Image acquisition system and method for metrology apparatus

Abstract

The embodiment of the present application discloses an image acquisition system and method of a metrology device, and the system comprises: a first defocus determination module, which is used for determining a first defocus amount of a target object; a second defocus determination module, which is used for determining a second defocus amount of the target object; a first movement control module, which is used for controlling the relative movement of a metrology objective lens and the target object in a first direction according to the first defocus amount to focus the target object for the first time, and controlling the relative movement of the metrology objective lens and the target object in the first direction according to the second defocus amount to focus the target object for the second time; an image acquisition module, which is used for acquiring the image of the target object after the first focusing, generating a first image to determine whether the target object is at a preset position, and acquiring the image of the target object after the second focusing to generate a second image after it is determined that the target object is at the preset position; the image acquisition time of the target object can be reduced, the alignment error measurement efficiency of the target object is improved, and the applicability is strong.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of semiconductor technology, and in particular to an image acquisition system and method of a measurement device. BACKGROUND

[0002] Semiconductor detection technology plays an important role in the processes of semiconductor production, packaging and testing, and the measurement of overlay error (OVL) is an important part of the key process in the semiconductor production process. The overlay error is one of the most important errors that need to be controlled in the key process, which refers to the pattern alignment error between the front layer and the current layer in the wafer alignment process, and there is a certain distribution rule on the wafer and the exposure field. In order to ensure that the overlay error is within the threshold range, the overlay error of a plurality of mark points needs to be measured on the alignment measurement machine after each batch of wafer exposure, and the measurement value is processed by mathematics to obtain the distribution model (OVL model terms) of the overlay error, which is used for the overlay error control of the next batch of wafer exposure. In order to obtain the distribution rule of the overlay error on the wafer and the exposure field, the mark points for overlay error measurement need to be distributed as evenly as possible on the whole wafer, and the wafer measurement image (i.e. the wafer scanning image containing the overlay error measurement mark points) containing the information of the front layer and the current layer is obtained by a camera in the process of overlay error measurement, and the overlay error is obtained through the wafer measurement image. Therefore, in order to improve the measurement accuracy of the overlay error, the positioning accuracy of the wafer measurement image acquisition also has very high requirements, and high-precision wafer image scanning positioning technology and auto-focusing technology are needed.

[0003] In the prior art, in the process of improving the positioning accuracy of wafer image scanning, target acquisition (TA) (including wafer measurement image acquisition) operation is needed when positioning the mark points for overlay error measurement, and in order to improve the accuracy of wafer image scanning, focusing is performed once before and after the TA operation by using white light interference focusing method. White light interference focusing is a focusing technology with very high precision (about 10nm), but it needs a large-load and large-stroke Z motor (i.e. precision motor) to perform a scanning motion of about 20um stroke each time focusing is performed, and after waiting for the solution result, a step setting of the Z motor needs to be performed, which causes each flow of white light interference focusing to consume 70ms~80ms of time, and twice white light interference focusing also makes the wafer measurement image acquisition time-consuming and the overlay error measurement efficiency of the wafer low. SUMMARY

[0004] The present application provides an image acquisition system and method of a measurement device, which can reduce the image acquisition time of the target object, improve the overlay error measurement efficiency of the target object based on image acquisition, and has strong applicability.

[0005] In a first aspect, the present application provides an image acquisition system of a metrology device, a first defocus determination module configured to determine a first defocus amount of a target object; a second defocus determination module configured to determine a second defocus amount of the target object; a first movement control module configured to control a relative movement between a measurement objective lens and the target object in a first direction according to the first defocus amount to perform a first focusing on the target object, and control the relative movement between the measurement objective lens and the target object in the first direction according to the second defocus amount to perform a second focusing on the target object; an image acquisition module configured to acquire an image of the target object after the first focusing to generate a first image, the first image being used to determine whether the target object is at a preset position, and acquire an image of the target object after the second focusing to generate a second image after determining that the target object is at the preset position; wherein a determination speed of the first defocus amount is greater than a determination speed of the second defocus amount, and a resolution of the first image is less than a resolution of the second image. By using the image acquisition system provided by the present application, the first defocus determination module can acquire the first defocus amount of the target object at a high speed, so that the image acquisition system can quickly perform the first focusing on the target object. On the basis of the first focusing, the second defocus determination module can acquire the second defocus amount of the target object at a higher accuracy, so that the image acquisition module can acquire the second image at a higher resolution after the second focusing. Therefore, the image acquisition time of the target object can be reduced, the alignment error measurement efficiency of the target object can be improved, and the structures of the modules in the image acquisition system are simple and have strong applicability.

[0006] In a possible implementation of the first aspect, the first defocus determination module includes a first light emitting unit and a first light receiving unit. During the determination of the first defocus amount of the target object, the first light emitting unit is configured to emit a first light beam, the first light beam generates a first reflected light signal after being reflected by the target object, and the first light receiving unit is configured to determine the first defocus amount of the target object according to the received first reflected light signal. By using the present application, the first light emitting unit emits the first light beam, the first light receiving unit receives the first reflected light signal after the first light beam is reflected by the target object, the image acquisition system can quickly acquire the first reflected light signal of the target object, the first light receiving unit can quickly and accurately calculate the first defocus amount of the target object based on the first reflected light signal, and the direct optical measurement method can improve the determination speed of the first defocus amount, further reduce the image acquisition time of the target object, and improve the alignment error measurement efficiency of the target object.

[0007] In a possible implementation of the first aspect, the first defocus determination module determines the first defocus amount by using one of the following methods: an eccentric mask, differential confocal, chopping method, and coaxial laser triangulation. The present application can use specific optical effects or principles to accurately measure the first defocus amount of the target object. The method has high measurement accuracy and high stability, and can effectively reduce the measurement deviation caused by external interference or system error, thereby improving the determination accuracy of the first defocus amount.

[0008] In a possible implementation of the first aspect, the second defocus determination module includes a second light emitting unit, an interference unit, and a second light receiving unit. The interference unit and the measurement objective lens are fixedly connected. The interference unit includes a first beam splitter and a reference mirror. The second light emitting unit is configured to emit a second light beam. The second light beam generates a third light beam and a fourth light beam after passing through the first beam splitter. The third light beam generates a second reflected light signal after being reflected by the reference mirror. The fourth light beam generates a third reflected light signal after being reflected by the target object. The first movement control module is further configured to control the interference unit and the measurement objective lens to move a preset distance during the determination of the second defocus amount of the target object. During the movement of the interference unit and the measurement objective lens from a first position (initial position) to a second position (first position), the second light signal receiving unit is configured to receive the second reflected light signal and the third reflected light signal when the interference unit and the measurement objective lens are at different positions, and determine the second defocus amount according to the second reflected light signal and the third reflected light signal. The present application uses the principle of optical interference to accurately calculate the second defocus amount by measuring the change of interference fringes, and can achieve high-precision measurement of the second defocus amount of the target object, thereby further improving the accuracy of the second focusing.

[0009] In a possible implementation of the first aspect, the second light signal receiving unit is configured to determine the second position of the interference unit or the measurement objective lens when the image acquisition module is in a focus state according to the second reflected light signal and the third reflected light signal received when the interference unit and the measurement objective lens are at different positions, and determine the second defocus amount according to the second position and the initial position of the interference unit or the measurement objective lens. The present application uses the principle of interference and light signal analysis to accurately measure the position change of the interference unit or the measurement objective lens, thereby achieving high-precision determination of the second defocus amount of the target object, and further improving the accuracy of the second focusing.

[0010] In a possible implementation of the first aspect, the first movement control module includes a first control unit and a first driving unit, the first driving unit is connected with the second light emitting unit and the interference unit, and the first control unit is configured to control the first driving unit to drive the second light emitting unit and the interference unit to move in the first direction. By introducing the first control unit and the first driving unit, the image acquisition system can accurately control the movement of the interference unit in the first direction. This accurate control ensures that the interference unit moves according to a predetermined trajectory and speed, thereby further improving the accuracy and stability of the second defocus amount determination.

[0011] In a possible implementation of the first aspect, the image acquisition system includes a second beam splitter, the target object, the measurement objective, the first beam splitter, the second beam splitter, and the image acquisition module are located on a first optical axis, the second light emitting unit, the first beam splitter, and the reference mirror are located on a second optical axis, and the first optical axis is perpendicular to the second optical axis. By using the second beam splitter and reasonably arranging the related components on the first optical axis and the second optical axis, the image acquisition system can accurately separate and combine the light paths, thereby improving the accuracy and efficiency of image acquisition.

[0012] In a possible implementation of the first aspect, the image acquisition system includes a third beam splitter, the second beam splitter, the third beam splitter, and the second light receiving unit are located on a third optical axis, and the third beam splitter and the first defocus determination module are located on a fourth optical axis, the third optical axis is parallel to the second optical axis, and the fourth optical axis is parallel to the first optical axis. By introducing the third beam splitter and arranging the third optical axis and the second optical axis in parallel, the image acquisition system can more effectively separate and combine light rays in different directions, avoid mutual interference of the light paths, improve the clarity of image acquisition, and enhance the stability and reliability of the image acquisition system.

[0013] In a possible implementation of the first aspect, the first movement control module is connected with the target object, and when the target object is not in the preset position, the first movement control module is configured to control the target object to move in a second direction, so that the target object is in the preset position, and the second direction is a plane perpendicular to the first direction. By connecting the first movement control module with the target object, the image acquisition system can detect the current position of the target object and determine whether the target object is in the preset position. If the target object is not in the preset position, the first movement control module can control the target object to move in the second direction until the target object reaches the preset position, thereby improving the automation degree of the image acquisition system and further improving the image acquisition efficiency of the target object.

[0014] In a possible implementation of the first aspect, the image acquisition system further includes a second movement control module, the second movement control module is connected with the target object, and the second movement control module is configured to control the target object to move in a second direction to make the target object be at the preset position when the target object is not at the preset position. With the application, the image acquisition system has two independent control modules, i.e., the first movement control module and the second movement control module, to ensure that the target object can be accurately moved to the preset position. This double protection mechanism improves the accuracy and reliability of the positioning of the target object. Even if one control module fails or makes an error, the other module can ensure the correct positioning of the target object.

[0015] In a possible implementation of the first aspect, the second movement control module includes a second control unit and a second driving unit, the second control unit is connected with the second driving unit, the second driving unit is connected with the target object, and the second control unit is configured to control the second driving unit to drive the target object to move in the second direction, wherein the second direction is a plane perpendicular to the first direction. With the application, the second control unit can send accurate instructions, and the second driving unit can accurately convert the instructions into actual movement of the target object, thereby ensuring that the target object can be accurately moved to the preset position, and realizing accurate control of the movement of the target object in the second direction.

[0016] In a possible implementation of the first aspect, the image acquisition module further includes a position judgment module, the position judgment module is configured to determine whether the target object is at the preset position according to the first image. With the application, through accurate analysis of the first image, the position judgment module can identify the current position of the target object and compare it with the preset position, thereby ensuring that the target object is accurately positioned, and improving the image acquisition accuracy of the target object.

[0017] In a possible implementation of the first aspect, the target object is provided with a graphic mark, and the preset position is the position of the target object in the second direction when the graphic mark is at the center of the field of view of the image acquisition module, wherein the second direction is a plane perpendicular to the first direction. With the application, by providing a graphic mark on the target object and ensuring that the mark is at the position of the center of the field of view of the image acquisition module, the positioning accuracy of the target object and the identification efficiency of the first image can be improved.

[0018] In a second aspect, the application further provides an image acquisition method of a metrology device, comprising: determining a first defocus amount of a target object; based on the first defocus amount, controlling relative movement between a measurement objective lens and the target object in a first direction to focus the target object for a first time; acquiring an image of the target object after the first time of focusing, generating a first image, and determining whether the target object is at a preset position using the first image; after determining that the target object is at the preset position, obtaining a second defocus amount of the target object; based on the second defocus amount, controlling relative movement between the measurement objective lens and the target object in the first direction to focus the target object for a second time; acquiring an image of the target object after the second time of focusing, generating a second image; wherein the determination speed of the first defocus amount is greater than the determination speed of the second defocus amount, and the resolution of the first image is less than the resolution of the second image. By using the application, the target object is first focused quickly, and then fine focusing is performed for image acquisition. The first stage of quick focusing reduces the focusing time required for target object image acquisition, and the second stage of fine focusing ensures the high resolution of the second image, thereby ensuring the measurement accuracy of the error measurement based on the second image, so as to reduce the image acquisition time of the target object and improve the alignment error measurement efficiency of the target object based on image acquisition.

[0019] In a possible implementation of the second aspect, the metrology device comprises a first defocus determination module, and the first defocus determination module comprises a first light emitting unit and a first light receiving unit. The method for determining the first defocus amount of the target object comprises: controlling the first light emitting unit to emit a first light beam, the first light beam generates a first reflected light signal after being reflected by the target object; and determining the first defocus amount of the target object based on the first reflected light signal received by the first light receiving unit. By using the application, the first light emitting unit emits a light beam, the first light receiving unit receives a first reflected light signal, and the first defocus amount is calculated based on the first reflected light signal. This process can quickly and efficiently determine the first defocus amount without moving the devices in the metrology device, thereby shortening the overall error measurement time.

[0020] In a possible implementation of the second aspect, the method for determining the first defocus amount of the target object based on the first reflected light signal received by the first light receiving unit comprises: determining the first defocus amount using one of an eccentric mask, differential confocal, chopping method, and coaxial laser triangulation method based on the first reflected light signal. By using the application, the first defocus amount of the target object can be accurately and quickly determined based on the first reflected light signal by using measurement methods such as eccentric mask, differential confocal, chopping method, and coaxial laser triangulation method, thereby reducing measurement errors and improving the accuracy of the first defocus amount.

[0021] In a possible implementation of the second aspect, the measurement device includes a second defocus determination module, the second defocus determination module includes a second light emitting unit, an interference unit, and a second light receiving unit, the interference unit includes a first beam splitter and a reference mirror, and the second defocus amount of the target object is obtained by: controlling the second light emitting unit to emit a second light beam during relative movement of the interference unit and the measurement objective lens relative to the target object in the first direction, the second light beam generates a third light beam and a fourth light beam after passing through the first beam splitter, the third light beam generates a second reflected light signal after being reflected by the reference mirror, and the fourth light beam generates a third reflected light signal after being reflected by the target object; and determining the second defocus amount of the target object based on the second reflected light signal and the third reflected light signal received by the second light receiving unit. According to the application, the second defocus amount of the target object is measured with high precision based on the principle of optical interference, and the focusing accuracy of the second focusing is further improved.

[0022] In a possible implementation of the second aspect, the method for determining the second defocus amount of the target object based on the second reflected light signal and the third reflected light signal received by the second light receiving unit includes: determining a first focusing position of the interference unit or the measurement objective lens when the image acquisition module is in a focusing state based on the second reflected light signal and the third reflected light signal received by the second light receiving unit; and determining the second defocus amount based on the first focusing position and an initial position of the interference unit or the measurement objective lens. According to the application, the position change of the interference unit or the measurement objective lens is measured with high precision based on the principle of interference and light signal analysis, and the second defocus amount of the target object is determined with high precision.

[0023] In a possible implementation of the second aspect, before the relative movement between the measurement objective lens and the target object in the first direction is controlled, the method includes: determining a target movement position of the measurement objective lens or the target object based on the first defocus amount. According to the application, the target movement position is determined to avoid inaccurate second focusing caused by excessive movement or insufficient movement of the measurement objective lens or the target object without determining the target movement position in advance. After the target movement position is determined, the image acquisition system can directly move the measurement objective lens or the target object to the position without multiple trial movements and adjustments, which greatly reduces the number of movements and time and further improves the error measurement efficiency of the target object.

[0024] In a possible implementation of the second aspect, the method for controlling the relative movement between the metrology objective and the target object in the first direction includes: controlling the movement of the metrology objective relative to the target object in the first direction, or / and controlling the movement of the target object relative to the metrology objective in the first direction. With the present application, the metrology objective and / or the target object can be moved in the first direction, and the most suitable movement mode can be selected to achieve the first focusing and the second focusing according to the specific measurement scene and requirements, thereby improving the applicability.

[0025] In a possible implementation of the second aspect, after determining that the target object is not in the preset position, the method includes: controlling the relative movement between the target object and the metrology objective in the second direction, so that the target object is in the preset position. With the present application, by controlling the movement of the target object in the second direction, the measurement error caused by directly performing the second focusing and image acquisition when the target object is not in the preset position can be eliminated, and the accuracy and reliability of the error measurement of the target object can be further improved.

[0026] In a possible implementation of the second aspect, the metrology device includes an image acquisition module, and before the image acquisition of the target object after the first focusing or before the image acquisition of the target object after the second focusing, the method includes: sending a control signal indicating that the focusing is completed to the image acquisition module. With the present application, by sending the control signal indicating that the focusing is completed, it can be ensured that the image acquisition module performs image acquisition only after the first focusing or the second focusing is completed, thereby avoiding the image blur or distortion problem caused by incomplete focusing, and improving the accuracy and quality of image acquisition.

[0027] In a possible implementation of the second aspect, the target object has a graphic mark, and the determination of whether the target object is in the preset position includes: determining whether the graphic mark is located at the center of the field of view of the image acquisition module; and if the graphic mark is located at the center of the field of view of the image acquisition module, determining that the target object is in the preset position. With the present application, the introduction of the graphic mark provides an intuitive visual basis for the position judgment of the target object, and the current position of the target object can be more accurately determined, thereby reducing the positioning error of the target object and improving the positioning accuracy of the target object. BRIEF DESCRIPTION OF DRAWINGS

[0028] Figure 1 is a structural schematic diagram of an image acquisition system provided by the present application;

[0029] Figure 2 is another structural schematic diagram of an image acquisition system provided by the present application;

[0030] Figure 3is another structural schematic diagram of an image acquisition system provided by the present application;

[0031] Figure 4 is a light path schematic diagram of a first light beam provided by the present application;

[0032] Figure 5 is a flow schematic diagram of an image acquisition method provided by the present application. DETAILED DESCRIPTION

[0033] The technical solutions in the present application will be described below in combination with the drawings in the present application.

[0034] For the convenience of understanding, first, some nouns are simply explained as follows:

[0035] 1. Defocus amount, also known as defocus height, refers to the data indicating the focus offset difference when an image of a target object (such as a target wafer) is acquired in the scanning process of the target object, which can be used to adjust the distance between the target object and the measurement objective lens so that the image of the target object reaches a preset sharpness. The preset sharpness refers to the specified value of the sharpness of the image of the target object, which can be determined according to the specific form of the product.

[0036] 2. Image marker, which can also be called a scanning feature point, an ideal feature point or a target feature point, can be a marker pattern used for alignment and needs to have unique features that are easy to identify. The image marker can be obtained from the feature points used for alignment of the target object, or can be obtained by artificial intelligence labeling in the design drawing of the target object.

[0037] 3. First light beam, which can be a structured light, a partially coherent light, a laser and the like. Among them, the structured light usually has the characteristic of narrow line width, and can get high contrast and high definition imaging effect when captured; the partially coherent light is a light beam between completely coherent light and incoherent light, and its coherence can be controlled by adjusting the light source or using a scatterer; the laser is a highly coherent monochromatic light with extremely high directivity and brightness, and the phase and frequency of the laser remain consistent in space and time.

[0038] Taking the structured light as the first light beam as an example, the structured light can be projected to project a specific optical pattern onto the surface of the target object, and then the processor can calculate the three-dimensional information of the target object according to the returned light beam data (light signal) to restore the entire three-dimensional space and obtain the defocus amount of the target object. Among them, the optical pattern projected by the structured light can be a plane, a grid, a straight line and the like, and the height change of the surface of the target object can be calculated by observing the distortion of the light.

[0039] 4. Second light beam, refers to the light beam used to generate light beam interference, usually monochromatic laser light beam (the above-mentioned monochromatic laser light beam can also be called monochromatic light beam), for example, the above-mentioned monochromatic light beam can be visible light, infrared light, etc. The monochromatic light beam has high precision and strong stability, has a specific wavelength and coherence, and can generate a specific interference pattern by adjusting the phase and amplitude of the light beam.

[0040] 5. Light beam interference, refers to light beam interference experiment, generally using monochromatic light beam to carry out experiment, such as white light interference, red light interference, etc. Light beam interference experiment relies on the interference phenomenon of light, that is, the phenomenon that interference pattern is generated when two monochromatic light beams meet. In this application, one monochromatic light beam (such as white light) can be split into two light beams by a beam splitter, one of which is reflected by a reference mirror, and the other is reflected by a target object, and finally converges at a photodiode to generate bright and dark stripes. These stripes are caused by the phase difference of the two monochromatic light beams, and the phase difference depends on the optical path difference of the two monochromatic light beams. The intensity of the interference fringes depends on the optical path difference of the two light beams. According to the brightness and darkness of the white light interference fringes and the position of the interference fringes, the height of the target object can be analyzed. Among them, only when the optical path difference of the reference arm and the measurement arm is within one coherence length of the light source, the backscattering light (i.e. the reflected light of the target object) and the reference light (i.e. the reflected light of the reference mirror) will interfere, and the optical path difference is equal to 0, that is, the optical path of the two light beams is completely consistent, and the coherence intensity reaches the maximum. This signal is the light beam interference signal.

[0041] Example one

[0042] For ease of understanding, the architecture of the image acquisition system is first described. The above-mentioned image acquisition system can be applied to the production scene of the wafer, the processing scene of the wafer, etc. Taking the wafer as the target object as an example, the image acquisition scene of the wafer measurement device is taken as an example for description. Please refer to Figure 1 , Figure 1 is a structural schematic diagram of the image acquisition system provided by the present application. As Figure 1As shown, the image acquisition system can include an image acquisition module, a first defocus determination module, a second defocus determination module, and a first movement control module. The first defocus determination module is configured to determine a first defocus amount of the target object. The second defocus determination module is configured to determine a second defocus amount of the target object. The first movement control module is configured to control the relative movement between the measurement objective lens and the target object in the first direction according to the first defocus amount, so as to focus the target object for the first time, and control the relative movement between the measurement objective lens and the target object in the first direction according to the second defocus amount, so as to focus the target object for the second time. The image acquisition module is configured to acquire the image of the target object after the first focusing, to generate a first image. The first image is used to determine whether the target object is at a preset position, and is used to acquire the image of the target object after the second focusing, to generate a second image, after it is determined that the target object is at the preset position. The determination speed of the first defocus amount is greater than the determination speed of the second defocus amount, and the resolution of the first image is less than the resolution of the second image.

[0043] In some possible embodiments, the first defocus determination module can include a focus pursuit sensor or the like. The first defocus determination module can be configured to determine the first defocus amount of the target object, and transmit the first defocus amount to the first movement control module. The first defocus amount is the first distance between the focal point of the light and the surface of the target object. The first defocus determination module can be configured to emit a light beam to the target object, and receive and analyze the data of the light beam reflected by the target object. For example, the first defocus amount of the target object can be quickly obtained by using a high-speed optical focusing technology. For example, the high-speed optical focusing technology can include an eccentric mask method (the time for a single measurement is about 1 ms), a differential confocal method (the time for a single measurement is about 2 ms), a chopping method (the time for a single measurement is about 0.1 ms), and a coaxial laser triangulation method (the time for a single measurement is about 1 ms). Since the first image has a low focusing accuracy requirement, the light beam interference focusing method (the time for a single measurement is about 100 ms) with high accuracy and long time is not used, but the first defocus amount is obtained by using the high-speed optical focusing technology, so as to greatly improve (about 100 ms for each measurement) the acquisition speed of the first defocus amount on the basis that the accuracy of the first defocus amount meets the focusing accuracy requirement of the first image. By improving the acquisition speed of the first defocus amount, the acquisition speed of the first image can be improved, so as to improve the positioning speed of the target object, and further improve the image acquisition speed of the image acquisition system.

[0044] The second defocus determination module can include a light tracking device, a photoelectric acquisition board, or the like. The second defocus determination module can be used to determine the second defocus amount of the target object, for example, by a light beam interference focusing method. The second defocus amount can be transmitted to the first movement control module. It can be understood that the second defocus amount is also the second distance between the focal point of the light and the surface of the target object. The second defocus determination module is fixedly connected to the measurement objective lens. Through the second defocus determination module, the second defocus amount with higher focusing accuracy can be obtained on the basis of the first defocus amount with lower focusing accuracy. For example, a more accurate second defocus amount can be obtained by using a higher-precision algorithm or a higher-precision sensor. For example, the second defocus determination module can obtain the second defocus amount by a light beam interference focusing method (with higher precision than the high-speed optical focusing technology) and a fine adjustment motor (which can adjust the position of the measurement objective lens or the target object with high precision) so that the focusing accuracy of the second defocus amount meets the precision requirement of the product for image acquisition.

[0045] The first movement control module can be used to control the relative movement between the measurement objective and the target object in the first direction according to the first defocus amount, so as to perform the first focusing on the target object. For example, the first movement control module can generate a motion control instruction based on the first defocus amount to accurately control the movement of the measurement objective in the first direction, or to accurately control the movement of the target object in the first direction, or to accurately control the movement of both the measurement objective and the target object in the first direction. The relative movement distance of the measurement objective and / or the target object can compensate for the first defocus amount, so that the target object and / or the measurement objective can reach the in-focus position to perform the first focusing on the target object. The first movement control module can accurately control the movement of the measurement objective and / or the target object by a distance indicated by the first defocus amount through a high-precision position adjustment device (such as a fine adjustment motor), so as to ensure the accuracy of the first focusing, and the movement of the measurement objective and / or the target object can be accurately controlled through the motion control instruction to perform the precise position movement. The first movement control module can also be used to control the relative movement between the measurement objective and the target object in the first direction according to the second defocus amount, so as to perform the second focusing on the target object. Similarly to the first focusing, the first movement control module can accurately control the relative movement between the measurement objective and / or the target object in the first direction based on the second defocus amount, so as to compensate for the second defocus amount to perform the second focusing. The first movement control module can accurately control the movement of the measurement objective and / or the target object by a distance indicated by the second defocus amount through a high-precision position control device (such as a fine adjustment motor), so as to meet the high-precision requirement of the second focusing. The second focusing is performed on the basis of the first focusing, the first movement control module moves the target object and / or the measurement objective to the in-focus position with lower accuracy through the first focusing with higher speed, and then obtains the in-focus position with higher accuracy through the second defocus amount, so as to control the relative movement between the measurement objective and / or the target object in the first direction through the high-precision position adjustment device such as the fine adjustment motor, thereby completing the second focusing with higher accuracy. The fast focusing in the first focusing reduces the overall measurement time, and the second focusing is performed on the basis of the first focusing, so as to improve the focusing accuracy while ensuring the focusing accuracy, thereby improving the working efficiency of the image acquisition system.

[0046] It should be noted that the determination speed of the first defocus amount is greater than the determination speed of the second defocus amount. That is, the first movement control module can control the first relative movement of the measurement objective lens and the target object in the first direction based on the first defocus amount when the first defocus amount is received, and control the second relative movement of the measurement objective lens and the target object in the first direction based on the second defocus amount on the basis of the first relative movement when the second defocus amount is received. It can be understood that the first relative movement can be used for preliminary focusing of the target object. Through the preliminary focusing (i.e., the first focusing), the relative distance between the target object and the measurement objective lens can be adjusted to the vicinity of the relative distance required for accurate focusing (i.e., the second focusing), so that long-distance movement is not required when the target object is accurately focused, and the time for accurate focusing of the target object can be reduced. It should be noted that the first direction can be a vertical direction in space, and alternatively, the first direction can also be a horizontal direction, which should be determined according to the specific product form, and the present application does not make any limitation.

[0047] In some possible embodiments, the image acquisition module can include an image acquisition device such as a camera. The image acquisition module can be used to scan the target object to acquire an image of the target object after the first focusing, to generate a first image. The first image can be used to determine whether the target object is at a preset position. For example, it is determined whether a certain position on the target object is at the center of the field of view of the image acquisition module. The image acquisition module can also be used to acquire an image of the target object after the second focusing when it is determined that the target object is at the preset position, to generate a second image. The second image can serve as a reference image to provide alignment reference for superimposing another target object on the target object. The resolution of the first image is less than the resolution of the second image. It can be understood that the first image is used to quickly identify the current position of the target object, to ensure that the target object is accurately positioned. Since an image recognition algorithm can be used to identify whether the target object is at the preset position, the image recognition algorithm has a lower resolution requirement for the first image and a lower focusing accuracy requirement for the first image, so that the first defocus determination module can quickly determine the first defocus amount with lower accuracy than the second defocus amount, without using a beam interference focusing method with high focusing accuracy but slow focusing speed. Moreover, since the first image generated based on the first defocus amount has a smaller resolution, the first image can be generated at a faster speed, so that whether the target object is at the preset position can be quickly identified, thereby improving the acquisition efficiency of the image acquisition system for the second image. On the basis of ensuring that the target object is at the preset position through the first image, the image acquisition module can acquire the second image with higher resolution than the first image, to meet the image quality requirement of the target object of the product.

[0048] It can be understood that the first defocus determination module obtains the first defocus amount quickly and transmits the first defocus amount to the first movement control module, the first movement control module controls the relative movement between the measuring objective lens and the target object in the first direction according to the first defocus amount to perform the first focusing (preliminary focusing), so that the image acquisition module obtains the first image with low resolution after the first focusing, and then determines whether the target object is in the preset position according to the first image. The second defocus determination module can be used to obtain the second defocus amount on the basis of the first focusing and transmit the second defocus amount to the first movement control module, the first movement control module controls the relative movement between the measuring objective lens and the target object in the first direction again based on the second defocus amount to perform the second focusing (precise focusing) on the target object after the image acquisition module determines that the target object is in the preset position, and then the image acquisition module obtains the second image with high resolution.

[0049] In some possible embodiments, the image acquisition system can comprise a focusing control module. If the image acquisition system comprises the focusing control module, the focusing control module can receive the first reflected light signal transmitted by the first defocus determination module and generate the first defocus amount and return the first defocus amount to the first defocus determination module. The focusing control module can also receive the second reflected light signal and the third reflected light signal transmitted by the second defocus determination module to generate the second defocus amount and return the second defocus amount to the second defocus determination module. The focusing control module can also receive the first image transmitted by the image acquisition module, determine whether the target object is in the preset position based on the first image, and trigger the second movement control module to move the target object in the second direction if it is determined that the target object is not in the preset position. The focusing control module can also trigger the image acquisition module to perform image acquisition and generate the second image after it is determined that the target object is in the preset position.

[0050] By using the image acquisition system provided in the present application, the first defocus determination module can obtain the first defocus amount of the target object at a high speed, so that the image acquisition system can quickly perform the first focusing on the target object. On the basis of the first focusing, the second defocus determination module can obtain the second defocus amount of the target object with higher precision, so that the second image acquired by the image acquisition module after the second focusing is a higher definition image. Therefore, the image acquisition time of the target object can be reduced, and the efficiency of measuring the alignment error of the target object can be improved. In addition, the structures of the modules in the image acquisition system are simple, and the applicability is strong.

[0051] To facilitate the understanding of the internal structures of the first defocus determination module, the second defocus determination module, the first movement control module and the image acquisition module, the following will be combined with Figures 2 to 4 The implementation modes of the modules will be described by way of example.

[0052] Please refer to Figure 2 ,Figure 2 This is another structural schematic diagram of the image acquisition system provided in this application.

[0053] In some feasible implementations, including Figure 1 Based on the implementation of the image acquisition system shown, such as Figure 2 As shown, the aforementioned first defocus determination module includes a first light emitting unit and a first light receiving unit. During the process of determining the first defocus amount of the target object, the first light emitting unit emits a first light beam. After being reflected by the target object, the first light beam generates a first reflected light signal. The first light receiving unit determines the first defocus amount of the target object based on the received first reflected light signal. The first light emitting unit can be a light source capable of emitting a first light beam, such as a laser. The first light beam is used to measure the first defocus amount. The first light beam can be structured light, partially coherent light, laser light, or other high-intensity light beams. The characteristics of the first light beam, such as beam type, wavelength, intensity, and beam emission angle, should be determined according to the high-speed optical focusing technology applicable to the actual product. For example, selecting a suitable wavelength to improve the resolution of the first image, selecting a suitable light intensity to ensure the signal-to-noise ratio and suppress thermal drift, and selecting a suitable emission angle to enhance the measurement sensitivity, etc. The first light emitting unit can emit a first light beam during the process of determining the first defocus amount of the target object, so that the first light beam is reflected by the target object after illuminating it, generating a first reflected light signal. The aforementioned first light receiving unit may include a photoelectric acquisition board, a photodiode, or other devices that can convert optical signals into electrical signals or other types of optical path data; this application does not impose any limitations. Optionally, the first light beam emitted by the first light emitting unit may be irradiated onto the target object through a beam splitter or other device in the second defocusing module, and then reflected by the target object to generate a first reflected light signal. The reflected light signal may be transmitted to the first light receiving unit through a beam splitter or other device in the second defocusing module. Optionally, the first light emitting unit may also directly emit the first light beam onto the target object without passing through a beam splitter or other device in the second defocusing module, and the first light receiving unit may also directly receive the first reflected light signal without passing through a beam splitter or other device in the second defocusing module; this application does not impose any limitations. The aforementioned first light receiving unit can determine the first defocus amount of the target object based on the received first reflected light signal.

[0054] In some feasible implementations, the first optical receiving unit may further include a processor ( Figure 2The first light receiving unit can be connected to a processor, and the processor can be configured to process the received first reflected light signal to determine the first defocus amount of the target object. For example, if the first light emitting unit emits structured light, the first reflected light signal generated after the structured light is irradiated on the target object includes information such as the light intensity and the light angle of the structured light. The first light receiving unit can determine the deformation or the light intensity change of the structured light on the target object according to the information such as the light intensity and the light angle indicated in the first reflected light signal (for example, by receiving the first reflected light signal through an optical sensor), and thus can determine the first defocus amount based on the degree of deformation and the degree of light intensity change. According to the present application, since the time for the first light emitting unit to emit the light beam and the first light receiving unit to receive the first reflected light signal generated after the light beam is reflected is extremely short, and the propagation speed of light is extremely fast, the first defocus amount of the target object can be quickly measured through the first light emitting unit and the first light receiving unit. The first light receiving unit can quickly obtain the first reflected light signal of the target object, and based on the first reflected light signal, the first light receiving unit can quickly and accurately calculate the first defocus amount of the target object. This direct optical measurement method can significantly improve the determination speed of the first defocus amount, so that the image acquisition system can respond more quickly and perform subsequent focusing and image acquisition operations.

[0055] Optionally, in some possible embodiments, the first light beam can be structured light, the first defocus determining module can emit the structured light, irradiate the structured light on the target object, and obtain the first reflected light signal based on the reflection of the structured light by the target object. The first defocus determining module can calculate the first defocus amount based on the received first reflected light signal by the coaxial laser triangulation method. When the first defocus determining module calculates the first defocus amount based on the coaxial laser triangulation method, the first defocus determining module can calculate the three-dimensional topographic information of the target object surface based on the position, shape, light intensity, and other optical path data of the light spot indicated by the first reflected light signal by the triangulation principle, so as to determine the first defocus amount of the target object based on the three-dimensional topographic information of the target object surface. Optionally, the first defocus determining module can emit the structured light by the first light emitting unit, irradiate the structured light on the target object, and obtain the first reflected light signal based on the reflection of the structured light by the target object. The first light receiving unit in the first defocus determining module can calculate the first defocus amount based on the received first reflected light signal by the coaxial laser triangulation method. When the first light receiving unit calculates the first defocus amount based on the coaxial laser triangulation method, the first light receiving unit can calculate the three-dimensional topographic information of the target object surface based on the position, shape, light intensity, and other optical path data of the light spot indicated by the first reflected light signal by the triangulation principle, so as to determine the first defocus amount of the target object based on the three-dimensional topographic information of the target object surface. The structured light can be a point structured light, a line structured light, a surface structured light, and the like, which is used to illuminate the target object and generate the first reflected light signal by the reflection of the target object to indicate the optical path data; the optical path data includes at least one of the spot size, shape, or light intensity signal of the light spot.

[0056] Optionally, in some possible implementations, the first light beam can also be partially coherent light, and the image acquisition system can further include a mask plate aligned with the target object. The first defocus determination module can obtain the first defocus amount by the eccentric mask method, and can calculate the defocus amount according to the change in the light intensity signal generated by the imaging misalignment of the mask plate. For example, after the mask plate is aligned with the target object, the first defocus determination module can irradiate partially coherent light onto the mask plate to generate beam diffraction through the mask plate, the partially coherent light is projected onto the target object through the mask plate, the first defocus determination module receives the first reflected light signal generated after the target object and the mask plate are reflected, and determines the first defocus amount by analyzing the change in the light intensity signal in the light path data indicated by the first reflected light signal. Optionally, the first light receiving unit in the first defocus determination module can obtain the first defocus amount by the eccentric mask method, and can calculate the defocus amount according to the change in the light intensity signal generated by the imaging misalignment of the mask plate when the first light receiving unit obtains the first defocus amount by the eccentric mask method. For example, after the mask plate is aligned with the target object, the first light emitting unit in the first defocus determination module can irradiate partially coherent light onto the mask plate to generate beam diffraction through the mask plate, the partially coherent light is projected onto the target object through the mask plate, the first light receiving unit in the first defocus determination module receives the first reflected light signal generated after the target object and the mask plate are reflected, and determines the first defocus amount by analyzing the change in the light intensity signal in the light path data indicated by the first reflected light signal.

[0057] Optionally, in some possible implementations, the first light beam can also be laser light, and the image acquisition system can further include at least two photodiodes. The first defocus determination module can obtain the first defocus amount by the differential confocal method, and can calculate the defocus amount according to the difference between the light intensity signals detected by the two photodiodes when the first light receiving unit obtains the first defocus amount by the differential confocal method. For example, the first light emitting unit in the first defocus determination module emits laser light and converges the laser light on the target object, the laser light reflected by the target object is received by the two photodiodes respectively to generate two light intensity signals as two first reflected light signals, and then the in-focus position of the target object can be determined by the difference between the two light intensity signals to generate the first defocus amount of the target object. Optionally, the first light receiving unit in the first defocus determination module can obtain the first defocus amount by the differential confocal method, and can calculate the defocus amount according to the difference between the light intensity signals detected by the two photodiodes when the first light receiving unit obtains the first defocus amount by the differential confocal method. For example, the first light emitting unit in the first defocus determination module emits laser light and converges the laser light on the target object, the laser light reflected by the target object is received by the two photodiodes respectively to generate two light intensity signals as two first reflected light signals, and then the in-focus position of the target object can be determined by the difference between the two light intensity signals to generate the first defocus amount of the target object.

[0058] Optionally, in some possible embodiments, the first light beam can also be other high-intensity light beams, and the image acquisition system can further include a chopper (e.g., a knife edge). The first defocus determination module can obtain the first defocus amount by the chopping method. In the process of obtaining the first defocus amount by the chopping method, the phase change of the light intensity signal of the light beam passing through the knife edge of the chopper can be measured by the movement of the chopper in the laser light beam or other high-intensity light beam, so as to calculate the defocus amount based on the phase change. For example, the first defocus determination module can output the laser light beam or other high-intensity light beam to converge on the target object. The light intensity signal can be generated after the light beam passes through the knife edge of the chopper. The first defocus determination module calculates the defocus amount by analyzing the phase change of the light intensity signal. Optionally, the first light receiving unit in the first defocus determination module can obtain the first defocus amount by the chopping method. In the process of obtaining the first defocus amount by the chopping method, the phase change of the light intensity signal of the light beam passing through the knife edge of the chopper can be measured by the movement of the chopper in the laser light beam or other high-intensity light beam, so as to calculate the defocus amount based on the phase change. For example, the first light emitting unit in the first defocus determination module can output the laser light beam or other high-intensity light beam to converge on the target object. The light intensity signal can be generated after the light beam passes through the knife edge of the chopper. The first light receiving unit in the first defocus determination module calculates the defocus amount by analyzing the phase change of the light intensity signal.

[0059] In the present application, the first defocus determination module can use eccentric mask, differential confocal, chopping method, coaxial laser triangulation, etc. as precise optical measurement methods to measure the first defocus amount of the target object. Because these optical measurement methods have high measurement accuracy and stability, they can effectively reduce the measurement deviation caused by external interference or system error, thereby improving the determination accuracy of the first defocus amount. It should be noted that the present application does not limit the type of light beam used by the first light beam and the defocus amount generation method. For example, the first defocus determination module can determine the first defocus amount by using at least one of the eccentric mask, differential confocal, chopping method, and coaxial laser triangulation, and the first light beam can be a laser, structured light, partially coherent light, etc. For ease of description, the process of determining the defocus amount by the first defocus determination module is described below by taking structured light as the first light beam as an example, and will not be described again.

[0060] Optionally, in some possible embodiments, as described above, the first defocus determination module can output the first light beam to converge on the target object, and the first light receiving unit in the first defocus determination module can receive the light beam reflected by the target object. The first light receiving unit can generate a first light intensity signal based on the received light beam. The first defocus determination module can analyze the first light intensity signal to determine the first defocus amount of the target object. Figure 2As shown, the second defocus determination module includes a second light emitting unit, an interference unit, and a second light receiving unit. The interference unit and the measuring objective are fixedly connected. The interference unit includes a first beam splitter and a reference mirror. The second light emitting unit emits a second light beam. After passing through the first beam splitter, the second light beam generates a third light beam and a fourth light beam. The third light beam is reflected by the reference mirror to generate a second reflected light signal, and the fourth light beam is reflected by the target object to generate a third reflected light signal. The first movement control module is also used to control the interference unit and the measuring objective to move a preset distance during the process of determining the second defocus amount of the target object. During the process of controlling the interference unit and the measuring objective to move from the first position to the second position, the second light receiving unit receives the second reflected light signal and the third reflected light signal when the interference unit and the measuring objective are at different positions, and determines the second defocus amount based on the second reflected light signal and the third reflected light signal. The aforementioned second light emitting unit may include a light source such as a laser, and is used to emit a second light beam, which may be a laser beam. Please refer to [link / reference needed]. Figure 3 , Figure 3 This is another structural schematic diagram of the image acquisition system provided in this application. Figure 3 Only some components of the image acquisition system are shown; not all components are depicted. For example... Figure 3 As shown, the interference unit and the measuring objective lens are fixedly connected. The interference unit may include a first beam splitter and a reference mirror, and the second light receiving unit may include a photodiode and a processor. The first beam splitter splits the passing light beam into two beams of equal intensity but different angles. The reference mirror reflects the light beam and provides the reference phase required by the second light receiving unit to determine the second defocus amount. The first beam splitter and the reference mirror are located on the same optical axis. For example, if the second light emitting unit emits a second light beam from left to right, the second light beam converges onto the reference mirror after passing through the first beam splitter. That is, the first beam splitter is located between the second light emitting unit and the reference mirror. If the second light emitting unit is located to the left of the reference mirror, then the first beam splitter is located to the left of the reference mirror. Optionally, if the second light emitting unit is located to the right of the reference mirror, then the first beam splitter is also located to the right of the reference mirror and to the left of the second light emitting unit. The second beam generates a third beam and a fourth beam after passing through the first beam splitter. The third beam generates a second reflected light signal after being reflected by the reference mirror, and the fourth beam generates a third reflected light signal after being reflected by the target object.

[0061] In such Figure 3 Based on the implementation method of the second defocus determination module shown, as Figure 2The first movement control module can control the interference unit to move a preset distance with the measurement objective lens during the process in which the interference unit determines the second defocus amount of the target object. The first movement control module obtains the defocus amount corresponding to different distances between the measurement objective lens and the target object by moving the measurement objective lens, so that the second light receiving unit can determine the second defocus amount based on the second reflected light signal and the third reflected light signal received when the measurement objective lens is located at different positions. For example, the second light receiving unit can determine a reference phase based on the second reflected light signal and a measurement phase based on the third reflected light signal, and then generate a phase difference based on the reference phase and the measurement phase, so as to determine the second defocus amount of the current position of the target object or the measurement objective lens based on the phase difference. It can be understood that when the positions of the target object and / or the measurement objective lens change, the measurement phase indicated by the third reflected light signal will also change, so that the in-focus position (the position at which the phase difference is 0) can be determined based on the phase difference between the reference phase and the measurement phase, and the second defocus amount can be generated based on the in-focus position and the initial position of the target object or the measurement objective lens. The preset distance is the predicted distance between the in-focus position of the measurement objective lens and the initial position of the measurement objective lens, which should be determined according to the actual product form to avoid the situation that the measurement objective lens cannot find the in-focus position due to the too small movement distance of the measurement objective lens, so that the second defocus amount cannot be determined, or the situation that the determination speed of the second defocus amount is affected due to the too large movement distance of the measurement objective lens. The preset distance can be a pre-set value or a value identified by artificial intelligence, which is not limited in the present application. Since the interference phenomenon is extremely sensitive to the phase difference of light waves, the present application adopts the principle of optical interference to accurately calculate the second defocus amount by measuring the change of interference fringes, so that high-precision measurement of the second defocus amount of the target object can be realized, and the precision of the second focusing can be further improved.

[0062] In some feasible implementations, the second optical signal receiving unit is used to determine the second position of the interferometer or the measuring objective when the image acquisition module is in a focusing state, based on the second reflected light signal and the third reflected light signal received when the interferometer and the measuring objective are at different positions. The second defocus amount is then determined based on the second position and the initial position of the interferometer or the measuring objective. For example, by moving the measuring objective a preset distance, the measuring objective can be moved from its initial position to a first position. Since the measuring objective is fixedly connected to the interferometer, the interferometer can also be moved from its initial position to the first position. During the process of controlling the interferometer and the measuring objective to move from their initial positions to the first position, the second optical signal receiving unit is used to receive the second reflected light signal and the third reflected light signal when the interferometer and the measuring objective are at different positions, to determine the position of the interferometer or the measuring objective when the image acquisition module is in a focusing state based on the second reflected light signal and the third reflected light signal, and to define this position as the second position. The second optical signal receiving unit can determine the second defocus amount based on the aforementioned second position and the initial position of the interferometer or measuring objective lens. This second defocus amount indicates the difference between the focusing position (i.e., the second position) of the measuring objective lens and its initial position. By employing this application, the second defocus amount of the target object can be accurately determined by precisely measuring the positional changes of the interferometer or measuring objective lens using the principles of interference and optical signal analysis, thus further improving the accuracy of the second focusing.

[0063] Optionally, in some feasible implementations, such as Figure 3 The interference unit shown may further include a collimating lens and a reference objective. The collimating lens generates an illumination collimated optical path when the light beam passes through, and the reference objective focuses the light beam onto a reference mirror. At this time, the light source in the second light emitting unit emits a monochromatic light beam as a second beam. This second beam, after passing through the collimating lens, generates an illumination collimated optical path. This illumination collimated optical path, after passing through the first beam splitter, splits into a third beam and a fourth beam. The fourth beam, after passing through the measurement objective, converges onto the target object (such as a target wafer), and the third beam, after passing through the reference objective, converges onto the reference mirror. The third beam, after being reflected by the reference mirror, generates a second reflected light signal, and the fourth beam, after being reflected by the target object, generates a third reflected light signal.

[0064] Optionally, in some feasible embodiments, the image acquisition system described above may further include a second beam splitter. Optionally, the second beam splitter may also be integrated into the second receiving unit or the interferometer unit; this application does not impose any limitations. Figure 3The target object, the measurement objective lens, the first beam splitter, the second beam splitter and the image acquisition module are located on the first optical axis. If the first optical axis is perpendicular to the horizontal direction in space, and the target object is located at the lowermost part of the first optical axis, then the target object, the measurement objective lens, the first beam splitter, the second beam splitter and the image acquisition module are sequentially arranged from bottom to top in the first optical axis. It should be noted that the relative positions of the target object, the measurement objective lens, the first beam splitter, the second beam splitter and the image acquisition module in the first optical axis remain unchanged when the angle of the first optical axis changes. The second light emitting unit, the first beam splitter and the reference mirror are located on the second optical axis, and the first optical axis is perpendicular to the second optical axis. If the second optical axis is the horizontal direction in space, and the second light emitting unit is located at the leftmost part of the second optical axis, then the second light emitting unit, the first beam splitter and the reference mirror are sequentially arranged from left to right in the second optical axis. It should be noted that the relative positions of the second light emitting unit, the first beam splitter and the reference mirror in the second optical axis remain unchanged when the angle of the second optical axis changes. Therefore, the image acquisition module can acquire images of the target object based on the first beam splitter, the second beam splitter and the measurement objective lens. By using the second beam splitter and reasonably arranging the related components on the first optical axis and the second optical axis, the image acquisition system can accurately separate and combine the optical paths, thereby improving the accuracy and efficiency of image acquisition.

[0065] Optionally, in some possible embodiments, the image acquisition system can further include a third beam splitter. Optionally, the third beam splitter can be integrated in the second receiving unit or the interference unit, which is not limited in the present application. The second beam splitter, the third beam splitter and the second light receiving unit are located on the third optical axis. If the third optical axis is the horizontal direction in space, and the second beam splitter is located at the leftmost part of the third optical axis, then the second beam splitter, the third beam splitter and the second light receiving unit are sequentially arranged from left to right in the third optical axis. It should be noted that the relative positions of the second beam splitter, the third beam splitter and the second light receiving unit in the third optical axis remain unchanged when the angle of the third optical axis changes. The third beam splitter and the first defocus determination module are located on the fourth optical axis, the third optical axis is parallel to the second optical axis, and the fourth optical axis is parallel to the first optical axis. If the fourth optical axis is perpendicular to the horizontal plane in space, and the third beam splitter is located at the lowermost part of the fourth optical axis, then the third beam splitter and the first defocus determination module are sequentially arranged from bottom to top in the fourth optical axis. It should be noted that the relative positions of the third beam splitter and the first defocus determination module in the fourth optical axis remain unchanged when the angle of the fourth optical axis changes. Therefore, the first defocus determination module can obtain the first defocus amount of the target object based on the third beam splitter, the second beam splitter, the first beam splitter and the measurement objective lens.

[0066] Optionally, the image acquisition system can further comprise an imaging lens group, which can be used to converge the light beams to the photodiode in the second light signal receiving unit to generate the light beam interference. For example, if the image acquisition system comprises the imaging lens group, the third light beam converges on the reference mirror and is reflected by the reference mirror to generate a second reflected light signal, which converges on the photodiode in the second light signal receiving unit by sequentially passing through the reference objective lens, the first beam splitter, the second beam splitter, the third beam splitter, and the imaging lens group. The fourth light beam converges on the target object and is reflected by the target object to generate a third reflected light signal, which converges on the photodiode by sequentially passing through the measurement objective lens, the first beam splitter, the second beam splitter, the third beam splitter, and the imaging lens group.

[0067] For example, the second reflected light signal and the third reflected light signal can interfere on the photodiode to generate an interference signal, and the intensity of the interference signal reflects the optical path difference between the reference arm and the measurement arm when the monochromatic light beam irradiates the target object. The photodiode can transmit the interference signals generated when the measurement objective lens is at different positions to the processor, and the processor can determine the optical path difference between the reference arm and the measurement arm based on the intensity of the interference signal and generate an interference signal curve. The processor can obtain the position of the measurement objective lens corresponding to the peak value of the interference signal intensity by algorithmically processing the light beam interference signal curve, at which time the optical path difference between the reference arm and the measurement arm is zero, and this position can also be used to indicate the focusing position of the measurement objective lens. Therefore, the processor can determine the second defocus amount by obtaining the difference between the focusing position and the initial position of the measurement objective lens. By using the interference principle and optical signal analysis, the position change of the interference unit or the measurement objective lens can be accurately measured to determine the defocus amount of the target object with high precision.

[0068] To facilitate understanding of the process of the first defocus determination module for obtaining the first defocus amount of the target object based on the third beam splitter, the second beam splitter, the first beam splitter, and the measurement objective lens, please refer to Figure 4 , Figure 4 is a schematic diagram of the optical path of the first light beam provided by the present application. As shown in Figure 4 , the optical path of the first light beam comprises a first beam splitter, a second beam splitter, a third beam splitter, and a measurement objective lens. The first light beam emitted by the first defocus determination module converges on the target object by sequentially passing through the third beam splitter, the second beam splitter, the third beam splitter, and the measurement objective lens, and generates a first reflected light signal after being reflected by the target object, which returns to the first defocus determination module by sequentially passing through the measurement objective lens, the first beam splitter, the second beam splitter, and the third beam splitter. Among them, the first beam splitter belongs to the second defocus determination module, Figure 4Only the first beam splitter in the second defocus determination module is shown, and other devices in the second defocus determination module are not shown. By introducing the third beam splitter and arranging the fourth optical axis parallel to the first optical axis, the image acquisition system can more effectively separate and combine light beams in different directions according to the application, avoiding mutual interference of light beams in different directions, not only improving the clarity of image acquisition, but also enhancing the stability and reliability of the image acquisition system.

[0069] In some possible embodiments, as shown in Figure 2 The first movement control module includes a first control unit and a first driving unit. It can be understood that, in the case of Figures 3 to 4The implementation manners of the first defocus determination module, the second defocus determination module, and the image acquisition module are shown. The implementation manners of the first movement control module including the first control unit and the first driving unit are also applicable. Here, the first driving unit can be a fine adjustment motor, a motion table, or the like, and the first control unit can be a motor controller, a motion table controller, or the like. It can be understood that the first control unit can include multiple independent controllers or a controller integrated with multiple controller functions, which are not limited in the present application. The controller can be a central processing unit (CPU), a microcontroller unit (MCU), or the like. The first control unit can be used to generate a motion control instruction (or other types of control instructions) to trigger the first driving unit to control the second light emitting unit and the interference unit to move in the first direction based on the motion control instruction. The first driving unit controls the second light emitting unit and the interference unit to move in the first direction by a distance indicated by the motion control instruction (or other types of control instructions). The first driving unit is connected to the second light emitting unit and the interference unit, so the first driving unit can drive the second light emitting unit and the interference unit to move in the first direction at the same time, thereby ensuring that the second light emitting unit and the interference unit remain synchronized when moving in the first direction to avoid motion errors, thereby ensuring the accuracy of the target focus. The first control unit can receive the first defocus amount and the second defocus amount, thereby controlling the first driving unit to move the second light emitting unit in the first direction based on the first defocus amount when the first defocus amount is received, and controlling the first driving unit to move the second light emitting unit in the first direction based on the second defocus amount when the second defocus amount is received. For example, the first control unit can generate a motion control instruction and send the motion control instruction to the first driving unit to trigger the first driving unit to move in the first direction by a distance corresponding to the first defocus amount. If the measuring objective lens and the target object are placed vertically in space (for example, the measuring objective lens is above the target object), the first direction can be the vertical direction in space; if the measuring objective lens and the target object are placed horizontally in space (for example, the measuring objective lens is to the right of the target object), the first direction can be the horizontal direction in space, or the first direction can be a direction at a specific angle, which should be determined according to the actual product form, and the present application is not limited. Optionally, when the first driving unit moves, a first arrival signal can be sent to the image acquisition module, and the first arrival signal is used to indicate that the relative movement of the measuring objective lens and the target object in the first direction has been completed. By introducing the first control unit and the first driving unit, the image acquisition system can accurately control the movement of the interference unit in the first direction.This precise control ensures that the interference unit can move according to the pre-set target trajectory and speed, thereby improving the accuracy and stability of the second defocus amount determination.

[0070] In some feasible implementations, the first motion control module can be connected to the target object. When the target object is not in the preset position, the first motion control module can control the target object to move in a second direction, so that the target object moves to the preset position. The second direction is a plane perpendicular to the first direction. The preset position can be determined based on the target object's trajectory, and the second direction is a plane perpendicular to the first direction. It should be noted that if the first direction is a vertical direction in space, the second direction can be a horizontal direction in space; conversely, if the first direction is a horizontal direction in space, the second direction can be a vertical direction in space. Alternatively, the first and second directions can be directions at other angles; this application does not impose any limitations. For example, the first motion control module can transmit motion control commands to the first drive unit based on the preset position, through the first control unit, to trigger the first drive unit to control the target object to move in the second direction to the preset position. Using this application, through the connection between the first motion control module and the target object, the image acquisition system can detect the current position of the target object and determine whether the target object is in the preset position. If the target object is not in the preset position, the first motion control module can control the target object to move in the second direction until the target object reaches the preset position, which improves the automation level of image acquisition and reduces manual intervention.

[0071] In some feasible implementations, such as Figure 2 As shown, the image acquisition system described above may also include a second motion control module. Similarly, it can be understood that, in situations such as... Figures 3 to 4 Based on the implementation of the first defocus determination module, the second defocus determination module, and the image acquisition module shown, the image acquisition system also includes a second motion control module, which remains applicable. The second motion control module can also be connected to the target object. When the target object is not in the preset position, the second motion control module can be used to control the target object to move in a second direction to bring it to the preset position. By introducing the second motion control module, the image acquisition system has two independent control mechanisms to ensure that the target object can be accurately moved to the preset position. This dual-protection mechanism improves the accuracy and reliability of positioning; if either the first or second motion control module malfunctions or errs, the other module can ensure the correct positioning of the target object.

[0072] In some possible embodiments, the second movement control module can include a second control unit and a second driving unit. The second control unit is connected to the second driving unit. The second driving unit is connected to the target object. The second control unit is configured to control the second driving unit to move the target object in the second direction. The second control unit can be a motion controller or the like. The second driving unit can be a motion stage or the like. For example, the second control unit can be a motion controller, and the second driving unit can be a motion stage. The motion stage is connected to the target object and is configured to carry the target object. The motion stage can be an X / Z / Theta motion stage or another motion stage that can carry the target object. For example, the motion stage can be an X / Z / Theta motion stage, which has an X-axis (horizontal translation), a Z-axis (vertical lifting), and a Theta-axis (rotation around the central axis). The motion stage is configured to carry the target object and adjust the position of the target object. Optionally, the motion stage can further include a Y-axis motion stage, which is configured to carry the target object and move the target object in the Y-axis direction.

[0073] In some possible embodiments, the motion controller can send a motion control instruction of the motion stage to the motion stage to drive the motion stage to move in the second direction, which is perpendicular to the first direction. The motion control instruction can be used to indicate a preset target motion track, which includes at least one preset position. The motion stage can carry the target object to sequentially pass through the at least one preset position in the target motion track. The second movement control module includes the second control unit and the second driving unit. The second control unit can send accurate instructions, and the second driving unit can accurately convert the instructions into actual movement of the target object, so that the target object can be accurately positioned at the preset position, and accurate control of the movement of the target object in the second direction is achieved.

[0074] In some possible embodiments, the image acquisition module can include an image acquisition device and a position determining module, and the position determining module is configured to determine whether the target object is at the preset position according to the first image. For example, the position determining module can be configured to receive the first image transmitted by the image acquisition device such as a camera, and determine whether the target object is at the preset position according to the first image. Optionally, when the position determining module detects that the second driving unit moves to the preset position, the position determining module can generate a control signal (e.g., a second arrival signal) indicating that the focusing is completed, and the second arrival signal is configured to indicate that the movement of the target object in the second direction is completed. When the position determining module obtains the first arrival signal and the second arrival signal, the position determining module can trigger the image acquisition device such as the camera to collect the image of the target object to generate a second image. The position determining module can accurately analyze the first image to identify the current position of the target object, and compare the current position with the preset position, so as to accurately determine whether the target object is at the preset position. According to the present application, the position determining module can identify the current position of the target object and compare the current position with the preset position by accurately analyzing the first image, so as to accurately position the target object and improve the image collection accuracy of the target object.

[0075] In some possible embodiments, the target object is provided with a graphic mark, and when the graphic mark is at the center of the field of view of the image acquisition module, the position of the target object in the second direction is the preset position, and the second direction is perpendicular to the first direction. For example, the position determining module can obtain the imaging position deviation between the imaging position of the target object and the center of the field of view of the image acquisition module by using an image recognition algorithm, and if the imaging position deviation is 0, it indicates that the second driving unit has moved to the preset position. If the imaging position deviation is not 0, the imaging position deviation can be transmitted to the second control unit, so that the second control unit controls the second driving unit to move in the second direction by a distance corresponding to the imaging position deviation. Since the image recognition algorithm runs at a high speed, the present application can improve the positioning accuracy and recognition efficiency of the target object by setting the graphic mark on the target object and ensuring that the mark is at the center of the field of view of the image acquisition module.

[0076] In some possible embodiments, the processors or controllers (e.g., the first control unit in the first movement control module, the second control unit in the second movement control module, the processor in the interference unit, etc.) in the first defocus determining module, the second defocus determining module, the first movement control module, the second movement control module, and the position determining module in the image acquisition module can be integrated into a focusing control module, and the focusing control module is configured to perform signal processing and control.

[0077] The image acquisition system provided in the application can obtain the first defocus amount of the target object at a very high speed through the first defocus determination module, so that the image acquisition system can quickly focus on the target object for the first time. On the basis of the first focusing, the second defocus determination module obtains the second defocus amount of the target object with higher precision, so that the second image acquired by the image acquisition module after the second focusing is a high-definition image. At the same time, this hierarchical focusing strategy significantly reduces the time required for overall focusing and improves work efficiency.

[0078] Embodiment two

[0079] The application also provides an image acquisition method of a metrology device, wherein the metrology device comprises an image acquisition system as described above. Figures 1 to 4 Any provided image acquisition system, the image acquisition method is suitable for the image acquisition system. In the present application, the image acquisition method can be executed by the focusing control module in the above-mentioned image acquisition system as the execution subject, and the focusing control module can cooperate with other modules in the image acquisition system to realize image acquisition. For the convenience of description, the focusing control module is taken as an example for description. Referring to Figure 5 , Figure 5 is a flowchart of the image acquisition method provided in the application. As shown in Figure 5 , the image acquisition method can include the following steps:

[0080] Step S101, determining the first defocus amount of the target object.

[0081] In some possible embodiments, the target object can be carried by the second movement control module and moved in the second direction based on the target motion trajectory by the second movement control module to pass through a plurality of preset positions in the target motion trajectory in sequence. When the target object reaches a preset position, the focusing control module can trigger focusing on the target object and image acquisition.

[0082] In some possible embodiments, the focus control module can generate a focus pursuit control instruction to trigger the first defocus determination module to emit a first light beam and obtain a first defocus amount of the target object by the first defocus determination module, wherein the first defocus amount of the target object can be obtained by the first defocus determination module analyzing light beam data of the returned first light beam, and the light beam data includes at least one of a spot size, a spot shape, and a light intensity signal. Optionally, the focus control module obtains the first defocus amount by the first defocus determination module through an artificial intelligence algorithm such as image recognition, for example, by recognizing the size of the spot through an image recognition algorithm, and then inferring the first defocus amount of the target object according to the size of the spot. The first defocus amount can be distinguished by direction through "+" and "-" methods, for example, if the relative distance between the target object and the measuring objective lens is 3 mm, and the first defocus amount is +1 mm, then the focusing distance between the target object and the measuring objective lens is 4 mm. The "+" and "-" are only used to distinguish the direction, and do not refer to the specific size of the value, and the same applies hereinafter, which will not be described again.

[0083] Optionally, in some possible embodiments, the focus control module can store the obtained first defocus amount data to obtain at least two first defocus amounts of the target object at at least two preset positions. The focus control module can predict a predicted first defocus amount of the target object at the next preset position based on the obtained historical data of the at least two first defocus amounts, so as to trigger the target object to move in the first direction based on the predicted first defocus amount before the target object reaches the next preset position, so that the target object only needs to move a small distance when performing the first focusing, and therefore, the speed of the first focusing of the target object can be further improved.

[0084] In some feasible implementations, the aforementioned measuring device includes a first defocus determination module, which comprises a first light emitting unit and a first light receiving unit. The method for determining the first defocus amount of a target object includes: controlling the first light emitting unit to emit a first light beam, the first light beam being reflected by the target object to generate a first reflected light signal; and determining the first defocus amount of the target object based on the first reflected light signal received by the first light receiving unit. For example, when the first defocus determination module includes a first light emitting unit and a first light receiving unit, a focus control module can control the first light emitting unit to emit the first light beam, so that the first light beam converges onto the target object and is reflected by the target object to generate a first reflected light signal. The focus control module can also control the first light receiving unit to receive the first reflected light signal and feed the received first reflected light signal back to the focus control module. The focus control module can determine the first defocus amount based on the first reflected light signal. By employing this application, a light beam is emitted by a first light emitting unit, a first light receiving unit receives a first reflected light signal, and a first defocus amount is calculated based on the first reflected light signal. This process can quickly and efficiently determine the first defocus amount without moving the components in the measuring equipment, thus shortening the overall error measurement time.

[0085] For example, if the focus control module includes a focus controller, the focus control module can trigger the first defocus determination module to emit a first light beam through the focus controller. For instance, the focus control module can generate a tracking focus control command through the focus controller in the focus control module and send the tracking focus control command to the first defocus determination module to trigger the first defocus determination module to emit the first light beam. Further, the focus controller can acquire at least two defocus values ​​of the target object generated by the first defocus determination module based on the optical path data (e.g., the size, shape, intensity, etc. of the light spot) indicated by the first reflected light signal returned by the first light beam.

[0086] In some feasible implementations, the method for determining the first defocus amount of the target object based on the first reflected light signal received by the first light receiving unit includes: according to the first reflected light signal, the focus control module can determine the first defocus amount using one of the following methods: eccentric masking, differential confocal focusing, chopper method, and coaxial laser triangulation method; this application does not impose any limitation on this method. Specific implementations of the eccentric masking, differential confocal focusing, chopper method, and coaxial laser triangulation method can be found in the above description. Figures 1 to 4 The descriptions in the corresponding embodiments will not be repeated. By employing optical measurement methods such as eccentric masking, differential confocal, chopper method, and coaxial laser triangulation, the first defocus amount of the target object can be accurately and quickly determined based on the first reflected light signal, reducing measurement errors and improving the accuracy of the first defocus amount.

[0087] In some possible embodiments, before determining the first defocus amount of the target object, the focus control module can calibrate the equipment in the image acquisition system, such as the first defocus determination module and the image acquisition module, to ensure the accuracy of the measurement of the first defocus amount and the like. For example, the focus control module can calibrate the focal length, resolution and the like of the image acquisition equipment in the image acquisition module by using a calibration plate (for example, a standard grid plate for geometric distortion correction and pixel calibration, a star plate for resolution and focal length correction), and can also correct the image by using the calibration plate to eliminate the inherent system error caused by the equipment due to its own characteristics, and further improve the accuracy of the measurement of the alignment error.

[0088] In step S102, based on the first defocus amount, the focus control module controls the relative movement between the measurement objective lens and the target object in the first direction to perform the first focusing on the target object.

[0089] In some possible embodiments, the focus control module can control the movement of the measurement objective lens relative to the target object in the first direction, or / and control the movement of the target object relative to the measurement objective lens in the first direction. For example, the focus control module can control the movement of the target object in the first direction based on the first defocus amount, and control the measurement objective lens to be stationary to adjust the relative distance between the target object and the measurement objective lens; or the focus control module can control the target object to be stationary in the first direction, and control the movement of the measurement objective lens in the first direction to adjust the relative distance between the target object and the measurement objective lens; or the focus control module can control the target object and the measurement objective lens to move in the first direction at the same time to adjust the relative distance between the target object and the measurement objective lens, and then perform the first focusing on the target object. The present application does not make any limitation, and the movement of the measurement objective lens and the stationarity of the target object are taken as an example for description.

[0090] In some possible embodiments, before the relative movement between the metrology objective and the target object in the first direction is controlled, the focus control module can determine a target movement position of the metrology objective or the target object based on the first defocus amount. Specifically, the focus control module can obtain the first defocus amount of the target object from the first defocus determination module, and then determine the target movement position of the metrology objective based on the first defocus amount, and control the relative movement between the metrology objective and the target object in the first direction based on the target movement position to focus the target object for the first time. If the target object remains stationary in the first direction, the focus control module can determine the target movement position of the metrology objective based on the first defocus amount to drive the first movement control module to move in the first direction. It can be understood that when the distance between the target object and the metrology objective is equal to the focal length of the metrology objective, the metrology objective is located at the target movement position. If the metrology objective and the target object are placed in a vertical direction in space (for example, the metrology objective is above the target object), the first direction can be a vertical direction in space; if the metrology objective and the target object are placed in a horizontal direction in space (for example, the metrology objective is to the right of the target object), the first direction can be a horizontal direction in space. By using the present application, the target movement position can be determined to avoid inaccurate second focusing caused by excessive movement or insufficient movement of the metrology objective or the target object without determining the target movement position in advance, and after the target movement position is determined, the image acquisition system can directly move the metrology objective or the target object to the position, without the need for multiple trial movements and adjustments, greatly reducing the number of movements and time, and further improving the error measurement efficiency of the target object.

[0091] For example, if the target object remains stationary in the first direction, the first defocus amount of the target object at the preset position is +1 mm, and the metrology objective is located at +3 mm of the target object, the target movement position of the metrology objective is located at +4 mm of the target object, and the focus control module can control the metrology objective to move +1 mm to focus the target object for the first time. Alternatively, if the metrology objective remains stationary in the first direction, the focus control module can also determine the target movement position of the target object, and control the target object to move in the first direction to the target movement position, so that the relative distance between the target object and the metrology objective is the focal distance. Alternatively, the focus control module can also determine the target movement positions of the target object and the metrology objective respectively, so that the target object and the metrology objective are moved in the first direction to the respective target movement positions, so that the relative distance between the target object and the metrology objective is the focal distance, which will not be described herein. By using the present application, the metrology objective and / or the target object are allowed to move in the first direction, and the most suitable movement mode can be selected according to the specific measurement scene and requirements to achieve focusing, which has strong applicability.

[0092] In some possible embodiments, the focus control module can detect the focus condition of the metrology objective lens and the target object in real time during the relative movement of the metrology objective lens and the target object. The focus condition can include the movement speed of the target object and / or the metrology objective lens, the position of the target object and / or the metrology objective lens, and the like. By detecting the focus condition in real time, the focus control module can adjust the movement speed and the distance to be moved of the target object and / or the metrology objective lens according to the focus condition, so as to ensure the accuracy of the first focus. For example, the focus control module can acquire a real-time image of the target object by using the image acquisition module, and determine whether the target object reaches the target movement position (the first direction) or whether the first focus of the target object is accurate based on the real-time image of the target object. If the focus of the target object is still not accurate when the target object reaches the target movement position (i.e., the focus requirement of the first focus is not met), the focus control module can control the first defocus determination module to determine the defocus amount again, so as to re-focus the target object for the first time. When the target object and / or the metrology objective lens reaches the target movement position, it indicates that the first focus is completed, and the focus control module can send a control signal (e.g., a first arrival signal) to the image acquisition module to trigger the image acquisition module to acquire an image of the target object. Optionally, in some possible embodiments, the focus control module can also save the real-time image and data when the first focus is completed. The saved real-time image and data can be used for product update or other functions.

[0093] According to the present application, the focus control module can control the target object and / or the metrology objective lens to move in the first direction by using the first movement control module, so as to focus the target object for the first time. The first focus for the target object by acquiring the first defocus amount of the target object and performing the first focus can meet the focus accuracy requirement of the image processing of the first image, and there is no need to perform the time-consuming white light interference focus. Therefore, the efficiency of the first focus can be improved, the acquisition time of the wafer metrology image can be reduced, and the alignment error measurement efficiency of the wafer can be improved.

[0094] In step S103, an image of the target object after the first focus is acquired, a first image is generated, and whether the target object is at a preset position is determined by using the first image.

[0095] In some possible embodiments, the above measuring device can comprise an image acquisition module. Before the above image acquisition of the target object after the first focusing, the focusing control module can send a focusing completion control signal to the image acquisition module. The focusing control module can trigger the image acquisition module to acquire the image of the target object after the target object completes the first focusing, to generate a first image. For example, the focusing control module can detect the focusing state of the target object and / or the measuring objective lens. When the motion controller detects that the target object and / or the measuring objective lens has reached the target moving position, a focusing completion control signal (such as a first arrival signal) is generated and transmitted to the image acquisition module, to trigger the image acquisition device to acquire the image of the target object. Further, the focusing control module can also determine whether the target object is at a preset position based on the first image. The target object moves according to a pre-set target motion trajectory, and the target motion trajectory comprises a plurality of preset positions.

[0096] In some possible embodiments, the target object can comprise a graphic mark, and the focusing control module can determine whether the target object is at a preset position by using a position determination module. The focusing control module can determine whether the graphic mark is at the center of the field of view of the image acquisition module; if the graphic mark is at the center of the field of view of the image acquisition module, it is determined that the target object is at the preset position. For example, the focusing control module can obtain the imaging position deviation of the graphic mark of the target object and the center of the field of view of the image acquisition module by using the position determination module.

[0097] In some possible embodiments, the imaging position of the graphical mark of the target object and the center of the field of view of the image acquisition module can be recorded in the form of coordinates. For example, the center of the field of view of the image acquisition module can be recorded as (0, 0), and if the imaging position is identified as (1, -1), the imaging position deviation can be recorded as (+1, -1). The above (+1, -1) is used to indicate that the imaging position is located at a unit length in the positive half-axis direction of the horizontal axis of the center of the field of view of the image acquisition module and at a unit length in the negative half-axis direction of the vertical axis of the center of the field of view of the image acquisition module. The above "+" and "-" are only used to indicate the direction and do not refer to the specific numerical value. The recording manner of the imaging position, the center of the field of view of the image acquisition module and the imaging position deviation is not limited to the recording manner provided in the present application, and the present application is not limited thereto. The imaging position deviation can be used to determine the deviation of the target object in the second direction. If the imaging position deviation is 0, that is, the imaging position of the target object is located at the center of the field of view of the image acquisition module, the focus control module determines that the target object is at the preset position; if the imaging position deviation is not 0, that is, the imaging position of the target object is not located at the center of the field of view of the image acquisition module, the focus control module determines that the target object is not at the preset position. By using the present application, the introduction of the graphical mark provides an intuitive visual basis for the position judgment of the target object, which can more accurately determine the current position of the target object, reduce the positioning error of the target object, and improve the positioning accuracy of the target object.

[0098] In some possible embodiments, if the focus control module determines that the target object is not at the preset position, the first movement control module or the second movement control module can be triggered to control the target object to move relative to the measuring objective lens in the second direction, so that the target object is at the preset position. For example, if the imaging position deviation is identified as (+1, -1), the focus control module can trigger the first movement control module or the second movement control module to control the target object to move to the negative half-axis direction of the horizontal axis of the center of the field of view of the image acquisition module by a unit length and to the positive half-axis direction of the vertical axis of the center of the field of view of the image acquisition module by a unit length. By using the present application, by controlling the target object to move in the second direction, the measurement error caused by directly performing the second focusing and image acquisition when the target object is not at the preset position can be eliminated, so that the accuracy and reliability of the error measurement of the target object can be further improved.

[0099] In some possible implementations, the focus control module can acquire a real-time image of the target object through the image acquisition module. Before the image acquisition module acquires the image of the target object after the first focusing, the focus control module can detect whether the image acquisition device in the image acquisition module is in good condition, for example, whether the lens of the image acquisition device is contaminated (which can be determined by whether there is a foreign object in the real-time image), whether the focal length and other parameters are calibrated (which can be determined by the blurring degree of the real-time image), and the like. The focus control module can also detect whether the light condition of the light source in the first defocus determination module is suitable for image acquisition to avoid overexposure or underexposure. The focus control module can also set the center of the field of view of the image acquisition module, for example, when the image acquisition module acquires the real-time image of the target object, if the target object is located at a specific position (i.e., the center of the field of view) in the real-time image, it indicates that the target object has reached the preset position.

[0100] In some possible implementations, during the process in which the focus control module controls the image acquisition module to acquire the image of the target object after the first focusing, the focus control module can detect the image quality of the acquired real-time image. If the quality of the real-time image does not meet the requirements (such as image blurring, image overexposure, image underexposure, and the like), the focus control module can adjust the relative distance between the target object and the measuring objective lens through the first movement control module to re-focus.

[0101] In some possible implementations, since there can be motion deviation during the movement of the target object and / or the measuring objective lens, the focus control module can detect, after the first image is generated, whether the target object meets the acquisition requirements of the second image after moving to the preset position, and if not, the focus control module can re-determine the preset position of the target object, re-adjust the parameters of the devices in the image acquisition system, or re-focus. For example, after the target object moves to the preset position, if the signal-to-noise ratio of the background and the target object does not meet the requirements (such as image overexposure or underexposure), the focus control module can adjust the illumination parameters of the image acquisition module in the image acquisition system. If the field of view offset and the angle deviation of the target object do not meet the requirements, the focus control module can re-determine the preset position and trigger the first movement control module or the second movement control module to control the target object to move to the re-determined preset position. If the focusing accuracy does not meet the requirements after the target object moves again, the focus control module can re-focus the target object.

[0102] Step S104, after determining that the target object is at the preset position, a second defocus amount of the target object is acquired.

[0103] In some possible embodiments, the focus control module can trigger the second defocus determination module to obtain the second defocus amount of the target object after determining that the target object is in the preset position. The second defocus determination module can emit a second light beam to generate a third light beam and a fourth light beam, wherein the third light beam converges on the reference mirror and is reflected by the reference mirror to generate a second reflected light signal, and the fourth light beam converges on the target object and is reflected by the target object to generate a third reflected light signal. The focus control module can trigger the second defocus determination module to determine the second defocus amount of the target object based on the received second reflected light signal and third reflected light signal.

[0104] In some possible embodiments, the measurement device comprises the first defocus determination module, the second defocus determination module comprises a second light emitting unit, an interference unit and a second light receiving unit, the interference unit comprises a first beam splitter and a reference mirror, and the second defocus amount of the target object is obtained by: controlling the second light emitting unit to emit a second light beam during relative movement of the interference unit and the measurement objective lens in a first direction relative to the target object, the second light beam generating a third light beam and a fourth light beam after passing through the first beam splitter, the third light beam being reflected by the reference mirror to generate a second reflected light signal, and the fourth light beam being reflected by the target object to generate a third reflected light signal; and determining the second defocus amount of the target object based on the second reflected light signal and the third reflected light signal received by the second light receiving unit. For example, based on the second defocus determination module comprising the second light emitting unit, the interference unit and the second light receiving unit, if the interference unit comprises a collimating lens and the light source in the second light emitting unit emits a monochromatic light beam, the monochromatic light beam can generate an illumination collimated light path after passing through the collimating lens, the illumination collimated light path is divided into two light beams after passing through the first beam splitter, one of the light beams (e.g., the fourth light beam) converges on the target object (e.g., a target wafer) after passing through the measurement objective lens, and the other light beam (e.g., the third light beam) converges on the reference mirror after passing through the reference objective lens. The third light beam is reflected by the reference mirror to generate the second reflected light signal, and the fourth light beam is reflected by the target object to generate the third reflected light signal. The focus control module can receive the second reflected light signal and the third reflected light signal through the second light receiving unit, thereby determining the second defocus amount of the target object. According to the present application, high-precision measurement of the second defocus amount of the target object is achieved by the principle of optical interference, and the focus accuracy of the second focusing can be further improved.

[0105] In some possible embodiments, the method for determining the second defocus amount of the target object based on the second reflected light signal and the third reflected light signal received by the second light receiving unit, comprises: determining a first in-focus position of the interference unit or the measurement objective lens when the image acquisition module is in a focus state based on the second reflected light signal and the third reflected light signal received by the second light receiving unit; and determining the second defocus amount according to the first in-focus position and an initial position of the interference unit or the measurement objective lens. For example, in the image acquisition system, a second beam splitter and a third beam splitter are further included, and if the image acquisition system includes an imaging lens group, a monochromatic light beam converges on the target object and is reflected by the target object, passes through the measurement objective lens, the first beam splitter, the second beam splitter, the third beam splitter and the imaging lens group in sequence, and converges on a photodiode to generate a second reflected light signal; the monochromatic light beam converges on a reference mirror and is reflected by the reference mirror, passes through the reference objective lens, the first beam splitter, the second beam splitter, the third beam splitter and the imaging lens group in sequence, and converges on a photodiode in the second light signal receiving unit to generate a third reflected light signal. The second reflected light signal and the third reflected light signal can interfere with each other on the photodiode to generate an interference signal, and the intensity of the interference signal reflects the optical path difference between the reference arm and the measurement arm when the monochromatic light beam irradiates the target object. During the determination of the second defocus amount of the target object by the interference unit, the focus control module can further trigger the first movement control module to control the interference unit and the measurement objective lens to move a preset distance. The preset distance is a predicted distance between the in-focus position of the measurement objective lens and the initial position of the measurement objective lens, and should be determined according to the actual product form. During the control of the interference unit and the measurement objective lens to move the preset distance, the focus control module can receive the interference signal generated by the second reflected light signal and the third reflected light signal when the measurement objective lens is located at different positions, determine the optical path difference between the reference arm and the measurement arm according to the intensity of the interference signal, and generate an interference signal curve. The focus control module can obtain the position of the measurement objective lens corresponding to the peak value of the intensity of the interference signal by performing algorithm processing on the light beam interference signal curve, and at this time, the optical path difference between the reference arm and the measurement arm is zero, and the position can also be used to indicate the in-focus position of the measurement objective lens. Therefore, the focus control module can determine the second defocus amount by obtaining the difference between the in-focus position and the initial position of the measurement objective lens. The determination speed of the first defocus amount is greater than that of the second defocus amount. By using the interference principle and optical signal analysis, the position change of the interference unit or the measurement objective lens is accurately measured, and the high-precision determination of the defocus amount of the target object is realized.

[0106] In step S105, the measurement objective lens and the target object are controlled to move relative to each other in the first direction based on the second defocus amount, so as to focus the target object for the second time.

[0107] In some possible embodiments, the focus control module can transmit the second defocus amount to the first movement control module to trigger the first movement control module to control the relative movement between the measurement objective lens and the target object in the first direction. For example, the focus control module triggers the first movement control module to determine the movement speed, movement distance, focus accuracy, etc. of the measurement objective lens and / or the target object based on the second defocus amount. For example, if the second defocus amount is +1 mm, it indicates that the relative distance between the measurement objective lens and the target object is 1 mm greater than the focal distance of the measurement objective lens, and thus the measurement objective lens and the target object need to move relative to each other by 1 mm in the first direction. Optionally, the focus control module can trigger the first movement control module to control the measurement objective lens to move relative to the target object by 1 mm, and the target object remains stationary in the first direction; or control the target object to move relative to the measurement objective lens by 1 mm, and the measurement objective lens remains stationary; or control the target object and the measurement objective lens to move relative to each other respectively, and the sum of the movement distances of the target object and the measurement objective lens is 1 mm. The actual product form should be determined, and the present application does not make any limitation.

[0108] In some possible embodiments, before the image acquisition module acquires the image of the target object after the second focusing, the focus control module can send a control signal indicating that the focusing is completed to the image acquisition module. For example, when the relative distance between the target object and the measurement objective lens is equal to the focal distance, it indicates that the second focusing of the target object is completed. The focus control module can send a control signal indicating that the focusing is completed to the image acquisition module to trigger the image acquisition module to acquire the image of the target object.

[0109] In some possible embodiments, during the relative movement between the measurement objective lens and the target object in the first direction controlled by the first movement control module, the focus control module can detect the focus state of the target object and the measurement objective lens in real time (for example, by acquiring the real-time image of the target object) to ensure the accuracy and stability of the movement. The focus control module can also adjust the movement speed and / or movement distance of the target object and / or the measurement objective lens in a timely manner according to the focus state to ensure that the image acquisition system can capture the best focus position of the target object and / or the measurement objective lens. If the focus control system detects that the focus is inaccurate (for example, as the target object and the measurement objective lens move relative to each other, the real-time image becomes more blurred) or the imaging quality of the real-time image is poor (for example, the image is overexposed or underexposed), the focus control system can adjust the parameters of the devices in the image acquisition system or re-focus in a timely manner.

[0110] In some possible implementation manners, the focus control module can further perform imaging quality assessment on the obtained second image after the second focusing is completed. If the imaging quality assessment on the second image does not meet the requirement, the parameters of the devices in the image acquisition system can be adjusted again or the focusing can be performed again to reacquire the second image.

[0111] In summary, before the image acquisition on the target object after the first focusing or before the image acquisition on the target object after the second focusing, the focus control module can send the focus completion control signal to the image acquisition module. By sending the focus completion control signal, the image acquisition module can perform the image acquisition only after the first focusing or the second focusing is completed, so that the image blur or distortion problem caused by incomplete focusing is avoided, and the accuracy and quality of the image acquisition are improved.

[0112] In step S106, the image acquisition on the target object after the second focusing is performed to generate a second image.

[0113] In some possible implementation manners, the focus control module can trigger the image acquisition module to perform the image acquisition on the target object to generate a second image with a higher resolution than the first image through the focus completion control signal.

[0114] By using the present application, the first defocus amount of the target object can be acquired at a very high speed by the first defocus determination module, so that the image acquisition system can quickly perform the first focusing on the target object. On the basis of the first focusing, the second defocus amount of the target object can be acquired at a higher precision by the second defocus determination module, so that the second image acquired by the image acquisition module after the second focusing is a high-definition image. Meanwhile, the hierarchical focusing strategy significantly reduces the time required for the overall focusing and improves the work efficiency.

[0115] Those skilled in the art can realize that the system and algorithm steps of each example described in combination with the embodiments disclosed herein can be realized by electronic hardware, computer software or a combination of both. In order to clearly illustrate the interchangeability of hardware and software, the components and steps of each example have been described in the above description in general terms. The skilled person can use different methods to realize the described functions for each specific application, but such implementation should not be considered beyond the scope of the present application.

Claims

1. An image acquisition system of a metrology apparatus, characterized in that, The application relates to a method for determining the defocus amount of a target object, comprising the following steps: a first defocus determining module is used for determining the first defocus amount of the target object; a second defocus determining module is used for determining the second defocus amount of the target object; a first movement control module is used for controlling the relative movement between the measuring objective lens and the target object in a first direction according to the first defocus amount, so as to focus the target object for the first time, and controlling the relative movement between the measuring objective lens and the target object in the first direction according to the second defocus amount, so as to focus the target object for the second time; an image acquisition module is used for collecting the image of the target object after the first time of focusing, and generating a first image, wherein the first image is used for determining whether the target object is in a preset position in a second direction, and the second direction is a plane perpendicular to the first direction; and the image of the target object after the second time of focusing is collected to generate a second image after it is determined that the target object is in the preset position in the second direction; wherein the determination speed of the first defocus amount is greater than the determination speed of the second defocus amount, and the resolution of the first image is less than the resolution of the second image.

2. The image acquisition system of claim 1, wherein, The first defocus determining module comprises a first light emitting unit and a first light receiving unit, wherein the first light emitting unit is used for emitting a first light beam during the determination of the first defocus amount of the target object, the first light beam generates a first reflected light signal after being reflected by the target object, and the first light receiving unit is used for determining the first defocus amount of the target object according to the received first reflected light signal.

3. The image acquisition system of claim 2, wherein, The first defocus determining module adopts one of the following methods to determine the first defocus amount: eccentric mask, differential confocal, chopping method and coaxial laser triangulation.

4. The image acquisition system of any one of claims 1 to 3, characterized in that, The second defocus determining module comprises a second light emitting unit, an interference unit and a second light receiving unit, the interference unit and the measuring objective lens are fixedly connected, and the interference unit comprises a first beam splitter and a reference mirror; the second light emitting unit is used for emitting a second light beam, the second light beam generates a third light beam and a fourth light beam after passing through the first beam splitter, the third light beam generates a second reflected light signal after being reflected by the reference mirror, and the fourth light beam generates a third reflected light signal after being reflected by the target object; the first movement control module is further used for controlling the movement of the interference unit and the measuring objective lens by a preset distance during the determination of the second defocus amount of the target object by the interference unit; during the control of the movement of the interference unit and the measuring objective lens from an initial position to a first position, the second light receiving unit is used for receiving the second reflected light signal and the third reflected light signal when the interference unit and the measuring objective lens are at different positions, and determining the second defocus amount according to the second reflected light signal and the third reflected light signal.

5. The image acquisition system of claim 4, wherein, The second light receiving unit is configured to determine a second position of the interference unit or the measurement objective lens when the image acquisition module is in a focus state according to the second reflected light signal and the third reflected light signal received when the interference unit and the measurement objective lens are at different positions, and determine the second defocus amount according to the second position of the interference unit and an initial position of the interference unit, or determine the second defocus amount according to the second position of the measurement objective lens and an initial position of the measurement objective lens.

6. The image acquisition system of claim 4, wherein, The first movement control module includes a first control unit and a first driving unit, and the first driving unit is connected with the second light emitting unit and the interference unit. The first control unit is configured to control the first driving unit to drive the second light emitting unit and the interference unit to move in the first direction.

7. The image acquisition system of claim 4, wherein, The image acquisition system includes a second beam splitter, and the target object, the measurement objective lens, the first beam splitter, the second beam splitter and the image acquisition module are located on a first optical axis. The second light emitting unit, the first beam splitter and the reference mirror are located on a second optical axis. The first optical axis is perpendicular to the second optical axis.

8. The image acquisition system of claim 7, wherein, The image acquisition system includes a third beam splitter, and the second beam splitter, the third beam splitter and the second light receiving unit are located on a third optical axis. The third beam splitter and the first defocus determination module are located on a fourth optical axis. The third optical axis is parallel to the second optical axis, and the fourth optical axis is parallel to the first optical axis.

9. The image acquisition system of any one of claims 1 to 3, wherein, The first movement control module is connected with the target object. When the target object is not in the preset position in a second direction, the first movement control module is configured to control the target object to move in the second direction, so that the target object is in the preset position in the second direction.

10. The image acquisition system of any one of claims 1 to 3, wherein, The image acquisition system further includes a second movement control module, and the second movement control module is connected with the target object. When the target object is not in the preset position in the second direction, the second movement control module is configured to control the target object to move in the second direction, so that the target object is in the preset position in the second direction.

11. The image acquisition system of any one of claims 1 to 3, wherein, The image acquisition system further includes a second movement control module, and the second movement control module includes a second control unit and a second driving unit. The second control unit is connected with the second driving unit, and the second driving unit is connected with the target object. The second control unit is configured to control the second driving unit to drive the target object to move in a second direction.

12. The image acquisition system of any one of claims 1 to 3, wherein, The image acquisition module further includes a position determination module, and the position determination module is configured to determine whether the target object is in the preset position in the second direction according to the first image.

13. The image acquisition system of any one of claims 1 to 3, wherein, The target object is provided with a graphic mark, and the preset position is a position of the target object in the second direction when the graphic mark is in the center of the field of view of the image acquisition module. The second direction is a plane perpendicular to the first direction.

14. An image acquisition method of a metrology apparatus, characterized by, The method includes: determining a first defocus amount of a target object; controlling relative movement between the target object and the measurement objective lens in a first direction based on the first defocus amount to focus the target object for a first time; acquiring an image of the target object focused for the first time by an image acquisition module to generate a first image, and determining whether the target object is in a preset position in a second direction using the first image, the second direction being a direction perpendicular to the first direction; acquiring a second defocus amount of the target object after determining that the target object is in the preset position in the second direction; controlling relative movement between the target object and the measurement objective lens in the first direction based on the second defocus amount to focus the target object for a second time; acquiring an image of the target object focused for the second time by the image acquisition module to generate a second image; wherein a determination speed of the first defocus amount is greater than a determination speed of the second defocus amount, and a resolution of the first image is less than a resolution of the second image.

15. The image acquisition method of claim 14, wherein, The measurement device comprises a first defocus determination module, the first defocus determination module comprises a first light emitting unit and a first light receiving unit, and the method for determining the first defocus amount of the target object comprises: controlling the first light emitting unit to emit a first light beam, the first light beam generates a first reflected light signal after being reflected by the target object; determining the first defocus amount of the target object based on the first reflected light signal received by the first light receiving unit.

16. The image acquisition method of claim 15, wherein, The method for determining the first defocus amount of the target object based on the first reflected light signal received by the first light receiving unit comprises: determining the first defocus amount by using one of the following methods: eccentric mask, differential confocal, chopping method, and coaxial laser triangulation method.

17. The image acquisition method according to any one of claims 14 to 16, characterized in that, The measurement device comprises a second defocus determination module, the second defocus determination module comprises a second light emitting unit, an interference unit, and a second light receiving unit, the interference unit comprises a first beam splitter and a reference mirror, and the method for acquiring the second defocus amount of the target object comprises: controlling the second light emitting unit to emit a second light beam during relative movement between the interference unit and the measurement objective lens in the first direction relative to the target object, the second light beam generates a third light beam and a fourth light beam after passing through the first beam splitter, the third light beam generates a second reflected light signal after being reflected by the reference mirror, and the fourth light beam generates a third reflected light signal after being reflected by the target object; determining the second defocus amount of the target object based on the second reflected light signal and the third reflected light signal received by the second light receiving unit.

18. The image acquisition method of claim 17, wherein, The method for determining the second defocus amount of the target object based on the second reflected light signal and the third reflected light signal received by the second light receiving unit comprises: determining a focus position of the interference unit or the measurement objective lens when the image acquisition module is in a focus state based on the second reflected light signal and the third reflected light signal received by the second light receiving unit. determining the second defocus amount according to a position where the interferometer unit is focused and an initial position of the interferometer unit, or determining the second defocus amount according to a position where the measurement objective lens is focused and an initial position of the measurement objective lens.

19. The image acquisition method according to any one of claims 14 to 16, characterized in that, before the control of the relative movement between the measurement objective lens and the target object in the first direction, comprising: determining a target movement position of the measurement objective lens or the target object based on the first defocus amount.

20. The image acquisition method according to any one of claims 14 to 16, characterized in that, the method for controlling the relative movement between the measurement objective lens and the target object in the first direction, comprising: controlling the movement of the measurement objective lens relative to the target object in the first direction, or / and controlling the movement of the target object relative to the measurement objective lens in the first direction.

21. The image acquisition method according to any one of claims 14 to 16, characterized in that, after the determination that the target object is not in the preset position in the second direction, comprising: controlling the relative movement between the target object and the measurement objective lens in the second direction so that the target object is in the preset position in the second direction.

22. The image acquisition method according to any one of claims 14 to 16, characterized in that, before the image acquisition of the target object after the first focusing or before the image acquisition of the target object after the second focusing, comprising: sending a control signal of completion of focusing to the image acquisition module.

23. The image acquisition method according to any one of claims 14 to 16, characterized in that, the target object has a graphic mark thereon, and the determination of whether the target object is in the preset position in the second direction, comprising: determining whether the graphic mark is in a center of a field of view of the image acquisition module; if the graphic mark is in the center of the field of view of the image acquisition module, determining that the target object is in the preset position in the second direction.

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