JP5338556B2 - Cleaning method for photomask blanks - Google Patents

Description

The present invention relates to a photomask blank cleaning method.
More specifically, the present invention relates to a method for cleaning a reflective mask blank in which a reflective layer and an absorption layer are formed in this order on a film formation surface of a glass substrate, and a conductive film is formed on the back surface of the film formation surface.

  2. Description of the Related Art Conventionally, in the semiconductor industry, a photolithography method using visible light or ultraviolet light has been used as a technique for transferring a fine pattern necessary for forming an integrated circuit having a fine pattern on a Si substrate or the like. However, while miniaturization of semiconductor devices is accelerating, the exposure limit of conventional light exposure has been approached. In the case of light exposure, the resolution limit of the pattern is about ½ of the exposure wavelength, and it is said that the immersion wavelength is about ¼ of the exposure wavelength. The immersion method of ArF laser (193 nm) Even if is used, the limit of about 45 nm is expected. Therefore, EUV lithography, which is an exposure technique using EUV light having a wavelength shorter than that of an ArF laser, is promising as an exposure technique for 45 nm and beyond. EUV light refers to light having a wavelength in the soft X-ray region or the vacuum ultraviolet region, and specifically refers to light having a wavelength of about 10 to 20 nm, particularly about 13.5 nm ± 0.3 nm.

  Since EUV light is easily absorbed by any material and has a refractive index close to 1, conventional refractive optical systems such as photolithography using visible light or ultraviolet light cannot be used. For this reason, in the EUV light lithography, a reflective optical system, that is, a reflective photomask and a mirror are used.

  The mask blank is a laminated body before patterning for manufacturing a photomask. In the case of a mask blank for a reflective photomask, a reflective layer that reflects EUV light and an absorption layer that absorbs EUV light are formed on a glass substrate in this order. As the reflective layer, by alternately laminating high refractive layers and low refractive layers, the light reflectance when irradiating the surface of the layer with light rays, more specifically, the light rays when irradiating the layer surface with EUV light. A multilayer reflective film with an increased reflectivity is usually used. For the absorption layer, a material having a high absorption coefficient for EUV light, specifically, a material mainly composed of Cr or Ta, for example, is used.

The multilayer reflection film and the absorption layer are formed on the film formation surface of the glass substrate using an ion beam sputtering method or a magnetron sputtering method. When forming the multilayer reflective film and the absorbing layer, the glass substrate is held by a holding means. As a glass substrate holding means, there are a mechanical chuck and an electrostatic chuck. From the problem of dust generation, suction holding by an electrostatic chuck is preferably used. As shown in Patent Document 1, an electrostatic chuck mainly includes a dielectric having an electrode embedded therein, and the surface of the dielectric forms an adsorption holding surface. For example, inorganic dielectrics such as alumina, aluminum nitride, silicon carbide, and glass, and organic dielectrics such as polyimide and polytetrafluoroethylene are used as the dielectric that forms the adsorption holding surface. In the case of electrostatic chucks used to hold and hold mask blanks, since they have plasticity, there are few scratches and rubbing during suction, and therefore there is little dust generation, and it is easy to regenerate by replacing the dielectric, etc. For this reason, it is preferable that an organic dielectric is used for the adsorption holding surface.
It should be noted that suction holding by an electrostatic chuck is preferably used also during the patterning process of the manufactured reflective mask blank or during exposure of the mask after patterning.
However, since the glass substrate has a low dielectric constant and electrical conductivity, it is necessary to apply a high voltage to obtain a sufficient chucking force, and there is a risk of causing dielectric breakdown.

  In order to solve such a problem, a film (conductive film) of a material having a higher dielectric constant and higher conductivity than a glass substrate is used as a back surface (hereinafter referred to as “glass substrate” with respect to the film formation surface of the glass substrate. It is usually performed to increase the chucking force of the glass substrate (refer to Patent Document 2).

JP 2006-40993 A No. 2007-069417

  As described above, from the viewpoint of dust generation, suction holding by an electrostatic chuck, particularly suction holding by an electrostatic chuck using an organic dielectric on the suction holding surface is a preferable method. It cannot be avoided that dust is generated due to mutual contact when the substrate is sucked and held, and dust generated here may exist as foreign matter on the surface of the conductive film.

Dust generation due to suction holding by an electrostatic chuck, especially dust generation due to suction holding by an electrostatic chuck using an organic dielectric on the suction holding surface, is extremely light compared to dust generation by a mechanical chuck, For mask blanks, what has been regarded as a problem so far is a multilayer reflective film that functions as a reflective optical system and foreign substances present on the film formation surface of the glass substrate on which the multilayer reflective film is formed. Foreign matter on the surface of the conductive film formed on the back side of the film formation surface by the dust generated by the suction holding by the electrostatic chuck, particularly the dust generated by the suction holding by the electrostatic chuck using an organic dielectric on the suction holding surface Even if it exists, it has never been regarded as a problem at all.
Hereinafter, in the present specification, dust generated by suction holding by an electrostatic chuck is present as foreign matter, which is referred to as “foreign matter resulting from suction holding by an electrostatic chuck”.

  However, since the demand for the defect of the mask blanks has become stricter, it has become a problem that the foreign matter resulting from the adsorption holding by the electrostatic chuck exists on the surface of the conductive film. Specifically, when foreign matter having a size on the order of μm is present on the surface of the conductive film, the appearance of the mask blank is deteriorated, and the mask after patterning is sucked and held by an electrostatic chuck for exposure. Since a finely deformed portion is formed on the exposed surface and there is a possibility of causing problems such as transfer defects, it becomes a defect of mask blanks. Further, although it is not a foreign matter having a size on the order of μm, it is preferable that the number of foreign matters having a size of 200 nm or more existing on the surface of the conductive film is suppressed to less than 100.

Therefore, it is necessary to remove foreign matters resulting from the adsorption holding by the electrostatic chuck when they exist on the surface of the conductive film.
However, when attracting and holding the electrostatic chuck, a strong chucking force is applied between the electrostatic chuck and the conductive film, so that the foreign matter present at the interface between the electrostatic chuck and the conductive film is deposited on the surface of the conductive film. It becomes a fixed state and is difficult to remove.

  In order to solve the above-described problems of the prior art, the present invention relates to foreign matter caused by suction holding by an electrostatic chuck, more specifically, foreign matter caused by suction holding by an electrostatic chuck using an organic dielectric on the suction holding surface. An object of the present invention is to provide a photomask blank cleaning method capable of easily removing the film from the surface of the conductive film.

As a result of diligent study, the inventor of the present application has found that in the case of an electrostatic chuck using an organic dielectric on the suction holding surface, most of the foreign matters resulting from the suction holding by the electrostatic chuck are used on the suction holding surface. It was found that a part of the organic dielectric was generated by peeling.
The present invention has been made on the basis of such findings. A conductive film is formed on one surface of a glass substrate, and the conductive film is formed by an electrostatic chuck using an organic dielectric on an adsorption holding surface. Is a method of cleaning a reflective mask blank that is adsorbed and held,
A reflective mask blank cleaning method (hereinafter referred to as “the mask blank of the present invention”), wherein the conductive film surface is cleaned using an aqueous 0.1-5 N alkali metal hydroxide solution. Cleaning method ").

  In the mask blank cleaning method of the present invention, the alkali metal hydroxide aqueous solution is preferably a 0.1 to 5 N sodium hydroxide aqueous solution or a 0.1 to 5 N potassium hydroxide aqueous solution.

  In the mask blank cleaning method of the present invention, scrub cleaning is preferably performed on the surface of the conductive film after cleaning with the alkali metal hydroxide aqueous solution.

  In the mask blank cleaning method of the present invention, after the conductive film surface is cleaned with the alkali metal hydroxide aqueous solution, the constituent elements of the reflective mask blank formed on the back side with respect to the conductive film are made of ammonia. It is preferable to perform cleaning using a cleaning liquid containing hydrogen peroxide.

  Moreover, this invention provides the manufacturing method of the reflective mask blank which uses the cleaning method of the mask blank of this invention for the cleaning process implemented at the manufacturing process of a reflective mask blank.

  Moreover, this invention provides the manufacturing method of the reflective mask which uses the cleaning method of the mask blanks of this invention for the cleaning process implemented by the manufacturing process of a reflective mask.

According to the method for cleaning a mask blank of the present invention, it is possible to easily remove foreign matters from the surface of the conductive film by suction holding by an electrostatic chuck using an organic dielectric on the suction holding surface.
The cleaning method for mask blanks of the present invention uses an aqueous 0.1-5N alkali metal hydroxide solution for cleaning the surface of the conductive film, and therefore does not adversely affect the conductive film itself. Further, it does not adversely affect the main components of the mask blank such as the multilayer reflective film and the absorption layer, and various functional films formed as necessary such as the cap layer, the buffer layer, and the low reflective layer.

FIG. 1 is a schematic diagram showing a general configuration of a reflective mask blank. FIG. 2 is a schematic view of a branch-and-leaf type spin cleaning apparatus used in the mask blank cleaning method of the present invention.

The present invention will be described below with reference to the drawings.
FIG. 1 is a schematic diagram showing a general configuration of a reflective mask blank. In the mask blank 10 shown in FIG. 1, a multilayer reflective film 12 and an absorption layer 13 are formed in this order on the film formation surface of a glass substrate 11 serving as a base. On the other hand, a conductive film 14 is formed on the back surface of the glass substrate 11.
Hereinafter, each component of the mask blank 10 shown in FIG. 1 will be described.

The glass substrate 11 that forms the base of the mask blank 10 preferably has a low coefficient of thermal expansion (0 ± 1.0 × 10 ⁻⁷ / ° C., more preferably 0 ± 0.3 × 10 ⁻⁷ / ° C., further preferably Is 0 ± 0.2 × 10 ⁻⁷ / ° C., more preferably 0 ± 0.1 × 10 ⁻⁷ / ° C., particularly preferably 0 ± 0.05 × 10 ⁻⁷ / ° C.).
Further, the glass substrate 11 is preferably excellent in resistance to an alkaline cleaning liquid usually used for cleaning a mask blank or a photomask after pattern formation.
As the glass substrate 11 satisfying the above, a glass substrate having a low thermal expansion coefficient, for example, a SiO ₂ —TiO ₂ glass substrate can be used. However, the present invention is not limited to this, and a crystallized glass substrate or a quartz glass substrate on which a β quartz solid solution is deposited can also be used.
Moreover, it is preferable that the glass substrate 11 is excellent in smoothness and flatness. As an example, in the case of a glass substrate used as a base of a reflective mask blank for EUV lithography, the film-forming surface has a smooth surface with an Rms of 0.15 nm or less and a flatness of 100 nm or less. Is preferable because high reflectivity and transfer accuracy can be obtained in a photomask after pattern formation.
The size, thickness, and the like of the glass substrate 11 are appropriately determined depending on the design value of the mask. For example, the outer diameter is 6 inches (152.4 mm) square and the thickness is 0.25 inches (6.3 mm). It is.

The multilayer reflective film 12 formed on the film formation surface of the substrate 11 is one in which a high refractive layer and a low refractive layer are alternately laminated to increase the light reflectance when a light beam is irradiated on the layer surface. It is required to show a high light reflectance with respect to the wavelength of the exposure light source when the lithography process is performed using the reflective mask created using the mask blanks 10. For example, when used in an EUV lithography process, it is required to be a film having a high EUV light reflectance. Specifically, when the surface of a multilayer reflective film is irradiated with light in the wavelength region of EUV light, the wavelength The maximum value of the light reflectance near 13.5 nm is preferably 60% or more, and more preferably 65% or more.
As the multilayer reflective film 12 exhibiting such a high EUV light reflectance, a Si / Mo multilayer reflective film in which Si films and Mo films are alternately laminated, and Be / Mo in which Be and Mo films are alternately laminated. Multi-layer reflective film, Si compound / Mo compound multilayer reflective film in which Si compound and Mo compound layer are alternately laminated, Si / Mo / Ru multilayer reflective film in which Si film, Mo film and Ru film are laminated in this order, Examples include a Si / Ru / Mo / Ru multilayer reflective film in which a Si film, a Ru film, a Mo film, and a Ru film are laminated in this order.

  As a constituent material of the absorption layer 13 formed on the multilayer reflective film 12, the absorption coefficient is high with respect to the wavelength of the exposure light source when the lithography process is performed using the reflective mask created using the mask blank 10 The material is selected. As an example, when used in an EUV lithography process, a material having a high absorption coefficient for EUV light is selected, and specifically, Ta and nitrides thereof may be used.

The mask blank 10 shown in FIG. 1 has a structure in which a multilayer reflective film 12 and an absorption layer 13 are formed in this order on the film formation surface of a glass substrate 11, but between the multilayer reflective film 12 and the absorption layer 13, or In addition, a functional film other than these may be formed on the absorption layer 13.
For example, a cap layer for preventing oxidation of the surface of the multilayer reflective film may be formed on the multilayer reflective film. In addition, a buffer layer may be formed on the multilayer reflective film in order to prevent the multilayer reflective film from being damaged during the etching process. In addition, in order to increase the contrast at the time of inspection of the mask pattern, a low reflection layer having a low reflectance with respect to inspection light used for inspection of the mask pattern may be formed on the absorption layer.
The multilayer reflective film, the absorption layer, and various functional films can be formed on the film formation surface of the glass substrate by various film formation methods such as sputtering.

On the other hand, the conductive film 14 formed on the back surface of the glass substrate attracts the glass substrate 11 that is the base of the mask blank 10 with an electrostatic chuck when the mask blank 10 is attracted and held with an electrostatic chuck. It is a film of a material having a higher dielectric constant and higher conductivity than the glass substrate, which is formed for the purpose of increasing the chucking force of the glass substrate 11 when held.
In the above description, the mask blank 10 is described as being held by suction with an electrostatic chuck. However, when the mask blank 10 is formed by forming the multilayer reflective film 12 and the absorption layer 13 on the film formation surface of the glass substrate 11. Also, the glass substrate 11 as a base is attracted and held by an electrostatic chuck. Therefore, the conductive film 14 is formed on the back surface of the glass substrate 11 from the stage of the glass substrate 11 before forming the multilayer reflective film 12 and the absorption layer 13.

As the material of the conductive film 14, a material having a higher dielectric constant and conductivity than the glass substrate 11 is used. Specific examples of such materials include Cr, Si, Mo, Ti, Zr, Nb, Ni, V, and borides, boronitrides, oxynitrides, and the like thereof.
Among these, the reason why the sheet resistance of the conductive film can be lowered, is inexpensive, has excellent adhesion to a glass substrate, and is widely used as a mask material, so that knowledge on film formation has been accumulated. To a conductive film containing Cr as a main component. Note that in this specification, a conductive film containing Cr as a main component means a conductive film containing 55 at% or more, preferably 65 at% or more, more preferably 70 at% or more in the film material.
The conductive film containing Cr as a main component may contain a material other than Cr as long as the characteristics are not impaired. Specific examples of materials other than Cr that may be included in the conductive film include B, N, Si, and the like.

The mask blank cleaning method of the present invention is intended for a method in which the conductive film 14 is attracted and held by an electrostatic chuck using an organic dielectric on the attracting and holding surface.
As described above, an electrostatic chuck using an organic dielectric on the suction holding surface is more in comparison with an electrostatic chuck using an inorganic dielectric such as alumina, aluminum nitride, silicon carbide, or glass on the suction holding surface. Since it has plasticity, it is preferable for reasons such as few scratches and rubbing at the time of adsorption, and therefore less dust generation, and easy reproduction by replacing the dielectric.
Examples of the organic dielectric used for the adsorption holding surface include polyimide, polytetrafluoroethylene, and polyolefin. Among these, polyimide is preferable for reasons of tensile strength and tear strength.

The foreign matter to be removed by the mask blank cleaning method of the present invention is a foreign matter existing on the surface of the conductive film, and more specifically, a foreign matter present on the surface of the conductive film by suction holding by an electrostatic chuck. is there. There are various kinds of foreign matters generated during the manufacture of the mask blanks in addition to the foreign matters caused by the suction holding by the electrostatic chuck. For example, a multilayer reflective film, an absorption layer, and various functional films are formed on a glass substrate on a glass substrate by using various film forming methods such as a sputtering method when manufacturing a reflective mask blank. However, foreign matter that exists in the deposition chamber at this time, or foreign matter that is generated in the course of the deposition process, that is, deposition that adheres to the wall surface of the deposition chamber when a deposition method such as sputtering is performed. The foreign material etc. which arises when material falls for some reason are mentioned.
However, when viewed from the viewpoint of the number of foreign substances existing on the surface of the conductive film, the frequency of occurrence, and the size of the foreign substances, the foreign substances due to these other factors can be ignored as compared to the foreign substances caused by electrostatic chucking and holding. .

Even when foreign matter is present on the surface of the conductive film, there may be no problem depending on its size. Such foreign matter does not need to be removed using the mask blank cleaning method of the present invention.
On the other hand, if there is a foreign matter with a size on the order of μm on the surface of the conductive film, the appearance of the mask blanks deteriorates, and when the patterned mask is attracted and held by an electrostatic chuck for exposure, Since there is a possibility that a finely deformed portion may be generated to cause a problem such as a transfer failure, it is removed using the mask blank cleaning method of the present invention.
Further, although it is not a foreign matter having a size on the order of μm, it is preferable that the number of foreign matters having a size of 200 nm or more existing on the surface of the conductive film is suppressed to less than 100.

In the mask blank cleaning method of the present invention, the surface of the conductive film is cleaned by using an alkali metal hydroxide aqueous solution of 0.1 to 5 N, and is thereby attracted and held by the electrostatic chuck. Remove foreign material.
As described above, in the case of an electrostatic chuck using an organic dielectric on the suction holding surface, most of the foreign matters resulting from the suction holding by the electrostatic chuck are organic dielectrics used on the suction holding surface. This is caused by part of the peeling. In the mask blank cleaning method of the present invention, the surface of the foreign material generated by peeling off a part of such an organic dielectric was changed to a highly water-soluble state, and the bonding force with the conductive film surface was weakened. By using an alkali metal hydroxide aqueous solution that facilitates diffusion in water as a cleaning liquid, foreign substances present on the surface of the conductive film are removed.

Therefore, the cleaning method of the mask blank of the present invention is not intended to remove from the surface of the conductive film by dissolving the foreign substance itself generated by peeling off a part of the organic dielectric.
As described above, the foreign matter existing on the surface of the conductive film adheres to the surface of the conductive film as a result of applying a strong chucking force between the electrostatic chuck and the conductive film when attracted and held by the electrostatic chuck. It has become. The cleaning method for mask blanks of the present invention is such that the surface of such a foreign substance adhered to the surface of the conductive film is transformed into a highly water-soluble state, weakening the bonding force with the surface of the conductive film and easily diffusing into water. By doing this, the foreign matter present on the surface of the conductive film is removed.
Here, it is not always necessary to remove the foreign matter fixed to the surface of the conductive film by cleaning with the aqueous alkali metal hydroxide solution, and scrub cleaning is performed on the surface of the conductive film whose bonding force to the foreign matter has been reduced by the cleaning. Further, foreign matter may be removed from the surface of the conductive film.
When using a cleaning solution that can dissolve the organic dielectric itself, it is necessary to add a substance having a strong chemical action that cuts the molecular chain of the constituent material of the organic dielectric. However, since such a substance is very likely to cause a chemical reaction with the conductive film, the multilayer reflective film formed on the back side of the conductive film, the absorption layer, etc. It is not suitable for the purpose of cleaning.
Therefore, it is not preferable that the alkali metal hydroxide aqueous solution in the present invention contains an oxidizing agent or a reducing agent contained in a cleaning solution used for removing a polyimide precursor or a polyimide film etching solution in the semiconductor manufacturing field. Specific examples of such oxidizing agent and reducing agent include ethylenediamine and hydrazine.

As is apparent from the above, the alkali metal hydroxide aqueous solution used as the cleaning liquid for the conductive film surface in the mask blank cleaning method of the present invention is the surface of the foreign material generated by peeling off a part of the organic dielectric. As long as it can remove foreign matter from the surface of the conductive film by altering the water into a highly water-soluble state and weakening the bonding force with the surface of the conductive film. I just need it. If the alkali metal hydroxide aqueous solution is less than 0.1 N, the surface of the foreign material generated by the separation of a part of the organic dielectric is insufficiently modified. It is not possible to reduce the bonding force of foreign matter to the conductive film surface to the extent that it can be done. If the alkali metal hydroxide aqueous solution exceeds 5 N, cleaning residues are likely to remain, and the conductive film, the multilayer reflective film formed on the back side of the conductive film, and the absorbing layer are damaged. There is a problem of worsening.
The alkali metal hydroxide aqueous solution used as the cleaning liquid is preferably 0.2 to 2N, and more preferably 0.5 to 1N.

As the alkali metal hydroxide aqueous solution used as the cleaning liquid, a 0.1 to 5 N sodium hydroxide aqueous solution and a 0.1 to 5 N potassium hydroxide aqueous solution can be used.
Even if hydrogen peroxide is added to these aqueous solutions in an amount of 4 vol% or less, the conductive film, the multilayer reflective film formed on the back side of the conductive film, the absorbing layer, etc. are not damaged. The same degree of cleaning effect can be obtained.

In the mask blank cleaning method of the present invention, the apparatus used for cleaning the conductive film surface is not particularly limited, but it is preferable to use a branch-and-leaf type spin cleaning apparatus.
FIG. 2 is a schematic diagram showing a configuration example of a branch and leaf type spin cleaning apparatus. However, the branch and leaf type spin cleaning apparatus used in the mask blank cleaning method of the present invention is not limited to this.
When carrying out the mask blank cleaning method of the present invention using the branch-and-leaf type spin cleaning apparatus 20 shown in FIG. 2, the surface to be cleaned with an alkali metal hydroxide aqueous solution (that is, the surface of the conductive film 14) is directed upward. Then, the mask blanks 10 are installed on the substrate installation unit 21 of the cleaning apparatus 20. For easy understanding, in the mask blank 10 shown in FIG. 1, the substrate 11, the multilayer reflective film 12, and the absorption layer 13 are shown as one component without being distinguished from each other.
Next, in a state where the mask blank 10 is rotated by the rotation mechanism 24, an alkali metal hydroxide aqueous solution is supplied from the cleaning liquid discharge port 23 to clean the surface of the conductive film 14.
After cleaning the surface of the conductive film 14, it is preferable to supply pure water from the pure water discharge port 22 to replace the alkali metal hydroxide aqueous solution, and after supplying pure water to replace the alkali metal hydroxide aqueous solution It is more preferable to perform spin drying.
2 has a mechanism for supplying pure water also to the back side of the mask blank 10 with respect to the surface of the conductive film 14 (below the mask blank 10 in the drawing). In this case, it is preferable to clean the surface of the conductive film 14 using an aqueous alkali metal hydroxide solution while supplying pure water to the back side of the mask blank 10.

When the branch-and-leaf type spin cleaning apparatus 20 shown in FIG. 2 has a mechanism (hereinafter referred to as “reversing mechanism”) that vertically inverts the mask blanks 10 placed on the substrate placement portion 21. With the mask blanks 10 installed in the cleaning device 20, both surfaces of the mask blanks 10 can be cleaned. That is, as shown in FIG. 2, after the mask blank 10 is placed on the substrate placement portion 21 with the surface of the conductive film 14 facing upward, and the surface of the conductive film 14 is cleaned using an alkali metal hydroxide aqueous solution, The mask blank 10 is turned upside down using the reversing mechanism to clean the surface of the absorption layer 14 of the mask blank 10 shown in FIG. 1 (or the surface of the low reflection layer when a low reflection layer is formed on the absorption layer). be able to. In this case, a cleaning liquid containing ammonia and hydrogen peroxide is preferably used as the cleaning liquid. In the cleaning liquid containing ammonia and hydrogen peroxide, the ammonia concentration is preferably 0.02 to 1 wt%, and the hydrogen peroxide concentration is preferably 0.02 to 1 wt%.
In addition, when cleaning both surfaces of the mask blank 10, it is a constituent element of the mask blank formed on the back surface side of the conductive film 14 after cleaning the surface of the conductive film 14 using an alkali metal hydroxide aqueous solution. It is preferable to clean the surface of the absorption layer 14 (or the surface of the low reflection layer when a low reflection layer is formed on the absorption layer).

  As described above, the mask blank cleaning method of the present invention changes the surface of a foreign material generated by peeling off a part of an organic dielectric material into a highly water-soluble state, and increases the bonding strength with the conductive film surface. Since the foreign matter is removed from the surface of the conductive film by weakening, it is preferable to perform scrub cleaning on the surface of the conductive film after cleaning with an aqueous alkali metal hydroxide solution. Here, scrub cleaning refers to physical cleaning in which cleaning is performed by pressing a cleaning tool such as a rotating brush against the surface to be cleaned.

  In addition, as described above, when creating mask blanks, a multilayer reflective film, an absorption layer, and various functional films are formed on the film formation surface of the glass substrate while the glass substrate is attracted and held by an electrostatic chuck. Therefore, there may be a case where foreign matter due to adsorption holding by the electrostatic chuck exists on the surface of the conductive film before the mask blanks are completely created. For example, at the stage where a multilayer reflective film is formed on the film formation surface of a glass substrate, or when a cap layer or buffer layer is further formed on the multilayer reflective film, foreign matter due to adsorption holding by an electrostatic chuck exists on the surface of the conductive film. Sometimes it is. The mask blank cleaning method of the present invention may be applied to such a substrate with a multilayer reflective film or a substrate in which a cap layer or a buffer layer is further formed on the multilayer reflective film. When the mask blank cleaning method of the present invention is applied to a substrate with a multilayer reflective film or a substrate in which a cap layer or a buffer layer is further formed on the multilayer reflective film, the same as described for the mask blanks You may perform double-sided cleaning in the procedure. That is, after cleaning the surface of the conductive film 14 using an alkali metal hydroxide aqueous solution, the multilayer reflective film surface, the cap layer surface, or the buffer layer, which is a constituent element of the mask blank formed on the back surface side of the conductive film 14 The surface may be cleaned using a cleaning solution containing ammonia and hydrogen peroxide.

  Thus, in the manufacturing method of the mask blank of this invention, the cleaning method of the mask blank of this invention is used for the cleaning process implemented by the manufacturing process of a mask blank. Similarly, in the reflective mask manufacturing method of the present invention, the mask blank cleaning method of the present invention is used for the cleaning process performed in the reflective mask manufacturing process.

Example 1
In this example, cleaning of the conductive film 14 of the mask blank 10 having the configuration shown in FIG. 1 and cleaning of the surface of the absorption layer 13 were performed using the branch-and-leaf type spin cleaning apparatus 20 shown in FIG. The configuration of the mask blank 10 is as follows.
Glass substrate 11: SiO ₂ —TiO ₂ glass substrate (outer dimensions 6 inches (152.4 mm) square, thickness 6.3 mm)
Multilayer reflective film 12: Si / Mo multilayer reflective film (film thickness 272 nm ((4.5 + 2.3) × 40)
Cap layer (not shown): Si layer (film thickness 11.0 nm)
Absorption layer 13: TaN layer (film thickness 70 nm)
Conductive film 14: CrN film (Cr85at%) (film thickness 100nm)
When the mask blanks 10 are produced, the glass substrate 11 as a base is formed and held by an electrostatic chuck using an organic dielectric (polyimide film) on the suction holding surface. On the film surface, a multilayer reflective film 12, a cap layer (not shown), and an absorption layer 13 were formed. A composition analysis of additional defects on the surface of the conductive film 14 was performed on 10 substrates formed in the same batch, and C, N, and O were detected in all. Since C and N were not detected in a place where there was no additional defect, it was determined that the dominant component of the additional defect on the surface of the conductive film 14 was polyimide.

First, as shown in FIG. 2, the mask blank 10 is placed on the substrate placement portion 21 of the cleaning device 20 with the surface of the conductive film 14 facing upward. Next, in a state where the mask blank 10 is rotated at a rotation speed of 100 rpm by the rotation mechanism 24, an alkali metal hydroxide aqueous solution (potassium hydroxide 2.0 N aqueous solution) is projected 1.0 L / min from the cleaning liquid discharge port 23. The pure water was supplied from the pure water discharge port 22 at a protruding amount of 1.0 L / min, and the concentration of the alkali metal hydroxide aqueous solution on the surface of the conductive film 14 was set to 1.0 normal.
After cleaning the surface of the conductive film 14, pure water was supplied from the pure water discharge port 22 to replace the cleaning liquid, and then spin-dried at a rotational speed of 1000 rpm.
Thereafter, the mask blanks 10 were turned upside down using an inversion mechanism (not shown), and the surface of the absorption layer 13 was spin cleaned. The conditions for spin cleaning are as follows.
Rotation speed: 100rpm
Cleaning liquid: ammonia water (0.1 wt%) + hydrogen peroxide water mixture (0.1 wt%)
Cleaning liquid discharge rate: 1.0 L / min
Pure water discharge rate: 1.0 L / min
After cleaning the surface of the absorption layer 13, pure water was supplied from the pure water discharge port 22 to replace the cleaning liquid, and then spin-dried at a rotational speed of 1000 rpm. This procedure was performed on three mask blanks.
As a result of inspecting the conductive film surface of the mask blanks after spin drying with a defect inspection machine (M1350A manufactured by Lasertec), the number of additional defects of 200 nm or more, that is, the number of foreign matters having a size of 200 nm or more fixed to the conductive film surface is The average of 3 sheets was 21.

(Comparative Example 1)
As an alkali metal hydroxide aqueous solution, a 0.1 N potassium hydroxide aqueous solution is supplied from the cleaning liquid discharge port 23 at a protruding amount of 1.0 L / min, and pure water is supplied from the pure water discharge port 22 at a protruding amount of 1.0 L / min. The same procedure as in Example 1 was performed, except that the concentration of the aqueous alkali metal hydroxide solution on the surface of the conductive film 14 was 0.05N.
As a result of inspecting the conductive film surface of the mask blank after spin drying with a defect inspection machine, the number of additional defects of 200 nm or more, that is, the number of foreign matters having a size of 200 nm or more fixed on the conductive film surface was an average of three. There were 677.

(Comparative Example 2)
As an alkali metal hydroxide aqueous solution, an 8.0 normal potassium hydroxide aqueous solution is supplied from the cleaning liquid discharge port 23 at a protruding amount of 1.0 L / min, and pure water is not supplied from the pure water discharge port 22. The same procedure as in Example 1 was performed, except that the concentration of the aqueous alkali metal hydroxide solution on the 14 surface was 8.0 N.
A cleaning residue was visually confirmed on the surface of the conductive film of the mask blank after spin drying, and the purpose of cleaning the surface of the conductive film could not be achieved.

(Comparative Example 3)
Instead of cleaning the surface of the conductive film 14 using an alkali metal hydroxide aqueous solution, the same procedure as in Example 1 was performed, except that the surface of the conductive film 14 was subjected to spin cleaning under the following conditions.
Rotation speed: 100rpm
Cleaning liquid: KS-3053 (polyoxyethylene alkyl ether surfactant) (manufactured by Kao Corporation) (1.0 wt%)
Cleaning liquid discharge rate: 1.0 L / min
Pure water discharge rate: 1.0 L / min
In addition, as a result of inspecting the conductive film surface of the mask blank after spin drying with a defect inspection machine (M1350A, manufactured by Lasertec), the number of additional defects of 200 nm or more, that is, foreign matter having a size of 200 nm or more fixed on the conductive film surface. The number of the three sheets was 823 on average.

(Comparative Example 4)
The electrostatic chuck was changed to one using an inorganic dielectric (alumina (aluminum substrate surface anodized)) on the adsorption holding surface, and the same procedure as in Example 1 was performed except that. As a result of inspecting the conductive film surface of the mask blank after spin drying with a defect inspection machine (M1350A manufactured by Lasertec), the number of additional defects of 200 nm or more, that is, the number of foreign matters having a size of 200 nm or more fixed to the conductive film is The average of 3 sheets was 8744.

10: Mask blanks 11: Glass substrate 12: Multi-layer reflective film 13: Absorbing layer 14: Conductive film 20: Branched leaf type spin cleaning device 21: Substrate installation part 22: Pure water discharge port 23: Cleaning liquid discharge port 24: Rotation mechanism

Claims (5)

A method of cleaning a reflective mask blank in which a conductive film is formed on one surface of a glass substrate, and the conductive film is sucked and held by an electrostatic chuck using an organic dielectric on a sucking and holding surface,
After cleaning the surface of the conductive film with an aqueous 0.1-5N alkali metal hydroxide solution, the components of the reflective mask blanks formed on the back side of the conductive film are combined with ammonia and peroxide. A method for cleaning a reflective mask blank , comprising cleaning with a cleaning liquid containing hydrogen .   The method for cleaning a reflective mask blank according to claim 1, wherein the alkali metal hydroxide aqueous solution is a 0.1 to 5 N sodium hydroxide aqueous solution or a 0.1 to 5 N potassium hydroxide aqueous solution.   The method of cleaning a reflective mask blank according to claim 1 or 2, wherein scrub cleaning is performed on the surface of the conductive film that has been cleaned with the alkali metal hydroxide aqueous solution. The manufacturing method of the reflective mask blank which uses the cleaning method of the mask blank in any one of Claims 1-3 for the cleaning process implemented at the manufacturing process of a reflective mask blank . The manufacturing method of the reflective mask which uses the cleaning method of the mask blanks in any one of Claims 1-3 for the cleaning process implemented at the manufacturing process of a reflective mask .

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