Breakdown properties of metal/NIDOS SiO2/silicon structures

NIDOS/SiO2/silicon structures have been annealed in a nitrogen (N2) ambient and X-ray photoelectron spectroscopy (XPS) characterization has been performed in order to definitively demonstrate the nitrogen atoms out-diffusion from the nitrogen doped silicon (NIDOS) film towards the buried oxide layer. The nitridation of the SiO2 layer is related to the competition between nitrogen atoms out-diffusion phenomena on one side into the underlying oxide layer and on the other side into an oxynitride layer grown during annealing. In order to analyse and optimize the corresponding MIS process, different structures such as metal/SiO2/silicon, metal/(NH3"nitrided")SiO2/silicon, metal/(N2O-nitrided)SiO2/silicon. metal/poly-Si*/SiO2/silicon (* indicates deposited from disilane Si2H6) and metal/NIDOS/SiO2/silicon have been realized and compared by capacitance-voltage, currentvoltage and ageing under constant current injection experiments. The optimization of the NIDOS-nitridation process gives the highest charge-to-breakdown for the lowest nitridation level or even for no intentional nitridation. The dielectric breakdown improvement should therefore not be related to the nitridation phenomena alone but also to the intrinsic properties of the polysilicon layer itself.