Performance of micro-optics imprint technology

Micro-optical components have been getting more and more popular in various applications in projection illumination. Often Microlens arrays are used to realize particular projection functions such as slanted angle street projection. Important is the lens surface definition and the quality of the array with respect to lens position and uniformity. To realize demanding applications of such array projectors the optical surface parameters are most important. Such projectors can contain more than 1000 lenses in a single optical component and if variation of the lens shape gets predominant the optical function will fail. In mass fabrication one has therefore to assure that no deviation happens in the whole fabrication process from mastering to imprint. During the fabrication process of the micro-optical components the surface is subject to geometrical deformations caused by shrinkage and aging of the tooling for instance. Changes are small but relevant and need a complex model that allows to include analysis of optical characteristics. At the quality level of today’s wafer level UV replication process, which can also realize freeform structures a simple analysis of radius of curvature and conic constant is not sufficient. It is therefore important to investigate at which point (or replication cycle) a controlled production is still possible. Only until this point than a correction of the surface shape is still possible. We have implemented an approach using Zernike polynomial fitting which allows us to see all changes down to noise of our metrology toolset and applied the model to a production data.