JP2010111540A - Method for growing silicon carbide single crystal, seed crystal, and silicon carbide single crystal - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for growing a silicon carbide single crystal, by which a high quality silicon carbide single crystal having low crystal defect density is grown with a satisfactory reproducibility. <P>SOLUTION: The method for growing the silicon carbide single crystal includes an etching-treated surface-forming process for forming an etching-treated surface 4a by subjecting a crystal growth surface of a seed crystal 4 to an etching treatment; and a crystal growth process for growing the silicon carbide single crystal on the etching-treated surface 4a by a sublimation method. By the method, factors inhibiting crystal growth, such as dust or polishing scratch damage, are removed by performing the etching treatment before crystal growth, and lateral growth is accelerated to grow the high quality silicon carbide single crystal having few crystal defects. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a method for growing a silicon carbide single crystal, a seed crystal, and a silicon carbide single crystal. In particular, the present invention relates to a crystal growth method of a high-quality silicon carbide single crystal used for an optical device or a semiconductor element for high withstand voltage and high power.

Silicon carbide has high heat conductivity, excellent heat resistance and mechanical strength, and is resistant to radiation, and is physically and chemically stable and has a wide energy band gap (forbidden band width). .
In particular, 4H-type silicon carbide single crystal has a wide forbidden band of about 3 eV at room temperature, so that it can be used as a rectifier and switching element with high withstand voltage and low loss, and can withstand use at high temperatures. It can be used for environmental element materials and radiation resistant elements.

In Non-Patent Document 1, as a method for producing a silicon carbide single crystal having the above-mentioned excellent characteristics, a silicon carbide single crystal is grown on a crystal growth surface of a seed crystal by sublimating a raw material silicon carbide powder at a high temperature. A sublimation method is disclosed.
In the production of a silicon carbide single crystal by the sublimation method, first, a silicon carbide powder as a raw material is filled in a crucible on which a seed crystal (substrate) is placed, and then this crucible is placed in an apparatus for crystal growth. . Next, after the inside of the crystal growth apparatus is made an inert gas atmosphere, the pressure is reduced. Thereafter, the temperature of the crystal growth apparatus is raised to 1800 to 2400 ° C. As a result, the silicon carbide powder inside the crucible is decomposed and sublimated to generate sublimation chemical species (gas), which reach the crystal growth surface of the seed crystal held in the crystal growth temperature range and form the silicon carbide single crystal. Epitaxially grow. By this method, silicon carbide single crystal wafers having a size of up to about 4 inches are currently obtained and are commercially available.

However, in the manufacturing process of the silicon carbide single crystal by the sublimation method, when foreign matter is present on the crystal growth surface or there is damage such as polishing scratches, the crystal growth is inhibited, and a high quality silicon carbide single crystal is produced. In some cases, it was not possible to grow.
Normally, with temperature rising heating for crystal growth, not only Si contributing to crystal growth but also various vapors such as Si ₂ C, SiC ₂ and SiC are generated from silicon carbide powder as a raw material, and sublimation vapor is generated. Generate pressure fluctuation. The sublimation vapor pressure fluctuation causes abnormal nuclei to be formed with a focus on damage such as foreign matter and polishing scratches. When the abnormal nuclei are formed, crystal growth along the creepage (hereinafter, creeping growth) is inhibited. Thereby, crystal defects such as different polytypes and micropipes are induced from the crystal growth surface of the seed crystal, and a high-quality silicon carbide single crystal cannot be grown.

In order to suppress the above crystal defects, it is necessary to remove damage such as foreign matter and polishing scratches. Further, a step shape unique to the crystal may be formed on the crystal growth surface.
Patent Documents 1 to 3 disclose a method for removing crystal growth inhibiting factors such as damage such as foreign matter and polishing scratches, and a method for forming a step shape.

For example, Patent Document 1 describes a method of forming a step shape on the crystal growth surface by providing an off angle with respect to the crystal growth surface. However, when the off angle is provided, the step shape remains disordered only by machining, and thus it has been necessary to prepare by some method.
Patent Document 2 discloses a method for removing damage by molten KOH etching. However, this method has a problem that the Si surface is selectively etched, linear defects are likely to remain, the C surface is etched unevenly, and undulation is likely to occur.
Further, Patent Document 3 discloses a reactive ion etching method. This method has a problem that the surface remains damaged during ion irradiation.
JP 2004-99340 A JP-A-7-97299 JP-A-9-183700 Yu. M.M. Tailov and V.M. F. Tsvetkov, Journal of Crystal Growth, Vol. 52 (1981), p. 146-p. 150.

  The present invention has been made in view of the above circumstances. A silicon carbide single crystal that removes a factor that inhibits crystal growth, promotes creeping growth, and grows a high-quality silicon carbide single crystal having a low crystal defect density with good reproducibility. An object is to provide a crystal growth method of crystals.

As a result of intensive studies to solve the above problems, the present inventors have obtained knowledge for forming a step shape unique to a crystal on the crystal growth surface of the seed crystal regardless of the off angle of the seed crystal. .
That is, the present invention provides the following means.

(1) An etching treatment surface forming step for forming an etching treatment surface by etching a crystal growth surface of a seed crystal, and a crystal growth step for crystal growth of a silicon carbide single crystal on the etching treatment surface. A method for growing a silicon carbide single crystal.
(2) The method for growing a silicon carbide single crystal according to (1), wherein the etched surface has a step shape.
(3) The crystal growth method for a silicon carbide single crystal according to (1) or (2), wherein a step shape having a surface roughness Ra of 0.03 nm to 2 nm is formed by the etching process.
(4) The method for growing a silicon carbide single crystal according to any one of (1) to (3), wherein the etching process is a dry etching process using hydrogen gas as an etching gas.
(5) The crystal growth method for a silicon carbide single crystal according to (4), wherein the etching gas contains a hydrocarbon gas of 0.01 vol% to 0.5 vol%.
(6) The crystal growth method of a silicon carbide single crystal according to (4), wherein the etching gas contains 1 vol% to 10 vol% of a halogen gas or a halogen compound gas.
(7) The silicon carbide single crystal according to any one of (1) to (6), wherein the seed crystal is etched to a depth of 0.2 μm to 1.0 μm in the etching treatment surface forming step. Crystal growth method.
(8) A step of removing the sacrificial oxide film after the sacrificial oxidation of the crystal growth surface to form a sacrificial oxide film before the etching treatment surface forming step is performed. 7) The crystal growth method for a silicon carbide single crystal according to any one of 7).
(9) A seed crystal comprising a silicon carbide single crystal and having an etching surface having a step shape with a surface roughness Ra of 0.03 nm to 2 nm.
(10) The crystal growth is performed using the silicon carbide single crystal crystal growth method according to any one of (1) to (8), and the dislocation density is 1 × 10 ⁴ pieces / cm ² or less. Silicon carbide single crystal.

  According to the above configuration, there is provided a method for growing a silicon carbide single crystal that removes a factor that hinders crystal growth, promotes creeping growth, and grows a high-quality silicon carbide single crystal having a low crystal defect density with good reproducibility. can do.

  The method of growing a silicon carbide single crystal according to the present invention includes an etching treatment surface forming step of forming an etching treatment surface by etching a crystal growth surface of a seed crystal, and growing a silicon carbide single crystal on the etching treatment surface. The crystal growth process, the etching process can be performed before crystal growth to remove crystal growth hindrance factors such as dust and polishing scratches damage, promote creeping growth, and increase the number of crystal defects. A quality silicon carbide single crystal can be grown. In addition, since the crystal growth surface is modified, dislocations generated during the crystal growth process can be suppressed, and a high-quality silicon carbide single crystal having a low dislocation density can be grown.

Hereinafter, modes for carrying out the present invention will be described. However, the present invention is not limited to the following embodiments.
(First embodiment)
<Crystal growth method of silicon carbide single crystal>
In the crystal growth method of a silicon carbide single crystal according to an embodiment of the present invention, a sacrificial oxide film is formed by sacrificing a crystal growth surface of a seed crystal, and then the sacrificial oxide film is removed to clean the crystal growth surface. A crystal growth surface cleaning step, an etching treatment surface formation step of etching the crystal growth surface to form an etching treatment surface, a crystal growth step of growing a silicon carbide single crystal on the etching treatment surface, Have

<Crystal growth surface cleaning process>
First, after cutting into a thickness of about 0.3 to 5 mm from a substantially cylindrical silicon carbide single crystal ingot, the surface is polished and molded to form a substantially disk-shaped silicon carbide single crystal wafer. One surface of the silicon carbide single crystal wafer having a substantially circular shape is a crystal growth surface on which a silicon carbide seed crystal is grown by a sublimation method. As this crystal growth surface, a (0001) plane or a (000-1) plane is used. Here, “−1” in the notation of (000-1) plane is a place where “−1” is originally written with a horizontal line on the number. The crystal growth plane may be inclined from {0001} to about 30 °.
Further, as the silicon carbide single crystal ingot, for example, one made by the Atchison method, the Rayleigh method or the sublimation method is used.

Next, the silicon carbide single crystal wafer is cleaned with an organic solvent, an acid or / and an alkali to remove contamination on the surface.
Next, for example, the substrate is heated to about 1000 to 1200 ° C. in an oxygen atmosphere to form an oxide film (hereinafter referred to as a sacrificial oxide film) on the surface of the silicon carbide single crystal wafer. Next, the sacrificial oxide film is removed with hydrofluoric acid to completely remove dirt and processing damage that cannot be removed by washing with an organic solvent, acid or / and alkali in the previous stage.
Thereby, a seed crystal composed of a silicon carbide single crystal wafer is formed.

<Etching surface formation process>
Next, the crystal growth surface of the seed crystal is etched by a vapor phase method to form an etched crystal growth surface (hereinafter, etched surface). If an active molecular species (hydrogen radical or the like) is obtained in the etching process, either plasma excitation or thermal excitation can be used, but thermal excitation capable of more stable etching is preferable. As a method of thermal excitation, high-frequency heating or resistance overheating is possible as long as it can be heated to 1000 ° C. or higher.

FIG. 1 is a schematic cross-sectional view showing an example of a silicon carbide single crystal etching apparatus used in a silicon carbide single crystal crystal growth method according to an embodiment of the present invention.
As shown in FIG. 1, the etching apparatus 100 includes a reaction vessel 11 having a cavity 11c in which a material to be etched such as a seed crystal 4 can be placed. As a material of the reaction vessel 11, quartz glass, stainless steel, or the like can be used. The reaction vessel 11 is provided with a gas inlet 17 and a gas outlet 18. By introducing or exhausting a predetermined gas, the cavity portion 11c can be brought into a predetermined gas atmosphere at a predetermined pressure. Further, a heating device (not shown) is disposed outside the reaction vessel 11, and the material to be etched such as the seed crystal 4 can be heated by heating the reaction vessel 11. As the heating device, a high-frequency heating coil or a heater can be used.

As shown in FIG. 1, the seed crystal 4 as the material to be etched is disposed on a graphite susceptor (not shown) in the cavity 11 c of the reaction vessel 11 with the crystal growth surface as the surface to be etched facing up. . In this state, hydrogen gas, hydrocarbon gas, halogen gas, or the like introduced from the gas inlet 17 into the cavity portion 11c is flowed on the crystal growth surface of the seed crystal 4 at a predetermined temperature and pressure, and then gas exhaust is performed. By exhausting from the mouth 18, the crystal growth surface of the seed crystal 4 can be etched to form an etching treatment surface 4a.
As specific etching conditions, for example, an etching gas is blown onto the crystal growth surface of the seed crystal at a temperature of 1400 to 1700 ° C. in an environment of a pressure of 15 to 35 kPa for 5 to 20 minutes to perform an etching process. Form a surface.

The etching gas used for forming the etching treatment surface is preferably hydrogen gas. Thereby, a seed crystal can be etched rapidly.
The etching gas may be mainly hydrogen gas, and a hydrocarbon gas, a halogen gas or a halogen compound gas may be added. At this time, the hydrocarbon-based gas is preferably added in a concentration range of 0.01 to 0.5 vol%. The halogen gas or the halogen compound gas is preferably added in a concentration range of 1 to 10% vol%. Thereby, an etching rate can be controlled suitably.

The etching rate of the seed crystal varies depending on the concentration of impurities contained in the seed crystal. For example, when the impurity concentration is low, the etching rate is increased. At this time, it is possible to control the etching rate to be appropriate by adding a hydrocarbon gas to reduce the etching rate.
Conversely, when the impurity concentration is high, the etching rate is slow. At this time, the etching rate can be increased by adding halogen or a halogen compound gas, and the etching amount can be controlled to be appropriate.

  The etching amount of the seed crystal is preferably 0.2 to 1.0 μm, and more preferably 0.4 to 0.6 μm. As a result, damage such as polishing scratches can be eliminated from the etched surface, and a step shape unique to the crystal can be formed on the etched surface.

  The surface roughness Ra of the etched surface is preferably 0.03 to 2 nm, and more preferably 0.1 to 1 nm. When the surface roughness Ra is less than 0.03 nm, the etching effect is too small, and damage such as polishing scratches may not be removed. On the contrary, when the surface roughness Ra exceeds 2 nm, abnormal nuclei are likely to be generated.

<Crystal growth process>
Next, a crystal growth process for growing a silicon carbide single crystal on the etched surface of the seed crystal by a sublimation method will be described.
FIG. 2 is a schematic cross-sectional view showing an example of a silicon carbide single crystal crystal growth apparatus used in the silicon carbide single crystal crystal growth method according to the embodiment of the present invention.
As shown in FIG. 2, the crystal growth apparatus 101 is schematically configured from a vacuum vessel 1 provided with a gas inlet 7 and a gas outlet 8, and a heating device 3 disposed outside the vacuum vessel 1. . The vacuum container 1 is made of a material that maintains a high vacuum such as quartz or stainless steel. A crucible 6 is arranged inside the vacuum apparatus 1.

  The crucible 6 includes a cylindrical main body portion 6a that is open only on one end side, and a disc-shaped lid portion 6b that covers the main body portion 6a. A part of the lid portion 6b protrudes in a columnar shape, and serves as a base portion 6c to which a seed crystal is attached. As a material of the crucible 6, for example, a carbon material such as graphite can be used. The carbon material is preferably subjected to a purification treatment with a halogen gas or the like. Thereby, generation | occurrence | production of impurity gas can be suppressed.

  First, the seed crystal 4 is fixed to the base portion 6c of the lid portion 6b of the crucible 6 with an adhesive or a screw. At this time, it arrange | positions so that the etching process surface 4a of the seed crystal 4 may face the bottom face side of the main-body part 6a of the crucible 6. FIG.

  Next, a sufficient amount of silicon carbide powder 5 for crystal growth of a silicon carbide single crystal is filled as a raw material on the bottom surface side of main body portion 6 a of crucible 6 so as to face seed crystal 4. And the main-body part 6a is covered with the cover part 6b.

Next, the crucible 6 is surrounded by the heat insulating material 2. As a material of the heat insulating material 2, for example, a carbon material such as carbon fiber can be used. The carbon material is also preferably subjected to a purification treatment with a halogen gas or the like. Thereby, generation | occurrence | production of impurity gas can be suppressed. By surrounding the crucible 6 with the heat insulating material 2 in this manner, the temperature control of the crucible 6 brought into a high temperature state becomes easy.
Next, the crucible 6 provided with the seed crystal 4 and the silicon carbide powder 5 is disposed inside the vacuum vessel 1.

Next, using a turbo molecular pump (not shown) connected to the gas discharge port 8, the air in the vacuum container 1 is exhausted, and the inside of the vacuum container 1 is, for example, 4.0 × 10 ⁻³ Pa˜ The pressure is reduced to 6.7 × 10 ⁻³ Pa.
Next, an inert gas such as high-purity argon (Ar) gas is introduced into the vacuum vessel 1 from the gas introduction port 7, and the inside of the vacuum vessel is brought to normal pressure to create an inert gas atmosphere.
Next, the pressure is reduced again to 6.7 × 10 ⁻³ Pa from the gas discharge port, and the inside of the vacuum vessel 1 is brought into a reduced pressure state of an inert gas atmosphere.
Next, an inert gas such as high-purity argon (Ar) gas is reintroduced through the gas inlet 7 to set the inside of the vacuum vessel 1 to 93.3 kPa. Thereby, for example, an environment of an inert gas atmosphere of 93.3 kPa is obtained.

  Next, the heating device 3 composed of a high-frequency heating coil disposed so as to surround the vacuum vessel 1 is heated to heat the vacuum vessel 1 and the crucible 6 inside thereof. The heating device 3 is not limited to the high frequency heating coil, and may be a resistance heating type device.

  At this time, the position of the high-frequency heating coil of the heating device 3 is adjusted so that the upper part of the crucible 6 is a low temperature part and the lower part of the crucible 6 is a high temperature part. Thereby, sublimation gas is efficiently generated from the silicon carbide powder 5 at the lower part of the crucible 6, the sublimation gas is cooled at the upper part of the crucible 6, and a silicon carbide single crystal is crystallized on the etching surface 4 a of the seed crystal 4. Can be grown.

The temperature of the high temperature part is set to a temperature at which sublimation gas is generated from the silicon carbide powder 5 filled in the crucible 6, for example, 1900 ° C. or more. It is preferable to set it as 2000 degreeC-2400 degreeC, and it is more preferable to set it as 2250-2300 degreeC.
Moreover, it is preferable that the temperature of the said low-temperature part shall be lower than the temperature of the said high-temperature part, and shall be 1800-2300 degreeC.
In addition, the temperature of the said high temperature part and the said low temperature part is measured with the radiation thermometer 9 arrange | positioned up and down on the outer side of the vacuum vessel 1. FIG.

Next, in a state where the crucible 6 is set to the above set temperature, the inert gas is again discharged from the gas discharge port 8 so that the inside of the vacuum vessel 1 is brought into a reduced pressure state of 133.3 to 13332.2 Pa. Crystal growth of a silicon carbide single crystal is performed on the etched surface 4 a of the crystal 4. By performing crystal growth for a certain period of time, a silicon carbide single crystal having a predetermined size can be grown.
At this time, if necessary, impurities such as nitrogen and aluminum can be added to adjust the electrical conductivity of the crystal.

The etched surface 4a of the seed crystal 4 is cleaned so that no foreign matter or the like exists, and a step shape is formed to remove damage such as polishing scratches. Therefore, even if sublimation vapor pressure fluctuations occur in the crystal growth step, abnormal nuclei are not formed on the etched surface 4 a of the seed crystal 4. Therefore, crystal defects such as different polytypes and micropipes due to the occurrence of abnormal nuclei are not induced. By forming the etched surface 4a in this manner, the crystal growth inhibiting factor is removed, and the creeping growth can be promoted, so that a high quality silicon carbide single crystal can be stably grown.
Furthermore, since the etched surface 4a of the seed crystal 4 is modified, dislocations and the like generated in the normal crystal growth process are suppressed, and high-quality silicon carbide having a dislocation density of 1 × 10 ⁴ pieces / cm ² or less. Single crystals can be grown.

  In order to form a silicon carbide single crystal wafer from the obtained silicon carbide single crystal, for example, the silicon carbide single crystal obtained as described above is cut perpendicularly to the crystal growth direction, and the cut surface Is polished to form a silicon carbide single crystal wafer.

  The crystal growth method of a silicon carbide single crystal according to an embodiment of the present invention includes an etching treatment surface forming step of forming an etching treatment surface 4a by etching a crystal growth surface of the seed crystal 4, and silicon carbide on the etching treatment surface 4a. It has a crystal growth process for growing a single crystal, so that it can be etched before crystal growth to remove foreign factors and damage to polishing crystals, etc. A high quality silicon carbide single crystal with few crystal defects can be grown. In addition, since the crystal growth surface is modified, dislocations generated during the crystal growth process can be suppressed, and a high-quality silicon carbide single crystal having a low dislocation density can be grown.

  In the crystal growth method of a silicon carbide single crystal according to an embodiment of the present invention, since the etching treatment surface 4a has a step shape, a high-quality silicon carbide single crystal is obtained by removing a crystal growth inhibiting factor and promoting creeping growth. Can grow.

  The crystal growth method of a silicon carbide single crystal according to an embodiment of the present invention has a configuration in which a step shape having a surface roughness Ra of 0.03 nm to 2 nm is formed by the etching process. Can be promoted to grow a high-quality silicon carbide single crystal.

  In the crystal growth method for a silicon carbide single crystal according to an embodiment of the present invention, since the etching process is a dry etching process using hydrogen gas as an etching gas, the crystal growth inhibiting factor is removed and the creeping growth is promoted. High quality silicon carbide single crystal can be grown.

  In the method for growing a silicon carbide single crystal according to an embodiment of the present invention, the etching gas contains a hydrocarbon-based gas of 0.01 vol% to 0.5 vol%. It can be promoted to grow a high quality silicon carbide single crystal.

  In the crystal growth method of a silicon carbide single crystal according to an embodiment of the present invention, the etching gas contains 1 vol% to 10 vol% of a halogen gas or a halogen compound gas. Thus, a high quality silicon carbide single crystal can be grown.

  The crystal growth method of a silicon carbide single crystal according to an embodiment of the present invention is configured to etch the seed crystal to a depth of 0.2 μm to 1.0 μm in the etching treatment surface formation step, thereby removing a crystal growth inhibiting factor. It is possible to promote creeping growth and grow a high-quality silicon carbide single crystal.

  In the method for growing a silicon carbide single crystal according to an embodiment of the present invention, the sacrificial oxide film is formed by sacrificing the crystal growth surface before the etching treatment surface forming step, and then the sacrificial oxide film is removed. Therefore, it is possible to grow a high-quality silicon carbide single crystal by cleaning the crystal growth surface, removing the crystal growth-inhibiting factor, and promoting the creeping growth.

  The seed crystal according to the embodiment of the present invention is composed of a silicon carbide single crystal and has an etching treatment surface having a step shape with a surface roughness Ra of 0.03 nm to 2 nm. Growth can be promoted to grow a high quality silicon carbide single crystal.

Since the silicon carbide single crystal according to the embodiment of the present invention has a structure in which crystal growth is performed using the above-described crystal growth method for silicon carbide single crystal and the dislocation density is 1 × 10 ⁴ pieces / cm ² or less, It can be used as a high-quality silicon carbide single crystal used for an optical device or semiconductor element for high withstand voltage and high power.

Hereinafter, the present invention will be specifically described based on examples. However, the present invention is not limited only to these examples.
Example 1
<Crystal growth surface cleaning process>
First, a φ2 inch 4H-silicon carbide seed crystal substrate (thickness 0.5 mm) is washed with a sulfuric acid-hydrogen peroxide mixed solution at 100 to 130 ° C. for 10 minutes, and then washed with running ultrapure water for 5 minutes. , Washed with ammonia-hydrogen peroxide mixed solution at 75-85 ° C. for 10 minutes, washed again with running ultrapure water for 5 minutes, and washed with hydrochloric acid-hydrogen peroxide mixed solution at 75-85 ° C. for 10 minutes. Then, running water was washed again with ultrapure water for 5 minutes, and further washed with an HF solution.
Thereafter, the surface was oxidized (sacrificial oxidation) at 1200 ° C., and then washed with HF again to clean the crystal growth surface of the seed crystal.

<Etching surface formation process>
After the seed crystal is placed in a quartz reaction vessel of an etching apparatus, the gas inside the reaction vessel is exhausted. After exhausting sufficiently, hydrogen gas is introduced to bring the atmospheric pressure to 25 kPa.
Next, while flowing a hydrogen flow rate of 10 SLM, the substrate was heated to a processing temperature of 1535 ° C. and etched for 10 minutes.

The crystal growth surfaces before and after the seed crystal etching were observed with an atomic force scanning microscope (hereinafter, AFM). FIG. 3 is an AFM photograph before the etching process, and FIG. 4 is an AFM photograph after the etching process. As shown in FIG. 4, after the etching process, a step shape that could not be observed before the etching process could be observed.
Further, the surface roughness Ra after the etching treatment was in the range of 0.17 nm to 1.04 nm.

<Crystal growth process>
A graphite crucible having an inner diameter of 100 mm and a depth of 120 mm was filled with silicon carbide powder (Showa Denko # 240) as a raw material to a depth of 60 mm. Subsequently, the seed crystal was stuck and held on the lower surface of the lid of the graphite crucible.

After the lid of the opening of the graphite crucible was covered with the lid, the entire graphite crucible was wrapped with a carbon fiber heat insulating material and set inside a vacuum vessel in a high-frequency heating furnace.
Next, air is exhausted from the gas discharge port of the vacuum vessel, the inside of the vacuum vessel is depressurized to 6.7 × 10 ⁻³ Pa, and then argon gas is introduced from the gas introduction port, so that the inside of the vacuum vessel is normally maintained. After the pressure was reached, the pressure was again reduced to 6.7 × 10 ⁻³ Pa from the gas discharge port, and the inside of the vacuum vessel was brought into a reduced pressure state of an argon atmosphere.
Then, argon gas was reintroduced from the gas inlet, and the temperature of the upper portion of the graphite crucible was increased to 2200 ° C. and the lower portion to 2250 to 2300 ° C. in a state where the inside of the vacuum vessel was 93.3 kPa. .
Thereafter, the argon gas was again discharged from the gas discharge port, and a silicon carbide single crystal was grown under reduced pressure in the range of 133.3 to 13332.2 Pa. The crystal growth rate at this time was 0.05 to 1.0 mm / h.
The silicon carbide single crystal thus obtained was cut perpendicularly to the growth direction and then polished and further subjected to molten KOH etching to produce a silicon carbide single crystal (Example 1 sample).
The dislocation density of the silicon carbide single crystal (Example 1 sample) was 10 ³ pieces / cm ² .

(Example 2)
Example 4 is the same as Example 1 except that a 4H-silicon carbide seed crystal substrate (thickness 0.8 mm) with a nitrogen impurity concentration of 7 × 10 ¹⁹ atoms / cc was used and etching was performed at a hydrogen flow rate of 10 SLM and a propane flow rate of 5 sccm at a processing temperature of 1535 ° C. Crystal growth was performed in the same manner to produce a silicon carbide single crystal (Example 2 sample).
The dislocation density of the silicon carbide single crystal (Example 2 sample) was 10 ³ pieces / cm ² .

(Example 3)
Example 4 except that etching was performed using a 4H-silicon carbide seed crystal substrate (thickness 0.8 mm) with a nitrogen impurity concentration of 2 × 10 ¹⁶ atoms / cc and a hydrogen flow rate of 10 SLM and a chlorine flow rate of 200 sccm at a treatment temperature of 1535 ° C. Crystal growth was performed in the same manner to produce a silicon carbide single crystal (Example 3 sample).
The dislocation density of the silicon carbide single crystal (Example 3 sample) was 10 ³ pieces / cm ² .

Example 4
A 4H-silicon carbide seed crystal substrate (thickness 0.8 mm) having a crystal thickness of 0.8 mm and a nitrogen impurity concentration of 2 × 10 ¹⁹ atoms / cc is used. Crystal growth was performed in the same manner as in Example 1 except that etching was performed at a flow rate of 10 SLM and a hydrocarbon flow rate of 2 sccm at a processing temperature of 1535 ° C., thereby producing a silicon carbide single crystal (Example 4 sample).
The surface roughness Ra after the etching treatment was 0.04 nm.
The dislocation density of the silicon carbide single crystal (Example 4 sample) was 10 ³ pieces / cm ² .

(Comparative Example 1)
A silicon carbide single crystal (Comparative Example 1 sample) was prepared by performing crystal growth in the same manner as in Example 1 except that the etching treatment surface forming step was not performed.
The dislocation density of the silicon carbide single crystal (sample of Comparative Example 1) was about 2 × 10 ⁴ pieces / cm ² .

FIG. 5 is a graph showing measured values of the dislocation density with respect to the sample cutting position from the seed crystal, and the measured values of Example 1 and Comparative Example 1 are described.
As shown in FIG. 5, the dislocation density of the silicon carbide single crystal (Example 1 sample) was 10 ³ pieces / cm ² , and the dislocation density could be suppressed low. On the other hand, the dislocation density of the silicon carbide single crystal (Comparative Example 1 sample) was about 2 × 10 ⁴ pieces / cm ² , and the dislocation density could not be suppressed low.

  The silicon carbide single crystal growth method of the present invention can promote creeping growth and obtain a high-quality silicon carbide single crystal with few crystal defects and a low dislocation density. Alternatively, it may be used in the semiconductor industry that manufactures and uses high-quality silicon carbide single crystals used for semiconductor elements and the like.

It is a cross-sectional schematic diagram which shows an example of the etching apparatus used with the crystal growth method of the silicon carbide single crystal which is embodiment of this invention. It is a cross-sectional schematic diagram which shows an example of the crystal growth apparatus used with the crystal growth method of the silicon carbide single crystal which is embodiment of this invention. It is an AFM photograph before the etching process of the crystal growth surface of a seed crystal. It is the AFM photograph after the etching process of the crystal growth surface of a seed crystal. It is a graph which shows the measured value of the dislocation density with respect to the sample cutting position from a seed crystal, Comprising: It is a graph which compares the effect of the presence or absence of an etching process.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Vacuum container, 2 ... Heat insulating material, 3 ... Heating apparatus (high frequency heating coil), 4 ... Seed crystal, 4a ... Etching surface, 5 ... Silicon carbide powder, 6 ... Crucible, 6a ... Main-body part, 6b ... Cover part , 6c ... Stand, 7 ... Gas inlet, 8 ... Gas outlet, 9 ... Radiation thermometer, 11 ... Reaction vessel, 11c ... Cavity, 17 ... Gas inlet, 18 ... Gas outlet, 100 ... Etching device 101 ... Crystal growth apparatus.

Claims (10)

An etching treatment surface forming step of etching the crystal growth surface of the seed crystal to form an etching treatment surface;
And a crystal growth step of growing a silicon carbide single crystal on the etched surface. A method for growing a crystal of a silicon carbide single crystal, comprising:   The method for growing a silicon carbide single crystal according to claim 1, wherein the etched surface has a step shape.   3. The method for growing a silicon carbide single crystal according to claim 1, wherein a step shape having a surface roughness Ra of 0.03 nm to 2 nm is formed by the etching process.   The method for growing a silicon carbide single crystal according to claim 1, wherein the etching process is a dry etching process using hydrogen gas as an etching gas.   The method for growing a silicon carbide single crystal according to claim 4, wherein the etching gas contains a hydrocarbon gas of 0.01 vol% to 0.5 vol%.   The method for growing a silicon carbide single crystal according to claim 4, wherein the etching gas contains 1 vol% to 10 vol% of a halogen gas or a halogen compound gas.   The method for growing a silicon carbide single crystal according to claim 1, wherein the seed crystal is etched to a depth of 0.2 μm to 1.0 μm in the etching treatment surface forming step. .   8. The method according to claim 1, further comprising a step of removing the sacrificial oxide film after forming the sacrificial oxide film by sacrificing the crystal growth surface before the etching treatment surface forming step. 2. A method for growing a silicon carbide single crystal according to item 1.   A seed crystal comprising a silicon carbide single crystal and having an etched surface having a step shape with a surface roughness Ra of 0.03 nm to 2 nm. Silicon carbide, which has been crystal-grown using the method for growing a silicon carbide single crystal according to any one of claims 1 to 8 and has a dislocation density of 1 × 10 ⁴ pieces / cm ² or less. Single crystal.

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