Process optimization of DLC films by unbalanced magnetron sputtering for laser-induced damage threshold improvement

Diamond-like carbon films (DLC) have been widely used in the fields of optics, mechanics and materials science due to the high optical transparency, high mechanical hardness and excellent chemical inertness. On the other hand, the laser-induced damage threshold of DLC films, which are used for infrared antireflection protection coatings, is an important index to evaluate the quality of film. However, the films prepared by various processes have different laser-induced damage threshold. Therefore, it is necessary to investigate the damage properties of DLC films under different deposition conditions. Unbalanced magnetron sputtering (UBMS), on the other hand, combines the advantages of conventional magnetron sputtering (MS) and ion beam assistant deposition. Applying this technique, it is promising to prepare hydrogen-free carbon films with excellent characteristics by physical vapor deposition method. In this paper described an UBMS system in details. Hydrogen-free DLC films were prepared by this system under various processes arranged according to the orthogonal experiments method. The laser-induced damage threshold of DLC films were investigated by using a 1064 nm pulsed laser at a pulse width of 12 ns following ISO standard 11254. The results indicated that the damage threshold of the DLC films is about 0.2-0.7 J/cm 2 . It was found that the target current is the most important factor which affects the threshold of DLC films based on orthogonal experiments, compared with other experiment parameters such as argon gas flow rate, substrate bias and excitation current. A optimization process was obtained in this study at a mass flow of 200 sccm, excitation current of 120 A, bias of about -30 ~ -80 V and target current of 8 A. The higher damage threshold of 0.7 J/cm 2 was achieved by depositing DLC film under the optimization process.