Young Matthias J, Bedford Nicholas M, Yanguas-Gil Angel, Letourneau Steven, Coile Matthew, Mandia David J, Aoun Bachir, Cavanagh Andrew S, George Steven M, Elam Jeffrey W
Department of Biomedical, Biological, and Chemical Engineering, University of Missouri, Columbia 65211, Missouri, United States.
Department of Chemistry, University of Missouri, Columbia 65211, Missouri, United States.
ACS Appl Mater Interfaces. 2020 May 20;12(20):22804-22814. doi: 10.1021/acsami.0c01905. Epub 2020 May 6.
Atomic layer deposition (ALD) is a well-established technique for depositing nanoscale coatings with pristine control of film thickness and composition. The trimethylaluminum (TMA) and water (HO) ALD chemistry is inarguably the most widely used and yet to date, we have little information about the atomic-scale structure of the amorphous aluminum oxide (AlO) formed by this chemistry. This lack of understanding hinders our ability to establish process-structure-property relationships and ultimately limits technological advancements employing AlO made ALD. In this work, we employ synchrotron high-energy X-ray diffraction (HE-XRD) coupled with pair distribution function (PDF) analysis to characterize the atomic structure of amorphous AlO ALD coatings. We combine and HE-XRD measurements on ALD AlO and fit these experimental data using stochastic structural modeling to reveal variations in the Al-O bond length, Al and O coordination environment, and extent of Al vacancies as a function of growth conditions. In particular, the local atomic structure of ALD AlO is found to change with the substrate and number of ALD cycles. The observed trends are consistent with the formation of bulk AlO surrounded by an O-rich surface layer. We deconvolute these data to reveal atomic-scale structural information for both the bulk and surface phases. Overall, this work demonstrates the usefulness of HE-XRD and PDF analysis in improving our understanding of the structure of amorphous ALD thin films and provides a pathway to evaluate how process changes impact the structure and properties of ALD films.
原子层沉积（ALD）是一种成熟的技术，可用于沉积纳米级涂层，能够精确控制薄膜厚度和成分。三甲基铝（TMA）和水（H₂O）的ALD化学过程无疑是应用最为广泛的，然而迄今为止，我们对通过这种化学过程形成的非晶态氧化铝（Al₂O₃）的原子尺度结构了解甚少。这种认知上的不足阻碍了我们建立工艺-结构-性能关系的能力，最终限制了采用ALD制备的Al₂O₃的技术进步。在这项工作中，我们采用同步加速器高能X射线衍射（HE-XRD）结合对分布函数（PDF）分析来表征非晶态Al₂O₃ ALD涂层的原子结构。我们对ALD Al₂O₃进行了HE-XRD测量，并结合这些测量结果，使用随机结构模型拟合这些实验数据，以揭示Al-O键长、Al和O配位环境以及Al空位程度随生长条件的变化。特别是，发现ALD Al₂O₃的局部原子结构会随着衬底和ALD循环次数而变化。观察到的趋势与由富O表面层包围的块状Al₂O₃的形成一致。我们对这些数据进行反卷积，以揭示体相和表面相的原子尺度结构信息。总体而言，这项工作证明了HE-XRD和PDF分析在增进我们对非晶态ALD薄膜结构理解方面的有用性，并提供了一条评估工艺变化如何影响ALD薄膜结构和性能的途径。
