Ga+ beam lithography for nanoscale silicon reactive ion etching

Abstract

By using a dry etch chemistry which relies on the highly preferential etching of silicon, overthat of gallium (Ga), we show resist-free fabrication of precision, high aspect rationanostructures and microstructures in silicon using a focused ion beam (FIB) and aninductively coupled plasma reactive ion etcher (ICP-RIE). Silicon etch masks are patterned viaGa + ion implantation in a FIB and then anisotropically etched in an ICP-RIE using fluorinatedetch chemistries. We determine the critical areal density of the implanted Ga layerin silicon required to achieve a desired etch depth for both a Pseudo Bosch (SF6/C4F8) and cryogenicfluorine (SF6/O2) silicon etching. High fidelity nanoscale structures down to 30 nm and high aspect ratiostructures of 17:1 are demonstrated. Since etch masks may be patterned on unevensurfaces, we utilize this lithography to create multilayer structures in silicon. The linearselectivity versus implanted Ga density enables grayscale lithography. Limitson the ultimate resolution and selectivity of Ga lithography are also discussed.