AVS 51st International Symposium
    Surface Science Wednesday Sessions
       Session SS2-WeM

Paper SS2-WeM7
STM Study of Silicon Surfaces at P-N Junctions Prepared by Low-Temperature Processing

Wednesday, November 17, 2004, 10:20 am, Room 210C

Session: Semiconductor Surface and Interface Structure
Presenter: T.-C. Shen, Utah State University
Authors: T.-C. Shen, Utah State University
J.S. Kline, University of Illinois at Urbana-Champaign
J.R. Tucker, University of Illinois at Urbana-Champaign
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Dopant distribution at p-n junctions has been extensively studied by many techniques. Recent advance of electron devices further demands a thorough understanding and precise control of the dopant behavior at nanometer scale. Feenstra et al. pioneered the technique of cross-sectional STM to image the p- and n-type GaAs interface. To examine planar p-n junctions in Si, conventional high temperature surface preparation in ultrahigh vacuum is not suitable due to enhanced dopant diffusion and desorption. In this presentation, we report some of our experimental findings based on a previously developed low-temperature surface preparation technique involving 300eV Ar ion sputtering and 600-700°C annealing. The B-doped substrates used in this work are either at an impurity level of 3x10@super 17@ cm@super -3@ or 1x10@super 19@cm@super -3@. N-type patterns are fabricated by implanting 40-50 keV As ions at a dose of 1x10@super 15@cm@super -2@ into the B-doped substrates. The atomically clean and flat surfaces prepared at low temperatures allow us to obtain atom-resolving images both in the As-implanted region and the B-doped substrate as well as their original interface. We observe for the first time that heavily B-doped substrates lead to c(4x4) patterns on the surface the same as the result of diborane exposure. When terminating the surface with H, we find that the dangling bonds in the As-region are much brighter than those on the substrate. More c(4x4) regions and less C and H-induced clustering are observed in the As region. Surface topography at different annealing conditions, the role of dopant atoms in the diffusion of other impurities and their electronic effect will be discussed. This work is supported by DARPA-QuIST program under ARO contract DAAD 19-01-1-0324.