| 摘要 |
PURPOSE:To detect the position of a pattern with high S/N by removing noises so effectively as not to cause distortion to a signal waveform. CONSTITUTION:A photoelectric signal from a photodetecting element 22 is input to a high-speed A/D converter 24A within a waveform detecting part 24, and converted to a digital value in correspondence to the position of coordinates of a stage ST in the A/D converter 24A. The digitally sampled waveform data is loaded in an address in a RAM 24B corresponding to the position of coordinates of the stage ST. Accordingly, a measuring pulse from an interferometer 12 is input to the waveform detecting part 24 through a stage controller 25 for obtaining timing of the digital sampling of the waveform etc. A computer 26 performs a pretreatment (averaging, synchronous addition (synthesizing), smoothing) for the waveform signal stored in the RAM 24B to remove noises, and obtains the center of the signal waveform, which is stored as the position of the pattern into the RAM 24B. |
