Second breakdown and crystallographic defects in transistors

Abstract

A study was conducted to determine the effect, on second breakdown in transistors, of some of the crystallographic defects that can develop during handling and fabricating procedures. X-ray diffraction microscopy was used to detect these defects. The susceptibility to second breakdown of about 1500 epitaxial planar silicon transistors diffused on two wafers was measured and the site of the current constriction of second breakdown was registered on most of these transistors. These data were then compared with the X-ray topographs. Any effect of the observed gross dislocations was masked by other factors, such as apparent surface induced effects, that were not discernible hi the X-ray topographs. It is proposed that a faulted emitter structure, that has been correlated with the emitter diffusion step, may be of importance in affecting the susceptibility of the transistor to second breakdown. The heating in the transistor at the second breakdown current constriction site to temperatures above 600°C and recrystallized laser-induced melt regions smaller that about 30 µm in diameter produced no crystallographic changes nor any frozen-in strain fields detectable in the X-ray topographs.