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 crysta ls were mechanically and chemo-mechanically polished, and additionally exposed to a microwave-assisted hydrogen plasma. The resulting roughn ess and surface topology was analyzed on a macroscopic scale by stylus profilometry (PFM), and on microscopic scales by STM and AFM. The fol lowing results have been observed: the surface roughness (rms-value) i s reduced by mechanical polishing from 4 nm(rms) (as received) to abou t 2 nm(rms) (PFM). This step, however, leads to scratches with depths up to 40 nm(pp). Chemo-mechanical polishing with KNO3 reduces the surf ace roughness further to typically 100 pm(rms) (PFM), usually eliminat ing 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 ro ughness increases up to 4 nm(rms) and a ''brick-wall'' pattern appears formed by weak cusps running along [110]. After exposure for an addit ional 5 min, the surface roughness of the B-doped samples increases fu rther to 20-40 nm(rms) and exhibits a regular pattern frequently with characteristic structures of 60 nm width, 250 nm length, and 160 nm he ight running along approximately [110]. The ''roofs'' are faceted with faces of approximately {XX1}. These results will be discussed in term s of strain relaxation, similar to the surface roughening observed on SiGe/Si and anisotropic etching of defects. (C) 1998 Published by Else vier Science S.A.