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A study on Si/Al2O3 paramagnetic point defects

: Kühnhold-Pospischil, S.; Saint-Cast, P.; Hofmann, M.; Weber, S.; Jakes, P.; Eichel, R.-A.; Granwehr, J.


Journal of applied physics 120 (2016), Nr.19, Art. 195304, 12 S.
ISSN: 0021-8979
ISSN: 1089-7550
Fraunhofer ISE ()

In this contribution, negative charges and electronic traps related to the Si/Al2O3 interface were measured and related to paramagnetic point defects and molecular vibrations. To this end, contactless capacitance voltage measurements, X-band electron paramagnetic resonance (EPR), and infrared spectroscopy were carried out, and their results were compared. A change in the negative charge density and electron trap density at the Si/Al2O3 interface was achieved by adding a thermally grown SiO2 layer with varying thicknesses and conducting an additional temperature treatment. Using EPR, five paramagnetic moments were detected in Si/(SiO2)/Al2O3 samples with g values of g1 = 2.0081 ± 0.0002 , g2 = 2.0054 ± 0.0002 , g3 = 2.0003 ± 0.0002 , g4 = 2.0026 ± 0.0002, and g5 = 2.0029 ± 0.0002. Variation of the Al2O3 layer thickness shows that paramagnetic species associated with g1, g2, and g3 are located at the Si/Al2O3 interface, and those with g4 and g5 are located within the bulk Al2O3. Furthermore, g1, g2, and g3 were shown to originate from oxygen plasma exposure during Al2O3 deposition. Comparing the g values and their location within the Si/Al2O3 system, g1 and g3 can be attributed to Pb0 centers, g3 to Si dangling bonds (Si-dbs), and g4 and g5 to rotating methyl radicals. All paramagnetic moments observed in this contribution disappear after a 5-min temperature treatment at 450 ° C. The deposition of an additional thermal SiO2 layer between the Si and the Al2O3 decreases the negative fixed charge density and defect density by about one order of magnitude. In this contribution, these changes can be correlated with a decrease in amplitude of the Si-db signal. Pb0 and the methyl radical signals were less affected by this additional SiO2 layer. Based on these observations, microscopic models for the negative fixed charge density (Qtot) and the interface trap density (DQit) and the connection between these values are proposed.