A STUDY OF X-RAY-DAMAGE EFFECTS ON OPEN-BOTTOM TRENCH ISOLATION FOR BIPOLAR-DEVICES

The x-ray radiation damage effects on trench isolation for bipolar devices have been studied using the vacuum ultra-violet storage ring of the National Synchrotron Light Source at the Brookhaven National Laboratory. The bipolar devices under study incorporated "open-bottom" trench structures and were exposed to x-ray radiation of 1-2 keV. Leakage measurements were performed from device to trench before and after irradiation, and were performed again after the devices were annealed in forming gas at 400-degrees-C for 30 min. NPN and lateral PNP transistors and Schottky barrier diodes were all used for the investigation. The study shows that x-ray radiation, although producing observable effects, does not fundamentally alter the trench leakage characteristics. The effects observed are primarily due to the interface states generated by irradiation at the interface between Si and SiO2 in the isolation region. Upon annealing, the radiation effects are completely removed. The open-bottom trench scheme employed for isolation in this work should be superior to that of recessed oxide or a closed-bottom trench.