COMPOSITE COLOR ILLUMINATION METHOD AND BAND LIGHT ILLUMINATION IN A DOUBLE-FOCUS DETECTOR UTILIZING CHROMATIC ABERRATION

摘要

This invention relates to a lens system having chromatic aberration on the axis of a double-focus detector which utilizes chromatic aberration. One focal plane of the lens system consists of a light image forming plane of a short wavelength corresponding to a first object which is, for example, a mask and the other focal plane consists of the same image forming plane of a wavelength having a predetermined band corresponding to a second object which is, for example, a wafer. The first object is illuminated with the light of a wavelength shorter than 500 nm and the second object is illuminated in a predetermined band of wave-lengths greater than 500 nm.