The influence of boron induced and oxidation induced defects on bipolar transistor slice yield

Abstract

Silicon lattice defects induced by high concentration boron diffusion, or by oxidation, are a major cause of high leakage currents in bipolar transistors. The incidence of such defects in narrow base, high frequency, transistors is investigated using Sirtl etch and the transmission electron microscope, and related to the transistor leakage currents. Boron induced defects are found to cause high emitter-base leakage, but it is shown that their density may be reduced by a nitric acid boron glass strip prior to base drive. A particular type of oxidation induced defect is found to cause high collector-emitter leakage, and appearance of this defect is correlated with silicon material batch. As an example, yields of slices of the British Telecom 40 Type submarine cable transistor meeting a specification including low leakage currents, are shown to be related closely to the silicon material/boron glass strip combination used.