JP2012031046A - Crystal growth method, method of manufacturing semiconductor device, and high-pressure device used for implementation of the crystal growth method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To grow a crystal at further high temperature and high pressure, in crystal growth using a solvothermal method.SOLUTION: In a so-called solvothermal method for growing a crystal by putting an appropriate solvent in a high-pressure vessel, and putting appropriate basic, neutral and acidic mineralizers and a compound therein to pressurize and heat them, a high-pressure vessel of a double structure including an internal vessel 1 for heating and an external vessel 9 for placing the internal vessel 1 therein to pressurize the outside thereof is used for the high-pressure vessel; the internal vessel 1 is heated; the external vessel 9 is pressurized with the increase of the internal pressure of the internal vessel 1 by the heating to prevent generation of a difference between the pressure of the internal vessel 1 and that of the external vessel 9; and, when the temperature of the internal vessel 1 reaches a predetermined value, crystal growth is performed by keeping that condition.

Description

  The present invention relates to a crystal growth method by a solvothermal method, a semiconductor device manufacturing method, and a high-pressure apparatus used for carrying out the crystal growth method.

  Single crystals including quartz that can be grown by a solvothermal method are applied as various functional elements such as piezoelectric elements. Recently, group III nitride semiconductor single crystals such as zinc oxide and GaN have attracted attention. Since these semiconductors have a large band gap, high breakdown electric field strength, and high melting point, various applications such as piezoelectric elements, electronic devices, light emitting elements, and lasers have been researched and developed as devices that make use of these physical properties. ing.

  In the solvothermal method, an appropriate solvent is placed in a high-pressure vessel, an appropriate basic, neutral or acidic mineralizer and a raw material element or compound are added, and this is pressurized and heated. Grow crystals.

  Actually, in a hydrothermal synthesis method using water as a solvent, single crystals such as quartz and zinc oxide are grown, and quartz is manufactured industrially. In addition, the ammonothermal method using ammonia as a solvent has been researched and developed for the growth of GaN single crystals (see, for example, Patent Documents 1-6 and 1-6).

JP 2003-277182 A Japanese Patent Laid-Open No. 2004-2152 JP 2007-39321 A JP 2007-238347 A JP 2008-143778 A Japanese Patent No. 4229624

K. Byrappa, "Hydrothermal Growth of Crystals", Handbook of Crystal Growth, Vol.2, ed. By D.T.J.Hurle, (1994, Elsebvier Science), Ch.9, pp. 465-562. Akira Yoshikawa et al., “Preparation of ZnO Parc Crystal by Solvothermal Method and Its Application to GaN Crystal”, Journal of Crystal Growth Society of Japan, Vol3 (2005) p.15-19. D. Ehrentraut et al., "Solvothermal Growth of ZnO", Prog. Crystal Growth Charact. Mater., 52 (2006), 280-335. R. Swilinski et al., "Bulk Ammonothermal GaN", J. Crystal Growth, 31 (2009), 3015-3018. T. Hashimoto et al. "Growth of Bulk GaN Crystals by the Basit Ammonothermal Method", Jpn. J. Appl. Phys., 46 (2007), L889-891. D. Ehrentraut et al., "Physico-chemical Featuers of the Acid Ammonothermal Growth of GaN", J. Crystal Growth, 310 (2008) 891-895.

  In the solvothermal method, high-pressure vessels are used for pressurization and heating, but these high-pressure vessels require the approval of the high-pressure gas method. In fact, all high-pressure vessels that have been used industrially or for research and development have been carried out based on the high-pressure gas method. For this reason, the manufacturing cost of the high pressure device is high, and there is a limit to the cost reduction of the product.

  In the conventional method, the pressure of the high-pressure vessel is set to a high pressure and the crystal is grown by heating from the outside of the vessel. For this reason, since the temperature and pressure of the container material are increased and there is a risk of destruction, the high-pressure gas method could not be pressurized or heated above a predetermined temperature and pressure, depending on the size of the container.

  In addition, when the pressurization and heating conditions were not recognized by the high pressure gas method, the experiment itself could not be carried out, which hindered the research and development of crystal growth of a new material.

  The present invention has been made in view of the above points, and an object of the present invention is to enable crystal growth at higher temperatures and pressures in crystal growth using the solvothermal method.

In order to achieve the above object, in the invention described in claim 1, in a crystal growth method using a solvothermal method in which a crystal and a solvent are put in a high-pressure vessel, and the crystal is grown by pressurization and heating.
As the high-pressure vessel, using a double-structured high-pressure vessel having an inner vessel for containing the crystal and solvent, and an outer vessel for putting the inner vessel and pressurizing the outside thereof,
The inner container is heated, and as the internal pressure of the inner container increases due to the heating, the outer container is pressurized to prevent a pressure difference between the inner container and the outer container. When the temperature reaches a predetermined temperature, the state is maintained and crystal growth is performed.

  According to this invention, as the high-pressure vessel, a double-structured high-pressure vessel having an inner vessel for containing crystals and a solvent and an outer vessel for putting the inner vessel and pressurizing the outside thereof is used. Since the inner container can be almost at the same pressure as the outer container, crystals can be grown at a higher temperature and pressure than in the prior art. For this reason, the growth rate can be made faster than before and the crystal quality can be improved.

  According to a second aspect of the present invention, there is provided a semiconductor device manufacturing method for manufacturing a semiconductor device from a crystal obtained by the crystal growth method according to the first aspect.

  According to the present invention, a semiconductor device such as a wafer and a device can be manufactured using the crystal having improved crystal quality obtained by the crystal growth method according to claim 1.

The invention described in claim 3 is a high-pressure apparatus used for carrying out a crystal growth method using a solvothermal method in which a crystal and a solvent are placed in a high-pressure vessel, and pressurized and heated to grow the crystal.
The high-pressure vessel is a double-structured high-pressure vessel having an inner vessel for containing crystals and a solvent, and an outer vessel for putting the inner vessel and pressurizing the outside thereof,
The high-pressure device further includes heating means for heating the inner container,
A pressurizing means for pressurizing the external container;
Pressure detecting means for obtaining a pressure difference between the inner container and the outer container.

  According to the present invention, the crystal growth method according to claim 1 can be appropriately performed.

  The heating means is an electric furnace installed in an external container as in the invention described in claim 4, and the internal container is installed in the electric furnace to heat the internal container. Can do. Moreover, as a pressurizing means for pressurizing the external container, a compressor, a high-pressure valve, or the like can be used as shown in an embodiment described later. In addition, as a pressure detection means for obtaining a pressure difference between the inner container and the outer container, as shown in an embodiment described later, in addition to a pressure gauge for detecting the respective pressures of the inner container and the outer container, A differential pressure gauge or the like that detects the pressure difference of the external container can be used.

It is a schematic diagram which shows the structure (high pressure apparatus) of the solvothermal method by this invention. It is a schematic diagram which shows the structure (high pressure apparatus) of the conventional solvothermal method.

  In the conventional solvothermal method, as shown in FIG. 2, heating is performed from the outside of the high-pressure vessel in a state where the high-pressure vessel is pressurized. In the present embodiment, as shown in FIG. That is, the high-pressure vessel is a double-structured high-pressure vessel having an inner vessel (internal high-pressure vessel) 1 and an outer vessel (external high-pressure vessel) 9 for putting the inner vessel 1 and pressurizing the outside thereof. The external container 1 is provided with pressurizing means such as a compressor 12 and a high-pressure valve 11 and a pressure gauge 10 for detecting the pressure inside the container. In FIGS. 1 and 2, 2 is a seed crystal, 3 is a raw material, 4 is a baffle plate, 5 is an upper heater, 6 is a lower heater, 7 is a pressure gauge, and 8 is a high-pressure valve.

  In the high-pressure apparatus shown in FIG. 1, the inner container 1 is filled with water or ammonia as a solvent. At this time, the solvent is filled through the high-pressure valve 8 so as to reach a predetermined pressure at a predetermined temperature. In an unheated state, even if pressure is applied to the inner container 1, it can be pressurized to a considerably high pressure in the high pressure method because it is at room temperature depending on the size of the container. Actually, the pressure is increased to an allowable pressure when the temperature reaches a predetermined temperature in view of the pressure increase when heated. Alternatively, the solvent is filled so that an allowable pressure is reached when a predetermined temperature is reached.

In the above state, heating of the inner container 1 is started, but the pressure inside the inner container 1 increases with heating. As the pressure increases, the external container 9 is pressurized. For this pressurization, an inert gas such as nitrogen or argon is preferably used. Although the internal pressure of the internal container 1 rises to a predetermined temperature for crystal growth, the external container 9 is pressurized so that a pressure difference between the internal container 1 and the external container 9 does not occur. At this time, the outer container 9 is pressurized using an inert gas whose pressure has been increased to, for example, 2000 atmospheres by the compressor 12. Then, when the temperature of the inner container 1 reaches a predetermined temperature, the state is maintained and crystal growth is performed. Since the pressure is reduced so that the pressure difference between the inner container 1 and the outer container 9 does not occur in the reverse procedure when cooling, the inner container 1 is hardly pressurized, so there is no risk of container breakage, higher pressure than before, Crystal growth is possible at a high temperature.
(Example)
Specific embodiments for carrying out the present invention will be described below. The present invention is not limited to these methods and can be carried out by methods similar to these. A GaN polycrystal having a particle size of about 0.05 to 5 mm is filled as a raw material 3 at the bottom of an inner vessel 1 (autoclave) made of a predetermined high-pressure vessel alloy, and about 10% of Ga is added. Next, a baffle plate 4 having an aperture ratio of about 6% is placed in the middle of the inner vessel 1 and the inner vessel is divided into a raw material filling portion and a crystal growth portion. Next, a plate-like GaN single crystal of about 100 mm × 150 mm cut and mirror-polished as a seed crystal 2 in a plane perpendicular to the C-axis direction is suspended on a Pt frame in several steps so that the C-axis faces the horizontal direction. This frame is disposed in the crystal growth part. NH3 as a solvent is poured into the inner container 1 together with NH4Cl as an acidic curing agent at a filling rate of about 80% and sealed with a cap.

  This inner container 1 is installed in an electric furnace composed of two upper and lower heaters 5 and 6 installed in an outer container 9 and connected to high-pressure piping and heater electrodes connected to the outer container 9. To do. Thereafter, piping is performed so that the outer container 9 can be sealed and pressurized.

  While keeping the temperature of the crystal growth part always higher than the temperature of the raw material filling part, the temperature of the raw material filling part is raised to about 650 ° C. and the crystal growth part is raised to about 700 ° C. At this time, the pressure of the inner container 1 is increased to about 3000 atm. However, the outer container 9 is pressurized in accordance with the temperature rise of the inner container 1, and the pressure in the inner container 1 and the pressure in the outer container 9 are increased. The inner container 1 is heated while adjusting the pressure gauge 7 and the pressure gauge 10 so as to be substantially the same. When a predetermined temperature is reached, the state is maintained for about 90 days to grow crystals. At this time, the pressure gauge 7 and the pressure gauge 10 are always adjusted so that the pressure in the inner container 1 and the pressure in the outer container 9 are substantially the same. This adjustment may be automatically adjusted based on the signal from the pressure gauge.

When cooling, the pressure gauge 7 and the pressure gauge 10 are viewed and adjusted so that the pressure in the inner container 1 and the pressure in the outer container 9 are substantially the same as when the temperature is raised. Cool to room temperature and take out the grown GaN single crystal. By this method, a GaN single crystal having a length of about 100 mm is obtained on both sides of the seed crystal 2, so that a large crystal of 100 × 150 × 200 mm is obtained as a bulk single crystal. This bulk crystal is cylindrically ground, sliced to a thickness of about 400 μm, and then mirror-polished with colloidal silica to obtain a wafer for device fabrication. Usually, the GaN single crystal wafer is cut out at the C-plane. However, if the orientation to be cut out is selected, a GaN single crystal wafer of either antipolarity or nonpolarity can be obtained.
(Comparative example)
As shown in FIG. 2, crystals are grown only in the inner container 1. About filling of a raw material, it carries out similarly to the above-mentioned Example. At this time, since the high-pressure vessel 1 is heated as it is, depending on the material of the inner vessel in the high-pressure method, the upper limit is about 1500 atm. Therefore, NH3 as a solvent and NH4Cl as an acidic mineralizer are used. At the same time, the filling rate is about 65%. In addition, since the pressure is limited, the temperature can only be increased to about 550 ° C. Crystal growth is carried out at about 500 ° C., and this temperature is maintained for about 90 days as in the above-described embodiment to grow crystals. Since the GaN single crystal grown by cooling to room temperature has a very low crystal growth temperature, only a GaN single crystal having a length of about 3 mm could be grown on both sides of the seed crystal 2. Many examples of growth under similar conditions are described in the literature, but since all growth is performed by heating and pressurizing in a single container, the growth temperature cannot be increased, so the maximum temperature growth rate is slow and only small crystals can be obtained. There wasn't.

  Thus, in the conventional method, the pressure of the high-pressure vessel is set to a high pressure, and the crystal is grown from the outside of the vessel. For this reason, the temperature and pressure of the container material become high and there is a risk of destruction. Depending on the size of the container in the high-pressure gas method, the temperature could not be raised or pressurized above the predetermined temperature and pressure. However, if the method according to the present embodiment described above is used, the inner container can be brought to almost the same pressure as the outer container during the heating, so that the temperature can be raised and pressurized above the conventional temperature and pressure. .

  As a result, the crystal can be grown at a higher temperature and pressure, so that the growth rate can be made faster than before and the crystal quality can be improved.

DESCRIPTION OF SYMBOLS 1 Internal container 2 Seed crystal 3 Raw material 4 Paffle board 5 Upper heater 6 Lower heater 7 Pressure gauge 8 High pressure valve 9 External container 10 Pressure gauge 11 High pressure valve 12 Compressor

Claims (5)

In a crystal growth method using a solvothermal method in which a crystal and a solvent are placed in a high-pressure vessel, and the crystal is grown by pressurization and heating.
As the high-pressure vessel, using a double-structured high-pressure vessel having an inner vessel for containing the crystal and solvent, and an outer vessel for putting the inner vessel and pressurizing the outside thereof,
The inner container is heated, and as the internal pressure of the inner container increases due to the heating, the outer container is pressurized to prevent a pressure difference between the inner container and the outer container. When the temperature reaches a predetermined temperature, crystal growth is performed while maintaining the state.   A semiconductor device manufacturing method for manufacturing a semiconductor device from a crystal obtained by the crystal growth method according to claim 1. A high-pressure apparatus used for carrying out a crystal growth method using a solvothermal method in which a crystal and a solvent are placed in a high-pressure vessel, and pressurized and heated to grow the crystal,
The high-pressure vessel is a double-structured high-pressure vessel having an inner vessel for containing crystals and a solvent, and an outer vessel for putting the inner vessel and pressurizing the outside thereof,
The high-pressure device further includes heating means for heating the inner container,
A pressurizing means for pressurizing the external container;
And a pressure detection means for obtaining a pressure difference between the inner container and the outer container.   4. The high-pressure apparatus according to claim 3, wherein the heating means is an electric furnace installed in the outer container, and the inner container is installed in the electric furnace.   In the content of Claim 1-4, when growing a GaN single crystal using ammonia as a solvent and an acidic mineralizer as a mineralizer, the temperature is 580 ° C. or higher and the pressure is 1700 atmospheres or higher. A crystal growth method, a semiconductor device manufacturing method, and a high-pressure apparatus.