C60 molecular depth profiling of a model polymer

The bombardment of a 26 nm poly(methyl methacrylate) (PMMA) film has been studied as a model for depth profiling of polymeric samples using a newly developed C60+ ion source. Experiments were conducted on a ToF-SIMS instrument equipped with C60+and Ga+ ion sources. A focused dc C60+ 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 C60+ 20 keV and Ga+ 15 keV 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 1014 ions/cm2. Depth resolution as determined by the interfacial region is found to be about 14 nm. A >10-fold increase in sputter yield for C60+ ion bombardment over Ga+ ions under similar conditions is observed from quartz crystal microbalance (QCM) measurements and our findings compare to enhanced SF5+ cluster bombardment yields of organic species