CN114488685A - A method for locating defects in EUV photomasks - Google Patents

Abstract

The application provides a method for positioning defects of an EUV photomask, which belongs to the technical field of EUV lithography and comprises the following steps: preparing an alignment graph required by a photoetching machine on an EUV photomask substrate; detecting the position of the defect to obtain coordinates (x, y); aligning by the photoetching machine according to the alignment pattern; writing a regular pattern by the photoetching machine by taking the defect position as a fixed point and developing; obtaining the transverse distance delta x and the longitudinal distance delta y of the defect from the fixed point in the regular graph; and calculating to obtain the accurate coordinates (x + delta x, y + delta y) of the defect in the coordinate system of the photoetching machine. By the processing scheme, the equipment is saved, the manufacturing time of the EUV photomask is shortened, and the accuracy of the defect position is improved.

Description

A method for locating defects in EUV photomasks

technical field

The present application relates to the technical field of EUV lithography, and in particular, to a method for locating defects in an EUV photomask.

Background technique

Defect-free EUV (extremely ultraviolet) mask preparation is one of the key issues restricting EUV lithography towards mass production, and EUV mask defect detection is the key core technology for EUV lithography. The deviation of the energy of the lithography machine will affect the performance and electrical properties of the chip, and will seriously cause 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. , the current defect location process is very complex and time-consuming.

SUMMARY OF THE INVENTION

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

An embodiment of the present application provides a method for locating defects in an EUV photomask, and the method includes the following steps:

Prepare the alignment pattern required by the lithography machine on the EUV photomask substrate;

Detect the defect position and get the coordinates (x, y);

The lithography machine performs alignment according to the alignment pattern;

The lithography machine writes a regular pattern with the defect position as a fixed point and develops it;

Obtain the lateral distance Δx and the longitudinal distance Δy of the defect from the fixed point in the regular pattern;

Calculate the exact coordinates (x+Δx, y+Δy) of the defect in the lithography machine coordinate system.

According to a specific implementation manner of the embodiment of the present application, the lateral distance Δx and the longitudinal distance Δy of the obtained defect from the fixed point in the regular graph include:

Use atomic force microscope to scan the developed regular patterns to obtain images;

Image analysis to obtain the lateral distance Δx and the longitudinal distance Δy.

According to a specific implementation manner of the embodiment of the present application, the fixed point is a center point of the regular graph.

According to a specific implementation manner of the embodiment of the present application, the regular figure is a square, a circle, a triangle or a hexagon.

According to a specific implementation manner of the embodiment of the present application, the regular figure is a square, and the side length of the square ranges from 3 to 10 um.

According to a specific implementation of the embodiment of the present application, the alignment pattern required for preparing the lithography machine on the EUV photomask substrate specifically includes:

Coating photoresist on the EUV photomask substrate;

Use a lithography machine to lithography to align the topography of the pattern;

Baking the EUV photomask substrate after photolithography;

Develop the topography of the alignment pattern formed by photolithography;

Etch the topography of the alignment pattern formed by photolithography;

The remaining photoresist is removed to obtain an EUV photomask substrate with an alignment pattern.

According to a specific implementation manner of the embodiment of the present application, after the step of calculating and obtaining the precise coordinates (x+Δx, y+Δy) of the defect, the method further includes:

Matching a suitable circuit design according to the precise coordinates of the defect;

cleaning the EUV photomask substrate;

After cleaning, photoresist is applied for standby.

According to a specific implementation manner of the embodiment of the present application, the defect location is detected by using a defect detection device.

beneficial effect

The EUV photomask defect positioning method in the embodiment of the present application omits the production of the first alignment pattern of the defect detection equipment, and the defect detection and the electron beam lithography machine share the same set of alignment patterns, which saves the use of the equipment And shorten the time of EUV photomask fabrication and improve the accuracy of defect location.

Description of drawings

In order to illustrate the technical solutions of the embodiments of the present application more clearly, the following briefly introduces the drawings that are used in the embodiments. Obviously, the drawings in the following description are only some embodiments of the present application. For those of ordinary skill in the art, other drawings can also be obtained from these drawings without any creative effort.

1 is a flowchart of a method for locating defects in an EUV photomask according to an embodiment of the present invention;

2 to 5 are schematic structural diagrams corresponding to each step of a method for locating defects in an EUV photomask according to an embodiment of the present invention;

6 is a schematic diagram of a coordinate system deviation of a method for locating defects in an EUV photomask according to an embodiment of the present invention.

In the figure: 1. EUV photomask substrate; 2. Alignment pattern; 3. Defects; 4. Regular pattern.

Detailed ways

The embodiments of the present application will be described in detail below with reference to the accompanying drawings.

The embodiments of the present application are described below through specific specific examples, and those skilled in the art can easily understand other advantages and effects of the present application from the contents disclosed in this specification. Obviously, the described embodiments are only a part of the embodiments of the present application, but not all of the embodiments. The present application can also be implemented or applied through other different specific embodiments, and various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present application. It should be noted that the following embodiments and features in the embodiments may be combined with each other under the condition of no conflict. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative work fall within the protection scope of the present application.

To illustrate, various aspects of embodiments within the scope of the appended claims are described below. It should be apparent that the aspects described herein may be embodied in a wide variety of forms and that any specific structure and/or function described herein is illustrative only. Based on this application, one skilled in the art should appreciate that an aspect described herein may be implemented independently of any other aspects and that two or more of these aspects may be combined in various ways. For example, an apparatus may be implemented and/or a method may be practiced using any number of the aspects set forth herein. Additionally, such an apparatus may be implemented and/or such a method may be practiced using other structure and/or functionality in addition to one or more of the aspects set forth herein.

It should also be noted that the drawings provided in the following embodiments only illustrate the basic concept of the present application in a schematic way, and the drawings only show the components related to the present application rather than the number, shape and the number of components in actual implementation. For dimension drawing, the type, quantity and proportion of each component can be changed at will in actual implementation, and the component layout may also be more complicated.

Additionally, in the following description, specific details are provided to facilitate a thorough understanding of the examples. However, one skilled in the art will understand that aspects may be practiced without these specific details.

The current defect location method mainly includes the following steps:

Step 1: First, laser burn out the first alignment pattern used by the defect detection equipment, and perform defect detection based on the first alignment pattern to obtain the first coordinates (X, Y) of the defect.

Step 2: Prepare the second alignment pattern used by 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. '),

X'=a ₀ +a ₁ X+a ₂ Y,

Y'=b ₀ +b ₁ X+b ₂ Y,

Among them, a ₀ , a ₁ , a ₂ , b ₀ , b ₁ , and b ₂ are all constants.

Step 3: Coat photoresist and use a photolithography machine to write a square pattern according to the defect position and then develop.

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

For the above method, after research, it is found that due to the inaccuracy of the coordinates of the defect detection equipment and the deviation from the coordinate system of the photomask lithography machine, as shown in Figure 6, for example, there is a deviation of the origin of the coordinate system between the two coordinate systems ( offset), coordinate system rotation (rotation) and unit length inconsistency (scale) problems, resulting in the location of the defect is not very accurate, so it cannot be directly used to match the layout.

Based on the above problems, the present application improves the EUV photomask defect location method, which will be described in detail below with reference to FIGS. 1-5 .

In the present embodiment, the specific flow of the EUV photomask defect positioning method refers to FIG. 1, and specifically includes the following steps:

S101. Prepare an alignment pattern 2 required by the lithography machine on the EUV photomask substrate 1. Referring to FIG. 2, the square outer frame is the EUV photomask substrate 1, and the four “+” marks on the corners are for alignment Quasi-Graphics 2. Since the alignment of the electron beam lithography machine uses electron beam scanning, the pattern needs to have a surface material with different heights in order to have a sufficiently obvious signal.

Therefore, in this embodiment, the alignment pattern 2 is prepared by etching, which specifically includes the following steps:

S1011, coating photoresist on the EUV photomask substrate 1;

S1012, using a photolithography machine to perform photolithography to align the morphology of the pattern 2;

S1013, baking the EUV photomask substrate 1 after photolithography;

S1014, developing the alignment pattern morphology formed by photolithography;

S1015, etching the alignment pattern morphology formed by photolithography;

S1016 , removing the remaining photoresist to obtain an EUV photomask substrate 1 with an alignment pattern 2 .

The position detection of the defect 3 is performed below, referring to FIG. 3 , the circle in the figure represents the defect 3, and there may be several defects 3 in different positions on different substrates.

S102 , use the defect detection equipment to detect the position of defect 3 to obtain coordinates (x, y). It should be explained that at this time, the defect detection equipment aligns with the alignment pattern 2 prepared in step S101 and detects defect 3 . However, due to the insufficient coordinate accuracy of the defect detection equipment, there may be an error of 1-2um, and the error between the defect coordinates and the layout is smaller than 300nm, so the defect coordinates measured by the defect detection equipment cannot be used for the layout. alignment, so more precise coordinates are required, and continue with the following steps.

S103, the lithography machine performs alignment according to the alignment pattern 2;

S104, coating photoresist, the photolithography machine writes and develops a regular pattern 4 with the coordinates (x, y) of the position of the defect 3 as a fixed point, and the regular pattern 4 can be a square, a circle, a triangle or a hexagon.

Preferably, the regular pattern 4 is a square, and the fixed point is the center point of the square. Considering that it is more complicated and time-consuming for the lithography machine to process circle/arc/triangle/polygon, it is better to set the regular pattern 4 as a square. . Referring to Figure 4, the defect 3 will fall into the square. Since the coordinates (x, y) of the position of the defect 3 are measured by the defect detection equipment, the detection error of the defect detection equipment is relatively large, and when the lithography machine uses this coordinate When writing a square as the center point, that is, the lithography machine is operating with a defect coordinate (x, y) with deviation, and the actual position of defect 3 is a certain distance from the coordinate (x, y), so It occurs that the defect 3 in Figure 4 is not at the center point of the square.

S105 , obtaining the lateral distance Δx and the longitudinal distance Δy of the defect 3 from the fixed point in the regular pattern 4 , referring to FIG. 5 . In this embodiment, the defect 3 is scanned by an atomic force microscope, which specifically includes:

S1051 , using an atomic force microscope to scan the developed regular pattern 4 to obtain an image with defects 3 . It needs to be explained that the multilayer structure of the EUV photomask substrate 1 will eventually have bumps on the surface if there are coated particles during the production process, and if there is a shortage, there will finally be depressions on the surface, so the atomic force microscope is used to scan. The surface morphology can show the location of defect 3.

S1052 , image analysis, to obtain a lateral distance Δx and a longitudinal distance Δy. The measurement after this step is because the coordinate accuracy of the atomic force microscope is not enough, and it is impossible to obtain more accurate coordinates from its coordinates, so the coordinates of the lithography machine are ultimately used as the criterion.

S106, calculate and obtain the precise coordinates (x', y') of defect 3 in the lithography machine coordinate system, where x'=x+Δx, y'=y+Δy, because the error after alignment of the lithography machine is less than 40nm, so the lithography machine writes a square at the defect 3 position, then scans it by an atomic force microscope, and then measures the scanned image to obtain more accurate defect coordinates.

In a preferred embodiment, the regular pattern 4 is a square, and the side length of the square is in the range of 3-10um.

Preferably, the side length of the square is 6um.

It should be explained that, for different detection scenarios, the size of the regular pattern 4 needs to be determined according to 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 pattern 4 as the basis.

In one embodiment, after step S106, it further includes:

S107. Match a suitable circuit design drawing (layou) according to the precise coordinates (x', y') of defect 3. Specifically, in the circuit design drawing, if there is no pattern in the area or some patterns are not affected by the defect, in the matching When laying, it can overlap with the defect 3 position. Because the EUV photomask substrate 1 is a 6-inch square, you can try to compare four angles of 0°, 90°, 180° and 270°, and each angle can also be translated up, down, left and right to see if There are defect locations to be avoided, try to avoid defect 3 as much as possible.

S108 , after matching, the EUV photomask substrate 1 is cleaned.

S109 , after cleaning, apply photoresist to the EUV photomask substrate 1 for use.

In the embodiment provided by the present invention, the defect location process of EUV photomask substrate is improved, and the first alignment pattern of the defect detection equipment and the second alignment pattern of the lithography machine are combined, so there is no need for position measurement equipment to measure and Perform coordinate conversion to save the measurement time of Registration equipment (such as KLA IPOR or ZEISS PROVE). Differences in scale, rotation, etc. Therefore, the present application omits the production of the first alignment pattern of the defect detection equipment, and shares the same set of alignment patterns for the defect detection and the electron beam lithography machine, which saves the use of the equipment and shortens the time for EUV photomask manufacturing. .

The above are only specific embodiments of the present application, but the protection scope of the present application is not limited thereto. Any person skilled in the art who is familiar with the technical field disclosed in the present application can easily think of changes or substitutions. All should be covered within the scope of protection of this application. Therefore, the protection scope of the present application shall be subject to the protection scope of the claims.

Claims (8)

1. An EUV photomask defect locating method, comprising the steps of:

preparing an alignment graph required by a photoetching machine on an EUV photomask substrate;

detecting the position of the defect to obtain coordinates (x, y);

aligning by the photoetching machine according to the alignment pattern;

writing a regular pattern by the photoetching machine by taking the defect position as a fixed point and developing;

obtaining the transverse distance delta x and the longitudinal distance delta y of the defect from the fixed point in the regular graph;

and calculating to obtain the accurate coordinates (x + delta x, y + delta y) of the defect in the coordinate system of the photoetching machine.

2. An EUV photomask defect locating method according to claim 1, wherein the obtaining of the lateral distance Δ x and the longitudinal distance Δ y of a defect in the regular pattern from the fixed point comprises:

scanning the developed regular pattern by using an atomic force microscope to obtain an image;

and analyzing the image to obtain the transverse distance delta x and the longitudinal distance delta y.

3. The EUV photomask defect locating method of claim 1, wherein the fixed point is a center point of the regular pattern.

4. The EUV photomask defect locating method of claim 3, wherein the regular pattern is a square, circle, triangle or hexagon.

5. An EUV photomask defect locating method according to claim 4, characterized in that the regular pattern is a square, the side length of the square being in the range 3-10 um.

6. The method for positioning defects of an EUV photomask according to claim 1, wherein the preparing of the alignment pattern required by the lithography machine on the EUV photomask substrate specifically comprises:

coating photoresist on the EUV photomask baseplate;

photoetching the appearance of the alignment graph by using a photoetching machine;

baking the EUV photomask substrate after photoetching;

developing the appearance of the alignment graph formed by photoetching;

etching the shape and appearance of the alignment pattern formed by photoetching;

and removing the remaining photoresist to obtain the EUV photomask blank with the alignment pattern.

7. The EUV photomask defect locating method of claim 1, further comprising after the step of calculating the precise coordinates (x + Δ x, y + Δ y) of the defect:

matching a proper circuit design drawing according to the accurate coordinates of the defects;

cleaning the EUV photomask substrate;

after cleaning, photoresist is coated for standby.

8. The EUV photomask defect locating method of claim 1, wherein the detected defect position is detected using a defect detection apparatus.

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