Multiple-level phase gratings fabricated using focused ion-beam milling and electron-beam lithography

Abstract

The fabrication of eight-level reflective phase gratings in Si by electron-beam lithography and reactive ion etching, and focused ion-beam milling, has been investigated. Electron-beam lithography and reactive ion etching were used to fabricate gratings with 0.5-μm feature sizes. Alignment of successive levels was held to 50 nm by careful control of proximity effects. Focused ion-beam milling was used to fabricate continuously blazed surface reliefs. The effects of binary and continuously blazed surface reliefs on the first-order diffraction efficiency were determined. Eight-level binary reliefs produced efficiencies of 75% and were limited by phase errors while continuously blazed reliefs produced efficiencies of 90%.

Specifying and Testing Digital Optics

“…When a field is misaligned to a previously transferred field on the wafer, high-frequency artifacts appear on the structures [20][21][22]. These artifacts can be much smaller than the resolution of the lithographic tool.…”

“…22 An example of an interferometric plot through a Mirau confocal interferometric white light microscopeFigure 15.23 An interferometric scan over an array of high aspect ratio binary lenses…”

Fabrication of diffractive optical elements with arbitrary surface-relief profile by direct laser writing

“…The lithography process can be carried out in a number of ways: direct laser writing, 1-4 direct electronbeam writing, 5 gray scale masks, 6 shadow mask printing, 7 focused ion beam writing, 8,9 laser ablation, 10,11 or diamond turning. [12][13][14] Among these techniques, direct laser writing has become a powerful technique for making such micro-optical elements with arbitrary surface-relief profiles over the past few years.…”

Investigation of direct milling of micro-optical elements with continuous relief on a substrate by focused ion beam technology

“…Similar work was reported by Shank et al for multilevel DOEs fabrication in 1994. 11,12 DOEs with four and eight levels were manufactured by FIB technology in their work. With the development of integrated devices, the requirement for diffraction efficiency is becoming higher and higher.…”