Study On The Loss Of Free-hydrogen Diamond-like Carbon Films

Diamond like-carbon thin film is widely used a lot of fields. It is mainly used as high hardness and anti-reflection films in optical field. In general, the optical thin film has the specific spectral characteristic indicators requests, such as geometry thickness, refractive index and extinction coefficient should be control strictly by fabrication process. The extinction coefficient reflects the absorption characteristics of optical thin films, and has a direct impact on the optical transmittance of the film. Therefore, accurate determination of the extinction coefficient of the film is a key part of the evaluation of thin-film absorption properties.The thesis discusses the method of physical model established by ellipsometric technology, and analysis the accuracy of the model results. A single physical model Si/EMA (na+nb mixed material) is established by using equivalent medium theory. The effectiveness of using double layer model of high and low refractive index ratio instead of different components ratio is explored based on this new model. The extinction coefficient of DLC thin film is represented from on macroscopic using single layer model. The extinction coefficient and refractive index of single layer are obtained by using this new model. The optical constants of hydrogen-free DLC films are obtained by using the particle swarm algorithm for inverse calculation of the transmittance spectra. The accuracy of the ellipsometric model test results is verified by transmittance and Raman spectroscopy. The relationship between the hydrogen-free DLC thin film deposition process parameters and absorption characteristics is established to characteristic of the absorption loss of a hydrogen-free DLC films.The results show that the settings of the initial range of parameters directly affect the calculation accuracy of the results in particle swarm optimization algorithm. The initial parameters include film thickness, refractive index, extinction coefficient and thickness choice of which affect the calculation results. By ellipsometric analysis techniques can be qualitative characterization of the UBMS prepared free-hydrogen hydrogen DLC film structure component, the measurement accuracy and the accuracy of the Raman spectrum at the same level. The experimental results show that, when DLC films have been prepared by (Unbalance Magnetron Sputtering, UBMS), absorption coefficient initially increase and then decrease with the increasing of vacuum gas pressure and exciting current, and absorption coefficient increase with the increasing targer current. With the increasing of ID/IG ratio, the refractivity is rising and the absorption coefficient showed a trend of decrease.