GB756195A - Improvements in or relating to methods and apparatus for cutting semi-conductor crystals - Google Patents

Abstract

756,195. Pickling. SIEMENS & HALSKE AKT.-GES. Feb. 18, 1954 [Feb. 18, 1953], No. 4855/54. Class 82(2). [Also in Groups XXII, XXIII and XXXVI] Semi-conductor crytals are cut by a band, wire, thread or the like of high tensile strength, on which a grinding and/or corrosive agent is placed during the cutting operation. The grinding agent may be moistened with water, oil or alcohol. The wire may have a surface coating of soft material, e.g. copper or silver, in which the grinding agent, e.g. emery, carborundum powder or diamond dust may be held. The wire may be of steel, molybdenum or bronze ; nylon, perlon, or natural silk may be used. When the wire is of magnetisable material, e.g. steel or iron, a magnetisable grinding agent, e.g. ferrite powder, is used ; by magnetising the wire, at least at the cutting position, the grinding agent is caused to adhere to the wire ; if the crystal is non-magnetic the magnetic grinding powder can easily be removed from the cut surface. A semi-conductor monocrystal 1 is divided into portions by endless steel wires 2, 3, 4 each passing around idler pulleys 10 and driving pulley 11. Each wire passes over a roller 5 which draws ferrite powder from a container 6. The wire is magnetised by a head 7 before it reaches the roller 5 and is demagnetised by a head 12 after it has left the cut. The ferrite powder may alternatively be dusted on or otherwise applied. When non-magnetic material is used it may be removed from the wire after it has left the cut by a stream of liquid. A corrosive agent, e.g. liquid, may be applied to the wire additionally to the grinding agent in some cases simultaneously. The corrosive agent may be used in place of the grinding agent. The corrosive agent and/or the grinding agent may be removed from the wire, e.g. by washing, after it has left the cut. The cutting action may be increased by moistening the wire with an electrolyte and applying a voltage between the wire and the material being cut. The cutting action may be improved by exciting the wire with mechanical vibrations, e.g. ultrasonic longitudinal vibrations. In place of the endless wire, a long wire may be wound from a supply reel on to a take-up reel ; the wire may be wound back again at high speed without any cutting action. A frame may be used on which separate wires are stretched adjacent one another, the frame being so driven that the wires reciprocate, one or both strokes being cutting strokes. The thickness of the wire is preferably less than 0À5 mm.; it may be 0À2 mm. or even less than 0À1 mm.