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

Ohio State University Research Foundation -Do Not Use, Columbus OH

Investigators

Abstract

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. ***