CN115145128A - Focusing and leveling device and method - Google Patents

Focusing and leveling device and method Download PDF

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Publication number
CN115145128A
CN115145128A CN202210932314.XA CN202210932314A CN115145128A CN 115145128 A CN115145128 A CN 115145128A CN 202210932314 A CN202210932314 A CN 202210932314A CN 115145128 A CN115145128 A CN 115145128A
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target object
image
imaging system
measured
optical imaging
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崔国栋
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Hefei Yuwei Semiconductor Technology Co ltd
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Hefei Yuwei Semiconductor Technology Co ltd
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    • G—PHYSICS
    • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
    • G03F—PHOTOMECHANICAL PRODUCTION OF TEXTURED OR PATTERNED SURFACES, e.g. FOR PRINTING, FOR PROCESSING OF SEMICONDUCTOR DEVICES; MATERIALS THEREFOR; ORIGINALS THEREFOR; APPARATUS SPECIALLY ADAPTED THEREFOR
    • G03F9/00—Registration or positioning of originals, masks, frames, photographic sheets or textured or patterned surfaces, e.g. automatically
    • G03F9/70—Registration or positioning of originals, masks, frames, photographic sheets or textured or patterned surfaces, e.g. automatically for microlithography
    • G03F9/7003—Alignment type or strategy, e.g. leveling, global alignment
    • G03F9/7023—Aligning or positioning in direction perpendicular to substrate surface
    • G03F9/7034—Leveling
    • G—PHYSICS
    • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
    • G03F—PHOTOMECHANICAL PRODUCTION OF TEXTURED OR PATTERNED SURFACES, e.g. FOR PRINTING, FOR PROCESSING OF SEMICONDUCTOR DEVICES; MATERIALS THEREFOR; ORIGINALS THEREFOR; APPARATUS SPECIALLY ADAPTED THEREFOR
    • G03F7/00—Photomechanical, e.g. photolithographic, production of textured or patterned surfaces, e.g. printing surfaces; Materials therefor, e.g. comprising photoresists; Apparatus specially adapted therefor
    • G03F7/70—Microphotolithographic exposure; Apparatus therefor
    • G03F7/708—Construction of apparatus, e.g. environment aspects, hygiene aspects or materials
    • G03F7/7085—Detection arrangement, e.g. detectors of apparatus alignment possibly mounted on wafers, exposure dose, photo-cleaning flux, stray light, thermal load
    • G—PHYSICS
    • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
    • G03F—PHOTOMECHANICAL PRODUCTION OF TEXTURED OR PATTERNED SURFACES, e.g. FOR PRINTING, FOR PROCESSING OF SEMICONDUCTOR DEVICES; MATERIALS THEREFOR; ORIGINALS THEREFOR; APPARATUS SPECIALLY ADAPTED THEREFOR
    • G03F9/00—Registration or positioning of originals, masks, frames, photographic sheets or textured or patterned surfaces, e.g. automatically
    • G03F9/70—Registration or positioning of originals, masks, frames, photographic sheets or textured or patterned surfaces, e.g. automatically for microlithography
    • G03F9/7088—Alignment mark detection, e.g. TTR, TTL, off-axis detection, array detector, video detection

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Abstract

The invention discloses a focusing and leveling device and a method, and the device comprises: the displacement platform is used for bearing a target object to be measured; the optical imaging system is positioned on one side of the target object to be measured, which is far away from the displacement table; the vertical displacement sensor is used for measuring the surface type of the target object to be measured; a drive mechanism for moving the displacement table along the transverse axis and/or the longitudinal axis; a vertical axis such that the optical imaging system moves with the vertical axis; the controller is respectively connected with the optical imaging system, the vertical displacement sensor and the driving mechanism, calculates the fuzzy scale of the image of the target object to be detected based on the image of the target object to be detected acquired by the optical imaging system, calculates the feedback compensation defocusing amount by combining the actual mapping relation between the fuzzy scale and the defocusing amount, and updates the expected position of the vertical axis according to the feedback compensation defocusing amount. So as to realize online defocus compensation.

Description

Focusing and leveling device and method
Technical Field
The invention relates to the technical field of semiconductors, in particular to a focusing and leveling device and a method.
Background
With the deepening and popularization of industrial automation and intellectualization, the use of Automatic Optical Inspection (AOI) instead of the traditional manual visual Inspection has become a technological development trend. The AOI equipment is widely used in the fields of automobiles, medicines, traffic, semiconductors and the like by virtue of the rapid and accurate defect identification and positioning capability of the AOI equipment.
In the semiconductor integrated circuit process, the wafer is subjected to glue coating, exposure, development, high temperature oxidation, diffusion and other processes. With the rapid development of moore's law, the size of microelectronic devices is continuously reduced, the process is more and more complex, the requirement for the quality of the finished product in a single step process is higher and higher, and the finished quality of each step needs to be detected and feedback controlled. AOI is an extremely important detection means, and plays an irreplaceable role in each process link.
Due to the continuous reduction of the size of microelectronic devices, the horizontal dimension resolution of AOI must be increased continuously to perform better resolution of the measurement object. With the increase of resolution, the vertical focal depth of the AOI is continuously compressed, and is reduced from hundreds of micrometers to several micrometers. Meanwhile, due to the existence of unavoidable astigmatism, the optical system has different resolving power for lines in two directions perpendicular to each other. This puts higher demands on the conventional vertical focal plane control method, and on one hand, it is necessary to find out the focal plane position having a better resolving power for the lines in the mutually perpendicular directions, and on the other hand, it is necessary to have the capability of accurately reaching the optimal focal plane in the dynamic photographing process.
The traditional focusing and leveling method in the detection equipment comprises the steps of firstly determining the optimal focal plane of an optical imaging system off line; in the detection process of the detection equipment, the height of a target object carried on the motion platform relative to the optimal reference focal plane is measured on line by using a displacement sensor, and the defocusing amount is calculated; in the process of motion detection, the defocusing amount is compensated through a motion executing mechanism.
In the method, because the focal plane measurement position is carried out in an off-line state and is not in the same state as the actual photographing position in the operation process of the equipment, errors are introduced to the estimation of the defocusing amount, and the finally calculated optimal imaging position also introduces measurement errors; in addition, the defocus compensation is performed by a motion actuator, and online real-time evaluation and feedback control cannot be realized.
Disclosure of Invention
The invention provides a focusing and leveling device and a method, which are used for realizing on-line defocusing compensation, so that the surface of a target object to be measured is positioned at the optimal focal plane of an optical imaging system, and the definition of an image of the target object to be measured is ensured.
In order to achieve the above object, an embodiment of the present invention provides a focusing and leveling device, including:
the displacement table is used for bearing a target object to be measured;
the optical imaging system is positioned on one side of the target object to be measured, which is far away from the displacement table;
the driving mechanism comprises a transverse shaft, a longitudinal shaft and a vertical shaft, and the transverse shaft and the longitudinal shaft are respectively connected with the displacement table so as to enable the displacement table to move along with the transverse shaft and/or the longitudinal shaft; the vertical shaft is connected with the optical imaging system so that the optical imaging system moves along with the vertical shaft;
and the controller is respectively connected with the optical imaging system and the driving mechanism, calculates the fuzzy scale of the image of the target object to be detected based on the image of the target object to be detected acquired by the optical imaging system, and calculates the feedback compensation defocusing amount by combining the actual mapping relation between the fuzzy scale and the defocusing amount so as to update the expected position of the vertical axis according to the feedback compensation defocusing amount.
According to an embodiment of the present invention, further comprising:
the vertical displacement sensor is used for measuring the surface type of the target object to be measured;
the controller is configured to determine a desired position of the vertical axis based on the face type of the object to be measured and the optimal focal plane position of the marker in the object to be measured.
According to one embodiment of the invention, the drive mechanism further comprises: the controller is further used for calculating the inclination of the image of the object to be detected relative to the optimal focal plane corresponding to the mark in the object to be detected according to the measuring points of at least three different straight lines in the image of the object to be detected acquired by the optical imaging system, and controlling the leveling of the leveling device of the transverse shaft to be connected with the transverse shaft and/or controlling the leveling device of the longitudinal shaft to be connected with the longitudinal shaft to be leveled with the displacement table.
According to one embodiment of the invention, the marks comprise at least one of spatially periodically distributed polygon marks, spatially periodically distributed transverse bar marks or spatially periodically distributed longitudinal bar marks.
In order to achieve the above object, an embodiment of another aspect of the present invention provides a focusing and leveling method, which is implemented based on the foregoing focusing and leveling device; the focusing and leveling method comprises the following steps:
calculating the fuzzy scale of the target object image to be detected according to the target object image to be detected acquired by the optical imaging system, and calculating feedback compensation defocusing amount by combining the actual mapping relation between the fuzzy scale and the defocusing amount so as to update the expected position of the vertical axis according to the compensation defocusing amount.
According to an embodiment of the present invention, before calculating a blur scale of an image of an object to be measured according to the image of the object to be measured acquired by the optical imaging system, the focusing and leveling device further includes:
and determining the expected position of the vertical shaft according to the surface type data of the target object to be detected acquired by the vertical displacement sensor and the optimal focal plane position of the mark in the target object to be detected.
According to an embodiment of the present invention, before the determining the expected position of the vertical axis according to the surface type data of the target object to be measured acquired by the vertical displacement sensor and the optimal focal plane position corresponding to the mark, the method includes:
controlling the vertical shaft to move up and down, controlling the optical imaging system to image the mark, and acquiring the position of the vertical shaft corresponding to the optimal focal plane corresponding to the mark;
further comprising: and controlling the vertical shaft to be immobile, controlling the transverse shaft and/or the longitudinal shaft to control the displacement table to move transversely and/or longitudinally, and controlling the vertical displacement sensor to acquire surface type data of the target object to be detected positioned on the displacement table at different positions.
According to an embodiment of the present invention, the determining the expected position of the vertical axis according to the plane type data of the target object to be measured acquired by the vertical displacement sensor and the optimal focal plane position corresponding to the mark in the target object to be measured includes:
calculating feedforward compensation defocusing amount according to the optimal focal plane position corresponding to the surface type data and the mark;
and determining the expected position of the vertical axis according to the optimal focal plane position and the feedforward compensation defocusing amount.
According to an embodiment of the present invention, before the calculating the blur scale of the image of the object to be measured according to the image of the object to be measured acquired by the optical imaging system, the method further includes:
controlling the transverse shaft and/or the longitudinal shaft to control the displacement table to move along the transverse direction and/or the longitudinal direction so that the optical imaging system is aligned with at least one mark in the target object to be measured;
controlling the vertical shaft to move up and down, controlling the optical imaging system to image at least one mark of the target object to be detected, and acquiring a reference image corresponding to the at least one mark;
acquiring the fuzzy scale and the defocusing amount corresponding to each reference image according to an image processing algorithm;
and fitting the fuzzy scale and the defocusing amount to obtain an actual mapping relation between the fuzzy scale and the defocusing amount.
According to an embodiment of the present invention, further comprising:
and calculating the inclination of the surface of the target object to be detected relative to the optimal focal plane according to the image of the target object to be detected acquired by the optical imaging system so as to control the leveling of the transverse shaft leveling device to the transverse shaft connected with the transverse shaft leveling device and/or the leveling of the longitudinal shaft leveling device to the longitudinal shaft connected with the longitudinal shaft leveling device to level the displacement table.
The focusing and leveling device and the method provided by the embodiment of the invention comprise: the displacement table is used for bearing a target object to be measured; the optical imaging system is positioned on one side of the target object to be measured, which is far away from the displacement table; the driving mechanism comprises a transverse shaft, a longitudinal shaft and a vertical shaft, and the transverse shaft and the longitudinal shaft are respectively connected with the displacement table so as to enable the displacement table to move along with the transverse shaft and/or the longitudinal shaft; the vertical shaft is connected with the optical imaging system so that the optical imaging system moves along with the vertical shaft; and the controller is respectively connected with the optical imaging system and the driving mechanism, calculates the fuzzy scale of the image of the target object to be detected based on the image of the target object to be detected acquired by the optical imaging system, and calculates the feedback compensation defocusing amount by combining the actual mapping relation between the fuzzy scale and the defocusing amount so as to update the expected position of the vertical axis according to the feedback compensation defocusing amount. The defocusing amount is compensated on line, so that the surface of the target object to be measured is positioned at the optimal focal plane of the optical imaging system, and the definition of the image of the target object to be measured is ensured.
It should be understood that the statements in this section do not necessarily identify key or critical features of the embodiments of the present invention, nor do they necessarily limit the scope of the invention. Other features of the present invention will become apparent from the following description.
Drawings
In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings required to be used in the description of the embodiments are briefly introduced below, and it is obvious that the drawings in the description below are only some embodiments of the present invention, and it is obvious for those skilled in the art that other drawings can be obtained according to the drawings without creative efforts.
Fig. 1 is a schematic structural view of a focusing and leveling device according to an embodiment of the present invention;
fig. 2 is a schematic structural diagram of an object to be measured in the focusing and leveling device according to the embodiment of the present invention;
FIG. 3 is a flowchart of a focusing and leveling method according to an embodiment of the present invention;
FIG. 4 is a flowchart of a focusing and leveling method according to an embodiment of the present invention;
FIG. 5 is a flowchart of a focusing and leveling method according to an embodiment of the present invention;
fig. 6 is a schematic diagram illustrating the effect of an embodiment of the present invention.
Detailed Description
In order to make those skilled in the art better understand the technical solutions of the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
It should be noted that the terms "first," "second," and the like in the description and claims of the present invention and in the drawings described above are used for distinguishing between similar elements and not necessarily for describing a particular sequential or chronological order. It is to be understood that the data so used is interchangeable under appropriate circumstances such that the embodiments of the invention described herein are capable of operation in sequences other than those illustrated or described herein. Moreover, the terms "comprises," "comprising," and "having," and any variations thereof, are intended to cover a non-exclusive inclusion, such that a process, method, system, article, or apparatus that comprises a list of steps or elements is not necessarily limited to those steps or elements expressly listed, but may include other steps or elements not expressly listed or inherent to such process, method, article, or apparatus.
Fig. 1 is a schematic structural diagram of a focusing and leveling device according to an embodiment of the present invention. As shown in fig. 1, the focusing and leveling apparatus 100 includes:
the displacement table 101 is used for bearing a target object 102 to be measured;
the optical imaging system 103 is positioned on one side of the target object 102 to be measured, which is far away from the displacement table 101;
a driving mechanism 105, including a transverse axis x, a longitudinal axis y and a vertical axis z, wherein the transverse axis x and the longitudinal axis y are respectively connected with the displacement table 101, so that the displacement table 101 moves along with the transverse axis x and/or the longitudinal axis y; the vertical axis z is connected with the optical imaging system 103 so that the optical imaging system 103 moves along with the vertical axis z;
and the controller 106 is respectively connected with the optical imaging system 103 and the driving mechanism 105, calculates the fuzzy scale of the image of the target object to be detected based on the image of the target object to be detected acquired by the optical imaging system 103, and calculates the feedback compensation defocusing amount by combining the actual mapping relation between the fuzzy scale and the defocusing amount so as to update the expected position of the vertical axis z according to the feedback compensation defocusing amount.
It can be understood that fig. 1 shows a schematic view of the focusing and leveling device, which mainly includes an optical imaging and collecting system for imaging, collecting and calculating the image of the target to be measured, in addition to the necessary electrical and frame supporting components; a Z axis for bearing the optical imaging system to perform vertical motion is used for performing focal plane compensation; x and Y axes for carrying a test object and performing horizontal movement; and the vertical displacement sensor is used for detecting the height of the material and roughly measuring defocusing amount.
The working principle of the device is as follows: the displacement table 101 carries the object 102 to be detected to move along with the x-axis and/or the y-axis, so that the optical imaging system 103 can image the object 102 to be detected, thereby detecting the object to be detected. During the imaging process of the optical imaging system 103 on the object 102 to be measured, for example, the optical imaging system 103 images a first region on the object 102 to be measured, after imaging, the controller 106 may calculate a blur scale of the first region according to the image, and obtain a defocus amount corresponding to the blur scale of the first region according to an actual mapping relationship between the blur scale and the defocus amount pre-stored in the controller 106, that is, obtain a feedback compensation defocus amount, update a desired position of the vertical axis z according to the feedback compensation defocus amount, re-image the first region, repeat the above process until a clear image of the first region is obtained, and then control the driving mechanism 105 to move the horizontal axis and/or the vertical axis to move to a next region.
The actual mapping relation between the fuzzy scale and the defocusing amount can be obtained in advance through a fitting algorithm. It should be noted that, under normal conditions, when the object to be measured is in the best focal plane of the imaging system, the image acquisition system can obtain a clear and sharp high-quality image information, and can analyze and measure the object to be measured with high fidelity. When the measured object is not coincident with the optimal focal plane of the imaging system, defocusing is generated, the imaging becomes fuzzy, and the measured pairSpatial high frequency information of the image will be lost, thereby reducing the defect resolution capability of the inspection system. For Image blur caused by defocus, description can be made using the following mathematical expression, image Detection (u,v)＝Image ideal (u, v) PSF (u, v) + Noise (u, v); wherein (u, v) represents lateral and vertical coordinates in an Image coordinate system, image Detection Representing the Image information, image, actually acquired by the imaging system via the optical system ideal Representing image information of an object under test at an optimal focal plane of an optical imaging system, PSF being a point spread function representing characteristics of the optical imaging system, noise representing Noise generated due to factors such as illumination, environment, image sensor, and optical imaging system. In the actual use process, the Image information Image actually acquired by the system is detected Detection Is an Image containing Noise ideal Convolution with the PSF.
In general, when the object is out of focus, the blurred PSF of the image can be described by the following mathematical expression,
Figure BDA0003781963040000081
where the blur scale ρ represents the magnitude of the blur and is a function of the defocus amount.
Therefore, the reference images of the marks with different heights can be obtained in the early stage of real-time focusing, so that the fuzzy scale of the point spread function can be obtained according to the corresponding reference images, finally, fitting is carried out according to the reference images of the marks with different vertical heights and the fuzzy scale calculated by the corresponding reference images, the corresponding relation between the fuzzy scale and the vertical height is obtained, and then the corresponding relation between the fuzzy scale and the defocusing amount is obtained and prestored in the controller 106.
In addition, the marked image can be obtained in the same optical imaging system, the feedback compensation defocusing amount can be calculated by calculating the fuzzy scale of the image and combining the corresponding relation between the fuzzy scale and the defocusing amount, the feedback compensation defocusing amount is not directly connected with the driving mechanism, and the expected position of the vertical axis can be updated after the feedback compensation defocusing amount is calculated.
Therefore, the embodiment realizes real-time online defocus compensation, and improves the imaging quality.
According to an embodiment of the present invention, further comprising: a vertical displacement sensor 104 for measuring the surface type of the target object 102 to be measured;
the controller 106 is configured to determine the desired position of the vertical axis based on the face type of the object to be measured and the optimal focal plane position of the marks in the object to be measured.
That is, after the surface type of the object 102 to be measured is measured, the feedforward compensation defocus amount can be estimated according to the optimal focus surface in the coordinate system of the vertical displacement sensor 104, and finally the expected position of the vertical axis can be determined according to the optimal focus surface in the coordinate system of the vertical displacement sensor 104 and the feedforward compensation defocus amount.
After the desired position of the vertical axis is determined, the feedback compensated defocus amount is determined again through the actual mapping relationship between the blur scale and the defocus amount in the optical imaging system 103 to correct the desired position of the vertical axis.
According to one embodiment of the present invention, the drive mechanism 105 further comprises: the controller 106 is further configured to calculate an inclination of the image of the target object to be measured with respect to an optimal focal plane corresponding to the mark according to at least three measurement points of different straight lines in the image of the target object to be measured acquired by the optical imaging system 103, and control the horizontal axis leveling device to level a horizontal axis connected thereto, and/or the longitudinal axis leveling device to level a longitudinal axis connected thereto, so as to level the displacement table 101.
That is, after the target object 102 to be measured is imaged, the tilt of the optimal focal plane corresponding to the plane and the mark may be calculated according to an image processing algorithm, so that the horizontal axis leveling device and/or the vertical axis leveling device may be controlled to move up and down to adjust the tilt of the translation stage 101. For example, the transverse shaft leveling device may be an electric lifting mechanism located at the end of the transverse shaft, and the longitudinal shaft leveling device may be an electric lifting mechanism located at the end of the longitudinal shaft, and after the inclination angle is calculated, the lifting distance may be calculated according to a positional relationship such as a trigonometric function, so as to control the transverse shaft leveling device and/or the longitudinal shaft leveling device to move up and down. Therefore, the subsequent imaging quality can be improved.
According to one embodiment of the invention, the indicia 107 comprises at least one of spatially periodically distributed polygon markers, spatially periodically distributed transverse bar markers, or spatially periodically distributed longitudinal bar markers.
It can be understood that, the marks 107 are arranged on the target object 102 to be measured, and in order to fit the corresponding relationship between different defocus amounts and the blur scale, the more the marks 107 are, the better the fit is, and the more the actual mapping relationship between the blur scale and the defocus amount is made to be closer to reality. For example, FIG. 2 shows a target for vertical control performance testing, with the left side showing the entire target being generated by repeated traversal of the same pattern; the right side represents a repeating pattern composition consisting primarily of both transverse and longitudinal lines, the lines used matching the resolution of the imaging system, optionally satisfying but not limited to a resolution test pattern in accordance with the MIL-STD-150A standard, the main principle being to include as many corners as possible.
Fig. 3 is a flowchart of a focusing and leveling method according to an embodiment of the present invention. The method is realized based on the previous focusing and leveling device; as shown in fig. 3, the focusing and leveling method includes the following steps:
s101, calculating a fuzzy scale of an image of a target object to be detected according to the image of the target object to be detected acquired by an optical imaging system, and calculating a feedback compensation defocusing amount by combining an actual mapping relation between the fuzzy scale and the defocusing amount;
and S102, updating the expected position of the vertical axis according to the compensated defocus amount.
It can be understood that the displacement table carries the object to be detected to move along the x-axis and/or the y-axis, so that the optical imaging system can image the object to be detected, and thus the object to be detected is detected. In the process of imaging the target object to be measured by the optical imaging system, for example, the optical imaging system images a first region on the target object to be measured, after imaging, the controller may calculate a blur scale of the first region according to the image, acquire a defocus amount corresponding to the blur scale of the first region according to an actual mapping relationship between the blur scale and the defocus amount pre-stored in the controller, acquire a feedback compensation defocus amount, update an expected position of the vertical axis according to the feedback compensation defocus amount, re-image the first region, repeat the above process until a clear image of the first region is acquired, and then control the driving mechanism to move the horizontal axis and/or the vertical axis to move to the next region.
The actual mapping relation between the fuzzy scale and the defocus amount can be obtained in advance through a fitting algorithm. Therefore, the embodiment realizes real-time online defocus compensation, and improves the imaging quality.
According to an embodiment of the present invention, as shown in fig. 4, the focusing and leveling apparatus further includes a vertical displacement sensor, and before S101 calculating a blur scale of an image of an object to be measured according to an image of the object to be measured acquired by an optical imaging system, the method further includes:
s100, determining the expected position of the vertical axis according to the surface type data of the target object to be detected acquired by the vertical displacement sensor and the optimal focal plane position of the mark in the target object to be detected.
That is, the desired position of the vertical axis may be initially set to the position of the optimal focal plane (optimal focal plane in the vertical displacement sensor coordinate system). Therefore, in the subsequent focusing process, the focusing can be performed more quickly, and the focusing efficiency is improved.
According to an embodiment of the present invention, before S100 determining the initial position of the vertical axis according to the surface type data of the target object to be measured acquired by the vertical displacement sensor and the best focal plane position corresponding to the mark, the method includes:
controlling the vertical shaft to move up and down, controlling the optical imaging system to image the mark, and acquiring the position of the vertical shaft corresponding to the optimal focal plane corresponding to the mark;
further comprising: and controlling the vertical shaft to be immobile, controlling the transverse shaft and/or the longitudinal shaft to control the displacement table to move transversely and/or longitudinally, and controlling the vertical displacement sensor to acquire surface type data of different positions of the target object to be detected on the displacement table.
According to an embodiment of the present invention, the step S100 of controlling the initial position of the vertical axis according to the surface type data of the target object to be measured acquired by the vertical displacement sensor and the best focal plane position corresponding to the mark comprises:
calculating feedforward compensation defocusing amount according to the optimal focal plane position corresponding to the surface type data and the mark;
and determining the expected position of the vertical axis according to the optimal focal plane position and the feedforward compensation defocusing amount.
That is to say, through vertical axle reciprocating, can obtain the corresponding vertical axis position of the best focal plane that the mark corresponds to obtain the best focal plane position of the target object surface that awaits measuring, can set for the expectation position of vertical axle with best focal plane position directly so as to shorten focusing time. After the model data is acquired, the desired position of the vertical axis can be determined with the best focal plane position and the profile data.
According to an embodiment of the present invention, before S101 calculating a blur scale of an image of an object to be measured according to an image of the object to be measured acquired by an optical imaging system, the method further includes:
controlling the transverse axis and/or the longitudinal axis to control the displacement table to move along the transverse direction and/or the longitudinal direction so as to enable the optical imaging system to be aligned with at least one mark in the target object to be measured;
controlling the vertical shaft to move up and down, controlling the optical imaging system to image at least one mark, and acquiring a reference image of an optimal focal plane corresponding to the at least one mark;
acquiring a fuzzy scale and a defocusing amount corresponding to each reference image according to an image processing algorithm;
and fitting the fuzzy scale and the defocusing amount to obtain the actual mapping relation between the fuzzy scale and the defocusing amount.
The actual mapping relation between the fuzzy scale and the defocus amount can be obtained in advance through a fitting algorithm. It should be noted that, under normal conditions, when the measured object is in the best focal plane of the imaging system, the optical imaging acquisition system can obtain a clear and sharp high-quality image information, and can achieve high fidelity to the measured objectAnd (5) analyzing and measuring the degree. When the optimal focal plane of the detected object and the imaging system is not coincident, defocusing is generated, the imaging becomes fuzzy, and the spatial high-frequency information of the detected object is lost, so that the defect analysis capability of the detection system is reduced. For Image blur caused by defocus, description can be made using the following mathematical expression, image Detection (u,v)＝Image ideal (u, v) PSF (u, v) + Noise (u, v); wherein (u, v) represents lateral and vertical coordinates in an Image coordinate system, image Detection Image representing the Image information actually acquired by the imaging system via the optical system ideal Representing image information of an object under test at an optimal focal plane of an optical imaging system, PSF being a point spread function representing characteristics of the optical imaging system, noise representing Noise generated due to factors such as illumination, environment, image sensor, and optical imaging system. In the actual use process, the Image information Image actually acquired by the system is detected Detection Is an Image containing Noise ideal Convolution with the PSF.
In general, when the object is out of focus, the blurred PSF of the image can be described by the following mathematical expression,
Figure BDA0003781963040000121
where the blur scale ρ represents the magnitude of the blur and is a function of the defocus amount.
Therefore, the reference images of the marks with different heights can be obtained in the early stage of real-time focusing, so that the fuzzy scale of the point spread function can be obtained according to the corresponding reference images, finally, fitting is carried out according to the reference images of the marks with different vertical heights and the fuzzy scale calculated by the corresponding reference images, the corresponding relation between the fuzzy scale and the vertical height is obtained, and then the corresponding relation between the fuzzy scale and the defocusing amount is obtained and prestored in the controller.
In addition, the marked image can be obtained in the same optical imaging system, the feedback compensation defocusing amount can be calculated by calculating the fuzzy scale of the image and combining the corresponding relation between the fuzzy scale and the defocusing amount, the feedback compensation defocusing amount is not directly connected with the driving mechanism, and the expected position of the vertical axis can be updated after the feedback compensation defocusing amount is calculated.
Therefore, the embodiment realizes real-time online defocus compensation, and improves the imaging quality.
According to an embodiment of the present invention, further comprising:
and calculating the inclination of the surface of the object to be measured relative to the optimal focal plane according to the image of the object to be measured acquired by the optical imaging system so as to control the transverse shaft leveling device to level the transverse shaft connected with the transverse shaft leveling device and/or the longitudinal shaft leveling device to level the longitudinal shaft connected with the longitudinal shaft leveling device so as to level the displacement table.
That is, after the target object to be measured is imaged, the inclination of the optimal focal plane corresponding to the plane and the mark can be calculated according to an image processing algorithm, so that the transverse axis leveling device and/or the longitudinal axis leveling device can be controlled to move up and down to adjust the inclination of the displacement table. For example, the transverse shaft leveling device may be an electric lifting mechanism located at the end of the transverse shaft, and the longitudinal shaft leveling device may be an electric lifting mechanism located at the end of the longitudinal shaft, and after the inclination angle is calculated, the lifting distance may be calculated according to a positional relationship such as a trigonometric function, so as to control the transverse shaft leveling device and/or the longitudinal shaft leveling device to move up and down. Therefore, after focusing, the displacement table is leveled, so that subsequent focusing is more accurate, and the imaging quality is higher.
More specifically, as shown in fig. 5, the focus and leveling method includes:
s1, uploading a target object to be detected; namely, after the mechanical and electrical devices in fig. 1 can work normally, the target object to be measured is uploaded to the motion platform; the target to be detected can be a silicon wafer or a mask plate and the like.
S2, single-point automatic focusing;
s21, selecting the calibration marks or the polygon marks shown in the figure 2, and moving to the central position of the optical imaging system;
s22, moving the Z axis up and down to approximately find the range of the focal plane, moving from top to bottom, simultaneously taking pictures, and recording the Z axis position of each picture and the measurement value of the corresponding vertical displacement sensor FLS when each picture is at the corresponding Z axis position;
s23, finding out the picture with the clearest and sharpest line by using an Image processing algorithm, finding out the corresponding Z-axis position and the measured value of the vertical displacement sensor FLS, recording the Z-BF and FLS-BF as the position of the optimal focal plane, and recording the picture as Image at the moment ideal As a reference picture.
Furthermore, the optimal positions of the imaging system for imaging can be calculated for the horizontal and vertical lines respectively, and recorded as the optimal focal planes Z _ BF _ H and FLS _ BF _ H of the horizontal line and the optimal focal planes Z _ BF _ V and FLS _ BF _ V of the vertical line, and the corresponding picture is recorded as Image at this time ideal _H、Image ideal And V as a reference picture.
Furthermore, different areas of the Image can be selected for optimal focal plane calculation to obtain Z _ BF _ V (u, V), FLS _ BF _ H (u, V) and Image ideal _H(u,v)、Image ideal _V(u,v)。
And S24, calculating the fuzzy scale of the point spread function by using the reference image. For different heights, and different lines, different ρ (z) can be obtained i )，ρ(z i ) H ，ρ(z i ) V Further, fitting with higher position accuracy can be performed on the obtained blur scale.
Furthermore, horizontal and vertical lines can be selected, and fuzzy scale calculation can be carried out on different areas of the image, so that positions (x) with different heights of the target to be measured can be obtained i ,y i ) Is the fuzzy scale value ρ (z) i ,x i ,y i )，ρ(z i ,x i ,y i ) H ，ρ(z i ,x i ,y i ) V Further, an actual mapping relation between the fuzzy scale and the defocus amount can be obtained.
S3, measuring the surface shape;
and S31, the Z axis is fixed, the X/Y axis carries the target to be detected to move in the horizontal plane, and the vertical displacement sensor FLS is used for measuring the surface height FLS _ Substrate (X, Y) of the target to be detected at different positions (X, Y).
S32, the defocus amount is estimated approximately by the following formula, and compensation is performed. Defocus _ FLS (x, y) = FLS _ BF-FLS _ Substrate (x, y).
S4, taking a picture in a sport mode;
s41, calculating the defocusing amount according to the surface type measured in S3, and setting the position of the Z axis: z _ Set (x, y) = FLS _ BF-focus _ FLS (x, y).
And S42, carrying the target to be detected by X \ Y, moving in a horizontal plane, photographing simultaneously, and recording the horizontal position (X, Y) at the moment.
S5, calculating the defocusing amount;
s51, after the picture is collected, the fuzzy scale rho (x) of the picture can be calculated i ,y i ) (ii) a Further, for different image areas and different lines, corresponding blur scales, ρ (x) can be obtained respectively i ,y i )，ρ(x i ,y i ) H ，ρ(x i ,y i ) V Therefore, when the position is photographed, the corresponding defocusing photographing position can be calculated as follows:
Z(x,y),＝ρ -1 (z i ,x,y)；
where ρ (z) i X, y) is defocus as z i And (x, y) is the horizontal position of the target to be measured.
And S52, according to the relation between the fuzzy scale and the height obtained in the S24, the defocusing amount can be more accurately inverted.
Defocus (x, y) = Z (x, y) -Z _ BF; wherein Z (x, y) represents a picture taken at the (x, y) position, and the computed imaging position is inverted according to the fuzzy scale.
Further, for different image areas and different lines, the Defocus _ H (x, y) and the Defocus _ V (x, y) can be obtained respectively;
further, for different regions of the image (more than 3 measurement points not on the same line), fitting is performed
Kx*X+Ky*Y+Kz*Z+C＝0；
The tilt of the surface to be measured with respect to the optimal focal plane can be calculated. Kx, ky, kz can be further compensated for by fine adjustment of X _ Z and Y _ Z.
S6, judging whether the imaging meets the requirements or not; if not, executing S7, if yes, executing S8;
s7, compensating defocusing amount in a feedback mode;
and judging whether the imaging requirement is met or not, and if the imaging requirement is not met, judging whether the imaging requirement is met. The Z-axis position needs to be reset,
Z_Set_update(x,y)＝Z_Set(x,y)-Defocus(x,y)；
and repeating the steps S4, S5 and S6 until the imaging control requirement is met.
S8, feedforward compensation defocusing amount;
when the defocusing amount meets the imaging control requirement, recording the vertical motion axis at the moment, and setting Z _ Set _ update (x, y), wherein the vertical motion axis at the moment is the optimal photographing position in the motion process of the motion platform.
Furthermore, kx, ky, kz can be further compensated by fine adjustment of X _ Z and Y _ Z.
Fig. 6 shows the spatial distribution of defocus over 300mm using the solution of the present invention, after using feed forward compensation. In the current mechanical structure, the distance between a focal plane detector and the center of an optical machine is about 10cm, the posture change of a guide rail is about 100urad, and the focal plane measurement error caused by the change is about 10 um. After the current coaxial focusing scheme is used, the defocusing distribution in the whole target object range is within the range of 2.5um, and the defocusing distribution is improved by 4 times compared with the original data; the accuracy of the method only depends on the processing accuracy of the defocus algorithm and the positioning accuracy of the motion table.
Based on the image processing technology, the optimal imaging focal plane position and the vertical control effect of the imaging system can be dynamically evaluated and feedback-controlled on line in real time; through an optical imaging system, based on the image actually acquired on line, the optimal imaging position is judged by using an image processing method, and the influence of an optical machine and motion errors is integrated, so that the optimal imaging position is more in line with the actual situation; through online and dynamic measurement of defocusing amount and feed-forward compensation, the focal plane control can be more accurate. And errors caused by different axes of the vertical displacement sensor and the optical imaging system are solved through the arrangement of the vertical displacement sensor and the optical imaging system and two sets of defocus compensation modes.
In summary, according to the focusing and leveling apparatus and method provided by the embodiment of the present invention, the apparatus includes: the displacement table is used for bearing a target object to be measured; the optical imaging system is positioned on one side of the target object to be measured, which is far away from the displacement table; the driving mechanism comprises a transverse shaft, a longitudinal shaft and a vertical shaft, and the transverse shaft and the longitudinal shaft are respectively connected with the displacement table so as to enable the displacement table to move along with the transverse shaft and/or the longitudinal shaft; the vertical shaft is connected with the optical imaging system so that the optical imaging system moves along with the vertical shaft; and the controller is respectively connected with the optical imaging system and the driving mechanism, calculates the fuzzy scale of the image of the target object to be detected based on the image of the target object to be detected acquired by the optical imaging system, and calculates the feedback compensation defocusing amount by combining the actual mapping relation between the fuzzy scale and the defocusing amount so as to update the expected position of the vertical axis according to the feedback compensation defocusing amount. The defocusing amount is compensated on line, so that the surface of the target object to be measured is positioned at the optimal focal plane of the optical imaging system, and the definition of the image of the target object to be measured is ensured.
It should be understood that various forms of the flows shown above may be used, with steps reordered, added, or deleted. For example, the steps described in the present invention may be executed in parallel, sequentially, or in different orders, and are not limited herein as long as the desired results of the technical solution of the present invention can be achieved.
The above-described embodiments should not be construed as limiting the scope of the invention. It should be understood by those skilled in the art that various modifications, combinations, sub-combinations and substitutions may be made in accordance with design requirements and other factors. Any modification, equivalent replacement, and improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims (10)

1. A focusing and leveling device, comprising:
the displacement table is used for bearing a target object to be measured;
the optical imaging system is positioned on one side of the target object to be measured, which is far away from the displacement table;
the driving mechanism comprises a transverse shaft, a longitudinal shaft and a vertical shaft, and the transverse shaft and the longitudinal shaft are respectively connected with the displacement table so as to enable the displacement table to move along with the transverse shaft and/or the longitudinal shaft; the vertical shaft is connected with the optical imaging system so that the optical imaging system moves along with the vertical shaft;
and the controller is respectively connected with the optical imaging system and the driving mechanism, calculates the fuzzy scale of the image of the target object to be detected based on the image of the target object to be detected acquired by the optical imaging system, and acquires the feedback compensation defocusing amount by combining the actual mapping relation between the fuzzy scale and the defocusing amount so as to update the expected position of the vertical axis according to the feedback compensation defocusing amount.
2. The focusing and leveling device according to claim 1, further comprising:
the vertical displacement sensor is used for measuring the surface type of the target object to be measured;
the controller is used for determining the expected position of the vertical axis based on the surface type of the object to be measured and the optimal focal plane position of the mark in the object to be measured.
3. The focusing and leveling device of claim 1, wherein the drive mechanism further comprises: the controller is further used for calculating the inclination of the image of the target object to be detected relative to the optimal focal plane of the mark in the target object to be detected according to the measuring points of at least three different straight lines in the image of the target object to be detected acquired by the optical imaging system, controlling the leveling of the leveling device of the transverse shaft to be connected with the transverse shaft, and/or controlling the leveling device of the longitudinal shaft to be connected with the longitudinal shaft to be leveled with the displacement table.
4. A focusing and leveling device according to claim 2 or 3 wherein the markings comprise at least one of spatially periodically distributed polygon markings, spatially periodically distributed transverse bar markings or spatially periodically distributed longitudinal bar markings.
5. A focusing and leveling method, which is realized based on the focusing and leveling device according to any one of claims 1-4; the focusing and leveling method comprises the following steps:
calculating the fuzzy scale of the target object image to be detected according to the target object image to be detected acquired by the optical imaging system, and calculating feedback compensation defocusing amount by combining the actual mapping relation between the fuzzy scale and the defocusing amount so as to update the expected position of the vertical axis according to the compensation defocusing amount.
6. The focusing and leveling method according to claim 5, wherein the focusing and leveling device further comprises a vertical displacement sensor, and before calculating a blur scale of the target object image to be measured according to the target object image to be measured acquired by the optical imaging system, the method further comprises:
and determining the expected position of the vertical shaft according to the surface type data of the target object to be detected acquired by the vertical displacement sensor and the optimal focal plane position of the mark in the target object to be detected.
7. The focusing and leveling method according to claim 6, wherein before determining the expected position of the vertical axis according to the surface type data of the object to be measured acquired by the vertical displacement sensor and the optimal focal plane position of the mark in the object to be measured, the method comprises:
controlling the vertical shaft to move up and down, controlling the optical imaging system to image the mark, and acquiring the position of the vertical shaft corresponding to the optimal focal plane corresponding to the mark;
further comprising: and controlling the vertical shaft to be immobile, controlling the transverse shaft and/or the longitudinal shaft to control the displacement table to move transversely and/or longitudinally, and controlling the vertical displacement sensor to acquire surface type data of the target object to be detected positioned on the displacement table at different positions.
8. The focusing and leveling method according to claim 6, wherein the determining the expected position of the vertical axis according to the surface type data of the target object to be measured acquired by the vertical displacement sensor and the optimal focal plane position of the mark in the target object to be measured comprises:
calculating feedforward compensation defocusing amount according to the optimal focal plane position corresponding to the surface type data and the mark;
and determining the expected position of the vertical axis according to the optimal focal plane position and the feedforward compensation defocusing amount.
9. The focusing and leveling method according to claim 5, wherein before the calculating a blur scale of the image of the object to be measured according to the image of the object to be measured acquired by the optical imaging system, the method further comprises:
controlling the transverse shaft and/or the longitudinal shaft to control the displacement table to move along the transverse direction and/or the longitudinal direction so that the optical imaging system is aligned with at least one mark in the target object to be measured;
controlling the vertical shaft to move up and down, controlling the optical imaging system to image at least one mark in the target object to be detected, and acquiring a reference image corresponding to the at least one mark;
acquiring the fuzzy scale and the defocusing amount corresponding to each reference image according to an image processing algorithm;
and fitting the fuzzy scale and the defocusing amount to obtain an actual mapping relation between the fuzzy scale and the defocusing amount.
10. The focus leveling method according to claim 5, further comprising:
and calculating the inclination of the surface of the target object to be detected relative to the optimal focal plane according to the image of the target object to be detected acquired by the optical imaging system so as to control the leveling of the transverse shaft leveling device to the transverse shaft connected with the transverse shaft leveling device and/or the leveling of the longitudinal shaft leveling device to the longitudinal shaft connected with the longitudinal shaft leveling device to level the displacement table.
CN202210932314.XA 2022-08-04 2022-08-04 Focusing and leveling device and method Pending CN115145128A (en)

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