亚十纳米相区嵌段共聚物/离子液体薄膜的热退火相分离研究

Poly (styrene-b-methyl methacrylate) (PS-b-PMMA) block copolymer has shown excellent promise as templates for nanomanufacturing by integrated into existing manufacturing processes, but weak block incompatibility limits its utility for the next generation lithographic applications. For PS-b-PMMA, limit of the minimum feature size is about ~12 nm by thermally annealing at 200 °C.To find a block copolymer with domain size less than 10 nm under thermal annealing and capability of pattern transfer is the key factor and a big challenge for the area of directed self-assembly technology. In our previous work, a room temperature ionic liquid, i.e., hexyl methylimidazoliumhexafluorophosphate (HMHF) has been employed to increase block incompatibility of PS-b-PMMA under thermally annealing conditions. HMHF preferentially pervades the PMMA block domain in PS-b-PMMA because of their compatility. With the aid of HMHF, perpendicular orientation of PS-b-PMMA thin films is achieved on silicon substrates, which is grafted with hydroxyl terminated random copolymers of styrene and methyl methacrylate.The HMHF facilitates the enhancement of effective interaction parameter (χeff) between the PS and PMMA block, resulting in the formation of enlarged domain period and modified interphase. In this project,we will systematically study the role of the ionic liquid and the interaction between ionic liquid and PS-b-PMMA on the phase separation of block copolymer under thermal annealing. In order to simulate the χeff value, charge effect will be considered to construct new model of phase separation under different thermal annealing conditions. The small angle X-ray scattering and rheometer will be used to detect the order-disorder transition of PS-b-PMMA and ionic liquid system. Moreover, by carefully design the chemical composition of the substrate, thin film of PS-b-PMMA and ionic liquid system with perpendicular sub-10nm lamellar domain will be attained through thermal annealing.

能通过热退火形成亚十纳米垂直相区的嵌段共聚物薄膜是目前引导组装领域的研究热点。聚苯乙烯/聚甲基丙烯酸甲酯（PS-b-PMMA）是迄今用于嵌段共聚物引导组装最为成功的品种，但其相互作用参数较低，因而通常认为临界相区尺寸无法突破十纳米以下。前期工作通过采用一种高沸点离子液体己基甲基咪唑六氟磷酸盐（HMHF）与PS-b-PMMA简单掺混，HMHF与PMMA嵌段微区相容，痕量离子液体通过热退火处理提高PS与PMMA的不相容性，使其能够相分离形成亚十纳米尺寸相区。本项目拟深入探索离子液体与PMMA链结合作用对不同热退火条件下薄膜相分离的影响机制，考虑长程电荷作用建立模型，归纳出有效相互作用参数的经验方程。使用旋转流变仪和小角X射线衍射仪研究嵌段共聚物/离子液体体系的有序无序转变规律，通过界面化学调控在优化的热退火条件下得到亚十纳米尺寸垂直相区的PS-b-PMMA嵌段共聚物薄膜。

嵌段共聚物引导组装是半导体光刻工艺重要备选技术之一。遴选出能满足热退火、刻蚀工艺要求，且相区为亚十纳米或更低尺寸的嵌段共聚物是当前国际研究热点。聚苯乙烯/聚甲基丙烯酸甲酯（PS-b-PMMA）与现有光刻工艺相容性最佳，是广泛应用在引导组装的一种嵌段共聚物，但其相互作用参数较低，半节距尺寸难以达到十纳米以下。针对此挑战，本项目的主要研究工作是通过离子液体掺混，促使无序态PS-b-PMMA嵌段共聚相分离形成亚十纳米垂直结构薄膜。主要开展了三个方面的研究工作：第一，利用差式扫描量热，接触角等表征了离子液体己基甲基咪唑六氟磷酸盐（HMHF）在嵌段共聚物中热退火后的分布，通过旋转流变仪和小角X射线衍射仪研究嵌段共聚物/离子液体带电体系的有序-无序转变规律，考察了不同热退火温度下相区尺寸的变化得出相互作用参数受温度的影响规律，并考虑长程电荷作用针对有效相互作用参数进行拟合，建立模型归纳出有效相互作用参数的经验方程；第二，通过合成不同MMA含量的含羟基P(S-r-MMA)无规共聚物，通过接触角测试定量分析其极性变化规律，就各个体系的界面能进行调试从而得到小尺寸垂直相区结构的中性化学基底，研究不同薄膜厚度下界面性质对薄膜表面形貌的影响规律；第三，与国外课题组合作，通过遴选出适用的离子液体，在大面积基底上引导组装制备出了半节距尺寸低至8.25纳米的PS-b-PMMA层状有序图案。本项目的重要研究结果为下一代半导体光刻工艺提供了一种重要的添加剂解决方案。