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、自组织和远程图案形成。该方法包括：(1)表面分解二硼烷(B2H6)，以可控的方式直接在表面添加硼，而不是使用重掺硼的硅片。“热”扫描隧道显微镜(STM)将被用来对B2H6的分解、硼的掺入(在有或没有额外的硅助熔剂的情况下)以及由此产生的原子尺度台阶形成和/或表面粗糙进行实时原子分辨率测量。(2)“扁平”的Si(001)衬底(阶梯宽达20微米)将被用来研究长程台阶组织现象，以避免“邻近”台阶带来的复杂情况。平坦化的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，并确定在平台上形成的大规模台阶“上层建筑”的平衡形状。(3)低能电子显微镜(LEEM)将用于实时研究在表面添加硼时的大规模台阶形成。第二个研究方向是由于表面电迁移力的作用，导致Si(001)表面台阶的大规模组织。对Si(001)表面电迁移现象的定量测量和模型研究包括几种方法。(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错切和外加电流之间的夹角。(2)对Si(001)表面的“交叉台阶”进行了详细的测量和模拟，以提取有关表面硅原子的“有效电荷”(及其可能的各向异性)的定量信息。(3)将进行表面电迁移现象的LEEM测量。交叉步演化的实时测量将被用于直接测试交叉步模型，并提取关于产生表面电迁移现象的重要表面过程的定量信息。这项研究将利用现有的三个超高真空扫描隧道显微镜(UHV)扫描隧道显微镜设备(一个商用变温扫描隧道显微镜系统和两个定制的室温扫描隧道显微镜系统)，以及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超高压LEEM系统。%该项目解决具有高度技术相关性的材料科学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了解，这些工艺是硅基微电子微电子小型化最终限制的几个问题的关键。现在可以使用实验工具对基本的表面过程进行原子水平的观察，如果更好地了解这些过程，就可以推动基础科学和技术的进步。该计划的一个重要特点是通过在一个具有根本意义和技术意义的领域对学生进行培训，将研究和教育结合起来。***

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. ***