緩衝液及二氧化矽對(100)單晶矽KOH濕蝕刻形成之微結構及反射性研究

THE EFFECTS OF IPA BUFFER AND SiO2 ON MICROSTRUCTURE AND REFLECTIVITY IN (100) SINGLE CRYSTALLINE SILICON WITH KOH WET ETCHING

錢佑欣(Yuhsin Chien)

指導教授 ： 魏哲弘

大同大學/工程學院/機械工程學系所/碩士(2010年)

摘要

由於無汙染及可以無限制的提供能源，太陽能電池將是未來能源的主流。為了能增大其效率，在太陽能電池表面製造微結構使其反射率減至最低及增加光吸收為常見方法，而我們提出的實驗方法可以有效的增加表面微結構。第一個實驗使用30wt%的氫氧化鉀(KOH)蝕刻液，並加入不同濃度的緩衝液(異丙醇Isopropyl Alcohol,簡稱IPA)對貼附軟式光阻的(100)矽晶圓蝕刻。第二個實驗為在30wt%的KOH蝕刻液中蝕刻表面塗佈二氧化矽(SiO2)奈米粒子並貼附一層軟式光阻的矽晶圓。經過蝕刻產生微結構後利用反射儀對矽晶圓表面進行反射率的量測，並使用掃描式電子顯微鏡(SEM)、原子力顯微鏡(AFM)、光學顯微鏡(OM)觀察表面其特徵。實驗中與其他方法不同的特徵為在晶圓上長一層二氧化矽並使用軟式光阻代替遮罩。
結果顯示當30wt% KOH蝕刻液、蝕刻時間20分鐘、蝕刻溫度70度時，加入濃度為1wt%的IPA可以使反射率從38%降至9%。另一個塗佈0.01克二氧化矽奈米粒子(0.00674% SiO2/Si)及貼附軟式光阻的實驗中，當30wt% KOH蝕刻液、蝕刻時間20分鐘、蝕刻溫度70度時，反射率可降至14%。在蝕刻過程中可以觀察到蝕刻機制分為兩步驟。一開始KOH蝕刻液蝕刻時會先從光阻的周圍開始向內蝕刻，之後軟式光阻因KOH蝕刻液蝕刻剝落，最後產生的微結構經實驗證實可以將光捕捉效益增至最大。

關鍵字

濕蝕刻 ； 二氧化矽 ； 緩衝液

並列摘要

Solar cells have been regarded the future power source due to its clean nature and unlimited supply. To increase the efficiency, it is a common practice to fabricate microstructures on solar cell surface to minimize the reflectivity and increase the light absorption. In this thesis, we propose cost-effective recipes to fabricate the microstructures. The first recipe is using 30wt% KOH with different isopropyl concentrations in etching photoresist covered (100) silicon. The second recipe is by spin coating SiO2 nanoparticles over silicon covered with photoresist and was etched by 30wt% KOH. The microstructure was examined and the associated reflectivity was measured by reflectometer. The surface morphology was characterized by atomic force microscopy (AFM), scanning electron microscopy (SEM) and optical microscopy (OM). A distinct feature in these recipes is instead of growing a hard SiO2 etching mask, a soft photoresist film was taped on the silicon wafer.
The results show that for 30 wt% KOH with 1 wt% isopropyl buffer and etching time 20 min and etching temperature 70 , the reflectivity is reduced from 38% to 9%. On the other hand, for SiO2/photoresist soft etching mask, the reflectivity is reduced 14% for 0.01g SiO2 (0.00674% SiO2/Si) for 30 wt% KOH, etching time 20 min and etching temperature 70 . The etching mechanism is characterizes as two step etching process. In the beginning, the KOH etching from the photoresist periphery, and as etching progresses, the soft mask was etched away and secondary features were fabricated. This recipes demonstrates the soft etching mask is able to fabricate microstructure that can maximize the light trapping in a cost effective way.

並列關鍵字

wet etch ； SiO2 ； IPA

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