Multizone Modeling of Impurity Redistribution in Ion‐Implanted Materials

Abstract

Implanted impurity redistribution has been observed during annealing of many ion‐implanted materials. Experimental evidence suggests some position dependence in the redistribution process. The tail region of ion‐implanted impurity profiles usually exhibits faster diffusion than the near‐surface region. In this paper, a multizone model for the redistribution of implanted impurities is presented. The implanted substrate is considered as a stratified medium with zones where a local diffusion equation is obeyed, and an effective diffusion coefficient is defined within each zone. The basic formulation of the model and its mathematical background are discussed. The multizone equations are solved using the Crank‐Nicolson method. A computer program is used to generate a plot of the post‐annealing redistributed impurity profile. The model is applied to the case of sulfur‐implanted normalGaAs for dose range of 4×1013 normalto 4×1015 cm−2 , with energies of 120 and 300 keV. Good agreement is obtained between the computer generated profile and the SIMS experimental profile.

Simulation of Anomalous Be Diffusion in Semi‐Insulating InP

“…Diffusion simulation is accomplished with a discrete transformation of the continuity equation for the position-dependent diffusion coefficient, reported previously in this journal (Ref. 8,Eq.[16]). In our model we assume that the diffusion coefficient is reduced in regions where the impurity concentration is larger than a specified value Cma x The shape of simulated profiles was found to be largely dependent on the degree to which the diffusion coefficient was reduced at high concentrations.…”