JP5076620B2 - Method for smoothing glass substrate surface - Google Patents

Description

The present invention relates to a method for smoothing the surface of a glass substrate. More specifically, the present invention relates to a method for smoothing the surface of a glass substrate for a reflective mask blank for EUV (Extreme Ultraviolet) lithography (hereinafter referred to as “EUV mask blank” in this specification). More specifically, the present invention relates to a method for smoothing the surface of a glass substrate for EUV mask blank having a concave defect.
The present invention also relates to an EUV mask blank using an EUV mask blank substrate whose surface has been smoothed by the smoothing method, and an EUV mask obtained by patterning the EUV mask blank.

  The EUV mask blank is manufactured by forming a reflective layer that reflects EUV light and an absorber layer that absorbs EUV light in this order on a glass substrate. As the reflective layer, a molybdenum (Mo) layer, which is a high refractive layer, and a silicon (Si) layer, which is a low refractive layer, are alternately laminated, thereby increasing the light reflectance when EUV light is irradiated on the surface of the layer. The multilayer reflective film formed is most common.

  If minute irregularities exist on the surface of the substrate used for manufacturing the EUV mask blank, the reflective layer and the absorber layer formed on the substrate are adversely affected. For example, if minute irregularities exist on the surface of the substrate, the periodic structure of the multilayer reflective film formed as a reflective layer on the substrate is disturbed, and the pattern on the mask is exposed to a photosensitive organic film on the Si wafer using an exposure apparatus. When transferred to (so-called photoresist film), a part of a desired pattern may be lost or an extra pattern may be formed in addition to the desired pattern. Disturbance of the multilayer reflective film periodic structure caused by unevenness present on the substrate is called a phase defect and is a serious problem, and it is desirable that there is no unevenness of a predetermined size or more on the substrate.

Non-Patent Documents 1 and 2 describe requirements regarding defects of EUV masks and EUV mask blanks, and the requirements regarding these defects are very strict. Non-Patent Document 1 is acceptable because if a defect exceeding 50 nm exists on the substrate, the structure of the multilayer reflective film is disturbed, and an unexpected shape is generated in the pattern projected onto the resist on the Si wafer. It is stated that it is not possible. Non-Patent Document 1 discloses that the surface roughness of the substrate is rms (root mean square roughness) in order to prevent the line edge roughness from increasing in the pattern projected onto the resist on the Si wafer. It is described that it is necessary to be less than 0.15 nm. Non-Patent Document 2 describes that a mask blank used for EUV lithography coated with a multilayer reflective film cannot have a defect exceeding 25 nm.
Non-Patent Document 3 describes how large a defect on a substrate can be transferred. Non-Patent Document 3 describes that there is a possibility of changing the line width of an image printed with phase defects. A phase defect having a surface bump with a height of 2 nm and a FWHM (full width at half maximum) of 60 nm is a boundary that determines whether or not the defect may be transferred. It is described as causing an unacceptable line width change of 20% (140 nm on the mask) for a 35 nm line.

SEMI, P37-1102 (2002), “Specification for extreme ultraviolet lithography mask substrate” SEMI, P38-1102 (2002), “Specification for absorbing film stacks and multilayers on extreme ultraviolet lithography mask blanks” SPIE, vol. 4889, Alan Stivers., Et. Al., P.408-417 (2002), “Evaluation of the Capability of a Multibeam”. Confocal Inspection System for Inspection of EUVL Mask Blanks)

Convex defects such as particles such as foreign matter and fibers, and bumps on the substrate itself, among the minute irregularities present on the substrate surface, can be removed by conventional wet cleaning methods using hydrofluoric acid or ammonia water, brush cleaning, or precision polishing. Etc. can be removed.
However, concave defects such as pits and scratches cannot be removed by these methods. In addition, when a wet cleaning method using hydrofluoric acid or ammonia water is used to remove the convex defects, it is necessary to slightly etch the substrate surface in order to lift off the convex defects from the substrate. For this reason, a new concave defect may be generated on the substrate surface. Even when brush cleaning is used to remove the convex defect, there is a possibility that a new concave defect is generated on the substrate surface.

An object of the present invention is to provide a method for smoothing the surface of a substrate having a concave defect such as a pit or a scratch in order to solve the above-described problems in the prior art.
Another object of the present invention is to provide a glass substrate for an EUV mask blank obtained by a method of smoothing the substrate surface.
Another object of the present invention is to provide a substrate with a reflective layer for EUV mask blanks and an EUV mask blank using the EUV mask blank substrate.

To achieve the above object, the present invention is a method of smoothing a glass substrate surface for a reflective mask blank for EUV lithography,
Forming a thin film on a glass substrate;
Detecting a concave defect present on the glass substrate;
A step of locally heating the thin film directly above the detected concave defect to cause a chemical reaction accompanied by an increase in volume in the material constituting the thin film, and a reflective mask for EUV lithography, comprising: A method of smoothing the glass substrate surface for blank (hereinafter referred to as “substrate smoothing method (1) of the present invention”) is provided.

  In the substrate smoothing method (1) of the present invention, the chemical reaction is preferably an oxidation reaction.

  In the substrate smoothing method (1) of the present invention, the chemical reaction is preferably a nitriding reaction.

  Further, in the substrate smoothing method (1) of the present invention, the thin film is selected from the group consisting of Al, B, Co, Cr, Ge, Hf, Mo, Nb, Ni, Ru, Si, Ta, Ti, Zn, and Zr. It is preferable that at least one selected as a main constituent material.

In the substrate smoothing method (1) of the present invention, the thin film includes at least two layers of films having different constituent materials,
The chemical reaction may be accompanied by mutual diffusion between materials constituting the two-layer film.

  When the thin film includes at least two layers having different constituent materials, one of the at least two layers is formed of Al, B, Co, Cr, Ge, Hf, Mo, Nb, Ni, It is preferable that at least one selected from the group consisting of Ru, Si, Ta, Ti, Zn and Zr is a main constituent material.

  Moreover, in the board | substrate smoothing method (1) of this invention, it is preferable that the thickness of the said thin film is 0.5 to 10 times the maximum depth of the concave defect which exists in the said glass substrate.

  Moreover, in the board | substrate smoothing method (1) of this invention, it is preferable that the crystalline state of the site | part heated locally of the said thin film becomes amorphous by the said chemical reaction.

  Moreover, in the board | substrate smoothing method (1) of this invention, it is preferable that the crystalline state of the said thin film after the said local heating is amorphous.

  Moreover, in the board | substrate smoothing method (1) of this invention, it is preferable to perform the said local heating by irradiating a laser beam to the thin film immediately above the concave defect of the said glass substrate.

  In the case where the local heating is performed by laser light irradiation, it is preferable that the diameter of the laser light is not more than twice the diameter of the concave defect existing in the glass substrate.

In the case where the local heating is performed by laser light irradiation, the detection of the concave defect is performed by laser light irradiation,
It is preferable that the laser light source used for the local heating and the laser light source used for detecting the concave defect are the same laser light source.

Further, in the substrate smoothing method (1) of the present invention, an atomic force microscope (AFM), a scanning tunneling microscope (STM) or a stylus step meter having a heatable probe is used to detect the concave defect. use,
It is preferable that the local heating is performed by heating the probe approaching or contacting the thin film immediately above the concave defect.

  Moreover, in the board | substrate smoothing method (1) of this invention, you may grind the said thin film surface after the said local heating using a needle-shaped member.

  When the detection of the concave defect and the local heating are performed with a heatable probe of AFM, STM or a stylus step meter, the surface of the thin film after the local heating is ground using the probe. It is preferable.

In order to achieve the above object, the present invention is a method of smoothing a glass substrate surface for a reflective mask blank for EUV lithography,
Forming a thin film on a glass substrate;
Detecting a concave defect present on the glass substrate;
A step of locally anodizing the thin film immediately above the detected concave defect to cause a chemical reaction accompanied by an increase in volume in the material constituting the thin film, and a reflective type for EUV lithography, A method of smoothing the glass substrate surface for mask blank (hereinafter referred to as “substrate smoothing method (2) of the present invention”) is provided.

  Further, in the substrate smoothing method (2) of the present invention, the thin film is selected from the group consisting of Al, B, Co, Cr, Ge, Hf, Mo, Nb, Ni, Ru, Si, Ta, Ti, Zn, and Zr. It is preferable that at least one selected as a main constituent material.

  Moreover, in the board | substrate smoothing method (2) of this invention, it is preferable that the thickness of the said thin film is 0.5 times or more of the maximum depth of the concave defect which exists in the said glass substrate.

  In the substrate smoothing method (2) of the present invention, it is preferable that the crystalline state of the locally anodized portion of the thin film becomes amorphous due to the chemical reaction.

  In the substrate smoothing method (2) of the present invention, it is preferable that the crystalline state of the thin film after the local anodic oxidation is amorphous.

In the substrate smoothing method (2) of the present invention, an atomic force microscope (AFM), a scanning tunneling microscope (STM) or a stylus type step gauge having a probe that can be energized is used to detect the concave defect. ,
It is preferable that the local heating is performed by applying a voltage between the probe and the thin film approaching or contacting the thin film immediately above the concave defect.

  In the substrate smoothing method (2) of the present invention, the surface of the thin film after the local anodic oxidation may be ground using a needle-like member.

  When detecting the concave defect and the local anodization with an AFM, STM or stylus probe, the thin film surface after the local anodization is ground using the probe. Is preferred.

  In the present invention, a reflective layer for reflecting EUV light is formed on a reflective mask blank substrate for EUV lithography, the substrate surface of which is smoothed by the substrate smoothing methods (1) and (2) of the present invention. A substrate with a reflective layer for EUV lithography (hereinafter referred to as “substrate with a reflective layer of the present invention”) is provided.

  Further, the present invention provides a reflective mask blank for EUV lithography (hereinafter referred to as “the EUV mask blank of the present invention”) in which an absorber layer that absorbs EUV light is formed on the reflective layer of the substrate with a reflective layer of the present invention described above. ").

  The present invention also provides a reflective mask for EUV lithography (hereinafter referred to as “the EUV mask of the present invention”) obtained by patterning the above EUV mask blank of the present invention.

In the substrate smoothing method of the present invention, a thin film is formed on the surface of a glass substrate for EUV mask blank having a concave defect, and the thin film immediately above the concave defect, that is, the portion where the concave defect appears on the thin film is locally heated. Then, by causing a chemical reaction accompanied by an increase in volume to the material constituting the thin film (substrate smoothing method (1) of the present invention), or locally anodizing a site where a concave defect appears on the thin film Then, by causing a chemical reaction accompanied by an increase in volume in the material constituting the thin film (substrate smoothing method (2) of the present invention), the concave defects appearing on the thin film are reduced or eliminated. Thereby, the thin film surface used as the film-forming surface in which a reflective layer and an absorber layer are formed at the time of manufacture of an EUV mask blank can be smoothed, and smoothness can be improved to the level which does not have a problem as an EUV mask blank.
Convex defects present on the substrate surface can be removed by a conventional wet cleaning method using hydrofluoric acid or aqueous ammonia, brush cleaning or precision polishing. However, when these methods are carried out for the purpose of removing convex defects, new concave defects may occur on the substrate surface. In the substrate smoothing method of the present invention, the film-forming surface of the glass substrate on which such a new concave defect has occurred can be smoothed, and the smoothness can be improved to a level where there is no problem as an EUV mask blank.

Hereinafter, the substrate smoothing method of the present invention will be described with reference to the drawings.
In the substrate smoothing method of the present invention, the glass substrate surface for EUV mask blank, more specifically, the glass substrate surface (hereinafter referred to as “film formation” on the side where the reflective layer and the absorption layer are formed during the production of EUV mask blank). Used for the purpose of smoothing the surface. However, the surface of the glass substrate on the side where the conductive film for the electrostatic chuck is to be formed may be smoothed by the substrate smoothing method of the present invention when manufacturing the EUV mask blank. The case where the film-forming surface of the glass substrate for EUV mask blanks is smoothed is demonstrated below as an example.

When carrying out the substrate smoothing method of the present invention, first, the film formation surface of a glass substrate for EUV mask blank prepared in advance is polished using polishing abrasive grains such as cerium oxide, zirconium oxide, colloidal silica, Thereafter, the film formation surface is cleaned using an acidic solution such as hydrofluoric acid, silicic hydrofluoric acid, and sulfuric acid, an alkaline solution such as ammonia water, or pure water, and dried. When there are convex defects such as foreign matter, particles such as fibers, and bumps on the substrate itself on the film formation surface, they are removed by these procedures.
The substrate smoothing method of the present invention is preferably used for a film-formed surface from which convex defects have been removed by performing surface polishing and cleaning in the above-described procedure.

  A glass substrate for an EUV mask blank is required to have high smoothness and flatness over the entire film formation surface. Specifically, the film formation surface of the glass substrate is required to have a smooth surface with an rms (root mean square roughness) of 0.15 nm or less and a flatness of 50 nm or less. Even when these required values are satisfied, localized concave defects called pits and scratches may still exist on the film formation surface.

When the size of the concave defects existing on the film formation surface of the glass substrate is very small, there is no possibility that the EUV mask blank manufactured using the glass substrate will be adversely affected. However, if there are concave defects larger than a certain size on the film formation surface of the glass substrate, the concave defects appear on the surface of the reflective layer and the absorber layer formed on the film formation surface, and are manufactured using the glass substrate. This may cause defects in the EUV mask blank.
How large a concave defect exists on the film-forming surface of the glass substrate, but the defect of the EUV mask blank is unclear because it is affected by the diameter, depth, and shape of the concave defect. For example, when a concave defect having a diameter of 30 nm or more and a depth of 3 nm or more exists on the film formation surface of the glass substrate, a concave defect appears on the surface of the reflective layer or the absorber layer formed on the film formation surface, The multilayer structure may be disturbed, which may cause defects in the EUV mask blank manufactured using the glass substrate.

In addition to being excellent in smoothness and flatness, the glass substrate for EUV mask blank preferably has a low thermal expansion coefficient (0 ± 1.0 × 10 ⁻⁸ / ° C., more preferably 0 ± 0). .3 × 10 ⁻⁸ / ° C.) is preferable. Specific examples of the glass substrate having such a low thermal expansion coefficient include a glass substrate made of SiO ₂ —TiO ₂ glass and a glass substrate made of crystallized glass on which β-quartz solid solution is deposited.
Moreover, it is preferable that the glass substrate for EUV mask blanks is excellent in the tolerance to the washing | cleaning liquid used for the washing | cleaning etc. of the EUV mask blank or the photomask after pattern formation.
In addition, the glass substrate for EUV mask blank preferably has high rigidity in order to prevent deformation due to film stress of the reflective layer and the absorber layer formed on the glass substrate. In particular, those having a high specific rigidity of 3 × 10 ⁷ m ² / s ² or more are preferable.
The size, thickness and the like of the glass substrate for EUV mask blank are appropriately determined depending on the design value of the mask. As a specific example, for example, there is an external shape of about 6 inches (152.4 mm) square and a thickness of about 0.25 inches (6.3 mm).

  FIG. 1 is a schematic diagram showing the vicinity of a portion of a glass substrate where a concave defect exists. In FIG. 1, a concave defect 2 exists on the film forming surface 1 a of the glass substrate 1. The diameter of the concave defect 2 is, for example, 100 nm, and the depth is, for example, 30 nm.

In the substrate smoothing method (1) of the present invention, first, a step of forming a thin film on a glass substrate is performed. In this step, the thin film 3 is formed on the film formation surface 1 a of the glass substrate 1. FIG. 2 shows a state in which the thin film 3 is formed on the film forming surface 1a of the glass substrate 1 of FIG. In FIG. 2, the thickness of the thin film 3 is about 1.5 times the depth of the concave defect 2 and is about 45 nm. Since the thin film 3 spreads along the shape of the film formation surface 1 a of the glass substrate 1, the concave defect 4 appears in the thin film 3 immediately above the concave defect 2. In the substrate smoothing method (1) of the present invention, the surface of the thin film 3 is smoothed by reducing or eliminating the concave defects 4 appearing on the surface of the thin film 3.
In addition, the thin film 3 plays the role which reduces or eliminates the concave defect 4 by increasing a volume so that it may mention later. In addition to this function, the thin film 3 also has an effect of facilitating detection of very small concave defects 2 formed on the film formation surface 1a of the substrate 1. In applications where even a very small defect becomes a problem, such as a substrate for an EUV mask blank, even a defect that is difficult to detect with a normal optical inspection apparatus is regarded as a problem. However, by forming the thin film 3 as in the present invention, it becomes possible to detect the minute concave defect 2 formed on the film formation surface 1a of the substrate 1. The reason why it is possible to detect the minute concave defect 2 formed on the film formation surface 1a of the substrate 1 by forming the thin film 3 is that the defect detection is performed by irradiating the surface of the substrate with a laser, The reflection image is analyzed, but when such a thin film is formed on the substrate, the light reflectance of general glass increases from 4% to 10% or more, and a higher signal / noise ratio is obtained. This is because a defect image can be obtained.

The constituent material of the thin film 3 is not particularly limited as long as it causes a chemical reaction accompanied by an increase in volume during heating. Here, the chemical reaction that occurs at the time of heating is not particularly limited as long as it involves an increase in volume, but it can proceed only by heating and can proceed locally only at the heated part, and the chemical reaction Oxidation reaction or nitridation reaction is preferred because the accompanying increase in volume can be easily controlled. Note that when the oxidation reaction is performed, local heating may be performed in air or in an oxygen atmosphere. When performing the nitriding reaction, local heating may be performed in a nitrogen atmosphere.
However, the constituent material of the thin film 3 is likely to cause a chemical reaction during heating, and is excellent in the smoothness of the surface of the thin film 3 after causing a chemical reaction accompanied by an increase in volume by heating (hereinafter referred to as “thin film 3 after heating”). It is said that it is excellent in surface smoothness ”). Among them, at least one selected from the group consisting of Al, B, Co, Cr, Ge, Hf, Mo, Nb, Ni, Ru, Si, Ta, Ti, Zn, and Zr (hereinafter referred to as “Group A”). As a main constituent material, a chemical reaction is likely to occur during heating, the surface of the thin film 3 after heating is excellent in smoothness, and a reflective layer and an absorber layer formed on the thin film 3 when manufacturing an EUV mask blank. It is excellent in that it does not adversely affect Among them, the thin film 3 mainly composed of Hf, Nb, Si, Ta, Ti and Zr has an amorphous crystalline state after heating, particularly a crystalline state after an oxidation reaction by heating, and a crystalline state after a nitriding reaction by heating. It is more preferable because it tends to be.

The material constituting the thin film 3 is preferably a material having a high volume increase rate due to a chemical reaction that occurs during heating. Specifically, the material is preferably a material having a volume increase rate ΔV during heating calculated by the following formula of 10% or more, more preferably 30% or more.
ΔV (%) = (V ₂ −V ₁ ) / V ₁ × 100
Here, V ₁ is the volume of the material at normal temperature (20 ° C.), and V ₂ is the volume of the material after heating. Heating is preferably performed in the range of 50 to 500 ° C.
Hereinafter, in the present specification, the phrase “volume increase during heating” refers to volume increase due to a chemical reaction that occurs during heating.
In addition, all the materials of A group are (DELTA) V 50 to 250%.

As the thin film 3 satisfying the above conditions, it is preferable that at least one selected from “Group A” is a main constituent material. Therefore, the thin film 3 may use only one type of the group A as a constituent material or two or more types as a constituent material. Moreover, the thin film 3 may contain materials other than A group as a constituent material. However, when the thin film 3 includes a material other than the group A, it is preferable that 50 atomic% or more of the constituent materials of the thin film 3 is the material of the group A.
When the thin film 3 contains a material other than the group A, it is more preferable that 80 atomic% or more of the constituent materials of the thin film 3 is the material of the group A.
Of the Group A materials, Si, Ta, and Ti are preferable because both the oxidation reaction and the nitridation reaction proceed easily. Furthermore, Si is preferable in terms of productivity because the material of the film constituting the reflective multilayer film can be used as it is.

The thin film 3 may include at least two layers of films having different constituent materials. That is, the thin film 3 may be a laminate of two or more films. However, in this case, it is necessary that the materials constituting the laminated film are different from each other, cause a chemical reaction accompanied by mutual diffusion during heating, and that the chemical reaction is accompanied by an increase in volume. It becomes. Hereinafter, in the present specification, such a thin film 3 is referred to as a “thin film 3 made of a laminated body”. In the thin film 3 made of a laminated body, the above-mentioned group A materials can be used as materials constituting the individual films. However, even if it is a material other than the group A material, it can be used as a film material constituting the thin film 3 made of a laminate as long as it causes a chemical reaction accompanied by mutual diffusion with the material of the group A during heating. Can do.
Note that when the thin film 3 is a laminate of three or more layers, it is sufficient that the materials constituting the films in a stacked relationship are different from each other. For example, in the case of a configuration in which three layers are laminated, The uppermost film and the lowermost film may be made of the same material. In this case, the film positioned in the middle is made of a material different from the films positioned above and below the film.

The thickness of the thin film 3 formed on the film formation surface 1a of the glass substrate 1 varies depending on the depth of the concave defect 2 existing on the film formation surface 1a, but is about 0.5 to 10 times the depth of the concave defect 2. It is preferable that If the thickness of the thin film 3 is in the above range, the thin film 3 immediately above the concave defect 2 is locally heated by the procedure described later, thereby reducing or eliminating the concave defect 4 appearing on the surface of the thin film 3. The surface can be smoothed. If the thickness of the thin film 3 is less than 0.5 times the depth of the concave defect 2, the thin film 3 directly above the concave defect 2 is locally localized, depending on the volume increase rate during heating of the material constituting the thin film 3. There is a possibility that the concave defect 4 appearing on the surface of the thin film 3 cannot be sufficiently reduced when heated to a low temperature. On the other hand, if the thickness of the thin film 3 is more than 10 times the depth of the concave defect 2, heat spreads over a wide range due to the thermal conductivity of the material constituting the thin film 3, and only the thin film 3 directly above the concave defect 2 is present. It becomes difficult to locally heat. Also in this case, there is a possibility that the concave defect 4 appearing on the surface of the thin film 3 cannot be sufficiently reduced.
When a plurality of concave defects 2 are present on the film formation surface 1a of the glass substrate 1, the thin film 3 is about 0.5 to 10 times the depth of the concave defect having the largest depth (maximum depth of the concave defect). The thickness of. In the case of the thin film 3 made of a laminate, the thickness of the entire laminate is about 0.5 to 10 times the depth of the concave defect 2. The thickness of the thin film 3 is more preferably about 1 to 5 times the depth of the concave defect 2.

  However, in the substrate smoothing method (1) of the present invention, since the concave defects appearing on the surface of the thin film 3 are detected after the thin film 3 is formed, the concaves present on the film formation surface 1a of the glass substrate 1 when the thin film 3 is formed. The depth of defect 2 is unknown. For this reason, the thickness of the thin film 3 is such that the depth of the concave defect 2 that normally exists on the film formation surface 1a of the glass substrate 1, more specifically, the film formation surface 1a from which the convex defects have been removed by surface polishing and cleaning. It will be based on. On the film-forming surface 1a from which the convex defects have been removed by surface polishing and cleaning, there are usually concave defects 2 having a depth of about 1 to 50 nm. For this reason, the thickness of the thin film 3 is preferably about 5 to 500 nm, and more preferably about 5 to 250 nm, in view of facilitating detection of concave defects. In addition, in the case of the thin film 3 which consists of a laminated body, it is preferable that the thickness of the whole laminated body is about 5-100 nm, and it is more preferable that it is about 5-250 nm.

  In the substrate smoothing method (1) of the present invention, as a method of forming the thin film 3, various dry film forming methods such as a sputtering method such as a magnetron sputtering method and an ion beam sputtering method, a vacuum evaporation method, a CVD method, and the like are used. Can do. Among these, the sputtering method or the CVD method is preferable because there is little possibility of generating new convex defects (particles) at the time of forming a thin film. From the viewpoint of preventing the generation of new convex defects, the CVD method is suitable for the film formation surface 1a. From the viewpoint of the adhesion of the thin film 3, the sputtering method is particularly preferable. However, when the reflective layer and the absorber layer are formed on the thin film 3 after the substrate smoothing method of the present invention is performed, the sputtering method is preferable in that the same apparatus can be used.

In the substrate smoothing method (1) of the present invention, following the step of forming a thin film on a glass substrate, a step of detecting a concave defect present on the glass substrate is performed. Specifically, the position, diameter, depth, etc. of the concave defect existing on the glass substrate are measured. However, in this process, the concave defect 2 present on the surface of the thin film 3 is detected after the formation of the thin film 3 instead of detecting the concave defect 2 existing on the film formation surface 1a of the glass substrate 1 and then In the process to be performed, data necessary for locally heating the thin film 3 immediately above the concave defect 2 (hereinafter referred to as “concave defect data” in this specification) is collected. Specifically, data such as the position of the concave defect 4 on the glass substrate 1 and the shape and size (diameter, depth) of the concave defect 4 are collected.
As described above, by forming the thin film 3 on the film formation surface 1a of the substrate 1, a very small concave defect 2 (actually appeared on the surface of the thin film 3) formed on the film formation surface 1a. The concave defect 4) is easy to detect.
The detection of the concave defect 4 can be performed by a method that is usually used when detecting the concave defect existing on the glass substrate. Specifically, stylus profilometer, atomic force microscope (AFM), scanning tunneling microscope (STM), light cutting method (triangulation method), defocus detection method, optical stylus tracking method (focusing method) , Focus scanning method (scanning laser microscope), confocal laser defect inspection method, Nomarski differential interference method, and fringe scanning method. Among these, a method using laser light irradiation, that is, a confocal laser defect inspection method, a method in which a probe such as an AFM, STM, or a stylus profilometer is brought close to or in contact with the surface of the thin film 3 is next. It is preferable to perform the step of locally heating the thin film immediately above the concave defect to be performed. A method using a probe is more preferable in that the diameter and depth of the concave defect can be measured more accurately.

  In the substrate smoothing method (1) of the present invention, the material constituting the thin film is obtained by locally heating the thin film immediately above the detected concave defect following the step of detecting the concave defect existing on the glass substrate. A step of causing a chemical reaction with an increase in volume is performed. However, what is detected in the previous step is not the concave defect 2 present on the film formation surface 1 a of the glass substrate 1 but the concave defect 4 appearing on the surface of the thin film 3. Therefore, in this step, the thin film 3 immediately below the concave defect 4 is locally heated based on the concave defect data obtained in the previous step.

  Since the material constituting the thin film 3 causes a chemical reaction accompanied by an increase in volume during heating, when the thin film 3 directly below the concave defect 4 is locally heated, the thin film 3 immediately below the concave defect 4 forms the thin film 3. The volume increases locally due to the chemical reaction of the material. As a result, as shown in FIG. 3, the concave defect 4 is eliminated and the surface of the thin film 3 is smoothed.

In this step, the means for locally heating the thin film 3 immediately below the concave defect 4 is not particularly limited as long as it is a method capable of locally heating the thin film 3 immediately below the concave defect 4. As an example of a suitable method for locally heating the thin film 3 immediately below the concave defect 4, a method of irradiating the concave defect 4 with laser light can be mentioned. The condition for irradiating the concave defect 4 with laser light is not particularly limited as long as the thin film 3 directly under the concave defect 4 can be locally heated. However, if the diameter of the irradiated laser beam is too large with respect to the diameter of the concave defect 4, not only the thin film 3 directly under the concave defect 4 but also a wide range of thin film 3 is heated. It becomes difficult to heat only the thin film 3 locally. For this reason, it is preferable that the diameter of the laser beam to be irradiated is not more than twice the diameter of the concave defect 4. If the diameter of the laser beam to irradiate is 2 times or less than the diameter of the concave defect 4, when the diameter of the concave defect 4 is relatively small, for example, even when the diameter of the concave defect 4 is 30 nm or less, The concave defect 4 can be eliminated by laser light irradiation, and the thin film 3 can be flattened. The diameter of the laser beam to be irradiated is more preferably 1 times or less than the diameter of the concave defect 4.
However, if the diameter of the laser beam is too smaller than the diameter of the concave defect 4, it is preferable because it takes a long time to heat the thin film 3 immediately below the concave defect 4 or it is necessary to move the irradiation position of the laser beam. Absent. For this reason, the diameter of the laser beam is preferably 0.5 times or more the diameter of the concave defect 4.

In the substrate smoothing method (1) of the present invention, when both the detection of the concave defect 4 appearing on the surface of the thin film 3 and the local heating of the thin film 3 immediately below the detected concave defect 4 are performed by laser light irradiation, The laser light sources are preferably the same. In other words, it is preferable to use the same laser beam irradiation apparatus. After the concave defect 4 is detected by laser light irradiation, if the thin film 3 directly under the concave defect 4 is irradiated with laser light from the same laser light source, the concave defect data obtained by detecting the concave defect 4 can be used as it is. Further, it is possible to more accurately perform laser beam irradiation on the thin film 3 immediately below the concave defect 4.
When the same laser light irradiation apparatus is used for detection of the concave defect 4 and local heating of the thin film 3 immediately below the concave defect 4, the thin film 3 is not heated when the concave defect 4 is detected. 3 may be scanned with laser light, and when the thin film 3 directly under the concave defect 4 is locally heated, the concave defect 4 may be irradiated with laser light for a certain period of time.

  As another example of a method suitable for locally heating the thin film 3 directly below the concave defect 4, a concave defect existing on the surface of the thin film 3 using an AFM, STM or stylus step meter having a heatable probe There is a method of locally heating the thin film 3 immediately below the concave defect 4 by detecting 4 and then bringing the probe close to or in contact with the detected concave defect 4 and heating the probe. FIG. 4 shows a state in which the heatable probe 5 is brought into contact with the concave defect 4 to locally heat the thin film 3 immediately below the concave defect 4. Also in this method, since the concave defect data obtained by detecting the concave defect 4 can be used as it is, the local heating of the thin film 3 immediately below the concave defect 4 can be performed more accurately. Examples of AFM and STM having a heatable probe include a nano-TA local thermal analysis system manufactured by Anasys Instruments of the United States. As the probe material that can be heated, single crystal Si, SiN, or the like is preferable.

  As a result of locally heating the thin film 3 immediately below the concave defect 4 by the above procedure, it is preferable that the heated portion of the thin film 3 has an amorphous crystalline state. In other words, it is preferable that the crystalline state of the material constituting the thin film 3 is amorphous due to a chemical reaction that occurs during heating. The heated portion of the thin film 3 is a portion that is smoothed by eliminating the portion that was the concave defect 4 by locally increasing the volume by a chemical reaction of the material constituting the thin film 3. If the crystal state of this part is amorphous, the smoothed thin film surface will be in a more smooth state. Specifically, the surface roughness of the surface of the thin film 3 after smoothing is 0.5 nm rms or less. If the surface roughness of the surface of the thin film 3 after smoothing is 0.5 nm rms or less, the surface of the thin film 3 is sufficiently smooth, so that the multilayer structure of the reflective layer formed on the thin film 3 is disturbed. There is no fear. If disorder occurs in the multilayer structure of the reflective layer, there is a risk that the manufactured EUV mask blank will be defective. Further, in the manufactured EUV mask blank, the edge roughness of the pattern does not increase and the dimensional accuracy of the pattern is good. When the surface roughness of the thin film 3 is large, the surface roughness of the reflective layer formed on the thin film 3 is large, and the surface roughness of the absorber layer formed on the reflective layer is large. As a result, the edge roughness of the pattern formed on the absorber layer is increased, and the dimensional accuracy of the pattern is deteriorated. The surface roughness of the surface of the thin film 3 is more preferably 0.4 nm rms or less, and further preferably 0.3 nm rms or less.

In this specification, the phrase “crystalline state is amorphous” includes a microcrystalline structure other than an amorphous structure having no crystal structure. Note that whether the crystal state is amorphous, that is, an amorphous structure or a microcrystalline structure can be confirmed by an X-ray diffraction (XRD) method. If the crystal state is an amorphous structure having no crystal structure or a microcrystalline structure, a sharp peak is not observed in a diffraction peak obtained by XRD measurement.
In terms of the smoothness of the surface of the thin film 3, it is preferable that the crystalline state of the entire thin film 3 after heating is amorphous. In this case, when the thin film 3 is formed, the crystal state of the entire thin film 3 is amorphous. And even after the material which comprises the thin film 3 just under the concave defect 4 chemically reacts by heating, the crystal state of the thin film 3 whole maintains amorphous.

Next, the substrate smoothing method (2) of the present invention will be described. Also in the substrate smoothing method (2) of the present invention, first, a step of forming a thin film 3 'on a glass substrate is performed. However, in the substrate smoothing method (2) of the present invention, the constituent material of the thin film 3 'undergoes a chemical reaction accompanied by an increase in volume by anodic oxidation. Here, the chemical reaction caused by anodization is not particularly limited as long as it involves an increase in volume, but it proceeds only by anodization, and the chemical reaction can proceed locally only at the anodized site, And it is preferable that the volume increase accompanying a chemical reaction is easy to control.
The constituent material of the thin film 3 ′ is easy to cause a chemical reaction at the time of anodizing and excellent in smoothness of the surface of the thin film after causing a chemical reaction accompanied by an increase in volume by anodizing (hereinafter referred to as “thin film after anodizing” It is said that it is excellent in surface smoothness ”). In particular, at least one selected from the above-mentioned group A is a main constituent material, which easily causes a chemical reaction during anodization, has excellent smoothness of the surface of the thin film 3 'after anodization, and manufactures an EUV mask blank. This is superior in that it sometimes does not adversely affect the reflective layer and the absorber layer formed on the thin film 3 '. Among these, the thin film 3 ′ containing Hf, Nb, Si, Ta, Ti, and Zr as main constituent materials is more preferable because the crystal state after anodization tends to be amorphous.

The material constituting the thin film 3 ′ is preferably a material having a high volume increase rate due to a chemical reaction that occurs during anodization. Specifically, the material is preferably a material in which the volume increase rate ΔV ′ during anodization obtained by the following formula is 10% or more, and more preferably 30% or more.
ΔV ′ (%) = (V ₂ ′ −V ₁ ) / V ₁ × 100
Here, V ₁ is the volume of the material at normal temperature (20 ° C.), and V ₂ ′ is the volume of the material after anodic oxidation.
Hereinafter, in the present specification, the phrase “volume increase during anodization” refers to a volume increase due to a chemical reaction that occurs during anodization.
In addition, as for the material of A group, all are (DELTA) V '50 to 250%.

As the thin film 3 ′ satisfying the above conditions, it is preferable that at least one selected from “Group A” is a main constituent material. Therefore, the thin film 3 ′ may include only one type of the A group as a constituent material, or two or more types as the constituent material. Moreover, thin film 3 'may contain materials other than A group as a constituent material. However, when thin film 3 'contains materials other than A group, it is preferable that 50 atomic% or more is the material of A group in all the constituent materials of thin film 3'.
When thin film 3 'contains materials other than A group, it is more preferable that 80 atomic% or more is material of A group in all the constituent materials of thin film 3'.
Among the materials of group A, Si, Ta and Ti are preferable because the chemical reaction easily proceeds during anodic oxidation. Furthermore, Si is preferable in terms of productivity because the material of the film constituting the reflective multilayer film can be used as it is.

The thickness of the thin film 3 ′ formed on the film formation surface 1 a of the glass substrate 1 varies depending on the depth of the concave defect 2 existing on the film formation surface 1 a, but is 0.5 times or more the depth of the concave defect 2. Preferably there is. If the thickness of the thin film 3 ′ is within the above range, the thin film 3 ′ immediately above the concave defect 2 is locally anodized by the procedure described later, thereby reducing or eliminating the concave defect 4 appearing on the surface of the thin film 3 ′. Thus, the surface of the thin film 3 'can be smoothed. If the thickness of the thin film 3 ′ is less than 0.5 times the depth of the concave defect 2, the thin film 3 immediately above the concave defect 2 depends on the volume increase rate during the anodic oxidation of the material constituting the thin film 3 ′. When ′ is locally anodized, the concave defects 4 appearing on the surface of the thin film 3 ′ may not be sufficiently reduced.
When a plurality of concave defects 2 are present on the film formation surface 1a of the glass substrate 1, the thickness of the thin film 3 'is more than 0.5 times the depth of the concave defect having the largest depth (maximum depth of the concave defect). Make the thickness.
More preferably, the thickness of the thin film 3 ′ is one or more times the depth of the concave defect 2.

  As a method for forming the thin film 3 ′, various dry film forming methods can be used as in the method for forming the thin film 3 in the substrate smoothing method (1) of the present invention. Among these, sputtering method or CVD method is preferable because there is little possibility of generating new convex defects (particles) at the time of thin film formation. From the viewpoint of preventing new convex defects from being generated, the CVD method is suitable for the thin film 3 on the film formation surface 1a. Sputtering is particularly preferred from the viewpoint of 'adhesive strength'. However, after forming the substrate smoothing method (2) of the present invention, the sputtering method is preferable in that the same apparatus can be used when forming the reflective layer and the absorber layer on the thin film 3 ′.

  Following the step of forming the thin film 3 ′ on the glass substrate, the step of detecting the concave defects existing on the glass substrate existing on the glass substrate is performed in the same procedure as the substrate smoothing method (1) of the present invention. To do.

  Subsequent to the step of detecting the concave defects existing on the glass substrate, the thin film 3 'immediately above the detected concave defects is locally anodized, whereby a chemical reaction accompanied by an increase in volume occurs in the material constituting the thin film 3'. A step of generating is performed. However, what is detected in the previous step is not the concave defect 2 existing on the film formation surface 1a of the glass substrate 1, but the concave defect 4 appearing on the surface of the thin film 3 '. Therefore, in this step, the thin film 3 ′ immediately below the concave defect 4 is locally anodized based on the concave defect data obtained in the previous step.

  Since the material constituting the thin film 3 ′ causes a chemical reaction accompanied by an increase in volume during anodic oxidation, when the thin film 3 ′ immediately below the concave defect 4 is locally anodized, the thin film 3 ′ immediately below the concave defect 4 becomes The volume is locally increased by the chemical reaction of the material constituting the thin film 3 '. As a result, as shown in FIG. 3, the concave defect 4 is eliminated and the surface of the thin film 3 'is smoothed.

  In this step, the means for locally anodizing the thin film 3 ′ directly under the concave defect 4 is not particularly limited as long as it is a method capable of locally anodizing the thin film 3 ′ directly under the concave defect 4. As an example of a suitable method for locally anodizing the thin film 3 ′ immediately below the concave defect 4, the concave defect 4 existing on the surface of the thin film 3 ′ using an AFM, STM, or stylus step meter having a probe that can be energized. Then, the probe is brought close to or brought into contact with the detected concave defect 4, and a voltage is applied between the probe and the thin film 3 ', so that the thin film 3' directly under the concave defect 4 is localized. And anodizing. FIG. 5 shows that an anodizable probe 6 is brought into contact with the concave defect 4 and a DC voltage is applied between the probe 6 and the thin film 3 ′ using the probe 6 as a positive electrode and the thin film 3 ′ as a negative electrode. The state in which the thin film 3 directly under the concave defect 4 is locally anodized is shown. Since this method can use the concave defect data obtained by detecting the concave defect 4 as it is, the local anodic oxidation of the thin film 3 directly under the concave defect 4 can be performed more accurately. The anodizable probe material needs to be conductive, and single crystal Si or SiN is preferable.

As a result of locally anodizing the thin film 3 ′ immediately below the concave defect 4 by the above procedure, it is preferable that the crystal state of the anodized portion of the thin film 3 ′ becomes amorphous. In other words, it is preferable that the crystal state of the material constituting the thin film 3 ′ is amorphous due to a chemical reaction that occurs during anodic oxidation.
The anodized portion of the thin film 3 ′ is a portion that is smoothed by eliminating the portion that was the concave defect 4 by locally increasing the volume by a chemical reaction of the material constituting the thin film 3. If the crystal state of this part is amorphous, the smoothed thin film surface will be in a more smooth state. Specifically, the surface roughness of the surface of the thin film 3 ′ after smoothing is 0.5 nm rms or less. If the surface roughness of the smoothed thin film 3 ′ surface is 0.5 nm rms or less, the surface of the thin film 3 ′ is sufficiently smooth, so that the multilayer structure of the reflective layer formed on the thin film 3 is disturbed. There is no risk of occurrence. If disorder occurs in the multilayer structure of the reflective layer, there is a risk that the manufactured EUV mask blank will be defective. Further, in the manufactured EUV mask blank, the edge roughness of the pattern does not increase and the dimensional accuracy of the pattern is good. When the surface roughness of the thin film 3 ′ is large, the surface roughness of the reflective layer formed on the thin film 3 ′ is large, and further, the surface roughness of the absorber layer formed on the reflective layer is large. Become. As a result, the edge roughness of the pattern formed on the absorber layer is increased, and the dimensional accuracy of the pattern is deteriorated. The surface roughness of the surface of the thin film 3 ′ is more preferably 0.4 nm rms or less, and further preferably 0.3 nm rms or less.

  In terms of the smoothness of the surface of the thin film 3 ′, it is preferable that the crystal state of the entire thin film 3 ′ after anodization is amorphous. In this case, when the thin film 3 ′ is formed, the crystal state of the entire thin film 3 ′ is amorphous. Even after the material constituting the thin film 3 ′ immediately below the concave defect 4 chemically reacts by anodic oxidation, the crystal state of the entire thin film 3 ′ remains amorphous.

In the substrate smoothing method (1) of the present invention, when the probe 5 that can be heated is used for local heating of the thin film 3 immediately below the concave defect 4, the hardness of the probe 5 is higher than that of the material of the thin film 3. By selecting one, convex defects present on the surface of the thin film 3 after heating can be removed. When the thin film 3 directly under the concave defect 4 is locally heated, a convex defect may occur on the surface of the thin film 3 due to an excessive volume increase. Further, it may be difficult to control the shape change of the defect due to the volume increase when locally heating the thin film 3 immediately below the concave defect 4 to make it flat by a single process. In some cases, a convex defect is generated on the surface of the thin film 3 due to an excessive increase in volume.
Similarly, in the substrate smoothing method (2) of the present invention, when the probe 6 that can be energized for local anodic oxidation of the thin film 3 ′ immediately below the concave defect 4 is used, the material of the thin film 3 ′ is used as the probe 6 material. By selecting a material whose hardness is higher than that of the material, convex defects present on the surface of the thin film 3 'after anodization can be removed. When the thin film 3 ′ directly under the concave defect 4 is locally anodized, a convex defect may occur on the surface of the thin film 3 ′ due to excessive volume increase. Further, it may be difficult to control the shape change of the defect due to the volume increase when the thin film 3 ′ directly under the concave defect 4 is locally anodized and to flatten it by a single treatment. In some cases, a convex defect is generated on the surface of the thin film 3 ′ due to an excessive volume increase in order to make the surface flat by processing as described later.
In the above case, the convex defects newly generated on the surfaces of the thin films 3 and 3 ′ can be removed using the probes 5 and 6, as shown in FIG. In FIG. 6, 7 indicates a convex defect removed using the probes 5 and 6. Thereby, the smoothness of the surfaces of the thin films 3 and 3 ′ can be further improved. Even when local heating of the thin film 3 immediately below the concave defect 4 is performed by laser light irradiation, if a new convex defect occurs on the surface of the thin film 3 after heating, it should be removed using a needle-like member. Can do.

  When manufacturing an EUV mask blank using a glass substrate having a smooth surface on the thin films 3 and 3 ′ by the above procedure, a reflective layer that reflects EUV light is formed on the surface of the thin films 3 and 3 ′. An absorber layer that absorbs EUV light is formed.

  The reflective layer formed on the surfaces of the thin films 3 and 3 ′ is not particularly limited as long as it has desired characteristics as the reflective layer of the EUV mask blank. Here, the characteristic particularly required for the reflective layer is a high EUV light reflectance. Specifically, when the surface of the reflective layer is irradiated with light in the wavelength region of EUV light, the maximum value of light reflectance near the wavelength of 13.5 nm is preferably 60% or more, and 65% or more. Is more preferable. Even when a protective layer, which will be described later, is provided on the reflective layer, the maximum value of the light reflectance near the wavelength of 13.5 nm is preferably 60% or more, and more preferably 65% or more. .

  Since the reflective layer can achieve a high EUV light reflectance, a multilayer reflective film in which a high refractive layer and a low refractive index layer are alternately laminated a plurality of times is usually used. In the multilayer reflective film constituting the reflective layer, Mo is widely used for the high refractive index layer, and Si is widely used for the low refractive index layer. That is, the Mo / Si multilayer reflective film is the most common. However, the multilayer reflective film is not limited to this, and a Mo compound / Si compound multilayer reflective film or a Si / Mo / Ru multilayer reflective film can also be used.

  The film thickness of each layer constituting the multilayer reflective film constituting the reflective layer and the number of repeating units of the layers can be appropriately selected according to the film material used and the EUV light reflectance required for the reflective layer. Taking a Mo / Si multilayer reflective film as an example, in order to obtain a reflective layer having a maximum EUV light reflectance of 60% or more, the multilayer reflective film comprises a Mo layer with a film thickness of 2.3 ± 0.1 nm, A Si layer having a thickness of 4.5 ± 0.1 nm may be laminated so that the number of repeating units is 30 to 60.

In addition, what is necessary is just to form each layer which comprises the multilayer reflective film which comprises a reflective layer so that it may become desired thickness using well-known film-forming methods, such as a magnetron sputtering method and an ion beam sputtering method. For example, when an Si / Mo multilayer reflective film is formed by ion beam sputtering, an Si target is used as a target, and Ar gas (gas pressure 1.3 × 10 ⁻² Pa to 2.7 × 10 ⁻ is used as a sputtering gas. ² Pa), an Si film is formed to have a thickness of 4.5 nm at an ion acceleration voltage of 300 to 1500 V and a film formation rate of 0.03 to 0.30 nm / sec. using a target, using an Ar gas (gas pressure ^{1.3 × 10 -2 Pa~2.7 × 10 -2} Pa), an ion acceleration voltage 300 to 1,500 V, the deposition rate of 0.03 to 0 It is preferable to form the Mo film so that the thickness is 2.3 nm at 30 nm / sec. With this as one period, the Si / Mo multilayer reflective film is formed by laminating the Si film and the Mo film for 40 to 50 periods.

  In order to prevent the surface of the reflective layer from being oxidized, it is preferable that the outermost layer of the multilayer reflective film constituting the reflective layer be a layer made of a material that is difficult to be oxidized. The layer of material that is not easily oxidized functions as a cap layer for the reflective layer. As a specific example of the layer of a material that hardly functions to be oxidized and functions as a cap layer, a Si layer can be exemplified. When the multilayer reflective film forming the reflective layer is an Si / Mo film, the uppermost layer can be made to function as a cap layer by making the uppermost layer Si. In that case, the thickness of the cap layer is preferably 11.0 ± 1.0 nm.

  Examples of the constituent material of the absorber layer formed on the reflective layer include materials having a high absorption coefficient for EUV light, specifically, Cr, Ta, and nitrides thereof. Among these, TaN is preferable because it tends to be amorphous and the surface shape is smooth. The thickness of the absorber layer is preferably 50 to 100 nm. The method for forming the absorber layer is not particularly limited as long as it is a sputtering method, and may be either a magnetron sputtering method or an ion beam sputtering method.

When a TaN layer is formed as an absorber layer using an ion beam sputtering method, a Ta target is used as a target, and a N ₂ gas (gas pressure 1.3 × 10 ⁻² Pa to 2.7 × 10 6) is used as a sputtering gas. ^-2 Pa) is preferably used to form a film at a voltage of 300 to 1500 V and a film formation rate of 0.01 to 0.1 nm / sec to a thickness of 50 to 100 nm.
When forming the absorption layer using the sputtering method, it is preferable to perform the film formation while rotating the substrate using a rotating body in order to obtain a uniform film formation.

A buffer layer may be formed between the reflective layer and the absorbing layer. Examples of the material constituting the buffer layer include Cr, Al, Ru, Ta, and nitrides thereof, and SiO ₂ , Si ₃ N ₄ , Al ₂ O _{3, and the} like. The buffer layer is preferably 10 to 60 nm thick.

FIG. 1 is a schematic diagram showing the vicinity of a portion of a glass substrate where a concave defect exists. FIG. 2 shows a state in which a thin film is formed on the film formation surface of the glass substrate of FIG. FIG. 3 shows a state in which the concave defects appearing on the thin film surface are eliminated and the thin film surface is smoothed by the substrate smoothing method of the present invention. FIG. 4 shows a state in which a heatable probe is brought into contact with a concave defect appearing on the surface of the thin film and the thin film immediately below the concave defect is locally heated. FIG. 5 shows a state in which the energizable probe is brought into contact with a concave defect appearing on the surface of the thin film, and the thin film immediately under the concave defect is locally anodized. FIG. 6 shows a state where convex defects newly generated on the surface of the thin film are removed using a probe.

Explanation of symbols

1: Substrate 1a: Film formation surface 2: Concave defect (concave defect existing on the film formation surface of the substrate)
3, 3 ′: thin film 4: concave defect (concave defect appearing on the thin film surface)
5: Heatable probe 6: Energizable probe 7: Convex defect removed using probes 5 and 6

Claims (23)

A method of smoothing a glass substrate surface for a reflective mask blank for EUV lithography,
Forming a thin film on a glass substrate;
Detecting a concave defect present on the glass substrate;
A step of locally heating the thin film directly above the detected concave defect to cause a chemical reaction accompanied by an increase in volume in the material constituting the thin film, and a reflective mask for EUV lithography, comprising: A method of smoothing the glass substrate surface for blanks.   The method for smoothing a glass substrate surface for a reflective mask blank for EUV lithography according to claim 1, wherein the chemical reaction is an oxidation reaction.   The method for smoothing a glass substrate surface for a reflective mask blank for EUV lithography according to claim 1, wherein the chemical reaction is a nitriding reaction.   The thin film is mainly composed of at least one selected from the group consisting of Al, B, Co, Cr, Ge, Hf, Mo, Nb, Ni, Ru, Si, Ta, Ti, Zn, and Zr. Item 4. A method for smoothing a glass substrate surface for a reflective mask blank for EUV lithography according to any one of Items 1 to 3. The thin film includes at least two layers of films having different constituent materials,
4. The glass substrate surface for a reflective mask blank for EUV lithography according to claim 1, wherein the chemical reaction is accompanied by mutual diffusion between materials constituting the two-layer film. how to.   One of the at least two layers is selected from the group consisting of Al, B, Co, Cr, Ge, Hf, Mo, Nb, Ni, Ru, Si, Ta, Ti, Zn, and Zr. 6. The method of smoothing a glass substrate surface for a reflective mask blank for EUV lithography according to claim 5, wherein at least one is a main constituent material.   The reflective mask for EUV lithography according to any one of claims 1 to 6, wherein the thickness of the thin film is 0.5 to 10 times the maximum depth of a concave defect existing in the glass substrate. A method of smoothing the glass substrate surface for blanks.   The glass substrate surface for a reflective mask blank for EUV lithography according to any one of claims 1 to 7, wherein the crystalline state of the locally heated portion of the thin film becomes amorphous by the chemical reaction. How to smooth.   The method for smoothing a glass substrate surface for a reflective mask blank for EUV lithography according to any one of claims 1 to 7, wherein the crystalline state of the thin film after the local heating is amorphous.   10. The reflective mask blank glass for EUV lithography according to claim 1, wherein the local heating is performed by irradiating a thin film immediately above a concave defect of the glass substrate with a laser beam. A method of smoothing the substrate surface.   11. The method for smoothing a glass substrate surface for a reflective mask blank for EUV lithography according to claim 10, wherein the diameter of the laser beam is not more than twice the diameter of a concave defect existing in the glass substrate. . Detection of the concave defect is performed by laser light irradiation,
The reflective mask for EUV lithography according to claim 10 or 11, wherein the laser light source used for the local heating and the laser light source used for the detection of the concave defect are the same laser light source. A method of smoothing the glass substrate surface for blanks. For detecting the concave defect, an atomic force microscope (AFM) having a heatable probe, a scanning tunneling microscope (STM) or a stylus step meter is used.
10. The reflective mask for EUV lithography according to claim 1, wherein the local heating is performed by heating the probe approaching or contacting the thin film immediately above the concave defect. A method of smoothing the glass substrate surface for blanks.   13. The glass substrate surface for a reflective mask blank for EUV lithography according to claim 1, wherein the surface of the thin film after the local heating is ground using a needle-like member. how to.   14. The method of smoothing a glass substrate surface for a reflective mask blank for EUV lithography according to claim 13, wherein the thin film surface after the local heating is ground using the probe. A method of smoothing a glass substrate surface for a reflective mask blank for EUV lithography,
Forming a thin film on a glass substrate;
Detecting a concave defect present on the glass substrate;
A step of locally anodizing the thin film immediately above the detected concave defect to cause a chemical reaction accompanied by an increase in volume in the material constituting the thin film, and a reflective type for EUV lithography, A method of smoothing the surface of a mask blank glass substrate.   The thin film is mainly composed of at least one selected from the group consisting of Al, B, Co, Cr, Ge, Hf, Mo, Nb, Ni, Ru, Si, Ta, Ti, Zn, and Zr. Item 17. A method for smoothing a glass substrate surface for a reflective mask blank for EUV lithography according to Item 16.   18. The glass substrate for a reflective mask blank for EUV lithography according to claim 16, wherein a thickness of the thin film is 0.5 times or more a maximum depth of a concave defect existing in the glass substrate. A method of smoothing the surface.   19. The glass substrate surface for a reflective mask blank for EUV lithography according to claim 16, wherein the crystalline state of the locally anodized portion of the thin film becomes amorphous by the chemical reaction. How to smooth.   19. The method of smoothing a glass substrate surface for a reflective mask blank for EUV lithography according to claim 16, wherein the crystal state of the thin film after the local anodic oxidation is amorphous. An atomic force microscope (AFM) having a probe that can be energized, a scanning tunneling microscope (STM), or a stylus type step gauge is used to detect the concave defect,
21. The local anodic oxidation is performed by applying a voltage between the probe approaching or contacting the thin film immediately above the concave defect and the thin film. The method of smoothing the glass substrate surface for reflective mask blanks for any one of EUV lithography.   21. The glass substrate surface for a reflective mask blank for EUV lithography according to claim 16, wherein the surface of the thin film after the local anodization is ground using a needle-like member. How to turn.   The method of smoothing a glass substrate surface for a reflective mask blank for EUV lithography according to claim 21, wherein the thin film surface after the local anodization is ground using the probe.

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