Pulsed CVD-W Nucleation Layer Using WF6 and B2H6 for Low Resistivity W

Abstract

Tungsten (W) thin films were deposited using the modified chemical vapor deposition (CVD), the so-called pulsed CVD, and their properties were characterized as nucleation layers for the chemical vapor deposited W (CVD-W) technology of sub-50 nm memory devices. W growth per cycle was extremely linear with a higher growth rate of similar to 0.58 nm/cycle as compared to that (similar to 0.28 nm/cycle) of the atomic layer deposition (ALD) process using the same chemistry. From the X-ray diffractometry, the pulsed CVD-W film was formed as an amorphous structure, which was the same as the atomic layer deposited W. This led to the formation of a low resistivity bulk CVD-W film deposited on it with the grain size of similar to 180 nm at 200 nm thick film, and its resistivity was further decreased with the B2H6 post-treatment before the deposition of bulk CVD-W film (similar to 13 mu cm at a 50 nm thick film). However, we found that the adhesion performances of CVD-W growing on the B2H6-based pulsed CVD-W nucleation layer were significantly degraded as both the deposition temperature of the nucleation layer and the B2H6 post-treatment time increased. High resolution transmission electron microscopy and energy-dispersive spectroscopy analysis clearly demonstrated that a discontinuous boron layer was formed at the bulk CVD-W/nucleation layer interface, which was dominantly due to the B2H6 decomposition during the B2H6 post-treatment. We strongly suggest that a boron-containing discontinuous layer degrades the adhesion properties of CVD-W films growing on it. Considering the thermodynamics of the B2H6 decomposition, we can improve the adhesion properties by increasing the H-2 flow rate at the post-treatment step.