Pattern forming apparatus

A pattern forming apparatus for projecting a pattern formed on a reticle onto a photoresist layer formed on a substrate, comprising illuminating means for illuminating the pattern to project an optical pattern image, and image forming optic means having a numerical aperture, the image forming optic means including lens means having at least one reduction lens for projecting the optical pattern image at a predetermined reduction ratio onto the photoresist layer formed on the substrate for exposing the photoresist layer, liquid sustaining means for filling a gap between the at least one reduction leans and the photoresist layer with an optically transparent liquid having a refractive index of more than 1 (one) for enabling the optical pattern image to be projected onto the photoresist layer with improved resolution of the image forming optic means of the pattern forming apparatus by varying the numerical aperture of the image forming optic means with respect to an image forming optic means in which the gap is not filled with a liquid, and pattern detector means for detecting the alignment of patterns between the reticle and the substrate by light reflected from the substrate and incident upon the pattern detector means along a path through the photoresist layer, the liquid and the lens means, the refractive index of the liquid being substantially equal to a refractive index of a material of the photoresist layer so that the light incident upon the photodetector means is not influenced by unevenness of the photoresist layer and substantially no error occurs in the pattern detection alignment.