Hole injection and dielectric breakdown in 6H–SiC and 4H–SiC metal–oxide–semiconductor structures during substrate electron injection via Fowler–Nordheim tunneling

Abstract

Hole injection into silicon dioxide (SiO2) films (8–40nm thick) is investigated for the first time during substrate electron injection via Fowler–Nordheim (FN) tunneling in n-type 4H- and 6H–SiC (silicon carbide) based metal–oxide–semiconductor (MOS) structures at a wide range of temperatures (T) between 298 and 598K and oxide electric fields Eoxfrom 6 to 10MV/cm. Holes are generated in heavily doped n-type polycrystalline silicon (n+-polySi) gate serving as the anode as well as in the bulk silicon dioxide (SiO2) film via hot-electron initiated band-to-band ionization (BTBI). In absence of oxide trapped charges, it is shown that at a given temperature, the hole injection rates from either of the above two mechanisms are higher in n-4H–SiCMOS devices than those in n-6H–SiCMOS structures when compared at a given Eoxand SiO2thickness (tox). On the other hand, relative to n-4H–SiCdevices, n-6H–SiCstructures exhibit higher hole injection rates for a given toxduring substrate electron injection at a given FN current density je,FNthroughout the temperature range studied here. These two observations clearly reveal that the substrate material (n-6H–SiCand n-4H–SiC) dependencies on time-to-breakdown (tBD) or injected charge (electron) to breakdown (QBD) of the SiO2film depend on the mode of FN injections (constant field/voltage and current) from the substrate which is further verified from the rigorous device simulation as well.