C-V Hysteresis Instability in Aluminum/Tantalum Oxide/Silicon Oxide/Silicon Capacitors due to Postmetallization Annealing and Co-60 Irradiation

The C-V hysteresis instability in the capacitors consisting of tantalum oxide layers was studied by postmetallization annealing at various temperatures below 400°C and by Co-60 irradiation with a total dose of 10⁶RAD(Si0₂). It was found that the directions of the C-V hysteresis loops of an aluminum/tantalum oxide/silicon oxide/silicon(n) capacitor can be changed from counterclockwise to clockwise when the annealing temperature varies from 200° to 400°C gradually. After receiving a Co-60 irradiation, the C-V hysteresis loops of the samples under testing became much larger under the same measurement condition. A model consisting of the leakage property of tantalum oxide and the generation of slow trap states at the silicon oxide/silicon interface due to negative charge-temperature effect was proposed in this work, and explained the observations quite well.