Materials Science Forum Vol. 924

Abstract: TLM structures on Al-implanted regions with different implanted Al concentrations and different annealing temperatures were processed and characterized by electrical measurements in order to determine the influence of these parameters on the ohmic resistivity. Based on these results, a TCAD model was developed that considers the carrier concentration of the implanted region, the effective density of states for holes and the hole tunneling mass at the Ti₃SiC₂-SiC interface. It could be shown that Ti₃SiC₂ allows to form ohmic contacts on Al implanted samples with an effective doping concentration down to 3·10¹⁷ cm^-3. Furthermore the effective density of states for holes in Ti₃SiC₂ was determined to 8.5·10¹⁸ cm^-3 and the hole tunneling mass in SiC and Ti3SiC2 in the range of 2·10^-34 kg to 6·10^-33 kg depending on the sample.

Abstract: Nickel (Ni) is the most widely used metal for the formation of ohmic contact on n-type SiC. However, the irregular contact can potentially cause degradation in the device performance. To form the uniform ohmic interface, titanium (Ti) was applied as a barrier layer. Ni/Ti/SiC and Ti/Ni/SiC contact metal structures were prepared, and ohmic contacts were formed using a rapid thermal annealing process. The interfacial properties of both contact metal structures were enhanced by applying the Ti layer. The specific contact resistance of ohmic contacts showed a slightly lower or similar value (~ low 10⁵ Ωcm²) compared with the specific contact resistance values formed from only the Ni contact metal.

Abstract: Studying the ohmic contacts formed on ion-implanted SiC layers is fundamental to understand and to predict the behavior of practical devices. Ohmic contacts to n- (1×10¹⁹ cm⁻³) and p-type (1×10²⁰ cm⁻³) ion-implanted 4H-SiC using Ni/W/TaSi₂/Pt were investigated. No degradation of the specific contact resistance nor a minute change of the surface morphologies was observed after 300 h of 500 oC thermal treatment in air. From auger electron spectroscopy (AES) depth profiles, it was found that the oxidation of the protective platinum silicide overlayer significantly slowed down further migration of oxygen to the SiC interface. In addition, Pt and W played the role of mutual blocking, which guarantees the stability of the contact. This research suggests that the contacts are very promising for applications in harsh environments, where the simultaneously completed both on n-and p-type stability ohmic contacts is crucial.

Abstract: A sandwich structure of Ni/Nb/4H-SiC was prepared and annealed at different temperature from 750°C to 1050°C. The electrical property and crystalline structure of Ni/Nb electrode was characterized by transmission line method and X-ray diffraction. It was found that the annealing temperature and the thickness of Ni/Nb layer played an important role in obtaining Ohmic contact. A low specific contact resistance of 1.1×10^-5 Ω·cm² was obtained when the Ni(50nm)/Nb(50nm) electrode was annealed at 1050°C. The Ohmic contact mechanism of Ni/Nb/4H-SiC was proposed.

Abstract: Low-resistance Ohmic contact on n⁺ 4H-SiC C-face with Titanium was demonstrated. In a conventional NiSi Ohmic contat on n-type 4H-SiC, a carbon agglomeration at the silicide/SiC interface occurs, and contact resistance becomes larger. For suppressing the carbon agglomeration, laser annealing and Ti metal were introduced to form both silicide and carbide. Ti (75 nm)/SiC and Ni (75 nm)/SiC Ohmic contacts were formed on backside C-face of high concentration impurity doped 4H-SiC substrates with and without activation annealing. Electrical properties were investigated after 40 nanoseconds pulse laser annealing in Ar ambient. As the result, the lowest specific contact resistance of 7.9×10^-5 Ωcm² was obtained in Ti (75 nm)/SiC sample in the case of ion implanted sample at 500°C and with activation annealing at a laser power of 2.2 J/cm².

Abstract: The formation of Ohmic contacts to n-type 4H-SiC layers at low annealing temperature using dopant segregation technique is reported. n-SiC epilayer was implanted with phosphorous and subsequently activated at 1700 °C. Ni metal contacts fabricated on phosphorous implanted and annealed epilayers produced Ohmic contacts with a specific contact resistivity (ρ_c) of ~7.2x10^-5 Ω.cm² at an annealing temperature of 550 °C. ρ_c decreased with further annealing temperature reaching a value of ~2.1x10^-5 Ω.cm² at 1000 °C. XRD analysis showed that nickel silicide phase was formed at both 550 °C and 1000 °C.

Abstract: The incorporation of Germanium (Ge) in 4H-SiC has recently being reported as enabling an increase of the electron mobility in n-type doped layers. The present work aims at evaluating the impact of the Ge doping on two types of SiC devices: Merged PiN-Schottky (MPS) diodes and Trench MOSFETs.

Abstract: 4H-SiC pMOSFETs with Al-doped S/D and NbNi silicide ohmic contacts were demonstrated and were characterized at up to a temperature of 200 °C. For the pMOSFETs, silicides on p-type 4H-SiC with Nb/Ni, NbNi alloy, Ni and Nb/Ti were investigated, and the Nb/Ni silicide with the contact resistance of 5.04×10^-3 Ωcm² were applied for the pMOSFETs.

Abstract: In this work we have studied the influence of design and process variations on electrical performance of 1.7 kV 4H-SiC Schottky diodes. Diodes with two variations in their active region design namely, stripe design and segment design, were fabricated in this study. Field Limiting Rings (FLRs) or Junction Termination Extension (JTE) were used as edge termination design to achieve a blocking voltage of 1.7 kV. In addition to these designs an extra processing step of nitrous oxide (N₂O) annealing was performed on some of the diodes. The study has shown that there is no extra beneficial effect of nitrous oxide annealing on device characteristics.

Abstract: Carrier lifetime in low carrier concentration 4H-SiC epitaxial layers grown on the C-face was enhanced by using carbon implantation and post annealing. The measured carrier lifetime increased with the thickness of the epitaxial layer and was 11.4 µs for the 150 µm thick epitaxial layer. The internal carrier lifetime was estimated as 21 µs from the dependence of the measured carrier lifetime on the epitaxial layer thickness. This value is almost comparable to the reported values of the internal carrier lifetime for the layers grown on the Si-face.