Dislocation pinning effect of oxygen atoms in silicon

Abstract

A definitive proof has now been obtained of the existence of a dislocation pinning effect by oxygen atoms in silicon. Ambiguities caused by uncertain material variables in different crystals or different parts of a crystal are avoided in this investigation by making oxygen out-diffusion from a wafer, creating a continuous variation of oxygen concentration in a ∼60-μm-deep surface layer. Dislocation movement at different depths of this layer was studied using indentation dislocation rosettes (IDR) on a 2° beveled surface. The method of IDR is uniquely suitable for this study because microdislocation half-loops are generated and confined to move within each ∼10-μm-deep layer in a series of precisely determined microregions down the bevel. The size of IDR increases steadily toward the sample surface, in good correlation with the steady decrease of oxygen concentration toward the same sample surface. The effect at the maximum oxygen concentration in this case increases the critical resolved shear stress in silicon by a factor of 4. This is a most beneficial effect in reducing thermal slip in the practical matter of silicon wafer processing.