Title of Invention: Temporary adhesion method and method for producing thin wafer Abstract: The present invention is a temporary adhesion method for temporarily bonding a support and a wafer via a temporary adhesive material, including attaching the wafer to the support via the temporary adhesive material including a complex temporary adhesive material layer that consists of a thermoplastic resin layer (A) exhibiting a storage modulus E′ of 1 to 500 MPa and a tensile rupture strength of 5 to 50 MPa at 25° C. and a thermosetting polymer layer (B) exhibiting a storage modulus E′ of 1 to 1000 MPa and a tensile rupture strength of 1 to 50 MPa at 25° C. after curing, wherein the attaching is performed by forming the layer (A) on the front surface of the wafer from a liquid composition (A′), forming the layer (B) on the support by laminating a film resin (B′), and then heating the wafer and the support under reduced pressure, or forming the layer (A) on the front surface of the wafer from the liquid composition (A′), forming the layer (B) on the layer (A) by laminating the film resin (B′), and then heating the wafer and the support under reduced pressure, and heat curing the layer (B). This temporary adhesion method facilitates temporary adhesion and separation and can increase productivity of thin wafers. Detailed Description: Part general_description_paragraphs: Part TECHNICAL FIELD: The present invention relates to a temporary adhesion method between a wafer and a support and a method for producing a thin wafer. Part BACKGROUND ART: Three-dimensional semiconductor mounting has become essential for higher density and larger capacity. The three-dimensional mounting technique is a semiconductor production technique for thinning a semiconductor chip and connecting the chip to another chip by a through silicon via (TSV) to form a multilayer. To realize this technique, steps of grinding a non-circuit-forming surface (also referred to as “back surface”) of a substrate on which a semiconductor circuit has been formed to thin the substrate, and then forming an electrode including a TSV on the back surface, are required. In the step of grinding the back surface of a silicon substrate, a protective tape for the back surface is conventionally attached to a back side of the surface to be ground to prevent the wafer from breaking during grinding. However, this tape uses an organic resin film as its supporting base, which has flexibility, but inadequate strength and heat resistance. Thus, this tape is not suited to the steps of forming a TSV and forming a wiring layer on the back surface. In this context, there has been proposed a system in which a semiconductor substrate is bonded to a support made of silicon, glass or the like, through an adhesive layer to sufficiently withstand the steps of grinding the back surface and forming a TSV and an electrode on the back surface. In this system, the adhesive layer used for bonding the substrate to the support is important. The adhesive layer requires a sufficient durability to bond the substrate and the support without gaps and to withstand subsequent steps, and also requires an ability to easily detach a thin wafer from the support finally. The adhesive layer, which is finally removed, is hence referred to as “temporary adhesive layer” (or temporary adhesive material layer) herein. With respect to the conventionally known temporary adhesive layer and a method for removing this layer, the following techniques have been proposed: an adhesive material containing a light-absorbing substance is irradiated with high intensity light to decompose the adhesive material layer, whereby the adhesive material layer is removed from the support (Patent Literature 1); a heat fusible hydrocarbon compound is used for the adhesive material, and bonding and removal are carried out in a heat-molten state (Patent Literature 2). The former technique has problems of requiring expensive tools such as laser, and a long treatment time per substrate. The latter technique is simple because of control only by heat, but thermal stability is insufficient at a high temperature exceeding 200° C., and thus the applicable range is limited. Furthermore, these temporary adhesive layers are not adequate to form a film with uniform thickness on a heavily stepped substrate and to provide a complete adhesion to the support. Moreover, it has been proposed to use a silicone pressure sensitive adhesive for the temporary adhesive material layer (Patent Literature 3). In this technique, a substrate is bonded to a support with an addition-curable silicone pressure sensitive adhesive, and on the removal, the assembly is immersed in a chemical solution capable of dissolving or decomposing the silicone resin to separate the substrate from the support. Thus, this method takes a very long time for separation and is difficultly applied to the actual producing process. Moreover, a method of applying a liquid composition by spin coating and removing a solvent to form a resin layer on the wafer has problems of decrease in yield and increase in cost. Moreover, it has been proposed to use a silicone adhesive for semiconductor (Patent Literature 4). However, this technique causes cracks when the adhesive is formed into a film on a protective film due to an extremely high elastic modulus after curing, thus failing in lamination process. Part CITATION LIST: Part Patent Literature: PATENT LITERATURE 1: Japanese Unexamined Patent publication (Kokai) No. 2004-64040 PATENT LITERATURE 2: Japanese Unexamined Patent publication (Kokai) No. 2006-328104 PATENT LITERATURE 3: U.S. Pat. No. 7,541,264 PATENT LITERATURE 4: Japanese Unexamined Patent publication (Kokai) No. 2010-043211 Part SUMMARY OF INVENTION: Part Technical Problem: The present invention was accomplished in view of the above-described problems. It is an object of the present invention to provide a temporary adhesion method and a method for producing a thin wafer that facilitate temporary adhesion, allow formation of a layer with uniform film thickness on a heavily stepped substrate, are highly compatible with the steps of forming a TSV and forming a wiring on the back surface of the wafer, have excellent resistance to a thermal process for wafer such as chemical vapor deposition (CVD), allow easy separation, and can increase productivity of thin wafers. Part Solution to Problem: To achieve this object, the present invention provides a temporary adhesion method for temporarily bonding a support and a wafer having a front surface on which a circuit is formed and a back surface to be processed via a temporary adhesive material for a wafer processing, the method comprising the steps of: attaching the wafer to the support via the temporary adhesive material for a wafer processing including a two-layered complex temporary adhesive material layer that consists of a first temporary adhesive layer composed of a thermoplastic resin layer (A) exhibiting a storage modulus E′ of 1 to 500 MPa and a tensile rupture strength of 5 to 50 MPa at 25° C. and a second temporary adhesive layer composed of a thermosetting polymer layer (B) exhibiting a storage modulus B′ of 1 to 1000 MPa and a tensile rupture strength of 1 to 50 MPa at 25° C. after curing, wherein the attaching is performed by forming the thermoplastic resin layer (A) on the front surface of the wafer from a liquid composition (A′) containing a thermoplastic resin, forming the thermosetting polymer layer (B) on the support by laminating a film resin (B′) that has been formed from a composition containing a thermosetting polymer, and then heating the wafer and the support under reduced pressure, or forming the thermoplastic resin layer (A) on the front surface of the wafer from the liquid composition (A′), forming the thermosetting polymer layer (B) on the resin layer (A) by laminating the film resin (B′), and then heating the wafer and the support under reduced pressure; and adhesively bonding the thermoplastic resin layer (A) and the thermosetting polymer layer (B) by heat curing the thermosetting polymer layer (B). Such a temporary adhesion method facilitates temporary adhesion between the wafer and the support, allows formation of the layer with uniform film thickness on a heavily stepped substrate, enables high compatibility with the steps of forming a TSV and forming a wiring on the back surface of the wafer and excellent resistance to a thermal process such as CVD, allows easy separation, and can increase productivity of thin wafers. In the step of attaching, the attaching is preferably performed under heating at 40 to 200° C. Such a temporary adhesion method enables the wafer to be surely attached to the support via the temporary adhesive material for a wafer processing. The thermoplastic resin layer (A) is preferably a non-silicone thermoplastic resin layer. The complex temporary adhesive material layer including a non-silicone thermoplastic resin layer facilitates, after a thin wafer is produced, separating the wafer from the support and cleaning the wafer. Thus, a fragile thin wafer can be more easily handled. The thermosetting polymer layer (B) is preferably a thermosetting siloxane-modified polymer layer. The thermosetting siloxane-modified polymer layer is excellent in heat resistance and thus preferable. In addition, a composition containing a thermosetting siloxane-modified polymer can be easily formed into a film resin. Thus, when the thermosetting polymer layer (B) is a thermosetting siloxane-modified polymer layer, yield can be improved. The thermosetting siloxane-modified polymer layer is preferably a layer of a composition containing 100 parts by mass of a siloxane bond-containing polymer having a repeating unit shown by the following general formula (1) and a weight average molecular weight of 3,000 to 500,000, and 0.1 to 50 parts by mass of one or more crosslinkers selected from the group consisting of an amino condensate, a melamine resin, a urea resin each modified with formalin or formalin-alcohol, a phenol compound having on average two or more methylol or alkoxymethylol groups per molecule, and an epoxy compound having on average two or more epoxy groups per molecule, wherein R1 to R4 may be the same or different, and represent a monovalent hydrocarbon group having 1 to 8 carbon atoms; “m” is an integer of 1 to 100; B is a positive number; A is 0 or a positive number, provided that A+B=1; and X is a divalent organic group shown by the following general formula (2), wherein Z represents a divalent organic group selected from any of N represents 0 or 1; R5 and R6 each represent an alkyl or alkoxy group having 1 to 4 carbon atoms, and may be the same or different from each other; and “k” represents any of 0, 1, and 2. Such a thermosetting siloxane-modified polymer layer is more excellent in heat resistance and thus preferable. The thermosetting siloxane-modified polymer layer is preferably a layer of a composition containing 100 parts by mass of a siloxane bond-containing polymer having a repeating unit shown by the following general formula (3) and a weight average molecular weight of 3,000 to 500,000, and 0.1 to 50 parts by mass of one or more crosslinkers selected from the group consisting of a phenol compound having on average two or more phenol groups per molecule and an epoxy compound having on average two or more epoxy groups per molecule, wherein R1 to R4 may be the same or different, and represent a monovalent hydrocarbon group having 1 to 8 carbon atoms; “m” is an integer of 1 to 100; B is a positive number; A is 0 or a positive number, provided that A+B=1; and Y is a divalent organic group shown by the following general formula (4), wherein V represents a divalent organic group selected from any of “p” represents 0 or 1; R7 and R8 each represent an alkyl or alkoxy group having 1 to 4 carbon atoms, and may be the same or different from each other; and “h” represents any of 0, 1, and 2. Such a thermosetting siloxane-modified polymer layer is more excellent in heat resistance and thus preferable. The thermosetting polymer layer (B) preferably exhibits a 180° peeling force of 2 gf to 50 gf after heat curing, the 180° peeling force being measured with a polyimide test piece having a width of 25 mm. The thermosetting polymer layer (B) exhibiting such a peeling force prevents the wafer from slipping at the time of grinding the wafer, and facilitates separation. Thus, it is preferable. Furthermore, the present invention provides a method for producing a thin wafer, comprising the steps of: (a) grinding or polishing the back surface of the wafer temporarily bonded to the support via the temporary adhesive material for a wafer processing by the inventive temporary adhesion method; (b) processing the back surface of the wafer; and (c) separating the processed wafer from the temporary adhesive material for a wafer processing and the support. Such a method for producing a thin wafer, which uses the inventive two-layered temporary adhesive material layer to bond the wafer and the support, can easily manufacture a thin wafer having a through electrode structure or a bump interconnect structure. The method preferably further comprises (d) cleaning a separation plane of the processed wafer after the step (c). Such a method for producing a thin wafer can yield a wafer from which the thermoplastic resin layer (A) is completely removed even if the thermoplastic resin layer (A) remains on the front surface of the wafer after the separating step (c). The step (c) preferably includes immersing the whole of the processed wafer in a solvent before the separating. When the whole of the wafer is immersed in a solvent, the temporary adhesive material at the periphery of the wafer is swollen and decomposed. Thus, the wafer can be easily separated from the temporary adhesive material for a wafer processing and the support. The step (d) preferably includes cleaning by two-fluid cleaning. Two-fluid cleaning allows cleaning under high pressure. Thus, cleaning by two-fluid cleaning enables a residual resin to be removed in a short time. Part Advantageous Effects of Invention: The complex temporary adhesive material layer in the present invention has the two-layered structure, and particularly uses the thermosetting polymer layer (B) as a supporting layer for bonding a substrate. This resin does not thermally decompose, does not flow especially at a high temperature of 200° C. or higher, and has excellent heat resistance. The temporary adhesive material layer is thus applicable to a wide range of semiconductor film-forming process. After the thin wafer is produced, the wafer can be easily separated from the support, for example, at room temperature. Thus, the thin wafer, which is easy to break, can be easily produced without breakage. In addition, the method includes laminating the film resin (B′) to form the thermosetting polymer layer (B) on the thermoplastic resin layer (A) or the support and then heating them under reduced pressure for attaching. This procedure prevents voids from occurring at the bonding interface on wafer side, etc., due to unevenness of the wafer. Moreover, this procedure to form the thermosetting polymer layer (B) and perform attaching allows the temporary adhesive material layer to be formed with high film-thickness uniformity even on a stepped wafer. This film-thickness uniformity enables easy production of a uniform thin wafer 50 μm or less thick. Furthermore, forming the thermosetting polymer layer (B) by this procedure reduces loss (cost) of the resin due to spin coating, improves flatness of the film thickness, eliminates a wafer cleaning solution for backside rinse, etc., and thus reduces the amount of waste liquid. When a thermosetting siloxane-modified polymer layer is used as the thermosetting polymer layer (B), a temporary adhesive material layer more excellent in CVD resistance can be formed. Part DESCRIPTION OF EMBODIMENTS: Hereinafter, the present invention will be described in detail. As described above, there are demands for a temporary adhesion method and a method for producing a thin wafer that facilitate temporary adhesion, allow formation of the layer with uniform film thickness on a heavily stepped substrate, are highly compatible with the steps of forming a TSV and forming a wiring on the back surface of the wafer, have excellent resistance to a wafer thermal process such as CVD, allow easy separation, and can increase productivity of thin wafers. The present inventors earnestly studied to accomplish the above object. Consequently, the inventors found that the object can be accomplished by a temporary adhesion method for temporarily bonding a support and a wafer having a front surface on which a circuit is formed and a back surface to be processed via a temporary adhesive material for a wafer processing, the method comprising the steps of: attaching the wafer to the support via the temporary adhesive material for a wafer processing including a two-layered complex temporary adhesive material layer that consists of a first temporary adhesive layer composed of a thermoplastic resin layer (A) exhibiting a storage modulus E′ of 1 to 500 MPa and a tensile rupture strength of 5 to 50 MPa at 25° C. and a second temporary adhesive layer composed of a thermosetting polymer layer (B) exhibiting a storage modulus E′ of 1 to 1000 MPa and a tensile rupture strength of 1 to 50 MPa at 25° C. after curing, wherein the attaching is performed by forming the thermoplastic resin layer (A) on the front surface of the wafer from a liquid composition (A′) containing a thermoplastic resin, forming the thermosetting polymer layer (B) on the support by laminating a film resin (B′) that has been formed from a composition containing a thermosetting polymer, and then heating the wafer and the support under reduced pressure, or forming the thermoplastic resin layer (A) on the front surface of the wafer from the liquid composition (A′), forming the thermosetting polymer layer (B) on the resin layer (A) by laminating the film resin (B′), and then heating the wafer and the support under reduced pressure; and adhesively bonding the thermoplastic resin layer (A) and the thermosetting polymer layer (B) by heat curing the thermosetting polymer layer (B), thereby bringing the present invention to completion. Hereinafter, a laminated material obtained by the attaching step in the inventive temporary adhesion method is also referred to as a wafer processing laminate. FIG. 1 is a cross-sectional view of an exemplary wafer processing laminate obtained by the attaching step in the inventive temporary adhesion method. As shown in FIG. 1, the wafer processing laminate has a wafer (device wafer) 1 having a front surface on which a circuit is formed and a back surface to be processed, a support 3 for supporting the wafer 1 during processing the wafer 1, and a complex temporary adhesive material layer 2 placed between the wafer 1 and the support 3. The complex temporary adhesive material layer 2 has a two-layered structure consisting of a thermoplastic resin layer (A) (first temporary adhesive layer) and a thermosetting polymer layer (B) (second temporary adhesive layer). The first temporary adhesive layer releasably adheres to the front surface of the wafer 1, and the second temporary adhesive layer releasably adheres to the support 3. The temporary adhesive material for a wafer processing used in the inventive temporary adhesion method is composed of a laminated material of the layers (A) and (B). The first temporary adhesive layer in the temporary adhesive material for a wafer processing exhibits a storage modulus E′ of 1 to 500 MPa and a tensile rupture strength of 5 to 50 MPa at 25° C. When the storage modulus E′ is less than 1 MPa, separation ability of the thermoplastic resin layer (A) decreases. When the storage modulus E′ is more than 500 MPa, back surface grinding resistance of the wafer in the laminated material deteriorates, and CVD resistance cannot be achieved. Additionally, cracks can occur on the surface of the thermoplastic resin layer (A). When the tensile rupture strength is less than 5 MPa, separation ability decreases. When the tensile rupture strength is more than 50 MPa, many defects occur due to high rigidity, and adhesion property cannot be achieved. The second temporary adhesive layer in the temporary adhesive material for a wafer processing exhibits a storage modulus E′ of 1 to 1000 MPa and a tensile rupture strength of 1 to 50 MPa at 25° C. after curing. When the storage modulus E′ after curing is less than 1 MPa, the wafer is likely to be separated during grinding the back surface of the wafer. When the storage modulus E′ after curing is more than 1000 MPa, voids can occur at the bonding interface on wafer side, etc., due to unevenness of the wafer. When the tensile rupture strength after curing is less than 1 MPa, the wafer is likely to be separated during grinding the back surface of the wafer. When the tensile rupture strength after curing is more than 50 MPa, voids can occur at the bonding interface on wafer side, etc., due to unevenness of the wafer. The storage modulus E′ of the first temporary adhesive layer is preferably 5 to 300 MPa, more preferably 5 to 100 MPa, much more preferably 10 to 80 MPa. The tensile rupture strength of the first temporary adhesive layer is preferably 10 to 50 MPa. The storage modulus E′ of the cured second temporary adhesive layer is preferably 5 to 800 MPa, more preferably 10 to 800 MPa, much more preferably 10 to 600 MPa. The tensile rupture strength of the cured second temporary adhesive layer is preferably to 40 MPa. Use of such a temporary adhesive material for a wafer processing more greatly prevents separation and cracking of the wafer during grinding the back surface of the wafer, enabling the wafer to be processed more stably. A method of measuring the storage modulus E′ and tensile rupture strength in the present invention will be now described. In the present invention, the storage modulus E′ and tensile rupture strength are measured on respective films of the thermoplastic resin layer (A) and the thermosetting polymer layer (B). Hereinafter, the present invention will be described in more detail, but the present invention is not limited thereto. [Complex Temporary Adhesive Material Layer] First, each layer constituting the complex temporary adhesive material layer (the temporary adhesive material for a wafer processing) used in the inventive adhesion method will be described. —First Temporary Adhesive Layer (A)/Thermoplastic Resin Layer— The thermoplastic resin layer (A) is a layer containing a thermoplastic resin. The thermoplastic resin layer (A) is preferably a non-silicon thermoplastic resin layer that contains an organopolysiloxane-free thermoplastic resin (a thermoplastic organopolysiloxane-free polymer layer). In view of applicability to stepped silicon wafers, etc., a non-silicone thermoplastic resin having a good spin coating property is suitably used as a material for forming the thermoplastic resin layer. In particular, the non-silicone thermoplastic resin preferably has a glass transition temperature of about −80 to 120° C. Examples thereof include an olefin type thermoplastic elastomer, a polybutadiene type thermoplastic elastomer, a styrene type thermoplastic elastomer, a styrene-butadiene type thermoplastic elastomer, and a styrene-polyolefin type thermoplastic elastomer. A hydrogenated polystyrene type elastomer excellent in heat resistance is particularly suitable. More specifically, there may be mentioned Tuftec (Asahi Kasei Chemicals Corporation), ESPOLEX SB series (Sumitomo Chemical Co., Ltd.), RABALON (Mitsubishi Chemical Corporation), SEPTON (Kuraray Co., Ltd.), and DYNARON (JSR Corporation). In addition, there may be mentioned a cycloolefin polymer represented by ZEONEX (ZEON Corporation) and a cyclic olefin copolymer represented by TOPAS (Nippon Polyplastics Co., Ltd.). As descried above, the non-silicone thermoplastic resin is preferably a non-silicone thermoplastic elastomer. The complex temporary adhesive material layer including such a non-silicone thermoplastic elastomer enables, after a thin wafer is produced, the wafer to be easily separated from the support. Thus, a fragile thin wafer can be easily handled. To the thermoplastic resin may be added an antioxidant for improving heat resistance, a surfactant for improving coating property, or a release agent for improving separation ability. Examples of the antioxidant that can be suitably used include di-tert-butylphenol. Examples of the surfactant that can be suitably used include a fluorinated silicone surfactant X-70-1102 (available from Shin-Etsu Chemical Co., Ltd.). Examples of the release agent that can be suitably used include KF-96 (available from Shin-Etsu Chemical Co., Ltd.). —Second Temporary Adhesive Layer (B)/Thermosetting Polymer Layer— The thermosetting polymer layer (B) is a layer containing a thermosetting polymer. The thermosetting polymer layer (B) is preferably a thermosetting siloxane-modified polymer layer. More specifically, a layer of a siloxane-containing composition mainly consisting of a thermosetting siloxane-modified polymer shown by the following general formula (1) or (3) is preferable. Polymer of Formula (1) (Phenolic Siloxane Polymer): A polymer of the general formula (1) is a siloxane bond-containing polymer. This polymer has a repeating unit shown by the general formula (1) and a weight average molecular weight of 3,000 to 500,000, preferably 10,000 to 100,000, wherein R1 to R4 may be the same or different, and represent a monovalent hydrocarbon group having 1 to 8 carbon atoms; “m” is an integer of 1 to 100; B is a positive number; A is 0 or a positive number, provided that A+B=1; and X is a divalent organic group shown by the following general formula (2), wherein Z represents a divalent organic group selected from any of N represents 0 or 1; R5 and R6 each represent an alkyl or alkoxy group having 1 to 4 carbon atoms, and may be the same or different from each other; and “k” represents any of 0, 1, and 2. In this case, illustrative examples of R1 to R4 include a methyl group, an ethyl group, and a phenyl group. “m” preferably represents an integer of 3 to 60, more preferably 8 to 40. B/A ranges from 0 to 20, particularly from 0.5 to 5. A is preferably 0 to 0.9; B is preferably 0.1 to 1. When A is larger than 0, A is preferably 0.1 to 0.7 and B is preferably 0.3 to 0.9. Polymer of Formula (3) (Epoxy-Modified Siloxane Polymer): A polymer of the general formula (3) is a siloxane bond-containing polymer. This polymer has a repeating unit shown by the general formula (3) and a weight average molecular weight of 3,000 to 500,000, wherein R1 to R4 may be the same or different, and represent a monovalent hydrocarbon group having 1 to 8 carbon atoms; “m” is an integer of 1 to 100; B is a positive number; A is 0 or a positive number, provided that A+B=1; and Y is a divalent organic group shown by the following general formula (4), wherein V represents a divalent organic group selected from any of “p” represents 0 or 1; R7 and R8 each represent an alkyl or alkoxy group having 1 to 4 carbon atoms, and may be the same or different from each other; and “h” represents any of 0, 1, and 2. In this case, illustrative examples of R1 to R4, “m” A, and 3 are the same as in the general formula (1). The thermosetting siloxane-containing composition mainly consisting of the thermosetting siloxane-modified polymer of the general formula (1) or (3) contains one or more crosslinkers for heat curing. In the case of the phenolic siloxane polymer of the general formula (1), the crosslinker is selected from an amino condensate, a melamine resin, a urea resin each modified with formalin or formalin-alcohol, a phenol compound having on average two or more methylol or alkoxymethylol groups per molecule, and an epoxy compound having on average two or more epoxy groups per molecule. Here, the amino condensate, the melamine resin, the urea resin each modified with formalin or formalin-alcohol may be exemplified by the following. For example, the melamine resin (condensate) modified with formalin or formalin-alcohol can be obtained by addition condensation polymerization of a modified melamine monomer (e.g. trimethoxymethyl monomethylol melamine), or a polymer thereof (e.g. oligomer such as dimer and trimer) with formaldehyde until a desired molecular weight is achieved, according to a known method. These compounds may be used alone or in combination of two or more kinds. The urea resin (condensate) modified with formalin or formalin-alcohol can be prepared by modifying a urea condensate having a desired molecular weight with formalin into a methylol form, and optionally, further modifying the resultant compound with an alcohol into an alkoxy form, according to a known method. Illustrative examples of the urea resin modified with formalin or formalin-alcohol include methoxymethylated urea condensate, ethoxymethylated urea condensate, and propoxymethylated urea condensate. These compounds may be used alone or in combination of two or more kinds. Illustrative examples of the phenol compound having on average two or more methylol or alkoxymethylol groups per molecule include (2-hydroxy-5-methyl)-1,3-benzenedimethanol and 2,2′,6,6′-tetramethoxymethyl-bisphenol A. These phenol compounds may be used alone or in combination of two or more kinds. On the other hand, in the case of the epoxy-modified siloxane polymer of the general formula (3), the composition contains one or more crosslinkers selected from an epoxy compound having on average two or more epoxy groups per molecule and a phenol compound having on average two or more phenol groups per molecule. The epoxy compound having a polyfunctional epoxy group used in the polymers of the general formulae (1) and (3) is not particularly limited. In particular, a bi-functional, a tri-functional, a tetra-functional or more polyfunctional epoxy resins, for example, EOCN-1020, EOCN-102S, XD-1000, NC-2000-L, EPPN-201, GAN, and NC6000, all available from Nippon Kayaku Co., Ltd., or a crosslinker shown by the following formula may be contained. In the case that the thermosetting siloxane-modified polymer is the epoxy-modified siloxane polymer of the general formula (3), examples of its crosslinker include m- or p-cresol-novolac resins such as EP-6030G available from Asahi Organic Chemicals Industry Co., Ltd., tri-functional phenol compounds such as Tris-P-PA available from Honshu Chemical Industry Co., Ltd., and tetra-functional phenol compounds such as TEP-TPA available from Asahi Organic Chemicals Industry Co., Ltd. The formulation amount of the crosslinker is 0.1 to 50 parts by mass, preferably 0.1 to 30 parts by mass, more preferably 1 to 20 parts by mass based on 100 parts by mass of the thermosetting siloxane-modified polymer. Two, three or more crosslinkers may be blended in combination. A curing catalyst such as an acid anhydride may be added in an amount of 10 parts by mass or less based on 100 parts by mass of the thermosetting siloxane-modified polymer. A known antioxidant and a filler such as silica may be added in an amount of 50 parts by mass or less based on 100 parts by mass of the thermosetting siloxane-modified polymer to improve heat resistance. Moreover, a surfactant may be added to improve coating uniformity. Illustrative examples of the antioxidant that can be added into the siloxane-containing composition include hindered phenol compounds such as tetrakis[methylene-(3,5-di-tert-butyl-4-hydroxyhydrocinnamate)]methane (product name: Adekastab AO-60). The thermosetting polymer layer (B) typically exhibits a 180° peeling force of 2 gf to 50 gf, preferably 3 gf to 30 gf, more preferably 5 gf to 20 gf after heat curing when the 180° peeling force is measured with a polyimide test piece having a width of 25 mm. When the peeling force is 2 gf or more, the wafer is prevented from slipping at the time of grinding the wafer. When the peeling force is 50 gf or less, the wafer can be easily separated. In the case that the temporary adhesive material for a wafer processing and the support are separated after the wafer processing laminate is immersed in a solvent, a peeling force of 70 gf or less enables the temporary adhesive material for a wafer processing and the support to be easily separated. [Temporary Adhesion Method] Each step of the inventive temporary adhesion method using the above temporary adhesive material for a wafer processing will be now described. [Attaching Step] In this step, the wafer is attached to the support via the temporary adhesive material for a wafer processing by heating them under reduced pressure. More specifically, attaching is performed by either procedure: forming the thermoplastic resin layer (A) on the front surface of the wafer from a liquid composition (A′), forming the thermosetting polymer layer (B) on the support by laminating a film resin (B′), and then attaching the wafer to the support; or forming the thermoplastic resin layer (A) on the front surface of the wafer from the liquid composition (A′), forming the thermosetting polymer layer (B) on the resin layer (A) by laminating the film resin (B′), and then attaching the wafer to the support. Herein, the liquid composition (A′) is a liquid composition containing a thermoplastic resin. The film resin (B′) is a film formed from the composition containing a thermosetting polymer. The wafer used in this step has a circuit-forming surface on one surface and a non-circuit-forming surface on the other surface. The wafer to which the present invention can be applied is typically a semiconductor wafer. Examples of the semiconductor wafer include not only a silicon wafer, but also a germanium wafer, a gallium-arsenic wafer, a gallium-phosphorus wafer, and a gallium-arsenic-aluminum wafer. The thickness of the wafer is typically, but not particularly limited to, 600 to 800 μm, more typically 625 to 775 μm. As the support, a substrate such as a silicon wafer, a glass plate, and a quartz wafer can be used without any limitation. In the present invention, it is not necessary to irradiate the temporary adhesive material layer with an energy beam through the support, so that the support does not require light transmittance. The thermoplastic resin layer (A) is formed on the front surface of, for example, a semiconductor substrate such as a silicon wafer from the liquid composition (A′). As described above, the liquid composition (A′) contains a thermoplastic resin. For example, the liquid composition can be obtained by dissolving a thermoplastic resin in a solvent. In this case, the thermoplastic resin layer (A) can be formed on the front surface of the wafer by applying the liquid composition (A′) onto the front surface of the wafer by, for example, spin coating, spray coating, or roll coating, followed by pre-baking. Alternatively, the thermoplastic resin layer (A) can be formed on the front surface of the wafer by forming a film of the liquid composition (A′), laminating this film on the front surface of the wafer, and pre-baking the film. Preferable examples of the solvent include hydrocarbon solvents such as nonane, p-menthane, pinene, isooctane, toluene, xylene, and mesitylene. Among them, nonane, p-menthane, isooctane, and mesitylene are more preferable because of their coating properties. Although the thickness of the film to be formed is not limited, the resin film is desirably formed according to unevenness of the substrate. The thermoplastic resin layer (A) is preferably formed on the front surface of the wafer with a thickness of 0.5 to 50 μm, more preferably 0.5 to 10 μm. The thermosetting polymer layer (B) is formed on the support or the thermoplastic resin layer (A) formed on the front surface of the wafer by laminating the film resin (B′). This reduces loss (cost) of the resin due to spin coating, improves flatness of the film thickness, eliminates a wafer cleaning solution for backside rinse, etc., and thus reduces the amount of waste liquid. The film resin (B′) is obtained by forming the composition containing a thermosetting polymer into a film. When the composition containing a thermosetting polymer is formed into a film, an organic solvent for dissolving the composition containing a thermosetting polymer may be optionally used. In other words, the composition containing a thermosetting polymer may be used without solvent, or may be used after dissolving or dispersing in an organic solvent to prepare a solution or dispersion (a composition solution), as described below. Examples of the organic solvent include N,N-dimethyl acetamide, methyl ethyl ketone, N,N-dimethyl formamide, cyclohexanone, cyclopentanone, N-methyl-2-pyrrolidone, toluene, methanol, ethanol, isopropanol, acetone, propylene glycol monomethyl ether, and propylene glycol monomethyl ether acetate. Preferable examples include methyl ethyl ketone, cyclopentanone, propylene glycol monomethyl ether, and propylene glycol monomethyl ether acetate. These organic solvents may be used alone or in combination of two or more kinds. The thickness of the film resin (B′) is preferably, but not particularly limited to, 10 μm to 200 μm, more preferably 20 μm to 120 μm. When the thickness is 10 μm or more, it can sufficiently withstand a grinding step for thinning the wafer. When the film thickness is 200 μm or less, the film resin is prevented from deforming in a heat treatment process such as TSV formation process, and can be put to practical use. Thus, this range is preferable. Protective layers may be laminated on the film resin (B′). The protective layers that can be used will be described below. A film having the film resin (B′) and the protective layers (a protective layer-attached resin film) can be produced by the following procedure. [Method for Producing Protective Layer-Attached Resin Film] The thermosetting polymer, the crosslinker, and if necessary, optional components and an organic solvent are previously mixed to prepare a solution of resin composition. This resin composition solution is applied to a protective layer (a protective film or a release film) by a die coater, a reverse roll coater, a comma center, or the like. The protective layer to which the resin composition solution is applied is made to pass through an inline dryer, and the organic solvent is removed to dry the layer at 80 to 160° C. over 2 to 20 minutes. The layer is then pressure-bonded and laminated to another protective layer by a roll laminator. The protective layer-attached resin film can be thus obtained. The pressure bonding condition for laminating is not particularly limited. Preferable condition is as follows: temperature, 50 to 100° C.; linear pressure, 0.5 to 5 kgf/cm; speed, 0.1 to 5 m/min. In another aspect, a complex film formed of multiple resin films is obtained by the following procedure. Two or more identical or different protective layer-attached resin films are prepared. The protective layers are removed from the respective resin films such that the film resins (B′) to be laminated are uncovered. The film resins (B′) of the resin films are then laminated to form a complex film. In laminating, the films are preferably laminated while heating at 30 to 120° C. If two or more different film resins (B′) are laminated, protective layers (protective films/release films) having different peeling force may be used as needed. Protective Layer (Protective Film/Release Film) The protective layers, which are used as a protective film and a release film for a wafer, are not particularly limited as long as the layers can be separated without deforming the film resin (B′). Examples thereof include plastic films such as a polyethylene (PE) film, a polypropylene (PP) film, a polymethylpentene (TPX) film, and a polyester film subjected to releasing treatment. The peeling force is preferably 50 to 300 mN/min. The thickness is 25 to 100 μm, preferably 38 to 75 μm. The method of laminating the wafer with the film resin (B′) is not particularly limited. For example, one of protective layers is removed from the protective layer-attached resin film. The protective layer-attached resin film on which the other protective layer remains is pressure-bonded to the support or the wafer having the thermoplastic resin layer (A) at once by a roll laminator, for example, a vacuum laminator TEAM-100RF, manufactured by Takatori Corporation in a vacuum chamber with a vacuum of 50 to 1,000 Pa, preferably 50 to 500 Pa, for example 250 Pa, at 80 to 200° C., preferably 80 to 130° C., for example 100° C. After the pressure is restored to normal pressure, the wafer is cooled to room temperature and taken out from the vacuum laminator. The other protective layer is then removed. When the thermoplastic resin layer (A) and the thermosetting polymer layer (B) are formed, prebaking is preferably performed at 80 to 200° C., more preferably 100 to 180° C. depending on the volatile conditions of the solvent, although the temperature condition is not particularly limited thereto. For example, when the thermosetting polymer layer (B) is formed, the laminated film resin (B′) laminated by the above method may be dried by heating at 100 to 180° C. for 1 to 5 minutes to form the thermosetting polymer layer (B). The wafer and the support on which the layers (A) and (B) have been formed are joined via the layers (A) and (B) to form a substrate. The substrate is uniformly compressed under reduced pressure preferably at 40 to 200° C., more preferably 60 to 180° C. to form a wafer processing laminate (laminated substrate) in which the wafer and the support are joined. The reduced pressure condition is a reduced pressure atmosphere, preferably 0.01 to 500 Pa, more preferably 0.01 to 100 Pa. The compression condition is preferably 0.1 to 50 kN. An apparatus for attaching the wafer may be a commercially available wafer-bonding apparatus, such as EVG520IS and 850 TB manufactured by EV Group. [Bonding Step] In this step, the thermoplastic resin layer (A) and the thermosetting polymer layer (B) are adhesively bonded by heat curing the thermosetting polymer layer (B). After the wafer processing laminate (laminated substrate) is formed, the wafer processing laminate is heated at 120 to 220° C., preferably 150 to 200° C., for 10 minutes to 4 hours, preferably 30 minutes to 2 hours to cure the thermosetting polymer layer (B). [Method for Producing Thin Wafer] Next, the inventive method for producing a thin wafer will be described. The inventive method for producing a thin wafer includes the steps (a) to (c) and optional steps (d) to (g). The thickness of a thin wafer obtained by the inventive producing method is typically 5 to 300 μm, more typically 10 to 100 μm. [Step (a)] The step (a) is a step of grinding or polishing the back surface of the wafer temporarily bonded to the support via the temporary adhesive material for a wafer processing by the inventive temporary adhesion method, i.e., a step of grinding or polishing the wafer processing laminate, which has been subjected to the bonding step in the inventive temporary adhesion method, from the wafer back surface side to reduce the thickness of the wafer. The technique for grinding the wafer back surface is not particularly limited, and known grinding techniques may be used. The grinding is preferably performed while water is fed to the wafer and a grinding wheel (e.g. diamond) for cooling. Examples of an apparatus for grinding the wafer back surface include DAG-810 (product name) manufactured by DISCO Co., Ltd. The wafer back surface side may be subjected to CMP polishing. [Step (b)] Step (b) is a step of processing the back surface of the wafer, i.e., a step of processing the non-circuit-forming surface of the wafer that has been thinned by grinding the back surface. This step includes various processes applied in the wafer level. Examples thereof include electrode formation, metal wiring formation, and protective film formation. More specifically, there may be mentioned well-known processes including metal sputtering for forming electrodes or the like, wet etching for etching a sputtered metal layer, patterning process in which a resist is applied and subjected to exposure and development to form a pattern used as a mask for metal wiring formation, resist removal, dry etching, plating with metal, silicon etching for forming a TSV, and formation of an oxide film on silicon surface. [Step (c)] Step (c) is a step of separating the wafer processed in the step (b) from the temporary adhesive material for a wafer processing and the support, i.e., a step of separating the thinned wafer, which has been subjected to various processes, from the temporary adhesive material for a wafer processing and the support before dicing. This separating step is generally carried out under relatively low temperature condition from room temperature to about 60° C. This step may be performed by a procedure in which one of the wafer and the support of the wafer processing laminate is horizontally fixed, and the other is lifted at a certain angle with respect to the horizontal direction; or a procedure in which a protective film is bonded to the ground surface of the wafer, and then the wafer and the protective film are separated from the wafer processing laminate by peeling. Both the separating procedures can be applied to the present invention, although it is not limited to these procedures. These separating procedures are usually carried out at room temperature. The step (c), separating the processed wafer from the temporary adhesive material for a wafer processing and the support, preferably includes the steps of: (e) bonding a dicing tape to the processed surface (back surface) of the processed wafer; (f) attaching the dicing tape surface by vacuum suction to a suction surface; and (g) separating the temporary adhesive material for a wafer processing and the support from the processed wafer by lift-off in a temperature range of the suction surface of 10° C. to 100° C. These steps enable the temporary adhesive material for a wafer processing and the support to be easily separated from the processed wafer, and facilitate a subsequent dicing step. The step (c) preferably includes immersing the whole of the processed wafer in a solvent before the processed wafer is separated from the temporary adhesive material for a wafer processing and the support. This causes the temporary adhesive material at the periphery of the wafer to be swollen and decomposed. Thus, the wafer can be easily separated from the temporary adhesive material for a wafer processing and the support. The solvent is any solvent that can swell and dissolve the thermoplastic resin layer (A) in the complex temporary adhesive material layer. Illustrative examples thereof include pentane, hexane, cyclohexane, decane, isononane, p-menthane, pinene, isododecane, limonene, toluene, xylene, and mesitylene. These solvents may be used alone or in combination of two or more kinds thereof. Additionally, the method preferably includes (d) cleaning a separation plane of the processed wafer after the processed wafer is separated from the temporary adhesive material for a wafer processing and the support by the step (c). The circuit-forming surface of the wafer separated from the support by the step (c) can have residue of the thermoplastic resin layer (A) in some cases. This thermoplastic resin layer (A) can be removed by, for example, cleaning the wafer. In the step (d), any cleaning solution capable of dissolving the thermoplastic resin layer (A) in the complex temporary adhesive material layer can be used. Illustrative examples thereof include pentane, hexane, cyclohexane, decane, isononane, p-menthane, pinene, isododecane, limonene, toluene, xylene, and mesitylene. These solvents may be used alone or in combination of two or more kinds thereof. If removal is difficult, a base or an acid may be added to the solvent. Examples of the usable base include amines such as ethanolamine, diethanolamine, triethanolamine, triethylamine, and ammonia; and ammonium salts such as tetramethylammonium hydroxide. Examples of the usable acid include organic acids such as acetic acid, oxalic acid, benzenesulfonic acid, and dodecylbenzenesulfonic acid. The amount thereof is 0.01 to 10 mass %, preferably 0.1 to 5 mass % in terms of concentration in the cleaning solution. To improve removal efficiency of residual matters, an existing surfactant may be added thereto. The cleaning may be performed by a known method, such as paddling, spraying, or dipping in a cleaning tank with the above solution. Above all, the cleaning is preferably performed by two-fluid cleaning. Two-fluid cleaning allows cleaning under high pressure, thus enabling a residual resin to be removed in a short time. In this operation, nitrogen is preferably mixed. The cleaning time is preferably about 5 seconds to 10 minutes, more preferably 10 seconds to 5 minutes. The cleaning temperature is preferably 10 to 80° C., more preferably 15 to 65° C. If necessary, the layer (A) may be dissolved in the dissolving solution, and the wafer may be finally rinsed with water or alcohol (preferably having 1 to 5 carbon atoms) and dried to obtain a thin wafer. Part EXAMPLES: In the following, the present invention will be specifically described with reference to examples and comparative examples, but the present invention is not limited to these examples. Part Resin Solution Production Example 1: 16 g of a hydrogenated polystyrene-based thermoplastic resin, SEPTON8007 (available from Kuraray Co., Ltd.), was dissolved in 184 g of p-menthane to obtain a p-menthane solution containing 8 mass % SEPTON8007. The obtained solution was filtered through a 0.2-μm membrane filter to obtain a p-menthane solution of the non-silicone thermoplastic resin (A′-1). Part Resin Solution Production Example 2: 24 g of a hydrogenated polystyrene-based thermoplastic resin, SEPTON4033 (available from Kuraray Co., Ltd.), was dissolved in 176 g of p-menthane to obtain a p-menthane solution containing 12 mass % SEPTON4033. The obtained solution was filtered through a 0.2-μm membrane filter to obtain a p-menthane solution of the non-silicone thermoplastic resin (A′-2). Part Resin Solution Production Example 3: 10 g of a hydrogenated polystyrene-based thermoplastic resin, SEPTON4033 (available from Kuraray Co., Ltd.), and 10 g of a hydrogenated polystyrene-based thermoplastic resin, Tuftec H1043 (Asahi Kasei Chemicals Corporation), were dissolved in 180 g of p-menthane to obtain a p-menthane solution containing 10 mass % mixture of SEPTON4033 and Tuftec H1043. The obtained solution was filtered through a 0.2-μm membrane filter to obtain a p-menthane solution of the non-silicone thermoplastic resin
{'bibliographic_information': "{'country': 'US', 'doc-number': '15271056', 'kind': 'B2', 'date': '20160920', 'invention_title': 'Temporary adhesion method and method for producing thin wafer'}", 'source_file': './grant/2018/ipg180206.xml', 'source_data': 'USPTO-Grant'}