Low-resistivity α-phase tungsten films grown by hot-wire assisted atomic layer deposition in high-aspect-ratio structures

In this work, the so-called hot-wire (HW) assisted atomic layer deposition (HWALD) technique is employed to grow high-purity α-phase tungsten (W) films at a substrate temperature of 275 °C. The films are deposited on thermally grown silicon dioxide (SiO2) in a home-built hot-wall reactor, using alternating pulses of WF6 and HW-generated atomic hydrogen in the self-limiting surface-reaction manner characteristic for ALD. A W seed layer, needed to enable the HWALD-W process on a SiO2 surface, is formed prior to each deposition. In-situ spectroscopic ellipsometry is used to monitor the growth behavior and film properties. The films exhibit a high-purity (99 at.%) W, according to X-ray photoelectron spectroscopy. The X-ray diffraction scans reveal the existence of α-phase W. The resistivity measurements by means of four point probe, transfer length method test structures and the Drude-Lorentz SE model all reveal a low resistivity of 15 μΩ·cm. The high-resolution transmission electron microscopy analysis shows a uniform and conformal coverage of high aspect ratio structures, confirming the effective ALD process and the sufficient diffusion of both WF6 and at-H into deep trenches.