WO2014148158A1 - サファイア単結晶育成用坩堝およびサファイア単結晶育成方法 - Google Patents
サファイア単結晶育成用坩堝およびサファイア単結晶育成方法 Download PDFInfo
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- WO2014148158A1 WO2014148158A1 PCT/JP2014/053309 JP2014053309W WO2014148158A1 WO 2014148158 A1 WO2014148158 A1 WO 2014148158A1 JP 2014053309 W JP2014053309 W JP 2014053309W WO 2014148158 A1 WO2014148158 A1 WO 2014148158A1
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- crucible
- single crystal
- sapphire single
- tungsten
- growing
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- C—CHEMISTRY; METALLURGY
- C30—CRYSTAL GROWTH
- C30B—SINGLE-CRYSTAL GROWTH; UNIDIRECTIONAL SOLIDIFICATION OF EUTECTIC MATERIAL OR UNIDIRECTIONAL DEMIXING OF EUTECTOID MATERIAL; REFINING BY ZONE-MELTING OF MATERIAL; PRODUCTION OF A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; SINGLE CRYSTALS OR HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; AFTER-TREATMENT OF SINGLE CRYSTALS OR A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; APPARATUS THEREFOR
- C30B29/00—Single crystals or homogeneous polycrystalline material with defined structure characterised by the material or by their shape
- C30B29/10—Inorganic compounds or compositions
- C30B29/16—Oxides
- C30B29/20—Aluminium oxides
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C1/00—Making non-ferrous alloys
- C22C1/04—Making non-ferrous alloys by powder metallurgy
- C22C1/045—Alloys based on refractory metals
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C27/00—Alloys based on rhenium or a refractory metal not mentioned in groups C22C14/00 or C22C16/00
- C22C27/04—Alloys based on tungsten or molybdenum
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- C—CHEMISTRY; METALLURGY
- C30—CRYSTAL GROWTH
- C30B—SINGLE-CRYSTAL GROWTH; UNIDIRECTIONAL SOLIDIFICATION OF EUTECTIC MATERIAL OR UNIDIRECTIONAL DEMIXING OF EUTECTOID MATERIAL; REFINING BY ZONE-MELTING OF MATERIAL; PRODUCTION OF A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; SINGLE CRYSTALS OR HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; AFTER-TREATMENT OF SINGLE CRYSTALS OR A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; APPARATUS THEREFOR
- C30B11/00—Single-crystal growth by normal freezing or freezing under temperature gradient, e.g. Bridgman-Stockbarger method
- C30B11/002—Crucibles or containers for supporting the melt
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- C—CHEMISTRY; METALLURGY
- C30—CRYSTAL GROWTH
- C30B—SINGLE-CRYSTAL GROWTH; UNIDIRECTIONAL SOLIDIFICATION OF EUTECTIC MATERIAL OR UNIDIRECTIONAL DEMIXING OF EUTECTOID MATERIAL; REFINING BY ZONE-MELTING OF MATERIAL; PRODUCTION OF A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; SINGLE CRYSTALS OR HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; AFTER-TREATMENT OF SINGLE CRYSTALS OR A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; APPARATUS THEREFOR
- C30B15/00—Single-crystal growth by pulling from a melt, e.g. Czochralski method
- C30B15/10—Crucibles or containers for supporting the melt
Definitions
- the present invention relates to a crucible for growing a sapphire single crystal and a method for growing a sapphire single crystal.
- Sapphire single crystal is a material excellent in transmittance and mechanical properties, and is widely used, for example, as an optical material, and has been increasingly used as an epitaxial substrate for GaN growth.
- This sapphire single crystal has been conventionally used by using a pulling method (also called Czochralski method, CZ method, etc.) EFG method (Edge-defined.fFilm-fed Growth) method or Kyropoulos method using a crucible made of iridium, tungsten, molybdenum or the like. It was obtained by growing from a seed crystal.
- a pulling method also called Czochralski method, CZ method, etc.
- EFG method Edge-defined.fFilm-fed Growth
- Kyropoulos method using a crucible made of iridium, tungsten, molybdenum or the like. It was obtained by growing from a seed crystal.
- sapphire single crystals have become larger in order to improve the yield of sapphire, and sizes that are difficult to grow using conventional sapphire single crystal manufacturing methods, such as the pulling method described above, have appeared.
- Non-patent Document 1 HEM (Heat Exchange Method) method has come to be used as a growth method that can cope with the increase in size of such sapphire single crystals.
- molybdenum is widely used as a crucible material because it is less expensive than iridium and tungsten (Patent Document 1).
- the crucible described in the above literature requires the sapphire to be destroyed after the sapphire is grown, and it is not assumed that the crucible will be reused. Therefore, it is necessary to discard the crucible every time sapphire is grown, and it is difficult to reduce the cost of sapphire growth.
- the present invention has been made in view of the above problems, and an object of the present invention is to provide a crucible for growing a sapphire single crystal having a structure capable of reducing the cost of growing sapphire as compared with the prior art.
- the present inventor has made the crucible reusable and the crucible inner peripheral surface that is in contact with sapphire, particularly for the conditions necessary for the crucible that can suppress the mixing of the crucible components into the melted sapphire. The shape of was examined again.
- the present invention is It came to do.
- the first aspect of the present invention is composed of tungsten and unavoidable impurities, or composed of tungsten-molybdenum alloy containing 3 mass% to 60 mass% of tungsten and unavoidable impurities, the cylindrical portion, A crucible for growing a sapphire single crystal, having a bottom provided so as to be connected to a cylindrical portion, and having at least an inner circumference having a surface roughness with a maximum height Ry of 7 ⁇ m or less and an arithmetic average roughness Ra of 1 ⁇ m or less.
- a second aspect of the present invention is a sapphire single crystal growth method using the sapphire single crystal growth crucible described in the first aspect.
- the present invention it is possible to provide a crucible for growing a sapphire single crystal having a structure capable of reducing the cost of sapphire growth compared to the conventional case.
- a crucible 1 for growing a sapphire single crystal a crucible for growing a single crystal by the HEM method is illustrated.
- a crucible 1 for growing a sapphire single crystal has a cylindrical portion 3 and a bottom portion 7 having a circular truncated cone shape that is continuous with the cylindrical portion 3, and is further provided with a flange 9 at the opening. ing.
- a material constituting the sapphire single crystal growth crucible 1 As a material constituting the sapphire single crystal growth crucible 1, a material that can withstand the melting temperature of sapphire (alumina), has excellent high-temperature strength, and has a temperature change of thermal expansion coefficient close to that of sapphire (or the thermal expansion coefficient itself is as small as possible). Thing) is desirable.
- Such a material is preferably tungsten. That is, tungsten has the highest melting point of 3400 ° C. among metals and has high high-temperature strength.
- an alloy containing molybdenum in an amount of 3% by mass to 30% by mass. This is because if the tungsten content is less than 3 mass, the effect of containing tungsten cannot be obtained, and if it exceeds 30 mass%, the characteristics, particularly the workability, are very similar to tungsten. This is because the significance of the target is lowered. In addition, the alloying of the tungsten component and the molybdenum component is insufficient during sintering and unalloyed particles are scattered, and the crystal grain size of the sintered body is too small, so that the formability is lowered.
- the purity of the above material is preferably 99.9% by mass or more, and the remainder is inevitable impurities. This is because erosion of the molten sapphire on the inner surface of the crucible is unavoidable, but a high-purity material of this level requires very little impurity contamination, and problems such as coloring can be avoided.
- TMIAS tungsten-molybdenum industry association standard
- the cylindrical portion 3 has an inner diameter (opening portion diameter D) corresponding to the diameter of the sapphire single crystal wafer to be grown.
- the diameter of the wafer include a 4-inch wafer and a 6-inch wafer. In order to cope with these wafer sizes, it is desirable that the diameter is at least 200 mm.
- there are openings having diameters corresponding to these diameters 200 mm or more and 660 mm or less).
- the bottom 7 is a truncated cone-shaped bottom here. This is a characteristic shape of a crucible used in the HEM method, and can be seamlessly formed by a spatula drawing method as will be described later. However, when using a growth method other than the HEM method, the bottom 7 does not necessarily have a truncated cone shape.
- the cylindrical portion 3 and the flat bottom 7 have a thickness of 1 mm or more and 5 mm or less, and the thickness is reduced from the bottom portion 7 toward the cylindrical portion 3 (the opening thereof). This is because, in the case of a spatula stop, it is necessary to make the shape thinner toward the opening, considering the formation of the flange 9 described later.
- the ridge 9 is a holding part when the crucible 1 for growing a sapphire single crystal is incorporated into a growth apparatus, and is preferably provided.
- ⁇ 9 can be formed without a seam from the cylindrical portion 3 by means of a spatula as will be described later.
- the surface shape of the sapphire single crystal growth crucible 1 is desirably a shape that can suppress the mixing of the crucible components into the melted sapphire and can be reused. Specifically, it is Ry 7 ⁇ m or less, Ra 1 ⁇ m or less. It is desirable.
- the surface roughness within the above range, the surface of the sapphire crystal after growth becomes smooth and can be seen through to the inside, so that the defect confirmation becomes easy and an effect of providing a high-quality crystal is also produced.
- the hardness of the material constituting the crucible 1 for sapphire single crystal growth is preferably Hv 420 or more and 500 or less in terms of Vickers hardness (measurement load 10 kg).
- H / D which is a ratio of the crucible height (H) and the opening diameter (D)
- H / D which is a ratio of the crucible height (H) and the opening diameter (D)
- the aspect ratio of the crystal grains of the material constituting the crucible 1 for sapphire single crystal growth is desirably 5 or less. This is because when the aspect ratio exceeds 5, the anisotropy of the metal structure becomes remarkable, and as a result, the difference in the crystal grain boundary strength becomes large. Because there is.
- the aspect ratio here means a measurement result by a grain boundary intercept method in a metal structure view of 500 ⁇ m ⁇ 500 ⁇ m.
- the method for producing the sapphire single crystal growth crucible 1 is not particularly limited as long as the sapphire single crystal growth crucible having the above-mentioned shape and composition can be produced. Examples thereof are as follows. be able to. Hereinafter, an example of the manufacturing method will be described with reference to FIG.
- raw materials for the crucible are prepared. Specifically, when pure tungsten is used as the material for the sapphire single crystal growth crucible 1, the raw material is a tungsten powder having an Fsss (Fisher Sub-Sieve Sizer) particle size of 2 to 3 ⁇ m and a purity of 99.9% by mass or more. It is desirable to use it.
- Fsss Fisher Sub-Sieve Sizer
- tungsten-molybdenum alloy when used, a tungsten powder having a Fsss particle size of 2 to 3 ⁇ m and a purity of 99.9% by mass or more as a raw material for the crucible, and a molybdenum having an Fsss particle size of 4 to 5 ⁇ m and a purity of 99.9% by mass or more.
- the powder is weighed at the desired alloy weight ratio.
- Typical alloy types are 90 mass% Mo-10 mass% W (abbreviated as 9 MW), 70 mass% Mo-30 mass% W (7 MW), 50 mass% Mo-50 mass% W (5 MW).
- the tungsten content is desirably 3% by mass or more and 60% by mass or less.
- the raw material powder is filled into a rubber in the shape of a desired molded body, the open port is sealed with a stopper, and then the rubber is evacuated. After the evacuation is completed, the rubber is loaded into a CIP (Cold Isostatic Pressing) apparatus, and molding is performed by applying water pressure according to a predetermined procedure. After depressurization, the rubber is taken out from the CIP device to wipe off moisture on the surface, the stopper is opened, and the powder compact is taken out.
- CIP Cold Isostatic Pressing
- the powder compact is sintered at 2000 ° C. or higher for 20 hours in a batch type or continuous hydrogen sintering furnace. A higher temperature and longer sintering treatment is preferable for improving the sintered density.
- the sintered material is, for example, a plate-like sintered body having a thickness of approximately 30 mm, a width of 300 mm, a length of 300 mm, and a weight of 28 kg.
- the theoretical density ratio of the obtained sintered body is 95% or more. This is because if the theoretical density ratio is 95% or more, the densification of the powder particles proceeds, or the high-density strength is improved by high densification due to plastic deformation, and the erosion resistance is further improved.
- the theoretical density ratio here means a value obtained by measurement by the Archimedes method.
- the above-described hot-rolled material has an oxidized surface and is covered with a light yellow or dark oxide. Therefore, after the surface oxide is reduced at a temperature of 850 ° C. in a hydrogen reduction furnace, this is dissolved and removed with a strong acid to form the surface of the metal background.
- the rolled sheet is cut by an appropriate cutting method such as discharge wire cutting or plasma cutting to obtain a disk-shaped blank for drawing.
- spatula drawing is performed. Specifically, first, a mold is set on a spatula squeezing device, a blank material is pressed against this, and the blank material is fixed with a push bar. Next, the mold, blank material, and push rod are rotated together.
- the blank material can be finished in a crucible shape by an ordinary spatula drawing method in which the blank material is heated in the atmosphere to the level of red heat and the roller (scalar) is fed out to follow the mold while being shaped into a crucible shape.
- the crucible 1 for growing sapphire single crystal is composed of tungsten and inevitable impurities, or a tungsten-molybdenum alloy and inevitable impurities containing 3 to 60% by mass of tungsten. And has a cylindrical portion and a bottom portion that is continuous with the cylindrical portion, and at least the inner circumference has a surface roughness with a maximum height Ry of 7 ⁇ m or less and an arithmetic average roughness Ra of 1 ⁇ m or less.
- the crucible 1 for growing sapphire single crystal has a structure capable of reducing the cost of growing sapphire than before.
- Example 1 An attempt was made to produce a crucible 1 for growing a sapphire single crystal using a 7 MW alloy and alloys of various compositions. The specific procedure is as follows.
- this mixed powder was filled into a flat plate molding rubber, and after sealing the rubber with a die, the rubber was evacuated for about 30 minutes to confirm that there was no air leakage.
- the rubber surface was washed with water to remove the adhering powders, and then inserted into a CIP apparatus and subjected to hydrostatic pressure. After holding at a pressure of 2 ton / cm 2 for about 10 minutes, the pressure was released and the CIP molding operation was completed. Next, the rubber was taken out from the CIP apparatus, the surface moisture was wiped off and removed, and then the base was removed and opened. Thereafter, the tungsten-molybdenum mixed powder molded body was taken out from the rubber, and burrs and protrusions were removed by sanding or the like.
- this molded body was inserted into a hydrogen sintering furnace and sintered at 2000 ° C. for 20 hours.
- the specific gravity was about 11.3 (theoretical density ratio was about 95%), the thickness was 30 mm, the length was 300 mm, and the width was 290 mm.
- 7MW alloy (theoretical density: 11.88 g / cm 3 ) was obtained.
- the obtained sintered material was rolled. Specifically, rolling was performed using a four-high rolling mill for hot rolling. First, the size of the blank material required for molding into a crucible having a diameter of 300 mm and a height of 300 mm was set to a thickness of 5 mm and a diameter of 550 mm, and rolling was performed based on the following rolling schedule.
- a sintered body heated to 1400 ° C. in a hydrogen furnace is stripped to about 600 mm and hot-rolled, then the rolling direction is changed, and finally the heating temperature is lowered by heating at 800 ° C. as appropriate.
- Direction rolling was repeated to obtain a hot-rolled alloy plate having a thickness of approximately 5 mm, a width of 600 mm, and a length of 800 mm.
- the reason for rolling while lowering the heating temperature is to prevent the recrystallization phenomenon that occurs during the rolling process.
- This alloy plate whose surface is covered with a light yellow oxide is inserted into a hydrogen annealing furnace for annealing treatment that is maintained at 930 ° C., heated and held for about 30 minutes, and then moved into a hydrogen atmosphere cooling zone to reach room temperature. It was cooled and taken out of the furnace. After this treatment, the reduced surface deposits were dissolved and removed in strong acid, washed with water and dried to obtain an alloy plate with a flat alloy background.
- the 9MW alloy sheet was rolled in the same procedure to obtain a rolled sheet having a theoretical density ratio of 99.9% by mass (specific gravity 10.6), purity of 99.9% by mass, Vickers hardness Hv440, and aspect ratio of 5. .
- a 5 MW alloy plate was obtained as a rolled plate having a theoretical density ratio of 98.9% (specific gravity 13.2), a purity of 99.9% by mass, a Vickers hardness of Hv500, and an aspect ratio of 4.4.
- Table 1 shows the properties of the obtained rolled sheet.
- a spatula drawing process was performed on the obtained rolled plate.
- a blank material to be subjected to a spatula drawing process having a thickness of 5 mm and a diameter of 550 mm was cut out from the rolled plate using a discharge wire cutting machine.
- This blank was applied to the portion corresponding to the bottom of the drawing-type crucible attached to the spatula drawing machine, and the blank was fixed with a push rod while leaving the center of rotation.
- the blank material was heated in a red hot state of 600 ° C. to 700 ° C. with a burner while simultaneously rotating the drawing die / blank material / push bar integrated in series. In this state, the roller (spar) was drawn out and formed into a crucible shape following the drawing die. At this time, the crucible whose thickness is continuously reduced from the bottom part to the opening part can be finished by increasing the number of times of ironing compared with the normal spatula drawing procedure.
- the phenomenon caused by the characteristics and quality of the blank material is caused by intragranular cracks that appear in the process of following the outer corner R of the drawing die that hits the bottom of the crucible, and opening near the end of processing. It is delamination and grain boundary cracking appearing in the part.
- the causes of these are mainly low blank material strength (hardness as an alternative characteristic) and crystal grain shape (substitute with aspect ratio). However, if the material strength is too high, the deformation does not proceed.
- the material strength is high and can withstand deformation if it is a fine particle of about 10 ⁇ m to 50 ⁇ m, but it is resistant to deformation if it is a coarse particle of about 300 ⁇ m to 500 ⁇ m. It will not break.
- Table 2 shows the relationship between the spatula drawing ability and the aspect ratio.
- a crucible having an inner diameter of 300 mm and a height of 300 mm obtained by a spatula squeezing is inserted into a hydrogen annealing furnace for annealing treatment, the surface oxide film is reduced, and then the surface deposits are dissolved and removed with strong acid. It carried out in the liquid and obtained the crucible of the alloy ingot.
- the obtained crucible was placed in a wet blasting apparatus, and surface treatment was performed by spraying alumina abrasive grains (particle size 100 mesh) on the inner and outer surfaces. Thereafter, the abrasive grains remaining on the crucible surface were removed with jet water and dried.
- a negative electrode material is placed in the electrolyte solution inside the crucible, electric connection is made so that the crucible becomes a positive electrode, and voltage is applied to perform electropolishing. Started. After processing for about 1 hour, the connection was removed, the electrode was removed, the chemical solution was discharged, and the crucible was taken out from the liquid bath. Thereafter, the crucible was placed in a neutralization chemical solution tank, neutralized with the adhering chemical solution, and then washed with water, washed with hot water, and dried. The crucible was completed by the above processing.
- the obtained crucible was assembled in a sapphire growing apparatus, sapphire was dissolved, held at 2150 degrees for 50 hours, sapphire was taken out, and the presence or absence of coloring on sapphire was observed by visual observation.
- Table 3 shows a summary of changes in surface roughness before and after electropolishing and the effect of surface roughness on poor sapphire coloring.
- the obtained sapphire ingot was not colored and was a normal sapphire ingot.
- Example 2 As described above, in Example 1, drawing molding of a 70 mass% Mo-30 mass% W alloy (theoretical density: 11.88 g / cm 3 , 7 MW) having a tungsten content of 30 mass% is the limit. Alloys with higher tungsten content cracked during spatula drawing. On the other hand, the sample using pure tungsten did not crack.
- Example 2 instead of producing an alloy using metal powders as raw materials, an alloy was produced using alloyed metal powders as raw materials, and thought and trial were repeated. As a result, a sintered body in which both the causes A and B were eliminated could be made, and a blank material suitable for drawing was obtained by repeating plastic working by hot rolling and warm rolling.
- the mixture was mixed with a V-shaped mixer, and 27 kg was taken and filled in a flat plate molding rubber, inserted into a CIP apparatus, and hydrostatic pressure was applied to form a molded body.
- This molded body was subjected to a hydrogen sintering process at 2200 ° C. for 30 hours to obtain a sintered alloy sintered material for rolling having a specific gravity of about 13.5 (theoretical density ratio of about 95%), a thickness of 30 mm, a width of 300 mm, and a length of 220 mm. It was.
- the sintered material was rolled. Specifically, the rolling was performed using a hot four-high rolling mill, the sintered body was heated to 1500 ° C. in a hydrogen furnace, and rolling was performed up to a plate width of about 600 mm. Thereafter, the rolling direction is changed, and the unidirectional rolling is repeated by heating at 800 ° C. while appropriately lowering the heating temperature to obtain a hot rolled finish alloy plate having a thickness of approximately 5 mm, a width of 600 mm, and a length of 800 mm. It was. The reason for rolling while lowering the heating temperature is to prevent the recrystallization phenomenon that occurs during the rolling process.
- This alloy plate whose surface is covered with a light yellow oxide is inserted into a hydrogen annealing furnace for annealing that is maintained at 1030 ° C., held for about 30 minutes, then moved into a hydrogen atmosphere cooling zone and cooled to room temperature. And taken out of the furnace. After this treatment, the reduced surface deposits were dissolved and removed in strong alkali, washed with water and dried to obtain an alloy plate with a flat alloy background.
- Tungsten-molybdenum alloy plates having the following different tungsten contents were produced in the same process.
- Example 2 advanced pre-alloying until the raw material powder stage. Furthermore, since the alloy powder particles are fine, the sintering temperature was increased and the sintering time was extended as a method for increasing the sintered particle size. Also, the rolling rate during hot rolling is increased, the heating temperature is increased (about 100 ° C higher than before), and the annealing temperature is also set and processed to improve the plastic workability and tensile strength. It was.
- Example 1 Other conditions such as CIP molding, warm rolling, blank material cutting, etc. are the same as in Example 1. However, when the tungsten content in the tungsten-molybdenum alloy exceeds 30% by mass, the characteristics approximate to those of tungsten. Come. Therefore, the following three points were performed following the tungsten plate material processing conditions.
- Rolling heating temperature 1400 ° C. in Example 1, but 1500 ° C. in Example 2 (By increasing the heating temperature, the deformation resistance of the sintered body and the material during rolling plastic working is reduced. To prevent the occurrence of processing defects).
- Example 2 Annealing after hot rolling: In Example 1, it was 30 minutes at 930 ° C., but in Example 2, it was 30 minutes at 1030 ° C. (By increasing the tungsten content, work strain was released. Because the temperature that can be increased also).
- Example 2 Oxide dissolution / removal treatment: In Example 1, it was carried out in strong acid, but in Example 2, it was carried out in strong alkali (because the alkaline solution is highly effective).
- Table 4 and Table 5 summarize the results of molding blank materials (thickness 5 mm ⁇ diameter 550 mm) cut into a container shape into a diameter of 300 mm and a height of 300 mm.
- the alloy having a tungsten content of 60% by mass or less could be molded normally, but the 70% by mass tungsten-containing alloy was cracked.
- Table 6 shows the results of investigating the influence of surface roughness on the sapphire coloring defects after annealing, blasting, and electropolishing as usual.
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Abstract
Description
サファイア単結晶育成用坩堝1を構成する材料としては、サファイア(アルミナ)の溶融温度に耐え高温強度に優れ、かつ、熱膨張率の温度変化がサファイアに近いもの(あるいは熱膨張率自体が極力小さいもの)が望ましい。
円筒部3は、育成するサファイア単結晶のウェハの直径に対応した内径(開口部径D)を有する。ウェハの直径としては4インチウエハ、6インチウエハが挙げられるが、これらのウエハサイズに対応するためには少なくとも200mm径であるのが望ましい。また、将来的には直径400mm坩堝、更に直径660mm坩堝の需要が生じると予測されているため、これらの直径に対応した開口部径(200mm以上、660mm以下)を有するものも想定される。
鍔9はサファイア単結晶育成用坩堝1を育成装置に組み込む際の保持部であり、設けられるのが望ましい。
サファイア単結晶育成用坩堝1の表面形状は、溶解したサファイアへの坩堝成分の混入を抑制可能で、かつ坩堝を再利用可能な形状であるのが望ましく、具体的にはRy7μm以下、Ra1μm以下であるのが望ましい。
サファイア単結晶育成用坩堝1を構成する材料の硬度は、ビッカース硬度(測定荷重10Kg)でHv420以上、500以下であるのが望ましい。
本発明のサファイア単結晶育成用坩堝1において、坩堝高さ(H)と開口部径(D)の比率であるH/Dは1.35以下であるのが望ましい。これは、ヘラ絞りでは2程度も可能ではあるが、厚さ不等の坩堝成形の場合、1.35が成型限界であるためである。
サファイア単結晶育成用坩堝1を構成する材料の結晶粒のアスペクト比は、5以下であるのが望ましい。これは、アスペクト比が5を超えると金属組織の異方性が顕著となり、その結果、結晶粒界強度にも差が大きくなり、ヘラ絞りを行うと、粒界に亀裂を生じて割れるおそれがあるためである。
サファイア単結晶育成用坩堝1の製造方法は、上記の形状、組成を有するサファイア単結晶育成用坩堝が製造できるものであれば、特に限定されるものではないが、以下のようなものを例示することができる。
以下、図2を参照して製造方法の一例を説明する。
まず、坩堝の原料を用意する。
具体的には、サファイア単結晶育成用坩堝1の材料として、純タングステンを用いる場合は、原料はFsss(Fisher Sub-Sieve Sizer)粒度で2~3μm、純度99.9質量%以上のタングステン粉末を用いるのが望ましい。
次に、サファイア単結晶育成用坩堝1の材料として、タングステン-モリブデン合金を用いる場合、計量された2種類の粉末を適当な装置(例えば、ボールミル、V型ミキサー、ダブルコーンミキサーなど)で混合し、合金用原料粉末とする。
次に、原料粉末を所望する成形体の形状のラバー内に充填し、開放口を止め具でシールした後ラバーを真空引きする。真空引きを終えた後、ラバーをCIP(Cold Isostatic Pressing、冷間等方圧加圧、)装置内に装填し、所定の手順で水圧を掛けて成形を行う。除圧後、CIP装置内からラバーを取り出して表面の水気を拭き取り、止め具を開放し、粉末成形体を取り出す。
次に、粉末成形体をバッチ式或いは連続式水素焼結炉で、2000℃以上で20時間焼結する。より高温度、長時間の焼結処理が、焼結密度向上に好ましい。焼結素材は例えば、大略厚さ30mm、幅300mm、長さ300mm、重量28kgの板状の焼結体である。
次に、焼結体を坩堝形状に加工するため、板圧延を4段式熱間圧延機で行う。この熱間圧延による塑性加工工程において、ブランク材並びに絞り成型後の坩堝の品質を作り出す。パススケジュール(落とし率、加熱温度×時間、通し方向など)に工夫を行うことで、理論密度比98%以上、ビッカース硬度Hv420~500、アスペクト比5以下の絞り加工に好適な圧延材が得られる。
上記した熱間圧延を行った材料は表面が酸化し、薄黄色ないし浅黒い酸化物で覆われている。そのため、水素還元炉で温度850℃で表面の酸化物を還元した後、強酸によってこれを溶解除去し金属地肌の表面とする。この圧延板を放電ワイヤカット或いはプラズマ切断など適宜の切断法で切断して、円盤状の絞り加工用ブランク材を得る。
次に、ブランク材を坩堝形状に加工するため、ヘラ絞りを行う。
具体的には、まず、ヘラ絞り装置に金型をセットし、これにブランク材を押し当て、押し棒でブランク材を固定する。次に、金型、ブランク材、押し棒を一体回転させる。ブランク材を赤熱程度に大気中加熱しながら、ローラー(ヘラ)を繰り出して金型に倣わせながら、坩堝形状に成形する通常のヘラ絞り工法で坩堝形状に仕上げることができる。
先ず、S6(表面酸化物除去処理)と同様の処理によって、金属地肌の表面を出す。その後、ブラスト処理を行い、電解研磨処理の下準備を行う。切削加工仕上げでは、バイト目などの模様が残るため、ブラスト処理を行う。ブラスト処理は乾式あるいは湿式いずれの処理でも同様な効果が得られる。電解研磨処理は坩堝内面に対してのみ実施する。このブラスト処理と電解研磨処理の結果、Ry7μm以下、Ra1μm以下の表面粗さの坩堝製品が完成する。
以上がサファイア単結晶育成用坩堝1の製造方法の一例である。
7MW合金および種々の組成の合金を用いたサファイア単結晶育成用坩堝1の製造を試みた。具体的な手順は以下の通りである。
得られた圧延板の特性を表1に示す。
まず、圧延板から、放電ワイヤカット機で厚さ5mm、直径550mmのヘラ絞り加工に供するブランク材を切り出した。このブランク材をヘラ絞り加工機に取り付けた絞り型の坩堝底部に相当する部分にあてがい、回転中心を出しながら押し棒でブランク材を固定した。直列に一体化させた絞り型/ブランク材/押し棒を同時に回転させながら、ブランク材をバーナーで600℃~700℃の赤熱状態に加熱した。その状態でローラー(ヘラ)を繰り出して、絞り金型に倣わせながら坩堝形状に成形した。この際通常のヘラ絞り手順よりもしごきの回数を多くすることで、底部から開口部へと厚さが連続的に減少する坩堝に仕上げることができる。
以上のヘラ絞り性とアスペクト比の関係を表2に示す。
以上の加工により、坩堝が完成した。
上記の通り、実施例1においては、タングステン含有量が30質量%である70質量%Mo-30質量%W合金(理論密度:11.88g/cm3、7MW)の絞り成型が限界であり、これよりもタングステン含有量の多い合金はヘラ絞りの際に亀裂が生じた。一方で純タングステンを用いた試料は亀裂は生じなかった。
まず、原料としては金属粉末を用いず、三酸化タングステン粉末と二酸化モリブデン粉末を採用した(図3のS11)。ここでは40質量%Mo-60質量%W合金(理論密度:14.22g/cm3、4MW)粉末100kgの作製を例に詳述する。
(2)50質量%Mo-50質量%W合金板(5MW):理論密度比99.0%(比重13.23)、純度99.9質量%
(3)40質量%Mo-60質量%W合金板(4MW):理論密度比99.0%(比重14.08)、純度99.9質量%
(4)30質量%Mo-70質量%W合金板(3MW):理論密度比99.0%(比重15.08)、純度99.9質量%
3 :円筒部
7 :底部
9 :鍔
Claims (8)
- タングステンと不可避不純物で構成されるか、もしくはタングステンを3質量%以上、60質量%以下含むタングステン-モリブデン合金と不可避不純物で構成され、
円筒部と、前記円筒部に連なるように設けられた底部を有し、
少なくとも内周が、最大高さRyが7μm以下、算術平均粗さRaが1μm以下の表面粗さである、サファイア単結晶育成用坩堝。 - 前記底部は、前記円筒部に連なるように、つなぎ目なしで設けられている、請求項1に記載のサファイア単結晶育成用坩堝。
- 高さ/開口部径の比率が1.35以下であり、底部から開口部への厚さが5mm~1mmであり、かつ底部から開口部にかけて、厚さが薄くなるように形成されている、請求項1または2に記載のサファイア単結晶育成用坩堝。
- 硬度がビッカース硬度で420~500、アスペクト比5以下の金属組織を有し、理論密度比98%以上、純度99.9質量%以上である、請求項1~3のいずれか一項に記載のサファイア単結晶育成用坩堝。
- 開口部径が200mm以上である、請求項1~4のいずれか一項に記載のサファイア単結晶育成用坩堝。
- 前記底部は、円錐台形状である、請求項1~5のいずれか一項に記載のサファイア単結晶育成用坩堝。
- ヘラ絞り工法によって成型され、前記開口部に設けられた鍔を有する、請求項1~6のいずれか一項に記載のサファイア単結晶育成用坩堝。
- 請求項1~7のいずれか一項に記載のサファイア単結晶育成用坩堝を用いたサファイア単結晶育成方法。
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