Restorative Self-Image of Rough-Line Grids: Application to Coherent EUV Talbot Lithography

Abstract

Self-imaging is a well-known optical phenomenon produced by diffraction of a coherent beam in a periodic structure. The self-imaging effect (or Talbot effect) replicates the field intensity at a periodic mask in certain planes, effectively producing in those planes an image of the mask. However, the effect has not been analyzed for a rough-line grid from the point of view of the fidelity of the image. In this paper, we investigate the restorative effect of the self-image applied to the lithography of gratings with rough lines. This paper is applied to characterize a Talbot lithography experiment implemented in the extreme ultraviolet. With the self-imaging technique, a mask with grid patterns having bumps randomly placed along the line edges reproduces a grid pattern with smoothed line edges. Simulation explores the approach further for the cases of sub-100-nm pitch grids.