We investigated the line edge roughness (LER) of chemically amplified resist (CAR) in the high-sensitivity resist process in low-energy electron beam lithography (LEEBL). We have confirmed that a sub-100 nm pattern having a small line edge roughness could be obtained at the exposure dose below sub-1 µC/cm2 for LEEBL. In order to explain the experimental results, we have proposed a resist exposure model, considering the generation yield and diffusion of secondary electrons (SEs). Based on the proposed model, we analyzed the LER for LEEBL using a simulation. When the beam blur and the acceptable LER were 30 nm (σ) and 2 nm (σ), the acceptable exposure doses for 2–5 keV and 50 keV were 0.3 µC/cm2 and 2.5 µC/cm2, respectively. This means that a high-sensitivity CAR process at the exposure dose below 0.5 µC/cm2 can be achieved in LEEBL.