Collaborative Research: A Combined Experimental and Theoretical Investigation of Plasma Deposition of Nanocrystalline Silicon Films

合作研究：纳米晶硅薄膜等离子体沉积的实验与理论相结合的研究

• 批准号: 0549310
• 负责人: Eray Aydil
• 金额: $ 20.14万
• 依托单位: University of Minnesota-Twin Cities
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2005
• 资助国家: 美国
• 起止时间: 2005-07-01 至 2007-09-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0549310&HistoricalAwards=false
• 关键词: Collaborative; Research; Combined; Experimental; Theoretical

Hydrogenated nanocrystalline silicon (nc-Si:H) thin films grown by plasma-enhanced chemical vapordeposition (PECVD) from feed gases containing silane (SiH4) and hydrogen (H2) have tremendous potential for electronic, optoelectronic, and photovoltaic device fabrication technologies. Plasma-surface interactions during PECVD and subsequent H2 plasma treatment of these films determine their structure and properties. The films may be either polycrystalline, where nanometer-size grains are separated by grain boundaries, or polymorphous where the nanocrystals are embedded in a hydrogenated amorphous Si (a-Si:H) matrix. Fundamental understanding of the plasma-surface interactions that govern the nucleation and growth of the nanocrystalline phase during deposition or post-deposition processing, as well as control of the nanocrystalline grain size distribution are essential for tailoring the electronic and optical properties of the deposited films.This research aims at developing strategies for controlling the grain size and crystalline fraction in nc-Si:Hfilms formed through low-temperature PECVD from SiH4 heavily diluted in H2 or through post treatment of a-Si:H films with H atoms created by plasma dissociation of H2. Toward these goals, the PIs propose a research plan that integrates in situ plasma and surface diagnostics with atomic-scale simulations. They seek a fundamental and quantitative understanding of the role of hydrogen in the nucleation and growth of nanocrystalline silicon films that will aid in manipulating synthesis methods and choosing plasma-processing parameters to gain a better control over the film properties than is currently possible. As a result, the proposed study will set the stage for establishing quantitative relationships between the film's structure (e.g., grain size and crystalline fraction) and plasma processing parameters, such as the H flux and the substrate temperature.The proposed experimental work will focus on synthesizing silicon films containing nanocrystals throughH-atom post treatment of a-Si:H films deposited by PECVD. Fluxes of H atoms will be measured using line-of-sight threshold-ionization mass spectrometry. In situ multiple total internal reflection Fourier transform infrared (MTIR-FTIR) specroscopy will be used to detect silicon hydrides in the growing film and on its grain boundaries. High-resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD), and Raman spectroscopy will provide information on the grain sizes and grain-size distribution, as well as crystalline fraction; spectroscopic ellipsometry will be used in situ during deposition and post treatment to monitor the evolution of these same parameters. In conjunction with the experimental work, molecular-dynamics (MD) simulations of a-Si:H film growth and H2 plasma post treatment will be carried out aiming at both fundamental understanding of the growth and crystallization mechanisms and comprehensive identification of chemical reaction and diffusion processes for subsequent quantitative energetic and rate analysis. The resulting reaction/diffusion database will be used as input for implementing hybrid off-lattice kinetic Monte Carlo (KMC) simulations that are capable of capturing the long-time-scale dynamics of silicon film growth and H2 plasma post treatment. The computational results will becompared directly with the experimental data; the insights gained from the simulations will be used to guide new experimental studies and design new deposition strategies.Intellectual Merit - The proposed research is pioneering in linking experimental diagnostic measurements and structural characterization analyses with computational atomic-scale studies of chemical reactions and crystallization mechanisms. The research is particularly timely given our recent developments of in situ experimental techniques for monitoring plasma-surface interactions and atomic-scale simulation tools. The PIs anticipate that their research findings will enable systematic engineering strategies for controlling thin-film crystallinity and the grain size distribution of nanocrystalline silicon films, which in turn determine the films' electronic and optical properties. In addition, they expect that their research strategy and methodology will be applicable to studying the growth and processing of various other technologically important materials.Broader Impact - The scientific underpinnings of nanostructured materials synthesis and thin-film deposition & processing are multidisciplinary and cut across traditional boundaries between physics, chemistry, chemical engineering, materials science, as well as applied and numerical mathematics. Thus, the proposed systematic study of silicon thin-film deposition and post-deposition processing provides ideal means for training students to address technologically important problems using an integrated, state-of-the-art experimental and computational approach. The results of the research will be disseminated broadly in the physics, chemistry, electronic materials, and plasma engineering communities through publications and conference presentations. The proposed research has the potential to enable technological advancements in low-temperature plasma deposition of nc-Si:H films which will have tremendous impact on fabrication of solar cells for renewable energy production and flexible display manufacturing for consumer electronics.

采用等离子体增强化学气相沉积（PECVD）技术，以硅烷（SiH 4）和氢气（H2）为原料制备氢化纳米晶硅（nc-Si：H）薄膜，在电子、光电和光伏器件制造技术中具有巨大的应用潜力。PECVD和随后的H2等离子体处理这些薄膜过程中的等离子体-表面相互作用决定了它们的结构和性能。薄膜可以是多晶的，其中纳米尺寸的晶粒被晶界分开，或者是多晶的，其中纳米晶体嵌入氢化的非晶Si（a-Si：H）基质中。对等离子体-表面相互作用的基本理解是控制沉积或沉积后处理过程中纳米晶相的成核和生长，以及控制纳米晶晶粒尺寸分布对于定制沉积薄膜的电子和光学性质是必不可少的。通过低温PECVD从在H2中严重稀释的SiH 4形成H膜，或者通过用H2的等离子体解离产生的H原子对a-Si：H膜进行后处理形成H膜。为了实现这些目标，PI提出了一项研究计划，将原位等离子体和表面诊断与原子级模拟相结合。他们寻求对氢在纳米晶硅薄膜的成核和生长中的作用的基本和定量的理解，这将有助于操纵合成方法和选择等离子体处理参数，以获得比目前可能的更好地控制薄膜性能。因此，拟议的研究将为建立薄膜结构（例如，晶粒尺寸和晶化率）和等离子体处理参数（如氢流量和衬底温度）的影响，本论文的实验工作将集中于通过氢原子后处理PECVD沉积的a-Si：H薄膜来合成含纳米晶的硅薄膜。氢原子的通量将使用视线阈值电离质谱法测量。原位多重全内反射傅里叶变换红外光谱（MTIR-FTIR）将用于检测生长膜中及其晶界上的硅杂质。 高分辨率透射电子显微镜（HRTEM）、X射线衍射（XRD）和拉曼光谱将提供有关晶粒尺寸和晶粒尺寸分布以及结晶分数的信息;在沉积和后处理期间将原位使用光谱椭圆偏振法来监测这些相同参数的演变。结合实验工作，a-Si：H薄膜生长和H2等离子体后处理的分子动力学（MD）模拟将进行旨在生长和结晶机制的基本理解和化学反应和扩散过程的全面识别，为随后的定量能量和速率分析。由此产生的反应/扩散数据库将被用作输入，用于实施混合非晶格动力学蒙特卡罗（KMC）模拟，能够捕获长时间尺度的动态硅膜生长和H2等离子体后处理。计算结果将直接与实验数据相结合;从模拟中获得的见解将用于指导新的实验研究和设计新的沉积策略。智力优点-拟议的研究是开创性的，将实验诊断测量和结构表征分析与化学反应和结晶机制的计算原子尺度研究联系起来。这项研究是特别及时的，因为我们最近发展了原位实验技术，用于监测等离子体表面相互作用和原子尺度的模拟工具。PI预计，他们的研究结果将使系统的工程策略，控制薄膜结晶度和纳米晶硅薄膜的晶粒尺寸分布，这反过来又决定了薄膜的电子和光学性能。更广泛的影响-纳米结构材料合成和薄膜沉积工艺的科学基础是多学科的，跨越了物理学、化学、化学工程、材料科学以及应用数学和数值数学之间的传统界限。因此，拟议的硅薄膜沉积和沉积后处理的系统研究为培训学生使用集成的、最先进的实验和计算方法解决重要的技术问题提供了理想的手段。 研究结果将通过出版物和会议报告在物理，化学，电子材料和等离子体工程界广泛传播。拟议的研究有可能实现nc-Si：H薄膜低温等离子体沉积的技术进步，这将对可再生能源生产的太阳能电池制造和消费电子产品的柔性显示器制造产生巨大影响。