Sacrificial composition, method for producing device, and acoustic wave device

Abstract

Provided is a sacrificial composition. The sacrificial composition comprises a polymer (A) that undergoes acid-catalyzed decomposition, a compound (B) that generates an acid by heat, and a solvent (C), wherein the compound (B) that generates the acid by heat consists of a carboxylic acid and a base, and a content of the compound (B) is 1 to 60 parts by mass based on 100 parts by mass of the polymer (A). The sacrificial composition may exhibit at least one of properties as an advanced material or as a high performance material. The sacrificial composition may be used in the nanotechnology process to make semiconductor device / display device application, for example semiconductor chip, or a liquid crystal, quantum dot, OLED display fabricated on a substrate controlled by semiconductors.

Description

[DESCRIPTION][Title of Invention]SACRIFICIAL COMPOSITION, METHOD FOR PRODUCING DEVICE, AND ACOUSTIC WAVE DEVICE[Technical Field]

[0001] The present disclosure relates to a sacrificial composition, a method for producing a device, and an acoustic wave device.[Background Art]

[0002] Acoustic wave devices are widely used, for example, as devices having filter functions in high-frequency circuits of wireless devices, typically cellular phones.In an acoustic wave device, it is necessary to provide a cavity near the electrode surface where the acoustic wave is excited to secure a vibration space and to seal this vibration space. As a method for forming a cavity, a method comprising forming a sacrificial layer from a sacrificial material, such as silicon dioxide, and removing the sacrificial layer by wet etching, dry etching, or the like in the subsequent step has been proposed (for example, PTL 1).

[0003] As a sacrificial material for forming a sacrificial layer, PTL 2 describes a composition containing a sacrificial polymer that undergoes acid-catalyzed decomposition and a catalytic amount of a photo-acid generator. PTL 3 describes a coating composition containing a polycarbonate having an aliphatic ring in a polymer main chain as a sacrificial polymer. PTL 4 describes a resin layer containing a photo-acid generator and a resin component.[Citation List][Patent Literature]

[0004] [PTL 1 ] JP 2012-182854 A[PTL 2] JP 2006-504853 A[PTL 3] JP 2004-207475 A[PTL 4] JP 2012-222174 A[Summary of Invention][Technical Problem]

[0005] The inventors believed that one or more problems that require improvement still exist in a sacrificial composition. Examples of the problems include the following:residue of films (darkened portion) occurs upon removal of the sacrificial layer; a long time is required to remove the sacrificial layer; a high temperature heat treatment is required to remove the sacrificial layer; a removing agent is required to remove the sacrificial layer; a thick sacrificial layer cannot be used; production costs are high; long time is required for production; and device yields are low.

[0006] The present invention has been made on the basis of the above technical background, and provides a sacrificial composition, a method for producing a device, and an acoustic wave device.[Solution to Problem]

[0007] A sacrificial composition of one embodiment comprises a polymer (A) that undergoes acid-catalyzed decomposition, a compound (B) that generates an acid by heat, and a solvent (C),whereinthe compound (B) that generates the acid by heat consists of a carboxylic acid and a base, and a content of the compound (B) is 1 to 60 parts by mass based on 100 parts by mass of the polymer (A).

[0008] The method for producing a device of one embodiment comprises the steps of:applying the sacrificial composition above a substrate to form a sacrificial layer;forming a lid above the sacrificial layer; andremoving the sacrificial layer by heating to form a cavity.

[0009] An acoustic wave device of one embodiment has a cavity formed by the method for producing a device.[Techinical Effects of Invention]

[0010] According to the present disclosure, it is possible to desire one or more of the following effects:the occurrence of residue of films (darkened portion) during the removal of the sacrificial layer can be suppressed; the sacrificial layer can be removed in a sufficiently short time; the sacrificial layer can be removed at sufficiently low temperature; no removing agent is required to remove the sacrificial layer; a sufficiently thick sacrificial layer can be used; production costs are sufficiently low; production time is reduced; and device yields are sufficiently high.

[0011] The above description is not to be construed as disclosing all embodiments of the present invention and all advantages related to the present invention.[Brief Description of Drawings]

[0012] [Fig. 1 A] Fig. 1 A is an exemplary explanatory view of a method for producing an acoustic wave device of a first embodiment.[Fig. 1 B] Fig. 1 B is an exemplary explanatory view of a method for producing an acoustic wave device of a first embodiment.[Fig. 2A] Fig. 2A is an exemplary explanatory view of a method for producing an acoustic wave device of a second embodiment.[Fig. 2B] Fig. 2B is an exemplary explanatory view of a method for producing an acoustic wave device of a second embodiment.[Fig. 2C] Fig. 2C is an exemplary explanatory view of a method for producing an acoustic wave device of a second embodiment.[Description of Embodiments]

[0013] Embodiments of the present invention will be described below, but the present invention is not limited to these embodiments, and variousapplications can be made within the spirit and scope of the present invention.

[0014] [Definitions]In the present disclosure, unless otherwise specifically stated, terms and symbols follow the definitions or examples described in this paragraph. The singular form includes the plural form, and the terms “a / an” and “the” mean “at least one.” An element of a certain concept can be expressed as a plurality of types, and when an amount thereof (for example, mass% or mol%) is expressed, the amount is the sum of the amounts of the plurality of types.The term “and / or” includes all combinations of elements, or also includes the use of a single element.When a numerical range is expressed using “to” or the range includes values at both ends, and the units are the same. For example, 5 to 25 mol% is 5 mol% or more and 25 mol% or less.Notations such as “Cx-y”, “Cx to Cy”, and “Cx” refer to the number of carbon atoms in a molecule or substituent. For example, C1-6 alkyl refers to an alkyl chain having 1 or more and 6 or less carbon atoms (methyl, ethyl, propyl, butyl, pentyl, hexyl, and the like).Aromatic hydrocarbons include polycyclic aromatic hydrocarbons.When a polymer has a plurality of structural units, monomers that form these structural units are copolymerized in the polymer. The copolymerization may be any of alternating copolymerization, random copolymerization, block copolymerization, graft copolymerization, or a mixture thereof. When polymers and resins are represented by structural formulae, the symbols n, m, and the like in parentheses indicate the number of structural units.Degrees Celsius is used as the temperature unit. For example, 20 degrees is 20 degrees Celsius.An additive means a compound itself that exhibits the function. For example, a base generator is a compound itself that generates a base. The compound may be in a dissolved or dispersed form in a solvent, which is tobe added to a composition. In one embodiment, such a solvent is preferably contained in the composition of the present disclosure as the solvent (C) or another component.

[0015] <Sacrificial Composition>The sacrificial composition of one embodiment comprises a polymer (A) that undergoes acid-catalyzed decomposition (hereinafter simply referred to as “polymer (A)”), a compound (B) that generates an acid by heat (hereinafter simply referred to as “compound (B)”), and a solvent (C). The compound (B) that generates an acid by heat consists of a carboxylic acid and a base.

[0016] Combining the polymer (A)with the compound (B) makes it possible to completely eliminate the residual film that occurs before the completion of the thermal decomposition in a short time when the sacrificial layer formed using the sacrificial composition of the present disclosure is thermally decomposed. The residual film is a thin film with a thickness of several nanometers to several tens of nanometers and may be visible as a darkened portion. A darkened portion is observed, in particular, when sulfonic acid-based acids are used as the decomposition catalyst for the polymer (A). Without being bound by theory, in the case that a photo-acid generator is used, a lot of acids are generated near the surface of the sacrificial layer on which radiation, such as an ultraviolet ray, is incident. The photo-acid generator absorbs radiation while the radiation travels through the thickness direction of the sacrificial layer. As a result, the amount of acid generated decreases in the deep portion of the sacrificial layer. Therefore, in order to decompose the polymer (A) in the deep portion of the sacrificial layer, it takes time for the acid to diffuse from near the surface of the sacrificial layer toward the deep portion of the sacrificial layer. As a result, the decomposition of the polymer (A) progresses non-uniformly in the depth direction of the sacrificial layer. Meanwhile, the compound (B) of the present disclosure is a thermal acid generator (TAG), and TAG generates an acid throughout the thickness of the sacrificial layer upon heating the sacrificial layer. Thus, the decomposition of the polymer(A) also progresses at the deep portion of the sacrificial layer from the initial stage of heating. It is believed that this can decompose even a thick sacrificial layer in a short time and effectively eliminate the residual film. In addition, by using a carboxylic acid as the acid, it is possible to suppress the residual film from forming a darkened portion.

[0017] (A) Polymer That Undergoes Acid-Catalyzed Decomposition ReactionThe polymer (A) is not particularly limited as long as it is decomposed by an acid-catalyzed reaction. The polymer (A) preferably comprises at least one selected from the group consisting of polycarbonates, polyesters, polyethers, polyamides, polyimides, and polyurethanes. These polymers have chemical bonds that are decomposed in the presence of an acid within the structural units thereof. The polymer (A) may be used alone or in combination of two or more thereof.

[0018] The polymer (A) is more preferably a polycarbonate selected from the group consisting of polyethylene carbonate, polypropylene carbonate, poly(1 ,2-cyclohexene carbonate), poly(1 ,2-cyclohexene carbonate-co-propylene carbonate), polynorbornene carbonate, and combinations thereof, still more preferably a polycarbonate selected from the group consisting of polypropylene carbonate, poly(1 ,2-cyclohexene carbonate), and combinations thereof, and particularly preferably polypropylene carbonate. The polycarbonate is decomposed by heating in the presence of an acid via two reaction mechanisms: (i) the formation of ketones and CO2 by main chain cleavage and (ii) the formation of oxirane compounds and CO2 via a cyclization reaction.

[0019] The glass transition temperature of the polymer (A) is preferably -50 to 200°C, more preferably -50 to 180°C, and still more preferably -45 to 150°C. The polymer (A) with a glass transition temperature of -50°C or higher can enhance the shape retention of the sacrificial layer formed using the sacrificial composition. The polymer (A) with a glass transition temperature of 200°C or lower can suppress the excessive increase in internal stress of the sacrificial layer and prevent peeling of the sacrificiallayer from the substrate, breakage of a structure adjacent to the sacrificial layer, and the like. Furthermore, if the glass transition temperature is 200°C or lower, the fluidity of the sacrificial layer is increased during the thermal decomposition, so that the thermal decomposition can progress efficiently. The glass transition temperature of the polymer (A) is a value measured in air at a rate of temperature rise of 5°C / min by a thermogravimetric differential thermal analyzer (TG-DTA).

[0020] The mass average molecular weight (Mw) of the polymer (A) is preferably 5,000 to 300,000, and more preferably 10,000 to 300,000. Mw is measured by gel permeation chromatography (GPC) using polystyrene as a standard. GPC is performed using an Alliance™ e2695-type high-speed GPC system (Nihon Waters) and a Super Multipore HZ-M type GPC column (Tosoh). The measurement is performed under measurement conditions of a flow rate of 0.6 mL / min and a column temperature of 40°C with monodispersed polystyrene as a standard sample and tetrahydrofuran as an eluent, and the Mw is then calculated as the relative molecular weight to the standard sample. By setting the Mw of the polymer (A) to 5,000 or more, the film-forming property and the wettability to the substrate of the sacrificial composition can be enhanced. By setting the Mw of the polymer (A) to 300,000 or less, the solubility of the polymer (A) in the solvent (C) can be increased, and the thermal decomposability can be increased.

[0021] The content of the polymer (A) is preferably 1.0 to 50 mass%, more preferably 2.0 to 40 mass%, and still more preferably 5.0 to 35 mass%, based on the total mass of the sacrificial composition.

[0022] (B) Compound That Generates Acid by HeatThe compound (B) that generates an acid by heat consists of a carboxylic acid and a base. The compound (B) is preferably present in the form of a salt of the carboxylic acid and the base in the sacrificial composition. Heating the sacrificial layer formed using the sacrificial composition dissociates the carboxylic acid and the base, and the released carboxylic acid promotes the thermal decomposition of the polymer (A). The compound (B) may be used alone or in combination of two or more thereof.The compound (B) is preferably decomposed at 70 to 250°C to generate an acid. The decomposition temperature of the compound (B) is more preferably 80 to 200°C, and still more preferably 80 to 180°C. The decomposition temperature of the compound (B) is a value determined by the weight loss onset temperature of TG-DTA.

[0023] The compound (B) preferably generates a carboxylic acid with a pKa of 6.3 or lower. A carboxylic acid with a pKa of 6.3 or lower can effectively promote the thermal decomposition of the polymer (A). The lower limit of the pKa of the carboxylic acid is not particularly limited, and can be, for example, -10 or higher. The pKa of carboxylic acid is more preferably 0 to 5, and still more preferably 1 to 5. The pKa of the carboxylic acid is a value measured by neutralization titration.

[0024] The compound (B) preferably contains an amine with a boiling point of 70 to 400°C as a base. An amine with a boiling point of 400°C or lower can promote the evaporation of the amine upon heating to shift the equilibrium of the salt formation of the amine and the carboxylic acid toward a direction advantageous to the generation of the carboxylic acid, thereby further promoting the thermal decomposition of the polymer (A). An amine with a boiling point of 70°C or more can suppress the evaporation of the amine at room temperature and enhance the storage stability of the sacrificial composition. The boiling point of the amine is more preferably 75 to 300°C, and still more preferably 80 to 250°C.

[0025] The compound (B) is preferably a salt represented by formula (B-1).whereinn01 is 1 , 2, or 3; preferably 1 or 2; and more preferably 1 ;n02 is 0, 1 , 2, 3, or 4; preferably 0, 1 , or 2; and more preferably 0 or 1 ;X is a single bond, H, a saturated or unsaturated linear C1-20 hydrocarbon group, a saturated or unsaturated C5-10 cycloaliphatic hydrocarbon group, or a C6-10 aromatic hydrocarbon group;(i) when n01 is 1 , X is a monovalent group, and preferably C1-20 alkyl, C2-20 alkenyl, C2-20 alkynyl, C5-10 cycloalkyl, or Ce-io aryl;(ii) when n01 is 2, X is a divalent group, and preferably C1-20 alkanediyl, C2-20 alkenediyl, C2-20 alkynediyl, C5-10 cycloalkanediyl, or Ce-io aryldiyl; (iii) when n01 is 3, X is a trivalent group, and preferably C1-20 alkanetriyl, C2-20 alkenetriyl, C2-20 alkynetriyl, C5-10 cycloalkanetriyl, or Ce-io aryltriyl; X is more preferably C1-20 alkyl or Ce-io aryl; still more preferably C1-16 alkyl or phenyl;Y is a substituent on X, each independently hydroxy or C1-4 alkyl; preferably hydroxy;Z is each independently a primary amine, a secondary amine, a tertiary amine, or an alkanolamine; preferably a C2-20 secondary amine, a C3-30 tertiary amine, or a C1-30 alkanolamine; more preferably a C2-12 secondary amine, a C3-18 tertiary amine or a C3-18 alkanolamine. The number of carbon atoms of the amine is the sum of the number of carbon atoms of all hydrocarbon groups on an N atom.

[0026] Examples of preferred acids constituting the salt represented by formula (B-1) include C1-16 monocarboxylic acids such as formic acid, acetic acid, propanoic acid, butanoic acid, pentanoic acid, hexanoic acid, heptanoic acid, octanoic acid, nonanoic acid, decanoic acid, and lauric acid; C1-16 dicarboxylic acids such as oxalic acid, malonic acid, succinic acid, glutaric acid, fumaric acid, maleic acid, malic acid, tartaric acid, citraconic acid, mesaconic acid, and phthalic acid; C1-16 tricarboxylic acids such as aconitic acid; C2-16 aliphatic hydroxy carboxylic acids such as glycolic acid and lactic acid; and Ce-io aromatic hydroxy carboxylic acids such as salicylic acid and gallic acid. The aforementioned acid is preferably a C1-16 monocarboxylic acid, a C1-16 dicarboxylic acid, a C2-12 aliphatic hydroxy carboxylic acid, or a Ce-io aromatic hydroxycarboxylic acid.

[0027] Examples of amines constituting the salt represented by formula (B-1) include C1-10 primary amines such as butylamine, pentylamine, hexylamine, octylamine, decylamine, benzylamine, cyclohexylamine, aniline, toluidine, propargylamine, phenethylamine, and naphthyl amine; C2-20 secondary amines such as di-n-propylamine, diisopropylamine, dibutylamine, N-methylaniline, N-methyltoluidine, pyrrolidine, piperidine, dicyclohexylamine, dibenzylamine, N-methylcyclohexylamine, N-methylpyrrolidine, N-ethylpiperidine, and N-phenylpiperidine; C3-30 tertiary amines such as triethylamine, dimethylethylamine, tripropylamine, diisopropylmethylamine, dimethylisopropylamine, tributylamine, trihexylamine, trioctylamine, tricyclohexylamine, dimethylphenylamine, and tris(2-methoxyethoxy)ethylamine; and C1-30 alkanolamines such as ethanolamine, propanolamine, diethanolamine, triethanolamine, butanolamine, pentanolamine, and hexanolamine. The aforementioned base is preferably a C2-20 secondary amine, a C3-30 tertiary amine, or a C1-30 alkanolamine; more preferably a C2-12 secondary amine, a C3-18 tertiary amine, or a C3-18 alkanolamine.

[0028] Examples of suitable salts represented by formula (B-1 ) include a salt of octanoic acid and triethylamine, a salt of octanoic acid and tripropylamine, a salt of octanoic acid and dibutylamine, a salt of octanoic acid and tributylamine, a salt of octanoic acid and triethanolamine, a salt of lauric acid and triethylamine, a salt of lauric acid and tripropylamine, a salt of lauric acid and dibutylamine, a salt of lauric acid and tributylamine, a salt of lauric acid and triethanolamine, a salt of malonic acid and triethylamine, a salt of malonic acid and tripropylamine, a salt of malonic acid and dibutylamine, a salt of malonic acid and tributylamine, a salt of malonic acid and triethanolamine, a salt of maleic acid and triethylamine, a salt of maleic acid and tripropylamine, a salt of maleic acid and dibutylamine, a salt of maleic acid and tributylamine, a salt of maleic acid and triethanolamine, a salt of salicylic acid and triethylamine, a salt of salicylic acid and tripropylamine, a salt of salicylic acid and dibutylamine, a salt of salicylic acid and tributylamine, a salt of salicylic acid and triethanolamine, a salt oflactic acid and triethylamine, a salt of lactic acid and tripropylamine, a salt of lactic acid and dibutylamine, a salt of lactic acid and tributylamine, and a salt of lactic acid and triethanolamine.

[0029] The content of the compound (B) is preferably 1 to 60 parts by mass, more preferably 1 to 50 parts by mass, and further preferably 1 to 40 parts by mass, based on 100 parts by mass of the polymer (A). Thermal decomposition of the polymer (A) can be promoted by setting the content of the compound (B) to 1 part by mass or more based on 100 parts by mass of the polymer (A). The film-forming property of the sacrificial composition can be ensured by setting the content of the compound (B) to 60 parts by mass or less based on 100 parts by mass of the polymer (A).

[0030] The content of the acid constituting the compound (B) is preferably 0.4 to 40 parts by mass, more preferably 0.5 to 38 parts by mass, and still more preferably 0.5 to 35 parts by mass, based on 100 parts by mass of the polymer (A). Thermal decomposition of the polymer (A) can be promoted by setting the content of the acid to 0.4 parts by mass or more based on 100 parts by mass of the polymer (A). The film-forming property of the sacrificial composition can be ensured by setting the content of the acid to 40 parts by mass or less based on 100 parts by mass of the polymer (A).

[0031] (C) SolventThe solvent (C) is not particularly limited as long as it dissolves the polymer (A). The solvent (C) preferably dissolves the compound (B). The solvent (C) preferably comprises at least one selected from the group consisting of alcohols, aliphatic hydrocarbons, ethers, esters, aromatic hydrocarbons, ketones, amides, and lactones, and more preferably comprises at least one selected from the group consisting of ethers and ketones.Examples of ethers include tetrahydrofuran, tetrahydropyran, anisole, diisopropyl ether, and tert-butyl methyl ether.Examples of ketones include cyclopentanone and methyl isobutyl ketone.The solvent (C) may be used alone or in combination of two or more thereof.The content of the solvent (C) is preferably 20 to 98.99 mass%, more preferably 36 to 97.98 mass%, and still more preferably 44 to 94.95 mass%, based on the total mass of the sacrificial composition.

[0032] (D) AdditiveThe sacrificial composition may further comprise an additive (D). The additive (D) preferably comprises at least one selected from the group consisting of a surfactant, an acid, a base, an antibacterial agent, a sterilizing agent, a preservative, and an antifungal agent. The additive (D) is different from the polymer (A), the carboxylic acid and the base of the compound (B), and the solvent (C) described above.The content of the additive (D) (in the case where a plurality of additives are used, the total content thereof) is preferably 0 to 10 parts by mass, and more preferably 0 to 5 parts by mass, based on 100 parts by mass of the polymer (A). It is also a suitable embodiment that the sacrificial composition does not contain any additive (D).

[0033] <Method for Producing Device>The method for producing a device of one embodiment comprises the steps of:applying the sacrificial composition above a substrate to form a sacrificial layer;forming a lid above the sacrificial layer; andremoving the sacrificial layer by heating to form a cavity.

[0034] The material of the substrate is preferably selected from the group consisting of lithium tantalate, lithium niobate, lithium tetraborate, quartz, lanthanum gallium silicate, lanthanum gallium tantalate, aluminum nitride, aluminum scandium nitride, silicon, and sapphire.

[0035] The removal of the sacrificial layer by heating is preferably performed at 150 to 400°C, and more preferably at 180 to 400°C.

[0036] In one embodiment, the device is an acoustic wave device. The following is an illustrative description of the steps of the method forproducing a device, with reference to a plurality of embodiments of the method for producing an acoustic wave device.

[0037] <Method for Producing Acoustic Wave Device of First EmbodimentThe method for producing an acoustic wave device of a first embodiment comprises the following steps:(la) forming an electrode on a piezoelectric substrate;(Ila) forming a protective layer frame surrounding the electrode;(Illa) applying a sacrificial composition onto the electrode to form a sacrificial layer;(IVa) forming a protective layer lid on the sacrificial layer; and(Va) removing the sacrificial layer by heating to form a cavity.The steps (la) to (Va) may be performed in any order. In one preferred embodiment, the steps (la) to (Va) are performed in the stated order.

[0038] Step (la)In step (la), an electrode is formed on a piezoelectric substrate.The material of the piezoelectric substrate is preferably selected from the group consisting of lithium tantalate, lithium niobate, lithium tetraborate, quartz, lanthanum gallium silicate, lanthanum gallium tantalate, aluminum nitride, and aluminum scandium nitride, and more preferably lithium tantalate and lithium niobate. The piezoelectric substrate may be joined to a support substrate of silicon, a ceramic such as glass, quartz, sapphire, or the like, for example.Examples of the electrode formed on the piezoelectric substrate include an Interdigital Transducer (IDT), a reflective electrode, a wiring electrode, and the like. Examples of the electrode include those made of an aluminum alloy composed of Al, Au, and Al-Cu, and may be formed by forming a thin film using sputtering, vapor deposition, or a CVD method, and then patterning the thin film using photolithography. Preferably, a positive lift-off resist film is formed, then a lift-off resist pattern is formed using a photolithography method, and thereafter, an aluminum alloy thin film composed of Al-Cu is formed. The resist is removed with a resist stripper toform an electrode. The electrode preferably includes a comb-shaped electrode, and more preferably is a comb-shaped electrode.A silicon oxide film, a silicon nitride film, and the like may be formed on the electrode. The silicon oxide film, the silicon nitride film, and the like are formed by a thin film forming method such as a CVD method or a vapor deposition method. The silicon oxide film and the silicon nitride film may also be processed by a photolithography method so that at least a portion of the wiring electrode is exposed.

[0039] Step (Ila)In step (Ila), a protective layer frame surrounding the electrode is formed. The protective layer preferably comprises a protective layer frame and a protective layer lid (hereinafter simply referred to as a “frame” and a “lid”, respectively), and the lid is formed on the frame. It is more preferable that the frame is in the form surrounding the electrode, and the lid has a through hole.The protective layer frame may be processed by a photolithography method using a photosensitive composition, such as a polyimide resin, an epoxy resin, a siloxane resin, or a benzocyclobutene resin.

[0040] Step (Illa)In step (Illa), a sacrificial composition is applied to form a sacrificial layer. A sacrificial composition is applied onto the electrode. The application method is not particularly limited, and may be an ordinary application method, such as a spin coating method, an immersion method, a spraying method, a transfer method, a slit coating method, and the like.The film thickness of the sacrificial layer formed is not particularly limited, and preferably 2.0 to 50.0 pm, and more preferably 3.0 to 40.0 pm.

[0041] Step (IVa)In step (IVa), a protective layer lid is formed on the sacrificial layer.The protective layer lid is, for example, formed by a photolithography method using a photosensitive composition such as a polyimide resin, an epoxy resin, a siloxane resin, or a benzocyclobutene resin. The lid is formed preferably by using a thermosetting film, more preferably aphotosensitive polyimide film. The through hole is formed by a photolithography method or laser processing.

[0042] Step (Va)In step (Va), the sacrificial layer is removed by heating to form a cavity. In this embodiment, the sacrificial layer does not need to be dry-etched or wet-etched, and can be removed by heating. The heating temperature is preferably 150 to 400°C, and more preferably 180 to 400°C. The heating time is preferably 2 to 60 minutes, and more preferably 3 to 30 minutes. This heating dissociates the carboxylic acid and the amine of the compound (B), and the released carboxylic acid promotes the thermal decomposition of the polymer (A). As a result, the polymer is removed. In this step, it is sufficient that at least a portion of the sacrificial layer is removed and a cavity is formed. Preferably 80 vol% or more, more preferably 90 vol% or more, still more preferably 95 vol% or more of the sacrificial layer is removed. In one preferred embodiment, all (100 vol%) of the sacrificial layer is removed.

[0043] It is preferable to form the sealing layer using a resin solution such as an epoxy resin after the formation of the cavity by removing the sacrificial layer by heating. When the sealing layer is formed by applying and then curing a resin solution, it is preferable, in order to seal the through hole, to use a resin solution having a viscosity such that the resin solution does not flow into the through hole during baking.Further, a metal post is preferably formed using a metal such as Cu, Au, Ni, Al, and SnAgCu. The metal post can be formed by an electroplating method, an electroless plating method, a stud bump method, or the like. An adhesion layer of Cr or Ti may also be interposed for adhesion between the electrode and the metal post. Furthermore, it is preferable that the solder ball is formed of an alloy such as SnAgCu, SnAgln, SnCuNi, SnCuBi, SnSb, and SnBi. A thin film may be formed from a conductive material to form a flat pad.

[0044] Figs. 1 A and 1 B are exemplary explanatory views of a method for producing an acoustic wave device of a first embodiment. 1-k in Fig. 1B is aschematic cross-sectional view of an acoustic wave device of one embodiment. This figure shows only one acoustic wave device, assuming that a plurality of acoustic wave devices formed on a wafer at the same time are diced into individual pieces upon completion of production.

[0045] A substrate in which a LiTaOs piezoelectric substrate 102 is joined to a Si wafer as a support substrate 101 is prepared (1-a in Fig. 1A). A positive lift-off resist composition is coated by a spin coating method to form a resist layer 103, and the resist layer 103 is then dried. The resist layer is selectively exposed using a mask with a pattern corresponding to the IDT and the reflective electrode. Next, the resist layer is developed with an alkaline developer containing 2.38 mass% tetramethylammonium hydroxide (TMAH). An aluminum alloy film 104 composed of Al-Cu is formed by a sputtering method (1-b in Fig. 1A). The resist layer is removed with a resist stripper to form a wiring electrode for connecting the IDT and the reflective electrode with the outside (1-c in Fig. 1A). A silicon oxide film 105 made of silicon oxide is formed on the IDT, the reflective electrode, and the wiring electrode by TEOS-CVD. A part of the silicon oxide film is removed by a photolithography method so that at least a part (end) of the wiring electrode is exposed (1-d in Fig. 1A).

[0046] A photosensitive negative polyimide composition is spin-coated on a piezoelectric substrate. The protective layer frame 106 is formed by patterning exposure and development. Thereafter, a frame in which the IDT, the reflective electrode, and the wiring electrode portion are not covered with a polyimide is formed by heating (1-e in Fig. 1A).

[0047] A sacrificial composition is applied on the piezoelectric substrate on which the frame is formed, and a sacrificial layer 107 is formed by spin coating. The sacrificial layer 107 is etched back to the top surface of the polyimide frame (1-f in Fig. 1A).

[0048] A photosensitive negative polyimide film, which will form a protective layer lid, is attached onto the polyimide frame using an applicator to form a protective layer composed of the frame and the lid (1-g in Fig. 1A). The polyimide film in the wiring electrode portion and the through holeportion with a diameter of 10 pm is removed by patterning exposure and development (1-h in Fig. 1A).

[0049] The sacrificial layer is thermally decomposed by heating in air at 250°C for 360 seconds and removed through the through hole (1-i in Fig.1A). As a result, the IDT and the reflective electrode form a hollow structure with a through hole.

[0050] The through hole is sealed with a photosensitive epoxy resin to form a sealing layer 108. A part of the sealing layer located on the wiring electrode portion is removed by a patterning process using a photolithography method to expose the wiring electrode portion. Heat treatment forms a hollow portion (cavity) of the IDT and the reflective electrode (1-j in Fig. 1B).A nickel metal post 109 is formed, and a SnAgCu alloy solder ball 110 is formed thereon (1-k in Fig. 1B).An acoustic wave device can be produced in this manner.

[0051] <Method for Producing Acoustic Wave Device of Second EmbodimentThe method for producing an acoustic wave device of a second embodiment comprises the following steps:(lb) applying a sacrificial composition to a recess of a support substrate with the recess on a top surface to form a sacrificial layer;(lib) joining a piezoelectric substrate above the support substrate; and (I lib) removing the sacrificial layer by heating to form a cavity.The steps (lb) to (lllb) may be performed in any order. In one preferred embodiment, the steps (lb) to (lllb) are performed in the stated order.

[0052] Step (lb)In step (lb), a sacrificial composition is applied to the recess of the support substrate to form a sacrificial layer.Examples of the support substrate include silicon, a ceramic such as glass, quartz, sapphire, and the like, and is preferably a Si wafer. The recesses in the support substrate may be formed by, for example, applying a resist composition, such as a negative resist composition, to the supportsubstrate to form a resist pattern and dry-etching the support substrate. The application method of the sacrificial composition is not particularly limited, and may be an ordinary application method, such as a spin coating method, an immersion method, a spray method, a transfer method, a slit coating method, and the like. Thereafter, a planarization process can be performed by etching back.

[0053] Step (lib)In step (lib), the support substrate and the piezoelectric substrate are joined.The material of the piezoelectric substrate is preferably selected from the group consisting of lithium tantalate, lithium niobate, lithium tetraborate, quartz, lanthanum gallium silicate, lanthanum gallium tantalate, aluminum nitride, and aluminum scandium nitride, and more preferably lithium tantalate, and lithium niobate.Electrodes may be formed on the piezoelectric substrate. Examples of the electrode include those made of an aluminum alloy composed of Al, Au, Mo, Ta, Ru, W, Pt, and Al-Cu. The electrode may be formed by sputtering, vapor deposition, a CVD method, or the like.The joining method is not particularly limited. These substates can be joined by a conventionally used method. For example, these substrates may be joined using an adhesive, a solder, ultrasonic joining, friction stir welding, or expanded surface-activated bonding with a nanoadhesion layer. A through hole may be formed in the piezoelectric substrate so that the sacrificial layer is exposed. The through hole can be formed by, for example, laser processing or ion milling.

[0054] Step (lllb)In step (lllb), the sacrificial layer is removed by heating to form a cavity. In this embodiment, the sacrificial layer does not need to be dry-etched or wet-etched, and can be removed by heating. The heating temperature is preferably 150 to 400°C, and more preferably 180 to 400°C. The heating time is preferably 2 to 60 minutes, and more preferably 3 to 30 minutes. This heating dissociates the carboxylic acid and the amine of thecompound (B), and the released carboxylic acid promotes the thermal decomposition of the polymer (A). As a result, the polymer is removed. In this step, it is sufficient that at least a portion of the sacrificial layer is removed and a cavity is formed. Preferably 80 vol% or more, more preferably 90 vol% or more, still more preferably 95 vol% or more of the sacrificial layer is removed. In one preferred embodiment, all (100 vol%) of the sacrificial layer is removed.

[0055] Step (IVb)The method for producing an acoustic wave device of a second embodiment may further comprise the following step:(IVb) forming a cavity (hollow portion) above the side of the piezoelectric substrate to which the support substrate is not joined.

[0056] In step (IVb), a cavity (hollow portion) is formed above the side of the piezoelectric substrate to which the support substrate is not joined. The formation of the cavity can be achieved, for example, by forming a second sacrificial layer and then removing the second sacrificial layer. Examples of sacrificial materials for the second sacrificial layer include a polymer, silicon, and silicon dioxide. As the removal method, a method depending on materials, for example, removal by heating, dry etching, or wet etching, can be used. It is preferred that the sacrificial composition of the present disclosure is used as a sacrificial material for the second sacrificial layer and removed by heating.

[0057] It is preferable to form the sealing layer using a resin solution such as an epoxy resin after the formation of the cavity by removing the sacrificial layer by heating. When the sealing layer is formed by applying and then curing a resin solution, it is preferable, in order to seal the through hole, to use a resin solution having a viscosity such that the resin solution does not flow into the through hole during baking.Further, a metal post is preferably formed using a metal such as Cu, Au, Ni, Al, and SnAgCu. The metal post can be formed by an electroplating method, an electroless plating method, a stud bump method, or the like. An adhesion layer of Cr or Ti may also be interposed for adhesion between theelectrode and the metal post. Furthermore, it is preferable that the solder ball is formed of an alloy such as SnAgCu, SnAgln, SnCuNi, SnCuBi, SnSb, and SnBi. A thin film may be formed from a conductive material to form a flat pad.

[0058] Figs. 2A to 2C are exemplary explanatory views of a method for producing an acoustic wave device of a second embodiment. 2-r in Fig. 2C is a schematic cross-sectional view of an acoustic wave device of one embodiment. Only one acoustic wave device is shown for the same purpose as Fig. 1C.

[0059] A negative resist composition is coated on a Si wafer as a support substrate 201 by a spin coating method to form a resist layer 202, and a resist pattern is formed by patterning exposure and development (2-a in Fig. 2A). After the Si wafer is etched by dry etching, the resist is removed to form a recess in the Si wafer (2-b in Fig. 2A).Next, a silicon oxide film 203 is formed by TEOS-CVD from the upper end of the Si wafer with a recess, and planarized by CMP (2-c in Fig. 2A). A negative resist composition is coated on the silicon oxide film 203 by a spin coating method to form a resist layer 204, and a resist pattern is formed by patterning exposure and development (2-d in Fig. 2A). After the silicon oxide film is etched by dry etching, the resist pattern is removed (2-e in Fig.2A).A sacrificial composition is applied thereon, and a sacrificial layer 205 is formed by spin coating. The sacrificial layer 205 is etched back to the top surface of the silicon oxide film (2-f in Fig. 2A).

[0060] A support substrate 201 is joined to a LiTaOs piezoelectric substrate 206 (2-g in Fig. 2A). A positive lift-off resist composition is coated on the piezoelectric substrate by a spin coating method to form a resist layer 207, and the resist layer 207 is then dried. The resist layer is selectively exposed using a mask with a pattern corresponding to the IDT and the reflective electrode. Next, the resist layer is developed with an alkaline developer containing 2.38 mass% TMAH for one minute. An aluminum alloy film 208 composed of Al-Cu is formed by a sputteringmethod (2-h in Fig. 2A). The resist layer is removed with a resist stripper to form a wiring electrode for connecting the IDT and the reflective electrode with the outside (2-i in Fig. 2A). A silicon oxide film 209 made of silicon oxide is formed on the IDT, the reflective electrode, and the wiring electrode by TEOS-CVD. A part of the silicon oxide film is removed by a photolithography method so that at least a part (end) of the wiring electrode is exposed (2-j in Fig. 2B).

[0061] A photosensitive negative polyimide composition is spin-coated on a piezoelectric substrate. The protective layer 210 is formed by patterning exposure and development. Thereafter, a frame in which the IDT, the reflective electrode, and the wiring electrode portion are not covered with a polyimide is formed by heating (2-k in Fig. 2B).A through hole is formed in the piezoelectric substrate by ion milling (2-I in Fig. 2B). A sacrificial composition is applied onto the piezoelectric substrate on which the frame is formed, and a sacrificial layer 211 is formed by spin coating. The sacrificial layer 211 is etch-backed to the top surface of the polyimide frame (2-m in Fig. 2B). A photosensitive negative polyimide film, which will form a lid, is attached onto the polyimide frame by using an applicator (2-n in Fig. 2B).

[0062] The polyimide film in the wiring electrode portion and the through hole portion is removed by patterning exposure and development (2-o in Fig. 2B). The sacrificial layer is then thermally decomposed by heating in air at 280°C for 20 minutes and removed through the through hole (2-p in Fig.2B). As a result, the IDT and the reflective electrode form a hollow structure with a through hole.

[0063] The through hole is sealed with a photosensitive epoxy resin to form a sealing layer 212. A part of the sealing layer located on the wiring electrode portion is removed by a patterning process using a photolithography method to expose the wiring electrode portion. Heat treatment forms a hollow portion of the IDT and the reflective electrode (2-q in Fig. 2C).A nickel metal post 213 is formed, and a SnAgCu alloy solder ball 214 isformed thereon (2-r in Fig. 2C).An acoustic wave device can be produced in this manner.

[0064] <Acoustic Wave Device>According to one embodiment, an acoustic wave device with a cavity formed by the above method is provided. The structure of the cavity is not particularly limited, and examples thereof include a cavity with a longitudinal or lateral width of 50 to 500 pm and a height of 2.0 to 50.0 pm.[Examples]

[0065] The present invention will be described below using various examples. Here, the embodiments of the present invention are not limited to these examples.

[0066] In the following examples, a mass average molecular weight (Mw) of the polymer (A) is measured by gel permeation chromatography (GPC) using polystyrene as a standard. GPC is performed using an Alliance™ e2695-type high-speed GPC system (Nihon Waters) and a Super Multipore HZ-M type GPC column (Tosoh). The measurement is performed under measurement conditions of a flow rate of 0.6 mL / min and a column temperature of 40°C with monodispersed polystyrene as a standard sample and tetrahydrofuran as an eluent, and the Mw is then calculated as the relative molecular weight to the standard sample.

[0067] The glass transition temperature of the polymer (A) is measured by TG-DTA in air at a rate of temperature rise of 5°C / min.

[0068] Preparation Example of Sacrificial Composition>The components are listed in Table 1.

[0069] [Table 1]Table 1

[0070] To anisole as the solvent (C), the components listed in Tables 2-1 , 2-2, or 3 are added in the blending amounts listed in these tables(expressed in mass% relative to the total mass of the sacrificial composition), and the resulting mixture is stirred at 25°C for 24 hours.Complete dissolution of the components is visually confirmed. The mixture is then filtered (pore size = 10 nm) to obtain a sacrificial composition.

[0071] <250°C Thermal Decomposability and 300°C Thermal Decomposability>A sacrificial composition is applied onto a Si wafer, and a sacrificial layer of the thickness listed in Table 2-1 , 2-2, or 3 is formed by spin coating (500 rpm). The initial film thickness To of the sacrificial layer is measured using DektakXT (Bruker). After the sacrificial layer is heat-treated at 250°C or300°C for 1 minute or 10 minutes, the film thickness Ti after the 1-minute heat treatment or the film thickness T10 after the 10-minute heat treatment is measured by DektakXT. The residual rate after 1 minute or 10 minutes is calculated for the film thickness according to the following equations. ForComparative Example 105, exposure at an exposure dose of 200 mJ / cm2in an open shot using a KrF stepper (FPA 300-EX5, CANON), followed by the above heat treatment, are performed, and the same calculation is performed on the film thickness in the exposed region.Residual rate after 1 minute = T1 / T0 (%)Residual rate after 10 minutes = T / To (%)

[0072] <Complete Elimination Time Evaluation>A sacrificial composition is applied onto a Si wafer, and a sacrificial layer of the thickness listed in Table 2-1 , 2-2, or 3 is formed by spin coating (500 rpm). The sacrificial layer is heat-treated at 250°C or 300°C, and the time at which the sacrificial layer is completely decomposed and eliminated by visual observation (complete elimination time) is recorded and evaluated on the following criteria. For comparative example 105, exposure at an exposure dose of 200 mJ / cm2in an open shot using a KrF stepper (FPA 300-EX5, CANON), followed by the above heat treatment, are performed, and the same evaluation is performed in the exposed region.A: The complete elimination time is within 45 minutesB: The complete elimination time is over 45 minutes and within 60 minutes C: The complete elimination time is over 60 minutes

[0073] The compositions and results of the sacrificial compositions are listed in Tables 2-1 , 2-2, and 3.

[0074] [Table 2-1]

[0075] [Table 2-1 ] - continued

[0076] [Table 2-2]

[0077] [Table 2-2] - continued* Darkened spots remain on a Si wafer after thermal decomposition.

[0078] [Table 3]

[0079] [Table 3] - continued[Reference Signs List]

[0080] 101 Support substrate102 Piezoelectric substrate103 Resist layer104 Aluminum alloy film105 Silicon oxide film106 Protective layer107 Sacrificial layer108 Sealing layer109 Metal post110 Solder ball201 Support substrate 202 Resist layer203 Silicon oxide film204 Resist layer205 Sacrificial layer206 Piezoelectric substrate 207 Resist layer208 Aluminum alloy film 209 Silicon oxide film 210 Protective layer211 Sacrificial layer212 Sealing layer213 Metal post214 Solder ball

Claims

[CLAIMS]

1. A sacrificial composition comprising:a polymer (A) that undergoes acid-catalyzed decomposition, a compound (B) that generates an acid by heat, and a solvent (C), whereinthe compound (B) that generates the acid by heat consists of a carboxylic acid and a base, and a content of the compound (B) is 1 to 60 parts by mass based on 100 parts by mass of the polymer (A).

2. The sacrificial composition according to claim 1 , wherein the polymer (A) comprises at least one selected from the group consisting of polycarbonates, polyesters, polyethers, polyamides, polyimides, and polyurethanes.

3. The sacrificial composition according to claim 1 or 2, wherein the polymer (A) has a glass transition temperature of -50 to 200°C.

4. The sacrificial composition according to any one of claims 1 to 3, wherein the compound (B) is a salt represented by formula (B-1):( B — 1 )whereinn01 is 1, 2, or 3;n02 is 0, 1, 2, 3, or 4;X is a single bond, H, a saturated or unsaturated linear C1-20 hydrocarbon group, a saturated or unsaturated C5-10 cycloaliphatic hydrocarbon group, or a C6-10 aromatic hydrocarbon group;Y is a substituent on X, each independently hydroxy or C1-4 alkyl; and Z is each independently a primary amine, a secondary amine, a tertiary amine, or an alkanolamine.

5. The sacrificial composition according to any one of claims 1 to 4, wherein the compound (B) is decomposed at a temperature of 70 to 250°C to generate an acid.

6. The sacrificial composition according to any one of claims 1 to 5, wherein the compound (B) comprises an amine with a boiling point of 70 to 400°C.

7. The sacrificial composition according to any one of claims 1 to 6, wherein the compound (B) generates a carboxylic acid with a pKa of 6.3 or less.

8. The sacrificial composition according to any one of claims 1 to 7, wherein the polymer (A) has a mass average molecular weight (Mw) of 5,000 to 300,000.

9. The sacrificial composition according to any one of claims 1 to 8, wherein the solvent (C) comprises at least one selected from the group consisting of alcohols, aliphatic hydrocarbons, ethers, esters, aromatic hydrocarbons, ketones, amides, and lactones.

10. The sacrificial composition according to any one of claims 1 to 9, further comprising a solvent (D),wherein the additive (D) comprises at least one selected from the group consisting of a surfactant, an acid, a base, an antibacterial agent, a sterilizing agent, a preservative, and an antifungal agent, and a content of the additive (D) is 0 to 10 parts by mass based on 100 parts by mass of the polymer (A).

11. A method for producing a device comprising the steps of:applying the sacrificial composition according to any one of claims 1 to 10 above a substrate to form a sacrificial layer;forming a lid above the sacrificial layer; andremoving the sacrificial layer by heating to form a cavity.

12. The method according to claim 11 , wherein a material of the substrate is selected from the group consisting of lithium tantalate, lithium niobate, lithium tetraborate, quartz, lanthanum gallium silicate, lanthanum gallium tantalate, aluminum nitride, aluminum scandium nitride, silicon, and sapphire.

13. The method according to claim 11 or 12, wherein the removal of the sacrificial layer by heating is performed at 150 to 400°C.

14. The method according to any one of claims 11 to 13, wherein the device is an acoustic wave device.

15. An acoustic wave device with a cavity formed by the method according any one of claims 11 to 13.

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