Dissolution of thin SiO2-coatings - Characterization and evaluation

The hydrolytic attack by liquid solutions was investigated for two different SiO₂-coatings deposited by plasma enhanced chemical vapor deposition using a pulsed microwave plasma (PICVD) on a polymer substrate. The extent of hydrolysis was determined by the thickness reduction of the SiO₂-layer. Measurements were performed before and after aqueous contact with two independent methods, scanning electron microscopy (SEM) and reflectometry. Before storage the morphology of the coatings deposited with a HMDSO-concentration of 3% tend to be columnar, whereas the coatings produced with 1.5% appear almost untextured. After hydrolytic attack the systems feature enhanced thickness reduction with increasing pH and temperature. Significant differences between the two systems were observed regarding the dissolution rate and the appearance of the corroded surface. The dissolution rates were determined after storage in aqueous buffer-systems (pH = 5.5 and pH = 7.0) at temperatures of 60 and 90 °C. Under appropriate analysis conditions it was found, that the error of these difference measurements is dominated by the thickness variation. The observed dissolution rates vary between 0.1 and >50 nm/h.