A method for locating defects in EUV photomasks

Abstract

This application provides a method for locating defects in EUV photomasks, belonging to the field of EUV lithography technology. The method includes the following steps: preparing an alignment pattern required by the lithography machine on an EUV photomask substrate; detecting the defect position and obtaining coordinates (x, y); aligning the lithography machine according to the alignment pattern; writing a regular pattern with the defect position as a fixed point and developing it; obtaining the lateral distance Δx and longitudinal distance Δy of the defect from the fixed point in the regular pattern; and calculating the precise coordinates (x+Δx, y+Δy) of the defect in the lithography machine coordinate system. This method saves on equipment usage, shortens the EUV photomask manufacturing time, and improves the accuracy of defect location.

Description

Technical Field

[0001] This application relates to the field of EUV lithography technology, and in particular to a method for locating defects in EUV photomasks. Background Art

[0002] The fabrication of defect-free EUV (extremely ultraviolet) masks is one of the key issues restricting the mass production of EUV lithography. Defect detection of EUV masks is a key core technology for realizing EUV lithography. Defects on the EUV photomask substrate can cause deviations in the energy of the EUV lithography machine, affecting the performance and electrical properties of the chip, and in severe cases, causing the chip to be scrapped. However, it is very difficult to produce a completely defect-free EUV photomask substrate. Therefore, it is necessary to accurately locate the coordinates of the defects first. The current defect location process is very complex and time-consuming. Summary of the Invention

[0003] In view of this, embodiments of this application provide a method for locating defects in EUV photomasks, which at least partially solves the problem of complex and time-consuming defect location processes in the prior art.

[0004] This application provides a method for locating defects in an EUV photomask, the method comprising the following steps:

[0005] Prepare alignment patterns required for lithography on EUV photomask substrates;

[0006] The defect location is detected, and the coordinates (x, y) are obtained;

[0007] The lithography machine aligns itself according to the alignment pattern;

[0008] The lithography machine writes a regular pattern using the defect location as a fixed point and then develops it.

[0009] Obtain the lateral distance Δx and vertical distance Δy of the defect from the fixed point in the regular graphic;

[0010] The precise coordinates (x+Δx, y+Δy) of the defect in the lithography machine coordinate system were calculated.

[0011] According to a specific implementation of this application, obtaining the lateral distance Δx and vertical distance Δy of the defect from the fixed point in the regular graphic includes:

[0012] An image is obtained by scanning the developed regular pattern using an atomic force microscope;

[0013] Image analysis is used to obtain the horizontal distance Δx and the vertical distance Δy.

[0014] According to one specific implementation of an embodiment of this application, the fixed point is the center point of the regular graphic.

[0015] According to one specific implementation of the embodiments of this application, the regular graphic is a square, circle, triangle or hexagon.

[0016] According to a specific implementation of an embodiment of this application, the regular graphic is a square, and the side length of the square ranges from 3 to 10 μm.

[0017] According to a specific implementation of an embodiment of this application, the fabrication of the alignment pattern required for the lithography machine on the EUV photomask substrate specifically includes:

[0018] Photoresist is applied to the EUV photomask substrate;

[0019] The morphology of the photolithographic alignment pattern is determined using a photolithography machine;

[0020] Bake the EUV photomask substrate after photolithography;

[0021] The alignment pattern formed by photolithography is developed;

[0022] Etching is performed on the alignment pattern formed by photolithography;

[0023] Remove the remaining photoresist to obtain an EUV photomask substrate with alignment patterns.

[0024] According to a specific implementation of this application, after the step of calculating the precise coordinates (x+Δx, y+Δy) of the defect, the method further includes:

[0025] Match a suitable circuit design based on the precise coordinates of the defect;

[0026] The EUV photomask substrate is cleaned;

[0027] After cleaning, apply photoresist for later use.

[0028] According to one specific implementation of an embodiment of this application, the location of the detected defect is detected using a defect detection device.

[0029] Beneficial effects

[0030] The EUV photomask defect location method in this application eliminates the need for the fabrication of the first alignment pattern of the defect detection equipment. It allows the defect detection and electron beam lithography machine to share the same set of alignment patterns, saving equipment usage, shortening the EUV photomask manufacturing time, and improving the accuracy of defect location. Attached Figure Description

[0031] To more clearly illustrate the technical solutions of the embodiments of this application, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0032] Figure 1 This is a flowchart of an EUV photomask defect localization method according to an embodiment of the present invention;

[0033] Figures 2 to 5 This is a schematic diagram of the structure corresponding to each step of the EUV photomask defect localization method according to an embodiment of the present invention;

[0034] Figure 6 This is a schematic diagram of coordinate system deviation in an EUV photomask defect localization method according to an embodiment of the present invention.

[0035] In the figure: 1. EUV photomask substrate; 2. Alignment pattern; 3. Defect; 4. Regular pattern. Detailed Implementation

[0036] The embodiments of this application will now be described in detail with reference to the accompanying drawings.

[0037] The following specific examples illustrate the implementation of this application. Those skilled in the art can easily understand other advantages and effects of this application from the content disclosed in this specification. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of them. This application can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of this application. It should be noted that, in the absence of conflict, the following embodiments and features in the embodiments can be combined with each other. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0038] It should be noted that various aspects of embodiments within the scope of the appended claims are described below. It will be apparent that the aspects described herein can be embodied in a wide variety of forms, and any particular structure and / or function described herein is merely illustrative. Based on this application, those skilled in the art will understand that one aspect described herein can be implemented independently of any other aspect, and two or more of these aspects can be combined in various ways. For example, any number of aspects set forth herein can be used to implement the device and / or practice the method. Additionally, this device and / or method can be implemented using structures and / or functionalities other than one or more of the aspects set forth herein.

[0039] It should also be noted that the illustrations provided in the following embodiments are only schematic representations of the basic concept of this application. The drawings only show the components related to this application and are not drawn according to the actual number, shape and size of the components in the actual implementation. In the actual implementation, the form, quantity and proportion of each component can be arbitrarily changed, and the layout of the components may also be more complex.

[0040] Furthermore, specific details are provided in the following description to facilitate a thorough understanding of the examples. However, those skilled in the art will understand that these aspects can be practiced without these specific details.

[0041] The currently used defect location methods mainly include the following steps:

[0042] Step 1: First, use laser to burn out the first alignment pattern for the defect detection equipment. Then, perform defect detection based on the first alignment pattern to obtain the first coordinates (X, Y) of the defect.

[0043] Step 2: Prepare the second alignment pattern for the lithography machine, measure the position of the first alignment pattern / second alignment pattern, and convert the defect coordinates into coordinates (X', Y') aligned with the second alignment pattern.

[0044] X' = ​​a0 + a1X + a2Y,

[0045] Y' = b0 + b1X + b2Y,

[0046] Where a0, a1, a2, b0, b1, and b2 are all constants.

[0047] Step 3: Apply photoresist and use a photolithography machine to write a square pattern according to the defect location, then develop.

[0048] Step 4: Obtain the position of the defect in the square pattern and calculate the precise coordinates of the defect.

[0049] Research has shown that the above methods have limitations due to the imprecise coordinates of the defect detection equipment and discrepancies with the coordinate system of the photomask lithography machine. Figure 6 As shown, for example, there are issues such as offset of the coordinate system origin, rotation of the coordinate system, and inconsistent unit length between the two coordinate systems, which makes the location of the defect not very accurate, so it cannot be directly used to match the layout.

[0050] Based on the above-mentioned problems, this application improves the method for locating defects in EUV photomasks, as detailed below with reference to the appendix. Figure 1-5 Provide a detailed description.

[0051] In this embodiment, the specific process of the EUV photomask defect localization method is as follows: Figure 1 Specifically, it includes the following steps:

[0052] S101. Prepare the alignment pattern 2 required for the lithography machine on the EUV photomask substrate 1, referring to... Figure 2 As shown, the square outer frame is the EUV photomask substrate 1, and the four "+" marks on the corners are the alignment pattern 2. Since the alignment of the electron beam lithography machine is done by scanning with an electron beam, the pattern needs to have different surface materials and heights to produce a sufficiently clear signal.

[0053] Therefore, in this embodiment, the alignment pattern 2 is prepared by etching, specifically including the following steps:

[0054] S1011. Coat the EUV photomask substrate 1 with photoresist;

[0055] S1012. The morphology of the photolithographic alignment pattern 2 is determined using a photolithography machine;

[0056] S1013. Bake the EUV photomask substrate 1 after photolithography;

[0057] S1014. Develop the alignment pattern formed by photolithography;

[0058] S1015. Etch the alignment pattern formed by photolithography;

[0059] S1016. Remove the remaining photoresist to obtain an EUV photomask substrate 1 with alignment pattern 2.

[0060] The location of defect 3 will be detected next, referring to... Figure 3 The circle in the figure represents defect 3. There may be several defects 3 in different locations on different substrates.

[0061] S102. The defect 3 position is detected using a defect detection device to obtain coordinates (x, y). It should be explained that at this point, the defect detection device is aligned with the alignment pattern 2 prepared in step S101 and then used to detect defect 3. However, due to insufficient coordinate accuracy of the defect detection device, there may be an error of 1-2 μm. Since the error between the defect coordinates and the layout should be less than 300 nm, the defect coordinates measured by the defect detection device cannot be used for comparison with the layout. Therefore, more accurate coordinates are needed, and the following steps continue.

[0062] S103, The lithography machine aligns itself according to alignment pattern 2;

[0063] S104. Coating photoresist: The photolithography machine writes the regular pattern 4 with the coordinates (x, y) of the defect 3 position as a fixed point and develops it. The regular pattern 4 can be a square, circle, triangle or hexagon, etc.

[0064] Preferably, the regular shape 4 is square, and the fixed point is the center point of the square. Considering that lithography machines are more complex and time-consuming in processing circles / arcs / triangles / polygons, it is preferable to set the regular shape 4 as square. (Refer to...) Figure 4 Defect 3 will fall within the square. Since the coordinates (x, y) of defect 3 are measured by the defect detection equipment, which has a large detection error, when the lithography machine writes into the square using these coordinates as the center point, it's essentially operating with a flawed defect coordinate (x, y). The actual position of defect 3 is some distance from these coordinates, thus causing the defect to fall within the square. Figure 4 The case where defect 3 is not located at the center point of the square.

[0065] S105. Obtain the lateral distance Δx and longitudinal distance Δy of defect 3 from the fixed point in the regular graphic 4, referring to... Figure 5 In this embodiment, the defect 3 is scanned using an atomic force microscope, specifically including:

[0066] S1051. Using an atomic force microscope to scan the developed regular pattern 4, an image with defect 3 is obtained. It should be explained that if there are coated particles in the multilayer structure of the EUV photomask substrate 1 during the manufacturing process, there will be a protrusion on the surface. If there are any defects, there will be a depression on the surface. Therefore, scanning the surface morphology with an atomic force microscope can reveal the location of defect 3.

[0067] S1052. Image analysis to obtain the lateral distance Δx and longitudinal distance Δy. This step is necessary because the coordinate accuracy of the atomic force microscope is insufficient to obtain more precise coordinates; therefore, the coordinates of the lithography machine are ultimately used as the standard.

[0068] S106. The precise coordinates (x', y') of defect 3 in the lithography machine coordinate system are calculated, where x' = x + Δx and y' = y + Δy. Since the alignment error of the lithography machine is less than 40nm, a square is drawn at the position of defect 3 by the lithography machine, and then scanned by an atomic force microscope. The more accurate defect coordinates can be obtained by measuring the scanned image.

[0069] In a preferred embodiment, the regular pattern 4 is a square, and the side length of the square ranges from 3 to 10 μm.

[0070] Preferably, the side length of the square is 6µm.

[0071] It should be explained that, for different detection scenarios, the size of the regular graphic 4 needs to be determined based on the degree of deviation of the defect position detected by the defect detection equipment, so as to ensure that the defect 3 can fall into the regular graphic 4.

[0072] In one embodiment, the method further includes the following step after step S106:

[0073] S107. Match a suitable circuit design diagram (LAY) based on the precise coordinates (x', y') of defect 3. Specifically, in the circuit design diagram, areas without graphics or where some graphics are unaffected by the defect can overlap with the position of defect 3 when matching the LAI. Since the EUV photomask substrate 1 is a 6-inch square, you can try comparing four angles: 0°, 90°, 180°, and 270°. For each angle, you can also make slight up, down, left, and right translations to see if you can avoid the defect position and try to avoid defect 3.

[0074] S108. After matching, the EUV photomask substrate 1 is cleaned.

[0075] S109. After cleaning, apply photoresist to EUV photomask substrate 1 for later use.

[0076] The embodiments provided by this invention improve the defect localization process of EUV photomask substrates by merging the first alignment pattern of the defect detection equipment and the second alignment pattern of the lithography machine. Therefore, coordinate transformation is not required using position measurement equipment, saving the measurement time of registration equipment (such as KLA IPOR or ZEISS PROVE). The reason for coordinate transformation is that the first and second alignment patterns are manufactured by different equipment, resulting in differences in offset, scale, rotation, etc. Therefore, this application eliminates the need for fabricating the first alignment pattern of the defect detection equipment, allowing defect detection and electron beam lithography to share the same set of alignment patterns, saving equipment usage and shortening the EUV photomask manufacturing time.

[0077] The above description is merely a specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A method for locating defects in an EUV photomask, characterized in that, The method includes the following steps: Prepare alignment patterns required for lithography on EUV photomask substrates; The defect location is detected using a defect detection device to obtain the coordinates (x, y) of the defect location. The defect detection device is aligned with the alignment pattern and the defect is detected. There is an error between the coordinates (x, y) of the defect location and the actual coordinates of the defect location. The lithography machine aligns itself according to the alignment pattern; The lithography machine writes a regular pattern and develops it using the coordinates of the defect location as a fixed point, where the fixed point is the center point of the regular pattern; An image is obtained by scanning the developed regular pattern using an atomic force microscope. After image analysis, the lateral distance Δx and longitudinal distance Δy of the defect from the fixed point in the regular pattern are obtained. The precise coordinates (x+Δx, y+Δy) of the defect in the lithography machine coordinate system were calculated.

2. The EUV photomask defect localization method according to claim 1, characterized in that, The regular shape is a square, circle, triangle or hexagon.

3. The EUV photomask defect localization method according to claim 2, characterized in that, The regular shape is a square, and the side length of the square ranges from 3 to 10 μm.

4. The EUV photomask defect localization method according to claim 1, characterized in that, The specific steps involved in fabricating the alignment pattern required for the lithography machine on the EUV photomask substrate include: Photoresist is applied to the EUV photomask substrate; The morphology of the photolithographic alignment pattern is determined using a photolithography machine; Bake the EUV photomask substrate after photolithography; The alignment pattern formed by photolithography is developed; Etching is performed on the alignment pattern formed by photolithography; Remove the remaining photoresist to obtain an EUV photomask substrate with alignment patterns.

5. The EUV photomask defect localization method according to claim 1, characterized in that, The step following the calculation of the precise coordinates (x+Δx, y+Δy) of the defect also includes: Match a suitable circuit design based on the precise coordinates of the defect; The EUV photomask substrate is cleaned; After cleaning, apply photoresist for later use.

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