Papers by Keyword: NO Annealing

Abstract: This work investigates the impact of different gate oxide fabrication schemes on the electrical characteristics of 4H-SiC planar MOSFETs. Three processes were implemented: (1) 50 nm thermal oxidation with NO annealing at 1350°C, (2) 50 nm ALD-grown oxide with NO annealing at 1250°C, and (3) a stacked 20 nm thermal/30 nm ALD oxide structure with NO annealing at 1250°C. Electrical characterization included I_dV_g, CV, and I_gE_ox measurements. Results show that Condition 1 exhibits the lowest leakage and best uniformity, and demonstrates strong oxide integrity without soft breakdown events. In contrast, Condition 2 and 3 show increased leakage, higher variability, and evidence of soft breakdown, suggesting greater interfacial weakness. However, a surprising trend was observed in the CV analysis: Condition 2’s flat band voltage (VFB​) is closest to the ideal 0V, indicating a lower fixed charge density than Condition 1 [1], which has the most negative VFB​ (≈ -2V). The hysteresis results further highlight differences, with Condition 3 showing the largest hysteresis window (ΔVth​=0.13V). These findings suggest that while the ALD process coupled with a lower-temperature NO anneal (Condition 2) can effectively reduce fixed charges, it does not fully eliminate interfacial defects responsible for increased leakage and soft breakdown. Our results underscore the complex trade-offs in different fabrication schemes, emphasizing that careful interface engineering beyond conventional NO annealing is required to ensure reliable performance in SiC MOSFETs.

Abstract: We have used molecular dynamics simulations to investigate the decomposition mechanisms of residual C defects near the interface of 4H-SiC/SiO₂ during NO annealing. We have observed drastically rapid defect decomposition by NO and O₂ mixed gas, which is thermodynamically more realistic, compared with single NO or O₂ gas annealing. We have constructed simplified defect decomposition model. This model numerically reproduced the simulation results, suggesting that multi-step and cooperative reactions caused by the coexistence of NO and O₂ during NO annealing effectively promote the decomposition of residual C defects.

Abstract: The threshold voltage of 4H-SiC metal-oxide-semiconductor field-effect transistors (MOSFETs) show instability during normal operation, especially after bias temperature stress (BTS), and this phenomenon is called bias temperature instability (BTI). In this work, to study the factors affecting threshold voltage (V_th) instability of SiC MOSFETs, flat-band voltage (V_fb) instability of 4H-SiC metal-oxide-semiconductor (MOS) capacitors is discussed instead. Some factors, including the polarity of gate bias stress, stress time, and stress temperature, are analyzed by performing one-way bias stress C-V measurements in the devices. Firstly, positive bias stress leads to a positive V_fb shift, and negative bias stress leads to a negative one. Moreover, the V_fb shift appears to exhibit a linear relationship with log (stress time). Furthermore, the V_fb shift decreases over the temperature range of 225 K to 400 K, but slightly increases at 475 K. Finally, the V_fb stability of the MOS devices fabricated by 1200 °C NO post-oxidation annealing (POA) and those fabricated by 1250 °C NO POA is similar.

Abstract: We have developed a new interatomic potential of Si-O-C-N with newly added N for classical molecular dynamics simulation of NO annealing at 4H-SiC/SiO₂ interface. By adjusting the potential parameters to reproduce the material properties obtained from first-principles calculations for various kinds of structures, the accuracy of the potential has improved well enough to reproduce the formation of Si₃N termination at the 4H-SiC/SiO₂ interface during NO annealing. We have also observed that the defects with C=C double bonds have been modified into C-N bonds, which is supposed to be the decomposition process of residual C atoms in the NO annealing of 4H-SiC/SiO₂.

Abstract: Effects of combination of NO and POCl₃ annealing on electrical properties and their stability of 4H-SiC MOS capacitors and MOSFETs were investigated. Channel mobility of MOSFETs processed with both NO and POCl₃ annealing did not exceed that of POCl₃ annealed MOSFETs. As for the stability of flat-band voltage and threshold voltage using a constant field stress test, the combined annealed sample indicated very stable characteristics compared with single annealed devices with NO or POCl₃. The reason for obtaining stable electrical properties is discussed based on nitridation and phosphorization effects at the interface.

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: This paper describes the influence of the geometric component in the charge-pumping measurement of 4H-SiC MOSFETs. Charge-pumping measurements were conducted on 4H-SiC MOSFETs with and without NO annealing. Charge-pumping measurements with different pulse-fall times revealed that the geometric component exists in 4H-SiC MOSFETs and is especially large in the unannealed MOSFETs. A sufficiently long fall-time is needed to minimize its effect, which is expected to be 1–10 μs for 4H-SiC MOSFETs with a gate length of 10 μm.

Abstract: The effects of gamma radiation on field effect mobility and threshold voltage have been studied for lateral n-channel 4H-SiC MOSFETs passivated with nitric oxide. MOS capacitors (n and p) and n-channel lateral MOSFETs were irradiated unbiased (floating contacts) for a total gamma dose of 6.8Mrad (Si). The MOS capacitors were used to study the radiation-induced interface traps and fixed oxide charge that affect the performance of the MOSFETs. Radiationinduced interface traps were observed near the SiC valence band edge and just above mid-gap, and field effect channel mobility was reduced by 18-20% following irradiation. Even so, 4HMOSFETs appear to be more radiation tolerant than Si devices.

Abstract: High temperature (1250 oC) NO annealing was performed for deposited oxide (SiO2) and oxynitride (SiON) films on n-type 4H-SiC. Interface state density of SiO2 samples was dramatically reduced (one order of magnitude) by NO annealing compared to N2 annealing, resulting in 1x1011 cm-2eV-1 at 0.2 eV below the conduction band edge. In contrast, that of NO annealed SiON samples showed only 30% decrease and was still in the range of 1x1012 cm-2eV-1. These different effects of NO annealing against SiO2 and SiON are probably due to different reaction mechanism at the interface. Breakdown field of SiO2 samples annealed in NO was as high as 10 MV/cm. Barrier height of this sample was 2.86eV, which is close to the ideal value.