GLOBAL AND STOCHASTIC SPACE-CHARGE EFFECTS IN ION-BEAM LITHOGRAPHY

Ion projection lithography (IPL) is a candidate technology for meeting expected circuit design rules (less than 0.18 mu m) for future genera tions of semiconductor devices. The Advanced Lithography Group (ALG), a consortium of industrial and U. S. government laboratories and unive rsities, is developing IPL technology with funding from the Advanced R esearch Projects Agency (ARPA) and the state of Maryland. A prototype IPL device, the ALG-1000, is being developed to demonstrate the capabi lity of IPL to meet future requirements for pattern overlay. To realiz e IPL technology requires control of space charge effects in the ion o ptical column. Due to the length of the IPL system (several meters), t he precision of the calculation to predict distortion at the wafer pla ne becomes difficult to perform. Including the effects of the space ch arge is even more difficult. Both global and stochastic space-charge p henomena 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-con sistent equilibrium ray tracing code, where the applied fields are cal culated from the actual lens column geometry. For global space charge, the model also includes optimization of the lens electrode voltages t o minimize pattern distortion at the wafer plane. (C) 1995 American Va cuum Society.