設計與製造多樣化應用的大面積週期性奈米結構

Abstract

大面積週期性半導體奈米結構因為其獨特的機械、光學和電學特性引起廣泛的討論，從而實現許多應用，包括電子、光電、生化感測器、高密度資料儲存及超薄顯示器等元件。目前，奈米壓印技術(nanoimprint lithography , NIL)和光學微影技術(photolithography, PL)是製造大面積週期性奈米結構最常用的方法。然而，NIL模板的製造往往需要昂貴的電子束微影技術製程，而PL則會受限於光學解析度的限制。因此，低成本、高產量的大面積週期奈米結構製造方法對於奈米技術的發展至關重要。在本研究中，我們使用低成本的i-line stepper光學微影技術和快速、全水容易製成的金屬輔助蝕刻(metal-assisted chemical etching , MacEtch)，透過調變製程參數，被定義的圖型可調性高且快速的於晶圓上製作幾近完美的週期性奈米結構。 首先，利用i-line stepper 光學微影技術在6吋矽基板上銜接曝光場來實現大面積圖案化，為臨界尺寸400nm，週期800nm的三角晶格點狀圖形。在目標CD+/-10%的容忍範圍內，得到橢圓形製程窗口內的聚焦深度(depth of focus, DOF) -0.2um，曝光容忍度(exposure latitude, EL)1350J/m2。並利用金屬輔助蝕刻成功的製作大面積週期性奈米柱結構，此結構在800nm光波段有6%的低反射率。而此製造方法也可以有效的降低NIL母模之製作成本。 此外，我們透過調變銀粒子的沉積時間和多步驟的非等向性蝕刻(AgNO3+HF+H2O2)可以精確的調節奈米結構的傾斜角度，以改變奈米結構的側壁輪廓，成功的製作筆柱狀奈米結構與錐狀奈米結構。再者，通過混合不同的氧化劑加上光阻的保留，可以以一步驟簡單製作筆柱狀奈米結構。也可以利用MacEtch的蝕刻機制，透過調變蝕刻液比例得到更多樣化的表面形貌。 最後，我們將導入解析度增益技術(resolution enhancement techniques, RETs)修正曝光場邊緣的尺寸誤差並可以更進一步的縮小臨界尺寸。此外，可以利用側牆製程技術(spacer technique)，縮小奈米陣列結構的間距以提高結構的光管理能力。

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.