Conventional fabrication of top
oxide in an ONO-type
memory cell stack usually produces Bird's
Beak. Certain materials in the stack such as
silicon nitrides are relatively difficult to oxidize. As a result oxidation does not proceed uniformly along the multi-layered height of the ONO-type stack. The present disclosure shows how radical-based fabrication of top-
oxide of an ONO stack (i.e. by ISSG method) can help to reduce formation of Bird's
Beak. More specifically, it is indicated that short-lived oxidizing agents (e.g.,
atomic oxygen) are able to better oxidize difficult to oxidize materials such as
silicon nitride and the it is indicated that the short-lived oxidizing agents alternatively or additionally do not diffuse deeply through already oxidized
layers of the ONO stack such as the lower
silicon oxide layer. As a result, a more uniform top oxide
dielectric can be fabricated with more uniform breakdown voltages along its height. Additionally, adjacent low and
high voltage transistors may benefit from simultaneous formation of their gate dielectrics with use of the radical-based oxidizing method.