Effect of applying ultrasonic vibration in thermal nanoimprint lithography
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In our previous works we had shown that the use of ultrasonic vibration in micro hot embossing processes proved to be effective in improving the molding accuracy. We then decided to extend this technology of ultrasonic vibration to nanoimprint lithography also, and investigate its effect on nanoimprints experimentally. This task also required the use of a heater capable of sustaining three kinds of stresses, namely loading force, thermal stress, and ultrasonic vibration in the molding process. This work led to the development of an ultrasonic nanoimprint system with a built-in pyrolytic graphite/pyrolytic boron nitride all-in-one heater. The material chosen for nanoimprinting was polycarbonate with its glass transition temperature being 150°C. The research in the area showed that the timing point at which an impression of ultrasonic vibration begins is an important factor. When an ultrasonic vibration was impressed at an early stage in a molding process the height of the imprinted pattern seemed to increase where high amplitudes of the acoustical vibration were involved. Moreover, when the molding accuracies of line/space pattern with line widths of 500, 750 nm, and 1 μm were compared among themselves, the effect of assistance from ultrasonic vibration became quite noticeable in the case of small lines patterns; this was the case even where the amplitudes of the ultrasonic vibration were small. As for the application of ultrasonic vibration on nanoimprinting is concerned, it was found to greatly improve the molding accuracy of the process.
KeywordsContact Force Line Width Molding Process High Aspect Ratio Ultrasonic Vibration
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