Three-dimensional Monte Carlo calculation of Ga+ ion penetration in an a-Se75Ge25 thin film

Three-dimensional (3D) Monte Carlo (MC) simulation for Ga+ ion penetration in an amorphous Se75Ge25 thin film which acts as a positive resist in focused ion beam lithography is presented. For 3D MC simulation, both the depth and the lateral distance in the resist are divided into discrete cubic pixels with 25×25×25 Å. Scattering and stop positions as well as deposited energy density by ∼104 ion trajectories are summed up in these pixels. Also, these MC data are expanded for a focused ion beam with a proper ion dose. Therefore, the 3D stop-ion distributions and the 3D deposited energy profiles by ions implanted into the resist are obtained. The peak concentration of MC simulation associated with a dose of 1015/cm2 and an incident energy of 80 keV amounts to 2×1020 ions/cm3 and is located at a distance of about 400 Å from the surface which is shifted about 40 Å to the surface in comparison with Lindhard, Scharff, and Schiott-based calculation.