Impact energy dependence of SF5+-induced damage in poly(methyl methacrylate) studied using time-of-flight secondary ion mass spectrometry

Ion-induced damage of polymers is a critical factor in the depth profiling of polymer surfaces using polyatomic primary ions. In this study, time-of-flight secondary ion mass spectrometry was used to measure the damage of spin-cast poly(methyl methacrylate) (PMMA) films under 5-keV Cs+ and 2.5-8.75-keV SF5+ bombardment. Under 5-keV Cs+ bombardment, the characteristic PMMA secondary ion intensities decreased rapidly for primary ion doses above 5 x 10(13) ionS/cm(2). The damage profiles of PMMA under SF5+ bombardment contained three distinct regions as a function of SF5+ ion dose: a surface transient, an extended quasi-stabilization of the characteristic PMMA secondary ion intensities, and the decay of these intensities as the silicon substrate was reached. The PMMA film sputtered in a controlled manner for SF5+ ion doses up to 4 x 10(14) ions/cm(2), with the maximum ion dose limited by the thickness of the PMMA film. Furthermore, the chemistry at the bottom of the sputter crater was significantly less modified by SF5+ bombardment when compared with Cs+ bombardment. The sputter rate was linearly correlated with the SF5+ impact energy while the damage to the PMMA film varied minimally with the SF5+ impact energy. These results were compared with Monte Carlo (SRIM) calculations of the penetration depth and vacancy production for SF5+ at different impact energies. Since the SF5+ impact energy only affected the sputter rate, selection of the appropriate SF5+ impact energy for polymer depth profiling depends solely on the desired sputter rate.