Process optimization of plasma-enhanced chemical vapor deposited passivation thin films for improving nonvolatile memory IC performance

Characteristics of plasma-enhanced chemical vapor deposited (PECVD) SiO2/Si Nx passivation layers are modified to improve and optimize electrical perfo rmances such as program/erase cycle and hot carrier reliability of floating -gate nonvolatile memory devices. SiH4/N2O gas mixtures are utilized as pre cursors for oxide CVD process. Higher SiH4/N2O flow rate ratios render the resulting oxide films more silicon-rich, as manifested by their higher refr active index (RI) and wet etch rates. These modifications in film character istics also correspond to increased program/erase cycles and lower % hot-ca rrier linear drain current (I-dlin) degradation An increase in RI from 1.52 0 to 1.675 translates to a rise in program/erase cycles from 17.3 K to 32 K and a fall in I-dlin from 8.2% to 4.9%. Further improvement in device perf ormance is fulfilled by modifying the stoichiometry of the overlying nitrid e passivation layer. Water diffusion from oxide and hydrogen release from n itride are both responsible for hot carrier drain current degradation and l oss in program/erase cycles. The utilization of a high-RI oxide in conjunct ion with a low hydrogen content nitride would give rise to the optimal devi ce reliability.