High-efficiency planarization method combining mechanical polishing and atmospheric-pressure plasma etching for hard-to-machine semiconductor substrates

A high-efficiency planarization technique for preprocessing before final polishing is needed for hard-to-machine wide-band-gap semiconductors, such as silicon carbide (SiC), gallium nitride, and diamond. We proposed a novel planarization method that combines chemical mechanical polishing (CMP) and atmospheric-pressure plasma etching (plasma chemical vaporization machining [P-CVM]) and developed a prototype of the basic type CMP/P-CVM combined processing system. This prototype has a mechanical polishing part for introducing a damaged layer on the convex part of the sample surface and a P-CVM part for efficient etching of the damaged layer. Process conditions for plasma generation were determined in order to minimize the optical emission intensity ratio of nitrogen to helium because nitrogen comes from circumstance air and should not exist in the plasma region. Process conditions for mechanical polishing were determined in order to efficiently generate a damaged layer only on the convex part of the sample surface. The combined process was performed using a SiC substrate on which the mesa structure was fabricated as a sample. As a result, we found that the convex parts of the mesa structure were preferentially removed and the surface of the sample was planarized. We also found that the decreasing rate of the peak-to-valley value of the mesa structure obtained by CMP/P-CVM combined processing was approximately seven times greater than that during mechanical polishing.