奈米多孔材料應用相當廣泛，其高面積體積比之結構特性可以增加表面接觸面積，可應用於氣體感測器、質譜儀、質量傳輸膜及太陽能面板抗反射層等，另外因孔隙率增加及奈米結構尺寸效應導致有效熱傳導係數大幅下降，使之成為良好的絕熱材料。常見的多孔矽製程包括電化學蝕刻、乾蝕刻、金屬輔助化學蝕刻等。本研究利用金屬輔助化學蝕刻法具有製程相對簡單、製程設備成本低之優點，研究探討蝕刻參數與孔隙之關係以製備高深宽比之奈米多孔矽結構，並分析其熱傳導性質。 實驗利用硝酸銀溶液混和氫氟酸在矽表面形成奈米銀粒子作為蝕刻之催化劑，接著在添加過氧化氫之蝕刻液中進行非等向性蝕刻，形成奈米多孔結構，透過控制過氧化氫濃度達到均勻奈米多孔結構。結果顯示在長時間蝕刻下，蝕刻深度會趨緩；而因結構頂部蝕刻影響，多孔層的成長率最後會逐漸下降。所製備之結構利用不同的熱傳模型計算熱傳導係數分析，結果顯示未考慮孔徑的簡化模型在分析極小孔徑結構時有較大的差異；在考量製程上孔隙率與孔徑的相依性下，在低孔隙率時反而會因其小孔徑影響，使得有效熱傳係數比預期還低。 ;Nanoporous material has been widely used in various applications. It has high area-to-volume ratio that increases surface area and can be used in gas sensors, mass spectrometers, mass-transferring films, and anti-reflection coating on solar panels. Due to the increasing porosity and the size effects of nano-structures, it leads to an effective decreasing in the heat conduction coefficient and makes it a good thermal insulating material. Typical porous silicon fabrication processes include electrochemical etching, dry etching, and metal-assisted chemical etching. Among them, metal-assisted chemical etching has the advantages of simple process and low equipment cost. In this study, we use metal-assisted chemical etching to prepare high aspect ratio nanoporous silicon, explore the relation between etching parameters and porosities, and analyze its heat conduction properties. The silver nitrate solution and hydrofluoric acid were used to form the Ag nanoparticles on silicon surface as the catalyst for etching. The anisotropic etching was performed in the etching solution with hydrogen peroxide to form nanoporous structures. A well-distributed nanoporous structure was achieved through controlling the concentration of hydrogen peroxide. The results showed that for a long etching time, the etching rate became slower and the porous layer growth rate gradually decreased due to the etching on top structure. Different heat transfer models were used to analyze the thermal transfer coefficient. The results showed for the simplified models that do not consider the pore size exhibited a significant difference in thermal conductivity for small pore size samples. Considering of dependence of porosity and pore size in the process perspective, the effective thermal conductivity was lower than expected due to the impact of the small pore size structure.
