Transient measurement of resist charging during electron beam exposure

Charging of resist films during electron beam exposure has been believed to cause significant (up to 500 nm) pattern displacement. However, our own modeling and direct measurements of pattern, displacement have suggested that the pattern displacement is less than 20 nm under typical mask making conditions (10 keV electrons exposing 400 nm polymeric resist on chromium). Here we describe the use of a custom-designed secondary electron collector to measure surface potential during electron beam exposure. We observed essentially no surface potential change (less than 0.2 V) on poly(methylmethacrylate) (PMMA) resists up to 1 mum thick, when exposed by 10 and 25 keV electrons. However, significant,charging occurs when the beam energy is reduced to 5 or 3 keV and the thickness of the PMMA resist film is comparable 'with, or larger than, the maximum beam penetration depth. (C) 2003 American Vacuum Society.