Neutral atom lithography using the 389 nm transition in metastable helium.

摘要

Resist based neutral atom lithography with metastable 23 S1 Helium (He*) has been used to produce small structures in both gold and palladium. A beam of He* from a reverse flow, DC discharge source is collimated by the bichromatic optical force followed by three optical molasses velocity compression stages. The He* beam then crosses a region where a mechanical or optical mask creates the desired pattern.;In the first experiments, a self assembled monolayer (SAM) of nonanethiol is grown on a gold coated silicon wafer and then exposed to the bright, collimated beam of He* after a nickel micro mesh mask. The mesh protects parts of the SAM from the 20 eV of internal energy deposited by the impact of a He* atom onto the sample surface. The pattern of the mesh is transferred into the ∼200 A gold layer with a standard selective etch that removes the gold from under the damaged SAM molecules. The samples were analyzed with an Atomic Force Microscope and Scanning Electron Microscope.;The second set of experiments were performed using an optical mask to pattern a gold coated silicon wafer. In the optical mask, the He* atoms experience the dipole force while traversing a standing light wave of lambda1 = 1083 nm light tuned 490 MHz above the 23S1 → 23P2 transition or, in separate experiments, lambda 2 = 389 nm light tuned 80 MHz below the 23S1 → 33P2 transition. Using the optical masks, He* can be focused or channeled into parallel lines separated by lambda/2 by varying the intensity of the standing light wave.;The small structures created by the 389 nm optical mask began approaching the gold surface granularity. A ∼ 200A layer of palladium on silicon was chosen as the palladium granularity is much smaller and the SAM of nonanethiol will still form on the surface. Experiments using a nickel micro mesh as a mechanical mask have demonstrated similar features to those in gold.