Fabrication And Test Of X-Ray Self-Standing Transmission Gratings

To break foreign export prohibitions of high-density diffractive optical elements (DOE), as well as to meet the urgent needs of our inertial confinement fusion (ICF) plasma diagnostic studies and space X-ray spectra, based on the diffraction simulation results by using the scalar diffraction theory and finite difference time domain ( FDTD) algorithm, which is established on the theory of vector, 2000 l/mm, 3333 l/mm self-standing transmission gratings and 1000 l/mm single-order diffraction transmission gratings were designed. Combining on the advantage of high resolution and almost infinite numbers of patterns of e-beam lithography and high efficiency, low cost and easily forming high aspect ratio of X-rays lithography as a means of reproduction, these three kinds of gratings mentioned above were fabricated. Firstly, using the e-beam lithography and micro-electroplating technology a master mask of gratings was fabricated on polyimide membrane substrate. Then using X-rays lithography and micro-electroplating, child gratings was replicated basing on the master mask. And then the self-standing mesh structure was transferred to the child gratings using U-V lithography and micro-electroplating. Finally, with the technology of etching and inductively coupled plasma (ICP), the fabrication of X-rays self-standing transmission gratings was fulfilled. During the fabrication process, several key technical issues, such as the grating duty cycle control, the fabrication of self-standing structure mesh and etching hollow polyimide substrates were analysized and solved. Diffraction efficiency of these three kinds of gratings mentioned above was conducted and analysed in the National Synchrotron Radiation Laboratory (NSRL).The major works in this article are listed as follows:1. Based on the scalar diffraction theory and vector theory of FDTD algorithm, self-supporting transmission gratings models were designed and the diffraction simulation was conducted in X-ray band. According to the simulation results and the limit of fabricating techniques, the map of transmission gratings was designed to get the maximum diffraction efficiency;2. The masks of 2000 l/mm and 3333 l/mm soft X-ray transmission grating as well as that of 1000 l/mm single-order diffraction gratings were fabricated, including fabricating the supporting membrane of polyimide (PI), electron beam proximity effect correction, Micro-Nano Resist graphics technology of electron beam lithography, micro-plating technology and plasma etching micro-nano-graphics technology, etc.;3. Small-batch of 2000 l/mm and 3333 l/mm transmission gratings as well as 1000 l/mm single-order diffraction gratings on PI supporting membrane were replicated successfully by using contact X-ray exposure. Graphics broadening problem caused by Fresnel diffraction during the process of exposure was resolved;4. 2000 l/mm and 3333 l/mm self-standing transmission gratings, as well as 1000 l/mm self-standing single-order diffraction gratings were prepared successfully. Self-standing structure mesh, optical lithography, micro-plating , mechanical properties and etching of PI membrane were all studied. These samples were all used in SGⅢPrototype Laser Facility respectively, which have a great significance for the next study.5. The three types of gratings mentioned above were tested in NSRL, the test results show that the diffraction efficiency of transmission gratings and the duty cycle are almost close to the ideal value according to the theoretical analysis. From the SEM pictures, we can see that the bars of 2000 l/mm and 3333 l/mm transmission gratings are all smooth; wall is steep and the duty cycle is close to 1:1;6. Studied manufacturing process of the large area gratings by using sensitive photo-resist and initially a 15mm×15mm 2000 l/mm X-ray transmission grating masks were prepared.