Reactive sputtering of SixNy for MONOS memory fabrication

Reactive sputtering deposition of Si_xN_y layers for application in MONOS memory fabrication was studied. The optical, electrical and compositional properties of these silicon nitride films were investigated by spectral ellipsometry measurements, I-V measurements and MEIS. Two films with different deposition regimes are described: sample A with a lack of silicon, and sample B with an excess of silicon. The compositional results obtained by MEIS showed the stoichiometry of Si_2.6N₄ for sample A and Si_3.3N₄ for sample B. Silicon excess in sample B results in a less resistive film as compared to sample A. Two memory devices have been fabricated for comparison, using both deposition regimes. Retention and endurance measurements have been performed and it was observed that memory B has a Program/Erase window of 10 V, approximately 3 times larger than that of memory A. Endurance measurements revealed that memory B has non-zero window after 10 000 cycles, while memory A window is practically zero after 200 cycles. These results point to an improvement of memory characteristics with the use of silicon rich sputtered Si_xN_y layers.