SPATIAL VARIATIONS IN OXYGEN PRECIPITATION IN SILICON AFTER HIGH-TEMPERATURE RAPID THERMAL ANNEALING

Spatial variations of oxygen precipitation have been studied in silico n wafers submitted to rapid thermal annealing (RTA) in nitrogen ambien ts at a temperature above 1150 degrees C prior to a two-step precipita tion treatment. The samples submitted to high temperature preannealing show a consistent enhancement of oxygen precipitation, which is depen dent on the RTA time and temperature. Oxygen precipitate density measu rements show that oxygen precipitation is not homogeneous inside the w afer, but peaks near the surfaces, with a minimum in the bulk. The hig h treatment in N-2 results in the formation of defects which act as pr ecursors for the subsequent nucleation and growth of oxygen precipitat es. There is strong evidence that these precursors are generated by th e thermal nitridation of the silicon surface and subsequent vacancy in jection into the bulk of the wafer. (C) 1997 American Institute of Phy sics.