  In situ plasma etching is a common method to prepare diamond substrates for
epitaxial overgrowth to effectuate higher quality. However, there is no
practical, direct, qualitative method established so far to assess the
performance of the etching pretreatment. We propose an optimization of the
pretreatment process on grounds of high-resolution X-ray diffraction
measurements to judge the structural quality gain of the diamond substrates and
the effectiveness of the polishing-induced subsurface damage removal. The
obtained data shows, that parameters like thickness nor misorientation angle of
the diamond substrates seem to influence the gain of the structural quality.
The process duration, however, is an important key factor, when the amount of
material removal and the arising roughness are discussed. Furthermore, the
impact of the oxygen-to-hydrogen ratio is examined. And with rising oxygen
percentage, the structural quality gain remains similar, only the overall as
well as local mean roughness increases exponentially. Within the utilized
reactor setup, the best results are obtained after a 20-minute in situ hydrogen
plasma-etching step. The optimal pretreatment process, however, will always
embody a tradeoff and needs to be optimized for each reactor type. Due to the
introduced method a better evaluation and comparison of the achievements is
accomplishable.
