JP2003226600A - Seed crystal for growing silicon carbide single crystal, silicon carbide single crystal ingot, and methods of producing them - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To form a good protective film with a good reproducibility, and to provide a seed crystal for growing an SiC single crystal with which the deterioration of the crystal quality caused by the occurrence of voids is suppressed, an SiC single crystal ingot having a good appearance free from structural defects over the whole surface, and methods for producing them with good reproducibilities. <P>SOLUTION: When the silicon carbide single crystal is grown by a sublimation recrystallization method using the seed crystal, an organic thin film having a thickness within a predetermined range is formed at the rear surface of the growth surface of the seed crystal. Thereby, the departure of atoms from the rear surface is suppressed during growth, and a high quality silicon carbide single crystal ingot having extremely less structural defects can be obtained. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a seed crystal for growing a silicon carbide single crystal, a method for producing the same, and a method for producing a silicon carbide single crystal using the seed crystal, as well as a blue light emitting diode and an electronic device. And a large-sized silicon carbide single crystal ingot to be a substrate wafer of the above and a method for manufacturing the same.

[0002]

2. Description of the Related Art Silicon carbide (SiC) has been attracting attention as an environment-resistant semiconductor material because of its excellent heat resistance and mechanical strength and physical and chemical properties such as resistance to radiation. SiC
Is a typical substance having a polymorphic (polytype) structure that has many different crystal structures even if the chemical composition is the same.
Polytype means that when a molecule in which Si and C are bonded is considered as one unit in the crystal structure, the unit structure molecule has a different periodic structure when stacked in the c-axis direction ([0001] direction) of the crystal. Occurs. Representative polytypes include 6H, 4H, 15R or 3C. here,
The first number indicates the repetition cycle of stacking, and the alphabet indicates a crystal system (H is a hexagonal system, R is a rhombohedral system, and C is a cubic system). Each polytype has different physical and electrical characteristics, and it is considered to be applied to various applications by utilizing the difference. For example, 6H has recently been used as a substrate for short wavelength optical devices in the blue to ultraviolet range.
H is considered to be applied as a substrate wafer for high-frequency high-voltage electronic devices and the like.

However, high quality S having a large area
A crystal growth technique capable of stably supplying an iC single crystal on an industrial scale has not yet been established. Therefore, SiC
Despite its many advantages and potentials mentioned above, its practical use has been hindered.

Conventionally, on a scale of a laboratory, for example, a SiC single crystal was grown by a sublimation recrystallization method (Rayleigh method) to obtain an SiC single crystal having a size capable of producing a semiconductor device. However, with this method, the area of the obtained single crystal is small, and it is difficult to control the size and shape with high accuracy. Moreover, it is not easy to control the crystal polymorphism and the impurity carrier concentration of SiC. Further, a cubic silicon carbide single crystal is also grown by performing heteroepitaxial growth on a heterogeneous substrate such as silicon (Si) using a chemical vapor deposition method (CVD method). With this method, a large-area single crystal can be obtained, but many defects (~) due to the lattice mismatch with the substrate of about 20%.
Only a SiC single crystal containing 10 ⁷ cm ⁻² ) can be grown, and it is not easy to obtain a high quality SiC single crystal. In order to solve these problems, an improved Rayleigh method of sublimation recrystallization using a SiC single crystal {0001} wafer as a seed crystal has been proposed (Yu. M. T.
airov and VF Tsvetkov, Journal of Crystal Growt
h, vol. 52 (1981) pp.146-150). In this method, since the seed crystal is used, the nucleation process of the crystal can be controlled, and the atmosphere pressure is 100 Pa to 15 k due to the inert gas.
By controlling to about Pa, the crystal growth rate and the like can be controlled with good reproducibility. The principle of the modified Rayleigh method will be described with reference to FIG. The SiC single crystal 1 as a seed crystal and the SiC crystal powder 2 as a raw material are housed in a crucible 3 (usually made of graphite) and placed in an inert gas atmosphere such as argon (13).
3 Pa to 13.3 kPa) and 2000 to 2400 ° C. At this time, the temperature gradient is set so that the seed crystal 1 has a slightly lower temperature than the SiC crystal powder 2 as the raw material. After sublimation, the SiC crystal powder 2 is diffused and transported in the seed crystal 1 direction by a concentration gradient (formed by a temperature gradient). Single crystal growth is realized by recrystallizing on the seed crystal 1 the gas formed by sublimation of the SiC crystal powder 2 that has reached the seed crystal 1. At this time, the resistivity of the crystal is determined by adding an impurity gas into an atmosphere of an inert gas or mixing an impurity element or its compound into the SiC crystal powder to obtain silicon (Si) in the SiC single crystal structure.
Alternatively, it can be controlled by substituting (doping) the position of the carbon atom (C) with an impurity element. Nitrogen (n-type) is a typical substitution type impurity in a SiC single crystal.
There are boron and aluminum (p type). A SiC single crystal can be grown while controlling the carrier type and concentration.

Currently, the S produced by the improved Rayleigh method described above is used.
A SiC single crystal wafer having a diameter of 1 inch (25 mm) to 3 inches (75 mm) is cut out from an iC single crystal, and is used for epitaxial thin film growth and device fabrication.

As mentioned above, at present, SiC single crystals are
Although it is produced by the modified Rayleigh method utilizing the sublimation phenomenon from the raw material, it will be described with reference to FIG. 1 that a specific problem occurs when the seed crystal 1 is actually mounted and grown on the crucible 3. One of such problems is that the sublimation phenomenon also occurs from the back surface of the seed crystal 1 toward the crucible material (made of graphite) such as the crucible lid 4 having the seed crystal mounted thereon during the crystal growth. Usually, the seed crystal 1 is mounted inside the crucible lid 4 (on the side facing the raw material) by a mechanical mounting method. At this time, since it is a mechanical mounting method, strictly speaking, there is a very small gap (gap) between the seed crystal 1 and the crucible lid 4. Crystal growth requires a high temperature of 2000 ° C. or higher in order to sublimate the SiC crystal powder 2. However, like the SiC crystal powder 2, the seed crystal 1 is also SiC, so the back surface of the seed crystal 1 and the crucible lid 4
If there is a very small gap between the seed crystal 1 and the seed crystal 1 due to the temperature gradient between the back surface of the seed crystal 1 and the crucible lid 4 (the back surface of the seed crystal has a higher temperature).
Si atoms sublimate from the backside of the crucible lid 4 at a lower temperature
Recrystallize on the surface of. As a result, holes (voids) having a diameter of about 5 to 100 μm and having Si removed are formed from the back surface of the seed crystal 1 to the growth surface. Since Si is removed and C remains in this hole, the surface thereof is carbonized and has a black color. The void reaching the growth surface naturally affects the crystal growth, and in particular, a hollow defect with a diameter of about 0.1 to 10 μm called a micropipe defect is often generated from the carbonized portion, which significantly deteriorates the crystal quality. There is a problem. Also, since the voids appear black, the appearance of the wafer is significantly impaired, and the number of wafers that can be taken out as samples from the region where the voids exist (from the bottom to the middle of the growth crystal ingot) decreases, and the yield in sample preparation decreases. Was a problem.

As a method of mounting the seed crystal on the crucible material, there is a method of carbonizing sugar and using it as an adhesive material. However, in the same method, the above-mentioned problem of void generation similarly occurs and the crystal quality is deteriorated. Was connected to.

In response to this problem, EK Sanchez, T. Ku
hr, VD Heydemann, DW Snyder, GS Rohrer an
d M. Skowronski, Journal of Electronic Materials,
As reported in vol.29, No.3 (2000) pp.347-352, it is protected by carbonizing (hereinafter also referred to as annealing) after applying a photosensitive resist that is an organic film on the back surface of the seed crystal. A method of forming a film has been proposed. According to the report, after applying a photosensitive resist having a thickness of about 15 μm on the back surface of the seed crystal, it is dried at 120 ° C. for 5 minutes, and then 1200 ° C. under high vacuum (2 × 10 ⁻³ Pa or less). Annealing is performed by a lamp heating method at a heating rate of 400 ° C./hour) to obtain a graphite protective film having gloss. It has been reported that, when crystal growth was performed using this seed crystal provided with the protective film, the release of Si from the back surface of the seed crystal was suppressed by the protective film, and void generation was prevented.

However, when the protective film is actually formed by such a method, it is dried at 120 ° C. for 5 minutes, and then 1200 ° C. (lamp heating under high vacuum (2 × 10 ⁻³ Pa or less)). When annealed at a temperature rising rate of 400 ° C./hour by the method), a phenomenon was observed that voids were formed at the interface between the seed crystal back surface and the resist or inside the resist. The cause of this void generation is that when the solvent volatilizes from the resist in the above-mentioned drying step and annealing step,
This is because the solidification of the resist proceeds before the organic solvent gas generated inside the resist reaches the surface and completely volatilizes, and the gas remains without being exhausted. As a result, there arises a problem that a uniform protective film is not formed on the entire back surface of the seed crystal. In such a phenomenon, when the generated cavity is in contact with the back surface of the seed crystal, a void is generated, which is the same phenomenon as when a conventional gap is present during crystal growth, and the crystal quality is deteriorated. Further, even if the gas does not contact the back surface of the seed crystal and remains as a cavity inside the resist, the presence of the cavity causes uneven heat transfer in the back surface of the seed crystal during crystal growth, resulting in a Has a problem that the crystal growth is disturbed and the crystal growth cannot be performed well. Thus, EK Sa
Even with the method by nchez et al., it has not been achieved to suppress the generation of voids over the entire surface of the grown crystal.

[0010]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a seed crystal for growing a SiC single crystal in which the deterioration of crystal quality due to the occurrence of voids is suppressed and the production thereof. It is another object of the present invention to provide a method, in addition, an SiC single crystal having a good appearance with no structural defects over the entire surface, an ingot produced from the same, and a production method capable of producing these with good reproducibility.

[0011]

Means for Solving the Problems The inventors of the present invention have made earnest studies on a protective film of a seed crystal, and as a result, in the conventional method described above, gas was generated when the solvent volatilized from the protective film during drying and carbonization. Based on the knowledge that the thickness of the protective film is not completely removed, it is because the thickness of the protective film is thick, and by strictly controlling the thickness of the organic thin film, it is possible to suppress the voids generated during the growth of the SiC single crystal. did.

Therefore, the gist of the present invention is the following means.

(1) A seed crystal for growing a silicon carbide single crystal, wherein the back surface side of the single crystal growth surface of the seed crystal is covered with an organic thin film.

(2) The seed crystal for growing a silicon carbide single crystal according to (1), wherein the organic thin film is made of an organic resin.

(3) The seed crystal for growing a silicon carbide single crystal according to (2), wherein the organic resin is a photosensitive resin.

(4) The thickness of the organic thin film is 0.5 to 5 μm.
The seed crystal for growing a silicon carbide single crystal according to any one of (1) to (3), wherein m is m.

(5) A seed crystal for growing a silicon carbide single crystal, wherein the back surface side of the single crystal growth surface of the seed crystal is covered with a carbon thin film.

(6) The seed crystal for growing a silicon carbide single crystal according to (5), wherein the carbon thin film is formed by carbonizing an organic thin film.

(7) The carbon thin film has a thickness of 0.5 to 5 μm.
The seed crystal for growing a silicon carbide single crystal according to (5) or (6), wherein m is m.

(8) The diameter is 25 mm or more (1) to
A seed crystal for growing a silicon carbide single crystal according to any one of (7).

(9) A silicon carbide characterized in that an organic thin film is formed by performing a carbonization treatment at least once by applying a composition for forming an organic thin film on the back surface side of a single crystal growth surface of a seed crystal. A method for producing a seed crystal for growing a single crystal.

(10) The method according to (9), wherein the method for applying the composition for forming an organic thin film is spin coating.

(11) A seed crystal produced by the production method described in (9) or (10), in which an organic thin film is formed on the back surface side of the single crystal growth surface, is at a temperature equal to or higher than the temperature at which the organic thin film is carbonized. A method for producing a seed crystal for growing a silicon carbide single crystal, comprising heating the organic thin film to a carbon thin film by heating the organic thin film to a temperature lower than the sublimation temperature.

(12) A method for producing a silicon carbide single crystal, which comprises a step of growing a silicon carbide single crystal on a seed crystal by a sublimation recrystallization method, wherein the seed crystal (1) to
A method for producing a silicon carbide single crystal, which comprises using the seed crystal for growing a silicon carbide single crystal according to any one of (8).

(13) A silicon carbide single crystal ingot made of the silicon carbide single crystal obtained by the manufacturing method according to (12), characterized in that the diameter of the ingot is 25 mm or more. Crystal ingot.

(14) A silicon carbide single crystal wafer obtained by cutting and polishing the silicon carbide single crystal ingot according to (13).

[0027]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention relates to a seed crystal for growing a silicon carbide single crystal in which the back surface side of the seed crystal single crystal growth surface is covered with an organic thin film, and the back surface side of the seed crystal single crystal growth surface is a carbon thin film. It is a seed crystal for growing a silicon carbide single crystal coated with.
In the present invention, a high-quality organic thin film whose thickness is strictly controlled, or a carbon thin film formed by carbonizing the organic thin film (hereinafter also referred to as annealing) is formed on the back surface side of the single crystal growth surface of the seed crystal. By manufacturing, it is possible to suppress sublimation of Si atoms from the back surface of the seed crystal during crystal growth and suppress generation of voids during crystal growth.

The effects of forming the organic thin film in the present invention will be described below with reference to FIGS. 2A and 2B are schematic diagrams for explaining the mechanism of suppressing the generation of voids by the organic thin film, where FIG. 2A is a sectional view of a part of the seed crystal growth crucible, and FIG. It is an enlarged view of a portion between the lid and (c) is an enlarged view of the same portion when further covered with an organic thin film. Crystal growth is carried out by mechanically attaching a seed crystal to a graphite crucible lid with screws or the like, as shown in FIG. At this time, as shown in FIG. 2B, there is actually a minute gap of the μm unit level between the back surface of the seed crystal and the crucible lid to be mounted. Due to the existence of this gap, S is introduced from the back surface of the seed crystal during crystal growth.
The i atom sublimes and recrystallizes on the crucible lid surface at a lower temperature. As a result, from the seed crystal back surface to the growth surface,
Diameter 5-100m caused by the elimination of Si atoms
A hole (void) of about m is generated. Therefore, if an organic thin film is formed on the back surface of the seed crystal as shown in FIG. 2C, the Si atoms that are going to sublimate are blocked and cannot escape, so that the generation of voids is suppressed.

Next, referring to FIG. 3, the effect of forming the thin organic thin film in the present invention will be described. FIG. 3A shows a conventional thick protective film (15 μm).
FIG. 4B is a cross-sectional view of a case where the organic thin film (5 μm or less) of the present invention is formed. When the protective film is thick (15 μm) as shown in FIG.
During the process in which the gas generated by the volatilization of the organic solvent inside the film reaches the surface during drying, surface solidification of the protective film proceeds while the gas is not exhausted, and the gas remains inside the film. As a result, a cavity is formed at a position where the gas remains (a portion in contact with the back surface of the seed crystal or a position inside the film and not in contact with the back surface of the seed crystal). The cavities remain even after the carbonization treatment of the organic thin film by the subsequent annealing, and in addition to this, a new gas is generated in the annealing, so that further cavities are generated. A space is partially provided on the back surface of the seed crystal by the portion where the above-mentioned cavity is in contact with the back surface of the seed crystal, and Si atoms can be sublimated toward the space during crystal growth, resulting in a void, Crystal quality deteriorates. Even if the cavity does not contact the backside of the seed crystal and remains inside the carbonized thin film, the state of heat conduction on the backside of the seed crystal changes due to the presence of the cavity during crystal growth. Will be disturbed. Furthermore, due to the thermal expansion of the cavities, the phenomenon that stress strain is applied to the crystal growth surface also overlaps,
For these reasons, the crystal growth conditions are disturbed and the crystal quality is degraded.

On the other hand, in the case of the organic thin film used in the present invention as shown in FIG. 3B, the gas generated during the drying and annealing is a thin organic thin film, so that the organic thin film is thin. Since all of the solids escape to the surface before solidification, no voids are formed and a dense protective film without pores can be obtained. In the crystal growth using the seed crystal with the dense protective film formed, the entire back surface of the seed crystal is covered with the dense protective film.
Generation of voids can be completely suppressed over the entire surface of the crystal. At the same time, since the protective film has no cavities inside, has a uniform thickness, and is dense, it is uniform in terms of heat conduction over the entire back surface of the wafer, which may adversely affect the temperature distribution during crystal growth. There is no. As a result, deterioration of crystal quality during growth can be prevented, and the yield of the number of wafers that can be taken out from an ingot can be improved. From such a viewpoint, the thickness of the organic thin film used in the present invention is
The thickness is not particularly limited as long as the above effect can be achieved,
It is preferably adjusted appropriately according to the material of the organic thin film, reaction conditions and the like, but specifically, it is preferably 0.5 to 5 μm. If the thickness of the organic thin film is 5 μm or less, the gas generated by the evaporation of the organic solvent during the drying or annealing, which has conventionally been the cause of the voids in the thin film, can be generated before the organic thin film solidifies during the drying or annealing. The reason is that it is possible to prevent the generation of cavities, since it is possible to prevent almost all of them from volatilizing and remaining in the film. The thickness of the organic thin film is preferably thinner because the time for volatilizing the organic solvent can be shortened, and is, for example, 2 μm or 1 μm. However, if the thickness is too thin, the entire surface is not completely covered and a continuous film cannot be obtained. Therefore, it is preferable to secure at least 0.5 μm in thickness.

The material constituting the organic thin film in the present invention is not particularly limited as long as it is an organic substance capable of forming a thin film (hereinafter referred to as "composition for organic thin film production"), but is preferably made of an organic resin. . As the organic resin, any one can be used as long as it is used at the time of manufacturing a semiconductor element, and examples thereof include a photosensitive resin in addition to various resins such as an acrylic resin, a phenol resin, a urea resin, and an epoxy resin. In particular, the photosensitive resin is preferable because the coating conditions by the spin coating method have been established and the thickness control is easy. The photosensitive resin is a resin that is crosslinked or decomposed by the action of light, and any known resin can be used. Among them, a photoresist used at the time of manufacturing a semiconductor element is preferable, and either a positive type or a negative type can be used.

Next, a specific method for producing the seed crystal for growing a silicon carbide single crystal of the present invention will be described. The diameter of the single crystal substrate used as the seed crystal may be a wafer cut out from the growth crystal and has a size suitable for the subsequent semiconductor element manufacturing process, but preferably the crystal diameter is 25 mm or more. The following SiC seed crystal is used.

Then, the composition for producing an organic thin film is applied to the back surface of the seed crystal to form an organic thin film. As a coating method, a conventionally known method can be used, but a spin coating method is particularly preferable because it can form a sufficiently thin and uniform thin film. Hereinafter, an embodiment in which the composition is applied using a spin coating method will be described in detail.

First, the seed crystal is adsorbed to the holder, the composition for producing an organic thin film is dropped while rotating at a predetermined rotation speed, and the composition is kept for a predetermined time to form a thin film having a thin and uniform control. It Regarding the rotation speed of the thin film formation, in order to secure the uniformity over the entire surface of the seed crystal, the primary rotation speed is set to 50 to 500 rotations / minute, and the rotation speed is set to 5 hours.
It is desirable that the secondary rotation speed is 1000 to 10,000 rotations / minute for 30 seconds, and the time is adjusted within the range of 15 to 60 seconds. Under such conditions, a sufficiently thin and uniform thin film can be obtained. Can be formed.

Subsequently, the obtained organic thin film is dried to be solidified. Here, the drying temperature and time are
It is preferable to select appropriately depending on the material and thickness of the organic thin film. To give a specific example, normally, when drying at 120 ° C., the time required for volatilization is 5 μm in thickness for 15 minutes,
The thickness is 2 μm for 8 minutes, and the thickness is 1 μm for 3 minutes, but it is not limited to this.

In the present invention, the step of applying the composition for forming an organic thin film and drying the formed organic thin film as described above is performed at least once, but this step (that is, coating and drying) is repeated a plurality of times. The organic thin film may be adjusted to have a predetermined film thickness. However, if the number of times is increased too much, it takes too much time to prepare the seed crystal.
It is preferable to keep repeating up to about 3 times.

The present invention is further characterized in that the organic thin film formed as described above is further carbonized (annealed) to carbonize the organic thin film to form a carbon thin film. The step of annealing the organic thin film to form the carbonized thin film is usually performed efficiently with the seed crystal on which the organic thin film is formed set in a crucible for single crystal growth. When annealing is performed in this state, it may be performed before the single crystal growth step or at the same time as the temperature raising step in the single crystal growth step. Hereinafter, the case where the annealing treatment is performed before the single crystal growth step will be specifically described. First, as described above, the seed crystal having the organic thin film formed on the back surface side is mounted in a graphite crucible, the crucible is covered with a heat insulating material, and then the chamber is evacuated in a vacuum apparatus. Subsequently, the seed crystal is annealed to carbonize the organic thin film to form a carbon thin film. The annealing described above is preferably performed by raising the seed crystal to a temperature not lower than the temperature at which the organic thin film is carbonized but not higher than the sublimation temperature of silicon carbide, specifically, a temperature in the range of 1200 to 2000 ° C. The rate of temperature rise in the annealing is not particularly limited, but it is preferable to raise the temperature from room temperature to 2000 ° C. within a range of 15 minutes to 90 minutes in order to form a good carbon thin film. By this annealing, the organic thin film covering the back surface of the seed crystal is carbonized to form a carbon thin film as a protective film. The pressure in annealing is not particularly limited, but under high vacuum exhaust (10 ⁻³ Pa or less) to 1
It is preferably in the range of 3.3 kPa, and stable carbonization treatment is possible in this range.

In the above-described evaporation of the organic solvent and carbonization by annealing, the thickness of the previously applied organic thin film does not change. Therefore, the thickness of the carbon thin film after the annealing is the same as the above-mentioned organic thin film formation. It may be 0.5 to 5 μm as well as the preferred coating thickness of the composition.
By the above method, by suppressing the generation of cavities due to gas, a carbon thin film having a predetermined thickness and excellent thickness uniformity can be obtained.

The annealing treatment may be combined with the temperature raising step in the single crystal growth step and the annealing treatment of the organic thin film. In this case, since the seed crystal having the organic thin film can be used as it is without being carbonized, there is an advantage that the process time can be shortened.

Further, the present invention is a method for producing a SiC single crystal including a step of growing a SiC single crystal on a seed crystal by a sublimation recrystallization method, wherein the S crystal described above is used as the seed crystal.
Si using an iC single crystal growing seed crystal
This is a method for producing a C single crystal. The details will be described below. Using the seed crystal (SiC single crystal) having the organic thin film or the carbon thin film obtained by the above method, single crystal growth is performed by the improved Rayleigh method described in detail in the related art. A SiC single crystal as a seed crystal and a SiC crystal powder as a raw material are placed in a graphite crucible. After that, high vacuum exhaust (10 ^-3 P
a) or less) and then in an atmosphere of an inert gas such as argon (1
33 Pa to 13.3 kPa) and 2000 to 240
The temperature is raised to 0 ° C. to sublimate the SiC crystal powder. Si
The gas formed by sublimation of C crystal powder (hereinafter referred to as raw material gas) is
A concentration gradient (formed by a temperature gradient) causes diffusion and transport in the seed crystal direction. The growth of the single crystal is realized by recrystallizing the source gas that has reached the seed crystal on the seed crystal. At this time, the back surface of the seed crystal is covered with an organic thin film or a carbon thin film as a protective film, and Si from the back surface side is
Since sublimation of atoms is prevented, a high quality SiC single crystal is produced.

The present invention also provides the S obtained by the above manufacturing method.
A SiC single crystal ingot made of iC single crystal,
The ingot has a diameter of 25 mm or more. The SiC single crystal ingot has a feature that voids (large hole defects with a diameter of 5 to 100 μm) are not generated over the entire surface and the crystal quality is good. Therefore, the ratio of non-defective wafers that can be cut out from this ingot can be increased, and the productivity of SiC single crystal wafers can be significantly improved. The SiC single crystal wafer obtained by cutting and polishing this ingot also has no voids, and the yield of semiconductor elements fabricated on this wafer can be improved.

Next, a method for producing a SiC single crystal by growing the SiC single crystal of the present invention will be described with reference to FIG. FIG. 4 shows a single crystal growth apparatus used in the present invention, which is an example of an apparatus for growing an SiC single crystal by an improved Rayleigh method using a seed crystal. First, the single crystal growth apparatus will be briefly described. Seed crystals (here, S
It is performed by subliming and recrystallizing SiC crystal powder 2 on iC single crystal 1. Seed crystal 1 is attached to the inner surface of crucible lid 4 of graphite crucible 3. The SiC crystal powder 2 is filled in the crucible 3. Such a crucible 3 is installed inside a double quartz tube 5 by a graphite support rod 6. Around the crucible 3, a graphite felt 7 for heat shield is installed. The double quartz tube 5 can be evacuated to high vacuum (10 ⁻³ Pa or less) by the vacuum exhaust device 11, and the internal atmosphere can be pressure-controlled by Ar gas or the like by the gas flow controller 10. Further, a work coil 8 is installed on the outer periphery of the double quartz tube 5, and a high-frequency current is passed to heat the crucible 3 and
C crystal powder 2 and seed crystal 1 can be heated to a desired temperature. The crucible temperature is measured by providing a light path having a diameter of 2 to 4 mm in the center of the graphite felt 7 covering the upper and lower portions of the crucible, taking out light from the upper and lower portions of the crucible, and using a two-color thermometer. The temperature of the lower part of the crucible is set to the raw material temperature (here, S
The temperature of the iC crystal powder) and the temperature of the upper part of the crucible are used as the seed temperature. In addition to Ar gas for controlling the internal atmosphere, various doping gases are introduced into the gas pipe 9 to the manufacturing apparatus through the gas flow rate controller 10. The introduced gas is exhausted by the vacuum exhaust device 11 and the gas pressure is adjusted by adjusting the exhaust amount of the exhaust device by an exhaust amount variable valve (not shown).

[0043]

EXAMPLES Hereinafter, the seed crystal for growing a silicon carbide single crystal, the silicon carbide single crystal ingot of the present invention, and a method for producing them will be described with reference to examples.

First, as a seed crystal, Si having a diameter of 50 mm was used.
A C single crystal wafer was prepared. The seed crystal was sufficiently washed in ethanol for 5 minutes under application of ultrasonic waves so that the composition for producing an organic thin film could be uniformly applied. This wafer was set on a rotary holder (vacuum chuck adsorption type) of a spin coater with the side that would be the back surface during growth facing up.
Positive-type and negative-type photosensitive resins were used as the photosensitive resins for forming the organic thin film. The photosensitive resin was prepared by absorbing a required amount with a dropper. Next, the rotation speed and time of the spin coater were such that the primary rotation was 200 rpm for 10 seconds, and the secondary rotation was 7500 rpm for 30 seconds. With this setting, the composition for producing an organic thin film having a thickness of about 1 μm was applied over the entire surface of the wafer. The dropping of the above-mentioned photosensitive resin with a dropper was performed after the secondary rotation, and was dropped onto the central portion of the wafer. After the rotation,
By visual confirmation under light irradiation, it was confirmed that the organic thin film was formed evenly over the entire surface of the wafer. Next, the wafer having the organic thin film formed thereon was heated in a constant temperature heating furnace at 120 ° C. for 3 minutes to dry the organic thin film. In the same step, so-called degassing is carried out, in which the organic solvent contained in the photosensitive resin is volatilized. At this time, since the photosensitive resin thickness is sufficiently thin as 1 μm, the photosensitive resin does not solidify during the desorption of the gas. Generation of cavities in the organic thin film due to completion was suppressed, and a uniform and dense protective film was formed over the entire back surface of the wafer. After drying, the wafer was naturally cooled.

The following steps will be described below with reference to FIG. The wafer obtained above was used as a seed crystal. The seed crystal 1 was attached to the inner surface of the lid 4 of the graphite crucible 3 by a mechanical attachment method. Inside the crucible 3, SiC crystal powder 2 was filled. Next, the crucible 3 filled with the SiC crystal powder 2 is closed with the lid 4 having the seed crystal 1 attached thereto, covered with the graphite felt 7, and then placed on the graphite support rod 6 to form the double quartz tube 5. Installed inside. Then, after the inside of the quartz tube was evacuated by the vacuum exhaust device 11, a current was passed through the work coil 8 to raise the temperature of the SiC crystal powder 2 to 2000 ° C. over 30 minutes. Carbonization of the organic thin film was performed in this step. After that, Ar gas was used as the atmospheric gas by the gas flow controller 10 and the flow rate was 2.33 × 10 ⁻⁶ m ^3.
/ Sec, while keeping the pressure in the quartz tube at about 80 kPa, the raw material temperature (here, the temperature of the SiC crystal powder)
Was raised to the target temperature of 2400 ° C. The growth pressure was reduced to 1.3 kPa over about 30 minutes, and then the growth was continued for about 20 hours. The temperature gradient in the crucible at this time was 15 ° C./cm, and the growth rate was about 1 mm / hour. The obtained crystal had a diameter of 51 mm and a height of about 20 mm.

Wafers were cut out from both the SiC single crystal ingots using the positive type and negative type photosensitive resins as protective films on the backsides of the seed crystals thus obtained, and observed. From this, it was confirmed that a wafer with very good crystal quality, which was very transparent and had no voids, was obtained.

On the other hand, when the seed crystal having no protective film was used for the growth, voids were generated at a high density (about 100 / cm ² ) almost uniformly over the entire surface of the wafer. Also,
For comparison, thickness 1 applied using spray or brush
When grown using a seed crystal with a protective film formed of an organic thin film of 5 μm, the void generation density is reduced as compared with the case without the protective film, but the voids generated inside the protective film cause local voids. There are places where voids occur,
When converted to the entire surface of the wafer, about 10 voids / cm ² were observed. That is, it was found that the spin coating method is preferable for applying the composition for forming an organic thin film. From the above results, it was confirmed that the SiC single crystal ingot obtained by the seed crystal using the protective film made of the organic thin film or the carbon thin film whose thickness was controlled to be thin was of high quality.

[0048]

As described above, according to the present invention, in the improved Rayleigh method using a seed crystal, a protective film capable of preventing sublimation of Si atoms from the back surface of the seed crystal at the time of growing the crystal in the seed crystal rear surface at the time of crystal growth. By forming (thickness of 5 μm or less), void formation in the crystal can be suppressed. By controlling the thickness of the organic thin film to be formed thinly, it is possible to prevent the generation of cavities on the back surface of the seed crystal due to gas generation during the annealing process after coating, and to completely suppress the void generation during crystal growth by the same seed crystal. To be Further, this method is a very simple method because the annealing treatment after coating the organic thin film is sufficient only at 120 ° C. for 15 minutes in a constant temperature oven, and no special treatment under high vacuum is required thereafter. . The crystal obtained in this way is a high-quality SiC single crystal with no mixed defects throughout the entire crystal, and a large number of high-quality single-crystal wafers can be taken out from the same ingot, so it is also extremely productive. It can be said that the method.

By using such a SiC single crystal wafer, it is possible to manufacture a high voltage / environment resistant electronic device having excellent electrical characteristics and a blue light emitting element having excellent optical characteristics.

[Brief description of drawings]

FIG. 1 is a schematic diagram for explaining the principle of an improved Rayleigh method.

FIG. 2 is an explanatory diagram of a void formation mechanism by sublimation of Si atoms from the back surface of the seed crystal and a void formation prevention mechanism by a protective film.

FIG. 3 is a diagram for explaining the influence of the thickness of the organic thin film on the generation of gas and the formation of cavities due to the generation of gas at the stage of drying after forming the organic thin film.

FIG. 4 is a schematic view showing an example of a single crystal growth apparatus used in the method for producing a silicon carbide single crystal of the present invention.

[Explanation of symbols]

1 seed crystal 2 SiC crystal powder 3 crucible 4 Crucible lid 5 Double quartz tube 6 Support rod 7 Graphite felt 8 work coil 9 gas piping 10 Gas flow controller 11 Vacuum exhaust device

Continued front page    (72) Inventor Tatsuo Fujimoto             20-1 Shintomi, Futtsu-shi, Chiba Nippon Steel shares             Company Technology Development Division (72) Inventor Hirokatsu Yashiro             20-1 Shintomi, Futtsu-shi, Chiba Nippon Steel shares             Company Technology Development Division F-term (reference) 4G077 AA02 BE08 DA02 DA18 DA19                       EA02 ED01 ED04 HA02 HA06                       HA12 SA04

Claims (14)

[Claims] 1. A seed crystal for growing a silicon carbide single crystal, wherein the rear surface side of the single crystal growth surface of the seed crystal is covered with an organic thin film. 2. The seed crystal for growing a silicon carbide single crystal according to claim 1, wherein the organic thin film is made of an organic resin. 3. The seed crystal for growing a silicon carbide single crystal according to claim 2, wherein the organic resin is a photosensitive resin. 4. The seed crystal for growing a silicon carbide single crystal according to claim 1, wherein the organic thin film has a thickness of 0.5 to 5 μm. 5. A seed crystal for growing a silicon carbide single crystal, wherein the back surface side of the single crystal growth surface of the seed crystal is covered with a carbon thin film. 6. The seed crystal for growing a silicon carbide single crystal according to claim 5, wherein the carbon thin film is formed by carbonizing an organic thin film. 7. The seed crystal for growing a silicon carbide single crystal according to claim 5, wherein the carbon thin film has a thickness of 0.5 to 5 μm. 8. A caliber having a diameter of 25 mm or more.
A seed crystal for growing a silicon carbide single crystal according to any one of 1. 9. An organic thin film is formed by applying a composition for forming an organic thin film to the back surface side of a single crystal growth surface of a seed crystal and performing a carbonization treatment at least once. A method for producing a seed crystal for growing a crystal. 10. The manufacturing method according to claim 9, wherein the coating method of the composition for forming an organic thin film is a spin coating method. 11. A sublimation temperature of silicon carbide, which is equal to or higher than a temperature at which the organic thin film carbonizes a seed crystal produced by the manufacturing method according to claim 9 or having an organic thin film formed on a back surface side of a single crystal growth surface. A method for producing a seed crystal for growing a silicon carbide single crystal, which comprises subjecting the organic thin film to a carbon thin film by carbonizing the organic thin film by heating the organic thin film to a temperature lower than below. 12. A method for producing a silicon carbide single crystal, which comprises a step of growing a silicon carbide single crystal on a seed crystal by a sublimation recrystallization method, wherein the seed crystal is any one of claims 1 to 8. A method for producing a silicon carbide single crystal, which comprises using the seed crystal for growing a silicon carbide single crystal according to 1. 13. A silicon carbide single crystal ingot made of the silicon carbide single crystal obtained by the manufacturing method according to claim 12, wherein the ingot has a diameter of 25 mm or more. ingot. 14. A silicon carbide single crystal wafer obtained by cutting and polishing the silicon carbide single crystal ingot according to claim 13.