An operational definition for breakdown of thin thermal oxides of silicon

As MOS devices with thinner gate oxides are put into production, the high-field oxide breakdown definition used for process monitoring must be revised to account for noncatastrophic electrical conduction. This conduction is due to electron injection by Fowler-Nordheim tunneling into the oxide conduction band, and it can be as large as 0.1 A/cm²without causing irreversible breakdown of thin oxides. We propose that breakdown should be defined as the passage of a large current at a low value of applied electric field, after stressing of the oxide at a high field. We show that this definition represents a truly irreversible catastrophic breakdown, that it can be adapted easily for automated testing, and that it yields reliable results for breakdown of thin (less than 500 Å) gate oxides.