Demonstration and analysis of channel mobility, trapped electron density and Hall effect at SiO2/SiC (0$\bar{3}$3$\bar{8}$) interfaces (original) (raw)
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Atomic scale characterization of SiO2/4H-SiC interfaces in MOSFETs devices
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The breakthrough of 4H-SiC MOSFETs is stemmed mainly due to the mobility degradation in their channel in spite of the good physical intrinsic material properties. Here, two different n-channel 4H-SiC MOSFETs are characterized in order to analyze the elemental composition at the SiC/SiO 2 interface and its relationship to their electrical properties. Elemental distribution analyses performed by EELS reveal the existence of a transition layer between the SiC and the SiO 2 regions of the same width for both MOSFETs despite a factor of nearly two between their electron mobility. Additional 3D compositional mapping by atom probe tomography corroborates these results, particularly the absence of an anomalous carbon distribution around the SiC/SiO 2 interface.
IEEE Electron Device Letters, 2000
In the family of wide band gap materials (silicon carbide, the group III nitrides and diamond), SiC is the only semiconductor that has a native oxide, and metal-oxide-semiconductor field effect transistors (MOSFETs) have been fabricated using both 4H-and 6H-SiC. The 4H polytype has higher bulk carrier mobility [1], and is hence the polytype of choice for power MOSFET fabrication. However, reported channel mobilities for 4H n-channel, inversion mode devices are substantially lower than for 6H-MOSFETs. For power device applications, the advantage provided by 4H-SiC of lower epilayer resistance for a given operating voltage is compromised by the low channel mobility. Schorner, et al. [2] attribute the poorer performance of 4H devices to a large, broad interface state density located at approximately 2.9eV above the valence band edge in both polytypes. More of these states lie in the band gap for 4H-SiC (Egap ~ 3.3eV) compared to 6H-SiC (Egap ~ 3eV) where they act to reduce channel mobility through field termination, carrier trapping and Coulomb scattering. Afanasev, et al. proposed that interface states in SiC/SiO2 structures result from carbon clusters at the interface and defects in a nearinterface sub-oxide that is produced when the oxidation process is terminated. The large interface trap density near the conduction band edge proposed by Schorner, et al. has been observed experimentally for both n-SiC and p-SiC . Li, et al. [7] originally reported improvements in the electrical performance of dry oxides on 6H-SiC annealed in nitric oxide (NO). We have grown oxides on 4H-SiC using standard thermal techniques [8] and conducted post oxidation anneals in . We find that the interface state density near the conduction band edge in n-4H-SiC can be reduced to levels comparable to the interface state density near the conduction band edge in 6H-SiC. Furthermore, the effective channel mobility for inversionmode 4H-SiC MOSFETs improves significantly following high temperature anneals in nitric oxide.