OFF-AXIS ILLUMINATION SYSTEM WITH ANNULAR ILLUMINATION APERTURE AND OFF-AXIS ILLUMINATION METHOD TO IMPROVE RESOLUTION AND DOF OF OFF-AXIS ILLUMINATION SYSTEM

摘要

PURPOSE: An off-axis illumination system with an annular illumination aperture is provided to improve resolution and a DOF(depth of focus) of an off-axis illumination system by increasing the intensity of light while using an oblique angle component of the light incident upon the center part of an annular illumination aperture. CONSTITUTION: A substrate is prepared. A plurality of band-type rings are formed in the center of the substrate to transmit only the light of an oblique angle component. An annular part(100a) has a cross section of a roughness type to make the incident light have a phase difference of a predetermined dimension, including an amplitude of lambda/2(n-1)(lambda is a wavelength of light and n is an index of refraction of the substrate) and a pitch(P) of n*lambda/sine*alpha(lambda is a wavelength of light, n is an index of refraction of the substrate, and alpha is a diffraction angle of the light passing through an aperture). The annular part is surrounded by a light transmitting part of a doughnut type that transmits light by a hundred percent. The light transmitting part is surrounded by a light isolating part that isolates light by a hundred percent.