Stability of TiB2 as a Diffusion Barrier on Silicon

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Abstract
The stability of low‐pressure chemical vapor‐deposited films has been investigated for their potenital use as diffusion barriers between Al or Cu metallurgy and the Si substrate during post‐metal annealing at temperatures ranging from 450–640°C for Al, and 500–800°C for Cu. Although no evidence of intermixing was observed via Rutherford backscattering spectroscopy (RBS) for samples rapid thermal‐annealing (RTA) up to 1080°C, pyramid‐shape pits in the Si, bounded by (111) planes, were observed using transmission electron microscopy for the samples annealed above 950°C. Secondary ion mass spectroscopy depth profiles of B in Si originating from the solid source suggested enhanced diffusion after RTA. According to RBS spectra coupled with scanning electron microscopy (SEM) examination, (pre‐annealed) stacks appeared to be stable up to 500°C for 30 min in forming gas. For the stacks with as‐deposited (amorphous) films, plan‐view SEM of showed very limited reaction with Al up to 600°C, in good agreement with sheet resistance measurements. The as‐deposited, amorphous films were superior diffusion barriers compared to the annealed, polycrystalline . No interaction took place between sputtered Cu and an underlying, amorphous film up to 750°C, 30 min in vacuum. Plan‐view SEM, RBS, and sheet resistance measurements showed that the structure started to break down at 775°C.

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