JP2014045075A - Reflective mask blank for euv lithography and reflective mask for euv lithography - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an EUV mask blank excellent in cleaning resistance, and suitable for pattern inspection utilizing a phase effect.SOLUTION: A reflective mask blank for EUV lithography includes: a reflective layer reflecting EUV light, on a substrate; an absorption layer absorbing EUV light, on the reflective layer; and an outermost surface protective layer including tantalum (Ta) and oxygen (O), on the absorption layer. In the outermost surface protective layer, the percentage content of tantalum (Ta) is 15-60 at%, and the percentage content of oxygen (O) is 40-85 at%. The outermost surface protective layer has a thickness of 1 nm or more and less than 3 nm.

Description

  The present invention relates to a reflective mask blank for EUV lithography, which is a precursor of a mask mainly used in the manufacture of a semiconductor device utilizing an EUV (Extreme Ultra-Violet) exposure technique. In addition, the reflective mask blank for EUV lithography may be referred to as “EUV mask blank” in this specification.

  In the exposure system, the resolution limit is determined according to the wavelength of light irradiated to a semiconductor substrate such as a Si substrate. In this exposure system, a transmission optical system exposure technique using a KrF laser with a wavelength of 248 nm, an ArF laser with a wavelength of 193 nm, or the like has been put into practical use. In this exposure system, a transmissive mask is used which has a predetermined pattern formed by a portion that transmits the irradiated light and a portion that absorbs the irradiated light. Transcription is performed.

  On the other hand, in order to realize a higher resolution of a pattern transferred to a semiconductor substrate or the like, an exposure technique using EUV light has attracted attention as an exposure technique using light having a shorter wavelength than an ArF laser. The EUV light is light in the wavelength region of soft X-rays or vacuum ultraviolet rays, specifically, light having a wavelength of about 10 to 20 nm, particularly 13.2 to 13.8 nm (13.13 nm centered on 13.5 nm (13 .5 nm ± 0.3 nm).

  In the exposure technique using EUV light, a transmission optical system exposure system using a KrF laser light source, an ArF laser light source, or the like cannot be applied due to the property of EUV light, and therefore a reflection optical system exposure system is applied. In the reflective optical system exposure system, a reflective mask for EUV lithography or a reflective mirror for EUV is used. Note that the reflective mask for EUV lithography may be referred to as an “EUV mask” in this specification.

  As described above, the EUV mask blank is a patterned EUV mask precursor and includes a layer that reflects EUV light. Specifically, the EUV mask blank has at least a reflective layer that reflects EUV light on a flat substrate such as glass, and has an absorption layer that absorbs EUV light on the reflective layer. The EUV mask has a predetermined pattern formed on the absorption layer of the EUV mask blank, and absorbs EUV light that is irradiated in a portion where the absorption layer is present and is irradiated in a portion where there is no absorption layer. The predetermined pattern can be transferred to a semiconductor substrate or the like by reflecting the light.

  The reflective layer is usually a multilayer reflective film having a structure in which a high refractive index layer showing a high refractive index with respect to EUV light and a low refractive index layer showing a low refractive index with respect to EUV light are alternately laminated. Is used. Examples of the multilayer reflective film include a Mo / Si multilayer reflective film composed of a silicon (Si) layer as a high refractive index layer and a molybdenum (Mo) layer as a low refractive index layer. Reflectivity can be realized. The absorption layer is made of a material having a low reflectance with respect to EUV light, that is, a material having a high absorption coefficient with respect to EUV light, and examples thereof include a material mainly composed of Ta or Cr.

  In the EUV mask blank, a substrate, a reflective layer on the substrate, and an absorption layer on the reflective layer are indispensable components. In addition to this, on the absorption layer, light for mask pattern inspection (hereinafter, “ In many cases, it has a low reflection layer exhibiting low reflection characteristics with respect to “inspection light”. In this specification, for example, when “B on A” is expressed as “absorbing layer on the reflective layer”, not only the configuration in which A and B are adjacent to each other, but also between A and B. A configuration having another functional layer is also included. In other words, when the “absorbing layer on the reflecting layer” is taken as an example, not only the structure in which the absorbing layer is laminated adjacently on the reflecting layer but also another functional layer between the reflecting layer and the absorbing layer. It means that the configuration is also included.

  The low reflection layer exhibits low reflectance characteristics with respect to light having a wavelength of 190 nm to 260 nm, which can be exemplified as inspection light. The EUV mask having the low reflection layer has a predetermined pattern formed by a portion where both the absorption layer and the low reflection layer are present and a portion where both the absorption layer and the low reflection layer are absent. By including the layer, the difference between the reflectance of the inspection light in the former portion and the reflectance of the inspection light in the latter portion can be increased. That is, the inspection light is used to obtain information on the presence or absence of pattern defects in the EUV mask. In particular, when the difference in reflectance is large, the contrast is increased, so that the inspection sensitivity is improved. For this reason, the low reflection layer is required to have a characteristic that provides a low reflectance with respect to the inspection light.

  As an EUV mask blank having a low reflection layer on the absorption layer in this manner and exhibiting a low reflectance with respect to inspection light, Patent Document 1 includes nitrides, oxides containing Ta (tantalum), An example of using a nitrided oxide or a material of a low reflection layer further containing Si is described. Patent Document 2 describes an example in which tantalum oxide (TaO) or tantalum oxygen nitride (TaON) is used as the low reflection layer. Further, Patent Document 3 describes an example in which a material containing H (hydrogen) or H and nitrogen (N) in addition to Ta (tantalum) and O (oxygen) is used as the low reflection layer. In Patent Documents 1 to 3, it is described that each of the low reflection layers exhibits low reflection characteristics with respect to inspection light of about 190 to 260 nm. In each example, evaluation was mainly performed with inspection light of 257 nm. Results are shown.

Japanese Patent Laid-Open No. 2004-6798 International Publication No. 2009/116348 Pamphlet International Publication No. 2010/50520 Pamphlet

  As described above, in the conventional EUV mask blank having a low reflection layer, the low reflection layer is required to have a characteristic of low reflectance with respect to inspection light. And as one specification for implement | achieving this characteristic, in patent documents 1-3, it describes that the film thickness of a low reflection layer and the reflectance of inspection light shall be made into a predetermined range. Specifically, in both inspection lights having a wavelength of 257 nm, Patent Document 1 can realize a reflectance of 20% or less in a range where the film thickness of the low reflection layer is 5 to 30 nm. A reflectance of 15% or less can be realized when the film thickness is in the range of 5 to 30 nm, and Patent Document 3 describes that a reflectance of 15% or less can be realized when the film thickness of the low reflective layer is 3 to 30 nm. Has been.

  However, as an EUV mask pattern inspection, an inspection using an electron beam is also in practical use. If pattern inspection of the EUV mask is useful in all inspection processes by inspection with an electron beam, a configuration including a low reflection layer as in the EUV mask blanks of Patent Documents 1 to 3 is not essential. However, from the aspect of improving inspection throughput, a multi-faceted pattern inspection can be carried out if the EUV mask has an optical characteristic that can be used not only for inspection with an electron beam but also for inspection with light of about 190 to 260 nm. It is preferable because it can

  In addition, inspection using light of about 190 to 260 nm is not limited to inspection using characteristics that provide low reflectivity with respect to inspection light by including a low reflection layer as in Patent Documents 1 to 3. That is, the inspection using the phase effect generated between the reflected light from the reflecting layer and the reflected light from the absorbing layer is also being put into practical use. Typically, the inspection uses light having a wavelength of about 193 nm. The machine is also being developed. In particular, in the case of pattern inspection using this phase effect, for example, when inspection light having a wavelength of about 193 nm is irradiated, the phase difference between the light reflected by the reflective layer and the light reflected by the absorption layer is about When the angle is 180 °, the reflectivity is lowered. On the other hand, since the reflection due to the inspection light is enhanced in the portion where there is no absorption layer, the contrast due to the difference in reflectivity can be used. In this case, the reflectance at the surface of the absorption layer with respect to the inspection light is not low, but rather, the reflectance as high as the reflectance at the surface of the reflection layer with respect to the inspection light is required. A low reflective layer having the described low reflectivity characteristics is not required. In addition, in the inspection using the electron beam, which is considered to be used in combination with the above inspection, sufficient contrast can be obtained in the inspection when there is no low reflection layer as described above, that is, even when the outermost layer is an absorption layer. .

  On the other hand, when the outermost surface of the EUV mask blank or EUV mask is the surface of the absorbing layer, there is a concern that the surface state may change over time due to the cleaning process performed in the manufacturing process of the EUV mask blank or EUV mask. As an example of the cleaning liquid, an acidic solution in which sulfuric acid and hydrogen peroxide are mixed is used to remove organic substances on the surface. In particular, such an acidic solution may oxidize the absorption layer surface over time. .

  In the case of a conventional transmissive mask, the transmittance for exposure light is as high as 90% or more. Therefore, even when exposure light such as an ArF excimer laser is irradiated on the transmissive mask, the temperature of the transmissive mask increases. Is not considered. On the other hand, in the case of a reflective EUV mask, the reflectance when irradiated with EUV light is at most 67%, the remaining EUV light is absorbed by the EUV mask, and part of it becomes thermal energy, and the temperature of the EUV mask surface. To raise. In particular, the energy of short wavelength light is high, and the heat energy when irradiated with EUV light is ten to several tens of times higher than that of an ArF excimer laser. There is a risk of thermal oxidation of the surface.

  As described above, when the surface of the absorption layer is oxidized, there is a possibility that optical characteristics such as absorption characteristics with respect to EUV light may be changed, which hinders the realization of EUV mask blanks and EUV masks having stable optical characteristics over the long term. Cause. Therefore, the EUV mask blank and EUV mask are different from the absorption layer so that the outermost surface thereof does not become the absorption layer surface. The functional layer has excellent cleaning resistance and suppression of thermal oxidation of the absorption layer by EUV exposure. The structure which makes the surface of this the outermost surface is required.

  As described above, as a functional layer that has cleaning resistance and suppresses thermal oxidation of the absorption layer by EUV exposure, if it is a material containing O (oxygen), a stable EUV mask blank, EUV mask as the outermost layer Is obtained. On the other hand, when the surface of the functional layer containing O (oxygen) is at the outermost surface, it may cause a charge-up in an electron beam inspection, resulting in a decrease in contrast. Off relationship. Further, even when an EUV mask blank having the functional layer is applied to a pattern inspection using a phase effect, as described above, for example, a high reflectance characteristic can be exhibited with respect to an inspection light of 193 nm. desired.

  The present invention can be applied to both a pattern inspection using an electron beam and a pattern inspection using a phase effect using light having a wavelength of about 193 nm as a representative inspection light in the inspection of a mask pattern. An object of the present invention is to provide a reflective mask blank for EUVL and a reflective mask for EUVL, which are excellent in properties and suppress thermal oxidation of the absorption layer with respect to exposure light using EUV light.

  In order to achieve the above object, the present invention provides a reflective layer for reflecting EUV light on a substrate, an absorbing layer for absorbing EUV light on the reflective layer, and the absorbing layer on the absorbing layer. And the outermost surface protective layer contains tantalum (Ta) and oxygen (O), and the outermost surface protective layer has a tantalum (Ta) content of 15 to 60 at%. There is provided a reflective mask blank for EUV lithography, wherein the oxygen (O) content is 40 to 85 at%, and the film thickness of the outermost protective layer is 1 nm or more and less than 3 nm.

  Further, the substrate has a reflective layer that reflects EUV light, an absorbing layer that absorbs EUV light on the reflective layer, and an outermost surface protective layer that protects the absorbing layer on the absorbing layer. The outermost surface protective layer has a total content of tantalum (Ta) and oxygen (O) of 80 to 99.9 at%, a composition ratio of Ta and O of 3: 2 to 3:17, and nitrogen. The total content of at least one element selected from (N), hydrogen (H), and boron (B) is 0.1 to 20 at%, and the film thickness of the outermost protective layer is 1 nm or more and less than 3 nm. A reflective mask blank for EUV lithography is provided.

  Moreover, in the said outermost surface protective layer, the content rate of nitrogen (N) is 1-15 at%, the content rate of hydrogen (H) is 0.1-10 at%, and the composition ratio of N and H is N: The reflective mask blank for EUV lithography, wherein H = 19: 1 to 1:10, is provided.

  Further, the outermost surface protective layer provides the above reflective mask blank for EUV lithography having a surface roughness of 0.5 nm rms or less.

  Moreover, the reflective mask blank for EUV lithography according to the above, wherein the film thickness of the outermost protective layer is 1.7 to 2.8 nm.

  The above-mentioned outermost protective layer provides the reflective mask blank for EUV lithography, wherein the crystalline state is amorphous.

Further, when the outermost surface protective layer is not provided, the reflectance of the surface of the absorbing layer with respect to light having a wavelength of 193 nm is _RA , and the outermost surface protection with respect to light having a wavelength of 193 nm when the outermost surface protective layer is provided. Provided is the above reflective mask blank for EUV lithography, where (R _A −R _S ) / R _A showing the attenuation rate is 0.2 or less, where R _S is the reflectance of the layer surface.

  Further, the present invention provides the above-described reflective mask blank for EUV lithography, which has a protective layer for protecting the reflective layer between the reflective layer and the absorbent layer when forming a pattern on the absorbent layer.

  The absorption layer is mainly composed of tantalum (Ta) and has hafnium (Hf), silicon (Si), zirconium (Zr), germanium (Ge), boron (B), nitrogen (N) and hydrogen (H). The reflective mask blank for EUV lithography comprising at least one element selected from the above is provided.

The protective layer may provide the above-described reflective mask blank for EUV lithography having at least one material of Ru, Ru compound, SiO ₂ and CrN.

  Furthermore, a reflective mask for EUV lithography in which the thin film protective layer and the absorption layer of the reflective mask blank for EUV lithography are patterned is provided.

  The EUV mask blank and the EUV mask according to the present invention have an outermost surface protective layer on the absorption layer, and the outermost surface protective layer is configured to have a specific material and thickness, thereby providing cleaning resistance. At the same time, it is possible to suppress a decrease in reflectance with respect to inspection light. As a result, stable optical characteristics can be realized with respect to EUV light, and high-precision pattern inspection can be realized.

The cross-sectional schematic diagram of the EUV mask blank which concerns on 1st Embodiment. The cross-sectional schematic diagram of the EUV mask blank which concerns on 2nd Embodiment.

(First embodiment of EUV mask blank)
FIG. 1 is a schematic diagram showing a cross-sectional structure of an EUV mask blank 10 according to this embodiment. The EUV mask blank 10 includes a reflective layer 12 that reflects EUV light on a substrate 11, an absorbing layer 13 that absorbs EUV light on the reflective layer 12, and an outermost surface protective layer that has cleaning resistance on the absorbing layer 13. 14 is laminated in this order. In the EUV mask blank, particularly when considering only the accuracy (sensitivity) of pattern inspection using the phase effect, if the outermost surface is the absorbing layer surface, the effect can be maximized. The EUV mask blank 10 according to the present embodiment has an outermost surface on the absorption layer 13 in order to exhibit cleaning resistance of the mask blank, suppression of thermal oxidation of the absorption layer by EUV light irradiation, and stable optical characteristics of the absorption layer. A protective layer 14 is provided.

As a substrate used for an EUV mask blank, the substrate 11 is required to have a low coefficient of thermal expansion, excellent smoothness and flatness, and have as few surface defects as possible. Specifically, the thermal expansion coefficient at room temperature (20 ° C.) are preferably be in the range of ^{-0.05 × 10 -7 /℃~+0.05×10 -7 / ℃} , -0.03 × 10 -7 / C to + 0.03 × 10 ⁻⁷ / ° C. is more preferable. As the material having the above-described thermal expansion coefficient, for example, SiO ₂ —TiO ₂ glass or the like can be preferably used, but is not limited thereto, and is not limited to this, crystallized glass, quartz glass, silicon, metal, etc. in which β quartz solid solution is precipitated. Can also be used.

  Further, the smoothness and flatness required for the substrate 11 are specifically such that the surface roughness is 0.15 nm rms or less in the standard of JIS-B0601, and the flatness is 100 nm or less. Satisfying these ranges is preferable because the pattern transfer accuracy by EUV light when an EUV mask is manufactured can be improved. The size and thickness of the substrate 11 are determined as appropriate according to the design values of the EUV mask blank. For example, the outer shape is about 6 inches (152 mm) square and the thickness is about 0.25 inches (6.3 mm). ).

  In particular, it is preferable that no defect is present on the surface of the substrate 11 on which the reflective layer 12 is formed (sometimes referred to as “main surface”). It only needs to be within a size that does not cause defects. Specifically, the surface state in which the depth of the concave defect and the height of the convex defect on the main surface are 2 nm or less, and the half width of the concave defect and the convex defect is 60 nm or less. Is preferred. In addition, the substrate 11 is not limited to the main surface, but also has defects on the surface opposite to the main surface (sometimes referred to as “back surface”) and side surfaces due to particles or the like when forming a reflective layer or the like. It is required to ensure flatness and smoothness as much as possible.

  The reflective layer 12 is required to have a characteristic that exhibits high reflectance when irradiated with EUV light. As a specific characteristic, the maximum value of the reflectance obtained when the EUV light having a wavelength of about 13.5 nm is irradiated is preferably 60% or more, more preferably 63% or more, and further preferably 65% or more. Here, the reflectance is obtained as the reflectance intensity when EUV light is incident on the surface of the reflective layer 12 from a direction inclined by 6 degrees from the normal direction. This angle condition is based on the fact that EUV light is incident from a direction inclined by 6 degrees from the normal direction of the EUV mask surface in an exposure system of a reflective optical system using EUV light.

  Thus, in order to obtain a high reflectance for EUV light, the reflective layer 12 includes a high refractive index layer that exhibits a high refractive index for EUV light and a low refractive index that exhibits a low refractive index for EUV light. A multilayer reflective film in which a rate layer is alternately laminated a plurality of times is preferably used. In particular, a Mo / Si multilayer reflective film comprising a Si layer as a high refractive index layer and a Mo layer as a low refractive index layer is preferably used. The reflective layer 12 is not limited to the Mo / Si multilayer reflective film, but is a Ru / Si multilayer reflective film, a Mo / Be multilayer reflective film, a Mo compound / Si compound multilayer reflective film, a Si / Mo / Ru multilayer reflective film, Si / Mo / Ru / Mo multilayer reflective films and Si / Ru / Mo / Ru multilayer reflective films can also be used.

  In addition, the thickness of each of the high refractive index layer and the low refractive index layer, and the number of repetitions using the adjacent high refractive index layer and low refractive index layer as one unit are required for materials constituting the multilayer reflective film and It can be designed according to the reflectance of EUV light. For example, in the case of a Mo / Si multilayer reflective film, when the thickness of the Si layer is 4.5 nm, the thickness of the Mo layer is 2.3 nm, and the number of repetitions is 30 to 60, the wavelength is 13. A characteristic with a reflectance of 60% or more for EUV light of about 5 nm is obtained.

  The uppermost layer of the multilayer reflective film constituting the reflective layer 12 may be selected from materials that do not oxidize the reflective film, and a specific example of the cap layer having this function is an Si layer. In the case where the reflective layer 12 is a Mo / Si multilayer reflective film, it is preferable that the uppermost layer is a Si layer because this layer can function as a cap layer. The thickness of the cap layer at this time is preferably about 9 to 13 nm. For the Mo / Si multilayer reflective film, a film forming method such as an ion beam sputtering method or a magnetron sputtering method can be used as a known film forming method. In each film forming method, a sputtering gas, a gas pressure, a film forming speed, a sputtering target, and the like are appropriately selected, and the Mo layer and the Si layer may be alternately formed by a predetermined number of repetitions.

  The absorption layer 13 is required to exhibit high light absorption characteristics (low reflectance) when irradiated with EUV light. That is, when an EUV mask is used, high reflectance (60% or more) can be obtained by irradiating EUV light and the reflective layer 12 can obtain high reflectance, while the absorbing layer 13 can obtain low reflectance. Can be realized. Specifically, the reflectance on the surface of the absorption layer 13 when irradiated with EUV light is about 0.5 to 15%. For example, the reflectance on the surface of the absorption layer 13 is relatively high at about 15%. Even so, if the phase difference between the reflected light on the surface of the reflective layer 12 and the reflected light on the surface of the absorbing layer 13 is designed to be about 175 to 185 degrees with respect to the EUV light, a high contrast is obtained using the phase effect. Can be realized.

  The absorption layer 13 may be made of a material having a high absorption coefficient with respect to EUV light. For example, a material containing tantalum (Ta) as a main component, a material containing chrome (Cr) as a main component, palladium (Pd) It is preferable to use a material containing as a main component. Here, the material containing tantalum (Ta) as a main component refers to a material in which the Ta content in the absorption layer 13 is 40 at% or more. Moreover, when the absorption layer 13 is comprised with the material which has Ta as a main component, the content rate of Ta is preferable 50 at% or more, and 55 at% or more is more preferable.

  Moreover, the material which has chromium (Cr) as a main component refers to the material from which the Cr content rate in the absorption layer 13 becomes 40 at% or more, In this case, the Cr content rate in the absorption layer 13 is 50 at% or more. Preferably, 55 at% or more is more preferable. Furthermore, the material having palladium (Pd) as a main component refers to a material in which the Pd content in the absorption layer 13 is 40 at% or more. In this case, the Pd content in the absorption layer 13 is 50 at% or more. Preferably, 55 at% or more is more preferable.

  In addition to Ta, the material that constitutes the absorption layer 13 is mainly hafnium (Hf), silicon (Si), zirconium (Zr), germanium (Ge), boron (B), palladium (Pd), chromium. It is preferable to contain at least one component among (Cr), hydrogen (H) and nitrogen (N). Specific examples of materials containing the above elements other than Ta include TaN, TaNH, TaHf, TaHfN, TaBSi, TaBSiN, TaB, TaBN, TaSi, TaSiN, TaGe, TaGeN, TaZr, TaZrN, TaPd, TaPdN, TaCr, TaCrN etc. are mentioned.

  In addition to Cr, the material that constitutes the absorption layer 13 is mainly hafnium (Hf), silicon (Si), zirconium (Zr), germanium (Ge), boron (B), palladium (Pd). ), Tantalum (Ta), hydrogen (H) and nitrogen (N). Specific examples of the material containing the above-described elements other than Cr include CrN, CrNH, CrHf, CrHfN, CrBSi, CrBSiN, CrB, CrBN, CrSi, CrSiN, CrGe, CrGeN, CrZr, CrZrN, CrPd, CrPdN, CrTa, CrTaN etc. are mentioned.

  In addition to Pd, the material constituting the absorption layer 13 containing Pd as a main component includes hafnium (Hf), silicon (Si), zirconium (Zr), germanium (Ge), boron (B), chromium ( It is preferable to contain at least one component of Cr), tantalum (Ta), hydrogen (H), and nitrogen (N). Specific examples of the material containing the above elements other than Pd include PdN, PdNH, PdHf, PdHfN, PdBSi, PdBSiN, PdB, PdBN, PdSi, PdSiN, PdGe, PdGeN, PdZr, PdZrN, PdCr, PdCrN, PdCr, PdTaN etc. are mentioned.

  Moreover, the thickness of the absorption layer 13 should just be the range of 20-100 nm. If the thickness of the absorption layer 13 is less than 20 nm, sufficient absorption characteristics for EUV light cannot be obtained, and sufficient contrast cannot be obtained even when the phase effect is used. Further, if the thickness of the absorption layer 13 exceeds 100 nm, the pattern accuracy at the time of manufacturing the EUV mask deteriorates, and the pattern is used to irradiate the EUV mask with oblique incidence (6 degrees) in the reflective exposure system. There is a risk that the transfer accuracy will deteriorate. Moreover, the thickness of the absorption layer 13 is preferably in the range of 20 to 90 nm, and more preferably in the range of 20 to 80 nm. In addition, the absorption layer 13 can utilize film-forming methods, such as an ion beam sputtering method and a magnetron sputtering method, for example as a well-known film-forming method. In each film forming method, a sputtering gas, a gas pressure, a film forming speed, a sputtering target, and the like may be appropriately selected to form a film having a predetermined thickness.

  If the surface of the absorbing layer 13 has a large surface roughness, the edge roughness of the pattern formed on the absorbing layer 13 becomes large and the dimensional accuracy of the pattern deteriorates, so that smoothness is required. Specifically, the surface roughness may be 0.5 nm rms or less, preferably 0.4 nm rms or less, and more preferably 0.3 nm rms. In order to obtain such a smooth surface, the crystal structure of the absorption layer 13 is preferably amorphous.

  Next, the outermost surface protective layer 14 laminated on the absorption layer 13 will be described. The outermost surface protective layer 14 has an effect of preventing the absorption layer 13 from being oxidized. In particular, the outermost protective layer 14 has resistance to an EUV mask blank, an acidic solution mixed with sulfuric acid and hydrogen peroxide used to remove organic substances on the surface of the EUV mask. That is required. The material of the outermost surface protective layer 14 having excellent cleaning resistance is a material containing tantalum (Ta) and oxygen (O), and the content of tantalum (Ta) is 15 to 60 at%. The oxygen (O) content may be 40 to 85 at%. If the O content is less than 40 at%, that is, if the Ta content exceeds 60 at%, sufficient cleaning resistance cannot be obtained. On the other hand, when the O content is more than 85 at%, that is, when the Ta content is less than 15 at%, there is a problem that, when a film is formed by sputtering according to the procedure described later, the discharge becomes unstable. In the surface protective layer 14 described above, the Ta content is preferably 15 to 55 at%, the O content is preferably 45 to 85 at%, the Ta content is 15 to 50 at%, and the O content is More preferably, the rate is 50 to 85 at%. The cleaning resistance can be evaluated, for example, by examining changes in (surface) optical properties before and after cleaning.

  The material constituting the outermost protective layer 14 contains at least one element selected from nitrogen (N), hydrogen (H) and boron (B) in addition to tantalum (Ta) and oxygen (O). Also good. In this case, the total content of tantalum (Ta) and oxygen (O) is 80 to 99.9 at%, and the total content of elements of nitrogen (N), hydrogen (H) and boron (B) is 0. .1 to 20 at% is sufficient. Here, the total content of Ta and O is 80 to 99.5 at%, the total content of N, H and B is preferably 0.5 to 20 at%, and the total content of Ta and O Is more preferably 80 to 99.0 at%, and the total content of N, H and B is more preferably 1.0 to 20 at%. In this case, the composition ratio of Ta and O may be in the range of 3: 2 to 3:17, preferably in the range of 3: 4 to 3:17, and more preferably in the range of 3: 4 to 3:16. preferable.

  When the outermost protective layer 14 contains nitrogen (N), the surface can be smoothed, and when it contains hydrogen (H), dangling bonds existing on the surface of the outermost protective layer 14 are made of hydrogen. Termination provides chemical stability. Further, when boron (B) is contained, the surface can be smoothed, and it can be easily amorphized. When the outermost surface protective layer 14 contains nitrogen (N) and hydrogen (H), the nitrogen (N) content is in the range of 1 to 15 at%, and the hydrogen (H) content is 0.1 to 10 at. % Is preferable. At this time, the composition ratio of N and H is preferably N: H = 19: 1 to 1:10.

  Further, if the surface of the outermost surface protective layer 14 has a large surface roughness, the edge roughness of the pattern formed on the outermost surface protective layer 14 increases and the dimensional accuracy of the pattern deteriorates, so that smoothness is required. The Specifically, the surface roughness may be 0.5 nm rms or less, preferably 0.4 nm rms or less, and more preferably 0.3 nm rms. In order to obtain such a smooth surface, the crystal structure of the outermost protective layer 14 is preferably amorphous.

  The thickness of the outermost protective layer 14 may be 1 nm or more and less than 3 nm. When the thickness of the outermost surface protective layer 14 is 3 nm or more, in the pattern inspection using the phase effect, the reflectance of the inspection light on the surface of the outermost surface protective layer 14 may be lowered and a good inspection may not be performed. As the thickness of the outermost protective layer 14 increases, the pattern accuracy at the time of EUV mask fabrication deteriorates, and the pattern exposure pattern is irradiated with EUV light obliquely incident (6 degrees) on the EUV mask in a reflective exposure system. It is desired that the thickness is small in that transfer accuracy may be deteriorated. In addition, since the outermost protective layer 14 contains oxygen (O), if the thickness of the outermost protective layer 14 increases, the electron beam image may become unclear due to charge-up in the inspection by the electron beam, and the resolution may be lowered. Therefore, it is desired that the thickness is small. Further, in the pattern inspection using the phase effect, if the thickness of the outermost protective layer 14 is increased, a change in the phase difference with respect to the phase difference set to about 180 degrees may occur, and the contrast may be lowered. Is desired to be small. On the other hand, if the thickness of the outermost protective layer 14 is less than 1 nm, the cleaning resistance may be deteriorated and the surface may be damaged, or film peeling may occur. Further, the thickness of the outermost protective layer 14 is preferably 1.2 nm or more and less than 3.0 nm, more preferably 1.5 nm or more and 2.8 nm or less, and further preferably 1.7 nm or more and 2.8 nm or less.

  In addition, as described above, in the EUV mask blank, when considering the improvement of the accuracy of pattern inspection using the phase effect without considering the washing resistance, if the outermost surface is the absorption layer surface, the inspection is performed. Although high reflectance with respect to light is obtained, stable optical characteristics of the absorption layer cannot be obtained due to the problem of washing resistance. Therefore, by providing the outermost surface protective layer 14 having the cleaning resistance like the EUV mask blank 10 according to the present embodiment, stable optical characteristics can be obtained, while the EUV mask blank 10 (outermost surface protective layer 14 The reflectance with respect to the inspection light in) is reduced to some extent. Therefore, when the outermost surface protective layer 14 is not provided, that is, when the reflectance for the inspection light when the absorption layer 13 is the outermost surface is used as a reference, the reflection with respect to the inspection light when the outermost surface protective layer 14 is provided. It is preferable to suppress the decrease in the rate because the inspection accuracy in the pattern inspection using the phase effect does not greatly decrease.

Here, when the outermost surface of the EUV mask blank is the absorption layer 13, the reflectance for the inspection light is _RA, and the EUV mask blank according to the present embodiment, that is, the mask blank having the outermost surface protective layer 14, Let the reflectance for the inspection light be R _S. At this time, when an attenuation factor (R _A −R _S ) / R _A is given as an index indicating a decrease in reflectance with respect to inspection light, this value may be 0.2 or less, preferably 0.18 or less, and 0 .15 or less is more preferable. As described above, when the attenuation rate of the reflectance with respect to the inspection light when the outermost surface protective layer 14 is provided is 0.2 or less, the contrast in the pattern inspection using the phase effect is not greatly reduced, and the inspection sensitivity is deteriorated. Can be suppressed. In the pattern inspection using the phase effect, light having a wavelength of 190 to 260 nm is used, and in particular, light having a wavelength of 190 to 200 nm, and further, light having a wavelength of about 193 nm is often used.

  As described above, the thickness of the outermost surface protective layer 14 is preferably adjusted so that the washing resistance is obtained and the decrease in the reflectance with respect to the inspection light used for the pattern inspection using the phase effect is suppressed. The outermost protective layer 14 may be a film forming method such as an ion beam sputtering method or a magnetron sputtering method as a known film forming method. In each film forming method, a sputtering gas, a gas pressure, a film forming speed, a sputtering target, and the like may be appropriately selected to form a film having the above thickness.

  Moreover, the EUV mask blank 10 according to the present embodiment may have a functional layer known in the field of EUV mask blanks in addition to the reflective layer 12, the absorption layer 13, and the outermost surface protective layer 14. For example, a conductive coating layer having a sheet resistance of 100Ω / □ or less may be provided on the back side of the substrate 11 in order to promote electrostatic chucking of the EUV mask blank. In this case, the conductive coating layer may be formed by a known method such as a magnetron sputtering method or an ion beam sputtering method.

(Second Embodiment of EUV Mask Blank)
FIG. 2 is a schematic diagram showing a cross-sectional structure of the EUV mask blank 20 according to the present embodiment. The EUV mask blank 20 is different from the EUV mask blank 10 in that a protective layer 21 for protecting the reflective layer 12 is formed between the reflective layer 12 and the absorbent layer 13 when a mask pattern is formed on the absorbent layer. . The substrate 11 other than the protective layer 21, the reflective layer 12, the absorption layer 13, the outermost surface protective layer 14, and the functional layer known in the field of EUV mask blanks constituting the EUV mask blank 20 are the first The configuration is the same as that of the EUV mask blank 10 according to the embodiment, and the same numbers are assigned to avoid duplication of explanation. Further, the optical characteristics such as the reflectance of each wavelength of the reflective layer 12, the absorption layer 13 and the outermost surface protective layer 14 in the EUV mask blank 20 are also the same as the ranges described in the first embodiment. Therefore, the duplicate description is omitted.

The protective layer 21 is provided to prevent damage to the reflective layer 12 in an etching process when forming a pattern on the absorption layer 13 and the outermost surface protective layer 14. Therefore, the protective layer 21 is preferably made of a material that is slower than the etching rate with respect to the absorption layer 13 and is not easily damaged in the etching process when the absorption layer 13 is etched. Examples of the protective layer 21 include Cr, Al, Ta and nitrides thereof, Ru and Ru compounds, and SiO ₂ , Si ₃ N ₄ , Al ₂ O _3, and mixtures thereof. Among these, Ru and Ru compounds, CrN and SiO ₂ are preferable, and Ru and Ru compounds are more preferable. Examples of the Ru compound include RuB and RuSi.

  Further, in the case of the EUV mask blank according to the present embodiment having the protective layer 21, it is required that the EUV light reflectivity at the surface of the protective layer 21 is high. As a specific characteristic, the maximum value of the reflectance obtained when the EUV light having a wavelength of about 13.5 nm is irradiated is preferably 60% or more, more preferably 63% or more, and further preferably 65% or more. In realizing such reflectance to EUV light, the protective layer 21 is preferably a Ru or Ru compound, and the thickness at that time may be in the range of 1 to 10 nm, and may be in the range of 1 to 5 nm. The range of 2 to 4 nm is more preferable. The protective layer 21 can be formed by a known film formation method such as an ion beam sputtering method or a magnetron sputtering method. In each film forming method, a sputtering gas, a gas pressure, a film forming speed, a sputtering target, and the like may be appropriately selected to form a film having a predetermined thickness.

(Example 1)
In this example, the EUV mask blank 20 shown in FIG. 2 was produced. As the substrate 11, a SiO ₂ —TiO ₂ glass substrate having an outer shape of 6 inches (152 mm) square and a thickness of 0.25 inches (6.3 mm) was used. This glass substrate has a thermal expansion coefficient at 20 ° C. of 0.05 × 10 ⁻⁷ / ° C., a Young's modulus of 67 GPa, a Poisson's ratio of 0.17, and a specific rigidity of 3.07 × 10 ⁷ m ² / s. ² . Then, by polishing this glass substrate, it was confirmed that the surface roughness of the main surface was 0.15 nm rms or less and the flatness was 100 nm or less.

  Next, a CrN film having a thickness of about 200 nm was formed on the back surface of the glass substrate (substrate 11) by a magnetron sputtering method to obtain a conductive coating layer having a sheet resistance of 100Ω / □ or less. Thereafter, with the conductive coating layer side fixed to the electrostatic chuck, a reflective layer 12 made of a Mo / Si multilayer reflective film was formed on the main surface of the substrate 11 by ion beam sputtering. Specifically, a 4.5 nm thick Si layer and a 2.3 nm thick Mo layer were alternately formed by ion beam sputtering so that the number of repetitions was 40 (40 cycles). The thickness of the reflective layer (Mo / Si multilayer film) at this time was 272 nm ((4.5 nm + 2.3 nm) × 40). Further, a protective layer 21 made of a Ru layer was formed to a thickness of 2.5 nm on the reflective layer by ion beam sputtering. Specific film forming conditions of the reflective layer 12 and the protective layer 21 are as shown in Table 1.

  Next, a TaNH film containing Ta, N, and H was formed to a thickness of 70 nm as the absorption layer 13 on the protective layer 21 made of the Ru layer by using a magnetron sputtering method. Further, a TaONH film containing Ta, O, N, and H was formed as the outermost surface protective layer 14 with a thickness of 2.5 nm on the absorption layer 13 made of TaNH using the magnetron sputtering method. Specific film forming conditions for the absorption layer 13 and the outermost surface protective layer 14 are as shown in Table 2.

  The film composition of TaNH which is the absorption layer 13 and TaONH which is the outermost protective layer 14 is an X-ray photoelectron spectrometer (manufactured by PERKIN ELEMER-PHI), a Rutherford backscattering spectrometer (Rutherford Back Scattering). Measurement was carried out using Spectroscopy (manufactured by Kobe Steel). Further, the film composition of TaNH serving as the absorption layer 13 was further measured using a secondary ion mass spectrometer (manufactured by PHI-ATOMIKA). As a result, the composition of TaNH as the absorption layer 13 was Ta: N: H = 55: 42: 3, and the oxygen (O) content was 0.05 at% or less. Moreover, the composition of TaONH which is the outermost surface protective layer 14 was Ta: O: N: H = 22: 64: 6: 8.

  With respect to the EUV mask blank 20 thus obtained, the crystal state of the outermost surface protective layer 14 made of TaONH was confirmed with an X-ray diffractometer (manufactured by RIGAKU). As a result, since no sharp peak was observed in the diffraction peak, it was confirmed that the crystal state of the outermost surface protective layer made of TaONH was an amorphous structure or a microcrystalline structure.

  Next, the surface roughness of the outermost protective layer 14 made of TaONH was measured with a dynamic force mode using an atomic force microscope (SII, SPI-3800). In addition, the measurement area | region of surface roughness shall be 1 micrometer x 1 micrometer, and SI-DF40 (product made from SII) was used for the cantilever. As a result, the surface roughness was 0.30 nm rms.

  Next, in order to evaluate the cleaning resistance of the obtained EUV mask blank 20, it is immersed in an acidic solution at about 100 ° C. containing sulfuric acid for 30 minutes, and the optical properties of the surface state of the outermost protective layer 14 are confirmed. did. Specifically, the average reflectance of light having a wavelength of 190 to 300 nm in the outermost protective layer 14 before and after immersion is measured and evaluated using a spectrophotometer (manufactured by Hitachi High-Technologies Corporation, UV-4100). did. As a result, the change in average reflectance with respect to light in the above wavelength range was 0.1% or less, and no significant change in reflectance was confirmed.

Further, by forming the outermost surface protective layer 14 made of TaONH, the spectrophotometer (UV-4100 manufactured by Hitachi High-Technologies Corporation, UV-4100) is used to determine the reflectance attenuation rate ((R _A −R _S ) / R _A ). ). First, the reflectance (R _A ) with respect to light having a wavelength of 193 nm when the outermost protective layer 14 was not present, that is, when the surface was the absorption layer 13 made of TaNH, was 35.1%. In this example in which TaONH having a thickness of 2.5 nm is formed, the reflectance (R _S ) with respect to light with a wavelength of 193 nm is 28.6%, and the reflectance decay rate ((R _A −R _S ) / R _A ) was 0.19.

(Examples 2 to 6)
Next, based on the configuration of the EUV mask blank in Example 1, an EUV mask blank 20 in which only the thickness of the outermost surface protective layer 14 made of TaONH was changed was produced, and each evaluation was performed. Specific thickness conditions and evaluation results are as shown in Table 3. In Table 3, the conditions of Example 1 are also shown. In Examples 2 to 6, the crystal state of TaONH was examined by the same method as in Example 1. As a result, no sharp peak was observed in the diffraction peak. The crystal structure was confirmed. Furthermore, when the surface roughness of TaONH was examined in the same manner as in Example 1 in Examples 2 to 6, it was confirmed that the surface roughness was 0.4 nm rms or less and the surface was smooth. did.

  In Example 2 and Example 3, the thickness of TaONH which is the outermost surface protective layer 14 was 1.0 nm and 2.0 nm, respectively. At this time, the attenuation factor of the reflectance with respect to light having a wavelength of 193 nm was 0.11 and 0.17, respectively, and no significant reduction in reflectance was confirmed. Moreover, when the immersion process by the acidic solution was performed on the same conditions as Example 1, the average reflectance with respect to the light of wavelength 190-300 nm before and behind immersion is 0.1% or less, and the big change of a reflectance is confirmed. Was not.

  In Example 4, the thickness of TaONH which is the outermost surface protective layer 14 was set to 0.5 nm. At this time, the attenuation factor of the reflectance with respect to light having a wavelength of 193 nm was 0.06, and no significant reduction in reflectance was confirmed. On the other hand, when the immersion treatment using the same acidic solution as in Example 1 was performed, it was confirmed that the average reflectance with respect to light having a wavelength of 190 to 300 nm before and after the immersion was greatly changed to 2.7%. As a result, the EUV mask blank based on Example 4 had a portion that was not covered with TaONH on the surface after immersion, and a portion of TaNH (absorbing layer) was exposed. It was confirmed that it was sufficient.

  In Examples 5 and 6, the thickness of TaONH, which is the outermost surface protective layer 14, was 4.0 nm and 7.0 nm, respectively. At this time, the attenuation factor of the reflectance with respect to light having a wavelength of 193 nm was 0.25 and 0.39, respectively, and a large decrease in reflectance was confirmed. In addition, when the immersion process by the acidic solution similar to Example 1 was performed, the average reflectance with respect to the light of wavelength 190-300 nm before and behind immersion is 0.1% or less, and the big change of a reflectance is confirmed. There wasn't.

10, 20 EUV mask blank 11 Substrate 12 Reflective layer 13 Absorbing layer 14 Outermost surface protective layer 21 Protective layer

Claims (11)

A reflective layer for reflecting EUV light on the substrate;
An absorbing layer that absorbs EUV light on the reflective layer;
On the absorbent layer, having an outermost surface protective layer that protects the absorbent layer,
The outermost protective layer includes tantalum (Ta) and oxygen (O),
In the outermost surface protective layer, the content of tantalum (Ta) is 15 to 60 at%, the content of oxygen (O) is 40 to 85 at%, and the film thickness of the outermost surface protective layer is 1 nm or more and less than 3 nm. A reflective mask blank for EUV lithography. A reflective layer for reflecting EUV light on the substrate;
An absorbing layer that absorbs EUV light on the reflective layer;
On the absorbent layer, having an outermost surface protective layer that protects the absorbent layer,
The outermost surface protective layer has a total content of tantalum (Ta) and oxygen (O) of 80 to 99.9 at%, a composition ratio of Ta and O of 3: 2 to 3:17, and nitrogen (N ), The total content of at least one element selected from hydrogen (H) and boron (B) is 0.1 to 20 at%, and the film thickness of the outermost protective layer is 1 nm or more and less than 3 nm, EUV A reflective mask blank for lithography.   In the outermost surface protective layer, the content of nitrogen (N) is 1 to 15 at%, the content of hydrogen (H) is 0.1 to 10 at%, and the composition ratio of N and H is N: H = The reflective mask blank for EUV lithography according to claim 2, which is 19: 1 to 1:10.   The reflective mask blank for EUV lithography according to any one of claims 1 to 3, wherein the outermost surface protective layer has a surface roughness of 0.5 nm rms or less.   The reflective mask blank for EUV lithography of any one of Claims 1-4 whose film thickness of the said outermost surface protective layer is 1.7-2.8 nm.   The reflective mask blank for EUV lithography according to any one of claims 1 to 5, wherein the outermost protective layer has an amorphous crystal state. When the outermost surface protective layer is not provided, the reflectance of the surface of the absorbing layer with respect to light having a wavelength of 193 nm is _RA, and the surface of the outermost surface protective layer with respect to light having a wavelength of 193 nm when the outermost surface protective layer is provided. when reflectance of the _{R S,} indicating an attenuation factor _{(R a -R S) / R} a is reflective mask blank for EUV lithography according to any one of claims 1 to 6 is 0.2 or less .   The reflective type for EUV lithography according to claim 1, further comprising a protective layer for protecting the reflective layer when forming a pattern on the absorbent layer, between the reflective layer and the absorbent layer. Mask blank.   The absorption layer is mainly composed of tantalum (Ta) and selected from hafnium (Hf), silicon (Si), zirconium (Zr), germanium (Ge), boron (B), nitrogen (N) and hydrogen (H). The reflective mask blank for EUV lithography according to any one of claims 1 to 8, comprising at least one kind of element. 10. The reflective mask blank for EUV lithography according to claim 1, wherein the protective layer includes at least one material of Ru, Ru compound, SiO _2, and CrN.   The reflective mask for EUV lithography which patterned the thin film protective layer and absorption layer of the reflective mask blank for EUV lithography in any one of Claims 1-10.

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