Characteristics of a Schottky barrier diode and the SiC wafers sliced by wire electrical discharge machining

摘要

The multi-wire electrical discharge slicing (multi-wire EDS), which is a brand-new method for fabricating wafers, is expected to considerably reduce the production cost of SiC wafers by decreasing in the width of kerf and kerf loss. We evaluated, for the first time, the influences of a wire electrical discharge machining (WEDM) on the SiC wafers based on experiments using WEDM equipped with a power supply of EDS. Although the analyses by transmission electron microscopy (TEM) and energy dispersive X-ray (EDX) revealed that the WEDM influenced layer consisted of a contamination layer including several kinds of metals and a layer having crystal defects was certainly formed near the wafer surfaces, the width of the influenced layers was only 3μm, and the layer could be easily removed by the grinding process. Furthermore, characteristics of Schottky barrier diodes (SBDs) fabricated with removing the influenced layer formed by WEDM are comparable to those fabricated with using conventional wafers. 1. Introduction SiC is an attractive material for power devices, because of its excellent electrical properties. While the demand of SiC for power devices is increasing, reduction of wafer production cost is required due to a valuable SiC ingot. Hence, it is effective to increase, numbers of wafers which are obtained from one ingot. The increase in wafers can be expected by reduction of kerf loss during slicing, whereas it is very difficult to slice a SiC ingot into wafers with a narrow kerf due to its hardness. It is difficult for conventional multi-wire saw to use thin line wires which is effective to reduce kerf loss. In the case of slicing of SiC ingot by wire-saw with thin line wire, the slicing speed must be slow to prevent wire breakage. In order to resolve this problem, we have proposed the multi-wire EDS for wafer manufacturing method as shown in the Fig. 1 [1]. In the multi-wire EDS, a large reactive force does not act on the wire throughout the process because of noncontact removal machining with the heat of electrical discharge. Essentially, thin line wires can be used on the multi-wire EDS, since the wire is not influenced by hardness of a SiC ingot. In particular, the multi-wire EDS is expected as the effective method for slicing the large-diameter wafers from the large SiC ingot. On the other hand, the multi-wire EDS might spoil the attractive characteristic of SiC wafers due to contaminations of several kinds of metals which are mixed in a processing atmosphere or due to considerably local high temperature more than sublimation temperature. In this paper, we report the characteristics of a SBD fabricated with SiC wafers sliced by WEDM based on the investigation about properties of the influenced layer.