Direct imaging of dopant distributions in silicon by scanning transmission electron microscopy

The first direct images of dopant distributions in Si have been observed using scanning transmission electron microscopy, by detecting Rutherford-scattered transmitted electrons. Strong atomic number (Z) contrast is obtained allowing images to be formed of Bi at concentrations of the order of 0.2 to 1 at. % and of Sb at concentrations of 0.5 to 6 at. %. The image contrast from cross-section specimens correlated closely with the dopant concentration profiles determined by x-ray microanalysis and with Rutherford ion backscattering analysis of the bulk materials. This technique should prove extremely valuable for studying dopant segregation phenomena in semiconductors.