Spectral analysis and correction of the structure of computer-generated fan-out Dammann gratings at their fabrication

Abstract

A technique for quickly finding the optimal time of liquid etching the amplitude masks of two-dimensional Dammann gratings, the structure of which is synthesized by direct laser writing in a polar coordinate system, is studied theoretically and experimentally. Thin chromium films are used as the recording material for laser writing, which are oxidized during laser writing and form an amplitude mask during their liquid etching (when using the thermochemical technology for their processing). The change in the etching time here occurs in the form of etching and displacement of the edges of the exposed zones. To find the optimal etching time for chromium films, it is proposed to use a procedure of measuring the spectra of amplitude gratings, by quick operational measurement and analysis of the intensity distribution of high diffraction orders, and by minimization of the root-mean-square deviation of these intensities. It is shown that higher diffraction orders in the spectra of binary-amplitude structures correlate well with the same orders of binary-phase structures. This conclusion can be effectively used to determine the moment when the optimum zone size is reached during liquid etching.