Plasma diagnosis of tetrahedral amorphous carbon films by filtered cathodic vacuum arc deposition

Filtered cathodic vacuum arc (FCVA) deposition is regarded as an important technique for the synthesis of tetrahedral amorphous carbon (ta-C) films due to its high ionization rate, high deposition rate and effective filtration of macroparticles. Probing the plasma characteristics of arc discharge contributes to understanding the deposition mechanism of ta-C films on a microscopic level. This work focuses on the plasma diagnosis of an FCVA discharge using a Langmuir dual-probe system with a discrete Fourier transform smoothing method. During the ta-C film deposition, the arc current of graphite cathodes and deposition pressure vary from 30 to 90 A and from 0.3 to 0.9 Pa, respectively. The plasma density increases with arc current but decreases with pressure. The carbon plasma density generated by the arc discharge is around the order of 10¹⁰ cm⁻³. The electron temperature varies in the range of 2‒3.5 eV. As the number of cathodic arc sources and the current of the focused magnetic coil increase, the plasma density increases. The ratio of the intensity of the D-Raman peak and G-Raman peak (I_D/I_G) of the ta-C films increases with increasing plasma density, resulting in a decrease in film hardness. It is indicated that the mechanical properties of ta-C films depend not only on the ion energy but also on the carbon plasma density.