WO2018062318A1

WO2018062318A1 - METHOD AND APPARATUS FOR PRODUCING SiC SINGLE CRYSTAL, AND SEED SHAFT USED IN PRODUCTION OF SiC SINGLE CRYSTAL

Info

Publication number: WO2018062318A1
Application number: PCT/JP2017/035055
Authority: WO
Inventors: 楠　一彦; 和明関; 寛典大黒; 幹尚加渡; 雅喜土井
Original assignee: トヨタ自動車株式会社
Priority date: 2016-09-27
Filing date: 2017-09-27
Publication date: 2018-04-05
Also published as: JP6627984B2; JPWO2018062318A1

Abstract

Provided is a production method with which it is possible to produce an SiC single crystal of high quality and high crystal thickness. A method for producing an SiC single crystal by a solution growth method in which the crystal growth plane (81) of a seed crystal (8) attached to the lower-end surface of a seed shaft is brought into contact with an Si-C solution (7) to grow an SiC single crystal, wherein the production method is provided with a step for heating and melting a raw material housed in a crucible (2) to produce an Si-C solution (7), and a step for bringing the crystal growth plane (81) into contact with the Si-C solution (7) and growing an SiC single crystal on the crystal growth plane (81). The seed shaft (6) has a surface layer gas permeability of 5 × 10^-5m²/s or less in regions other than the region to which the seed crystal (8) is attached, at least in the region (61) between the lower end and a position 30 mm from the lower end.

Description

Method and apparatus for producing SiC single crystal, and seed shaft used for producing SiC single crystal

The present invention relates to a method and an apparatus for manufacturing a SiC single crystal, and a seed shaft used for manufacturing a SiC single crystal.

Silicon carbide (SiC) is a thermally and chemically stable compound semiconductor. The SiC single crystal has excellent physical properties as compared with the Si single crystal. For example, a SiC single crystal has a large band gap, a high breakdown voltage, a high thermal conductivity, and a high electron saturation rate compared to a Si single crystal. For this reason, SiC single crystals are attracting attention as next-generation semiconductor materials.

Sublimation recrystallization and solution growth methods are known as methods for producing SiC single crystals. In the sublimation recrystallization method, an SiC single crystal is grown on a seed crystal by supplying a raw material onto the SiC seed crystal in a gas phase state. In the solution growth method, a SiC seed crystal is brought into contact with a Si—C solution to grow a SiC single crystal on the seed crystal. Specifically, a raw material containing Si is placed in a crucible, and the crucible is heated to melt the raw material, thereby producing a Si—C solution. The SiC single crystal is manufactured by bringing the seed crystal into contact with the Si—C solution and supersaturating the Si—C solution in the vicinity of the seed crystal. Here, the Si—C solution refers to a solution in which carbon is dissolved in a melt of Si or Si alloy.

The solution growth method has a lower crystal growth rate than the recrystallization method, and it is a problem to increase the crystal growth rate. Japanese Patent Application Laid-Open No. 2013-147397 discloses a method for producing an SiC single crystal using a seed crystal holding shaft whose side surface is covered with a reflecting member. According to this manufacturing method, the heat removal through the seed crystal holding shaft is improved by the reflecting member, and the growth rate is increased. In this manufacturing method, the reflecting member is disposed with a gap between the reflecting member and the single crystal so as not to come into direct contact with the seed crystal.

The solution growth method also has a problem that polycrystals precipitate at a low temperature portion in the solution, and it is also a problem to prevent the polycrystals from adhering to the grown crystals. Japanese Patent Application Laid-Open No. 2010-184838 discloses a SiC single crystal manufacturing apparatus in which a polycrystal generation inhibiting portion having lower wettability with respect to a solution than a carbon rod is provided on a side surface portion at the lower end of the carbon rod. Japanese Patent Laid-Open No. 2013-1619 discloses a SiC single crystal manufacturing apparatus including a crucible including an inner lid and an upper lid.

When a SiC single crystal is manufactured, regardless of the manufacturing method, polycrystal generation, mixing of different crystal polymorphs, introduction of crystal defects and dislocations, etc. may occur, and the quality of the SiC single crystal may deteriorate. The SiC single crystal is required to be further improved in quality. In addition, from the viewpoint of productivity improvement, there is a demand for a crystal lengthening technique.

Recently, in the solution growth method, it has been studied to increase the thickness of the SiC single crystal formed on the crystal growth surface of the seed crystal. In order to increase the thickness of the SiC single crystal, it is necessary to increase the growth rate of the SiC single crystal or lengthen the growth time of the SiC single crystal. However, when the growth time of the SiC single crystal is lengthened, there is a problem that the quality of the SiC single crystal is lowered.

Japanese Patent Application Laid-Open No. 2014-201508 discloses a method for producing a SiC single crystal that can increase the thickness of the SiC single crystal formed on the crystal growth surface of the SiC seed crystal. This manufacturing method includes a preparation process, a generation process, and a growth process. In the preparation step, a manufacturing apparatus including a crucible in which a raw material of the Si—C solution is accommodated and a high-frequency coil disposed around the side wall of the crucible is prepared. In the production step, the raw material in the crucible is heated and melted by a high frequency coil to produce a Si—C solution. In the growth step, a SiC seed crystal is brought into contact with the Si—C solution to grow a SiC single crystal on the seed crystal. The growth process includes a maintenance process. In the maintaining step, at least one of the crucible and the high frequency coil is moved relative to the other in the height direction, and the separation distance in the height direction between the liquid level of the Si—C solution and the height center of the high frequency coil is within a predetermined range. Keep in.

When the growth time of the SiC single crystal is lengthened, the growth of the SiC single crystal proceeds or the Si—C solution evaporates, so that the liquid level of the Si—C solution decreases. When the liquid level of the Si—C solution decreases, the heating condition of the Si—C solution by the high frequency coil changes, and the temperature of the Si—C solution near the SiC seed crystal changes. Thereby, the supersaturation degree of SiC in the region changes. Therefore, stable growth of the SiC single crystal is inhibited, and the quality of the SiC single crystal is lowered.

In the above manufacturing method, when the SiC single crystal is grown, the separation distance in the height direction between the liquid surface of the Si—C solution and the height center of the high-frequency coil is maintained within a predetermined range. Therefore, the heating condition of the Si—C solution by the high frequency coil is difficult to change. As a result, it is possible to suppress a change in the temperature near the SiC single crystal and, in turn, the degree of supersaturation near the SiC single crystal.

The manufacturing method of the SiC single crystal described in JP 2014-151509 A also includes a preparation step, a generation step, and a growth step. In this manufacturing method, the growth process includes a formation process and a maintenance process. In the forming step, a meniscus is formed between the growth interface of the SiC single crystal and the liquid surface of the Si—C solution. In the maintaining step, at least one of the seed shaft and the crucible is moved relative to the other in the height direction to maintain the fluctuation range of the meniscus height within a predetermined range.

In the above manufacturing method, when the SiC single crystal is grown, the fluctuation range of the meniscus height is maintained within a predetermined range. Therefore, it is possible to suppress a change in the degree of supersaturation in the vicinity of the seed crystal due to the fluctuation of the meniscus height.

The techniques disclosed in Japanese Patent Application Laid-Open Nos. 2014-201508 and 2014-201509 are effective means for manufacturing a SiC single crystal having a large crystal thickness. However, it has become clear that there are more growth condition parameters that must be controlled to increase the crystal thickness.

An object of the present invention is to provide a manufacturing method and a manufacturing apparatus capable of manufacturing a SiC single crystal having a high quality and a large crystal thickness, and a seed shaft used in these.

A manufacturing method according to an embodiment of the present invention includes a method for growing a SiC single crystal by a solution growth method, in which a crystal growth surface of a seed crystal attached to a lower end surface of a seed shaft is brought into contact with a Si—C solution to grow a SiC single crystal. A method for producing a Si—C solution by heating and melting a raw material contained in a crucible; bringing the crystal growth surface into contact with the Si—C solution; And growing the SiC single crystal. The seed shaft has a gas permeability of 5 × 10 ⁻⁵ m ² / s or less in at least a region between the lower end and a position 30 mm from the lower end other than the region to which the seed crystal is attached. It is.

A manufacturing apparatus according to an embodiment of the present invention is a manufacturing apparatus used for manufacturing a SiC single crystal by a solution growth method, a crucible in which a Si—C solution is accommodated, and a seed shaft to which a seed crystal is attached at a lower end surface. Is provided. The seed shaft has a gas permeability of 5 × 10 ⁻⁵ m ² / s or less in at least a region between the lower end and a position 30 mm from the lower end other than the region to which the seed crystal is attached. It is.

A seed shaft according to an embodiment of the present invention is a method for producing a SiC single crystal by a solution growth method in which a seed crystal is attached to a lower end surface, and a SiC single crystal is grown by bringing a crystal growth surface of the seed crystal into contact with a Si—C solution. The gas permeability of the surface layer is 5 × 10 ⁻⁵ m ² at least in the region between the lower end and the position 30 mm from the lower end other than the region to which the seed crystal is attached. / S or less.

According to the present invention, a manufacturing method and a manufacturing apparatus capable of manufacturing a SiC single crystal having a high quality and a large crystal thickness, and a seed shaft used for these can be obtained.

FIG. 1 is a flowchart of a method for producing a SiC single crystal according to the first embodiment of the present invention. FIG. 2 is a schematic cross-sectional view of an example of a manufacturing apparatus used for manufacturing a SiC single crystal by a solution growth method. FIG. 3 is a schematic view of a gas permeability measuring device. FIG. 4 is a schematic diagram of a gas permeability measuring device. FIG. 5 is a schematic cross-sectional view of another example of a manufacturing apparatus used for manufacturing a SiC single crystal by a solution growth method. FIG. 6 is a schematic diagram of a gas permeability measuring device. FIG. 7 is a schematic cross-sectional view of another example of a manufacturing apparatus used for manufacturing a SiC single crystal by a solution growth method. FIG. 8 is a schematic diagram of a meniscus of a Si—C solution. FIG. 9 is a schematic cross-sectional view of the grown SiC single crystal.

The present inventors examined a method for stably producing a SiC single crystal by a solution growth method for a long time. As a result, the following knowledge was obtained.

In the solution growth method, a SiC seed crystal is attached to the lower end surface of the seed shaft, and the SiC crystal is grown by bringing the crystal growth surface of the seed crystal into contact with the Si—C solution. The seed shaft is generally made of a carbonaceous material such as graphite and has a porous structure having pores. When the growth time of the SiC single crystal is increased, the vapor penetrates into the seed shaft. The invading steam may chemically react with carbon or the like constituting the seed shaft, or it may be liquefied inside the seed shaft and remain as a metal (hereinafter referred to as both steam and seed shaft). Are referred to as “reactive”).

Thus, when the seed shaft is exposed to the vapor of the Si—C solution for a long time, a kind of composite material is formed, and the thermal characteristics change from the initial state. For example, when a metal or the like enters the pores, the thermal conductivity of the seed shaft is increased. As a result, during the growth of the SiC single crystal, the amount of heat removed from the seed shaft increases, and the degree of supersaturation near the seed crystal increases. When the supersaturation degree in the vicinity of the seed crystal becomes excessively large, the two-dimensional growth changes to a three-dimensional growth surface form. As a result, solvent inclusion is easily formed, and the quality of the SiC single crystal is lowered.

By using a seed shaft having a reduced gas permeability compared to the conventional one, it is possible to suppress the reaction between the vapor of the Si—C solution and the seed shaft. As a result, the change in the thermal characteristics of the seed shaft due to the reaction with the vapor and the change in the supersaturation degree in the vicinity of the seed crystal due to the change can be suppressed, and the SiC single crystal can be stably grown for a long time.

The present invention has been completed based on the above findings. Hereinafter, with reference to drawings, the manufacturing method and manufacturing apparatus of SiC single crystal by one embodiment of the present invention, and the seed shaft used for these are explained. The drawings do not necessarily faithfully represent actual dimensional ratios and the like.

[First Embodiment]
FIG. 1 is a flowchart of a method for producing a SiC single crystal according to the first embodiment of the present invention. This manufacturing method is a method for manufacturing a SiC single crystal by a solution growth method, and includes a preparation step (Step S1), a generation step (Step S2) for generating a Si—C solution, and a seed crystal in a Si—C solution. And a growth step (step S3) in which a SiC single crystal is grown in contact with each other. Hereinafter, each process is explained in full detail.

[Preparation process (step S1)]
In this step, a manufacturing apparatus, a SiC seed crystal, and a raw material for the Si—C solution are prepared.

[Configuration of manufacturing equipment]
FIG. 2 is a schematic cross-sectional view of a manufacturing apparatus 100 which is an example of a manufacturing apparatus used for manufacturing a SiC single crystal by a solution growth method. The configuration of the manufacturing apparatus 100 illustrated in FIG. 2 is an exemplification, and the configuration of the manufacturing apparatus used in the present embodiment is not limited to this.

The manufacturing apparatus 100 includes a chamber 1, a crucible 2, a heat insulating material 3, a high frequency coil 4, a rotating shaft 5, and a seed shaft 6.

The chamber 1 accommodates the crucible 2, the heat insulating material 3, and the high frequency coil 4. When manufacturing a SiC single crystal, the chamber 1 is water-cooled.

The crucible 2 includes a cylinder part 21 and a bottom part 22 arranged at the lower end of the cylinder part 21. The crucible 2 accommodates the raw material for the Si—C solution 7. The crucible 2 preferably contains carbon. When the crucible 2 contains carbon, the crucible 2 becomes a carbon supply source to the Si—C solution 7.

The heat insulating material 3 is disposed so as to surround the crucible 2. The heat insulating material 3 keeps the crucible 2 warm. The high frequency coil 4 is disposed outside the crucible 2 and the heat insulating material 3. The high frequency coil 4 induction-heats the crucible 2. The vertical length of the high-frequency coil 4 is preferably longer than the vertical length of the Si—C solution 7. More preferably, the vertical length of the high-frequency coil 4 is equal to or greater than the vertical length of the crucible 2.

The rotary shaft 5 is arranged so that the axial direction is parallel to the vertical direction. The rotating shaft 5 supports the crucible 2 at one end. The other end of the rotating shaft 5 is connected to a drive device 59 disposed below the chamber 1. The drive device 59 rotates the rotating shaft 5 around the axial direction. According to this configuration, the crucible 2 can be rotated. The drive device 59 may have a function of moving the rotary shaft 5 up and down. According to this configuration, the temperature distribution of the Si—C solution 7 can be adjusted by changing the relative position of the crucible 2 and the coil 4.

The seed shaft 6 is arranged so that the axial direction is parallel to the vertical direction. An SiC seed crystal 8 is attached to the lower end surface of the seed shaft 6. The other end of the seed shaft 6 is connected to a driving device 69 disposed above the chamber 1. The drive device 69 moves the seed shaft 6 up and down. As will be described later, in the growth process, after the Si—C solution 7 is generated, the seed shaft 6 is lowered to bring the seed crystal 8 and the Si—C solution 7 into contact with each other. The drive device 69 may have a function of rotating the seed shaft 6 around the axial direction.

As will be described later, the growth process is performed at 1600 to 2050 ° C., for example. At least a portion of the seed shaft 6 located inside the heat insulating material 3 is formed of a material that can withstand such a high temperature. The seed shaft 6 is made of, for example, a refractory metal, a refractory metal carbide, or carbon. The seed shaft 6 is preferably made of carbon from an economical viewpoint.

The seed shaft 6 preferably has an outer diameter of 25 mm or more, more preferably an outer diameter of 40 mm or more, and further preferably an outer diameter of 45 mm or more.

In the present embodiment, the gas permeability of the surface layer in the vicinity of the lower end of the seed shaft 6 is set to 5 × 10 ⁻⁵ m ² / s or less. Specifically, in a region between the lower end and a position separated by a height h from the lower end (hereinafter referred to as “region 61”), the gas permeability of the surface layer is set to 5 × 10 ⁻⁵ m ² / s or less. To do. The gas permeability of the surface layer is preferably 5 × 10 ⁻⁶ m ² / s or less, more preferably 5 × 10 ⁻⁷ m ² / s or less.

It is possible to suppress the vapor of the Si—C solution 7 from entering the inside of the seed shaft 6 by reducing the gas permeability of the surface layer of the seed shaft 6. Here, the “surface gas permeability” refers to the gas permeability in a region from the surface to a depth of 3 mm. If the gas permeability of the surface layer is high, even if the internal gas permeability is low, the seed shaft 6 reacts with the vapor of the Si—C solution 7 in the surface layer, so that the change in the thermal characteristics of the seed shaft 6 cannot be suppressed. . On the other hand, if the gas permeability of the surface layer is low, the internal gas permeability may be high.

The seed shaft 6 may be formed of different materials for the surface layer and the inside. The seed shaft 6 may be hollow. By forming the inside of the seed shaft 6 from another material or making it hollow, the amount of heat removed from the seed shaft 6 during crystal growth can be adjusted.

The height h of the region 61 is at least 30 mm. As the height h is larger, the influence of the vapor of the Si—C solution 7 can be reduced. The height h is preferably 40 mm or more, and more preferably 50 mm or more. The seed shaft 6 may have a gas permeability of 5 × 10 ⁻⁵ m ² / s or less over the entire length.

A portion of the region 61 where the seed crystal 8 is attached may have a high gas permeability. This is because this portion is covered with the seed crystal 8 and does not come into contact with the vapor of the Si—C solution 7. In other words, the seed shaft 6 may have a surface layer gas permeability of 5 × 10 ⁻⁵ m ² / s or less in at least the region 61 other than the region where the seed crystal 8 is attached. In the example shown in FIG. 2, the diameter of the seed crystal 8 is larger than the diameter of the seed shaft 6. Therefore, the lower end surface of the seed shaft 6 is entirely covered with the seed crystal 8. In this case, the gas permeability of the surface layer on the lower end surface may be 5 × 10 ⁻⁵ m ² / s or less, or may be higher than 5 × 10 ⁻⁵ m ² / s.

The gas permeability of the surface layer of the seed shaft 6 can be controlled by, for example, applying a carbon adhesive to the surface of the seed shaft 6 and reducing the open porosity of the seed shaft 6. The carbon adhesive is obtained by kneading carbon powder into a resin. In this case, the gas permeability can be adjusted depending on the blending and application amount of the carbon adhesive.

When a carbon adhesive is applied to the surface of the seed shaft 6 to reduce the open porosity, it is necessary to apply the carbon adhesive throughout the region 61 other than the region where the seed crystal 8 is attached. If there is even a portion where the carbon adhesive is not applied, the gas permeates from that portion, so that the gas permeability cannot be reduced to 5 × 10 ⁻⁵ m ² / s or less. Therefore, for example, using a brush or the like, the carbon adhesive is applied to the entire surface of the region 61 other than the region where the seed crystal 8 is attached.

Alternatively, the gas permeability of the surface layer of the seed shaft 6 can be controlled by coating with SiC or pyrolytic graphite (PG). For the coating, for example, a chemical vapor deposition (CVD) method can be used. In this case, the gas permeability can be adjusted by the mixing ratio and flow rate of the gas used in the CVD method.

As another means for reducing the gas permeability of the surface layer of the seed shaft 6, it is conceivable to cover the seed shaft 6 with a shielding member having a low gas permeability (for example, a carbon sheet). However, with this means, since gas enters from the end of the shielding member, it is difficult to reduce the gas permeability to 5 × 10 ⁻⁵ m ² / s or less.

The gas permeability of the surface layer of the seed shaft 6 is described in Toshiaki Sogabe, Masaki Okada, “Gas Permeability of Large Cylindrical Isotropic Graphite”, Carbon, 1995 (No. 168), pp. 176-178. According to, measurement is performed as follows.

FIG. 3 is a schematic diagram of the gas permeability measuring device 9. The measuring device 9 includes a first chamber 91 and a second chamber 92.

The cylindrical test piece 6A including the surface layer is collected from the region 61 (FIG. 2) of the seed shaft 6. When the seed shaft 6 is solid, the inside is cut out into a cylindrical shape. One opening of the test piece 6 </ b> A is arranged so as to communicate with the chamber 92, and the other opening is closed with a lid 93. The end of the test piece 6A is sealed with a packing 94. In this state, the test piece 6A is accommodated in the first chamber 91.

The first chamber 91 is filled with nitrogen, and a predetermined pressure (for example, 100 to 300 kPa) is applied to the outside of the test piece 6A. On the other hand, the inside of the second chamber 92 is evacuated and decompressed. Thereby, the nitrogen gas in the first chamber 91 flows to the second chamber 92 through the test piece 6A, and the pressure in the second chamber 92 increases. At this time, the gas permeability K (m ² / s) of the test piece 6A is obtained by the following equation.

Here, ΔP is the pressure difference (Pa) between the inside and outside of the test piece 6A, L is the thickness (m) of the test piece 6A, A is the gas permeation area (m ² ), and P _B1 is the pressure in the second chamber 92 at time t1 ( Pa) and P _B2 are the pressure (Pa) of the second chamber 92 at time t2, and V _B is the volume (m ³ ) of the second chamber 91. In addition, let a gas permeation | transmission area be the logarithm average of the surface area of the outer periphery and inner periphery of 6 A of test pieces.

As described above, the gas permeability is an amount normalized by the reciprocal of the thickness of the test piece and the gas permeation area. Theoretically, the gas permeability value does not depend on the dimension of the test piece 6A if the gas permeability of the test piece 6A is uniform throughout.

When the gas permeability of the test piece 6A has a distribution, the measured gas permeability value is an average value of the gas permeability in the entire test piece 6A. When the gas permeability is controlled by the above-described method of applying a carbon adhesive to the seed shaft 6 or the method of coating the seed shaft 6, the gas permeability of the seed shaft 6 is considered to be lower as it is closer to the surface. Therefore, if the gas permeability is 5 × 10 ⁻⁵ m ² / s or less as measured with a test piece including a region 3 mm or more from the surface, the gas permeability in a region from the surface to a depth of 3 mm is also 5 × 10. ^It can be concluded that it is ⁻⁵ m ² / s or less.

When measuring the gas permeability including the lower end surface of the seed shaft 6, as shown in FIG. 4, a bottomed cylindrical test piece 6 </ b> B including the bottom is collected from the seed shaft 6 and measured in the same manner as described above. Good.

[Seed crystal]
Next, a SiC seed crystal 8 is prepared. The seed crystal 8 is a single crystal of SiC. The seed crystal 8 is attached to the lower end surface of the seed shaft 6 so that the crystal growth surface 81 faces the bottom 22 of the crucible 2.

The seed crystal 8 is preferably an SiC single crystal having the same crystal structure as the SiC single crystal to be manufactured. For example, when producing a 4H polymorphic SiC single crystal, it is preferable to use a 4H polymorphic seed crystal. When a 4H polymorphic seed crystal is used, the crystal growth surface 81 is a (0001) plane or (000-1) plane, or a plane inclined at an angle of 8 ° or less from the (0001) plane or (000-1) plane; It is preferable to do. By using these surfaces, the SiC single crystal can be stably grown.

[Si-C raw material]
Next, the raw material of the Si—C solution 7 is placed in the crucible 2. The raw material may be, for example, only silicon, or a mixture of silicon and other metal elements. Examples of the metal element include titanium, manganese, chromium, cobalt, vanadium, and iron. The raw material may be, for example, a lump or a powder.

[Generation Step (Step S2)]
The chamber 1 is filled with an inert gas. The crucible 2 is induction-heated by the high-frequency coil 4 and the raw material in the crucible 2 is heated to the melting point or higher. When the crucible 2 contains carbon, when the crucible 2 is heated, the carbon is dissolved from the crucible 2 into the melt, and the Si—C solution 7 is generated. When the crucible 2 does not contain carbon, carbon may be supplied from the outside. When carbon dissolves in the Si—C solution 7, the carbon solubility in the Si—C solution 7 approaches the saturation concentration.

[Growth process (step S3)]
The seed shaft 6 is lowered by the driving device 69, and the crystal growth surface 81 of the seed crystal 8 is brought into contact with the Si—C solution 7. In this state, the high frequency coil 4 is controlled to keep the Si—C solution 7 in the vicinity of the seed crystal 8 at the crystal growth temperature. The crystal growth temperature is, for example, 1600 to 2050 ° C., preferably 1850 to 2000 ° C. At this time, the vicinity of the seed crystal 8 is set to a low temperature, and SiC is supersaturated. When SiC becomes supersaturated, a SiC single crystal grows on the crystal growth surface 81.

The method for lowering the temperature near the seed crystal 8 is not particularly limited. For example, the high-frequency coil 4 may be controlled so that the temperature in the vicinity of the seed crystal 8 is lower than the temperature in other regions. Alternatively, the vicinity of the seed crystal 8 may be cooled by a refrigerant. Specifically, a coolant may be circulated inside the seed shaft 6. The refrigerant is, for example, an inert gas such as helium or argon. By circulating the refrigerant inside the seed shaft 6, the seed crystal 8 is cooled, and the temperature in the vicinity of the seed crystal 8 can be lowered.

At this time, it is preferable to rotate the rotating shaft 5 and the crucible 2 by the driving device 59. Further, it is preferable to rotate the seed shaft 6 and the seed crystal 8 by the driving device 69. The rotation direction of the crucible 2 and the rotation direction of the seed crystal 8 may be the same or opposite. Each rotation speed may be constant or may be varied.

[Effect of the first embodiment]
By increasing the time for maintaining the vicinity of the seed crystal 8 in the supersaturated state (hereinafter referred to as “growth time”), the thickness of the SiC single crystal formed on the crystal growth surface 81 can be increased. On the other hand, when the growth time is lengthened, the reaction between the vapor of the Si—C solution 7 and the seed shaft 6 proceeds, and the thermal characteristics of the seed shaft 6 change from the initial state.

When the thermal characteristics of the seed shaft 6 change, the amount of heat removed from the seed shaft 6 due to heat transfer and radiation changes. As a result, the supersaturation degree of the Si—C solution 7 in the vicinity of the seed crystal 8 also changes. If the supersaturation is outside the proper range, stable SiC single crystals cannot be grown. Specifically, different types of polymorphs and crystals with different orientations are likely to be formed, and solvent inclusions are likely to be formed.

According to the manufacturing method according to the present embodiment, the seed shaft 6 has a gas permeability of 5 × 10 ⁻⁵ m ² / s or less at least in the region 61 other than the region to which the seed crystal 8 is attached. It is. By reducing the gas permeability of the surface layer of the seed shaft 6, it is possible to suppress the vapor of the Si—C solution 7 from entering the inside of the seed shaft 6.

By carrying out the growth process using the seed shaft 6, it is possible to suppress the reaction of the vapor of the Si—C solution 7 and the seed shaft 6 even if the growth time is lengthened. Therefore, the thermal characteristics of the seed shaft 6 can be maintained in the initial state for a long time. Thereby, the production of the SiC single crystal by the solution growth method can be carried out stably for a long time. Therefore, a SiC single crystal having a high quality and a large crystal thickness can be manufactured.

The manufacturing method according to the present embodiment is not limited to this, but is suitable when the diameter of the seed shaft 6 is large, for example, when the diameter of the seed shaft is 25 mm or more. The larger the diameter of the seed shaft 6, the larger the amount of heat removed from the seed shaft 6, and the greater the influence on the crystal growth due to the change in the characteristics of the seed shaft 6. The manufacturing method according to the present embodiment is particularly suitable when the diameter of the seed shaft 6 is 40 mm or more.

The manufacturing method according to the present embodiment is not limited to this, but is suitable when the growth time is long, for example, when the growth time is 30 hours or more. This is because the longer the growth time, the more obvious the influence of the reaction between the seed shaft 6 and the steam. The manufacturing method according to the present embodiment is particularly suitable when the growth time is 40 hours or more.

[Other example 1 of manufacturing apparatus]
FIG. 5 is a schematic cross-sectional view of a manufacturing apparatus 200 as another example of a manufacturing apparatus used for manufacturing a SiC single crystal by a solution growth method. The manufacturing apparatus 200 differs in the structure of the crucible compared with the manufacturing apparatus 100 (FIG. 2). The manufacturing apparatus 200 includes a crucible 25 instead of the crucible 2 of the manufacturing apparatus 100.

The crucible 25 further includes an inner lid 23 in addition to the cylindrical portion 21 and the bottom portion 22 disposed at the lower end of the cylindrical portion 21. The inner lid 23 is disposed so as to be positioned above the liquid surface of the Si—C solution 7 in a state where the Si—C solution 7 is accommodated in the main body of the crucible 25 including the cylindrical portion 21 and the bottom portion 22. . The inner lid 23 has a through hole 23 a through which the seed shaft 6 is passed.

According to the structure of the crucible 25, radiation from the liquid surface of the Si—C solution 7 is blocked by the inner lid 23. Therefore, the space between the liquid level of the Si—C solution 7 and the inner lid 23 is kept warm. According to this configuration, the temperature of the region other than the vicinity of the seed crystal 8 of the Si—C solution 7 can be made uniform.

The inner lid 23 is made of a material that can withstand high temperatures, like the seed shaft 6. The inner lid 23 is preferably made of carbon. As with the seed shaft 6, the inner lid 23 reacts with the vapor of the Si—C solution 7 when the growth time is lengthened, and the thermal characteristics change from the initial state. As a result, the temperature distribution in the space between the liquid level of the Si—C solution 7 and the inner lid 23 also changes from the initial state.

In the present embodiment, the gas permeability of the surface layer of at least the lower surface 231 of the inner lid 23 is set to 5 × 10 ⁻⁵ m ² / s or less. According to this configuration, the reaction of the vapor of the Si—C solution 7 and the inner lid 23 can be suppressed even if the growth time is extended. Therefore, the thermal characteristics of the inner lid 23 can be maintained in the initial state for a long time. The gas permeability of the surface layer of the lower surface 231 of the inner lid 23 is preferably 5 × 10 ⁻⁶ m ² / s or less, more preferably 5 × 10 ⁻⁷ m ² / s or less.

The inner lid 23 only needs to have a gas permeability of 5 × 10 ⁻⁵ m ² / s or less on the surface layer on the lower surface in contact with the vapor of the Si—C solution 7. The gas permeability of the inside and upper surfaces of the inner lid 23 is arbitrary.

As in the case of the seed shaft 6, the gas permeability of the surface layer on the lower surface of the inner lid 23 can be controlled by applying a carbon adhesive to the inner lid 23 or coating the inner lid 23 with SiC or PG. .

As shown in FIG. 6, the gas permeability of the surface layer of the inner lid 23 can be measured in the same manner as in the case of the seed shaft 6 (FIGS. 3 and 4) by collecting a test piece 23A from the inner lid 23. .

[Other example 2 of manufacturing apparatus]
FIG. 7 is a schematic cross-sectional view of a manufacturing apparatus 300 which is another example of a manufacturing apparatus used for manufacturing a SiC single crystal by a solution growth method. The manufacturing apparatus 300 differs from the manufacturing apparatus 100 (FIG. 2) in the configuration of the seed shaft. The manufacturing apparatus 300 includes a seed shaft 65 instead of the seed shaft 6 of the manufacturing apparatus 100.

The seed shaft 65 includes a main body 66 and a pedestal 67 attached to the lower end surface of the main body 66. The main body 66 and the pedestal 67 may be connected by screws, for example, or may be fixed by an adhesive. Further, the main body 66 and the pedestal 67 may be configured integrally. That is, the seed shaft 65 may be composed of a single member.

The seed crystal 8 is attached to the lower end surface of the pedestal 67. According to this configuration, the amount of heat removed from the seed shaft 65 can be adjusted by adjusting the diameters of the main body 66 and the pedestal 67, and the degree of supersaturation in the vicinity of the seed crystal 8 can be controlled. In the example shown in FIG. 7, the diameter of the seed crystal 8 is smaller than the diameter of the main body 66 and larger than the diameter of the pedestal 67.

Also in the present embodiment, the gas permeability of the surface layer of the seed shaft 65 is set to 5 × 10 ⁻⁵ m ² / s or less in a region between the lower end of the seed shaft 65 and a position separated from the lower end by the height h. . A region between the lower end of the seed shaft 65 and a position away from the lower end by a height h includes a partial region 661 of the main body 66 and a pedestal 67. That is, in this embodiment, the gas permeability of the surface layer of the region 661 and the pedestal 67 is 5 × 10 ⁻⁵ m ² / s or less.

Also in this embodiment, the portion to which the seed crystal 8 is attached may have a high gas permeability. In the example shown in FIG. 7, since the diameter of the seed crystal 8 is larger than the diameter of the pedestal 67, the lower end surface of the pedestal 67 is entirely covered with the seed crystal 8. Therefore, the surface layer of the lower end surface of the pedestal 67 may have a high gas permeability. On the other hand, since the lower end surface of the main body 66 is partially exposed, the gas permeability of the surface layer needs to be 5 × 10 ⁻⁵ m ² / s or less in this portion.

As with the seed shaft 6, the seed shaft 65 can suppress the reaction with the vapor of the Si—C solution 7 even if the growth time is lengthened. Therefore, the thermal characteristics of the seed shaft 65 can be maintained in the initial state for a long time.

[Second Embodiment]
The method for producing a SiC single crystal according to the second embodiment of the present invention differs from the first embodiment in the growth process (step S3 in FIG. 1).

In this embodiment, after the seed crystal 8 is brought into contact with the Si—C solution 7 in the growth process, the seed shaft 6 is raised by a predetermined distance. As a result, a meniscus 71 is formed between the seed crystal 8 and the Si—C solution 7 as shown in FIG. The height of the meniscus 71 can be controlled by the distance d between the seed crystal 8 and the liquid surface of the Si—C solution 7.

According to the present embodiment, the enlargement angle of the SiC single crystal can be adjusted by the meniscus 71.

If the growth time of the SiC single crystal is lengthened, the growth of the SiC single crystal proceeds or the Si—C solution 7 evaporates, so that the liquid level of the Si—C solution 7 decreases. As the liquid level of the Si—C solution 7 decreases, the distance d between the seed crystal 8 and the liquid level of the Si—C solution 7 changes, and the shape of the meniscus 71 changes from the initial state. When the shape of the meniscus 71 changes, the supersaturation degree in the vicinity of the seed crystal 8 also changes accordingly. In order to perform stable growth for a long time, it is preferable to move the seed shaft 6 and / or the crucible 2 in a direction to compensate for the drop in the liquid level of the Si—C solution 7. That is, it is preferable to estimate in advance the speed at which the liquid level of the Si—C solution 7 is lowered and to lower the seed shaft 6 at the same speed or raise the crucible 2 at the same speed. Alternatively, both the seed shaft 6 and the crucible 2 may be moved so that the distance d between the seed crystal 8 and the liquid surface of the Si—C solution 7 is constant.

Hereinafter, the present invention will be described more specifically with reference to examples. The present invention is not limited to these examples.

The SiC single crystal was manufactured by changing the gas permeability of the seed shaft and the quality of the manufactured SiC single crystal was evaluated.

[Example 1]
The SiC single crystal was manufactured using the apparatus according to the manufacturing apparatus 100 (FIG. 2). The composition of the raw material of the Si—C solution was Si: Cr = 0.6: 0.4 in atomic ratio. The seed crystal was a 4H polymorphic SiC single crystal having a diameter of 50.8 mm, and the crystal growth plane was a (000-1) plane.

The seed shaft made of isotropic graphite and having a diameter of 46 mm was used. The seed shaft was coated with a thin and thin carbon adhesive on the side and bottom surfaces to close the open pores and reduce the gas permeability. The application area of the carbon adhesive was an area between the lower end of the seed shaft and 50 mm from the lower end. After applying the carbon adhesive, the seed shaft was baked at 250 ° C. for 1 hour in an air atmosphere to volatilize the binder component of the carbon adhesive. A specimen was collected from the seed shaft adjusted under the same conditions, and the gas permeability of the surface layer was measured at room temperature. The gas permeability was 5 × 10 ⁻⁵ m ² / s.

Using this seed shaft, crystal growth was performed by bringing the seed crystal into contact with the Si—C solution. The crystal growth temperature was 1950 ° C., and the temperature gradient near the seed crystal was 12 ° C./cm. After bringing the seed crystal into contact with the Si—C solution, the seed shaft was raised by 0.5 mm to form a meniscus. After 40 hours from the start of growth, the seed shaft was raised to separate the seed crystal from the Si—C solution, thereby terminating the crystal growth.

[Example 2]
The amount of carbon adhesive applied to the seed shaft was changed to improve the degree of opening of the open pores. The gas permeability of the surface layer at room temperature measured with a test piece collected from a seed shaft adjusted under the same conditions was 5 × 10 ⁻⁶ m ² / s. Other conditions were the same as in Example 1 to produce a SiC single crystal.

[Example 3]
Instead of applying the carbon adhesive to the seed shaft, about 10 μm of SiC was coated by the CVD method. The gas permeability of the surface layer at room temperature measured with a test piece collected from a seed shaft adjusted under the same conditions was 5 × 10 ⁻⁷ m ² / s. Other conditions were the same as in Example 1 to produce a SiC single crystal.

[Example 4]
The SiC single crystal was manufactured using the apparatus according to the manufacturing apparatus 200 (FIG. 5). A graphite inner lid having a thickness of 5 mm was placed at a position 10 mm above the surface of the Si—C solution. A carbon adhesive was applied to both sides (including side surfaces) of the inner lid. After applying the carbon adhesive, the inner lid was baked at 250 ° C. for 1 hour in an air atmosphere to volatilize the binder component of the carbon adhesive. The gas permeability of the surface layer at room temperature measured with a test piece collected from the inner lid adjusted under the same conditions was 5 × 10 ⁻⁵ m ² / s. Other conditions were the same as in Example 1 to produce a SiC single crystal.

[Example 5]
A SiC single crystal was manufactured using an apparatus according to the manufacturing apparatus 300 (FIG. 7). The seed shaft used was a solid body with a diameter of 75 mm and a base with a diameter of 46 mm and a height of 5 mm attached to the lower end. The body and pedestal are both isotropic graphite. A seed crystal having a diameter of 50.8 mm was attached to the lower end surface of the pedestal. A carbon adhesive was applied thinly and thinly on the side and bottom surfaces of the main body and the side surface of the pedestal to close the open pores and reduce the gas permeability. The application area of the carbon adhesive was an area between the lower end of the seed shaft and a position 50 mm from the lower end. After applying the carbon adhesive, the seed shaft was baked at 250 ° C. for 1 hour in an air atmosphere to volatilize the binder component of the carbon adhesive. A specimen was collected from the seed shaft adjusted under the same conditions, and the gas permeability of the surface layer was measured at room temperature. The gas permeability was 5 × 10 ⁻⁵ m ² / s. Other conditions were the same as in Example 1 to produce a SiC single crystal.

[Example 6]
The main body of the seed shaft has a hollow structure with an outer diameter of 75 mm and an inner diameter of 69 mm. Other conditions were the same as in Example 5 to produce a SiC single crystal.

[Example 7]
During the crystal growth, the seed shaft was driven to descend 1.0 mm so that the meniscus height coincided with the initial state. Other conditions were the same as in Example 6 to produce a SiC single crystal.

[Comparative example]
The graphite material was used as it was as a seed shaft. The gas permeability of the surface layer at room temperature measured by a test piece collected from a seed shaft adjusted under the same conditions was 8 × 10 ⁻⁴ m ² / s. Other conditions were the same as in Example 1 to produce a SiC single crystal.

[Evaluation methods]
The manufactured SiC single crystal was cut, the cut surface was polished, and the growth thickness of the SiC single crystal was measured. As shown in FIG. 9, when a polycrystal or inclusion is formed on the surface of the SiC single crystal, the thickness up to that is defined as “uniform growth thickness”, and the uniform growth thickness of each SiC single crystal was measured. . The case where the uniform growth thickness was 3.0 mm or more was evaluated as “excellent”, the case where it was 2.0 mm or more and less than 3.0 mm was evaluated as “good”, and the case where it was less than 2.0 mm was evaluated as “impossible”.

Manufacturing conditions and evaluation results are summarized in Table 1.

From the comparison of Examples 1 to 3 and the comparative example, it can be seen that the uniform growth thickness can be increased by lowering the gas permeability. It can also be seen that by setting the gas permeability to 5 × 10 ⁻⁵ m / s or less, the uniform growth thickness can be set to 2.0 mm or more. Furthermore, as shown in Example 7, it can be seen that the uniform growth thickness can be increased to 3.0 mm or more by combining the meniscus height control.

As mentioned above, although embodiment of this invention was described, embodiment mentioned above is only the illustration for implementing this invention. Therefore, the present invention is not limited to the above-described embodiment, and can be implemented by appropriately modifying the above-described embodiment without departing from the spirit thereof.

Claims

A method for producing a SiC single crystal by a solution growth method, wherein a crystal growth surface of a seed crystal attached to a lower end surface of a seed shaft is brought into contact with a Si—C solution to grow a SiC single crystal,
Heating and melting the raw material contained in the crucible to produce the Si-C solution;
Contacting the crystal growth surface with the Si-C solution and growing the SiC single crystal on the crystal growth surface,
The seed shaft has a gas permeability of 5 × 10 −5 m 2 / s or less in at least a region between the lower end and a position 30 mm from the lower end other than the region to which the seed crystal is attached. A manufacturing method.
The manufacturing method according to claim 1,
The crucible is
A main body including a cylindrical portion and a bottom portion disposed at a lower end portion of the cylindrical portion;
An inner lid having a through-hole passing through the seed shaft and positioned in the cylindrical portion above the Si-C solution level in a state where the Si-C solution is accommodated in the main body;
The manufacturing method wherein the gas permeability of the surface layer on at least the lower surface of the inner lid is 5 × 10 −5 m 2 / s or less.
The manufacturing method according to claim 1 or 2,
The seed shaft has an outer diameter of 25 mm or more.
The production method according to any one of claims 1 to 3,
In the growing step, the time for bringing the crystal growth surface into contact with the Si—C solution is 30 hours or more.
A manufacturing apparatus used for manufacturing a SiC single crystal by a solution growth method,
A crucible containing a Si-C solution;
A seed shaft to which a seed crystal is attached to the lower end surface;
The seed shaft has a gas permeability of 5 × 10 −5 m 2 / s or less in at least a region between the lower end and a position 30 mm from the lower end other than the region to which the seed crystal is attached. Is a manufacturing device.
The manufacturing apparatus according to claim 5,
The seed shaft is a manufacturing apparatus having an outer diameter of 25 mm or more.
A seed shaft used for manufacturing a SiC single crystal by a solution growth method in which a seed crystal is attached to a lower end surface and a crystal growth surface of the seed crystal is brought into contact with a Si-C solution to grow a SiC single crystal,
A seed shaft having a gas permeability of 5 × 10 −5 m 2 / s or less in a region other than a region to which the seed crystal is attached, at least in a region between a lower end and a position 30 mm from the lower end .
The seed shaft according to claim 7,
A seed shaft having an outer diameter of 25 mm or more.