The Research Of Microlens Arrays Based On SU-8Photoresist

With the development of MOEMS (Micro-Optical-Electro-Mechanical System), the demand for miniaturization of the optical element is increasing. As lens is one of the most crucial element of the optical system, miniaturization of the lens has become the research focus. In recent years, many research institutions and universities have been conducting the research about the microlens and many microlens fabrication methods have been proposed. Among them, the photoresist reflow method has become the focus of many researchers’ study. Based on the deep ultraviolet lithography, a new photoresist fabrication method is proposed in this thesis. The microlens arrays were fabricated based on surface tension when heating temperature is over glass transition temperature of SU-8photoresist. The main contents of this thesis are summarized as follows:1. The microlens fabrication methods were researched and analyzed and the domestic and foreign research status and progress of microlens fabrication methods were investigated. The SU-8resist fabrication process has been studied. Based on the conventional photoresist reflow method, a new method for fabricating the microlens has been proposed in this thesis. The theoretical analysis of the formation mechanism of microlens has been conducted. Theoretically, the influence factors to control the morphology of the microlens were discussed. The fabrication process tolerance and consistency were analyzed. Based on the proposed photoresist fabrication method, several experiments have been made to explore and study the effect of various process parameters on the morphology of the microlens.2. The morphology of the microlens was measured by three measure methods. The measure methods were with the surface profiler, optical microscopy/scanning electron microscopy and the built up optical setup, respectively. According to a large amount of experimental data, the effect of various process parameters on the morphology of the microlens has been analyzed. The effect of the width of photoresist microstructure, the height of coating photoresist, post-baking procedure on the morphology of microlens have been discussed and analyzed. The focal length of microlens were obtained by two methods and the optical performance has been analyzed and evaluated. Finally, the fill factors of the microlens array were analyzed. It is concluded that this fabrication method has the following advantages:1. The ultra-long-focal-length microlens arrays can be fabricated by this method.2. This method has good reliability and large process tolerance.3. The fill factor is very large and the largest fill factor in experiment can be up to98.5%.3.The formation mechanism was also studied by simulation based on finite element method (FEM). The simulation of microlens has been carried out by Surface Evolver. The experimental result agrees well with the result of simulation, which proves that the assumption that surface tension is the most crucial impact element of MLA’s formation procedure is correct. It is concluded that the formation mechanism of microlens is that the unexposed photoresist reflowed to form a spherical lens shape which minimized the energy of surface due to surface tension. The formation mechanism was validated by the simulation of software.