Characterizations of Pulsed Chemical Vapor Deposited-Tungsten Thin Films for Ultrahigh Aspect Ratio W-Plug Process

Abstract

Tungsten (W) thin films were deposited using a modified chemical vapor deposition (CVD) process, called pulsed CVD, and the film properties were characterized as nucleation layers for a W-plug fill process. In this study, the deposition stage is composed of four steps, resulting in one deposition cycle: (i) reaction of with , (ii) inert gas purge, (iii) exposure, and (iv) inert gas purge. The W growth per cycle was extremely linear with a growth rate of at 400°C. The growth rate was further enhanced to by increasing the flow rate in the first step and/or by adding in the first and the third steps. The W film deposited by pulsed CVD showed a much lower roughness and a better conformality at the contact holes with an aspect ratio of 14, compared to W films deposited by conventional CVD using and . The film resistivity was closely related with its phase (body-centered cubic or primitive cubic ) and microstructure characterized by grain size as well as the film thickness (the "size effect"). Transmission electron microscopy analysis showed that addition into the first and third steps increased the grain size from to and prevented the film from forming a phase with high resistivity, resulting in a lower resistivity of compared to that of the W film deposited without addition . addition was also effective in reducing the F and Si impurities in the films. Finally, the film resistivity was discussed on the basis of impurity, roughness, microstructure, and film phase.