以不同濃度的結構導向試劑TPAOH製備多孔型低介電薄膜

Abstract

近年來有很多文獻利用純二氧化矽沸石的鍍膜溶液，製備出孔洞型二氧化矽低介電薄膜。而根據本實驗室過去的研究，已發展出使用短時間水熱程序，製備出非結晶型二氧化矽奈米顆粒的鍍膜溶液，並可製備出介電係數小於2、且高機械強度的薄膜。本研究承接前人的研究成果，將探討不同濃度的結構導向試劑對低介電係數薄膜所造成的影響。 本研究使用TPAOH (Tetrapropylammonium hydroxide) 作為結構導向試劑，在水熱程序的前驅液中，改變TPAOH/TEOS的莫耳比作為變因，使用比例為0.15、0.25與0.36，並研究所製備出的非結晶型二氧化矽奈米顆粒與薄膜。研究的方向將針對不同莫耳比例(TPAOH/TEOS)對於二氧化矽奈米顆粒粒徑、顆粒表面的鍵結、孔洞型薄膜的孔徑分佈、介電係數、漏電流密度、機械強度與薄膜表面型態等性質所造成的影響，供日後改善製程及其他應用的參考。 實驗結果發現，隨著TPAOH濃度的增加，將使奈米顆粒粒徑縮小。另外，TPAOH濃度也會影響奈米顆粒表面的Si-OH基團數量，導致顆粒表面的親水性質不同，進而影響界面活性劑形成不同程度的聚集。當TPAOH濃度愈低，顆粒表面Si-OH基團越少，親水性較低，而傾向驅使鍍膜溶液中的界面活性劑形成較大的團聚，所製備出的薄膜表面會產生微米級孔洞，而此孔洞會導致薄膜的電性與機械強度不佳；另外，顆粒表面含有較少的Si-OH基團，亦會使顆粒彼此間不易形成縮合鍵結，而降低薄膜機械強度。反之，當TPAOH濃度愈高時，顆粒表面Si-OH基團越多，顆粒表面較親水而傾向使界面活性劑分子吸附於顆粒表面，鍍膜溶液中的微胞較小，因此製備出的薄膜較平整，且薄膜k值為1.94，硬度是1.50 GPa，彈性模數是13.36 GPa，漏電流密度為5.69×10-9A/cm2，其性質皆符合工業標準。

The syntheses of coating solutions with pure silica MFI-type zeolite for the preparation of porous low dielectric constant (low-k) films were reported in literatures. In our previous study, short hydrothermal process for producing coating solutions mainly containing noncrystalline silica has been developed for the preparation of low-k films. The films with not only a k value below 2 but also a high mechanical strength can be obtained. To continue with the research, the effect of concentration of tetrapropylammonium hydroxide (TPAOH, as structure directing agent) on properties of low-k films has been investigated. In this research, the motivation is to study the effect of TPAOH concentration on properties of noncrystalline silica nanoparticles (such as particle size and surface hydrophilic property) and on properties of corresponding low-k films (such as pore properties, dielectric constant, leakage current density, mechanical properties and surface morphology). The properties were examined and discussed in details. It is found that the nanoparticle size decreases with the increase of the TPAOH concentration in the precursor solution. In addition, the content of silanol groups on the surface of silica nanoparticles would also be influenced by the TPAOH concentration. They increase with the increase of the TPAOH concentration. The silica nanoparticles with different surface silanol groups should possess different hydrophilic properties, and therefore would influence the behavior of surfactants in the coating solutions. The lower content of surface silanol groups would lead to the formation of more aggregates of surfactants, resulting in the existence of micro-sized pore on the film surface and thereby causing the electrical properties and mechanical properties of the films to become worse. In addition, the lower content of surface silanol groups on silica nanoparticles would have a negative effect on crosslink formation between different silica nanoparticles, which would contribute to the decrease of mechanical strength of the films. In contrast, the films preprared form silica nanoparticles with higher content of surface silanol groups can possess a uniform surface, an ultra-low k value of 1.94, a high hardness of 1.50 GPa, a high elastic modulus of 13.36 GPa, and a low leakage current density of 5.69×10-9A/cm2.