Fabrication of near-infrared and optical meta-materials on insulating substrates by lift-off using PMMA/Al stack

A novel lift-off process using PMMA/Al bi-layer stack is presented. The aluminium sacrificial layer underneath PMMA layer functions as a conducting layer so that e-beam exposure can be performed on an insulating substrate. Furthermore, it helps to create an undercut profile in an alkaline solution with appropriate conditions. The dissolution rates of aluminium layer were measured. Other conditions for controlling the undercut profile were investigated. A meta-material consisting of silver U-shape array with minimum feature dimension of 40 nm for near-infrared and optical wavelength has been successfully fabricated on a quartz substrate using the novel process.