Studies On Optical Constants And Thickness Uniformity Of The Laser Thin Films

The fabrication technology of optical thin films is more foundational and important than the design of optical thin films. The fabrication technology decides the realization of the design, while the new design will ask for the fabrication technology preciser. As for the fabrication technology of laser thin films, it mainly includes: film thickness monitoring, the control of film thickness uniformity, the measurement of optical constants of thin films, ion assistant deposition technique and fabricated thin films testing and so on. For fabricating large area, high quality laser thin films and improving the good product rate of coating machines, the accurate measurement of optical constants of thin films and good film thickness uniformity is most important. Starting from these points, The paper makes systemic theory analysis and in-depth experiment research for optical constants of thin films and film thickness uniformity. Introduce and compare the common value simulated ways of optical constants of thin films, and on the basis of Sellmeier formula, an extended optimization method is gotten, which is able to calculate optical constants n, k and film thickness d of thin dielectric films on wide spectrum only from transmission spectrum. The method is simple, precise and less restrained on film thickness, and because it thinks of the influence of extinction coefficient on transmission spectrum and the physical constraints, the method is preciser, more efficient and especially fit for thin weakly absorbing films. In this paper through the example of Ta2O5 thin weakly absorbing film, the optimization method is introduced from principle to application in detail. The experiment of Ta2O5 provides a refractive index error of 0.004, an extinction coefficient error of 1e-4, and a film thickness error of 0.32%. The theory of cosine emitted character and its correct model is analyzed, and the calculation formulas of some kinds of general fixture are given. With the fact of coating machines author used, author makes the simulated calculation of film thickness uniformity and the analysis of experiment results, which provides a good basis for improving film thickness uniformity. The film thickness uniformity of flat and spherical planetary fixture is emphasized, and their calculation formula is given. For perfecting the calculation model of film thickness uniformity, we analyze the influence of low background gas and ion assistant deposition technique on film thickness uniformity, and summarize two useful correct ways, virtual source and cosnφdistribution. By the optimization method some common laser thin film materials (MgF2,ZnS,Ta2O5 and SiO2) are analyzed, and these materials'optical constants are gotten, and then the film design database of our laboratory is built. Through the improving project of film thickness uniformity on DYC-900 large caliber coating machine, the film thickness uniformity increase to 98% in the cone radius of 0~150mm, which can satisfy the batch manufacture requirement of optical thin films. Especially, a flat planetary fixture is designed and made for ES-26CB coating machine, and the experiment proves its film thickness uniformity reaches 98.5%. Presently, this planetary fixture is in gear, and provides guarantee of depositing high quality and large area thin films for our laboratory.