Nanofabrication by Ion Beam

Abstract

Ions are different from electrons because of their heavy mass. A hydrogen ion is 1840 times heavier than an electron. The heavy mass of ions makes them particularly suitable for nanofabrication by direct structuring of material, rather than by exposure of a polymer resist as e-beam lithography does. Ions were discovered and made use of in many applications other than nanofabrication many years earlier than electrons. The application of ion beam has nearly a hundred years of history. Since Thomson developed gas discharge ion source in 1910, ion beam technology was mainly used in material analysis, separation of isotopes and modification of material property by ion implantation. In the early days, fabrication utilizing ion beam in nanometer scale was hampered because a fine size of ion beam was difficult to achieve from the early gas discharge ion sources. Focused ion beam (FIB) really became a nanofabrication tool following the introduction of liquid metal ion sources (LMIS) [1]. The LMIS made it possible to focus an ion beam to less than 5 nm in beam size. On the one hand, a focused ion beam can machine a material by sputtering away the material. On the other hand, a focused ion beam combined with chemically active gases can deposit materials onto a substrate. A focused ion beam can also implant different atomic species into a substrate by using ion sources consisting of different liquid materials. All the above processes are based on the high resolution capability of an FIB system, which enables the processed structures to be in micrometer and nanometer dimensions. FIB system is truly a flexible and versatile nanofabrication tool.