In critical-dimension (CD) measurements of resist patterns, CD deviation dependent on measurement time and adjacent pattern effect are major problems created by using an electron beam. We studied the mechanism of these effects. The dependence of CD deviation on measurement time may be caused as a result of compound effects of resist thickening due to surface contamination and resist thinning due to electron-beam induced resist contraction. The adjacent pattern effect is mainly produced by surface charging. The surface charge may distort the electron-beam trajectory.