Functional Polymers for Advanced Lithography
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Functional Polymers for Advanced Lithography Kyung M. Choi Chemistry, University of California, Irvine, CA 92697, U. S. A.
ABSTRACT In nanotechnology, many scientists have been seeking for new functional polymers, which can replica nano-sized features to achieve improved performances of nano-devices. Soft lithography has been widely used in replica of small features as a low cost alternative to conventional UV photolithography. However, commercial silicon rubbers, PDMS polymers, which have been used in current soft lithography, show limitations, especially for nanoresolution soft lithography. These limitations have motivated us to develop a new version of PDMS polymers to overcome those limitations and thus to extend current technology in soft lithography to the advanced level. Since the resolution of soft lithography significantly relies on stamping performance, we designed a novel PDMS prepolymer, which has photocurable crosslinkers to enhance mechanical property to improve lithographic performance and also to create photocurable capability. ` INTRODUCTION Nanotechnology is promising due to unprecedented applications arise from their small scale in sizes [1-16]. Novel approaches in nanotechnology have been developed including nanofabrication, soft lithography, plastic/flexible electronics, and microfluidic synthesis. In materials science, development of new materials for nanotechnology applications has taken attractive attentions to improve the performance of nano-devices. Intensive efforts have been taken to seek for novel materials; because, development of novel materials is the most challenging key contributor to achieve high performances. Soft lithography is a technique of transferring patterns from the original masters to substrates (Figure 1). It employs silicon rubbers as stamps or photomasks to replicate small features [4-9]. As shown in Figure 1, soft lithography consists of three processes; making stamps, stamping process, and micro-contacting process. The technique, which generates small features on flexible substrates, is crucial for flexible electronics applications at low-cost.
Figure 1. Soft lithography processes. Silicon elastomers have been widely used for soft lithographic purposes due to their high elasticity, chemical stability, and good optical transparency. However, commercial silicon elastomers have been initially developed for some other applications and thus often show limitations for high-fidelity soft lithographic tasks, especially at the nano-scale. For example, Sylgard 184 stamp has shown a low compressive modulus and thus limits high fidelity lithographic tasks at the submicro-scale; due to the limitations, Sylgard 184 stamps often collapse, merge, and disconnect during lithographic process and thus result in poor lithographic performances. To overcome these limitations, we modified the chemical structure of PDMS prepolymers to develop a new version of silicon rubbers, specifically designed for soft lithographic purposes.
EXPERIMENTAL DETAILS[15] Synthesis of photocu
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