Focusing method and focusing system for object to be measured, equipment and storage medium

Abstract

The invention discloses a focusing method and system for a to-be-measured object, equipment and a storage medium. The focusing method comprises the following steps: acquiring calibration images of the to-be-measured object at different focusing heights; acquiring a distribution relationship between a first focusing degree parameter and a focusing height of each layer of calibration graph according to the calibration image, wherein the distribution relationship is Gaussian distribution; the logarithm of the distribution relation of the multiple layers of calibration graphs is solved, then weighting processing is carried out, and a calibration curve in a linear relation with the focusing height is obtained; obtaining an optimal focusing height reference value; shooting to obtain a to-be-detected image of the to-be-detected object; acquiring a second focusing degree parameter of each layer of calibration graph according to the to-be-detected image; carrying out logarithm solving on the second focusing degree parameter of each layer of calibration graph in the to-be-tested image, and then carrying out weighting processing to obtain a test difference value; and determining the actual height corresponding to the test difference value by using the calibration curve, and calculating the difference value between the optimal focusing height reference value and the actual height as the defocusing amount of the to-be-tested image. According to the invention, the focusing speed is improved while the focusing precision is ensured.

Description

technical field [0001] Embodiments of the present invention relate to the field of measurement, and in particular, to a method for focusing an object to be measured, a focusing system, a device, and a storage medium. Background technique [0002] In the application of measurement based on high-magnification microscopic imaging, the accuracy of focusing often directly affects the accuracy of measurement. For example, in overlay error measurement, even if the difference is only a few tens of nanometers at different heights, the measured There will be differences in overlay errors. On the other hand, the focusing speed directly affects the measurement efficiency, and if the focusing time is too long, the measurement efficiency will decrease. [0003] There are usually two types of traditional focusing algorithms. One is to use the imaging method to determine the optimal focus height based on the image captured at different heights, and to use the response of the image focus (f...

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Problems solved by technology

On the other hand, the focusing speed directly affects the measurement efficiency, too long focusing time will lead to lower measurement efficiency

[0003] There are usually two traditional focusing algorithms. One is to use imaging based on images taken at different heights, and use the response of image focus (for example, image sharpness) to height to determine the best focus height. However, this approach In order to achieve higher measurement accuracy, it is often necessary to take multiple images at a smaller step size, which leads to long data acquisition time and low measurement efficiency

The other is to use a non-imaging method (such as the method of interference) to measure the distance between the object and the lens, but this method needs to be equipped with an additional optical system (such as an interference system), which is costly and the overall system is relatively large. complex

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