Two-Dimensional Numerical Simulation of Impurity Redistribution in VLSI Processes

A numerical simulation program is presented which predicts two-dimensional impurity distributions resulting from a sequence of ion-implantation and drive-in steps. Oxidation is not included. The program aims at a closer understanding of the lateral-diffusion effect, which is an important factor in the design of minimum-size devices. Its output provides the input data for a two-dimensional device-simulation program. The algorithm is based on an implicit finite-difference analog of the transport equation, including both the diffusion and the field term. The interaction of different impurities as well as their partial activation at high concentrations are considered. The models used in the program are discussed and a brief description of the main equations is given. As a practical application, the critical steps of a DIMOS process are simulated. The results reveal the complexity of the redistribution of implanted profiles near a mask edge.