Electron beam lithography tri-layer lift-off to create ultracompact metal/metal oxide 2D patterns on CaF sub(2) substrate for surface-enhanced infrared spectroscopy

We developed a tri-layer electron beam lithography lift-off process to improve the resolution of metal film patterning for 100 nm thick films. The limitation of the bi-layer lift-off process is related to the trade-off in the thickness of the resist with high resolution requiring thin resist and lift-off ability requiring thick resist. A SiO sub(2) layer sandwiched between top and bottom layer of the bi-layer resist breaks this limitation. The top layer resist which influences the lift-off resolution can be much thinner without influencing the lift-off ability which is now determined by the thickness of the bottom layer. Using this tri-layer method, we have achieved 2 dimensional structures with 100 nm half pitch in both directions for 100 nm thick Au or ITO layers on CaF sub(2) substrate. We have used these structures to show resonant plasmonic features.