Kinetics of Lateral Autodoping in Silicon Epitaxy

Abstract

The kinetics of lateral autodoping in silicon epitaxy over silicon substrates containing localized arsenic diffusions was studied as a function of deposition temperature, growth rate, and preepitaxial heat cycling. The lateral autodoping increases either with the decrease of deposition temperature or with the increase in growth rate. The autodoping vs. temperature plot yields an enthalpy of ∼ −64 kcal/mole for the process in the temperature range 950°–1100°C and at 0.08 μm/min growth rate. Thermodynamic calculations showed that the arsenic redistribution during lateral autodoping cannot be completely described by equilibria considerations and that an incorporation model based on dopant trapping during epitaxy is capable of explaining quantitatively the growth rate and temperature effects observed here. The effect of preepitaxial baking is such that the lateral autodoping decreases with the increase in either the bake temperature for constant bake time or the bake time for constant bake temperature. These results were analyzed in terms of the evaporation of arsenic during prebake and consequent surface depletion in the diffused regions. Arsenic evaporation velocity was calculated for several temperatures, which yields an activation energy of 5.16 eV for arsenic evaporation from (100) silicon surface in an flow ambient. This high activation barrier pertains to the evaporation of arsenic from the silicon surface through a nearly stagnant boundary layer in a typical CVD epitaxial system.