| Summary: | 碩士 === 國立交通大學 === 光電工程研究所 === 106 === Large-scale periodical semiconductor nanostructures have attracted considerable interest due to their extraordinary mechanical, optical, and electrical properties, thus enabling many applications including electronics, optoelectronics, bio-/ chemical- sensors, high-density storage, and ultra-thin display devices. Currently, nanoimprint lithography (NIL) and photolithography (PL) are the most commonly used methods for fabricating ordered nanostructures in large area. However, the fabrication of NIL mold usually requires costly e-beam lithography and PL is limited by its resolution. As a result, a low-cost and high-throughput fabrication method for large area periodic nanostructures will be vital to the development of nanotechnology. In this study, we report a low-cost method by means of photolithography using i-line stepper and metal-assisted chemical etching (MacEtch). By carefully tuning the process conditions, near perfectly ordered Si nanostructure arrays of user-defined patterns can be controllably and rapidly produced on a wafer scale.
First, large area patterning has been implemented by stitching exposed fields using i-line stepper lithography on a 6 inch Si substrate. The critical dimension of periodic dots is 400nm in diameter and 800nm in pitch arranged a triangular lattice. The target CD tolerance was +/- 10%, yielding a depth of focus (DOF) of -0.2 um and exposure latitude (EL) of 1350 J/m2 in elliptical process window. By means of MacEtch, we have successfully fabricated large area nanorod arrays which shows a low reflectance of 6% at 800nm wavelength. This approach offers a solution to reducing the cost of NIL molds.
Second, we could tailor the side wall profile of Si nanorods by varying the Ag deposition time and using multiple-step anisotropic etching (AgNO3+HF+H2O2). We can regulate the tilt angle of Si nanostructures precisely and obtain different side wall profiles such as nanopencils and nanocones. Furthermore, by mixing different kinds of oxidants and retaining the photoresist during etch, we can successfully fabricate nanopencil structures in one single step. We show that in the case of MacEtch, a large variety of surface morphologies can be produced by changing the etching solution composition.
For future work, resolution enhancement techniques (RETs) can be introduced to correct the CD-error at the edge of exposure field and further reduce the CD. Also, the spacer technique can be employed to shrink the spacing of nanostructure arrays which could improve the light management capability.
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