Method for producing semiconductor wafer and substrate used for producing the semiconductor

Abstract: In a method for forming a semiconductor wafer with a cleavage plane as an orientation flat, a groove or a hole is formed through the substrate so that it may be on a line along which the substrate is cleaved to form an orientation flat, and surface treatment is applied to the substrate to provide a mirrorlike surface of the substrate. Then, the substrate having the mirrorlike surface is cleaved from the groove or hole to form the orientation flat. Accordingly, edges of the cleavage plane are not rounded due to the surface treatment. In addition, the substrate is easily cleaved along the cleavage plane from the groove or the hole. As the result, a semiconductor wafer having a sharp cleavage plane as an orientation flat is produced with improved yield, and an alignment is performed with high precision in a subsequent process, such as a photolithography.

Description: FIELD OF THE INVENTION The present invention relates to a method for producing a semiconductor wafer having an orientation flat formed by cleaving a portion of the wafer along a cleavage plane. The invention also relates to a substrate used for producing the semiconductor wafer. BACKGROUND OF THE INVENTION Figures 5(a)-5(e) illustrate a method for forming a GaAs epitaxial wafer having a cleavage plane of crystal as an orientation flat. In these figures, reference numeral 1 designates a GaAs monocrystalline ingot. This GaAs monocrystalline ingot 1 is formed by a boat grown method in which GaAs is melted in an electric furnace and a crystalline germ is moved from a high temperature region to a low temperature region in the furnace to grow the GaAs ingot with the crystalline germ as a core. Alternatively, it may be formed by a pull method in which GaAs is melted in a crucible and the melted GaAs is slowly pulled up by a seed crystal bar. Reference numeral 2 designates a cylindrical GaAs monocrystalline ingot made of the GaAs monocrystalline ingot 1. Reference numeral 3 designates a GaAs substrate obtained by slicing the cylindrical GaAs monocrystalline ingot 3 in a prescribed thickness. Reference numeral 4 designates a GaAs wafer having an orientation flat 4a formed by cleaving a portion of the GaAs substrate 3 along a cleavage plane. Generally, the orientation flat 4a is formed at a position relating to a crystal orientation of the GaAs substrate 3 and serves as a mark when the orientation of the wafer is detected in a subsequent process. Reference numeral 5 designates a GaAs epitaxial wafer in which an epitaxial layer 51 is grown on the GaAs wafer 4. A description is given of the production process. Initially, as illustrated in figure 5(a), a high quality GaAs monocrystalline ingot 1 is formed by the above-described boat grown method or the pull method. Then, as illustrated in figure 5(b), opposite end portions of the ingot 1 are cut off to remove deformed portions of the ingot 1. Then, the ingot 1 is formed into a cylindrical shape by polishing its periphery, whereby a diameter of a wafer to be formed is determined. Preferably, the diameter is a few inches (note: 1 inch = 2.54 cm). Thereafter, the cylindrical GaAs monocrystalline ingot 2 is sliced using a very thin diamond cutter, providing a GaAs substrate 3 shown in figure 5(c). When the diameter of the wafer is 2 inches, it is sliced in a thickness of about 400 microns. When the diameter is 3 inches, it is sliced in a thickness of about 600 microns. Then, as illustrated in figure 5(d), an end portion of the GaAs substrate 3 is cleaved along a cleavage plane to form an orientation flat 4a. Since there are differences in thicknesses of a plurality of GaAs substrates 4 with the orientation flat 4a due to the slicing process, both surfaces of the GaAs substrates 4 are lapped by a solution comprising aluminium oxide and glyceline or the like with applying pressure thereto, whereby the thicknesses of the GaAs substrates 4 are made even. Then, a broken layer and a contaminated layer each about 10 microns thick generated on the surface and the periphery of the substrate 4 due to the machine work are removed by etching. Then, abrasive is dropped onto the substrate and the substrate is polished using a porous pad or the like to improve the flatness of the substrate, resulting in a mirrorlike surface of the GaAs substrate 4. Thereafter, as illustrated in figure 5(e), an epitaxial layer 51 is grown on the surface of the GaAs substrate 4 by MOCVD or the like, resulting in a GaAs epitaxial wafer 5 with the cleavage plane serving as the orientation flat. Figures 6(a)-6(e) illustrate another conventional method for producing the GaAs epitaxial substrate with the cleavage plane as the orientation flat. In this method, after directly slicing a GaAs monocrystalline ingot, a prescribed diameter of a wafer to be formed is obtained by stamping and then an orientation flat is formed. In figures 6(a)-6(e), reference numeral 6 designates a GaAs substrate for stamping obtained by directly slicing the GaAs monocrystalline ingot 1. Initially, as illustrated in figure 6(a), a GaAs monocrystalline ingot 1 is formed by the boat grown method, the pull method, or the like. Then, the ingot 1 is sliced in a prescribed thickness, providing a GaAs substrate 6 shown in figure 6(b). Then, as illustrated in figure 6(c), a GaAs substrate 3 is stamped out from the GaAs substrate 6 using a trimming die (not shown) having a diameter equal to a desired diameter of a wafer to be formed. Then, as illustrated in figure 6(d), an end portion of the GaAs substrate 3 is cleaved along a cleavage plane to form an orientation flat 4a. Thereafter, lapping, etching, and polishing processes are applied to the GaAs substrate 4 with the orientation flat 4a to provide a mirrorlike surface of the GaAs substrate 4. Then, as illustrated in figure 6(e), an epitaxial layer 51 is grown on the GaAs substrate 4 by MOCVD or the like, resulting in a GaAs epitaxial wafer 5 with the cleavage plane as the orientation flat. In the above-described conventional methods, since the orientation flat is produced by cleaving the substrate along the cleavage plane, the orientation flat is produced with high precision. However, since the surface treatment like the polishing is performed after the formation of the orientation flat 4a, edges of the cleavage plane of the orientation flat are rounded as shown in figure 7. In addition, when the epitaxial layer 51 is grown on the substrate 4, the edges of the cleavage plane of the orientation flat 4a are also rounded due to the grown epitaxial layer 51. Therefore, when a position of the GaAs epitaxial wafer 5 is detected on the basis of the orientation flat 4a, precision of the detection is lowered. In addition, when the orientation flat 4a is formed by cleaving the GaAs substrate 4, the GaAs substrate 4 is unfavorably cracked or broken, resulting in a poor production yield. SUMMARY OF THE INVENTION It is an object of the present invention to provide a method for forming a semiconductor wafer in which a semiconductor wafer having a sharp cleavage plane as an orientation flat is produced in a simple process with a good yield. It is another object of the present invention to provide a substrate used for forming such a semiconductor wafer. Other objects and advantages of the present invention will become apparent from the detailed description given hereinafter; it should be understood, however, that the detailed description and specific embodiment are given by way of illustration only, since various changes and modifications within the spirit and the scope of the invention will become apparent to those skilled in the art from this detailed description. According to a first aspect of the present invention, in a method for producing a semiconductor wafer having a cleavage plane as an orientation flat, a semiconductor monocrystalline ingot is formed into a cylindrical shape, a groove is formed at the side of the cylindrical ingot in a direction parallel with a cleavage direction, the cylindrical ingot having the groove is sliced in a prescribed thickness to form a substrate for a semiconductor wafer, surface treatment is applied to the substrate to provide a mirrorlike surface of the substrate, and the substrate having the mirrorlike surface is cleaved from the groove, resulting in a semiconductor wafer with a cleavage plane as an orientation flat. According to a second aspect of the present invention, in a method for producing a semiconductor wafer having a cleavage plane as an orientation flat, a semiconductor monocrystalline ingot is sliced in a prescribed thickness to form a substrate, a circular substrate is stamped out from the substrate, a groove or a hole is formed through the circular substrate so that the groove or hole may be on a line along which the substrate is cleaved to form an orientation flat, surface treatment is applied to the substrate to provide a mirrorlike surface of the substrate, and the substrate having the mirrorlike surface is cleaved from the groove or hole, resulting in a semiconductor wafer having a cleavage plane as an orientation flat. According to a third aspect of the present invention, a substrate used for producing a semiconductor wafer having a cleavage plane as an orientation flat includes a groove or a hole formed through the substrate, on a line along which the substrate is cleaved to form the orientation flat. According to the present invention, the substrate is easily cleaved from the groove or the hole, so that breakage in the substrate is significantly decreased. In addition, since the substrate is cleaved after the surface treatment, the edges of the cleavage plane are not rounded due to the surface treatment, resulting in a sharp cleavage plane as an orientation flat. BRIEF DESCRIPTION OF THE DRAWINGS Figures 1(a)-1(f) are diagrams illustrating steps in a method for producing a semiconductor wafer in accordance with a first embodiment of the present invention; Figures 2(a)-2(e) are diagrams illustrating steps in a method for producing a semiconductor wafer in accordance with a second embodiment of the present invention; Figures 3(a)-3(d) are diagrams illustrating various examples of grooves and holes which are formed in a substrate in the method according to the embodiment 1 or 2; Figure 4 is a diagram showing a semiconductor wafer having a second flat; Figures 5(a)-5(e) are diagrams illustrating steps in a method for producing a semiconductor wafer in accordance with the prior art; Figures 6(a)-6(e) are diagrams illustrating steps in a method for producing a semiconductor wafer in accordance with another prior art; and Figure 7 is an enlarged view of a part of the prior art semiconductor wafer in the vicinity of the orientation flat. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Figures 1(a)-1(f) are diagrams illustrating steps in a method for producing a semiconductor wafer in accordance with a first embodiment of the present invention. In these figures, the same reference numerals as those in figures 5(a)-5(e) designate the same or corresponding parts. Reference numeral 8 designates a GaAs substrate having a V-shaped groove 7 from which the substrate 8 is cleaved to form an orientation flat. Reference numeral 9 designates a GaAs substrate on which an epitaxial layer 51 is formed. A description is given of the production process. Initially, as illustrated in figure 1(a), a GaAs monocrystalline ingot 1 is formed by the conventional boat grown method, pull method, or the like. Then, as illustrated in figure 1(b), opposite end portions of the ingot 1 are cut off to remove deformed portions of the ingot 1. Then, the periphery of the ingot 2 is polished to form the ingot 2 into a cylindrical shape, whereby a diameter of a wafer to be formed is determined. Preferably, the diameter is a few inches. Then, as illustrated in figure 1(c), a crystal orientation of the cylindrical GaAs monocrystalline ingot 2 is detected by X-ray analysis or the like. Thereafter, a V-shaped groove 7 having a depth of about 0.1 mm is formed at the side of the ingot 2 so that a side surface of the groove 7 may accord with a cleavage plane along which the substrate 8 is cleaved to form an orientation flat. Preferably, the groove 7 is formed by dicing or etching. Thereafter, the GaAs monocrystalline ingot 2 with the V-shaped groove 7 is sliced using a very thin diamond cutter, providing a GaAs substrate 8 shown in figure 1(d). When the diameter of the wafer is 2 inches, it is sliced in a thickness of about 400 microns. When the diameter is 3 inches, it is sliced in a thickness of about 600 microns. Then, surface treatment, such as chamfering, etching, polishing or the like, is applied to the GaAs substrate 8 with the groove 7 to provide a mirrorlike surface of the GaAs substrate 8. Then, as illustrated in figure 1(e), an epitaxial layer 51 having a desired layer structure, for example, a laser structure is grown on the GaAs substrate 8 by MOCVD or the like, resulting in a GaAs substrate 9 with the epitaxial layer 51. Thereafter, the GaAs substrate 9 is cleaved from the V-shaped groove 7 to form an orientation flat 4a. Thus, a GaAs epitaxial wafer 5 with the cleavage plane as the orientation flat 4a is achieved as shown in figure 1(f). In this case, although the epitaxial layer 51 formed on the GaAs substrate 9 is also cleaved when the GaAs substrate 9 is cleaved, since crystal of the epitaxial layer 51 is uniformly oriented, the epitaxial layer 51 is not broken by a crack or the like generated in a direction different from the orientation flat 4a. According to the first embodiment of the present invention, edges of the orientation flat 4a are not rounded due to the surface treatment and the growth of the epitaxial layer 51. In addition, the GaAs substrate 9 is easily cleaved from the groove 7, so that breakage in the GaAs substrate is significantly decreased. Figures 2(a)-2(e) are diagrams illustrating steps in a method for producing a semiconductor wafer in accordance with a second embodiment of the present invention. In this method, a GaAs monocrystalline ingot is directly sliced and then a desired diameter of a wafer to be formed is obtained by stamping. Initially, as illustrated in figure 2(a), a GaAs monocrystalline ingot 1 is formed by the conventional boat grown method, pull method, or the like. Then, the ingot 1 is sliced in a prescribed thickness, providing a GaAs substrate 6 shown in figure 2(b). Then, as illustrated in figure 2(c), a crystal orientation of the GaAs substrate 6 is detected by X-ray analysis or the like. Then, a GaAs substrate with a desired shape and a desired diameter is stamped out from the GaAs substrate 6 using a trimming die (not shown), ultrasonic wave, or the like. Then, a V-shaped groove 7 having a depth of about 0.1 mm is formed in the GaAs substrate so that a side wall of the groove may accord with a cleavage plane along which the substrate is cleaved to form an orientation flat. Preferably, the groove 7 is formed by dicing or etching. Thus, a GaAs substrate 8 shown in figure 1(d) is formed. Then, as illustrated in figure 2(d), surface treatment, such as lapping, etching, polishing or the like, is performed to the GaAs substrate 8 to provide a mirrorlike surface of the GaAs substrate 8. Thereafter, an epitaxial layer 51 having a desired layer structure, for example, a laser structure is grown on the substrate 8 by MOCVD or the like. Thereafter, the GaAs substrate 9, on which the epitaxial layer 51 is present, is cleaved from the V-shaped groove 7 to form an orientation flat 4a. Thus, a GaAs epitaxial wafer 5 having a sharp cleavage plane of the orientation flat 4a is achieved (refer to figure 2(e)). According to the second embodiment of the present invention, the GaAs epitaxial wafer 5 having a sharp cleavage plane of the orientation flat is formed using the stamping method with an improved production yield. While in the above-described first and second embodiments the V-shaped groove 7 is formed as a clue for cleaving the substrate to form the orientation flat 4a, a U-shaped groove 7a may be formed as shown in figure 3(a). Also in this case, a GaAs epitaxial wafer having a sharp cleavage plane as an orientation flat is formed with an improved production yield. In addition, by employing the U-shaped groove, the GaAs substrate is prevented from cracking or breaking when the GaAs ingot with the groove 7a is sliced to provide the substrate 8 or when a stress is applied to the substrate 8 by a handling during the surface treatment in the step of forming the epitaxial layer. While in the above-described second embodiment the V-shaped groove 7 is formed at an end of a line along which the substrate is cleaved to form the orientation flat, an oval hole 10 shown in figure 3(b), a rhomboid hole 10b shown in figure 3(c), or a triangular hole 10c shown in figure 3(d) may be formed so that a major axis thereof may accord with the line along which the substrate is cleaved to form an orientation flat. Also in this case, a GaAs epitaxial wafer having a sharp cleavage plane as an orientation flat is formed with an improved production yield. In addition, the GaAs substrate is prevented from cracking or breaking when the GaAs ingot with the hole 10, 10b, or 10c is sliced to provide the GaAs substrate or when a stress is applied to the GaAs substrate by a handling during the surface treatment in the step of forming the epitaxial layer. In the above-described first and second embodiments, the GaAs epitaxial wafer 5 is formed by growing the epitaxial layer 51 on the GaAs substrate 8. However, if the GaAs substrate 8 is cleaved from the groove or the hole after the surface treatment of the substrate 8 without growing the epitaxial layer 51 thereon, a GaAs wafer with a sharp cleavage plane as an orientation flat is achieved. In the above-described first and second embodiments, the orientation flat 4a relating to the crystal orientation (first flat) is formed in the wafer. As shown in figure 4, a second flat 4b which is smaller than the first flat 4a and shows a conductivity type of the wafer may be formed in addition to the first flat 4a. While in the first and second embodiments the GaAs wafer is described, other compound semiconductor materials like InP may be used with the same effects as described above. In addition, while in the first and second embodiments the GaAs substrate 8 is formed in a circle, it may be formed in an oval or in a shape obtained by removing a portion of a circle along a prescribed arc. As is evident from the foregoing description, according to the present invention, when a substrate for a semiconductor wafer is formed, a groove or a hole is formed through the substrate so that it may be on a line along which the substrate is cleaved to form an orientation flat, surface treatment is applied to the substrate to provide a mirrorlike surface of she substrate, and then the substrate having the mirrorlike surface is cleaved from the groove or hole to form the orientation flat. Therefore, edges of the cleavage plane are not rounded due to the surface treatment. In addition, the substrate is easily cleaved along the cleavage plane from the groove or the hole. As the result, a semiconductor wafer having a sharp cleavage plane as an orientation flat is produced with improved yield, and an alignment is performed with high precision in a subsequent process, such as a photolithography.

Claims: A method for producing a semiconductor wafer having a cleavage plane serving as an orientation flat, comprising: forming a semiconductor monocrystalline ingot into a cylindrical shape; forming a groove at the side of said cylindrical ingot in a direction parallel with a cleavage direction; slicing said cylindrical ingot having said groove in a prescribed thickness to form a substrate for a semiconductor wafer; applying surface treatment to said substrate to provide a mirrorlike surface of said substrate; and cleaving said substrate having said mirrorlike surface from said groove, resulting in a semiconductor wafer with a cleavage plane as an orientation flat. A method for producing a semiconductor wafer having a cleavage plane serving as an orientation flat, comprising: slicing a semiconductor monocrystalline ingot in a prescribed thickness to form a substrate; stamping out a circular substrate from said substrate; forming a groove or a hole through said circular substrate so that said groove or hole may be on a line along which said substrate is cleaved to form an orientation flat; applying surface treatment to said substrate to provide a mirrorlike surface of said substrate; and cleaving said substrate having said mirrorlike surface from said groove or hole, resulting in a semiconductor wafer having a cleavage plane as an orientation flat. The method of claim 1 wherein an epitaxial layer is grown on said mirrorlike surface of said substrate. The method of claim 2 wherein an epitaxial layer is grown on said mirrorlike surface of said substrate. The method of claim 1 wherein said groove is formed by detecting crystal orientation of said cylindrical semiconductor monocrystalline ingot by X-ray analysis and removing a prescribed portion of said ingot by dicing or etching. A substrate used for producing a semiconductor wafer having a cleavage plane as an orientation flat wherein a groove is formed through said substrate, at an end of a line along which said substrate is cleaved to form said orientation flat, in a direction parallel to a cleavage direction. A substrate used for producing a semiconductor wafer having a cleavage plane as an orientation flat wherein a hole is formed through said substrate, on a line along which said substrate is cleaved to form said orientation flat. The substrate of claim 6 wherein said groove is a V-shaped groove formed so that a side surface of said groove may accord with said line along which said substrate is cleaved to form said orientation flat. The substrate of claim 6 wherein said groove is a U-shaped groove formed so that a side surface of said groove may accord with said line along which said substrate is cleaved to form said orientation flat. The substrate of claim 7 wherein said hole is an oval hole formed so that a major axis thereof may accord with said line along which said substrate is cleaved to form said orientation flat. The substrate of claim 7 wherein said hole is a triangular hole formed so that a major axis thereof may accord with said line along which said substrate is cleaved to form said orientation flat. The substrate of claim 7 wherein said hole is a rhomboid hole formed so that a major axis thereof may accord with said line along which said substrate is cleaved to form said orientation flat. A method of forming a semiconductor wafer comprising slicing an ingot to obtain a wafer, cleaving the wafer along a cleavage plane to provide a straight edge portion, and treating the wafer after it is obtained from the ingot by slicing, characterised in that: a hole or notch defining the cleavage plane is formed in the wafer after slicing or in the ingot before slicing and the wafer is subsequently cleaved along the plane defined by the hole or notch, and the wafer is treated between formation of the hole or notch and cleaving of the wafer.

Inventors: HAYAFUJI NORIO, MIHASHI YUTAKA, MIYASHITA MOTOHARU, HAYAFUJI, NORIO, MIHASHI, YUTAKA, MIYASHITA, MOTOHARU, Hayafuji, Norio, c/o Mitsubishi Denki K. K., Mihashi, Yutaka, c/o Mitsubishi Denki K. K., Miyashita, Motoharu, c/o Mitsubishi Denki K. K.
Applicants: MITSUBISHI ELECTRIC CORP, MITSUBISHI DENKI KABUSHIKI KAISHA
Application year: 1992
Main classification: C30B33
IPC codes: H01L21, B28D5, C30B33