Heterogeneous decomposition of trimethylaluminum and trimethylgallium on silicon surfaces
Gow, Thomas Richard, Jr
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Permalink
https://hdl.handle.net/2142/19884
Description
Title
Heterogeneous decomposition of trimethylaluminum and trimethylgallium on silicon surfaces
Author(s)
Gow, Thomas Richard, Jr
Issue Date
1990
Doctoral Committee Chair(s)
Masel, Richard I.
Department of Study
Chemical and Biomolecular Engineering
Discipline
Chemical and Biomolecular Engineering
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Engineering, Chemical
Engineering, Materials Science
Language
eng
Abstract
Trimethylaluminum (TMAl) and trimethylgallium (TMGa) are important source gases for use in MOCVD and MOMBE. This study uses thermal desorption spectroscopy, x-ray photoelectron spectroscopy, and electron energy loss spectroscopy to examine the decomposition of TMAl at low coverages on heated silicon substrates. In addition, molecular beam methods are employed to investigate the decomposition of TMGa directly on a heated surface at higher TMGa exposures. The decomposition mechanisms are identified through characterization of the intermediate species produced during decomposition. Carbon deposition is found to be an intrinsic part of the decomposition of TMAl and TMGa on silicon under the conditions used in this work.
TMAl adsorbs molecularly as dimers on clean silicon below 300 K. The dimers dissociate into monomers upon heating to 300-400 K. At temperatures above 400 K, the adsorbed TMAl monomers begin to decompose forming methane via hydrogen transfer from one methyl group to another. The methane desorbs while the dialkyl intermediate remains on the surface. Further heating causes decomposition of some of the surface intermediates to produce additional methane via hydrogen transfer, while the rest of the surface intermediates decompose into aluminum atoms and CH$\sb{\rm x}$ (x = 1 to 3) on the surface. The CH$\sb{\rm x}$ fragments are strongly bound to the silicon and subsequently decompose above 700 K yielding hydrogen and carbon. The hydrogen desorbs between 750 and 800 K, but the carbon remains on the surface to high temperatures. More than one third of the carbon initially present in the TMAl is left on the surface.
In the decomposition of TMGa at high exposures on a silicon surface, the first step is again the production of a dialkylgallium species and CH$\sb{\rm x}$ (x = 3 or 4) at temperatures above 400 K. However, in the presence of several layers of TMGa, or gallium and carbon containing species on the surface, the dialkylgallium readily desorbs. In addition, above 500 K, small amounts of monomethylgallium are produced. Some of the CH$\sb{\rm x}$ species desorb as methane between 400 and 700 K, while desorption of methyl radicals is observed at higher temperatures. However, much of the CH$\sb{\rm x}$ appears to remain on the surface under the conditions of these molecular beam experiments.
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