Cleaning of an Optical Filter

ToF-SIMS was used to monitor the cleaning efficiency during the production of an optical filter. In an initial experiment, surface spectrometry was used to identify the nature of contaminants present on the sample before and after the final cleaning following the polishing of the substrate (in preparation for layer deposition). The analysis clearly identified a contamination of triglycerides and dodecylbenzenesulfonate salts before the cleaning. The amount of both was greatly reduced after the final drop-and-wipe cleaning with acetone.
However, mass spectrometry without localisation did not give the full picture. Therefore, in a second experiment, ToF-SIMS imaging in macroscan mode (i.e. imaging of the chemical composition on large areas, in this case 60 x 60 mm2) was performed. Dodecylbenzenesulfonate salt was still detected in localised spots. Other compounds like smaller oxygen containing hydrocarbon fragments were also detected with inhomogeneous distributions. Therfore, ToF-SIMS analysis revealed that the conventional drop-and-wipe method as a final cleaning step was not performing efficiently.