Papers by Author: Sokrates T. Pantelides

Abstract: The defects at the interface and in the oxide have been considered as the sources of mobility degradation at the SiC/SiO₂ interface as in the case of Si/SiO₂ system. By examining available experimental and theoretical results and performing new calculations, we show that thermal oxidation creates immobile carbon di-interstitial defects inside the semiconductor substrate, which are a major cause of the poor mobility in SiC/SiO₂ structures.

Abstract: Phosphorous passivation of the SiO2/4H-SiC interface lowers the interface trap density and increases the field effect mobility for n-channel MOSFETs to twice the value of 30-40cm2/V-s obtained using standard NO nitridation. Passivation using P2O5 introduced with an SiP2O7 planar diffusion source (PDS) converts the oxide layer to phosphosilicate glass (PSG) which is a polar material. BTS (bias‐temperature‐stress) measurements with MOS capacitors and FETs show that the benefits of reduced interface trap density and increased mobility are offset by unstable flat band and threshold voltages. This instability can be removed by etching away the PSG oxide and depositing a replacement SiO2 layer. However, trap densities for etched MOS capacitors are "NO-like" (i.e., higher), which would lead one to expect a lower mobility if MOSFETs are fabricated with the PSG / etch / deposited oxide process.

Abstract: We report on the effect of nitridation on the negative and positive charge buildup in SiC gate oxides during carrier injection. We observe that the incorporation of nitrogen at the SiO2/SiC interface can enhance the reliability of the interface by suppressing the generation of interface states upon electron injection but that it can also degrade the oxide by creating additional hole traps. We relate these phenomena to the passivation of atomic-level defects by nitrogen.

Abstract: Post-oxidation anneals that introduce nitrogen at the SiO2/4H-SiC interface have been most effective in reducing the large interface trap density near the 4H-SiC conduction band-edge for (0001) Si face 4H-SiC. Herein, we report the effect of nitridation on interfaces created on the (11 20) a-face and the (0001) C-face of 4H-SiC. Significant reductions in trap density (from >1013 cm-2 eV-1 to ~ 1012 cm-2 eV-1 at EC-E ~0.1 eV) were observed for these different interfaces, indicating the presence of substantial nitrogen susceptible defects for all crystal faces. Annealing nitridated interfaces in hydrogen results in a further reduction of trap density (from ~1012 cm-2 eV-1 to ~5 x 1011 cm-2 eV-1 at EC-E ~0.1 eV). Using sequential anneals in NO and H2, maximum field effect mobilities of ~55 cm-2 V-1s-1 and ~100 cm-2 V-1s-1 have been obtained for lateral MOSFETs fabricated on the (0001) and (11 20) faces, respectively. These electronic measurements have been correlated to the interface chemical composition.

Abstract: 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.