A Study of Loading Effect during Electron-Beam Exposure and Etching Process in Photomask Fabrication

Abstract

As the requirements of critical dimension (CD) uniformity on photomasks continue to tighten with advanced logic and memory devices, the dry etching process should be adopted to meet the needs of the optical proximity effect correction (OPC) and reduced bias process [W. T. Chen and M. Kamma: Proc. SPIE 3412 (1998) 149.]. There are severe CD variations in the dry etching process due to chrome (Cr) pattern density with various clear and dark fields. Through experiments, on the CD variation was investigated in the wet etching process, as well as in the dry etching process. This work focused on the tracing-determining the actual cause of the loading effect. It was revealed that what accounts for a major portion of the loading effect is not the Cr dry etching process, but the rescattering of electrons of the electron-beam exposure system. Rescattered electrons in this article refers to electrons that are reflected between the specimen and the lower parts of the electron-beam column and expose the unexposed area. In this paper, the existence of rescattered electrons was experimentally confirmed with a 10 kV acceleration-voltage system and the CD variation by reflected electrons was also investigated.