Tungsten silicide ($WSi_x$) films in Polycide structure were fabricated by low-pressure chemical-vapor-deposition (LPCVD) method and were annealed in $N_2$ for 30 mins at various temperatures.
The annealing behavior of tungsten silicide films have been investigated by electrical resistivity measurements, X-ray diffraction methods, Scanning Electron Microscopy (SEM), Hall measurements, Auger Electron Spectroscopy (AES) and by Secondary Ion Mass Spectrometry (SIMS).
The electrical resistivity of films decreased with increasing annealing temperature, and reached to 35 μ$\Omega-cm$ in the films that annealed at 1000°C, regardless the doping conditions of the polysilicon substrate. The X-ray and SEM analyses indicate that crystallization of tetragonal $WSi_2$ takes place at 560°C and grain size increases with increasing annealing temperature up to 1000°C. The variation of electrical resistivity with annealing temperature is closely related to that of grain size. Depth profile analysis by AES method indicates that the excess Si atoms in the as-deposited $WSi_x$ films were redistributed onto polysilicon substrate layer during the annealing.
By Hall measurements, it was found that the carriers for specimens annealed above 900°C were positive holes while the carriers were electrons for specimens annealed below 800°C. The explanation of such a critical behavior in electronic transport property of films is attributed to excess Si redistribution.
From SIMS analyses, P, F and H elements are identified to reside near the $SiO_2$ films through annealing process and may have an subtle effect on the properties of gate device.
