A Rapid Hot-Embossing Prototyping Approach Using SU-8 Molds Coated With Metal and Antistick Coatings

In this paper, we have developed a rapid prototyping process using hybrid master molds for hot-embossing lithography. The hybrid master mold developed here typically consists of a structural layer of SU-8, an overlayer of copper, and a top layer of antistick compound. The structure is first formed by the negative photoresist SU-8 layer with conventional photolithography. On the structural SU-8 layer, a nanoscale copper thin film is deposited to enhance the mechanical strength of the mold and improve heat transfer during the hot-embossing process. Finally, an outermost antistick layer is formed by the reaction of trichloro-(1H,1H,2H,2H-perfluoroctyl)-silane with the oxidized copper surface. These three layers cooperatively yield a hybrid mold which can be fabricated on a silicon wafer or any other suitable substrates for subsequent hot-embossing lithography. Our tests have verified that the molds fabricated with this method do not show any degradation of their structural design features and surface smoothness after 30 hot-embossing cycles. In comparison to other methods of making master molds for hot-embossing lithography such as laser machining and electroplating, the present method is simple and fast, with no reliance on any additional replication steps and fabrication procedures. Hence, the present method can remarkably reduce cost and the processing time in hot embossing, which is particularly attractive in prototyping or small volume production.

I. Introduction

Over the past several decades, microelectromechanical systems (MEMS) technology has developed rapidly. Numerous MEMS applications have been demonstrated in a wide spectrum of business sectors such as manufacturing, electronics, automotive, information technology, and chemical and biomedical industries. Nowadays, most MEMS devices are based on the silicon- and glass-based processes. Although silicon- and glass-based microfabrications are still mainstream MEMS techniques, the construction materials are being extended from silicon and glass to polymers. In comparison to silicon- and glass-based microfabrication, polymer-based microfabrication, e.g., that with polymethylmethacrylate (PMMA), shows advantages in cost (e.g., 0.2–2 for polymer versus 15–20 for silicon and 10–20 for glass), simplicity in microfabrication procedures, and less consumption of harmful chemicals [1]. More importantly, polymer is transparent and flexible, which eliminates the limitations of optical barriers and mechanical stiffness of silicon in many applications. In addition, fabrication of polymer-based devices does not suffer from the geometrical design limitations and does not involve the usage of many harmful chemicals required by the silicon- and glass-based processes. Thus, microfabrication using polymer as construction materials emerges as a very promising technique for making low-cost and flexible microdevices [2]–[4].