| AVS 63rd International Symposium & Exhibition | |
| Applied Surface Science | Thursday Sessions |
| Session AS+SS-ThM |
| Session: | Depth Profiling, Buried Interfaces, and 3D Analyses |
| Presenter: | Alexander Pirkl, ION-TOF GmbH, Germany |
| Authors: | A. Pirkl, ION-TOF GmbH, Germany R. Moellers, ION-TOF GmbH, Germany H.F. Arlinghaus, ION-TOF GmbH, Germany N.J. Havercroft, ION-TOF USA E. Niehuis, ION-TOF GmbH, Germany A.A. Makarov, Thermo Fisher Scientific S. Horning, Thermo Fisher Scientific R. Havelund, National Physical Laboratory, UK M.K. Passarelli, National Physical Laboratory, UK A.G. Shard, National Physical Laboratory, UK I.S. Gilmore, National Physical Laboratory, UK |
| Correspondent: | Click to Email |
Introduction
Depth profiling of organic layers for optical and electronic devices can be ideally performed using gas cluster ion beams (GCIB) in combination with time-of-flight secondary ion mass spectrometry (TOF-SIMS). For optimum performance a dual beam approach is utilized, employing a lower energetic quasi DC sputter beam for material removal and a short pulsed small spot analysis beam for optimal mass spectral and imaging performance.
However molecular identification of unknown substances, e.g. contaminants, is usually hampered by constraints in mass resolution and mass accuracy of the TOF analyser. Furthermore ions generated in the sputter phase of the dual beam experiment are lost for the MS analysis. In order to overcome these limitations a TOF/OrbitrapTM-SIMS hybrid mass analyser instrument was developed.
Methods
A prototype SIMS instrument with a hybrid TOF/Orbitrap mass analyser was utilized for acquisition of organic depth profiles. During sputtering with 5-20 keV argon clusters secondary ions can be detected using the Q ExactiveTM HF mass analyser. Selective ion gating was implemented to avoid artefacts from the crater walls. In situ tandem MS analyses of the most abundant peaks were used to confirm the mass assignments. Imaging TOF analysis with high lateral resolution was performed on the same instrument using short pulses from a 30-60 keV Bi-liquid metal ion gun (LMIG) and a dedicated TOF.SIMS V analyser for comparative measurements.
Preliminary Data
Molecular depth profiles were acquired using GCIB induced desorption in a single beam approach from organic test structures and organic LED materials. The high mass resolution of 240 000 of the Q Exactive HF mass spectrometer proved to be essential for separation of otherwise overlapping ion signals. Molecular assignments based on the high mass accuracy below 3 ppm were validated using tandem MS analysis. Up to 5 decades of dynamic range and a depth resolution below 8 nm were found to be possible with this approach leading to unprecedented depth profiling results.
Depth profiles and according spectra are compared to the classical dual beam approach. While depth resolution is similar, differences in the relative signal intensities were observed in spectra from the two different ion beams. Implications for the analysis of biological samples will be discussed.