Sanwu Wang

Increase in oxide hole trap density associated with nitrogen incorporation at the SiO2/SiC interface

Nitrogen incorporation at the SiO2/SiC interface via high temperature nitric oxide annealing leads to the passivation of electrically active interface defects, yielding improved inversion mobility in the semiconductor. However, we find that such nitrided oxides can possess a larger density of hole traps than as-grown oxides, which is detrimental to the reliability of devices (e.g., can lead to large threshold voltage instabilities and to accelerated failure). Three different charge injection techniques are used to characterize this phenomenon in metal–oxide–semiconductor structures: x-ray irradiation, internal photoemission and Fowler–Nordheim tunneling. Some nitrogen-based atomic configurations that could act as hole traps in nitrided SiO2 are discussed based on first-principles density functional calculations.

Si/SiO2 and SiC/SiO2 Interfaces for MOSFETs – Challenges and Advances

Silicon has been the semiconductor of choice for microelectronics largely because of the unique properties of its native oxide (SiO2) and the Si/SiO2 interface. For high-temperature and/or high-power applications, however, one needs a semiconductor with a wider energy gap and higher thermal conductivity. Silicon carbide has the right properties and the same native oxide as Si. However, in the late 1990’s it was found that the SiC/SiO2 interface had high interface trap densities, resulting in poor electron mobilities. Annealing in hydrogen, which is key to the quality of Si/SiO2 interfaces, proved ineffective. This paper presents a synthesis of theoretical and experimental work by the authors in the last six years and parallel work in the literature. High-quality SiC/SiO2 interfaces were achieved by annealing in NO gas and monatomic H. The key elements that lead to highquality Si/SiO2 interfaces and low-quality SiC/SiO2 interfaces are identified and the role of N and H treatments is described. More specifically, optimal Si and SiC surfaces for oxidation are identified and the atomic-scale processes of oxidation and resulting interface defects are described. In the case of SiC, we conclude that excess carbon at the SiC/SiO2 interface leads to a bonded Si-C-O interlayer with a mix of fourfold- and threefold-coordinated C and Si atoms. The threefold coordinated atoms are responsible for the high interface trap density and can be eliminated either by H-passivation or replacement by N. Residual Si-Si bonds, which are partially passivated by H and N remain the main limitation. Perspectives for the future for both Si- and SiC-based MOSFETs are discussed.

Effects of device aging on microelectronics radiation response and reliability.

Recent work is reviewed that shows that MOS and bipolar device radiation response can change significantly with aging time after device fabrication and/or packaging. Effects include changes in radiation response due to burn-in, pre-irradiation elevated temperature stress, and/or long-term storage. These changes are attributed experimentally and theoretically to the motion and reactions of water and other hydrogen-related species. Similar hydrogen-related reactions can also affect the long-term reliability of MOS devices and integrated circuits, as illustrated in detail here for negative-bias temperature instability

Thermal donor formation processes in silicon and the catalytic role of hydrogen

We report the results of first-principles calculations on the interactions of hydrogen with oxygen clusters in silicon and other processes that relate to the formation of thermal donors (TD). We find that pre-existing small O clusters transform to thermal donors with a low activation energy of 1.15 eV. Clusters formed due to O–H codiffusion bind H strongly in TD precursor configurations and H release requires high temperatures to overcome a 1.9 eV barrier, a value in agreement with experiments on the dissociation of TD-H complexes. Repeated trapping and release from such clusters establish a catalytic role for H in TD formation.

Suppression of interface state generation upon electron injection in nitrided oxides grown on 4H-SiC

The flatband voltage stability of SiO2∕SiC metal-oxide-semiconductor capacitors upon electron injection can be enhanced by the introduction of nitrogen in a thermal gate oxide. We show that it is due to the suppression of negative charge buildup in interface states during injection. We discuss the role of nitrogen in this effect and how it might be linked to the passivation of interface defects.

First-principles calculations for the adsorption of water molecules on the Cu(100) surface

First-principles density-functional theory and supercell models are employed to calculate the adsorption of water molecules on the

The effects of aging on MOS irradiation and annealing response

\mathrm{Cu}(100)

Total Dose Radiation Response of Nitrided and Non-nitrided SiO

surface. In agreement with the experimental observations, the calculations show that a

_{2}

{\mathrm{H}}_{2}\mathrm{O}

/4H-SiC MOS Capacitors

molecule prefers to bond at a onefold on-top