Institute for Molecular Engineering , University of Chicago , Chicago , Illinois 60637 , United States.
imec , Kapeldreef 75 , B-3001 Leuven , Belgium.
ACS Appl Mater Interfaces. 2018 Jul 11;10(27):23414-23423. doi: 10.1021/acsami.8b05247. Epub 2018 Jun 27.
Directed self-assembly (DSA) of block copolymers (BCPs) can achieve perfectly aligned structures at thermodynamic equilibrium, but the self-assembling morphology can become kinetically trapped in defective states. Understanding and optimizing the kinetic pathway toward domain alignment is crucial for enhancing process throughput and lowering defectivity to levels required for semiconductor manufacturing, but there is a dearth of experimental, three-dimensional studies of the kinetic pathways in DSA. Here, we combined arrested annealing and TEM tomography to probe the kinetics and structural evolution in the chemoepitaxy DSA of PS- b-PMMA with density multiplication. During the initial stages of annealing, BCP domains developed independently at first, with aligned structures at the template interface and randomly oriented domains at the top surface. As the grains coarsened, the assembly became cooperative throughout the film thickness, and a metastable stitch morphology was formed, representing a kinetic barrier. The stitch morphology had a three-dimensional structure consisting of both perpendicular and parallel lamellae. On the basis of the mechanistic information, we studied the effect of key design parameters on the kinetics and evolution of structures in DSA. Three types of structural evolutions were observed at different film thicknesses: (1) immediate alignment and fast assembly when thickness < L ( L = BCP natural periodicity); (2) formation of stitch morphology for 1.25-1.45 L; (3) fingerprint formation when thickness >1.64 L. We found that the DSA kinetics can be significantly improved by avoiding the formation of the metastable stitch morphology. Increasing template topography also enhanced the kinetics by increasing the PMMA guiding surface area. A combination of 0.75 L BCP thickness and 0.50 L template topography achieved perfect alignment over 100 times faster than the baseline process. This research demonstrates that an improved understanding of the evolution of structures during DSA can significantly improve the DSA process.
定向自组装（DSA）可以在热力学平衡时实现完美排列的结构，但自组装形态可能会在动力学上被困在缺陷状态。理解和优化向畴对齐的动力学途径对于提高工艺吞吐量和降低缺陷率以达到半导体制造要求至关重要，但在 DSA 中，对动力学途径的实验、三维研究还很缺乏。在这里，我们结合了 arrested annealing 和 TEM 断层扫描来探测 PS-b-PMMA 在密度倍增的化学外延 DSA 中的动力学和结构演变。在退火的初始阶段，BCP 畴首先独立发展，在模板界面处具有对齐的结构，在顶部表面处具有随机取向的畴。随着晶粒粗化，组装在整个薄膜厚度上变得协作，形成了一种亚稳态缝合形态，代表了一个动力学障碍。缝合形态具有由垂直和平行层片组成的三维结构。基于机械信息，我们研究了关键设计参数对 DSA 中动力学和结构演变的影响。在不同的薄膜厚度下观察到了三种类型的结构演变：（1）当厚度<L（L=BCP 自然周期）时，立即对齐和快速组装；（2）在 1.25-1.45 L 时形成缝合形态；（3）当厚度>1.64 L 时形成指纹形态。我们发现通过避免形成亚稳态缝合形态，可以显著改善 DSA 的动力学。增加模板形貌也通过增加 PMMA 导向表面积来增强动力学。将 0.75 L 的 BCP 厚度和 0.50 L 的模板形貌相结合，可以实现比基线工艺快 100 多倍的完美对齐。这项研究表明，对 DSA 过程中结构演变的理解的提高可以显著改善 DSA 过程。
