Plasma passivation of near-interface oxide traps and voltage stability in SiC MOS capacitors

Abstract

Near-interface oxide traps severely affect the voltage stability of silicon carbide metal-oxide-semiconductor devices. In this work, electron cyclotron resonance microwave nitrogen plasma and electron cyclotron resonance microwave nitrogen-hydrogen-mixed plasma were used to passivate near-interface oxide traps in silicon carbide metal-oxide-semiconductor capacitors. An improved low-temperature midgap voltage drift method was proposed to evaluate the voltage stability of silicon carbide metal-oxide-semiconductor capacitors. Results showed that the effect of passivating near-interface oxide traps and voltage stability could be improved by increasing the nitrogen passivation time. However, excessive nitrogen passivation created deep-level interface traps that degraded the interface quality, and a small amount of hydrogen could passivate the deep-level traps produced by the excess nitrogen. As a result, the samples subjected to the passivation process with the nitrogen-hydrogen-mixed plasma had a smaller flat-band voltage drift and more stable carbide metal-oxide-semiconductor capacitors than the samples subjected to nitrogen plasma. However, the excessive introduction of hydrogen also produced additional defects, consequently making the stability of the metal-oxide-semiconductor devices sensitive to the time of the passivation process by nitrogen-hydrogen-mixed plasma. Therefore, the suitable time of mixed plasma passivation is crucial to the improvement of the stability of devices.

Reliability and Stability Improvement of MOS Capacitors via Nitrogen–Hydrogen Mixed Plasma Pretreatment for SiC Surfaces

“…Δ N ot can be calculated by normalΔ N normalo normalt = normalΔ V normalm normalg , normalh normaly normals normalt normale normalr normale normals normali normals × C normalo normalx italicAq where C ox is the oxide capacitance, A is the electrode area, and q is the elementary charge. The blue dashed line in Figure b represents the Δ N ot of all samples under alternate bias stress at 100 K. The Δ N ot is decreased for the samples pretreated by NH plasma, and the Δ N ot of NH-8 min is the lowest (8.28 × 10 10 cm –2 , as shown in Table S3), which is lower than that of the samples prepared by NH and NO postoxidation annealing. , The results demonstrate that NH plasma pretreatment could effectively inhibit oxide traps generated by thermal oxidation by reducing defects on the SiC surface.…”

“…In addition, the improvement of BTI of the SiC MOS device is ascribed to the passivation of C-related defects by N atoms and the reduction of interfacial defects. SiO x C y and C–C generally exist as near-interface oxide traps, and the corresponding defective energy levels are located near the CBM in the SiC band gap, which seriously affects BTI . NH plasma pretreatment suppressed the generation of these interface electroactive traps by eliminating surface contaminants and passivating surface defects; the introduced N atoms at the interface could also effectively passivate these defects, converting the defect energy level from near the CBM to the lower half of the SiC band gap or outside of the band gap, thus limiting the capture of defect carriers and further improving the BTI of the device …”

“…The blue dashed line in Figure 7b represents the ΔN ot of all samples under alternate bias stress at 100 K. The ΔN ot is decreased for the samples pretreated by NH plasma, and the ΔN ot of NH-8 min is the lowest (8.28 × 10 10 cm −2 , as shown in Table S3), which is lower than that of the samples prepared by NH and NO postoxidation annealing. 13,44 The results demonstrate that NH plasma pretreatment could effectively inhibit oxide traps generated by thermal oxidation by reducing defects on the SiC surface.…”

“…SiO x C y and C−C generally exist as near-interface oxide traps, and the corresponding defective energy levels are located near the CBM in the SiC band gap, which seriously affects BTI. 44 NH plasma pretreatment suppressed the generation of these interface electroactive traps by eliminating surface contaminants and passivating surface defects; the introduced N atoms at the interface could also effectively passivate these defects,…”

Ozone oxidation of 4H-SiC and flat-band voltage stability of SiC MOS capacitors

“…[9,34] Second, a low temperature can reduce the de-trapping rate of trapped carriers. [9,35] Therefore, the electrical signals of many traps can be tested by C-V curves. We observed that ∆V fb decreases with the increase in O 3 oxidation temperature, indicating that V fb BTI can be effectively improved by O 3 oxidation at high temperatures.…”