Effects of Titanium Layer as Diffusion Barrier in Ti/Pt/Au Beam Lead Metallization on Polysilicon

The effect of a titanium layer as a diffusion barrier in Ti/Pt/Au beam lead metallization on polysilicon was investigated. A critical temperature, defined as the beginning of Au-Si eutectic reaction, was investigated for specimens with electron-beam (EB) evaporated and radio frequency (RF) sputtered titanium films 23-- 3000 Å thick deposited onto polysilicon films 0.2-2 µm thick. Polysilicon surface roughness was characterized by grain step height as a function of grain size and polysilicon film thickness. The titanium film thickness required to retain the same metallization integrity during heat treatment became greater with increase in the polysilicon film thickness. At the polysilicon surface, the grain size and the grain step height became greater with increase in the polysilicon film thickness. The mechanism of increased heat resistance with increased titanium film thickness was examined relative to grain step coverage effect.