Second breakdown and crystallographic defects in transistors

A study was conducted to determine the effect on second breakdown of crystallographic defects dectectable by means of x-ray diffraction microscopy. The susceptibility of 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 compared with x-ray topographs which indicated the kind and location of defects existing initially and those that were introduced during fabrication. Any effect of these defects was masked by other factors, such as surface induced effects, that were not discernible in the x-ray topographs. The heating at the second breakdown current construction site to temperature above 600°C and recrystallized laser-induced melt regions smaller than about 25 µm in diameter produced no crystallographic changes nor any frozen-in strain fields detectable in the x-ray topographs. Comments will be made about the significance to the second breakdown problem of these and other results obtained from this study.