Contact metallurgy development for VLSI logic

Abstract

The criteria involved with the choice of an ohmic contact material for VLSI logic are discussed. The problems of aluminum penetration encountered with Al metallization and solid-phase epitaxy associated with Al-Si metallization make these interconnect materials incompatible with VLSI technology. The contact resistance characteristics of palladium and platinum silicides were compared to the contact resistance obtained using a titanium contact layer. The contact resistance of palladium silicide increased with extended annealing at 400°C, while the PtSi and Ti contact materials exhibited stable contact resistance under these conditions. A Ti/Al-Cu/Si process which is compatible with a lift-off patterning technique and partial coverage of contacts is described. Rutherford backscattering results indicate that copper and silicon additions to the aluminum metallization retard the Ti-Al reaction. SIMS data show that silicon in Ti/Al-Cu/Si films redistributes during heat treatment, accumulating at the Ti/Al-Cu interface.