Method of producing single crystal of high-pressure phase material

Abstract: Disclosed herein is a method of producing a single crystal of a high-pressure phase material having a pressure region of at least 1000 atm. in an equilibrium state at 25°C. This method is characterized in that a plurality of single-crystalline plates (3, 16) of the high-pressure phase material, being so formed that crystal orientations thereof are substantially equal to each other, are arranged so that single major surfaces (3a) thereof are substantially flush with each other and crystal orientations thereof are substantially along the same direction to define a substrate (1) for serving as a core for vapor-phase growth, and a single-crystalline layer (4) of the high-pressure phase material is formed on the substrate (2) by a vapor-phase synthesis process. According to the inventive method, a single-crystalline layer (4) of the high-pressure phase material is integrally formed on the major surfaces (3a) of the plurality of single-crystalline plates (3, 16) of the high-pressure phase material whose major surfaces (3a) are substantially flush with each other. Thus, it is possible to easily obtain a homogeneous and large-sized single crystal of the high-pressure phase material having a large area.

Description: BACKGROUND OF THE INVENTION Field of the Invention The present invention relates to a method of producing a single crystal of a high-pressure phase material such as diamond, cubic boron nitride or the like, and more particularly, it relates to a method of producing a relatively large-sized single crystal, being at least about 10 mm x 10 mm, of a high-pressure phase material, which is applied to a cutting tool, a precision tool, a semiconductor material, an electronic component, an optical component or the like. Description of the Background Art High-pressure phase materials such as diamond and cubic boron nitride are excellent in hardness, heat conductivity, transparency and the like, and widely applied to various tools, optical components, semiconductor materials, electronic components and the like. Such high-pressure phase materials may increasingly gain in importance from now on. Within the high-pressure phase materials, diamond has various excellent properties such as the highest hardness among already-known materials, a function as an excellent electric insulator, high heat conductivity of about five times that of copper under a high temperature, and the like. Further, diamond has good light transmittance over a wide range of wavelengths of ultraviolet, visible and infrared rays excluding part of the infrared region, while the same is brought into a semiconductor state by addition of an impurity. With such properties, diamond has already been applied to a coating material for a tool surface, an electronic material, a heat radiator for a particularly high-output semiconductor laser or LSI, and the like. Further, also studied is application of diamond to a high-temperature semiconductor material, which is operable in a high-temperature region. While natural diamond was applied to industrial use in the past, artificially synthesized diamond is mainly employed nowadays. Fig. 1 shows relatively large-sized polycrystalline diamond, which has generally been artificially produced by a vapor-phase synthesis process such as plasma CVD (chemical vapor deposition) or the like (refer to "Oyo Butsuri" Vol. 55, No. 7, 1986, pp. 640 to 653, for example). In relation to such polycrystalline diamond, however, it is impossible to attain a sufficiently smooth surface by polishing since polycrystalline diamond layers 2 formed on a substrate 1 are heterogeneous. Therefore, it is necessary to employ single-crystalline diamond, which is homogeneous in crystal orientation, for a super-precision tool, an optical component or a semiconductor material particularly requiring a smooth surface within applications of diamond. Since natural output of such single-crystalline diamond is extremely scarce, awaited is a method of artificially producing single-crystalline diamond. At present, artificial synthesis of diamond is implemented by a superhigh-pressure method and the aforementioned vapor-phase synthesis process. As to the superhigh-pressure method, it has been reported that a diamond single crystal of at least 10 ct. (carats: 1 carat = 200 mg) under a superhigh pressure for maintaining the diamond in a stable state (refer to "Indiaqua" No. 50, 1988, p. 126, for example). As to the vapor-phase synthesis process, on the other hand, it has been confirmed that a single-crystalline layer of diamond is grown on single crystals of natural or artificial diamond (refer to "Journal of Crystal Growth" Vol. 31, 1975, p. 44, for example), while there has been developed a method of growing a single crystal of diamond on a dissimilar substrate (refer to Japanese Patent Laying-Open Gazette No. 224225/1988 and "Science" Vol. 243, 1989, p. 1047, for example). However, this method has not yet succeeded in attaining a large-sized diamond single crystal of good quality having a thickness of tens of micrometers. Cubic boron nitride (CBN) has extremely high heat conductivity (about five times that of Al) and high hardness, although the values thereof are inferior to those of diamond. While it is difficult for diamond to work a ferrous material which reacts with diamond by heat generated in cutting, cubic boron nitride is effective for working such a ferrous material. Further, cubic boron nitride may possibly be applied to a heat radiator for an electronic element of an LSI or the like in the future through high resistivity and heat conductivity thereof. In addition, it may be possible to form a p-type or n-type semiconductor material of cubic boron nitride with a doping material. In order to apply cubic boron nitride to the field of electronics, it is necessary to develop a technique of forming a single-crystalline thin film. There has been developed a method of vapor-phase synthesizing a polycrystalline film of cubic boron nitride by plasma CVD or the like (refer to "Shinkuu" Vol. 31, No. 6, 1988, p. 14, for example). Since a sintered body of cubic boron nitride is more suitable for working iron and steel materials as compared with that of diamond, polycrystalline substances are mass-produced. However, the aforementioned conventional methods of synthesizing single crystals of diamond or cubic boron nitride have the following problems: As to the superhigh-pressure method of producing a single crystal of diamond, it is difficult to grow a diamond single crystal having a large area since a superhigh-pressure container is restricted in size. On the other hand, an apparatus for vapor-phase synthesis is large-scaled and costly. When a single-crystalline layer of diamond is grown on a core which is formed by a single-crystalline substrate of natural or artificial diamond by vapor-phase synthesis, a large area cannot be attained since it is difficult to obtain a large-sized single crystal of artificial diamond in the existing circumstances. While artificial diamond can be grown up to a diameter of 10 mm by the superhigh-pressure method, it costs a great deal, and a single crystal of natural diamond is more costly. If a diamond single crystal is grown on a dissimilar substrate by vapor-phase synthesis, on the other hand, distortion is caused due to difference in lattice constant and thermal expansion coefficient between diamond and the material for the substrate, leading to a significantly defective single crystal. As to growth of single crystals having different lattice constants, deviation takes place in atomic arrangement, to cause a defect called lattice misfit dislocation. Further, difference in thermal expansion coefficient leads to difference in degree of shrinkage upon temperature reduction from a growth temperature of 700 to 1000°C to the room temperature, to cause distortion. However, it is noted that combination of high-pressure phase materials themselves is relatively nonproblematic since the materials are similar in lattice constant to each other such that difference in lattice constant between diamond and cubic boron nitride is 1.4 %, while thermal expansion coefficients thereof are also similar to each other. Although cubic boron nitride is relatively easily synthesized by CVD or the like similarly to diamond, there has not yet been established a technique of readily controlling crystal states (single-crystalline, polycrystalline and amorphous states) for implementing functional improvement. As to a single crystal of cubic boron nitride, which is indispensable for application to an electronic element for an LSI or the like, merely a fine one has been attained by vapor-phase synthesis. Thus, cubic boron nitride has not been employed in the field of super-precision working, which requires single crystals. Table 1 shows levels of surface roughness (R max ) required for diamond and cubic boron nitride materials as to main applications thereof, and levels after polishing (1Å=10⁻¹⁰m). Application Required Level R max (Å) Optical Application (Lenses, etc.) 100 Semiconductor Substrate 50 Semiconductor Device Component 500 Super-Precision Tool 300 Material Polished Level R max (Å) Diamond Single Crystal 200 Diamond Polycrystal 700 Diamond Sintered Body 2000 CBN Single Crystal 300 CBN Polycrystal 1000 CBN Sintered Body 2000 SUMMARY OF THE INVENTION An object of the present invention is to provide a method of producing a single crystal of a high-pressure phase material capable of obtaining a homogeneous and large-sized single crystal of a high-pressure phase material, which is applicable to the electronic field of electronic elements, super-precision components and the like, by vapor-phase synthesis. The present invention is directed to a method of producing a single crystal of a high-pressure phase material whose pressure region is at least 10⁸Pa (1000 atm.) in an equilibrium state at 25°C. The inventive method of producing a single crystal of a high-pressure phase material resides in that a substrate for serving as a core for vapor-phase growth is prepared by forming a plurality of single-crystalline plates of a high-pressure phase material to be substantially equal in crystal orientation to each other so that single major surfaces thereof are substantially flush with each other and crystal orientations thereof are substantially along the same direction, thereby forming a single-crystalline layer of the high-pressure phase material on the substrate. According to the present invention, a single-crystalline layer 4 of a high-pressure phase material is integrally formed on major surfaces 3a, which are substantially flush with each other, of a plurality of single-crystalline plates 3 of a high-pressure phase material, as shown in Fig. 2. It is preferable that both of an angle α (Fig. 3) formed between crystal orientations of each adjacent pair of the single-crystalline plates 3 along normal directions of growth planes and an angle β (Fig. 4) formed between such crystal orientations in planes parallel to the growth planes are within 5°. The reason for this is as follows: If the angle α formed between the crystal orientations of the adjacent pair of single-crystalline plates 3 of the high-pressure phase material along the normal directions of the growth planes is within 5°, no grain boundary is observed in upper parts of grown phases although a clear grain boundary is observed immediately after integration of adjacent grown phases. Then, a substantially homogeneous single-crystalline layer 4 of the high-pressure phase material is grown although minor twin crystals and defects are observed. If the angle α exceeds 5°, grain boundaries are apt to remain while twin crystals and defects increase. If the angle β formed between the crystal orientations in the planes which are parallel to the growth planes of adjacent single-crystalline plates 3 of the high-pressure phase material exceeds 5°, on the other hand, twin crystals and defects are apt to take place in the boundary between the pair of single-crystalline plates 3 of the high-pressure phase material. It is considered that, when the angles α and β are not more than 5°, twin crystals and defects hardly take place since unconformability is absorbed by defects or the like to remove grain boundaries. Further, it is preferable to arrange the single-crystalline plates 3 of the high-pressure phase material so that a clearance δ (Fig. 4) between each pair of the single-crystalline plates 3 is not more than 300 µm. If the clearance δ exceeds 300 µm, a defect is easily caused in the boundary between the adjacent pair of single-crystalline plates 3 of the high-pressure phase material. It is also preferable that the crystal orientation of each surface for serving as a growth plane for a single crystal of the high-pressure phase material is along the (100) plane or the (111) plane for serving as a major surface of a substrate. This is because the (100) and (111) planes are relatively workable and hence it is easy to produce a single crystal for serving as a substrate by using one of these planes as the growth plane, while a relatively smooth and polishable surface is attained after growth of the single-crystalline layer 4. It is ideally preferable to arrange the plurality of single-crystalline plates 3 of the high-pressure phase material for defining the substrate so that angles (including both α and β) formed between crystal orientations thereof are within 2°. If both the angles α and β are within 2°, the single-crystalline layer 4 of the high-pressure phase material is homogeneously grown immediately after integration in an integrated state with no turbulence. These and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a sectional view showing the state of crystal growth of polycrystalline diamond which is grown on a substrate by a conventional vapor-phase synthesis process; Fig. 2 is a sectional view typically showing a state of crystal growth according to the inventive method of producing a diamond single crystal with no dispersion in crystal orientation of a substrate; Fig. 3 is a sectional view typically showing a state of crystal growth with dispersion in crystal orientation of a substrate along normal directions of growth planes; Fig. 4 is a plan view showing arrangement of single-crystalline plates of diamond for defining a substrate in the inventive method of producing a diamond single crystal; Fig. 5 is a perspective view for illustrating indications of crystal planes of a single-crystalline plate 3 of a high-pressure phase material employed in each Example of the present invention; Fig. 6 is a perspective view for illustrating a method of measuring dispersion along normal directions of (100) planes of single crystals of a high-pressure phase material in each Example of the present invention using X-ray diffraction; Fig. 7 schematically illustrates the structure of a microwave plasma CVD apparatus employed for vapor-phase synthesizing a diamond single crystal in Example 1 of the present invention; Fig. 8 is a perspective view for illustrating arrangement of a cubic boron nitride single crystal employed in Example 2 of the present invention and indications of crystal planes thereof; and Fig. 9 schematically illustrates the structure of a high-frequency plasma CVD apparatus employed in Example 2 of the present invention. DESCRIPTION OF THE PREFERRED EMBODIMENTS Examples of the present invention are now described with reference to the drawings. Example 1 Single crystals of the so-called type Ib diamond, which was artificially synthesized by the superhigh-pressure method to contain at least 5 p.p.m. of nitrogen, were compacted to 4 mm by 4 mm in size and 0.3 mm in thickness and polished to prepare single-crystalline plates 3 of diamond. 16 such single-crystalline plates 3 of diamond were arranged in a four-by-four array, to define a substrate 1 for vapor-phase synthesis. These plates were so arranged that dispersion of angles formed between crystal orientations of adjacent single crystals was within 1.5°. The dispersion of the angles formed between the crystal orientations was measured by a method using X-ray diffraction, as shown in Fig. 6. Referring to Fig. 6, positions of an X-ray generator 11 and an X-ray detector 12 are fixed and a sample table 15 is translated or rotated so that a (400) diffracted X-ray 13 enters the X-ray detector 12 when the (100) plane of each single-crystalline plate 3 serves as the major surface. In this state, the normal direction of the single-crystalline plate 3 is temporarily determined as a direction along a straight line MN in Fig. 6. Referring to Fig. 6, symbol M denotes a point of incidence of the X-ray upon the (100) plane, symbol ϑ denotes an angle formed by the X-ray 14 and the (400) diffracted X-ray 13 and the (100) plane, symbols H₁ and H₂ denote points on the X-ray 14 and the (400) diffracted X-ray 13 which are at equal intervals from the point M, and symbol N denotes an intersection between perpendiculars drawn from the points H₁ and H₂ in a plane defined by the X-ray 14 and the (400) diffracted X-ray 13. Since the X-ray generator 11 and the X-ray detector 12 are fixed, it is possible to detect dispersion of the (100) planes of the single-crystalline plates 3 along the normal directions by measuring the rotational angle of the sample table 15. Accuracy of measurement by this measuring method is about 0.1°. Hydrogen and methane gas were supplied onto the as-formed substrate 1 by a well-known microwave plasma CVD process so that the mole ratio of methane gas to hydrogen was 1.5 %, to grow diamond under a gas pressure of 7x10³ Pa (60 Torr) at a substrate temperature of 870°C for a period of 200 hours. After the diamond was completely grown, the substrate 1 was taken out to observe that all diamond crystals grown on the substrate 1, which was defined by the 16 single-crystalline plates 3 of diamond, were integrated to form a diamond single crystal. The determination as to whether or not the diamond crystals were integrated to form a single crystal was made through X-ray diffraction. This determination can also be made through electron beam diffraction. The amount of growth was estimated to be 2.0 ct. from increase in weight. This single crystal was divided for examination, to confirm that the thickness of the integrally grown layer was at least 150 µm in every portion. Six portions of the single crystal were arbitrarily extracted for observing crystal directions by X-ray diffraction, to confirm that dispersion of crystal orientations along the normal directions of the growth planes thereof was 1.3° at the maximum. The Raman spectrum of this single crystal exhibited no scattering which indicated properties other than those of diamond. Thus, it has been proved that a diamond single crystal of good quality, having an area of 16 mm square and a thickness of at least 150 µm, was obtained. It is possible to obtain a diamond single crystal having a larger area and smaller dispersion of crystal orientations by slicing the as-formed diamond single crystal layer 4 into plates for defining a substrate 1, arranging the plates to be flush with each other and performing vapor-phase synthesis similarly to the above. Further, an impurity such as boron or nitride can be easily homogeneously contained in the single-crystalline layer 4 of diamond which is grown in the aforementioned manner. While the (100) plane has been selected as the growth plane for the single crystal of diamond in the above Example, it is also possible to select the (110) plane, the (111) plane or other plane as the growth plane. However, it is most preferable to select the (100) plane as the growth plane, in consideration of the facts that the as-formed single crystal is easy to work and the growth plane is excellent in flatness. In the above Example, vapor-phase synthesis has been carried out using a microwave plasma CVD apparatus, the structure of which is schematically shown in Fig. 7. In this microwave plasma CVD apparatus, a gas supply system 21 supplies gas which is required for the CVD process to a reaction tube 22, while a pressure gauge 23 monitors the pressure to adjust exhaust from an exhaust system 24, thereby maintaining a prescribed pressure. Microwaves oscillated from a microwave oscillator 25 are monitored and adjusted by a microwave output meter 26, to generate a plasma 28 around a sample 27 which is placed in the reaction tube 22. Although the plasma CVD process is employed in this Example as the vapor-phase synthesis process, it is also possible to use other processes such as a thermal CVD process of heating a thermoionic emission material for decomposing/exciting gas, an ion beam method of ionizing gas and applying the same to a substrate, a laser CVD process of decomposing and exciting gas with a laser beam, and the like, for example. Within these vapor-phase synthesis processes, it is preferable to use the plasma CVD process or the thermal CVD process in consideration of the fact that diamond can be homogeneously grown on a substrate 1 having a large area. Example 2 A single-crystalline plate 16 of cubic boron nitride artificially synthesized by the superhigh-pressure method was cut into an equilateral triangle so that its (111) plane served as the growth plane, and the side surfaces thereof were polished to be orthogonal to the growth plane. Four such single-crystalline plates 16 of cubic boron nitride, which were so compacted and polished that each equilateral triangle had sides of 0.8 mm and a thickness of 0.3 mm, were arranged to define a substrate 1 shown in Fig. 8. Dispersion angles along the normal directions of the (111) planes of the single-crystalline plates 16 were measured using X-ray diffraction similarly to Example 1, to find that the maximum dispersion angle was 3.5°. A single-crystalline layer of cubic boron nitride was grown on the substrate 1 defined by the single-crystalline plates 16, by a high-frequency plasma CVD process using an apparatus shown in Fig. 9. 10 sccm. of diborane (B₂H₆), 100 sccm. of nitrogen, 1000 sccm. of hydrogen and 50 sccm. of argon were supplied as raw material gases to a reaction tube 29 of quartz, to grow the single-crystalline layer under a gas pressure of 2,7 x 10⁻³ Pa (20 Torr) with an output of 1200 W from a high-frequency oscillator 30 (13.56 MHz) at a substrate temperature of 970°C for 100 hours. A cooling pipe 32 for supplying cooling water was arranged along an induction coil 31, which was supplied with a high frequency. Consequently, a single-crystalline layer of cubic boron nitride having a thickness of 35 µm was obtained on the substrate 1. Surface roughness of this single-crystalline layer was 1,5 µm (15000 Å) in R max after the growth, while it was possible to obtain a smooth surface whose surface roughness was 60 nm (600 Å) in R max by polishing the layer. In this single-crystalline layer, dispersion in inclination of crystal axes of the (111) planes was 2.4°. Example 3 Six single-crystalline plates 3 of diamond, having the same dimensions as those employed in Example 1, were arranged flush in a three-by-two array, to examine the growth rate of a single crystal, inclination of crystal axes of the grown single-crystalline layer and surface roughness after polishing in the same apparatus as that in Example 1 with variations of conditions for vapor-phase synthesis. Table 2 (1Å=10⁻¹⁰m) shows the results of this Example with growth times of 120 hours. Conditions not listed in Table 2 were identical to those of Example 1. It is understood from Table 2 that, if dispersion of the angles α or β exceeds 5° or a clearance between each adjacent pair of single-crystalline plates 3 exceeds 300 µm, a smooth surface cannot be obtained even if the grown layer is polished, and the inclination α of the crystal axes in the grown layer tends to increase. In the sample No. 14 listed in Table 2, three ones of the six single-crystalline plates 3 were made different in growth plane orientation from the remaining ones. It is understood that surface roughness after polishing became consequently higher as compared with the remaining samples, whose orientations of growth planes were unified, although the angles α and β and the clearance δ between each adjacent pair of single-crystalline plates 3 were set at preferable values. No. Orientation of Growth Plane Angle α (deg) Angle β (deg) Clearance (µm) Methane-to-Hydrogen Ratio (%) Growth Rate (µm/h) Dispersion in Crystal Axes in Growth Layer (deg) Surface Roughness After Polishing Rmax(Å) 1 100 2.5 2.2 80 1.0 0.6 2.2 100 2 100 3.7 3.2 170 1.0 0.6 3.0 230 3 100 4.2 3.3 150 1.5 0.8 3.1 280 4 111 2.2 2.3 70 1.5 1.0 1.7 80 5 111 3.8 4.0 210 1.0 0.7 3.4 190 6 111 4.8 4.5 220 1.5 1.0 4.4 250 7 110 1.8 2.2 120 1.5 1.6 1.7 280 8 110 3.3 4.5 140 1.0 1.2 3.1 300 9 111 2.4 3.1 110 1.0 0.9 2.2 170 10 100 5.6 4.0 220 1.5 0.8 5.9 370 11 100 4.3 6.2 360 1.5 0.8 5.3 630 12 111 4.5 5.5 200 1.0 0.7 4.7 360 13 111 6.2 7.1 420 1.5 1.0 6.8 1100 14 100-3 pieces (3.8) (4.4) 130 1.0 0.7 (4.4) 740 111-3 pieces Example 4 60 p.p.m. of diborane (B₂H₆) gas was mixed into raw material gases with respect to hydrogen, to make growth under conditions similar to those of Example 1. A single-crystalline diamond film thus obtained was entirely in a semiconductor state with average resistivity of 2 x 10³ Ω·cm. It is understood that a single-crystalline substrate for a diamond semiconductor element having an unprecedented large area can be thus obtained according to the inventive method. Example 5 A single-crystalline diamond layer was grown on a substrate 1 defined by the single-crystalline plates 16 of cubic boron nitride used in Example 2 under conditions similar to those of Example 1. The thickness of this single-crystalline diamond layer was 47 µm and the plane orientation of its major surface was (111), while dispersion in inclinations of (111) planes in the single-crystalline diamond layer examined by X-ray diffraction was 4.4°. As understood from the aforementioned Examples, a homogeneous and relatively thick high-pressure phase single crystal having a large area can be easily obtained by adjacently arranging a plurality of single-crystalline plates of the high-pressure phase material so that crystal orientations thereof are substantially equal to each other to define a substrate 1, and growing a high-pressure phase material on the substrate 1 by vapor-phase synthesis. According to the present invention, it is possible to obtain a workable single crystal since the crystal orientation can be arbitrarily selected to grow the high-pressure phase single crystal. Further, the high-pressure phase single crystal obtained according to the inventive method can easily contain boron and nitrogen. Thus, the high-pressure phase single crystal obtained according to the inventive method can be widely applied to the tip of a precision tool, a wear resisting tool, a heat resisting tool, a semiconductor base material, a heat radiator, a high-pressure phase semiconductor material, an optical material, an acoustic diaphragm and the like. While above examples refer to diamond or cubic boron nitride only, the present invention can also be applied to any other high pressure-phase materials, such as wurtzite boron nitride. Furthermore, the technology of the present invention can be applied for producing large scale single crystal of such non high pressure-phase materials as Si, SiC, GaAs, ZnO or the like. However, the present invention is not necessarily suitable for these materials, because their single crystal of high quality can be synthesized under normal pressure at lower cost.

Claims: A method of producing a single crystal of a high-pressure phase material having a pressure region of at least 10⁸ Pa (1000 atm.) in an equilibrium state at 25°C, said method comprising: a step of arranging a plurality of single-crystalline plates (3, 16) of said high-pressure phase material, being formed to be substantially equal in crystal orientation to each other, so that single major surfaces (3a) thereof are substantially flush with each other and crystal orientations thereof are substantially along the same direction, thereby defining a substrate (1) for serving as a core for vapor-phase growth; and a step of forming a single-crystalline layer (4) of said high-pressure phase material on said substrate by a vapor-phase synthesis process. A method of producing a single crystal of a high-pressure phase material in accordance with claim 1, wherein adjacent ones of said single-crystalline plates (3, 16) of said high-pressure phase material have the same crystal planes of surfaces (3a) for serving as growth planes, and an angle formed between crystal orientations of said adjacent single-crystalline plates is within 5°. A method of producing a single crystal of a high-pressure phase material in accordance with claim 1, wherein said substrate (1) for serving as a core for vapor-phase growth is so formed that crystal planes of surfaces (3a) for serving as respective growth planes are identical to each other and a clearance between each adjacent pair of said single-crystalline plates (3, 16) is within 300 µm. A method of producing a single crystal of a high-pressure phase material in accordance with claim 1, wherein single crystals of diamond are used for said single-crystalline plates (3, 16) of said high-pressure phase material for defining said substrate (1), to form a single-crystalline layer (4) of diamond on said substrate (1). A method of producing a single crystal of a high-pressure phase material in accordance with claim 1, wherein single crystals of cubic boron nitride are employed for said single-crystalline plates (3, 16) of said high-pressure phase material for defining said substrate (1), to form a single-crystalline layer (4) of cubic boron nitride on said substrate (1). A method of producing a single crystal of a high-pressure phase material in accordance with claim 1, wherein a plasma CVD process is employed as said vapor-phase synthesis process for said single crystal of said high-pressure phase material. A method of producing a single crystal of a high-pressure phase material in accordance with claim 1, wherein growth planes (3a) of said single-crystalline plates (3, 16) are prepared by (100) planes or (111) planes. A method of producing a single crystal of a high-pressure phase material in accordance with claim 1, wherein dispersion along the normal directions of said single-crystalline plates (3, 16) is detected using X-ray diffraction in said step of arranging a plurality of single-crystalline plates of said high-pressure phase material for defining a substrate (1). A method of producing a single crystal of a high-pressure phase material in accordance with claim 4, wherein said single-crystalline layer of diamond is vapor-phase grown by a plasma CVD process using hydrogen and hydrocarbon gas as raw material gases. A method of producing a single crystal of a high-pressure phase material in accordance with claim 5, wherein diborane, nitrogen, hydrogen and argon are used as raw material gases to vapor-phase grow said single-crystalline layer of cubic boron nitride by a high-frequency plasma CVD process. A method of producing a single crystal of a high-pressure phase material in accordance with claim 1, wherein a plurality of single-crystalline plates of cubic boron nitride are arranged flush to define a substrate (1), and a single crystal of diamond is vapor-phase grown on said substrate. A method of producing a single crystal of a high-pressure phase material, comprising: a step of arranging major surfaces (3a) of a plurality of single-crystalline plates (3, 16) of diamond substantially flush so that crystal planes of respective said major surfaces (3a) are (100) planes and an angle formed between crystal orientations of adjacent ones of said single-crystalline plates (3, 16) is within 2° while a clearance between said adjacent ones of said single-crystalline plates (3, 16) is within 300 µm, thereby defining a substrate (1) for serving as a core for vapor-phase growth; and a step of vapor-phase growing a single crystal of diamond by a plasma CVD process using hydrogen and methane gas as raw material gases.

Inventors: FUJIMORI NAOJI C O ITAMI WORKS, IMAI TAKAHIRO C O ITAMI WORKS, FUJIMORI, NAOJI, C/O ITAMI WORKS OF, IMAI, TAKAHIRO, C/O ITAMI WORKS OF
Applicants: SUMITOMO ELECTRIC INDUSTRIES, SUMITOMO ELECTRIC INDUSTRIES, LTD.
Application year: 1990
Main classification: C30B25
IPC codes: C30B25