The Research Of Structural Uniformity Of Large Area And High Aspect Ratio Gratings

Over the past decades,X-ray grating phase contrast imaging technology has been rapidly developed.The core optical component in the phase contrast imaging system,the large area and high aspect ratio gratings,play an indispensable role in phase contrast imaging systems.At present,the traditional high aspect ratio grating fabrication methods are silicon deep-processing technology and LIGA technology,but the gratings produced by these two methods are difficult to meet the needs of high energy and large view field of phase contrast imaging devices.Corresponding to the needs of the phase contrast imaging system,the grating size needs to be at least 100 mm × 100 mm,and it needs to have good structural uniformity.UV-LIGA technology can produce large area and high aspect ratio gratings,but the uniformity of the grating structure is still difficult to meet the needs of phase contrast imaging systems.Therefore,in order to improve the uniformity of the large area and high aspect ratio grating structure,this thesis proposes optimization research on the key fabrication process of UV-LIGA technology,and effectively improves the structural uniformity of large area and high aspect ratio gratings.The main contents of this thesis are summarized as follows:1.In order to reduce the diffraction effect caused by the uneven gap,this thesis optimizes the exposure process and adopts the back-exposure method.In order to verify the feasibility of this method,the consistency of the sidewall inclination angles and the consistency of the linewidths were used to evaluate the uniformity of exposure.Large area and high aspect ratio gratings with different linewidths were fabricated respectively based on the traditional contact exposure process and the back exposure process.The experimental results show that under different line width conditions,the inclination angles of the high aspect ratio gratings prepared by the back exposure process are close to 90°and the angles consistency is good.Besides,the large area gratings can also obtain good linewidths consistency.It proves that the back exposure process adopted in this thesis can effectively improve the uniformity of large area and high aspect ratio gratings.2.In order to improve the uniformity of the development,this thesis developes a rocker-type shaker-assisted development method that uses the up and down swing of the rocker-type shaker to achieve uniform flow of the developer.The finite element method is used to simulate the flow field distribution on the surface of the substrate and the different aspect ratios microstructure gratings.The simulation results show that the swinging up and down rocker-bed can achieve uniform flow of the developer.In order to give suitable development parameters efficiently,this thesis proposes a rapid development parameters determination method.The experiments show the relationship between the aspect ratios of the trenchs and the development rates,and provide the suitable development process parameters.3.In order to solve the problem that gratings will swing during the electroplating process,this thesis introduces the reinforcing ribs to the gratings.The gratings with different reinforcing ribs were simulated using ANSYS software.The simulation results show that the introduction of the reinforcing ribs can effectively prevent the grating from swinging during the electroplating process.The effects of different rib structures on the strength of the grating structure were also analyzed through simulation,and the optimal number and position of ribs were obtained.The experimental results show that by introducing the reinfocing ribs structure into the grating structure,the structural uniformity of the large area and high aspect ratio metal grating can be effectively improved.