Techniques for Screening Bipolar Transistor Degradation Due to Ionizing Radiation.

Two methods for screening bipolar parameter degradation due to exposure to ionizing radiation were explored. These were the use of a scanning electron microscope SEM as a controlled simulator of a Co60 source irradiation and the use of surface sensitive test devices to assess the potential hardness of bipolar oxides. The goal was the development of screening techniques which could be applied in a production environment to evaluate hardness to ionizing radiation while the devices were in slice form. The technique of using the SEM as a simulator for a Co60 source, delivering a total ionizing dose, was shown to be feasible. The second screening method involved the design and implementation of a test bar which placed a number of experimental devices on a common die with two p-n-p transistors. The structures on the test bar which were to characterize the oxides and the Si-SiO2 interface of the transistor pair included dated diodes, a p-n-p tetrode, MOS capacitors, and an N-channel MOSFET. Pre-irradiation characterization of the oxides was explored as a measure of post-irradiation degradation of the p-n-p transistors. The data presented here shows only limited success in the use of this method as a screen.