A Technique for Characterizing Ionization and Displacement Defects in NPN Transistors Induced by 1-MeV Electron Irradiation

In this paper, characteristics of damage defects in 3DG110 NPN transistors induced by 1-MeV electrons were investigated by deep-level transient spectroscopy (DLTS) with the various period widths and reverse biases. The curve slope corresponding to the ideality factor for the irradiated NPN transistor by 1-MeV electrons at different fluences does not vary with the emitter-base voltage. The oxide-trapped charge, interface traps, and displacement defect centers in the NPN transistor are detected by DLTS simultaneously. These results show that unlike Co-60 gamma ray and low-energy electrons with less than 170 keV which can cause only ionization damage, 1-MeV electrons can produce both ionization and displacement damage on Si BJTs. With decreasing period width of DLTS measurement, the height of ionization defect (including oxide-trapped charge and interface traps) peaks increases, while the height of the displacement defect (VO center) peak remains unchanged. Meanwhile, with increasing reverse biases, the position of ionization defect peaks moves to rightward, while the position of displacement peaks keeps unchanged. Moreover, based on the annealing experimental results, with increasing the annealing temperature and time, both the concentration and the energy levels for oxide-trapped charge, the energy level of interface traps obviously change, and the energy level of VO center does not change. These experimental results show DLTS can be used to identify the ionization and displacement defects in bipolar transistors accurately and conveniently.