Global and stochastic space-charge effects in ion beam lithography

Abstract

Ion projection lithography (IPL) is a candidate technology for meeting expected circuit design rules (less than 0.18 μm) for future generations of semiconductor devices. The Advanced Lithography Group (ALG), a consortium of industrial and U. S. government laboratories and universities, is developing IPL technology with funding from the Advanced Research Projects Agency (ARPA) and the state of Maryland. A prototype IPL device, the ALG-1000, is being developed to demonstrate the capability of IPL to meet future requirements for pattern overlay. To realize IPL technology requires control of space charge effects in the ion optical column. Due to the length of the IPL system (several meters), the precision of the calculation to predict distortion at the wafer plane becomes difficult to perform. Including the effects of the space charge is even more difficult. Both global and stochastic space-charge phenomena occur. This article presents a system of computer models that allows simulations of both global and stochastic space-charge effects. In particular, the models will be used on the ion beam projector in the ALG-1000 device. The calculations are carried out using a self-consistent equilibrium ray tracing code, where the applied fields are calculated from the actual lens column geometry. For global space charge, the model also includes optimization of the lens electrode voltages to minimize pattern distortion at the wafer plane.