Study On The Fabrication Of X-Ray Absorption Grating With Large Area And High Aspect Ratio

Since X-ray was discovered by Roentgen in 1895,X-ray-based image measurements have been widely used in medical diagnosis,non-destructive detection and other fields.Traditional X-ray absorption imaging method cannot provide high quality imaging for weakly absorbed structures,such as biological soft tissues mainly consist of light elements.Unlike conventional X-ray imaging based on attenuation property,X-ray phase contrast imaging technology utilizes the phase shift information of X-ray,so for weak absorbing sample,X-ray phase contrast imaging has a higher sensitivity.Over the past years,X-ray phase contrast imaging technology has been developed rapidly.Among those imaging technologies,X-ray differential interference based on gratings is the most promising technology.The introduction of this technology makes X-ray imaging method get rid of the limitation of the synchrotron radiation source and the micro focus source,and can be implemented in ordinary laboratories.This technology provide the possibility for application of X-ray phase contrast method in clinical medicine.Based on the X-ray grating phase contrast imaging device constructed by the National Synchrotron Radiation Laboratory of the University of Science and Technology of China,in this paper,we studied the fabrication of the core components of the imaging system.In order to meet the needs of high energy and large field of view in clinical application,the study of fabricating the large area and high aspect ratio X-ray absorption gratings is indispensable.UV lithography was adopted to carry out the research on the fabrication process of X-ray absorption grating,the main contents of this thesis were summarized as follows:In order to fabricate photoresist grating structure with large area and high aspect ratio,the parameters of exposure and development were studied and optimized.In this paper,we studied the relationship between linewidth broadening and exposure dose,and realized the precise control of the line width;a new method of developing using tilting table was presented in this paper,so that effectively improve the uniformity of development of large area grating microstructure,we used the COMSOL software to analyze the velocity distribution during the developing process and obtained the development parameters combined with the rotary stirring assisted developing;in consideration of pattern collapse of high aspect ratio microstructures,a reinforcement structure was introduced in experiments to solve this problem effectively.The electroplating process of gratings with large area and high aspect ratio were studied.And the parameters of the gold potassium citrate plating process were described in detail.The influence of surface tension caused by developing drying process is effectively avoided by using the whole water electroplating process.We discussed the problem of internal stress in electroplating process and analyzed the influencing parameters and forming reasons of internal stress.This study investigated the effect of current density on the internal stress by the bent strip method,and controlled the deposit stress effectively by optimizing the current density.Due to the special microstructure of large area and high aspect ratio,the solution was prone to transfer difficultly during the electroplating process and the uniformity of the deposit cannot be guaranteed.By optimizing the experimental design and parameters,the X-ray absorption gratings with good uniformity were successfully fabricated.According to the structure characteristics of X-ray absorption grating in this paper,the detection scheme of gratings were given.An optical detection method for high aspect ratio grating structure was presented and the validity of this method was verified by experiments.Based on the modulation of the photoresist grating structure to the incident light,the change of the grating structure can be judged by observing the distribution of the outgoing light on the upper surface of the grating,and the detection of X-ray absorption grating with large aspect ratio can be realized.