Effects of oxidation on optical properties of polymer-like and diamond-like amorphous hydrogenated carbon films

Abstract

Diamond-like carbon (DLC) film has attracted considerable attention because of its extreme properties such as hardness, thermal conductivity, optical transparency and chemical resistance. Applications include scratch-resistant coating, microelectronics packaging, optical coating and coating on plastics [1-3]. DLC film belongs to the amorphous hydrogenated carbon (a-C:H) family whose properties depend strongly on the method and conditions used for the deposition. Methods such as plasma:enhanced chemical vapour deposition (PECVD), ion beam deposition and sputtering have been used for the deposition. Ion-assisted PECVD is advantageous for depositing a-C:H films because ion bombardment can be used for modifying film properties [4-6]. The degree of the ion bombardment on the substrate can be adjusted by changing the r.f. power, reactor geometry and gas pressure. Depending on the magnitude of the ion energy, the deposited films are classified as polymer-like, diamond-like or graphite-like. At low ion energy, soft, polymer-like carbon (PLC) films are formed, while at moderately high ion energy the hydrogen content in the film decreases and a dense and hard film [1] called diamond-like carbon (DLC) is formed. Because of the ion bombardment used, a-C:H films generally have high residual stress. Heat treatment is often used to relieve this stress. It is thus of interest how the properties of these films change upon oxidation. In this letter, we compare the oxidation behaviours of PLC and DLC films.