Shape deviations in masks for optical structures produced by electron beam lithography

Abstract

E-beam lithography is a well-known technology used in the structuring of resist for mask fabrication. In the LIGA process E-beam lithography is used to fabricate the first X-ray mask. Due to the high precision of X-ray lithography patterning errors and defects are transformed into the several hundred micrometers thick resist structures. The side walls of these high-aspect-ratio structures are often used as optical mirrors, for which very good surface properties are essential. Deviations in the shape of the side walls even far below the wavelength of the used light lead to spurious strayed or misguided light. For grating microspectrometers the requirements are particularly stringent. The width of the grating teeth does not only have to be precise, but also the grating teeth have to be positioned accurately along the entire grating width. Using LIGA microspectrometers as an example, deviations in masks and LIGA-structured side walls were studied and subsequent correlations made with the corresponding e-beam writing pattern.