Influence of gamma irradiation on the C-V characteristics of the Al/SiNx/Si MIS capacitors

The authors studied effects of gamma radiation on the electrical properties of the MOS capacitor made on SiNx thin films with thickness of 100 nm deposited on p-type (100) silicon wafer using plasma-enhanced chemical vapor deposition method. The authors investigated the chemical bonds and their densities inside the films using Fourier transform infrared (FTIR) spectroscopy. The as-deposited and annealed samples with Al/SiNx/Si structure as metal-insulator-semiconductor (MIS) capacitors were exposed to a 60-Co gamma radiation source with a dose rate of 0.015 Gy/S. The authors performed capacitance-voltage measurements at frequencies 10, 100, and 1000 kHz before and after radiation exposure with doses of up to 40 Gy. It was found that before gamma irradiation compared with as-deposited sample, the annealed samples exhibit less negative flatband voltages (V-fb) shift. This indicates the relative reduction in positive charge in the SiNx:H samples. After gamma irradiation, for all samples a negative shift has been observed in V-fb, being more pronounced in the samples annealed at 700 degrees C. The more striking feature is that the amount of shift does not change by increasing radiation dose after first irradiation, in which we attributed what to the radiation hardening in Al/SiNx/Si MIS capacitors. (C) 2012 American Vacuum Society. [http://dx.doi.org/10.1116/1.4720351]