Imprint wafer alignment method, system, and storage medium for nanoimprint

Abstract

The application discloses a nano-imprint imprint wafer alignment method, a system and a storage medium, and relates to the technical field of nano-imprint technology.The nano-imprint imprint wafer alignment system comprises an imprint template, an imprint wafer, a multi-camera imaging module and a wafer motion module, position information of template alignment marks is acquired, the imprint wafer is moved to a preset initial position, at least one wafer alignment mark on the imprint wafer is located in a field of view, the wafer alignment mark in the field of view is moved to the center of the field of view, position information of wafer alignment marks adjacent to the same-angle point of the imprint wafer is determined, and a first alignment is performed based on the difference between the positions of the two groups of wafer alignment marks and the template alignment marks thereof.According to the number of wafer alignment marks appearing in the field of view, the alignment strategy is executed, full-field scanning of two sets of imaging systems in pre-alignment is saved, the repeated alignment process is saved, and the alignment speed and efficiency are effectively improved.

Description

Technical Field

[0001] This application relates to the field of nanoimprint technology, specifically to a nanoimprint wafer alignment method, system, and storage medium. Background Technology

[0002] Nanoimprint lithography, as an advanced micro-nano manufacturing technology, has been widely used in many fields such as semiconductors, optical components, and biochips in recent years. The core of this technology lies in high-precision alignment. During nanoimprint lithography, precise alignment between the wafer and the template is crucial to ensuring processing quality and the performance of the final product. Poor alignment can easily lead to pattern distortion, poor repeatability, and even production defects.

[0003] For example, CN114326340A, "Nanoimprint Alignment Method and System," discloses a high-precision nanoimprint alignment method and system. The nanoimprint alignment system includes an imprint template, an imprint adhesive layer, a light source, and a light intensity measurement device. The imprint template includes a first reference grating; the imprint adhesive layer has a first alignment grating; the light source provides a light beam, which forms an interference pattern after passing through the first reference grating and the first alignment grating; the light intensity measurement device obtains the light intensity distribution map of the interference pattern based on the interference pattern. High-precision alignment can be achieved directly through the corresponding set of interference light intensities based on the phase difference calculation. However, this method requires that the target alignment mark be within the target's field of view during alignment, thus limiting the alignment efficiency.

[0004] For example, CN118444541A, "Wafer Alignment and Calibration Method and Wafer Exposure Method," discloses a wafer alignment and calibration method and a wafer exposure method. Two alignment marks are selected on a photomask, each including two calibration points. Left and right cameras display screenshots of the alignment marks on the terminal. The left camera screenshot shows the coordinates of the two calibration points (x1, y1) and (x2, y2), while the right camera screenshot shows the coordinates of the two calibration points (x3, y3) and (x4, y4). The left camera screenshot shows the x... s =x2-x1,y s =y2-y1, the pixel distance between the two calibration points is x in the screenshot of the right camera r =x4-x3,y r =y4-y3, the pixel distance between the two calibration points is This solution requires manual calibration to resolve situations where the calibration point is not in the field of view. Furthermore, the mask needs to be removed and the wafer installed during the alignment process between the template and the wafer, making the alignment process quite cumbersome.

[0005] For example, CN114667485A, "Alignment Control in Nanoimprint Lithography Using Feedback and Feedforward Control," provides a method and system for controlling the position of a movable stage supporting a substrate. First position information indicating the position of the substrate relative to a mark on an object is obtained from a sensor. Alignment prediction information is generated based on the obtained first position, and the generated alignment prediction information includes at least one parameter value. First trajectory information is generated based on the obtained first position information and the generated alignment prediction information, and the first trajectory information includes at least one parameter value. Second trajectory information is generated based on the generated alignment prediction information, the first trajectory information, and the second position information, and the second position information represents the position of the movable stage. An output control signal is generated based on the second trajectory information and used to control the movable stage to approach a target position based on the generated output signal. This scheme uses feedforward control to generate trajectory information based on position information and prediction information, and the calculation process is relatively complex.

[0006] Existing wafer alignment systems design at least one or two levels. In a two-level alignment system, a module needs to be designed first to align the wafer with the wafer motion module to ensure that the wafer marker can directly enter the two-level alignment system. In a system with only a one-level alignment module, the wafer marker may not be able to enter the measurement field of view of the two-level alignment system at once due to the limited motion accuracy and repeatability of the wafer motion module, which requires more alignment time. Summary of the Invention

[0007] The main objective of this application is to provide a nanoimprint wafer alignment method, system, and storage medium, in order to at least partially solve the aforementioned technical problems.

[0008] To solve the above-mentioned technical problems, as a first aspect of the present invention, the following is proposed:

[0009] A nanoimprint wafer alignment method includes the following steps:

[0010] S1: Obtain the position information of the template alignment mark;

[0011] S2: Move the imprinted wafer to a preset initial position so that at least one wafer alignment mark on the imprinted wafer is within the field of view, wherein the wafer alignment mark on the imprinted wafer corresponds to the template alignment mark;

[0012] S3: Move the wafer alignment mark in the field of view to the center of the field of view, determine the position information of the adjacent wafer alignment marks at the same corner point of the imprinted wafer, and perform the first alignment according to the offset of the position information of the two sets of wafer alignment marks at the same corner point and their template alignment marks.

[0013] S4: Determine if all wafer alignment marks are within the field of view. If yes, proceed to the final alignment step and end the alignment process.

[0014] As a second aspect of the present invention, an imprint wafer alignment system for nanoimprinting is also proposed, comprising an imprint template, an imprint wafer, a multi-camera imaging module, a wafer motion module, and a data processing module, wherein:

[0015] The embossing template has template alignment marks;

[0016] The imprinted wafer has wafer alignment marks;

[0017] The multi-camera imaging module is used to capture raw images of the template alignment marks and wafer alignment marks;

[0018] The data processing module performs image processing on the raw images captured by the multi-camera imaging module to obtain the position information of the template alignment mark and the wafer alignment mark, and uses the imprint wafer alignment method for nanoimprinting as described above to determine the translation vector and rotation angle.

[0019] The wafer motion module drives the imprint wafer to align it relative to the imprint template based on the translation vector and rotation angle output by the data processing module.

[0020] As a third aspect of the invention, a computer-readable storage medium is also provided, on which a computer program is stored, which, when executed by a processor, implements the steps of the method described above.

[0021] Based on the above technical solutions, it can be seen that the nanoimprint wafer alignment method, system, and storage medium of this application have at least one of the following beneficial effects compared with the prior art:

[0022] Based on the pre-installed position of the imprinted wafer, this application moves at least two wafer markers into the field of view. After 1 to 2 successive alignments, it ensures that all 8 sets of alignment markers are displayed in the camera's field of view. Finally, the center position and rotation angle offset of the 8 sets of alignment markers are obtained. The wafer markers are moved to the target point through the wafer motion module, thereby realizing the rapid alignment of the imprinted wafer.

[0023] This application only requires movement within a defined offset, solving the problem that traditional two imaging systems need to perform full-field scanning and repeated alignment during pre-alignment, effectively improving the speed and efficiency of alignment. Attached Figure Description

[0024] The accompanying drawings are provided to further illustrate the present application and form part of the specification. They are used together with the embodiments of the present application to explain the application and do not constitute a limitation thereof. In the drawings:

[0025] Figure 1 This is a schematic flowchart of an embodiment of a nanoimprint wafer alignment method according to this application;

[0026] Figure 2 This is a schematic diagram of the image processing flow of an imprint wafer alignment method for nanoimprinting according to this application;

[0027] Figure 3 This is a schematic diagram of the structural principle of a nanoimprint wafer alignment system according to this application;

[0028] Figure 4 This is a schematic diagram of the structure of a multi-camera imaging module of a nanoimprint wafer alignment system according to this application;

[0029] Figure 5 This is a schematic diagram of the structure of an imprint template for an imprint wafer alignment system of nanoimprinting according to this application;

[0030] Figure 6 This is a schematic diagram of the structure of an imprinted wafer in a nanoimprinted wafer alignment system according to this application;

[0031] Figure 7 This is a schematic diagram of the world coordinate system constructed in the nanoimprint wafer alignment method of this application;

[0032] Figure 8 This is a schematic flowchart of a second embodiment of a nanoimprint wafer alignment method according to this application;

[0033] Figure descriptions: 100, Imprint template; 200, Imprint wafer; 300, Multi-camera imaging module; 400, Wafer motion module; 101-108, Template alignment marks; 201-208, Wafer alignment marks; 301-308, Imaging lens. Detailed Implementation

[0034] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0035] It should be noted that when a component is described as "fixed to" another component, it can be directly on the other component or may have a component in between. When a component is considered "connected to" another component, it can be directly connected to the other component or may have a component in between. When a component is considered "set on" another component, it can be directly set on the other component or may have a component in between. The terms "vertical," "horizontal," "left," "right," and similar expressions used in this document are for illustrative purposes only.

[0036] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used herein in the specification of this application is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0037] In multi-stage wafer alignment, two imaging systems are typically required. The first pre-alignment process requires an independent imaging system to scan the wafer's position on the wafer motion module, and then move the wafer motion module to the accurate position. Building upon this, a simplified approach is considered: a final second-step alignment system is used. This system moves the wafer to an initial preset position. However, errors due to tolerances in the wafer imprinting process may result in exposed portions of the wafer. The question then arises: how can the alignment process between the imprinted wafer and the imprinting template be achieved?

[0038] After in-depth research and numerous experiments, the applicant considered how to find the precise position of the exposed portion of the wafer to achieve alignment. Specifically, such as... Figure 1 As shown, to address the problem that the alignment process of traditional dual-imaging systems is complex and requires full-field scanning and repeated alignment during pre-alignment, this application provides a nanoimprint wafer alignment method, comprising the following steps:

[0039] S1: Obtain the position information of template alignment marks 101-108. The position information of both template alignment marks 101-108 and wafer alignment marks 201-208 includes coordinates and rotation angles. Template alignment marks 101-108 are set on the imprinting template, and the pattern shape of template alignment marks 101-108 includes at least one line segment. This is to facilitate obtaining the rotation angles before and after alignment. Figure 7As shown, before extracting the position information of template alignment marks 101-108, a world coordinate system is constructed with the center point of the imprint template 100 as the origin, the horizontal direction as the x-axis, and the vertical direction as the y-axis. The correspondence between the world coordinate system and the multi-camera coordinate system built into the multi-camera imaging module 300 is determined. Then, the coordinate transformation relationship between the multi-camera coordinate system and the wafer motion module 400 is established. After the imprint template 100 is installed, the position of the multi-camera imaging module 300 is adjusted so that the template alignment marks 101-108 appear in the center of the field of view.

[0040] Example 1

[0041] Specifically, before alignment, the imprint template 100 is first installed in a fixed position using a tooling fixture. Then, a vacuum is drawn to fix the position of the imprint template 100. During subsequent alignment, the imprint template 100 does not move. The imprint template 100 has alignment marks 101-108, and the imprint wafer 200 has alignment marks 201-208. Figure 5 and Figure 6 As shown, the eight points of wafer alignment marks 201-208 are distributed in pairs at the four corner points. The patterns of template alignment marks 101-108 and wafer alignment marks 201-208 include at least one line segment. This means that the pattern can be set as a cross mark, square mark, triangular mark, "L" pattern, polygon mark or moiré mark. These patterns are used for any mark or feature to perform alignment, and there is no restriction on the specific shape. To distinguish between template alignment marks 101-108 and wafer alignment marks 201-208, numerical markers are placed around each mark. The position information of both template alignment marks 101-108 and wafer alignment marks 201-208 is acquired by a multi-camera imaging module 300. The multi-camera imaging module 300 includes a detector, an imaging lens, and an imaging adjustment assembly. Due to installation tolerances during the mounting of the imprint template 100, the camera adjustment assembly is adjusted to move the imaging lens, ensuring that template alignment marks 101-108 appear as close to the center of the field of view as possible. The imaging lens captures the original image including template alignment marks 101-108. The center point coordinates of the i-th template alignment mark in the world coordinate system are represented as follows: After image processing, the coordinates of the center point of the i-th template alignment mark in the camera coordinate system are obtained as follows: And the rotation angle is expressed as

[0042] S2: Move the imprinted wafer 200 to a preset initial position so that at least one wafer alignment mark 101-108 on the imprinted wafer 200 is within the field of view. The wafer alignment marks 201-208 on the imprinted wafer 200 correspond to the template alignment marks 101-108. The center point coordinates of the wafer alignment marks 201-208 in the multi-camera coordinate system are represented as (x′). j ,y′ j and the rotation angle θ of the center point j In this embodiment, taking the exposure of a wafer alignment mark 201 as an example, the offset between the wafer alignment mark 201 and the template alignment mark 101, i.e., the distance difference of the horizontal component, is determined and denoted as... The distance difference between the vertical component and the vertical component is denoted as The difference in rotation angle is denoted as The wafer motion module 400 drives the wafer alignment mark 201 to move from the current real-time position to the target position P. 目标 =P 实时 +(Δx, Δy) each time the wafer is moved.

[0043] The position information of wafer alignment mark 201 in the multi-camera coordinate system is obtained using the same process as obtaining the position information of template alignment marks 101-108. Then, the position information of wafer alignment marks 202-208 is obtained based on the position information of wafer alignment mark 201. The wafer alignment marks 201-208 are then aligned in... Convert to world coordinate system The formula is:

[0044]

[0045] S3: Move the wafer alignment mark 201 in the field of view to the center of the field of view, determine the position information of the adjacent wafer alignment marks 208 at the same corner point of the imprinted wafer, and perform the first alignment based on the difference between the positions of the two sets of wafer alignment marks at the same corner point and their template alignment marks. The difference refers to the relative distance between the position information of the two sets of wafer alignment marks 201, 208 at the same corner point and the template alignment marks 101, 108.

[0046] S4: If all wafer alignment marks are within the field of view, the alignment process ends. In this embodiment, when all eight wafer alignment marks 201 to 208 appear within the field of view, the final alignment step is performed to achieve alignment. Specifically, the alignment of the imprinted wafer relative to the imprinting template is achieved by determining the translation vector and rotation angle of each template alignment mark and the corresponding wafer alignment mark, and by using the translation vector and rotation angle.

[0047] Example 2

[0048] like Figure 8As shown, when not all eight wafer alignment marks 201 to 208 appear in the field of view, it is detected whether there are wafer alignment marks of at least two corner points in the field of view. If the wafer alignment marks of at least two corner points are present in the field of view, the position offset between the wafer alignment marks of the at least two corner points and their template alignment marks is determined, and a second alignment is performed. In this embodiment, the case where three wafer alignment marks 201, 202, and 203 are exposed is taken as an example for description. As can be seen from the foregoing, the center point coordinates of the i-th wafer mark in the world coordinate system are obtained from n (1<n≤8) wafer alignment marks 201, 202, and 203

[0049] The non-linear least squares method is used for motion alignment. Under this motion alignment condition, the coordinates of the wafer alignment marks 201 to 208 in the world coordinate system are The coordinates of the template alignment mark in the world coordinate system For translation and rotation alignment in a two-dimensional space, let the rotation matrix be R and the translation vector be t. Then for each wafer alignment mark, the error vector is expressed as The sum of squared errors is expressed as A non-linear optimization algorithm including a gradient descent method or a Newton method is adopted to minimize the value of the sum of squared errors S and obtain the minimum value, and the rotation matrix R and the translation vector t are solved according to the minimum value. Finally, the wafer motion module 400 drives the imprint wafer 200 to move to a target point, and the coordinates of the target point are expressed as P 目标 =RP 实时 +t.

[0050] As Figure 2 shown, in this embodiment, further, the image processing process includes the following steps:

[0051] After the captured original image including the template alignment mark and the wafer alignment mark is subjected to Gaussian denoising, the position information of the template alignment mark and the position information of the wafer alignment mark are determined. The steps of Gaussian denoising include: converting the original image into a grayscale image; the original image is an original color image including the template alignment mark and the wafer alignment mark, and the original color image is regarded as a three-dimensional array, each element of the array represents a pixel point, which contains the values of the R, G, and B channels; traversing each pixel point in the image, for each pixel point, obtaining its R, G, and B values, then determining the grayscale value according to different weights assigned to the three R, G, and B channels, finally assigning the obtained grayscale value to the pixel point at the corresponding position, and finally obtaining a two-dimensional array, that is, the grayscale image;

[0052] To obtain a denoised image, a Gaussian filter is applied to the grayscale image. First, the size and standard deviation of the Gaussian kernel are determined. Then, the value of each element in the Gaussian kernel matrix is ​​determined based on the Gaussian function. After determining all elements, the matrix is ​​normalized so that the sum of all elements is 1, resulting in a normalized Gaussian kernel matrix. Next, each pixel in the grayscale image is traversed, and a neighborhood of the same size as the Gaussian kernel is selected centered on that pixel. The pixel values ​​within this neighborhood are multiplied by the corresponding element of the Gaussian kernel, and all products are summed. The result is then used as the new value for that pixel. After convolution, all pixels are updated to the new value, thus obtaining the denoised image.

[0053] The process of extracting the target contours of template alignment marks and wafer alignment marks is as follows: A binary image is generated based on a preset threshold and the grayscale distribution in the denoised image; the target contour is obtained based on the edges of the binary image. Specifically, the preset threshold can be automatically determined according to the Otsu method, or it can be adjusted according to application requirements; the grayscale value of each pixel in the denoised image is compared with the preset threshold. Pixels with a grayscale value greater than the preset threshold are assigned a value of 255 (white, representing the target), and pixels with a grayscale value less than the preset threshold are assigned a value of 0 (black, representing the background), thus obtaining the binary image; starting from the edge of the binary image, the image is scanned row by row and column by column. When a pixel with a value of 255 is encountered, it is used as the starting point of the contour. A boundary tracking algorithm is used to sequentially visit adjacent pixels along the boundary of the target region until the starting point is returned, forming a closed contour. This process is repeated until the entire binary image is scanned, and all target contours are found.

[0054] Based on the target contour, the coordinates of the center point of the minimum bounding rectangle and the rotation angle can be obtained using the rotating caliper algorithm. The rotating caliper algorithm is relatively mature and will not be elaborated further here.

[0055] The center point of the smallest bounding rectangle of the target contour is the center point of the corresponding template alignment mark or wafer alignment mark.

[0056] like Figure 3 As shown, an imprinted wafer alignment system for nanoimprinting employs the imprinted wafer alignment method for nanoimprinting described above, including an imprinting template, an imprinted wafer, a multi-camera imaging module, a wafer motion module, and a data processing module, wherein:

[0057] The impression template 100 is provided with template alignment marks 101 to 108;

[0058] The imprinted wafer 200 is provided with wafer alignment marks 201-208;

[0059] The multi-camera imaging module 300 is used to capture raw images of template alignment marks 101-108 and wafer alignment marks 201-208;

[0060] The data processing module performs image processing on the raw images captured by the multi-camera imaging module 300 to obtain the position information of template alignment marks 101-108 and wafer alignment marks 201-208, and uses the wafer alignment method for nanoimprinting as described above to determine the translation vector and rotation angle.

[0061] The wafer motion module 400 drives the imprint wafer 200 to align it relative to the imprint template 100 based on the translation vector and rotation angle output by the data processing module. The multi-camera imaging module 300 includes a detector, imaging lenses, and imaging adjustment components, with at least one imaging lens positioned directly above each of the four corner points of the imprint template. Figure 4 The diagram shows a case where two imaging lenses are set for a corner point, with a total of eight imaging lenses 301 to 308.

[0062] A computer-readable storage medium having a computer program stored thereon, which, when executed by a processor, implements the steps of the method described above.

[0063] The key feature of this application is that, in traditional single-stage multi-camera alignment systems, the motion accuracy and repeatability of the wafer motion module 400 cannot guarantee that all wafer alignment marks will enter the field of view of the alignment camera at once. Specifically, these systems first obtain the coordinates of all alignment marks one by one, and then calculate the alignment position after a full-field scan, requiring at least two to three minutes to achieve alignment. This application proposes an imprint wafer alignment method for nanoimprint lithography. Based on the pre-installed position of the imprint wafer 200, at least two wafer alignment marks are moved into the field of view, and after 1 to 2 successive alignments, alignment is achieved. All eight alignment marks are displayed within the camera's field of view. The final processing yields the center position and rotation angle offset of the eight alignment marks. The wafer motion module 400 moves the wafer alignment marks to the target point, thereby achieving rapid alignment of the imprinted wafer 200. This application only requires movement within a specific area, with a maximum movement on the order of 0.5 millimeters. The alignment method disclosed in this application can achieve the alignment process of the imprinted wafer 200 relative to the imprinting template 100 in just a few seconds, solving the problem that traditional two imaging systems require full-field scanning and repeated alignment during pre-alignment, effectively improving the speed and efficiency of alignment.

[0064] The embodiments of this application have been described in detail above, but the content described is only a preferred embodiment of this application and should not be considered as limiting the scope of this application. All equivalent changes and improvements made within the scope of this application should still fall within the scope of this application.

Claims

1. A method for aligning imprinted wafers for nanoimprinting, characterized in that, Includes the following steps: S1: Obtain the position information of the template alignment mark; S2: Move the imprinted wafer to a preset initial position so that at least one wafer alignment mark on the imprinted wafer is within the field of view, wherein the wafer alignment mark on the imprinted wafer corresponds to the template alignment mark; S3: Move the wafer alignment mark in the field of view to the center of the field of view, determine the position information of the adjacent wafer alignment marks at the same corner point of the imprinted wafer, and perform the first alignment based on the difference between the positions of the two sets of wafer alignment marks at the same corner point and their template alignment marks. S4: If all wafer alignment marks are within the field of view, the alignment process ends.

2. The wafer alignment method according to claim 1, characterized in that, Step S4 also includes: If not all wafer alignment marks are within the field of view, then it is checked whether there are wafer alignment marks at least two corner points within the field of view. If so, the offset of the wafer alignment marks at at least two corner points and their template alignment marks is determined and a second alignment is performed.

3. The wafer alignment method according to claim 1, characterized in that, The template alignment mark is set on the imprinting template. A world coordinate system is constructed with the center point of the imprinting template as the origin. The center point coordinates of the template alignment mark and the wafer alignment mark in the world coordinate system are converted into the center point coordinates in the camera coordinate system.

4. The wafer alignment method according to claim 1, characterized in that, Each corner of the imprinted wafer has at least two of the wafer alignment marks.

5. The imprint wafer alignment method according to claim 1, characterized in that, The first and second alignments include: determining the translation vector and rotation angle between the template alignment mark and the corresponding wafer alignment mark, and aligning the imprinted wafer relative to the imprinting template according to the translation vector and rotation angle.

6. The imprint wafer alignment method according to claim 1, characterized in that, The position information of the template alignment mark and the wafer alignment mark are determined based on the original image. The position information of the template alignment mark and the wafer alignment mark includes the center point coordinates and rotation angle. The original image includes the template alignment mark and the wafer alignment mark.

7. The wafer alignment method according to claim 6, characterized in that, After the original image undergoes Gaussian denoising, the position information of the template alignment mark and the wafer alignment mark is determined. The Gaussian denoising includes the following steps: Convert the original image to a grayscale image; The grayscale image is denoised to obtain a denoised image; Extract the target contours of template alignment marks and wafer alignment marks from the denoised image; The center point coordinates and rotation angle of the minimum bounding rectangle are obtained based on the target contour.

8. The wafer alignment method according to claim 7, characterized in that, The process of extracting the target contours of the template alignment marks and wafer alignment marks is as follows: A binary image is generated based on a preset threshold and the grayscale distribution in the denoised image; The target contour is obtained based on the edges of the binary image.

9. An imprint wafer alignment system for nanoimprinting, characterized in that, It includes an imprinting template, an imprinting wafer, a multi-camera imaging module, a wafer motion module, and a data processing module, among which: The multi-camera imaging module is used to acquire raw images containing the template alignment marks and wafer alignment marks; The data processing module performs image processing on the original image to obtain the position information of the template alignment mark and the wafer alignment mark, and uses the imprint wafer alignment method for nanoimprinting as described in any one of claims 1 to 8 to determine the translation vector and rotation angle; The wafer motion module drives the imprint wafer to align it relative to the imprint template based on the translation vector and rotation angle output by the data processing module.

10. A computer-readable storage medium having a computer program stored thereon, characterized in that, When the computer program is executed by a processor, it implements the steps of the method according to any one of claims 1 to 8.

Images