TW201921085A - Reflective mask blank, reflective mask, and process for producing reflective mask blank - Google Patents

Abstract

A reflective mask blank includes, on/above a substrate in the following order from the substrate side, a reflective layer which reflects EUV light, and an absorber layer which absorbs EUV light. The absorber layer contains Sn as a main component and Ta in an amount of 25 at % or more.

Description

Reflective reticle base, reflective reticle, and reflective reticle substrate manufacturing method

The present invention relates to a method of manufacturing a reflective reticle substrate, a reflective reticle, and a reflective reticle substrate.

In recent years, with the miniaturization of integrated circuits constituting semiconductor elements, ultra-violet light (Etreme Ultra Violet: hereinafter referred to as "EUV") lithography has been studied instead of using visible light or ultraviolet light (wavelength 365 to 193 nm) or An exposure method of a prior exposure technique such as ArF (argon fluoride) excimer laser light (wavelength 193 nm).

In EUV lithography, EUV light of a shorter wavelength than ArF excimer laser light is used as a light source for exposure. In addition, the EUV light refers to light of a wavelength of a soft X-ray region or a vacuum ultraviolet region, and specifically, light having a wavelength of about 0.2 to 100 nm. As the EUV light, for example, EUV light having a wavelength of about 13.5 nm is used.

Since EUV light is easily absorbed for most substances, the refractive optical system used in the prior exposure technique cannot be used. Therefore, a reflective optical system including a reflective mask or a mirror is used in the EUV lithography. In EUV lithography, a reflective reticle is used as a mask for pattern transfer.

The reflective reticle is formed with a reflective layer that reflects EUV light on the substrate, and an absorbing layer that absorbs EUV light is formed in a pattern on the reflective layer. The reflective reticle is obtained by using a reflective reticle substrate formed by sequentially laminating a reflective layer and an absorbing layer on a substrate as an original plate, and partially removing the absorbing layer to form a specific pattern. Wash with a cleaning solution.

The EUV light incident on the reflective mask is absorbed in the absorption layer and reflected on the reflective layer. The reflected EUV light is imaged by the optical system on the surface of the exposed material (the wafer coated with the resist). Thereby, the pattern of the absorbing layer is transferred to the surface of the exposed material.

In EUV lithography, EUV light is typically incident on the reflective reticle from a tilt of about 6° and is also reflected obliquely. Therefore, if the film thickness of the absorption layer is thick, the light path (shadowing) of the EUV light may be blocked. If a portion that becomes a projection of the absorbing layer is formed on the substrate due to the influence of the shadow, the pattern of the reflective reticle is not faithfully transferred onto the surface of the exposed material, and the pattern accuracy may be deteriorated. On the other hand, if the film thickness of the absorbing layer is made thinner, the light-shielding performance of the reflective reticle against EUV light is lowered, and the reflectance of the EUV light is increased, so that the pattern portion of the reflective reticle may be removed. The contrast of the other parts will decrease.

Therefore, a reflective reticle substrate which faithfully transfers the pattern of the reflective reticle and suppresses the decrease in contrast has been studied. For example, Patent Document 1 discloses a reflective photomask substrate which contains 50 atom% (at%) or more of Ta as a main component and further contains Te, Sb, Pt, I, Bi, Ir, and A material of at least one of Os, W, Re, Sn, In, Po, Fe, Au, Hg, Ga, and Al constitutes an absorber film.

However, in the reflective photomask substrate described in Patent Document 1, the absorption film film has no resistance to cleaning liquid (washing resistance) when the reflective mask is manufactured. Therefore, it may be impossible to form a pattern stably on the absorber film. [Prior Technical Literature] [Patent Literature]

[Patent Document 1] Japanese Patent Laid-Open Publication No. 2007-273678

[The problem that the invention wants to solve]

An aspect of an aspect of the present invention is to provide a reflective reticle substrate having an absorbing layer excellent in cleaning resistance at the time of manufacture of a reflective reticle. [Technical means to solve the problem]

A reflective reticle substrate according to an aspect of the present invention is characterized in that, on the substrate, a reflective layer that reflects EUV light and an absorbing layer that absorbs EUV light are sequentially provided from the substrate side, and the absorbing layer contains Sn as a main component and contains Ta at 25 at% or more. [Effects of the Invention]

According to an aspect of the invention, it is possible to provide a reflective mask substrate having an absorbing layer excellent in cleaning resistance at the time of manufacture of a reflective reticle.

Hereinafter, embodiments of the present invention will be described in detail. Furthermore, for ease of understanding, the reduction ratio of each component in the drawing is sometimes different from the actual one. In the present specification, a three-dimensional orthogonal coordinate system in the three-axis direction (X-axis direction, Y-axis direction, and Z-axis direction) is used, and the coordinates of the main surface of the glass substrate are set to the X-axis direction and the Y-axis direction, and the height direction is used. (Thickness direction) is set to the Z-axis direction. The direction from the lower side of the glass substrate upward (the direction from the main surface of the glass substrate toward the reflective layer) is set to the +Z axis direction, and the opposite direction is set to the -Z axis direction. In the following description, there is a case where the +Z-axis direction is referred to as the upper and the -Z-axis direction is referred to as the lower.

[First Embodiment] <Reflective reticle base> The reflective reticle base of the first embodiment will be described. Fig. 1 is a schematic cross-sectional view showing a reflective mask base of the first embodiment. As shown in FIG. 1, the reflective reticle base 10A has a substrate 11, a reflective layer 12, a protective layer 13, and an absorbing layer 14. The reflective reticle base 10A is formed by sequentially laminating the substrate 11, the reflective layer 12, the protective layer 13, and the absorbing layer 14 from the substrate 11 side.

(Substrate) The substrate 11 preferably has a small coefficient of thermal expansion. The small coefficient of thermal expansion of the substrate 11 suppresses strain generated by the pattern formed on the absorbing layer 14 due to heat during exposure of the EUV light. Specifically, the thermal expansion coefficient of the substrate 11 is preferably 0 ± 1.0 × 10 ^-7 / ° C at 20 ° C, more preferably 0 ± 0.3 × 10 ^-7 / ° C. As a material having a small coefficient of thermal expansion, for example, SiO ₂ -TiO ₂ -based glass or the like can be used. As the SiO ₂ -TiO ₂ -based glass, quartz glass containing 90 to 95% by mass of SiO ₂ and 5 to 10% by mass of TiO ₂ is preferably used. When the content of TiO ₂ is 5 to 10% by mass, the coefficient of thermal expansion near room temperature is substantially zero, so that a dimensional change hardly occurs near room temperature. Further, the SiO ₂ -TiO ₂ -based glass may contain a trace amount of components other than SiO ₂ and TiO ₂ .

The first main surface 11a on the side of the laminated reflective layer 12 of the substrate 11 preferably has a high surface smoothness. The surface smoothing performance of the first main surface 11a was evaluated by surface roughness. The surface roughness of the first main surface 11a is preferably 0.15 nm or less in terms of the root mean square roughness Rq. Further, the surface smoothness can be measured by an atomic force microscope.

It is preferable that the first main surface 11a is subjected to surface processing so as to have a specific flatness. The reason is that the reflective mask achieves higher pattern transfer accuracy and positional accuracy. The substrate 11 preferably has a flatness of 100 nm or less, more preferably 50 nm or less, and still more preferably 30 nm or less in a specific region (for example, a region of 132 mm × 132 mm) of the first main surface 11a.

Further, the substrate 11 is preferably resistant to a cleaning liquid used for cleaning the reflective mask base, the reflective mask base after pattern formation, or the reflective mask.

Further, in order to prevent deformation of the substrate 11 due to film stress of the film (reflection layer 12 or the like) formed on the substrate 11, the substrate 11 preferably has high rigidity. For example, the substrate 11 preferably has a higher Young's modulus of 65 GPa or more.

The size, thickness, and the like of the substrate 11 are appropriately determined depending on the design value of the reflective mask or the like.

The first main surface 11a of the substrate 11 is formed in a rectangular shape or a circular shape in plan view. In the present specification, a rectangle includes a rectangle or a square, and includes a shape formed by an arc at a corner of a rectangle or a square.

(Reflective Layer) The reflective layer 12 has a high reflectance for EUV light. Specifically, when the EUV light is incident on the surface of the reflective layer 12 at an incident angle of 6°, the maximum value of the reflectance of the EUV light having a wavelength of 13.5 nm is preferably 60% or more, more preferably 65% or more. Further, even when the protective layer 13 and the absorbing layer 14 are laminated on the reflective layer 12, the maximum value of the reflectance of the EUV light having a wavelength of 13.5 nm is preferably 60% or more, more preferably More than 65%.

The reflective layer 12 is a multilayer film in which a plurality of layers are periodically laminated with layers each having an element having a different refractive index as a main component. The reflective layer 12 is generally formed of a plurality of layers in which a high refractive index layer having a refractive index higher in EUV light and a low refractive index layer having a lower refractive index in EUV light are alternately laminated from the substrate 11 side. Reflective film.

The multilayer reflective film may have a laminated structure in which a high refractive index layer and a low refractive index layer are sequentially laminated from the substrate 11 side, and may have a plurality of cycles as one cycle, or may have a low refractive index layer and a high refractive index layer. The laminated structure in which the layers are sequentially stacked from the side of the substrate 11 is stacked as a single cycle. Further, in this case, it is preferable that the multilayer reflective film has a layer (the uppermost layer) of the outermost surface as a high refractive index layer. The reason for this is that since the low refractive index layer is easily oxidized, if the low refractive index layer becomes the uppermost layer of the reflective layer 12, the reflectance of the reflective layer 12 may be reduced.

As the high refractive index layer, a layer containing Si can be used. As the material containing Si, in addition to the Si element, one or more Si compounds selected from the group consisting of B, C, N, and O may be used. By using a high refractive index layer containing Si, a reflective mask excellent in reflectance of EUV light can be obtained. As the low refractive index layer, an alloy selected from the group consisting of Mo, Ru, Rh, and Pt or an alloy thereof can be used. In the present embodiment, it is preferable that the low refractive index layer is a Mo layer and the high refractive index layer is a Si layer. Furthermore, in this case, by forming the uppermost layer of the reflective layer 12 as a high refractive index layer (Si layer), a tantalum oxide containing Si and O is formed between the uppermost layer (Si layer) and the protective layer 13. The layer of matter improves the cleaning resistance of the reflective mask.

In the reflective layer 12, the high refractive index layer and the low refractive index layer each have a plurality of layers, but the thickness of the high refractive index layers or the thickness of the low refractive index layers may not necessarily be the same.

The film thickness and period of each layer constituting the reflective layer 12 can be appropriately selected depending on the film material to be used, the reflectance of the EUV light required for the reflective layer 12, the wavelength of the EUV light (exposure wavelength), and the like. For example, when the maximum value of the reflectance of the EUV light having a wavelength of 13.5 nm is set to 60% or more, the low refractive index layer (Mo layer) and the high refractive index layer (Si layer) are preferably used. A Mo/Si multilayer reflective film formed by alternately laminating 30 to 60 cycles.

Further, each layer constituting the reflective layer 12 can be formed into a film so as to have a desired film thickness by a known film forming method such as a magnetron sputtering method or an ion beam sputtering method. For example, when the reflective layer 12 is formed by ion beam sputtering, it is carried out by supplying ion particles to the target of the high refractive index material and the target of the low refractive index material from the ion source. In the case where the reflective layer 12 is a Mo/Si multilayer reflective film, a Si layer having a specific film thickness is formed on the substrate 11 by ion beam sputtering, for example, first using a Si target. Thereafter, a Mo layer having a specific film thickness was formed using a Mo target. A Mo/Si multilayer reflective film is formed by laminating the Si layer and the Mo layer as one cycle for 30 to 60 cycles.

(Protective Layer) When the reflective mask 20 (see FIG. 7) is manufactured, the absorber layer 14 is etched (usually dry etching) to form the absorber pattern 141 in the absorber layer 14 (see FIG. 7). The protective layer 13 suppresses the surface of the reflective layer 12 from being damaged by etching, thereby protecting the reflective layer 12. Further, when the resist layer 18 (see FIG. 8) remaining on the reflective mask base after etching is peeled off using the cleaning liquid to clean the reflective mask substrate, the protective layer 13 protects the reflective layer 12 from the cleaning liquid. Therefore, the obtained reflective mask 20 (see FIG. 7) has a good reflectance for EUV light.

In FIG. 1, the case where the protective layer 13 is one layer is shown, but the protective layer 13 may also be a plurality of layers.

As a material for forming the protective layer 13, a material which is less susceptible to damage by etching during etching of the absorbing layer 14 is selected. As a substance satisfying the above conditions, for example, a Ru metal element and one or more selected from the group consisting of B, Si, Ti, Nb, Mo, Zr, Y, La, Co, and Re are contained in addition to Ru. a Ru alloy of a metal, a Ru-based material such as a nitride of nitrogen containing a nitride of the above-mentioned Ru alloy; Cr, Al, Ta, and a nitride containing nitrogen on the basis of the above; SiO ₂ , Si ₃ N ₄ , Al ₂ A mixture of O ₃ or the like, and the like. Among them, Ru metal element and Ru alloy, CrN and SiO _{2 are} preferable. The Ru metal element and the Ru alloy are difficult to be etched with respect to the oxygen-free gas, and it is particularly preferable as the etching stopper layer in the processing of the reflective mask.

In the case where the protective layer 13 is formed of a Ru alloy, the Ru content in the Ru alloy is preferably 95 at% or more and less than 100 at%. When the Ru content is within the above range, when the reflective layer 12 is a Mo/Si multilayer reflective film, diffusion of Si from the Si layer of the reflective layer 12 to the protective layer 13 can be suppressed. Further, the protective layer 13 has a function as an etching stopper layer for etching the absorption layer 14 while sufficiently ensuring the reflectance of the EUV light. Further, it is possible to have the cleaning resistance of the reflective reticle and to prevent deterioration of the temporal deterioration of the reflective layer 12.

The film thickness of the protective layer 13 is not particularly limited as long as it functions as the protective layer 13. The film thickness of the protective layer 13 is preferably 1 nm or more, more preferably 1.5 nm, and still more preferably 2 nm in terms of the reflectance of the EUV light reflected in the reflective layer 12. The film thickness of the protective layer 13 is preferably 8 nm or less, more preferably 6 nm or less, and still more preferably 5 nm or less.

As a method of forming the protective layer 13, a known film formation method such as a magnetron sputtering method or an ion beam sputtering method can be used.

(Absorbing Layer) For the reflective reticle for EUV lithography, the absorbing layer 14 must have characteristics such as high absorption coefficient of EUV light, high cleaning resistance to the cleaning liquid, and easy etching.

The absorbing layer 14 absorbs EUV light, and the reflectance of the EUV light is extremely low. Specifically, the maximum value of the reflectance of the EUV light having a wavelength of 13.5 nm when the EUV light is irradiated onto the surface of the absorption layer 14 is preferably 10% or less, more preferably 5% or less, still more preferably 2% or less. , especially good for 1% or less. Therefore, the absorption layer 14 must have a high absorption coefficient of EUV light.

Further, in the production of the reflective mask 20 (see FIG. 7) described below, the absorbing layer 14 is exposed to the resist pattern 181 (see FIG. 8) remaining on the reflective mask base after etching by the cleaning liquid. In the cleaning solution. At this time, as the cleaning liquid, a sulfuric acid hydrogen peroxide mixture (SPM), sulfuric acid, ammonia, an aqueous ammonia hydrogen peroxide mixture (APM), OH (hydroxyl) radical washing water, ozone water or the like is used. In EUV lithography, SPM is generally used as a cleaning solution for a resist. Further, the SPM is a solution in which sulfuric acid and hydrogen peroxide are mixed, and sulfuric acid and hydrogen peroxide may be mixed in a volume ratio, for example, at 3:1. At this time, from the viewpoint of increasing the etching rate, the temperature of the SPM is preferably controlled to 100 ° C or higher. Therefore, the absorbing layer 14 must have high cleaning resistance to the cleaning liquid. The absorbing layer 14 is preferably, for example, a etch rate which is low (for example, 0.10 nm/min or less) when immersed in a solution of 75 vol% of sulfuric acid and 25 vol% of hydrogen peroxide.

Further, the absorption layer 14 is processed by etching using a chlorine (Cl)-based gas such as Cl ₂ , SiCl _{4 or} CHCl ₃ or a dry etching of a fluorine (F)-based gas such as CF ₄ or CHF ₃ . Therefore, the absorbing layer 14 must be easily etched.

In order to achieve the characteristics as described above, the absorption layer 14 contains Sn as a main component and contains Ta at 25 at% or more. The absorbing layer 14 may be formed of a Sn-Ta alloy. The Sn-Ta alloy is present in a state containing at least one selected from the group consisting of Ta, Sn, TaSn ₂ and Ta ₃ Sn depending on the film formation conditions of Sn and Ta or the respective contents thereof.

In the present specification, the term "Sn" as a main component means that the material contains at most Sn in terms of at% of other metal elements. In the case where the absorption layer 14 contains a non-metal element such as N or O in addition to a metal element such as Sn or Ta, the main component means a metal element which is the most contained when at% is calculated by excluding a non-metal element, that is, The main component means the main component of the metal element excluding the non-metallic element. The content of Sn (Sn content) is preferably 30 at% or more, more preferably 40 at% or more, further preferably 50 at% or more, and particularly preferably 55 at% or more. The Sn content is preferably 75 at% or less, more preferably 70 at% or less, and particularly preferably 65 at% or less.

When the Sn content is 30 at% or more, the absorption coefficient of the EUV light of Sn is high, so that the absorption layer 14 has a high light absorption amount even if the film thickness of the absorption layer 14 is made thin. Therefore, the film thickness of the absorbing layer 14 can be made thin.

When the Sn content is 75 at% or less, the content of Ta (Ta content) is set to 25 at% or more. In this case, in the manufacture of the reflective mask 20 (see FIG. 7) described below, when the reflective mask substrate is cleaned using SPM as a cleaning liquid, the absorption layer is as shown in FIG. A surface oxide film (passive film) 15 containing yttrium oxide (Ta ₂ O ₅ ) is formed on the surface of 14. Thereby, the absorbing layer 14 is protected, so that the etching of the absorbing layer 14 is suppressed, so that the absorbing layer 14 has high washing resistance.

When the reflective mask 20 (see FIG. 7) is manufactured, the resist layer 18 (refer to FIG. 8) formed on the reflective mask substrate 10A (see FIG. 1) is drawn (exposed) by an electron beam (EB). (electron-beam, electron beam) exposure). After the EB exposure, the absorption layer 14 is dry etched (see FIG. 8), and the resist layer 18 is peeled off (see FIG. 7). Ashing is used when the resist layer 18 is peeled off, but in order to completely remove the resist residue, it is necessary to perform cleaning using SPM. The absorption layer 14 can improve the washing resistance against a cleaning liquid such as SPM by setting the Sn content to 75 at% or less and the Ta content to 25 at% or more. Thereby, the absorbing layer 14 can satisfy the washing resistance required for the reflective reticle 20 (refer to FIG. 7).

Further, if the passivation film 15 formed by the cleaning of the reflective mask substrate after etching is too thick, the reflectance of the absorption layer 14 may fluctuate. When the Sn content is 75 at% or less and the Ta content is 25 at% or more, the film thickness of the passivation film 15 formed on the surface of the absorption layer 14 can be suppressed to be small. Thereby, the fluctuation of the reflectance of the absorbing layer 14 can be suppressed. The upper limit of the Ta content is not particularly limited. As described above, since the absorbing layer 14 contains Sn as a main component, the Ta content is smaller than the Sn content.

Here, an example of the relationship between the Ta content of the absorption layer and the film thickness of the passive film 15 formed on the surface of the absorption layer 14 is shown in FIG. A natural oxide film of about 2 nm is formed on the surface of the absorber layer 14 before SPM cleaning. After the SPM cleaning, the film thickness of the oxide film is increased by the oxidation of SPM, thereby protecting the inside. Further, the natural oxide film becomes the passive film 15. As shown in FIG. 3, when the Ta content of the absorption layer is 25 at% or more, the film thickness of the passive film 15 can be suppressed to 6 nm or less. Further, the natural oxide film is formed on the surface of the absorption layer because the absorption layer is exposed to the atmosphere after sputtering. At this time, the composition of the natural oxide film is SnTaO. Thereafter, it is considered that the natural oxide film is eluted by Sn during the SPM cleaning to become TaO, thereby becoming the passive film 15.

In the present specification, the film thickness of the passive film 15 means the length in the direction perpendicular to the surface of the absorption layer 14. The film thickness of the passive film 15 is, for example, the thickness at the time of measuring the arbitrary position in the cross section of the passive film 15. When a plurality of locations are measured at any position in the cross section of the passive film 15, the average thickness of the measurement sites may be set.

In addition, when Sn is used as the main component and the Ta content is 25 at% or more, since Sn is easily etched by the Cl-based gas, Ta is easily etched by the Cl-based gas or the F-based gas, and the absorption layer 14 can be made of a Cl-based system. The gas is easily etched.

The absorbing layer 14 preferably has an etching rate for SPM of 0.10 nm/min or less. More preferably, it is 0.09 nm/min or less, further preferably 0.07 nm/min or less, and particularly preferably 0.05 nm/min or less. When the etching rate of the absorbing layer 14 for SPM is 0.10 nm/min or less, the reflective mask 20 (see FIG. 7) may be substantially equal to the resist pattern provided on the absorbing layer 14 at the time of manufacture of the reflective mask 20 (see FIG. 7). The absorber pattern 141 is formed in the ground (see FIG. 7). Further, the etching rate of the absorbing layer 14 with respect to SPM can be determined, for example, by immersing in SPM having sulfuric acid of 75 vol%, hydrogen peroxide of 25 vol%, and heating to 100 °C. The slower the etching rate for SPM, the lower the lower limit is 0 nm/min.

The absorption layer 14 may further contain one or more elements selected from the group consisting of N, O, B, Hf, Si, Zr, Ge, Pd, and H in addition to Sn and Ta. Among them, it is preferred to contain N, O or B. By containing at least one of N and O on the basis of Sn and Ta, the resistance of the absorbing layer 14 to oxidation can be improved, and thus the stability over time can be improved. By including B on the basis of Sn and Ta, the absorption layer 14 can be made into a structure in which the crystal state is amorphous or crystallite. The absorbing layer 14 is preferably amorphous in a crystalline state. Therefore, the absorbing layer 14 has excellent surface smoothness and flatness. Moreover, the surface smoothness and flatness of the absorbing layer 14 are improved, and the edge roughness of the absorber pattern 141 (see FIG. 7) is reduced, so that the dimensional accuracy of the absorber pattern 141 (see FIG. 7) can be improved.

The absorbing layer 14 may be a single layer film or a multilayer film including a plurality of layers. When the absorbing layer 14 is a single-layer film, the number of processes at the time of manufacturing the reticle base can be reduced, and the production efficiency can be improved. In the case where the absorbing layer 14 is a multilayer film, by appropriately setting the optical constant or film thickness of the layer on the upper layer side of the absorbing layer 14, it is possible to use the inspection light to inspect the absorber pattern 141 (refer to FIG. 7). Anti-reflective film. Thereby, the inspection sensitivity at the time of inspection of the absorber pattern can be improved.

The film thickness of the absorbing layer 14 can be appropriately designed according to the composition of the absorbing layer 14, etc., but it is preferably thinner in terms of suppressing the thickness of the reflective reticle substrate 10A. The film thickness of the absorption layer 14 is preferably, for example, 40 nm or less in terms of maintaining the reflectance of the absorption layer 14 at 10% or less and obtaining sufficient contrast. The film thickness of the absorption layer 14 is more preferably 35 nm or less, further preferably 30 nm or less, particularly preferably 25 nm or less, and most preferably 20 nm or less. The lower limit of the film thickness of the absorbing layer 14 is determined by the reflectance, and is preferably as thin as possible within a range of 10% or less of the reflectance of EUV light having a wavelength of 13.5 nm, and is preferably 10 nm or more. Since the film thickness of the absorption layer 14 is preferably thin, the lower limit of the film thickness of the absorption layer 14 is more preferably 5 nm or more, further preferably 3 nm or more, and particularly preferably 1 nm or more. The film thickness of the absorption layer 14 can be measured, for example, by X-ray reflectance method (XRR), TEM (Transmission Electron Microscopy) or the like.

The absorbing layer 14 can be formed by a known film forming method such as a magnetron sputtering method or an ion beam sputtering method. For example, when a SnTa film is formed as the absorption layer 14 by magnetron sputtering, the absorber layer 14 can be formed by sputtering using argon gas using a target containing Sn and Ta.

As described above, the reflective mask substrate 10A includes the absorption layer 14 containing Sn as a main component and containing Ta at 25 at% or more as described above. The absorbing layer 14 contains Sn and Ta in a specific range, and can have excellent washing durability in the production of a reflective reticle (see FIG. 7). Therefore, the reflective reticle base 10A can stably form the absorber pattern 141 on the absorbing layer 14 (refer to FIG. 7).

Further, since the reflective mask base 10A can make the EUV light absorption rate higher even if the absorption layer 14 is made thinner, the EUV light in the absorption layer 14 can be reduced while thinning the reflective mask base 10A. Reflectivity.

Further, since the reflective mask base 10A can easily etch the absorbing layer 14, it is excellent in workability.

<Method of Manufacturing Reflective Photomask Base> Next, a method of manufacturing the reflective mask base 10A shown in Fig. 1 will be described. Fig. 4 is a flow chart showing an example of a method of manufacturing the reflective mask substrate 10A. As shown in FIG. 4, a reflective layer 12 is formed on the substrate 11 (forming process of the reflective layer 12: step S11). The reflective layer 12 is formed on the substrate 11 so as to have a desired film thickness by a known film formation method as described above.

Then, a protective layer 13 is formed on the reflective layer 12 (the formation process of the protective layer 13: step S12). The protective layer 13 is formed on the reflective layer 12 so as to have a desired film thickness by a known film formation method.

Then, an absorbing layer 14 is formed on the protective layer 13 (forming process of the absorbing layer 14: step S13). The absorbing layer 14 is formed on the protective layer 13 so as to have a desired film thickness by a known film forming method.

Thereby, the reflective mask substrate 10A as shown in FIG. 1 is obtained.

(Other Layers) The reflective mask substrate 10A may have a hard mask layer 16 on the absorption layer 14 as shown in FIG. As the hard mask layer 16, a material having high resistance to etching such as a Cr-based film or a Si-based film can be used. Examples of the Cr-based film include a Cr element and a material obtained by adding O or N to Cr. Specifically, CrO, CrN, etc. are mentioned. Examples of the Si-based film include a Si element and a material obtained by adding one or more selected from the group consisting of O, N, C, and H to Si. Specific examples thereof include SiO ₂ , SiON, SiN, SiO, Si, SiC, SiCO, SiCN, and SiCON. Among them, the Si-based film is preferable because it is less likely to cause the side wall to retreat when the absorption layer 14 is dry-etched.

By forming the hard mask layer 16 on the absorption layer 14, dry etching can be performed even if the minimum line width of the absorber pattern 141 (refer to FIG. 7) becomes small. Therefore, it is effective to refine the absorber pattern 141 (refer to FIG. 7). Further, in the case where another layer is laminated on the absorbing layer 14, the hard mask layer 16 may be provided on the layer on the most surface side of the absorbing layer 14.

As shown in FIG. 6, the reflective reticle base 10A may include a back surface conductive layer 17 for an electrostatic chuck on the second main surface 11b on the side opposite to the side of the substrate 11 on which the reflective layer 12 is laminated. As the characteristics of the back surface conductive layer 17, the sheet resistance value is required to be low. The sheet resistance value of the back surface conductive layer 17 is, for example, 250 Ω/□ or less, preferably 200 Ω/□ or less.

As the material contained in the back surface conductive layer 17, for example, a metal such as Cr or Ta or an alloy thereof can be used. As the alloy containing Cr, a Cr compound containing one or more selected from the group consisting of B, N, O, and C on the basis of Cr can be used. Examples of the Cr compound include CrN, CrON, CrCN, CrCON, CrBN, CrBON, CrBCN, and CrBOCN. As the alloy containing Ta, a Ta compound containing one or more selected from the group consisting of B, N, O, and C on the basis of Ta can be used. Examples of the Ta compound include TaB, TaN, TaO, TaON, TaCON, TaBN, TaBO, TaBON, TaBCON, TaHf, TaHfO, TaHfN, TaHfON, TaHfCON, TaSi, TaSiO, TaSiN, TaSiON, and TaSiCON.

The film thickness of the back surface conductive layer 17 is not particularly limited as long as it satisfies the function as an electrostatic chuck, and is, for example, 10 to 400 nm. Further, the back surface conductive layer 17 may also include stress adjustment on the second main surface 11b side of the reflective mask substrate 10A. In other words, the back surface conductive layer 17 can be adjusted so as to balance the stresses of the various layers formed on the side of the first main surface 11a and to make the reflective mask base 10A flat.

As a method of forming the back surface conductive layer 17, a known film formation method such as a magnetron sputtering method or an ion beam sputtering method can be used.

The back surface conductive layer 17 can be formed on the second main surface 11b of the substrate 11, for example, before the protective layer 13 is formed.

<Reflective Mask> Next, a reflection type mask obtained by using the reflection type mask base 10A shown in Fig. 1 described above will be described. Fig. 7 is a schematic cross-sectional view showing an example of a configuration of a reflective mask. As shown in Fig. 7, the reflective mask 20 is formed by forming the desired absorber pattern 141 on the absorbing layer 14 of the reflective reticle base 10A shown in Fig. 1.

An example of a method of manufacturing the reflective mask 20 will be described. FIG. 8 is a view for explaining a manufacturing process of the reflective reticle 20. As shown in Fig. 8(a), a resist layer 18 is formed on the absorbing layer 14 of the reflective reticle base 10A shown in Fig. 1 described above.

Thereafter, the resist layer 18 is exposed to a desired pattern. After the exposure, the exposed portion of the resist layer 18 is developed and rinsed with pure water, whereby a specific resist pattern 181 is formed on the resist layer 18 as shown in Fig. 8(b).

Thereafter, the resist layer 18 on which the resist pattern 181 is formed is used as a mask, and the absorption layer 14 is dry-etched. Thereby, as shown in FIG. 8(c), the absorber pattern 141 corresponding to the resist pattern 181 is formed on the absorption layer 14.

As the etching gas, an F-based gas, a Cl-based gas, or a mixed gas of a Cl-based gas and O ₂ , He or Ar may be used in a specific ratio.

Thereafter, the resist layer 18 is removed by a resist stripper or the like to form a desired absorber pattern 141 on the absorber layer 14. Thereby, the reflective mask 20 in which the desired absorber pattern 141 is formed in the absorption layer 14 as shown in FIG. 7 can be obtained.

The illumination optical system of the self-exposure device irradiates the obtained reflective mask 20 with EUV light. The EUV light incident on the reflective mask 20 is reflected in a portion of the non-absorptive layer 14 (portion of the absorber pattern 141), and is absorbed in a portion having the absorption layer 14. As a result, the reflected light of the EUV light reflected in the reflective layer 12 is irradiated to the exposure material (for example, a wafer or the like) by the reduced projection optical system of the exposure device. Thereby, the absorber pattern 141 of the absorbing layer 14 is transferred onto the exposed material to form a circuit pattern on the exposed material.

In the reflective reticle 20, since the absorbing layer 14 has high washing resistance, the absorber pattern 141 can be stably formed in the absorbing layer 14. Therefore, the reflective reticle 20 has a higher pattern accuracy.

Further, the reflective mask 20 can thin the absorption layer 14. Therefore, even if the line width of the absorber pattern 141 of the absorbing layer 14 becomes small, the influence of the shadow can be alleviated. Therefore, the reflective mask 20 can faithfully transfer the absorber pattern 141 of the absorbing layer 14 on the surface of the exposed material while reducing the film thickness of the layer. Further, since the reflective mask 20 can reduce the reflectance of the EUV light in the absorbing layer 14, even if the absorbing layer 14 is made thin, it has a high contrast.

[Second Embodiment] A reflective mask base according to a second embodiment will be described with reference to the drawings. It is to be noted that the same reference numerals are given to members having the same functions as those of the above-described embodiment, and the detailed description is omitted. Fig. 9 is a schematic cross-sectional view showing a reflective mask base according to a second embodiment. As shown in FIG. 9, the reflective reticle base 10B has a stabilizing layer 19 on the absorbing layer 14 of the reflective reticle base 10A shown in FIG. In other words, the reflective reticle base 10B is formed by sequentially laminating the substrate 11, the reflective layer 12, the protective layer 13, the absorbing layer 14, and the stabilizing layer 19 from the substrate 11 side.

The stabilizing layer 19 may contain an oxide, a nitride, a boride, an oxynitride and a boron oxide, a oxide of Ta, a nitride, a boride, an oxynitride, and a borooxide, and the like containing Ta and Sn. One or more compounds of the group consisting of Ru-based materials (Ru-based compounds).

When the stabilizing layer 19 is a compound selected from the group consisting of one or more of an oxide, a nitride, a boride, an oxynitride, and a boron oxide containing Ta and Sn, the oxide containing Ta and Sn is used. Examples of the nitride, boride, oxynitride, and borooxide include TaSnO, TaSnN, TaSnB, TaSnON, TaSnBO, TaSnBN, and TaSnBON.

When the stabilizing layer 19 is an oxide film or an oxynitride film containing Ta and Sn as an oxide, a nitride, a boride, an oxynitride or a boron oxide of Ta and Sn, the stabilizing layer 19 can be used and absorbed. Layer 14 is formed from the same material. Therefore, the target used in forming the stabilizing layer 19 can use the target used when forming the absorbing layer 14. As a result, the stabilizing layer 19 can be easily formed on the main surface of the absorbing layer 14, and thus the productivity is excellent. In this case, the stable layer 19 does not change in film thickness even after washing, but the composition of the film sometimes changes.

Here, when the stabilization layer 19 is a film containing Ta and Sn (Ta content is 50 at%), X-ray photoelectron spectroscopy (XPS) is used to measure the surface of the stabilization layer 19 before and after SPM cleaning. An example of the intensity ratio of Sn to Ta is shown in Table 1. The XPS spectrum measured by XPS reflects the intensity ratio of the composition of the film surface of the stabilizing layer 19. In Table 1, the Sn system measures the intensity of the photoelectron spectrum corresponding to the 3d _5/2 orbital, and the Ta system measures the intensity of the photoelectron spectrum corresponding to the 4d _5/2 orbit.

[Table 1]

As can be seen from Table 1, the Sn content on the surface of the film was greatly reduced by SPM cleaning, and the composition of the components on the surface of the film was changed. This is because the surface of the stabilizing layer 19 is similar to the case where the passive film 15 containing Ta ₂ O ₅ is formed on the surface of the absorbing layer 14 during the cleaning of the reflective reticle base after etching (see FIG. 2). The Ta is oxidized, and a passivation film 15 containing Ta ₂ O ₅ is formed on the surface of the stabilization layer 19 (see Fig. 2). Therefore, when the stabilizing layer 19 is an oxide film or an oxynitride film containing Ta and Sn, the passivation film 15 (see FIG. 2) is formed on the surface of the stabilizing layer 19, and the composition of the film changes.

When the stabilizing layer 19 is a compound selected from the group consisting of oxides, nitrides, borides, oxynitrides, and oxyborides of Ta, an oxide film or a nitride film of Ta may be used. A boride film, an oxynitride film, and a boron oxide film are used as the stabilizing layer 19. Examples of the oxide, nitride, boride, oxynitride, and borooxide of Ta include TaO, Ta ₂ O ₅ , TaN, TaB ₂ , TaON, TaCON, TaBN, TaBO, TaBON, TaBCON, and TaHfO. TaHfN, TaHfON, TaHfCON, TaSiO, TaSiN, TaSiON, and TaSiCON. When the oxide film of Ta or the oxynitride film is used as the stabilizing layer 19, the change in composition in the stabilizing layer 19 is not caused by cleaning, so that a more stable stabilizing layer 19 can be formed.

Further, a film (Ru-based film) containing a Ru-based material can be used as the stabilizing layer 19. When a Ru-based film is used as the stabilizing layer 19, the absorbing layer 14 can be further thinned while maintaining the reflectance at 10% or less (particularly preferably 1% or less).

The film thickness of the stabilizing layer 19 is preferably 10 nm or less. The film thickness of the stabilizing layer 19 is more preferably 7 nm or less, further preferably 6 nm or less, particularly preferably 5 nm or less, and most preferably 4 nm or less. The film thickness of the stabilizing layer 19 is more preferably 1 nm or more, further preferably 2 nm or more, and particularly preferably 3 nm or more.

The stabilization layer 19 can be formed by a known film formation method such as a magnetron sputtering method, an ion beam sputtering method, or a reactive sputtering method. Further, the reactive sputtering method is a method in which, for example, Ta, Sn or SnTa is used as a target, and a mixed gas obtained by mixing oxygen or nitrogen into an inert gas such as Ar (argon gas) or Kr (helium gas) is used as a sputtering gas. .

The reflective reticle base 10B can further improve the washing resistance of the absorbing layer 14 by having the stabilizing layer 19 on the absorbing layer 14. By having the stabilizing layer 19, a strong and stable film can be formed with good reproducibility, and the characteristics of the reflective reticle base and the reflective reticle can be stabilized. Further, as shown in FIG. 10, the sidewall of the absorption layer 14 is exposed after dry etching. However, since the passivation film 15 is formed on the side wall of the absorption layer 14 after cleaning, the absorption layer 14 can be prevented from being etched by cleaning, and the absorption layer 14 can be protected.

[Third Embodiment] A reflective mask base according to a third embodiment will be described with reference to the drawings. It is to be noted that the same reference numerals are given to members having the same functions as those of the above-described embodiment, and the detailed description is omitted. Figure 11 is a schematic cross-sectional view showing a reflective mask base of a third embodiment. As shown in FIG. 11, the reflective reticle base 10C has a barrier layer 21 between the absorbing layer 14 and the stabilizing layer 19 of the reflective reticle base 10B shown in FIG. 9, that is, over the absorbing layer 14. In other words, the reflective reticle base 10C is formed by sequentially laminating the substrate 11, the reflective layer 12, the protective layer 13, the absorbing layer 14, the preventing layer 21, and the stabilizing layer 19 from the substrate 11 side.

As a material for forming the prevention layer 21, Ta, Cr or Si can be used. These elements may be contained alone or in combination of two or more.

As the prevention layer 21, a Ta element, a Cr element, a Si element, a nitride of Ta, a nitride of Cr, a nitride of Si, a boride of Ta, a boride of Cr, a boride of Si, or a boron nitride of Ta can be used. These may be contained alone or in combination of two or more.

A preferred composition of the prevention layer 21 is, for example, Ta, TaN, TaB or TaBN. For example, it is assumed that the stabilizing layer 19 contains an oxide of Ta, an oxynitride or a boron oxide. In this case, if the prevention layer 21 is such a material, the same target can be used in the film formation preventing layer 21 and the stabilization layer 19. Therefore, it is possible to reduce the productivity of the reflective mask substrate 10C such as the number of film forming chambers required.

The prevention layer 21 may further contain an element such as He, Ne, Ar, Kr or Xe.

The prevention layer 21 is a layer which does not contain oxygen. The absence of oxygen means that the sputtering gas does not contain oxygen, and after the film formation preventing layer 21 is formed, oxygen is not present on the surface and inside of the prevention layer 21. When the stabilization layer 19 is formed, if a reactive sputtering method containing oxygen is used, the component contained in the layer 21 is prevented from reacting (oxidizing) with oxygen on the surface where the layer 21 is prevented from contacting oxygen, so that it is prevented. The case where the surface of the layer 21 forms a film of an oxide. In addition, the term "containing no oxygen" refers to a film which does not include the oxide in the film which is formed on the surface of the layer 21 which is in contact with oxygen in the process after the film formation preventing layer 21 is formed. Oxygen. On the other hand, the interface between the absorbing layer 14 and the preventing layer 21 is not in contact with oxygen, so that oxygen is not contained at the interface between the preventing layer 21 and the absorbing layer 14 and its vicinity. In addition, the term "near" refers to a range within 0.5 nm from the interface in the depth direction of the prevention layer 21.

The prevention layer 21 can be formed by a known film formation method such as a magnetron sputtering method or an ion beam sputtering method. For example, when a Ta film, a TaB film, or a Si film is formed as the prevention layer 21 by magnetron sputtering, an inert gas such as He, Ar, or Kr is used as a sputtering by using a target containing Ta, TaB, or Si. The gas film formation preventing layer 21 is formed.

The thickness of the layer 21 can be reduced to about several nm, and preferably 10 nm or less, in terms of suppressing the thickness of the pattern of the reflective mask substrate 10C. The film thickness of the prevention layer 21 is more preferably 8 nm or less, further preferably 6 nm or less, particularly preferably 5 nm or less, and most preferably 4 nm. The film thickness of the prevention layer 21 is more preferably 0.5 nm or more, further preferably 1 nm or more, particularly preferably 1.5 nm or more, and most preferably 2 nm or more. The film thickness of the prevention layer 21 can be measured, for example, by XRR, TEM or the like.

When the absorbing layer 14 is in contact with oxygen, there is a possibility that a part of Sn existing on the surface of the absorbing layer 14 reacts with oxygen, and a precipitate containing fine particles of Sn is generated on the surface of the absorbing layer 14. For example, when the stabilization layer 19 is formed by a reactive sputtering method, as described above, a mixed gas obtained by mixing oxygen gas with an inert gas such as He, Ar or Kr is used as a sputtering gas. If the surface of the absorbing layer 14 is in contact with a mixed gas as a sputtering gas, precipitates may be generated on the surface of the absorbing layer 14.

As described above, the prevention layer 21 is formed on the absorption layer 14 by using only an inert gas such as He, Ar or Kr as a sputtering gas. Therefore, by forming the prevention layer 21 before the absorption layer 14 comes into contact with a gas such as oxygen, the absorption layer 14 can be prevented from coming into contact with oxygen, so that precipitation of precipitates on the surface of the absorption layer 14 can be prevented.

Therefore, since the reflective mask base 10C has the prevention layer 21 on the absorption layer 14, it is possible to prevent the occurrence of precipitates on the surface of the absorption layer 14, and therefore it is possible to suppress the reflection type in the production of the reflective mask. The mask creates defects. Thereby, a defect-free film can be stably formed.

The reflective photomask substrate 10C may contain at least one of Ta, Cr, or Si to form the prevention layer 21. These elements are easy to dry-etch and have excellent washing durability. When the layer 21 is made of Ta or the like, the absorber layer 14 can prevent the oxidation of the surface of the absorber layer 14 and form the absorber pattern 141 having a high cleaning resistance (see FIG. 7). .

The reflective photomask substrate 10C may use Ta element, Cr element, Si element, nitride of Ta, nitride of Cr, nitride of Si, boride of Ta, boride of Cr, boride of Si or boron of Ta The prevention layer 21 is formed by nitride. Since these elements, nitrides, borides, and boron nitrides are amorphous, the edge roughness of the absorber pattern 141 (see FIG. 7) can be suppressed. When the barrier layer 21 is formed by containing a nitride of Ta or the like, it is possible to form a highly accurate absorber pattern 141 while preventing oxidation of the surface of the Sn-containing absorber layer 14 (see FIG. 7).

The reflective photomask substrate 10C can be formed by preventing the layer 21 from containing at least one of He, Ne, Ar, Kr, or Xe. By using these elements as a sputtering gas in the formation of the prevention layer 21, there is a case where these elements are contained in a trace amount in the prevention layer 21. In this case as well, the function of the prevention layer 21 can be exerted without affecting the properties of the prevention layer 21.

The reflective photomask substrate 10C can set the film thickness of the prevention layer 21 to 10 nm or less. Thereby, the thickness of the preventing layer 21 can be suppressed. Therefore, the reflective mask base 10C can suppress the overall thickness of the pattern of the absorber pattern 141 (see FIG. 7) and the preventing layer 21 and the stabilizing layer 19 formed thereon. [Examples]

<Example 1> Example 1-1 is an example, and Example 1-2 is a comparative example.

[Example 1-1] (Production of Reflective Photomask Base) A SiO ₂ -TiO ₂ -based glass substrate (having an outer shape of approximately 152 mm square and a thickness of approximately 6.3 mm) was used as a substrate for film formation. Further, the glass substrate has a thermal expansion coefficient of 0.02 × 10 ^-7 /°C. The glass substrate is polished to have a smooth surface having a surface roughness of 0.15 nm or less and a flatness of 100 nm or less with a root mean square roughness Rq. On the back surface of the glass substrate, a Cr layer having a film thickness of about 100 nm was formed by magnetron sputtering to form a back surface conductive layer (conductive film) for the electrostatic chuck. The sheet resistance of the Cr layer is about 100 Ω/□. After the glass substrate was fixed by using a Cr film, the operation of alternately forming a Si film and a Mo film by ion beam sputtering on the surface of the glass substrate was repeated for 40 cycles. The film thickness of the Si film was set to be about 4.5 nm, and the film thickness of the Mo film was set to be about 2.3 nm. Thereby, a reflection layer (multilayer reflection film) having a total film thickness of about 272 nm ((Si film: 4.5 nm + Mo film: 2.3 nm) × 40) was formed. Thereafter, a Ru layer (having a film thickness of about 2.5 nm) was formed on the reflective layer by ion beam sputtering to form a protective layer (protective film). Next, an absorber layer (absorber film) containing a Sn-Ta alloy was formed on the protective layer by magnetron sputtering. The sputtering gas system uses argon. The target system Sn used for sputtering was 60 at% and Ta was 40 at%, but the Ta content in the absorbing layer after sputtering was 48 at%. Further, the Sn content and the Ta content in the absorption layer were measured by a fluorescent X-ray analysis method (XRF) (manufactured by Olympus Co., Ltd., Delta). By stopping the rotation of the stage during sputtering of the absorbing layer, an absorbing layer having a large film thickness distribution of 30 to 53 nm in the plane is obtained. Thereby, the reflective mask substrate 10A shown in Fig. 6 was produced. The film thickness of the absorption layer was measured by XRR using an X-ray diffraction apparatus (manufactured by RIGAKU Co., Ltd., SmartLab HTP). Further, from the results of X-ray diffraction (XRD) measurement using the same apparatus, it was confirmed that the absorption layer containing the Sn-Ta alloy was amorphous.

(Relationship between film thickness of the absorption layer and reflectance) The relationship between the film thickness of the absorption layer of the reflective mask base and the reflectance was measured. In the measurement of the reflectance, a mask base was used using an EUV reflectometer (manufactured by AIXUV Co., Ltd., MBR). The wavelength of the EUV light is set to 13.5 nm. The relationship between the film thickness of the absorption layer and the reflectance is shown in Fig. 12. In order to obtain sufficient contrast of the reflective mask, it is preferred to have a reflectance of 1% or less.

[Example 1-2] The same procedure as in Example 1-1 was carried out except that in Example 1-1, TaN was used instead of the Sn-Ta alloy to prepare an absorbing layer. The relationship between the film thickness of the absorption layer and the reflectance is shown in Fig. 12.

As shown in Fig. 12, the reflectance of Example 1-1 was smaller than that of Example 1-2. The reason is considered to be that the extinction coefficient of Sn is larger than the extinction coefficient of Ta. In Example 1-2, in order to maintain the reflectance of the absorbing layer at 1% or less, only the film thickness of the absorbing layer can be reduced to about 62 nm. On the other hand, in Example 1-1, the film thickness of the absorption layer was made thin to about 40 nm.

Therefore, when an absorber layer is formed using an alloy containing Sn 52 at% and Ta 48 at%, even if the thickness of the absorption layer is 40 nm, the reflectance of EUV light can be made 1% or less, so that sufficient absorption can be obtained. Contrast. Thus, it was confirmed that the thickness of the absorption layer was 40 nm or less with respect to the absorption layer.

<Example 2> Examples 2-1 to 2-5 are examples, and examples 2-6 are reference examples.

[Example 2-1] (Refractive index and extinction coefficient of the absorbing layer) The reflectance of the absorbing layer containing the Sn-Ta alloy was simulated. The Sn content of the absorption layer was set to 30 at% and the Ta content was set to 70 at%. The refractive index (n) and extinction coefficient (k) of the absorber layer are required in the simulation. Use the Center for X-Ray Optics, the value of the database of the Lawrence Berkeley National Laboratory as the refractive index and extinction coefficient of Sn and Ta. At a wavelength of 13.5 nm, the refractive index n of Sn is 0.9416, the extinction coefficient k is 0.0725, the refractive index n of Ta is 0.9429, and the extinction coefficient is 0.0408. The refractive index and extinction coefficient of the Sn-Ta alloy can be calculated using the density of the alloy. The density of the alloy was calculated by interpolating the density of the composition ratio Sn (7.365 g/cm ³ ) and the density of Ta (16.69 g/cm ³ ).

(Relationship between film thickness of the absorption layer and reflectance) The film thickness of the absorption layer is set to 30 to 60 nm, and simulation is performed, that is, the reflection of the reflection type photomask substrate 10A with respect to the reflection type photomask substrate 10A is assumed. The case where the angle is 6° to illuminate EUV light. The wavelength of the EUV light is set to 13.5 nm. The simulation results of the relationship between the film thickness of the absorption layer and the reflectance are shown in Fig. 13 . In the same manner as in Example 1-1, in order to obtain a sufficient contrast of the reflective mask, it is preferred to have a reflectance of 1% or less.

[Example 2-2 to Example 2-6] In Example 2-1, the Sn content of the absorption layer was changed to 40 at% (Example 2-2), 50 at% (Example 2-3), 60 at% ( The simulation was carried out in the same manner as in Example 2-1 except for Example 2-4), 70 at% (Example 2-5), or 80 at% (Example 2-6). The simulation result of the relationship between the film thickness of the absorption layer of the reflective reticle base and the reflectance is shown in Fig. 13 .

As shown in Fig. 13, in Examples 2-1 to 2-6, the thickness of the absorbing layer was about 40 nm and the reflectance of EUV light was 1.0% or less. In Examples 2-4 to 2-6, even if the film thickness of the absorption layer is about 32 nm, the reflectance of EUV light is 1.0% or less. Therefore, when the Sn content of the absorption layer is 30 to 80 at%, even if the thickness of the absorption layer is reduced to about 40 nm, the reflectance of the absorption layer can be maintained at 1% or less, so that sufficient absorption can be obtained. Contrast. Further, when the Sn content of the absorption layer is 60 to 80 at%, the reflectance of the absorption layer can be maintained at 1% or less even if the thickness of the absorption layer is further set to about 32 nm. However, in the case of Example 2-6, since the Sn content of the absorption layer was 80 at%, the film reduction was large when cleaning with SPM as described below (see Fig. 15).

Thus, it has been confirmed that when the Sn content of the absorption layer is 30 at% or more, the reflectance of the absorption layer can be made 1% or less even if the thickness of the absorption layer is made thinner to 40 nm.

<Example 3> Example 3-1 and Example 3-2 are examples.

[Example 3-1] The film thickness of the absorption layer was fixed to 40 nm, and the Sn content was changed to simulate the reflectance of EUV light in the same manner as in Example 2-1. The simulation results of the relationship between the Sn content and the reflectance are shown in Fig. 14.

[Example 3-2] The same procedure as in Example 3-1 was carried out except that the film thickness of the absorption layer was fixed to 33 nm. When the Sn content is 60 at%, the reflectance of the EUV light is about 1.0%. When the Sn content is 70 at%, the reflectance of EUV light is about 0.8%. When the Sn content is 80 at%, the reflectance of the EUV light is about 0.6%.

(Relationship between Sn content and reflectance) As shown in Fig. 14, in order to set the reflectance of the absorption layer to 1% or less in Example 3-1, it is sufficient that the Sn content is 30 at% or more. Therefore, when the film thickness of the absorption layer is 40 nm, it is confirmed that when the Sn content is 30 at% or more, the reflectance of EUV light can be made 1% or less. In the case of the example 3-2, when the film thickness of the absorption layer is further reduced, for example, when the film thickness of the absorption layer is 33 nm, it is confirmed that the Sn content is 60 at% or more. The reflectance of the EUV light can be made 1% or less (refer to Example 2-4, Example 2-5, and Example 2-6 of Fig. 13).

Therefore, when the film thickness of the absorption layer is 40 nm, the reflectance of the EUV light can be made 1% or less by adjusting the Sn content to 30 at% or more. Further, if the Sn content is further increased to 60 at% or more, the film thickness of the absorption layer can be made thinner to 33 nm.

<Example 4> Examples 4-1 to 4-4 are examples, and examples 4-5 are comparative examples, and examples 4-6 are reference examples. [Example 4-1] (Production of Absorbing Layer +) A Si substrate was used as a substrate for film formation. On the surface of the Si substrate, an absorber film containing a Sn-Ta alloy was formed by magnetron sputtering. The sputtering gas system uses argon. With the double sputtering of the Ta target and the Sn target, the absorption layer was formed to a film thickness of 40 nm so that the Ta content in the absorption layer became about 30 at% and the Sn content was about 70 at%.

(Relationship between Ta content and film reduction of the absorption layer) Thereafter, SPM (75 vol% of sulfuric acid and 25 vol% of hydrogen peroxide) was used as a cleaning liquid, and the Si substrate on which the absorption layer was formed was immersed and heated to 100. About 20 minutes in the SPM of °C. After the Si substrate was pulled out from the SPM, the film thickness of the absorber layer formed on the Si substrate was measured, and the amount of decrease in film thickness (film reduction) was determined. The relationship between the Ta content and the film reduction of the absorption layer is shown in Table 2 and Figure 15. Further, the film reduction must be reduced to the film of the Cr film previously used as the absorption layer. The film thickness of the Cr film was set to 2.2 nm. In Fig. 15, the film of the Cr film is shown by a broken line.

[Examples 4-2 to 4-6] In the same manner as in Example 4-1, except that the Ta content and the Sn content in the absorption layer were changed to the values shown in Table 2, respectively, in Example 4-1. get on. The relationship between the Ta content and the film reduction of the absorption layer is shown in Table 2 and Figure 15.

[Table 2]

As shown in Fig. 15, the film reduction of Examples 4-1 to 4-3 was smaller than that of the Cr film. On the other hand, the film reduction of Examples 4-5 was larger than that of the Cr film. The film thicknesses of the absorption layers of Examples 4-4 and 4-6 were increased. The reason is considered to be that when immersed in the cleaning liquid, a passive film is formed on the surface of the absorbing layer, and the passive film grows. Although the absorption layer of Example 4-6 has washing resistance, since the Sn content is low, the reflectance becomes large.

As is clear from Fig. 15, when the Ta content in the absorbing layer is 25 at% or more, the washing resistance of the Cr film or the like which has been used as the absorbing layer or more can be obtained. Therefore, it was confirmed that the absorber layer can stably form the absorber pattern.

<Example 5> Example 5-1 is an example, and Example 5-2 is a comparative example.

[Example 5-1] (Production of absorption layer) An absorption layer similar to that of Example 4-1 was formed on a Si substrate. (Relationship between Ta content and etching rate) An Si substrate on which an absorption layer is formed is etched using an ICP (Inductively Coupled Plasma) plasma etching apparatus. The etching gas system uses chlorine gas (Cl ₂ ). The ICP source power is set to 100 W and the bias power is set to 40 W. The film thickness of the absorption layer and the TaN film was measured using XRR. The film thickness of the absorbing layer after etching was measured, and the etching rate of the absorbing layer was measured. The measurement result of the etching rate is shown in FIG.

[Example 5-2] The same procedure as in Example 5-1 was carried out except that in Example 5-1, an insulating layer was produced by using TaN instead of the Sn-Ta alloy. The measurement result of the etching rate is shown in FIG.

As shown in Fig. 16, the etching speed of Example 5-1 was faster than that of Example 5-2. Thus, if an absorber layer is formed using a Sn-Ta alloy containing 70 at% of Sn and 30 at% of Ta, the Cl ₂ can be easily utilized as compared with an absorber layer formed of a material previously used such as TaN. The gas is etched. Thereby, the absorbing layer is easily subjected to etching processing.

<Example 6> Example 6 is an example.

(Production of Reflective Photomask Base) A reflective mask substrate was produced in the same manner as in Example 1-1. Thereafter, a stable layer containing TaO of about 4 nm was formed on the absorber layer by magnetron sputtering. Thereby, the reflective mask substrate 10B shown in Fig. 9 was produced.

(Measurement of reflectance) EUV light having an incident angle of 13.53 nm was incident on the surface of the reflective reticle from the surface of the reflective reticle base (at the direction of +Z-axis) at an incident angle of 6°, and the reflected light was measured. The reflectivity of the EUV light reflected by the cover substrate. As a result, the reflectance of the EUV light was about 0.8% in the portion where the total thickness of the absorption layer and the stabilization layer was 40 nm.

Thereby, even if the total thickness of the absorbing layer and the stabilizing layer is about 40 nm, the reflectance of the EUV light can be 10% or less (particularly preferably 1% or less). Therefore, the reflective mask base of the present embodiment can be made thinner than the conventional reflective mask base.

<Example 7> Example 7 is an example. (Production of Reflective Photomask Base) A reflective mask substrate was produced in the same manner as in Example 1-1. At this time, the thermal expansion coefficient of the glass substrate was 0.02 × 10 ^-7 /° C. or less, and the thickness of the absorption layer (absorber film) was 40 nm. Thereafter, on the absorption layer (absorber film), a 2 nm-preventing layer containing Ta was formed by magnetron sputtering, and a 2 nm film was formed on the prevention layer by reactive sputtering. Stable layer of TaO. Thereby, the reflective mask substrate 10C shown in Fig. 11 was produced. Further, when a film formation preventing layer is formed by magnetron sputtering, argon gas is used as the sputtering gas system. When a stable layer was formed by a reactive sputtering method, a mixed gas obtained by mixing Ar and oxygen was used as a sputtering gas, and the flow rate of Ar was 40 sccm, and the flow rate of oxygen was 30 sccm.

The anti-layer and the stabilizing layer of the reflective reticle base after the film formation were measured by XRR. As a result, the film thickness of Ta was 0.9 nm, and the film thickness of TaO was 4.6 nm. The reason for this is that when a TaO film is formed on a Ta film, oxygen contained in the sputtering gas reacts with Ta of the Ta film to form a TaO film, and expands.

Thereafter, the reflective mask substrate 10C shown in Fig. 11 is dry etched using a dry etching apparatus. After the dry etching is performed using the F-based gas removal preventing layer and the stabilizing layer, the absorption layer is removed using a Cl-based gas.

(Observation of the surface of the reflective reticle base) The surface of the reflective reticle base was observed using a scanning electron microscope (manufactured by Carl Zeiss, Ultra 60), and as a result, precipitates such as fine particles were not observed. In this example, in the case of forming a film formation preventing layer, only Ar is used as a sputtering gas. Therefore, the surface of the absorbing layer is not exposed to an atmosphere containing oxygen, so Sn existing on the surface of the absorbing layer does not react with oxygen. Thereby, it can be said that the occurrence of precipitates on the surface of the absorption layer is suppressed.

Although the embodiment has been described above, the above embodiment has been proposed as an example, and the present invention is not limited to the above embodiment. The above-described embodiments can be implemented in various other forms, and various combinations, omissions, substitutions, changes, and the like can be made without departing from the scope of the invention. These embodiments and variations thereof are included in the scope of the invention and the scope of the invention as set forth in the appended claims. The present application is based on Japanese Patent Application No. Hei. No. Hei. No. Hei. No. Hei. No. Hei. No. Hei. No. Hei. No. Hei. In this article.

10A‧‧‧Reflective reticle base

10B‧‧‧Reflective reticle base

10C‧‧‧Reflective reticle base

11‧‧‧Substrate

11a‧‧‧1st main face

11b‧‧‧2nd main face

12‧‧‧reflective layer

13‧‧‧Protective layer

14‧‧‧absorbing layer

15‧‧‧ Surface oxide film (passive film)

16‧‧‧hard mask layer

17‧‧‧ Back conductive layer

18‧‧‧resist

19‧‧‧Steady layer

20‧‧‧reflective mask

21‧‧‧Protection layer

141‧‧‧Absorber pattern

181‧‧‧resist pattern

S11～S13‧‧‧Steps

X‧‧‧ axis

Y‧‧‧ axis

Z‧‧‧ axis

Fig. 1 is a schematic cross-sectional view showing a reflective mask base of the first embodiment. Fig. 2 is an explanatory view showing a state in which a passive film is formed on the surface of the absorption layer. Fig. 3 is a view showing an example of the relationship between the Ta content and the film thickness of the passive film formed on the surface of the absorption layer. Fig. 4 is a flow chart showing an example of a method of manufacturing a reflective reticle base. Fig. 5 is a schematic cross-sectional view showing an example of another embodiment of a reflective reticle base. Fig. 6 is a schematic cross-sectional view showing an example of another embodiment of a reflective reticle base. Fig. 7 is a schematic cross-sectional view of a reflective reticle. Fig. 8 is a view showing the manufacturing process of the reflective reticle. Fig. 9 is a schematic cross-sectional view showing a reflective mask base according to a second embodiment. Fig. 10 is an explanatory view showing a state of a reflective mask base before and after cleaning. Figure 11 is a schematic cross-sectional view showing a reflective mask base of a third embodiment. Fig. 12 is a view showing the relationship between the film thickness of the absorption layer and the reflectance. Fig. 13 is a view showing a simulation result of the relationship between the film thickness of the absorption layer and the reflectance. Fig. 14 is a graph showing the relationship between the Sn content and the reflectance. Fig. 15 is a graph showing the relationship between the Ta content of the SnTa film and the film reduction. Fig. 16 is a view showing the measurement results of the etching rate of the absorption layer and TaN.

Claims (19)

A reflective reticle substrate which is provided on a substrate having a reflective layer for reflecting EUV light and an absorbing layer for absorbing EUV light from the substrate side, wherein the absorbing layer contains Sn as a main component and contains 25 at% or more Ta. The reflective reticle substrate of claim 1, wherein the content of Sn in the absorbing layer is 30 at% or more. The reflective reticle substrate of claim 1 or 2, wherein the absorbing layer has a film thickness of 40 nm or less. The reflective reticle substrate of any one of claims 1 to 3, wherein the absorbing rate of the absorbing layer for the sulfuric acid hydrogen peroxide mixture is 0.10 nm/min or less. The reflective reticle substrate according to any one of claims 1 to 4, wherein the absorbing layer contains one or more selected from the group consisting of N, O, B, Hf, Si, Zr, Ge, Pd, and H. element. A reflective reticle substrate according to any one of claims 1 to 5, which has a stabilizing layer above the absorbing layer. The reflective reticle substrate of claim 6, wherein the stabilizing layer comprises an oxide, a nitride, a boride, an oxynitride and a boride, an oxide of a Ta, a nitride, a boride And one or more compounds selected from the group consisting of nitrogen oxides, boron oxides, and Ru-based materials containing Ru. The reflective reticle substrate of claim 6 or 7, wherein the stable layer has a film thickness of 10 nm or less. The reflective reticle substrate of any of claims 6 to 8 having a barrier layer over the absorbing layer. The reflective reticle substrate of claim 9, wherein the barrier layer is formed between the absorbing layer and the stabilizing layer. The reflective reticle substrate of claim 9 or 10, wherein the prevention layer contains one or more elements selected from the group consisting of Ta, Cr, and Si. The reflective reticle substrate of claim 11, wherein the preventing layer contains a boron selected from the group consisting of Ta element, Cr element, Si element, nitride of Ta, nitride of Cr, nitride of Si, boride of Ta, and boron of Cr One or more components selected from the group consisting of a compound, a boride of Si, and a boron nitride of Ta. The reflective photomask substrate according to any one of claims 9 to 12, wherein the prevention layer contains one or more elements selected from the group consisting of He, Ne, Ar, Kr, and Xe. The reflective reticle substrate of any one of claims 9 to 13, wherein the film thickness of the above-mentioned prevention layer is 10 nm or less. The reflective reticle substrate of any one of claims 1 to 14, which has a protective layer between the reflective layer and the absorbing layer. A reflective reticle substrate according to any one of claims 1 to 15, which has a hard mask layer on the layer above the absorbing layer or on the most surface side of the absorbing layer. The reflective reticle substrate of claim 16, wherein the hard reticle layer contains at least one of Cr or Si. A reflective reticle obtained by patterning the above-described absorbing layer of the reflective reticle substrate according to any one of claims 1 to 17. A method for manufacturing a reflective reticle substrate, which is a method for manufacturing a reflective reticle substrate having a reflective layer for reflecting EUV light and an absorbing layer for absorbing EUV light from a substrate side on a substrate, and comprising the following process Forming the reflective layer on the substrate; and forming an absorbing layer on the reflective layer, the absorbing layer containing Sn as a main component and containing Ta at 25 at% or more.