Influences of the chemical vapor deposition (CVD)-TiN gate process on gate oxide integrity have been studied. The gate leakage characteristic and reliability of the gate oxide were drastically degraded by 1000°C annealing for thick oxide as compared to for thin oxide. By X-ray photoelectron spectroscopy (XPS) and thermal desorption spectroscopy (TDS) analyses, the oxide degradation is confirmed to be due to the formation of a weak spot induced by out-diffusion of residual Cl from the TiN gate electrode into the gate oxide. Out-diffused Cl reacts with defects in the oxide during the high-temperature anneal and forms trap sites. The weak spot which acts as a leakage path appears to be the local spot which has a larger amount of Cl-related trap sites. Controlling of impurities in the CVD metal gate is a key for realizing future multiple-thickness gate oxide technology.
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Moriwaki et al. (2001) studied this question.