Position detecting method and apparatus using optical system with oblique optical axes

Abstract

A wafer with an exposure surface having a wafer mark formed thereon for scattering incidence light for position alignment and an exposure mask with a mask surface having a mask mark formed thereon for scattering incidence light for position alignment, are disposed facing each other with a predetermined distance being set between the exposure surface and the mask surface. An illumination optical system applies illumination light to the wafer mark and the mask mark along an optical axis which is oblique relative to the exposure surface. An observation optical system focuses scattered light from the wafer mark and mask mark on a light reception surface. The optical axis of the observation optical system is slanted in a direction opposite to the direction of the optical axis of the illumination optical system, relative to a normal direction to the exposure surface of the wafer. Regular reflection light of the illumination light applied to the wafer and the mask is set so as not to become incident upon the light reception surface. A controller controls to detect a positional relation between the wafer and the mask in accordance with images formed by scattered light from the wafer mark and mask mark. A contract between a background and an image formed by scattered light from alignment marks is increased to easily detect the positions of the wafer and mask.