Patent ID: 11199401

Abstract:
A method of evaluating a region of a sample that includes a first sub-region and a second sub-region, adjacent to the first sub-region, the region comprising a plurality of sets of vertically-stacked double-layers extending through both the first and second sub-regions with a geometry or orientation of the vertically-stacked double layers in the first sub-region being different than a geometry or orientation of the vertically-stacked double layers in the second region resulting in the first sub-region having a first milling rate and the second sub-region having a second milling rate different than the first milling rate, the method including: milling the region of a sample by scanning a focused ion beam over the region a plurality of iterations in which, for each iteration, the focused ion beam is scanned over the first sub-region and the second sub-region generating secondary electrons and secondary ions from each of the first and second sub-regions; detecting, during the milling, at least one of the generated secondary electrons or the secondary ions; generating, in real-time, an endpoint detection signal from the at least one of detected secondary electrons or secondary ions, the endpoint detection signal including a fast oscillating signal having a first frequency and a slow oscillating signal having a second frequency, slower than the first frequency; analyzing the fast and slow oscillating signals to determine original first and second frequencies of the fast and slow oscillating signals; and estimating, in real-time, a depth of each of the first and second sub-regions based on the determined first and second frequencies.