JP7597305B1 - Reflective photomask blank, reflective photomask, and method for manufacturing reflective photomask - Google Patents

Abstract

The present invention provides a reflective photomask that uses light with a wavelength in the extreme ultraviolet region as a light source and has an absorbing 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.
[Solution] A reflective photomask blank 10 according to an embodiment of the present invention has a substrate 1, a reflective layer 2, and an absorbing layer 4, the absorbing layer 4 being formed from a material containing 50 atomic % or more of platinum (Pt) and 5 atomic % or more and less than 50 atomic % of tantalum (Ta), the film thickness of the absorbing layer 4 being in the range of 17 nm or more and 50 nm or less, the extinction coefficient of the absorbing layer 4 with respect to EUV light being 0.049 or more, and the surface roughness of the absorbing layer 4 being 0.4 nm or less.
[Selected Figure] Figure 1

Description

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

In the manufacturing process of semiconductor devices, the demand for finer photolithography technology is increasing as semiconductor devices become finer. The minimum resolution dimension of the transfer pattern in photolithography depends heavily on the wavelength of the exposure light source, and the shorter the wavelength, the smaller the minimum resolution dimension can be. For this reason, exposure light sources are being replaced from the conventional 193 nm wavelength ArF excimer laser light to light in the EUV (Extreme Ultra Violet) range with a wavelength of 13.5 nm.

Light in the EUV region is absorbed at a high rate by most materials, so reflective photomasks are used as photomasks for EUV exposure (EUV masks) (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) on top of that, and forming a pattern on this light absorbing layer.

As mentioned above, EUV lithography cannot use refractive optics that utilize the transmission of light, so the optical components of the exposure machine are reflective (mirrors) rather than lenses. This creates the problem that the light incident on a reflective photomask (EUV mask) and the light reflected by the EUV mask cannot be designed to be coaxial, so EUV lithography typically employs a method in which the optical axis is tilted 6 degrees from the vertical direction of the EUV mask, and the reflected light reflected at an angle of minus 6 degrees is guided to the semiconductor substrate.

As described above, in EUV lithography, the optical axis is tilted via a mirror, which can cause a problem known as the "projection 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.
In current EUV mask blanks, a film mainly composed of tantalum (Ta) with a thickness of 60 to 90 nm is used as the light absorbing layer. When an EUV mask manufactured using this mask blank is used for pattern transfer exposure, there is a risk of causing a decrease in contrast at the edge portion of the mask pattern that is in the shadow, depending on the relationship between the incident direction of the EUV light and the orientation of the mask pattern. This can lead to problems such as an increase in line edge roughness of the transfer pattern on the semiconductor substrate and an inability to form the line width to the targeted dimension, resulting in a deterioration in transfer performance.

Therefore, reflective photomask blanks have been considered in which the light absorption layer is changed from tantalum (Ta) to a material with high absorptivity (extinction coefficient) for EUV light, or a material with high absorptivity is added to tantalum (Ta). For example, Patent Document 2 describes a reflective photomask blank in which the light absorption layer is made of an alloy containing at least two materials selected from Pt, Zn, Au, NiO, Ag ₂ O, Ir, Fe, SnO ₂ , Co, etc.

However, some materials that are highly absorptive of EUV light are difficult to process using dry etching, and even if a photomask blank is formed (produced), the light absorbing layer on the photomask blank cannot be patterned, which is a problem.

Patent No. 5418293 Special table 2019-527382 publication

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 absorbing 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.

The present disclosure has been made to solve the above 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, and is characterized in that it has 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 and 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 for EUV light being 0.049 or more, and the surface roughness of the absorbing layer being 0.4 nm or less.

In addition, 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, and includes a substrate, a reflective layer including a multilayer film formed on the substrate, and an absorbing pattern layer formed on the reflective layer, the absorbing pattern layer being formed of a material containing 50 atomic % or more of platinum (Pt) and 5 atomic % or more and less than 50 atomic % of tantalum (Ta), the thickness of the absorbing pattern layer being in the range of 17 nm or more and 50 nm or less, the extinction coefficient of the absorbing layer for EUV light being 0.049 or more, and the surface roughness of the absorbing pattern layer being 0.4 nm or less.

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

The reflective photomask blank according to one embodiment of the present disclosure makes it possible to create an absorption layer with good pattern processability. In other words, the reflective photomask blank according to one embodiment of the present disclosure can provide a reflective photomask blank with excellent pattern processability for the absorption layer. In other words, the reflective photomask blank according to one embodiment of the present disclosure can provide a reflective photomask blank with an absorption layer that can provide 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.

In addition, the reflective photomask according to one embodiment of the present disclosure can provide a reflective photomask having an absorption layer with good patterning processability, which is to say, the reflective photomask according to one embodiment of the present disclosure can be expected to improve the transfer performance onto a semiconductor substrate in patterning using light in the extreme ultraviolet region as a light source.
Furthermore, the method for producing a reflective photomask according to an embodiment of the present disclosure can produce a reflective photomask having an absorption layer with good pattern processability. In other words, the method for producing a reflective photomask according to an embodiment of the present disclosure can produce a reflective photomask that is expected to have improved transfer performance to a semiconductor substrate in patterning using light in the extreme ultraviolet region as a light source.

Thus, 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.

1 is a schematic cross-sectional view showing a structure of a reflective photomask blank according to an embodiment of the present invention. 1 is a schematic cross-sectional view showing a structure of a reflective photomask according to an embodiment of the present invention. 1 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 a structure of a reflective photomask blank according to another embodiment of the present invention. FIG. 1 is a schematic cross-sectional view showing a structure of a reflective photomask blank according to an embodiment of the present invention. 1A to 1C are schematic cross-sectional views showing a manufacturing process of a reflective photomask according to an embodiment of the present invention. 1A to 1C are schematic cross-sectional views showing a manufacturing process of a reflective photomask according to an embodiment of the present invention. 1A to 1C are schematic cross-sectional views showing a manufacturing process of a reflective photomask according to an embodiment of the present invention. 1 is a schematic cross-sectional view showing a structure of a reflective photomask according to an embodiment of the present invention. 1 is a schematic plan view showing the shape of a design pattern of a reflective photomask according to an embodiment of the present invention.

The following describes an embodiment of the present invention with reference to the drawings, but the present invention is not limited to the embodiment shown below. In the embodiment shown below, technically preferable limitations are imposed for implementing the present invention, but these limitations are not essential requirements for the present invention.

Figure 1 is a schematic cross-sectional view showing the structure of a reflective photomask blank 10 according to an embodiment of the present invention. Also, Figure 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 Figure 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 Figure 1.

(Overall structure)
As shown in FIG. 1, a reflective photomask blank 10 according to an embodiment of the present invention comprises 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.

(substrate)
For example, a flat Si substrate, a synthetic quartz substrate, etc. can be used for the substrate 1 according to the embodiment of the present invention. In addition, low thermal expansion glass containing titanium can 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.

(Reflective Layer)
The reflective layer 2 according to the embodiment of the present invention may be any layer that reflects the EUV light (extreme ultraviolet light) that is the 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 the 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.

(Capping Layer)
The capping layer 3 according to the embodiment of the present invention is made of a material that is resistant to dry etching 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 made of, 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. In addition, although not shown, a back conductive film can be formed on the surface of the substrate 1 on which the reflective layer 2 is not formed. The back conductive film is a film for fixing the reflective photomask 20 by utilizing the principle of an electrostatic chuck when the reflective photomask 20 is placed in an exposure machine.

(Absorption layer)
As shown in Fig. 2, an absorption pattern (absorption pattern layer) 41 of the reflective photomask 20 is formed by removing a part of the absorption layer 4 of the reflective photomask blank 10, i.e., by patterning the absorption layer 4. In EUV lithography, EUV light is incident at an angle and reflected by the reflective layer 2, but due to a projection effect in which the absorption pattern 41 obstructs the optical path, the transfer performance onto the wafer (semiconductor substrate) may deteriorate. This deterioration in transfer performance can be reduced by reducing the thickness of the absorption layer 4 that absorbs EUV light. In order to reduce the thickness of the absorption layer 4, it is preferable to use a material that is more absorbent for EUV light than conventional materials, that is, a material with a high extinction coefficient k for a wavelength of 13.5 nm.

Figure 3 is a graph showing the optical constants of each metal material for the 13.5 nm wavelength of EUV light. 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), the main material of the conventional absorption layer 4, is 0.041. If a compound material has a larger extinction coefficient k than this, it is possible to make the thickness of the absorption layer 4 thinner than before.

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

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

In order 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 of a material (alloy) containing platinum (Pt) and tantalum (Ta). Platinum (Pt) alone has high resistance to liquids used for cleaning photomasks and also has high resistance 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 and the absorption pattern layer 41, it is possible to process the absorption layer 4 by dry etching while maintaining high hydrogen radical resistance.

In this embodiment, "poor dry etching properties" refers to a state in which, when the absorption 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 of the absorption pattern layer 41 in the pattern formation portion, that is, the elevation angle (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°.
In this embodiment, "high hydrogen radical resistance" means that the film reduction rate is 0.01 nm/s or less in a hydrogen radical environment where the hydrogen pressure is 0.36 millibars (mbar) or less and a power of 1 kW is used by using microwave plasma.

The material constituting the absorbing layer 4 contains platinum (Pt) at 50 atomic % or more relative to the number of atoms constituting the entire absorbing layer 4. Note that the material constituting the absorbing layer 4 preferably contains platinum (Pt) in the range of 50 atomic % or more and 95 atomic % or less relative to the number of atoms constituting the entire absorbing layer 4, more preferably contains platinum (Pt) in the range of 55 atomic % or more and 90 atomic % or less, and even more preferably contains platinum (Pt) in the range of 60 atomic % or more and 80 atomic % or less.
The absorbing layer 4 contains 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 absorbing layer 4. This is because, although there is a possibility that the EUV light absorption properties will decrease if the absorbing layer 4 contains components other than platinum (Pt), if the components other than platinum (Pt) are less than 50 atomic %, the decrease in EUV light absorption properties will be very slight, and there will be almost no decrease in performance as the absorbing layer 4 of the EUV mask.

Furthermore, while platinum (Pt) alone is difficult to process by dry etching, adding tantalum (Ta) to platinum (Pt) improves processability by dry etching, and enables dry etching using a chlorine-based gas, a fluorine-based gas, or a mixed gas, so that a reflective photomask blank can be processed into a reflective photomask. Specifically, if the content of tantalum (Ta) contained in the absorption layer 4 is within a range of 5 atomic % or more and less than 50 atomic % of the number of atoms constituting the entire absorption layer 4, the processability of the absorption layer 4 by dry etching can be improved while maintaining hydrogen radical resistance.

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

The above composition ratio of the materials constituting the absorption layer 4 is calculated based on the analysis results by Rutherford backscattering spectrometry (RBS), and the content may vary depending on the analysis method. For example, a material with a platinum (Pt) content of 50 atomic % to 99 atomic % of all metal elements by Rutherford backscattering spectrometry (RBS) may be analyzed using X-ray photoelectron spectroscopy (XPS) to find that it is 40 atomic % to 75 atomic % of all metal elements, or analyzed using energy dispersive X-ray spectrometry (EDX) to find that it is 45 atomic % to 100 atomic % of all metal elements.

The processability of the absorbing 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 absorbing pattern layer 41. For the above reasons, it is desirable that the absorbing layer 4 in this embodiment is formed of an amorphous film with low crystallinity. A material with high crystallinity also has a large surface roughness due to the formation of crystal grain boundaries. Therefore, the surface roughness (RMS) of the absorbing layer 4 is preferably 0.4 nm or less, and more preferably 0.2 nm or less. Here, the "surface roughness (RMS) of the absorbing layer 4" means the roughness (RMS) of the surface (surface) of the absorbing layer 4 (absorbing pattern layer 41) opposite to the reflective layer 2 side.
In this embodiment, the surface roughness (RMS) may be measured using, for example, an atomic force microscope (AFM).

As described above, the material constituting the absorption layer 4 preferably contains platinum (Pt) at 50 atomic % or more and tantalum (Ta) in the range of 5 atomic % or more and less than 50 atomic % relative to the number of atoms constituting the entire absorption layer 4, but may further contain 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 the "additive element group"). In other words, the absorption layer 4 may further contain, in addition to platinum (Pt) and tantalum (Ta), one or more elements selected from the above-mentioned group of additive elements.

For example, by adding tellurium (Te), silver (Ag), nickel (Ni), or indium (In) from the group of additive elements described above to the absorption pattern layer 41, the absorption of EUV light can be further improved and the film can be made thinner.
Alternatively, among the elements included in the above-mentioned group of additive elements, iron (Fe), palladium (Pd), gold (Au), cobalt (Co), or iridium (Ir) can be added to the absorption pattern layer 41 to provide electrical conductivity to the absorption pattern layer 41 while ensuring high absorption of EUV light. This makes it possible to improve the inspectability in mask pattern inspection.

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

The total content of the elements contained in the above-mentioned additive element group 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 additive element group, and the total content of the elements contained in the above-mentioned additive element group may be equal to or less than the content of tantalum (Ta). More preferably, the total content of the elements contained in the above-mentioned additive element group is within a range of 0.9 times or less of the content of tantalum (Ta), and even more preferably, the total content of the elements contained in the above-mentioned additive element group is within a range of 0.6 times or less of the content of tantalum (Ta). With the above-mentioned configuration, it is possible to provide the absorption layer 4 with excellent pattern processability while having excellent transfer performance, and further provide the various functions described above.

The OD value in the absorbing pattern layer 41 will be described below.
The intensity of reflected light from the reflective portion, which is an area where the reflective layer 2 and the capping layer 3 are exposed by removing a part of the absorbing layer 4, is Rm, and the intensity of reflected light from the absorbing portion, which is an area where the absorbing layer 4 remains, is 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 (Formula 1). The larger the OD value, the better the contrast and the higher the transferability. If the OD value is less than 1, sufficient contrast cannot be obtained and the transferability tends to decrease. For pattern transfer, OD>1 is preferable, and 1.5 or more is even more preferable.
Therefore, the OD value of the absorbent layer 4 (absorbent 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) (Formula 1)

The absorption layer 4 (absorption pattern layer 41) of the conventional EUV reflective photomask has been formed of a compound material mainly composed of tantalum (Ta) as described above. In this case, the thickness of the absorption layer 4 needs to be 40 nm or more to obtain an OD value of 1 or more. The extinction coefficient k of the conventional material is 0.031, but by forming the absorption layer 4 from a compound material mainly composed of platinum (Pt) whose extinction coefficient k is 0.058 by itself, it is possible to thin the thickness of the absorption layer 4 to 17 nm if the OD value is 1 or more. However, the extinction coefficient k of the entire absorption layer 4 varies greatly depending on the mixture ratio of tantalum (Ta) to platinum (Pt) and the crystallinity of the formed material, and if the extinction coefficient k of the entire absorption layer 4 is less than 0.049, a sufficient thinning effect cannot be expected in many cases. Therefore, in order to achieve a thinner film than the conventional one, the extinction coefficient k of the entire absorption layer 4 is preferably 0.049 or more, and more preferably 0.051 or more.

Furthermore, if the thickness of the absorption layer 4 exceeds 50 nm, the projection effect will be about the same as that of a conventional absorption layer having a thickness of 60 nm and made of a compound material mainly composed of tantalum (Ta). Also, if the thickness of the absorption layer 4 exceeds 50 nm, the pattern processability of the absorption layer 4 may be degraded.
Therefore, the thickness of the absorption layer 4 according to the present embodiment is in the range of 17 nm to 50 nm. In other words, when the thickness of the absorption layer 4 is in the range of 17 nm to 50 nm, the projection effect can be sufficiently reduced and the transfer performance is improved, compared to a conventional absorption layer formed of a compound material mainly composed of tantalum (Ta).
The thickness of the absorbing layer 4 is more preferably in the range of 25 nm to 40 nm. If the thickness of the absorbing layer 4 is in the range of 25 nm to 40 nm, the projection effect can be further reduced compared to conventional absorbing layers, and the transfer performance can be further improved.
The above-mentioned "main component" refers to a component that is contained in an amount of 50 atomic % or more based on the number of atoms in the entire absorbing layer.

Also, an oxide film (not shown) may be formed by oxidizing at least one of the upper surface of the absorption layer 4 or the upper surface and side surface of the absorption pattern layer 41. Also, an oxide film (not shown) may be separately formed on at least one of the upper surface of the absorption layer 4 or 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.
In addition, the above-mentioned oxide film may be a natural oxide film that is formed naturally 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.

(Hard Mask)
4, the reflective photomask blank 10 according to the embodiment of the present invention may have a hard mask 5 formed on the absorbing layer 4. The hard mask 5 according to this embodiment, when formed on the absorbing layer 4, has the function of further enhancing the processability of the absorbing layer 4.
The material constituting the hard mask 5 is desirably a material that can be dry etched with a gas different from the gas used when dry etching the absorption layer 4. That is, when the material containing platinum (Pt) and tantalum (Ta) which is the material forming the absorption 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. Also, when the material containing platinum (Pt) and tantalum (Ta) which is the material forming the absorption 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.

Therefore, it is preferable that the material constituting the hard mask 5 contains 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 their oxides, nitrides, borides, oxynitrides, oxyborides, and oxynitride boride compounds. That is, the absorption layer 4 may contain platinum (Pt), tantalum (Ta), and one or more elements selected from the above-mentioned group of additive 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.

In general, dry etching occurs when the 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, and the boiling point and vapor pressure of the reaction products of the material to be etched and the introduced gas serve as indicators of this. In other words, the lower the boiling point of the reaction product, the more it vaporizes, the higher the vapor pressure, and the easier it is to exhaust.

In the etching of the absorbing layer 4 in producing the reflective photomask 20, the above definition of "easily etched" or "hardly etched" means that when it is easily etched by a chlorine-based gas, at least one chlorine-based compound produced by etching has a boiling point of 250° C. or lower, and when it is hard to etch by a chlorine-based gas, the boiling point of a chloride in a stoichiometric form produced by etching is 300° C. or higher. The same applies to fluorine-based gas.
Therefore, the material used for the hard mask 5 is preferably a material that is easily etched by a fluorine-based gas or a chlorine-based gas, that is, a substance having a low boiling point as a fluorine-based compound or a chlorine-based compound.

Table 1 shows the boiling points of metal halogen compounds. The values in Table 1 are taken from various documents (CRC Handbook of Chemistry and Ochemicals, 97th Edition, Vol. 13, No. 1, pp. 1171-1175).
This table summarizes the values found in the International Publication No. 2016 (2016) and other 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.

However, the above is an example of the 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 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 or chlorine-based compound is not 250°C or lower.

The hard mask 5 must remain on the absorption layer 4 until etching of the absorption layer 4 is completed. However, if the thickness of the hard mask 5 exceeds 30 nm, it may be difficult to form a fine pattern. Also, if the 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 the hard mask 5 having a uniform thickness.
Therefore, the 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.
In this embodiment, the processing of the absorption layer 4 is not limited to dry etching. For example, the absorption layer 4 can be processed by atomic layer etching (ALE).

Below, we will explain examples of the reflective photomask blank and reflective photomask according to the present invention.

[Example 1]
First, a method for producing the reflective photomask blank 10 will be described with reference to FIG.
First, as shown in Fig. 5, a reflective layer 2 formed by stacking 40 layers of a laminate film, each of which is a pair of silicon (Si) and molybdenum (Mo), is formed on a synthetic quartz substrate 1 having low thermal expansion characteristics. The thickness of the reflective layer 2 is set to 280 nm.
Next, a capping layer 3 made of ruthenium (Ru) was formed as an intermediate film on the reflective layer 2 to a thickness of 3.5 nm.
Next, an absorbing layer 4 containing platinum (Pt) and tantalum (Ta) was formed to a thickness of 33 nm on the capping layer 3. When the formed absorbing layer 4 was subjected to composition analysis using Rutherford backscattering spectroscopy (RBS), the platinum (Pt) content in the entire absorbing layer 4 was 55 atomic %, and the tantalum (Ta) content was 45 atomic %.

Furthermore, the surface roughness (RMS) of the absorbing layer 4 was measured using an atomic force microscope (AFM) and found to be 0.1 nm.
Furthermore, when the crystallinity of the absorbing layer 4 was measured by XRD (X-ray diffraction), it was found to be amorphous although slight crystallinity was observed.
Next, a back 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 a reflective photomask blank 10 of Example 1.
A sputtering device was used to deposit each film (form each layer) on the substrate 1. The thickness of each film was controlled by the sputtering time.

Next, a method for producing the reflective photomask 20 will be described with reference to FIGS.
First, as shown in FIG. 6 , a positive chemically amplified resist (SEBP9012: manufactured by Shin-Etsu Chemical Co., Ltd.) was applied by spin coating 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 drawn on the resist film 7 by 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 by using a spray developer (SFG3000: manufactured by Sigma Meltec Co., Ltd.). As a result, a resist pattern 71 was formed as shown in FIG.

Next, the absorbing layer 4 was patterned by dry etching mainly using a chlorine-based gas, using the resist pattern 71 as an etching mask. As a result, an absorbing pattern (absorbing pattern layer) 41 was formed in the absorbing layer 4, as shown in FIG.
Next, the resist pattern 71 was peeled off in a cleaning process, and the reflective photomask 20 of this embodiment was fabricated as shown in Fig. 9. In this embodiment, the absorbing pattern 41 formed in the absorbing layer 4 includes a 64 nm line width LS (line and space) pattern, a 200 nm line width LS pattern for measuring the thickness of the absorbing layer using an AFM, and a 4 mm square absorbing layer removed portion for measuring the EUV reflectance on the reflective photomask 20 for transfer evaluation. In this embodiment, the 64 nm line width LS pattern was designed in each of the x and y directions as shown in Fig. 10 so that the influence of the projection effect due to EUV irradiation can be easily seen.

[Example 2-1]
The absorbing layer 4 was formed so that the platinum (Pt) content of the absorbing layer 4 was 90 atomic % of the entire absorbing layer 4, and the tantalum (Ta) content of the absorbing layer 4 was 10 atomic % of the entire absorbing layer 4. The absorbing layer 4 was formed to a thickness of 28 nm. The surface roughness (RMS) of the absorbing 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 absorbing layer 4.

[Example 2-2]
The absorbing layer 4 was formed so that the platinum (Pt) content of the absorbing layer 4 was 90 atomic % of the entire absorbing layer 4, and the tantalum (Ta) content of the absorbing layer 4 was 10 atomic % of the entire absorbing layer 4. The absorbing layer 4 was formed to a thickness of 28 nm. The surface roughness (RMS) of the absorbing layer 4 thus formed was measured and found to be 0.3 nm.
Next, a hard mask (HD: not shown) made of silicon dioxide (SiO ₂ ) was formed on the absorbing layer 4 to a thickness of 10 nm.
The 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 .

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 removed in a cleaning process.
Finally, the hard mask used as the etching mask was removed by dry etching mainly using a fluorine-based gas.
Except for the above, the reflective photomask 20 of Example 2-2 was produced in the same manner as in Example 1.

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

[Example 4]
An absorbing 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 absorbing layer 4 thus formed was measured and found to be 0.1 nm. In addition, a composition analysis was performed on the absorbing layer 4 formed using Rutherford backscattering spectroscopy (RBS), and the content of platinum (Pt) in the entire absorbing layer 4 was 60 atomic %, the content of tantalum (Ta) was 30 atomic %, and the content of hafnium (Hf) was 10 atomic %.
The reflective photomask blank 10 and the reflective photomask 20 of Example 4 were produced in the same manner as in Example 1, except for the formation of the absorbing layer 4.

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

[Example 6-1]
The absorbing layer 4 was formed so that the platinum (Pt) content of the absorbing layer 4 was 70 atomic % of the entire absorbing layer 4, and the tantalum (Ta) content of the absorbing layer 4 was 30 atomic % of the entire absorbing layer 4. The absorbing layer 4 was formed to a thickness of 33 nm. The surface roughness (RMS) of the absorbing 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 absorbing layer 4.

[Example 6-2]
The absorbing layer 4 was formed so that the platinum (Pt) content of the absorbing layer 4 was 70 atomic % of the entire absorbing layer 4, and the tantalum (Ta) content of the absorbing layer 4 was 30 atomic % of the entire absorbing layer 4. The absorbing layer 4 was formed to a thickness of 33 nm. The surface roughness (RMS) of the absorbing 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 absorbing layer 4.

[Example 7-1]
The absorbing layer 4 was formed so that the platinum (Pt) content of the absorbing layer 4 was 70 atomic % of the entire absorbing layer 4, and the tantalum (Ta) content of the absorbing layer 4 was 30 atomic % of the entire absorbing layer 4. The absorbing layer 4 was formed to a thickness of 48 nm. The surface roughness (RMS) of the absorbing 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 absorbing layer 4.

[Example 7-2]
The absorbing layer 4 was formed so that the platinum (Pt) content of the absorbing layer 4 was 70 atomic % of the entire absorbing layer 4, and the tantalum (Ta) content of the absorbing layer 4 was 30 atomic % of the entire absorbing layer 4. The absorbing layer 4 was formed to a thickness of 48 nm. The surface roughness (RMS) of the absorbing 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 absorbing layer 4.

[Example 8-1]
The absorbing layer 4 was formed so that the platinum (Pt) content of the absorbing layer 4 was 90 atomic % of the entire absorbing layer 4, and the tantalum (Ta) content of the absorbing layer 4 was 10 atomic % of the entire absorbing layer 4. The absorbing layer 4 was formed to a thickness of 45 nm. The surface roughness (RMS) of the absorbing 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 absorbing layer 4.

[Example 8-2]
The absorbing layer 4 was formed so that the platinum (Pt) content of the absorbing layer 4 was 90 atomic % of the entire absorbing layer 4, and the tantalum (Ta) content of the absorbing layer 4 was 10 atomic % of the entire absorbing layer 4. The absorbing layer 4 was formed to a thickness of 45 nm. The surface roughness (RMS) of the absorbing 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 absorbing layer 4.

[Example 9]
An absorbing 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 absorbing layer 4 thus formed was measured and found to be 0.1 nm. In addition, a composition analysis was performed on the absorbing layer 4 formed using Rutherford backscattering spectroscopy (RBS), and the content of platinum (Pt) in the entire absorbing layer 4 was 70 atomic %, the content of tantalum (Ta) was 20 atomic %, and the content of iodine (I) was 10 atomic %.
The reflective photomask blank 10 and the reflective photomask 20 of Example 9 were produced in the same manner as in Example 1, except for the formation of the absorbing layer 4 .

[Example 10]
An absorbing 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 absorbing layer 4 thus formed was measured and found to be 0.2 nm. In addition, a composition analysis was performed on the absorbing layer 4 formed by Rutherford backscattering spectroscopy (RBS), and the content of platinum (Pt) in the entire absorbing layer 4 was 60 atomic %, the content of tantalum (Ta) was 20 atomic %, and the content of cobalt (Co) was 20 atomic %.
The reflective photomask blank 10 and the reflective photomask 20 of Example 10 were produced in the same manner as in Example 1, except for the formation of the absorbing layer 4 .

[Example 11]
An absorbing 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 absorbing layer 4 thus formed was measured and found to be 0.3 nm. In addition, a composition analysis was performed on the absorbing layer 4 formed using Rutherford backscattering spectroscopy (RBS), and the content of platinum (Pt) in the entire absorbing layer 4 was 70 atomic %, the content of tantalum (Ta) was 15 atomic %, and the content of tellurium (Te) was 15 atomic %.
The reflective photomask blank 10 and the reflective photomask 20 of Example 11 were produced in the same manner as in Example 1, except for the formation of the absorbing layer 4 .

[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. In addition, a composition analysis was performed on the absorber layer 4 formed using Rutherford backscattering spectroscopy (RBS), and the content of platinum (Pt) in the entire absorber layer 4 was 70 atomic %, the content of tantalum (Ta) was 25 atomic %, and the content of boron (B) was 5 atomic %.
The reflective photomask blank 10 and the reflective photomask 20 of Example 12 were produced in the same manner as in Example 1, except for the formation of the absorbing layer 4.

[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. In addition, a composition analysis was performed on the absorber layer 4 formed using Rutherford backscattering spectroscopy (RBS), and the content of platinum (Pt) in the entire absorber layer 4 was 75 atomic %, the content of tantalum (Ta) was 15 atomic %, and the content of rhenium (Re) was 10 atomic %.
The reflective photomask blank 10 and the reflective photomask 20 of Example 13 were produced in the same manner as in Example 1, except for the formation of the absorbing layer 4.

[Comparative Example 1]
The absorbing layer 4 was formed so that the platinum (Pt) content of the absorbing layer 4 was 45 atomic % and the tantalum (Ta) content of the absorbing layer 4 was 55 atomic % of the entire absorbing layer 4. The absorbing layer 4 was formed to a thickness of 29 nm. The surface roughness (RMS) of the absorbing layer 4 thus formed 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 absorbing layer 4 .

[Comparative Example 2]
The absorbing layer 4 was formed so that the platinum (Pt) content of the absorbing layer 4 was 30 atomic % of the entire absorbing layer 4, and the tantalum (Ta) content of the absorbing layer 4 was 70 atomic % of the entire absorbing layer 4. The absorbing layer 4 was formed to a thickness of 28 nm. The surface roughness (RMS) of the absorbing 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 absorbing layer 4 .

[Comparative Example 3]
The absorbing layer 4 was formed so that the platinum (Pt) content of the absorbing layer 4 was 70 atomic % of the entire absorbing layer 4, and the tantalum (Ta) content of the absorbing layer 4 was 30 atomic % of the entire absorbing layer 4. The absorbing layer 4 was formed to a thickness of 15 nm. The surface roughness (RMS) of the absorbing layer 4 thus formed 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 absorbing layer 4 .

[Comparative Example 4]
The absorbing layer 4 was formed so that the platinum (Pt) content of the absorbing layer 4 was 70 atomic % of the entire absorbing layer 4, and the tantalum (Ta) content of the absorbing layer 4 was 30 atomic % of the entire absorbing layer 4. The absorbing layer 4 was formed to a thickness of 55 nm. The surface roughness (RMS) of the absorbing layer 4 thus formed 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 absorbing layer 4.

[Comparative Example 5]
The absorbing layer 4 was formed so that the platinum (Pt) content of the absorbing layer 4 was 55 atomic % of the entire absorbing layer 4, and the tantalum (Ta) content of the absorbing layer 4 was 45 atomic % of the entire absorbing layer 4. The absorbing layer 4 was formed to a thickness of 33 nm. The surface roughness (RMS) of the absorbing 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 absorbing layer 4 .

[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 formed so that the film thickness of the absorbing layer 4 was 33 nm. The surface roughness (RMS) of the absorbing layer 4 thus formed 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 .

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. The reflective photomask blank, like the above-mentioned examples and comparative examples, has 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 having low thermal expansion characteristics, a ruthenium (Ru) capping layer 3 having a thickness of 3.5 nm, and an absorption layer 4 formed on the capping layer 3.
The absorber layer 4 thus formed had a surface roughness (RMS) of 0.1 nm.
As in the above-mentioned Examples and Comparative Examples, the absorber layer 4 was patterned and used for the evaluation.
In the above-mentioned examples and comparative examples, the film thickness of the absorbing layer 4 was measured by a transmission electron microscope.

The evaluation items evaluated in this example will be described below.
(Processability)
In the above-mentioned examples and comparative examples, analysis was performed using a SEM to check whether there were any breaks or missing defects (so-called pattern defects) in the pattern in the absorbing pattern layer 41. In addition, the cross-sectional shape of the pattern in the absorbing pattern layer 41 was also confirmed.
If the formed pattern had no abnormalities, it was deemed that there was no problem with the processing suitability (transfer performance) and was rated as "pass (△)" in this evaluation. If the formed pattern had no abnormalities and the sidewall angle (the elevation angle based on the surface of the capping layer 3) confirmed from the cross-sectional image was 80° or more, it was deemed that there was no problem with the processing suitability (transfer performance) and was rated as "pass (◯)" in this evaluation.
That is, in each of the embodiments of Example 2-1, Example 6-1, Example 7-1, and Example 8-1, it is suggested that the processing suitability (transfer performance) is improved by providing a hard mask (HD).

(Reflectance)
In the above-mentioned 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 by a reflectance measuring device using EUV light. Also, the reflectance Rm of the reflective portion 8 (see FIG. 10) where the absorption pattern layer 41 was not formed was measured by the reflectance measuring device using EUV light. In this way, the OD values of the reflective photomasks 20 according to the examples and comparative examples were calculated using the above-mentioned formula 1.
As described above, when the OD value is less than 1.0, sufficient contrast cannot be obtained and the transfer performance is deteriorated. Therefore, when the OD value is 1.0 or more, there is no problem with the transfer performance, and the evaluation was made "pass" in this evaluation.

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

The HV bias value is the line width difference of the transferred 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 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 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.

The evaluation method was based on the HV bias value of the existing tantalum (Ta) photomask shown in Table 2 as "existing mask" and the HV bias value was used as a standard.
In this evaluation, a case in which the LS pattern in the y direction is transferred as designed and the HV bias is smaller than that in the case of using an existing tantalum (Ta)-based photomask is judged as "passed." In addition, a case in which the LS pattern in the x direction is transferred as designed and the HV bias is not transferred as designed (the LS pattern in the y direction is not resolved) or the HV bias is larger than that in the case of using an existing tantalum (Ta)-based photomask is judged as "failed."
The evaluation results are shown in Table 1. In addition to the evaluation results, the table also shows the refractive index n and the extinction coefficient k.

A comparison of the OD values of each of the Examples and Comparative Examples is shown in Table 2. As described above, when the OD value is less than 1.0, sufficient contrast cannot be obtained, and the transfer performance is reduced.
The OD value of a conventional reflective photomask (existing reflective photomask) having a tantalum (Ta)-based absorption pattern layer with a 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 1.02. 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. 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. That is, 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.

Table 2 shows a comparison of the HV bias for each of the examples and comparative examples.
As a result of patterning by EUV light using a reflective photomask having a conventional 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 the comparative examples, the HV bias was 0.81 nm in Comparative Example 4, 1.47 nm in Comparative Example 5, and 0.98 nm in Comparative Example 6, which met the criteria for "pass" in this evaluation.

In contrast, the HV bias in Comparative Example 1 was 1.85 nm, and as a result of patterning using EUV light, the transferability was deteriorated compared to the conventional tantalum (Ta)-based photomask.
In addition, in Comparative Examples 2 and 3, the OD values were small, the absorbing layer 4 could not be patterned, and the HV bias could not be measured.

Here, in this embodiment, 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 a hard mask). The reason is that, in the configurations of Example 2-1, Example 6-1, Example 7-1, and Example 8-1 (i.e., configurations without a hard mask), which have excellent processing characteristics and satisfy the criteria for the HV bias evaluation of "pass", the HV bias value does not decrease even in the configurations further including a hard mask, and the HV bias evaluation does not result in a "fail" result.
In other words, the HV bias values of the embodiments having a hard mask (Example 2-2, Example 6-2, Example 7-2, Example 8-2) are equivalent to the HV bias values of the embodiments not having a hard mask (Example 2-1, Example 6-1, Example 7-1, Example 8-1), and therefore are omitted in Table 2.

Table 2 shows the overall evaluation of the processability, OD value, and HV bias. Reflective photomasks 20 that can suppress or reduce the projection effect and have the processability of the absorbing layer are marked with "○" in the "Judgment" 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 "Judgment" column. Conventional tantalum (Ta)-based photomasks are used for comparison, so they are marked with "△" in the "Judgment" column.

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. If an RMS of 0.4 nm or less is considered a "pass" in order to reduce the influence of the reflectance of EUV light, the reflective photomasks 20 of Examples 1 to 13 and Comparative Examples 1 to 4 met the criteria for a "pass" in this evaluation, while Comparative Examples 5 and 6 were "failed."

As a result, if the absorption pattern layer 41 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 absorption pattern layer 41 is in the range of 17 nm to 50 nm, 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, then 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.

Furthermore, for example, the reflective photomask blank, the reflective photomask, and the 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;
an absorbing layer formed on the reflective layer,
The absorption layer is formed of a material containing platinum (Pt) at 50 atomic % or more and tantalum (Ta) in a range of 5 atomic % or more and less than 50 atomic %;
The thickness of the absorption layer is in the range of 17 nm to 50 nm,
The extinction coefficient of the absorption layer for EUV light is 0.049 or more,
A reflective photomask blank, wherein the surface roughness of the absorber layer is 0.4 nm or less.
(2)
The reflective photomask blank according to (1) above, wherein the absorption layer is formed of a material containing tantalum (Ta) in a range of 20 atomic % to 40 atomic %.
(3)
The reflective photomask blank according to (1) or (2) above, 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)
a hard mask over the absorbing layer;
The reflective photomask blank according to any one of (1) to (3) above, wherein the hard mask has a thickness 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 is composed 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 boron oxynitrides thereof.
(6)
The reflective photomask blank according to any one of (1) to (5) above, which has an oxide film on the absorption layer.
(7)
The reflective photomask blank according to any one of the above (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,
A substrate;
a reflective layer including a multilayer film formed on the substrate;
an absorbing pattern layer formed on the reflective layer;
The absorption pattern layer is formed of a material containing platinum (Pt) at 50 atomic % or more and tantalum (Ta) in the range of 5 atomic % or more and less than 50 atomic %;
The thickness of the absorption pattern layer is in the range of 17 nm to 50 nm,
The extinction coefficient of the absorption layer for EUV light is 0.049 or more,
A reflective photomask, wherein the surface roughness of the absorption pattern layer is 0.4 nm or less.
(9)
The reflective photomask according to (8) above, wherein the absorption pattern layer is formed of a material containing tantalum (Ta) in the range of 20 atomic % to 40 atomic %.
(10)
The reflective photomask according to (8) or (9) above, 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) above, which has an oxide film on at least one of the top surface of the absorbing pattern layer and the side surface of the absorbing pattern layer.
(12)
The reflective photomask according to any one of the above (8) to (11), further comprising 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;
forming an absorbing pattern layer on the reflective layer;
The absorption pattern layer is formed of a material containing platinum (Pt) at 50 atomic % or more and tantalum (Ta) in the range of 5 atomic % or more and less than 50 atomic %;
The thickness of the absorption pattern layer is in the range of 17 nm to 50 nm,
The extinction coefficient of the absorption pattern layer for EUV light is 0.049 or more;
A method for manufacturing a reflective photomask, wherein the surface roughness of the absorption pattern layer is 0.4 nm or less.

The reflective photomask of 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.

1... Substrate 2... Reflective layer 3... Capping layer 4... Absorbing layer 41... Absorbing pattern (absorbent 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 (14)

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;
an absorbing layer formed on the reflective layer,
The absorption layer is formed of a material containing platinum (Pt) at 50 atomic % or more and tantalum (Ta) in the range of 5 atomic % to 45 atomic % or less,
The thickness of the absorption layer is in the range of 17 nm to 50 nm,
A reflective photomask blank, wherein the surface roughness of the absorber layer is 0.4 nm or less. The 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 %. 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). a hard mask over the absorbing layer;
4. The reflective photomask blank according to claim 3, wherein the hard mask has a thickness in the range of 2 nm to 30 nm. The reflective photomask blank according to claim 4, wherein the hard mask is made of 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 their oxides, nitrides, borides, oxynitrides, oxyborides, and oxynitride boride compounds. The reflective photomask blank according to claim 3, which has an oxide film on the absorbing layer. 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. A reflective photomask for pattern transfer using extreme ultraviolet light as a light source,
A substrate;
a reflective layer including a multilayer film formed on the substrate;
an absorbing pattern layer formed on the reflective layer;
The absorption pattern layer is formed of a material containing platinum (Pt) at 50 atomic % or more and tantalum (Ta) in the range of 5 atomic % to 45 atomic % or less,
The thickness of the absorption pattern layer is in the range of 17 nm to 50 nm,
A reflective photomask, wherein the surface roughness of the absorption pattern layer is 0.4 nm or less. The reflective photomask according to claim 8, wherein the absorption pattern layer is formed from a material containing tantalum (Ta) in the range of 20 atomic % to 40 atomic %. The reflective photomask of 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). The reflective photomask according to claim 10, which has an oxide film on at least one of the absorbing pattern layer and the side surface of the absorbing pattern layer. 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. 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;
forming an absorbing pattern layer on the reflective layer;
The absorption pattern layer is formed of a material containing platinum (Pt) at 50 atomic % or more and tantalum (Ta) in the range of 5 atomic % to 45 atomic % or less,
The thickness of the absorption pattern layer is in the range of 17 nm to 50 nm,
A method for manufacturing a reflective photomask, wherein the surface roughness of the absorption pattern layer is 0.4 nm or less. The method for manufacturing a reflective photomask according to claim 13, wherein the absorption pattern layer is formed from a material containing tantalum (Ta) in the range of 20 atomic % to 40 atomic %.

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