JP5367996B2 - Adhesive sheet base film and adhesive sheet - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a base film for an adhesive sheet and an adhesive sheet which enable grinding a wafer to a wafer with an extremely small thickness while preventing bending of the wafer, and prevent the development of air bubbles due to heat resulting from grinding. <P>SOLUTION: The base film for the adhesive sheet is made of an urethane acrylate oligomer and an energy-rays copolymerizing monomer. An acrylic ester compound not containing a hydroxyl group is used as the energy-rays copolymerizing monomer. This prevents the infiltration of moisture into the base film, thus prevents development of air bubbles when the adhesive sheet is heated. Use of the energy-rays copolymerizing monomer having a bulky molecule structure improves a stress relaxation property of the base film. <P>COPYRIGHT: (C)2010,JPO&amp;INPIT

Description

  The present invention relates to a base film for an adhesive sheet and an adhesive sheet, and in particular, a base film for an adhesive sheet for processing a semiconductor wafer that is suitably used for a process of grinding a semiconductor wafer to an extremely thin thickness and increasing the temperature, and It relates to an adhesive sheet.

  There is an increasing need to embed an IC in a card such as a money card. With the spread of such ICs, it has become necessary to reduce the thickness of a semiconductor chip, which was conventionally about 350 μm, to 50 to 100 μm or less. For this reason, thinning of the wafer is required. In addition, in order to improve productivity, the wafer diameter is being increased.

  In wafer grinding, it is known to grind the back surface of a wafer while protecting the circuit surface using a protective adhesive sheet (see, for example, Patent Document 1). In particular, in the back surface grinding of a thin film wafer or a large-diameter wafer, an adhesive sheet having high stress relaxation properties is required in order to grind the wafer to a very thin thickness without bending the wafer. This is because if the adhesive sheet has a large residual stress, the wafer may be bent or damaged.

On the other hand, in recent years, in a wafer ground to an extremely thin thickness, a die bonding tape for transferring an adhesive layer is affixed to the back surface with the above-mentioned protective adhesive sheet affixed to the circuit surface, and a protective adhesive sheet is attached. After peeling, a dicing process, a pick-up process, etc. may be performed. Since the die bonding tape may be attached to the back surface of the wafer by thermocompression bonding with the protective adhesive sheet attached to the circuit surface of the wafer, the protective adhesive sheet is also heated. In addition, plasma treatment or the like may be performed on the back surface of the wafer after grinding, and in this case as well, heat is applied to the protective adhesive sheet attached to the circuit surface.
JP 2002-246345 A

  When the protective adhesive sheet affixed to the wafer is heated, bubbles may be generated inside the protective adhesive sheet or at the interface between the protective adhesive sheet and the wafer. Such bubbles may cause wafer cracking, wafer transfer error, and adsorption error on the chuck table, and may cause a decrease in productivity.

  In particular, it is conceivable that the influence of minute bubbles generated in the protective pressure-sensitive adhesive sheet increases due to the recent trend of wafer thinning. For this reason, the problem of air bubbles may also occur in the protective adhesive sheet that has been used without problems.

  Therefore, the present invention aims to realize a base film for an adhesive sheet and an adhesive sheet that can be ground to an extremely thin thickness while preventing the wafer from being bent, and that can prevent the generation of bubbles due to subsequent heating. To do.

  The base film of the pressure-sensitive adhesive sheet of the present invention is a base film of a pressure-sensitive adhesive sheet that is attached to a semiconductor wafer. The base film is formed by energy ray curing of at least a urethane acrylate oligomer and an energy ray polymerizable monomer, and the energy ray polymerizable monomer is an acrylic ester compound not containing a hydroxyl group. To do.

  The energy ray polymerizable monomer is, for example, at least one of cresol ethylene oxide-modified acrylate and phenoxyethyl acrylate. The urethane acrylate oligomer includes, for example, an isocyanate urethane oligomer composed of a polycarbonate diol and a polyvalent isocyanate.

  The water absorption when the substrate film is immersed in pure water for 120 minutes is preferably 0.5% by weight or less. Moreover, it is preferable that the stress relaxation property after 1 minute when extending | stretching a base film 10% is 40% or more.

  The pressure-sensitive adhesive sheet of the present invention includes the above-described base film and a pressure-sensitive adhesive layer. And in an adhesive sheet, in order to protect the circuit surface of a semiconductor wafer when grinding the back surface of a semiconductor wafer, it is preferable that an adhesive layer is affixed on a circuit surface.

  ADVANTAGE OF THE INVENTION According to this invention, the base film for adhesive sheets and an adhesive sheet which can be ground to ultrathin while preventing the curvature of a wafer and can prevent generation | occurrence | production of the bubble by subsequent heating are realizable.

  Hereinafter, embodiments of the pressure-sensitive adhesive sheet according to the present invention will be described. The pressure-sensitive adhesive sheet includes a sheet-like base film and a pressure-sensitive adhesive layer formed on the surface of the base film. The pressure-sensitive adhesive layer is laminated on the base film so as to have a uniform thickness over the entire region of the base film. The pressure-sensitive adhesive sheet is used by being attached to a semiconductor wafer such that the pressure-sensitive adhesive layer is in contact with the circuit surface.

  Next, the base film will be described. The base film is formed by forming a curable resin into a film. As the curable resin, an energy beam curable resin or the like is used.

  As the energy ray curable resin, for example, a resin composition mainly composed of an energy ray polymerizable urethane acrylate oligomer or a polyene / thiol resin is preferably used. The urethane acrylate oligomer includes a polyol compound such as a polycarbonate type, a polyester type or a polyether type, and a polyvalent isocyanate compound such as isophorone diisocyanate, 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate. An acrylate having a terminal hydroxyl group on a terminal isocyanate urethane prepolymer obtained by reacting narate, 1,3-xylylene diisocyanate, 1,4-xylylene diisocyanate, diphenylmethane 4,4-diisocyanate, etc. Alternatively, methacrylates such as 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, 2-hydroxypropyl acrylate, 2-hydroxypropyl methacrylate, 2-hydroxybutyl acrylate DOO, 2-hydroxybutyl methacrylate, polyethylene glycol acrylate, obtained by further reacting a polyethylene glycol methacrylate. Such a urethane acrylate oligomer has an energy ray-polymerizable double bond in the molecule and is polymerized and cured by energy ray irradiation to form a film.

  The urethane acrylate oligomer may be formed by combining a plurality of the aforementioned compounds. The molecular weight of the urethane acrylate oligomer is generally 1000 to 50000, preferably in the range of 2000 to 30000.

  Only urethane acrylate oligomers may be difficult to form due to their high viscosity. In addition, physical properties such as flexibility suitable for the base film may not be obtained. For this reason, usually, a low-viscosity energy ray-polymerizable monomer is mixed to form a film, which is then cured to form a base film. The energy ray polymerizable monomer has an energy ray polymerizable double bond in the molecule. As the energy ray polymerizable monomer, an acrylate ester compound having a relatively bulky group is particularly preferably used. This is because, when an acrylic ester compound having a bulky group is used, the stress relaxation property of the base film is improved as described later.

  Specific examples of energy beam polymerizable monomers for mixing with urethane acrylate oligomers include phenoxyethyl (meth) acrylate, p-cresol ethylene oxide modified (meth) acrylate, o-cresol ethylene oxide modified (meth) acrylate, m-cresol. Aromatic compounds such as ethylene oxide modified (meth) acrylate, phenol ethylene oxide modified (meth) acrylate, benzyl acrylate, isobornyl (meth) acrylate, dicyclopentenyl (meth) acrylate, dicyclopentanyl (meth) acrylate, dicyclopentenyloxy Alicyclic compounds such as (meth) acrylate, cyclohexyl (meth) acrylate, adamantane (meth) acrylate, or tetrahydrofurfuryl (Meth) acrylate, morpholine acrylate, heterocyclic compounds such as N- vinyl pyrrolidone or N- vinyl caprolactam. Among these, phenoxyethyl acrylate and p-cresol ethylene oxide modified acrylate are preferable, and p-cresol ethylene oxide modified acrylate is particularly preferable. Moreover, you may use polyfunctional (meth) acrylate as an energy-beam polymerizable monomer as needed.

  These energy beam polymerizable monomers are preferably used in a proportion of 5 to 900 parts by weight, more preferably 10 to 500 parts by weight, and particularly preferably 30 to 200 parts by weight with respect to 100 parts by weight of the urethane acrylate oligomer. .

  The energy beam curable resin may contain a photopolymerization initiator. By containing a photopolymerization initiator, the irradiation amount and irradiation time of energy rays necessary for polymerization and curing can be reduced. Examples of the photopolymerization initiator include benzophenone, acetophenone, benzoin, benzoin methyl ether, benzoin ethyl ether, benzoin isopropyl ether, benzoin isobutyl ether, benzoin benzoic acid, methyl benzoin benzoate, benzoin dimethyl ketal, and 2,4-diethylthioxan. Son, 1-hydroxycyclohexyl phenyl ketone, benzyldiphenyl sulfide, tetramethylthiuram monosulfide, azobisisobutyronitrile, benzyl, dibenzyl, diacetyl, 2-chloranthraquinone, or 2,4,6-trimethylbenzoyldiphenylphosphine Examples include oxides. These photopolymerization initiators are preferably used in a proportion of 0.05 to 15 parts by weight, more preferably 0.1 to 10 parts by weight, with respect to 100 parts by weight of the energy beam curable resin.

  The base film may be colorless or colored. It may be transparent or opaque. When the pressure-sensitive adhesive layer to be described later is an energy ray curable type, it is preferable that the pressure-sensitive adhesive layer has transparency to the wavelength of the energy rays to be used. That is, in the case where the pressure-sensitive adhesive layer is cured using ultraviolet rays as energy rays, the substrate film preferably has ultraviolet transparency. Moreover, when hardening an adhesive layer using an electron beam as an energy beam, a base film may be opaque.

  The thickness of a base film is adjusted according to the performance etc. which are requested | required of an adhesive sheet, Preferably it is 20-500 micrometers, Especially preferably, it is 50-400 micrometers. As a method for forming a base film, a liquid resin (resin before curing, resin solution, etc.) is cast into a thin film on, for example, a process sheet, and then cured by irradiation with energy rays to form a film. .

  Moreover, a base film can also be manufactured by extrusion molding by a T-die or an inflation method, or a calendar method. Further, the upper surface of the base film, that is, the surface on which the pressure-sensitive adhesive layer is provided is subjected to plasma treatment, corona treatment, or other layers such as a primer are laminated in order to improve adhesion to the pressure-sensitive adhesive. May be.

  Next, the pressure-sensitive adhesive layer will be described. The pressure-sensitive adhesive layer is formed of a pressure-sensitive adhesive such as rubber, acrylic, silicone, or polyvinyl ether, for example. In addition, the pressure-sensitive adhesive layer can be formed using an energy ray-curable pressure-sensitive adhesive, a heat-foaming-type, a water-swelling-type, or a low-viscosity-type pressure-sensitive adhesive. The energy ray curable pressure-sensitive adhesive layer is mainly composed of an acrylic copolymer and an energy ray curable resin, and contains components such as a crosslinking agent and a photopolymerization initiator as necessary. Moreover, as an acrylic copolymer, you may use the acrylic copolymer which has an energy-beam curable group in a side chain. As the energy rays, ultraviolet rays, electron beams and the like are used, and it is particularly preferable to use ultraviolet rays for the ultraviolet curable pressure-sensitive adhesive layer.

  The thickness of the energy ray curable pressure-sensitive adhesive layer in the pressure-sensitive adhesive sheet is determined according to the required surface protection performance of a semiconductor wafer or the like, and is preferably 10 to 200 μm, and particularly preferably 20 to 100 μm.

  The pressure-sensitive adhesive sheet is coated on the above-mentioned base film with an appropriate thickness by a known method such as roll coater, knife coater, roll knife coater, bar coater, gravure coater, die coater, reverse coater, etc. It is obtained by drying to form a pressure-sensitive adhesive layer, and then bonding a release sheet on the pressure-sensitive adhesive layer as necessary. The pressure-sensitive adhesive sheet of this embodiment is suitably used for protecting the surface of a semiconductor wafer.

  That is, the adhesive sheet is attached to the surface of an adherend such as a circuit surface of a semiconductor wafer, and the back surface of the wafer is ground with the circuit surface protected. A thermocompression-bonding sheet such as a die-bonding sheet is thermocompression bonded to the back surface that has been subjected to processing such as grinding. Then, the semiconductor wafer on which the adhesive sheet and the thermocompression bonding sheet are further adhered is heated to cure the thermosetting component of the thermocompression bonding sheet. As described above, the pressure-sensitive adhesive sheet of the present embodiment is preferably used for a process including a step of grinding the back surface of the semiconductor wafer while protecting the circuit surface of the semiconductor wafer, and thermocompression bonding and heat curing the die bonding sheet on the ground back surface. . The thickness of the semiconductor wafer after back grinding is not particularly limited, but is preferably 1 to 300 μm, particularly preferably about 10 to 100 μm.

  The thermocompression bonding temperature of the die bonding sheet is adjusted according to the type, but is generally about 100 to 180 ° C. Moreover, the heat-curing temperature of the sheet | seat for die bonding is about 120-200 degreeC in general. For this reason, when a conventional pressure-sensitive adhesive sheet is used for protecting the surface of a wafer, stress is generated due to shrinkage due to heating, and deformation (warping) may occur in the wafer whose strength is reduced due to grinding. There is a possibility that bubbles may be generated in the material film. Therefore, in the pressure-sensitive adhesive sheet of the present embodiment, a base film that has excellent stress relaxation properties and can prevent generation of bubbles is used as follows.

  Hereinafter, the Example and comparative example of the base film of the adhesive sheet in this embodiment are demonstrated. Table 1 shows the composition of the base film in Examples and Comparative Examples.

The base film of Examples 1-4 shown in Table 1 and Comparative Examples 1-3 is produced | generated as follows. First, the base film of Example 1 will be described.
Example 1
A terminal isocyanate urethane prepolymer obtained by polymerizing polycarbonate diol and isophorone diisocyanate was reacted with 2-hydroxyethyl acrylate to obtain a urethane acrylate oligomer having a weight average molecular weight of about 5,000. 40 parts by weight of this urethane acrylate oligomer, 20 parts by weight of p-cresol ethylene oxide-modified acrylate, 40 parts by weight of isobornyl acrylate, and 1-hydroxycyclohexyl phenyl ketone (Irgacure 184, Ciba Specialty as a photopolymerization initiator) Chemicals) 2.0 parts by weight (solid ratio) was blended to obtain an energy ray curable resin composition.

  The obtained energy ray curable resin composition was coated on a polyethylene terephthalate (PET) film, which is a process sheet for casting, by a fountain die method so as to have a thickness of 160 μm to form a resin composition layer. . The same PET film was further laminated on the resin composition layer semi-cured using a high-pressure mercury lamp immediately after coating, and then the resin composition was further crosslinked and cured using a high-pressure mercury lamp. Then, the PET films on both sides were peeled to obtain a film having a thickness of 160 μm. This is the base film of Example 1.

  Furthermore, the acrylic adhesive was adjusted as follows. That is, a copolymer having a weight average molecular weight of about 300,000 consisting of 84 parts by weight of butyl acrylate, 10 parts by weight of methyl methacrylate, 1 part by weight of acrylic acid and 5 parts by weight of 2-hydroxyethyl acrylate was used as the acrylic pressure-sensitive adhesive. . 100 parts by weight of this copolymer was dissolved in an organic solvent (ethyl acetate: toluene = 1: 1) to give a 40% by weight solution, and 3 parts by weight of a polyisocyanate compound (Coronate L, manufactured by Nippon Polyurethane Industry Co., Ltd.) as a crosslinking agent. Part (solid ratio) was added and mixed to obtain an adhesive composition. This pressure-sensitive adhesive composition was applied to one side of the above-mentioned base film and dried to form a pressure-sensitive adhesive having a thickness of 20 μm to obtain a pressure-sensitive adhesive sheet.

(Example 2)
The base film of Example 2 was formed in the same manner as the base film of Example 1 except that the same part by weight of phenoxyethyl acrylate was used instead of p-cresol ethylene oxide-modified acrylate to obtain an adhesive sheet.
(Example 3)
A terminal isocyanate urethane prepolymer obtained by polymerizing polyester diol and isophorone diisocyanate was reacted with 2-hydroxyethyl acrylate to obtain a urethane acrylate oligomer having a weight average molecular weight of about 5,000. 40 parts by weight of this urethane acrylate oligomer, 20 parts by weight of p-cresol ethylene oxide-modified acrylate, 40 parts by weight of isobornyl acrylate, and 1-hydroxycyclohexyl phenyl ketone (Irgacure 184, Ciba Specialty as a photopolymerization initiator) Chemicals) 2.0 parts by weight (solid ratio) was blended to obtain an energy ray curable resin composition. Using the obtained energy ray curable resin composition, it was formed in the same manner as the base film of Example 1 to obtain an adhesive sheet.
Example 4
The base film of Example 4 was formed in the same manner as the base film of Example 3 except that the same part by weight of phenoxyethyl acrylate was used instead of p-cresol ethylene oxide-modified acrylate to obtain an adhesive sheet.

(Comparative Example 1)
On the other hand, the base film of Comparative Example 1 was formed in the same manner as the base film of Example 1 except that the same part by weight of phenylhydroxypropyl acrylate was used instead of p-cresol ethylene oxide-modified acrylate, and an adhesive sheet was formed. Obtained.
(Comparative Examples 2 and 3)
The base film of Comparative Example 2 is a low density polyethylene ethylene film having a thickness of 110 [mu] m, the base film of Comparative Example 3, it is polyethylene terephthalate film of 100μm thickness. Also from the base film of Comparative Example 2 and Comparative Example 3, an adhesive sheet was obtained in the same manner as in Example 1.

  Next, the evaluation results of the base film and the pressure-sensitive adhesive sheet in Examples and Comparative Examples of the present embodiment will be described. Table 2 shows the evaluation results of the base film or the pressure-sensitive adhesive sheet in Examples and Comparative Examples.

  Water absorption: Samples were formed by cutting the substrate films of Examples and Comparative Examples into 100 mm × 100 mm. This sample was immersed in pure water at 23 ° C. for 2 hours. From the weight A (g) measured before immersion and the weight B (g) after immersion, (B−A) / A × 100 was absorbed. Calculated as a percentage (%).

  Foaming during heating: The above-mentioned pressure-sensitive adhesive sheets (protective pressure-sensitive adhesive sheets) including the base film of Examples and Comparative Examples were respectively attached to the surfaces of two silicon wafers (thickness: 750 μm) having a diameter of 12 inches. Then, the back surface of the silicon wafer was ground by a back surface polishing apparatus (DGP 8760, manufactured by Disco Corporation) until the finished thickness became 75 μm. The protective adhesive sheet on the surface of one of the wafers thus ground was heated at 150 ° C. for 1 minute and the other at 180 ° C. for 1 minute by RAD-2700 manufactured by Lintec. Thereafter, the protective pressure-sensitive adhesive sheet was visually observed to confirm whether bubbles having a diameter of 0.5 mm or more were generated.

Stress relaxation rate: Samples were formed by cutting the substrate films of Examples and Comparative Examples into 15 mm × 140 mm. Using a universal tensile testing machine (Autograph AG-10kNIS manufactured by SHIMADZU), gripping both ends 20 mm of this sample, pulling at a speed of 200 mm per minute, stress A (N / m ² ) when stretched 10%, The stress B (N / m ² ) 1 minute after the stop of the tape stretching was measured. From the values of these stresses A and B, (A−B) / A × 100 (%) was calculated as the stress relaxation rate.

  Wafer warpage after grinding: precision of flatness grade 1 conforming to JIS B 7513 for a wafer (see paragraph [0047]) ground with an adhesive sheet using the base film of Examples and Comparative Examples attached The pressure-sensitive adhesive sheet was placed on the surface plate for inspection, and the maximum height (mm) from the surface of the surface plate was measured as the amount of warpage of the wafer. In addition, the amount of warpage of the wafer was similarly measured for the wafer heated at 180 ° C. for 1 minute after grinding.

  As is clear from the results in Table 2, the base film of Example 1 has the lowest water absorption (%), and in the pressure-sensitive adhesive sheet, foaming during heating is not recognized. Furthermore, since the stress relaxation rate (%) is high, the warpage amount (mm) of the wafer after grinding is also suppressed. Thus, Example 1 shows the best results.

  About Examples 2-4, although the water absorption rate (%) of a base film is a little higher than Example 1, generation | occurrence | production of the bubble under the high temperature of 180 degreeC is recognized for this reason, The bubble generation | occurrence | production at 150 degreeC is It is prevented. The stress relaxation rate (%) and the warpage amount (mm) of the wafer are good values almost equivalent to those of the first embodiment. Thus, it can be said that Examples 2 to 4 also show generally good results such as a water absorption rate of 0.5% by weight or less and a stress relaxation property of 40% or more. It can be said that it can be used without any problem under the above heating conditions.

  On the other hand, the substrate film of Comparative Example 1 has a water absorption rate (%) that is significantly higher than that of the Examples and exceeds 0.5% by weight, which is a standard for usable standards. Sometimes foaming is also observed. For this reason, although the stress relaxation rate (%) and the amount of warpage of the wafer (mm) have shown good results, the pressure-sensitive adhesive sheet of Comparative Example 1 was subjected to wafer cracking due to use under conditions exposed to high temperatures. There is a risk of causing problems such as wafer transfer errors.

  Moreover, the base film of the comparative example 2 and the comparative example 3 which respectively used typical low density polyethylene and polyethylene terephthalate as a raw material of the base film of an adhesive sheet is excellent in water absorption (%) and foaming prevention property. . However, since these substrate films have a stress relaxation property after 1 minute after 10% elongation of less than 40%, which is a standard of usable standards, and stress is easily accumulated, when used as an adhesive sheet, It will be greatly warped. In particular, at a temperature as high as 180 ° C., the amount of warpage of the wafer is too large, causing wafer cracks. Such warpage and wafer cracks become prominent when the wafer is thin. Therefore, the pressure-sensitive adhesive sheets of Comparative Example 2 and Comparative Example 3 may not be able to sufficiently protect a thin wafer, particularly when used at high temperatures.

  From the above experimental results, in order to realize a base film and an adhesive sheet that suppresses the water absorption rate of the base film and does not cause problems even when grinding water is used in grinding, It can be said that it is effective to use an acrylate compound containing no hydroxyl group as the monomer. This is based on the test results of Examples 3 and 4 using p-cresol ethylene oxide-modified acrylate and phenoxyethyl acrylate, which are acrylic acid ester compounds containing no hydroxyl group, and phenylhydroxypropyl acrylate having a hydroxyl group. It is clear by comparing the results of Comparative Example 1 having the same composition as Examples 3 and 4.

  The above effect is considered to be due to the fact that the polarity of the base film is prevented from being increased by the hydroxyl group, and the water absorption (hygroscopicity) in the base film and the pressure-sensitive adhesive sheet is lowered. In the same manner as in Examples 3 and 4, not only Examples 1 and 2 in which an acrylic ester compound having no hydroxyl group was used, but also Comparative Examples 2 and 3 containing no hydroxyl group were water absorption (%). This is because good results are shown for the antifoaming property.

  Moreover, in order to implement | achieve the base film and adhesive sheet which are excellent in stress relaxation property and suppress the curvature of a wafer, it can be said that it is effective to use the energy ray polymerizable monomer which has a bulky molecular structure. This is a stress relaxation rate in the base film of Examples 1 to 4 and Comparative Example 1 using bulky molecules such as p-cresol ethylene oxide modified acrylate, phenoxyethyl acrylate, phenylhydroxypropyl acrylate, and isobornyl acrylate. It is clear from the low stress relaxation rate (%) in Comparative Example 2 and Comparative Example 3 using low density polyethylene and polyethylene terephthalate having a high (%), extremely small branched chain, and having a substantially linear molecular structure. It is.

  In addition, Example 1 and Example 2 using polycarbonate diol and isophorone diisocyanate as urethane acrylate oligomers have a lower water absorption rate than Example 3 and Example 4 using polyester diol instead of polycarbonate diol, It is possible to prevent foaming. In particular, in Example 1, this tendency is clear. For this reason, it can be said that polycarbonate diol is more suitable than polyester diol as a diol compound contained in a urethane acrylate oligomer. This may be due to the difference in polarity or molecular structure between polycarbonate diol and polyester diol.

  Further, when Example 1 and Example 3 are compared with Example 2 and Example 4, p-cresol ethylene oxide-modified acrylate is more energy ray polymerizable than phenoxyethyl acrylate with respect to water absorption and antifoaming properties. It can be said that it is suitable as a monomer. This is because p-cresol ethylene oxide-modified acrylate having a methyl group is slightly less polar than phenoxyethyl acrylate in both cases where the difference in molecular structure is only the presence or absence of a methyl group in the phenol moiety. It is considered that there is a possibility that the molecular structure is slightly higher than the latter.

  As described above, according to the present embodiment, by using a urethane acrylate oligomer and an acrylic ester compound having no hydroxyl group, which is an energy ray polymerizable monomer, as a base film, it is possible to prevent bubbles due to heating of the pressure-sensitive adhesive sheet. It is possible to prevent the occurrence. Furthermore, by using an energy beam polymerizable monomer having a relatively bulky molecular structure, it is excellent in stress relaxation, and can be ground to an extremely thin thickness while preventing the wafer from being bent, And an adhesive sheet can be formed.

  The material and the amount of the base film and the pressure-sensitive adhesive sheet are not limited to those exemplified in the present embodiment. For example, a base film may be formed by mixing p-cresol ethylene oxide-modified acrylate that has shown good results as an energy beam polymerizable monomer and phenoxyethyl acrylate. Further, the amount of each component contained in the base film is not limited to those exemplified in Table 1. For example, the ratio of the urethane acrylate oligomer and the energy ray polymerizable monomer is within the range shown in paragraph [0019]. You may adjust with.

Claims (6)

It is a base film of an adhesive sheet to be attached to a semiconductor wafer,
At least urethane acrylate oligomer and energy ray polymerizable monomer are formed by energy ray curing,
The energy ray polymerizable monomer is cresol ethylene oxide-modified acrylate,
The base film of an adhesive sheet, wherein the urethane acrylate oligomer includes an isocyanate urethane oligomer composed of a polycarbonate diol or polyester diol and a polyvalent isocyanate .   The base film of the pressure-sensitive adhesive sheet according to claim 1, wherein a water absorption when the base film is immersed in pure water for 120 minutes is 0.5% by weight or less.   The base film of the pressure-sensitive adhesive sheet according to claim 1, wherein the stress relaxation property after 1 minute when the base film is stretched by 10% is 40% or more.   A pressure-sensitive adhesive sheet comprising the base film according to claim 1 and a pressure-sensitive adhesive layer. The pressure-sensitive adhesive sheet according to claim 4 , wherein the pressure-sensitive adhesive layer is attached to the circuit surface to protect the circuit surface of the semiconductor wafer when the back surface of the semiconductor wafer is ground. It is a base film of an adhesive sheet to be attached to a semiconductor wafer,
At least urethane acrylate oligomer and energy ray polymerizable monomer are formed by energy ray curing,
The energy ray polymerizable monomer is cresol ethylene oxide-modified acrylate,
The base film of the pressure-sensitive adhesive sheet, wherein the urethane acrylate oligomer contains a polycarbonate diol, has a water absorption of 0.11% by weight or less, and has a stress relaxation property of 79% or more.