Abstract: Different SiC thermal oxide passivation techniques were characterized using UV-induced hysteresis to estimate the fixed charge, Qf, and interface-trapped charge, Qit. Steam-grown oxides have a fixed charge density of Qf=-1x1012 cm-2, and a net interface-trapped charge density of Qit=4x1011cm-2. Addition of a thin low-pressure chemical-vapor deposited (LPCVD) silicon nitride layer decreased these parameters to Qf=-2x1011 cm-2 and Qit=4x1010 cm-2. Dry oxide shows a fixed charge density, Qf=-3x1012 cm-2 and interface-trapped charge density, Qit=4x1011 cm-2 which changes to Qf=+7x1010 cm-2 and Qit=1x1010 cm-2 with the addition of a LPCVD silicon nitride cap. Dry thermal oxide with a silicon nitride cap was used to passivate SiC MESFETs to achieve a power-added efficiency of 60% in pulsed operation at 3 GHz in Class AB bias conditions.
Abstract: Utilizing an very sensitive electron spin resonance (ESR) technique, spin dependent recombination (SDR) we have identified interface and near interface trapping centers in 4H and 6H SiC/SiO2 metal oxide semiconductor field effect transistors (MOSFETs). We extend our group’s earlier observations on 6H devices to the more technologically important 4H system and find that several centers can play important roles in limiting the performance of SiC based
Abstract: Technological aspects of ion implantation in SiC device processes are described.
Annealing techniques to suppress surface roughening of implanted SiC (0001) are demonstrated. Trials to achieve a low sheet resistance are described for n-type and p-type doping. Implantation into the (11-20) face is also presented. Electrical behaviors of implants near implanted tail regions are discussed based on experiments.
Abstract: Most of the ion implanter is large scale, high acceleration voltage and expensive. For research and development, such a huge implanter is not required. Our motivation is to make desktop type ion implanter for SiC device. We report the fabrication of a compact 100 kV ion implanter. In order to miniaturize the equipment,
an ion source, an accelerator tube and a main chamber were vertically arranged. We implanted Argon (Ar) and Nitrogen (N) ions to 6H-SiC substrate and the implanted 6H-SiC substrates were characterized by Fourier Transform Infrared Spectrometer (FTIR), Rutherford Backscattering Spectrometry (RBS) and Secondary Ion Mass Spectrometry (SIMS). In this report, concept of desktop ion implanter, evaluation of implanted substrate and its device application are presented. In order to characterize capability, with using the newly made compact ion implanter, it was possible to make implantation on SiC to get amorphous layer suitable for deices.
Abstract: We develop the rapid thermal anneal system of the implanted SiC, Electron Bombardment Anneal System (EBAS), which is able to heat up to 1900 oC with a rate of 320 oC/min in vacuum. Using this novel system, the annealing of N+ implanted SiC samples (total dose: 2.4 x 1015 cm-2, thickness: 220 nm) at 1900 oC for 0.5 min results in a low sheet resistance of 1.39 x 103 ohm/sq. with
extremely low roughness of the surface (RMS value: 0.32 nm). It is also demonstrated that EBAS can anneal the sample with low electric power consumption.
Abstract: New results are presented of a surface trench defect observed during anneal of
room temperature Al implants. The size of the surface defect is proportional to anneal
temperature and occurs predominantly in the implanted zone. Signs of lattice strain are observed outside the implanted zone as well.
Abstract: The authors have investigated electrical behavior of implanted Al and B atoms near a “tail” region in 4H-SiC (0001) after high-temperature annealing. For aluminum-ion (Al+) implantation, slight in-diffusion of Al implants occurs in the initial stage of annealing at 1700 °C. Nearly all of implanted Al atoms, including the in-diffused Al atoms were activated by annealing at 1700 °C for 1 min. Several electrically deep centers are formed by Al+ implantation. The concentrations of the centers are 3-4 orders-of-magnitude lower than that of implanted Al-atom concentration. For boron-ion (B+) implantation, significant out- and in-diffusion of B implants occur in the initial stage of annealing at 1700 °C. Most of the in-diffused B implants work as B acceptors. A high density of B-related D center exists near the tail region. To suppress the B diffusion, a ten-times higher dose of carbon-ion (C+) co-implantation is effective. However, high concentrations of additional deep centers
are introduced by such high-dose C+ co-implantation.
Abstract: Furnace annealing and lamp annealing of aluminum implanted layers in 4H silicon carbide (SiC) were investigated with respect to surface degradation and electrical parameters. A sheet resistance of about 20kW/ı was obtained for an aluminum implantation dose of 1.2×1015cm-2 and annealing in the furnace at 1700°C for 30min. For the same implantation dose, lamp annealing at 1770°C for 5min resulted in a three times higher sheet resistance of 60kW/ı. The surface roughness
was best for the lamp system and stayed below 1nm for Al doses lower than 1×1015cm-2.
Abstract: We report on the electrical characterization of Al+ implanted p+/n 4H-SiC diodes via a planar technology. Hot implantation at 400°C and post implantation annealing at 1600°C and 1650°C in high purity Argon ambient were done for the realization of p+/n diodes. The current voltage characteristics of the p+/n diodes and the resistivity of the implanted layer were measured at room temperature. The majority of the 136 measured diodes had a turn on voltage of 1.75 V for both annealing temperatures. The 1600°C annealed diodes showed an almost exponential forward
characteristic with ideality factor equal to 1.4, an average reverse leakage current density equal to (4.8 ± 0.1)×10-9 A/cm2 at –100 V, and a break down voltage between 600 and 900V. The 1650°C annealed diodes often had forward “excess current component” that deviates from the ideal forward exponential trend. The average reverse leakage current density was equal to (2.7 ± 0.5)×10-8 A/cm2
at –100 V, and the breakdown voltage was between 700 and 1000V, i.e. it approached the theoretical value for the epitaxial 4H-SiC layer.
Abstract: Al+ implanted p+/n 4H-SiC diodes were realized via planar technology. The p+/n
junctions were obtained by hot implantation at 400°C, followed by a post implantation annealing at 1600°C in Silane ambient. 136 diodes and other test structures were measured: the current voltage^curves and the resistivity of the implanted layer were investigated at room temperature. The majority of the measured diodes had a turn on voltage of about 1.75 V, a forward characteristic with exponential trend and ideality factor equal to 1.2, and a very low spread in the distribution of the
reverse leakage current values at –100V. The average reverse leakage current value is (9.7 ± 0.4) × 10-9 A/cm2. The breakdown voltage of these diodes approached the theoretical value for the use epitaxial 4H-SiC layer, i.e. 0.75 – 1.0 kV. All these positive results are penalized by the high resistivity value of the implanted Al+ layer, which amounts to 11 W·cm that is one order of
magnitude higher than the desired value.