Development of an energy-resolved method for SIMS in-depth analysis of metal-polymer interfaces

Energy-resolved SIMS depth profiling has been succesfully applied in the analysis of Al-metalized polypropylene films used in the capacitor industry. The accurate identification of the metal-polymer interface was not straightforward due to the simultaneous contribution of isobaric ions coming from each layer (²⁷Al⁺/⁴³AlO⁺ ions from the aluminium layer and ²⁷C₂H₃⁺/ ⁴³C₃H₇⁺ from the polymer substrate). Kinetic energy filtering by means of a 45° electrostatic analyzer (ESA) has allowed the resolution of the metal-polymer interface by selecting a suitable kinetic energy corresponding to the ions generated in the metallized layer but not on the polymer. Owing to the dielectric polymeric substrate, charge effects might be produced during depth profiling. These charge buildup effects are minimized by flooding the surface with low-energy electrons (500 eV) and a specific sample-mounting procedure assuring grounded conditions. The excellent repeatability and sensibility of the technique allows studying the degradative process in the capacitor films and the accurate location of the metal-polymer interface, and therefore, the nanometric metal thickness variations. These factors drastically affect the capacitor's performance and they will determine the potential failures that could be developed during the capacitor's life cycle.