The deposition of tungsten films divide into two catagories. First, blanket tungsten were deposited on Si and $SiO_2$ by the Si, $H_2$, and $SiH_4$ reduction of $WF_6$ to investigate the crystal structure, chemical composition, microstructure, surface roughness, preferred orientation, residual stress, adhesion, and resistivity. Secondly, selective tungsten were deposited on contact holes (patterned $SiO_2$/Si) by the Si, $H_2$, and $SiH_4$ reduction of $WF_6$ for the purpose of studying selective deposition characteristics, microstructure, and encroachment.
The crystal structure of tungsten films deposited by Si reduction of $WF_6$ changes from $\alpha$ to $\beta$ as the deposition temperature increase from 330℃to 400℃, but it has $\alpha$ structure independent of $WF_6$ input flow rate at deposition temperature of 330℃. The Si-reduced tungsten films increases with a square root dependence on deposition time which is up to 120 sec. Above the deposition time of 120sec, the deposition thickness increases with a power of 1.64 of deposition time.
From the results of AES, the oxide exists in Si-reduced tungsten films as well as tungsten/Si interface. This result means that the deposited tungsten has a porous structure and the oxide is formed in the surface of the deposited porous tungsten film.
The crystal structures of tungsten films deposited by $H_2$ and/or $SiH_4$ reduction of $WF_6$ are the only $\alpha$ structure independent of deposition temperature and flow rates of input gas ($WF_6/H_2$ and $SiH_4/WF_6$) in these experimental conditions. The tungsten films reduced by $H_2$ and/or $SiH_4$ have porous structures, and the grain sizes increase with the deposition temperature. The tungsten films reduced by $H_2$ have a preferred oriented plane of (200) independent of deposition temperature. However the films reduced by $SiH_4$ have random orientation. $R_a$(surface roughness) of tungsten films reduced by $H_2$ and $SiH_4$ are $100-200Å and 200-300Å, respectively.
The residual stress of the films were measured by $\sin^2 \psi$ method. The previously reported $\sin^2 \psi$ method was modified by considering the stress gradient with the thickness as the expressed following equation.
$\sigma$ (mean stress) = $\sigma$ (surface) +$\sigma$ (Stress gradient)
The residual stresses of $H_2$-reduced and $SiH_4$-reduced tungsten on Si decrease in tensile stress with increasing deposition temperature. In the case of $SiO_2$ substrates, $SiH_4$-reduced tungsten deposits show monotonic decrease in the tensile stress with increasing deposition temperature. Whereas, $H_2$-reduced tungsten deposits show the constant tensile stress of $1\times10^9 dyn/cm^2$ until deposition temperature reaches 470℃, and then the stress increases rapidly with deposition temperature. From the above results, the residual stress of the tungsten film is not affected by the thermal stress, but is mainly affected by internal stress which results from the microstructure of the depostis, and the inclusion of the impurity.
The peel strength (adhesion) is inverely propertional to the residual stress independent of $WF_6-H_2$ and $WF_6-SiH_4$ reaction systems. The deposits on TiN/$SiO_2$ substrates have the higher peel strength than on Si and $SiO_2$. The peel strength is affected by the microstructure and the interfacial phase. The porous microstructure, and brittle oxide phases ($WO_3$ and $Si_xWO_y$) existed at W/Si and $W/SiO_2$ result in a deterioration of peel strength.
The resistivity of the tungsten films decreases until the thickness reaches 4000Å, and then it is constant of 10 $\mu\Omega$cm. The $H_2$-reduced tungsten film has a constant resistivity of $10 \pm 2 \mu\Omega cm$ independent of the deposition temperature and input flow rates. The resistivity of $SiH_4$-reduced tungsten is not affected by deposition temperature but it increases with $SiH_4/WF_6$ input gas ratios.
The selective loss time of the deposits reduced by $H_2$ and $SiH_4$ decreases with increasing deposition temperature, but the maximum selective thickness increase with deposition temperature.
The encroachment of $H_2$-reduced tungsten film is occurred, and the encroachment length decrease with deposition temperature and $H_2$ flow rate. By calculation, the thickness of 68-133A is necessary for $H_2$-reduced tungsten to prevent $WF_6$ gas from reaction with Si substrate.
