Overlay measurement method and related equipment

Abstract

The invention discloses an overlay measurement method and related equipment, and relates to the technical field of photoetching. In response to a measurement request for a to-be-measured overlay mark in a to-be-measured silicon wafer, a target height value corresponding to a measurement position where the to-be-measured overlay mark is located is determined based on a pre-established target function corresponding to the to-be-measured silicon wafer, and the target function is based on measurement positions of a plurality of measurement points in the to-be-measured silicon wafer. And a function obtained by data fitting of the measurement positions and the height values corresponding to the measurement positions is used for representing the function relationship between the measurement positions of the measurement points in the silicon wafer to be measured and the height values. And controlling the imaging objective lens to move to a target focusing position corresponding to the target height value according to the target height value and the measurement position, and performing overlay measurement on the overlay mark to be measured. According to the invention, adaptive focusing is carried out according to the height of each overlay mark, so that each to-be-measured overlay mark can be imaged at the corresponding optimal focal length, the imaging effect is improved, and the accuracy of overlay measurement is improved.

Description

Technical Field

[0001] The present application relates to the field of photolithography technology, and more specifically, to an overlay measurement method and related equipment. Background Art

[0002] Imaging overlay measurement uses an objective lens to image the overlay mark, and uses the image of the overlay mark obtained by imaging to calculate the overlay accuracy. Among them, the focusing accuracy determines whether the light can be accurately focused on the overlay mark during the imaging process, thereby affecting the clarity of the overlay mark image. In overlay measurement, if the focus is inaccurate, the image will be blurred and the edge will be unclear, which will affect the accuracy and reliability of the measurement. Therefore, high-precision focusing is the basis for ensuring the accuracy of imaging overlay measurement.

[0003] The commonly used focusing methods are focusing based on white light interferometer or imaging contrast. These two focusing methods only require the height of the silicon wafer to be tested on the silicon wafer stage to be used as the height value of all measurement points and input into the measurement prescription for focusing, which means that the focusing parameters for each measurement point of the silicon wafer to be tested are consistent. However, in reality, due to the inclination of the objective lens motion stage and the silicon wafer stage, and the height difference of the surface of the silicon wafer itself, the height of each measurement point on the silicon wafer to be tested is not consistent. If the same focusing parameters are used for imaging, the focusing of some measurement points may fail, resulting in the failure of the overlay measurement of the silicon wafer to be tested, or inaccurate overlay measurement results. Summary of the invention

[0004] In view of the above problems, this application provides an overlay measurement method and related equipment to achieve the purpose of precise focusing. The specific solution is as follows:

[0005] The first aspect of the present application provides an overlay measurement method, comprising:

[0006] In response to a measurement request for an overlay mark to be measured in a silicon wafer to be measured, determining a measurement position of the overlay mark to be measured;

[0007] Input the measurement position into a pre-established target function corresponding to the silicon wafer to be tested, and determine a target height value corresponding to the measurement position, wherein the target function is a function obtained by performing data fitting on the measurement positions of multiple measurement points in the silicon wafer to be tested and the height value corresponding to each measurement position, and is used to characterize the corresponding relationship between the measurement position and the height value of each measurement point in the silicon wafer to be tested, wherein the height value is the height difference between the measurement point and an imaging objective lens located at a preset height;

[0008] According to the target height value and the measurement position, the imaging objective lens is controlled to move to a target focusing position corresponding to the target height value, and overlay measurement is performed on the overlay mark to be measured.

[0009] In a possible implementation, the process of pre-establishing the objective function corresponding to the silicon wafer to be tested includes:

[0010] Determining measurement positions of a preset number of measurement points evenly distributed in the silicon wafer to be measured according to the size of the silicon wafer to be measured;

[0011] Obtaining a height value corresponding to the measurement position of each measurement point;

[0012] Data fitting is performed on the measurement position and the height value corresponding to each measurement point to obtain an objective function that characterizes the corresponding relationship between the measurement position and the height value in the silicon wafer to be measured.

[0013] In a possible implementation, controlling the imaging objective lens to move to a target focusing position corresponding to the target height value based on the target height value and the measurement position, and performing overlay measurement on the overlay mark to be measured, includes:

[0014] Controlling the imaging objective lens to move to the measuring position of the overlay mark to be measured;

[0015] Determining an initial focus height corresponding to the overlay mark to be measured according to the target height value corresponding to the measuring position;

[0016] Controlling the imaging objective lens to move within a preset height range of the initial focusing height according to a preset step distance, and controlling the imaging objective lens to capture an image of the overlay mark to be measured at the height of the preset step distance;

[0017] From the captured images, a height value corresponding to an image with the highest definition is determined as a target focal length position of the imaging objective lens;

[0018] The imaging objective lens is controlled to move to the target focal length position.

[0019] In a possible implementation, determining the initial focus height corresponding to the overlay mark to be measured according to the target height value corresponding to the measurement position includes:

[0020] Obtain the height value and focus position corresponding to the last overlay mark to be measured, as the historical height value and historical focus position respectively;

[0021] Determine whether the difference between the historical altitude value and the target altitude value is less than a preset threshold;

[0022] When the difference between the historical height value and the target height value is less than the preset threshold, the focus height of the historical focus position is determined as the initial focus height corresponding to the overlay mark to be measured in this measurement;

[0023] When the difference between the historical height value and the target height value is not less than the preset threshold, the preset focus height corresponding to the target height value is determined as the initial focus height corresponding to the overlay mark to be measured this time.

[0024] In a possible implementation, before determining the measurement position of the overlay mark to be measured, the method further includes:

[0025] Aligning the silicon wafer to be tested with the mask according to the alignment marks on the silicon wafer to be tested and the alignment marks on the mask;

[0026] The measurement position of the overlay mark to be tested in the aligned silicon wafer to be tested is obtained.

[0027] In a possible implementation, aligning the silicon wafer to be tested with the mask according to the alignment mark on the silicon wafer to be tested and the alignment mark on the mask includes:

[0028] Acquire the mark position of each alignment mark on the silicon wafer to be tested, and a preset focus position corresponding to the mark position;

[0029] Controlling the imaging objective lens to move to the mark position of each alignment mark and the preset focus position corresponding to the mark position, and collecting a mark image of each alignment mark, wherein the mark image at least includes: the alignment mark of the silicon wafer to be tested and the alignment mark of the mask;

[0030] According to the deviation between the alignment mark of the silicon wafer to be tested and the alignment mark of the mask in all the mark images, the position of the silicon wafer to be tested is adjusted so that the deviation between the alignment mark of the silicon wafer to be tested and the alignment mark of the mask meets a preset deviation threshold.

[0031] A second aspect of the present application provides an overlay measurement device, comprising:

[0032] A position determination unit, configured to determine a measurement position of an overlay mark to be measured in response to a measurement request for the overlay mark to be measured in the silicon wafer to be measured;

[0033] a height value determination unit, used for inputting the measurement position into a pre-established target function corresponding to the silicon wafer to be tested, and determining a target height value corresponding to the measurement position, wherein the target function is a function obtained by performing data fitting on the measurement positions of a plurality of measurement points in the silicon wafer to be tested, and the height value corresponding to each of the measurement positions, and is used for characterizing the correspondence between the measurement position and the height value of each measurement point in the silicon wafer to be tested, wherein the height value is the height difference between the measurement point and an imaging objective lens located at a preset height;

[0034] The overlay measurement unit is used to control the imaging objective lens to move to a target focusing position corresponding to the target height value according to the target height value and the measurement position, and to perform overlay measurement on the overlay mark to be measured.

[0035] 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:

[0036] The memory is used to store computer programs;

[0037] The processor is used to execute the computer program so that the overlay measurement device can implement the overlay measurement method of the above-mentioned first aspect or any implementation manner of the first aspect.

[0038] 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 perform the overlay measurement method of the first aspect or any implementation of the first aspect.

[0039] A fifth aspect of the present application provides a computer program product, including a computer program, which, when executed by a processor, implements the overlay measurement method of the above-mentioned first aspect or any implementation manner of the first aspect.

[0040] It can be seen from the above technical solutions that the overlay measurement method provided in the embodiment of the present application, before the overlay measurement of the overlay mark to be measured in the silicon wafer, obtains the height value of the overlay mark to be measured according to the pre-established objective function of the height of different measurement positions in the silicon wafer to be measured and the distance thereto from the imaging objective lens. Further, according to the height value of the overlay mark to be measured, the imaging objective lens is adjusted to the target focusing position for overlay measurement. Based on this, in the case where the silicon wafer has a plurality of overlay marks of non-uniform heights, the embodiment of the present application can perform adaptive focusing according to the height of each overlay mark. Compared with the measurement method of the unified focal length in the prior art, each overlay mark to be measured can be imaged at the corresponding optimal focal length, thereby improving the imaging effect, thereby improving the accuracy of the overlay measurement of each overlay mark in the silicon wafer to be measured. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] 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.

[0042] Figure 1 A schematic diagram of a flow chart of a method for implementing overlay measurement provided in an embodiment of the present application;

[0043] Figure 2 A schematic diagram showing the positional relationship between the overlay mark and the imaging objective lens provided in an embodiment of the present application;

[0044] Figure 3 An example diagram of measurement point locations provided in an embodiment of the present application;

[0045] Figure 4 Another schematic diagram of a flow chart of a method for implementing overlay measurement provided in an embodiment of the present application;

[0046] Figure 5 A schematic diagram of the structure of the overlay measurement device provided in an embodiment of the present application;

[0047] Figure 6 A schematic diagram of the structure of the overlay measurement device provided in an embodiment of the present application. DETAILED DESCRIPTION

[0048] 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.

[0049] The embodiments of the present application take into account factors such as the height difference of the surface of the silicon wafer to be measured, as well as the slight height difference caused by the tilt of hardware equipment such as the imaging objective lens and the silicon wafer stage. Different overlay marks in the same silicon wafer have different corresponding height values. If a unified focusing parameter is used to capture images of all overlay marks, some overlay marks will fail to focus, affecting the results of the overlay measurement.

[0050] To solve the above problems, an embodiment of the present application proposes an overlay measurement method. Before overlay measurement is performed on each overlay mark in the silicon wafer to be measured, the height value of each overlay mark is obtained in advance, and the focusing position of the imaging objective lens is adaptively adjusted according to the height value, so that the imaging objective lens can capture each overlay mark in the best focusing state, thereby improving the accuracy of the overlay measurement result.

[0051] Reference Figure 1 , a flow chart of implementing the overlay measurement method provided in an embodiment of the present application, which illustrates the process of implementing the overlay measurement method, wherein the following steps are specifically included:

[0052] Step S110 , in response to a measurement request for an overlay mark to be measured in a silicon wafer to be measured, determining a measurement position of the overlay mark to be measured.

[0053] Step S120 , inputting the measurement position into a pre-established target function corresponding to the silicon wafer to be measured, and determining a target height value corresponding to the measurement position.

[0054] Step S130, according to the target height value and the measurement position, the imaging objective lens is controlled to move to the target focusing position corresponding to the target height value, and overlay measurement is performed on the overlay mark to be measured.

[0055] The objective function is a function obtained by data fitting based on the measurement positions of multiple measurement points in the silicon wafer to be tested and the height value corresponding to each measurement position. It is used to characterize the correspondence between the measurement position and the height value of each measurement point in the silicon wafer to be tested, and the height value is the height difference between the measurement point and the imaging objective lens at a preset height.

[0056] There are multiple overlay marks to be measured on the silicon wafer to be tested, and there are slight differences in the height of each overlay mark. If the height values ​​of the overlay marks are measured one by one, the efficiency of the overlay measurement will be greatly reduced. Therefore, the embodiment of the present application adopts a data fitting method to determine the objective function that characterizes the relationship between the position and height of each measurement point in the silicon wafer to be tested. Among them, the measurement point refers to any position point on the silicon wafer to be tested where the overlay measurement is performed, and the position of the measurement point refers to the position coordinate in the two-dimensional coordinate system established with the plane where the silicon wafer to be tested is located. Based on this, when the overlay mark is subsequently overlaid, the height value corresponding to the position of the overlay mark can be determined according to the objective function, which is more efficient than manually measuring the height value.

[0057] Reference Figure 2 , a schematic diagram showing the positional relationship between the overlay mark and the imaging objective lens provided in an embodiment of the present application, wherein the height value of the overlay mark can be taken as a reference to the plane where the silicon wafer stage is located, and the distance between the plane where the highest point of the overlay mark is located and the plane where the silicon wafer stage is located is taken as the height value of the overlay mark, that is, Figure 2 h in . The positions of multiple measurement points and their corresponding height values ​​h are fitted to obtain a functional relationship. According to the functional relationship, before the overlay mark is overlaid, the height of the overlay mark from the silicon wafer stage can be obtained in advance, and the imaging objective lens can be focused according to the height.

[0058] Considering that the focusing of the imaging objective lens mainly refers to the distance between the overlay mark and the objective lens, even if the height h of the overlay mark is obtained according to the above-mentioned fitting function relationship, it is necessary to further measure the distance H between the imaging objective lens and the silicon wafer stage, and further determine the focusing strategy of the imaging objective lens according to the difference between h and H. Based on this, the difference between the height value h of the measuring point and the height value H of the imaging objective lens, that is, the height value Z of the measuring point, is fitted with the position of the measuring point. It can be understood that in order to ensure the reliability and accuracy of the height value, the height value H of the imaging objective lens remains unchanged. Optionally, the imaging objective lens is located at the initial position pre-calibrated by the imaging overlay device, or the imaging overlay objective lens is located at the optimal focal plane position, etc.

[0059] Specifically, the process of pre-establishing the objective function corresponding to the silicon wafer to be tested may include: determining the measurement positions of a preset number of measurement points evenly distributed in the silicon wafer to be tested based on the size of the silicon wafer to be tested; obtaining the height value corresponding to the measurement position of each measurement point; performing data fitting on the measurement position and height value corresponding to each measurement point to obtain the objective function that characterizes the correspondence between the measurement position and the height value in the silicon wafer to be tested.

[0060] Reference Figure 3 , an example diagram of the measurement point position provided in the embodiment of the present application, first, a plurality of measurement points are randomly selected from the silicon wafer to be measured, and the measurement position of the measurement point is obtained, wherein the measurement position refers to the position coordinate (x i ,y i ). Optionally, in order to ensure that the height of the measuring point can reflect the overall height distribution of the silicon wafer to be measured as much as possible, multiple measuring points evenly distributed on the silicon wafer to be measured can be selected according to the size of the silicon wafer to be measured. Figure 3 The silicon wafer is usually circular, and multiple measurement points and the measurement positions of the measurement points can be determined based on the radius of the silicon wafer and the angle of the measurement point. Optionally, the measurement points on the silicon wafer can be determined based on equally spaced angles. For example, the detection points can be determined at intervals of 120 degrees, with reference to the calculation formula for the measurement position of the measurement point shown in the following formula (1):

[0061] (1)

[0062] Among them, x i ,y i represent the abscissa and ordinate of the measurement position of the ith measurement point respectively, n represents the total number of measurement points in the silicon wafer to be measured, and r represents the radius of the silicon wafer to be measured.

[0063] Furthermore, the height value Z of each measuring point is measured, and the height value Z of each measuring point and the measuring position (x i ,y i) is used to perform data fitting processing to obtain the functional relationship shown in formula (2).

[0064] (2)

[0065] Among them, the function f(x i ,y i ) can be a linear function, a quadratic fitting function (quadratic polynomial), or a high-order polynomial fitting function. Figure 3 Taking the three measurement points shown as an example, according to the positions and height values ​​corresponding to the three measurement points, a linear function fitting is adopted to obtain the following equation group (3).

[0066] (3)

[0067] Among them, (x1, y1), (x2, y2), (x3, y3) represent the plane coordinates of the measurement positions corresponding to the three measurement points, respectively, and K0, K1, K2 are the linear function coefficients. Solving the equation group of the above formula (3), we can obtain the values ​​of the linear function coefficients K0, K1, K2, and thus determine the objective function f(x i ,y i ). Wherein, K0 represents the overall height of the silicon wafer or wafer to be tested, and K1 and K2 represent the overall wedge tilt angles of the wafer in the Y direction and the X direction, respectively.

[0068] According to the objective function f(x i ,y i ), determine the height value Z corresponding to the measurement position (x, y) where the overlay mark to be measured in the silicon wafer to be measured is located. Further, first control the imaging objective lens to move to the measurement position (x, y), then adjust the imaging objective lens according to the height value Z, so that it performs focus scanning in the Z direction, determine the focus position with the best focusing effect on the overlay mark at the measurement position, then control the imaging objective lens to collect the image of the overlay mark at the focus position, and perform subsequent operations such as overlay measurement.

[0069] In summary, the overlay measurement method provided in the embodiment of the present application, before the overlay measurement of the overlay mark to be measured in the silicon wafer is performed, obtains the height value of the overlay mark to be measured according to the pre-established objective function of the height of different measurement positions in the silicon wafer to be measured and the distance thereto from the imaging objective lens. Further, according to the height value of the overlay mark to be measured, the imaging objective lens is adjusted to the target focusing position for overlay measurement. Based on this, in the case where the silicon wafer has a plurality of overlay marks of non-uniform heights, the embodiment of the present application can perform adaptive focusing according to the height of each overlay mark. Compared with the measurement method of uniform focal length in the prior art, each overlay mark to be measured can be imaged at the corresponding optimal focal length, thereby improving the imaging effect, thereby improving the accuracy of the overlay measurement of each overlay mark in the silicon wafer to be measured.

[0070] Next, the embodiments of the present application illustrate other possible implementations of the overlay measurement method described above.

[0071] In a possible implementation, step S130 controls the imaging objective lens to move to a target focusing position corresponding to the target height value based on the target height value and the measurement position, and performs overlay measurement on the overlay mark to be measured, including: controlling the imaging objective lens to move to the measurement position of the overlay mark to be measured; determining an initial focusing height corresponding to the overlay mark to be measured based on the target height value corresponding to the measurement position; controlling the imaging objective lens to move according to a preset step distance within a preset height range of the initial focusing height, and controlling the imaging objective lens to capture an image of the overlay mark to be measured at a height of the preset step distance; determining the height value corresponding to the image with the highest clarity from the captured image as the target focal length position of the imaging objective lens; and controlling the imaging objective lens to move to the target focal length position.

[0072] It is understandable that although conventional imaging overlay measurement equipment uses a uniform focusing height to image the silicon wafer to be measured, the focusing height is usually an optimal focusing height determined in advance for the overall height of the silicon wafer to be measured. The embodiment of the present application can utilize the correspondence between the overall height of the silicon wafer and the optimal focusing height in the past to determine the optimal focusing height corresponding to the overall height equal to the target height Z as the focusing height for the overlay measurement corresponding to the target height Z. Based on this, the imaging objective lens is directly moved to the focusing height of the test position to photograph the overlay mark, which can save the process of focusing the imaging objective lens and improve the efficiency of the overlay measurement.

[0073] However, considering that focusing is not only related to the position of the objective lens such as the focal plane position and focal length, but also to the external lighting environment, the reflectivity of the silicon wafer material, etc., the above-obtained focusing height is not necessarily the best for the focusing effect of the overlay mark. Therefore, the embodiment of the present application uses the focusing height as the initial focusing height, adjusts the height of the imaging objective lens within the preset range of the initial focusing height, and determines the optimal focusing height corresponding to the target height value Z of the overlay mark. Based on this, compared with the method of re-controlling the imaging objective lens in the Z direction to perform focusing scanning and find the optimal focusing height, the method of adjusting the height of the imaging objective lens within the preset range of the initial focusing height to find the optimal focusing height narrows the range of the focusing scan, thereby reducing the time for finding the optimal focusing height and improving the focusing efficiency.

[0074] During focusing scanning, the imaging objective lens is controlled to move within the preset range of the initial focusing height with a preset step distance, and after each step distance is moved, the imaging objective lens is controlled to collect the image of the overlay mark at the height after the movement, and the focusing degree, clarity, etc. of the image at each height are identified and compared, and the height with the best focusing effect is determined as the target focusing height corresponding to the overlay mark. Among them, since the focusing after determining the initial focusing height is fine focusing, the step distance can be set smaller to improve the focusing accuracy.

[0075] In another possible implementation, the initial focusing height corresponding to the overlay mark to be measured is determined based on the target height value corresponding to the measurement position, including: obtaining the height value and focusing position corresponding to the previous overlay mark to be measured, as the historical height value and the historical focusing position, respectively; judging whether the difference between the historical height value and the target height value is less than a preset threshold; when the difference between the historical height value and the target height value is less than the preset threshold, determining the focusing height of the historical focusing position as the initial focusing height corresponding to the overlay mark to be measured this time; when the difference between the historical height value and the target height value is not less than the preset threshold, determining the pre-set focusing height corresponding to the target height value as the initial focusing height corresponding to the overlay mark to be measured this time.

[0076] If the difference between the height value of the overlay mark measured last time and the height value of the overlay mark measured this time is small, or they are almost the same height, the target focusing height corresponding to the overlay mark measured last time can be directly used as the initial focusing height of the overlay mark measured this time, saving the process of adjusting the imaging objective lens from the initial focusing height to the target focusing height, thereby improving the focusing efficiency.

[0077] However, considering the slight differences in the heights of the overlay marks and the impact of changes in the positions of the overlay marks, the target focusing height corresponding to the overlay mark measured last time may only be close to the target focusing height of this measurement, but not completely equal. Therefore, in order to improve the focusing accuracy, the focusing height corresponding to the overlay mark measured last time is used as the initial focusing height of this measurement.

[0078] For example, if the height value of the overlay mark a in the same silicon wafer to be tested measured last time is 10, and the height value of the overlay mark b measured this time is 10.2, the height values ​​between the two are almost equal, and the corresponding optimal focusing heights of the imaging objective lens are also almost the same. The focusing height in the target focusing position corresponding to the overlay mark a is 40, so the focusing height of the overlay mark b can also be set to 40, but considering that there is a height difference of 0.2 between the overlay mark a and the overlay mark b, there may be a slight difference in the optimal focusing height, and the imaging objective lens may not be able to achieve the best focus on the overlay mark b at the focusing height of 40. Therefore, the focusing height of 40 is used as the initial focusing height of the overlay mark b, and subsequent focusing is performed. Assuming that the optimal focusing height of the overlay mark d is 40.2 after the final focusing, the focusing scanning process of the imaging objective lens is only 0.2. If the optimal focusing height 41 determined by the height of 10.2 is used as the initial focusing height, the focusing scanning process required for the imaging objective lens to adjust to the optimal focusing height is 0.8. Based on this, when the height difference between two adjacent overlay marks is less than a certain threshold, the target focus height corresponding to the previous overlay mark can be used as the initial focus height corresponding to the current overlay mark, which can effectively improve the focusing efficiency.

[0079] According to the initial focusing height determined above, the imaging objective lens is focused to determine the focusing height with the best focusing effect on the overlay mark at the measurement position, which is used as the target focusing height for subsequent image acquisition and overlay measurement.

[0080] In another possible implementation, before obtaining the measurement position of the overlay mark to be tested, it also includes: aligning the silicon wafer to be tested and the mask according to the alignment marks on the silicon wafer to be tested and the alignment marks on the mask; and obtaining the measurement position of the overlay mark to be tested in the aligned silicon wafer to be tested.

[0081] The overlay measurement process for the silicon wafer to be tested includes alignment and overlay mark measurement. Among them, alignment is the process of aligning the positioning points or alignment marks on the silicon wafer with the positioning points or alignment marks on the photoresist or mask. In this process, the images of the silicon wafer and the alignment marks on the mask are captured by the imaging objective lens, and the placement of the silicon wafer is adjusted according to the displacement deviation of the two marks in the image to achieve alignment. Therefore, both alignment and overlay mark measurement require focusing and collecting images at different positions of the silicon wafer to be tested.

[0082] Based on this, before focusing the overlay mark on the silicon wafer to be tested, align the silicon wafer to be tested with the mask first. It can be understood that the imaging objective, silicon wafer stage, etc. all use the same two-dimensional coordinate system in the horizontal direction. On the basis of silicon wafer alignment, the measurement position of each overlay mark is more accurately positioned. Moreover, after alignment, the deviation value obtained after overlay measurement of the overlay mark only refers to the deviation between the overlay marks. Otherwise, the deviation value still has the deviation introduced by the misalignment of the silicon wafer, resulting in incorrect results of the overlay mark. Therefore, focusing and overlay measurement of the overlay mark after alignment can improve the accuracy of the overlay measurement.

[0083] Optionally, the silicon wafer to be tested and the mask are aligned based on the alignment marks on the silicon wafer to be tested and the alignment marks on the mask, including: obtaining the mark position of each alignment mark on the silicon wafer to be tested, and a preset focusing position corresponding to the mark position; controlling the imaging objective lens to move to the mark position of each alignment mark, and the preset focusing position corresponding to the mark position, and collecting a mark image of each alignment mark, the mark image including at least: the alignment mark of the silicon wafer to be tested and the alignment mark of the mask; based on the deviation between the alignment mark of the silicon wafer to be tested and the alignment mark of the mask in all the mark images, adjusting the position of the silicon wafer to be tested, so that the deviation between the alignment mark of the silicon wafer to be tested and the alignment mark of the mask meets the preset deviation threshold.

[0084] There are usually multiple alignment marks between the silicon wafer to be tested and the mask. According to the placement of the silicon wafer to be tested, the alignment marks in the silicon wafer to be tested and the mask are aligned. It can be understood that the alignment marks on the silicon wafer to be tested are similar to the overlay marks, and both have different heights. Therefore, focusing is still required during the process of capturing the alignment mark image.

[0085] Specifically, the alignment process of any alignment mark in the silicon wafer to be tested is taken as an example to illustrate that the height value of the alignment mark is determined according to the objective function obtained in the above step S110 and the measurement position of the alignment mark in the silicon wafer to be tested. The control stage drives the imaging objective lens to move to the measurement position, and performs focus scanning in the Z direction at the initial focus position corresponding to the height value to determine the best focus position for collecting the alignment mark image.

[0086] The captured alignment mark image includes at least: the alignment mark of the silicon wafer to be tested and the alignment mark of the mask, and there may be a deviation between the two. According to the deviation shown in the image, the position of the silicon wafer to be tested is adjusted to align the two alignment marks as much as possible, for example: the deviation value between the two alignment marks does not exceed the preset threshold. Furthermore, the image of the alignment mark can be captured again for alignment verification, and the alignment position of the two alignment marks can be adjusted until the positional relationship between the two alignment marks meets the alignment requirements, and then the imaging objective lens is controlled to move to the measurement position where the next alignment mark is located, and the above alignment process is repeated, based on which the alignment of each alignment mark is achieved.

[0087] In summary, the embodiment of the present application samples the height values ​​between a plurality of different measuring positions in the silicon wafer to be measured and the imaging objective lens before the overlay measurement, and obtains height prior information by fitting the height of all positions in the silicon wafer to be measured from the imaging objective lens according to the measurement results. Based on the prior information, it can ensure that all measuring points are focused successfully, thereby improving the focusing stability. During the overlay measurement, the focusing height of the imaging objective lens at the measuring position of the overlay mark is set according to the height value obtained by fitting, and a small-range focusing scan is performed near the focusing height, which can shorten the focusing stroke and increase the focusing speed. In addition, before performing the overlay measurement, the silicon wafer to be measured and the mask are first aligned to reduce the influence of the alignment error on the overlay measurement result and improve the accuracy of the overlay measurement.

[0088] Reference Figure 4 , another flow chart of implementing the overlay measurement method provided in an embodiment of the present application is used to exemplify the practical application of the above-mentioned overlay measurement method.

[0089] First, according to the pre-fitted objective function f(x i ,y i ), solve the height values ​​corresponding to all alignment marks and all overlay marks in the silicon wafer to be tested. Further, align each alignment mark first, set the initial position of the Z-axis motion stage of the imaging objective lens according to the height value corresponding to the alignment mark, that is, the initial focusing position, and start scanning and focusing near the initial focusing position to find the best focusing position. Based on the image of the alignment mark taken at the best focusing position, align the silicon wafer to be tested and the mask. After alignment, determine whether all alignment marks have been aligned. If the judgment result is no, control the imaging objective lens to move to the next alignment mark to perform the above alignment process; if the judgment result is yes, start the overlay measurement of the overlay mark.

[0090] According to the measurement order of the overlay marks, the imaging objective lens is moved to the measurement position where the first overlay mark to be measured is located, and the position of the Z-direction motion stage of the imaging objective lens, i.e., the initial focusing height, is controlled according to the height value corresponding to the measurement position obtained in advance. Furthermore, the imaging objective lens is driven to perform scanning and focusing by a PZT nano-displacement stage, wherein the PZT nano-displacement stage refers to a piezoelectric nano-displacement stage, and the PZT nano-displacement stage is usually mounted on the Z-direction motion stage as a Z-direction fine-tuning mechanism, which has higher precision than a conventional Z-direction motion stage. The PZT nano-displacement stage can drive the imaging objective lens to move up and down in the Z direction, so that the imaging objective lens scans images at different positions in the Z direction to obtain a high-precision focal plane position and achieve precise focusing. At the focal plane position obtained by precise focusing, i.e., the optimal focusing position, the first overlay mark to be measured is subjected to image acquisition and overlay measurement.

[0091] Further, after the measurement is completed, the measurement position of the next overlay mark is moved to the measurement position, and the initial focusing position of the corresponding imaging objective lens is determined according to the height value corresponding to the next overlay mark. When determining the initial focusing position, it can be first determined whether the height difference between the next overlay mark and the previous overlay mark is less than the stroke of the PZT nano displacement stage. The stroke can be understood as the displacement of the PZT from the initial focusing position to the optimal focusing position during the fine focusing process of the previous overlay mark. If the height difference between the previous overlay mark and the next overlay mark is less than the displacement, it proves that the height difference between the two overlay marks is small and the optimal focusing position is close, then the fine focusing focusing position of the previous overlay mark can be used as the initial focusing position of the next overlay mark. When adjusting the imaging objective lens to measure the next overlay mark, the imaging objective lens can be moved only in the horizontal direction to the measurement position corresponding to the next overlay mark. The height of the imaging objective lens does not need to be adjusted and is maintained at the optimal focusing position of the previous overlay mark. When fine focusing is performed on the next overlay mark, scanning focusing is performed at the optimal focusing position to improve focusing efficiency.

[0092] On the contrary, if the height difference between the previous overlay mark and the next overlay mark is not less than the displacement, it proves that the height difference between the two overlay marks is large, and the difference between the best focus positions is far, and the initial focus position can be reset according to the height value of the next overlay mark. Based on this, the embodiment of the present application focuses on each overlay mark in a targeted manner according to the height value between each overlay mark in the silicon wafer. Compared with the prior art using a unified focusing parameter, the present application improves the flexibility of overlay measurement, so that each overlay mark is imaged at the best focus state of the imaging objective lens, and the obtained image is clearer, thereby improving the accuracy of the overlay measurement result.

[0093] 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.

[0094] 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:

[0095] A position determination unit 100 is used to determine a measurement position of an overlay mark to be measured in a silicon wafer to be measured in response to a measurement request for the overlay mark to be measured;

[0096] A height value determination unit 200 is used to input the measurement position into a pre-established target function corresponding to the silicon wafer to be tested, and determine a target height value corresponding to the measurement position, wherein the target function is a function obtained by performing data fitting on the measurement positions of multiple measurement points in the silicon wafer to be tested and the height value corresponding to each measurement position, and is used to characterize the correspondence between the measurement position and the height value of each measurement point in the silicon wafer to be tested, and the height value is the height difference between the measurement point and an imaging objective lens located at a preset height;

[0097] The overlay measurement unit 300 is used to control the imaging objective lens to move to a target focusing position corresponding to the target height value according to the target height value and the measurement position, and perform overlay measurement on the overlay mark to be measured.

[0098] In summary, before the overlay measurement of the overlay mark to be measured in the silicon wafer is performed, the embodiment of the present application obtains the height value of the overlay mark to be measured according to the pre-established objective function of the height of different measurement positions in the silicon wafer to be measured and the distance thereto from the imaging objective lens. Further, according to the height value of the overlay mark to be measured, the imaging objective lens is adjusted to the target focusing position for overlay measurement. Based on this, when the silicon wafer has a plurality of overlay marks with non-uniform heights, the embodiment of the present application can perform adaptive focusing according to the height of each overlay mark. Compared with the measurement method of the unified focal length in the prior art, each overlay mark to be measured can be imaged at the corresponding optimal focal length, thereby improving the imaging effect, thereby improving the accuracy of the overlay measurement of each overlay mark in the silicon wafer to be measured.

[0099] In a possible implementation, the functional unit for pre-establishing the objective function corresponding to the silicon wafer to be tested includes:

[0100] A measuring point determination unit, used to determine the measuring positions of a preset number of measuring points evenly distributed in the silicon wafer to be measured according to the size of the silicon wafer to be measured;

[0101] A height value acquisition unit, used to acquire a height value corresponding to the measurement position of each measurement point;

[0102] The data fitting unit is used to perform data fitting on the measurement position and the height value corresponding to each measurement point to obtain an objective function that characterizes the corresponding relationship between the measurement position and the height value in the silicon wafer to be measured.

[0103] In a possible implementation, the overlay measurement unit 300 includes:

[0104] A position moving subunit, used for controlling the imaging objective lens to move to the measuring position of the overlay mark to be measured;

[0105] An initial height determination subunit, used for determining an initial focus height corresponding to the overlay mark to be measured according to the target height value corresponding to the measurement position;

[0106] An image acquisition subunit, used to control the imaging objective lens to move within a preset height range of the initial focusing height according to a preset step distance, and to control the imaging objective lens to capture an image of the overlay mark to be measured at the height of the preset step distance;

[0107] A target focus position determination subunit, used to determine the height value corresponding to the image with the highest definition from the captured image as the target focal length position of the imaging objective lens;

[0108] The control moving subunit is used to control the imaging objective lens to move to the target focal length position.

[0109] In a possible implementation, the initial height determination subunit includes:

[0110] A historical focus information acquisition subunit is used to acquire the height value and focus position corresponding to the last overlay mark to be measured, as the historical height value and historical focus position respectively;

[0111] A threshold judgment subunit, used to judge whether the difference between the historical altitude value and the target altitude value is less than a preset threshold;

[0112] The first initial height determination subunit is used to determine the focus height of the historical focus position as the initial focus height corresponding to the overlay mark to be measured in this measurement when the threshold judgment subunit is yes;

[0113] The second initial height determination subunit is used to determine, when the threshold judgment subunit is negative, a preset focus height corresponding to the target height value as the initial focus height corresponding to the overlay mark to be measured this time.

[0114] In a possible implementation, the method further includes:

[0115] An alignment unit, used for aligning the silicon wafer to be tested with the mask according to the alignment mark on the silicon wafer to be tested and the alignment mark on the mask;

[0116] The position acquisition unit is used to acquire the measurement position of the overlay mark to be tested in the aligned silicon wafer to be tested.

[0117] In a possible implementation, the alignment unit includes:

[0118] A mark position acquisition subunit, used to acquire the mark position of each alignment mark on the silicon wafer to be tested, and a preset focus position corresponding to the mark position;

[0119] An alignment image acquisition subunit, used to control the imaging objective lens to move to the mark position of each alignment mark and the preset focus position corresponding to the mark position, and to acquire a mark image of each alignment mark, wherein the mark image at least includes: the alignment mark of the silicon wafer to be tested and the alignment mark of the mask;

[0120] The silicon wafer alignment subunit is used to adjust the position of the silicon wafer to be tested according to the deviation between the alignment mark of the silicon wafer to be tested and the alignment mark of the mask in all the mark images, so that the deviation between the alignment mark of the silicon wafer to be tested and the alignment mark of the mask meets a preset deviation threshold.

[0121] The overlay measurement device provided in the embodiment of the present application can be applied to overlay measurement equipment.

[0122] 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.

[0123] 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 .

[0124] 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.

[0125] 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.

[0126] 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 above-mentioned overlay measurement method.

[0127] A computer storage medium is also provided in an embodiment of the present application. The storage medium carries one or more computer programs. When the one or more computer programs are executed by the overlay measurement device, the overlay measurement device can implement any one of the overlay measurement methods provided in the embodiment of the present application.

[0128] An embodiment of the present application also provides a computer program product including computer-readable instructions. When the computer-readable instructions are executed on an overlay measurement device, the overlay measurement device implements any one of the overlay measurement methods provided in the embodiments of the present application.

[0129] It should also be noted that the device embodiments described above are merely schematic, wherein the units described as separate components may or may not be physically separated, and the components displayed as units may or may not be physical units, that is, they may be located in one place, or they may be distributed over multiple network units. Some or all of the modules may be selected according to actual needs to achieve the purpose of the scheme of this embodiment. In addition, in the drawings of the device embodiments provided by the present application, the connection relationship between the modules indicates that there is a communication connection between them, which may be specifically implemented as one or more communication buses or signal lines.

[0130] Through the description of the above implementation mode, the technicians in the field can clearly understand that the present application can be implemented by means of software plus necessary general hardware, and of course, it can also be implemented by special hardware including special integrated circuits, special CPUs, special memories, special components, etc. In general, all functions completed by computer programs can be easily implemented by corresponding hardware, and the specific hardware structure used to implement the same function can also be various, such as analog circuits, digital circuits or special circuits. However, for the present application, software program implementation is a better implementation mode in more cases. Based on such an understanding, the technical solution of the present application is essentially or the part that contributes to the prior art can be embodied in the form of a software product, which is stored in a readable storage medium, such as a computer floppy disk, a U disk, a mobile hard disk, a ROM, a RAM, a disk or an optical disk, etc., including a number of instructions to enable a computer device (which can be a personal computer, a training device, or a network device, etc.) to execute the methods described in each embodiment of the present application.

[0131] In the above embodiments, all or part of the embodiments may be implemented by software, hardware, firmware or any combination thereof. When implemented by software, all or part of the embodiments may be implemented in the form of a computer program product.

[0132] The computer program product includes one or more computer instructions. When the computer program instructions are loaded and executed on a computer, the process or function described in the embodiment of the present application is generated in whole or in part. The computer may be a general-purpose computer, a special-purpose computer, a computer network, or other programmable devices. The computer instructions may be stored in a computer-readable storage medium, or transmitted from one computer-readable storage medium to another computer-readable storage medium. For example, the computer instructions may be transmitted from a website site, a computer, a training device, or a data center by wired (e.g., coaxial cable, optical fiber, digital subscriber line (DSL)) or wireless (e.g., infrared, wireless, microwave, etc.) mode to another website site, computer, training device, or data center. The computer-readable storage medium may be any available medium that a computer can store or a data storage device such as a training device, a data center, etc. that includes one or more available media integrations. The available medium may be a magnetic medium, (e.g., a floppy disk, a hard disk, a tape), an optical medium (e.g., a DVD), or a semiconductor medium (e.g., a solid-state drive (SSD)), etc.

[0133] 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.

[0134] 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.

[0135] 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: include: In response to a measurement request for an overlay mark to be measured in a silicon wafer to be measured, determining a measurement position of the overlay mark to be measured; Input the measurement position into a pre-established target function corresponding to the silicon wafer to be tested, and determine a target height value corresponding to the measurement position, wherein the target function is a function obtained by performing data fitting on the measurement positions of a plurality of measurement points in the silicon wafer to be tested, and the height value corresponding to each measurement position, and is used to characterize the corresponding relationship between the measurement position and the height value of each measurement point in the silicon wafer to be tested, wherein the height value is the height difference between the measurement point and an imaging objective lens located at a preset height; According to the target height value and the measurement position, the imaging objective lens is controlled to move to a target focusing position corresponding to the target height value, and overlay measurement is performed on the overlay mark to be measured.

2. The overlay measurement method according to claim 1, characterized in that: The process of pre-establishing the objective function corresponding to the silicon wafer to be tested includes: Determining measurement positions of a preset number of measurement points evenly distributed in the silicon wafer to be measured according to the size of the silicon wafer to be measured; Obtaining a height value corresponding to the measurement position of each measurement point; Data fitting is performed on the measurement position and the height value corresponding to each measurement point to obtain an objective function that characterizes the corresponding relationship between the measurement position and the height value in the silicon wafer to be measured.

3. The overlay measurement method according to claim 1, characterized in that: According to the target height value and the measurement position, controlling the imaging objective lens to move to the target focusing position corresponding to the target height value, and performing overlay measurement on the overlay mark to be measured, comprises: Controlling the imaging objective lens to move to the measuring position of the overlay mark to be measured; Determining an initial focus height corresponding to the overlay mark to be measured according to the target height value corresponding to the measuring position; Controlling the imaging objective lens to move within a preset height range of the initial focusing height according to a preset step distance, and controlling the imaging objective lens to capture an image of the overlay mark to be measured at the height of the preset step distance; From the captured images, a height value corresponding to an image with the highest definition is determined as a target focal length position of the imaging objective lens; The imaging objective lens is controlled to move to the target focal length position.

4. The overlay measurement method according to claim 3, characterized in that: Determining the initial focus height corresponding to the overlay mark to be measured according to the target height value corresponding to the measurement position includes: Obtain the height value and focus position corresponding to the last overlay mark to be measured, as the historical height value and historical focus position respectively; Determine whether the difference between the historical altitude value and the target altitude value is less than a preset threshold; When the difference between the historical height value and the target height value is less than the preset threshold, the focus height of the historical focus position is determined as the initial focus height corresponding to the overlay mark to be measured in this measurement; When the difference between the historical height value and the target height value is not less than the preset threshold, the preset focus height corresponding to the target height value is determined as the initial focus height corresponding to the overlay mark to be measured this time.

5. The overlay measurement method according to claim 1, characterized in that: Before determining the measurement position of the overlay mark to be measured, the method further includes: Aligning the silicon wafer to be tested with the mask according to the alignment marks on the silicon wafer to be tested and the alignment marks on the mask; The measurement position of the overlay mark to be tested in the aligned silicon wafer to be tested is obtained.

6. The overlay measurement method according to claim 5, characterized in that: The step of aligning the silicon wafer to be tested with the mask according to the alignment mark on the silicon wafer to be tested and the alignment mark on the mask comprises: Acquire the mark position of each alignment mark on the silicon wafer to be tested, and a preset focus position corresponding to the mark position; Controlling the imaging objective lens to move to the mark position of each alignment mark and the preset focus position corresponding to the mark position, and collecting a mark image of each alignment mark, wherein the mark image at least includes: the alignment mark of the silicon wafer to be tested and the alignment mark of the mask; According to the deviation between the alignment mark of the silicon wafer to be tested and the alignment mark of the mask in all the mark images, the position of the silicon wafer to be tested is adjusted so that the deviation between the alignment mark of the silicon wafer to be tested and the alignment mark of the mask meets a preset deviation threshold.

7. An overlay measurement device, characterized in that: include: A position determination unit, configured to determine a measurement position of an overlay mark to be measured in response to a measurement request for the overlay mark to be measured in the silicon wafer to be measured; a height value determination unit, used for inputting the measurement position into a pre-established target function corresponding to the silicon wafer to be tested, and determining a target height value corresponding to the measurement position, wherein the target function is a function obtained by performing data fitting on the measurement positions of a plurality of measurement points in the silicon wafer to be tested, and the height value corresponding to each measurement position, and is used for characterizing the correspondence between the measurement position of each measurement point in the silicon wafer to be tested and the height value, wherein the height value is a height difference between the measurement point and an imaging objective lens located at a preset height; The overlay measurement unit is used to control the imaging objective lens to move to a target focusing position corresponding to the target height value according to the target height value and the measurement position, and to perform overlay measurement on the overlay mark to be measured.

8. 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 6.

9. A 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 6.

10. A computer program product, comprising a computer program, characterized in that When the computer program is executed by a processor, each step of the overlay measurement method according to any one of claims 1 to 6 is implemented.

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