新穎混合型與奈米群聚型多孔隙低介電材料之結構與性質關係研究

Abstract

本研究針對使用延後移除高溫起孔洞劑製程（post-integration porogen removal scheme）的混合型低介電材料，以及使用奈米群聚（nano-clustering）技術的多孔隙二氧化矽低介電材料進行了一連串結構與性質間關係的研究，期望能夠應用於未來半導體製程中。首先，兩種不同的高溫起孔洞劑（porogen）探討起孔洞劑結構對混合型與其相對應的多孔隙低介電材料性質的影響。實驗發現，相對於結構對稱且不具極性官能基的poly(styrene-block-butadiene-block-styrene)（PS-b-PB-b-PS），混合型低介電材料中若使用如poly(styrene-b-4-vinylpyridine)（PS-b-P4VP）此種結構中含有極性官能基的雙嵌段共聚高分子（di-block copolymer）作為起孔洞劑，將會有比較高的薄膜吸水性和介電常數。然而從水氣吸脫附的實驗曲線可以得知，水氣是以物理吸附的方式附著於混合型低介電材料內部，可藉由抽氣或加熱移除。而且薄膜的介電常數在起孔動劑移除後僅和孔隙率有關，不會受到起孔洞劑類型影響。以本研究為例，當基材中添加入40.1 vol%的孔隙率時，介電常數也從原本的2.89下降至2.44。 研究也發現高溫起孔洞劑對於低介電基材「甲基矽氧烷（MSQ，methylsilsesquioxane）」的交聯反應，會因添加量多寡而有不同的影響。以MSQ/PS-b-P4VP系統為例，當起孔洞劑的添加量少於16.7 vol%時，起孔洞劑產生的塑化效應（Plasticization）會促進了MSQ基材的交聯程度。當添加量多於16.7 vol%時，大量的起孔洞劑反而會形成立體障礙，阻止MSQ基材交聯。只要起孔洞劑的添加量低於某一臨界值（在MSQ/PS-b-P4VP系統中約為69.5 vol%），混合型低介電材料的機械強度高於其相對應的多孔隙材料，甚至純MSQ基材。 另一方面，本研究以甲基三甲氧基矽烷（MTMS，methyltrimethoxysilane）添加入沸石材料中，再利用奈米群聚（nano-clustering）技術形成改良型矽氧基沸石（MSZ，modified silica zeolite）材料，探討添加大量MTMS對MSZ材料的基材結構、介電常數和機械強度和孔洞形貌的影響。研究發現雖然添加大量的MTMS可以將MSZ的介電常數降至2.0，但同時也將其機械強度降至2.7 GPa。而根據低入射角小角X光散射（GISAXS，grazing-incidence small-angle X-ray scattering）實驗的分析顯示，MSZ內部的奈米孔洞不是圓球狀而是橢球狀（Rin-plane ~3.75 nm; Rout-of-plane ~3.04 nm）。這是由於在150–160°C時，起孔洞劑tetra-n-propylammonium hydroxide（TPAOH）發生熱裂解反應，同時間MSZ薄膜亦開始大量的交聯反應，使得MSZ薄膜產生約32%的膜厚收縮，造成孔洞形貌改變。綜合GISAXS、29Si-NMR和FT-IR等分析結果，吾人認為大量來自MTMS中的甲基（CH3）是造成MSZ薄膜機械強度下降與孔洞形貌改變的主要原因。

This work examines the structure-property relationship of porous low-k dielectrics such as novel MSQ/high-temperature porogen hybrid materials and nano-clustering materials, and explores their integration feasibility for future technology node. Specifically, the effect of porogen structure on the structure-property relationship in MSQ/porogen hybrid films and their corresponding porous films by using a post-integration porogen removal scheme is investigated. Poly(styrene-b-4-vinylpyridine) containing di-block structure and pyridine polar group possesses higher moisture uptake and k-value in the hybrid films as compared to poly(styrene-block-butadiene-block-styrene) with symmetrical structure and non-polar groups. Moreover, the moisture uptake behavior in both as-prepared hybrid films is in physical sorption mode based on their reversible adsorption-desorption curve measured by quartz-crystal-microbalance. After porogen removal, the k-values of porous films are favorably not influenced by porogen structures. The k-value decreases from 2.89 to 2.44 when a porosity of 40.1 vol% is introduced into a dense MSQ matrix. Furthermore, the moduli of the hybrid films were found to be higher than their porous forms, and even better than the dense MSQ film, for porogen loading below a critical level (~69.5 vol%). This could be attributed to their enhanced degree of crosslinking in MSQ as evidenced by the network/cage structural ratios. Besides, high-temperature porogen plays different roles during the crosslinking of MSQ depending on its loadings. In our study, with immediate loading at 16.7 vol%, PS-b-P4VP can serve as plasticizer to enhance the degree of crosslinking, but at a large loading >16.7 vol%, it becomes a steric hindrance reducing the degree of crosslinking. On the other hand, a methyltrimethoxysilane (MTMS) modified silica zeolite (MSZ) film was prepared using a high ratio of MTMS/tetraethyl orthosilicate (TEOS) to study the structure-property relationship. The study investigated the effect of MTMS addition on the low-k matrix structure, elastic modulus, and pore geometry. High MTMS loading reduced the k-value of MSZ film down to 2.0, but yielded a lower elastic modulus, 2.7 GPa. Based on grazing-incidence small-angle X-ray scattering (GISAXS) analysis, the pore geometry of the MSZ film was found to be small but elliptical (Rin-plane ~3.75 nm; Rout-of-plane ~3.04 nm). The elliptical pore shape was formed by a collapse of film structure at 150–160°C as a result of ~32% thickness shrinkage due to the decomposition of tetra-n-propylammonium hydroxide (TPAOH), a structure directing catalyst, and due to a large degree of crosslinking reaction in the silica matrix. Combining GISAXS, 29Si-NMR, and FT-IR results, we propose that the lower elastic modulus was caused by the incorporation of a large amount of methyl groups from the MTMS precursor and the elliptic pores.