JP7386117B2 - Photomask and exposure method - Google Patents

Description

The present disclosure relates to a photomask and an exposure method.

In the technology (photolithography) in which a photosensitive substance is applied to the surface of an object such as an electronic component, printed circuit board, or display panel, and then exposed to light to form a pattern, a pattern is formed on one side called a photomask. A transparent substrate is used.

In recent years, as exposure patterns have become more precise, the use of shorter wavelength EUV (Extreme Ultra Violet) light has expanded as an exposure light source instead of DUV (Deep Ultra Violet) light. ing. In an exposure method using EUV light, a photomask including a reflective layer that reflects exposure light is used (see, for example, Patent Document 1).

Japanese Patent Application Publication No. 2017-191285

A photomask provided with a reflective layer is generally used with the surface opposite to the surface on which a pattern is formed fixed to a photomask stage of an exposure machine using an electrostatic chuck. At this time, if foreign matter adheres to the photomask, the foreign matter may become caught between the photomask and the photomask stage, causing problems such as distortion of the photomask and the inability to perform exposure. Measures to avoid the adhesion of foreign matter to photomasks include installing dustproof covers called pellicles and conducting inspections, but with changes in pattern forming technology, photomasks (especially those with patterns formed Strategies to avoid contamination on both sides (front and opposite sides) are becoming increasingly important.

In view of the above circumstances, an object of an embodiment of the present disclosure is to provide a photomask in which contamination of the photomask is effectively suppressed, and an exposure method using this photomask.

Means for solving the above problems include the following embodiments.
<1> A photomask substrate with a pattern formed on one side,
A photomask, comprising: a protective film that is disposed in contact with a surface of the photomask substrate opposite to the surface on which the pattern is formed, and that is removable from the photomask substrate.
<2> The photomask according to <1>, further comprising a pellicle arranged to cover the surface of the photomask substrate on which the pattern is formed.
<3> The photo according to <1> or <2>, wherein the surface of the protective film in contact with the photomask substrate has an adhesive force of 0.1 N/25 mm to 10 N/25 mm as measured in accordance with JIS Z0237. mask.
<4> The photomask according to any one of <1> to <3>, wherein the protective film has a base layer and an adhesive layer.
<5> The photo according to <4>, wherein the protective film further includes an uneven absorption layer and an antistatic layer, and includes the base layer, the uneven absorption layer, the antistatic layer, and the adhesive layer in this order. mask.
<6> The photomask according to <5>, wherein the uneven absorption layer contains a thermoplastic resin.
<7> The photomask according to <5> or <6>, wherein the antistatic layer contains a conductive polymer.
<8> The photomask according to any one of <1> to <3>, wherein the protective film is formed by coating the photomask substrate with an adhesive.
<9> The photomask according to any one of <1> to <3>, wherein the protective film includes a base material having an uneven shape on at least one surface.
<10> The photomask according to <9>, wherein the protective film further includes a surface layer that covers at least a portion of the uneven surface of the base material.
<11> The photomask according to <10>, wherein the protective film has a hollow structure between the base material and the surface layer.
<12> The photomask according to any one of <1> to <11>, wherein the photomask substrate has a reflective layer that reflects exposure light.
<13> A step of arranging a protective film so as to be in contact with a surface opposite to the surface on which the pattern is formed of a photomask substrate having a pattern formed on one surface;
Peeling the protective film from the photomask;
An exposure method comprising the step of attaching the photomask from which the protective film has been peeled off to an exposure device and performing exposure.
<14> The exposure method according to <13>, wherein the protective film is placed by attaching the protective film to the photomask substrate.
<15> The exposure method according to <13>, wherein the protective film is placed by coating the photomask substrate with an adhesive.
<16> Any one of <13> to <15>, wherein the photomask is attached such that the surface opposite to the surface on which the pattern of the photomask substrate is formed is in contact with the photomask stage of the exposure apparatus. Exposure method described in section.

According to the present disclosure, a photomask in which contamination of the photomask is effectively suppressed and an exposure method using this photomask are provided.

FIG. 1 is a schematic cross-sectional view showing the configuration of a photomask according to an embodiment of the present disclosure. 1 is a schematic cross-sectional view showing an example of a protective film used in a photomask according to an embodiment of the present disclosure.

In the present disclosure, a numerical range expressed using "~" means a range that includes the numerical values written before and after "~" as the minimum and maximum lower and upper limits, respectively. In the numerical ranges described step by step in the present disclosure, the upper limit or lower limit described in a certain numerical range may be replaced with the upper limit or lower limit of another numerical range described step by step. Furthermore, in the numerical ranges described in this disclosure, the upper limit or lower limit described in a certain numerical range may be replaced with the value shown in the Examples.
In this disclosure, combinations of preferred aspects are more preferred aspects.
In this disclosure, the term "step" is used not only to refer to an independent process, but also to include a process that is not clearly distinguishable from other processes as long as the intended purpose of the process is achieved. .

In the present disclosure, EUV light refers to light with a wavelength of 5 nm to 30 nm, for example, 5 nm to 13.5 nm.
In this disclosure, EUV light and light having a shorter wavelength than EUV light may be collectively referred to as "EUV light, etc.".

The term "photomask" in the present disclosure is a concept that also includes a reticle.
In the present disclosure, "pellicle" refers to an embodiment including a pellicle frame and a pellicle membrane.
In the present disclosure, "(meth)acrylic" means either or both of acrylic and methacrylic, and "(meth)acrylate" means either or both of acrylate and methacrylate.

<Photomask>
A photomask according to an embodiment of the present disclosure includes a photomask substrate having a pattern formed on one surface, and a photomask substrate arranged so as to be in contact with a surface opposite to the surface on which the pattern is formed of the photomask substrate, and The present invention is a photomask that includes a protective film that can be peeled off from a photomask substrate.

In the photomask having the above configuration, a protective film is disposed on the surface (hereinafter also referred to as the back surface) opposite to the surface on which the pattern of the photomask substrate is formed (hereinafter also referred to as the pattern surface). Further, since the protective film can be peeled off from the photomask substrate, even if foreign matter adheres to the back surface of the photomask substrate, the foreign matter will be removed along with the protective film if the protective film is peeled off.
For example, adhesion of foreign matter to the back surface of the photomask substrate can be avoided by pasting a protective film on the back surface of the photomask substrate after cleaning and peeling off the protective film immediately before installing the photomask substrate in an exposure machine.

The photomask may further include a pellicle arranged to cover the patterned surface of the photomask substrate. By arranging the pellicle, it is possible to prevent foreign matter from adhering to the patterned surface of the photomask substrate.

FIG. 1 shows an example of the configuration of a photomask according to an embodiment of the present disclosure. The photomask shown in FIG. 1 includes a photomask substrate 100 with a pattern (not shown) formed on one surface, a protective film 200 disposed on the back surface of the photomask substrate 100, and a patterned surface of the photomask substrate 100. and a pellicle 300 arranged to cover the. The pellicle 300 is composed of a pellicle membrane 301 and a pellicle frame 302.
The pellicle 300 can be separated from the photomask substrate 100 and replaced with a new one.

(Photomask substrate)
The photomask substrate constituting the photomask is not particularly limited, and may be selected from those commonly used in photolithography. For example, a pattern formed using a material with low exposure light transmittance may be formed on one surface of a substrate such as glass that has high exposure light transmittance.

The photomask substrate may have a reflective layer that reflects exposure light, which is used when EUV light or the like is used as a light source.
A photomask substrate having a reflective layer may include, for example, a supporting substrate, a reflective layer laminated on the supporting substrate, and an absorber layer formed on the reflective layer.
In the photomask substrate having the above structure, the surface on which the reflective layer and the absorber layer are provided becomes the light irradiation surface, and the absorber layer absorbs a portion of the irradiated light. A desired image is formed on the semiconductor substrate).
A preferred example of the reflective layer is a multilayer film of molybdenum (Mo) and silicon (Si).
As the absorber layer, a layer made of a material with high absorbency for EUV light, such as chromium (Cr) and tantalum nitride, is preferably mentioned.

(Protective film)
The protective film is not particularly limited as long as it is made of a material that can be peeled off from the photomask substrate.
The protective film preferably has an adhesive force of 0.1 N/25 mm to 10 N/25 mm as measured in accordance with JIS Z0237 on the surface in contact with the photomask substrate (in the case of the first embodiment, the adhesive layer).
When the adhesive force is 0.1 N/25 mm or more, sufficient adhesion to the photomask substrate can be obtained, and when it is 10 N/25 mm or less, peeling from the photomask substrate can be performed well.

The manner in which the protective film exhibits adhesiveness is not particularly limited. For example, the adhesive may be exhibited by containing an adhesive, or the adhesive may be exhibited by fine convex portions formed on the surface.

Hereinafter, as examples of specific embodiments of the protective film, one having a base material layer and an adhesive layer (first embodiment), one formed by coating a photomask substrate with an adhesive (second embodiment), and at least one A structure having a base material having an uneven shape on one surface (third embodiment) will be described.

(First form)
The protective film of the first form has a base layer and an adhesive layer, and may have other layers as necessary.

The material of the base layer is not particularly limited. Examples include resins such as thermoplastic resins and thermoplastic elastomers. Specifically, polyolefins such as polyethylene, polypropylene, poly(4-methyl-1-pentene), and poly(1-butene); polyesters such as polyethylene terephthalate, polybutylene terephthalate, and polyethylene naphthalate; nylon-6, nylon- 66, polyamide such as polymethaxylene adipamide; polyacrylate; polymethacrylate; polyvinyl chloride; polyetherimide; ethylene/vinyl acetate copolymer; polyacrylonitrile; polycarbonate; polystyrene; ionomer; polysulfone; polyethersulfone; Examples include polyphenylene ether. The base material layer may contain only one type of resin or two or more types of resin.

When the protective film includes an adhesive layer containing a radiation-curable adhesive described below, the base layer is preferably made of a material that can transmit at least the radiation. Such resins include polyolefins and polyesters.

The density of the resin contained in the base material layer is preferably 900 kg/m ³ or more. When the density of the resin contained in the base layer is 900 kg/m ³ or more, the storage modulus is not too low and sufficient shape retention tends to be obtained. The upper limit of the density of the resin contained in the base material layer is not particularly limited, but from the viewpoint of ensuring flexibility, it is preferably 1450 kg/m ³ or less.

The base material layer may be a single layer or a combination of multiple layers. When the base layer is a combination of multiple layers, each layer may include different materials.

The thickness of the base layer is not particularly limited. From the viewpoint of suppressing warping of the photomask substrate, the thickness is preferably 5 μm or more, and more preferably 10 μm or more. The upper limit of the thickness of the base material layer is not particularly limited, but from the viewpoint of ease of handling, it is preferably 100 μm or less.

The adhesive layer included in the protective film has a function of maintaining the state in which the protective film is attached to the photomask substrate.
The adhesive layer may include an adhesive. The type of adhesive (adhesive main agent) is not particularly limited, and may include silicone adhesives, acrylic adhesives, urethane adhesives, polyamide adhesives, polyester adhesives, ethylene-vinyl acetate copolymers, and olefin adhesives. , polybutadiene-based adhesives, rubber-based adhesives, styrene-based adhesives, and the like. Among these, acrylic adhesives, silicone adhesives, and rubber adhesives are preferred, and acrylic adhesives are preferred from the viewpoint of facilitating adjustment of adhesive strength.
The adhesive layer may contain only one type of adhesive or two or more types of adhesives.

The adhesive layer may include a radiation-curable adhesive. When the adhesive layer includes a radiation-curable adhesive, for example, when removing the protective film, the adhesive is cured by irradiation with radiation to reduce the adhesive force and facilitate peeling from the photomask substrate. I can do it. The radiation to be irradiated is not particularly limited, and ultraviolet rays, electron beams, infrared rays, etc. can be used.

Examples of radiation-curable adhesives include those containing the above-mentioned adhesive base, a compound having a carbon-carbon double bond in the molecule, and a radiation polymerization initiator, and those containing a polymer having a carbon-carbon double bond in the molecule. Examples include those containing an adhesive main agent as a base polymer and a radiation polymerization initiator.

Examples of compounds having a carbon-carbon double bond in the molecule include trimethylolpropane tri(meth)acrylate, pentaerythritol tri(meth)acrylate, dipentaerythritol hexa(meth)acrylate, and tetraethylene glycol di(meth)acrylate. The following (meth)acrylate compounds are mentioned. The content of the compound having a carbon-carbon double bond in the molecule may be, for example, 30 parts by mass or less based on 100 parts by mass of the adhesive base agent. Further, the amount may be 5 parts by mass or more based on 100 parts by mass of the adhesive base agent.

Examples of radiation polymerization initiators include acetophenone photopolymerization initiators such as methoxyacetophenone; α-ketol compounds such as 4-(2-hydroxyethoxy)phenyl (2-hydroxy-2-propyl) ketone; ketals such as benzyl dimethyl ketal; Examples include benzoin-based photopolymerization initiators such as benzoin and benzoin methyl ether; benzophenone-based photopolymerization initiators such as benzophenone and benzoylbenzoic acid.

The radiation-curable adhesive may further contain a crosslinking agent, if necessary. Examples of the crosslinking agent include isocyanate crosslinking agents such as diphenylmethane diisocyanate, tolylene diisocyanate, hexamethylene diisocyanate, and polyisocyanate.

The thickness of the adhesive layer is not particularly limited. For example, it may be 5 μm to 200 μm.

The protective film of the first form may have at least one of an uneven absorption layer and an antistatic layer between the base layer and the adhesive layer.
In one embodiment, the protective film includes a base layer, an uneven absorption layer, an antistatic layer, and an adhesive layer in this order.

The material of the uneven absorption layer is not particularly limited. For example, it may contain a resin that exhibits unevenness absorbability.
Resins that exhibit unevenness absorption include olefin resins, ethylene/polar monomer copolymers, ABS resins, vinyl chloride resins, vinylidene chloride resins, (meth)acrylic resins, polyamide resins, fluorine resins, and polycarbonate resins. Examples include thermoplastic resins such as resins and polyester resins. Among these, olefin resins and ethylene/polar monomer copolymers are preferred. The uneven absorbing layer may contain only one type of resin or two or more types.

Examples of olefin-based resins include linear low-density polyethylene (LLDPE), low-density polyethylene, high-density polyethylene, polypropylene, ethylene/α-olefin copolymers containing ethylene and α-olefin having 3 to 12 carbon atoms, and propylene. and an α-olefin having 4 to 12 carbon atoms, propylene/α-olefin copolymers, ethylene/cyclic olefin copolymers, ethylene/α-olefin/cyclic olefin copolymers, and the like.

Examples of ethylene/polar monomer copolymers include ethylene/ethyl (meth)acrylate copolymer, ethylene/methyl (meth)acrylate copolymer, ethylene/propyl (meth)acrylate copolymer, and ethylene/(meth)acrylate copolymer. ) Ethylene/unsaturated carboxylic acid ester copolymers such as butyl acrylate copolymers; ethylene/vinyl acetate copolymers, ethylene/vinyl propionate copolymers, ethylene/vinyl butyrate copolymers, ethylene/vinyl stearate Examples include ethylene/vinyl ester copolymers such as copolymers.

The α-olefin having 3 to 12 carbon atoms in the ethylene/α-olefin copolymer includes propylene, 1-butene, 1-pentene, 3-methyl-1-butene, 1-hexene, 4-methyl-1- Examples include pentene, 3-methyl-1-pentene, 1-heptene, 1-octene, 1-decene, 1-dodecene, and among them, propylene and 1-butene are preferred.

Among these, low-density polyethylene; polypropylene; ethylene/propylene copolymer, ethylene/1-butene copolymer, ethylene/propylene/α having 4 to 12 carbon atoms, and - Ethylene/α-olefin copolymers such as olefin terpolymers; propylene/1-butene/α-olefin terpolymers having 5 to 12 carbon atoms; and ethylene/vinyl acetate copolymers are preferred, and ethylene/propylene copolymers and ethylene/vinyl acetate copolymers are more preferred.

The thickness of the uneven absorption layer is not particularly limited. From the viewpoint of the balance between uneven absorbability and other properties, it may be 10 μm to 500 μm, 20 μm to 400 μm, 30 μm to 300 μm, or 50 μm to 250 μm.

The density of the uneven absorption layer is not particularly limited. From the viewpoint of the balance between mechanical strength and unevenness absorbability, the weight may be 800 kg/m ³ to 990 kg/m 3 , ⁸³⁰ kg/m ³ to 980 kg/m ³ , or 850 kg/m ³ to It may be 970 kg/m ³ .

The antistatic layer serves to suppress the amount of static electricity generated when the protective film is peeled off from the photomask substrate.

The material of the antistatic layer is not particularly limited. For example, it may contain a conductive polymer.
Examples of conductive polymers include polythiophene-based conductive polymers, polypyrrole-based conductive polymers, polyaniline-based conductive polymers, poly(p-phenylene vinylene)-based conductive polymers, polyquinoxaline-based conductive polymers, etc. Can be mentioned. The antistatic layer may contain only one type of conductive polymer or two or more types.

From the viewpoint of a good balance of optical properties, appearance, antistatic properties, coatability, stability, etc., polythiophene-based conductive polymers are preferred. Examples of polythiophene-based conductive polymers include polyethylenedioxythiophene and polythiophene.

The antistatic layer may include a doping agent. A doping agent is a substance that more reliably imparts conductivity (doping) to a conductive polymer.
Examples of doping agents include sulfonic acid compounds. When a sulfonic acid compound is added as a doping agent, the conductive polymer and the sulfonic acid compound partially react to form a sulfonate, and the action of this sulfonate improves the antistatic function of the antistatic layer. do.

Examples of sulfonic acid compounds include p-toluenesulfonic acid, benzenesulfonic acid, ethylbenzenesulfonic acid, octylbenzenesulfonic acid, dodecylbenzenesulfonic acid, mesitylenesulfonic acid, m-xylenesulfonic acid, polystyrenesulfonic acid, polyvinylsulfonic acid, etc. Can be mentioned. From the viewpoint of improving the solubility or water dispersibility of the conductive polymer, polystyrene sulfonic acid and polyvinyl sulfonic acid are preferred.
The content of the doping agent is, for example, 100 parts by mass to 300 parts by mass based on 100 parts by mass of the conductive polymer.

As a combination of a conductive polymer and a doping agent, a combination of polyethylene dioxythiophene (PEDOT) and polystyrene sulfonic acid (PSS) is preferable because it has better antistatic properties.

The antistatic layer may include a binder resin. When the antistatic layer contains a binder resin, film-forming properties, adhesion, etc. tend to improve.
Binder resins include polyurethane resins, polyester resins, (meth)acrylic resins, polyether resins, cellulose resins, polyvinyl alcohol resins, epoxy resins, polyvinylpyrrolidone, polystyrene resins, polyethylene glycol, pentaerythritol, etc. can be mentioned. The antistatic layer may contain only one kind of binder resin or two or more kinds of binder resins.
The content of the binder resin may be, for example, 10 parts by mass to 500 parts by mass based on 100 parts by mass of the conductive polymer.

The thickness of the antistatic layer 30 is not particularly limited. From the viewpoint of the balance between antistatic performance and other properties, the thickness may be 0.01 μm to 10 μm, 0.01 μm to 5 μm, or 0.01 μm to 1 μm.

(Second form)
The second type of protective film is formed by coating a photomask substrate with an adhesive. The type of adhesive used for coating is not particularly limited, and may be selected from the adhesives included in the adhesive layer described above.

The coating method is not particularly limited, and spray coating, brush coating, etc. can be used. From the viewpoint of forming a film with uniform thickness, spray coating is preferred.

From the viewpoint of forming a film with a uniform thickness, the adhesive is preferably coated in the form of an adhesive solution dissolved in a known solvent.
The solvent used in the adhesive solution is not particularly limited, and any known solvent can be used. For example, acetone, methyl ethyl ketone (2-butanone), cyclohexane, ethyl acetate, ethylene dichloride, tetrahydrofuran, toluene, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol dimethyl ether, propylene glycol monomethyl ether, propylene glycol monoethyl ether, acetylacetone , cyclohexanone, diacetone alcohol, ethylene glycol monomethyl ether acetate, ethylene glycol ethyl ether acetate, ethylene glycol monoisopropyl ether, ethylene glycol monobutyl ether acetate, 1-methoxy-2-propanol, 3-methoxy-1-propanol, methoxy Methoxyethanol, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, propylene glycol monomethyl ether acetate, propylene glycol monoethyl ether acetate, 3-methoxypropyl acetate, N,N-dimethylformamide, dimethyl sulfoxide, γ- Examples include butyrolactone, methyl lactate, ethyl lactate, and the like. The number of solvents used in the adhesive solution may be one, or two or more.

The solid content concentration of the adhesive solution is not particularly limited. For example, it is preferable that the solid content concentration is about 1% by mass to 50% by mass.

The thickness of the coating containing the adhesive is not particularly limited. Depending on the balance between strength and removability, the thickness may be 10 μm to 200 μm, or 25 μm to 100 μm.

If desired, another material such as a resin film may be placed over the adhesive-containing coating.

(Third form)
The third embodiment of the protective film includes a base material having an uneven shape on at least one surface.
The protective film having the above structure exhibits adhesiveness due to the physical action derived from the uneven shape of the base material. Since the protective film configured as described above does not contain an adhesive, it is possible to avoid the adhesive from remaining on the photomask substrate after the protective film is peeled off.

Regarding adhesive materials that utilize physical effects derived from uneven shapes, for example, International Publication No. 2014/124352, Adv. Mater. 19, 1973-1977 (2007), etc.

The uneven shape of the base material is not particularly limited as long as it exhibits the necessary adhesiveness to the photomask substrate. Moreover, the uneven shape may be formed only on one side of the base material, or may be formed on both sides.

The shape of the convex portion is not particularly limited, and may be any shape such as a columnar shape, a conical shape, a tapered shape, an inverted tapered shape, a rectangular parallelepiped shape, a polygonal columnar shape, a mushroom shape, and a dumbbell shape. Further, the central axis of the convex portion on the base material may be inclined with respect to the vertical direction (thickness direction of the base material).

The width of the convex portion is preferably 0.1 μm to 500 μm, more preferably 0.5 μm to 400 μm, and even more preferably 1 μm to 300 μm.
In the present disclosure, the width of a convex portion refers to the length at which the distance between the surfaces is maximum when the periphery of the bottom of the convex portion is sandwiched between two parallel surfaces.
For example, if the convex part is cylindrical or conical, the diameter of the bottom corresponds to the width of the convex part, if it is rectangular parallelepiped, the length of the diagonal of the bottom corresponds to the width of the convex part, and if it is triangular prism-shaped, the diameter of the bottom corresponds to the width of the convex part. , the maximum value of the distance between one side of the bottom and the vertices that do not constitute the certain side corresponds to the width of the convex portion.

The distance between the protrusions on the base material is preferably 0.1 μm to 500 μm, preferably 1 μm to 400 μm, and more preferably 2 μm to 300 μm.
In the present disclosure, the distance between convex portions refers to the length at which the distance between the side surfaces of two convex portions is the shortest among adjacent convex portions.

The height of the convex portion on the base material is preferably 0.1 μm to 2000 μm, preferably 1 μm to 1000 μm, and more preferably 2 μm to 500 μm.

The ratio of the height of the protrusion to the width of the protrusion (height of the protrusion/width of the protrusion) is preferably 0.5 to 15, more preferably 0.8 to 10, and 1 It is more preferable that it be 5 to 5. When the ratio is 0.5 or more, the adhesion to the adherend tends to be better, and when it is 15 or less, the strength of the convex portion tends to be better.

The ratio of the distance between the protrusions to the width of the protrusions (distance between the protrusions/width of the protrusions) is preferably 0.2 to 10, more preferably 0.5 to 8, and 0. More preferably, it is between .8 and 5. When the ratio is 0.2 or more, the processability and shape stability of the convex portions tend to be excellent, and when it is 10 or less, the adhesion to the adherend tends to be better.

The ratio of the total area of the bottoms of the recesses to the total area of the bottoms of the projections (total area of the bottoms of the recesses/total area of the bottoms of the projections) is from 1 to 100 in terms of adhesiveness and shape retention of the protective film. It is preferably from 1.5 to 50, even more preferably from 2 to 20.

In the area occupied by the uneven shape of the base material (the total area occupied by the protrusions and the area occupied by the recesses), the ratio (volume ratio) occupied by the protrusions is 0.5% from the viewpoint of adhesiveness and shape retention of the protective film. It is preferably from 0.0001 to 0.5, more preferably from 0.02 to 0.4, even more preferably from 0.05 to 0.33.

The materials included in the base material having an uneven shape are not particularly limited, and include olefin resins, polyester resins, polyurethane resins, polyimide resins, silicone resins, styrene resins, acrylic resins, epoxy resins, and amide resins. Examples include resins such as resins, ester resins, and carbonate resins. Among these, olefin resins, polyurethane resins, acrylic resins, polyimide resins, and silicone resins are preferred from the viewpoint of maintaining the shape of the convex portions.

The base material having an uneven shape is preferably formed from a material having a high elastic modulus and low tackiness, from the viewpoint of maintaining the shape of the convex portions and suppressing stickiness.

The storage modulus of the above-mentioned base material at 25°C is preferably 1 MPa to 1 GPa, more preferably 5 MPa to 1 GPa, and more preferably 10 MPa to 50 MPa, from the viewpoint of achieving both imprint processability and adhesiveness. It is even more preferable that there be.
The storage modulus of the base material can be measured according to the method for measuring the storage modulus of the base material layer of the protective film of the first embodiment described above.

The method of forming the uneven shape on the base material is not particularly limited, and any known method can be used. For example, convex portions may be formed by patterning on the surface of the base material using nanoimprint technology.

The base material may contain a substance whose chemical structure changes when stimulated by ultraviolet light, heat, or the like. Thereby, for example, a structure may be adopted in which when stimulation is applied to the base material, the adhesive force to the photomask substrate is reduced.

The protective film may further include a surface layer that covers at least a portion of the uneven surface of the base material. The surface layer may have any configuration as long as it is disposed on the tip of the convex portion of the base material and covers at least a portion of the surface having an uneven shape.

The surface layer is preferably disposed over the tips of a plurality of convex portions on the base material, and may be placed, for example, over the tip portions of 10 or more convex portions on the base material. . Here, "the surface layer is disposed straddling the tips of the plurality of convex parts on the base material" means that at least one surface layer is disposed straddling the tips of the plurality of convex parts. It means there is. It is preferable that the surface layer is a continuous layer disposed over the tips of the plurality of convex portions and covering the plurality of convex portions. The protective film may have a plurality of surface layers disposed over the tips of the plurality of protrusions. When a plurality of surface layers are provided, it is preferable that the plurality of surface layers exist separately and are respectively disposed over the tips of the plurality of convex portions.

The protective film may have a hollow structure between the base material and the surface layer.
For example, as shown in FIG. 2, between a base material 1 having an uneven shape consisting of a convex part 2 and a concave part 6, and a surface layer 3 disposed so as to cover the concave and convex shape of the base material 1, a concave part 6 is formed. It may have a hollow structure consisting of a space corresponding to .
The shape of the space formed between the base material 1 and the surface layer 3 may change when attaching the protective film to the photomask substrate.

The ratio of the height of the protrusions on the base material to the thickness of the surface layer (height of the protrusions/thickness of the surface layer) is preferably 0.2 to 1000, and preferably 0.5 to 500. is more preferable, and even more preferably 1.0 to 100.

The thickness of the surface layer is preferably 0.1 μm to 50 μm, more preferably 1 μm to 20 μm, and 3 μm to 15 μm from the viewpoint of further increasing the adhesiveness to the photomask substrate and processability. It is even more preferable.

The materials contained in the surface layer are not particularly limited, and include olefin resins, polyester resins, polyurethane resins, polyimide resins, silicone resins, styrene resins, acrylic resins, epoxy resins, amide resins, and ester resins. Examples include resins such as resins and carbonate resins. Among these, olefin resins, polyimide resins, acrylic resins, and silicone resins are preferable because of their excellent low contamination properties on the photomask substrate.

The base material and the surface layer may contain the same type of material, for example, both the base material and the surface layer may contain a silicone resin.

The surface layer is preferably formed from a material having a high elastic modulus and low tackiness from the viewpoint of maintaining the shape of the convex portions and suppressing stickiness.

The storage modulus of the surface layer at 25° C. is preferably 1 MPa to 1 GPa, more preferably 5 MPa to 1 GPa, and even more preferably 10 MPa to 50 MPa. Further, the storage modulus of the surface layer at 25°C is preferably smaller than the storage modulus of the base material at 25°C.
The storage modulus of the surface layer can be measured according to the method for measuring the storage modulus of the base layer of the protective film of the first embodiment described above.

(pellicle)
When the photomask includes a pellicle, the type of pellicle is not particularly limited and can be selected depending on the application and the like.
The material of the pellicle film constituting the pellicle is not particularly limited, and may be an organic material, an inorganic material, or a combination of an organic material and an inorganic material.
Examples of organic materials include fluorine-based polymers and the like.
Examples of inorganic materials include crystalline silicon (monocrystalline silicon, polycrystalline silicon, etc.), diamond-like carbon (DLC), graphite, amorphous carbon, graphene, silicon carbide, silicon nitride, aluminum nitride, and the like.
The pellicle film may contain only one kind of the above-mentioned materials, or may contain two or more kinds of materials.

The pellicle film may be a single layer or may have a structure consisting of two or more layers.
The thickness of the pellicle film (total thickness in the case of two or more layers) is preferably 10 nm to 200 nm, more preferably 10 nm to 100 nm, even more preferably 10 nm to 70 nm, and even more preferably 10 nm to 50 nm. It is particularly preferable that

The material of the pellicle frame constituting the pellicle is not particularly limited. Examples include aluminum, aluminum alloys (5000 series, 6000 series, 7000 series, etc.), stainless steel, silicon, silicon alloys, iron, iron alloys, carbon steel, tool steel, ceramics, metal-ceramic composite materials, resins, etc. . Among these, aluminum and aluminum alloys are preferred from the viewpoint of light weight and rigidity.

The pellicle frame may have a protective film on its surface. The protective film is preferably resistant to hydrogen radicals present in the exposure atmosphere and to exposure.
Examples of the protective film include an oxide film. The oxide film can be formed by a known method such as anodic oxidation. Further, the oxide film may be colored with a black dye. When the pellicle frame has an oxide film colored with a black dye, it becomes easier to detect foreign substances on the pellicle frame.

<Exposure method>
An exposure method according to an embodiment of the present disclosure includes a step of arranging a protective film so as to be in contact with a surface opposite to the surface on which the pattern is formed of a photomask substrate having a pattern formed on one surface;
Peeling the protective film from the photomask substrate;
The exposure method includes the step of attaching the photomask substrate from which the protective film has been peeled off to an exposure device and performing exposure.

According to the above method, contamination of the surface opposite to the patterned surface of the photomask substrate before being attached to the exposure apparatus is effectively suppressed.

The method of arranging the protective film on the photomask substrate is not particularly limited, and can be selected depending on the form of the protective film used, etc. For example, when using the above-mentioned protective film of the first form or the third form, the protective film can be attached to the photomask substrate while being heated as necessary. When using the second type of protective film, the photomask substrate can be coated with an adhesive.

From the viewpoint of suppressing contamination of the photomask substrate, it is preferable that the step of peeling off the protective film from the photomask substrate is performed immediately before the operation of attaching the photomask substrate to the exposure apparatus.

The method may include the step of cleaning the photomask substrate. In this case, from the viewpoint of suppressing contamination of the photomask substrate, the step of disposing the protective film on the photomask substrate is preferably performed immediately after the step of cleaning the photomask substrate.

The method may include a step of arranging a pellicle so as to cover the patterned surface of the photomask substrate. The method for arranging the pellicle is not particularly limited, and can be performed by a known method using an adhesive or the like. Either the protective film or the pellicle may be placed first.

The method may include a step of inspecting whether foreign matter is attached to the photomask substrate. The inspection may be performed before the protective film is placed, after the protective film is placed and before peeling off, or after the protective film is peeled off, and the test may be performed once or multiple times.

In the above method, the method of attaching the photomask substrate to the exposure apparatus is not particularly limited. For example, the photomask substrate may be fixed using an electrostatic chuck or the like so that the surface opposite to the surface on which the pattern is formed contacts the photomask stage of the exposure machine.

In the above method, since the protective film prevents foreign matter from adhering to the surface of the photomask substrate opposite to the pattern-formed surface, foreign matter is less likely to get caught between the photomask and the photomask stage. Problems are less likely to occur. Therefore, productivity is improved compared to the conventional method that does not use a protective film.

EXAMPLES Hereinafter, the present invention will be explained in more detail with reference to Examples, but the present invention is not limited to the following Examples unless the gist thereof is exceeded.

<Example 1>
An adhesive tape (ICROS tape, SB-150HND-R2, Mitsui Chemicals Tohcello Co., Ltd.), which has an adhesive layer formed on a base material cut out to 200 mm x 200 mm, was placed on the back side of a pre-cleaned photomask substrate at room temperature. I applied a roll and placed a protective film.
The photomask substrate with the protective film placed thereon was left in a clean room for 24 hours. Thereafter, the protective film was peeled off from the photomask substrate, and the number of foreign particles with a maximum diameter of 3 μm or more existing on the exposed surface was measured using a surface particle scanner (YPI-200MX, Yamanashi Gijutsu Kobo Co., Ltd.). The number of foreign particles was similarly measured on the back surface of the photomask substrate immediately after cleaning (before the protective film was placed). The results are shown in Table 1.

<Example 2>
The same process as Example 1 was carried out, except that instead of pasting adhesive tape, the back side of the photomask substrate was coated with an adhesive (manufactured by LFT Co., Ltd., product name: Liquid Film Spray) to form a protective film. went.

<Example 3>
A protective film having the structure shown in FIG. 2 was produced by the following method.
100 parts by mass of epoxy acrylate (Daicel Allnex, EBERCRYL3500) and 2 parts by mass of a photopolymerization initiator (IGM Resins B.V., Omnirad 184) were mixed and stirred to obtain a resin composition. The obtained resin composition was molded into a 300 mm square mold made of nickel (concave pattern arranged in a two-dimensional square grid, height difference of concave portions: 15 μm, shape of concave portions: holes, width of concave portions (diameter of holes): 5 μm, Width of the recess (hole spacing): 5 μm, aspect ratio (depth/diameter) of the recess 3:1), coated with a gap of 50 μm, and attached a polyester release film (TN100 manufactured by Toyobo Co., Ltd.). UV irradiation (1000 mJ/cm ² ) was applied to the combined state. After that, the cured resin sheet was peeled off from the mold, and a base material having cylindrical convex shapes (width: 5 μm, height: 15 μm) arranged in a two-dimensional square lattice shape (distance between convex parts: 5 μm) on one side was removed. Obtained.
Next, a film serving as a surface layer was created as follows. The resin composition was dropped into a Teflon (registered trademark) Petri dish and UV irradiated (500 mJ/cm ² ) to obtain a 10 μm thick film.
Subsequently, a film that will become the surface layer is attached to the convex surface side of the base material, and main curing is performed with UV irradiation (1000 mJ/cm ² ) to form a hollow structure between the base material and the surface layer. A protective film (thickness of the base material portion excluding the release film: 50 μm, thickness of the surface layer portion: 10 μm) was produced.
The same process as in Example 1 was carried out except that the surface layer side of the produced protective film was attached to the back surface of the photomask substrate instead of the adhesive tape.

<Comparative example 1>
The same process as in Example 1 was performed except that a protective film was not placed on the back surface of the photomask substrate.

As shown in Table 1, in the photomask substrate of the comparative example in which no protective film was placed, the number of foreign substances increased after being left in a clean room for 24 hours compared to immediately after cleaning. In contrast, in the photomask substrate of the example in which the protective film was disposed, the number of foreign particles after being left standing in a clean room for 24 hours was almost unchanged from immediately after cleaning, and surface contamination was effectively suppressed.

DESCRIPTION OF SYMBOLS 100... Photomask substrate 200... Protective film 300... Pellicle 301... Pellicle membrane 302... Pellicle frame 1... Base material 2... Convex part 3... Surface layer 6... Concave part

Claims (16)

a photomask substrate with a pattern formed on one side;
A photomask, comprising: a protective film that is disposed in contact with a surface of the photomask substrate opposite to the surface on which the pattern is formed, and that is removable from the photomask substrate. The photomask according to claim 1, further comprising a pellicle arranged to cover the surface of the photomask substrate on which the pattern is formed. The photomask according to claim 1 or 2, wherein the surface of the protective film in contact with the photomask substrate has an adhesive force of 0.1 N/25 mm to 10 N/25 mm as measured in accordance with JIS Z0237. The photomask according to any one of claims 1 to 3, wherein the protective film has a base layer and an adhesive layer. The photomask according to claim 4, wherein the protective film further includes an uneven absorption layer and an antistatic layer, and includes the base layer, the uneven absorption layer, the antistatic layer, and the adhesive layer in this order. The photomask according to claim 5, wherein the uneven absorption layer contains a thermoplastic resin. The photomask according to claim 5 or 6, wherein the antistatic layer contains a conductive polymer. The photomask according to claim 1, wherein the protective film is formed by coating the photomask substrate with an adhesive. The photomask according to any one of claims 1 to 3, wherein the protective film includes a base material having an uneven shape on at least one surface. The photomask according to claim 9, wherein the protective film further includes a surface layer that covers at least a portion of the uneven surface of the base material. The photomask according to claim 10, wherein the protective film has a hollow structure between the base material and the surface layer. The photomask according to any one of claims 1 to 11, wherein the photomask substrate has a reflective layer that reflects exposure light. arranging a protective film so as to be in contact with a surface opposite to the surface on which the pattern is formed of a photomask substrate having a pattern formed on one surface;
Peeling the protective film from the photomask substrate ;
An exposure method comprising the step of attaching the photomask substrate from which the protective film has been peeled off to an exposure device and performing exposure. 14. The exposure method according to claim 13, wherein the protective film is placed by attaching the protective film to the photomask substrate. 14. The exposure method according to claim 13, wherein the protective film is placed by coating the photomask substrate with an adhesive. According to any one of claims 13 to 15, the photomask substrate is attached such that the surface of the photomask substrate opposite to the surface on which the pattern is formed is in contact with the photomask stage of the exposure apparatus. Exposure method described.