Materials Science Forum Vols. 778-780

Abstract: ZrO₂ films were deposited on C-face 4H-SiC substrates by using an RF sputter at a temperature of 200°C. Then, ZrO₂ films were treated with RTA (rapid thermal annealing) process in Argon (Ar) ambient at 600°C, 700°C and 800°C for 4 minutes, respectively. The samples with RTA process show the lower leakage currents. As the measure temperature increases from room temperature (RT) to 150°C, the dielectric breakdown voltage reduces from 3 V to 1 V. The difference between quasi C-V characteristics and high frequency C-V characteristics at 1 MHz becomes larger with increasing RTA temperature. The C-V curves also shift to the left side as the measure temperature increases from RT to 150°C. It also shows the ledge on the C-V curves of samples with RTA at elevated measure temperature.

Abstract: This work deals with two applications of the Selective Epitaxial Growth of highly p-type doped buried 4H-SiC in Vapor-Liquid-Solid configuration (SEG-VLS). The first application is the improvement of the Specific Contact Resistance (SCR) of contacts made on such p-type material. As a result of the extremely high doping level, SCR values as low as 1.3x10^-6 Ω.cm² have been demonstrated. Additionally, the high Al concentration of the SEG-VLS 4H-SiC material induces a lowering of the Al acceptor ionization energy down to 40 meV. The second application is the fabrication of PiN diodes with SEG-VLS emitter and guard-rings peripheral protection. Influence of some process parameters and crystal orientation on the forward and reverse characteristics of the PiN diodes is discussed.

Abstract: Silicon carbide (SiC) is a promising semiconductor for high-power devices due to its superior material properties; high breakdown field, high electron saturation velocity, and high thermal conductivity. To implement SiC power devices, pn junction must be formed in the SiC. However, ion implantation for impurity doping has several issues for the SiC. For example, while a high-temperature (~1700 °C) post-implantation annealing is required to electrically activate implanted species [, it induces generation of crystallographic defects in the SiC, such as segregation of carbon atoms at the surface from the SiC bulk [. Therefore, development of new technology for local doping of SiC is highly demanded.

Abstract: Contact property of aluminum and 4H-SiC wafer with crystallized amorphous-silicon (a-Si) interlayer was investigated. A phosphorus-doped a-Si layer on SiC wafer was crystallized by annealing at 1377 °C. Good ohmic contact behavior and contact resistivity of 2.1 × 10^-6 Ωcm² were obtained without silicidation annealing process. Furthermore, non-doped crystallized a-Si layer insertion layer also showed ohmic contact property. However, high contact resistivity of 8.2×10^-4 Ωcm² was obtained in the non-doped a-Si sample. X-ray photo-electron spectroscopy analysis suggests that conduction band offset is significantly reduced between crystallized a-Si and SiC wafer. Therefore, a-Si insertion layer is effective for Schottky barrier height decreasing and high doping into Si layer forms low contact resistivity between Al and SiC, indirectly.

Abstract: Carrier transport in Al⁺ implanted 4H-SiC for Al concentrations in the 5 × 10¹⁹ 5 × 10²⁰ cm^-3 range and after 2000°C/30s microwave annealing are characterized. Each sample resistivity decreases with increasing temperature and attains values of about 10² Ωcm for temperatures > 600 K. At room temperature, resistivity decreases from 4 × 10^-1 Ωcm to 3 × 10² Ωcm with the increase of implanted Al concentration. The onset of an impurity band conduction around room temperature takes place for implanted Al concentrations > 3 × 10²⁰ cm^-3. Al⁺ implanted and microwave annealed 4HSiC vertical p⁺-i-n diodes have shown promising forward characteristics.

Abstract: Two families of Al⁺ implanted vertical p⁺in diodes that have been processed all by identical steps except the post implantation annealing one have been characterized with current voltage measurements from -100 to +5V at different temperatures. Analysis of the static forward current voltage characteristics shows two different ideality factor regions, which are distinct for each family. The reverse current voltage characteristics reveals corresponding two different activation energies. These are assumed to be correlated to the Z_1/2 defect for the one case and another one with an activation energy of 0.25eV.

Abstract: Temperature dependence of the femtosecond laser modified region on silicon carbide was measured. The current-voltage characteristics showed the ohmic properties and thus we could evaluate the specific resistance for each irradiation conditions and the measured temperatures. The specific resistance was increased with decreasing temperature. From the double exponential fit to the temperature dependence of the specific resistance, the trapping energy of the impurity levels formed by the femtosecond laser modification was found to be 4.5 meV and 51.4 meV.

Abstract: The knowledge of the temperature behavior of Ohmic contacts is an important issue to understand the device operation. This work reports an electrical characterization as a function of the temperature carried out on nickel silicide (Ni₂Si) Ohmic contacts, used both for n-type and p-type implanted 4H-SiC layers. The temperature dependence of the specific contact resistance suggested that a thermionic field emission mechanism dominates the current transport for contacts on p-type material, whereas a current transport by tunneling is likely occurring in the contacts on n-type implanted SiC. Furthermore, from the temperature dependence of the electrical characteristics, the activation energies for Al and P dopants were determined, resulting of 145 meV and 35 meV, respectively. The thermal stability of the electrical parameters has been demonstrated upon a long-term (up to ~100 hours) cycling in the temperature range 200-400°C.

Abstract: An ohmic contact process by using tri-layer materials for a source contact of a silicon carbide (SiC) metal oxide semiconductor field effect transistor (MOSFET) is proposed. The authors validate its extremely low contact resistance for both n-type and p-type SiC by a simple process. The characteristics of Ti/Al/Si ohmic contacts were measured by using the transfer length method (TLM). We examined the dependence of the contact resistance on the thickness of each layer of Ti/Al/Si. Then, it is found that Ti/Al/Si contacts with an appropriate thickness show excellent ohmic properties for both n-type and p-type SiC. N-type specific contact resistance (ρ_n) of 3.7 × 10^-6 Ω cm² and p-type specific contact resistance (ρ_p) of 1.7 × 10^-4 Ω cm² are obtained with Ti (20 nm) /Al (30 nm) /Si (30 nm).

Abstract: As a new post-implantation activation annealing of Silicon Carbide (SiC), we propose the Si-vapor ambient anneal using Tantalum Carbide / metal Tantalum composite materials (TaC/Ta). In this technique, semi-closed TaC/Ta container which can supply Si-vapor ambient is used, and Si vapor compensates thermal desorption Si atoms from the SiC surface above 1500°C and can maintain the original surface morphology by controlling a process temperature and Ar back pressure. Therefore the Si-vapor ambient anneal is able to simplify the process of conventional activation anneal methods using refractory cap-layers for protecting SiC surface from thermal damage of Si-atom desorption. Experiments were performed under Ar 1.3kPa at 1600/1700°C for 5min optimized conditions in a 6inch TaC/Ta container, and the Al⁺ ion-implanted 4H-SiC properties after annealing were characterized by atomic force microscopy (AFM), Rutherford Back-scattering Spectrometry (RBS) channeling method, and four-point probe method. According to evaluation, there was no roughening of SiC surface from AFM topographic images and recovery of crystallinity at the ion-implanted layer was equivalent to by the conventional cap-layer method from RBS channeling measurement. The sheet resistance of 12kΩ/ at 1700°C equal to the typical Al⁺ ion implanted p-type SiC is confirmed by four-point probe method.