On the Kinetics of the Thermal Oxidation of Silicon: II . Some Theoretical Evaluations

Abstract

A steady‐state transport analysis, including electric field effects, leads to orientation‐dependent linear and parabolic rate constants. A free energy budget accounting indicates that neutral oxygen diffusion in the SiO2 cannot alone account for the oxidation reaction. An analysis of the system relaxation associated with the normalSi/SiO2 interface disregistry indicates that a network of extra half‐planes forms at the interface to reduce the stored strain energy and that movement of the interface requires the influx of vacancies from the Si, egress of Si interstitials from the interface back into the bulk Si, or free volume influx from the SiO2 to remove the extra half‐plane segments. This tends to become a dominant feature of the kinetics of oxidation. An analysis of the proportioning of the total driving force into its component contributions and their relative magnitudes is given. The coordination of a variety of diverse oxidation studies is indicated.

Intrinsic SiO2 film stress measurements on thermally oxidized Si

“…Now, however, our stress measurements show that the (111) has a small relative stress. Therefore, we now conclude that both areal density and measured oxide stress are important at the outset of the oxidation, and their product scales initially with the oxidation rates according to equation (9). This conclusion is reasonable since the intrinsic stress is tensile in the Si and thus the stretched Si-Si bonds on the surface are likely easier to react.…”

“…The kinetics of the thermal oxidation of Si have been explained using the A number of models have been proposed which consider stress to be influential on either the interface reaction (9,10) or the diffusivity of oxidant species through a strained oxide (11,12,13 (14) observations have included the effects of mechanical properties on the Si-SiO 2 interface and on the early stages of oxidation.…”

A Measurement of the Effect of Intrinsic Film Stress on the Overall Rate of Thermal Oxidation of Silicon

“…k= kC C I [2] where k is a constant, C and C Si are the oxygen and silicon concentrations, o-is the intrinsic stress and is the viscosity of SiO 2 . The compressive SiO 2 stress is tensile in Si thereby stretching the Si -Si bonds and increasing the likelihood for '1 ,.oxidation.…”

In-Situ Stress Measurements during Thermal Oxidation of Silicon

“…It is observed that a, is larger nearer the Si-SiOe interface where SiOe is produced via the interface reaction between Si and oxidant. The origin of at has been attributed to the partial confinement of the molar volume change accompanying the transformation (5,7,9). Based on the fact that the maximum a, found from extrapolation to zero SiO* thickness is substantially less that the theoretical value of more than 10"1 dynes/cma (7), an initially fast stress relaxation was suggested for the SiOa as it is formed which is followed by a much slower relaxation that is characteristic of the bulk SiOa viscosity (22).…”