Fundamental Mechanisms of Photo-Stimulated Surface Reactions During Laser-Induced and Laser-Assisted Crystal Growth
Lubben, Daniel C.
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https://hdl.handle.net/2142/71848
Description
Title
Fundamental Mechanisms of Photo-Stimulated Surface Reactions During Laser-Induced and Laser-Assisted Crystal Growth
Author(s)
Lubben, Daniel C.
Issue Date
1987
Doctoral Committee Chair(s)
Greene, J.E.
Department of Study
Metallurgy and Mining Engineering
Discipline
Metallurgical Engineering
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Engineering, Materials Science
Abstract
The use of ultra-violet lasers to alter the chemistry of surfaces during vapor-phase crystal growth and the fundamental mechanisms of these interactions during the growth of thin films has been examined. Three growth techniques have been studied. These are: laser-induced chemical vapor deposition (LCVD), laser-assisted low-pressure chemical vapor deposition (LA-LPCVD), and laser-induced primary-ion deposition.
The interaction of the laser beam and adsorbed layers of parent gas during growth by LCVD plays an important role in the composition and quality of the resulting film. As a model system, we chose to investigate the dissociation of trimethylaluminum (TMA) adsorbed on Si(100)(2 x 1) substrates by both ArF (193 nm, 6.4 eV) and KrF (248 nm, 5.0 eV) laser irradiation. By examining the surfaces before and after laser-irradiation with XPS, AES and (EELS) we determined that the dissociation of TMA, which adsorbs as a dimer, takes place by monomerization followed by successive removal of the methyl ligands. The C and Al atoms present on the surface form strong bonds which prevent the removal of C-containing species, resulting in the incorporation of C into the resulting film.
Intensities in the range of 10$\sp6$ to 10$\sp7$ W-cm$\sp{-2}$ were used to melt Si films deposited by LPCVD, and the subsequent resolidification gave rise to polycrystalline films on amorphous substrates and single-crystals on Si(100) wafers for growth temperatures at which the films would normally be amorphous. By irradiating the films during growth, problems associated with post-deposition laser-annealing such as surface damage due to the high intensities required for large melt depths were avoided. A theoretical model based on optical absorption and heat flow was developed which explains the results.
High-intensity ($>$10$\sp7$W-cm$\sp{-2}$) KrF laser irradiation was used to evaporate and ionize Ge and Si targets, and the resulting plasma was used as a source for primary-ion deposition. The kinetic energies of ions in the plasma, which depend strongly on the laser intensity, were typically tens of eV, and were accelerated to higher energies by placing a bias on the substrate. The electrical and spatial characteristics of the plasma as well as the properties of the deposited films are discussed.
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