Research On Reflective Overlapping Diffraction Imaging Technology Based On Oblique Illumination

The fabrication of defect-free mask is an significant part of extreme ultraviolet lithography(EUVL)technology.Therefore,the defect detection of the EUVL mask is very important.The substrate of the extreme ultraviolet lithography mask absorbs ultraviolet light,therefore,the defect detection of the EUVL mask generally applies reflective optical system.This paper studies the technology of reflection ptychographical iterative engine via tilted illumination under the visible light condition result from the lack of EUV experimental condition,which provides the theoretical and experimental basis for the defect detection of EUVL mask.The tilted angular spectrum transmission theory is deduced based on the traditional optical transmission theories between parallel planes.And the model of reflective ptychographical iterative engine via tilted illumination is established.The correct of the tilted angular spectrum transmission theory is verified.The two-dimensional image and the phase component are used as samples to verify the feasibility of reflective ptychographical iterative engine.Futhermore,the influence of reflection angle on the recovery result is studied by simulation,which can provide a theoretical base for the selection of the reflection angle in the experiment.The factors that affect the recovery quality of reflective ptychographical iterative engine is analyzed,including the scanning position error,axial distance error and reflection angle error.In order to suppress the influence of various factors on recovery quality,this paper introduces the scanning position error correction method based on simulated annealing algorithm,the axial distance error correction method based on iterative self-focusing and the reflection angle error correction method based on MSE value.The feasibility of these correction methods are verified by simulation as wellThe reflective ptychography optical system is built under the visible light condition.The resolution test target is used as the amplitude-type sample and the step plate is used as the phasetype sample,they are experimentally measured respectively.The experimental results show that the error between the recovered value and the nominal value(1.4 cycles/mm)of the resolution test target line pair is 0.63% while the error between the recovered value and the nominal value(90.5 nm)of the step plate height is 1.15%.It is verified that the method we proposed can be used to recover the amplitude and phase information of the sample,so that the defect information of the sample can be obtained.