Thermal nanoimprint resist for the fabrication of high-aspect-ratio patterns M. Messerschmidt a,⇑ , A. Schleunitz a,b , C. Spreu b , T. Werner c , M. Vogler a , F. Reuther a , A. Bertz c , H. Schift b , G. Grützner a a micro resist technology GmbH, 12555 Berlin, Köpenicker Straße 325, Germany b Paul Scherrer Institute, Laboratory for Micro- and Nanotechnology, 5232 Villigen, Switzerland c Fraunhofer-Institut für Elektronische Nanosysteme ENAS, 09126 Chemnitz, Technologie-Campus 3, Germany article info Article history: Available online 27 July 2012 Keywords: Nanoimprint lithography Si-containing resist Oxygen RIE High aspect ratio abstract We report a newly developed thermal nanoimprint (T-NIL) resist specifically engineered for the imple- mentation in a bilayer system rendering the fabrication of high-aspect-ratio patterns. The synthesis of the T-NIL resist was accomplished by applying a free radical copolymerization of adequate comonomers. Due to the modular architecture of the terpolymer, the rather different material properties are directly adjusted by varying the amount of the comonomers and also by tuning the polymerization conditions like temperature and the amount of initiator. Following this synthetic strategy, the Si content for a sufficient oxygen plasma resistance as well as an excellent flowability behavior for a significant reduction of the overall processing cycle time could be easily achieved. Moreover, the already good mould release prop- erties of the pure T-NIL resist can be further improved by the addition of a small amount of a fluorinated additive leading to a very low defect rate of the imprinted structures. Ó 2012 Elsevier B.V. All rights reserved. 1. Introduction Nanoimprint lithography (NIL) has emerged as a powerful tech- nique in the fabrication of micro- and nanostructures [1]. Up to now, most of the commonly used NIL resists work satisfactorily for the imprinting of patterns with moderate aspect ratios of max- imum three. But for specific applications, e.g. high-brightness LEDs, features with higher aspect ratios are highly advantageous or even necessary. Generally, the manufacturing of such high-aspect-ratio patterns demands specially designed resists which are applicable in bilayer systems [2]. In such systems, firstly a thick organic under layer or transfer-layer (ca. 1 lm) is spin-coated onto the substrate followed by the preparation of a thinner layer consisting of a Si- containing resist. As the Si-containing resist features a significantly higher resistance toward oxygen plasma compared to the purely organic material of the transfer layer, the relief of the imprinted sil- icon-containing layer can be strongly magnified by applying an oxygen reactive ion etching (RIE) step. The obtained high-aspect- ratio patterns can then further transferred into the underlying sub- strate employing additional etching procedures [2]. Such bilayer systems are already established for UV-based NIL [3], but only few literature has been published for thermal nanoimprint lithog- raphy (T-NIL) [4]. An industrial applicability of such a T-NIL resist requires additionally short processing cycles and a high patterning fidelity. Accordingly, the T-NIL resist needs an excellent inherent flowability to ensure a fast filling of the structures, whereas a low polarity of the material is favorable to minimize surface ener- gies and thus defects during the demoulding step. In this contribu- tion, we present the synthetic approach and the characterization of a new T-NIL resist as well as the investigated film forming proper- ties, the imprinting behavior and the plasma etch resistance toward RIE with oxygen and a mixture of fluorinated gases. 2. Experimental 2.1. Materials All employed chemicals were of analytical grade and used as received except for the initiator 2,2 0 -azobis(isobutyronitrile) (AIBN) which was purified by recrystallization from ethanol prior to use. 2.2. Polymer synthesis and characterization The preparation of the terpolymer SiPol was performed analo- gously as described elsewhere [5]. The glass transition temperature (T g ) of SiPol was investigated by a DSC822e from Mettler Toledo employing the Star e Software (Version 9.01). The measurement was run under a nitrogen atmo- sphere with a flow rate of 10 K/min. For determination of the T g only the second heating cycle was applied using the half-step method. The molecular weight and the polydispersity index (PDI) of SiPol was determined by GPC analysis using the integrated 0167-9317/$ - see front matter Ó 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.mee.2012.07.098 ⇑ Corresponding author. E-mail address: m.messerschmidt@microresist.de (M. Messerschmidt). Microelectronic Engineering 98 (2012) 107–111 Contents lists available at SciVerse ScienceDirect Microelectronic Engineering journal homepage: www.elsevier.com/locate/mee