The line edge roughness (LER) of ultrathin chemically amplified (CA) KrF-resist-based films was investigated using exposure to extreme ultraviolet (EUV) radiation (13.5nm). For the films between 0.09micrometers and 0.13micrometers thick, the LER was about 5~7% for a target critical dimension (CD) of 70nm and exposure to coherent illumination ((sigma) =0.01). The LER was found to be smaller in samples containing a relatively strong-acid photo-acid generator (PAG). The use of baking conditions producing greater acid diffusivity and the use of weak developer were very effective in reducing the LER of thin resist films. Atomic force microscope (AFM) observations showed the surface morphology of samples with a small LER to be very uniform. These results suggest that the use of a high-sensitivity resist and a weak developer may help to create an environment promoting uniform dissolution, thus resulting in a smaller LER in thin resist films.