FOCUSED ION-BEAMS MICROFABRICATION METHODS AND APPLICATIONS (INVITED)

Focused ion beams generated from liquid metal field emission ion sources enable high resolution microfabrication by sputter machining, deposition and ion implantation. Beams are focused by electrostatic lenses to form probes as small as tens of nanometres with current densities of several A cm-2. Energies in the range 20-50 keV are commonly used for micromachining and microdeposition. Machining rates can be significantly increased over pure sputtering rates by chemical assistance. Microdeposition through ion-induced decomposition of a precursor gas is increasingly used in R&D for a range of applications. Fundamental work has been relatively neglected, but an understanding of mechanisms is emerging and preliminary models proposed. Among the more immediate applications are the repair of photomasks used in optical lithography of microcircuits, using carbon deposition, and repair of gold-on-membrane masks for X-ray lithography, for which tungsten is deposited, Tungsten deposition is also used in the modification and repair of integrated circuits. Recent work in this field has included the modification of an advanced prototype IC with three layers of metal, each requiring precisely located repairs on the micron scale.