FLUX DISTRIBUTIONS AND DEPOSITION PROFILES FROM HEXAGONAL COLLIMATORSDURING SPUTTER-DEPOSITION

We use the Monte Carlo method to simulate transport through a single h exagonal collimator cell and transport from the exit of the cell to th e substrate. We assume a distribution function for the species enterin g the collimator, and that the pressure is low enough so that the tran sport inside the collimator cells is free molecular flow. Three-dimens ional flux distributions of species exiting the collimator cell are ob tained as functions of the sticking factor of the sputtered material i n the collimator and the collimator aspect ratio. Specular as well as diffuse re-emission, for species which have subunity sticking factors, are considered. The larger the sticking coefficient and the higher th e aspect ratio, the higher the ''beaming'' effect of the collimator an d the smaller the fraction of species which make it through the collim ator. For nonunity sticking factors, diffuse re-emission produces a mo re collimated beam than specular re-emission, and the fraction of the species which make it through the collimator are lower for diffuse re- emission. Collisional transport is tracked from the collimator exit to the substrate using Monte Carlo simulations for each species. The dep osited film profile from a single collimator cell is computed by assum ing a sticking factor of one on the substrate. The film profile over m acroscopic regions of the wafer is obtained by summing the fluxes from all the collimator cells. Calculated variations in film thickness are explained in terms of collimator to wafer distance and mean free path of the sputter gas. (C) 1995 American Vacuum Society.