Interfacial Adhesion Studies for Step and Flash Imprint Lithography Michael W. Lin 1 , Daniel J. Hellebusch 1 , Kai Wu 1 , Eui Kyoon Kim 1 , Kuan Lu 2 , Li Tao 3 , Kenneth M. Liechti 4 , John G. Ekerdt 1 , Paul S. Ho 2 , Walter Hu 3 , C. Grant Willson 1 1 Dept of Chemical Engineering, The University of Texas at Austin, Austin, TX 78712 2 Dept of Mechanical Engineering, The University of Texas at Austin, Austin, TX 78712 3 Dept of Electrical Engineering, The University of Texas at Dallas, Richardson, TX 75080 4 Dept of Aerospace Engineering and Engineering Mechanics, The University of Texas at Austin, Austin, TX 78712 ABSTRACT The step and flash imprint lithography (SFIL) process requires the clean separation of a quartz template from a polymer imprint, and the force required to create this separation must be minimized to prevent the generation of defects. According to fracture mechanics principles, decreasing both the imprint polymer modulus and the interfacial fracture energy are beneficial for reducing the separation force. Adjusting the crosslinker concentration in the imprint formulation decreases the modulus but does not significantly impact the facture energy. On the other hand, fluorinated surfactant additives to the imprint fluid lower the modulus of the imprint polymer and decrease the fracture energy. The fracture energy is further decreased by using a nonreactive, liquid surfactant versus a surfactant that reacts with the polymer matrix. Angle-resolved X-ray photoelectron spectroscopy (XPS) results indicate that surfactant migration is more effective with a fluorinated surface treatment compared to an untreated quartz surface. This result shows that the use of fluorinated surfactants must be accompanied by a surface treatment that produces a similar energy or polarity to induce migration and lower the adhesive strength. Keywords: adhesion, SFIL, fracture, surfactant, imprint lithography 1. INTRODUCTION The step and flash imprint lithography (SFIL) process was developed in 1999 at The University of Texas at Austin as a high resolution, cost-effective alternative to photolithography for nanoscale patterning. Unlike current projection steppers, which are resolution limited by diffraction phenomena, the resolution of SFIL tools are only limited by the template and patterning capability down to 20 nm has been demonstrated. 1 The combination of high resolution and low cost of ownership make SFIL a strong candidate for future semiconductor IC manufacturing. SFIL is a contact lithographic process in which a pattern is transferred from a rigid quartz template to a liquid resist through mechanical molding techniques. The imprint fluid, also known as the etch barrier, is dispensed onto a substrate, and the template is then brought into contact with the liquid, such that the recesses in the quartz are filled through capillary force. Once the etch barrier has completely filled the features on the mold, UV radiation is projected through the backside of the template to polymerize the material. The template is then removed to leave a polymer imprint that is a replica of the template. Subsequent dry etch processes are used to transfer the pattern into the underlying substrate. A successful imprint is dependent on perfect adhesive failure at the quartz-polymer interface when the template is removed from the imprint. Removal involves applying tensile forces on the template to propagate a crack along the often-complex topography of the quartz mold. If excessive force is required, cohesive failure of the polymer can occur and thereby generate defects on the polymer and quartz surfaces resulting in poor imprints and fouling of the template as shown in Figure 1. Emerging Lithographic Technologies XII, edited by Frank M. Schellenberg Proc. of SPIE Vol. 6921, 69210E, (2008) · 0277-786X/08/$18 · doi: 10.1117/12.772797 Proc. of SPIE Vol. 6921 69210E-1 2008 SPIE Digital Library -- Subscriber Archive Copy