Interfacial Reaction in Polycide MOS Gate Structure Employing CVD Tungsten Silicide

Interfacial reaction of a CVD WSi x polycide gate structure, WSi x (2200 Å)/polysilicon (4500 Å)/SiO2 (500 Å)/Si, has been studied by Rutherford backscattering spectroscopy technique. Annealing was done at temperatures of 900–1100°C in flowing dry N2. Slight interfacial reaction was observed at the WSi x -polysilicon interface with 1000°C annealing. At 1100°C annealing, however, in addition to this reaction, other reaction was also observed in gate oxide-polysilicon and/or gate oxide-substrate silicon interfaces. Composition of WSi x changed from nonstoichiometric (x=2.5) for as-deposited to stoichiometric (x=2.0–2.1) with annealing at temperatures above 900°C. Resistivity of CVD WSi x polycide layer was around 900 µΩ·cm for as-deposited, and decreased rapidly to 80, 60 and 42 µΩ·cm with 900, 1000 and 1100°C annealing, respectively.