Effects of rapid thermal annealing on cobalt silicided p⁺ poly-Si gates fabricated by BF₂⁺ implantation into bilayered CoSi/a-Si films

The cobalt polycide gate formed by implanting BF₂⁺ ions into the bilayered CoSi/a-Si films and the subsequent rapid thermal anneal has been studied. The resulting gate oxide integrity is characterized with respect to various silicide thicknesses and implantation energies. Significant degradation in gate oxide integrity and flat-band voltage shift were found with increasing suicide thickness and annealing temperature, especially for the thicker CoSi₂ films, which is attributable to severe boron penetration. Although a thinner silicide can achieve excellent gate dielectric reliability, it will lead to poor high-temperature thermal stability. Moreover, shallower implantation depth and lower annealing temperature, which sustain less boron penetration, would cause the poly-Si gate depletion effects. Therefore, appropriate conditions, which comprise the CoSi₂ thickness, the implantation energy, and the annealing temperature, should be employed to optimize the device performance while retaining the thin dielectric reliability.