Controlled nanostructuring of a gold film covered with alkanethiol SAM by low energy cluster implantation
Size matters in scandium doped copper clusters
Ostwald ripening - Movie
Doped AunX+ clustersRIMS and SIMS
When a particle impinges with sufficiently high energy on a surface, material will be removed from the upper layers of the solid.
The fundamental processes that occur strongly depend on a complex interplay between physical and chemical properties of the surface
and of the projectiles. We intend to contribute experimentally to a more fundamental insight in particle-induced desorption phenomena
of material from ultra thin overlayers. Our methodological approach is based on the determination of differential sputtering yields
of neutral particles (e.g. population partitions, state selective flight-time distributions, and fragmentation patterns) using resonance
enhanced photoionization in combination with mass spectrometry (REMPI, RIMS).
Have a look at our RIMS and
SIMS setups.
Current research topics
Photon induced desorption of copper halides
In today’s microchips, copper is one of the most important materials. There are, however, quite some challenges related to the processing of this material. Therefore a study is carried out in collaboration with IMEC on the topic of photon induced desorption of copper halides. If such a process would be feasible on industrial scale, new etching or cleaning processes for copper could be developed. Besides the practical application, the interaction of photons with copper halides is a particularly interesting scientific topic, which might lead to further insight in so-called DIET mechanisms (desorption induced by electronic transitions).
Zero energy SIMS
Secondary ion mass spectrometry (SIMS) is a technique used to analyze the composition of solid surfaces and thin films by sputtering the surface of the specimen with a focused primary ion beam and collecting and analyzing ejected secondary ions. These secondary ions are measured with a mass spectrometer to determine the elemental, isotopic, or molecular composition of the surface. SIMS is the most sensitive surface analysis technique, being able to detect elements present in the parts per billion range.
Due to the scaling of CMOS devices, the surface and interface properties of the semiconductor structures together with an accurate
dopant profiling will become more important. This has triggered a continuing research for metrology methods that can determine
quantitatively the composition of complex heterogeneous materials, shallow surface layers, and interfaces with very high depth
resolution (sub-nm) and lateral resolution (nm). Due to its high sensitivity and depth resolution, SIMS still has a leading role
in compositional analysis. However, there is an increasing difficulty for SIMS to meet those targets due to the fundamental aspects
concerning SIMS depth profiling. These include the limited depth resolution to approximately 2 nm/dec even if low energy ion beams
are used, which also limits the lateral resolution. Finally, the ionization process is closely linked to the surface chemistry which
makes quantitative depth profiles at the surface and interfaces more difficult.
To overcome these fundamental limitations, a highly challenging new approach (called Zero-Energy SIMS) was proposed at IMEC.# The
concept eliminates the ion beam (collision cascade) and induces the material removal (only from the upper monolayer) by the formation
of volatile species through the chemical reaction of a precursor species at the substrate surface. As the reaction requires the concurrent
impact of an electron beam (electron beam induced etching, EBIE), the material removal is also highly localized providing a high spatial
resolution (in principle down to a few nm). Quantitative identification of the volatile reaction products (partly composed of substrate material)
is further based on photoionization of the elements by using ultra-short high-power laser pulses and subsequent mass selection.
Etching monolayer by monolayer will finally result into quantitative 3D depth profiles with high (ultimately atomic) depth and spatial resolution (1-3 nm).
This research is carried out in collaboration with Imec vzw, Materials and Components Analysis group (Prof. Wilfried Vandervorst).
# W. Vandervorst, Method and apparatus for local surface analysis, US patent nr. 20030127591 (2003)
- Particle emission from chemically enhanced electron-beam-induced etching of Si: an approach for zero-energy secondary-ion mass spectrometry, N. Vanhove, P. Lievens, W. Vandervorst, Phys. Rev. B 79 (2009) 035305
- Towards quantitative depth profiling with high spatial and high depth resolution, N. Vanhove, P. Lievens, W. Vandervorst, Appl. Surf. Sci. 255 (2008) 1360
Desorption of thin molecular overlayers on metallic substrates
We investigate the lift-off of molecular fragments from ion-bombarded surfaces to obtain a better fundamental understanding on the interplay
of the different processes that occur while a molecule leaves the surface. This research might lead to further developments in surface analytical
techniques. The mechanisms by which organic molecules desorb from the surface strongly depend on the physical and chemical properties of both the
overlayer and the substrate, and can include collisional, thermal or even chemical triggered events. Molecular dynamics simulations are employed to
model these processes at a molecular level.
Our RIMS setup is well equipped to experimentally assess the main observables involved. Mass spectra, time-of-flight distributions, and population
partitions of small molecules can be accurately determined. Moreover, the experimental procedure is sensitive to detect molecules ejected from overlayers
with submonolayer thickness.
Substrates are covered with an ultrathin layer of molecules carrying a chromophore. By a suitable choice of the functional group of the adsorbate and by
strictly controlling other physical properties such as the temperature and the thickness of the overlayer, the adsorption process can be varied from
physisorption to chemisorption. Parametric studies of the effect of the bond strength between the adsorbate and the substrate on the total lift-off
process were undertaken.
This research is performed in collaboration with the research groups of Prof. Zbigniew Postawa
and Dr. Piotr Cyganik (Jgellonian University, Krakow)
- Phase-dependent desorption from biphenyl-substituted alkanethiol self-assembled monolayers induced by ion irradiation, F. Vervaecke, S. Wyczawska, P. Cyganik, Z. Postawa, M. Buck, R.E. Silverans, P. Lievens, E. Vandeweert, J. Phys. Chem. C 112 (2008) 2248
