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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.
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