Experimental study of surface performance of monocrystalline 6H-SiC substrates in plane grinding with a metal-bonded diamond wheel

Monocrystalline SiC has long been recognised as an ideal third-generation semiconductor material for application in situations where there is high frequency, high power and high voltage. Because of the hardness, stiffness and strength of monocrystalline SiC, these materials are extremely difficult to machine in order to produce the extremely flat, smooth and damage-free surfaces required in many industrial applications. This paper presents the results of plane grinding experiments which were carried out using a metal-bonded diamond wheel. The process parameters of these have demonstrated a significant influence on surface roughness. Surface quality improved and roughness decreased as the wheel feed rate decreased. On the substrate surfaces, the particle trajectory density increased closer to the centre, producing better surface quality. At large feed rates, the material removed is mainly brittle fracture, and the plough scratch widths and gully depths on the ground surface are greater. At small feed rates, plastic removal predominates, becoming more significant closer to the centre and giving a smoother surface. Median and transverse cracks occur in the subsurface damaged layer, and the crack depths are consistent with the surface roughness Rz and gully morphology. Then, the critical grit depth of cut and the maximum undeformed substrate thickness values under different grinding conditions were calculated in order to analyse the characteristics of the subsurface damage and the material removal mechanism. Finally, an optimised process was achieved using orthogonal experiments, with processing parameters for rough, half-fine and fine grinding. This process gives flat substrates with surface roughness Ra 0.012 μm, SSD < 4 μm and TTV < 3 μm, which achieves the same level of precision as lapping.

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