The Characteristics of Chemical Vapor Deposited Amorphous-like Tungsten Film as a Gate Electrode

Abstract

Tungsten films are often advantageously formed by the chemical vapor deposition system which using WF6 gas through SiH4 or H2 reduction. The fluorine species will diffuse into poly-Si/SiO2/<Si> multilayers by a driving force which is the reaction of WF6 and poly-Si gate. When too many fluorine atoms diffused into the gate oxide, the fluorine atoms will cause more strain in the gate oxide and the electrical characteristics of device will shift. An amorphous-like tungsten layer was deposited at a flow rate ratio of 2.5 of SiH4/WF6. The driving force in the amorphous-like tungsten film deposition is far less than that in selective tungsten film deposition; therefore, the concentration of fluorine atoms in the amorphous-like tungsten film is much less than in the selective tungsten film. We proved that only few fluorine atoms were incorporated in amorphous-like tungsten film which has good characteristics in the application of gate electrode.