| The existing lithography technology adopts deep ultraviolet light(DUV)with wavelength of 193 nm to make a 22 nm minimum line width that is approaching the limit.In order to etch smaller line widths on the same chip,the shorter wavelength needs to be used.The next-generation lithography technology will use extreme ultraviolet light(EUV)with wavelength of 13.5 nm,which is predicted to reduce the line width in the chip to 5 nm or less.At present,the extreme ultraviolet lithography technology(EUVL)has initially formed an internationally recognized final scheme.Made in China 2025 lists EUVL technology as an important development technology in the field of integrated circuit manufacturing,and plans to achieve the localization of EUV lithography machines by 2030.The EUV collector optics is one of the important components in the EUVL system and is formed by plurality of monolithic Wolter-Ⅰ type optical collection mirrors combined in a nested manner.The monolithic Wolter-Ⅰ type collection mirror adopts an X-ray grazing incidence optical design.It is composed of two coaxial confocal axisymmetric aspheric surfaces.The steepness or ratio of length to diameter of the aspherical surface is relatively large,and the processing precision is very high.Internationally,the mandrel with the same surface form and processing quality as the collection mirror is often used to manufacture by the replication process.The manufacturing process is complicated,the process chain is long,and many links are involved.The key technical problems involved in the manufacturing process are difficult and the manufacturing cost is high.Currently,the research on the replication manufacturing method and the whole set of replication process of this collection mirror is not yet mature and perfect,lack of corresponding engineering experience and technical base.There are many key technical problems in the replication manufacturing process that need to be solved.These technical problems directly determines the accuracy and efficiency of the replication manufacturing of Wolter-Ⅰ type EUV collector optics.Therefore,the main research of this paper is effectively solving the key problems that currently exists in the manufacturing process of the Wolter-Ⅰ type EUV collector optics,improving the level of manufacturing technology,breaking through the traditional processing technology,completing the whole set of replication manufacturing process of the collection mirror,and realizing the replication manufacture of collection mirror.The research of the paper mainly includes the following parts:(1)In order to solve the problem of the traditional CNC trajectory equidistant interpolation method of inconsistent roughness around the surface of the mandrel after turning,to reduce the difficulty of mandrel surface subsequent polishing and improve the polishing quality.A calculation method for tool trajectory on the surface of a turning Wolter-Ⅰ type structure mandrel is putted forward.Keeping the center of the center of the circular edge diamond tool moving along the equidistant line of the meridian contour curve of the mandrel.Make the circular edge and the mandrel meridian contour curve is tangent at the interpolation point.The calculation method of approximation error is given.The simulation analysis software is designed and developed.The approximation error and the tool movement trajectory are simulated and analyzed.Through theoretically calculating the approximation error and densifying the interpolation points to meet the surface form accuracy machining requirements,the diamond turning machining of Wolter-Ⅰ type mandrel parts is completed.(2)Aiming at the problem that the measurement coordinate system cannot be established,for the aspheric surface of the mandrel forming the Wolter-Ⅰ type structure doesn’t contain vertices,a method for testing the surface of the Wolter-Ⅰ type structure mandrel after diamond turning using a high-accuracy contact profilometer is proposed.Design and build an adjustment device for auxiliary measurement to complete the accurate measurement of the mandrel meridional contour curve.Based on the Haar wavelet transform method,the method of extracting the intersection point R of the ellipsoid and hyperbola meridian contour curves on the surface of the Wolter-Ⅰ type structure mandrel is putted forward.The R coordinate is used as the reference point to establish the measurement coordinate system and the mandrel dimension error is accurately calculated.Based on the sym5 wavelet transform,the method of separately extracting the high-frequency and low-frequency components of the contour error signal of the mandrel surface from the original measurement data of the profilometer is presented.Statistically calculating performance index of the surface roughness and shape error of the mandrel,and analyzing by the profilometer built-in analysis software to verify this method.(3)In order to effectively reduce the surface roughness of the Wolter-Ⅰ type structure mandrel after diamond turning,to make the turning trajectory the same as the polishing trajectory,and to avoid or reduce the damage caused by the contour form of the surface of the mandrel after diamond turning in the polishing process,a polishing method is proposed.This method to control the movement of the center of the spherical tool along the equidistant contour curve of the mandrel meridional curve can keep the tool tangential to the mandrel contour curve.The mathematic model of the removal function of the polishing mandrel material was established,and the calculation method of the trajectory of the spherical polishing tool was given.Through Matlab software simulated analyzes the influence of the polishing parameters on the material removal depth,to complete the ultra-precision polishing of the Wolter-Ⅰ type mandrel surface and carried out surface roughness test.Based on the sym5 wavelet analysis method,the method of extracting the roughness from the raw data of the test polished mandrel from profilometer was given,and the correctness of this method was verified.(4)Established a whole set of replication process including a surface rough machining process for Wolter-Ⅰ type structure mandrel,electroless nickel-phosphorus alloy plating on the surface of the mandrel,a surface finishing process of the mandrel,a process of replicating a gold film on the surface of the mandrel,electroplating after gold plating on the surface of the mandrel mirror shell technology,mandrel and mirror shell separation process.The key technical problems are analyzed in the various stages of the process chain improve and optimize.The manufacturing process of the Wolter-Ⅰ type EUV collector optics is perfected,the replication of the collection mirror is completed.Test the duplicated reflective gold film and the surface roughness is consistent with the surface of the mandrel. |
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