Analysis And Suppression Of Interference Fringe Drift Error In Scanning Interference Photolithography

Large size and high-precision flat grating is irreplaceable in major national defense,science and technology fields such as the high-speed and high-precision displacement measurement of lithography workpiece table,inertial confinement nuclear fusion and large telescope.So there is a very urgent demand of this kind of gratings in our country's strategic planning.However,due to technology and product embargo,we have to develop our own production of such high-tech grating.Among the methods of grating fabrication,scanning interference photolithography used by Schattenburg research group from MIT has made great achievements in the larg and highest precision flat gratings fabrication.Workpiece-stage is used to hold the wafer and move so that small size interferegrams can step and scan on the wafer which result in large size grating image's exposure.The most important technology of this scanning interference photolithography is using interference pattern locking system to suppress the drift of the interferegram.The key point of increasing the precision of pattern locking system is how to suppress the drift error of interference fringe drift while many accuracy indicators of gratings is linked closely with it.In this paper,the drift error of interference fringe in scanning interference photolithography which use the homodyne pattern locking system put forward by Wangleijie is classified into three general types.And according this kind of category,I analyse the fringe drift error caused by the rigid body error motion of interferegram phase measurement frame and grating interferometer used to measure displacement of XY motion stage.And then,these measurement errors that significantly introduce the fringe drift are summed up.This paper also analyse the fringe drift caused by vibration of optical components in high frequency and summaries the structural weaknesses which introduce the should be avoided.According to the analysis of fringe drift error early,I establish an optimized design scheme of scanning interference photolithography which aims at suppressing the drift error of interference fringe.These optimized scheme contains the suppression of measurement error caused by the rigid body error motion and directly fringe shift error in high frequency which can't be suppressed by control system.Furthermore some experiments were designed to verify feasibility of optimized design scheme put forward in this paper.According to the results of experiments,the displacement measurement error has significantly reduced when grating interferometer rotate relative to the grating.At the same time,pattern locking system error has been suppressed under 6.5 mrad(3?)from 46.1mrad(3?)compare to the original system.These results well validate the feasibility of optimized design scheme which I established in this paper and give good ideas to suppress fringe drift in actual design of scanning interference photolithography mechanical.