TW202415697A - Semiconductor substrate manufacturing method, composition and polymer - Google Patents

Abstract

The object of the present invention is to provide a method for manufacturing a semiconductor substrate using a composition capable of forming a film having excellent bending resistance, a composition and a polymer. A method for manufacturing a semiconductor substrate comprises: a step of directly or indirectly coating a composition for forming an anti-etching agent base film on a substrate; a step of directly or indirectly forming an anti-etching agent pattern on the anti-etching agent base film formed by the coating step; and a step of performing etching using the anti-etching agent pattern as a mask, wherein the composition for forming an anti-etching agent base film contains a polymer having a structural unit represented by the following formula (1) and a solvent. (In formula (1), ^Ar1 is a divalent group having an aromatic ring having 5 to 40 ring members. ^X1 is a divalent group represented by the following formula (i)) (In formula (i), ^R1 and ^R2 are independently a hydrogen atom or a monovalent organic group having 1 to 20 carbon atoms, or these groups are bonded to each other and together with the carbon atoms to which they are bonded, form a divalent alicyclic hydrocarbon group having 3 to 20 carbon atoms. * and ** are bonding bonds in formula (1))

Description

Semiconductor substrate manufacturing method, composition and polymer

The present invention relates to a method for manufacturing a semiconductor substrate, a composition and a polymer.

In the manufacture of semiconductor devices, for example, a multi-layer resist process is used, wherein a resist film deposited on a substrate through an organic bottom layer film, a silicon-containing film, etc. is exposed and developed to form a resist pattern. In this process, the resist bottom layer film is etched using the resist pattern as a mask, and the substrate is further etched using the obtained resist bottom layer film pattern as a mask, thereby forming a desired pattern on a semiconductor substrate (see Japanese Patent Publication No. 2004-177668).

Various studies have been conducted on the materials used in the composition for forming the anti-corrosion agent base film (see International Publication No. 2011/108365). [Prior Art Literature] [Patent Literature]

[Patent document 1] Japanese Patent Publication No. 2004-177668 [Patent document 2] International Publication No. 2011/108365

[Problem to be solved by the invention] In the multi-layer anti-corrosion process, the organic base film serving as the anti-corrosion base film is required to have bending resistance.

The present invention is based on the above-mentioned situation, and its purpose is to provide a method for manufacturing a semiconductor substrate using a composition capable of forming a film with excellent bending resistance, a composition, and a polymer. [Means for Solving the Problem]

The present invention, in one embodiment, relates to a method for manufacturing a semiconductor substrate, comprising: a step of directly or indirectly coating an anti-etching agent base film forming composition on a substrate; a step of directly or indirectly forming an anti-etching agent pattern on the anti-etching agent base film formed by the coating step; and a step of etching using the anti-etching agent pattern as a mask, wherein the anti-etching agent base film forming composition contains: a polymer having a structural unit represented by the following formula (1) (hereinafter also referred to as "[A] polymer"); and a solvent (hereinafter also referred to as "[B] solvent"). (In formula (1), ^Ar1 is a divalent group having an aromatic ring having 5 to 40 ring members. ^X1 is a divalent group represented by the following formula (i)) (In formula (i), ^R1 and ^R2 are independently a hydrogen atom or a monovalent organic group having 1 to 20 carbon atoms, or represent a divalent alicyclic hydrocarbon group having 3 to 20 carbon atoms formed by combining these groups with the carbon atoms to which they are bonded. * and ** represent bonding bonds in formula (1))

In this specification, the term "ring member number" refers to the number of atoms constituting a ring. For example, a biphenyl ring has 12 ring members, a naphthyl ring has 10 ring members, and a fluorene ring has 13 ring members.

In another embodiment, the present invention relates to a composition comprising: a polymer having a structural unit represented by the following formula (1); and a solvent. (In formula (1), ^Ar1 is a divalent group having an aromatic ring having 5 to 40 ring members. ^X1 is a divalent group represented by the following formula (i)) (In formula (i), ^R1 and ^R2 are independently a hydrogen atom or a monovalent organic group having 1 to 20 carbon atoms, or these groups are bonded to each other and together with the carbon atoms to which they are bonded, form a divalent alicyclic hydrocarbon group having 3 to 20 carbon atoms. * and ** are bonding bonds in formula (1))

In another embodiment, the present invention relates to a polymer having a structural unit represented by the following formula (1). (In formula (1), ^Ar1 is a divalent group having an aromatic ring having 5 to 40 ring members. ^X1 is a divalent group represented by the following formula (i)) (In formula (i), ^R1 and ^R2 are independently a hydrogen atom or a monovalent organic group having 1 to 20 carbon atoms, or these groups are bonded to each other and together with the carbon atoms to which they are bonded, form a divalent alicyclic hydrocarbon group having 3 to 20 carbon atoms. * and ** are bonding bonds in formula (1)) [Effects of the Invention]

By the method for manufacturing a semiconductor substrate, an anti-etching agent bottom layer film having excellent bending resistance is formed, so that a good semiconductor substrate can be obtained. By the composition, a film having excellent bending resistance can be formed. The polymer is preferably a composition capable of forming a film having excellent bending resistance. Therefore, these can be preferably used in the manufacture of semiconductor elements that are expected to be further miniaturized in the future.

Hereinafter, the manufacturing method, composition and polymer of the semiconductor substrate of each embodiment of the present invention are described in detail. In addition, the combination of the preferred aspects in the embodiment is also preferred.

《Method for manufacturing semiconductor substrate》 The method for manufacturing semiconductor substrate includes: a step of directly or indirectly coating a composition for forming an anti-etching agent bottom layer film on a substrate (hereinafter, also referred to as "coating step"); a step of directly or indirectly forming an anti-etching agent pattern on the anti-etching agent bottom layer film formed by the coating step (hereinafter, also referred to as "anti-etching agent pattern forming step"); and a step of performing etching using the anti-etching agent pattern as a mask (hereinafter, also referred to as "etching step").

According to the method for manufacturing a semiconductor substrate, the composition described below is used as a composition for forming an anti-corrosion agent base film in the coating step, thereby forming an anti-corrosion agent base film with excellent bending resistance, thereby manufacturing a semiconductor substrate with a good pattern shape.

The method for manufacturing the semiconductor substrate may further include, if necessary, a step of directly or indirectly forming a silicon-containing film relative to the anti-etching agent bottom layer film (hereinafter also referred to as "silicon-containing film forming step").

Hereinafter, the composition and each step used in the method for manufacturing the semiconductor substrate will be described.

<Composition> The composition for forming an anti-corrosion agent base film contains [A] a polymer and [B] a solvent. The composition may contain any component within the range that does not impair the effect of the present invention.

The composition can form a film having excellent bending resistance by containing [A] a polymer and [B] a solvent. Therefore, the composition can be used as a composition for forming a film. More specifically, the composition can be preferably used as a composition for forming an anti-corrosion agent bottom layer film in a multi-layer anti-corrosion agent process.

Hereinafter, each component contained in this composition will be described.

<[A] Polymer> The [A] polymer has a structural unit represented by the following formula (1). The [A] polymer may have two or more structural units represented by the following formula (1). The composition may contain one or more [A] polymers. (In formula (1), ^Ar1 is a divalent group having an aromatic ring having 5 to 40 ring members. ^X1 is a divalent group represented by the following formula (i)) (In formula (i), ^R1 and ^R2 are independently a hydrogen atom or a monovalent organic group having 1 to 20 carbon atoms, or represent a divalent alicyclic hydrocarbon group having 3 to 20 carbon atoms formed by combining these groups with the carbon atoms to which they are bonded. * and ** represent bonding bonds in formula (1))

In the above formula (1), examples of the aromatic ring having 5 to 40 ring members in ^Ar1 include aromatic hydrocarbon rings such as benzene ring, naphthalene ring, anthracene ring, phenanthrene ring, phenanthrene ring, pyrene ring, fluorene ring, perylene ring, coronene ring, furan ring, pyrrole ring, thiophene ring, phosphole ring, pyrazole ring, oxazole ring, isooxazole ring, thiazole ring, pyridine ring, pyrazine ring, pyrimidine ring, oxazine ring, triazine ring, carbazole ring, dibenzofuran ring, and heteroaromatic rings, or combinations thereof. The aromatic ring in Ar ¹ is preferably at least one aromatic hydrocarbon ring selected from the group consisting of a benzene ring, a naphthalene ring, an anthracene ring, a phenanthrene ring, a phenanthrene ring, a pyrene ring, a fluorene ring and a perylene ring. More preferably, the aromatic ring in Ar ¹ is a benzene ring, a naphthalene ring, a pyrene ring or a fluorene ring.

In the above formula (1), the divalent group having an aromatic ring having 5 to 40 ring members represented by ^Ar1 preferably includes a group (q) obtained by removing two hydrogen atoms from the aromatic ring having 5 to 40 ring members in ^Ar1 , or a group obtained by combining the group (q) with a divalent organic group having 1 to 20 carbon atoms represented by ^R7 described later.

In the above formula (i), examples of the monovalent organic group having 1 to 20 carbon atoms represented by ^R1 and ^R2 include: a monovalent hydrocarbon group having 1 to 20 carbon atoms, a group having a divalent impurity-containing group between carbon atoms of the hydrocarbon group or at the end of the hydrocarbon group, a group in which a part or all of the hydrogen atoms of the hydrocarbon group are substituted with a monovalent impurity-containing group, or a combination thereof.

Examples of the monovalent hydrocarbon group having 1 to 20 carbon atoms include a monovalent chain hydrocarbon group having 1 to 20 carbon atoms, a monovalent alicyclic hydrocarbon group having 3 to 20 carbon atoms, a monovalent aromatic hydrocarbon group having 6 to 20 carbon atoms, and combinations thereof.

In this specification, the term "alkyl group" includes chain alkyl groups, alicyclic alkyl groups, and aromatic alkyl groups. The term "alkyl group" includes saturated alkyl groups and unsaturated alkyl groups. The term "chain alkyl group" refers to a alkyl group that does not include a ring structure but only includes a chain structure, and includes both straight chain alkyl groups and branched chain alkyl groups. The term "alicyclic alkyl group" refers to a alkyl group that includes only an alicyclic structure as a ring structure and does not include an aromatic ring structure, and includes both monocyclic alicyclic alkyl groups and polycyclic alicyclic alkyl groups (wherein, it is not necessary to include only an alicyclic structure, and a chain structure may be included in part thereof). The "aromatic alkyl group" refers to a alkyl group containing an aromatic ring structure as a ring structure (however, it does not necessarily contain only an aromatic ring structure, and may contain an alicyclic structure or a chain structure in part).

Examples of the monovalent chain hydrocarbon group having 1 to 20 carbon atoms include alkyl groups such as methyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, and tert-butyl; alkenyl groups such as vinyl, propenyl, and butenyl; and alkynyl groups such as ethynyl, propynyl, and butynyl.

Examples of the monovalent alicyclic alkyl group having 3 to 20 carbon atoms include cycloalkyl groups such as cyclopentyl and cyclohexyl; cycloalkenyl groups such as cyclopropenyl, cyclopentenyl and cyclohexenyl; bridged cyclic saturated alkyl groups such as norbornyl, adamantyl and tricyclodecanyl; and bridged cyclic unsaturated alkyl groups such as norbornyl and tricyclodecanyl.

Examples of the monovalent aromatic hydrocarbon group having 6 to 20 carbon atoms include phenyl, tolyl, naphthyl, anthracenyl, and pyrene.

Examples of the impurity atom constituting the divalent or monovalent impurity-atom-containing group include oxygen, nitrogen, sulfur, phosphorus, silicon, halogen, and boron atoms. Examples of the halogen atom include fluorine, chlorine, bromine, and iodine atoms.

Examples of the divalent impurity-containing group include -CO-, -CS-, -NR'-, -O-, -S-, and groups obtained by combining these groups. R' is a hydrogen atom or a monovalent hydrocarbon group having 1 to 10 carbon atoms.

Examples of the monovalent impurity-containing group include a hydroxyl group, a sulfonyl group, a cyano group, a nitro group, and a halogen atom.

As the divalent alicyclic hydrocarbon group having 3 to 20 carbon atoms formed by ^R1 and ^R2 bonding to each other and the carbon atoms to which they are bonded, a structure obtained by removing one hydrogen atom from the monovalent alicyclic hydrocarbon group having 3 to 20 carbon atoms in ^R1 and ^R2 of the above formula (i) can be preferably used.

Preferably, both R ¹ and R ² are hydrogen atoms.

The * is preferably a bond to a carbon atom in the aromatic ring of Ar ¹ in the formula (1).

Ar ¹ preferably has at least one group (hereinafter also referred to as a "specific substituent") selected from the group consisting of a hydroxyl group, a group represented by the following formula (2-1) and a group represented by the following formula (2-2). (In formula (2-1) and formula (2-2), ^R7 is independently a divalent organic group having 1 to 20 carbon atoms or a single bond. * is a bond to a carbon atom in an aromatic ring)

As the divalent organic group having 1 to 20 carbon atoms represented by ^R7 , a group obtained by removing one hydrogen atom from the monovalent organic group having 1 to 20 carbon atoms represented by ^R1 and ^R2 can be preferably used.

The above R ⁷ is preferably a divalent hydrocarbon group having 1 to 10 carbon atoms such as methanediyl, ethanediyl, phenylene, -O-, or a combination thereof, and more preferably methanediyl, or a combination of methanediyl and -O-.

It is preferred that Ar ¹ has a group represented by the formula (2-1), and the group is represented by the following formula (2-1-1): wherein * has the same meaning as in the formula (2-1).

^Ar1 may have the above-mentioned specific substituent and may have other substituents instead of the above-mentioned specific substituents. Examples of other substituents include monovalent chain hydrocarbon groups having 1 to 10 carbon atoms, halogen atoms such as fluorine atoms, chlorine atoms, bromine atoms, and iodine atoms, alkoxy groups such as methoxy groups, ethoxy groups, and propoxy groups, aryloxy groups such as phenoxy groups and naphthoxy groups, alkoxycarbonyl groups such as methoxycarbonyl groups and ethoxycarbonyl groups, alkoxycarbonyloxy groups such as methoxycarbonyloxy groups and ethoxycarbonyloxy groups, acyl groups such as formyl groups, acetyl groups, propionyl groups, and butyryl groups, cyano groups, nitro groups, and carboxyl groups.

Examples of the structural unit represented by the formula (1) include the structural units represented by the following formulas (1-1) to (1-21).

Among them, preferred are the structural units represented by the above formulae (1-1) to (1-18), and preferred are the structural units represented by the above formulae (1-2), (1-3), and (1-7).

The [A] polymer may further have a structural unit represented by the following formula (2). (In formula (3), ^Ar2 is a divalent group having an aromatic ring with 5 to 40 ring members. ^R3 is a hydrogen atom or a monovalent organic group with 1 to 60 carbon atoms)

As the aromatic ring having 5 to 40 ring members in Ar ² , the aromatic ring having 5 to 40 ring members in Ar ¹ of the above formula (1) can be preferably used.

Preferred examples of the divalent group having an aromatic ring having 5 to 40 ring members represented by Ar ² include a group obtained by removing two hydrogen atoms from the aromatic ring having 5 to 40 ring members in Ar ² and the like.

Examples of the monovalent organic group having 1 to 60 carbon atoms represented by ^R3 include a monovalent alkyl group having 1 to 60 carbon atoms, a group having a divalent impurity-containing group between carbon atoms of the alkyl group, a group in which a part or all of the hydrogen atoms of the alkyl group are substituted with a monovalent impurity-containing group, or a combination thereof. As these groups, a group obtained by expanding the groups exemplified as the group consisting of the monovalent organic group having 1 to 20 carbon atoms represented by ^R1 and ^R2 in the above formula (i) to 60 carbon atoms can be preferably used.

Examples of the structural unit represented by the formula (2) include structural units represented by the following formulas (2-1) to (2-6).

The lower limit of the weight average molecular weight of the polymer [A] is preferably 800, more preferably 1200, further preferably 1600, and particularly preferably 2000. The upper limit of the molecular weight is preferably 10000, more preferably 8000, further preferably 6000, and particularly preferably 4000. The method for measuring the weight average molecular weight is based on the description of the Examples.

The lower limit of the content ratio of the [A] polymer in the composition is preferably 2 mass %, more preferably 4 mass %, further preferably 6 mass %, and particularly preferably 8 mass % based on the total mass of the [A] polymer and the [B] solvent. The upper limit of the content ratio is preferably 30 mass %, more preferably 25 mass %, further preferably 20 mass %, and particularly preferably 15 mass % based on the total mass of the [A] polymer and the [B] solvent.

<Method for producing [A] polymer> The [A] polymer can be produced representatively by the following reaction, namely, a nucleophilic addition reaction of an aromatic ring compound having a phenolic hydroxyl group as a precursor providing Ar ¹ of the formula (1) to a pyruvic acid derivative as a precursor providing X ¹ of the formula (1) under an acid catalyst, and the subsequent removal of water and carbon monoxide. The acid catalyst is not particularly limited, and known inorganic acids and organic acids can be used. After the reaction, the [A] polymer can be obtained through separation, purification, drying, etc. As the reaction solvent, the [B] solvent described later can be preferably used.

<[B] Solvent> The [B] solvent is not particularly limited as long as it can dissolve or disperse the [A] polymer and any components contained therein as necessary.

Examples of the [B] solvent include hydrocarbon solvents, ester solvents, alcohol solvents, ketone solvents, ether solvents, nitrogen-containing solvents, etc. The [B] solvent may be used alone or in combination of two or more.

Examples of the hydrocarbon solvent include aliphatic hydrocarbon solvents such as n-pentane, n-hexane, and cyclohexane, and aromatic hydrocarbon solvents such as benzene, toluene, and xylene.

Examples of the ester solvent include carbonate solvents such as diethyl carbonate, monoacetic acid ester solvents such as methyl acetate and ethyl acetate, lactone solvents such as γ-butyrolactone, polyol partial ether carboxylic acid ester solvents such as diethylene glycol monomethyl ether acetate and propylene glycol monomethyl ether acetate, and lactic acid ester solvents such as methyl lactate and ethyl lactate.

Examples of the alcohol solvent include monoalcohol solvents such as methanol, ethanol, and n-propanol, and polyol solvents such as ethylene glycol and 1,2-propylene glycol.

Examples of the ketone solvent include chain ketone solvents such as methyl ethyl ketone and methyl isobutyl ketone, and cyclic ketone solvents such as cyclohexanone.

Examples of the ether solvent include chain ether solvents such as n-butyl ether, polyol ether solvents such as cyclic ether solvents such as tetrahydrofuran, and polyol partial ether solvents such as diethylene glycol monomethyl ether.

Examples of the nitrogen-containing solvent include chain nitrogen-containing solvents such as N,N-dimethylacetamide and the like, and cyclic nitrogen-containing solvents such as N-methylpyrrolidone and the like.

The solvent [B] is preferably an ester solvent or a ketone solvent, more preferably a polyol partial ether carboxylate solvent or a cyclic ketone solvent, and further preferably propylene glycol monomethyl ether acetate or cyclohexanone.

The lower limit of the content ratio of the [B] solvent in the composition is preferably 60% by mass, more preferably 70% by mass, and further preferably 80% by mass. The upper limit of the content ratio is preferably 99.9% by mass, more preferably 99% by mass, and further preferably 95% by mass.

[Optional components] The composition may contain optional components within the range that does not impair the effects of the present invention. Examples of optional components include acid generators, crosslinking agents, surfactants, etc. The optional components may be used alone or in combination of two or more. The content ratio of the optional components in the composition may be appropriately determined according to the type of the optional components, etc.

[Method for preparing the composition] The composition can be prepared by mixing [A] a polymer, [B] a solvent, and any other components as required in a predetermined ratio, and preferably filtering the obtained mixture using a membrane filter having a pore size of 0.5 μm or less.

[Coating step] In this step, the anti-corrosion agent bottom layer film forming composition is directly or indirectly coated on the substrate. In this step, the composition is used as the anti-corrosion agent bottom layer film forming composition.

The method for applying the anti-corrosion agent underlayer film-forming composition is not particularly limited, and it can be implemented by appropriate methods such as spin coating, cast coating, roll coating, etc. A coating film is formed in this way, and the anti-corrosion agent underlayer film is formed by the volatilization of the solvent [B].

As the substrate, for example, metal or semi-metal substrates such as silicon substrates, aluminum substrates, nickel substrates, chromium substrates, molybdenum substrates, tungsten substrates, copper substrates, tantalum substrates, and titanium substrates can be listed, among which silicon substrates are preferred. The substrate may also be a substrate formed with a silicon nitride film, an aluminum oxide film, a silicon dioxide film, a tantalum nitride film, a titanium nitride film, and the like.

As an example of indirectly applying the composition for forming an anti-etching agent underlayer film on a substrate, there can be cited a case where the composition for forming an anti-etching agent underlayer film is applied on a silicon-containing film to be described later formed on the substrate.

In this embodiment, a heating step of heating the coating film formed by the coating step may be performed. The heating of the coating film can promote the formation of the anti-corrosion agent base film. More specifically, the heating of the coating film can promote the volatilization of the [B] solvent, etc.

The coating film may be heated in an atmospheric environment or in a nitrogen environment. The lower limit of the heating temperature is preferably 300°C, more preferably 320°C, and further preferably 350°C. The upper limit of the heating temperature is preferably 600°C, and more preferably 500°C. The lower limit of the heating time is preferably 15 seconds, and more preferably 30 seconds. The upper limit of the time is preferably 1,200 seconds, and more preferably 600 seconds.

Furthermore, after the coating step, the anti-etching agent bottom layer film may be exposed. After the coating step, the anti-etching agent bottom layer film may be exposed to plasma. After the coating step, the anti-etching agent bottom layer film may be ion-implanted. If the anti-etching agent bottom layer film is exposed to light, the etching resistance of the anti-etching agent bottom layer film is improved. If the anti-etching agent bottom layer film is exposed to plasma, the etching resistance of the anti-etching agent bottom layer film is improved. If the anti-etching agent bottom layer film is ion-implanted, the etching resistance of the anti-etching agent bottom layer film is improved.

The radiation used for exposure of the resist base film can be appropriately selected from electromagnetic waves such as visible light, ultraviolet light, far ultraviolet light, X-rays, and gamma rays; and particle beams such as electron beams, molecular beams, and ion beams.

As a method for exposing the resist base film to plasma, for example, there is a direct method based on placing the substrate in various gas environments and performing plasma discharge. As conditions for plasma exposure, the gas flow rate is usually 50 cc/min or more and 100 cc/min or less, and the supplied power is 100 W or more and 1,500 W or less.

The lower limit of the plasma exposure time is preferably 10 seconds, more preferably 30 seconds, and further preferably 1 minute. The upper limit of the time is preferably 10 minutes, more preferably 5 minutes, and further preferably 2 minutes.

Regarding plasma, for example, plasma is generated in an environment of a mixed gas of _H2 gas and Ar gas. In addition, in addition to introducing _H2 gas and Ar gas, carbon-containing gases such as _CF4 gas or _CH4 gas may be introduced. Furthermore, at least one of _CF4 gas, _NF3 gas, _CHF3 gas, _CO2 gas, _CH2F2 gas, _CH4 gas _{and C4F8 gas} may be introduced to replace either or both of _H2 gas and Ar gas.

Ion implantation into the resist bottom layer is implanting dopants into the resist bottom layer. The dopants may be selected from the group consisting of boron, carbon, nitrogen, phosphorus, arsenic, aluminum, and tungsten. The implantation energy for applying a voltage to the dopants may be about 0.5 keV to 60 keV, depending on the type of dopants used and the desired implantation depth.

The lower limit of the average thickness of the formed anti-etching agent bottom layer film is preferably 30 nm, more preferably 50 nm, and further preferably 100 nm. The upper limit of the average thickness is preferably 3,000 nm, more preferably 2,000 nm, and further preferably 500 nm. The method for measuring the average thickness is based on the description of the embodiments.

[Silicon-containing film formation step] In this step, a silicon-containing film is directly or indirectly formed on the anti-etching agent bottom layer film formed by the coating step or the heating step. As a case where a silicon-containing film is indirectly formed on the anti-etching agent bottom layer film, for example, a case where a surface modification film of the anti-etching agent bottom layer film is formed on the anti-etching agent bottom layer film can be cited. The so-called surface modification film of the anti-etching agent bottom layer film is, for example, a film having a different contact angle with water than the anti-etching agent bottom layer film.

The silicon-containing film can be formed by applying a silicon-containing film-forming composition, chemical vapor deposition (CVD), atomic layer deposition (ALD), etc. As a method of forming a silicon-containing film by applying a silicon-containing film-forming composition, for example, there can be cited a method of directly or indirectly applying the silicon-containing film-forming composition to the anti-etching agent base film, exposing and/or heating the formed coated film to harden it, etc. As commercial products of the silicon-containing film-forming composition, for example, "NFC SOG01", "NFC SOG04", "NFC SOG080" (all JSR (Co., Ltd.)) and the like can be used. Silicon oxide film, silicon nitride film, silicon oxynitride film, and amorphous silicon film can be formed by chemical vapor deposition (CVD) or atomic layer deposition (ALD).

Examples of the radiation used for the exposure include visible light, ultraviolet light, far ultraviolet light, electromagnetic waves such as X-rays and gamma rays, and particle beams such as electron beams, molecular beams, and ion beams.

The lower limit of the temperature when the coating film is heated is preferably 90° C., more preferably 150° C., and further preferably 200° C. The upper limit of the temperature is preferably 550° C., more preferably 450° C., and further preferably 300° C. The heating may be performed in one stage or in multiple stages.

The lower limit of the average thickness of the silicon-containing film is preferably 1 nm, more preferably 10 nm, and further preferably 20 nm. The upper limit is preferably 20,000 nm, more preferably 1,000 nm, and further preferably 100 nm. The average thickness of the silicon-containing film is a value measured using the spectroscopic ellipse circular polarimeter in the same manner as the average thickness of the anti-etching agent underlayer film.

[Anti-etching agent pattern forming step] In this step, an anti-etching agent pattern is directly or indirectly formed on the anti-etching agent bottom layer film. As a method for performing this step, for example, there can be listed: a method using an anti-etching agent composition, a method using a nano-imprinting method, a method using a self-organized composition, etc. As a case of indirectly forming an anti-etching agent pattern on the anti-etching agent bottom layer film, for example, there can be listed a case of forming an anti-etching agent pattern on the silicon-containing film, etc.

Examples of the anti-etching agent composition include a positive or negative chemically amplified anti-etching agent composition containing a radiation-sensitive acid generator, a positive anti-etching agent composition containing an alkali-soluble resin and a quinone diazide-based photosensitive agent, a negative anti-etching agent composition containing an alkali-soluble resin and a crosslinking agent, and a metal-containing anti-etching agent composition containing a metal such as tin, zirconium, and einsteinium.

As a method for applying the anti-corrosion agent composition, for example, a spin coating method can be cited. The temperature and time of the pre-baking can be appropriately adjusted according to the type of the anti-corrosion agent composition used.

Next, the formed resist film is exposed by selective radiation irradiation. The radiation used in the exposure can be appropriately selected according to the type of the radiation-sensitive acid generator used in the resist composition, and examples thereof include visible light, ultraviolet light, far ultraviolet light, X-rays, electromagnetic waves such as gamma rays, and particle beams such as electron beams, molecular beams, and ion beams. Among these, far ultraviolet light is preferred, and KrF excimer laser light (wavelength 248 nm), ArF excimer laser light (wavelength 193 nm), _F2 excimer laser light (wavelength 157 nm), _Kr2 excimer laser light (wavelength 147 nm), ArKr excimer laser light (wavelength 134 nm) or extreme ultraviolet light (wavelength 13.5 nm, etc., hereinafter also referred to as "EUV (extreme ultraviolet)") is more preferred, and KrF excimer laser light, ArF excimer laser light or EUV is further preferred.

After the exposure, post-baking may be performed to improve resolution, pattern outline, developability, etc. The temperature and time of the post-baking may be appropriately determined according to the type of the anti-etching agent composition used.

Next, the exposed anti-etchant film is developed with a developer to form an anti-etchant pattern. The development may be alkaline development or organic solvent development. In the case of alkaline development, examples of the developer include alkaline aqueous solutions such as ammonia, triethanolamine, tetramethyl ammonium hydroxide (TMAH), and tetraethyl ammonium hydroxide. Appropriate amounts of water-soluble organic solvents such as alcohols such as methanol and ethanol, surfactants, etc., may also be added to these alkaline aqueous solutions. In addition, in the case of organic solvent development, examples of the developer include various organic solvents exemplified as the [B] solvent of the composition.

After developing with the developer, a predetermined resist pattern can be formed by washing and drying.

[Etching step] In this step, etching is performed using the anti-etching agent pattern as a mask. The number of etchings may be one or multiple times, that is, etching may be performed sequentially using the pattern obtained by etching as a mask. Multiple times are preferred from the viewpoint of obtaining a pattern with a better shape. When etching is performed multiple times, etching is performed sequentially in the order of, for example, a silicon-containing film, an anti-etching agent bottom layer film, and a substrate. Etching methods include dry etching, wet etching, and the like. From the viewpoint of making the shape of the pattern of the substrate better, dry etching is preferred. In the dry etching, gas plasma such as oxygen plasma can be used. A semiconductor substrate having a predetermined pattern can be obtained by the etching.

As dry etching, for example, a known dry etching apparatus can be used. Etching gases used in dry _{etching can be appropriately selected according to the mask pattern, the element composition of the film to be etched, etc., and examples thereof include: fluorine-based gases such as CHF3, CF4, C2F6 , C3F8 , and SF6} , chlorine-based gases such as _Cl2 and _BCl3 , oxygen-based gases such _{as O2} , _{O3 , and H2O ,} reducing gases such as _H2 , CO, _{CO2 , CH4} , _C2H2 , _C2H4 , _C2H6 , _C3H4 , _C3H6 , _C3H8 , HF, HI, HBr, HCl, NO, _NH3 , and _BCl3 , and inert gases such as He, _N2 , and Ar. These gases may also be used _{in combination} . When etching a substrate using a resist bottom film pattern as a mask, a fluorine-based gas is generally used.

<<Composition>> The composition contains [A] a polymer and [B] a solvent. As the composition, it is preferably used as a composition used in the method for manufacturing the semiconductor substrate.

"Polymer" The polymer has a structural unit represented by the formula (1). As the polymer, the polymer [A] used in the method for manufacturing the semiconductor substrate can be preferably used. [Example]

Hereinafter, the present invention will be specifically described based on embodiments, but the present invention is not limited to these embodiments.

[Weight average molecular weight (Mw)] The Mw of the polymer was measured by gel permeation chromatography (GPC) columns (two "G2000HXL", one "G3000HXL", and one "G4000HXL") manufactured by Tosoh Corporation under the analytical conditions of flow rate: 1.0 mL/min, elution solvent: tetrahydrofuran, column temperature: 40°C, using monodisperse polystyrene as the standard (detector: differential refractometer).

[Average thickness of anti-corrosion primer film] The average thickness of the anti-corrosion primer film is obtained by measuring the film thickness at any 9 points at intervals of 5 cm including the center of the anti-corrosion primer film formed on the silicon wafer using a spectroscopic elliptical polarimeter ("M2000D" produced by J. A. WOOLLAM), and calculating the average value of these film thicknesses.

[Example 1-1] (Synthesis of polymer (A-1)) In a nitrogen environment, 10.0 g of phenol, 14.1 g of pyruvic acid, and 100 g of nitrobenzene were added to a reaction vessel, heated to 70°C, and the compounds were dissolved. After adding 7.97 g of trifluoromethanesulfonic acid to the reaction vessel, the reaction was allowed to proceed at 70°C for 6 hours. After cooling the reaction solution to 30°C, it was added to a large amount of hexane to obtain a precipitate. After washing the obtained precipitate several times with methanol, the solid was recovered by suction filtration and dried to obtain a polymer (A-1) having a structural unit represented by the following formula (A-1). The Mw of the obtained polymer (A-1) was 3,300.

[Example 1-2] (Synthesis of polymer (A-2)) Except for adding 17.0 g of 2,7-dihydroxynaphthalene instead of reacting 10.0 g of phenol, the reaction was carried out under the same conditions as [Example 1-1] to obtain a polymer (A-2) having a structural unit represented by the following formula (A-2). The Mw of the obtained polymer (A-2) was 2,600.

[Example 1-3] (Synthesis of polymer (A-3)) Except for adding 23.2 g of 1-hydroxypyrene instead of reacting 10.0 g of phenol, the reaction was carried out under the same conditions as [Example 1-1] to obtain a polymer (A-3) having a structural unit represented by the following formula (A-3). The Mw of the obtained polymer (A-3) was 2,000.

[Example 1-4] (Synthesis of polymer (A-4)) Except for adding 24.3 g of 2,2-bis(4-hydroxyphenyl)propane instead of reacting 10.0 g of phenol, the reaction was carried out under the same conditions as [Example 1-1] to obtain a polymer (A-4) having a structural unit represented by the following formula (A-4). The Mw of the obtained polymer (A-4) was 2,700.

[Example 1-5] (Synthesis of polymer (A-5)) Except for adding 17.7 g of fluorene instead of reacting 10.0 g of phenol, the reaction was carried out under the same conditions as [Example 1-1] to obtain a polymer (A-5) having a structural unit represented by the following formula (A-5). The Mw of the obtained polymer (A-5) was 2,500.

[Example 1-6] (Synthesis of polymer (A-6)) Except for adding 17.8 g of carbazole instead of reacting 10.0 g of phenol, the reaction was carried out under the same conditions as [Example 1-1] to obtain a polymer (A-6) having a structural unit represented by the following formula (A-6). The Mw of the obtained polymer (A-6) was 2,300.

[Example 1-7] (Synthesis of polymer (A-7)) 10.0 g of the polymer (A-2), 17.2 g of propargyl bromide, 20 g of methyl isobutyl ketone, and 10.0 g of methanol were added to a reaction vessel under a nitrogen atmosphere, and after stirring, 52.7 g of a 25% by mass aqueous solution of tetramethylammonium hydroxide was added, and the mixture was reacted at 50°C for 6 hours. After the reaction solution was cooled to 30°C, 100.0 g of a 5% by mass aqueous solution of oxalic acid was added. After removing the aqueous phase, the obtained organic phase was concentrated using an evaporator, and the residue was added dropwise to a large amount of hexane to obtain a precipitate. The obtained precipitate was washed several times with methanol, and then the solid was recovered by suction filtration and dried to obtain a polymer (A-7) having a structural unit represented by the following formula (A-7). The Mw of the polymer (A-7) was 3,200.

[Example 1-8] (Synthesis of polymer (A-8)) 10.0 g of the polymer (A-5), 100 g of tetrahydrofuran and 13.0 g of potassium tert-butoxide were added to a reaction vessel under a nitrogen atmosphere and stirred at room temperature for 30 minutes. Then, after cooling to 0°C, 13.8 g of propargyl bromide was added dropwise and reacted at room temperature for 2 hours. After the reaction was completed, 200 g of a 5% by mass aqueous oxalic acid solution and 100 g of methyl isobutyl ketone were added. After removing the aqueous phase, separation extraction was performed with water, and the organic layer was added dropwise to a large amount of hexane to obtain a precipitate. The precipitate was recovered by suction filtration and dried to obtain a polymer (A-8) having a structural unit represented by the following formula (A-8). The Mw of the polymer (A-8) is 3,000.

[Example 1-9] (Synthesis of polymer (A-9)) Except for adding 37.3 g of 9,9-bis(4-hydroxyphenyl)fluorene instead of reacting 10.0 g of phenol, the reaction was carried out under the same conditions as [Example 1-1] to obtain a polymer (A-9) having a structural unit represented by the following formula (A-9). The Mw of the obtained polymer (A-9) was 3,500.

[Example 1-10] (Synthesis of polymer (A-10)) In a nitrogen environment, 10.0 g of the polymer (A-5), 100 g of tetrahydrofuran, 9.0 g of naphthaldehyde, and 1.7 g of tetrabutylammonium bromide were added to a reaction vessel and stirred at room temperature for 30 minutes. Then, after cooling to 0°C, 42.2 g of a 25% by mass aqueous solution of tetramethylammonium hydroxide was added dropwise, and the mixture was reacted at room temperature for 2 hours. After the reaction was completed, 200 g of a 5% by mass aqueous solution of oxalic acid and 100 g of methyl isobutyl ketone were added. After removing the aqueous phase, separation extraction was performed using water, and the organic layer was added dropwise to a large amount of hexane to obtain a precipitate. The precipitate was recovered by suction filtration and dried to obtain a polymer (A-10) having a structural unit represented by the following formula (A-10). The Mw of the polymer (A-10) was 3,400.

[Example 1-11] (Synthesis of polymer (A-11)) Indole-2-carboxaldehyde 8.4 g, 1,8-diazabicyclo[5.4.0]-7-undecene 17.6 g were added respectively, and 9.0 g of naphthaldehyde and 42.2 g of 25 mass % tetramethylammonium hydroxide aqueous solution were reacted, and the reaction was carried out under the same conditions as [Example 1-10] to obtain a polymer (A-11) having a structural unit represented by the following formula (A-11). The Mw of the obtained polymer (A-11) was 3,100.

[Comparative Example 1-1] (Synthesis of polymer (x-1)) In a nitrogen atmosphere, 250.0 g of m-cresol, 125.0 g of 37% by mass formalin, and 2 g of oxalic anhydride were added to a reaction vessel, reacted at 100°C for 3 hours and at 180°C for 1 hour, and then unreacted monomers were removed under reduced pressure to obtain a polymer (x-1) having a structural unit represented by the following formula (x-1). The Mw of the obtained polymer (x-1) was 11,000.

<Preparation of composition> The following shows [A] polymer, [B] solvent, [C] acid generator, and [D] crosslinking agent used in the preparation of the composition.

[[A] Polymer] Example: The synthesized polymer (A-1) to polymer (A-11) Comparative example: The synthesized polymer (x-1)

[[B] Solvent] B-1: Propylene glycol monomethyl ether acetate B-2: Cyclohexanone

[[C] Acid Generator] C-1: Bis(4-tert-butylphenyl)iodonium nonafluoro-n-butanesulfonate (a compound represented by the following formula (C-1))

[[D] Crosslinking agent] D-1: A compound represented by the following formula (D-1)

D-2: Compound represented by the following formula (D-2)

[Example 2-1] 10 parts by mass of (A-1) as the polymer [A] was dissolved in 90 parts by mass of (B-1) as the solvent [B]. The obtained solution was filtered using a polytetrafluoroethylene (PTFE) membrane filter with a pore size of 0.45 μm to prepare a composition (J-1).

[Example 2-2 to Example 2-13 and Comparative Example 2-1] Except for using the types and contents of each component shown in Table 1 below, the composition (J-1) to composition (J-13) and composition (CJ-1) were prepared in the same manner as in Example 2-1. The "-" in the "[C] Acid Generator" and "[D] Crosslinking Agent" rows in Table 1 indicates that the corresponding component was not used.

<Evaluation> The obtained composition was used to evaluate the bending resistance by the following method. The evaluation results are shown in Table 1 below.

[Bending resistance] The prepared composition was applied to a silicon substrate having a silicon dioxide film with an average thickness of 500 nm by a spin coating method using a spin coater ("CLEAN TRACK ACT12" manufactured by Tokyo Electron). Next, the substrate was heated at 400°C for 60 seconds in an atmospheric environment and then cooled at 23°C for 60 seconds to obtain a substrate with an anti-corrosion agent base film with an average thickness of 200 nm. A silicon-containing film-forming composition ("NFC SOG080" of JSR Co., Ltd.) was applied to the obtained substrate with the film by spin coating, and then heated at 200°C for 60 seconds in an atmospheric environment, and then heated at 300°C for 60 seconds to form a silicon-containing film with an average thickness of 50 nm. An ArF anti-etching agent composition ("AR1682J" of JSR Co., Ltd.) was applied to the silicon-containing film by spin coating, and then heated (calcined) at 130°C for 60 seconds in an atmospheric environment to form an anti-etching agent film with an average thickness of 200 nm. Using an ArF excimer laser exposure device (lens numerical aperture 0.78, exposure wavelength 193 nm), a 1:1 line and space mask pattern with a target size of 100 nm was used to expose the resist film by varying the exposure amount. The film was then heated (post-baked) at 130°C for 60 seconds in an atmospheric environment, developed at 25°C for 1 minute using a 2.38 mass% tetramethylammonium hydroxide (TMAH) aqueous solution, and then rinsed and dried to obtain a substrate with a line pattern having a line width of 30 nm to 100 nm and a line and space spacing of 200 nm.

The silicon-containing film was etched using the resist pattern as a mask using an etching apparatus ("TACTRAS" manufactured by Tokyo Electron) under the conditions of _CF4 = 200 sccm, PRESS. = 85 mT, HF RF (high frequency power for plasma generation) = 500 W, LF RF (high frequency power for bias) = 0 W, DCS = -150 V, and RDC (gas sensor flow ratio) = 50%, thereby obtaining a substrate having a pattern formed on the silicon-containing film. Next, the silicon-containing film pattern was used as a mask and the etching device was used to etch the resist bottom film under the conditions of O ₂ = 400 sccm, PRESS. = 25 mT, HF RF (high frequency power for plasma generation) = 400 W, LF RF (high frequency power for bias) = 0 W, DCS = 0 V, and RDC (gas sensor flow ratio) = 50%, thereby obtaining a substrate with a pattern formed on the resist bottom film. The silicon dioxide film was etched using the etching device with the anti-etching agent bottom layer film pattern as a mask under the conditions of CF ₄ =180 sccm, Ar=360 sccm, PRESS.=150 mT, HF RF (high frequency power for plasma generation)=1,000 W, LF RF (high frequency power for bias)=1,000 W, DCS=-150 V, RDC (gas sensor flow ratio)=50%, and 60 seconds to obtain a substrate with a pattern formed on the silicon dioxide film.

Then, with respect to the substrate having the pattern formed on the silicon dioxide film, an image of the shape of the anti-etching agent bottom layer film pattern of each line width was obtained by using a scanning electron microscope ("CG-4000" manufactured by Hitachi High-tech Co., Ltd.), and the image was processed. As shown in FIG. 1, the cross-sectional view 3a of the anti-etching agent bottom layer film pattern 3 (line pattern) having a length of 1,000 nm was obtained based on the 100-fold magnification. The standard deviation calculated from the position Xn (n=1 to 10) in the line width direction obtained by measuring 10 positions at intervals of 10 nm and the position Xa of the average value of these positions in the line width direction was amplified 3 times to obtain a value of 3 sigma, and this value was set as the line edge roughness (LER). LER, which represents the degree of bending of the anti-etching agent bottom layer film pattern, increases as the line width of the anti-etching agent bottom layer film pattern becomes thinner. Regarding bending resistance, the film pattern with an LER of 5.5 nm is evaluated as "A" (good) when the line width is less than 35.0 nm, and the case of 35.0 nm or more and less than 40.0 nm is evaluated as "B" (slightly good), and the case of 40.0 nm or more is evaluated as "C" (poor). Furthermore, the curvature of the film pattern shown in FIG. 1 is exaggerated compared to reality.

[Table 1] Composition [A] Polymer [B] Solvent [C] Acid generator [D] Crosslinking agent Bending resistance Type Content (weight) Type Content (weight) Type Content (weight) Type Content (weight) Example 2-1 J-1 A-1 10 B-1 90 - - - - A Example 2-2 J-2 A-2 10 B-2 90 - - - - A Embodiment 2-3 J-3 A-3 10 B-2 90 - - - - A Embodiment 2-4 J-4 A-4 10 B-1 90 - - - - A Embodiment 2-5 J-5 A-5 10 B-2 90 - - - - A Embodiment 2-6 J-6 A-6 10 B-2 90 - - - - A Embodiment 2-7 J-7 A-7 10 B-2 90 - - - - A Embodiment 2-8 J-8 A-8 10 B-2 90 - - - - A Embodiment 2-9 J-9 A-9 10 B-2 90 - - - - A Embodiment 2-10 J-10 A-10 10 B-2 90 - - - - A Embodiment 2-11 J-11 A-11 10 B-2 90 - - - - A Embodiment 2-12 J-12 A-2 10 B-2 88.5 C-1 0.50 D-1 1 B Embodiment 2-13 J-13 A-2 10 B-2 88.5 C-1 0.50 D-2 1 B Comparison Example 2-1 CJ-1 x-1 10 B-1 88.5 C-1 0.50 D-1 1 C

According to the results in Table 1, the anti-corrosion base film formed by the composition of the embodiment has superior bending resistance compared to the anti-corrosion base film formed by the composition of the comparative example. [Industrial Applicability]

By the method for manufacturing a semiconductor substrate of the present invention, a patterned substrate can be obtained well. The composition of the present invention can form an anti-corrosion agent bottom layer film with excellent bending resistance. The polymer of the present invention is preferably used for the composition capable of forming an anti-corrosion agent bottom layer film with excellent bending resistance. Therefore, these can be preferably used for the manufacture of semiconductor elements that are expected to be further miniaturized in the future.

3: Anti-corrosion agent bottom film pattern 3a: Horizontal view of anti-corrosion agent bottom film pattern X1~X10, Xa: Position

FIG. 1 is a schematic plan view for explaining a method for evaluating bending resistance.

3: Anti-corrosion agent bottom layer film pattern

3a: Horizontal view of the anti-corrosion agent bottom film pattern

X1~X10, Xa: Position

Claims (15)

A method for manufacturing a semiconductor substrate comprises: a step of directly or indirectly coating a composition for forming an anti-etching agent bottom layer film on a substrate; a step of directly or indirectly forming an anti-etching agent pattern on the anti-etching agent bottom layer film formed by the coating step; and a step of performing etching using the anti-etching agent pattern as a mask, wherein the composition for forming an anti-etching agent bottom layer film comprises: a polymer having a structural unit represented by the following formula (1); and a solvent, In formula (1), ^Ar1 is a divalent group having an aromatic ring with 5 to 40 ring members; ^{X1 is} a divalent group represented by the following formula (i), In formula (i), ^R1 and ^R2 are independently a hydrogen atom or a monovalent organic group having 1 to 20 carbon atoms, or represent a divalent alicyclic hydrocarbon group having 3 to 20 carbon atoms formed by combining these groups with the carbon atoms to which they are bonded; * and ** are bonding bonds in formula (1). A method for manufacturing a semiconductor substrate as described in claim 1, wherein R ¹ and R ² are hydrogen atoms. The method for manufacturing a semiconductor substrate according to claim 1, wherein the * is a bond to a carbon atom in the aromatic ring in Ar ¹ of the formula (1). The method for manufacturing a semiconductor substrate as described in any one of claims 1 to 3 further includes a step of directly or indirectly forming a silicon-containing film relative to the anti-etching agent bottom layer film before the anti-etching agent pattern is formed. A composition comprising: a polymer having a structural unit represented by the following formula (1); and a solvent, In formula (1), ^Ar1 is a divalent group having an aromatic ring with 5 to 40 ring members; ^{X1 is} a divalent group represented by the following formula (i), In formula (i), ^R1 and ^R2 are independently a hydrogen atom or a monovalent organic group having 1 to 20 carbon atoms, or represent a divalent alicyclic hydrocarbon group having 3 to 20 carbon atoms formed by combining these groups with the carbon atoms to which they are bonded; * and ** are bonding bonds in formula (1). The composition as described in claim 5, wherein the aromatic ring is at least one aromatic hydrocarbon ring selected from the group consisting of a benzene ring, a naphthalene ring, an anthracene ring, a phenanthrene ring, a phenanthrene ring, a pyrene ring, a fluorene ring and a perylene ring. The composition according to claim 5 or 6, wherein ^Ar1 has at least one group selected from the group consisting of a hydroxyl group, a group represented by the following formula (2-1) and a group represented by the following formula (2-2), In formula (2-1) and formula (2-2), ^R7 is independently a divalent organic group having 1 to 20 carbon atoms or a single bond; * is a bond to a carbon atom in an aromatic ring. The composition as described in claim 5 or 6, wherein R ¹ and R ² are hydrogen atoms. The composition according to claim 5 or 6, wherein the * is a bond to a carbon atom in the aromatic ring in Ar ¹ of the formula (1). The composition as described in claim 5 or 6 is used to form an anti-corrosion agent bottom layer film. A polymer having a structural unit represented by the following formula (1): In formula (1), ^Ar1 is a divalent group having an aromatic ring with 5 to 40 ring members; ^{X1 is} a divalent group represented by the following formula (i), In formula (i), ^R1 and ^R2 are independently a hydrogen atom or a monovalent organic group having 1 to 20 carbon atoms, or represent a divalent alicyclic hydrocarbon group having 3 to 20 carbon atoms formed by combining these groups with the carbon atoms to which they are bonded; * and ** are bonding bonds in formula (1). A polymer as described in claim 11, wherein the aromatic ring is at least one aromatic hydrocarbon ring selected from the group consisting of a benzene ring, a naphthalene ring, an anthracene ring, a phenanthrene ring, a phenanthrene ring, a pyrene ring, a fluorene ring and a perylene ring. The polymer according to claim 11 or 12, wherein ^Ar1 has at least one group selected from the group consisting of a hydroxyl group, a group represented by the following formula (2-1) and a group represented by the following formula (2-2), In formula (2-1) and formula (2-2), ^R7 is independently a divalent organic group having 1 to 20 carbon atoms or a single bond; * is a bond to a carbon atom in an aromatic ring. A polymer as described in claim 11 or 12, wherein R ¹ and R ² are hydrogen atoms. A polymer as described in claim 11 or 12, wherein the * is a bond to a carbon atom in the aromatic ring in Ar ¹ of the formula (1).