Optical module for optical height measurement

An optical module for optical height measurement that optically measures only a surface height of a layer-structured specimen including a transparent or semi-transparent thin film, comprising:

• a laser light source configured to irradiate the layer-structured specimen with a light beam;
• an irradiation optical system that includes an objective lens, the objective lens being located to be approximately perpendicular to the layer-structured specimen;
• a detection optical system configured to guide a light having passed through an aperture-restrictor-for-return to a detector, a reflected light reflected by the layer-structured specimen passing through the objective lens and the aperture-restrictor-for-return, the aperture-restrictor-for-return being located immediately after the objective lens, the aperture-restrictor-for-return being configured to restrict the reflected light and cause only a light in a high NA region to pass through;
• and
• the detector configured to convert an entered light into a light detection signal,
• wherein the detector includes a multi-divided detector array, and
• a surface reflected light from the layer-structured specimen and a deep surface reflected light from a deep layer other than the surface reflected light are separated and detected on the detector.