探討製備孔洞型二氧化矽低介電薄膜前驅液組成及製程對薄膜性質的影響

Study the Effect of Composition and Preparation Process of Precursor Solution on the Properties of Porous Low-k Silica Thin Films

黃啟達(Qi-Da 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(2005年)

https://doi.org/10.6342/NTU.2005.10374

摘要

本研究主要是探討製備孔洞型二氧化矽低介電薄膜前驅液中，各組成對前驅液pH值的影響，前驅液的配製及靜置對薄膜性質的影響。孔洞型二氧化矽薄膜是近年一項相當有應用性的研究題目。增加孔洞體積能使介電係數有效地降低，但也造成材料的機械強度不足，因此本研究藉由量測前驅液的pH值及改變製備前驅液的製程，嘗試研發改善孔洞型二氧化矽低介電薄膜的性質的方法。
　　由迴流前、後的pH值變化及比較不同溶液在迴流後攪拌期間的pH值，發現當前驅液加入鹼性有機鹽TPAOH時，不只是與HCl有酸鹼中和的反應，也會與模板試劑Tween80所形成的微胞發生作用。另外，本研究發現當TPAOH在迴流後隨著Tween80一同加入前驅液中，旋塗薄膜表面有明顯的二氧化矽顆粒，發現此現象所形成的原因是，由於TPAOH無法即刻均勻溶解於溶液中，使局部溶液具較高的鹼性，因此形成較大顆粒狀之二氧化矽。
　　由改變前驅液配製的製程，本研究發現較多酸量的前驅液經迴流程序後，所製備的薄膜雖有較低的介電係數及較高的機械強度，但由電性曲線也發現其結構有較多的缺陷。以Tween80作為模板試劑時，前驅液中添加分子較大的有機鹽所製備的薄膜介電係數較低，機械強度略有改善。若以Brij56作為模板試劑，以不迴流、HCl/TEOS=0.25（高酸量）所製備的薄膜整體性質為較佳；而迴流程序中，有機鹽類添加的時機對於薄膜性質的影響並不明顯。以Brij56為模板試劑且使用具高酸量的前驅液，在靜置六日後所製備的薄膜介電係數會明顯提高；而具低酸量（HCl/TEOS=0.03）且使用迴流程序製備的前驅液，靜置前驅液的時間對於薄膜介電性質的影響並不明顯。
　　本研究結論出前驅液中的酸量是影響二氧化矽結構最主要的因素。在前驅液不靜置的前提下，以前驅液組成為：Brij56作為模板試劑、不迴流、HCl/TEOS=0.25（高酸量）、不添加任何有機鹽，所製備的薄膜性質較佳，其薄膜具有以下性質：介電係數及漏電流為：1.94及2.23E-07 A/cm2；硬度及彈性係數為：0.758 GPa及8.034 GPa。

關鍵字

低介電 ； 孔洞材料 ； 薄膜 ； 旋轉塗佈 ； 界面活性劑模板法 ； 模板

並列摘要

The pH values of precursor solutions and the effect of preparation processes for precursor solutions on the properties of porous low-k silica thin film were studied in this research. Porous silica thin film has been widely studied; for it can possess low dielectric constant under appropriate preparation conditions. The increasing number of pores can effectively lower dielectric constant; however, the insufficient mechanical strength is sequential shortcoming. It was found that the composition of precursor solution and the process for preparing precursor solution would have great influence on mechanical strength of porous silica thin film. Therefore, the properties improvement of porous silica thin film was carried out by observing pH values of precursor solutions and by altering the processes for preparing the precursors.

　　From observing the variation of pH values through reflux process and comparing the pH values among different solutions during reflux process, it was found that the added basic organic salt not only reacted with HCl but also with the micelles that formed from the template, Tween80. Furthermore, when the basic organic salt, TPAOH, was added along with Tween 80 into the coating (precursor) solution after the reflux, there were apparent silica particles formed on the spin-on thin film. They came from the local higher basic region in the solution, because TPAOH could not be dissolved in the coating solution immediately.

　　By altering the process for preparing precursor solution, it was found that the thin films possessed lower dielectric constant and higher mechanical strength from the precursor solution, which contained more HCl and went through the reflux process; however due to imperfect SiO2 structure, the film was observed with more trapped charges from C-V curve. When Tween80 was used as the template, the thin films possessed lower dielectric constant. And the mechanical strength was slightly improved by adding organic salt, TBAOH (with a molecule size larger than TPAOH), to the precursor solution. When Brij56 was used as the template in the precursor containing HCl/TEOS=0.25, which did not go through the reflux process, the resulting thin films possessed better properties. The timing for adding organic salt was not an apparent factor for changing the properties of thin films. However, the dielectric constants of thin films were increased after the precursor solution aged for 6 days.

　　In this research it was found that the most significant factor affecting the properties of SiO2 film was the amount of HCl added in the precursor solution. When the precursor solutions are fresh (before aging), the thin films with the best performance among those tested in this study are produced under the following conditions: non-reflux, non-adding organic salt, and HCl/TEOS=0.25 in the precursor solution. The resulting properties are the followings: dielectric constant= 1.94, leakage current density= 2.23E-07 A/cm2, hardness= 0.758 GPa and elastic modulus= 8.034 GPa.

並列關鍵字

low dielectric constant ； low-k ； porous material ； thin film ； spin coating ； surfactant-templated method ； template

參考文獻

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