Method for manufacturing magnetic tunnel junction element

Abstract

Provided is a method for manufacturing a magnetic tunnel junction element provided with a magnetic tunnel junction layer and a metal layer in the stated order directly or indirectly on a substrate, the method comprising: a step for applying, to the metal layer, a resist composition containing a polymer that has a structural unit containing an aromatic ring; a step for exposing a resist film formed through the application step; a step for developing the exposed resist film; and a step for etching the magnetic tunnel junction layer and the metal layer using, as a mask, a resist pattern formed through the development step.

Description

Method for manufacturing a magnetic tunnel junction element

[0001] The present invention relates to a method for manufacturing a magnetic tunnel junction element.

[0002] In recent years, application of magnetic tunnel junction (MTJ) elements, which utilize resistance changes due to differences in magnetization direction, to magnetoresistive random access memories (MRAMs) has been attracting attention.

[0003] An MTJ element used in an MRAM includes, for example, a fixed magnetic layer (fixed magnetic layer) whose magnetization direction is fixed, a free magnetic layer (free magnetic layer) whose magnetization direction is variable, and a tunnel insulating layer disposed between them.

[0004] The resistance of the MTJ element is low when the magnetization directions of the free magnetic layer and the fixed magnetic layer are parallel (same direction) and high when they are antiparallel (opposite directions), so the parallel and antiparallel states correspond to, for example, data "0" and "1."

[0005] MRAMs are classified into two types based on the write method: write-wire type and spin-transfer type. In write-wire type MRAM, the magnetization direction of the free magnetic layer is controlled based on the magnetic field generated by a current flowing through a write word line. On the other hand, in spin-transfer type MRAM, the magnetization direction of the free magnetic layer is controlled by the spin transfer effect that occurs when a current is passed through the MTJ element.

[0006] Various methods have been proposed for manufacturing a magnetic memory element (magnetoresistive memory) using an MTJ element.

[0007] Japanese Patent Application Laid-Open No. 2006-060044 Japanese Patent Application Laid-Open No. 2002-305290 Japanese Patent Application Laid-Open No. 2002-038285 International Publication No. 2009 / 096328

[0008] Since magnetic memory elements using MTJ elements change the magnetization direction (resistance state) by passing a current through the MTJ element, they have the problem of high power consumption. Therefore, attempts have been made to change the magnetization direction of the free magnetic layer by using a voltage instead of a current.

[0009] As a magnetic memory element that changes the magnetization direction (resistance state) of the MTJ element by this voltage, various types of magnetic memory elements, such as two-terminal and three-terminal magnetic memory elements, have been proposed. However, in these magnetic memory elements, the upper electrode (first electrode) and lower electrode (second electrode) that sandwich the MTJ element are made of, for example, conductive tantalum (Ta).

[0010] When manufacturing magnetic memory devices (MRAMs), the MTJ elements use magnetic materials, making it difficult to remove them using reactive ion etching (RIE), a method typically used in microfabrication. Furthermore, in microfabrication processes, resist films become thinner as dimensions become smaller, and as the aspect ratio of the processed pattern (the ratio of pattern dimensions to depth) increases, a phenomenon known as the microloading effect occurs, which reduces the etching rate. This lengthens the etching time and can lead to problems such as the collapse of the resist mask.

[0011] If etching is performed using a sufficiently thick resist mask, the etching time will be long and the resist mask will collapse. If the resist film is made thin in an attempt to speed up the etching speed, the etching will no longer function properly, and for example, the resist mask will also be removed in the width direction, making it difficult to manufacture magnetic memory elements with high precision.

[0012] An object of the present invention is to provide a method for manufacturing a magnetic tunnel junction element that can manufacture a magnetic tunnel junction element with high precision.

[0013] The invention made to solve the above problem is a method for manufacturing a magnetic tunnel junction element having a magnetic tunnel junction layer and a metal layer directly or indirectly on a substrate in this order, the method comprising the steps of: applying a resist composition containing a polymer having a structural unit including an aromatic ring onto the metal layer; exposing the resist film formed by the application step; developing the exposed resist film; and etching the magnetic tunnel junction layer and the metal layer using the resist pattern formed by the development step as a mask.

[0014] According to the method for manufacturing a magnetic tunnel junction element of the present invention, it is possible to manufacture a magnetic tunnel junction element with high precision.

[0015] Fig. 1 is a schematic diagram showing a magnetic tunnel junction element, Fig. 2 is a schematic diagram showing a magnetic tunnel junction layer, and Fig. 3 is a schematic diagram showing a patterned magnetic tunnel junction element.

[0016] A method for manufacturing a magnetic tunnel junction element according to the present invention will be described in detail below. Note that the magnetic tunnel junction element may be referred to as an "MTJ element" below.

[0017] <MTJ Element> The MTJ element will be described using Fig. 1. The MTJ element 1 includes a magnetic tunnel junction layer 10 (hereinafter also referred to as "MTJ layer 10") and a metal layer 21, in this order, directly or indirectly on a substrate 5. In Fig. 1, the MTJ element 1 includes an interlayer film 42 provided on the substrate 5 as needed, and a metal layer 22, the MTJ layer 10, and the metal layer 21 stacked in this order.

[0018] The substrate 5 may be made of silicon, for example.

[0019] The material of the interlayer film 42 is, for example, SiO ２ , SiN. The interlayer film 42 is an optional layer.

[0020] Examples of materials for the metal layer 21 (first electrode) include aluminum (Al), tungsten (W), titanium (Ti), ruthenium (Ru), and tantalum (Ta). Tantalum is preferred because it functions as a stop layer when forming the MTJ element 1 by etching and can improve adhesion with the interlayer film 42. Examples of materials for the metal layer 22 (second electrode) include ruthenium (Ru), platinum (Pt), and iridium (Ir). Ruthenium is preferred because it can reduce the resistance of the metal layer 22. The metal surfaces of the metal layers 21 and 22 can be chemically treated to prevent oxidation. Examples of chemical treatments include nitriding.

[0021] 2 includes a free magnetic layer 11, an insulating layer 13, and a fixed magnetic layer 12. In FIG. 1, the MTJ layer 10 has the free magnetic layer 11 on the metal layer 21 side, but the MTJ layer 10 may have the fixed magnetic layer 12 on the metal layer 21 side.

[0022] Various magnetic materials are used as the materials for the free magnetic layer 11 and the pinned magnetic layer 12 depending on the specifications required for the MTJ element, the data writing and reading method, etc. For example, ferromagnetic materials such as CoFeB (cobalt iron boron), CoFe (cobalt iron), NiFe, etc. are used for the pinned magnetic layer 11 and / or the free magnetic layer 12. In addition, Mn, which can detect the magnetization direction by utilizing the anomalous Hall effect, can be used for the pinned magnetic layer 11 and / or the free magnetic layer 12. ３ At least one of the pinned magnetic layer 11 and the free magnetic layer 12 may be made of an antiferromagnetic metal compound such as Sn. ３＋ｒ X １－ｒ (X represents Sn, Ge, Ga, Pt, Rh, Ir, or Pd, and r is a number satisfying −0.2≦r≦0.2) may be used.

[0023] The size of the MTJ element 1 is, for example, about 20 nm to 50 nm, but to increase the density of the magnetic memory element (to increase the capacity of the magnetoresistive memory (MRAM)), it is preferable to have a smaller size of the MTJ element 1. For example, to reduce the magnetization reversal current (=power consumption) that reverses the magnetization of the free magnetic layer 11, it is preferable to have a smaller size of the MTJ element 1.

[0024] The MTJ element 1 can be obtained, for example, by depositing a metal layer 22, a fixed magnetic layer 12, an insulating layer 13, a free magnetic layer 11, and a metal layer 21 in this order on a wafer having an interlayer film 42 formed on a substrate 5.

[0025] <Method for Manufacturing MTJ Element> The method for manufacturing an MTJ element is a method for manufacturing a magnetic tunnel junction element having a magnetic tunnel junction layer and a metal layer directly or indirectly on a substrate in this order, and includes the steps of: applying a resist composition containing a polymer having a structural unit containing an aromatic ring onto the metal layer (hereinafter also referred to as a “coating step”); exposing the resist film formed by the coating step (hereinafter also referred to as an “exposing step”); developing the exposed resist film (hereinafter also referred to as a “developing step”); and etching the magnetic tunnel junction layer and the metal layer using the resist pattern formed by the developing step as a mask (hereinafter also referred to as an “etching step”).

[0026] According to this method for manufacturing an MTJ element, the use of a specific resist composition in the coating process allows the MTJ element to be manufactured with high precision. The resist mask formed from the resist composition has high processing resistance against etching, allowing the MTJ element 1 to be manufactured with high precision. This reduces the size of the MTJ element 1, enabling higher density magnetic memory elements, larger capacity MRAMs, and lower power consumption.

[0027] Each step of the method for manufacturing the MTJ element will be described below.

[0028] [Coating Step] In this step, a resist composition containing a polymer having a structural unit containing an aromatic ring is coated on the metal layer 21 of the MTJ element 1. By this step, a coating film (resist film) is formed on the metal layer 21.

[0029] Examples of coating methods include spin coating, casting coating, and roll coating. After coating, pre-baking (PB) may be performed, if necessary, to volatilize the solvent in the coating film. The lower limit of the PB temperature is preferably 60°C, more preferably 80°C. The upper limit of the temperature is preferably 150°C, more preferably 140°C. The lower limit of the PB time is preferably 5 seconds, more preferably 10 seconds. The lower limit of the time is preferably 600 seconds, more preferably 300 seconds. The lower limit of the average thickness of the resist film to be formed is preferably 10 nm, more preferably 20 nm. The upper limit of the average thickness is preferably 1,000 nm, more preferably 500 nm.

[0030] <Resist Composition> The resist composition used in this process contains a polymer having a structural unit containing an aromatic ring (hereinafter also referred to as "polymer [A]"). By including polymer [A], the microloading effect can be suppressed, and as a result, the MTJ element can be manufactured with high precision.

[0031] [Polymer (A)] The polymer (A) has a structural unit containing an aromatic ring. Examples of the aromatic ring include an aromatic hydrocarbon ring having 6 to 20 ring members and an aromatic heterocycle having 5 to 20 ring members. The "number of ring members" refers to the number of atoms constituting the ring structure, and in the case of a polycyclic ring, refers to the total number of atoms constituting the polycyclic ring.

[0032] Examples of aromatic hydrocarbon rings having 6 to 20 ring members include a benzene ring, a naphthalene ring, a biphenyl ring, an anthracene ring, a phenanthrene ring, a fluorene ring, a tetracene ring, and a pyrene ring.

[0033] Examples of the aromatic heterocyclic ring having 5 to 20 ring members include a furan ring, a benzofuran ring, a pyrrole ring, an indole ring, a thiophene ring, a benzothiophene ring, a dibenzothiophene ring, an imidazole ring, a pyrazole ring, and an oxazole ring.

[0034] The aromatic ring is preferably an aromatic hydrocarbon ring having 6 to 20 ring members or a polycyclic aromatic heterocycle containing an aromatic hydrocarbon ring having 6 to 20 ring members.

[0035] An example of the aromatic ring-containing structural unit is a first structural unit containing a phenolic hydroxyl group. In this case, the resist composition preferably contains a radiation-sensitive acid generator (hereinafter also referred to as "acid generator [B]"). The resist composition preferably contains an acid diffusion controller (hereinafter also referred to as "acid diffusion controller [C]").

[0036] The polymer (A) preferably further includes a second structural unit containing an acid-dissociable group. The polymer (A) may include structural units other than the first structural unit and the second structural unit. The polymer (A) may include one or more types of each structural unit.

[0037] The lower limit of the weight average molecular weight (Mw) of the polymer [A], as measured by gel permeation chromatography (GPC) in terms of polystyrene, is preferably 2,000, more preferably 3,000, even more preferably 4,000, and particularly preferably 5,000. The upper limit of the Mw is preferably 50,000, more preferably 30,000, even more preferably 15,000, and particularly preferably 8,000. By setting the Mw of the polymer [A] within the above range, the coatability of the resist composition can be further improved.

[0038] The lower limit of the dispersity of the polymer [A], i.e., the ratio of Mw to the polystyrene-equivalent number average molecular weight (Mn) measured by GPC (Mw / Mn), is preferably 1.1, more preferably 1.25, even more preferably 1.4, and particularly preferably 1.5. The upper limit of the dispersity is preferably 5, more preferably 3, and even more preferably 2. By setting the Mw / Mn of the polymer [A] within the above range, the CDU performance of the resist composition can be further improved.

[0039] The Mw and Mn of the polymer in this specification are values ​​measured using gel permeation chromatography (GPC) under the following conditions: GPC columns: two "G2000HXL" columns, one "G3000HXL" column, and one "G4000HXL" column, all manufactured by Tosoh Corporation; flow rate: 1.0 mL / min; elution solvent: tetrahydrofuran; sample concentration: 1.0 mass%; sample injection volume: 100 μL; column temperature: 40° C.; detector: differential refractometer; standard material: monodisperse polystyrene.

[0040] Each structural unit contained in the polymer (A) will be described below.

[0041] (First structural unit) The first structural unit is a structural unit containing a phenolic hydroxyl group. The term "phenolic hydroxyl group" refers not only to a hydroxyl group directly bonded to a benzene ring, but also to any hydroxyl group directly bonded to an aromatic ring. By including the first structural unit in the polymer (A), the hydrophilicity of the resist film can be increased, the solubility in a developer can be appropriately adjusted, and the adhesion of the resist pattern to the substrate can be improved. Furthermore, in the case of KrF exposure, EUV exposure, or electron beam exposure, the sensitivity of the resist composition can be further increased.

[0042] The first structural unit may be, for example, a structural unit represented by the following formula (1).

[0043]

[0044] In the above formula (1), R １ is a hydrogen atom, a fluorine atom, a methyl group, or a trifluoromethyl group. ２ is a single bond, -O-, -COO-*, or -CONH-*. * indicates the bonding site with Ar. Ar is a group obtained by removing (p+q+1) hydrogen atoms on an aromatic ring from an aromatic hydrocarbon ring having 6 to 20 ring members. p is an integer from 0 to 10. When p is 1, R ３ is a monovalent organic group having 1 to 20 carbon atoms or a halogen atom. When p is 2 or more, a plurality of R ３ are the same or different and are a monovalent organic group having 1 to 20 carbon atoms or a halogen atom, or a plurality of R ３two or more of the following are combined with each other to form a ring structure having 4 to 20 ring members together with the carbon atoms to which they are attached. q is an integer of 1 to 11, with the proviso that p+q is 11 or less.

[0045] R １ From the viewpoint of copolymerizability of the monomer that provides the first structural unit, a hydrogen atom or a methyl group is preferred as the alkyl group, and a hydrogen atom is more preferred.

[0046] R ２ is preferably a single bond or —COO—*, and more preferably a single bond.

[0047] Examples of aromatic hydrocarbon rings having 6 to 20 ring members that give Ar include those mentioned above. Among these, a benzene ring or a naphthalene ring is preferred, and a benzene ring is more preferred.

[0048] "Organic group" refers to a group containing at least one carbon atom. ３ Examples of the monovalent organic group having 1 to 20 carbon atoms represented by the formula (I) include a monovalent hydrocarbon group having 1 to 20 carbon atoms, a group containing a divalent heteroatom-containing group between carbon atoms or at the terminal on the bond side of the hydrocarbon group, and groups in which some or all of the hydrogen atoms in the hydrocarbon group and the group containing the divalent heteroatom-containing group have been substituted with monovalent heteroatom-containing groups.

[0049] "Hydrocarbon group" includes linear hydrocarbon groups, alicyclic hydrocarbon groups, and aromatic hydrocarbon groups. This "hydrocarbon group" may be a saturated hydrocarbon group or an unsaturated hydrocarbon group. "Linear hydrocarbon group" refers to a hydrocarbon group that does not contain a cyclic structure and is composed only of a linear structure, and includes both linear hydrocarbon groups and branched hydrocarbon groups. "Alicyclic hydrocarbon group" refers to a hydrocarbon group that contains only an alicyclic structure as a ring structure and does not contain an aromatic ring structure, and includes both monocyclic alicyclic hydrocarbon groups and polycyclic alicyclic hydrocarbon groups. However, it does not have to be composed only of an alicyclic structure, and may contain a linear structure as part of it. "Aromatic hydrocarbon group" refers to a hydrocarbon group that contains an aromatic ring structure as a ring structure. However, it does not have to be composed only of an aromatic ring structure, and may contain a linear structure or an alicyclic structure as part of it.

[0050] 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, and a monovalent aromatic hydrocarbon group having 6 to 20 carbon atoms.

[0051] Examples of the monovalent chain hydrocarbon group having 1 to 20 carbon atoms include alkyl groups such as a methyl group, an ethyl group, an n-propyl group, and an i-propyl group; alkenyl groups such as an ethenyl group, a propenyl group, and a butenyl group; and alkynyl groups such as an ethynyl group, a propynyl group, and a butynyl group.

[0052] Examples of the monovalent alicyclic hydrocarbon group having 3 to 20 carbon atoms include alicyclic saturated hydrocarbon groups such as a cyclopentyl group, a cyclohexyl group, a norbornyl group, an adamantyl group, a tricyclodecyl group, and a tetracyclododecyl group; and alicyclic unsaturated hydrocarbon groups such as a cyclopentenyl group, a cyclohexenyl group, a norbornenyl group, a tricyclodecenyl group, and a tetracyclododecenyl group.

[0053] Examples of the monovalent aromatic hydrocarbon group having 6 to 20 carbon atoms include aryl groups such as phenyl, tolyl, xylyl, naphthyl, and anthryl; and aralkyl groups such as benzyl, phenethyl, naphthylmethyl, and anthrylmethyl.

[0054] Examples of heteroatoms constituting the monovalent or divalent heteroatom-containing group include oxygen atoms, nitrogen atoms, sulfur atoms, phosphorus atoms, silicon atoms, and halogen atoms. Examples of halogen atoms include fluorine atoms, chlorine atoms, bromine atoms, and iodine atoms.

[0055] Examples of the divalent heteroatom-containing group include —O—, —CO—, —S—, —CS—, —NR′—, and groups formed by combining two or more of these, where R′ is a hydrogen atom or a monovalent hydrocarbon group.

[0056] Examples of the monovalent heteroatom-containing group include halogen atoms such as fluorine atom, chlorine atom, bromine atom and iodine atom, hydroxy group, carboxy group, cyano group, amino group and sulfanyl group.

[0057] R３ As the alkyl group, a monovalent hydrocarbon group is preferred, and an alkyl group is more preferred.

[0058] Multiple R ３ Examples of the ring structure having 4 to 20 ring members formed by combining two or more of the above include alicyclic structures such as a cyclopentane structure, a cyclohexane structure, a cyclopentene structure, and a cyclohexene structure, as well as aliphatic heterocyclic structures such as a lactone structure and a cyclic ether structure.

[0059] p is preferably 0 to 2, more preferably 0 or 1, and even more preferably 0.

[0060] q is preferably 1 to 3, and more preferably 1 or 2.

[0061] Examples of the first structural unit include structural units represented by the following formulas (1-1) to (1-12).

[0062]

[0063] In the above formulas (1-1) to (1-12), R １ is synonymous with the above formula (1).

[0064] The lower limit of the content of the first structural unit relative to all structural units constituting the polymer (A) is preferably 10 mol%, more preferably 20 mol%, and even more preferably 30 mol%. The upper limit of this content is preferably 80 mol%, more preferably 70 mol%, and even more preferably 60 mol%. By keeping the content of the first structural unit within this range, the CDU performance of the resist composition can be further improved.

[0065] (Second structural unit) The second structural unit is a structural unit containing an acid-dissociable group. The "acid-dissociable group" refers to a group that substitutes a hydrogen atom of a carboxy group, a sulfo group, a phenolic hydroxyl group, or the like, and that dissociates under the action of an acid. The acid-dissociable group is dissociated by the action of the acid generated from the acid generator (B) upon exposure, and the solubility of the polymer (A) in a developer changes, thereby forming a resist pattern.

[0066] Examples of the second structural unit include structural units represented by the following formula (2-1A), formula (2-1B), formula (2-1C), formula (2-2A), and formula (2-2B). In the following formulas (2-1A) to (2-2B), -CR bonded to an oxyoxygen atom derived from a carboxy group or a phenolic hydroxyl group is Ｘ R Ｙ R Ｚ , a group containing an unsaturated alicyclic structure, or —CR Ｕ R Ｖ (OR Ｗ ) corresponds to the acid-dissociable group.

[0067]

[0068] In the above formulas (2-1A), (2-1B), (2-1C), (2-2A) and (2-2B), R Ｔ are each independently a hydrogen atom, a fluorine atom, a methyl group, or a trifluoromethyl group.

[0069] In the above formulas (2-1A) and (2-1B), R Ｘ are each independently a monovalent hydrocarbon group having 1 to 20 carbon atoms. Ｙ and R Ｚ are each independently a monovalent hydrocarbon group having 1 to 20 carbon atoms, or are part of an alicyclic structure having 3 to 20 ring members formed by combining these groups together with the carbon atoms to which they are attached.

[0070] In formula (2-1C), R Ａ is a hydrogen atom. Ｂ and R Ｃ are each independently a hydrogen atom or a monovalent hydrocarbon group having 1 to 20 carbon atoms. Ｄ is R Ａ , R Ｂ and R Ｃ are divalent hydrocarbon groups having 1 to 20 carbon atoms which, together with the carbon atoms to which they are bonded, constitute an unsaturated alicyclic structure having 4 to 20 ring members.

[0071] In the above formulas (2-2A) and (2-2B), R Ｕ and R Ｖ are each independently a hydrogen atom or a monovalent hydrocarbon group having 1 to 20 carbon atoms, and R Ｗare each independently a monovalent hydrocarbon group having 1 to 20 carbon atoms, or R Ｕ and R Ｖ are combined with each other and are part of an alicyclic structure having 3 to 20 ring members formed together with the carbon atoms to which they are attached, or R Ｕ and R Ｗ are aligned with each other and R Ｕ and the carbon atom to which R Ｗ is part of an aliphatic heterocyclic structure having 5 to 20 ring members, which is formed together with the oxygen atom to which it is bonded.

[0072] R Ｔ From the viewpoint of copolymerizability of the monomer that provides the second structural unit, a hydrogen atom or a methyl group is preferred.

[0073] R Ｘ , R Ｙ , R Ｚ , R Ｂ , R Ｃ , R Ｕ , R Ｖ and R Ｗ Examples of the monovalent hydrocarbon group having 1 to 20 carbon atoms represented by the formula (1) include R ３ Examples of the hydrocarbon groups include the same groups as those exemplified as the hydrocarbon groups.

[0074] R Ｄ Examples of the divalent hydrocarbon group having 1 to 20 carbon atoms represented by the formula (1) include R ３ Examples of the monovalent hydrocarbon groups include those exemplified above in which one hydrogen atom has been removed.

[0075] R Ｘ is preferably an alkyl group or an aryl group.

[0076] R Ｙ and R Ｚ As the alkyl group, an alkyl group or an alicyclic saturated hydrocarbon group is preferred.

[0077] R Ｙ and R Ｚ or R Ｕ and R ＶExamples of the alicyclic structure having 3 to 20 ring members include saturated alicyclic structures such as a cyclopropane structure, a cyclobutane structure, a cyclopentane structure, a cyclohexane structure, a norbornane structure, and an adamantane structure; and unsaturated alicyclic structures such as a cyclopropene structure, a cyclobutene structure, a cyclopentene structure, a cyclohexene structure, and a norbornene structure. Among these, a cyclopentane structure, a cyclohexane structure, a cyclohexene structure, or an adamantane structure is preferred.

[0078] R Ｄ is R Ａ , R Ｂ and R Ｃ Examples of the unsaturated alicyclic structure having 4 to 20 ring members formed together with the carbon atoms to which they are bonded include unsaturated alicyclic structures such as a cyclobutene structure, a cyclopentene structure, a cyclohexene structure, and a norbornene structure.

[0079] R Ｕ and R Ｗ Examples of the aliphatic heterocyclic structure having 5 to 20 ring members constituted by include saturated oxygen-containing heterocyclic structures such as an oxacyclobutane structure, an oxacyclopentane structure, and an oxacyclohexane structure; and unsaturated oxygen-containing heterocyclic structures such as an oxacyclobutene structure, an oxacyclopentene structure, and an oxacyclohexene structure.

[0080] The structural unit represented by the formula (2-1A) is preferably a structural unit derived from 1-alkylcycloalkane-1-yl(meth)acrylate, a structural unit derived from 1-arylcycloalkane-1-yl(meth)acrylate, or a structural unit derived from 2-adamantylpropan-2-yl(meth)acrylate. The structural unit represented by the formula (2-1B) is preferably a structural unit derived from t-alkyloxystyrene. The structural unit represented by the formula (2-1C) is preferably a structural unit derived from cyclohexen-3-yl(meth)acrylate. The structural unit represented by the formula (2-2A) is preferably (1-ethoxy)ethoxy(meth)acrylate. The structural unit represented by the formula (2-2B) is preferably p-(1-ethoxy)ethoxystyrene.

[0081] The second structural unit is preferably a structural unit represented by the above formula (2-1A).

[0082] The lower limit of the content of the second structural unit is preferably 5 mol%, more preferably 10 mol%, even more preferably 15 mol%, and particularly preferably 20 mol%, based on all structural units constituting the polymer [A]. The upper limit of the content is preferably 90 mol%, more preferably 80 mol%, even more preferably 70 mol%, and particularly preferably 65 mol%. By setting the content within the above range, the sensitivity of the radiation-sensitive composition can be further increased, and as a result, the CDU performance can be further improved.

[0083] (Other structural units) The other structural units are structural units other than the first structural unit and the second structural unit. Examples of the other structural units include a third structural unit including a lactone structure, a cyclic carbonate structure, a sultone structure, or a combination thereof. When the polymer (A) includes the third structural unit, the solubility in a developer can be improved, and as a result, the CDU performance of the resist composition can be further improved.

[0084] The third structural unit is preferably a structural unit containing a lactone structure, more preferably a structural unit containing a lactone structure and an aromatic ring. Examples of the structural unit containing a lactone structure and an aromatic ring include structural units represented by the following formula:

[0085]

[0086] In the above formula, R Ｌ１ is a hydrogen atom, a fluorine atom, a methyl group, or a trifluoromethyl group.

[0087] When the polymer (A) has a third structural unit, the upper limit of the content of the third structural unit relative to all structural units constituting the polymer (A) is preferably 60 mol %, more preferably 50 mol %, and even more preferably 30 mol %. The lower limit of the content is, for example, 1 mol %.

[0088] Examples of structural units other than the third structural unit include a structural unit containing an alcoholic hydroxy group and a structural unit containing a non-acid dissociable hydrocarbon group.

[0089] [[B] Acid Generator] The [B] acid generator is a substance that generates an acid when irradiated with radiation. Examples of the radiation include the radiation used in the exposure step described below. Examples of the acid generated from the [B] acid generator include sulfonic acid and imide acid. The acid generated from the [B] acid generator dissociates the acid-dissociable group of the [A] polymer to generate a carboxyl group or the like, which changes the solubility of the [A] polymer in a developer, allowing the formation of a resist pattern. The resist composition can contain one or more [B] acid generators.

[0090] Examples of the acid generator (B) include an onium salt compound, an N-sulfonyloxyimide compound, a sulfonimide compound, a halogen-containing compound, and a diazoketone compound.

[0091] Examples of the onium salt compound include sulfonium salts, tetrahydrothiophenium salts, iodonium salts, phosphonium salts, diazonium salts, and pyridinium salts.

[0092] Specific examples of the acid generator (B) include the compounds described in paragraphs

[0080] to

[0113] of JP-A No. 2009-134088.

[0093] Examples of the acid generator [B] that generates a sulfonic acid upon irradiation with radiation include compounds represented by the following formula (3): When the acid generator [B] has the following structure, it is believed that the diffusion length of the generated acid in the resist film is suitably shortened due to, for example, interaction with the first structural unit of the polymer [A], and as a result, the CDU performance can be further improved.

[0094]

[0095] In the above formula (3), R ｐ１ is a monovalent group containing a ring structure having 5 or more ring members. ｐ２ is a divalent linking group. ｐ３ and Rｐ４ are each independently a hydrogen atom, a fluorine atom, a monovalent hydrocarbon group having 1 to 20 carbon atoms, or a monovalent fluorinated hydrocarbon group having 1 to 20 carbon atoms. ｐ５ and R ｐ６ are each independently a fluorine atom or a monovalent fluorinated hydrocarbon group having 1 to 20 carbon atoms. ｐ１ is an integer from 0 to 10. ｐ２ is an integer from 0 to 10. ｐ３ is an integer from 0 to 10. ｐ１ +n ｐ２ +n ｐ３ is 1 or more and 30 or less. ｐ１ If there are two or more R ｐ２ are the same or different. ｐ２ If there are two or more R ｐ３ are the same or different, and multiple R ｐ４ are the same or different. ｐ３ If there are two or more R ｐ５ are the same or different, and multiple R ｐ６ are the same or different. ＋ is a monovalent radiation-sensitive onium cation.

[0096] R ｐ１ Examples of the monovalent group having a ring structure of 5 or more ring members, represented by the formula (I), include a monovalent group having an alicyclic structure of 5 or more ring members, a monovalent group having an aliphatic heterocyclic structure of 5 or more ring members, a monovalent group having an aromatic ring structure of 5 or more ring members, and a monovalent group having an aromatic heterocyclic structure of 5 or more ring members.

[0097] Examples of the alicyclic structure having 5 or more ring members include: monocyclic saturated alicyclic structures such as a cyclopentane structure, a cyclohexane structure, a cycloheptane structure, a cyclooctane structure, a cyclononane structure, a cyclodecane structure, and a cyclododecane structure; monocyclic unsaturated alicyclic structures such as a cyclopentene structure, a cyclohexene structure, a cycloheptene structure, a cyclooctene structure, and a cyclodecene structure; polycyclic saturated alicyclic structures such as a norbornane structure, an adamantane structure, a tricyclodecane structure, and a tetracyclododecane structure; and polycyclic unsaturated alicyclic structures such as a norbornene structure and a tricyclodecene structure.

[0098] Examples of the aliphatic heterocyclic structure having 5 or more ring members include lactone structures such as a hexanolactone structure and a norbornanelactone structure; sultone structures such as a hexanosultone structure and a norbornanesultone structure; oxygen atom-containing heterocyclic structures such as an oxacycloheptane structure and an oxanorbornane structure; nitrogen atom-containing heterocyclic structures such as an azacyclohexane structure and a diazabicyclooctane structure; and sulfur atom-containing heterocyclic structures such as a thiacyclohexane structure and a thianorbornane structure.

[0099] Examples of aromatic ring structures having 5 or more ring members include a benzene structure, a naphthalene structure, a phenanthrene structure, and an anthracene structure.

[0100] Examples of aromatic heterocyclic structures having 5 or more ring members include oxygen atom-containing heterocyclic structures such as a furan structure, a pyran structure, a benzofuran structure, and a benzopyran structure; and nitrogen atom-containing heterocyclic structures such as a pyridine structure, a pyrimidine structure, and an indole structure.

[0101] R ｐ１ The lower limit of the number of ring members in the ring structure is preferably 6, more preferably 8, even more preferably 9, and particularly preferably 10. The upper limit of the number of ring members is preferably 15, more preferably 14, even more preferably 13, and particularly preferably 12. By setting the number of ring members within the above range, the diffusion length of the acid can be further suitably shortened, and as a result, the CDU performance and the like of the resist composition can be further improved.

[0102] R ｐ１ Some or all of the hydrogen atoms in the ring structure may be substituted with a substituent. Examples of the substituent include halogen atoms such as fluorine atom, chlorine atom, bromine atom, and iodine atom, hydroxy group, carboxy group, cyano group, nitro group, alkoxy group, alkoxycarbonyl group, alkoxycarbonyloxy group, acyl group, and acyloxy group. Among these, a hydroxy group is preferred.

[0103] R ｐ１is preferably a monovalent group containing an alicyclic structure having 5 or more ring members or a monovalent group containing an aliphatic heterocyclic structure having 5 or more ring members, more preferably a monovalent group containing an alicyclic structure having 9 or more ring members or a monovalent group containing an aliphatic heterocyclic structure having 9 or more ring members, and is preferably an adamantyl group, a hydroxyadamantyl group, a norbornane lactone-yl group, a norbornane sultone-yl group, or a 5-oxo-4-oxatricyclo[4.3.1.1 ３，８ ]undecanyl is more preferred, and adamantyl is especially preferred.

[0104] R ｐ２ Examples of the divalent linking group represented by the formula (I) include a carbonyl group, an ether group, a carbonyloxy group, a sulfide group, a thiocarbonyl group, a sulfonyl group, a divalent hydrocarbon group, etc. Among these, a carbonyloxy group, a sulfonyl group, an alkanediyl group, or a divalent alicyclic saturated hydrocarbon group is preferred, a carbonyloxy group or a divalent alicyclic saturated hydrocarbon group is more preferred, a carbonyloxy group or a norbornanediyl group is even more preferred, and a carbonyloxy group is particularly preferred. ｐ２ is a carbonyloxy group, the orientation of the carbonyloxy group is not particularly limited. ｐ１ and the oxyoxygen atom may be bonded to R ｐ１ It may be bonded to.

[0105] R ｐ３ or R ｐ４ Examples of the monovalent hydrocarbon group having 1 to 20 carbon atoms represented by R include an alkyl group having 1 to 20 carbon atoms. ｐ３ and R ｐ４ Examples of the monovalent fluorinated hydrocarbon group having 1 to 20 carbon atoms represented by the formula (R) include a fluorinated alkyl group having 1 to 20 carbon atoms. ｐ３ and R ｐ４ is preferably a hydrogen atom, a fluorine atom or a fluorinated alkyl group, more preferably a fluorine atom or a perfluoroalkyl group, and even more preferably a fluorine atom or a trifluoromethyl group.

[0106] R ｐ５ or R ｐ６Examples of the monovalent fluorinated hydrocarbon group having 1 to 20 carbon atoms represented by the formula (R) include a fluorinated alkyl group having 1 to 20 carbon atoms. ｐ５ and R ｐ６ As the alkyl group, a fluorine atom or a fluorinated alkyl group is preferable, a fluorine atom or a perfluoroalkyl group is more preferable, a fluorine atom or a trifluoromethyl group is further preferable, and a fluorine atom is particularly preferable.

[0107] n ｐ１ is preferably 0 to 5, more preferably 0 to 3, still more preferably 0 to 2, and particularly preferably 0 or 1.

[0108] n ｐ２ is preferably 0 to 5, more preferably 0 to 2, still more preferably 0 or 1, and particularly preferably 0.

[0109] n ｐ３ The lower limit of n is preferably 1, and more preferably 2. ｐ３ By making n equal to or greater than 1, the strength of the acid generated from compound (3) can be increased, and as a result, the CDU performance of the resist composition can be further improved. ｐ３ The upper limit of is preferably 4, more preferably 3, and even more preferably 2.

[0110] n ｐ１ +n ｐ２ +n ｐ３ The lower limit of n is preferably 2, more preferably 4. ｐ１ +n ｐ２ +n ｐ３ The upper limit of is preferably 20, more preferably 10.

[0111] T ＋ Examples of the monovalent radiation-sensitive onium cation represented by the formula (r-a) below (hereinafter also referred to as "cation (r-a)"), a cation represented by the formula (r-b) below (hereinafter also referred to as "cation (r-b)"), and a cation represented by the formula (r-c) below (hereinafter also referred to as "cation (r-c)"):

[0112]

[0113] In the above formula (r-a), RＢ３ and R Ｂ４ are each independently a monovalent organic group having 1 to 20 carbon atoms. b3 is an integer of 0 to 11. When b3 is 1, R Ｂ５ is a monovalent organic group having 1 to 20 carbon atoms, a hydroxy group, a nitro group, or a halogen atom. Ｂ５ are the same or different and are a monovalent organic group having 1 to 20 carbon atoms, a hydroxy group, a nitro group, or a halogen atom, or are parts of a ring structure having 4 to 20 ring members formed by combining these groups together with the carbon chain to which they are bonded. ｂｂ is an integer from 0 to 3.

[0114] The above R Ｂ３ , R Ｂ４ or R Ｂ５ Examples of the monovalent organic group having 1 to 20 carbon atoms represented by the formula (I) include a monovalent hydrocarbon group having 1 to 20 carbon atoms, a monovalent group (g) containing a divalent heteroatom-containing group between carbon atoms or at the terminal on the bond side of the hydrocarbon group, and a monovalent group in which some or all of the hydrogen atoms in the hydrocarbon group and group (g) have been substituted with heteroatom-containing groups.

[0115] R Ｂ３ and R Ｂ４ As the alkyl group, a monovalent unsubstituted hydrocarbon group having 1 to 20 carbon atoms or a hydrocarbon group in which a hydrogen atom is substituted with a substituent is preferred, a monovalent unsubstituted aromatic hydrocarbon group having 6 to 18 carbon atoms or an aromatic hydrocarbon group in which a hydrogen atom is substituted with a substituent is more preferred, a substituted or unsubstituted phenyl group is further preferred, and an unsubstituted phenyl group is particularly preferred.

[0116] The above R Ｂ３ and R Ｂ４ Examples of the substituent that may substitute a hydrogen atom of the monovalent hydrocarbon group having 1 to 20 carbon atoms, represented by ２ -R ｋ , -SO ２ -R ｋ , -OR ｋ , -COOR ｋ , —O—CO—R ｋ , -O-R ｋｋ -COORｋ , -R ｋｋ -CO-R ｋ or -S-R ｋ is preferred. ｋ is a monovalent hydrocarbon group having 1 to 10 carbon atoms. ｋｋ is a single bond or a divalent hydrocarbon group having 1 to 10 carbon atoms.

[0117] R Ｂ５ is a substituted or unsubstituted monovalent hydrocarbon group having 1 to 20 carbon atoms, -OSO ２ -R ｋ , -SO ２ -R ｋ , -OR ｋ , -COOR ｋ , —O—CO—R ｋ , -O-R ｋｋ -COOR ｋ , -R ｋｋ -CO-R ｋ or -S-R ｋ is preferred. ｋ is a monovalent hydrocarbon group having 1 to 10 carbon atoms. ｋｋ is a single bond or a divalent hydrocarbon group having 1 to 10 carbon atoms.

[0118] In the above formula (r-b), b4 is an integer of 0 to 9. When b4 is 1, R Ｂ６ is a monovalent organic group having 1 to 20 carbon atoms, a hydroxy group, a nitro group, or a halogen atom. Ｂ６ are the same or different and are a monovalent organic group having 1 to 20 carbon atoms, a hydroxy group, a nitro group, or a halogen atom, or are parts of a ring structure having 4 to 20 ring members formed by combining these groups together with the carbon chain to which they are bonded. b5 is an integer of 0 to 10. When b5 is 1, R Ｂ７ is a monovalent organic group having 1 to 20 carbon atoms, a hydroxy group, a nitro group, or a halogen atom. Ｂ７ are the same or different and are a monovalent organic group having 1 to 20 carbon atoms, a hydroxy group, a nitro group, or a halogen atom, or are parts of a ring structure having 3 to 20 ring members formed by combining these groups together with the carbon atoms or carbon chains to which they are attached. ｂ２is an integer from 0 to 3. Ｂ８ is a single bond or a divalent organic group having 1 to 20 carbon atoms. ｂ１ is an integer from 0 to 2.

[0119] The above R Ｂ６ and R Ｂ７ is a substituted or unsubstituted monovalent hydrocarbon group having 1 to 20 carbon atoms, -OR ｋ , -COOR ｋ , —O—CO—R ｋ , -O-R ｋｋ -COOR ｋ or -R ｋｋ -CO-R ｋ is preferred. ｋ is a monovalent hydrocarbon group having 1 to 10 carbon atoms. ｋｋ is a single bond or a divalent hydrocarbon group having 1 to 10 carbon atoms.

[0120] In the above formula (rc), b6 is an integer of 0 to 5. When b6 is 1, R Ｂ９ is a monovalent organic group having 1 to 20 carbon atoms, a hydroxy group, a nitro group, or a halogen atom. Ｂ９ are the same or different and are a monovalent organic group having 1 to 20 carbon atoms, a hydroxy group, a nitro group, or a halogen atom, or are parts of a ring structure having 4 to 20 ring members formed by combining these groups together with the carbon chain to which they are bonded. b7 is an integer of 0 to 5. When b7 is 1, R Ｂ１０ is a monovalent organic group having 1 to 20 carbon atoms, a hydroxy group, a nitro group, or a halogen atom. Ｂ１０ are the same or different and are a monovalent organic group having 1 to 20 carbon atoms, a hydroxy group, a nitro group, or a halogen atom, or are parts of a ring structure having 4 to 20 ring members formed by combining these groups together with the carbon chain to which they are bonded.

[0121] The above R Ｂ９ and R Ｂ１０ is a substituted or unsubstituted monovalent hydrocarbon group having 1 to 20 carbon atoms, -OSO ２ -R ｋ , -SO ２ -R ｋ , -ORｋ , -COOR ｋ , —O—CO—R ｋ , -O-R ｋｋ -COOR ｋ , -R ｋｋ -CO-R ｋ , -S-R ｋ Alternatively, a ring structure formed by combining two or more of these groups is preferred. ｋ is a monovalent hydrocarbon group having 1 to 10 carbon atoms. ｋｋ is a single bond or a divalent hydrocarbon group having 1 to 10 carbon atoms.

[0122] R Ｂ５ , R Ｂ６ , R Ｂ７ , R Ｂ９ or R Ｂ１０ Examples of the monovalent hydrocarbon group having 1 to 20 carbon atoms represented by the formula (I) include: linear alkyl groups such as methyl, ethyl, n-propyl, and n-butyl; branched alkyl groups such as i-propyl, i-butyl, sec-butyl, and t-butyl; aryl groups such as phenyl, tolyl, xylyl, mesityl, and naphthyl; and aralkyl groups such as benzyl and phenethyl.

[0123] R Ｂ８ Examples of the divalent organic group represented by the formula (r-a) include R Ｂ３ , R Ｂ４ and R Ｂ５ Examples of such groups include groups in which one hydrogen atom has been removed from the monovalent organic groups having 1 to 20 carbon atoms exemplified above.

[0124] The above R Ｂ５ , R Ｂ６ , R Ｂ７ , R Ｂ９ or R Ｂ１０ Examples of the substituent that may substitute a hydrogen atom of the hydrocarbon group represented by the formula (I) include a halogen atom such as a fluorine atom, a chlorine atom, a bromine atom, or an iodine atom, a hydroxy group, a carboxy group, a cyano group, a nitro group, an alkoxy group, an alkoxycarbonyl group, an alkoxycarbonyloxy group, an acyl group, an acyloxy group, etc. Among these, a halogen atom is preferred, and a fluorine atom is more preferred.

[0125] R Ｂ５ , R Ｂ６ , R Ｂ７ , R Ｂ９ and R Ｂ１０ Examples of the alkyl group include an unsubstituted linear or branched monovalent alkyl group, a monovalent fluorinated alkyl group, an unsubstituted monovalent aromatic hydrocarbon group, and —OSO ２ -R ｋ or -SO ２ -R ｋ is preferred, a fluorinated alkyl group or an unsubstituted monovalent aromatic hydrocarbon group is more preferred, and a fluorinated alkyl group is even more preferred.

[0126] In formula (r-a), b3 is preferably 0 to 2, more preferably 0 or 1, and even more preferably 0. ｂｂ is preferably 0 or 1, more preferably 0. b4 in formula (r-b) is preferably 0 to 2, more preferably 0 or 1, and even more preferably 0. b5 is preferably 0 to 2, more preferably 0 or 1, and even more preferably 0. n ｂ２ is preferably 2 or 3, and more preferably 2. ｂ１ is preferably 0 or 1, and more preferably 0. b6 and b7 in formula (rc) are preferably 0 to 2, more preferably 0 or 1, and even more preferably 0.

[0127] T ＋ Among these, the cation (r-a) is preferred, and the triphenylsulfonium cation is more preferred.

[0128] The acid generator (B) is an acid generator that generates sulfonic acid, and examples thereof include compounds represented by the following formula (3-1).

[0129]

[0130] In the above formula (3-1), T ＋ is a monovalent radiation-sensitive onium cation.

[0131] The lower limit of the content of the acid generator [B] is preferably 0.1 parts by mass, more preferably 1 part by mass, even more preferably 5 parts by mass, and particularly preferably 10 parts by mass, relative to 100 parts by mass of the polymer [A]. The upper limit of the content is preferably 50 parts by mass, more preferably 40 parts by mass, even more preferably 30 parts by mass, and particularly preferably 25 parts by mass. By setting the content of the acid generator [B] within the above range, the resist composition can have improved sensitivity and developability, and as a result, can have further improved CDU performance.

[0132] [Acid Diffusion Controller (C)] The acid diffusion controller (C) controls the diffusion phenomenon in the resist film of the acid generated from the acid generator (B) upon exposure, thereby suppressing undesirable chemical reactions in unexposed regions. This also improves the storage stability of the resist composition and further improves the resolution of the resist. Furthermore, it is possible to suppress changes in the line width of the resist pattern due to variations in the exposure time between exposure and development, thereby obtaining a resist composition with excellent process stability.

[0133] Examples of the acid diffusion controller (C) include nitrogen atom-containing compounds and photodecomposable bases that are photosensitive to light upon exposure to generate weak acids.

[0134] Examples of the nitrogen atom-containing compound include amine compounds such as tripentylamine and trioctylamine; amide group-containing compounds such as formamide and N,N-dimethylacetamide; urea compounds such as urea and 1,1-dimethylurea; and nitrogen-containing heterocyclic compounds such as pyridine, N-(undecylcarbonyloxyethyl)morpholine, and N-t-pentyloxycarbonyl-4-hydroxypiperidine.

[0135] Examples of photodegradable bases include compounds containing an onium cation that decomposes upon exposure and an anion of a weak acid. In the photodegradable base, a weak acid is generated from a proton generated by decomposition of the onium cation and the anion of the weak acid in the exposed area, resulting in a decrease in acid diffusion controllability.

[0136] Examples of the photodegradable base include compounds represented by the following formula:

[0137]

[0138] When the resist composition contains the acid diffusion controller (C), the lower limit of the content of the acid diffusion controller (C) is preferably 1 mol %, more preferably 5 mol %, and even more preferably 10 mol %, relative to 100 mol % of the acid generator (B), and the upper limit of the content is preferably 250 mol %, more preferably 150 mol %, and even more preferably 100 mol %.

[0139] [Organic Solvent (D)] The resist composition typically contains an organic solvent (D). The organic solvent (D) is not particularly limited as long as it is a solvent that can dissolve or disperse at least the optional components such as the polymer (A), the acid generator (B), and the acid diffusion controller (C).

[0140] [D] Examples of the organic solvent include alcohol solvents, ether solvents, ketone solvents, amide solvents, ester solvents, and hydrocarbon solvents.

[0141] Examples of alcohol-based solvents include aliphatic monoalcohol-based solvents having 1 to 18 carbon atoms, such as 4-methyl-2-pentanol and n-hexanol; alicyclic monoalcohol-based solvents having 3 to 18 carbon atoms, such as cyclohexanol; polyhydric alcohol-based solvents having 2 to 18 carbon atoms, such as 1,2-propylene glycol; and polyhydric alcohol partial ether-based solvents having 3 to 19 carbon atoms, such as 1-methoxy-2-propanol.

[0142] Examples of ether solvents include dialkyl ether solvents such as diethyl ether, dipropyl ether, dibutyl ether, dipentyl ether, diisoamyl ether, dihexyl ether, and diheptyl ether; cyclic ether solvents such as tetrahydrofuran and tetrahydropyran; and aromatic ring-containing ether solvents such as diphenyl ether and anisole.

[0143] Examples of ketone solvents include chain ketone solvents such as acetone, methyl ethyl ketone, methyl-n-propyl ketone, methyl-n-butyl ketone, diethyl ketone, methyl-iso-butyl ketone, 2-heptanone, ethyl-n-butyl ketone, methyl-n-hexyl ketone, di-iso-butyl ketone, and trimethylnonanone; cyclic ketone solvents such as cyclopentanone, cyclohexanone, cycloheptanone, cyclooctanone, and methylcyclohexanone; and 2,4-pentanedione, acetonylacetone, and acetophenone.

[0144] Examples of the amide solvent include cyclic amide solvents such as N,N'-dimethylimidazolidinone and N-methylpyrrolidone; and chain amide solvents such as N-methylformamide, N,N-dimethylformamide, N,N-diethylformamide, acetamide, N-methylacetamide, N,N-dimethylacetamide, and N-methylpropionamide.

[0145] Examples of ester solvents include monocarboxylic acid ester solvents such as n-butyl acetate and ethyl lactate; polyhydric alcohol carboxylate solvents such as propylene glycol acetate; polyhydric alcohol partial ether carboxylate solvents such as propylene glycol monomethyl ether acetate; polycarboxylic acid diester solvents such as diethyl oxalate; and carbonate solvents such as dimethyl carbonate and diethyl carbonate.

[0146] Examples of hydrocarbon solvents include aliphatic hydrocarbon solvents having 5 to 12 carbon atoms, such as n-pentane and n-hexane; and aromatic hydrocarbon solvents having 6 to 16 carbon atoms, such as toluene and xylene.

[0147] The resist composition can be prepared, for example, by mixing the polymer (A), the acid generator (B), the organic solvent (D), and optional components such as the acid diffusion controller (C) in a predetermined ratio, and then filtering the resulting mixture preferably through a membrane filter having a pore size of about 0.2 μm.

[0148] The resist composition can be used for forming a positive pattern using an alkaline developer, or for forming a negative pattern using an organic solvent-containing developer.

[0149] [Exposure Step] In this step, the resist film formed in the coating step is exposed to light. This exposure is carried out by irradiating with radiation through a photomask (or, in some cases, through an immersion medium such as water). Examples of radiation include electromagnetic waves such as visible light, ultraviolet light, far ultraviolet light, extreme ultraviolet light (EUV), X-rays, and gamma rays; and charged particle beams such as electron beams and alpha rays, depending on the line width and other factors of the desired pattern. Among these, far ultraviolet light, EUV, or electron beams are preferred, with ArF excimer laser light (wavelength 193 nm), KrF excimer laser light (wavelength 248 nm), EUV (wavelength 13.5 nm), or electron beams being more preferred, and ArF excimer laser light, EUV, or electron beams being even more preferred.

[0150] After the exposure, post-exposure baking (hereinafter also referred to as "PEB") is preferably performed to promote dissociation of acid-dissociable groups in the polymer (A) or the like in the exposed portions of the resist film by the acid generated from the acid generator (B) or the like upon exposure. This PEB can increase the difference in solubility in a developer between the exposed and unexposed portions. The lower limit of the PEB temperature is preferably 50°C, more preferably 80°C, and even more preferably 100°C. The upper limit of the temperature is preferably 180°C, and more preferably 130°C. The lower limit of the PEB time is preferably 5 seconds, more preferably 10 seconds, and even more preferably 30 seconds. The upper limit of the time is preferably 600 seconds, more preferably 300 seconds, and even more preferably 100 seconds.

[0151] [Development Step] In this step, the exposed resist film is developed. This allows a predetermined resist pattern to be formed. After development, the resist film is generally washed with a rinse solution such as water or alcohol, and then dried. The development method in the development step may be either alkali development or organic solvent development, but alkali development is preferred.

[0152] In the case of alkaline development, examples of the developer used for development include an alkaline aqueous solution containing at least one alkaline compound dissolved therein, such as sodium hydroxide, potassium hydroxide, sodium carbonate, sodium silicate, sodium metasilicate, aqueous ammonia, ethylamine, n-propylamine, diethylamine, di-n-propylamine, triethylamine, methyldiethylamine, ethyldimethylamine, triethanolamine, tetramethylammonium hydroxide (hereinafter also referred to as "TMAH"), pyrrole, piperidine, choline, 1,8-diazabicyclo-[5.4.0]-7-undecene, and 1,5-diazabicyclo-[4.3.0]-5-nonene. Among these, an aqueous TMAH solution is preferred, and a 2.38 mass % aqueous TMAH solution is more preferred.

[0153] In the case of organic solvent development, examples of the developer include the solvents exemplified as the organic solvent (D) in the resist composition described above. Examples of components in the developer other than the organic solvent include water and silicone oil.

[0154] Examples of development methods include a method in which the substrate is immersed in a tank filled with developer for a certain period of time (dip method), a method in which developer is piled up on the surface of the substrate by surface tension and left to stand for a certain period of time (puddle method), a method in which developer is sprayed onto the surface of the substrate (spray method), and a method in which developer is continuously dispensed onto a substrate rotating at a constant speed while a developer dispensing nozzle is scanned at a constant speed (dynamic dispense method).

[0155] [Etching Step] In this step, the resist pattern formed in the development step is used as a mask to etch the metal layer 21 and the MTJ layer 10. This step makes it possible to obtain the patterned MTJ element 1 shown in FIG.

[0156] Examples of etching methods include reactive ion etching (RIE) and ion beam etching. Reactive ion etching is performed using sulfur hexafluoride (SF ６ ), chlorine and argon (Cl ２Examples of the dry etching include dry etching using an ion beam such as an argon ion beam as an etching gas. The resist mask formed from the resist composition described above has high resistance to these etching methods, so the resist mask does not collapse and the MTJ element 1 can be formed in a desired shape with high precision.

[0157] The present invention will be specifically described below based on examples, but the present invention is not limited to these examples.

[0158] <Synthesis of Polymer [A]> Polymer (A-1) was synthesized as Polymer [A] according to the following method. Compounds represented by the following formulas (M-1) to (M-3) (hereinafter also referred to as "monomers (M-1) to (M-3)") were used in the synthesis of Polymer [A]. In the following synthesis examples, unless otherwise specified, "parts by mass" means a value when the total mass of the monomers used is taken as 100 parts by mass, and "mol %" means a value when the total number of moles of the monomers used is taken as 100 mol %.

[0159]

[0160] Synthesis Example: Synthesis of Polymer (A-1) Monomer (M-1), monomer (M-2), and monomer (M-3) were dissolved in 60 parts by mass of 1-methoxy-2-propanol so that the molar ratio of the structural units in the final polymer was 35 / 45 / 20. Next, 3.5 mol % of 2-cyano-2-propyldodecyl trithiocarbonate as a chain transfer agent and 0.7 mol % of azobisisobutyronitrile (AIBN) as a polymerization initiator were added to the solution to prepare a monomer solution. After purging the monomer solution with nitrogen for 30 minutes, the monomer solution was heated to 80°C with stirring. The polymerization reaction was initiated when the temperature of the monomer solution reached 80°C, and the polymerization reaction was carried out for 6 hours. After completion of the polymerization reaction, a solution prepared by dissolving 14.3 mol % of AIBN based on all monomers and 17.8 mol % of tert-dodecanethiol based on all monomers in 50 parts by mass of 1-methoxy-2-propanol was added dropwise over 15 minutes while the temperature of the polymerization reaction solution was maintained at 80° C. After completion of the dropwise addition, the mixture was heated at 80° C. for 2 hours to perform terminal treatment, and then the polymerization reaction solution was cooled with water to 30° C. or less.

[0161] The cooled polymerization reaction solution was added to 500 parts by mass of hexane per 100 parts by mass of the polymerization reaction solution, and the precipitated white powder was filtered off. The filtered white powder was washed twice with 100 parts by mass of hexane per 100 parts by mass of the polymerization reaction solution, then filtered off and dissolved in 300 parts by mass of 1-methoxy-2-propanol. Next, 500 parts by mass of methanol, 50 parts by mass of triethylamine, and 10 parts by mass of ultrapure water were added, and a hydrolysis reaction was carried out at 70°C for 6 hours with stirring. After completion of the reaction, the remaining solvent was distilled off, and the resulting product was purified again with an organic solvent, separated, and dried to synthesize a white powdery polymer (A-1).

[0162] <Preparation of Resist Composition> The acid generator [B] and acid diffusion controller [C] used in the preparation of the resist composition are shown below. As the acid generator [B], a compound represented by the following formula (B-1) (hereinafter also referred to as "acid generator (B-1)") was used. As the acid diffusion controller [C], a compound represented by the following formula (C-1) (hereinafter also referred to as "acid diffusion controller (C-1)") was used. In the following examples, unless otherwise specified, "parts by mass" means the value when the mass of the polymer [A] used is taken as 100 parts by mass, and "mol %" means the value when the number of moles of the acid generator [B] used is taken as 100 mol %.

[0163]

[0164] [Example] Preparation of Resist Composition (R-1) [A] 100 parts by mass of (A-1) as a polymer, [B] 20 parts by mass of (B-1) as an acid generator, [C] 30 mol % of (C-1) as an acid diffusion controller relative to the (B-1), and [D] 4,800 parts by mass of propylene glycol monomethyl ether acetate and 2,000 parts by mass of cyclohexanone as a solvent were mixed. The resulting mixture was filtered through a membrane filter with a pore size of 0.2 μm to prepare a radiation-sensitive resin composition (R-1).

[0165] <Formation of Resist Pattern> The MTJ element was formed by laminating a 30 nm thick metal layer (second electrode) containing tungsten, an MTJ layer, and a 10 nm thick metal layer (first electrode) containing tantalum on a silicon substrate in this order. The MTJ layer had a free magnetic layer and a fixed magnetic layer made of Mn with a thickness of 30 nm. ３The insulating layer was a layer containing Sn, and the insulating layer was a 2 nm thick layer containing magnesium oxide. The resist composition (R-1) prepared above was applied to the first electrode on the MTJ element, and then subjected to PB at 130°C for 60 seconds, followed by cooling at 23°C for 30 seconds to form a 55 nm thick resist film. Next, this resist film was irradiated with EUV using an EUV exposure machine (model "NXE3300", manufactured by ASML, NA = 0.33, illumination conditions: Conventional s = 0.89). Next, PEB was performed at 110°C for 60 seconds, followed by cooling at 23°C for 30 seconds, and development was performed using a 2.38 mass% TMAH aqueous solution at 23°C for 30 seconds to form a positive 40 nm pillar pattern.

[0166] <Evaluation> The 40-nm pillar pattern formed above was observed from above the pattern, and the diameter was measured at a total of 50 arbitrary points. The 3-sigma value was calculated from the distribution of the measured values, and this 3-sigma value was designated as CDU (unit: nm). The smaller the CDU value, the smaller the diameter variation, indicating better CDU performance. CDU performance can be evaluated as "good" when it is 3.1 nm or less, and as "poor" when it exceeds 3.1 nm. If the CDU performance of the resist pattern is poor, i.e., if the diameter variation is large, the variation will be transferred to the MTJ element during the etching process, increasing the variation in the MTJ element, making it difficult to manufacture the MTJ element with high precision. The CDU value of the 40-nm pillar pattern formed above was 3.0 nm, indicating good CDU performance.

[0167] Next, using the formed resist film as a mask, the MTJ layer was etched by argon ion beam etching together with the silicon oxide film and the first electrode to pattern the MTJ element 1. As a result, it was possible to manufacture the MTJ element with high precision without transferring roughness to the MTJ element.

[0168] REFERENCE SIGNS LIST 1 MTJ element 10 MTJ layer 11 free magnetization layer 12 fixed magnetization layer 13 insulating layer 21 metal layer (first electrode) 22 metal layer (second electrode) 42 interlayer film 5 substrate

Claims

1. A method for manufacturing a magnetic tunnel junction element having a magnetic tunnel junction layer and a metal layer directly or indirectly on a substrate in this order, the method comprising the steps of: applying a resist composition containing a polymer having a structural unit including an aromatic ring onto the metal layer; exposing the resist film formed by the application step; developing the exposed resist film; and etching the magnetic tunnel junction layer and the metal layer using the resist pattern formed by the development step as a mask.

2. The method of claim 1, wherein said metal layer contains at least one selected from the group consisting of aluminum, tungsten, titanium, ruthenium and tantalum.

3. The method for producing a magnetic tunnel junction element according to claim 1, wherein the polymer has a first structural unit containing a phenolic hydroxyl group, and the resist composition contains a radiation-sensitive acid generator.

4. The method for producing a magnetic tunnel junction element according to claim 3, wherein the polymer further comprises a second structural unit containing an acid dissociable group.

5. The magnetic tunnel junction layer includes a free magnetic layer, an insulating layer, and a fixed magnetic layer, and at least one of the free magnetic layer and the fixed magnetic layer is made of Mn. ３＋ｒ X １－ｒ 6. The method for manufacturing a magnetic tunnel junction element according to claim 1, further comprising: forming an antiferromagnetic material represented by the formula: (X represents Sn, Ge, Ga, Pt, Rh, Ir, or Pd; r is a number satisfying −0.2≦r≦0.2).

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