Studies on charge trapping and interface state generation in MOS capacitors at low temperatures

Abstract

We have studied electrical phenomena caused by Fowler-Nordheim tunneling injection of electrons in metal-oxide-semiconductor (MOS) capacitors at temperatures of 77–300 K. The phenomena have been examined by measuring the shift of the flat-band voltages (ΔVFB) and that in gate voltage-gate current characteristics (ΔVG). We have found a simple method using ΔVFB and ΔVG to obtain information on the location of positive charges trapped in the oxide without suffering the influence of interface states, and it can be derived that the positive charge is located at about 60 Å from the Si-SiO2 interface. The determination of the location gives us explicit information on the charge trapping in the oxide and the interface state generation. The positive charge trapping is enhanced, but the interface state generation is suppressed with decreasing injection temperature. In spite of these dependences, a proportional relationship is found between the trapped charge density and the interface state charge density.