Mechanism of dense silicon dioxide films deposited under 100 °C via inductively coupled plasma chemical vapor deposition

High density of the inductively coupled plasma chemical vapor deposition (ICPCVD) enables growth of films on soft substrate such as polyethylene terephthalate (PET) that otherwise curls at temperatures higher than 100 °C. In this study, dense silicon oxide (SiO_x) films are prepared on PET by ICPCVD. Intrusive optical emission spectroscopy is employed to monitor distribution of the plasma radicals during the deposition process. The study discovers a direct relationship between the dense structure of the deposited film and the CH/(CH + OH) plasma radical intensity ratio. The deposition plasma with the lowest CH radical ratio results in the SiO_x film with the least CH_x incorporation and densest film structure. The film exhibits the smallest etched area in hydrochloric acid etching tests and the minimal water-vapor transmission rate of about 1.5 × 10⁻¹ g/m²/day.