Effects of thermal history on stress-related properties of very thin films of thermally grown silicon dioxide

Abstract

This paper presents studies of the infrared (IR) absorbance and the intrinsic stress in thermally grown very thin films (60 to 700 Å) of SiO2. These data are combined with previously obtained data for thicker thermally grown films (∼1300 Å) to study the variation in intrinsic growth stress close to the Si/SiO2 interface. The combined data indicate that the intrinsic stress at Si/SiO2 interfaces extrapolates to the same relatively high values for oxides grown at 700 and 1000 °C, and that the distribution of Si–O–Si bond angles close to the Si/SiO2 interface, as deduced from the IR data, is quantitatively different than in the bulk of the oxide film. These two observations are explained in terms of a model based on a temperature dependent viscoelastic relaxation of the oxide stress. This model emphasizes differences in the thermal history of the SiO2 near the Si/SiO2 interface, as compared to the SiO2 that is well removed from that interface and is in the bulk of the film and/or close to the ‘‘top’’ surface of the film. The observed differences between the 700 and 1000 °C bulk oxides, and the associated Si/SiO2 interfaces are explained in terms of a renormalized time scale that is defined by the ratio of the growth time to the viscoelastic relaxation time at the growth temperature.