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. Most dry O2 oxidations are really only partially dry and the presence of as little as ~20 ppm H2O 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. It is proposed that these differences as well as the m>2 observed in high concentration B2O3 diffusion source oxidations are determined by the formation thermodynamics of the B compounds created during segregation. Quantitative agreement with m values obtained from directly measured B distributions across the SiO2/Si interface are obtained
