Inner peripheral type thin plate blade: method of producing the same

Abstract: An annular thin plate blade (K1) having a cutting edge at its inner periphery and a method of producing the thin plate blade (K1) in which an annular member (40) made of polycrystalline diamond formed by vapor phase synthesis is provided at the inner periphery of the thin plate blade (K1) and the thin plate blade (K1) has a thickness of 20 to 300 µm.

Description: The present invention generally relates to cutting of an ingot and particularly, to a method of producing an inner peripheral type thin plate blade suitable for cutting a large-diameter ingot of single-crystal semiconductor. Conventionally, when ICs (integrated circuits) or LSIs (large scale integrated circuits) are produced by using semiconducting materials such as Si, Ge, GaAs, InP, etc., a cutting process of cutting a synthesized single-crystal ingot into wafers is quite vital in determination of production cost, quality and yield. In this known cutting process, a cylindrical ingot is cut into disklike wafers of 0.3 to 0.5 mm in thickness by using an inner peripheral type diamond whetstone, a multiwire, a multiband steel, etc. In view of slicing efficiency, cutting cost and cutting allowance, slicing by an inner peripheral type whetstone has come into commonest use. Generally, in the known inner peripheral type whetstone of Figs. 1 and 2, a cutting edge 2 constituted by diamond abrasive grains 4 of about 50 µm in diameter and a nickel electrodeposition layer 5 is formed at an inner periphery of an annular metal base 1. In the known inner peripheral type whetstone, since the diamond abrasive grains 4 subjected to nickel electrodeposition is employed, it is difficult to control thickness of the cutting edge 2 due to electrodeposition. Therefore, the known inner peripheral type whetstone has such drawbacks as wide distribution of thickness of the cutting edge 2, large cutting allowance, separation of the diamond abrasive grains 4 from the cutting edge 2 and wear of the nickel electrodeposition layer 5, thereby resulting in aggravation of its cutting accuracy and service life. DE-U-8806254 discloses a thin blade plate of annular shape, having a cutting edge at its inner periphery and faces coated by vapour phase deposition with diamond to reduce friction. SUMMARY OF THE INVENTION Accordingly, an essential object of the present invention is to provide an inner peripheral type thin plate blade for cutting an ingot, whose cutting accuracy, wear resistance and resistance to failure are excellent. Another important object of the present invention is to provide a method of producing the inner peripheral type thin plate blade at low cost. In order to accomplish these objects of the present invention, a thin plate blade of annular shape is made, according to the present invention, wholly of polycrystalline diamond formed by vapor phase synthesis and with a thickness of 20 to 300 µm. BRIEF DESCRIPTION OF THE DRAWINGS These objects and features of the present invention will become apparent from the following description taken in conjunction with the preferred embodiments thereof with reference to the accompanying drawings, in which: Figs. 1a and 1b are a side sectional view and a bottom plan view of a prior art inner peripheral type cutting blade, respectively (already referred to); Fig. 2 is an enlarged sectional view of a cutting edge portion of the prior art cutting blade of Fig. 1a (already referred to); Figs. 3a and 3b are a side sectional view and a bottom plan view of an inner peripheral type cutting blade according to a first embodiment of the present invention, respectively; Fig. 4 is an enlarged sectional view of a cutting edge portion of the cutting blade of Fig. 3a; Figs. 5a and 5b are a side sectional view and a bottom plan view of an inner peripheral type cutting blade according to a second embodiment of the present invention, respectively; Fig. 6 is an enlarged sectional view of a cutting edge portion of the cutting blade of Fig. 5a; Figs. 7, 8 and 9 are schematic views showing three examples of a filament CVD apparatus for coating diamond, which is applicable to production of the cutting blade of the present invention, respectively; Figs. 10a(1) and 10b(1), Figs. 10a(2) and 10b(2) and Figs. 10a(3) and 10b(3) are views showing first, second and third steps of a method of producing the cutting blade of Fig. 4, according to the present invention, respectively; and Figs. 11a(1) and 11b(1) are views similar to Figs. 10a(1) and 10b(1), respectively, particularly showing a modification thereof. Before the present invention proceeds, it is to be noted that like parts are designated by like reference numerals throughout several views of the accompanying drawings. DETAILED DESCRIPTION OF THE INVENTION Referring now to the drawings, there is shown in Figs. 3a, 3b and 4, an inner peripheral type cutting blade K1 suitable for cutting a large-diameter ingot of single-crystal semiconductor, according to a first embodiment of the present invention. The cutting blade K1 has a thickness of 20-300 µm and includes an annular metal base 30. An annular polycrystalline diamond film 40 formed by vapor phase synthesis is bonded to an inner periphery of the metal base 30 by a bonding layer 80. Meanwhile, Figs. 5a, 5b and 6 show an inner peripheral type cutting blade K2 according to a second embodiment of the present invention. The cutting blade K2 has also a thickness of 20-300 µm and is wholly made of polycrystalline diamond formed by vapor phase synthesis. Generally, in order to increase rigidity of an inner peripheral type diamond whetstone, the diamond whetstone is strained by applying a tensile stress to an outer periphery of a metal base of the diamond whetstone. However, the tensile stress at an inner periphery of the diamond whetstone becomes larger than that of the outer periphery of the diamond whetstone. Therefore, the diamond whetstone is likely to be distorted and thus, a work hardened surface layer of wafers is also increased. In order to reduce this distortion of the diamond whetstone, a cutting edge portion should be strained by a large force. The cutting blades K1 and K2 of the present invention are partially and wholly made of polycrystalline diamond formed by vapor phase synthesis, respectively and therefore, have high tensile strengths. Accordingly, the cutting blades K1 and K2 can be strained by a large force, thereby resulting in improvement of cutting accuracy of wafers and enabling slicing of the wafers for a long period. Namely, since the cutting blades K1 and K2 are partially and wholly made of diamond formed by vapor phase synthesis, the cutting blades K1 and K2 have the following features (1) to (7) in comparison with an earlier mentioned known cutting blade having a cutting edge formed by diamond grains and a nickel electrodeposition layer. (1) Since the outer peripheral portion can be strained by a larger force, distortion of the inner peripheral portion is reduced, thereby resulting in improvement of cutting accuracy of wafers. (2) Since binder (electrodeposition layer) is not employed, amount of wear of the cutting blade is reduced. Hence, it becomes possible to perform slicing operation for a long period. Therefore, the number of replacement of the cutting edge can be reduced, thus resulting in great reduction in cost of cutting operation. (3) In the case where diamond is formed on a base member and one side face of the diamond adjacent to the base member is used as a cutting edge after removing the base member through its melting, the cutting edge is capable of having a surface roughness Rmax of about 0.05 µm. Therefore, a finished surface of a workpiece can be improved remarkably. As a result, the workpiece can be cut to finish state at a time without hitherto required multiple steps from rough cutting to finish cutting. In addition, cutting allowance can be reduced and cutting accuracy can be improved. (4) Even a large-diameter inner peripheral type cutting blade can be produced at high accuracy. (5) Since failure of the abrasive grains of the prior art cutting blade does not take place, the cutting blade has excellent wear resistance and durability. (6) Since grain diameter of diamond can be controlled arbitrarily in accordance with vapor phase synthesis conditions, a diamond film of ever about 20 to 30 µm in thickness can be obtained. Accordingly, it becomes possible to reduce cutting allowance and improve cutting accuracy. (7) Grain diameter of diamond can be controlled only by vapor phase synthesis conditions such that an inner peripheral portion of the cutting edge is increased in thickness, while grain diameter of diamond is reduced further towards an outer peripheral portion of the cutting edge. Thus, quality and yield of the cutting blade can be improved. The cutting blades K1 and K2 have a thickness of 20-300 µm as described earlier. This thickness is selected on the following ground. Namely, if thickness of the cutting blade is less than 20 µm, and metal base and diamond itself have insufficient strength and therefore, is readily subjected to failure. On the other hand, if thickness of the cutting blade exceeds 300 µm, cutting allowance is increased, thereby resulting in drop of yield. Hereinbelow, a method of producing the cutting blade K1, according to the present invention is described with reference to Figs. 10a(1) and 10b(1) to Figs. 10a(3) and 10b(3). The method includes a first step of Figs. 10a(1) and 10b(1) in which diamond is formed on a side face of a cylindrical base member 60, a second step of Figs. 10a(2) and 10b(2) in which the base member 60 is removed through its melting by acid treatment or the like such that the annular diamond film 40 is obtained and a third step of Figs. 10a(3) and 10b(3) in which the annular diamond film 40 is secured to the inner periphery of the annular metal base by the bonding layer 80. In the first step, diamond is coated on the side face of the cylindrical base member 60 by using a filament CVD (chemical vapor deposition) apparatus of Fig. 7 acting as a diamond synthesis apparatus. The filament CVD apparatus includes an apparatus housing 9, a stand 10 for supporting the base member 60, a pair of filaments 11 for activating gas, a pair of electrodes 12, three gas inlets 13, a pair of cooling water passages 14, a pair of gas outlets 15 and a pressure gauge 17. It may also be so arranged that a cutting operation for adjusting thickness A of the diamond film 40 by laser beams is performed between the second and third steps. Figs. 11a(1) and 11b(1) show a modified first step in which diamond is formed on an inner periphery of an annular base member 60′. In this first step, diamond is coated on the inner periphery of the annular base member 60′ by using a filament CVD apparatus of Fig. 8 acting as a diamond synthesis apparatus. The base members 60 and 60′ may be made of ordinary materials for synthesizing diamond, for example, Mo, W, Si, Ta, Nb, Cu, Al, B, Be, Au, Pt, Fe, Ti, C, C having Si deposited thereon, SiC, AIN, SiN, WC, MoC, BN, BC, NbC, TaC or the like. The metal base 30 is usually made of carbon tool steel, stainless steel, etc. The bonding layer 80 for securing the diamond film 40 to the metal base 30 may be formed by adhesive but is desirably formed by solder in view of its excellent heat resistance and durability. Meanwhile, the annular diamond film 40 is produced by the above two procedures of Figs. 10a(1) and 10b(1) and Figs. 11a(1) and 11b(1). In the case of Figs. 10a(1) and 10b(1), an inner side face of the diamond film 40 confronting the base member 60 at the time of deposition of diamond on the base member 60 is used as the cutting edge, while an outer side face of the diamond film 40 on which diamond is grown has a rough surface and is attached to the metal base 30. Thus, by improving surface roughness of the inner side face of the diamond film 40, it becomes possible to improve surface roughness of the cutting edge of diamond, so that roughness of a cut surface of a workpiece can be improved and thus, the cutting blade K1 can also be used for finishing. On the other hand, in the case of Figs. 11a(1) and 11b(1), the cutting edge portion and the bonding portion are disposed opposite to those of Figs. 10a(1) and 10b(1). Thus, an inner side face of the diamond film 40 on which diamond film is grown has a rough surface and is used as the cutting edge. Therefore, roughness of the cut surface of the workpiece is slightly deteriorated and thus, the cutting blade K1 is suitable for rough cutting. The cutting blade K2 wholly made of diamond formed by vapor phase synthesis is produced in the same manner as tha method of Figs. 10a(1) and 10b(1) to Figs. 10a(3) and 10b(3) and the method of Figs. 11a(1) and 11b(1). The cutting blade K2 is produced by using, for example, a filament CVD apparatus of Fig. 9. The filament CVD apparatuses shown in Figs. 7 to 9 are operated under vacuum and include the several filaments 11 to several tens of the filaments 11. The stand 10 for supporting the base member 60 or 60′ may be provided rotatably. In Figs. 7 to 9, character D denotes a distance between the filament 11 and the base member 60 or 60′. Hereinbelow, examples 1 and 2 of production of the cutting blade of the present invention are described. [Example 1] The cutting blade K1 was produced by using the filament CVD apparatus of Fig. 7 and employing as the base member 60, a cylinder shown in Table 1 below and having an outside diameter of 1840 mm. In Table 1, C/Si represents material in which 5000 Å Si has bean deposited on a carbon member by sputtering. Under synthesis conditions shown in Table 1, diamond was deposited on the side face of the cylindrical base member 60 as shown in Fig. 10. Sample No. Supply gas (SCCM) Pressure (Torr) D (mm) Base member Material Thickness (mm) 1 H₂-1000 80 7 Si 80 CH₄-20 2 H₂-500 40 8 Si 25 CH₄-15 3 H₂-200 50 10 C/Si 200 CH₄-20 4 H₂-600 120 5 W 50 CH₄-12 O₂-2 5 H₂-1000 100 6 Mo 80 C₂H₅OH-20 Sample No. Thickness of portion A (µm) Thickness of portion B (µm) 1 80 200 2 25 120 3 200 280 4 50 400 5 80 80 Comparative example 3000 4200 Then, the diamond film 40 obtained by the first and second steps of Figs. 10a(1) and 10b(1) and Figs. 10b(1) and 10b(2) have dimensions shown in Table 2 above. In Table 2, the prior art cutting blade of Fig. 2 is recited as a comparative example. By using the thus obtained cutting blade K1, an ingot of single-crystal silicon and of 1800 mm in diameter was cut by slicing conditions of peripheral speed of the cutting blade of 1000 m/min. and feed rate of 40 mm/min. Results of this cutting is shown in Table 3 below. Meanwhile, in Table 3, the prior cutting blade of Fig. 2 is recited as a comparative example. Sample No. of slicing Accuracy of wafer Parallelism (µm) Distortion (µm) Scatter of thickness (µm) 1 4000 4±0.5 3.0±0.7 3.0±0.8 2 4300 7±1.0 4.0±0.9 4.2±0.9 3 1800 8±2.0 8.5±1.2 6.0±1.3 4 3000 5±1.1 4.0±1.2 3.0±0.4 5 2600 8±1.2 10.0±2.2 3.1±0.8 Comparative example 1000 25±5 20.0±3.5 18.0±3.0 Table 3 reveals that the cutting blade K1 in which the diamond film 40 is formed at the cutting edge improves cutting accuracy remarkably and lengthens service life greatly. [Example 2] The cutting blade K2 was produced by using the filament CVD apparatus of Fig. 9. The annular base member 60′ is made of polycrystalline silicon and has an inside diameter of 1840 mm, an outside diameter of 4930 mm and a thickness of 0.1 mm. It was found from the same cutting operation as Example 1 performed by using the obtained cutting blade K2 that 2000 wafers can be sliced. As is clear from the foregoing, in the thin plate blade for cutting the single-crystal ingot, according to the present invention, the diamond film formed by vapor phase synthesis is provided at the cutting edge. Hence, in the thin plate blade of the present invention, binder such as Ni or Co and the electrodeposition layer are not employed, so that partial wear or failure of the cutting blade does not take place and thus, cutting operation can be performed at high accuracy for a long period. Accordingly, the number of replacement of the cutting edge is reduced and yield of the cutting blade is improved, thereby resulting in great reduction of cost of cutting operation. Although the present invention has been fully described by way of example with reference to the accompanying drawings, it is to be noted here that various changes and modifications will be apparent to those skilled in the art. Therefore, unless otherwise such changes and modifications depart from the scope of the present invention, they should be construed as being included therein. Reference signs in the claims are intended for better understanding and shall not limit the scope.

Claims: A method of forming a thin annular blade plate (K1) with an inner annular cutting edge portion having a thickness in a range of from 20 to 300 µm and characterised in that said portion is made wholly of polycrystalline diamond formed by vapour phase synthesis. A method according to claim 1 wherein the whole plate is formed by vapour phase synthesis. A method according to claim 1 wherein the inner annular cutting edge portion is attached to the inner periphery of a separate annular member of the plate. A method according to claim 3 wherein the annular cutting edge portion is formed on an annular base member, then removed from the base member, then attached to the annular blade plate member. A method according to claim 4 wherein the annular member is removed from the base member by dissolution. A method according to claim 5 wherein the dissolution is by acid treatment. A method according to claim 3, 4, 5 or 6 wherein the annular member is soldered to the annular blade plate member. A method according to any one of the preceding claims wherein the grain diameter of the diamond is reduced towards an outer peripheral portion of the cutting edge. A method according to claim 8 including the step of increasing the thickness of the inner peripheral portion. A method of producing an annular thin plate blade having a cutting edge at its inner periphery, comprising the steps of: forming a diamond film on the surface of the annulus of an annular base member by vapour phase synthesis; and separating the diamond film from the base member by dissolution of the base member. A method according to claim 10, and including the step of mounting the separated diamond film to the inner periphery of an annular blade plate member.

Inventors: FUJIMORI NAOJI C O ITAMI WORKS, TANABE KEIICHIRO C O ITAMI WOR, FUJIMORI, NAOJI, C/O ITAMI WORKS OF SUMITOMO, TANABE, KEIICHIRO, C/O ITAMI WORKS OF SUMITOMO
Applicants: SUMITOMO ELECTRIC INDUSTRIES, SUMITOMO ELECTRIC INDUSTRIES, LTD.
Application year: 1990
Main classification: B28D5
IPC codes: B24D18, B23P5, B24D5, B23P15