Focused ion beam methods of nanofabrication: Room at the bottom

Various focused ion beam (FIB) processes, which can generate two- or three-dimensional (2D or 3D) features on surfaces by removing or depositing material, are reviewed for their efficiency, Processes for removing material include direct ion milling, chemical etching with a reactive gas, reactive ion etching, ion implantation with post chemical etch, and ion resist lithography. Processes to deposit material on a surface include direct ion deposition, FIB chemical deposition (simultaneous FIB and gas jet), FIB induced nucleation, and ion resist lithography. Surface material removal and deposition efficiencies (cubic microns per nano-coulomb of ion beam current) are examined, and their ability to form 2D and 3D surface structures is analyzed. In general, the ion lithography processes are the most efficient, whereas direct ion deposition is very inefficient. FIB instrument capabilities are examined including their focused ion beam size and beam current characteristics. These FIB instruments commonly employ field emission LMIS's (liquid metal ion sources), can focus beams to less than 10 nm diameter, and can rapidly mill in the 100 nm beam range. The removal and addition rates of material (cubic microns per second) are then examined for the various surface modification processes using these instruments. Since the milling throughput of FIB instruments has increased by two orders of magnitude in the last decade, new nanofabrication applications are rapidly unfolding. Direct FIB milling, FIB chemical etching, and FIB deposition are now common processes in the semiconductor industry for circuit modification, defect analysis, and process control. Production applications include thin film magnetic head trimming and aperture fabrication.