Interface behaviour and electrical performance of ruthenium Schottky contact on 4H-SiC after argon annealing

Rutherford backscattering spectrometry(RBS) analysis , carried out at various annealing temperatures, of a thin film of ruthenium on n-type 4-hexagonal silicon carbide (4H-SiC) showed evidence of ruthenium oxidation, ruthenium silicide formation and diffusion of ruthenium into silicon carbide starting from an annealing temperature of 400oC. Ruthenium oxidation was more pronounced, and ruthenium and Silicon inter-diffusion was very deep after annealing at 800oC. Raman analysis of some samples also showed ruthenium silicide formation and oxidation. The Schottky barrier diodes showed very good linear capacitance-voltage characteristics and excellent forward current-voltage characteristics, despite the occurrence of the chemical reactions and inter-diffusion of ruthenium and silicon at ruthenium-silicon-carbide interface, up to an annealing temperature of 800oC.http://link.springer.com/journal/12034hb201

Solid state reaction and operational stability of ruthenium Schottky contact-on-6H-SiC under argon annealing

Thin films of ruthenium-on-6-hexagonal silicon carbide (6H-SiC) were analysed by Rutherford backscattering spectroscopy (RBS) at various annealing temperatures. Some thin film samples were also analysed by scanning electron microscope (SEM). RBS analysis indicated minimal element diffusion, and formation of ruthenium oxide after annealing at 500 oC. Large scale diffusion of ruthenium (Ru) was observed to commence at 700 oC. The SEM images indicated that the as-deposited Ru was disorderly and amorphous. Annealing of the thin film improved the grain quality of Ru. The fabricated Ru-6H-SiC Schottky barrier diodes (SBD) with nickel ohmic contacts showed excellent rectifying behaviour and linear capacitance-voltage characteristics up to an annealing temperature of 900 oC. The SBDs degraded after annealing at 1000 oC. The degradation of the SBDs is attributed to the inter-diffusion of Ru and Si at the Schottky-substrate interface.http://link.springer.com/journal/116642016-10-31hb201

Structural and electrical properties of annealed Ru thin films on SiC

Silicon carbide (SiC) is both used as a diffusion barrier in Tristructural Isotropic (TRISO) coated nuclear fuel particles in nuclear reactors and as a wide band gap semiconductor in microelectronics applications. SiC has physical properties of high strength and hardness, high melting point and is chemically inert. This thesis investigates the effectiveness of SiC as a barrier to ruthenium diffusion in TRISO coated nuclear fuel particles. In addition, the electrical performance and degradation mechanism of ruthenium-SiC based Schottky barrier diodes (SBDs), and their ability to operate at extremely high temperatures are also investigated. In TRISO coated fuel particles, the high strength SiC layer acts as a containment layer to the high pressure generated in the kernel by the fission nuclear reaction. One element produced during the nuclear fission reaction is ruthenium (Ru). In this thesis, the Ru solid state reaction with SiC has been investigated by annealing a thin film of Ru on 4H-SiC and 6H-SiC in the air, argon and a vacuum. Analysis of the thin films after various annealing temperatures were performed by Rutherford Backscattering Spectrometry, X-Ray Diffraction analysis, Scanning electron microscopy, and Raman Spectroscopy. The study has shown that diffusion of Ru into SiC starts at a much higher annealing temperature in a vacuum, whereas, in air annealing, diffusion commences at a much lower temperature. The study has shown that SiC is not a perfect barrier to the diffusion of metallic fission products. Due to its wide band gap property, electronic devices made from SiC can operate at very high temperatures, with very high power and fast switching times. Ru also happens to be a suitable material for making Schottky contacts with SiC. Due to its high melting temperature (2250oC), and chemical inertness, the Ru Schottky contact can function at very high operating temperatures. The electrical characteristics of Ru/SiC SBDs have been investigated by annealing the diodes in various environments namely air, argon and vacuum. The electrical characterisation of the SBDs after each annealing temperature was done by using current-voltage (IV) and capacitance-voltage (CV) characterisation techniques. This study has shown that Ru/4H-SiC SBDs will remain operational after annealing in vacuum up to temperatures of above 1000 oC and that the diodes degrade at a very low temperature of 400 oC when annealed in air. Ru/4H-SiC SBDs under argon annealing degrade at a temperature of 1000 oC. The degradation of the Ru/4H-SiC SBDs, when annealed in air, is explained by the fact that there is a possibility of formation of an oxide of Ru which is not conducting which leads to a high series resistance of the diode at the degradation temperature of 400 oC. In the case of argon annealing, the degradation of Ru/4H-SiC SBDs is due to the diffusion of Ru into 4H-SiC. In a vacuum, the Ru/6H-SiC SBDs degrade at a temperature of 800 oC. The IV data show that Ru Schottky contact on 6H-SiC becomes ohmic at 900 oC. The formation of an ohmic contact is attributed to the formation of graphite flakes as evidenced by Raman analysis of Ru/6H-SiC thin films. In atmospheric annealing environment, the Ru/6H-SiC SBDs degrade at a higher temperature (of 700 oC) than that of Ru/4H-SiC SBDs (400 oC). Under argon annealing, there is very little difference in the degradation temperature between Ru-4H-SiC and Ru/6H-SiC SBDs. This study has shown that, in general, the SBDs degrade at higher temperatures when annealed in vacuum and argon while in air degradation takes place at a very much lower temperature.Thesis (PhD)--University of Pretoria, 2016.tm2016PhysicsPhDUnrestricte

Solid state reaction of ruthenium with silicon carbide, and the implications for its use as a Schottky contact for high temperature operating Schottky diodes

A thin film of ruthenium was deposited on n-type-4-hexagonal-silicon- carbide (4H-SiC) so as to studythe interface behaviour of the ruthenium Schottky contact with silicon carbide. Ruthenium (Ru) Schottkydiode dots were also fabricated by deposition of ruthenium on n-type-4H-SiC which had nickel as aback ohmic contact. The Ru-4H-SiC Schottky barrier diodes (SBDs) and thin films were both annealedisochronally in a vacuum furnace at various temperatures. Rutherford-backscattering-spectrometry anal-ysis of the thin film sample showed evidence of formation of ruthenium silicide (Ru2Si3) and diffusionof ruthenium into silicon carbide at annealing temperatures of 700?C and 600?C respectively. Ramananalysis of the sample that was annealed in a vacuum at 1000?C showed evidence of the formation ofgraphite, and Ru2Si3. Despite the occurrence of the chemical reactions and diffusion of ruthenium into4H-SiC, the SBDs were operationally stable up to the final annealing temperature of 1000?C

Microstructure evolution and diffusion of ruthenium in silicon carbide, and the implications for structural integrity of SiC layer in TRISO coated fuel particles

A thin film of ruthenium (Ru) was deposited on n-type 4H-SiC and 6H-SiC by electron beam deposition technique so as to study interface reaction of ruthenium with silicon carbide at various annealing temperatures, and in two annealing environments namely vacuum and air. The Ru-4H-SiC and Ru-6H-SiC films were both annealed isochronally in a vacuum furnace at temperatures ranging from 500 to 1000 C, and the second set of samples were also annealed in air for temperatures ranging from 100 C to 600 C. After each annealing temperature, the films were analysed by Rutherford Backscattering spectrometry (RBS). Raman analysis and X-ray diffraction analysis were also used to analyse some of the samples. RBS analysis of 4H-SiC annealed in a vacuum showed evidence of formation of ruthenium silicide (Ru2Si3) and diffusion of Ru into SiC starting from annealing temperature of 700 C going upwards. In the case of Ru-6H-SiC annealed in a vacuum, RBS analysis showed formation of Ru 2Si3 at 600 C, in addition to the diffusion of Ru into SiC at 800 C. Raman analysis of the Ru-4H-SiC and Ru-6H-SiC samples that were annealed in a vacuum at 1000 C showed clear D and G carbon peaks which was evidence of formation of graphite. As for the samples annealed in air ruthenium oxidation started at a temperature of 400 C and diffusion of Ru into SiC commenced at temperatures of 500 C for both Ru-4H-SiC and Ru-6H-SiC. X-ray diffraction analysis of samples annealed in air at 600 C showed evidence of formation of ruthenium silicide in both 4H and 6H-SiC but this was not corroborated by RBS analysis

Solid state reaction of ruthenium with 6H-SiC under vacuum annealing and the impact on the electrical performance of its Schottky contact for high temperature operating SiC-based diodes

Thin films and Schottky diodes dots of ruthenium (Ru) on bulk-grown n-type-6-hexagonal-silicon carbide (6H-SiC) were annealed isochronally in a vacuum furnace at temperatures ranging from 500-1,000 °C. Rutherford backscattering spectroscopy analysis of the thin films showed formation of ruthenium silicide (Ru2Si3) at 800 °C, while diffusion of Ru into 6H-SiC commenced at 800 °C. Raman analysis of the thin films annealed at 1,000 °C showed clear D and G carbon peaks which was evidence of formation of graphite. At this annealing temperature, the Schottky contact was observed to convert to an ohmic contact, as evidenced by the linearity of current-voltage characteristic, thereby, rendering the diode unusable. The transformation from Schottky contact to ohmic contact is attributed to graphite formation at the interface