Ionized physical vapor deposition of Cu for high aspect ratio damascene trench fill applications

Abstract

The ionized physical vapor deposition technique is used to fill high aspect ratio trenches with copper. This technique allows directional filling of embedded features, known as damascene, by sputtering metal atoms into a high density plasma. Large metal-atom ionized-flux fractions are achievable (≊85%) leading to high directionality of deposition at the biased substrate. In this article, we report quantitative measurements of fill directionality of Cu using an inductively coupled plasma (ICP) high density source. Copper is deposited into fairly aggressive (depth/width ≤1.5) damascene trenches. Metal ion flux fractions are estimated from direct measurement of the trench step coverage and compared to simulation. Estimates of the Cu+/Ar+ density ratios are also made to understand the influence of applied ICP power and Cu atom density (magnetron power) on fill directionality. It is found that at high magnetron powers (high copper atom densities) the plasma becomes ‘‘copper rich,’’ where the flux of copper ions exceeds that of the argon ions. At low magnetron power and high ICP power, we find the trench fill to be highly directional. As magnetron power is increased, directionality suffers due to cooling of the plasma by higher copper atom flux.