A method for overlay measurement

Abstract

The present invention discloses a method for overlay measurement. The method includes: obtaining a first image formed by a first layer of patterns and a first intermediate layer of patterns adjacent to the first layer of patterns; sequentially obtaining an (i + 2)-th image formed by an (i + 1)-th intermediate layer of patterns and an (i + 2)-th intermediate layer of patterns adjacent to the (i + 1)-th intermediate layer of patterns; obtaining an (i + 3)-th image formed by the (i + 2)-th intermediate layer of patterns and a second layer of patterns adjacent to the (i + 2)-th intermediate layer of patterns, wherein the intermediate layers of patterns are sequentially stacked on the first layer of patterns; the second layer of patterns is stacked on the (i + 2)-th intermediate layer of patterns; obtaining a first overlay error to an (i + 3)-th overlay error based on the first image to the (i + 3)-th image, and further accumulating the first overlay error to the (i + 3)-th overlay error to obtain the overlay error of the first image relative to the second image. By adding an intermediate layer between the inner and outer ring patterns of the overlay mark in the embodiments of the present invention, the complexity of the overlay measurement process is simplified, and the overlay measurement accuracy and measurement throughput are improved.

Description

Technical Field

[0001] The present invention relates to the technical field of overlay measurement, and in particular, to an overlay measurement method. Background Art

[0002] As an optical measurement tool, an overlay measurement device is widely used in industries such as solar cells, integrated circuits, and display panels. The overlay measurement device measures the position deviation between the overlay patterns prepared by the previous process and the current process through an optical detection device, so as to measure the overlay alignment deviation between two process layers.

[0003] For a scenario where the thickness difference between two process layers is less than the available focal depth of the optical lens, usually the focal plane of the optical lens is placed at the 1 / 2 thickness position between the front and back two process layers, then a photo is taken, and the deviation between the center positions of the overlay patterns of the front and back two process layers in this picture is calculated by using image processing. For a scenario where the thickness difference between two process layers is greater than the available focal depth of the optical lens, clear images of the overlay patterns of the front and back two process layers cannot be obtained simultaneously through a single picture. At this time, usually the optical lens is focused on the two process layers, a picture is taken respectively, the center position of the overlay pattern is calculated respectively, and then the deviation between the overlay center positions of the two layers is calculated. Since the Z-axis height of the optical lens is different and the pictures of the two process layers are not taken simultaneously in this scheme. Therefore, crosstalk of systematic errors and random errors in the horizontal position is inevitably introduced into the measurement result of the overlay error. In order to reduce the influence of this crosstalk, the existing scheme reduces the systematic error through a higher-precision and more complex calibration process, and reduces the influence of the random error through a scheme of taking the average value by measuring multiple times. However, the former will increase the measurement complexity, and the latter will increase the time cost of measurement. Summary of the Invention

[0004] The present invention provides an overlay measurement method to solve the problem of large overlay errors when the distance between double-layer patterns is greater than the focal depth of the image acquisition device in related technologies. By using this overlay measurement method to measure the overlay error of double-layer patterns, the deviation brought by the overlay measurement device itself is reduced, and the accuracy of overlay measurement is improved.

[0005] An embodiment of the present invention provides an overlay measurement method, which is characterized by including:

[0006] Obtaining a first image formed by a first-layer pattern and a first-layer intermediate pattern adjacent to the first-layer pattern;

[0007] Successively obtain the second image formed by the intermediate layer pattern of the first layer and the intermediate layer pattern of the second layer adjacent to the intermediate layer pattern of the first layer, the third image formed by the intermediate layer pattern of the second layer and the intermediate layer pattern of the third layer adjacent to the intermediate layer pattern of the second layer,..., the (i + 2)-th image formed by the intermediate layer pattern of the (i + 1)-th layer and the intermediate layer pattern of the (i + 2)-th layer adjacent to the intermediate layer pattern of the (i + 1)-th layer;

[0008] Obtain the (i + 3)-th image formed by the intermediate layer pattern of the (i + 2)-th layer and the second layer pattern adjacent to the intermediate layer pattern of the (i + 2)-th layer; wherein, the intermediate layer patterns of each layer are successively stacked on top of the first layer pattern; the second layer pattern is stacked on top of the intermediate layer pattern of the (i + 2)-th layer; the distance between adjacent two layer patterns is less than the depth of focus of the image acquisition device;

[0009] Obtain the first set of registration errors to the (i + 2)-th set of registration errors based on the first image to the (i + 3)-th image, and then accumulate the first set of registration errors to the (i + 2)-th set of registration errors to obtain the registration error of the first image relative to the second image; i is an integer and i ≥ 0.

[0010] Optionally, when the image acquisition device acquires an image each time, and when acquiring images twice in succession, the defocus amount of the focal plane of the image acquisition device from the top of the intermediate layer pattern is the same.

[0011] Optionally, the distance between the first layer pattern and the second layer pattern in the stacking direction is the first height, and the height ratios of the intermediate layer patterns between the first layer pattern and the second layer pattern are the same.

[0012] Optionally, the focal plane of the image acquisition device is located at the middle height position of each layer pattern, and the number of times the image acquisition device takes pictures is one less than the total number of layers of the layer patterns.

[0013] Optionally, when the image acquisition device acquires an image each time, the focal plane of the image acquisition device is located at the top of the layer pattern.

[0014] Optionally, each intermediate layer pattern includes an intermediate registration mark, the first layer pattern includes a first registration mark, and the second layer pattern includes a second registration mark; the shapes of each of the intermediate registration marks, the first registration mark, and the second registration mark are the same.

[0015] Optionally, the first registration mark, each of the intermediate registration marks, and the second registration mark are all one of a closed rectangular frame registration mark or a short line broken rectangular frame registration mark.

[0016] Optionally, the first registration mark, each of the intermediate registration marks, and the second registration mark form a first region, a second region, a third region, and a fourth region;

[0017] In the first region, the first set of alignment marks, each of the intermediate alignment marks, and the second set of alignment marks are arranged in sequence along a first direction, and each type of alignment mark is also arranged along a second direction. The second region is formed by rotating the first region clockwise by 90 degrees. The third region is formed by rotating the second region clockwise by 90 degrees. The fourth region is formed by rotating the third region clockwise by 90 degrees.

[0018] Optionally, the first set of alignment marks, each of the intermediate alignment marks, and the second set of alignment marks form the first region, the second region, the third region, and the fourth region.

[0019] In the first region, the first set of alignment marks and the second set of alignment marks are arranged in sequence along a first direction, and each type of alignment mark is also arranged along a second direction. The first set of alignment marks and the intermediate alignment marks are arranged along the second direction. The second set of alignment marks and the intermediate alignment marks are arranged along the second direction. The second region is formed by rotating the first region clockwise by 90 degrees. The third region is formed by rotating the second region clockwise by 90 degrees. The fourth region is formed by rotating the third region clockwise by 90 degrees.

[0020] Optionally, the method further includes: obtaining a first deviation according to the first-layer intermediate-layer pattern in the first image and the first-layer intermediate-layer pattern in the second image, obtaining a second deviation according to the second-layer intermediate-layer pattern in the second image and the second-layer intermediate-layer pattern in the third image,..., obtaining an (i + 2)-th deviation according to the (i + 2)-th layer intermediate-layer pattern in the (i + 2)-th image and the (i + 2)-th layer intermediate-layer pattern in the (i + 3)-th image.

[0021] Obtaining a precise alignment error between the first-layer pattern and the second-layer pattern according to the alignment error, the first deviation, the second deviation,..., and the (i + 2)-th deviation.

[0022] Wherein, obtaining the precise alignment error between the first-layer pattern and the second-layer pattern according to the alignment error, the first deviation, the second deviation,..., and the (i + 2)-th deviation includes:

[0023] The precise alignment error = the alignment error - the first deviation - the second deviation -... - the (i + 2)-th deviation.

[0024] The technical solution of the embodiment of the present invention adds an intermediate layer between the inner and outer ring patterns of the overlay mark, eliminates the overlay crosstalk caused by horizontal displacement due to factors such as the stage, improves the overlay measurement accuracy, simplifies the complexity of the overlay measurement process, and avoids the overlay measurement error caused by calibration.

[0025] It should be understood that the content described in this part is not intended to identify the key or important features of the embodiments of the present invention, nor is it used to limit the scope of the present invention. Other features of the present invention will become easily understood through the following description. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following will briefly introduce the drawings required for the description of the embodiments. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0027] Figure 1 is a schematic diagram of a device in an overlay measurement method provided by the related art;

[0028] Figure 2 is a schematic side view structure diagram of an overlay mark in an overlay measurement method provided by the related art;

[0029] Figure 3 is a schematic top view structure diagram of an overlay mark in an overlay measurement method provided by the related art;

[0030] Figure 4 is a flowchart of an overlay measurement method provided according to an embodiment of the present invention;

[0031] Figure 5 is a flowchart of an overlay measurement method provided by an embodiment of the present invention;

[0032] Figure 6 is a schematic diagram of a device in an overlay measurement method provided according to an embodiment of the present invention;

[0033] Figure 7 is another schematic diagram of a device in an overlay measurement method provided according to an embodiment of the present invention;

[0034] Figure 8 is a schematic diagram of a device in another overlay measurement method provided according to an embodiment of the present invention;

[0035] Figure 9 is a schematic diagram of a device in another overlay measurement method provided according to an embodiment of the present invention;

[0036] Figure 10It is a top view of a registration mark in a registration measurement method provided according to an embodiment of the present invention;

[0037] Figure 11 It is a top view of another registration mark in a registration measurement method provided according to an embodiment of the present invention;

[0038] Figure 12 It is a top view of yet another registration mark in a registration measurement method provided according to an embodiment of the present invention;

[0039] Figure 13 It is a side view of a registration mark in a registration measurement method provided according to an embodiment of the present invention;

[0040] Figure 14 It is a top view of yet another registration mark in a registration measurement method provided according to an embodiment of the present invention. Detailed implementation manners

[0041] In order to enable those skilled in the art to better understand the solutions of the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0042] It should be noted that the terms "first", "second", etc. in the specification and claims of the present invention and the above-mentioned drawings are used to distinguish similar objects, and do not necessarily need to describe a specific order or sequence. It should be understood that such data can be interchanged under appropriate circumstances so that the embodiments of the present invention described here can be implemented in an order different from those illustrated or described here. In addition, the terms "comprising" and "having" and any variations thereof are intended to cover non-exclusive inclusion.

[0043] The schematic diagram of the detection principle of the existing device is as Figure 1As shown in the figure. For scenarios where the thickness of the inner and outer layer patterns is relatively large (close to the order of the depth of focus), it is usually necessary to take pictures on two planes at different heights for the inner and outer layers respectively. Then, based on the difference in the center positions of the inner and outer layer images obtained through calculation, the overlay error between the inner and outer layer processes can be obtained. This process may introduce two types of errors. One type of error is the systematic error, including the non-perpendicularity of the Z-axis driven by the motor to move the camera up and down with respect to the wafer surface, and the non-parallelism between the optical axis of the lens and the Z-axis, resulting in a position offset between the upper and lower layer patterns captured. This type of error can be minimized by fine calibration to adjust the parallelism between the Z-axis, the wafer normal, and the optical axis of the lens to meet the set threshold. Another type of error is the random position error, including the random jitter of the Z-axis, the position jitter of the wafer stage, etc. To solve this type of error, the existing method is to repeat the test multiple times and use the average effect of the repeated tests to reduce the influence of the random jitter error. This method cannot completely solve the influence of random jitter. To obtain the best effect, more rounds of tests are required, resulting in an increase in the overall test time. The extension of the overall test time may, at the same time, exacerbate the influence of error sources that increase over time, such as hardware drift and thermal noise.

[0044] A side view of a typical implementation of the overlay mark of the existing device is as Figure 2 shown, and the top view is as Figure 3 shown. Generally speaking, Figure 3 in the outer circle pattern is prepared by the previous process, and the inner circle pattern is prepared by the current process. The detection method obtains the overlay error between the inner and outer layer processes by calculating the difference in the center positions of the inner and outer circle patterns.

[0045] Figure 4 The present invention provides a flowchart of an overlay measurement method in an embodiment. This embodiment is applicable to the situation of overlay measurement. As Figure 4 shown, the method includes:

[0046] S101, obtaining a first image formed by the first layer pattern 105 and the first layer intermediate layer pattern 103 adjacent to the first layer pattern 105;

[0047] S102, sequentially obtaining a second image formed by the first layer intermediate layer pattern 103 and the second layer intermediate layer pattern adjacent to the first layer intermediate layer pattern, a third image formed by the second layer intermediate layer pattern and the third layer intermediate layer pattern adjacent to the second layer intermediate layer pattern,..., and an (i + 2)th image formed by the (i + 1)th layer intermediate layer pattern and the (i + 2)th layer intermediate layer pattern adjacent to the (i + 1)th layer intermediate layer pattern;

[0048] S103. Obtain the (i + 3)-th image formed by the intermediate layer pattern of the (i + 2)-th layer and the second layer pattern 102 adjacent to the intermediate layer pattern of the (i + 2)-th layer. Among them, the intermediate layer patterns of each layer are stacked on the first layer pattern 105 in sequence; the second layer pattern 102 is stacked on the intermediate layer pattern of the (i + 2)-th layer; the distance between adjacent two-layer patterns is less than the depth of focus of the image acquisition device 100.

[0049] S104. Obtain the first set of registration errors to the (i + 3)-th set of registration errors based on the first image to the (i + 3)-th image, and then accumulate the first set of registration errors to the (i + 3)-th set of registration errors to obtain the registration error of the first image relative to the second image. i is an integer and i ≥ 0.

[0050] Thus, through the medium of multiple intermediate layer patterns, the first set of registration errors can be obtained based on the first image in sequence, the second set of registration errors can be obtained based on the second image, and so on, until the (i + 3)-th set of registration errors is obtained through the (i + 3)-th image, and by performing accumulation, the registration error between the first layer pattern 105 and the second layer pattern 102 can be obtained.

[0051] Figure 5 The figure is a flowchart of a registration measurement method provided by an embodiment of the present invention. This embodiment is applicable to the situation of registration measurement. As Figure 5 shown, the method includes:

[0052] S201. Obtain the first image formed by the first layer pattern 105 and the first intermediate layer pattern 103 adjacent to the first layer pattern 105.

[0053] S202. Sequentially obtain the second image formed by the first intermediate layer pattern 103 and the second intermediate layer pattern adjacent to the first intermediate layer pattern, the third image formed by the second intermediate layer pattern and the third intermediate layer pattern adjacent to the second intermediate layer pattern,..., the (i + 2)-th image formed by the (i + 1)-th intermediate layer pattern and the (i + 2)-th intermediate layer pattern adjacent to the (i + 1)-th intermediate layer pattern.

[0054] S203. Obtain the (i + 3)-th image formed by the intermediate layer pattern of the (i + 2)-th layer and the second layer pattern 102 adjacent to the intermediate layer pattern of the (i + 2)-th layer. Among them, the intermediate layer patterns of each layer are stacked on the first layer pattern 105 in sequence; the second layer pattern 102 is stacked on the intermediate layer pattern of the (i + 2)-th layer; the distance between adjacent two-layer patterns is less than the depth of focus of the image acquisition device 100.

[0055] S204. Obtain the first set of registration errors to the (i + 3)-th set of registration errors based on the first image to the (i + 3)-th image, and then accumulate the first set of registration errors to the (i + 3)-th set of registration errors to obtain the registration error of the first image relative to the second image. i is an integer and i ≥ 0.

[0056] S205. Obtain a first deviation based on the first-layer intermediate-layer pattern 103 in the first image and the first-layer intermediate-layer pattern 103 in the second image, obtain a second deviation based on the second-layer intermediate-layer pattern in the second image and the second-layer intermediate-layer pattern in the third image,......, obtain an (i + 2)-th deviation based on the (i + 2)-th layer intermediate-layer pattern in the (i + 2)-th image and the (i + 2)-th layer intermediate-layer pattern in the (i + 3)-th image;

[0057] S206. Obtain the precise registration error between the first-layer pattern 105 and the second-layer pattern 102 according to the registration error, the first deviation, the second deviation,......, the (i + 2)-th deviation, where i is an integer and i ≥ 0.

[0058] Among them, in the above two embodiments, the image acquisition device 100 can be a device that uses optical principles to collect and convert the target to be collected into an image and store it, such as a mobile camera or other devices.

[0059] Among them, the depth of focus of the optical imaging system refers to the range within which the image plane can move when the change in the system wavefront aberration caused by the movement of the system image plane does not exceed one-quarter wavelength. Figure 5 In the shown embodiment, the distance between adjacent two-layer patterns is less than the depth of focus of the image acquisition device, so that when the image acquisition device 100 acquires an image of one layer of patterns, it can acquire an image of the patterns of the layer adjacent to this layer. Furthermore, when the distance between two-layer patterns is greater than the depth of focus of the image acquisition device 100, the deviation brought by the registration device itself can be obtained through the intermediate-layer patterns of each layer, thereby removing the registration crosstalk caused by the horizontal displacement caused by factors such as the stage, and improving the registration measurement accuracy.

[0060] It can be understood that in the registration patterns, the number of intermediate-layer patterns between the first-layer pattern 105 and the second-layer pattern 101 can be determined according to the distance between the first-layer pattern 105 and the second-layer pattern 101 and the depth of focus of the image acquisition device 100, n = ceiling(d / f) - 1, where ceiling represents rounding up, and the intermediate-layer patterns are at least set to one layer.

[0061] Exemplarily, such as Figure 6As shown, taking the middle layer as an example of one layer, first, the image acquisition device 100 is used to obtain the first image of the first layer pattern 105 and the middle layer pattern 103; then, the second image of the middle layer pattern 103 and the second layer pattern 102 is obtained. Among them, the distance between the middle layer pattern 103 and the first layer pattern 105 is less than the depth of focus of the image acquisition device 100, and the distance between the middle layer pattern 103 and the second layer pattern 102 is less than the depth of focus of the image acquisition device 100. After that, the position of the middle layer pattern 103 and the position of the first layer pattern 105 are obtained according to the first image, and the position of the middle layer pattern 103 and the position of the second layer pattern 102 are obtained according to the second image. Finally, the device deviation caused by the overlay device can be obtained according to the position of the middle layer pattern 103 in the first image and the second image, and the overlay error of the positions of the first layer pattern 105 and the second layer pattern 102 can be obtained according to each image. After that, the precise overlay error is calculated according to the device deviation and the overlay error.

[0062] Among them, the deviation can be the horizontal displacement caused by factors such as the stage during the acquisition by the image acquisition device 100, and can be represented by (dx, dy). The precise overlay error can be the alignment deviation of the overlay during the measurement of the previous process and the current process during the optical detection process, and can be represented by (misRx, misRy).

[0063] It can be understood that S206 obtaining the precise overlay error of the first layer pattern and the second layer pattern according to the overlay error, the first deviation, the second deviation,..., the (i + 2)-th deviation includes:

[0064] Precise overlay error = overlay error - first deviation - second deviation -... - (i + 2)-th deviation.

[0065] Still taking Figure 6 the middle layer pattern of one layer shown as an example, the first deviation obtained according to the image of the middle layer pattern 103 obtained from the first image and the overlay mark of the middle layer pattern 103 obtained from the second image can be recorded as (dx, dy), and the overlay error caused by the offset between the centers of the first layer pattern 105 and the second layer pattern 102 can be recorded as (misRx0, misRy0). Then, the precise overlay error between the first layer pattern and the second layer pattern obtained according to the first deviation and the overlay error can be recorded as (misRx, misRy) = (misRx0, misRy0) – (dx, dy).

[0066] In other embodiments, the middle layer pattern can also be two layers, three layers, etc. Exemplarily, such as Figure 7As shown, taking two middle layers as an example, first, the image acquisition device 100 is used to obtain the first image of the first layer pattern 105 and the first middle layer pattern 103 of the first layer, then obtain the second image of the first middle layer pattern 103 of the first layer and the second middle layer pattern 108 of the second layer, and obtain the third image of the second middle layer pattern 108 of the second layer and the second layer pattern 102. Among them, the distance between the first middle layer pattern 103 and the first layer pattern 105 is less than the depth of focus of the image acquisition device 100, the distance between the second middle layer pattern 108 and the second layer pattern 102 is less than the depth of focus of the image acquisition device 100, and the distance between the first middle layer pattern 105 and the second middle layer pattern 102 of the first layer is less than the depth of focus of the image acquisition device 100. The first deviation (dx1, dy1) is obtained according to the image of the first middle layer pattern 103 obtained from the first image and the image of the first middle layer pattern 103 obtained from the second image, the second deviation (dx2, dy2) is obtained according to the image of the second middle layer pattern 108 obtained from the second image and the image of the second middle layer pattern 108 obtained from the third image, and the overlay error (misRx0, misRy0) is obtained according to each image; finally, the precise overlay error (misRx, misRy) between the first layer pattern 105 and the second layer pattern 102 is obtained according to the first deviation (dx1, dy1) and the second deviation (dx2, dy2) = (misRx0, misRy0) – (dx1, dy1) - (dx2, dy2).

[0067] When there are multiple middle layers, reference can be made to Figure 6 and Figure 7 the description of the example, which will not be elaborated here.

[0068] In the embodiment of the present invention, by adding a middle layer between the inner and outer ring patterns of the overlay mark, the overlay crosstalk caused by horizontal displacement caused by factors such as the stage is removed, the overlay measurement accuracy is improved, the complexity of the overlay measurement process is simplified, and the overlay measurement error caused by calibration is avoided.

[0069] Optionally, each time the image acquisition device 100 acquires an image, the defocus amount of the focal plane of the image acquisition device 100 from the top of the middle layer pattern is the same during two adjacent acquisitions of images.

[0070] Among them, the defocus amount can be the distance between the focus of the image acquisition device and the corresponding pattern layer.

[0071] Exemplarily, such as Figure 6As shown, taking the middle layer as one layer as an example, first use the image acquisition device 100 to obtain the first image of the first layer pattern 105 and the middle layer pattern 103; then obtain the second image of the middle layer pattern 103 and the second layer pattern 102. Among them, when shooting the first image, the distance between the focus of the image acquisition device 103 and the top of the middle layer pattern 103 is the same as the distance between the focus of the image acquisition device 103 and the top of the middle layer pattern 103 when shooting the second image. Thus, when collecting images twice in succession, the defocus amount of the focal plane of the image acquisition device 100 from the top of the middle layer pattern 103 is the same, so that the size of the middle layer pattern 103 can be imaged consistently in the two images (for example, spherical aberration, coma, etc. can be the same), which is convenient for obtaining the corresponding deviation by using the middle layer pattern 103, and then obtaining the overlay error, improving the measurement accuracy.

[0072] Optionally, the distance between the first layer pattern 105 and the second layer pattern 102 in the stacking direction is the first height, and the height ratios of the respective middle layer patterns between the first layer pattern 105 and the second layer pattern 102 are the same.

[0073] That is to say, when the height between the first layer pattern 105 and the second layer pattern 102 is h and there are i layers of middle layers, the height of each middle layer pattern is h / i. In this way, when using the optical system to collect images, it is easier to ensure that each middle layer can be at the same defocus position, that is, each time the image acquisition device is moved, it moves the same distance in the height direction, which is convenient for controlling the movement of the image acquisition device. In addition, due to the principle that the optical properties of images at the same defocus position are similar, the imaging characteristics of the images of the middle layer are ensured to be the same, reducing the measurement deviation.

[0074] Exemplarily, as Figure 6 shown, taking the middle layer as one layer as an example, the distance between the first layer pattern 105 and the second layer pattern 102 is the first height d, the distance between the middle layer pattern 103 and the first layer pattern 105 is d1, and the distance between the middle layer pattern 103 and the second layer pattern 102 is d2, that is, d = d1 + d2. To ensure that the defocus amount of the focal plane of the image acquisition device 100 from the top of the middle layer pattern 103 is the same, it is necessary to ensure that the distance d1 between the middle layer pattern 103 and the first layer pattern 105 and the distance d2 between the middle layer pattern 103 and the second layer pattern 102 are the same, that is, d1 = d2.

[0075] Optionally, the focal plane of the image acquisition device 100 is located at the middle height position of each layer pattern, and the number of shooting times of the image acquisition device 100 is one less than the total number of layers of the layer patterns.

[0076] That is to say, if there are i layers of middle layer patterns between the first layer pattern 105 and the second layer pattern 102, then there are a total of i + 2 layer patterns, and the number of shooting times of the image acquisition device 100 is i + 1 times.

[0077] Exemplarily, as Figure 6 shown, taking the middle layer as one layer as an example, the image acquisition method may be to first use the image acquisition device 100 to obtain a first image of the first layer pattern 105 and the middle layer pattern 103; then obtain a second image of the middle layer pattern 103 and the second layer pattern 102. The distance between the first layer pattern 105 and the second layer pattern 102 is the first height d, the distance between the middle layer pattern 103 and the first layer pattern 105 is d1, and the distance between the middle layer pattern 103 and the second layer pattern 102 is d2. When acquiring the first image, the focusing position is at the middle height between the first layer pattern 105 and the middle layer pattern 103, that is, at the position of d1 / 2, which is 111; when acquiring the second image, the focusing position is at the middle height between the second layer pattern 102 and the middle layer pattern 103, that is, at the position of d2 / 2, which is 112. When the middle layer pattern 103 is one layer and the layer patterns are three layers, the number of shooting times is two times.

[0078] As Figure 7 shown, taking the middle layer as two layers as an example, the image acquisition method may be: first use the image acquisition device 100 to obtain a first image of the first layer pattern 105 and the first middle layer pattern 103, then obtain a second image of the first middle layer pattern 103 and the second middle layer pattern 108, and obtain a third image of the second middle layer pattern 108 and the second layer pattern 102. The distance between the first layer pattern 105 and the second layer pattern 102 is the first height d, the distance between the first middle layer pattern 103 and the first layer pattern 105 is d1, the distance between the first middle layer pattern 105 and the second middle layer pattern 108 is d2, and the distance between the second middle layer pattern 108 and the second layer pattern 102 is d3. When acquiring the first image, the focusing position is at the middle height between the first layer pattern 105 and the first middle layer pattern 103, that is, at the position of d1 / 2, which is 113; when acquiring the second image, the focusing position is at the middle height between the second middle layer pattern 108 and the first middle layer pattern 103, that is, at the position of d2 / 2, which is 114; when acquiring the third image, the focusing position is at the middle height between the second middle layer pattern 108 and the second layer pattern 102, that is, at the position of d3 / 2, which is 115. When the middle layer is two layers and the layer patterns are four layers, the number of shooting times is three times.

[0079] Collecting images at the middle positions of each layer pattern reduces the moving distance of the image acquisition device, reduces the measurement time, and improves the measurement efficiency.

[0080] Optionally, each time the image acquisition device 100 acquires an image, the focal plane of the image acquisition device 100 is located at the top of the layer pattern.

[0081] Exemplarily, as Figure 8As shown, when there is one intermediate layer, the total number of layers is three. First, the image acquisition device 100 is used to obtain the first image of the first layer pattern 105 and the intermediate layer pattern 103; then, the second image of the intermediate layer pattern 103 and the second layer pattern 102 is obtained. The distance between the first layer pattern 105 and the second layer pattern 102 is the first height d, the distance between the intermediate layer pattern 103 and the first layer pattern 105 is d1, and the distance between the intermediate layer pattern 103 and the second layer pattern 102 is d2. When acquiring the first image, the focusing position is at the top of the first pattern layer 105, that is, at 121 where d1 is located; when acquiring the second image, the focusing position is at the top of the second pattern layer, that is, at 122 where d2 is located. Among them, during the two image acquisitions, the defocus amount of the focus from the intermediate layer pattern is d1 = d2. Then, the first deviation is obtained based on the image of the intermediate layer pattern 103 obtained from the first image and the image of the intermediate layer pattern 103 obtained from the second image, and then the precise registration error between the first layer pattern 105 and the second layer pattern 102 is obtained based on the first deviation.

[0082] When the distance d between the first layer pattern 105 and the second layer pattern 102 is larger, an intermediate layer needs to be added to ensure that the distance between adjacent layer patterns is less than the depth of focus of the image acquisition device 100.

[0083] As Figure 9 shown, taking the case where there are two intermediate layers as an example, first, the image acquisition device 100 is used to obtain the first image of the first layer pattern 105 and the first intermediate layer pattern 103 of the first layer, then the second image of the first intermediate layer pattern 103 of the first layer and the second intermediate layer pattern 108 of the second layer is obtained, and the third image of the second intermediate layer pattern 108 of the second layer and the second layer pattern 102 is obtained. The distance between the first layer pattern 105 and the second layer pattern 102 is the first height d, the distance between the first intermediate layer pattern 103 of the first layer and the first layer pattern 105 is d1, the distance between the first intermediate layer pattern 103 of the first layer and the second intermediate layer pattern 108 of the second layer is d2, and the distance between the second intermediate layer pattern 108 of the second layer and the second layer pattern 102 is d3. When acquiring the first image, the focusing position is at the top of the first layer pattern 105, that is, at 123 where d1 is located; when acquiring the second image, the focusing position is at the top of the first intermediate layer pattern 103 of the first layer, that is, at 124 where d2 is located; when acquiring the third image, the focusing position is at the top of the second layer pattern 102, that is, at 125 where d3 is located. The first deviation is obtained based on the image of the first intermediate layer pattern 103 of the first layer obtained from the first image and the first intermediate layer image 103 obtained from the second image, the second deviation is obtained based on the image of the second intermediate layer pattern 108 of the second layer obtained from the second image and the image of the second intermediate layer pattern 108 obtained from the third image, and based on the first deviation and the second deviation, as well as the registration error between the first layer pattern 105 and the second layer pattern 102, the precise registration error between the first layer pattern 105 and the second layer pattern 102 is obtained. In the embodiments of the present invention, there is no specific limitation on the total number of layers.

[0084] When the layer pattern is four layers, the focal plane of the image acquisition device can be located at the top of the first layer pattern 105, the top of the second layer pattern 102, and the top of any one of the two intermediate layer patterns; when the layer pattern is five layers, the focal plane of the image acquisition device can be located at the top of the first layer pattern 105, the top of the second layer pattern 102, and the top of any two of the three intermediate layer patterns. When the layer pattern is i layers, the focal plane of the image acquisition device can be located at the top of the first layer pattern 105, the top of the second layer pattern 102, and the top of any intermediate layer pattern among i - 3 intermediate layer patterns.

[0085] In the embodiment of the present invention, by adding an intermediate layer between the graphic layers, the horizontal displacement error caused by the stage factor is removed, the accuracy of the overlay measurement is improved, the complexity of the overlay process is simplified, and the measurement efficiency is increased.

[0086] Optionally, in the above embodiment, each intermediate layer pattern includes an intermediate overlay mark, the first layer pattern 105 includes a first overlay mark 104, and the second layer pattern 102 includes a second overlay mark 101; each intermediate overlay mark, the first overlay mark 104, and the second overlay mark 102 are the same.

[0087] Among them, the overlay mark can be a pattern on the graphic layer specifically used to measure the overlay error, that is, the center of each layer pattern can be calculated through the overlay marks collected by the image acquisition device 100.

[0088] Specifically, taking one intermediate layer as an example, after the image acquisition device 100 acquires the first image and the second image, the first deviation (dx, dy) is obtained according to the first intermediate overlay mark 106 obtained from the first image and the first intermediate overlay mark 106 obtained from the second image. Then, the precise overlay error (misRx, misRy) between the first layer pattern 105 and the second layer pattern 102 is obtained according to the first deviation, where (misRx, misRy) = (misRx0, misRy0) - (dx, dy).

[0089] Among them, (misRx0, misRy0) can be the overlay error caused by the offset between the center of the first layer pattern 105 and the center of the second layer pattern 102.

[0090] Adding an overlay mark in the intermediate layer pattern helps to calculate the deviation between the acquired images, reduces the accuracy of the overlay measurement, and improves the efficiency of the overlay measurement.

[0091] In one embodiment, the first overlay mark 104, each intermediate overlay mark, and the second overlay mark 101 are all one of a closed rectangular frame overlay mark or a short line broken rectangular frame overlay mark.

[0092] Exemplarily, as Figure 10 shown, taking one layer of the intermediate layer as an example, the horizontal direction in the image is the x-direction, and the vertical direction is the y-direction. The first set of alignment marks 104, the first intermediate alignment marks 106, and the second set of alignment marks 101 are all closed rectangular frames, and the edges of the rectangular frames are all in the x-direction or the y-direction. After the image acquisition device 100 acquires the first image and the second image, the center of the first intermediate alignment mark 106 obtained from the first image and the first intermediate alignment mark 106 obtained from the second image is obtained, and the comparison is performed along the x-direction and the y-direction respectively to obtain the deviation (dx, dy) in the x and y directions between the two layers of images. The center deviation between the first layer pattern and the second layer pattern is also obtained through the first set of alignment marks 104 and the second set of alignment marks 101, and then the precise alignment error (misRx, misRy) between the first layer pattern and the second layer pattern is obtained according to the deviation in the x and y directions = (misRx0, misRy0) – (dx, dy).

[0093] In one embodiment, the first set of alignment marks 104, each intermediate alignment mark, and the second set of alignment marks 101 form a first region 131, a second region 132, a third region 133, and a fourth region 134;

[0094] In the first region 131, the first set of alignment marks 104, each intermediate alignment mark, and the second set of alignment marks 101 are arranged in sequence along the first direction, and each type of alignment mark is also arranged along the second direction. The second region 132 is formed by rotating the first region 131 clockwise by 90 degrees, the third region 133 is formed by rotating the second region 132 clockwise by 90 degrees, and the fourth region 134 is formed by rotating the third region 133 clockwise by 90 degrees.

[0095] Exemplarily, as Figure 11As shown, taking the middle layer as an example, the horizontal direction in the image is the x - direction, and the vertical direction is the y - direction. The first set of alignment marks 104, the first intermediate alignment marks 106, and the second set of alignment marks 101 are concentrated in the corresponding areas and arranged along the x - direction or y - direction within the corresponding areas. In the first area 131, the first set of alignment marks 104, the first intermediate alignment marks 106, and the second set of alignment marks 101 are all arranged along the y - direction, and in the x - direction, the first set of alignment marks 104, the first intermediate alignment marks 106, and the second set of alignment marks 101 are arranged in sequence; in the second area 132, the first set of alignment marks 104, the first intermediate alignment marks 106, and the second set of alignment marks 101 are all arranged along the x - direction, and the three are arranged in sequence along the y - direction; the second area 132 is formed by rotating the first area 131 clockwise by 90 degrees; in the third area 133, the first set of alignment marks 104, the first intermediate alignment marks 106, and the second set of alignment marks 101 are all arranged along the y - direction, and the three are also arranged in sequence along the negative x - direction; the third area 133 is formed by rotating the second area 132 clockwise by 90 degrees; in the fourth area 134, the first set of alignment marks 104, the first intermediate alignment marks 106, and the second set of alignment marks 101 are all arranged along the x - direction, and the three are also arranged in sequence along the negative y - direction; that is, the fourth area 134 is formed by rotating the third area 133 clockwise by 90 degrees and is arranged along the x - direction.

[0096] Among them, after the image acquisition device 100 acquires the first image and the second image, the first intermediate alignment marks 106 along the x - direction obtained from the first image are compared with the first intermediate alignment marks 106 along the x - direction obtained from the second image to obtain dx in the first deviation (i.e., the first intermediate alignment marks 106 in the first area 131 and the third area 133); the first intermediate alignment marks 106 along the y - direction obtained from the first image are compared with the first intermediate alignment marks 106 along the y - direction obtained from the second image to obtain dy in the first deviation (i.e., the first intermediate alignment marks 106 in the second area 132 and the fourth area 134). Then, according to the first area 131 and the third area 133 in the first image, the center of the first set of alignment marks 104 in the x - direction is obtained, and according to the second area 132 and the fourth area 134, the center of the first set of alignment marks 104 in the y - direction is obtained. Then, according to the first area 131 and the third area 133 in the second image, the center of the second set of alignment marks 101 in the x - direction is obtained, and according to the second area 132 and the fourth area 134, the center of the second set of alignment marks 101 in the y - direction is obtained. Then, the registration error (misRx0, misRy0) is obtained according to the center of the first set of alignment marks 104 and the center of the second set of alignment marks 101. Finally, according to the first deviation and the registration error, the precise registration error (misRx, misRy) between the first - layer pattern 105 and the second - layer pattern 102 is obtained as (misRx, misRy)=(misRx0, misRy0)-(dx, dy).

[0097] In one embodiment, the first set of alignment marks 104, each intermediate alignment mark, and the second set of alignment marks 101 form a first region 131, a second region 132, a third region 133, and a fourth region 134;

[0098] In the first region 131, the first set of alignment marks 104 and the second set of alignment marks 101 are arranged in sequence along a first direction, and each type of alignment mark is also arranged along a second direction. The first set of alignment marks 104 and the intermediate alignment marks are arranged along the second direction, and the second set of alignment marks 101 and the intermediate alignment marks are arranged along the second direction. The second region 132 is formed by rotating the first region 131 clockwise by 90 degrees. The third region 133 is formed by rotating the second region 132 clockwise by 90 degrees. The fourth region 134 is formed by rotating the third region 133 clockwise by 90 degrees.

[0099] Exemplarily, as Figure 12 shown, taking one layer of the intermediate layer as an example, the first set of alignment marks 104 are arranged along the y direction in the first region 131, and the second set of alignment marks 101 are arranged along the y direction in the first region 131. Moreover, the two are arranged in sequence along the x direction. The first intermediate alignment mark 106 is arranged along the x direction. Then, the first set of alignment marks 104 and the first intermediate alignment mark 106 are also arranged in sequence along the y direction, and the second set of alignment marks 101 and the first intermediate alignment mark 106 are also arranged in sequence along the y direction.

[0100] The second region 132 is formed by rotating the first region 131 clockwise by 90 degrees. The third region 133 is formed by rotating the second region 132 clockwise by 90 degrees. The fourth region 134 is formed by rotating the third region 133 clockwise by 90 degrees.

[0101] Similarly, dx in the first deviation can be obtained from the first intermediate alignment marks 106 in the first region 131 and the third region 133; dy in the first deviation can be obtained from the first intermediate alignment marks 106 in the second region 132 and the fourth region 134. Then, the x-direction center of the first alignment mark 104 is obtained based on the first region 131 and the third region 133 in the first image, and the y-direction center of the first alignment mark 104 is obtained based on the second region 132 and the fourth region 134. The x-direction center of the second alignment mark 101 is obtained based on the first region 131 and the third region 133 in the second image, and the y-direction center of the second alignment mark 101 is obtained based on the second region 132 and the fourth region 134. Then, the alignment error (misRx0, misRy0) is obtained based on the centers of the first alignment mark 104 and the second alignment mark 101. Finally, the precise alignment error (misRx, misRy) between the first layer pattern and the second layer pattern is obtained according to the first deviation, where (misRx, misRy) = (misRx0, misRy0) – (dx, dy).

[0102] Figure 13 FIG. is a schematic side view structure of an alignment mark in an alignment measurement method provided by an embodiment of the present invention. Among them Figure 13 FIG. 1 and FIG. 2 in are provided by an embodiment of the present invention Figure 10 schematic side view structure; among them Figure 13 FIG. 3 in is provided by an embodiment of the present invention Figure 11 and Figure 12 schematic side view structure.

[0103] Figure 14 FIG. is a schematic top view structure of an alignment mark in another alignment measurement method provided by an embodiment of the present invention. That is, it is a top view of an alignment mark with two intermediate layers. In the embodiment of the present invention, the number of intermediate layers is not specifically limited.

[0104] In the embodiment of the present invention, the arrangement of the alignment marks is not specifically limited. For different arrangements of alignment marks, the method of obtaining the deviation is different, and the alignment error is obtained based on the arrangements of different alignment marks. For the alignment mark with an intermediate layer, the alignment measurement method in the prior art is improved, and the complexity of the alignment measurement process is reduced. Thus, by adding an intermediate layer between the inner and outer ring patterns of the alignment mark, and calculating the horizontal position error using the position offset of the intermediate layer pattern obtained simultaneously when photographing the inner and outer ring patterns, the crosstalk between the systematic error and the random error of the horizontal position is reduced, and a simpler and more accurate alignment measurement method can be provided. And there is no need for multiple repeated tests. In one embodiment, the moving distance of the machine in the Z direction is reduced from d to d / 2, so the measurement time is reduced and the measurement throughput is increased; there is no need for a complex systematic error calibration process, which simplifies the complexity of the alignment measurement process and avoids the alignment measurement error caused by imperfect calibration.

[0105] A method for overlay measurement provided by an embodiment of the present invention adds an intermediate layer containing overlay marks between patterns of different pattern layers, eliminates the horizontal displacement deviation caused by factors such as the stage, simplifies the complexity of the overlay measurement process, and improves the measurement efficiency and the accuracy of overlay measurement.

[0106] It should be understood that the various methods shown above can be used to reorder, add, or delete steps. As long as the desired results of the technical solution of the present invention can be achieved, no limitations are imposed herein.

[0107] The above specific embodiments do not constitute a limitation on the protection scope of the present invention. Those skilled in the art should understand that various modifications, combinations, sub - combinations, and substitutions can be made according to design requirements and other factors. Any modifications, equivalent substitutions, and improvements made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A lithography measurement method, characterized in that, Including: Obtaining a first image formed by a first-layer pattern and a first-layer intermediate pattern adjacent to the first-layer pattern; Successively obtaining a second image formed by the first-layer intermediate pattern and a second-layer intermediate pattern adjacent to the first-layer intermediate pattern, a third image formed by the second-layer intermediate pattern and a third-layer intermediate pattern adjacent to the second-layer intermediate pattern,..., an (i + 2)-th image formed by an (i + 1)-th layer intermediate pattern and an (i + 2)-th layer intermediate pattern adjacent to the (i + 1)-th layer intermediate pattern; Obtaining an (i + 3)-th image formed by the (i + 2)-th layer intermediate pattern and a second-layer pattern adjacent to the (i + 2)-th layer intermediate pattern; wherein, the intermediate patterns of each layer are successively stacked on the first-layer pattern; the second-layer pattern is stacked on the (i + 2)-th layer intermediate pattern; the distance between adjacent two-layer patterns is less than the depth of focus of the image acquisition device; i is an integer and i ≥ 0; Obtaining a first set of registration errors to an (i + 3)-th set of registration errors according to the first image to the (i + 3)-th image, and further accumulating the first set of registration errors to the (i + 3)-th set of registration errors to obtain the registration error between the first-layer pattern and the second-layer pattern.

2. The overlay measurement method according to claim 1, wherein When the image acquisition device acquires an image each time, and during two adjacent image acquisitions, the defocus amount of the focal plane of the image acquisition device from the top of the intermediate pattern is the same.

3. The overlay measurement method according to claim 2, wherein The distance between the first-layer pattern and the second-layer pattern in the stacking direction is a first height, and the height ratios of the intermediate patterns between the first-layer pattern and the second-layer pattern are the same.

4. The overlay measurement method according to claim 3, characterized in that The focal plane of the image acquisition device is located at the middle height position of each layer pattern, and the number of times the image acquisition device takes pictures is one less than the total number of layers of the layer patterns.

5. The overlay measurement method according to claim 3, wherein When the image acquisition device acquires an image each time, the focal plane of the image acquisition device is located at the top of the layer pattern.

6. The overlay measurement method according to claim 1, wherein Each intermediate pattern includes an intermediate registration mark, the first-layer pattern includes a first registration mark, and the second-layer pattern includes a second registration mark; the shapes of each intermediate registration mark, the first registration mark, and the second registration mark are the same.

7. The overlay measurement method according to claim 6, wherein The first registration mark, each intermediate registration mark, and the second registration mark are all one of a closed rectangular frame registration mark or a short-line broken rectangular frame registration mark.

8. The overlay measurement method according to claim 6, characterized in that The first registration mark, each intermediate registration mark, and the second registration mark form a first region, a second region, a third region, and a fourth region; In the first region, the first registration mark, each intermediate registration mark, and the second registration mark are successively arranged along a first direction, and each type of registration mark is also arranged along a second direction. The second region is formed by rotating the first region clockwise by 90 degrees, the third region is formed by rotating the second region clockwise by 90 degrees, and the fourth region is formed by rotating the third region clockwise by 90 degrees.

9. The overlay measurement method according to claim 6, wherein The first registration mark, each intermediate registration mark, and the second registration mark form a first region, a second region, a third region, and a fourth region; In the first region, the first set of alignment marks and the second set of alignment marks are arranged in sequence along a first direction, and each type of alignment mark is also arranged along a second direction. The first set of alignment marks and the intermediate alignment marks are arranged along the second direction, and the second set of alignment marks and the intermediate alignment marks are arranged along the second direction. The second region is formed by rotating the first region clockwise by 90 degrees, the third region is formed by rotating the second region clockwise by 90 degrees, and the fourth region is formed by rotating the third region clockwise by 90 degrees.

10. The overlay measurement method according to claim 1, wherein, It further includes: Obtaining a first deviation based on the first-layer intermediate layer pattern in the first image and the first-layer intermediate layer pattern in the second image, obtaining a second deviation based on the second-layer intermediate layer pattern in the second image and the second-layer intermediate layer pattern in the third image,..., obtaining an (i + 2)-th deviation based on the (i + 2)-th layer intermediate layer pattern in the (i + 2)-th image and the (i + 2)-th layer intermediate layer pattern in the (i + 3)-th image; Obtaining the precise registration error between the first-layer pattern and the second-layer pattern based on the registration error, the first deviation, the second deviation,..., and the (i + 2)-th deviation.

Images