Characteristics of low - resistive plasma enhanced chemical vapor deposited tungsten (PECVD - W) thin films

Abstract

The resistivity of plasma enhanced chemical vapor deposited tungsten thin films (PECVD-W) which has been known to be $50 \sim 100\mu \Omega{cm}$ can be reduced to $10 \sim 11 \mu \Omega{cm}$. The theoretical and experimental comparisons of deposition kinetics between LPCVD-W and PECVD-W are studied. The deposition rates of LPCVD-W calculated by the rate equation $(R = 4.08 \times 10^7 \exp(-0.73/kT)[H_2]^1$[nm/Torr.minl]) and obtained by experiment are both proportional to square root of $H_2$ partial pressure, while the deposition rate of PECVD-W shows no distingurshable relation with the $H_2$ partial pressure. The difference between the hot plate temperature and the wafer temperature leads quite erroneous result to the control of real deposition temperature, because the wafer temperature is lower than the hot plate temperature at the low pressure of sub-Torr. Therefore, in this work, the deposition temperature by the thermocouple inserted into a cabity formed in the monitoring Si wafer. The optimum deposition temperature for producing the low resisitive PECVD-W films is $300 \sim 400\,^\circ\!C$. The fragmentation process of $WF_6-H_2$ reactant system is explained by using the optical emission actinometry, and it is found that the relative concentration of F atoms i sincreased when the $H_2/WF_6$ partial pressure ratio is decreased. Corresponding the results of x-ray diffraction, TEM, and AES measurements with the deposition parameters, it can be concluded that the low resistivity of PECVD-W films is attributed to the growth of not porous but dense grains, and (110) and (200) preferentially oriented bcc structure grains when F atoms are effectively removed by the increase of the $H_2/WF_6$ partial pressure ratio or by the assition of $SiH_4$ at the deposition temperatures of $300 \sim 400\,^\circ\!C$. However, when the $H_2/WF_6$ is lower than 10, or the deposition temperature is higher than $450\,^\circ\!C$, the resistivity of PECVD-W is increased due to $\...