Improved alignment accuracy using lens-distortion correction for electron-beam lithography in mix-and-match with an optical stepper

The mix-and-match use of an electron-beam (EB) lithography system and an optical stepper is an effective approach to achieving higher resolution while maintaining high throughput in the fabrication of Gbit DRAMs and advanced ASIC devices. In this approach, the highly accurate alignment of patterns exposed by different lithography methods is essential. In this paper, the lens distortion of the optical stepper is examined and distorted patterns are aligned with an EB lithography system. The overlay accuracy in this mix-and-match application was 51.4 nm (3 sigma) which corresponds to Gbit DRAMs fabrication.