Theory and Direct Measurement of Boron Segregation in SiO2 during Dry, Near Dry, and Wet O 2 Oxidation

A theory of B segregation is developed which accounts for the differences in m observed in, for example, diffusion from a highly doped B 2 O 3 source as compared to oxidation of B‐doped Si in wet and dry oxidizing ambients. We have found that most dry O 2 oxidations are really only partially dry and that the presence of as little as ∼ 20 ppm H 2 O 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 B 2 O 3 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 SiO 2 / 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 O 2 case even though the subsequent oxidations were performed in O 2 ambients with trace amounts of H 2 O . Examples are presented which illustrate the effect of trace amounts of H 2 O on B diffusion during oxidation.