The increased process and material complexity linked to further device scaling and the strong size dependence of many material problems and phenomena has led to the need for metrology applicable to devices with nm-scale dimensions. The emergence of small 3D-devices with the need of probing doping and composition in very small, heterogeneous 3D-devices (< 20 nm), led to the paradox of performing analysis with the required 3D-spatial resolution (nm) versus the limited statistical relevance of analyzing one small single (nm) device.
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 concept and the 3D-heterogeneity problem by performing these measurements in a novel prototype 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 (< 0.5 nm). 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 20 nm. 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 performance (depth resolution, sensitivity, accuracy, extension to doping) and application to 3D-devices (FINFET, nanowires, TFETs) and concepts like area selective deposition of inorganic (Cu,W, Al2O3) as well as organic films (Sell-assembled monolayers) still need to be explored.
The limits of SF-Sims lies in the heterogeneous 3D-nature of many devices as this leads to a rapid topography development jeopardizing the depth resolution attainable with SF-SIMS. The novel instrumentation at imec combine SF-SIMS profiling with in-situ AFM enabling to observe the topographical evolution as a function of erosion depth. Algorithms to cope with the evolution of surface topography in heterogeneous system provide then an opportunity to reach a novel degree in accuracy for 3D-metrology.
Experimental parameters to be studied include the optimum cluster ion detection, the use of small (monoatomic) (Ar, O2) versus large cluster ions (Ar3000, O3-5000) as bombarding beam, the control and monitoring surface topography with in-situ AFM when dealing with heterogeneous non-planar devices and developing the required topography correction, combined electrical and chemical analysis.. All in relation to studying advanced devices and process technologies.
1 A.Franquet, B, Douhard, D. Melkonyan, P Favia, T. Conard, W Vandervorst, Appl. Surf.Sci (2015)
2 W.Vandervorst et al., Plenary lecture SIMS-19, Korea (2013)
Physics, material science.
Type of work:
60% experimental, 40% theoretical.
Supervisor: Wilfried Vandervorst
Daily advisor: Valentina Spampinato and Kristof Paredis
When you apply for this PhD project, mention the following reference code in the imec application form: ref. STS 1704-18.