JP6965833B2 - Manufacturing method of reflective mask blank, reflective mask and reflective mask blank - Google Patents

Description

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

In recent years, with the miniaturization of integrated circuits constituting semiconductor devices, it has become an extreme exposure method as an alternative to the conventional exposure technique using visible light, ultraviolet light (wavelength 365 to 193 nm), ArF excimer laser light (wavelength 193 nm), or the like. Ultraviolet light (Etreme Ultra Violet: hereinafter referred to as "EUV") lithography is being studied.

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

Since EUV light is easily absorbed by all substances, the refractive optics system used in the conventional exposure technique cannot be used. Therefore, in EUV lithography, a reflective optical system such as a reflective mask or a mirror is used. In EUV lithography, a reflective mask is used as a transfer mask.

In the reflective mask, a reflective layer that reflects EUV light is formed on a substrate, and an absorbent layer that absorbs EUV light is formed in a pattern on the reflective layer. The reflective mask uses a reflective mask blank formed by laminating a reflective layer and an absorbent layer on a substrate in this order as a base plate, removes a part of the absorbent layer to form a predetermined pattern, and then a cleaning liquid. Obtained by washing with.

The EUV light incident on the reflective mask is absorbed by the absorbing layer and reflected by the reflecting layer. The reflected EUV light is imaged on the surface of the exposure material (wafer coated with resist) by the optical system. As a result, the pattern of the absorbing layer is transferred to the surface of the exposure material.

In EUV lithography, EUV light is usually incident on the reflective mask from a direction inclined by about 6 ° and is reflected obliquely as well. Therefore, if the thickness of the absorption layer is large, the optical path of EUV light may be blocked (Shadowing). If a portion that becomes a shadow of the absorption layer is generated on the substrate or the like due to the influence of shadowing, the pattern of the reflective mask is not faithfully transferred on the surface of the exposure material, and the pattern accuracy may deteriorate. On the other hand, if the thickness of the absorption layer is reduced, the light-shielding performance of EUV light by the reflective mask is lowered and the reflectance of EUV light is increased, so that the contrast between the pattern portion of the reflective mask and the other portions is increased. May decrease.

Therefore, a reflective mask blank that can suppress a decrease in contrast while faithfully transferring the pattern of the reflective mask has been studied. For example, Patent Document 1 contains an absorber film containing Ta as a main component in an amount of 50 atomic% (at%) or more, and further includes Te, Sb, Pt, I, Bi, Ir, Os, W, Re, Sn, In. , Po, Fe, Au, Hg, Ga and a reflective mask blank made of a material containing at least one element selected from Al.

However, in the reflective mask blank described in Patent Document 1, it has not been studied that the absorber film has resistance to a cleaning liquid (cleaning resistance) when the reflective mask is manufactured. Therefore, it may not be possible to stably form a pattern on the absorber membrane.

Japanese Unexamined Patent Publication No. 2007-273678

One aspect of the present invention is to provide a reflective mask blank having an absorbent layer having excellent cleaning resistance during the production of the reflective mask.

The reflective mask blank according to one aspect of the present invention is a reflective mask blank having a reflective layer for reflecting EUV light and an absorbing layer for absorbing EUV light on the substrate in this order from the substrate side. The absorption layer contains Sn as a main component and Ta in 25 at% or more.

According to one aspect of the present invention, it is possible to provide a reflective mask blank having an absorbent layer having excellent cleaning resistance during the production of the reflective mask.

It is the schematic sectional drawing of the reflection type mask blank which concerns on 1st Embodiment. It is explanatory drawing which shows the state which the passivation film is formed on the surface of the absorption layer. It is a figure which shows an example of the relationship between the Ta content and the film thickness of the passivation film formed on the surface of an absorption layer. It is a flowchart which shows an example of the manufacturing method of a reflective mask blank. It is a schematic cross-sectional view which shows an example of another form of a reflective mask blank. It is a schematic cross-sectional view which shows an example of another form of a reflective mask blank. It is a schematic cross-sectional view of a reflective mask. It is a figure explaining the manufacturing process of a reflective mask. It is the schematic sectional drawing of the reflection type mask blank which concerns on 2nd Embodiment. It is explanatory drawing which shows the state of the reflective mask blank before and after cleaning. It is the schematic sectional drawing of the reflection type mask blank which concerns on 3rd Embodiment. It is a figure which shows the relationship between the film thickness of the absorption layer and the reflectance. It is a figure which shows the result of simulating the relationship between the film thickness of the absorption layer and the reflectance. It is a figure which shows the relationship between the Sn content and the reflectance. It is a figure which shows the relationship between the Ta content of a SnTa film and the film loss. It is a figure which shows the result of having measured the etching rate of the absorption layer and TaN.

Hereinafter, embodiments of the present invention will be described in detail. For ease of understanding, the scale of each member in the drawing may differ from the actual scale. In the present specification, a three-dimensional Cartesian coordinate system in the three-axis directions (X-axis direction, Y-axis direction, Z-axis direction) is used, and the coordinates on the main surface of the glass substrate are the X-axis direction and the Y-axis direction, and the height direction. (Thickness direction) is the Z-axis direction. The direction from the bottom to the top of the glass substrate (the direction from the main surface of the glass substrate to the reflective layer) is the + Z-axis direction, and the opposite direction is the −Z-axis direction. In the following description, the + Z-axis direction may be referred to as "up" and the -Z-axis direction may be referred to as "down".

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

(substrate)
The substrate 11 preferably has a small coefficient of thermal expansion. When the coefficient of thermal expansion of the substrate 11 is small, it is possible to suppress distortion of the pattern formed on the absorption layer 14 due to heat during exposure with EUV light. Specifically, the coefficient of thermal expansion of the substrate 11 ^{is preferably 0 ± 1.0 × 10 -7} / ° C., more preferably 0 ± 0.3 × 10 ^-7 / ° C. at 20 ° C. As a material having a small coefficient of thermal expansion, for example, SiO _2- TIO _2- based glass or the like can be used. SiO ₂ -TiO ₂ based glass, a SiO ₂ 90-95 mass%, it is preferable to use a quartz glass containing TiO ₂ 5 to 10 wt%. When _{the content of TiO 2} is 5 to 10% by mass, the coefficient of linear expansion near room temperature is substantially zero, and there is almost no dimensional change near room temperature. The SiO _2- TiO ₂ system glass may contain trace components other than _{SiO 2} and TiO _2.

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

The first main surface 11a is preferably surface-treated so as to have a predetermined flatness. This is because the reflective mask obtains high pattern transfer accuracy and position accuracy. The flatness of the substrate 11 is preferably 100 nm or less, more preferably 50 nm or less, still more preferably 30 nm or less in a predetermined region (for example, a region of 132 mm × 132 mm) of the first main surface 11a. ..

Further, the substrate 11 preferably has resistance to a cleaning liquid used for cleaning the reflective mask blank, the reflective mask blank after pattern formation, the reflective mask, and the like.

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

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

The first main surface 11a of the substrate 11 is formed in a rectangular shape or a circular shape in a plan view. As used herein, the term "rectangle" includes a rectangle or a square, as well as a shape in which the corners of the rectangle or the square are rounded.

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

The reflective layer 12 is a multilayer film in which a plurality of layers each containing elements having different refractive indexes as main components are periodically laminated. The reflective layer 12 is generally a multilayer in which a plurality of high refractive index layers exhibiting a high refractive index with respect to EUV light and a plurality of low refractive index layers exhibiting a low refractive index with respect to EUV light are alternately laminated from the substrate 11 side. A reflective film is used.

The multilayer reflective film may be laminated for a plurality of cycles with a laminated structure in which a high refractive index layer and a low refractive index layer are laminated in this order from the substrate 11 side as one cycle, or may be a low refractive index layer and a high refractive index layer. May be laminated in a plurality of cycles with the laminated structure in which the above-mentioned ones are laminated in this order as one cycle. In this case, it is preferable that the outermost surface layer (top layer) of the multilayer reflective film is a high refractive index layer. This is because the low refractive index layer is easily oxidized, and when the low refractive index layer becomes the uppermost layer of the reflective layer 12, the reflectance of the reflective layer 12 may decrease.

As the high refractive index layer, a layer containing Si can be used. As the material containing Si, in addition to Si alone, a Si compound containing at least one selected from the group consisting of B, C, N and O in Si can be used. By using a high refractive index layer containing Si, a reflective mask having excellent reflectance of EUV light can be obtained. As the low refractive index layer, a metal selected from the group consisting of Mo, Ru, Rh and Pt or an alloy thereof can be used. In the present embodiment, it is preferable that the low refractive index layer is the Mo layer and the high refractive index layer is the Si layer. In this case, by forming the uppermost layer of the reflective layer 12 as a high refractive index layer (Si layer), a silicon oxide layer containing Si and O is provided between the uppermost layer (Si layer) and the protective layer 13. And improve the cleaning resistance of the reflective mask.

Although the reflective layer 12 includes a plurality of high refractive index layers and a plurality of low refractive index layers, the film thickness of the high refractive index layers or the film thickness of the low refractive index layers does not necessarily have to be the same.

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

Each layer constituting the reflective layer 12 can be formed into a desired film thickness by using a known film forming method such as a magnetron sputtering method or an ion beam sputtering method. For example, when the reflective layer 12 is produced by using the ion beam sputtering method, it is performed by supplying ion particles from an ion source to a target of a high refractive index material and a target of a low refractive index material. When the reflective layer 12 is a Mo / Si multilayer reflective film, a Si layer having a predetermined film thickness is first formed on the substrate 11 by an ion beam sputtering method, for example, using a Si target. Then, using the Mo target, a Mo layer having a predetermined film thickness is formed. A Mo / Si multilayer reflective film is formed by laminating the Si layer and the Mo layer for 30 to 60 cycles with one cycle as one cycle.

(Protective layer)
The protective layer 13 is formed by etching (usually dry etching) the absorbing layer 14 to form an absorber pattern 141 (see FIG. 7) on the absorbing layer 14 at the time of manufacturing the reflective mask 20 (see FIG. 7) described later. At that time, the surface of the reflective layer 12 suppresses damage due to etching and protects the reflective layer 12. Further, the resist layer 18 (see FIG. 8) remaining on the reflective mask blank after etching is peeled off with a cleaning liquid to protect the reflective layer 12 from the cleaning liquid when cleaning the reflective mask blank. Therefore, the reflectance of the obtained reflective mask 20 (see FIG. 7) with respect to EUV light is good.

Although FIG. 1 shows a case where the protective layer 13 is one layer, the protective layer 13 may be a plurality of layers.

As the material for forming the protective layer 13, a substance that is not easily damaged by etching when the absorbing layer 14 is etched is selected. As a substance satisfying this condition, for example, Ru metal alone, Ru contains one or more metals selected from the group consisting of B, Si, Ti, Nb, Mo, Zr, Y, La, Co and Re. Ru alloys, ru-based materials such as nitrides containing nitrogen in the Ru alloys; Cr, Al, Ta and nitrides containing nitrogen; SiO ₂ , Si ₃ N ₄ , Al ₂ O ₃ or a mixture thereof, etc. Is exemplified. Among these, Ru metal alone, Ru alloy, CrN and SiO ₂ are preferable. The Ru metal simple substance and the Ru alloy are particularly preferable because they are difficult to be etched with respect to a gas containing no oxygen and function as an etching stopper when processing a reflective mask.

When the protective layer 13 is made of a Ru alloy, the Ru content in the Ru alloy is preferably 95 at% or more and less than 100 at%. When the Ru content is within the above range, when the reflective layer 12 is a Mo / Si multilayer reflective film, it is possible to suppress the diffusion of Si from the Si layer of the reflective layer 12 to the protective layer 13. Further, the protective layer 13 can have a function as an etching stopper when the absorbing layer 14 is etched while ensuring sufficient reflectance of EUV light. Further, it is possible to have the cleaning resistance of the reflective mask and prevent the reflective layer 12 from deteriorating with time.

The film thickness of the protective layer 13 is not particularly limited as long as it can function as the protective layer 13. From the viewpoint of maintaining the reflectance of EUV light reflected by the reflective layer 12, the film thickness of the protective layer 13 is preferably 1 nm or more, more preferably 1.5 nm, and even more preferably 2 nm. The film thickness of the protective layer 13 is preferably 8 nm or less, more preferably 6 nm or less, and even more preferably 5 nm or less.

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

(Absorption layer)
The absorption layer 14 has desired characteristics such as a high absorption coefficient of EUV light, high cleaning resistance to a cleaning liquid, and easy etching for use in a reflective mask for EUV lithography. There is a need.

The absorption layer 14 absorbs EUV light, and the reflectance of EUV light is extremely low. Specifically, when the surface of the absorption layer 14 is irradiated with EUV light, the maximum value of the reflectance of EUV light having a wavelength of around 13.5 nm is preferably 1% or less. Therefore, the absorption layer 14 needs to have a high absorption coefficient of EUV light.

Further, the absorption layer 14 is a cleaning liquid when the resist pattern 181 (see FIG. 8) remaining on the reflective mask blank after etching is removed with the cleaning liquid at the time of manufacturing the reflective mask 20 (see FIG. 7) described later. Be exposed to. At that time, as the cleaning liquid, sulfuric acid hydrogen peroxide (SPM), sulfuric acid, ammonia, ammonia hydrogen peroxide (APM), OH radical cleaning water, ozone water and the like are used. In EUV lithography, SPM is generally used as a cleaning solution for resists. SPM is a solution in which sulfuric acid and hydrogen peroxide are mixed, and sulfuric acid and hydrogen peroxide can be mixed in a volume ratio of, for example, 3: 1. At this time, the temperature of SPM is preferably controlled to 100 ° C. or higher from the viewpoint of improving the etching rate. Therefore, the absorption layer 14 needs to have high cleaning resistance to the cleaning liquid. The absorption layer 14 preferably has a low etching rate (for example, 0.10 nm / min or less) when immersed in a solution of 75 vol% sulfuric acid and 25 vol% hydrogen peroxide at 100 ° C.

Further, the absorption layer 14 is processed by etching by dry etching or the like using a chlorine (Cl) gas such as _{Cl 2} , SiC ₄ and CHCl ₃ , _{or a fluorine (F) gas such as CF 4 or CHF 3.} .. Therefore, the absorption layer 14 needs to be easily etched.

In order to achieve the above characteristics, the absorption layer 14 contains Sn as a main component and Ta in an amount of 25 at% or more. The absorption layer 14 can be formed of a Sn—Ta alloy. The Sn—Ta alloy exists in a state of containing at least one selected from the group consisting of _{Ta, Sn, TaSn 2} and Ta ₃ Sn, depending on the film formation conditions of Sn and Ta and the respective contents. ..

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

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

When the Sn content is 75 at% or less, the Ta content (Ta content) is 25 at% or more. In this case, when the reflective mask 20 (see FIG. 7) to be described later is manufactured, when the reflective mask blank after etching is washed with SPM as a cleaning liquid, as shown in FIG. 2, the surface of the absorption layer 14 is covered. A surface oxide film (passivation film) 15 made of tantalum oxide (Ta ₂ O _{5) is formed.} As a result, the absorption layer 14 is protected, so that etching of the absorption layer 14 is suppressed, and the absorption layer 14 has high cleaning resistance.

When the reflective mask 20 (see FIG. 7) is manufactured, the resist layer 18 (see FIG. 8) formed on the reflective mask blank 10A (see FIG. 1) is drawn (exposed) by an electron beam (EB exposure). After EB exposure, the absorption layer 14 is dry-etched (see FIG. 8) to peel off the resist layer 18 (see FIG. 7). Ashing is used to peel off the resist layer 18, but further cleaning with SPM is required to completely remove the resist residue. By setting the Sn content of the absorption layer 14 to 75 at% or less and the Ta content to 25 at% or more, the cleaning resistance to a cleaning liquid such as SPM can be increased. As a result, the absorption layer 14 can satisfy the cleaning resistance required for the reflective mask 20 (see FIG. 7).

Further, if the passivation film 15 formed by cleaning the reflective mask blank after etching is too thick, the reflectance of the absorption layer 14 may fluctuate. When the Sn content is 75 at% or less and the Ta content is 25 at% or more, the film thickness of the passivation film 15 formed on the surface of the absorption layer 14 can be kept small. As a result, it is possible to suppress fluctuations in the reflectance of the absorption layer 14.

Here, FIG. 3 shows an example of the relationship between the Ta content of the absorption layer and the film thickness of the passivation film 15 formed on the surface of the absorption layer 14. A natural oxide film of about 2 nm is formed on the surface of the absorption layer 14 before SPM cleaning. After SPM cleaning, the film thickness of the oxide film increases due to the oxidizing action of SPM to protect the inside. Then, this natural oxide film becomes the passivation film 15. As shown in FIG. 3, when the Ta content of the absorption layer is 25 at% or more, the film thickness of the passivation film 15 can be suppressed to 6 nm or less. The natural oxide film is generated on the surface of the absorption layer when the absorption layer is exposed to the atmosphere after sputtering. At that time, the composition of this natural oxide film is SnTaO. After that, it is considered that Sn is eluted from the natural oxide film during SPM washing and changed to TaO to become a passivation film 15.

In the present specification, the film thickness of the passivation film 15 means the length in the direction perpendicular to the surface of the absorption layer 14. The film thickness of the passivation film 15 is, for example, the thickness of the passivation film 15 when measured at an arbitrary location in the cross section of the passivation film 15. When several points are measured in the cross section of the passivation film 15 at arbitrary places, the average value of the film thicknesses at these measurement points may be used.

Further, when Sn is the main component and the Ta content is 25 at% or more, Sn is easily etched by Cl-based gas, and Ta is easily etched by Cl-based gas, F-based gas, or the like. It can be easily etched with Cl-based gas.

The absorption layer 14 preferably has an etching rate with respect to SPM of 0.10 nm / min or less. It is more preferably 0.09 nm / min, still more preferably 0.07 nm / min, and particularly preferably 0.05 nm / min. If the etching rate of the absorption layer 14 with respect to SPM is 0.10 nm / min or less, the absorber corresponds to the resist pattern provided on the absorption layer 14 at the time of manufacturing the reflective mask 20 (see FIG. 7). Pattern 141 (see FIG. 7) can be formed substantially evenly. The etching rate of the absorption layer 14 with respect to SPM can be determined by immersing the absorption layer 14 in SPM heated to 100 ° C., for example, 75 vol% for sulfuric acid and 25 vol% for hydrogen peroxide.

In addition to Sn and Ta, the absorption layer 14 may contain one or more elements selected from the group consisting of N, O, B, Hf, Si, Zr, Ge, Pd and H. Above all, it is preferable to contain N, O or B. By containing at least one element of N and O in Sn and Ta, the resistance of the absorption layer 14 to oxidation can be improved, so that the stability over time can be improved. By including B in Sn and Ta, the absorption layer 14 can have an amorphous or microcrystalline structure. The absorption layer 14 is preferably amorphous in crystal state. Therefore, the absorption layer 14 has excellent surface smoothness and flatness. Further, by improving the surface smoothness and flatness of the absorbent layer 14, the edge roughness of the absorber pattern 141 (see FIG. 7) is reduced, and the dimensional accuracy of the absorber pattern 141 (see FIG. 7) can be improved.

The absorption layer 14 may be a single-layer film or a multilayer film composed of a plurality of films. When the absorption layer 14 is a single-layer film, the number of steps in manufacturing the mask blank can be reduced and the production efficiency can be improved. When the absorbent layer 14 is a multilayer film, when the absorber pattern 141 (see FIG. 7) is inspected using the inspection light by appropriately setting the optical constant and the film thickness of the upper layer of the absorbent layer 14. Can be used as an antireflection film. Thereby, the inspection sensitivity at the time of inspection of the absorber pattern can be improved.

The film thickness of the absorption layer 14 can be appropriately designed depending on the composition of the absorption layer 14 and the like, but it is preferably thinner from the viewpoint of suppressing the thickness of the reflective mask blank 10A. The film thickness of the absorption layer 14 is preferably 40 nm or less, for example, from the viewpoint of obtaining sufficient contrast while maintaining the reflectance of the absorption layer 14 of 1% or less. The film thickness of the absorption layer 14 is more preferably 35 nm or less, further preferably 30 nm or less, particularly preferably 25 nm or less, and most preferably 20 nm or less. The film thickness of the absorbing layer 14 is determined by the reflectance, and the thinner the film thickness, the better. The film thickness of the absorption layer 14 can be measured by using, for example, the X-ray reflectivity method (XRR) or TEM.

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

As described above, the reflective mask blank 10A includes an absorption layer 14 containing Sn as a main component and Ta at 25 at% or more, as described above. By containing Sn and Ta in their respective predetermined ranges, the absorption layer 14 can have excellent cleaning resistance during the production of the reflective mask (see FIG. 7). Therefore, the reflective mask blank 10A can stably form the absorber pattern 141 (see FIG. 7) on the absorbing layer 14.

Further, since the reflective mask blank 10A can increase the EUV light absorption rate even if the absorption layer 14 is made thinner, the reflectance of EUV light in the absorption layer 14 is reduced while the reflective mask blank 10A is made thinner. Can be lowered.

Further, the reflective mask blank 10A is excellent in workability because the absorption layer 14 can be easily etched.

<Manufacturing method of reflective mask blank>
Next, a method for manufacturing the reflective mask blank 10A shown in FIG. 1 will be described. FIG. 4 is a flowchart showing an example of a method for manufacturing the reflective mask blank 10A. As shown in FIG. 4, the reflective layer 12 is formed on the substrate 11 (reflective layer 12 forming step: step S11).
As described above, the reflective layer 12 is formed on the substrate 11 so as to have a desired film thickness by using a known film forming method.

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

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

As a result, the reflective mask blank 10A as shown in FIG. 1 is obtained.

(Other layers)
As shown in FIG. 5, the reflective mask blank 10A can include the hard mask layer 16 on the absorbing layer 14. As the hard mask layer 16, a material having high resistance to etching such as a Cr-based film or a Si-based film is used. Examples of the Cr-based film include Cr alone and a material obtained by adding O or N to Cr. Specific examples thereof include CrO and CrN. Examples of the Si-based film include Si alone and a material obtained by adding one or more selected from the group consisting of O, N, C and H to Si. Specific examples thereof include SiO ₂ , SiON, SiN, SiO, Si, SiC, SiCO, SiCN and SiCON. Above all, the Si-based film is preferable because the side wall is unlikely to recede when the absorption layer 14 is dry-etched.

By forming the hard mask layer 16 on the absorption layer 14, dry etching can be performed even if the minimum line width of the absorber pattern 141 (see FIG. 7) becomes small. Therefore, it is effective for miniaturization of the absorber pattern 141 (see FIG. 7). When another layer is laminated on the absorption layer 14, the hard mask layer 16 may be provided on the outermost surface side layer of the absorption layer 14.

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

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

The film thickness of the back surface conductive layer 17 is not particularly limited as long as it satisfies the function for the electrostatic chuck, but is, for example, 10 to 400 nm. Further, the back surface conductive layer 17 can also be provided with stress adjustment on the second main surface 11b side of the reflective mask blank 10A. That is, the back surface conductive layer 17 can be adjusted so as to flatten the reflective mask blank 10A by balancing the stress from various layers formed on the first main surface 11a side.

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

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

<Reflective mask>
Next, the reflective mask obtained by using the reflective mask blank 10A shown in FIG. 1 will be described. FIG. 7 is a schematic cross-sectional view showing an example of the configuration of the reflective mask. As shown in FIG. 7, the reflective mask 20 has a desired absorber pattern 141 formed on the absorbent layer 14 of the reflective mask blank 10A shown in FIG.

An example of a method for manufacturing the reflective mask 20 will be described. FIG. 8 is a diagram illustrating a manufacturing process of the reflective mask 20. As shown in FIG. 8A, the resist layer 18 is formed on the absorption layer 14 of the reflective mask blank 10A shown in FIG. 1 described above.

Then, the resist layer 18 is exposed to a desired pattern. After the exposure, the exposed portion of the resist layer 18 is developed and washed (rinsed) with pure water to form a predetermined resist pattern 181 on the resist layer 18 as shown in FIG. 8 (b).

Then, the resist layer 18 on which the resist pattern 181 is formed is used as a mask to dry-etch the absorption layer 14. As a result, as shown in FIG. 8C, an absorber pattern 141 corresponding to the resist pattern 181 is formed on the absorption layer 14.

As the etching gas, a mixed gas containing F-based gas, Cl-based gas, Cl-based gas and O ₂ , He or Ar in a predetermined ratio can be used.

After that, the resist layer 18 is removed with a resist stripping solution or the like to form a desired absorber pattern 141 on the absorption layer 14. As a result, as shown in FIG. 7, it is possible to obtain the reflective mask 20 in which the desired absorber pattern 141 is formed on the absorption layer 14.

The obtained reflective mask 20 is irradiated with EUV light from the illumination optical system of the exposure apparatus. The EUV light incident on the reflective mask 20 is reflected at the portion without the absorbing layer 14 (the portion of the absorber pattern 141) and absorbed at the portion with the absorbing layer 14. As a result, the reflected light of the EUV light reflected by the absorption layer 14 is applied to the exposure material (for example, a wafer or the like) through the reduced projection optical system of the exposure apparatus. As a result, the absorber pattern 141 of the absorption layer 14 is transferred onto the exposure material, and a circuit pattern is formed on the exposure material.

In the reflective mask 20, since the absorption layer 14 has high cleaning resistance, the absorber pattern 141 can be stably formed on the absorption layer 14. Therefore, the reflective mask 20 has high pattern accuracy.

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

[Second Embodiment]
The reflective mask blank according to the second embodiment will be described with reference to the drawings. Members having the same functions as those in the above embodiment are designated by the same reference numerals, and detailed description thereof will be omitted. FIG. 9 is a schematic cross-sectional view of the reflective mask blank according to the second embodiment. As shown in FIG. 9, the reflective mask blank 10B has a stabilizing layer 19 on the absorbing layer 14 of the reflective mask blank 10A shown in FIG. That is, the reflective mask blank 10B is configured by laminating the substrate 11, the reflective layer 12, the protective layer 13, the absorbing layer 14, and the stabilizing layer 19 in this order from the substrate 11 side.

The stable layer 19 contains oxides, nitrides, borides, oxynitrides and acid borides containing Ta and Sn, Ta oxides, nitrides, borides, oxynitrides and acid borides, and Ru. It can contain one or more compounds selected from the group consisting of Ru-based materials (Ru-based compounds).

When the stable layer 19 is one or more compounds selected from the group consisting of oxides containing Ta and Sn, nitrides, borides, oxynitrides and acid borides, oxides containing Ta and Sn. As nitrides, borides, oxynitrides and acid borides, for example, TaSnO, TaSnN, TaSnB, TaSnON, TaSnBO, TaSnBN, TaSnBON and the like can be mentioned.

When the stable layer 19 is an oxide film or an oxynitride film composed of Ta and Sn as an oxide, a nitride, a boride, an oxynitride and an acid boride containing Ta and Sn, the stable layer 19 absorbs. It can be formed using the same material as layer 14. Therefore, as the target used when forming the stable layer 19, the target used when forming the absorbing layer 14 can be used. As a result, the stable layer 19 can be easily formed on the main surface of the absorption layer 14, so that the productivity is excellent. In this case, the film thickness of the stable layer 19 does not change even after washing, but the composition of the film may change.

Here, when the stable layer 19 is a film composed of Ta and Sn (Ta content 50 at%), the surface of the stable layer 19 before and after SPM cleaning is measured by X-ray photoelectron spectroscopy (XPS). Table 1 shows an example of the intensity ratio of Sn and Ta. The XPS spectrum measured using XPS reflects the intensity ratio of the composition of the film surface of the stable layer 19. In Table 1, Sn _{measured the intensity of the photoelectron spectrum corresponding to the 3d 5/2} orbit, and Ta measured the intensity of the photoelectron spectrum corresponding to the 4d _5/2 orbit.

From Table 1, by SPM cleaning, the Sn content on the film surface is significantly reduced, and the composition of the components on the film surface is changed. This is the same as the case where the passivation film 15 made _{of Ta 2} O ₅ is formed on the surface of the absorption layer 14 when the reflective mask blank is washed after etching (see FIG. 2). Is oxidized to form a passivation film 15 (see FIG. 2) made _{of Ta 2} O _{5 on} the surface of the stable layer 19. Therefore, when the stable layer 19 is an oxide film or an oxynitride film composed of Ta and Sn, a passivation film 15 (see FIG. 2) may be formed on the surface of the stable layer 19, and the composition of the film may change.

When the stable layer 19 is one or more compounds selected from the group consisting of Ta oxides, nitrides, borides, oxynitrides and acid borides, the stable layer 19 is Ta oxide film or nitride film. , Boride film, oxynitride film and acid boride film can be used. Oxides of Ta, nitride, boride, oxynitride and acid borides, _{e.g., TaO, Ta 2 O 5,} TaN, TaB 2, TaON, TaCON, TaBN, TaBO, TaBON, TaBCON, TaHfO, TaHfN , TaHfON, TaHfCON, TaSiO, TaSiN, TaSiON, TaSiCON and the like. If a Ta oxide film or an oxynitride film is used as the stable layer 19, the composition of the stable layer 19 does not change due to washing, so that a more stable stable layer 19 can be formed.

Further, a film containing a Ru-based material (Ru-based film) can be used as the stable layer 19. If a Ru-based film is used as the stable layer 19, the absorption layer 14 can be further thinned while maintaining the reflectance at 1% or less.

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

The stable layer 19 can be formed by using a known film forming method such as a magnetron sputtering method, an ion beam sputtering method, or a reactive sputtering method. The reactive sputtering method is, for example, a method in which Ta, Sn or SnTa is used as the target, and a mixed gas in which oxygen or nitrogen is mixed with an inert gas such as Ar or Kr is used as the sputtering gas.

The reflective mask blank 10B has the stabilizing layer 19 on the absorbing layer 14, so that the cleaning resistance of the absorbing layer 14 can be further improved. By having the stable layer 19, a strong and stable film can be formed with good reproducibility, and the characteristics of the reflective mask blank and the reflective mask can be stabilized. Further, as shown in FIG. 10, the side wall of the absorption layer 14 is exposed after dry etching. However, since the passivation film 15 is formed on the side wall of the absorption layer 14 after cleaning, it is possible to prevent the absorption layer 14 from being etched by cleaning, and the absorption layer 14 is protected.

[Third Embodiment]
The reflective mask blank according to the third embodiment will be described with reference to the drawings. Members having the same functions as those in the above embodiment are designated by the same reference numerals, and detailed description thereof will be omitted. FIG. 11 is a schematic cross-sectional view of the reflective mask blank according to the third embodiment. As shown in FIG. 11, the reflective mask blank 10C is between the absorption layer 14 and the stable layer 19 of the reflection mask blank 10B shown in FIG. 9, and has a prevention layer 21 on the absorption layer 14. That is, the reflective mask blank 10C is configured by laminating the substrate 11, the reflective layer 12, the protective layer 13, the absorbing layer 14, the preventing layer 21, and the stabilizing layer 19 in this order from the substrate 11 side.

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

The prevention layer 21 contains Ta simple substance, Cr simple substance, Si simple substance, Ta nitride, Cr nitride, Si nitride, Ta boride, Cr boride, Si boride or Ta boron nitride. Can be used. These may be contained alone or in combination of two or more.

The preferred composition of the prevention layer 21 is, for example, Ta, TaN, TaB or TaBN. For example, assume that the stable layer 19 contains an oxide of Ta, an oxynitride or an acid boride. In this case, if the preventive layer 21 is made of these materials, the same target can be used when forming the preventive layer 21 and the stable layer 19. Therefore, the productivity of the reflective mask blank 10C is excellent, such as reducing the number of required film forming chambers.

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

The prevention layer 21 is a layer that does not contain oxygen. "Oxygen-free" means that oxygen does not exist on the surface and inside of the prevention layer 21 immediately after the film is formed on the prevention layer 21. When the reactive sputtering method containing oxygen is used when forming the stable layer 19, the components contained in the prevention layer 21 react (oxidize) with oxygen on the surface where the prevention layer 21 comes into contact with oxygen. , An oxide film may be formed on the surface of the prevention layer 21. In addition, oxygen-free means that if there is an oxide film formed on the surface where the prevention layer 21 is in contact with oxygen in the step after the prevention layer 21 is formed, the oxygen contained in the oxide film is present. Does not include. On the other hand, since the interface between the absorption layer 14 and the prevention layer 21 does not come into contact with oxygen, oxygen is not contained in the interface between the absorption layer 21 and the prevention layer 14 and its vicinity. The term "neighborhood" refers to a range of several nm from the interface in the depth direction of the prevention layer 21.

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

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

When the absorption layer 14 comes into contact with oxygen, some Sn existing on the surface of the absorption layer 14 may react with oxygen to generate precipitates such as fine particles containing Sn on the surface of the absorption layer 14. .. For example, when the stable layer 19 is formed by using the reactive sputtering method, as described above, a mixed gas obtained by mixing oxygen with an inert gas such as He, Ar or Kr is used as the sputtering gas. When the surface of the absorption layer 14 comes into contact with a mixed gas which is a sputtering gas, precipitates may be generated on the surface of the absorption layer 14.

As described above, the prevention layer 21 is formed on the absorption layer 14 by using only an inert gas such as He, Ar or Kr as a sputtering gas. Therefore, by forming the prevention layer 21 before the absorption layer 14 comes into contact with a gas such as oxygen, it is possible to prevent the absorption layer 14 from coming into contact with oxygen, thereby preventing precipitation from being generated on the surface of the absorption layer 14. can.

Therefore, since the reflective mask blank 10C has the prevention layer 21 on the absorption layer 14 to prevent the formation of precipitates on the surface of the absorption layer 14, the reflection type mask is produced when the reflection type mask is manufactured. It is possible to suppress the occurrence of defects in the mask. As a result, a defect-free film can be stably formed.

The reflective mask blank 10C can form the prevention layer 21 containing at least one or more elements of Ta, Cr or Si. These elements are easy to dry etch and have excellent cleaning resistance. Therefore, if the prevention layer 21 is configured to include Ta or the like, even if the absorption layer 14 contains Sn, the absorber pattern 141 having strong cleaning resistance while preventing oxidation of the surface of the absorption layer 14 (see FIG. 7). ) Can be formed.

In the reflective mask blank 10C, the prevention layer 21 is provided with Ta simple substance, Cr simple substance, Si simple substance, Ta nitride, Cr nitride, Si nitride, Ta boride, Cr boride, and Si boride. Alternatively, it can be formed using Ta boron nitride. Since these simple substances, nitrides, borides and boron nitrides are amorphous, the edge roughness of the absorber pattern 141 (see FIG. 7) can be suppressed. Therefore, if the prevention layer 21 is configured to contain Ta nitride or the like, a highly accurate absorber pattern 141 (see FIG. 7) can be formed while preventing oxidation of the surface of the absorption layer 14 containing Sn.

The reflective mask blank 10C can be formed by containing at least one or more elements of He, Ne, Ar, Kr or Xe in the prevention layer 21. Since these elements are used as a sputtering gas during the film formation of the prevention layer 21, a small amount of these elements may be contained in the prevention layer 21. Even in this case, the function of the prevention layer 21 can be exhibited without affecting the properties of the prevention layer 21.

The reflective mask blank 10C can have the prevention layer 21 film thickness of 10 nm or less. As a result, the thickness of the preventive layer 21 can be suppressed, so that the reflective mask blank 10C has the absorber pattern 141 (see FIG. 7) and the patterns of the preventive layer 21 and the stable layer 19 formed on the absorber pattern 141. The overall thickness of the can be suppressed.

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

[Example 1-1]
(Making a reflective mask blank)
As a substrate for film formation, a SiO _2- TiO ₂ system glass substrate (outer shape: about 152 mm square, thickness: about 6.3 mm) was used. The coefficient of thermal expansion of the glass substrate was 0.02 × 10 ^-7 / ° C. The glass substrate was polished to obtain a smooth surface having a surface roughness of 0.15 nm or less in a root mean square roughness Rq and a flatness of 100 nm or less. A Cr layer having a film thickness of about 100 nm was formed on the back surface of the glass substrate by using a magnetron sputtering method to form a back surface conductive layer (conductive film) for an electrostatic chuck. The sheet resistance value of the Cr layer was about 100Ω / □. After fixing the glass substrate with the Cr film, the Si film and the Mo film were alternately formed on the surface of the glass substrate by the ion beam sputtering method for 40 cycles. The film thickness of the Si film was about 4.5 nm, and the film thickness of the Mo film was about 2.3 nm. As a result, a reflective layer (multilayer reflective film) having a total film thickness of about 272 nm ((Si film: 4.5 nm + Mo film: 2.3 nm) × 40) was formed. Then, a Ru layer (thickness: about 2.5 nm) was formed on the reflective layer by using an ion beam sputtering method to form a protective layer (protective film). Next, an absorption layer (absorber film) made of a Sn—Ta alloy was formed on the protective layer by a magnetron sputtering method. Ar gas was used as the sputtering gas. The target used for the sputtering had Sn of 60 at% and Ta of 40 at%, but the Ta content in the sputtered absorption layer was 48 at%. The Sn content and Ta content in the absorption layer were measured by using a fluorescent X-ray analysis method (XRF) (manufactured by Olympus Corporation, Delta). By stopping the rotation of the stage during sputtering of the absorption layer, an absorption layer having a large film thickness distribution of 30 to 53 nm was obtained in the plane. As a result, the reflective mask blank 10A shown in FIG. 6 was produced. The film thickness of the absorption layer was measured by XRR using an X-ray diffractometer (SmartLab HTP, manufactured by Rigaku Co., Ltd.). From the results of X-ray diffraction (XRD) measurement using the same device, it was confirmed that the absorption layer made of Sn—Ta alloy was amorphous.

(Relationship between absorption layer film thickness and reflectance)
The relationship between the film thickness of the absorbent layer of the reflective mask blank and the reflectance was measured. The reflectance was measured using an EUV reflectance meter for mask blanks (MBR, manufactured by AIXUV). The wavelength of EUV light was 13.5 nm. The relationship between the film thickness of the absorbing layer and the reflectance is shown in FIG. In order for the reflective mask to obtain sufficient contrast, it is necessary to reduce the reflectance to 1% or less.

[Example 1-2]
In Example 1-1, the same procedure as in Example 1-1 was carried out except that the absorption layer was prepared using TaN instead of the Sn—Ta alloy. The relationship between the film thickness of the absorbing layer and the reflectance is shown in FIG.

As shown in FIG. 12, the reflectance of Example 1-1 was smaller than that of Example 1-2. It is considered that this is because the extinction coefficient of Sn is larger than the extinction coefficient of Ta. In Example 1-2, in order to maintain the reflectance of the absorbing layer at 1% or less, the film thickness of the absorbing layer could only be thinned to about 62 nm. On the other hand, in Example 1-1, the film thickness of the absorption layer could be reduced to about 40 nm.

Therefore, if the absorption layer is formed by using an alloy containing Sn52at% and Ta48at%, the reflectance of EUV light can be reduced to 1% or less even if the thickness of the absorption layer is 40 nm, so that sufficient contrast can be obtained. Therefore, it was confirmed that the absorption layer can have a film thickness of 40 nm or less.

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

[Example 2-1]
(Refractive index and extinction coefficient of absorption layer)
The reflectance of the absorbent layer made of Sn—Ta alloy was simulated. The Sn content of the absorption layer was 30 at%, and the Ta content was 70 at%. The simulation requires the refractive index (n) and the extinction coefficient (k) of the absorption layer. As the refractive index and extinction coefficient of Sn and Ta, the values in the database of Center for X-Ray Optics and Lawrence Berkeley National Laboratory were used. At a wavelength of 13.5 nm, the refractive index n of Sn is 0.9416, the extinction coefficient k is 0.0725, the refractive index n of Ta is 0.9429, and the extinction coefficient is 0.0408. .. The refractive index and extinction coefficient of the Sn—Ta alloy can be calculated using the density of the alloy. The density of the alloy was calculated by interpolating the density of Sn (7.365 g / cm ³ ) and the density of Ta (16.69 g / cm ³ ) with the composition ratio.

(Relationship between absorption layer film thickness and reflectance)
A simulation was performed assuming that the film thickness of the absorption layer was 30 to 60 nm and EUV light was applied to the reflective mask blank 10A so that the angle of incidence on the reflective mask blank 10A was 6 °. The wavelength of EUV light was 13.5 nm. The result of simulating the relationship between the film thickness of the absorption layer and the reflectance is shown in FIG. Similar to Example 1-1, the reflectance needs to be 1% or less in order for the reflective mask to obtain sufficient contrast.

[Example 2-2 to Example 2-6]
In Example 2-1 the simulation was performed in the same manner as in Example 2-1 except that the Sn content of the absorption layer was changed to 40 at%, 50 at%, 60 at%, 70 at% or 80 at%. FIG. 13 shows the result of simulating the relationship between the film thickness of the absorption layer of the reflective mask blank and the reflectance.

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

Therefore, it was confirmed that if the Sn content of the absorbing layer is 30 at% or more, the reflectance of the absorbing layer can be reduced to 1% or less even if the film thickness of the absorbing layer is reduced to 40 nm.

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

[Example 3-1]
The film thickness of the absorption layer was fixed at 40 nm, the Sn content was changed, and the reflectance of EUV light was simulated in the same manner as in Example 2-1. The result of simulating the relationship between the Sn content and the reflectance is shown in FIG.

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

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

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

<Example 4>
Examples 4-1 to 4-4 are examples, Example 4-5 is a comparative example, and Example 4-6 is a reference example.
[Example 4-1]
(Preparation of absorption layer)
A Si substrate was used as the substrate for film formation. An absorber film made of a Sn—Ta alloy was formed on the surface of the Si substrate by a magnetron sputtering method. Ar gas was used as the sputtering gas. The absorption layer was formed to a film thickness of 40 nm so that the Ta content in the absorption layer was about 30 at% and the Sn content was about 70 at% by the dual sputtering of the Ta target and the Sn target.

(Relationship between Ta content and film loss of absorption layer)
Then, SPM (75 vol% of sulfuric acid and 25 vol% of hydrogen peroxide) was used as a cleaning liquid, and the glass substrate on which the absorption layer was formed was immersed in SPM heated to 100 ° C. for about 20 minutes. After pulling up the Si substrate from the SPM, the film thickness of the absorption layer formed on the Si substrate was measured, and the amount of decrease in the film thickness (film reduction) was determined. The relationship between the Ta content and the film loss of the absorption layer is shown in Table 2 and FIG. It is necessary that the film loss is less than or equal to the film loss of the Cr film that has been conventionally used as an absorption layer. The reduction of the Cr film was set to 2.2 nm. In FIG. 15, the film loss of the Cr film is shown by a broken line.

[Example 4-2-4-6]
In Example 4-1 the same procedure as in Example 4-1 was carried out except that the Ta content and Sn content in the absorption layer were changed to the values shown in Table 2, respectively. The relationship between the Ta content and the film loss of the absorption layer is shown in Table 2 and FIG.

As shown in FIG. 15, in Examples 4-1 to 4-3, the film loss was smaller than that of the Cr film. On the other hand, in Example 4-5, the film loss was larger than that of the Cr film. In Examples 4-4 and 4-6, the film thickness of the absorption layer increased. It is considered that this is because a passivation film was formed and grew on the surface of the absorption layer when immersed in the cleaning liquid. The absorption layer of Example 4-6 has cleaning resistance, but has a high reflectance due to its low Sn content.

From FIG. 15, when the Ta content in the absorption layer is 25 at% or more, it is possible to obtain cleaning resistance higher than that of the Cr film conventionally used as the absorption layer. Therefore, it was confirmed that the absorbent layer can stably form the absorber pattern.

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

[Example 5-1]
(Preparation of absorption layer)
An absorption layer similar to Example 4-1 was formed on the Si substrate.
(Relationship between Ta content and etching rate)
The glass substrate on which the absorption layer was formed was etched using an ICP plasma etching apparatus. Chlorine (Cl ₂ ) gas was used as the etching gas. The ICP source power was 100 W and the bias power was 40 W. The film thicknesses of the absorption layer and the TaN film were measured using an XRR. The film thickness of the absorbing layer after etching was measured, and the etching rate of the absorbing layer was measured. The result of measuring the etching rate is shown in FIG.

[Example 5-2]
In Example 5-1 the same procedure as in Example 5-1 was carried out except that the absorption layer was prepared using TaN instead of the Sn—Ta alloy. The result of measuring the etching rate is shown in FIG.

As shown in FIG. 16, the etching rate of Example 5-1 was higher than that of Example 5-2. Therefore, if the absorption layer is formed by using a Sn—Ta alloy containing 70 at% of Sn and 30 at% of Ta, it is possible to use Cl ₂ gas as compared with the absorption layer formed of a conventionally used material such as TaN. Can be easily etched. Therefore, the absorption layer is easy to be etched.

<Example 6>
Example 6 is an example.

(Making a reflective mask blank)
A reflective mask blank was prepared in the same manner as in Example 1-1. Then, a stable layer made of TaO was formed on the absorption layer by a magnetron sputtering method to form a film of about 4 nm. As a result, the reflective mask blank shown in FIG. 9 was produced.

(Measurement of reflectance)
From above the prepared reflective mask blank (+ Z-axis direction), EUV light with a wavelength of 13.53 nm is incident on the surface of the reflective mask blank at an incident angle of 6 °, and the UV light reflected by the reflective mask is reflected. The rate was measured. As a result, the reflectance of EUV light was about 0.8% in the portion where the total film thickness of the absorption layer and the stable layer was 40 nm.

Therefore, the reflectance of EUV light can be reduced to 1% or less even with a reflective mask blank in which the total film thickness of the absorbing layer and the stable layer is about 40 nm. Therefore, the reflective mask blank of the present embodiment can make the absorption layer thinner than the conventional reflective mask blank.

<Example 7>
Example 7 is an example.
(Making a reflective mask blank)
A reflective mask blank was prepared in the same manner as in Example 1-1. At that time, the coefficient of thermal expansion of the glass substrate was 0.02 × ^10-7 / ° C. or less, and the film thickness of the absorption layer (absorbent film) was 40 nm. Then, a prevention layer made of Ta is formed on the absorption layer (absorbent film) by a magnetron sputtering method at 2 nm, and a stable layer made of TaO is formed on the prevention layer by a reactive sputtering method at 2 nm. Membrane. As a result, the reflective mask blank 10C shown in FIG. 11 was produced. When the prevention layer was formed into a film by the magnetron sputtering method, Ar gas was used as the sputtering gas. When the stable layer was formed into a film by the reactive sputtering method, a mixed gas in which Ar and oxygen were mixed was used as the sputtering gas, the flow rate of Ar was 40 sccm, and the flow rate of oxygen was 30 sccm.

When the preventive layer and the stable layer of the reflective mask blank after the film formation were measured by XRR, the film thickness of Ta was 0.9 nm and the film thickness of TaO was 4.6 nm. It is considered that this is because when the TaO film is formed on the Ta film, oxygen contained in the sputtering gas reacts with Ta of the Ta film to form a TaO film, which expands.

Then, the reflective mask blank 10C shown in FIG. 11 was dry-etched using a dry etching apparatus. In dry etching, the prevention layer and the stable layer were removed using an F-based gas, and then the absorption layer was removed using a Cl-based gas.

(Observation of the surface of the reflective mask blank)
When the surface of the reflective mask blank was observed using a scanning electron microscope (Carl Zeiss, Ultra60), no precipitates such as fine particles were observed. In this example, when the prevention layer is formed, only Ar is used as the sputtering gas. Therefore, since the surface of the absorption layer is not exposed to an atmosphere containing oxygen, Sn existing on the surface of the absorption layer does not react with oxygen. As a result, it can be said that the generation of precipitates on the surface of the absorption layer was suppressed.

Although the embodiments have been described above, the above-described embodiments are presented as examples, and the present invention is not limited to the above-described embodiments. The above-described embodiment can be implemented in various other forms, and various combinations, omissions, replacements, changes, etc. can be made without departing from the gist of the invention. These embodiments and modifications thereof are included in the scope and gist of the invention, and are also included in the scope of the invention described in the claims and the equivalent scope thereof.

10A-10C Reflective mask blank 11 Substrate 12 Reflective layer 13 Protective layer 14 Absorbent layer 15 Surface oxide film (passivation film)
16 Hard mask layer 17 Back surface conductive layer 18 Resist layer 19 Stable layer 20 Reflective mask 21 Prevention layer

Claims (19)

A reflective mask blank having a reflective layer that reflects EUV light and an absorbent layer that absorbs EUV light on the substrate in this order from the substrate side.
The absorption layer is a reflective mask blank containing Sn as a main component and Ta at 25 at% or more. The reflective mask blank according to claim 1, wherein the Sn content of the absorption layer is 30 at% or more. The reflective mask blank according to claim 1 or 2, wherein the absorption layer has a film thickness of 40 nm or less. The reflective mask blank according to any one of claims 1 to 3, wherein the etching rate of the absorption layer with respect to sulfuric acid hydrogen peroxide is 0.10 nm / min or less. The reflective type according to any one of claims 1 to 4, wherein the absorption layer contains one or more elements selected from the group consisting of N, O, B, Hf, Si, Zr, Ge, Pd and H. Mask blank. The reflective mask blank according to any one of claims 1 to 5, which has a stable layer on the absorption layer. The stable layer contains oxides containing Ta and Sn, nitrides, borides, oxynitrides and acid borides, Ta oxides, nitrides, borides, oxynitrides and acid borides, and Ru. The reflective mask blank according to claim 6, which contains one or more compounds selected from the group consisting of Ru-based materials. The reflective mask blank according to claim 6 or 7, wherein the stable layer has a film thickness of 10 nm or less. The reflective mask blank according to any one of claims 6 to 8, which has an prevention layer on the absorption layer. The reflective mask blank according to claim 9, wherein the prevention layer is formed between the absorption layer and the stable layer. The reflective mask blank according to claim 9 or 10, wherein the prevention layer contains one or more elements selected from the group consisting of Ta, Cr and Si. The preventive layer is made of Ta simple substance, Cr simple substance, Si simple substance, Ta nitride, Cr nitride, Si nitride, Ta boride, Cr boride, Si boride and Ta boron nitride. The reflective mask blank according to claim 11, which contains one or more components selected from the group. The reflective mask blank according to any one of claims 9 to 12, wherein the prevention layer contains one or more elements selected from the group consisting of He, Ne, Ar, Kr, and Xe. The reflective mask blank according to any one of claims 9 to 13, wherein the film thickness of the prevention layer is 10 nm or less. The reflective mask blank according to any one of claims 1 to 14, which has a protective layer between the reflective layer and the absorbent layer. The reflective mask blank according to any one of claims 1 to 15, which has a hard mask layer on the absorption layer or on the layer on the outermost surface side of the absorption layer. The reflective mask blank according to claim 16, wherein the hard mask layer contains at least one element of Cr or Si. A reflective mask in which a pattern is formed on the absorbent layer of the reflective mask blank according to any one of claims 1 to 17. A method for manufacturing a reflective mask blank, which has a reflective layer that reflects EUV light and an absorbent layer that absorbs EUV light on a substrate in this order.
The step of forming the reflective layer on the substrate and
A step of forming an absorption layer containing Sn as a main component and 25 at% or more of Ta on the reflective layer.
A method for manufacturing a reflective mask blank including.

Images