Temporary adhesion method and method for producing thin wafer

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 removing a first protective layer from a protective layer-attached resin film, which has a film resin (B′) that has been formed from a composition containing a thermosetting polymer and the protective layers formed on the front and back surfaces of the film resin (B′), 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′) on which a second protective layer remains, and removing the second protective layer, 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′) on which the second protective layer remains, and removing the second protective layer, 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).