A study of diffused bipolar transistors by electron microscopy

Abstract

Shallow junction bipolar transistors have been fabricated on bulk (001) silicon starting material using a diffusion processing technology. The resultant junction depths were about 0.5 and 0.8 μ m respectively for the emitter-base and base-collector junctions. The crystallographic defects present have been detected and characterized using a combination of electrical measurements, the electron beam induced current (EBIC) mode of the scanning electron microscope (SEM) and both conventional and high voltage transmission electron microscopy (TEM). Two types of dislocations were identified in the TEM. The first consisted of an orthogonal array of sessile, diffusion-induced edge dislocations located about halfway down in the heavily doped emitter. The second type consisted of 60° glissile dislocations that looped down from the orthogonal array and in some cases penetrated the emitter-base junction. Observations of a number of 60° dislocations yielded a good correlation between their depth and their contrast when imaged in the EBIC mode of the SEM. The 60° dislocations locally retard the emitter diffusion when they lie near to the emitter-base junction. Local breakdown effects under reverse bias were observed at the sites of these dislocations.