Impact energy dependence of SF 5+ ion beam damage of poly(methyl methacrylate) studied by time-of-flight secondary ion mass spectrometry

Abstract

Recent advances in instrumentation for secondary ion mass spectrometry (SIMS) have focused on the application of polyatomic primary ions for enhancing molecular secondary ion signals of organic materials. A few studies have also noted that some polymers, in particular poly(methyl methacrylate) (PMMA), display the unusual characteristic of maintaining their molecular ion signals after extended bombardment with polyatomic ion beams. In this study, ion-induced damage of spin-cast PMMA films by 2.5, 5, and 7.5 keV SF 5 + and 5 keV Cs + was studied using time-of-flight SIMS (ToF-SIMS). After a surface transient regime, the characteristic molecular ion signals for PMMA remained relatively stable during extended SF 5 + bombardment. Increased SF 5 + impact energy increased the sputter rate with a slight increase in the damage of the polymer films. Additionally, neither fluorocarbon cations nor anions were observed in the ToF-SIMS spectra of the damaged PMMA films. Monte Carlo calculations of the primary ion penetration into the polymeric material showed that an increased penetration depth and depth of vacancy production was correlated with increased sputter and damage rates observed in the SIMS data.