以不同的四烷基氫氧化銨為鹼性試劑製備孔洞型二氧化矽低介電薄膜

Preparation of Porous Silica Low-k Film by Using Different Tetraalkylammonium Hydroxide

黃瀚友(Han-Yeou Huang)

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(2012年)

https://doi.org/10.6342/NTU.2012.00214

摘要

近年來有很多文獻利用純二氧化矽沸石之鍍膜溶液，製備孔洞二氧化矽低介電(low-k)薄膜。但是發展至今，僅四丙基氫氧化銨(TPAOH)所製備的MFI沸石薄膜能符合未來積體電路工業應用條件(介電係數小於2，硬度大於1 GPa，彈性係數大於10 GPa)。然而比起MFI沸石，BEA和MEL沸石的結構密度更低，應更有潛力製備二氧化矽低介電薄膜。因此本研究是利用不同的四烷基氫氧化銨(TEAOH、TPAOH、TBAOH)當作鹼性試劑，以水熱24小時及水熱36小時程序，分別合成BEA、MFI、MEL沸石並用來製備低介電薄膜，除了期望能符合工業應用條件之外，還要分析BEA、MFI以及MEL沸石在薄膜製備過程中可能發生的機制，供日後改善製程以及其他應用的參考。
　　實驗結果發現，僅MFI沸石薄膜能符合工業需求。而MEL沸石薄膜除了k值偏高之外，其他條件也能符合工業需求；BEA沸石薄膜最大的問題是漏電流普遍偏高。整體來說，這些不同沸石薄膜最大的差異在於k值以及漏電流，為了探究造成電性差異的原因，本研究以FTIR分析薄膜中尚未被修飾的Si-OH基團，並證實了的確是這些Si-OH基團造成薄膜電性差異的主因。
　　為了分析造成差異的原因，本研究先以solid state 29Si NMR分析鍍液於鍛燒前的Si-OH基團比例，結果發現鍛燒前Si-OH基團比例較高的鍍液，其製備的薄膜經鍛燒修飾後的Si-OH基團比例反而最低，呈現相反趨勢。因此本研究進一步以TGA/DTA及solid state 29Si NMR討論鍍液中界面活性劑Tween80與這些不同表面特性沸石之作用力，再推論鍛燒前，到鍛燒修飾後可能發生的機制。本研究推論，當沸石與Tween80作用力越強，其Si-OH基團可能裸露於孔壁上，因此比較容易修飾為疏水基，使薄膜有較低之k值以及漏電流。
　　本研究結果發現，薄膜內殘留的Si-OH基團比例、沸石與Tween80之作用力、沸石的熱膨脹係數薄膜皆會影響薄膜性質。而本研究中最佳的薄膜是MFI沸石薄膜，k值為1.94，硬度是1.72 GPa，彈性係數是14.95 GPa，漏電流1.24×10^(-8) A/cm2，均能符合未來工業需求。

關鍵字

MFI沸石 ； MEL沸石 ； BEA沸石 ； 界面活性劑 ； 低介電係數薄膜

並列摘要

The synthesis of coating solutions with pure silica zeolite (PSZ) for porous low dielectric constant (low-k) films has been reported in literatures. However, only MFI zeolite low-k films were reported to solve the requirements of future integrated circuit (IC) industry, which are that k values below 2, elastic modulus higher than 10 GPa and hardness more than 1 GPa. The other types of zeolite (such as BEA and MEL) which have lower framework densities than that of MFI zeolite should have possessed higher porosity for making films with lower k values, but have not been thoroughly investigated. Therefore, in this research, by using TPAOH, TBAOH and TEAOH as templates, PSZ MFI, MEL, and BEA colloidal solutions have been synthesized through hydrothermal processes. Different zeolite type low-k films have been coated. The properties of those films were examined and discussed in details.
　　It has been found from this research that the films prepared with BEA and MEL zeolites still cannot meet the requirements of future IC industry. In general, k values and leakage current densities are higher than those expected. FTIR experiments were carried out to investigate the causes. It has been found that they are correlated to the Si-OH groups remaining within the films after the surface modification by using silane. More Si-OH groups within the films would be resulting higher k values and leakage current.
　　Experiments of solid state 29Si NMR have also been employed to study Si-OH of dried powder samples (without calcined) from coating solutions. However, the results of dried powder samples were opposite to the results from the films. To study the phenomena, the interaction between surfactants and silica particles was checked by using thermal analyses. It has been inferred from this research that the stronger interaction strength can cause more Si-OH groups to expose on the surface of pore walls and to be easier modified to be hydrophobic. Therefore, the resulting films can contain less Si-OH remaining and can possess both of lower k values and lower leakage current.
　　It has been found in this research that the Si-OH remaining within the films, the thermal expansion coefficient of silica species, and the interaction between surfactants and silica species are important factors to influence the properties of low-k films. It is still that only low-k film synthesized from PSZ MFI can meet the requirements of future IC industry, with k value lower than 2, leakage current densities lower than 10^(-6) A/cm2, elastic modulus higher than 10 GPa and hardness higher than 1 GPa.

並列關鍵字

Pure silica zeolite (PSZ) MFI ； PSZ MEL ； PSZ BEA ； surfactant ； low dielectric constant (low-k) film

參考文獻

[78] Ralph K. Iler, The chemistry of silica1979: Wiley. 377.

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