Patent ID: 8218138

Claim:
A defect inspection apparatus comprising: an irradiation optical system that focuses a beam flux emitted from a laser light source and formed into a slit-shaped beam by fluxes of light that are substantially parallel in a longitudinal direction, from a direction having a required inclination with respect to a surface of a substrate to be inspected, so as to irradiate the beam flux onto the surface of the substrate to be inspected; a detection optical system that detects light from the substrate that has been irradiated with the slit-shaped beam; and a signal processor that processes a signal output from the detection optical system; wherein the irradiation optical system includes a cylindrical lens for focusing the beam flux that has been emitted from the laser light source onto the substrate to be inspected, as the slit-shaped beam; wherein the cylindrical lens is disposed so as to obtain a distance between an incidence surface or emitting surface thereof and the slit-shaped beam upon the substrate to be inspected to be equal to a focal distance of the cylindrical lens; and wherein the cylindrical lens is set at an inclination angle with respect to an optical axis of the beam flux emitted from the laser light source.