Simulation of three-dimensional refractory metal step coverage over contact cuts and vias

In very large scale integration metalization processes, thin diffusion barrier metal films deposited over vias and contacts are used to inhibit the diffusion of the top metal layer into the underlying junctions. These thin films are normally sputter deposited and their reliability is crucial to die yield and device lifetime. As wafer sizes increase, die at the wafer edge receive a directionally asymmetrical sputter flux, leading to nonuniform and asymmetrical film coverage over vias and contacts. Two three-dimensional (3D) extensions of the two-dimensional (2D) him growth program SIMBAD are presented. The first extension (quasi-3D) assumes a radially symmetrical adatom flux distribution and would be appropriate for the simulation of film deposition on regions near the central axis of a radially symmetrical target. Due to the assumption of a symmetrical flux distribution, the resulting film growth is symmetrical. The second extension (interpolated-3D) does not assume that the flux is symmetrical and is intended for the simulation of asymmetrical him growth off-axis. Both extensions provide a 3D surface of the deposited him and the microstructure and profile of 2D slices through the via or contact. In order to determine the accuracy of the two models, simulations were compared to W films sputter deposited over contacts having an aspect ratio of 3:1. The models were tested for a substrate placed directly under the center of the target. The interpolated-3D model was also tested for asymmetrical fluxes by placing the substrate off-axis by 2.2, 5.0, and 8.1 cm. The comparisons with the experimental results indicate that both the surface profiles and the microstructure of the deposited films were predicted well by the two models. The interpolated 3D model was very successful at predicting deposition profiles for off-axis deposition flux. (C) 1996 American Vacuum Society.