Density variation of tungsten films sputtered over topography

Abstract

Density and resistivity of sputtered tungsten films are directly measured as a function of angle-of-vapor incidence. The film density is found to drop off quickly at deposition angles greater than 50°, and the resistivity rises sharply at angles greater than 70°. These deposition angle effects in films deposited over topography can be predicted using simulation by ballistic deposition (SIMBAD), a two-dimensional computer simulation of thin-film growth using ballistic deposition of hard disks. Simulated film structure and density is in good agreement with real tungsten films deposited over vias. To confirm density predictions, etch rate measurements made on planar films are presented which confirm the dependence of etch rate on film density. The results of the measurement are used to develop an etching algorithm using SIMBAD density predictions. Films deposited over vias are etched to reveal the presence of low-density regions of film covering the via sidewalls, showing excellent agreement with the simulation results.