To elucidate the linewidth variation caused by postexposure delay (PED) in resist films, the distribution of photogenerated acid, the role of additional base component, and the affect of exposure energy were investigated in tert-butoxycarbonyl protected-type chemically amplified positive deep ultraviolet resist. The resist system included an N-methyl pyrrolidone organic base which was evaluated via KrF excimer laser lithography. Using various line-and-space patterns formed with a KrF scanner, this work also investigated the change of linewidth caused by the delay time between exposure and postexposure bake. Experimental results indicate that the linewidth broadened immediately following exposure and became a constant value rather than continuously expanding for various pattern sizes. Based on the mechanism of neutralizing organic base and photogenerated acid, a model was established to describe the linewidth according to FED time. Moreover, the effect of exposure energy on linewidth variation was investigated to not only assess the influence of exposure energy but also clarify the relationship between linewidth broadening and delay rime. Experimental analysis demonstrates that the exposure latitude and depth of focus can be improved by employing FED.