{'fraction_non_alphanumeric': 0.025552825552825554, 'fraction_numerical': 0.002457002457002457, 'mean_word_length': 4.850574712643678, 'pattern_counts': {'":': 0, '<': 0, '<?xml version=': 0, '>': 0, 'https://': 0, 'lorem ipsum': 0, 'www.': 0, 'xml': 0}, 'pii_count': 0, 'substrings_counts': 0, 'word_list_counts': {'cursed_substrings.json': 0, 'profanity_word_list.json': 0, 'sexual_word_list.json': 0, 'zh_pornsignals.json': 0}}
Local Lattice Strain Measurement using Geometric Phase Analysis of Annular Dark Field Images from Scanning Transmission Electron Microscopy

Strain engineering to improve device performance is now widespread in the Si-based device industry. As such, there is a need for a technique that measures the local lattice strain on a routine basis at the size scale of the device. This metrology should be sensitive to small strains and should be able to resolve the spatial variations of the strain across the device. It should be practical and reproducible to apply it on a routine basis. All techniques that map strains at the sub-100 nm scale rely on some form of transmission electron microscopy or diffraction. [1-4] Although the high angle annular dark field mode of a scanning transmission electron microscope (HAADF-STEM) is common for high-resolution imaging, geometric phase analysis (GPA) of HAADF-STEM has not been used extensively. HAADF-STEM imaging has two strong advantages compared to normal high-resolution transmission electron microscopy (HRTEM). One is that more reproducible images can be recorded from HAADF-STEM images because it is less sensitive to experimental parameters. The other is that thicker samples can be imaged in HAADF-STEM, which can reduce strain relaxation effects due to sample thinning. However, hysteresis in scanning is a critical defect in the application of GPA to HAADF-STEM images. This paper shows how GPA of high-resolution images acquired in the HAADF-STEM can map strains at levels of accuracy and reproducibility needed for strained silicon device development. The largest potential source of error in strain measurement in HAADF-STEM is the beam shift between scan lines due to the lens hysteresis. That is, when the beam reaches the end of its scan across the specimen, it should fly back the start. If it fails the start, the subsequent line will be displaced, ∆ u x (y), in This “fly-back” involves a relatively large beam displacement; it the largest defect at modest magnifications.