Annealing and oxidation behavior of low‐pressure chemical vapor deposited tungsten slicide layers on polycrystalline silicon gates

A WSi_x≊2.6 film was deposited by low‐pressure chemical vapor deposition at 350–420 °C onto a P‐doped polycrystalline silicon/SiO₂/Si substrate. This polycide structure (with or without a subsequent As⁺ source/drain implant) was heat treated in the following manner: (i) 1000 °C/N₂ anneal for 20 min, (ii) oxidation both in dry oxygen and in steam ambients at 920–950 °C (50 min–8 h), and (iii) N₂ anneal as well as dry oxidation at 920 °C/50 min. Cross‐sectional transmission electron microscopy, Rutherford backscattering, secondary ion mass spectrometry, and sheet resistance measurements were used for characterization. The as‐deposited film was mostly amorphous with a fine grain structure. The N₂ anneal caused the formation of a polycrystalline WSi_x>2 film containing tetragonal WSi₂. Dry oxidation produced a void‐containing SiO₂ layer atop the silicide film. However, the SiO₂ layer was impregnated with W particles when the silicide film was steam oxidized. The role of excess Si in refractory metal silicide films during annealing and oxidation is discussed. The effect of stress at the corners of a step in a patterned wafer during the oxidation of tungsten polycide is also demonstrated.