THE TECHNOLOGY OF FINELY FOCUSED ION-BEAMS

Focused ion beam machine technology is generally divided into two distinct categories according to the intended applications. These are: (1) low-energy (10-30 keV) heavy-ion beam (usually Ga) systems used in sputtering and ion-induced material deposition and (2) high-energy (50-200 keV) systems with generally more complex ion optics for implantation and lithography applications. State-of-the-art focused ion beam systems are capable of minimum beam diameters (FWHM) on the order of 500 angstrom with a chromatic aberration-limited current density of about 1 A/cm2. While continuing progress in ion optics and the computer automation of both these types of focused ion beam systems has enabled them to emerge from the laboratory and into limited production uses, some new approaches are also on the horizon. These new approaches include the use of achromatic quadrupole lenses to improve the maximum achievable beam current density perhaps by a factor of 10, and the use of immersion lenses for producing finely focused beams at very low (100 eV or less) energy to minimize substrate damage during processing. This paper will review some of the recent developments in focused ion beam machine technology in the context of existing and emerging processing techniques.