Papers by Keyword: Wafer Processing

Abstract: The research and commercialization of SiC based power device have been burgeoning over the last decade worldwide, which is bringing about an increasing demand on lost-cost and low-defect SiC wafers. To meet this challenge, we have been continuously making efforts on improving the crystal growth and wafer processing techniques. Now, the mass-production of high quality 4-inch, 6-inch n-type and semi-insulating SiC wafers has been realized. Statistically, the micropipe density is lower than 0.5 cm^-2. The resistivity of the wafers is lower than 0.02 Ω·cm and up to 10⁸ Ω·cm for n-type and semi-insulating SiC single crystals, respectively. A state of the art processing technique has been developed to control wafer deformation and thickness within the desired values for subsequent epitaxy. The total defect number of the epitaxial layers grown on the "epi-ready" 4-inch SiC wafer is 63, and the usable area is 97.6%, indicating the high quality of our SiC substrates.

Abstract: 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.

Abstract: In order to slice the larger size ingot toward 6 inch of silicon carbide (SiC), we are developing Multi-wire Electric Discharge Machining (EDM). To prevent wire break during slicing, we have developed the electric discharge pulse control system. So far, with 10 multi-wires, we have succeeded in slicing of 4 inch SiC balk single crystal without wire break. High quality slicing surface (e.g. small value of around 10 μm of SORI for 3 inchi wafer) was also achieved. By polishing methode, EDM-sliced wafer was estimated to have the uniform thickness of damaged layer over the entire surface. We confirmed that the wafer sliced by EDM can be processed in the later process, by grinding the 3 inch wafer. And it was confirmed that 6 inch ingot can be sliced with 10 multi-wire EDM, by slicing the boule of SiC poly crystal. For the larger diameter ingot than 4 inch, Multi-wire EDM will be practically used by the effective removal of machining chips from the machining clearance between the wire and work.

Abstract: In this study, we report electric discharge machining (EDM) as a new cutting method for silicon carbide (SiC) single crystals. Moreover, we discuss characteristics and usefulness of the EDM for the SiC. The EDM realized not only high speed and smooth cutting but also lower surface damage. Defect propagation in the EDM SiCs have been also estimated by etch pits observation using molten KOH, however, we confirmed the EDM has caused no damage inside the SiCs in spite of high voltage and high temperature during the machining.