Molybdenum and tungsten–10% titanium deposition characterization

Abstract

Refractory metal interconnects are of interest for very large scale integration to obtain reliable electromigration resistant conductors. GE has developed and characterized deposition processes for these films in a Varian 3180 cassette-to-cassette sputtering system. The base metal is tungsten containing 10 wt. % titanium. The bulk resistivity varies slightly (7%) with deposition pressure. The bulk resistivity minimum value has a deposition rate dependence as well. The functional form of RB seems to be independent of deposition temperature, while the absolute value depends very strongly on temperature. Bulk resistivity is a monotonically decreasing function with increasing temperature. All RB values were taken in the as-deposited condition and remeasured after a 400 °C forming gas anneal. Step coverage appears to be independent of deposition conditions in the range of operating parameters accessible to the 3180. Contact resistance is also a function of deposition temperature, roughly tracking the bulk resistivity. Stress in the TiW was in the mid 109 dyn/cm2 range, and was compressive in all cases. Stress versus deposition rate and temperature was measured. The stress appears to be independent of deposition pressure. Molybdenum deposition has been characterized as a function of deposition temperature. The bulk resistivity decreases strongly with increasing temperature, but shows almost no variation with pressure outside the measurement uncertainty. Stress increases with increasing deposition pressure. The bulk resistivity is apparently not a function of deposition rate. Step coverage of moly is equal to or slightly worse than aluminum step coverage. The optimum deposition window for aluminum step coverage is much narrower than that for moly. Any deposition condition we had access to in the 3180 had no effect on moly step coverage.