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

Abstract

Moiré fringes are used throughout a wide variety of applications in physics and engineering to bring out small variations in an underlying lattice by comparing with another reference lattice. This method was recently demonstrated in Scanning Transmission Electron Microscopy imaging to provide local strain measurement in crystals by comparing the crystal lattice with the scanning raster that then serves as the reference. The images obtained in this way contain a beating fringe pattern with a local period that represents the deviation of the lattice from the reference. In order to obtain the actual strain value, a region containing a full period of the fringe is required, which results in a compromise between strain sensitivity and spatial resolution. In this paper we propose an advanced setup making use of an optimised scanning pattern and a novel phase stepping demodulation scheme. We demonstrate the novel method on a series of 16 nm Si-Ge semiconductor FinFET devices in which strain plays a crucial role in modulating the charge carrier mobility. The obtained results are compared with both Nano-beam diffraction and the recently proposed Bessel beam diffraction technique. The setup provides a much improved spatial resolution over conventional moiré imaging in STEM while at the same time being fast and requiring no specialised diffraction camera as opposed to the diffraction techniques we compare to.

Linearized radially polarized light for improved precision in strain measurements using micro-Raman spectroscopy

“…The precision measured as the standard deviation of strain over the reference Si area on the two perpendicular lamellae under the same illumination conditions is 7 x 10 -4 for NBD and 9 x 10 -4 for Bessel. The precision measured for Bessel is lower in comparison to our previously reported values [44] and the variations can be attributed to the thickness of the sample under investigation, the electron dose used [45] for acquisition and hence the overall SNR (signal to noise ratio) of the dataset. Hence, a determination of optimal electron dose level prior to the measurement to get good SNR aids to achieve the best possible precision depending on thickness of the sample of interest.…”

Comparison Between Moiré Sampling Scanning Transmission Electron Microscopy Geometrical Phase Analysis Strain Characterization Method and Dark-Field Electron Holography

“…For example, an experimental match between the established HR-STEM Geometric Phase Analysis method (HR-STEM GPA) and the Moiré sampling Scanning Transmission Electron Microscopy Geometrical Phase Analysis technique (STEM Moiré GPA) was recently demonstrated [7] and provides confidence in using the recently developed method. The reliability of STEM Moiré GPA was further confirmed with another experimental match with the NB(P)ED technique [8].…”

Evaluation of different rectangular scan strategies for STEM imaging

“…Indeed, rather than a line modulation as in raster and snake scanning, the modulation due to sample drift is now smeared over the image with approximately equal weight in all directions, leading to a better behaviour when calculating the diffractogram. Atomic resolution images contain direct information about strain, which can be very relevant in many material systems [18]. STEM images are however often problematic for this application as the sequential scanning mixes actual strain with artefacts caused by sample drift during the recording time.…”