SPUTTER DEPTH PROFILING OF SURFACE-POTENTIALS IN SILICON SEMICONDUCTORS

This work is a study of depth-dependent changes in surface electrical potential observed during secondary ion mass spectroscopy (SIMS) sputt er profiling of doped, recrystallized silicon semiconductor samples. T hese changes are measured indirectly, using spectrometer energy filtra tion to detect changes in secondary ion energy as changes in signal tr ansmission. The effect is caused by carrier-depleted zones in samples containing n-p junctions, which become reverse-biased diodes due to th e ion bombardment-induced surface charge. These profiles are qualitati vely similar to spreading resistance probe (SRP) profiles and are indi cative of the dynamic carrier profile as erosion removes the overlying doped silicon, as in the concept of an on-bevel SRP carrier profile. However, the amount of biasing surface charge is highly dependent on b ombardment and instrumental conditions, so the same sample can be made to exhibit much different potential profiles. By optimizing these con ditions, the signals can give useful information about the sample carr ier profile at the same time that the SIMS dopant profile is directly measured. (C) 1996 American Vacuum Society.