The effect of incident electron-beam conditions, which are acceleration voltage and beam blur of variable-shaped electron-beam direct writing, is investigated using the deposited energy distribution to realize a fine pattern of less-than-or-equal-to 0.25 mum in trilayer resist process. The deposited energy distribution is calculated using a three-dimensional Monte Carlo method. In a trilayer resist system, a thin bottom resist layer can be used, because the contrast value derived from the Monte Carlo calculation is independent of the bottom layer thickness. The beam blur of 0.05 mum does not degrade 0.25 mum line-and-space (L/S) patterns, but seriously degrades 0.1 mum L/S patterns. Higher acceleration voltage is effective for improving the contrast. At lower acceleration voltage, the slope of the deposited energy profile defined at the resist bottom is mainly influenced by electron scattering. On the other hand, at higher acceleration voltage, the slope of deposited energy profile mainly depends on the beam blur. The 0.1 mum L/S patterns are expected to be resolved at 30 kV when there is less than 0.02 mum beam blur with trilayer resist system. The possibility of using a single layer resist process for 0.1 mum L/S pattern will be barely realized at the conditions of 50 kV and 0.02 mum beam blur.