鑑定與製備微孔型非結晶二氧化矽低介電薄膜

Characterization and Preparation of Microporous Non-crystalline Silica Low-k Films

陳翰儀(Han-Yi Chen)

指導教授 ： 萬本儒

國立臺灣大學/工學院/化學工程學研究所/碩士(2016年)

https://doi.org/10.6342/NTU201602638

摘要

本實驗室過去已發展出使用短時間水熱製做非結晶二氧化矽沸石前驅液，製備介電常數小於2之中孔型高機械強度低介電薄膜。然而未來介電薄膜孔洞需在微孔範圍，故本研究目標為研發微孔型高機械強度低介電薄膜。
本研究利用蒸發及刮除法從鍍膜液中收集粉末樣品，以氬氣吸脫附與非局部密度泛函理論模擬，量測薄膜孔洞大小與體積。鍍膜液由沸石顆粒加界面活性劑組成，沸石顆粒由四丙基氫氧化銨(TPAOH)做為MFI微孔結構導向試劑，經水熱程序合成。界面活性劑能使薄膜均勻，但若聚集成微胞，鍛燒後會形成中孔。當薄膜孔隙度提高，藉由空氣之低介電常數(κ=1)，可降低薄膜κ值。
為了增加微孔洞，增加TPAOH之比例，發現TPAOH/Si比例增加無法增加7Å下之微孔體積，但過多TPAOH(鹼)會改變合成結果，孔洞分析顯示，當TPAOH比例提高達0.36，顆粒已不具MFI之結構。另外，界面活性劑會與沸石顆粒作用，改變微孔、破壞MFI結構後，聚集形成中孔。顆粒或界面活性劑之親水性上升可縮小聚集之中孔，故本研究嘗試縮短水熱時間(少於24 h)期望合成親水性更高之沸石顆粒，但研究結果發現過短的水熱時間(6小時)可能會保留矽源TEOS(tetraethyl orthosilicate)與水反應之散亂二氧化矽結構，無法增加親水性。
12小時水熱顆粒做為前驅液，減少四倍界面活性劑，可製備最大孔洞在17.3Å之微孔型低介電薄膜。減少的薄膜孔洞由分子量200，親水性較高之聚乙二醇(PEG200)做為成孔劑，增加孔隙度。為更精確得到薄膜孔洞分佈，改用刮除法收集粉末，經量測可得最大孔洞17.3Å，孔隙度0.31或0.32(PEG200濃度決定)之微孔薄膜。然而這些薄膜κ值大於2，未達未來工業需求，原因可能來自鍍膜的異質性或HMDS無法修飾。
本研究另外發現，加入成孔劑減少界面活性劑會造成薄膜不均勻，但當滴上鍍膜液後等待五秒，可塗佈出均勻薄膜。12小時水熱顆粒親水性高，但會造成界面活性劑形成大微胞，使薄膜產生不均勻條紋。使用短時間水熱時，TEOS的新舊會改變水熱顆粒性質，造成孔洞分佈及孔洞體積的改變。

關鍵字

水熱法 ； 非結晶二氧化矽 ； 界面活性劑 ； 成孔劑 ； 微孔低介電常數薄膜 ； 吸脫附

並列摘要

In our previous study, coating solution containing non-crystalline silica for preparing mesoporous low k film with k value below 2 and high mechanical strength has been made. However, microporous low k films is necessary for future needs. Therefore, the goal of this research is to make microporous low k film with high mechanical strength.
In this research, pore size distribution (PSD) and pore volume of powders made from coating solution by evaporation method or scraping method were measured by argon adsorption/desorption and analyzed by non local density functional theory (NLDFT) simulation. Coating solution consist of synthesized silica, tetrapropylammonium hydroxide (TPAOH) and surfactant. TPAOH was used as a structure directing agent to synthesis MFIlike microporous silica during hydrothermal process. Surfactant added in the solution can form pores between silica particles after the calcination. As the porosity increases, dielectric constant of the film should decrease.
In order to increase the micropore volume, the molar ratio of TPAOH to TEOS (tetraethyl orthosilicate) was increased from 0.15 to 0.36. Nevertheless, the micropore volume was not successfully increased. Instead, the surfactant interacted with silica strongly, resulting in destroying micropores of MFI structure. On the other hand, because increasing hydrophilicities of silica and surfactant (or porogen) can increase the interaction between these two, decrease the formation of micelles and mesopores, and resulting more micropores, shortening hydrothermal period (less than 24 hours) was adopted to manufacture more hydrophilic silica. It was found that micropore volume was increased and mesopore volume was decreased successfully. However, that from too short hydrothermal period (i.e., 6 hours) was not, may be because synthesized silica would maintain amorphous structure from incomplete reaction between TEOS and water.
In this research, the low k film with the largest micropore size of 13.6Å has been produced from the coating solution containing silica (synthesized from 12 hours hydrothermal process) and the surfactant with a reduced amount (i.e., ratio of surfactant to TEOS decreases from 0.41 to 0.1). In order to increase the micropore volume, poly(ethylene glycol) with molecular weight 200 (PEG200) acting as hydrophilic porogen was added to coating solution. It was found that the largest micropore increased to 17.3Å and the porosity increased to 0.31 or 0.32, which is close for making low-k value less than 2. Nevertheless, the measured k values are all well above 2, which are not suit for the future needs of IC industry. One of the reasons may be because of the non-uniform coating. Although it can be solved by waiting 5 seconds after dispersing coating solution to wafer before the spinning, the k values are still unexpectedly large.

並列關鍵字

hydrothermal ； non-crystalline silica ； surfactant ； porogen ； microporous low k film ； adsorption/desorption

參考文獻

[34] 蔡承宗, 改良孔洞型二氧化矽低介電係數薄膜機械性質. 國立台灣大學化學工程學系碩士論文, 2004.

[61] 張瓊云, 以不同濃度的結構導向試劑TPAOH製備多孔型低介電薄膜. 國立台灣大學化學工程學系碩士論文, 2013

[62] 余俊賢, 以聚氧化乙烯型界面活性劑為模板試劑製備含MFI沸石之中孔洞型低介電薄膜. 國立台灣大學化學工程學系碩士論文, 2010

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