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%.