Abstract: A semiconductor memory device such as a flash Electrically Erasable Programmable Read-Only Memory (Flash EEPROM) includes a floating gate with high data retention. A tungsten damascene local interconnect structure includes a silicon oxynitride etch stop layer which is formed using Plasma Enhanced Chemical Vapor Deposition (PECVD) at a temperature of at least 480.degree. C. such that the etch stop layer has a very low concentration of hydrogen ions. The minimization of hydrogen ions, which constitute mobile positive charge carriers, in the etch stop layer, minimizes recombination of the hydrogen ions with electrons on the floating gate, and thereby maximizes data retention of the device.