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: 0317459
• 负责人: Eray Aydil
• 金额: $ 30.01万
• 依托单位: University of California-Santa Barbara
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2003
• 资助国家: 美国
• 起止时间: 2003-10-01 至 2005-11-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0317459&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.

以硅烷(SiH4)和氢气(H2)为原料，等离子体增强化学气相沉积(PECVD)法制备的氢化纳米硅(nc-Si：H)薄膜在电子学、光电子学和光伏器件制造技术中具有巨大的潜力。PECVD过程中的等离子体-表面相互作用以及随后的氢等离子体处理决定了这些薄膜的结构和性能。薄膜可以是多晶膜，其中纳米尺寸的颗粒被晶界分开，或者是多晶性的，其中纳米晶嵌入到氢化的非晶硅(a-Si：H)基质中。在沉积或后沉积过程中，控制纳米晶相成核和长大的等离子体-表面相互作用以及纳米晶尺寸分布的控制对于调整沉积薄膜的电学和光学性能是至关重要的。本研究旨在开发控制nc-Si：H薄膜的晶粒尺寸和晶化分数的策略，所述nc-Si：H薄膜是通过低温PECVD从氢气中大量稀释的SiH4形成的，或者通过对含有氢的a-Si：H薄膜进行后处理而形成的。为了实现这些目标，PI提出了一项将原位等离子体和表面诊断与原子尺度模拟相结合的研究计划。他们试图从根本上和定量地了解氢在纳米硅薄膜成核和生长中的作用，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的薄膜性能控制。因此，这项研究将为建立薄膜结构(如晶粒度和晶化分数)与等离子体工艺参数(如氢通量和衬底温度)之间的定量关系奠定基础。拟议的实验工作将集中在通过对PECVD沉积的a-Si：H薄膜进行原子后处理来合成含有纳米晶的硅薄膜。氢原子的通量将用视线阈值电离质谱仪测量。利用多重全内反射傅里叶变换红外光谱(MTIR-FTIR)原位检测生长薄膜及其晶界上的硅氢化物。高分辨率电子显微镜(HRTEM)、X射线衍射仪(X射线衍射仪)和拉曼光谱将提供晶粒度和晶粒度分布以及结晶分数的信息；椭圆偏振光谱将在沉积和后处理过程中原位使用，以监测这些参数的演变。结合实验工作，将对a-Si：H薄膜生长和氢等离子体后处理进行分子动力学(MD)模拟，以期从根本上理解生长和结晶机制，并全面识别化学反应和扩散过程，以便随后进行定量的能量和速率分析。得到的反应/扩散数据库将被用作实施混合非晶格动力学蒙特卡罗(KMC)模拟的输入，该模拟能够捕捉硅薄膜生长和氢等离子体后处理的长时间尺度动力学。计算结果将直接与实验数据进行比较；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。智能价值-建议的研究在将实验诊断测量和结构表征分析与化学反应和结晶机理的计算原子尺度研究相结合方面具有开创性。鉴于我们在监测等离子体-表面相互作用的现场实验技术和原子尺度模拟工具方面的最新发展，这项研究尤其及时。PIs预计，他们的研究成果将使控制薄膜结晶度和纳米晶硅薄膜的颗粒尺寸分布的系统工程策略成为可能，这反过来又决定了薄膜的电子和光学特性。此外，他们预计他们的研究策略和方法将适用于研究各种其他重要技术材料的生长和加工。博德影响-纳米结构材料合成和薄膜沉积与加工的科学基础-是多学科的，跨越了物理、化学、化学工程、材料科学以及应用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、电子材料和等离子工程界广泛传播。所提出的研究有可能使低温等离子体沉积nc-Si：H薄膜的技术进步，这将对用于可再生能源生产的太阳能电池的制造和消费电子产品的柔性显示器制造产生巨大影响。