Depth profiling studies of multilayer films with a C60+ ion source

Abstract

A newly developed C 60 + primary ion beam source for time-of-flight secondary ion mass spectrometry has been employed for depth profiling analysis of organic and inorganic multilayer films. In particular, the C 60 + ion beam is used in the dc mode to sputter the surface for depth profiling while spectra are taken both with Ga + 15 keV and C 60 + 20 keV projectiles between sputtering cycles. From C 60 + bombardment of Langmuir–Blodgett films of barium arachidate, we find that cluster beams increase the secondary ion yields and ion formation efficiencies compared to monoatomic projectiles. For a 15-layer film, a barium arachidate fragment ion at m / z =208.9 was monitored as a function of C 60 + dose to determine that the sputtering rate is about 1.54 nm/s and that the film interface position can be determined with a depth resolution of 16 nm. For comparison purposes, a depth resolution of 8.7 nm was measured for a sample consisting of 66 nm of Ni and 53 nm of Cr on Si(1 0 0) at a C 60 + beam energy of 20 keV. The neutral atom yield was monitored via laser postionization to avoid matrix effects. These experiments show great promise for the use of C 60 + for depth profiling studies of multilayer targets.