Research On Fabrication Of Continuous Relief Micro Optical Element In Fused Silica Based On Hot Embossing

The thesis"Research on fabrication of continuous relief micro optical element in fused silica based on hot embossing"includes the theoretical analysis, model building and experiment research work. It covers technological base for the mass production of micro optical element (MOE) used hard substrate material with high precision, high repeatability and low costs. What is more, it will also improve the level of processing in the realm of modern optics in our country.Together with DRIE, hot embossing is able to fulfill the mass production of continuous relief MOE on the quartz material with high precision, high repeatability and low costs. However, there still exist two problems in the hot embossing when replicating continuous relief structure to the photoresist on the substrate. First, it is very difficult to get both the prolonged utilization life of stamp and the perfect filling efficiency. It mainly focused on the fragility of the sharp ridge on the continuous relief during the traditional imprinting of positive stamp and the incomplete filling of the negative stamp. Second, simulation method of imprint parameter's effect on the recovery is not ripe. Research on the reduction of the 3D polymer structure's recovery is still in short of experimental and theoretical evidence. These two problems have become the bottlenecks of the mass production of continuous relief MOE with high precision.The following is the innovational work we have done so far to resove these two problem.1. An improved method of filling process using continuous relief negative mold is put forward based on resist shaping. This method firstly shaped the resist layer into a 2D geometry pattern which is the same as the pattern area of the mold by dry etching, then align the mold with the shaped resist. This method can move the resist layer away under the protrution before imprinting, consequently, avoid long distance displacement of the resist under the inhabitation of non-slip bondary and the impediment on filling process. Therefore this method can realize a filling effect similar as the one using positive stamp, and reduce the residual layer of resist. The experimental results indicate: this method can realize complete filling into pattern of continuous relief MOE with the structure of 10nm diameter and 795nm depth in 15 minute, and reduce the redidual layer from 466nm using traditional imprint to 206nm.2. A cut-off grating structure used to protect continuous relief positive mold is advanced in this paper. This grating is less higher than the pattern area and can undertake the stress on mold. And this grating can reduce the required distances under the grating when resist flow laterally, and overcome the problem that the fragile tip of continuous relief positive mold is prone to be damaged during imprinting, and at the same time maintaine the advantages of positive mold in filling process. The experimental results indicate: by using the positive mold with cut-off grating, polymer can be completely filled into a pattern area with 8mm diameter, 1390nm depth continuous relief MOE.3. An integrated model of Cross-WLF equation and linear elastomer model which can be used for Deform simulation is advanced in this paper. This model describes the non-recoverable viscous flow in polymer and recoverable elastic deformation during filling process by using Cross-WLF equation and linear elastomer model. This model also can be used to analyze the action rules that imprinting parameters affect the recovery in polymer, on the condition that demolding temperature is below Tg. The experimental results indicate: the release of accumulated elastic stress after demolding is the internal reseason which caused recovery phenomenon; compared with the experimental results, the simulation results using this model under imprinting time 100s, 200s and 400s show that relative errors in depth are completely less than 4%.Finally, the continuous relief of resist was transferred into fused silica by reactive ion etching. The corresponding etching selectivity is 1: 1.01, and the roughness is 2nm. The profile of the final replica result at center shows the largest error. And its root-mean-square error relative to the mould profile is 5.41%, corresponding to a mean absolute height error of 40 nm, about 2.9% of the mould profile.