The fabrication of aspherical microlenses using focused ion-beam techniques |
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| Institution: | 1. Advanced Technology Institute, Faculty of Engineering and Physical Sciences, University of Surrey, Guildford GU2 7XH, UK;2. National Physical Laboratory, Hampton Road, Teddington, Middlesex TW11 0LW, UK;3. Surrey Ion Beam Centre, Nodus Laboratory, University of Surrey, Guildford, Surrey GU2 7XH, UK;1. Belarusian State University, Minsk, Belarus;2. Belarusian State University of Informatics and Radioelectronics, Minsk, Belarus;3. Al-Balqa Applied University, Salt, Jordan;4. Scientific-Practical Materials Research Center of NAS of Belarus, Minsk, Belarus;5. Lublin University of Technology, Lublin, Poland;1. Department of Physics, Mohanlal Sukhadia University, Udaipur 313001, India;2. Microelectronics Research Center, Iowa State University of Science and Technology, Ames, IA 50011, USA;1. Departamento de Matemáticas and GISC, Universidad Carlos III de Madrid, E-28911 Leganés, Spain;2. Instituto de Ciencia de Materiales de Madrid (CSIC), Cantoblanco, E-28049 Madrid, Spain;3. Grupo de Dinámica No-Lineal and Grupo Interdisciplinar de Sistemas Complejos (GISC), Escuela Técnica Superior de Ingeniería (ICAI), Universidad Pontificia Comillas, E-28015 Madrid, Spain;4. Departamento de Física Aplicada, Universidad Autónoma de Madrid, Cantoblanco, E-28049 Madrid, Spain;1. School of Biomedical Engineering, McMaster University, Hamilton, Canada;2. Department of Materials Science and Engineering, McMaster University, Hamilton, Canada;3. Canadian Centre for Electron Microscopy, McMaster University, Hamilton, Canada;4. Univ. Grenoble Alpes, LIPHY, F-38000 Grenoble, France;5. CNRS, LIPHY, F-38000 Grenoble, France |
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| Abstract: | Aspheric lenses are the most common method for correcting for spherical aberrations but, in microlens production, highly-controlled lens profiles are hard to achieve. We demonstrate a technique for creating bespoke, highly-accurate aspheric or spherical profile silicon microlens moulds, of almost any footprint, using focused ion-beam milling. Along with this, we present a method of removing induced ion-beam damage in silicon, via a hydrofluoric acid etch, helping to recover the surface's optical and chemical properties.In this paper, we demonstrate that our milled and etched moulds have a roughness of 4.0–4.1 nm, meaning they scatter less than 1% of light, down to wavelengths of 51 nm, showing that the moulds are suitable to make lenses that are able to handle light from UV up to infra-red.Using empirical experiments and computer simulations, we show that increasing the ion-dose when milling increases the amount of gallium a hydrofluoric acid etch can remove, by increasing the degree of amorphisation within the surface. For doses above 3000 μC/cm2 this restores previous surface properties, reducing adhesion to the mould, allowing for a cleaner release and enabling higher quality lenses to be made.Our technique is used to make aspheric microlenses of down to 3 μm in size, but with a potential to make lenses smaller than 1 μm. |
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| Keywords: | Aspheric micro-lenses Micro-fabrication Focused ion beam lithography Chemical etching |
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