Proton-enhanced diffusion and vacancy migration in silicon

Abstract

Single crystals of silicon containing prediffused arsenic, boron, and phosphorus profiles are bombarded at 600–900 °C with 250–360-keV protons. Under conditions approaching ideality (low impurity concentration and less than 1013 protons/cm2 sec) enhanced impurity diffusion appears to proceed in an uncomplicated manner which is well described by steady-state kinetic treatment. At high temperatures and very low bombardment fluxes the enhanced-diffusion coefficients are observed to be temperature independent and first-order dependent upon flux. At moderately increased damage rates, particularly at lower temperatures, the diffusivities become temperature dependent and a half-order flux dependence is observed. The results are explained by assuming proton-enhanced diffusion to be controlled by the migration of split monovacancies (semivacancy pairs). Consistency with annealing studies of radiation-induced defects at much lower temperatures and with thermally activated diffusion studies at higher temperatures is attained by assuming a 1.47-eV migrational enthalpy and a 3.66-eV enthalpy of formation for the uncharged defect.