Overlay measurement method, device, equipment and storage medium

Abstract

The present application discloses an overlay measurement method, device, equipment and storage medium, and relates to the field of overlay measurement technology. The present application is applied to a controller of an imaging overlay measurement device, which responds to a test instruction for a wafer to be tested, moves the focal plane to multiple test positions, and obtains overlay measurement data corresponding to each test position respectively; according to each overlay measurement data, determines the focal plane corresponding to each test position, which is used to evaluate the measurement effect evaluation factor when the focal plane is located at the test position; according to the influence of the test position change on the measurement effect reflected by all evaluation factors, determines the target focal plane position that matches the wafer to be tested; controls the focal plane to adjust to the target focal plane position, and controls the imaging overlay measurement device to perform overlay measurement on the overlay mark in the wafer to be tested. The evaluation parameters of the present application integrate the measurement effect of the overlay measurement, so that the focal plane position finally adjusted can take into account the accuracy of the overlay measurement.

Description

Technical Field

[0001] The present application relates to the technical field of overlay measurement, and more specifically, to an overlay measurement method, device, equipment and storage medium. Background Art

[0002] Imaging overlay measurement uses a large numerical aperture objective to image the overlay mark, and uses the center deviation of the inner and outer overlay marks in the image to calculate the overlay value. Different imaging effects will result in different accuracy of the calculated overlay value. Usually, the objective lens used in imaging overlay measurement has a high-magnification imaging system with a numerical aperture of more than 0.5NA. The focal depth of the imaging system is usually only a few hundred nanometers. Therefore, the focal plane position determines the clarity, size ratio, and imaging surface shape of the image, which affects the measurement result of the overlay value.

[0003] In the prior art, the focal plane is usually adjusted by image contrast or white light interferometer, and the focal plane position with the best contrast or feedback from the white light interferometer is used as the focal plane position for overlay measurement. However, in reality, the focal plane position with the best overlay measurement performance may not be the focal plane position with the best image contrast or the focal plane position measured by the white light interferometer, and there is often a deviation between the two.

[0004] Based on this, there is an urgent need for a method for determining the focal plane position so that the accuracy of the overlay value measured by the imaging overlay measurement device at the focal plane position is optimal. Summary of the invention

[0005] In view of the above problems, the present application provides an overlay measurement method, device, equipment and storage medium to adjust the focal plane to the position with the best measurement effect and improve the overlay measurement accuracy of the imaging overlay measurement device. The specific scheme is as follows:

[0006] In a first aspect, the present application provides an overlay measurement method, which is applied to a controller of an imaging overlay measurement device. The overlay measurement method includes:

[0007] In response to the test instruction, a plurality of test positions are acquired, wherein the test positions are positions within a preset range of an initial position of a pre-calibrated focal plane;

[0008] Control the focal plane to move to each of the test positions in sequence to perform overlay measurement on the wafer to be tested, and respectively obtain overlay measurement data corresponding to each of the test positions;

[0009] Determine, according to each of the overlay measurement data, an evaluation factor corresponding to the focal plane at each of the test positions, wherein the evaluation factor is used to evaluate a measurement effect when the focal plane is located at the test position;

[0010] Determining a target focal plane position that matches the wafer to be tested according to the influence of the test position change on the measurement effect reflected by all the evaluation factors;

[0011] The focal plane is controlled to be adjusted to the target focal plane position, and the imaging overlay measurement device is controlled to perform overlay measurement on the overlay mark in the wafer to be measured.

[0012] In a possible implementation, the evaluation factors include at least: an imaging effect factor and an overlay measurement factor;

[0013] The imaging effect factor is a parameter characterizing the imaging effect of the image obtained by the focal plane at the test position, and the overlay measurement factor is a parameter characterizing the measurement effect of the focal plane of the imaging overlay measurement device at the test position.

[0014] In a possible implementation, the imaging effect factor includes: image contrast, and the overlay measurement factor includes: measurement accuracy and measurement uncertainty;

[0015] The image contrast represents the clarity of the image at the test position, the measurement accuracy represents the accuracy of the overlay value measured at the test position, and the measurement uncertainty represents the stability of the overlay measurement at the test position.

[0016] In a possible implementation, determining the measurement accuracy corresponding to the focal plane at the test position according to the overlay measurement data includes:

[0017] From the overlay measurement data, obtaining an overlay value of each overlay mark in the wafer to be tested at the test position;

[0018] Calling a pre-established overlay value compensation model, processing the test position and the overlay value of each overlay mark at the test position, and obtaining a theoretical overlay value corresponding to each overlay mark, wherein the overlay value compensation model is used to perform data fitting on the test position and the overlay value of the overlay mark, and determine the theoretical overlay value at the test position;

[0019] Determine the difference between the overlay value corresponding to each overlay mark and the theoretical overlay value as the overlay value accuracy rate corresponding to each overlay mark;

[0020] The average value of all the overlay value accuracy is determined as the measurement accuracy corresponding to the test position.

[0021] In a possible implementation, determining the image contrast corresponding to the focal plane at the test position according to the overlay measurement data includes:

[0022] acquiring an image of each overlay mark from the overlay measurement data;

[0023] Identify the grayscale value in the ROI area in the image of the overlay mark, and obtain the maximum grayscale value and the minimum grayscale value in the ROI area;

[0024] Determine the quotient of the difference between the maximum grayscale value and the minimum grayscale value and the total value as the contrast corresponding to the image of the overlay mark;

[0025] The average value of the contrasts corresponding to the images of all the overlay marks is determined as the image contrast corresponding to the test position.

[0026] In a possible implementation, determining the measurement uncertainty corresponding to the focal plane at the test position according to the overlay measurement data includes:

[0027] From the overlay measurement data, obtaining an overlay value of each overlay mark in the wafer to be tested at the test position, the overlay value at least comprising: an overlay value in a first direction and an overlay value in a second direction;

[0028] Based on the overlay value in the first direction corresponding to each of the overlay marks, determine a first device error parameter in the first direction and a first repeatability parameter of the overlay value, wherein the first device error parameter is a parameter characterizing an average level and a degree of fluctuation of a measurement error introduced by the focal plane, and the first repeatability parameter is a parameter value characterizing a repetition rate and a degree of discreteness of the overlay value in all the overlay values ​​in the first direction;

[0029] Determine a first measurement uncertainty corresponding to the first direction according to the first device error parameter and the first repeatability parameter, wherein the first measurement uncertainty is used to characterize the stability of the overlay measurement in the first direction of the test position;

[0030] Determine, based on the overlay value in the second direction corresponding to each of the overlay marks, a second device error parameter in the second direction and a second repeatability parameter of the overlay value;

[0031] determining a second measurement uncertainty corresponding to the second direction according to the second device error parameter and the second repeatability parameter;

[0032] An average of the first measurement uncertainty and the second measurement uncertainty is determined as the measurement uncertainty corresponding to the test position.

[0033] In one possible implementation, the evaluation factor is a performance parameter corresponding to the test position determined based on the weight values ​​corresponding to the measurement uncertainty, the measurement accuracy and the image contrast respectively contained in the evaluation factor, and the weight value represents the influence of the measurement uncertainty or the measurement accuracy or the image contrast on the overlay measurement result.

[0034] In a possible implementation, determining the target focal plane position matching the wafer to be tested according to the influence of the test position change reflected by all the evaluation factors on the measurement effect includes:

[0035] Performing data fitting on each of the test positions and the performance parameters corresponding to each of the test positions to obtain an objective function corresponding to the wafer to be tested, wherein the objective function represents a functional relationship between the test position and the performance parameters corresponding to the wafer to be tested;

[0036] The test position corresponding to when the performance parameter in the objective function is at a maximum value is determined as the target focal plane position corresponding to the wafer to be tested.

[0037] In a possible implementation, obtaining multiple test positions includes:

[0038] Obtaining a pre-calibrated initial position of the focal plane;

[0039] The initial position is adjusted according to a preset step distance to obtain a preset number of test positions.

[0040] A second aspect of the present application provides an overlay measurement device, which is applied to a controller of an imaging overlay measurement device, and the overlay measurement device comprises:

[0041] A test position acquisition unit, configured to acquire a plurality of test positions in response to a test instruction, wherein the test positions are positions within a preset range of an initial position of a pre-calibrated focal plane;

[0042] A measurement data acquisition unit, used for controlling the focal plane to move to each of the test positions in sequence to perform overlay measurement on the wafer to be measured, and respectively acquiring overlay measurement data corresponding to each of the test positions;

[0043] An evaluation factor determination unit, used to determine the evaluation factor corresponding to the focal plane at each of the test positions according to each of the overlay measurement data, wherein the evaluation factor is used to evaluate the measurement effect when the focal plane is located at the test position;

[0044] A target position determination unit, configured to determine a target focal plane position that matches the wafer to be tested according to the influence of the test position change reflected by all the evaluation factors on the measurement effect;

[0045] The control and measurement unit is used to control the focal plane to adjust to the target focal plane position, and control the imaging overlay measurement device to perform overlay measurement on the overlay mark in the wafer to be measured.

[0046] In a third aspect, the present application provides an overlay measurement device, comprising at least one processor and a memory connected to the processor, wherein:

[0047] The memory is used to store computer programs;

[0048] The processor is used to execute the computer program so that the overlay measurement device can implement any one of the overlay measurement methods.

[0049] A fourth aspect of the present application provides a computer storage medium, which carries one or more computer programs. When the one or more computer programs are executed by an overlay measurement device, the overlay measurement device can implement any one of the overlay measurement methods.

[0050] It can be seen from the above technical solutions that the overlay measurement method provided in the embodiment of the present application responds to the test instructions for the wafer to be tested, moves the focal plane to multiple test positions, obtains the evaluation factors of the measurement effect for overlay measurement corresponding to each measurement position, and determines the best measurement position for the best measurement effect of the wafer to be tested, that is, the target focal plane position, based on the impact of the test position change on the measurement effect reflected by the evaluation factors corresponding to each measurement position. Compared with the prior art that only adjusts the focal plane position with reference to the image clarity, the evaluation factors of the present application integrate the measurement effect of overlay measurement, so that the focal plane position finally adjusted can take into account the accuracy of overlay measurement.

[0051] Furthermore, the focal plane of the imaging overlay measurement device is adjusted to the target focal plane position, and the wafer is overlaid with the best measurement effect, so as to improve the accuracy of the overlay measurement. In addition, considering the differences between wafers, the best focal plane position will also change. Therefore, the embodiment of the present application locates the best focal plane position suitable for the wafer to be measured based on the overlay measurement result of the wafer to be measured, and locates the best focal plane position for each wafer in a personalized manner, thereby improving the flexibility of the imaging overlay measurement device. BRIEF DESCRIPTION OF THE DRAWINGS

[0052] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying any creative work.

[0053] Figure 1 A schematic diagram of a flow chart of a method for implementing overlay measurement provided in an embodiment of the present application;

[0054] Figure 2 A schematic diagram of an overlay mark image provided in an embodiment of the present application;

[0055] Figure 3 A statistical graph of the grayscale values ​​of various regions of a single overlay mark provided in an embodiment of the present application;

[0056] Figure 4 The function graph of the objective function provided in the embodiment of the present application;

[0057] Figure 5 A schematic diagram of the structure of an overlay measurement device provided in an embodiment of the present application;

[0058] Figure 6 A schematic diagram of the structure of an overlay measurement device provided in an embodiment of the present application. DETAILED DESCRIPTION

[0059] The following will be combined with the drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0060] In the embodiment of the present application, in the scenario where only the focal plane position affects the measurement result of the overlay measurement, all structural parameters and positions of the imaging overlay measurement device except the focal plane are preset as the measurement parameters or positions, and only the focal plane position is adjusted. Since only the focal plane position of the imaging overlay measurement device changes, the factor affecting the measurement result is only the measurement position of the focal plane.

[0061] Furthermore, an embodiment of the present application proposes an overlay measurement method, which is applied to a controller of an imaging overlay measurement device, wherein the imaging overlay measurement device also includes at least: a focal plane, and the focal plane position in the imaging overlay measurement device is adjusted by the controller to locate the optimal focal plane position for measuring the wafer to be measured, so that the accuracy of the overlay value measured by the imaging overlay measurement device at the optimal focal plane position is optimal.

[0062] Specifically, refer to Figure 1 , a flow chart of a method for implementing overlay measurement provided in an embodiment of the present application is provided, and each step of the overlay measurement method is described, which specifically includes the following steps:

[0063] Step S110, in response to the test instruction, obtaining a plurality of test positions.

[0064] The test position refers to a position within a preset range of an initial position of a pre-calibrated focal plane.

[0065] Usually, the focal plane in the imaging overlay measurement device corresponds to a calibrated initial position. In the absence of position adjustment, the wafer to be measured is measured at the calibrated initial position. The present application takes into account that the initial position is not necessarily the best measurement position for different wafers to be measured. Therefore, the present application determines multiple test positions within a preset range of the initial position to test which position is the best measurement position for the wafer to be measured.

[0066] Optionally, after determining the initial position, multiple non-repetitive positions are randomly selected within a preset range as test positions. In one possible implementation, the process of obtaining multiple test positions may also include: obtaining a pre-calibrated initial position of the focal plane; adjusting the initial position according to a preset step distance to obtain a preset number of test positions.

[0067] First, determine the default calibrated focal plane position of the imaging overlay device, that is, the initial position Z0. The focal plane position scheduling is only in the vertical direction, and the lateral position does not need to be changed. Therefore, in the vertical direction of Z0, multiple test positions near Z0 are determined according to the preset step distance. Specifically, refer to formula (1) and determine the starting point and end point of the focal plane position test based on the initial position Z0.

[0068] (1)

[0069] Among them, Z start Indicates the test position corresponding to the starting point of the focus plane position test, Z end Indicates the test position of the end point of the focus plane position test, Step indicates the preset step distance, and n indicates 1 / 2 of the preset number. It can be understood that the above parameters can be set according to the actual situation of the imaging overlay measurement device and are not unique and unchanging.

[0070] Step S120 , controlling the focal plane to move to each test position in sequence to perform overlay measurement on the wafer to be tested, and respectively obtaining overlay measurement data corresponding to each test position.

[0071] According to the order of the test positions in the interval from the starting point to the end point determined in step S110, the position of the vertical focal plane is adjusted in sequence, the focal plane is controlled to move to each test position, and the imaging overlay measurement device is controlled to perform overlay measurement on the overlay mark on the wafer to be tested at each test position to obtain the overlay measurement data corresponding to each test position. The overlay measurement data at least includes: the overlay measurement result, i.e., the overlay value, and the imaging of the overlay mark.

[0072] It can be understood that in order to verify the accuracy of the overlay value measured at the test position, the embodiment of the present application performs overlay measurement on the wafer to be tested at 0° and 180° at the test position, respectively, and uses the overlay values ​​corresponding to 0° and 180° as the overlay measurement results of the test position. Among them, 0° and 180° represent the placement angles of the wafer to be tested on the wafer placement plane of the imaging overlay measurement device. If the front side of the wafer to be tested is placed upward as 0°, then the back side of the wafer to be tested is placed upward as 180°.

[0073] Step S130: determining the evaluation factor corresponding to the focal plane at each test position according to each overlay measurement data.

[0074] Based on the collected overlay measurement data corresponding to the focal plane at each test position, the measurement effect reflected by the overlay measurement data at each test position is evaluated to obtain an evaluation factor, wherein the evaluation factor is used to evaluate the measurement effect when the focal plane is located at the test position.

[0075] Optionally, the evaluation factor may include multiple parameters that can reflect the measurement effect, such as a parameter reflecting the imaging effect of the overlay mark, a parameter reflecting the accuracy of the overlay value, an evaluation parameter that comprehensively evaluates the measurement performance of the focal plane at each test position, etc. In a possible implementation, the evaluation factor includes at least: an imaging effect factor and an overlay measurement factor; wherein the imaging effect factor is a parameter that characterizes the imaging effect of the image obtained by the focal plane at the test position, and the overlay measurement factor is a parameter that characterizes the measurement effect of the focal plane of the imaging overlay measurement device at the test position.

[0076] It is understandable that the imaging effect of the imaging overlay measurement device on the overlay mark directly affects the accuracy of the overlay measurement result. Therefore, the embodiment of the present application comprehensively evaluates the overlay measurement effect of the focal plane at each test position from the two perspectives of imaging effect and overlay measurement result.

[0077] The imaging effect factor is a parameter that characterizes the imaging effect of the image obtained by the focal plane at the test position, wherein the image imaging effect may include: image clarity, image brightness, the degree of deviation of the overlay mark image collected at 0° and 180°, etc. The parameters that can reflect the above image imaging effects are used as the imaging effect factor.

[0078] The overlay measurement factor is a parameter that characterizes the measurement effect of the focal plane of the imaging overlay measurement device at the test position, wherein the measurement effect can be: the deviation between the overlay values ​​corresponding to 0° and 180°, the degree of deviation of the overlay measurement results from the average level, etc. The parameter that can reflect the above measurement effects is used as the overlay measurement factor.

[0079] In one possible implementation, the imaging effect factor includes: image contrast, and the overlay measurement factor includes: measurement accuracy and measurement uncertainty; wherein, the image contrast represents the clarity of the imaging at the test position, the measurement accuracy represents the accuracy of the overlay value measured at the test position, and the measurement uncertainty represents the stability of the overlay measurement at the test position.

[0080] The embodiment of the present application determines the imaging effect factor and the overlay measurement factor corresponding to each test position, which characterize the imaging effect and the measurement effect, based on the overlay measurement data corresponding to each test position. It can be understood that the evaluation factor is obtained by independently evaluating the overlay measurement data corresponding to each test position. Therefore, the following process of determining the image contrast, measurement accuracy and measurement uncertainty corresponding to the focal plane at the test position based on the overlay measurement data is an independent processing process of the overlay measurement data corresponding to a test position among multiple test positions.

[0081] Specifically, based on the overlay measurement data, the image contrast corresponding to the focal plane at the test position is determined, including: acquiring the image of each overlay mark from the overlay measurement data; identifying the grayscale value in the ROI area in the image of the overlay mark, and obtaining the maximum grayscale value and the minimum grayscale value in the ROI area; determining the quotient of the difference between the maximum grayscale value and the minimum grayscale value and the total value as the contrast corresponding to the image of the overlay mark; and determining the average value of the contrast corresponding to the images of all the overlay marks as the image contrast corresponding to the test position.

[0082] First, obtain the overlay mark image collected by the imaging overlay measurement device from the overlay measurement data corresponding to the test position, and refer to Figure 2 , a schematic diagram of an overlay mark image provided in an embodiment of the present application, wherein the overlay mark image contains multiple overlay marks. Identify the grayscale value of the ROI area in the overlay mark image, the ROI area is the region of interest (Region of Interest), in the embodiment of the present application, the ROI area is the area where the overlay mark is located. Figure 2 The overlay mark image is larger than the ROI area. Therefore, the grayscale value of the complete overlay mark can be identified by changing the position of the ROI area.

[0083] The gray value of each overlay mark area in the identified overlay mark image is counted to obtain Figure 3 , the embodiment of the present application provides a statistical graph of the grayscale values ​​of each area of ​​a single overlay mark, in which the horizontal axis represents the position coordinates in the overlay mark image, and the vertical axis represents the grayscale value, and the curve in the statistical graph represents the grayscale change of the overlay mark. Based on this, the maximum grayscale value Max_Gray and the minimum grayscale value Min_Gray of the image of the single overlay mark are determined.

[0084] Further, referring to formula (2), the contrast of a single overlay mark in the overlay mark image is determined:

[0085] (2)

[0086] Wherein, Contrast represents the contrast of a single overlay mark.

[0087] The mean value Contrast_M of the contrast Contrast of all the overlay marks in the overlay mark image is taken as the image contrast of the overlay mark image. The image contrast can comprehensively reflect the average level of brightness and clarity of the overlay mark image collected at the test position.

[0088] Specifically, based on the overlay measurement data, the measurement accuracy corresponding to the focal plane at the test position is determined, including: obtaining the overlay value of each overlay mark in the wafer to be tested at the test position from the overlay measurement data; calling a pre-established overlay value compensation model to process the test position and the overlay value of each overlay mark at the test position to obtain a theoretical overlay value corresponding to each overlay mark, the overlay value compensation model is used to perform data fitting on the test position and the overlay value of the overlay mark to determine the theoretical overlay value at the test position; the difference between the overlay value corresponding to each overlay mark and the theoretical overlay value is determined as the overlay value accuracy corresponding to each overlay mark; and the average value of all overlay value accuracy rates is determined as the measurement accuracy corresponding to the test position.

[0089] Overlay value refers to the deviation in the alignment of patterns or overlay marks between different layers during the multi-layer lithography process. This deviation may cause circuit connection errors and even affect the function of the chip in the wafer. By performing overlay value compensation, this deviation can be significantly reduced or eliminated, thereby improving the accuracy of chip manufacturing. It can be understood that the smaller the value of overlay value compensation, the more accurate the overlay value measurement result. The compensated overlay value can also be understood as a theoretically accurate overlay value. If the difference between the overlay value actually measured by the imaging overlay measurement device and the compensated overlay value is smaller, the measurement accuracy of the imaging overlay measurement device is more accurate. Optionally, it is usually adopted to call a pre-established overlay value compensation model to compensate for the overlay value and obtain a theoretical overlay value.

[0090] Based on this, the embodiment of the present application first obtains the overlay value corresponding to each overlay mark in the overlay measurement image from the overlay measurement data, and calls a pre-built overlay value compensation model to compensate the overlay value of each overlay mark to obtain the theoretical overlay value corresponding to each overlay mark.

[0091] Among them, the overlay value compensation model can adopt a six-parameter overlay model, that is, a six-parameter overlay value compensation model, wherein the model function of the six-parameter overlay value compensation model includes three parts: translation, scaling, and rotation, each part has two directions, X and Y, and a total of 6 parameters, namely, the translation amount Tx in the X direction, the translation amount Ty in the Y direction, the scaling amount Mx in the X direction, the scaling amount My in the Y direction, the rotation amount Rx in the X direction, and the rotation amount Ry in the Y direction.

[0092] Specifically, the process of calling the six-parameter overlay value compensation model to process the input raw overlay value, that is, the overlay value measured by the imaging overlay measurement device, may include: first, using a functional form to describe the relationship between the raw overlay value RawOV (RawOVx, RawOVy) and the silicon wafer / wafer position coordinate (Posx, Posy), and obtaining the function expression of the following formula (3).

[0093] (3)

[0094] Among them, RawOVx and RawOVy respectively represent the overlay values ​​of the overlay mark measured by the imaging overlay detection equipment in the X direction and the Y direction; PosX and PosY respectively represent the coordinates of the overlay mark in the X direction and the Y direction on the wafer or silicon wafer.

[0095] Furthermore, each overlay measurement point can establish an equation group based on the above 6 parameters. Based on this, a linear equation group is constructed corresponding to multiple overlay measurement points to obtain the following equation (4), and the 6 parameters in the linear equation group (4) are solved using the least squares method.

[0096] (4)

[0097] Among them, RawOVxi and RawOVyi represent the overlay values ​​of the i-th overlay mark in the X direction and Y direction respectively measured by the imaging overlay detection equipment; PosXi and PosYi represent the coordinates of the i-th overlay mark in the X direction and Y direction on the wafer or silicon wafer respectively.

[0098] Considering that the six parameter solutions obtained by the least squares method have errors, after the six parameters are solved, the six parameters and the wafer position coordinates (Posx, Posy) can be used to solve the overlay value ModelOV obtained by fitting the six-parameter overlay value compensation model, i.e., the overlay value compensation value, by referring to the following formula (5).

[0099] (5)

[0100] Wherein, ModelOVxi and ModelOVyi represent the overlay values ​​of the i-th overlay mark respectively in the X direction and the Y direction obtained by fitting the six-parameter overlay value compensation model.

[0101] Based on the overlay value compensation value corresponding to the overlay value of each overlay mark obtained above, the measurement accuracy of the overlay measurement at the test position is determined with reference to the following formula (6).

[0102] (6)

[0103] Among them, Accuracy represents the measurement accuracy; ModelOV i,j represents the overlay compensation value of the overlay value obtained by measuring the i-th overlay mark in the overlay mark image j times in the above six-parameter overlay value compensation model; RawOVi,j represents the overlay value obtained by measuring the i-th overlay mark in the overlay mark image j times in the overlay mark image; n is the total number of overlay marks in the overlay mark image, and m is the total number of measurements of the overlay marks.

[0104] Specifically, according to the overlay measurement data, the measurement uncertainty corresponding to the focal plane at the test position is determined, including: obtaining the overlay value of each overlay mark in the wafer to be tested at the test position from the overlay measurement data, the overlay value at least including: the overlay value in the first direction and the overlay value in the second direction; based on the overlay value in the first direction corresponding to each overlay mark, determining the first device error parameter in the first direction and the first repeatability parameter of the overlay value, the first device error parameter characterizing the average level and fluctuation degree of the measurement error introduced by the focal plane, the first repeatability parameter characterizing the overlay value in all the overlay values ​​in the first direction. The parameter values ​​of repetition rate and discreteness are determined; based on the first device error parameter and the first repeatability parameter, a first measurement uncertainty corresponding to the first direction is determined, and the first measurement uncertainty characterizes the stability of the overlay measurement in the first direction of the test position; based on the overlay value in the second direction corresponding to each overlay mark, a second device error parameter in the second direction and a second repeatability parameter of the overlay value are determined; based on the second device error parameter and the second repeatability parameter, a second measurement uncertainty corresponding to the second direction is determined; and the average of the first measurement uncertainty and the second measurement uncertainty is determined as the measurement uncertainty corresponding to the test position.

[0105] From the overlay measurement data corresponding to the test position, obtain the overlay values ​​obtained by multiple measurements of all the overlay marks in the overlay mark image at the test position. Optionally, three times the standard deviation of all the above overlay values ​​can be used as the repeatability parameter of the overlay measurement at the test position. It can be understood that the standard deviation of a group of data can measure the degree of discreteness or dispersion of the group of data. If the repeatability of the overlay value obtained by testing at the test position is high, it proves that the test performance of the imaging overlay measurement equipment is relatively stable when the focal plane is at the test position.

[0106] In addition, the embodiment of the present application also introduces the TIS (Tool Introduced Shift) parameter, that is, the device error parameter, which is the error introduced by the device itself to the measurement result. In the embodiment of the present application, it is the error caused by the focal plane to the measurement result of the imaging overlay device at the current test position. The overlay value obtained by multiple measurements of the focal plane at the test position is used to determine the measurement error introduced by the focal plane, that is, the device error parameter corresponding to each measurement. Similarly, determining three times the standard deviation of the device error parameter corresponding to multiple measurements at the test position can also reflect the degree of stability or fluctuation of the influence of the focal plane on the test error at the test position.

[0107] The overlay value is a measurement of the offset between overlay marks on a horizontally placed wafer, referring to Figure 2 , the overlay value can be quantified from the horizontal plane in two directions, the horizontal direction X and the vertical direction Y. Therefore, the overlay value measured by the imaging overlay measurement device at the test position of each focal plane includes at least: the overlay value in the first direction X and the overlay value in the second direction Y. Based on this, the repeatability parameters, device error parameters, etc. determined based on the overlay value can also be divided into two directions for calculation to obtain the repeatability parameters and device error parameters corresponding to the first direction X, and the mean value can be calculated based on the device error parameter and the repeatability parameter to determine the average level of the measurement error introduced by the focal plane.

[0108] Based on the overlay value, repeatability parameter of the overlay value, device error parameter, repeatability parameter of the device error parameter, etc. corresponding to the first direction X and the second direction Y determined in the above manner, the measurement uncertainty corresponding to the test position is determined with reference to the following formula (7).

[0109] (7)

[0110] Wherein, TU represents the measurement uncertainty corresponding to the test position, TU_X represents the first measurement uncertainty corresponding to the first direction X, and TU_Y represents the second measurement uncertainty corresponding to the second direction Y; TISX and TISY represent the equipment error parameters corresponding to the first direction X and the second direction Y, respectively; Static Precision represents the mean of the overlay value repeatability parameters (three times the standard deviation) obtained by multiple measurements of all overlay marks, where Static PrecisionX and Static PrecisionY represent the mean of the overlay value repeatability parameters corresponding to the first direction X and the second direction Y, respectively; TIS M is the mean value of all overlay marks TIS, then TISX M TISY M are the mean values ​​of TISX and TISY corresponding to all overlay marks; TIS 3σ is three times the standard deviation of all overlay marks TIS, then TISX 3σ is three times the standard deviation of TISX for all overlay marks, TISY 3σ It is three times the standard deviation of TISY of all overlay marks.

[0111] In summary, the image contrast, measurement accuracy and measurement uncertainty included in the evaluation factors comprehensively evaluate the imaging of the wafer to be tested, the accuracy of the measurement results, the stability of the measurement effect, etc. of the imaging overlay measurement equipment at the test position of the focal plane, and the evaluation factors can comprehensively reflect the measurement performance of the imaging overlay measurement equipment at the test position of the focal plane. Compared with the prior art, which only adjusts the focal plane position based on the brightness and contrast of the imaging, the adjustment basis of the embodiment of the present application is more comprehensive.

[0112] Step S140 , determining a target focal plane position that matches the wafer to be tested according to the influence of the test position change on the measurement effect reflected by all evaluation factors.

[0113] Step S150, controlling the focal plane to adjust to the target focal plane position, and controlling the imaging overlay measurement equipment to perform overlay measurement on the overlay mark in the wafer to be measured.

[0114] It can be understood that the evaluation factors corresponding to each test position reflect different measurement effects. By visually counting the evaluation factors at different test positions in the form of a line graph or other statistical graphs, it can be observed that the changing trend of the evaluation factors changes with the test position, and the evaluation factors can reflect the measurement effect at the test position. Similarly, based on the changing trend of the evaluation factors, it is also possible to determine the impact of the change in the test position on the measurement effect, that is, the changing trend of the measurement effect with the change of the test position.

[0115] Optionally, when the evaluation factor is a single value, the evaluation factor is proportional to the measurement effect, that is, the larger the value of the evaluation factor, the better the corresponding measurement effect. Based on this, the relationship diagram between the test position and the evaluation factor can be statistically calculated in the form of a line graph, and because the evaluation factor is proportional to the measurement effect, the relationship diagram can intuitively reflect the impact of the change in the test position on the measurement effect, and there is no need to convert the relationship diagram into a relationship diagram between the test position and the measurement effect. Assume that as the focal plane test position moves downward, the measurement effect becomes better, or as the focal plane test position moves downward, the measurement effect presents a parabolic change trend, the measurement effect becomes better and better, and when it moves down to a certain test position, the measurement effect reaches a peak value, and then moves down and the measurement effect shows a downward trend.

[0116] Based on this, according to the changing trend of the measurement effect under the change of the test position, the test position with the best measurement effect is determined as the best focal plane position for overlay measurement of the wafer to be tested, that is, the target focal plane position.

[0117] Referring to the above step S130 , the evaluation factors include image contrast, measurement accuracy and measurement uncertainty. The relationship between each parameter and the measurement effect is not uniform, so the above statistical method is no longer applicable.

[0118] For the case where the evaluation factors include image contrast, measurement accuracy and measurement uncertainty, the process of implementing step S140 can firstly comprehensively consider multiple parameters included in the evaluation factors to determine the measurement effect at the test position reflected by the evaluation factors. Specifically, based on the weight values ​​corresponding to the measurement uncertainty, measurement accuracy and image contrast included in the evaluation factors, the performance parameters corresponding to the test position are determined, and the weight values ​​represent the influence of the measurement uncertainty or measurement accuracy or image contrast on the overlay measurement results.

[0119] It is understandable that the various parameters in the evaluation factors have different degrees of influence on the measurement effect. For example, during the measurement process, the clarity of the image directly affects the accuracy of the deviation detection between the overlay marks, that is, it directly affects the accuracy of the overlay value, which will also affect the measurement uncertainty and measurement correctness. Based on this, it can be determined that the influence of image contrast on the measurement effect is higher than that of the other two parameters.

[0120] Based on this, the degree of influence of image contrast, measurement uncertainty and measurement accuracy on the overlay measurement results is objectively evaluated to characterize the degree of influence on the measurement effect. Based on the degree of influence of each parameter on the measurement effect, the corresponding weight value is set respectively. Based on the weight value, the three parameters are weighted and summed. The evaluation factor including the three parameters of image contrast, measurement uncertainty and measurement accuracy is quantified into a performance parameter that can comprehensively reflect the measurement effect of the imaging overlay measurement equipment. The embodiment of the present application can be recorded as Focus. KPI Specifically, according to the following formula (8), the KPI is determined by weighted summing of the three parameters of image contrast, measurement uncertainty and measurement accuracy.

[0121] (8)

[0122] Among them, A, B, and C are their corresponding weight values. The weight values ​​can be pre-configured in the system parameters of the imaging overlay device according to the influence of each parameter on the measurement effect, and the default values ​​are 0.5, 0.3, and 0.2.

[0123] Furthermore, data fitting is performed on each test position and the performance parameters corresponding to each test position to obtain the objective function corresponding to the wafer to be tested, and the objective function represents the functional relationship between the test position and the performance parameters corresponding to the wafer to be tested; the test position corresponding to the maximum value of the performance parameter in the objective function is determined as the target focal plane position corresponding to the wafer to be tested.

[0124] Data fitting is performed on the performance parameters corresponding to multiple test positions to obtain an objective function that characterizes the functional relationship between the test position of the focal plane and the performance parameters, as shown in the following formula (9).

[0125] (9)

[0126] Among them, Focus_Pos represents the test position of the focus plane.

[0127] Optionally, f(Focus_Pos) is generally fitted in the form of a quadratic function to obtain the objective function of the following formula (10).

[0128] (10)

[0129] Among them, a, b, and c are the coefficients of the quadratic term, the linear term, and the constant term, respectively. The specific values ​​are determined according to the data fitting results.

[0130] According to the objective function (10) obtained by fitting, the peak value of the objective function, i.e. Focus KPI The focal position at the maximum value, refer to Figure 4, the function graph of the objective function provided in the embodiment of the present application, the function graph of the objective function (10) is parabolic and has a peak value. If the imaging overlay device allows, the focal plane position corresponding to the peak value is used as the target focal plane position. If the imaging overlay device cannot adjust the focal plane to the focal plane position corresponding to the peak value, then according to the focal plane position range allowed by the imaging overlay measurement device, determine the corresponding Focus within the position range. KPI The position corresponding to the maximum value is taken as the target focal plane position.

[0131] Furthermore, the focal plane is controlled to be adjusted to the target focal plane position determined above, and overlay measurement is performed on the overlay mark in the wafer to be measured.

[0132] In summary, the overlay measurement method provided in the embodiment of the present application responds to the test instruction of the wafer to be tested, moves the focal plane to multiple test positions, obtains the evaluation factor of the measurement effect for overlay measurement corresponding to each measurement position, and determines the best measurement position for the best measurement effect of the wafer to be tested, that is, the target focal plane position, based on the influence of the test position change on the measurement effect reflected by the evaluation factor corresponding to each measurement position. Compared with the prior art that only adjusts the focal plane position with reference to the image clarity, the performance parameters of the present application also integrate the measurement effect of overlay measurement, so that the focal plane position finally adjusted can take into account the accuracy of overlay measurement.

[0133] Furthermore, the focal plane of the imaging overlay measurement device is adjusted to the target focal plane position, and the wafer is overlaid with the best measurement effect, so as to improve the accuracy of the overlay measurement. In addition, considering the differences between wafers, the best focal plane position will also change. Therefore, the embodiment of the present application locates the best focal plane position suitable for the wafer to be measured based on the overlay measurement result of the wafer to be measured, and locates the best focal plane position for each wafer in a personalized manner, thereby improving the flexibility of the imaging overlay measurement device.

[0134] The following is a description of the overlay measurement device provided in an embodiment of the present application. The overlay measurement device described below and the overlay measurement method described above can be referenced to each other.

[0135] First, combine Figure 5 , an overlay measurement device for a controller used in an imaging overlay measurement device is introduced, such as Figure 5 As shown, the overlay measurement device may include:

[0136] A test position acquisition unit 100, for acquiring a plurality of test positions in response to a test instruction, wherein the test positions refer to positions within a preset range of an initial position of a pre-calibrated focal plane;

[0137] A measurement data acquisition unit 200 is used to control the focal plane to move to each of the test positions in sequence to perform overlay measurement on the wafer to be measured, and respectively acquire overlay measurement data corresponding to each of the test positions;

[0138] An evaluation factor determination unit 300, used to determine the evaluation factor corresponding to the focal plane at each of the test positions according to each of the overlay measurement data, wherein the evaluation factor is used to evaluate the measurement effect when the focal plane is located at the test position;

[0139] A target position determination unit 400, configured to determine a target focal plane position that matches the wafer to be tested according to the influence of the test position change on the measurement effect reflected by all the evaluation factors;

[0140] The control and measurement unit 500 is used to control the focal plane to adjust to the target focal plane position, and control the imaging overlay measurement device to perform overlay measurement on the overlay mark in the wafer to be measured.

[0141] In a possible implementation, the evaluation factors include at least: an imaging effect factor and an overlay measurement factor;

[0142] The imaging effect factor is a parameter characterizing the imaging effect of the image obtained by the focal plane at the test position, and the overlay measurement factor is a parameter characterizing the measurement effect of the focal plane of the imaging overlay measurement device at the test position.

[0143] In a possible implementation, the imaging effect factor includes: image contrast, and the overlay measurement factor includes: measurement accuracy and measurement uncertainty;

[0144] The image contrast represents the clarity of the image at the test position, the measurement accuracy represents the accuracy of the overlay value measured at the test position, and the measurement uncertainty represents the stability of the overlay measurement at the test position.

[0145] In a possible implementation, the evaluation factor determination unit 300 includes:

[0146] An overlay value acquisition subunit, used for acquiring the overlay value of each overlay mark in the wafer to be tested at the test position from the overlay measurement data;

[0147] A model calling subunit, used to call a pre-established overlay value compensation model, process the test position and the overlay value of each overlay mark at the test position, and obtain a theoretical overlay value corresponding to each overlay mark, wherein the overlay value compensation model is used to perform data fitting on the overlay value of the test position and the overlay mark, and determine the theoretical overlay value at the test position;

[0148] An accuracy determination subunit, used to determine the difference between the overlay value corresponding to each overlay mark and the theoretical overlay value as the accuracy of the overlay value corresponding to each overlay mark;

[0149] The accuracy determination subunit is used to determine the average value of the accuracy of all overlay values ​​as the measurement accuracy corresponding to the test position.

[0150] In a possible implementation, the evaluation factor determination unit 300 includes:

[0151] An image acquisition subunit, used for acquiring an image of each overlay mark from the overlay measurement data;

[0152] A grayscale recognition subunit, used to recognize the grayscale value in the ROI area in the image of the overlay mark, and obtain the maximum grayscale value and the minimum grayscale value in the ROI area;

[0153] a contrast determination subunit, configured to determine the quotient of the difference between the maximum grayscale value and the minimum grayscale value and the total value as the contrast corresponding to the image of the overlay mark;

[0154] The image contrast determination subunit is used to determine the average value of the contrasts corresponding to the images of all the overlay marks as the image contrast corresponding to the test position.

[0155] In a possible implementation, the evaluation factor determination unit 300 includes:

[0156] An overlay value acquisition subunit is used to acquire the overlay value of each overlay mark in the wafer to be tested at the test position from the overlay measurement data, wherein the overlay value at least includes: an overlay value in a first direction and an overlay value in a second direction;

[0157] a first direction parameter determination subunit, configured to determine a first device error parameter in the first direction and a first repeatability parameter of the overlay value based on the overlay value in the first direction corresponding to each of the overlay marks, wherein the first device error parameter represents a parameter of an average level and a degree of fluctuation of the measurement error introduced by the focal plane, and the first repeatability parameter represents a parameter value of a repetition rate and a degree of discreteness of the overlay value in all the overlay values ​​in the first direction;

[0158] A first parameter determination subunit, configured to determine a first measurement uncertainty corresponding to the first direction according to the first device error parameter and the first repeatability parameter, wherein the first measurement uncertainty represents a stability of the overlay measurement in the first direction of the test position;

[0159] A second direction parameter determination subunit, configured to determine a second device error parameter in the second direction and a second repeatability parameter of the overlay value based on the overlay value in the second direction corresponding to each of the overlay marks;

[0160] A second parameter determination subunit, configured to determine a second measurement uncertainty corresponding to the second direction according to the second device error parameter and the second repeatability parameter;

[0161] The uncertainty determination subunit is used to determine the average of the first measurement uncertainty and the second measurement uncertainty as the measurement uncertainty corresponding to the test position.

[0162] In one possible implementation, the evaluation factor is a performance parameter corresponding to the test position determined based on the weight values ​​corresponding to the measurement uncertainty, the measurement accuracy and the image contrast respectively contained in the evaluation factor, and the weight value represents the influence of the measurement uncertainty or the measurement accuracy or the image contrast on the overlay measurement result.

[0163] In a possible implementation, the target position determination unit 400 includes:

[0164] A data fitting subunit is used to perform data fitting on each of the test positions and the performance parameters corresponding to each of the test positions to obtain an objective function corresponding to the wafer to be tested, wherein the objective function represents a functional relationship between the test position and the performance parameters corresponding to the wafer to be tested;

[0165] The target focal plane position determination subunit is used to determine the test position corresponding to the maximum value of the performance parameter in the objective function as the target focal plane position corresponding to the wafer to be tested.

[0166] In a possible implementation, the test position acquisition unit 100 includes:

[0167] An initial position acquisition subunit, used to acquire a pre-calibrated initial position of the focal plane;

[0168] The position adjustment subunit is used to adjust the initial position according to a preset step distance to obtain a preset number of test positions.

[0169] In summary, the embodiment of the present application responds to the test instructions for the wafer to be tested, moves the focal plane to multiple test positions, obtains the evaluation factors of the measurement effect for overlay measurement corresponding to each measurement position, and determines the best measurement position for the best measurement effect of the wafer to be tested, that is, the target focal plane position, based on the impact of the test position change on the measurement effect reflected by the evaluation factors corresponding to each measurement position. Compared with the prior art that only adjusts the focal plane position with reference to the image clarity, the performance parameters of the present application also integrate the measurement effect of overlay measurement, so that the focal plane position finally adjusted can take into account the accuracy of overlay measurement.

[0170] Furthermore, the focal plane of the imaging overlay measurement device is adjusted to the target focal plane position, and the wafer is overlaid with the best measurement effect, so as to improve the accuracy of the overlay measurement. In addition, considering the differences between wafers, the best focal plane position will also change. Therefore, the embodiment of the present application locates the best focal plane position suitable for the wafer to be measured based on the overlay measurement result of the wafer to be measured, and locates the best focal plane position for each wafer in a personalized manner, thereby improving the flexibility of the imaging overlay measurement device.

[0171] The overlay measurement device provided in the embodiment of the present application can be applied to overlay measurement equipment.

[0172] Figure 6 The schematic diagram of the structure of the overlay measurement device is shown. Figure 6 The structure of the overlay measurement device may include: at least one processor 10, at least one memory 20, at least one communication bus 30 and at least one communication interface 40.

[0173] In the embodiment of the present application, the number of the processor 10 , the memory 20 , the communication bus 30 , and the communication interface 40 is at least one, and the processor 10 , the memory 20 , and the communication interface 40 communicate with each other through the communication bus 30 .

[0174] The processor 10 may be a central processing unit (CPU), or an application specific integrated circuit (ASIC), or one or more integrated circuits configured to implement the embodiments of the present invention.

[0175] The memory 20 may include a high-speed RAM memory, and may also include a non-volatile memory (non-volatile memory), etc., such as at least one disk memory.

[0176] The memory stores a program, and the processor can call the program stored in the memory, and the program is used to implement each processing flow in the aforementioned overlay measurement method.

[0177] An embodiment of the present application also provides a computer storage medium, which can store a program suitable for execution by a processor, and the program is used to implement each processing flow in the aforementioned overlay measurement method.

[0178] Finally, it should be noted that, in this article, relational terms such as first and second, etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions, the elements defined by the sentence "comprise a ..." do not exclude the presence of other identical elements in the process, method, article or device including the elements.

[0179] The various embodiments in this specification are described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same or similar parts between the various embodiments can be referenced to each other.

[0180] The above description of the disclosed embodiments enables those skilled in the art to implement or use the present application. Various modifications to these embodiments will be apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present application. Therefore, the present application will not be limited to the embodiments shown herein, but will conform to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. An overlay measurement method, characterized in that: A controller applied to an imaging overlay measurement device, wherein the overlay measurement method comprises: In response to the test instruction, a plurality of test positions are acquired, wherein the test positions are positions within a preset range of an initial position of a pre-calibrated focal plane; Control the focal plane to move to each of the test positions in sequence to perform overlay measurement on the wafer to be tested, and respectively obtain overlay measurement data corresponding to each of the test positions; Determine, according to each of the overlay measurement data, an evaluation factor corresponding to the focal plane at each of the test positions, wherein the evaluation factor is used to evaluate a measurement effect when the focal plane is located at the test position; Determining a target focal plane position that matches the wafer to be tested according to the influence of the test position change on the measurement effect reflected by all the evaluation factors; The focal plane is controlled to be adjusted to the target focal plane position, and the imaging overlay measurement device is controlled to perform overlay measurement on the overlay mark in the wafer to be measured.

2. The overlay measurement method according to claim 1, characterized in that: The evaluation factors at least include: imaging effect factor and overlay measurement factor; The imaging effect factor is a parameter characterizing the imaging effect of the image obtained by the focal plane at the test position, and the overlay measurement factor is a parameter characterizing the measurement effect of the focal plane of the imaging overlay measurement device at the test position.

3. The overlay measurement method according to claim 2, characterized in that: The imaging effect factor includes: image contrast, and the overlay measurement factor includes: measurement accuracy and measurement uncertainty; The image contrast represents the clarity of the image at the test position, the measurement accuracy represents the accuracy of the overlay value measured at the test position, and the measurement uncertainty represents the stability of the overlay measurement at the test position.

4. The overlay measurement method according to claim 3, characterized in that: Determining the measurement accuracy corresponding to the focal plane at the test position according to the overlay measurement data includes: From the overlay measurement data, obtaining an overlay value of each overlay mark in the wafer to be tested at the test position; Calling a pre-established overlay value compensation model, processing the test position and the overlay value of each overlay mark at the test position, and obtaining a theoretical overlay value corresponding to each overlay mark, wherein the overlay value compensation model is used to perform data fitting on the test position and the overlay value of the overlay mark, and determine the theoretical overlay value at the test position; Determine the difference between the overlay value corresponding to each overlay mark and the theoretical overlay value as the overlay value accuracy rate corresponding to each overlay mark; The average value of all the overlay value accuracy is determined as the measurement accuracy corresponding to the test position.

5. The overlay measurement method according to claim 3, characterized in that: Determining the image contrast corresponding to the focal plane at the test position according to the overlay measurement data includes: acquiring an image of each overlay mark from the overlay measurement data; Identify the grayscale value in the ROI area in the image of the overlay mark, and obtain the maximum grayscale value and the minimum grayscale value in the ROI area; Determine the quotient of the difference between the maximum grayscale value and the minimum grayscale value and the total value as the contrast corresponding to the image of the overlay mark; The average value of the contrasts corresponding to the images of all the overlay marks is determined as the image contrast corresponding to the test position.

6. The overlay measurement method according to claim 3, characterized in that: Determining the measurement uncertainty corresponding to the focal plane at the test position according to the overlay measurement data includes: From the overlay measurement data, obtaining an overlay value of each overlay mark in the wafer to be tested at the test position, the overlay value at least comprising: an overlay value in a first direction and an overlay value in a second direction; Based on the overlay value in the first direction corresponding to each of the overlay marks, determine a first device error parameter in the first direction and a first repeatability parameter of the overlay value, wherein the first device error parameter is a parameter characterizing an average level and a degree of fluctuation of a measurement error introduced by the focal plane, and the first repeatability parameter is a parameter value characterizing a repetition rate and a degree of discreteness of the overlay value in all the overlay values ​​in the first direction; Determine a first measurement uncertainty corresponding to the first direction according to the first device error parameter and the first repeatability parameter, wherein the first measurement uncertainty is used to characterize the stability of the overlay measurement in the first direction of the test position; Determine, based on the overlay value in the second direction corresponding to each of the overlay marks, a second device error parameter in the second direction and a second repeatability parameter of the overlay value; determining a second measurement uncertainty corresponding to the second direction according to the second device error parameter and the second repeatability parameter; An average of the first measurement uncertainty and the second measurement uncertainty is determined as the measurement uncertainty corresponding to the test position.

7. The overlay measurement method according to claim 3, characterized in that: The evaluation factor is a performance parameter corresponding to the test position determined based on the weight values ​​corresponding to the measurement uncertainty, the measurement accuracy and the image contrast respectively included in the evaluation factor, and the weight value represents the influence of the measurement uncertainty or the measurement accuracy or the image contrast on the overlay measurement result.

8. The overlay measurement method according to claim 7, characterized in that: The step of determining a target focal plane position matching the wafer to be tested according to the influence of the test position change reflected by all the evaluation factors on the measurement effect includes: Performing data fitting on each of the test positions and the performance parameters corresponding to each of the test positions to obtain an objective function corresponding to the wafer to be tested, wherein the objective function represents a functional relationship between the test position and the performance parameters corresponding to the wafer to be tested; The test position corresponding to when the performance parameter in the objective function is at a maximum value is determined as the target focal plane position corresponding to the wafer to be tested.

9. The overlay measurement method according to claim 1, characterized in that: The obtaining of multiple test positions comprises: Obtaining a pre-calibrated initial position of the focal plane; The initial position is adjusted according to a preset step distance to obtain a preset number of test positions.

10. An overlay measurement device, characterized in that: A controller applied to an imaging overlay measurement device, the overlay measurement device comprising: A test position acquisition unit, configured to acquire a plurality of test positions in response to a test instruction, wherein the test positions are positions within a preset range of an initial position of a pre-calibrated focal plane; A measurement data acquisition unit, used for controlling the focal plane to move to each of the test positions in sequence to perform overlay measurement on the wafer to be measured, and respectively acquiring overlay measurement data corresponding to each of the test positions; An evaluation factor determination unit, used to determine the evaluation factor corresponding to the focal plane at each of the test positions according to each of the overlay measurement data, wherein the evaluation factor is used to evaluate the measurement effect when the focal plane is located at the test position; A target position determination unit, configured to determine a target focal plane position that matches the wafer to be tested according to the influence of the test position change reflected by all the evaluation factors on the measurement effect; The control and measurement unit is used to control the focal plane to adjust to the target focal plane position, and control the imaging overlay measurement device to perform overlay measurement on the overlay mark in the wafer to be measured.

11. An overlay measurement device, characterized in that: The method comprises at least one processor and a memory connected to the processor, wherein: The memory is used to store computer programs; The processor is used to execute the computer program so that the overlay measurement device can implement the overlay measurement method according to any one of claims 1 to 9.

12. A computer storage medium, characterized in that: The storage medium carries one or more computer programs, and when the one or more computer programs are executed by the overlay measurement device, the overlay measurement device can implement the overlay measurement method as described in any one of claims 1 to 9.

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