JP4061319B2 - REFLECTIVE MASK BLANK, REFLECTIVE MASK, MANUFACTURING METHOD THEREOF, AND SEMICONDUCTOR MANUFACTURING METHOD - Google Patents

Description

  The present invention relates to a reflective mask and mask blanks preferably used in a lithography method using exposure light in a short wavelength region such as extreme ultraviolet light, and a method for manufacturing the same. The present invention relates to a reflective mask that can be performed.

In recent years, as seen in semiconductor memories, ultra-LSIs (Large Scale Integrated Circuits), etc., with the high integration of semiconductor products, fine patterns exceeding the transfer limit of photolithography are required. Therefore, in order to enable transfer of such a fine pattern, a lithography method using extreme ultraviolet light (Extreme Ultra Violet, hereinafter referred to as EUV light) having a shorter wavelength has been proposed.
By the way, a reflection type mask used as an exposure mask in a short wavelength region such as EUV light or X-ray has been conventionally proposed. The basic structure of this reflective mask has, for example, a reflective layer that reflects EUV light or X-rays on a substrate such as Si or quartz, and an absorber pattern that absorbs EUV light or X-rays thereon. Yes. The reflective layer is generally a multilayer film in which thin films of at least two kinds of substances are alternately stacked. Then, the exposure light is incident on the mask from a direction inclined several degrees (usually 2 to 5 degrees) from the vertical direction of the mask, the exposure light is absorbed in a portion where the absorber pattern is present, and the exposure light is absorbed in other portions. Since it is reflected by the reflective layer, a reflected image reflecting the absorber pattern is formed. Transfer is performed by projecting the reflected image on a silicon wafer by reduction through an appropriate optical system.

In addition to such a basic structure of the reflective mask, a configuration in which an intermediate layer is provided between the reflective layer and the absorber is disclosed in Japanese Patent Laid-Open Nos. 7-333829 and 8-213303. Yes. That is, when the absorber is patterned, an intermediate layer is provided for the purpose of protecting the reflective layer so that the lower reflective layer is not damaged by etching, particularly during etching.
Here, a manufacturing method of a reflective mask used in lithography using EUV light (for example, EUV light in a soft X-ray region having a wavelength of about 13.4 nm) as exposure light will be described with reference to FIG. FIG. 13 is a schematic cross-sectional view sequentially showing a manufacturing process of a conventional reflective mask.
On a substrate 11 made of quartz or the like, a laminated film 12 which is an EUV light reflecting layer (hereinafter referred to as an EUV reflecting layer) in sequence, and a buffer layer for the purpose of protecting the EUV reflecting layer in the absorber pattern forming step. (Corresponding to the above-described intermediate layer) 13 and a mask blank 101 on which an absorber layer (hereinafter referred to as EUV absorber layer) 14 that absorbs EUV light is formed (see FIG. 13A). ).

Next, the EUV absorber layer 14 which is an EUV light absorber is processed to form an EUV absorber pattern having a predetermined pattern (see FIG. 5B).
Next, an inspection is performed to determine whether this EUV absorber pattern is formed as designed. As a result of this pattern inspection, for example, as shown in FIG. 4B, pinhole defects (also referred to as white defects) 21 due to adhesion of foreign matters to the resist layer at the time of pattern formation and insufficient etching defects (black) When the 22) occurs, the pinhole defect 21 is repaired by depositing a carbon film 23 on the pinhole by a focused ion beam (FIB) assisted deposition method. Further, for the etching deficiency defect 22, the removal portion 25 of the absorber layer 14 is obtained by removing and repairing the residual portion 22a by FIB-excited gas-assisted etching. There is a damaged portion 24 (a portion 24a removed by FIB and a portion 24b into which FIB ions have entered) (see FIG. 5C).

Thereafter, a pattern 26 from which the buffer layer 13 corresponding to the portion 25 from which the EUV absorber layer 14 has been removed is formed to form a reflective mask for EUV light (see FIG. 4D).
When this reflective mask is exposed to EUV light 31, it is absorbed in a portion where the absorber pattern is present, and EUV light 31 is reflected by the exposed reflective layer 12 in the other portions where the absorber 14 and buffer layer 13 are removed. (See (e) in the figure), it can be used as a mask for lithography with EUV light.

JP-A-7-333829 JP-A-8-213303

  In the above mask manufacturing process, after the pattern is formed on the EUV absorber layer 14, it is as described above that the inspection of whether or not the EUV absorber pattern is formed as designed is performed. In this inspection, an inspection machine using light of about 257 nm is usually used. That is, the light of about 257 nm is applied to the mask and the pattern of the reflected image is inspected. Then, as described above, this mask pattern inspection is performed after completion of the pattern formation process of the surface EUV absorber layer 14 (process of FIG. 13B), and necessary pattern repair is performed based on the inspection result. It is carried out. Therefore, specifically, when the light used for the inspection (hereinafter referred to as inspection light) is applied to the mask, the surface of the buffer layer 13 exposed by removing the surface absorber by patterning and the pattern remain. Inspection is performed by the difference in reflectance from the absorber surface, so if the difference in reflectance between the buffer layer surface and the absorber surface with respect to the wavelength of the inspection light is small, the contrast at the time of inspection deteriorates and accurate inspection is performed. It will not be possible.

By the way, in the case of a conventional reflective mask, for example, it is typically composed of a tantalum or tantalum nitride film as a surface EUV absorber and a SiO ₂ film as a buffer layer, but for inspection light having a wavelength of 257 nm or the like. The difference between the reflectivity of the absorber surface and the reflectivity of the buffer layer surface is small, and the contrast at the time of inspection cannot be obtained sufficiently. As a result, pattern defects cannot be sufficiently identified in mask inspection, and accurate defect inspection can be performed. There was no problem.
In addition, in an inspection with an electron microscope using an electron beam, the EUV absorption film is damaged by the irradiation electron beam, and it is difficult to put it to practical use.
Also, a method of using the above-described light of about 13.4 nm, which is the EUV light wavelength, for mask pattern inspection has been proposed. However, installation of an EUV light source in an inspection machine requires a very large equipment cost. In addition, a structure for holding the entire optical system in a vacuum is required to avoid absorption in the atmosphere as compared with a conventional inspection machine using an ultraviolet light wavelength, and the pattern inspection process becomes large and complicated. Furthermore, there is a problem that the throughput due to the evacuation time is lowered.
The present invention has been made to solve such a conventional problem, and an object of the present invention is to provide a reflective mask and a mask blank capable of accurately and quickly inspecting a mask pattern, a manufacturing method thereof, and An object of the present invention is to provide a semiconductor manufacturing method using the reflective mask.

As a result of diligent research to solve the above-mentioned problems, the conventional absorber layer on the mask surface is composed of a layer that separates the function into a layer that absorbs exposure light and a layer that has a low reflectance with respect to the mask pattern inspection wavelength. As a result, it was found that sufficient contrast at the time of pattern inspection can be obtained, and the present invention has been completed.
That is, the first invention provides a reflective layer for reflecting exposure light in a short wavelength region including the extreme ultraviolet region in order on the substrate, a buffer layer for protecting the reflective layer when forming a pattern on the absorber layer, and exposure. A mask blank having an absorber layer that absorbs light, wherein the absorber layer is composed of an absorber layer of an exposure light in a short wavelength region including an extreme ultraviolet region, and a mask pattern. It is at least a two-layer structure with a low reflection layer composed of an inspection light absorber used for the inspection as an upper layer, and the upper layer is made of a material containing tantalum (Ta), boron (B), and oxygen (O). The reflective mask blank is characterized in that the buffer layer is made of Cr or a substance containing Cr as a main component.
A second invention is a mask blank comprising a reflective layer for reflecting exposure light in a short wavelength region including an extreme ultraviolet region in order and an absorber layer for absorbing exposure light on a substrate, wherein the absorber The layer is an absorber layer composed of an absorber of exposure light in a short wavelength region including the extreme ultraviolet region as a lower layer, and a low reflection layer composed of an absorber of inspection light used for mask pattern inspection as an upper layer It has a two-layer structure, and the upper layer is made of a material containing tantalum (Ta), boron (B), and oxygen (O), and contains oxygen (O) in a range of 30 at% to 70 at%. This is a reflective mask blank.

A third invention is a mask blank comprising a reflective layer for reflecting exposure light in a short wavelength region including an extreme ultraviolet region in order and an absorber layer for absorbing exposure light on a substrate, wherein the absorber The layer is an absorber layer composed of an absorber of exposure light in the short wavelength region including the extreme ultraviolet region as a lower layer, and a low reflection layer composed of an absorber of inspection light used for inspection of the mask pattern is at least an upper layer The upper low reflection layer is made of chromium, manganese, cobalt, copper, zinc, gallium, molybdenum, palladium, silver, cadmium, tin, antimony, tellurium, iodine, hafnium, tungsten, titanium, gold and It is composed of an oxide of at least one substance selected from an alloy containing these elements, or at least one substance selected from materials containing silicon in addition to the oxide. A reflective mask blank according to symptoms.
According to a fourth aspect of the present invention, a buffer layer is provided between the reflective layer and the absorber layer to protect the reflective layer when forming a pattern on the absorber layer, and the buffer layer mainly contains Cr or Cr. The reflective mask blank according to the second or third aspect, wherein the reflective mask blank is formed of a substance as a component.
According to a fifth aspect of the present invention, the absorber of the exposure light in the lower layer in the absorber layer is a metal element contained in the upper layer or an alloy containing the metal element, or the metal element or an alloy containing the metal element and nitrogen and The reflective mask blank according to the third aspect of the invention is characterized by comprising at least one material selected from materials containing oxygen.

According to a sixth aspect of the present invention, there is provided a reflective layer that sequentially reflects exposure light in a short wavelength region including an extreme ultraviolet region, a buffer layer for protecting the reflective layer when forming a pattern on the absorber layer, and exposure light on the substrate. Mask blanks comprising an absorber layer that absorbs, wherein the absorber layer comprises an absorber layer composed of an absorber of exposure light in a short wavelength region including an extreme ultraviolet region, and a mask pattern is inspected. The buffer has at least a two-layer structure including an inspection light absorber used as an upper layer, and the upper layer is made of a material containing at least one of Ta and Si or Ge and oxygen, and the buffer. The reflective mask blank is characterized in that the layer is made of Cr or a substance containing Cr as a main component.
A seventh invention is the reflective mask blank according to any one of the first to sixth inventions, characterized in that a lower layer of the absorber layer is a material containing Ta.
An eighth invention is the reflective mask blank according to the seventh invention, wherein the lower layer of the absorber layer is a material containing Ta and at least B.
In a ninth aspect of the present invention, the first to eighth aspects are characterized in that an intermediate region in which the composition continuously changes from the lower layer composition to the upper layer composition is provided between the lower layer and the upper layer of the absorber layer. The reflective mask blank according to any one of the above.
In a tenth aspect of the invention, a contrast between reflected light on the surface of the reflective layer and reflected light on the surface of the absorber layer with respect to a wavelength of light used for inspection of a pattern formed on the absorber layer is 40% or more. The reflective mask blank according to any one of the first to ninth inventions.

An eleventh aspect of the invention includes a buffer layer for protecting the reflective layer when forming a pattern on the absorber layer between the reflective layer and the absorber layer, and a pattern formed on the absorber layer. Any of the first to tenth inventions, wherein the contrast between the reflected light on the surface of the buffer layer and the reflected light on the surface of the absorber layer with respect to the wavelength of the light used for the inspection is 40% or more This is a reflective mask blank described in the above.
In a twelfth aspect of the invention, the reflectance of the surface of the absorber layer is 20% or less with respect to the wavelength of light used for inspection of a pattern formed on the absorber layer. The reflective mask blank according to any one of the above.
A thirteenth invention is the reflective mask blank according to any one of the first to twelfth inventions, wherein the surface roughness of the absorber layer surface is 0.5 nmRms or less.
In a fourteenth aspect of the present invention, the material forming the upper layer of the absorber layer has a refractive index n and an extinction coefficient k at the wavelength of the inspection light, where n is 1.5 to 3.5 and k is 0.7 or less. The reflective mask blank according to any one of the first to thirteenth inventions, characterized in that:

According to a fifteenth aspect of the present invention, the absorber for the inspection light wavelength is based on the relationship between the reflectance of the surface of the absorber layer with respect to the wavelength of the inspection light and the film thickness of the low reflection layer. The reflective mask blank according to any one of the first to fourteenth aspects, wherein the surface reflectance is selected to be minimal.
A sixteenth aspect of the present invention is the reflective mask blank according to the fifteenth aspect, wherein the thickness of the upper low reflection layer is 5 to 30 nm.
A seventeenth aspect of the present invention is a reflective mask characterized in that the absorber layer of the reflective mask blank according to any one of the first to sixteenth aspects of the present invention is formed in a pattern.
According to an eighteenth aspect of the present invention, the reflective mask blank according to any one of the first to sixteenth aspects further includes a step of forming at least the low reflection layer and the exposure light absorber layer in a pattern. It is a manufacturing method.

A nineteenth aspect of the invention is a method for manufacturing a reflective mask blank comprising a reflective layer for reflecting exposure light in a short wavelength region including the extreme ultraviolet region and an absorber layer for absorbing exposure light on a substrate in order. The lower layer of the absorber layer is made of a material containing nitrogen (N), the upper layer is a two-layer structure made of a material containing oxygen (O), and the upper layer of the absorber layer contains oxygen (O). The reflective mask blank manufacturing method is characterized in that it is formed by reactive sputtering in an atmosphere, and the formation of the lower layer and the upper layer of the absorber layer are continuously performed in the same film forming chamber.
According to a twentieth aspect of the invention, there is provided the reflective mask blank manufacturing method according to the nineteenth aspect, wherein the upper layer and the lower layer each contain a metal element, and the metal elements are the same. .
A twenty-first aspect of the invention is the reflective type according to the twentieth aspect, wherein the same target containing the metal element is used in the formation of the upper layer and the lower layer of the absorber layer, and the gas used for film formation is changed. It is a manufacturing method of mask blanks.

A twenty-second invention is a method of manufacturing a reflective mask blank according to any one of the first to sixteenth inventions, wherein a reflective layer that reflects exposure light in a short wavelength region including an extreme ultraviolet region is formed on a substrate. A step of forming an absorber layer that absorbs the exposure light on the reflective layer; and a mask pattern inspection near the surface of the absorber layer by treating the surface of the absorber layer. A method for producing a reflective mask blank is characterized in that a low reflective layer for the inspection light used in the method is formed.
A twenty-third invention is a method for manufacturing a semiconductor, wherein a pattern is transferred onto a semiconductor substrate using the reflective mask according to the seventeenth invention.

The reflective mask of the present invention is applied as a mask for EUV light. The wavelength of the exposure light is in the EUV light region, specifically a wavelength region of about several nm to 100 nm.
The uppermost low reflection layer can be formed of a material having a low reflectance with respect to the wavelength of the mask pattern inspection light.
In the present invention, the absorber layer has a laminated structure in which the function is separated into the exposure light absorption layer and the inspection light low reflection layer as described above, so that the original exposure light absorption function is not impaired at all. The reflectance with respect to the pattern inspection wavelength is remarkably lowered by the low reflection layer formed on the surface.
As a result, the difference in reflectance at the pattern inspection wavelength between the surface of the low reflection layer and the exposure layer exposed by removing the absorber layer by pattern formation becomes large, so that sufficient contrast at the time of inspection can be obtained. Therefore, a high-contrast reflection image pattern is formed.

In the case where a buffer layer is provided between the absorber layer and the reflective layer, the reflectance at the pattern inspection wavelength between the surface of the low reflective layer and the surface of the buffer layer exposed by removing the absorber layer by pattern formation is as follows. Since the difference becomes large and sufficient contrast at the time of inspection is obtained, a high-contrast reflection image pattern is formed.
Therefore, the mask pattern can be accurately and quickly inspected by a conventionally used mask inspection machine.
In addition, by separating the function of the absorber layer into an absorption layer for exposure light and a low reflection layer for inspection light, the absorption and reflection characteristics of the light of the exposure light and inspection light can be optimized. It is possible to reduce the value of the film thickness, and even if the absorber layer has a laminated structure, it can be suppressed to a film thickness equivalent to the conventional single layer structure. For this reason, it is possible to suppress blurring of the edge portion of the pattern at the time of exposure, and it is possible to minimize the pattern damage by shortening the processing time for pattern formation and to improve the quality.

For example, the present invention can be configured as follows.
On the substrate, a reflective layer that reflects exposure light in a short wavelength region including the extreme ultraviolet region, a buffer layer that protects the reflective layer when forming a mask pattern, and an absorber layer that absorbs the exposure light are sequentially formed on the substrate. It is a mask blank, and the absorber layer is composed of an absorber of inspection light used for mask pattern inspection, with an absorber layer formed of an absorber of exposure light in a short wavelength region including the extreme ultraviolet region as a lower layer. This is a mask blank having at least a two-layer structure with the low reflection layer as an upper layer.
The absorber of the exposure light in the lower layer in the absorber layer is chromium, manganese, cobalt, copper, zinc, gallium, germanium, molybdenum, palladium, silver, cadmium, tin, antimony, tellurium, iodine, hafnium, tantalum, tungsten, It can be composed of at least one material selected from titanium, gold and alloys containing these elements, and these elements or alloys containing these elements and substances containing nitrogen and / or oxygen.
The upper inspection light absorber in the absorber layer is composed of at least one substance selected from an oxide of a substance constituting the lower exposure light absorber or a material further containing silicon in the oxide. can do.

It is a reflective mask in which at least a low reflection layer and an exposure light absorber layer in the mask blank are formed in a pattern.
Forming a reflective layer on the substrate that reflects exposure light in a short wavelength region including an extreme ultraviolet region, forming a buffer layer on the reflective layer to protect the reflective layer during mask pattern formation, and Forming a mask layer having a step of forming an absorber layer for exposure light in the short wavelength region including the extreme ultraviolet region on the buffer layer, and forming a low reflection layer for the inspection light used for the inspection of the mask pattern on the buffer layer. Is the method.
After forming an absorber layer for exposure light in the short wavelength region including the extreme ultraviolet region on the buffer layer, the surface of the absorber layer is processed to form a low reflection layer for inspection light used for inspection of the mask pattern. It is a manufacturing method of the mask blanks to form.
The relationship between the film thickness of the low reflection layer formed on the absorber layer of the exposure light and the reflectance on the low reflection layer with respect to the wavelength of the inspection light is obtained, and the reflectance on the low reflection layer with respect to the wavelength of the inspection light is This is a mask blank manufacturing method in which the thickness of the low reflection layer is selected so as to be minimized.
It is a manufacturing method of the reflective mask which has the process of forming at least the low reflection layer and exposure light absorber layer in the said mask blanks in pattern shape.
In this method, the low reflection layer and the exposure light absorber layer are formed in a pattern, and then the portion of the buffer layer from which the low reflection layer and the exposure light absorber layer have been removed is removed.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
FIG. 1 is a schematic sectional view showing an embodiment of the mask blank of the present invention, and FIG. 2 is a schematic sectional view showing an embodiment of the reflective mask of the present invention.
One embodiment of the mask blank according to the present invention is configured as shown in FIG. That is, on the substrate 11, in order, a reflective layer 12 that reflects exposure light in a short wavelength region including the EUV region, a buffer layer 13 that protects the reflective layer 12 when forming a mask pattern, and an absorber layer that absorbs exposure light In this embodiment, the absorber layer 16 has a lower layer as an absorber layer 14 for exposure light in a short wavelength region including the EUV region, and an upper layer as a low layer for inspection light used for mask pattern inspection. This is a mask blank 1 having a two-layer structure as a reflective layer 15.

As shown in FIG. 2, the reflective mask 2 of the present invention has at least the absorber layer 16, that is, the low reflective layer 15 and the exposure light absorber layer 14 in such a mask blank 1 formed in a pattern. It is a thing.
The reflective mask according to the present invention has a structure in which the absorber layer on the mask surface is divided into a layer that absorbs exposure light and a layer that has a low reflectivity with respect to the mask pattern inspection wavelength, so that the mask layer is inspected. The contrast is sufficiently obtained.
The reflective mask of the present invention is used for lithography using light in a short wavelength region including EUV light region in order to enable transfer of a finer pattern exceeding the transfer limit by the conventional photolithography method. , And can be used as a reflective mask for EUV light.

Next, the configuration of each layer will be described.
As the substrate 11, a substrate obtained by appropriately optically polishing quartz glass, a silicon wafer or the like is usually used. The size, thickness, etc. of the substrate 11 are appropriately determined according to the design value of the mask, etc., and are arbitrary in the present invention.
The exposure light reflecting layer 12 is made of a material that reflects exposure light in a short wavelength region including the EUV region, but naturally, it is made of a material having a very high reflectance with respect to light in a short wavelength region such as EUV light. It is particularly preferable to increase the contrast when used as a reflective mask. For example, a typical example of the EUV light reflecting layer which is a soft X-ray region of about 12 to 14 nm is a periodic laminated film in which thin films of silicon (Si) and molybdenum (Mo) are alternately laminated. Usually, these thin films (thickness of about several nm) are repeatedly laminated for 40 to 50 periods (number of layers) to form a multilayer film. The multilayer film is formed using, for example, ion beam sputtering or magnetron sputtering.

The buffer layer 13 is provided for the purpose of protecting the lower reflective layer 12 from being damaged by the etching process when the mask pattern is formed on the absorber layer 16 of the surface exposure light as described above. It is done.
Therefore, the material of the buffer layer 13 is not easily affected by the etching process of the absorber layer 16 on the mask surface, that is, the etching rate is slower than the absorber layer 16 and is not easily damaged by etching. Possible substances are selected. For example, materials such as Cr, Al, Ru, Ta and nitrides thereof, SiO ₂ , Si ₃ N ₄ , and Al ₂ O ₃ are preferable. select. The reason why the buffer layer 13 can be removed later is that after the absorber layer 16 is formed in a pattern, the portion of the buffer layer 13 from which the absorber layer 16 has been removed is further removed to remove the reflection layer. This is because, by exposing the surface 12, it is possible to improve the reflection characteristic of exposure light as a reflective mask, which is more desirable. Further, for example, when a substance such as Cr is selected, since it has an EUV light absorption characteristic, the buffer layer 13 can also have the function of an exposure light absorption layer, and the upper absorber layer accordingly. Since the film thickness of 16 can be further reduced, blurring of the edge portion of the pattern at the time of exposure can be suppressed, and pattern damage can be reduced by shortening the processing time for pattern formation. However, in this case, it is essential to remove the portion of the buffer layer 13 from which the absorber layer 16 has been removed by patterning.

Note that the thickness of the buffer layer 13 is preferably small. This is because, as is clear from FIG. 2, when the thickness of the buffer layer 13 is large, the difference in height between the surface of the reflective layer 12 and the surface of the absorber layer 16 becomes large, and the incident angle is about 5 degrees. This is because the edge portion of the mask pattern is blurred due to the optical path of the EUV exposure. Further, even when the buffer layer 13 is removed later by etching, it is desirable that the film thickness is small because the processing time can be shortened. Therefore, the thickness of the buffer layer 13 is 100 nm or less, preferably 80 nm or less.
The buffer layer 13 can be formed by using a well-known film forming method such as a magnetron sputtering method or an ion beam sputtering method as in the case of the reflection layer 12 described above.
In addition, what is necessary is just to provide a buffer layer as needed, and depending on the pattern formation method and conditions to an absorber layer, you may provide an absorber layer directly on a reflection layer.

As described above, the absorber layer 16 has a lower layer as the absorber layer 14 for exposure light in the short wavelength region including the EUV region, and an upper layer as the inspection light low reflection layer 15 used for mask pattern inspection. It consists of a layer structure. In the present invention, the absorber layer 16 has a laminated structure in which the function is separated into the exposure light absorption layer and the inspection light low reflection layer.
The lower exposure light absorber layer 14 is made of a material that absorbs light in a short wavelength region such as EUV. Examples of such exposure light absorbers include chromium, manganese, cobalt, copper, zinc, gallium, germanium, molybdenum, palladium, silver, cadmium, tin, antimony, tellurium, iodine, hafnium, tantalum, tungsten, titanium, and gold. And an alloy containing these elements, and at least one material selected from these elements or alloys containing these elements and substances containing nitrogen and / or oxygen.
For example, in the case of tantalum, tantalum alone (Ta), tantalum nitride (TaN), tantalum oxide (TaO), tantalum silicon alloy (TaSi), tantalum silicon alloy nitride (TaSiN), tantalum boron alloy (TaB), Examples thereof include tantalum boron alloy nitride (TaBN), tantalum germanium alloy (TaGe), tantalum germanium alloy nitride (TaGeN), and the like.

Further, the minimum required characteristics of the upper inspection light low reflection layer 15 are low reflection with respect to the mask pattern inspection wavelength, pattern formation processing is possible, and when the buffer layer is removed by etching. (There is an etching selectivity with the buffer layer). Furthermore, it is more preferable to have an EUV light absorption function because the total film thickness of the absorber layer 16 can be reduced.
For mask pattern inspection, deep ultraviolet (Deep Ultra Violet) light of about 190 to 260 nm, for example, light having a wavelength of about 257 nm or 193 nm is used. Therefore, as a material having a low reflectance with respect to such inspection light wavelength, For example, oxides, nitrides, nitride oxides of materials constituting the above-described exposure light absorber, or materials further containing silicon can be used.

  As a material for the low reflection layer, nitride has the effect of reducing the reflectance at the inspection wavelength, and in the case of a polycrystalline film, it has the effect of reducing the crystal grain size and improving the smoothness. In addition, the oxide has a greater effect of reducing the reflectance at the inspection wavelength than the nitride. In addition, the silicide has little effect of lowering the reflectance at the inspection wavelength, but has the effect of expanding the wavelength region where the reflectance is lowered. That is, in the case of nitride or oxide, a curve having a minimum value of reflectance is obtained only in a specific wavelength portion, but when silicon is further added to these materials, low reflectance can be obtained in a wide wavelength range. (See FIG. 9 in Example 1 described later). If low reflectance is obtained in such a wide wavelength range, it can flexibly respond to changes in the inspection wavelength, and the change in reflectance is small even when the minimum value shifts due to the change in the film thickness of the uppermost layer. There is an advantage that the allowable value of deviation from the design value of the film thickness is increased, and the manufacturing restrictions are eased.

Therefore, it is necessary for the material of the low reflection layer to contain oxygen or nitrogen in the compound. As described above, the oxide, nitride, nitride oxide, or the substance constituting the exposure light absorber, or In addition, it is preferable that these are made of at least one substance selected from materials further containing silicon.
Although boride does not contribute much to reflectivity, it contributes to the smoothness of the film in relation to the crystallinity (amorphization) of the film. Therefore, by including boron in the compound, the smoothness of the film of the low reflection layer can be improved. Improved.
Here, specific examples of the material of the low reflection layer include metal oxides, nitrides, oxynitrides used for the lower exposure light absorber layer, metals and boron used for the lower absorber layer Oxide, nitride, oxynitride of alloy and metal used for lower absorber layer and oxide of oxide and nitride, oxynitride of metal and silicon, metal used for lower absorber layer And oxides, nitrides, oxynitrides, and the like of alloys of silicon and boron. For example, when tantalum is used as the exposure light absorber metal, tantalum oxide (TaO), tantalum nitride (TaN), tantalum oxynitride (TaNO), tantalum boron alloy oxide (TaBO), tantalum boron alloy nitride (TaBN), tantalum boron alloy oxynitride (TaBNO), tantalum silicon alloy oxide (TaSiO), tantalum silicon alloy nitride (TaSiN), tantalum silicon alloy oxynitride (TaSiON), tantalum silicon boron alloy Oxide (TaSiBO), tantalum silicon boron alloy nitride (TaSiBN), tantalum silicon boron alloy oxynitride (TaSiBNO), tantalum germanium alloy nitride (TaGeN), tantalum germanium alloy oxide (TaGeO), Tantalum germanium Oxynitride of an alloy (TaGeNO), a nitride of tantalum germanium silicon alloy (TaGeSiN), oxides of tantalum germanium silicon alloy (TaGeSiO), oxynitride of tantalum germanium silicon alloy (TaGeSiNO), and the like.

  When the film thickness of the low reflection layer is changed, the position of the minimum value of the reflectance curve is shifted. For example, in the case of a tantalum or molybdenum system such as TaO or TaSiON, there is a tendency to shift to the longer wavelength side when the film thickness is increased. Therefore, since the reflectance at a specific wavelength also changes when the film thickness of the low reflective layer is changed, it is possible to control the reflectance at the inspection wavelength to be minimized by adjusting the film thickness to some extent. However, as will be described later, if the film thickness of the low reflection layer is too large, it is not preferable, so the adjustment is made between about 5 and 30 nm. Preferably it is 10-20 nm. Further, when the composition ratio of the low reflective layer material, for example, the composition ratio of metal, oxygen, nitrogen, or the like is changed, the reflectance changes. In general, when the composition ratio of oxygen or nitrogen increases, the reflectance decreases, but the EUV light absorption rate tends to decrease.

As described above, since the effect of lowering the reflectivity of nitride and oxide tends to be larger in oxide, the material of the low reflection layer may be a material containing metal, oxygen and silicon (for example, metal and A material containing oxygen and silicon as main components, a material containing metal, silicon, oxygen and nitrogen as main components, etc.) are most preferable from the viewpoints of a decrease in reflectance and a wide range of wavelengths at which the reflectance decreases. In addition, by using the metal element used as the exposure light absorber here, the low reflection layer also has an EUV light absorption function, which is more preferable.
Of course, although the wavelength region in which the reflectance is reduced is a little narrow, an oxide that does not contain silicon can provide a low reflectance in a specific wavelength region. Further, although depending on the material, a sufficient decrease in reflectance may not be obtained only by containing nitrogen, but the reflectance of nitride is lower than that of a single metal. Moreover, the effect of improving the smoothness of the film can be obtained by adding nitrogen as described above. If the smoothness of the film is poor, the edge roughness of the pattern increases and the dimensional accuracy of the mask deteriorates. Therefore, it is desirable that the film be as smooth as possible.
Further, as the material of the low reflection layer, for example, a material containing no metal, for example, a material composed of silicon, nitrogen, and oxygen (silicon oxynitride) can be used. However, in this case, the effect of absorbing EUV light in the low reflection layer is small.

When the low reflection layer is made of a material containing, for example, metal, Si, N, and O, the composition ratio for obtaining low reflectivity with deep ultraviolet light of about 190 to 260 nm, which is the inspection wavelength, is, for example, tantalum, It is preferable that metals such as molybdenum and chromium are 20 to 25 at%, Si is 17 to 23%, N is 15 to 20%, and the rest is O. The ratio of Si and O is preferably about 1: 1.5 to 1: 2.
In order to make the surface of the absorber layer smooth, the low reflection layer is preferably an amorphous structure film. For example, in the case of Ta, it can be amorphized by appropriately containing B. It is also preferable to add Si or Ge to Ta because an amorphous film can be obtained.
Further, when the low reflective layer is made of, for example, a tantalum boron alloy nitride (TaBN), N is preferably 30 to 70 at% as a composition ratio for obtaining a low reflectance at the above-described inspection wavelength, Furthermore, it is preferable that it is 40-60 at%. If the amount of N is small, sufficient low reflection characteristics cannot be obtained. Further, when both the low reflection layer and the underlying absorber layer are nitrides of the tantalum boron alloy, the N of the low reflection layer is 30 to 70 at%, more preferably 40 to 60 at%. Is 0 to 25 at%, more preferably 5 to 20 at%. If the amount of N in the absorber layer is small, it is not preferable in terms of surface roughness, and conversely if it is large, the absorption coefficient of EUV light decreases. In the case of a TaBN film, it is preferable that B is 5 to 30 at%, preferably 5 to 25 at%, and the composition ratio of Ta and N is 8: 1 to 2: 7.

When the low reflective layer is an oxide of tantalum boron alloy (TaBO), O is 30 to 70 at%, more preferably 40 to 60 at%. If the amount of O is small, low reflection characteristics cannot be obtained. Conversely, if the amount of O is large, the insulating property becomes high, and charge-up occurs due to electron beam irradiation. Furthermore, when the low reflective layer is a tantalum boron alloy oxynitride (TaBNO), N is preferably 5 to 70 at% and O is preferably 5 to 70 at%. In the case of a TaBO film, it is preferable that B is 5 to 25 at% and the composition ratio of Ta and O is in the range of 7: 2 to 1: 2. In the case of a TaBNO film, it is preferable that B is 5 to 25 at% and the composition ratio of Ta and N + O is within a range of Ta: (N + O) of 7: 2 to 2: 7.
In any case, these boron-containing substances preferably have a B content of about 5 to 30%, more preferably 5 to 25%, from the viewpoint of forming an amorphous structure.

By the way, the combination of materials in the lower exposure light absorber layer 14 and the upper low reflection layer 15 will be described. The low reflection layer 15 preferably contains the metal used for the exposure light absorber layer 14. For example, when a material containing tantalum is used as the exposure light absorber layer, the low reflection layer is also made of a material containing tantalum. Specifically, the exposure light absorber layer is made of a material containing tantalum, for example, Ta single substance, TaN, TaB, TaBN, TaBO, TaBNO or the like, and the low reflection layer contains tantalum and nitrogen or oxygen. One kind of material can be used among the materials to be included, such as TaO, TaBO, TaBNO, TaNO, TaSiO, TaSiON, and the like. In this way, by using the same metal as the exposure light absorber layer for the low reflection layer, the low reflection layer has a function of absorbing EUV light to some extent because it contains a metal having an EUV light absorption function. Since a material with a high etching selectivity is selected for the layer and the exposure light absorber layer, basically a large etching selectivity can be obtained even between the buffer layer and the low reflection layer, and the exposure light absorber layer and the low reflection layer are formed. Can be performed in the same film forming chamber, and the exposure light absorber layer and the low reflection layer can be patterned under the same etching conditions.
In addition, if the lower layer material is a film having an amorphous structure or a microcrystalline structure, a film having excellent smoothness can be obtained, which is more preferable.
Regarding the reflectance, a low reflectance can be obtained at the inspection wavelength to be used by obtaining the relationship between the composition of the material of the low reflection layer and the reflectance on the absorber surface, and the relationship between the film thickness and the reflectance. It is possible to determine the composition and film thickness.

In the reflective mask and reflective mask blank of the present invention, the surface roughness of the absorber layer is preferably 0.5 nmRms or less, more preferably 0.4 nmRms or less, and 0.3 nmRms or less. If the surface roughness of the surface of the absorber layer is large, the edge roughness of the absorber pattern is increased and the dimensional accuracy of the pattern is deteriorated. As the pattern becomes finer, the influence of edge roughness becomes more prominent, so the absorber surface is required to be smooth.
In order to reduce the surface roughness on the surface of the absorber layer, it is effective to make the upper layer (low reflection layer) of the absorber layer an amorphous structure film. The lower layer of the absorber layer is more preferably a film excellent in smoothness of an amorphous structure or a microcrystalline structure. Further, when a buffer layer is provided, it is also necessary to use a smooth film for the buffer layer.
Next, a combination of materials in the exposure light absorber layer 14 and the low reflection layer 15 and the buffer layer 13 will be described. In the present invention, it is preferable that the exposure light absorber layer 14 and the low reflection layer 15 are formed of a material containing tantalum, and the buffer layer 13 is made of a material containing chromium. By using a chromium-based material for the buffer layer, the buffer layer can have an EUV light absorption function as described above, and the reflectivity for inspection light in the deep ultraviolet region is about 40%. Easy to design multilayer reflective film surface, buffer layer surface, and absorber layer surface so that the reflectivity for the inspection wavelength decreases sequentially, large etching selectivity with absorber layer containing tantalum, and buffer There are advantages such as that the layer can be removed with little damage to the multilayer reflective film when the layer is removed.

As the material containing chromium used as the buffer layer, a material containing at least one element selected from Cr and N, O, and C can be preferably used in addition to Cr alone. Examples thereof include chromium nitride (CrN), chromium oxide (CrO), chromium carbide (CrC), chromium oxynitride (CrNO), and carbon nitride nitride oxide (CrCNO).
For example, in the case of chromium nitride (CrN), a preferred composition ratio of chromium and _nitrogen, when expressed in _{Cr 1-X N} X, is 0.05 ≦ X ≦ 0.5, more preferably 0.05 ≦ X ≦ 0.2. When X is smaller than 0.05, it is not preferable in terms of acid resistance, film stress, and surface roughness. When X is larger than 0.5, the reflectance with respect to the inspection light is too low. It becomes impossible to take large contrast. Further, a small amount of about 5% of oxygen, carbon, etc. may be added to chromium nitride.
In addition, it is preferable to use a CrN film having a microcrystalline structure because of excellent smoothness.
It is preferable that the entire thickness of the absorber layer 16 composed of the lower exposure light absorber layer 14 and the upper inspection light low reflection layer 15 is smaller. This is because the etching process time during patterning of the absorber layer 16 is proportional to the film thickness. In this etching process, the resist pattern surface is damaged for an etching process time proportional to the thickness of the absorber layer 16. Due to this, in-plane distribution defects of etching are likely to occur, mask pattern defects increase due to the increased occurrence frequency of white and black defects, and mass productivity is reduced due to the time required to repair these defects, and the resulting cost A serious problem such as an increase occurs. Furthermore, if the film thickness of the entire absorber layer 16 is large, the difference in height between the surface of the reflective layer 12 and the surface of the absorber layer 16 becomes large, as in the case where the film thickness of the buffer layer 13 is large. Sometimes the edge of the mask pattern is blurred.

Therefore, the total film thickness of the absorber layer 16 is 100 nm or less, preferably 80 nm or less, and more preferably 60 nm or less. However, if the value of the film thickness of the absorber layer 16 is too small, the exposure light absorption characteristic is deteriorated.
In the absorber layer 16, it is desirable that the thickness of the upper low reflection layer 15 is smaller than the thickness of the lower exposure light absorber layer 14. If the upper low reflection layer 15 is too thick, the EUV light absorption characteristics of the absorber layer 16 as a whole may be degraded. Therefore, the film thickness of the upper low reflection layer 15 is preferably about 5 to 30 nm, and the film thickness of the lower exposure light absorber layer 14 is preferably about 30 to 60 nm. As described above, the absorber layer 16 has a laminated structure, but can be suppressed to a thickness as much as the conventional single layer structure. Further, the buffer layer 13 has a function as an exposure light absorbing layer. Therefore, even if the absorption characteristic of the upper exposure light absorber layer 14 is lowered, the film thickness can be reduced.
Moreover, the preferable range of the total film thickness of the buffer layer 13 and the absorber layer 16 is 60 nm-130 nm. Although depending on the material, if the total film thickness is less than 60 nm, sufficient absorption characteristics of EUV light may not be obtained. If the total film thickness is greater than 130 nm, the problem of shadow of the pattern itself increases.

The exposure light absorber layer 14 and the inspection light absorber layer 15 are also well-known film formation methods such as magnetron sputtering, ion beam sputtering, CVD, vapor deposition, and the like, similar to the reflection layer 12 and the buffer layer 13 described above. Film formation can be performed using the method.
By the way, it is preferable to design the reflectance with respect to the pattern inspection light wavelength so as to decrease in the order of the exposure light reflection layer surface, the buffer layer surface, and the low reflection layer surface. Because, in both the inspection between the buffer layer surface and the low reflection layer surface after pattern formation and the inspection between the exposure light reflection layer surface and the low reflection layer surface after removal of the buffer layer, the portion with the pattern is Since it becomes dark and the pattern contrast does not invert, it is not necessary to change the setting of the inspection machine, and the result is easy to understand. Further, in the case of the Mo / Si multilayer film used as the exposure light reflecting layer, the reflectance is as high as about 60%. Therefore, in order to obtain sufficient contrast with each layer, it is advantageous to lower the reflectance of other layers. .
Next, the relationship between the refractive index n and extinction coefficient k of the material of the low reflective layer 15 and the reflectance with respect to the inspection wavelength will be described.
3 to 6 show a case in which chromium nitride is used as a buffer layer (50 nm), and an exposure light absorber layer is formed of tantalum boron alloy nitride (TaBN) (N is about 18%) 50 nm, and a low reflection layer is formed thereon. As shown, the reflectance R at 190 nm and 260 nm inspection wavelengths when materials having various refractive indexes n and extinction coefficients k are formed to a thickness of 10 nm or 20 nm are plotted with n and k as axes. From this result, it is understood that a low reflectance can be obtained when a material satisfying a specific range of n and k is used.

That is, the relationship between the inspection wavelength and film thickness and the preferred n and k ranges is as follows.
(1) When the film thickness is 10 nm and 20 nm, the reflectance is 10% or less if the extinction coefficient k is approximately 0.7 or less for both film thicknesses. When the reflectance is allowed to 20% or less, k is 1.2 or less. At this time, the preferable range of the refractive index n is slightly different between the case of a film thickness of 10 nm and the case of 20 nm. When the film thickness is 20 nm, n is about 1.5 to 2.5 and the reflectance R is 10% or less. When the reflectance is allowed to 20% or less, n is about 1 to 3. When the film thickness is 10 nm, n is about 2.0 to 3.5 and the reflectance R is 10% or less. When the reflectance is 20% or less, n is about 1.5 to 4.0.
(2) The inspection wavelength of 190 nm and 260 nm do not change so much, but the 260 range tends to slightly shift the preferred range of n.
(3) Considering the above as a whole, when the film thickness is 10 nm to 20 nm, the extinction coefficient k is 0.7 or less and the refractive index n is set to be 10% or less in the deep ultraviolet region. What is necessary is just to select the material which is 1.5-3.5.

The absorber layer 16 may have a so-called laminated structure such as a two-layer structure as in the present embodiment. For example, oxygen may flow from the buffer layer 13 side of the absorber layer 16 toward the absorber layer surface. It may have a distribution. In this case, the reflectance with respect to the inspection light on the surface of the absorber layer 16 can be reduced by increasing the amount of oxygen toward the surface of the absorber layer. The composition distribution of oxygen in the thickness direction of the absorber layer may continuously change linearly or in a curve, or may change stepwise. Such a composition distribution of oxygen in the thickness direction of the absorber layer can be realized by controlling the amount of element added during film formation. For example, in the case of a TaBO film, oxygen is continuously formed in the thickness direction of the absorber layer 16 by performing film formation while changing the amount of oxygen gas to be added in the sputtering method using a target containing Ta and B. A target or stepwise composition distribution can be formed.
Furthermore, the reflective mask blank and the reflective mask of the present invention may have an intermediate region whose composition changes continuously from the lower layer composition to the upper layer composition between the lower layer and the upper layer of the absorber layer. good. This intermediate region is a transition region in which elements contained in the lower layer and elements contained in the upper layer are mixed. By having such an intermediate region, it is easy to obtain a pattern having a smooth cross-sectional structure without forming a boundary between the upper layer and the lower layer when forming a pattern in the absorber layer. When the metal elements contained in the upper layer and the lower layer are the same, it is preferable because a pattern can be continuously formed on the absorber layer. There is also an advantage that the adhesion between the upper layer and the lower layer is improved. The thickness of the intermediate region may be about 2 to 15 nm.

Next, a method for manufacturing a reflective mask according to the present invention will be described with reference to FIG. FIG. 7 is a schematic cross-sectional view showing the manufacturing process of the reflective mask of the present invention.
FIG. 1A shows the configuration of the mask blank 1. The configuration has already been described above. This mask blank 1 is formed by laminating an exposure light reflection layer 12, a buffer layer 13, an exposure light absorber layer 14, and an inspection light low reflection layer 15 in this order on a substrate 11.
Here, it is possible to employ a method in which an absorber layer 14 for exposure light is first formed on the buffer layer 13 and then a low reflection layer 15 for inspection light is formed thereon, but depending on the material of the low reflection layer, For example, in the case of using the same metal oxide as the lower exposure light absorber layer 14 as the upper low reflection layer 15, after the exposure light absorber layer 14 is formed on the buffer layer 13, the absorber layer 14. It is also possible to form the low reflection layer 15 for the inspection light on the outermost surface by subjecting the surface to oxidation treatment using a process gas containing oxygen gas or oxidation treatment with an acid solution. According to the latter method, the time required for changing the film formation conditions can be shortened, the number of material types and the number of film formation chambers can be reduced, and the work can be simplified and the work time can be shortened.

Further, it is preferable to continuously form the upper low reflection layer and the lower exposure light absorber layer in the same film forming chamber. By doing so, a good interface between the lower layer and the upper layer can be obtained between the lower layer and the upper layer by preventing the adsorption of impurities / foreign matter to the lower layer surface and the alteration (oxidation) of the surface. . If there is an adsorption or alteration of impurities at the interface between the upper layer and the lower layer, the stress of the absorber layer will change and it will affect the optical properties such as the reflectance of the inspection light. The interface parameters must be taken into account, and the designed characteristics cannot be obtained, resulting in poor reproducibility and controllability.
On the other hand, if the lower layer and the upper layer are continuously formed in the same film formation chamber, the substrate is not taken out of the film formation chamber or left unattended. Therefore, the absorber layer can be formed with good reproducibility and controllability. In addition, there is an advantage that the film forming process is not complicated.
The continuous formation of the upper layer and the lower layer in the same film formation chamber is particularly effective when the upper layer and the lower layer contain metal elements, respectively, and these metal elements are the same. This is because, by using a common metal element supply source and changing the gas supplied during film formation, film formation can be performed continuously. For example, when a reactive sputtering method is used, continuous film formation can be easily performed by using a target containing a common metal element in the upper layer and the lower layer and changing the content of the supplied gas (oxygen, etc.). Can do.
For example, when a material containing Ta is used for the upper layer and the lower layer, a target containing Ta is commonly used, and the content and type of gas (oxygen, etc.) to be introduced for low reflection are set at the time of forming the lower layer, and the upper layer. What is necessary is just to change at the time of formation.
Further, by performing continuous film formation in the same film formation chamber, it is possible to intentionally introduce an intermediate region in which the above composition continuously changes between the upper layer and the lower layer. Specifically, the film formation conditions may be continuously changed from the film formation conditions for the lower layer to the film formation conditions for the upper layer. If the metal elements contained in the lower layer and the upper layer are the same, the metal element source such as the target may be made common and the gas flow rate such as oxygen to be introduced may be changed. At this time, the formation of the lower layer and the formation of the upper layer In the meantime, the flow rate of the gas used for forming the lower layer is decreased or stopped, the amount of gas used for forming the upper layer is increased, or the introduction is started, and the gas flow rate is continuously changed, If the film formation is performed in a state where the gases used for forming both layers exist at the same time, the intermediate region can be easily formed.

Next, an absorber pattern having a predetermined pattern is formed by processing the absorber layer 16 including the exposure light absorber layer 14 which is an EUV light absorber and the low reflection layer 15 of inspection light (patterning step, same pattern). (Refer figure (b)). Usually, a resist pattern having a predetermined pattern is formed on the surface of the absorber layer 16 by an electron beam drawing process, and then the absorber layer is etched. The etching process may be dry etching or wet etching, and an appropriate method and its conditions are selected depending on the material. Finally, the remaining resist pattern is removed.
Next, at this stage, it is inspected whether the absorber pattern is formed as designed. As a result of this pattern inspection, for example, as shown in FIG. 5B, pinhole defects (also referred to as white defects) 21 caused by adhesion of foreign matters to the resist layer at the time of pattern formation and etching deficient defects (also referred to as black defects). If it exists, the necessary repair is performed. The pinhole defect 21 is repaired by depositing a carbon film 23 on the pinhole by a focused ion beam (FIB) assisted deposition method, and the etching deficiency defect 22 remains by gas-assisted etching with FIB excitation. The removed portion 25 of the absorber layer 16 having a two-layer structure is obtained by removing and repairing the portion 22a. Damaged portions 24 (portions 24a removed by FIB and portions 24b into which FIB ions have entered) are present on the surface of the buffer layer 13 due to the energy of ion irradiation at this time (see FIG. 5C).

Next, the buffer layer 13 corresponding to the portion 25 from which the absorber layer 16 has been removed is removed by, for example, dry etching (buffer layer removing step). At this time, it is important to set the etching conditions so that the etching proceeds only to the buffer layer 13 and the other layers are not damaged. Thus, the reflective mask 2 is produced by forming the pattern 26 of the exposure light reflecting layer 12 (see FIG. 4D).
When the thus prepared reflective mask 2 is exposed to EUV light 31, it is absorbed at a portion of the mask surface where the absorber pattern is present, and is exposed at portions other than the absorber layer 16 and the buffer layer 13 that are exposed. 12, the EUV light 31 is reflected (see FIG. 5E), and can be used as a mask for lithography using EUV light.

Thus, the reflective mask of the present invention has a laminated structure in which the function of the absorber layer, which has conventionally been a single layer, is separated into a lower exposure light absorber layer 14 and an upper inspection light low reflection layer 15. As a result, the reflectivity at the pattern inspection light wavelength of the surface of the low reflection layer 15 of the upper inspection light formed on the outermost surface has a sufficiently reduced exposure light absorption function. Thereby, the difference in reflectance at the pattern inspection light wavelength between the surface of the low reflection layer 15 of the inspection light and the surface of the buffer layer 13 exposed by removing the absorber layer 16 by mask pattern formation (see FIG. 7B). Increases and sufficient contrast is obtained during inspection. For this reason, a reflected image pattern with high contrast is obtained. Therefore, it is possible to accurately and quickly inspect a mask pattern, which has been difficult in the past, by using a conventional mask inspection machine using light having a wavelength in the deep ultraviolet region such as 257 nm.
Further, the contrast will be further described. For example, the ratio of the reflectance values of the surface of the inspection light absorber layer 15 and the surface of the buffer layer 13 described above can be generally used as an index of the magnitude of contrast. The following defining formula is also known, and a value based on this formula can be used as an index of the magnitude of contrast.
That is, R ₁ and R ₂ are each reflectance at a certain wavelength, and when R ₂ is larger than R ₁ ,
Contrast (%) = ((R ₂ −R ₁ ) / (R ₂ + R ₁ )) × 100

  A sufficient contrast may be obtained in the pattern inspection, but as a guideline, it is preferably 1: 3 or less, more preferably 1: 4 or less, and even more preferably 1:10 or less when expressed by the above-described reflectance ratio. It is. The contrast value represented by the above definition formula is 40% or more, preferably 50% or more, more preferably 60% or more, and still more preferably 80% or more. The contrast value here is the contrast between the absorber layer and the reflective layer, or the contrast between the absorber layer and the buffer layer. The preferred reflectance of the low reflective layer 15 is 20% or less, more preferably 10% or less, and even more preferably 5% or less.

Hereinafter, the present invention will be described more specifically with reference to examples. For convenience of explanation, the symbols shown in FIGS. 1, 2 and 7 are appropriately used.
Example 1
Each layer was formed on the substrate 11 to produce mask blanks. Here, a low expansion SiO ₂ —TiO ₂ glass substrate having an outer shape of 6 inches square and a thickness of 6.3 mm was used as the substrate 11. This glass substrate had a smooth surface of 0.12 nmRms (Rms: root mean square roughness) and a flatness of 100 nm or less by mechanical polishing.
First, a laminated film Mo / Si of molybdenum (Mo) and silicon (Si) was laminated on the substrate 11 as a EUV light reflecting layer 12 by a DC magnetron sputtering method. First, using a Si target, a Si film having a thickness of 4.2 nm was formed at an Ar gas pressure of 0.1 Pa. Next, using a Mo target, a Mo film having a thickness of 2.8 nm was formed at a Ar gas pressure of 0.1 Pa. After 40 cycles were stacked as one cycle, a 7 nm Si film was finally formed. The total film thickness is 287 nm. The reflectance of this multilayer reflective film with respect to light having a wavelength of 257 nm is 60%.
On top of this, a SiO ₂ thin film having a thickness of 50 nm was formed as a buffer layer 13. This was formed by a DC magnetron sputtering method using a Si target and a mixed gas of argon (Ar) and oxygen (O ₂ ). The surface roughness on the SiO ₂ buffer layer was 0.4 nm Rms.

Further, a tantalum (Ta) thin film having a thickness of 50 nm was formed thereon as an EUV light absorber layer 14. This was formed using a Ta target and a DC magnetron reactive sputtering method using argon gas.
Further thereon, a TaO thin film having a thickness of 10 nm was formed as a low reflection layer 15 for inspection light having a wavelength of 257 nm. The film was formed by DC magnetron reactive sputtering using a mixed gas of argon and oxygen using the same Ta target in the same film forming chamber as the lower layer Ta. The film composition was Ta ₃₈ O ₆₂ . This TaO film has a refractive index of 2.68 and an extinction coefficient of 0.18 for light having a wavelength of 260 nm, and a refractive index of 2.04 and an extinction coefficient of 0.87 for light having a wavelength of 190 nm. The surface roughness of the TaO film surface was 0.7 nmRms.
When the same metal oxide as the EUV light absorber layer is used as the low reflection layer for the inspection light as in this embodiment, the surface of the EUV light absorber layer is oxidized using a process gas containing oxygen gas. You may form by a process or the oxidation process by an acid solution.

Next, the mask blank produced as described above was used, and a predetermined mask pattern was formed thereon. Here, an EUV mask having a pattern for 16 Gbit-DRAM having a design rule of 0.07 μm was produced. The mask pattern was formed as follows. First, an electron beam resist material was uniformly applied to the surface of the mask blank with a spinner or the like, and after prebaking, electron beam drawing and development were performed to form a resist pattern. Next, dry etching using chlorine gas was performed, and the resist pattern was removed after the etching was completed. Thus, a mask pattern was formed on the absorber layer 14 and the low reflection layer 15 above the buffer layer 13.
As a result of inspecting the formed mask pattern by a mask inspection machine using light having a wavelength of 257 nm, pinhole defects (white defects) and etching deficiencies (black defects) were confirmed.
Next, the pattern defect was repaired based on the inspection result. That is, for the white defect, a carbon film was deposited on the pinhole by the focused ion beam (FIB) assisted deposition method, and for the black defect, the remaining part was removed by FIB-excited gas-assisted etching. In the surface of the buffer layer 13 due to the energy by irradiation at this time, there was a damaged portion whose optical characteristics were changed due to the change in the film structure (see FIGS. 7B and 7C).

Next, the buffer layer 13 exposed in the patternless portions of the absorber layer 14 and the low reflection layer 15 was removed by etching (see (d) of FIG. 7 described above). At this time, only the SiO ₂ buffer layer was dry-etched with a fluorine-based gas so that the absorber pattern was not damaged and the pattern became an etching mask. Thus, the reflective mask of this example was produced.
When this mask is irradiated with EUV light, the EUV light is reflected only at the pattern portion on the surface of the reflective layer 12, thereby fulfilling a function as a reflective mask.
For comparison, a sample of a single EUV light absorption layer without the uppermost low reflection layer 15 of this example was prepared. The film thickness of the single EUV light absorption layer at this time was formed as 60 nm, which is the same value as the total film thickness of the two layers of the EUV light absorber layer and the low reflection layer according to this example.
FIG. 9 shows the reflectance values on the absorber pattern surface of the mask with respect to light having a wavelength from 190 nm to 690 nm. In the case of the present embodiment, it can be seen that the wavelength region showing the minimum value of the reflectance is extremely narrow.
From this result, when the pattern inspection light wavelength is 257 nm, the reflectance of the low reflective layer surface of the mask of this example at this wavelength is 4.0%, and the reflectance of the buffer layer (SiO ₂ ) at this wavelength is also the same. Since it was 42.1%, the contrast between the low reflection layer surface and the buffer layer surface at this wavelength was 1:10 in terms of the ratio of these reflectances, and the contrast value was 83%. The reflectance ratio between the low reflective layer and the multilayer reflective film surface was 1:15, and the contrast value was 88%.

On the other hand, the reflectance of the absorption layer surface of the conventional mask at the above wavelength is 44%, and the contrast between the absorption layer surface and the buffer layer surface at this wavelength is 1: 0 in terms of the ratio of these reflectances. The contrast value was 2.2%. The reflectance ratio between the absorption layer and the surface of the multilayer reflective film was 1: 1.4, and the contrast value was as low as 15%.
In the mask of this example, the reflectance of EUV light with a wavelength of 13.4 nm on the surface of the low reflection layer on the absorber layer 16 and the reflection layer surface of the EUV light was 0.5% and 62.4%, respectively. Therefore, the contrast between the surface of the absorber layer 16 and the surface of the reflective layer with respect to EUV light is 1: 125 in terms of the ratio of reflectance, and the contrast value is 98%. Similarly, the contrast between the surface of the single-layer absorption layer and the surface of the reflective layer with respect to EUV light of the conventional mask was 1: 105, and the contrast value was 98%.

Next, a method for transferring a pattern by EUV light to a semiconductor substrate with a resist (silicon wafer) using the reflective mask of this embodiment will be described. FIG. 8 shows a schematic configuration of the pattern transfer apparatus. The pattern transfer apparatus 50 is schematically configured by a laser plasma X-ray source 32, a reflective mask 2, a reduction optical system 33, and the like. The reduction optical system 33 uses an X-ray reflection mirror, and the pattern reflected by the reflective mask 2 is usually reduced to about ¼. Since the wavelength band of 13 to 14 nm is used as the exposure wavelength, it was set in advance so that the optical path was in vacuum.
In this state, EUV light obtained from the laser plasma X-ray source 32 is incident on the reflective mask 2, and the light reflected here is transferred onto the silicon wafer 34 through the reduction optical system 33. The light incident on the reflective mask 2 is absorbed and not reflected by the absorber at a portion having the absorber pattern, and the light incident on the portion without the absorber pattern is reflected by the reflective layer of EUV light. . In this way, an image formed by the light reflected from the reflective mask 2 enters the reduction optical system 33. The exposure light passing through the reduction optical system 33 exposes the transfer pattern on the resist layer on the silicon wafer 34. Then, a resist pattern was formed on the silicon wafer 34 by developing the exposed resist layer.
As a result of pattern transfer onto the semiconductor substrate as described above, it was confirmed that the accuracy of the reflective mask of this example was 16 nm or less, which is the required accuracy of the 70 nm design rule.
From the above results, the mask of this embodiment can obtain high contrast with respect to EUV light, and also can obtain high contrast with respect to the pattern inspection wavelength. On the other hand, the conventional mask can obtain a high contrast for EUV light, but has a very poor contrast for the pattern inspection wavelength.

(Example 2)
A multilayer film Mo / Si of molybdenum (Mo) and silicon (Si) is formed as a EUV light reflecting layer 12 on the same substrate 11 as in Example 1, and a Cr thin film is formed as a buffer layer 13 on the DC magnetron. A film having a thickness of 50 nm was formed by sputtering. The surface roughness of the Cr thin film surface was 0.5 nmRms.
A tantalum (Ta) thin film is formed thereon as the EUV light absorber layer 14 and the TaO thin film is further formed thereon as the low reflection layer 15 for the inspection light having a wavelength of 257 nm. Was deposited. However, in this embodiment, the tantalum film has a thickness of 40 nm. The surface roughness of the TaO film surface was 0.7 nmRms.
An EUV reflective mask having a pattern for a 16 Gbit DRAM having a design rule of 0.07 μm was produced in the same manner as in Example 1 using the mask blank produced as described above.

For comparison, a sample of an EUV light absorption layer single layer without the low reflection layer 15 of the uppermost inspection light of this example was prepared. The film thickness of the single EUV light absorption layer at this time was set to 50 nm, which is equal to the total film thickness of the two layers of the EUV light absorber layer according to this example and the low reflection layer for inspection light.
FIG. 10 shows the reflectance values on the absorber pattern surface of the mask with respect to light having a wavelength from 190 nm to 690 nm.
From this result, when the pattern inspection light wavelength is 257 nm, the reflectance of the surface of the low reflective layer of the mask of this embodiment at this wavelength is 4.0%, and the reflectance of the buffer layer (Cr) at this wavelength is also 57%. Therefore, the contrast between the low reflection layer surface and the buffer layer surface at this wavelength was 1:14 in terms of the ratio of these reflectances, and the contrast value was 87%. The ratio of the reflectance of the low reflective layer to the surface of the multilayer reflective film was 1:15, and the contrast value was 88%.

On the other hand, the reflectance of the absorption layer surface of the conventional mask at the above wavelength is 44%, and the contrast between the absorption layer surface and the buffer layer surface at this wavelength is 1: 1 when expressed by the ratio of these reflectances. .3 and the contrast value was 13%. The reflectance ratio between the absorbing layer and the multilayer reflective film was 1: 1.4, and the contrast value was as low as 15%.
In the mask of this example, the reflectivity for EUV light having a wavelength of 13.4 nm on the surface of the low reflection layer and the EUV light reflection layer on the absorber layer 16 was 0.5% and 62.4%, respectively. The contrast between the surface of the absorber layer 16 and the EUV light reflection layer surface with respect to EUV light was 1: 125 in terms of reflectance ratio, and the contrast value was 98%. Similarly, the contrast between the surface of the single-layer absorption layer and the surface of the reflective layer with respect to EUV light of the conventional mask was 1: 105, and the contrast value was 98%.
Furthermore, as a result of performing exposure transfer to the semiconductor substrate shown in FIG. 8 by the same method as in Example 1 using the reflective mask of this example, it was confirmed that the film had sufficient exposure characteristics. That is, it was confirmed that the accuracy of the EUV reflective mask of this example was 16 nm or less, which is the required accuracy of the 70 nm design rule.

  From the above results, the mask of this embodiment can obtain high contrast with respect to EUV light, and also can obtain high contrast with respect to the pattern inspection wavelength. In addition, since the mask of this embodiment uses a Cr film as the buffer layer, the buffer layer also has a function as an EUV light absorbing layer, so that the upper EUV light absorbing layer does not deteriorate the contrast. Can be made thinner. On the other hand, the conventional mask can obtain a high contrast for EUV light, but has a very poor contrast for the pattern inspection wavelength.

(Example 3)
In the same manner as in Example 1, an EUV light reflection layer 12 was formed on the substrate 11.
A chromium nitride film was formed as a buffer layer 13 on the reflective layer 12 to a thickness of 50 nm. This chromium nitride film was formed by a DC magnetron sputtering method, a Cr target was used for film formation, and a gas in which 10% of nitrogen was added to Ar was used as a sputtering gas.
In the formed chromium nitride film, X was 0.1 in Cr _1-X N _X. The film stress of this chromium nitride film was +40 MPa in terms of 100 nm. The reflectance of this chromium nitride film with respect to light having a wavelength of 257 nm is 52%. The surface roughness of the chromium nitride film surface was 0.27 nmRms.
Next, a nitride (TaBN) film of tantalum boron alloy was formed to a thickness of 50 nm as the EUV light absorber layer 14 on the buffer layer 13 composed of a chromium nitride film. This TaBN film was formed by DC magnetron sputtering using a target containing Ta and B, adding 10% nitrogen to Ar. The composition ratio of this TaBN film was 0.8 for Ta, 0.1 for B, and 0.1 for N. The crystal state of the TaBN film was amorphous.

A tantalum boron alloy oxide (TaBO) film having a thickness of 12 nm was formed as a low reflection layer 15 on the TaBN absorber layer. This TaBO film was formed by adding 30% of oxygen to Ar using a target containing Ta and B by DC magnetron sputtering. During the formation of the EUV light absorber layer and the formation of the low reflection layer, the DC power was temporarily stopped and the gas used for film formation was switched. The composition ratio of the TaBO film of the low reflection layer formed here was 0.4 for Ta, 0.1 for B, and 0.5 for O. The crystal state of the TaBO film was amorphous. The lower layer and the upper layer of the absorber layer were continuously formed using the same target in the same film forming chamber and changing the type of gas.
The TaBO film has a refractive index of 2.5 and an extinction coefficient of 0.3 for light having a wavelength of 257 nm. Moreover, the absorption coefficient with respect to EUV light with a wavelength of 13.4 nm is 0.035. The surface roughness of this TaBO film was 0.25 nmRms and was very smooth.

The reflectance with respect to light having a wavelength of 257 nm on the low reflection layer thus obtained was 5%. Further, the total stress of the EUV light absorber layer and the low reflection layer was −50 MPa in terms of 100 nm.
The reflective mask blanks of this example were obtained as described above.
Next, an EUV reflective mask having a pattern for 16 Gbit-DRAM having a design rule of 0.07 μm was produced in the same manner as in Example 1 using the produced mask blanks.
First, an absorber pattern was formed on the low reflection layer and the absorber layer in the same manner as in Example 1. Here, the absorber pattern was inspected using light having a wavelength of 257 nm as inspection light. The ratio of the reflectance of the buffer layer to the inspection light and the reflectance on the low reflection layer was 1: 0.10, and the contrast value was 82%, so that a sufficient contrast was obtained in the inspection.
Next, the buffer layer made of chromium nitride was removed by dry etching according to the absorber pattern. For dry etching, a mixed gas of chlorine and oxygen was used.

A reflective mask of this example was obtained as described above. When the inspection of the absorber pattern was performed again using the inspection light having a wavelength of 257 nm on the obtained reflective mask, the ratio between the reflectance of the EUV reflection layer and the reflectance on the low reflection layer with respect to the inspection light is It was 1: 0.08, the contrast value was 85%, and a sufficient contrast was obtained even in the confirmation inspection. Further, when the reflectance of the obtained reflective mask was measured with EUV light having a wavelength of 13.4 nm and an incident angle of 5 degrees, it had a good reflection characteristic of 65%.
Furthermore, as a result of performing exposure transfer to the semiconductor substrate shown in FIG. 8 by the same method as in Example 1 using the reflective mask of this example, it was confirmed that the film had sufficient exposure characteristics. That is, it was confirmed that the accuracy of the EUV reflective mask of this example was 16 nm or less, which is the required accuracy of the 70 nm design rule.

Example 4
In the same manner as in Example 3, an absorber lower layer composed of a Mo / Si reflective multilayer film, a CrN buffer layer 50 nm, and a TaBN film 50 nm was formed on a glass substrate.
Next, a chromium oxide film (CrO) was formed to a thickness of 20 nm as an upper low reflection layer. The film forming method was a DC magnetron sputtering method using a target containing Cr and a gas containing argon and oxygen. The composition of the obtained CrO film was Cr: O = 46: 54. Further, the refractive index in light having a wavelength of 260 nm is 2.37, the extinction coefficient is 0.72, the refractive index in light having a wavelength of 190 nm is 1.91, and the extinction coefficient is 1.13.
The surface roughness on the surface of the CrO film was 0.3 nmRms. The reflectivity of the CrO film surface with respect to the inspection light having a wavelength of 257 nm was 14%.
In this way, a reflective mask blank of this example was obtained.
Next, using this mask blank, a reflective mask having a pattern for 16 Gbit-DRAM having a design rule of 0.07 μm was produced.
First, in the same manner as in Example 1, a resist pattern was formed on the low reflective layer. Subsequently, a CrO low reflection layer was formed in a pattern along the resist pattern by dry etching using chlorine and oxygen, and a part of the TaBN film under the absorber was exposed.
Next, the exposed TaBN film was formed into the same pattern as the CrO film by dry etching using chlorine gas, and a part of the CrN buffer layer was exposed.

Here, in the same manner as in Example 1, the absorber pattern was inspected using inspection light having a wavelength of 257 nm. The ratio of the reflectivity to the inspection light on the absorber layer surface and the buffer layer surface was 1: 3.7, and the contrast value was 58%, so that a sufficient contrast was obtained.
Similarly to Example 1, after the defect was corrected using FIB, the exposed CrN buffer layer was removed in the same pattern as the absorber by dry etching using chlorine and oxygen.
As described above, the reflective mask of this example was obtained.
The reflective mask was subjected to a final pattern inspection using inspection light having a wavelength of 257 nm. The ratio of the reflectivity to the inspection light on the absorber layer surface and the multilayer reflective film surface was 1: 4.3, and a good contrast of 62% was obtained.
Similarly to Example 1, when a pattern was transferred to a semiconductor substrate with a resist (silicon wafer) using the reflective mask of this example, the accuracy of the reflective mask of this example was 70 nm design rule. It was confirmed that the required accuracy was 16 nm or less.

(Example 5)
In the same manner as in Example 3, an EUV light reflecting layer made of a Mo / Si periodic laminated film and a buffer layer made of a chromium nitride film were formed on the substrate.
Next, a tantalum boron alloy nitride (TaBN) film was formed as a lower layer of the absorber layer. This TaBN film was formed by a DC magnetron sputtering method using a target containing Ta and B and using a gas in which 10% of nitrogen was added to Ar. When the TaBN film is formed to have a thickness of about 50 nm, the supply of Ar and nitrogen gas is gradually reduced and stopped during 10 seconds while DC is applied, and at the same time, oxygen is added to Ar in this 10 seconds without exhausting. %, And film formation with the same target was continued in the same film formation chamber. After introducing oxygen, a film was formed about 15 nm. The roughness of the formed absorber layer surface was 0.25 nmRms, which was very smooth. The crystal structure of the absorber layer was amorphous.
Further, when the nitrogen and oxygen composition in the film thickness direction of the absorber layer was analyzed by X-ray photoelectron spectroscopy (XPS), it was as shown in FIG. 11, and the lower layer composition was changed from the lower layer to the upper layer. It was found that an intermediate region in which the composition continuously changes was formed. The thickness of this intermediate region was about 5 nm. In the intermediate region, nitrogen gradually decreased from the lower layer side to the upper layer side, the oxygen content increased, and the composition continuously changed. The composition of the lower layer on the buffer layer side is a TaBN film of Ta: B: N = 0.5: 0.1: 0.4, and the upper layer near the surface of the absorber layer is Ta: B: O = The TaBO film was 0.4: 0.1: 0.5.

The reflectance of the surface of the absorber layer with respect to inspection light having a wavelength of 257 nm was 5%. The upper layer TaBO film has a refractive index of 2.5 and an extinction coefficient of 0.3 for a wavelength of 257 nm.
As described above, a reflective mask blank of this example was obtained.
Next, using this reflective mask blank, a reflective mask having a pattern for 16 Gbit-DRAM having a design rule of 0.07 μm was produced.
First, in the same manner as in Example 1, a resist pattern was formed on the low reflective layer. Subsequently, the absorber layer was formed in a pattern along the resist pattern by dry etching using a gas containing chlorine. The upper layer, middle region, and lower layer of the absorber layer were continuously patterned by dry etching to expose a part of the CrN buffer layer. Since the intermediate region having a continuous composition change was provided between the upper layer and the lower layer, the absorber layer could be patterned into a continuous good rectangular shape having no step in the cross-sectional shape.
Here, in the same manner as in Example 1, the absorber pattern was inspected using inspection light having a wavelength of 257 nm. The ratio of the reflectance to the inspection light on the absorber layer surface and the buffer layer surface was 1: 10.4, and a good contrast of 82% was obtained.

Similarly to Example 1, after the defect was corrected using FIB, the exposed CrN buffer layer was removed in the same pattern as the absorber by dry etching using chlorine and oxygen.
As described above, the reflective mask of this example was obtained.
The reflective mask was subjected to a final pattern inspection using inspection light having a wavelength of 257 nm. The ratio of the reflectance to the inspection light on the absorber layer surface and the multilayer reflective film surface was 1:12, and a good contrast value of 85% was obtained.
Similarly to Example 1, when a pattern was transferred to a semiconductor substrate with a resist (silicon wafer) using the reflective mask of this example, the accuracy of the reflective mask of this example was 70 nm design rule. It was confirmed that the required accuracy was 16 nm or less.

(Reference Example 1)
Each layer was formed on the substrate 11 to produce mask blanks. Here, a low expansion SiO ₂ —TiO ₂ glass substrate having an outer shape of 6 inches square and a thickness of 6.3 mm was used as the substrate 11. This glass substrate had a smooth surface of 0.12 nmRms (Rms: root mean square roughness) and a flatness of 100 nm or less by mechanical polishing.
First, a laminated film Mo / Si of molybdenum (Mo) and silicon (Si) was laminated on the substrate 11 as a EUV light reflecting layer 12 by a DC magnetron sputtering method. First, using a Si target, a Si film having a thickness of 4.2 nm was formed at an Ar gas pressure of 0.1 Pa. Next, using a Mo target, a Mo film having a thickness of 2.8 nm was formed at a Ar gas pressure of 0.1 Pa. After 40 cycles were stacked as one cycle, a 7 nm Si film was finally formed. The total film thickness is 287 nm. The reflectance of this multilayer reflective film with respect to light having a wavelength of 257 nm is 60%.
On top of this, a SiO ₂ thin film having a thickness of 50 nm was formed as a buffer layer 13. This was formed by a DC magnetron sputtering method using a Si target and a mixed gas of argon (Ar) and oxygen (O ₂ ). The surface roughness on the SiO ₂ buffer layer was 0.4 nm Rms.

Further, a tantalum nitride (TaN) thin film having a thickness of 50 nm was formed thereon as an EUV light absorber layer 14. This was formed by a DC magnetron sputtering method using a Ta target and a mixed gas of argon and nitrogen (N ₂ ). The film composition was Ta ₆₁ N ₃₉ .
Finally, a TaSiON thin film having a thickness of 20 nm was formed thereon as a low reflection layer 15 for inspection light having a wavelength of 257 nm. This was formed by a DC magnetron reactive sputtering method using a TaSi alloy target and a mixed gas of argon, oxygen and nitrogen. The film composition was Ta ₂₁ Si ₁₇ O ₄₇ N ₁₅ . This TaSiON film has a refractive index of 2.09 for light with a wavelength of 260 nm and an extinction coefficient of 0.24, and has a refractive index of 2.00 for light with a wavelength of 190 nm and an extinction coefficient of 0.59. The TaSiON film has an amorphous structure. The surface roughness of the TaSiON film surface was 0.45 nmRms.

Next, the mask blank produced as described above was used, and a predetermined mask pattern was formed thereon. Here, an EUV mask having a pattern for 16 Gbit-DRAM having a design rule of 0.07 μm was produced. The mask pattern was formed as follows. First, an electron beam resist material was uniformly applied to the surface of the mask blank with a spinner or the like, and after prebaking, electron beam drawing and development were performed to form a resist pattern. Next, dry etching using chlorine gas was performed, and the resist pattern was removed after the etching was completed. Thus, a mask pattern was formed on the absorber layer 14 and the low reflection layer 15 above the buffer layer 13.
As a result of inspecting the formed mask pattern by a mask inspection machine using light having a wavelength of 257 nm, pinhole defects (white defects) and etching deficiencies (black defects) were confirmed.
Next, the pattern defect was repaired based on the inspection result. That is, for the white defect, a carbon film was deposited on the pinhole by the focused ion beam (FIB) assisted deposition method, and for the black defect, the remaining part was removed by FIB-excited gas-assisted etching. In the surface of the buffer layer 13 due to the energy by irradiation at this time, there was a damaged portion whose optical characteristics were changed due to the change in the film structure (see FIGS. 7B and 7C).

Next, the buffer layer 13 exposed in the patternless portions of the absorber layer 14 and the low reflection layer 15 was removed by etching (see (d) of FIG. 7 described above). At this time, only the SiO ₂ buffer layer was dry-etched with a fluorine-based gas so that the absorber pattern was not damaged and the pattern became an etching mask. Thus, the reflective mask of this example was produced.
When this mask is irradiated with EUV light, the EUV light is reflected only at the pattern portion on the surface of the reflective layer 12, thereby fulfilling a function as a reflective mask.
For comparison, a sample of a single EUV light absorption layer in which the uppermost low reflection layer 15 of Reference Example 1 was not provided was manufactured by the conventional process shown in FIG. The film thickness of the single EUV light absorption layer at this time was set to 70 nm, which is the same value as the total film thickness of the two layers of the EUV light absorber layer according to this reference example and the low reflection layer for inspection light.

FIG. 12 shows the reflectance values on the absorber pattern surface of the mask with respect to light having a wavelength of 190 nm to 690 nm. In the figure, the two layers are the reflectance of the surface of the two-layer absorption layer of this reference example mask, and the single layer is the reflectance of the surface of the single-layer absorption layer of the conventional mask. Further, ML in the figure is a reflection layer of EUV light. In the case of this reference example mask, it can be seen that the wavelength region having a low reflectance is relatively wide.
From this result, when the pattern inspection light wavelength is 257 nm, the reflectance of the low reflective layer surface of this reference example mask at this wavelength is 5.2%, and the reflectance of the buffer layer (SiO ₂ ) at this wavelength is also the same. Since it was 42.1%, the contrast between the low reflection layer surface and the buffer layer surface at this wavelength is 1: 8.1 in terms of the ratio of these reflectances, and the contrast value represented by the above definition formula Was 78%. Further, the reflectance ratio between the low reflective layer and the multilayer reflective film was 1: 11.5, and the contrast was 84%.
On the other hand, the reflectance of the absorption layer surface of the conventional mask at the above wavelength is 43.4%, and the contrast between the absorption layer surface and the buffer layer surface at this wavelength is expressed by the ratio of these reflectances. : 0.97, and the contrast value was 1.5%. Further, the reflectance ratio between the absorbing layer and the multilayer reflective film was 1: 1.4, and the contrast was as low as 16%.

Further, in this reference example mask, the reflectivity of the EUV light with respect to the EUV light having a wavelength of 13.4 nm on the surface of the low reflective layer on the absorber layer 16 and the surface of the reflective layer was 0.6% and 62.4%, respectively. Therefore, the contrast between the surface of the absorber layer 16 and the surface of the reflective layer with respect to EUV light is represented as 1: 104, and the contrast value is 98%. Similarly, the contrast between the surface of the single-layer absorption layer and the surface of the reflective layer with respect to EUV light of the conventional mask was 1: 105, and the contrast value was 98%.
Next, as a result of pattern transfer onto the semiconductor substrate using the apparatus of FIG. 8 using the reflective mask of this reference example, the accuracy of the reflective mask of this reference example is 16 nm or less, which is the required precision of the 70 nm design rule. It was confirmed that.
From the above results, the mask of this reference example can obtain a high contrast with respect to EUV light and also a high contrast with respect to the pattern inspection wavelength, so that the pattern inspection can be performed accurately and rapidly. On the other hand, the conventional mask can obtain a high contrast with respect to EUV light, but has a very poor contrast with respect to the pattern inspection wavelength, so that an accurate pattern inspection is difficult.
It should be noted that when a mask was fabricated in exactly the same manner as in this reference example except that a MoSiON thin film was formed as the low reflection layer 15 for the inspection light in this reference example, the inspection wavelength and EUV light were also the same as in this reference example. High contrast was obtained for both.

(Reference Example 2)
In the same manner as in Reference Example 1, a reflective layer 12 for EUV light was formed on the substrate 11.
A chromium nitride film was formed as a buffer layer 13 on the reflective layer 12 to a thickness of 50 nm. This chromium nitride film was formed by a DC magnetron sputtering method, a Cr target was used for film formation, and a gas in which 10% of nitrogen was added to Ar was used as a sputtering gas.
In the formed chromium nitride film, X was 0.1 in Cr _1-X N _X. The film stress of this chromium nitride film was +40 MPa in terms of 100 nm. The reflectance of this chromium nitride film with respect to light having a wavelength of 257 nm is 52%. The surface roughness of the chromium nitride film surface was 0.27 nmRms.
Next, a nitride (TaBN) film of tantalum boron alloy was formed to a thickness of 50 nm as the EUV light absorber layer 14 on the buffer layer 13 composed of a chromium nitride film. This TaBN film was formed by DC magnetron sputtering using a target containing Ta and B, adding 10% nitrogen to Ar. The composition ratio of this TaBN film was 0.8 for Ta, 0.1 for B, and 0.1 for N. The crystal state of the TaBN film was amorphous.

A tantalum boron alloy nitride (TaBN) film having a thickness of 15 nm was further formed as a low reflection layer 15 on the TaBN absorber layer. The TaBN film as the low reflective layer was formed by adding 40% nitrogen to Ar using a target containing Ta and B by DC magnetron sputtering. At this time, the same target was used in the same deposition chamber as the lower TaBN film, and the lower layer and the upper layer were continuously formed by changing the amount of nitrogen gas. The composition ratio of the TaBN film as the low-reflection layer formed here is such that the proportion of nitrogen is larger than that of the TaBN film of the EUV light absorber layer, Ta is 0.5, B is 0.1, N was set to 0.4. This upper TaBN film was also amorphous.
This TaBN film has a refractive index of 2.3 and a extinction coefficient of 1.0 in light with a wavelength of 257 nm. Moreover, the absorption coefficient with respect to EUV light with a wavelength of 13.4 nm is 0.036. Further, the surface roughness was 0.25 nmRms, and it was very smooth.
The reflectance with respect to light having a wavelength of 257 nm on the low reflection layer thus obtained was 18%. Further, the total stress of the EUV light absorber layer and the low reflection layer was −50 MPa in terms of 100 nm.
The reflective mask blanks of Reference Example 2 were obtained as described above.

Next, an EUV reflective mask having a pattern for 16 Gbit-DRAM having a design rule of 0.07 μm was produced using the produced mask blanks as in Reference Example 1.
First, an absorber pattern was formed on the low reflection layer and the absorber layer in the same manner as in Reference Example 1. Here, the absorber pattern was inspected using light having a wavelength of 257 nm as inspection light. The ratio between the reflectance of the buffer layer and the reflectance on the low-reflection layer with respect to the inspection light was 1: 0.35, and the contrast value was 48%. Thus, sufficient contrast was obtained in the inspection.
Next, the buffer layer made of chromium nitride was removed by dry etching according to the absorber pattern. For dry etching, a mixed gas of chlorine and oxygen was used.
As described above, the reflective mask of Reference Example 2 was obtained. When the inspection of the absorber pattern was performed again using the inspection light having a wavelength of 257 nm on the obtained reflective mask, the ratio between the reflectance of the EUV reflection layer and the reflectance on the low reflection layer with respect to the inspection light is It was 1: 0.3, the contrast value was 50%, and a sufficient contrast was obtained even in the confirmation inspection. Further, when the reflectance of the obtained reflective mask was measured with EUV light having a wavelength of 13.4 nm and an incident angle of 5 degrees, it had a good reflection characteristic of 65%.
Furthermore, as a result of performing exposure transfer to the semiconductor substrate shown in FIG. 8 using the reflective mask of this reference example, it was confirmed that the film had sufficient exposure characteristics. That is, it was confirmed that the accuracy of the EUV reflective mask of this reference example was 16 nm or less, which is the required accuracy of the 70 nm design rule.

(Reference Example 3)
This reference example is different from the reference example 2 in that a tantalum boron alloy oxynitride (TaBNO) film is used as the low reflection layer.
In the same manner as in Reference Example 2, an EUV light reflection layer 12, a buffer layer 13, and an EUV light absorber layer 14 were formed on a substrate 11.
Next, a tantalum boron alloy oxynitride (TaBNO) film having a thickness of 15 nm was formed as a low reflection layer 15 on the EUV light absorber layer 14. This TaBNO film was formed by adding 10% nitrogen and 20% oxygen to Ar using a target containing Ta and B by DC magnetron sputtering. The composition ratio of the TaBNO film of the low reflection layer formed here was 0.4 for Ta, 0.1 for B, 0.1 for N, and 0.4 for O. The surface roughness of the TaBNO low reflection layer was 0.25 nmRms and was very smooth. The crystalline state of this TaBNO film was amorphous. The lower TaBN film and the upper TaBNO film were continuously formed using the same target while changing the type of gas in the same film formation chamber.

This TaBNO film has a refractive index of 2.4 and an extinction coefficient of 0.5 for light having a wavelength of 257 nm. Moreover, the absorption coefficient with respect to EUV light with a wavelength of 13.4 nm is 0.036.
The reflectance with respect to light having a wavelength of 257 nm on the low reflection layer thus obtained was 10%. Further, the total stress of the EUV light absorber layer and the low reflection layer was −50 MPa in terms of 100 nm.
As described above, a reflective mask blank of Reference Example 3 was obtained.
Next, an EUV reflective mask having a pattern for 16 Gbit-DRAM having a design rule of 0.07 μm was produced using the produced mask blanks as in Reference Example 1.
First, an absorber pattern was formed on the low reflection layer and the absorber layer in the same manner as in Reference Example 1. Here, the absorber pattern was inspected using light having a wavelength of 257 nm as inspection light. The ratio between the reflectance of the buffer layer and the reflectance on the low reflection layer with respect to the inspection light was 1: 0.19, and the contrast value was 68%. Thus, sufficient contrast was obtained in the inspection.
Next, as in Reference Example 2, the buffer layer made of chromium nitride was removed by dry etching according to the absorber pattern.

As described above, a reflective mask of this reference example 3 was obtained. When the inspection of the absorber pattern was performed again on the obtained reflective mask using inspection light having a wavelength of 257 nm, the ratio between the reflectance of the EUV reflection layer and the reflectance on the low reflection layer with respect to the inspection light was It was 1: 0.17, the contrast value was 71%, and sufficient contrast was obtained even in the confirmation inspection. Further, when the reflectance of the obtained reflective mask was measured with EUV light having a wavelength of 13.4 nm and an incident angle of 5 degrees, it had a good reflection characteristic of 65%.
Furthermore, as a result of performing exposure transfer to the semiconductor substrate shown in FIG. 8 using the reflective mask of this reference example, it was confirmed that the film had sufficient exposure characteristics. That is, it was confirmed that the accuracy of the EUV reflective mask of this reference example was 16 nm or less, which is the required accuracy of the 70 nm design rule.

(Reference Example 4)
Similarly to Reference Example 2, an absorber lower layer composed of a Mo / Si reflective multilayer film, a CrN buffer layer of 50 nm, and a TaBN film of 50 nm was formed on a glass substrate.
Next, a film made of Mo, Si, and N (MoSiN) was formed to a thickness of 10 nm as an upper low reflection layer. The film formation method was a DC magnetron sputtering method using a target containing Si and Mo and a gas containing argon and nitrogen. The composition of the obtained MoSiN film was Mo: Si: N = 23: 27: 50, and the crystal state was amorphous.
Further, the refractive index in light having a wavelength of 260 nm is 2.56, the extinction coefficient is 0.97, the refractive index in light having a wavelength of 190 nm is 2.39, and the extinction coefficient is 1.05. Further, the surface roughness on the surface of the MoSiN film was very smooth at 0.25 nmRms. The reflectance of the MoSiN film surface with respect to the inspection light having a wavelength of 257 nm was 17%.
In this way, a reflective mask blank of Reference Example 4 was obtained.
Next, using this mask blank, a reflective mask having a pattern for 16 Gbit-DRAM having a design rule of 0.07 μm was produced.
First, in the same manner as in Reference Example 1, a resist pattern was formed on the low reflective layer. Subsequently, the MoSiN low reflection layer was formed in a pattern along the resist pattern by dry etching using fluorine gas, and a part of the TaBN film under the absorber was exposed.

Next, the exposed TaBN film was formed in the same pattern as the MoSiN film by dry etching using chlorine gas, and a part of the CrN buffer layer was exposed.
Here, the absorber pattern was inspected using inspection light having a wavelength of 257 nm. The ratio of the reflectivity to the inspection light on the absorber layer surface and the buffer layer surface was 1: 3, and a contrast value of 50% was sufficient.
Similarly to Reference Example 1, after the defect was corrected using FIB, the exposed CrN buffer layer was removed in the same pattern as the absorber by dry etching using chlorine and oxygen.
As described above, the reflective mask of Reference Example 4 was obtained.
The reflective mask was subjected to a final pattern inspection using inspection light having a wavelength of 257 nm. The ratio of the reflectance to the inspection light on the surface of the absorber layer and the surface of the multilayer reflective film was 1: 3.5, and a contrast value of 56% was sufficient.
When the pattern was transferred to the resist-coated semiconductor substrate (silicon wafer) using the reflective mask of Reference Example 4, the accuracy of the reflective mask of this example was 16 nm or less, which is the required accuracy of the 70 nm design rule. I was able to confirm that there was.

(Reference Example 5)
Similarly to Reference Example 2, an absorber lower layer composed of a Mo / Si reflective multilayer film, a CrN buffer layer of 50 nm, and a TaBN film of 50 nm was formed on a glass substrate.
Next, a film (MoSiON) made of Mo, Si, O, and N was formed to a thickness of 20 nm as an upper low reflection layer. The film forming method was a DC magnetron sputtering method using a target containing Si and Mo and a gas containing argon, nitrogen and oxygen. The composition of the obtained MoSiON film was Mo: Si: O: N = 19: 19: 19: 43 and had an amorphous structure. Further, the refractive index in light having a wavelength of 260 nm is 2.01, the extinction coefficient is 0.46, the refractive index in light having a wavelength of 190 nm is 1.91, and the extinction coefficient is 0.52.
Further, the surface roughness on the surface of the MoSiON film was very smooth at 0.25 nmRms. The reflectance of the MoSiON film surface with respect to the inspection light having a wavelength of 257 nm was 4.4%.
In this way, a reflective mask blank of Reference Example 5 was obtained.
Next, using this mask blank, a reflective mask having a pattern for 16 Gbit-DRAM having a design rule of 0.07 μm was produced.
First, in the same manner as in Reference Example 1, a resist pattern was formed on the low reflective layer. Subsequently, the MoSiON low reflection layer was formed in a pattern along the resist pattern by dry etching using fluorine gas, and a part of the TaBN film under the absorber was exposed.
Next, the exposed TaBN film was formed in the same pattern as the MoSiON film by dry etching using chlorine gas, and a part of the CrN buffer layer was exposed.

Here, the absorber pattern was inspected using inspection light having a wavelength of 257 nm. The ratio of the reflectance to the inspection light on the surface of the absorber layer and the surface of the buffer layer was 1:12, and the contrast value was 84%, and a good contrast was obtained.
Similarly to Reference Example 1, after the defect was corrected using FIB, the exposed CrN buffer layer was removed in the same pattern as the absorber by dry etching using chlorine and oxygen.
As described above, the reflective mask of Reference Example 5 was obtained.
The reflective mask was subjected to a final pattern inspection using inspection light having a wavelength of 257 nm. The ratio of the reflectance to the inspection light on the absorber layer surface and the multilayer reflective film surface was 1:14, and a good contrast of 86% was obtained.
Further, when the pattern was transferred to the resist-coated semiconductor substrate (silicon wafer) using the reflective mask of this reference example, the accuracy of the reflective mask of this reference example 5 was 16 nm, which is the required accuracy of the 70 nm design rule. It was confirmed that the following.

(Reference Example 6)
Similarly to Reference Example 2, an absorber lower layer composed of a Mo / Si reflective multilayer film, a CrN buffer layer of 50 nm, and a TaBN film of 50 nm was formed on a glass substrate.
Next, a film made of Si, O, and N (SiON) was formed to a thickness of 22 nm as an upper low reflection layer. The film forming method was a DC magnetron sputtering method using a Si target and using a gas containing argon, oxygen and nitrogen. The composition of the obtained SiON film was Si: O: N = 28: 62: 10. Further, the refractive index in light having a wavelength of 260 nm is 1.74, the extinction coefficient is 0.0018, the refractive index in light having a wavelength of 190 nm is 1.86, and the extinction coefficient is 0.0465.
The surface roughness on the SiON film surface was 0.3 nmRms. The reflectance of the SiON film surface with respect to the inspection light having a wavelength of 257 nm was 5%.
In this way, a reflective mask blank of Reference Example 6 was obtained.
Next, using this mask blank, a reflective mask having a pattern for 16 Gbit-DRAM having a design rule of 0.07 μm was produced.
First, in the same manner as in Reference Example 1, a resist pattern was formed on the low reflective layer. Subsequently, the SiON low reflection layer was formed in a pattern along the resist pattern by dry etching using a gas containing fluoride, and a part of the TaBN film under the absorber was exposed.
Next, the exposed TaBN film was formed in the same pattern as the SiON film by dry etching using chlorine gas, and a part of the CrN buffer layer was exposed.

Here, the absorber pattern was inspected using inspection light having a wavelength of 257 nm. The ratio of the reflectance to the inspection light on the absorber layer surface and the buffer layer surface was 1: 10.4, and the contrast value was 82%, which was a good contrast.
Similarly to Reference Example 1, after the defect was corrected using FIB, the exposed CrN buffer layer was removed in the same pattern as the absorber by dry etching using chlorine and oxygen.
As described above, the reflective mask of Reference Example 6 was obtained.
The reflective mask was subjected to a final pattern inspection using inspection light having a wavelength of 257 nm. The ratio of the reflectance to the inspection light on the absorber layer surface and the multilayer reflective film surface was 1:12, and a good contrast value of 85% was obtained.
Further, when the pattern was transferred to the semiconductor substrate with a resist (silicon wafer) using the reflective mask of this reference example, the accuracy of the reflective mask of this reference example 6 was 16 nm, which is the required accuracy of the 70 nm design rule. It was confirmed that the following.

(The invention's effect)
As described above in detail, according to the present invention, the substrate has a reflection layer that reflects exposure light in a short wavelength region including the EUV region, and an absorber layer that absorbs the exposure light, and this absorption. The body layer has at least a two-layer structure in which the exposure light absorber layer in the short wavelength region including the EUV region is the lower layer, the inspection light low reflection layer used for the mask pattern inspection is the upper layer, and the upper layer has a low reflection property. By selecting a specific material as a layer, the function of the absorber layer on the surface of the reflective mask to be formed is separated into a layer that absorbs exposure light and a layer that has a low reflectance with respect to the mask pattern inspection light wavelength. As a result, it has a sufficient exposure light absorption function and remarkably reduces the reflectance with respect to the inspection light wavelength on the surface of the absorber pattern. Since the difference in reflectance with respect to the inspection light wavelength from the surface of the reflective layer becomes large and sufficient contrast is obtained during pattern inspection, a conventional mask inspection machine that uses light in the deep ultraviolet region as inspection light is used. Thus, the mask pattern can be accurately and quickly inspected.

In addition, the effect of the present invention is further exhibited by selecting a specific substance as the lower exposure light absorber layer in the absorber layer in consideration of the material of the upper low reflection layer.
In addition, by having an intermediate region in which the composition continuously changes from the lower layer composition to the upper layer composition between the lower layer and the upper layer of the absorber layer, the upper layer and the lower layer are formed when the pattern is formed on the absorber layer. Therefore, a pattern having a smooth cross-sectional structure is easily obtained, and the adhesion between the upper layer and the lower layer is improved.
Further, by providing a buffer layer between the exposure light reflection layer and the absorber layer, the reflection layer can be protected during pattern formation on the absorber layer. In the present invention, even in the case of having such a buffer layer, in order to significantly reduce the reflectance with respect to the inspection light wavelength on the surface of the absorber pattern, it is exposed on the absorber pattern surface of the uppermost layer and a portion without this pattern. The difference in reflectance with respect to the inspection light wavelength with respect to the buffer layer surface can be made large, and sufficient contrast can be obtained during pattern inspection.

In addition, the reflective mask blank of the present invention is manufactured by forming a reflective layer that reflects exposure light on the substrate, an exposure light absorber layer, and a low-reflection layer for inspection light thereon. A well-known film forming method can be applied, and manufacturing is easy and inexpensive mask blanks can be provided. By continuously forming the upper low-reflection layer and the lower absorber layer in the same film formation chamber, the substrate is not taken out of the film formation chamber or left unattended. In addition, a good interface can be obtained without alteration, an absorber layer can be formed with good reproducibility and controllability, and the advantage that the film forming process is not complicated is also obtained.
In addition, after forming the exposure light absorber layer, by processing the surface of the absorber layer to form a low reflection layer for inspection light, it is possible to shorten the time required for changing the film formation conditions, etc. Simplify and reduce work time.
In addition, the reflective mask of the present invention is manufactured by forming at least the absorber layer in a mask blank in a pattern. However, the reflective mask can be easily manufactured by applying a known patterning means, and an inexpensive reflective mask is provided. it can.
Further, by transferring a pattern onto a semiconductor substrate using the reflective mask of the present invention, a semiconductor having a highly accurate pattern can be obtained.

It is a schematic sectional drawing which shows one Embodiment of the mask blank which concerns on this invention. It is a schematic sectional drawing which shows one Embodiment of the reflective mask which concerns on this invention. It is the figure which plotted the reflectance R in the inspection wavelength of 190 nm on the axis of n and k when the material which has various refractive index n and extinction coefficient k as a low reflection layer was formed at 10 nm. It is the figure which plotted the reflectance R in the inspection wavelength of 260 nm on the axis of n and k at the time of forming the material which has various refractive index n and extinction coefficient k as a low reflection layer at 10 nm. It is the figure which plotted the reflectivity R in the test | inspection wavelength of 190 nm on the axis of n and k when the material which has various refractive index n and extinction coefficient k was formed at 20 nm as a low reflection layer. It is the figure which plotted the reflectance R in the inspection wavelength of 260 nm on the axis of n and k at the time of forming the material which has various refractive index n and extinction coefficient k as 20 nm as a low reflection layer. It is a schematic sectional drawing which shows the manufacturing process of the reflective mask of this invention. It is a schematic block diagram of the pattern transfer apparatus using a reflective mask. It is a figure which shows the value of the reflectance with respect to the light of the wavelength of 190 nm to 690 nm in Example 1 of this invention and the conventional reflective mask. It is a figure which shows the value of the reflectance with respect to the light of the wavelength from 190 nm to 690 nm in Example 2 of this invention and the conventional reflective mask. 6 is a nitrogen and oxygen composition diagram in the film thickness direction of the absorber layer in Example 5. FIG. It is a figure which shows the value of the reflectance with respect to the light of the wavelength of 190 nm to 690 nm in the reference example 1 and the conventional reflective mask. It is a schematic sectional drawing which shows the manufacturing process of the conventional reflective mask.

Explanation of symbols

1 Mask Blanks 2 Reflective Mask 11 Substrate 12 Reflective Layer 13 Buffer Layer 14 Exposure Light Absorber Layer 15 Low Reflective Layer 16 Absorber Layer 21 Pinhole Defect 22 Insufficient Etching 26 Reflective Layer Pattern 31 EUV Light 50 Pattern Transfer Device

Claims (16)

On the substrate, a reflective layer that reflects exposure light in a short wavelength range including the extreme ultraviolet region in order, a buffer layer for protecting the reflective layer when forming a pattern on the absorber layer, and an absorber layer that absorbs the exposure light The mask blank has an absorber layer composed of an absorber of exposure light in a short wavelength region including an extreme ultraviolet region as a lower layer, and an inspection light used for inspection of a mask pattern. It has at least a two-layer structure with a low reflection layer made of an absorber as an upper layer, the upper layer is made of a material containing tantalum (Ta), boron (B), and oxygen (O), and the buffer layer is made of Cr or It is made of a material mainly composed of Cr ,
The reflectance for the inspection light decreases in the order of the multilayer reflective film surface, the buffer layer surface, and the absorber layer surface, and the surface of the absorber layer with respect to the wavelength of the light used for the inspection of the pattern formed on the absorber layer. A reflective mask blank characterized by having a reflectance of 20% or less . A mask blank comprising a reflective layer that reflects exposure light in a short wavelength region including an extreme ultraviolet region and an absorber layer that absorbs exposure light on a substrate in order, wherein the absorber layer has an extreme ultraviolet region It is an at least two-layer structure in which an absorber layer composed of an absorber of exposure light in a short wavelength region including a lower layer and a low reflection layer composed of an absorber of inspection light used for mask pattern inspection as an upper layer, the upper layer is made of a material containing tantalum (Ta) and boron (B) and oxygen (O), see containing oxygen (O) in the range of 30at% ~70at%,
A buffer layer is provided between the reflective layer and the absorber layer to protect the reflective layer when forming a pattern on the absorber layer, and the buffer layer is formed of Cr or a substance containing Cr as a main component. Has been
The reflectance for the inspection light decreases in the order of the multilayer reflective film surface, the buffer layer surface, and the absorber layer surface, and the surface of the absorber layer with respect to the wavelength of the light used for the inspection of the pattern formed on the absorber layer. A reflective mask blank characterized by having a reflectance of 20% or less . On the substrate, a reflective layer that reflects exposure light in a short wavelength region including the extreme ultraviolet region in order, a buffer layer for protecting the reflective layer when forming a pattern on the absorber layer, and an absorber layer that absorbs the exposure light The mask blank has an absorber layer composed of an absorber of exposure light in a short wavelength region including an extreme ultraviolet region as a lower layer, and an inspection light used for inspection of a mask pattern. It has at least a two-layer structure with a low reflection layer made of an absorber as an upper layer, the upper layer is made of a material containing at least one of Ta and Si or Ge, and oxygen, and the buffer layer is Cr or Cr are formed of a material mainly composed of,
The reflectance for the inspection light decreases in the order of the multilayer reflective film surface, the buffer layer surface, and the absorber layer surface, and the surface of the absorber layer with respect to the wavelength of the light used for the inspection of the pattern formed on the absorber layer. A reflective mask blank characterized by having a reflectance of 20% or less . The reflective mask blank according to any one of claims 1 to 3 , wherein the lower layer of the absorber layer is made of a material containing Ta. 5. The reflective mask blank according to claim 4, wherein the lower layer of the absorber layer is made of a material containing Ta and at least B. The reflection according to any one of claims 1 to 5 , wherein an intermediate region whose composition continuously changes from a lower layer composition to an upper layer composition is provided between the lower layer and the upper layer of the absorber layer. Type mask blanks. The contrast between the reflected light on the surface of the reflective layer and the reflected light on the surface of the absorber layer with respect to the wavelength of light used for inspection of the pattern formed on the absorber layer is 40% or more, The reflective mask blank according to any one of claims 1 to 6 . A buffer layer is provided between the reflective layer and the absorber layer to protect the reflective layer during pattern formation on the absorber layer, and is used for inspection of the pattern formed on the absorber layer. the reflective mask according to any one of claims 1 to 7 and reflected light, the contrast of the reflected light at the surface of the absorber layer, characterized in that at least 40% in the buffer layer surface to the wavelength of Blanks. The reflective mask blank according to any one of claims 1 to 8 wherein the surface roughness of the absorber layer surface to equal to or less than 0.5 nm RMS. The material forming the upper layer of the absorber layer has a refractive index n and an extinction coefficient k at the wavelength of the inspection light satisfying the condition that n is 1.5 to 3.5 and k is 0.7 or less. the reflective mask blank according to any one of claims 1 to 9, wherein. Based on the relationship between the reflectance of the absorber layer surface with respect to the wavelength of the inspection light and the thickness of the low reflection layer, the reflectance of the absorber surface with respect to the inspection light wavelength is minimal. the reflective mask blank according to any one of claims 1 to 10, characterized in that it is chosen to be. The reflective mask blank according to claim 11, wherein the thickness of the upper low reflection layer is 5 to 30 nm. A reflection type mask blank according to any one of claims 1 to 12 , wherein the absorber layer is formed in a pattern. Method for producing a reflective mask characterized by having a step of forming at least low reflection layer and the exposure light absorbing layer in pattern in the reflective mask blank according to any one of claims 1 to 12. A method for producing a reflective mask blank according to any one of claims 1 to 12 , wherein a reflective layer for reflecting exposure light in a short wavelength region including an extreme ultraviolet region is formed on a substrate, and the reflection is performed. By forming an absorber layer that absorbs the exposure light on the layer, and by treating the surface of the absorber layer, the surface near the surface of the absorber layer has a low resistance to inspection light used for mask pattern inspection. A method for producing a reflective mask blank, comprising forming a reflective layer. A method for manufacturing a semiconductor, comprising: transferring a pattern onto a semiconductor substrate using the reflective mask according to claim 13 .

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