Pulsed chemical vapor deposition of tungsten (W) thin film as a nucleation layer for W-plug fill of sub-100 nm dynamic random access memory technology

Tungsten (W) thin film was deposited using pulsed chemical vapor deposition (pulsed CVD) and evaluated as a nucleation layer for W-plug deposition at the contact with an ultrahigh aspect ratio (contact height: 3.51 μm and aspect ratio: 13.7-14.9) for sub-100 nm dynamic random access memory technology (DRAM). The deposition stage for pulsed CVD-W film is composed of 4 sequential steps, resulting one deposition cycle; (1) Reaction of tungsten hexafluoride (WF ₆) with silane (SiH₄) (2) Inert gas purge (3) SiH ₄ exposure (4) Inert gas purge while the deposition of conventional CVD-W nucleation is based on the simultaneous flow of SiH₄ and WF₆. W growth per cycle was extremely linear with growth rate of -1.32 -1.5 nm/cycle at 400°C. W film deposited by pulsed CVD showed a better conformality at the contact holes with an aspect ratio of ∼14 as compared to W film deposited by conventional CVD. It was found that a resistivity of pulsed CVD-W film 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 impurity content. The integration results showed that a lower contact resistance was obtained when pulsed CVD-W film was used as a nucleation layer even though pulsed CVD-W film has a higher film resistivity (∼100 mΩ-cm) compared to conventional CVD-W nucleation layer (∼25 μΩ-cm). It was found that a lower contact resistance of pulsed CVD-W based plug fill scheme was mainly due to its better plug filling capability.