Influence of ion bombardment on the surface functionalization of plasma deposited coatings

This paper investigates the influence of ion bombardment on surface functionalization of hybrid organic–inorganic coatings deposited by plasma enhanced chemical vapor deposition. The experiment involves simultaneous deposition of silicon based coatings on Si substrates at the live and a floating electrode of 13.56 MHz asymmetric capacitive coupled plasma. The films were characterized using Fourier Transform Infrared Spectroscopy (FTIR) spectroscopy, which shows the presence of both inorganic Si–O–Si and organic Si–OH groups. By increasing the RF power we observe a consistent increase in nano-hardness of the film at the powered electrode, however the OH functional group is found to reduce drastically. In contrast, the nano-hardness of the films deposited at the floating electrode remains constant throughout the range of the applied RF power and it also retains the OH functional groups. At a typical RF power, above 200 W, we observe a decrease in deposition rate at the powered electrode. This is attributed to film densification by ion bombardment in conjunction with sputtering. Based on these observations, a qualitative discussion is presented to account for the differences in the chemical and mechanical properties of the films deposited at the floating and the live electrodes.