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

Chemo-mechanical polishing (CMP) of silicon with a colloidal suspension 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, little is known about the microscopic removal mechanism during CMP that controls the resulting surface properties. With infrared spectroscopy we find that, after CMP, a surface termination by hydrogen predominates on Si(111) and Si(100). This H-termination is responsible for the observed strong hydrophobicity of the surface and its chemical stability (passivation) in air. Hydrophobicity (contact angle) and polishing removal rate strongly depend on the slurry pH and peak at pH approximate to 11. At this optimum pH a nearly "ideal" termination by monohydride is found on Si(111) which points to perfect atomic-scale surface planarity and chemical homogeneity. Si(100), after CMP, exhibits a more complex H-termination by mono-, di-, and trihydrides. At higher or lower 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.