Impact of ALD Al₂O₃ Dielectrics on the Device Performance of SiC-Based Field-Effect Transistors (FETs): A Study of Atomic Diffusion

We investigated double-diffused (D)-MOSFETs based on 4H-SiC with an atomic-layer-deposited (ALD) 30 nm-thick Al 2 O 3 /15 nm-thick SiO 2 bi-layer to improve the microstructure and electrical properties, particularly the subthreshold swing (S) and atomic diffusion behavior of phosphorus (P) in the P-doped poly-Si gates. Stacking the 30 nm-thick ALD Al 2 O 3 on the SiO 2 layer reduced the subthreshold swing (S) of the bi-layer film (Al 2 O 3 /SiO 2 ) by approximately 53% compared to that of the SiO 2 single dielectric film, demonstrating a reduction from 732.3 to 345.7 (mV/decade) at room measuring temperature of about 25 °C. The device performance of gate improved by Al 2 O 3 dielectrics blocking of the atomic diffusions of phosphorus (P) and carbon (C). This effect was analyzed in more detail using atom probe tomography (APT). The penetration depth of P atoms in bilayer of Al 2 O 3 /SiO 2 was about 8.4 nm less than that in the single layer of SiO 2 , owing to the blocking of the P atomic diffusion by the ALD Al 2 O 3 film.