Manufacturing and Thermal Property Analysis of Porous Silicon Structure by Metal Assisted Chemical Etching

• Main Authors: PAN,XIANG-QIN, 潘詳親
• Other Authors: 洪銘聰
• Format: Others
• Language: en_US
• Published: 2017
• Online Access: http://ndltd.ncl.edu.tw/handle/z9zg43

碩士 === 國立中央大學 === 機械工程學系 === 106 === 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.