JP2013077758A - Base film and pressure-sensitive adhesive sheet with base film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a base film of a pressure-sensitive adhesive sheet capable of suppressing dimpling and cracking of a wafer by dispersing grinding stress applied to a step on a wafer surface.SOLUTION: There is provided a base film 22 comprising (A) a step absorption layer which is 100-400 μm thick and has a storage elastic modulus of 0.2-6.0 MPa at 23°C and (B) a layer made of thermoplastic resin. In a reverse-surface grinding process in which a top-surface side of the wafer having a device region where a plurality of devices are sectioned with streets and an outer peripheral surplus region surrounding the device region is held on a holding table of a grinding device so as to form a recessed part by grinding a region 16 of a reverse surface of the wafer which corresponds to the device region and also to form a ring-shaped reinforcement part 17 on an outer peripheral side of the recessed part, the base film is used for the pressure-sensitive adhesive sheet stuck on the wafer surface.

Description

  The present invention relates to a base film used as a base material of an adhesive sheet used to protect a circuit surface of a semiconductor wafer having a circuit formed on the surface, and in particular, a ring-shaped reinforcing portion is formed on the outer periphery of the back surface. The present invention relates to a base film used as a base of an adhesive sheet used when manufacturing a semiconductor wafer. The present invention also relates to a pressure-sensitive adhesive sheet comprising a pressure-sensitive adhesive layer on the film and used as a surface protection sheet for a semiconductor wafer.

  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.

  For this reason, it has been demanded that a wafer, which has been polished to a finish thickness of about 350 μm in the past, be reduced to 50 to 100 μm or less. However, as the semiconductor wafer becomes thinner, the risk of breakage increases during processing and transportation.

  For this reason, as shown in FIGS. 3 to 5, when grinding the back surface of the wafer, only the back inner peripheral portion 16 is ground, and the ring-shaped reinforcing portion 17 is left on the back outer peripheral portion to make the wafer rigid. A grinding method has been proposed (Patent Documents 1 and 2). As shown in FIG. 3, the surface of the wafer 10 has an outer peripheral portion 15 in which a circuit (device) 13 is not formed within a range of several mm from the outer peripheral end, and the circuit 13 is an inner peripheral portion of the wafer excluding the outer peripheral portion 15. 14 is formed. In the wafer having the ring-shaped reinforcing portion 17, the back inner peripheral portion 16 corresponding to the front surface circuit forming portion (wafer inner peripheral portion 14) is ground to a predetermined thickness, and the outer peripheral portion 15 where no circuit is formed is formed. The corresponding outer peripheral portion of the back surface remains without being ground and becomes a ring-shaped reinforcing portion 17. Since the ring-shaped reinforcing portion 17 has a relatively high rigidity, the wafer 10 ground in the above-described form can be stably transported and stored, and damage during processing is reduced. 4 is a perspective view from the back side of the wafer on which the ring-shaped reinforcing portion 17 is formed, and FIG. 5 is a cross-sectional view of FIG.

  However, the wafer grinding method as described above has a greater load on the inner peripheral portion of the wafer back surface than the conventional method of grinding the entire back surface of the wafer. This is because such a grinding wheel for grinding a wafer revolves within a limited region corresponding to the inner peripheral portion of the back surface of the wafer, and therefore its size is usually small. This is because, in order to perform grinding while maintaining the production speed with such a small grinding wheel, it is necessary to perform grinding while partially applying a high load. For this reason, even if the level difference is caused by a circuit on the wafer surface, which is not a problem with the conventional grinding method, the dimples and cracks may occur due to concentration of grinding stress on the level difference.

JP 2007-27309 A JP 2007-59829 A

  The present invention disperses the grinding stress applied to the step on the front surface of the wafer, which was not a problem with the conventional method of grinding the entire back surface of the wafer, and suppresses the occurrence of dimples and cracks on the wafer. The purpose is to provide a film.

  As a result of intensive research aimed at solving the above-mentioned problems, the present inventors have suppressed the occurrence of dimples and cracks on the grinding surface by arranging a resin layer having specific physical properties as the base film of the pressure-sensitive adhesive sheet. As a result, the present invention has been completed.

The present invention for solving the above problems includes the following gist.
[1] A base film of an adhesive sheet to be attached to a semiconductor wafer,
(A) a step absorption layer having a thickness of 100 to 400 μm and a storage elastic modulus at 23 ° C. of 0.2 to 6.0 MPa;
(B) It is comprised from the layer which consists of thermoplastic resins,
A wafer is formed by holding a surface of the wafer having a device region formed by dividing a plurality of devices by streets and an outer peripheral surplus region surrounding the device region on a surface by a holding table of a grinding apparatus, In the back surface grinding step, a region corresponding to the device region is ground to form a recess and a ring-shaped reinforcing portion is formed on the outer peripheral side of the recess. Base film.

[2] The base film according to [1], wherein the step absorption layer (A) is made of a cured product obtained by energy beam curing a blend containing a polyether polyol polyurethane and an energy beam curable monomer.

[3] The base film according to [1] or [2], in which the thickness of the concave portion on the back surface of the wafer is ground to 75 μm or less in the back surface grinding step.

[4] A pressure-sensitive adhesive sheet further comprising a pressure-sensitive adhesive layer (C) on the base film according to any one of [1] to [3].

[5] A semiconductor wafer grinding method in which the pressure-sensitive adhesive sheet according to [4] is attached to a front surface of a wafer and the back surface of the wafer is ground.

[6] A method for manufacturing a semiconductor device, comprising a step of attaching the pressure-sensitive adhesive sheet according to [4] to a surface of a wafer.

  According to the present invention, by using a specific base material film, it is possible to absorb a step on the wafer surface, which has not been a problem with the conventional grinding method, and to suppress the generation of dimples. In addition, the depression of the pressure-sensitive adhesive sheet using the base film due to the stress (grinding stress) generated during grinding can be alleviated, and cracking of the wafer can be prevented. That is, when the back surface of the wafer is ground so that the ring-shaped reinforcing portion remains on the outer periphery of the back surface while protecting the circuit surface of the semiconductor wafer using the adhesive sheet using the base film, the dimples on the ground surface And the generation of cracks can be suppressed.

It is sectional drawing of the state which has stuck the adhesive sheet which concerns on this invention to the semiconductor wafer. It is sectional drawing of the state which has stuck the adhesive sheet which concerns on this invention to the semiconductor wafer. The top view of the circuit formation surface of a semiconductor wafer is shown. The perspective view of the semiconductor wafer in which the ring-shaped reinforcement part was formed in the back surface outer peripheral part is shown. FIG. 5 shows a cross-sectional view of FIG. 4.

Hereinafter, the present invention will be described more specifically, including its best mode. The base film according to the present invention is a base film of an adhesive sheet to be attached to a semiconductor wafer,
(A) a step absorption layer having a thickness of 100 to 400 μm and a storage elastic modulus at 23 ° C. of 0.2 to 6.0 MPa (hereinafter sometimes abbreviated as “step absorption layer”);
(B) is composed of a layer made of a thermoplastic resin (hereinafter sometimes abbreviated as “thermoplastic resin layer”),
A wafer is formed by holding a surface of the wafer having a device region formed by dividing a plurality of devices by streets and an outer peripheral surplus region surrounding the device region on a surface by a holding table of a grinding apparatus, In the back surface grinding step, a region corresponding to the device region is ground to form a recess, and a ring-shaped reinforcing portion is formed on the outer peripheral side of the recess. It is a base film.

[(A) Step absorption layer]
The thickness of the step absorption layer (A) is 100 to 400 μm, and the storage elastic modulus at 23 ° C. is 0.2 to 6.0 MPa.

  The step absorption layer (A) exhibits unique viscoelasticity when the device region formed on the wafer surface is pressed, deforms rapidly according to the shape of the device, and stress caused by the height difference (step) of the device. For relaxation, the device will not be crushed when pressed. Further, since the residual stress after deformation is small, the wafer can be stably held and the occurrence of dimples and cracks in the wafer can be suppressed. When the thickness of the step absorption layer (A) is less than 100 μm, or when the storage elastic modulus at 23 ° C. of the step absorption layer (A) exceeds 6.0 MPa, the stress due to the height difference of the device is sufficiently relieved. And dimples are likely to occur on the wafer. On the other hand, when the thickness of the step absorption layer (A) exceeds 400 μm or when the storage elastic modulus at 23 ° C. of the step absorption layer (A) is less than 0.2 MPa, in the wafer back grinding process, Of these, the grinding wheel is pressed only to the concave portion (back surface inner peripheral portion) formed by grinding the region corresponding to the device region, so that the adhesive tape sinks locally and the wafer is likely to crack.

  The thickness of the step absorption layer (A) is preferably 150 to 350 μm, more preferably 150 to 250 μm. Moreover, the storage elastic modulus at 23 ° C. of the step absorption layer (A) is preferably 0.2 to 2.5 MPa, more preferably 0.5 to 1.5 MPa. By setting the thickness of the step absorption layer (A) and the storage elastic modulus at 23 ° C. within the above range, the step on the wafer surface is embedded in the step absorption layer (A) and absorbs the step, thereby producing dimples on the wafer. Can be suppressed. Moreover, excessive sinking of the adhesive tape in the wafer back grinding process can be suppressed, and cracking of the wafer can be prevented.

  As long as the step absorption layer (A) satisfies the above thickness and storage modulus, the material is not particularly limited, but a cured product obtained by energy beam curing a blend containing a polyether polyol polyurethane and an energy beam curable monomer. It is preferable that

  The polyether polyol-based polyurethane may be a high molecular weight substance or an oligomer as long as it is obtained by polycondensation of a polyether polyol and a polyvalent isocyanate compound. When it is an oligomer, it preferably has a polymerizable functional group, and examples of the polymerizable functional group include a (meth) acryloyl group. Examples of such a polyether polyol-based polyurethane include polyether polyol-based urethane (meth) acrylate oligomers.

  The polyether polyol-based urethane (meth) acrylate oligomer is a compound having a structural unit derived from a polyether polyol in the molecule, an energy ray polymerizable (meth) acryloyl group, and a urethane bond. The polyether polyol urethane (meth) acrylate oligomer is obtained by reacting, for example, a terminal isocyanate urethane prepolymer obtained by reacting a polyether polyol compound and a polyvalent isocyanate compound with a (meth) acrylate having a hydroxy group. can get. By using a polyether polyol-based urethane (meth) acrylate oligomer having two or more (meth) acryloyl groups, the tack of the step absorption layer (A) can be suppressed, and the base film is made into a roll-shaped raw material. In this case, it is preferable that the end portion is difficult to adhere to an operator or equipment. In addition, in this specification, (meth) acryl is used in the meaning including both acryl and methacryl.

  The polyether type polyol compound is not particularly limited, and may be a bifunctional diol, a trifunctional triol, or a tetrafunctional or higher polyol, but from the viewpoint of availability, versatility, reactivity, and the like. It is particularly preferred to use a diol. Accordingly, polyether type diols are preferably used.

  The polyether type diol is generally represented by HO-(-R-O-) n-H. Here, R is a divalent hydrocarbon group, preferably an alkylene group, more preferably an alkylene group having 1 to 6 carbon atoms, and particularly preferably an alkylene group having 2 or 3 carbon atoms. Among the alkylene groups having 1 to 6 carbon atoms, ethylene, propylene, butylene or tetramethylene is preferable, and ethylene or propylene is particularly preferable. n is the number of repetitions of (—R—O—), preferably about 10 to 250, more preferably about 25 to 205, and particularly preferably about 40 to 185. When n is smaller than 10, the urethane bond concentration of the urethane (meth) acrylate oligomer becomes high, and the storage elastic modulus at 23 ° C. of the step absorption layer (A) becomes high. When n is larger than 250, there is a concern that the storage elastic modulus at 23 ° C. is difficult to decrease.

  The molecular weight of the polyether-type polyol compound is preferably about 1000 to 10000, and more preferably about 2000 to 8000. When the molecular weight is lower than 1000, the crosslinking density of the urethane (meth) acrylate oligomer increases, and the storage elastic modulus at 23 ° C. of the step absorption layer (A) tends to increase. When the weight average molecular weight is too high, there is a concern that the storage elastic modulus at 23 ° C. is hardly lowered due to polymer interaction between the polyether chains.

  The molecular weight of the polyether-type polyol compound is the number of polyether-type polyol functional groups × 56.11 × 1000 / hydroxyl value [mgKOH / g], which is a value calculated from the hydroxyl value of the polyether-type polyol compound.

  The polyether-type polyol compound generates a terminal isocyanate urethane prepolymer having an ether bond (-(-R-O-) n-) introduced by urethanation with a polyvalent isocyanate compound. Such an ether bond may have a structure derived from a ring-opening reaction of a cyclic ether such as ethylene oxide, propylene oxide, and tetrahydrofuran. By using such a polyether type polyol compound, the urethane (meth) acrylate oligomer contains a structural unit derived from the polyether type polyol compound.

  Examples of the polyvalent isocyanate compound include aliphatic polyisocyanates such as tetramethylene diisocyanate, hexamethylene diisocyanate, and trimethylhexamethylene diisocyanate; isophorone diisocyanate, norbornane diisocyanate, dicyclohexylmethane-4,4′-diisocyanate, dicyclohexylmethane-2,4. Alicyclic diisocyanates such as' -diisocyanate, ω, ω'-diisocyanate dimethylcyclohexane; 4,4'-diphenylmethane diisocyanate, tolylene diisocyanate, xylylene diisocyanate, tolidine diisocyanate, tetramethylene xylylene diisocyanate, naphthalene-1, And aromatic diisocyanates such as 5-diisocyanate. Among these, it is preferable to use isophorone diisocyanate, hexamethylene diisocyanate, or xylylene diisocyanate because the viscosity of the urethane (meth) acrylate oligomer can be kept low and the handleability becomes good.

  In addition, you may use various well-known catalysts for the said urethanation reaction as needed. Examples of the catalyst include tin compounds such as dibutyltin oxide and stannous octylate, and alkoxytitanium such as tetrabutyl titanate and tetrapropyl titanate. When a catalyst is used, the amount used is not particularly limited, but about 10 to 500 ppm is reasonable from the viewpoint of reaction rate and reaction control. The reaction temperature of the esterification reaction is not particularly limited, but 150 to 300 ° C. is reasonable from the viewpoint of reaction rate and reaction control.

  A polyether polyol-based urethane (meth) acrylate obtained by reacting a hydroxyl-containing (meth) acrylate with a terminal isocyanate urethane prepolymer obtained by reacting the above polyether-type polyol compound with a polyvalent isocyanate compound. An oligomer is obtained.

  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, α-hydroxymethyl acrylate, 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, 4-hydroxybutyl (meth) acrylate, 4-hydroxycyclohexyl (meth) acrylate, 5 -Alkylene ethers such as hydroxycyclooctyl (meth) acrylate, 2-hydroxy-3-phenyloxypropyl (meth) acrylate, pentaerythritol tri (meth) acrylate, polyethylene glycol mono (meth) acrylate, polypropylene glycol mono (meth) acrylate Group-containing (meth) acrylate; Hydroxy group-containing (meth) acrylamide such as N-methylol (meth) acrylamide; Vinyl alcohol, vinyl phenol, bisphenol The diglycidyl ester of A (meth) reacting the acrylic acid and the 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 may be reacted in the presence of a solvent and a catalyst, if necessary. The reaction may be performed at about 60 to 100 ° C. for about 1 to 4 hours.

  Although the usage-amount of the (meth) acrylate which has a terminal isocyanate urethane prepolymer and a hydroxy group is not specifically limited, Usually, (equivalent of the isocyanate group of a terminal isocyanate urethane prepolymer) / (hydroxy of the (meth) acrylate which has a hydroxy group) The group equivalent) is preferably about 0.5 to 1.0.

  The weight average molecular weight Mw of the polyether polyol-based urethane (meth) acrylate oligomer thus obtained (polystyrene converted value by gel permeation chromatography, the same shall apply hereinafter) is not particularly limited, but is usually weight. The average molecular weight Mw is preferably about 35000 to 100,000, more preferably about 40000 to 80000, and particularly preferably about 45000 to 70000. When the weight average molecular weight Mw is in such a range, it becomes easy to adjust the storage elastic modulus at 23 ° C. of the step absorption layer (A) to the above preferable range. Moreover, the break elongation of a level | step difference absorption layer (A) can be improved by making the weight average molecular weight Mw 35000 or more, and the resin viscosity of a urethane (meth) acrylate oligomer is made low by setting it as 100,000 or less. Therefore, the handleability of the coating solution for film formation is improved.

  The resulting polyether polyol-based 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 polyether polyol-based urethane (meth) acrylate oligomer has a polyether polyol moiety 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 step absorption layer (A) containing a cured product of a (meth) acrylate oligomer exhibits unique viscoelasticity.

  Said polyether polyol type 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, the energy ray-curable monomer is mixed to form a film and then cured to obtain the step absorption layer (A). . 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, hexadecyl (Meth) acrylates having 1-30 carbon atoms in the alkyl group such as meth) acrylate, octadecyl (meth) acrylate, eicosyl (meth) acrylate, etc .; isobornyl (meth) acrylate, dicyclopentenyl (meth) acrylate, dicyclopentanyl (Meth) acrylate, dicyclopentenyloxy (meth) acrylate, cyclohexyl (meth) acrylate, (meth) acrylate having an alicyclic structure such as adamantane (meth) acrylate; phenoxyethyl acrylate, phenylhydroxypropyl (meth) acrylate, (Meth) acrylate having an aromatic structure such as benzyl (meth) acrylate, 2-hydroxy-3-phenoxypropyl (meth) acrylate; or tetrahydrofurfuryl (meth) (Meth) acrylates having a heterocyclic structure such as acrylate, (meth) acryloylmorpholine, N-vinylpyrrolidone, N-vinylcaprolactam; vinyl compounds such as styrene, hydroxyethyl vinyl ether, hydroxybutyl vinyl ether, N-vinylformamide It is done. Moreover, you may use polyfunctional (meth) acrylate as needed.

  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

  10-500 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, 30-400 mass parts is more preferable.

As the film forming method, a technique called casting film formation (cast film formation) can be preferably employed. Specifically, a liquid compound (a liquid product obtained by diluting a mixture of the above components with a solvent if necessary) is cast into a thin film on a process sheet, for example, and then the coating film is irradiated with energy rays for polymerization. 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. Further, the irradiation amount is different depending on the type of the energy ray, for example, when ultraviolet rays are used, the ultraviolet intensity is 50~300mW / cm ^2, the amount of ultraviolet irradiation is preferably about 100~1200mJ / 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.

  Moreover, you may add metal fillers, such as inorganic fillers, such as a calcium carbonate, a silica, and a mica, iron, and lead, in the above-mentioned compound. In addition to the above components, the step absorption layer (A) may contain additives such as colorants such as pigments and dyes.

  Said level | step difference absorption layer (A) is laminated | stacked with the thermoplastic resin layer (B) mentioned later, and comprises a base film. The step absorption layer (A) may be laminated with the thermoplastic resin layer (B) after being formed on the process sheet as described above, and the step absorption layer directly on the thermoplastic resin layer (B). (A) may be formed.

[(B) Thermoplastic resin layer]
The thermoplastic resin layer (B) is a layer for imparting shape maintenance to the substrate film of the present invention. The storage elastic modulus of the thermoplastic resin layer (B) is preferably 6.0 MPa or more, more preferably 15 MPa or more, and particularly preferably 50 MPa or more. Examples of the thermoplastic resin layer (B) having such characteristics include polyester resins such as polyethylene terephthalate (PET), polyolefin resins such as polyethylene (PE) and polypropylene (PP), polyimide (PI), and polyether ether. Thermoplastic resins such as ketone (PEEK), polyvinyl chloride (PVC), polyvinylidene chloride resin, polyamide resin, polyurethane resin, polystyrene resin, acrylic resin, fluorine resin, cellulose resin, polycarbonate resin, etc. Is used. These thermoplastic resins can be used as a single layer or a multilayer product by laminating.

  The thermoplastic resin layer (B) may be formed on one side of the step absorption layer (A) or may be formed on both sides.

  Since the step absorption layer (A) deforms relatively easily as described above, it is difficult to maintain the shape. Therefore, when a base film is formed only by a level | step difference absorption layer (A), handling property is bad and working efficiency may fall. By laminating a relatively hard thermoplastic resin layer (B) on the step-absorbing layer (A), a base film having an appropriate shape retaining property and excellent handling properties can be obtained.

  Although the thickness of a thermoplastic resin layer (B) is not specifically limited, Preferably it is 10-1000 micrometers, More preferably, it exists in the range of 20-500 micrometers.

[Base film]
As described above, the base film is formed by laminating the step absorption layer (A) and the thermoplastic resin layer (B). The step absorption layer (A) and the thermoplastic resin layer (B) may be directly laminated, or may be bonded via an adhesive layer.

  Although the manufacturing method of a base film is not specifically limited, a level | step difference absorption layer (A) may be laminated | stacked on a thermoplastic resin layer (B) by the extrusion lamination method etc., and the material of a level | step difference absorption layer (A) When has thermal softening properties, it may be laminated with the thermoplastic resin layer (B) by a heat laminating method or the like. Further, the step absorption layer (A) may be provided on the thermoplastic resin layer (B) by a solution casting method, or by a dry laminating method or the like. Among these, it is possible to carry out with simple equipment, the material of the step absorption layer (A) is not required to have a separate characteristic such as thermal softening property, and the step absorption layer (A) and the thermoplastic resin layer (B It is preferable to employ a solution casting method because an adhesive is not required for laminating.

  As a method of providing the step absorption layer (A) on the thermoplastic resin layer (B) by a solution cast method, for example, a blend containing the polyether polyol urethane (meth) acrylate oligomer and an energy ray curable monomer, After casting into a thin film on the process sheet, the coating is dried if necessary, and a small amount of energy rays are irradiated to partially polymerize and cure the coating to form a semi-cured layer. There is a method obtained by laminating the plastic resin layer (B), irradiating energy rays to cure the semi-cured layer, obtaining the step absorption layer (A), and removing the process sheet.

  Further, the step absorption layer (A) is obtained by laminating the thermoplastic resin layer (B) on the step absorption layer (A) surface of the laminate comprising the step absorption layer (A) and the thermoplastic resin layer (B). The base film in which the thermoplastic resin layer (B) is formed on both sides can also be obtained.

  The pressure-sensitive adhesive sheet according to the present invention has a pressure-sensitive adhesive layer (C) formed on one side of the base film. The surface of the base film on which the pressure-sensitive adhesive layer (C) is provided, preferably the surface of the step absorption layer (A), is subjected to corona treatment in order to improve the adhesion with the pressure-sensitive adhesive layer (C), A primer layer may be provided.

[(C) Adhesive layer]
The type of the pressure-sensitive adhesive layer (C) is not specified as long as it has an appropriate removability to the wafer, and can be formed of various conventionally known 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.

  Although the thickness of an adhesive layer (C) is not specifically limited, Preferably it is 5-200 micrometers, More preferably, it exists in the range of 10-120 micrometers.

  Note that a release sheet may be laminated on the pressure-sensitive adhesive layer (C) in order to protect the pressure-sensitive adhesive layer (C) 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 carbamates.

  As a method of providing the pressure-sensitive adhesive layer (C) on the surface of the base film, the pressure-sensitive adhesive layer (C) formed so as to have a predetermined thickness on the release sheet may be transferred to the surface of the base film. The pressure-sensitive adhesive layer (C) may be formed by directly applying to the surface of the base film.

[Adhesive sheet]
The pressure-sensitive adhesive sheet according to the present invention has a pressure-sensitive adhesive layer (C) formed on one side of the base film. When the base film has a two-layer structure in which the thermoplastic resin layer (B) is laminated on one side of the step absorption layer (A), the pressure-sensitive adhesive layer (C) is provided on the surface of the step absorption layer (A). It is preferable to be made.

[Semiconductor wafer processing method]
In the semiconductor wafer processing method as described below, the pressure-sensitive adhesive sheet can be suitably used.
(Wafer back grinding method)
In the wafer back surface grinding, as shown in FIG. 1, the pressure-sensitive adhesive layer 21 of the pressure-sensitive adhesive sheet 20 according to the present invention is attached to the surface of the semiconductor wafer 10 on which the circuit (device) 13 is formed. The sticking of the adhesive sheet to the semiconductor wafer is performed by a general-purpose method using a tape mounter or the like. Moreover, the adhesive sheet 20 may be cut in advance in substantially the same shape as the semiconductor wafer 10, and after sticking the adhesive sheet to the wafer, an excess sheet may be cut and removed along the outer periphery of the wafer.

  Next, as shown in FIGS. 2 and 3, a region (back surface inner peripheral portion) 16 corresponding to the device region 14 in the back surface of the semiconductor wafer 10 is ground to a predetermined thickness. Thereafter, the adhesive sheet 20 is peeled from the semiconductor wafer 10. A semiconductor device is manufactured through processes such as dicing, die bonding, and resin sealing of the obtained wafer 10. In FIG. 3, a device region (inner peripheral portion) 14 formed by dividing a plurality of devices 13 by streets 18 and an outer peripheral surplus region (outer peripheral portion) 15 surrounding the device region 14 are formed on the surface. FIG. 4 is a plan view of the semiconductor wafer 10, and FIG. 4 shows a wafer 10 in which a concave portion is formed by grinding the back inner peripheral portion 16 of the semiconductor wafer 10, and a ring-shaped reinforcing portion 17 is formed on the outer peripheral side (back peripheral portion) of the concave portion. FIG. 5 is a cross-sectional view of FIG. 4.

  The semiconductor wafer 10 may be a silicon wafer or a compound semiconductor wafer such as gallium / arsenic. The formation of the circuit 13 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 circuit forming process of the semiconductor wafer, a predetermined circuit 13 is formed. The circuit 13 is formed in a lattice shape on the surface of the inner peripheral portion 14 of the wafer 10, and a surplus portion 15 in which no circuit is present remains in a range of several mm from the outer peripheral end. The thickness of the wafer 10 before grinding is not particularly limited, but is usually about 500 to 1000 μm.

  At the time of back surface grinding, an adhesive sheet 20 is attached to the circuit surface in order to protect the circuit 13 on the front surface. In the back surface grinding, a circuit surface side (that is, the adhesive sheet 20 side) of the wafer 10 is held by a holding table such as a chuck table, and the back surface side where the circuit 13 is not formed is ground by a grinder. At the time of back surface grinding, after grinding the entire back surface to a predetermined thickness or without grinding the entire back surface, only the back surface inner peripheral portion 16 corresponding to the circuit forming portion (inner peripheral portion 14) on the front surface is ground, The back region corresponding to the outer peripheral portion 15 where the circuit 13 is not formed is left without being ground. As a result, in the semiconductor wafer 10 after grinding, only the back inner peripheral portion 16 is thinly ground to form a recess, and the ring-shaped reinforcing portion 17 remains on the rear outer peripheral portion. Such back grinding can be performed by a known method described in, for example, Japanese Patent Application Laid-Open No. 2007-59829 and Japanese Patent Application Laid-Open No. 2007-27309.

  The total thickness T1 (see FIG. 5) of the ring-shaped reinforcing portion 17 is not particularly limited, as long as it provides the necessary rigidity to the wafer and does not impair handling properties, and is generally about 200 to 725 μm. is there. The width of the ring-shaped reinforcing portion 17 is about the width of the outer peripheral portion 15, and is generally about 2 to 8 mm. Further, the thickness T2 of the inner peripheral portion 16 depends on the design of the device, and is usually about 25 to 200 μm, preferably 75 μm or less.

  The pressure-sensitive adhesive sheet 20 of the present invention has the step absorption layer (A) and the pressure-sensitive adhesive layer (C) as described above, and has viscoelasticity that can sufficiently follow the steps of the device. For this reason, it is embedded in the wafer surface on which the device is formed, the step is eliminated, and the wafer can be held in a flat state. In addition, because of the high conformity to the surface shape of the wafer, even when a strong shearing force is applied to the wafer during grinding of the wafer back surface, the wafer can be prevented from vibrating and misaligned, and the inner periphery of the back surface of the wafer is flat and extremely thin. Can be ground up to. Further, since the thickness of the step absorption layer (A) and the storage elastic modulus at 23 ° C. are adjusted to a predetermined appropriate range, the wafer is subjected to a special grinding method for grinding only the inner periphery of the back surface. Even when a high load is applied, dimples and cracks are unlikely to occur. Also, the grinding water does not enter the circuit surface during wafer back surface grinding.

  After the back grinding process, a process of removing a crushed layer (micro crack) generated by grinding may be performed. Since the pressure-sensitive adhesive sheet 20 is adhered to the surface of the wafer 10, it can be stably conveyed to the crushing layer removal step, and the wafer surface can be protected when the crushing layer is removed. As a result of removing the fractured layer, the strength of the wafer 10 is improved. Then, the adhesive sheet 20 is peeled from the wafer 10 from which the crushed layer has been removed. Since the crushed layer is removed, the wafer 10 has a relatively high strength and does not break due to the stress when the pressure-sensitive adhesive sheet is peeled off. Therefore, according to the said manufacturing method, the semiconductor wafer 10 which has the ring-shaped reinforcement part 17 and the intensity | strength was maintained can be obtained easily. Thereafter, the semiconductor wafer 10 is diced to obtain a chip, and a semiconductor device is manufactured through processes such as die bonding of the chip and resin sealing.

  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.

<Storage modulus>
An energy ray cured layer having a diameter of 8 mm and a thickness of 3 mm was prepared, and a storage elastic modulus at 23 ° C. was measured at 1 Hz using a viscoelasticity measuring device (DYNAMIC ANALYZER RDA II (twisted shear method) manufactured by Rheometrics).

<Dimple and crack generation>
After affixing the pressure-sensitive adhesive layer of the pressure-sensitive adhesive sheet to the surface of a silicon wafer (8 inches) having a device formed on the surface using a tape laminator (RAD-3510F / 12 (manufactured by Lintec Corporation)), a wafer back surface grinding device ( Using DAG810 (manufactured by Disco Corporation), only the inner peripheral portion of the back surface of the wafer was ground into the following shape while spraying water.

(Wafer shape)
Outer diameter: 200mm
Inner diameter of ring-shaped reinforcement: 198mm
Inner peripheral thickness: 75 μm and 30 μm
Ring-shaped reinforcing part thickness: 725 μm

  After grinding the inner peripheral portion to a thickness of 75 μm and 30 μm, the back surface of the wafer was visually observed to check for the presence of dimples. A sample in which no dimples were generated was indicated as A, a sample in which slight dimples were generated but B was found to be practically acceptable, and C in which dimples were clearly generated or cracks were generated.

<Infiltration of grinding water>
After evaluating the occurrence of dimples and cracks, the adhesive sheet was peeled off from the wafer surface, and the presence or absence of intrusion of grinding water into the wafer surface was confirmed with an optical digital microscope (100 times magnification).

Example 1
2-hydroxyethyl methacrylate (hereinafter referred to as HEMA) is reacted at the terminal of a terminal isocyanate urethane prepolymer obtained by polymerizing polypropylene glycol having a molecular weight of 4000 (hereinafter described as PPG 4000) and isophorone diisocyanate (hereinafter referred to as IPDI), A polyether polyol urethane methacrylate oligomer having a weight average molecular weight of 47,000 was obtained. In addition, the said weight average molecular weight is a commercially available gel permeation chromatography (Body product name "HLC-8220GPC", the Tosoh Corporation make; column product name "TSKGel SuperHZM-M", the Tosoh Corporation make; developing solvent tetrahydrofuran ) (The same applies hereinafter).

  100 g (solid content) of the obtained polyether polyol-based urethane methacrylate oligomer, 140 g (solid content) of isobornyl acrylate as an energy ray-curable monomer, 160 g (solid content) of 2-hydroxy-3-phenoxypropyl acrylate, and photopolymerization 4 g of 2-hydroxy-2-methyl-1-phenyl-propan-1-one (manufactured by Ciba Specialty Chemicals: Darocur 1173, solid content concentration 100% by mass) is added as an initiator, and the composition (energy ray of room temperature liquid) A curable composition (viscosity η = 3400 mPa · s, 25 ° C.)) was obtained.

On the polyethylene terephthalate (PET) film release film (product of Lintec Corporation, product name “SP-PET3811” thickness 38 μm), which is a process sheet for casting, the above composition is applied to a thickness of 200 μm by a fountain die method. Then, a coating film was formed, and then a semi-cured layer was obtained by irradiation with ultraviolet rays from the coating film side. As the ultraviolet irradiation device, a belt conveyor type ultraviolet irradiation device (manufactured by Eye Graphics: ECS-401GX) and a high pressure mercury lamp (manufactured by Eye Graphics: H04-L41) were used as the ultraviolet light source {irradiation conditions: lamp height 150 mm, Lamp output: 3 kW (converted output: 120 mW / cm), illuminance of 271 mW / cm ^{2 with} a light wavelength of 365 nm, light amount of 177 mJ / cm ² (Oak Seisakusho's UV light meter: measured by UV-351)}. Then, immediately after irradiation, a polyethylene terephthalate (PET) film (Mitsubishi Chemical Polyester Co., Ltd .: T-100, thickness 75 μm) was laminated as a thermoplastic resin layer on the semi-cured layer, and further irradiated with ultraviolet rays from the laminated PET film side. {Irradiation conditions: Lamp height 150 mm, lamp output 3 kW (converted output 120 mW / cm), illuminance 271 mW / cm ^{2 with} a light wavelength of 365 nm, light quantity 1200 mJ / cm ² (measured with an UV light quantity meter manufactured by Oak Manufacturing Co., Ltd .: UV-351). )} Four times, the semi-cured layer is crosslinked and cured to obtain a step absorbing layer, the casting process sheet is removed, and the step absorbing layer (200 μm) and the thermoplastic resin layer (75 μm) are all laminated. A substrate film having a thickness of 275 μm was obtained.

  Apart from the above, an acrylic copolymer having a weight average molecular weight of 500,000 and a glass transition temperature of −7 ° C. is solution-polymerized in an ethyl acetate solvent using 70 parts by mass of butyl acrylate and 30 parts by mass of 2-hydroxyethyl acrylate. Was generated. 100 parts by mass of the solid content of this acrylic copolymer and 8 parts by mass of methacryloyloxyethyl isocyanate (80 equivalents with respect to 100 equivalents of hydroxyl groups in the acrylic copolymer) are reacted to form a polymerizable two molecule in the molecule. An ethyl acetate solution (30% solution) of an ultraviolet curable acrylic copolymer having a heavy bond was obtained.

  With respect to 100 parts by mass (solid content) of the ultraviolet curable acrylic copolymer, 2.0 parts by mass (solid ratio) of a polyvalent isocyanate compound (Coronate L, manufactured by Nippon Polyurethane Co., Ltd.) and a photopolymerization initiator as a crosslinking agent. (Irgacure 184, manufactured by Ciba Specialty Chemicals) 3.3 parts by mass (solid ratio) were mixed to obtain an ultraviolet curable pressure-sensitive adhesive composition. By applying and drying this ultraviolet curable pressure-sensitive adhesive composition on a release sheet (SP-PET 381031, manufactured by Lintec Corporation), forming a pressure-sensitive adhesive layer having a thickness of 50 μm, and bonding it to the step absorption layer side of the base film A pressure-sensitive adhesive sheet was obtained. Table 1 shows the evaluation results of the pressure-sensitive adhesive sheet.

(Example 2)
In Example 1, an adhesive sheet was obtained and evaluated by the same method as in Example 1 except that the thickness of the step absorption layer was 100 μm. The results are shown in Table 1.

(Example 3)
In Example 1, an adhesive sheet was obtained and evaluated in the same manner as in Example 1 except that the thickness of the step absorption layer was 300 μm. The results are shown in Table 1.

Example 4
In Example 1, an adhesive sheet was obtained and evaluated in the same manner as in Example 1 except that the thickness of the step absorption layer was 400 μm. The results are shown in Table 1.

(Example 5)
In Example 1, a pressure-sensitive adhesive sheet was obtained and evaluated in the same manner as in Example 1 except that the polyether polyol-based urethane methacrylate oligomer had a weight average molecular weight of 53,000. The results are shown in Table 1. The viscosity of the blend (room temperature liquid energy beam curable composition) was η = 4800 mPa · s and 25 ° C.

(Example 6)
In Example 1, instead of isophorone diisocyanate, hydrogenated xylylene diisocyanate (hereinafter referred to as HXDI) was used, and the weight average molecular weight of the polyether polyol-based urethane (meth) acrylate oligomer was changed to 46000. A pressure sensitive adhesive sheet was obtained by the same method and evaluated. The results are shown in Table 1. The viscosity of the blend (room temperature liquid energy beam curable composition) was η = 3400 mPa · s and 25 ° C.

(Example 7)
In Example 1, in place of isophorone diisocyanate, hexamethylene diisocyanate (hereinafter referred to as HDI) was used, and the weight average molecular weight of the polyether polyol urethane methacrylate oligomer was changed to 45,000. An adhesive sheet was obtained and evaluated. The results are shown in Table 1. The viscosity of the blend (room temperature liquid energy beam curable composition) was η = 3300 mPa · s and 25 ° C.

(Example 8)
In Example 1, instead of PPG 4000, a polypropylene glycol having a molecular weight of 8000 (hereinafter referred to as PPG 8000) was used, and the polyether polyol-based urethane methacrylate oligomer was made to have a weight average molecular weight of 68,000. Thus, an adhesive sheet was obtained and evaluated. The results are shown in Table 1. The viscosity of the blend (room temperature liquid energy beam curable composition) was η = 3700 mPa · s and 25 ° C.

Example 9
In Example 1, in place of PPG4000, poly (oxytetramethylene) glycol (hereinafter referred to as PTMG3000) having a molecular weight of 3000 was used, and the weight average molecular weight of the polyether polyol-based urethane methacrylate oligomer was changed to 45,000. A pressure-sensitive adhesive sheet was obtained in the same manner as described above and evaluated. The results are shown in Table 1. The viscosity of the blend (room temperature liquid energy beam curable composition) was η = 4100 mPa · s and 25 ° C.

(Example 10)
In Example 1, instead of PPG4000, a polypropylene glycol having a molecular weight of 2000 (hereinafter referred to as PPG2000) was used, and the weight average molecular weight of the polyether polyol-based urethane methacrylate oligomer was changed to 54,000. Thus, an adhesive sheet was obtained and evaluated. The results are shown in Table 1. The viscosity of the blend (room temperature liquid energy beam curable composition) was η = 4500 mPa · s and 25 ° C.

(Example 11)
Instead of the polyether polyol-based urethane methacrylate oligomer used in Example 1, a pressure-sensitive adhesive sheet was obtained in the same manner as in Example 1, except that a polyether polyol-based urethane methacrylate oligomer having a weight average molecular weight of 40,000 was used. Evaluation was performed. The results are shown in Table 1. The viscosity of the blend (room temperature liquid energy ray curable composition) was η = 2200 mPa · s and 25 ° C.

(Example 12)
In Example 1, instead of PPG4000, a polypropylene glycol having a molecular weight of 2000 (hereinafter referred to as PPG2000) was used, and the weight average molecular weight of the polyether polyol-based urethane methacrylate oligomer was changed to 41000. Thus, an adhesive sheet was obtained and evaluated. The results are shown in Table 1. In addition, the viscosity (eta) = 2300mPa * s and 25 degreeC of the compounding composition (room temperature liquid energy-beam curable composition) were obtained.

(Example 13)
In Example 1, in place of PPG4000, a polypropylene glycol having a molecular weight of 10,000 (hereinafter referred to as PPG10000) was used, and the weight average molecular weight of the polyether polyol-based urethane methacrylate oligomer was changed to 44,000. Thus, an adhesive sheet was obtained and evaluated. The results are shown in Table 1. The viscosity of the blend (room temperature liquid energy ray curable composition) was η = 2500 mPa · s and 25 ° C.

(Comparative Example 1)
In Example 1, an adhesive sheet was obtained and evaluated in the same manner as in Example 1 except that the thickness of the step absorption layer was 50 μm. The results are shown in Table 1.

(Comparative Example 2)
In Example 1, an adhesive sheet was obtained and evaluated in the same manner as in Example 1 except that the thickness of the step absorption layer was 500 μm. The results are shown in Table 1.

(Comparative Example 3)
Instead of the polyether polyol-based urethane methacrylate oligomer used in Example 1, a polyester-based urethane (meth) acrylate oligomer (weight average molecular weight 4000) was used, and the formulation (viscosity η = 4500 mPa · s, 25 ° C.). Except having used the obtained compound, the adhesive sheet was obtained by the same method as Example 1, and evaluated. The results are shown in Table 1.

(Comparative Example 4)
Instead of the polyether polyol urethane methacrylate oligomer used in Example 1, a polycarbonate urethane (meth) acrylate oligomer (weight average molecular weight 6000) was used, and the formulation (viscosity η = 4500 mPa · s, 25 ° C.). Except having used the obtained compound, the adhesive sheet was obtained by the same method as Example 1, and evaluated. The results are shown in Table 1.

(Comparative Example 5)
Polypropylene glycol having a molecular weight of 4000 (hereinafter referred to as PPG4000)
And isophorone diisocyanate (hereinafter referred to as IPDI) were polymerized to obtain a polyurethane having a weight average molecular weight of 40,000 and no polymerizable functional group. 100 g of the obtained polyurethane (solid content), 50 g (solid content) of isobornyl acrylate as an energy ray-curable monomer, 100 g (solid content) of 2-hydroxy-3-phenoxypropyl acrylate, and 2-hydroxy as a photopolymerization initiator 4 g of 2-methyl-1-phenyl-propan-1-one (Ciba Specialty Chemicals: Darocur 1173, solid content concentration: 100% by mass) was added, and an energy ray-curable composition (viscosity η = 4000 mPa) in a room temperature liquid. -S, 25 ° C). Except having used the obtained compound, the adhesive sheet was obtained by the same method as Example 1, and evaluated. The results are shown in Table 1.

(Comparative Example 6)
Using the same UV-curable pressure-sensitive adhesive composition as in Example 1, it was applied and dried on a release sheet (SP-PET 381031, manufactured by Lintec Corporation) so as to have a thickness of 120 μm, and directly provided in Example 1 without providing a step absorption layer. A pressure-sensitive adhesive sheet was obtained by directly bonding to a PET film and evaluated. The results are shown in Table 1.

(Comparative Example 7)
A pressure-sensitive adhesive sheet was obtained and evaluated in the same manner as in Comparative Example 6 except that the ultraviolet curable pressure-sensitive adhesive composition was applied and dried to a thickness of 180 μm. The results are shown in Table 1.

DESCRIPTION OF SYMBOLS 10 ... Semiconductor wafer 17 ... Ring-shaped reinforcement part 18 ... Street 20 ... Adhesive sheet 21 ... Adhesive layer 22 ... Base film

Claims (6)

It is a base film of an adhesive sheet to be attached to a semiconductor wafer,
(A) a step absorption layer having a thickness of 100 to 400 μm and a storage elastic modulus at 23 ° C. of 0.2 to 6.0 MPa;
(B) It is comprised from the layer which consists of thermoplastic resins,
A wafer is formed by holding a surface of the wafer having a device region formed by dividing a plurality of devices by streets and an outer peripheral surplus region surrounding the device region on a surface by a holding table of a grinding apparatus, In the back surface grinding step, a region corresponding to the device region is ground to form a recess and a ring-shaped reinforcing portion is formed on the outer peripheral side of the recess. Base film.   The base film according to claim 1, wherein the step absorption layer (A) is made of a cured product obtained by energy beam curing a blend containing a polyether polyol-based polyurethane and an energy beam curable monomer.   The base film according to claim 1 or 2, wherein in the back grinding step, the thickness of the concave portion on the back surface of the wafer is ground to 75 µm or less.   A pressure-sensitive adhesive sheet further comprising a pressure-sensitive adhesive layer (C) on the base film according to claim 1.   A method for grinding a semiconductor wafer, wherein the pressure-sensitive adhesive sheet according to claim 4 is affixed to the front surface of a wafer and the back surface of the wafer is ground. The manufacturing method of a semiconductor device including the process of sticking the adhesive sheet of Claim 4 on the surface of a wafer.

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