ROUGHNESS TRANSITIONS OF DIAMOND(100) INDUCED BY HYDROGEN-PLASMA TREATMENT

To investigate the influence of hydrogen-plasma treatment on diamond(1 00) surfaces, heavily boron (B)-doped HPHT diamond crystals were mecha nically and chemo-mechanically polished, and exposed to a microwave-as sisted hydrogen plasma on a time scale of several minutes. The resulti ng surface morphology was analyzed on macroscopic scales by stylus pro filometry (PFM) and on microscopic scales by STM and AFM. The polished samples have a roughness of typically 100 pm(rms) (PFM), with no obvi ous anisotropic structures at the surface. After exposure of the B-dop ed diamond(100) to the H-plasma, the roughness increases dramatically, and pronounced anisotropic structures appear, these being closely ali gned with the crystallographic axis' and planes. An exposure for 3 min utes to the plasma leads to an increase of the roughness to 2-4 nm(rms ) (STM), and a 'brick-wall' pattern appears, formed by weak cusps runn ing along [110]. Very frequently, the cusps are replaced by 'negative' pyramids that are bordered by {11X} facets. After an exposure of an a dditional 5 minutes, the surface roughness of the B-doped samples incr eases further to 20-40 nm,, (STM), and frequently exhibits a regular p attern with structures at a characteristic length scale of about 100 n m. Those structures are aligned approximately with [110] and they are faceted with faces of approximately {XX1}. These results will be discu ssed in terms of strain relaxation, similar to the surface roughening observed on SiGe/Si and anisotropic etching.