Applied Surface Science 258 (2012) 4191–4194 Contents lists available at SciVerse ScienceDirect Applied Surface Science j our nal ho me p age: www.elsevier.com/loc ate/apsusc Fabrication of metallic stamps for injection moulding applications by combining proton beam writing and UV lithography P. Malar a , Zhao Jianhong b , J.A. van Kan a,∗ a Centre for Ion Beam Applications, Department of Physics, National University of Singapore, Singapore 117542, Singapore b Singapore Institute of Manufacturing Technology, Singapore 638075, Singapore a r t i c l e i n f o Article history: Available online 31 October 2011 Keywords: Proton beam writing UV lithography Ni mould fabrication a b s t r a c t In this paper, we present the results of resist evaluation for the fabrication of metallic stamps used in the injection moulding of micro/nano fluidic devices. The resist was evaluated in terms of its suitability to combine direct proton beam writing (PBW) and UV lithography techniques for incorporating few tens of micron and micron- to millimeter sized features respectively. In a first step PBW is used to generate the fine features with smooth sidewall profiles in AR-P 3250, here the resist shows negative behavior. Following PBW, masked i-line UV lithography was used to create larger features to complete the device design, here the AR-P 3250 acts as a positive resist. After developing, the resist was used to generate the final mould through Ni electroplating, resulting in a high quality metallic stamp. © 2011 Elsevier B.V. All rights reserved. 1. Introduction Microfluidic systems have found exceptional success over a wide range of scientific fields including chemistry and biol- ogy [1–3]. The main advantages of microfluidic systems include high performance, versatility and fast processing. Conventionally microfluidic systems are fabricated on glass or Si substrates. How- ever, the systems made of glass or Si are relatively expensive because of contamination that renders the devices not suitable for multiple usages. As a result, polymers gained attention as an attrac- tive alternative to glass and Si as a substrate material due to their biocompatibility, disposability and low cost [4–6]. Moreover, repli- cation techniques such as soft lithography, contact imprinting and injection moulding enable low cost mass production of polymeric microfluidic systems. Apart from these advantages, polymers are suitable for rapid prototyping as well. For prototyping, direct write techniques have the advantage over the mass production techniques because masks or masters are not required [5]. Among the several next generation lithography methods (electron-beam writing, LIGA and UV lithog- raphy), proton beam writing (PBW), a novel technique developed at Centre for Ion Beam Applications (CIBA) [7], has attracted consid- erable attention. Compared to E-beam writing, PBW shows greatly reduced proximity effects [8], which allow the fabrication of high- density high aspect-ratio nano-structures, and secondly PBW has typically a 100 fold higher sensitivity compared with E-beam writ- ing in the same resist material [9]. CIBA holds the world record for ∗ Corresponding author. focusing protons down to 35 × 75 nm 2 [10] and have produced 3D high aspect ratio walls down to 22 nm in hydrogen silsesquioxane HSQ [11]. In this paper we aim to study the suitability of the polymer resist AR-P 3250 as master mould for making Ni stamp for replication applications. This work is in continuation with the previous one [12] to look for possible resists in which PBW and UV lithogra- phy can be combined. The reason for combining two lithography techniques arise from the fact that the final chip design consists of few tens of micron sized pillars (about 60 m) incorporated into the millimeter sized long channels (20 mm) with a final height of tens of microns (10–40 m). The strategy is to write the micro pil- lars having smooth and straight sidewalls by PBW and link the fine structures to the large area by UV lithography. In this way the short patterning time of UV lithography and the reliability of PBW for fine features can be combined to produce the master mould for electroplating Ni stamps. It has been a well-established fact that the polymer PMMA [11,13] a commonly used positive tone resist, can be easily used for this kind applications. PBW and electroplat- ing of PMMA resist can give smooth Ni moulds with sub-10 nm RMS side wall roughness and 20 nm details. Further, PMMA resist can be removed easily without compromising the fine details in the Ni stamp. The usage of PMMA resist for the present study is constrained by the fact that the maximum depth at which PMMA can be structured is limited to about 10 m if a 248 nm deep UV lithography is used. Therefore, to complete the chip design with heights up to 30 m or more, suitable resists have to be identified and thoroughly characterized for proton dosage, UV exposure con- ditions, developing, compatibility for electroplating metallic stamp and finally removal of the resist. To the best of our knowledge, the 0169-4332/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.apsusc.2011.10.014