Challenging atomistic processes in SiC (CapSiC) (completed)
This project deals with issues related to growth and modification of silicon carbide (SiC) - one of the most promising wide bandgap semiconductor for electronic device operation under demanding conditions (e.g., high temperatures, high frequencies and high voltages, and aggressive atmospheres). The SiC-technology has a key to energy saving by largely reducing the losses of electrical power transmission.
About the project
This project addresses fundamental issues regarding atomistic phenomena occurring during modification and processing of silicon carbide (SiC). SiC is a novel wide band gap semiconductor with an outstanding potential beyond the silicon era. However, to realize this potential, a number of critical scientific challenges need to be resolved, and two of the most commonly recognized ones are tackled here, i.e gate dielectrics and selective area doping.
Al2O3 and ZrO2 will be grown on epitaxial 4H-SiC layers by ALCVD, and the electrical and structural properties of the oxide/SiC interface will be studied in detail. AN ultimate goal is to gain understanding about the identity of near-interfacial electron traps and how their density and energy distribution can be controlled.
Focused beams of electrons/ions will be employed to reveal the intriguing phenomenon of long distance defect migration (>300 microns) outside the directly irradiaded area in SiC. The process is athermal and may be one of the very first confirmations of the Bourgoin-Corbett mechanism for charge-state driven migration. Laterally resolved electrical and optical characterization techniques are to be used, and the experimental concept is quite unique/original since it also facilitates identification of defects involving carbon interstitials.
The crucial but scarcely studied EH6/7 deep-level defect in 4H-SiC will be investigated with respect to identity and mechanisms for formation and annealing. In particular, epitaxial layers grown under different conditions, like variation of the C/Si ratio and using different n-type dopants, will be subjected to electron/ion irradiation and electrical characterization.
The project comprises extensive collaboration with leading international and national partners.
The overall objectives are:
- to investigate the electrical and structural properties of oxide/SiC interfaces, and especially Al2O3 and ZrO2 prepared by ALCVD on epitaxial layers of 4H- and 6H-SiC. An ultimate goal is identify the nature of near-interfacial electron traps and control their density and energy distribution
- to understand the mechanisms(s) for 'athermal' long distance (>300 microns) defect migration outside the directly irradiated area in SiC exposed to focused beams (<1 micron) of electrons/ions. Further, through combination of spatially resolved electrical and optical measurements the involvement of interstitial carbon during defect formation will be determined
- to reveal the identity of the prominent EH6/7 deep-level-defect in 4H-SiC and the mechanisms for its formation and annealing. A specific sub-goal is to control the formation of EH6/7 centers and thereby also the charge carrier lifetime in high purity SiC layers
Several fundamental issues related to growth and modification of silicon carbide remain to be resolved in order to explore the full potential of SiC for energy-efficient electronic devices. Some of these issues are addressed in this project and for the reporting period the following accomplishments can be highlighted: Substantial efforts have been made to characterize and understand the origin of the so-called near interface defects in SiO2/4H-SiC and Al2O3/4H-SiC structures. In particular, the energy distribution of these states near to the conduction band edge (Ec) has been studied in detail and the commonly accepted model of a strong increase in the concentration of the states close to Ec may not hold. The states are also found to be passivated by implanted nitrogen atoms, which is a very encouraging result for applications of metal-oxide-SiC field effect devices, like gas sensors, to be operated in harsh environments.
Employing a novel experimental concept of focused particle beams (beam diameter in the range of 1-10 microns) and laterally resolved electrical and optical spectroscopic techniques, fundamental carbon-related defects are revealed to migrate distances of several hundred of microns under ionizing conditions at room temperature. The migration occurs outside the directly irradiated volume and this effect is rather unique in such a thermally stable material as SiC. A likely explanation may be electronically stimulated motion of carbon-related defects. Two of the most prominent defects in 4H-SiC are the so-called Z1/2 and EH6/7 centers; they display long-distance migration and are of unknown microscopic origin. With the help of large scale and highly accurate ab initio electronic structure calculations, we have investigated the properties of carbon and silicon vacancies in 4H-SiC and our results suggest that the Z1/2 and EH6/7 centers are very likely to originate from different charge states of the carbon vacancy.
Finally, it has very recently been discovered that thermal oxidation of the 4H-SiC surface suppresses the concentration of Z1/2 and EH6/7 centers in as-grown and irradiated/processed material. This implies a giant step forward for SiC device processing and an accurate/quantitative model for this process, involving defect injection from the surface during oxidation, has been developed.
The project was featured in the article "Temperature differences give rise to electricity" published by Apollon in 2011
The participants of this project organized the European Conference on Silicon and Related Materials (ECSCRM2010). This was held in Aug 29 to Sep 2 2010. About 380 participants from 30 countries attended this conference, all continents represented. In the course of this conference, it was demonstrated that the SiC-technology has a key to energy saving by largely reducing the losses of electrical power transmission. It is predicted that 10-15 % of all power plants can closed (reducing/eliminating the need of for example coal-based ones) if the SiC-technology is succesfully implented on power-transmission-system-level.
The Research Counsil of Norway