Investigation of the film properties and deposition process of hydrogenated amorphous carbon films deposited with a microwave ECR plasma reactor

Hydrogenated amorphous carbon (a-C:H) films are deposited from acetylene gas at pressures in the submillitorr range (0.2–0.6 mTorr), and methane-argon and acetylene-argon gas mixtures at pressures in the millitorr range (1–5 mTorr) in a microwave ECR plasma reactor operated with rf biased substrate holder. The films deposited at pressures in the submillitorr range showed a strong influence of ion energy and ion flux to neutral flux ratio on the deposition process and film properties. The films showed a peak value of optical bandgap when deposited at –200 V of rf induced substrate bias revealing the ion energy effect. The effect of ion flux to neutral flux ratio was seen in the depositions done with varied substrate positions from the discharge region and the threshold ratio of ion flux to neutral flux for deposition of films with the peak is found to be in the range of 0.06–0.1. Maintaining a low deposition pressure is found to be critical to obtain films of high optical bandgaps. The deposition rate (∼90 nm/min) at 7.0 sccm of acetylene flow rate is much higher than the filtered ion beam and plasma beam deposition systems used for tetrahedral (hydrogenated) amorphous carbon film depositions in the literature.; The films deposited at pressures in the millitorr range showed variation of the film properties dependent on the deposition condition. The films deposited with the two mainly explained with the consideration of the hydrogen content of the films. In contrast, the variation of film properties in the film deposition at submillitorr pressures is mainly different gas mixtures including argon-methane and argon-acetylene under similar input variable conditions have substantially different properties including deposition rate, mass density, optical absorption coefficient, refractive index, optical bandgap and hydrogen content. The deposition variables varied included rf induced do substrate bias voltage (0 to –100 V), argon/hydrocarbon gas flow ratio (0–1.0) and pressure (1–5 mTorr).; The variation of film properties in the film deposition at millitorr pressures can be mainly explained with the consideration of the hydrogen content of the films. In contrast, the variation of film properties in the film deposition at submillitorr pressures is mainly attributed to sp3 to sp 2 carbon bonding ratio changes in the film composition. (Abstract shortened by UMI.)...