C ₆₀ molecular depth profiling of a model polymer

The bombardment of a 26nm poly(methyl methacrylate) (PMMA) film has been studied as a model for depth profiling of polymeric samples using a newly developed C ₆₀ ⁺ ion source. Experiments were conducted on a ToF-SIMS instrument equipped with C ₆₀ ⁺ and Ga ⁺ ion sources. A focused dc C ₆₀ ⁺ ion beam was used to etch through the polymer sample at specified time intervals. Subsequent spectra were recorded after each individual etching cycle using both C ₆₀ ⁺ 20keV and Ga ⁺ 15keV ion beams at field-of-views smaller than the sputter area. PMMA fragment ion at m/z=69 and substrate Au m/z=197 were monitored with respect to primary ion doses of up to 10 ¹⁴ ions/ cm ² . Depth resolution as determined by the interfacial region is found to be about 14nm. A >10-fold increase in sputter yield for C ₆₀ ⁺ ion bombardment over Ga ⁺ ions under similar conditions is observed from quartz crystal microbalance (QCM) measurements and our findings compare to enhanced SF ₅ ⁺ cluster bombardment yields of organic species.