As Systems-In-Package (SiP) are evolving beyond just combining different integrated circuits within a package, the need to integrate non-semiconductor functional features such as optical components is increasing. In recent years a nonconventional lithographic technique has been established as the preferred way of directly forming micro-optical elements on wafer level. Imprint lithography, often also referred to as Nano Imprint Lithography (NIL), is a mechanical way of patterning polymer materials. The technique enables small feature sizes beyond the limitations of optical photo-mask based approaches. In most cases, the structures are directly replicated into a functional material hence avoiding the need for complex and costly post-litho processes such as developing and etching.
This work provides on overview of basic imprint principles on individual substrates and specifically discusses high volume manufacturing applications related to integration of Wafer Level Optics (WLO) which have now become commonplace. The requirements on masters, imprint molds, materials and process equipment are highlighted and the suitability of various imprint technologies is being assessed. Roll-to-roll imprint methods are not covered in this review.
One key driver for high volume manufacturing via Imprint Lithography has been the growing demand for Photonics components in Consumer Electronics, Automotive and Vision Systems. Standard manufacturing methods are usually too expensive. Wafer Level Optics (WLO) Imprint lithography allows to directly integrate refractive microlens arrays, diffractive optical elements (DOE), fiber couplers, gratings, beam-splitters, phase plates (free-form) and other planar or non-planar structured components at high throughput and relatively low cost. Subsequent Wafer Level Packaging further enhances the value of this approach.
In addition to the overview of the current status of wafer level imprint technology, an outlook of future technology developments in the field of imprint lithography for wafer level optics (WLO) applications and processes is given. The presentation also offers a perspective of the critical importance of optical system design, mastering, stamp manufacturing, stamp lifetime, process industrialization, wafer stacking, wafer-level packaging (WLP), metrology and inspection when manufacturing Photonics components as a part of an SiP.