JP6376027B2 - Silicon carbide single crystal manufacturing equipment - Google Patents

Description

  The present disclosure relates to an apparatus for manufacturing a silicon carbide single crystal.

  Japanese Unexamined Patent Publication No. 2011-213563 (Patent Document 1) discloses a method of growing a bulk single crystal of silicon carbide using a sublimation method.

JP 2011-213563 A

  The sublimation method (also called “improved Rayleigh method”) is a method of growing a bulk single crystal by obtaining a sublimation gas by heating a solid raw material and reprecipitating the sublimation gas on a seed crystal. .

  One object of the present disclosure is to improve controllability of a sublimation gas composition in the production of a bulk single crystal by a sublimation method.

  An apparatus for manufacturing a silicon carbide single crystal according to one embodiment of the present disclosure includes a graphite crucible having an upper surface, a bottom surface facing the upper surface, and a cylindrical inner wall interposed between the upper surface and the bottom surface. At least a part of the inner wall contains silicon.

  According to the above, the controllability of the sublimation gas composition is improved.

It is a schematic sectional drawing showing an example of the composition of the manufacture device of the silicon carbide single crystal concerning the embodiment of this indication. It is the schematic which shows one cross section of the extending direction of the inner wall of a crucible. It is a flowchart which shows the outline of the manufacturing method of a silicon carbide single crystal.

[Description of Embodiment of Present Disclosure]
First, embodiments of the present disclosure will be listed and described.

  [1] An apparatus for producing a silicon carbide single crystal according to one aspect of the present disclosure includes a graphite crucible having an upper surface, a bottom surface facing the upper surface, and a cylindrical inner wall interposed between the upper surface and the bottom surface Is provided. At least a part of the inner wall contains silicon.

  In the vapor phase growth of silicon carbide (SiC) single crystal, the composition of the raw material gas, that is, the ratio of the partial pressure of the silicon (Si) component in the raw material gas to the partial pressure of the carbon (C) component (hereinafter referred to as “C / Si”). The “ratio” is an important factor in determining crystal quality. For this reason, in a crystal growth method in which a silicon component gas and a carbon component gas can be separately supplied, such as a chemical vapor deposition (CVD) method, precise control of the C / Si ratio is achieved. Has been made. However, in the sublimation method, since the solid raw material of silicon carbide is sublimated in the graphite crucible and the sublimation gas is used as the raw material gas, it is not easy to control the C / Si ratio.

  The graphite constituting the crucible is a porous material. Therefore, the inner wall of the crucible includes a plurality of pores. Part of the silicon component in the sublimation gas is adsorbed on the inner wall of the crucible. The silicon component once adsorbed may be detached from the inner wall and become part of the sublimation gas again. At the initial stage of crystal growth, adsorption of silicon components tends to occur on the inner wall of the crucible. Therefore, it is considered that the partial pressure of the silicon component in the sublimation gas becomes unstable at the initial stage of crystal growth.

  Further, when the silicon carbide solid material is sublimated, the sublimation of the silicon component tends to precede the sublimation of the carbon component. Therefore, in the latter stage of crystal growth, it is considered that the sublimation amount of the silicon component from the solid raw material decreases and the partial pressure of the silicon component in the sublimation gas decreases.

  These factors are considered to make it difficult to control the C / Si ratio in the sublimation method. Thus, when the controllability of the sublimation gas composition is lowered, a problem such as the mixing of different types of polytypes into the grown crystal is expected.

  Therefore, in the silicon carbide single crystal production apparatus of [1], silicon is contained in at least a part of the inner wall of the graphite crucible. According to this silicon carbide single crystal manufacturing apparatus, an improvement in the controllability of the sublimation gas composition can be expected. In other words, it is considered that by containing silicon in the inner wall in advance, adsorption of the silicon component on the inner wall can be suppressed in the initial stage of crystal growth. This is considered to stabilize the C / Si ratio from the beginning of crystal growth.

  Further, in the latter stage of crystal growth in which the sublimation amount of the silicon component from the solid raw material decreases, it is considered that silicon is desorbed from the inner wall and compensates for the partial pressure of the silicon component in the sublimation gas. Thereby, it is considered that the C / Si ratio is stable even in the latter stage of crystal growth.

  Here, the “controllability” indicates the length of the period during which the deviation from the target value of the control target can be maintained within the allowable range. An improvement in controllability indicates that this period becomes longer. The controlled object in [1] is the C / Si ratio. By improving the controllability, for example, the bulk single crystal can be expected to be elongated.

  [2] In the above [1], the crucible is positioned on the upper surface side from the intermediate point of the inner wall and on the bottom surface side of the intermediate point of the inner wall in one cross section in the extending direction of the inner wall. A second region, and each of the first region and the second region may contain silicon.

  [3] In the above [2], the silicon concentration in the first region may be higher than the silicon concentration in the second region.

  [4] In the above [2], the silicon concentration in the first region may be lower than the silicon concentration in the second region.

  [5] The silicon carbide single crystal manufacturing apparatus according to [1] to [4] may further include a graphite resistance heater for heating the crucible. In this case, at least a part of the resistance heater may contain silicon.

[Details of Embodiment of the Present Disclosure]
Hereinafter, embodiments of the present disclosure (hereinafter referred to as “present embodiment”) will be described, but the present embodiment is not limited thereto.

[Silicon carbide single crystal manufacturing equipment]
FIG. 1 is a schematic cross-sectional view showing an example of the configuration of the silicon carbide single crystal manufacturing apparatus according to the present embodiment. As shown in FIG. 1, silicon carbide single crystal manufacturing apparatus 100 (hereinafter, also simply referred to as “manufacturing apparatus 100”) includes chamber 6. The chamber 6 is provided with a gas introduction port 7 and a gas exhaust port 8. An exhaust pump 9 is connected to the gas exhaust port 8.

  In the chamber 6, a crucible 5, a first resistance heater 2a, a second resistance heater 2b, a third resistance heater 2c, and a heat insulating material 10 are arranged. That is, the manufacturing apparatus 100 includes the crucible 5. The crucible 5 is made of graphite. The crucible 5 is manufactured, for example, by cutting isotropic graphite. Therefore, the crucible 5 has pores that communicate the inside and the outside.

  The crucible 5 is composed of a pedestal 3 and a housing part 4. The pedestal 3 is configured to hold a seed crystal 11 described later. The pedestal 3 also functions as a lid for the crucible 5. The crucible 5 has an upper surface 5a, a bottom surface 5b facing the upper surface 5a, and a cylindrical inner wall 5c interposed between the upper surface 5a and the bottom surface 5b. The inner wall 5c has, for example, a cylindrical shape. The inner diameter of the crucible 5 is, for example, 100 mm or more and 1000 mm or less.

  At least a part of the inner wall 5c contains silicon. The silicon content of the inner wall is, for example, atomic absorption spectrometry (AAS), inductively coupled plasma atomic emission spectroscopy (ICP-AES), XP-AES, X-ray fluorescence analysis (ICP-AES), X-ray fluorescence analysis (ICP-AES). XRF) and the like. The measurement sample may be collected by scraping off a part of the inner wall. The cutting depth may be, for example, in the range from the inner wall to about 1 mm in the wall thickness direction. The crucible 5 may contain a trace amount of impurities as the balance other than carbon and silicon. Examples of such impurities include metals derived from cutting tools used during crucible production. Silicon may be locally distributed on a part of the inner wall 5c, or may be distributed on the entire inner wall 5c. Further, not only the inner wall 5c but also at least a part of the upper surface 5a and the bottom surface 5b may contain silicon.

  FIG. 2 is a schematic view showing a cross section in the extending direction of the inner wall of the crucible. Here, in the extending direction D of the inner wall 5c, a region located on the upper surface 5a side from the middle point of the inner wall 5c is defined as a first region 5c1, and a region located on the bottom surface 5b side from the middle point is defined as a second region 5c2. That is, the crucible 5 includes a first region 5c1 and a second region 5c2. Each of first region 5c1 and second region 5c2 may contain silicon.

  H in FIG. 2 indicates the distance between the top surface 5a and the bottom surface 5b. H is, for example, about 100 to 500 mm. The intermediate point is at a position 0.5H away from the top surface 5a and the bottom surface 5b on the inner wall 5c.

  The silicon concentration in the first region 5c1 may be higher than the silicon concentration in the second region 5c2. Alternatively, the silicon concentration in the first region 5c1 may be lower than the silicon concentration in the second region 5c2.

  Thus, when there is a difference between the silicon concentration in the first region 5c1 and the silicon concentration in the second region 5c2, the silicon concentration may continuously increase or decrease in the extending direction D. However, it may increase or decrease stepwise.

  There may be no substantial difference between the silicon concentration in the first region 5c1 and the silicon concentration in the second region 5c2.

  In the extending direction D, the silicon concentration may have a maximum value or a minimum value. In the extending direction D, the silicon concentration may be repeatedly increased or decreased periodically or aperiodically.

  In FIG. 2, the wall thickness of the crucible 5 is denoted as T. T is, for example, about 5 to 50 mm. A concentration gradient of silicon concentration may be formed from the inner wall 5c over a certain range in the wall thickness direction. The certain range may be, for example, a range from the inner wall 5c to several tens of μm in the wall thickness direction. Such a concentration gradient can be measured by, for example, Secondary Ion Mass Spectrometry (SIMS). The primary ion of SIMS may be, for example, a cesium (Cs) ion.

  The concentration gradient in the wall thickness direction may extend over the entire region in the wall thickness direction from the inner wall to the outer wall. Such a concentration gradient can be confirmed, for example, by collecting measurement samples from the inner wall side and the outer wall side and measuring the silicon concentration using an analytical method such as AAS as described above.

  As shown in FIG. 1, the manufacturing apparatus 100 includes a first resistance heater 2a for heating the upper surface 5a, a second resistance heater 2b for heating the bottom surface 5b, and a third resistance heater for heating the inner wall 5c. 2c. That is, the manufacturing apparatus 100 includes a resistance heater for heating the crucible 5. The third resistance heater 2c has, for example, a cylindrical outer shape. The third resistance heater 2 c is arranged so as to surround the outer periphery of the crucible 5. Each resistance heater is made of graphite. Thus, when using a graphite resistance heater, at least a part of each resistance heater may contain silicon. For example, at least a part of the third resistance heater 2c for heating the inner wall 5c may contain silicon. As described above, the graphite constituting the crucible and the resistance heater is a porous material. Therefore, it can be expected that the silicon contributes to the partial pressure of the silicon component in the crucible by containing silicon in the resistance heater adjacent to the crucible. The silicon content of the resistance heater can also be measured in the same manner as the crucible.

  Note that the silicon carbide single crystal manufacturing apparatus of the present embodiment may include an induction heating type heater instead of the resistance heater.

  The heat insulating material 10 is arrange | positioned so that the crucible 5, the 1st resistance heater 2a, the 2nd resistance heater 2b, and the 3rd resistance heater 2c may be covered. The heat insulating material 10 is made of, for example, graphite. The heat insulating material 10 may also contain silicon. However, as can be seen from FIG. 1, there is a considerable distance between the heat insulating material 10 and a position where a seed crystal 11 to be described later is to be disposed, and there are also shielding objects such as crucibles and resistance heaters between them. To do. Therefore, even if silicon is contained in the heat insulating material 10, it cannot be expected that the silicon contributes to the partial pressure of the silicon component in the crucible.

[Method for producing silicon carbide single crystal]
Next, a bulk single crystal manufacturing method using the silicon carbide single crystal manufacturing apparatus will be described. FIG. 3 is a flowchart showing an outline of the manufacturing method. As shown in FIG. 3, the manufacturing method includes a preparation step (S01) and a crystal growth step (S02). Each process is performed in this order. Hereinafter, each step will be described.

[Preparation process (S01)]
In the preparation step, first, the silicon carbide single crystal manufacturing apparatus 100 described above is prepared. That is, as shown in FIG. 1, a graphite crucible 5 having a top surface 5a, a bottom surface 5b facing the top surface 5a, and a cylindrical inner wall 5c interposed between the top surface 5a and the bottom surface 5b is provided. A silicon carbide single crystal manufacturing apparatus 100 containing at least a part of silicon is prepared. The method for incorporating silicon into the inner wall is not particularly limited. As an example, for example, a gas containing silicon may be brought into contact with the inner wall. In this case, silicon is adsorbed in the pores near the inner wall, and the inner wall contains silicon. Examples of the gas containing silicon include silane (SiH ₄ ) gas.

  Next, seed crystal 11 and solid raw material 12 are placed in crucible 5. In the crucible 5, the seed crystal 11 and the solid raw material 12 are arranged so as to face each other. Seed crystal 11 is a silicon carbide single crystal substrate made of, for example, polytype 4H—SiC. The seed crystal 11 is fixed to the pedestal 3 with, for example, a carbon adhesive. The diameter of the seed crystal 11 is, for example, about 100 to 300 mm. Solid raw material 12 is, for example, powder obtained by pulverizing silicon carbide polycrystal. The solid raw material 12 is filled in the storage unit 4.

[Crystal growth step (S02)]
In the crystal growth step, a bulk single crystal 13 of silicon carbide is grown in the crucible 5.

  The crucible 5 is heated by the first resistance heater 2a, the second resistance heater 2b, and the third resistance heater 2c. The temperature of each part of the crucible 5 is monitored by a radiation thermometer (not shown). A temperature gradient is formed in the crucible 5 such that the temperature decreases from the bottom surface 5b toward the top surface 5a. At this time, the temperature around the solid raw material 12 is, for example, about 2300 to 2500 ° C. The temperature around the seed crystal 11 is, for example, about 2000 to 2300 ° C.

  An inert gas such as argon (Ar) gas is introduced from the gas inlet 7. The introduced inert gas is exhausted from the gas exhaust port 8 by the exhaust pump 9. The pressure in the chamber 6 is adjusted by the amount of inert gas introduced and the amount of exhaust. When the temperature gradient in the crucible 5 is formed and the pressure in the chamber 6 falls below a predetermined pressure, sublimation of the solid material 12 is started. The sublimation gas generated from the solid raw material 12 is transported in the direction from the bottom surface 5 b to the top surface 5 a and reaches the seed crystal 11. The sublimation gas reprecipitates on the seed crystal 11 and grows as a bulk single crystal 13. During crystal growth, the pressure in the chamber 6 is adjusted to 5 kPa or less, for example.

  In the initial stage of crystal growth, it is considered that the silicon component is easily adsorbed on the inner wall 5c including the pores, and the partial pressure of the silicon component in the sublimation gas becomes unstable. However, in this embodiment, since silicon is previously contained in the inner wall 5c, it is considered that the adsorption of the silicon component to the inner wall 5c can be suppressed at the initial stage of crystal growth. This is considered to stabilize the C / Si ratio from the beginning of crystal growth.

  In the solid raw material 12, the silicon component tends to sublime prior to the carbon component. Therefore, in the latter stage of crystal growth, it is considered that the sublimation amount of the silicon component from the solid raw material decreases and the partial pressure of the silicon component in the sublimation gas decreases. However, in this embodiment, when the partial pressure of the silicon component in the sublimation gas is reduced to some extent, it is considered that silicon is desorbed from the inner wall 5c and compensates for the partial pressure of the silicon component in the sublimation gas. Thereby, it is considered that the C / Si ratio is stable even in the latter stage of crystal growth.

  From the above, in this embodiment, it is considered that the C / Si ratio can be controlled within a desired range over a long period of time.

  It should be thought that embodiment disclosed this time is an illustration and restrictive at no points. The scope of the present disclosure is shown not by the above-described embodiment but by the scope of claims, and is intended to include all modifications within the meaning and scope equivalent to the scope of claims.

2a 1st resistance heater 2b 2nd resistance heater 2c 3rd resistance heater 3 Base 4 Accommodating part 5 Crucible 5a Upper surface 5b Bottom surface 5c Inner wall 5c1 1st area | region 5c2 2nd area | region 6 Gas chamber 8 Gas exhaust port 9 Exhaust pump 10 Heat insulating material 11 Seed crystal 12 Solid raw material 13 Bulk single crystal 100 Manufacturing apparatus D Extension direction

Claims (5)

A graphite crucible having an upper surface, a bottom surface facing the upper surface, and a cylindrical inner wall interposed between the upper surface and the bottom surface;
At least a part of the inner wall contains silicon ,
It further comprises a graphite resistance heater for heating the crucible,
An apparatus for producing a silicon carbide single crystal, wherein at least a part of the resistance heater contains silicon. The crucible includes, in one cross section in the extending direction of the inner wall, a first region located on the upper surface side from an intermediate point of the inner wall and a second region located on the bottom surface side from the intermediate point of the inner wall. Including
The silicon carbide single crystal manufacturing apparatus according to claim 1, wherein each of the first region and the second region contains silicon.   The silicon carbide single crystal manufacturing apparatus according to claim 2, wherein a silicon concentration in the first region is higher than a silicon concentration in the second region.   The silicon carbide single crystal manufacturing apparatus according to claim 2, wherein a silicon concentration in the first region is lower than a silicon concentration in the second region. Further comprising thermal insulation,
The said resistance heater is a manufacturing apparatus of the silicon carbide single crystal of any one of Claims 1-4 arrange | positioned between the said crucible and the said heat insulating material .

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