On the Segregation of Ca at SiO2/Si Interface During Oxygen Ion Bombardment

Abstract

Segregation of Ca in Si has been studied using SIMS and RBS. Pronounced Ca profile broadening is observed during SIMS measurements with oxygen ions under bombardment conditions, yielding the formation of a stoichiometric oxide layer at the surface. Additional profiling through the SiO2/Si interface showed that Ca segregates predominantly at the Si side of the interface, within an a-Si layer adjacent to the continuous SiO2 layer. We explain the migration behaviour of Ca in thermodynamic terms whereby segregation is driven by a large difference in solid solubilities of Ca in a-Si and SiO2. The influence of temperature on the segregation at the SiO2/a-Si interface is demonstrated. Evidence is also provided for the electric-field-induced migration of Ca. The discrepancy with previously reported results on the migration behaviour of Ca is discussed.