Papers by Author: Daniel Alquier

Abstract: Laser Thermal Annealing (LTA) is a necessary fabrication step to improve the 4H-SiC devices by reducing their ON-state resistance. Because the LTA annealing is achieved at the end of the front-end fabrication, the classical Radio Corporation of America cleaning (RCA) cannot be used without affecting the material deposited on the frontside. Therefore, in this study, we investigate the argon (Ar) plasma surface treatment, achieved in our sputtering tool, before the ohmic contact fabrication, as an alternative surface preparation to the RCA sequence. As the Ar plasma modifies the SiC surface morphology, it affects its wetting properties. That can play a key role in the ohmic contact formation by LTA since the nickel turns into liquid phase during the laser irradiation. For an Ar plasma treatment of 30 min, a specific contact resistance of 5.0×10^-5 Ω.cm² has been obtained for an annealing at 5.0 J.cm², which is in the same range than the contact fabricated by LTA involving a classical RCA cleaning.

Abstract: Laser Thermal Annealing (LTA) is a key process step to improve the 4H-SiC devices by reducing their on-state resistance. In this study, we investigate the electrical, structural and morphological properties of nickel contact fabricated by LTA. A contact formed by a classical Rapid Thermal Annealing (RTA) was also fabricated as reference. Based on structural analysis, the phases formed by LTA do not match with RTA sample ones that has better ohmic properties. Nevertheless, the LTA contacts reach a specific contact resistance of 2.4×10^-5 Ω.cm² for an annealing at 4.75 J.cm^‑2, which represents a significant improvement in comparison with our previous contacts fabricated with the same experimental protocol using titanium.

Abstract: This paper demonstrates the ability of 3CSiC microcantilevers (μCs) to monitor binary gas mixture without sensitive coating. Here, 3CSiC is chosen in particular, as the newly designed sensor will be placed in a radioactive environment. The change in gas concentration is identified using relative shifts in the cantilever’s mechanical resonance frequency (∆f_r). The presented microcantilevers work on electromagnetic actuation and inductive detection. In this paper, the fabrication process, optical characterization results using laser Doppler vibrometry and test results under a gas mixture environment are demonstrated. The presented limit of detection shows the ability of 3CSiCμCs to detect less than 1% of hydrogen in nitrogen, which makes them suitable for the targeted application.

Abstract: This work is focused on the fabrication of Titanium-based ohmic contacts by Laser Thermal Annealing (LTA) on n-type silicon carbide (4H-SiC). Their morphologies and electrical properties were studied by using two sets of parameters impacting the laser pulse overlap. With both sets, the ohmic contact transition was reached. The high overlap conditions produced a massive degradation of the contact morphology by leaving uncovered SiC. An optimisation of the annealing parameters was successfully performed by reducing the overlap. With the low overlap configuration, a specific contact resistance of 1.2×10^-4 Ω.cm² was measured for a fluence of 4.25 J.cm^-2 with a satisfying contact surface morphology.

Abstract: We present an epitaxy-based approach for designing a 3C-SiC Capacitive Micromachined Ultrasonic Transducer (CMUT). The design requires to consider a 3C-SiC/Si/3C-SiC heterostructure on a Si substrate. This implies to address different growth steps of SiC on Si and Si on SiC. We present some specific growth related issued, namely the control of selectively grown Si on a masked SiC(100) and the further regrowth of 3C-SiC on a Si (110) layer. The final release of the SiC membrane, to define a CMUT, is also addressed using a simple thermal treatment allowing to suppress several technological steps.

Abstract: In this work, an AlGaN/GaN HEMT structure is grown on a 0.8 μm thick 3C-SiC layer on high resistivity Silicon substrate. The RF propagation losses are investigated and compared with the ones of epi-layers grown directly on Silicon and on 6H-SiC substrates. Short gate length transistors are fabricated using e-beam lithography. In spite of ohmic contact resistance of 0.6 Ω.mm, a saturated current density of 0.7 A/mm at a gate bias of +1V and a transconductance peak higher to 250 mS/mm for 75 nm T-shaped gate transistors are reached on structure with thick 3C-SiC template. Moreover, for the first time, transition frequencies f_T/f_max of 60/98 GHz are reported on such 3C-SiC template.

Abstract: The silicon carbide cubic polytype (3C-SiC) is a material of choice to fabricate microelectromechanical systems. However, the mechanical properties of 3C-SiC-based devices are severely linked to the stress of the involved 3C-SiC material. Moreover, the stress level can hamper completing microsystems. As a consequence, in this study, we considered the influence of aluminum (Al) doping towards the mechanical properties of 3C-SiC epilayers and demonstrated a noticeable reduction of the Young’s modulus with a high Al incorporation.

Abstract: Based on finite elements method, thermal simulations were conducted to reproduce a laser annealing of several common metals deposited on 4H-SiC. We estimated the temperature reached at the metal/4H-SiC interface to check the possibility to achieve ohmic contact formation through laser annealing. An optimization of Al/Ti/4H-SiC stacking was also considered. Simulations highlighted the low temperature of the non-irradiated SiC face that allows using grinded wafer.

Abstract: Different methods for cross-section characterization of SiC Trenched-singly-implanted vertical junction field effect transistors (TSI-VJFETs) are presented with the purpose to determine the epitaxial structure in terms of doping topography.

Abstract: The silicon carbide cubic polytype (3C-SiC) is perfectly appropriate to fabricate microelectromechanical systems. However, for such applications, the stress can largely influence both the fabrication of 3C‑SiC‑based microsystems and their related mechanical properties. Accordingly, in this study, we investigated the influence of strong aluminum incorporation towards the mechanical properties of 3C-SiC epilayers grown on silicon substrates.