Full Wafer Double Sided Monolithic Lens
Fabrication Using UV-Imprint Lithography
Vijay.R. Kolli1, F. Pawlitzek, S. Drieschner, M. Zoberbier, E. Storace,
M. Hennemeyer

SUSS MicroTec Lithography GmbH
Schleißheimer Str. 90, 85748 Garching, Germany
E-mail: vijayramya.kolli@suss.com

Monolithic Lens Array (MLA) fabrication has emerged over the past decade as a constantly
growing market, as it eliminates the requirement of using glass substrates and thereby
increasing the scalability and material compatibility of optical devices. In this paper, we discuss
the capability of imprint lithography to manufacture double-sided monolithic wafer-leveloptics, which enables low cost of ownership and high throughput. MLAs are nowadays a key
component in next generation flashlights for mobile phones, high pixel wafer-level-cameras
and integration with LED arrays. However, the main challenges in manufacturing MLAs are:(1) obtaining arrays with low Total Thickness Variation (TTV) over large areas, (2) lowaberration and distortion of the lens geometry, (3) critical ultra-precision lens-to-lensalignment, and (4) interconnected MLAs. Traditionally, injection moulding and diamondmicro-milling techniques have been used in the production of MLAs [1, 2]. Whereas injection
moulding is a rather low cost manufacturing method when addressing low and medium volume
productions, it poses major disadvantages in term of production scalability. The moulds allow
for lens arrays of only few centimetres square at a time and, moreover, the thermal cycling of
the materials drastically limits the overall throughput. The different approach of micro-millingalso has a strong limitation in terms of scalability: these high-quality lens arrays would simply
be too costly for medium to large volume productions. Finally, both these traditional methods
are limited in fabricating interconnected and double sided MLAs in a single step, i.e. wherehigh alignment accuracy is required.
As it will be demonstrated in the presentation, the highly sophisticated SUSS UV- imprint
lithography equipment addresses and solves the challenges of high-volume MLAs
manufacturing: it allows for a very low TTV, for the accurate definition of the final thicknessof the monolithic layer and for precisely aligned and interconnected MLAs. The SUSS imprint
technique is based the use of UV-curable optical polymer material in combination with two
hybrid stamps. The stamps are made of a polymer layer on a glass carrier that providing thenecessary in-plane stiffness of the system leads to imprints without distortions in the lensgeometries. In the initial steps of the imprint procedure, the two stamps are set parallel torespect of each other and the UV-curable polymer material is dispensed on one of the stamps
and afterwards spread between the two stamps. The final thickness of the polymer’s monolithic
layer is obtained via the SUSS Active Wedge Error Compensation technology, that allows aconstant real-time control over the relative position of the two stamps.. Furthermore, theimprint process takes full advantage of the SUSS mask aligner hardware on which it is based,by leading to high-quality alignment results. In the final step, the imprint material is cured
using a high uniformity UV-LED exposure unit. Hence, by using SUSS imprint technology,
fabrication of full wafer double sided MLAs are achievable in a single and thereby enablinglow cost of ownership and high throughput. Fig 1. Shows a schematic of an imprint process.
Fig 2. Shows a picture of a full wafer-level MLA sheet as obtained with the SUSS imprint
lithography equipment.

Figure 1. (a)- (d): Process flow-monolithic lens imprinting

Figure 2. Picture of monolithic lens wafer

Reference:[1] Gih-Keong Lau and Milan Shrestha; “Ink-Jet Printing of Micro-Electro-Mechanical
Systems (MEMS)” Micromachines, doi: 10.3390/mi8060194 (2017).
[2] Scheiding, Sebastian, Yi, Allen, Loose, Roman, Gebhardt A, Li, Lei , Risse, Stefan,Eberhardt, Ramona and Tünnermann, Andreas; “Diamond milling or turning for the fabricationof micro lens arrays: comparing different diamond machining technologies” Proceedings of theSPIE, Volume 7927, id. 79270N (2011).