Depth profiling studies of multilayer films with a C ₆₀ ⁺ ion source

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 ⁺ 15keV and C ₆₀ ⁺ 20keV 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 1.54nm/s and that the film interface position can be determined with a depth resolution of 16nm. For comparison purposes, a depth resolution of 8.7nm was measured for a sample consisting of 66nm of Ni and 53nm of Cr on Si(100) at a C ₆₀ ⁺ beam energy of 20keV. 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.