Effects of preannealing on the diffusion barrier properties for ultrathin W-Si-N thin film

Ultrathin sputtered W-Si-N films (∼10 nm) were prepared for copper metallization. While copper was sequentially deposited onto some samples without breaking the vacuum, some samples underwent annealing before copper deposition. The precopper deposition annealing (simplified as preannealing) was carried out by rapid thermal annealing (RTA) in high purity N2 atmosphere. Sheet resistance measurement, Auger electron spectroscopy (AES) and X-ray diffraction (XRD) results all show that the preannealing procedure significantly increased the failure temperature for copper/diffusion barrier/Si structure by about 100 deg. C compared with those without preannealing. Bias leakage current versus time (I-t) measurement and bias temperature C-V measurement, which are very sensitive for mobile ions in the oxide, also show that the copper gate MOS structure with preannealing fails at temperatures ∼100 deg. C higher than those without preannealing. By preannealing, oxygen and nitrogen were stuffed into the grain boundaries of the nanocrystalline films, thus eliminating the rapid diffusion path for copper