JP6593212B2 - Method for producing silicon carbide single crystal - Google Patents

Description

  The present disclosure relates to a method for producing a silicon carbide single crystal.

  Japanese Patent Laying-Open No. 2015-030659 (Patent Document 1) discloses a method for producing a silicon carbide single crystal using a sublimation method. In Patent Document 1, a silicon carbide seed substrate is fixed to a pedestal using a carbon adhesive.

JP, 2015-030659, A

  An object of the present disclosure is to suppress a silicon carbide seed substrate from peeling from a pedestal when a silicon carbide single crystal is grown by a sublimation method.

  The method for producing a silicon carbide single crystal of the present disclosure is a method for producing a silicon carbide single crystal by growing a silicon carbide single crystal by a sublimation method on a silicon carbide seed substrate fixed to a pedestal. The manufacturing method of the present disclosure includes a step of preparing a silicon carbide seed substrate having a first main surface and a second main surface located on the opposite side of the first main surface, and in a chlorine-containing atmosphere, Heat treating the main surface, interposing an adhesive between the first main surface and the pedestal, and fixing the silicon carbide seed substrate to the pedestal via the adhesive. .

  According to the above, when the silicon carbide single crystal is grown by the sublimation method, it is possible to suppress the silicon carbide seed substrate from peeling from the pedestal.

It is a schematic sectional drawing which shows an example of a crystal growth apparatus. It is a 1st flowchart which shows the outline of the manufacturing method of the silicon carbide single crystal of this indication. It is a 2nd flowchart which shows the outline of the manufacturing method of the silicon carbide single crystal of this indication. It is a 3rd flowchart which shows the outline of the manufacturing method of the silicon carbide single crystal of this indication. It is a 4th flowchart which shows the outline of the manufacturing method of the silicon carbide single crystal of this indication.

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

  [1] The method for producing a silicon carbide single crystal of the present disclosure is a method for producing a silicon carbide single crystal by growing a silicon carbide single crystal by a sublimation method on a silicon carbide seed substrate fixed to a pedestal. The manufacturing method of the present disclosure includes a step of preparing a silicon carbide seed substrate having a first main surface and a second main surface located on the opposite side of the first main surface, and in a chlorine-containing atmosphere, Heat treating the main surface, interposing an adhesive between the first main surface and the pedestal, and fixing the silicon carbide seed substrate to the pedestal via the adhesive. .

  The sublimation method is a crystal growth method in which a solid raw material is sublimated at a high temperature and the sublimated raw material is recrystallized on a seed substrate. In the sublimation method, the solid raw material is disposed at the bottom of the crucible, and the seed substrate is fixed to a pedestal located at the top of the crucible. Conventionally, a carbon adhesive having heat resistance has been used for fixing a silicon carbide seed substrate. This is because when a silicon carbide single crystal is grown by the sublimation method, the silicon carbide seed substrate and the pedestal are exposed to a high temperature of 2000 ° C. or higher.

  However, with the increase in diameter of silicon carbide single crystals, even when a carbon adhesive having heat resistance is used, the silicon carbide seed substrate may be peeled off from the pedestal during crystal growth. Delamination significantly degrades the crystal quality of the single crystal, even if it is partial. Therefore, even when growing a large-diameter silicon carbide single crystal, a fixing method capable of suppressing the peeling of the silicon carbide seed substrate is required.

  There are various factors that cause the silicon carbide seed substrate to peel off from the pedestal. The present inventor has found that the influence of the residual stress accumulated in the silicon carbide seed substrate is large among them. That is, the silicon carbide seed substrate undergoes various processes such as grinding and polishing in the manufacturing process. By these processes, it is considered that residual stress is accumulated in the silicon carbide seed substrate. The residual stress is released by the high temperature during crystal growth. It is considered that peeling occurs because the silicon carbide seed substrate is deformed with the release of the residual stress.

  In the manufacturing method of the present disclosure shown in [1] above, the first main surface of the silicon carbide seed substrate is an adhesive surface to be fixed to the pedestal. The second main surface is a growth surface on which a silicon carbide single crystal is to be grown. In the manufacturing method of the present disclosure, the first main surface is heat-treated in a chlorine-containing atmosphere before the first main surface is fixed to the pedestal. When the first main surface, that is, silicon carbide (SiC) is heat-treated in a chlorine-containing atmosphere, the first main surface is etched. Thereby, the residual stress accumulated in the silicon carbide seed substrate is released. Thus, it is thought that peeling during crystal growth can be suppressed by releasing the residual stress in advance.

  [2] In the manufacturing method of the present disclosure, in the heat treatment step, silicon on at least the surface of the first main surface can be removed.

  [3] The manufacturing method of the present disclosure may further include a step of machining the first main surface before the step of heat treatment.

  [4] In the above machining step, the first main surface may be lapped or the first main surface may be ground.

  [5] In the manufacturing method of the present disclosure, the silicon carbide seed substrate may have a diameter of 75 mm or more.

[Details of Embodiment of the Present Disclosure]
Hereinafter, embodiments of the present disclosure will be described. However, the embodiment of the present disclosure is not limited to the following description. In the following description, the same or corresponding elements are denoted by the same reference numerals, and the same description is not repeated. In addition, a negative crystallographic index is usually expressed by adding a “-” (bar) above a number, but in this specification, for convenience, a negative sign is added before the number. To express a negative index in crystallography.

[Method for producing silicon carbide single crystal]
In the manufacturing method of the present disclosure, a bulk single crystal of silicon carbide is grown by a sublimation method. First, the outline of the sublimation method will be described with reference to FIG.

《Crystal manufacturing equipment》
FIG. 1 is a schematic cross-sectional view showing an example of a crystal manufacturing apparatus. As shown in FIG. 1, the crystal manufacturing apparatus 200 includes a chamber 201. The chamber 201 is provided with a gas introduction port 202 and a gas exhaust port 203. The gas exhaust port 203 is connected to the exhaust pump 204.

  In the chamber 201, a crucible 210, a resistance heater 205, and a heat insulating material 206 are arranged. The crucible 210 is made of, for example, graphite. The crucible 210 is composed of a housing part 211 and a pedestal 212. The pedestal 212 also functions as a lid for the crucible 210. The accommodating part 211 is a bottomed cylindrical shape. The outer shape of the accommodating part 211 is, for example, a cylindrical shape. The accommodating part 211 is filled with the solid raw material 10. Solid raw material 10 is, for example, powder obtained by pulverizing silicon carbide polycrystal.

  Silicon carbide seed substrate 100 is fixed to pedestal 212. Adhesive 20 is interposed between pedestal 212 and silicon carbide seed substrate 100. Silicon carbide seed substrate 100 has a first main surface 101 and a second main surface 102 located on the opposite side of first main surface 101. The first main surface 101 is a so-called adhesive surface. The first main surface 101 is fixed to the pedestal 212 via an adhesive. The second main surface 102 is a so-called growth surface. The second main surface 102 faces the solid raw material 10. During crystal growth, a predetermined temperature gradient is formed in the crucible 210 in the direction from the solid raw material 10 toward the silicon carbide seed substrate 100. In the temperature gradient, the solid raw material 10 is on the high temperature side, and the silicon carbide seed substrate 100 is on the low temperature side. The source gas generated by sublimation of the solid source 10 moves toward the silicon carbide seed substrate 100 and is recrystallized on the second main surface 102. Thus, silicon carbide single crystal 1 can be grown on second main surface 102.

  Next, the manufacturing method of this indication is demonstrated along a flowchart. FIG. 2 is a first flowchart illustrating an outline of the manufacturing method of the present disclosure. As shown in FIG. 2, the manufacturing method of the present disclosure includes a preparation step (S101), a machining step (S102), a heat treatment step (S103), an adhesion step (S104), a fixing step (S105), and a crystal growth step (S106). ). Hereinafter, each step will be described.

<< Preparation Step (S101) >>
In the preparation step (S101), silicon carbide seed substrate 100 having first main surface 101 and second main surface 102 located on the opposite side of first main surface 101 is prepared.

  The polytype of silicon carbide seed substrate 100 is typically 4H—SiC. The polytype of silicon carbide seed substrate 100 may be, for example, 3C—SiC, 6H—SiC, or the like. Silicon carbide seed substrate 100 is prepared, for example, by slicing a bulk single crystal of silicon carbide to a predetermined thickness. For the slice, for example, a wire saw can be used. The thickness of the silicon carbide seed substrate may be 0.5 mm or more, for example. The thickness of the silicon carbide seed substrate may be, for example, 5.0 mm or less, or 2.0 mm or less.

  The planar shape of silicon carbide seed substrate 100 is, for example, a circular shape. The manufacturing method of the present disclosure is expected to be applied to the silicon carbide seed substrate 100 having a large diameter. As the diameter of the silicon carbide seed substrate 100 is larger, peeling is more likely to occur. Therefore, a means for suppressing peeling becomes more important. The diameter of silicon carbide seed substrate 100 may be 75 mm or more. The diameter of silicon carbide seed substrate 100 may be, for example, 100 mm or more, or 150 mm or more. The diameter of silicon carbide seed substrate 100 may be, for example, 300 mm or less.

  Of the crystal planes of silicon carbide (SiC), the (0001) plane is sometimes referred to as a “Si (silicon) plane”. The (000-1) plane is sometimes referred to as a “C (carbon) plane”. In silicon carbide seed substrate 100, first main surface 101 may be a Si surface or a C surface. The second main surface 102 may be a C surface or a Si surface.

  The first main surface 101 and the second main surface 102 may be surfaces inclined at a predetermined angle from the Si surface or the C surface. The direction in which the first main surface 101 and the second main surface 102 are inclined from a predetermined crystal plane is also referred to as “off direction”. The off direction is typically the <11-20> direction.

  The angle at which the first main surface 101 and the second main surface 102 are inclined from the Si surface or the C surface is also referred to as an “off angle”. The off angle may be, for example, 1 ° or more, 2 ° or more, or 3 ° or more. The off angle may be 8 ° or less, 7 ° or less, 6 ° or less, or 5 ° or less.

<< Machining step (S102) >>
In the manufacturing method of the present disclosure, the first main surface 101 may be machined before a heat treatment step (S103) described later. Specifically, for example, the first main surface 101 may be lapped or the first main surface 101 may be ground. A lapping machine for a semiconductor substrate can be used for lapping. The lapping process may be performed by a loose abrasive method. For the free abrasive grains, for example, a slurry containing diamond particles can be used. A grinding machine for a semiconductor substrate can be used for the grinding process. For the grinding wheel, for example, a diamond wheel can be used.

  The finish of the first main surface 101 in machining may be a satin finish. Since the surface area of the first main surface 101 is increased by finishing the first main surface 101 into a surface having moderate unevenness, an improvement in adhesive strength can be expected. Moreover, since the convex part bites into the adhesive, an improvement in adhesive strength due to a so-called anchor effect can be expected. The surface roughness of the first main surface 101 after machining is, for example, about 0.1 to 1.0 μm in terms of arithmetic average roughness Ra.

  In this step, processing such as CMP (Chemical Mechanical Polishing) may be performed on the second main surface 102 which is a growth surface. Residual stress generated by CMP, lapping, grinding, or the like is released in a heat treatment step (S103) described later.

<< Heat treatment step (S103) >>
In the heat treatment step (S103), the first main surface 101 is heat-treated in a chlorine-containing atmosphere. For example, a tubular electric furnace can be used for the heat treatment. The material of the furnace wall may be quartz, for example.

The atmosphere in the furnace is a chlorine-containing atmosphere. The chlorine-containing atmosphere can be formed, for example, by circulating a gas containing chlorine atoms (Cl) in the furnace. As the gas containing chlorine atoms, for example, chlorine (Cl ₂ ) gas, boron trichloride (BCl ₃ ) gas, carbon tetrachloride (CCl ₄ ) gas, chlorine trifluoride (ClF ₃ ) gas, or the like can be used. . A carrier gas may be used in combination. As the carrier gas, for example, a rare gas such as nitrogen (N ₂ ) gas or argon (Ar) gas, oxygen (O ₂ ) gas, or the like can be used. The flow rate of the gas containing chlorine atoms is, for example, about 0.1 to 0.5 L / min. For example, when chlorine gas is used, the flow rate of chlorine gas is preferably about 0.2 L / min.

  The heat treatment temperature may be, for example, about 800 ° C. or more and 1200 ° C. or less. The heat treatment temperature is typically about 900 ° C. The pressure in the furnace is, for example, about 0.05 kPa to 150 kPa. The heat treatment time is, for example, about 30 minutes to 2 hours. The heat treatment time is typically about 45 minutes.

  By heat-treating the first main surface 101 under the above conditions, the first main surface 101 is etched. Thereby, the residual stress accumulated in silicon carbide seed substrate 100 is released.

  In the etching described above, silicon (Si) on at least the surface of the first main surface 101 can be removed. By removing silicon (Si) from silicon carbide (SiC), a carbon layer having a higher carbon (C) composition ratio than silicon carbide is formed over a certain depth range from first main surface 101. Will be. That is, the heat treatment step (S103) can include a step of forming a carbon layer having a higher carbon composition ratio than silicon carbide on the first main surface 101.

  Since the carbon layer has a high carbon composition ratio, the carbon layer has higher affinity with the carbon adhesive than silicon carbide. Therefore, the formation of the carbon layer can be expected to improve the adhesive strength due to the carbon adhesive. Furthermore, since the carbon layer is a layer obtained by removing Si from SiC, it is considered that the carbon layer has a more porous structure than SiC. Therefore, the carbon adhesive can easily penetrate into the first main surface 101, and it can be expected that the adhesive strength is improved.

  The thickness of the carbon layer formed in the heat treatment step (S103) is, for example, about 1 μm to 20 μm. The thickness of the carbon layer is typically about 5 μm or more and 10 μm or less. The carbon layer may be a layer consisting essentially of carbon. Alternatively, the carbon layer may contain chlorine. The thickness and composition of the carbon layer can be measured, for example, by analyzing a cross section in the thickness direction of the silicon carbide seed substrate 100 using SEM-EDX (Scanning Electron Microscope with Energy Dispersive X-ray spectroscopy) or the like.

  In the carbon layer, the surface shape of the first main surface 101 before etching is inherited. That is, the arithmetic average roughness of the first main surface 101 adjusted in the machining step (S102) can be maintained even after the heat treatment step (S103).

  In addition, since it is not preferable that the 2nd main surface 102 used as a growth surface is etched, it is good to perform a heat treatment step (S103) in the aspect in which the 2nd main surface 102 is not etched.

  FIG. 3 is a second flowchart showing an outline of a method for producing a silicon carbide single crystal of the present disclosure. As shown in FIG. 3, for example, a protective film covering the second main surface 102 may be formed in order to protect the second main surface 102 from etching. In other words, the manufacturing method of the present disclosure may include a protective film forming step (S111) that forms a protective film that covers the second main surface 102 between the preparation step (S101) and the heat treatment step (S103). . FIG. 3 shows a mode in which the protective film forming step (S111) is performed after the machining step (S102). However, the protective film forming step (S111) is performed before the machining step (S102). It may be broken.

The thickness of the protective film may be, for example, about 0.01 μm or more and 10 μm or less. The protective film may be, for example, an insulating film made of silicon dioxide (SiO ₂ ), silicon nitride (Si ₃ N ₄ ), or an organic film made of photoresist or the like. The protective film can be removed by, for example, ashing, acid treatment or the like after the heat treatment step (S103).

  FIG. 4 is a third flowchart illustrating an outline of the manufacturing method of the present disclosure. As shown in FIG. 4, when it is difficult to form a protective film, it is desirable to perform a process of planarizing the second main surface 102 after the heat treatment step (S103). That is, as shown in FIG. 4, the manufacturing method of the present disclosure may include a planarization step (S112) in which the second main surface 102 is planarized after the heat treatment step (S103). For example, the second main surface 102 may be planarized by performing processing such as mechanical polishing and CMP on the second main surface 102.

  FIG. 5 is a fourth flowchart showing an outline of the method for producing a silicon carbide single crystal of the present disclosure. In the protective film formation step (S111) described above, the second main surface 102 may be etched despite the formation of the protective film. As shown in FIG. 5, it is desirable to perform the planarization step (S112) also in that case. That is, the manufacturing method of the present disclosure can include both the protective film forming step (S111) and the planarization step (S112).

<< Adhesion Step (S104) >>
In the bonding step (S104), the adhesive 20 is interposed between the first main surface 101 and the base 212. The adhesive 20 may be applied to the first main surface 101, may be applied to the pedestal 212, or may be applied to both the first main surface 101 and the pedestal 212.

  The adhesive 20 is typically a carbon adhesive. The carbon adhesive includes an organic solvent and graphite fine particles dispersed in the organic solvent. The carbon adhesive may be, for example, “ST-201” manufactured by Nisshinbo Chemical Co., Ltd.

<< Fixed Step (S105) >>
In the fixing step (S 105), silicon carbide seed substrate 100 is fixed to pedestal 212 through adhesive 20. For example, the silicon carbide seed substrate 100 can be fixed to the pedestal 212 via the adhesive 20 by applying a load in the stacking direction of the silicon carbide seed substrate 100 and the pedestal 212. In this step, heat treatment may be further performed. The heat treatment may be performed in two stages, for example. First, the organic solvent contained in a carbon adhesive is vaporized by hold | maintaining at the temperature of about 150-300 degreeC. Subsequently, the remainder of the carbon adhesive is carbonized by holding at a temperature of about 500 to 1000 ° C. As a result, the carbon adhesive becomes an adhesive layer firmly bonded to both the silicon carbide seed substrate 100 and the pedestal 212. In the manufacturing method of the present disclosure, since the carbon layer, the carbon adhesive (adhesive layer), and the pedestal 212 formed on the first main surface 101 are all composed mainly of carbon, an improvement in adhesive strength can be expected.

<< Crystal Growth Step (S106) >>
In the crystal growth step (S106), a bulk single crystal of silicon carbide is grown on second main surface 102 of silicon carbide seed substrate 100 by a sublimation method.

  As shown in FIG. 1, silicon carbide seed substrate 100 fixed to pedestal 212 is arranged in crucible 210 so as to face solid raw material 10 filled in container 211.

  For example, argon gas is introduced into the chamber 201 from the gas inlet 202. The introduced argon gas is exhausted from the gas exhaust port 203. The pressure in the chamber 201 is adjusted by the balance between the amount of gas introduced and the amount of exhaust. During crystal growth, the pressure in the chamber 201 is, for example, about 0.1 kPa to 10 kPa.

  The resistance heater 205 heats each part of the crucible 210. Thereby, a temperature gradient is formed in the crucible 210. The temperature around the solid raw material 10 is adjusted to about 2200 to 2400 ° C., for example. The temperature around silicon carbide seed substrate 100 is adjusted to about 2000 to 2200 ° C., for example. The temperature of each part of the crucible 210 can be measured by, for example, a radiation thermometer.

  The solid raw material 10 is sublimated when the above pressure condition and temperature condition are satisfied. The source gas generated by the sublimation moves toward the silicon carbide seed substrate 100 and is recrystallized on the second main surface 102. Thus, silicon carbide single crystal 1 can be grown on second main surface 102. In the manufacturing method of the present disclosure, since silicon carbide seed substrate 100 is firmly fixed to pedestal 212, a large-diameter single crystal having a diameter of, for example, 100 mm or more can be grown. For example, a long single crystal can be grown.

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

DESCRIPTION OF SYMBOLS 1 Silicon carbide single crystal 10 Solid raw material 20 Adhesive 100 Silicon carbide seed board | substrate 101 1st main surface 102 2nd main surface 200 Crystal manufacturing apparatus 201 Chamber 202 Gas introduction port 203 Gas exhaust port 204 Exhaust pump 205 Resistance heater 206 Heat insulating material 210 Crucible 211 container 212 pedestal

Claims (5)

A silicon carbide single crystal manufacturing method for growing a silicon carbide single crystal by a sublimation method on a silicon carbide seed substrate fixed to a pedestal,
Providing the silicon carbide seed substrate having a first main surface and a second main surface located on the opposite side of the first main surface;
Heat-treating the first main surface in a chlorine-containing atmosphere;
Interposing an adhesive between the first main surface and the pedestal;
Fixing the silicon carbide seed substrate to the pedestal via the adhesive, and a method for producing a silicon carbide single crystal.   The method for manufacturing a silicon carbide single crystal according to claim 1, wherein in the heat treatment step, silicon on at least a surface of the first main surface is removed.   The method for manufacturing a silicon carbide single crystal according to claim 1, further comprising a step of machining the first main surface before the heat treatment step.   The method for producing a silicon carbide single crystal according to claim 3, wherein in the machining step, the first main surface is lapped or the first main surface is ground.   The method for producing a silicon carbide single crystal according to claim 1, wherein the silicon carbide seed substrate has a diameter of 75 mm or more.

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