A silicon/silver multilayer Fabry-Perot bandpass transmission filter for use near 28.4 nm.

摘要

A transmissive Fabry-Perot filter was designed, fabricated, and tested in an attempt to reduce the bandpass near the Fe XV spectral line in the extreme ultraviolet. The design of the filter involved analysis of the optical constants of the available materials, examination of binary alloy tables for candidate material pairs, and computer modeling of possible configurations. Of the materials available, silicon and silver were determined to best fit the requirements of high throughput, low off-peak transmissivity, and minimal rate of interdiffusion. The optical component was fabricated using radio frequency triode sputter deposition onto silicon wafer substrates. An effort was also made to produce a transmissive substrate consisting of a thin silicon nitride window on a silicon wafer support structure using standard photolithographic and wet-etch techniques. Testing of the fabricated multilayer device included x-ray diffractometry, Auger spectroscopy, transmission electron microscopy, and reflectometry in the extreme ultraviolet.; The designed Fabry-Perot multilayer filter had a theoretical peak transmission of 1.55% at 28.0 nm and a full width at half maximum of 2.0 nm. The fabricated filter suffered from oxidation of its exposed silicon layer, addition of an adsorbed water layer, an interfacial roughness of between 0.5 and 1.2 nm, and a thickness error of approximately 0.5 nm. If this filter were tested as a free-standing filter, its theoretical peak transmissivity would be between 1.05% and 0.75% at 27.0 nm with a full width at half maximum between 2.8 nm and 3.7 nm.