ArF resist-pattern shrinkage in critical-dimension scanning electron microscopy (CD-SEM) measurement is investigated, and its mechanism is discussed. In CD-SEM irradiation damage in the resist detected by Fourier transform infrared (FTIR) spectroscopy, we propose that C=O units of pendant polymer chains decompose COOH units at the first stage and that the COOH units finally decompose CO2 outgas at the second stage. We propose the mechanism of the ArF resist-pattern shrinkage in the CD-SEM measurement from experimental and simulation results of the FTIR spectroscopy and Monte Carlo simulation of electron scattering trajectories into the resist. The first resist polymer free volume shrinkage is caused by hydrogen bonds between the COOH units, as well as decomposition of dissolution inhibitor groups. The second resist polymer free volume shrinkage is caused by the CO2 outgas within 4-14 nm in depth from the resist surface depending on the CD-SEM acceleration voltages of 400 and 800 V, respectively, with probe current of 8 pA. Based on the mechanism, we also propose an improvement in the ArF resist material design to reduce the ArF resist-pattern shrinkage in the CD-SEM measurement. (C) 2004 American Vacuum Society.