KR20250152903A - EUV mask inspection device and inspection method - Google Patents

Abstract

An image resolution enhancement device is provided. The image resolution enhancement device may include a light source that generates EUV light, an optical system that controls a path of the EUV light generated from the light source to irradiate the EUV light to an EUV mask, a detector that collects first diffraction light reflected and diffracted after the EUV light is irradiated to a target area of the EUV mask for a first time and second diffraction light reflected and diffracted after the EUV light is irradiated to the target area of the EUV mask for a second time, thereby obtaining a first diffraction pattern image and a second diffraction pattern image for the target area, and an image acquisition unit that obtains a target diffraction pattern image using the first diffraction pattern image and the second diffraction pattern image, and obtains a target area image for the target area of the EUV mask by converting the target diffraction pattern image.

Description

EUV mask inspection device and inspection method

The present invention relates to an EUV mask inspection device and an inspection method, and more particularly, to an EUV mask inspection device and an inspection method using a high dynamic range (HDR) diffraction pattern.

To realize 3 nm node integrated semiconductor devices, the EUV lithography process, which secures resolution and is more efficient than conventional lithography processes, is being actively used in mass production. Due to the high photon energy of EUV, which is easily absorbed by all materials, the EUV optical system consists of a reflective multilayer thin-film mirror-based system. The mask for the EUV lithography process, which has a circuit pattern engraved on it, also has a structure in which the absorber material is patterned on a reflective multilayer thin-film mirror. Due to the structural characteristics of the reflective mask, the absorber has a thickness, which causes a shadowing effect that obscures the EUV light, resulting in problems such as reduced image contrast, changes in the critical dimension (CD), and shifts in the circuit pattern. In addition to the deterioration of image transfer characteristics due to this mask structure, the characteristics of EUV lithography equipment that uses a step-and-scan system cause various defects on the mask to be repeatedly transferred to the wafer, reducing the process yield. Therefore, prior verification of the mask for defects and contamination is essential.

While the EUV lithography process offers greater process efficiency than conventional lithography, its high cost has led to an increased demand and frequency of performance and defect inspection during the mask manufacturing process for the EUV process. In particular, multilayer mirror-based masks require verification to determine whether the numerous defects present between the multilayer films affect the patterned image on the wafer after the lithography process. Furthermore, mask pattern defects and imaging performance must be verified before they can be introduced into the lithography process. Mask patterns with CD sizes of several nm can be inspected using methods such as scanning electron microscopy and deep ultraviolet (DUV) imaging. However, considering the permeability of multilayer films, an actinic inspection method using 13.5 nm EUV light, which utilizes the wavelength range used in EUV lithography, and a 6-degree mask incidence angle is essential to inspect image transfer characteristics, including phase defects, in EUV masks.

Previously, high-NA EUV mask inspection technology using a 0.55 NA objective lens was studied to evaluate the transfer characteristics of the mask image transferred onto the wafer inside the exposure tool. However, problems such as the high manufacturing difficulty and price of the lens, the decrease in depth of focus due to the increase in NA, and the technical limitations for ultra-precision alignment occurred. Therefore, coherent diffraction imaging (CDI) technique has been actively studied and utilized, which uses a light trapping detector to replace expensive EUV objective optics and reconstructs the pattern image using a phase recovery algorithm based on the diffraction pattern of the mask pattern obtained through the light trapping detector. The use of coherent EUV is essential to utilize the CDI technique, but among the two representative light generation methods, the high-harmonic generation method has limitations in EUV photon flux, and the particle acceleration method has limitations in securing the scale of the accelerator facility.

In addition, conventional CDI technology has used methods such as removing detector noise, improving light source output, and extending exposure time to increase the signal-to-noise ratio (SNR) of high-order diffracted light when acquiring a diffraction pattern to improve resolution. However, this is limited by the dynamic range (DR) of the detector due to the limitations of diffraction. The DR of the detector is proportional to the capacity of photoelectrons that can be stored in one pixel constituting the detector, and is defined as the number of photoelectrons due to the detected diffraction signal compared to the number of electrons due to detector noise. Therefore, the DR of the detector causes limitations in securing the SNR of all signals for low-order to high-order diffracted light generated in the mask pattern. In other words, the intensity of the light diffracted by the mask pattern is such that low-order diffracted light has high light intensity due to the diffraction characteristics, while high-order diffracted light has very weak light intensity, which simultaneously limits the securing of the SNR of low-order to high-order diffracted light. If the exposure time is long to secure the SNR of the high-order diffracted light, the light intensity of the low-order diffracted light will exceed the DR of the detector, causing saturation and bleeding. The diffraction pattern with bleeding phenomenon cannot be used for mask inspection through image restoration because the diffraction signal is distorted. To overcome this, using a detector with high DR requires replacing it with an HDR detector, which costs hundreds of millions of won. In addition, the production and performance verification of the HDR detector also take a long time, consuming a lot of cost and time. In addition, since the HDR detector also has a fundamental limitation in that the SNR of the diffracted light is limited by the DR, a method to overcome this is required.

In conclusion, the EUV mask inspection technology utilizing conventional CDI technology has limitations in securing the SNR of high-order diffraction light that can affect the resolution of the inspection system due to the diffraction characteristics of light and the DR limitations of the detector, and therefore, there is a problem in that the image resolution of the EUV mask is also limited.

Accordingly, the present invention aims to provide a technology that can improve the image resolution of an EUV mask by overcoming the DR limitations of the detector and securing the SNR of high-order diffraction light while utilizing a detector that is currently in use by applying it to an actinic inspection technology using CDI-based coherent EUV light.

The technical problem to be solved by the present invention is to provide an EUV mask inspection device and inspection method.

Another technical problem to be solved by the present invention is to provide a device and method capable of improving the resolution of an EUV mask image.

Another technical problem to be solved by the present invention is to provide a device and method capable of suppressing saturation and bleeding phenomena due to an increase in light irradiation time.

Another technical problem that the present invention seeks to solve is to provide a device and method that can overcome the dynamic range (DR) limit of a detector.

Another technical problem to be solved by the present invention is to provide a device and method capable of securing a high signal to noise ratio (SNR) from the region appearing by low-order diffracted light to the region appearing by high-order diffracted light within a diffraction pattern.

The technical problems to be solved by the present invention are not limited to those described above.

To solve the above-described technical problems, the present invention provides an EUV mask inspection device.

According to one embodiment, the EUV mask inspection device may include a light source that generates EUV light, an optical system that controls a path of the EUV light generated from the light source to irradiate the EUV light to an EUV mask, a detector that collects first diffraction light reflected and diffracted after the EUV light is irradiated to a target area of the EUV mask for a first time and second diffraction light reflected and diffracted after the EUV light is irradiated to the target area of the EUV mask for a second time, thereby obtaining a first diffraction pattern image and a second diffraction pattern image for the target area, and an image acquisition unit that obtains a target diffraction pattern image using the first diffraction pattern image and the second diffraction pattern image, and converts the target diffraction pattern image to obtain a target area image for the target area of the EUV mask.

According to one embodiment, the target diffraction pattern image may include a composite of a corrected diffraction pattern image in which the first diffraction pattern image is corrected using the first time and the second time, and the second diffraction pattern image.

According to one embodiment, the above-described corrected diffraction pattern image may include one obtained from a target signal value calculated according to <Mathematical Formula 1> below.

<Mathematical Formula 1>

(TS: target signal value, DS ₁ : signal value of the first diffracted light, α: slope value of a linear graph obtained by applying the least squares method to the intensity profile of the first diffracted light, β: slope value of a linear graph obtained by applying the least squares method to the intensity profile of the second diffracted light)

In one embodiment, the second time period may be longer than the first time period.

According to one embodiment, the target diffraction pattern image may include a composite of a first area image within the corrected diffraction pattern image and a second area image within the second diffraction pattern image.

According to one embodiment, the corrected diffraction pattern image may include a first region and a second region excluding the first region, and the second diffraction pattern image may include a first region and a second region excluding the first region, wherein the first region of the corrected diffraction pattern image and the first region of the second diffraction pattern image represent the same region within the target region, and the second region of the corrected diffraction pattern image and the second region of the second diffraction pattern image represent the same region within the target region.

According to one embodiment, the first region of the corrected diffraction pattern image and the second diffraction pattern image may include an image by relatively low-order diffraction light, and the second region of the corrected diffraction pattern image and the second diffraction pattern image may include an image by relatively high-order diffraction light.

According to one embodiment, the method further includes an optical blocker disposed between the EUV mask and the detector to locally block diffracted light reflected and diffracted from the EUV mask, wherein the first diffraction pattern image is obtained by the first diffracted light in a state where the optical blocker is not disposed between the EUV mask and the detector, and the second diffraction pattern image is obtained by the second diffracted light in a state where the optical blocker is disposed between the EUV mask and the detector.

According to one embodiment, the method may further include a shutter disposed between the light source and the optical system to control the time at which the EUV light is irradiated to the EUV mask.

According to another embodiment, the EUV mask inspection device may include a light source that generates test light, an optical system that controls a path of the test light generated from the light source to irradiate the test light to an EUV mask, a detector that collects diffraction light reflected and diffracted after the test light is irradiated to a target area of the EUV mask to obtain a diffraction pattern image for the target area, and an optical blocker that is disposed between the EUV mask and the detector and locally blocks diffraction light reflected and diffracted from the EUV mask.

According to another embodiment, the optical blocker may be controlled to not block the diffracted light when the EUV light is irradiated to the target area for a relatively short time, and may be controlled to block a portion of the diffracted light when the EUV light is irradiated to the target area for a relatively long time.

According to another embodiment, the optical blocker may be controlled to block the center of the diffracted light and not block the edge portion excluding the center portion.

To solve the above-described technical problems, the present invention provides an EUV mask inspection method.

According to one embodiment, the EUV mask inspection method may include a step of irradiating EUV light to a target area of an EUV mask for a first time to obtain a first diffraction light reflected and diffracted from the target area, a step of irradiating the EUV light to the target area for a second time to obtain a second diffraction light reflected and diffracted from the target area, a step of obtaining a first diffraction pattern image and a second diffraction pattern image from the first diffraction light and the second diffraction light, respectively, a step of obtaining a target diffraction pattern image using the first diffraction pattern image and the second diffraction pattern image, and a step of converting the target diffraction pattern image to obtain a target area image for the target area.

According to one embodiment, the step of obtaining the target diffraction pattern image may include the step of obtaining a corrected diffraction pattern image in which the first diffraction pattern image is corrected using the first time and the second time, the step of extracting a first area image represented by relatively low-order diffraction light within the corrected diffraction pattern image, the step of extracting a second area image represented by relatively high-order diffraction light within the second diffraction pattern image, and the step of synthesizing the first area image and the second area image.

The present invention collects first diffraction light reflected and diffracted after EUV light is irradiated on a target area of an EUV mask for a first time and second diffraction light reflected and diffracted after EUV light is irradiated on the target area for a second time longer than the first time, thereby obtaining a first diffraction pattern image and a second diffraction pattern image for the target area, and synthesizes a corrected diffraction pattern image in which a difference between the first time and the second time is compensated for and the second diffraction pattern image to the first diffraction pattern image, thereby obtaining a target diffraction pattern image.

Accordingly, the target diffraction pattern image can be obtained from the diffraction light of EUV light irradiated for a relatively short time in a first region by relatively low-order diffraction light, while the second region by high-order diffraction light can be obtained from the diffraction light of EUV light irradiated for a relatively long time.

Due to this, the target diffraction pattern image can secure a high signal-to-noise ratio (SNR) in the first region while suppressing saturation and bleeding phenomena in the first region due to low-order diffraction light, and can also secure a high signal-to-noise ratio (SNR) in the second region due to high-order diffraction light, so that the resolution of the target region image converted from the target diffraction pattern image can be significantly improved.

FIG. 1 is a drawing for explaining an EUV mask inspection device according to an embodiment of the present invention.
FIG. 2 is a drawing for explaining a process of acquiring a first diffraction pattern image using an EUV mask inspection device according to an embodiment of the present invention.
FIG. 3 is a drawing for explaining a second diffraction pattern image acquisition process using an EUV mask inspection device according to an embodiment of the present invention.
Figures 4 and 5 are schematic diagrams for explaining the first diffraction pattern image and the second diffraction pattern image.
Figure 6 is a schematic diagram illustrating the process of acquiring a target diffraction pattern image.
Figure 7 is a graph for explaining α and β of <Mathematical Formula 1>.
Figure 8 is a schematic diagram illustrating the computational processing of a phase restoration algorithm used in the process of converting a target diffraction pattern image to obtain a target area image.
Figure 9 is a schematic diagram for explaining a target area image obtained by converting the first diffraction pattern image.
Figure 10 is a schematic diagram for explaining a target area image obtained by converting a target diffraction pattern image.
FIG. 11 is a flowchart for explaining an EUV mask inspection method according to an embodiment of the present invention.
FIG. 12 is a flowchart specifically explaining step S400 of an EUV mask inspection method according to an embodiment of the present invention.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the attached drawings. However, the technical concept of the present invention is not limited to the embodiments described herein and may be embodied in other forms. Rather, the embodiments introduced herein are provided to ensure that the disclosed content is thorough and complete and to sufficiently convey the spirit of the present invention to those skilled in the art.

In this specification, when a component is referred to as being on another component, it means that it can be formed directly on the other component, or a third component may be interposed between them. In addition, in the drawings, the thicknesses of films and regions are exaggerated for the purpose of effectively explaining the technical contents.

Also, although terms such as first, second, and third have been used to describe various components in various embodiments of this specification, these components should not be limited by these terms. These terms are only used to distinguish one component from another. Thus, what is referred to as a first component in one embodiment may be referred to as a second component in another embodiment. Each embodiment described and illustrated herein also includes its complementary embodiments. Also, the term "and/or" has been used herein to mean including at least one of the components listed before and after.

In the specification, singular expressions include plural expressions unless the context clearly dictates otherwise. In addition, terms such as "comprise" or "have" are intended to specify the presence of a feature, number, step, component, or combination thereof described in the specification, and should not be construed as excluding the presence or addition of one or more other features, numbers, steps, components, or combinations thereof. In addition, the term "connection" is used in the present specification to mean both indirectly connecting multiple components and directly connecting them.

In addition, when describing the present invention below, if it is determined that a detailed description of a related known function or configuration may unnecessarily obscure the gist of the present invention, the detailed description will be omitted.

FIG. 1 is a drawing for explaining an EUV mask inspection device according to an embodiment of the present invention.

Referring to FIG. 1, an EUV mask inspection device according to an embodiment of the present invention may include a light source (100), a shutter (200), an optical system (310, 320), a pinhole (400), a light blocker (500), a detector (600), and an image acquisition unit (not shown). Each component is described below.

The light source (100) can generate and radiate EUV light (L). According to one embodiment, the light source (100) can radiate coherent EUV light of 13.56 nm generated in a high-order harmonic manner. According to another embodiment, the light source (100) can generate and radiate light other than EUV light. That is, the light used in the EUV mask inspection device according to the embodiment of the present invention may include not only EUV light but also other light (e.g., E-beam, etc.).

The shutter (200) is arranged between the light source (100) and the optical system (310, 320) described below, and can transmit or block the EUV light (L) emitted from the light source (100). Accordingly, the time for which the EUV light (L) emitted from the light source (100) is irradiated to the EUV mask (M) described below can be controlled by the shutter (200).

The optical system (310, 320) can control the path of the EUV light (L) emitted from the light source (100) to irradiate the EUV light (L) to an EUV mask (M). According to one embodiment, the EUV mask (M) may be a reflective mask used in an EUV process.

According to one embodiment, the optical system (310, 320) may include a first mirror (310) and a second mirror (320). For example, the first mirror (310) may include a concave multilayer thin-film mirror for focusing the EUV light (L). Alternatively, the second mirror (320) may include a planar multilayer thin-film mirror for guiding the EUV light (L) focused from the first mirror (310) to a target area (TA) of the EUV mask (M).

According to one embodiment, the EUV light (L) irradiated onto the EUV mask (M) may be irradiated such that the direction in which the EUV light (L) is irradiated and the normal direction of the upper surface of the EUV mask (M) form an angle of 6°. That is, the EUV light (L) may be irradiated onto the EUV mask (M) so as to satisfy an oblique incidence condition of 6°.

The pinhole (400) may be placed between the optical system (310, 320) and the EUV mask (M). The pinhole (400) can confirm whether the EUV light (L) has been irradiated to the target area (TA) of the EUV mask (M).

The EUV light (L) irradiated onto the EUV mask (M) may be reflected and diffracted by the EUV mask (M). The EUV light (L) reflected and diffracted from the EUV mask (M) may be defined as diffracted light (DL).

The above optical blocker (500) can be placed between the EUV mask (M) and the detector (600) described later. The optical blocker (500) can locally block the diffracted light (DL) collected by the detector (600) described later.

The detector (600) can collect the diffraction light (DL) to obtain a diffraction pattern image. The image acquisition unit (not shown) can convert the diffraction pattern image to obtain a target area image. According to one embodiment, the target area image can be defined as an image of the target area (TA) of the EUV mask (M). Inspection of the EUV mask (M) can be performed through the target area image.

Above, each component of an EUV mask inspection device according to an embodiment of the present invention has been described. Below, the process of improving image resolution using the EUV mask inspection device is described in detail.

FIG. 2 is a diagram for explaining a process for obtaining a first diffraction pattern image using an EUV mask inspection device according to an embodiment of the present invention, FIG. 3 is a diagram for explaining a process for obtaining a second diffraction pattern image using an EUV mask inspection device according to an embodiment of the present invention, FIGS. 4 and 5 are schematic diagrams for explaining a first diffraction pattern image and a second diffraction pattern image, FIG. 6 is a schematic diagram for explaining a process for obtaining a target diffraction pattern image, FIG. 7 is a graph for explaining α and β of <Mathematical Formula 1>, FIG. 8 is a schematic diagram for explaining an operation processing process of a phase restoration algorithm used in a process for obtaining a target area image by converting a target diffraction pattern image, FIG. 9 is a schematic diagram for explaining a target area image obtained by converting a first diffraction pattern image, and FIG. 10 is a schematic diagram for explaining a target area image obtained by converting a target diffraction pattern image.

Referring to FIGS. 2 to 6, an EUV mask inspection device according to an embodiment of the present invention can obtain a target diffraction pattern image (TP) using a first diffraction pattern image (DP ₁ ) obtained by collecting a first diffraction light (DL ₁ ) and a second diffraction pattern image (DP ₂ ) obtained by collecting a second diffraction light (DL ₂ ).

According to one embodiment, the first diffracted light (DL ₁ ) may be defined as EUV light reflected and diffracted after the EUV light (L) is irradiated onto the target area (TA) of the EUV mask (M) for a first time. In contrast, the second diffracted light (DL ₂ ) may be defined as EUV light reflected and diffracted after the EUV light (L) is irradiated onto the target area (TA) of the EUV mask (M) for a second time that is longer than the first time.

That is, the first diffraction pattern image (DP ₁ ) can be obtained from light diffracted after being irradiated for a relatively short time, whereas the second diffraction pattern image (DP ₂ ) can be obtained from light diffracted after being irradiated for a relatively long time.

For example, when the mask pattern (MP) of the target area (TA) has a shape like (a) of FIG. 4, the first diffraction pattern image (DP ₁ ) may appear like (b) of FIG. 4, and the second diffraction pattern image (DP ₂ ) may appear like (c) of FIG. 4.

In addition, according to one embodiment, the first diffraction pattern image (DP ₁ ) can be obtained from the first diffraction light (DL 1 ) in a state where the optical blocker (500) is not disposed between the EUV mask (M) and the detector (600), as illustrated in FIG. 2 . In contrast, the second diffraction pattern image (DP ₂ ) can be obtained from the second diffraction light (DL ₂ ) in a state where the optical blocker (500) is disposed between the EUV mask (M) and the detector (600), as illustrated in FIG. ₃ .

According to one embodiment, the optical blocker (500) can block relatively low-order diffraction light among the second diffraction light (DL ₂ ). That is, the second diffraction pattern image (DP ₂ ) may have the center of the second diffraction light (DL ₂ ) blocked by the optical blocker (500), and the edge portion excluding the center may not be blocked. Accordingly, the second diffraction pattern image (DP ₂ ) may include only an image by high-order diffraction light. In contrast, the first diffraction pattern image (DP ₁ ) may include both an image by low-order diffraction light and an image by high-order diffraction light.

More specifically, the diffraction pattern image (DP ₁ ) obtained from the first diffraction light (DL ₁ ) and the diffraction pattern image (DP ₂ ) obtained from the second diffraction light (DL ₂ ) may include a first region (A ₁ , B ₁ ) by low-order diffraction light and a second region (A ₂ , B ₂ ) by high-order diffraction light, as shown in (a) and (b) of FIG. 5 , respectively.

As described above, since the first diffraction pattern image (DP ₁ ) is acquired in a state where the optical blocker (500) is not disposed, both the first region (A ₁ ) and the second region (B ₂ ) may appear in the first diffraction pattern image (DP ₁ ). In contrast, since the second diffraction pattern image (DP ₂ ) is acquired in a state where the optical blocker (500) is disposed, only the second region (B ₂ ) may appear in the second diffraction pattern image (DP ₂ ) and not the first region (B ₁ ).

The above target diffraction pattern image (TP) can be obtained by synthesizing the first diffraction pattern image (DP ₁ ) and the second diffraction pattern image (DP ₂ ). However, since the first diffraction pattern image (DP ₁ ) and the second diffraction pattern image (DP ₂ ) are obtained in a state where the times at which the EUV light (L) is irradiated to the EUV mask (M) are different, they can be synthesized in a state where compensation for the difference in irradiation times is made.

According to one embodiment, the target diffraction pattern image (TP) can be obtained by synthesizing the first diffraction pattern image (DP ₁ ) with a corrected diffraction pattern image (CP) and the second diffraction pattern image (DP ₂ ) using the first time and the second time.

For example, the above-mentioned corrected diffraction pattern image (CP) can be obtained from the target signal value calculated according to <Mathematical Formula 1> below. The α value and β value indicated in <Mathematical Formula 1> can be calculated as shown in Fig. 7.

<Mathematical Formula 1>

(TS: target signal value, DS ₁ : signal value of the first diffracted light, α: slope value of a linear graph obtained by applying the least squares method to the intensity profile of the first diffracted light, β: slope value of a linear graph obtained by applying the least squares method to the intensity profile of the second diffracted light)

In addition, the target diffraction pattern image (TP) is obtained by a method of synthesizing the corrected diffraction pattern image (CP) and the second diffraction pattern image (DP ₂ ), as illustrated in FIG. 6, and can be obtained by a method of synthesizing the first area (A ₁ ) image in the corrected diffraction pattern image (CP) and the second area (B ₂ ) image in the second diffraction pattern image (DP ₂ ).

Accordingly, the target diffraction pattern image (TP) can be obtained from the diffraction light of EUV light irradiated for a relatively short time in a first region (C ₁ ) by low-order diffraction light, while the second region (C ₂ ) by high-order diffraction light can be obtained from the diffraction light of EUV light irradiated for a relatively long time.

Due to this, the target diffraction pattern image (TP) can secure a high signal-to-noise ratio (SNR) of the first region (C ₁ ) while suppressing saturation and bleeding phenomena in the first region (C ₁ ) due to low-order diffraction light, and can also secure a high signal-to-noise ratio (SNR) of the second region (C ₂ ) due to high-order diffraction light, so that the resolution of the target region image converted from the target diffraction pattern image (TP) can be significantly improved.

More specifically, when simply synthesizing a diffraction pattern image obtained from the diffraction light of EUV light irradiated for a relatively short time and a diffraction pattern image obtained from the diffraction light of EUV light irradiated for a relatively long time, saturation and bleeding phenomena may occur in the region due to low-order diffraction light in the diffraction pattern image obtained from the diffraction light of EUV light irradiated for a relatively long time, and thus saturation and bleeding phenomena may also occur in the synthesized diffraction pattern image.

However, as described above, since the present invention blocks low-order diffraction light by using the optical blocker (500) in the process of obtaining the second diffraction pattern image (DP ₂ ), the first region (B ₁ ) in which saturation and bleeding phenomena may occur in the second diffraction pattern image (DP ₂ ) can be blocked. In addition, since only the second region (B ₂ ) in the second diffraction pattern image (DP ₂ ) is used in the process of obtaining the target diffraction pattern image (TP), the saturation and bleeding phenomena in the target diffraction pattern image (TP) can also be suppressed.

According to one embodiment, as illustrated in FIG. 8, an arbitrary value is assigned to the target diffraction pattern image (TP) (①), an amplitude and phase are calculated in a Fourier domain through Fourier transformation (②), the calculated amplitude value is replaced with an amplitude value measured from the target diffraction pattern image (TP) (③), an amplitude value in a real domain is calculated through inverse Fourier transformation, and then a probe constraint according to the shape of the EUV light irradiated on the EUV mask (M) is applied (④), the result in ④ is Fourier transformed to calculate the amplitude and phase in the Fourier domain, and then the process of ① to ④ is repeated until the difference between the value and the amplitude value measured from the target diffraction pattern image (TP) is within an allowable error range, thereby obtaining the target area image from the target diffraction pattern image (TP).

Referring to FIG. 9, a target area image and an intensity profile acquired using only the first diffraction light are shown, and referring to FIG. 10, a target area image and an intensity profile acquired using both the first diffraction light and the second diffraction light are shown. As can be seen in FIGS. 9 and 10, the target area image acquired using both the first diffraction light and the second diffraction light (acquired from the target diffraction pattern image) can be seen to have a finer CD size pattern resolution compared to the target area image acquired using only the first diffraction light (acquired from the first diffraction pattern image). In addition, the improvement in image performance can be confirmed once again through a comparison of the intensity profiles.

Above, an EUV mask inspection device according to an embodiment of the present invention has been described. Hereinafter, an EUV mask inspection method according to an embodiment of the present invention will be described. According to one embodiment, the EUV mask inspection method can be performed using an EUV mask inspection device according to the embodiment described with reference to FIGS. 1 to 10.

FIG. 11 is a flowchart for explaining an EUV mask inspection method according to an embodiment of the present invention, and FIG. 12 is a flowchart for specifically explaining step S400 of the EUV mask inspection method according to an embodiment of the present invention.

Referring to FIGS. 11 and 12, by irradiating EUV light (L) to a target area (TA) of an EUV mask (M) for a first time, a first diffracted light (DL ₁ ) reflected and diffracted from the target area (TA) can be obtained (S100).

In addition, by irradiating the EUV light (L) to the target area (TA) for a second time longer than the first time, second diffracted light (DL ₂ ) reflected and diffracted from the target area (TA) can be obtained (S200).

After obtaining the first diffraction light (DL ₁ ) and the second diffraction light (DL ₂ ), a first diffraction pattern image (DP ₁ ) and a second diffraction pattern image (DP ₂ ) can be obtained from the first diffraction light (DL ₁ ) and the second diffraction light (DL ₂ ), respectively (S300).

The target diffraction pattern image (TP) can be obtained using the first diffraction pattern image (DP ₁ ) and the second diffraction pattern image (DP ₂ ) (S400). According to one embodiment, the step of obtaining the target diffraction pattern image (TP) (S400) may include the steps of: obtaining a corrected diffraction pattern image (CP) in which the first diffraction pattern image is corrected using the first time and the second time (S410); extracting a first region (A ₁ ) image appearing by relatively low-order diffraction light within the corrected diffraction pattern image (CP) (S420); extracting a second region (B ₂ ) image appearing by relatively high-order diffraction light within the second diffraction pattern image (DP ₂ ) (S430); and synthesizing the first region image and the second region image (S440).

The target diffraction pattern image (TP) can be converted to obtain a target area image for the target area (TA) (S500). Finally, inspection of the target area (TA) of the EUV mask (M) can be performed through the target area image.

While the present invention has been described in detail using preferred embodiments, the scope of the present invention is not limited to the specific embodiments described above, and should be interpreted in accordance with the appended claims. Furthermore, those skilled in the art will appreciate that numerous modifications and variations are possible without departing from the scope of the present invention.

100: Light source
200: Shutter
310, 320: First mirror, second mirror (optical system)
400: Pinhole
500: Optical circuit breaker
600: Detector

Claims (14)

A light source that generates EUV light;
An optical system that controls the path of the EUV light generated from the light source and irradiates the EUV light onto an EUV mask;
A detector that collects first diffraction light reflected and diffracted after the EUV light is irradiated on the target area of the EUV mask for a first time and second diffraction light reflected and diffracted after the EUV light is irradiated on the target area of the EUV mask for a second time, thereby obtaining a first diffraction pattern image and a second diffraction pattern image for the target area; and
An EUV mask inspection device comprising an image acquisition unit that acquires a target diffraction pattern image using the first diffraction pattern image and the second diffraction pattern image, and converts the target diffraction pattern image to acquire a target area image for the target area of the EUV mask.
In the first paragraph,
An EUV mask inspection device comprising a target diffraction pattern image, wherein the target diffraction pattern image is a composite of a corrected diffraction pattern image obtained by correcting the first diffraction pattern image using the first time and the second time and the second diffraction pattern image.
In the second paragraph,
An EUV mask inspection device, wherein the above-mentioned correction diffraction pattern image is obtained from a target signal value calculated according to <Mathematical Formula 1> below.
<Mathematical Formula 1>

(TS: target signal value, DS ₁ : signal value of the first diffracted light, α: slope value of a linear graph obtained by applying the least squares method to the intensity profile of the first diffracted light, β: slope value of a linear graph obtained by applying the least squares method to the intensity profile of the second diffracted light)
In the second paragraph,
An EUV mask inspection device comprising the second time being longer than the first time.
In the second paragraph,
An EUV mask inspection device, wherein the target diffraction pattern image comprises a composite of a first area image within the corrected diffraction pattern image and a second area image within the second diffraction pattern image.
In paragraph 5,
The above-mentioned corrected diffraction pattern image includes a first region and a second region excluding the first region,
The above second diffraction pattern image includes a first region and a second region excluding the first region,
The first area of the above-mentioned correction diffraction pattern image and the first area of the above-mentioned second diffraction pattern image represent the same area within the above-mentioned target area,
An EUV mask inspection device comprising a second area of the above-described correction diffraction pattern image and a second area of the above-described second diffraction pattern image representing the same area within the above-described target area.
In paragraph 6,
The first region of the above-mentioned corrected diffraction pattern image and the second diffraction pattern image includes an image by relatively low-order diffracted light,
An EUV mask inspection device wherein the second area of the above-mentioned corrected diffraction pattern image and the second diffraction pattern image include images by relatively high-order diffraction light.
In the first paragraph,
Further comprising an optical blocker disposed between the EUV mask and the detector to locally block diffracted light reflected and diffracted from the EUV mask,
The first diffraction pattern image is obtained by the first diffracted light without the optical blocker being placed between the EUV mask and the detector,
An EUV mask inspection device, wherein the second diffraction pattern image is obtained by the second diffraction light while the optical blocker is placed between the EUV mask and the detector.
In the first paragraph,
An EUV mask inspection device further comprising a shutter disposed between the light source and the optical system, the shutter controlling the time at which the EUV light is irradiated onto the EUV mask.
A light source that generates test light;
An optical system that controls the path of the test light generated from the light source and irradiates the test light onto an EUV mask;
A detector that collects reflected and diffracted diffracted light after the test light is irradiated onto the target area of the EUV mask to obtain a diffraction pattern image for the target area; and
An EUV mask inspection device including an optical blocker positioned between the EUV mask and the detector to locally block diffracted light reflected and diffracted from the EUV mask.
In Article 10,
The above optical blocker is controlled so as not to block the diffracted light when the test light is irradiated to the target area for a relatively short time,
An EUV mask inspection device comprising a device controlled to block a portion of the diffracted light when the test light is irradiated to the target area for a relatively long period of time.
In Article 11,
An EUV mask inspection device including a light blocker that is controlled to block the center of the diffracted light and not block the edge portion excluding the center.
A step of irradiating EUV light to a target area of an EUV mask for a first time to obtain first diffracted light reflected and diffracted from the target area;
A step of irradiating the EUV light to the target area for a second time to obtain second diffracted light reflected and diffracted from the target area;
A step of obtaining a first diffraction pattern image and a second diffraction pattern image from the first diffraction light and the second diffraction light, respectively;
A step of obtaining a target diffraction pattern image using the first diffraction pattern image and the second diffraction pattern image; and
An EUV mask inspection method comprising a step of converting the target diffraction pattern image to obtain a target area image for the target area.
In the 13th paragraph,
The step of obtaining the above target diffraction pattern image is:
A step of obtaining a corrected diffraction pattern image in which the first diffraction pattern image is corrected using the first time and the second time;
A step of extracting a first area image represented by relatively low-order diffracted light within the above-mentioned corrected diffraction pattern image;
A step of extracting a second area image represented by relatively high-order diffraction light within the second diffraction pattern image; and
An EUV mask inspection method comprising a step of synthesizing the first area image and the second area image.