| Step-by-step projection and scanning lithography based on DMD(digital micro-mirror device)are the two most widely used exposure modes in large-area micro-structure processing.When the processing of large-area micro-structure is realized,the boundary of the adjacent field of view will be exposed.In this way,Splicing errors will be made,such as overlapping,misalignment of scribe lines,and severely limited exposure accuracy.Regardless of the exposure mode,in order to achieve high stitching accuracy in large-area micro-structure processing,it is necessary to test accurately the zoom ratio of the projection system,the inclination of the DMD projection image and the movement direction of the two-dimensional precision mobile platform,and make corresponding adjustments to the movement of the platform according to the test results to achieve higher precision stitching exposure and obtain an ideal large-area structure.Some researchers have also analyzed the errors of inclination angle and zoom magnification.Compared with zoom magnification,the test of inclination angle is more difficult.At present,the common methods of measuring inclination angle include metering process,moiré alignment method and automatic precise alignment.Nevertheless,the adjustment accuracy of the metering process and the moiréfringe alignment method are limited.Besides,the fully automated alignment system complicates the lithography equipment,and the cost is too high.Moreover,at present,there is no detailed analysis and discussion on the impact of the platform's movement accuracy limit and the uneven energy distribution of a single projection pattern.And barely have measurement schemes and solutions with strong feasibility,wide adaptability,accuracy and reliability been given.Therefore,based on the principle of step-by-step projection lithography,this thesis has made relevant research on the splicing accuracy problems of DMD-based maskless lithography systems in large-area micro-structure processing.And in terms of the defects of the existing solutions,corresponding new technologies are proposed to solve them.This method does not require large-scale DMD,long-distance movement and high-precision test equipment,and avoid complicated image processing.With better universality,it needs only one measurement to correct all subsequent stitching errors through the obtained error value.Specifically:(1)This thesis proposes a test method based on double exposure to get the main errors that cause stitching accuracy: the inclination angle is 0.05975°,and the zoom magnification is3.60399.And using these two quantized errors,the motion compensation method is employed to control the step distance of the platform movement,so that the side-to-side error is reduced to about 0.15 ?m,and the diagonal error is reduced to less than 0.5 ?m.Moreover,a simulation analysis is carried out for the sudden change caused by factors such as platform movement accuracy and energy unevenness.And the method of graphics preprocessing based on gradual gray scale is adopted to further optimize the stitching quality,and reduce the side-to-side error and the diagonal error to less than 0.15 ?m.Through the experiment,it is proved that this accuracy is sufficient to write large-area lithography pattern with high quality.In order to further verify the practical application value for the proposed method of testing,adjusting and optimizing the splicing error,the author makes the processing of square,hexagonal and circular microlens array with fit surface shape,even distribution,employing inverted thermal reflow technology and AZ50 XT thick photoresist.We have mastered the influence of the thermal reflow process on the various process parameters of the microlens array,and provided a valuable experimental reference basis for the subsequent optimization of the microlens array to achieve the ideal divergence angle and beam shaping spot. |
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