JP3330851B2 - Wafer grinding method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a wafer grinding method,
In particular, the present invention relates to a wafer grinding method capable of extremely thinly grinding a wafer having a circuit pattern formed on its surface.

[0002]

BACKGROUND OF THE INVENTION In recent years, there has been an increasing need to embed ICs in cards such as money cards. For this reason, it has become necessary to reduce the thickness of the semiconductor chip, which was conventionally about 350 μm, to 50 to 100 μm or less.

[0003] Grinding the back surface of a wafer after pattern formation has conventionally been performed, and its purpose is to remove an oxide film generated during pattern formation or to make the thickness uniform. When grinding the back surface of such a wafer, the surface of the circuit is coated with an ultraviolet-curable protective adhesive sheet (Japanese Patent Laid-Open No. 60-1985).
189938) and the like.

When such an ultraviolet-curable protective sheet is used, the sheet is adhered to a circuit surface, and after grinding the back surface, the sheet is peeled off by irradiating ultraviolet rays to reduce the adhesive force of the sheet. I was Therefore, the adhesive layer is in an uncured state during the back surface grinding. 35 as described above
When grinding to a thickness of about 0 μm, there was no problem if the pressure-sensitive adhesive layer remained flexible, but it was thinner (for example, 15 μm).
When trying to grind (to 0 μm or less), it was difficult to grind to a uniform thickness, and the wafer was sometimes damaged during the grinding. For this reason, if the back surface was ground by a conventional method using a conventional ultraviolet-curable pressure-sensitive adhesive sheet, it was not possible to produce an extremely thin IC chip with a high yield. Also, grinding dust generated during back surface grinding may adhere to the base material of the adhesive sheet, and even if irradiated with ultraviolet light, the ultraviolet light is blocked at a portion where the grinding dust is adhered. Was not sufficiently cured, the adhesive strength was not sufficiently reduced, and the adhesive was sometimes left behind.

The inventors of the present invention have conducted intensive studies on the mechanism of the non-uniformity of the thickness of the wafer and the damage of the wafer as described above. One of the causes is that if the pressure-sensitive adhesive layer is too soft, the grinding will occur. It was determined that the wafer was at a point where it was slightly displaced up and down or left and right during processing.

[0006]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a method of grinding a wafer capable of manufacturing an extremely thin IC chip with a high yield. I have.

[0007]

SUMMARY OF THE INVENTION In the wafer grinding method according to the present invention, an energy ray-curable pressure-sensitive adhesive sheet is adhered to a wafer surface on which a circuit is formed, and an energy ray is irradiated to cure the pressure-sensitive adhesive layer. The method is characterized in that the back surface of the wafer is ground in a state where the sheet is adhered to the front surface of the wafer.

According to the present invention, the wafer can be ground to a thickness of 50 to 250 μm. In the present invention, the adhesive strength of the pressure-sensitive adhesive layer of the energy ray-curable pressure-sensitive adhesive sheet is 100 to 100 before irradiation with energy rays.
2000g / 25mm, 10 after energy beam irradiation
It is preferably less than 0 g / 25 mm, the elastic modulus of the pressure-sensitive adhesive layer before irradiation with energy rays is less than 1 × 10 ⁷ dyn / cm ² , and the elastic modulus after irradiation with energy rays is 1 × 10 ⁷ dyn.
/ cm ² or more.

[0009]

DETAILED DESCRIPTION OF THE INVENTION Hereinafter, a wafer grinding method according to the present invention will be specifically described. In the wafer grinding method according to the present invention, first, an energy-ray-curable pressure-sensitive adhesive sheet is attached to the surface of a wafer on which a circuit has been formed.

The formation of the circuit pattern is performed by a conventionally known etching method, lift-off method or the like. On the wafer surface on which the circuit pattern is formed, unevenness having a step of about 10 to 60 μm is formed by the pattern.

Next, an energy-ray-curable pressure-sensitive adhesive sheet is attached to the circuit surface of the wafer. The energy ray-curable pressure-sensitive adhesive sheet used in the present invention is composed of a substrate film and an energy ray-curable pressure-sensitive adhesive layer formed thereon, and its shape can take any shape such as a tape shape, a label shape, and the like. .

As the substrate film, a film having excellent water resistance and heat resistance is suitable, and a synthetic resin film is particularly suitable. In the present invention, since an energy beam such as an electron beam (EB) or an ultraviolet ray (UV) is irradiated after the adhesive sheet is attached to the wafer, the substrate film needs to be transparent in the case of the EB irradiation. However, when performing UV irradiation, it is necessary to use a transparent material even if it is colored, as the base film.

Specific examples of such a base film include a polyethylene film, a polypropylene film, a polyvinyl chloride film, a polyethylene terephthalate film, a polybutylene terephthalate film,
Polybutene film, polybutadiene film, polyurethane film, polymethylpentene film, ethylene-vinyl acetate copolymer film, ethylene- (meth)
Acrylic acid copolymer films, ethylene-methyl (meth) acrylate copolymer films, ethylene-ethyl (meth) acrylate copolymer films and the like are used. Also, these laminated films may be used. The thickness of the base film is usually about 10 to 300 μm, preferably about 50 to 200 μm.

The energy-ray-curable pressure-sensitive adhesive layer formed on the substrate film comprises, for example, a pressure-sensitive adhesive and an energy-ray polymerizable compound. Acrylic,
Conventionally known pressure-sensitive adhesives such as polyester-based and natural rubber-based adhesives are used without any particular limitation. Among these, acrylic pressure-sensitive adhesives are preferable, and acrylic pressure-sensitive adhesives containing acrylate as a main constituent unit are particularly preferable.

As the acrylate, for example,
Acrylic acid esters of alkyl alcohols having 1 to 10 carbon atoms, methacrylic acid esters of alkyl alcohols having 1 to 10 carbon atoms and the like are used.

[0016] In addition, an acrylate ester containing a hydroxyl group, an amino group, a substituted amino group, a glycidyl group, etc .; and (meth) acrylic acid, vinyl acetate, acrylonitrile, as long as the object of the present invention is not impaired. And a structural unit derived from vinyl alkyl ether or the like may be contained in the acrylic pressure-sensitive adhesive.

The weight average molecular weight of the copolymer obtained by polymerizing these monomers is preferably from 5.0 × 10 ⁴ .
2.0 × 10 ⁶ , more preferably 1.0 × 10 6
^{It is 5 to} 1.0 × 10 ⁶ .

The acrylic pressure-sensitive adhesive as described above can set the adhesive strength and the cohesive strength to arbitrary values by using a crosslinking agent. Examples of such a crosslinking agent include a polyvalent isocyanate compound, a polyvalent epoxy compound, a polyvalent aziridine compound, a chelate compound and the like.

Examples of the energy ray-polymerizable compound used in the energy ray-curable pressure-sensitive adhesive layer include, for example, JP-A-60-196956 and JP-A-60-22.
Low-molecular-weight compounds having at least two or more photopolymerizable carbon-carbon double bonds in a molecule which can be three-dimensionally reticulated by light irradiation as disclosed in Japanese Patent No. 3,139 are widely used. , Trimethylolpropane triacrylate, pentaerythritol triacrylate,
Pentaerythritol tetraacrylate, dipentaerythritol monohydroxypentaacrylate, dipentaerythritol hexaacrylate or 1,4
-Butylene glycol diacrylate, 1,6-hexanediol diacrylate, polyethylene glycol diacrylate, commercially available oligoester acrylate and the like are used.

Further, as an energy ray polymerizable compound,
In addition to the acrylate compounds described above, urethane acrylate oligomers can also be used. The urethane acrylate oligomer includes a polyol compound such as a polyester type or a polyether type, and a polyvalent isocyanate compound such as 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, 1,3-
Xylylene diisocyanate, 1,4-xylylene diisocyanate, diphenylmethane 4,4-diisocyanate, etc. are reacted with an isocyanate-terminated urethane prepolymer to give an acrylate or methacrylate having a hydroxyl group such as 2-hydroxyethyl acrylate or 2-hydroxyethyl. It is obtained by reacting methacrylate, 2-hydroxypropyl acrylate, 2-hydroxypropyl methacrylate, polyethylene glycol acrylate, polyethylene glycol methacrylate and the like.

The mixing ratio of the acrylic pressure-sensitive adhesive and the energy ray polymerizable compound in the pressure-sensitive adhesive is 100
50 to 20 parts by weight of the energy beam polymerizable compound
It is desirable to use 0 parts by weight, preferably 50 to 150 parts by weight, particularly preferably 70 to 120 parts by weight.

The energy ray-curable pressure-sensitive adhesive layer may be formed from an energy ray-curable copolymer having an energy ray-polymerizable group in a side chain. Such an energy ray-curable copolymer has the property of having both adhesiveness and energy ray-curability. An energy ray-curable copolymer having an energy ray polymerizable group in a side chain is disclosed in, for example, JP-A-5-32946 and JP-A-8-2723.
No. 9 discloses such details.

The adhesive strength of the energy ray-curable pressure-sensitive adhesive layer having the above composition before irradiation with energy rays is usually 100 g / 25 mm or more, preferably 100 to 2000 g /.
25 mm, particularly preferably 200 to 1000 g / 25 mm
It is. The adhesive strength of the pressure-sensitive adhesive layer after irradiation with energy rays is usually less than 100 g / 25 mm, preferably 2 g / 25 mm.
mm or more and less than 100 g / 25 mm, particularly preferably 5 to 100 g / 25 mm.
It is 60 g / 25 mm.

Furthermore, the elastic modulus of the pressure-sensitive adhesive layer before curing with an energy ray is usually less than 1 × 10 ⁷ dyn / cm ² ,
Preferably 1 × 10 ⁵ dyn / cm ² or more and 1 × 10 ⁷ dyn / cm ²
Less than 5 × 10 ^{5 to} 5 × 10 ⁶ dyn / cm ²
The elastic modulus after curing is usually 1 × 10 ⁷ dy
n / cm ² or more, preferably 1 × 10 ⁷ to 1 × 10 ¹⁰ dyn / cm
² or more, particularly preferably 1 × 10 ⁸ to 1 × 10 ⁹ dyn / cm
²

Here, the elastic modulus is a value determined by the following method. That is, the energy ray-curable pressure-sensitive adhesive constituting the pressure-sensitive adhesive layer is made into a piece of pressure-sensitive adhesive having a diameter of 8 mm and a thickness of 3 mm. Made)
From the graph obtained by measuring at 1 Hz using
Is read and the energy ray is taken as the elastic modulus before irradiation.

The energy ray-curable pressure-sensitive adhesive constituting the pressure-sensitive adhesive layer is made into a piece of pressure-sensitive adhesive having a length of 50 mm, a width of 4 mm and a thickness of 0.2 mm, placed under a high-pressure mercury lamp of 80 W / cm, and irradiated with energy rays for one second. Then, the value of 25 ° C. was read from a graph obtained by measuring the elastic modulus of the cured small piece at 11 Hz using a viscoelasticity measuring device (Leo Vibron: DDV-II-EP, manufactured by Orientec Co., Ltd.). To the elastic modulus after irradiation with energy rays.

The thickness of the energy ray-curable pressure-sensitive adhesive layer is usually about 3 to 100 μm, and preferably about 5 to 50 μm. Furthermore, in the case of UV irradiation in the above-mentioned energy ray-curable pressure-sensitive adhesive layer, by mixing a UV initiator, the polymerization curing time by UV irradiation and the amount of UV irradiation can be reduced.

Specific examples of such a UV initiator include benzoin, benzoin methyl ether, benzoin ethyl ether, benzoin isopropyl ether,
Benzyldiphenyl sulfide, tetramethylthiuram monosulfide, azobisisobutyronitrile, dibenzyl, diacetyl, β-chloranthraquinone,
Examples include acetophenone, diethoxyacetophenone, 1-hydroxycyclohexylphenyl ketone, and the like.

The energy ray-curable pressure-sensitive adhesive sheet used in the present invention can be prepared by coating the above energy ray-curable pressure-sensitive adhesive on various substrates in accordance with a generally known method such as a comma coater, a gravure coater, a die coater, and a reverse coater. Apply in thickness and dry to form an adhesive layer,
Then, it is obtained by laminating a release sheet on the pressure-sensitive adhesive layer as required.

When an adhesive having the above-mentioned characteristics is used, it has flexibility before irradiation with energy rays, so that it undergoes plastic deformation corresponding to the unevenness of the circuit on the wafer surface and follows the unevenness of the circuit. The pressure-sensitive adhesive layer is deformed to buffer irregularities.

Next, when the pressure-sensitive adhesive layer is irradiated with energy rays in this state, the pressure-sensitive adhesive layer is cured while buffering the unevenness of the circuit. The irradiation amount of energy is sufficient if the physical properties of the pressure-sensitive adhesive after curing are within the above-described range,
Although it varies depending on the composition of the pressure-sensitive adhesive, generally, when ultraviolet rays are used as energy rays, 40 to 400 mJ /
cm ² and about 0.1 to 10 in the case of using an electron beam
It is about 0 kGy.

When the back surface of the wafer is ground in this state, the unevenness of the surface of the wafer is buffered due to the deformation of the adhesive layer. Therefore, the wafer is ground to a uniform thickness without being affected by the unevenness of the surface of the wafer. be able to. Further, since the pressure-sensitive adhesive layer is hardened and does not undergo plastic deformation, the wafer can be stably held and the wafer can be ground extremely thinly.

Further, conventionally, since the adhesive force is reduced by irradiating ultraviolet rays after grinding, if grinding chips adhere to the surface of the adhesive sheet, defective irradiation of ultraviolet rays occurs at the portion where the cutting chips are adhered, and glue residue remains. However, in the present invention, since ultraviolet irradiation is performed before grinding, irradiation failure of ultraviolet light does not occur, and adhesive does not remain on the wafer surface.

On the other hand, although the adhesive force is reduced by the irradiation of the energy rays, the adhesive can follow the unevenness of the circuit on the surface of the wafer and is in close contact therewith, so that the wafer can be sufficiently held during the wafer grinding. Also, there is no peeling during wafer grinding and no permeation of cooling water or cleaning water.

[0035]

According to the present invention, since the unevenness of the wafer surface is buffered by the adhesive layer and the wafer is ground while the adhesive layer is cured, the wafer can be ground extremely thinly. In addition, damage to the wafer can be prevented. Therefore, it becomes possible to manufacture an extremely thin IC chip with a high yield.

[0036]

EXAMPLES The present invention will be described below with reference to examples, but the present invention is not limited to these examples.

In the following Examples and Comparative Examples, the measurement of “180 ° peel adhesive strength” and the “wafer back surface grinding test” were performed as follows. 180 ° peel adhesive strength The energy-ray-curable adhesive sheet obtained in the example was 23
2 kg on the mirror surface of the semiconductor wafer in an atmosphere of 65 ° C. and 65% RH
After sticking by reciprocating a rubber roller and leaving it to stand for 30 minutes, the peeling rate is 30 using a universal type tensile tester (TENSILON / UTM-4-100 manufactured by Orientec Co., Ltd.).
The 180 ° peel adhesion was measured at 0 mm / min. Further, after being stuck and left under the same conditions, and irradiated with ultraviolet rays from the energy ray-curable pressure-sensitive adhesive sheet side with a high-pressure mercury lamp (80 W / cm) at an irradiation distance of 10 cm and a line speed of 5 m / min, similarly, 18
The 0 ° peel adhesion was measured. Wafer backside grinding test (1) A circuit is formed on the surface of the test wafer, and the step on the circuit surface is 30 μm and 50 μm.
μm 8-inch silicon wafer (average thickness 725 μm)
Were prepared and used for the test. (2) Wafer back surface grinding test Surface (circuit surface) of wafer sample created in (1) above
Then, an energy ray-curable pressure-sensitive adhesive sheet prepared according to the following example was adhered along a wafer shape using a 5 kg rubber roller.

A) In the example, after irradiating an ultraviolet ray at an irradiation distance of 10 cm and a line speed of 5 m with a high-pressure mercury lamp (80 W / cm) as a light source from the side of the energy ray-curable pressure-sensitive adhesive sheet, Was ground to a wafer thickness of 150 μm with a wafer grinder (DFG840 manufactured by Disco Corporation), the sheet was peeled off, and the state of the wafer was visually observed.

B) In the comparative example, after the back surface of the wafer to which no sheet was attached was ground to a wafer thickness of 150 μm with a wafer grinder (DFG840 manufactured by Disco Corporation), a high-pressure mercury lamp ( Using a light source of 80 W / cm), the sheet was peeled off by ultraviolet irradiation at an irradiation distance of 10 cm and a line speed of 5 m, and the state of the wafer was visually observed.

The following were used as the energy ray-curable pressure-sensitive adhesives in Examples and Comparative Examples. (A1) 100 parts by weight of a 25% ethyl acetate solution of a copolymer having a weight average molecular weight of 600,000 consisting of 70 parts by weight of butyl acrylate and 30 parts by weight of 2-hydroxyethyl acrylate, and 8.4 parts by weight of methacryloyloxyethyl isocyanate And reactants. (A2) Weight average molecular weight 400,000 comprising 50 parts by weight of butyl acrylate, 20 parts by weight of methyl methacrylate, and 30 parts by weight of 2-hydroxyethyl acrylate
Reaction product of 100 parts by weight of a 25% ethyl acetate solution of a copolymer of the above with 7.0 parts by weight of methacryloyloxyethyl isocyanate. (A3) A weight average molecular weight of 35 parts by weight of butyl acrylate, 10 parts by weight of 2-ethylhexyl acrylate, and 5 parts by weight of 2-hydroxyethyl acrylate.
A reaction product of 100 parts by weight of a 000 copolymer in a 25% ethyl acetate solution and 1.7 parts by weight of methacryloyloxyethyl isocyanate. (A4) A mixture of 100 parts by weight of an acrylic pressure-sensitive adhesive (Alon S-1511X, manufactured by Toa Gosei Chemical Industry Co., Ltd.) and 40 parts by weight of a urethane acrylate having an average molecular weight of about 3,000.

[0041]

Example 1 100 parts by weight of the above (A1), 0.1 part by weight of an acetophenone-based photopolymerization initiator (trade name: Irgacure 184, manufactured by Ciba-Geigy), polyvalent isocyanate compound (trade name, manufactured by Nippon Polyurethane Co., Ltd.) Name Coronate L)
0.5 parts by weight were mixed to obtain an energy ray-curable pressure-sensitive adhesive composition.

This energy ray-curable pressure-sensitive adhesive composition was
After coating on a polyethylene film having a thickness of 100 μm so that the coating thickness after drying was 30 μm, drying was performed at 100 ° C. for 1 minute to obtain an energy ray-curable pressure-sensitive adhesive sheet. Using the obtained energy ray-curable pressure-sensitive adhesive sheet, the “180 ° peeling pressure” before and after irradiation with ultraviolet light was measured. Further, "wafer back surface grinding test a)" was performed on a wafer sample having a step of 30 μm on the circuit surface. Table 1 shows the results.

[0043]

Example 2 An energy ray-curable pressure-sensitive adhesive sheet was obtained in the same manner as in Example 1 except that (A2) was used in place of (A1). Using this energy ray-curable pressure-sensitive adhesive sheet, the “180 ° peeling pressure” before and after irradiation with ultraviolet light was measured. Further, "wafer back surface grinding test a)" was performed on a wafer sample having a step of 30 μm on the circuit surface. Table 1 shows the results.

[0044]

Example 3 An energy ray-curable pressure-sensitive adhesive sheet was obtained in the same manner as in Example 1 except that (A3) was used instead of (A1). Using this energy ray-curable pressure-sensitive adhesive sheet, the “180 ° peeling pressure” before and after irradiation with ultraviolet light was measured. Further, "wafer back surface grinding test a)" was performed on a wafer sample having a step of 30 μm on the circuit surface. Table 1 shows the results.

[0045]

Example 4 An energy ray-curable pressure-sensitive adhesive sheet was obtained in the same manner as in Example 1 except that (A4) was used instead of (A1). Using this energy ray-curable pressure-sensitive adhesive sheet, the “180 ° peeling pressure” before and after irradiation with ultraviolet light was measured. Further, "wafer back surface grinding test a)" was performed on a wafer sample having a step of 30 μm on the circuit surface. Table 1 shows the results.

[0046]

Example 5 An energy-ray-curable pressure-sensitive adhesive sheet was obtained in the same manner as in Example 1, except that the energy-ray-curable pressure-sensitive adhesive composition of Example 1 was applied so that the coating amount after drying was 50 μm. Using this energy ray-curable pressure-sensitive adhesive sheet, the “180 ° peeling pressure” before and after irradiation with ultraviolet light was measured. Further, "wafer back surface grinding test a)" was performed on a wafer sample having a step of 50 μm on the circuit surface. Table 1 shows the results
Shown in

[0047]

Embodiments 6 to 8 Instead of (A1) in Embodiment 5, (A
2), (A3) and (A4) were used in the same manner as in Example 5 to obtain an energy-ray-curable pressure-sensitive adhesive sheet. Using this energy ray-curable pressure-sensitive adhesive sheet, the “180 ° peeling pressure” before and after irradiation with ultraviolet light was measured. Further, "wafer back surface grinding test a)" was performed on a wafer sample having a step of 50 μm on the circuit surface. Table 1 shows the results.

[0048]

[Table 1]

[0049]

Comparative Examples 1 to 8 In Examples 1 to 8, "Wafer backside grinding test b)" was used instead of "Wafer backside grinding test a)".
The same experiment was performed except that the above was performed. Table 2 shows the results.

[0050]

[Table 2]

──────────────────────────────────────────────────続 き Continued on the front page (58) Fields surveyed (Int.Cl. ⁷ , DB name) H01L 21/304

Claims (4)

(57) [Claims] 1. A state in which an energy-ray-curable pressure-sensitive adhesive sheet is adhered to the surface of a wafer on which circuits are formed, and the adhesive layer is cured by irradiating energy rays, and then the pressure-sensitive adhesive sheet is adhered to the wafer surface. Grinding the back surface of the wafer by using the method. 2. The wafer grinding method according to claim 1, wherein said wafer is ground to a thickness of 50 to 250 μm. 3. The adhesive force of the energy ray-curable pressure-sensitive adhesive sheet is 100 g / 25 mm or more before irradiation with energy rays and less than 100 g / 25 mm after irradiation with energy rays. 3. The wafer grinding method according to 2. 4. The pressure-sensitive adhesive layer of the energy ray-curable pressure-sensitive adhesive sheet has an elastic modulus of 1 × 10 ⁷ before irradiation with energy rays.
less than dyn / cm ² and 1 × 10
The wafer grinding method according to any one of claims 1 to 3, wherein the value is ⁷ dyn / cm ² or more.