Research On Micro-nano Structure Measurement Based On Digital Holography And Its Key Technologies

With the continuous development of science and technology,various functional micro-nano structures keep emerging,which play an important role in many fields,such as: precision instruments,aerospace,biomedicine,national defense and military industries etc.As a scientific and technological infrastructure,micro-nano structure is the driving force for the development of various disciplines,and the technological development level of micro-nano structure has become an important indicator for judging a country’s scientific and technological strength.High-precision measurement,as one of the prerequisites for the fabrication of micro-nano structures,is an important means of guaranteeing processing accuracy and device performance.Nowadays,in order to pursue more excellent performance,micro-nano structure is constantly developing in a more refined and complex direction.At the same time,the increasing demand for micro-nano structures has brought new challenges to the micro-nano measurement technology.Digital holographic microscopy restores the threedimensional information of the measured object through simulating the diffraction process in computer.Compared with other measurement methods,digital holographic microscopy eliminates the scanning steps,and can realize the rapid construction of surface information,with a wide measurement range and high resolution,The advantages of strong robustness and fast reconstruction speed have a great potential in the field of micro-nano structure measurement.In recent years,digital holographic microscopy has developed rapidly under the joint promotion of many researchers at home and abroad.The research content mainly focuses on system stability improvement,zero-order image and twin image elimination,phase aberration correction,noise suppression,and widened the longitudinal measurement range,increasing the lateral resolution,etc.Nevertheless,there are still some urgent problems to be solved in digital holographic microscopy,mainly including:(1)When digital holographic microscopy system measures the large gradient micro-nano structure,the high-frequency information generated by the large gradient region can’t enter the optical system,results in this method cannot realize the characterization of large gradient micro-nano structures.(2)In order to improve the real-time performance of the slightly off-axis digital holography method,predecessors proposed an interference structure with synchronous phase shift,but this structure will introduce an image matching problems.The existing spatial consistency calibration algorithm only has pixel-level accuracy,and the calibration accuracy still needs to be improved.(3)Although digital holographic microscopy can achieve super-resolution under the support of structured illumination,this method requires multiple phase shifts to complete the demodulation of super-resolution information.How to further improve its collection efficiency is a major problem at present.In view of the detection requirements of micro-nano devices and the existing problems in the current digital holography measurement method,the specific research work and research results obtained are as follows:First,in order to solve the measurement limitations of large gradient micro-nano structures,the generation principle of this problem is firstly analyzed,and a multiangle stitching digital holography measurement scheme is proposed,which reduces the gradient in different areas of the sample by adding a tilt angle to the sample.,so that the object wave in the area can be collected by the microscope objective lens,and then the complete three-dimensional topography of the large gradient micro-nano structure can be obtained by oblique diffraction,high-precision surface reconstruction and stitching algorithm based on overlapping regions.Second,a synchronous micro-off-axis digital holography system based on polarizing prism beam splitting is built,and in view of the existing problem of image space mismatch,a method based on the minimum phase difference is proposed.The spatial consistency calibration algorithm is optimized,and its sub-pixel calibration accuracy and algorithm effectiveness are proved through simulation and experiments.Third,the imaging model of structured illumination digital holography is established,and its 3D super-resolution capability is verified by simulation and experiment.On this basis,a fast structured illumination digital holography measurement method is proposed,which uses polarization multiplexing technology to modulate structured illumination.The field,together with the polarization beam splitter prism,realizes the synchronous acquisition of two phase-shifting images,which improves the real-time performance of structured illumination digital holography.Starting from the unsolved problems and difficulties of digital holographic microscopy,this paper gives the corresponding solutions,and proves the effectiveness of the method in multiple dimensions through theoretical modeling,computer simulation and experimental verification,and these methods are used to improve the application field,measurement accuracy and measurement efficiency of the traditional measurement method,the successful realization of the above methods provide new solutions for the increasingly urgent demands of micro-nano structure measurement,and promote the sustainable development of micro-nano technology.