CN112542396A

CN112542396A - Overlay mark and alignment error measuring method

Info

Publication number: CN112542396A
Application number: CN202010614218.1A
Authority: CN
Inventors: 陈鲁; 吕肃; 李青格乐; 江博闻; 张嵩
Original assignee: Shenzhen Zhongke Feice Technology Co Ltd
Current assignee: Shenzhen Zhongke Feice Technology Co Ltd
Priority date: 2020-06-30
Filing date: 2020-06-30
Publication date: 2021-03-23
Anticipated expiration: 2040-06-30
Also published as: CN112542396B

Abstract

The application discloses a method for measuring overlay marks and alignment errors. The overlay mark is positioned in the substrate and comprises a first mark and a second mark; the first mark and the second mark are respectively positioned on different layers of the substrate, and/or the first mark and the second mark are formed in different processes. The first mark and the second mark both contain feature structures, and the feature structures have feature points. The projection plane of the first mark and the second mark is the surface of the substrate, and the characteristic structure has discontinuity along any direction at the characteristic point. The information of the first identified feature points and the information of the second identified feature points are used to make alignment error measurements. Because the characteristic points are not easily influenced by illumination nonuniformity and operations such as rotation, translation, expansion and the like, the alignment error measurement is carried out by using the information of the characteristic points of the first identification and the information of the characteristic points of the second identification, and the stability of the measurement result is strong.

Description

Overlay mark and alignment error measuring method

Technical Field

The invention relates to the technical field of integrated circuit manufacturing, in particular to a method for measuring overlay marks and alignment errors.

Background

With the continuous progress of the integrated technology, the number of superposed layers of the circuits in the integrated circuit chip is more and more. In the process of multilayer patterning, in order to achieve good semiconductor performance, the photoetching patterns on the wafer not only need to have accurate characteristic line width dimensions, but also need to ensure the position alignment between the upper layer of patterns and the lower layer of patterns, and if the upper layer of patterns and the lower layer of patterns are not aligned, the reliable connection of circuits designed on the upper layer of patterns and the lower layer of patterns cannot be ensured. Therefore, it is an important factor to ensure the semiconductor yield that the offset (i.e., alignment error) of the patterns on the upper and lower layers of the wafer satisfies the error requirement. In order to measure whether the positions of the upper and lower patterns are shifted, overlay marks (i.e., patterns for measuring alignment errors) on the wafer may be detected.

Currently, alignment error is measured in two ways, one is Diffraction-Based alignment error measurement (DBO) and the other is Image-Based alignment error measurement (IBO). The former calculation needs modeling based on a diffraction model, and the calculation amount is large, so the alignment error measurement speed is slow. The latter determines the alignment error by comparing the peaks of the periodic signal. However, the stripe pattern in the commonly used overlay mark is more easily affected by the illumination nonuniformity and the operations such as rotation, translation and expansion when the alignment error measurement is performed, so that the stability of the measurement result is poor.

Disclosure of Invention

In view of the above problems, the present application provides a method for measuring overlay marks and alignment errors, so as to improve the stability of the measurement result of the alignment errors.

In a first aspect of the present application, an overlay mark is provided, where the overlay mark is located in a substrate and includes a first mark and a second mark; the first mark and the second mark are respectively positioned on different layers of the substrate, and/or the first mark and the second mark are formed in different processes;

the first mark and the second mark both comprise a feature structure, the feature structure is provided with a feature point, the projection plane of the first mark and the second mark is the surface of the substrate, and the feature structure is provided with discontinuity along any direction at the feature point; and the information of the characteristic points of the first identification and the information of the characteristic points of the second identification are used for carrying out alignment error measurement.

Optionally, the feature structures of the first marker are arranged periodically, and the feature structures of the second marker are arranged periodically.

Optionally, the projection of the feature structure in the projection plane is a feature pattern, the feature pattern is a polygon, and the projection of the feature point in the projection plane is a vertex of the polygon; or, the characteristic structure is a cone, and the characteristic point is a cone vertex.

Optionally, the first marker is centrosymmetric, and the second marker is centrosymmetric; when the first mark and the second mark have no alignment error, the symmetry center of the first mark and the symmetry center of the second mark are coincident in the projection plane.

Optionally, the first mark is still coincident with the first mark before rotation after rotating 90 degrees or 180 degrees along the symmetry center of the first mark; the second mark is still coincident with the second mark before the second mark rotates along the symmetry center of the second mark by 90 degrees or 180 degrees.

Optionally, the first marker and the second marker are offset from each other in the projection plane.

Optionally, the first marker comprises at least one first grid structure, and the second marker comprises at least one second grid structure; the first grid structure and the second grid structure each include the feature, and a first grid pattern formed by the first grid structure at the projection plane and a second grid pattern formed by the second grid structure at the projection plane each include a plurality of polygonal figures.

Optionally, the overlay mark comprises a plurality of identification sections, each of the identification sections comprises one of the first grid structures and one of the second grid structures, and the first grid pattern of the first grid structure is adjacent to the second grid pattern of the second grid structure in the projection plane.

Optionally, the vertices of the polygons in the first grid pattern meet, and the vertices of the polygons in the second grid pattern meet.

Alternatively, when the center of the first grid pattern of a certain first grid structure and the center of the second grid pattern of a certain second grid structure are overlapped in the projection plane, the polygon corresponding to the first grid pattern is overlapped with the polygon corresponding to the second grid pattern or the interval between the polygon corresponding to the first grid pattern and the polygon corresponding to the second grid pattern is overlapped.

Optionally, the side length of the polygon is in the interval of [2 μm, 6 μm ].

Optionally, the number of the features periodically arranged along the first direction in the first grid structure is greater than or equal to 3.

In a second aspect of the present application, there is provided a method for measuring an alignment error, including:

obtaining an image of the overlay mark provided in the first aspect;

acquiring a first relative position relation between the characteristic points of the first identifier and the second identifier according to the image; and acquiring the offset of the first identifier and the second identifier according to the first relative position relationship, and taking the offset as an alignment error.

Optionally, obtaining a first relative position relationship between the feature point of the first identifier and the feature point of the second identifier according to the image specifically includes: and extracting the actual position information of the characteristic points of the first identifier and the second identifier in a first coordinate system according to the image to obtain the first relative position relationship.

Optionally, obtaining an offset between the first identifier and the second identifier according to the first relative position relationship specifically includes:

obtaining a first position conversion matrix corresponding to the feature point of the first identifier according to the actual position information of the feature point of the first identifier and the preset position information of the feature point of the first identifier; obtaining a second position conversion matrix corresponding to the feature point of the second identifier according to the actual position information of the feature point of the second identifier and the preset position information of the feature point of the second identifier, wherein the preset position information of the feature point of the first identifier and the preset position information of the feature point of the second identifier are position information in a second coordinate system;

and obtaining a relative offset matrix according to the first position conversion matrix and the second position conversion matrix, wherein the relative offset matrix comprises the offset.

Optionally, a relative offset matrix is obtained according to the first position transformation matrix and the second position transformation matrix, and the method is specifically implemented according to the following formula: u ═ TM1 × inv (TM 2);

wherein the U represents the relative offset matrix, the TM1 represents the first position transition matrix, and the TM2 represents the second position transition matrix; the inv () function represents the inversion operation of the TM 2.

Optionally, obtaining a first position transformation matrix corresponding to the feature point of the first identifier according to the actual position information of the feature point of the first identifier and the preset position information of the feature point of the first identifier, specifically including:

calculating the actual offset of the characteristic point of the first identifier relative to the preset offset by using a least square method according to the actual position information of the characteristic point of the first identifier and the preset position information of the characteristic point of the first identifier to form a first position conversion matrix;

obtaining a second position conversion matrix corresponding to the feature point of the second identifier according to the actual position information of the feature point of the second identifier and the preset position information of the feature point of the second identifier, and specifically comprising:

and calculating the actual offset of the characteristic point of the second identifier relative to the preset offset by using a least square method according to the actual position information of the characteristic point of the second identifier and the preset position information of the characteristic point of the second identifier to form the second position conversion matrix.

Optionally, the first mark is centrosymmetric, the second mark is centrosymmetric, and a preset relative position relationship is formed between the symmetry center of the first mark and the symmetry center of the second mark;

the obtaining an offset between the first identifier and the second identifier according to the first relative position relationship, and taking the offset as an alignment error, includes:

acquiring a second relative position relation between the first identification symmetry center and a second identification symmetry center according to the first relative position relation;

and acquiring the offset of the first identifier and the second identifier according to the second relative position relationship and the preset relative position relationship between the first identifier symmetry center and the second identifier symmetry center.

Optionally, the offset includes: a translational offset and/or a rotational offset.

Compared with the prior art, the technical scheme of the application has the advantages that:

the application provides an overlay mark, which is positioned in a substrate and comprises a first mark and a second mark; the first mark and the second mark are respectively positioned on different layers of the substrate, and/or the first mark and the second mark are formed in different processes. The first mark and the second mark both contain feature structures, and the feature structures have feature points. The projection plane of the first mark and the second mark is the surface of the substrate, and the characteristic structure has discontinuity along any direction at the characteristic point. The information of the first identified feature points and the information of the second identified feature points are used to make alignment error measurements. Because the characteristic points are not easily influenced by illumination nonuniformity and operations such as rotation, translation, expansion and the like, the alignment error measurement is carried out by using the information of the characteristic points of the first identification and the information of the characteristic points of the second identification, and the stability of the measurement result is strong.

Drawings

In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings needed to be used in the description of the embodiments or the prior art will be briefly described below, it is obvious that the drawings in the following description are only some embodiments described in the present application, and other drawings can be obtained by those skilled in the art without creative efforts.

Fig. 1 is a schematic projection diagram of an overlay mark according to an embodiment of the present disclosure;

FIG. 2 is a schematic projection view of a first mark of the overlay mark of FIG. 1;

FIG. 3 is a schematic projection view of a second mark in the overlay mark of FIG. 1;

FIG. 4 is a schematic projection view of another overlay mark provided in an embodiment of the present application;

FIG. 5 is a schematic projection view of a first mark in the overlay mark of FIG. 4;

FIG. 6 is a schematic projection view of a second mark in the overlay mark of FIG. 4;

FIG. 7 is a schematic projection diagram of another overlay mark provided in the embodiments of the present application;

FIG. 8 is a schematic projection diagram of another alignment mark provided in an embodiment of the present application;

FIG. 9 is a flowchart of a method for measuring alignment error according to an embodiment of the present disclosure;

fig. 10 is a schematic diagram illustrating a preset position of a feature point of a first mark in an overlay mark according to an embodiment of the present disclosure;

fig. 11 is a schematic diagram of a relative shift between an actual position and a preset position of a feature point of a first identifier according to an embodiment of the present application.

Detailed Description

In order to determine whether the positions of the upper and lower patterns on the wafer are shifted, the overlay marks on the wafer need to be detected to obtain the alignment error. Currently, alignment errors are measured by using overlay marks based on the IBO technology. In order to improve the stability of the measurement result of the alignment error and reduce the influence of the illumination nonuniformity and the operations such as rotation, translation and expansion on the measurement result, the inventors have studied and provided a method for measuring the overlay mark and the alignment error in the present application.

In order to make the technical solutions of the present invention better understood, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

Overlay mark example:

the embodiment of the application provides an overlay mark. The overlay mark is specifically formed in the substrate. The overlay mark comprises two part marks which are respectively a first mark and a second mark.

In a possible implementation manner, the first identifier and the second identifier may be located at different layers of the substrate, for example, the first identifier is located at the ith layer of the substrate, the second identifier is located at the jth layer of the substrate, i and j are positive integers, and i ≠ j. The first mark and the second mark are formed in the same process. For example: the first mark and the second mark may be both formed by an etching process, or both formed by an ion implantation process.

In another possible implementation, the first and second marks are located on the same layer of the substrate, but the first and second marks are formed during different processes. The different processes comprise: the first mark and the second mark are formed using different masks, or are formed at different times.

In yet another possible implementation, the first mark and the second mark are respectively located on different layers of the substrate, and the first mark and the second mark are formed in different processes.

If the first marker and the second marker are located on the same layer or respectively located on different layers but the layer distance is small, a projection image of the first marker and the second marker on the same projection plane can be obtained through single-time focusing shooting. And the first mark and the second mark are positioned on different layers but have larger layer distance, so that the first mark and the second mark can be focused respectively to obtain a projected image of the first mark on the projection screen and a projected image of the second mark on the same projection plane. The projection plane of the first mark and the second mark is the surface of the substrate.

The first mark and the second mark both comprise feature structures, and the feature structures are provided with feature points. The feature points have discontinuities in the feature along either direction. Continuous means that the feature points are continuous along both sides of a straight line. By way of example, the features may be raised or recessed structures, as well as vertebral bodies. If the projection structure or the groove structure can form a polygonal feature pattern on the projection plane, the projection of the feature point of the feature structure on the projection plane is the vertex of the polygonal figure. If the feature structure is a cone, the vertex of the cone is a feature point. It will also be appreciated in connection with the above examples that the feature points have discontinuities in the feature structure in either direction.

The polygonal shapes may be triangles, rectangles (e.g., squares or rectangles), pentagons, and the like. The specific number of sides of the polygon is not limited here. The vertices of each polygon are taken as projections of feature points. That is, by forming the first mark and the second mark, a plurality of recognizable feature points are constructed. By capturing images with these feature points, information of the feature points on the projection plane, such as position information, distance information, and the like, can be recognized. This information may be useful in making alignment error measurements. As a possible implementation manner, the information of the feature points on the projection plane may be identified to obtain the translational offset and the rotational offset of the feature points of the first identifier relative to the feature points of the second identifier.

Because the characteristic points on the characteristic structure are not easily influenced by illumination nonuniformity and operations such as rotation, translation and expansion, the alignment error measurement is carried out by using the information of the characteristic points of the first identification and the information of the characteristic points of the second identification, and compared with the prior art, the stability of the measurement result is enhanced.

To improve the accuracy of alignment error measurements, periodically arranged features may be built on the substrate. That is, in a possible implementation, the first labeled features are arranged periodically, and the second labeled features are arranged periodically.

In the embodiment of the present application, it is not specifically limited whether the first mark and the second mark coincide with each other in the projection plane. For example, the first and second markers are offset from each other in the projection plane. As another example, the first indicia and the second indicia may partially overlap or completely overlap in the projection plane.

In the overlay mark provided in the embodiment of the present application, the first mark is centrosymmetric, and the second mark is also centrosymmetric. When the first mark rotates 90 degrees or 180 degrees along the symmetry center, the first mark can be coincided with the first mark before rotation, and when the second mark rotates 90 degrees or 180 degrees along the symmetry center, the second mark can also be coincided with the second mark before rotation. When the first mark and the second mark have no alignment error, the symmetry center of the first mark and the symmetry center of the second mark are coincident in the projection plane.

In the embodiment of the application, the first mark may include a plurality of first grid structures, and the second mark includes a plurality of second grid structures; the first lattice structure and the second lattice structure each include a feature. For ease of understanding, the following description will be made with reference to the accompanying drawings, in which two types of overlay marks provided by the embodiments of the present application are described.

Fig. 1 is a schematic projection diagram of an overlay mark 100 according to an embodiment of the present disclosure. Fig. 2 is a schematic projection view of a first mark 110 in the overlay mark 100, and fig. 3 is a schematic projection view of a second mark 120 in the overlay mark 100. As can be seen in connection with fig. 1 to 3, the projection of the first marker 110 includes projections of four first grid structures K11, K12, K13 and K14, and the projection of the second marker 120 includes projections of four second grid structures K21, K22, K23 and K24.

As can be seen from fig. 2 and 3, the first mark 110 is still overlapped with the first mark before rotation after rotating 90 degrees along the symmetry center; the second marker 120 is rotated 90 degrees along its center of symmetry and then still coincides with before rotation.

Take the projection of the first grid structure K12 as an example, which includes a plurality of polygon patterns. One of the darker regions may be considered as a polygon, or one of the lighter regions may be considered as a polygon. In the projection of the first grid structure K12, the regions are differently colored in different shades merely to distinguish different process effects, for example, darker regions are ion-etched regions and lighter regions are regions that are not etched by the examples. In a first grid pattern formed by the first grid structure, vertexes of the polygonal figures are connected; the second grid pattern is formed by the second grid structure, and the vertexes of the polygon are connected.

To facilitate description of the arrangement of the polygon pattern in the first grid pattern of the first grid structure K12, a first direction and a second direction are defined in fig. 1, wherein the first direction is a direction pointing from the first grid structure K11 to the first grid structure K12, and the second direction is a direction pointing from the first grid structure K12 to the first grid structure K13. As can be seen from fig. 1, the first direction and the second direction are perpendicular to each other. After the first direction and the second direction are defined, the arrangement of the polygon in the first grid pattern is described by taking the first grid structure K12 as an example. In this embodiment, the polygon is a square, and the sides of the square are perpendicular or parallel to the first direction, and correspondingly, perpendicular or parallel to the second direction.

In the first grid pattern of the first grid structure K12, darker squares are assumed to be polygonal as described in the embodiments of the present application. The polygon has a dimension in the first direction of L1 and a dimension in the second direction of L2. When the polygon is a square, L1 ═ L2. The polygonal patterns were arranged in the first direction at a period of 2 × L1 and in the second direction at a period of 2 × L2, and thus it was found that the first lattice structure K12 was a feature structure including two-dimensional periodic extensions. As can be seen from the projection of the first lattice structure K12 illustrated in the figure, the first direction in the first lattice structure K12 includes 6 or 7 features, and the second direction includes 6 or 7 features.

Similarly, the second grid pattern of the second grid structure K22 is taken as an example, and includes a plurality of polygonal figures. One of which a single dark area may be considered as one polygonal figure, or one of which a single clear area may be considered as one polygonal figure. In the projection of the second grid structure K22, the difference in color of the regions is merely to distinguish different process effects, for example, dark regions are ion-etched regions and colorless regions are regions that are not etched by the examples. The following describes the arrangement of the polygon in the second grid pattern by taking the second grid structure K22 as an example.

In the second grid pattern of the second grid structure K22, dark squares are assumed as the polygonal shapes described in the embodiments of the present application. The polygon has a dimension in the first direction of L1 and a dimension in the second direction of L2. When L1 is L2, the polygon is a square. The polygonal patterns were arranged in the first direction at a period of 2 × L1 and in the second direction at a period of 2 × L2, and thus it was found that the second lattice structure K22 was a feature structure including two-dimensional periodic extensions. As can be seen from the projection of the second lattice structure K22 illustrated in the figure, the first direction in the second lattice structure K22 includes 6 or 7 features, and the second direction includes 6 or 7 features.

If the darker squares in the first grid structures K11-K14 are used as the polygons (regions affected by the process), and the darker squares in the second grid structures K21-K24 are used as the polygons (regions affected by the process), as can be seen from fig. 1-3, when the center of the first grid structure in the first indicator 110 and the center of the second grid structure in the second indicator 120 coincide with each other in the projection plane, the polygons corresponding to the first grid structure and the polygons corresponding to the second grid structure coincide with each other at intervals (i.e., are complementary). Taking the first grid structure K12 and the second grid structure K22 as an example, when the centers of the two coincide in the projection plane, the polygonal figure corresponding to the first grid structure K12 is exactly complementary to the polygonal figure corresponding to the second grid structure K22 in the outline.

If (1) the darker squares in the first grid structures K11-K14 are used as the polygons (regions to be processed), and the colorless squares in the second grid structures K21-K24 are used as the polygons (regions to be processed); or, (2) the light-colored squares in the first grid structures K11 to K14 are polygonal patterns (regions to be processed), and the dark squares in the second grid structures K21 to K24 are polygonal patterns (regions to be processed); then, when a center of a first grid structure in the first indicator 110 and a center of a second grid structure in the second indicator 120 coincide with each other in a projection plane, a polygon corresponding to the first grid structure coincides with a polygon corresponding to the second grid structure.

As can be seen from fig. 1 and 2, the first lattice structures K11 to K14 are arranged in a dispersed manner. As can be seen from fig. 1 and 3, the second lattice structures K21 to K24 are arranged in a row. In one possible implementation, the size of the first grid structure in the first identifier 110 is the same as the size of the second grid structure in the second identifier 120.

The overlay mark may be considered to comprise a plurality of identification zones, wherein each identification zone comprises one first grid structure and one second grid structure, and the first grid pattern of the first grid structure and the second grid pattern of the second grid structure are adjacent in the projection plane. As the overlay mark 100 shown in fig. 1, (1) a first lattice structure K11 and a second lattice structure K21; (2) a first lattice structure K12 and a second lattice structure K22; (3) a first lattice structure K13 and a second lattice structure K23; (4) a first lattice structure K14 and a second lattice structure K24; respectively, as four distinct identification divisions within the overlay mark 100. The existence of the identification subarea enables measurement and comparison to be more convenient and faster when information of the characteristic points in the projection image is extracted to measure the overlay marks.

The side length of the polygon is too large, which easily increases the volume of the overlay mark. When the side length of the polygon pattern is too small, moire is likely to occur, and the accuracy of detecting the feature point information in the captured image is lowered. In the example illustrated in fig. 1 to 3, the side lengths of the polygon in the first mark 110 and the polygon in the second mark 120 of the overlay mark 100 take values within the interval of [2 μm, 6 μm ]. For example, L1 ═ L2 ═ 2 μm.

Another overlay mark provided by the present application is described below.

Fig. 4 is a schematic projection diagram of another overlay mark 400 provided in the embodiments of the present application. Fig. 5 is a schematic projection view of a first mark 410 in the overlay mark 400, and fig. 6 is a schematic projection view of a second mark 420 in the overlay mark 400. As can be seen in conjunction with fig. 4 to 6, the first flag 410 includes four first lattice structures D11, D12, D13, and D14, and the second flag 420 includes four second lattice structures D21, D22, D23, and D24. Each of the first grid structure and the second grid structure includes a plurality of polygonal figures therein. In practice, the multi-sided graphics may be triangular, rectangular (e.g., square or rectangular), pentagonal, etc. In the examples of fig. 4 to 6, only the square polygon is taken as an example for detailed description. As shown in fig. 4 to 6, in the first mark 410, the first grid pattern of each of the first grid structures D11-D14 includes 3 complete polygonal figures, wherein the vertices of the 3 complete polygonal figures are connected, and partial edges are adjacent to each other, so as to form 8 vertices. For example, the first grid pattern of the first grid structure D14 includes a polygon z1 and a polygon z2, wherein the sides of the polygon z1 are: b1, b2, b3 and b 4; the sides of polygon z2 are: b3, b5, b6 and b 7. The side b3 is a side where the polygon z1 and the polygon z2 are adjacent to each other. Similarly, in the second marker 420, the second grid pattern of each of the second grid structures D21-D24 includes 3 complete polygons, and the vertices of the 3 complete polygons are connected and some edges are adjacent to each other, forming 8 vertices. In practical applications, the first mark of the overlay mark may include at least one first grid structure, and the second mark may include at least one second grid structure. The number of the first lattice structure and the second lattice structure is not limited, respectively.

It should be noted that in the present embodiment, adjacent polygons are separated by mutually adjacent sides, such as the polygons z1 and z2, which are separated by the side b 3. In addition, as can be seen from fig. 4, the vertices of the polygon may be shared by four polygons having adjacent edges between two polygons. The vertex of the polygon in the figure is the projection of the feature point on the feature structure contained in the first mark or the second mark in the overlay mark.

The width of the sides of the polygon is much smaller than the side length of the polygon. As shown in the drawing, when the widths of b1 to b7 are equal and the polygon is a square, W1 is equal to W2. The width of b 1-b 7 is much less than W1 (i.e., also much less than W2). For example, W1 ═ W2 ═ 4 μm, and the sides b1 to b7 have a width of several tens of nanometers.

As can be seen from fig. 4 to 6, the first lattice structures D11 to D14 may be arranged in a scattered manner, and the second lattice structures D21 to D24 may be arranged in a gathered manner. In the present embodiment, the outer contours of the first grid structures D11 to D14 and the second grid structures D21 to D24 are both rectangular. Taking the first grid structure D11 and the second grid structure D21 as an example, when the two move and the centers coincide in the projection plane, the polygon shapes in the two coincide.

As can be seen from fig. 5 and 6, the first mark 410 is still coincident with the first mark before rotation after rotating 90 degrees or 180 degrees along the symmetry center; the second marker 420 may be rotated 90 degrees or 180 degrees along its center of symmetry and still coincide with the position before rotation.

A first direction and a second direction are defined in fig. 4, wherein the first direction is directed from the first grid structure D11 to the first grid structure D12, and the first direction is parallel to two opposite sides of the outer contour of any one of the first grid structures. The second direction is directed to the first grid structure D13 from the first grid structure D12, and the second direction is parallel to two opposite sides of the outer contour of any one of the first grid structures. The polygonal shapes corresponding to the first grid structures D11 to D14 and the second grid structures D21 to D24 may be rectangles, and the size of the rectangle in the first direction is W1 and the size of the rectangle in the second direction is W2. When W1 is W2, the polygon is a square.

As shown in fig. 4, the sides of the square polygon are parallel or perpendicular to the previously defined first direction. Since the first direction is perpendicular to the second direction in the embodiment of the present application, the sides of the polygonal figure of the square are parallel or perpendicular to the second direction accordingly.

In the first grid structures D12 and D14 and the second grid structures D22 and D24, the polygon patterns are arranged in the first direction according to a period of W1. In the first grid structures D11 and D13 and the second grid structures D21 and D23, the polygonal patterns are arranged in the second direction according to a period of W2. In this embodiment, the side length of the polygon is in the interval of [2 μm, 6 μm ]. For example, W1 ═ W2 ═ 4 μm.

In the embodiment of the present application, the overlay mark may be regarded as including a plurality of identification sections, wherein each identification section includes a first grid structure and a second grid structure, and a first grid pattern of the first grid structure and a second grid pattern of the second grid structure are adjacent in the projection plane. As shown in the overlay mark 400 of fig. 4, (1) a first lattice structure D11 and a second lattice structure D21; (2) a first lattice structure D12 and a second lattice structure D22; (3) a first lattice structure D13 and a second lattice structure D23; (4) a first lattice structure D14 and a second lattice structure D24; respectively, as four distinct identification divisions within the overlay mark 400. The existence of the identification subarea enables measurement and comparison to be more convenient and faster when the information of the characteristic points in the projection image is extracted to measure the overlay marks.

Of the above four marker sections (1) to (4) of the overlay mark 400 shown in fig. 4, (2) and (4) the long side of the outer contour of the first grid structure in the two marker sections is parallel to the first direction, and the long side of the outer contour of the second grid structure is parallel to the first direction; (1) and (3) the short side of the outline of the first grid structure in the two identification subareas is parallel to the first direction, and the short side of the outline of the second grid structure is parallel to the first direction.

In addition to the arrangement of the first grid structure and the second grid structure in the overlay mark 400 shown in fig. 4, the present application also shows the projection of an overlay mark 401 and an overlay mark 402 in conjunction with fig. 7 and 8, respectively. In the overlay mark 401 shown in fig. 7, (1) to (4) four mark sections indicate that the short sides of the outer contour of the first grid structure are parallel to the first direction, and the short sides of the outer contour of the second grid structure are parallel to the first direction. In the projection of the overlay mark 402 shown in fig. 8, the long sides of the outer contour of the first grid structure of (1) to (4) four marker sections are parallel to the first direction, and the long sides of the outer contour of the second grid structure are parallel to the first direction.

In the above embodiment, the number of the features periodically arranged in the first direction in the first lattice structure is greater than or equal to 3. Similarly, the number of the features periodically arranged along the second direction in the first lattice structure is greater than or equal to 3. The number of the features periodically arranged along the first direction in the second lattice structure is greater than or equal to 3. Similarly, the number of the features periodically arranged along the second direction in the second grid structure is greater than or equal to 3.

Based on the overlay mark provided by the foregoing embodiment, correspondingly, the application also provides a method for implementing alignment error measurement by using the overlay mark. Specific implementations of the method are described below in conjunction with the examples and figures.

The method comprises the following steps:

referring to fig. 9, it is a flowchart of a method for measuring an alignment error according to an embodiment of the present application.

As shown in fig. 9, the method includes:

step 901: an image of the overlay mark is obtained.

The overlay mark used in this step may be any one of the overlay marks provided in the foregoing embodiments, for example, the overlay marks shown in fig. 1, 4, 7, or 8. It should be noted that fig. 1, fig. 4, fig. 7, or fig. 8 are only examples, and in practical applications, these example overlay mark modifications may also be applied.

The projection plane of the first mark and the second mark of the overlay mark is the surface of the substrate. If the first indicia and the second indicia of the overlay mark are on the same layer of the substrate, or on different layers but spaced closer together, an image can be taken. If the first mark and the second mark of the overlay mark are located on different layers and the distance between the two layers is large, one image can be shot for the first mark, and the other image can be shot for the second mark.

The purpose of shooting the image is to extract the actual position information of the vertexes of the polygon in the feature pattern, i.e., the actual position information of the image formed by the feature points on the feature structure on the projection plane.

Step 902: and acquiring a first relative position relation between the characteristic point of the first identifier and the characteristic point of the second identifier according to the image.

Optionally, the actual position information of the feature points of the first identifier and the feature points of the second identifier in the first coordinate system is extracted according to the image, and a first relative position relationship is obtained according to the actual position information in the same coordinate system.

In a possible implementation manner, the pixel values of the pixel points in the image obtained in step 901 may be analyzed, so as to determine the positions of the pixel points corresponding to the feature points of the first identifier in the image and the positions of the pixel points corresponding to the feature points of the second identifier in the image. In a specific implementation, stable corner points can be found by an algorithm, for example, by using the symmetry of image gradients.

Therefore, the actual position information of the first identified feature point and the actual position information of the second identified feature point can be represented by the coordinates of the pixel points in the image coordinate system. Then, the first relative position relationship is obtained.

Step 903: and acquiring the offset of the first identifier and the second identifier according to the first relative position relationship, and taking the offset as an alignment error.

In a specific possible implementation manner, the step may include the following steps a and b:

a. obtaining a first position conversion matrix TM1 corresponding to the feature point of the first identifier according to the actual position information of the feature point of the first identifier and the preset position information of the feature point of the first identifier; and obtaining a second position conversion matrix TM2 corresponding to the feature point of the second identifier according to the actual position information of the feature point of the second identifier and the preset position information of the feature point of the second identifier.

And the preset position information of the characteristic points of the first identifier and the preset position information of the characteristic points of the second identifier are position information in a second coordinate system. The position information of the second coordinate system can be understood as ideal position information of the feature point in the image. That is, the second coordinate system is a coordinate system of the ideal position of the feature point. These ideal positions are named preset positions in the embodiments of the present application.

During specific implementation, the rotation amount and the translation amount of the actual feature point of the first identifier relative to the ideal feature point can be calculated by using a least square method according to the actual position information of the feature point of the first identifier and the preset position information of the feature point of the first identifier, so as to form a first position conversion matrix; and calculating the actual rotation amount and translation amount of the characteristic point of the second identifier relative to the ideal by using a least square method according to the actual position information of the characteristic point of the second identifier and the preset position information of the characteristic point of the second identifier to form a second position conversion matrix.

For ease of understanding, please refer to fig. 10 and 11. Fig. 10 is a schematic diagram of the preset positions of the feature points of the first mark in the overlay mark similar to the overlay mark 100. Wherein the solid dark colored dots represent characteristic points of the first marker. Fig. 11 is a schematic diagram illustrating a relative shift between an actual position and a preset position of a feature point of a first marker. In fig. 11, solid dark colored dots represent preset positions of the first-identified feature points, and open circles represent actual positions of the first-identified feature points. In practical applications, the actual rotation amount and the actual translation amount of the feature point of the first identifier with respect to the preset (ideal) amount can be obtained by using the position information of the solid color setting point and the position information of the hollow circle shown in fig. 11. The translation direction is the first direction or the opposite direction thereof, or the second direction or the opposite direction thereof.

b. A relative shift matrix U is derived from the first position transition matrix TM1 and the second position transition matrix TM2, and the relative shift matrix U includes an offset.

The method is realized according to the following formula:

U＝TM1*inv(TM2)；

where the inv () function represents the inversion operation on TM 2. That is, in the present embodiment, the TM1 is multiplied by the inverse matrix of the TM2 to obtain a relative offset matrix.

The offset may specifically include: a translational offset and/or a rotational offset. In practice, the translational offset and the rotational offset are usually present simultaneously.

In addition, the present application also proposes another implementation manner of step 903, which is described below. In this implementation, the alignment error measurement is performed with the aid of the centers of symmetry of the first marker and the second marker. Specifically, the method comprises the following steps:

A. and acquiring a second relative position relation between the first identification symmetry center and a second identification symmetry center according to the first relative position relation.

Since the first relative positional relationship is obtained in the first coordinate system, the first relative positional relationship represents actual positional information of the feature point, and the feature point has positional association with the first identifier symmetry center and the second identifier symmetry center, the second relative positional relationship, which is a relative positional relationship between the actual positions of the first identifier symmetry center and the second identifier symmetry center, can be easily obtained based on the first relative positional relationship.

B. And acquiring the offset of the first identifier and the second identifier according to the second relative position relationship and the preset relative position relationship between the first identifier symmetry center and the second identifier symmetry center.

The preset relative position relationship between the first identification symmetry center and the second identification symmetry center specifically refers to the relationship between the position of the first identification symmetry center in the second coordinate system and the position of the second identification symmetry center in the second coordinate system. Since the second coordinate system includes the ideal position of the point, the preset relative position relationship between the first mark symmetry center and the second mark symmetry center also represents the relative position relationship between the first mark symmetry center and the ideal position of the second mark symmetry center.

By using the second relative position relationship and the preset relative position relationship, the position relationship of the two symmetric centers in the first coordinate system and the position relationship of the two symmetric centers in the second coordinate system can be obtained. The symmetric center of the first mark is positioned on the first mark and is associated with the position of each feature point on the first mark, and the symmetric center of the second mark is positioned on the second mark and is associated with the position of each feature point on the second mark, so that the symmetric center can be used as a virtual feature point. And obtaining the offset of the first identifier and the second identifier by using the second relative position relation and the preset relative position relation.

In order to convert the offset into an actual physically measurable numerical value, the final offset of the first identifier and the second identifier can be obtained according to the number of the pixel points corresponding to the offset and the size of each pixel point after the offset of the first identifier and the second identifier is obtained. That is, the number of pixels corresponding to the offset is multiplied by the size of each pixel, and the obtained product is used as the final offset. The final offset is the measured alignment error.

In the overlay mark applied in this embodiment, the appearance of the feature point in the image is not easily affected by the illumination nonuniformity and the operations such as rotation, translation, expansion, and the like, so that the alignment error measurement is performed by using the information of the feature point of the first identifier and the information of the feature point of the second identifier, and the stability of the measurement result is strong.

The foregoing is only a specific embodiment of the present invention, and each embodiment in this specification is described in a progressive manner, and the same and similar parts among the embodiments are referred to each other, and each embodiment focuses on the differences from other embodiments. It should be noted that, for those skilled in the art, without departing from the principle of the present invention, several improvements and modifications can be made, and these improvements and modifications should also be construed as the protection scope of the present invention.

Claims

1. An overlay mark, wherein the overlay mark is located in a substrate and comprises a first mark and a second mark; the first mark and the second mark are respectively positioned on different layers of the substrate, and/or the first mark and the second mark are formed in different processes;

2. The overlay mark according to claim 1, wherein the features of the first indicia are arranged periodically and the features of the second indicia are arranged periodically.

3. The overlay mark according to claim 1 wherein the projection of the feature structure in the projection plane is a feature pattern, the feature pattern is a polygon, and the projection of the feature point in the projection plane is a vertex of the polygon; or, the characteristic structure is a cone, and the characteristic point is a cone vertex.

4. The overlay mark of claim 1 wherein said first mark is centrosymmetric and said second mark is centrosymmetric; when the first mark and the second mark have no alignment error, the symmetry center of the first mark and the symmetry center of the second mark are coincident in the projection plane.

5. The overlay mark according to claim 4 wherein said first indicia is rotated 90 degrees or 180 degrees along its center of symmetry and then coincides with before rotation; the second mark is still coincident with the second mark before the second mark rotates along the symmetry center of the second mark by 90 degrees or 180 degrees.

6. The overlay mark of claim 1 wherein said first indicia and said second indicia are offset from each other in said projection plane.

7. The overlay mark of claim 1 wherein said first indicia comprises at least one first lattice structure and said second indicia comprises at least one second lattice structure; the first grid structure and the second grid structure each include the feature, and a first grid pattern formed by the first grid structure at the projection plane and a second grid pattern formed by the second grid structure at the projection plane each include a plurality of polygonal figures.

8. The overlay mark according to claim 7, wherein said overlay mark comprises a plurality of identification sections, each of said identification sections comprising one of said first grid structure and one of said second grid structure, and wherein a first grid pattern of said first grid structure and a second grid pattern of said second grid structure are adjacent in said projection plane.

9. The overlay mark of claim 7 wherein the vertices of the polygons in the first grid pattern meet and the vertices of the polygons in the second grid pattern meet.

10. The overlay mark according to claim 7, wherein when a center of a first grid pattern of the first grid structure and a center of a second grid pattern of the second grid structure are overlapped in the projection plane with respect to a certain first grid structure and a certain second grid structure, a polygon corresponding to the first grid pattern is overlapped with a polygon corresponding to the second grid pattern or a space between a polygon corresponding to the first grid pattern and a polygon corresponding to the second grid pattern is overlapped.

11. The overlay mark according to claim 3 or 7 wherein the polygon has a side length in the interval of [2 μm, 6 μm ].

12. The overlay mark of claim 7 wherein the number of features in the first lattice structure that are periodically arranged along the first direction is greater than or equal to 3.

13. A method of measuring alignment error, comprising:

obtaining an image of the overlay mark of any one of claims 1-12;

14. The method according to claim 13, wherein the obtaining of the first relative position relationship between the feature point of the first identifier and the feature point of the second identifier according to the image specifically includes: and extracting the actual position information of the characteristic points of the first identifier and the second identifier in a first coordinate system according to the image to obtain the first relative position relationship.

15. The method according to claim 13, wherein the obtaining an offset between the first identifier and the second identifier according to the first relative position relationship specifically includes:

16. The method of claim 15, wherein the deriving the relative shift matrix from the first position transformation matrix and the second position transformation matrix is implemented according to the following formula: u ═ TM1 × inv (TM 2);

17. The method according to claim 15, wherein obtaining the first position transformation matrix corresponding to the feature point of the first identifier according to the actual position information of the feature point of the first identifier and the preset position information of the feature point of the first identifier specifically includes:

the obtaining of the second position conversion matrix corresponding to the feature point of the second identifier according to the actual position information of the feature point of the second identifier and the preset position information of the feature point of the second identifier specifically includes:

18. The method according to claim 13, wherein the first mark is symmetrical in center, the second mark is symmetrical in center, and the symmetrical center of the first mark and the symmetrical center of the second mark have a preset relative position relationship;

19. The method of any of claims 13-18, wherein the offset comprises: a translational offset and/or a rotational offset.