THE ATOMIC-SCALE REMOVAL MECHANISM DURING CHEMOMECHANICAL POLISHING OF SI(100) AND SI(111)

Chemo-mechanical polishing (CMP) of silicon with a colloidal suspensio n of silica (''Siton'') is the standard technology for the preparation of smooth, defect-free silicon starting surfaces for microelectronic device patterning. Despite its importance in device manufacturing, lit tle is known about the microscopic removal mechanism during CMP that c ontrols the resulting surface properties. With infrared spectroscopy w e find that, after CMP, a surface termination by hydrogen predominates on Si(111) and Si(100). This H-termination is responsible for the obs erved strong hydrophobicity of the surface and its chemical stability (passivation) in air. Hydrophobicity (contact angle) and polishing rem oval rate strongly depend on the slurry pH and peak at pH approximate to 11. At this optimum pH a nearly ''ideal'' termination by monohydrid e is found on Si(111) which points to perfect atomic-scale surface pla narity and chemical homogeneity. Si(100), after CMP, exhibits a more c omplex H-termination by mono-, di-, and trihydrides. At higher or lowe r pH, OH groups replace some of the hydride species both on CMP-Si(111 ) and CMP-Si(100). We present a microscopic removal mechanism which - on an atomic scale - is determined by an interplay of local oxidation by OH- and passivation by hydrogen.