CN-121986255-A - Pattern inspection apparatus, focus position adjustment method, and pattern inspection method

CN121986255ACN 121986255 ACN121986255 ACN 121986255ACN-121986255-A

Abstract

The pattern inspection apparatus according to one embodiment of the present invention includes a correlation data creation circuit that creates correlation data between an autofocus signal and a focus evaluation value for evaluating a focus position, using an autofocus signal and a focus evaluation value for each of the parameters of autofocus control acquired while changing the height position of a pattern formation surface of an evaluation substrate in a state in which the evaluation substrate on which an evaluation pattern is formed is placed on a table, and an autofocus signal calculation circuit that calculates an inspection autofocus signal for obtaining a focus evaluation value equal to or higher than a threshold value in the substrate to be inspected, using the autofocus signal and the focus evaluation value for each of the height positions acquired while changing the height position of the pattern formation surface of the substrate to be inspected in a state in which the pattern is formed on the table, and the correlation data of the evaluation substrate, and an autofocus mechanism that adjusts the height position of the pattern formation surface of the substrate to be inspected to a height position of the pattern formation surface corresponding to the value of the inspection autofocus signal.

Inventors

HIRANO RYOICHI
YAMASHITA YASUHIRO
Hisaaki Otaki
YASUI YOSHITAKA

Assignees

纽富来科技股份有限公司

Dates

Publication Date: 20260505
Application Date: 20241003
Priority Date: 20231010

Claims (10)

1. A pattern inspection device is characterized by comprising: A stage on which a substrate is placed; A driving mechanism for moving the height position of the workbench; a related data creation circuit that creates related data of an autofocus signal and a focus evaluation value for evaluating a focus position, using an autofocus signal serving as a parameter for autofocus control and a focus evaluation value for evaluating a focus position, which are acquired while changing a height position of a pattern formation surface of an evaluation substrate in a state in which the evaluation substrate on which an evaluation pattern is formed is placed on the stage; a storage device that stores the related data; an inspection autofocus signal calculation circuit that calculates an inspection autofocus signal that obtains a focus evaluation value equal to or higher than a threshold value in a substrate to be inspected, using the autofocus signal and the focus evaluation value for each height position obtained while changing the height position of a pattern formation surface of the substrate to be inspected, and the related data of the evaluation substrate, in a state in which the substrate to be inspected on which a pattern is formed is placed on the stage; An autofocus mechanism that adjusts a height position of a pattern formation surface of the inspected substrate to a height position of a pattern formation surface corresponding to a value of the inspection autofocus signal; A sensor for receiving light transmitted or reflected from the inspected substrate irradiated with the light to thereby capture an optical image of the inspected substrate in a state where the height position of the pattern formation surface of the inspected substrate is adjusted to the height position of the pattern formation surface corresponding to the value of the inspection autofocus signal, and And a comparison circuit for comparing the photographed optical pixel with the reference image using the reference image.
2. The pattern inspection apparatus according to claim 1, wherein, As the related data, a function obtained by approximating the autofocus signal and the focus evaluation value for each height position is used.
3. The pattern inspection apparatus according to claim 1, wherein, As the related data, a numerical sequence of the autofocus signal and the focus evaluation value for each height position is used.
4. The pattern inspection apparatus according to claim 1, wherein, The autofocus signal and the focus evaluation value for each height position of the inspected substrate are acquired at different height positions of 3 points or more.
5. The pattern inspection apparatus according to claim 1, wherein, The related data creation circuit includes: a plot processing circuit for plotting the obtained autofocus signal and focus evaluation value of each moving focus signal for each height position, and Fitting processing circuit approximates the focus evaluation value of each of the plotted autofocus signal values with a convex polynomial function.
6. The pattern inspection apparatus according to claim 1, wherein, The inspection autofocus signal calculation circuit plots a plurality of combinations of the autofocus signal and the focus evaluation value obtained on the inspected substrate to produce a graph, and applies a template represented by the correlation data to the plotted plurality of combinations.
7. The pattern inspection apparatus according to claim 6, wherein, The inspection autofocus signal calculation circuit calculates an inspection autofocus signal having a focus evaluation value equal to or greater than a threshold value in the graph to which the template is applied.
8. The pattern inspection apparatus according to claim 7, wherein, The inspection autofocus signal calculating circuit calculates the inspection autofocus signal corresponding to a maximum value of the template applied.
9. A focus position adjusting method is characterized in that, Using an autofocus signal for parameters for autofocus control and a focus evaluation value for evaluating a focus position, which are obtained while changing the height position of a pattern formation surface of an evaluation substrate on which an evaluation pattern is formed, in a state in which the evaluation substrate is mounted on a stage, to prepare data on the autofocus signal and the focus evaluation value, The relevant data are stored in a storage means, Calculating an inspection autofocus signal for obtaining a focus evaluation value equal to or higher than a threshold value on a substrate to be inspected by using the autofocus signal and the focus evaluation value for each height position and the correlation data of the evaluation substrate, which are obtained while changing the height position of a pattern formation surface of the substrate to be inspected, in a state in which the substrate to be inspected on which a pattern is formed is placed on the stage, Receiving light transmitted or reflected from the inspected substrate irradiated with the inspection light, thereby adjusting the height position of the pattern formation surface of the inspected substrate to the height position of the pattern formation surface corresponding to the value of the inspection autofocus signal when the optical image of the inspected substrate is captured by the sensor.
10. A pattern inspection method, characterized in that, Using an autofocus signal for parameters for autofocus control and a focus evaluation value for evaluating a focus position, which are obtained while changing the height position of a pattern formation surface of an evaluation substrate on which an evaluation pattern is formed, in a state in which the evaluation substrate is mounted on a stage, to prepare data on the autofocus signal and the focus evaluation value, The relevant data are stored in a storage means, Calculating an inspection autofocus signal for obtaining a focus evaluation value equal to or higher than a threshold value on a substrate to be inspected by using the autofocus signal and the focus evaluation value for each height position and the correlation data of the evaluation substrate, which are obtained while changing the height position of a pattern formation surface of the substrate to be inspected, in a state in which the substrate to be inspected on which a pattern is formed is placed on the stage, Receiving light transmitted or reflected from the inspected substrate irradiated with the inspection light while adjusting the height position of the pattern formation surface of the inspected substrate to the height position of the pattern formation surface corresponding to the value of the inspection autofocus signal, thereby capturing an optical image of the inspected substrate by a sensor, The photographed optical pixel is compared with the reference image using the reference image, and the result is output.

Description

Pattern inspection apparatus, focus position adjustment method, and pattern inspection method Technical Field The present application is an application claiming priority from JP2023-175426 (application number) filed on 10 months of 2023, on 10 days of japanese application. The entire contents described in JP2023-175426 are incorporated herein by reference. The invention relates to a pattern inspection apparatus, a focus position adjustment method, and a pattern inspection method. For example, the present invention relates to an apparatus for inspecting a pattern defect of an exposure mask used for semiconductor manufacturing, and a focus position adjustment method of the apparatus. Background In recent years, with the high integration and large capacity of large-scale integrated circuits (LSI), circuit line widths required for semiconductor elements are becoming narrower. These semiconductor elements are manufactured by using an original image pattern (also referred to as a mask or a reticle, hereinafter collectively referred to as a mask) on which a circuit pattern is formed, and exposing and transferring the pattern onto a wafer by a reduced projection exposure apparatus called a step exposure apparatus to form a circuit. Further, improvement in yield is indispensable for the manufacture of LSI that takes a lot of manufacturing cost. One of the main causes of the reduction in yield is pattern defects of a mask used for exposing and transferring an ultrafine pattern on a semiconductor wafer by a photolithography technique. In recent years, as the size of LSI patterns formed on a semiconductor wafer is miniaturized, the size required for pattern defect detection is becoming extremely small. Therefore, there is a need for a pattern inspection apparatus for inspecting defects of a transfer mask used for LSI manufacturing with high precision. Examples of the inspection method include a "die to die inspection" and a "die to database inspection", in which optical image data obtained by capturing the same pattern at different places on the same mask are compared with each other, and a "die to database inspection" in which CAD data of a pattern design is converted into drawing data (design data) in a device input format for drawing a pattern on the mask, and the drawing data (design data) is input to an inspection device, and a reference image is generated based on the drawing data and compared with an optical image which is measured data obtained by capturing the pattern. In this inspection apparatus, it is necessary to clearly acquire a pattern image on a mask as an inspection object. However, since the optical system of the inspection apparatus has a limited focal depth, it is necessary to keep the inspection surface of the inspection object within the focal depth of the optical system continuously during the inspection. In other words, it is required to keep the contrast of the captured image within an allowable range. In an inspection apparatus, it is necessary to scan a mask while moving a stage to continuously capture images, and it is not realistic to adjust the focal point (focus) of an optical system by successively calculating the image contrast during the inspection due to insufficient processing time. Therefore, in the inspection apparatus, an autofocus mechanism that detects a displacement of an inspection object with respect to a height direction of an inspection optical system and adjusts a height position is employed in addition to the inspection optical system for image capturing. With recent miniaturization of patterns, the inspection light has been shortened. With this, the focal depth of the inspection optical system becomes shallow. Therefore, although the accuracy of a measurement system of a separate autofocus mechanism provided In the vicinity of the inspection optical system is sufficient In the past, it is impossible to detect various fluctuation factors (dependency of temperature and mechanical deformation) of the inspection optical system without performing (In-situ) measurement using the inspection optical system itself, and it is impossible to perform focus adjustment with high accuracy. Therefore, as an autofocus mechanism, a system using a part of an inspection optical system is adopted (for example, refer to patent document 1). In the optical system of the autofocus mechanism, the amount of light passing through the slit disposed before and after the focus position of the image from the mask is measured, and the difference value between the amounts of light is calculated, thereby measuring the change in the height position of the mask. Here, an error occurs between a height position where the difference value of the measured light amounts is zero and a height position where the contrast of the image is maximum. Therefore, parameters required for the autofocus operation are required to obtain an image with a larger contrast for each mask to be inspected. On the other hand, in order