The effect of gate metal and SiO2 thickness on the generation of donor states at the Si-SiO2 interface

Abstract

Two experimental observations are reported concerning the degradation of the Si–SiO2 interface during electron injection in metal-oxide-semiconductor structures. First, the generation of the interfacial positive charge during avalanche injection can be strongly inhibited by employing magnesium, instead of aluminum, as gate metal, or enhanced by employing gold. This correlates with the different work functions of the metals. Second, during negative bias high-field injection in Al-gate capacitors with thin oxides (≲100 Å), a threshold in gate voltage, of 7–8 V, is found for the generation of the positive charge. Both observations are consistent with a model which assumes that holes generated in the anode by hot electrons, via emission of surface plasmons, are injected into the SiO2 and are subsequently trapped at the Si–SiO2 interface. Other possible mechanisms are also discussed.

Effects of gate material on Fowler-Nordheim stress induced thin silicon dioxide degradation under negative gate bias

“…This value of N T is also independently reported by Fischetti and co-workers. 4 Taking the gate material independent trap parameters from Table II and incorporating our AHI model in the average energy picture, 9,10 the two coupled first-order kinetic equations (1) and (4) can be numerically solved during both constant current and constant voltage FN stress. Throughout our simulation, we have chosen the initial applied electric field below the threshold field for TTBI in the bulk oxide to ensure the origin of trapped holes solely from AHI process.…”

Surface plasmons and breakdown in thin silicon dioxide films on silicon

“…[3][4][5][6] For thick oxides, the impact ionization model for electron-hole pair generation in the oxide bulk shows reasonable agreement with experiments when the breakdown voltage is larger than the band gap energy of SiO 2 . 3 For thin oxides, even though the apparent breakdown field is somewhat higher than that of thick oxides, the breakdown voltage is less than the threshold energy of impact ionization.…”

“…[4][5][6] The electrons do heat up in SiO 2 and their transport can be understood, to first order, without invoking collision events in the bulk SiO 2 in which several eV are released. However, as soon as the electrons enter the anode electrode, their energy must be somehow lost.…”

Density of ultradry ultrathin silicon oxide films and its correlation with reliability

“…[27][28][29][30][31] Actually, T TDDB has been improved by reducing the hydrogen invasion during oxidation 32,33 and annealing. 34 On the other hand, the thickness difference affects the generation and trapping of stress-induced positive charges, which are mainly produced near the anode-side oxide interface through the so-called surface plasmon mechanism 35 via Fowler-Nordheim ͑F-N͒ tunneling. 36 Even if the device structure used in the evaluation and the electrical condition during stressing are the same, slight differences in control of the defects and thickness ultimately result in large differences in reliability due to the differences in the stress-induced charge generation and trapping phenomena.…”