| In neutral particle proximity lithography (NPL), a broad beam of energetic neutral particles illuminates a stencil mask and transmitted beamlets transfer the mask pattern to resist on a substrate NPL preserves the advantages of ion beam proximity lithography, including nanoscale resist scattering, negligible diffraction, and large depth of field, but is completely free of charge-related artifacts, including line edge roughness due to mask and wafer charging. However, the brightness of the neutral particle source used in the preliminary study of NPL was extremely low, resulting in long exposure times and impractical proximity gaps. We have developed a new concept for a neutral particle source to address these issues.;In the new source, ions are extracted from an improved multi-cusp ion source and injected into a four-electrode lens that accelerates the beam to a final energy between 30--50 keV and bends the beam towards the optical axis. Instead of crossing over, however, space charge repulsion causes the formation of a beam waist without a crossover. Viewed from the substrate, ions appear to be emitted by a bright, compact virtual source about 23 cm downstream of the beam waist. The ions are neutralized by charge transfer scattering in a differentially pumped charge transfer cell positioned about 38 cm downstream of the virtual source.;A neutral particle proximity lithography system, using the new source with a 10 m long beam line, is expected to be able to print 10 nm features with 0.5 nm (1 sigma) penumbral blur and 16 s exposure times in PMMA using a 50 microm proximity gap and resist. |
