Ellipsometric studies of silicon dioxide films on silicon

Ellipsometry is demonstrated to be an appropriate technique for measuring the thickness of silicon dioxide films grown thermally and by an r.f. glow discharge deposition technique in commercial equipment. Optical anisotropy has been observed in thermally grown oxide layers on crystalline (111) and (100) silicon by rotating the samples (in an ellipsometer) about a normal to the sample surface. The degree of anisotropy of films on silicon (111) was found to be dependent on the oxide thickness and decreased to about zero with time at an annealing temperature of 950 °C. The changes in the optical constant produced by rotation increased from 1 × 10^-3 to 8 × 10^-3 with an increase in oxide thickness from 400 to 1000 nm and decreased for thicker films. No anisotropy was observed in thermally grown films or for films deposited by an r.f. glow discharge for thicknesses less than 400nm.