| 摘要 |
PURPOSE:To prepare a wafer which has a mirror surface on one-side surface has a large diameter with high precision by making difference in the polishing speed between on one surface and the other surface of the wafer interposed between the lower and the upper surface plates which revolve in the opposite direction and making one surface into mirror surface and the other surface into semipolished surface. CONSTITUTION:When the number of revolution of an internal gear 15 is 12rpm clockwise and the number of revolution of a sun gear 14 is 10rpm clockwise, a carrier 16 revolves 10.9rpm clockwise. Therefore, when polishing for a wafer is carried-out with the number of revolution of a lower surface plate 11 in 11rpm clockwise and the number of revolution of an upper surface plate 13 in 50rpm counterclockwise, the ratio between the speed difference between the upper surface of a wafer 17-upper surface plate 13 and the speed difference between the undersurface of the wafer 17-lower surface plate 11 becomes 510:1. Since the environment during machining is equal in the vertical direction, the ratio of the speed difference becomes nearly equal to the ratio of working speed on the upper and lower surfaces of the wafer 17, and only the upper surface of the wafer 17 is made mirror surface, and the undersurface is made semipolished surface. Therefore, even if the wafer 17 is made to a large diameter, a wafer having a mirror surface on one-side surface can be prepared with high precision similarly in the conventional method. |
