Image acquisition system and method of measuring equipment

Abstract

The embodiment of the invention discloses an image acquisition system and method of measurement equipment, and the system comprises a first defocus determination module which is used for determining a first defocus amount of a target object; the second defocusing determination module is used for determining a second defocusing amount of the target object; the first movement control module is used for controlling the measuring objective lens and the target object to move relatively in the first direction according to the first defocusing amount so as to focus the target object for the first time, and controlling the measuring objective lens and the target object to move relatively in the first direction according to the second defocusing amount so as to focus the target object for the second time; the image acquisition module is used for carrying out image acquisition on the target object after the first focusing to generate a first image so as to determine whether the target object is located at a preset position or not; the image acquisition module is used for performing image acquisition on the target object after the second focusing after determining that the target object is located at the preset position to generate a second image; the image acquisition duration of the target object can be reduced, the alignment error measurement efficiency of the target object is improved, and the applicability is high.

Description

Technical Field

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

[0002] Semiconductor inspection technology plays an important role in the processes of semiconductor production, packaging and testing. Among them, the measurement of alignment error (Overlay, OVL) is an important part of the key process in the semiconductor production process. Alignment error is one of the most important errors that need to be controlled in the key process. It refers to the pattern alignment error between the front layer and the current layer during the wafer alignment process. There is a certain distribution law on the wafer and the exposure field. In order to ensure that the alignment error is within the threshold range, after each batch of wafers is exposed, it is necessary to perform alignment error measurement on the alignment measurement machine for many marking points. After mathematical processing, the measurement value obtains the distribution model of alignment error (OVL model terms), which is used for the alignment error control of the next batch of wafer exposure. In order to obtain the distribution law of alignment error on the wafer and the exposure field, the marking points for alignment error measurement need to be distributed as evenly as possible on the entire wafer. In the process of alignment error measurement, the camera is mainly used to obtain a wafer measurement image containing information of both the front layer and the current layer (that is, a wafer scanning image containing alignment error measurement marking points), and the alignment error is obtained through the wafer measurement image. Therefore, in order to improve the measurement accuracy of alignment errors, the positioning accuracy of wafer measurement image acquisition also has extremely high requirements, requiring high-precision wafer image scanning positioning technology and autofocus technology.

[0003] In the prior art, in the process of improving the positioning accuracy of wafer image scanning, it is necessary to perform target acquisition (TA) (including the acquisition of wafer measurement images) when positioning the mark point of alignment error measurement. At the same time, in order to improve the accuracy of wafer image scanning, the white light interferometric focusing method is used to perform focusing once before and after the TA operation. White light interferometric focusing is a focusing technology with extremely high precision (approximately equal to 10nm), but each time it performs focusing, it requires a large-load and large-stroke Z-axis motor (i.e., a precision motor) to perform a scanning motion of about 20um stroke. After waiting for the solution result, it is necessary to perform a step adjustment of the Z-axis motor, which results in each process of white light interferometric focusing taking 70ms to 80ms. Two white light interferometric focusings also make the acquisition of wafer measurement images time-consuming and the wafer alignment error measurement efficiency is low. Summary of the invention

[0004] The present application provides an image acquisition system and method for a measurement device, which can reduce the image acquisition time of a target object, improve the efficiency of alignment error measurement 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 measuring device, comprising a first defocus determination module for determining a first defocus amount of a target; a second defocus determination module for determining a second defocus amount of the target; a first movement control module for controlling a measuring lens of the target to move relative to the target in a first direction according to the first defocus amount so as to focus on the target for the first time, and controlling a measuring lens to move relative to the target in the first direction according to the second defocus amount so as to focus on the target for the second time; an image acquisition module for acquiring an image of the target after the first focusing to generate a first image, wherein the first image is used to determine whether the target is at a preset position; and after determining that the target is at the preset position, acquiring an image of the target after the second focusing to generate a second image; wherein a speed of determining the first defocus amount is greater than a speed of determining the second defocus amount, and a resolution of the first image is less than a resolution of the second image. By adopting the image acquisition system provided by the present application, the first defocus amount of the target object can be obtained at a higher 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 accuracy, so that the second image acquired by the image acquisition module after the second focusing is an image with higher definition. 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 structure of each module in the image acquisition system is simple and the applicability is strong.

[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. In the process of determining the first defocus amount of the target object, the first light emitting unit is used to emit a first light beam, and the first light beam is reflected by the target object to generate a first reflected light signal. The first light receiving unit is used to determine the first defocus amount of the target object based on the received first reflected light signal. With the present application, the first light beam is emitted by the first light emitting unit and is reflected by the target object and then received by the first light receiving unit. The image acquisition system can quickly acquire the first reflected light signal of the target object. 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 increase the speed of determining the first defocus amount, further reduce the image acquisition time of the target object, and improve the efficiency of measuring the alignment error of the target object.

[0007] In a possible implementation of the first aspect, the first defocus determination module uses one of an eccentric mask, differential confocal, a chopping method, and a coaxial laser triangulation method to determine the first defocus amount. By using the present application, a specific optical effect or principle can be used to accurately measure the first defocus amount of the target object. The above method has high measurement accuracy and high stability, and can effectively reduce measurement deviations caused by external interference or system errors, 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 is fixedly connected to the measuring objective lens, and the interference unit includes a first beam splitter and a reference reflector; the second light emitting unit is used 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 reflector, and the fourth light beam generates a third reflected light signal after being reflected by the target object; the first movement control module is also used to control the interference unit and the measuring objective lens to move a preset distance during the process of the interference unit determining the second defocus amount of the target object; in the process of controlling the interference unit and the measuring objective lens to move from the first position initial position to the second position first position, the second light signal receiving unit is used to receive 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 determine the second defocus amount according to the second reflected light signal and the third reflected light signal. According to the present application, since the interference phenomenon is extremely sensitive to the phase difference of light waves, the implementation method of the present application adopts the principle of optical interference and accurately calculates the second defocus amount by measuring the changes in the interference fringes. This can achieve high-precision measurement of the second defocus amount of the target object and further improve the accuracy of the second focusing.

[0009] In a possible implementation of the first aspect, the second optical signal receiving unit is used to determine the second position of the interference unit or the measuring lens when the image acquisition module is in the focusing state according to the second reflected light signal and the third reflected light signal received when the interference unit and the measuring lens are in different positions, and determine the second defocus amount according to the second position and the initial position of the interference unit or the measuring lens. By adopting the present application, the interference principle and optical signal analysis can be used to accurately measure the position change of the interference unit or the measuring lens to achieve high-precision determination of the second defocus amount of the target object, thereby 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 to the second light emitting unit and the interference unit, and the first control unit is used to control the first driving unit to drive the second light emitting unit and the interference unit to move in the first direction. With the present application, the image acquisition system can accurately control the movement of the interference unit in the first direction through the introduction of the first control unit and the first driving unit. This precise control ensures that the interference unit can move according to a predetermined trajectory and speed, thereby further improving the accuracy and stability of determining the second defocus amount.

[0011] In a possible implementation of the first aspect, the image acquisition system includes a second beam splitter, the target object, the measuring 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 reflector are located on a second optical axis, wherein the first optical axis is perpendicular to the second optical axis. By adopting the present application, the image acquisition system realizes accurate separation and merging of optical paths by adopting a second beam splitter and rationally arranging relevant components on the first optical axis and the second optical axis, 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, wherein the third optical axis is parallel to the second optical axis, and the fourth optical axis is parallel to the first optical axis. With the present application, due to the introduction of the third beam splitter and the parallel layout of the third optical axis and the second optical axis, the image acquisition system can more effectively separate and merge light from different directions, avoiding mutual interference of optical paths, which not only improves the clarity of image acquisition, but also enhances the stability and reliability of the image acquisition system.

[0013] In a possible implementation of the first aspect, the first mobile control module is connected to the target object, and when the target object is not in the preset position, the first mobile control module is used to control the target object to move in a second direction so that the target object is in the preset position, wherein the second direction is a plane perpendicular to the first direction. With the present application, through the connection between the first mobile 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 mobile control module can control the target object to move in the second direction until the target object reaches the preset position, thereby improving the degree of automation 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 mobile control module, which is connected to the target object; when the target object is not in the preset position, the second mobile control module is used to control the target object to move in a second direction so that the target object is in the preset position. By adopting the present application, by introducing the second mobile control module, the image acquisition system can have two independent control modules, namely the first mobile control module and the second mobile control module, to ensure that the target object can be accurately moved to the preset position. This dual protection mechanism improves the accuracy and reliability of the target object positioning. Even when one control module fails or has 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 drive unit, the second control unit is connected to the second drive unit, the second drive unit is connected to the target object, and the second control unit is used to control the second drive unit to drive the target object to move in a second direction, wherein the second direction is a plane perpendicular to the first direction. With the present application, the second control unit can send precise instructions, and the second drive unit can accurately convert these instructions into actual movement of the target object, thereby ensuring that the target object can be accurately moved to a preset position, thereby achieving precise 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 determination module, which is used to determine whether the target object is in the preset position according to the first image. With the present application, by accurately analyzing the first image, the position determination 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 located and improving the accuracy of target object image acquisition.

[0017] In a possible implementation of the first aspect, a graphic mark is provided on the target object, 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. By adopting the present application, by providing a 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, the positioning accuracy of the target object and the recognition efficiency of the first image can be improved.

[0018] In the second aspect, the present application also provides an image acquisition method for a measuring device, comprising: determining a first defocus amount of a target; based on the first defocus amount, controlling the relative movement between the measuring lens of the target and the target in a first direction to focus the target for the first time; acquiring an image of the target after the first focus to generate a first image, and using the first image to determine whether the target is in a preset position; after determining that the target is in the preset position, obtaining a second defocus amount of the target; based on the second defocus amount, controlling the relative movement between the measuring lens and the target in a first direction to focus the target for the second time; acquiring an image of the target after the second focus to generate 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. Using the present application, the target is firstly focused quickly, and then finely focused for image acquisition. The fast focus in the first stage reduces the focusing time required for target image acquisition, while the fine focus in the second stage ensures the high resolution of the second image, thereby ensuring the measurement accuracy of the error measurement based on the second image. Therefore, it can reduce the image acquisition time of the target object and improve the efficiency of the alignment error measurement based on the image acquisition of the target object.

[0019] In a possible implementation of the second aspect, the measuring device includes a first defocus determination module, the first defocus determination module includes a first light emitting unit and a first light receiving unit, and the method for determining the first defocus amount of the target object includes: controlling the first light emitting unit to emit a first light beam, the first light beam is reflected by the target object to generate a first reflected light signal; based on the first reflected light signal received by the first light receiving unit, determining the first defocus amount of the target object. With the present application, the first light emitting unit emits a light beam, the first light receiving unit receives the first reflected light signal, and the first defocus amount is calculated based on the first reflected light signal. This process can achieve fast and efficient determination of the first defocus amount without moving the device in the measuring device, which can shorten 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 includes: determining the first defocus amount according to the first reflected light signal by using one of the methods selected from the group consisting of an eccentric mask, differential confocal, chopping method, and coaxial laser triangulation. By using the present application, the first defocus amount of the target object can be accurately and quickly determined according to the first reflected light signal by using measurement methods such as an eccentric mask, differential confocal, chopping method, and coaxial laser triangulation, thereby reducing measurement errors and improving the accuracy of the first defocus amount.

[0021] In a possible implementation of the second aspect, the measuring 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 spectroscope and a reference reflector, and the second defocus amount of the target object is obtained, including: in the process of controlling the interference unit and the measuring objective lens to move relative to the target object in the first direction, controlling the second light emitting unit 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 spectroscope, the third light beam generates a second reflected light signal after being reflected by the reference reflector, and the fourth light beam generates a third reflected light signal after being reflected by the target object; based on the second reflected light signal and the third reflected light signal received by the second light receiving unit, the second defocus amount of the target object is determined. By adopting the present application, the high-precision measurement of the second defocus amount of the target object is achieved through the principle of optical interference, which can further improve the focusing accuracy of the second focusing.

[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 the first focus position of the interference unit or the measuring objective lens when the image acquisition module is in the 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 based on the first focus position and the initial position of the interference unit or the measuring objective lens. The present application utilizes the interference principle and light signal analysis to accurately measure the position change of the interference unit or the measuring objective lens to achieve high-precision determination of the second defocus amount of the target object.

[0023] In a possible implementation of the second aspect, before the above-mentioned control of the relative movement between the above-mentioned measuring lens and the above-mentioned target object in the first direction comprises: determining the target movement position of the measuring lens or the above-mentioned target object based on the above-mentioned first defocus amount. With the present application, the target movement position can be determined to avoid the inaccurate second focusing caused by excessive or insufficient movement of the measuring lens or the target object without predetermining the target movement position, and after determining the target movement position, the image acquisition system can directly move the measuring lens or the target object to the position without multiple tentative movements and adjustments, which greatly reduces the number and time of movements 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 measuring lens of the target and the target in the first direction comprises: controlling the measuring lens to move relative to the target in the first direction, or / and controlling the target to move relative to the measuring lens in the first direction. By adopting the present application, the measuring lens and / or the target is allowed to move in the first direction, and the most appropriate movement mode can be selected to achieve the first focusing and the second focusing according to the specific measurement scene and requirements, which has strong 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 target object to move relative to the measuring objective lens in the second direction so that the target object is in the preset position. By adopting the present application, by controlling the target object to move in the second direction, the measurement error caused by directly performing a second focus and image acquisition when the target object is not in the preset position is 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 measuring device includes an image acquisition module, and before the image acquisition of the target after the first focusing or before the image acquisition of the target after the second focusing is performed, the device includes: sending a control signal indicating that the focusing is completed to the image acquisition module. By adopting the present application, by sending a control signal indicating that the focusing is completed, it is possible to ensure that the image acquisition module performs image acquisition only after the first focusing or the second focusing is completed, thereby avoiding the problem of image blur or distortion 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; 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 determining the position 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. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 It is a structural schematic diagram of the image acquisition system provided by the present application; Figure 2 is another structural schematic diagram of the image acquisition system provided by the present application; Figure 3 is another structural schematic diagram of the image acquisition system provided by the present application; Figure 4 is a schematic diagram of the optical path of the first light beam provided in this application; Figure 5 It is a flowchart of the image acquisition method provided in this application. DETAILED DESCRIPTION

[0029] The technical solution in this application will be described below in conjunction with the drawings in this application.

[0030] To facilitate understanding, some nouns are briefly explained as follows: 1. Defocus, also known as defocus height, refers to the data indicating the focus offset difference when acquiring the target image (such as the target wafer) during the scanning process of the target (such as the target wafer). It can be used to adjust the distance between the target and the measuring lens so that the target image reaches the preset clarity. The preset clarity refers to the specified value of the target image clarity, which can be determined according to the specific form of the product.

[0031] 2. Image markers, also known as scan feature points, ideal feature points or target feature points, can be marking patterns used for alignment and need to have unique features that are easy to identify. Image markers can be selected from the feature points used for target alignment, or they can be obtained by artificial intelligence annotation in the target design drawing.

[0032] 3. The first light beam can be a structured light, partially coherent light, laser or other light beams. Among them, structured light usually has the characteristics of narrow line width, which can obtain high contrast and high definition imaging effects when captured; partially coherent light is a light beam between fully coherent light and incoherent light, and its coherence can be controlled by adjusting the light source or using a scatterer; laser is a highly coherent monochromatic light with extremely high directionality and brightness, and the phase and frequency of the laser are consistent in space and time.

[0033] Taking structured light as the first light beam as an example, a specific optical pattern can be projected onto the surface of the target by projecting structured light, and then the processor calculates the three-dimensional information of the target based on the returned light beam data (light signal), and then restores the entire three-dimensional space to obtain the defocus amount of the target. Among them, the optical pattern projected by the structured light can be in the shape of a plane, a grid, a straight line, etc., and the height change of the target surface can be calculated by observing the distortion of the light.

[0034] 4. The second beam refers to the beam used for beam interference, which is usually a monochromatic laser beam (the monochromatic laser beam may also be referred to as a monochromatic beam). For example, the monochromatic beam may be visible light, infrared light, etc. Monochromatic beams have high precision, strong stability, specific wavelength and coherence, and can generate specific interference patterns by adjusting the phase and amplitude of the beam.

[0035] 5. Beam interference refers to the beam interference experiment, which is generally carried out using a monochromatic beam, such as white light interference, red light interference, etc. The beam interference experiment relies on the interference phenomenon of light, that is, the phenomenon of interference patterns when two monochromatic beams meet. In this application, a monochromatic beam (such as white light) can be divided into two beams of light through a spectroscope, one of which is reflected by a reference reflector and the other is reflected by the target object, and finally converges at a photodiode to produce light and dark stripes. These stripes are caused by the phase difference between the two monochromatic beams, which depends on the optical path difference of the two monochromatic beams. The intensity of the interference stripes depends on the optical path difference of the two beams of light. According to the brightness of the white light interference stripes and the position where the interference stripes appear, the height of the target object can be analyzed. Among them, only when the optical path difference between the reference arm and the measuring arm is within a coherent length of the light source, the backscattered light (i.e., the reflected light of the target object) and the reference light (i.e., the reflected light of the reference reflector) will interfere, and the optical path difference is equal to 0, that is, when the optical paths of the two beams are completely consistent, the coherence intensity reaches the maximum, and this signal is the beam interference signal.

[0036] Embodiment 1 For ease of understanding, this application first describes the architecture of the image acquisition system. The above image acquisition system can be applied to wafer production scenarios, wafer processing scenarios, etc. Taking the wafer as the target object, this application uses the image acquisition scenario of the wafer measurement equipment as an example to illustrate. Figure 1 , Figure 1 Schematic diagram of the structure of the image acquisition system provided by this application. Figure 1 As shown, the image acquisition system may include an image acquisition module, a first defocus determination module, a second defocus determination module and a first movement control module, wherein the first defocus determination module is used to determine a first defocus amount of a target object; the second defocus determination module is used to determine a second defocus amount of the target object; the first movement control module is used to control a measuring lens of the target object to move relative to the target object in a first direction according to the first defocus amount so as to focus on the target object for the first time, and to control a measuring lens to move relative to the target object in the first direction according to the second defocus amount so as to focus on the target object for the second time; the image acquisition module is used to perform image acquisition on 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 perform image acquisition on the target object after the second focusing to generate a second image after determining that the target object is at the preset position; 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.

[0037] In some feasible embodiments, the first defocus determination module may include devices such as a focus tracking sensor, and the first defocus determination module may be used to determine the first defocus amount of the target object and transmit the first defocus amount to the first mobile control module. The first defocus amount is the first distance of the focus of the light relative to the surface of the target object. The first defocus determination module may be used to emit a light beam to irradiate the target object, receive and analyze the data of the light beam reflected by the target object, for example, the first defocus amount of the target object may be quickly obtained through high-speed optical focusing technology. Exemplarily, the high-speed optical focusing technology may include: eccentric mask method (single measurement takes about 1ms), differential confocal method (single measurement takes about 2ms), chopping method (single measurement takes about 0.1ms), coaxial laser triangulation method (single measurement takes about 1ms). Since the first image has a low requirement for focusing accuracy, it is not necessary to use high-precision but long-time beam interference focusing (a single measurement takes about 100ms), but the first defocus amount is obtained by the above-mentioned high-speed optical focusing technology, so as to greatly improve the acquisition speed of the first defocus amount (about 100ms for each measurement) 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, thereby improving the positioning speed of the target object, and further improving the speed of the image acquisition system for acquiring the image of the target object.

[0038] The second defocus determination module may include a ray tracing device, an optoelectronic collection board and other devices. The second defocus determination module may be used to determine the second defocus amount of the target object, for example, the second defocus amount of the target object may be determined by beam interference focusing, and the second defocus amount may be transmitted to the first mobile control module. It is understandable that the second defocus amount is also the second distance of the focus of the light relative to the surface of the target object. The second defocus determination module is fixedly connected to the measuring lens. Through the second defocus determination module, a second defocus amount with a higher focusing accuracy can be obtained on the basis of the first defocus amount with a lower focusing accuracy. For example, a more accurate algorithm or a more accurate sensor may be used to obtain a more accurate second defocus amount. Exemplarily, the second defocus determination module may obtain the second defocus amount through a beam interference focusing method (with higher accuracy than the above-mentioned high-speed optical focusing technology) and a fine-tuning motor (which can adjust the position of the measuring lens or the target object with high accuracy) so that the focusing accuracy of the second defocus amount meets the product's accuracy requirements for image acquisition.

[0039] The first movement control module can be used to control the relative movement of the measuring lens of the target and the target in the first direction according to the first defocus amount, so as to focus on the target for the first time. 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 measuring lens in the first direction, or accurately control the movement of the target in the first direction, or accurately control the movement of the measuring lens and the target in the first direction. The relative movement distance of the measuring lens and / or the target can compensate for the first defocus amount, so that the target and / or the measuring lens can reach the in-focus position to focus on the target for the first time. Among them, the first movement control module can accurately control the measuring lens and / or the target to move the distance indicated by the first defocus amount through a high-precision position adjustment device (such as a fine-tuning motor), so as to ensure the accuracy of the first focus, and can accurately control the measuring lens and / or the target to move accurately through the motion control instruction. The first movement control module can also be used to control the relative movement of the measuring lens and the target in the first direction according to the second defocus amount, so as to perform a second focus on the target. Similar to the first focus, the first movement control module can accurately control the relative movement of the measuring lens and / or the target in the first direction based on the second defocus amount to compensate for the second defocus amount for the second focus. Among them, the first movement control module can accurately control the measuring lens and / or the target to move the distance indicated by the second defocus amount through a high-precision position control device (such as a fine-tuning motor), so as to meet the high-precision requirements of the second focus. The second focus is performed on the basis of the first focus. The first movement control module moves the target and / or the measuring lens to the vicinity of the low-accuracy focus position through the first focus at a faster speed, and then obtains a more accurate focus position through the second defocus amount, so as to control the relative movement of the measuring lens and / or the target in the first direction through a high-precision position adjustment device such as a fine-tuning motor, so as to complete a more accurate second focus. The fast focusing during the first focusing reduces the overall measurement time, while the second focusing is performed based on the first focusing, which can improve the focusing accuracy while ensuring the focusing accuracy, thereby improving the working efficiency of the image acquisition system.

[0040] 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 to say, when the first defocus amount with a faster determination speed is received, the first movement control module can first control the measurement lens and the target to move relative to each other for the first time in the first direction based on the first defocus amount, and then when the second defocus amount with a slower determination speed is received, the measurement lens and the target are controlled to move relative to each other for the second time in the first direction based on the second defocus amount. It can be understood that the first relative movement can be used to perform preliminary focusing on the target, and the relative distance between the target and the measurement lens can be adjusted to the relative distance required for precise focusing (i.e., the second focusing) in advance through preliminary focusing (i.e., the first focusing), so there is no need to move long distances when the target is precisely focused, which can reduce the time for precise focusing on the target. It should be noted that the first direction can be a vertical direction in space, and optionally, the first direction can also be a horizontal direction, which should be determined according to the specific product form, and this application does not limit it.

[0041] In some feasible embodiments, the image acquisition module may include an image acquisition device such as a camera. The image acquisition module may be used to scan the target to capture an image of the target after the first focus to generate a first image. The first image may be used to determine whether the target is in a preset position. For example, determine whether a certain position on the target is in the center of the field of view of the image acquisition module. The image acquisition module may also be used to capture an image of the target after the second focus after determining that the target is in the preset position to generate a second image. The second image may be used as a reference image to provide a reference for alignment of another target superimposed on this target. The resolution of the first image is less than the resolution of the second image. It is understandable that the first image is used to quickly identify the current position of the target to ensure that the target is accurately positioned. Since an image recognition algorithm may be used to identify whether the target is in a preset position, the image recognition algorithm has a low resolution requirement for the first image and a low focus accuracy requirement for the first image. Therefore, the first defocus determination module may be used to quickly determine the first defocus amount with a lower accuracy relative to the second defocus amount without using a beam interference focusing method with high focus accuracy but slow focus speed. And because the resolution of the first image generated based on the first defocus amount is relatively small, the first image is generated at a relatively fast speed, and it can quickly identify whether the target object is in the preset position, thereby improving the efficiency of the image acquisition system in acquiring the second image. On the basis of ensuring that the target object is in the preset position through the first image, the image acquisition module can acquire a second image with a higher resolution than the first image to meet the product's requirements for the image quality of the target object.

[0042] It can be understood that the first defocus determination module quickly obtains the first defocus amount and transmits the first defocus amount to the first mobile control module. The first mobile control module controls the measuring lens of the target object and the target object to move relative to each other in the first direction according to the first defocus amount to perform the first focusing (preliminary focusing), so that the image acquisition module obtains a first image with a lower resolution after the first focusing, and then determines whether the target object is in a preset position according to the first image. The second defocus determination module can be used to obtain the second defocus amount based on the first focusing and transmit the second defocus amount to the first mobile control module. After the image acquisition module determines that the target object is in the preset position, the first mobile control module controls the measuring lens of the target object and the target object to move relative to each other in the first direction based on the second defocus amount again to perform the second focusing (precise focusing) on ​​the target object, so that the image acquisition module obtains a second image with a high resolution.

[0043] In some feasible embodiments, the above-mentioned image acquisition system may include a focus control module. If the image acquisition system includes a focus control module, the focus control module may receive the first reflected light signal transmitted by the first defocus determination module and generate a first defocus amount and return it to the first defocus determination module. The focus control module may also receive the second reflected light signal and the third reflected light signal transmitted by the second defocus determination module to generate a second defocus amount, and return the second defocus amount to the second defocus determination module. The focus control module may also receive the first image transmitted by the image acquisition module, and determine whether the target object is in a preset position based on the first image. If it is determined that the target object is not in the preset position, the second movement control module may be triggered to carry the target object to move in the second direction. The focus control module may also trigger the image acquisition module to perform image acquisition and generate a second image after determining that the target object is in the preset position.

[0044] By adopting the image acquisition system provided by the present application, the first defocus amount of the target object can be obtained at a higher 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 accuracy, so that the second image acquired by the image acquisition module after the second focusing is an image with higher definition. 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 structure of each module in the image acquisition system is simple and the applicability is strong.

[0045] To facilitate 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 methods of the above modules are described with examples.

[0046] Please also see Figure 2 , Figure 2 It is another structural schematic diagram of the image acquisition system provided by this application.

[0047] In some possible implementations, in the Figure 1 Based on the implementation of the image acquisition system shown in FIG. Figure 2 As shown, the first defocus determination module includes a first light emitting unit and a first light receiving unit. In the process of determining the first defocus amount of the target object, the first light emitting unit is used to emit a first light beam, and the first light beam is reflected by the target object to generate a first reflected light signal. The first light receiving unit is used to determine the first defocus amount of the target object according to the received first reflected light signal. The first light emitting unit can be a light source such as a laser that can emit a first light beam, and the first light beam is used to measure the first defocus amount. The first light beam can be structured light, partially coherent light, laser or other high-intensity light beams. The first light beam should determine the characteristics of the beam type, wavelength, intensity and beam emission angle according to the high-speed optical focusing technology applicable to the actual product, such as 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 sensitivity of the measurement. The first light emitting unit can emit the first light beam in 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 irradiating the target object to generate a first reflected light signal. The above-mentioned first light receiving unit may include a photoelectric collection board, a photodiode and other devices that can convert optical signals into electrical signals or other types of optical path data, and the present application does not limit it. Optionally, the first light beam emitted by the first light emitting unit may be irradiated onto the target object through a device such as a spectroscope in the second defocus determination module, and then reflected by the target object to generate a first reflected light signal, and the above-mentioned reflected light signal may be transmitted to the first light receiving unit through a device such as a spectroscope in the second defocus determination module. Optionally, the first light emitting unit may not pass through a device such as a spectroscope in the second defocus determination module, but directly emit the first light beam to the target object, and the first light receiving unit may not pass through a device such as a spectroscope in the second defocus determination module, but directly receive the first reflected light signal, and the present application does not limit it. The above-mentioned first light receiving unit can determine the first defocus amount of the target object based on the received first reflected light signal.

[0048] In some feasible implementations, the first light receiving unit may further include a processor ( Figure 2(not shown) or connected to a processor, the processor can be used to perform signal processing on the received first reflected light signal, so as 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 illumination intensity and illumination angle of the structured light, and the first light receiving unit can determine the deformation or light intensity change caused by the structured light irradiating on the target object according to the illumination intensity, illumination angle and other information indicated in the first reflected light signal (for example, receiving the first reflected light signal through an optical sensor), so as to determine the first defocus amount based on the degree of deformation and the degree of light intensity change. With 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 by the first light emitting unit and the first light receiving unit. Among them, the first light receiving unit can quickly obtain the first reflected light signal of the target object. 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 speed of determining the first defocus amount, so that the image acquisition system can respond more quickly and perform subsequent focusing and image acquisition operations.

[0049] Optionally, in some feasible embodiments, the first light beam may be a structured light, and the first defocus determination module may emit a structured light, and irradiate the structured light on the target object and obtain a first reflected light signal based on the reflection of the structured light by the target object. The first defocus determination module may calculate the first defocus amount based on the received first reflected light signal by coaxial laser triangulation. When the first defocus determination module calculates the first defocus amount based on the coaxial laser triangulation, the three-dimensional morphology information of the surface of the target object may be calculated by the triangulation principle based on the optical path data such as the position, shape, and light intensity of the light spot indicated by the first reflected light signal, so as to determine the first defocus amount of the target object based on the three-dimensional morphology information of the surface of the target object. Optionally, the first defocus determination module may emit a structured light through a first light emitting unit, and irradiate the structured light on the target object and obtain a 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 determination module may calculate the first defocus amount based on the received first reflected light signal by coaxial laser triangulation. When the first light receiving unit calculates the first defocus amount based on the coaxial laser triangulation method, the three-dimensional shape information of the surface of the target object can be calculated based on the light path data such as the position, shape, and light intensity of the light spot indicated by the first reflected light signal through the triangulation principle, so that the first defocus amount of the target object can be determined based on the three-dimensional shape information of the surface of the target object. The above-mentioned structured light can be a light beam such as a point structured light, a line structured light, and a surface structured light, which is used to illuminate the target object and is reflected by the target object to generate a first reflected light signal to indicate the light path data; the above-mentioned light path data includes at least one of the light spot size, shape, or light spot intensity signal.

[0050] Optionally, in some feasible embodiments, the first light beam may also be partially coherent light, and the image acquisition system may further include a mask plate, which is aligned with the target. The first defocus determination module may obtain the first defocus amount by an eccentric mask method; the first defocus determination module may calculate the defocus amount according to the change of the light intensity signal generated by the imaging dislocation of the mask plate. For example, after the mask plate is aligned with the target, the first defocus determination module may irradiate the partially coherent light onto the mask plate to generate a light beam diffraction through the mask plate, and the partially coherent light is projected onto the target through the mask plate. The first defocus determination module receives the first reflected light signal generated after the target and the mask plate are reflected, and determines the first defocus amount by analyzing the change of the light intensity signal in the optical path data indicated by the first reflected light signal. Optionally, the first light receiving unit in the first defocus determination module may obtain the first defocus amount by an eccentric mask method; when the first light receiving unit obtains the first defocus amount by the eccentric mask method, the defocus amount may be calculated according to the change of the light intensity signal generated by the imaging dislocation of the mask plate. For example, after the above-mentioned mask plate is aligned with the target object, the first light emitting unit in the first defocus determination module can irradiate partial coherent light onto the mask plate to generate light beam diffraction through the mask plate, and the above-mentioned partial 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 reflection from the target object and the mask plate, and determines the first defocus amount by analyzing the change of the light intensity signal in the optical path data indicated by the first reflected light signal.

[0051] Optionally, in some feasible embodiments, the first light beam may also be a laser, and the image acquisition system may further include at least two photodiodes. The first defocus determination module may obtain the first defocus amount by the differential confocal method, and when the first defocus amount is obtained by the differential confocal method, the first defocus amount may be calculated according to the difference between the light intensity signals detected by the two photodiodes. For example, the first defocus determination module emits a laser and converges on the target object, and the laser reflected by the target object is received by two photodiodes respectively to generate two light intensity signals as two first reflected light signals, and then the 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 may obtain the first defocus amount by the differential confocal method, and when the first light receiving unit obtains the first defocus amount by the differential confocal method, the first defocus amount may be calculated according to the difference between the light intensity signals detected by the two photodiodes. For example, the first light emitting unit in the first defocus determination module emits a laser and converges it on the target object. The laser reflected by the target object is received by two photodiodes respectively to generate two light intensity signals as two first reflected light signals. The focus position of the target object can then be determined by the difference between the two light intensity signals to generate the first defocus amount of the target object.

[0052] Optionally, in some feasible embodiments, the first light beam may also be other high-intensity light beams, and the image acquisition system may further include a chopper (such as a knife edge). The first defocus determination module may obtain the first defocus amount by a chopping method. In the process of the first defocus determination module obtaining the first defocus amount by the chopping method, the movement of the chopper in the laser beam or other high-intensity light beam may measure the phase change of the light intensity signal of the light beam passing through the chopper blade, thereby calculating the defocus amount based on the phase change. For example, the first defocus determination module may output a laser beam or other high-intensity light beam to converge on the target object, and the light beam may generate a light intensity signal after passing through the chopper blade. 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 a chopping method. In the process of the first light receiving unit obtaining the first defocus amount by the above-mentioned chopping method, the phase change of the light intensity signal of the light beam passing through the chopper blade can be measured through the movement of the chopper in the laser 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 a laser beam or other high-intensity light beam to converge to the target object, and the above-mentioned light beam can generate a light intensity signal after passing through the chopper blade. The first light receiving unit in the first defocus determination module calculates the defocus amount by analyzing the phase change of the above-mentioned light intensity signal.

[0053] In the present application, the first defocus determination module can use eccentric mask, differential confocal, chopping method, coaxial laser triangulation method, etc., which are all 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, and 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 beam used for the first light beam and the defocus amount generation method used. For example, the first defocus determination module can use at least one of eccentric mask, differential confocal, chopping method, and coaxial laser triangulation method to determine the above-mentioned first defocus amount, and the first light beam can be a laser, structured light, partially coherent light, etc. beam. For the convenience of description, the following takes structured light as the first light beam as an example to illustrate the process of determining the defocus amount by the above-mentioned first defocus determination module, and no further details are given.

[0054] Optionally, in some feasible implementations, such as 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 is fixedly connected to the measuring objective lens, and the interference unit includes a first beam splitter and a reference reflector; the second light emitting unit is used 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 reflector, and the fourth light beam generates a third reflected light signal after being reflected by the target object; the first movement control module is also used to control the interference unit and the measuring objective lens to move a preset distance during the process of the interference unit determining the second defocus amount of the target object; in the process of controlling the interference unit and the measuring objective lens to move from the first position initial position to the second position first position, the second light signal receiving unit is used to receive 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 determine the second defocus amount according to the second reflected light signal and the third reflected light signal. The 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. Figure 3 , Figure 3 It is another structural schematic diagram of the image acquisition system provided by this application. Figure 3 Only some components in the image acquisition system are shown, not all. 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 reflector, and the second light receiving unit may include a photodiode and a processor. The first beam splitter is used to split the passing light beam into two light beams with the same intensity and different angles, and the reference reflector is used to reflect the light beam and provide the second light receiving unit with a reference phase required to determine the second defocus amount. The first beam splitter and the reference reflector are located on the same optical axis. For example, if the second light emitting unit emits the second light beam from the left to the right, the second light beam converges on the reference reflector after passing through the first beam splitter. In other words, the first beam splitter is located between the second light emitting unit and the reference reflector. If the second light emitting unit is located on the left side of the reference reflector, the first beam splitter is located on the left side of the reference reflector. Optionally, if the second light emitting unit is located on the right side of the reference reflector, the first beam splitter is also located on the right side of the reference reflector, and the first beam splitter is located on the left side of the second light emitting unit. 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 reflector, and the fourth light beam generates a third reflected light signal after being reflected by the target object.

[0055] In such Figure 3 Based on the implementation of the second defocus determination module shown, as Figure 2The first moving control module shown can control the interference unit and the measuring lens to move a preset distance during the process of the interference unit determining the second defocus amount of the target object. The first moving control module obtains the defocus amount corresponding to different distances between the measuring lens and the target object by moving the measuring lens, so that the second light signal receiving unit can determine the second defocus amount based on the second reflected light signal and the third reflected light signal received when the measuring lens is located at different positions. For example, the second light receiving unit can determine the reference phase based on the second reflected light signal, and determine the measured phase based on the third reflected light signal, and then generate a phase difference based on the reference phase and the measured phase, so as to determine the second defocus amount of the current position of the target object or the measuring lens based on the phase difference. It can be understood that when the position of the target object and / or the measuring lens changes, the measured phase indicated by the third reflected light signal will also change, so the focus position (the position where the phase difference is 0) can be determined by the phase difference between the reference phase and the measured phase, so as to generate the second defocus amount based on the focus position and the initial position of the target object or the measuring lens. The above-mentioned preset distance is the predicted distance between the focusing position of the measuring objective lens and the initial position of the measuring objective lens, and should be determined according to the actual product form to avoid the measuring objective lens moving too close, resulting in the inability to find the focusing position of the measuring objective lens, thereby failing to determine the second defocus amount, or the measuring objective lens moving too far, which affects the speed of determining the second defocus amount. The above-mentioned preset distance may be a pre-set value, or a value identified by artificial intelligence or the like, and this application does not impose any restrictions. Since the interference phenomenon is extremely sensitive to the phase difference of light waves, the embodiment of the present application adopts the principle of optical interference to accurately calculate the second defocus amount by measuring the changes in the interference fringes, thereby achieving high-precision measurement of the second defocus amount of the target object, which can further improve the accuracy of the second focus. ‌

[0056] In some feasible embodiments, the second optical signal receiving unit is used to determine the second position of the interference unit or the measuring objective lens when the image acquisition module is in the focusing state according to the second reflected light signal and the third reflected light signal received when the interference unit and the measuring objective lens are in different positions, and determine the second defocus amount according to the second position and the initial position of the interference unit or the measuring objective lens. Exemplarily, the measuring objective lens can be moved from the initial position to the first position by moving the measuring objective lens by a preset distance, wherein the measuring objective lens is fixedly connected to the interference unit, so the interference unit can also be moved from the initial position to the first position. In the process of controlling the interference unit and the measuring objective lens to move from the initial position 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 interference unit and the measuring objective lens are in different positions, so as to determine the position of the interference unit or the measuring objective lens when the image acquisition module is in the focusing state based on the second reflected light signal and the third reflected light signal, and determine the position as the second position. The second optical signal receiving unit can determine the second defocus amount based on the second position and the initial position of the interference unit or the measuring lens, and the second defocus amount is used to indicate the difference between the in-focus position (i.e., the second position) of the measuring lens and the initial position of the measuring lens. By adopting the present application, the interference principle and optical signal analysis can be used to accurately measure the position change of the interference unit or the measuring lens to achieve high-precision determination of the second defocus amount of the target object, thereby further improving the accuracy of the second focusing.

[0057] Optionally, in some feasible implementations, such as Figure 3 The interference unit shown may also include a collimating lens and a reference objective lens. The collimating lens is used to generate an illumination collimated light path when the light beam passes through, and the reference objective lens is used to converge the light beam onto the reference reflector. At this time, the light source in the second light emitting unit can emit a monochromatic light beam as the second light beam. The second light beam generates an illumination collimated light path after passing through the collimating lens. The illumination collimated light path is divided into a third light beam and a fourth light beam after passing through the first beam splitter. The fourth light beam converges on the target object (such as a target wafer) after passing through the measuring objective lens, and the third light beam converges on the reference reflector after passing through the reference objective lens. The third light beam generates a second reflected light signal after being reflected by the reference reflector, and the fourth light beam generates a third reflected light signal after being reflected by the target object.

[0058] Optionally, in some feasible implementations, the image acquisition system may further include a second beam splitter. Optionally, the second beam splitter may also be integrated into the second receiving unit or the interference unit, which is not limited in the present application. Figure 3As shown, the target object, the measuring objective lens, the first beam splitter, the second beam splitter and the image acquisition module are located on the first optical axis, wherein, if the first optical axis is perpendicular to the horizontal direction in space, the target object is located at the bottom of the first optical axis, and the first optical axis includes the target object, the measuring objective lens, the first beam splitter, the second beam splitter and the image acquisition module from bottom to top. It should be noted that if the angle of the first optical axis changes, the relative positions of the target object, the measuring objective lens, the first beam splitter, the second beam splitter and the image acquisition module in the first optical axis remain unchanged. The second light emitting unit, the first beam splitter and the reference reflector are located on the second optical axis, wherein the first optical axis is perpendicular to the second optical axis. If the second optical axis is the horizontal direction in space, the second light emitting unit is located at the leftmost of the second optical axis, and the second optical axis includes the second light emitting unit, the first beam splitter and the reference reflector from left to right. It should be noted that if the angle of the second optical axis changes, the relative positions of the second light emitting unit, the first beam splitter, and the reference reflector in the second optical axis remain unchanged. Therefore, the image acquisition module can capture 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 rationally arranging the relevant components on the first optical axis and the second optical axis, the image acquisition system can achieve accurate separation and merging of the optical path, thereby improving the accuracy and efficiency of image acquisition.

[0059] Optionally, in some feasible embodiments, the image acquisition system may further include a third beam splitter. Optionally, the third beam splitter may also 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, wherein, if the third optical axis is a horizontal direction in space, the second beam splitter is located at the leftmost of the third optical axis, and the third optical axis includes the second beam splitter, the third beam splitter and the second light receiving unit from left to right. It should be noted that if the angle of the third optical axis changes, 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. 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. Wherein, if the fourth optical axis is perpendicular to the horizontal plane in space, and the third beam splitter is located at the bottom of the fourth optical axis, the fourth optical axis includes the third beam splitter and the first defocus determination module from bottom to top. It should be noted that if the angle of the fourth optical axis changes, the relative position between the third beam splitter and the first defocus determination module in the fourth optical axis remains unchanged. Therefore, the first defocus determination module can obtain the first defocus value of the target object based on the third beam splitter, the second beam splitter, the first beam splitter and the measurement objective lens.

[0060] Optionally, the image acquisition system may further include an imaging lens group, which may be used to converge the light beam to the photodiode in the second light signal receiving unit to generate light beam interference. Exemplarily, if the image acquisition system includes an imaging lens group, the third light beam converges on the reference reflector and is reflected by the reference reflector to generate a second reflected light signal, and the second reflected light signal 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 the photodiode in the second light signal receiving unit. The fourth light beam converges on the target and is reflected by the target to generate a third reflected light signal, and the third reflected light signal passes through the measuring objective lens, the first beam splitter, the second beam splitter, the third beam splitter and the imaging lens group in sequence and converges on the photodiode.

[0061] Exemplarily, the second reflected light signal and the third reflected light signal may interfere with each other on a photodiode to generate an interference signal, and the intensity of the interference signal reflects the optical path difference between the reference arm and the measuring arm formed when the monochromatic light beam irradiates the target object. The photodiode may transmit the interference signal generated when the measuring lens is located at different positions to the processor, and the processor may determine the optical path difference between the reference arm and the measuring arm based on the intensity of the interference signal and generate an interference signal curve. The processor may obtain the position of the measuring lens corresponding to the peak value of the interference signal intensity by performing algorithm processing on the light beam interference signal curve, at which time the optical path difference between the reference arm and the measuring arm is zero, and the position may also be used to indicate the focusing position of the measuring lens. Therefore, the processor may determine the second defocus amount by obtaining the difference between the focusing position and the initial position of the measuring lens. By adopting the present application, the interference principle and light signal analysis may be utilized to accurately measure the position change of the interference unit or the measuring lens to achieve high-precision determination of the defocus amount of the target object.

[0062] To facilitate understanding of the process of obtaining the first defocus amount of the target object by the first defocus determination module based on the third beam splitter, the second beam splitter, the first beam splitter and the measuring objective lens, please refer to Figure 4 , Figure 4 is a schematic diagram of the optical path of the first light beam provided in this application. Figure 4 As shown, the optical path of the first light beam includes a first beam splitter, a second beam splitter, a third beam splitter and a measuring objective lens. The first light beam emitted by the first defocus determination module passes through the third beam splitter, the second beam splitter, the third beam splitter and the measuring objective lens in sequence and converges to the target object, and is reflected by the target object to generate a first reflected light signal, and the first reflected light signal passes through the measuring objective lens, the first beam splitter, the second beam splitter and the third beam splitter in sequence and returns to the first defocus determination module. 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 components in the second defocus determination module are not shown. With the present application, through the introduction of the third beam splitter and the parallel layout of the fourth optical axis and the first optical axis, the image acquisition system can more effectively separate and merge light beams in different directions, avoiding mutual interference between light beams in different directions, which not only improves the clarity of image acquisition, but also enhances the stability and reliability of the image acquisition system.

[0063] In some possible implementations, such as Figure 2 As shown, the first movement control module includes a first control unit and a first driving unit. Figure 3 to Figure 4On the basis of the implementation of the first defocus determination module, the second defocus determination module and the image acquisition module shown, the implementation of the first mobile control module including the first control unit and the first driving unit is still applicable. Here, the first driving unit may be a fine-tuning motor, a motion stage and other equipment, and the first control unit may be a motor controller, a motion stage controller and other equipment. It can be understood that the first control unit may include multiple independent controllers, or a controller integrating multiple controller functions, which is not limited in the present application, wherein the controller may be a central processing unit (CPU), a microcontroller unit (MCU) and other chips. The first control unit may 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 is used to control the second light emitting unit and the interference unit to move in the first direction by the distance indicated by the motion control instruction (or other types of control instructions). The above-mentioned first driving unit is connected to the second light emitting unit and the interference unit, so the first driving unit can simultaneously drive the second light emitting unit and the interference unit to move in the first direction, 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 focus of the target object. The above-mentioned first control unit can receive the first defocus amount and the second defocus amount, so that when the first defocus amount is received, the first driving unit can be controlled to drive the second light emitting unit to move in the first direction based on the first defocus amount, and when the second defocus amount is received, the first driving unit can be controlled to drive the second light emitting unit to move in the first direction based on the second defocus amount. Exemplarily, 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 a distance corresponding to the first defocus amount in the first direction. If the measuring objective lens and the target object are placed in a vertical direction in space (for example, the measuring objective lens is above the target object), the above-mentioned first direction may be the vertical direction in space; if the measuring objective lens and the target object are placed in a horizontal direction in space (for example, the measuring objective lens is to the right of the target object), the above-mentioned first direction may be the horizontal direction in space, or, the above-mentioned first direction may be the direction of other specific angles, which should be determined according to the actual product form, and this application does not limit it. Optionally, when the first drive unit completes the movement, a first in-position signal may be sent to the image acquisition module, and the above-mentioned first in-position 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. With the present application, through the introduction of the first control unit and the first drive 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 preset target motion trajectory and speed, thereby improving the accuracy and stability of determining the second defocus amount.

[0064] In some feasible embodiments, the first mobile control module may be connected to the target. When the target is not in the preset position, the first mobile control module may control the target to move in the second direction so that the target moves to the preset position. Wherein, the second direction is a plane perpendicular to the first direction. The preset position may be determined according to the target motion trajectory of the target, 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 may be a horizontal direction in space; conversely, if the first direction is a horizontal direction in space, the second direction may be a vertical direction in space, or the first direction and the second direction may be directions at other angles, which are not limited in this application. Exemplarily, the first mobile control module may transmit a motion control instruction to the first drive unit through the first control unit based on the preset position to trigger the first drive unit to control the target to move to the preset position in the second direction. With this application, through the connection between the first mobile control module and the target, the image acquisition system can detect the current position of the target and determine whether the target is in the preset position. If the target object is not at 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 of image acquisition and reducing manual intervention.

[0065] In some possible implementations, such as Figure 2 As shown, the above image acquisition system may further include a second mobile control module. Figure 3 to Figure 4 Based on the implementation of the first defocus determination module, the second defocus determination module and the image acquisition module shown, it is still applicable that the image acquisition system also includes a second mobile control module. The second mobile control module can also be connected to the target. When the above-mentioned target is not in the preset position, the second mobile control module can be used to control the target to move in the second direction so that the target is in the preset position. With the present application, by introducing the second mobile control module, the image acquisition system has two independent control mechanisms to ensure that the target can be accurately moved to the preset position. This dual protection mechanism improves the accuracy and reliability of positioning. When a failure or error occurs in the first mobile control module or the second mobile control module, the other module can ensure the correct positioning of the target.

[0066] In some feasible embodiments, the second mobile control module may include a second control unit and a second drive unit, the second control unit is connected to the second drive unit, the second drive unit is connected to the target, and the second control unit is used to control the second drive unit to drive the target to move in the second direction. The second control unit may be a device such as a motion controller, and the second drive unit may be a device such as a motion stage that can carry the target to move. Exemplarily, the second control unit may be a motion controller, and the second drive unit may be a motion stage. The motion stage is connected to the target and can be used to load the target and carry the target to move. The motion stage may be an X / Z / Theta axis motion stage, or other motion stages that can load the target. This application does not limit this. Take the X / Z / Theta axis motion stage as an example: its movement directions are X-axis (lateral translation), Z-axis (vertical lifting) and Theta axis (rotation around the central axis). The motion stage can be used to load wafers and adjust the wafer position by movement. Optionally, the motion stage may also include a Y-axis motion stage, which can load wafers to move the wafers longitudinally. In this application, the motion stage is responsible for carrying the target object to move in the X-axis and Y-axis directions.

[0067] In some feasible embodiments, the motion controller may send a motion control instruction of the motion stage to the motion stage to drive the motion stage to move in a second direction, wherein the second direction is a plane perpendicular to the first direction. The motion control instruction may be used to indicate a preset target motion trajectory, wherein the target motion trajectory includes at least one preset position, and the motion stage may carry the target object and sequentially pass through at least one preset position in the target motion trajectory according to the target motion trajectory. The second motion control module is integrated with a second control unit and a second drive unit, wherein the second control unit is capable of sending precise instructions, and the second drive unit is capable of accurately converting these instructions into actual movement of the target object, thereby ensuring that the target object can be accurately positioned at the preset position, thereby achieving precise control of the movement of the target object in the second direction.

[0068] In some feasible embodiments, the image acquisition module may include an image acquisition device and a position determination module, and the position determination module is used to determine whether the target is in the preset position according to the first image. Exemplarily, the position determination module can be used to receive the first image transmitted by an image acquisition device such as a camera, and determine whether the target is in the preset position according to the first image. Optionally, when the position determination module detects that the second drive unit moves to the preset position, it can generate a control signal (such as a second in-place signal) indicating that the focus is completed, and the second in-place signal is used to indicate that the movement of the target in the second direction has been completed. When the position determination module obtains the first in-place signal and the second in-place signal, it can trigger an image acquisition device such as a camera to capture the image of the target to generate a second image. The position determination module can accurately analyze the first image to identify the current position of the target, and compare the current position with the preset position, so as to accurately determine whether the target is in the preset position. With the present application, by accurately analyzing the first image, the position determination module can identify the current position of the target and compare it with the preset position, thereby ensuring that the target is accurately positioned and improving the accuracy of the target image acquisition.

[0069] In some feasible embodiments, a graphic mark is provided on the target object, and when the graphic mark is at the center of the field of view of the above-mentioned image acquisition module, the position of the target object in the second direction is a preset position, wherein the above-mentioned second direction is a plane perpendicular to the above-mentioned first direction. Exemplarily, the above-mentioned position judgment 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 through algorithms such as image recognition. If the imaging position deviation is 0, it indicates that the second drive 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 drive unit to move in the second direction by a distance corresponding to the imaging position deviation. Since the image recognition algorithm runs fast, the present application can improve the positioning accuracy and recognition efficiency of the target object by setting a 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.

[0070] In some feasible embodiments, the first defocus determination module, the second defocus determination module, the first movement control module, the processor or controller in the second movement control module (such as 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.) and the position judgment module in the image acquisition module can be integrated into a focus control module, and the above-mentioned focus control module performs signal processing and control. By adopting the image acquisition system provided by the present application, the first defocus amount of the target object can be acquired at an extremely 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. Based on the first focusing, the second defocus determination module acquires the second defocus amount of the target object with higher accuracy, 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.

[0071] Embodiment 2 The present application also provides an image acquisition method for a measuring device, wherein the measuring device includes: Figures 1 to 4 Any provided image acquisition system, the image acquisition method is applicable to the image acquisition system. In the present application, the image acquisition method can be executed by the focus control module in the above-mentioned image acquisition system as the execution subject, and the focus control module can cooperate with other modules in the image acquisition system to realize image acquisition. For the convenience of description, the focus control module is used as the execution subject for example. Figure 5 , Figure 5 is a flow chart of the image acquisition method provided by this application. Figure 5 As shown, the image acquisition method may include the following steps: Step S101, determining a first defocus amount of a target object.

[0072] In some feasible implementations, the target object may be carried by the second mobile control module and move with the second mobile control module in the second direction based on the target motion trajectory to sequentially pass through a plurality of preset positions in the target motion trajectory. When the target object reaches the preset position, the focus control module may trigger the focus and image acquisition of the target object.

[0073] In some feasible implementations, the focus control module may generate a focus tracking control instruction to trigger the first defocus determination module to emit a first light beam, and obtain the first defocus amount of the target object through the first defocus determination module, wherein the first defocus amount of the target object can be obtained by analyzing the beam data of the first light beam returned by the first defocus determination module, and the above-mentioned beam data includes at least one of the spot size, spot shape, and light intensity signal. Optionally, the focus control module obtains the first defocus amount through the first defocus determination module through artificial intelligence algorithms such as image recognition, for example, the size of the spot is identified through an image recognition algorithm, and then the first defocus amount of the target object is inferred according to the spot size. The above-mentioned first defocus amount can be distinguished in direction by the way of "+" and "-". For example, if the relative distance between the target object and the measuring objective lens is 3mm, the first defocus amount is +1mm, indicating that the focal distance between the target object and the measuring objective lens is 4mm. The above-mentioned "+" and "-" are only used to distinguish the direction, and do not refer to the size of the specific numerical value. The same applies to the following, and no further description is given.

[0074] Optionally, in some feasible implementations, the focus control module may store the data of the first defocus amount that has been obtained to obtain at least two first defocus amounts of the target at at least two preset positions. The focus control module may predict the predicted first defocus amount of the target at the next preset position based on the historical data of the at least two first defocus amounts that have been obtained, so as to trigger the target to move in the first direction based on the predicted first defocus amount before the target reaches the next preset position, so that the target only needs to move a short distance when performing the first focusing, thereby further improving the speed of the first focusing of the target.

[0075] In some feasible embodiments, the measurement device includes a first defocus determination module, the first defocus determination module includes a first light emitting unit and a first light receiving unit, and the method for determining the first defocus amount of the target object includes: controlling the first light emitting unit to emit a first light beam, the first light beam is reflected by the target object to generate a first reflected light signal; based on the first reflected light signal received by the first light receiving unit, determining the first defocus amount of the target object. Exemplarily, in the case where the first defocus determination module includes the first light emitting unit and the first light receiving unit, the focus control module can control the first light emitting unit to emit the first light beam so that the first light beam converges on the target object and generates a first reflected light signal after being reflected by the target object. 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 adopting the present 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 realize fast and efficient determination of the first defocus amount without moving devices in the measuring equipment, thereby shortening the overall error measurement time.

[0076] Exemplarily, if the focus control module includes a focus controller, the focus control module can trigger the first defocus determination module to emit the first light beam through the focus controller. For example, the focus control module can generate a focus tracking control instruction through the focus controller in the focus control module, and send the above focus tracking control instruction to the first defocus determination module to trigger the first defocus determination module to emit the first light beam. Furthermore, the focus controller can obtain at least two defocus amounts of the target object generated by the first defocus determination module based on the optical path data (such as the size, shape, intensity, etc. of the light spot) indicated by the first reflected light signal returned by the first light beam.

[0077] 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 may use one of the methods of eccentric mask, differential confocal, chopping method, and coaxial laser triangulation to determine the first defocus amount, and this application does not limit it. The specific implementation methods of the eccentric mask, differential confocal, chopping method, and coaxial laser triangulation can be referred to the above Figures 1 to 4 The description in the corresponding embodiment is not repeated here. By adopting the optical measurement methods such as eccentric mask, differential confocal, chopping method, coaxial laser triangulation method, etc., the first defocus amount of the target object can be accurately and quickly determined according to the first reflected light signal, thereby reducing the measurement error and improving the accuracy of the first defocus amount.

[0078] In some feasible implementations, before the focus control module determines the first defocus amount of the target object, the focus control module may calibrate the devices in the image acquisition system, such as the first defocus determination module and the image acquisition module, to ensure the measurement accuracy of the first defocus amount and other data. Exemplarily, the focus control module may calibrate the focal length, resolution and other parameters of the image acquisition device in the image acquisition module through a calibration plate (e.g., a standard grid plate for geometric distortion correction and pixel calibration, a star plate for correcting resolution and focal length), and may also perform image correction through the calibration plate to eliminate the inherent system error of the device due to its own characteristics, and further improve the measurement accuracy of the alignment error.

[0079] Step S102 , based on the first defocus amount, controlling the measuring lens of the target object and the target object to move relative to each other in a first direction, so as to focus the target object for the first time.

[0080] In some feasible implementations, the focus control module may control the measuring objective lens to move relative to the target object in the first direction, or / and control the target object to move relative to the measuring objective lens in the first direction. Exemplarily, the focus control module may control the target object to move in the first direction based on the first defocus amount, and control the measuring objective lens to be stationary to adjust the relative distance between the two; it may also control the target object to be stationary in the first direction, and control the measuring objective lens to move in the first direction to adjust the relative distance between the two; or it may also control both the target object and the measuring objective lens to move in the first direction to adjust the relative distance between the two, thereby focusing the target object for the first time. This application is not limited thereto, and takes controlling the measuring objective lens to move and controlling the target object to be stationary as an example for explanation.

[0081] In some feasible embodiments, before the above-mentioned control of the relative movement between the above-mentioned measuring objective lens and the above-mentioned target object in the first direction, the focus control module may determine the target movement position of the measuring objective lens or the above-mentioned target object based on the above-mentioned first defocus amount. Specifically, the focus control module may obtain the first defocus amount of the target object from the first defocus determination module, and then determine the target movement position of the measuring objective lens based on the above-mentioned first defocus amount, and control the relative movement between the measuring objective lens of the target object and the target object in the first direction based on the target movement position to focus on the target object for the first time. If the target object remains stationary in the first direction, the focus control module may determine the target movement position of the measuring objective lens based on the above-mentioned 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 measuring objective lens is equal to the focal length of the measuring objective lens, the measuring objective lens is located at the target movement position. If the measuring lens and the target are placed in a vertical direction in space (for example, the measuring lens is above the target), the first direction may be the vertical direction in space; if the measuring lens and the target are placed in a horizontal direction in space (for example, the measuring lens is to the right of the target), the first direction may be the horizontal direction in space. By adopting the present application, the target moving position can be determined to avoid inaccurate second focusing caused by excessive or insufficient movement of the measuring lens or the target without predetermining the target moving position. After determining the target moving position, the image acquisition system can directly move the measuring lens or the target to the position without multiple tentative movements and adjustments, which greatly reduces the number and time of movements and further improves the error measurement efficiency of the target.

[0082] For example, if the target remains stationary in the first direction, the first defocus amount of the target at the preset position is +1mm, and the measuring objective lens is located at +3mm of the target, then the target moving position of the measuring objective lens is located at +4mm of the target, and the focus control module can control the measuring objective lens to move +1mm to focus on the target for the first time. Optionally, if the measuring objective lens remains stationary in the first direction, the focus control module can also determine the target moving position of the target, and control the target to move to the target moving position in the first direction so that the relative distance between the target and the measuring objective lens is the focusing distance. Optionally, the focus control module can also determine the target moving position of the target and the measuring objective lens respectively, so that the target and the measuring objective lens are both moved to their respective target moving positions in the first direction, so that the relative distance between the target and the measuring objective lens is the focusing distance, which will not be repeated. The present application allows the measuring objective lens and / or the target to move in the first direction, and the most suitable moving method can be selected to achieve focusing according to the specific measurement scenario and requirements, which has strong applicability.

[0083] In some feasible implementations, the focus control module can detect the focus of the measuring lens and the target in real time during the relative movement of the measuring lens and the target, and the above-mentioned focus situation may include parameters such as the moving speed of the target and / or the measuring lens, the position of the target and / or the measuring lens. By detecting the above-mentioned focus situation in real time, the focus control module can adjust the moving speed and the distance to be moved of the target and / or the measuring lens according to the focus situation, so as to ensure the accuracy of the first focus. Exemplarily, the focus control module can obtain a real-time image of the target through the image acquisition module, and determine whether the target has reached the target moving position (first direction) based on the real-time image of the target, or determine whether the first focus of the target is accurate. If the focus of the target is still inaccurate when it reaches the target moving 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 re-determine the defocus amount to re-focus the target for the first time. When the target object and / or the measuring objective lens reaches the target moving position, it indicates that the first focusing is completed, and the focusing control module can send a control signal (such as a first in-position signal) indicating that the focusing is completed to the image acquisition module to trigger the image acquisition module to capture an image of the target object. Optionally, in some feasible implementations, the focusing control module can also save the real-time image and data of the first focusing completion, and the saved real-time image and data can be used for product updates or other functions.

[0084] By adopting the present application, the focus control module can control the target object and / or the measuring objective lens to move in the first direction by driving the first movement control module to perform a first focus on the target object. The focus accuracy requirement of image processing of the first image can be met by obtaining the first defocus amount of the target object and performing the first focus. There is no need to perform time-consuming white light interference focusing, thereby improving the efficiency of the first focus, reducing the acquisition time of the wafer measurement image, and improving the efficiency of measuring the alignment error of the wafer.

[0085] Step S103 , capturing an image of the target after the first focusing to generate a first image, and using the first image to determine whether the target is at a preset position.

[0086] In some feasible embodiments, the above-mentioned measuring device may include an image acquisition module. Before the above-mentioned target object after the first focusing is imaged, the focus control module may send a control signal of focusing completion to the above-mentioned image acquisition module. The focus control module may trigger the image acquisition module to capture the image of the target object after the target object completes the first focusing to generate a first image. Exemplarily, the focus control module may detect the focus 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 control signal of focusing completion (such as a first in-position signal) is generated and transmitted to the image acquisition module to trigger the image acquisition device to capture the image of the target object. Further, the focus control module may also determine whether the target object is in a preset position based on the first image. Wherein, the target object moves according to a preset target motion trajectory, and the target motion trajectory includes multiple preset positions.

[0087] In some feasible implementations, the target may include a graphic mark, and the focus control module may determine whether the target is in a preset position through a position judgment module. The focus control module may determine whether the graphic mark is located at the center of the field of view of the image acquisition module; if the graphic mark is located at the center of the field of view of the image acquisition module, it is determined that the target is in the preset position. Exemplarily, the focus control module may obtain the imaging position deviation between the graphic mark of the target and the center of the field of view of the image acquisition module through the position judgment module.

[0088] In some feasible embodiments, the imaging position of the graphic mark of the target object and the field of view center of the image acquisition module can be recorded in the form of coordinates. For example, the field of view center of the image acquisition module can be recorded as (0, 0). 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 semi-axis direction of the horizontal axis of the field of view center of the image acquisition module, and is located at a unit length in the negative semi-axis direction of the vertical axis of the field of view center 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 method of the above imaging position, the field of view center of the image acquisition module and the imaging position deviation is not limited to the recording method provided in the present application, and the present application does not impose any restrictions. The deviation of the target object in the second direction can be determined by the above imaging position deviation. If the above imaging position deviation is 0, that is, the imaging position of the target is located at the center of the field of view of the image acquisition module, the focus control module determines that the target is at the preset position; if the above imaging position deviation is not 0, that is, the imaging position of the target is not located at the center of the field of view of the image acquisition module, the focus control module determines that the target is not at the preset position. With the present application, the introduction of graphic marks provides an intuitive visual basis for the position judgment of the target, which can more accurately determine the current position of the target, reduce the positioning error of the target, and improve the positioning accuracy of the target.

[0089] In some feasible implementations, if the focus control module determines that the target object is not in the preset position, the first mobile control module or the second mobile control module may 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 in the preset position. Exemplarily, if the imaging position deviation is identified as (+1, -1), the focus control module may trigger the first mobile control module or the second mobile control module to control the target object to move one unit length in the negative semi-axis direction of the horizontal axis of the field of view center of the image acquisition module, and to move one unit length in the positive semi-axis direction of the vertical axis of the field of view center of the image acquisition module. By adopting the present application, by controlling the target object to move in the second direction, the measurement error caused by directly performing the second focus and image acquisition when the target object is not in the preset position can be eliminated, thereby further improving the accuracy and reliability of the error measurement of the target object.

[0090] In some feasible implementations, the focus control module can obtain a real-time image of the target object through the image acquisition module. Before capturing the image of the above-mentioned target object after the first focus, the focus control module can detect whether the image acquisition device in the image acquisition module is in a good state, such as determining whether the lens of the image acquisition device is uncontaminated (which can be determined by whether there are foreign objects in the real-time image), whether parameters such as focal length have been calibrated (which can be determined by the focus blur of the real-time image), etc. The focus control module can also detect whether the lighting conditions of the light source in the first defocus determination module are suitable for image acquisition to avoid overexposure or underexposure. The focus control module can also set the field of view center of the image acquisition module. For example, when the image acquisition module acquires a real-time image of the target object, if the target object is located at a specific position in the real-time image (i.e., the center of the field of view), it indicates that the target object has reached a preset position.

[0091] In some feasible implementations, during the process of the focus control module controlling the image acquisition module to collect images of the target object after the first focusing, the focus control module can detect the image quality of the collected real-time image. If the quality of the real-time image does not meet the requirements (such as image blur, image overexposure, image underexposure, etc.), the focus control module can readjust the relative distance between the target object and the measurement objective lens through the first mobile control module to refocus.

[0092] In some feasible implementations, since there may be motion deviations during the movement of the target object and / or the measuring objective lens, the focus control module may detect whether the target object meets the acquisition requirements of the second image after moving to the preset position through the first image after generating the first image. If it does not meet the requirements, the preset position of the target object may be re-determined, the parameters of the equipment in the image acquisition system may be re-adjusted, or the focus may be re-performed. Exemplarily, 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 the image is overexposed or underexposed), the focus control module may adjust the illumination parameters of the image acquisition module in the image acquisition system. If the field of view offset and angle deviation of the target object do not meet the requirements, the focus control module may re-determine the preset position and trigger the first mobile control module or the second mobile control module to control the target object to move to the above-mentioned re-determined preset position. If the focus accuracy does not meet the requirements after the target object moves again, the focus control module may re-focus the target object.

[0093] Step S104, after determining that the target object is at a preset position, obtaining a second defocus value of the target object.

[0094] In some feasible implementations, the focus control module may trigger the second defocus determination module to obtain a second defocus amount of the target object after determining that the target object is at a preset position. The second defocus determination module may emit a second light beam to generate a third light beam and a fourth light beam, the third light beam converges on a reference reflector and is reflected by the reference reflector 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 may 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 the third reflected light signal.

[0095] In some feasible embodiments, the measuring device includes a first 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 spectrometer and a reference reflector, and obtaining the second defocus amount of the target object includes: in the process of controlling the interference unit and the measuring objective lens to move relative to the target object in a first direction, controlling the second light emitting unit 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 spectrometer, the third light beam generates a second reflected light signal after being reflected by the reference reflector, and the fourth light beam generates a third reflected light signal after being reflected by the target object; 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 of the target object. Exemplarily, on the basis that the second defocus determination module may include a second light emitting unit, an interference unit, and a second light receiving unit, if the interference unit includes a collimating lens, and the second light beam emitted by the light source in the second light emitting unit is a monochromatic light beam, then the monochromatic light beam can generate an illumination collimated light path after passing through the collimating lens, and the illumination collimated light path is divided into two light beams after passing through the first beam splitter, one of which (such as the fourth light beam) converges on the target object (such as the target wafer) after passing through the measuring objective lens, and the other light beam (such as the third light beam) converges on the reference reflector after passing through the reference objective lens. The third light beam generates a second reflected light signal after being reflected by the reference reflector, and the fourth light beam generates a third reflected light signal after being reflected by the target object. 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. By adopting the present application, through the principle of optical interference, high-precision measurement of the second defocus amount of the target object is achieved, which can further improve the focusing accuracy of the second focusing.

[0096] In some feasible 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 includes: determining the first in-focus position of the interference unit or the measuring 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 in-focus position and the initial position of the interference unit or the measuring objective lens. Exemplarily, on the basis that the above-mentioned image acquisition system may also include a second beam splitter and a third beam splitter, if the above-mentioned image acquisition system includes an imaging lens group, the monochromatic light beam converges on the target object and is reflected by the target object, and then converges on the photodiode to generate a second reflected light signal after passing through the measuring objective lens, the first beam splitter, the second beam splitter, the third beam splitter and the imaging lens group in sequence; the monochromatic light beam converges on the reference reflector and is reflected by the reference reflector, and then converges on the photodiode in the second light signal receiving unit after passing through the reference objective lens, the first beam splitter, the second beam splitter, the third beam splitter and the imaging lens group in sequence to generate a third reflected light signal. The above-mentioned second reflected light signal and the third reflected light signal may interfere on the photodiode to generate an interference signal, and the intensity of the above-mentioned interference signal reflects the optical path difference between the reference arm and the measuring arm formed when the monochromatic light beam irradiates the target object. In the process of the interference unit determining the second defocus amount of the target object, the focus control module may also trigger the first movement control module to control the above-mentioned interference unit and the measuring objective lens to move a preset distance. The above-mentioned preset distance is the predicted distance between the focal position of the measuring lens and the initial position of the measuring lens, and should be determined according to the actual product form. In the process of controlling the interference unit and the measuring 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 measuring lens is located at different positions, and determine the optical path difference between the reference arm and the measuring arm by the intensity of the interference signal and generate an interference signal curve. The focus control module can obtain the position of the measuring lens corresponding to the peak value of the interference signal intensity by performing algorithm processing on the light beam interference signal curve. At this time, the optical path difference between the reference arm and the measuring arm is zero, and this position can also be used to indicate the focal position of the measuring lens. Therefore, the focus control module can determine the second defocus amount by obtaining the difference between the above-mentioned focal position and the initial position of the measuring lens. Among them, the determination speed of the first defocus amount is greater than the determination speed of the second defocus amount. With the present application, the interference principle and light signal analysis can be used to accurately measure the position change of the interference unit or the measuring lens to achieve high-precision determination of the defocus amount of the target object.

[0097] Step S105 , based on the second defocus amount, controlling the measuring lens and the target object to move relative to each other in a first direction, so as to perform a second focusing on the target object.

[0098] In some feasible implementations, the focus control module may transmit the second defocus amount to the first mobile control module to trigger the first mobile control module to control the relative movement between the measuring lens and the target object in the first direction. For example, the focus control module triggers the first mobile control module to determine the moving speed, moving distance, and focusing accuracy of the measuring lens and / or the target object based on the second defocus amount. Exemplarily, taking the first mobile control module determining the moving distance of the measuring lens and / or the target object as an example, if the second defocus amount is +1mm, it indicates that the relative distance between the measuring lens and the target object is greater than the focusing distance of the measuring lens of 1mm, so the measuring lens and the target object need to move 1mm relative to each other in the first direction. Optionally, the focus control module can trigger the first movement control module to control the measuring objective lens to move 1 mm relative to the target object, while the target object remains stationary in the first direction; it can also control the target object to move 1 mm relative to the measuring objective lens, while the measuring objective lens remains stationary; or separately control the target object and the measuring objective lens to move relative to each other, so that the sum of their moving distances is 1 mm. This should be determined based on the actual product form and is not limited in this application.

[0099] In some feasible implementations, before the above-mentioned target object after the second focusing is imaged, the focus control module may send a control signal indicating that the focus is completed to the above-mentioned image acquisition module. Exemplarily, when the above-mentioned target object and the measuring objective lens move relative to each other until the relative distance between the target object and the measuring objective lens is equal to the focal distance, it indicates that the second focusing of the target object is completed. The focus control module may send a control signal indicating that the focus is completed to the image acquisition module to trigger the image acquisition module to capture the image of the target object.

[0100] In some feasible implementations, during the process in which the first movement control module controls the relative movement between the measuring lens and the target object in the first direction, the focus control module can detect the focus state of the target object and the measuring lens in real time (for example, by obtaining a real-time image of the target object), thereby ensuring the accuracy and stability of the movement. The focus control module can also adjust the moving speed and / or moving distance of the target object and / or the measuring lens in a timely manner according to the focus state to ensure that the image acquisition system can capture the best focusing position of the target object and / or the measuring lens. If the focus control system detects that the focus is inaccurate (for example, as the target object and the measuring lens move relative to each other, the focus blur of the real-time image is higher) or the imaging quality of the real-time image is poor (such as overexposure or underexposure of the image), the focus control system can adjust the parameters of the equipment in the image acquisition system in a timely manner or refocus.

[0101] In some feasible implementations, the focus control module may also perform an imaging quality assessment on the second image obtained after the second focusing is completed. If the imaging quality assessment of the second image does not meet the requirements, the parameters of the device in the image acquisition system may be adjusted again or the focus may be re-performed to reacquire the second image.

[0102] In summary, before capturing an image of the target object after the first focusing or before capturing an image of the target object after the second focusing, the focus control module may send a control signal indicating that focusing is completed to the image acquisition module. By adopting the present application, by sending a control signal indicating that focusing is completed, it is possible to ensure that the image acquisition module performs image capture only after the first focusing or the second focusing is completed, thereby avoiding image blur or distortion problems caused by incomplete focusing and improving the accuracy and quality of image acquisition.

[0103] Step S106, capturing an image of the target object after the second focusing to generate a second image.

[0104] In some feasible implementations, the focus control module may trigger the image acquisition module to capture an image of the target object through a control signal indicating that the focus is completed, so as to generate a second image with a higher resolution than the first image.

[0105] By adopting the present application, the first defocus amount of the target object can be obtained at an extremely 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. Based on the first focusing, the second defocus determination module obtains the second defocus amount of the target object with higher accuracy, so that the second image captured 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.

[0106] Those skilled in the art will appreciate that the systems and algorithm steps of each example described in conjunction with the embodiments disclosed herein can be implemented with electronic hardware, computer software, or a combination of the two. In order to clearly illustrate the interchangeability of hardware and software, the composition and steps of each example have been generally described in terms of function in the above description. Professional and technical personnel may use different methods to implement the described functions for each specific application, but such implementation should not be considered beyond the scope of this application.

Claims

1. An image acquisition system for a measuring device, characterized in that: include: A first defocus determination module, used to determine a first defocus amount of the target object; A second defocus determination module, used to determine a second defocus amount of the target object; a first movement control module, configured to control the measuring lens of the target object to move relative to the target object in a first direction according to the first defocus amount, so as to focus on the target object for a first time, and to control the measuring lens of the target object to move relative to the target object in the first direction according to the second defocus amount, so as to focus on the target object for a second time; An image acquisition module is used to collect an image of the target object after the first focusing to generate a first image, wherein the first image is used to determine whether the target object is at a preset position; and for, after determining that the target object is at the preset position, capturing an image of the target object after the second focusing to generate a second image; Wherein, a speed of determining the first defocus amount is greater than a speed of determining the second defocus amount, and a resolution of the first image is smaller than a resolution of the second image.

2. The image acquisition system according to claim 1, characterized in that: The first defocus determination module includes a first light emitting unit and a first light receiving unit. In the process of determining the first defocus amount of the target object, the first light emitting unit is used to emit a first light beam, and the first light beam generates a first reflected light signal after being reflected by the target object. The first light receiving unit is used to determine the first defocus amount of the target object based on the received first reflected light signal.

3. The image acquisition system according to claim 2, characterized in that: The first defocus determination module uses one of an eccentric mask, differential confocal, a chopping method, and a coaxial laser triangulation method to determine the first defocus amount.

4. The image acquisition system according to any one of claims 1 to 3, characterized in that: The second defocus determination module comprises a second light emitting unit, an interference unit and a second light receiving unit, the interference unit is fixedly connected to the measuring objective lens, and the interference unit comprises a first beam splitter and a reference reflector; The second light emitting unit is used 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 reflector, 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 to control the interference unit and the measuring lens to move a preset distance during the process of the interference unit determining the second defocus amount of the target object; In the process of controlling the interference unit and the measuring objective lens to move from an initial position to a 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 interference unit and the measuring objective lens are at different positions, and determine the second defocus amount based on the second reflected light signal and the third reflected light signal.

5. The image acquisition system according to claim 4, characterized in that: The second light signal receiving unit is used to determine the second position of the interference unit or the measuring objective lens when the image acquisition module is in a focusing state according to the second reflected light signal and the third reflected light signal received when the interference unit and the measuring 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 measuring objective lens.

6. The image acquisition system according to claim 4, characterized in that: The first movement control module includes a first control unit and a first driving unit, the first driving unit is connected to the second light emitting unit and the interference unit, and the first control unit is used 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 according to claim 4, characterized in that: The image acquisition system includes a second beam splitter, the target object, the measuring 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 reflector are located on a second optical axis, wherein the first optical axis is perpendicular to the second optical axis.

8. The image acquisition system according to claim 7, characterized in that: 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, the third beam splitter and the first defocus determination module are located on a fourth optical axis, wherein 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 according to any one of claims 1 to 3, characterized in that: The first movement control module is connected to the target object. When the target object is not in the preset position, the first movement control module is used to control the target object to move in a second direction so that the target object is in the preset position, wherein the second direction is a plane perpendicular to the first direction.

10. The image acquisition system according to any one of claims 1 to 3, characterized in that: The image acquisition system also includes a second mobile control module, which is connected to the target object; when the target object is not in the preset position, the second mobile control module is used to control the target object to move in a second direction so that the target object is in the preset position.

11. The image acquisition system according to any one of claims 1 to 3, characterized in that: The second mobile control module includes 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, and the second control unit is used to control the second driving unit to drive the target object to move in a second direction, wherein the second direction is a plane perpendicular to the first direction.

12. The image acquisition system according to any one of claims 1 to 3, characterized in that: The image acquisition module further includes a position determination module, and the position determination module is used to determine whether the target object is at the preset position according to the first image.

13. The image acquisition system according to any one of claims 1 to 3, characterized in that: A graphic mark is provided on the target object, and the preset position is the position of the target object in a 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.

14. An image acquisition method for a measuring device, characterized in that: include: Determining a first defocus amount of the target object; Based on the first defocus amount, controlling a measuring lens of the target object and the target object to move relative to each other in a first direction, so as to focus the target object for the first time; Capturing an image of the target after the first focusing to generate a first image, and using the first image to determine whether the target is at a preset position; After determining that the target object is at a preset position, obtaining a second defocus value of the target object; Based on the second defocus amount, controlling the measuring objective lens and the target object to move relative to each other in a first direction, so as to perform a second focusing on the target object; Capturing an image of the target object after the second focusing to generate a second image; Wherein, a speed of determining the first defocus amount is greater than a speed of determining the second defocus amount, and a resolution of the first image is smaller than a resolution of the second image.

15. The image acquisition method according to claim 14, characterized in that: The measuring device includes a first defocus determination module, the first defocus determination module includes a first light emitting unit and a first light receiving unit, and the method for determining a first defocus amount of a target object includes: Controlling the first light emitting unit to emit a first light beam, wherein the first light beam is reflected by the target object to generate a first reflected light signal; A first defocus amount of the target object is determined based on the first reflected light signal received by the first light receiving unit.

16. The image acquisition method according to claim 15, characterized in that: The method for determining a first defocus amount of the target object based on the first reflected light signal received by the first light receiving unit includes: The first defocus amount is determined according to the first reflected light signal by using one of an eccentric mask, differential confocal, a chopping method, and a coaxial laser triangulation method.

17. The image acquisition method according to any one of claims 14 to 16, characterized in that: The measuring 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 reflector, and obtaining the second defocus value of the target object includes: In the process of controlling the interference unit and the measuring objective lens to move relative to the target object in the first direction, controlling the second light emitting unit 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 reflector, and the fourth light beam generates a third reflected light signal after being reflected by the target object; A second defocus amount of the object is determined 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 according to claim 17, characterized in that: The method for determining a 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: Based on the second reflected light signal and the third reflected light signal received by the second light receiving unit, determining the focusing position of the interference unit or the measuring objective lens when the image acquisition module is in a focusing state; The second defocus amount is determined according to the focus position and an initial position of the interference unit or the measuring objective lens.

19. The image acquisition method according to any one of claims 14 to 16, characterized in that: Before controlling the measuring objective lens and the target object to move relative to each other in the first direction, the method includes: Based on the first defocus amount, a target movement position of the measuring objective lens or the target object is determined.

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 measuring lens of the target and the target in a first direction comprises: The measuring lens is controlled to move relative to the target object in a first direction, or / and the target object is controlled to move relative to the measuring lens in the first direction.

21. The image acquisition method according to any one of claims 14 to 16, characterized in that: After determining that the target object is not at the preset position, the method includes: The target object is controlled to move relative to the measuring lens in a second direction so that the target object is at a preset position.

22. The image acquisition method according to any one of claims 14 to 16, characterized in that: The measuring device includes an image acquisition module, which includes: A control signal indicating that focusing is completed is sent 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, and determining whether the target object is at a preset position includes: Determining whether the graphic mark is located at the center of the field of view of the image acquisition module; If the graphic mark is located 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.

Images