多孔矽發現至今，由於其光學、光電、熱、化學等特性，因此多孔矽在很多領域上有廣泛之研究，例如光偵測器、生物及化學感測器、氣體感測器之應用。近年來，多孔矽也被研究在熱電材料上之應用，好的熱電材料需要好的導電及低的熱傳導率，使熱電優值提升。利用奈米結構降低熱傳導係數是具潛力的方式，多孔矽能具有奈米等級的孔洞，造成熱傳導值的降低。一般來說製作多孔矽的方法概略分成乾式蝕刻、濕式化學蝕刻與電化學蝕刻。電化學蝕刻保有濕式蝕刻的優點，且具有低設備成本、蝕孔異向性高等優點，是目前最常用於研究多孔矽的製程方法。本文利用電化學蝕刻方法，改變不同電流密度及時間，製備出不同厚度及孔隙率之多孔矽材料，並利用暫態式的雷射脈衝測定法(Lsaer Flash)量測多孔矽之熱擴散係數，具有非接觸式避免破壞材料結構之優點，由於本文材料為多孔矽-矽雙層材料，透過有限元素分析軟體COMSOL 建立模型，並利用雙層模型，與實際量測配合，進而計算出多孔矽之熱傳導係數。經由製程得知，利用不同電流密度大小，能提升蝕刻速率及製作出不同孔隙率之多孔矽，改變蝕刻時間，能得到不同厚度及孔隙率的多孔矽。由熱傳特性量測結果得知，當孔隙率越大，熱傳係數隨著下降。熱傳導係數自溫度150K 至400K 呈現上升趨緩的趨勢。

Porous silicon has unique characteristics of optics, photoelectric, thermal ,chemistry etc.. It has been used in different area, for example, in photodetectors, biosensors, chemical sensors, and gas sensor. Recently, porous silicon has been found as a potential thermoelectric material due to its low thermal conductivity. In general, porous silicon can be made using dry etching, wet etching, and electrochemical
etching, in which electrochemical etching is the most common method to fabricate directional pores due to its low-cost and etching anisotropy. In this study, we fabricate porous silicon on silicon wafer using electrochemical etching. Different porous layer thickness and porosity are made by adjusting the current density and etching time. Thermal diffusivity of porous silicon is measured using transient laser flash method that can avoid the damages of the sample. Since the measured sample is composed of the porous silicon layer and the silicon substrate. To obtain the thermal transport properties of the porous silicon, finite element simulation is performed with the two-layer construction model. In the fabrication of the porous silicon, it is shown that the change of current density can increase the etching rate and the increase in etching time can lead to thicker thickness and higher porosity. The measurement results show
that the thermal conductivity of the porous silicon increase from 150 K to 400 K and reach a plateau. In addition, the thermal conductivity decrease as the porosity increae.

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