High-speed, high-quality thinning processes of GaAs wafers for high-power FETs

This paper describes new machining processes for GaAs wafers. First, bonding accuracy of 1~2 μm in parallelism was achieved by using a specific wax and a glass base plate. Secondly, an efficient and ultraprecision grinding technique using metallic bond diamond wheels applied with electrolyticin-process dressing (ELID) was introduced for the high-speed thinning process of GaAs wafers. Through this process, metallic bond wheels with diamond grains from 12 to 2 μm reduced the thickness of wafers, and produced good mirror surfaces of 40 nm in Ry with low subsurface damage successfully. High surface accuracy of around 0.3 μm was also obtained for wafers 3 inches in diameter. Finally, a fluid containing of mainly NaBrO₂ was developed as a new polishing media, and proved that surface roughness smaller than 20 angstroms in Ry can be obtained effectively. Thus, this paper provides the concept of these new thinning processes for GaAs wafers for high-power FETs with high heat sinking function