Maskless electron beam lithography: prospects, progress, and challenges

The resolution of electron beams is unlimited, for practical purposes in lithography. The central problem of e-beam lithography remains throughput, which has been historically too slow for mainstream VLSI manufacturing. The rapidly escalating cost of masks has given rise to renewed interest in various maskless alternatives, including direct write e-beam lithography. Usable writing cut-rent in probe forming systems is limited by the Coulomb interaction in the beam path. The resulting writing speed increases roughly as the cube root of the pixel parallelism for these systems. In contrast, distributed systems are not limited in usable writing current by the Coulomb interaction. These systems scale more favorably in writing speed. The proposed DiVa (Distributed Variable shaped beam system) is projected to be capable of writing at a speed of 5.2 cm(2)/s with 1000 shaped beams. If this can be achieved in practice, it will open up the possibility of mainstream manufacturing of VLSI circuits using maskless e-beam lithography. Feasibility issues include the electron source, parallel operation, and lithography demonstration at 50 nm and below. An experimental apparatus has been constructed, and has achieved its first beam. (C) 2002 Published by Elsevier Science B.V.