Strain mapping of semiconductor specimens with nm-scale resolution in a transmission electron microscope

Abstract

The last few years have seen a great deal of progress in the development of transmission electron microscopy based techniques for strain mapping. New techniques have appeared such as dark field electron holography and nanobeam diffraction and better known ones such as geometrical phase analysis have been improved by using aberration corrected ultra-stable modern electron microscopes. In this paper we apply dark field electron holography, the geometrical phase analysis of high angle annular dark field scanning transmission electron microscopy images, nanobeam diffraction and precession diffraction, all performed at the state-of-the-art to five different types of semiconductor samples. These include a simple calibration structure comprising 10-nm-thick SiGe layers to benchmark the techniques. A SiGe recessed source and drain device has been examined in order to test their capabilities on 2D structures. Devices that have been strained using a nitride stressor have been examined to test the sensitivity of the different techniques when applied to systems containing low values of deformation. To test the techniques on modern semiconductors, an electrically tested device grown on a SOI wafer has been examined. Finally a GaN/AlN superlattice was tested in order to assess the different methods of measuring deformation on specimens that do not have a perfect crystalline structure. The different deformation mapping techniques have been compared to one another and the strengths and weaknesses of each are discussed.

Strain measurement in semiconductor FinFET devices using a novel moiré demodulation technique

“…Applying this method to moiré STEM images reveals the apparent strain which needs to be corrected back to the actual strain via eq. [12] as shown in fig.5. As the strain magnification is significantly higher for low frequency moiré fringes, it is tempting to choose the undersampling as demonstrated in fig.5.a where strain is readily apparent from the moiré image due to the boosting effect.…”

Optimizing disk registration algorithms for nanobeam electron diffraction strain mapping

“…With NBED this is not a problem and FOV is usually limited by the storage space of the data acquisition system or the sample stability. With the introduction of high speed direct electron detectors, a large number of diffraction patterns can be obtained from a single sample, covering a very large field of view without concerns for sample drift or other instabilities [10,2,11,12,13].…”

“…Cooper et al, have noted that NBED strain measurements can lose accuracy due to non-uniform disk intensity [12]. This non-uniformity is due to experimental limitations such as sample bending, dynamical effects, or imperfect alignment, resulting in more complicated data sets.…”

Electron Bessel beam diffraction for precise and accurate nanoscale strain mapping

“…Transmission electron microscopy (TEM) offers strain measurement with the highest spatial resolution and many methods have been developed or adapted to this purpose. Strain can be measured through convergent beam electron diffraction (CBED), high resolution conventional and scanning TEM imaging (HRTEM and HRSTEM) including Moiré fringe analysis (Moiré fringes appear when using a HRSTEM setup to scan at a lower magnification, due to the low-frequency sampling of the crystal lattice) as well as nano beam electron diffraction (NBED) which can also be performed in conjunction with precession electron diffraction (N-PED) [6][7][8][9][10] . Of these techniques, the best accuracy and precision are offered by nano beam precession electron diffraction with a spatial resolution better than 1nm, a strain sensitivity of σ = 2×10 −4 and an accuracy of ∆ = 1×10 −3 , though it requires additional specialised hardware 11,12 .…”