Research On Silicon Nanowire Sensors Fabricated By Nanoimprint Lithography Combined With Angle Deposition

In recent years, nanoimprint lithography (NIL) was applied in top-down fabrication of semiconductor nanowires. The reason is that, while NIL can achieve good resolution, it has lower cost, higher throughput than electron beam lithography (EBL) does. However, it is still very challenging to fabricate ultra thin linear patterns using NIL in a common laboratory.In this thesis, traditional nanoimprint lithography is combined together with angle physical vapor deposition (PVD) technique, in order to develop an approach to define ultra-thin nanowire patterns. The widths of nanowires fabricated by this approach can be adjusted conveniently by controlling the deposition angle and imprint depth, and can be much smaller than the width of original pattern on the imprint template. In this work, silicon nanowires with their widths ranging from 22nm to 110 nm are fabricated with the same template pattern using this approach,In order to verify the practicability of this approach in fabricating actual semiconductor nanowire devices, silicon nanowire gas sensors (with 60-nm-wide and 90-nm-wide nanowires) are also fabricated on SOI substrate using this approach, and are tested for their response to 250ppm NO2. And their relative sensitivities reach 155% and 44% respectively. The sensitivites of the sensors fabricated by our team with two different approaches are compared and analysed. Experiment results reveal that, the sensitivity to NO2, and its dependency on the widths of nanowires, varies a lot according to the fabrication approaches. Later analysis indicates that, on the surface of silicon nanowires, surface charges (primarily induced by etching process) greatly enhanced the ionization of surface energy level caused by absorbed NO2. This explains why silicon nanowire sensors made with dry etching possess much higher sensitivities than those wet etching samples do. And it also helps to understand why, for dry etching samples, relative sensitivities increase much faster than the widths of nanowire decrease.