JP5094811B2 - Single crystal manufacturing method and manufacturing apparatus - Google Patents

Description

  The present invention relates to a method and an apparatus for producing a single crystal such as silicon carbide.

  A silicon carbide (SiC) semiconductor has been attracting attention as a semiconductor material having excellent thermal and chemical properties and excellent electrical properties. For this reason, the request | requirement of the cost reduction of a SiC wafer is increasing.

  As a method for growing a silicon carbide single crystal, a sublimation method is widely used. In the sublimation method, a SiC single crystal seed substrate and a SiC raw material are placed opposite to each other in a graphite crucible, and the inside of the crucible is evacuated (exhausted) to air with an inert gas such as argon (Ar). After the substitution, the SiC raw material is sublimated by heating at a high temperature. At this time, by keeping the seed substrate in the SiC growth temperature region and keeping the raw material portion at a higher temperature than the seed substrate, the gas (raw material gas) obtained by sublimation of the SiC raw material reaches the surface of the seed substrate. A SiC single crystal ingot grows.

  One means for reducing the cost of SiC wafers is to increase the growth rate of ingots. In the sublimation method, the growth rate of the ingot is increased by increasing the vapor pressure of the source gas in the vicinity of the seed substrate in the crucible (lowering the pressure of the inert gas, increasing the temperature difference between the source and the seed substrate, etc.). Can be increased.

  However, when the vapor pressure of the raw material gas is increased, the raw material gas is likely to leak from the gap between the crucible lid and the main body, so that it is necessary to improve the airtightness of the crucible to suppress this. As a method for improving the airtightness, it is conceivable to increase the contact area between the lid and the main body by thickening the side wall of the crucible. As another method, it has been proposed to screw the crucible lid and the main body together (for example, Patent Document 1 below).

JP 2006-143497 A

  As described above, in order to increase the vapor pressure of the raw material gas in the crucible and increase the growth rate of the ingot, the hermeticity of the crucible is important. If the crucible side wall is made thicker, the hermeticity can be increased. However, if the outer diameter of the crucible is increased, a new large crystal growth furnace or a heat insulating material is required, which may increase the cost. If the outer diameter of the crucible is maintained and the side wall is thickened, this problem does not occur, but another problem arises that the inner diameter of the crucible is reduced and the ingot diameter that can be grown in the crucible is limited.

  Moreover, it is difficult to completely eliminate the gap between the lid, the main body, and the method of thickening the side wall of the crucible and the method of threading the crucible lid and the main body as in Patent Document 1. Even when threading is performed, the screw loosens due to thermal expansion after the temperature rises, and a gap is formed, from which a raw material gas leaks.

  The present invention has been made to solve the above-described problems. In the production of a single crystal, the crucible used for crystal growth is improved in hermeticity to prevent leakage of material gas, and sufficient in the crucible. The purpose is to enable easy vacuuming.

  The method for producing a single crystal according to the present invention includes a step of disposing a seed substrate and a raw material in a crucible and bonding the raw material storage container and the lid of the crucible using an adhesive, and the crucible inside the crucible. And a step of exhausting through the side wall.

  An apparatus for producing a single crystal according to the present invention includes a graphite raw material storage container having a thin wall portion having a thickness of 10 mm or less on a side wall, a crucible having a lid attached to an opening of the raw material storage container, and the lid. And an adhesive for fixing to the raw material storage container.

  According to the present invention, the gap between the raw material storage container and the lid is filled with the adhesive, and evacuation is performed through the side wall of the crucible. Therefore, the airtightness of the crucible is enhanced, and leakage of the raw material gas during crystal growth can be prevented. Therefore, the growth rate of the ingot can be increased. Further, since it is not necessary to increase the crucible side wall in order to improve the airtightness, a large crucible volume can be secured, and the ingot can be made large in diameter.

It is a figure which shows the structure of the principal part of the crystal growth apparatus which concerns on embodiment of this invention. It is a figure which shows the structure of the raw material storage container of the crucible of the crystal growth apparatus which concerns on embodiment of this invention.

  FIG. 1 is a diagram showing a configuration of a main part of a crystal growth apparatus which is a single crystal manufacturing apparatus according to an embodiment of the present invention. The crystal growth apparatus includes a graphite crucible 10 including a raw material storage container 1 and a lid 3. The raw material storage container 1 is provided with a thin part 1a thinner than other parts at the upper part of the side wall (in the vicinity of the opening).

  Although details will be described later, when crystal growth is performed, a crystal material 2 to be grown in the raw material storage container 1 is filled, and a seed substrate 4 is installed on a pedestal 3 a provided at the center of the lid 3. When the lid 3 is attached to the opening of the raw material container 1, the seed substrate 4 faces the raw material 2 as shown in FIG. At this time, the lid 3 is fixed to the raw material storage container 1 using an adhesive 5. The crucible 10 is covered with the heat insulating material 6 so that the temperature distribution in the overheated raw material 2 is uniform.

  In this embodiment, an example is shown in which a single crystal of silicon carbide (SiC) is grown using the growth apparatus of FIG.

FIG. 2 is a diagram showing the structure of the raw material storage container 1 used in the present embodiment. In the present embodiment, the outer diameter φ1 of the raw material storage container 1 is 116 mm, the inner diameter φ2 of the portion (bottom portion) other than the thin portion 1a is 92 mm, and the inner diameter of the portion (upper portion) provided with the thin portion 1a is 105 mm. That is, on the side wall of the raw material storage container 1, the thickness W of the thin portion 1a is 5.5 mm, and the thickness of the other portions is 12 mm. The height L1 of the raw material storage container 1 was 145 mm, and the height (height from the bottom in the raw material storage container 1) L2 of the position where the thin portion 1a was provided was 100 mm. As the graphite constituting the raw material storage container 1 and the lid 3, two types having a density of 1.75 g / cm ³ and 1.82 g / cm ³ were used. However, the dimensions of the raw material storage container 1 and the density of graphite are not limited to those shown above, and may be appropriately changed within a range in which the effects of the present invention can be obtained.

  The adhesive 5 may be any adhesive as long as it fixes the lid 3 to the raw material storage container 1 and can fill the gap between the lid 3 and the raw material storage container 1. In addition, it is necessary to have resistance to etching by a gas (raw material gas) in which the raw material 2 is sublimated.

  In the crystal growth of SiC, the crucible 10 is heated to a high temperature of 2000 to 2500 ° C. Therefore, in the present embodiment, a carbon adhesive is used as the adhesive 5 that can withstand it. In this specification, “carbon adhesive” is defined as an adhesive containing 20% or more of carbon (for example, carbon black) as a filler in a resin component such as phenol or novolac.

  The cured carbon adhesive has excellent resistance to etching with SiC source gas, and even if the surface is etched, carbon does not become an impurity when growing a SiC single crystal. Therefore, the carbon adhesive is particularly suitable as the adhesive 5 used for SiC crystal growth. Since the adhesive 5 is easily etched when it is too thick, the thickness is preferably 100 μm or less as long as sufficient adhesive force can be obtained.

  Hereinafter, a method for manufacturing a SiC single crystal according to the present embodiment will be described.

  First, the SiC raw material 2 is stored in the raw material storage container 1 of the crucible 10, and the seed substrate 4 is fixed to the base 3 a of the lid 3. In this embodiment, an SiC (4H—SiC) seed substrate 4 having a 4H type polytype is used. Then, in order to fill the gap between the raw material storage container 1 and the lid 3 with the seed substrate 4, an adhesive 5 is applied to the outer edge of the lid 3 (the part that contacts the raw material storage container 1), and the lid 3 is attached to the raw material storage container 1. And the adhesive 5 is cured.

The hardening process of the adhesive 5 which is a carbon adhesive was performed by the heat treatment of the following procedure. First, the temperature is raised from room temperature to 80 ° C. over 60 minutes and held at 80 ° C. for 360 minutes. Subsequently, the temperature is raised from 80 ° C. to 120 ° C. over 80 minutes and held at 120 ° C. for 360 minutes. Further, the temperature is raised from 120 ° C. to 200 ° C. over 360 minutes, and finally, 200 ° C. is maintained for 60 minutes. This heat treatment was performed in the atmosphere (N ₂ , O ₂ atmosphere) using a thermostatic bath.

After the adhesive 5 is cured, the crucible 10 is covered with a heat insulating material 6 and placed in a furnace (growth furnace) of a crystal growth apparatus, and the inside of the growth furnace is evacuated (exhaust). The graphite constituting the crucible 10 has fine holes, and the thin part 1a of the raw material container 1 has holes that penetrate the side walls. Therefore, when the inside of the growth furnace is evacuated, the air (N ₂ , O ₂ ) in the crucible 10 passes through the holes of the thin portion 1a, and the crucible 10 is also evacuated. The vacuuming time was 12 hours.

  After evacuating the growth furnace, the atmosphere in the growth furnace is replaced with high-purity argon gas. At this time, the argon gas passes through the holes of the thin portion 1a of the raw material storage container 1, and the inside of the crucible 10 is also in an argon gas atmosphere.

  In this argon gas atmosphere (600 Torr), the crucible 10 is heated using heating means such as an induction coil (not shown), and the temperature of the SiC raw material 2 is set to a temperature at which silicon carbide sublimates (2000 to 2500 ° C.). On the other hand, the temperature of the lid 3 to which the seed substrate 4 is attached is set lower than the temperature of the SiC raw material 2. When the argon atmosphere in the growth furnace is reduced in this state, the argon atmosphere in the crucible 10 is also reduced, so that the gas obtained by sublimation of the SiC raw material 2 reaches the seed substrate 4, and the SiC single substance is formed on the seed substrate 4 surface. Crystal ingot grows.

  According to the method for producing a SiC single crystal according to the present embodiment, since the gap between the raw material storage container 1 and the lid 3 of the crucible 10 is closed by the adhesive 5, the source gas leaks from the gap. The single crystal can be grown at high speed.

Specifically, by setting the bottom temperature of the raw material storage container 1 to 2260 ° C., the top temperature of the lid 3 to 2140 ° C., and the argon atmosphere pressure to 2.8 Torr, the growth rate is 1.53 mm / h and the height is 69 mm. An ingot was obtained. Further, after the crystal growth, the surface of the cured adhesive 5 was observed, but almost no trace of etching was observed. Also, good results were obtained in the same manner when the density of the graphite constituting the raw material container 1 was 1.75 g / cm ³ and 1.82 g / cm ³ .

  For comparison, the inventor also performed SiC crystal growth under the same conditions as described above without fixing the raw material storage container 1 and the lid 3 with an adhesive. In that case, the source gas leaks from the gap between the source container 1 and the lid 3, and SiC accumulates on the heat insulating material 6 outside the crucible 10 and the inner wall of the growth furnace, and does not grow on the surface of the seed substrate 4. .

  Further, when the inventor did not fix the raw material storage container 1 and the lid 3 with an adhesive, the growth rate was changed by changing the argon atmosphere pressure or the crucible temperature, and the growth rate of the ingot was 0.5 mm / h. To the extent, leakage of raw material gas was not a problem. However, if the argon atmosphere is further depressurized to grow at an ingot growth rate of 0.5 mm / h or more, the raw material gas leakage from the gap between the raw material container 1 and the lid 3 increases, and a desired growth rate is obtained. I can't.

  On the other hand, when the raw material storage container 1 and the lid 3 are fixed with the adhesive 5 as in the present embodiment, the raw material gas does not leak from the gap between the raw material storage container 1 and the lid 3, so that the growth rate is 1 mm / Ingots can be grown at h or higher. In addition, since the pressure of the source gas in the vicinity of the seed substrate 4 is stabilized, the growth rate of the ingot is also stabilized and the crystallinity of the ingot is improved. Furthermore, it is possible to greatly suppress the deterioration of the heat insulating material 6 due to the leakage of the raw material gas, thereby contributing to the reduction of the wafer manufacturing cost. Further, since the side wall of the crucible is not thickened to increase the airtightness as in the conventional case, the crucible 10 can have a large volume and can be used for manufacturing a large-diameter ingot.

  As described above, in the present embodiment, the gap between the raw material storage container 1 and the lid 3 is filled with an adhesive, and vacuuming in the crucible 10 cannot be performed through the gap. This is carried out through a hole in the thin part 1a on the side wall of the raw material container 1. Compared to the case where the raw material storage container 1 and the lid 3 are not bonded together, the inside of the crucible 10 is hard to be evacuated, so a sufficient time for evacuation should be secured. The evacuation time is preferably 12 hours or more. The longer the evacuation time, the better the evacuation can be performed, but it should be noted that if it is too long, the production efficiency of the wafer will be reduced.

  In order to evacuate the crucible 10 efficiently, the thickness of the thin portion 1a may be reduced. This is because if the thin portion 1a is thinned, the number of holes passing through the thin portion 1a increases. The optimum thickness of the thin portion 1a is preferably 10 mm or less, more preferably 5 mm or less, although it depends on the heat insulating material 6 and the structure of the growth furnace.

  However, since the inner wall of the crucible 10 is etched by the source gas, if the thin portion 1a is too thin, a hole is formed in the middle of crystal growth, and the source gas leaks out of the crucible 10 from there. For this reason, the thickness of the thin part 1a needs to be determined according to the time required for crystal growth and the length of the ingot to be grown. That is, when the ingot is grown for a long time, the crystal growth takes a long time. Therefore, the thin portion 1a is set to be thick so that it can withstand etching during that time. According to the verification by the present inventor, an ingot having a height of 70 mm could be grown using the crucible 10 having the thin part 1a having a thickness of 5 mm. In addition, when the thin part 1a is comparatively thick, since it becomes difficult to evacuate the raw material storage container 1, it is preferable to set a longer evacuation time to compensate for this.

  In the vicinity of the SiC raw material 2 (that is, in the vicinity of the bottom in the raw material storage container 1), the inner wall of the raw material storage container 1 is relatively intensely etched by the raw material gas. It is. That is, as shown in FIG. 2, the thin portion 1 a is preferably provided in the vicinity of the opening of the raw material storage container 1.

In order to increase the etching resistance of the inner wall of the crucible 10, it is also effective to increase the density of graphite (g / cm ³ ) constituting the raw material storage container 1. However, if the density of graphite is high, the number of vacancies will decrease and it will be difficult to evacuate. Therefore, it is preferable to set the thin part 1a thinner or set the evacuation time longer.

  In addition, when the crucible 10 is overheated during crystal growth, in order to prevent the crucible 10 from cracking due to the stress due to the difference in thermal expansion coefficient, the material of the raw material storage container 1 and the lid 3 should have the same thermal expansion coefficient. It is preferable to use it. Furthermore, in order to prevent the occurrence of defects such as cracks in the ingot due to the stress due to the difference in thermal expansion coefficient, it is preferable that the material of the lid 3 has the same thermal expansion coefficient as the seed substrate 4 attached thereto. Since the thermal expansion coefficient of the seed substrate 4 varies depending on the crystal axis direction, the material (thermal expansion coefficient) of the lid 3 and the raw material storage container 1 may be selected according to the plane orientation of the seed substrate 4.

  Although the 4H—SiC seed substrate 4 is used in the present embodiment, the present invention is also applicable to other polytype seed substrates 4 such as 6H—SiC. Further, the present invention is not limited to SiC crystal growth but can be applied to AlN or GaN crystal growth, for example.

  DESCRIPTION OF SYMBOLS 1 Raw material storage container, 1a Thin part, 2 Raw material, 3 Cover, 3a pedestal, 4 type | mold board | substrate, 5 Adhesive, 6 Heat insulating material, 10 Crucible.

Claims (6)

Placing the seed substrate and the raw material in the crucible, and bonding the raw material storage container and the lid of the crucible using an adhesive;
And a step of exhausting the inside of the crucible through the side wall of the crucible. The method for producing a single crystal according to claim 1, wherein the crucible raw material storage container is made of graphite, and has a thin wall portion having a thickness of 10 mm or less on a side wall. The method for producing a single crystal according to claim 1, wherein the adhesive is a carbon adhesive. A raw material storage container made of graphite having a thin wall portion having a thickness of 10 mm or less on the side wall, and a crucible having a lid attached to an opening of the raw material storage container;
An apparatus for producing a single crystal, comprising: an adhesive that fixes the lid to the raw material storage container. The single crystal manufacturing apparatus according to claim 4, wherein the thin portion is provided in the vicinity of the opening in the side wall. The single crystal manufacturing apparatus according to claim 4, wherein the adhesive is a carbon adhesive.

Images