Linewidth controllability depending on electron-beam blur and resist thickness

Abstract

When making photomasks for low-k1 lithography, critical dimension (CD) control is more important than pattern resolution on the photomask. Photomasks are written by an electron-beam (EB) writing system or a laser beam writing system. A high-acceleration-voltage EB writing system that has less beam blue is now expected to be a useful tool for fabricating photomasks with accurate CD control. To clarify the latitudes of dose accuracy and beam blue for photomasks of under 0.15 micrometers lithography, we studied Cd controllability for with dose fluctuation respect to beam blue and resist thickness using a 50 kV acceleration voltage EB writing system. The CD variation rate with does fluctuation strongly depends on pattern density, beam blue and resist thickness. The CD variation rate decreases with decreasing beam blur. Thinner resists, especially, are effective for improving CD control when beam blue is small enough. However, when beam blur is 70 nm, the effect of thinner resists in controlling CD is less because the origin of deposited energy blur is primarily the beam blur. To realize CD control within 10 nm, +/- -3 dose accuracy, 40 nm beam blur, and 30 nm resist thickness are necessary.