Effect of recoil atoms on resolution in ion-beam lithography

A previously developed computer simulation scheme of the Monte Carlo type which provides implantation and energy-loss distributions of ions implanted in amorphous materials is extended to include recoils. Damage produced by such recoil atoms can thus be simulated. Theoretical results are obtained using the Kalbitzer and Oetzmann empirical nuclear scattering potential. In the present work, primarily results concerning the effect of the inclusion of recoil atoms on the deposited energy distributions in organic resist materials are presented. In the case of heavy ions with energies in the range 200-300 keV there is a significant number of recoil atoms with energies of up to several keV. Our extended Monte Carlo simulation scheme is applied in the study of the effect of recoils on the lithographic resolution of focused ion-beam resist exposure, and in particular the effect of the inclusion of recoils in the case of Ga⁺ exposed PMMA. The model is also applied in a number of other cases such as damage produced in Si by Sb implantation, and recoil implantation of Al in Si.