| CPC H04N 23/11 (2023.01) [G01B 11/272 (2013.01); G02B 27/108 (2013.01); G02B 27/141 (2013.01); H04N 23/56 (2023.01); H04N 23/673 (2023.01)] | 18 Claims |
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1. An image acquisition method of acquiring images of a plurality of marks, which includes a mark covered with a mask layer, from a sample on which the plurality of marks are formed, the image acquisition method comprising:
a) acquiring a first optical signal by emitting a penetrative light beam, which is capable of penetrating the mask layer, to a measurement target mark that is one of the plurality of marks on the sample;
b) acquiring a second optical signal by emitting a reflective light beam, which reflects from the mask layer, to the measurement target mark;
c) determining whether the measurement target mark is covered with the mask layer by comparing the first optical signal and the second optical signal; and
d) acquiring a mark image by emitting a first light beam, which penetrates the mask layer, to the measurement target mark when the measurement target mark is covered with the mask layer, and acquiring a mark image by emitting a second light beam, which is different from the first light beam, to the measurement target mark when the measurement target mark is not covered with the mask layer,
wherein the first optical signal in the step a) represents an intensity of a reflected light beam from the sample produced by the penetrative light beam and the second optical signal acquired in the step b) represents an intensity of a reflected light beam from the sample produced by the reflective light beam, and
wherein when a ratio of the second optical signal to the first optical signal is a reference value or more, the measurement target mark is determined to be covered with the mask layer.
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