Study On Beam Quality Control Of The Scanning Beam Interference Lithography System

With the rapid development of science and technology,large size and high quality diffraction gratings have been widely used in many fields.The Scanning beam interference lithography technique is a new method of holographic grating fabrication.Its principle is to make two Gaussian laser beams pass through the waist of a smalldiameter optical system interference and by precise two-dimensional platform steppingand-scanning,record the interference fringes in a substrate coated with a photoresist,thus fabricating a large-area grating mask.The interference field formed by the superposition of the Gauss laser beam is the basic unit of the system,the quality of which directly determines the success or failure of the grating mask.The scanning interference lithography system is complex,and various parameters influence each other.It should not only consider the impact on the wavefront and energy distribution in the static holographic exposure,also need to consider the factors affecting exercise when fringe scanning.Therefore,it is great significance for the system to optimize the exposure interference field and control the errors of the beam.This paper mainly includes the following contents.First,according to the requirements of measurement,adjustment and exposure of the system,the system discussed the exposure beam size on the influence of fringe straightness,line error and exposure contrast by method of numerical simulation.Based on the analysis and the transmission characteristics of the Gauss beam in the lens,the optical layout of the system is calculated,designed and optimized,then the beam shape and nonlinear error of the fringe is measuredSecond,for the Gauss beam transmission system,a physical model of Gaussian beam modulation is developed with Fresnel diffraction theory and the corresponding analytical results are given.Based on the analytic expressions,details of the modulations introduced by defects are derived.Then the interference of two Gauss beams is extended by using the model.The effect of defects on the exposure contrast is analyzed and simulated and a corresponding evaluation factor is put forward.Third,according to the phenomenon of drift in the exposure light path,this article established a mathematical model of step-scanning exposure and analyzed the effects of the beam drift error on the interference image.Furthermore,taking advantage of the characteristics of a scanning beam interference lithography system,an exposed beam stable system was designed that can effectively suppress the low-frequency drift of the beam.The total beam angle control accuracy is better than the 2.7?rad,and position control accuracy is better than 3.9?m(both for 1?),which achieves the expected goal of the design.Fourth,in order to ensure the alignment accuracy of two exposure beam and improve the quality of grating mask groove in the scanning beam interference lithography system,this paper established a theoretical model between the beam alignment error with exposure contrast and designs the automatic alignment system for the exposure beam.Finally the beam angle alignment accuracy is better than 9?rad,beam position alignment accuracy is better than 10?m,which meet the exposure contrast and groove forming request.