Method for manufacturing magnetic tunnel junction element

Abstract

A method for manufacturing a magnetic tunnel junction element comprising a magnetic tunnel junction layer and a metal layer directly or indirectly on a substrate in this order, the method comprising: a step for forming a resist underlayer film on the metal layer; a step for forming a silicon oxide film on the resist underlayer film; and a step for forming a resist film on the silicon oxide film, wherein the resist underlayer film is formed from a resist underlayer film-forming composition containing a compound having an aromatic ring and a solvent.

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-mentioned problems 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 forming a resist underlayer film on the metal layer, forming a silicon oxide film on the resist underlayer film, and forming a resist film on the silicon oxide film, wherein the resist underlayer film is formed from a composition for forming a resist underlayer film, which contains a compound having an aromatic ring and a solvent.

[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. FIG. 3 is a schematic diagram showing a resist film patterning step. FIG. 4 is a schematic diagram showing a resist film patterning step. FIG. 5 is a schematic diagram showing a silicon oxide film etching step. FIG. 6 is a schematic diagram showing a resist underlayer film etching step. FIG. 7 is a schematic diagram showing an MTJ layer etching step. FIG. 8 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 with reference to 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, which are stacked in this order directly or indirectly on a substrate 5. In Fig. 1, the MTJ element 1 includes an interlayer film 42, a metal layer 22, the MTJ layer 10, and a metal layer 21 stacked in this order on the substrate 5.

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

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

[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 free magnetic layer 11 and / or the pinned magnetic layer 12. In addition, Mn, which makes it possible to detect the magnetization direction by utilizing the anomalous Hall effect, is used for the free magnetic layer 11 and / or the pinned magnetic layer 12. ３ At least one of the magnetic layers 31 and 33 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 a step of forming a resist underlayer film on the metal layer (hereinafter also referred to as a "resist underlayer film forming step"), a step of forming a silicon oxide film on the resist underlayer film (hereinafter also referred to as a "silicon oxide film forming step"), and a step of forming a resist film on the silicon oxide film (hereinafter also referred to as a "resist film forming step").

[0026] This MTJ element manufacturing method allows for high-precision manufacturing of MTJ elements. When miniaturizing MTJ elements, if the thickness of the resist film used is reduced without changing its thickness, i.e., if the pattern width is narrowed, the aspect ratio of the resist pattern after development increases, potentially resulting in pattern collapse. Therefore, the resist film thickness must be reduced as the miniaturization progresses to ensure that the aspect ratio of the resist pattern falls within an appropriate range. However, reducing the resist film thickness reduces the accuracy of pattern transfer to the workpiece. If the accuracy of pattern transfer decreases and the roughness of the MTJ element deteriorates, the magnetic properties of the MTJ element may deteriorate. One method for solving this problem is the multilayer resist method. In this method, a silicon oxide film, which has a different etching selectivity from the resist film, is interposed between the resist film and the resist underlayer film. After obtaining a pattern in the resist film, the pattern is transferred to the silicon oxide film by etching using the upper resist pattern as an etching mask, and then the pattern is transferred to the resist underlayer film by etching using the silicon oxide film as an etching mask. By adopting such a method in the miniaturization process of the MTJ element, it becomes possible to manufacture the MTJ element with high precision without causing the resist to collapse.

[0027] Preferably, the method for manufacturing the MTJ element further includes a step of patterning the resist film (hereinafter also referred to as a "resist film patterning step"), a step of etching the silicon oxide film with a gas containing fluorine using the patterned resist film as a mask (hereinafter also referred to as a "silicon oxide film etching step"), a step of etching the resist underlayer film with a gas containing at least one of oxygen and nitrogen using the silicon oxide film as a mask (hereinafter also referred to as a "resist underlayer film etching step"), and a step of etching the metal layer and the magnetic tunnel junction layer with an ion beam using the resist underlayer film as a mask (hereinafter also referred to as an "MTJ layer etching step").

[0028] Each step of the method for manufacturing the MTJ element will be described below.

[0029] [Resist Underlayer Film Forming Step] In this step, a resist underlayer film 62 is formed on the metal layer 21. The resist underlayer film 62 is formed from a composition for forming a resist underlayer film containing a compound having an aromatic ring and a solvent. The resist underlayer film 62 can be formed, for example, by coating the composition for forming a resist underlayer film on the metal layer 21 and heating it.

[0030] The compound having an aromatic ring may be a polymer or a low molecular weight compound, but is preferably a polymer. In this specification, "polymer" means a compound having a repeating unit, and "low molecular weight compound" means a non-polymer compound that does not have a molecular weight distribution and has a molecular weight of 1,000 or less.

[0031] Examples of aromatic rings include aromatic hydrocarbon rings having 6 to 20 ring members and aromatic heterocyclic rings having 5 to 20 ring members. The term "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] When the compound having an aromatic ring is a polymer, examples of the polymer (polymer having an aromatic ring) include novolak resin, resol resin, styrene resin, acenaphthylene resin, indene resin, arylene resin, triazine resin, and calixarene resin.

[0035] (Novolac Resin) A novolac resin is a resin obtained by reacting a phenolic compound with an aldehyde or a divinyl compound using an acid catalyst. A plurality of phenolic compounds and aldehydes or divinyl compounds may be mixed and reacted.

[0036] Examples of the phenolic compound include phenols such as phenol, cresol, xylenol, resorcinol, bisphenol A, p-tert-butylphenol, p-octylphenol, 9,9-bis(4-hydroxyphenyl)fluorene, 9,9-bis(3-hydroxyphenyl)fluorene, and 4,4'-(α-methylbenzylidene)bisphenol; naphthols such as α-naphthol, β-naphthol, 1,5-dihydroxynaphthalene, 2,7-dihydroxynaphthalene, and 9,9-bis(6-hydroxynaphthyl)fluorene; anthrols such as 9-anthrol; and pyrenols such as 1-hydroxypyrene and 2-hydroxypyrene.

[0037] Examples of aldehydes include aldehydes such as formaldehyde, benzaldehyde, 1-naphthaldehyde, 2-naphthaldehyde, and 1-formylpyrene, and aldehyde sources such as paraformaldehyde and trioxane.

[0038] Examples of divinyl compounds include divinylbenzene, dicyclopentadiene, tetrahydroindene, 4-vinylcyclohexene, 5-vinylnorborna-2-ene, divinylpyrene, limonene, and 5-vinylnorbornadiene.

[0039] Examples of novolak resins include resins having a structural unit derived from phenol and formaldehyde, resins having a structural unit derived from cresol and formaldehyde, resins having a structural unit derived from dihydroxynaphthalene and formaldehyde, resins having a structural unit derived from fluorene bisphenol and formaldehyde, resins having a structural unit derived from fluorene bisnaphthol and formaldehyde, resins having a structural unit derived from hydroxypyrene and formaldehyde, resins having a structural unit derived from hydroxypyrene and naphthaldehyde, resins having a structural unit derived from 4,4'-(α-methylbenzylidene)bisphenol and formaldehyde, resins having a structural unit derived from a phenol compound and formylpyrene, resins combining these, and resins in which some or all of the hydrogen atoms of the phenolic hydroxyl groups of these resins have been substituted with propargyl groups or the like.

[0040] (Resole Resin) A resole resin is a resin obtained by reacting a phenolic compound with an aldehyde using an alkaline catalyst.

[0041] (Styrene Resin) The styrene resin is a resin having a structural unit derived from a compound having an aromatic ring and a polymerizable carbon-carbon double bond. In addition to the above structural units, the styrene resin may also have a structural unit derived from an acrylic monomer, a vinyl ether, or the like.

[0042] Examples of styrene resins include polystyrene, polyvinylnaphthalene, polyhydroxystyrene, polyphenyl(meth)acrylate, and resins made by combining these.

[0043] (Acenaphthylene Resin) The acenaphthylene resin is a resin having a structural unit derived from a compound having an acenaphthylene skeleton.

[0044] Examples of acenaphthylene resins include copolymers of acenaphthylene and hydroxymethylacenaphthylene.

[0045] (Indene Resin) An indene resin is a resin having a structural unit derived from a compound having an indene skeleton.

[0046] (Arylene Resin) The arylene resin is a resin having a structural unit derived from a compound containing an arylene skeleton. Examples of the arylene skeleton include a phenylene skeleton, a naphthylene skeleton, and a biphenylene skeleton.

[0047] Examples of the arylene resin include polyarylene ether, polyarylene sulfide, polyarylene ether sulfone, polyarylene ether ketone, a resin having a structural unit containing a biphenylene skeleton, and a resin having a structural unit containing a biphenylene skeleton and a structural unit derived from a compound containing an acenaphthylene skeleton.

[0048] (Triazine Resin) The triazine resin is a resin having a structural unit derived from a compound having a triazine skeleton.

[0049] Examples of compounds having a triazine skeleton include melamine compounds and cyanuric acid compounds.

[0050] When the polymer is a novolac resin, a resol resin, a styrene resin, an acenaphthylene resin, an indene resin, an arylene resin, or a triazine resin, the lower limit of the weight average molecular weight (Mw) in terms of polystyrene measured by gel permeation chromatography (GPC) is preferably 1,000, more preferably 2,000, even more preferably 3,000, and particularly preferably 4,000. The upper limit of Mw is preferably 100,000, more preferably 60,000, even more preferably 30,000, and particularly preferably 15,000.

[0051] The upper limit of Mw / Mn (Mn is the number average molecular weight in terms of polystyrene measured by GPC) of the polymer is preferably 5, more preferably 3, and still more preferably 2. The lower limit of Mw / Mn is usually 1, and preferably 1.2.

[0052] In this specification, the Mw and Mn of a polymer are values ​​measured by gel permeation chromatography (detector: differential refractometer) using GPC columns (two "G2000HXL," one "G3000HXL," and one "G4000HXL" manufactured by Tosoh Corporation) under the analysis conditions of a flow rate of 1.0 mL / min, an elution solvent: tetrahydrofuran, and a column temperature of 40°C, with monodisperse polystyrene as a standard.

[0053] (Calixarene Resin) Calixarene resin is a cyclic oligomer in which multiple aromatic rings to which hydroxy groups are bonded are cyclically bonded via hydrocarbon groups, or a resin in which some or all of the hydrogen atoms of the hydroxy groups, aromatic rings, and hydrocarbon groups have been substituted.

[0054] Examples of calixarene resins include cyclic tetramers to dodecamers formed from phenolic compounds such as phenol and naphthol and formaldehyde, cyclic tetramers to dodecamers formed from phenolic compounds such as phenol and naphthol and benzaldehyde compounds, and resins in which the hydrogen atoms of the phenolic hydroxyl groups of these cyclic compounds have been substituted with propargyl groups or the like.

[0055] The lower limit of the molecular weight of the calixarene resin is preferably 500, more preferably 700, and even more preferably 1,000. The upper limit of the molecular weight is preferably 5,000, more preferably 3,000, and even more preferably 1,500.

[0056] The polymer is preferably a novolac resin.

[0057] The solvent is not particularly limited as long as it can dissolve or disperse at least the compound, and examples of the solvent include alcohol-based solvents, ether-based solvents, ketone-based solvents, amide-based solvents, ester-based solvents, and hydrocarbon-based solvents.

[0058] 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.

[0059] 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.

[0060] 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.

[0061] 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.

[0062] 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.

[0063] 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.

[0064] Specific examples of the composition for forming a resist underlayer film include those described in, for example, JP-A-2012-145897, JP-A-2013-253227, WO 2018 / 173446, WO 2018 / 179704, etc.

[0065] [Silicon oxide film forming step] In this step, a silicon oxide film 61 is formed on the resist underlayer film 62 formed in the resist underlayer film forming step. The silicon oxide film 61 is formed from a silicon oxide film forming composition. The silicon oxide film 61 preferably has a silicon content of 10 mass % or more. For example, the silicon oxide film 61 may be formed by applying the silicon oxide film forming composition on the resist underlayer film 62 and heating the composition.

[0066] Examples of the silicon oxide film-forming composition include a composition containing polysiloxane and a solvent. Specific examples of the silicon oxide film-forming composition include those described in JP-A-2007-302873.

[0067] [Resist Film Forming Step] In this step, a resist film 60 is formed on the silicon oxide film 61 formed in the silicon oxide film forming step. The resist film 60 is formed from a resist composition. For example, the resist film 60 can be formed by applying the resist composition onto the silicon oxide film 61 and heating it.

[0068] The resist composition may be, for example, a positive or negative KrF resist or ArF resist, or a resist material that is easily altered by halogens or ions. Resists for EUV exposure or nanoimprint resist materials may also be used. Specific examples of negative resist compositions include those described in JP-A-2003-076019.

[0069] [Resist Film Patterning Process] This process will be described with reference to FIGS. 3 and 4. In this process, the resist film 60 is patterned. As a method for patterning the resist film 60, for example, as shown in FIG. 3, the resist film 60 is patterned into a predetermined pattern using lithography technology via a photomask 63. For example, the resist film 60 is processed into a line and space pattern with a half pitch of about 50 nm. As a result, the resist film 60 is patterned as shown in FIG. 4.

[0070] More specifically, the resist film 60 can be patterned by exposing the resist film 60 to light and developing the exposed resist film 60 .

[0071] The radiation used for exposure is appropriately selected from, for example, 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, depending on the type of radiation-sensitive acid generator used in the resist film-forming composition. Among these, far ultraviolet light or electron beams are preferred, and KrF excimer laser light (248 nm), ArF excimer laser light (193 nm), extreme ultraviolet light (wavelength 13.5 nm, etc., EUV), or electron beams are more preferred.

[0072] In the case of alkaline development, examples of the developer include basic aqueous solutions of sodium hydroxide, potassium hydroxide, sodium carbonate, sodium silicate, sodium metasilicate, ammonia, ethylamine, n-propylamine, diethylamine, di-n-propylamine, triethylamine, methyldiethylamine, dimethylethanolamine, triethanolamine, tetramethylammonium hydroxide (TMAH), tetraethylammonium hydroxide, pyrrole, piperidine, choline, 1,8-diazabicyclo[5.4.0]-7-undecene, and 1,5-diazabicyclo[4.3.0]-5-nonene. These basic aqueous solutions may also contain an appropriate amount of a water-soluble organic solvent, such as an alcohol, for example, methanol or ethanol, or a surfactant. In the case of organic solvent development, examples include the organic solvents exemplified above as solvents for the composition for forming a resist underlayer film.

[0073] [Silicon Oxide Film Etching Step] This step will be described with reference to FIG. 5. In this step, the silicon oxide film 61 is etched with a gas containing fluorine using the patterned resist film 60 as a mask. The fluorine-containing gas is trifluoromethane (CHF ３ ), hydrogen bromide (HBr) and oxygen (O ２ ) can be used as a mixed gas.

[0074] After this process, the resist film 60 used as a mask is removed using, for example, a resist stripper. Examples of resist strippers include organic solvents such as aminoethanol, aminopropanol, aminoisopropanol, aminobutanol, aminopentanol, aminohexanol, propylene glycol monomethyl ether acetate, propylene glycol monomethyl ether, cyclohexanone, acetone, N-methyl-2-pyrrolidone, ethyl lactate, and methyl amyl ketone, or strippers made from combinations of these. The resist film 60 may also be removed using a gas such as plasma or ozone.

[0075] [Resist Underlayer Film Etching Step] This step will be described with reference to Fig. 6. In this step, the resist underlayer film 62 is etched with a gas containing at least one of oxygen and nitrogen, using the silicon oxide film 61 as a mask.

[0076] After this process, the silicon oxide film 61 used as a mask is removed with, for example, an APM cleaning solution (a cleaning solution composed of ammonia water, hydrogen peroxide water, and pure water in a volume ratio of 1:1 to 2:5 to 7).

[0077] 7 and 8. In this step, the metal layer 21 and the MTJ layer 1 are etched with an ion beam using the resist underlayer film 62 as a mask. The ion beam may be an argon ion beam or the like.

[0078] After this step, the resist underlayer film 62 used as a mask is removed, for example, with an etching gas containing oxygen, thereby obtaining the patterned MTJ element shown in Fig. 8. The resist underlayer film 62 may also be removed by wet etching using a stripping solution or the like.

[0079] The present invention will be specifically described below based on examples, but the present invention is not limited to these examples.

[0080] <Preparation of composition for forming resist underlayer film> A polymer having a structure represented by the following formula and triphenylsulfonium trifluoromethanesulfonate as an acid generator were mixed with propylene glycol methyl ether and propylene glycol monomethyl ether acetate as a solvent, and the mixture was stirred for 1 hour to prepare a composition for forming a resist underlayer film (U-1).

[0081]

[0082] <Preparation of Silicon Oxide Film-Forming Composition> A polysiloxane having a structure represented by the following formula was mixed with propylene glycol ethyl ether as a solvent, and the mixture was stirred for 1 hour to prepare a silicon oxide film-forming composition (S-1).

[0083]

[0084] <Preparation of Resist Composition> (Polymer Synthesis) 100 g of p-t-butoxystyrene, 10 g of styrene, and 9.0 g of azobisisobutyronitrile were dissolved in propylene glycol monomethyl ether and subjected to a polymerization reaction at 80°C for 9 hours. The polymerization solution was purified by reprecipitation with methanol, yielding 100 g of p-t-butoxystyrene / styrene copolymer with a Mw of 7,300 and a Mw / Mn of 1.80. This copolymer and 50 g of 10 wt% aqueous sulfuric acid were dissolved in 300 g of propylene glycol monomethyl ether and subjected to acid hydrolysis at 90°C for 6 hours. The reaction solution was purified by reprecipitation with a large amount of water until neutral, yielding a p-hydroxystyrene / styrene = 85 / 15 mol% copolymer with a Mw of 5,500 and a Mw / Mn of 1.55.

[0085] (Preparation of Resist Composition) The p-hydroxystyrene / styrene=85 / 15 mol % copolymer obtained above, diphenyl-4-hydroxyphenylsulfonium trifluoromethanesulfonate as an acid generator, N,N,N,N-tetra(methoxymethyl)glycoluril as an acid crosslinker, and triphenylsulfonium salicylate as an acid diffusion controller were dissolved in a mixed solvent of ethyl lactate and 3-ethoxyethyl propionate, and the resulting mixture was filtered through a membrane filter with a pore size of 0.2 μm to prepare resist composition (R-1).

[0086] <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 layer containing magnesium oxide and having a thickness of 2 nm. The resist underlayer film-forming composition (U-1) was applied onto the first electrode of the MTJ element, followed by 60 seconds of preheating at 300°C, followed by cooling at 23°C for 30 seconds, to form a resist underlayer film with an average film thickness of 85 nm. The silicon oxide film-forming composition (S-1) was applied onto the resist underlayer film, followed by 60 seconds of preheating at 200°C, followed by cooling at 23°C for 30 seconds, to form a silicon oxide film with an average film thickness of 15 nm. The resist composition (R-1) was applied onto the silicon oxide film, followed by 60 seconds of preheating at 110°C, followed by cooling at 23°C for 30 seconds, to form a resist film with an average film thickness of 50 nm.

[0087] The wafer 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. Development was then performed using a 2.38% by mass aqueous TMAH solution at 23°C for 30 seconds to form a 50 nm pillar pattern.

[0088] <Evaluation> The 50-nm pillar pattern formed above was observed from above the pattern, and the pillar 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 50-nm pillar pattern formed above was 3.0 nm, indicating good CDU performance.

[0089] Using the resist pattern formed above as a resist mask, trifluoromethane (CHF ３ ) and oxygen (O ２The silicon oxide film was etched using a gas mixture of oxygen and argon. Next, the resist underlayer film was etched using the processed silicon oxide film as a mask with an oxygen-containing gas. Using the resist underlayer film as a mask, the MTJ layer was etched together with the silicon oxide film and the first electrode by argon ion beam etching 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.

[0090] 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 60 resist film 61 silicon oxide film 62 resist underlayer film 63 photomask

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, comprising the steps of forming a resist underlayer film on the metal layer, forming a silicon oxide film on the resist underlayer film, and forming a resist film on the silicon oxide film, wherein the resist underlayer film is formed from a composition for forming a resist underlayer film, which contains a compound having an aromatic ring and a solvent.

2. The method for manufacturing a magnetic tunnel junction element according to claim 1, further comprising the steps of: patterning the resist film; etching the silicon oxide film with a gas containing fluorine using the patterned resist film as a mask; etching the resist underlayer film with a gas containing at least one of oxygen and nitrogen using the silicon oxide film as a mask; and etching the metal layer and the magnetic tunnel junction layer with an ion beam using the resist underlayer film as a mask.

3. The method for producing a magnetic tunnel junction element according to claim 1, wherein the silicon oxide film is formed from a composition for forming a silicon oxide film containing polysiloxane and a solvent.

4. 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.

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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