Fluorine distributions in a chemical vapor deposited tungsten silicide/polycrystalline silicon composite gate structure

A tungsten silicide/polycrystalline silicon composite gate structure has been fabricated in which tungsten silicide layers on polycrystalline silicon have been deposited by the low-temperature chemical vapor deposition method (at 360 °C) using a WF6/SiH4 gas mixture. The fluorine distributions in this structure have been studied by secondary ion mass spectrometry. In samples with as-deposited tungsten silicide, it has been confirmed clearly that almost all of the fluorine resides in the silicide layer. After high-temperature annealing (above 950 °C), however, fluorine is found to diffuse easily into the gate SiO2 through the polycrystalline silicon, that is, the gate oxide has been changed into the fluorine-doped oxide.