Interference lithography for nanostructure fabrication

Abstract

Some of the latest developments at CSEM Center Muttenz using diffraction gratings applied for a high resolution spectroscopy, light management in solar cells and LED, color filters, optical security, nano-membrane fabrication etc. will be presented. CSEM Center Muttenz has built a full chain for the grating fabrication, beginning with the design and ending with the optical device. The simulations are made to fulfill the appropriate properties of reflected/diffracted light for the planned application. This permits to fully specify the grating geometry: period, profile, duty cycle and depth. Gratings (linear or crossed) are initially fabricated in a photoresist using a Laser Interference Lithography (LIL) with periods going from 220nm up to 2000nm this on a surface of 5”. If needed the gratings can be transferred into the substrate (glass, Quartz, steel or dielectric) using a dry etching processes and a Cr masking. With this technology flat substrates can be structured with gratings, but also concave or convex surface can be processed. Different grating shapes are available like: sinusoidal or quasi-sinusoidal, triangle, rectangular, “U” type or blazed. This technology allows adjusting the duty cycle of the rectangular gratings, 20/80 is the minimum we can achieve but, this will depend on the depth to period ratio requested. A typical value we can achieve as “Depth to Period” ratio is 1.6. Most of the applications involving gratings will need a hard copy, the later can be made into glass, or a SolGel type of material like, Ormocer or also with a Ni shim. The Ni shims are useful for replication like hot embossing, including the Roll to Roll processes, UV casting. It allows transferring the grating structures into different flexible polymers, like PMMA, PC, PET etc. Specific metals or dielectric materials deposited on the gratings will permit to create different requested color effects.