JP2010111521A - Manufacturing apparatus of silicon carbide single crystal, and manufacturing method of silicon carbide single crystal - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an apparatus and a method for manufacturing a silicon carbide single crystal, which promote more homogeneous crystal growth. <P>SOLUTION: In the method for manufacturing a silicon carbide single crystal in which a raw material for sublimation 80 is heated to sublime the raw material for sublimation 80, and the sublimed raw material for sublimation 80 is recrystallized on a seed crystal 70 to manufacture a silicon carbide single crystal, at least a part of the raw material for sublimation 80 is of a cylindrical shape having a hollow portion formed, and the seed crystal 70 is disposed in the hollow portion of the raw material for sublimation 80. The positional relationship between the seed crystal 70 and the raw material for sublimation 80 is such that a heating position which varies along the extending direction of the hollow portion with the elapse of the heating time by an induction heating coil 30 and is heated at a predetermined temperature by the induction heating coil 30 moves along with the position of the seed crystal 70. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a silicon carbide single crystal comprising: a seed crystal containing silicon carbide; a housing part that houses a sublimation raw material used for seed crystal growth; and a heating part that heats the periphery of the side part of the housing part. The present invention relates to a manufacturing apparatus and a method for manufacturing a silicon carbide single crystal.

  Conventionally, a method of manufacturing a silicon carbide single crystal using a crucible (accommodating portion) in which a seed crystal formed of silicon carbide and a sublimation raw material are accommodated is known. For example, a powdery sublimation raw material is placed on the bottom of the crucible, and a seed crystal is disposed on the top of the crucible (see Patent Document 1). An induction heating coil for heating the crucible is disposed on the outer periphery of the crucible.

  The sublimation raw material sublimated in the crucible heated using the induction heating coil is recrystallized on the seed crystal by being cooled. By growing the seed crystal in this way, a silicon carbide single crystal ingot is manufactured.

  However, the conventional method for manufacturing a silicon carbide single crystal described above has the following problems. That is, since the temperature in the crucible heated using the induction heating coil varies depending on the position in the crucible, there is a problem that the sublimation raw material does not sublime uniformly. Specifically, the sublimation raw material disposed in the high temperature region sublimes quickly, and the sublimation raw material disposed in the low temperature region is difficult to sublime compared to other regions.

  For this reason, immediately after the start of heating of the crucible, the amount of sublimation raw material sublimates is large, and as the time elapses from the start of heating, the amount of sublimation raw material sublimates decreases. That is, since the growth rate of the silicon carbide single crystal gradually slows, there is a problem that the promotion of uniform crystal growth of the silicon carbide single crystal is hindered.

  Therefore, the present invention has been made in view of such a situation, and an object thereof is to provide a silicon carbide single crystal manufacturing apparatus and a silicon carbide single crystal manufacturing method that promote more uniform crystal growth. .

  In order to solve the above-described problems, the present invention has the following features. First, the first feature of the present invention is that a housing portion (housing portion) housing a seed crystal containing silicon carbide (seed crystal 70) and a sublimation raw material (sublimation raw material 80) used for growing the seed crystal. 14) and a silicon carbide single crystal manufacturing apparatus (manufacturing apparatus 1) comprising a heating section (induction heating coil 30) disposed around the side portion of the housing section and heating the housing section, At least a part of the sublimation raw material has a cylindrical shape in which a hollow portion (hollow portion 81) is formed, and the seed crystal is disposed in the hollow portion of the sublimation raw material, and the seed crystal and the The positional relationship with the sublimation raw material changes along the elongating direction (direction F) of the hollow portion with the elapse of the heating time by the heating unit, and the heating position heated to a predetermined temperature by the heating unit is The gist is to move with the position of the seed crystal.

  According to the first feature of the present invention, the heating position in the sublimation raw material and the position of the seed crystal in the hollow portion move as the heating time elapses. The source gas is sublimated from the heating position heated to a predetermined temperature by the heating unit.

  According to the first feature of the present invention, a part of the sublimation raw material is heated, and the heating position and the position of the seed crystal are correspondingly changed with the passage of time. That is, at the start of the reaction, the entire sublimation raw material necessary for obtaining a silicon carbide single crystal is not heated.

  Thus, since the heating position of the sublimation raw material changes, it is possible to prevent the sublimation raw material from remaining due to temperature unevenness occurring in the sublimation raw material throughout the reaction process. Thereby, it can prevent that the amount of sublimation of the sublimation raw material decreases as time elapses from the start of heating.

  Therefore, the growth rate of the silicon carbide single crystal can be prevented from gradually decreasing, and uniform crystal growth of the silicon carbide single crystal can be promoted.

  A second feature of the present invention relates to the first feature of the present invention, and is provided with a seed crystal moving mechanism (seed crystal moving mechanism 44) for moving the seed crystal along the extending direction (direction F). The gist.

  A third feature of the present invention relates to the second feature of the present invention, and is a heating unit moving mechanism (induction heating coil moving mechanism 140) that moves the heating unit in accordance with the movement of the seed crystal by the seed crystal moving mechanism. ).

  The fourth feature of the present invention relates to the second or third feature of the present invention, and is characterized by having a seed crystal placement part (seed crystal placement part 52) on which the seed crystal is placed. .

  A fifth feature of the present invention relates to any one of the second to fourth features of the present invention, comprising a pair of sealing portions (sealing portions 50, 60) for sealing the hollow portion, The sealing portion (sealing portion 50) is attached to the seed crystal moving mechanism, and seals one end portion side of the hollow portion, and the other sealing portion (sealing portion 60) The other end of the hollow portion is sealed, and the pair of sealing portions slides on the inner wall surface of the hollow portion in accordance with the movement of the seed crystal by the seed crystal moving mechanism.

  A sixth feature of the present invention relates to the fourth feature of the present invention, wherein the heating position is sealed between the end portion (crystal end portion 100a) in the growth direction of the seed crystal and the other end side of the hollow portion. The gist is that it is set between the sealing portion (sealing portion 50) to be stopped.

  A seventh feature of the present invention relates to the fifth or sixth feature of the present invention, wherein the sealing portion is formed of a member containing graphite, and a temperature measuring portion (temperature) that measures the temperature of the sealing portion. The gist is to include a measuring unit 90).

  An eighth feature of the present invention relates to the first feature of the present invention, and is characterized by comprising a raw material moving mechanism (raw material moving mechanisms 45, 46) for moving the sublimation raw material along the extending direction. To do.

  A ninth feature of the present invention relates to the eighth feature of the present invention, and is summarized in that the raw material moving mechanism moves the sublimation raw material upward along a vertical direction.

  A tenth feature of the present invention according to any one of the first to ninth aspects of the present invention is that the heating unit includes an induction coil that is rotated along the periphery of the housing unit. To do.

  An eleventh feature of the present invention is that a seed crystal containing silicon carbide and a sublimation raw material having a hollow part used for growth of the seed crystal are accommodated in a housing part, and the seed crystal of the sublimation raw material is The sublimation raw material is sublimated by heating the sublimation raw material by a heating unit disposed in a hollow portion and disposed along the outer periphery of the housing portion, and the sublimated raw material is sublimated with the seed crystal. A method for producing a silicon carbide single crystal, which is recrystallized to produce a silicon carbide single crystal, wherein the sublimation raw material is heated (step S3), and the heated sublimation raw material is used for the sublimation. Recrystallizing the seed crystal disposed in the hollow portion of the raw material, and growing the recrystallized silicon carbide single crystal (step S4). In the growing step, the seed crystal And the positional relationship between the sublimation raw material and the heating time Along the extending direction of the hollow portion changes, heating position of the sublimation raw material is heated to a predetermined temperature by the heating unit is summarized in that that moves with the position of the seed crystal.

  According to the present invention, it is possible to provide a silicon carbide single crystal manufacturing apparatus and a silicon carbide single crystal manufacturing method that promote more uniform crystal growth.

  Next, an embodiment of a method for producing silicon carbide powder according to the present invention will be described with reference to the drawings. Specifically, First Embodiment, 2. Second embodiment, 3. Third embodiment, 4. Other embodiments will be described.

  In the following description of the drawings, the same or similar parts are denoted by the same or similar reference numerals. However, it should be noted that the drawings are schematic and ratios of dimensions are different from actual ones.

  Accordingly, specific dimensions and the like should be determined in consideration of the following description. Moreover, it is a matter of course that portions having different dimensional relationships and ratios are included between the drawings.

1. First Embodiment (1) Schematic Configuration of Manufacturing Apparatus A silicon carbide single crystal manufacturing apparatus 1 shown as an embodiment of the present invention will be described with reference to FIGS. FIG. 1 is a configuration diagram illustrating a silicon carbide single crystal manufacturing apparatus 1.

  As shown in FIG. 1, a silicon carbide single crystal manufacturing apparatus 1 includes a reaction furnace 10, a quartz tube 20 covering at least a side surface of the reaction furnace 10, and an induction heating coil 30 disposed on the outer periphery of the quartz tube 20. Have.

  The reaction furnace 10 includes a cylindrical graphite partition 11, a graphite lid 12, and a graphite bottom 13. The graphite partition 11 constitutes the side surface of the reaction furnace 10. The graphite partition 11 has an outer surface covered with a heat insulating material (not shown). The graphite lid 12 constitutes the upper surface of the reaction furnace 10. The graphite bottom 13 constitutes the bottom surface of the reaction furnace 10.

  The upper surface outside the graphite lid 12 is covered with a heat insulating material 21. The upper surface outside the graphite bottom portion 13 is covered with a heat insulating material 22. An opening 12 a is provided on the outer upper surface of the graphite lid 12. A support bar 41 is inserted through the opening 12a. An opening 13 a is also provided on the outer upper surface of the graphite bottom portion 13. A support rod 42 is inserted through the opening 13a.

  A space between the openings 12a and 13a and the support rods 41 and 42 is sealed with a sealing material (not shown). Even if the support rods 41 and 42 move in the insertion / removal direction with respect to the openings 12a and 13a, the sealing performance is maintained.

  The graphite lid 12 and the graphite bottom 13 may be detachably provided on the graphite partition 11 by screwing.

  An accommodating portion 14 is formed by the graphite partition wall 11, the graphite lid portion 12, and the graphite bottom portion 13. The accommodating part 14 accommodates the seed crystal 70 containing silicon carbide and the sublimation raw material 80 used for the growth of the seed crystal 70. The sublimation raw material 80 is disposed along the inner wall surface of the graphite partition wall 11. That is, the sublimation raw material 80 is cylindrical.

  In the hollow portion 81 of the sublimation raw material 80 disposed in the accommodating portion 14, that is, in the cylinder, a graphite sealing portion 50 and a sealing portion 60 are disposed.

  The sealing portion 50 is disposed below the inside of the housing portion 14 and seals one end side (downward) of the hollow portion 81. The sealing portion 60 is disposed above the sealing portion 50 and seals the other end side (upper side) of the hollow portion 81.

  The sealing parts 50 and 60 have a planar shape substantially the same as the cross-sectional shape of the sublimation raw material 80 in plan view. It is preferable that the space | interval of the outer peripheral surface of the sealing part 50 and the sealing part 60 and the inner wall face of the sublimation raw material 80 is 0.5 mm or less. It is preferable that the outer peripheral surfaces of the sealing part 50 and the sealing part 60 are in contact with the inner wall surface of the sublimation raw material 80 so that the raw material gas sublimated from the sublimation raw material 80 does not leak.

  The sealing unit 50 includes a seed crystal mounting unit 52 on which the seed crystal 70 is mounted. The seed crystal mounting portion 52 is formed at a substantially central portion of the surface 51 of the sealing portion 50. The sealing part 50 is formed of a member containing graphite. A temperature measuring unit 90 that measures the temperature of the sealing unit 50 is provided on the surface opposite to the surface 51 of the sealing unit 50. The support bar 42 has a hollow structure. The temperature measuring unit 90 is disposed inside the support bar 42 in a state where the temperature measuring unit 90 is in contact with the sealing unit 50.

  A support rod 42 is connected to the sealing unit 50. The support bar 42 is connected to the seed crystal moving mechanism 44. Further, the support bar 41 is connected to the sealing portion 60. The support bar 41 is connected to the sealing unit moving mechanism 43.

  The sealing portions 50 and 60 slide on the inner wall surface of the sublimation raw material 80 as the heating time elapses inside the reaction furnace 10, and can move, for example, from above to below (see FIG. 1). Arrow direction shown).

  The induction heating coil 30 includes a first coil 31, a second coil 32, a third coil 33, a fourth coil 34, and a fifth coil 35. The induction heating coil 30 is wound along the outer peripheral portion of the quartz tube 20. The induction heating coil 30 heats the graphite partition 10.

  The position of the center line CL3 passing through the center of the coil diameter of the induction heating coil 30 overlaps with the center line CL1 of the accommodating portion 14 and the crystal center line CL2 passing through the center of the seed crystal 70.

  Each of the induction heating coils 30 is controlled by a control unit (not shown) in FIG. Therefore, the induction heating coil 30 can heat at least the outer periphery of the reaction furnace 10 corresponding to the position of the seed crystal 70 with the movement of the sealing portion 50 and the sealing portion 60 as the heating time elapses. The temperature in the reaction furnace 10 can be appropriately selected according to the crystal polymorph of the silicon carbide single crystal to be grown.

  Further, the center line CL3 of the induction heating coil 30 coincides with the center line CL4 of the cylinder of the sublimation raw material 80. When the center line CL3 of the induction heating coil 30, the center line CL1 of the accommodating portion 14, and the center line CL4 of the cylinder of the sublimation raw material 80 are matched, an induction current also flows through the sublimation raw material 80. Accordingly, the sublimation raw material 80 self-heats. Thereby, the heating efficiency of the sublimation raw material 80 can be improved.

  The smaller the gap between the inner surface 11a of the graphite partition wall 11 and the outer surface 80a of the cylindrical sublimation raw material 80, the better. Specifically, it is 0.5 mm or less. The inner diameter and the outer diameter of the cylindrical sublimation raw material 80 are preferably substantially the same. When the distance is 0.5 mm or less, an induction current from an induction heating coil 30 described later easily enters the sublimation raw material 80, and the heating efficiency of the sublimation raw material 80 is improved.

  Furthermore, considering the ease of flow of the induced current, it is preferable to use n-type or p-type silicon carbide having high conductivity as the sublimation raw material 80.

  Further, considering the ease of induction current flow in the sublimation raw material 80, the thickness of the side wall of the graphite partition 11 needs to be thinner, but considering the strength of the graphite partition 11, it is 5 mm. It is preferable to set it to 10 mm or less.

  Seed crystal 70 is, for example, a silicon carbide single crystal. The seed crystal 70 is disposed in the central portion of the accommodating portion 14. Mirror polishing is applied to the crystal growth surface. The seed crystal 70 is placed on the seed crystal placement portion 52 formed on the surface 51 of the sealing portion 50.

  Sublimation raw material 80 is a silicon carbide raw material containing silicon carbide. The sublimation raw material 80 is disposed along the inner surface of the graphite partition wall 10. That is, the sublimation raw material 80 is cylindrical.

  Sublimation raw material 80 is a silicon carbide sintered body produced by sintering silicon carbide. Since the silicon carbide sintered body has better formability than powder, the degree of freedom of the arrangement position of the sublimation raw material 80 in the reaction vessel main body 50 is increased. Therefore, it can be formed into a cylindrical shape as in this embodiment. The sublimation raw material 80 and the seed crystal 70 are preferably the same polymorph.

  FIG. 2 is a perspective view for explaining the positional relationship between sublimation raw material 80 and seed crystal 70 disposed in silicon carbide single crystal manufacturing apparatus 1.

  As shown in FIG. 2, the seed crystal 70 is surrounded by a sublimation raw material 80 having a cylindrical shape while being placed on the seed crystal placement portion 52. That is, the side of the seed crystal 70 is surrounded by the sublimation raw material 80. The center line CL4 of the cylinder of the sublimation raw material 80 substantially coincides with the crystal center line CL2 of the seed crystal 70.

  As shown in FIG. 2, a predetermined distance d is provided between the sealing portion 50 and the sealing portion 60 along the extending direction F of the cylindrical sublimation raw material 80. The sealing portions 50 and 60 can move, for example, from the top to the bottom as the heating time elapses while the interval d is constant inside the reaction furnace 10. That is, the space surrounded by sealing portion 50, sealing portion 60, and sublimation raw material 80 corresponds to reaction system 15 for sublimation and recrystallization of silicon carbide single crystal.

  The relationship between the inner diameter D1 of the sublimation raw material 80 and the radial length D2 of the seed crystal 70 is preferably 10 mm ≦ (D1−D2) ≦ 20 mm. If D1-D2 exceeds 20 mm, the sublimated silicon carbide tends to recrystallize on the surface 51 of the sealing portion 50 between the seed crystal 70 and the sublimation raw material 80, which is not preferable.

  On the other hand, when D1-D2 is 10 mm or less, the growth on the seed crystal proceeds, and when the crystal grows in the central axis direction and grows in the radial direction, the grown single crystal may come into contact with the sublimation raw material 80. This is not preferable.

  Next, an operation example of the silicon carbide single crystal manufacturing apparatus 1 will be described. FIG. 3 is a diagram showing a state after the elapse of a predetermined time t from the start of heating of the silicon carbide single crystal manufacturing apparatus 1.

  The sealing part 50 and the sealing part 60 move from top to bottom as the heating time elapses. The heating position in the reaction furnace 10 is set at least between the crystal end portion 100 a that is the end portion in the growth direction of the seed crystal 70 and the sealing portion 50. That is, in the state shown in FIG. 3, the third coil 33 and the fourth coil 34 are operating.

  The source gas is sublimated from the heating position of the sublimation raw material 80 heated by the selected induction heating coil, recrystallized based on the seed crystal 70, and a silicon carbide single crystal grows on the seed crystal 70.

  In the manufacturing apparatus 1, the heating position of the sublimation raw material 80 moves and the position of the seed crystal 70 moves. That is, the sublimation raw material 80 from which silicon has escaped by sublimation is sent out of the reaction system 15 and the unreacted sublimation raw material 80 is supplied to the reaction system 15. Therefore, according to the manufacturing apparatus 1, even if time elapses from the start of heating, the sublimation amount of the sublimation raw material 80 and the components of the sublimated raw material gas are kept constant.

(2) Production Method of Silicon Carbide Single Crystal (2-1) Production of Sublimation Raw Material Sublimation raw material 80 will be described. As the sublimation raw material 80, for example, it is preferable to use a high-purity silicon carbide sintered body. The sublimation raw material 80 is produced from a silicon-containing raw material and a carbon-containing raw material. A silicon carbide precursor is obtained by mixing a silicon-containing raw material and a carbon-containing raw material and crosslinking or polymerizing the mixed raw material mixture. When the obtained silicon carbide precursor is dried and fired at 1600 to 2000 ° C. in a non-oxidizing atmosphere, a high-purity silicon carbide powder (so-called high-purity precursor method powder) is obtained. This high-purity precursor method powder is formed into a cylindrical shape, and a sintered body obtained by firing is used as a sublimation raw material 80.

  The silicon-containing raw material is at least one silicon-containing raw material selected from the group comprising a liquid silicon compound and a silicon solid synthesized from a hydrolyzable silicon compound.

  Examples of the silicon-containing raw material include a group of polymers obtained by trimethylation of a hydrolyzable silicic acid compound, and an ester (for example, silicon tetrachloride) of a hydrolyzable silicic acid compound and a monovalent or polyhydric alcohol (eg, diol, triol). Ethyl silicate synthesized by the reaction of ethanol with ethanol), reaction products other than esters obtained by the reaction of hydrolyzable silicon compounds and organic compounds (for example, tetramethylsilane, dimethyldiphenylsilane, polydimethylsilane), etc. The silicon compound is mentioned.

  A silicon compound is a compound synthesized in a manufacturing process using a raw material not containing impurities and a catalyst containing no impurities. The content of impurities in this silicon compound is preferably 1 ppm or less.

  Here, an element harmful to semiconductor manufacturing (hereinafter referred to as an impurity) is an element that causes a decrease in electrical characteristics of a wafer by being incorporated into the wafer as an impurity in the wafer heat treatment process.

  As an example of an impurity, an element belonging to group 1 to group 17 in the periodic table of the 1989 IUPAC inorganic chemical nomenclature revised edition and having atomic number 3 or more (excluding carbon atom, oxygen atom and silicon atom) Say. In addition, in order to impart n-type or p-type conductivity to the growing silicon carbide single crystal, when a dopant element such as nitrogen or aluminum is intentionally added, these are also excluded.

  Similarly, the silicon solid synthesized from the hydrolyzable silicon compound preferably has an impurity content of 1 ppm or less. This silicon solid may be any material that reacts with carbon in a high-temperature non-oxidizing atmosphere to produce silicon carbide. A preferred example of the siliceous solid is amorphous silica fine powder obtained by hydrolysis of silicon tetrachloride.

  The carbon-containing raw material is a monomer that is synthesized using a catalyst that does not contain impurities, and is composed of any one or more organic compounds that can be cured by polymerization and crosslinking with heating and / or a catalyst or a crosslinking agent. , Oligomers and polymers.

  Preferable specific examples of the carbon-containing raw material include curable resins such as a phenol resin, a furan resin, a urea resin, an epoxy resin, an unsaturated polyester resin, a polyimide resin, and a polyurethane resin synthesized using a catalyst that does not contain impurities. Can be mentioned. In particular, a resol type or novolac type phenol resin having a high residual carbon ratio and excellent workability is preferable.

  The resol type phenolic resin useful in the present embodiment is monovalent or divalent such as phenol, cresol, xylenol, resorcin, bisphenol A, etc. in the presence of an impurity-free catalyst (specifically, ammonia or organic amine). This is produced by reacting phenolic compounds with aldehydes such as formaldehyde, acetaldehyde and benzaldehyde.

  The organic amine used as the catalyst may be any of primary, secondary, and tertiary amines. As the organic amine, dimethylamine, trimethylamine, diethylamine, triethylamine, dimethylmonoethanolamine, monomethyldiethanolamine, N-methylaniline, pyridine, morpholine and the like can be used.

  As a method of synthesizing a resol type phenol resin by reacting phenols and aldehydes in the presence of ammonia or an organic amine, conventionally known methods can be adopted except that the catalyst used is different.

  The novolak type phenolic resin useful in the present embodiment is a mixture of monovalent or divalent phenols and aldehydes similar to those described above, and contains no impurities (specifically, hydrochloric acid, sulfuric acid, p-toluenesulfone). Acid or oxalic acid) as a catalyst.

(2-2) Manufacturing method of silicon carbide single crystal Next, the manufacturing method of the silicon carbide single crystal which concerns on this embodiment is demonstrated. FIG. 4 is a diagram illustrating a method for manufacturing a silicon carbide single crystal.

  As shown in FIG. 4, the method for manufacturing a silicon carbide single crystal according to this embodiment includes steps S1 to S4. In addition, a semiconductor wafer can be manufactured by performing step S5 and step S6 shown in FIG. 4 continuously.

  Step S1 is a step of preparing the above-described sublimation raw material 80. The production of the sublimation raw material 80 is based on the production method of the sublimation raw material 80 described above.

  Step S2 is a step of arranging the sublimation raw material 80, the seed crystal 70, and the like produced in step S1 in the manufacturing apparatus 1.

  In step S <b> 2, the seed crystal 70 is placed on the seed crystal placement portion 52 formed on the surface 51 of the sealing portion 50. At this time, the crystal center line CL <b> 2 passing through the center of the seed crystal 70 is placed on the seed crystal placement unit 52 in a state where it matches the center line CL <b> 1 of the housing unit 14.

  In addition, the center line CL4 of the cylinder of the sublimation raw material 80 having a cylindrical shape is disposed so as to overlap the center line CL1 and the crystal center line CL2 of the accommodating portion 14. The center line CL1, the crystal center line CL2, and the center line CL4 of the cylinder of the sublimation raw material 80 substantially coincide with the center line CL3 of the coil of the induction heating coil 30.

  Step S3 is a step of heating the graphite partition wall 10 and sublimating the sublimation raw material 80. In silicon carbide single crystal manufacturing apparatus 1, current is passed through induction heating coil 30 to heat sublimation raw material 80.

  Step S4 is a step of growing a silicon carbide single crystal based on the seed crystal 70. The sublimation raw material 80 sublimated in step S3 is recrystallized based on the seed crystal 70 disposed in the central part of the graphite partition 10. That is, the source gas sublimated from the sublimation raw material 80 is recrystallized based on the seed crystal 70 disposed in the hollow portion 81 of the sublimation raw material 80 to grow the silicon carbide single crystal 100 on the seed crystal 70.

  Step S4 includes a step S41 in which the positional relationship between the seed crystal 70 and the sublimation raw material 80 changes along the extending direction F (see FIG. 2) of the hollow portion 81 with the passage of the heating time. In step S <b> 41, the heating position of the sublimation raw material 80 heated to a predetermined temperature by each coil of the induction heating coil 30 moves together with the position of the seed crystal 70.

  Thereby, a silicon carbide single crystal (referred to as a single crystal ingot) can be grown in the radial direction of the reaction vessel main body 50 with time. A single crystal ingot can be obtained by performing the above-described steps S1 to S4.

  Step S5 is a step of subjecting the single crystal ingot grown to a desired size to peripheral grinding. In step S5, orientation flat forming processing for forming an orientation flat (orientation flat) indicating a crystal orientation (for example, Si plane or C plane) may be performed on the single crystal ingot. Step S6 is a step of slicing (slicing) a semiconductor wafer from the single crystal ingot.

  According to the manufacturing method shown in FIG. 4, the raw material gas is sublimated from the heating position of the sublimation raw material 80 heated by the selected induction heating coil, and recrystallized based on the seed crystal 70. A silicon carbide single crystal grows. In the manufacturing method shown in FIG. 4, the heating position of the sublimation raw material 80 moves and the position of the seed crystal 70 moves.

  That is, the sublimation raw material 80 from which silicon has escaped by sublimation is sent out of the reaction system 15 and the unreacted sublimation raw material 80 is supplied to the reaction system 15. Therefore, according to the manufacturing method described above, the sublimation amount of the sublimation raw material 80 and the components of the sublimated raw material gas are kept constant even when time elapses from the start of heating.

(3) Modification (3-1) Modification 1
FIG. 5 is a view showing Modification 1 of the sealing portion in the silicon carbide single crystal manufacturing apparatus 1 according to the first embodiment. In the first embodiment, a seed crystal mounting portion 52 is formed on the surface 51 of the sealing portion 50. However, the sealing part 50a shown as the modification 1 may be formed with a concave part 53a that is recessed toward the lower side of the manufacturing apparatus 1 as a seed crystal mounting part. The seed crystal 70 is placed on the concave portion 53a.

  The concave portion 53 a has substantially the same shape as the planar shape of the seed crystal 70. Further, the depth d2 of the concave portion 53a is equal to or less than the thickness d1 of the seed crystal 70. The seed crystal 70 is placed on the concave portion 53a but is not bonded.

  In the first modification, the concave portion 53 a is formed in the sealing portion 50, so that the position where the seed crystal 70 is placed is determined. Thereby, the mounting position of the seed crystal 70 can be accurately determined without strictly performing the positioning operation in the step S2 of arranging the seed crystal 70. Therefore, in step S2 in which the seed crystal 70 is arranged, positioning can be performed accurately and work efficiency can be improved.

(3-2) Modifications 2 and 3
Fig.6 (a) is a figure which shows the modification 2 of a sealing part. The configuration for positioning may be a shape other than the concave portion 53a. For example, the sealing part 50b shown as the modification 2 has the seed crystal mounting part 52b. The seed crystal mounting part 52b is higher than the surface 51b of the sealing part 50b.

  FIG.6 (b) is a figure which shows the modification 3 of a sealing part. The sealing part 50c shown as the modification 3 has the seed crystal mounting part 52c. The seed crystal mounting part 52c is higher than the surface 51c of the sealing part 50c. In addition, a concave portion 53 c that is recessed downward of the manufacturing apparatus 1 is formed in the seed crystal mounting portion 52 c.

  In the second and third modifications, similarly to the first modification, the placement position of the seed crystal 70 can be accurately determined without strictly performing the positioning operation in the step S2 of arranging the seed crystal 70. Therefore, in step S2 in which the seed crystal 70 is arranged, positioning can be performed accurately and work efficiency can be improved.

(4) Action / Effect According to the silicon carbide single crystal manufacturing apparatus 1 described above, the heating position in the sublimation raw material 80 and the position of the seed crystal 70 in the hollow portion 81 move as the heating time elapses. The source gas is sublimated from the heating position where the induction heating coil 30 is heated to a predetermined temperature.

  According to the silicon carbide single crystal manufacturing apparatus 1 described above, a part of the sublimation raw material 80 is heated, and the heating position and the position of the seed crystal 70 are changed correspondingly over time. That is, at the start of the reaction, the entire sublimation raw material 80 necessary for obtaining a silicon carbide single crystal (single crystal ingot) is not heated.

  Thus, since the heating position of the sublimation raw material changes, it is possible to prevent the sublimation raw material 80 from remaining due to temperature unevenness in the sublimation raw material 80 throughout the reaction process. This can prevent the sublimation amount of the sublimation raw material 80 from decreasing as time elapses from the start of heating.

  Therefore, the growth rate of the silicon carbide single crystal can be prevented from gradually decreasing, and uniform crystal growth of the silicon carbide single crystal can be promoted.

  The manufacturing apparatus 1 according to the first embodiment includes a seed crystal moving mechanism 44 that moves the seed crystal 70 along the extending direction F of the sublimation raw material 80. In addition, the heating position of the sublimation raw material 80 is set between the crystal end portion 100 a in the growth direction of the seed crystal 70 and the sealing portion 50.

  Thus, in the manufacturing apparatus 1, the raw material for sublimation heated for recrystallization may be a part of the whole. Therefore, the electric power of the induction heating coil 30 necessary for heating the sublimation raw material 80 can be reduced.

  In the conventional method for producing a silicon carbide single crystal, silicon preferentially sublimates from the sublimation raw material near the sublimation temperature, so that in the latter half of the reaction, the proportion of carbon in the raw material gas increases, and the quality of the silicon carbide single crystal Is known to change. Further, it has been found that the growth rate of the silicon carbide single crystal is remarkably reduced because the sublimation amount of the sublimation raw material is reduced.

  In contrast, in the silicon carbide single crystal manufacturing apparatus 1 described above, the hollow portion 81 of the sublimation raw material 80 is sealed by the pair of sealing portions 50 and 60. The sealing portions 50 and 60 slide on the inner wall surface of the hollow portion 81 according to the movement of the seed crystal 70 while maintaining a predetermined distance d. The heating position is set between the crystal end portion 100 a in the growth direction of the seed crystal 70 and the sealing portion 50.

  That is, a closed reaction system 15 surrounded by the inner wall surface of the hollow portion 81 of the sublimation raw material 80 and the pair of sealing portions 50, 60 is formed, and the reaction system 15 extends in the extending direction F of the sublimation raw material 80. Change along.

  That is, according to the silicon carbide single crystal manufacturing apparatus 1 described above, the sublimation raw material 80 from which silicon has escaped by sublimation is sent out of the reaction system 15, and the unreacted sublimation raw material 80 is contained in the reaction system 15. To be supplied. Thereby, even if time passes from a heating start, the sublimation amount of the sublimation raw material 80 and the component of the sublimated raw material gas are kept constant.

  Therefore, the growth rate of the silicon carbide single crystal can be prevented from gradually decreasing, and uniform crystal growth of the silicon carbide single crystal can be promoted.

  In the conventional manufacturing apparatus, when the induced current flows through the side wall of the crucible, the crucible generates heat, and the heat is transmitted to the sublimation raw material by radiation or the like. Therefore, the heat conduction efficiency to the raw material for sublimation is poor, leading to energy loss.

  On the other hand, in the silicon carbide single crystal manufacturing apparatus 1 described above, the center line CL1 of the housing portion 14, the crystal center line CL2 of the seed crystal 70, the center line CL3 passing through the center of the coil diameter of the induction heating coil 30, and When the center line CL4 of the cylinder of the sublimation raw material 80 is matched, an induced current flows through the sublimation raw material 80 and the sublimation raw material 80 self-heats.

  Thus, in the silicon carbide single crystal manufacturing apparatus 1, an induction current can be supplied to the sublimation raw material 80 itself to generate heat, so that the heating efficiency of the sublimation raw material 80 can be improved. Therefore, it is possible to suppress power consumption for manufacturing the silicon carbide single crystal.

2. Second Embodiment (1) Schematic Configuration of Manufacturing Apparatus Next, a silicon carbide single crystal manufacturing apparatus 2 shown as a second embodiment of the present invention will be described with reference to FIG. FIG. 7 is a configuration diagram illustrating the silicon carbide single crystal manufacturing apparatus 2.

  In the following description of the drawings, the same or similar parts as those of the manufacturing apparatus 1 shown as the first embodiment are denoted by the same or similar reference numerals, and detailed description thereof is omitted.

  As shown in FIG. 7, the silicon carbide single crystal manufacturing apparatus 2 includes a reaction furnace 10, a quartz tube 20 covering at least a side surface of the reaction furnace 10, and a movable induction heating coil moving mechanism 140.

  In the manufacturing apparatus 1, the heating position was changed by operating the 1st coil 31, the 2nd coil 32, the 3rd coil 33, the 4th coil 34, and the 5th coil 35 of the induction heating coil 30 in order. However, the manufacturing apparatus 2 includes an induction heating coil moving mechanism 140 that moves the heating position in accordance with the movement of the seed crystal 70 by the seed crystal moving mechanism 44.

  The induction heating coil moving mechanism 140 includes an induction heating coil 130, a coil cover 131, a screw screw 141, a motor 142, and a coil guide 143.

  The induction heating coil 130 is wound along the outer periphery of the quartz tube 20. The induction heating coil 130 heats the graphite partition 10. The induction heating coil 130 is covered with a coil cover 131. The coil cover 131 is connected to the motor 142 via a screw screw 141. The coil cover 131 is supported by the coil guide 143 at a position different from the screw screw 141.

  According to the induction heating coil moving mechanism 140, when the motor 142 is rotated, the induction heating coil 130 moves in the vertical direction.

  FIG. 8 shows an operation explanatory diagram of the silicon carbide single crystal manufacturing apparatus 2. FIG. 8 is a diagram showing a predetermined time t after the start of heating of the silicon carbide single crystal manufacturing apparatus 2.

  The sealing unit 50 and the sealing unit 60 move from the upper side to the lower side as the heating time elapses. Further, the induction heating coil 130 moves from the upper side to the lower side corresponding to the position in the hollow part 81 of the sealing part 50 (that is, the seed crystal 70). At this time, the heating position in the reaction furnace 10 is set at least between the crystal end portion 100 a that is the end portion in the growth direction of the seed crystal 70 and the sealing portion 50.

  The source gas is sublimated from the heating position of the sublimation raw material 80 heated by the induction heating coil 130, recrystallized based on the seed crystal 70, and a silicon carbide single crystal grows on the seed crystal 70.

(2) Action / Effect According to the silicon carbide single crystal manufacturing apparatus 2 according to the second embodiment described above, the induction heating coil 130 moves in accordance with the movement of the seed crystal 70 by the seed crystal moving mechanism 44. Thereby, a part of the sublimation raw material 80 is heated, and the heating position and the position of the seed crystal 70 are changed correspondingly with the passage of time.

  In the manufacturing apparatus 2, the hollow portion 81 of the sublimation raw material 80 is sealed by the pair of sealing portions 50 and 60. The sealing portions 50 and 60 slide on the inner wall surface of the hollow portion 81 according to the movement of the seed crystal 70 while maintaining a predetermined distance d. The heating position is set between the crystal end portion 100 a in the growth direction of the seed crystal 70 and the sealing portion 50.

  That is, the closed reaction system 15 surrounded by the inner wall surface of the hollow portion 81 of the sublimation raw material 80 and the pair of sealing portions 50 and 60 is formed. The reaction system 15 and the induction heating coil 130 change along the extending direction F of the sublimation raw material 80.

3. Third Embodiment (1) Schematic Configuration of Manufacturing Apparatus Next, a silicon carbide single crystal manufacturing apparatus 2 shown as a third embodiment of the present invention will be described with reference to FIGS. 9 and 10. FIG. 9 is a configuration diagram illustrating the silicon carbide single crystal manufacturing apparatus 3. FIG. 10 is a diagram showing a state after the elapse of a predetermined time t from the start of heating of the silicon carbide single crystal manufacturing apparatus 3. In the following description of the drawings, the same or similar parts as those of the manufacturing apparatuses 1 and 2 shown as the first and second embodiments are denoted by the same or similar reference numerals, and detailed description thereof is omitted.

  As shown in FIG. 9, the silicon carbide single crystal manufacturing apparatus 3 includes a graphite crucible 200, a quartz tube 20 covering at least a side surface of the graphite crucible 200, and an induction heating coil 30 disposed on the outer periphery of the quartz tube 20. And have.

  At least the upper and lower surfaces of the graphite crucible 200 are covered with heat insulating materials 221 and 222. The graphite crucible 200 has a reaction vessel main body 250 and a lid portion 260. Reaction vessel main body 250 accommodates seed crystal 70 containing silicon carbide.

  The graphite crucible 200 is supported by a support part 452 and a support part 454. The graphite crucible 200 is fixed to the column portion 453.

  At least the inside of the reaction vessel main body 250 is cylindrical. The reaction vessel main body 250 has a reaction system 270. The reaction vessel main body 250 includes a seed crystal placement unit 252 on which the seed crystal 70 is placed. The seed crystal mounting portion 252 is formed at the bottom of the graphite crucible 200, that is, at the center of the bottom 251 of the reaction vessel main body 250.

  Sublimation raw material 180 used for growth of seed crystal 70 is a silicon carbide raw material containing silicon carbide. The sublimation raw material 180 is disposed on the outer peripheral side of the graphite crucible 200 with respect to the seed crystal 70, and surrounds at least a part of the periphery of the seed crystal 70.

  In this embodiment, the sublimation raw material 180 has a cylindrical shape, and the length in the extending direction is larger than the height of the graphite crucible 200.

  The bottom portion 251 and the lid portion 260 of the reaction vessel main body 250 are provided with an insertion port through which the cylindrical sublimation raw material 180 can be inserted. The sublimation raw material 180 is formed such that the gap is as small as possible with respect to the bottom portion 251 and the lid portion 260.

  The induction heating coil 30 is disposed along the outer periphery of the quartz tube 20 and heats the graphite crucible 10.

  The manufacturing apparatus 3 includes a raw material moving mechanism 45 that moves the sublimation raw material 180 along the extending direction. The raw material moving mechanism 45 is connected to a support portion 451 that supports the sublimation raw material 80. The raw material moving mechanism 45 moves the sublimation raw material 180 upward along the vertical direction as the heating time elapses.

(2) Action / Effect According to the silicon carbide single crystal manufacturing apparatus 3 described above, a part of the sublimation raw material 180 located inside the graphite crucible 200 is heated. The sublimation raw material 180 is moved by the raw material moving mechanism 45. That is, only the portion of the sublimation raw material 180 that has reached the inside of the graphite crucible 200 is heated.

4). Example A cylindrical sublimation raw material 80 made of n-type silicon carbide was used as a sublimation raw material, a silicon carbide single crystal was used as a seed crystal 70, and a single crystal ingot was produced under the following conditions.

Graphite partition wall 10: side wall thickness 5 mm
Raw material for sublimation 80 ... Inner diameter 60mm, Outer diameter 70mm, Length 200mm
The thickness of the hollow part 81 is 10 mm
Seed crystal 70: Diameter 50 mm, thickness 1 mm, circular shape With reference to Modification 1, a concave portion having a diameter slightly larger than 50 mm and a depth of 0.4 mm was formed on the surface 51 of the sealing portion 50. A seed crystal 70 was placed on the concave portion. The distance d between the sealing material 50 and the sealing material 60 was 30 mm.

  The temperature of the sealing part 50 measured by the temperature measuring part 90 was set to 2000 ° C., the pressure of the reaction furnace 10 was set to 1333.22 Pa, and held for 50 hours.

  A movable induction heating coil 30 was employed as the heating unit. That is, the sublimation raw material 80 was fixed, and the positions of the seed crystal 70 and the induction heating coil 30 were changed downward. The moving speed was 1 mm / hour, and 50 mm was moved (50 hours).

  As a result, a single crystal ingot having a length of 20 mm in the extending direction of the sublimation raw material 80 was obtained. The obtained crystal was sliced and processed into a wafer to examine the state of the wafer in the early, middle and late stages of growth. The number and density of crystal defects, and the density of nitrogen atoms incorporated into the crystal were grown. And uniform throughout the entire crystal. Therefore, according to the method for manufacturing a silicon carbide single crystal according to the present embodiment, it has been found that a single crystal can be obtained under a constant temperature environment through a growth process for a long time.

5). Other Embodiments As described above, the contents of the present invention have been disclosed through one embodiment of the present invention. However, it should be understood that the description and drawings constituting a part of this disclosure limit the present invention. Absent. From this disclosure, various alternative embodiments will be apparent to those skilled in the art.

  The silicon carbide single crystal manufacturing apparatus according to the present invention only needs to have a configuration in which the relative positional relationship between the heating unit, the seed crystal, and the sublimation raw material changes, and the first to third embodiments described above. It is not limited to the configuration shown in FIG.

  Although the heating unit is the induction heating coils 30 and 130, the heating unit is not limited to the induction heating coil. Resistance heating (carbon heater or the like) may be used. In the above-described embodiment, the number of turns of the induction heating coils 30 and 130 and the interval between the electric wires are not limited to those shown in FIGS. For example, the number of turns of the first coil 31, the second coil,... Is not limited to three. Moreover, the wire spacing is preferably as narrow as possible.

  In the embodiment described above, the graphite partition 11 is used as the side wall of the reaction furnace 10, but is not limited to graphite. It can be changed according to the composition of the sublimation raw material or seed crystal. Further, the crystal orientation of the seed crystal 70 can be arbitrarily selected.

  In the above-described embodiment, the sublimation raw material 80 has been described as a sintered body formed by sintering a high-purity precursor method powder into a cylindrical shape. However, the shape and raw material of the sublimation raw material 80 are not limited to this. The sublimation raw material 80 may be silicon carbide. Moreover, it is not limited to a cylindrical shape. The cross-sectional shape may be a rectangular cylinder. Moreover, the polymorph of the crystal, the amount used, the purity, the production method, and the like can be appropriately selected. For example, a silicon carbide hot press sintered body, a reaction sintered body, or a calcined body can be selected. The size, shape and the like of the sublimation raw material 80 can be appropriately selected according to the size of the single crystal to be grown.

  As described above, the present invention naturally includes various embodiments that are not described herein. Therefore, the technical scope of the present invention is defined only by the invention specifying matters according to the scope of claims reasonable from the above description.

It is a block diagram explaining the manufacturing apparatus of the silicon carbide single crystal which concerns on 1st Embodiment of this invention. It is a perspective view explaining the positional relationship of the raw material for sublimation and the seed crystal inside the graphite crucible of the manufacturing apparatus of the silicon carbide single crystal which concerns on 1st Embodiment of this invention. It is a figure which shows the state after predetermined time t progress from the heating start of the manufacturing apparatus of the silicon carbide single crystal which concerns on 1st Embodiment of this invention. It is a figure explaining the manufacturing method of the silicon carbide single crystal which concerns on embodiment of this invention. It is a figure explaining the modification 1 of the manufacturing apparatus of the silicon carbide single crystal which concerns on embodiment of this invention. (A) is a figure explaining the modification 2 of the manufacturing apparatus of the silicon carbide single crystal which concerns on embodiment of this invention, (b) is a figure explaining the modification 3. FIG. It is a block diagram explaining the manufacturing apparatus of the silicon carbide single crystal which concerns on 2nd Embodiment of this invention. It is operation | movement explanatory drawing of the manufacturing apparatus of the silicon carbide single crystal which concerns on 2nd Embodiment of this invention. It is a block diagram explaining the manufacturing apparatus of the silicon carbide single crystal which concerns on 3rd Embodiment of this invention. It is an operation view which shows after predetermined time t progress from the heating start of the manufacturing apparatus of the silicon carbide single crystal which concerns on 3rd Embodiment of this invention.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1, 2, 3 ... Manufacturing apparatus, 10 ... Reactor, 11 ... Graphite partition, 11a ... Inner surface of graphite partition, 12 ... Graphite lid part, 13 ... Graphite bottom part, 14 ... Storage part, 15 ... Reaction system 12a, 13a ... opening, 20 ... quartz tube, 21, 22 ... heat insulating material, 30 ... induction heating coil, 31 ... first coil, 32 ... second coil, 33 ... third coil, 34 ... fourth coil, 35 ... 5th coil, 41, 42 ... support rod, 43 ... sealing part moving mechanism, 44 ... seed crystal moving mechanism, 45, 46 ... raw material moving mechanism, 50, 50a, 50b ... sealing part, 51, 51a, 51b ... surface, 52, 52b, 52c ... seed crystal placement part, 53a, 53c ... concave part, 60 ... sealing part, 70 ... seed crystal, 80 ... sublimation raw material, 80a ... outer surface of sublimation raw material 80, 81 ... hollow part, 90 ... temperature measuring part, 100 ... silicon carbide single crystal, 100a ... Crystal end portion, 130 ... induction heating coil, 131 ... coil cover, 140 ... induction heating coil moving mechanism, 141 ... screw screw, 142 ... motor, 143 ... coil guide, 180 ... raw material for sublimation, 200 ... graphite crucible, 221 , 222 ... heat insulating material, 250 ... reaction vessel body, 252 ... seed crystal placement part, 251 ... bottom part, 260 ... lid part, F ... extending direction, d ... interval between the sealing part 50 and the sealing part 60, d1 ... thickness of seed crystal 70, d2 ... depth of concave portion 53a, CL1 ... center line of housing part 14, CL2 ... crystal center line of seed crystal 70, CL3 ... center line of coil diameter of induction heating coil 30, CL4: Center line of cylinder of sublimation raw material 80

Claims (11)

An accommodating portion for accommodating a seed crystal containing silicon carbide and a sublimation raw material used for growing the seed crystal;
A silicon carbide single crystal manufacturing apparatus provided with a heating unit that is disposed around a side portion of the housing unit and heats the housing unit;
At least a part of the sublimation raw material has a cylindrical shape in which a hollow portion is formed,
The seed crystal is disposed in a hollow portion of the sublimation raw material,
The positional relationship between the seed crystal and the raw material for sublimation changes along the extending direction of the hollow part with the elapse of the heating time by the heating part,
The apparatus for producing a silicon carbide single crystal, wherein a heating position heated to a predetermined temperature by the heating unit moves with the position of the seed crystal.   The silicon carbide single crystal manufacturing apparatus according to claim 1, further comprising a seed crystal moving mechanism that moves the seed crystal along the extending direction.   The silicon carbide single crystal manufacturing apparatus according to claim 2, further comprising a heating part moving mechanism that moves the heating part according to the movement of the seed crystal by the seed crystal moving mechanism.   4. The silicon carbide single crystal manufacturing apparatus according to claim 2, wherein the seed crystal moving mechanism includes a seed crystal placement portion on which the seed crystal is placed. A pair of sealing portions for sealing the hollow portion;
One of the sealing portions is attached to the seed crystal moving mechanism, and seals one end portion side of the hollow portion,
The other sealing part seals the other end part side of the hollow part,
5. The silicon carbide single crystal according to claim 2, wherein the pair of sealing portions slide on an inner wall surface of the hollow portion in accordance with the movement of the seed crystal by the seed crystal moving mechanism. Manufacturing equipment.   The said heating position is set between the edge part of the growth direction of the said seed crystal, and the said sealing part which seals the other end part side of the said hollow part. Manufacturing equipment. The sealing portion is formed of a member containing graphite,
The manufacturing apparatus of the silicon carbide single crystal of Claim 5 or 6 provided with the temperature measurement part which measures the temperature of the said sealing part.   The silicon carbide single crystal manufacturing apparatus according to claim 1, further comprising a raw material moving mechanism that moves the sublimation raw material along the extending direction.   The said raw material moving mechanism is a manufacturing apparatus of the silicon carbide single crystal of Claim 8 which moves the said sublimation raw material upward along a perpendicular direction.   The said heating part is a manufacturing apparatus of the silicon carbide single crystal as described in any one of Claim 1 thru | or 9 containing the induction coil rotated along the circumference | surroundings of the said accommodating part. A seed crystal containing silicon carbide and a sublimation raw material having a hollow part used for growth of the seed crystal are housed in a housing part, the seed crystal is disposed in the hollow part of the sublimation raw material, and the housing The sublimation raw material is heated by a heating unit disposed along the outer periphery of the part to sublimate the sublimation raw material, and the sublimated raw material is recrystallized on the seed crystal to form silicon carbide. A method for producing a silicon carbide single crystal for producing a single crystal,
Heating the sublimation raw material;
The heated sublimation material is recrystallized based on a seed crystal disposed in the hollow portion of the sublimation material, and the recrystallized silicon carbide single crystal is grown.
In the growing step, the positional relationship between the seed crystal and the raw material for sublimation changes along the extending direction of the hollow portion with the passage of heating time,
A method for producing a silicon carbide single crystal, wherein a heating position of the sublimation raw material heated to a predetermined temperature by the heating unit moves together with a position of the seed crystal.

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