Study On Wavefront Control Of Grating Diffraction On Scanning Beam Interference Lithography System

As a very important core device,large scale diffraction gratings are used in many fields,such as spectrometer,astronomy,metrology and inertial confinement fusion.When the traditional holographic lithography is used to manufacture large size and high quality holographic grating,it is limited by the acquisition,processing and adjustment of the large aperture lens.Scanning Beam Interference Lithography is a new type of large size holographic grating fabrication in recent years.It absorbs the advantages of mechanically ruling,holographic exposure and direct laser writing.The two small-size Gauss lights coincide at the grating substrate surface and generate interference fringes.A two-axis(x,y)air bearing stage is utilized to move the substrate in a step-and-scan fashion,stitching and exposing the interference fringe patterns in the photoresist in order to obtain the large size holographic gratings,the fringes of the phase distribution will directly affect the diffraction wavefront of holographic grating.The stage position measuring system is used to locate the stage position of the bearing grating substrate,and the phase of the latent image of the exposed area can be obtained.The exposure beam phase measurement system can obtain the phase of the interference fringes of the exposure area.The phase modulation of grating wavefront can be realized by phase locking system.Therefore,Therefore,the diffraction front of the grating in the Scanning Beam Interference Lithography System can be controlled by three steps,the position measurement of the worktable,the phase measurement of the interferometric fringe and the phase modulation of the grating wavefront.Thesis includes the following contents.Firstly,stage position measurement,in order to solve the aberration of grating diffraction wavefront and the low diffraction efficiency caused by the positioning inaccurate,heterodyne measurement method was proposed on the prototype device,and the refractive index change of the measured light path is compensated by wavelength tracker.A measuring system is designed and the accuracy is analyzed.The method of two-color measurement is proposed for the positive device,which can improve the resolution by adding an uncertainty correction system for the measured optical distances when measuring a long-distance stage in motion.Secondly,measurement of stage mirror profile,when patterning gratings via a parallel scan,the stage is scanned closely parallel to the Y axis.Since the stage mirror is scanned together with the stage,a profile of the stage mirror will be imprinted in the gratings,which results in a phase error whose amplitude is proportional to the current-location stage mirror profile,on the prototype device,two sets of original data of the profile are obtained by two sets of detectors of different spans composed by three interferometer and then through the relationship between the two sets of data,the detail profile deviation between the span was modified,improves the precision and accuracy of detection.Traditional method of measuring a stage mirror profile requires a Y-axis stage mirror on the vertical axis.The length of the Y-axis stage mirror is no less than 1700 mm if the length of the grating is 1500 mm,which is costly and difficult to manufacture and install.In this paper,we cut down the Y-axis stage mirror and measuring stage mirror profile using three-point method better than that using two-point method under the same condition.Thirdly,Fringe phase measurement,in order to solve the problem that the interference fringe measurement is low and the anti-interference ability is poor,the error source of the interference fringe phase measurement is analyzed.A symmetrical measurement method is proposed,and a set of high-precision phase measurement system is developed by using a four-in-one prism.And the accuracy analysis and stability analysis,the production of grating wavefront quality has improved significantly.Fourthly,grating diffraction wavefront modulation,the grating diffraction wavefront modulation theory model is established,and the holographic grating phase distribution is directly reflected by the grating diffraction wavefront.According to the principle of holographic grating exposure,the holographic grating phase distribution is determined by the three parts of the table measurement,phase measurement and phase lock.The grating diffraction wavefront control is measured by the table position measurement,the interference fringe phase measurement and the grating wavefront phase modulation Finally,the simulation and experimental verification of the grating diffraction wavefront modulation are carried out.The results show that the scanning interferometric field exposure system can control the grating diffraction wavefront well.