Acknowledgments

at ll5O ~ no impur i ty dr iven effect on oxidation is at-tr ibuted to the Si precipitation. Since this study deals with the oxidation of heavi ly B- and P-doped Si, the B203 phase separation effect and the Si precipitat ion effect wi l l be discussed at greater depth in a future publication. Conclusions From an extension of the oxidation data for heavi ly B- and P-doped Si to lower temperatures and an anal-ysis of the data in terms of the l inear-parabol ic model several conclusions are made: 1. P pr imar i ly increases the over-a l l oxidation rate at lower temperatures whi le B is more effective at the higher oxidation temperatures. 2. The accumulation of P and depletion of B at the Si surface explain the variat ion of kL values with tem-perature. 3. The enhancement effect of P on kp is due to a loosening of the SiO2 network. When P substitutes for Si in Si-O4 tetrahedra, fewer b idging oxygens are provided. The net loosening effect is most pronounced at]tower temperatures where other network loosening factors are smaller. 4. The enhancement of kp due to B is due to the creation of defects when B-O3 is oxidized to B-O4. This mechanism is favored at higher temperatures where bonds are more l ikely to be broken. 5. TEM supports the atomistic arguments to explain the kp results, since no morphological differences were found in the various oxides which could be correlated with an enhanced diffusion of oxidant. 6. Over the extended temperature range of the pres-ent study, the Arrhenius relationship is not obeyed. Hence there is no straightforward interpretat ion of Ea values. However, divergent results from two previous studies (7, 13) are explained based on the Arrhenius plots