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  Method of manufacturing silicon substrates for magnetic recording medium, silicon substrate for magnetic recording medium, magnetic recording medium, and magnetic recording apparatusUSPTO Application #: 20070270084Title: Method of manufacturing silicon substrates for magnetic recording medium, silicon substrate for magnetic recording medium, magnetic recording medium, and magnetic recording apparatus Abstract: A manufacturing method for silicon substrates for a magnetic recording medium has the steps of forming a stack body of a number of silicon substrates which are stacked via spacers therebetween, wherein each silicon substrate has a circular hole at a center of the substrate; immersing the stack body of the silicon substrates in a polishing liquid in which grains are suspended; and polishing inner peripheral end faces of the circular holes of the silicon substrates, wherein in polishing, a polishing brush contacts the end faces while performing a relative rotation between the end faces and the polishing brush, and the stack body of the silicon substrates is inverted during polishing. The step of polishing the inner peripheral end faces may be performed before inner and outer peripheries of the silicon substrate are subjected to chamfering. Preferably, the polishing brush is made of polyamide resin. (end of abstract) Agent: Sughrue Mion, PLLC - Washington, DC, US Inventor: Katsuaki Aida USPTO Applicaton #: 20070270084 - Class: 451036000 (USPTO) Related Patent Categories: Abrading, Abrading Process, Utilizing Fluent Abradant The Patent Description & Claims data below is from USPTO Patent Application 20070270084. Brief Patent Description - Full Patent Description - Patent Application Claims
[0001] Priority is claimed on Japanese Patent Application No. 2004-237340, filed Aug. 17, 2004, and U.S. Provisional Patent Application No. 60/603,566, filed Aug. 24, 2004, the contents of which are incorporated herein by reference. TECHNICAL FIELD [0002] The present invention relates to a silicon substrate for a small-sized magnetic recording medium, which is used as a recording medium for a data processing apparatus. BACKGROUND ART [0003] Accompanying recent progress in data processing apparatuses, data recording capacity of a magnetic recording medium has increased more and more. In particular, in magnetic disks, which are important media as external memory for computers, both storage capacity and data recording density increase every year, and development for recording data with higher density is required. For example, in accordance with development of notebook computers or palmtop computers, small-sized and impact-resistant magnetic recording media are required, and therefore small-sized magnetic recording media for recording data with higher density, which also have high mechanical strength, are required. More recently, navigation systems or portable music reproducing systems may employ ultra-small-sized magnetic recording media. [0004] A substrate made of aluminum alloy, which may be plated with NiP, or a glass substrate, is conventionally used as a substrate for a magnetic disk which is a magnetic recording medium as described above. A substrate made of aluminum alloy has inferior abrasion resistance and processibility, and plating with NiP is performed so as to solve this problem. However, a substrate which has been subjected to NiP plating tends to be warped, and may be magnetized when being processed at a high temperature. In addition, when the glass substrate is processed so as to be strengthened, a distortion layer may be produced in a surface of the substrate and the substrate may receive compressive stress, and the glass substrate also tends to be warped when being processed at a high temperature. [0005] Regarding an ultra-small-sized magnetic recording medium having a diameter of 1 inch (i.e., 25.4 mm) or 0.85 inches (i.e., 21.6 mm) which requires higher recording density, warp of the substrate is a fatal problem. Therefore, as a substrate for an ultra-small-sized recording medium, a thinner material, which is not easily deformed by external force and has a smooth surface on which a magnetic recording layer can be easily formed, is required. [0006] Accordingly, it has been proposed that a silicon substrate, which is popular as a substrate for semiconductor devices, be used as a magnetic recording medium (see, for example, Reference 1: Japanese Unexamined Patent Application, First Publication No. H06-076282). [0007] In comparison with aluminum, single crystal silicon has a larger specific gravity, a larger Young's modulus, a smaller coefficient of thermal expansion, a superior high-temperature characteristic, and electrical conductivity. Such single crystal silicon having many advantages is preferable as a material for a substrate for a magnetic recording medium. In addition, the smaller the diameter of the substrate, the smaller impact force the substrate receives, and a magnetic recording device having durability can be produced even from a silicon substrate. [0008] In order to manufacture the silicon substrate for a magnetic recording medium, generally, a single crystal silicon ingot is first produced by a pulling method, and the ingot is sliced into blank materials having a specific thickness. [0009] Each blank material is subjected to a lapping process, and a circular through hole is formed at the center of the blank material. The inner and outer peripheral edges are subjected to chamfering using a grindstone or the like. The inner and outer end faces and the chamfered portions are then subjected to polishing, so as to produce mirror-finished surfaces. Finally, the main surface is polished, and the substrate is used. [0010] The material for the silicon substrate is fragile; thus, cracks or chips tend to be produced in the above manufacturing processes. When cracks or chips are produced, the yield rate for manufacturing the magnetic recording medium is reduced, and generated particles may cause errors in a write/read process, or a crash of the magnetic head in the write/read process. [0011] In order to obtain a silicon substrate for the magnetic recording medium, which has no cracks or chips, from a fragile material, a method has been proposed in which for the inner periphery of the circular center hole and for the outer periphery of the substrate, the chamfering angle is set to be from 20.degree. to 24.degree., and the chamfering length is set to be from 0.03 mm to 0.15 mm (see, for example, Reference 2: Japanese Unexamined Patent Application, First Publication No. H07-249223). [0012] FIG. 12 is a longitudinal sectional view of a conventional silicon substrate for a magnetic recording medium. In FIG. 12, between an end face 4 and each of main surfaces 2 and 3 of the substrate 1, a chamfered portion 5 is formed, which is inclined at an angle from 20.degree. to 24.degree.. Similar chamfered portions (not shown) are also formed in the inner periphery of the substrate. [0013] According to the above form for the substrate, defects in the substrate, such as cracks or chips due to handling or dropping the substrate in the manufacturing process, are reduced, and the yield rate is remarkably improved. [0014] In addition, regarding the glass substrate, lower floating of the magnetic head has been planned so as to implement high density data recording, and the write/read method has been gradually switched from the CSS (contact start stop) method to the load and run method (or the ramp load method). These write/read methods also require a substrate which can be reliably installed and does not cause write/read errors, or a crash of the magnetic head in the write/read process. [0015] In order to satisfy the above requirements, a substrate has been proposed in which inner and outer peripheral end faces of the substrate are polished using a polishing liquid in which grains are suspended so that the arithmetic average roughness Ra for the surface roughness comes to 0.001 to 0.04 cam, and the maximum height Rmax for the surface roughness comes to 0.5 .mu.m or less (see, for example, Reference 3: Japanese Unexamined Patent Application, First Publication No. H11-221742). [0016] According to such a substrate, no cracks or chips are produced even when a substrate contained in a processing cassette (which is a case for storing and transferring a substrate in a manufacturing process) is transferred, and no write/read errors or crash of the magnetic head in the write/read process occurs, thereby providing a magnetic recording medium which can be reliably installed. [0017] In order to write or read data on the magnetic recording medium, the medium is rotated at a high speed while a center circular hole of the medium is fit around a spindle. Therefore, the accuracy for processing the center circular hole is important, and if this accuracy is inadequate, a problem may occur in assembling of a hard disk drive which can be rotated at high speed. [0018] The silicon substrate is fragile; thus, a hard disk drive having high accuracy cannot be obtained by only limiting the surface roughness of the finished inner peripheral end face as shown in Reference 3. [0019] In order to mass-producing hard disk drives having consistent quality and high performance, it is necessary to improve the accuracy and reduce dimensional variation of inner diameters of the center circular holes of the silicon substrates as respective magnetic recording media which are built into the hard disk drive. With inadequate accuracy in dimensions of the inner diameters, it is impossible to mass-produce hard disk drives having consistent quality and high performance. [0020] However, no trial or attempt for regulating the accuracy relating to the dimensional variation of the inner diameters of the center circular holes has been implemented. DISCLOSURE OF INVENTION [0021] In view of the above circumstances, an object of the present invention is to improve the accuracy and reduce dimensional variation of the inner diameters of the center circular holes of the silicon substrates, to efficiently manufacture silicon substrates suitable for hard disk drives which have consistent quality and can be rotated at high speed, and to provide a magnetic recording apparatus in which a magnetic recording medium using such silicon substrates is mounted. Continue reading... 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