COPPER ELECTROLESS DEPOSITION TECHNOLOGY FOR ULTRA-LARGE-SCALE-INTEGRATION (ULSI) METALLIZATION

In this paper we present the technology of electroless Cu deposition f or ultra-large-scale integration. The technology has several component s: the solution chemistry, the operation conditions, the seeding, the equipment and the process integration. Sodium-free solution was used a nd optimized to achieve a deposition rate in the range of 75-120 nm/mi n, resistivity rho less than 2 mu Omega cm, with a uniformity better t han 3% on 6'' wafers and 5% on 8'' wafers. The surface roughness of th e films was in the range of 10-15 nm for a 1.5 mu m thick layer. The h ighly uniform deposition is achieved by using a novel sacrificial alum inium protected copper seeding. This method protects the catalytic pro perties of the Cu, which is exposed to the solution after the aluminiu m dissolution. Another seeding method has been developed with Cu conta ct displacement deposition on a TiN layer using a solution that contai ns copper and fluorine ions. Several electroless Cu deposition process es have been developed in both blanket and selective deposition modes, using Al protected Cu seed and contact displacement seeding. The tech nology was capable of obtaining 0.3 mu m electroless Cu-filled trenche s and vias with an aspect ratio as high as 5:1. The process topography is modelled numerically for vias, trenches, and micro-tunnels with hi gh aspect ratio (up to 400:1). The copper diffusivity was found to be in the range of 10(-5) cm(2)/sec at 40 degrees C and it was used in th e 2-D modelling of copper deposition in via contacts and trenches.