Mo/TiW contact for VLSI applications

Abstract

A molybdenum and titanium-tungsten double-layer contact metallization was developed for VLSI circuit applications. A thin TiW contact layer produced good ohmic contact and thermal stability With n+silicon and p+silicon up to 650°C without spiking. Thick Mo over the TiW layer has high conductivity, good step coverage, low electromigration, and smooth surface morphology. Both metal layers are sequentially sputtered in one pumpdown. The pattern formation process, including the etching Of approximately 1-µm-size contacts and tightly pitched 1.5-µm-wide metal lines is described. The contact resistance was evaluated as a function of processing conditions and high-temperature annealing. The contact resistance values for n+silicon contacts were always less then 35 Ω . µm2and that for the p+silicon contact resistance was within a range of 35 to 85 Ω . µm2after annealing at 400°C. Annealing experiments showed that occasional larger values of p+contact rsistance could be reduced by annealing at 625°C. There was no junction leakage degradation for annealing temperatures below 600°C. The mechanism, and cause, of the contact resistance and leakage current change with sintering temperature was studied by means of X-ray, SIMS, TEM, and SEM.