Abstract: A projection apparatus is described having a reference plate with a set of grating marks in X and Y directions for aligning with an exposure mask having similar marks, and having four detectors for each mark, and having a lens system for projecting only the relevant mark on the relevant detector. A method of projecting is also described in which the detection signals are simultaneously processed with other signals to result in a control signal to adjust image quality.

Abstract: An optical imaging system is described which is provided with an opto-electronic detection system for determining a deviation between the image plane of the imaging system and a second plane on which an image is to be formed by the imaging system. After a first reflection on the second plane an auxiliary beam which is obliquely incident on said plane is reflected along itself and mirror-inverted, is subsequently reflected a second time on the second plane, and is finally incident on two detectors. The difference signal of the detectors, which is a measure of the deviation, is unaffected by tilting of the second plane and by local variations in reflectivity of in said plane.

Abstract: An apparatus is described for writing patterns in a layer on a substrate by using a beam of electrically-charged particles. The apparatus is provided with an optical height-measuring system for determining a deviation between the desired and the actual position of the surface to be inscribed relative to the charged particle lens system. The deviation can be measured accurately and continuously without the use of additional markers on the substrate.