Indian J Phys. 76B ( 6 ), 711-714 (2002) U P B • an international journal Computer aided design of an electrostatic FIB system i Ahmad K Ahmad*, Sabah M Juma an|l Ahmed A Al-Tabbakh Department of Physics, College of Science, Saddam Unilrcrsily, PO. Box 64055, Baghdad, Iraq E-mail : sadsci(a)uruk{ink.net Received 27 February* 2002, accepted 2<S August 2002 Abstract A computer-aided design of focused ion beam (FIB) system consisting of three electrostatic lenses approximated by the spline lens model, has been investigated in the present work In a lens system, there may exist between the electrostatic lenses either a collimated ion beam (a bundle o f charged particles travelling parallel to the optical axis) or a beam crossover. The two-interval spline lens model is used in the synthesis procedure to construct einzel and immersion electrostatic lenses with as small aberrations as possible. In the beam crossover system, the axial gap between the electrostatic lenses has been investigated as an important parameter for improving the performance of the lens system. Non-rclativistic velocities of charged particles and neglecting the space-charge ciTcct, arc the two main assumptions that have been taken into account throughout the work. A two-dimensional diagram of the electrodes has been determined which shows that they can be practically realized. Keywords FIB system, electrostatic lenses, beam crossover, ion beam and ion optics. PAC.S Sos, ' 41 «5. -p, 41 85.NC, 41 85 Gy I. Introduction I'ocused ion beam (FIB) system is a combination of electrostatic lenses and deflectors that can provide a beam of charged particles of high current density and small spherical and chromatic aberrations. It is one of the most promising technologies for submicron microfabrication, which has certain features for application to lithography and maskless processes 11,2). It may also be used for direct writing onto wafers, mask fabrication, implantation (doping), direct ion milling,, deposition, and for producing bombardment damage to enhance sputtering and etching. The bright ion source and the high resolution ion optics column with a wide scanning area are the most important and complimentary elements of the FIB systems [3]. In order to achieve a high current density beam, an electrostatic lens system with low aberrations is required. Hie einzel lens is typically used since the object-side and image-side beam energies are not affected by variations in its excitation, a desirable property for the objective lens of a focused ion beam system. Tsumagari et al [4] investigated the optimization of the relative displacement in an electrostatic "Corresponding Author two-lens system with an intermediate beam crossover. Many authors introduced various designs of electrostatic FIB sy.stem taking into account the beam spot size and the aberrations of the system [2,3,5]. Sometimes it is difficult to determine what is the optical system for the application at hand, becuase there are some controversial demands. The present work is aimed at putting forward a design of a focusing system with aberrations as small as possible. The effect of the axial gap between the electrostatic focusing elements where the ion beam crossover occurs on the optical properties, has been investigated. The importance of the present investigation lies in the possibility of studying the effect of the exial gap independently of the electrodes geometry with the aid of the two-interval spline lens model. 2. Design of electrostatic lenses Design of electrostatic lens& may be accomplished by following one of the two main procedures, namely analysis and synthesis [6]. In the present work, synthesis of electrostatic lenses have been considered as a design procedure with the aid of two-interval spline lens model. © 2002 lACS