BEAM SHAPE MEASURING APPARATUS

PURPOSE:To make it possible to obtain a differentiated signal excellent in SN ratio and having a reduced waveform distortion, by a method wherein a detection signal is converted into a digital data and arithmetially processed with a specific constant thereby simultaneously carrying out differentiation and smoothing processes. CONSTITUTION:When an electron beam 1 is arranged to scan across a reference mark 2 in the direction of the arrow, a detection signal waveform 17 is obtained by a sensor 3. The waveform is amplified as at 6 and then sampled by a sampling circuit 7 at predetermined intervals. The sampled values are converted into digital data in an A/D converter 8 and successively stored in a memory 9. When the number of data exceeds N, the contents of the memory 9 are stored in a register 10. A multiplier 12 multiplies the contents of the register 10 at addresses (n) and the contents of the memory 11 at address (n) together, respectively. The multiplication results are added together by an adder 13. The addition result is divided in a divider 14 by a normalizing constant stored in a memory 15. Then, the contents of the register 10 are shifted downward, one by one, and operations similar to the above are carried out.