烷基矽烷自組裝層於ITO薄膜之電化學特性及其於蝕刻製程之應用

The Electrochemical Characteristics of Alkyl Silane Self-Assembly Layers on ITO Film and Application to Etching Process

黃柏榮(Po-Rung Huang)

指導教授 ： 顏溪成

國立臺灣大學/工學院/化學工程學研究所/碩士(2009年)

https://doi.org/10.6342/NTU.2009.10705

摘要

本實驗分為三部份：第一部份為討論自組裝分子於不同反應條件下在ITO表面形成薄膜之型態，利用Contact angle、XPS、表面粗糙度、循環伏安法、交流阻抗分析對於自組裝層在不同反應條件下所生成之型態；第二部份針對自組裝前後ITO於不同比例之草酸蝕刻液之研究，利用蝕刻速率量測、開環電位量測、極化曲線分析自組裝前後對於蝕刻反應進行是否有明顯之效果；第三部份為結合第一部份以及第二部份之最適化條件進行自組裝層取代光阻之實驗，以SEM觀察自組裝層抗腐蝕效應，並且對於自組裝層脫附於ITO表面實驗，利用XPS表面化學成分分析以及循環伏安法觀察表面脫附情況。
第一部份實驗結果發現在ITO表面形成自組裝層操作兩個實驗變數：一為碳鏈長度；二為反應溫度。當使用碳鏈長度為18的ODTMS為自組裝層來源時，由於分子間作用力之關係，之間排列方式會趨於整齊排列，而且對於電化學反應的抑制現象較短碳鏈的OTMS（C8）來的明顯，而且接觸角的結果也以ODTMS的結果（110.54o）較OTMS高（93.83 o）；交流阻抗分析之結果ODTMS所造成之電荷轉移電阻為32100 Ω也較OTMS的18693Ω高，而對於薄膜電阻而言，隨碳鏈減少也從2285 Ω降至1280 Ω。而對於反應溫度而言，根據交流阻抗分析的結果發現，以ODTMS的結果來說，當反應溫度越高時，Rct從32100 ohm降至19480 ohm，而RSAM也從2285 ohm降至1547 ohm，主要原因在於在溫度提升的過程薄膜生成的型態從原先的低溫下所形成的LC型態轉換為LE型態所導致的結果，而從循環伏安分析的結果也有相同之趨勢，低溫所生成之薄膜其抑制電化學反應進行之能力越佳。
第二部份針對ITO在草酸蝕刻液中的行為進行研究，ITO蝕刻速度和草酸的濃度有相關，但卻不為正比關係，當濃度超過3.4 wt%時，蝕刻速率會趨向於一定值；在草酸蝕刻液中添加醋酸以及酒石酸對於蝕刻速率皆有明顯抑制的現象，而以酒石酸的抑制效果越強；而從極化曲線的結果發現，錯合劑的添加對於整體蝕刻反應進行方式沒有明顯之改變，但從腐蝕電位來看，添加錯合劑會造成腐蝕電位有下降之趨勢，從原本-0.331 V降至-0.38 V左右，而腐蝕電流也有下降趨勢，但其改變幅度不大，其中以添加0.34 wt%的結果變化最為明顯；而當有自組裝層在ITO表面時，腐蝕電位有明顯上升，而以有添加錯合劑上升的情況最為明顯（-0.38 V增加至-0.2 ~ 0 V左右），表示自組裝分子確實可以抑制蝕刻反應之進行，而從SEM的結果來看也證實同樣之結果；對於添加劑而言，以添加醋酸之結果較好，在蝕刻後之邊界會產生斜坡現象，對於半導體製程中，這樣的結果對於之後製程之加工性會有所幫助。
第三部份針對自組裝層脫附ITO表面實驗，由於自組裝分子和ITO為類似二氧化矽之鍵結，利用BOE蝕刻為脫附劑；經矽烷分子修飾之ITO浸至於BOE中1 min，從CV的結果已有明顯特性峰產生，當反應達5 min左右，表面自組裝分子大致脫離完全，而且利用BOE脫附劑對於ITO而言，利用CV以及XPS分析，對於ITO表面沒有蝕刻效果。

關鍵字

非晶型ITO玻璃 ； 自組裝薄膜 ； 草酸蝕刻液 ； 濕式蝕刻

並列摘要

Photo-lithography is an important process in the property of LED. There are three major parts in this process : 1. Photo-resist coating 2. Expoursion 3. Development. In fact, it will be finished the process with seven steps in detail. It will be more complex with whole process. In this experiment, we want to use the advantage of SAM to protect the ITO surface during etching process. Therer are three parts in this experiment : 1. Using contact angle, XPS, AFM, cyclic voltammetry and EIS analysis method discusses the property of SAM film with different conditions of SAM reation; 2. In the etchant of amorphous ITO, it analyzes etching rate, OCP and LSV method. It studies the properties of amorphous ITO in diffirent concentrations and types etchant, then finds the relationships between these experiment condition; 3. Combine the suitable condition of part 1 and part 2, using SEM, OCP and tafel method focuses on the level of protecting ITO then uses the BOE etchant to remove SAM on ITO. Furthermore, estimates the possibility of replacing the role of photo-resist.
Part I : In this experiment, we control two major conditions : 1. SAM chain length 2. The temperature of SAM reaction. From the result of SAM, longer self-assembly molecular owe to arrange in order and condenses tightly very much, cause by the force between each molecular. From the result of AFM and CV analysis, when the experiment of temperature is below Tc, the SAM film owns to perform uiniform.
Part II : In the process of etching with OXA solution, the etching rate of ITO will increase following the concentration of OXA. When the concentration of OXA is upward 3.4 wt%, the etching rate will approach constant. From tafel analysis method, adding acetic acid (AA) and tartaric acid (TA) , the corrosion potential will decrease from -0.331V to -0.38V. Adding AA and TA, it will change the ITO surface to remove easily, but for etching rate measurement, adding AA and TA will decrease the etching rate of ITO film. Cause of two results, adding chelate will change the proiperty of ITO surface, it will not increase the etching process. For the amount of chelate, when adding 0.34 wt% in OXA solution, it differs with the other one. From these results, choosing the 0.34 wt% chelate undergoes the etching process.
Part III : Focus on the ITO with protector-SAM in etching process. From tafel analysis result, SAM exists on ITO surface in the etchant will increase the corrosion potential from -0.38V to -0.2~0V. Only OXA 3.4 wt% system, from SEM result, the edge will occur default. If reducing the scale of element, this condition should not be accepted. At OXA 3.4 wt% + AA 0.34 wt% or OXA 3.4 wt% + TA 0.34 wt% condition, the edge of etching performs smooth one. For removal SAM, useing BOE etchant can remove SAM completely and BOE can not hurt ITO surface.

並列關鍵字

Amorphous ITO glass ； SAM ； Oxalic acid ； Wet etching

參考文獻

Allara, D.L. and R.G. Nuzzo, Langmuir, 1, 45 (1985).

Amick, J.A., Solid State Technology, Nov., 47 (1976).

Bain, C. D. and G. M. Whitesides, J. Am. Chem. Soc., 111, 7164 (1989).

Bard, A.J. and L.R. Faulkner, “Electrochemical Methods”, 2nd Ed., John Wiley & Sons, Inc., New York (2001).

Chen, K.; Caldwell, W.B., Mirkin, C.A. J. Am. Chem. Soc., 115, 1193 (1993).