Surface topography in mechanical polishing of 6H-SiC (0001) substrate

Silicon carbide (SiC) single crystals have been used as the substrates of a new generation of wide band-gap semiconductors due to their unparalleled combination of high breakdown voltage, extreme temperature tolerance, mobility and radiation hardness. For their applications, the SiC substrates need to be machined with nanometric surface quality as well as high form accuracy. However, the superior properties of the materials render their machinability extremely difficult. In this paper, we report the form error and surface roughness of the 6H-SiC (0001) substrate mechanically polished using 3 μm diamond powders in two different polishing processes. One process was concentrated-load polishing; the other was surface polishing. The polished surfaces were evaluated using white light interferometry and atomic force microscopy (AFM) for assessment of two- and three-dimensional topographies including form error and surface roughness. We found that a large form error was produced on the 6H-SiC (0001) substrate in the concentrated-load polishing. The root-mean-square (RMS) surface roughness of approximately 4 nm was resulted. Surface polishing of the 6H-SiC (0001) substrate remarkably improved form accuracy. The RMS surface roughness of approximately 2.5 nm was obtained.