Phase and microstructure of ALD-W films deposited using B2H6 and WF6 and their effects on CVD-W growth

Abstract

We report on the deposition properties of W nucleation layers prepared using a sequential supply of B2H6 and WF6 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, B2H6 flow rate, and B2H6 pulsing time. The formation of an amorphous and two forms of crystalline W film [primitive cubic beta-phase and body-centered-cubic (bcc) alpha-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 degrees C and that when the deposition temperature was increased to 395 degrees C, the film formed the beta-phase. At a deposition temperature of 425 degrees C, the phase of the film started to be transformed into beta-phase and was completely transformed to single phase alpha-W with a very large grain size of approximately 120-180 nm at 450 degrees C. We were also able to deposit the alpha-phase W film at 395 degrees C with a lower B2H6 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 B2H6-based nucleation layer was similar to 10 mu Omega cm, while the conventional CVD-W film with a SiH4-based nucleation layer showed a resistivity of 25 mu Omega cm at the same thickness. (c) 2007 The Electrochemical Society.