CORRELATION OF TRAP GENERATION TO CHARGE-TO-BREAKDOWN (QBD) - A PHYSICAL-DAMAGE MODEL OF DIELECTRIC-BREAKDOWN

Ultrathin gate and tunnel oxides in MOS devices are subjected to high- field stress during device operation, which degrades the oxide and eve ntually causes dielectric breakdown. Oxide reliability, therefore, is a key concern in technology scaling for ultra-large scale integration (ULSI). Here we provide critical new insight into oxide degradation (a nd consequently, reliability) by a systematic study of five technologi cally relevant parameters, namely, stress-current density, oxide thick ness, stress temperature, charge-injection polarity (gate versus subst rate), and nitridation of pure oxide. For all five parameters, a stron g correlation has been observed between oxide degradation and the gene ration of new traps (distinct from the filling of intrinsic traps). Fu rther, we observe that this correlation is independent of the trap pol arity (positive versus negative). Based on this correlation, and based on the fundamental link between electronic properties and atomic stru cture, a physical-damage model of dielectric breakdown has been propos ed. The concept of the physical-damage model is that the oxide suffers dielectric breakdown when physical damage due to broken bonds forms a defect-filled filamentary path in the oxide, that conducts excessive current. A good monitor of this physical damage is trap generation, wh ich we believe is caused by physical bond breaking in the oxide and at the interface. The model has been quantified empirically by the corre lation between trap generation and Q(bd).