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UNIVERSITY OF BUCHAREST
FACULTY OF PHYSICS Guest
2024-11-22 2:22 |
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Conference: Bucharest University Faculty of Physics 2003 Meeting
Section: Optics, Spectroscopy, Plasma and Lasers
Title:
Surface – plasma interactions in GaAs subjected to RF plasmas
Authors:
CC Surdu-Bob
Affiliation:
National Institute for Lasers, Plasma and Radiation Physics
E-mail
Keywords:
Abstract:
GaAs is used as base material in semiconductor processing industry for electronic device fabrication. The use of this material in industry is limited by a lack of precise identification and characterisation of the oxides formed on GaAs.
Reactive ion etching involves the use of complex plasmas and is widely used in the fabrication of III-V semiconductor devices. This method consists of a combination of physical and chemical interactions with the surface of semiconductor. For a complete understanding of the phenomena taking place when the semiconductor is exposed to energetic reactive ions, a separation of the physics and chemistry is necessary. In this study, GaAs surfaces exposed to less complex plasmas like inert gas plasmas as well as oxygen, hydrogen and plasmas of combinations of these gases were investigated.
The plasma etcher used was an asymmetrical capacitively copupled industrial plasma etcher powered at 13.56 MHz and the time of exposure to plasma was 30 minutes. The pressure and power ranges were 10 – 90 mT and 5 – 200 W, respectively. XPS and AFM were used for surface characterisation. The GaAs samples were polished clean wafers.
The Ga3d spectra of a clean GaAs sample contained the following major components with BEs of 19.1, 20.1, 20.7 and 21.6 eV corresponding to Ga(As), Ga2O, Ga2O3 and Ga(OH)3 respectively. Depending on plasma parameters, different amounts of these components were observed on the surface and a model of their formation was proposed.
Exposure of GaAs to inert plasma resulted mainly in physical etching with etch rates directly dependent on ion energy and ion flux. However, surface oxidation was also observed. The sample exposed for a long period of time to the ambient air after plasma treatment was key to the understanding of the results. The data showed that immediate sub-surface relaxation continues after plasma treatment and surface oxidation in air has also taken place.
With respect to the effect of the plasma upon the surface, two different plasma conditions were distinguished: weak and strong plasmas. Their delimitation point was the value of the power were, at a certain pressure, surface oxidation remained constant with further increase of the power.
Plasma treatment of the surface induced surface oxidation with oxide layers of tens of angstroms thickness. Most of the oxide was formed during plasma processing and consisted of a mixture of Ga and As oxides.
A very important factor in all surface – plasma interaction experiments was found to be the time elapsed between plasma treatment and surface investigation.
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