JP7314523B2 - Photomasks and photomask blanks for laser exposure - Google Patents

Description

The present disclosure relates to photomasks and photomask blanks for laser exposure.

2. Description of the Related Art A photomask for transferring a wiring pattern or the like, which is used in manufacturing a semiconductor element or the like, has a mask pattern including a light shielding portion and an opening corresponding to the wiring pattern or the like. 2. Description of the Related Art Along with miniaturization and high integration of wiring patterns, etc., in the photolithography technology used for pattern formation, KrF excimer laser (248 nm), ArF excimer laser (193 nm), etc. are used as the light source of the exposure apparatus in place of the g-line (436 nm) and i-line (365 nm) of the high pressure mercury lamp, and the wavelength of the light source of the exposure apparatus is shortened.

Since the light emitted from these short-wavelength exposure light sources has a high energy density (for example, about 5 mJ/cm ² ), ozone is generated in the exposure atmosphere, which gradually oxidizes the light-shielding material (metal compounds such as Cr and MoSi) contained in the light-shielding portion of the photomask. In order to solve such problems, conventional photomasks have been proposed in which the metal present on the surface of the light shielding portion is forcibly passivated by treatment with nitric acid (HNO ₃ ) or the like (see Patent Document 1).

Japanese Unexamined Patent Application Publication No. 2011-75808

According to the photomask described in Patent Literature 1, deterioration of the light shielding portion made of Cr or the like can be suppressed even when ArF laser or the like is irradiated. In recent years, not only photolithography but also glass substrates, silicon substrates, etc. have been directly microfabricated and modified by laser irradiation through a photomask as a method for pattern formation, etc., and it is expected that the use of laser processing will become more widespread in the future.

Photomasks used for these applications are exposed to a KrF excimer laser with a much higher energy density (e.g., about 200 mJ/cm ² ) compared to the conventional lithography process in the manufacture of semiconductor devices, so there is a risk that ozone will be generated in the exposure atmosphere, and the temperature will increase due to light absorption in the light shielding portion. Therefore, even in the photomask described in Patent Literature 1, the shape of the light-shielding portion may change, the light-shielding portion may become transparent, and the performance of the photomask (reflectance of the light-shielding portion, etc.) may be degraded.

In view of the above problems, an object of the present disclosure is to provide a photomask for laser exposure and a photomask blank that can suppress deterioration in performance even when irradiated with high energy density laser light or the like.

In order to solve the above problems, an embodiment of the present disclosure is a photomask for laser exposure, comprising: a transparent glass substrate having a first surface and a second surface facing the first surface; and a mask pattern provided on the first surface of the transparent glass substrate.and thickness t of each of the first dielectric layer and the second dielectric layer ₁ is 30 nm to 80 nm, and the arithmetic mean value t of the thickness of the first metal layer and the thickness of the second metal layer constituting the laminated film ₂ is 10 nm to 50 nm, and the optical density of the light shielding portion is 2.0 or more.A photomask for laser exposure is provided.

Al ₂ O ₃ can be used as the dielectric material forming the dielectric layer, and aluminum (Al) can be used as the material forming the metal layer.

An embodiment of the present disclosure is a photomask blank used for manufacturing a photomask for laser exposure, comprising: a transparent glass substrate having a first surface and a second surface facing the first surface; and a light shielding layer provided on the first surface side of the transparent glass substrate., thickness t of each of the first dielectric layer and the second dielectric layer ₁ is 30 nm to 80 nm, and the arithmetic mean value t of the thickness of the first metal layer and the thickness of the second metal layer constituting the laminated film ₂ is 10 nm to 50 nm, and the optical density of the light shielding layer is 2.0 or more.A photomask blank is provided.

Aluminum (Al) can be used as the material forming the metal layer, and Al ₂ O ₃ can be used as the dielectric forming the dielectric layer.

ADVANTAGE OF THE INVENTION According to this invention, the photomask and photomask blanks for laser exposure which can suppress the deterioration of performance even if it is irradiated with the laser beam etc. of high energy density can be provided.

FIG. 1 is a cut end view showing a schematic configuration of a first aspect of a photomask for laser exposure according to an embodiment of the present disclosure. FIG. 2 is a cut end view showing a schematic configuration of a second mode of a photomask for laser exposure according to an embodiment of the present disclosure. FIG. 3 is a cut end view showing a schematic configuration of another aspect of the second aspect of the photomask for laser exposure according to one embodiment of the present disclosure. FIG. 4 is a process flow diagram showing, in cross section, each process of a method for manufacturing a photomask for laser exposure (first aspect) according to an embodiment of the present disclosure. FIG. 5 is a process flow diagram showing, in cross-section, each process of a method for manufacturing a photomask for laser exposure (second aspect) according to an embodiment of the present disclosure. FIGS. 6A and 6B are cross-sectional views showing schematic configurations of other aspects of the photomask for laser exposure according to one embodiment of the present disclosure. 7 is a graph showing the simulation results in Test Examples 2 and 3. FIG. 8 is a graph showing simulation results in Test Example 4. FIG. 9 is a graph showing simulation results in Test Examples 2 and 6. FIG. 10 is a graph showing simulation results in Test Example 7. FIG. 11 is a graph showing simulation results in Test Example 8. FIG. 12 is a graph showing simulation results in Test Example 9. FIG. 13 is a graph showing a simulation result in Test Example 10. FIG.

Embodiments of the present disclosure will be described with reference to the drawings.
In the drawings, in order to facilitate understanding, the shape, scale, ratio of vertical and horizontal dimensions, etc. of each part may be changed from the real thing or exaggerated. In this specification and the like, a numerical range represented by "to" means a range including the numerical values described before and after "to" as lower and upper limits, respectively. In this specification and the like, terms such as "film", "sheet", and "plate" are not distinguished from each other based on the difference in designation. For example, "plate" is a concept that includes members that can be generally called "sheets" and "films."

A photomask for laser exposure according to this embodiment will be described. 1 and 2 are cross-sectional views showing schematic configurations of a first mode and a second mode of a photomask for laser exposure according to this embodiment, respectively.

As shown in FIGS. 1 and 2, the laser exposure photomask 1 according to the present embodiment includes a transparent glass substrate 2 having a first surface 21 and a second surface 22 opposite thereto, and a mask pattern 3 provided on the first surface 21 of the transparent glass substrate 2. The photomask 1 for laser exposure according to the present embodiment may be used for patterning a photosensitive resist layer formed on a substrate to be processed, or may be a laser processing mask used for direct microfabrication by irradiating a substrate to be processed with a laser.

The transparent glass substrate 2 is not particularly limited, and for example, non-flexible transparent rigid materials such as alkali-free glass, quartz glass, and synthetic quartz plate can be used. The transparent glass substrate 2 in the present embodiment may be transparent to the extent that the photosensitive resist can be exposed to the exposure light irradiated through the laser exposure photomask 1 or the substrate to be processed can be directly subjected to microfabrication. The transparent glass substrate 2 preferably has a transmittance of 80% or more, more preferably 90% or more, of exposure light (KrF excimer laser (wavelength: 248 nm), ArF excimer laser (wavelength: 193 nm), etc.). In particular, synthetic quartz glass has a high transmittance for a KrF excimer laser with a high energy density, and can be suitably used as the transparent glass substrate 2 .

The size of the transparent glass substrate 2 can be appropriately set depending on the size of an article to be manufactured using the laser exposure photomask 1 according to this embodiment, the exposure method of the exposure apparatus used for manufacturing the article, and the like. For example, when the laser exposure photomask 1 according to the present embodiment is used for manufacturing semiconductor elements, etc., the size of the transparent glass substrate 2 can be set to approximately 127 mm×127 mm to 228.6 mm×228.6 mm.

The thickness of the transparent glass substrate 2 is not particularly limited, but since it is necessary to hold the laser exposure photomask 1 without bending during exposure, it can be appropriately set according to the size of the transparent glass substrate 2. For example, it can be set in the range of 0.5 mm to 7 mm.

The mask pattern 3 includes a light blocking portion 3A capable of blocking exposure light and an opening 3B capable of transmitting exposure light. The optical density (OD value) of the light shielding portion 3A with respect to exposure light is preferably 2.0 or more. When the optical density (OD value) is 2.0 or more, necessary light shielding properties can be obtained in desired portions during exposure.

The light shielding portion 3A is composed of a laminated film in which at least one dielectric layer 31 and at least one metal layer 32 are alternately laminated. In this embodiment, the dielectric layer 31 is in contact with the first surface 21 of the transparent glass substrate 2. The number of laminated layers of the dielectric layer 31 and the metal layer 32 in the laminated film forming the light shielding portion 3A may be one layer each (see FIG. 1) or two layers each (see FIG. 2). That is, the first dielectric layer 311, the first metal layer 321, the second dielectric layer 312 and the second metal layer 322 may be laminated in this order on the first surface 21 of the transparent glass substrate 2 (see FIG. 2). Also, the number of layers may be three or more for each layer.

The dielectric layer 31 may be composed of _a dielectric such as _Al2O3 , for example. Aluminum (Al) or the like is suitable as a material for forming the metal layer 32, but aluminum bronze (AlCu), tungsten (W), or the like may also be used.

The thickness t ₁ of the dielectric layer 31 may be any thickness as long as the absorptance of the exposure light in the metal layer 32 when irradiated with the exposure light is equal to or less than a predetermined value (for example, 7.6% or less), and specifically, it is within the range represented by the following formula (1).

式（１）中、λは「露光光（レーザ）の波長」を表し、ｍは「１以上の整数」を表し、ｎ₁は「誘電体層３１を構成する誘電体の屈折率の実部」を表し、ｋ₂は「金属層３２を構成する金属の屈折率の虚部」を表す。

In formula (1), λ represents the “wavelength of the exposure light (laser)”, m represents an “integer of 1 or more”, n ₁ represents the “real part of the refractive index of the dielectric constituting the dielectric layer 31”, and k ₂ represents the “imaginary part of the refractive index of the metal constituting the metal layer 32”.

When the thickness t ₁ of the dielectric layer 31 is within the range represented by the above formula (1), the reflected light reflected at the interface between the first surface 21 and the dielectric layer 31 of the exposure light irradiated from the second surface 22 side of the transparent glass substrate 2 and the reflected light reflected by the metal layer 32 of the exposure light transmitted through the dielectric layer 31 interfere and strengthen each other. The ratio of light energy absorbed by 2 is reduced. Therefore, deterioration of the performance (reflectance) of the light shielding portion 3A can be suppressed. The value of m in formula (1) is preferably 2 or less, more preferably 1. The value of m may be 3 or more, but there is a tendency that the larger the value of m, the greater the demerit in manufacturing.

When a KrF excimer laser (wavelength λ=248 nm) is used as exposure light, the thickness t ₁ of the dielectric layer 31 may be 30 nm to 80 nm, preferably 40 nm to 75 nm, more preferably 50 nm to 60 nm. If the thickness t ₁ of the dielectric layer 31 is out of the above numerical range, the metal layer 32 will have a high absorption rate of the exposure light, which may deteriorate the performance of the light shielding portion 3A over time.

The thickness t ₂ of the metal layer 32 is appropriately set to such an extent that the light shielding portion 3A in the photomask 1 for laser exposure according to the present embodiment can exhibit the desired performance.

When a KrF excimer laser (wavelength λ=248 nm) is used as the exposure light, and the light shielding portion 3A is a laminated film in which the dielectric layer 31 and the metal layer 32 are laminated one by one (see FIG. 1), the thickness t ₂ of the metal layer 32 may be, for example, 20 nm to 200 nm, preferably 25 nm to 80 nm, and more preferably 30 nm to 40 nm. If the thickness t ₂ of the metal layer 32 is less than 20 nm, the transmittance of the exposure light increases, and there is a possibility that the desired performance of the light shielding portion 3A cannot be obtained. If the thickness t ₂ of the metal layer 32 exceeds 200 nm, it may be difficult to form the metal layer 32 with a uniform thickness and with high density.

When a KrF excimer laser (wavelength λ=248 nm) is used as the exposure light and the light shielding portion 3A is a laminated film formed by laminating the first dielectric layer ₃₁₁ , the first metal layer 321, the second dielectric layer 312 and the second metal layer 322 in this order (see FIG. ₂ ), the arithmetic mean value _t2 (=( _t21 +t ₂₂ )/2) may be, for example, 10 nm to 50 nm, preferably 15 nm to 40 nm, more preferably 18 nm to 30 nm. When the average thickness t ₂ of the first metal layer 321 and the second metal layer 322 is less than 10 nm, the transmittance of the exposure light increases, and the desired performance of the light shielding portion 3A may not be obtained. Even if the average thickness t ₂ of the first metal layer 321 and the second metal layer 322 exceeds 50 nm, the exposure light absorptance of the first metal layer 321 in particular hardly changes.

In the second embodiment shown in FIG. 2, the thickness t ₂₁ of the first metal layer 321 and the thickness t ₂₂ of the second metal layer 322 are the same, but are not limited to this, and the thickness t ₂₁ of the first metal layer 321 and the thickness t ₂₂ of the second metal layer 322 may be different from each other (see FIG. 3). When both thicknesses t ₂₁ and t ₂₂ are different from each other, the thickness t ₂₁ of the first metal layer 321 is preferably thinner than the thickness t ₂₂ of the second metal layer 322 . When the first metal layer 321 and the second metal layer 322 have the same thickness (see FIG. 2), the first metal layer 321 closer to the exposure light source has a higher absorptivity of the exposure light than the second metal layer 322 farther from the exposure light source. Therefore, the first metal layer 321 may deteriorate over time earlier than the second metal layer 322, and as a result, the light shielding performance of the light shielding portion 3A of the photomask 1 for laser exposure may deteriorate. However, by making the thickness t ₂₁ of the first metal layer 321 thinner than the thickness t ₂₂ of the second metal layer 322, the difference in the absorptivity of the exposure light between the two can be reduced, and deterioration over time of the first metal layer 321 can be suppressed.

In the photomask 1 for laser exposure shown in FIGS. 1 to 3, a protective layer (Al ₂ O 3 or _the like) is provided to cover the metal layer 32, the second metal layer 322, and the sidewalls of the light shielding portion 3A exposed at the top layer for the purpose of preventing oxidation (natural oxidation) of the metal layer 32, the second metal layer 322 exposed at the uppermost layer, and the metal layer 32, the first metal layer 321, and the second metal layer 322 exposed at the side walls of the light shielding portion 3A. may have been Alternatively, instead of the protective layer, an oxide film may be formed on the exposed surface layers of the metal layer 32, the first metal layer 321, and the second metal layer 322 by thermal oxidation (forced oxidation) of the metal layer 32 and the second metal layer 322 exposed on the uppermost layer, and the metal layer 32, the first metal layer 321, and the second metal layer 322 exposed on the side walls of the light shielding portion 3A.

The shape (planar view shape) of the opening 3B is not particularly limited, and can be appropriately set depending on the shape (planar view shape) of the pattern formed using the laser exposure photomask 1 according to the present embodiment. Examples of the shape of the opening 3B include, but are not limited to, a substantially circular shape, a substantially triangular shape, a substantially rectangular shape such as a square or a rectangular shape, and a substantially polygonal shape.

The dimensions of the opening 3B are also not particularly limited, and can be appropriately set according to the dimensions of the pattern formed using the photomask 1 for laser exposure according to the present embodiment (the design rule of the semiconductor device manufactured using the photomask 1 for laser exposure). For example, when the shape of the opening 3B is substantially circular, the diameter of the opening 3B may be about 1 μm to several mm.

According to the photomask 1 for laser exposure according to the present embodiment having the configuration described above, the dielectric layer 31 constituting the light shielding portion 3A of the mask pattern 3 has a desired thickness, so that the light shielding performance of the light shielding portion 3A can be prevented from deteriorating. Therefore, even if a KrF excimer laser or the like with a particularly high energy density (e.g., 200 mJ/cm ² or more) is irradiated, it is possible to suppress deterioration in the performance of the photomask 1 for laser exposure (decrease in reflectance, deformation, dimensional variation, etc. of the light shielding portion 3A due to an increase in temperature of the metal layer 32 (first metal layer 321 and second metal layer 322)).

[Photomask manufacturing method]
A method for manufacturing the photomask 1 for laser exposure according to the present embodiment described above will be described. 4 and 5 are cross-sectional process flow diagrams showing respective steps of the method for manufacturing a photomask for laser exposure according to this embodiment.

<Mask blank preparation process>
A transparent glass substrate 2 having a first surface 21 and a second surface 22 opposite thereto is prepared, and a dielectric film 31L and a metal film 32L, or a first dielectric film 311L, a first metal film 321L, a second dielectric film 312L and a second metal film 322L are formed in this order on the first surface 21 of the transparent glass substrate 2 to prepare a photomask blank 10. Then, a photosensitive resist layer 80 is formed on the metal film 32L or the second metal film 322L of the photomask blanks 10 (see FIGS. 4A and 5A).

Examples of materials forming the dielectric film 31L, the first dielectric film 311L, and the second dielectric film 312L include dielectrics such as Al ₂ O ₃ . Aluminum (Al) or the like is suitable as a material for forming the metal film 32L, the first metal film 321L, and the second metal film 322L, but aluminum bronze (AlCu), tungsten (W), or the like may also be used.

The thickness T ₁ of the dielectric film 31L, the first dielectric film 311L, and the second dielectric film 312L may be any thickness as long as the absorptivity of the exposure light in the metal layer 32 becomes a predetermined value or less (for example, 7.6% or less) when the photomask 1 for laser exposure to be manufactured is irradiated with the exposure light, and specifically, it is within the range shown by the following formula (2).

式（２）中、λは「露光光（レーザ）の波長」を表し、ｍは「１以上の整数」を表し、ｎ₁’は「誘電体膜３１Ｌを構成する誘電体の屈折率の実部」を表し、ｋ₂’は「金属膜３２Ｌを構成する金属の屈折率の虚部」を表す。

In formula (2), λ represents the "wavelength of the exposure light (laser)", m represents an "integer of 1 or more", n ₁ ' represents the "real part of the refractive index of the dielectric material forming the dielectric film 31L", and k ₂ ' represents the "imaginary part of the refractive index of the metal forming the metal film 32L".

When a KrF excimer laser (wavelength λ=248 nm) is used as the exposure light, the thickness T ₁ of the dielectric film 31L, the first dielectric film 311L and the second dielectric film 312L may be 30 nm to 80 nm, preferably 40 nm to 75 nm, more preferably 50 nm to 60 nm. If the thickness T ₁ of the dielectric film 31L, the first dielectric film 311L, and the second dielectric film 312L is out of the above numerical range, the absorptance of the exposure light in the metal layer 32 of the photomask 1 for laser exposure to be manufactured increases, and the performance of the light shielding portion 3A may deteriorate over time.

The thicknesses T ₂ , T ₂₁ , and T ₂₂ of the metal film 32L, the first metal film 321L, and the second metal film 322L are appropriately set to such an extent that the light shielding portion 3A in the photomask 1 for laser exposure to be manufactured can exhibit the desired performance.

When the photomask 1 for laser exposure to be manufactured uses a KrF excimer laser (wavelength λ=248 nm) as the exposure light, and the light shielding portion 3A is a laminated film in which the dielectric layer 31 and the metal layer 32 are laminated one by one (see FIG. 1), the thickness T ₂ (see FIG. 4A) of the metal film 32L may be, for example, 20 nm to 200 nm, preferably 25 nm to 80 nm, and 30 nm to 40 nm. nm is more preferred. If the thickness T ₂ of the metal film 32L is less than 20 nm, the transmittance of the exposure light increases, and there is a possibility that the desired performance of the light shielding portion 3A cannot be obtained. If the thickness T ₂ of the metal film 32L exceeds 200 nm, it may be difficult to form the metal film 32L with a uniform thickness and densely.

作製されるレーザ露光用フォトマスク１が、露光光としてＫｒＦエキシマレーザ（波長λ＝２４８ｎｍ）が用いられ、遮光部３Ａが第１誘電体層３１１、第１金属層３２１、第２誘電体層３１２及び第２金属層３２２をこの順で積層してなる積層膜である場合（図２参照）、第１金属膜３２１Ｌの厚みＴ ₂₁及び第２金属膜３２２Ｌの厚みＴ ₂₂ （図５（Ａ）参照）の算術平均値Ｔ ₂ （＝(Ｔ ₂₁ ＋Ｔ ₂₂ )／２）は、例えば、１０ｎｍ～５０ｎｍであればよく、１５ｎｍ～４０ｎｍであるのが好ましく、１８ｎｍ～３０ｎｍであるのがより好ましい。 If the arithmetic mean value _T2 of the thicknesses _T21 and _T22 of the first metal film 321L and the second metal film 322L is less than 10 nm, the transmittance of exposure light increases, and the desired performance of the light shielding portion 3A may not be obtained. Even if the arithmetic mean value T2 of the thicknesses _T21 and _T22 of the first metal film 321L and the second metal film 322L exceeds 50 nm, it is difficult to improve the effect (the effect of reducing the absorptivity _of exposure light) of the manufactured photomask 1 for laser exposure.

The thickness T ₂₁ of the first metal film 321L and the thickness T ₂₂ of the second metal film 322L are the same, but are not limited to this, and the thickness T ₂₁ of the first metal film 321L and the thickness T ₂₂ of the second metal film 322L may be different from each other. When both thicknesses T ₂₁ and T ₂₂ are different from each other, the thickness T ₂₁ of the first metal film 321L is preferably thinner than the thickness T ₂₂ of the second metal film 322L. When the first metal film 321L and the second metal film 322L have the same thickness, the first metal layer 321 and the second metal layer 322 forming the light shielding portion 3A of the manufactured laser exposure photomask 1 have the same thickness. In this case, the first metal layer 321 closer to the exposure light source has a higher absorbance of the exposure light than the second metal layer 322 farther from the exposure light source. Therefore, the first metal layer 321 may deteriorate over time earlier than the second metal layer 322, and as a result, the light shielding performance of the light shielding portion 3A of the photomask 1 for laser exposure may deteriorate. However, by making the thickness T ₂₁ of the first metal film 321L smaller than the thickness T ₂₂ of the second metal film 322L, the thickness t ₂₁ of the first metal layer 321 is also smaller than the thickness t ₂₂ of the second metal layer 322 in the manufactured photomask 1 for laser exposure. As a result, the difference in absorptivity of the exposure light between the two can be reduced, and deterioration of the first metal layer 321 over time can be suppressed.

As a method for forming the dielectric film 31L, the first dielectric film 311L, the second dielectric film 312L, the metal film 32L, the first metal film 321L, and the second metal film 322L on the first surface 21 of the transparent glass substrate 2, conventionally known methods can be applied, and examples thereof include sputtering, vacuum deposition, thermal CVD, plasma CVD, and the like.

The resist material constituting the photosensitive resist layer 80 is not particularly limited, but an electron beam sensitive positive resist material, an electron beam sensitive negative resist material, an ultraviolet sensitive positive resist material, an ultraviolet sensitive negative resist material, or the like can be used.

The thickness of the photosensitive resist layer 80 is not particularly limited as long as it is sufficiently thick as a mask for etching the dielectric film 31L, the first dielectric film 311L, the second dielectric film 312L, the metal film 32L, the first metal film 321L, and the second metal film 322L.

A hard mask layer (not shown) may be provided between the photosensitive resist layer 80 and the metal film 32L or the second metal film 322L. By providing the hard mask layer, the hard mask pattern formed by etching the hard mask layer using the resist pattern 81 (see FIGS. 4B and 5B) as a mask can be used as an etching mask for etching the dielectric film 31L, the first dielectric film 311L, the second dielectric film 312L, the metal film 32L, the first metal film 321L, and the second metal film 322L. Materials constituting such a hard mask layer may be appropriately set in consideration of the etching selectivity with respect to the materials constituting the dielectric film 31L, the first dielectric film 311L, the second dielectric film 312L, the metal film 32L, the first metal film 321L and the second metal film 322L, and the photosensitive resist layer 80.

<Resist pattern formation process>
The photosensitive resist layer 80 is exposed and developed through a predetermined photomask to form a resist pattern 81 (see FIGS. 4B and 5B). The dimensions of the resist pattern 81 may be substantially the same as the dimensions of the light shielding portion 3A of the photomask 1 for laser exposure according to this embodiment. The resist pattern 81 may be formed by imprinting using an imprint mold having an uneven pattern corresponding to the resist pattern 81, or may be formed by direct writing (direct writing) of an electron beam or the like on the photosensitive resist layer 80. When the resist pattern 81 is formed by imprinting, a resist layer made of a photo (UV) curable resin or the like may be formed instead of the photosensitive resist layer 80 .

<Etching process>
Next, using the resist pattern 81 formed as described above as an etching mask, the dielectric film 31L, the first dielectric film 311L, the second dielectric film 312L, the metal film 32L, the first metal film 321L, and the second metal film 322L are dry-etched using a predetermined etching gas (for example, a chlorine-based etching gas) to form the mask pattern 3 having the light shielding portion 3A and the opening portion 3B (see FIGS. 4C and 5C). After that, by removing the remaining resist pattern 81, the photomask 1 for laser exposure can be manufactured (see FIGS. 4(D) and 5(D)).

The embodiments described above are described to facilitate understanding of the present invention, and are not described to limit the present invention. Therefore, each element disclosed in the above embodiment is meant to include all design changes and equivalents that fall within the technical scope of the present invention.

In the above embodiment, the dielectric layer 31 or the first dielectric layer 311 is provided on the first surface 21 of the transparent glass substrate 2, but it is not limited to this aspect. For example, the light shielding portion 3A on the first surface 21 of the transparent glass substrate 2 may be a laminated film in which the metal layer 32 and the dielectric layer 31, or the first metal layer 321, the first dielectric layer 311, the second metal layer 322 and the second dielectric layer 312 are laminated in this order (see FIGS. 6A and 6B). In this embodiment, a protective layer (such as Al ₂ O ₃ ) may be provided between the first surface 21 of the transparent glass substrate 2 and the metal layer 32 or the first metal layer 321 to prevent interfacial reaction between the constituent material (e.g. quartz) of the transparent glass substrate 2 and the constituent material (e.g. aluminum) of the metal layer 32 or the first metal layer 321. If the first surface 21 of the transparent glass substrate 2 and the metal layer 32 or the first metal layer 321 are in contact with each other, the metal layer ₃₂ or the first metal layer 321 may be heated when irradiated with a KrF excimer laser or the like with a high energy density. If such an interfacial reaction occurs, the performance of the photomask 1 for laser exposure may be degraded. However, since the protective layer is provided between the first surface 21 of the transparent glass substrate 2 and the metal layer 32 or the first metal layer 321, it is possible to suppress the decrease in the reflectance of the light shielding portion 3A, the deformation of the light shielding portion 3A, the dimensional variation, etc., and prevent the deterioration of the performance of the photomask 1 for laser exposure. The laser exposure photomask 1 of this aspect can be used by irradiating laser light as exposure light from the first surface 21 side of the transparent glass substrate 2 toward the second surface 22 .

The present disclosure is not limited to the following examples and the like, although further detailed description will be given below with reference to examples and the like.

[Test Example 1]
A dielectric layer composed of Al ₂ O ₃ and a metal layer composed of Al were laminated in this order to form a laminated film on the first surface of a transparent glass substrate, and a KrF excimer laser (wavelength λ = 248 nm) as exposure light was irradiated from the second surface side of the transparent glass substrate. From the resulting contour plot (horizontal axis: dielectric layer thickness, vertical axis: metal layer thickness), the dielectric layer thickness t ₁ at which the exposure light absorbance (%) was minimized was 55 nm.

[Test Example 2]
A metal layer composed of Al was formed on the first surface of a transparent glass substrate, and a KrF excimer laser (wavelength: 248 nm) as exposure light was irradiated from the second surface side, and the exposure light absorption rate (%) of the metal layer was obtained by simulation when the thickness t ₂ of the metal layer was varied. The results are shown in FIG.

[Test Example 3]
A dielectric layer (thickness t ₁ =55 nm) composed of Al ₂ O ₃ and a metal layer composed of Al were laminated in this order to form a laminated film on the first surface of a _transparent glass substrate, and a KrF excimer laser (wavelength: 248 nm) as exposure light was irradiated from the second surface side. The results are also shown in FIG.

From the results shown in FIG. 7, it was confirmed that the exposure light absorptance (%) of the metal layer in the sample of Test Example 3 was lower than that of the sample of Test Example 2.

[Test Example 4]
A dielectric layer composed of _{Al O} and a metal layer composed of Al (thickness _t = 32 nm, 50 nm, 100 nm) were laminated in this order on the first surface of a transparent glass substrate to form a laminated film, and a KrF excimer laser (wavelength: 248 nm) as exposure light was irradiated from the second surface side, and the exposure light absorptance ( _% ) of the metal layer was obtained by simulation when the thickness t of the dielectric layer was varied. The results are shown in FIG.

From the results shown in FIGS. 7 and 8, it was confirmed that the minimum absorptivity (7.6%) in the sample of Test Example 2 can be achieved by setting the thickness of the dielectric layer to 44.4 nm to 65.8 nm in the sample of Test Example 4 (metal layer thickness t ₂ =32 nm).

Further, from the results shown in FIG. 8, it was understood that when the thickness t ₂ of the metal layer is 32 nm, the exposure light absorptance can be reduced by having the thickness t ₁ of the dielectric layer represented by the following formula (1).

式（１）中、λは「露光光（レーザ）の波長」を表し、ｍは「１以上の整数」を表し、ｎ₁は「誘電体層を構成する誘電体の屈折率の実部」を表し、ｋ₂は「金属層を構成する金属の屈折率の虚部」を表す。

In formula (1), λ represents the “wavelength of the exposure light (laser)”, m represents an “integer of 1 or more”, _n1 represents the “real part of the refractive index of the dielectric constituting the dielectric layer”, and _k2 represents the “imaginary part of the refractive index of the metal constituting the metal layer”.

[Test Example 5]
A first dielectric layer made of Al ₂ O ₃ , a first metal layer made of Al, a second dielectric layer made of Al ₂ O ₃ and a second metal layer made of Al were laminated in this order to form a laminated film on the first surface of a transparent glass substrate, and a KrF excimer laser (wavelength λ = 248 nm) as exposure light was irradiated from the second surface side of the transparent glass substrate. From the resulting contour diagram (horizontal axis: thickness of dielectric layer, vertical axis: thickness of metal layer), the thickness _t1 of the first dielectric layer and the second dielectric layer, which had the smallest exposure light absorption (%), was 54 nm.

[Test Example 6]
A first dielectric layer made of Al ₂ O ₃ (thickness t ₁ =54 nm), a first metal layer made of Al, a second dielectric layer made of Al ₂ O ₃ (thickness t ₁ =54 nm), and a second metal layer made of Al are laminated in this order on the first surface of a transparent glass substrate. The exposure light absorptivity (%) of the first metal layer was obtained by simulation when the thicknesses t ₂₁ and t ₂₂ of the second metal layer were varied. The results are shown in FIG.

The graph in FIG. 9 also shows the results of the sample of Test Example 2. From the results, it was confirmed that the exposure light absorptance (%) of the metal layer in the sample of Test Example 6 was lower than that of the sample of Test Example 2.

[Test Example 7]
A first dielectric layer made of Al ₂ O ₃ , a first metal layer made of Al, a second dielectric layer made of Al ₂ O ₃ and a second metal layer made of Al (thicknesses t ₂₁ , t ₂₂ of the first and second metal layers = 19 nm, 30 nm, 50 nm, 100 nm) were laminated in this order to form a laminated film on the first surface of a transparent glass substrate. 48 nm) from the second surface side, the exposure light absorptivity (%) of the first metal layer was obtained by simulation when the thickness t ₁ of the first dielectric layer and the second dielectric layer was varied. The results are shown in FIG.

From the results shown in FIGS. 9 and 10, it was confirmed that the minimum value (7.6%) of the absorptivity in the sample of Test Example 2 can be achieved by setting the thickness t ₁ of the first dielectric layer and the second dielectric layer to 48.1 nm to 66.8 nm in the sample of Test Example 7 (thicknesses t ₂₁ and t ₂₂ of the first metal layer and second metal layer = 19 nm).

Further, from the results shown in FIG. 10, it was understood that the exposure light absorptance can be reduced by having the thickness t ₁ of the first dielectric layer and the second dielectric layer represented by the following formula (1).

式（１）中、λは「露光光（レーザ）の波長」を表し、ｍは「１以上の整数」を表し、ｎ₁は「第１誘電体層及び第２誘電体層を構成する誘電体の屈折率の実部」を表し、ｋ₂は「第１金属層及び第２金属層を構成する金属の屈折率の虚部」を表す。

In the formula (1), λ represents the "wavelength of the exposure light (laser)", m represents an "integer of 1 or more", _n1 represents the "real part of the refractive index of the dielectrics constituting the first dielectric layer and the second dielectric layer", and _k2 represents the "imaginary part of the refractive index of the metals constituting the first metal layer and the second metal layer".

[Test Example 8]
Ａｌ ₂ Ｏ ₃により構成される第１誘電体層、Ａｌにより構成される第１金属層、Ａｌ ₂ Ｏ ₃により構成される第２誘電体層、Ａｌにより構成される第２金属層、Ａｌ ₂ Ｏ ₃により構成される第３誘電体層、Ａｌにより構成される第３金属層、Ａｌ ₂ Ｏ ₃により構成される第４誘電体層及びＡｌにより構成される第４金属層（第１～第４金属層の厚みｔ ₂₁ ，ｔ ₂₂ ，ｔ ₂₃ ，ｔ ₂₄ ＝１２ｎｍ，２０ｎｍ，４０ｎｍ）をこの順に積層してなる積層膜を透明ガラス基板の第１面上に形成し、露光光としてのＫｒＦエキシマレーザ（波長：２４８ｎｍ）を第２面側から照射した場合において、第１～第４誘電体層の厚みｔ ₁を変動させたときにおける第１金属層の露光光吸収率（％）をシミュレーションにより求めた。 The results are shown in FIG.

[Test Example 9]
A dielectric layer composed of _{Al O} and a metal layer composed of AlCu (thickness _t = 45.3 nm, 100 nm) were laminated in this order to form a laminated film on the first surface of a transparent glass substrate, and a _KrF excimer laser (wavelength: 248 nm) as exposure light was irradiated from the second surface side. The results are shown in FIG.

[Test Example 10]
A dielectric layer composed of Al ₂ O ₃ and a metal layer composed of W (thickness t ₂ =25.6 nm) were laminated in this order to form a laminated film on the first surface of a transparent glass substrate, and a KrF excimer laser (wavelength: 248 nm) as exposure light was irradiated from the second surface side, and the exposure light absorptance (%) of the metal layer was obtained by simulation when the thickness t ₁ of the dielectric layer was varied. The results are shown in FIG.

DESCRIPTION OF SYMBOLS 1... Photomask for laser exposure 2... Transparent glass substrate 3... Mask pattern 3A... Light-shielding part 31... Dielectric layer 32... Metal layer 3B... Opening part

Claims (6)

A photomask for laser exposure,
a transparent glass substrate having a first surface and a second surface facing the first surface;
a mask pattern provided on the first surface of the transparent glass substrate;
The mask pattern includes a light-shielding portion composed of a laminated film formed by laminating a first dielectric layer, a first metal layer, a second dielectric layer, and a second metal layer on the first surface in this order, and an opening,
the thickness _t1 of each of the first dielectric layer and the second dielectric layer is 30 nm to 80 nm;
an arithmetic mean value t ₂ of the thickness of the first metal layer and the thickness of the second metal layer constituting the laminated film is 10 nm to 50 nm;
A photomask for laser exposure, wherein the light shielding portion has an optical density of 2.0 or more . 2. The photomask for laser exposure according to claim 1, wherein the dielectric constituting said first dielectric layer and said _second dielectric layer is _Al2O3 . 3. The photomask for laser exposure according to claim 1, wherein a material forming said first metal layer and said second metal layer is aluminum (Al). A photomask blank used for manufacturing a photomask for laser exposure,
a transparent glass substrate having a first surface and a second surface facing the first surface;
A light shielding layer provided on the first surface side of the transparent glass substrate,
The light shielding layer is composed of a laminated film formed by laminating a first dielectric layer, a first metal layer, a second dielectric layer and a second metal layer on the first surface in this order ,
the thickness _t1 of each of the first dielectric layer and the second dielectric layer is 30 nm to 80 nm;
an arithmetic mean value t ₂ of the thickness of the first metal layer and the thickness of the second metal layer constituting the laminated film is 10 nm to 50 nm;
A photomask blank , wherein the light shielding layer has an optical density of 2.0 or more . 5. The photomask blank according to claim 4 , wherein the material forming said first metal layer and said second metal layer is aluminum (Al). 6. The photomask blanks according to claim 4 , _wherein a dielectric constituting said first dielectric layer and said second dielectric layer is _Al2O3 .

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