Charge trapping in thin SiO/sub 2/ layers: application to the breakdown of MOS

Positive and negative charging is commonly observed in thin SiO/sub 2/ layers subjected to high electric fields. Under Fowler-Nordheim electron injection that requires fields exceeding 7 MV/cm, positive charging is formed, whereas negative charging is produced at lower fields. In both cases breakdown is obtained after the injection of a critical amount of charges Q/sub BD/, called "charge to breakdown". Positive and negative charging induced breakdown is interpreted on the basis of the polarization/relaxation process developed to interpret breakdown in high voltage capacitors. In agreement with experiments, it is demonstrated that negative charging induced breakdown is due to the detrapping of a critical density of electrons. The consequence is that Q/sub BD/ is roughly constant when the current density J is less than a critical value J/sub c/ and decreases very rapidly when J>J/sub c/. When positive charging is formed, breakdown is attributed to the neutralization of positive charges by the injected electrons. In this case breakdown occurs when the product J/spl times/N/sub c//sup +/ (where N/sub c//sup +/ is the density of positive trapped charges) reaches a critical value. The charge to breakdown Q/sub BD/ decreases with J according to an expression of the form Q/sub BD//spl alpha/expJ/sub 0//J where J/sub 0/ is an appropriate parameter characteristic of the dielectric material.