Studying of physical characteristics and optimizing of gap filling for tungsten

The effect of process parameters on the physical properties of tungsten (W) thin film and the preferable condition for W-plug gap filling were investigated. Uniformity (U%) of resistance was found to improve with pressure. This can be explained by reactant gas flow change during the process due to the pressure altered, which further affects the behavior of film deposition. In addition, lower temperature and slower WF6 flow rate lead to better thickness U%, which is ascribed to a slower film growth rate. As to tensile stress, it decreased with the process temperature. It is presumable that there is less impurity in the film and less dislocation with higher temperature deposition. On the other hand, there was lower resistivity with higher temperatures because of larger grain size growth. Using the Taguchi method, pressure of 80 Torr, temperature of 370 °C, and WF6 flow rate of 150 sccm demonstrated the optimized condition to achieve the minimum seam size (6 and 10 nm in the top-view and cross-section, respectively) on the aspect ratio (A/R) 16 of the contact loop. Furthermore, the exposed seam ratio was also found to be the smallest.