Method and system for improving imaging performance of masks for EUV lithography

Abstract

A method for improving the imaging performance of a mask for EUV lithography is provided. The method for improving the imaging performance of the above-described EUV lithography mask may include the steps of: irradiating EUV light onto a sample mask comprising a reflective layer, a capping layer disposed on the reflective layer, and a sample absorption pattern disposed on the capping layer; deriving a phase difference value defined as the difference between the phase value at the maximum amplitude of a first diffracted light diffracted by the sample mask and the phase value at the maximum amplitude of a second diffracted light having a different order from the first diffracted light; deriving an image position difference value defined as the difference between the position value at the maximum intensity of a first aerial image formed by the interference of the first diffracted light and the second diffracted light at a first position and the position value at the maximum intensity of a second aerial image formed by the interference of the first diffracted light and the second diffracted light at a second position; and constructing a database in which the phase difference value and the image position difference value are stored for each of a plurality of sample masks comprising different sample absorption patterns.

Description

Technology Field

[0001] The present invention relates to a method and system capable of improving the imaging performance of a mask for EUV lithography. Background Technology

[0002] EUV lithography is a next-generation semiconductor lithography technology that utilizes a 13.5 nm EUV light source—which has a wavelength approximately 1 / 14th that of DUV—to achieve improved resolution. It is applied to mass production processes for semiconductors at the 7 nm node level and below, following the existing ArF 193 nm immersion double patterning technology. Because EUV light has a short wavelength, it is absorbed by most media, including air; consequently, a reflective mask is used instead of the transmissive mask used in conventional DUV lithography. The EUV lithography equipment consists of a total of 11 reflective mirrors (Multilayer Mirrors, ML), including the EUV mask, and is configured with an oblique incidence structure having an angle of incidence to prevent collisions between incident and reflected light at each reflective mirror.

[0003] The EUV mask is also designed with a Bragg reflector for application to a reflective optical system. The materials used in the reflective layer are determined by considering optical constants; to minimize EUV light absorption, the extinction coefficient (k) must have a low value, and to maximize reflectivity, there must be a large difference in the refractive indices between the two materials. Therefore, the most optimal combination, molybdenum (Mo) and silicon (Si), is used. The thickness of the two elements is determined by considering the Bragg equation and the concept that constructive interference occurs when the thickness of a pair corresponds to half the EUV wavelength, resulting in optimal reflectivity. Thus, a total of more than 40 pairs are stacked, with a Mo layer of 2.8 nm and a Si layer of 4.2 nm forming a single pair. The uppermost layer of the reflective film consists of a capping layer made of ruthenium (Ru) with a thickness of 2.5 nm. The capping layer above is composed of an absorber for absorbing light to form a pattern. In the case of a conventional general EUV exposure process mask, a tantalum (Ta)-based absorber with a thickness of about 70 nm is used to maximize the contrast ratio between the reflection region and the absorption region.

[0004] In the case of conventional Ta-based EUV masks, there are problems such as the Shadowing Effect, where the transferred line width becomes larger than the originally designed line width due to the oblique incidence optical system and the thick absorber thickness; the Telecentricity Error, where the pattern position changes depending on the focus; and the Best Focus Shift, where the optimal focus position changes depending on the pitch of the pattern.

[0005] This not only causes deterioration in pattern performance during the EUV lithography process but can also lead to a decrease in yield due to the reduction of the process window. In particular, the difference in exposure characteristics between vertical and horizontal patterns caused by the shadowing effect can lead to additional issues, such as increased difficulty in the pattern mask fabrication process, and when producing devices below a 3 nm node, the mask 3D effect intensifies to the point of directly affecting process yield.

[0006] The imaging performance of an EUV mask can be evaluated through aerial images. More specifically, an aerial image is the intensity distribution according to the position of EUV light containing pattern information, just before the light reflected and diffracted from the mask reaches the wafer. This can be evaluated using image contrast, which represents the difference between maximum and minimum intensity, and NILS (Normalized Image Log Slope), which represents the slope of that intensity. Conventional Ta-based masks exhibit measurement results showing a sharp decrease in image contrast and NILS when transferring fine patterns, indicating a degradation in the mask's imaging performance.

[0007] Therefore, to address the aforementioned problems, various studies are being conducted on the development of next-generation absorbent materials to replace Ta-based absorbers. The problem to be solved

[0008] The technical problem that the present invention aims to solve is to provide a method and system for improving the imaging performance of a mask for EUV lithography.

[0009] Another technical problem that the present invention aims to solve is to provide a method and system for selecting a material other than a tantalum (Ta)-based material as a material for an absorption pattern.

[0010] Another technical problem that the present invention aims to solve is to provide a method and system for manufacturing an absorption pattern with reduced thickness compared to a tantalum (Ta)-based absorption pattern.

[0011] Another technical problem that the present invention aims to solve is to provide a method and system capable of reducing the Mask 3D Effect.

[0012] Another technical problem that the present invention aims to solve is to provide a method and system capable of improving the yield of an EUV lithography process.

[0013] The technical problems that the present invention aims to solve are not limited to those described above. means of solving the problem

[0014] To solve the technical problems described above, the present invention provides a method for improving the imaging performance of a mask for EUV lithography.

[0015] According to one embodiment, a method for improving the imaging performance of an EUV lithography mask may include: a step of irradiating EUV light onto a sample mask comprising a reflective layer, a capping layer disposed on the reflective layer, and a sample absorption pattern disposed on the capping layer; a step of deriving a phase difference value defined as the difference between a phase value at the maximum amplitude of a first diffracted light diffracted by the sample mask and a phase value at the maximum amplitude of a second diffracted light having a different order from the first diffracted light; a step of deriving an image position difference value defined as the difference between a position value at the maximum intensity of a first aerial image formed by interference of the first diffracted light and the second diffracted light at a first position and a position value at the maximum intensity of a second aerial image formed by interference of the first diffracted light and the second diffracted light at a second position; and a step of constructing a database in which the phase difference value and the image position difference value are stored for each of a plurality of sample masks comprising different sample absorption patterns. there is.

[0016] According to one embodiment, the different sample absorption patterns included in the plurality of sample masks may include patterns with different thicknesses.

[0017] According to one embodiment, the different sample absorption patterns included in the plurality of sample masks each include first and second absorption patterns spaced apart from each other, and the distance between the first and second absorption patterns spaced apart from each other may be different.

[0018] According to one embodiment, the first and second absorption patterns may include having a line shape extending in the same direction.

[0019] According to one embodiment, the EUV light may be irradiated onto the sample mask through a dipole illumination system.

[0020] According to one embodiment, the method for improving the imaging performance of the EUV lithography mask may include, after the step of building the database, the step of deriving a target phase difference value from the database such that the image position difference value is minimized, the step of deriving a target refractive index and a target extinction coefficient having the target phase difference value, the step of selecting a target absorbing material having the target refractive index and the target extinction coefficient, and the step of manufacturing a target mask using the target absorbing material.

[0021] According to one embodiment, the target absorption material may include a single elemental material or a compound of different elements.

[0022] According to one embodiment, the step of manufacturing a target mask using the target absorption material may include the step of forming a reflective layer on a substrate, the step of forming a capping layer on the reflective layer, and the step of forming a target absorption pattern including the target absorption material on the capping layer.

[0023] According to one embodiment, the method for improving the imaging performance of the EUV lithography mask comprises, after the step of constructing the database, the step of deriving a sub-phase difference value different from a target phase difference value in which the image position difference value is minimized from the database, the step of deriving a sub-refractive index and a sub-extinction coefficient having the sub-phase difference value, the step of selecting a sub-absorbing material having the sub-refractive index and a sub-extinction coefficient, and the step of manufacturing a sub-mask by forming a sub-absorbing pattern with the sub-absorbing material on a reflective layer, wherein the line width of the sub-absorbing pattern is controlled so that the sub-phase difference value derived from the sub-mask becomes equal to the target phase difference value.

[0024] According to one embodiment, the method of controlling the linewidth of the sub-absorption pattern may vary depending on the type of sub-mask, such that the position of the photoresist pattern formed on the wafer by EUV light reflected and diffracted from the sub-mask changes.

[0025] According to one embodiment, when using a submask formed such that the position of the photoresist pattern formed on the wafer by EUV light reflected and diffracted from the submask corresponds to the position of the sub-absorption pattern of the submask, the method may include controlling the linewidth of the sub-absorption pattern to narrow so that the sub-phase difference value derived from the submask becomes equal to the target phase difference value.

[0026] According to one embodiment, when using a submask formed such that the position of a photoresist pattern formed on a wafer by EUV light reflected and diffracted from the submask corresponds to the position of a reflection layer exposed between the sub-absorption patterns of the submask, the method may include controlling the linewidth of the sub-absorption pattern to widen so that the sub-phase difference value derived from the submask is equal to the target phase difference value.

[0028] To solve the technical problems described above, the present invention provides a system for improving the imaging performance of a mask for EUV lithography.

[0029] According to one embodiment, the imaging performance enhancement system for the EUV lithography mask comprises: a light irradiation unit that irradiates EUV light onto a sample mask comprising a reflective layer, a capping layer disposed on the reflective layer, and a sample absorption pattern disposed on the capping layer; a phase difference value derivation unit that derives a phase difference value defined as the difference between the phase value at the maximum amplitude of a first diffracted light diffracted by the sample mask and the phase value at the maximum amplitude of a second diffracted light having a different order from the first diffracted light; an image position difference value derivation unit that derives an image position difference value defined as the difference between the position value at the maximum intensity of a first aerial image formed by interference of the first diffracted light and the second diffracted light at a first position and the position value at the maximum intensity of a second aerial image formed by interference of the first diffracted light and the second diffracted light at a second position; and the phase difference value and the image position difference value for each of a plurality of sample masks comprising different sample absorption patterns. It may include a database construction unit that builds a stored database.

[0030] According to one embodiment, the imaging performance enhancement system for the EUV lithography mask may further include a target absorption material selection unit that derives a target phase difference value from the database in which the image position difference value is minimized, derives a target refractive index and a target extinction coefficient having the target phase difference value, and selects a target absorption material having the target refractive index and the target extinction coefficient. Effects of the invention

[0031] The present invention allows for the selection of a material that can replace existing tantalum (Ta)-based materials as a material that can be used as an absorption pattern for a mask for EUV lithography. In addition, when an absorption pattern is manufactured using the selected material, the imaging performance of the mask can be maximized. Brief explanation of the drawing

[0032] FIG. 1 is a flowchart illustrating steps S110 to S140 of a method for improving the imaging performance of an EUV lithography mask according to an embodiment of the present invention. FIG. 2 is a drawing illustrating a sample mask used in a method for improving the imaging performance of an EUV lithography mask according to an embodiment of the present invention. FIG. 3 is a diagram illustrating the phase difference value derived in step S120 of the method for improving the imaging performance of an EUV lithography mask according to an embodiment of the present invention. FIG. 4 is a diagram illustrating the image position difference value derived in step S130 of the method for improving the imaging performance of an EUV lithography mask according to an embodiment of the present invention. FIG. 5 is a diagram illustrating the first aerial image and the second aerial image used to derive the position difference value. FIG. 6 is a flowchart illustrating step S200 of a method for improving the imaging performance of an EUV lithography mask according to an embodiment of the present invention. FIGS. 7 to 10 are drawings for explaining examples of a process for deriving a target phase difference value in which the image position difference value is minimized in step S210. Figures 11 and 12 are drawings for explaining the target absorbing materials selected through steps S220 and S230. FIG. 13 is a drawing for explaining the first area image and the second area image of a target mask manufactured using a target absorption material. Figure 14 is a simulation result comparing the trends of phase difference values, image position difference values, and NILS values ​​according to the thickness and refractive index conditions of an absorption pattern with an extinction coefficient of 0.01. Figure 15 is a simulation result comparing the trends of phase difference values, image position difference values, and NILS values ​​according to the thickness and refractive index conditions of an absorption pattern with an extinction coefficient of 0.03. Figure 16 is a simulation result comparing the trends of phase difference values, image position difference values, and NILS values ​​according to thickness and refractive index conditions of an absorption pattern with an extinction coefficient of 0.05. Figure 17 is a simulation result comparing the trends of phase difference values, image position difference values, and NILS values ​​according to thickness and refractive index conditions of an absorption pattern with an extinction coefficient of 0.07. Figure 18 is a simulation result comparing the trends of phase difference values, image position difference values, and NILS values ​​according to thickness and refractive index conditions of an absorption pattern with an extinction coefficient of 0.05 in a 0.33NA exposure system and a 0.55NA exposure system. FIG. 19 is a flowchart illustrating step S300 of a method for improving the imaging performance of an EUV lithography mask according to an embodiment of the present invention. FIG. 20 is a diagram illustrating the process of forming a photoresist pattern when a dark field mask is used as a sub-mask. Figure 21 is a simulation result comparing the trends of phase difference values ​​(a), image position difference values ​​(b), and NILS values ​​(c) according to the conditions of the thickness, refractive index, and linewidth (Mask bias) of the absorption pattern with an extinction coefficient of 0.01 in the dark field tone. Figure 22 is a simulation result comparing the trends of phase difference values ​​(a), image position difference values ​​(b), and NILS values ​​(c) according to the conditions of the thickness, refractive index, and linewidth (mask bias) of the absorption pattern with an extinction coefficient of 0.03 in the dark field tone. Figure 23 is a simulation result comparing the trends of phase difference values ​​(a), image position difference values ​​(b), and NILS values ​​(c) according to the conditions of the thickness, refractive index, and linewidth (mask bias) of the absorption pattern with an extinction coefficient of 0.05 in the dark field tone. Figure 24 is a simulation result comparing the trends of phase difference values ​​(a), image position difference values ​​(b), and NILS values ​​(c) according to the conditions of the thickness, refractive index, and linewidth (Mask bias) of the absorption pattern with an extinction coefficient of 0.07 in the dark field tone. FIG. 25 is a diagram illustrating the process of forming a photoresist pattern when a Bright field mask is used as a sub-mask. Figure 26 is a simulation result comparing the trends of phase difference values ​​(a), image position difference values ​​(b), and NILS values ​​(c) according to the conditions of the thickness, refractive index, and linewidth (Mask bias) of the absorption pattern with an extinction coefficient of 0.01 in the Bright field tone. Figure 27 is a simulation result comparing the trends of phase difference values ​​(a), image position difference values ​​(b), and NILS values ​​(c) according to the conditions of the thickness, refractive index, and linewidth (Mask bias) of the absorption pattern with an extinction coefficient of 0.03 in the Bright field tone. Figure 28 is a simulation result comparing the trends of phase difference values ​​(a), image position difference values ​​(b), and NILS values ​​(c) according to the conditions of the thickness, refractive index, and linewidth (Mask bias) of the absorption pattern with an extinction coefficient of 0.05 in the Bright field tone. Figure 29 is a simulation result comparing the trends of phase difference values ​​(a), image position difference values ​​(b), and NILS values ​​(c) according to the conditions of the thickness, refractive index, and linewidth (Mask bias) of the absorption pattern with an extinction coefficient of 0.07 in the Bright field tone. Figure 30 is a diagram illustrating the range of absorbent materials expanded through the S300 step. Specific details for implementing the invention

[0033] 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 concept of the present invention to those skilled in the art.

[0034] In this specification, when a component is described as being on another component, it means that it may be formed directly on the other component or that a third component may be interposed between them. Additionally, in the drawings, the thicknesses of the films and regions are exaggerated for the effective description of the technical content.

[0035] Additionally, although terms such as first, second, third, etc., have been used to describe various components in the various embodiments of this specification, these components should not be limited by such terms. These terms are used merely to distinguish one component from another. Accordingly, what is referred to as the first component in one embodiment may be referred to as the second component in another embodiment. Each embodiment described and illustrated herein also includes its complementary embodiment. Furthermore, in this specification, "and / or" is used to mean including at least one of the components listed before and after it.

[0036] In the specification, singular expressions include plural expressions unless the context clearly indicates otherwise. Furthermore, terms such as "include" or "have" are intended to specify the existence of the features, numbers, steps, components, or combinations thereof described in the specification, and should not be understood as excluding the existence or addition of one or more other features, numbers, steps, components, or combinations thereof. Additionally, in this specification, "connection" is used to include both indirectly connecting multiple components and directly connecting them.

[0037] In addition, in describing the present invention below, if it is determined that a detailed description of related known functions or configurations could unnecessarily obscure the essence of the invention, such detailed description will be omitted.

[0039] Database construction method (S110, S120, S130, S140)

[0040] FIG. 1 is a flowchart for explaining steps S110 to S140 of a method for improving the imaging performance of an EUV lithography mask according to an embodiment of the present invention, FIG. 2 is a diagram for explaining a sample mask used in a method for improving the imaging performance of an EUV lithography mask according to an embodiment of the present invention, FIG. 3 is a diagram for explaining a phase difference value derived in step S120 of a method for improving the imaging performance of an EUV lithography mask according to an embodiment of the present invention, FIG. 4 is a diagram for explaining an image position difference value derived in step S130 of a method for improving the imaging performance of an EUV lithography mask according to an embodiment of the present invention, and FIG. 5 is a diagram for explaining a first aerial image and a second aerial image used to derive this position difference value.

[0041] Referring to FIG. 1, a method for improving the imaging performance of an EUV lithography mask according to an embodiment of the present invention may include the steps of irradiating EUV light onto a sample mask (S110), deriving a phase difference value (S120), deriving an image position difference value (S130), and building a database (S140). Additionally, after step S140, a step of improving mask imaging performance using a target absorption material (S200) and / or a step of improving mask imaging performance using a sub-absorption material (S300) may be performed. Steps S110 through S140 are described in detail below.

[0042] In step S110 above, EUV light may be irradiated onto the sample mask (SM). According to one embodiment, the sample mask (SM) may include a substrate (100), a reflective layer (200) disposed on the substrate (100) and comprising a Mo / Si multilayer thin film, a capping layer (300) disposed on the reflective layer (200) and comprising ruthenium (Ru), and a sample absorption pattern (400) disposed on the capping layer (300), as shown in FIG. 2.

[0043] According to one embodiment, the sample absorption pattern (400) may have a line and space pattern shape. That is, the sample absorption pattern (400) may be arranged such that line-shaped patterns extending in the same direction are spaced apart from each other in the line width (w) direction.

[0044] According to one embodiment, the EUV light may be irradiated onto the sample mask (SM) through a dipole illumination system. The EUV light irradiated onto the sample mask (SM) may be provided to a wafer coated with photoresist after being reflected and diffracted from the sample mask (SM).

[0045] In the above S120 step, the EUV light irradiated onto the sample mask (SM) is diffracted by the sample mask (SM) into a first diffracted light (DL1) and a second diffracted light (D L2 A phase difference value (PD) can be derived using ). According to one embodiment, the first diffracted light (DL1) and the second diffracted light (DL2) may have different orders. For example, the first diffracted light (DL1) may be a zero-order diffracted light. Alternatively, the second diffracted light (DL2) may be a +1st-order or -1st-order diffracted light.

[0046] As illustrated in FIG. 3, the first diffracted light (DL1) and the second diffracted light (DL2) may have different amplitude changes according to phase, and the phase difference value (PD) can be derived from this. More specifically, the phase difference value (PD) can be derived through the difference between the phase value at the maximum amplitude of the first diffracted light (DL1) and the phase value at the maximum amplitude of the second diffracted light (DL2). That is, the phase difference value (PD) can be defined as the difference between the phase value at the maximum amplitude of the first diffracted light (DL1) and the phase value at the maximum amplitude of the second diffracted light (DL2).

[0047] In the above S130 step, an image position difference value (IP) can be derived using a plurality of aerial images formed by interference between the first diffracted light (DL1) and the second diffracted light (DL2) at different positions.

[0048] Referring to FIGS. 4 and 5, a plurality of diffracted lights (LDL1, LDL2, RDL1, RDL2) that are irradiated onto the sample mask (SM) through a dipole illumination system and then diffracted can form a first aerial image at a first position (P1) and a second aerial image at a second position (P2). More specifically, at the first position (P1), a first light diffracted light (RDL1, 0th order) formed by a right dipole (RP) and a second left diffracted light (LDL2, -1st order) formed by a left dipole (LP) can be interfered to form a first aerial image. In contrast, at the second position (P2), the first left diffracted light (LDL1, 0th order) formed by the left dipole (LP) and the second light diffracted light (RDL2, +1st order) formed by the right dipole (RP) can be interfered to form a second aerial image.

[0049] As illustrated in FIG. 5, the first aerial image (P1) and the second aerial image (P2) may have different changes in intensity according to position (x position, nm), and the image position difference value (IP) can be derived from this. More specifically, the image position difference value (IP) can be derived through the difference between the position value at maximum intensity of the first aerial image (P1) and the position value at maximum intensity of the second aerial image (P2). That is, the image position difference value (IP) can be defined as the difference between the position value at maximum intensity of the first aerial image (P1) and the position value at maximum intensity of the second aerial image (P2).

[0050] The final image used to evaluate the imaging performance of the sample mask (SM) may be formed by the interference of the first aerial image (P1) and the second aerial image (P2). The imaging performance of the sample mask (SM) is evaluated by measuring the image contrast and NILS (Normalized Image Log Slope) values ​​from the final aerial image (the lower the image contrast and NILS values, the lower the imaging performance, and the higher the image contrast and NILS values, the higher the imaging performance). As the image position difference value (IP) increases, the image contrast and NILS values ​​measured from the final aerial image decrease (imaging performance decreases), and as the image position difference value (IP) decreases, the image contrast and NILS values ​​measured from the final aerial image increase (imaging performance improves).

[0051] In step S140 above, a database can be constructed in which the phase difference value (PD) and the image position difference value (IP) are stored for each of the plurality of sample masks (SM) containing different sample absorption patterns (400). According to one embodiment, the different sample absorption patterns (400) included in the plurality of sample masks (SM) may include patterns with different thicknesses (t). Additionally, according to one embodiment, the different sample absorption patterns (400) included in the plurality of sample masks (SM) may each include first and second absorption patterns spaced apart from each other, wherein the distance (d) between the first and second absorption patterns spaced apart from each other may be different. Additionally, according to one embodiment, the different sample absorption patterns (400) included in the plurality of sample masks (SM) may include refractive index (n) and extinction coefficient (k) which are different.

[0052] That is, in the above S140 step, the phase difference value (PD) and the image position difference value (IP) can be measured for each of a plurality of sample masks (SM) that differ in the thickness (t) of the sample absorption pattern (400), the distance (d) between the sample absorption patterns (400), the refractive index, and the extinction coefficient, and the database can be constructed.

[0054] Method for improving mask imaging performance using target absorption material (S200)

[0055] FIG. 6 is a flowchart for explaining step S200 of a method for improving the imaging performance of an EUV lithography mask according to an embodiment of the present invention, FIG. 7 to 10 are drawings for explaining examples of a process for deriving a target phase difference value in which the image position difference value is minimized in step S210, FIG. 11 and FIG. 12 are drawings for explaining target absorption materials selected through steps S220 and S230, and FIG. 13 is a drawing for explaining a first area image and a second area image of a target mask manufactured using the target absorption material.

[0056] Referring to FIG. 6, after the database is established in step S140, a target phase difference value can be derived from the database such that the image position difference value (IP) is minimized (close to 0) (S210). According to one embodiment, the target phase difference value can be derived from the image position difference value (IP, Image split, nm) according to the distribution of the phase difference value (PD, Phase delta, °).

[0057] For example, as shown in FIG. 7, for a sample mask where the distance between sample absorption patterns is 14 nm in a 0.33 NA exposure system, the target phase difference value where the image position difference value is minimized can be derived as approximately -28°. Alternatively, as another example, as shown in FIG. 8, for a sample mask where the distance between sample absorption patterns is 15 nm in a 0.33 NA exposure system, the target phase difference value where the image position difference value is minimized can be derived as approximately -24°. Alternatively, as yet another example, as shown in FIG. 9, for a sample mask where the distance between sample absorption patterns is 16 nm in a 0.33 NA exposure system, the target phase difference value where the image position difference value is minimized can be derived as approximately -21°. In contrast, as another example, as shown in FIG. 10, for a sample mask in a 0.55 NA exposure system where the distance between sample absorption patterns is 12 nm, the target phase difference value in which the image position difference value is minimized can be derived as approximately -36°.

[0058] After the target phase difference value is derived through the above step S210, a target refractive index and a target extinction coefficient having the target phase difference value can be derived from the database (S220), and a target absorbing material having the target refractive index and the target extinction coefficient can be selected (S230). As shown in FIGS. 11 and 12, the target absorbing material (Phase shift optimization) can be selected differently depending on the thickness of the sample absorption pattern (400). In addition, according to one embodiment, the target absorbing material may be composed of a single elemental material or a compound of different elements.

[0059] After the above step S230, a target mask can be manufactured using the target absorption material. More specifically, a target mask can be manufactured by forming a reflective layer on a substrate, forming a capping layer on the reflective layer, and then forming a target absorption pattern containing the target absorption material on the capping layer. As shown in FIG. 13, the first aerial image (P1) and the second aerial image (P2) formed through the target mask can have their image position difference value (IP) minimized, thereby improving imaging performance.

[0060] That is, the present invention can maximize the imaging performance of an EUV lithography mask by providing a method for selecting a material that can be used as an absorption pattern for an EUV lithography mask and a method for reducing thickness compared to a conventional tantalum (Ta)-based absorption pattern.

[0061] Figure 14 is a simulation result comparing the trends of phase difference values, image position difference values, and NILS values ​​according to thickness and refractive index conditions of an absorption pattern with an extinction coefficient of 0.01; Figure 15 is a simulation result comparing the trends of phase difference values, image position difference values, and NILS values ​​according to thickness and refractive index conditions of an absorption pattern with an extinction coefficient of 0.03; Figure 16 is a simulation result comparing the trends of phase difference values, image position difference values, and NILS values ​​according to thickness and refractive index conditions of an absorption pattern with an extinction coefficient of 0.05; Figure 17 is a simulation result comparing the trends of phase difference values, image position difference values, and NILS values ​​according to thickness and refractive index conditions of an absorption pattern with an extinction coefficient of 0.07; and Figure 18 is a comparison of the trends of phase difference values, image position difference values, and NILS values ​​according to thickness and refractive index conditions of an absorption pattern with an extinction coefficient of 0.05 with a 0.33NA exposure system and a 0.55NA exposure This is the simulation result compared in the system.

[0062] As can be seen in FIGS. 14 to 17, depending on the optical constant and thickness conditions of each absorption pattern, the image split value is mitigated in the region where the phase delta value has a specific value, and the NILS value, which is the imaging performance, is also high. In addition, as can be seen in FIG. 18, a similar trend is observed not only in the 0.33NA system but also in the 0.55NA exposure system.

[0064] Method for improving mask imaging performance using sub-absorbing material (S300)

[0065] FIG. 19 is a flowchart illustrating step S300 of a method for improving the imaging performance of an EUV lithography mask according to an embodiment of the present invention.

[0066] Referring to FIGS. 1 and FIGS. 19, after the database is established in step S140, a sub-phase difference value different from the target phase difference value at which the image position difference value is minimized can be derived from the database (S310). According to one embodiment, the sub-phase difference value can be derived from the image position difference value (IP, Image split, nm) according to the distribution of the phase difference value (PD, Phase delta, °). That is, in step S300, mask imaging performance can be improved by using the sub-phase difference value instead of the target phase difference value. Accordingly, the range of types of absorption materials, which was limited by step S200 alone, can be further expanded.

[0067] More specifically, after the sub-phase difference value is derived through the above step S310, a sub-refractive index and a sub-extinction coefficient having the sub-phase difference value can be derived from the database (S320), a sub-absorbing material having the sub-refractive index and the sub-extinction coefficient can be selected (S330), and a sub-mask can be manufactured using the sub-absorbing material (S340).

[0068] However, in step S340 above, the submask is manufactured by forming a sub-absorption pattern with the sub-absorption material, and the line width (w) of the sub-absorption pattern can be controlled so that the sub-phase difference value derived from the submask becomes equal to the target phase difference value.

[0069] According to one embodiment, the method for controlling the linewidth of the sub-absorption pattern may vary depending on the type of sub-mask in which the position of the photoresist pattern formed on the wafer by EUV light reflected and diffracted from the sub-mask changes.

[0070] For example, when using the submask formed such that the position of the photoresist pattern formed on the wafer by EUV light reflected and diffracted from the submask corresponds to the position of the sub-absorption pattern of the submask, the linewidth of the sub-absorption pattern can be controlled to narrow so that the sub-phase difference value derived from the submask becomes equal to the target phase difference value.

[0071] In contrast, when using the submask formed such that the position of the photoresist pattern formed on the wafer by EUV light reflected and diffracted from the submask corresponds to the position of the reflection layer exposed between the sub-absorption patterns of the submask, the linewidth of the sub-absorption pattern can be controlled to widen so that the sub-phase difference value derived from the submask is equal to the target phase difference value.

[0072] With reference to FIGS. 20 to 24, a case in which a submask (dark field mask) is used such that the position of the photoresist pattern formed on the wafer by EUV light reflected and diffracted from the submask corresponds to the position of the sub-absorption pattern of the submask is described in more detail, and with reference to FIGS. 25 to 29, a case in which a submask (bright field mask) is used such that the position of the photoresist pattern formed on the wafer by EUV light reflected and diffracted from the submask corresponds to the position of the reflection layer exposed between the sub-absorption patterns of the submask is described in more detail.

[0073] FIG. 20 is a diagram illustrating the process of forming a photoresist pattern when a dark field mask is used as a sub-mask; FIG. 21 is a simulation result comparing the trends of phase difference values ​​(a), image position difference values ​​(b), and NILS values ​​(c) according to the conditions of the thickness, refractive index, and linewidth (mask bias) of an absorption pattern with an extinction coefficient of 0.01 in a dark field tone; FIG. 22 is a simulation result comparing the trends of phase difference values ​​(a), image position difference values ​​(b), and NILS values ​​(c) according to the conditions of the thickness, refractive index, and linewidth (mask bias) of an absorption pattern with an extinction coefficient of 0.03 in a dark field tone; FIG. 23 is a simulation result comparing the trends of phase difference values ​​(a), image position difference values ​​(b), and NILS values ​​(c) according to the conditions of the thickness, refractive index, and linewidth (mask bias) of an absorption pattern with an extinction coefficient of 0.05 in a dark field tone; and FIG. 24 is a dark field This is a simulation result comparing the trends of phase difference values ​​(a), image position difference values ​​(b), and NILS values ​​(c) according to the conditions of the thickness, refractive index, and linewidth (Mask bias) of the absorption pattern with an extinction coefficient of 0.07 in tone.

[0074] Referring to FIG. 20, when a dark field mask is used as a submask (dark field tone), it can be seen that the position of the photoresist pattern (PP) formed on the wafer (WF) by EUV light reflected and diffracted from the submask (M) corresponds to the position of the sub-absorption pattern (400) of the submask (M).

[0075] Referring to FIGS. 21 to 24, the results of applying a -12 nm open mask bias to a +12 nm close mask bias are shown for cases where the thickness of the sub-absorption pattern (400) is 31 nm, 36 nm, and 37 nm. A -12 nm open mask bias means that the linewidth of the sub-absorption pattern (400) is -12 nm narrower from the reference linewidth, and a +12 nm close mask bias means that the linewidth of the sub-absorption pattern (400) is +12 nm wider from the reference linewidth, and the reference linewidth means the linewidth of the sub-absorption pattern (400) before the linewidth is changed.

[0076] As can be seen in FIGS. 21 to 24, a specific linewidth change (Mask bias) occurs according to the thickness and optical constant conditions of the sub-absorption pattern (400), resulting in a specific phase difference value (phase delta), and it can be confirmed that the image position difference value (image split) is minimized in that region, thereby improving the NILS value. Specifically, when a mask bias of -2 nm to +4 nm is applied when k=0.01, -4 nm to +2 nm when k=0.03, -8 nm to 0 nm when k=0.05, and -10 nm to -2 nm when k=0.07, it can be confirmed that imaging performance is improved by minimizing the image position difference value (image split) along with the optimization of the phase difference value (phase delta).

[0077] That is, in the case of a dark field tone, it can be seen that the linewidth of the sub-absorption pattern is controlled to narrow as the extinction coefficient k increases, so that the sub-phase difference value derived from the sub-mask becomes equal to the target phase difference value.

[0078] FIG. 25 is a diagram illustrating the process of forming a photoresist pattern when a bright field mask is used as a sub-mask; FIG. 26 is a simulation result comparing the trends of phase difference values ​​(a), image position difference values ​​(b), and NILS values ​​(c) according to the conditions of thickness, refractive index, and linewidth (mask bias) of an absorption pattern with an extinction coefficient of 0.01 in a bright field tone; FIG. 27 is a simulation result comparing the trends of phase difference values ​​(a), image position difference values ​​(b), and NILS values ​​(c) according to the conditions of thickness, refractive index, and linewidth (mask bias) of an absorption pattern with an extinction coefficient of 0.03 in a bright field tone; FIG. 28 is a simulation result comparing the trends of phase difference values ​​(a), image position difference values ​​(b), and NILS values ​​(c) according to the conditions of thickness, refractive index, and linewidth (mask bias) of an absorption pattern with an extinction coefficient of 0.05 in a bright field tone; and FIG. 29 is a bright field This is a simulation result comparing the trends of phase difference values ​​(a), image position difference values ​​(b), and NILS values ​​(c) according to the conditions of the thickness, refractive index, and linewidth (Mask bias) of the absorption pattern with an extinction coefficient of 0.07 in tone.

[0079] Referring to FIG. 25, when a Bright field mask is used as a submask (Bright field tone), it can be seen that the position of the photoresist pattern (PP) formed on the wafer (WF) by EUV light reflected and diffracted from the submask (M) corresponds to the position of the reflection layer (200) exposed between the sub-absorption pattern (400) of the submask (M).

[0080] Referring to FIGS. 26 to 29, the results of applying a -12 nm open mask bias to a +12 nm close mask bias are shown for cases where the thickness of the sub-absorption pattern (400) is 31 nm, 36 nm, and 37 nm. A -12 nm open mask bias means that the linewidth of the sub-absorption pattern (400) is -12 nm narrower from the reference linewidth, and a +12 nm close mask bias means that the linewidth of the sub-absorption pattern (400) is +12 nm wider from the reference linewidth, and the reference linewidth means the linewidth of the sub-absorption pattern (400) before the linewidth is changed.

[0081] As can be seen in FIGS. 26 to 29, as a specific linewidth change (Mask bias) occurs according to the thickness and optical constant conditions of the sub-absorption pattern (400), a specific phase difference value (phase delta) is obtained, and it can be confirmed that the image position difference value (image split) is minimized in that region, thereby improving the NILS value. Specifically, when a mask bias of -4 nm to +2 nm is applied when k=0.01, -2 nm to +4 nm when k=0.03, -2 nm to +8 nm when k=0.05, and -2 nm to +12 nm when k=0.07, it can be confirmed that imaging performance is improved by minimizing the image position difference value (image split) along with the optimization of the phase difference value (phase delta).

[0082] That is, in the case of the Bright field tone, it can be seen that the linewidth of the sub-absorption pattern is controlled to widen as the extinction coefficient k increases, so that the sub-phase difference value derived from the sub-mask becomes equal to the target phase difference value.

[0083] Figure 30 is a diagram illustrating the range of absorbent materials expanded through the S300 step.

[0084] As can be seen in Fig. 30, in step S300, mask imaging performance can be improved by using the sub-phase difference value instead of the target phase difference value. Accordingly, the range of types of absorption materials, which was limited by step S200 alone, can be further expanded (from the blue area to the Phase shift optimization w / mask bias area).

[0086] Although the present invention has been described in detail using preferred embodiments, the scope of the invention is not limited to specific embodiments and should be interpreted by the appended claims. Furthermore, those skilled in the art will understand that many modifications and variations are possible without departing from the scope of the invention.

Claims

Claim 1 A step of irradiating EUV light onto a sample mask comprising a reflective layer, a capping layer disposed on the reflective layer, and a sample absorption pattern disposed on the capping layer; a step of deriving a phase difference value defined as the difference between the phase value at the maximum amplitude of a first diffracted light diffracted by the sample mask and the phase value at the maximum amplitude of a second diffracted light having a different order from the first diffracted light; a step of deriving an image position difference value defined as the difference between the position value at the maximum intensity of a first aerial image formed by the interference of the first diffracted light and the second diffracted light at a first position and the position value at the maximum intensity of a second aerial image formed by the interference of the first diffracted light and the second diffracted light at a second position; A method for improving the imaging performance of an EUV lithography mask, comprising the step of constructing a database in which the phase difference value and the image position difference value for each of a plurality of sample masks having different sample absorption patterns are stored, wherein the first diffracted light and the second diffracted light are defined as light diffracted by the EUV light reflected from the sample mask. Claim 2 A method for improving the imaging performance of an EUV lithography mask according to claim 1, wherein the different sample absorption patterns included in the plurality of sample masks include different pattern thicknesses. Claim 3 A method for improving the imaging performance of an EUV lithography mask according to claim 1, wherein the different sample absorption patterns included in the plurality of sample masks each include first and second absorption patterns spaced apart from each other, and the distance between the first and second absorption patterns spaced apart from each other is different. Claim 4 A method for improving the imaging performance of an EUV lithography mask according to claim 1, wherein the first and second absorption patterns have a line shape extending in the same direction. Claim 5 A method for improving the imaging performance of an EUV lithography mask according to claim 1, wherein the EUV light is irradiated onto the sample mask through a dipole illumination system. Claim 6 A method for improving the imaging performance of an EUV lithography mask according to claim 1, comprising: a step of constructing a database, a step of deriving a target phase difference value from the database in which the image position difference value is minimized; a step of deriving a target refractive index and a target extinction coefficient having the target phase difference value from the database; a step of selecting a target absorption material having the target refractive index and the target extinction coefficient; and a step of manufacturing a target mask using the target absorption material. Claim 7 In claim 6, the target absorption material comprises a single elemental material or a compound of different elements, a method for improving the imaging performance of an EUV lithography mask. Claim 8 A method for improving the imaging performance of an EUV lithography mask according to claim 6, wherein the step of manufacturing a target mask using the target absorption material comprises: forming a reflective layer on a substrate; forming a capping layer on the reflective layer; and forming a target absorption pattern including the target absorption material on the capping layer. Claim 9 A method for improving the imaging performance of an EUV lithography mask according to claim 1, comprising: a step of constructing a database, after which a sub-phase difference value different from a target phase difference value in which the image position difference value is minimized is derived from the database; a step of deriving a sub-refractive index and a sub-extinction coefficient having the sub-phase difference value from the database; a step of selecting a sub-absorbing material having the sub-refractive index and the sub-extinction coefficient; and a step of manufacturing a sub-mask by forming a sub-absorbing pattern with the sub-absorbing material on a reflective layer, wherein the line width of the sub-absorbing pattern is controlled so that the sub-phase difference value derived from the sub-mask becomes equal to the target phase difference value. Claim 10 A method for improving the imaging performance of an EUV lithography mask according to claim 9, wherein the method for controlling the linewidth of a sub-absorption pattern varies depending on the type of sub-mask, wherein the position of the photoresist pattern formed on a wafer by EUV light reflected and diffracted from the sub-mask varies. Claim 11 A method for improving the imaging performance of an EUV lithography mask according to claim 9, wherein when using a submask formed such that the position of a photoresist pattern formed on a wafer by EUV light reflected and diffracted from the submask corresponds to the position of the sub-absorption pattern of the submask, the method comprises controlling the linewidth of the sub-absorption pattern to be narrowed so that the sub-phase difference value derived from the submask becomes equal to the target phase difference value. Claim 12 A method for improving the imaging performance of an EUV lithography mask according to claim 9, wherein, when using a submask formed such that the position of a photoresist pattern formed on a wafer by EUV light reflected and diffracted from the submask corresponds to the position of a reflection layer exposed between the sub-absorption patterns of the submask, the linewidth of the sub-absorption pattern is controlled to be widened so that the sub-phase difference value derived from the submask is equal to the target phase difference value. Claim 13 A light irradiation unit for irradiating EUV light onto a sample mask comprising a reflective layer, a capping layer disposed on the reflective layer, and a sample absorption pattern disposed on the capping layer; a phase difference value derivation unit for deriving a phase difference value defined as the difference between the phase value at the maximum amplitude of a first diffracted light diffracted by the sample mask and the phase value at the maximum amplitude of a second diffracted light having a different order from the first diffracted light; and an image position difference value derivation unit for deriving an image position difference value defined as the difference between the position value at the maximum intensity of a first aerial image formed by the interference of the first diffracted light and the second diffracted light at a first position and the position value at the maximum intensity of a second aerial image formed by the interference of the first diffracted light and the second diffracted light at a second position. An imaging performance enhancement system for an EUV lithography mask, comprising a database construction unit that constructs a database storing the phase difference value and the image position difference value for each of a plurality of sample masks having different sample absorption patterns, wherein the first diffracted light and the second diffracted light are defined as light diffracted by the EUV light reflected from the sample mask. Claim 14 An imaging performance enhancement system for an EUV lithography mask according to claim 13, further comprising a target absorption material selection unit that derives a target phase difference value from the database in which the image position difference value is minimized, derives a target refractive index and a target extinction coefficient having the target phase difference value, and selects a target absorption material having the target refractive index and the target extinction coefficient.

Images