Reflective photomask

Abstract

To provide a reflective photomask that suppresses or reduces a projection effect of a reflective photomask for pattern transfer with light of a wavelength of an extreme-ultraviolet region as a light source and having durability to hydrogen radicals.SOLUTION: A reflective photomask 10 according to the present embodiment is a reflective photomask for pattern transfer using extreme-ultraviolet rays as a light source, and includes a substrate 1, a reflective layer 2 including a multilayer film formed on the substrate 1, and an absorption pattern layer 4 having a pattern formed on the reflection layer 2, in which the absorption pattern layer 4 is formed of a material containing a total of 50 atomic % or more of tin (Sn) and oxygen (o). Fluorine (F) is added to the absorption pattern layer 4, wherein a film thickness of the absorption pattern layer 4 is in the range of 17 nm or more and 45 nm or less, and atomic ratio (o / Sn) of oxygen (o) to tin (Sn) in the absorption pattern layer 4 is 1.0 or larger.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a reflective photomask used in lithography using light in the ultraviolet region as a light source.

Background Art

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

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

[0004] In addition, as described above, in EUV lithography, since a refractive optical system that utilizes light transmission cannot be used, the optical system members of the exposure machine are also reflective (mirrors) instead of lenses. For this reason, there is a problem that the incident light and the reflected light on the reflective photomask (EUV mask) cannot be designed to be coaxial. Usually, in EUV lithography, a method is adopted in which light is incident at an angle inclined by 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. Thus, in EUV lithography, since the optical axis is tilted via a mirror, a problem called the so-called "projection effect" may occur, in which the EUV light incident on the EUV mask creates a shadow of the mask pattern (patterned light absorption layer) of the EUV mask.

[0005] In the current EUV mask blank, a film mainly composed of tantalum (Ta) with a film thickness of 60 to 90 nm is used as the light absorption layer. When exposure for pattern transfer is performed on an EUV mask fabricated using this mask blank, depending on the relationship between the incident direction of the EUV light and the direction of the mask pattern, there is a risk of causing a decrease in contrast at the edge portion that becomes the shadow of the mask pattern. Along with this, problems such as an increase in the line edge roughness of the transferred pattern on the semiconductor substrate and the inability to form the line width to the targeted dimension may occur, and the transfer performance may deteriorate.

[0006] Therefore, a reflective photomask blank in which the light absorption layer is changed from tantalum (Ta) to a material with high absorbability (attenuation coefficient) for EUV light or a material with high absorbability is added to tantalum (Ta) has been studied. For example, Patent Document 2 describes a reflective photomask blank in which the light absorption layer is composed of a material containing 50 atomic percent (at%) or more of Ta as the main component and further containing at least one element selected from Te, Sb, Pt, I, Bi, Ir, Os, W, Re, Sn, In, Po, Fe, Au, Hg, Ga, and Al.

[0007] Furthermore, it is known that the mirror is contaminated by by-products of EUV generation (e.g., Sn) and carbon. The accumulation of contaminants on the mirror surface reduces the reflectivity of the mirror surface and decreases the throughput of the lithography apparatus. Regarding this problem, Patent Document 3 discloses a method of removing these contaminants from the mirror by generating hydrogen radicals in the apparatus and reacting the hydrogen radicals with the contaminants. However, in the reflective photomask blank described in Patent Document 2, the light absorption layer has not been examined for its resistance to hydrogen radicals (hydrogen radical resistance). Therefore, when introduced into an EUV exposure apparatus, the transfer pattern (mask pattern) formed in the light absorption layer cannot be stably maintained, and as a result, the transferability may deteriorate.

Prior Art Documents

Patent Documents

[0008]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0009] Therefore, an object of the present invention is to provide a reflective photomask for patterning transfer that suppresses or reduces the projection effect of a reflective photomask using light having a wavelength in the extreme ultraviolet region as a light source and has resistance to hydrogen radicals. That is, an object of the present invention is to provide a reflective photomask that reduces the possibility of deterioration in transferability by imparting hydrogen radical resistance to a transfer pattern (mask pattern).

Means for Solving the Problems

[0010] In order to solve the above problems, a reflective photomask according to one aspect of the present invention is a reflective photomask for pattern transfer using extreme ultraviolet rays as a light source, and includes a substrate, a reflective layer including a multilayer film formed on the substrate, and an absorption pattern layer having a pattern formed thereon. The absorption pattern layer is formed of a material containing a total of 50 atomic% or more of tin (Sn) and oxygen (O), fluorine (F) is added to the absorption pattern layer, the film thickness of the absorption pattern layer is in the range of 17 nm or more and 45 nm or less, and the atomic ratio (O / Sn) of oxygen (O) to tin (Sn) in the absorption pattern layer is 1.0 or more.

[0011] Further, in a reflective photomask according to one aspect of the present invention, the atomic ratio (O / Sn) of oxygen (O) to tin (Sn) in the absorption pattern layer may be 1.5 or more. Further, in a reflective photomask according to one aspect of the present invention, the fluorine (F) may be added at a depth of 2 nm or more from the outermost surface of the absorption pattern layer. Further, in a reflective photomask according to one aspect of the present invention, the fluorine (F) may be added at least in a region from the outermost surface of the absorption pattern layer to a depth of 2 nm.

[0012] Further, in a reflective photomask according to one aspect of the present invention, the absorption pattern layer is a layer containing the fluorine (F) in the depth direction from the outermost surface, and the content of the fluorine (F) may continuously change up to the depth at which the detection limit of the fluorine (F) is reached. Further, in a reflective photomask according to one aspect of the present invention, the absorption pattern layer is a layer containing the fluorine (F) in the depth direction from the outermost surface, the content of the fluorine (F) discontinuously changes at the depth at which the detection limit of the fluorine (F) is reached, and a boundary may exist between a region containing the fluorine (F) and a region not containing the fluorine (F) in the depth direction. Further, in a reflective photomask according to one aspect of the present invention, the entire absorption pattern layer may be formed of tin (Sn), oxygen (O), and fluorine (F).

[0013] In addition, in the reflective photomask according to one aspect of the present invention, the fluorine (F) may have a content rate of 30 atomic% or less with respect to the total number of atoms constituting the absorption pattern layer. In addition, in the reflective photomask according to one aspect of the present invention, the absorption pattern layer may further contain one or more elements selected from the group consisting of Ta, Pt, Te, In, Zr, Hf, Nb, Ti, W, Si, Cr, Mo, B, Sn, Pd, Ni, F, N, C, and H.

Advantages of the Invention

[0014] According to one aspect of the present invention, it is possible to expect a reflective photomask that improves the transfer performance to a semiconductor substrate in patterning using light having a wavelength in the extreme ultraviolet region as a light source and can be used even in a hydrogen radical environment. That is, for the reflective photomask according to one aspect of the present invention, the projection effect of the reflective photomask for patterning transfer using light having a wavelength in the extreme ultraviolet region as a light source is suppressed or reduced, and it has resistance to hydrogen radicals.

Brief Description of the Drawings

[0015]

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Embodiments for Carrying Out the Invention

[0016] Hereinafter, embodiments of the present invention will be described with reference to the drawings, but the present invention is not limited to the embodiments shown below. In the embodiments shown below, technically preferable limitations are made to implement the present invention, but this limitation is not an essential requirement of the present invention. FIG. 1 is a schematic cross-sectional view showing the structure of a reflective photomask 10 according to an embodiment of the present invention. Here, the reflective photomask 10 according to an embodiment of the present invention includes a substrate 1, a reflective layer 2 formed on the substrate 1, a capping layer 3 formed on the reflective layer 2, and an absorption pattern layer 4 formed on the capping layer 3.

[0017] (Substrate) For the substrate 1 according to the embodiment of the present invention, for example, a flat Si substrate, a synthetic quartz substrate, or the like can be used. Further, for the substrate 1, a low thermal expansion glass added with titanium can be used, but the present invention is not limited to these as long as the material has a small coefficient of thermal expansion.

[0018] (Reflection layer) The reflection layer 2 according to the embodiment of the present invention only needs to reflect EUV light (extreme ultraviolet light), which is the exposure light, and may be a multilayer reflection film formed by a combination of materials having significantly different refractive indices for EUV light. The reflection layer 2 including the multilayer reflection film may be formed, for example, by repeatedly laminating about 40 cycles of layers in a combination such as Mo (molybdenum) and Si (silicon), or Mo (molybdenum) and Be (beryllium).

[0019] (Capping layer) The capping layer 3 according to the embodiment of the present invention is formed of a material having resistance to dry etching performed when forming the absorption pattern layer 4, and functions as an etching stopper for preventing damage to the reflection layer 2 during etching. The capping layer 3 is formed of, for example, Ru (ruthenium). Here, depending on the material of the reflection layer 2 and the etching conditions, the capping layer 3 may not be formed. Further, a back surface conductive film 5 can be formed on the surface of the substrate 1 where the reflection layer 2 is not formed. The back surface conductive film 5 is a film for fixing the reflective photomask 10 to the exposure machine using the principle of an electrostatic chuck.

[0020] (Absorption pattern layer) The absorption pattern layer 4 of the reflective photomask 10 is formed by removing a part of the absorption layer of the reflective photomask blank, that is, by patterning the absorption layer. In EUV lithography, EUV light is incident obliquely and reflected by the reflective layer 2. However, due to the projection effect that the absorption pattern layer 4 obstructs the optical path, the transfer performance onto the wafer (semiconductor substrate) may deteriorate. This deterioration of the transfer performance is reduced by thinning the thickness of the absorption pattern layer 4 that absorbs EUV light. In order to thin the thickness of the absorption pattern layer 4, it is preferable to apply a material with higher absorbability to EUV light than conventional materials, that is, a material with a high extinction coefficient k for a wavelength of 13.5 nm.

[0021] Figure 2 is a graph showing the optical constants of each metal material with respect to the wavelength of 13.5 nm of EUV light. The horizontal axis in Figure 2 represents the refractive index n, and the vertical axis represents the extinction coefficient k. The extinction coefficient k of tantalum (Ta), which is the main material of the conventional absorption pattern layer 4, is 0.041. If it is a compound material having a larger extinction coefficient k, it is possible to reduce the thickness of the absorption pattern layer 4 compared to the conventional case. If the extinction coefficient k is 0.06 or more, it is possible to sufficiently thin the thickness of the absorption pattern layer 4 and reduce the projection effect.

[0022] Examples of materials that satisfy the combination of the above optical constants (nk values) include silver (Ag), platinum (Pt), indium (In), cobalt (Co), tin (Sn), nickel (Ni), and tellurium (Te) as shown in Figure 2. However, these metal materials have the problem that the volatility of the elemental halide is low and the dry etching property is poor. Therefore, even if a reflective photomask blank having an absorption layer formed of these metal materials is manufactured, an absorption layer pattern cannot be patterned on this absorption layer. As a result, there is a problem that this reflective photomask blank cannot be processed into a reflective photomask. Alternatively, since the melting points of these metal materials are low, they cannot withstand the heat during the production of the reflective photomask or during EUV exposure, resulting in a reflective photomask with poor practicality.

[0023] To avoid the above drawbacks, the absorption pattern layer 4 of the reflective photomask 10 in this embodiment is made of a material containing tin (Sn) and oxygen (O). Tin alone has a melting point of around 230°C, which is lower than the temperature of the heat during the production of the reflective photomask or EUV exposure, and there are problems with thermal stability. However, by forming it into tin oxide (SnO 2 ), the melting point of each can be significantly increased. Actually, multiple tin oxide (SnO 2 ) films were fabricated by reactive sputtering, and their melting points were measured with a thermal analyzer. It was found that the melting point was 1630°C, which is higher than that of the single element. Also, tin oxide (SnO 2 ) is chemically stable and can be dry-etched using chlorine-based gas, so the reflective photomask blank can be processed into a reflective photomask.

[0024] The material constituting the absorption pattern layer 4 preferably contains a total of 50 atomic% or more of tin (Sn) and oxygen (O). This is because if components other than tin (Sn) and oxygen (O) are included in the absorption pattern layer 4, the EUV light absorbency may decrease. However, if the components other than tin (Sn) and oxygen (O) are less than 50 atomic%, the decrease in EUV light absorbency and hydrogen radical resistance is very small, and there is almost no decrease in the performance of the absorption pattern layer 4 of the EUV mask.

[0025] Since the reflective photomask 10 is exposed to a hydrogen radical environment, if it is not made of a light-absorbing material with high hydrogen radical resistance, the reflective photomask 10 cannot withstand long-term use. In this embodiment, using microwave plasma, in a hydrogen radical environment with a hydrogen pressure of 0.36 millibar (mbar) or less at a power of 1 kW, a material with a film reduction rate of 0.01 nm / s or less or a layer formed of such a material is used as a material or layer with high hydrogen radical resistance.

[0026] Tin (Sn) is known to have low resistance to hydrogen radicals in its elemental form, but its resistance to hydrogen radicals increases by adding oxygen. Furthermore, adding fluorine (F) significantly increases the resistance to hydrogen radicals. Specifically, as shown in Table 1, excellent resistance to hydrogen radicals was confirmed under the condition that the atomic ratio of oxygen (O) to tin (Sn) (O / Sn) is 1.0 or more and fluorine (F) is detected in a region 2 nm or deeper from the outermost surface. This is considered to indicate that it is important for tin (Sn) and oxygen (O) to sufficiently form tin oxide (SnO 1~2 ) and for fluorine (F) to be present on the outermost surface of the absorption pattern layer 4. In the evaluation test of the film reduction rate shown in Table 1, when the measurement of the film reduction rate was repeated multiple times and the film reduction rate was 0.01 nm / s or less in all of them, it was evaluated as "○", when the film reduction rate exceeded 0.01 nm / s and was 0.1 nm / s or less, it was evaluated as "△", and when the film reduction rate exceeded 0.1 nm / s in all of them, it was evaluated as "×". "◎" represents the condition showing particularly excellent resistance to hydrogen radicals.

[0027] Also, the above atomic ratio (O / Sn) is the result measured by RBS (Rutherford backscattering spectroscopy), and the fluorine-containing film thickness (fluorine-detectable film thickness) is the result measured by TEM-EDX (energy-dispersive X-ray analysis). Here, the "fluorine-detectable film thickness" is the thickness (film thickness) of the region where fluorine could be detected in the absorption pattern layer 4, that is, the depth (layer thickness) from the outermost layer of the absorption pattern layer 4 until fluorine could no longer be detected, that is, the depth until the detection limit of fluorine is reached from the outermost layer of the absorption pattern layer 4.

[0028]

Table 1

[0029] As described above, the material containing tin (Sn) and oxygen (O) for forming the absorption pattern layer 4 is tin oxide (SnO with a stoichiometric composition 2It is desirable to be close to ). That is, the atomic number ratio (O / Sn) of tin (Sn) and oxygen (O) in the material constituting the absorption pattern layer 4 is preferably at least 1.0 or more, more preferably the atomic number ratio (O / Sn) is 1.5 or more, and it is more preferable that it approaches 2.0. However, it is important that the composition of the material is stable in tin oxide (SnO 2 ). Even if the atomic number ratio (O / Sn) exceeds 2.0 due to the detection of oxygen (O) trapped in the film or differences in analysis methods, there is no problem.

[0030] As described above, it is possible to improve the hydrogen radical resistance by adding fluorine (F) to the material containing tin (Sn) and oxygen (O) and forming FTO (Fluorine doped Tin Oxide) in the absorption pattern layer 4. The formation of FTO can add F to the raw material gas, for example, by treating it with a fluorine gas surface treatment apparatus at a pressure of 40 kPa with F 2 (about 100%). As described above, in order to improve the hydrogen radical resistance, the addition of fluorine (F) to the absorption pattern layer 4 according to the embodiment of the present invention is preferably added to a region with a depth of 2 nm or more from the outermost surface of the absorption pattern layer 4. By adding fluorine (F) to a depth of 2 nm or more from the outermost surface of the absorption pattern layer 4, it is possible to form an absorption pattern layer 4 that stably contains fluorine (F) throughout the mask.

[0031] However, the fluorine (F) added to the absorption pattern layer 4 preferably has a content rate of 30 atomic % or less with respect to tin (Sn) and oxygen (O). That is, the content rate of fluorine (F) is preferably 30 atomic % or less with respect to the total number of atoms constituting the absorption pattern layer 4. This is because if fluorine (F) is contained in excess, although the EUV light absorbency may decrease, if the content rate is 30 atomic % or less, the decrease in EUV light absorbency is extremely small, and there is almost no decrease in the performance of the absorption pattern layer 4 of the EUV mask. Note that the content of fluorine (F) is preferably 20 atomic % or less, and more preferably 10 atomic % or less.

[0032] Also, the content rate of fluorine (F) is preferably 0.1 atomic % or more with respect to the total number of atoms constituting the absorption pattern layer 4. If the content rate of fluorine (F) is less than 0.1 atomic %, it is difficult to obtain the effect of adding fluorine (F). The content rate of fluorine (F) is preferably 0.5 atomic % or more, and more preferably 1 atomic % or more. If the content rate of fluorine (F) is 0.5 atomic % or more, the effect of adding fluorine (F) can be surely obtained. Further, if the content rate of fluorine (F) is 1 atomic % or more, the effect of adding fluorine (F) can be remarkably obtained.

[0033] As described above, the material constituting the absorption pattern layer 4 preferably contains a total of 50 atomic % or more of tin (Sn) and oxygen (O), but as materials other than tin (Sn) and oxygen (O), for example, Ta, Pt, Te, Zr, Hf, Nb, Ti, W, Si, Cr, In, Pd, Ni, Mo, B, N, C, and H may be mixed. That is, the absorption pattern layer 4 may further contain one or more elements selected from the group consisting of Ta, Pt, Te, Zr, Hf, Nb, Ti, W, Si, Cr, In, Pd, Ni, Mo, B, N, C, and H in addition to tin (Sn) and oxygen (O).

[0034] For example, by mixing Ta, Pt, Te, In, Pd, and Ni into the absorption pattern layer 4, it is possible to impart conductivity to the film (absorption pattern layer 4) while ensuring high absorbability for EUV light. Therefore, in the mask pattern inspection using DUV (Deep Ultra Violet) light with a wavelength of 190 to 260 nm, it is possible to enhance the inspectability. Alternatively, when N, Hf, or Zr, Nb, Mo, Cr is mixed into the absorption pattern layer 4, it is possible to make the film quality more amorphous. Therefore, it is possible to improve the roughness, in-plane dimension uniformity of the absorption layer pattern (mask pattern) after dry etching, or the in-plane uniformity of the transferred image. Also, when Ti, W, Si is mixed into the absorption pattern layer 4, it is possible to enhance the resistance to cleaning.

[0035] In the present embodiment, as described above, in the absorption pattern layer 4, the atomic ratio (O / Sn) of oxygen (O) to tin (Sn) is 1.0 or more, and it is preferable that fluorine (F) is added at least in the region from the outermost surface of the absorption pattern layer 4 to a depth of 2 nm. The concentration distribution of fluorine (F) in the absorption pattern layer 4 is not limited. That is, there is no problem even if there is a clear boundary or the composition ratio changes continuously at the boundary between the outermost layer doped with fluorine (F) and the absorption pattern layer 4 mainly containing tin (Sn) and oxygen (O) inside. For example, there is no problem even if the composition ratio changes continuously as in the absorption pattern layer 4 shown in FIG. 1, or even if there is a clear boundary as in the absorption pattern layer 6 shown in FIG. 6 described later. Hereinafter, this point will be described in detail with reference to the drawings.

[0036] In this embodiment, as shown in FIG. 1, the absorption pattern layer 4 may contain fluorine (F) in the depth direction (the direction toward the capping layer 3) from the outermost surface, and the content of fluorine (F) may continuously change up to the depth D which is the detection limit of fluorine (F). More specifically, as shown in FIG. 1, in the region 4a from the outermost surface of the absorption pattern layer 4 to the depth D which is the detection limit of fluorine (F), the content of fluorine (F) may continuously change in the depth direction from the outermost surface of the absorption pattern layer 4. Here, the "depth D which is the detection limit of fluorine (F)" means the depth indicating the detection limit value of fluorine (F) when using TEM-EDX (energy dispersive X-ray analysis), and means the depth at which the content of fluorine (F) becomes 0.1 atomic% or less per unit area. That is, in the region deeper than the "depth D which is the detection limit of fluorine (F)" (the region on the capping layer 3 side), it means a region where substantially no fluorine (F) is added.

[0037] Hereinafter, in the absorption pattern layer 4, the distribution of the content (concentration) of the above-mentioned "continuously changing" fluorine (F) will be described. In this embodiment, it is preferable that the content of fluorine (F) decreases linearly (linearly), curvilinearly (for example, an S-shaped curve), or exponentially from the outermost surface of the absorption pattern layer 4 toward the depth D which is the detection limit of fluorine (F).

[0038] The distribution of the content (concentration) of fluorine (F) in the absorption pattern layer 4 will be described with reference to FIGS. 3 to 5. In this embodiment, the absorption pattern layer 4 contains fluorine (F) in the depth direction (the direction toward the capping layer 3), and contains fluorine (F) from the side surface of the absorption pattern layer 4, that is, from the surface where the absorption patterns face each other, toward the inside of the absorption pattern layer 4. Therefore, the concentration distribution of fluorine (F) from the side surface of the absorption pattern layer 4 toward the inside of the absorption pattern layer 4 is substantially the same as the concentration distribution of fluorine (F) from the outermost surface of the absorption pattern layer 4 toward the depth D which is the detection limit of fluorine (F). Therefore, in the present embodiment, only the concentration distribution of fluorine (F) from the outermost surface of the absorption pattern layer 4 toward the depth D at which the detection limit of fluorine (F) is reached will be described, and the description of the concentration distribution of fluorine (F) from the side surface of the absorption pattern layer 4 toward the inside of the absorption pattern layer 4 will be omitted.

[0039] Figures 3 to 5 are conceptual diagrams showing the content distribution (concentration distribution) of fluorine (F). The vertical axis in each of Figures 3 to 5 indicates the content (%) of fluorine (F) in the entire absorption pattern layer 4, and the horizontal axis indicates the depth direction of the entire absorption pattern layer 4. And "D" shown on the horizontal axis indicates "the depth at which the detection limit of fluorine (F) is reached". Figure 3 shows a form in which the content of fluorine (F) decreases linearly from the outermost surface of the absorption pattern layer 4 toward the depth D at which the detection limit of fluorine (F) is reached.

[0040] Figure 4 shows a form in which the content of fluorine (F) decreases exponentially from the outermost surface of the absorption pattern layer 4 toward the depth D at which the detection limit of fluorine (F) is reached, and the region near the depth D at which the detection limit of fluorine (F) is reached has a uniform composition. Figure 5 shows a form in which the content of fluorine (F) decreases curvilinearly (in the form of an S-curve) from the outermost surface of the absorption pattern layer 4 toward the depth D at which the detection limit of fluorine (F) is reached, and the composition is uniform near the depth D at which the detection limit of fluorine (F) is reached.

[0041] In the above form, since the reflective photomask 10 includes the absorption pattern layer 4 in which the content of fluorine (F) continuously decreases from the outermost surface of the absorption pattern layer 4 toward the depth D at which the detection limit of fluorine (F) is reached, it is possible to impart excellent hydrogen radical resistance to the absorption pattern layer 4. As a result, a reflective photomask that can be used for a long period can be manufactured. Note that even if the formation region of FTO has a film thickness of 2 nm or less from the outermost surface of the absorption pattern layer 4, there is no problem as long as FTO is uniformly present on the outermost surface and has hydrogen radical resistance.

[0042] In the absorption pattern layer 4 of the conventional EUV reflective photomask, a compound material mainly composed of Ta has been applied as described above. In this case, in order to obtain a value of 1 or more in the optical density OD (Equation 1), which is an index representing the contrast of the light intensity between the absorption pattern layer 4 and the reflective layer 2, the film thickness of the absorption pattern layer 4 needs to be 40 nm or more. In order to obtain a value of 2 or more in OD, the film thickness of the absorption pattern layer 4 needs to be 70 nm or more. Although the attenuation coefficient k of Ta is 0.041, by applying a compound material mainly containing tin (Sn) and oxygen (O) with an attenuation coefficient k of 0.06 or more to the absorption pattern layer 4, according to Beer's law, if at least OD is 1 or more, the film thickness of the absorption pattern layer 4 can be thinned to 17 nm or less, and if OD is 2 or more, the film thickness of the absorption pattern layer 4 can be made 45 nm or less. However, when the film thickness of the absorption pattern layer 4 exceeds 45 nm, the projection effect becomes the same as that of the absorption pattern layer 4 with a film thickness of 60 nm formed of a conventional compound material mainly composed of Ta. OD = -log(Ra / Rm) ···(Equation 1)

[0043] Therefore, the film thickness of the absorption pattern layer 4 according to the embodiment of the present invention is preferably 17 nm or more and 45 nm or less. That is, when the film thickness of the absorption pattern layer 4 is within the range of 17 nm or more and 45 nm or less, the projection effect can be sufficiently reduced compared to the conventional absorption pattern layer 4 formed of a compound material mainly composed of Ta, and the transfer performance is improved. The optical density (OD: Optical Density) value is the contrast between the absorption pattern layer 4 and the reflective layer 2. When the OD value is less than 1, sufficient contrast cannot be obtained, and the transfer performance tends to deteriorate.

[0044] In addition, the above-mentioned "main component" refers to a component contained in an amount of 50 atomic% or more with respect to the total number of atoms in the absorption layer. In addition, "Ra" in the above-mentioned Equation 1 means the reflectance in the region of the absorption pattern layer 4, and "Rm" means the reflectance in the region where the absorption pattern layer 4 is not formed, that is, the reflectance in the region composed of the exposed capping layer 3 and the reflective layer 2.

[0045] <Other Embodiments> In addition to the absorption pattern layer 4 shown in FIG. 1, the absorption pattern layer of this embodiment may be, for example, the absorption pattern layers shown in FIGS. 6 to 7. The absorption pattern layer 6 shown in FIG. 6 contains fluorine (F) in the depth direction from the outermost surface, and at the depth D where the detection limit of fluorine (F) is reached, the content of fluorine (F) changes discontinuously. In the depth direction, a boundary (interface) 6c is provided between the region 6a containing fluorine (F) and the region 6b not containing fluorine (F). Note that the content of fluorine (F) in the region 6a containing fluorine (F) may be uniform, or may continuously decrease in the depth direction from the outermost surface of the absorption pattern layer 6.

[0046] As described above, for the absorption pattern layer of this embodiment, it is desirable that fluorine (F) is added up to a region with a depth of 2 nm or more from the outermost surface. However, regarding the upper limit value of the depth, for example, there is no problem even if fluorine (F) is detected at the deepest part as in the absorption pattern layer 7 shown in FIG. 7. That is, as shown in FIG. 7, the entire absorption pattern layer 7 may be uniformly formed of a material containing tin (Sn), oxygen (O), and fluorine (F).

[0047] Hereinafter, examples of the reflective photomask blank and the reflective photomask according to the present invention will be described.

[0048] [Example 1] First, a method for manufacturing the reflective photomask blank 100 will be described with reference to FIG. 8. First, as shown in FIG. 8, a reflective layer 12 is formed by laminating 40 pairs of a silicon (Si) and molybdenum (Mo) laminated film on a synthetic quartz substrate 11 having low thermal expansion characteristics. The film thickness of the reflective layer 12 was 280 nm. Next, a capping layer 13 formed of ruthenium (Ru) as an intermediate film was formed on the reflective layer 12 to have a film thickness of 3.5 nm.

[0049] Next, an absorption layer 14 containing tin (Sn) and oxygen (O) was formed on the capping layer 13 to a film thickness of 26 nm. When the atomic number ratio of tin (Sn) and oxygen (O) was measured by RBS (Rutherford backscattering spectroscopy), it was O / Sn: 2.0. For the RBS analysis, 2.275 MeV 4He ++ was used as the incident ion. When the crystallinity of the absorption layer 14 was measured by XRD (X-ray diffractometer), although slight crystallinity was observed, it was amorphous.

[0050] Next, a back surface conductive film 15 formed of chromium nitride (CrN) was formed to a thickness of 100 nm on the surface of the substrate 11 on the side where the reflective layer 12 was not formed, and a reflective photomask blank 100 was produced. The film formation (layer formation) of each film on the substrate 11 was performed using a sputtering apparatus. The film thickness of each film was controlled by the sputtering time. The absorption layer 14 was formed by the reactive sputtering method by controlling the amount of oxygen introduced into the chamber during sputtering so that the O / Sn atomic number ratio became 2.0.

[0051] Next, a method for manufacturing the reflective photomask 200 will be described with reference to FIGS. 9 to 13. First, as shown in FIG. 9, a positive chemically amplified resist (SEBP9012: manufactured by Shin-Etsu Chemical Co., Ltd.) was spin-coated on the absorption layer 14 of the reflective photomask blank 100 to a film thickness of 120 nm, and baked at 110° C. for 10 minutes to form a resist film 16. Next, a predetermined pattern was drawn on the resist film 16 by an electron beam lithography machine (JBX3030: manufactured by JEOL Ltd.). Thereafter, a pre-bake treatment was performed at 110° C. for 10 minutes, and then development treatment was performed using a spray developer (SFG3000: manufactured by Sigma Meltech Co., Ltd.). As a result, as shown in FIG. 10, a resist pattern 16a was formed. Next, using the resist pattern 16a as an etching mask, the absorption layer 14 was patterned by dry etching mainly using a chlorine-based gas. As a result, as shown in FIG. 11, an absorption pattern (absorption pattern layer) 141 was formed in the absorption layer 14.

[0052] Next, as shown in FIG. 12, after peeling the resist pattern 16a, F was added to the raw material gas with a fluorine gas surface treatment apparatus 2 (approx. 100%) and treated at a pressure of 40 kPa to add fluorine (F) to the absorption pattern layer 141. As a result, as shown in FIG. 13, the reflective photomask 200 of Example 1 was fabricated. After cross-sectioning by FIB (focused ion beam apparatus), the detection limit film thickness of fluorine (F) from the outermost surface was measured using TEM-EDX (energy dispersive X-ray analysis), and it was 2 nm. Furthermore, when the bulk composition ratio (composition ratio in the entire absorption pattern layer 141) was measured using RBS (Rutherford backscattering spectroscopy), it was Sn+O / F: 98 / 2. That is, when the composition ratio in the entire absorption pattern layer 141 was measured, the content of tin (Sn) and oxygen (O) was 98 atomic%, and the content of fluorine (F) was 2 atomic%.

[0053] In this example, the absorption pattern 141 formed in the absorption layer 14 includes a line width 64 nm LS (line and space) pattern, a line width 200 nm LS pattern for measuring the film thickness of the absorption layer using AFM, and a 4 mm square absorption layer removal portion for EUV reflectivity measurement on the reflective photomask 200 for transfer evaluation. In this example, as shown in FIG. 14, the line width 64 nm LS pattern was designed in the x-direction and y-direction respectively so that the influence of the projection effect by EUV irradiation could be easily seen.

[0054] [Example 2] The absorption layer 14 was formed such that the atomic number ratio O / Sn of tin (Sn) and oxygen (O) in the absorption layer 14 was 1.0 and the film thickness was 26 nm. Also, in the same manner as in Example 1, after fabricating the absorption pattern layer 141, fluorine (F) was added so that the detection limit film thickness of fluorine (F) from the outermost surface was 2 nm and the bulk composition ratio was Sn+O / F: 98 / 2. That is, when the composition ratio in the entire absorption pattern layer 141 was measured, the content of tin (Sn) and oxygen (O) was 98 atomic%, and the content of fluorine (F) was 2 atomic%. As a result, the reflective photomask 200 of Example 2 was fabricated.

[0055] [Example 3] The absorption layer 14 was formed such that the atomic number ratio O / Sn of tin (Sn) and oxygen (O) in the absorption layer 14 became 2.5 and the film thickness became 26 nm. Also, in the same manner as in Example 1, after the absorption pattern layer 141 was formed, fluorine (F) was added such that the detection limit film thickness of fluorine (F) from the outermost surface became 2 nm and the bulk composition ratio became Sn+O / F: 98 / 2. That is, when the composition ratio in the entire absorption pattern layer 141 was measured, the content of tin (Sn) and oxygen (O) was 98 atomic% and the content of fluorine (F) was 2 atomic%. Thereby, the reflective photomask 200 of Example 3 was fabricated.

[0056] [Example 4] The absorption layer 14 was formed such that the atomic number ratio O / Sn of tin (Sn) and oxygen (O) in the absorption layer 14 became 2.0 and the film thickness became 26 nm. Also, in the same manner as in Example 1, after the absorption pattern layer 141 was formed, fluorine (F) was added such that the detection limit film thickness of fluorine (F) from the outermost surface became 26 nm and the bulk composition ratio became Sn+O / F: 80 / 20. That is, when the composition ratio in the entire absorption pattern layer 141 was measured, the content of tin (Sn) and oxygen (O) was 80 atomic% and the content of fluorine (F) was 20 atomic%. Thereby, as shown in FIG. 15, the reflective photomask 201 of Example 4 was fabricated.

[0057] [Example 5] The absorption layer 14 was formed such that the atomic ratio O / Sn of tin (Sn) and oxygen (O) was 2.5, the total content of tin (Sn) and oxygen (O) was 70 atomic % of the entire absorption layer 14, the remaining 30 atomic % was tantalum (Ta), and the film thickness was 26 nm. Also, in the same manner as in Example 1, after producing the absorption pattern layer 141, fluorine (F) was added such that the detection limit film thickness of fluorine (F) from the outermost surface was 2 nm and the bulk composition ratio was Sn+O / Ta / F: 69 / 29 / 2. That is, when the composition ratio in the entire absorption pattern layer 141 was measured, the content of tin (Sn) and oxygen (O) was 69 atomic %, the content of tantalum (Ta) was 29 atomic %, and the content of fluorine (F) was 2 atomic %. Thereby, the reflective photomask 200 of Example 5 was produced.

[0058] [Example 6] The absorption layer 14 was formed such that the atomic ratio O / Sn of tin (Sn) and oxygen (O) was 2.0, the total content of tin (Sn) and oxygen (O) was 70 atomic % of the entire absorption layer 14, the remaining 30 atomic % was chromium (Cr), and the film thickness was 26 nm. Also, in the same manner as in Example 1, after producing the absorption pattern layer 141, fluorine (F) was added such that the detection limit film thickness of fluorine (F) from the outermost surface was 2 nm and the bulk composition ratio was Sn+O / Cr / F: 69 / 29 / 2. That is, when the composition ratio in the entire absorption pattern layer 141 was measured, the content of tin (Sn) and oxygen (O) was 69 atomic %, the content of chromium (Cr) was 29 atomic %, and the content of fluorine (F) was 2 atomic %. Thereby, the reflective photomask 200 of Example 6 was produced.

[0059] [Comparative Example 1] The absorption layer 14 was formed such that the atomic number ratio O / Sn of tin (Sn) to oxygen (O) was 0, that is, it did not contain oxygen (O), and the film thickness was 26 nm. Also, in the same manner as in Example 1, after the absorption pattern layer 141 was fabricated, fluorine (F) was added such that the detection limit film thickness of fluorine (F) from the outermost surface was 2 nm, and the bulk composition ratio was Sn+O / F: 98 / 2. That is, when the composition ratio of the entire absorption pattern layer 141 was measured, the content of tin (Sn) was 98 atomic %, and the content of fluorine (F) was 2 atomic %. Thereby, the reflective photomask 200 of Comparative Example 1 was fabricated.

[0060] [Comparative Example 2] The absorption layer 14 was formed such that the atomic number ratio O / Sn of tin (Sn) to oxygen (O) was 1.5, and the film thickness was 26 nm. Also, in the same manner as in Example 1, after the absorption pattern layer 141 was fabricated, fluorine (F) was not added. That is, when the composition ratio of the entire absorption pattern layer 141 was measured, the contents of tin (Sn) and oxygen (O) were 100 atomic %, and the content of fluorine (F) was 0 atomic %. Thereby, the reflective photomask 200 of Comparative Example 2 was fabricated.

[0061] [Comparative Example 3] The absorption layer 14 was formed such that the atomic number ratio O / Sn of tin (Sn) to oxygen (O) was 2.0, and the film thickness was 15 nm. Also, in the same manner as in Example 1, after the absorption pattern layer 141 was fabricated, fluorine (F) was added such that the detection limit film thickness of fluorine (F) from the outermost surface was 2 nm, and the bulk composition ratio was Sn+O / F: 98 / 2. That is, when the composition ratio of the entire absorption pattern layer 141 was measured, the contents of tin (Sn) and oxygen (O) were 98 atomic %, and the content of fluorine (F) was 2 atomic %. Thereby, the reflective photomask 200 of Comparative Example 3 was fabricated.

[0062] [Comparative Example 4] The absorption layer 14 was formed such that the atomic number ratio O / Sn of tin (Sn) and oxygen (O) was 2.0 and the film thickness was 47 nm. Also, in the same manner as in Example 1, after the absorption pattern layer 141 was fabricated, fluorine (F) was added such that the detection limit film thickness of fluorine (F) from the outermost surface was 2 nm and the bulk composition ratio was Sn+O / F: 98 / 2. That is, when the composition ratio throughout the absorption pattern layer 141 was measured, the content of tin (Sn) and oxygen (O) was 98 atomic % and the content of fluorine (F) was 2 atomic %. Thereby, the reflective photomask 200 of Comparative Example 4 was fabricated.

[0063] [Comparative Example 5] The absorption layer 14 was formed such that the atomic number ratio O / Sn of tin (Sn) and oxygen (O) was 2.0, the total content of tin (Sn) and oxygen (O) was 30 atomic % of the entire absorption layer 14, the remaining 70 atomic % was silicon (Si), and the film thickness was 26 nm. Also, in the same manner as in Example 1, after the absorption pattern layer 141 was fabricated, fluorine (F) was added such that the detection limit film thickness of fluorine (F) from the outermost surface was 2 nm and the bulk composition ratio was Sn+O / Si / F: 29 / 69 / 2. That is, when the composition ratio throughout the absorption pattern layer 141 was measured, the content of tin (Sn) and oxygen (O) was 29 atomic %, the content of silicon (Si) was 69 atomic %, and the content of fluorine (F) was 2 atomic %. Thereby, the reflective photomask 200 of Comparative Example 5 was fabricated.

[0064] Separately from the foregoing Examples and Comparative Examples, a reflective photomask having a conventional tantalum (Ta)-based absorption layer was also compared as a Reference Example. Similar to the foregoing Examples and Comparative Examples, the reflective photomask blank was formed by laminating 40 pairs of silicon (Si) and molybdenum (Mo) films on a synthetic quartz substrate 11 having low thermal expansion characteristics to form a reflective layer 12, and a ruthenium (Ru) capping layer 13 with a thickness of 3.5 nm. The absorption layer 14 formed on the capping layer 13 was formed by depositing a 2-nm-thick TaO film on a 58-nm-thick TaN film. Also, similar to the foregoing Examples and Comparative Examples, a patterned absorption layer 14 was used for evaluation. In the foregoing Examples and Comparative Examples, the film thickness of the absorption layer 14 was measured by a transmission electron microscope.

[0065] Hereinafter, the evaluation items evaluated in this Example will be described. (Reflectivity) In the foregoing Examples and Comparative Examples, the reflectivity Ra of the absorption pattern layer 141 region of the fabricated reflective photomasks 200 and 201 was measured by a reflectivity measuring device using EUV light. Also, the reflectivity Rm in the region where the absorption pattern layer 141 was not formed, i.e., the reflectivity Rm in the region composed of the exposed capping layer 13 and the reflective layer 12, was measured by a reflectivity measuring device using EUV light. In this way, the OD values of the reflective photomasks 200 and 201 according to the Examples and Comparative Examples were obtained.

[0066] (Hydrogen radical resistance) Using microwave plasma, the reflective photomasks 200 and 201 fabricated in the Examples and Comparative Examples were placed in a hydrogen radical environment with a hydrogen pressure of 0.36 mbar or less and a power of 1 kW. The change in the film thickness of the absorption pattern layer 141 after hydrogen radical treatment was confirmed using an atomic force microscope (AFM). The measurement was performed on a 200-nm linewidth LS pattern.

[0067] (Wafer exposure evaluation) Using an EUV exposure apparatus (NXE3300B, manufactured by ASML), the absorption patterns 141 of the reflective photomasks 200 and 201 fabricated in the examples and comparative examples were transferred and exposed onto a semiconductor wafer coated with an EUV positive chemically amplified resist. At this time, the exposure dose was adjusted so that the LS pattern in the x-direction shown in FIG. 14 was transferred as designed. Specifically, in this exposure test, the LS pattern in the x-direction (line width 64 nm) shown in FIG. 14 was exposed so that the line width on the semiconductor wafer was 16 nm. The transferred resist pattern was observed and the line width was measured using an electron beam dimension measuring machine, and the change in the HV bias value was compared by simulation.

[0068] The HV bias value is the difference in line width of the transferred pattern depending on the orientation of the mask pattern, that is, the difference between the line width in the horizontal (Horizontal: H) direction and the line width in the vertical (Vertical: V) direction. The line width in the H direction indicates the line width of a linear pattern orthogonal 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 a linear pattern parallel to the incident plane. That is, 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 orthogonal to the incident plane. These evaluation results are shown in FIG. 16 and Table 2.

[0069]

Table 2

[0070] FIG. 13 shows the EUV light reflectance of each example and each comparative example. In the evaluation shown in Table 2, if the OD value was 1.50 or more, it was considered that there was no problem with the transfer performance, and it was judged as "pass". The OD value of the reflective photomask (reflective photomask of the reference example) with the conventional tantalum (Ta)-based absorption pattern layer having a film thickness of 60 nm is 1.58 (reflectance 1.7%), whereas the OD value of the reflective photomask 200 of Example 1 is 1.99 (reflectance 0.7%), the OD value of the reflective photomask 200 of Example 2 is 2.01 (reflectance 0.7%), the OD value of the reflective photomask 200 of Example 3 is 1.96 (reflectance 0.7%), the OD value of the reflective photomask 201 of Example 4 is 2.00 (reflectance 0.6%), the OD value of the reflective photomask 200 of Example 5 is 1.64 (reflectance 1.4%), and the OD value of the reflective photomask 200 of Example 6 is 1.50 (reflectance 2.0%), which was good. Also, in the comparative examples, the OD value of the reflective photomask 200 of Comparative Example 1 is 1.97 (reflectance 0.7%), the OD value of the reflective photomask 200 of Comparative Example 2 is 2.01 (reflectance 0.6%), and the OD value of the reflective photomask 200 of Comparative Example 4 is 2.46 (reflectance 0.2%), which was good. On the other hand, the OD value of the reflective photomask 200 of Comparative Example 3 is 0.77 (reflectance 10.7%), and the OD value of the reflective photomask 200 of Comparative Example 5 is 0.90 (reflectance 7.5%), which is lower than the OD value (1.58) of the conventional tantalum (Ta)-based photomask with a film thickness of 60 nm.

[0071] Table 2 shows a comparison of the HV biases of each example and each comparative example. As a result of patterning with EUV light using a reflective photomask having a conventional tantalum (Ta)-based absorption pattern with a film thickness of 60 nm, the HV bias was 7.57 nm. In contrast, the HV bias of Example 1 is 3.85 nm, the HV bias of Example 2 is 3.60 nm, the HV bias of Example 3 is 3.91 nm, the HV bias of Example 4 is 3.90 nm, the HV bias of Example 5 is 3.40 nm, and the HV bias of Example 6 is 3.20 nm. As a result, the effect of shadowing was reduced and the pattern transferability was improved as compared with the conventional Ta-based photomask.

[0072] Also, in Comparative Example 1, the HV bias was 3.59 nm, in Comparative Example 2, the HV bias was 3.79 nm, in Comparative Example 3, the HV bias was 1.99 nm, and in Comparative Example 5, the HV bias was 2.00 nm. As a result, the shadowing effect was reduced compared with the conventional Ta-based photomask, and the pattern transferability was improved. However, only in Comparative Example 4, the HV bias was 9.79 nm, and as a result of patterning with EUV light, the transferability deteriorated compared with the conventional Ta-based photomask.

[0073] In Table 2, the results of the hydrogen radical resistance of each example and each comparative example are shown. When the film reduction rate of the absorption pattern layer 141 was 0.01 nm / s or less, it was evaluated as "〇", when the film reduction rate exceeded 0.01 nm / s but was 0.1 nm / s or less, it was evaluated as "△", and when the film reduction rate exceeded 0.1 nm / s, it was evaluated as "×". As a result, for the reflective photomasks 200 and 201 of Examples 1 to 6 and Comparative Examples 3 to 5, that is, the examples and comparative examples other than Comparative Example 1 and Comparative Example 2, hydrogen radical resistance with a film reduction rate of 0.01 nm / s or less was confirmed.

[0074] In Table 2, the comprehensive evaluation of the HV bias and the hydrogen radical resistance is shown. For the reflective photomasks 200 and 201 that can suppress or reduce the projection effect and have hydrogen radical resistance, "○" is marked in the "judgment" column. For the reflective photomasks 200 and 201 that could not sufficiently suppress or reduce the projection effect or did not have hydrogen radical resistance, "×" was marked in the "judgment" column. Since the conventional Ta-based photomask is a comparison target, "△" was marked in the "judgment" column. As a result, if the absorption pattern layer 141 is formed of a material containing a total of 50 atomic% or more of tin (Sn) and oxygen (〇) and a material with fluorine (F) added, the optical density, HV bias, and hydrogen radical resistance are all good. Therefore, the projection effect can be reduced, the lifespan is long, and the transfer performance is high.

Industrial Applicability

[0075] The reflective photomask according to the present invention can be suitably used for forming a fine pattern by EUV exposure in a manufacturing process of a semiconductor integrated circuit or the like.

Explanation of Signs

[0076] 1... Substrate 2... Reflective layer 3... Capping layer 4... Absorption pattern layer 4a... Region containing fluorine (F) 5... Backside conductive film 6... Absorption pattern layer 6a... Region containing fluorine (F) 6b... Region not containing fluorine (F) 7... Absorption pattern layer 10... Reflective photomask 11... Substrate 12... Reflective layer 13... Capping layer 14... Absorption layer 15... Backside conductive film 16... Resist film 16a... Resist pattern 141... Absorption pattern layer (absorption pattern) 100... Reflective photomask blank 200... Reflective photomask 201... Reflective photomask D... Depth at which detection limit is reached

Claims

1. 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 absorption pattern layer having a pattern formed thereon, on the reflective layer; wherein the absorption pattern layer is formed of a material containing 50 atomic% or more in total of tin (Sn) and oxygen (O); fluorine (F) is added to the absorption pattern layer; the film thickness of the absorption pattern layer is in the range of 17 nm or more and 45 nm or less; the atomic ratio (O / Sn) of oxygen (O) to tin (Sn) in the absorption pattern layer is 1.0 or more; the absorption pattern layer contains the fluorine (F) in the depth direction from the outermost surface, and the content of the fluorine (F) continuously changes up to the depth at which the detection limit of the fluorine (F) is reached. A reflective photomask.

2. 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 absorption pattern layer having a pattern formed thereon, on the reflective layer; wherein the absorption pattern layer is formed of a material containing 50 atomic% or more in total of tin (Sn) and oxygen (O); fluorine (F) is added to the absorption pattern layer; the film thickness of the absorption pattern layer is in the range of 17 nm or more and 45 nm or less; the atomic ratio (O / Sn) of oxygen (O) to tin (Sn) in the absorption pattern layer is 1.0 or more; the entire absorption pattern layer is formed of tin (Sn), oxygen (O), and fluorine (F). A reflective photomask.

3. The reflective photomask according to claim 1 or claim 2, wherein the atomic ratio (O / Sn) of oxygen (O) to tin (Sn) in the absorption pattern layer is 1.5 or more.

4. The reflective photomask according to claim 1 or claim 2, wherein the atomic ratio (O / Sn) of oxygen (O) to tin (Sn) in the absorption pattern layer is 2.0 or more.

5. The reflective photomask according to any one of claims 1 to 4, wherein the fluorine (F) is added at a depth of 2 nm or more from the outermost surface of the absorption pattern layer.

6. The reflective photomask according to any one of claims 1 to 4, wherein the fluorine (F) is added at least in a region from the outermost surface of the absorption pattern layer to a depth of 2 nm.

7. The reflective photomask according to any one of claims 1 to 6, wherein the fluorine (F) has a content of 30 atomic% or less based on the total number of atoms constituting the absorption pattern layer. **Claim 8** The reflective photomask according to any one of claims 1 to 7, wherein the absorption pattern layer further contains one or more elements selected from the group consisting of Ta, Pt, Te, In, Zr, Hf, Nb, Ti, W, Si, Cr, Mo, B, Pd, Ni, N, C, and H. **Claim 9** The reflective photomask according to any one of claims 1 to 7, wherein the absorption pattern layer further contains one or more elements selected from the group consisting of Te, In, B, N, C, and H. **Claim 10** The reflective photomask according to any one of claims 1 to 9, wherein the absorption pattern layer is the outermost layer.

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