Time-of-flight secondary ion mass spectrometry depth profiling was used to study N distribution in SiO2/Si3N4/SiO2 (ONO) structures. An investigation was made of different factors that affected N accumulation at the Si/SiO2 interface of the ONO structure. In order to isolate the impact of ion beam enhanced N diffusion towards the Si/SiO2 interface in secondary ion mass spectrometry measurements, the top silicon oxide and silicon nitride layers were chemically etched before secondary ion mass spectrometry. Thermal diffusion effects were investigated by comparing specimens with different thermal budgets and different thicknesses of layers in the ONO stack. The results suggested that N could accumulate at the Si/SiO2 interface during ONO fabrication.

Nitrogen Diffusion and Accumulation at the Si/SiO2 Interface in SiO2/Si3N4/SiO2 Structures for Non-Volatile Semiconductor Memories. M.Saraf, R.Edrei, R.Shima-Edelstein, Y.Roizin, A.Hoffman: Journal of Vacuum Science & Technology B, 2005, 23[4], 1558-61