The Study Of Focused Ion Beam Milling Technology For Machining Three-dimensional Optical Microstructures

Traditional optical systems often use bulky curved lens combinations to improve image quality.This will result in a complicated structure and large occupation of the optical system,which is not possible to meet the requirements for high performance and light weight of optical systems in specific fields such as aerospace.Optical microstructures,especially three-dimensional optical microstructures,have the advantages of small size,light weight,and high integration.So it brings opportunities to break through the above technology and application bottlenecks.Its machining technology is also the focus of research in the field of micro-nano processing.Compared to other machining technologies,focused ion beam milling(FIBM)is a high-precision direct writing technology,which has unique advantages in microstructures machining,especially in three-dimensional optical microstructures machining.In this paper,the FIBM profile simulation model,FIBM machining experiment,FIBM profile error analysis and compensation for three-dimensional optical microstructures were studied.Firstly,based on the mechanism of focused ion beam milling,a process model of FIBM was established.Based on this process model,the two-dimensional and three-dimensional profile simulation model of bitmap patterning method was realized by using Python language programming.In the process of establishing simulation model,experiments on sputtering yield and spot distribution were carried out to improve the accuracy of simulation model.And also the running speed of the simulation model has been improved by using the matrix computation and sparse matrix storage.The process and simulation model realized the high-precision simulation of three-dimensional microstructures fabricated by FIBM bitmap patterning.Secondly,the experimental studies on FIBM of three-dimensional optical structure were carried out.For the concave spherical microlens,the effects of the ion beam current,maximum dwell time and beam spot overlap ratio on the surface quality of microstructures were studied.The influence of the these parameter was summarized by combining theory with simulation model.It was found that the surface quality of three-dimensional optical microstructures decreases significantly with ion beam current increases,too long or too small dwell time,and too large beam spot overlap ratio.Finally,for concave spherical lens and convex spherical lens which are two typical three-dimensional optical microstructures,the casuses of profile error of this two kinds of structures were analyzed by combining experimental results with simulation model.Based on the mechanism of profile error,two bitmap compensation methods to reduce the profile error of microstructures were proposed.And the feasibility of these two methods was verified by simulation and experiment.The error compensation proposed in this paper can improve the surface accuracy of microstructures by about 50%.