A graphical analysis of transient response curves at an early stage in SIMS depth profiling using a 133Cs+ beam

The behavior of transient response curves observed at an early stage of SIMS depth profiling contains much information on the characteristics of thin surface layers. An attempt has been made to determine the depth of the native silicon oxide layer of a silicon wafer from a graphical analysis of the behavior of transient response curves measured using a Cs+ primary ion beam. Three specified depths were found from the characteristic shapes of the 30Si− secondary ion intensity versus depth curves. The depths strongly depended upon the acceleration energy (E) of the Cs+ beam and did slightly so on the angle of incidence (θ). Good linear relationships were found between the specified parameters and E and low θ. The linear lines extrapolated coincided triply at E = 0 with each other, that is, resulted in “a triple intercept”, from which a value of 0.57 nm was obtained as the thickness of the native oxide layer. It was also found that the depth specified from the relative intensity of the 16O− secondary ion, which was measured together with 30Si−, was proportional to E. The thickness estimated from an extrapolation of the straight line to E = 0 was identical to the above.