Optimization of an electron beam lithography instrument for fast, large area writing at 10 kV acceleration voltage

Abstract

Electron beam lithography (EBL) is a maskless lithography technique used in numerous applications for fabrication of ultrahigh-resolution photolithography masks. The main disadvantage of EBL is that it is time-consuming, requiring the pattern to be written in a successive fashion. Various approaches are used to lower the write time. Throughput-oriented EBL instruments used in industrial applications typically apply a very high acceleration voltage (≥50 kV). However, in many research environments, more cost-effective instruments are used. These tools are usually optimized for high-resolution writing and are not very fast. Hence, they are normally not considered very suitable for writing large-scale structures with high pattern densities, even for limited resolution applications. In this paper, the authors show that a carefully considered optimization of the writing parameters in an EBL instrument (Raith e_LiNE) can improve the writing time to more than 40 times faster than commonly used instrument settings. The authors have applied the optimization procedure in the fabrication of high-precision photolithography masks. Chrome photolithography masks, 15 mm in diameter with a write resolution of 200 nm, were routinely produced during overnight exposures (less than 9 h). The write time estimated by the instrument software for most commonly used settings was close to 14 days. A comparison with conventional chrome masks fabricated using a high-resolution (128 000 dpi) photolithography mask printer showed that our pattern definition is significantly better.