Simulation of interface broadening of sputter profiled isotopic silicon layers

Abstract

The experimental SIMS profiles of Si³⁰/Si²⁸ multilayers depth profiled using 2–10 KeV Ne⁺, Ar⁺ and Xe⁺ (K. Wittmaack and D. B. Poker, Nucl. Instr. Meth. B47 (1990) 224) have been simulated using a diffusion approximation to ion mixing. Both the leading and trailing edges of peaks in the depth profiles could be fitted for all ion energies by mixing efficiencies of 25, 40 and 65 Å⁵ eV^?1 respectively. These values are larger than the estimates of 5, 11 and 15 Å⁵ eV^?1 from ballistic mixing. The additional contributions to the mixing, 20, 29 and 50 Å eV^?1, scale with cascade energy density, suggesting that stimulated motion in thermal spikes is important. A simple spike model in which cascade defects are trapped at fixed sinks agrees with the experimental mixing efficiencies.