Characterization of Al-1 wt% Y thin films for VLSI interconnects

Abstract The microstructure of an integrated circuit interconnect material significantly affects the reliability of the device. Narrow lines with near bamboo structure exhibit an increased mean time to failure (MTF) and a concomitant increase in the dispersion ( σ ). A critical stress concentration site forms at the boundary between a single crystal segment and a polycrystalline segment of the line which leads to early failure. Simulation results for a 1000 μ m long aluminum line (a rigidly confined line with blocked ends is assumed) show that, if the grains are uniform in size and small relative to the line width, a missing metal defect located at the center does not produce a stress concentration site. This paper reports on properties of Al-1 wt% Y films deposited by DC magnetron sputtering. The addition of yttrium reduces both the mean grain size (299 nm) of aluminum films and the standard deviation of the grain sizes (89 nm). As-deposited films consist of α -aluminum supersaturated with yttrium and Al 4 Y phase. After annealing at 450°C for 30 min, β -Al 3 Y is precipitated, grain growth is not significant and the electrical resistance drops from 6.05 to 2.95 μ Ωcm.