Oxidation of n-Type Silicon in the 10–1400-Å Oxide Thickness Range

The oxidation of the (111) surface of n-type silicon in oxygen and in steam has been followed by ellipsometry in the film thickness region of 10 to about 1400 Å. For very thin films (<300 Å), the real part of the complex index of refraction proves to be 4.08±0.02 as compared to 4.05 for films >300 Å. Oxidation between 30 and about 60 Å follows a logarithmictime relationship. As the film thickens above this the rate accelerates then decreases and the data do not follow any of the usual thickness-vs-time relationships. As a first approximation the average rate of oxidation (up to about 500 Å) is proportional to the square root of the oxygen partial pressure. Between about 890 and 1100°C the activation energy proves to be about 22 kcal/mole.