Abstract: Photolithographic processes require alignment of substrate to mask prior to exposure. Alignment accuracy becomes critical as feature size diminishes. For alignment tolerances above 1 &mgr;m, off-axis camera-based techniques are acceptable, but require frequent calibration. Through the lens (TTL) on-axis alignment is much preferred, not requiring frequent calibrations and having superior alignment accuracies, even though usually more complicated and expensive. This invention provides a simple, easy to incorporate TTL, on-axis alignment technique for alignment accuracies of 1 &mgr;m, such as scan-and-repeat patterning systems that employ a unitary mask-substrate stage and a folded projection imaging system. There is a master alignment mark adjacent to the mask, which is imaged onto a phosphor screen with the same radiation as is to be used for patterning.

Abstract: Photolithographic processes require alignment of substrate to mask prior to exposure. Alignment accuracy becomes critical as feature size diminishes. For alignment tolerances above 1&mgr;m, off-axis camera-based techniques are acceptable, but require frequent calibration. Through the lens (TTL) on-axis alignment is much preferred, not requiring frequent calibrations and having superior alignment accuracies, even though usually more complicated and expensive. This invention provides a simple, easy to incorporate TTL, on-axis alignment technique for alignment accuracies of 1&mgr;m, such as scan-and-repeat patterning systems that employ a unitary mask-substrate stage and a folded projection imaging system. There is a master alignment mark adjacent to the mask, which is imaged onto a phosphor screen with the same radiation as is to be used for patterning.