Nanoscale Structure and Dynamics of Self-Organized Steps on Silicon Surfaces

该项目旨在更好地理解硅表面台阶的自发形成、自组织和远程模式形成。该方法包括：(1)表面分解二硼烷（B2H6），以可控的方式直接向表面添加硼，而不是使用重硼掺杂的硅片。“热”扫描隧道显微镜（STM）将用于实时原子分辨率测量B2H6分解，硼掺入（有或没有额外的Si通量），以及由此产生的原子尺度台阶形成和/或表面粗糙化。(2)“扁平”Si（001）衬底（阶地宽度可达20微米）将用于研究长程阶梯组织现象，以避免“邻近”阶梯带来的复杂性。扁平的Si（001）衬底允许实验直接研究长程弛豫效应在台阶形成和组织过程中的作用，并确定在台阶上形成的大型台阶“上层结构”的平衡形状。(3)低能电子显微镜（LEEM）将用于实时研究向表面添加硼时大规模台阶形成的过程。第二项研究涉及由于表面电迁移力而导致的Si（001）表面上台阶的大规模组织。Si（001）表面电迁移现象的定量测量和建模研究包括几种方法。(1)“凹陷”硅片衬底，直接研究电迁移现象如何依赖于局部表面误切与施加电流之间的角度。(2)对Si（001）表面的“交叉步骤”进行详细的测量和建模，以提取表面硅原子的“有效电荷”（及其可能的各向异性）的定量信息。(3)对地表电迁移现象进行LEEM测量。跨步演化的实时测量将用于直接测试跨步模型，并提取有关产生表面电迁移现象的重要表面过程的定量信息。该研究将利用三个现有的超高真空（UHV） STM设备（一个商用变温STM系统和两个定制的室温STM系统）和一个现有的商用原子力显微镜（AFM）系统。亚利桑那州立大学的合作研究将使用两个独立的特高压LEEM系统。该项目涉及材料科学中具有高技术相关性的主题领域的基础研究问题。这些研究将提高对硅表面工艺的基本理解，这是硅基微电子微型化最终极限的几个问题的关键。现在有了实验工具，可以在原子水平上观察基本的表面过程，这些过程一旦得到更好的理解，就会促进基础科学和技术的进步。该计划的一个重要特点是通过培养学生在一个基础和技术上重要的领域的研究和教育的整合。* * *

This project aims for greater understanding of spontaneous formation, self-organization, and long-range pattern formation of steps on silicon surfaces. The approach includes: (1) Surface decomposition of diborane (B2H6) to directly add boron to the surface in a controlled manner, instead of using heavily boron-doped Si wafers. "Hot" scanning tunneling microscopy (STM) will be used to make real-time atomic-resolution measurements of B2H6 decomposition, boron incorporation (with and without an additional Si flux), and resulting atomic-scale step formation and/or surface roughening. (2) "Flattened" Si(001) substrates (with terraces up to 20 um wide) will be used to study long-range step organization phenomena so as to avoid complications imposed by "vicinal" steps. Flattened Si(001) substrates permit experiments to study directly the role of long-range relaxation effects in the step formation and organization process, and to determine the equilibrium shape of large-scale step "superstructures" that form on the terrace. (3) Low energy electron microscopy (LEEM) will be used for real-time studies of large-scale step formation as boron is added to the surface. A second line of research concerns large-scale organization of steps on Si(001) surfaces due to surface electromigration forces. Quantitative measurement and modeling studies of electromigration phenomena on Si(001) surfaces include several approaches. (1) "Dimpled" Si wafer substrates to directly study how electromigration phenomena depend on the angle between the local surface miscut and an applied current. (2) Detailed measurement and modeling of "crossing steps" on the Si(001) surface will be done to extract quantitative information about the "effective charge" (and its possible anisotropy) of surface silicon atoms. (3) LEEM measurements of surface electromigration phenomena will be conducted. Real-time measurements of crossing-step evolution will be used to directly test crossing-step models, and extract quantitative information about the important surface processes that produce surface electromigration phenomena. The research will make use of three existing ultra-high vacuum (UHV) STM facilities (a commercial variable-temperature STM system and two custom-built room-temperature STM systems), and an existing commercial atomic force microscopy (AFM) system. Collaborative studies at Arizona State University will use two separate UHV LEEM systems.%%% The project addresses basic research issues in a topical area of materials science with high technological relevance. These studies will improve fundamental understanding of silicon surface processes, which are key to several issues in ultimate limits of silicon-based microelectronics miniaturization. Experimental tools are now available to allow atomic level observation of elementary surface processes which when better understood allow advances in fundamental science and technology. An important feature of the program is the integration of research and education through the training of students in a fundamentally and technologically significant area. ***