Popular electron beam resists such as PMMA, ZEP and HSQ all use solvent or base solutions for processing, which may attack the sub-layers or substrate that are made out of organic semiconducting materials. In this study we show that water soluble poly(sodium 4-styrenesulfonate), or sodium PSS, can be used as a negative electron beam resist developed in water. Moreover, since PSS contains metal sodium, its dry etching resistance is much higher than PMMA. It is notable that sodium PSS's sensitivity and contrast is still far inferior to organic resists such as PMMA, thus it is not suitable for patterning dense and highresolution structures. Nevertheless, feature size down to 40 nm was achieved for sparse patterns. Lastly, using very low energy (here 2 keV) electron beam lithography and liftoff process using water only, patterning of metal layer on an organic conductive material P3HT was achieved. The metallization of an organic conducting material may find applications in organic semiconductor devices such as OLED.
Periodic tilted nanostructures over large area have various applications. In this work tilted nanostructures were created by SEM scanning of electron beam resists with the substrate tilted at 45. The key to the process is the usage of the dynamic focus function that is available for most SEM systems for imaging purpose (but not for lithography), as otherwise the tilted substrate will be out of focus of the electron beam. The pattern created by this method is limited to periodic pillar or hole array using negative or positive resist, respectively, with the number of pillars or holes per scan given by the image resolution (e.g., 1024 Â 768). The diameter of the pillars or holes was determined by the exposure dose, which is in turn determined by the beam current and scan speed (scanning time per frame). The array period is controlled by the magnification (that determines image area, e.g., 1 mm 2) and image resolution. The pillar or hole pattern in the resist can be further transferred to another material such as Au by electroplating. V
Low throughput is the major drawback for electron beam lithography. Chemically amplified resists that have high sensitivity are often used to keep the exposure time within practical limit. In this Letter the authors show that the popular non-chemically amplified electron beam resist ZEP-520A can achieve 2.6 mC/cm 2 sensitivity when using methyl ethyl ketone:methyl isobutyl ketone developer and 5 keV exposure, though at the cost of reduced contrast compared to standard developers xylene, n-amyl acetate or hexyl acetate. The achievable resolution was found to depend strongly on the resist's adhesion to the substrate or under-layer and thus obtained 40 nm half-pitch resolution using ZEP resist spun on a layer of anti-reflection coating that was treated by oxygen plasma.
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