FFT calculation of two-step semiconductor impurity diffusion

The fast Fourier transform (FFT) is used to efficiently calculate an approximation to the second step of the two-step semiconductor impurity atom diffusion. The linearized one-dimensional diffusion equation is assumed with zero oxide growth. The calculation is shown to be a convolution, and the criteria for minimizing aliasing and overlap are outlined. Calculations for erfc (error function) and ion-implanted profiles are shown. Computation time is about 800 ms for a 256-point profile, using APL on an IBM System/370 Model 168 computer. Less than 2-percent error occurs in curve area and surface concentration for typical profiles.