Microlens array fabrication by enhanced thermal reflow process: Towards efficient collection of fluorescence light from microarrays

• Published in: Microelectronic engineering 2009-11, Vol.86 (11), p.2255-2261
• Main Authors: Roy, E., Voisin, B., Gravel, J.-F., Peytavi, R., Boudreau, D., Veres, T.
• Format: Article
• Language: English
• Subjects: Applied sciences; Design. Technologies. Operation analysis. Testing; Electronics; Exact sciences and technology; Fundamental areas of phenomenology (including applications); Integrated circuits; Lenses, prisms, and mirrors; Micro optics integration; Microarray fluorescent detection; Microelectronic fabrication (materials and surfaces technology); Microlens; Optical elements, devices, and systems; Optics; Physics; Reflow method; Semiconductor electronics. Microelectronics. Optoelectronics. Solid state devices
• ISSN: 0167-9317; 1873-5568
• DOI: 10.1016/j.mee.2009.04.001

This paper describes two enhanced resist reflow methods for the fabrication of microlens arrays and demonstrates their use for integrated biomolecular fluorescence detection on printed microarrays. A PDMS (polydimethylsiloxane) microlens array was fabricated by a double soft lithography approach using a photoresist microlens array as master mold. Additionally, by using both a careful control of the surface wettability and thermal treatments, we demonstrate the possibility to extend the resist reflow process in order to tune the diameters of microlens array over a large range by using a unique photomask pattern. We introduce an enhanced reflow on hydrophobic surfaces obtained by fluorosilane treatment and identify a threshold shrinkage temperature (T shrinkage) of 140 °C, above which the diameter of microlenses can be then reduced down to 40% compared with the initial pattern on the photomask. Furthermore, on hydrophilic substrates, achieved by an accurate incomplete development of the photoresist, we demonstrate a nearly perfect linear dependency (1.4 μm/°C) of microlens diameter spreading up to 70% the initial diameter inside a temperature reflow window of 110–140 °C. For both approaches, above a freezing temperature (T freezing) of 170 °C, the microlens profile characteristics are temperature independent. By using high numerical aperture microlens array, we provide a proof of concept for the integration and enhanced light collection of the fluorescent signals collected form a microarray of fluorescent spots thus showing the potential of the concept for biophotonic integration.