The Step & Repeat process enables the parallel and cost-effective replication of micro-optical components for the production of large quantities.
Fraunhofer IOF offers customers from industry and research the direct replication of micro-optics, customized manufacturing of master wafers as well as consulting and process development e.g. for integration into own production lines.
Micro-optical components, e.g. micro-aspheres, micro-optical freeform surfaces or diffractive optical elements, are key enabling components in miniaturized imaging and sensing devices.
Wafer level replication methods can be used in order to ensure a cost-effective manufacturing of these elements in batch processes. Therefore, a master-wafer is required. Typical methods for the generation of master-wafers, e.g. grayscale photolithography, electron-beam lithography, ultraprecision-micromachining or two-photon-lithography often permit the manufacturing of small-sized single masters only.
The step-and-repeat replication process allows the transition from the single master to a wafer-master. Alternatively, micro-optical elements can be replicated directly on glass substrates with lithographically patterned diaphragms in order to produce prototypes or a small batch series.
The Fraunhofer IOF has extensive experience in the field of step and repeat replication processes for the production of microoptical components. The manufactured elements are used for example in artificial compound eye camera systems or miniaturized 3D cameras. The manufacturing process is based on a modified nanoimprint stepper, permitting the replication of microoptical elements on substrates up to 8 inch. For the characterization of produced structures a versatile arsenal of equipment such as an optical surface profilometer, a laser scanning microscope, and a tactile surface profilometer is used.
In the following video you can see an illustration of the process:
Sequence of the Step & Repeat process
The starting point of the process chain is a master structure of the micro-optical component which is to be replicated in the form of a small single master. This can be manufactured by us or our partners on the basis of the optical design or can be provided by our customers.
Using a casting process, a molding tool is first formed from this single master, which is then used for shaping in the subsequent replication process. For this purpose, a polymer drop is dispensed onto the substrate and then the molding tool is brought into contact with it. After UV exposure to cure the polymer, the molding tool and the replicated structure are separated again. This process sequence is repeated until the entire wafer is patterned with the element to be replicated.
The manufactured wafer can be used as a master wafer in further replication steps, enabling parallel and low-cost replication of the devices in large quantities. Alternatively, Step & Repeat replication can be performed on both sides of lithographically patterned aperture wafers. This approach allows the direct production of micro-objectives for prototypes or small series without an additional replication step. The micro-optical components produced with both process variants are then separated by a dicing process before they are integrated into miniaturized sensor systems.
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Fraunhofer Institute for Applied Optics and Precision Engineering IOF