Materials Science Forum Vol. 1192

Abstract: In this paper, we study high-temperature H₂, N₂, and H₂/N₂ surface conditioning processes prior to the SiO₂ deposition as a promising approach for SiO₂/4H-SiC interface preparation in metal-oxide-semiconductor field-effect transistors (MOSFET). A thorough electrical analysis is presented, consisting of temperature-dependent transfer characteristics as well as reliability studies regarding bias temperature instabilities (BTI) and dielectric breakdown behavior. Especially N₂-containing surface pretreatments were found to greatly suppress electron traps, whereas hole trapping is enhanced. Finally, X-ray photoelectron spectroscopy (XPS) was utilized to elucidate the elemental surface composition after the different annealing procedures. The obtained results are in good agreement with the electrical characterization and complement already published results regarding the formation of surface reconstructions on 4H-SiC through H₂ and H₂/N₂ annealings.

Abstract: In this work, the electrical properties of Mo₂C/4H-SiC Schottky contacts were studied at different annealing temperatures. In particular, the Schottky barrier height was derived by current-voltage measurements on as-deposited and 400 °C and 700 °C-annealed contacts. The Schottky barrier height was comparable for the as-deposited and 400°C-annealed Mo₂C/4H-SiC contact (0.94 and 0.96 eV, respectively), while it increased (1.07 eV) for the 700 °C-annealed Mo₂C/4H-SiC one. For the sample annealed at 700°C, the electrical characterization of the diodes was combined with the study of the surface and interface electrical properties, by Kelvin-probe force microscopy (KPFM) and frequency dependent capacitance-voltage measurements (C-f-V) and discussed assuming a Mo/4H-SiC Schottky contact (F_B =1.39 eV) as a reference. The KPFM measurements revealed a similar value of the surface potential, thus suggesting that the work function of the metal is the same in both cases. On the other hand, a higher density of interface state was obtained by C-f-V for the Mo₂C/4H-SiC system. This latter can explain the reduction of the Schottky barrier height observed for this system.

Abstract: Laser annealing is considered an enabling process for a new generation of SiC power devices, since it allows the formation of ohmic contacts on very thin wafers, significantly reducing their total ON resistance. Ni silicide and Ti silicide ohmic contacts have been widely investigated and reported in literature, exploring in detail the role of laser features, metal thickness and thinning process. Nevertheless, adding a small amount of Si to the contact layer could represent an opportunity to increase process options. In this work, a NiSi alloy has been used as a contact metal to study the role of the addition of Si to Ni in the reaction process under UV laser irradiation. Morphological and structural properties of the reacted layers have been investigated by means of Transmission Electron Microscopy (TEM) and X-Ray Diffraction (XRD) analyses. The electrical characterization of reacted contacts has been performed by measuring their Sheet Resistance (R_s) by Four Point Probe (FPP) method and, at device level, by measuring the forward voltage drop (V_f) of Schottky Barrier Diodes (SBDs) fabricated on 150 mm-diameter 4H-SiC wafers. Furthermore, a comparison has been made between Ni and NiSi alloy under the same irradiation conditions. It has been found that adding Si to Ni in the contact metal layer moves the silicide reaction forward, driving the strong relationship observed between structural, morphological and electrical properties of the reacted contacts.

Abstract: Accurate characterization of low-resistance ohmic contacts on 4H-SiC is crucial for devicedevelopment, but is complicated by the limitations of the standard Transfer Length Method (TLM).TLM test structures are widely used for extracting the specific contact resistivity (ρC) between metaland semiconductor layers, as well as the sheet resistance of doped layers. The contact formation pro-cess itself, particularly the annealing step, modifies the SiC layer under the contact. This results in asheet resistance below the contact (RSK) that deviates from the sheet resistance of interest between thecontacts (RSH), which invalidates a key assumption of the standard TLM evaluation of a constant RSHthroughout the whole TLM test structure. This study uses 2D TCAD simulation of TLM test structuresto investigate the influence of the contact length L, while using an advanced evaluation method forextracting ρC with the help of a third contact. Consequently, it is necessary to measure the contactend resistance RCE, which is derived from the potential at the end of the TLM contact. The findingsprovide a deeper understanding of the TLM technique’s robustness and offer valuable guidelines foroptimizing TLM test structures to ensure accurate characterization of ohmic contacts on 4H-SiC.

Abstract: In this study, 4H-SiC bonded substrates (bonded-SiC) with an average resistivity of 2.4–31.5 mΩ·cm were prepared, and attention has been directed toward the relationship between the resistivity of bonded-SiC and the contact resistance at the backside where metal Ti/Ni was applied. A circular transmission line model (cTLM) was used to accurately measure the backside contact resistance. A linear correlation was found between and the resistivity of bonded-SiCs at room temperature (RT). This result indicates the existence of a threshold resistivity at which the specific contact resistance in the range of 2.2 × 10⁻⁶ to 1.5 × 10⁻⁵ Ω·cm² can be achieved without contact annealing; it also indicates that the temperature dependence of between 17.4 and 34.4 mΩ·cm is eliminated. This phenomenon can occur because is dominated by tunneling current above the nitrogen concentration at the threshold resistivity, which is driven by the high nitrogen concentration and sufficient carrier activation in the polycrystalline portion (polycrystalline layer) of bonded-SiCs. These are important properties resulting from a polycrystalline layer with a 3C structure in bonded-SiC.