JP4054197B2 - Seed crystal for growing silicon carbide single crystal, method for producing the same, and method for producing silicon carbide single crystal ingot - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a seed crystal for growing a silicon carbide single crystal, a method for producing the seed crystal, and a method for producing a silicon carbide single crystal using the seed crystal. In addition, the present invention provides a high-quality substrate wafer for blue light-emitting diodes and electronic devices. And a large silicon carbide single crystal ingot and a manufacturing method thereof.
[0002]
[Prior art]
Silicon carbide (SiC) is attracting attention as an environmentally resistant semiconductor material because of its physical and chemical properties such as excellent heat resistance and mechanical strength and resistance to radiation. SiC is a representative substance having a crystal polymorphic (polytype) structure that has many different crystal structures even though the chemical composition is the same. The polytype is based on the difference in the periodic structure when this unit structure molecule is stacked in the c-axis direction ([0001] direction) of the crystal when the molecule in which the Si and C bonds are considered as one unit in the crystal structure. Arise. Typical polytypes include 6H, 4H, 15R or 3C. Here, the first number indicates the repetition period of the lamination, and the alphabet represents 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 application to various uses is considered using the difference. For example, 6H is recently used as a substrate for short-wavelength optical devices from blue to ultraviolet, and 4H is considered to be used as a substrate wafer for high-frequency, high-voltage electronic devices.
[0003]
However, a crystal growth technique that can stably supply a high-quality SiC single crystal having a large area on an industrial scale has not yet been established. Therefore, practical use of SiC has been hindered despite the semiconductor material having many advantages and possibilities as described above.
[0004]
Conventionally, on a laboratory scale scale, for example, a SiC single crystal was grown by a sublimation recrystallization method (Rayleigh method) to obtain a SiC single crystal of a size capable of producing a semiconductor element. However, with this method, the area of the obtained single crystal is small, and it is difficult to control its size and shape with high accuracy. Moreover, it is not easy to control the crystal polymorphism and impurity carrier concentration of SiC. Also, a cubic silicon carbide single crystal is grown by heteroepitaxial growth on a heterogeneous substrate such as silicon (Si) using chemical vapor deposition (CVD). In this method, a single crystal having a large area can be obtained, but a large number of defects (−10 to 10%) due to a lattice mismatch of about 20% with the substrate.⁷cm^-2Can be grown only, and it is not easy to obtain a high-quality SiC single crystal. In order to solve these problems, an improved Rayleigh method for performing sublimation recrystallization using a SiC single crystal {0001} wafer as a seed crystal has been proposed (Yu. M. Tairov and VF Tsvetkov, Journal of Crystal Growth, 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 by controlling the atmospheric pressure to about 100 Pa to 15 kPa with an inert gas, the crystal growth rate and the like can be controlled with good reproducibility. it can. The principle of the improved 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 in an inert gas atmosphere such as argon (133 Pa to 13.3 kPa), 2000 to 2400 ° C. To be heated. At this time, the temperature gradient is set so that the seed crystal 1 is slightly lower in temperature than the SiC crystal powder 2 as a raw material. After sublimation, SiC crystal powder 2 is diffused and transported in the direction of seed crystal 1 by a concentration gradient (formed by a temperature gradient). Single crystal growth is realized by recrystallization of a gas formed by sublimation of SiC crystal powder 2 arriving at seed crystal 1 on seed crystal 1. At this time, the resistivity of the crystal is determined by adding an impurity gas in an atmosphere made of an inert gas, or mixing an impurity element or a compound thereof in the SiC crystal powder to form silicon (Si) in the SiC single crystal structure. Alternatively, it can be controlled by replacing the position of the carbon atom (C) with an impurity element (doping). Typical substitutional impurities in the SiC single crystal include nitrogen (n-type), boron, and aluminum (p-type). A SiC single crystal can be grown while controlling the carrier type and concentration.
[0005]
Currently, SiC single crystal wafers having a diameter of 1 inch (25 mm) to 3 inches (75 mm) are cut out from the SiC single crystal produced by the above-described improved Rayleigh method, and are used for epitaxial thin film growth and device production.
[0006]
As described above, the SiC single crystal is currently produced by the improved Rayleigh method using the sublimation phenomenon from the raw material. However, referring to FIG. 1, the seed crystal 1 is actually attached to the crucible 3. A unique problem arises when growing. One of the problems is that a sublimation phenomenon occurs even from a back surface of the seed crystal 1 toward a crucible material (made of graphite) such as the crucible lid 4 on which the seed crystal is mounted during crystal growth. Usually, the seed crystal 1 is mounted inside the crucible lid 4 (side facing the raw material) by a mechanical mounting method. At this time, since it is a mechanical mounting method, strictly speaking, a very small gap exists between the seed crystal 1 and the crucible lid 4. In crystal growth, a high temperature of 2000 ° C. or higher is required to sublimate the SiC crystal powder 2, but since the seed crystal 1 is also SiC like the SiC crystal powder 2, the back surface of the seed crystal 1 and the crucible lid 4 As described above, if there is a slight gap as described above, the temperature gradient between the back surface of the seed crystal 1 and the crucible lid 4 (the back surface of the seed crystal becomes higher) is caused. Si atoms are sublimated from the back surface and recrystallized on the surface of the crucible lid 4 at a lower temperature. As a result, a hole (void) from which Si having a diameter of about 5 to 100 μm is removed from the back surface of the seed crystal 1 to the growth surface. Since this hole has C remaining due to the removal of Si, the surface is carbonized and black. The void reaching the growth surface naturally affects the crystal growth, and in particular, a hollow defect having a diameter of about 0.1 to 10 μm called a micropipe defect is often generated from the carbonized portion, and the crystal quality is significantly deteriorated. There is a problem. In addition, since the void is black, the appearance of the wafer is significantly impaired, and the number of wafers that can be taken out as a sample from the area where the void exists (from the bottom to the middle of the grown crystal ingot) decreases, resulting in a decrease in yield in sample preparation. Was a problem.
[0007]
As a method for attaching the seed crystal to the crucible material, there is a method in which sugar is carbonized and used as an adhesive material. However, in this method as well, the above-mentioned problem of void generation also occurs, leading to deterioration of crystal quality. It was.
[0008]
This problem was reported in EK Sanchez, T. Kuhr, VD Heydemann, DW Snyder, GS Rohrer and M. Skowronski, Journal of Electronic Materials, vol. 29, No. 3 (2000) pp.347-352. As described above, there has been proposed a method of forming a protective film by applying a photosensitive resist, which is an organic film, to the rear surface of the seed crystal, followed by carbonization (hereinafter also referred to as annealing). According to the report, a photosensitive resist having a thickness of about 15 μm was applied to the back surface of the seed crystal, and then dried at 120 ° C. for 5 minutes, and then under high vacuum (2 × 10^-3By annealing at 1200 ° C. (heated at a heating rate of 400 ° C./hour by a lamp heating method) at Pa or less, a glossy graphite protective film can be obtained. When crystal growth was carried out using the seed crystal with the protective film, it was reported that the above-mentioned Si detachment from the back surface of the seed crystal was suppressed by the protective film, and the generation of voids was prevented.
[0009]
However, when the protective film was actually produced by such a method, it was dried at 120 ° C. for 5 minutes and then subjected to high vacuum (2 × 10^-3When annealing was performed at 1200 ° C. (heated at a heating rate of 400 ° C./hour by a lamp heating method) at Pa or less), a phenomenon was observed in which cavities were generated at the interface between the back surface of the seed crystal and the resist or inside the resist. The cause of this void is that when the solvent evaporates from the resist in the drying process and annealing process described above, the solidification of the resist proceeds before the organic solvent gas generated inside the resist reaches the surface and completely evaporates. This is because the gas remains without being completely removed. As a result, there arises a problem that a uniform protective film is not formed over 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, voids are generated as the same phenomenon as when a conventional gap exists during crystal growth, and the crystal quality deteriorates. In addition, even when the gas does not contact the backside of the seed crystal and remains as a cavity inside the resist, during the crystal growth, due to the presence of the cavity, the way of heat transfer on the backside of the seed crystal becomes non-uniform, and within the seed crystal plane. This causes a problem that the temperature distribution of the crystal is disturbed and crystal growth cannot be performed satisfactorily. Thus, even with the technique by E. K. Sanchez et al., It has not been achieved to suppress the generation of voids over the entire surface of the grown crystal.
[0010]
[Problems to be solved by 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 an SiC single crystal in which deterioration of crystal quality due to generation of voids is suppressed, and a method for manufacturing the same, and a structure over the entire surface. It is to provide a SiC single crystal having a good appearance free from defects, an ingot produced therefrom, and a production method capable of producing them with good reproducibility.
[0011]
[Means for Solving the Problems]
As a result of earnest studies on the protective film of the seed crystal, the present inventors, as a result, in the conventional method described above, the cause that the gas remains without being completely removed when the solvent evaporates from the protective film in the drying and carbonization treatment is Based on the knowledge that the thickness of the protective film is large, the thickness of the organic thin film was strictly controlled to suppress voids generated during the growth of the SiC single crystal.
[0012]
Accordingly, the gist of the present invention is as follows.
[0013]
  (1) The back side of the single crystal growth surface of the seed crystal is0.5-5μm thickA seed crystal for growing a silicon carbide single crystal covered with an organic thin film.
[0014]
(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.
[0015]
(3) The seed crystal for growing a silicon carbide single crystal according to (2), wherein the organic resin is a photosensitive resin.
[0017]
  (4) The back side of the seed crystal single crystal growth surface is0.5-5 μm thick formed by carbonizing organic thin filmA seed crystal for growing a silicon carbide single crystal covered with a carbon thin film.
[0020]
  (5) The diameter is 25 mm or more (1) to (4) A seed crystal for growing a silicon carbide single crystal according to any one of the above.
[0021]
  (6) By applying the organic thin film forming composition to the back side of the single crystal growth surface of the seed crystal and performing the carbonization process at least once0.5-5μm thickA method for producing a seed crystal for growing a silicon carbide single crystal, comprising forming an organic thin film.
[0022]
  (7The coating method of the organic thin film forming composition is a spin coating method (6) Manufacturing method.
[0023]
  (8()6) Or (7) Produced on the back side of the single crystal growth surface,0.5-5μm thickA silicon carbide single crystal characterized by carbonizing the organic thin film into a carbon thin film by heating the seed crystal on which the organic thin film is formed to a temperature not lower than a temperature at which the organic thin film is carbonized and lower than a sublimation temperature of silicon carbide. A method for producing a seed crystal for crystal growth.
[0024]
  (9) A method for producing a silicon carbide single crystal comprising a step of growing a silicon carbide single crystal on a seed crystal by a sublimation recrystallization method, wherein (1) to (1)5A method for producing a silicon carbide single crystal comprising using the seed crystal for growing a silicon carbide single crystal according to any one of the above.
[0027]
DETAILED DESCRIPTION OF THE INVENTION
  In the present invention, the back side of the single crystal growth surface of the seed crystal is0.5-5μm thickThe seed crystal for growing silicon carbide single crystal covered with an organic thin film, and the back side of the single crystal growth surface of the seed crystal are0.5-5 μm thick formed by carbonizing organic thin filmA seed crystal for growing a silicon carbide single crystal covered with a carbon thin film. 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 provided on the back side of the single crystal growth surface of the seed crystal. By making it, sublimation of Si atoms from the back surface of the seed crystal can be suppressed during crystal growth, and void generation during crystal growth can be suppressed.
[0028]
Hereinafter, the effect of forming the organic thin film in the present invention will be described with reference to FIGS. FIG. 2 is a schematic diagram for explaining a mechanism for suppressing generation of voids by an organic thin film, wherein (a) is a cross-sectional view of a part of a seed crystal growth crucible, and (b) is a graph showing growth crystals and seed crystals. It is an enlarged view of a part between lid | covers, (c) is an enlarged view of the part at the time of coat | covering the organic thin film further. As shown in FIG. 2A, crystal growth is performed by mechanically attaching a seed crystal to a graphite crucible lid with a screw or the like. At this time, as shown in FIG. 2B, there is actually a minute gap of a μm unit level between the rear surface of the seed crystal and the crucible lid to be mounted. Due to the existence of this gap, Si atoms are sublimated from the back surface of the seed crystal during crystal growth and recrystallized on the crucible lid surface at a lower temperature. As a result, holes (voids) having a diameter of about 5 to 100 mm are generated from the back surface of the seed crystal to the growth surface due to the removal of Si atoms. Therefore, when an organic thin film is formed on the rear surface of the seed crystal as shown in FIG. 2C, the generation of voids is suppressed because Si atoms to be sublimated are blocked and cannot be removed.
[0029]
Next, with reference to FIG. 3, the effect of forming a thin organic thin film in the present invention will be described. 3A is a cross-sectional view when a conventional thick protective film (15 μm) is formed, and FIG. 3B is a cross-sectional view when an organic thin film (5 μm or less) of the present invention is formed. When the protective film is thick as shown in FIG. 3 (a) (15 μm), the surface of the protective film is formed while the gas generated by volatilization of the organic solvent inside the film reaches the surface during drying. Solidification proceeds and 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 in the film and not in contact with the back surface of the seed crystal). These cavities remain even when the organic thin film is carbonized by the subsequent annealing, and in addition to this, a new gas is generated even in the annealing, and thus further cavities are generated. A space is partially provided on the back surface of the seed crystal by the portion where the cavity described above is in contact with the back surface of the seed crystal, and Si atoms can sublime toward the space during crystal growth, resulting in the generation of voids. Crystal quality deteriorates. Even if the cavities are not in contact with the back surface of the seed crystal and remain inside the carbonized thin film, the temperature distribution in the seed crystal plane changes because the state of thermal conduction on the back surface of the seed crystal changes due to the presence of the cavities during crystal growth. Will be disturbed. Furthermore, due to the influence of the thermal expansion of the cavities, the phenomenon in which stress strain is applied to the crystal growth surface also overlaps, and due to these reasons, the crystal growth conditions are disturbed and the crystal quality is deteriorated.
[0030]
  On the other hand, as shown in FIG. 3B, in the case of the organic thin film used in the present invention, the gas generated during drying and annealing is sufficiently thin because the organic thin film is sufficiently thin. Since all of the surface is removed before, no voids are generated, and a non-porous dense protective film can be obtained. In the crystal growth using the seed crystal on which the dense protective film is formed, the entire back surface of the seed crystal is covered with the dense protective film, so that generation of voids is completely suppressed over the entire crystal surface. At the same time, the protective film has no cavities, is uniform in thickness, and is dense, so that heat conduction is uniform on the entire back surface of the wafer, which may adversely affect the temperature distribution during crystal growth. No. As a result, it is possible to prevent the deterioration of crystal quality during growth and to improve the yield of the number of wafers that can be taken out per ingot. From such a viewpoint, the thickness of the organic thin film used in the present invention isYesAlthough it is preferable to adjust appropriately according to the material of the mechanical thin film, reaction conditions, etc., specifically, it is 0.5-5 micrometers.TheIf the thickness of the organic thin film is 5 μm or less, the gas generated by volatilization of the organic solvent during drying or annealing, which has been a cause of cavities in the conventional thin film, is solidified before the organic thin film is solidified during drying or annealing. This is because the generation of cavities can be prevented because the evaporation to the film is suppressed. Further, the thinner organic thin film is preferable because the time for volatilizing the organic solvent can be shortened, for example, 2 μm or 1 μm. However, if the thickness is made too thin, the entire surface is not completely covered and a continuous film cannot be obtained, so at least a thickness of 0.5 μm is secured.The
[0031]
Although the material which comprises the organic thin film in this invention will not be specifically limited if it is an organic substance (henceforth "the composition for organic thin film manufacture") which can form a thin film, It is preferable to consist of organic resin. Any organic resin can be used as long as it is used at the time of semiconductor element fabrication. For example, in addition to various resins such as acrylic resin, phenol resin, urea resin, and epoxy resin, photosensitive resin can be used. In particular, the photosensitive resin is preferable because the coating conditions by the spin coating method are established and the thickness can be easily controlled. The photosensitive resin is a resin that crosslinks or decomposes under the action of light, and any conventionally 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.
[0032]
Next, a specific method for producing a 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 is not particularly limited as long as the wafer is cut out from the grown crystal and has a sufficient size suitable for the subsequent semiconductor element manufacturing process. Preferably, the crystal diameter is 25 mm or more. SiC seed crystal is used.
[0033]
Next, the said organic thin film manufacturing composition is apply | coated to this seed crystal back surface side, and an organic thin film is formed. As a coating method, a conventionally known method can be used, but a spin coating method capable of forming a sufficiently thin and uniform thin film is particularly preferable. Hereinafter, an embodiment in which the composition is applied using a spin coating method will be described in detail.
[0034]
First, a seed crystal is adsorbed on a holder, and the composition for producing an organic thin film is dropped while being rotated at a predetermined rotation speed, and a thin film with a thin and uniform thickness is formed by maintaining the composition for a predetermined time. As the rotation speed for thin film formation, in order to ensure uniformity over the entire surface of the seed crystal, the primary rotation speed is 50 to 500 rotations / minute, and the secondary rotation speed is 1000 to 500 seconds. It is desirable to adjust the rotation speed within a range of 15 to 60 seconds as 10,000 rotations / minute. Under such conditions, a sufficiently thin and uniform thin film can be formed.
[0035]
Subsequently, the obtained organic thin film is solidified by drying. Here, the drying temperature and time are preferably selected appropriately depending on the material and thickness of the organic thin film. Specifically, when drying at 120 ° C., the time required for volatilization is 15 minutes at a thickness of 5 μm, 8 minutes at a thickness of 2 μm, and 3 minutes at a thickness of 1 μm, but is not limited thereto. .
[0036]
In the present invention, as described above, the step of applying the composition for forming an organic thin film and drying the formed organic thin film is performed at least once, and this step (that is, coating and drying) is repeated a plurality of times. May be adjusted to a predetermined film thickness. However, if the number of times is increased too much, it will take too much time to prepare the seed crystal, so it is usually preferable to keep the number of repetitions about 2 to 3 times.
[0037]
Furthermore, the present invention is 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 efficient when the seed crystal on which the organic thin film is formed is set in a crucible for performing single crystal growth. When annealing is performed in this state, it may be performed before the single crystal growth step or may be performed simultaneously with the temperature raising step in the single crystal growth step. Hereinafter, the case where the annealing process is performed before the single crystal growth step will be specifically described. First, as described above, a seed crystal having an 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 evacuated in a vacuum apparatus. Subsequently, by annealing the seed crystal, the organic thin film is carbonized to form a carbon thin film. The annealing described above is preferably carried out by raising the seed crystal to a temperature not lower than the temperature at which the organic thin film is carbonized and not higher than the sublimation temperature of silicon carbide, specifically, in the range of 1200 to 2000 ° C. The rate of temperature increase in the annealing is not particularly limited, but it is preferable to increase the temperature from room temperature to 2000 ° C. within a range of 15 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^-3Pa or less) to 13.3 kPa is preferable, and stable carbonization is possible within this range.
[0038]
In the above-described volatilization of the organic solvent by drying and the carbonization step by annealing, the thickness of the organic thin film applied in advance does not change. Therefore, the thickness of the carbon thin film after the annealing is the same as that of the organic thin film forming composition described above. Similar to the preferred coating thickness, it may be 0.5-5 μm. 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.
[0039]
Further, the annealing treatment may serve both as a temperature raising step in the single crystal growth step and an organic thin film annealing treatment. 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.
[0040]
The present invention is also a method for producing an SiC single crystal including a step of growing an SiC single crystal on a seed crystal by a sublimation recrystallization method, wherein the aforementioned seed crystal for growing an SiC single crystal is used as the seed crystal. This is a method for producing an SiC single crystal. Details will be described below. Using a seed crystal (SiC single crystal) having an organic thin film or a carbon thin film obtained by the above method, single crystal growth is performed by the modified Rayleigh method detailed in the prior art. An SiC single crystal as a seed crystal and an SiC crystal powder as a raw material are placed in a graphite crucible. After that, high vacuum evacuation (10^-3Then, the temperature is raised to 2000 to 2400 ° C. in an inert gas atmosphere such as argon (133 Pa to 13.3 kPa), and the SiC crystal powder is sublimated. A gas obtained by sublimating SiC crystal powder (hereinafter referred to as source gas) is diffused and transported in the seed crystal direction by a concentration gradient (formed by a temperature gradient). Single crystal growth is realized by recrystallizing the source gas that has arrived at 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 carbon thin film that is a protective film, and sublimation of Si atoms from the back surface side is prevented, so that a high-quality SiC single crystal is manufactured.
[0041]
  MaTheA SiC single crystal ingot made of a SiC single crystal obtained by the above production method, wherein the ingot has a diameter of 25 mm or moreSThe iC single crystal ingot is characterized in that there is no generation of voids (large pore defects having a diameter of 5 to 100 μm) over the entire surface and the crystal quality is good. Therefore, the proportion 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 greatly improved. Further, the SiC single crystal wafer obtained by cutting and polishing the ingot has no voids, and the yield of semiconductor elements fabricated on the wafer can be improved.
[0042]
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 a SiC single crystal by an improved Rayleigh method using a seed crystal. First, this single crystal growth apparatus will be briefly described. Crystal growth is performed by sublimating and recrystallizing SiC crystal powder 2 on seed crystal (here, SiC single crystal) 1. The seed crystal 1 is attached to the inner surface of the crucible lid 4 of the 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 support rod 6 made of graphite. Around the crucible 3, a graphite felt 7 for heat shielding is installed. The double quartz tube 5 is subjected to high vacuum exhaust (10^-3Pa or less) and the internal atmosphere can be pressure controlled by the gas flow rate controller 10 with Ar gas or the like. In addition, a work coil 8 is installed on the outer periphery of the double quartz tube 5 to heat the crucible 3 by flowing a high-frequency current and to heat the SiC crystal powder 2 and the seed crystal 1 to a desired temperature. it can. The temperature of the crucible is measured using a two-color thermometer by providing an optical path having a diameter of 2 to 4 mm at the center of the graphite felt 7 covering the upper and lower parts of the crucible, taking out light from the upper and lower parts of the crucible. The temperature at the bottom of the crucible is the raw material temperature (here, the temperature of the SiC crystal powder), and the temperature at the top of the crucible is 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 11 vacuum exhaust devices, and the gas pressure is adjusted by adjusting the exhaust amount in the exhaust device by an exhaust amount variable valve (not shown).
[0043]
【Example】
Hereinafter, the seed crystal for silicon carbide single crystal growth, the silicon carbide single crystal ingot of the present invention, and the production methods thereof will be described with examples.
[0044]
First, an SiC single crystal wafer having a diameter of 50 mm was prepared as a seed crystal. The seed crystal was washed in ethanol for 5 minutes under application of ultrasonic waves sufficiently so that the composition for producing an organic thin film could be evenly applied uniformly. This wafer was set in a spin coater rotary holder (vacuum chuck suction type) with the back side facing up during growth. As the photosensitive resin for forming the organic thin film, positive and negative photosensitive resins were used, respectively. The photosensitive resin was prepared by sucking a required amount with a dropper. Next, the rotation speed and time of the spin coater were set to 10 seconds at a primary rotation of 200 rpm and 30 seconds at a secondary rotation of 7500 rpm. With this setting, a composition for producing an organic thin film having a thickness of about 1 μm was applied over the entire surface of the wafer. The photosensitive resin was dropped by a dropper at the center of the wafer after entering the secondary rotation. After completion of the rotation, it was confirmed by visual confirmation under light irradiation that an organic thin film was formed evenly over the entire wafer surface. Next, the wafer on which the organic thin film was formed was heated in a constant temperature heating furnace at 120 ° C. for 3 minutes to dry the organic thin film. In this process, so-called degassing is performed to volatilize the organic solvent contained in the photosensitive resin. At this time, since the photosensitive resin thickness is sufficiently thin as 1 μm, the photosensitive resin is solidified during gas separation. 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.
[0045]
Hereinafter, the subsequent steps will be described 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 mounting method. The inside of the crucible 3 was filled with SiC crystal powder 2. Next, the crucible 3 filled with the SiC crystal powder 2 is closed with the lid 4 to which the seed crystal 1 is attached, covered with the graphite felt 7, and then placed on the graphite support rod 6. Installed inside. And after evacuating the inside of a quartz tube with the vacuum exhaust apparatus 11, an electric current was sent through the work coil 8, and the temperature of the SiC crystal powder 2 was raised to 2000 degreeC over 30 minutes. In this step, the organic thin film was carbonized. Thereafter, Ar gas is supplied as an atmospheric gas by the gas flow rate controller 10 at a flow rate of 2.33 × 10 6.^-6m^ThreeThe raw material temperature (here, the temperature of the SiC crystal powder) was raised to the target temperature of 2400 ° C. while maintaining the pressure in the quartz tube at about 80 kPa. The growth pressure was reduced to 1.3 kPa over about 30 minutes, and then the growth was continued for about 20 hours. At this time, the temperature gradient in the crucible was 15 ° C./cm, and the growth rate was about 1 mm / hour. The diameter of the obtained crystal was 51 mm, and the height was about 20 mm.
[0046]
When the wafer was cut out and observed from both of the SiC single crystal ingots using positive and negative photosensitive resins as a protective film on the back surface of the seed crystal thus obtained, voids were found from directly above the seed crystal from any ingot. It was confirmed that a wafer with good crystal quality that was not visually generated and was very transparent was obtained.
[0047]
On the other hand, when grown with a seed crystal without a protective film, it is almost uniformly high in density (about 100 / cm) over the entire wafer surface.²), Voids occurred. As a comparison, when growing using a seed crystal formed with a protective film formed from an organic thin film having a thickness of 15 μm applied by spraying or printing, the void generation density is higher than that without the protective film. However, there are places where voids are locally generated due to the influence of cavities generated inside the protective film, and about 10 / cm2 when converted to the entire wafer surface.²A degree of voiding was observed. That is, it was found that the spin coating method is preferable for applying the organic thin film forming composition. 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 high quality.
[0048]
【The invention's effect】
As described above, according to the present invention, in the improved Rayleigh method using a seed crystal, a protective film (thickness of 5 μm or less) that can prevent sublimation of Si atoms from the back surface during growth on the back surface of the seed crystal during crystal growth. ) Can suppress void formation in the crystal. By controlling the thickness of the organic thin film to be formed, 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 generation of voids during crystal growth of the same crystal. It is done. Further, in this method, the annealing process after coating the organic thin film is sufficient only at 120 ° C. for 15 minutes in a constant temperature furnace, and after that, a special process under a high vacuum is unnecessary, so that it is a very simple method. . The crystal obtained in this way is a high-quality SiC single crystal with no mixed defects over the entire crystal, and a large number of high-quality single crystal wafers can be taken out from the ingot. It can be said that
[0049]
By using such a SiC single crystal wafer, it is possible to produce a high voltage / environment resistant electronic device having excellent electrical characteristics and a blue light emitting element having excellent optical characteristics.
[Brief description of the 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 rear surface of the seed crystal and a void shape prevention mechanism by a protective film.
FIG. 3 is a diagram for explaining the influence of the thickness of an organic thin film on the generation of gas generated in the drying step after the formation of the organic thin film and the formation of cavities thereby.
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 system

Claims (9)

  A seed crystal for growing a silicon carbide single crystal, wherein the back side of the single crystal growth surface of the seed crystal is coated with an organic thin film having a thickness of 0.5 to 5 μm.   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.   The silicon carbide single crystal growing seed crystal according to claim 2, wherein the organic resin is a photosensitive resin.   A seed crystal for growing a silicon carbide single crystal, wherein the back side of the single crystal growth surface of the seed crystal is coated with a carbon thin film having a thickness of 0.5 to 5 μm formed by carbonizing an organic thin film.   The diameter is 25 mm or more, The seed crystal for silicon carbide single crystal growth as described in any one of Claims 1-4.   An organic thin film having a thickness of 0.5 to 5 μm is formed by applying a composition for forming an organic thin film on the back side of a single crystal growth surface of a seed crystal and performing a carbonization process at least once. A method for producing a seed crystal for growing a silicon carbide single crystal.   The manufacturing method according to claim 6, wherein the coating method of the composition for forming an organic thin film is a spin coating method.   Silicon carbide at a temperature above the temperature at which the organic thin film carbonizes the seed crystal formed by the manufacturing method according to claim 6 or 7 on which the organic thin film having a thickness of 0.5 to 5 μm is formed on the back side of the single crystal growth surface. A method for producing a seed crystal for growing a silicon carbide single crystal, wherein the organic thin film is carbonized to a carbon thin film by heating to a temperature lower than the sublimation temperature.   A method for producing a silicon carbide single crystal comprising a step of growing a silicon carbide single crystal on a seed crystal by a sublimation recrystallization method, wherein the silicon carbide according to any one of claims 1 to 5 is used as the seed crystal. A method for producing a silicon carbide single crystal, comprising using a seed crystal for growing a single crystal.

Images