Impact ionization and positive charge in thin SiO2 films

• Published in: Journal of applied physics 1976-01, Vol.47 (7), p.3192-3202
• Main Authors: Shatzkes, Morris, Av-Ron, Moshe
• Format: Article
• Language: English
• ISSN: 0021-8979; 1089-7550
• DOI: 10.1063/1.323115

The magnitude and the centroid of the positive charge induced in the SiO2 layer of an MOS capacitor have been determined from measurements of deviations of the fields at the electrodes from the average field in the oxide. The field at the metal electron-injecting electrode is found from the current density, which deviates from a Fowler-Nordheim characteristic with respect to the average field at high fields; the field at the SiO2-Si interface is found from the shift of the high-frequency capacitance-voltage curve. For cathode fields ≳10 MV/cm, the charge is linearly related to the cathode field and is the same for both of the film thicknesses used, 494 and 263 Å. The centroid, measured from the injecting electrode, is a decreasing function of the cathode field. From these results, the average field can be derived as a function of the cathode field and the film thickness, even for cathode fields beyond breakdown. A maximum average field is found to exist, which is identified as the average field at breakdown. The average field and the cathode field (and thus the current) at breakdown are determined as a function of film thickness. Good agreement is found between our results and computations based on a model by DiStefano and Shatzkes involving electron impact ionization and electron-hole recombination.