Tungsten (W) thin films were deposited using a modified chemical vapor deposition (CVD) process, called pulsed CVD, and the film properties were characterized as nucleation layers for a W-plug fill process. In this study, the deposition stage is composed of four steps, resulting in one deposition cycle: (i) reaction of WF6 with SiH4, (ii) inert gas purge, (iii) SiH4 exposure, and (iv) inert gas purge. The W growth per cycle was extremely linear with a growth rate of ∼ 1.32nm/cycle at 400°C. The growth rate was further enhanced to 1.5-1.9 nm/cycle by increasing the SiH4 flow rate in the first step and/or by adding H2 in the first and the third steps. The W film deposited by pulsed CVD showed a much lower roughness (∼0.7 nm) and a better conformality at the contact holes with an aspect ratio of 14, compared to W films deposited by conventional CVD using WF6 and SiH4. The film resistivity was closely related with its phase (body-centered cubic α-W or primitive cubic β-W) and microstructure characterized by grain size as well as the film thickness (the "size effect"). Transmission electron microscopy analysis showed that H2 addition into the first and third steps increased the grain size from ∼7 to ∼13 nm and prevented the film from forming a β-W phase with high resistivity, resulting in a lower resistivity of 100 μΩ-cm compared to that of the W film deposited without H2 addition (210 μΩ-cm). H2 addition was also effective in reducing the F and Si impurities in the films. Finally, the film resistivity was discussed on the basis of impurity, roughness, microstructure, and film phase.
All Science Journal Classification (ASJC) codes
- Electronic, Optical and Magnetic Materials
- Renewable Energy, Sustainability and the Environment
- Surfaces, Coatings and Films
- Materials Chemistry