No Defect Goes Undetected – Inspection of Micro-optic Components


Lithography, fusion or replication

The technology for producing micro-optic components depends on the specific application, the required surface quality, desired reliability and final cost of these components. The three most common production techniques are lithography, fusion and replication.The lithographic method was originally developed in microelectronics for the production of structured coatings or surface profiles. With this method, a laser or electron beam is used to write 3D patterns in a photoresistant film which, after development, are applied to the substrate by means of a reactive ion process. This lithographic technique is suitable for wave guide structures, micro-optic free-space elements and diffractive optic elements.

The fusion technique is used to produce refractive components. It delivers high-quality results and is appealingly simple. Small cylinders are made in a traditional lithographic method. Due to the surface tension caused by the melting process, small plano-convex lenses of extremely high quality are produced. Lithography and fusion are extremely precise methods. In view of the rising demand for microlenses however, some manufacturers use the replication technique to obtain higher quantities. As a rule, molding processes are applied to produce replicas in silicon oxide or epoxy resin on hard glass with a high-quality master.

Fig. 2 (right): Linear lens array. Copy of an array of cylindrical lenses on epoxide material (ion etch master). The data were recorded with a 50x, 0.8 NA objective using the topography stitching method. The total field of view of the sample measures 0.4 × 3.18 mm and the surface slope is more than 30° in places. Topography stitching is therefore necessary to depict the entire lens group. The spacing between the lenses is 1 mm, the total height is over 90 µm.



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