Contact pattern sensitivity and precision machine control in roll-to-roll microcontact printing
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Contact pattern sensitivity and precision machine control in roll-to-roll microcontact printing Joseph E. Petrzelka, Melinda R. Hale, and David E. Hardt Massachusetts Institute of Technology, 77 Massachusetts Ave., Cambridge, MA 02139, U.S.A.
ABSTRACT Scaling contact lithography (microcontact printing, microflexography, and nanoimprint lithography) to large roll-to-roll platforms will enable high speed, low cost lithographic patterning of surfaces. However, many details of robust implementations at the roll-to-roll scale remain an engineering challenge, including precise regulation of printing pressures and the stamp-substrate interaction. This paper introduces a method for precise control of contact pressure that can accommodate large dimensional variations, i.e. varying stamp and substrate thicknesses. This control algorithm is implemented on a simply supported roll positioning stage. Experimental results for microcontact printing and microflexography are shown both with in situ contact measurements on a pseudo substrate and with 5 um silver nanoparticle prints. Ultimately, this approach enables robust printing despite sensitive stamp patterns and large dimensional variations (> 10 μm) in substrates, stamps, and roll equipment. INTRODUCTION Adapting contact lithography (microcontact printing, microflexography, and nanoimprint lithography) to roll-based platforms is a promising technique for large area, high rate patterning of micron and sub-micron features. This paper addresses precise control of the stamp contact pressure in rolling machinery, which in turn influences pattern integrity, residual layer thickness, and the overall quality of pattern transfer. The large size of roll-to-roll equipment makes uniform nip strain and pressure distributions difficult to attain across the entire width of substrates. This work is motivated by patterning of metallic conductors on photovoltaic or flexible electronic devices by soft lithography. Sparse networks of metallic wires can be economically patterned over large areas through either microcontact printing or microflexography. These sparse networks represent a very sensitive printing configuration, where successful pattern transfer depends on positioning the roll and substrate within only a few microns of error. a
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Figure 1. Patterned polymer stamps can deform and cause printing defects. Possible deformation modes include (a) sidewall collapse, (b) roof collapse, (c) buckling, and (d) lateral collapse. Pattern integrity is a major concern in soft lithography. The compliant elastomeric stamps employed (typically polydimethylsiloxane, PDMS) can deform significantly under ordinary printing pressures. The failure modes shown in Figure 1 will occur under load and degrade pattern integrity; the onset of these different modes has been the subject of prior studies [1,2]. Even optimally designed features (e.g. optimal aspect ratio) collapse under pressures that are
only a fraction of the stamp elastic modulus. Analytical and experimental approaches show that these press
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