Underlying physics of the thermochemical E model in describing low-field time-dependent dielectric breakdown in SiO2 thin films

The underlying physics behind the success of the thermochemical E model in describing time-dependent dielectric breakdown (TDDB) in SiO2 thin films is presented. Weak bonding states can be broken by thermal means due to the strong dipolar coupling of intrinsic defect states with the local electric field in the dielectric. This dipole-field coupling serves to lower the activation energy required for thermal bond-breakage and accelerates the dielectric degradation process. A temperature-independent field acceleration parameter gamma and a field-independent activation energy Delta H can result when different types of disturbed bonding states are mixed during TDDB testing of SiO2 thin films. While gamma for each defect type alone has the expected 1/T dependence and Delta H shows a linear decrease with electric field, a nearly temperature-independent gamma and a field-independent Delta H can result when two or more types of disturbed bonding states are mixed. The good agreement between long-term TDDB data and the thermochemical model suggest strongly that the oxygen vacancy is an important intrinsic defect for breakdown and that field, not current, is the primary cause of TDDB under low-field conditions. (C) 1998 American Institute of Physics. [S0021-8979(98)07515-X].