Ion energy and momentum flux dependence of diamond-like carbon film synthesis in radio frequency discharges

An investigation of the ion energy and ion momentum flux dependence of the properties of plasma-deposited diamond-like carbon (DLC) films is presented. The DLC films are deposited in low:pressure radio frequency (RF) discharges operating at 13.3 Pa with methane as the source gas. The discharge is characterized in situ for the negative direct current (d.c.) self-bias voltage at the powered electrode, the average discharge current, and the total power, from which the average ion energy and average incident momentum flux can be determined. Ion energies explored in this study range from 50 to 250 eV. Films are deposited on [100] n-type silicon wafers and are characterized by a variety of analytical methods to determine film hardness, density, and stress. It is shown that the maximum film density (1.7 g/cm(3)) and hardness (18 GPa) correspond to conditions of maximum deposition rate (5 x 10(-6) g/s) and maximum film stress (1.8 GPa) all at ion energies of approximately 160 eV. These values are comparable with those previously reported in the literature. The relationship between film properties and impinging ion energy and ion momentum flux is discussed within the framework of existing models of diamond-like carbon formation. (C) 1999 Published by Elsevier Science S.A. All rights reserved.