Reduction of selectivity loss probability on dielectric surface during chemical vapor deposition of tungsten using fluorinated oxide and removing silanol units on dielectric surface

Abstract

Dielectric materials and surface pretreatment are important for the control of selectivity loss during the chemical vapor deposition (CVD) of W in SiH4/H-2/WF6 ambient. Water-related silanol (SiOH) units on an oxide surface, which come from a wet cleaning step and moisture in clean room air, are found to act as nucleation centers, resulting in selectivity loss. Removing these silanol units by in situ NF3 plasma pretreatment effectively inhibits the nucleation of W. Reduction of the dielectric constant, as well as doping of fluorine in oxide, was shown to suppress the selectivity loss. This is due to the high electronegativity of the FxSiOy film surface, which repels the WF6 molecules. The resistance to selectivity loss of W on FxSiOy is better than that on BPSG. From these results, nucleation of W is inferred to initiate from the adsorption of WF6 on the insulator surface in the WF6/SiH4/H-2 ambient. On the other hand, a novel method that uses FxSiOy as an intermetal dielectric (IMD) or that involves capping on a dielectric material (e.g., BPSG), was proposed to reduce the selectivity loss probability during selective growth processes.