EPL electron optics performance on test stand: 1. resolution results

The performance of the electron optical (EO) column of Nikon's EB-stepper mounted on its test stand is reported, mainly focusing on the subject of resolution as preliminary results. Stitching data will be presented in the next paper at MNE2002. Resolution performance data are presented with SEM photos of line/space patterns and contact hole features, printed in both positive and negative resists. EO adjustment techniques were established to obtain the maximum resolution with best trajectory optimisation so that both resolution and distortion can meet their specifications. It is essential to have a metrology capability to measure, distortion as well as resolution. Good resolution results have been achieved over the large deflection (5 mm) field of the EO column using the curvilinear variable axis lens (CVAL) concept, which has been demonstrated by IBM theoretically and experimentally. Current beam blur, depth of focus (DOF) and some characteristic features of the EO conditions are also demonstrated. Image blur at small-deflected positions has also been determined by a direct measurement method. The minimum feature size of 50 nm and a large depth of focus over 5 µm, have been obtained. Overall performance over the whole 5 mm deflected range has not been accomplished yet due to stability limitations of the test stand stage, but good 80-nm line and space resist images have been obtained for the whole deflected range.