Comparison of diamond-like carbon films synthesized by 2.45 GHz microwave and 13.56 MHz multi-jet radiofrequency plasma sources

摘要

Diamond-like carbon films (DLC) were grown by two different plasm deposition systems: the RF-MW system employing a radio frequency (RF) powered substrate holder with an additional 2.45 GHz slot antenna (SLAN) microwave (MW) plasma source and the RF-RF system employing a RF powered substrate holder with an additional RF (13.56 MHz) jet matrix plasma source (JeMPS). Helium and methane were used as carrier gas and carbon source, respectively. When operating the RF-MW system, ion densities approached 4 * 10~(10) cm~(-3). Because of the large working distance used in our experiments the MW plasma did not contribute significantly to the charged particle density. In the RF-RF system substantially higher ion concentrations of up to 1.6 * 10~(11) cm~(-3) were measured. Optical and structural properties of the coatings deposited were compared using ellipsometry, Raman spectroscopy and Fourier transform infrared (FTIR). When depositing with the RF-MW system a gradual and controllable change from polymer-like to DLC-based films with increasing substrate RF-power was obtained. This is reflected by a refractive index variation from 1.6 to 2.1. Furthermore, the film growth rates decreased with increasing RF-bias. Typical growth rates were 30 nm min~(-1) at -400 to -500 V bias. A similar change of the films deposited in the RF-RF system was not observed. Instead, DLC films were produced in all cases. The growth rate peaked at 70-80 nm min~(-1) when using -350 to -450 V bias. The refractive index (at λ = 632 nm) and Vickers hardness were approximately 2.3 and 30 GPa, respectively.