Water Absorption Properties of Fluorine-Doped SiO₂ Films Using Plasma-Enhanced Chemical Vapor Deposition

The water absorption properties of a PE-CVD (plasma-enhanced chemical vapor deposition) fluorine-doped SiO 2 film with a low dielectric constant were studied. It was concluded that highly stable F-doped SiO 2 film was obtained at F contents from 2.0% to 4.2% (3.2≤ k ≤3.6) using high-density plasma CVD. However, at F contents higher than 4.2% ( k <3.2), the amount of water absorption was markedly increased due to the presence of Si–F bonds, such as Si(–F) 2 bonds, which are highly reactive with water. On the other hand, water absorption was observed at every F content for conventional plasma CVD films. Through gas phase component analysis and investigation of the incident ion energy distribution using a quadrupole mass spectrometer, it was confirmed that a high efficiency of gas dissociation and high-energy ion bombardment are the keys to obtaining high-quality films with a high resistance to water absorption.