Simulation of physical vapor deposition into trenches and vias: Validation and comparison with experiment

Abstract

We have performed two-dimensional (2D) and three-dimensional (3D) (axisymmetric) numerical simulations of physical vapor deposition into high aspect ratio trenches and vias used for modern very large-scale integration interconnects. The topographic evolution is modeled using (continuum) level set methods. The level set approach is a powerful computational technique for accurately tracking moving interfaces or boundaries, where the advancing front is embedded as the zero level set (isosurface) of a higher dimensional mathematical function. We have validated both codes against analytic formulas for step coverage. First, we study the 2D case of long rectangular trenches including 3D out-of-plane target flux. The 3D flux can be obtained from molecular dynamics computations, and hence our approach represents a hybrid atomistic/continuum model. Second, we report results of axisymmetric 3D simulations of high aspect ratio vias, which we compare with experimental data for Ti/TiN barrier layers. We find that the simulations (using a cosine angular distribution for the flux from the target) overpredict bottom coverage in some cases by approximately 20%–30% for both collimated and uncollimated deposition, but in other cases provide a reasonably accurate comparison with experiment.