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Micro lenses
Form precision of micro lenses
Micro lenses are used for the collimation, focusing or imaging of light. Micro lens technology holds great potential for the miniaturization of components, reduction of production costs, and increase in performance of products. Micro optics allows to mass-produce high-quality miniaturized optical systems that are applied in a wide range of innovations. The important role of micro optics is based on different motivations: miniaturization, high functionality and packaging aspects.
The performance of micro lenses depends crucially on their actual optical properties which are defined by the structure and form of the lenses. For development processes and the detection of defects in production the right measurement technology is required.
Applied measurement system:
Real 3D data, non-destructive and precise measurements
Neither the test equipment from semiconductor industry nor the test equipment from classical optics manufacturing completely addresses the metrology requirements of wafer-level micro optics. Interferometers designed for large classical lenses cannot resolve the profile of tiny micro lenses. Mechanical stylus profilometers do not provide 3D profile information about a structure and quite often the measurement resolution of tools like a stylus profiler is limited due to the small object size. Furthermore, the sample is likely to be damaged during the measurement process.
Using the confocal 3D measurement system µsurf custom of NanoFocus micro lens arrays can be analyzed fast, precisely and non-destructively at different points during production.
The high reproducibility and repeatability of the NanoFocus measurement technology guarantees stable and reliable measurement data. Additionally, due to its non-contact measurements µsurf custom does not require previous sample preparation. The major advantage of the confocal µsurf technology is that it provides real 3D data, and provides the opportunity for automated full-wafer mapping and automatable measurements.
Measurement and analysis:
Wafermapping, automated measurement and evaluation
Small-size micro lenses are in general difficult to fabricate and not easy to characterize. With diameters below 100 micrometers, measuring the surface structure and form of the lenses is a challenge. The shape of the lenses, defined by the radius of curvature (ROC) and the conic constant of the surface, a precise positioning of the lenses on the micro lens array as well as the form precision of the wafer are aspects that need to be determined.
The mapping ability using NanoFocus technology makes more dense measurement grids available. This results in the identification and detection of defected micro lenses out of thousands of lenses. With the aim of integrating the measurement technology into the production process and of achieving fast automated measurements, the autofocus function and the stitching function play an important role. Employing the autofocus function, µsurf custom does not require any specific alignment or focusing adjustment for each lens. The measurement head is automatically moved to the right measurement position without manual interference.
The wafer mapping is also supported by the stitching function of the NanoFocus software, meaning the combination of different measurement fields into a single dataset. The software also enables wafermap imports and using reference data from a data bank.
