High efficiency penetration boring of single crystalline silicon ingot by EDM

In the manufacturing process of integrated circuit, graphite plate with many fine holes has been used as an electrode in plasma etching process. Recently, it is examined to use a single crystalline silicon as the electrode in order to minimize the contamination However, it is difficult to machine accurately by the conventional methods, since the material removal is due to brittle fracture. The machining force in EDM is very small compared with that in conventional machining, therefore the possibility of high efficiency and high accuracy boring hole in a silicon ingot by EDM is experimentally investigated in this study. The removal rate of silicon is from 4 to 8 times higher than that of steel, while the electrode wear is from one-fifteenth to one-seventh times smaller. When the electrode advances at the exit of hole, stagnation region appears in which the electrode retracts suddenly and the machining becomes unstable. In order to prevent this phenomenon, the copper plate is closely attached under silicon ingot firmly. In this method, better hole can be obtained without chipping. Besides, there is no sticking of insulator which contains silicon oxide and copper oxide on the wall of hole in this case. Furthermore, it is proved that even high aspect ratio over 200 boring is possible.