Effect of surface steps on oxide-cluster nucleation and sticking of oxygen on Si(001) surfaces

The effect of surface steps on the O₂ reactive surface sticking coefficient and oxide-cluster nucleation on Si(001)-(2×1) surfaces at 690 ^∘{}C sample temperature has been investigated for surfaces miscut 0.2^∘{}--6.5^∘{} away from (001), oxidation pressures 3×10^-8--6×10^-8Torr and O₂ doses {}800 L. Scanning tunneling microscopy and atomic force microscopy were used to determine oxidation-induced vertical etch rates (used to determine reactive sticking coefficients) and oxide-cluster densities. The reactive sticking coefficient and oxide cluster nucleation were found to be strongly enhanced in regions of higher step density. A comparison with model simulations of oxide cluster nucleation indicates that the increased nucleation rate is not simply due to the enhanced reactive sticking coefficient, but rather must be partially due to a step-related enhanced nucleation mechanism. Our measurements suggest that the atomic structure of the step (e.g., ``A type,'' ``B type,'' ``mixed,'' single height, double height, etc.) may also have an effect on the enhanced nucleation. The average diffusion length of surface oxygen is found to be much longer than the average step spacing for high surface miscut indicating that the nucleation enhancement at individual steps is weak.