The net sputter coating flux at the surface being coated can be conceptually divided into two constituent fluxes: the directed flux, and the diffusional flux. The former is due to the high initial velocities of the sputtered target atoms, which tend to move in their original direction even after several collisions with the background gas atoms. The latter exists because of the eventual slowing down of the target atoms to the velocities of equilibrium distribution. At a given sputtering pressure, the directed flux dominates in the vicinity of the target, whereas the diffusional flux dominates away from the target. Coating uniformity on nonplanar substrates depends on the relative contributions from these two fluxes. These two contributions have been extensively modeled in the literature. However, to use the models for any specific situation, one needs to make an a priori assumption about the dominant contribution. In many situations, both these mechanisms are equally significant. It is then difficult to decide which model to apply. We have developed a simplified model that takes into account the gradual transition between the two mechanisms, and thus covers the entire range of relative flux distributions. A decay parameter calculated from experimental data is used to determine the relative contributions from the fluxes. Therefore, with this model, one need not resort to arbitrary assumptions about the controlling contributions, and thus the coating uniformity. We will present the development of the model, computation of the decay parameter, and experimental data that support the model. © 1990, American Vacuum Society. All rights reserved.
