Formation of Al-Cu via/interconnect by low-pressure collimated sputtering

This paper describes the effect of low-pressure collimated sputtering (LPCS) on deposition rates, step coverages, and electrical properties of Al-Cu. The LPCS deposition is achieved in a magnetron sputter deposition system with a hollow cathode and collimator. The deposition results show that as the via or line size reduces, a complete fill requires a monotonic increase in the aspect ratio of the collimator which limits the throughput for a thick deposition, especially at high pressures (≳1 mT). The benefit of the LPCS is the improved deposition rate (scaled to power) of 1.5–2× compared to the conventional high-pressure collimated deposition. The integration of LPCS process to fabricate a two-level Al-Cu metal structure with submicron Al-Cu studs (aspect ratio of 2) shows excellent via and electromigration resistances.