(Invited) Interface Defects in C-face 4H-SiC MOSFETs: An Electrically-Detected-Magnetic-Resonance Study

Abstract

Using electrically-detected-magnetic-resonance spectroscopy and a device simulation, we studied dominant interface defects, named "C-face defects," in C-face 4H-SiC metal-oxide-semiconductor field-effect transistors (MOSFETs). The C-face defects act as hole traps via their donor levels, when they are not passivated by hydrogen atoms. The densities of unpassivated C-face defects were estimated to be from 4×10 12 cm -2 to 13×10 12 cm -2 in various C-face MOSFETs, which correlated with negative thresholdvoltage (V th ) shifts. We explained influences of the C-face defects on the V th instability and the channel mobility of C-face MOSFETs. C-face 4H-SiC MOSFETsSilicon carbide metal-oxide-semiconductor field-effect transistors (SiC-MOSFETs) are promising for low-energy-loss and high-power-density power transistors. SiC-MOSFETs are usually fabricated using a 4H-SiC(0001) ("Si face") surface to ensure a stability in their threshold voltages (V th ) (1,2). In contrast, a 4H-SiC(0001 _ ) ("C face") surface exhibits a wider range of the V th instability (2,3), although C-face MOSFETs can achieve a much higher field-effect mobility (µ FE = 60-100 cm 2 V -1 s -1 ) than the standard Si-face MOSFETs (µ FE = 20-30 cm 2 V -1 s -1 ) (1-4). Figure 1 shows a typical example of the V th instability observed in C-face MOSFETs. In MOSFET (a) which we call "bad type," the drain-current (I d ) versus gate-voltage (V g ) curve is horizontally shifted toward the negative direction after applying a negative V g stress (-30 V) for 1800 sec. On the contrary, in MOSFET (b) or "good type," the negative V th shift is drastically reduced even against a much longer stress time (20480 sec). However, the microscopic origin of such V th instability as well as microscopic differences between C-face and Si-face MOS interfaces is still unclear.In this paper, we present an electrically-detected-magnetic-resonance (EDMR) and device-simulation study on C-face MOSFETs. EDMR spectroscopy detected a large number of hole traps at the C-face MOS interface, which we have named the "C-face defects" (2,5). They were only observed on oxidized C face, and deeply connect with the characteristic properties of C-face MOSFETs. For instance, a primary difference in the samples shown in Figs. 1(a) and (b) was found in the densities of the C-face defects. We also found that their densities correlated with the negative V th shifts in C-face MOSFETs. Accordingly, we propose a microscopic model for the V th instability that the C-face

Anomalous carbon clusters in 4H-SiC/SiO2 interfaces

“…In the Dry sample, a single broad Lorentzian signal appeared at an isotropic g factor of 2.0024. In contrast, the Wet sample revealed sharper anisotropic EDMR signals, which were named "C-face defects," 11 and they showed a c-axial g tensor of g // = 2.0016 and g ⊥ = 2.0023. 11 We tentatively attribute the broadened signal of the Dry sample to high-density 2D electron spins because a similar phenomenon was determined for the P b centers at Si(111)/SiO 2 interfaces, if their density is ≳10 13 cm −2 .…”

“…In contrast, the Wet sample revealed sharper anisotropic EDMR signals, which were named "C-face defects," 11 and they showed a c-axial g tensor of g // = 2.0016 and g ⊥ = 2.0023. 11 We tentatively attribute the broadened signal of the Dry sample to high-density 2D electron spins because a similar phenomenon was determined for the P b centers at Si(111)/SiO 2 interfaces, if their density is ≳10 13 cm −2 . 13,14 Such high-density 2D electron spins reveal a broadened ESR signal due to 2D dipolar broadening.…”

“…For maximizing the signal-to-noise ratio of EDMR signals in the Dry MOSFETs, I d was set to be 100 μA, and the I was 750-780 nA, in the V g range between −30 and +15 V. For the case of the wet MOSFETs, the details of the optimizing EDMR setup were already reported in Ref. 11. All measurements were performed at room temperature and with a microwave of 9.462 GHz and 200 mW.…”

“…2(c)]. 11 Basically, a peak-shaped V g dependence is associated with a particular energy level of the interface defect; e.g., in Ref.…”

“…[3][4][5] The identification of interface defects in this system is a timely issue. Electron spin resonance (ESR) and electrically detected magnetic resonance (EDMR) spectroscopy have so far revealed various interface defects such as carbon clusters (C clusters), 6,7 P bC centers (interfacial carbon dangling bonds), 8,9 Si-vacancy centers, 10 C-face defects, 11 and carbon-related defects. 12 In this paper, we identify another key defect in the SiC-MOS system, which was found in dry-oxidized 4H-SiC(000 1)/SiO 2 interfaces that are known as the most deteriorated SiC-MOS interfaces.…”