Large-area uniform hydrogen-free diamond-like carbon films prepared by unbalanced magnetron sputtering for infrared anti-reflection coatings

The hydrogen-free diamond-like carbon (DLC) films are potential materials to be used as infrared anti-reflection protective coatings if their optical absorption can be reduced to get relatively thick films needed. In this study, hydrogen-free DLC films were deposited by the physical vapor deposition (PVD) method in an unbalanced magnetron sputtering (UBMS) system with a rectangle graphite target of 440 × 80 mm in the argon atmosphere. The UBMS system was described in detail and the magnetron field distribution of the target was denoted in this work. The film thickness uniformity was investigated and the results showed that this system is capable of depositing uniform films larger than 150 mm in diameter. The infrared transmission spectra of DLC films were analyzed by a FTIR spectrometer, the results indicating that transparent films were obtained in the infrared region for the single side DLC coated on the silicon and germanium substrates, and about 68.83% and 63.05% transmittance were achieved respectively at the wave number of 2983 /cm, close to theoretical value for non-absorption carbon material. No obvious absorption peaks were found between 5000 and 800 /cm. The refractive index and extinction coefficient of the DLC films deposited under optimized conditions were about 2.08 and 0.067 respectively at the wavelength of 1600 nm. These important optical characteristics showed that the hydrogen-free DLC films prepared in the UBMS system were suitable for infrared transmission enhancement applications.