The formation of surface nanostructures on As-S-Ge chalcogenide film after e-beam exposure

Abstract

Background. Chalcogenide glasses comprise a unique materials platform and are attractive in view of various applications that make use their intriguing characteristic, the ability to form surface-relief patterns. The interaction of these materials with the electron beam is of interest due to diversity of physical phenomena induced in chalcogenide films by laser irradiation. Objective. The purpose of the paper is to study direct (without selective etching) surface relief formation of optical elements periodic nanostructures on thermal vacuum evaporated film As3S77Ge20 of ∼8.3 μm thickness using electron beam lithography, as well as investigate the changes in surface nanostructures height and shape depending on exposure. Methods. The chemical composition was determined by energy dispersive analysis of X-rays. The film was irradiated by an electron beam using a scanning electron microscope. The influence of electron beam irradiation on As3S77Ge20 amorphous chalcogenide thin film was investigated. Surface relief of the film was tapped by atomic force microscope. Results. The exposure dose G varied from 12 mC·cm−2 to 12 C·cm−2. The formation of cones with Gaussian profile on the surfaces of the films was detected after local electron irradiation. Exposition dependent evolution of height surface nanostructures has been detected. It can be seen that for G < 2400 mC·cm−2 the height of the surface relief gradually grows to 100–125 nm and for G > 2400 mC·cm−2, relief height decreases. The initial and inversion doses of relief formation on this film have found. For 6,6 μm pitch is equal to G0 = 9,60 mC·cm-2, and the inversion dose of the surface relief shape G1= 31.18 C·cm−2. At d = 10 μm, these parameters are G0 = 6,98 mC·cm−2 and G1 = 36.19 C·cm−2. The dependences ()h=FG at increasing interval (16 mC·cm−2 – 1200 mC·cm−2) for d = 6.6 μm and d = 10 μm were fitted by exponential function. Conclusions. The changing of shape and parameters of the obtained surface relief on As3S77Ge20 film can be explained by the charge model. Our investigations have demonstrated that studied As3S77Ge20 composition is suitable for e-beam recording. These results show that As3S77Ge20 films can be used for fabrication of the optical elements.