SILICON NANOSTRUCTURES GENERATED USING METASTABLE HELIUM ATOM LITHOGRAPHY AND PLASMA ETCHING

W. Lu*, K.G.H. Baldwin, M.D. Hoogerland, S.J. Buckman, T.J. Senden, T.E. Sheridan and R. Boswell

We have combined atom lithography, using a metastable helium atomic beam, with an isotropic plasma etching process to transfer a mask pattern into a silicon wafer. He atoms in the 23S state with 19.8 eV internal energy are generated by an expanding nozzle discharge source (brightness ~ 10^15 atoms/s/str). The source is used to expose Au/Ti coated Si substrates (protected by a Self-Assembled Monolayer (SAM) resist of thiol molecules) through a mask for ~ 1000 s. The exposed substrates are wet chemically etched to remove the Au in the damaged SAM regions, generating an intermediate Au mask on the Si. The substrates are then dry etched in a low pressure helicon plasma reactor for 2 minutes. This etching process shows a selectivity greater than 19 with respect to the Au mask. The final structure has a depth of 580 nm and an aspect ratio better than 14. In addition, we use laser cooling techniques to develop an intensified metastable He beam source to enhance the lithography exposure rate.