System for detecting a latent image using an alignment apparatus

In an apparatus for forming an image, by means of projection radiation of a feature on a mask in a photosensitive layer on a substrate, is comprising a mask holder, a substrate holder in spaced relationship to said mask holder, projection lens means mounted between the mask holder and the substrate holder, and latent image detection means mounted in spaced relationship to said substrate holder for detecting an undeveloped image, formed by means of the projection light, of the mask feature in the photosensitive layer, wherein the latent-image detection device comprises alignment means including a source of non-actinic projection radiation for irradiating said substrate photosensitive layer, intended for aligning, via the projection lens system, the mask pattern with respect to the substrate and is designed for detecting the measure of coincidence of a mask alignment feature and a substrate alignment feature, which alignment device is nonactinic radiation-sensitive detection means and means for detecting the nonactinic radiation reflected from said substrate photosensitive layer and producing electrical signal indicative of the amplitude of the radiation incident on the nonactinic radiation-sensitive detection means reflected from an area of the photosensitive layer onto which there is projected an image of the mask feature,

• the improvement wherein said mask feature is a first feature having a spatial frequency which is approximately equal to the useful resolving power of the projection lens means and considerably greater than the resolving power of the alignment means, and said mask has a second feature disposed between said substrate holder and said detection means for superimposition upon an aerial image of said first feature reflected from said photoresistive layer.