Test Methods for Measuring Bulk Copper and Nickel in Heavily Doped p-Type Silicon Wafers

The goal of this work was to optimize the existing test methods for measuring bulk copper and nickel impurities in the heavily doped p-type silicon wafers and to assess their sensitivity, recovery rate, and correlation. Three test methods were studied; low-temperature out-diffusion, polysilicon ultratrace profiling, and wafer digestion. The bulk copper and nickel recovery rates of low-temperature out-diffusion were improved by one order of magnitude in the concentration around 2 X 10 12 atoms/cm 3 . Among the three test methods, polysilicon ultratrace profiling and wafer digestion were found to be most sensitive and the method detection limit of 5 X 10 11 atoms/cm 3 or better was achieved after optimization. The optimized wafer digestion and polysilicon ultraprofiling also correlated well across six laboratories with a bias less than ±50% for both bulk copper and nickel.