Analysis of hydrogenated amorphous carbon films deposited by middle frequency pulsed unbalanced magnetron sputtering

Hydrogenated amorphous carbon (a-C:H) films were deposited by middle frequency pulsed unbalanced magnetron sputtering with a mixture gas of argon and methane. The effects of working pressure on the structure, surface morphology, mechanical and optical properties of the a-C:H films were investigated by Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), Atomic force microscopy (AFM), Auger electron microscopy (AES), nanoindentation and spectroscopic ellipsometry (SE). It has been found that the film thickness, bonded hydrogen content and RMS surface roughness of a-C:H films increase with increasing working pressure from 0.2 to 1.33 Pa, while the sp3 content decreases with the increase of working pressure. AES depth profile exhibits that the C element distributes uniformly across the film thickness, and the transitional layer width between a-C:H film and Si substrate decreases with increasing working pressure. Nanoindentation and spectroscopic ellipsometry measurements indicate that the nanohardness and refractive index of the film decrease with increasing working pressure. IR transmission spectra show that a-C:H film exhibits quite higher transmission in near IR region. The Ge1 − xCx/a-C:H multilayer antireflection protective films can effectively improve the transmittance of Ge substrate within the broad band of 2.5–14 μm, and a-C:H film can resist rain erosion.