FOCUSING EQUIPMENT

摘要

PURPOSE:To obtain a focusing equipment capable of effective focusing operation in a short time independently of the change of reflectivity of a wafer, by installing a means for focusing detection which performs phase-locked loop detection of the value of a division means by setting the vibration frequency of a vibration mirror as a reference signal. CONSTITUTION:Light outputted from a light emitting element 4 is reflected by a wafer 1; the reflected light is divided into a reflected light and a transmitted light by a half mirror 9; the reflected light is detected by a photodetector 10 for monitoring; the transmitted light is reflected by a vibration mirror 11; the reflected light is made to pass a slit 13 and detected by a photodetector 14; the output of the photodetector 14 after amplification is set as a dividend input; the output of the photo detector 10 for monitoring after amplification is set as a divisor input; normalization is achieved by the division using a divider 17; the vibration frequency signal of the vibration mirror 11 is set as a reference signal; the normalized value is detected by a phase- locked loop detector 18 and then smoothed by a low pass filter 19; the transferring distance of the wafer 1 as far as a focusing point is obtained by a wafer stage control circuit 20; a wafer stage 2 is moved and subjected to focusing by a wafer stage vibrating circuit 21. Hence S-shape characteristics are not necessary to be again obtained in the case of different reflectivity of a wafer.