Patent US 5,347,118

A method of aligning a substrate includes the steps of detecting misalignment of the substrate using an image signal from a charge coupled device (CCD) camera which receives light reflected by an alignment mark on the substrate illuminated by pulse light, and moving the substrate in accordance with the detected misalignment. If the amount of light received by the camera during a predetermined time period does not reach a predetermined value, the predetermined time period is increased. If the amount of light exceeds the predetermined value, the amount of light emitted by the source of the pulse light for each pulse is reduced. An aligning apparatus for carrying out the method includes a light source for generating pulse light for illuminating an alignment mark on a substrate, a camera for receiving light reflected by the alignment mark to generate an image signal, a signal processing circuit for detecting misalignment of the substrate based on the image signal, a driver for moving the substrate in accordance with the output from the signal processing circuit, a detector for monitoring the amount of light received by the camera, and a light modulating mechanism for adjusting the amount of light emitted by the light source in accordance with the output from the light amount detector.