Experiments on the origin of process−induced recombination centers in silicon

Abstract

Densities of recombination centers obtained by the transient capacitance technique in diffused p⁺n junctions and Al−nSi Schottky barriers are correlated with process variables of more than 70 diffusion and heat−treatment experiments. Results show that the two process−induced donor defect centers reported previously are generated at the strained and disordered silicon surface layers either from high−surface concentration phosphorus or boron diffusion or from mechanical lapping. Chemically polished surfaces appear to act neither as a source nor a sink of these defect centers. The defects are not related to oxygen in the original silicon nor oxygen introduced during oxidation or diffusion. The effects of phosphorus and boron surface concentrations, phosphosilicate surface glass layers, and diffusion temperatures on the concentrations of these two centers are investigated. Nearly constant defect concentration profiles at depth more than 50 μ from the surfaces are observed, suggesting an L−shaped defect concnetration profile in samples with one−sided surface defect source and U−shaped profile for two−sided surface defect sources. These characteristics suggest that the defect centers are vacancies or vacancy complexes formed by vacancies diffused into silicon from the surface sources.