Measurement method of overlay alignment mark and overlay error

Abstract

An overlay alignment mark and an overlay error measurement method, the overlay alignment mark comprising: a front-layer mark having a first geometric center in a direction parallel to the surface of the front-layer mark; the current-layer mark is located above the front-layer mark, the current-layer mark has a second geometric center in the direction parallel to the surface of the current-layer mark and is located on the same projection plane, and the projection pattern of the current-layer mark is located in the projection pattern of the front-layer mark. According to the embodiment of the invention, the offset vector between the first coordinate and the second coordinate can be determined by acquiring the first coordinate of the first geometric center and the second coordinate of the second geometric center, and is used for representing the overlay error, so that the error numerical values including the transverse overlay error and the longitudinal overlay error can be acquired at the same time; compared with the scheme that transverse and longitudinal overlay alignment marks need to be arranged respectively, the area of the overlay alignment marks is saved, and then the performance of the overlay alignment marks is improved.

Description

Technical Field

[0001] This invention relates to the field of semiconductor manufacturing, and more particularly to a method for measuring overlay alignment marks and overlay errors. Background Technology

[0002] With the rapid development of the integrated circuit (IC) industry, semiconductor technology, driven by Moore's Law, continues to advance towards smaller process nodes, enabling integrated circuits to develop in the direction of smaller size, higher circuit precision, and higher circuit complexity.

[0003] In IC manufacturing, photolithography is one of the most complex and critical process steps, and overlay accuracy is one of its important performance indicators. As integrated circuits evolve towards smaller size, higher circuit precision, and greater circuit complexity, the feature size of photolithography processes in IC manufacturing continues to shrink, leading to increasingly higher requirements for overlay accuracy. If the overlay accuracy does not meet design specifications, the circuits between different layers of the device cannot be accurately connected, potentially resulting in short circuits or open circuits, thus causing losses in production yield and device performance. Only by accurately measuring the actual overlay error can effective compensation and correction be achieved in subsequent processes. Overlay error (OVL) is an important parameter describing the accuracy of overlay between the current layer pattern and the previous layer pattern.

[0004] Currently, with the continuous shrinking of technology nodes, higher requirements are being placed on the overlay alignment marks. Summary of the Invention

[0005] The problem solved by the embodiments of the present invention is to provide a method for measuring overprint alignment marks and overprint errors, so as to save the area of ​​overprint alignment marks and improve the measurement efficiency of overprint errors.

[0006] To address the aforementioned problems, embodiments of the present invention provide an overlay alignment mark, comprising: a front layer mark having a first geometric center in a direction parallel to the surface of the front layer mark; and a current layer mark located above the front layer mark, having a second geometric center in a direction parallel to the surface of the current layer mark, and on the same projection plane, the projected image of the current layer mark being located inside the projected image of the front layer mark.

[0007] Optionally, the preset relative positional relationship between the current layer mark and the previous layer mark includes: the geometric centers of the current layer mark and the previous layer mark are set concentrically.

[0008] Optionally, the area of ​​the projected graphic of the current layer mark accounts for 50% to 80% of the area of ​​the projected graphic of the previous layer mark.

[0009] Optionally, the overlay alignment mark is of multiple types, and in each type of the overlay alignment mark, the projected area of the current layer mark accounts for a different proportion of the projected area of the previous layer mark.

[0010] Optionally, the overlay alignment mark comprises a first overlay alignment mark, a second overlay alignment mark, a third overlay alignment mark and a fourth overlay alignment mark; in the first overlay alignment mark, the projected area of the previous layer mark is a first area, and the projected area of the current layer mark is a second area; in the second overlay alignment mark, the projected area of the previous layer mark is a third area, and the projected area of the current layer mark is a fourth area; in the third overlay alignment mark, the projected area of the previous layer mark is the first area, and the projected area of the current layer mark is the fourth area; in the fourth overlay alignment mark, the projected area of the previous layer mark is the third area, and the projected area of the current layer mark is the second area; wherein the first area is smaller than the third area, and the second area is smaller than the fourth area.

[0011] Optionally, the vertical distance between the top surface of the previous layer mark and the top surface of the current layer mark is less than or equal to 2 microns.

[0012] Optionally, the overlay alignment mark further comprises a medium layer on the previous layer mark on the side of the current layer mark, and the medium layer is different from the material of the previous layer mark.

[0013] Optionally, the material of the previous layer mark is a metal material.

[0014] Optionally, the projected pattern of the previous layer mark and the projected pattern of the current layer mark are of the same shape.

[0015] Optionally, the projected pattern of the previous layer mark comprises one or more of a circle, a square and a rectangle, and the projected pattern of the current layer mark comprises one or more of a circle, a square and a rectangle.

[0016] Optionally, the projected pattern of the previous layer mark and the projected pattern of the current layer mark are both circles.

[0017] Correspondingly, the embodiment of the present application further provides an overlay error measurement method, which is suitable for measuring the overlay alignment mark of any embodiment of the present application, and the measurement method comprises the following steps: obtaining the first plane coordinates of the first geometric center of the previous layer mark; obtaining the second plane coordinates of the second geometric center of the current layer mark; and obtaining the offset vector of the first geometric center and the second geometric center based on the first plane coordinates and the second plane coordinates, wherein the offset vector is used to represent the overlay error.

[0018] Optionally, the first planar coordinate and the second planar coordinate are coordinate points in a same planar rectangular coordinate system.

[0019] Optionally, the manner of obtaining the first planar coordinate comprises: identifying an outline of the front layer mark, and positioning the first geometric center based on the outline of the front layer mark.

[0020] Optionally, the manner of obtaining the second planar coordinate comprises: identifying an outline of the current layer mark, and positioning the second geometric center based on the outline of the current layer mark.

[0021] Optionally, the types of the overlay alignment marks are multiple, and in the various types of the overlay alignment marks, the projection pattern area of the current layer mark occupies different proportions of the projection pattern area of the front layer mark in the corresponding overlay alignment mark; the measurement method further comprises: selecting one overlay alignment mark to be measured from the multiple overlay alignment marks; based on the selected overlay alignment mark, obtaining the first planar coordinate of the first geometric center of the front layer mark, and obtaining the second planar coordinate of the second geometric center of the current layer mark.

[0022] Optionally, one overlay alignment mark to be measured is determined by one or more of the following: when the number of each type of the overlay alignment mark is multiple, one overlay alignment mark to be measured is selected by linear correlation analysis; wherein the step of selecting one overlay alignment mark to be measured by linear correlation analysis comprises: taking the overlay error of each overlay alignment mark along a preset direction as a variable, and taking the overlay error between the actual product layers corresponding to each overlay alignment mark along the preset direction as a dependent variable, performing linear correlation analysis on the overlay error measurement results corresponding to each type of the overlay alignment mark respectively, and obtaining a linear correlation degree; selecting one overlay alignment mark with the best linear correlation degree as the overlay alignment mark to be measured; one overlay alignment mark to be measured is selected by error analysis; wherein the step of selecting one overlay alignment mark to be measured by error analysis comprises: obtaining the measurement results of multiple overlay errors along a preset direction corresponding to each type of the overlay alignment mark, and the measurement results of multiple overlay errors corresponding to each type of the overlay alignment mark are obtained by measuring the overlay error multiple times; selecting one overlay alignment mark with the minimum error of multiple overlay error measurement results as the overlay alignment mark to be measured; one overlay alignment mark to be measured is selected by size comparison; wherein the step of selecting one overlay alignment mark to be measured by size comparison comprises: obtaining the ratio of the overlay error difference value along a preset direction corresponding to each type of the overlay alignment mark to the mark size difference value, the mark size difference value being half of the size difference value along the preset direction between the front layer mark and the current layer mark of the overlay alignment mark; and selecting one overlay alignment mark with the ratio closest to 50% as the overlay alignment mark to be measured.

[0023] Optionally, the step of selecting one overlay alignment mark to be measured from multiple types of the overlay alignment mark comprises: when linear correlation analysis is available, one overlay alignment mark to be measured is selected by linear correlation analysis; when the type of the overlay alignment mark with the best linear correlation degree is multiple, one overlay alignment mark to be measured is selected from the multiple overlay alignment marks with the best linear correlation degree by error analysis; when the type of the overlay alignment mark with the minimum error is multiple, one overlay alignment mark to be measured is selected from the multiple overlay alignment marks with the minimum error by size comparison; or when linear correlation analysis is not available, one overlay alignment mark to be measured is selected by error analysis; when the type of the overlay alignment mark with the minimum error is multiple, one overlay alignment mark to be measured is selected from the multiple overlay alignment marks with the minimum error by size comparison.

[0024] Optionally, the projection pattern of the front layer mark and the projection pattern of the same layer mark are in the same shape.

[0025] Optionally, the projection pattern of the front layer mark comprises one or more of a circle, a square and a rectangle; and the projection pattern of the same layer mark comprises one or more of a circle, a square and a rectangle.

[0026] Compared with the prior art, the technical scheme of the embodiment of the present application has the following advantages:

[0027] In the overlay alignment mark provided by the embodiment of the present application, the front layer mark has a first geometric center, and the same layer mark has a second geometric center, and the same layer mark is located above the front layer mark. Since the front layer mark and the same layer mark both have geometric centers, the first coordinate of the first geometric center of the front layer mark and the second coordinate of the second geometric center of the same layer mark are obtained, and the offset vector of the first geometric center and the second geometric center is determined by the first coordinate and the second coordinate. The offset vector is used to represent the overlay error, and the error value including the lateral overlay error and the longitudinal overlay error can be obtained at the same time. Compared with the scheme in which the lateral overlay alignment mark and the longitudinal overlay alignment mark are respectively arranged, the area of the overlay alignment mark is saved, and the measurement efficiency of the overlay error is improved.

[0028] In the measurement method of the overlay alignment mark provided by the embodiment of the present application, since the front layer mark and the same layer mark both have geometric centers, the first coordinate of the first geometric center of the front layer mark and the second coordinate of the second geometric center of the same layer mark are obtained, and the offset vector of the first geometric center and the second geometric center is determined by the first coordinate and the second coordinate. The offset vector is used to represent the overlay error, and the error value including the lateral overlay error and the longitudinal overlay error can be obtained at the same time. Compared with the scheme in which the lateral overlay alignment mark and the longitudinal overlay alignment mark are respectively arranged, the area of the overlay alignment mark is saved, and the measurement method of the overlay alignment mark is simplified, and the measurement efficiency of the overlay error is improved. BRIEF DESCRIPTION OF DRAWINGS

[0029] Figure 1 is a top view structural schematic diagram of an overlay alignment mark;

[0030] Figure 2 is a structural schematic diagram of an embodiment of the overlay alignment mark of the present application;

[0031] Figure 3 is Figure 2 is a sectional view along the X direction;

[0032] Figure 4is Figure 2 a sectional view along the Y direction;

[0033] Figure 5 is a structural schematic diagram of another embodiment of the overlay alignment mark of the present application;

[0034] Figure 6 is a flow chart of an embodiment of the measurement method of overlay error of the present application. DETAILED DESCRIPTION

[0035] At present, with the rapid development of the semiconductor integrated circuit industry, higher requirements are put forward for the area of the overlay alignment mark and the efficiency of the overlay error.

[0036] Figure 1 is a top view structural schematic diagram of an overlay alignment mark.

[0037] Reference Figure 1 , an overlay alignment mark, comprising: a transverse overlay alignment mark (not indicated) and a longitudinal overlay alignment mark (not indicated) arranged separately.

[0038] Among them, the transverse overlay alignment mark is used to measure the overlay error in the first direction x, and the longitudinal overlay alignment mark is used to measure the overlay error in the second direction y.

[0039] Specifically, the transverse overlay alignment mark comprises: a first front layer mark 11, which has a first width interval w11 in the first direction x in the direction parallel to the surface of the first front layer mark 11; and a first when layer mark 12, which is located above the first front layer mark 11 and has a second width interval w12 in the first direction x in the direction parallel to the surface of the first when layer mark 11.

[0040] In the first direction x, the overlay error in the first direction x can be obtained by obtaining the positional deviation amount of the midline of the first width interval w11 and the midline of the second width interval w12.

[0041] Specifically, the longitudinal overlay alignment mark comprises: a second front layer mark 21, which has a third width interval l21 in the second direction y in the direction parallel to the surface of the second front layer mark 21; and a second when layer mark 22, which is located above the second front layer mark 21 and has a fourth width interval l22 in the second direction y in the direction parallel to the surface of the second when layer mark 22.

[0042] In the second direction y, the overlay error in the second direction y can be obtained by obtaining the positional deviation amount of the midline of the third width interval l21 and the midline of the fourth width interval l22.

[0043] It is found through research that only overlay error in the first direction x, i.e. lateral overlay error, of the first front layer mark 11 and the first current layer mark 12 can be obtained through lateral overlay alignment marks, and only overlay error in the second direction y, i.e. longitudinal overlay error, of the second front layer mark 21 and the second current layer mark 22 can be obtained through longitudinal overlay alignment marks. That is, to obtain the lateral overlay error and the longitudinal overlay error, lateral overlay alignment marks for measuring the lateral overlay error are needed, and longitudinal overlay alignment marks for measuring the longitudinal overlay error are needed, so that the area of the overlay alignment marks is easily large; and the lateral overlay alignment marks and the longitudinal overlay alignment marks need to be measured respectively, so that the measurement process of the overlay alignment marks is complex, and thus the measurement efficiency of the overlay alignment marks is not improved.

[0044] To solve the above technical problems, an embodiment of the present application provides an overlay alignment mark, comprising: a front layer mark, the front layer mark has a first geometric center in a direction parallel to a surface of the front layer mark; a current layer mark, the current layer mark is located above the front layer mark, the current layer mark has a second geometric center in a direction parallel to a surface of the current layer mark, and a projection pattern of the current layer mark is located inside a projection pattern of the front layer mark on a same projection plane.

[0045] The overlay alignment mark provided by the embodiment of the present application comprises the front layer mark having the first geometric center and the current layer mark having the second geometric center, the current layer mark is located above the front layer mark, because the front layer mark and the current layer mark both have geometric centers, so that the first coordinate of the first geometric center of the front layer mark and the second coordinate of the second geometric center of the current layer mark are obtained, the offset vector of the first geometric center and the second geometric center can be determined through the first coordinate and the second coordinate, the offset vector is used to represent the overlay error, and the error value including the lateral overlay error and the longitudinal overlay error can be obtained at the same time, compared with the scheme of respectively setting the lateral overlay alignment marks and the longitudinal overlay alignment marks, the area of the overlay alignment marks is saved, and the measurement efficiency of the overlay error is improved.

[0046] In order to make the above-mentioned purposes, features and advantages of the embodiments of the present application more obvious and easy to understand, the specific embodiments of the present application are described in detail below with reference to the drawings.

[0047] Figure 2 is a structural schematic diagram of an embodiment of the overlay alignment mark of the present application, Figure 3 is Figure 2 is a sectional view along the X direction, Figure 4 is Figure 2 is a sectional view along the Y direction.

[0048] ReferenceFigure 2 to Figure 4 In the embodiment, the overlay alignment mark 500 comprises: a front layer mark 510, the front layer mark 510 has a first geometric center 515 in a direction parallel to a surface of the front layer mark 510; an in-layer mark 520, the in-layer mark 520 is above the front layer mark 510, the in-layer mark 520 has a second geometric center 525 in a direction parallel to a surface of the in-layer mark 520, and a projection pattern of the in-layer mark 520 is inside a projection pattern of the front layer mark 510 in the same projection plane.

[0049] It should be noted that, since the front layer mark 510 and the in-layer mark 520 both have geometric centers, by obtaining a first coordinate of the first geometric center 515 of the front layer mark 510 and a second coordinate of the second geometric center 525 of the in-layer mark 520, an offset vector of the first geometric center 515 and the second geometric center 525 can be determined by the first coordinate and the second coordinate, the offset vector is used to represent an overlay error, and error values including a lateral overlay error and a longitudinal overlay error can be obtained at the same time, compared with a scheme of respectively setting a lateral overlay alignment mark and a longitudinal overlay alignment mark, the area of the overlay alignment mark 500 can be saved, and the measurement efficiency of the overlay error can be improved.

[0050] Here, since a vector can be formed from the first geometric center 515 to the second geometric center 525, a component of the vector in the first direction X can represent the overlay error in the first direction X, and a component of the vector in the second direction Y can represent the overlay error in the second direction Y, therefore, the offset vector can be used to represent the overlay error.

[0051] In the embodiment, the overlay mark further comprises: a substrate (not shown in the figure), the substrate comprises an alignment mark area I; the front layer mark 510 is arranged on the substrate of the alignment mark area I.

[0052] The substrate provides a process platform for arranging the overlay alignment mark 500.

[0053] The alignment mark area I is used to arrange the front layer mark 510 and the in-layer mark 520.

[0054] The substrate further comprises a device area (not shown in the figure), the substrate of the device area can be provided with semiconductor devices such as transistors and capacitors, and the substrate of the device area can be further provided with functional structures such as resistance structures and conductive structures.

[0055] In the embodiment, as shown in FIG. 5, the overlay alignment mark 500 comprises: Figure 2 and Figure 3As shown, the overlay alignment mark 500 further comprises a medium layer 530 on the front layer mark 510 at the side of the current layer mark 520, the medium layer 530 being different from the material of the front layer mark 510.

[0056] The medium layer 530 provides a process basis for setting the current layer mark 520.

[0057] The medium layer 530 being different from the material of the front layer mark 510, easily makes the detection condition (e.g. detection voltage, detection current, etc.) of the front layer mark 510 different from the detection condition of the medium layer 530, thereby facilitating the identification of the profile of the front layer mark 510 and the profile of the current layer mark 520.

[0058] As an example, the medium layer 530 being different from the material of the front layer mark 510, according to the material corresponding to the medium layer 530 and the material corresponding to the front layer mark 510, by setting different detection conditions for a scanning electron microscope (SEM), the profile of the front layer mark 510 is identified, the first geometric center 515 of the front layer mark 510 is obtained, the first coordinate of the first geometric center 515 is correspondingly obtained, and the profile of the current layer mark 520 is identified, the second geometric center 525 of the current layer mark 520 is obtained, and the second coordinate of the second geometric center 525 is correspondingly obtained.

[0059] Moreover, the material of the medium layer 530 is dielectric material, thereby being able to reduce the shielding of the front layer mark 510.

[0060] Specifically, taking the front layer mark 510 used in the back-end-of-line process in a semiconductor process as an example, the material of the front layer mark 510 is metal material.

[0061] Generally, the material of the medium layer 530 is dielectric material, when the material of the front layer mark 510 is metal material, it is convenient to make the material of the medium layer 530 different from the material of the front layer mark 510. In other embodiments, the front layer mark can also be other materials suitable for the semiconductor process.

[0062] In this embodiment, the front layer mark 510 is a certain metal layer in the back-end-of-line process, and the current layer mark 520 is a via interconnection structure (Via) electrically connecting the front layer mark 510 and another metal layer.

[0063] As an example, the front layer mark 510 is a first layer metal layer (M1), and the current layer mark 520 is a via interconnection structure (V1) electrically connecting the first layer metal layer and a second layer metal layer (M2). It should be noted that the front layer mark 510 is not limited to M1, and the current layer mark 520 is not limited to V1. In other embodiments, the front layer mark and the current layer mark can also be other suitable film layers.

[0064] It should be noted that the medium layer 530 is also located on the substrate on the side of the front layer mark 510 and the current layer mark 520.

[0065] It can be understood that when the widths of the front layer marks 510 located on both sides of the current layer mark 520 are inconsistent in the first direction X, it indicates that there is an overlay error in the first direction X (as shown in FIG. 5B). Figure 3 When the widths of the front layer marks 510 located on both sides of the current layer mark 520 are inconsistent in the second direction Y, it indicates that there is an overlay error in the second direction Y (as shown in FIG. 5C). Figure 4

[0066] In the projection plane parallel to the top surface of the front layer mark 510, the projection pattern of the front layer mark 510 satisfies that the first geometric center 515 of the front layer mark 510 can be extracted. In this embodiment, the projection pattern of the front layer mark 510 includes one or more of a circle, a square, and a rectangle.

[0067] When the projection pattern of the front layer mark 510 includes one or more of a circle, a square, and a rectangle, it is advantageous to reduce the difficulty of forming the front layer mark 510, and it is also convenient to determine the first geometric center 515 of the front layer mark 510, thereby facilitating the obtaining of the first coordinates of the first geometric center 515.

[0068] In the projection plane parallel to the top surface of the current layer mark 520, the projection pattern of the current layer mark 520 satisfies that the second geometric center 525 of the current layer mark 520 can be extracted. In this embodiment, the projection pattern of the current layer mark 520 includes one or more of a circle, a square, and a rectangle.

[0069] The reason why the projection pattern of the current layer mark 520 includes one or more of a circle, a square, and a rectangle is similar to the reason why the projection pattern of the front layer mark 510 includes one or more of a circle, a square, and a rectangle, which will not be described here again.

[0070] Specifically, the projection pattern of the front layer mark 510 and the projection pattern of the current layer mark 520 are both circles.

[0071] ​In a plane, a closed curve formed by rotating a point around a point and a length as a distance is called a circle, that is, the distance from any point on the circumference to the center of the circle is equal. Therefore, when the projection pattern of the front layer mark 510 and the projection pattern of the current layer mark 520 are both circles, the center of the circle of the front layer mark 510 is the first geometric center 515, and the center of the circle of the current layer mark 520 is the second geometric center 525, which is beneficial to further reduce the difficulty of positioning the first geometric center 515 and the second geometric center 525.

[0072] In this embodiment, the projection pattern of the front layer mark 510 and the projection pattern of the current layer mark 520 are the same shape.

[0073] The projection pattern of the front layer mark 510 and the projection pattern of the current layer mark 520 are the same shape, which is beneficial to reduce the error of the offset vector between the first geometric center 515 and the second geometric center 525, thereby improving the accuracy of the offset vector between the first geometric center 515 and the second geometric center 525, and further improving the accuracy of the overlay error value.

[0074] In this embodiment, on the same projection plane, the projection pattern of the current layer mark 520 is located inside the projection pattern of the front layer mark 510.

[0075] It should be noted that the projection plane is parallel to the top surface of the current layer mark 520.

[0076] On the same projection plane, the projection pattern of the current layer mark 520 is located inside the projection pattern of the front layer mark 510, so that the current layer mark 520 is not easy to block the outline of the front layer mark 510, which is convenient for identifying the outline of the front layer mark 510, thereby extracting the first geometric center of the front layer mark 510; and the projection pattern of the current layer mark 520 is located inside the projection pattern of the front layer mark 510, which is also beneficial to further save the area of the overlay mark.

[0077] In this embodiment, the preset relative position relationship between the current layer mark 520 and the front layer mark 510 includes that the geometric centers of the current layer mark 520 and the front layer mark 510 are concentrically arranged.

[0078] The geometric centers of the current layer mark 520 and the front layer mark 510 are designed to be concentrically arranged, which is beneficial to increase the uniformity of the distance between the outline of the front layer mark 510 and the outline of the current layer mark 520, thereby improving the probability that the projection pattern of the current layer mark 520 is located inside the projection pattern of the front layer mark 510, and further increasing the monitoring window of the overlay error in different directions.

[0079] It should be noted that, on the projection plane parallel to the top surface of the current layer mark 520, the proportion of the projection area of the current layer mark 520 to the projection area of the front layer mark 510 should not be too small or too large. If the proportion of the projection area of the current layer mark 520 to the projection area of the front layer mark 510 is too small, it is easy to increase the difficulty of forming the current layer mark 520; if the proportion of the projection area of the current layer mark 520 to the projection area of the front layer mark 510 is too large, it is easy to cause the difficulty of the projection pattern of the current layer mark 520 being located inside the projection pattern of the front layer mark 510 to be large, thereby causing the effect of increasing the monitoring window of the overlay error to be poor. Therefore, in the embodiment, the projection area of the current layer mark 520 accounts for 50% to 80% of the projection area of the front layer mark 510.

[0080] It should also be noted that the longitudinal distance between the top surface of the front layer mark 510 and the top surface of the current layer mark 520 should not be too large. If the longitudinal distance between the top surface of the front layer mark 510 and the top surface of the current layer mark 520 is too large, it is easy to increase the difficulty of identifying the contour of the front layer mark 510, and accordingly increase the difficulty of obtaining the first geometric center 515 of the front layer mark 510, thereby increasing the difficulty of obtaining the overlay error value. Therefore, in the embodiment, the longitudinal distance between the top surface of the front layer mark 510 and the top surface of the current layer mark 520 is less than or equal to 2 microns.

[0081] Reference Figure 5 , Figure 5 is a structural schematic diagram of another embodiment of the overlay alignment mark of the application.

[0082] The same as the previous embodiment, this will not be repeated here. The difference between the embodiment and the previous embodiment is that the type of the overlay alignment mark 600 is multiple, and in various types of the overlay alignment mark 600, the proportion of the projection area of the current layer mark 620 to the projection area of the front layer mark 610 in the corresponding overlay alignment mark 600 is different.

[0083] Here, the type of the overlay alignment mark 600 refers to the proportion of the projection area of the current layer mark 620 of the overlay alignment mark 600 to the projection area of the front layer mark 610 in the corresponding overlay alignment mark 600.

[0084] In the various types of the overlay alignment marks 600, the projection pattern area of the current layer mark 620 accounts for different proportions of the projection pattern area of the previous layer mark 610 in the corresponding overlay alignment mark 600, and correspondingly, the monitoring window of the overlay error of the various types of the overlay alignment marks 600 is also different. In the case of different monitoring windows, it is easy to make the offset vectors corresponding to the various types of the overlay alignment marks 600 also different, so as to make the error values between each offset vector and the actual overlay error value corresponding thereto different in degree, and then facilitate determining the overlay alignment mark 600 suitable for the actual product according to the absolute value of the error value.

[0085] It should be noted that when the monitoring window of the overlay error is small, the size difference between the current layer mark 620 and the previous layer mark 610 is small, which is beneficial to reduce the process error caused by the size difference, and correspondingly, it is easy to make the error value between the offset vector and the actual overlay error value corresponding thereto smaller. Therefore, according to the actual situation, selecting a suitable overlay alignment mark can obtain a more ideal monitoring window in the case of obtaining an offset vector with a smaller difference degree from the actual overlay error value.

[0086] Specifically, the overlay alignment mark 600 includes a first overlay alignment mark 601, a second overlay alignment mark 602, a third overlay alignment mark 603, and a fourth overlay alignment mark 604. In the first overlay alignment mark 601, the projection pattern area of the previous layer mark 610 is a first area S1, and the projection pattern area of the current layer mark 620 is a second area S2. In the second overlay alignment mark 602, the projection pattern area of the previous layer mark 610 is a third area S3, and the projection pattern area of the current layer mark 620 is a fourth area S4. In the third overlay alignment mark 603, the projection pattern area of the previous layer mark 610 is the first area S1, and the projection pattern area of the current layer mark 620 is the fourth area S4. In the fourth overlay alignment mark 604, the projection pattern area of the previous layer mark 610 is the third area S3, and the projection pattern area of the current layer mark 620 is the second area S2. Wherein, the first area S1 is smaller than the third area S3, and the second area S2 is smaller than the fourth area S4.

[0087] It can be understood that, in the same set of alignment marks 600, when the proportion of the projection area of the layer mark 620 to the projection area of the front layer mark 610 is the projection area proportion, the set of alignment marks 600 includes the first set of alignment marks 601, the second set of alignment marks 602, the third set of alignment marks 603, and the fourth set of alignment marks 604, therefore, the projection area of the front layer mark 610 can be the first area S1 or the third area S3, the projection area of the layer mark 620 can be the second area S2 or the fourth area S4, the set of alignment marks 600 capable of obtaining four projection area proportions, thereby improving the type diversity of the set of alignment marks 600, and facilitating to meet different needs.

[0088] It should be noted that the type of the set of alignment marks 600 is not limited to four, and in other embodiments, the type of the set of alignment marks for measurement can also be two, three, or any number greater than four.

[0089] As an example, in the set of alignment marks 600, the shapes of the projection patterns of each front layer mark 610 are the same, and the shapes of the projection patterns of each layer mark 620 are also the same. In a specific embodiment, the shapes of the projection patterns of each front layer mark 610 are circular, and the shapes of the projection patterns of each layer mark 620 are also circular.

[0090] Correspondingly, the application also provides a set of alignment mark measurement method for measuring the set of alignment marks of any embodiment of the application. Figure 6 is a flowchart corresponding to an embodiment of the set of alignment mark measurement method of the application.

[0091] Reference Figure 6 , and in combination with reference Figure 2 to Figure 4 , perform step S1: obtain the first plane coordinates of the first geometric center 515 of the front layer mark 510.

[0092] The first plane coordinates are used to represent the position of the first geometric center 515 on the horizontal plane.

[0093] In this embodiment, the manner of obtaining the first plane coordinates includes identifying the contour of the front layer mark 510, and positioning the first geometric center 515 based on the contour of the front layer mark 510.

[0094] Since the front layer mark 510 has the first geometric center 515, that is, the front layer mark 510 is a closed pattern, by identifying the contour of the front layer mark 510, the position of the first geometric center 515 can be extracted, and the first plane coordinates can be obtained, which is conducive to reducing the difficulty of obtaining the first plane coordinates.

[0095] Reference is made to Figure 6 , and in combination with reference Figure 2 to Figure 4 , a step S2 is performed: obtaining a second planar coordinate of a second geometric center 525 of the in-layer mark 520.

[0096] The second planar coordinate is used to represent the position of the second geometric center 525 on the horizontal plane.

[0097] In this embodiment, the manner of obtaining the second planar coordinate includes: identifying the contour of the in-layer mark 520, and positioning the second geometric center 525 based on the contour of the in-layer mark 520.

[0098] Since the in-layer mark 520 has a second geometric center 525, that is, the in-layer mark 520 is also a closed figure, by identifying the contour of the in-layer mark 520, the position of the second geometric center 525 can be extracted, and the second planar coordinate can be obtained, which is conducive to reducing the difficulty of obtaining the second planar coordinate.

[0099] In this embodiment, the first planar coordinate and the second planar coordinate are coordinate points in the same planar rectangular coordinate system.

[0100] The planar rectangular coordinate system defines the position of a point through two perpendicular number axes with a common origin, which is convenient for calculating and understanding the positional relationship between different points, so as to facilitate the determination of the offset vector between the first coordinate and the second coordinate.

[0101] The projection pattern of the front layer mark 510 satisfies that the first geometric center 515 of the front layer mark 510 can be extracted, and the projection pattern of the in-layer mark 520 satisfies that the second geometric center 525 of the in-layer mark 520 can be extracted. In this embodiment, the projection pattern of the front layer mark 510 includes one or more of a circle, a square and a rectangle; and the projection pattern of the in-layer mark 520 includes one or more of a circle, a square and a rectangle.

[0102] When the projection patterns of the front layer mark 510 and the in-layer mark 520 each include one or more of a circle, a square and a rectangle, it is conducive to reducing the difficulty of forming the front layer mark 510 and the in-layer mark 520, and it is also convenient to determine the first geometric center 515 of the front layer mark 510 and the second geometric center 525 of the in-layer mark 520, so as to facilitate obtaining the first coordinate of the first geometric center 515 and the second coordinate of the second geometric center 525.

[0103] Specifically, the shapes of the projection pattern of the front layer mark 510 and the projection pattern of the in-layer mark 520 are both circles.

[0104] In a plane, a closed curve formed by rotating a point around a certain length as a distance is called a circle, that is, the distance from any point on the circumference to the center of the circle is equal. Therefore, when the projection pattern of the front layer mark 510 and the projection pattern of the same layer mark 520 are both circles, the center of the circle of the front layer mark 510 is the first geometric center 515, and the center of the circle of the same layer mark 520 is the second geometric center 525, which is beneficial to further reduce the difficulty of positioning the first geometric center 515 and the second geometric center 525.

[0105] In this embodiment, the projection pattern of the front layer mark 510 and the projection pattern of the same layer mark 520 are the same shape.

[0106] The projection pattern of the front layer mark 510 and the projection pattern of the same layer mark 520 are the same shape, which is beneficial to reduce the error of the offset vector between the first geometric center 515 and the second geometric center 525, thereby improving the accuracy of the offset vector between the first geometric center 515 and the second geometric center 525, and further improving the accuracy of the overlay error value.

[0107] Reference Figure 6 , and in combination with reference Figure 2 to Figure 4 , step S3 is performed: based on the first plane coordinates and the second plane coordinates, an offset vector of the first geometric center 515 and the second geometric center 525 is obtained, and the offset vector is used to represent the overlay error.

[0108] Here, since the vector from the first geometric center 515 to the second geometric center 525 can be constructed, the component of the vector in the first direction X can represent the overlay error in the first direction X, and the component of the vector in the second direction Y can represent the overlay error in the second direction Y, so the offset vector can be used to represent the overlay error.

[0109] By obtaining the first coordinates of the first geometric center 515 of the front layer mark 510 and obtaining the second coordinates of the second geometric center 525 of the same layer mark 520, the offset vector between the first coordinates and the second coordinates for representing the overlay error can be determined, so that the error value including the lateral overlay error and the longitudinal overlay error can be obtained at the same time. Compared with the scheme of needing to set lateral overlay alignment marks and longitudinal overlay alignment marks, it is beneficial to save the area of the overlay alignment mark 500, and further improve the performance of the overlay alignment mark 500.

[0110] In other embodiments, the type of the overlay alignment mark that can be used for measurement is multiple, and in multiple different types of the overlay alignment mark, the area of the projection pattern of the same layer mark occupies different proportions of the area of the projection pattern of the front layer mark in the corresponding overlay alignment mark. For example, as Figure 5As shown, the types of the overlay alignment marks used for measurement are four. It can be understood that the types of the overlay alignment marks used for measurement are not limited to four, and in other embodiments, the types of the overlay alignment marks used for measurement can also be two, three, or any number greater than four.

[0111] Correspondingly, before the first plane coordinate and the second plane coordinate are acquired, the measurement method can further include: selecting one type of overlay alignment mark to be measured from the plurality of types of overlay alignment marks.

[0112] Specifically, the selected overlay alignment mark has the best measurement accuracy of overlay error. Here, the measurement accuracy refers to that the overlay error corresponding to the offset vector acquired by the overlay alignment mark has the smallest error.

[0113] Correspondingly, based on the selected overlay alignment mark, the first plane coordinate of the first geometric center of the front layer mark is acquired, and the second plane coordinate of the second geometric center of the current layer mark is acquired.

[0114] In this embodiment, one type of overlay alignment mark to be measured is determined by one or more of the following ways:

[0115] Way one: in the case where the number of each type of overlay alignment mark is multiple, one type of overlay alignment mark to be measured is selected by using linear correlation analysis; wherein, the step of selecting one type of overlay alignment mark to be measured by using linear correlation analysis includes: in the same type of overlay alignment mark, taking the overlay error of each overlay alignment mark along the preset direction as the variable, and taking the overlay error along the preset direction between the actual product layers corresponding to each overlay alignment mark as the dependent variable, respectively performing linear correlation analysis on the overlay error measurement results corresponding to each type of overlay alignment mark to obtain the linear correlation degree; selecting one type of overlay alignment mark with the best linear correlation degree as the overlay alignment mark to be measured.

[0116] Here, the best linear correlation degree refers to that the absolute value of the linear correlation coefficient is closest to 1, and the slope is also close to 1.

[0117] As an example, the linear correlation degree refers to the Pearson correlation coefficient.

[0118] It should be noted that the preset direction refers to the first direction X or the second direction Y.

[0119] It should be further noted that the actual product layer refers to: two product layers in the chip area corresponding to the overlay alignment mark. As an example, the actual product layer can be located in the chip area adjacent to the overlay alignment mark. As an example, the overlay error between the actual product layers in the preset direction can be obtained by transmission electron microscopy (TEM) technology.

[0120] Method two: selecting an overlay alignment mark to be measured by error analysis; wherein the step of selecting an overlay alignment mark to be measured by error analysis includes: obtaining a plurality of measurement results of overlay errors in a preset direction corresponding to each type of overlay alignment mark, the plurality of measurement results of overlay errors corresponding to each type of overlay alignment mark being obtained by measuring the overlay error of the overlay alignment mark multiple times; selecting an overlay alignment mark with the smallest error of the plurality of measurement results of overlay errors as the overlay alignment mark to be measured.

[0121] As an example, the error analysis of the measurement results of the overlay errors corresponding to the same type of overlay alignment mark 600 includes: according to the three standard deviation (3σ) principle, obtaining the three times range of the standard deviation (σ) of the measurement results corresponding to the same type of overlay alignment mark 600, i.e. the 3σ value. Correspondingly, according to the 3σ value, the overlay alignment mark with the smallest 3σ value is selected as the overlay alignment mark to be measured.

[0122] Method three: selecting an overlay alignment mark to be measured by size comparison; wherein the step of selecting an overlay alignment mark to be measured by size comparison includes: obtaining the ratio of the overlay error in the preset direction corresponding to each type of overlay alignment mark to the mark size difference value, the mark size difference value being half of the size difference value in the preset direction between the front layer mark and the current layer mark of the overlay alignment mark; selecting an overlay alignment mark with a ratio closest to 50% as the overlay alignment mark to be measured.

[0123] As an example, in the case where the projection patterns of the front layer mark and the current layer mark are both circular, half of the size difference value in the preset direction between the front layer mark and the current layer mark of the overlay alignment mark refers to the difference value between the front layer mark radius and the current layer mark radius.

[0124] Specifically, in one embodiment, the step of selecting one overlay alignment mark to be measured from the plurality of types of overlay alignment marks includes: under the condition of having linear correlation analysis, selecting one overlay alignment mark to be measured by using linear correlation analysis; when the type of the overlay alignment mark with the best linear correlation degree is multiple, selecting one overlay alignment mark to be measured from the multiple overlay alignment marks with the best linear correlation degree by using error analysis; when the type of the overlay alignment mark with the minimum error is multiple, selecting one overlay alignment mark to be measured from the multiple overlay alignment marks with the minimum error by using size comparison.

[0125] Alternatively, in another embodiment, under the condition of not having linear correlation analysis, selecting one overlay alignment mark to be measured by using error analysis; when the type of the overlay alignment mark with the minimum error is multiple, selecting one overlay alignment mark to be measured from the multiple overlay alignment marks with the minimum error by using size comparison.

[0126] It should be noted that, the step of selecting one overlay alignment mark to be measured by using linear correlation analysis is beneficial to make the measurement result of the selected overlay alignment mark have a smaller difference degree with the overlay error along the preset direction between the corresponding actual product layer, so as to facilitate the selected overlay alignment mark to have the best measurement accuracy of overlay error.

[0127] It should be further noted that, the step of selecting one overlay alignment mark to be measured by using error analysis before the step of selecting one overlay alignment mark to be measured by using size comparison is beneficial to improve the accuracy of the measurement result of the selected overlay alignment mark.

[0128] It should be further noted that, the step of selecting one overlay alignment mark to be measured by using size comparison is beneficial to reduce the process error caused by the size difference.

[0129] Although the present application is disclosed as above, the present application is not limited to this. Any person skilled in the art, without departing from the spirit and scope of the present application, can make various changes and modifications, therefore the protection scope of the present application should be subject to the range defined by the claims.

Claims

1. A lithography overlay mark, characterized by, The overlay alignment mark comprises: a front layer mark, the front layer mark having a first geometric center in a direction parallel to a surface of the front layer mark; a current layer mark, located above the front layer mark, the current layer mark having a second geometric center in a direction parallel to a surface of the current layer mark, and a projection pattern of the current layer mark being located inside a projection pattern of the front layer mark in a same projection plane.

2. The overlay alignment mark of claim 1, wherein, The preset relative position relationship between the current layer mark and the front layer mark comprises that the geometric centers of the current layer mark and the front layer mark are concentrically arranged.

3. The overlay alignment mark of claim 1, wherein, An area of the projection pattern of the current layer mark accounts for 50% to 80% of an area of the projection pattern of the front layer mark.

4. The overlay alignment mark of claim 1, wherein, The overlay alignment mark comprises multiple types of overlay alignment marks, and in each type of the overlay alignment mark, a proportion of the area of the projection pattern of the current layer mark to the area of the projection pattern of the front layer mark in the corresponding overlay alignment mark is different.

5. The overlay alignment mark of claim 4, wherein, The overlay alignment mark comprises a first overlay alignment mark, a second overlay alignment mark, a third overlay alignment mark and a fourth overlay alignment mark. In the first overlay alignment mark, the area of the projection pattern of the front layer mark is a first area, and the area of the projection pattern of the current layer mark is a second area. In the second overlay alignment mark, the area of the projection pattern of the front layer mark is a third area, and the area of the projection pattern of the current layer mark is a fourth area. In the third overlay alignment mark, the area of the projection pattern of the front layer mark is the first area, and the area of the projection pattern of the current layer mark is the fourth area. In the fourth overlay alignment mark, the area of the projection pattern of the front layer mark is the third area, and the area of the projection pattern of the current layer mark is the second area. The first area is smaller than the third area, and the second area is smaller than the fourth area.

6. The overlay alignment mark of claim 1, wherein, A vertical distance between a top surface of the front layer mark and a top surface of the current layer mark is less than or equal to 2 microns.

7. The overlay alignment mark of claim 1, wherein, The overlay alignment mark further comprises a medium layer located on the front layer mark at a side of the current layer mark, and the medium layer is different in material from the front layer mark.

8. The overlay alignment mark of claim 7, wherein, The material of the front layer mark is a metal material.

9. The overlay alignment mark of any of claims 1-8, wherein, The projection pattern of the front layer mark and the projection pattern of the current layer mark are of the same shape.

10. The overlay alignment mark of any one of claims 1 to 8, wherein, The projection pattern of the front layer mark comprises one or more of a circle, a square and a rectangle, and the projection pattern of the current layer mark comprises one or more of a circle, a square and a rectangle.

11. The overlay alignment mark of claim 10, wherein, The projection pattern of the front layer mark and the projection pattern of the current layer mark are both of a circular shape.

12. A method of measuring overlay error, the method comprising: The overlay alignment mark comprises a front layer mark and a current layer mark located above the front layer mark, the front layer mark having a first geometric center in a direction parallel to a surface of the front layer mark, the current layer mark having a second geometric center in a direction parallel to a surface of the current layer mark, and a projection pattern of the current layer mark being located inside a projection pattern of the front layer mark in a same projection plane. The measurement method comprises: obtaining a first plane coordinate of the first geometric center of the front layer mark; obtaining a second plane coordinate of the second geometric center of the current layer mark; and Based on the first planar coordinate and the second planar coordinate, an offset vector of the first geometric center and the second geometric center is obtained, and the offset vector is used to represent the overlay error.

13. The method of measuring overlay error of claim 12, wherein, The first planar coordinate and the second planar coordinate are coordinate points in the same planar rectangular coordinate system.

14. The method of measuring overlay error of claim 12, wherein, The manner of obtaining the first planar coordinate includes identifying the contour of the front layer mark and positioning the first geometric center based on the contour of the front layer mark.

15. The method of measuring overlay error of claim 12, wherein, The manner of obtaining the second planar coordinate includes identifying the contour of the current layer mark and positioning the second geometric center based on the contour of the current layer mark.

16. The method of measuring overlay error of claim 12, wherein, The types of the overlay alignment marks are multiple, and in the multiple types of the overlay alignment marks, the projection pattern area of the current layer mark accounts for different proportions of the projection pattern area of the front layer mark in the corresponding overlay alignment mark. The measurement method further includes selecting one overlay alignment mark to be measured from the multiple types of the overlay alignment marks. Based on the selected overlay alignment mark, the first planar coordinate of the first geometric center of the front layer mark is obtained, and the second planar coordinate of the second geometric center of the current layer mark is obtained.

17. The method of overlay error measurement of claim 16, wherein, One overlay alignment mark to be measured is determined by one or more of the following manners: In the case where the number of the various types of the overlay alignment marks is multiple, one overlay alignment mark to be measured is selected by using linear correlation analysis, and the step of selecting one overlay alignment mark to be measured by using linear correlation analysis includes: in the same type of the overlay alignment marks, taking the overlay error of each overlay alignment mark along a preset direction as a variable and taking the overlay error between the actual product layers corresponding to each overlay alignment mark along the preset direction as a dependent variable, respectively performing linear correlation analysis on the overlay error measurement results corresponding to the various types of the overlay alignment marks to obtain linear correlation degrees; and selecting one overlay alignment mark with the best linear correlation degree as the overlay alignment mark to be measured. One overlay alignment mark to be measured is selected by using error analysis, and the step of selecting one overlay alignment mark to be measured by using error analysis includes: obtaining multiple overlay error measurement results corresponding to each type of the overlay alignment marks along a preset direction, the multiple overlay error measurement results corresponding to each type of the overlay alignment marks being obtained by performing multiple overlay error measurements on the overlay alignment marks; and selecting one overlay alignment mark with the minimum error of the multiple overlay error measurement results as the overlay alignment mark to be measured. The method comprises the following steps: selecting one overlay alignment mark to be measured by size comparison; wherein, the step of selecting one overlay alignment mark to be measured by size comparison comprises: obtaining the ratio of overlay error along a preset direction and mark size difference value corresponding to each type of overlay alignment mark, the mark size difference value being half of the size difference value along the preset direction between the front layer mark and the current layer mark of the overlay alignment mark; selecting one overlay alignment mark with a ratio closest to 50% as the overlay alignment mark to be measured.

18. The method of overlay error measurement of claim 17, wherein, The step of selecting one overlay alignment mark to be measured from a plurality of types of overlay alignment marks comprises: under the condition of linear correlation analysis, selecting one overlay alignment mark to be measured by linear correlation analysis; when the type of overlay alignment mark with the best linear correlation degree is multiple, selecting one overlay alignment mark to be measured from the multiple overlay alignment marks with the best linear correlation degree by error analysis; when the type of overlay alignment mark with the minimum error is multiple, selecting one overlay alignment mark to be measured from the multiple overlay alignment marks with the minimum error by size comparison; or, under the condition of no linear correlation analysis, selecting one overlay alignment mark to be measured by error analysis; when the type of overlay alignment mark with the minimum error is multiple, selecting one overlay alignment mark to be measured from the multiple overlay alignment marks with the minimum error by size comparison.

19. The method of measuring overlay according to any one of claims 12-18, wherein, The projection pattern of the front layer mark and the projection pattern of the current layer mark are of the same shape.

20. The method of measuring overlay of any one of claims 12-18, wherein, The projection pattern of the front layer mark comprises one or more of a circle, a square and a rectangle; and the projection pattern of the current layer mark comprises one or more of a circle, a square and a rectangle.

Images