Kinetics of Thermal Growth of Ultra-Thin Layers of SiO₂ on Silicon Part II. Theory

The thermally activated growth of oxide on silicon as a function of time obeys a linear-parabolic relationship, the linear part of which stems from interface limited reactions. In Part I of this paper, it has been reported that this linear part cannot result from a single rate-limiting reaction step, because the order of the over-all reaction rate differs for different substrate orientations at a fixed temperature and varies for a given orientation as a function of temperature. A kinetic model for the reaction between silicon and oxygen at the Si-Si02 interface is now presented to account for the experimental data (dsio2 300A, Tox = 700°-1000°C, po2 = 0.01-1.0 atm). Two parallel, competing reactions are postulated to occur. In the first of these, molecular oxygen reacts directly with silicon to form silicon dioxide and atomic oxygen; the second reaction involves the dissociation of O2. The atomic oxygen thus formed, may either react with silicon or recombine to molecular oxygen. An analysis of the data shows that a difference in the activation energies (i.e., 1.91 vs. 0.58 eV) associated with these competing reaction steps is responsible for the shift in their relative importance as a function of temperature. © 1972, The Electrochemical Society, Inc. All rights reserved.