Planarized aluminum deposition on TiW and TiN layers by high temperature evaporation

The evaporation of Al onto a heated TiW- or TiN-coated substrate is used to planarize topography. The final temperature of 450°C provides enough Al mobility to planarize 2-μm-wide features. The deposition of 1.5-2.0 times the feature depth with a >250/450°C two-temperature process and a deposition rate ≈100 angstrom/s gives good planarization uniformity over >6-cm wafer radius. Submicron trenches are planarized without voids, whereas windows with h/w > 1 have voids. Also, 1-μm-deep trenches are filled, whereas 2-μm-deep trenches are not filled with a similar process. Scanning electron microscopy correlates planarization and via filling with the evaporation process and substrate topography. The effect of high-temperature evaporation on materials integrity is studied with diode leakage measurements. At 450°C for <2 min required for the second step, there is no Al/(TiW or TiN)/Si interaction. However, the process is close to the failure temperature of the 1000-angstrom-thick (less than or approximately equal to 500 angstrom thick in 1-gmm features) TiW barrier layer since Al spiking is seen when the final step is ≳500°C.