Journal of Applied Physics vol:73 issue:5 pages:2477-2485
The mechanism of plasma afterglow oxidation of silicon by atomic oxygen is discussed in terms of a physical model that includes recombination of the oxidant atoms during their diffusion through the SiO2 layer. Inclusion of a first-order O loss term in the continuity equation that governs the unbound O atoms leads to a biexponential concentration profile in the oxide. The corresponding time-dependent O flux across the SiO2/Si interface results in an oxide growth equation that is a more general form of the classical Deal-Grove model. Confrontation with available experimental data shows that the general expression can be abbreviated for oxide widths w greater-than-or-equal-to 0.1 nm as t = (A2/B)[exp(w/A) + exp(-w/A) - exp(w(i)/A) - exp(-w(i)/A)], where w(i) is the native oxide width. The two model parameters are A = square-root D/k and B = 2HD[O]g/n(b), with D being the diffusivity and k the first-order loss rate constant of unbound O atoms in SiO2, H the SiO2/gas Henry equilibrium ratio of free O atoms, [O]g = the gas-phase O atom concentration, and n(b) = the bound-O number density in SiO2. The two-parameter model provides excellent fits (sigma congruent-to 2% of final w) to the available data on both n- and p-type Si, strikingly better than fits obtained by the Deal-Grove equation in particular for p-type Si. The values deduced for the model parameters A and B provide proof for the controlling importance of the 0-atom recombination process, especially for p-type Si. The model parameters also allow values to be derived for other pertaining physical constants; e.g., the product HD is deduced to be 2.4 X 10(-9) cm2 s-1 at T congruent-to 850 K, in close agreement with the known HD value for neon atoms in SiO2, equal to 5.2 X 10(-9) cm2 s-1.