Plasma deposition and characterization of silicon oxide-containing diamond-like carbon films obtained from CH 4:SiH 4:O 2 gas mixtures

Abstract

In this work silicon oxide-containing diamond-like carbon films were deposited from gaseous mixtures of CH 4 + SiH 4 + O 2 and characterized. The effects of the self-bias voltage and O 2 content on deposition and properties of the films were investigated. At low self-bias voltages (| V B| < 200 V) films present reduced residual stress due to the smaller internal stress of a silicon oxide-rich (SiO x ) network. At high values of self-bias (| V B| > 200 V), on the other hand, the film residual stress is comparable to oxygen-free films although a considerable concentration of oxygen is present. Hardness of the films are somewhat reduced by oxygen incorporation in the whole range of bias voltages investigated. An increasing value of hardness was observed as | V B| is increased. The refractive index of films increased with increasing | V B| due to both the relative reduction of the SiO x content and to the increased sp 2 character of the diamond-like carbon network. Oxygen incorporation results in important structural changes: i. a strong reduction of the density of C–H bonds with a reduction of C–H n sp 3/sp 2 ratio and ii. a dramatic increase of Si–O bonds that substitute Si–H n ones, suggesting the formation of a non-hydrogenated a–SiO x -rich network. Refractive index measurements indicated a strong decrease of the material density as a result of the formation of Si–O–Si bonds. Scratch hardness measurements revealed that the obtained films can be used as highly transparent scratch resistant coatings for polycarbonate substrates. These results show that films with properties equivalent to those obtained with liquid siloxane precursors can be produced when using CH 4 + SiH 4 + O 2 mixtures as gas feeds.