Phase and microstructure of ALD-W films deposited using B₂H ₆ and WF₆ and their effects on CVD-W growth

We report on the deposition properties of W nucleation layers prepared using a sequential supply of B2 H6 and W F6 and their effects on the growth of the subsequent chemical vapor deposited (CVD)-W. The structural properties of the W nucleation layers such as their phase, crystallinity, and grain size depended on the deposition temperature, B2 H6 flow rate, and B2 H6 pulsing time. The formation of an amorphous and two forms of crystalline W film [primitive cubic Β -phase and body-centered-cubic (bcc) α -one] was observed, depending on the deposition temperature. X-ray diffractometry and transmission electron microscopy diffraction analysis showed that the amorphous W was dominantly deposited at temperatures of up to 350°C and that when the deposition temperature was increased to 395°C, the film formed the Β -phase. At a deposition temperature of 425°C, the phase of the film started to be transformed into α -phase and was completely transformed to single phase α-W with a very large grain size of approximately 120-180 nm at 450°C. We were also able to deposit the α -phase W film at 395°C with a lower B2 H6 flow rate, but its grain size was only approximately 20-30 nm. The W nucleation layers had a significant effect on the final grain size and resistivity of the CVD-W films deposited on them. The minimum resistivity of the 50 nm thick CVD-W film with the optimized B2 H6 -based nucleation layer was ∼10 μ cm, while the conventional CVD-W film with a Si H4 -based nucleation layer showed a resistivity of 25 μ cm at the same thickness.