Fabrication of high-aspect-ratio silicon nanostructures using near-field scanning optical lithography and silicon anisotropic wet-etching process
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A new process in which near-field scanning optical lithography (NSOL) is combined with anisotropic wet-etching of (110) silicon is developed for the fabrication of high-aspect-ratio (HAR) nanochannels. In the proposed process, NSOL is applied to produce nanopatterns on a commercial positive photoresist as in an optical lithography. The use of a commercial photoresist is an advantage of this process because it allows the direct application of many photoresists currently available without pretreatment, saving cost and time. A bare (110) silicon wafer coated with a thin Si3N4 layer, of approximately 10 nm thickness, is used as the sample and the photoresist is spincoated on the Si3N4 layer to a thickness of about 50–80 nm. Nanopatterning of the photoresist using a contact mode NSOL, transfer of the photoresist pattern onto the Si3N4 layer by reactive ion etching, and anisotropic wet etching of the silicon wafer using the patterned Si3N4 layer as an etch mask, lead to the intended HAR nanostructures. Fabrication of silicon nanochannels with a channel width below 150 nm and an aspect ratio greater than 3 is demonstrated.
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