JP7263908B2 - Reflective mask blank, reflective mask, and method for manufacturing 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 that make up semiconductor devices, extreme exposure methods have been developed as alternatives to conventional exposure techniques using visible light, ultraviolet light (wavelength 193 to 365 nm), ArF excimer laser light (wavelength 193 nm), etc. Ultraviolet (Etreme Ultra Violet: hereinafter referred to as "EUV") lithography is being considered.

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

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

A reflective mask has a reflective layer that reflects EUV light formed on a substrate, and an absorption layer that absorbs EUV light is formed in a pattern on the reflective layer. The reflective mask was formed in a predetermined pattern by removing part of the absorbing layer from a reflective mask blank, which was constructed by laminating a reflective layer and an absorbing layer on a substrate in this order from the substrate side. After that, it is obtained by washing with a washing liquid.

The EUV light incident on the reflective mask is absorbed by the absorbing layer and reflected by the reflective layer. The reflected EUV light is imaged onto the surface of the exposure material (wafer coated with resist) by an optical system. This transfers the pattern of the absorbing layer to the surface of the exposed material.

In EUV lithography, EUV light is typically incident on a reflective mask from an oblique direction of about 6° and is reflected obliquely as well. Therefore, if the thickness of the absorption layer is large, the optical path of the EUV light may be blocked (shadowing). If shadowing occurs on the substrate or the like due to the influence of the absorption layer, the pattern of the reflective mask may not be faithfully transferred onto the surface of the exposure material, resulting in deterioration of pattern accuracy. On the other hand, if the thickness of the absorption layer is reduced, the EUV light shielding performance of the reflective mask decreases, and the reflectance of the EUV light increases. may decline.

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

However, in the reflective mask blank described in Patent Document 1, the surface of the absorber film may be oxidized to generate fine particles on the surface of the absorber film and cause defects on the surface of the absorber film. For example, when the absorber film is made of an alloy of Ta and Sn, the surface of the absorber film may be oxidized to generate fine particles of tin oxide on the surface of the absorber film. When producing a reflective mask, if fine particles are present in a portion where the absorber film should be removed by dry etching, there is a possibility that this portion will not be etched and the absorber film will remain, resulting in a pattern defect. In this case, pattern defects on the reflective mask are transferred to the exposure material (resist) applied to the wafer during wafer exposure, which is not preferable.

JP 2007-273678 A

An object of one embodiment of the present invention is to provide a reflective mask blank that can suppress the occurrence of defects on the surface of the absorbing layer due to oxidation of the surface of the absorbing layer.

One aspect of the reflective mask blank according to the present invention is a reflective mask blank having, on a substrate, a reflective layer for reflecting EUV light and an absorbing layer for absorbing EUV light in this order from the substrate side, The absorption layer contains Sn and has an anti-oxidation layer on the absorption layer to prevent oxidation of the absorption layer.

According to one aspect of the present invention, it is possible to provide a reflective mask blank capable of suppressing defects on the surface of the absorbing layer due to oxidation of the surface of the absorbing layer.

1 is a schematic cross-sectional view of a reflective mask blank according to a first embodiment; FIG. 4 is a flow chart showing an example of a method for manufacturing a reflective mask blank; FIG. 4 is a schematic cross-sectional view showing an example of another form of a reflective mask blank; FIG. 4 is a schematic cross-sectional view showing an example of another form of a reflective mask blank; It is a schematic sectional drawing which shows an example of a structure of a reflective mask. It is a figure explaining the manufacturing process of a reflective mask. FIG. 5 is a schematic cross-sectional view of a reflective mask blank according to a second embodiment; FIG. 4 is a schematic cross-sectional view showing an example of another form of a reflective mask blank; 2 is a schematic cross-sectional view of a reflective mask blank of Comparative Example 1; FIG. FIG. 10 is a diagram showing observation results of the surface of the absorption layer of the reflective mask blank of Comparative Example 1; FIG. 4 is a diagram showing observation results of the surface of the absorption layer of the reflective mask blank of Example 1; FIG. 10 is a diagram showing observation results of the surface of the absorption layer of the reflective mask blank of Example 2;

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described in detail. In addition, in order to facilitate understanding of the description, the same components are denoted by the same reference numerals in each drawing, and overlapping descriptions are omitted. Also, the scale of each member in the drawings may differ from the actual scale. In this specification, a three-dimensional orthogonal coordinate system with three axial directions (X-axis direction, Y-axis direction, Z-axis direction) is used, the coordinates on the main surface of the 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 substrate (the direction from the main surface of the substrate toward 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." In this specification, the tilde "~" indicating a numerical range means that the numerical values before and after it are included as lower and upper limits unless otherwise specified.

<Reflective mask blank>
A reflective mask blank according to the first embodiment will be described. FIG. 1 is a schematic cross-sectional view of a reflective mask blank according to the first embodiment. As shown in FIG. 1, the reflective mask blank 10A is constructed by stacking a reflective layer 12, a protective layer 13, an absorbing layer 14, and an anti-layer 15 on a substrate 11 in this order.

(substrate)
The substrate 11 preferably has a small coefficient of thermal expansion. A smaller coefficient of thermal expansion of the substrate 11 can suppress the distortion of the pattern formed in the absorption layer 14 due to heat during exposure to 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 with a small thermal expansion coefficient, for example, SiO ₂ —TiO ₂ based glass or the like can be used. As the SiO ₂ —TiO ₂ -based glass, it is preferable to use quartz glass containing 90% to 95% by mass of SiO ₂ and 5% to 10% by mass of TiO ₂ . When the content of TiO ₂ is 5% by mass to 10% by mass, the coefficient of linear expansion near room temperature is approximately zero, and dimensional change hardly occurs near room temperature. The SiO ₂ —TiO ₂ -based glass may contain minor components other than SiO ₂ and TiO ₂ .

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

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

Further, the substrate 11 is preferably resistant to a cleaning solution used for cleaning a reflective mask blank, a reflective mask blank after pattern formation, or a reflective mask.

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

The size, thickness, etc. of the substrate 11 are appropriately determined according to the design values of the reflective mask.

The first main surface 11a of the substrate 11 is formed in a rectangular or circular shape in plan view. In this specification, a rectangle includes not only rectangles and squares, but also rectangles and squares with rounded corners.

(reflective layer)
The reflective layer 12 has a high reflectance for EUV light. Specifically, when the EUV light is incident on the surface of the reflective layer 12 at an incident angle of 6°, the maximum reflectance of the EUV light near a wavelength of 13.5 nm is preferably 60% or more, and more preferably 65% or more. preferable. Also, 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 around a wavelength of 13.5 nm is preferably 60% or more. % or more is more preferable.

The reflective layer 12 is a multilayer film in which a plurality of layers whose main components are elements having different refractive indices are periodically laminated. The reflective layer 12 is generally a multi-layer structure in which high refractive index layers exhibiting a high refractive index with respect to EUV light and 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 periods 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 period, or a low refractive index layer and a high refractive index layer may be laminated. A lamination structure in which layers are laminated in this order may be laminated in a plurality of cycles as one cycle. In this case, the outermost layer (uppermost layer) of the multilayer reflective film is preferably a high refractive index layer. This is because the low refractive index layer is easily oxidized, and if the low refractive index layer is the uppermost layer of the reflective layer 12, the reflectance of the reflective layer 12 may decrease.

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

The reflective layer 12 includes a plurality of high refractive index layers and a plurality of low refractive index layers, but the thicknesses of the high refractive index layers or the thicknesses of the low refractive index layers may not necessarily 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 reflectance of 60% or more for EUV light near a wavelength of 13.5 nm, a low refractive index layer (a layer containing Mo) and a high refractive index layer (a layer containing Si) A Mo/Si multilayer reflective film obtained by alternately stacking 30 to 60 cycles of the layers is preferably used.

Each layer constituting the reflective layer 12 can be formed to have a desired film thickness using a known film forming method such as magnetron sputtering or ion beam sputtering. For example, when the reflective layer 12 is produced using the ion beam sputtering method, ion particles are supplied from an ion source to a high refractive index material target and a low refractive index material target. When the reflective layer 12 is a Mo/Si multilayer reflective film, a Si-containing layer having a predetermined thickness is formed on the substrate 11 by ion beam sputtering, for example, using a Si target. After that, a Mo target is used to form a layer containing Mo with a predetermined film thickness. A Mo/Si multilayer reflective film is formed by laminating the layer containing Si and the layer containing Mo as one period for 30 to 60 periods.

(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. 5) in the absorbing layer 14 at the time of manufacturing the reflective mask 20 (see FIG. 5), which will be described later. At this time, the surface of the reflective layer 12 is prevented from being damaged by etching, and the reflective layer 12 is protected. Also, the resist layer 19 (see FIG. 6) remaining on the reflective mask blank after etching is removed with a cleaning liquid to protect the reflective layer 12 from the cleaning liquid when the reflective mask blank is cleaned. Therefore, the obtained reflective mask 20 (see FIG. 5) has a good reflectance for EUV light.

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

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

When the protective layer 13 is made of Ru alloy, the Ru content in the Ru alloy is preferably 95 at % or more and less than 100 at %. If the Ru content is within the above range, it is possible to suppress the diffusion of Si from the Si layer of the reflective layer 12 to the protective layer 13 when the reflective layer 12 is a Mo/Si multilayer reflective film. In addition, the protective layer 13 can function as an etching stopper when the absorption layer 14 is etched while sufficiently ensuring the reflectance of EUV light. Further, the reflective mask can be washed tolerant and the reflective layer 12 can be prevented from deteriorating over 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 the 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 or more, and even more preferably 2 nm or more. The 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.

(absorbent layer)
The absorption layer 14 must have properties such as a high absorption coefficient of EUV light, easy etching, and high cleaning resistance to a cleaning liquid in order to be used in a reflective mask for EUV lithography.

The absorption layer 14 absorbs EUV light and has extremely low EUV light reflectance. Specifically, when the surface of the absorption layer 14 is irradiated with EUV light, the maximum reflectance of EUV light having a wavelength of about 13.5 nm is preferably 2% or less, more preferably 1% or less. Therefore, the absorption layer 14 needs to have a high absorption coefficient for EUV light.

The absorption layer 14 is processed by dry etching using a chlorine (Cl)-based gas such as Cl ₂ , SiCl ₄ and CHCl ₃ or a fluorine (F)-based gas such as CF ₄ or CHF ₃ . . Therefore, the absorbing layer 14 should be easily etched.

Further, the absorption layer 14 is removed by a cleaning liquid when the resist pattern 191 (see FIG. 6) remaining on the reflective mask blank after etching is removed with a cleaning liquid during the manufacture of the reflective mask 20 (see FIG. 5), which will be described later. exposed to At that time, as a cleaning liquid, sulfuric acid peroxide mixture (SPM), sulfuric acid, ammonia, ammonia peroxide mixture (APM), OH radical cleaning water, ozone water, and the like are used. In EUV lithography, SPM is commonly used as a resist cleaning solution. SPM is a mixed solution of sulfuric acid and hydrogen peroxide, for example, a mixed solution of sulfuric acid and hydrogen peroxide at a volume ratio of 3:1. At this time, the temperature of the SPM is preferably controlled to 100° C. or higher from the viewpoint of improving the etching rate. Therefore, the absorbent 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 100° C. solution containing 75 vol % sulfuric acid and 25 vol % hydrogen peroxide.

The absorption layer 14 contains Sn in order to achieve the above properties. Since Sn has a large absorption coefficient, the absorption layer 14 containing Sn can reduce the reflectance of the absorption layer 14 . Also, since the absorption layer 14 contains Sn, it can be easily etched with a Cl-based gas or the like.

Absorption layer 14 preferably contains Ta, Cr, or Ti in addition to Sn. These elements may be contained individually by 1 type, and may contain 2 or more types. The absorption layer 14 further contains one or more of these elements in addition to Sn, thereby enhancing washing resistance.

Absorbing layer 14 may further contain N, B, Hf, or H in addition to Sn. These elements may be contained individually by 1 type, and may contain 2 or more types. In particular, the absorption layer 14 preferably contains at least one of N and B among these elements. Since the absorption layer 14 contains at least one of N and B, the crystalline state of the absorption layer 14 can be an amorphous or microcrystalline structure.

A preferred composition for the absorber layer 14 is, for example, SnTa, SnTaN, SnTaB or SnTaBN.

The absorption layer 14 preferably has an amorphous crystalline state. Thereby, the absorption layer 14 can have excellent smoothness and flatness. Further, by improving the smoothness and flatness of the absorption layer 14, the edge roughness of the absorber pattern 141 (see FIG. 5) is reduced, and the dimensional accuracy of the absorber pattern 141 (see FIG. 5) can be increased.

The absorption layer 14 may be a single layer film or a multilayer film composed of a plurality of films. If the absorption layer 14 is a single-layer film, the number of steps in manufacturing the mask blank can be reduced, and production efficiency can be improved. When the absorption layer 14 is a multilayer film, by appropriately setting the optical constants and film thickness of the layers on the upper layer side of the absorption layer 14, the layers on the upper layer side of the absorption layer 14 can be formed into an absorber pattern using inspection light. It can be used as an antireflection film when inspecting 141 (see FIG. 5). This can improve the inspection sensitivity when inspecting the absorber pattern.

The film thickness of the absorption layer 14 can be appropriately designed according to the composition of the absorption layer 14, etc., but a thinner one is preferable from the viewpoint of suppressing the influence of shadowing. 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 at 1% or less. The film thickness of the absorption layer 14 is preferably 35 nm or less, more preferably 30 nm or less, even more preferably 25 nm or less, and particularly preferably 20 nm or less. The film thickness of the absorption layer 14 is determined by the reflectance, and the thinner the better. The film thickness of the absorption layer 14 can be measured using, for example, X-ray reflectometry (XRR) or TEM.

The absorption layer 14 can be formed using a known film formation method such as magnetron sputtering or ion beam sputtering. For example, when a SnTa film is formed as the absorption layer 14 by magnetron sputtering, the absorption layer 14 can be formed by sputtering using Ar gas with a target containing Sn and Ta. The absorption layer 14 can also be formed by binary sputtering using a Sn target and a Ta target at the same time.

(Prevention layer)
The prevention layer 15 is formed on the main surface above the absorption layer 14 (in the +Z-axis direction).

Ta, Ru, Cr, Ti or Si can be used as a material for forming the prevention layer 15 . These elements may be contained individually by 1 type, and may be contained 2 or more types.

The prevention layer 15 is made of Ta elemental, Ru elemental, Cr elemental, Ti elemental, Si elemental, Ta nitride, Ru nitride, Cr nitride, Ti nitride, Si nitride, Ta boride, Ru-boride, Cr-boride, Ti-boride, Si-boride or Ta-boron nitride can be used. These may be contained individually by 1 type, and may be contained 2 or more types.

A preferred composition for the blocking layer 15 is, for example, Ta, TaN, TaB or TaBN. For example, assume that a reflective mask blank 10B (see FIG. 7) according to the second embodiment having a stabilizing layer 21 on the blocking layer 15 is formed, as will be described later. Suppose that the stable layer 21 contains an oxide containing Ta, an oxynitride, or an oxyboride. In this case, if the prevention layer 15 is made of these materials, the same target can be used when forming the prevention layer 15 and the stable layer 21 . Therefore, the productivity of the reflective mask blank 10B (see FIG. 7) is excellent, for example, the number of required film formation chambers can be reduced.

The blocking layer 15 may further contain elements such as He, Ne, Ar, Kr or Xe.

The prevention layer 15 is a layer containing no Sn and oxygen. "Containing no Sn and oxygen" means that Sn and oxygen do not exist on the surface and inside of the prevention layer 15 immediately after the formation of the prevention layer 15 . When the prevention layer 15 is exposed to an atmosphere containing oxygen, the components contained in the prevention layer 15 react (oxidize) with oxygen on the surface of the prevention layer 15 that comes into contact with oxygen. Oxide films may form. At this time, if Sn is contained in the prevention layer 15, Sn existing on the surface of the prevention layer 15 reacts with oxygen, and fine particles containing Sn such as tin oxide are precipitated on the surface of the prevention layer 15. The prevention layer 15 does not contain Sn, as it may occur as a material.

Note that the prevention layer 15 does not contain oxygen means that if there is an oxide film formed on the surface of the prevention layer 15 in contact with oxygen in the process after the formation of the prevention layer 15, the oxide film does not include the oxygen contained in On the other hand, since the interface between the absorption layer 14 and the prevention layer 15 does not come into contact with oxygen, the interface between the prevention layer 15 and the absorption layer 14 does not contain oxygen.

The prevention layer 15 can be formed in an inert gas atmosphere or in a gas atmosphere obtained by selectively adding nitrogen to an inert gas using a known film forming method such as magnetron sputtering or ion beam sputtering. For example, when a Ta film, Ru film, Cr film, or Si film is formed as the prevention layer 15 by magnetron sputtering, a target containing Ta, Ru, Cr, or Si is used, and the sputtering gas is He, Ar, or Si. The protective layer 15 is formed by using an inert gas such as Kr or a gas obtained by selectively adding nitrogen to the inert gas.

As for the film thickness of the prevention layer 15, if the prevention layer 15 is too thick, etching of the prevention layer 15 takes time. Also, shadowing and the like may increase. On the other hand, if the prevention layer 15 is too thin, the function of the prevention layer 15 may not be stably and sufficiently exhibited. Therefore, the film thickness of the prevention layer 15 may be about several nanometers, preferably 10 nm or less, in order to suppress the thickness of the pattern of the reflective mask blank 10A. The film thickness of the prevention layer 15 is preferably 8 nm or less, more preferably 6 nm or less, still more preferably 5 nm or less, and particularly preferably 4 nm. The film thickness of the prevention layer 15 is preferably 0.5 nm or more, more preferably 1 nm or more, even more preferably 1.5 nm or more, and particularly preferably 2 nm or more. The film thickness of the prevention layer 15 can be measured using XRR, TEM, or the like, for example.

Thus, the reflective mask blank 10A has the blocking layer 15 on the absorbing layer 14 containing Sn. When the absorption layer 14 comes into contact with oxygen, part of Sn present on the surface of the absorption layer 14 reacts with oxygen, and fine particles containing Sn, such as tin oxide, are formed on the surface of the absorption layer 14 as precipitates. can occur as As described above, the prevention layer 15 is formed on the absorption layer 14 using only an inert gas such as He, Ar, or Kr, or a gas obtained by selectively adding nitrogen to an inert gas as a sputtering gas. filmed. Therefore, by forming the prevention layer 15 before the absorption layer 14 contacts gas such as oxygen, the absorption layer 14 can be prevented from coming into contact with oxygen or the like. This prevents the surface of the absorption layer 14 from being oxidized and deposits on the surface of the absorption layer 14 , and suppresses the occurrence of defects on the surface of the absorption layer 14 .

Therefore, when the reflective mask 20 (see FIG. 5) is manufactured using the reflective mask blank 10A, the occurrence of defects in the reflective mask 20 (see FIG. 5) can be suppressed. Therefore, by using the reflective mask blank 10A, a defect-free pattern can be stably formed.

The reflective mask blank 10A can form the prevention layer 15 containing at least one element of Ta, Ru, Cr, or Si. These elements are easy to dry-etch and have excellent washing resistance. Therefore, if the prevention layer 15 contains Ta or the like, even if the absorption layer 14 contains Sn, the surface of the absorption layer 14 is prevented from being oxidized while the absorber pattern 141 (see FIG. 5) having high washing resistance is used. ) can be formed.

In the reflective mask blank 10A, the prevention layer 15 is made of Ta elemental, Ru elemental, Cr elemental, Si elemental, Ta nitride, Ru nitride, Cr nitride, Si nitride, Ta boride, Ru boride, Cr boride, Si boride, or Ta boron nitride. Since these simple substances, nitrides, borides and boron nitrides are amorphous, edge roughness of the absorber pattern 141 (see FIG. 5) can be suppressed. Therefore, if the prevention layer 15 contains a nitride of Ta or the like, it is possible to form a highly accurate absorber pattern 141 (see FIG. 5) while preventing oxidation of the surface of the absorber layer 14 containing Sn.

The reflective mask blank 10A can be formed by including at least one element of He, Ne, Ar, Kr, and Xe in the prevention layer 15 . These elements may be contained in the prevention layer 15 in trace amounts by using these elements as a sputtering gas when forming the prevention layer 15 . Even in this case, the function of the prevention layer 15 can be exhibited without affecting the properties of the prevention layer 15 .

In the reflective mask blank 10A, the film thickness of the prevention layer 15 can be set to 10 nm or less. As a result, the thickness of the prevention layer 15 can be suppressed, so that the reflective mask blank 10A has a total thickness of the absorber pattern 141 (see FIG. 5) and the pattern of the prevention layer 15 formed thereon. can be reduced.

The reflective mask blank 10A can comprise the absorption layer 14 containing one or more elements selected from the group consisting of Ta, Cr and Ti. By including these elements in the absorbing layer 14, the washing resistance of the absorbing layer 14 can be further improved, so that the absorbing layer 14 can be made thinner. As a result, it is possible to obtain the absorption layer 14 having a high absorption rate of EUV light even if it is thin. Therefore, the reflectance of the EUV light in the absorption layer 14 can be lowered while reducing the thickness of the reflective mask blank 10A and the pattern of the reflective mask 20 (see FIG. 5).

The reflective mask blank 10A preferably has a protective layer 13 between the reflective layer 12 and the absorbing layer 14 . Thereby, the reflective layer 12 can be protected during the etching of the absorbing layer 14 and the cleaning of the reflective mask blank during the manufacture of the reflective mask 20 (see FIG. 5). Therefore, the reflectance of the obtained reflective mask 20 (see FIG. 5) with respect to EUV light can be improved.

<Manufacturing method of reflective mask blank>
Next, a method of manufacturing the reflective mask blank 10A shown in FIG. 1 will be described. FIG. 2 is a flow chart showing an example of a method for manufacturing the reflective mask blank 10A.

As shown in FIG. 2, the reflective layer 12 is formed on the substrate 11 (process for forming the reflective layer 12: step S11). The reflective layer 12 is formed on the substrate 11 to a desired film thickness using a known film forming method as described above.

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

Next, the absorbing layer 14 is formed on the protective layer 13 (step of forming the absorbing layer 14: step S13). The absorption layer 14 is formed on the protective layer 13 to a desired film thickness using a known film formation method. For example, the absorption layer 14 can be formed in a film forming chamber of a film forming apparatus using a known film forming apparatus.

After the absorption layer 14 is formed, the film formation chamber of the film formation apparatus used for the formation of the absorption layer 14 is removed from the film formation chamber and transferred to a storage chamber. It may be stored until use, such as until layer 15 is formed.

Next, the prevention layer 15 is formed on the absorption layer 14 (step of forming the prevention layer 15: step S14). The prevention layer 15 is formed on the absorption layer 14 using a known film formation method in an inert gas atmosphere or in a gas atmosphere in which nitrogen is selectively added to the inert gas, to a desired film thickness. A film is formed as follows.

Thereby, a reflective mask blank 10A as shown in FIG. 1 is obtained.

Further, in the present embodiment, the method of manufacturing the reflective mask blank 10A can continuously perform the process of forming the absorbing layer 14 (step S13) and the process of forming the blocking layer 15 (step S14). In this case, a binary sputtering method using a target such as a metal such as a Sn target forming the absorption layer 14 and a target such as a metal forming the prevention layer 15 such as a Ta target can be used. By using the binary sputtering method, the charging of the target such as the metal constituting the absorption layer 14 is completed earlier than the charging of the target such as the metal constituting the prevention layer 15. , the formation of the absorption layer 14 and the formation of the prevention layer 15 can be performed continuously.

(Other layers)
The reflective mask blank 10A may comprise a hard mask layer 17 over the blocking layer 15, as shown in FIG. As the hard mask layer 17, a material having high resistance to etching, such as a Cr-based film, a Si-based film, and a Ru-based film, is used.

As the Cr-based film, for example, a material obtained by adding O or N to Cr alone and Cr can be used. Specific examples include CrO, CrN and CrON.

Examples of the Si-based film include Si alone and materials obtained by adding one or more selected from the group consisting of O, N, C and H to Si. Specific examples include SiO ₂ , SiON, SiN, SiO, Si, SiC, SiCO, SiCN and SiCON. Among them, a Si-based film is preferable because recession of the sidewall hardly occurs when the absorption layer 14 is dry-etched.

Examples of the Ru-based film include Ru and materials obtained by adding O or N to Ru. Specific examples include RuO, RuN, and RuON.

By forming the hard mask layer 17 on the prevention layer 15, dry etching can be performed even if the minimum line width of the absorber pattern 141 is small. Therefore, it is effective for miniaturization of the absorber pattern 141 . When another layer is laminated on the prevention layer 15 , the hard mask layer 17 may be provided on the outermost layer of the prevention layer 15 .

As shown in FIG. 4, the reflective mask blank 10A can have a back conductive layer 18 for electrostatic chuck on the second main surface 11b of the substrate 11 opposite to the side on which the reflective layer 12 is laminated. can. The back conductive layer 18 is required to have a low sheet resistance as a characteristic. The sheet resistance value of the back conductive layer 18 is, for example, 250Ω/□ or less, preferably 200Ω/□ or less.

A material including the back conductive layer 18 can be, for example, a metal such as Cr or Ta, or an alloy thereof. As an alloy containing Cr, a Cr compound containing Cr and one or more selected from the group consisting of B, N, O and C can be used. Examples of Cr compounds include CrN, CrON, CrCN, CrCON, CrBN, CrBON, CrBCN and CrBOCN. As the alloy containing Ta, a Ta compound containing Ta and at least one selected from the group consisting of B, N, O and C can be used. Examples of Ta compounds include TaB, TaN, TaO, TaON, TaCON, TaBN, TaBO, TaBON, TaBCON, TaHf, TaHfO, TaHfN, TaHfON, TaHfCON, TaSi, TaSiO, TaSiN, TaSiON and TaSiCON. .

The film thickness of the back surface conductive layer 18 is not particularly limited as long as it satisfies the function for the electrostatic chuck, but is, for example, 10 to 400 nm. The back conductive layer 18 can also provide stress adjustment on the side of the second major surface 11b of the reflective mask blank 10A. That is, the back conductive layer 18 can be adjusted 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 18, a known film forming method such as a magnetron sputtering method or an ion beam sputtering method can be used.

The back conductive layer 18 can be formed on the second main surface 11 b of the substrate 11 , for example, before forming the protective layer 13 .

<Reflective mask>
Next, a reflective mask obtained using the reflective mask blank 10A shown in FIG. 1 will be described. FIG. 5 is a schematic cross-sectional view showing an example of the configuration of a reflective mask. As shown in FIG. 5, the reflective mask 20 is obtained by forming a desired absorber pattern 141 on the absorbing 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. 6A and 6B are diagrams for explaining the manufacturing process of the reflective mask 20. FIG. As shown in FIG. 6A, a resist layer 19 is formed on the absorption layer 14 of the reflective mask blank 10A shown in FIG.

After that, the resist layer 19 is exposed to a desired pattern. After the exposure, the exposed portion of the resist layer 19 is developed and washed (rinsed) with pure water to form a predetermined resist pattern 191 on the resist layer 19 as shown in FIG. 6B.

Thereafter, using the resist layer 19 with the resist pattern 191 formed thereon as a mask, the absorption layer 14 is dry-etched. As a result, an absorber pattern 141 corresponding to the resist pattern 191 is formed in the absorber layer 14, as shown in FIG. 6(c).

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

After that, the resist layer 19 is removed with a resist remover or the like, and a desired absorber pattern 141 is formed on the absorber layer 14 . Thereby, as shown in FIG. 5, a reflective mask 20 in which a desired absorber pattern 141 is formed in the absorber layer 14 can be obtained.

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 by the portion without the absorption layer 14 (the portion of the absorber pattern 141 ) and is absorbed by the portion with the absorption layer 14 . As a result, the EUV light reflected by the absorption layer 14 passes through the reduction projection optical system of the exposure apparatus and is irradiated onto the exposure material (for example, a wafer or the like). As a result, the absorber pattern 141 of the absorber layer 14 is transferred onto the exposed material, forming a circuit pattern on the exposed material.

[Second embodiment]
A reflective mask blank according to the second embodiment will be described with reference to the drawings. Members having the same functions as those of the above-described embodiment are denoted by the same reference numerals, and detailed description thereof will be omitted.

FIG. 7 is a schematic cross-sectional view of a reflective mask blank according to the second embodiment. As shown in FIG. 7, reflective mask blank 10B has a stabilizing layer 21 on top of blocking layer 15 of reflective mask blank 10A shown in FIG. That is, the reflective mask blank 10B is configured by laminating a substrate 11, a reflective layer 12, a protective layer 13, an absorbing layer 14, an anti-layer 15, and a stabilizing layer 21 in this order from the substrate 11 side.

As the stable layer 21, an oxide containing Ta, an oxynitride and an oxyboride can be used. Examples of Ta-containing oxides, oxynitrides and oxyborides include TaO, Ta ₂ O ₅ , TaON, TaCON, TaBO, TaBON, TaBCON, TaHfO, TaHfON, TaHfCON, TaSiO, TaSiON and TaSiCON. can be done.

The film thickness of the stable layer 21 is preferably 10 nm or less. The thickness of the stable layer 21 is preferably 7 nm or less, more preferably 6 nm or less, even more preferably 5 nm or less, and particularly preferably 4 nm or less. The film thickness of the stable layer 21 is preferably 1 nm or more, more preferably 2 nm or more, and particularly preferably 3 nm or more.

The stable layer 21 can be formed using a known film formation method such as magnetron sputtering or ion beam sputtering.

Thus, the reflective mask blank 10B has the stabilizing layer 21 on the prevention layer 15, so that the washing resistance of the prevention layer 15 can be further improved. By having the stabilizing layer 21, 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.

Since the reflective mask blank 10B has the prevention layer 15 on the absorption layer 14 containing Sn, the surface of the absorption layer 14 is exposed to oxygen when forming the stable layer 21 on the prevention layer 15. never. For example, when the stable layer 21 is formed using a reactive sputtering method, as described above, the sputtering gas may be a mixed gas in which an inert gas such as He, Ar, or Kr is mixed with oxygen, or a mixed gas in which an inert gas is mixed with nitrogen. is selectively added, and a mixed gas further mixed with oxygen is used. Since the prevention layer 15 is formed on the absorption layer 14, the surface of the absorption layer 14 does not come into contact with the mixed gas, which is the sputtering gas, when the stable layer 21 is formed. Therefore, the surface of the absorption layer 14 is not oxidized, and the generation of precipitates on the surface of the absorption layer 14 can be prevented.

In the reflective mask blank 10B, the stabilizing layer 21 is formed using an oxide containing Ta, an oxynitride, or an oxyboride. A reflective mask blank and a reflective mask having excellent washability can be obtained.

In the reflective mask blank 10B, the film thickness of the stabilizing layer 21 is set to 10 nm or less, so that the thickness of the reflective mask blank 10B and the pattern of the reflective mask can be reduced while improving the washing resistance of the prevention layer 15. can be maintained.

As shown in FIG. 8, the reflective mask blank 10B may include a hard mask layer 17 on the stabilizing layer 21, like the reflective mask blank 10A according to the first embodiment shown in FIG. .

Example 1 is a comparative example, and Examples 2 to 4 are examples.

[Example 1]
A reflective mask blank 100 is shown in FIG. The reflective mask blank 100 does not have the blocking layer 15 on the absorbing layer 14 in the reflective mask blank 10A according to the first embodiment shown in FIG.
(Production of reflective mask blank)
A SiO ₂ —TiO ₂ -based glass substrate (outer shape: about 152 mm square, thickness: about 6.3 mm) was used as a substrate for film formation. The thermal expansion coefficient of the glass substrate was 0.02×10 ⁻⁷ /° C. or less. The glass substrate was polished to obtain a smooth surface with a root-mean-square roughness Rq of 0.15 nm or less 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 using a Cr film, alternately forming a Si film and a Mo film on the surface of the glass substrate using an ion beam sputtering method was repeated 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. Thereafter, a Ru layer (with a film thickness of about 2.5 nm) was formed on the reflective layer using an ion beam sputtering method to form a protective layer (protective film). Next, an absorption layer (absorber film) made of Sn—Ta alloy and having a thickness of 40 nm was formed on the protective layer by magnetron sputtering. Ar gas was used as the sputtering gas. The target used for sputtering was 60 at % Sn and 40 at % Ta, and the Ta content in the sputtered absorption layer was 48 at %. The Sn content and Ta content in the absorption layer were measured using X-ray fluorescence spectroscopy (XRF) (manufactured by Olympus, Delta). Thus, a reflective mask blank 100 shown in FIG. 9 was produced. The film thickness of the absorption layer was measured by XRR using an X-ray diffractometer (SmartLab HTP, manufactured by Rigaku Corporation). From the result of X-ray diffraction (XRD) measurement using the same apparatus, it was confirmed that the absorption layer made of the Sn--Ta alloy was amorphous.

(Observation of surface of reflective mask blank)
The surface of the reflective mask blank 100 was observed using a scanning electron microscope (Carl Zeiss, Ultra60). FIG. 10 shows observation results of the surface of the reflective mask blank. As shown in FIG. 10, fine particles were observed on the surface of the reflective mask blank. As a result of analyzing the fine particles by energy dispersive X-ray spectroscopy (EDX), it was confirmed that the fine particles were formed of tin oxide. It is considered that the fine particles on the surface of the absorbing layer are produced by reaction of Sn contained in the absorbing layer with oxygen in the atmosphere when the absorbing layer is exposed to the atmosphere. Such fine particles are not preferable because they may remain as pattern defects in the reflective mask after etching of the absorbing layer.

[Example 2]
In this example, a reflective mask blank 10A shown in FIG. 1 was fabricated by depositing a TaN film of 4 nm as a blocking layer on the absorption layer of the reflective mask blank 100 fabricated in Example 1. FIG. The prevention layer was formed by reactive sputtering, using a mixed gas of Ar and nitrogen as a sputtering gas, with the flow rate of Ar being 70 sccm and the flow rate of nitrogen being 2 sccm. The reflective mask blank 100 produced in Example 1 was moved from the film forming chamber of the film forming apparatus used for forming the absorbing layer to a storage chamber until the blocking layer was formed on the absorbing layer. was stored under high vacuum.

(Observation of surface of reflective mask blank)
The surface of the reflective mask blank 10A was observed using a scanning electron microscope. FIG. 11 shows the result of observing the surface of the absorption layer of the reflective mask blank 10A. As shown in FIG. 11, no fine particles were generated on the surface of the absorption layer of the reflective mask blank 10A. It can be said that this is because oxygen in the atmosphere does not come into contact with Sn contained in the absorption layer due to the presence of the prevention layer on the surface of the absorption layer.

[Example 3]
In this example, in Example 1, on the absorption layer of the reflective mask blank 100 produced, a Ta blocking layer of 2 nm was formed by magnetron sputtering, and further a TaO stable layer was formed on the blocking layer. A film of 2 nm was formed using a reactive sputtering method. Thus, a reflective mask blank 10B shown in FIG. 7 was produced. Ar gas was used as the sputtering gas when forming the protective layer using the magnetron sputtering method. When the stable layer was formed by reactive sputtering, a mixed gas of Ar and oxygen was used as a sputtering gas, and the flow rate of Ar was set at 40 sccm and the flow rate of oxygen was set at 30 sccm. The reflective mask blank 100 produced in Example 1 was moved from the film forming chamber of the film forming apparatus used for forming the absorbing layer to a storage chamber until the blocking layer was formed on the absorbing layer. was stored under high vacuum.

XRR measurement of the prevention layer and the stabilization layer of the reflective mask blank 10B after film formation revealed that the film thickness of Ta was 0.9 nm and the film thickness of TaO was 4.6 nm. This is probably because oxygen contained in the sputtering gas and Ta in the Ta film react with each other to form a TaO film when the TaO film is formed on the Ta film, and the film expands.

After that, the reflective mask blank 10B shown in FIG. 7 was dry etched using a dry etching apparatus. In the dry etching, after removing the prevention layer and the stable layer using an F-based gas, the absorption layer was removed using a Cl-based gas.

(Observation of surface of reflective mask blank)
The surface of the reflective mask blank 10B was observed using a scanning electron microscope. FIG. 12 shows the observation result of the absorption layer on the surface of the reflective mask blank 10B. As shown in FIG. 12, no precipitate such as fine particles was observed on the surface of the reflective mask blank. In this example, only Ar is used as the sputtering gas when forming the prevention layer. Therefore, since the surface of the absorption layer is not exposed to an oxygen-containing atmosphere, Sn present on the surface of the absorption layer does not react with oxygen. Thus, it can be said that the generation of precipitates on the surface of the absorption layer was suppressed.

[Example 4]
(Production of reflective mask blank)
In this example, a binary sputtering method using a Sn target and a Ta target at the same time was used instead of the Sn—Ta alloy target in forming the absorption layer made of the Sn—Ta alloy in Example 3. Ar gas was used as the sputtering gas, the Ar flow rate was 70 sccm, the input power to the Sn target was 130 W, and the input power to the Ta target was 200 W. When binary sputtering was performed, the charging of the Sn target and the Ta target started at the same time. The end time of charging the Sn target and the Ta target was 520 seconds after the start of charging for the Sn target, and 608 seconds after the start of charging for the Ta target. As a result, a 35-nm-thick absorption layer made of Sn--Ta alloy and a 2-nm-thick blocking layer made of Ta on the absorption layer were successively formed by one-time sputtering. After that, a stabilizing layer of TaO was deposited to a thickness of 2 nm on the blocking layer by reactive sputtering in the same manner as in Example 3. Thus, a reflective mask blank 10B shown in FIG. 7 was produced. When the Ta content in the sputtered absorption layer was measured using XRF, it was 35%.

(Observation of surface of reflective mask blank)
When the surface of the reflective mask blank 10B produced in this example was observed using a scanning electron microscope, no precipitates such as fine particles were observed on the surface of the reflective mask blank 10B. When the absorption layer and the prevention layer are formed by sputtering twice as in Example 2 or Example 3, the reflective mask blank 100 prepared by forming the absorption layer in Example 1 is used for forming the absorption layer. It is necessary to return the film from the film forming chamber of the film forming apparatus to the storage room. Although the storage room is kept in a high vacuum, there is a risk that small amounts of residual oxygen will generate oxide particles on the surface of the absorbing film. In this example, since the absorption layer and the prevention layer are continuously formed in the film forming chamber of the film forming apparatus to fabricate the reflective mask blank 10B, generation of fine particles of oxide in the storage chamber can be reduced. Moreover, since only one sputtering operation is required, the time required to manufacture the reflective mask blank 10B can be shortened.

As described above, the embodiment has been described, but the above embodiment is presented as an example, and the present invention is not limited by the above embodiment. The above embodiments can be implemented in various other forms, and various combinations, omissions, replacements, changes, etc. can be made without departing from the scope of the invention. These embodiments and modifications thereof are included in the scope and gist of the invention, and are included in the scope of the invention described in the claims and equivalents thereof.

This application claims priority based on Japanese Patent Application No. 2018-112601 filed with the Japan Patent Office on June 12, 2018, and the entire contents of Japanese Patent Application No. 2018-112601 are incorporated into this application. .

10A, 10B reflective mask blank 11 substrate 12 reflective layer 13 protective layer 14 absorbing layer 15 blocking layer 17 hard mask layer 18 back conductive layer 19 resist layer 20 reflective mask 21 stabilizing layer

Claims (14)

A reflective mask blank having, on a substrate, a reflective layer for reflecting EUV light and an absorbing layer for absorbing EUV light in this order from the substrate side,
the absorbing layer contains Sn,
Having a prevention layer on the absorption layer for preventing oxidation of the absorption layer,
A reflective mask blank in which the prevention layer contains Ta and does not contain Sn and oxygen . 2. The reflective type according to claim 1 , wherein the prevention layer contains one or more components selected from the group consisting of simple Ta , a nitride of Ta , a boride of Ta , and a boron nitride of Ta. mask blank. 3. The reflective mask blank according to claim 1, wherein said blocking layer contains one or more elements selected from the group consisting of He, Ne, Ar, Kr and Xe. 4. The reflective mask blank according to any one of claims 1 to 3 , wherein the film thickness of the prevention layer is 10 nm or less. 5. The reflective mask blank according to any one of claims 1 to 4 , wherein said absorption layer contains one or more elements selected from the group consisting of Ta, Cr and Ti. The reflective mask blank according to any one of claims 1 to 5 , further comprising a stabilizing layer on the blocking layer. 7. The reflective mask blank according to claim 6 , wherein the stable layer contains one or more selected from the group consisting of Ta-containing oxides, oxynitrides and oxyborides. 8. The reflective mask blank according to claim 6 , wherein the stabilizing layer has a thickness of 10 nm or less. The reflective mask blank according to any one of claims 1 to 8 , further comprising a protective layer between said reflective layer and said absorbing layer. 10. The reflective mask blank according to any one of claims 1 to 9 , further comprising a hard mask layer on the prevention layer or on the outermost layer of the prevention layer. 11. The reflective mask blank according to claim 10 , wherein said hard mask layer contains at least one element selected from the group consisting of Cr, Si and Ru. A reflective mask, wherein a pattern is formed in the absorbing layer of the reflective mask blank according to any one of claims 1 to 11 . A method for manufacturing a reflective mask blank having, on a substrate, a reflective layer for reflecting EUV light and an absorbing layer for absorbing EUV light in this order from the substrate side, comprising:
forming the reflective layer on the substrate;
forming the absorbing layer containing Sn on the reflective layer;
forming an anti-oxidation layer on the absorption layer to prevent oxidation of the absorption layer;
including
The method for manufacturing a reflective mask blank , wherein the prevention layer contains Ta and does not contain Sn and oxygen . 14. The reflective mask blank according to claim 13 , wherein the step of forming the absorbing layer and the step of forming the blocking layer are continuously performed in a deposition chamber by using a binary sputtering method. Production method.

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