Photonic applications for 3D sensing, biometric authentication and spectral imaging have emerging rapidly through the use of wafer-level optics fabrication. To date, sensing in consumer electronics has mainly been dominated by MEMS providing high performance in the smallest form factors for many applications. This has been enabled by using the fabrication infrastructure of the semiconductor industry and in particular by implementing wafer bonding technologies. To manufacture these novel optical modules, wafer-level technologies are also required to achieve the smallest form factors and high performance combined with high-volume parallel processing. In particular, lens molding and nanoimprint lithography play an essential role in this new field of sensing applications.
Lens molding allows the replication of a wide range of lens shapes and sizes at the wafer level with a high degree of freedom for various optical designs. The process uses a single lens master template, which is scaled to a wafer scale master by step and repeat imprinting. Then, the wafer scale master is used for the actual lens molding process, where hundreds or thousands of lenses are replicated into a UV-curable resist in a single step. As the resist provides required optical properties and reliability, no further steps are required to define the optical structures. Subsequently, the lenses are precisely stacked by using wafer bonding. To implement more complex structures as diffractive optical elements (DOEs) or nano photonics, an alternative technology based on UV nanoimprint lithography can be used, which offers high pattern fidelity using a field-proven and robust process.
Equipment and processes are closely related to manufacture novel optical devices on a wafer level. Thus, recent developments in wafer-level optics manufacturing using lens molding and nanoimprint lithography in volume manufacturing are reviewed and described in more detail.