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

Diamond-like carbon films (DLC) were grown by two different plasma depositi on systems: the RF-MW system employing a radio frequency (RF) powered subst rate 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 x 10(10) cm(-3). Bec ause of the large working distance used in our experiments the MW plasma di d not contribute significantly to the charged particle density. In the RF-R F system substantially higher ion concentrations of up to 1.6 X 10(11) cm(- 3) were measured. Optical and structural properties of the coatings deposit ed were compared using ellipsometry, Raman spectroscopy and Fourier transfo rm infrared (FTIR). When depositing with the RF-MW system a gradual and con trollable change from polymer-like to DLC-based films with increasing subst rate RF-power was obtained. This is reflected by a refractive index variati on from 1.6 to 2.1. Furthermore, the film growth rates decreased with incre asing RF-bias. Typical growth rates were 30 nm min(-1) at -400 to -500 V bi as. A similar change of the films deposited in the RF-RF system was not obs erved. Instead, DLC films were produced in all cases. The growth rate peake d at 70-80 nm min(-1) when using -350 to -450 V bias. The refractive index (at lambda = 632 nm) and Vickers hardness were approximately 2.3 and 30 GPa , respectively. (C) 2001 Elsevier Science B.V. All rights reserved.