Process optimization on mask fabrication

Recently, next-generation mask fabrication processes have been actively examined for application with Electron Beam (EB) writing tools and chemically amplified resist. In this study, we used a variable shaped electron beam (VSB) writing system with an accelerating voltage (50 keV) and chemically amplified resist to investigate the dependence of the CD error in a localized area of a 6025 mask on the process factors, with the goal of fabricating more accurate masks with improving sensitivity. Our results indicated that CD error in a localized area didn't depend on the resist thickness. Higher sensitivity and CD uniformity were achieved simultaneously. Moreover, we could isolate the CD error caused by the resist heating effect((1)(2)). Generally, the resist heating effect is more apparent for higher doses than lower doses. However, a higher dose gives rise to a small CD change rate. In this experiment, the effect of the lower CD change rate at a higher dose counterbalances the resist heating effect. By decreasing CD error in a localized area, we obtained a CD uniformity of 14 nm (3 sigma) in a 100 mm(square) area on the mask.