Scattering effects in ion beam exposure of photoresist polymer films

Abstract

By applying the large-angle elastic scattering theory of Rutherford and a modified energy loss law of the Thomson-Whiddington type, expressions are obtained for the fraction of an ion beam transmitted through a target, the rate of energy dissipation with depth and the backscattering coefficient. The model is found to be in good agreement with experiment. It is shown that an etch-resisting polymer (photoresist film) can be cross-linked by an ion beam as well as by an electron beam. The exposure characteristics of KTFR and AZ photoresists for 30-50 kev argon ions are very similar to those for electron beam exposure. On the basis of a quantitative discussion of ion beam scattering it is concluded that ion beam exposure is of great value in producing semiconductors in integrated circuits, because the resolution (or smoothness) at an edge is very high due to the small back-scattering effect, and also the penetration range is considerably greater than predicted by the theory of electronic stopping.