Study On The Key Technology Of Ultrasmooth Surface Fabrication Based On The Material Removal In Elastic Mode

The development of modern optics has put extremely high requirements on surface quality on the components. As one of the promising technologies for next generation lithography, extreme ultraviolet lithography(EUVL) requires the mirror substrate to be fabricated with the roughness at atomic level and almost no surface defects. Although the low surface roughness can be obtained with plastic removal mode in the traditional ultrasmooth surface fabrication method, it unavoidably causes the surface/subsurface damages induced deteriation and residual stress layers. It is the key research point that how to realize defect-free surface fabrication to meet the requirement for ultrasmooth surface in modern optical system. Within elastic deformation, the arrangement of each atom can be recovered back to its original position. So if we can remove the material in its elastic region defect-free surface is possible to be obtained.A newly developed ultrasmooth surface fabrication method is presented based on the material removal in elastic mode in our research. It is deeply studied that bond energy decline of the surface atoms during the chemisorption process and critical elastic contact condition. Based on the elastic removal mechanism, the hydrodynamic effect polishing(HEP) equipment is designed in detail. The key problem in HEP such as material removal characteristic, process optimization and machinability of the material are primarily studied. According to application requirement, polishing experiments are conducted to verity ultrasmooth capability of HEP. The major research points are listed as follows:1. The mechanism of the material removal in elastic mode is studied. Firstly, the chemisorption process between the nanoparticle and workpiece surface is studied, and the bond energy decline of the surface atoms at different locations has been investigated accordingly. Secondly, the impact analytic mode between the nanoparticle and workpiece surface has been established, and the elastic contact condition is fixed accordingly. Thirdly, through the research of the nanoparticle jet polishing, the feasibility and excellent performance of the material removal mechanism are validated. At last, the material removal characteristic of the nanoparticle with different type has been researched, and it gives instructions how to select the proper type of the nanoparticle for the subsequent research.2. Based on the fundamentals of fluid dynamic lubrication and fluid dynamic simulations, HEP in which the material removal is confined in elastic zone is presented. The original HEP equipment has designed, and the structures of the polishing head and wheel have been given optimum design. The rotational accuracy affected by the wheel speed and the heat expansion during the machining process has been studied. The excellent ultrasmooth capability has been verified by the sample polishing experiment.3. The material removal characteristic in HEP has been studied. Firstly, according to theory analysis and exploratory experiment, the three-dimensional material removal model of HEP has been established. Material removal affected by the combination of the hydrodynamic pressure and shear stress. Secondly, the surface evolution during HEP process has been studied. Based on the experiment result, the effect of the HEP ultrasmooth capability influenced by the direction of the defect in the original surface has been researched. At last, the surface and subsurface quality machined by HEP has been evaluated through hydrofluoric(HF) acid solution and nano-indentation technology, from which the excellent machinability has been demonstrated.4. The effect of the machining process is researched. On the one side, the effect of the different process parameters in HEP on the material removal efficiency has been studied. According to the analysis, the optimum parameters have been selected. On the other hand, the generation of the micro polishing marks on the processed surface has been studied. The strategies to restrain the micro polishing marks have been presented accordingly, and their feasibilities have been verified by the related experiments.5. Application experiments for HEP technique are carried out. Firstly, the machinability on different types of material in HEP has been investigated experimentally, and the material structure that can be used for ultrasmooth polishing is presented. Secondly, the ultrasmooth capabilities for ion beam figuring(IBF) and magnetorheological finishing(MRF) are investigated experimentally, and the Rms roughness of the processed nearly reached to 0.1nm. Thirdly, ultrasmooth polishing experiment was conducted on a circular quartz glass mirror, and the results show that the mid-frequency and high-frequency surface roughness have been greatly depressed while the low-frequency surface figure error is well maintained after the HEP process. At last, Laser induced damage threshold(LIDT) of the quartz glass before and after HEP process have been measured respectively, and the results show the LIDT has been improved when surface was processed by HEP.