Projects

When manufacturing microstructures using direct laser exposure, it is essential for reproducible, high-resolution exposure to be able to control the focal position of the laser beam relative to the substrate surface. Optical single-point sensors based on astigmatism, confocal or oblique illumination concepts are usually used to determine the substrate position.

Common to all of these principles is the requirement that the substrate surface must have a known angle (usually perpendicular) to the optical axis of the exposure system. If non-planar surfaces such as optical lenses are to be exposed, the tilted substrate surface leads to measurement errors when determining the substrate position.

As part of this project, a detection principle was implemented that allows the determination of the substrate position independent of the surface angle. The optical system developed is based on wavefront measurement methods and was seamlessly integrated into the laser lithography system.

Using a tailor-made detector and a hybrid positioning unit (consisting of a linear axis and a piezo actuator), a focus position control was implemented that is able to follow a monotonous surface profile fully automatically and without knowledge of the topography. The permissible surface angle achieved is in a range of +/- 15°.