JP5951216B2 - Adhesive sheet and method of using the same - Google Patents

Description

  The present invention relates to a pressure-sensitive adhesive sheet, and more particularly, is preferably used as a surface protective sheet for protecting a circuit surface when grinding a back surface of a semiconductor wafer having a circuit formed on the surface and having bumps with large height differences on the circuit surface. It relates to an adhesive sheet. Moreover, this invention relates to the usage method of this adhesive sheet.

  As information terminal devices are rapidly becoming thinner, smaller, and multifunctional, semiconductor devices mounted on them are also required to be thinner and denser. In order to reduce the thickness of an apparatus, it is desired to reduce the thickness of a semiconductor wafer on which semiconductors are integrated. Further, as the density increases, there is a need for further improvement of a semiconductor chip mounting technique in which spherical bumps made of solder or the like and having a diameter of about several hundreds μm, which are used for joining a semiconductor chip and a substrate, are mounted on a circuit surface. Usually, the bumps are bonded to the semiconductor wafer at a high density in advance. When the back surface of such a wafer with bumps is ground, the pressure difference caused by the difference in height between the portion where the bumps are present and the portion where the bumps are not present directly affects the back surface of the wafer. Will eventually break the semiconductor wafer.

  For this reason, when grinding the back surface of the wafer with bumps, a surface protection sheet composed of a base film and an adhesive layer is attached to the circuit surface to absorb and alleviate the height difference of the circuit surface. In particular, for wafers with a large bump height difference, the pressure-sensitive adhesive layer of the surface protective sheet is made thicker and the flowability of the pressure-sensitive adhesive is further increased, thereby bringing the pressure-sensitive adhesive layer and the wafer into close contact with each other. This is dealt with by eliminating the pressure difference due to bump bumps due to the cushioning properties of the layers. However, if the pressure-sensitive adhesive layer is made thick and its fluidity is increased, the pressure-sensitive adhesive easily wraps around the base portion of the bump. For this reason, the adhesive adhered to the base portion of the bump may cause cohesive failure by the peeling operation of the surface protective sheet, and a part of the adhesive may remain on the circuit surface. This is a problem that may occur even with a surface protective sheet using an energy ray curable adhesive. If the adhesive remaining on the circuit surface is not removed by solvent cleaning or the like, it remains as a foreign substance in the device and impairs the reliability of the completed device.

  Therefore, it has been proposed to provide an intermediate layer for absorbing and mitigating bump height differences between the base film of the surface protection sheet and the pressure-sensitive adhesive layer, rather than increasing the thickness of the pressure-sensitive adhesive layer.

  For example, Patent Document 1 (Japanese Patent Application Laid-Open No. 2000-17239) discloses a thermoplastic resin intermediate layer having a JIS-A hardness of 10 to 55 and a thickness of 28 to 400 μm between a base material and an adhesive layer. A pressure-sensitive adhesive sheet in which is disposed is disclosed. Patent Document 2 (Japanese Patent Laid-Open No. 2001-203255) discloses a surface protective sheet having an intermediate layer having an elastic modulus of 30 to 1000 kPa and a gel content of 20% or more.

  These pressure-sensitive adhesive sheets proposed in Patent Documents 1 and 2 are premised on being attached to a semiconductor wafer at room temperature. Since the intermediate layer is formed to absorb and relax the height difference of the semiconductor wafer surface, it is designed to have flexibility at room temperature. When such a pressure-sensitive adhesive sheet is applied to the wafer surface and backside grinding is performed, the intermediate layer is softened by the heat generated during grinding, which may reduce the grinding accuracy. Furthermore, when the pressure-sensitive adhesive sheet is rolled up, transported, stored, etc., it is exposed to high temperatures, particularly in the summer, and the intermediate layer and the pressure-sensitive adhesive layer soften and the resin component oozes out from the side of the roll. There was a case.

A surface protective sheet having an intermediate layer exhibiting flexibility under heating conditions, although having low flexibility at low temperatures, has been proposed. For example, in Patent Document 3 (Japanese Patent Laid-Open No. 2005-48039), as an intermediate layer, the storage elastic modulus at 50 ° C. is 3.0 × 10 ⁵ [Pa] or less and the storage elastic modulus at 23 ° C. is 2. A surface protective sheet having an intermediate layer composed of a side-chain crystalline polymer that is 0 × 10 ⁶ [Pa] or higher and has a primary melting transition temperature higher than room temperature (23 ° C.) has been proposed. Further, Patent Document 4 (Republished Patent: International Publication No. WO2006 / 088074) discloses that the storage elastic modulus G ′ (25) at 25 ° C. and the storage elastic modulus G ′ (60) at 60 ° C. are G ′ (60). A surface protective sheet provided with an intermediate layer having a relationship of /G′(25)<0.1 is disclosed.

  According to such a surface protective sheet, since the intermediate layer is softened by heating, the surface protective sheet can be adhered in close contact with the irregularities on the surface of the semiconductor wafer. In addition, since the wafer can be stably held during back grinding or conveyance, the grinding accuracy is high and the wafer can be prevented from being damaged.

JP 2000-17239 A JP 2001-203255 A JP-A-2005-48039 Republished patent: International Publication Number WO2006 / 088074

  In the surface protective sheet of Patent Document 3, the surface followability at the time of attaching the wafer is improved because the intermediate layer is softened by heating. However, if the sticking temperature is too high, the intermediate layer may be fluidized, the thickness uniformity of the pressure-sensitive adhesive sheet may be reduced, or the resin component may ooze out from the edge of the pressure-sensitive adhesive sheet. For this reason, it is necessary to strictly control the sticking temperature near the primary melting transition temperature of the side chain crystalline polymer, and the degree of freedom of the process is low. In addition, the storage modulus at room temperature is high, and such a side chain crystalline polymer is so low in surface adhesion that it may be used as a release agent, and an intermediate layer made of such a material is adjacent. In some cases, the adhesion to the layer was poor. In addition, an etching process or the like may be performed on the back surface of the wafer while the wafer surface is protected with an adhesive sheet. At this time, the wafer may be heated or generate heat. In the pressure-sensitive adhesive sheet as in Patent Document 4, the intermediate layer may be fluidized in such a back surface processing step, and the protection function of the wafer may be reduced.

  Therefore, the present invention can absorb and mitigate the difference in height of the surface of the bump wafer or the like in the surface protection sheet for protecting the surface of the semiconductor wafer when processing the back surface of the semiconductor wafer, and does not excessively soften in a high temperature environment. It aims at providing the surface protection sheet which has an intermediate | middle layer.

  As a result of earnest research for the purpose of solving the above-mentioned problems, the present inventors include a heat-meltable resin as an intermediate layer of the surface protection sheet, and by disposing an intermediate layer exhibiting a specific elastic behavior, The present inventors have found that the problem can be solved and have completed the present invention.

The present invention for solving the above problems includes the following gist.
(1) A base film, an intermediate layer, and an adhesive layer are laminated in this order,
The intermediate layer includes a heat-meltable resin having a melting point (Tm);
The storage elastic modulus G ′ (Tm + 6) of the intermediate layer at a temperature 6 ° C. higher than the melting point Tm (Tm + 6) and the storage elastic modulus G ′ of the intermediate layer at a temperature 6 ° C. lower than the melting point Tm (Tm−6). About Tm-6), G '(Tm-6) / G' (Tm + 6) is an adhesive sheet having 2.0 or more.

(2) The pressure-sensitive adhesive sheet according to (1), wherein the heat-meltable resin has a melting point in the range of (Tm) 45 to 90 ° C.

(3) The pressure-sensitive adhesive sheet according to (1) or (2), wherein the melting start temperature of the heat-meltable resin is (Tm-8) ° C. or higher.

(4) The adhesive sheet according to any one of (1) to (3), wherein the hot-melt resin is an olefin-based material.

(5) The pressure-sensitive adhesive sheet according to (4), wherein the olefin-based material is an α-olefin polymer having 14 to 30 carbon atoms.

(6) The intermediate sheet is the pressure-sensitive adhesive sheet according to any one of (1) to (5), wherein the hot-melt resin is dispersed in a matrix resin.

(7) The pressure-sensitive adhesive sheet according to (6), wherein the matrix resin does not have a melting point, or the melting point exceeds a temperature for sticking the pressure-sensitive adhesive sheet to the adherend.

(8) The pressure-sensitive adhesive sheet according to (6) or (7), wherein the matrix resin comprises an energy ray curable resin.

(9) The pressure-sensitive adhesive sheet according to (8), wherein the energy beam curable resin is a cured product obtained by energy beam curing a compound containing a urethane resin and an energy beam curable monomer.

(10) The pressure-sensitive adhesive sheet according to (1), wherein the intermediate layer is a cured product obtained by energy-beam curing a blend containing the heat-meltable resin, a urethane resin, and an energy beam-curable monomer.

(11) The storage elastic modulus G ′ (25) at 25 ° C. of the intermediate layer is 0.05 MPa to 20 MPa, the storage elastic modulus G ′ (50) at 50 ° C. is 0.01 MPa to 15 MPa, and the storage elastic modulus G at 80 ° C. The pressure-sensitive adhesive sheet according to (1), wherein “(80) is 0.001 MPa to 1 MPa and satisfies a relationship of G ′ (25)> G ′ (50)> G ′ (80)”.

(12) The pressure-sensitive adhesive sheet according to any one of (1) to (11), wherein the base film has a thickness of 50 to 200 μm, the intermediate layer has a thickness of 50 to 500 μm, and the pressure-sensitive adhesive layer has a thickness of 1 to 150 μm.

(13) The pressure-sensitive adhesive sheet according to any one of (1) to (12), wherein the pressure-sensitive adhesive sheet is a surface protective sheet for protecting the surface of the semiconductor wafer when processing the back surface of the semiconductor wafer.

(14) A step of applying the adhesive sheet according to (13) to a surface of a semiconductor wafer on which a circuit having bumps is formed, and grinding the back surface of the semiconductor wafer while protecting the circuit surface of the semiconductor wafer. A method for processing a semiconductor wafer, comprising:

(15) The semiconductor wafer processing method according to (14), wherein the adhesive sheet is attached to the semiconductor wafer at a temperature not lower than the melting point (Tm) of the heat-meltable resin and not higher than 50 ° C. higher than Tm.

(16) A groove having a depth of cut shallower than the wafer thickness is formed from the surface of the semiconductor wafer on which a circuit having bumps is formed, and the adhesive sheet according to (13) is pasted on the circuit forming surface, A method of manufacturing a semiconductor chip, comprising the steps of reducing the thickness of the wafer by grinding the back surface of the semiconductor wafer and finally dividing the wafer into individual chips.

(17) The method for manufacturing a semiconductor chip according to (16), wherein the adhesive sheet is attached to the semiconductor wafer at a temperature not lower than the melting point (Tm) of the hot-melt resin and not higher than 50 ° C. higher than Tm.

  In the present invention, as an intermediate layer of the surface protection sheet, an intermediate layer containing a heat-meltable resin and exhibiting a unique elastic behavior is disposed. The intermediate layer can absorb and alleviate the height difference of the wafer surface, and does not excessively soften in a high temperature environment. For this reason, it is not necessary to strictly control the sticking temperature, and the degree of freedom of the process is high. Further, the surface protection sheet can be adhered and adhered to the circuit surface of the wafer with bumps, and the wafer can be stably held even when processing involving heating and heat generation is performed on the back surface of the wafer.

  Hereinafter, the present invention will be described more specifically, including its best mode. The pressure-sensitive adhesive sheet according to the present invention is formed by laminating a base film, an intermediate layer, and a pressure-sensitive adhesive layer in this order.

(Base film)
The base film is not particularly limited, and various synthetic resin films that have been used as the base material of the surface protective sheet are used without any particular limitation. Examples of such a base film include polyethylene film, polypropylene film, polybutene film, polybutadiene film, polymethylpentene film, ethylene / vinyl acetate copolymer film, ionomer resin film, and ethylene / (meth) acrylic acid copolymer. Polyester film such as coalesced film, polyolefin film such as ethylene / (meth) acrylate copolymer film, polyvinyl chloride film, vinyl chloride copolymer film, polyethylene terephthalate film, polyethylene naphthalate film, polybutylene terephthalate film A film such as a film, a polyurethane film, a polystyrene film, a polycarbonate film, or a polyimide film is used. Among these, a relatively hard film is preferable from the viewpoint of stably holding the wafer, and for example, a polyester film is more preferable. Among polyester films, it is particularly preferable to use a polyethylene terephthalate film. These crosslinked films are also used. Furthermore, these laminated films may be sufficient. In addition, it is preferable to laminate a relatively hard film such as a polyester film and a relatively soft film such as a polyolefin film. By setting it as such a structure, it is easy to prevent the curvature of the semiconductor wafer in the grinding process of the semiconductor wafer using the adhesive sheet which concerns on this invention. In addition to the above films, films colored with these, fluororesin films, and the like can be used.

  The pressure-sensitive adhesive sheet according to the present invention is produced by providing a pressure-sensitive adhesive layer on the intermediate layer formed on the base film as described above. In the case where the pressure-sensitive adhesive layer is composed of an energy ray-curable pressure-sensitive adhesive, the base film and the intermediate layer need to have energy ray permeability necessary for curing.

  In addition, the upper surface of the base film, that is, the surface on the side where the intermediate layer is provided may be subjected to corona treatment or other layers such as a primer layer and a barrier layer in order to improve adhesion to the intermediate layer. Good.

  The thickness of the substrate film is preferably 20 to 200 μm, more preferably 30 to 160 μm, and particularly preferably 50 to 140 μm. If the substrate film is extremely thin or too thick, the operability of the pressure-sensitive adhesive sheet is lowered.

(Middle layer)
An intermediate layer is formed between the base film and the pressure-sensitive adhesive layer. The intermediate layer includes a heat-meltable resin having a melting point (Tm, ° C.) and is designed to exhibit a unique elastic behavior. Here, having a melting point means that a clear and sharp melting peak is observed in DSC measurement, and the melting point indicates the temperature of the melting peak. The fact that a clear and sharp melting peak is observed indicates that the difference between the rising temperature of the melting peak and the temperature at the peak apex is small. Specifically, the melting start temperature (Ti, ° C) of the hot-melt resin ) Is close to the melting peak temperature (Tm), preferably Ti ≧ (Tm-8), more preferably Ti ≧ (Tm-6), and particularly preferably Ti ≧ (Tm-3). Means that. The melting start temperature is a temperature at which a melting peak starts to rise in DSC measurement of a heat-meltable resin. Moreover, it is preferable that a melting peak is single and does not have a shoulder etc.

  The melting point (Tm) of the heat-meltable resin is a melting peak temperature in DSC measurement, and is preferably in the range of 45 to 90 ° C, more preferably 50 to 80 ° C. When the melting point is in such a range, the temperature at which the storage elastic modulus of the intermediate layer, which will be described later, drops significantly is set to a temperature suitable for application of the adhesive sheet, and the adhesive sheet of the present invention is applied to the semiconductor wafer. It becomes easy to be positioned in the middle of the temperature at which the back surface processing is performed.

  By containing the above-described hot-melt resin in the intermediate layer, the storage elastic modulus of the intermediate layer is significantly different before and after the melting point of the hot-melt resin. That is, the storage elastic modulus gradually changes until the intermediate layer is heated and reaches Tm, the storage elastic modulus is remarkably lowered near Tm, and thereafter the storage elastic modulus gradually changes again. In the pressure-sensitive adhesive sheet of the present invention, the storage elastic modulus G ′ (Tm + 6) of the intermediate layer at a temperature 6 ° C. higher than the melting point Tm (Tm + 6) and the temperature 6 ° C. lower than the melting point Tm of the heat-meltable resin (Tm-6). With respect to the storage elastic modulus G ′ (Tm-6) of the intermediate layer, G ′ (Tm-6) / G ′ (Tm + 6) is 2.0 or more, preferably 2.4 or more, more preferably 2 0.5 to 30.0, particularly preferably in the range of 2.8 to 25.0.

  Thus, in the pressure-sensitive adhesive sheet of the present invention, the storage elastic modulus of the intermediate layer largely fluctuates at a certain temperature (Tm), and is relatively stable in both the temperature range lower than Tm and the temperature range higher than Tm. The storage elastic modulus tends to change gradually, and the storage elastic modulus in the temperature region lower than Tm is higher than the storage elastic modulus in the temperature region higher than Tm. And the said property can be expressed notably by measuring the storage elastic modulus of an intermediate | middle layer at 2 points | pieces of 6 degreeC above and below melting | fusing point (Tm).

That is, the storage elastic modulus of the intermediate layer of the pressure-sensitive adhesive sheet is high on the low temperature side, low on the high temperature side, and changes greatly in Tm. Looking at the temperature characteristics of the storage elastic modulus of the intermediate layer at 25 ° C, 50 ° C and 80 ° C,
Preferably, the storage elastic modulus G ′ (25) at 25 ° C. is 0.05 MPa to 20 MPa, the storage elastic modulus G ′ (50) at 50 ° C. is 0.01 MPa to 15 MPa, and the storage elastic modulus G ′ (80) at 80 ° C. Is 0.001 MPa to 1 MPa,
More preferably, G ′ (25) is 0.08 MPa to 10 MPa, G ′ (50) is 0.04 MPa to 5 MPa, G ′ (80) is 0.001 MPa to 0.1 MPa,
Particularly preferably, G ′ (25) is 0.1 MPa to 5 MPa, G ′ (50) is 0.075 MPa to 3 MPa, and G ′ (80) is 0.005 MPa to 0.02 MPa.

  In the above, the relationship of G ′ (25)> G ′ (50)> G ′ (80) is satisfied. When G ′ (25) is in the above range, the rigidity of the intermediate layer is maintained at the grinding temperature, the grinding accuracy is improved, and the adhesion of the intermediate layer to the substrate at room temperature is maintained. When G ′ (50) is in the above range, the hardness of the intermediate layer is maintained even when the ambient temperature during grinding rises and falls, and good grinding accuracy is easily maintained. When G ′ (80) is in the above range, it is easy to follow the unevenness of the adherend surface during sticking, and thickness unevenness due to the unevenness is unlikely to occur, so that the grinding accuracy is easily maintained. On the other hand, if G ′ (80) is too low, the intermediate layer may protrude during the sticking, or the intermediate layer may adhere to the cutting blade during the cutting after the sticking.

  In the pressure-sensitive adhesive sheet of the present invention, the tendency for the storage elastic modulus of the intermediate layer to gradually change in a temperature region higher than Tm is 24 ° C. or more higher than the above-described storage elastic modulus G ′ (Tm + 6) and the melting point (Tm). Also confirmed by the ratio of the storage elastic modulus G ′ (Tm + 24) of the intermediate layer at temperature, G ′ (Tm + 6) / G ′ (Tm + 24), preferably 3.25 or less, more preferably 2.5 or less. can do.

  Therefore, according to the pressure-sensitive adhesive sheet of the present invention, if the temperature range is Tm or higher, the intermediate layer is in a softened state, so that the height difference of the wafer surface can be absorbed and relaxed, and adhered to the bump wafer in close contact. Can do. Moreover, in the temperature range where Tm is exceeded and the heat-meltable resin is melted, the storage elastic modulus of the intermediate layer changes gently and does not change rapidly. This means that the intermediate layer once softened is not excessively softened or fluidized in the softened state. For this reason, it is not necessary to strictly control the sticking temperature, and the degree of freedom of the process is high. In addition, the wafer can be stably held even when the back surface of the wafer is processed with heating and heat generation.

  The intermediate layer is not particularly limited as long as it contains a heat-meltable resin as described above and exhibits a specific elastic behavior. However, it is often difficult to form a film with a heat-meltable resin alone, and it may be excessively fluidized in a heating environment. Therefore, as a preferred configuration example of the intermediate layer, a structure in which a hot-melt resin is dispersed in a matrix resin can be exemplified. As described above, when the heat-meltable resin is dispersed in the matrix resin, the storage elastic modulus changes greatly in the low-temperature region and the high-temperature region of the melting point (Tm) of the heat-meltable resin. In the region, an intermediate layer whose elastic modulus changes gradually is obtained. This is presumably because the properties of the hot-melt resin become obvious near the melting point (Tm), whereas the elastic behavior of the matrix resin mainly dominates in other temperature ranges. Therefore, if the melting point is not included between the upper limit and the lower limit of the processing temperature, the elastic modulus of the intermediate layer during processing remains in a stable region. Conditions can be set and process flexibility is increased.

  The ratio of the matrix resin and the heat-meltable resin in the intermediate layer is not particularly limited, but from the viewpoint of easily realizing the specific elastic behavior as described above, the heat-meltable resin is based on 100 parts by weight of the matrix resin. The amount is preferably 5 to 70 parts by mass, more preferably 10 to 50 parts by mass, and still more preferably 10 to 35 parts by mass. When the heat-meltable resin is too small relative to the matrix resin, the effect that the storage elastic modulus causes a discontinuous change near Tm may not be sufficiently obtained. Moreover, when there are too many heat-meltable resins with respect to a matrix resin, there exists a tendency for an intermediate | middle layer to become brittle and to become easy to break, or for the adhesiveness to a base film to fall.

  As described above, the heat-meltable resin applicable to the present invention is not particularly limited as long as it has a clear and sharp melting point. As the polymer material having a clear and sharp melting point, for example, an acrylic polymer or an olefin material is preferably used, and among these, an olefin material is preferably used. Acrylic polymers with a clear and sharp melting point are generally waxy at room temperature, and evenly distributed in the composition for forming the matrix resin described later when the content in the intermediate layer is increased. It may be difficult to do. On the other hand, when the composition for forming the matrix resin and the heat-meltable resin are in a compatible state, the intermediate layer does not exhibit a significant decrease in storage elastic modulus at the melting point Tm of the heat-meltable resin, and storage elasticity The rate drop tends to occur over a wide temperature range. The acrylic polymer and the matrix resin are likely to form a compatible state, whereas such problems are unlikely to occur in the olefin material. As a result of diligent investigations by the present inventors, among the olefin-based materials, a poly α-olefin obtained by polymerizing a higher α-olefin using a specific bridged metallocene catalyst exhibits a clear melting point and at room temperature. The present inventors have found that it is solid and can be easily distributed uniformly in a composition for forming a matrix resin such as an energy beam curable resin. Here, the α-olefin is an α-olefin having 14 to 30, preferably 16 to 28 carbon atoms. The poly α-olefin may be a homopolymer of the α-olefin or a copolymer, but a homopolymer is preferable from the viewpoint of showing a clear melting point. More specific examples of such poly α-olefins include poly (docose-1), poly (eicosen-1), poly (octadecene-1), poly (hexadecene-1), etc., and Idemitsu Kosan Co., Ltd. Poly α-olefins having various melting points can be obtained from the company under the trade name “Erycrista”. As the acrylic polymer, ST-100 (trade name) manufactured by Nippon Shokubai Co., Ltd. is used.

  The crystalline structure of the heat-meltable resin is considered to be a structure in which the main chain portion is not crystallized, and only the side chain alkyl portion is crystallized in a metastable manner, and exhibits a sharp melting behavior at a low melting point. In general, a low melting point resin is often soft even below the melting point, but this heat-meltable resin exhibits fastness below the melting point despite having a low melting point. That is, the penetration of the heat-meltable resin used in the present invention is preferably 6 or less, and more preferably 3 or less. By setting the hot-melt resin to such a penetration, the storage elastic modulus of the intermediate layer at a temperature of Tm or less is kept higher, and the grinding accuracy is further improved. The penetration is a characteristic value obtained on the basis of the measurement performed by adopting 25 ° C. as the test temperature by the penetration test method of JIS K-2235.

  In the intermediate layer, the above-described hot-melt resin is preferably dispersed in the matrix resin. From the viewpoint of realizing an appropriate storage modulus under the heating environment of the intermediate layer, the matrix resin preferably has a melting point or a resin whose melting point exceeds the temperature for sticking the adherend to the adherend. . If the matrix resin has a melting point, the resin will flow above the melting point of the matrix resin, and the holding function cannot be performed, the conditions for sticking to the wafer can be easily set, and the degree of freedom of the process is increased. There is a risk that it will not be possible. For this reason, the matrix resin is preferably made of a resin having no melting point. However, in the case where the matrix resin has a melting point, the holding function of the intermediate layer needs to be maintained at the temperature at which the adhesive sheet is applied to the wafer. Therefore, if the matrix resin has a melting point that exceeds the temperature at which the pressure-sensitive adhesive sheet is stuck to the adherend, the holding function is easily maintained without fluidizing when sticking to the wafer.

  Such a matrix resin serves as a binder for the heat-meltable resin, maintains the shape retention of the intermediate layer, and is intermediate at the temperature at the time of sticking to the wafer surface (that is, a temperature higher than the melting point of the heat-meltable resin). It is possible to prevent the layer from fluidizing excessively and the intermediate layer from sticking out at the time of sticking, or from adhering to the cutting blade in the cutting after the sticking. Further, at normal temperature, the intermediate layer can be prevented from being embrittled and the adhesion to the substrate can be maintained.

  The matrix resin is not particularly limited as long as the heat-meltable resin is uniformly dispersed and exhibits the elastic behavior as described above. However, a urethane resin or an energy ray-curable component that can easily control the flexibility and storage elastic modulus is used. It is preferable to consist of an energy beam curable resin formed by curing a blended composition.

  By using a urethane resin as the main component of the matrix resin, the intermediate layer can suppress excessive fluidization at the temperature at the time of sticking, and also exhibits appropriate flexibility, and the unevenness of the adherend surface is reduced. Followability is improved. As the urethane resin, a urethane polymer or an oligomer can be used.

  The matrix resin may be a urethane resin alone, but preferably has an appropriate cross-linked structure in order to control flexibility, shape retention and the like. The crosslinked structure may be formed by polymerizing and curing an energy ray-polymerizable urethane resin obtained by introducing an energy ray-polymerizable group into a urethane resin, or by mixing a urethane resin and an energy ray-curable monomer, A crosslinked structure may be introduced into the matrix resin by curing the mixture. Furthermore, an energy ray curable monomer and an energy ray polymerizable urethane resin may be used in combination. A matrix resin that contains an energy ray-polymerizable urethane resin or a polyfunctional energy ray-curable monomer and is cured with energy rays will form a crosslinked three-dimensional network structure. It will not have.

  In particular, in the intermediate layer of the present invention, the matrix resin is obtained by curing a blend of a urethane (meth) acrylate oligomer and an energy ray curable monomer described later, and the hot-melt resin is dispersed in the matrix resin. It is preferable that

  As the energy ray polymerizable urethane resin, a urethane (meth) acrylate oligomer is preferably used. The urethane (meth) acrylate oligomer is a compound having an energy ray polymerizable (meth) acryloyl group in the molecule and further having a urethane bond. The urethane (meth) acrylate oligomer is obtained, for example, by reacting a terminal isocyanate urethane prepolymer obtained by reacting a polyol compound and a polyvalent isocyanate compound with a (meth) acrylate having a hydroxy group. As the polyol, various polyols such as polyether type polyol and polyester type polyol are used, and diols are particularly preferably used.

  A terminal isocyanate urethane prepolymer is produced by the reaction of the polyol and the polyvalent isocyanate compound. Examples of polyisocyanates include aliphatic polyisocyanates such as tetramethylene diisocyanate, hexamethylene diisocyanate, and trimethylhexamethylene diisocyanate, isophorone diisocyanate, norbornane diisocyanate, and dicyclohexylmethane-4. , 4′-diisocyanate, dicyclohexylmethane-2,4′-diisocyanate, ω, ω′-diisocyanate dimethylcyclohexane, etc., 4,4′-diphenylmethane diisocyanate And aromatic diisocyanates such as tolylene diisocyanate, xylylene diisocyanate, tolidine diisocyanate, tetramethylene xylylene diisocyanate, naphthalene-1,5-diisocyanate, and the like.

  A urethane (meth) acrylate oligomer is obtained by reacting the obtained terminal isocyanate urethane prepolymer with a (meth) acrylate having a hydroxy group.

  The (meth) acrylate having a hydroxy group is not particularly limited as long as it is a compound having a hydroxy group and a (meth) acryloyl group in one molecule, and known ones can be used. Specifically, for example, 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, 4-hydroxybutyl (meth) acrylate, 4-hydroxycyclohexyl (meth) acrylate, 5-hydroxycyclooctyl (meta ) Acrylate, 2-hydroxy-3-phenyloxypropyl (meth) acrylate, pentaerythritol tri (meth) acrylate, polyethylene glycol mono (meth) acrylate, polypropylene glycol mono (meth) acrylate and other hydroxyalkyl (meth) acrylates, N -Hydroxy group-containing (meth) acrylamide such as methylol (meth) acrylamide, vinyl alcohol, vinylphenol, diglycidyl ester of bisphenol A (meth) actyl Reacting the Le acids like reaction product obtained.

  As conditions for reacting the terminal isocyanate urethane prepolymer and the hydroxy group-containing (meth) acrylate, the terminal isocyanate urethane prepolymer and the hydroxy group-containing (meth) acrylate are optionally mixed with a solvent and a catalyst. What is necessary is just to make it react for about 1 to 4 hours at about 60-100 degreeC in presence.

  The weight average molecular weight Mw of the urethane (meth) acrylate oligomer thus obtained (polystyrene converted value by gel permeation chromatography, hereinafter the same) is not particularly limited, but usually the weight average molecular weight Mw is 40000 to 100000, preferably about 41000 to 80000, more preferably about 45000 to 70000. By setting the weight average molecular weight Mw to 40000 or more, the elongation at break of the intermediate layer can be improved, and by setting the weight average molecular weight Mw to 100000 or less, the resin viscosity of the urethane (meth) acrylate oligomer can be lowered. The handling property of the forming coating solution is improved.

  The obtained urethane (meth) acrylate oligomer has a photopolymerizable double bond in the molecule, and has a property of being polymerized and cured by irradiation with energy rays to form a film. Such a urethane (meth) acrylate oligomer has a flexible portion having a relatively long chain length in the molecule, and the number of acryloyl groups serving as polymerization points is small compared to the molecular weight. The intermediate layer containing the cured product as a matrix resin exhibits the unique elastic behavior as described above.

  Said urethane (meth) acrylate oligomer can be used individually by 1 type or in combination of 2 or more types. Since only the urethane (meth) acrylate oligomer as described above is often difficult to form a film, it is preferably mixed with an energy ray-curable monomer and then cured to obtain a matrix resin. The energy ray curable monomer has an energy ray polymerizable double bond in the molecule, and particularly in the present invention, an acrylate ester compound having a relatively bulky group is preferably used.

  Specific examples of energy ray curable monomers include methyl (meth) acrylate, ethyl (meth) acrylate, n-propyl (meth) acrylate, isopropyl (meth) acrylate, n-butyl (meth) acrylate, and isobutyl (meth) acrylate. , T-butyl (meth) acrylate, n-pentyl (meth) acrylate, n-hexyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, n-octyl (meth) acrylate, isooctyl (meth) acrylate, nonyl (meth) ) Acrylate, decyl (meth) acrylate, isodecyl (meth) acrylate, undecyl (meth) acrylate, dodecyl (meth) acrylate, tridecyl (meth) acrylate, tetradecyl (meth) acrylate, hexadec (Meth) acrylates such as (meth) acrylates, octadecyl (meth) acrylates, eicosyl (meth) acrylates and the like having 1-30 carbon atoms; isobornyl (meth) acrylates, dicyclopentenyl (meth) acrylates, dicyclopentas (Meth) acrylates having an alicyclic structure such as nyl (meth) acrylate, dicyclopentenyloxy (meth) acrylate, cyclohexyl (meth) acrylate, adamantane (meth) acrylate; phenoxyethyl acrylate, phenylhydroxypropyl acrylate, benzyl acrylate (Meth) acrylate having an aromatic structure such as 2-hydroxy-3-phenoxypropyl acrylate, or tetrahydrofurfuryl (meth) acrylate, acrylo Having a heterocyclic structure such as Rumoruhorin (meth) acrylate, styrene, hydroxyethyl vinyl ether, hydroxybutyl vinyl ether, N- vinyl formamide, vinyl compounds such as N- vinyl pyrrolidone or N- vinyl caprolactam. Moreover, you may use polyfunctional (meth) acrylate as needed, but when polyfunctional (meth) acrylate is used abundantly, there exists a possibility that a crosslinked structure may become excessive in matrix resin and an intermediate | middle layer may become hard too much.

  Among these, from the point of compatibility with urethane (meth) acrylate oligomer, (meth) acrylate having an alicyclic structure having a relatively bulky group, (meth) acrylate having an aromatic structure, and heterocyclic structure (Meth) acrylate having

  100-700 mass parts is preferable with respect to 100 mass parts (solid content) of a urethane (meth) acrylate oligomer, and, as for the usage-amount of this energy-beam curable monomer, 200-600 mass parts is more preferable.

  The method for forming the intermediate layer is not particularly limited, and an intermediate layer may be formed by forming a coating liquid composed of a heat-meltable resin, a matrix resin, and a suitable solvent on the base film and drying it. Alternatively, the coating solution may be applied onto another release sheet and dried, and the resulting coating film may be transferred onto the substrate film. However, in this method, the heat-meltable resin is melted by heating at the time of drying, but it is not easy to control the separation state between the heat-meltable resin solidified after cooling and the matrix resin. For this reason, the hot-melt resin is compatible with the matrix resin, or the size of the hot-melt resin separation domains is not constant, domains with large size differences are mixed, and the dispersion of the hot-melt resin is uneven. It may become. In addition, when the drying time becomes long, the resin moves due to the difference in density between the matrix resin and the heat-meltable resin, and the composition and thickness of the intermediate layer may become uneven. Furthermore, since the preferable thickness of the intermediate layer is considerably large as will be described later, the productivity by the coating and drying method is poor and the drying time becomes long, so that the control of the distribution of the hot-melt resin as described above can be performed. Difficulty and non-uniformity may be further increased.

  In order to obtain an intermediate layer in which a heat-meltable resin is uniformly dispersed in a matrix resin, a matrix resin precursor containing the energy ray-polymerizable urethane (meth) acrylate oligomer and an energy ray-curable monomer, heat-meltable It is preferable to form a composition comprising a resin and other polymer components used as necessary and a dispersion medium on the base film, and then cure the film by irradiation with energy rays to form an intermediate layer. You may apply | coat the said composition on another peeling sheet, energy ray hardening, and may transfer the obtained coating film to a base film. According to energy ray curing, the temperature rise of the compound is small compared to the heat drying step, and the intermediate layer can be obtained in a short time. For this reason, the malfunction by the said coating method can be avoided, and a hot-melt resin can be uniformly disperse | distributed in matrix resin. In addition, by dispersing the heat-meltable resin in a particle state in a liquid compound and curing it in advance, the particle state of the heat-meltable resin before compounding is maintained and the separated state from the matrix resin is constituted. Therefore, the dispersion size of the hot-melt resin and the state of the interface with the matrix resin hardly change before and after the film formation, and an intermediate layer in which the hot-melt resin is dispersed in the expected separated state can be easily obtained. Even when the intermediate layer is thick, it is easy to obtain an intermediate layer having excellent productivity and uniform properties in the thickness direction.

As the film forming method, a technique called casting film formation (cast film formation) can be preferably employed. Specifically, after casting a liquid compound (a liquid material obtained by diluting a mixture of the above components with a solvent if necessary) into a thin film on, for example, a base film or a release sheet, energy rays are applied to the coating film. Irradiation is polymerized and cured to form a film. According to such a manufacturing method, the stress applied to the resin during film formation is small, and the formation of fish eyes is small. Moreover, the uniformity of the film thickness is also high, and the thickness accuracy is usually within 2%. Specifically, ultraviolet rays, electron beams, etc. are used as the energy rays. The irradiation amount varies depending on the type of energy beam. For example, when ultraviolet rays are used, the ultraviolet ray intensity is preferably 50 to 300 mW / cm ² and the ultraviolet ray irradiation amount is preferably about 100 to 1800 mJ / cm ² .

  When ultraviolet rays are used as energy rays during film formation, it is possible to react efficiently by blending a photopolymerization initiator into the blend. Examples of such photopolymerization initiators include photopolymerization initiators such as benzoin compounds, acetophenone compounds, acylphosphinoxide compounds, titanocene compounds, thioxanthone compounds and peroxide compounds, and photosensitizers such as amines and quinones. Specific examples include 1-hydroxycyclohexyl phenyl ketone, 2-hydroxy-2-methyl-1-phenyl-propan-1-one, benzoin, benzoin methyl ether, benzoin ethyl ether, and benzoin isopropyl ether.

  The use amount of the photopolymerization initiator is preferably 0.05 to 15 parts by mass, more preferably 0.1 to 10 parts by mass with respect to 100 parts by mass in total of the urethane (meth) acrylate oligomer and the energy ray curable monomer. Particularly preferred is 0.3 to 5 parts by mass.

  The intermediate layer may contain additives such as inorganic fillers such as calcium carbonate, silica and mica, metal fillers such as iron and lead, and colorants such as pigments and dyes.

  The thickness of the intermediate layer is preferably 50 to 500 μm, more preferably 100 to 400 μm, and particularly preferably 200 to 350 μm.

(Adhesive layer)
An adhesive layer is formed on the intermediate layer. The type of the pressure-sensitive adhesive layer is not specified as long as it has an appropriate removability to the wafer, and can be formed of various pressure-sensitive adhesives. Such an adhesive is not limited at all, but an adhesive such as rubber-based, acrylic-based, silicone-based, or polyvinyl ether is used. In addition, an energy ray curable pressure-sensitive adhesive that is cured by irradiation with energy rays and becomes removable, a heat-foaming type, or a water swelling type pressure-sensitive adhesive can also be used.

  As the energy ray curable (ultraviolet ray curable, electron beam curable) pressure-sensitive adhesive, it is particularly preferable to use an ultraviolet curable pressure-sensitive adhesive. Specific examples of such energy beam curable pressure-sensitive adhesives are described in, for example, JP-A-60-196956 and JP-A-60-223139. Moreover, as a water swelling type adhesive, what is described, for example in Japanese Patent Publication No. 5-77284, Japanese Patent Publication No. 6-101455, etc. is used preferably.

  The method of providing the pressure-sensitive adhesive layer on the surface of the intermediate layer may be to transfer the pressure-sensitive adhesive layer formed by applying the pressure-sensitive adhesive composition so as to have a predetermined film thickness on the release sheet to the surface of the intermediate layer. You may form an adhesive layer by apply | coating an adhesive composition directly on the surface of a layer.

  The thickness of the pressure-sensitive adhesive layer is 1 to 150 μm, more preferably 20 to 100 μm, and particularly preferably 40 to 80 μm.

(Adhesive sheet)
The pressure-sensitive adhesive sheet according to the present invention is formed by laminating a base film, an intermediate layer, and a pressure-sensitive adhesive layer in this order. In addition, a barrier layer may be provided between the intermediate layer and the pressure-sensitive adhesive layer in order to prevent migration of components between the intermediate layer and the pressure-sensitive adhesive layer.

  According to the preferable range of the thickness of the intermediate layer and the preferable range of the thickness of the pressure-sensitive adhesive layer, the total thickness of the intermediate layer and the pressure-sensitive adhesive layer is preferably 51 to 650 μm, more preferably 120. It is -500 micrometers, Most preferably, it exists in the range of 240-430 micrometers. In addition, when providing a barrier layer, the thickness of a barrier layer is also included in the total thickness of an intermediate | middle layer and an adhesive.

  The total thickness of the intermediate layer and the pressure-sensitive adhesive layer is appropriately selected in consideration of the bump height of the adherend to which the pressure-sensitive adhesive sheet is adhered, the bump shape, the pitch of the bump interval, and the like. The total thickness of the layer and the pressure-sensitive adhesive layer is desirably selected so as to be 110% or more, preferably 130 to 500% of the bump height. When the total thickness of the intermediate layer and the pressure-sensitive adhesive layer is selected in this way, the pressure-sensitive adhesive sheet follows the unevenness on the circuit surface, and the unevenness difference can be eliminated. The bump height is the height from the flat surface of the circuit surface (portion where no bump is formed) to the top of the bump, and is defined by the arithmetic average of the heights of a plurality of bumps.

  A release sheet may be laminated on the pressure-sensitive adhesive layer in order to protect the pressure-sensitive adhesive layer before use. The release sheet is not particularly limited, and a release sheet base material treated with a release agent can be used. Examples of the release sheet substrate include films made of resins such as polyethylene terephthalate, polybutylene terephthalate, polypropylene, and polyethylene, or foamed films thereof, and papers such as glassine paper, coated paper, and laminated paper. Examples of the release agent include release agents such as silicone-based, fluorine-based, and long-chain alkyl group-containing carbamate.

  Although the method of manufacturing the adhesive sheet which concerns on this invention is not specifically limited, For example, it can manufacture with the following method. First, an intermediate layer is formed on a base film. As the method for forming a film, the above-described preferable method for forming the intermediate layer can be employed. Next, as a temporary protective material, a release sheet or the like is bonded to the surface opposite to the surface in contact with the base material of the intermediate layer. By providing the protective material, the intermediate layer-coated substrate can be wound up and stored as a roll, or can be stored in a stacked state in a sheet state. Next, the protective material is removed, and the pressure-sensitive adhesive layer prepared in advance by a conventional method is bonded to the intermediate layer, and the pressure-sensitive adhesive sheet is laminated in the order of the base film, the intermediate layer, and the pressure-sensitive adhesive layer. obtain.

  The pressure-sensitive adhesive sheet according to the present invention can take any shape such as a tape. Moreover, the pre-cut shape by which the adhesive sheet previously die-cut by the shape of the to-be-adhered body was hold | maintained on the peeling sheet may be sufficient. The pre-cut pressure-sensitive adhesive sheet is obtained by a so-called half-cut method in which, after an uncut pressure-sensitive adhesive sheet is provided on the release sheet, only the pressure-sensitive adhesive sheet is completely punched into the adherend shape and the release sheet is not completely cut. . At this time, in order to completely cut the pressure-sensitive adhesive sheet, it is preferable to cut slightly into the release sheet. However, if the release sheet is cut excessively, the strength is lowered and the operability is impaired. Therefore, the depth of cut into the release sheet is 30% or less, more preferably 20% or less of the total thickness of the release sheet.

(Usage form of adhesive sheet)
The pressure-sensitive adhesive sheet of the present invention is used for surface protection of various articles and for temporary fixing during precision processing. In particular, the pressure-sensitive adhesive sheet of the present invention is preferably used as a surface protective sheet for articles having a large difference in unevenness on the surface or a dicing sheet for cutting and separating a semiconductor wafer into chips. When used as a surface protection sheet, it is particularly preferable for a process including a step of attaching the pressure-sensitive adhesive sheet as a surface protection sheet to the surface of the adherend and performing the back surface processing while protecting the surface of the adherend. Used. Here, as the adherend, a semiconductor wafer on which a circuit having bumps is formed on the surface is particularly suitable, and as the back surface processing, back surface grinding of the semiconductor wafer on which the circuit having bumps is formed on the surface is performed. Particularly preferred. Here, the height of the bump is not particularly limited, but according to the method of the present invention, a semiconductor wafer on which a circuit having a bump of 40 μm or more, 50 to 400 μm, particularly 70 to 300 μm is formed. Can also be used for machining.

(Wafer back grinding method)
First, the wafer back surface grinding method using the adhesive sheet of this invention is demonstrated in detail. In wafer backside grinding, an adhesive sheet is applied to the circuit surface of a semiconductor wafer having a circuit formed on the surface to protect the circuit surface and grind the backside of the wafer to obtain a wafer having a predetermined thickness.

  The semiconductor wafer may be a silicon wafer or a compound semiconductor wafer such as gallium / arsenic. Formation of a circuit on the wafer surface can be performed by various methods including conventionally used methods such as an etching method and a lift-off method. In the semiconductor wafer circuit forming step, a predetermined circuit is formed. The thickness of such a wafer before grinding is not particularly limited, but is usually about 500 to 1000 μm. The surface shape of the semiconductor wafer is not particularly limited, but the pressure-sensitive adhesive sheet of the present invention is preferably used for protecting the surface of a wafer having bumps formed on the circuit surface.

  The pressure-sensitive adhesive sheet of the present invention has an intermediate layer and a pressure-sensitive adhesive layer that exhibit the above-described unique elastic behavior, and exhibits viscoelasticity that can sufficiently follow bump irregularities under heating conditions. When sticking the pressure-sensitive adhesive sheet of the present invention, it is preferable that the storage elastic modulus of the intermediate layer is lowered. Therefore, it is preferable to stick the adhesive sheet to the semiconductor wafer at a temperature equal to or higher than the melting point (Tm) of the heat-meltable resin, and the influence on the change in storage elastic modulus due to the melting of the heat-melting resin is reduced. It is more preferable to carry out at a temperature of 6 ° C. or higher. However, if the temperature at the time of application is too high, the intermediate layer and the pressure-sensitive adhesive layer will be excessively softened and fluidized and may ooze out from the side surface of the pressure-sensitive adhesive sheet. It is preferable to apply at a temperature not higher than 30 ° C. higher than Tm.

  When the pressure-sensitive adhesive sheet is attached under heating, the pressure-sensitive adhesive layer and the intermediate layer are embedded in the wafer surface on which the bumps are formed, and the unevenness difference is eliminated. Further, by allowing to cool after sticking, the elastic modulus of the intermediate layer is recovered and the intermediate layer becomes hard, so that the wafer can be held in a flat state. In addition, the pressure-sensitive adhesive sheet of the present invention has high followability to the surface shape of the wafer, and the intermediate layer is normally relatively hard, so even if a strong shearing force is applied to the wafer during wafer back grinding, Misalignment can be prevented, and the back surface of the wafer can be ground to a flat and extremely thin thickness.

  The back surface grinding is performed by a known method using a grinder, a suction table for fixing the wafer, or the like with the adhesive sheet attached. After the back grinding process, a process of removing the crushed layer generated by grinding may be performed. The thickness of the semiconductor wafer after back grinding is not particularly limited, but is preferably 10 to 400 μm, and particularly preferably about 25 to 300 μm.

  After the back grinding process, the adhesive sheet is peeled off from the circuit surface. At the time of peeling of the pressure-sensitive adhesive sheet, the intermediate layer is softened by heating to a temperature equal to or higher than the Tm, and peeling becomes easy. According to the pressure-sensitive adhesive sheet of the present invention, it is possible to securely hold the wafer during backside grinding of the wafer and to prevent cutting water from entering the circuit surface.

(Pre-dicing method)
Furthermore, the pressure-sensitive adhesive sheet of the present invention is preferably used in making a wafer with a high bump by a so-called tip dicing method, specifically,
A groove having a depth of cut shallower than the wafer thickness is formed from the surface of the semiconductor wafer on which a circuit having bumps is formed,
Affixing the adhesive sheet as a surface protective sheet on the circuit forming surface,
Then, the wafer is thinned by grinding the back surface of the semiconductor wafer, and finally divided into individual chips.
It is preferably used in a method for manufacturing a semiconductor chip.

  The preferable aspect in sticking of an adhesive sheet is the same as the above. By using the pressure-sensitive adhesive sheet of the present invention, high adhesion can be obtained between the wafer (chip) and the pressure-sensitive adhesive layer, so that grinding water does not enter the circuit surface and chip contamination can be prevented.

  Thereafter, the chip is picked up by a predetermined method. In addition, prior to chip pickup, the chips in a wafer shape may be transferred to another pressure-sensitive adhesive sheet, and then chip pickup may be performed.

  EXAMPLES Hereinafter, although an Example demonstrates this invention, this invention is not limited to these Examples. In the following examples and comparative examples, various physical properties were evaluated as follows.

(Dimple and crack generation)
An adhesive sheet was affixed and fixed to a wafer with solder bumps (8-inch silicon wafer in which chips of 10 mm length × 10 mm width were aligned, bump height 250 μm, bump pitch 500 μm, total thickness 720 μm). Adhesion of the pressure-sensitive adhesive sheet is performed by using a laminator “RAD3510F / 12” manufactured by Lintec Corporation at a temperature shown in Table 3 below the melting point (Tm) of the hot-melt resin contained in the intermediate layer and 50 ° C. higher than Tm. Used. After grinding to a thickness of 200 μm (using Grinder DGP8760 manufactured by DISCO Corporation) and then peeling off the adhesive sheet using RAD2700F / 12 manufactured by Lintec Corporation, the back surface of the wafer was visually observed, and the back surface of the wafer It was confirmed that dimples did not occur in the parts corresponding to the bumps.

  The case where no dimples were generated was designated as A, the case where slight dimples were confirmed to be produced but B which was not practically problematic was designated as C, and the case where obvious dimples were produced was designated as C. Also, the presence or absence of wafer cracks (wafer cracks) was visually confirmed.

(Difference in height)
Adhesive sheet was affixed to a bumped wafer with a bump height of 250 μm in the same manner as described above. Immediately after that, the total thickness “A” (the back side of the wafer) was measured with a constant pressure thickness measuring instrument: PG-02 manufactured by Teclock. To the base film surface of the pressure-sensitive adhesive sheet), the total thickness “B” of the portion without the bump was measured, and “AB” was calculated as the height difference. It means that the unevenness | corrugation resulting from bump height is eased by the adhesive sheet, so that a height difference is small.

(Infiltration of grinding water)
After affixing an adhesive sheet to the circuit surface of a bumped wafer with a bump height of 250 μm, grinding the backside of the wafer to a total thickness of 200 μm while spraying water, peeling off the adhesive sheet from the wafer surface, and entering the grinding water into the wafer surface The presence or absence of was confirmed with an optical digital microscope (magnification 100 times).

(Embeddability)
An adhesive sheet was affixed to the circuit surface of the bumped wafer having a bump height of 250 μm, and immediately after that, it was observed with an optical digital microscope (300 × magnification) to measure the embedding distance between the bumps. The embedding distance between the bumps is defined as follows.

  Four adjacent bump tops are connected by a straight line to create a virtual square. The square diagonal is measured, and the bump diameter is subtracted from the diagonal length to obtain the bump interval. The distance at which the pressure-sensitive adhesive layer and the wafer surface are in close contact with each other on the diagonal line is measured and set as the embedding distance between the bumps.

  (Embedding distance / bump interval) × 100 is calculated and set as embeddability (%). The embedding property is an index of the adhesiveness of the adhesive sheet with respect to the gap between the bumps. The higher the embedding property, the more closely the adhesive sheet and the bumped wafer are in close contact with each other. When the embedding property is low, it means that the adhesion of the adhesive sheet is insufficient at the base portion of the bump.

(Adhesion)
In the same manner as in the evaluation of the occurrence of dimples and cracks, the adhesive sheet was attached to the semiconductor wafer, the semiconductor wafer was ground, and the adhesive sheet was peeled off. At the time of peeling, the case where the intermediate layer is good without peeling off from the base material is A, the case where the intermediate layer is peeled off from the base material film is B, and the case where the intermediate layer is always peeled off from the base material is C It was.

(Dispersion uniformity of matrix resin precursor and heat-meltable resin)
In the examples, after filtering the mixture in which the hot-melt resin was added to the matrix resin precursor using a # 120 mesh, the dispersion uniformity was visually evaluated, and neither dispersion failure nor filtration failure was observed. The case was designated as A, the case where some dispersion failure or filtration failure was slightly observed, and the case where dispersion failure or filtration failure was remarkable was designated as C.

(Viscoelasticity measurement)
On the release film (product name “SP-PET 381031”, manufactured by Lintec Co., Ltd., thickness 38 μm), a material composition for forming an intermediate layer is applied to a thickness of 300 μm by a fountain die method, and a belt conveyor type as an ultraviolet irradiation device Using an ultraviolet irradiation device (product name “US2-0801 <2>” manufactured by Eye Graphics Co., Ltd.), with a high pressure mercury lamp (product name “H04-L41” manufactured by Eye Graphics Co., Ltd.), the height of the UV lamp is 180 mm, The composition layer is crosslinked and cured by irradiating with ultraviolet light under the apparatus conditions of an ultraviolet lamp output of 120 W / cm, a light wavelength of 365 nm of illuminance of 150 mW / cm ² , and a light amount of 112 mJ / cm ^2. A release film (product name “SP-PET381031”, manufactured by Lintec Corporation, thickness 38 μm) on the physical layer The release surface of the) was laminated. The light quantity was measured using an ultraviolet light quantity meter (product name “UVPF-A1” manufactured by Eye Graphics Co., Ltd.).

Next, using the same UV irradiation device, the UV lamp height is 150 mm, the UV lamp output is 160 W / cm, the light wavelength is 365 nm, the illuminance is 285 mW / cm ² , and the light quantity is 387 mJ / cm ² ) Was irradiated with ultraviolet rays four times from the substrate side, the total amount of ultraviolet rays irradiated was 1660 mJ / cm ^2, and a single-layer intermediate layer sandwiched between release films was obtained.

  The release film was peeled off, an intermediate layer was laminated, and the lamination was repeated so that the thickness became 1 to 2 mm. Using the laminate of the obtained intermediate layer, storage elasticity at −20 to 120 ° C. at a frequency of 1 Hz (6.28 rad / sec.) Using a viscoelasticity measuring device (ARES (twist shear method) manufactured by Rheometric). The rate was measured.

(Hot-melting resin)
The following resins were used as the hot-melt resin.

Example 1
A commercially available energy ray polymerizable composition (made by Arakawa Chemical Co., Ltd .: Beam Set 520MA-9) containing a urethane acrylate, an acrylate monomer, and a photopolymerization initiator is used as a matrix resin precursor, and the matrix resin precursor After adding 20 parts by mass of crystalline poly α-olefin (made by Idemitsu Kosan Co., Ltd .: ELCRYSTA X-W-6100) to 100 parts by mass, filtration is performed using # 120 mesh to form an intermediate layer of room temperature liquid. A material composition was prepared.

As a base film, PET38 T-100 (Mitsubishi Resin Chemical Co., Ltd., thickness 38 μm) was used, and the composition was applied on the base film so as to have a thickness of 300 μm by a fountain die method. Using a belt conveyor type ultraviolet irradiation device (product name “US2-0801 <2>” manufactured by Eye Graphics Co., Ltd.), a high pressure mercury lamp (product name “H04-L41” manufactured by Eye Graphics Co., Ltd.) The composition layer is crosslinked and cured by performing ultraviolet irradiation under the apparatus conditions of 180 mm in length, an ultraviolet lamp output of 120 W / cm, an illuminance of a light wavelength of 365 nm of 150 mW / cm ² , and a light amount of 112 mJ / cm ^2. A release film on the cured composition layer (manufactured by Lintec, product name “SP-PET 381031”, thickness 38 μm) The release surface was laminated. The light quantity was measured using an ultraviolet light quantity meter (product name “UVPF-A1” manufactured by Eye Graphics Co., Ltd.).

Next, using the same UV irradiation device, the UV lamp height is 150 mm, the UV lamp output is 160 W / cm, the light wavelength is 365 nm, the illuminance is 285 mW / cm ² , and the light quantity is 387 mJ / cm ² ) Was irradiated with ultraviolet rays four times from the substrate film side, and the total amount of irradiated ultraviolet rays was set to 1660 mJ / cm ² to obtain a laminate of substrate film / intermediate layer / release film.

  Next, the release film laminated on the intermediate layer side of the laminate was peeled off, and a film-like acrylic pressure-sensitive adhesive having a thickness of 50 μm prepared in advance was laminated to obtain an adhesive sheet. The sheet-like pressure-sensitive adhesive is an acrylic pressure-sensitive adhesive (a copolymer of 2-ethylhexyl acrylate and hydroxyethyl acrylate, in which 80% IEM (isocyanatoethyl methacrylate) is added to the hydroxyl group of hydroxyethyl acrylate) 100 A pressure-sensitive adhesive composition obtained by mixing 1 part by mass of a mass part, 1 part by mass of a curing agent (diisocyanate type) and 3.1 parts by mass of a photopolymerization initiator (Irgacure 184, manufactured by Ciba Specialty Chemicals) is used as a release film. It was applied and dried so that the thickness after drying was 50 μm.

  Table 3 shows the viscoelasticity measurement results of the intermediate layer and the evaluation results of the pressure-sensitive adhesive sheet.

(Example 2)
A pressure-sensitive adhesive sheet was obtained in the same manner as in Example 1 except that the compounding amount of the crystalline poly α-olefin (Idemitsu Kosan Co., Ltd .: ELCRYSTA X-W-6100) was changed to 40 parts by mass. The results are shown in Table 3.

Example 3
Instead of the crystalline poly α-olefin used in Example 1, a pressure sensitive adhesive sheet was obtained in the same manner as in Example 1 except that crystalline poly α-olefin (Idemitsu Kosan Co., Ltd .: Elkrista X-W-7100) was used. Obtained. The results are shown in Table 3.

Example 4
A pressure-sensitive adhesive sheet was obtained in the same manner as in Example 3 except that the amount of the crystalline poly α-olefin (Idemitsu Kosan Co., Ltd .: ELCRYSTA X-W-7100) was changed to 40 parts by mass. The results are shown in Table 3.

(Example 5)
100 parts by mass of a commercially available energy ray polymerizable composition (Arakawa Chemical Co., Ltd .: Beam Set 520MA-9), 60 parts by mass of the energy ray polymerizable composition, and 40 parts by mass of phenoxyethyl acrylate (Sartomer Inc .: SR339A) A pressure-sensitive adhesive sheet was obtained in the same manner as in Example 1 except that the matrix resin precursor changed to the mixture was used. The results are shown in Table 3.

(Example 6)
A pressure-sensitive adhesive sheet was obtained in the same manner as in Example 5 except that the amount of the crystalline poly α-olefin (Idemitsu Kosan Co., Ltd .: ELCRYSTA X-W-6100) was changed to 25 parts by mass. The results are shown in Table 3.

(Example 7)
A pressure-sensitive adhesive sheet was obtained in the same manner as in Example 5 except that the amount of the crystalline poly α-olefin (Idemitsu Kosan Co., Ltd .: ELCRYSTA X-W-6100) was changed to 30 parts by mass. The results are shown in Table 3.

(Example 8)
Example 5 except that 40 parts by mass of phenoxyethyl acrylate was changed to 30 parts by mass of phenoxyethyl acrylate (manufactured by Sartomer: SR339A) and 10 parts by mass of isooctyl acrylate (manufactured by Sartomer: SR440). In the same manner, an adhesive sheet was obtained. The results are shown in Table 3.

Example 9
In Example 8, the amount of phenoxyethyl acrylate (Sartomer: SR339A) was changed to 20 parts by mass, and the amount of isooctyl acrylate (Sartomer: SR440) was changed to 20 parts by mass. In the same manner, an adhesive sheet was obtained. The results are shown in Table 3.

(Example 10)
Example 5 except that 40 parts by mass of phenoxyethyl acrylate was changed to 30 parts by mass of phenoxyethyl acrylate (manufactured by Sartomer: SR339A) and 10 parts by mass of isodecyl acrylate (manufactured by Sartomer: SR395). In the same manner, an adhesive sheet was obtained. The results are shown in Table 3.

(Example 11)
Example 10 except that the blending amount of phenoxyethyl acrylate (manufactured by Sartomer: SR339A) was changed to 20 parts by mass and the blending amount of isodecyl acrylate (manufactured by Sartomer: SR395) was changed to 20 parts by weight. In the same manner, an adhesive sheet was obtained. The results are shown in Table 3.

(Example 12)
Example 10 except that the blending amount of phenoxyethyl acrylate (manufactured by Sartomer: SR339A) was changed to 10 parts by mass and the blending amount of isodecyl acrylate (manufactured by Sartomer: SR395) was changed to 30 parts by weight. In the same manner, an adhesive sheet was obtained. The results are shown in Table 3.

(Example 13)
A pressure-sensitive adhesive sheet was obtained in the same manner as in Example 5 except that phenoxyethyl acrylate (manufactured by Sartomer: SR339A) was changed to stearyl acrylate (manufactured by Sartomer: SR257) in Example 5. The results are shown in Table 3.

(Example 14)
Example 1 except that 5 parts by mass of an acrylic polymer (manufactured by Nippon Shokubai Co., Ltd .: ST-100) was used in place of 20 parts by mass of crystalline poly α-olefin (Idemitsu Kosan Co., Ltd .: ELCRYSTA X-W-6100). Similarly, an adhesive sheet was obtained. The results are shown in Table 3.

(Example 15)
A pressure-sensitive adhesive sheet was obtained in the same manner as in Example 14 except that the blending amount of the acrylic polymer (manufactured by Nippon Shokubai: ST-100) was changed to 13.63 parts by mass. The results are shown in Table 3.

(Comparative Example 1)
A pressure-sensitive adhesive sheet was obtained in the same manner as in Example 1 except that the crystalline poly α-olefin (Idemitsu Kosan Co., Ltd .: ELCRYSTA X-W-6100) was not blended. The results are shown in Table 3.

Claims (15)

A base film, an intermediate layer, and an adhesive layer are laminated in this order,
The intermediate layer includes a heat-meltable resin having a melting point (Tm);
The intermediate layer is formed by dispersing the hot-melt resin in a matrix resin.
The storage elastic modulus G ′ (Tm + 6) of the intermediate layer at a temperature 6 ° C. higher than the melting point Tm (Tm + 6) and the storage elastic modulus G ′ of the intermediate layer at a temperature 6 ° C. lower than the melting point Tm (Tm−6). For Tm-6), G ′ (Tm-6) / G ′ (Tm + 6) is 2.0 or more,
The storage elastic modulus G ′ (25) at 25 ° C. of the intermediate layer is 0.05 MPa to 20 MPa, the storage elastic modulus G ′ (50) at 50 ° C. is 0.01 MPa to 15 MPa, and the storage elastic modulus G ′ at 80 ° C. (80 ) Is 0.001 MPa to 1 MPa, and satisfies the relationship of G ′ (25)> G ′ (50)> G ′ (80).   The pressure-sensitive adhesive sheet according to claim 1, wherein the heat-meltable resin has a melting point (Tm) in a range of 45 to 90 ° C.   The pressure-sensitive adhesive sheet according to claim 1 or 2, wherein a melting start temperature of the heat-meltable resin is (Tm-8) ° C or higher.   The pressure-sensitive adhesive sheet according to claim 1, wherein the heat-meltable resin is an olefin-based material.   The pressure-sensitive adhesive sheet according to claim 4, wherein the olefin-based material is an α-olefin polymer having 14 to 30 carbon atoms. The pressure-sensitive adhesive sheet according to any one of claims 1 to 5 , wherein the matrix resin comprises an energy ray curable resin. The pressure-sensitive adhesive sheet according to claim 6 , wherein the energy beam curable resin is a cured product obtained by energy beam curing a compound containing a urethane resin and an energy beam curable monomer.   The pressure-sensitive adhesive sheet according to claim 1, wherein the intermediate layer is a cured product obtained by energy-beam curing a blend containing the heat-meltable resin, a urethane resin, and an energy beam-curable monomer. The pressure-sensitive adhesive sheet according to the thickness of the base film is 50 to 200 [mu] m, the thickness of the intermediate layer 50 to 500 [mu] m, claim 1-8 thickness of the adhesive layer is 1-150 [mu] m. The base film is a polyester film,
The intermediate layer is a cured product obtained by energy ray curing a compound containing a heat-meltable resin, a urethane resin, and an energy ray curable monomer,
The pressure-sensitive adhesive sheet according to any one of claims 1 to 9 , wherein the pressure-sensitive adhesive layer comprises an acrylic pressure-sensitive adhesive. The pressure-sensitive adhesive sheet according to any one of claims 1 to 10 , wherein the pressure-sensitive adhesive sheet is a surface protective sheet for protecting the surface of the semiconductor wafer when the back surface processing of the semiconductor wafer is performed. A pressure-sensitive adhesive sheet according to claim 11 is attached to the surface of a semiconductor wafer on which a circuit having bumps is formed, and the semiconductor wafer circuit surface is protected and the back surface is ground. A method for processing a semiconductor wafer. The semiconductor wafer processing method according to claim 12 , wherein the adhesive sheet is attached to the semiconductor wafer at a temperature not lower than the melting point (Tm) of the heat-meltable resin and not higher than 50 ° C. higher than Tm. A groove having a depth of cut smaller than the wafer thickness is formed from the surface of the semiconductor wafer on which a circuit having bumps is formed, and the adhesive sheet according to claim 11 is attached to the circuit forming surface, and then the semiconductor wafer is formed. A method of manufacturing a semiconductor chip, comprising a step of reducing the thickness of a wafer by performing back surface grinding and finally dividing into individual chips. The manufacturing method of the semiconductor chip of Claim 14 which affixes an adhesive sheet on a semiconductor wafer at the temperature below melting | fusing point (Tm) of a thermomeltable resin, and 50 degrees C or more higher than Tm.