Synthesis and fundamental studies of chlorinated Si-Ge hydride macromolecules for strain engineering and selective-area epitaxial applications

Jesse B. Tice, Y. Y. Fang, John Tolle, Andrew Chizmeshya, John Kouvetakis

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8 Scopus citations

Abstract

We recently demonstrated the low-temperature (400-450°C) deposition of high-purity, Ge-rich crystalline and stoichiometric Si0.5Ge 0.50 films on Si(100) using a new designer class of highly reactive, selectively chlorinated silylgermane compounds, such as ClH 2SiGeH3 and Cl2HSiGeH3. Here we extend the synthetic "palette" of chlorinated Si-Ge analogs to the Ge-rich propane- and butane-like family of molecules including SiH 2(GeH3)2, SiH(GeH)3, and (SiH 2)2(GeH3)2. Our approach involves the controlled and selective chlorination of the -SiH2, -SiH, and -SiH2-SiH2- bridging ligands and leads to the pure compounds ClHSi(GeH3)2 (1), Cl2Si(GeHj) 2 (2), ClSi(GeH3)3 (3), and ClHSiSiH 2(GeHj)2 (4) in practical yields. The dichlorinated butane-like species (ClHSi)2(GeH3)2 and Cl 2SiSiH2(GeH3)2 are also obtained as isomeric mixtures. Here the availability of two equivalent Si sites has allowed us to investigate the order and degree of chlorination and establish that full substitution is preferred. AU compounds were characterized by NMR, FTIR, and mass spectroscopy. First-principles density functional theory is used to elucidate the structural and vibrational trends of compounds 1-4 as well as a range of isomers of the dichlorinated butane-like derivatives. The observed FTIR frequencies and intensities of compounds 1-4 are accurately reproduced using the B3LYP/6-311N++G(3df,3pd) model chemistry, thus confirming the molecular structures, and our simulations are then used to obtain reliable vibrational mode assignments. Finally, we used Cl2Si(GeH3)2 (2) to selectively grow silicon-germanium alloy semiconductors in the "source" and "drain" regions of simple transistor structures at 420°C. XTEM imaging indicates commensurate growth of this material on the Si platform of the device. Experiments involving the more reactive ClHSi(GeH3)2 (1) analog produced Si0.33Ge 0.67 layers with novel epitaxy-stabilized tetragonal structures exhibiting unprecedented compressive strain approaching -2.4%. This is ∼90% of the maximum value (2.75%) expected for this composition, and it is obtained in film thicknesses of 20-25 nm that far exceed the equilibrium critical value of the same material grown pseudomorphically on Si(100). The external stress required to achieve this deformation in free-standing samples is ∼4 GPa, which underscores the extreme strain state achieved in our films. This type of single-source deposition completely circumvents the need for the usual multicomponent reactions and corrosive Cl2 etchants necessary to promote selective, strained-layer deposition in conventional processes.

Original languageEnglish (US)
Pages (from-to)4374-4385
Number of pages12
JournalChemistry of Materials
Volume20
Issue number13
DOIs
StatePublished - Jul 8 2008

ASJC Scopus subject areas

  • Chemistry(all)
  • Chemical Engineering(all)
  • Materials Chemistry

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