Tungsten films deposited by LPCVD on TiN glue layers were studied in order to improve its properties such as adherence to substrate, residual stress and surface morphology through optimizing the deposition condition.
Silicon wafer specimens on which TiN had been deposited through the reactive sputtering were exposed to argon plasma before the deposition of tungsten for the purpose of native $TiO_2$ elimination. Varying the deposition temperature and $WF_6/SiH_4$ input gas ratio, the deposition of tungsten films was performed. The residual stresses and adhesion strengths of the films were measured. The surface morphologies of tungsten deposits were observed by SEM and the textures and the crystal structures were analysed by XRD.
The deposition reaction is typical thermally-activated process and its apparent activation energy is around 0.47eV. The electrical resistivity of the film is 8-9μΩ·㎝.
With the increase of deposition temperature, residual tensile stress reduces and adhesion strength increases. $WF_6/SiH_4$ input gas ratio less than 1 induces higher residual stress within the deposits. The higher $WF_6/SiH_4$ input gas ratio, the better the adherence of the tungsten film to TiN surface.
Especially, the tungsten films grown at $WF_6/SiH_4$ input ratio less than 1, show different morphologies and textures from those of the films deposited at higher $WF_6/SiH_4$ ratio.
From the results above mentioned, it is found that the deposition conditions, temperature higher than 340℃ and $WF_6/SiH_4$ input gas ratio larger than 1, would be available for the blanket tungsten deposition as a 1st level interconnection in ULSI.
