Monte Carlo Modelling of BSE Reflection in E-Beam Writers

摘要

The reflection of back-scattered electrons (BSE) at the objective lens of an electron beam writer leads to a diffuse resist exposure which extends over several millimetres. The deposed energy of this unintentional exposure is much lower than the direct one. However, if the area of the direct electron beam exposure is large enough the accumulated energy is no longer negligible and may cause significant CD variations. Therefore, it is of crucial importance to study possible ways of reducing this dose contribution to a minimum and in order to perform a correct proximity correction targeting to determine its radial distribution. In this work a model of a 50kV E-Beam writer was developed, consisting of a resist-coated silicon wafer and an opposing low-reflection disk mounted at the pole piece of the objective lens. In order to improve the low-reflection disk, different material compositions as well as an optimized surface topography of the disk are modelled.