QUANTITATIVE 2-DIMENSIONAL DOPANT PROFILES OBTAINED DIRECTLY FROM SECONDARY-ELECTRON IMAGES

Doping-dependent contrast in secondary electron images of p/n junction s in silicon obtained in a field-emission scanning electron microscope was observed and characterized. The optimum experimental conditions f or observing this ''electronic'' contrast were established by investig ating the effect of microscope and material parameters on the magnitud e of the contrast. The contrast between the bright p-type areas and th e darker n-type areas was maximized at an accelerating voltage of simi lar to 1 kV, and when a through-the-lens detector configuration was em ployed. Secondary electron contrast profiles of boron doped p(+)/n jun ctions in silicon showed a good correlation with secondary ion mass sp ectroscopy depth profiles of the atomic concentration down to the 10(1 7) cm(-3) level. However, similar results were not obtainable for n(+) /p junctions. It is demonstrated that this contrast effect may he expl oited for obtaining two-dimensional dopant profiles directly from seco ndary electron images of p(+)/n junctions provided that the technique is empirically calibrated against a one-dimensional dopant profiling m ethod. (C) 1996 American Vacuum Society.