超低介電孔洞材料MSQ薄膜中起孔洞劑聚集行為及孔洞形貌控制之研究

Abstract

本研究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，主要分為三個部份:(1)探討起孔洞劑(poorgen)於低介電母材中團聚的行為;(2)分散porogen於低介電母材中，並有效控制porogen以及最後孔洞的尺寸;(3)提高母材中porogen的含量，致使更有效降低介電常數維持更小孔洞，並探討其結構與性質間之關係。首先，選用methylsilsesquioxane (MSQ)為母材，polystyrene-b-polybutadiene-b-polystyrene (SBS)作為高溫起孔洞劑，使之形成混合型低介電材料薄膜。在不同升溫速率條件下利用即時動態的grazing incidence small angle X-ray scattering (GISAXS)量測porogen尺寸變化;並以黏度變化和紅外線光譜儀(FT-IR)分析母材結構對porogen尺寸的影響。藉由其交互行為可得知SBS的團聚主要受三個關鍵的溫度影響; (1)母材的玻璃轉換溫度，此時開始有團聚現象，(2)母材開始大量產生交鏈的溫度(或結構由cage轉換成network時)，此時團聚現象更甚，(3) 母材完成交鏈的溫度，此時結構固化，團聚不易產生。確定團聚機制後，第二部分使用polystyrene(PS)作為porogen，並使用陰離子型的dodecylbenzenesulfonate (NaDBS)以及陽離子型的domiphen bromide (DB)界面活性劑將porogen進行表面改質，然後檢測慢速升溫(2oC/min)過程中的porogen尺寸及黏度的變化。研究結果指出，改質過的porogen表面帶有電荷，並存在庫倫力將其排斥並穩定分散於母材中，而且在改質過後的porogen造成的電滯效應使母材整體黏度上昇，使之更不容易擴散或聚集於母材內。另一方面帶有正電的PS會與MSQ母材中的Si−OH有吸引作用，位置會被母材固定住致使更不易團聚，故可達到更佳控制孔洞大小的效果。最後研究將DB改質的PS增量於低介電母材中，用以增加孔隙率並降低介電常數，結果指出孔隙率達到45vol.%以上，介電常數可有效降低，且孔洞呈現獨立圓形，其機械性質因無內連結大型孔洞可維持強度。以往文獻指出porogen的含量大於25wt%或孔隙率達到30vol.%以上時，因為porogen大量聚集而造成熱移除後的大型孔洞，本研究發展一個表面改質方法使porogen可以有效分散porogen於母材中並能提高最後之孔隙率。

This work focuses on the hybrid low-k film in a late-porogen removal scheme. There are three parts are discussed including: (1) the aggregation behavior of porogen in the hybrid film; (2) disperses the porogen in the low-k precursor and control the porogne size (later pore size); (3) increases the loading of porogen in the low-k materials to reduce k value and try to remain the small pore size. Firstly, the interaction between polystyrene-b-polybutadiene-b-polystyrene (SBS) porogen and low-k methylsilsesquioxane (MSQ) matrix under different curing profiles and their impact on porogen size were studied by grazing incidence small angle X-ray scattering (GISAXS), viscosity measurement, and Fourier transform infrared analysis. The aggregation of SBS porogen was greatly influenced by the microstructure of MSQ matrix at three controlling temperatures; namely (1) glass transition temperature, Tg (~100oC), (2) onset temperature (160oC) for transforming cage to network structure, and (3) immobilization temperature (170oC). Secondly, an anionic surfactant, sodium dodecylbenzenesulfonate (NaDBS) and a cationic surfactant, domiphen bromide (DB) were used to modify the surface potential of PS porogen in the low-k film. The NaDBS- and DB-modified porogens with higher surface potential impede their aggregation within the cross-linking MSQ matrix, resulting in a smaller porogen size, by electrostatic repulsion and increased viscosity due to the electroviscous effect. In addition, the columbic attraction between Si−OH groups of MSQ matrix and the positively charged, DB-modified PS, restrains the PS porogen, thus reduces its aggregation during the curing step, leading to small porogen size and tight distribution at 200oC and later a similar pore size after removal of porogen at 400oC. Finally, the different loading of polystyrene (PS) porogen with/without cationic surfactant, domiphen bromide (DB) modification in MSQ appeared for porous low-k films. The pore size, morphology, mechanical strength and k of porous low-k films with different porosity were investigated. The porosity could be increased above 45 vol.% by porogen surface modification, and reduced k from 2.6 to 1.9. The porous film appear the no interconnect pore and maintain the sphere shape. The past paper indicates that porogen occur obvious aggregation at porogen loading>25 wt% (or porosity >30 vol.%). In this work, we develop a method of porogen surface-modification to disperse the porogen in the low-k materials and increase the porogen loading (porosity) effectively.