JP2006151756A - Method for fixing seed crystal - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for fixing a seed crystal, by which impurities are prevented from being present between the seed crystal and a seed crystal mounting face and the occurrence of a linear penetrating defect can be suppressed. <P>SOLUTION: A seed crystal mount 2 whose seed crystal mounting face 3 has an area smaller than the seed crystal 5 is used. The seed crystal 5 and the seed crystal mounting face 3 are adhered by using a first adhesive 4. Then, a second adhesive 6 is applied so that a part not adhered with the first adhesive 4 in the surface of the seed crystal 5 at the seed crystal mounting face 3 side and the side wall of the seed crystal mount 2 are connected. After hardening the second adhesive 6, the first adhesive 4 is heated, decomposed and removed. The elution or infiltration of the second adhesive 6 inbetween the seed crystal 5 and the seed crystal mounting face 3 can be prevented by the first adhesive 4. Further, after hardening the second adhesive 6, when heating treatment is performed at a high temperature, the first adhesive 4 is heated, decomposed and removed. Thereby, the impurities can be prevented from being present between the seed crystal 5 and the seed crystal mounting face 3, and a silicon carbide single crystal free from a linear penetrating defect can be produced. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a seed crystal fixing method for fixing a seed crystal to a seed crystal base when a silicon carbide single crystal is manufactured by a sublimation method.

  Silicon carbide is a semiconductor with a wide forbidden band and is physically and chemically stable, and thus has attracted attention as an environment-resistant semiconductor material and a short wavelength light emitting diode material. There is a need for the development of crystal substrates. As a method for growing a silicon carbide single crystal, an improved Lely method, which is a sublimation recrystallization method using a seed crystal, is widely used.

  The principle of the improved Lely method will be described with reference to FIG. A silicon carbide single crystal substrate as a seed crystal 5 and a silicon carbide crystal powder 8 as a raw material are placed in a crucible 7 with a lid made of graphite or a refractory metal such as tantalum. The crucible is heated at 2000 to 2400 ° C. in an inert gas atmosphere such as argon under reduced pressure. At this time, the temperature gradient is set so that the seed crystal 5 is slightly lower in temperature than the silicon carbide crystal powder 8. After sublimation, the raw material is diffused and transported in the direction in which the seed crystal 5 having a slightly low temperature is installed. The silicon carbide single crystal 9 is obtained by recrystallizing the diffused and transported sublimation gas on the seed crystal 5.

  In the improved Lely method, the seed crystal is fixed to the crucible lid portion or a mounting portion formed on the lid portion by a mechanical method or a chemical method using a seed crystal fixing agent. As an example of the mechanical method, there is a method in which the seed crystal back surface and the seed crystal mounting portion surface are flattened, and the two are physically attached to each other (see, for example, Patent Document 1).

  On the other hand, as an example of a chemical method using a seed crystal fixing agent, a carbonized layer obtained by high-temperature carbonization treatment of a liquid adhesive containing a polymer material such as a phenol resin or a novolac resin includes a seed crystal and a mounting portion. The seed crystal is seeded using a method of growing a single crystal with a seed crystal bonded to the mounting portion by the carbonized layer or a seed crystal fixing agent comprising a carbohydrate, a heat-resistant fine particle, and a solvent. There is a method of fixing to the crystal mounting part (for example, see Patent Documents 2 and 3).

A silicon carbide single crystal wafer is cut out from a silicon carbide single crystal produced using these seed crystal fixing methods, and is used for epitaxial thin film growth and device production. However, when a silicon carbide single crystal is produced by the modified Lely method using the mechanical or chemical seed crystal fixing method, penetration defects are observed inside the single crystal. This penetration defect is often near the seed crystal and often extends linearly from the back surface of the seed crystal in the growth direction.
JP 2002-308697 A Japanese Patent Laid-Open No. 9-110584 Japanese Patent Laid-Open No. 11-171691

  The linear penetration defect is due to non-uniform decomposition / sublimation phenomenon of the silicon carbide single crystal from the surface of the seed crystal fixed to the seed crystal mounting surface (RA Stein, Physica B, vol. 185 (1993) pp. 211-216), the non-uniform contact between the seed crystal and the seed crystal mounting surface is the main factor. In the region where the contact is insufficient, heat removal from the growth crystal to the crucible lid becomes insufficient, and as a result, a large temperature gradient is generated in the growth crystal, particularly in the vicinity of the seed crystal. In a region where such a large temperature gradient is generated, the decomposition / sublimation phenomenon of silicon carbide is promoted, and linear penetrating defects are generated and elongated. Further, if a gap is formed between the seed crystal and the seed crystal mounting surface due to non-uniform contact, the sublimation gas easily escapes to the outside of the system through this gap or through the gap. The decomposition and sublimation of silicon carbide is promoted, and a linear through defect is generated in the seed crystal and is elongated. Linear penetrating defects generated in the seed crystal rarely stay in the seed crystal and extend into the grown crystal.

  These linear penetration defects become hollow defects that penetrate the wafer in the thickness direction when the grown crystal is processed into a wafer shape. It is difficult to epitaxially grow a thin film on such a hollow defect, and further, characteristics deterioration of a device manufactured on such a hollow defect is inevitable.

  In the fixing method described in Patent Document 1, the seed crystal and the seed crystal placement surface are flattened to obtain uniform contact between the seed crystal and the seed crystal placement surface. Since it cannot be fixed to the seed crystal mounting surface, it is necessary to fix the end portion of the seed crystal with a holding member such as a high heat-resistant screw made of graphite or an L-shaped member. The holding member itself used for fixing and the vicinity of the holding member have locally different temperature distributions. Crystallinity such as precipitation of polycrystals on the holding member and increase of defects in the single crystal near the holding member. The deterioration is inevitable.

  Further, the chemical fixing method described in Patent Document 2 requires a carbonization step of a seed crystal fixing agent by high-temperature heat treatment prior to the single crystal growth step. In this carbonization process, the volume of the fixing agent is greatly reduced. Therefore, undesired seed crystal distortion due to non-uniform fixation between the seed crystal and the seed crystal mounting surface, and the gap generated as a result of the volume reduction. Sublimation recrystallization of the seed crystal occurs, and there is a risk of causing a linear penetration defect. In addition, since there may be linear penetration defects originally in the seed crystal, a part of the fixing agent penetrates into the linear penetration defects in the seed crystal during high-temperature heat treatment, and further overflows to the surface of the seed crystal. There is also a possibility that the inside and surface of the seed crystal may be contaminated due to the release, and as a result, there is a high possibility that the quality of the grown crystal will be deteriorated.

  Furthermore, the chemical fixing method described in Patent Document 3 is a method in which the seed crystal fixing agent is composed of a carbohydrate, a heat-resistant fine particle, and a solvent, and realizes pressure bonding at room temperature or low temperature. No carbonization process is required. However, when growing a silicon carbide single crystal, it is exposed to a high temperature of 2000 ° C. or higher, so it cannot escape decomposition and carbonization of the constituent carbohydrates. The gap between the crystal mounting portions increases, and as a result, linear penetration defects are generated. Further, when the decomposition of carbohydrate progresses at a high temperature, the residual component becomes only heat-resistant fine particles, so it is difficult to obtain a fixing strength that can withstand single crystal growth.

  The present invention solves the above-mentioned conventional problems, prevents impurities from interposing between the seed crystal and the seed crystal mounting surface, suppresses the occurrence of linear through defects, and at the same time, introduces polycrystals during growth. It aims at providing the seed crystal fixing method which can be suppressed.

  In order to solve the above-described conventional problems, the seed crystal fixing method of the present invention includes a bonding step of bonding a seed crystal mounting surface of a seed crystal base and a seed crystal using a first adhesive, and the seed crystal An application step of applying a second adhesive so as to connect a portion of the seed crystal base that is not covered with the first adhesive, and a drying step of drying the second adhesive A thermosetting step of curing the second adhesive by applying a predetermined pressure at a temperature of 300 ° C. or lower for a predetermined time, and removing the first adhesive by heating at a temperature of 500 ° C. or higher. It consists of a decomposition and removal step.

  Furthermore, the area of the seed crystal mounting surface of the seed crystal fixing method of the present invention is smaller than the area of the seed crystal on the surface bonded to the seed crystal mounting surface.

  Further, in the bonding step of the seed crystal fixing method of the present invention, the center of the seed crystal surface of the surface bonded to the seed crystal mounting surface is arranged so that the center of the seed crystal mounting surface substantially coincides. It is characterized by.

  Furthermore, the first adhesive of the seed crystal fixing method of the present invention is characterized in that an organic substance that can be easily removed by thermal decomposition is a main component.

  According to the seed crystal fixing method of the present invention, a high-quality silicon carbide single crystal that prevents the inclusion of impurities between the seed crystal and the seed crystal mounting surface of the seed crystal pedestal and suppresses the occurrence of linear through defects is obtained. Obtainable.

  Hereinafter, embodiments of the seed crystal fixing method of the present invention will be described in detail with reference to the drawings.

  FIG. 1 is a process diagram showing a seed crystal fixing method according to Example 1 of the present invention. In the seed crystal pedestal 2 formed on the graphite crucible lid 1, the area of the seed crystal mounting surface 3 shown in FIG. 1 a is larger than the area of the crystal surface of the seed crystal that is bonded to the seed crystal mounting surface 3. Also prepare a small one. As shown in FIG. 1 b, the first adhesive 4 is applied to the seed crystal mounting surface 3 of the seed crystal base 2. As the first adhesive 4, rosin was used in this example. Since rosin is solid at room temperature, the graphite crucible lid 1 is heated at approximately 120 ° C., which is a temperature sufficient for softening of the rosin, and is brought into contact with and applied to the seed crystal mounting surface 3.

  Next, as shown in FIG. 1c, after the crystal pedestal 2 and the seed crystal 5 are aligned, the seed crystal 5 is placed and bonded. At this time, it is desirable that the seed crystal 5 and the seed crystal mounting surface 3 are aligned so that the center of the seed crystal mounting surface 3 and the center of the seed crystal 5 are substantially coincident with each other. What is necessary is just to be attached so that all the mounting surfaces 3 may be covered. Note that the bonding step of the seed crystal 5 shown in FIG. 1c must be performed in a state where the rosin is softened.

  Next, the crucible lid 1 to which the seed crystal 5 is bonded is cooled to room temperature, and the rosin as the first adhesive is solidified. Thereafter, as shown in FIG. 1 d, the portion of the seed crystal surface bonded to the seed crystal mounting surface 3 that is not covered with the first adhesive 4 and the side wall of the seed crystal base 2. Then, the second adhesive 6 in the form of a liquid adhesive is applied. At this time, since the first adhesive 4 is applied, the second adhesive 6 can prevent elution and permeation between the seed crystal 5 and the seed crystal mounting surface 3. In the present embodiment, the second adhesive 6 is an adhesive containing phenol resin and formaldehyde as main components, furfuryl alcohol as a solvent, and graphite particles that are heat-resistant fine particles. In addition, a resist whose main component is a novolac resin may be used. Further, a resist containing a novolac resin as a main component may contain heat-resistant fine particles such as graphite fine particles.

After the second adhesive 6 is applied, it is left at room temperature in an atmospheric pressure or reduced pressure atmosphere for 1 hour or longer to dry the applied second adhesive 6. When drying in an atmospheric pressure atmosphere, it is not particularly necessary, but when drying in a reduced pressure atmosphere, as shown in the parentheses of FIG. 1d, it is better to pressurize at 200 g / cm ² or more. Good. When pressure is not applied at 200 g / cm ² or more, when the solvent component contained in the second adhesive 6 volatilizes, the seed crystal 5 that is adhered is pushed up, and the seed crystal 5 and the seed crystal are mounted. There is a possibility that a large gap is generated between the mounting surfaces 3 or the fixing position of the seed crystal 5 is shifted.

Thereafter, as shown in FIG. 1e, the phenol resin used as the second adhesive 6 was heated at about 130 ° C. for 4 hours and then at about 260 ° C. for 2 hours under a pressure of 200 g / cm ² or more. And thermosetting the adhesive mainly composed of formaldehyde. As the second adhesive 6, it is possible to use a resist whose main component is a novolak resin and whose solvent is ethyl cellosolve acetate. In this case, the main component can be obtained if the heating condition is approximately 300 ° C. for 3 hours or more. Can be carbonized. When these heating conditions are not satisfied, the thermosetting or carbonization becomes insufficient, or rapid thermal decomposition or foaming of the first and second adhesives occurs, and a preferable adhesion state cannot be obtained. . Note that, when the second adhesive 6 is thermally cured or carbonized, most of the first adhesive 4 is removed by combustion or thermal decomposition, but the residue of the first adhesive 4 remains. Since it is difficult to completely remove the residue below 500 ° C., the residue is decomposed and removed by heating at a high temperature of 500 ° C. or more for 1 hour or more. When performing the high temperature heat treatment at 500 ° C. or higher, it is not necessary to perform pressurization as shown in FIGS. 1d and 1e. However, the high temperature heat treatment at 500 ° C. or higher may cause deterioration of the graphite crucible lid 1 or complete burning of the second adhesive 6 if the heat treatment environment is not under reduced pressure in an inert gas atmosphere. Therefore, it is necessary to carry out under reduced pressure in an inert gas atmosphere.

  FIG. 2a is a schematic view of a crucible configuration used for silicon carbide single crystal production using the seed crystal fixing method of the present invention. The side wall of the seed crystal pedestal 2 formed on the graphite crucible lid 1 and the seed crystal 5 are bonded by a second adhesive 6, and a predetermined amount of silicon carbide powder 8 as a raw material is contained in the crucible 7. . By heating the crucible having the structure shown in FIG. 2a to an inert gas atmosphere, an atmospheric pressure of 20 Torr, a crucible lower temperature of about 2200 to 2400 ° C., and a crucible upper temperature of about 2000 to 2200 ° C., as shown in FIG. The portion of the seed crystal protruding from the seed crystal pedestal 2 is subjected to sublimation etching, and the silicon carbide single crystal 9 can be grown on the seed crystal 5 existing on the seed crystal pedestal 2. In this embodiment, since a holding member such as a screw for fixing the seed crystal is not used, naturally, there is no polycrystalline precipitation on the holding member and its vicinity. The produced silicon carbide single crystal was cut in parallel with the growth direction, then polished, and the cross section was observed. As a result, linear through defects penetrating the seed crystal could be completely prevented, and high quality from the start to the end of growth. As a result, it was found that a single crystal was maintained.

  Next, a seed crystal fixing method according to Example 2 of the present invention will be described. The difference from Example 1 is the first adhesive 4 and contains a solvent, so that it is liquid at room temperature. Therefore, it is not necessary to heat the crucible lid 1 in order to apply the first adhesive 4. In this example, the first adhesive 4 was prepared by dissolving ethyl cellulose in acetone. As in the case of Example 1, in the seed crystal base 2 formed on the graphite crucible lid 1, a seed crystal mounting surface 3 having an area smaller than that of the seed crystal 5 is prepared. In the case of the present embodiment, since the first adhesive 4 is in a liquid state at room temperature, the step of applying the first adhesive 4 to the seed crystal mounting surface 3 shown in FIG. 1b may be performed at room temperature.

  Next, as shown in FIG. 1c, the seed crystal 5 is aligned and placed on the seed crystal mounting surface 3 to which the first adhesive 4 has been applied, and adhesion is performed. After bonding, if it is allowed to stand at room temperature, acetone in the first adhesive volatilizes, and ethyl cellulose having a solid shape remains at room temperature between the seed crystal 5 and the seed crystal mounting surface 3. Since acetone, which is a solvent, may dissolve the second adhesive, the acetone must be volatilized and the process cannot proceed to the next step unless the first adhesive is completely dried.

  Next, in order to fix the side wall of the seed crystal base 2 and the seed crystal 5, a second adhesive 6 in the form of a liquid adhesive is applied as shown in FIG. 1d. From the application step of the second adhesive 6 to the silicon carbide single crystal growth, the same steps as those in Example 1 were performed. As a result of cross-sectional observation of the obtained silicon carbide single crystal, as in Example 1, no single line defect penetrating the seed crystal 5 was observed, and a single crystal maintained in a high quality state from the start to the end of the growth was obtained. It turns out that it is obtained.

  In order to verify the effect of the present invention, a silicon carbide single crystal manufactured using the seed crystal fixing method of Examples 1 and 2 was compared with a silicon carbide single crystal manufactured by a conventional method shown in a comparative example. A manufacturing method of a comparative example is shown below.

(Comparative example)
FIG. 3 is a process diagram showing a seed crystal fixing method according to this comparative example. This comparative example is based on a conventional chemical method. As the seed crystal fixing agent 10, the same adhesive as that used as the second adhesive in the present example, which is mainly composed of phenol resin and formaldehyde and furfuryl alcohol as a solvent, was used. A seed crystal fixing agent 10 is applied to the seed crystal mounting surface 3 of the seed crystal base 2 shown in FIG. A diagram with the seed crystal fixer 10 applied is shown in FIG. 3b.

Next, as shown in FIG. 3c, the seed crystal 5 is placed and fixed. As in the thermosetting process in this example, the seed crystal fixer 10 is thermoset by heating at approximately 130 ° C. for 4 hours and further at approximately 260 ° C. for 2 hours in a state where the pressure is 200 g / cm ² or more. I let you. In the case of this comparative example, the seed crystal fixing agent 10 remains between the seed crystal 5 and the seed crystal placement surface 3. A single crystal was grown under the same conditions as in this example. As a result of cross-sectional observation of the obtained single crystal, many linear defects penetrating the seed crystal were observed.

  FIG. 4 is a diagram comparing cross sections of silicon carbide single crystals manufactured by the conventional method shown in the examples of the present invention and the comparative examples. FIG. 4 a is a cross section of a silicon carbide single crystal obtained using Example 1, and shows that no linear defects penetrating the seed crystal 5 are generated. The same result was obtained with respect to the cross section of the silicon carbide single crystal obtained using Example 2. FIG. 4b is a cross section of a silicon carbide single crystal obtained by using this comparative example, in which a large number of linear through crystals 11 penetrating the seed crystal are generated, and the linear through defects 11 are formed of silicon carbide single crystals. It extends into the crystal 9.

  As described above, in this embodiment, since impurities are prevented from intervening between the seed crystal and the seed crystal mounting surface, generation of defects such as linear through defects can be suppressed. A high-quality silicon carbide single crystal can be obtained.

  In the seed crystal fixing method for growing a silicon carbide single crystal according to the present invention, a seed crystal fixing agent that can be an impurity is interposed at the contact interface between the seed crystal and the seed crystal base without using a holding member such as a screw. It has a technique for fixing a seed crystal without any problem, and is useful for producing a high-quality silicon carbide single crystal that suppresses the occurrence of linear penetration defects and the precipitation of polycrystals during the growth of the silicon carbide single crystal.

Schematic of seed crystal fixing method in Embodiment 1 of the present invention Schematic of silicon carbide single crystal manufacturing method using seed crystal fixing method of the present invention Schematic of seed crystal fixing method in comparative example The figure which compares the cross section of the silicon carbide single crystal obtained using the seed crystal fixing method of this invention and the conventional method shown by the comparative example Diagram explaining the principle of the improved Lely method

Explanation of symbols

1 crucible lid 2 seed crystal base 3 seed crystal mounting surface 4 first adhesive 5 seed crystal 6 second adhesive 7 crucible 8 silicon carbide crystal powder 9 silicon carbide single crystal 10 seed crystal fixing agent 11 linear penetration defect

Claims (16)

A bonding step of bonding the seed crystal mounting surface of the seed crystal base and the seed crystal using the first adhesive;
An application step of applying a second adhesive so as to connect a portion of the seed crystal that is not covered with the first adhesive and a side wall of the seed crystal base;
A drying step of drying the second adhesive;
A thermosetting step of curing the second adhesive by heating at a temperature of 300 ° C. or lower for a predetermined time while applying a predetermined pressure;
It comprises a decomposition and removal step of removing the first adhesive by heating at a temperature of 500 ° C. or higher.
A seed crystal fixing method characterized by the above. 2. The seed crystal fixing method according to claim 1, wherein an area of the seed crystal mounting surface is smaller than an area of a seed crystal on a surface bonded to the seed crystal mounting surface. 2. The bonding step according to claim 1, wherein the center of the seed crystal surface of the surface bonded to the seed crystal mounting surface and the center of the seed crystal mounting surface are substantially aligned. Seed crystal fixing method. 2. The seed crystal fixing method according to claim 1, wherein the first adhesive contains an organic substance that can be easily removed by thermal decomposition as a main component. 5. The seed crystal fixing method according to claim 4, wherein the organic substance that can be easily removed by thermal decomposition is at least one of rosin and ethyl cellulose. The seed crystal fixing method according to claim 1, wherein the second adhesive is made of a thermosetting resin. The seed crystal fixing method according to claim 6, wherein the second adhesive contains heat-resistant fine particles. The seed crystal fixing method according to claim 7, wherein the heat-resistant fine particles are graphite fine particles. The seed crystal fixing method according to claim 6, wherein the thermosetting resin includes at least one of a phenol resin and a novolac resin. 2. The seed crystal fixing method according to claim 1, wherein the drying step is allowed to stand for 1 hour or more under atmospheric pressure or reduced pressure at room temperature. 2. The seed crystal fixing method according to claim 1, wherein the thermosetting step maintains a temperature of about 300 ° C. or less for about 3 hours or more. The seed crystal fixing method according to claim 11, wherein, in the thermosetting step, the seed crystal is pressed with a force of 200 g / cm ² or more between the seed crystal pedestal and the seed crystal pedestal. The seed crystal fixing method according to claim 1, wherein the decomposition and removal step is performed in an inert gas atmosphere under reduced pressure. A silicon carbide single crystal ingot produced using the seed crystal fixing method according to claim 1. A silicon carbide single crystal wafer obtained by cutting and polishing the silicon carbide single crystal ingot according to claim 14. A silicon carbide single crystal epitaxial wafer obtained by epitaxial growth on the silicon carbide single crystal wafer according to claim 15.

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