JP2006117441A - Method for preparing silicon carbide single crystal - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To manufacture a good quality silicon carbide single crystal free from inclusions at a high crystal growth speed even when the single crystal has such a large size that the diameter is ≥1 in and the thickness is ≥5 μm, in the manufacturing of the silicon carbide single crystal by a solution growth method comprising immersing an SiC seed crystal fixed to a seed stem in a solution of SiC in an Si or Si alloy melt in a rotating crucible, and growing an SiC single crystal layer on the SiC seed crystal by making SiC into a supersaturated state by the supercooling of at least solution around the seed crystal. <P>SOLUTION: In a method for manufacturing the silicon carbide single crystal, the single crystal is grown while utilizing an accelerated crucible rotation technique wherein acceleration of the rotation of the crucible to a prescribed rotation number, retention at the rotation number and deceleration to a low or zero rotation number are repeated. The rotation direction of the crucible may be reversed at every acceleration. Further, the seed stem may be rotated in synchronization with the rotation of the crucible in the direction being the same with or reverse to that of the rotation of the crucible. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a method for producing a high-quality silicon carbide single crystal suitable as a material for optical devices and electronic devices, and in particular, a high-quality silicon carbide single crystal can be reliably produced at a high growth rate by a solution growth method. Regarding the method.

  Silicon carbide (SiC) is one of the thermally and chemically stable compound semiconductors. Compared to silicon (Si), the band gap is about 3 times, the breakdown voltage is about 10 times, and the electron saturation rate is about. It has characteristics that are more advantageous than Si, about twice as much and about three times as large in thermal conductivity. Due to such excellent characteristics, SiC is expected to be applied as an electronic device material such as a power device that breaks the physical limits of Si devices and an environment-resistant device that operates at high temperatures.

  On the other hand, for optical devices, nitride-based materials (GaN, AlN) aiming at shorter wavelengths are being developed. SiC is attracting attention as a substrate material for epitaxial growth of nitride-based materials, since the lattice mismatch with respect to nitride-based materials is much smaller than other compound semiconductor materials.

  However, SiC is also famous as a substance exhibiting a crystalline polymorph (polytype). Crystal polymorphism is a phenomenon that can take many crystal structures in which the stacking mode of atoms differs only in the C-axis direction while having the same stoichiometric composition. Typical crystal polymorphs of SiC are 6H type (hexagonal system with 6 molecules as one period), 4H type (hexagonal system with 4 molecules as 1 period), and 3C type (3 molecules as 1 period). Cubic system). Mixing two or more crystal forms is not preferable for application to a device.

  Application of SiC to electronic and optical devices requires high-quality bulk single crystals and / or thin films of SiC that have a single crystal form (no intermingling of polymorphs) and have few or very few defects. It becomes.

Conventionally known SiC production methods include a sublimation method and chemical vapor deposition (CVD method) belonging to vapor phase growth, and a solution growth method which is liquid phase growth.
In the sublimation method, a raw material SiC powder is sublimated at a high temperature of 2200 to 2500 ° C., and a SiC single crystal is recrystallized on a seed crystal composed of a SiC single crystal arranged in a low temperature part.

In the CVD method, a silane-based gas and a hydrocarbon-based gas are used as raw materials, and a SiC single crystal is epitaxially grown on a substrate made of silicon or a SiC single crystal.
In the solution growth method, carbon is dissolved in a silicon or silicon alloy melt to prepare a solution in which SiC is dissolved in the melt. An SiC seed crystal is immersed in a melt in which SiC is dissolved, and at least a solution near the seed crystal is brought into a supercooled state to create a supersaturated state of SiC, and an SiC single crystal is grown on the seed crystal.

  In the solution growth method, a temperature gradient is provided in the melt so that the melt temperature in the vicinity of the seed crystal is lower than the melt temperature in the other part, so-called temperature difference method (only the solution in the vicinity of the seed crystal becomes supersaturated. ) And a so-called slow cooling method in which the entire melt soaked with the seed crystal is cooled to form a supersaturated solution of SiC. Since the slow cooling method is a batch method, it is preferable as a method for obtaining a single crystal of a thin film. On the other hand, the former temperature difference method which is continuous growth is preferred for obtaining a bulk single crystal.

  Since it is easy to obtain large bulk crystals by the sublimation method, industrial production of SiC single crystal wafers is currently performed by the sublimation method. However, SiC single crystals grown by the sublimation method tend to cause crystal defects such as hollow through defects, screw dislocations, and stacking faults, which are called micropipe defects, and have a problem in crystal quality.

  Since the CVD method has a relatively slow growth rate, it is mainly used for the growth of thin-film SiC crystals. Although the thin film SiC single crystal is affected by the substrate, the quality of the SiC substrate produced mainly by the sublimation method has the above-mentioned problems, so that there is a restriction on the high quality of the thin film.

  In the solution growth method, which is liquid phase growth, crystal growth occurs in a state close to thermal equilibrium, so a single crystal with significantly better crystallinity (no mixing of different crystal forms) is formed compared to vapor phase growth. Obtainable. As described above, as the solvent for the SiC solution, a Si melt or a Si alloy melt is used.

However, various technical problems still remain in order to obtain a large-area SiC crystal with a high quality and a high growth rate by the solution growth method.
For example, Materials Science and Engineering, B61-62 (1999) 29-39 is a technical problem related to SiC high-quality, and includes the inclusion of Si in a SiC crystal during the growth of a SiC single crystal from a solution using a Si solvent. (inclusion) occurs. This inclusion is caused by a non-uniform surface at the growth interface called morphological instability. This non-uniform surface has a macrostep structure, and it is considered that the solvent Si that has entered between the macrosteps is confined in the crystal by the lateral growth of the steps.

  On the other hand, in J. Crystal Growth 197 (1999) 147-154, in the liquid phase epitaxial growth from the Si-Sc-C ternary system solution, a circular pit (pit) is formed on the crystal surface, and this dent is crystal growth. It is described that it is caused by foreign matters such as carbon particles sometimes attached to the growth interface.

  Inclusion is a general term for phases that are inherent in SiC single crystals and that are different from SiC single crystals. That is, it is a different phase mixed in the SiC single crystal. Typical examples are particles derived from small liquids (droplets) of Si and C, but also include silicides, carbides, nitrides, oxides, and the like. Furthermore, an SiC crystal different from a predetermined crystal polymorph, for example, a 3C—SiC crystal mixed in a 6H—SiC single crystal, or a gas (bubble) confined in the crystal is also included.

  FIG. 1 shows an optical micrograph of a cross section of a SiC single crystal including inclusions generated by incorporation of a Si solvent into the crystal, which was found in a growth experiment conducted by the present inventors. In the figure, the black part shown at the end of ↓ is an inclusion generated due to the confinement of the solution.

  The occurrence of inclusions and depressions (pits) is a macro defect for a single crystal and an unacceptable defect as a device material. These also occur in crystal growth where the research-level single crystal size is 2 inches or less. In addition, if the temperature condition and the solute supply condition are not uniform at the growth interface where the crystal growth is performed, the resulting crystal thickness may be unevenly distributed. Particularly in a thin film single crystal, if the crystal thickness is non-uniform, the desired device performance cannot be achieved, and such non-uniformity is unacceptable for the device material.

  On the other hand, as a technical problem related to high-speed growth of SiC single crystal, increasing the growth rate while maintaining high crystal quality is cited. In general, the growth rate of SiC single crystal by the solution growth method is low. For example, in the case of solution growth using Si as a solvent, the growth rate is about 5 to 12 microns / hr at a melt temperature of 1650 ° C. This growth rate is 1 to 2 orders of magnitude smaller than the sublimation method. Thus, it is thought that the cause of the slow growth rate of the SiC crystal in the solution growth method is that the solubility of carbon in the solution is low. Therefore, the present inventors have succeeded in growing a SiC bulk single crystal by increasing the carbon solubility in the solution by using a Si—Ti or Si—Mn solvent (Japanese Patent Laid-Open No. 2004-2173). . However, even in this method, when the growth rate is increased, there is a possibility that the above-mentioned inclusion and the problem of non-uniformity in the crystal plane of the growth rate may occur, and the stable quality of 100 microns / hr or more is maintained while maintaining the crystal quality. Achieving fast growth is difficult.

As described above, in recent years, there has been a demand for industrially increasing the size of SiC single crystals, but as the size of the crystals increases, defects such as inclusions, depressions, and uneven crystal thickness become more apparent. For this reason, it is difficult to stably produce SiC single crystals having a size of 1 inch or more with no inclusions or depressions and a uniform growth thickness by high-speed growth of 100 microns / hr or more by the solution growth method. Has been.
Materials Science and Engineering, B61-62 (1999) 29-39 J. Crystal Growth 197 (1999) 147-154 JP 2004-2173 A

  An object of the present invention is to provide a method for producing a SiC single crystal capable of producing a high-quality SiC single crystal having no inclusion in the crystal at a high speed. As a result, it is possible to industrially manufacture a high-quality SiC single crystal grown by a solution growth method, which has been considered difficult to put into practical use.

  In the present invention, a SiC seed crystal fixed to a seed shaft is immersed in a melt containing SiC and containing Si and C or Si and C and one or more metals in a rotating crucible. Production of a silicon carbide single crystal by growing a SiC single crystal layer on the seed crystal by making SiC supersaturated by supercooling the solution around the seed crystal--ie, production of a silicon carbide single crystal by a solution growth method -The method for producing a silicon carbide single crystal, wherein the melt is stirred by periodically changing the number of revolutions or the number of revolutions and the direction of rotation of the crucible.

The melt containing Si, C, and one or more metals may be any combination of constituent elements as long as it is a liquid phase that is in thermodynamic equilibrium with SiC (solid phase). It is better that the melt has a large amount of SiC dissolved in the liquid and has a steep inclination of the liquidus. This is because such a melt can efficiently grow SiC crystals from the liquid phase. Examples of such melts include binary melts of Si _1-x Ti _x (0.1 ≦ x ≦ 0.25) and Si _1-x Mn _x (0.1 ≦ x ≦ 0.7). Fe and Co are other suitable alloy elements other than Ti and Mn of the Si alloy. The alloy element may be one type or two or more types.

  The present invention improves the stirring effect in the melt by applying a so-called crucible accelerated rotation technique (ACRT) in the production of a silicon carbide single crystal by a solution growth method, thereby generating inclusions. At the same time, the crystal growth was unexpectedly successful.

  The “ACRT” method is a method of changing the rotational speed or rotational speed and rotational direction of a crucible serving as a container when growing a single crystal from a melt in a crucible, that is, accelerating change. This method was proposed by Sheel and Shulz-DuBois (J. Crystal Growth 8 (1971) 304) and is a known technique per se. However, until now, ACRT has never been applied to the growth of SiC single crystals by a solution growth method, and has not been considered to be effective in solving the various problems described above. In the present invention, the ACRT technology is combined with the growth of an SiC single crystal by a solution growth method for the first time. By this combination, the SiC single crystal growth by the solution growth method and the ACRT technology alone can be predicted. It was confirmed that a remarkable effect (specifically, not only the occurrence of inclusion but also a significant increase in the crystal growth rate) was achieved.

  "At least the solution around the seed crystal substrate is supercooled" is (1) a so-called slow cooling method in which the entire melt is substantially uniformly cooled to a supercooled state, or (2) a temperature gradient in the melt. And a temperature difference method (temperature gradient method) in which the periphery of the seed crystal substrate becomes a low temperature portion and only this portion is in a supercooled state of the solution.

  In the slow cooling method, the cooling of the melt is finished at a temperature higher than the solidus temperature of the melt, and then the supercooling is repeated by repeating heating and cooling of the melt, so that the SiC single crystal is deposited on the seed crystal. By continuing the growth, it is possible to obtain a bulk (long) single crystal. However, since repeated heating and cooling consumes a large amount of heat energy, the temperature difference method is more advantageous for the growth of bulk single crystals. The slow cooling method is suitable for obtaining an epitaxial thin film single crystal by a batch method by finishing the cooling to a temperature higher than the solidus temperature only once. According to the present invention, even if a large-diameter thin film is epitaxially grown, a thin film without inclusion can be obtained.

  The temperature difference method is a method suitable for obtaining a bulk single crystal because crystal growth is performed continuously, but it is possible to obtain an epitaxial film by shortening the growth time even with the temperature difference method. It is.

  In either method, carbon is supplied into the melt by using a crucible containing the melt as a carbonaceous crucible (eg, a graphite crucible) and by supplying the melt by melting the crucible or through a gas phase such as hydrocarbon gas. In addition, a method in which a solid carbon source is introduced into a melt and dissolved can be used. Two or more methods may be combined.

In the crucible accelerated rotation (ACRT) method, when only the rotation speed of the crucible is changed periodically, the change in the rotation speed is
(1) Acceleration up to the first set speed A1,
(2) rotation holding at the first rotation speed A1, and
(3) Deceleration to the second set rotational speed A2 (A2 <A1),
Repeat this cycle for each cycle (however, the set values of the rotational speeds A1 and A2 do not need to be the same in each cycle, and these set values can be varied from cycle to cycle). Can do.

On the other hand, when both the rotation speed and the rotation direction of the crucible are changed periodically, this change is
(1) Acceleration up to the set speed B1 in the first rotation direction,
(2) Rotation holding at the rotation speed B1 in the first rotation direction,
(3) Deceleration to 0 rpm,
(4) Acceleration up to the set rotation speed B2 (B2 may be the same as or different from B1) in the second rotation direction in the reverse direction;
(5) Maintaining rotation at the set value B2 in the second rotation direction,
(6) Deceleration to 0 rpm,
, And repeat this cycle (however, the set values of the rotational speeds B1 and B2 do not have to be the same in each cycle, and these set values can be changed for each cycle). Can do.

  As the set rotational speeds A1, B1, and B2 are all larger, the stirring effect in the melt can be expected. However, if the rotational speed is too large, the melt surface shape becomes unstable, and the crystal growth may be adversely affected. A preferable range of A1, B1, and B2 is a range of 15 to 100 rpm. The set rotational speed A2 only needs to be smaller than A1, and may be 0 rpm. A preferable range of A2 is from 0 rpm to 1/2 of A1.

In the case of a method that changes only the rotation speed,
(1) Acceleration time to reach the first set speed A1: 1 second to 10 minutes
(2) Rotation holding time at the first set rotational speed A1: 0 seconds to 10 minutes
(3) It is preferable that the deceleration time from the end of holding until reaching the second set rotational speed A2 is 1 second to 10 minutes. It is substantially difficult to realize that the acceleration time to A1 is shorter than 1 second, and when it is longer than 10 minutes, the acceleration is small and the forced stirring effect is reduced. The longer the rotation holding time at A1, the longer the stirring effect can be obtained. This holding time may be instantaneous, ie substantially 0 seconds. The range of the deceleration time from A1 to A2 is also preferable for the same reason as the acceleration time to A1. A large forced stirring effect can be obtained during deceleration as well as during acceleration.

In the method of changing both the rotation speed and the rotation direction, for the same reason as the above method,
(1) Acceleration time to reach the set rotation speed B1 in the first direction: 1 second to 10 minutes
(2) Rotation holding time at the set rotation speed B1 in the first direction: 0 seconds to 10 minutes
(3) Deceleration time from the end of rotation holding in the first direction until reaching 0 rpm: 1 second to 10 minutes
(4) Acceleration time to reach the set rotation speed B2 in the reverse second direction: 1 second to 10 minutes
(5) Rotation holding time at the set rotation speed B2 in the second direction: 0 seconds to 10 minutes
(6) Deceleration time from the end of rotation holding in the second direction until reaching 0 rpm is preferably 1 second to 10 minutes.

In the latter method, the stirring effect in the melt is increased by the amount of inversion compared to the former.
In the method of the present invention, the stirring in the melt is promoted by the accelerated rotation of the crucible, but the seed shaft (seed crystal holding jig) for fixing the seed crystal is also in the same direction as or opposite to the rotation direction of the crucible. It may be rotated in the direction. The rotation of the seed shaft is preferably an acceleration rotation synchronized with the rotation of the crucible. Thereby, the stirring in the melt can be further increased.

  According to the method of the present invention, an SiC single crystal having an area of 1 inch diameter or more and a thickness of 5 microns or more and having no inclusions can be stably and reliably produced at a high crystal growth rate. . As a result, a high-quality SiC single crystal can be grown at a high speed by a solution growth method, which has been difficult to put into practical use.

  According to the present invention, it is possible to industrially manufacture a SiC single crystal having a diameter of 1 inch or more and a thickness of 5 microns or more, which is difficult in the past and does not include inclusions. When the thickness is 200 microns or less, it is used as a thin film (epi film) epitaxially grown on the SiC single crystal used as the substrate. When the thickness is 200 microns or more, the seed crystal is removed as needed and used as a substrate material. It becomes possible to do. That is, the single crystal obtained by the present invention can be used as a bulk single crystal for substrate use, or can be used as an epitaxial crystal for device use using a seed crystal as a substrate.

  Inclusion includes everything that is different from a crystal taken into the crystal by some action. For example, the solvent is trapped within the crystal during crystal growth, which is caused by inhomogeneities at the crystal growth interface. In particular, when growing SiC crystals from a solution, the solubility of SiC in the melt of Si or Si alloy is small, and therefore the degree of supersaturation of the solution is often low. Is left behind and becomes inclusion. In addition to the solvent, bubbles, graphite particles mixed in the solution, and the like are typical inclusions. If inclusions are mixed, the device cannot be used for its intended purpose.

  In the following examples, experiments were conducted using the crystal growth apparatus shown in FIG. The illustrated apparatus includes a rotatable high-purity graphite crucible containing a high-temperature SiC solution. The solution in the crucible is immersed with a seed crystal attached to a rotatable seed shaft that passes through the crucible lid and is inserted into the crucible. The graphite crucible is surrounded by a heat insulating material, and a heating coil for high frequency induction heating is disposed around the heat insulating material. The entirety of the above elements is accommodated in the water cooling chamber. The water-cooled chamber includes a gas inlet and a gas outlet, and can control the composition and pressure of the atmosphere gas for crystal growth. Although not shown, the back surface of the side of the graphite crucible 2 is directly measured by a pyrometer such as a two-color pyrometer. A plurality of pyrometers may be installed at the top and bottom to measure the melt temperature at different positions on the top and bottom.

  In the experiment, Si or Si serving as a solvent and Ti of an alloy element were charged in a graphite crucible, and the material charged by high-frequency induction heating was melted by energizing a high-frequency coil to form a melt. C was supplied into the melt by melting a high-purity graphite crucible as a container. By adjusting the relative positional relationship between the graphite crucible and the high-frequency coil, the melt can be brought into a soaking state, or an appropriate temperature gradient can be formed. Accordingly, the illustrated apparatus can perform SiC crystal growth by either the slow cooling method or the temperature difference method.

  Each of the crucible and the seed shaft starts accelerated rotation at least immediately before immersing the seed crystal in the solution, and when the seed crystal is immersed and a new SiC crystal grows on the seed crystal, the accelerated rotation is performed. To be.

  In the examples, growth experiments by the temperature difference method are illustrated, but similar results can be obtained by the slow cooling method. The temperature of the solution is adjusted so that the vicinity of the liquid surface of the solution where the seed crystal is located is lower in temperature than the inside (lower part) of the solution, and the seed crystal is immersed in a relatively low temperature region near the liquid surface for 5 hours. . A 1-inch diameter single crystal was used as a seed crystal. After the experiment, the seed crystal was pulled up from the melt and the seed crystal was recovered. The seed crystal was washed with hydrofluoric acid to remove the adhering melt coagulum. The growth rate was obtained from the growth thickness of a single crystal newly grown on the seed crystal. In addition, the occurrence state of inclusion of the obtained single crystal was examined.

  As a result, when the crucible accelerated rotation (ACRT) method is applied to the SiC single crystal solution growth method, the conventional solution growth method can realize crystals that do not contain inclusions with very small crystal growth of about several millimeters square. In contrast, it has been found that single crystals having no inclusions grow in large crystals having a diameter of 1 inch or more.

  This is presumably because the forced flow of the melt occurs due to the accelerated rotation of the crucible, so that the uniform supply of the solute to the seed crystal is promoted. As a result, uneven solute supply at the growth interface is remarkably improved, step bunching is suppressed, solvent uptake between steps can be completely suppressed, and the occurrence of inclusions is prevented It is guessed.

  It was also found that the in-plane thickness distribution of the resulting crystal was greatly improved by the uniform supply of the solute to the growth interface. Furthermore, the supply of the solute by forced flow brings about an increase in the crystal growth rate in the crystal growth in which the transport to the growth interface of the solute is the limiting process like SiC, and at least compared with the growth not applying the ACRT method. An increase in the growth rate of about 2 times was confirmed. Since uniform step flow growth at the atomic level is realized under a large area, the surface morphology of the SiC single crystal obtained by applying the ACRT method is visually observed even when grown with a crystal length of cm order. It was also confirmed that the mirror surface was held.

  The fact that the ACRT method not only prevents the inclusion but also provides a significant increase in the crystal growth rate has been hardly known so far, which is an unexpected effect unique to the growth of SiC single crystals. This is because, as described above, the solubility of SiC, which is a solute, is very small, and supply to the growth interface of the solute is significantly increased by forced flow.

As a method for generating forced flow in the melt, there are a first method for changing only the rotation speed of the graphite crucible (same direction rotation method) and a second method for changing the rotation speed and rotation direction of the graphite crucible ( Both of them were carried out.

In the first method,
(1) Acceleration up to the first set speed A1,
(2) Rotation holding at the first rotation speed A1, and
(3) Deceleration to the second set rotational speed A2 (A2 <A1),
This cycle was repeated with 1 cycle.

In the second method,
(1) Acceleration up to the set rotational speed B1 in the first rotational direction,
(2) Rotation holding at rotation speed B1,
(3) Deceleration to 0 rpm
(4) Acceleration up to the second rotational direction setting rotational speed B2 in the reverse direction (B2 may be different from B1, but the same in the experiment)
(5) Rotation holding at set value B2,
(6) Deceleration to 0 rpm,
This cycle was repeated with 1 cycle.

  Agitation in the melt is accelerated by the accelerated rotation of the crucible, but in some embodiments, in order to further increase the stirring, the seed shaft on which the seed crystal is attached may be rotated at an accelerated speed in synchronization with the rotation of the crucible. went.

This example illustrates the production of an SiC single crystal by the solution growth method using the crystal growth apparatus shown in FIG. In this example, the crucible accelerated rotation was performed by rotating only the graphite crucible.
The crystal growth apparatus includes a graphite crucible having an inner diameter of 80 mm and a height of 150 mm containing a melt, and this crucible is arranged in a water-cooled stainless steel chamber. The outer periphery of the graphite crucible is kept warm by a heat insulating material, and a high frequency coil for induction heating is provided on the outer periphery. The atmosphere in the crystal growth apparatus is adjusted using the gas inlet and the gas outlet.

An alloy raw material having a composition of Si _0.8 Ti _0.2 was charged into a graphite crucible and melted. A temperature gradient was provided in the depth direction of the melt by adjusting the relative positions of the high-frequency coil and the graphite crucible. The temperature gradient was adjusted so that the temperature near the crystal growth interface was about 1700 ° C. and the bottom of the solution was about 1750 ° C. A SiC seed crystal (1 inch diameter 6H-SiC) was attached to the seed shaft.

  The crucible was rotated counterclockwise without rotating the seed crystal (seed shaft). The ultimate rotation speed of the crucible was set to 30 rpm, and the time required to reach the set rotation speed was 5 seconds. After the number of rotations of the crucible reached the set number of rotations, the rotation was performed for 10 seconds, and then the rotation was stopped in 5 seconds. Next, the direction of rotation of the crucible was reversed to the right, and in the same manner as described above, 30 rpm was reached in 5 seconds, the rotation at 30 rpm was held for 10 seconds, and then the rotation was stopped in 5 seconds. With the above as one cycle, the cycle was repeated during crystal growth. In this example, the seed shaft was not rotated, and only the graphite crucible was rotated in reverse. The time for one cycle is 40 seconds.

After 5 hours from the seed crystal immersion, the seed axis was raised and the crystal was pulled away from the melt to terminate the growth. Thereafter, the rotation of the crucible was stopped.
After gradually cooling the crucible to room temperature, the crystal was recovered from the seed shaft. A SiC single crystal was newly grown on the seed crystal, and its growth area was the same 1 inch diameter as the seed crystal. The presence or absence of inclusion in the grown crystal was examined by observing in detail with an optical microscope (× 200) from the surface and cross section of the crystal. If there is a magnification of × 200, the inclusion of micron order can be distinguished.

Judgment is that the inclusion does not exist in the total area of the grown crystal,
X where inclusions exist
It was.

  The growth rate was determined by determining the growth thickness by observation with an optical microscope from a cross section and dividing by the growth time. For the case where a growth rate of 2 times or more was obtained with respect to the same growth condition (Comparative Example 1 described later) to which ACRT is not applied, ◎, 1 time or more, 2 times or less, ○, 1 time or less. The results are summarized in Table 1.

This example illustrates the growth of a SiC single crystal by crucible acceleration rotation in which the rotation direction of the graphite crucible and the seed crystal (seed axis) is reversed so as to be the same direction.
The seed crystal and the crucible were first rotated to the same left rotation. The arrival speed of the seed crystal and the crucible was set to 30 rpm, and the time required to reach the set speed was 5 seconds. After reaching the reached rotation speed, the rotation was performed for 10 seconds, and then the rotation was stopped in 5 seconds. Next, the direction of rotation of the seed crystal and the crucible was reversed to the right, and reached 30 rpm in 5 seconds, and the rotation at 30 rpm was held for 10 seconds, and then the rotation was stopped in 5 seconds. . With the above as one cycle, the cycle was repeated during crystal growth. The seed shaft and the crucible were repeatedly rotated in reverse while being synchronized so as to always have the same rotational direction. The time for one cycle is 40 seconds.

  Except for the above rotation conditions, SiC crystal growth was performed by the solution growth method in the same manner as in Example 1. After 5 hours from the seed crystal immersion, the seed axis was raised and the crystal was pulled away from the melt to terminate the growth. Thereafter, the rotation of the seed shaft and the crucible was stopped.

  After gradually cooling the crucible to room temperature, the crystal was recovered from the seed shaft. A SiC single crystal was newly grown on the seed crystal, and its growth area was the same 1 inch diameter as the seed crystal. Table 1 shows the results of investigating the presence or absence of inclusion in the grown crystal and the crystal growth rate in the same manner as in Example 1.

This example illustrates the growth of a SiC single crystal by crucible acceleration rotation in which the rotation direction of the graphite crucible and the seed crystal (seed axis) is reversed (opposite).
That is, first, the seed crystal was rotated clockwise and the crucible was rotated counterclockwise. Each reached rotation speed was set to 30 rpm, and the time to reach the set rotation speed was 5 seconds. After reaching the set rotation speed, the rotation was performed at the rotation speed for 10 seconds, and then the rotation was stopped at 5 seconds. Next, the direction of rotation is reversed, the seed shaft is rotated to the left, the crucible is rotated to the right, and 30 rpm is reached in 5 seconds, and the rotation at 30 rpm is held for 10 seconds. The rotation stopped at. With the above as one cycle, the cycle was repeated during crystal growth. The rotation of the seed shaft and the crucible was repeatedly reversed while synchronizing the rotation so that the rotation directions were always opposite to each other. This situation is shown in FIG. As shown in the figure, the time for one cycle is 40 seconds.

  Except for the above rotation conditions, SiC crystal growth was performed by the solution growth method in the same manner as in Example 1. After 5 hours from the seed crystal immersion, the seed axis was raised and the crystal was pulled away from the melt to terminate the growth. Thereafter, the rotation of the seed shaft and the crucible was stopped.

  After gradually cooling the crucible to room temperature, the crystal was recovered from the seed shaft. A SiC single crystal was newly grown on the seed crystal, and its growth area was the same 1 inch diameter as the seed crystal. Table 1 shows the results of investigating the presence or absence of inclusion in the grown crystal and the crystal growth rate in the same manner as in Example 1.

  In this example, the rotation direction of the graphite crucible and the seed crystal (seed axis) is the same direction, and the same direction rotation type crucible acceleration rotation that repeats acceleration and deceleration while maintaining the rotation in the same direction without reversing the rotation direction. 3 illustrates the growth of a SiC single crystal by the above.

  Both the seed crystal (seed shaft) and the crucible were rotated counterclockwise, and the number of revolutions reached was set to 30 rpm. The time required to reach the set rotational speed was 5 seconds. After reaching the reached rotation speed, the rotation was performed at the rotation speed for 10 seconds, and then the rotation speed was reduced to 0 rpm in 5 seconds (that is, the rotation was stopped). Immediately after the rotation stopped, the rotation speed was accelerated to 30 rpm in 5 seconds while maintaining the same left rotation, and the rotation was stopped in 5 seconds after maintaining the rotation at 30 rpm for 10 seconds. In this example, acceleration to 30 rpm, rotation holding at 30 rpm, and deceleration to 0 rpm are one cycle, so the time for one cycle is 20 seconds. The rotation of the seed shaft and the crucible was always synchronized in the same rotation direction.

  Except for the above rotation conditions, SiC crystal growth was performed by the solution growth method in the same manner as in Example 1. After 5 hours from the seed crystal immersion, the seed axis was raised and the crystal was pulled away from the melt to terminate the growth. Thereafter, the rotation of the seed shaft and the crucible was stopped.

  After gradually cooling the crucible to room temperature, the crystal was recovered from the seed shaft. A SiC single crystal was newly grown on the seed crystal, and its growth area was the same 1 inch diameter as the seed crystal. Table 1 shows the results of investigating the presence or absence of inclusion in the grown crystal and the crystal growth rate in the same manner as in Example 1.

  A SiC single crystal was produced on the seed crystal in the same manner as in Example 1 except that the graphite crucible was filled only with Si. That is, the seed shaft was not rotated, and only the graphite crucible was rotated in reverse. In the examples so far, the solvent is a Si—Ti alloy, but in this example, it is Si.

After 5 hours from the seed crystal immersion, the seed axis was raised and the crystal was pulled away from the melt to terminate the growth. Thereafter, the rotation of the crucible was stopped.
After gradually cooling the crucible to room temperature, the crystal was recovered from the seed shaft. A SiC single crystal was newly grown on the seed crystal, and its growth area was the same 1 inch diameter as the seed crystal. Table 1 shows the results of investigating the occurrence of inclusions in the grown crystal in the same manner as in Example 1.

As shown in Table 1, in this example, the crystal growth rate was lower than in Examples 1 to 4, but this was because the solvent of the SiC solution was Si—Ti alloy in Examples 1 to 4. In contrast, in this example, Si alone is used, and the concentration of SiC in the solution is lowered. Compared with the case where the solvent is Si alone and acceleration rotation is not performed, the crystal growth rate in this example is also twice or more.
[Comparative Example 1]

  In this example, as in Example 3, the seed crystal was rotated to the right and the crucible was rotated to the left to rotate in opposite directions. However, the number of rotations during crystal growth was kept constant at 30 rpm for the seed crystal and the crucible, and accelerated rotation was not performed. Other than that was carried out similarly to Example 3, and performed the crystal growth of SiC by the solution growth method.

After 5 hours from the seed crystal immersion, the seed axis was raised and the crystal was pulled away from the melt to terminate the growth. Thereafter, the rotation of the seed shaft and the crucible was stopped. After gradually cooling the crucible to room temperature, the crystal was recovered from the seed shaft. A SiC single crystal was newly grown on the seed crystal, and its growth area was the same 1 inch diameter as the seed crystal. Table 1 shows the results of investigating the occurrence of inclusions in the grown crystal in the same manner as in Example 1.
A new SiC single crystal was grown on the seed crystal.

  As shown in Table 1, in Comparative Example 1 in which the crucible accelerated rotation was not performed, the inclusion as shown in FIG. 1 was observed in the crystal. On the other hand, when applying crucible accelerated rotation according to the present invention, the type of solvent (Si or Si alloy), rotation method (reversing the rotation direction or keeping it in the same direction), or rotation of the seed axis (seed crystal) Regardless of the presence or absence of the crystal, the inclusion-free crystal could be grown at a speed twice as high as that without acceleration rotation under any rotation condition. In particular, when the solvent was a Si alloy, it was possible to achieve a high crystal growth rate of 150 microns / hr or more, and at most 200 microns / hr or more, while maintaining good crystal quality.

  As mentioned above, although this invention was demonstrated about the specific form, embodiment and the Example which were disclosed here are illustrations in all the points, Comprising: It is not restrictive. The scope of the present invention includes meanings equivalent to the claims and all modifications within the scope.

It is an optical microscope photograph of the section of SiC crystal containing inclusion grown by the conventional solution growth method. It is a schematic explanatory drawing which shows the single crystal growth apparatus by the solution growth method suitable for using for the method of this invention. It is a figure which shows the rotation profile of the crucible and seed shaft which were employ | adopted in the Example of this invention.

Claims (5)

  A SiC seed crystal fixed to a seed shaft is immersed in a melt containing SiC and containing Si and C or Si and C and one or more metals in a rotating crucible, and at least around the seed crystal. In the manufacture of a silicon carbide single crystal by growing a SiC single crystal layer on the seed crystal by making SiC supersaturated by supercooling the solution, the rotational speed or rotational speed and rotational direction of the crucible are periodically changed. The method for producing a silicon carbide single crystal, wherein the melt is stirred. The number of revolutions of the crucible,
(1) Acceleration up to the first set speed A1,
(2) rotation holding at the first rotation speed A1, and
(3) Deceleration to the second set rotational speed A2 (A2 <A1),
The method according to claim 1, wherein the cycle is periodically changed by repeating the cycle (however, the set values of the rotational speeds A1 and A2 can be changed for each cycle). The rotation speed and rotation direction of the crucible
(1) Accelerate to the set speed B1 in the first rotation direction,
(2) Rotation holding in the first rotation direction at the rotation speed B1,
(3) Deceleration to 0 rpm,
(4) Acceleration up to the set rotation speed B2 (B2 may be the same as or different from B1) in the second rotation direction in the reverse direction;
(5) Maintaining rotation in the second rotational direction at the set value B2.
(6) Deceleration to 0 rpm,
The method according to claim 1, wherein the cycle is periodically changed by repeating this cycle (however, the set values of the rotation speeds B <b> 1 and B <b> 2 can be changed for each cycle).   The method according to any one of claims 1 to 3, wherein the seed shaft is rotated in the same or opposite direction as the crucible together with the rotation of the crucible.   The method according to claim 4, wherein the rotation of the seed shaft is synchronized with the rotation of the crucible.

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