溴化十二烷基二甲胺致孔劑 對低介電多孔性MSQ結構與性質的影響

Abstract

旋塗式低介電材料的水氣吸附以及致孔劑量增加後，致孔劑群聚，孔洞變大等問題急待解決。致孔劑群聚的問題，可利用帶有電荷以及高電位的界面活性劑改質致孔劑，或是直接利用界面活性劑形成微胞作為致孔劑。本研究以溶膠凝膠法合成MSQ (methyl silsesquioxane)基材，溴化十二烷基二甲胺為致孔劑，乙酸乙酯當作溶劑。另製備不同致孔劑含量的MSQ/DB混合薄膜, 再燒結形成多孔性MSQ低介電材料薄膜。也分析及探討其結構(包括孔洞大小、孔隙率)及材料特性(介電常數、楊氏彈性係數,光學性質) 。 吾人發現在高致孔劑含量（25 wt% DB）下,多孔性MSQ膜含有相常高的孔隙率(~39%) ， 其介電常數由3.15 (0 wt% DB)下降至2.2, 楊氏彈性係數也降至1.4 GPa。藉由同步輻射光源的小角度X光散射分析,得到的孔洞結構是均勻分散而且孔洞大小控制在3.1-5.8 nm。此可歸究於DB的雙親特性，其於乙酸乙酯溶劑中，微胞間產生的靜電排斥性, 在初成膜與高溫熱處理過程中， 避免或減緩群聚發生。因而,致孔劑含量增加時，孔洞可以被控制在一個較小的尺寸。

The moisture-induced dielectric degradation and aggregated pore/porgen sizes are two challenging issues for the spin-on porous low-k dielectric films. For the aggregated pore/progen, the porogen can be modified by a surfactant with a charge and high zeta potential or a surfactant capable of forming micelle structures as the porogen directly. In this study, porous low-k silsesquioxane (MSQ) films are fabricated using sol-gel MTMS as the matrix, domiphen bromide (DB) as template or porogen, and ethyl acetate (EA) as the solvent. The structure (including pore size and porosity) and properties such as dielectric constant, Young’s modulus, refractive index are characterized and discussed. Domiphen bromide is found to be a promising porogen to spin-on MSQ matrix for fabricating a nanoporous low-k thin film. Under a relatively high porogen loading (25 wt%), the porous low-k film possesses a high porosity, ~39%, and a dielectric constant of 2.2, which shows 28% reduction compared to 3.15 for a solid MSQ film. Moreover, the pore sizes measured by grazing incidence small angle X-ray scattering (GISAXS) at NSRRC, are spherical and uniform in 3.1-5.8 nm range. The pore size and distribution behavior can be attributed to amphiphilic property of DB dissolved in ethyl acetate (EA), in which the electrorepulsive micelles do not aggregate or delay the aggregation during the drying of as-deposited film and thermal curing step. As a result, the pore size of porous low-k MSQ films in this study can be contained at a small size, i.e. 3.1-5.8 nm even the porogen loading is increased up to 25 wt% (or 39% porosity).