The correlation between thermal oxide reliability and dislocations in n-type 4H-SiC (0001) epitaxial wafers has been investigated. The thermal oxides were grown by dry oxidation at 1200°C followed by nitrogen postoxidation annealing. Charge-to-breakdown values of thermal oxides decrease with an increase in the number of the dislocations in a gate-oxide-forming area. Two types of dielectric breakdown modes, edge breakdown and dislocation-related breakdown, were confirmed by Nomarski microscopy. In addition, it is revealed that basal plane dislocation is the most common cause of the dislocation-related breakdown mode.

We investigated the effects of the interface state density (DIT) at the interfaces between SiO2 and the Si-, C-, and a-faces of 4H-SiC in n-channel metal-oxide-semiconductor field-effect transistors that were subjected to dry/nitridation and pyrogenic/hydrotreatment processes. The interface state density over a very shallow range from the conduction band edge (0.00 eV < EC − ET) was evaluated on the basis of the subthreshold slope deterioration at low temperatures (11 K < T). The interface state density continued to increase toward EC, and DIT at EC was significantly higher than the value at the conventionally evaluated energies (EC − ET = 0.1–0.3 eV). The peak field-effect mobility at 300 K was clearly inversely proportional to DIT at 0.00 eV, regardless of the crystal faces and the oxidation/annealing processes.

Time-dependent dielectric breakdown (TDDB) measurement of MOS capacitors on an n-type 4 ° off-axis 4H-SiC(0001) wafer free from step-bunching showed specific breakdown in the Weibull distribution plots. By observing the as-grown SiC-epi wafer surface, two kinds of epitaxial surface defect, Trapezoid-shape and Bar-shape defects, were confirmed with confocal microscope. Charge to breakdown (Qbd) of MOS capacitors including an upstream line of these defects is almost the same value as that of a Wear-out breakdown region. On the other hand, the gate oxide breakdown of MOS capacitors occurred at a downstream line. It has revealed that specific part of these defects causes degradation of oxide reliability. Cross-sectional TEM images of MOS structure show that gate oxide thickness of MOS capacitor is non-uniform on the downstream line. Moreover, AFM observation of as-grown and oxidized SiC-epitaxial surfaces indicated that surface roughness of downstream line becomes 3-4 times larger than the as-grown one by oxidation process.

The reliability of thermal oxides grown on an n-type 4H-SiC(0001) was investigated using an area-scaling method, and the influence of dislocation defects on the time-dependent dielectric breakdown characteristics of thermal oxides was examined. A thermal oxide was grown by dry oxidation at 1200 C followed by nitrogen post-oxidation annealing. Using the area-scaling method, the time-to-breakdown (t BD ) distribution curves of metal-oxide-semiconductor (MOS) capacitors with different gate area sizes were converged to a single one. It was clearly shown that origins of dielectric breakdown are edge breakdown and dislocation-related breakdown for steep and gradual slopes of the area-scaling normalized t BD distribution curve, respectively. In addition, a yield analysis of MOS capacitors quantitatively indicated that both threading screw dislocation and basal plane dislocation are predominant killer defects for the dielectric breakdown of thermal oxides on the 4H-SiC(0001) face.

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