Synthesis of MFI Zeolite Mesoporous Low-k Films Using Poly (ethylene oxide)-based Surfactants as Template

近年有很多文獻提到利用MFI沸石溶液作為塗佈液體，製作超低介電常數薄膜。雖然可做出介電常數大約2左右的薄膜，但其表面卻有不平整的現象。本研究在MFI沸石溶液中添加聚氧化乙烯型界面活性劑 (Tween80、Tween60、Tween40、Tween20)以解決表面不平整的問題，而且可以增加薄膜之中孔洞體積以進一步降低介電常數，所加入界面活性劑/ 四乙基矽的比例為0.41。本研究是以24小時水熱時間之小沸石晶種溶液及42小時水熱時間製作的大沸石結晶溶液為基礎，研究不同的聚氧化乙烯型界面活性劑對塗佈溶液的影響，以及對薄膜性質的影響。研究中並以氮氣吸脫附法量測孔洞體積及孔徑分佈，以了解這些界面活性劑對相關性質的影響。 由實驗結果發現，在塗佈溶液中加入Tween80所製作出來的薄膜有最低的介電常數值以及最高的機械強度 (Elastic modulus, hardness)。氮氣吸脫附實驗結果顯示孔洞體積和所加入的界面活性劑的分子大小有關係；加入的界面活性劑分子愈大，孔洞體積也愈大。然而，薄膜的介電常數值並不隨著孔洞體積的大小而變化。在實驗結果中，孔洞體積較大的薄膜，所製成薄膜的介電常數值較高；而孔洞體積較小的薄膜，反而有較低的介電常數值。本研究以TGA/ DTA量測來討論加入不同界面活性劑塗佈溶液中的氫氧基團和界面活性劑的分子或微胞之間的作用力。結果顯示這些作用力會影響氫氧基團與微胞在塗佈溶液中的位置，若是這些氫氧基團分佈在距離孔洞較遠的位置，會較難完全被修飾成疏水基團，而使薄膜有較高的介電常數值；相反的，若是氫氧基團分佈在較好修飾的位置，則薄膜會有相對較低的介電常數值。 薄膜的機械強度也會被氫氧基團和界面活性劑的分子或微胞之間的作用力所影響。從固態核磁共振儀 (29Si solid state NMR) 的結果顯示，在加入界面活性劑後的攪拌時，較強的作用力會限制氫氧基團的聚合反應，因此在薄膜鍛燒的時候，顆粒和顆粒之間會有較多的氫氧基團進行聚合反應，所以薄膜會有相對較高的機械強度。 本研究中以聚氧化乙烯型界面活性劑為模板試劑所製做的薄膜都符合IC工業的基本需求；介電常數值小於2或是2左右，彈性模數大於10 GPa且硬度大於1 GPa，漏電流也符合低於10-7 (A/cm2)的需求。The synthesis of coating solutions with pure-silica-zeolite (PSZ) of MFI structure for low-k (dielectric constant) films applications was reported a few years ago. Although the k values can be around 2, the morphology of the films was poor. In order to solve this problem and to increase the mesopore volume in the films, the poly (ethylene oxide)-based non-ionic surfactants (such as Tween80, Tween60, Tween40 and Tween20) were added in the coating solution (with PSZ and MFI structure) in this research. The weight ratio of surfactant to tetraethylorthosilicate (TEOS, a silicon source) is 0.41. Two types of coating solutions with small crystalline particles or with large crystalline particles prepared through hydrothermal process were studied. The physical properties (dielectric constant, elastic modulus and harness) of the low-k films were characterized to make a comparison. Moreover, by burning away Tween in the films, the mesopores formed and the pore volume in the films should be increased, which may lower the k values of the films. Therefore, the nitrogen adsorption/ desorption measurements on different films were carried out at 77 K to characterize the effect of different Tweens on the pore volume and pore sizes in the low-k films. It was found in this research that the films synthesized with the addition of Tween80 had the lower k value and the higher mechanical strength (Elastic modulus and hardness), as compared with those prepared with the addition of the other types of Tween. Nitrogen adsorption/ desorption results indicate that the total pore volume is consistent with the molecular size of Tween; in other words, a larger molecular size of Tween possesses a higher total pore volume. However, the dielectric constants are not consistent with the porosity (total pore volume) variation of the low-k films. In order to address the phenomena, TGA/ DTA results were provided to study the interaction between hydroxyl groups and surfactant molecules or surfactant micelles in the coating solutions. The results suggest that the interaction result in that the hydroxyl groups would be located in the position where is hard to be modified to become hydrophobic after the surfactant were removed. Therefore, the k values would be influenced. The mechanical strength was also affected by the interactions between hydroxyl groups and the surfactant. From the results of 29Si solid state NMR spectra, a higher interaction would limit the polycondension reaction between hydroxyl groups during the stirring step. As a result, the low-k films would have a more completed polycondensation reaction among the hydroxyl groups after the calcinations, and the low-k film possessed a higher mechanical strength. All of the low-k films synthesized with the addition of poly (ethylene oxide)-based surfactant met the requirements of IC industry; the low-k value were lower than 2 or around 2, elastic modulus were of > 10 GPa and hardness were of > 1 Gpa, and the values of leakage current density were under the order of 10-7 (A/cm2)