Reflective mask, reflective mask blank, and method for manufacturing a reflective mask

Abstract

The present invention pertains to a reflection-type mask blank (10) obtained by forming, on a substrate (11) in the following order, a multilayer reflection film (12) for reflecting EUV light, a phase shift film (14) for shifting a phase of EUV light, and a semi-light shielding film (15) for providing shielding from EUV light. The reflection-type mask blank is characterized in that the reflectance is less than 7% at a wavelength of 13.5 nm when a surface of the semi-light shielding film is irradiated with EUV light, and that the reflectance is not less than 9% but less than 15% at a wavelength of 13.5 nm when a surface of the phase shift film is irradiated with EUV light.

Description

[Technical Field]

[0001] The present invention relates to a reflective mask used in an EUV (Etreme Ultra Violet) exposure process in semiconductor manufacturing, a reflective mask blank that is the original plate thereof, and a method for manufacturing a reflective mask. [Background technology]

[0002] Conventionally, ultraviolet light with a wavelength of 365 to 193 nm has been used as the light source for exposure equipment used in semiconductor manufacturing. The shorter the wavelength, the higher the resolution of the exposure equipment. Therefore, in recent years, exposure equipment using EUV light with a central wavelength of 13.53 nm as the light source has been put into practical use.

[0003] EUV light is easily absorbed by many materials, making it impossible to use refractive optics in exposure equipment, so reflective optics and reflective masks are used for EUV exposure.

[0004] In a reflective mask, a multilayer reflective film that reflects EUV light is formed on a substrate, and an absorber film that absorbs EUV light is formed in a pattern on the multilayer reflective film.

[0005] EUV light incident on a reflective mask is absorbed by the absorber film and reflected by the multilayer reflective film. The EUV light reflected by the multilayer reflective film passes through the reduced projection optical system of the exposure tool and is imaged onto the surface of the exposure material (a wafer coated with resist).

[0006] The absorber film is formed in a pattern on the multilayer reflective film, so that EUV light incident on the reflective mask from the reflective optical system of the exposure tool is reflected in areas where there is no absorber film (openings) and absorbed in areas where there is an absorber film (non-openings). As a result, the openings in the absorber film are transferred as a mask pattern onto the surface of the exposure material.

[0007] In EUV lithography, EUV light typically enters a reflective mask from a direction tilted at about 6° and is reflected in a direction tilted at about 6°.

[0008] The exposure area of the reflective mask is determined by a mask blade installed in the exposure tool. The mask blade is installed a few mm above the reflective mask so as not to come into contact with the reflective mask. The mask blade blocks light from reaching the non-exposure area of the reflective mask.

[0009] However, because there is a gap of several millimeters between the reflective mask and the mask blade, light diffraction occurs, causing light leakage from adjacent shots. To prevent light leakage from adjacent shots, the non-exposed area of the reflective mask, or at least the exposure frame area, must have a reflectance of less than 0.5% at a wavelength of 13.5 nm when EUV light is irradiated onto the surface (hereinafter sometimes referred to as "reflectance of EUV light" in this specification).

[0010] In order to reduce the reflectance of EUV light in the non-exposure region of the reflective mask to less than 0.5%, Patent Document 1 proposes a reflective mask shown in FIGS. 2(a) and 2(b). 2(a) and 2(b), a reflective mask 30 has a multilayer reflective film 32 that reflects EUV light, a protective film 33 for the multilayer reflective film 32, and an absorber film 36 that absorbs EUV light, formed in this order on a substrate 31. In an exposure region 100 of the reflective mask 30, the absorber film 36 is formed in a pattern. In a non-exposure region 200 of the reflective mask 30, a light-shielding film 37 is formed on the absorber film 36. However, to reduce the reflectance of the non-exposed region 200 to less than 0.5%, the total thickness of the absorber film 36 and the light-shielding film 37 needs to be 70 nm or more. Such a large film thickness makes it difficult to etch fine patterns inside the chip, and therefore this technology is not currently in practical use.

[0011] In order to reduce the reflectance of the exposure frame portion of the reflective mask to EUV light to less than 0.5%, Patent Document 1 proposes a reflective mask shown in FIGS. 3(a) and 3(b). The reflective mask 40 shown in FIGS. 3(a) and 3(b) includes a multilayer reflective film 42 that reflects EUV light, a protective film 43 for the multilayer reflective film 42, and an absorber film 46 that absorbs EUV light, which are formed in this order on a substrate 41. In the exposure region 100 of the reflective mask 40, the absorber film 46 is formed in a pattern. In the exposure frame region 300, located between the exposure region 100 and the non-exposure region 200 of the reflective mask 30, the multilayer reflective film 42, the protective film 43, and the absorber film 46 are removed by etching, exposing the surface of the substrate 41. Because the width of the exposure frame is as wide as several hundred μm, a thick resist can be used for etching until the surface of the substrate 41 is exposed. The reflectivity of the surface of the substrate 41 to EUV light is sufficiently low, less than 0.1%. Therefore, the exposure frame region 300 is almost completely shielded from light. For this reason, this technology is currently in practical use.

[0012] Conventionally, tantalum-based materials containing tantalum have been used for absorber films. Absorber films using tantalum-based materials are used under the conditions of binary reflective masks, and typically have a reflectance of 2% or less for EUV light.

[0013] In recent years, development of reflective masks utilizing the phase shift effect has progressed by adjusting the reflectivity of EUV light and the amount of phase shift of EUV light. By using reflective masks utilizing the phase shift effect, the contrast of the optical image on the wafer is improved, and the exposure margin is increased.

[0014] In the case of a transmissive phase-shift mask used in ultraviolet light exposure, the transmittance of the phase-shift film is high in order to obtain the phase-shift effect, and as with a reflective mask, overlapping light between adjacent shots becomes a problem. In the phase-shift mask of Patent Document 2, as in the reflective mask 30 shown in Figures 2(a) and (b), the exposure frame is covered with a light-shielding film to suppress overlapping light between adjacent shots.

[0015] In addition to the chips, the exposure area also contains scribe lines that cut the chips in the final process of semiconductor manufacturing. Alignment marks, as shown in Figure 4(a), and overlay marks, as shown in Figure 4(b), are located within the scribe lines. The alignment marks are used to align the exposure tool with the wafer, and the overlay marks are used to measure the overlay error between the lower layer pattern P2 and the upper layer pattern P1. The line width of these marks is on the order of several μm to several tens of μm, which is much larger than the fine patterns on the order of several tens of nm within the chip.

[0016] In a transmissive phase-shift mask, if the transmittance of the phase-shift film is increased to obtain a phase-shift effect, the side lobes of large patterns with wide line widths, such as alignment marks and overlay marks, become large, causing problems with transfer to the resist on the wafer.

[0017] To solve this problem, in a transmission type phase shift mask used with ultraviolet light, a light-shielding film is provided also on the alignment marks and overlay marks in the scribe line, as in the phase shift mask of Patent Document 3. [Prior art documents] [Patent documents]

[0018] [Patent Document 1] Japanese Patent Application Publication No. 2009-141223 [Patent Document 2] Japanese Patent Publication No. 6-282063 [Patent Document 3] Japanese Patent No. 2942816 Summary of the Invention [Problem to be solved by the invention]

[0019] Even in the case of reflective phase-shift masks used in EUV exposure, if the reflectivity of the phase-shift film to EUV light is increased to enhance the phase-shift effect, the side lobes of large patterns such as alignment marks and overlay marks within the scribe line will become larger, causing problems with transfer to the resist on the wafer.

[0020] However, in the case of a reflective phase-shift mask for EUV exposure, forming a pattern by etching becomes difficult when a thick light-shielding film 37 is formed on the scribe lines, as in the reflective mask 30 shown in Figures 2(a) and 2(b). Also, etching the areas to be shielded until the substrate surface is exposed, as in the reflective mask 40 shown in Figures 3(a) and 3(b), is difficult because of the presence of alignment marks and overlay marks within the scribe lines.

[0021] An object of the present invention is to provide a reflective mask blank, a reflective mask, and a method for manufacturing a reflective mask that can produce a reflective mask that can suppress the transfer of side lobes of a large pattern. [Means for solving the problem]

[0022] As a result of extensive research into solving the above problems, the present inventors have found that the above problems can be solved by the following configuration. [1] A reflective mask blank having a multilayer reflective film that reflects EUV light, a phase shift film that shifts the phase of EUV light, and a semi-light-shielding film that shields EUV light formed in this order on a substrate, the reflectance at a wavelength of 13.5 nm when the surface of the semi-light-shielding film is irradiated with EUV light is less than 7%, A reflective mask blank characterized in that the reflectance at a wavelength of 13.5 nm when the surface of the phase shift film is irradiated with EUV light is 9% or more and less than 15%. [2] The reflective mask blank according to [1], wherein the semi-light-shielding film has a thickness of 3 nm or more and 10 nm or less. [3] The reflective mask blank according to [1] or [2], wherein the phase shift amount of the phase shift film for EUV light is 210 degrees or more and 250 degrees or less. [4] The reflective mask blank according to any one of [1] to [3], wherein the phase shift film is made of a Ru-based material containing Ru. [5] The reflective mask blank according to any one of [1] to [4], wherein the semi-light-shielding film is made of a Cr-based material containing Cr or a Ta-based material containing Ta. [6] The reflective mask blank according to any one of [1] to [5], wherein the phase shift film has a thickness of 20 nm or more and 60 nm or less. [7] The reflective mask blank according to any one of [1] to [6], which has a protective film for the multilayer reflective film between the multilayer reflective film and the phase shift film. [8] A reflective mask in which a pattern having a chip region and a scribe line region is formed in the semi-light-shielding film and the phase shift film of the reflective mask blank according to any one of [1] to [7], a reflective mask, wherein the chip region of the pattern does not have the semi-light-shielding film on the phase shift film, and the scribe line region of the pattern has the semi-light-shielding film on the phase shift film. [9] The reflective mask according to [8], wherein the pattern has an exposure frame area, and the exposure frame area does not have the multilayer reflective film, the phase shift film, or the semi-light-shielding film, and the substrate surface is exposed.

[10] A method for manufacturing a reflective mask, comprising the steps of: forming a pattern having a chip region and a scribe line region in the semi-light-shielding film and the phase shift film of the reflective mask blank according to any one of [1] to [7]; removing the semi-light-shielding film in the chip region; and etching the semi-light-shielding film, the phase shift film, and the exposure frame region of the multilayer reflective film until the surface of the substrate is exposed. [Effects of the Invention]

[0023] The reflective mask of the present invention can suppress the transfer of side lobes of large patterns. According to the reflective mask blank and the method for manufacturing a reflective mask of the present invention, a reflective mask that can suppress the transfer of side lobes of large patterns can be manufactured. [Brief explanation of the drawings]

[0024] [Figure 1] FIG. 1 is a schematic cross-sectional view of one example of the configuration of a reflective mask blank of the present invention. [Figure 2] FIG. 2 shows an example of the structure of the reflective mask described in Patent Document 1, where FIG. 2(a) is a plan view and FIG. 2(b) is a schematic cross-sectional view. [Figure 3] FIG. 3 shows another example of the structure of the reflective mask described in Patent Document 1, where FIG. 3(a) is a plan view and FIG. 3(b) is a schematic cross-sectional view. [Figure 4] FIG. 4(a) is a diagram showing an example of the configuration of an alignment mark, and FIG. 4(b) is a diagram showing an example of the configuration of an overlay mark. [Figure 5] Figure 5 is a graph comparing phase shift films with different alloy ratios of Ru and Cr. Figure 5(a) is a graph showing the relationship between the film thickness of the phase shift film and the reflectance of EUV light, and Figure 5(b) is a graph showing the relationship between the film thickness of the phase shift film and the phase shift amount of EUV light. [Figure 6] FIG. 6 shows the mask pattern used in the exposure simulation. [Figure 7] FIG. 7 is a graph showing the relationship between the thickness of a phase shift film and the NILS for phase shift films having different alloy ratios of Ru and Cr. [Figure 8] FIG. 8 is a graph showing the relationship between the reflectance of EUV light and the maximum NILS. [Figure 9] FIG. 9 is a cross-sectional view of the light intensity on a wafer of a 22 nm dense hole pattern, which is a mask pattern used in the exposure simulation. [Figure 10] FIG. 10(a) is an enlarged view of the periphery of a corner of the pattern HP used in the exposure simulation, and FIG. 10(b) is a diagram showing the light intensity distribution on the wafer around the corner of the pattern HP. [Figure 11] FIG. 11 is a diagram showing the relationship between the reflectance of EUV light and the side lobe light intensity. [Figure 12]FIG. 12 is a graph showing the relationship between the thickness of a CrN film as a semi-light-shielding film provided on a 45 nm thick Ru80Cr20 alloy phase shift film and the reflectance of EUV light. [Figure 13] 13A and 13B are diagrams showing an example of the structure of a reflective mask of the present invention, with FIG. 13A being a plan view and FIG. 13B being a schematic cross-sectional view. [Figure 14] 14(a) to 14(f) are diagrams showing the manufacturing procedure of the reflective mask 20 shown in FIG. [Figure 15] FIG. 15 is a schematic cross-sectional view of the reflective mask blank of Example 1. [Figure 16] FIG. 16 is a diagram showing the relationship between the thickness of the TaON film and the reflectance of EUV light in Example 3. DETAILED DESCRIPTION OF THE INVENTION

[0025] To investigate the phase shift effect of the reflective mask, an alloy of Ru and Cr was used as the material for the phase shift film, and exposure simulations were performed in which the refractive index and absorption coefficient were changed by changing the alloy ratio of Ru and Cr. Table 1 shows the refractive index n and absorption coefficient k of Ru and Cr alloys. In the table, the numbers attached to Ru and Cr indicate the alloy ratio (atomic ratio). In the table, the Ru listed at the top is a Ru metal film, and the Cr listed at the bottom is a Cr metal film. Figure 5 is a graph comparing phase shift films with different Ru and Cr alloy ratios. Figure 5(a) is a graph showing the relationship between the phase shift film thickness and the reflectance of EUV light, and Figure 5(b) is a graph showing the relationship between the phase shift film thickness and the phase shift amount of EUV light. As shown in Figures 5(a) and 5(b), the reflectance of EUV light and the phase shift amount change significantly depending on the alloy ratio. Therefore, the phase shift effect also varies significantly depending on the alloy material used in the phase shift film.

[0026] [Table 1]

[0027] The optical conditions for the exposure simulation were annular illumination with NA 0.33 and σ 0.6 / 0.3. The mask pattern was a dense hole pattern (HP) with a CD (Critical Dimension) of 22 nm as shown in Figure 6. The results of the exposure simulation are shown in Figure 7. Figure 7 shows the relationship between the thickness of the phase shift film and NILS for phase shift films with different alloy ratios of Ru and Cr. NILS (Normalized Image Loss) The larger the Log Slope, the greater the phase shift effect. NILS depends on the thickness of the phase shift film, and the film thickness at which NILS is maximized varies depending on the alloy material used in the phase shift film.

[0028] Table 2 shows the maximum NILS values of phase shift films with different alloy ratios of Ru and Cr, as well as the film thickness, EUV light reflectivity, and phase shift amount at that time.

[0029] [Table 2]

[0030] In both cases, the phase shift amount for EUV light is 217 to 247 degrees, which is different from the optimal value of 180 degrees for the phase shift amount in ultraviolet light exposure. This is because the phase shift film used in the reflective mask for EUV exposure is thick, and the mask three-dimensional effect cannot be ignored. The mask three-dimensional effect refers to the effect that the three-dimensional structure of the phase shift film pattern has on the mask pattern projected onto the wafer.

[0031] Figure 8 shows the relationship between the reflectance of EUV light and the maximum NILS. As shown in Figure 8, the maximum NILS increases as the reflectance of EUV light increases. However, if the reflectance of EUV light becomes too high, the maximum NILS decreases. Figure 8 shows that the optimal reflectance of EUV light is greater than or equal to 9% and less than 15%.

[0032] We investigated whether side lobes occurring in large patterns within scribe lines would be transferred when the reflectivity of EUV light was 13%. The phase shift film material was a Ru80Cr20 alloy, with a film thickness of 45 nm. Figure 9 shows a cross-sectional view of the light intensity on a wafer for a 22 nm dense hole pattern (HP) present within a chip. The light intensity I when CD = 22 nm is 0.17, the light intensity I when 22 nm + 10% is 0.14, and the light intensity I when 22 nm + 20% is 0.11. The light intensity is a relative value where the intensity of the incident light is set to 1.

[0033] Within the scribe line, there are large patterns such as alignment marks (see Figure 4(a)) and overlay marks (see Figure 4(b)). Side lobes are most likely to occur at the corners of the large patterns, as shown in Figure 10(a). Note that Figure 10(a) shows the large pattern P1, an overlay pattern shown in Figure 4(b). Figure 10(b) shows the results of a simulation of the light intensity distribution on the wafer. Figure 10(b) shows the light intensity distribution on the wafer around the corner of pattern P1. Figure 10(b) also shows the areas where the light intensity I is greater than 0.17 and areas where the light intensity I is less than 0.17 when transferring a 22-nm hole pattern HP within a chip. Side lobes sl occur at the corners of the large patterns, where the light intensity I exceeds 0.17. These areas are transferred to the resist.

[0034] We investigated how much the reflectance should be reduced to prevent the side lobes of large patterns from being transferred. Figure 11 shows the relationship between the reflectance of EUV light and the side lobe intensity. In Figure 11, the side lobe intensity increases as the reflectance of EUV light increases. If the exposure dose margin is CD+20%, the reflectance must be less than 7% to suppress the side lobes.

[0035] In order to reduce the reflectance, the reflective mask 30 of Patent Document 1 shown in FIGS. 2(a) and 2(b) has a light-shielding film 37 provided on an absorber film 36. In this case, when EUV light is irradiated onto the surface of the light-shielding film 37, the reflectance at a wavelength of 13.5 nm is less than 0.5%. In this case, the total thickness of the absorber film 36 and the light-shielding film 37 needs to be 70 nm or more. With such a thick film, it is difficult to form a pattern by etching. In contrast, side lobe transfer of large patterns can be suppressed by keeping the reflectance of EUV light below 7%, so by providing a semi-light-shielding film on the phase shift film, it is possible to suppress side lobe transfer.

[0036] Figure 12 shows the relationship between the thickness of a CrN film and the reflectance of EUV light when a CrN film is provided as a semi-light-shielding film on a 45-nm-thick Ru80Cr20 alloy phase shift film. Figure 12 shows that a 4-nm-thick CrN film is sufficient to achieve an EUV reflectance of less than 7%. In this case, the total thickness of the phase shift film and semi-light-shielding film is 50 nm or less, allowing for easy patterning by etching.

[0037] As described above, the present inventors have found that the side lobes of a large pattern can be suppressed by setting the reflectance of EUV light to less than 7%. For this purpose, a semi-light-shielding film having a thickness of 10 nm or less may be formed on the phase shift film. Since the semi-light-shielding film is thin, it is easy to form a pattern by etching.

[0038] The reflective mask blank of the present invention and the reflective mask of the present invention will be described below with reference to the drawings.

[0039] Fig. 1 is a schematic cross-sectional view showing one example of the configuration of a reflective mask blank of the present invention. The reflective mask blank 10 shown in Fig. 1 has a multilayer reflective film 12 that reflects EUV light, a protective film 13 for the multilayer reflective film 12, a phase shift film 14 that shifts the phase of EUV light, and a semi-light-shielding film 15 that shields EUV light, formed in this order on a substrate 11. However, in the reflective mask blank of the present invention, of the configuration shown in Fig. 1, only the substrate 11, the multilayer reflective film 12, the phase shift film 14, and the semi-light-shielding film 15 are essential, and the protective film 13 is an optional component. The protective film 13 of the multilayer reflective film 12 is a layer provided for the purpose of protecting the multilayer reflective film 12 when the phase shift film 14 is patterned.

[0040] The individual components of the reflective mask blank 10 will now be described.

[0041] (substrate) The substrate 11 preferably has a small thermal expansion coefficient. A substrate with a small thermal expansion coefficient can prevent distortion of the pattern formed in the phase shift film due to heat generated during exposure to EUV light. Specifically, the thermal expansion coefficient of the substrate is 0±0.05×10 at 20°C. -7 / ℃ is preferred, 0±0.03×10 -7 / °C is more preferred.

[0042] As a material with a small thermal expansion coefficient, for example, SiO2-TiO2-based glass can be used. The SiO2-TiO2-based glass is preferably quartz glass containing 90 to 95 mass % of SiO2 and 5 to 10 mass % of TiO2. When the TiO2 content is 5 to 10 mass %, the temperature is low at around room temperature. The coefficient of linear expansion of SiO2-TiO2 is approximately zero, and there is almost no change in dimension at around room temperature. Note that the SiO2-TiO2-based glass may contain trace components other than SiO2 and TiO2.

[0043] The first main surface of the substrate 11, on which the multilayer reflective film 12 is to be laminated, preferably has high surface smoothness. The surface smoothness of the first main surface can be evaluated by surface roughness. The surface roughness of the first main surface is preferably 0.15 nm or less in terms of root-mean-square roughness Rq. The surface smoothness can be measured using an atomic force microscope. The first main surface is preferably surface-processed to a predetermined flatness. This is to ensure that the reflective mask achieves high pattern transfer accuracy and positional accuracy. In a predetermined area of the first main surface (e.g., a 132 mm × 132 mm area), the substrate preferably has a flatness of 100 nm or less, more preferably 50 nm or less, and even more preferably 30 nm or less.

[0044] Furthermore, the substrate 11 preferably has resistance to cleaning solutions used for cleaning reflective mask blanks and reflective masks after pattern formation. Furthermore, the substrate 11 preferably has high rigidity to prevent deformation due to film stress of films formed on the substrate (such as the multilayer reflective film 12 and the phase shift film 14). For example, the substrate 11 preferably has a high Young's modulus of 65 GPa or more.

[0045] (Multilayer reflective film) The multilayer reflective film 12 has high reflectivity for EUV light. Specifically, when EUV light is incident on the surface of the multilayer reflective film at an incident angle of 6°, the maximum reflectivity for EUV light is preferably 60% or more, more preferably 65% or more. Similarly, even when a protective film 13 is laminated on the multilayer reflective film 12, the maximum reflectivity for EUV light is preferably 60% or more, more preferably 65% or more.

[0046] The multilayer reflective film 12 is a multilayer film in which multiple layers each composed mainly of elements with different refractive indices are periodically stacked. Generally, the multilayer reflective film is formed by alternately stacking multiple high-refractive-index films that exhibit a high refractive index to EUV light and multiple low-refractive-index films that exhibit a low refractive index to EUV light from the substrate side. The multilayer reflective film 12 may be formed by laminating multiple periods, each period consisting of a high-refractive index film and a low-refractive index film stacked in this order from the substrate side, or may be formed by laminating multiple periods consisting of a low-refractive index film and a high-refractive index film stacked in this order. In this case, it is preferable that the outermost layer (top layer) of the multilayer reflective film be a high-refractive index film. Because low-refractive index films are easily oxidized, if a low-refractive index film is the top layer of the multilayer reflective film, the reflectance of the multilayer reflective film may decrease.

[0047] The high-refractive index film can be a film containing Si. Examples of materials containing Si include elemental Si and Si compounds containing one or more elements selected from the group consisting of B, C, N, and O. The use of a high-refractive index film containing Si enables the production of a reflective mask with excellent reflectivity for EUV light. The low-refractive index film can be a metal selected from the group consisting of Mo, Ru, Rh, and Pt, or an alloy thereof. In the reflective mask blank of the present invention, it is preferable that the low-refractive index film is a Mo layer and the high-refractive index film is a Si layer. In this case, by using a high-refractive index film (Si film) as the top layer of the multilayer reflective film, a silicon oxide layer containing Si and O is formed between the top layer (Si film) and the protective film 13, thereby improving the cleaning resistance of the reflective mask blank.

[0048] The thickness and period of each layer constituting the multilayer reflective film 12 can be appropriately selected depending on the film material used, the EUV light reflectivity required of the multilayer reflective film 12, the wavelength of the EUV light (exposure wavelength), and other factors. For example, if the multilayer reflective film 12 is to have a maximum EUV light reflectivity of 60% or more, a Mo / Si multilayer reflective film is preferably used, in which low-refractive-index films (Mo layers) and high-refractive-index films (Si layers) are alternately stacked for 30 to 60 periods. To achieve high reflectivity, the thickness of one period of the Mo / Si multilayer film is preferably 6.0 nm or more, more preferably 6.5 nm or more. To achieve high reflectivity, the thickness of one period of the Mo / Si multilayer film is preferably 8.0 nm or less, more preferably 7.5 nm or less.

[0049] Each layer constituting the multilayer reflective film 12 can be deposited to a desired thickness using a known deposition method such as magnetron sputtering or ion beam sputtering. For example, when fabricating a multilayer reflective film using ion beam sputtering, ion particles are supplied from an ion source to a target of a high refractive index material and a target of a low refractive index material. When the multilayer reflective film 12 is a Mo / Si multilayer reflective film, for example, a Si layer with a predetermined thickness is first deposited on a substrate using ion beam sputtering, for example, using a Si target. Then, a Mo layer with a predetermined thickness is deposited using a Mo target. This Si layer and Mo layer constitute one cycle, and 30 to 60 cycles are stacked to form a Mo / Si multilayer reflective film.

[0050] (protective film) The protective film 13 protects the multilayer reflective film by suppressing damage to the surface of the multilayer reflective film 12 caused by etching (usually dry etching) the phase shift film 14 to form a pattern during the manufacture of the reflective mask described below. The protective film 13 also protects the multilayer reflective film from the cleaning solution when the resist film remaining on the reflective mask after etching is removed with a cleaning solution to clean the reflective mask. Therefore, the resulting reflective mask has good reflectivity for EUV light. Although FIG. 1 shows a case where the protective film 13 is a single layer, the protective film may be a multi-layer film.

[0051] The material for forming the protective film 13 is selected from those that are resistant to etching damage when the phase shift film 14 is etched. Examples of materials that satisfy this condition include Ru metal alone, Ru alloys containing one or more metals selected from the group consisting of Si, Ti, Nb, Rh, Ta, and Zr in Ru, and Ru-based materials such as nitrides of Ru alloys containing nitrogen; Cr, Al, and Ta metal alone, and nitrides of these metals containing nitrogen; SiO2, Si3N4, Al2O3, and mixtures thereof. Among these, Ru metal Ru metal and its alloys, CrN and SiO2 are preferred. It is particularly preferable because it is difficult to etch with a gas that does not contain oxygen and functions as an etching stopper when etching the phase shift film 14 .

[0052] When the protective film 13 is made of a Ru alloy, the Ru content in the Ru alloy is preferably 30 at % or more and less than 100 at %. If the Ru content is within the above range, when the multilayer reflective film 12 is a Mo / Si multilayer reflective film, diffusion of Si from the Si film of the multilayer reflective film 12 into the protective film 13 can be suppressed. Furthermore, the protective film 13 functions as an etching stopper when etching the phase shift film 14 while ensuring sufficient reflectivity for EUV light. Furthermore, the cleaning resistance of the reflective mask can be improved and deterioration of the multilayer reflective film 12 over time can be prevented.

[0053] The thickness of the protective film 13 is not particularly limited as long as it can function as the protective film 13. In order to maintain the reflectance of EUV light reflected by the multilayer reflective film 12, the thickness of the protective film 13 is preferably 1 to 8 nm, more preferably 1.5 to 6 nm, and even more preferably 2 to 5 nm.

[0054] (Phase shift film) The use of phase shift film 14 improves the contrast of the optical image on the wafer and increases the exposure margin. This effect depends on the reflectance of EUV light, as shown in Figure 8, which shows the relationship between the reflectance of EUV light and the maximum NILS. To obtain a sufficient phase shift effect, the reflectance of phase shift film 14 to EUV light should be 9% or more and less than 15%, and preferably 9% or more and 13% or less. Furthermore, the phase shift film 14 preferably has a phase shift amount of EUV light of 210 degrees or more and 250 degrees or less, and more preferably 220 degrees or more and 240 degrees or less.

[0055] In addition to the above characteristics, the phase shift film 14 must have other desirable properties, such as ease of etching and high cleaning resistance against cleaning solutions. Preferred materials for the phase shift film 14 include Ru-based materials such as Ru oxide, Ru oxynitride, Ru alloys containing Ru and one or more metals selected from the group consisting of Cr, Au, Pt, Re, Hf, Ti, and Si, and Ru alloy oxides containing oxygen, nitrides containing nitrogen, and oxynitrides containing oxygen and nitrogen. Ru alloys, particularly alloys with an atomic ratio of Ru to Cr of 60:40 to 80:20, are preferred because they have a large NILS and maximize the phase shift effect.

[0056] When the phase shift film 14 is formed from a Ru-based material, the inclusion of at least one of oxygen and nitrogen improves the oxidation resistance of the phase shift film 14, thereby improving stability over time. Furthermore, the inclusion of at least one of oxygen and nitrogen in the Ru-based material causes the phase shift film 14 to have an amorphous or microcrystalline structure. This improves the surface smoothness and flatness of the phase shift film 14. The improved surface smoothness and flatness of the phase shift film 14 reduces edge roughness of the phase shift film pattern, improving dimensional accuracy. Therefore, the material for forming the phase shift film 14 is preferably Ru oxide, Ru oxynitride, the above-mentioned Ru alloy containing oxygen, nitride containing nitrogen, or oxynitride containing oxygen and nitrogen, and Ru oxide is even more preferable.

[0057] The phase shift film 14 may be a single-layer film or a multilayer film made up of multiple films. When the phase shift film 14 is a single-layer film, the number of steps in mask blank manufacturing can be reduced, improving production efficiency. When the phase shift film 14 is a multilayer film, by appropriately setting the optical constants and film thicknesses of the upper layers of the phase shift film 14, it can be used as an anti-reflection film when inspecting the phase shift film pattern using inspection light. This improves inspection sensitivity when inspecting the phase shift film pattern. The thickness of the phase shift film 14 is preferably 20 nm or more and 60 nm or less. The optimum thickness varies depending on the refractive index of the phase shift film 14.

[0058] The phase shift film 14 can be formed by a known film formation method such as magnetron sputtering, ion beam sputtering, etc. For example, when a Ru oxide film is formed as the phase shift film by magnetron sputtering, the phase shift film can be formed by sputtering using a Ru target, Ar gas, and oxygen gas.

[0059] Phase shift film 14 made of a Ru-based material can be etched by dry etching using oxygen gas or a mixed gas of oxygen gas and a halogen-based gas (chlorine-based gas, fluorine-based gas) as an etching gas.

[0060] (semi-shielding film) Because the phase shift film 14 has a high reflectance, side lobes occur around the pattern in the light intensity distribution on the wafer during exposure. The light intensity of the side lobes increases as the pattern becomes larger, and the side lobes of the large pattern may be transferred to the resist on the wafer. In order to suppress the side lobes of the large pattern within the scribe line, it is effective to provide a semi-light-shielding film 15 in the scribe line area. In order to suppress the side lobes of the large pattern within the scribe line from being transferred to the resist, it is preferable that the semi-light-shielding film 15 have a reflectance of EUV light of less than 7%. Unlike the light-shielding film 37 of Patent Document 1, the semi-light-shielding film 15 does not need to block EUV light to a reflectance of less than 0.5%, and it is sufficient if it can block EUV light to a reflectance of less than 7%.

[0061] The semi-light-shielding film 15 is required to be easily patterned by etching. Therefore, it is preferable that the film thickness of the semi-light-shielding film 15 is as thin as possible as long as the reflectance of EUV light is less than 7%. The film thickness of the semi-light-shielding film 15 is preferably 10 nm or less, and more preferably 5 nm or less. In order to make the reflectance of EUV light less than 7%, the film thickness of the semi-light-shielding film 15 is preferably 3 nm or more.

[0062] When manufacturing a reflective mask, the semi-light-shielding film 15 on the phase shift film 14 must be removed by etching in the chip region of the reflective mask to obtain a phase shift effect. During this etching, it is required that the phase shift film 14 is not easily affected.

[0063] The semi-light-shielding film 15 can be formed from Cr-based materials such as Cr, CrO, CrN, and CrON, which satisfy the above conditions. These Cr-based materials can be easily removed by wet etching. For example, cerium ammonium nitrate can be used as an etching solution. When the material forming the semi-light-shielding film 15 is a Cr-based material, containing at least one of oxygen and nitrogen can improve the oxidation resistance of the semi-light-shielding film 15, thereby improving stability over time. Furthermore, when the Cr-based material contains at least one of oxygen and nitrogen, the crystalline state of the semi-light-shielding film 15 becomes an amorphous or microcrystalline structure. This improves the surface smoothness and flatness of the semi-light-shielding film 15. The improved surface smoothness and flatness of the semi-light-shielding film 15 reduces the edge roughness of the semi-light-shielding film pattern, improving dimensional accuracy. Therefore, when the semi-light-shielding film 15 is made of a Cr-based material, CrO, CrN, and CrON are preferable. Furthermore, Ta-based compounds such as Ta, TaO, TaN, and TaON can be used for the semi-light-shielding film 15. These Ta-based materials can be easily removed by dry etching using a fluorine-based gas as an etching gas. When the material forming the semi-light-shielding film 15 is a Ta-based material, containing at least one of oxygen and nitrogen can improve the oxidation resistance of the semi-light-shielding film 15, thereby improving stability over time. Furthermore, when the Ta-based material contains at least one of oxygen and nitrogen, the semi-light-shielding film 15 has an amorphous or microcrystalline structure. This improves the surface smoothness and flatness of the semi-light-shielding film 15. The improved surface smoothness and flatness of the semi-light-shielding film 15 reduces the edge roughness of the semi-light-shielding film pattern and improves dimensional accuracy. Therefore, when the material for forming the semi-light-shielding film 15 is a Ta-based material, TaO, TaN, or TaON is preferable.

[0064] The reflective mask blank 10 of the present invention may have, in addition to the multilayer reflective film 12, the protective film 13, the phase shift film 14, and the semi-light-shielding film 15, a functional film known in the field of EUV mask blanks.

[0065] (Backside conductive film) The reflective mask blank 10 of the present invention may be provided with a back surface conductive film for electrostatic chucking on the second main surface of the substrate 11 opposite to the side on which the multilayer reflective film 12 is laminated. The back surface conductive film is required to have a low sheet resistance as a characteristic. The sheet resistance of the back surface conductive film is preferably, for example, 200 Ω / □ or less.

[0066] The backside conductive film may be made of a metal such as Cr or Ta, or an alloy or compound containing at least one of Cr and Ta. Examples of Cr-containing compounds include Cr-based materials containing Cr and one or more elements selected from the group consisting of B, N, O, and C. Examples of Cr-based materials include CrN, CrON, CrCN, CrCON, CrBN, CrBON, CrBCN, and CrBOCN. Examples of Ta-containing compounds include Ta-based materials containing Ta and one or more elements selected from the group consisting of B, N, O, and C. Examples of Ta-based materials include TaB, TaN, TaO, TaON, TaCON, TaBN, TaBO, TaBON, TaBCON, TaHf, TaHfO, TaHfN, TaHfON, TaHfCON, TaSi, TaSiO, TaSiN, TaSiON, and TaSiCON.

[0067] The thickness of the back surface conductive film is not particularly limited as long as it satisfies the function of the electrostatic chuck, but is, for example, 10 to 400 nm. This back surface conductive film can also adjust the stress on the second main surface side of the reflective mask blank. That is, the back surface conductive film can be adjusted to balance the stress from various layers formed on the first main surface side and flatten the reflective mask blank.

[0068] <Reflective mask> Next, we will explain a reflective mask obtained using the above-mentioned reflective mask blank shown in Fig. 1. Fig. 13 shows an example of the configuration of a reflective mask of the present invention, with Fig. 13(a) being a plan view and Fig. 13(b) being a schematic cross-sectional view. In the exposure frame region 300 of the reflective mask 20, the multilayer reflective film 12, the protective film 13, the phase shift film 14, and the semi-light-shielding film 15 are removed to expose the surface of the substrate 11. This almost completely suppresses the overlay light from adjacent shots.

[0069] The exposure area 100 of the reflective mask 20 has a chip C area and a scribe line S area. The semi-light-shielding film 15 is removed above the chip C area, exposing the phase shift film 14. As a result, for the fine pattern of the chip C area, the contrast of the optical image is improved due to the phase shift effect, and the exposure margin is increased. The scribe line S region has a semi-light-shielding film 15. Therefore, the light intensity of the side lobes for the large pattern within the scribe line is reduced, and transfer to the resist is suppressed.

[0070] <Method of manufacturing a reflective mask> An example of a method for manufacturing the reflective mask 20 of Fig. 13 will be described below. Fig. 14(a) to Fig. 14(f) are diagrams showing the manufacturing procedure for the reflective mask 20. First, as shown in FIG. 14(a), a resist film is applied onto a reflective mask blank 10, exposed to light, and developed to form a resist 60 pattern corresponding to the fine pattern of the chip C region and the pattern of the scribe line S region. Next, as shown in Fig. 14(b), the semi-light-shielding film 15 and the phase shift film 14 are dry-etched using the resist pattern as a mask to form a pattern of the semi-light-shielding film 15 and a pattern of the phase shift film 14. Note that the resist pattern has been removed in Fig. 14(b). Next, as shown in FIG. 14(c), a resist film is applied onto the reflective mask blank, and is exposed and developed to form a resist 60 pattern corresponding to the scribe line region. Thereafter, as shown in FIG. 14(d), the semi-light-shielding film 15 in the chip area is removed by wet etching or dry etching using the resist pattern as a mask. Next, as shown in FIG. 14(e), a resist film is applied onto the reflective mask blank, and then exposed. The resist 60 is patterned by exposure to light and development to form a pattern corresponding to the area other than the exposure frame area. Then, as shown in Figure 14(f), the exposure frame area 300 is dry-etched using the resist pattern as a mask until the surface of the substrate 11 is exposed. In this way, the reflective mask 20 shown in Figure 13 can be manufactured. [Example]

[0071] The present invention will be described in more detail below using examples, but the present invention is not limited to these examples. Among examples 1 to 4, example 1 is a comparative example, and examples 2 to 4 are working examples.

[0072] <Example 1> In Example 1, a reflective mask blank 50 shown in FIG. 15 was produced. A SiO2-TiO2 glass substrate (approximately 152 mm square and approximately 6.3 mm thick) was used as the substrate 11 for film formation. The thermal expansion coefficient of the glass substrate was 0.02 × 10 -7The temperature was 100°C. The glass substrate was polished to a smooth surface with a root-mean-square roughness (Rq) of 0.15 nm or less and a flatness of 100 nm or less. A 100-nm-thick Cr layer was deposited on the rear surface of the glass substrate using magnetron sputtering to form a rear conductive film for an electrostatic chuck. The sheet resistance of the Cr layer was approximately 100 Ω / □. After the glass substrate was fixed using the Cr film, 40 cycles of alternately depositing Si and Mo films on the surface of the glass substrate using ion beam sputtering were performed. The Si film had a thickness of approximately 4.5 nm, and the Mo film had a thickness of approximately 2.3 nm. This resulted in a multilayer reflective film 12 with a total thickness of approximately 272 nm ((Si film: 4.5 nm + Mo film: 2.3 nm) × 40). Thereafter, a Ru layer (thickness: about 2.5 nm) was formed on the multilayer reflective film 12 by ion beam sputtering, thereby forming the protective film 13. Next, a phase shift film 14 made of a RuCr film was formed on the protective film 13 by magnetron sputtering. Ar gas was used as the sputtering gas. Two types of targets, Ru and Cr, were used for sputtering. By adjusting the input power to the Ru target and the input power to the Cr target, a film with a Ru:Cr atomic ratio of 80:20 was formed with a thickness of 45 nm. The phase shift film 14 had a reflectance of 13% for EUV light. The film thickness was measured by X-ray reflectometry (XRR) using an X-ray diffractometer. The reflectivity was measured using an EUV reflectometer for mask blanks. 15 does not have a semi-light-shielding film. Therefore, when a reflective mask is produced using the reflective mask blank 50, side lobes are transferred from large patterns such as alignment marks within the scribe lines during exposure.

[0073] <Example 2> In Example 2, a reflective mask blank 10 shown in FIG. 1 was produced. The same procedures as in Example 1 were followed up to the formation of the phase shift film 14. A semi-light-shielding film 15 made of a CrN film was formed on the phase shift film 14 by magnetron sputtering. A mixed gas of Ar gas and nitrogen gas was used as the sputtering gas. A Cr target was used for sputtering. A 4 nm thick CrN film was formed. The semi-light-shielding film 15 had a reflectance of 6% for EUV light. When the reflective mask blank 10 is used to fabricate the reflective mask 20 shown in FIG. 13, the scribe line S region has a semi-light-shielding film 15, which prevents side lobes from being transferred during exposure.

[0074] <Example 3> In Example 3, a reflective mask blank 10 shown in FIG. 1 was produced. In Example 3, a RuO2 film was used as the phase shift film 14, and a TaON film was used as the semi-light-shielding film 15. The thickness of the TaON film and Figure 16 shows the results of a simulation of the relationship with the reflectance of EUV light. The same procedures as in Example 1 were carried out up to the formation of the protective film 13. The phase shift film 14 was formed by magnetron sputtering. A mixture of Ar gas and oxygen gas was used as the sputtering gas. A Ru target was used for sputtering. A RuO2 film was formed as the phase shift film 14 to a thickness of 52 nm. The phase shift film 14 was formed by E The reflectance of UV light was 9%. A semi-light-shielding film 15 made of a TaON film was formed on the phase shift film 14 by magnetron sputtering. A mixture of Ar gas, oxygen gas, and nitrogen gas was used as the sputtering gas. A Ta target was used for sputtering. A TaON film with a thickness of 3 nm was formed as the semi-light-shielding film 15. The semi-light-shielding film 15 had a reflectance of 5% for EUV light. When the reflective mask blank 10 is used to fabricate the reflective mask 20 shown in FIG. 13, the scribe line S region has a semi-light-shielding film 15, which prevents side lobes from being transferred during exposure.

[0075] <Example 4> In Example 4, the reflective mask blank produced in Example 3 was used to produce the reflective mask shown in FIG. In Figure 13, the size of each chip C is 40 mm in the X direction and 32 mm in the Y direction. These dimensions are the values on the mask, and are reduced to 1 / 4 when transferred to the wafer, to 10 mm in the X direction and 8 mm in the Y direction. The width of the scribe line S is 200 μm on the mask (50 μm on the wafer). When eight chips C are arranged on the mask as shown in Figure 13, the size of the exposure area 100 including the scribe line S is 80.4 mm in the X direction and 128.8 mm in the Y direction (20.1 mm in the X direction and 32.2 mm in the Y direction on the wafer). A 1 mm wide exposure frame is placed outside the exposure area 100. The manufacturing procedure for the reflective mask was as shown in Figures 14(a) to 14(f). First, a resist was applied, and the fine patterns in the chip area and the patterns in the scribe lines were exposed using EB. After resist development, the resist 60 pattern was used as a mask to dry-etch the semi-light-shielding film 15 made of a TaON film and the phase shift film 14 made of a RuO2 film. Fluorine gas is used to etch N film, and a mixture of chlorine and oxygen gas is used to etch RuO2 film. After dry etching, the resist film was removed by ashing and cleaning. After that, resist was applied and the chip area was exposed. Because the exposure area was large, a laser exposure machine was used. After development, the resist 60 pattern exposed the entire chip area. The semi-light-shielding film 15 made of TaON film in the chip area was removed by dry etching using fluorine-based gas. Resist was applied again, and the exposure frame region 300 was exposed to laser light. Physical dry etching with increased bias power was used to etch the exposure frame region 300, removing even the multilayer reflective film and exposing the substrate surface. In this way, the reflective mask 20 shown in FIG. 13 was obtained.

[0076] Although the present invention has been described in detail and with reference to specific embodiments, it will be apparent to those skilled in the art that various changes and modifications can be made without departing from the spirit and scope of the invention. This application is based on Japanese Patent Application No. 2020-148984 filed on September 4, 2020, the contents of which are incorporated herein by reference. [Explanation of symbols]

[0077] 10: EUV mask blank 11: Circuit board 12: Multilayer reflective film 13:Protective film 14: Phase shift film 15: Semi-shading film 20: EUV mask 30: EUV mask 31: Circuit board 32: Multilayer reflective film 33:Protective film 36: Absorber membrane 37: Light-shielding film 100: Exposure area 200:Outside exposure area 40: EUV mask 41: Circuit board 42: Multilayer reflective film 43:Protective film 46: Absorber membrane 60: Resist 100: Exposure area 200:Outside exposure area 300: Exposure frame area C: Chip P1: Upper layer pattern P2: Lower layer pattern HP: Hole pattern sl: side lobe S: Scribe line

Claims

1. A reflective mask blank comprising a substrate on which a multilayer reflective film that reflects EUV light, a phase shift film that shifts the phase of the EUV light, and a semi-light-shielding film that shields the EUV light are formed in this order, the reflectance at a wavelength of 13.5 nm when the surface of the semi-light-shielding film is irradiated with EUV light is less than 7%, the reflectance at a wavelength of 13.5 nm when the surface of the phase shift film is irradiated with EUV light is 9% or more and less than 15%, the phase shift amount of the phase shift film for EUV light is 210 degrees or more and 250 degrees or less, the phase shift film is made of a Ru-based material containing Ru, The reflective mask blank, wherein the semi-light-shielding film is made of a Cr-based material containing Cr or a Ta-based material containing Ta.

2. 2. The reflective mask blank according to claim 1, wherein the semi-light-shielding film has a thickness of 3 nm or more and 10 nm or less.

3. 3. The reflective mask blank according to claim 1, wherein the phase shift film has a thickness of 20 nm or more and 60 nm or less.

4. 4. The reflective mask blank according to claim 1, further comprising a protective film for the multilayer reflective film between the multilayer reflective film and the phase shift film.

5. A reflective mask in which a pattern having a chip region and a scribe line region is formed in the semi-light-shielding film and the phase shift film of the reflective mask blank according to any one of claims 1 to 4, a reflective mask, wherein the chip region of the pattern does not have the semi-light-shielding film on the phase shift film, and the scribe line region of the pattern has the semi-light-shielding film on the phase shift film.

6. 6. The reflective mask according to claim 5, wherein the pattern has an exposure frame area, the exposure frame area does not have the multilayer reflective film, the phase shift film, or the semi-light-shielding film, and the substrate surface is exposed.

7. 5. A method for manufacturing a reflective mask, comprising the steps of: forming a pattern having a chip region and a scribe line region in the semi-light-shielding film and the phase shift film of the reflective mask blank according to any one of claims 1 to 4; removing the semi-light-shielding film in the chip region; and etching the semi-light-shielding film, the phase shift film, and an exposure frame region of the multilayer reflective film until the surface of the substrate is exposed.

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