Untersuchung von Grenzflächen zwischen kristallinem Silicium und Al2O3-Passivierungsschichten
Zusammenfassung der Projektergebnisse
The passivation mechanisms of Al2O3 on Si were studied on a microscopic scale with experimental and simulation methods. Experimentally, Si/Al2O3 interfaces and Al2O3 bulk properties were studies using QSSPC, COCOS, FTIR, EPR, ellipsometry, and XRD. Here, the main focus was set on the temperature induced activation and degradation of Al2O3 passivation qualities on Si. In the frame of this work, the theoretical description of X-band EPR spectra obtained for Si/Al2O3 samples for varies Al2O3 layer thicknesses and additional SiO2 layer thicknesses in-between Si and Al2O3 were realized. With these, five paramagnetic moments, namely Pb0, Si-db and CH3 radicals were detected. Further, the main paramagnetic moment contributing to Dit was determined to be Si-dbs. In addition, the activation of passivation was observed to be connected to changes of an electronical level instead of structural changes. The corresponding activation energy for Th-ALD Al2O3 layers which is connected to an increase in Qtot and Dit was estimated. Due to nearly equivalent activation energies for the increase of Dit and Qtot, a connection between both values can be assumed. In contrast to the activation of passivation, the temperature-induced degradation of the Al2O3 passivation was shown to be connected to the crystallization of Al2O3 layers. It is further shown, that the crystallization process is enhanced for thicker Al2O3 layers compared to thinner Al2O3 layers. This observation might be connected to a higher oxygen or hydrogen concentration at the Si/Al2O3 interface for thick Al2O3 layers compared to thin Al2O3 layers. Another possibility to explain this thickness dependency might be connected to internal Al2O3 layer stress. Internal layer stress decreases with increasing Al2O3 layer thickness. Thus, crystallization might be enhanced for thicker Al2O3 layers. The correlation between those changes in the interface structure and the degradation of passivation were studied by means of ab-initio simulation (DFT). In particular, the influence of hydrogen on the structural transition and the formation of electronic gap states were extensively investigated. We found that hydrogen facilitates structural transitions at the interface, which in turn causes defects in the Si subsurface near the interface to Al2O3. Ab initio simulations (selfinteraction corrected DFT) were also used to elucidate the role of defects in the formation of deep electronic states, leading to a qualitative understanding of the passivation mechanism. We found that hydrogen-induced defects are related to electronic gap states acting as electron-hole recombination centers. These can be passivated by H atoms moving from the interface into the subsurface for a sufficiently high H concentration.
Projektbezogene Publikationen (Auswahl)
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Atomistische Strukturmodelle für Grenzflächen zwischen kristallinem Silicium und Al2O3-Passivierungsschichten, FMF Report 2013, S. 89f.
F. Colonna und C. Elsässer
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Atomistische und elektronische Strukturen an Grenzflächen von kristallinem Silicium und Al2O3-Passivierungschichten, FMF Report 2014, S. 104f.
F. Colonna und C. Elsässer
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High-temperature degradation in plasma-enhanced chemical vapor deposition Al2O3 surface passivation layers on crystalline silicon, J. Appl. Phys. 116, Art.-No. 054507 (2014)
S. Kühnhold, F. Colonna et al.
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A study on Si/Al2O3 paramagnetic point defects, J. Appl. Phys. 120, Art.-No. 195304 (2016)
S. Kühnhold-Pospischil et al.
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Activation energy of negative fixed charges in thermal ALD Al2O3, Appl. Phys. Letters, 109, Art.-No. 061602 (2016)
S. Kühnhold-Pospischil et al.
