Theory and Direct Measurement of Boron Segregation in SiO2 during Dry, Near Dry, and Wet O2 Oxidation

A theory of B segregation is developed which accounts for the differences in m observed in, for example, diffusion from a highly doped B2O3 source as compared to oxidation of B-doped Si in wet and dry oxidizing ambients. We have found that most dry O2 oxidations are really only partially dry and that the presence of as little as ~20 ppm H2 0 results in an m essentially the same as oxidation in 100% steam, i.e., m = 0.58 at 1200°C with an “effective” activation energy of 0.64 eV. However, in a truly dry oxidation, the B segregation coefficient at 1200°C is ~1 with an effective activation energy of 0.33 eV. We propose that these differences as well as the m > 2 observed in high concentration B2 O3 diffusion source oxidations are determined by the formation thermodynamics of the B compounds that are created during segregation. Quantitative agreement with m values obtained from directly measured B distributions across the SiO2/Si interface are obtained (SIMS measurements with oxygen leak). Also, through-oxide B implants were observed to have segregation coefficients equal to the pure dry Oa case even though the subsequent oxidations were performed in O2 ambients with trace amounts of H20. Examples are presented which illustrate the effect of trace amounts of H2O on B diffusion during oxidation. © 1978, The Electrochemical Society, Inc. All rights reserved.

Duke Scholars

Author Richard B. Fair Electrical and Computer Engineering