{'fraction_non_alphanumeric': 0.02342786683107275, 'fraction_numerical': 0.002466091245376079, 'mean_word_length': 5.444444444444445, '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}}
Recovery of SEM Image by In-Situ Cleaning of Contaminated Objective Aperture

We studied the effect of in-situ cleaning of a contaminated scanning electron microscope (SEM) objective aperture, applying the down-flow ashing process with a O2+CF4 gas mixture. Model experiments, using resists instead of contamination layers, were carried out and empirical equations which describe the dependence of etching rates on experimental parameters were obtained. A conversion factor between resist and contamination layer etching rates was experimentally obtained, and the conditions required for in-situ cleaning were determined. By applying in-situ cleaning, the SEM images, which had deteriorated after two weeks of operation, were recovered to nearly the same level of quality as those obtained using a new aperture.