Abstract:
A cover member ( 40 ) of an apparatus ( 1 ) for producing single crystals is provided with a projection ( 41 ) generally in the center. The projection ( 41 ) is disposed so as to protrude toward the inside of a crucible main body ( 30 ) through a cover member opening ( 40   a ). A seed crystal ( 10 ) is disposed between a supporting portion ( 432 ) and a contact surface ( 41   a ) of the projection ( 41 ) which is inserted into a guide opening ( 43   h ). The apparatus ( 1 ) for producing single crystals is configured such that the contact surface ( 41   a ) presses the entire back surface of the seed crystal ( 10 ), said back surface being on the reverse side of the crystal growth surface of the seed crystal ( 10 ), against the projection ( 41 ) when a screw thread ( 41   s ) that is formed on the projection ( 41 ) is screwed to a thread groove ( 43   g ) that is formed on an engaging portion ( 431 ).

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to a single crystal manufacturing apparatus employing a modified Rayleigh&#39;s method. 
       BACKGROUND ART 
       [0002]    Conventionally, there is disclosed a method of causing a support portion provided at a capping member to mechanically retain a seed crystal without a need to adhere the seed crystal to the capping member (for example, refer to Patent Literature 1), in a single crystal manufacturing apparatus of obtaining a bulky single crystal by sublimating a sublimation raw material including silicon carbide and then growing a silicon carbide single crystal on a silicon carbide single crystal substrate (referred to as a seed crystal). 
         [0003]    In a technique disclosed in Patent Literature 1, a protection member is disposed between a back face of the seed crystal and the capping member, and a gap for temperature control is formed between a back face side of the protection member and the capping member. A growth velocity of a single crystal can be controlled by adjusting intervals of the gap. 
       CITATION LIST 
     Patent Literature 
       [0004]    Patent Literature 1: Japanese Patent No. 4275308 
       SUMMARY OF INVENTION 
       [0005]    However, the conventional single crystal manufacturing apparatus described above has entailed the following problem. That is, since a thermal expansion coefficient of a graphite (carbon) crucible is greater than that of a seed crystal (silicon carbide), a gap is produced between a support portion and an outer edge of the seed crystal. Therefore, there will be a concern about entry of a sublimation gas produced when a sublimation raw material sublimates in a space between the back face of the seed crystal provided for temperature control (the back face of the protection member) and the capping member. 
         [0006]    In addition, since the seed crystal is not adhered to the support portion, if a gap on the back face side is heterogeneous due to a warp of an error level of the order of some microns to some tens of microns existing in advance in seed crystal, there has been a case in which the quality of the single crystal grown may be heterogeneous. Further, if a diameter of the seed crystal increases, since the seed crystal is likely to warp, cracking of a protection layer on the back face of the seed crystal or lowering of the quality of the single crystal has been likely to significantly occur. 
         [0007]    Accordingly, it is an object of the present invention to provide a single crystal manufacturing apparatus that is capable of preventing the damage to a seed crystal or the lowering of quality of the single crystal in a single crystal manufacturing apparatus of such a type that the seed crystal is not to be adhered to the capping member. 
         [0008]    To solve the above problem, the present invention has following feature. A feature of the present invention is summarized as a single crystal manufacturing apparatus (single crystal manufacturing apparatus  1 ) comprising: a crucible main body (crucible main body  30 ) that having a substantially cylindrical shape in which a bottom portion (bottom portion  30   b ) is formed at one end portion of the crucible main body and an opening portion (opening portion  30   u ) is formed at another end of the crucible main body, a sublimation raw material (sublimation raw material  20 ) being disposed at the bottom portion; and a capping member (capping member  40 ) that closes the opening portion, on which a seed crystal (seed crystal  10 ,  11 ) being disposed at a position facing the sublimation raw material, wherein the single crystal manufacturing apparatus sublimates the sublimation raw material and then recrystallizing a single crystal on the seed crystal, a guide portion (guide portion  43 ) having a conical face (conical face  43   a ) is mounted on the capping member, a diameter of the conical face being increased as going down in a growing direction of the single crystal, the capping member has a substantially columnar projection portion (projection portion  41 ) projecting inward of the crucible main body, a contacting face having a diameter that is equal to a diameter of the seed crystal or greater than the diameter of the seed crystal is formed at the projection portion, the guide portion has: an engagement portion (engagement portion  431 ) which has an aperture fitting to an outer diameter of the projection portion, and a guide opening portion (guide opening portion  43   h ) through which the projection portion is inserted; and a support portion (support portion  432 ) supporting the seed crystal that narrows at least a part of the guide opening portion formed in the engagement portion, a screw thread (screw thread  41   s ) is formed outside of the projection portion, a screw groove (screw groove  43   g ) screwed with the screw thread is formed at the engagement portion, the seed crystal is disposed between an end portion of the projection portion inserted through the guide opening portion and the support portion, and the screw thread formed at the projection portion is screwed with the screw groove formed at the engagement portion, whereby the contacting face is formed so as to compress an entire portion of aback face opposite to a crystalline growth face of the seed crystal against the projection portion. 
         [0009]    According to the single crystal manufacturing apparatus, the seed crystal is supported by means of the support portion which narrows at least the part of the guide opening portion formed at the engagement portion, and the screw thread formed at the projection portion is screwed with the screw groove formed at the engagement portion, whereby the contacting face is formed so as to compress the entire portion of the back face opposite to the crystal growth face in the seed crystal against the projection portion. 
         [0010]    Thus, in the single crystal manufacturing apparatus, since the seed crystal is not to be adhered to the support portion, the seed crystal can be prevented from being damaged due to a difference in stress exerted by a difference in thermal expansion coefficient between a capping member to which the seed crystal is mounted and the seed crystal itself. 
         [0011]    In addition, since an outer edge of the seed crystal is compressed against the support portion by means of the contacting face, gapping between the support portion and the outer edge of the seed crystal  10  can be prevented. Further, entry of the sublimation gas as a sublimation raw material between the support portion and the outer edge of the seed crystal can also be prevented. 
         [0012]    In the single crystal manufacturing apparatus, the full back face of the seed crystal is compressed against the contacting face, whereby warping of the seed crystal is corrected, cracking of the protection layer of the back face of the seed crystal can be prevented, and a single crystal of its homogenous quality can be produced. 
         [0013]    In the above feature of the present invention, a protection member may be disposed between the contacting face and the back face of the seed crystal. 
         [0014]    In the above feature of the present invention, the seed crystal may be curved so as to be convex in an opposite direction to the growing direction of the single crystal. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0015]    [ FIG. 1 ]  FIG. 1  is a sectional view illustrating an outline of a single crystal manufacturing apparatus according to an embodiment of the present invention. 
           [0016]    [ FIG. 2 ]  FIG. 2  is a sectional view illustrating a single crystal grown in the single crystal manufacturing apparatus according to the embodiment of the present invention. 
           [0017]    [ FIG. 3 ]  FIG. 3  ( a ) is a dissembled view showing a guide portion, a seed crystal, and a protection member in a dissembled manner in a capping member of the single crystal manufacturing apparatus, and  FIG. 3  ( b ) is an assembled view of the guide portion, the seed crystal, and the protection member that are assembled in the capping member of the single crystal manufacturing apparatus. 
           [0018]    [ FIG. 4 ]  FIG. 4  ( a ) is a dissembled view when another seed crystal is applied to the single crystal manufacturing apparatus, and  FIG. 4  ( b ) is a view illustrating a modification example of the seed crystal. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0019]    An embodiment of a single crystal manufacturing apparatus according to the embodiments of the present invention will be described with reference to the drawings. Specifically, a description will be given with respect to (1) Description of Configuration of Single Crystal Manufacturing apparatus, (2) Description of Configuration of Capping Member, (3) Functions/Advantageous Effects, (4) Modification Example of Seed Crystal, and (5) Other Embodiments. 
         [0020]    In the following description of the drawings, same or like constituent elements are designated by same or like reference numerals. However, it is to be noted that the drawings are merely schematic, and ratios of the respective dimensions or the like are different from actual ones. Therefore, specific dimensions or the like should be determined in consideration of the following description. In addition, in amongst the drawings as well, the constituent elements in which dimensional interrelationships or ratios are different from each other are included. 
       (1) Description of Configuration of Single Crystal Manufacturing Apparatus 
       [0021]    A configuration of the single crystal manufacturing apparatus of producing a silicon carbide single crystal, which is shown as an embodiment, will be described with reference to  FIG. 1  and  FIG. 2 .  FIG. 1  is a sectional view illustrating an outline of the single crystal manufacturing apparatus  1 .  FIG. 2  is a sectional view illustrating a state in which a single crystal is grown by means of the single crystal manufacturing apparatus  1  according to the embodiment of the present invention. 
         [0022]    As shown in  FIG. 1  and  FIG. 2 , the single crystal manufacturing apparatus  1  is an apparatus applying the modified Rayleigh&#39;s method of sublimating a sublimation raw material  20  and then recrystallizing a single crystal on a seed crystal  10  inside of a graphite crucible  50  in which the sublimation raw material  20  is disposed. 
         [0023]    The crucible  50  has a crucible main body  30  and a capping member  40  where the seed crystal  10  is to be disposed. The crucible main body  30  has a substantially cylindrical shape in which a bottom portion  30   b  is formed at one end portion and an opening portion  30   u  is formed at another end portion. The sublimation raw material  20  is disposed at the bottom portion  30   b.  The capping member  40  closes the opening portion  30   u,  and the seed crystal  10  is disposed at an opposite position to the sublimation raw material  20 . 
         [0024]    The capping member  40  has a projection portion  41 . A guide portion  43  having a conical face  43   a  is mounted on the capping member  40 , and a diameter of conical face  43   a  increases as going down in a growing direction D of a silicon carbide single crystal is mounted. 
         [0025]    The crucible  50  is covered with a heat insulation member (not shown). In addition, the crucible  50  is fixed to the inside of a quartz tube  80  via the support rod  70 . At an outer circumference of the quartz tube  80 , a heating coil  90  to heat the crucible  50  is provided. 
         [0026]    In the embodiment, the diameter of the seed crystal  10  is 76.2 mm, and the thickness is 500 microns. 
       (2) Description of Configuration of Capping Member 
       [0027]      FIG. 3  ( a ) is a dissembled view showing the capping member  40 , the guide portion  43 , the seed crystal  10 , and a protection member  100  of the single crystal manufacturing apparatus  1  in a dissembled manner, and  FIG. 3  ( b ) is an assembled view in which the capping member  40 , the guide portion  43 , the seed crystal  10 , and the protection member  100  of the single crystal manufacturing apparatus  1  are assembled. 
         [0028]    The projection portion  41  is provided at a substantial center part of the capping member  40 . The projection portion  41  is formed in a substantially columnar shape in which a contacting face  41   a  having a diameter that is equal to a diameter of the seed crystal  10  or greater than the diameter of the seed crystal  10  is formed. 
         [0029]    The projection portion  41  of the capping member  40  is disposed so as to project inside of the crucible main body  30  via the capping member opening portion  40   a.  A screw thread  41   s  is formed outside of the projection portion  41 . 
         [0030]    The guide portion  43  has an engagement portion  431  to engage with the projection portion  41  and a support portion  432  to support the seed crystal  10 . At the engagement portion  431 , a guide opening portion  43   h  having a diameter fitting to an outer diameter of the projection portion  41  is formed. At the guide opening portion  43   h  of the engagement portion  431 , a screw groove  43   g  to be screwed with the screw thread  41   s  is formed. The projection portion  41  is inserted through the guide opening portion  43   h.  The support portion  432  is formed to narrow at least a part of the guide opening portion  43   h  formed at the engagement portion  431 . 
         [0031]    In the embodiment, the support portion  432  is formed in a peaked shape in which an edge of the guide opening portion  43   h  extends to an opening center of the opening portion. The support portion  432  is an aperture that is smaller than an aperture of the guide opening portion  43   h,  and forms an opening having a diameter that is smaller than the diameter of the seed crystal  10 . 
         [0032]    The seed crystal  10  is disposed between the contacting face  41   a  of the projection portion  41  inserted through the guide opening portion  43   h  and the support portion  432 . The seed crystal  10  is inserted from a top side of the guide opening portion  43   h,  whereby the seed crystal is supported by means of the support portion  432 . 
         [0033]    The screw thread  41   s  formed at the projection portion  41  is screwed with the screw groove  43   g  formed at the engagement portion  431 , whereby the contacting face  41   a  is formed so as to compress the entire portion of the back face opposite to the crystalline growth face in the seed crystal  10  against the projection portion  41 . 
         [0034]    In the embodiment, the protection member  100  is disposed between the contacting face  41   a  and the back face of the seed crystal  10 , and the contacting face  41   a  is formed so as to compress the full back face of the seed crystal  10  via the protection member  100 . The protection member  100  is a carbon fiber, for example. It is preferable that the protection member  100  be made of a material having its flexibility. 
       (3) Functions/Advantageous Effects 
       [0035]    According to the single crystal manufacturing apparatus  1 , the seed crystal  10  is supported by means of the support portion  432  formed after at least a part of the guide opening portion  43   h  formed at the engagement portion  431  has been narrowed, and the screw thread  41   s  formed at the projection portion  41  is screwed with the screw groove  43   g  formed at the engagement portion  431 , whereby the contacting face  41   a  is formed so as to compress the entire portion of the back face opposite to the crystalline growth face in the seed crystal  10  against the projection portion  41 . 
         [0036]    In the single crystal manufacturing apparatus  1 , since the seed crystal  10  is not adhered to the support portion  432 , the seed crystal can be prevented from being damaged due to a difference in stress exerted by a difference in thermal expansion coefficient between the capping member to which the seed crystal is mounted and the seed crystal itself. 
         [0037]    In addition, in the single crystal manufacturing apparatus  1 , the seed crystal  10  is not adhered to the support portion  432 . The full back face of the seed crystal  10  is compressed against the contacting face  41   a,  whereby the outer edge of the seed crystal  10  is compressed against the support portion  432  by means of the contacting face  41   a.  Thus, gapping between the support portion  432  and the outer edge of the seed crystal  10  can be prevented. In this manner, entry of the sublimation gas as a sublimation raw material between the support portion  432  and the outer edge of the seed crystal  10  can be prevented. 
         [0038]    Further, in the single crystal manufacturing apparatus  1 , the full back face of the seed crystal  10  is compressed against the contacting face  41   a,  whereby warping of the seed crystal  10  is corrected. Cracking of the protection layer on the back face of the seed crystal  10  can be prevented, and a single crystal of its homogenous quality can be produced. 
         [0039]    Furthermore, in the embodiment, the protection member  100  is disposed between the contacting face  41   a  and the back face of the seed crystal  10 . The contacting face  41   a  is formed so as to compress the full back face of the seed crystal  10  via the protection member  100  made of a carbon fiber. 
         [0040]    In this manner, by interposing the carbon fiber, a gap between a part of the capping member  40  and the seed crystal  10  can be reduced more reliably, and macroscopic defects can be prevented. 
       (4) Modification Example of Seed Crystal 
       [0041]      FIG. 4  ( a ) is a dissembled view when another seed crystal  11  is applied to the single crystal manufacturing apparatus  1 , and  FIG. 4  ( b ) is a view illustrating the seed crystal  11  for use in the single crystal manufacturing apparatus  1 . The seed crystal  11  is curved so as to be convex in an opposite direction to the growing direction D of the single crystal. 
         [0042]    In the embodiment, the diameter of the seed crystal  11  is 76.2 mm, and its thickness is 500 microns. Its warping is of the order of 30 microns. 
         [0043]    The thus curved seed crystal  11  is compressed against the contacting face  41   a  of the projection portion  41 , whereby a curved face protruded in the opposite direction to the growing direction is flattened. In addition, by means of compression, curving in the growing direction side can be prevented, and the growth face in the seed crystal  11  can be retained so as to be flat. Therefore, cracking of the protection layer on the back face of the seed crystal  11  can be prevented, and a single crystal of its homogenous quality can be produced. 
       (5) Other Embodiments 
       [0044]    As described above, while the contents of the present invention were disclosed through the embodiment of the present invention, it is not to be understood that the discussion and drawings forming part of this disclosure limit the present invention. From this disclosure, a variety of alternate embodiments or examples would be self-evident to one skilled in the art. For example, the embodiment of the present invention can be altered as follows. 
         [0045]    The embodiment described that the protection member  100  was disposed between the contacting face  41   a  and the back face of the seed crystal  10 . However, the protection member  100  does not always need to be disposed. 
         [0046]    In a case where the protection member  100  is not provided, it is preferable to apply a refinement treatment to a surface of the capping member  40  abutting against the seed crystal  10  to thereby achieve a refined structure. By refining the surface, even if a slight gap still remains between the seed crystal  10  and the capping member  40  (contacting face  41   a ), generation of macroscopic defects can be prevented. 
         [0047]    Thus, it is a matter of course that the present invention includes a variety of embodiments or the like that are not described herein. Therefore, the technical scope of the present invention is defined only by the specified matters of the invention related to the claims reasonable from the foregoing description. 
         [0048]    All the contents of Japanese Patent Application No. 2010-212339 (filed on Sep. 22, 2010) are incorporated in the present specification by way of reference. 
         [0049]    According to the present invention, in the single crystal manufacturing apparatus of such a type that a seed crystal is not adhered to a capping member, the damage to the seed crystal or the lowering of the quality of the single crystal can be prevented.