Analysis of errors and correction of topology of computer-generated two-dimensional fan-out gratings

Abstract

A procedure is proposed and investigated for correction of direct laser writing of the topology of two-dimensional diffraction fan-out gratings with the use of a laser-lithographic system DWL66+ operating in the Cartesian system. Thin films of photoresist and chromium on a quartz substrate were used as recording materials. The required binary-phase structures were obtained by subsequent ion-plasma etching of the amplitude structures recorded by the system. The minimum feature size of the binary zones of synthesized structures was 1500´1500 nm. It has been found that, in order to obtain the stability of the reproduction of the synthesized structures and to approach these structures to the calculated ones, it is necessary to use a regime with partial overexposure of photoresist and correction of position of transition boundaries of exposed zones. The specified correction of position of transition boundaries was experimentally implemented by software, with a modification of the topology of written structures and with experimental founding the optimal diffraction fan-out gratings accounting for their response, with the maximization of efficiency in useful diffraction orders and minimization of the root-mean-square deviation between intensity maxima in useful orders. Taking into account the size of a focused spot (about 550 nm), as well as the recording materials and the regime of photoresist overexposure, it was found that the optimal correction for the displacement of the boundaries of the exposed zones amounts to 200 nm, with the boundaries being shifted to the centers (inside) of the zones.