Materials Science Forum Vols. 717-720

Abstract: We show that it is possible to obtain information relating to deep level interface traps, or so called ‘slow states’, by using the photo-CV characterisation method. Sub-bandgap illumination has been chosen in order to avoid band-to-band excitation for the creation of minority carriers. This enables information to be extracted from trapping states at the SiO2/SiC interface that are energetically deep within the band gap. Empirical observations of deep level trapping states with life times in the order of tens of hours are reported and the interface trap density as a function of energy has been extracted using the Terman method. Characterisation of these interface states will aid the development of new fabrication processes, with the aim of reducing the interface trap density to the same level as that of the SiO2/Si interface and facilitating the production of higher quality SiC based devices.

Abstract: The radiation hardness of Al2O3 as a dielectric for SiC surface passivation is studied and compared to SiO2 for potential application in radiation hard SiC devices. SiO2 is deposited on 4H-SiC by PECVD and post annealed in N2O, whereas Al2O3 is deposited by atomic layer deposition (ALD). The oxides are bombarded with Ar ions in an energy range to produce maximum damage near the oxide/SiC interface. Metal-insulator-semiconductor structures are prepared and their dielectric characteristics are analyzed using capacitance-voltage measurements. Additionally, the effect of the interface damage on surface recombination is studied using the optical free carrier absorption method for the same samples. The results indicate that the SiO2/SiC interface is significantly affected at 1×1011 cm-2 fluence of Ar ions, however, the dielectric properties of Al2O3/SiC interface remain unaffected even for ten times higher fluences. Similar observations are made for the surface recombination measurements.

Abstract: In this work a Pt/HfO₂/SiO₂/SiC MIS capacitor is exposed in air at 400°C for 1000 hours, with its oxide capacitance, flatband voltage and density of interface traps being measured at various time intervals. After the structure has been shown to operate reliably for extensive periods of time at 400°C, the C-V characteristics of a device from the same fabrication batch are measured at 300°C in different concentrations of H2 and examined for sensitivity. The results demonstrate that gas sensitive MIS capacitors incorporating high-ĸ dielectrics, have the potential to operate at extreme temperatures for long periods of time. This makes them suitable for deployment in hostile conditions, where regular servicing may not be possible.

Abstract: This paper investigates n-type doping of point-defect compensated high purity semi-insulating (HPSI) 4H-SiC using a pulsed laser (10 ns FWHM @ 260 nm) for the introduction of nitrogen to shallow depths. A thermal model is presented using COMSOL Multiphysics featuring nonlinear temperature dependent material properties and a volumetric heat source term that takes into account the laser absorption depth for common ultraviolet irradiating wavelengths. The temperature distribution in the material and the amount of time that the surface and near-surface regions are at high temperature determines how many laser pulses are required to dope to the desired depth, and simulation results are presented and fit to measured data. The simulations and measured data show that for shallow doping a short wavelength ultraviolet laser should be used to localize the heat at the surface so the dopant can’t diffuse deep into the material. The laser enhanced diffusion process has been used to incorporate nitrogen into HPSI 4H-SiC with a measured surface concentration greater than 10²⁰ cm^-3 and a nonlinear thermal model was built.

Abstract: A post implantation microwave annealing technique has been applied for the electrical activation of Al⁺ implanted ions in semi-insulating 4H-SiC. The annealing temperatures have been 2000-2100°C. The implanted Al concentration has varied from 5 x 10¹⁹ to 8 x 10²⁰ cm^-3. A minimum resistivity of 2 x 10^-2 Ω∙cm and about 70% electrical activation of the implanted Al has been measured at room temperature for an implanted Al concentration of 8 x 10²⁰ cm^-3 and a microwave annealing at 2100°C for 30 s.

Abstract: In this paper, we demonstrate the fabrication of SBD utilizing SiC process line specially designed for mass production of SiC power device. In SiC power device process, ion implantation and activation annealing are key technologies. Details of ion implantation system and activation annealing system designed for SiC power device production are shown. Further, device characteristics of SBD fabricated using this production line is also shown briefly.

Abstract: This paper reports on the effects of different post-implantation annealings on the electrical properties of interfaces to p-type implanted 4H-SiC. The morphology of p-type implanted 4H-SiC was controlled using a capping layer during post-implantation activation annealing of the dopant. Indeed, the surface roughness of Al-implanted regions strongly depends on the use of the protective capping layer during the annealing. However, while the different morphological conditions do not affect the macroscopical electrical properties of the implanted SiC (such as the sheet resistance), they led to an improvement of the morphology and of the specific contact resistance of Ti/Al Ohmic contacts formed on the implanted regions. These electrical and morphologic improvements were associated with a lowering of Schottky barrier height. Preliminary results showed that the different activation annealing conditions of p-type implanted SiC can affect also the electrical parameters (like threshold voltage and mobility) of lateral MOSFETs.

Abstract: The thickness-ratio effects of Ni/Nb bi-layer electrodes were studied for power device applications. The reaction microstructure and electrical contact property were investigated after annealing at 1000 °C and compared with the results of an Ni electrode. Microstructure-related problems of the Ni electrode could be successfully resolved without sacrificing ohmic contact behavior by the addition of Nb to a Ni based electrode. Carbon precipitation was reduced with increasing Nb thickness by the formation of carbides, which led to good adhesion between the electrode and a wiring pad. High shear strength of the bonded wire was also obtained by the elimination of the carbon precipitates on the electrode surface.

Abstract: In this work the electrical properties of Ni and Ni₂Si contacts on n-type 4H-SiC were correlated to the strong structural changes at the contact/SiC interface upon annealing. We can conclude that only δ-Ni₂Si grains play a main role in determining electrical transport properties of the Ni-based ohmic contacts to n-SiC. It is presumed that a recrystallization and texturization of δ-Ni₂Si phase on (0001)SiC-surface during high temperature annealing (> 900°C) contributes to the change of barrier heights, as well as specific contact resistance of contacts.

Abstract: An electroless nickel film contains 5-14% by weight of phosphorus. Because of the presence of such a high concentration of phosphorus, electroless nickel can be a useful and convenient source of phosphorus dopant in the fabrication of n-type ohmic contacts for SiC. This paper describes the successful deposition of a Ni:P layer on 4H-SiC through electroless nickel plating followed by a discussion of the results of surface science and electrical measurements. Specific contact resistivity on lightly-doped samples with carrier concentration of 2.5 ´ 10¹⁶ cm^-3 has been found to be about 4.8 ´ 10^-6 Ωcm² without any need for ion implantation. This metallization technique is especially useful in broad area ohmic contact formation on the back of n-type SiC substrate.