Properties of diamond-like carbon films deposited by ion plating with a pulsed substrate bias

Abstract

Diamond-like carbon films of high quality were deposited using CH4 by a magnetically enhanced ion plating system with a bipolar pulsed substrate bias (0–1000 V, 0–33 kHz). The flux and energy distribution of impinging ions could be individually controlled by the bias voltage and the duty cycle, defined as the percentage of ion acceleration time in the total pulse period. The effects of bias voltage and duty cycle on the structure and properties of film were studied. Owing to charge accumulation on the surface, ion bombardment energy increases with decreasing the duty cycle. The film's hydrogen content decreases with decreasing the duty cycle. The film having the highest growth rate and the lowest internal stress can be obtained at a duty cycle of 88%, suggesting possible charge neutralization on the surface. In addition, the hydrogen content decreases with increasing the substrate bias and the film having the highest growth rate and high hardness can be deposited at a substrate bias of 600 V. A lower bias reduces the ion flux and ion energy forming a softer hydrogen-containing film, and a higher bias induces the re-sputtering effect and the formation of sp2 carbon bonding in the film. Hardness and adhesion increase with increasing the substrate bias, except that hardness slightly decreases at the highest bias of 800 V, owing to the extremely high ion energy bombardment enhancing the formation of sp2 bonding. Ion energy is concluded to be crucial in determining the structure and properties of diamond-like carbon films.