JP2021157114A - Photomask and exposure method - Google Patents

Abstract

To provide a photomask which effectively suppresses the contamination of a photomask and to provide an exposure method using the photomask.SOLUTION: There is provided a photomask which has a photomask substrate on one surface of which a pattern is formed and a protective film which is arranged so as to contact with a surface opposite to a surface on which the pattern on the photomask substrate is formed and can be peeled off from the photomask substrate.SELECTED DRAWING: Figure 1

Description

The present disclosure relates to photomasks and exposure methods.

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

In recent years, as the definition of exposure patterns has increased, the use of shorter wavelength EUV (Extreme Ultra Violet) light has expanded in place of DUV (Deep Ultra Violet) light as a light source for exposure. ing. In the exposure method using EUV light, a photomask provided with a reflective layer that reflects the exposure light is used (see, for example, Patent Document 1).

JP-A-2017-191285

A photomask provided with a reflective layer is generally used by fixing a surface opposite to the surface on which the pattern is formed to a photomask stage of an exposure machine by an electrostatic chuck. At this time, if foreign matter adheres to the photomask, the foreign matter may be caught between the photomask and the photomask stage, causing problems such as the photomask being distorted and exposure not being possible. As a measure to prevent foreign matter from adhering to the photomask, a dustproof cover called a pellicle has been installed and inspections have been carried out so far. However, as the pattern forming technology changes, the photomask (particularly, a pattern is formed). Measures to avoid pollution on the opposite side) are becoming more important.

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

Means for solving the above problems include the following embodiments.
<1> A photomask substrate having a pattern formed on one surface and
A photomask having a protective film that is arranged so as to be in contact with a surface of the photomask substrate that is opposite to the surface on which the pattern is formed and that can be peeled off from the photomask substrate.
<2> The photomask according to <1>, further comprising a pellicle arranged so as to cover the surface of the photomask substrate on which the pattern is formed.
<3> The photo according to <1> or <2>, wherein the adhesive strength of the surface of the protective film in contact with the photomask substrate is 0.1 N / 25 mm to 10 N / 25 mm 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 material layer and an adhesive layer.
<5> The photo according to <4>, wherein the protective film further has an uneven absorption layer and an antistatic layer, and includes the base material 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 has a surface layer that covers at least a part 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 the protective film so as to be in contact with the surface of the photomask substrate having the pattern formed on one surface and the surface opposite to the surface on which the pattern is formed.
The step of peeling the protective film from the photomask and
An exposure method comprising a step of attaching the photomask from which the protective film has been peeled off to an exposure apparatus and performing exposure.
<14> The exposure method according to <13>, wherein the protective film is arranged by attaching the protective film to the photomask substrate.
<15> The exposure method according to <13>, wherein the protective film is arranged by coating the photomask substrate with an adhesive.
<16> The photomask is attached so 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, any one of <13> to <15>. The exposure method according to the section.

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

It is a schematic cross-sectional view which shows the structure of the photomask which concerns on one Embodiment of this disclosure. It is a schematic cross-sectional view which shows the example of the protective film used for the photomask which concerns on one Embodiment of this disclosure.

In the present disclosure, the numerical range represented by using "~" means a range including the numerical values before and after "~" as the minimum value, the maximum value lower limit value, and the upper limit value, respectively. In the numerical range described stepwise in the present disclosure, the upper limit value or the lower limit value described in a certain numerical range may be replaced with the upper limit value or the lower limit value of another numerical range described stepwise. Further, in the numerical range described in the present disclosure, the upper limit value or the lower limit value described in a certain numerical range may be replaced with the value shown in the examples.
In the present disclosure, the combination of preferred embodiments is a more preferred embodiment.
In the present disclosure, the term "process" is included in this term not only as an independent process but also as long as the intended purpose of the process is achieved even if it cannot be clearly distinguished from other processes. ..

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

The "photomask" in the present disclosure is a concept including a reticle.
In the present disclosure, "pellicle" indicates an embodiment including a pellicle frame and a pellicle film.
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>
The photomask according to the embodiment of the present disclosure is arranged so as to be in contact with a photomask substrate having a pattern formed on one surface and a surface opposite to the surface on which the pattern is formed. A photomask having a protective film that can be peeled off from a photomask substrate.

In the photomask having the above configuration, the protective film is arranged on the surface (hereinafter, also referred to as the back surface) opposite to the surface (hereinafter, also referred to as the pattern surface) on which the pattern of the photomask substrate is formed. 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 is also removed together with the protective film by peeling off the protective film.
For example, by attaching a protective film to the back surface of the photomask substrate after cleaning and peeling off the protective film immediately before installing the photomask substrate, it is possible to prevent foreign matter from adhering to the back surface of the photomask substrate.

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

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

(Photomask board)
The photomask substrate constituting the photomask is not particularly limited, and may be selected from those generally used for photolithography. For example, it may have a pattern formed on one surface of a substrate having a high transparency of exposure light such as glass by using a material having a low transparency of exposure light.

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.
The photomask substrate having a reflective layer may include, for example, a support substrate, a reflective layer laminated on the support substrate, and an absorber layer formed on the reflective layer.
In the photomask substrate having the above configuration, the surface on the side where the reflective layer and the absorber layer are provided becomes a light irradiation surface, and the absorber layer partially absorbs the irradiation light, so that the sensitive substrate (for example, a photoresist film) A desired image is formed on the attached semiconductor substrate).
As the reflective layer, a multilayer film of molybdenum (Mo) and silicon (Si) is preferably used.
As the absorber layer, a layer made of a material having high absorbency such as 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 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 measured in accordance with JIS Z0237 on the surface in contact with the photomask substrate (adhesive layer in the case of the first form).
When the adhesive strength 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 satisfactorily.

The mode in which the protective film exhibits adhesiveness is not particularly limited. For example, it may be adhesive by containing an adhesive, or may be adhesive by fine protrusions formed on the surface.

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

(First form)
The protective film of the first form has a base material layer and an adhesive layer, and may have another layer if necessary.

The material of the base material is not particularly limited. For example, resins such as thermoplastic resins and thermoplastic elastomers can be mentioned. 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, Polyolefins such as Polymethaxylene adipamide; Polyacrylate; Polymethacrylate; Polyvinyl chloride; Polyetherimide; Ethylene-vinyl acetate copolymer; Polyacrylonitrile; Polycarbonate; Polycarbonate; Ionomer; Polysulfone; Polyethersulfone; Examples include polyphenylene ether and the like. The resin contained in the base material layer may be only one type or two or more types.

When the protective film includes a pressure-sensitive adhesive layer containing a radiation-curable pressure-sensitive adhesive described later, the base material layer is preferably a material capable of transmitting the radiation at least. Examples of 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 material layer is 900 kg / m ³ or more, the storage elastic 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 it is preferably ^{1450 kg / m 3 or less from the viewpoint of ensuring flexibility.}

The base material layer may be a single layer or a combination of a plurality of layers. When the base material layer is a combination of a plurality of layers, each layer may contain a different material.

The thickness of the base material layer is not particularly limited. From the viewpoint of suppressing the warp of the photomask substrate, it 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 it is preferably 100 μm or less from the viewpoint of handleability.

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

The pressure-sensitive adhesive layer may contain a radiation-curable pressure-sensitive adhesive. When the pressure-sensitive adhesive layer contains a radiation-curable pressure-sensitive adhesive, for example, when the protective film is peeled off, the pressure-sensitive adhesive is cured by irradiating with radiation to reduce the adhesive strength and easily peel off from the photomask substrate. Can be done. The radiation to be irradiated is not particularly limited, and ultraviolet rays, electron beams, infrared rays and the like can be used.

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

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. (Meta) acrylate compound of. The content of the compound having a carbon-carbon double bond in the molecule may be, for example, 30 parts by mass or less with respect to 100 parts by mass of the pressure-sensitive adhesive base material. Further, it may be 5 parts by mass or more with respect to 100 parts by mass of the pressure-sensitive adhesive main agent.

Examples of the radiation polymerization initiator include an acetophenone-based photopolymerization initiator such as methoxyacetophenone; an α-ketol compound such as 4- (2-hydroxyethoxy) phenyl (2-hydroxy-2-propyl) ketone; and a ketal such as benzyldimethyl ketal. Phenyl compounds; benzoin-based photopolymerization initiators such as benzoin and benzoin methyl ether; benzophenone-based photopolymerization initiators such as benzophenone and benzoylbenzoic acid can be mentioned.

The radiation-curable pressure-sensitive adhesive may further contain a cross-linking agent, if necessary. Examples of the cross-linking agent include isocyanate-based cross-linking 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 material layer and the adhesive layer.
In one embodiment, the protective film has a base material 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 absorption.
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, fluororesins, and polycarbonate resins. Examples thereof include thermoplastic resins such as resins and polyester resins. Among these, olefin resins and ethylene / polar monomer copolymers are preferable. The resin contained in the uneven absorption layer may be only one type or two or more types.

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

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

Examples of the α-olefin having 3 to 12 carbon atoms in the ethylene / α-olefin copolymer include propylene, 1-butene, 1-pentene, 3-methyl-1-butene, 1-hexene and 4-methyl-1-. Examples thereof include pentene, 3-methyl-1-pentene, 1-heptene, 1-octene, 1-decene and 1-dodecene, and propylene and 1-butene are preferable.

Among these, low-density polyethylene; polypropylene; ethylene / propylene copolymer, ethylene / 1-butene copolymer, ethylene / propylene / α having 4 to 12 carbon atoms, in that it has excellent unevenness absorption during pasting. Ethylene / α-olefin copolymers such as −olefin ternary copolymers; propylene / 1-butene / α-olefin ternary copolymers with 5 to 12 carbon atoms; and ethylene / vinyl acetate copolymers Is preferable, and ethylene / propylene copolymer and ethylene / vinyl acetate copolymer are more preferable.

The thickness of the uneven absorption layer is not particularly limited. From the viewpoint of the balance between unevenness absorption 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 balance between the mechanical strength and unevenness absorbability ^may be a ^{800kg / m 3 ~990kg / m 3} , may be a ^{830kg / m 3 ~980kg / m 3} , 850kg / m 3 ~ It may be 970 kg / m ^3.

The antistatic layer plays a role of suppressing the amount of static electricity generated when the protective film is peeled from the photomask substrate.

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

A polythiophene-based conductive polymer is preferable from the viewpoint of having a good balance of optical properties, appearance, antistatic property, coatability, stability and the like. Examples of the polythiophene-based conductive polymer include polyethylene dioxythiophene and polythiophene.

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

Examples of the sulfonic acid-based compound include p-toluene sulfonic acid, benzene sulfonic acid, ethyl benzene sulfonic acid, octyl benzene sulfonic acid, dodecyl benzene sulfonic acid, mesitylen sulfonic acid, m-xylene sulfonic acid, polystyrene sulfonic acid, polyvinyl sulfonic acid and the like. Can be mentioned. Polystyrene sulfonic acid and polyvinyl sulfonic acid are preferable from the viewpoint of improving the solubility or water dispersibility of the conductive polymer.
The content of the doping agent is, for example, 100 parts by mass to 300 parts by mass with respect to 100 parts by mass of the conductive polymer.

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

The antistatic layer may contain a binder resin. When the antistatic layer contains a binder resin, the film-forming property, adhesion, and the like tend to be improved.
Binder resins include polyurethane resins, polyester resins, (meth) acrylic resins, polyether resins, cellulose resins, polyvinyl alcohol resins, epoxy resins, polyvinylpyrrolidone, polystyrene resins, polyethylene glycols, pentaerythritol, etc. Can be mentioned. The binder resin contained in the antistatic layer may be only one type or two or more types.
The content of the binder resin may be, for example, 10 parts by mass to 500 parts by mass with respect to 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 the antistatic performance and other characteristics, it may be 0.01 μm to 10 μm, 0.01 μm to 5 μm, or 0.01 μm to 1 μm.

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

The coating method is not particularly limited, and spray coating, brush coating, or the like can be used. From the viewpoint of forming a film having a uniform thickness, spray coating is preferable.

From the viewpoint of forming a film having a uniform thickness, the pressure-sensitive adhesive is preferably coated in the state of a pressure-sensitive adhesive solution dissolved in a known solvent.
The solvent used for the pressure-sensitive adhesive solution is not particularly limited, and a 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, acetyl acetone. , 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 thereof include butyrolactone, methyl lactate and ethyl lactate. The solvent used in the pressure-sensitive adhesive solution may be only one type or two or more types.

The solid content concentration of the pressure-sensitive adhesive solution is not particularly limited. For example, the solid content concentration is preferably about 1% by mass to 50% by mass.

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

If necessary, another material such as a resin film may be placed on the coating containing the adhesive.

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

For the adhesive material utilizing the physical action derived from the uneven shape, for example, International Publication No. 2014/124352, Adv. Mater. 19, 1973-1977 (2007) and the like can be referred to.

The uneven shape of the base material is not particularly limited as long as it has a shape that exhibits the necessary adhesiveness to the photomask substrate. Further, the uneven shape may be formed on only one side of the base material or 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, a reverse 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 of 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 the convex portion refers to the length at which the inter-plane distance is maximized when the periphery of the bottom portion of the convex portion is sandwiched between two parallel surfaces.
For example, when the convex portion is columnar or conical, the diameter of the bottom corresponds to the width of the convex portion, and when the convex portion is rectangular parallelepiped, the diagonal length of the bottom corresponds to the width of the convex portion, and when the convex portion is triangular columnar. , The maximum value of the distance between one side with the bottom and the vertices that do not form the one side corresponds to the width of the convex part.

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

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 even more preferably 2 μm to 500 μm.

The ratio of the height of the convex portion to the width of the convex portion (height of the convex portion / width of the convex portion) is preferably 0.5 to 15, more preferably 0.8 to 10 and 1 It is more preferably ~ 5. When the ratio is 0.5 or more, the adhesiveness to the adherend tends to be excellent, and when the ratio is 15 or less, the strength of the convex portion tends to be excellent.

The ratio of the distance between the convex portions to the width of the convex portions (distance between the convex portions / width of the convex portions) is preferably 0.2 to 10, more preferably 0.5 to 8, and 0. It is more preferably .8-5. When the ratio is 0.2 or more, the workability and the shape stability of the convex portion tend to be excellent, and when the ratio is 10 or less, the adhesiveness to the adherend tends to be excellent.

The total area ratio of the bottom surface of the recess to the total area of the bottom of the convex portion (total area of the bottom surface of the recess / total area of the bottom of the convex portion) is 1 to 100 from the viewpoint of the adhesiveness and shape retention of the protective film. It is preferably 1.5 to 50, more preferably 2 to 20.

In the region occupied by the uneven shape of the base material (the total of the region occupied by the convex portion and the region occupied by the concave portion), the ratio (volume ratio) occupied by the convex portion is 0. It is preferably 0001 to 0.5, more preferably 0.02 to 0.4, and even more preferably 0.05 to 0.33.

The material contained in the base material having an uneven shape is not particularly limited, and is olefin resin, polyester resin, polyurethane resin, polyimide resin, silicone resin, styrene resin, acrylic resin, epoxy resin, amide resin. Examples thereof include resins such as resins, ester resins and carbonate resins. Of these, olefin resins, polyurethane resins, acrylic resins, polyimide resins and silicone resins are preferable from the viewpoint of maintaining the shape of the convex portion.

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

The storage elastic 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 10 MPa to 50 MPa from the viewpoint of achieving both imprint processability and adhesiveness. It is more preferable to have.
The storage elastic modulus of the base material can be measured according to the method for measuring the storage elastic modulus of the base material layer of the protective film of the first form described above.

The method for forming the uneven shape on the base material is not particularly limited, and a known method can be used. For example, the convex portion may be patterned and formed on the surface of the base material by nanoimprint technology.

The base material may contain a substance whose chemical structure is changed by giving a stimulus such as ultraviolet rays or heat. As a result, for example, the adhesive force to the photomask substrate may be reduced when the substrate is stimulated.

The protective film may further have a surface layer that covers at least a part of the concave-convex surface of the substrate. The surface layer may be arranged on the tip of the convex portion of the base material and may cover at least a part of the surface having the uneven shape.

The surface layer is preferably arranged over the tips of a plurality of protrusions on the substrate, and may be, for example, over the tips of 10 or more protrusions on the substrate. .. Here, "the surface layer is arranged over the tips of the plurality of protrusions on the base material" means that at least one surface layer is arranged over the tips of the plurality of protrusions. Means to be. The surface layer is preferably a continuous layer that is arranged over the tips of the plurality of convex portions and covers the plurality of convex portions. The protective film may have a plurality of surface layers arranged over the tips of the plurality of convex portions. When a plurality of surface layers are provided, it is preferable that the plurality of surface layers exist separately and are arranged 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, a concave portion 6 is formed between a base material 1 having an uneven shape composed of a convex portion 2 and a concave portion 6 and a surface layer 3 arranged so as to cover the uneven shape of the base material 1. It may have a hollow structure composed of a space corresponding to.
The shape of the space formed between the base material 1 and the surface layer 3 may change when the protective film is attached to the photomask substrate.

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

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 enhancing the adhesiveness to the photomask substrate and the processability. Is even more preferable.

The material contained in the surface layer is not particularly limited, and is olefin resin, polyester resin, polyurethane resin, polyimide resin, silicone resin, styrene resin, acrylic resin, epoxy resin, amide resin, ester resin. Examples thereof include resins and resins such as carbonate-based resins. Of these, an olefin resin, a polyimide resin, an acrylic resin, or a silicone resin is preferable from the viewpoint of excellent low contamination 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-based resin.

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

The storage elastic 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 elastic modulus of the surface layer at 25 ° C. is preferably smaller than the storage elastic modulus of the base material at 25 ° C.
The storage elastic modulus of the surface layer can be measured according to the method for measuring the storage elastic modulus of the base material layer of the protective film of the first form described above.

(Pellicle)
When the photomask is provided with a pellicle, the type of the pellicle is not particularly limited and can be selected according to 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 the organic material and the inorganic material.
Examples of the organic material include a fluorine-based polymer and the like.
Examples of the inorganic material include crystalline silicon (single crystal 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 one of the above materials alone, or may contain two or more of the above materials.

The pellicle film may be a single layer or may be composed of two or more layers.
The thickness of the pellicle film (total thickness when composed of two or more layers) is preferably 10 nm to 200 nm, more preferably 10 nm to 100 nm, further preferably 10 nm to 70 nm, and 10 nm to 50 nm. Is particularly preferable.

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

The pellicle frame may have a protective film on the surface. The protective film is preferably resistant to hydrogen radicals present in the exposure atmosphere and to be used for 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 matter on the pellicle frame.

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

According to the above method, contamination of the surface opposite to the surface on which the pattern of the photomask substrate is formed 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 according to the form of the protective film to be used and the like. For example, when the protective film of the first form or the third form described above is used, the protective film can be attached to the photomask substrate while heating as necessary. When the protective film of the second form is used, it can be carried out by coating the photomask substrate with an adhesive.

From the viewpoint of suppressing contamination of the photomask substrate, the step of peeling the protective film from the photomask substrate is preferably immediately before the work of attaching the photomask substrate to the exposure apparatus.

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

A step of arranging the pellicle so as to cover the surface on which the pattern of the photomask substrate is formed may be included. The method of arranging the pellicle is not particularly limited, and it can be carried out by a known method using an adhesive or the like. Either the protective film or the pellicle may be arranged first.

The above method may include a step of inspecting whether or not foreign matter is attached to the photomask substrate. The inspection may be performed before arranging the protective film, after arranging the protective film and before peeling, or after peeling the protective film, and the number of inspections may be one or a plurality of times.

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

In the above method, since the protective film suppresses the adhesion of foreign matter to the surface opposite to the surface on which the pattern of the photomask substrate is formed, it is difficult for foreign matter to get caught between the photomask and the photomask stage, and during exposure. Trouble is less likely to occur. Therefore, the productivity is improved as compared with the conventional method that does not use a protective film.

Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited to the following Examples as long as the gist of the present invention is not exceeded.

<Example 1>
An adhesive tape (Icross tape, SB-150HND-R2, Mitsui Chemicals Tohcello Co., Ltd.) having an adhesive layer formed on a 200 mm × 200 mm substrate was placed on the back surface of a pre-cleaned photomask substrate at room temperature. A roll was attached and a protective film was placed.
The photomask substrate on which the protective film was placed was allowed to stand in a clean room for 24 hours. Then, the protective film was peeled off from the photomask substrate, and the number of foreign substances having a maximum diameter of 3 μm or more existing on the exposed surface was measured using a surface particle scanner (YPI-200MX, Yamanashi Technical Studio Co., Ltd.). Similarly, the number of foreign substances was 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>
Instead of sticking the adhesive tape, the same process as in Example 1 was performed except that the back surface 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 a structure as shown in FIG. 2 was produced by the following method.
100 parts by mass of epoxy acrylate (Dycel Ornex, EBERCRYL3500) and 2 parts by mass of photopolymerization initiator (IGM Resins VV, Omnirad 184) were mixed and stirred to obtain a resin composition. The obtained resin composition was molded into a nickel 300 mm square mold (concave pattern arranged in a two-dimensional square lattice, height difference of recesses: 15 μm, shape of recesses: holes, width of recesses (hole diameter): 5 μm, The width of the recess (hole spacing): 5 μm, the aspect ratio of the recess (depth / diameter) 3: 1) is dropped, coated with a gap of 50 μm, and a polyester-based release film (TN100 manufactured by Toyobo Co., Ltd.) is attached. UV irradiation (1000 mJ / cm ² ) was performed in the combined state. After that, the cured resin sheet is peeled off from the mold, and a base material having a columnar convex shape (width: 5 μm, height: 15 μm) arranged in a two-dimensional square lattice pattern (distance between convex portions: 5 μm) is provided on one side. Obtained.
Next, a film to be a surface layer was prepared as follows. The resin composition was dropped onto a petri dish made of Teflon (registered trademark) and irradiated with UV (500 mJ / cm ² ) to obtain a film having a thickness of 10 μm.
Subsequently, a film to be a surface layer is attached to the surface side having a convex shape of the base material, and the film is ^{main-cured by UV irradiation (1000 mJ / cm 2} ) to have 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 prepared.
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 carried out except that the protective film was not arranged on the back surface of the photomask substrate.

As shown in Table 1, in the photomask substrate of the comparative example in which the protective film was not arranged, the number of foreign substances after being allowed to stand in the clean room for 24 hours increased as compared with that immediately after cleaning. On the other hand, in the photomask substrate of the example in which the protective film was placed, the number of foreign substances after standing in a clean room for 24 hours was almost unchanged immediately after cleaning, and surface contamination was effectively suppressed.

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

Claims (16)

A photomask substrate with a pattern formed on one side,
A photomask having a protective film that is arranged so as to be in contact with a surface of the photomask substrate that is opposite to the surface on which the pattern is formed and that can be peeled off from the photomask substrate. The photomask according to claim 1, further comprising a pellicle arranged so as to cover the surface of the photomask substrate on which the pattern is formed. The photomask according to claim 1 or 2, wherein the adhesive strength of the surface of the protective film in contact with the photomask substrate is 0.1 N / 25 mm to 10 N / 25 mm measured in accordance with JIS Z0237. The photomask according to any one of claims 1 to 3, wherein the protective film has a base material layer and an adhesive layer. The photomask according to claim 4, wherein the protective film further has an uneven absorption layer and an antistatic layer, and includes the base material 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 any one of claims 1 to 3, 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 has a surface layer that covers at least a part 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. A step of arranging the protective film so as to be in contact with the surface of the photomask substrate having the pattern formed on one surface and the surface opposite to the surface on which the pattern is formed.
The step of peeling the protective film from the photomask and
An exposure method comprising a step of attaching the photomask from which the protective film has been peeled off to an exposure apparatus and performing exposure. The exposure method according to claim 13, wherein the protective film is arranged by attaching the protective film to the photomask substrate. The exposure method according to claim 13, wherein the protective film is arranged by coating the photomask substrate with an adhesive. The aspect according to any one of claims 13 to 15, wherein the photomask is attached so 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.

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