WO2012102313A1

WO2012102313A1 - Method for manufacturing photomask

Info

Publication number: WO2012102313A1
Application number: PCT/JP2012/051574
Authority: WO
Inventors: 生田　順亮; 直弘梅尾
Original assignee: 旭硝子株式会社
Priority date: 2011-01-26
Filing date: 2012-01-25
Publication date: 2012-08-02
Also published as: TW201243487A; TWI572974B; JP5880449B2; JPWO2012102313A1

Abstract

The present invention relates to a method for manufacturing a photomask, in which a mask pattern is drawn, according to a mask pattern design, on a mask blank comprising at least a polishing substrate and a light absorption film disposed on the polishing substrate, wherein at least one of the surface shape of a plurality of the polishing substrates and the surface shape of a plurality of the mask blanks is measured, a reference surface shape or reference substrate thickness distribution is calculated based on the measured surface shape, and based on the calculated reference surface shape or reference substrate thickness distribution, a mask pattern-forming position is adjusted when the mask pattern is drawn.

Description

Photomask manufacturing method

The present invention relates to a photomask manufacturing method, and more particularly to a manufacturing method suitable for a reflective photomask for EUV lithography (EUVL) using EUV (Extreme Ultra Violet) light.

Conventionally, in lithography technology, an exposure apparatus for transferring a fine circuit pattern onto a wafer to manufacture a semiconductor device has been widely used. As semiconductor devices are highly integrated, speeded up, and power saved, semiconductor devices are becoming finer. In response to this trend, the exposure apparatus is required to form an image of a finer semiconductor device circuit pattern on the wafer surface with a greater depth of focus, and the wavelength of the exposure light source is being shortened. Specifically, the light used as the exposure light source proceeds from the conventional g-line (wavelength 436 nm), i-line (wavelength 365 nm) and KrF excimer laser (wavelength 248 nm), and ultraviolet light from an ArF excimer laser (wavelength 193 nm). Is used.

However, even with lithography technology using such light having a wavelength of 193 nm, only semiconductor devices having circuit dimensions of 32 to 45 nm can be produced at the most, and development of techniques capable of producing semiconductor devices having circuit dimensions of 30 nm or less is required. It has been. Against this background, lithography technology using extreme ultraviolet light (EUV light) has attracted attention as a promising candidate and is being actively developed. EUV light refers to light in the wavelength band of the soft X-ray region or the vacuum ultraviolet region, specifically, light having a wavelength of about 0.2 to 100 nm. At present, the use of light having a wavelength near 13.5 nm as a lithography light source is mainly studied.

The exposure principle of EUV lithography (hereinafter also abbreviated as “EUVL”) is the same as that of conventional lithography in that a mask pattern is reduced and projected onto a wafer using a projection optical system, but in the energy region of EUV light, Because there is no light-transmitting material, a transmission / refraction optical system using a transmission type photomask usually used in an exposure apparatus that uses light of wavelength 193 to 436 nm as a light source cannot be used, and a reflection optical system is used. Has been. The optical member of the reflective optical system is composed of a reflective photomask and a plurality of reflective mirrors, and the ratio of the pattern formed on the mask to the resist formed on the wafer via the reflective mirror is 1/4. Projected at a reduced magnification of ~ 1/5.

Here, the reflection type photomask mainly includes four procedures (first procedure; preparation of polishing substrate, second procedure; creation of ML blank, third procedure; creation of mask blank, and fourth procedure; photomask It is a kind of optical member (optical member for EUVL) obtained through preparation.

For reference, the cross-sectional structures of a mask blank and a reflective photomask are schematically shown in FIGS. 1 and 2, respectively. 1 and 2, 1 is a polishing substrate, 2 is a multilayer reflective film (hereinafter abbreviated as “ML film”) formed on the surface on which the polishing substrate is formed, and 3 is a protection formed on the ML film surface. 4 is an absorption film formed on the protective film surface, 5 is an antireflection film formed on the absorption film surface, 6 is a resist film formed on the antireflection film, and 7 is formed on the back surface of the polishing substrate. The conductive film made is shown.

FIG. 4 shows a side view of the polishing substrate (in the drawing, exaggerated expression is shown for easy understanding of the deformation mode). FIG. 4A shows a polishing substrate before final (local) polishing, and FIG. 4B shows a polishing substrate after local polishing.

In the reflection type photomask, a mask pattern is formed on the EUV light absorption film of the mask blank, the EUV light reflection layer is exposed and the EUV light is reflected, and the reflection layer is covered with the absorption film so that the EUV light is hardly reflected. It has a part.

In addition, since an electrostatic chuck is generally used to hold the reflective photomask on the mask stage of the exposure apparatus, a conductive film having a sheet resistance of 100Ω or less (for example, CrN, Cr, CrO, CrON, TaN, etc.) are usually formed.

By the way, in an exposure apparatus using EUV light as a light source, the reflective photomask is attracted and held by an electrostatic chuck using a conductive film formed on the back surface thereof, and the mask pattern formed on the film formation surface is formed on the wafer. Reduced projection and transfer to a resist film. At this time, the flatter the mask pattern formation surface of the reflective photomask is, the more faithfully transferred and formed the mask pattern formed on the reflective photomask deposition surface onto the resist film on the wafer at a desired position. Therefore, it is preferable.

In particular, in the case of a semiconductor device having a circuit dimension of 30 nm or less for which application of EUVL is being studied, the required accuracy with respect to the circuit pattern formation position is 5 nm or less, and further, 3 nm or less, which is extremely strict. Therefore, for the flatness of the surface on which the polishing substrate is formed and the back surface, the conventional required level of 250 nm or less is extremely low, such as 100 nm or less, further 50 nm or less, and further 30 nm or less for the EUVL polishing substrate. Strict levels have been required.

Here, as shown in FIG. 4 of Non-Patent Document 1, the flatness of the polishing substrate is the maximum value of the height difference in the gentle irregularities having a spatial wavelength of 0.1 mm or more on the surface on which the polishing substrate is formed and the back surface. (See FIG. 4 of Non-Patent Document 1). In addition to the flatness, there are no defects such as scratches or leaks having a depth of 1 nm or more and defects such as minute irregularities having a polystyrene latex particle diameter conversion size of 50 nm or more on the surface on which the polishing substrate is formed. That is also sought.

The strict requirements as described above are mainly due to the fact that the wavelength of light used for exposure is extremely short, 1/10 or less compared with 193 nm of the current mainstream ArF lithography. It is unique to photomasks.

On the other hand, the level of the processing method does not always catch up with the above required level, and in reality, it is possible to obtain a polished substrate that satisfies all of the mirror surface (smoothness), the number of low defects, and the high flatness at the same time. It is extremely difficult. Therefore, a method of using a reflective mask using a polishing substrate that does not reach the required flatness has been proposed (see

Patent Documents

1 and 2, Non-Patent Document 1). Specifically, when drawing a mask pattern using an electron beam or the like, the mask pattern depends on the flatness of the surface and the back surface of the polishing substrate constituting the mask blank or the thickness distribution of the polishing substrate. This is a method of adjusting the formation position.

For example, when the method for adjusting the mask pattern forming position as described above is adopted, for example, the demand for the flatness of the polishing substrate constituting the mask blank is reduced to 300 nm or less. In this case, a polishing substrate having a small number of defects such as a flatness of 300 nm or less on the surface to be formed and a back surface, a surface roughness (RMS) of 0.15 nm or less on the surface to be formed, and a size of 50 nm or more on the surface to be formed. The polishing substrate can be processed considerably easily because it can be realized by focusing only on the surface roughness and defects.

However, in the proposed method, when the mask pattern of the reflective photomask is drawn on the mask blank using an electron beam or the like, the mask pattern forming position is set flat for each mask blank. There is a problem in that it takes a considerable amount of time and labor to form a mask pattern because it is necessary to individually adjust the surface shape such as the degree. For this reason, there is a strong demand for improvements in terms of productivity and cost.

The adjustment of the mask pattern formation position is not used only for the EUVL reflective photomask, but other photomasks, i.e., i-line (wavelength 365 nm), KrF excimer laser (wavelength 248 nm), ArF excimer Needless to say, the present invention can also be applied to a transmissive photomask for lithography using a laser (wavelength: 193 nm) as a light source.

Japanese Unexamined Patent Publication No. 2006-39223 (US7703066) Japanese Unexamined Patent Publication No. 2008-103512

In a conventional method for manufacturing a photomask (particularly, a reflective photomask for EUVL), when a mask pattern of a photomask (particularly, a reflective photomask for EUVL) is drawn on a mask blank using an electron beam or the like, The mask pattern formation position is individually adjusted according to the flatness and thickness distribution of the polishing substrate for each mask blank, that is, the mask pattern formation position needs to be adjusted for each mask blank. Therefore, there is a problem that the mask pattern forming operation becomes complicated, and improvement is strongly demanded from the viewpoint of productivity and cost.

Therefore, the present invention provides a photomask (particularly, a reflective type for EUVL) in which the mask pattern forming position does not have to be individually adjusted according to the flatness and thickness distribution of the polishing substrate for each mask blank. An object of the present invention is to provide a manufacturing method of a photomask.

A photomask manufacturing method according to the present invention (hereinafter referred to as the present manufacturing method) draws a mask pattern on a mask blank having at least a polishing substrate and a light absorption film formed on the polishing substrate based on the mask pattern design. A method of manufacturing a photomask,
Measured at least one of the surface shape of a plurality of polishing substrates or the surface shape of a plurality of mask blanks, and after calculating a reference surface shape or a reference plate thickness distribution based on the measured surface shape, the calculated A mask pattern forming position at the time of drawing the mask pattern is adjusted based on a reference surface shape or a reference plate thickness distribution.

In this manufacturing method, the photomask is a reflective photomask for EUVL, and the mask blank has a multilayer reflective film (ML film) between the polishing substrate and the light absorption film, and light formed on the ML film. The absorption film is preferably an EUV light absorption film.

In the present manufacturing method, the reference surface shape is the average shape of the surface shapes of the surface and the back surface of the plurality of polishing substrates, or the film formation surface and the back surface of the mask blanks, respectively. The average shape of the surface shape is preferably itself. Alternatively, in the present manufacturing method, the reference surface shape is an average shape of the surface shapes of the surface and the back surface of the plurality of polishing substrates or each of the film formation surface and the back surface of the plurality of mask blanks. It is also preferable that the average shape of the surface shape is calculated, and the calculated average shape is approximated by a polynomial such as a Legendre polynomial or a Zernike polynomial. Further, in the present manufacturing method, the reference surface shape is a surface shape of each of the surface and the back surface of the plurality of polishing substrates or a surface shape of each of the film formation surfaces and the back surface of the plurality of mask blanks. It is also preferable that at least one of these be approximated by a polynomial such as a Legendre polynomial or a Zernike polynomial, and obtained by averaging them.

In this manufacturing method, it is preferable that the reference plate thickness distribution is an average of plate thickness distributions of the plurality of polishing substrates or an average of plate thickness distributions of the plurality of mask blanks. Alternatively, in the present manufacturing method, the reference plate thickness distribution is calculated by calculating an average plate thickness distribution of the plurality of polishing substrates or an average plate thickness distribution of the plurality of mask blanks, and calculating the calculated average plate thickness distribution. It is also preferable that it is obtained by approximation with a polynomial such as a Legendre polynomial or a Zernike polynomial. Further, in the present manufacturing method, the reference plate thickness distribution is a polynomial such as a Legendre polynomial or a Zernike polynomial, wherein at least one of the plate thickness distribution of the plurality of polishing substrates or the plate thickness distribution of the plurality of mask blanks. It is also preferable that they are approximated and obtained by averaging them.

Compared with the conventional technique in which the surface shape measurement or the plate thickness distribution measurement is performed for each polishing substrate, the mask pattern formation position is adjusted based on the measurement data, and the mask pattern is drawn, in this manufacturing method, Since a plurality of polishing substrates are drawn by adjusting the mask pattern formation position based on the same reference surface shape or the same reference plate thickness distribution, the mask pattern formation position adjustment time is greatly shortened.

For example, in the case of manufacturing five photomasks, in the conventional method, it is necessary to adjust the mask pattern formation position five times. According to this method, however, the reference surface shape or the reference of the five polishing substrates is used. It only needs to be adjusted once based on the plate thickness distribution. As a result, the productivity of the photomask is significantly improved.

This manufacturing method makes it possible to achieve both high productivity of a photomask and provision of a photomask having sufficient accuracy for EUVL, and stably improve the transfer accuracy during EUVL implementation.

FIG. 1 is a schematic diagram showing a cross-sectional structure of a mask blank (for EUVL). FIG. 2 is a schematic diagram showing a cross-sectional structure of a photomask (reflection type for EUVL). FIG. 3 is a top view of the mask blank as viewed from the pattern forming surface side of the photomask (EUVL reflective type). 4 (a) and 4 (b) are side views of the polishing substrate. FIGS. 5A to 5D are diagrams for explaining the procedure for calculating the plate thickness distribution of the polishing substrate used for the mask blank. FIG. 6 is a conceptual diagram illustrating a method for adjusting the formation position of the mask pattern. FIG. 7 shows the measurement result of the surface shape of the surface on which five polishing substrates are deposited and the average shape (reference surface shape). FIG. 8 shows the measurement results of the surface shape of the back surface of five polishing substrates and the average shape (reference surface shape). FIG. 9 is an example in which the average surface shape of each of the surfaces on which the five polishing substrates are deposited is approximated by a Legendre polynomial to obtain the respective reference surface shapes. FIG. 10 shows the thickness distribution of the polishing substrate calculated by adding the measurement result of the surface shape of the surface to be deposited after reversing the measurement result of the surface shape of the back surface of the five polishing substrates, It is an average plate thickness distribution (reference plate thickness distribution) of the polishing substrate. FIG. 11 is an example in which the average plate thickness distribution of five polishing substrates is approximated by a Legendre polynomial to obtain a reference plate thickness distribution.

The present invention relates to a photomask manufacturing method. First, an outline of a photomask manufacturing method is described in the following four procedures (first procedure; preparation of polishing substrate, second procedure; creation of ML blank, third procedure; creation of mask blank, and fourth procedure; photomask ). Note that the second procedure (creating an ML blank) is indispensable in the EUVL photomask manufacturing method, but is not necessary in any photomask manufacturing method other than EUVL.

First, as a first procedure, two opposing surfaces having a smooth and flat surface with a very small surface roughness and no gentle irregularities with a spatial wavelength of 0.1 mm or more and four side surfaces connecting the two opposing surfaces A substrate having the following (hereinafter referred to as a polishing substrate) is prepared. Of the two opposing surfaces having the flat surface, one surface finally becomes a surface on which a semiconductor device circuit pattern is formed (hereinafter referred to as a film formation surface), and the remaining surface on which no pattern is formed (hereinafter referred to as a surface). Called the back side).

The polishing substrate is required to have low thermal expansion so that expansion and contraction due to temperature change does not occur as much as possible. Therefore, for example, silica glass containing TiO ₂ (hereinafter abbreviated as TiO ₂ —SiO ₂ glass), silica glass (SiO ₂ glass), and the like are preferable materials. A rectangular parallelepiped made of the material is manufactured, cut and processed into a slice substrate, and polished to create a polished substrate.

As a second procedure (in the case of a photomask for EUVL), an ML blank is produced in which an ML film that reflects EUV light is formed on the surface of the polishing substrate obtained in the first procedure. As the ML film, a multilayer reflective film having a high reflectance by stacking alternately a high refractive index film (for example, Si) and a low refractive index layer (for example, Mo) in EUV light is usually used. In order to prevent deterioration such as oxidation of the ML film, a protective film (eg, Ru, Si, TiO ₂ or the like) may be usually formed on the ML film.

Next, as a third procedure, in the case of a photomask other than for EUVL, a light absorption film is formed on the polishing substrate obtained in the first procedure. In the case of a photomask for EUVL, EUV light is absorbed on the ML film of the ML blank obtained in the second procedure (or on the protective film if a protective film is formed on the ML film). An absorption film (for example, Ta or TaN) is formed. If necessary, an antireflection film (for example, TaON or TaO) having a low reflectance at the wavelength of the mask pattern inspection light may be formed on the absorption film. Next, a resist film is formed on the absorption film (on the antireflection film if an antireflection film is formed). A mask blank (see FIG. 1 for the cross-sectional structure) is such that an absorption film, an antireflection film, and a resist film are formed in this order on the ML blank in this order.

The final fourth procedure is the formation of a mask pattern. That is, (4-1) using a drawing apparatus that uses an electron beam or ultraviolet light as a light source, clamping the side of the mask blank or the vicinity of the outer periphery of the front and back surfaces, and holding the mask blank in some way, Drawing the designed mask pattern on the film, (4-2) heating, (4-3) removing the unnecessary resist film, (4-4) removing the unnecessary resist film, and exposing it This process consists of a series of processes such as etching away the absorbed film (both antireflective film and absorption film when antireflection film is formed) and (4-5) removing the remaining resist film. .

The present invention relates to a method of manufacturing a photomask, and is particularly characterized by adjusting a mask pattern forming position. Hereinafter, the present invention will be described in detail focusing on this.

[Preparation of polishing substrate (first procedure)]
A polishing substrate is obtained by obtaining a substrate processed to a desired shape accuracy from a lump of material, and using a double-sided lapping (polishing) machine on the surface of the substrate on which the polishing substrate is to be formed and the back surface. A polishing slurry containing water and water can be supplied to a polishing pad or the like to simultaneously polish both surfaces. Thereafter, it is preferable to use a local polishing method in which the surface and / or the back surface of the obtained polishing substrate is locally partially polished. Examples of the local polishing method include mechanical, chemical mechanical, MRF using magnetic abrasive grains, a beam (laser) irradiation method, a gas cluster ion beam etching method, and the like.

[Characteristics required for polishing substrate]
In the present invention, the polishing substrate is required to have excellent surface smoothness on the surface to be formed and the back surface. Specifically, in the case of a photomask for EUVL, the result (RMS) of the surface roughness of the surface to be deposited and the back surface in the quality assurance region measured with an atomic force microscope in a 10 μm × 10 μm square region is 0. It is preferably 0.5 nm or less, more preferably 0.3 nm or less, and further preferably 0.15 nm or less.

Here, in the case of a surface on which a film is formed, the quality assurance region is a region in which light such as EUV light for exposure or alignment is irradiated and alignment in a mask blank and a photomask manufactured using the polishing substrate. This is a region irradiated with EUV light or ultraviolet to visible light for mask identification.

Also, the quality assurance area on the back surface is an area for attracting and holding the EUVL mask blank and the reflective mask with an electrostatic chuck. In the case of the mask blank (for EUVL) 10 shown in FIG. 3, the quality assurance area 11 is the quality assurance area. The range of the quality assurance region varies depending on the dimensions of the mask blank (for EUVL), more specifically, the dimensions of the surface and the back surface on which the polishing substrate is formed. In the case of 152 × 152 mm square, the range of the quality assurance region is a 142 mm × 142 mm square region excluding the outer edge portion of 5 mm from the end.

In the present invention, the polishing substrate is required to have no convex defects such as particles and concave defects such as scratches, leaks, and pits on the surface of the surface on which the film is formed. Specifically, in the surface quality region of the surface to be deposited, the number of both concave and convex defects having a polystyrene latex particle size conversion size of 150 nm or more is preferably 10 or less, and more preferably 5 or less. Preferably, it is 0. Further, in the surface quality region of the surface on which the film is formed, the number of both concave and convex defects having a silica particle diameter conversion size of 70 nm or more is preferably 100 or less, more preferably 80 or less, and 60 or less. More preferably.

[Method for measuring surface shape of polishing substrate (mask blank)]
In the present invention, the apparatus for measuring the surface shape of the surface on which the polishing substrate is formed and the back surface is a laser interference type flatness meter (for example, Verifire, Mark IV manufactured by Zygo, G310S manufactured by Fujinon, FlatMaster manufactured by Tropel, etc. ), A laser displacement meter, an ultrasonic displacement meter, a contact displacement meter, or the like can be used. Here, the residue obtained by removing the tilt component from the results obtained using various measuring devices is the surface shape, and the difference between the maximum value and the minimum value of the surface shape is the flatness.

In the present invention, as a method for measuring the thickness distribution of the polishing substrate, when the substrate has a sufficient light transmittance of 30% or more in the visible light region having a wavelength of 300 to 800 nm, the wavelength of 300 to 800 nm is used. By using an interferometer that uses visible light as a light source (for example, Zirgo Verifire, Mark IV, Fujinon G310S, Tropel FlatMaster, etc.) There is a method of measuring a plate thickness distribution of a substrate and obtaining a plate thickness distribution as a residue obtained by subtracting a tilt component from the obtained plate thickness distribution.

In the present invention, the surface shape of the surface on which another polishing substrate is formed and the surface shape of the back surface are measured by the above-described laser interference type flatness measuring machine, and the thickness is calculated by adding them together. You can also Here, in order to calculate the plate thickness distribution of the polishing substrate, the surface shape measurement result of one of the surface shape (or the surface profile) of the surface to be deposited and the back surface is reversed, and then the other surface It is necessary to add to the shape measurement result. In the former method, since the obtained maximum plate thickness distribution includes the refractive index distribution of the substrate material, the latter is preferable in the case of a substrate obtained using a material having a refractive index distribution. Hereinafter, the latter measurement method will be described in more detail.

FIG. 5 is a diagram illustrating a procedure for calculating a plate thickness distribution of the polishing substrate (for EUVL). The procedure will be described below with reference to FIG. First, as shown in FIG. 5A and FIG. 5B, after measuring the surface shapes (or surface profiles) of the surface C and the back surface D to be formed, as shown in FIG. 5C. Invert the measurement result of the surface shape (or surface profile) of the back surface D, add the measurement result of the surface shape (or surface profile) of the surface C to be deposited, and add the tilt component from the addition result. By removing, the plate thickness distribution of the polishing substrate for EUVL shown in FIG. 5D is calculated.

The maximum thickness distribution is obtained as the difference between the maximum value and the minimum value of the thickness distribution obtained by both methods. Moreover, the surface shape measuring method described here can be applied as it is as a surface shape measuring method of a mask blank by changing a measuring object from a polishing substrate to a mask blank.

[ML blank creation (second procedure; photomask for EUVL)]
A multilayer reflective film in which a high refractive index film and a low refractive index film are alternately laminated a plurality of times is formed as an ML film 2 having a high reflectance in EUV reflected light on the surface on which the polishing substrate 1 is formed. Here, EUV reflected light refers to reflected light generated when a light ray in the wavelength range of EUV light is irradiated at an incident angle of 6 to 10 degrees, and the reflectance of EUV reflected light refers to EUV reflected light at a wavelength of 12 to 15 nm. It is intended to reflect light having a wavelength of around 13.5 nm.

The EUV reflected light from the ML film surface preferably has a maximum reflectance of 60% or more, and more preferably 63% or more. Si (refractive index = 0.999 (λ = 13.5 nm)) is widely used for the high refractive index film of the ML film, and Mo (same refractive index = 0.924) is widely used for the low refractive index film ( Mo / Si multilayer reflective film).

However, the ML film is not limited to this, and the Ru / Si multilayer reflective film, the Mo / Be multilayer reflective film, the Rh / Si multilayer reflective film, the Pt / Si multilayer reflective film, the Mo compound / Si compound multilayer reflective film, the Si / Mo / Ru multilayer reflective films, Si / Mo / Ru / Mo multilayer reflective films, Si / Ru / Mo / Ru multilayer reflective films, and the like can also be used.

The film thickness of each layer constituting the ML film and the number of repeating units of the layer can be appropriately selected according to the film material to be used and the reflectance of EUV reflected light required for the ML film. Taking a Mo / Si multilayer reflective film as an example, in order to set the maximum reflectance of EUV reflected light to 60% or more, a Si layer with a film thickness of 4.5 ± 0.1 nm and a film thickness of 2.3 It is preferable to stack a Mo layer of ± 0.1 nm in this order so that the number of repeating units is 30 to 60.

Note that each layer constituting the ML film may be formed to have a desired film thickness using a known film forming method such as a magnetron sputtering method or an ion beam sputtering method.

The protective film 3 can be provided on the surface of the ML film 2 in order to prevent the surface of the ML film 2 and the vicinity thereof from being naturally oxidized during storage or oxidized during cleaning. As the protective film 3, Si, Ti, Ru, Rh, C, SiC, a mixture of these elements / compounds, or those obtained by adding N, O, B or the like to these elements / compounds can be used.

When Ru is used as the protective film, the film thickness can be as thin as 2 to 3 nm, which is particularly preferable because it can also function as a buffer film described later. When the ML film is a Mo / Si multilayer reflective film, the uppermost layer can be made to function as a protective film by making the uppermost layer an Si film. In this case, the thickness of the uppermost Si film that also serves as a protective film is preferably 5 to 15 nm, which is larger than the usual 4.5 nm. Further, after forming a Si film as a protective film, a Ru film serving as both a protective film and a buffer film may be formed on the Si film.

Note that the film such as the ML film or the protective film is not necessarily one layer, and may be two or more layers. When a protective film is provided on the ML film, the maximum value of the reflectance of EUV reflected light from the surface of the protective film needs to satisfy the above range. That is, the maximum value of the reflectance of EUV reflected light from the protective film surface is preferably 60% or more, and more preferably 63% or more. Note that the protective film may be formed to have a desired film thickness using a known film formation method such as a magnetron sputtering method or an ion beam sputtering method.

[Formation of mask blank (third procedure)]
Next, in the case of a photomask other than for EUVL, a light absorption film is formed on the polishing substrate obtained in the first procedure. In the case of an EUVL photomask, the absorption film 4 is formed on the ML blank surface (on the ML film or on the protective film when a protective film is formed on the ML film). The characteristic particularly required for the absorption film 4 is that the pattern formed on the EUV reflection mask is transferred from the absorption film 4 so that the pattern is faithfully transferred to the resist film on the wafer via the projection optical system of the EUVL exposure machine. Adjusting the intensity and phase of the reflected light.

There are two specific methods. The first method is to reduce the intensity of reflected light from the absorption film 4 as much as possible. The absorption film 4 (when an antireflection film is formed on the absorption film surface) The film thickness and material of the absorption film 4 are adjusted so that the reflectance of EUV light from the antireflection film) surface is 1% or less, particularly 0.7% or less. The second is a method that uses the interference effect of the reflected light from the ML film 2 and the reflected light from the absorption film 4 (or the antireflection film when an antireflection film is formed on the absorption film surface), The reflectance of EUV light from the absorption film 4 (antireflection film when an antireflection film is formed on the absorption film surface) is set to 5 to 15%, and the reflected light from the ML film 2 and the absorption film 4 (absorption) When an antireflection film is formed on the film surface, the film thickness and material of the absorption film 4 are adjusted so that the phase difference of reflected light from the antireflection film) is 175 to 185 degrees.

In any method, the material constituting the absorption film 4 is preferably a material containing Ta at least 40 at%, preferably at least 50 at%, more preferably at least 55 at%. The material mainly composed of Ta used for the absorption film 4 preferably contains at least one element of Hf, Si, Zr, Ge, B, Pd, H, and N in addition to Ta.

Specific examples of the material containing the above elements other than Ta include TaN, TaNH, TaHf, TaHfN, TaBSi, TaBSiN, TaB, TaBN, TaSi, TaSiN, TaGe, TaGeN, TaZr, TaZrN, TaPd, and the like. It is done. However, it is preferable that the absorption film 4 does not contain oxygen. Specifically, the oxygen content in the absorption film 4 is preferably less than 25 at%.

When an EUV mask is formed by forming a mask pattern on an absorption film of a mask blank, a dry etching process is usually used. As an etching gas, chlorine gas (including mixed gas) or fluorine-based gas (mixed gas) is used. Are usually used.

In order to prevent damage to the ML film due to the etching process, when a film containing Ru or a Ru compound is formed on the ML film as a protective film, the protective film is less damaged. Is used. However, when the dry etching process of the absorption film 4 is performed using chlorine gas, if the absorption film 4 contains oxygen, the etching rate is lowered, and the damage to the resist film is increased. The oxygen content in the absorption film 4 is more preferably 15 at% or less, further preferably 10 at% or less, and particularly preferably 5 at% or less.

In the case of the first method described above, the thickness of the absorption film 4 is 60 nm or more so that the reflectance of EUV light from the surface of the absorption film 4 is 1% or less, particularly 0.7% or less. It is particularly preferable that the thickness is 70 nm or more. In the case of the second method described above, the range of 40 nm to 60 nm is preferable, and the range of 45 nm to 55 nm is particularly preferable.

The absorption film 4 having the above-described configuration can be formed by a known film formation method, for example, a magnetron sputtering method or an ion beam sputtering method.

In the present invention, in order to prevent the ML film 2 from being damaged by an etching process, usually a dry etching process, performed when forming an EUV mask by forming a mask pattern on the absorption film 4 of the mask blank, A buffer film serving as an etching stopper may be provided between the ML film 2 (the protective film 3 when the protective film 3 is formed on the ML film) and the absorption film 4. As the material of the buffer film, a material that is not easily affected by the etching process of the absorption film 4, that is, the etching rate is slower than that of the absorption film 4 and is not easily damaged by this etching process is selected. Examples of the material satisfying this condition include Cr, Al, Ru, Ta, and nitrides thereof, and SiO ₂ , Si ₃ N ₄ , Al ₂ O _3, and mixtures thereof. Among these, Ru, CrN, and SiO ₂ are preferable, CrN and Ru are more preferable, and Ru is particularly preferable because it combines the functions of a protective film and a buffer film. The thickness of the buffer film is preferably 1 to 60 nm. The buffer film can be formed using a known film formation method such as a magnetron sputtering method or an ion beam sputtering method.

In the present invention, a low-reflective antireflection film may be provided on the absorption film 4 as a mask blank. The antireflection film provides a good contrast when inspecting the mask pattern and facilitates accurate mask pattern defect inspection. Specifically, the reflectance of the reflected light generated when the mask pattern inspection light is irradiated on the surface of the antireflection film is preferably 15% or less, more preferably 10% or less, and more preferably 5% or less. More preferably it is. As inspection light, light of about 257 nm is usually used. In order to achieve the above characteristics, the antireflection film is preferably made of a material whose refractive index at the wavelength of the inspection light is lower than that of the absorption film. Specifically, a material mainly containing Ta can be used. In addition to Ta, at least one element of Hf, Ge, Si, B, N, H, and O can be contained. Specific examples include TaO, TaON, TaONH, TaHfO, TaHfON, TaBSiO, TaBSiON, SiN, and SiON.

When an antireflection film is formed on the absorption film, the total thickness of the absorption film and the antireflection film is preferably 10 to 65 nm, more preferably 30 to 65 nm, and further preferably 35 to 60 nm. In addition, if the thickness of the antireflection film is larger than the thickness of the absorption film, the EUV light absorption characteristics in the absorption film may be deteriorated. Therefore, the thickness of the antireflection film is smaller than the thickness of the absorption film. It is preferable. Therefore, the thickness of the antireflection film is preferably 1 to 20 nm, more preferably 3 to 15 nm, and further preferably 5 to 10 nm.

In the present invention, a functional film such as a hard mask may be provided. The hard mask is formed on the surface of an absorption film (an antireflection film when an antireflection film is formed on the absorption film and the hard mask does not have an antireflection film function). Since the dry etching rate described above is slower than that of the absorption film and / or the antireflection film, the resist film can be made thinner and a finer pattern can be produced. As a material for such a hard mask, Cr ₂ O ₃ , Ru, Cr (N, O) or the like can be used, and the film thickness is preferably 2 to 10 nm.

In the present invention, in the case of a photomask other than for EUVL, the basic configuration of the mask blank is to have at least a light absorption film on the surface of the polishing substrate. In the case of a photomask for EUVL, the basic structure is to have at least an ML film that reflects EUV light on the surface of the polishing substrate and an absorption film that absorbs EUV light on the ML film. A protective film may be formed, both the protective film and the buffer film may be formed, or an antireflection film and a hard mask may be formed on the surface of the absorption film.

[Formation of conductive film]
In order to attract and hold an EUVL mask blank or a reflective photomask with an electrostatic chuck, it is preferable to form a conductive film made of a high dielectric material on the back surface of the polishing substrate. As the conductive film, the electrical conductivity and thickness of the constituent materials are selected so that the sheet resistance is 100Ω / □ or less. Specifically, a single layer film made of Si, Mo, Cr, TiN, CrO, CrN, CrON, or TaSi or a laminated film thereof can be applied as the constituent material.

The thickness of the conductive film is preferably 10 to 1000 nm, for example. As a method for forming the conductive film, the film can be formed using a known film forming method, for example, a sputtering method such as a magnetron sputtering method or an ion beam sputtering method, a CVD method, a vacuum evaporation method, or an electrolytic plating method. The conductive film may be formed during any one of procedures 1 to 4. For example, it may be performed between the procedure 1 and the procedure 2, that is, before the procedure 2 in which the ML film is formed on the surface to be formed on the back surface of the polishing substrate prepared in the procedure 1. Moreover, you may implement between the procedure 2 and the procedure 3, ie, before the procedure 3 which forms an absorption film etc. in the surface formed into a film on the back surface of the ML blank produced by the procedure 2. Moreover, you may implement between the procedure 3 and the procedure 4, ie, before the procedure 4, such as resist film formation, on the back surface of the mask blank created by the procedure 3.

[Create photomask (fourth procedure)]
In the present invention, the photomask manufacturing method adjusts the mask pattern formation position according to the reference surface shape of the surface and the back surface on which the polishing substrate is formed, or the reference plate thickness distribution of the polishing substrate. Except for the point of performing line drawing, the mask can be manufactured in accordance with a conventional mask manufacturing process.

In other words, a resist film is applied to the mask blank produced by the above-described method and heated. Then, according to the reference surface shape of the surface and the back surface of the polishing substrate to be formed or according to the reference plate thickness distribution of the polishing substrate, the mask pattern formation position is adjusted to perform drawing with an electron beam or ultraviolet light, Subsequent development and etching remove unnecessary absorption films, antireflection films, and resists to obtain a photomask.

[Mask pattern formation position adjustment method]
This will be specifically described with reference to FIG. Here, for simplicity, it is assumed that the surface flatness of the mask stage of the exposure apparatus using EUV light as a light source is 0 nm, and the reflective photomask is adsorbed to the mask stage without a gap. When an ideal reflective photomask manufactured using a polishing substrate having a flatness of 0 nm on the front and back surfaces and a thickness distribution of 0 nm is adsorbed to the mask stage of the exposure apparatus, the surface of the reflective photomask is As indicated by the broken line 6, the mask pattern of the reflective photomask is formed so as to transfer the pattern to a desired position on the wafer in this state because it is parallel to the surface of the electrostatic chuck.

For example, EUV light incident on the reflective photomask at an angle inclined from the mask stage normal by θ from the point A is reflected at the point B on the ideal reflective photomask surface, and is a point of the projection optical system. Projected to point D on the wafer through C. Since the magnification of the projection optical system of this aspect is ¼, a pattern to be formed at the point D on the wafer is formed at the point B of the ideal reflection type photomask by equaling four times. . Note that θ is, for example, about 6 °.

However, in an actual reflective photomask, at least one of the front and back flatness and the maximum thickness distribution of the polishing substrate constituting the reflective photomask is not 0 nm, so that the reflection in the state of being adsorbed to the mask stage of the exposure apparatus As shown by the solid line in FIG. 6, the surface of the mold photomask has gentle irregularities and is shifted from the broken line in FIG.

For this reason, the EUV light incident from the point A is similarly reflected from the surface of the reflective photomask at a point B ′ shifted in the height direction from the broken line, passes through the point C ′ of the projection optical system, and is on the wafer. Projected to point D ′. For this reason, the pattern that should be formed at the point D on the wafer is projected to the point D ′ that is shifted by ΔX, and a fine circuit pattern cannot be formed at a desired position, which is not preferable. Here, the relationship between ΔX and z is ΔX = (z · tan θ) / 4.
It becomes.

As a mask pattern formation position adjusting method, in this example, the reflective photomask pattern formation position is adjusted by δx (= z · tan θ) in accordance with the displacement z in the height direction from the broken line. In this case, the pattern on the reflective photomask can be formed at a desired position on the wafer.

This is a simple case based on the above assumption, and the actual adjustments include the surface shape of the mask stage of the exposure apparatus in addition to the surface shape and thickness distribution of the polishing substrate constituting the reflective photomask. Further, it is necessary to consider the gap when the reflective photomask is sucked and held on the mask stage, the deformation of the reflective photomask due to the gravity at the time of drawing the pattern on the reflective photomask, etc., which is a more complicated adjustment.

Assuming that the mask pattern formation position is adjusted, the demand for the flatness of the polishing substrate is reduced to 300 nm or less. In this case, it is only necessary to realize a polished substrate having a flatness of 300 nm or less, a surface roughness (RMS) of 0.15 nm or less, and a size of 50 nm or more on the surface to be formed and the back surface, focusing only on the surface roughness and the defects. Therefore, the polishing substrate can be processed relatively easily.

In the present invention, the amount of deviation is calculated by calculating the reference surface shape or reference plate thickness distribution on the surface and the back surface of the polishing substrate, or the reference surface shape or reference plate thickness distribution on the film forming surface and the back surface of the mask blank. Based on. In addition, the reference surface shape and the reference plate thickness distribution are determined not for a single polishing substrate or a single mask blank but for a plurality of polishing substrates or a plurality of mask blanks. Has characteristics.

[Reference surface shape in the present invention]
In the present invention, it is preferable to define the following three types of reference surface shapes as the reference surface shape, and use one of them. The first method for determining the reference surface shape (hereinafter referred to as the first reference surface shape) is the average shape of the surface shapes of the surface and the back surface of the plurality of polishing substrates or the mask blanks. The average shape of the surface shapes of the film formation surface and the back surface is defined as a reference surface shape of the film formation surface (or film formation surface) and the back surface. The number of sheets is not particularly limited as long as it is 2 or more, but 4 to 15 sheets, for example, are preferable examples. The average shape is obtained by simply averaging a plurality of target surface shapes.

A second method for determining a reference surface shape (hereinafter referred to as a second reference surface shape) is an average shape of the surface shapes of the surface and the back surface of a plurality of polishing substrates or a plurality of mask blanks. An average shape of the surface shapes of the film formation surface and the back surface is calculated, and a fitting (approximation) of the surface shape is expressed as a reference surface shape of the film formation surface (or film formation surface) and the back surface. As a polynomial, a Legendre polynomial, a Zernike polynomial, etc. are mentioned as a preferable polynomial. The Legendre polynomial (up to the 6th order) and the Zernike polynomial (up to the 8th order) in the xyz orthogonal coordinate system are shown in the following

formulas

1 and 2, respectively. As a polynomial approximation, for example, in the case of a Legendre polynomial, it is preferable to use an approximation up to the sixth order in terms of balance between accuracy and time.

[Formula 1]
Z (x, y) =
a ₀
+ A ₁
+ A ₂ (3x ² -1) (3y ² -1) / 4
+ A ₃ (5x ³ -3x) (5y ³ -3y) / 4
+ A ₄ (35x ⁴ -30x ² +3) (35y ⁴ -30y ² +3) / 64
+ A ₅ (63x ⁵ -70x ³ + 15x) (63y ⁵ -70y ³ + 15x) / 64
+ A ₆ (231x ⁶ −315x ⁴ + 105x ² −5) (231y ⁶ −315y ⁴ + 105y ² −5) / 256
Here, _{a n} is a coefficient.

[Formula 2]
Z (x, y) =
a ₀
+ A ₁ (x ² + y ² ) ^0.5 cos (tan ⁻¹ (y / x))
+ A ₂ (x ² + y ² ) ^0.5 sin (tan ⁻¹ (y / x))
+ A ₃ (2 (x ² + y ² ) -1)
+ A ₄ (x ² + y ² ) cos ( ² tan ⁻¹ (y / x))
+ A ₅ (x ² + y ² ) sin ( ² tan ⁻¹ (y / x))
+ A ₆ (3 (x ² + y ² ) −2) (x ² + y ² ) ^0.5 cos (tan ⁻¹ (y / x))
+ A ₇ (3 (x ² + y ² ) −2) (x ² + y ² ) ^0.5 sin (tan ⁻¹ (y / x))
+ A ₈ (6 (x ² + y ² ) ² -6 (x ² + y ² ) +1)
Here, _{a n} is a coefficient.

A third method for determining a reference surface shape (hereinafter referred to as a third reference surface shape) is a method of forming a surface of a plurality of polishing substrates and a surface shape of each of a back surface or a film formation surface of a plurality of mask blanks. And at least one of the surface shapes of the back surface and the back surface is approximated by a polynomial, and the average of them is defined as the surface (or film forming surface) on which the film is formed and the reference surface shape of the back surface. As the polynomial, those listed in the second reference surface shape are preferably used.

[Reference thickness distribution in the present invention]
In the present invention, as the reference plate thickness distribution, the following three types of reference plate thickness distributions are defined, and any one of them is preferably used. The plate thickness distribution is determined by measuring the surface shape of each surface on the polishing substrate and the back surface, or measuring the surface shape of each mask blank film forming surface and the back surface, and reversing the measurement results of the back surface shape. The thickness distribution of the polishing substrate or the mask blank was calculated by subtracting the tilt component from the sum of the measurement results of the surface shape of the surface to be deposited (or the deposition surface). The maximum thickness distribution is obtained as the difference between the maximum value and the minimum value of the obtained thickness distribution.

The first method for determining the reference plate thickness distribution (hereinafter referred to as the first reference plate thickness distribution) uses the average of the thickness distribution of a plurality of polishing substrates or the average of the thickness distribution of a plurality of mask blanks as a reference plate. The thickness distribution is assumed. The second method for determining the reference plate thickness distribution (hereinafter referred to as the second reference plate thickness distribution) is to fit (approximate) an average plate thickness distribution of a plurality of polishing substrates or an average plate thickness distribution of a plurality of mask blanks with a polynomial. ) Is used as a reference thickness distribution. The third method for determining the reference plate thickness distribution (hereinafter referred to as the third reference plate thickness distribution) is at least either the plate thickness distribution of a plurality (n) of polishing substrates or the plate thickness distribution of a plurality of mask blanks. These are fitted (approximate) with a polynomial, and the average of them is used as a reference plate thickness distribution.

In the second reference plate thickness distribution and the third reference plate thickness distribution, as a polynomial, a Legendre polynomial, a Zernike polynomial, or the like can be cited as a preferable polynomial, as in the case of the reference surface shape described above. As the polynomial approximation, for example, in the case of Legendre polynomial, it is preferable to use approximation up to the sixth order in terms of balance between accuracy and time. Further, the number of polishing base plates or mask blanks for calculating the reference plate thickness distribution is not particularly limited as long as it is 2 or more, but 4 to 15 is an example of a preferable number.

In the present invention, the mask pattern formation position adjustment method is preferably adjusted based on at least one of the aforementioned reference surface shape or reference plate thickness distribution. That is, the adjustment may be made based on either the reference surface shape or the reference plate thickness distribution, or may be adjusted based on both the reference surface shape and the reference plate thickness distribution.

The above-mentioned reference surface shape or reference plate thickness distribution is obtained by measuring at least one of a plurality of polishing substrates or a plurality of mask blanks and calculating a reference surface shape and / or a reference plate thickness distribution based on the measured shape. Alternatively, the shapes of both the plurality of polishing substrates and the plurality of mask blanks may be measured, and the reference surface shape and / or the reference plate thickness distribution may be calculated based on them.

Hereinafter, the present invention will be described more specifically based on examples (Examples 1 to 10). However, the present invention is not limited to this.

[Polishing substrate preparation method]
A slice substrate (size: 153 mm square x thickness: 6.75 mm) made of TiO ₂ —SiO ₂ glass (TiO ₂ doped amount: 7% by mass) obtained by flame hydrolysis of silicon tetrachloride and titanium tetrachloride is prepared. To do. This sliced substrate is chamfered using an NC chamfering machine with a # 120 diamond grindstone so that the chamfering width becomes 0.2 to 0.4 mm, the outer diameter is 152 mm square, and the thickness is 6. Finishing was performed to 75 mm. Subsequently, the slice substrate was sandwiched between cast iron surface plates, a polishing slurry containing abrasive grains mainly composed of Al ₂ O ₃ was supplied, and the surface of the slice substrate was lapped. The side surface of the slice substrate was subjected to side surface polishing using a nylon brush and cerium oxide slurry, and the surface roughness was mirrored to 1 nm (RMS) or less. After that, both the film forming surface and the back surface of the sliced substrate subjected to the side polishing were subjected to first-stage polishing using a hard foam polyurethane pad and a cerium oxide slurry, a soft foam polyurethane suede pad and a cerium oxide slurry. Second stage polishing, soft foamed polyurethane suede pad, third stage polishing using colloidal silica are sequentially polished using a double-side polishing machine, and the surface roughness of the film-formed surface and the back surface is 0.15 nm ( RMS) The following polishing substrates (Examples 1 to 5) were obtained.

[Surface properties of polishing substrate]
After scrub cleaning the obtained polishing substrate using an alkaline detergent and PVA sponge, using a batch type cleaning machine, ultrapure water, sulfuric acid / hydrogen peroxide mixed solution, ultrapure water, alkaline detergent, ultrapure water Each solution was dipped in this order, dipped in isopropyl alcohol (IPA), and then dried at 80 ° C. The surface shape and flatness of the surface quality area (center 142 mm square) on the surface and the back surface of the obtained polishing substrate were measured using a Fizeau laser interference flatness measuring machine (manufactured by Fujinon, trade name: G310S). And measured. Both the surface shape of the surface on which the polishing substrate is formed and the back surface are concave shapes having a relatively low center and a relatively high periphery, and the flatness of the film forming surface is 200 to 300 nm. The flatness of the film was 500 to 600 nm.

[Processing method of polishing substrate]
As the polishing substrate for EUVL, the flatness of the surface to be formed and the back surface is relatively large, and the difference in surface shape between the substrates is not suitable for use. Local polishing was performed using cluster ion beam etching (trade name: US50XP, manufactured by Epion). Here, the local polishing amount of each part is a desired surface shape of the surface and the back surface of the polishing substrate after the correction polishing step (a concave shape having a relatively low center and a relatively high periphery). The flatness of the surface to be polished and the back surface is 330 nm and 600 nm, respectively, and the difference between the surface shape measurement results of the surface and the back surface of the polishing substrate before the local polishing is formed. This was done by adjusting the scan speed. Other main local polishing processing conditions are shown below.

<Local polishing conditions>
Source gas: NF ₃ 5% and N ₂ 95% mixed gas,
Accelerating voltage: 30 kV
Ionization current: 100 μA,
Gas cluster ion beam diameter (FWHM value): 6 mm
Etching rate: 50 nm · cm ² / sec.

The surface roughness of the polishing substrate that has been locally polished is as large as about 0.5 nm (RMS) and is not suitable as a polishing substrate for EUVL. Therefore, the polishing substrate is formed under the following conditions. Final polishing was performed on the surface and the back surface, and the surface roughness was adjusted to 0.15 nm (RMS) or less.

<Finishing polishing conditions>
Polishing tester: Double-sided 24B polishing machine manufactured by Hamai Sangyo Co., Ltd.
Polishing pad: Bellatrix N7512 manufactured by Kanebo Corporation
Polishing plate rotation speed: 10 rpm
Polishing time: 30 minutes,
Polishing load: 51 cN / cm ²
Polishing amount: 0.06 μm / surface,
Dilution water: Pure water (0.1 μm or more foreign matter filtration),
Slurry flow rate: 10 l / min,
Polishing slurry: 20% by mass of colloidal silica having an average primary particle size of less than 20 nm,
Polishing amount: 0.02 μm.

[Surface properties of the polished substrate after processing]
The obtained polishing substrate was washed by the same method as described above, and the surface shape and flatness of the surface quality regions (center 142 mm square) on the surface to be formed and the back surface were measured by the same method as described above. 7 and 8 and Table 1 show measured values of the surface shape and the flatness of the surfaces and back surfaces of the five EUVL polishing substrates thus obtained.

[Difference from the first reference surface shape]
The reference surface shapes of the surface and the back surface to be formed are obtained from the average shape of the surface shapes of the surface and the back surface of the five polishing substrates, which are shown in FIGS. 7 and 8, respectively. In the figure, the second column from the left indicates the surface shape, and the third column indicates the difference between the surface shape and the reference surface shape (reference; second column in the last row). The flatness of the reference surface shape of the surface to be formed and the back surface was 68 nm and 56 nm. Table 1 shows the result of calculating the maximum value of the difference between the surface shapes of the five polishing substrates to be formed and the back surface from the first reference surface shape. The difference is 46 nm or less, and EUVL having sufficient transfer accuracy when EUVL is performed by adjusting the mask pattern formation position based on the reference surface shape of the film formation surface and the back surface and performing mask pattern drawing. A reflective photomask manufacturing method can be obtained.

[Difference from the second reference surface shape]
The second method for determining the reference surface shape is to fit (approximate) the average shape of each surface shape of the surface on which the five polishing substrates are deposited and the back surface with a Legendre polynomial (function) up to the fifth order. The reference surface shape of the surface to be filmed and the back surface is used. FIG. 9 shows the reference surface shapes of the surface (Front surface) and the back surface (Back surface) to be formed. The flatness of the reference surface shape of the surface to be formed and the back surface was 52 nm and 45 nm.

Table 2 shows the result of calculating the maximum value of the difference between the surface shape of the surface to be deposited and the back surface of the five polishing substrates from the second reference surface shape. The difference is 57 nm or less, and EUVL having sufficient transfer accuracy when EUVL is performed by adjusting the mask pattern formation position based on the reference surface shape of the film formation surface and the back surface and performing mask pattern drawing. A reflective photomask manufacturing method can be obtained.

[Thickness distribution of the polished substrate after processing]
A polishing substrate was produced in the same manner as in Examples 1-5. The surface shapes of the surface and the back surface of the five polishing substrates thus obtained were measured by the same method as in Examples 1 to 5, and the film was formed after reversing the measurement results of the surface shape of the back surface. The thickness distribution of the polishing substrate was calculated by subtracting the tilt component from the measurement result of the surface shape of the surface (Examples 6 to 10). The maximum sheet thickness distribution was obtained as the difference between the maximum value and the minimum value of the obtained sheet thickness distribution. FIG. 10 shows the plate thickness distribution of five polishing substrates, and Table 3 shows the maximum plate thickness distribution. In the figure, the second column from the left shows the plate thickness distribution (Thickness variation), and the third column shows the difference between the plate thickness distribution and the reference plate thickness distribution (reference; second column in the last row).

[Difference from the first reference plate thickness distribution]
The first reference plate thickness distribution was determined from the average plate thickness distribution of the five polishing substrates. The reference plate thickness distribution is shown in FIG. The maximum value of the reference plate thickness distribution was 93 nm. Table 3 shows the result of calculating the maximum difference between the thickness distributions of the five polishing substrates from the first reference thickness distribution. The difference is 50 nm or less, and the production of a reflective photomask for EUVL having sufficient transfer accuracy during EUVL by adjusting the mask pattern formation position based on the reference plate thickness distribution and performing mask pattern drawing. You can get the method.

[Difference from the second reference plate thickness distribution]
The second method for determining the reference plate thickness distribution is a method of fitting (approximate) an average plate thickness distribution of five EUVL polishing substrates with a Legendre polynomial (function) up to the fifth order to obtain a reference plate thickness distribution (second Reference thickness distribution). The reference plate thickness distribution is shown in FIG. The maximum value of the reference plate thickness distribution was 75 nm. Table 4 shows the result of calculating the maximum value of the difference in thickness from the reference thickness distribution of the five prepared EUVL polishing substrates. The difference is 75 nm or less in all cases, and the production of a reflective photomask for EUVL having sufficient transfer accuracy during EUVL by adjusting the mask pattern formation position based on the reference plate thickness distribution and performing mask pattern drawing You can get the method.

Although the invention has been described in detail and with reference to specific embodiments, it will be apparent to those skilled in the art that various modifications and variations can be made without departing from the spirit and scope of the invention.
This application is based on Japanese Patent Application No. 2011-014460 filed on Jan. 26, 2011, the contents of which are incorporated herein by reference.

By using the polishing substrate and mask blank of the present invention and producing a reflective photomask for EUVL according to the present invention, the transfer accuracy during EUVL can be stably improved.

1: Polishing substrate, 2: Multi-layer reflection film, 3: Protection film, 4: Absorption film, 5: Antireflection film, 6: Resist film, 7: Conductive film, 10: Mask blank, 11: Quality assurance area

Claims

A photomask manufacturing method for drawing a mask pattern based on a mask pattern design on a polishing substrate and a mask blank having at least a light absorbing film formed on the polishing substrate,
Measured at least one of the surface shape of a plurality of polishing substrates or the surface shape of a plurality of mask blanks, and after calculating a reference surface shape or a reference plate thickness distribution based on the measured surface shape, the calculated A method for manufacturing a photomask, comprising adjusting a mask pattern formation position at the time of drawing the mask pattern based on a reference surface shape or a reference plate thickness distribution.
The photomask is a reflective photomask for EUVL, the mask blank has a multilayer reflective film (ML film) between the polishing substrate and the light absorption film, and the light absorption film formed on the ML film is EUV light The photomask manufacturing method according to claim 1, wherein the photomask is an absorption film.
The reference surface shape is an average shape of the surface shape of the surface and the back surface of the plurality of polishing substrates, or an average of the surface shape of the surface and the back surface of the plurality of mask blanks. The method for producing a photomask according to claim 1, wherein the shape is the shape itself.
The reference surface shape is an average shape of the surface shapes of the surface and the back surface of the plurality of polishing substrates or an average shape of the surface shapes of the film surface and the back surface of the plurality of mask blanks. The photomask manufacturing method according to claim 1, wherein the photomask is calculated and obtained by approximating the calculated average shape with a polynomial.
The method of manufacturing a photomask according to claim 4, wherein the polynomial is a Legendre polynomial or a Zernike polynomial.
The reference surface shape is a polynomial in at least one of the surface shape of each of the surface and the back surface of the plurality of polishing substrates or the surface shape of each of the film surface and the back surface of the plurality of mask blanks. The photomask manufacturing method according to claim 1, wherein the photomask manufacturing method is obtained by approximating and averaging.
The method for producing a photomask according to claim 6, wherein the polynomial is a Legendre polynomial or a Zernike polynomial.
The photomask manufacturing method according to claim 1, wherein the reference plate thickness distribution is an average of the plate thickness distribution of the plurality of polishing substrates or the average of the plate thickness distribution of the plurality of mask blanks.
The reference plate thickness distribution is obtained by calculating an average plate thickness distribution of the plurality of polishing substrates or an average plate thickness distribution of the plurality of mask blanks, and approximating the calculated average plate thickness distribution by a polynomial expression. The method for producing a photomask according to claim 1, wherein:
The method for manufacturing a photomask according to claim 9, wherein the polynomial is a Legendre polynomial or a Zernike polynomial.
The reference plate thickness distribution is obtained by approximating at least one of the plate thickness distribution of the plurality of polishing substrates or the plate thickness distribution of the plurality of mask blanks by a polynomial and averaging them. The manufacturing method of the photomask as described.
The photomask manufacturing method according to claim 11, wherein the polynomial is a Legendre polynomial or a Zernike polynomial.