Thermal and field enhanced emission of trapped holes in thin SiO/sub 2/ films

Abstract

Thermal and electric field enhanced emission of trapped holes in thin SiO/sub 2/ films of MOS devices has been investigated. Emission characteristics showed a different type of response with time under different oxide field polarity. A gradual deviation from the linearity in logarithmic time scale can be interpreted as meaning that a total recovery of the threshold property is rather difficult due to a possible permanent trapping of some holes in deep trap centers. Two different mechanisms for the field enhanced emission of trapped holes are found to exist with respect to the polarity of oxide electric field during emission. Emission under elevated temperatures demonstrated the presence of both shallow and deep level trap centers in the oxide films. Shallow traps which exist just above the oxide valence band can be emitted with relatively low thermal activation, while considerably higher thermal activation is required to initiate emission from deep trap centers. Trapped hole emission for long times at higher temperatures is explained by a hopping transport of deep trap holes towards the interface.