Alain Blosse

Improved Thermal Stability of CVD WSi. During Furnace Oxidation by a Rapid Thermal Anneal Pretreatment

In this paper, we report new results on tungsten silicide ( WSi x ) degradation during furnace oxidation. During Poly-oxidation step performed after gate patterning, a deformed oxide is grown on WSi x /Poly gate lines giving rise to protrusions (or nodules) at the interface between the two materials. Different parameters were evaluated including oxidation conditions, WSi x deposition parameters, WSi x capping dielectric and thermal treatments. The first conclusion of these experiments is that protrusions can be eliminated if Si/W ratio in as-deposited material is greater than 2.6 when no furnace thermal treatment is done on the WSi x . /Poly stack before furnace oxidation. The more important conclusion is that addition of a Rapid Thermal pretreatment with a temperature range between 700 and 1000 degrees done just after WSi x /Poly etch and before furnace oxidation eliminates totally the defects. Both results can be explained with internal stress reduction in the WSi x film which lead to suppression of accelerated oxidation kinetics at the interface between polysilicon and WSi x films during furnace oxidation after gate patterning.