Improving the resolution and throughput of achromatic Talbot lithography

Abstract

High-resolution patterning of periodic structures over large areas has several applications in science and technology. One such method, based on the long-known Talbot effect observed with diffraction gratings, is achromatic Talbot lithography (ATL). This method offers many advantages over other techniques, such as high resolution, large depth-of-focus, and high throughput. Although the technique has been studied in the past, its limits have not yet been explored. Increasing the efficiency and the resolution of the method is essential and might enable many applications in science and technology. In this work, the authors combine this technique with spatially coherent and quasimonochromatic light at extreme ultraviolet (EUV) wavelengths and explore new mask design schemes in order to enhance its throughput and resolution. They report on simulations of various mask designs in order to explore their efficiency. Advanced and optimized nanofabrication techniques have to be utilized to achieve high quality and efficient masks for ATL. Exposures using coherent EUV radiation from the Swiss light source have been performed, pushing the resolution limits of the technique for dense hole or dot patterning down to 40 nm pitch. In addition, through extensive simulations, alternative mask designs with rings instead of holes are explored for the efficient patterning of hole/dot arrays. They show that these rings exhibit similar aerial images to hole arrays, while enabling higher efficiency and thereby increased throughput for ATL exposures. The mask designs with rings show that they are less prone to problems associated with pattern collapse during the nanofabrication process and therefore are promising for achieving higher resolution.