Atsushi Itokazu

Multi-Wire Electrical Discharge Slicing for Silicon Carbide

In this paper, we propose a new wafer slicing method for silicon carbide(SiC). SiC is well-known as a difficult-to-cut material, and a conventional slicing via multi-wire saw becomes more difficult with increasing ingot size. To solve this problem, the multi-wire electrical discharge slicing (EDS) method is applied to 100 mm-square SiC polycrystalline block. We successfully obtained the average thickness of 385 μm for nine sliced plates by ten-wires EDS. The thickness variation was measured to be less than 11.2 μm. This is the first demonstration of ten-wires EDS for 100 mm-square SiC material.

Multi-Wire Electrical Discharge Slicing for Silicon Carbide Part 2: Improvement on Manufacturing Wafers by Forty-Wire EDS

In this paper, a machining energy control slicing method for cylindrical shaped ingots and forty-wire electrical discharge slicing (EDS) technology are investigated. Our recent study in [4], ten-wire EDS was applied to 100 mm-square polycrystalline SiC material. Applying this technology to ingot slicing, an appropriate process technology for cylindrical shaped SiC materials which are the same as an actual ingot is required. The slicing of cylindrical shaped SiC using conventional multi-wire EDS causes the increase of sori, or wire break with unstable machining process since wasteful machining power is not controlled as a function of machining length. To resolve this problem, we applied the machining energy control method which varies machining power with machining position. Using proposed method, ten-simultaneous slicing of cylindrical shaped SiC material is obtained with 80 μm/min in machining speed. The sori of machined surface is 34 μm, and TV5 is 28 μm as a result. Moreover, forty-wire EDS technology is applied to SiC slicing for improving wafer productivity. We successfully verified forty-simultaneous slicing of 100 mm-square poly-crystal SiC material without wire break. The sliced 39 thin plates are obtained 385 μm in average thickness, and 16 μm in maximum thickness variation.

Characteristics of a Schottky Barrier Diode and the SiC Wafers Sliced by Wire Electrical Discharge Machining

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 consists 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.