Tungsten Cap Metallization for 0.5 μm Via Fill Technology

A metallization stack is fabricated using a tungsten cap layer on top of the aluminum interconnect. Utilizing this stack significantly reduces the possibility of process-induced defectivity problems : formation of via veils, metal extrusions, and breakdown in the via glue layer. Conventional via etching is shown to stop successfully on the tungsten capping layer without forming via veils or resputtering the underlying aluminum substrate. Experimentally, the tungsten cap is shown to provide superior resistance to metal extrusion phenomena which are associated with high temperature chemical vapor deposition tungsten processing. Integrated with tungsten via fill technology and using only a sputtered titanium nitride via glue layer, acceptable via resistance is demonstrated. Electrical performance shows the tungsten-capped via resistance to be 0.60 Ω/via higher than conventional metallization scheme for a 0.65 x 0.65 μm sized via. Metal snake and comb tests show no difference between the standard metallization stack and the tungsten cap structure indicating differences in patterning defectivity to be statistically insignificant. Normalized static random access memory (SRAM) yield is shown to be equivalent between the two splits.