The Effects of Substrate Oxygen Content and Preannealing on the Properties of Silicon Epitaxial Layers

A study was carried out to evaluate whether the quality of Si epitaxial layers could improve if they were deposited on substrates intrinsically gettered through thermal annealing. Three different two‐step procedures were used to preanneal the substrates prior to deposition. Optical microscopy revealed the presence of defect‐free (denuded) zones at the surfaces of preannealed substrates only when the initial concentrations of interstitial oxygen in the substrates were , and if the high temperature step of the preannealing was carried out in a nonoxygen ambient. While the density of oxidation‐induced stacking faults in the epitaxial layers showed no such dependence, the minority carrier generation lifetimes in the layers were strongly dependent on the oxygen content and thermal history of the substrates. Layers deposited on preannealed substrates of high initial oxygen content exhibited the greatest lifetimes. It is believed that oxygen precipitates and related defects, when present in a substrate, getter metallic impurities introduced during processing away from the epitaxial layer and thus improve lifetimes. Such gettering appeared to be most effective when the substrates had both surface denuded zones and high densities of bulk defects.