Surface decomposition studies of trimethylgallium on silicon(100)
Lee, Fourmun
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Permalink
https://hdl.handle.net/2142/19156
Description
Title
Surface decomposition studies of trimethylgallium on silicon(100)
Author(s)
Lee, Fourmun
Issue Date
1989
Doctoral Committee Chair(s)
Masel, Richard I.
Department of Study
Engineering, Chemical
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, Electronics and Electrical
Engineering, Materials Science
Language
eng
Abstract
The trimethylgallium/silicon system is fundamentally and industrially important in microelectronics processing. In this study, the decomposition of trimethylgallium (TMG) on silicon (100) was investigated using thermal desorption spectroscopy (TDS), x-ray photoelectron spectroscopy (XPS), infrared spectroscopy (IR), and electron energy loss spectroscopy (EELS).
TMG adsorbs intact on silicon (100) at 300 K. It undergoes continuous decomposition between 400 K and 800 K which is accompanied by the evolution of methane over the entire temperature range. Hydrogen is liberated between 700 and 880 K. The adsorbed TMG is completely decomposed above 850 K, leaving only carbon and gallium atoms on the surface.
Adsorption of multilayers of TMG is observed at 100 K. Heating to 150 K causes the multilayers to evaporate, leaving only the layer immediately adjacent to the surface. Decomposition of the remaining material proceeds as described above.
The adsorbed TMG molecule lies flat on the silicon surface. This orientation together with the planar geometry of TMG limits the surface coverage to about 1 $\times$ 10$\sp{14}$ molecules/cm$\sp2$.
A mechanism for the surface decomposition of TMG is proposed which is consistent with all observed experimental results. In this mechanism, adsorbed TMG initially decomposes via extraction of a hydrogen atom from a methyl group by an adjacent methyl group within the same molecule. Methane is liberated, leaving one methyl group and a CH$\sb2$ group bound to the gallium. Additional heating causes the remaining TMG fragments to undergo to further decomposition via the same process, producing more methane. This is accompanied by the transfer of carbon-containing fragments to the surface. At higher temperatures, the decomposition of CH$\sb{\rm x}$ fragments forms surface hydrogen and carbon. After TMG is completely decomposed, only carbon and gallium are left on the surface. It is believed that two moles of methane and one-half mole of hydrogen is produced for each mole of TMG which decomposes.
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