Alignment mark detecting optical system

Claim 1

A projection exposure apparatus, comprising: a projection optical system through which an image of a pattern of a first article is projected on a second article; a polarization beam splitter disposed in an optical path of the projection optical system; an auxiliary optical system disposed outside the optical path, the auxiliary optical system including a mirror and a λ/4 plate disposed between the mirror and the polarization beam splitter; means for illuminating the first and second articles, wherein said illuminating means directs a beam to said beam splitter, which splits the beam into two beams, one of which is directed to one of the first and second articles and the other of which is directed to the other of the articles with said auxiliary optical system and said beam splitter, wherein said mirror of said auxiliary optical system receives the other beam from said beam splitter through said λ/4 plate and reflects said other beam to be incident on said beam splitter through said λ/4 plate, by which the other beam is directed to the other article through said beam splitter, and wherein at least one of the beams is incident on the associated one of the articles through at least a part of said projection optical system, wherein said illuminating means includes a laser source for producing the beam comprising a laser beam and a rotational mirror for receiving and reflecting the laser beam which is produced by said laser source, and wherein the first and second articles are scanned with the laser beam by rotation of said rotational mirror; and means for detecting a positional relation between the first and second articles using the beam, wherein said detecting means receives through said polarization beam splitter said one of the beams reflected by said one of the articles and receives through said polarization beam splitter and through said auxiliary optical system the beam reflected by the other one of the articles.