Abstract: An apparatus and a method for detecting an optimal focal plane of a lithographic projection objective lens, the apparatus including: an illumination device, a beam splitting device, a lens array, a mask plate, a reflecting device, a photoelectric detector and a controller. The illumination device generates a collimated beam, which is transmitted through the beam splitting device, focused by the lens array to the mask plate for spatial-filtering, and delivered to the lithographic projection objective lens. The reflecting device reflects a focused beam passing through the lithographic projection objective lens to generate a reflected beam. The photoelectric detector detects an intensity of the reflected beam from the reflecting device after being spatial-filtered via the mask plate and generates a beam intensity signal. The controller controls a movement of a workpiece table and/or collects the beam intensity signal generated by the photoelectric detector.

Abstract: The present disclosure provides an apparatus and a method for detecting an optimal focal plane of a lithographic projection objective lens, the apparatus comprising: an illumination means, a beam splitting means, a lens array, a mask plate, a reflecting device, a photoelectric detector and a controller. The illumination means may generate a collimated beam, which is transmitted through the beam splitting means, focused by the lens array to the mask plate for spatial-filtering, and then delivered to the lithographic projection objective lens. The reflecting device reflects a focused beam passing through the lithographic projection objective lens to generate a reflected beam. The photoelectric detector detects an intensity of the reflected beam from the reflecting device after being spatial-filtered via the mask plate and generates a beam intensity signal.