Basic Issues On Soft X-ray Diffraction Gratings Using Near-field Holography

As key elements of spectrometers, soft X-ray diffraction gratings play an important role in the field of synchrotron radiation, plasma diagnosis, and so on. In order to overcome the problems of mechanical ruling and holographic lithography, near-field holography (NFH) combined with electron-beam lithography (EBL) will be a very promising tool to realize soft X-ray gratings, especially soft X-ray varied-line-spacing gratings (VLSGs). In this thesis, aiming at the fabrication of soft X-ray VLSGs, two basic issues were investigated. One is the method to control the resist grating profile during NFH, considering the effect of efficiency contrast uniformity of fused silica VLSG mask and the parameter optimization of exposure and development during NFH. The other is the comparison of two kinds of method to suppress the interface reflections during NFH.1. Since interface reflections is a common issue during NFH, which significantly degrade the quality of resist grating from NFH and affects the measurement precision of spatial distribution of line density. Hence, the comparison of two different ways of suppressing interface reflections, including antireflection coating (ARC) and refractive index matching liquid (RIL), and the selection of a proper way of suppressing interface reflections are important to the investigation of the relations of line density of fused silica mask and resist grating. A fused silica grating mask with constant line density of 2400 lines/mm were utilized to compare the far field patterns of resist grating by using the above methods, respectively. Moreover, using such resist masks from the above methods, gratings followed by ion beam etching and Au coating were fabricated. Then their diffraction efficiency was compared at the spectral range of 5-20 nm. The experimental data implies that both ARC and RIL show a comparable effect of suppressing interface reflection. At the condition of a similar effect of suppressing interface reflection, the method of ARC can make the NFH process more simple and controllable than that of RIL. The straylight of gratings is reduced one level of magnitude by the suppression of the interface reflections during NFH.2. Considering the NFH of soft X-ray VLSGs, a fused silica VLSG mask with center density of 2400 lines/mm was taken as an example. First, the profile of efficiency contrast was simulated as functions of duty cycle and line density. Together with empiric value of efficiency contrast of common holographic lithography, the profile parameter of the VLSG mask was obtained. Based on the above simulation, fused silica VLSG masks were fabrication by EBL-etching method. Afterwards, a series of NFH with VLSG masks were performed. The preliminary NFH data show that, in order to tailor the profile of resist grating, on one hand, the efficiency contrast of fused silica mask is needed as high as possible during the its fabrication. On the other hand, a low and uniform efficiency contrast of the mask can be compensated by the parameter optimization of exposure and development during NFH.