Effect of rf bias (ion current density) on the hardness of amorphous silicon oxide films deposited by plasma enhanced chemical vapor deposition

Silicon oxide thin films are transparent protective coatings with anti-scratch, chemical resistant, barrier properties that have recently emerged as one of the prime coating technologies for depositing a range of functional optical coatings on polymer substrates in mobile electronics, digital cameras and other digital applications. Many optically transparent and protective coating materials as well as low temperature plasma processes have been developed for these applications. In this study, amorphous silicon oxide (a-SiO2) thin films were deposited on polycarbonate (PC) substrates by plasma enhanced chemical vapor deposition (PE-CVD) for applications as protective coatings. The coating layer deposited by low temperature plasma processes was electronically meta-stable because the process temperature was too low and the substrate temperature was always < 100 °C for the formation of a thermodynamically stable structure with a stoichiometric electronic bonding that can prevent the deterioration of the polymer substrate. This paper reports a coating technique for producing a denser structure with high hardness by controlling the rf bias (ion current density). The ion current density on the substrate was controlled by the rf power and an additional bias through the rf power.