Phase mask diffraction grating printing of extreme area and period
This PhD thesis presents a bench capable to write highly coherent diffraction gratings on a large area (potentially one square meter) with periods varying from 100 nm to several micrometers. The strategy is based on the "write on the ﬂy" method, which allows writing long and stitchingless gratings by scanning a photoresist-coated substrate under a small area interferogram generated by a phase mask. The main object of this thesis concerns the design of the phase-mask. Two different types have been developed. The first type can be described as a monolithic Mach-Zehnder interferometer comprising three diffraction gratings at the same side of a thick fused silica substrate. This approach has the advantage of writing large periods without any upper limitation. Standard lithography techniques (e-beam, RIE) have been used to fabricate the mask during a two months stay at UEF at Joensuu. At the wavelength of 442 nm, a large 2 µm period grating has been made with exposure by a divergent beam. The second type of mask is binary and made in a layer of high refractive index material. It has been used at the 244 nm wavelength and under immersion to write a 100 nm period grating. The modeling was performed to find the optimal structure capable of suppressing the zeroth transmitted order. The masks were made by three European partners within the Network of Excellence NEMO. The etching of LuAG has also been studied in view of making a 193 nm phase-mask. To write large and homogeneous gratings, various methods of beam expansion were compared to generate a light line with a homogeneous intensity proﬁle (top-hat). Solutions for the fabrication of long phase-masks have also been demonstrated