The Effects of Intrinsic In-Plane Stress on the Local Atomic Structure of Thermally Grown SiO 2

The effect of thermal history on the local atomic structure of thermally grown and annealed SiO2 films is discussed. Thin films of SiO2 were prepared for study by (1) thermal oxidation of silicon at 850°C and 1050°C in a dry oxygen ambient and, (2) by subsequent rapid thermal annealing at temperatures between 850°C and 1200°C. After thermal processing, the film thickness was reduced incrementally by a wet chemical etchback technique to within 50 A of the growth interface. Relief of intrinsic growth stress by viscous flow was investigated, at each thickness increment, on a local atomic scale by infrared spectroscopy and on a macroscopic scale by beam-bending type stress measurements. Results were analyzed in terms of a Maxwell model. Changes in film thickness and refractive index resulting from viscous flow during annealing were shown to obey a Clausius-Mossotti relationship. Local atomic strain values, calculated from shifts in the IR bond-stretching frequency, showed a linear correlation with measured stress values giving a value for a plane-strain Young’s modulus of 4.7 × 1011 dynes/cm2. This compares favorably with the literature value of 8.8 × 1011 dynes/cm2.