AlO Layers Grown by Atomic Layer Deposition as Gate Insulator in 3C-SiC MOS Devices.

Metal-oxide-semiconductor (MOS) capacitors with AlO as a gate insulator are fabricated on cubic silicon carbide (3C-SiC). AlO is deposited both by thermal and plasma-enhanced Atomic Layer Deposition (ALD) on a thermally grown 5 nm SiO interlayer to improve the ALD nucleation and guarantee a better band offset with the SiC. The deposited AlO/SiO stacks show lower negative shifts of the flat band voltage V (in the range of about -3 V) compared with the conventional single SiO layer (in the range of -9 V). This lower negative shift is due to the combined effect of the AlO higher permittivity (ε = 8) and to the reduced amount of carbon defects generated during the short thermal oxidation process for the thin SiO. Moreover, the comparison between thermal and plasma-enhanced ALD suggests that this latter approach produces AlO layers possessing better insulating behavior in terms of distribution of the leakage current breakdown. In fact, despite both possessing a breakdown voltage of 26 V, the T-ALD AlO sample is characterised by a higher current density starting from 15 V. This can be attributable to the slightly inferior quality (in terms of density and defects) of AlO obtained by the thermal approach and, which also explains its non-uniform dC/dV distribution arising by SCM maps.