Paper AS-MoM9
Quantification of the Layer Thickness of Thin Organic Layers by Secondary Ion Mass Spectrometry Depth Profiling

Monday, November 7, 2016, 11:00 am, Room 101B

Secondary ion mass spectrometry depth profiling using argon gas cluster sputtering is increasingly applied for the analysis of organic materials including layer stacks used in organic electronic devices. The depth profiles provide valuable information about layer diffusion, segregation, chemical degradation and contaminants in the stack but are generally not quantitative.

We report a study of the quantification of the amount of matter by secondary ion mass spectrometry (SIMS) when depth profiling a nominally 3.1 nm delta layer of fmoc-pentafluoro-L-phenylalanine in Irganox 1010. The depth profiles are made using 5 keV Ar₂₃₀₀⁺ sputtering with analysis by 25 keV ions. Data for 89 negative secondary ions shows profiles whose integrated areas, when normalized to the intensity for the pure material, vary over a factor of 12. This variation mainly arises from matrix effects that are measured here using separate samples with mixed layers of 3 intermediate compositions of the two materials. Strong effects can cause the delta layer signal to show structure that may be misinterpreted. The compositional profile is established by using trial profiles, representing the composition, which are then enhanced or reduced according to the measured matrix effect and the result is fitted to the normalized intensity data. It is critical to include the roughening caused by the ion beam. When this is included, the amount of matter is found to be equivalent to 3.25 ± 0.05 nm.

It is concluded that the matrix terms used are a good description of the phenomenon and that SIMS profiles may be made quantitative if suitable secondary ions are available and the matrix terms measured.