Strain visualization using large-angle convergent-beam electron diffraction

Abstract

In this study, we report a strain visualization method using large-angle convergent-beam electron diffraction (LACBED).11large-angle convergent-beam electron diffraction (LACBED); scanning transmission electron microscopy (STEM); nanobeam electron diffraction (NBD); personal computer (PC); diffraction pattern (DP); transmission electron microscopy (TEM); convergent beam electron diffraction (CBED); four-dimensional (4D); gigabytes (GB); region of interest (ROI); Gatan Microscopy Suite (GMS); selected area (SA); focused ion beam (FIB); embedded SiGe (eSiGe); complementary metal-oxide semiconductor (CMOS); full width at half maximum (FWHM); cross-correlation (CC); shallow trench isolations (STIs). We compare the proposed method with the strain maps acquired via STEM-NBD, a combination of scanning transmission electron microscopy (STEM) and nanobeam electron diffraction (NBD). Although STEM-NBD can precisely measure the lattice parameters, it requires a large amount of data and personal computer (PC) resources to obtain a two-dimensional strain map. Deficiency lines in the transmitted disk of LACBED reflect the crystalline structure information and move, curve, or disappear in the deformed area. Properly setting the optical conditions makes it possible to acquire real-space images over a broad area in conjunction with deficiency lines on the transmitted disk. The proposed method acquires images by changing the relative position between the specimen and the deficiency line and can grasp the strain information with a small number of images. In addition, the proposed method does not require high-resolution images. It can reduce the required PC memory or storage consumption in comparison with that of STEM-NBD, which requires a high-resolution diffraction pattern (DP) from each point of the region of interest. Compared with the two-dimensional maps of LACBED and NBD, NBD could detect large distortions in the area where the deficiency line curved, moved, or disappeared. The curving or moving direction of the deficiency line is qualitatively consistent with the NBD results. If quantitative strain values are not essential, strain visualization using LACBED can be considered an effective technique. We believe that the strain information of a sample can be obtained effectively using both methods.