Liu Cunding, Guo Qinmin, Wei Ming, Ai Wanjun, Xu Xu
Opt Express. 2022 Feb 28;30(5):7772-7781. doi: 10.1364/OE.452062.
Simulation based on Knudsen's law shows that film thickness uniformity above 99% can be realized on spherical substrates with optimized profiles of shadowing masks. However, a type of optical thickness nonuniformity is revealed when the masks are applied for thickness correction of MgF films experimentally. The optical thickness nonuniformity depends on steepness of the spherical surfaces and reaches 5% approximately for surfaces with CA/RoC = 1.22. Porosity of the MgF film is superimposed on Knudsen's law to interpret the optical thickness nonuniformity. For theoretical simulation, the influence of porosity on optical thickness distribution is characterized by a new parameter that describes nonlinear dependence of deposition rate on cosine function of molecular injection angles in Knudsen's law. Utilizing the optimized deposition model, optical thickness uniformity of MgF films approaching to or above 99% has been achieved for surfaces of different steepness in a single coating run.
基于克努森定律的模拟表明，通过优化荫罩轮廓，在球形衬底上可实现高于99%的膜厚均匀性。然而，在实验中将荫罩应用于MgF薄膜的厚度校正时，发现了一种光学厚度不均匀性。光学厚度不均匀性取决于球形表面的陡度，对于CA/RoC = 1.22的表面，该不均匀性约达到5%。将MgF薄膜的孔隙率叠加到克努森定律上，以解释光学厚度不均匀性。在理论模拟中，孔隙率对光学厚度分布的影响由一个新参数表征，该参数描述了克努森定律中沉积速率对分子注入角余弦函数的非线性依赖关系。利用优化的沉积模型，在单次镀膜过程中，对于不同陡度的表面，MgF薄膜的光学厚度均匀性已达到或接近99%。
