Silma Alberton Corrêa

Effects of nitrogen incorporation on the interfacial layer between thermally grown dielectric films and SiC

C-containing interlayers formed between the SiC substrate and dielectric films thermally grown in O2, NO, and in O2 followed by annealing in NO were investigated. X-ray reflectometry and x-ray photoelectron spectroscopy were used to determine N and C incorporation in dielectric films and interlayers, as well to determine their mass densities and thicknesses. The thickest C-containing interlayer was observed for films thermally grown in O2, whereas the thinnest one was observed for films directly grown in NO, evidencing that the presence of N decreases the amount of carbonaceous compounds in the dielectric/SiC interface region.

Presence and Resistance to Wet Etching of Silicon Oxycarbides at the SiO2 / SiC Interface

The formation and solubility of silicon oxycarbides at the SiO 2 /SiC interface was investigated using nuclear reaction analyses. The amount of silicon oxycarbides formed by thermal oxidation of SiC in dry O 2 was seen to be independent of substrate polytype, surface termination, and oxidation temperature. Oxide growth was retarded on surfaces containing residual silicon oxycarbides, and none of several acid and oxidizing wet etch chemistries was able to remove them.

Water vapor interaction with silicon oxide films thermally grown on 6H-SiC and on Si

Thermally induced incorporation of isotopically labeled water vapor (D2 O18) species in 7 nm thick SiO2 films thermally grown on 6H-SiC(0001) and on Si(001) were investigated. Higher incorporation of hydrogen and higher isotopic exchange were observed in SiO2/SiC as compared to SiO2/Si, at temperatures above 600 °C, which can lead to electrical instabilities, especially in high-temperature devices. At any annealing temperature, oxygen is incorporated in the oxide films, reaching the SiO2/SiC interface, in contrast with SiO2/Si. The present observations show that strict control of water vapor contents in SiO2/SiC is mandatory in order to achieve further improvements in the SiC-based device technology.

Enhancement in interface robustness regarding thermal oxidation in nanostructured Al2O3 deposited on 4H-SiC

Experimental evidences of enhanced stability of Al2O3/SiC structures following thermal annealing are presented. 5- and 40-nm-thick Al2O3 films evaporated on the Si- and C-terminated faces of 4H-SiC were annealed up to 1000 °C in different atmospheres, leading to crystallization and densification of Al2O3, with an increase in the band gap. Exposure to O2 at high temperatures produced SiO2 and AlSixOy at the Al2O3/SiC interface, with less silicate on the Si-terminated face. Annealing in N2 before exposure to O2 hindered oxygen diffusion and exchange, leading to more stable thin film structures from the point of view of atomic transport.

SiO2/SiC structures annealed in D218O: Compositional and electrical effects

Effects of water vapor annealing on SiO2/4H-SiC structures formed following different routes were investigated using water isotopically enriched in 18O and 2H (D). Isotopic exchange between oxygen from the water vapor and oxygen from SiO2 films deposited on 4H-SiC was observed in the whole depth of the films, differently from the behavior of SiO2 films thermally grown on 4H-SiC. The highest amount of D was obtained in the sample with the highest negative fixed charge concentration, suggesting that the D incorporation occurs in defects in the structure that exist prior to the annealing. As a consequence of the water annealing, a significant reduction in the negative effective charge in metal-oxide-semiconductor capacitors and the removal of the SiO2/SiC interfacial region was observed, attributed to the reduction of the amount of SiOxCy compounds in the interfacial region.

H Quantification and Profiling in SiO2 / SiC Submitted to Annealing in Water Vapor

The incorporation and depth distribution of hydrogen, after annealings in low pressure water vapor of Si0 2 films thermally grown in O 2 on SiC and on Si, are determined using nuclear reaction analyses. Water isotopically enriched simultaneously in deuterium ( 2 H or D) and in 18 O was used. While in Si0 2 /SiC, the amount of incorporated hydrogen increases continuously with temperature and with initial oxide thickness; in SiO 2 /Si, there is no such dependence. In SiO 2 /SiC, hydrogen profiling reveals its presence in the surface, bulk, and interface regions, whereas in SiO 2 /Si, hydrogen is observed only in near-surface regions of the oxide film.

Consequences of NO Thermal Treatments in the Properties of Dielectric Films / SiC Structures

The consequences of thermal treatments in nitric oxide atmospheres on the characteristics of dielectric films / SiC structures was investigated by high-frequency capacitance-voltage measurements, X-ray photoelectron spectroscopy, and X-ray reflectometry techniques. It was observed that nitrogen incorporation in dielectric films / SiC structures leads to the formation of a thinner interfacial layer that contains carbon. This fact was related to the improvement of electrical properties of those structures.

SiO2/SiC Interfacial Region: Presence of Silicon Oxycarbides and Effects of Hydrogen Peroxide and Water Vapor Thermal Treatments

This work provides data corroborating the presence of silicon oxycarbides (SiOxCy) in the SiO2/SiC interface region. Besides, it presents results on the efficiency of hydrogen peroxide annealings for reducing the SiO2/SiC interfacial region thickness. Finally, influences of water vapor thermal treatments on dielectric films thermally grown are presented. In most of the samples, isotopes rare in nature (18O and 2H) were used in thermal treatments associated with ion beam analyses.

Improvement in the SiO2/4H-SiC Interfacial Region by Thermal Treatments with Hydrogen Peroxide

The effect of sequential thermal treatments with growth/removal steps of SiO2 films intercalated with hydrogen peroxide treatments on the SiO2/4H-SiC interfacial region thickness were investigated on both Si and C faces. In the Si face case, samples that were submitted to more H2O2 treatments presented thinner interfacial region thicknesses. In the C face case, on the other hand, no significant alteration in this region was observed.