Tungsten silicide films ($WSi_{x$}) on heavily doped n-type polysilicon layer deposited by low-pressure chemical vapor deposition (LPCVD) method were annealed by rapid thermal process in a nitrogen atmosphere.
Electrical properties of annealed specimens have been investigated by measurements of electrical resistivity, Hall voltage and Capacitance-Voltage along with analyses of X-ray diffraction patterns, SEM photographs and depth profiles by secondary ion mass spectrometry (SIMS).
The electrical resistivity of the specimens decreases with increasing annealing temperature or time, and the reached to 168 μΩ-cm in the specimen annealed at 1000℃ for 15 seconds. The X-ray and SEM analyses indicated that crystallization of tetragonal $WSi_{2}$ takes place and grain size increases with increasing annealing temperature. These results suggest that the variation of electrical resistivity with annealing temperature is closely related to grain size. Hall measurements of the tungsten silicide films deposited by LPCVD on $SiO_{2}$/Si-substrate followed by thermal annealing show that the majority carrier is hole in all the tungsten silicide films independent of the annealing conditions. Hall measurements of tungsten silicide films in polycide structure, however, show that the majority carrier is electron in the specimens annealed below 950℃ while it is hole in the specimens annealed above 950℃. It appears that the negative Hall voltage observed in the tungsten silicide films in polycide structure that were annealed below 950℃ was caused by large contribution of Hall voltage by n-type polysilicon layer.
From SIMS analyses, it was found that P, F and H elements diffuse outward and reside near the oxide films through annealing process. Capacitance-Voltage measurements show that flat band voltage shift to the right with increasing annealing temperature. It was considered that these variations result from decreasing work function difference ($\phi_{MS}$) caused by outdiffusion of P atoms and increasing fixed oxide charge ($Q_{f}$) caused by segregation of F atoms in $SiO_{2}$/Si-substrate.
