Reactive ion beam etching of large-aperture multilayer diffraction gratings by radio frequency ion beam source

Abstract

The major etching processes of a large-aperture multilayer diffraction grating, including the uniformity of the ion beam current along the major axis and the on-line measurement of the diffraction intensity distribution are described. A largeaperture ion beam etcher with radio frequency linear source has been developed to fabricate large-aperture diffractive optical elements. The length with ±5.1% uniformity of the ion beam current distribution along the major axis is 30 cm. A series of multilayer diffraction gratings were etched successfully by using this etcher with CHF 3 chemistry. Multilayer diffraction gratings on a 80 mm×150 mm BK7 substrate etched for laser systems are shown. The grating exhibits an averaged diffraction efficiency about 96% at TE polarization of 1 064 nm light viewed at Littrow angle.

Methods for improving ion beam etching uniformity of large-sized DOEs

“…The etching depth in the K9 glass is measured with Alpha step500 of Tencor. The etching depth is directly proportional to the beam current along the major axis of the ion source [9] . By moving the position of the DOE sample on the working platform and controlling the etching time of each position, the curve of the beam current in figure 4 is considered as the ion beam current for etching.…”