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Published June 18, 2010 | public
Journal Article

Ga^+ beam lithography for nanoscale silicon reactive ion etching


By using a dry etch chemistry which relies on the highly preferential etching of silicon, over that of gallium (Ga), we show resist-free fabrication of precision, high aspect ratio nanostructures and microstructures in silicon using a focused ion beam (FIB) and an inductively coupled plasma reactive ion etcher (ICP-RIE). Silicon etch masks are patterned via Ga^+ ion implantation in a FIB and then anisotropically etched in an ICP-RIE using fluorinated etch chemistries. We determine the critical areal density of the implanted Ga layer in silicon required to achieve a desired etch depth for both a Pseudo Bosch (SF_6/C_4F_8) and cryogenic fluorine (SF_6/O_2) silicon etching. High fidelity nanoscale structures down to 30 nm and high aspect ratio structures of 17:1 are demonstrated. Since etch masks may be patterned on uneven surfaces, we utilize this lithography to create multilayer structures in silicon. The linear selectivity versus implanted Ga density enables grayscale lithography. Limits on the ultimate resolution and selectivity of Ga lithography are also discussed.

Additional Information

© 2010 IOP Publishing Ltd. Received 9 February 2010, in final form 28 April 2010. Published 20 May 2010. M David Henry gratefully acknowledges the support of the Fannie and John Hertz Foundation. Michael Shearn acknowledges the support of the National Science Foundation under their Graduate Research Fellowship program. This work was performed at the Kavli Nanoscience Institute at Caltech and the authors are grateful to the staff for their assistance. The authors also acknowledge funding from NSF Science and Technology Center under DMR-0120967 and CIAN NSF under EEC-0812072 program.

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