JP2007119273A - Method for growing silicon carbide single crystal - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for growing a silicon carbide single crystal of high quality which is free from the occurrence of micropipes, almost free from dislocation densities such as screw dislocations and edge dislocations, and free from mixing of different orientation crystals. <P>SOLUTION: The method contains a first growing process where a silicon carbide single crystal is grown by heating in an inert atmosphere a silicon carbide raw material at a first temperature of 2,200-2,300°C and a silicon carbide seed crystal at a second temperature of lower than the first temperature and ≥2,200°C and controlling the growing rate of the silicon carbide single crystal to be 80 μm/h or less at pressure in the range of 13.3-26.6 kPa, a pressure reducing process where the pressure is reduced from the pressure at the first growing process at a rate of ≤0.93 kPa/h so as to accelerate the growing rate to be faster than the first growing process, and a second growing process where the silicon carbide single crystal is grown at a rate faster than the first growing process by heating the silicon carbide raw material at the first temperature and the silicon carbide seed crystal at the second temperature at pressure after reducing the pressure. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a crystal growth method for growing a high-quality single crystal particularly when a silicon carbide single crystal substrate used for a semiconductor device for high voltage and high power such as an optical device and a power transistor is manufactured by a sublimation method. It is about.

In recent years, a silicon carbide single crystal substrate has been developed as a semiconductor substrate of a semiconductor device for high withstand voltage and high power such as a high withstand voltage power transistor and a high withstand voltage diode. And as a manufacturing method of this silicon carbide single crystal substrate, a sublimation method (improved Rayleigh method) is mainly adopted. FIG. 5 is a schematic view of an apparatus used in this sublimation method, and SiC powder 21 is contained as a raw material in the lower half of a graphite crucible comprising a container body 19 and a lid body 20 provided with a pedestal. A seed crystal 22 is disposed on the lower surface of the lid 20 facing the surface. This graphite crucible is placed in an inert gas atmosphere, the pressure is reduced, and the whole is heated to 1800 to 2400 ° C. The SiC powder 21 side is kept at a high temperature and the seed crystal 22 side is kept at a low temperature, and the sublimation gas from the SiC powder 21 is recrystallized on the low temperature seed crystal 22, whereby a single crystal 23 grows. As the temperature rises, the SiC powder 21 generates vapors such as Si, Si ₂ C, SiC ₂ , and SiC that contribute to growth, and in particular, a large amount of Si vapor with a low melting point of about 1400 ° C. is generated at the initial stage. At the same time, impurity fine particles and crystalline interfering fine particles contained in the raw material etc. also float in the crucible. As a result, it is said that Si droplets and impurity fine particles adhere to the surface of the single crystal growing on the seed crystal, and this is the starting point, leading to the generation of micropipes and dislocations.

  On the other hand, in order to produce a seed crystal substrate from a silicon carbide single crystal, processing is performed by slicing, polishing, cleaning, and the like, and a work-affected layer is introduced on the surface of the seed crystal during this processing. The work-affected layer does not have an appropriate etchant because silicon carbide is chemically stable, and is difficult to remove. For this reason, many defects such as micropipes and screw dislocations are generated in the grown crystal from the surface of the seed crystal. Further, in the sublimation method, it is difficult to control the crystal form (polytype) and the crystal plane due to spontaneous nucleation.

  In order to solve this, after forming a growth initial layer at a seed crystal substrate temperature of 2250 ° C. to 2350 ° C. and a growth pressure of 13.3 to 40 kPa in the initial stage of growth, the substrate temperature and the growth pressure are finally adjusted to 2200 to 2250. A silicon carbide single crystal is grown while gradually reducing the temperature to 0.13 to 2.7 kPa at C (see Patent Document 1).

In addition, a substrate having an off angle of 4 to 45 ° with respect to the (0001) plane or the (000-1) plane is used as a seed crystal, and after growing at a growth rate of 0.05 mm / h or less in the initial stage of growth, Thereafter, growth is performed at a growth rate of 1 mm / h or less (see Patent Document 2).
JP 2002-284599 A JP 2005-29459 A

  However, both methods can produce high-quality single crystals, but when the pressure is gradually reduced from the initial stage of growth, crystals with different orientations different from the orientation of the seed crystals are likely to be mixed into the growth crystals depending on this speed. This crystal cannot be used as a wafer, and has a problem of causing a decrease in yield and an increase in cost.

  The present invention solves this conventional problem, and is a growth method for reproducibly growing a high-quality single crystal called a micropipe, which has very few hollow defects and dislocations and does not contain different orientation crystals. The purpose is to provide.

  In order to solve the above-described conventional problems, a silicon carbide single crystal growth method of the present invention supplies a sublimation gas from a silicon carbide raw material to a seed crystal made of a silicon carbide single crystal at a predetermined temperature, thereby producing a silicon carbide single crystal. In the method for growing a silicon carbide single crystal for growing a crystal, in an inert atmosphere, the silicon carbide raw material is set to a first temperature within a range of 2200 to 2300 ° C., and the silicon carbide seed crystal is set to be lower than the first temperature. And heating to a second temperature of 2200 ° C. or higher and adjusting the pressure so that the growth rate of the silicon carbide single crystal is 80 μm / h or less within the range of 13.3 kPa to 26.6 kPa. In order to make a growth rate faster than the first growth step following the first growth step, a first growth step for growing a single crystal is 0.93 kPa / h ( 7 To r / h) Depressurization step of depressurizing at a rate of less than or equal to the above, and maintaining the silicon carbide raw material at the first temperature and the silicon carbide seed crystal at the second temperature at the pressure after depressurization, And a second growth step for growing the silicon carbide single crystal at a growth rate faster than the growth rate in the growth step.

  Further, in the method for growing a silicon carbide single crystal, a reduced pressure width that is a difference between the pressure in the first growth step and the pressure in the second growth step is 17.3 kPa (130 Torr) or less. It is a thing.

  Furthermore, in the method for growing a silicon carbide single crystal, the temperature gradient between the silicon carbide raw material and the silicon carbide seed crystal in the first growth step is 5 ° C./cm or less.

  Furthermore, in the method for growing a silicon carbide single crystal, the silicon carbide seed crystal is a seed crystal whose surface roughness Ra has been previously processed in the range of 0.3 to 0.8 nm. .

  According to the method for growing a silicon carbide single crystal of the present invention, the process from the first growth step of growing at a growth rate of 80 μm / h to the second growth step of growing at a growth rate faster than the first growth step. By setting the decompression speed in the decompression step to 0.93 kPa / h (7 Torr / h) or less, a high-quality single crystal having very few micropipes and dislocations and having no foreign crystals mixed is grown with good reproducibility. be able to.

  Hereinafter, embodiments of a method for growing a silicon carbide single crystal of the present invention will be described in detail with reference to the drawings. FIG. 1 shows a crystal growth apparatus used when growing a silicon carbide single crystal in an embodiment of the present invention. In FIG. 1, reference numeral 1 denotes a vacuum vessel, which is made of a material that maintains a high vacuum such as quartz or stainless steel, and is water-cooled as necessary. 2 is a heat insulating material, 3 is a graphite crucible. The heat insulating material 2 is provided with holes in the upper and lower central portions in order to measure the upper temperature and lower temperature of the graphite crucible 3 with the upper pyrometer 4 and the lower pyrometer 5. A silicon carbide seed crystal 6 as a seed crystal is fixed to the upper part of the graphite crucible where crystal growth is performed, and a silicon carbide raw material 7 is accommodated in the lower part of the crucible. In order to heat the graphite crucible 3, a high-frequency heating coil 8 is installed via the vacuum vessel 1. The vacuum vessel 1 is exhausted by a vacuum pump through the exhaust port 9. Further, high-purity argon gas or the like is supplied from the gas introduction port 10 and is maintained at a predetermined pressure by a pressure regulating valve provided in the middle of the exhaust port, although not shown.

  Subsequently, in order to bring the silicon carbide source material 7 side to a high temperature and the silicon carbide seed crystal 6 side to a low temperature, the silicon carbide source material 7 in the graphite crucible 3 is heated by using the high-frequency heating coil 8 to generate sublimation gas. For example, the silicon carbide single crystal 11 is grown by recrystallizing the sublimation gas on the silicon carbide seed crystal 6 at a temperature of 2000 ° C. or higher.

  Hereinafter, a specific method for growing a silicon carbide single crystal will be described in detail using the silicon carbide single crystal manufacturing apparatus shown in FIG.

As the silicon carbide seed crystal 6, a single crystal made by the Atchison method, the Rayleigh method, and the sublimation method is used. These are cut and polished to obtain a shape necessary as a seed crystal. In order to remove polishing damage completely as the final finishing of the seed crystal, the chemical mechanical polishing: performed until (CMP C hemical M echanical P olish ). In the present invention, CMP is used as the final finish of the silicon carbide seed crystal 6, but the work-affected layer is similarly obtained by using a method such as reactive ion etching (RIE) or thermal etching in a hydrogen atmosphere. Can be removed. Subsequently, in order to remove organic substances and metal impurities adhering to the surface of the silicon carbide seed crystal 6 by polishing, cleaning with a mixed solution of sulfuric acid and hydrogen peroxide, cleaning with ammonia and hydrogen peroxide, hydrochloric acid and peroxidation Wash with hydrogen water. This cleaning method is generally called RCA cleaning. Thereafter, sacrificial oxidation is further performed at about 1100 ° C., the sacrificial oxide film is removed with hydrofluoric acid, and the silicon carbide seed crystal 6 is used. By performing the surface treatment of the silicon carbide seed crystal 6, it is possible to grow a high-quality single crystal with very few micropipes and dislocations with good reproducibility.

The surface-treated silicon carbide seed crystal 6 is fixed to the upper part of the inner surface of the graphite crucible 3 in the crystal growth portion by using a bonding method using mechanical or carbon-based adhesive. The graphite crucible 3 in which the silicon carbide raw material 7 is placed so as to face the silicon carbide seed crystal 6 is placed in the vacuum vessel 1 and evacuated to a vacuum degree of 3 × 10 ⁻⁴ Pa using a rotary pump and a turbo molecular pump. I do. Subsequently, the temperature of the graphite crucible 3 is heated by the high-frequency coil 8 installed outside the graphite crucible 3 up to about 1200 ° C., which is a measurable temperature of the pyrometer, and the degree of vacuum is increased to 3 × 10 ⁻⁴ Pa for baking. stand by. In baking, gas or moisture adsorbed on the graphite crucible 3, the silicon carbide raw material 7, the heat insulating material 2, and the like can be discharged.

  Next, high-purity Ar gas is introduced and the pressure in the vacuum vessel 1 is adjusted to 80 to 93.3 kPa (600 to 700 Torr). In this state, the temperature on the silicon carbide raw material powder 7 side is heated to a predetermined temperature within 2200 to 2300 ° C., for example, 2230 ° C. And the relative position of the high frequency coil 8 and the graphite crucible 3 is adjusted so that the temperature by the side of the silicon carbide seed crystal 6 is lower than 2230 degreeC which is the temperature by the side of the silicon carbide raw material 7, and becomes 2200 degreeC or more.

  Here, only high-purity Ar gas is used as the inert gas, but nitrogen gas or the like can be added as necessary.

  Subsequently, in the initial stage of growth, the Ar atmosphere pressure is adjusted to 13.3 to 26.6 kPa so that the growth rate of the silicon carbide single crystal is 80 μm / h or less, and an initial growth layer is formed in this state.

Here, by setting the temperature on the silicon carbide seed crystal 6 side to be lower than the temperature on the silicon carbide source material 7 side and 2200 ° C. or higher, the migration of source molecules attached to the substrate surface becomes active and unnecessary. Generation of heterogeneous polytypes such as two-dimensional nuclei and 15R and 3C can be suppressed, and sublimation recrystallization of the surface of the single crystal substrate becomes active, and the disordered portion of the surface is reconstructed. At this time, if the vapor pressure of the sublimation gas in the vicinity of the Si, Si ₂ C, SiC ₂ , and SiC seed crystals at the silicon carbide seed crystal temperature becomes excessively higher than the saturated vapor pressure, the crystal molecules of the source molecules are moved to the crystal surface. The amount of deposition of the sublimation gas at the silicon carbide seed crystal temperature does not become excessively higher than the saturation vapor pressure, because the amount of adhesion of the material increases momentarily and hinders the migration of source molecules on the substrate surface. It is necessary to set the pressure to 13.3 to 26.6 kPa and the growth rate to 80 μm / h.

  By these actions, crystal defects such as micropipes and screw dislocations that have conventionally occurred from the surface of the seed crystal substrate are suppressed. Further, when forming the initial growth layer, a temperature gradient obtained by dividing the difference between the silicon carbide source temperature and the silicon carbide seed crystal temperature by the distance between the source surface and the seed crystal substrate surface is set to 5 ° C./cm. It is preferable. This is because when the temperature gradient is large, 15R, which is a different polytype, is likely to be mixed, and a large number of micropipes are generated from this portion.

  Thereafter, the pressure is reduced within a range of 17.3 kPa (130 Torr) or less at a decompression rate of 0.93 kPa / h (7 Torr / h) or less until a pressure at which the growth rate becomes higher than the rate of forming the initial growth layer. Do. Further, crystal growth is performed in order to obtain a desired growth amount while maintaining the temperature on the silicon carbide seed crystal 6 side lower than the temperature on the silicon carbide raw material 7 side and 2200 ° C. or higher. By reducing the decompression rate to 0.93 kPa / h (7 Torr / h) or less, a rapid change in the growth rate is suppressed from the stable state during initial growth layer formation, and two-dimensional or three-dimensional nucleation is suppressed. It is possible to suppress the introduction of different orientation crystals in the subsequent growth from the initial growth layer. Further, by setting the reduced pressure range to 17.3 kPa (130 Torr) or less within the range of the reduced pressure rate, mixing of differently oriented crystals can be suppressed. Of course, if the pressure of the initial growth layer is 13.3 kPa, the reduced pressure range is up to 13.3 kPa in MAX.

According to these embodiments of the present invention, a silicon carbide single crystal having no dislocation density <5 × 10 ³ pieces / cm ² and having no misorientation crystals is produced with good reproducibility without the occurrence of a hollow shape called a micropipe. can do.

  The decompression speed of the decompression step in the silicon carbide single crystal growth method of the present invention will be specifically described.

As the silicon carbide seed crystal, a Rayleigh substrate having a diameter of about 10 mm, a thickness of 0.3 to 0.5 mm, and a polytype 6H was used. This is because the quality of the Rayleigh substrate is 0 for micropipes and the dislocation density is stable at 5 × 10 ³ to 1 × 10 ⁴ / cm ² , so that defects in the grown crystal can be accurately compared and evaluated. Because.

  For a Rayleigh substrate, a carbon surface not used as a growth surface is polished to about Ra = 1.7 nm with a diamond slurry, and a Si surface used as a growth surface is polished to Ra = 0.3 to 0.8 nm by CMP to 1% HF For 10 min, flowing water cleaning with ultrapure water for 5 min, ammonia and hydrogen peroxide mixed solution at 140 ° C. for 10 min, flowing water cleaning with ultrapure water for 5 min, 5% HF for 5 min, flowing water cleaning with ultrapure water for 5 min, hydrochloric acid and hydrogen peroxide Treatment with mixed solution at 140 ° C. for 10 min, flowing water cleaning with ultrapure water for 5 min, 5% HF for 5 min, flowing water cleaning with ultrapure water for 5 min, 1100 ° C. for 6 h sacrificial oxidation, 5% HF for 10 min, flowing water cleaning with ultrapure water for 10 min Was given.

  A graphite crucible having an inner diameter of 24 mm and a depth of 80 mm was filled with a silicon carbide raw material (GMF-SP manufactured by Taihei Random Co., Ltd.) so as to have a height of 52 mm. The seed crystal was pasted and held on the bottom surface of a pedestal having a diameter of 10 mm and a height of 8 mm protruding from the center of the lid of the graphite crucible.

The graphite crucible was covered with a heat insulating material and set in a vacuum container. Vacuuming is performed with a turbo molecular pump until 2 × 10 ⁻⁴ Pa, the temperature is raised to 1200 ° C., baking is performed until 3 × 10 ⁻⁴ Pa, and Ar gas is introduced to reach 80 kPa (600 Torr). The temperature is raised until the lower part of the graphite crucible reaches 2230 ° C. At this time, the coil position is adjusted so that the upper temperature of the graphite crucible becomes 2220 ° C. Thereafter, the pressure is reduced to 25.3 kPa (190 Torr) over 50 minutes, and growth is performed in this state for 5 hours.

  Then, pressure reduction was performed at a pressure reduction rate of 0.13 to 1.33 kPa / h (1 to 10 Torr / h) up to 12 kPa (90 Torr), and mixing of differently oriented crystals was confirmed. Between the initial growth layer and the decompression step, nitrogen gas was added to the growth atmosphere gas to color the silicon carbide single crystal, and a nitrogen marker was introduced so that the position where the growth conditions changed could be seen. The grown crystal was sliced parallel to the growth direction, mirror-polished, and subjected to cross-sectional observation by transmission microscope observation. The growth rate of the initial growth layer and the number of micropipes generated were also examined.

  Table 1 shows the results of the presence or absence of different orientation crystals, the growth rate of the initial growth layer, and the number of generated micropipes when the decompression rate was changed.

減圧速度１．０７ｋＰａ／ｈ（８Ｔｏｒｒ／ｈ）以上において、図２に示すように初期成長層１２と減圧工程のほぼ界面の窒素マーカー１３の近傍から異方位結晶１４が混入されているという結果が得られた。この理由として、以下のようなことが考えられる。昇華法において、種結晶としてｃ面を成長面として使用する場合、種結晶は面方位が（０００１）からずれの無いジャスト基板や（０００１）から方位を故意にずらしたオフ基板が使用される。ジャスト基板といっても、完全にジャストにすることは難しく、０．５°程度のオフ角が存在してしまう。このため、種結晶表面としては、図３（ａ）に示すように、原子ステップ１５とテラス１６から構成されるような表面状態になる。この上に単結晶を安定した成長条件で成長させているときは、図３（ｂ）に示すように、テラス１６に原料分子１７が吸着し、途中で脱離する分子もあるが、この原料分子１７が基板表面でマイグレーションし、原子ステップ１５に到達しステップフロー的に結晶成長が進行するという過程をたどる。しかしながら、安定した成長条件から成長条件を変化させ、急激にテラス１６上に吸着する原料分子１７が増加すると、図３（ｃ）に示すように、吸着した原料分子１７が原子ステップ１５に向かってマイグレーションしていく途中で他の原料分子と結びつき、そこで新たな成長核１８の発生を起こしてしまう。この成長核１８は、テラス１６上で発生するため、種結晶の結晶構造の情報が受継がれにくく、これが異方位結晶の核の原因となってしまう。この図３（ｃ）に示した状態が、減圧速度１．０７ｋＰａ／ｈ（８Ｔｏｒｒ／ｈ）以上の減圧速度の条件に相当していると予想される。

As shown in FIG. 2, when the decompression speed is 1.07 kPa / h (8 Torr / h) or more, as shown in FIG. 2, the result is that the differently oriented crystal 14 is mixed from the vicinity of the nitrogen marker 13 at the interface between the initial growth layer 12 and the decompression process. Obtained. The following can be considered as this reason. In the sublimation method, when the c-plane is used as a growth surface as a seed crystal, a just substrate in which the plane orientation is not deviated from (0001) or an off-substrate whose orientation is intentionally deviated from (0001) is used. Even if it is a just substrate, it is difficult to make it completely just, and an off angle of about 0.5 ° exists. For this reason, the seed crystal surface is in a surface state composed of atomic steps 15 and terraces 16 as shown in FIG. When a single crystal is grown on this under stable growth conditions, as shown in FIG. 3 (b), there are molecules that adsorb raw material molecules 17 on terraces 16 and desorb in the middle. The molecule 17 migrates on the surface of the substrate, reaches the atomic step 15 and follows the process of crystal growth in a step flow. However, when the growth conditions are changed from a stable growth condition and the number of raw material molecules 17 adsorbed on the terrace 16 abruptly increases, the adsorbed raw material molecules 17 move toward the atomic step 15 as shown in FIG. In the course of migration, it is combined with other raw material molecules, where new growth nuclei 18 are generated. Since the growth nuclei 18 are generated on the terrace 16, information on the crystal structure of the seed crystal is difficult to be inherited, and this causes the nuclei of differently oriented crystals. It is expected that the state shown in FIG. 3C corresponds to a pressure reduction speed condition of 1.07 kPa / h (8 Torr / h) or higher.

  In addition, the growth rate of the initial growth layer was about 70 μm / h, and the number of micropipes generated at this time was zero although it was from cross-sectional observation.

  From these facts, it was found that the pressure reduction rate after forming the initial growth layer is preferably 0.93 kPa / h (7 Torr / h) or less.

  The reduced pressure range of the reduced pressure step in the silicon carbide single crystal growth method of the present invention will be specifically described.

  As the silicon carbide seed crystal, a Rayleigh substrate having a diameter of about 10 mm, a thickness of 0.3 to 0.5 mm, and a polytype 6H is used.

  A graphite crucible having an inner diameter of 24 mm and a depth of 80 mm was filled with a silicon carbide raw material (GMF-SP manufactured by Taihei Random Co., Ltd.) so as to have a height of 52 mm. The seed crystal was pasted and held on the bottom surface of a pedestal having a diameter of 10 mm and a height of 8 mm protruding from the center of the lid of the graphite crucible.

The graphite crucible was covered with a heat insulating material and set in a vacuum container. Vacuuming is performed with a turbo molecular pump until 2 × 10 ⁻⁴ Pa, the temperature is raised to 1200 ° C., baking is performed until 3 × 10 ⁻⁴ Pa, and Ar gas is introduced to reach 80 kPa (600 Torr). The temperature was raised until the lower part of the graphite crucible reached 2230 ° C. At this time, the coil position was adjusted so that the upper temperature of the graphite crucible was 2220 ° C. Thereafter, the pressure was reduced to 25.3 kPa (190 Torr) over 50 minutes, and growth was performed for 5 hours under this pressure. Thereafter, the pressure is reduced by changing the pressure reduction range from 6.7 to 22 kPa (50 to 165 Torr) at a pressure reduction rate of 0.67 kPa / h (5 Torr / h) from the pressure of 25.3 kPa. When the pressure reached the target pressure, the growth was stopped and mixed with different orientation crystals was confirmed. The boundary between the initial growth layer and the depressurization process, and the position where the growth conditions have changed by introducing nitrogen gas into the growth atmosphere gas by coloring nitrogen gas into the growth atmosphere gas every 1.33 kPa (10 Torr) and introducing nitrogen markers I was able to understand. The grown crystal was sliced parallel to the growth direction, mirror-polished, and subjected to cross-sectional observation by transmission microscope observation. This time, we also investigated the growth rate of the initial growth layer and the number of micropipes.

  Table 2 shows the results of the presence / absence of mixing of differently oriented crystals, the growth rate of the initial growth layer, and the number of generated micropipes when the decompression width is changed.

減圧幅１８．７ｋＰａ(１４０Ｔｏｒｒ)以上において、異方位結晶が混入されていることがわかった。減圧幅１８．７ｋＰａ（１４０Ｔｏｒｒ）では、断面観察より成長終了間際に異方位結晶が混入しており、減圧幅２０ｋＰａ（１５０Ｔｏｒｒ）、２１．３ｋＰａ（１６０Ｔｏｒｒ）、２２ｋＰａ（１６５Ｔｏｒｒ）では、減圧幅が１８．７ｋＰａ(１４０Ｔｏｒｒ)になった近辺から異方位結晶が混入しているという結果が得られた。昇華法による単結晶の成長において、図４に示すように、成長温度が一定の条件化では、成長圧力が減少していくとともに成長速度が反比例的あるいは指数関数的に速くなる関係がある。これは、原料粉末から昇華する原料分子が圧力の減少とともに急激に増加することを意味している。このことから、減圧幅１８．７ｋＰａ(１４０Ｔｏｒｒ)以上において異方位結晶が混入した理由は、１７．３ｋＰａ(１３０Ｔｏｒｒ)の減圧幅を越えた圧力での成長において、急激に原料粉末から昇華した原料分子が成長単結晶表面に到達し、図３（ｃ）における現象と同様のことが起こったためと考えられる。

It was found that different orientation crystals were mixed at a reduced pressure width of 18.7 kPa (140 Torr) or more. In the reduced pressure width 18.7 kPa (140 Torr), different orientation crystals are mixed just before the end of the growth from the cross-sectional observation, and in the reduced pressure width 20 kPa (150 Torr), 21.3 kPa (160 Torr), and 22 kPa (165 Torr), the reduced pressure width is 18 The result was that differently oriented crystals were mixed from around 7 kPa (140 Torr). In the growth of a single crystal by the sublimation method, as shown in FIG. 4, there is a relationship in which the growth pressure decreases and the growth rate increases inversely or exponentially when the growth temperature is constant. This means that the raw material molecules sublimated from the raw material powder increase rapidly as the pressure decreases. From this, the reason why the hetero-oriented crystal was mixed at a reduced pressure width of 18.7 kPa (140 Torr) or more is that the raw material molecules rapidly sublimated from the raw material powder during growth at a pressure exceeding the reduced pressure width of 17.3 kPa (130 Torr). This is thought to be due to the fact that the same phenomenon as that in FIG.

  In addition, the growth rate in the initial growth layer was about 65 to 77 μm / h, and the number of micropipes that were generated was 0, although from the cross-sectional observation.

  From these facts, it was found that the pressure reduction width at the optimum pressure reduction speed after the formation of the initial growth layer is preferably 17.3 kPa (130 Torr) or less.

  The temperature gradient between the silicon carbide raw material and the silicon carbide seed crystal in the first growth step in the method for growing a silicon carbide single crystal of the present invention will be specifically described.

  As the silicon carbide seed crystal, a Rayleigh substrate having a diameter of about 10 mm, a thickness of 0.3 to 0.5 mm, and a polytype 6H is used.

  A graphite crucible having an inner diameter of 24 mm and a depth of 80 mm was filled with silicon carbide raw material powder (GMF-SP manufactured by Taiyo Random Co., Ltd.) to a height of 60 mm. The seed crystal was stuck and held on the lower surface of the lid of the graphite crucible. The distance between the silicon carbide raw material powder surface and the seed crystal surface was set to 20 mm.

The graphite crucible was covered with a heat insulating material and set in a vacuum container. Vacuuming is performed with a turbo molecular pump until 2 × 10 ⁻⁴ Pa, the temperature is raised to 1200 ° C., baking is performed until 3 × 10 ⁻⁴ Pa, and Ar gas is introduced to reach 80 kPa (600 Torr). The temperature was raised until the lower part of the graphite crucible reached 2230 ° C. At this time, the coil position was adjusted so that the upper temperature of the graphite crucible varied between 2210 ° C and 2230 ° C. Thereafter, the pressure was reduced to 25.3 kPa (190 Torr) over 50 minutes, and growth was performed in this state for 5 hours. Thereafter, the pressure was reduced to 8 kPa (60 Torr) at a pressure reduction rate of 0.67 kPa / h (5 Torr / h), and growth was performed at this pressure for 64 hours. The grown crystal was polished by cutting a part of the crystal surface side in a direction perpendicular to the growth direction and the remaining crystal in a direction parallel to the growth direction. For crystals sliced in the parallel direction, it was confirmed by observation with a transmission deflection microscope whether different types of polytypes such as 15R were mixed in the initial growth layer. The crystal sliced in the vertical direction was etched with molten KOH at 500 ° C. for 5 min, the number of micropipes and dislocations was measured by microscopic observation, and the density was calculated.

  Table 3 shows the results of presence / absence of mixing of different polytypes at the initial stage of growth, micropipe density, and dislocation density when the temperature gradient was changed at 0 to 10 ° C./cm. The temperature gradient was calculated by dividing the difference between the crucible lower temperature and the crucible upper temperature by the distance of 20 mm between the raw material surface and the seed crystal surface.

７℃／ｃｍ以上の温度勾配において、種結晶表面と成長単結晶の界面から１５Ｒ異種ポリタイプが混入していることが観察でき、この領域からマイクロパイプが発生していた。転位密度としては、０〜１５℃／ｃｍの間のすべての温度勾配条件において、５×１０³／ｃｍ²以下となっていた。７℃／ｃｍ以上の温度勾配において１５Ｒ異種ポリタイプが混入した理由としては、温度勾配が大きいということは原料側温度と成長結晶との間の温度差が大きいということであり、これは種結晶周辺の過飽和度が大きいということを意味している。過飽和度が大きいということは、種結晶表面に到達する原料から昇華した原料分子の量が多くなり、図３（ｃ）に示した現象と同様のことが起こり、テラス上に種結晶の結晶構造を受継がない核が発生し、これにより１５Ｒが混入したものと考えられる。

In a temperature gradient of 7 ° C./cm or more, it was observed that a 15R heteropolytype was mixed from the interface between the seed crystal surface and the grown single crystal, and micropipes were generated from this region. The dislocation density was 5 × 10 ³ / cm ² or less under all temperature gradient conditions between 0 ° C. and 15 ° C./cm. The reason why the 15R heteropolytype is mixed in a temperature gradient of 7 ° C./cm or more is that the large temperature gradient means that the temperature difference between the raw material side temperature and the grown crystal is large. This means that the degree of supersaturation in the surrounding area is large. A large degree of supersaturation means that the amount of raw material molecules sublimated from the raw material reaching the surface of the seed crystal increases, and the same phenomenon as shown in FIG. 3C occurs, and the crystal structure of the seed crystal on the terrace It is considered that nuclei that do not inherit are generated and 15R is mixed in.

  From these facts, it was found that the temperature gradient is preferably 5 ° C./cm or less in the first growth step.

  As described above, the temperature gradient becomes a problem in the first growth step. In the second growth step, the silicon carbide seed crystal is brought to the first temperature within the range of 2200 to 2300 ° C. It is sufficient that 6 is heated to a second temperature lower than the first temperature and 2200 ° C. or higher, and there is no problem even if the temperature gradient is changed under a reduced pressure and the temperature gradient is slightly changed.

  The surface state of the silicon carbide seed crystal in the silicon carbide single crystal growth method of the present invention will be specifically described.

  As the silicon carbide seed crystal, a Rayleigh substrate having a diameter of about 10 mm, a thickness of 0.3 to 0.5 mm, and a polytype 6H was used. A carbon surface that is not a growth surface is polished to about Ra = 1.7 nm with diamond slurry, a Si surface that is a growth surface is polished to Ra = 0.3 to 0.8 nm by CMP, and a carbon surface that is not a growth surface is diamond slurry. Two types were prepared: polishing to Ra = 1.7 nm by polishing, and polishing the Si surface as a growth surface to Ra = 1 nm by polishing with a diamond slurry using a pad. Since cleaning of the seed crystal is exactly the same as in Example 1, it is omitted.

  A graphite crucible having an inner diameter of 24 mm and a depth of 80 mm was filled with silicon carbide raw material powder (GMF-SP manufactured by Taiyo Random Co., Ltd.) to a height of 60 mm. The seed crystal was stuck and held on the lower surface of the lid of the graphite crucible. The distance between the silicon carbide raw material powder surface and the seed crystal surface was set to 20 mm.

The graphite crucible was covered with a heat insulating material and set in a vacuum container. Vacuuming is performed with a turbo molecular pump until 2 × 10 ⁻⁴ Pa, the temperature is raised to 1200 ° C., baking is performed until 3 × 10 ⁻⁴ Pa, and Ar gas is introduced to reach 80 kPa (600 Torr). The temperature was raised until the lower part of the graphite crucible reached 2230 ° C. At this time, the coil position was adjusted so that the upper temperature of the graphite crucible was 2220 ° C. Thereafter, the pressure was reduced to 25.3 kPa (190 Torr) over 50 minutes, and growth was performed in this state for 5 hours. Thereafter, the pressure was reduced to 8 kPa (60 Torr) at a pressure reduction rate of 0.67 kPa / h (5 Torr / h), and growth was performed at this pressure for 64 hours. The grown crystal was sliced in the direction perpendicular to the growth direction and mirror polished. For this crystal, etching was performed at 500 ° C. for 5 minutes with molten KOH, the number of micropipes and dislocations was measured with a microscope, and the density was calculated.

  Crystal defects were evaluated for each of the case where the seed crystal that had been subjected to CMP was used and the case where the seed crystal that was subjected to diamond polishing was used. Moreover, in order to take reproducibility, three times of growth and evaluation were performed for each. The results are shown in Table 4.

種結晶をＣＭＰ処理まで施した場合は、マイクロパイプ密度０本／ｃｍ²、転位密度＜４×１０³個／ｃｍ²が再現性よく得られた。種結晶の処理がダイヤモンドのポリッシュまでの場合は、マイクロパイプ密度＜５本／ｃｍ²、転位密度＜１．９×１０⁴個／ｃｍ²と欠陥が多く、成長ごとに非常に値がばらついており、非常に不安定であった。これらのことから、種結晶の単結晶を成長させる表面をＣＭＰ処理まで行い、Ｒａ＝０．３〜０．８ｎｍとすることにより、マイクロパイプ密度０本／ｃｍ²、転位密度＜４×１０³個／ｃｍ²が再現性よく得られることがわかった。

When the seed crystal was subjected to CMP treatment, a micropipe density of 0 pieces / cm ² and a dislocation density of <4 × 10 ³ pieces / cm ² were obtained with good reproducibility. When the processing of the seed crystal is up to diamond polish, there are many defects such as micropipe density <5 / cm ² and dislocation density <1.9 × 10 ⁴ / cm ^2, and the value varies greatly with each growth. It was very unstable. From these facts, the surface on which the single crystal of the seed crystal is grown is subjected to CMP treatment, and Ra = 0.3 to 0.8 nm, whereby the micropipe density is 0 / cm ² and the dislocation density is less than 4 × 10 ^3. It was found that pieces / cm ² can be obtained with good reproducibility.

  The silicon carbide single crystal growth method according to the present invention grows a high-quality single crystal without generating new defects in the crystal growth process when a single crystal is grown from a seed crystal using a sublimation method. Therefore, the present invention can also be applied to cadmium sulfide (CdS), cadmium selenide (CdSe), zinc sulfide (ZnS), aluminum nitride (AlN), boron nitride (BN), and the like which are single crystals that can be grown by a sublimation method.

Schematic configuration diagram of a growth apparatus for silicon carbide single crystal growth in an embodiment of the present invention The figure which shows the cross section of the silicon carbide single crystal in which the different direction crystal was mixed in the case of the decompression speed | rate in the silicon carbide growth in Example 1 of this invention being large The figure for demonstrating the mechanism of the hetero-oriented crystal mixing in Example 1 of this invention Figure showing the relationship between the growth rate and growth pressure of silicon carbide single crystals Schematic diagram of a sublimation apparatus for growing silicon carbide single crystals

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Vacuum vessel 2 Heat insulating material 3 Graphite crucible 4 Upper pyrometer 5 Lower pyrometer 6 Silicon carbide seed crystal 7 Silicon carbide raw material 8 High frequency heating coil 9 Exhaust port 10 Gas inlet 11 Silicon carbide single crystal 12 Initial growth layer 13 Nitrogen marker 14 Different orientation Crystal 15 Atomic step 16 Terrace 17 Raw material molecule 18 Growth nucleus 19 Container body 20 Lid body 21 SiC powder 22 Seed crystal 23 Single crystal

Claims (4)

In a silicon carbide single crystal growth method of supplying a sublimation gas from a silicon carbide raw material to a seed crystal composed of a silicon carbide single crystal at a predetermined temperature to grow a silicon carbide single crystal,
In an inert atmosphere, the silicon carbide raw material is set to a first temperature within a range of 2200 to 2300 ° C., and the silicon carbide seed crystal is set to a second temperature lower than the first temperature and higher than 2200 ° C. A first growth step of growing the silicon carbide single crystal by heating and adjusting the pressure so that the growth rate of the silicon carbide single crystal is 80 μm / h or less within the range of 13.3 kPa to 26.6 kPa;
In order to make the growth rate higher than that of the first growth step following the first growth step, the pressure reduction step of reducing pressure from the pressure in the first growth step at a rate of 0.93 kPa / h (7 Torr / h) or less. When,
The silicon carbide raw material is heated to the first temperature and the silicon carbide seed crystal is heated to the second temperature at a pressure after the pressure reduction, and the silicon carbide single crystal is grown at a growth rate faster than the growth rate in the first growth step. And a second growth step for growing the crystal. A method for growing a silicon carbide single crystal, comprising: 2. The silicon carbide single crystal according to claim 1, wherein a reduced pressure width that is a difference between the pressure in the first growth step and the pressure in the second growth step is 17.3 kPa (130 Torr) or less. Growth method. The method for growing a silicon carbide single crystal according to claim 1, wherein a temperature gradient between the silicon carbide raw material and the silicon carbide seed crystal in the first growth step is 5 ° C / cm or less. 2. The method for growing a silicon carbide single crystal according to claim 1, wherein the silicon carbide seed crystal is a seed crystal whose surface roughness Ra is previously processed in a range of 0.3 to 0.8 nm.

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