Pulsed CVD of tungsten thin film as a nucleation layer for tungsten plug-fill

Tungsten (W) thin film as a nucleation layer for a W plug-fill process was deposited using a modified chemical vapor deposition (CVD) called pulsed CVD, and properties of the films were investigated. Basically, the deposition stage was composed of four separate steps for one deposition cycle: (i) reaction of WF₆ with SiH₄; (ii) inert gas purge; (iii) SiH₄ exposure without WF₆; and (iv) inert gas purge. A higher deposition rate, ∼1.5 nm/cycle, was obtained as compared to that of atomic layer deposition (ALD) (∼0.25 nm/cycle). The film deposited by pulsed CVD showed a much lower root mean square (rms) roughness (0.87 nm) and better conformality at the contact holes with an aspect ratio of 14 (contact height: 3.51 μm and top diameter: 240 nm) as compared to the layer deposited by conventional CVD using WF₆ and SiH₄.