Development of post-irradiation interface traps and oxide charges in thin thermal oxide and thermal oxinitride MOS structures

Nitrided oxides not only show greater radiation hardness than pure oxides, as has often been reported, but also behave differently after the end of irradiation. We irradiated a number of MOS structures with oxide and oxinitride dielectrics with 2.2 MeV electrons. The samples then were kept with different oxide fields for up to more than a year, repeatedly determining oxide charges and interface trap density. In oxides we find interface trap transformation and a decrease of oxide charges with simultaneous increase of interface traps, both processes being bias dependent. In oxinitrides there is no interface trap transformation and (except for a radiation independent increase with negative bias only) oxide charge remains almost constant