Hydrogen passivation effects under negative bias temperature instability stress in metal/silicon-oxide/silicon-nitride/silicon-oxide/silicon capacitors for flash memories

The paper presents the passivation effect of post-annealing gases on the negative bias temperature instability of metal/silicon-oxide/silicon-nitride/silicon-oxide/silicon (MONOS) capacitors. MONOS samples annealed at 850 °C for 30 s by a rapid thermal annealing (RTA) are treated by additional annealing in a furnace, using annealing gases N2 and N2–H2 (2% hydrogen and 98% nitrogen gas mixture) at 450 °C for 30 min. MONOS samples annealed in an N2–H2 environment are found to have lowest oxide trap charge density shift, ΔNot = 8.56 × 1011 cm−2, and the lowest interface-trap density increase, ΔNit = 4.49 × 1011 cm−2 among the three samples as-deposited, annealed in N2 and N2–H2 environments. It has also been confirmed that the same MONOS samples have the lowest interface-trap density, Dit = 0.834 × 1011 eV−1 cm−2, using small pulse deep level transient spectroscopy. These results indicate that the density of interface traps between the silicon substrate and the tunneling oxide layer are significantly reduced by the additional furnace annealing in the N2–H2 environment after the RTA.