support  6  is inserted and the purge gas is introduced. The purge gas in introduced into a lower reaction chamber part  64  formed by the apparatus bottom portion  61 , the lower side wall  32 , and the platform  45  from purge gas introducing means not shown and disposed in the purge gas introducing portion. The purge hole  44  communicates with the lower reaction chamber part  64 . 
       Summary of Film Forming Method Using Epitaxial Growth 
       [0053]    A film forming method using the epitaxial growth apparatus according to this embodiment will be described below. 
         [0054]    First, the susceptor  3  is moved to the substrate-carrying position P 2 , a substrate W is put in from the substrate carrying port  30 , and the susceptor  3  is moved to the film-forming position P 1 . For example, a silicon substrate with a diameter of 200 mm is used as the substrate W. Then, the substrate is heated from the standby temperature (for example, 800° C.) to the growth temperature (for example, 1100° C.) by the use of the heating means  23  and  62 . The purge gas (for example, hydrogen) is introduced into the lower reaction chamber portion  64  from the purge gas introducing portion. The reactant gas (for example, trichlorosilane as the first source gas and hydrogen as the second source gas) is introduced into the reaction chamber  2  through the reactant gas supply path  41  from the reactant gas introducing portion  54 . The reactant gas forms a boundary layer on the surface of the substrate W and a reaction occurs in the boundary layer. Accordingly, a silicon film is formed on the substrate W. The reactant gas is discharged from the gas discharge path  42  communicating with the reaction chamber  2 . The purge gas is discharged to the gas discharge path  42  through the purge hole  44 . After the epitaxial growth ends in this way, the temperature falls to the standby temperature and the substrate W is taken out and is moved to another chamber of a semiconductor manufacturing apparatus. 
       Details of Film Forming Method Using Epitaxial Growth Apparatus 
       [0055]    Details of the constituent members of the epitaxial growth apparatus  1  according to this embodiment and details of the film forming method according to this embodiment will be described below. 
         [0056]      FIG. 4  is a perspective cross-sectional view illustrating the configuration of the ceiling portion  5  in this embodiment. As shown in the drawing, the inner edge of the support  22  supporting the ceiling plate  21  has a diameter slowing decreasing toward the substrate. The ceiling plate  21  is fixed to an end portion of the inner edge facing the substrate W. When the support  22  is viewed from the rear side (bottom side), the inner circumferential portion protrudes to form a protrusion  25 . The protrusion  25  is formed to have a diameter slowly decreasing in the protruding direction. In this way, the support  22  includes two slope portions. That is, the support  22  supports the ceiling plate  21  from the upper side and the outer side of the circumferential edge at the circumferential edge of the ceiling plate  21 . On the other hand,  FIG. 20  is a perspective cross-sectional view illustrating an example of a ceiling portion  5 ′ of an epitaxial growth apparatus according to the related art. As shown in the drawing, in the ceiling portion  5 ′ of the apparatus according to the related art, a support  22 ′ supports a ceiling plate  21 ′ in the same plane as the ceiling plate  21 ′ at the circumferential edge of the ceiling plate  21 ′, and the support  22 ′ has a shape having a substantially rectangular corner  25 ′. 
         [0057]    In this way, in this embodiment, since the support  22  is formed in such a shape on which a stress is less concentrated than that in the related art, the distance H between the substrate W and the ceiling plate  21  can be reduced, that is, less than 10 mm. 
         [0058]    Specifically, most infrared rays from the heating means  23  passes through the ceiling plate  21  ( 21 ′), but the ceiling plate  21  ( 21 ′) absorbs radiant heat from the susceptor  3  or the substrate W. The absorbed heat is input to the support  22  ( 22 ′) through the joint with the support  22  ( 22 ′) from the ceiling plate  21  ( 21 ′). Here, when the distance H between the substrate W and the ceiling plate  21  ( 21 ′) is reduced, the amount of radiant heat absorbed increases and the amount of heat input to the support  22  ( 22 ′) increases. Therefore, when the support  22 ′ has a substantially rectangular corner  25 ′ as in the ceiling portion  5 ′ in the related art, a stress may be concentrated on the corner  25 ′ to generate cracks or the like. 
         [0059]    On the other hand, in this embodiment, by forming the protrusion  25  in the support  22  and supporting the ceiling plate  21  from the upper side and the outer side of the circumferential edge at the circumferential edge of the ceiling plate  21 , the ceiling plate  21  can be supported to the substrate side without forming the corner ( 25 ′) on which a stress is easily concentrated as small as possible. 
         [0060]    In this embodiment, since the distance between the ceiling place  21  and the substrate W is reduced to narrow the boundary layer as described above, the reactant gas is likely to escape to the outside of the substrate W and the film thickness distribution of the substrate may not be uniformized well, which should be preferably prevented. Accordingly, in this embodiment, a guide portion is disposed in the reactant gas supply path  41  to uniformize the gas flow, as described below. 
         [0061]    The guide portion disposed in the reactant gas supply path  41  will be described below in detail with reference to  FIGS. 5 to 7B . As described above, the reactant gas supply path  41  is formed by the first concave portion  34  of the lower side wall  32  and the first convex portion  36  of the upper side wall  31  and communicates with the reactant gas introducing portion  54  through the gas introducing tube  55  in the supply-side communication path  52 . The reactant gas supply path  41  includes a first supply path  71  extending in the direction (horizontal direction) corresponding to the gas introduction direction from the reactant gas introducing portion  54 , a second supply path  72  communicating with the first supply path  71  and extending the direction (vertical direction) perpendicular to the gas introduction direction, and a third supply path  73  communicating with the second supply path  72  and extending in the direction (horizontal direction) parallel to the gas introduction direction. The third supply path  73  communicates with the reaction chamber  2 . That is, the reactant gas supply path  41  is formed in a step shape ascending from the supply-side communication path  52  which is the entrance of the reactant gas to the exit which is the exit of the reactant gas and is connected to the reaction chamber  2 . 
         [0062]    Here, since the second supply path  72  extends in the vertical direction as described above, the gas introduced from the reactant gas introducing portion comes in contact with a wall surface  74  of the second supply path  72  facing the reactant gas introducing portion  54 . Accordingly, the reactant gas is diffused and the mixing property of the reactant gas is improved. That is, the second supply path  72  serves as a mixing chamber of the reactant gas. In this case, a groove  75  extending in the vertical direction is formed in the wall surface  74  of the second supply path  72  in this embodiment so as for the reactant gas no to stay in the second supply path  72 , and the groove  75  serves as a guide portion. Since the groove  75  is formed in this way, the gas diffused by contact with the wall surface  74  of the second supply path  72  can easily flow into the third supply path  73 , can be rectified along the groove  75  to improve the rectilinear flowing property of the reactant gas, thereby suppressing diffusion of the reactant gas when the reactant gas flows in the reaction chamber  2 . 
         [0063]    The groove  75  will be described below in detail. Plural grooves  75  are continuously formed as a concave portion in the entire surface of the wall surface  74  of the second supply path  72 . As shown in  FIG. 7B , the grooves  75  as the concave portion are curved in the width direction of the grooves in this embodiment, each groove  75  as an arc shape when viewed from the top side. Since the groove  75  is curved in the width direction, the reactant gas is not likely to be diffused (is likely to be concentrated) when the reactant gas comes in contact with the bottom of the grooves  75  of the wall surface  74 , and is not likely to be diffused to the outside of the substrate W when the reactant gas flows in the reaction chamber  2 . When the depth of the grooves  75  is excessively large, the diffusion can be suppressed but the first source gas and the second source gas in the reactant gas is not likely to be mixed. In an embodiment of the present invention, that the depth of the grooves  75  is preferably set to a range of 1 mm to 5 mm and more preferably 3 mm. 
         [0064]    The grooves  75  are formed toward the center c in the in-plane direction of the lower sidewall  32 . That is, the grooves  75  are arranged along the circumferential direction of the lower side wall  32 . By arranging the grooves in this way, the rectification property can be enhanced so that the horizontal component in the flow direction of the reactant gas guide by the grooves  75  and introduced into the reaction chamber  2  corresponds to the horizontal component in the direction extending from the center of the opening of the reactant gas supply path  41  facing the reactant chamber  2  to the center of the reaction chamber  2 , thereby suppressing diffusion of the reactant gas in the reaction chamber  2 . 
         [0065]    The grooves  75  are formed at positions at which the center in the width direction of each groove  75  substantially agrees (corresponds) to the center of each hole  56   a  of the rectifying plate  56  disposed in the reactant gas introducing portion  54 . That is, in this embodiment, the number of grooves  75  in the wall surface  74  is equal to the number of holes  56   a . Accordingly, since the reactant gas rectified by the rectifying plate  56  flows in the grooves  75 , the rectification performance is further enhanced to improve the rectilinear flowing property of the reactant gas. 
         [0066]    In this embodiment, the grooves  75  are formed in the entire surface of the wall surface  74  of the second supply path  72 , but may be formed at least in an end portion of the wall surface  74  of the second supply path  72 . The end portion means a portion corresponding to the extreme end region of plural regions into which the holes of the rectifying plate  56  are divided. For example, in the example shown in  FIGS. 7A and 7B , the rectifying plate  56  are divided into three regions  81  and the grooves  75  have only to be formed to correspond to the holes of the extreme end regions  82  and  83 . Since the reactant gas is likely to escape to the outside of the substrate W as described above, it is particularly preferable that the grooves  75  are formed to enhance the rectilinear flowing property of the reactant gas in the end portions of the reactant gas supply path  41 . In this case, by forming the grooves  75  serving as a guide in the form of a concave portion, it is possible to easily obtain such an effect. For example, when a rectifying member is separately disposed in the second supply path  72 , a problem may occur in the mixing property of the reactant gas or the manufacturing cost. However, such as problem is solved by forming the grooves  75  as a concave portion as in this embodiment. 
         [0067]      FIG. 8A  has  8 B are perspective views illustrating an example of the rectifying plate  56 . As shown in the drawings, the rectifying plate  56  has only to be ready to follow the pattern of the grooves  75 . The opening ratio of the rectifying plate  56  is preferably determined to be an optimal value in consideration of incidental equipment such as a scrubber or the shape, the length, and the like of an external pipe, as well as the viewpoint of growth rate. 
         [0068]    In this embodiment, since the distance between the ceiling plate  21  and the substrate W is reduced to narrow the boundary layer as described above, the reactant gas may easily flow into the lower part of the reaction chamber  2  and the temperature distribution of the substrate W may not be likely to be uniformized. As a result, the degradation in the film thickness distribution or the film quality at the time of forming a thick film (for example, distribution of resistivity or occurrence of crystal defects) may be caused. In this embodiment, in order to prevent these problems, the susceptor ring  7  is formed by two members. This point will be described below. 
         [0069]    As enlarged in  FIG. 9 , the first ring  11  of the susceptor ring  7  is disposed spaced apart from the outer circumference of the susceptor and a stepped portion  91  having a low top surface is formed in the inner circumference of the first ring. The second ring  12  is placed on the stepped portion  91  and the second ring  12  is formed to face a clearance portion  92  formed between the first ring  11  and the susceptor  3 , that is, to protrude to the clearance portion  92 . The second ring  12  is disposed so that the top surface thereof is flush with the top surface of the susceptor  3 . By making the top surface of the second ring  12  flush with the top surface of the susceptor  3  in this way, the reactant gas which is maintained in a state mixed and rectified in the reactance gas supply path  41  or the like can be smoothly supplied to the substrate W without lowering the flow rate as much as possible. The top surface of the susceptor  3  mentioned herein means a top surface of the susceptor  3  in a region in which the substrate concave portion  3   a  (see  FIGS. 1 ,  2 ,  11 , and  12 ) is not formed. The second ring  12  in this embodiment is formed of silicon carbide in consideration of thermal conductivity. 
         [0070]    By forming the second ring  12  and the first ring  11  out of different members in this way, the susceptor ring  7  can be constructed with more accuracy. That is, the distance between the susceptor ring  7  and the susceptor  3  can be reduced to the limit and it is thus possible to reduce flowing of the reactant gas to the rear side of the substrate W, that is, to the bottom side  64  of the reaction chamber and to uniformize the temperature distribution of the substrate W. As a result, according to this embodiment, the film thickness distribution of the film quality distribution of the formed film is uniformized. 
         [0071]    By providing two members of the first ring  11  and the second ring  12 , the conduction of heat between the first ring  11  and the second ring  12  can be suppressed more than the case where the first ring  11  and the second ring  12  are formed of a single member. 
         [0072]    By causing the second ring  12  to face the clearance portion  92  in this way, it is possible to reduce leakage of the reactant gas from between the susceptor ring  7  and the susceptor  3  toward the lower side at the time of forming a film and thus the flow of the reactant gas is not likely to be disturbed. Since leakage of the reactant gas to the lower side can be reduced, it is possible to reduce particles. 
         [0073]    In this case, the second ring  12  is thinner than the first ring  11 . Accordingly, it is possible to suppress heat loss from the susceptor  3  by radiation. Since the second ring  12  is thinner, it is possible to reduce the amount of heat for maintaining (pre-heating) the second ring  12  at a predetermined high temperature. In another embodiment, when the first ring  11  is formed of a material having small thermal conductivity, the first ring  11  serves as a thermal insulator, thereby further enhancing the above-mentioned effect. 
         [0074]    In this embodiment, the second ring  12  is configured to face the clearance portion  92 , but the invention is not limited to this configuration. The susceptor ring  7  can be constructed with high precision as long as the second ring  12  is placed at least on the stepped portion  91  of the first ring  11 . Accordingly, the distance between the susceptor ring  7  and the susceptor  3  can be reduced to the limit and it is thus possible to reduce flowing of the reactant gas to the rear side of the substrate W and to uniformize the temperature distribution of the substrate. 
         [0075]    In this embodiment, since the distance between the ceiling plate  21  and the substrate W is reduced to narrow the boundary layer, the ceiling surface of the ceiling plate  21  can be easily coated with the reactant gas. When the ceiling surface is coated, the ceiling surface is bedimmed and thus a film may not be satisfactorily formed using a cold wall type epitaxial growth apparatus that is heated using heating means  23  via the ceiling plate  21 . On the contrary, in this embodiment, by forming the grooves  75  in the wall surface of the reactant gas supply path  41  and forming the susceptor ring  7  out of two members as described above, the reactant gas is not likely to stay in the reaction chamber  2  and it is thus possible to suppress attachment of a coating material. As a result, it is possible to form a film continuously and satisfactorily. 
         [0076]      FIG. 10  shows a modification example of the susceptor ring  7 . This modification example is different from the embodiment shown in  FIG. 9 , in that a second ring  12 A is disposed to cover a clearance portion  92 A. In this modification example, a first ring  11 A is placed on a flange portion  13 A of a side wall  32 A. The second ring  12 A is placed on a stepped portion  91 A of the first ring  11 A and the inner circumference faces the outer circumference of the susceptor  3 A. 
         [0077]    In this modification example, since the second ring  12 A is disposed to cover the clearance portion  92 A, it is possible to further suppress flowing of the reactant gas flowing into the reaction chamber  2 A to the lower reaction chamber part  64 A. Here, in order to prevent the second ring  12 A from blocking heating of the susceptor  3 A from the heating means  23  not shown in  FIG. 10 , it is preferable that the overlap area of the second ring  12 A and the susceptor  3 A be small. 
         [0078]    In this modification example, the thickness of the second ring  12 A is preferably set to, for example, a range of 0.5 mm to 2 mm and more preferable about 0.8 mm. By setting this thickness, it is possible to suppress heat loss due to radiation from the susceptor  3 A to the second ring  12 A as much as possible. 
         [0079]      FIGS. 11 and 12  are plan views illustrating examples of the susceptor  3  according to an embodiment of the present invention. As shown in the drawings, susceptors  3 A and  3 B are provided with lift-pin through-holes  110 A and  110 B through which lift pins  123  (see  FIG. 13 ) pass. As shown in  FIG. 12 , plural through-holes  111 B may be formed. A problem that gas therebetween may be let out at the time of placing the substrate on the susceptor and the substrate W slides in the horizontal direction can be solved by the through-holes  111 B. When this susceptor  3 B is used, the uniformization in film thickness distribution or resistivity distribution of the substrate W is superior to the case where the susceptor  3 A is used. This is more marked when the diameter of the through-holes  111 B becomes smaller and the number of through-holes  111 B becomes larger. It is preferable that the opening ratio be more than 4% and it is more preferable that the through-holes  111 B be formed around the substrate concave portion  3 Ba of the susceptor as well as in the substrate concave portion. 
         [0080]      FIGS. 13 to 16  show examples of the susceptor support  6 . As shown in  FIG. 13 , the susceptor support  6  includes a susceptor shaft  121 , a substrate lift  122 , and lift pins  123 . The susceptor  3  is supported by three arms of the susceptor shaft  121 . Three arms of the substrate life  122  are provided with pedestals  124  having a concave portion on which the lower end of the corresponding lift pin  123  is placed, respectively. The axis portion of the substrate lift  122  is formed in a cylindrical shape, and the axis portion of the susceptor shaft  121  can be inserted into the axis portion of the substrate lift  122 . 
         [0081]    In this embodiment, the arms in the susceptor support  6  have a thickness smaller than in the related art. Accordingly, since the influence of the susceptor support  6  can be reduced at the time of heating the substrate W on the susceptor  3  by the use of the heating means  62 , it is possible to uniformize the temperature distribution of the susceptor  3 . The detailed configuration and the lifting operation of the susceptor support  6  in the embodiment are the same as in the susceptor apparatus described in Pamphlet of International Publication WO2013/005481 filed by the applicant of the present invention. However, the susceptor apparatus described the Pamphlet of International Publication includes a single susceptor shaft (platform shaft), but the susceptor support  6  in this embodiment includes three susceptor shafts (arms)  121 . 
         [0082]      FIG. 16  is a perspective cross-sectional view illustrating an example of the gas discharge tube  58  in this embodiment. As shown in the drawing, the gas discharge tube  58  is formed so that the opening is narrowed toward the center from the reaction chamber  2  to the gas discharge portion  57 . Accordingly, exhaust is rectified at the center, thereby improving the exhaust efficiency. 
         [0083]      FIG. 21  is an exploded perspective view illustrating the outer configuration of the reaction chamber  2  in the epitaxial growth apparatus according to the related art. As shown in the drawing, comparing the gas introduction tube  55  and the gas discharge tube  58  with the gas introduction tube  55 ′ and the gas discharge tube  58 ′, finished portions at the central portions thereof are removed in this embodiment. Accordingly, the flow of gas affecting the film thickness distribution is smoothed. 
         [0084]    The reactant gas flows into the lower reaction chamber part  64  when the opening ratio of the gas discharge path  42  and the purge hole  44  is excessively large, and the purge gas affects the film forming process in the reaction chamber  2  when the opening ratio is excessively small. Accordingly, the openings thereof are formed so that the opening ratios have the optimal values. 
         [0085]      FIG. 17  is a perspective view illustrating an example of the upper reflector  26  according to the embodiment of the present invention. As shown in drawing, the upper reflector  26  includes slope portions  26   a  reflecting hear waves from the heating means  23  to the center of the reaction chamber  2  and flat portions  26   b  reflecting heat waves from the heating means  23  in the vertically-falling direction. On the other hand,  FIG. 22  is a perspective view illustrating an example of the upper reflector  26 ′ in the epitaxial growth apparatus according to the related art. As shown in the drawing, the upper reflector  26 ′ in the related art includes slope portions  26   a ′ and flat portions  26   b ′, but is different from the upper reflector  26  according to the embodiment of the present invention in the arrangement of the slope portions  26   a . Specifically, the upper reflector  26  according to the embodiment of the present invention has an arrangement in which a slope portion is added to the center of a flat portion  26   b ′ of the upper reflector  26 ′ in the related art. In this way, by arranging the slope portions  26   a  and the flat portions  26   b  so that the area ratio of the slope portions  26   a  and the flat portions  26   b  is a predetermined ratio and the distribution of the slope portions  26   a  and the flat portions  26   b  is not biased, the uniformization of the temperature distribution of the substrate W is achieved. 
         [0086]      FIG. 18  is a perspective view illustrating an example of the lower reflector  65  according to the embodiment of the present invention.  FIG. 23  is a perspective view illustrating an example of the lower reflector  65 ′ in the epitaxial growth apparatus according to the related art. Similarly to the upper reflector  26 , the lower reflector  65  includes slope portions  65   a  reflecting heat waves from the heating means  62  to the center of the reaction chamber  2  and flat portions  65   b  reflecting heat waves from the heating means  62  in the vertically-rising direction, and has an arrangement in which a slope portion is added to the center of a flat portion  65   b ′ of the lower reflector according to the related art. In this way, by arranging the slope portions  65   a  and the flat portions  65   b  so that the area ratio of the slope portions  65   a  and the flat portions  65   b  is a predetermined ratio and the distribution of the slope portions  65   a  and the flat portions  65   b  is not biased, the uniformization of the temperature distribution of the substrate W is achieved. 
         [0087]    In the epitaxial growth apparatus according to this embodiment, since the support  22  supports the ceiling plate  21 , the distance H between the ceiling surface of the central portion of the ceiling surface of the central portion of the ceiling plate  21  facing the reaction chamber and the substrate W can be set to be less than 10 mm. Accordingly, the epitaxial growth apparatus  1  according to this embodiment can prevent the boundary layer formed by the reactant gas flowing between the ceiling plate  21  and the susceptor  3  from spreading toward the ceiling and thus the boundary layer is narrowed. Then, since the gas flow rate in the boundary layer increases, the gas density increases as a result and it is thus possible to enhance the reaction efficiency on the surface of the substrate W. Accordingly, in the epitaxial growth apparatus  1 , it is possible to enhance the growth rate. 
         [0088]    In the embodiment of the present invention, the distance H between the ceiling plate  21  and the substrate W is less than 10 mm, and it is preferable that the distance H between the ceiling plate  21  and the substrate W be less than 10 mm and the distance from the film formed on the substrate W to the ceiling plate  21  be equal to or more than 1 mm. By setting this range, it is possible to smooth the gas flow of the reactant gas while forming the boundary layer. 
         [0089]    That is, in the reaction chamber  2  of this embodiment, by setting the distance between the substrate W and the ceiling plate  21  to be smaller than that in the related art (about 20 mm in the related art), it is possible to narrow the boundary layer to enhance the reaction efficiency on the surface of the substrate and thus to raise the growth rate. 
       EXAMPLES 
       [0090]    The invention will be described below in detail with reference to examples. 
       Example 1 
       [0091]    Epitaxial growth was carried out under the following growth conditions by the use of an epitaxial growth apparatus  1 A (in which the distance H between the surface the substrate W and the ceiling plate  21  is 9.27 mm) employing the susceptor ring shown in  FIG. 10 . 
         [0092]    Amount of first source gas (trichlorosilane): 8.5 SLM 
         [0093]    Amount of purge gas (hydrogen): 15.0 SLM 
         [0094]    Growth time: 600.0 seconds 
         [0095]    Growth temperature: 1100.0° C. 
         [0096]    Rotation speed: 20.0 RPM 
       Example 2 
       [0097]    Epitaxial growth was carried out under the same conditions as in Example 1, except that the amount of the first source gas was changed to 13.5 SLM. 
       Example 3 
       [0098]    Epitaxial growth was carried out under the same conditions as in Example 1, except that the amount of the first source gas was changed to 17.0 SLM. 
       Comparative Example 1 
       [0099]    Epitaxial growth was carried out under the same conditions as in Example 1 using an epitaxial growth apparatus (in which the distance H between the surface of a substrate W and the ceiling plate  21  was 20 mm, there was no groove  75 , and the susceptor ring was formed of a single member) according to the related art, except the rotation speed was changed to 35.0 RPM. 
       Comparative Example 2 
       [0100]    Epitaxial growth was carried out under the same conditions as in Example 2 using an epitaxial growth apparatus (in which the distance H between the surface of a substrate W and the ceiling plate  21  was 20 mm, there was no groove  75 , and the susceptor ring was formed of a single member) according to the related art, except the rotation speed was changed to 35.0 RPM. 
       Comparative Example 3 
       [0101]    Epitaxial growth was carried out under the same conditions as in Example 3 using an epitaxial growth apparatus (in which the distance H between the surface of a substrate W and the ceiling plate  21  was 20 mm, there was no groove  75 , and the susceptor ring was formed of a single member) according to the related art, except the rotation speed was changed to 35.0 RPM. 
         [0102]    The film growth rate in the examples and the comparative examples was detected. The relationship between the detected growth rates and the first source gas is shown in  FIG. 19 . 
         [0103]    As shown in  FIG. 19 , by employing the epitaxial growth apparatus  1 A according to the embodiment of the present invention, the growth rate was improved by 50% and the improvement of the growth rate increased when the amount of the first source gas increased. Therefore, the growth rate was enhanced by using the epitaxial growth apparatus according to this embodiment.