A study of grown-in impurities in silicon by deep-level transient spectroscopy

Abstract

Deep levels due to various impurities incorporated into Czochralski silicon ingots during crystal growth have been delineated. The largest impurity-induced deep-level concentration, defined as the electrically active impurity concentration, is found to be a fraction of the metallurgical impurity content of the crystals. This fraction for a specific impurity depends on the thermal history of the sample and the ability of the impurity to diffuse. POCl 3 gettering of Ti and V produces a decreasing electrically active impurity concentration toward the surface of a silicon wafer, while there is no observable effect of this heat treatment on the Mo concentration. In the case of Cr, which diffuses much more rapidly than Mo, Ti, or V in silicon, a very significant reduction in the electrically active concentration is observed after heat treatment. Similarly, in metal-doped polysilicon wafers the electrically active Mo concentration appears unaffected by grain boundaries, but the electrically active Cr concentration at or near some grain boundaries is reduced by more than an order of magnitude compared to that at grain centers.