Self-focusing SIMS with in-situ SPM: a paradigm shift in 3D-metrology
Imec has recently proposed an integrated solution to this paradox by solving the resolution and statistics problem using the so called Self-Focusing SIMS (SF-SIMS)1,2,3 concept and the 3D-heterogeneity problem by performing these measurements in a novel system based on the combination of a ToF-SIMS (Time of Flight - Secondary Ions Mass Spectrometry) and an in-situ AFM (Atomic Force Microscope) instrument. This does lead to a metrology concept and instrumentation optimized for full 3D chemical analysis with nm-accuracy. Moreover when using the SPM in electrical mode (SSRM, KPFM, C-AFM) in combination with the ion beam erosion and chemical analysis, a complete chemical and electrical 3D-characterization can be performed. The innovation of SF-SIMS lies in exploiting the physics of cluster ion (AxBy+) formation which states that to form a cluster ion the constituents must originate from the same collision cascade in very close proximity (<1nm). Hence by selecting a cluster ion (AxBy+) which does contain one element (A or B) originating solely from the region of interest (i.e. Ge from the 10-20nm SiGe trench), the analytical information is self-focused to that region. Using SF-SIMS one could determine the composition of SiGe- layers in trenches as narrow as 20nm. These results have triggered a strong industrial interest with several semiconductor manufacturers attempting to implement the technique, and with SIMS instrument manufacturers adapting their instrument for its routine applications. Notwithstanding these early success and industrial interest, a detailed understanding of the physics of the entire concept, its performances and applications to 3D-devices (FINFET, nanowires, ...), area selective deposition of inorganic (Cu, W, Al2O3) as well as organic films (Self-Assembled Monolayers) still needs to be explored. The instrumentation at Imec is the first one world wide, combining large cluster ions (Ar3000, O2-5000) as bombarding beam in a TOFSIMS (ideally suited for SF-SIMS analysis) with in-situ (electrical) AFM enabling to observe the chemical and functional properties a function of erosion depth and does represent a unique opportunity to reach a novel degree in accuracy for 3D-metrology. Within the research project the candidate will explore the fundamental aspects of (cluster beam) SF-SIMS (large cluster ions (Ar3000, O2-5000) when applied to nanoscale heterogeneous systems addressing issues such as cluster selection, topography development (probed by the AFM), redeposition, proximity effects on ionization, quantification etc as well as experimental aspects such as the interplay between AFM measurements and SIMS transients but also aspects of data fusion (sims & e-SPM). Ultimately the project will provide fundamental insight in the various aspects of SF-SIMS and the added value of the hybrid SIMS-SPM metrology when applied to advanced semiconductor devices.