The fabrication of aspherical microlenses using focused ion-beam techniques.
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/cm(2) 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.
Advanced Technology Institute, Faculty of Engineering and Physical Sciences, University of Surrey, Guildford GU2 7XH, UK.
M T
MT
Langridge
Advanced Technology Institute, Faculty of Engineering and Physical Sciences, University of Surrey, Guildford GU2 7XH, UK; National Physical Laboratory, Hampton Road, Teddington, Middlesex TW11 0LW, UK.
D C
DC
Cox
Surrey Ion Beam Centre, Nodus Laboratory, University of Surrey, Guildford, Surrey GU2 7XH, UK.
R P
RP
Webb
Advanced Technology Institute, Faculty of Engineering and Physical Sciences, University of Surrey, Guildford GU2 7XH, UK. Electronic address: v.stolojan@surrey.ac.uk.
V
V
Stolojan
Aspheric micro-lenses; Chemical etching; Focused ion beam lithography; Micro-fabrication