Implications in the use of secondary ion mass spectrometry to investigate impurity concentration profiles in solids

Using a recently developed high sensitivity secondary ion mass spectrometer the influence of the sputtering ion energy (5 to 50 keV argon) on the original range distribution has been investigated with a standard implantation profile as a reference (20 keV boron in amorphous silicon). It was found that recoil processes change the distribution only in the long range tail so that projected range and standard deviation are not influenced by this effect within the limits of experimental accuracy. Because of the low sputtering yield of silicon (S ≃ 2 atoms/ion), however, there is a change in sputtering rate at the beginning of layer removal until equilibrium between implantation and release of argon is obtained. This effect results in an increase in the measured value of the projected range which can be corrected by extrapolation to zero sputtering energy (Rp = 690 Å, ΔRp =280 Å). Neither scanning electron microscopy nor talysurf measurements showed any indication for the development of a surface topography after sputtering silicon layers up to 5000 Å in thickness.