Stability requirements for two-beam interference lithography diffraction grating manufacturing

Reproducible manufacturing especially of large diffraction gratings using two-beam laser interference lithography gives rise to exceptional requirements on the stability of environmental conditions like temperature, air pressure, humidity, vibrations as well as a robust exposure setup using stable components, a highly coherent, frequency-stable laser and highquality optics. In our contribution, these requirements are reviewed systematically. The influences of atmospheric refractive index, laser frequency fluctuations, and thermomechanical drifts on the exposed dose contrast and hence on profile variations for surface-corrugated gratings are discussed. Moreover, mid-spatial frequency surface-errors of the used optical elements are identified as a main cause for local dose variations. Reasonable specifications for series manufacturing of grating masters are given and real-world measurement data from a holography laboratory is presented to illustrate the interplay between these different influences. This experimental data includes atomic force microscope scans of highgroove density resist gratings, spatially resolved diffraction efficiency measurements and moiré-interferometric measurements of the fringe stability. The results of our analysis are also useful for other holographic manufacturing facilities, including the manufacturing of surface and volume holographic optical elements of any kind.