On the roughness of hydrogen-plasma treated diamond(100) surfaces

To investigate the possibility of influencing the roughness of diamond(100) surfaces, type Ib or heavily boron (B)-doped HPHT diamond crystals were mechanically and chemo-mechanically polished, and additionally exposed to a microwave-assisted hydrogen plasma. The resulting roughness and surface topology was analyzed on a macroscopic scale by stylus profilometry (PFM), and on microscopic scales by STM and AFM. The following results have been observed: the surface roughness (rms-value) is reduced by mechanical polishing from 4 nm(rms) (as received) to about 2 nm(rms) (PFM). This step, however, leads to scratches with depths up to 40 nm(pp). Chemo-mechanical polishing with KNO3 reduces the surface roughness further to typically 100 pm(rms) (PFM), usually eliminating the above scratches. The roughness determined by STM is typically 5-10-times higher than measured by PFM. After exposing B-doped samples for 3 min to the H-plasma under typical CVD growth conditions, the roughness increases up to 4 nm(rms) and a "brick-wall" pattern appears formed by weak cusps running along [110]. After exposure for an additional 5 min, the surface roughness of the B-doped samples increases further to 20-40 nm(rms) and exhibits a regular pattern frequently with characteristic structures of 60 nm width, 250 nm length, and 160 nm height running along approximately [110]. The "roofs" are faceted with faces of approximately {XX1}. These results will be discussed in terms of strain relaxation, similar to the surface roughening observed on SiGe/Si and anisotropic etching of defects. (C) 1998 Published by Elsevier Science S.A.