Reflective photomask blank, reflective photomask, and reflective photomask production method

Abstract

The present invention provides: a reflective photomask that uses light having a wavelength in the extreme ultraviolet region as a light source, said reflective photomask comprising an absorption layer having good pattern processability; a reflective photomask blank that is used for producing said reflective photomask; and a reflective photomask production method that uses said reflective photomask blank. A reflective photomask blank (10) according to an embodiment of the present invention comprises a substrate (1), a reflective layer (2), and an absorption layer (4), wherein: the absorption layer (4) is formed from a material which contains not less than 50 at% of platinum (Pt) and which contains tantalum (Ta) in the range of not less than 5 at% but less than 50 at%; the film thickness of the absorption layer (4) is in the range of 17-50 nm; the extinction coefficient of the absorption layer (4) with respect to EUV light is not less than 0.049; and the surface roughness of the absorption layer (4) is not more than 0.4 nm.

Description

Reflective photomask blank, reflective photomask, and method for manufacturing reflective photomask

[0001] The present invention relates to a reflective photomask blank, a reflective photomask, and a method for manufacturing a reflective photomask.

[0002] In the manufacturing process of semiconductor devices, the miniaturization of semiconductor devices has led to an increasing demand for miniaturization of photolithography technology. The minimum resolution dimension of a transfer pattern in photolithography is highly dependent on the wavelength of the exposure light source, and the shorter the wavelength, the smaller the minimum resolution dimension. For this reason, the exposure light source has been replaced from the conventional 193 nm wavelength ArF excimer laser light to light in the EUV (Extreme Ultra Violet) region with a wavelength of 13.5 nm.

[0003] Since light in the EUV region is absorbed at a high rate by most materials, a reflective photomask is used as a photomask for EUV exposure (EUV mask) (see, for example, Patent Document 1). Patent Document 1 discloses an EUV photomask obtained by forming a reflective layer made of a multilayer film in which molybdenum (Mo) layers and silicon (Si) layers are alternately stacked on a glass substrate, forming a light absorbing layer mainly composed of tantalum (Ta) thereon, and forming a pattern on this light absorbing layer.

[0004] Furthermore, as mentioned above, EUV lithography cannot use refractive optical systems that utilize the transmission of light, and therefore the optical components of the exposure machine are reflective (mirrors) rather than lenses. This poses the problem that the light incident on the reflective photomask (EUV mask) and the light reflected from the EUV mask cannot be designed to be coaxial. Normally, EUV lithography employs a method in which the optical axis is tilted 6 degrees from the perpendicular direction of the EUV mask, and the reflected light reflected at an angle of minus 6 degrees is guided onto the semiconductor substrate.

[0005] As described above, in EUV lithography, the optical axis is tilted via a mirror, which can cause a problem known as the "shadow effect," in which the EUV light incident on the EUV mask casts a shadow on the mask pattern (patterned light-absorbing layer) of the EUV mask. Current EUV mask blanks use a tantalum (Ta)-based film with a thickness of 60 to 90 nm as the light-absorbing layer. When pattern transfer exposure is performed using an EUV mask fabricated using this mask blank, depending on the relationship between the incident direction of the EUV light and the orientation of the mask pattern, a decrease in contrast may occur at the edge portions of the mask pattern that are shadowed. This can lead to problems such as increased line edge roughness of the transferred pattern on the semiconductor substrate and an inability to form the desired line width, resulting in a deterioration in transfer performance.

[0006] Therefore, a change of the light absorbing layer from tantalum (Ta) to a material having a high absorbency (extinction coefficient) for EUV light, or a reflective photomask blank in which a material having a high absorbency is added to tantalum (Ta) is being considered. For example, Patent Document 2 discloses a reflective photomask blank in which the light absorbing layer is made of Pt, Zn, Au, NiO, Ag ２ O, Ir, Fe, SnO ２ and a reflective photomask blank made of an alloy containing at least two materials selected from the group consisting of Ni, Ni, Co, and the like.

[0007] However, some materials that are highly absorptive of EUV light are difficult to process by dry etching, and there has been a problem in that even if a photomask blank is formed (fabricated), the light absorbing layer provided on the photomask blank cannot be patterned.

[0008] Patent No. 5418293 Special Publication No. 2019-527382

[0009] The present disclosure has been made in light of the above circumstances, and aims to provide a reflective photomask for patterning transfer that uses light with a wavelength in the extreme ultraviolet region as a light source, the reflective photomask having an absorption layer with good pattern processability, a reflective photomask blank used to manufacture the reflective photomask, and a method for manufacturing a reflective photomask using the reflective photomask blank.

[0010] The present disclosure has been made to solve the above-mentioned problems, and a reflective photomask blank according to one aspect of the present disclosure is a reflective photomask blank for producing a reflective photomask for pattern transfer using extreme ultraviolet light as a light source, the reflective photomask blank comprising: a substrate; a reflective layer including a multilayer film formed on the substrate; and an absorbing layer formed on the reflective layer, the absorbing layer being formed of a material containing 50 atomic % or more of platinum (Pt) and 5 atomic % or more but less than 50 atomic % of tantalum (Ta), the film thickness of the absorbing layer being in the range of 17 nm or more and 50 nm or less, the extinction coefficient of the absorbing layer with respect to EUV light being 0.049 or more, and the surface roughness of the absorbing layer being 0.4 nm or less.

[0011] Furthermore, a reflective photomask according to one aspect of the present disclosure is a reflective photomask for pattern transfer using extreme ultraviolet light as a light source, comprising: a substrate; a reflective layer including a multilayer film formed on the substrate; and an absorbing pattern layer formed on the reflective layer, wherein the absorbing pattern layer is formed of a material containing 50 atomic % or more of platinum (Pt) and 5 atomic % or more but less than 50 atomic % of tantalum (Ta), the film thickness of the absorbing pattern layer is in the range of 17 nm or more and 50 nm or less, the extinction coefficient of the absorbing layer for EUV light is 0.049 or more, and the surface roughness of the absorbing pattern layer is 0.4 nm or less.

[0012] Furthermore, a method for manufacturing a reflective photomask according to one aspect of the present disclosure is a method for manufacturing a reflective photomask for pattern transfer using extreme ultraviolet light as a light source, and includes the steps of forming a reflective layer including a multilayer film on a substrate, and forming an absorbing pattern layer on the reflective layer, wherein the absorbing pattern layer is formed from a material containing 50 atomic % or more of platinum (Pt) and 5 atomic % or more but less than 50 atomic % of tantalum (Ta), the film thickness of the absorbing pattern layer is in the range of 17 nm or more and 50 nm or less, the extinction coefficient of the absorbing pattern layer for EUV light is 0.049 or more, and the surface roughness of the absorbing pattern layer is 0.4 nm or less.

[0013] The reflective photomask blank according to one embodiment of the present disclosure makes it possible to create an absorbing layer with good pattern processability. That is, the reflective photomask blank according to one embodiment of the present disclosure can provide a reflective photomask blank with excellent pattern processability for the absorbing layer. In other words, the reflective photomask blank according to one embodiment of the present disclosure can provide a reflective photomask blank with an absorbing layer that can achieve good pattern processability and is expected to improve transfer performance to a semiconductor substrate in patterning using light with a wavelength in the extreme ultraviolet region as a light source.

[0014] Furthermore, a reflective photomask according to an embodiment of the present disclosure can provide a reflective photomask having an absorbing layer with good pattern processability. That is, a reflective photomask according to an embodiment of the present disclosure can be expected to improve transfer performance to a semiconductor substrate in patterning using light with a wavelength in the extreme ultraviolet region as a light source. Furthermore, a manufacturing method for a reflective photomask according to an embodiment of the present disclosure can manufacture a reflective photomask having an absorbing layer with good pattern processability. That is, a manufacturing method for a reflective photomask according to an embodiment of the present disclosure can manufacture a reflective photomask that can be expected to improve transfer performance to a semiconductor substrate in patterning using light with a wavelength in the extreme ultraviolet region as a light source.

[0015] As described above, one aspect of the present disclosure can provide a reflective photomask for patterning transfer that uses light with a wavelength in the extreme ultraviolet region as a light source, the reflective photomask having an absorption layer with good pattern processability, a reflective photomask blank used to manufacture the reflective photomask, and a method for manufacturing a reflective photomask using the reflective photomask blank.

[0016] FIG. 1 is a schematic cross-sectional view showing the structure of a reflective photomask blank according to an embodiment of the present invention. FIG. 2 is a schematic cross-sectional view showing the structure of a reflective photomask according to an embodiment of the present invention. FIG. 3 is a graph showing the optical constants of each metal material at the wavelength of EUV light. FIG. 4 is a schematic cross-sectional view showing the structure of a reflective photomask blank according to another embodiment of the present invention. FIG. 5 is a schematic cross-sectional view showing the structure of a reflective photomask blank according to an example of the present invention. FIG. 6 is a schematic cross-sectional view showing the manufacturing process of a reflective photomask according to an example of the present invention. FIG. 7 is a schematic cross-sectional view showing the manufacturing process of a reflective photomask according to an example of the present invention. FIG. 8 is a schematic cross-sectional view showing the manufacturing process of a reflective photomask according to an example of the present invention. FIG. 9 is a schematic cross-sectional view showing the structure of a reflective photomask according to an example of the present invention. FIG. 10 is a schematic plan view showing the shape of a design pattern of a reflective photomask according to an example of the present invention.

[0017] Hereinafter, embodiments of the present invention will be described with reference to the drawings, but the present invention is not limited to the embodiments shown below. In the embodiments shown below, technically preferable limitations are imposed for carrying out the present invention, but these limitations are not essential requirements for the present invention.

[0018] Fig. 1 is a schematic cross-sectional view showing the structure of a reflective photomask blank 10 according to an embodiment of the present invention. Fig. 2 is a schematic cross-sectional view showing the structure of a reflective photomask 20 according to an embodiment of the present invention. Here, the reflective photomask 20 according to the embodiment of the present invention shown in Fig. 2 is formed by patterning the absorption layer 4 of the reflective photomask blank 10 according to the embodiment of the present invention shown in Fig. 1.

[0019] (Overall Structure) As shown in FIG. 1 , a reflective photomask blank 10 according to an embodiment of the present invention includes a substrate 1, a reflective layer 2 formed on the substrate 1, a capping layer 3 formed on the reflective layer 2, and an absorbing layer 4 formed on the capping layer 3.

[0020] (Substrate) For example, a flat Si substrate, a synthetic quartz substrate, etc. may be used for the substrate 1 according to the embodiment of the present invention. Furthermore, low thermal expansion glass containing titanium may be used for the substrate 1, but the present invention is not limited to these as long as the material has a small thermal expansion coefficient.

[0021] (Reflective Layer) The reflective layer 2 according to the embodiment of the present invention may be any layer that reflects EUV light (extreme ultraviolet light), which is exposure light, and may be a multilayer reflective film made of a combination of materials that have significantly different refractive indices for EUV light. The reflective layer 2 including a multilayer reflective film may be formed by repeatedly stacking layers of a combination of Mo (molybdenum) and Si (silicon) or Mo (molybdenum) and Be (beryllium) for about 40 periods.

[0022] (Capping Layer) The capping layer 3 according to the embodiment of the present invention is formed from a material that is resistant to the dry etching that is performed when forming a transfer pattern (mask pattern) on the absorption layer 4, and functions as an etching stopper that prevents damage to the reflective layer 2 when etching the absorption layer 4. The capping layer 3 is formed from, for example, Ru (ruthenium). Here, depending on the material of the reflective layer 2 and the etching conditions, the capping layer 3 may not be formed. Furthermore, although not shown, a back surface conductive film can be formed on the surface of the substrate 1 on which the reflective layer 2 is not formed. The back surface conductive film is a film that uses the principle of an electrostatic chuck to fix the reflective photomask 20 when it is placed in an exposure machine.

[0023] (Absorbing Layer) As shown in Figure 2, an absorbing pattern (absorbing pattern layer) 41 of the reflective photomask 20 is formed by removing a portion of the absorbing layer 4 of the reflective photomask blank 10, i.e., by patterning the absorbing layer 4. In EUV lithography, EUV light is incident at an angle and reflected by the reflective layer 2. However, due to a projection effect in which the absorbing pattern 41 obstructs the light path, transfer performance onto the wafer (semiconductor substrate) may be deteriorated. This deterioration in transfer performance can be reduced by reducing the thickness of the absorbing layer 4 that absorbs EUV light. In order to reduce the thickness of the absorbing layer 4, it is preferable to use a material that has a higher absorbency for EUV light than conventional materials, that is, a material with a high extinction coefficient k at a wavelength of 13.5 nm.

[0024] Figure 3 is a graph showing the optical constants of various metal materials for EUV light with a wavelength of 13.5 nm. The horizontal axis of Figure 3 represents the refractive index n, and the vertical axis represents the extinction coefficient k. The extinction coefficient k of tantalum (Ta), which is the main material of the conventional absorber layer 4, is 0.041. If a compound material has a larger extinction coefficient k, it will be possible to make the absorber layer 4 thinner than conventional materials.

[0025] Materials that satisfy the above-described extinction coefficient k include, for example, silver (Ag), platinum (Pt), indium (In), cobalt (Co), tin (Sn), nickel (Ni), and tellurium (Te), as shown in Figure 3. However, some of these metal materials have the problem of low cleaning resistance and low hydrogen radical resistance, which are required in the environment in which the photomask is used. For this reason, even if a reflective photomask blank having an absorption layer formed from these metal materials is produced, the reflective photomask produced using the reflective photomask blank may not be usable in the exposure environment.

[0026] Furthermore, even if a material has no problem in terms of resistance to hydrogen radicals, many of these materials often have the problem of poor dry etching properties due to low halide volatility. In other words, an absorbing layer formed from a material that is resistant to hydrogen radicals but has low halide volatility cannot be patterned, which can result in the problem that a reflective photomask blank cannot be processed into a reflective photomask.

[0027] To avoid the above-mentioned drawbacks, the absorption layer 4 of the reflective photomask blank 10 of this embodiment or the absorption pattern layer 41 of the reflective photomask 20 of this embodiment is formed from a material (alloy) containing platinum (Pt) and tantalum (Ta). Platinum (Pt) alone is highly resistant to liquids used in cleaning photomasks and also highly resistant to hydrogen radicals, but is known to have poor dry etching properties. The inventors of the present application have discovered that by using a material containing platinum (Pt) and tantalum (Ta) in a specific ratio as the material for forming the absorption layer 4 or the absorption pattern layer 41, it is possible to process the absorption layer 4 by dry etching while maintaining high hydrogen radical resistance.

[0028] In this embodiment, "poor dry etching properties" refers to a state in which, when the absorbing pattern layer 41 is formed, the angle formed between the surface of the reflective layer 2 or the surface of the capping layer 3 and the side surface of the absorbing pattern layer 41 in the pattern formation portion, that is, the angle of elevation (so-called sidewall angle) based on the surface of the reflective layer 2 or the surface of the capping layer 3, is less than 80°. Also, in this embodiment, "high hydrogen radical resistance" refers to a film reduction rate of 0.01 nm / s or less in a hydrogen radical environment using microwave plasma at a power of 1 kW and a hydrogen pressure of 0.36 millibars (mbar) or less.

[0029] The material constituting the absorber layer 4 contains platinum (Pt) at 50 atomic % or more relative to the total number of atoms constituting the absorber layer 4. The material constituting the absorber layer 4 preferably contains platinum (Pt) at a concentration in the range of 50 atomic % to 95 atomic % relative to the total number of atoms constituting the absorber layer 4, more preferably at a concentration in the range of 55 atomic % to 90 atomic % relative to the total number of atoms constituting the absorber layer 4, and even more preferably at a concentration in the range of 60 atomic % to 80 atomic % relative to the total number of atoms constituting the absorber layer 4. Furthermore, the absorber layer 4 contains tantalum (Ta) at a concentration in the range of 5 atomic % to less than 50 atomic % relative to the total number of atoms constituting the absorber layer 4. This is because, although the EUV light absorption may be reduced if the absorber layer 4 contains components other than platinum (Pt), the reduction in EUV light absorption is negligible if the content of components other than platinum (Pt) is less than 50 atomic %, and there is almost no reduction in performance as the absorber layer 4 of an EUV mask.

[0030] Furthermore, although processing by dry etching is difficult with platinum (Pt) alone, adding tantalum (Ta) to platinum (Pt) improves processability by dry etching, making dry etching using a chlorine-based gas, a fluorine-based gas, or a mixed gas possible, thereby enabling the reflective photomask blank to be processed into a reflective photomask. Specifically, if the content of tantalum (Ta) in the absorber layer 4 is within a range of 5 atomic % or more and less than 50 atomic % with respect to the number of atoms constituting the entire absorber layer 4, the processability of the absorber layer 4 by dry etching can be improved while maintaining hydrogen radical resistance.

[0031] If the tantalum (Ta) content is less than 5 atomic % relative to the total number of constituent atoms of the absorber layer 4, the processability of the absorber layer 4 by dry etching may not be improved. Furthermore, if the tantalum (Ta) content is 50 atomic % or more relative to the total number of constituent atoms of the absorber layer 4, the absorbency of EUV light may decrease, making it impossible to achieve a thin absorber layer 4. Furthermore, if the tantalum (Ta) content exceeds 50 atomic % relative to the total number of constituent atoms of the absorber layer 4, the contrast in DUV (Deep Ultra Violet) light with a wavelength of 190 to 260 nm may decrease, thereby deteriorating inspectability. Therefore, the tantalum (Ta) content is preferably in the range of 5 atomic % to less than 50 atomic % relative to the total number of constituent atoms of the absorber layer 4, more preferably in the range of 10 atomic % to 45 atomic % and even more preferably in the range of 20 atomic % to 40 atomic %.

[0032] The above composition ratios of the materials constituting the absorption layer 4 are calculated based on the analysis results obtained by Rutherford backscattering spectroscopy (RBS), and the contents may vary depending on the analysis method. For example, a material whose platinum (Pt) content is 50 atomic % to 99 atomic % of all metal elements as determined by Rutherford backscattering spectroscopy (RBS) may be found to contain 40 atomic % to 75 atomic % of all metal elements as a result of analysis using X-ray photoelectron spectroscopy (XPS), or may be found to contain 45 atomic % to 100 atomic % of all metal elements as a result of analysis using energy dispersive X-ray spectroscopy (EDX).

[0033] The processability of the absorber layer 4 is also affected by the crystallinity of the constituent material. Furthermore, the crystallinity also affects the smoothness of the film and the line edge roughness of the formed absorber pattern layer 41. For the reasons mentioned above, the absorber layer 4 in this embodiment is preferably formed from an amorphous film with low crystallinity. Materials with high crystallinity also have increased surface roughness due to the formation of crystal grain boundaries. Therefore, the surface roughness (RMS) of the absorber layer 4 is preferably 0.4 nm or less, and more preferably 0.2 nm or less. Here, the "surface roughness (RMS) of the absorber layer 4" refers to the roughness (RMS) of the surface (surface) of the absorber layer 4 (absorber pattern layer 41) opposite the reflective layer 2. In this embodiment, the surface roughness (RMS) may be measured using, for example, an atomic force microscope (AFM).

[0034] As described above, the material constituting the absorption layer 4 preferably contains platinum (Pt) at 50 atomic % or more and tantalum (Ta) in a range of 5 atomic % or more and less than 50 atomic % with respect to the number of atoms constituting the entire absorption layer 4. However, as a material other than platinum (Pt) and tantalum (Ta), for example, one or more elements selected from the group consisting of ruthenium (Ru), iridium (Ir), titanium (Ti), chromium (Cr), indium (In), nickel (Ni), cobalt (Co), bismuth (Bi), iron (Fe), gold (Au), silver (Ag), iodine (I), tellurium (Te), hafnium (Hf), tungsten (W), palladium (Pd), rhenium (Re), aluminum (Al), nitrogen (N), zinc (Zn), gallium (Ga), and boron (B) (hereinafter, for convenience, referred to as a "group of additional elements"). That is, the absorption layer 4 may further contain one or more elements selected from the above-mentioned group of additional elements in addition to platinum (Pt) and tantalum (Ta).

[0035] For example, among the elements included in the group of additive elements described above, adding tellurium (Te), silver (Ag), nickel (Ni), or indium (In) to the absorption pattern layer 41 further improves the absorption of EUV light and enables further thinning. Alternatively, among the elements included in the group of additive elements described above, adding iron (Fe), palladium (Pd), gold (Au), cobalt (Co), or iridium (Ir) to the absorption pattern layer 41 makes it possible to provide electrical conductivity to the absorption pattern layer 41 while ensuring high absorption of EUV light. This makes it possible to improve inspectability during mask pattern inspection.

[0036] Alternatively, when nitrogen (N), hafnium (Hf), tungsten (W), iodine (I), chromium (Cr), boron (B), or ruthenium (Ru) among the elements included in the above-described group of additional elements is added to the absorber layer 4, it is possible to make the film quality more amorphous. This makes it possible to improve the roughness and in-plane dimensional uniformity of the absorber layer pattern (mask pattern) 41 after dry etching, or the in-plane uniformity of the transferred image.

[0037] The total content of the elements included in the above-mentioned group of additive elements may be the same as the content of tantalum (Ta). That is, the absorption layer 4 and the absorption pattern layer 41 contain platinum (Pt), tantalum (Ta), and one or more elements selected from the above-mentioned group of additive elements, and the total content of the elements included in the above-mentioned group of additive elements may be equal to or less than the content of tantalum (Ta). More preferably, the total content of the elements included in the above-mentioned group of additive elements is within a range of 0.9 times or less the content of tantalum (Ta), and even more preferably, the total content of the elements included in the above-mentioned group of additive elements is within a range of 0.6 times or less the content of tantalum (Ta). With the above-mentioned configuration, the absorption layer 4 can be provided with excellent pattern processability while maintaining excellent transfer performance, and further provided with the various functions described above.

[0038] The OD value of the absorbing pattern layer 41 will be explained below. The intensity of reflected light from the reflective portion, which is the region where a portion of the absorbing layer 4 has been removed to expose the reflective layer 2 and capping layer 3, is defined as Rm, and the intensity of reflected light from the absorbing portion, which is the region where the absorbing layer 4 remains, is defined as Ra. The optical density (OD) value, which is an index representing the contrast in light intensity between the reflective portion and the absorbing portion, is defined by (Equation 1). The larger the OD value, the better the contrast and high transferability can be obtained. If the OD value is less than 1, sufficient contrast cannot be obtained and transfer performance tends to deteriorate. For pattern transfer, OD>1 is preferable, and 1.5 or more is even more preferable. Therefore, the OD value of the absorbing layer 4 (absorbing pattern layer 41) on which the transfer pattern is formed is preferably 1.0 or more, and more preferably 1.5 or more. OD=-log(Ra / Rm) (Equation 1)

[0039] As described above, the absorber layer 4 (absorber pattern layer 41) of conventional EUV reflective photomasks has been formed from a compound material primarily composed of tantalum (Ta). In this case, a thickness of 40 nm or greater is required for the absorber layer 4 to achieve an OD value of 1 or greater. While the extinction coefficient k of conventional materials is 0.031, forming the absorber layer 4 from a compound material primarily composed of platinum (Pt), whose extinction coefficient k is 0.058, makes it possible to reduce the thickness of the absorber layer 4 to 17 nm for an OD value of 1 or greater. However, the extinction coefficient k of the entire absorber layer 4 varies significantly depending on the mixing ratio of tantalum (Ta) to platinum (Pt) and the crystallinity of the deposited material. Therefore, if the extinction coefficient k of the entire absorber layer 4 is less than 0.049, a sufficient thinning effect is often not achieved. Therefore, to achieve a thinner layer than conventional layers, the extinction coefficient k of the entire absorber layer 4 is preferably 0.049 or greater, and more preferably 0.051 or greater.

[0040] Furthermore, if the thickness of the absorption layer 4 exceeds 50 nm, the projection effect will be similar to that of a conventional 60 nm absorption layer formed from a compound material primarily containing tantalum (Ta). Furthermore, if the thickness of the absorption layer 4 exceeds 50 nm, the pattern processability of the absorption layer 4 may be reduced. Therefore, the thickness of the absorption layer 4 according to this embodiment is in the range of 17 nm to 50 nm. In other words, if the thickness of the absorption layer 4 is in the range of 17 nm to 50 nm, the projection effect can be sufficiently reduced compared to conventional absorption layers formed from compound materials primarily containing tantalum (Ta), and the transfer performance can be improved. It is more preferable that the thickness of the absorption layer 4 is in the range of 25 nm to 40 nm. If the thickness of the absorption layer 4 is in the range of 25 nm to 40 nm, the projection effect can be further reduced compared to conventional absorption layers, and the transfer performance can be further improved. Furthermore, the "main component" mentioned above refers to a component that is contained in an amount of 50 atomic % or more of the total number of atoms in the absorption layer.

[0041] Alternatively, an oxide film (not shown) may be formed by oxidizing the upper surface of the absorption layer 4 or at least one of the upper surface and side surface of the absorption pattern layer 41. Alternatively, an oxide film (not shown) may be separately formed on the upper surface of the absorption layer 4 or at least one of the upper surface and side surface of the absorption pattern layer 41. The thickness of this oxide film is not particularly limited, but is, for example, in the range of 1 nm to 5 nm. The oxide film may be a natural oxide film that is naturally formed when the reflective photomask blank 10 or the reflective photomask 20 is stored or when the reflective photomask blank 10 or the reflective photomask 20 is cleaned.

[0042] (Hard Mask) As shown in FIG. 4 , the reflective photomask blank 10 according to an embodiment of the present invention may have a hard mask 5 formed on the absorber layer 4. The hard mask 5 according to this embodiment, when formed on the absorber layer 4, has the function of further enhancing the processability of the absorber layer 4. The material constituting the hard mask 5 is preferably a material that can be dry-etched with a gas different from the gas used to dry-etch the absorber layer 4. That is, when a material containing platinum (Pt) and tantalum (Ta), which is the material forming the absorber layer 4, is etched with a chlorine-based gas, it is preferable to use a gas other than a chlorine-based gas as the etching gas for the hard mask 5. Furthermore, when a material containing platinum (Pt) and tantalum (Ta), which is the material forming the absorber layer 4, is etched with a fluorine-based gas, it is preferable to use a gas other than a fluorine-based gas as the etching gas for the hard mask 5.

[0043] Therefore, it is preferable that the material constituting the hard mask 5 contains one or more selected from the group consisting of ruthenium (Ru), titanium (Ti), chromium (Cr), nickel (Ni), cobalt (Co), bismuth (Bi), iron (Fe), gold (Au), silver (Ag), hafnium (Hf), tantalum (Ta), aluminum (Al), and silicon (Si), as well as oxides, nitrides, borides, oxynitrides, oxyborides, and oxynitride boride thereof. That is, the absorption layer 4 may contain platinum (Pt), tantalum (Ta), and one or more elements selected from the above-described group of additional elements, and the hard mask 5 may contain one or more elements selected from the group consisting of ruthenium (Ru), titanium (Ti), chromium (Cr), nickel (Ni), cobalt (Co), bismuth (Bi), iron (Fe), gold (Au), silver (Ag), hafnium (Hf), tantalum (Ta), aluminum (Al), and silicon (Si), as well as oxides, nitrides, borides, oxynitrides, oxyborides, and oxynitride boride thereof.

[0044] Generally, dry etching occurs when introduced gas collides with electrons in the plasma, generating active radicals and reactive ions dissociated into various forms, which then cause etching. Therefore, the more volatile products with a low boiling point are formed on the etching surface, the more easily the material is etched. The boiling point and vapor pressure of the reaction products between the material to be etched and the introduced gas are indicators of this. In other words, the lower the boiling point of the reaction product, the more it vaporizes, the higher its vapor pressure and the easier it is to exhaust.

[0045] In etching the absorber layer 4 when fabricating the reflective photomask 20, the definitions of "easily etchable" and "resistant to etching" above mean that when the absorber layer 4 is easily etched by a chlorine-based gas, the boiling point of at least one chlorine-based compound produced by etching is 250°C or lower, and when the absorber layer 4 is resistant to etching by a chlorine-based gas, the boiling point of a stoichiometric chloride produced by etching is 300°C or higher. The same applies to fluorine-based gases. Therefore, it is desirable that the material used for the hard mask 5 is easily etched by a fluorine-based gas or a chlorine-based gas, that is, a substance whose fluorine-based compound or chlorine-based compound has a low boiling point.

[0046] Table 1 shows the boiling points of metal halogen compounds. The values ​​in Table 1 are a compilation of values ​​found in various literature (e.g., CRC Handbook of Chemistry and Ochemicals, 97th Edition (2016)) and websites. As shown in Table 1, examples of mixed materials that are easily etched with fluorine-based gases include ruthenium (Ru), bismuth (Bi), tantalum (Ta), and silicon (Si). Examples of mixed materials that are easily etched with chlorine-based gases include titanium (Ti), chromium (Cr), gold (Au), tantalum (Ta), aluminum (Al), and silicon (Si). Oxides, nitrides, oxynitrides, and boron nitrides of these mixed materials may also be used.

[0047]

[0048] However, the above is an example of an etching gas and its reactivity, and the etching gas in this embodiment is not limited to two types, fluorine-based gas and chlorine-based gas. In addition to fluorine-based gas and chlorine-based gas, a mixed gas of these may be used, and may contain a non-halogen gas such as oxygen gas or hydrogen gas to promote the reaction. By using the above mixed gas, it is possible to etch materials in which the boiling point of the fluorine-based compound or chlorine-based compound is not 250°C or lower.

[0049] The hard mask 5 must remain on the absorption layer 4 until etching of the absorption layer 4 is complete. However, if the film thickness of the hard mask 5 exceeds 30 nm, it may be difficult to form a fine pattern. Furthermore, if the film thickness of the hard mask 5 is less than 2 nm, the hard mask 5 may be too thin and it may be difficult to form a hard mask 5 having a uniform film thickness. Therefore, the film thickness of the hard mask 5 is preferably in the range of 2 nm to 30 nm, and more preferably in the range of 5 nm to 10 nm. Note that the processing of the absorption layer 4 in this embodiment is not limited to dry etching. For example, it is also possible to process the absorption layer 4 using atomic layer etching (ALE).

[0050] Examples of the reflective photomask blank and the reflective photomask according to the present invention will be described below.

[0051] Example 1 First, a method for fabricating a reflective photomask blank 10 will be described with reference to FIG. 5 . First, as shown in FIG. 5 , a reflective layer 2 was formed on a synthetic quartz substrate 1 having low thermal expansion characteristics, with 40 stacked layers each including a pair of silicon (Si) and molybdenum (Mo). The thickness of the reflective layer 2 was 280 nm. Next, a capping layer 3 made of ruthenium (Ru) was formed on the reflective layer 2 as an intermediate film to a thickness of 3.5 nm. Next, an absorption layer 4 containing platinum (Pt) and tantalum (Ta) was formed on the capping layer 3 to a thickness of 33 nm. Composition analysis of the formed absorption layer 4 using Rutherford backscattering spectroscopy (RBS) revealed that the platinum (Pt) content and tantalum (Ta) content of the entire absorption layer 4 were 55 atomic % and 45 atomic %, respectively.

[0052] Furthermore, the surface roughness (RMS) of the absorber layer 4 was measured using an atomic force microscope (AFM) and found to be 0.1 nm. Furthermore, when the crystallinity of the absorber layer 4 was measured using an XRD (X-ray diffraction) device, it was found to be amorphous, although slight crystallinity was observed. Next, a back surface conductive film 6 made of chromium nitride (CrN) was formed to a thickness of 100 nm on the surface of the substrate 1 on which the reflective layer 2 was not formed, thereby producing the reflective photomask blank 10 of Example 1. A sputtering device was used to form each film (layer) on the substrate 1. The film thickness of each film was controlled by the sputtering time.

[0053] Next, a method for fabricating a reflective photomask 20 will be described with reference to FIGS. 6 to 9 . First, as shown in FIG. 6 , a positive chemically amplified resist (SEBP9012, manufactured by Shin-Etsu Chemical Co., Ltd.) was spin-coated to a thickness of 120 nm on the absorption layer 4 of the reflective photomask blank 10, and baked at 110° C. for 10 minutes to form a resist film 7. Next, a predetermined pattern was written on the resist film 7 using an electron beam lithography machine (JBX3030, manufactured by JEOL Ltd.). Thereafter, a pre-baking process was performed at 110° C. for 10 minutes, and then a development process was performed using a spray developer (SFG3000, manufactured by Sigma Meltec Co., Ltd.). As a result, a resist pattern 71 was formed as shown in FIG. 7 .

[0054] Next, using the resist pattern 71 as an etching mask, the absorber layer 4 was patterned by dry etching using a chlorine-based gas. As a result, an absorber pattern (absorber pattern layer) 41 was formed in the absorber layer 4, as shown in FIG. 8 . Next, the resist pattern 71 was removed in a cleaning process, and the reflective photomask 20 of this example was fabricated, as shown in FIG. 9 . In this example, the absorber pattern 41 formed in the absorber layer 4 included, on the reflective photomask 20 for transfer evaluation, a 64-nm line-and-space (LS) pattern, a 200-nm line-width LS pattern for measuring the absorber layer thickness using an AFM, and a 4-mm square absorber layer removal portion for measuring EUV reflectivity. In this example, the 64-nm line-width LS pattern was designed in both the x and y directions, as shown in FIG. 10 , to make it easier to see the impact of the projection effect due to EUV irradiation.

[0055] Example 2-1 The absorber layer 4 was formed so that the platinum (Pt) content of the absorber layer 4 was 90 atomic % of the entire absorber layer 4 and the tantalum (Ta) content was 10 atomic % of the entire absorber layer 4. The absorber layer 4 was also formed to a film thickness of 28 nm. The surface roughness (RMS) of the absorber layer 4 thus formed was measured and found to be 0.3 nm. A reflective photomask blank 10 and a reflective photomask 20 of Example 2-1 were produced in the same manner as in Example 1, except for the formation of the absorber layer 4.

[0056] [Example 2-2] The absorber layer 4 was formed so that the platinum (Pt) content of the absorber layer 4 was 90 atomic % of the entire absorber layer 4, and the tantalum (Ta) content was 10 atomic % of the entire absorber layer 4. The absorber layer 4 was also formed to a thickness of 28 nm. The surface roughness (RMS) of the absorber layer 4 thus formed was measured and found to be 0.3 nm. Next, a silicon dioxide (SiO ２ A hard mask (HD: not shown) formed of the absorbing layer 4 was formed to a film thickness of 10 nm. A reflective photomask blank 10 of Example 2 was produced in the same manner as in Example 1, except for the formation of the absorbing layer 4.

[0057] Next, a resist pattern 71 was formed in the same manner as in Example 1. Thereafter, using the resist pattern 71 as an etching mask, a hard mask was patterned by dry etching mainly using a fluorine-based gas. Next, using the patterned hard mask as an etching mask, the absorbing layer 4 was patterned by dry etching mainly using a chlorine-based gas. As a result, an absorbing pattern (absorbing pattern layer) 41 was formed in the absorbing layer 4. Next, the resist pattern 71 was peeled off in a cleaning process. Finally, the hard mask used as the etching mask was removed by dry etching mainly using a fluorine-based gas. Otherwise, a reflective photomask 20 of Example 2-2 was fabricated in the same manner as in Example 1.

[0058] Example 3 The absorber layer 4 was formed so that the platinum (Pt) content of the absorber layer 4 was 60 atomic % of the entire absorber layer 4 and the tantalum (Ta) content was 40 atomic % of the entire absorber layer 4. The absorber layer 4 was also formed to a thickness of 39 nm. The surface roughness (RMS) of the absorber layer 4 thus formed was measured and found to be 0.1 nm. A reflective photomask blank 10 and a reflective photomask 20 of Example 3 were produced in the same manner as in Example 1, except for the formation of the absorber layer 4.

[0059] Example 4 An absorber layer 4 containing platinum (Pt), tantalum (Ta), and hafnium (Hf) was formed on the capping layer 3 to a thickness of 40 nm. The surface roughness (RMS) of the absorber layer 4 thus formed was measured and found to be 0.1 nm. Furthermore, composition analysis of the formed absorber layer 4 using Rutherford backscattering spectroscopy (RBS) revealed that the platinum (Pt) content in the entire absorber layer 4 was 60 atomic %, the tantalum (Ta) content was 30 atomic %, and the hafnium (Hf) content was 10 atomic %. A reflective photomask blank 10 and a reflective photomask 20 of Example 4 were produced in the same manner as in Example 1, except for the formation of the absorber layer 4.

[0060] Example 5 The absorber layer 4 was formed so that the platinum (Pt) content of the absorber layer 4 was 70 atomic % of the entire absorber layer 4 and the tantalum (Ta) content was 30 atomic % of the entire absorber layer 4. The absorber layer 4 was also formed to a thickness of 19 nm. The surface roughness (RMS) of the absorber layer 4 thus formed was measured and found to be 0.2 nm. A reflective photomask blank 10 and a reflective photomask 20 of Example 5 were produced in the same manner as in Example 1, except for the formation of the absorber layer 4.

[0061] Example 6-1 The absorber layer 4 was formed so that the platinum (Pt) content of the absorber layer 4 was 70 atomic % of the entire absorber layer 4 and the tantalum (Ta) content was 30 atomic % of the entire absorber layer 4. The absorber layer 4 was also formed to a thickness of 33 nm. The surface roughness (RMS) of the absorber layer 4 thus formed was measured and found to be 0.1 nm. A reflective photomask blank 10 and a reflective photomask 20 of Example 6-1 were produced in the same manner as in Example 1, except for the formation of the absorber layer 4.

[0062] Example 6-2 The absorber layer 4 was formed so that the platinum (Pt) content of the absorber layer 4 was 70 atomic % of the entire absorber layer 4 and the tantalum (Ta) content was 30 atomic % of the entire absorber layer 4. The absorber layer 4 was also formed to a thickness of 33 nm. The surface roughness (RMS) of the absorber layer 4 thus formed was measured and found to be 0.1 nm. A reflective photomask blank 10 and a reflective photomask 20 of Example 6-2 were produced in the same manner as in Example 2-2, except for the formation of the absorber layer 4.

[0063] Example 7-1 The absorber layer 4 was formed so that the platinum (Pt) content of the absorber layer 4 was 70 atomic % of the entire absorber layer 4 and the tantalum (Ta) content was 30 atomic % of the entire absorber layer 4. The absorber layer 4 was also formed to a thickness of 48 nm. The surface roughness (RMS) of the absorber layer 4 thus formed was measured and found to be 0.3 nm. A reflective photomask blank 10 and a reflective photomask 20 of Example 7-1 were produced in the same manner as in Example 1, except for the formation of the absorber layer 4.

[0064] Example 7-2 The absorber layer 4 was formed so that the platinum (Pt) content of the absorber layer 4 was 70 atomic % of the entire absorber layer 4 and the tantalum (Ta) content was 30 atomic % of the entire absorber layer 4. The absorber layer 4 was also formed to a thickness of 48 nm. The surface roughness (RMS) of the absorber layer 4 thus formed was measured and found to be 0.3 nm. A reflective photomask blank 10 and a reflective photomask 20 of Example 7-2 were produced in the same manner as in Example 2-2, except for the formation of the absorber layer 4.

[0065] Example 8-1 The absorber layer 4 was formed so that the platinum (Pt) content of the absorber layer 4 was 90 atomic % of the entire absorber layer 4 and the tantalum (Ta) content was 10 atomic % of the entire absorber layer 4. The absorber layer 4 was also formed to a film thickness of 45 nm. The surface roughness (RMS) of the absorber layer 4 thus formed was measured and found to be 0.4 nm. A reflective photomask blank 10 and a reflective photomask 20 of Example 8-1 were produced in the same manner as in Example 1, except for the formation of the absorber layer 4.

[0066] Example 8-2 The absorber layer 4 was formed so that the platinum (Pt) content of the absorber layer 4 was 90 atomic % of the entire absorber layer 4 and the tantalum (Ta) content was 10 atomic % of the entire absorber layer 4. The absorber layer 4 was also formed to a thickness of 45 nm. The surface roughness (RMS) of the absorber layer 4 thus formed was measured and found to be 0.4 nm. A reflective photomask blank 10 and a reflective photomask 20 of Example 8-2 were produced in the same manner as in Example 2-2, except for the formation of the absorber layer 4.

[0067] Example 9 An absorber layer 4 containing platinum (Pt), tantalum (Ta), and iodine (I) was formed on the capping layer 3 to a thickness of 26 nm. The surface roughness (RMS) of the absorber layer 4 thus formed was measured and found to be 0.1 nm. Furthermore, composition analysis of the formed absorber layer 4 using Rutherford backscattering spectroscopy (RBS) revealed that the platinum (Pt) content in the entire absorber layer 4 was 70 atomic %, the tantalum (Ta) content was 20 atomic %, and the iodine (I) content was 10 atomic %. A reflective photomask blank 10 and a reflective photomask 20 of Example 9 were produced in the same manner as in Example 1, except for the formation of the absorber layer 4.

[0068] Example 10 An absorber layer 4 containing platinum (Pt), tantalum (Ta), and cobalt (Co) was formed on the capping layer 3 to a thickness of 36 nm. The surface roughness (RMS) of the absorber layer 4 thus formed was measured and found to be 0.2 nm. Furthermore, composition analysis of the formed absorber layer 4 using Rutherford backscattering spectroscopy (RBS) revealed that the platinum (Pt) content in the entire absorber layer 4 was 60 atomic %, the tantalum (Ta) content was 20 atomic %, and the cobalt (Co) content was 20 atomic %. A reflective photomask blank 10 and a reflective photomask 20 of Example 10 were produced in the same manner as in Example 1, except for the formation of the absorber layer 4.

[0069] Example 11 An absorber layer 4 containing platinum (Pt), tantalum (Ta), and tellurium (Te) was formed on the capping layer 3 to a thickness of 24 nm. The surface roughness (RMS) of the absorber layer 4 thus formed was measured and found to be 0.3 nm. Furthermore, composition analysis of the formed absorber layer 4 using Rutherford backscattering spectroscopy (RBS) revealed that the platinum (Pt) content in the entire absorber layer 4 was 70 atomic %, the tantalum (Ta) content was 15 atomic %, and the tellurium (Te) content was 15 atomic %. A reflective photomask blank 10 and a reflective photomask 20 of Example 11 were produced in the same manner as in Example 1, except for the formation of the absorber layer 4.

[0070] Example 12 An absorber layer 4 containing platinum (Pt), tantalum (Ta), and boron (B) was formed on the capping layer 3 to a thickness of 41 nm. The surface roughness (RMS) of the absorber layer 4 thus formed was measured and found to be 0.1 nm. Furthermore, composition analysis of the formed absorber layer 4 using Rutherford backscattering spectroscopy (RBS) revealed that the platinum (Pt) content in the entire absorber layer 4 was 70 atomic %, the tantalum (Ta) content was 25 atomic %, and the boron (B) content was 5 atomic %. A reflective photomask blank 10 and a reflective photomask 20 of Example 12 were produced in the same manner as in Example 1, except for the formation of the absorber layer 4.

[0071] Example 13 An absorber layer 4 containing platinum (Pt), tantalum (Ta), and rhenium (Re) was formed on the capping layer 3 to a thickness of 33 nm. The surface roughness (RMS) of the absorber layer 4 thus formed was measured and found to be 0.2 nm. Furthermore, composition analysis of the formed absorber layer 4 using Rutherford backscattering spectroscopy (RBS) revealed that the platinum (Pt) content in the entire absorber layer 4 was 75 atomic %, the tantalum (Ta) content was 15 atomic %, and the rhenium (Re) content was 10 atomic %. A reflective photomask blank 10 and a reflective photomask 20 of Example 13 were produced in the same manner as in Example 1, except for the formation of the absorber layer 4.

[0072] Comparative Example 1 The absorber layer 4 was formed so that the platinum (Pt) content of the absorber layer 4 was 45 atomic % of the entire absorber layer 4 and the tantalum (Ta) content was 55 atomic % of the entire absorber layer 4. The absorber layer 4 was also formed to a thickness of 29 nm. The surface roughness (RMS) of the absorber layer 4 formed in this manner was measured and found to be 0.2 nm. A reflective photomask blank 10 and a reflective photomask 20 of Comparative Example 1 were produced in the same manner as in Example 1, except for the formation of the absorber layer 4.

[0073] Comparative Example 2 The absorber layer 4 was formed so that the platinum (Pt) content of the absorber layer 4 was 30 atomic % of the entire absorber layer 4 and the tantalum (Ta) content was 70 atomic % of the entire absorber layer 4. The absorber layer 4 was also formed to a film thickness of 28 nm. The surface roughness (RMS) of the absorber layer 4 thus formed was measured and found to be 0.3 nm. A reflective photomask blank 10 and a reflective photomask 20 of Comparative Example 2 were produced in the same manner as in Example 1, except for the formation of the absorber layer 4.

[0074] [Comparative Example 3] The absorber layer 4 was formed so that the platinum (Pt) content of the absorber layer 4 was 70 atomic % of the entire absorber layer 4 and the tantalum (Ta) content was 30 atomic % of the entire absorber layer 4. The absorber layer 4 was also formed to a film thickness of 15 nm. The surface roughness (RMS) of the absorber layer 4 formed in this manner was measured and found to be 0.2 nm. A reflective photomask blank 10 and a reflective photomask 20 of Comparative Example 3 were produced in the same manner as in Example 1, except for the formation of the absorber layer 4.

[0075] Comparative Example 4 The absorber layer 4 was formed so that the platinum (Pt) content of the absorber layer 4 was 70 atomic % of the entire absorber layer 4 and the tantalum (Ta) content was 30 atomic % of the entire absorber layer 4. The absorber layer 4 was also formed to a film thickness of 55 nm. The surface roughness (RMS) of the absorber layer 4 formed in this manner was measured and found to be 0.4 nm. A reflective photomask blank 10 and a reflective photomask 20 of Comparative Example 4 were produced in the same manner as in Example 1, except for the formation of the absorber layer 4.

[0076] Comparative Example 5 The absorber layer 4 was formed so that the platinum (Pt) content of the absorber layer 4 was 55 atomic % of the entire absorber layer 4 and the tantalum (Ta) content was 45 atomic % of the entire absorber layer 4. The absorber layer 4 was also formed to a thickness of 33 nm. The surface roughness (RMS) of the absorber layer 4 thus formed was measured and found to be 0.5 nm. A reflective photomask blank 10 and a reflective photomask 20 of Comparative Example 5 were produced in the same manner as in Example 1, except for the formation of the absorber layer 4.

[0077] [Comparative Example 6] The absorbing layer 4 was formed so that the platinum (Pt) content of the absorbing layer 4 was 100 atomic % of the entire absorbing layer 4. The absorbing layer 4 was also formed so that its film thickness was 33 nm. The surface roughness (RMS) of the absorbing layer 4 formed in this manner was measured and found to be 0.6 nm. A reflective photomask blank 10 and a reflective photomask 20 of Comparative Example 6 were produced in the same manner as in Example 1, except for the formation of the absorbing layer 4.

[0078] In addition to the above-mentioned examples and comparative examples, a reflective photomask (existing mask) having an absorption pattern layer composed of TaBO / TaBN, which is a conventional tantalum (Ta)-based absorption pattern layer, was also compared as a reference example. Similar to the above-mentioned examples and comparative examples, the reflective photomask blank had a reflective layer formed by stacking 40 laminated films each consisting of a pair of silicon (Si) and molybdenum (Mo) on a synthetic quartz substrate with low thermal expansion characteristics, and a ruthenium (Ru) capping layer 3 with a thickness of 3.5 nm. The absorption layer 4 formed on the capping layer 3 was formed by depositing TaBO with a thickness of 2 nm on TaBN with a thickness of 58 nm. The surface roughness (RMS) of the thus-formed absorption layer 4 was measured and found to be 0.1 nm. Furthermore, similar to the above-mentioned examples and comparative examples, a patterned absorption layer 4 was used for evaluation. In the above-mentioned examples and comparative examples, the thickness of the absorption layer 4 was measured using a transmission electron microscope.

[0079] The evaluation items evaluated in this example are described below. (Processability) In the above-described examples and comparative examples, SEM analysis was performed to check for disconnections or missing defects (so-called pattern defects) in the pattern in the absorption pattern layer 41. The cross-sectional shape of the pattern in the absorption pattern layer 41 was also confirmed. If the formed pattern had no abnormalities, it was deemed that there were no problems with processing suitability (transfer performance), and the evaluation was rated "pass (△)." Furthermore, if the formed pattern had no abnormalities and the sidewall angle (the angle of elevation based on the surface of the capping layer 3) confirmed from the cross-sectional image was 80° or greater, it was deemed that there were no problems with processing suitability (transfer performance), and the evaluation was rated "pass (◯)." In other words, it is suggested that the processing suitability (transfer performance) is improved by providing a hard mask (HD) in each of the embodiments of Example 2-1, Example 6-1, Example 7-1, and Example 8-1.

[0080] (Reflectance) In the above-described Examples and Comparative Examples, the reflectance Ra of the absorption pattern layer 41 region (see FIG. 10 ) of the fabricated reflective photomask 20 was measured using a reflectance measurement device for EUV light. The reflectance Rm of the reflective portion 8 (see FIG. 10 ) where the absorption pattern layer 41 was not formed was also measured using a reflectance measurement device for EUV light. The OD values ​​of the reflective photomasks 20 according to the Examples and Comparative Examples were calculated using the above-described formula 1. As described above, if the OD value is less than 1.0, sufficient contrast cannot be obtained, and transfer performance deteriorates. Therefore, if the OD value is 1.0 or more, there is no problem with transfer performance, and the mask was rated "pass" in this evaluation.

[0081] (Wafer Exposure Evaluation) Using an EUV exposure apparatus (NXE3300B: manufactured by ASML), the absorption patterns 41 of the reflective photomasks 20 produced in the examples and comparative examples were transferred and exposed onto a semiconductor wafer coated with an EUV positive chemically amplified resist. At this time, the exposure dose was adjusted so that the x-direction LS pattern shown in FIG. 10 was transferred as designed. Specifically, in this exposure test, the x-direction LS pattern (line width 64 nm) shown in FIG. 10 was exposed so that it had a line width of 16 nm on the semiconductor wafer. The transferred resist patterns were observed and line widths were measured using an electron beam dimension measuring machine, and changes in the HV bias value were compared by simulation.

[0082] The HV bias value is the line width difference of the transfer pattern that depends on the orientation of the mask pattern, that is, the difference between the line width in the horizontal (H) direction and the line width in the vertical (V) direction. The line width in the H direction indicates the line width of the linear pattern that is perpendicular to the plane formed by the incident light and the reflected light (hereinafter sometimes referred to as the "incident plane"), and the line width in the V direction indicates the line width of the linear pattern that is parallel to the incident plane. In other words, the line width in the H direction is the length in the direction parallel to the incident plane, and the line width in the V direction is the length in the direction perpendicular to the incident plane.

[0083] The evaluation method was based on the HV bias value of the existing tantalum (Ta)-based photomask shown in Table 2 as "Existing Mask," and the evaluation was based on the magnitude of the HV bias value. In other words, in a state where the LS pattern in the x direction was adjusted to be transferred as designed, the LS pattern in the y direction was transferred as designed, and the HV bias was smaller than when using an existing tantalum (Ta)-based photomask, the evaluation was deemed "pass." In addition, in a state where the LS pattern in the x direction was adjusted to be transferred as designed, the LS pattern was not transferred as designed (the LS pattern in the y direction was not resolved), or the HV bias was larger than when using an existing tantalum (Ta)-based photomask, the evaluation was deemed "fail." These evaluation results are shown in the table. In addition to the above evaluation results, the table also shows the refractive index n and extinction coefficient k.

[0084]

[0085] Table 2 shows a comparison of the OD values ​​of each Example and each Comparative Example. As mentioned above, when the OD value is less than 1.0, sufficient contrast cannot be obtained, and transfer performance deteriorates. The OD value of a conventional reflective photomask (existing reflective photomask) having a tantalum (Ta)-based absorption pattern layer with a film thickness of 60 nm is 1.69, whereas the OD value of the reflective photomask 20 of Example 1 is 1.67, the OD values ​​of the reflective photomasks 20 of Examples 2-1 and 2-2 are 1.39, the OD value of the reflective photomask 20 of Example 3 is 1.57, the OD value of the reflective photomask 20 of Example 4 is 1.95, the OD value of the reflective photomask 20 of Example 5 is 1.02, and the OD value of the reflective photomask 20 of Examples 6-1 and 6-2 is 1.69. The OD value of the reflective photomask 20 of Example 0 was 1.74, the OD values ​​of the reflective photomasks 20 of Examples 7-1 and 7-2 were 2.67, the OD values ​​of the reflective photomasks 20 of Examples 8-1 and 8-2 were 1.58, the OD value of the reflective photomask 20 of Example 9 was 1.46, the OD value of the reflective photomask 20 of Example 10 was 1.45, the OD value of the reflective photomask 20 of Example 11 was 1.13, the OD value of the reflective photomask 20 of Example 12 was 2.46, and the OD value of the reflective photomask 20 of Example 13 was 1.71. Furthermore, in the comparative examples, the OD value of the reflective photomask 20 of Comparative Example 1 was 1.00, the OD value of the reflective photomask 20 of Comparative Example 2 was 0.98, the OD value of the reflective photomask 20 of Comparative Example 3 was 0.57, the OD value of the reflective photomask 20 of Comparative Example 4 was 2.45, the OD value of the reflective photomask 20 of Comparative Example 5 was 1.67, and the OD value of the reflective photomask 20 of Comparative Example 6 was 1.74. In other words, the OD values ​​of Comparative Examples 2 and 3 were each less than 1.0, and did not satisfy the criteria for "pass" in this evaluation.

[0086] A comparison of the HV bias between each example and each comparative example is shown in Table 2. As a result of patterning with EUV light using a conventional reflective photomask having a tantalum (Ta)-based absorption pattern layer with a thickness of 60 nm, the HV bias was 1.80 nm. In contrast, the HV bias of Example 1 was 1.47 nm, the HV bias of Example 2-1 was 1.78 nm, the HV bias of Example 3 was 1.23 nm, the HV bias of Example 4 was 1.18 nm, the HV bias of Example 5 was 1.46 nm, the HV bias of Example 6-1 was 1.38 nm, the HV bias of Example 7-1 was 0.85 nm, the HV bias of Example 8-1 was 0.77 nm, the HV bias of Example 9 was 1.43 nm, the HV bias of Example 10 was 1.62 nm, the HV bias of Example 11 was 1.44 nm, the HV bias of Example 12 was 1.15 nm, and the HV bias of Example 13 was 1.32 nm. In addition, in the comparative examples, the HV bias of Comparative Example 4 was 0.81 nm, the HV bias of Comparative Example 5 was 1.47 nm, and the HV bias of Comparative Example 6 was 0.98 nm, which met the "pass" criteria in this evaluation.

[0087] In contrast, the HV bias of Comparative Example 1 was 1.85 nm, and as a result of patterning with EUV light, the transferability was worse than that of a conventional tantalum (Ta)-based photomask. Note that for Comparative Examples 2 and 3, the OD values ​​were small, and the absorber layer 4 could not be patterned, so the HV bias could not be measured.

[0088] Here, in this example, the HV bias was not evaluated for each of the configurations of Example 2-2, Example 6-2, Example 7-2, and Example 8-2 (i.e., configurations with hard masks). The reason for this is that, as long as each of the configurations of Example 2-1, Example 6-1, Example 7-1, and Example 8-1 (i.e., configurations without hard masks) has excellent processing characteristics and meets the criteria for a "pass" HV bias evaluation, the HV bias value does not decrease even when a hard mask is further provided, and the HV bias evaluation does not result in a "fail" HV bias. In other words, the HV bias values ​​of each configuration with a hard mask (Example 2-2, Example 6-2, Example 7-2, and Example 8-2) are equivalent to the HV bias values ​​of each configuration without a hard mask (Example 2-1, Example 6-1, Example 7-1, and Example 8-1), and therefore are omitted from Table 2.

[0089] Table 2 shows a comprehensive evaluation of the processability, OD value, and HV bias. Reflective photomasks 20 that can suppress or reduce the projection effect and have a processable absorbing layer are marked with "○" in the "Evaluation" column, and reflective photomasks 20 that cannot sufficiently suppress or reduce the projection effect or have low processability of the absorbing layer are marked with "×" in the "Evaluation" column. Since conventional tantalum (Ta)-based photomasks were used for comparison, they were marked with "△" in the "Evaluation" column.

[0090] Furthermore, the surface roughness (RMS) of Examples 1 to 13 and Comparative Examples 1 to 6 was also confirmed as a supplementary measure. An atomic force microscope (AFM) was used for the measurements. In order to suppress the influence of the reflectivity of EUV light, if an RMS of 0.4 nm or less is considered "pass," the reflective photomasks 20 of Examples 1 to 13 and Comparative Examples 1 to 4 met the "pass" criteria in this evaluation, while Comparative Examples 5 and 6 were "failed."

[0091] As a result, in a reflective photomask in which the absorption pattern layer 41 is formed from a material containing 50 atomic % or more of platinum (Pt) and tantalum (Ta) in the range of 5 atomic % or more but less than 50 atomic %, the film thickness of the absorption pattern layer 41 is in the range of 17 nm or more and 50 nm or less, the extinction coefficient of the absorption pattern layer 41 for EUV light is 0.049 or more, and the surface roughness of the absorption pattern layer 41 is 0.4 nm or less, the processability (pattern processability), optical density (OD value), and HV bias of the absorption layer 4 are all good, so that a transfer pattern can be reliably formed on the reflective photomask blank, the projection effect can be reduced, and transfer performance is improved.

[0092] Furthermore, for example, the reflective photomask blank, reflective photomask, and method for manufacturing a reflective photomask according to the present disclosure can have the following configurations: (1) A reflective photomask blank for producing a reflective photomask for pattern transfer using extreme ultraviolet light as a light source, comprising: a substrate; a reflective layer including a multilayer film formed on the substrate; and an absorbing layer formed on the reflective layer, wherein the absorbing layer is formed of a material containing 50 atomic % or more of platinum (Pt) and 5 atomic % or more but less than 50 atomic % of tantalum (Ta), the film thickness of the absorbing layer is in the range of 17 nm or more and 50 nm or less, the extinction coefficient of the absorbing layer for EUV light is 0.049 or more, and the surface roughness of the absorbing layer is 0.4 nm or less. (2) The reflective photomask blank according to (1) above, wherein the absorbing layer is formed of a material containing 20 atomic % or more and 40 atomic % or less of tantalum (Ta). (3) The reflective photomask blank according to (1) or (2), wherein the absorption layer further contains one or more elements selected from the group consisting of ruthenium (Ru), iridium (Ir), titanium (Ti), chromium (Cr), indium (In), nickel (Ni), cobalt (Co), bismuth (Bi), iron (Fe), gold (Au), silver (Ag), iodine (I), tellurium (Te), hafnium (Hf), tungsten (W), palladium (Pd), rhenium (Re), aluminum (Al), nitrogen (N), zinc (Zn), gallium (Ga), and boron (B). (4) The reflective photomask blank according to any one of (1) to (3), further comprising a hard mask on the absorption layer, wherein the film thickness of the hard mask is in the range of 2 nm to 30 nm.(5) The reflective photomask blank according to any one of (1) to (4), wherein the hard mask comprises one or more elements selected from the group consisting of ruthenium (Ru), titanium (Ti), chromium (Cr), nickel (Ni), cobalt (Co), bismuth (Bi), iron (Fe), gold (Au), silver (Ag), hafnium (Hf), tantalum (Ta), aluminum (Al), and silicon (Si), as well as oxides, nitrides, borides, oxynitrides, oxyborides, and oxynitride boride thereof. (6) The reflective photomask blank according to any one of (1) to (5), wherein an oxide film is provided on the absorption layer. (7) The reflective photomask blank according to any one of (1) to (6), wherein a capping layer is formed between the reflective layer and the absorption layer. (8) A reflective photomask for pattern transfer using extreme ultraviolet light as a light source, comprising: a substrate; a reflective layer including a multilayer film formed on the substrate; and an absorbing pattern layer formed on the reflective layer, wherein the absorbing pattern layer is formed of a material containing 50 atomic % or more of platinum (Pt) and 5 atomic % or more but less than 50 atomic % of tantalum (Ta), the film thickness of the absorbing pattern layer is in the range of 17 nm or more and 50 nm or less, the extinction coefficient of the absorbing layer for EUV light is 0.049 or more, and the surface roughness of the absorbing pattern layer is 0.4 nm or less. (9) The reflective photomask according to (8) above, wherein the absorbing pattern layer is formed of a material containing 20 atomic % or more and 40 atomic % of tantalum (Ta). (10) The reflective photomask according to (8) or (9), wherein the absorption pattern layer further contains one or more elements selected from the group consisting of ruthenium (Ru), iridium (Ir), titanium (Ti), chromium (Cr), indium (In), nickel (Ni), cobalt (Co), bismuth (Bi), iron (Fe), gold (Au), silver (Ag), iodine (I), tellurium (Te), hafnium (Hf), tungsten (W), palladium (Pd), rhenium (Re), aluminum (Al), nitrogen (N), zinc (Zn), gallium (Ga), and boron (B).(11) The reflective photomask according to any one of (8) to (10), which has an oxide film on at least one of the top and side surfaces of the absorbing pattern layer. (12) The reflective photomask according to any one of (8) to (11), which has a capping layer formed between the reflective layer and the absorbing pattern layer. (13) A method for manufacturing a reflective photomask for pattern transfer using extreme ultraviolet light as a light source, comprising the steps of: forming a reflective layer including a multilayer film on a substrate; and forming an absorbing pattern layer on the reflective layer, wherein the absorbing pattern layer is formed of a material containing 50 atomic % or more of platinum (Pt) and 5 atomic % or more but less than 50 atomic % of tantalum (Ta), the film thickness of the absorbing pattern layer is in the range of 17 nm to 50 nm, the extinction coefficient of the absorbing pattern layer for EUV light is 0.049 or more, and the surface roughness of the absorbing pattern layer is 0.4 nm or less.

[0093] The reflective photomask according to the present invention can be suitably used to form fine patterns by EUV exposure in the manufacturing process of semiconductor integrated circuits and the like.

[0094] REFERENCE SIGNS LIST 1 substrate 2 reflective layer 3 capping layer 4 absorbing layer 41 absorbing pattern (absorbing pattern layer) 5 hard mask 10 reflective photomask blank 20 reflective photomask 6 back surface conductive film 7 resist film 71 resist pattern 8 reflective portion

Claims

1. A reflective photomask blank for producing a reflective photomask for pattern transfer using extreme ultraviolet light as a light source, comprising: a substrate; a reflective layer including a multilayer film formed on the substrate; and an absorbing layer formed on the reflective layer, wherein the absorbing layer is formed of a material containing 50 atomic % or more of platinum (Pt) and 5 atomic % or more but less than 50 atomic % of tantalum (Ta), the film thickness of the absorbing layer is in the range of 17 nm or more and 50 nm or less, the extinction coefficient of the absorbing layer for EUV light is 0.049 or more, and the surface roughness of the absorbing layer is 0.4 nm or less.

2. A reflective photomask blank according to claim 1, wherein the absorption layer is formed from a material containing tantalum (Ta) in the range of 20 atomic % to 40 atomic %.

3. The reflective photomask blank according to claim 1, wherein the absorption layer further contains one or more elements selected from the group consisting of ruthenium (Ru), iridium (Ir), titanium (Ti), chromium (Cr), indium (In), nickel (Ni), cobalt (Co), bismuth (Bi), iron (Fe), gold (Au), silver (Ag), iodine (I), tellurium (Te), hafnium (Hf), tungsten (W), palladium (Pd), rhenium (Re), aluminum (Al), nitrogen (N), zinc (Zn), gallium (Ga), and boron (B).

4. The reflective photomask blank according to claim 3, further comprising a hard mask on the absorption layer, the hard mask having a thickness in the range of 2 nm to 30 nm.

5. The reflective photomask blank according to claim 4, wherein the hard mask is made of one or more elements selected from the group consisting of ruthenium (Ru), titanium (Ti), chromium (Cr), nickel (Ni), cobalt (Co), bismuth (Bi), iron (Fe), gold (Au), silver (Ag), hafnium (Hf), tantalum (Ta), aluminum (Al), and silicon (Si), as well as oxides, nitrides, borides, oxynitrides, oxyborides, and oxynitride boride products thereof.

6. The reflective photomask blank according to claim 3, which has an oxide film on the absorption layer.

7. The reflective photomask blank according to any one of claims 1 to 6, wherein a capping layer is formed between the reflective layer and the absorbing layer.

8. A reflective photomask for pattern transfer using extreme ultraviolet light as a light source, comprising: a substrate; a reflective layer including a multilayer film formed on the substrate; and an absorbing pattern layer formed on the reflective layer, wherein the absorbing pattern layer is formed of a material containing 50 atomic % or more of platinum (Pt) and 5 atomic % or more but less than 50 atomic % of tantalum (Ta), the film thickness of the absorbing pattern layer is in the range of 17 nm or more and 50 nm or less, the extinction coefficient of the absorbing pattern layer for EUV light is 0.049 or more, and the surface roughness of the absorbing pattern layer is 0.4 nm or less.

9. The reflective photomask according to claim 8, wherein said absorption pattern layer is formed from a material containing tantalum (Ta) in the range of 20 atomic % to 40 atomic %.

10. The reflective photomask according to claim 9, wherein the absorption pattern layer further contains one or more elements selected from the group consisting of ruthenium (Ru), iridium (Ir), titanium (Ti), chromium (Cr), indium (In), nickel (Ni), cobalt (Co), bismuth (Bi), iron (Fe), gold (Au), silver (Ag), iodine (I), tellurium (Te), hafnium (Hf), tungsten (W), palladium (Pd), rhenium (Re), aluminum (Al), nitrogen (N), zinc (Zn), gallium (Ga), and boron (B).

11. The reflective photomask according to claim 10, further comprising an oxide film on at least one of the top surface of said absorbing pattern layer and the side surface of said absorbing pattern layer.

12. The reflective photomask according to any one of claims 8 to 11, wherein a capping layer is formed between the reflective layer and the absorbing pattern layer.

13. A method for manufacturing a reflective photomask for pattern transfer using extreme ultraviolet light as a light source, comprising the steps of: forming a reflective layer including a multilayer film on a substrate; and forming an absorbing pattern layer on the reflective layer, wherein the absorbing pattern layer is formed from a material containing 50 atomic % or more of platinum (Pt) and 5 atomic % or more but less than 50 atomic % of tantalum (Ta), the film thickness of the absorbing pattern layer is in the range of 17 nm or more and 50 nm or less, the extinction coefficient of the absorbing pattern layer for EUV light is 0.049 or more, and the surface roughness of the absorbing pattern layer is 0.4 nm or less.

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