Jeong Hyuk Yim

Comparison of thermal and atomic-layer-deposited oxides on 4H-SiC after post-oxidation-annealing in nitric oxide

The electrical properties of thermally grown and atomic-layer-deposition (ALD) oxides, followed by nitridation treatment, on 4H-SiC substrate were compared. The nitridation treatment was performed with post oxidation annealing in NO atmosphere (NO POA). The best electrical characteristics of the thermally grown and ALD oxides were observed at 120 and 180 min NO POA, respectively. The NO POA treated ALD oxide showed extremely low interface trap density (Dit), less than 1011 eV−1 cm−1. A metal-oxide-semiconductor field-effect-transistor with the ALD oxide showed high field effect mobility, especially in the high electric field region. The reasons for these superior results were also discussed.

Electrical Properties of the La2O3/4H-SiC Interface Prepared by Atomic Layer Deposition Using La(iPrCp)3 and H2O

The La2O3 and Al2O3/La2O3 layers were grown on 4H-SiC by atomic layer deposition (ALD) method. The electrical properties of La2O3 on 4H-SiC were examined using metal-insulator-semiconductor (MIS) structures of Pt/La2O3(18nm)/4H-SiC and Pt/Al2O3(10nm)/La2O3(5nm)/4H-SiC. For the Pt/La2O3(18nm)/4H-SiC structure, even though the leakage current density was slightly reduced after the rapid thermal annealing at 500 oC, accumulation capacitance was gradually increased with increasing bias voltage due to a high leakage current. On the other hand, since the leakage current in the accumulation regime was decreased for the Pt/Al2O3/La2O3/4H-SiC MIS structure owing to the capped Al2O3 layer, the capacitance was saturated. But the saturation capacitance was strongly dependent on frequency, indicating a leaky interfacial layer formed between the La2O3 and SiC during the fabrication process of Pt/Al2O3(10nm)/ La2O3(5nm)/ 4H-SiC structure.

Homoepitaxial growth and electrical characterization of iron-doped semi-insulating 4H-SiC epilayer

The authors attempted to grow a semi-insulating silicon carbide (SiC) epitaxial layer by in situ iron doping. The homoepitaxial growth of the iron-doped 4H-SiC layer was performed by metal-organic chemical vapor deposition using the organo-silicon precursor bis(trimethylsilylmethane) (C7H20Si2) and the metal-organic precursor t-butylferrocene (C14H17Fe). For the measurement of the resistivity of the iron-doped 4H-SiC epilayers, the authors used the on resistance of Schottky barrier diode. Based on the measurement of the on resistance, it is shown that the free carrier concentration was decreased with increasing partial pressure of t-butylferrocene. The resistivity of the iron-doped 4H-SiC epilayer was about 108Ωcm.

Electrical Properties of Atomic-Layer-Deposited La2O3/Thermal-Nitrided SiO2 Stacking Dielectric on 4H-SiC(0001)

We have investigated the electrical properties of metal-oxide-semiconductor (MOS) capacitors with atomic-layer-deposited La2O3, thermal-nitrided SiO2, and atomic-layer-deposited La2O3/thermal-nitrided SiO2 on n-type 4H-SiC. A significant reduction in leakage current density has been observed in La2O3 structure when a 6-nm thick thermal nitrided SiO2 has been sandwiched between the La2O3 and SiC. However, this reduction is still considered high if compared to sample having thermal-nitrided SiO2 alone. The reasons for this have been explained in this paper.

Effect of Postoxidation Annealing on High Temperature Grown SiO2 / 4H-SiC Interfaces

SiO 2 was grown by dry (O 2 ) thermal oxidation (at 1175, 1300, or 1400°C) on n-type 4H-SiC substrates. The samples were prepared by subsequently exposing the grown Si0 2 film on 4H-SiC to postoxidation annealing (POA) treatment using nitric oxide (NO) gas. The SiC-Si0 2 interfaces were characterized by high frequency capacitance-voltage measurements, X-ray photoelectron spectroscopy (XPS), and ellipsometry. The interface trap density of the dry oxide grown at 1300°C was much lower than others. At a higher grown temperature (1400°C), the electrical and physical properties of the oxide were not improved compared to those oxides grown at 1175°C. The XPS measurements provided evidence for the presence of intermediate oxidation states of Si oxycarbide in all samples. The areal densities of the intermediate oxidation states affected the interface trap density. The NO POA treatment significantly improved the interface trap density, the near-interface trap density, and the effective oxide charge density of the oxides grown at 1175 and 1300°C. But, this improvement was not observed for the oxide grown at 1400°C. The electrical properties of the metal-oxide-semiconductor devices fabricated using these oxides have also been discussed in terms of the oxide chemical compositions, which were determined by XPS and an oxide etching test.

Homoepitaxial Growth of Vanadium-Doped Semi-insulating 4H-SiC Using Bis-trimethylsilylmethane and Bis-cyclopentadienylvanadium Precursors

The authors attempted to grow a semi-insulating 4H-SiC epitaxial layer by in situ vanadium doping. The homoepitaxial growth of the vanadium-doped 4H-SiC layer was performed by metallorganic chemical vapor deposition using the organosilicon precursor bis-trimethylsilylmethane (BTMSM, C 7 H 20 Si 2 ) and the metallorganic precursor bis-cyclopentadienylvanadium (Verrocene, C 10 H 10 V). The vanadium doping effect on the crystallinity of the epi layer was very destructive. Vanadium-doped epi layers grown under normal conditions had various crystal defects such as micropipes and polytype inclusions, but this crystallinity degradation was overcome by elevating the growth temperature. For measurement of the resistivity of the highly resistive vanadium-doped 4H-SiC epi layers, the authors used the on-resistance technique. Based on the measurements of the on-resistance of the Schottky barrier diode fabricated using the vanadium-doped epi layers, it was revealed that the residual donor concentration of the epi layers was decreased with increasing partial pressure of verrocene. The resistivity of the in situ vanadium-doped 4H-SiC epi layer was about 10 7 -10 12 Ω cm.

4H-SiC Planar MESFETs on High-Purity Semi-Insulating Substrates

Planar MESFETs were fabricated on high-purity semi-insulating (HPSI) 4H-SiC substrates. The saturation drain current of the fabricated MESFETs with a gate length of 0.5 μm and a gate width of 100 μm was 430 mA/mm, and the transconductance was 25 mS/mm. The maximum oscillation frequency and cut-off frequency were 26.4 GHz and 7.2 GHz, respectively. The power gain was 8.4 dB and the maximum output power density was 2.8 W/mm for operation of class A at CW 2 GHz. MESFETs on HPSI substrates showed no current instability and much higher output power density in comparison to MESFETs on vanadium-doped SI substrates.

Effects of thermally oxidized-SiN gate oxide on 4H-SiC substrate

We have investigated and reported the results on oxidized-SiN gate oxides on n-type 4H-SiC. The quality of this oxide has been compared with thermal nitrided and dry oxides. In the oxidized-SiC sample, a significant improvement in oxide deposition/growth rate has been obtained while the metal-oxide-semiconductor characteristics of the oxide are comparable to the thermal-nitrided oxide and much better than dry oxide. This achievement has been explained using a proposed chemical model.

Improved 4H-SiC MOS Interface Produced by Oxidized-SiN Gate Oxide

We have investigated the electrical and physical properties of the oxidized-SiN with or without post oxidation annealing (POA) in N2 gas. A significant reduction in interface-trap density (Dit) has been observed in the oxidized-SiN with N2 POA for 60 min if compared with other oxides. The reason for this has been explained in this paper.

Effects of rapid thermal annealing on Al2O3/SiN reaction barrier layer/thermal-nitrided SiO2 stacking gate dielectrics on n-type 4H-SiC

In this letter, we have reported electrical and physical properties of rapid thermal annealed (RTA) Al2O3 stacking dielectric on n-type 4H-SiC. The effects of SiN-reaction barrier layer (RBL) between Al2O3 and thermal-nitrided SiO2 on SiC-based metal-oxide-semiconductor characteristics have been investigated and compared. A significant reduction in oxide-semiconductor interface-trap density (Dit), improvement in dielectric breakdown field and reliability has been observed after the SiN-RBL has been introduced between Al2O3 and SiO2. High-resolution transmission electron microscope and Auger electron spectroscopy analyses reveal that the SiN-RBL suppresses Al diffusion into the nitrided SiO2 during RTA process.