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Title:Mechanisms and kinetics of silicon atomic-layer epitaxy on silicon(001)2x1 and germanium(001)2x1
Author(s):Tsu, Robert Yung-Hsi
Doctoral Committee Chair(s):Greene, Joseph E.
Department / Program:Materials Science and Engineering
Discipline:Materials Science and Engineering
Degree Granting Institution:University of Illinois at Urbana-Champaign
Subject(s):Physics, Condensed Matter
Engineering, Metallurgy
Engineering, Materials Science
Abstract:Single-crystal Si films have been grown on Si(001)2x1 substrates by UV-photostimulated atomic-layer epitaxy (ALE) from Si$\sb2$H$\sb6.$ The ALE deposition rate R per growth cycle remains constant at 0.43 monolayers (ML), 1 ML = $6.8\times10\sp{14}$ cm$\sp{-2}$, over a wide range of deposition parameters: growth temperature (T$\sb{\rm S}$ = 180-400$\sp\circ$C), Si$\sb2$H$\sb6$ exposure, UV laser energy density, and number of UV laser pulses per cycle. A film growth model, based upon the results of adsorption/desorption measurements, film growth experiments, and Monte Carlo simulations, is used to describe the reaction pathway for the process.
Si$\sb2$H$\sb6$ is dissociatively adsorbed on Si surface dimers as two SiH$\sb3$ radicals which, as shown by electron energy loss spectroscopy (EELS) and reflection high-energy electron diffraction (RHEED), subsequently dissociate to SiH$\sb2$ and H. The saturated H-terminated surface is stable and passive to further Si$\sb2$H$\sb6$ exposure. ArF or KrF laser pulses $(\simeq$20 ns) are used to desorb H, following a Si$\sb2$H$\sb6$ exposure, and the growth is repeated until the desired film thickness is obtained. Transmission electron microscopy (TEM) and cross-sectional TEM together with selective area and convergent-beam electron diffraction patterns show that the ALE films are epitaxial layers with no observed extended defects or strain.
The Si$\sb2$H$\sb6$ sticking probability at 25$\sp\circ$C is found to be $\simeq$0.5 while the saturation coverage is $\simeq$0.5 ML on Ge(001)2x1. Scanning tunneling microscopy (STM) observations show the adsorbed overlayers exhibit regions of local ordering, in contrast to the case for Si$\sb2$H$\sb6$ on Si(001), and are composed of SiH$\sb2$ and GeH with evidence of residual SiH$\sb3.$ Hydrogen desorption is observed at temperatures as low as 150$\sp\circ$C, admolecules are mobile at 270$\sp\circ$C, and complete ordering is observed by 330$\sp\circ$C. Film growth on Ge(001) is observed to proceed via a mixed mode.
Issue Date:1993
Rights Information:Copyright 1993 Tsu, Robert Yung-Hsi
Date Available in IDEALS:2011-05-07
Identifier in Online Catalog:AAI9411805
OCLC Identifier:(UMI)AAI9411805

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