INFRARED-ABSORPTION SPECTROSCOPY OF SI(100) AND SI(111) SURFACES AFTER CHEMOMECHANICAL POLISHING

The mechanism of silicon stock removal in chemomechanical polishing (C MP) is studied by characterizing surface chemical species with infrare d-absorption measurements and the corresponding degree of hydrophobici ty with contact angle measurements immediately after CMP. Surface prop erties and stock removal rates are found to depend strongly on the pH of the silica slurry used in this ''syton polishing'' technique. At th e peak of the removal rate [pH similar to 11 for both Si(100) and Si(1 11)], the surfaces have the highest hydrophobicity and the highest hyd rogen coverage. Si(111) has an ideal monohydride termination, while Si (100) is characterized by a variety of hydrides (mono-, di-, and trihy drides), suggesting different morphologies for the surfaces: atomicall y flat domains on Si(111) and rougher areas on Si(100). Away from the optimum slurry pH (at lower stock removal rates), a higher concentrati on of hydroxyl groups is observed, increasing the surface hydrophilici ty. At all pH, some oxidation occurs beneath the H-terminated Si surfa ce, as evidenced by a characteristic frequency shift of oxygen-backbon ded hydrides. The mechanisms of stock removal are considered in view o f these observations for the different ranges of slurry pH. In particu lar, at the highest removal rates, an interplay of surface oxidation, removal of oxidized silicon, and subsequent H termination is suggested . Based on the spectroscopic characterization of surface morphologies, the relevance of CMP to prepare atomically smooth silicon surfaces is discussed. (C) 1995 American Institute of Physics.