| AVS 63rd International Symposium & Exhibition | |
| Applied Surface Science | Tuesday Sessions |
| Session AS-TuP |
| Session: | Applied Surface Science Division Poster Session |
| Presenter: | Nathan Havercroft, ION-TOF USA |
| Authors: | P. Bruener, ION-TOF GmbH, Germany T. Grehl, ION-TOF GmbH, Germany N.J. Havercroft, ION-TOF USA J.Z. Mundy, North Carolina State University G.N. Parsons, North Carolina State University |
| Correspondent: | Click to Email |
Low Energy Ion Scattering (LEIS) is uniquely able to provide quantitative elemental characterization of the outermost atomic layer of a sample. In addition, the LEIS spectra contain information about the composition of the first few nm of the samples. These properties make it an ideal tool for the characterization of thin films, from the initial nucleation stage to complete films. The analysis gives insight into growth modes (island vs. layer-by-layer), growth rates and impurities, as well as accurate information about layer closure.
For the LEIS analysis, noble gas ions with kinetic energy of a few keV are scattered by individual atoms in the sample surface. The energy loss of the ions in this scattering process is dependent on the mass of the surface atom it was scattered from. The peaks in the energy spectrum of the backscattered ions are used to identify and quantify the elemental composition of the outer surface.
Ions that are scattered in deeper atomic layers are first of all efficiently neutralized and lose energy by nuclear and electronic stopping on their way through the sample. This causes a shift in energy proportional to the distance traveled in the solid, and a lower intensity of those ions. Due to this, the scattering from the first atomic layer can be distinguished from sub-surface scattering, leading to the extreme surface sensitivity of just one atomic layer [1].
However, even ions scattered below the surface can be detected if the surface promotes the reionization of neutralized primary ions after their travel through sub-surface layers. This can be used to determine layer thickness and elemental distribution in the first few nm of the sample in a fast and non-destructive measurement. The required stopping power values are calculated using SRIM [2].
In this study we applied LEIS to a range of samples of ALD deposited Pd on Al2O3 substrates. The currently used process for the Pd deposition requires high temperatures to facilitate the desorption of residuals from the Pd precursor, which poison the substrate surface and inhibit the further nucleation of Pd. This leads to island growth of Pd clusters. We demonstrate how LEIS can be used to analyze the surface coverage of the deposited Pd, the Pd cluster dimensions, and the amount of precursor residual. This information is crucial to develop a lower temperature process for the deposition on temperature sensitive substrates, such as polymers.
[1] Surface composition analysis by low-energy ion scattering, Brongersma, H. H.; Draxler et al., Surf Sci Reports, 62, 2007, 63-109
[2] The Stopping and Range of Ions in Solids (Pergamon, New York, 1985)