Advantages of isofocal printing in maskmaking with the ALTA 3500

The ALTA 3500, an advanced scanned-laser mask lithography tool produced by Etec, was introduced to the marketplace in 1997. The system architecture was described and an initial performance evaluation was presented. This system, based on the ALTA 3000 system, uses a new 33.3X, 0.8 NA final reduction lens to reduce the spot size to 0.27 micrometers FWHM, thereby affording improved resolution and pattern acuity on the mask. An anisotropic chrome etch process was developed and introduced along with a TOK iP3600 resist to take advantage of the improved resolution. In this paper we will more extensively describe the performance of the ALTA 3500 scanned laser system and the performance of these new processes. In addition, an investigation of the benefits of operating in the optimal isofocal print region is examined and compared to printing at the nominal process conditions.