CONSTANT CURRENT STRESS BREAKDOWN IN ULTRATHIN SIO2-FILMS

Ultrathin dielectric films play an important role in integrated circuits (ICs), both as gate dielectrics for MOS technologies, and as tunnel dielectrics for nonvolatile erasable memory (e.g. EEPROM) technologies. We have characterized charge-to-breakdown (Q(bd)) using constant-current stress in such films for a range of thicknesses, temperatures, and stress-current densities. This comprehensive characterization reveals several trends not observed previously While we briefly allude to possible implications on breakdown mechanisms, the focus of this paper is delineating the observed trends. At room temperature, Q(bd) values depend on thickness in a complex manner, with Q(bd) decreasing with increasing thickness in certain regimes, and staying constant in other regimes. Q(bd) falls dramatically with increasing temperature for all thicknesses, but the magnitude of the effect differs for each thickness. We believe that this characterization contributes significantly to predicting reliability of devices employing ultrathin oxides.