{"title":"Conformal polishing of NiP grating microstructures using SiO2/Al2O3 mixed abrasive slurry","authors":"Chuhong He , Quanpeng He , Yinhui Wang , Hui Deng","doi":"10.1016/j.precisioneng.2025.06.017","DOIUrl":null,"url":null,"abstract":"<div><div>Nickel-phosphorus (NiP) coatings are widely used for surface modification of metal mirrors due to their excellent physical and chemical properties, such as in the collector mirrors of extreme ultraviolet (EUV) lithography machines. Grating microstructures can be fabricated on NiP coatings using Single-Point Diamond Turning (SPDT) to enhance the optical performance of mirrors. However, the SPDT process often introduces periodic marks on the surface, increasing surface roughness, causing optical flux loss, and reducing reflectance, which negatively impact the performance of mirrors. In this study, SiO<sub>2</sub>/Al<sub>2</sub>O<sub>3</sub> mixed abrasive is employed for Chemical Mechanical Polishing (CMP) to investigate conformal polishing processes for NiP grating microstructures. The mixed abrasive leverages the advantages of both abrasives: Al<sub>2</sub>O<sub>3</sub> abrasive effectively removes periodic marks and reduces the spatial frequency errors in the 10<sup>1</sup>∼10<sup>2</sup> mm<sup>−1</sup> range, while SiO<sub>2</sub> abrasive further smooths the surface and reduces the spatial frequency errors in the 10<sup>2</sup>∼10<sup>3</sup> mm<sup>−1</sup> range. Through experiments, factors such as Al<sub>2</sub>O<sub>3</sub> particle size, Al<sub>2</sub>O<sub>3</sub> abrasive concentration, pH, and H<sub>2</sub>O<sub>2</sub> concentration are comprehensively considered to precisely control the synergistic effects of the mechanical removal and chemical reactions of CMP, balancing the optimization of surface quality and conformality of microstructures. By optimizing the polishing slurry and utilizing a combination of soft and hard polishing pads, a uniform RMS roughness of 0.8 nm (scanned area: 218 × 218 μm<sup>2</sup>) was achieved across a 100 mm diameter NiP grating microstructures sample. Importantly, the grating microstructures retained their shape, with only an 84 nm reduction in the grating height and a 12.98 μm increase in the transition area width after polishing. These results highlight the excellent conformal polishing capability of the process. This study provides a promising strategy for the conformal polishing of large-area and high-precision NiP grating microstructures on EUV collector mirrors, while also offering an important reference for the industrial-scale production of other optical microstructures.</div></div>","PeriodicalId":54589,"journal":{"name":"Precision Engineering-Journal of the International Societies for Precision Engineering and Nanotechnology","volume":"96 ","pages":"Pages 257-276"},"PeriodicalIF":3.7000,"publicationDate":"2025-06-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":"0","resultStr":null,"platform":"Semanticscholar","paperid":null,"PeriodicalName":"Precision Engineering-Journal of the International Societies for Precision Engineering and Nanotechnology","FirstCategoryId":"5","ListUrlMain":"https://www.sciencedirect.com/science/article/pii/S0141635925002053","RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":null,"EPubDate":"","PubModel":"","JCR":"Q2","JCRName":"ENGINEERING, MANUFACTURING","Score":null,"Total":0}
引用次数: 0
Abstract
Nickel-phosphorus (NiP) coatings are widely used for surface modification of metal mirrors due to their excellent physical and chemical properties, such as in the collector mirrors of extreme ultraviolet (EUV) lithography machines. Grating microstructures can be fabricated on NiP coatings using Single-Point Diamond Turning (SPDT) to enhance the optical performance of mirrors. However, the SPDT process often introduces periodic marks on the surface, increasing surface roughness, causing optical flux loss, and reducing reflectance, which negatively impact the performance of mirrors. In this study, SiO2/Al2O3 mixed abrasive is employed for Chemical Mechanical Polishing (CMP) to investigate conformal polishing processes for NiP grating microstructures. The mixed abrasive leverages the advantages of both abrasives: Al2O3 abrasive effectively removes periodic marks and reduces the spatial frequency errors in the 101∼102 mm−1 range, while SiO2 abrasive further smooths the surface and reduces the spatial frequency errors in the 102∼103 mm−1 range. Through experiments, factors such as Al2O3 particle size, Al2O3 abrasive concentration, pH, and H2O2 concentration are comprehensively considered to precisely control the synergistic effects of the mechanical removal and chemical reactions of CMP, balancing the optimization of surface quality and conformality of microstructures. By optimizing the polishing slurry and utilizing a combination of soft and hard polishing pads, a uniform RMS roughness of 0.8 nm (scanned area: 218 × 218 μm2) was achieved across a 100 mm diameter NiP grating microstructures sample. Importantly, the grating microstructures retained their shape, with only an 84 nm reduction in the grating height and a 12.98 μm increase in the transition area width after polishing. These results highlight the excellent conformal polishing capability of the process. This study provides a promising strategy for the conformal polishing of large-area and high-precision NiP grating microstructures on EUV collector mirrors, while also offering an important reference for the industrial-scale production of other optical microstructures.
期刊介绍:
Precision Engineering - Journal of the International Societies for Precision Engineering and Nanotechnology is devoted to the multidisciplinary study and practice of high accuracy engineering, metrology, and manufacturing. The journal takes an integrated approach to all subjects related to research, design, manufacture, performance validation, and application of high precision machines, instruments, and components, including fundamental and applied research and development in manufacturing processes, fabrication technology, and advanced measurement science. The scope includes precision-engineered systems and supporting metrology over the full range of length scales, from atom-based nanotechnology and advanced lithographic technology to large-scale systems, including optical and radio telescopes and macrometrology.