JP4556634B2 - Seed crystal fixing part and seed crystal fixing method - Google Patents

Description

  The present invention relates to a fixing structure and a fixing method for fixing a seed crystal for growing a silicon carbide single crystal to a seed crystal support, and a method for manufacturing a silicon carbide single crystal using them.

  Silicon carbide (SiC) has a large thermal conductivity, a low dielectric constant, a wide band gap, and has thermally and mechanically stable characteristics. Therefore, a semiconductor element using silicon carbide has higher performance than a semiconductor element using conventional silicon (Si). The range of use is expected to be environment-resistant device materials, radiation-resistant device materials, power device materials for power control, high-frequency device materials, etc. used in high-temperature environments. As a method for producing this silicon carbide single crystal substrate, a sublimation recrystallization method (also called “improved Rayleigh method”) is mainly employed.

  FIG. 7 is a schematic view of an apparatus used for this sublimation recrystallization method. In the lower half of the graphite crucible 7 comprising the crucible 7 and the lid 1 having a seed crystal support, silicon carbide powder is used as a raw material powder. 6 is accommodated, and a seed crystal 4 is arranged on the seed crystal support portion of the lid 1 facing this. In the crucible, the silicon carbide powder 6 side is held at a high temperature and the seed crystal 4 side is held at a low temperature, and the sublimation gas of the silicon carbide powder 6 is recrystallized on the low temperature seed crystal 4 to grow a single crystal 5. .

  In the above method, the seed crystal 4 is usually fixed to the seed crystal support provided on the lid 1 using the adhesive 2. As the fixing method, for example, as an adhesive used when fixing the seed crystal support part and the seed crystal, there is a method of carbonizing the adhesive by high-temperature treatment using an adhesive containing a polymer material. (Patent Document 1).

  Also disclosed is a method of drying an adhesive (fixing agent) comprising a carbohydrate, heat-resistant fine particles and a solvent at room temperature (Patent Document 2).

Also, the surface layer on the side of the seed crystal that adheres to the seed crystal support is removed, and the new surface from which the surface layer is removed and the seed crystal support are composed of carbon powder, a polymer material, and an organic solvent. The method of arrange | positioning through an adhesive agent and fixing by heat-processing is disclosed (patent document 3).
Japanese Patent Laid-Open No. 9-110584 Japanese Patent Laid-Open No. 11-171691 Japanese Patent Laid-Open No. 2003-119098

  However, in the case of the method for fixing the seed crystal in Patent Documents 1 to 3 described above, as shown in FIG. 8A, in the step of drying and curing the adhesive 2, air bubbles are easily generated in the adhesive layer 2, The void 8 remains in the layer 2. When the single crystal is grown in the presence of the void 8, heat is conducted to the lid 1 in a place where there is no void 8 and is in close contact with the adhesive 2, so the temperature gradient between the seed crystal 4 and the lid 1 is In addition, since the seed crystal 4 does not release heat to the lid 1 in the place where the void 8 exists, a temperature gradient is locally generated between the seed crystal 4 and the lid 1. As a result, as shown in FIG. 8B, sublimation of the seed crystal 4 occurs from the seed crystal 4 toward the lid 1 having a low temperature in the gap 2 portion. Since the graphite lid 1 is not gas-impermeable, the sublimation gas passes through the lid 1 and goes out. The back surface sublimation that occurs on the back surface of the seed crystal 4 occurs at a plurality of locations on the bonding surface of the seed crystal 4 and the lid 1 and continuously occurs during the single crystal growth. As shown in FIG. A large defect (macro defect) 9 that penetrates the crystal 4 and propagates to the grown crystal is caused. The macro defect 9 becomes a hollow defect penetrating in the thickness direction when the wafer is cut out from the grown crystal. When a device is formed on such a hollow defect, there is a problem that the device characteristics are extremely deteriorated or even the device does not operate.

  The present invention solves this conventional problem, prevents back surface sublimation that occurs between the seed crystal back surface and the seed crystal support part, and can more reliably suppress the occurrence of macro defects extending in the grown crystal. It is an object of the present invention to provide a seed crystal fixing part and a fixing method for growing a single crystal, and a method for producing a single crystal using them.

Seed crystal fixed part of the present invention, the seed crystal fixing unit for fixing the seed crystal to a support portion made of carbon, a first silicon carbide substrate through the adhesive to the surface of the support portion is bonded, said first The silicon carbide substrate and the second silicon carbide substrate which is a single crystal are bonded with an adhesive whose heat-resistant fine particles are graphite particles or ceramic particles .

  Moreover, the seed crystal fixing method of the present invention includes a step of disposing a first silicon carbide substrate on a surface of a support portion made of carbon via a first adhesive, and the bonding on the first silicon carbide substrate. Including a step of disposing a second silicon carbide substrate that is a single crystal through a second adhesive that is the same as the agent, and a step of curing the first and second adhesives. To do.

  In the seed crystal fixing portion of the present invention, the first silicon carbide substrate is bonded to the surface of the seed crystal support portion via an adhesive, and the second silicon carbide is bonded to the first silicon carbide substrate via an adhesive. The substrate is bonded. Therefore, in the step of curing the adhesive, even if a gap is formed in the adhesive between the seed crystal support portion and the first silicon carbide substrate, the first silicon carbide substrate is sublimated, but the first carbonization is performed. Since there is an adhesive between the silicon substrate and the second silicon carbide substrate, the back surface sublimation of the second silicon carbide substrate, which is a seed crystal substrate for producing a silicon carbide crystal in the sublimation recrystallization method, is prevented, and the grown crystal The occurrence of macro defects extending inward can be suppressed.

  Further, even if a gap is formed in the adhesive between the first silicon carbide substrate and the second silicon carbide substrate that is a seed crystal, the first silicon carbide substrate is located on the lower temperature side than the adhesive in which the gap is formed. Therefore, sublimation of the back surface of the second silicon carbide substrate, which is a seed crystal substrate, is prevented, and generation of macro defects extending into the grown crystal can be suppressed.

  Hereinafter, embodiments of a seed crystal fixing structure and fixing method and a single crystal manufacturing method using them will be described in detail with reference to the drawings.

  FIG. 1 shows a fixed structure of a seed crystal in Example 1 of the present invention. First, the adhesive 2 is applied to the seed crystal support portion provided on the graphite lid 1 so as to have a uniform thickness. As the adhesive 2, a trade name GRAPHYBOND 551-RN (made by Alemco Products) containing phenol resin and formaldehyde as main components, furfuryl alcohol as a solvent, and graphite particles as heat-resistant fine particles was used. . Thereafter, the polycrystalline silicon carbide substrate 3 having a thickness of about 600 μm is adhered and adhered to the adhesive applied to the seed crystal support.

  Thereafter, the adhesive 2 is applied on the polycrystalline silicon carbide substrate 3 so as to have a uniform thickness, and the seed crystal 4 is adhered and bonded thereto. In this example, a Rayleigh substrate having a thickness of about 400 μm manufactured by the Rayleigh method was used as the seed crystal 4, and the (000-1) carbon surface was used as an adhesive surface.

  Thereafter, the pressure member 5 is disposed on the seed crystal in order to pressurize the bonding surface and improve the adhesion of the bonded portion.

  Next, the pressure member 5 is placed on the thermostat bath as described above, and the adhesive is dried and cured by heat treatment. This is because the solvent contained in the adhesive 2 is evaporated and the phenol resin is cured. This drying / curing heat treatment is carried out in air, and the heat treatment temperature and time are maintained at room temperature for about 4 hours, then increased to about 129 ° C. at a rate of 10 ° C./min, and maintained at about 129 ° C. for about 4 hours. The temperature is raised from about 129 ° C. to about 260 ° C. at a rate of 10 ° C./min and held at about 260 ° C. for about 2 hours, followed by natural cooling.

  In addition, about the application | coating thickness of the above-mentioned adhesive 2, and the load added to a seed crystal by the pressurization member 5, the application | coating thickness of the adhesive 2 and the load added to a seed crystal by the pressurization member 5 are changed, and it heat-processes. After curing, the adhesive strength was evaluated and the optimum conditions were determined. The curing condition of the adhesive 2 was the same as the curing condition of the adhesive 2 of the present embodiment described above. The results are shown in Table 1.

  When the weight applied to the seed crystal was 0.3 MPa, the adhesive strength was weak regardless of the applied thickness of the adhesive, and the adhesive surface was easily peeled off by applying a little force with tweezers or the like. In this case, many voids were observed in the cured adhesive. When the weight applied to the seed crystal was 0.5 MPa or more, sufficient adhesive strength was obtained if the coating thickness of the adhesive was 50 μm or more. However, when the weight applied to the seed crystal is 0.5 MPa or more, the adhesive overflowed from the edge of the pasting surface during curing when the applied thickness of the adhesive was 300 μm or more. When crystal growth as described later is performed in this state, polycrystalline silicon carbide grows on the overflowing adhesive, and comes into contact with the silicon carbide single crystal grown from the seed crystal. Deteriorated crystal quality. Therefore, the best range of the coating thickness of the adhesive 2 is 50 μm to 200 μm, and the weight applied to the seed crystal by the pressure member 5 is preferably 0.5 MPa or more.

  In this example, the applied thickness of the adhesive was 200 μm, and the load applied to the seed crystal by the pressure member 5 was 1.0 MPa. In the present example, the trade name GRAPHYBOND 551-RN (made by Alemco Products) was used as the adhesive 2. However, the present invention is not limited to this, and high heat-resistant fine particles such as graphite fine particles and ceramic fine particles and thermosetting resin are used. Can be used as long as they are mixed with an organic solvent. Further, the curing conditions of the adhesive are not limited to the conditions described in this embodiment, and may be appropriately adjusted according to the material of the adhesive.

  As described above, a seed crystal fixed structure as shown in FIG. 1b was obtained. Thereafter, a silicon carbide single crystal was grown using a sublimation recrystallization method. FIG. 2 is a schematic view of the growth apparatus used in this example. The silicon carbide raw material 6 is accommodated in the crucible 7, and the seed crystal 4 fixed to the seed crystal support portion of the lid 1 is disposed so as to face the silicon carbide raw material 6.

  In silicon carbide single crystal growth using the sublimation recrystallization method, the silicon carbide raw material 6 must be sublimated, but sublimation of silicon carbide requires a high temperature of 2000 ° C. or higher. At a high temperature of 2000 ° C. or higher, the radiant heat is lost in proportion to the fourth power of the temperature. Therefore, it is necessary to cover the crucible 7 and the lid 1 with the heat insulating material 8. The crucible 7 and the lid 1 covered with the heat insulating material 8 are placed in a quartz reaction tube 9. The reaction tube 9 has a double tube structure, and is cooled by flowing cooling water 10 during crystal growth. A gas inlet 11 is provided at the top of the reaction tube 9 and a gas exhaust 12 is provided at the bottom.

  Thereafter, the inside of the reaction tube 9 is replaced with an inert gas, and argon (Ar) is suitable as the inert gas in terms of cost, purity, and the like. In this inert gas replacement, first, the inside of the reaction tube 9 is evacuated to a high vacuum from the gas exhaust port 12, and then the inert gas is filled from the gas inlet port 11 to normal pressure. In order to sufficiently replace the inside of the reaction tube 9 with argon gas, it is better to repeat this process several times.

  Thereafter, the crucible 7 and the lid 1 are heated at a high frequency by flowing a high-frequency current through a coil 13 spirally wound around the reaction tube 9 to raise the temperature. When raising the temperature, the inside of the reaction tube 9 needs to be kept at a pressure of about several tens of kPa. This is to prevent sublimation of the silicon carbide raw material 6 at low temperatures (below the desired crystal growth temperature) and prevent crystal growth from starting.

  The temperature control at the time of heating is performed with a radiation thermometer 15 through a temperature measuring window 14 made of quartz provided in the upper and lower portions of the reaction tube 9 and a temperature measuring hole provided in the upper and lower portions of the heat insulating material 8. The temperature at the lower part of the crucible 7 and the upper part of the lid 1 is measured, feedback is applied to a high-frequency power source (not shown), and the high-frequency current flowing through the coil 13 is controlled. Thus, after raising the temperature to a desired temperature, the pressure is gradually reduced to start crystal growth. In this example, the temperature of the crucible 7 lower part was 2250 ° C., the temperature at the center point of the crucible upper part was 2200 ° C., the pressure inside the reaction tube 9 was 0.665 kPa, and crystal growth was carried out while maintaining for 20 hours.

  At the end of crystal growth, contrary to the start of growth, the pressure inside the reaction tube 9 is increased to 80 kPa over 1 hour to stop the sublimation of the raw material from the silicon carbide raw material 6 and then slowly cooled to room temperature. did.

  The silicon carbide single crystal obtained as described above was sliced parallel to the growth direction and observed with a transmission optical microscope. The photograph is shown in FIG. As is apparent from FIG. 3, no sublimation from the back surface of the seed crystal was observed, and therefore there was no macro defect in the grown silicon carbide single crystal.

  As described above, a silicon carbide polycrystalline substrate is bonded to the surface of the seed crystal support portion via an adhesive, and the seed crystal is bonded to the silicon carbide polycrystalline substrate via an adhesive, thereby producing a silicon carbide single crystal. By growing the crystal, macro defects can be suppressed and a high-quality single crystal can be obtained.

  FIG. 4 shows a fixed structure of a seed crystal in Example 2 of the present invention. First, the adhesive 2 is applied to the seed crystal support portion provided on the graphite lid 1 so as to have a uniform thickness. In this embodiment, as the adhesive 2, the trade name GRAPHYBOND 551-RN (Alemco Products), which contains phenol resin and formaldehyde as main components, furfuryl alcohol as a solvent, and graphite particles as heat-resistant fine particles, is included. Made). The coating thickness was 200 μm. Thereafter, silicon carbide single crystal substrate 16 is adhered and bonded to adhesive 2 applied to the seed crystal support. As this silicon carbide single crystal substrate 16, a Rayleigh substrate having a thickness of about 400 μm manufactured by the Rayleigh method was used, and the (000-1) carbon surface was bonded to the seed crystal support portion side.

  Thereafter, the adhesive 2 is applied to the (0001) silicon surface of the silicon carbide single crystal substrate 16 so as to have a uniform thickness, and the seed crystal 4 is adhered and bonded thereto. In this example, the application thickness of the adhesive 2 was set to 200 μm, and a Rayleigh substrate having a thickness of about 400 μm manufactured by the Rayleigh method as the seed crystal 4 was used, and the (000-1) carbon surface was used as the adhesive surface.

  Thereafter, the pressing member 5 is disposed on the seed crystal 4. In this example, a graphite block was used as the pressure member 5, and 1.0 MPa was applied to the seed crystal as a load. Next, the pressure member 5 is placed on the thermostat bath as described above, and the adhesive is dried and cured by heat treatment. This is because the solvent contained in the adhesive 2 is evaporated and the phenol resin is cured. This drying / curing heat treatment is performed in air, and the heat treatment temperature and time are maintained at room temperature for 4 hours, then increased to about 129 ° C. at 10 ° C./min, maintained at about 129 ° C. for 4 hours, about The temperature was raised from 129 ° C. to about 260 ° C. at a rate of 10 ° C./min, maintained at about 260 ° C. for 2 hours, and then naturally cooled.

  In this example, the trade name GRAPHYBOND 551-RN (made by Alemco Products) was used as the adhesive 2. However, the present invention is not limited to this, and high heat-resistant fine particles such as graphite fine particles and ceramic fine particles are combined with thermosetting resin. It may be mixed with a solvent. Further, the curing condition of the adhesive is not limited to the conditions described in this embodiment, and may be adjusted according to the material of the adhesive.

    As described above, a seed crystal fixing structure as shown in FIG. Thereafter, a silicon carbide single crystal was grown using a sublimation recrystallization method. The growth of this silicon carbide single crystal was carried out using exactly the same growth apparatus and growth conditions as in Example 1.

  Thus, the obtained silicon carbide single crystal was sliced parallel to the growth direction and observed with a transmission optical microscope. As a result, sublimation from the back surface of the seed crystal was not observed, and therefore there was no macro defect in the grown silicon carbide single crystal.

  As described above, a silicon carbide single crystal substrate is bonded to the surface of the seed crystal support portion via an adhesive, and the seed crystal is bonded to the silicon carbide single crystal substrate via an adhesive, thereby obtaining a silicon carbide single crystal. By growing the crystal, macro defects can be suppressed and a high-quality single crystal can be obtained.

(Comparative example)
A comparison was made between the silicon carbide single crystals produced in Example 1 and Example 2 above and the silicon carbide single crystals produced by the conventional method. FIG. 5 shows the fixed structure of the seed crystal in this comparative example. First, the adhesive 2 is applied to the seed crystal support portion provided on the graphite lid 1 so as to have a uniform thickness. Adhesive 2 is the same as that used in Example 1 and Example 2, and is a product containing phenolic resin and formaldehyde as main components, furfuryl alcohol as a solvent, and graphite particles as heat-resistant fine particles. The name GRAPHIC BOND 551-RN (Alemco Products) was used. The coating thickness was set to 200 μm as in the case of Example 1 and Example 2. Thereafter, the seed crystal is brought into close contact and bonded. As a seed crystal, a Rayleigh substrate having a thickness of about 400 μm manufactured by the Rayleigh method was used, and the (000-1) carbon surface was used as an adhesive surface.

  Thereafter, the pressure member 5 is disposed on the seed crystal. A graphite block was used as the pressing member, and 1.0 MPa was applied to the seed crystal as a load as in Examples 1 and 2.

  Next, the pressure member 5 is placed on the thermostat bath as described above, and the adhesive is dried and cured by heat treatment. This drying / curing heat treatment was performed in the same manner as in Example 1 and Example 2, and then naturally cooled.

  A structure as shown in FIG. 5b was obtained as described above. Thereafter, a silicon carbide single crystal was grown using a sublimation recrystallization method. Crystal growth was performed under exactly the same growth conditions as in Example 1 and Example 2.

  The silicon carbide single crystal obtained as described above was sliced parallel to the growth direction and observed with a transmission optical microscope. The photograph is shown in FIG. As described above, the silicon carbide single crystal obtained in Example 1 and Example 2 shown in FIG. 3 does not show any sublimation of the seed crystal and no macro defect extending in the single crystal. However, as is apparent from FIG. 6, the silicon carbide single crystal obtained by the conventional method shown in the comparative example penetrates through the seed crystal from the adhesive between the seed crystal support portion of the lid and the seed crystal. Many macro defects extending to the crystal part have been observed.

  From the above, the silicon carbide single crystal manufactured using the present invention is prevented by the sublimation of the seed crystal, so that no macro defects elongating to the single crystal portion are generated and obtained by the prior art. Compared with the silicon carbide single crystal, a very high quality silicon carbide single crystal can be produced.

  The seed crystal fixing structure and fixing method according to the present invention and the single crystal manufacturing method using them can prevent sublimation from the back surface of the seed crystal and suppress the introduction of macro defects into the grown crystal. The present invention can also be applied to cadmium sulfide (CdS), cadmium selenide (CdSe), zinc sulfide (ZnS), aluminum nitride (AlN), boron nitride (BN), and the like that are single crystals.

The figure which shows the seed crystal fixing method and fixing | fixed part in Example 1 of this invention Schematic of the manufacturing apparatus of the silicon carbide single crystal in Example 1 of this invention The figure which shows the cross-sectional photograph of the silicon carbide single crystal obtained in Example 1 of this invention The figure which shows the seed crystal fixing method and fixing | fixed part in Example 2 of this invention. Diagram showing seed crystal fixing method and fixing structure in conventional method The figure which shows the cross-sectional photograph of the silicon carbide single crystal obtained by the conventional method Illustration of sublimation recrystallization method Explanatory diagram of macro defect generation mechanism in the conventional method

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Cover body 2 Adhesive 3 Silicon carbide polycrystalline substrate 4 Silicon carbide single crystal substrate (seed crystal)
DESCRIPTION OF SYMBOLS 5 Pressurization member 6 Silicon carbide raw material 7 Crucible 8 Heat insulating material 9 Reaction tube 10 Cooling water 11 Gas inlet 12 Gas exhaust 13 Coil 14 Temperature measuring window 15 Radiation thermometer 16 Silicon carbide single crystal substrate

Claims (11)

In the seed crystal fixing part for fixing the seed crystal to the support part made of carbon,
A first silicon carbide substrate is bonded to the surface of the support portion via an adhesive;
A seed crystal fixing part, wherein the first silicon carbide substrate and a second silicon carbide substrate which is a single crystal are bonded together with an adhesive whose heat-resistant fine particles are graphite particles or ceramic particles . The seed crystal fixing portion according to claim 1, wherein the first silicon carbide substrate is a polycrystalline substrate. The seed crystal fixing portion according to claim 1, wherein the first silicon carbide substrate is a single crystal substrate. Disposing a first silicon carbide substrate on a surface of a support portion made of carbon via a first adhesive;
Disposing a second silicon carbide substrate that is a single crystal on the first silicon carbide substrate via a second adhesive that is the same as the adhesive; and
Curing the first and second adhesives;
A seed crystal fixing method comprising the steps of: The seed crystal fixing method according to claim 4, wherein the first silicon carbide substrate is a polycrystalline substrate. The seed crystal fixing method according to claim 4, wherein the first silicon carbide substrate is a single crystal substrate. The seed crystal fixing method according to claim 4, wherein the adhesive contains heat-resistant fine particles, a thermosetting resin, and an organic solvent, and is cured by heating. The seed crystal fixing method according to claim 7, wherein the heat-resistant fine particles are graphite fine particles, the thermosetting resin is a phenol resin, and the organic solvent is furfuryl alcohol. The seed crystal fixing method according to claim 4, wherein a coating thickness of the first and second adhesives is in a range of 50 μm to 200 μm. The step of curing the adhesive comprises:
Leaving it at room temperature for 4 hours ;
Increasing the temperature from room temperature to 129 ° C. at 10 ° C. per minute;
Holding at 129 ° C. for 4 hours ;
Increasing the temperature from 129 ° C. to 260 ° C. at 10 ° C. per minute;
The seed crystal fixing method according to claim 4, comprising a step of holding at 260 ° C. for 2 hours . In the step of curing the first and second adhesives, a pressure member is disposed on the second silicon carbide substrate and a pressure of 0.5 MPa or more is applied to the second silicon carbide substrate. The seed crystal fixing method according to claim 4.