Effects of N-Face Finishing on Geometry of Double-Side Polished GaN Substrate
Koji Koyama*, Hideo Aida*,**, Michio Uneda***, Hidetoshi Takeda*, Seong-Woo Kim*, Hiroki Takei*, Tsutomu Yamazaki**, and Toshiro Doi**
*Namiki Precision Jewel Co., Ltd., 3-8-22 Shinden, Adachi, Tokyo 123-8511, Japan
**Kyushu University, 6-1 Kasuga Kouen, Kasuga, Fukuoka 816-8580, Japan
***Kanazawa Institute of Technology, 7-1 Ogigaoka, Nonoichi, Ishikawa 921-8501, Japan
Difficulties involved in producing Double-Side Polished (DSP) GaN substrate are extracted and approaches to overcoming them are reported in this paper. Mechanical polishing with a neutral diamond slurry of pH 7.0 for the N-face and CMP for the Ga-face are widely applied to obtain DSP GaN substrates. Accordingly, the substrate exhibits transparency. However, this is accompanied by approximately 100 µm of bowing due to the Twyman effect. In this paper, the reduction of the substrate bowing to 10 µm is successfully achieved through the use of an acidic diamond slurry with a pH of 1.8 instead of a neutral slurry. Cathode luminescence reveals that an acidic diamond slurry also induces less subsurface damage in the N-face than does the neutral one. We conclude that the stress on the N-face induced by the subsurface damage in the case of polishing with an acidic diamond slurry comes closer to that of the Gaface finished via CMP.
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