Sima Dimitrijev

Effects of nitridation in gate oxides grown on 4H-SiC

Experiments have demonstrated that nitridation provides critically important improvements in the quality of SiO2–SiC interface. This article provides results and analysis aimed at developing the much needed understanding of the mechanisms and effects associated with both annealing of pregrown oxides and direct growth in NO and N2O environments. According to the model proposed in the article, nitridation plays a double role: (1) creation of strong Si≡N bonds that passivate interface traps due to dangling and strained bonds, and (2) removal of carbon and associated complex silicon–oxycarbon bonds from the interface. This understanding of the effects of nitridation is experimentally verified and used to design a superior process for gate oxide growth in the industry-preferred N2O environment.

INTERFACIAL CHARACTERISTICS OF N2O AND NO NITRIDED SIO2 GROWN ON SIC BY RAPID THERMAL PROCESSING

Interfacial characteristics of Al/SiO2/n-type 6H–SiC metal–oxide–semiconductor capacitors fabricated by rapid thermal processing (RTP) with N2O and NO annealing are investigated. Interface state density was measured by a conductance technique at room temperature. RTP oxidation in pure O2 leads to an excellent SiO2/n-type 6H–SiC interface with interface state density in the order of 1010–1011 eV−1 cm−2. NO annealing improves the SiO2/n-type 6H–SiC interface, while N2O annealing increases the interface state density.

Physical properties of N2O and NO-nitrided gate oxides grown on 4H SiC

N2O and NO nitridation by either annealing or direct growth of gate oxides on 4H SiC is analyzed in this letter. The analysis is based on x-ray photoelectron spectroscopy binding energies and secondary ion mass spectroscopy depth profiles of nitrogen at the SiO2–SiC interface. A clean SiO2–SiC interface is found in both NO and N2O annealed/grown samples, as opposed to the interface annealed in Ar which exhibits complex suboxides and oxide–carbon compounds. The results demonstrate that nitridation in the industry-preferred N2O ambient could be as effective as nitridation in NO, provided appropriate process optimization is performed.

Mechanisms responsible for improvement of 4H-SiC/SiO2 interface properties by nitridation

An analysis of fast and slow traps at the interface of 4H–SiC with oxides grown in O2, N2O, and NO reveals that the dominant positive effect of nitridation is due to a significant reduction of the slow electron trap density. These traps are likely to be related to defects located in the near-interfacial oxide layer. In addition, the analysis confirms that the fast interface states related to clustered carbon are also reduced by nitridation.

Nitridation of silicon-dioxide films grown on 6H silicon carbide

This letter addresses the question of why it is possible to grow high-quality oxide films on N-type but not on P-type SiC. It provides results which indicate that the oxide/SiC interface would be inferior to the oxide/Si interface for both N-type and P-type SiC, if it were not for the beneficial effects of nitrogen incorporation. The letter presents, for the first time, results on nitridation of thermally grown oxides in NO and N/sub 2/O. The results demonstrate that the oxides grown on P-type can be improved by NO annealing, but not by N/sub 2/O annealing.

Band alignment and defect states at SiC/oxide interfaces

Comparative analysis of the electronic structure of thermally oxidized surfaces of silicon and silicon carbide indicates that in both cases the fundamental (bulk-band-related) spectrum of electron states is established within less than 1 nm distance from the interface plane. The latter suggests an abrupt transition from semiconductor to insulator. However, a large density of interface traps is observed in the oxidized SiC, which are mostly related to the clustering of elemental carbon during oxide growth and to the presence of defects in the near-interfacial oxides. Recent advancements in reducing the adverse effect of these traps suggest that the SiC oxidation technology has not reached its limits yet and fabrication of functional SiC/oxide interfaces is possible.

Electrical and physical characterization of gate oxides on 4H-SiC grown in diluted N2O

A systematic electrical and physical characterization of gate oxides on 4H-SiC, grown in diluted N2O at 1300 °C, has been performed. Electrical characterization by the high-frequency C-V technique, conductance technique, and slow trap profiling method reveals that the densities of interface and near-interface traps, and the effective oxide charge for gate oxides grown in 10% N2O are the lowest, compared to gate oxides grown in 100% and 0.5% N2O. These results are supported by physical characterizations using x-ray photoelectron spectroscopy, secondary ion mass spectroscopy, and atomic force microscopy. It has been shown that carbon clusters, accumulated at the SiC-SiO2 interface, directly influence the roughness of the interface and the densities of the interface and near-interface traps.

High quality ultrathin dielectric films grown on silicon in a nitric oxide ambient

High quality ultrathin silicon oxynitride films (3.5 nm) have been grown in a nitric oxide ambient using rapid thermal processing. The physical and electrical properties of these films are compared with those formed in a nitrous oxide environment. X‐ray photoelectron spectroscopy (XPS) results show that the nitric oxide (NO) grown films have a significantly different nitrogen distribution compared to the nitrious oxide (N2O) grown films. The capacitance‐voltage and current‐voltage characteristics of the NO grown and NO‐modified films are, in general, better than those of the same thickness grown in either N2O or O2.

Investigation of nitric oxide and Ar annealed SiO2/SiC interfaces by x-ray photoelectron spectroscopy

Silicon dioxide (SiO2)/silicon carbide (SiC) structures annealed in nitric oxide (NO) and argon gas ambiences were investigated using x-ray photoelectron spectroscopy (XPS). The XPS depth profile analysis shows a nitrogen pileup of 1.6 at. % close to the NO annealed SiO2/SiC interface. The results of Si 2p, C 1s, O 1s, and N 1s core-level spectra are presented in detail to demonstrate significant differences between NO and Ar annealed samples. A SiO2/SiC interface with complex intermediate oxide/carbon states is found in the case of the Ar annealed sample, while the NO annealed SiO2/SiC interface is free of these compounds. The Si 2p spectrum of the Ar annealed sample is much broader than that of the NO annealed sample and can be fitted with three peaks compared with the two peaks in the NO annealed sample, indicating a more complex interface in the Ar annealed sample. Also the O 1s spectrum of the NO annealed samples is narrow and symmetrical and can be fitted with only one peak whereas that of the Ar an...

Analysis of CMOS transistor instabilities

Abstract A method for separation and calculation of gate oxide and surface state charges in CMOS transistors have been developed, leading to a significant improvement of the analysis of CMOS integrated circuit instabilities. In order to demonstrate the usefulness of the method, an analysis of instabilities in transistors subject to high electric field and high temperature-bias stress has been carried out. Four instability mechanisms associated with high electric field stress are observed. Successively we consider a positive gate oxide charge increase due to hole tunneling from the silicon valence band into oxide hole traps (in case of negative gate bias), electron tunneling from oxide electron traps into the oxide conduction band (in case of positive gate bias), and a surface state charge increase due to tunneling of electrons from the metal to the silicon (in case of negative gate bias) or from the silicon to the metal (in case of positive gate bias). In addition instabilities associated with high temperature-bias stress are observed: drift of mobile ions in the gate oxide, increase of positive trapped charge in the gate oxide and simultaneous increase of the surface state and negative gate oxide charges.