Quality degradation for gate oxides grown on slightly damaged silicon surfaces

The quality of the gate oxide grown on a damaged silicon surface is investigated. The damage was created by exposing samples to CF₄ or C₂ClF₅ plasmas prior to the gate oxidation. Although only a slight change in C-V characteristics was observed in the damaged samples, both leakage current and breakdown voltage were significantly degraded for most of the conditions investigated. The leakage current mechanism was identified to be trap-assisted tunneling. We also observed that the damaged samples were more vulnerable to later plasma process damage, i.e. the damage is latent when it is created and can become active when subjected to electrical stress during subsequent plasma processing. This suggests that one can have oxide degradation due to the combination of pre-oxidation surface damage and the subsequent process damage even if one uses low damage plasma processing for cleaning or etching