Tungsten silicide($Wsi_x$) films deposited by low pressure chemical vapor deposition method on heavily doped p-type polysilicon layers were annealed by rapid thermal process in a nitrogen atmosphere. The effects of annealing of the $WSi_x$-polysilicon compositcs(tungsten polycides) have been investigated by stress measurements, electrical resistivity and Hall measurements, and by analyses X-ray diffraction patterns, scanning electron microscopy(SEM), Auger electron spectroscopy(AES) and secondary ion mass spectrometry(SIMS) data.
The stress in the $WSi_x$ films was found to be nearly $1\times10^{10}dynes/cm^2$, tensile. The electrical resistivity of the specimens with polycide structure decreased with an increase in annealing temperature or time, and decreased to 190μΩ-cm in the specimen annealed at 1000℃ for 60 seconds. The analyses of X-ray diffraction patterns and SEM photographs indicate 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 the 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 annealed up to 1000℃. Hall measurements of the specimens with polycide structure also show that the majority carrier is hole in all the specimens independent of the annealing conditions.
Depth profile analysis by AES method indicates that the excess Si atoms in $WSi_x$ layer accumulated in the middle of $WSi_x$ layer so that the $WSi_x$ films do not have homogeneous composition after annealing at 1000℃ for 30 seconds. This result show that the homogenization of $WSi_x$ film requires the annealing at high temperature for a long time. From SIMS analyses, it was found that B and F elements diffuses outward and resides inside the oxide films during annealing process. The penetration of B atoms from polysilicon layer into the Si-substrate does not take place during rapid thermal annealing of 30 seconds.
