JP2006261467A - Adhesive sheet for sticking wafer and process for machining wafer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an adhesive sheet for sticking a wafer in which production of thread-like chips can be reduced during dicing at a low cost without requiring an electron beam irradiation process. <P>SOLUTION: The adhesive sheet for sticking a wafer consists of a substrate film, and an adhesive layer formed thereon wherein the thickness of the adhesive layer is 20-50 μm. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an adhesive sheet for adhering a wafer, and more particularly to an adhesive sheet for adhering a wafer that can reduce chip contamination and breakage due to thread-like dicing waste generated when a semiconductor wafer is cut and separated into small pieces.

In a manufacturing process of a semiconductor device such as an IC or LSI, the semiconductor wafer such as silicon or gallium arsenide is cut and separated (diced) into small pieces and then subjected to a pickup process. A general semiconductor wafer dicing step and pick-up step will be described with reference to FIG.
First, the semiconductor wafer 31 is stuck to the wafer sticking sticking sheet 33 whose both ends are fixed to the holder 32 (FIG. 1-a), and dicing is performed to divide the wafer 31 into element pieces (chips) 31a. (Figure 1-b). Next, in order to pick up the chip 31a, the distance between the chips is expanded by expanding in the direction of the dotted arrow A (FIG. 1-c), and pickup of all chips or part of the chips is performed (FIG. 1-d). In some cases, the expand is once unwound (FIG. 1-e) and stored in the cassette 41 for later pickup (FIG. 2).

In a process from a semiconductor wafer dicing process to a pick-up process, an adhesive sheet in which an adhesive is applied on a base material has been used. In such an adhesive sheet, in consideration of expandability, a base material made of a relatively soft resin is used, and for example, a polyethylene film may be used.
At the time of dicing, the dicing blade may cut into the base material to generate thread-like cutting waste. The thread-shaped cutting waste often has a length of about 300 μm or more, and is accompanied by the adhesive of the adhesive sheet. For this reason, thread-like debris easily adheres to the chip, which causes chip reliability and yield reduction.

In order to solve such problems, a method for reducing the generation of thread-like cutting waste as described above by irradiating a soft polyethylene film with an electron beam to crosslink is disclosed (Patent Document 1). ). However, this method requires an electron beam irradiation step, which increases the number of steps and is disadvantageous in terms of cost.
Japanese Patent Laid-Open No. 5-21234

  The present invention is intended to solve the problems associated with the prior art as described above, and is advantageous in terms of cost without passing through a process such as electron beam irradiation, and is also effective for thread-like cutting waste generated during dicing. It aims at providing the adhesive sheet for wafer sticking which can reduce generation | occurrence | production.

  As a result of intensive studies on the above-mentioned problems, the present inventors have found that the pressure-sensitive adhesive layer has a specific thickness, and further, the pressure-sensitive adhesive sheet for sticking a wafer having a specific Young's modulus of the base film is the above-mentioned problem. The present invention has been made based on such findings.

That is, the present invention
(1) A wafer sticking adhesive sheet comprising a base film and a pressure sensitive adhesive layer formed on the base film, wherein the pressure sensitive adhesive layer has a thickness of 20 to 50 μm. Sheet,
(2) The adhesive sheet for adhering a wafer according to claim 1, wherein Young's modulus of the base film is 130 MPa or less,
(3) The adhesive film for wafer sticking according to (1) or (2), wherein the substrate film has at least one layer containing an ionomer resin,
(4) The adhesive sheet for adhering a wafer according to any one of (1) to (3), which is used for dicing a wafer.
(5) When the wafer is bonded to the adhesive sheet for sticking a wafer according to any one of (1) to (4) and the wafer is diced, the base material of the adhesive sheet is not cut. A wafer processing method characterized by
Is to provide.

  In the pressure-sensitive adhesive sheet for sticking a wafer according to the present invention, the thickness of the pressure-sensitive adhesive layer is set to 20 to 50 μm to suppress the generation of dicing waste, and even when the dicing blade penetrates the pressure-sensitive adhesive layer, the dicing waste is greatly increased. It is possible to reduce to

The adhesive sheet for sticking a wafer according to the present invention comprises a base film and an adhesive layer formed on the base film, and the thickness of the adhesive layer is 20 to 50 μm. The pressure-sensitive adhesive layer may be in the range of this thickness, and the pressure-sensitive adhesive layer may be a single layer or a multilayer pressure-sensitive adhesive layer formed by laminating two or more types of pressure-sensitive adhesive layers.
The thickness of the pressure-sensitive adhesive is preferably 20 to 40 μm, which is about the thickness of the cutting edge of the dicing blade, without cutting the dicing blade up to the surface of the substrate during dicing. When the thickness of the pressure-sensitive adhesive layer is 20 μm or more, the amount of whiskers generated from the base film can be significantly suppressed. In order to completely suppress the generation of whiskers from the substrate, it is preferable that the thickness be equal to or greater than the cutting depth of the blade cut into the substrate, and the thickness of the pressure-sensitive adhesive layer is desirably 30 μm or more.

When the thickness of the pressure-sensitive adhesive layer exceeds 50 μm, chipping and cracking of the chip end due to dicing called chipping increase. Although the cause of chipping is not clear, the pressure-sensitive adhesive layer is often softer than the base material, and the chip cannot be held during dicing, so that the thickness of the pressure-sensitive adhesive layer is set to 50 μm or less. In order to make chipping smaller, the thickness of the pressure-sensitive adhesive layer is preferably 40 μm or less.
In the wafer sticking pressure-sensitive adhesive sheet according to the present invention, by making the pressure-sensitive adhesive layer have a certain thickness as described above, at the time of dicing, it becomes possible that the dicing blade does not cut to the surface of the base material. Chips are not generated, and chip reliability and yield can be improved.

  After the wafer stuck to the adhesive sheet for wafer sticking of the present invention is cut into chips (dicing), it is pushed up from the adhesive tape side by a push-up pin called a needle, and a suction machine called a collet is used. The cut chip is peeled off from the adhesive tape. In that case, it is required that the chip is easily peeled off from the adhesive tape when pushed up by the needle, that is, the pickup property is good.

In the present invention, the thickness of the pressure-sensitive adhesive layer is 20 to 50 μm, and the Young's modulus of the base film is further set to 130 MPa or less. Preferably, it is 60-125 MPa. If it exists in this range, the deterioration of the pick-up property by a comparatively thick adhesive layer can be supplemented with the softness | flexibility of a base film.
The Young's modulus in the present invention is based on the tensile test method of JIS K 7127 (Plastic film and sheet tensile test method), the base film is made into a test piece having a width of 25 mm and a length of 100 mm, a temperature of 23 ± 2 ° C., The test is performed at a humidity of 50 ± 5%, a distance between marked lines of 50 mm and a distance between grips, and a speed of 300 mm / min, and is defined by the formula Em = Δσ / Δε using the first linear portion of the tensile stress-strain curve. It is an average value of a measured value in a machining direction (MD) and a measured value in a transverse method (TD) orthogonal to the machining method. Here, Em: Young's modulus (tensile elastic modulus, Pa), Δσ: Stress value (modulus value) due to the original average cross-sectional area between two linear points was also measured by the same tensile test, and the formula σ = F / A. Here, σ: stress value (Pa), F: load at that time (N), and A: minimum cross-sectional area (m ² ) of the test piece.

  A base film having excellent water resistance and heat resistance is suitable, and a synthetic resin film is particularly suitable. When an extensible film is interposed, expansion can be easily performed. Specific examples of such stretchable films include low density polyethylene (LDPE), linear low density polyethylene (LLDPE), ethylene / propylene copolymer, propylene copolymer, and ethylene-propylene-diene copolymer. Combined vulcanizate, polybutene, polybutadiene, polymethylpentene, ethylene-vinyl acetate copolymer, ethylene- (meth) acrylic acid copolymer, ethylene- (meth) acrylic acid methyl copolymer, ethylene- (meth) acrylic Ethyl acid copolymer, polyvinyl chloride, vinyl chloride-vinyl acetate copolymer, ethylene-vinyl chloride-vinyl acetate copolymer, polyurethane, polyamide, ionomer, nitrile rubber, butyl rubber, styrene isoprene rubber, styrene butadiene rubber, natural From rubber and its water additives or modified products That film and the like can be used. These stretchable films can be used in combination of two or more kinds.

  In the case of the adhesive tape for sticking a wafer according to the present invention, since the thickness of the adhesive is as thick as 20 to 50 μm, the amount of sag after expansion (FIG. 1-e) becomes large. As in the case where the cassette is accommodated in the second stage of the cassette, the adhesive tape cannot be accommodated because it comes into contact with a wafer on another adhesive tape as indicated by a broken line in the third stage. To prevent this, it is preferable to have at least one layer containing an ionomer resin as the base film. More preferably, the thickness of the layer containing the ionomer resin is more desirably 50% or more of the total thickness of the base film.

  In general, an ionomer resin refers to a metal orientation resin of an ethylene-methacrylic acid copolymer. In the present invention, an ionomer resin used for a base film is an ethylene-acrylic acid copolymer system. , A ternary polymer obtained by polymerizing, for example, an acrylic acid ester or a methacrylic acid ester as a third component on a copolymer such as ethylene-methacrylic acid and ethylene-acrylic acid, and further a metal orientation of a multi-component copolymer higher than that. Resin is also included. That is, it refers to a metal-oriented resin of a multi-component copolymer having a carboxyl group in a broad sense. Specifically, ethylene-acrylic acid ionomer, ethylene-methacrylic acid ionomer, ethylene-methacrylic acid-propyl methacrylate ionomer, ethylene-methacrylic acid-butyl methacrylate ionomer, ethylene-methacrylic acid-hexyl methacrylate ionomer, ethylene-acrylic Acid-acrylic acid 2-methylpropyl ionomer, ethylene-methacrylic acid-acrylic acid 2-methylpropyl ionomer, ethylene-methacrylic acid-methacrylic acid 2-methylbutyl ionomer, ethylene-methacrylic acid-methacrylic acid 2-ethylbutyl ionomer, ethylene -Methacrylic acid-methacrylic acid 2-methylhexyl ionomer etc. are mentioned.

  The base film constituting the present invention may have at least one layer containing an ionomer resin and may have a multilayer structure with other resin layers. In this case, the thickness of the layer containing the ionomer resin is preferably 50% or more, more preferably 60% or more of the total thickness of the base film. This is because if the thickness of the layer containing the ionomer resin is too thin, the intended sagging may not be sufficiently restored. In the case of a multi-layer structure, the layer arrangement is not particularly limited and can be arbitrarily selected according to required characteristics. However, a layer containing an ionomer resin is preferably a central layer. Moreover, in order to prevent breakage of the base film due to the difference in strength of each layer, it is desirable to heat-bond each layer to a multilayer.

  In order to improve adhesion, the surface in contact with the substrate may be subjected to corona treatment or other layers such as a primer. Although the thickness in particular of a base film is not restrict | limited, Preferably it is 30-200 micrometers, Most preferably, it is 50-100 micrometers.

  The pressure-sensitive adhesive layer can be formed of various conventionally known pressure-sensitive adhesives. The pressure-sensitive adhesive is not limited at all, but rubber-based, acrylic-based, silicone-based, polyvinyl ether-based, and the like are used. A radiation-curing type or heat-foaming type pressure-sensitive adhesive can also be used. As the radiation curable adhesive, it is possible to use an adhesive that is cured by ultraviolet rays, electron beams, etc., and easily peels off at the time of peeling. An adhesive that easily peels can be used. Furthermore, the adhesive may be an adhesive that can be used for dicing and dyne bonding. As the radiation curable pressure-sensitive adhesive, for example, those described in JP-B-1-56112 and JP-A-7-135189 are preferably used, but are not limited thereto. However, in the present invention, it is particularly preferable to use an ultraviolet curable pressure-sensitive adhesive.

  Moreover, an initial stage adhesive force can be set to arbitrary values by mixing an isocyanate type hardening | curing agent in said adhesive. Specific examples of such curing agents include polyvalent isocyanate compounds such as 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, 1,3-xylylene diisocyanate, 1,4-xylene diisocyanate, diphenylmethane. -4,4'-diisocyanate, diphenylmethane-2,4'-diisocyanate, 3-methyldiphenylmethane diisocyanate, hexamethylene diisocyanate, isophorone diisocyanate, dicyclohexylmethane-4,4'-diisocyanate, dicyclohexylmethane-2,4'-diisocyanate, Lysine isocyanate and the like are used.

In the case of an ultraviolet curable pressure-sensitive adhesive, by mixing a photopolymerization initiator in the pressure-sensitive adhesive, it is possible to reduce the polymerization curing time and the amount of ultraviolet irradiation by ultraviolet irradiation.
Specific examples of such a photopolymerization initiator include benzoin, benzoin methyl ether, benzoin ethyl ether, benzoin isopropyl ether, benzyl diphenyl sulfide, tetramethyl thiuram monosulfide, azobisisobutyronitrile, dibenzyl, diacetyl, β-chloranthraquinone and the like can be mentioned.

  When a peelable sheet is provided on the upper surface of the pressure-sensitive adhesive layer of the pressure-sensitive adhesive sheet for wafer bonding according to the present invention, the sheet is removed, and then placed with the pressure-sensitive adhesive layer of the pressure-sensitive adhesive sheet facing upward. A semiconductor wafer to be diced is attached to the upper surface of the agent layer. Dicing, cleaning, and drying steps are added to the wafer in this attached state. At this time, since the wafer chip is sufficiently adhered and held to the adhesive sheet by the adhesive layer, the wafer chip does not fall off during each of the above steps. Further, in the wafer sticking pressure-sensitive adhesive sheet of the present invention, in this configuration, most of the portion to be cut is the pressure-sensitive adhesive layer, and the pressure-sensitive adhesive layer has better cutting properties than the base material, so that no thread-like cutting waste is generated. . For example, even if the dicing blade penetrates the pressure-sensitive adhesive layer, very little thread-like dicing dust is generated and does not deposit to the pressure-sensitive adhesive sheet surface.

Next, each wafer chip is picked up from the adhesive sheet and mounted on a predetermined base. At this time, if the adhesive layer is made of a radiation curable adhesive or an electron beam curable adhesive, Prior to or at the time of pickup, the pressure-sensitive adhesive layer of the pressure-sensitive adhesive sheet can be irradiated with ionizing radiation such as ultraviolet rays or electron beams to polymerize and cure the radiation-polymerizable compound contained in the pressure-sensitive adhesive layer. In this way, when the pressure-sensitive adhesive layer 2 is irradiated with radiation and the radiation-polymerizable compound is polymerized and cured, the adhesive strength of the pressure-sensitive adhesive is greatly reduced, and only a slight adhesive strength remains.

It is preferable to perform radiation irradiation to the pressure-sensitive adhesive sheet from the side where the pressure-sensitive adhesive layer of the base film is not provided. Therefore, as described above, when ultraviolet rays are used as radiation, the substrate film needs to be light transmissive, but when using electron beams as radiation, the substrate film needs to be light transmissive. There is no.
After irradiating the adhesive layer where the wafer chip is provided in this way to reduce the adhesive strength of the adhesive layer, the adhesive sheet is transferred to the pickup die bonder and pushed up from the lower surface of the base film. A tip to be picked up is pushed up by a needle pin, this tip is picked up by a suction collet, and this is mounted on a predetermined base. When the wafer chip is picked up in this way, the adhesive can be easily picked up without any adhesion on the wafer chip surface, and a good quality chip without contamination can be obtained.

  EXAMPLES The present invention will be described below with reference to examples, but the present invention is not limited to these examples. In addition, the adhesive and base material constituent resin used in Examples and Comparative Examples are as follows.

(Adhesive)
Polyisocyanate compound (manufactured by Nippon Polyurethane Co., Ltd.) in 100 parts by mass of acrylic pressure-sensitive adhesive (copolymer comprising 2-ethylhexyl acrylate, methyl acrylate, 2-hydroxyethyl acrylate, weight average molecular weight 200,000, glass transition point = -35 ° C.) , Trade name Coronate L) 3 parts by mass, 10 parts by mass of tetramethylolmethane tetraacrylate as a compound having a photopolymerizable carbon-carbon double bond, 1 part by mass of α-hydroxycyclohexyl phenyl ketone as a photopolymerization initiator, Obtained by mixing.

(Substrate constituent resin)
Polypropylene (PP): melting point = 160 ° C., elastic modulus = 140 MPa
Blend of PP (75 wt%) and hydrogenated styrene-butadiene copolymer (HSBR, 25 wt%): elastic modulus = 125 MPa
Low density polyethylene (LDPE): melting point = 105 ° C., elastic modulus = 100 MPa
Single layer ionomer resin: ethylene-methacrylic acid- (2-methylpropyl acrylate) Zn ²⁺ ionomer resin, melting point = 70 ° C., elastic modulus = 65 MPa
Three-layer ionomer resin: (Center layer) Ethylene-methacrylic acid- (2-methylpropyl acrylate) Zn ²⁺ ionomer resin, wall thickness 70 μm (both side sublayers) ethylene-vinyl acetate copolymer, wall thickness 15 μm, elastic modulus = 70 MPa

A wafer having a diameter of 6 inches and a thickness of 350 μm is bonded to the dicing tapes of the examples and comparative examples as shown in Table 1, and a chip size is 5 mm square using a dicing apparatus (manufactured by DISCO, DAD-340). Dicing was performed so that The dicing conditions are: a rotating round blade rotation speed: 40000 rpm, a cutting speed: 100 mm / s, and a cutting water flow rate of 20 mL. In addition, the depth at which the rotating round blade cut into the dicing tape during dicing was 30 μm.
Various characteristics were evaluated as follows.

(Dicing waste)
After dicing as described above using a wafer (8 inches) with gold vapor deposited on the surface, the adhesive layer was cured by irradiating with ultraviolet light having an intensity of 500 mJ / m ² for 14 seconds, and then the chip was peeled off and observed with a microscope. Was used to measure the surface of the release tape, and the number of dicing scraps was counted.

(Chipping)
After dicing as described above using a wafer with gold deposited on the surface, the adhesive layer was cured by irradiating with ultraviolet light having an intensity of 500 mJ / m ² for 14 seconds, and then 50 chips were randomly picked up. . The maximum chipping value (size of chip) on each side of the surface of the chip bonded to the dicing tape was measured by microscopic observation, and the average of the chipping values for 50 chips was calculated. A chipping average value of 40 μm or less was rated as ◎, a 40-50 μm value as ◯, and a 50 μm or more value as x.

(Pickup property)
After dicing the wafer (6 inches), irradiating ultraviolet rays with an intensity of 500 mJ / m ² for 14 seconds and curing the adhesive layer, the fixing ring is lowered by 3 mm with a die bonder (CPS-100FM manufactured by NEC Machinery). The tip was pushed up with a needle, and the chip was picked up by a vacuum pyramid collet, and the presence or absence of a pickup mistake was confirmed. In the pick-up property, ○ indicates that no pickup mistake occurred in the pickup of 100 chips, Δ indicates 1-2 pickup errors in the pickup of 100 chips, and × indicates 100 chips. This indicates that three or more pickup mistakes have occurred in the pickup.

(Flexibility)
An adhesive tape was attached to a metal frame, a 6-inch silicon wafer was attached to the adhesive layer side of the dicing tape, and the silicon wafer was diced into 5 × 5 mm ² chips by a dicing saw. The adhesive tape to which the diced chip was attached was attached to a die bonder (CPS-100FM manufactured by NEC Machinery) together with the frame, and expanded by being pushed down with a stroke of 20 mm. In the expanded state, all the chips were picked up in about 30 minutes and removed from the tape, and then the expanded state was released and a normal dryer was used to apply hot air to the entire surface of the adhesive tape for 30 seconds from a distance of 30 cm. . To determine the slack, take out the entire frame when hot air from the dryer is applied, float it horizontally, measure the displacement in the vertical direction from the bottom of the frame to the largest part of the slack in the adhesive tape, and measure it. The amount of slack was taken. For the determination of the storage property, after measuring the amount of sag, it was stored in a frame storage cassette having a width of 1.3 mm, and the degree of hooking was observed. The case where there was no catch at all and storable was taken as ◯, and the case where it was necessary to house every other piece was taken as △ because it was caught at the time of storage.

As is clear from any of the examples, the wafer sticking adhesive sheet according to the present invention has no particular problem.
On the other hand, in the case of Comparative Example 1 where the thickness of the pressure-sensitive adhesive is as thin as 10 μm, dicing scraps are often generated. Occurred.

It is process drawing explaining the dicing and pick-up process of a semiconductor wafer. It is a figure which shows the state in which the semiconductor wafer is accommodated in the cassette after the dicing process.

Claims (5)

A wafer sticking pressure-sensitive adhesive sheet comprising a base film and a pressure-sensitive adhesive layer formed on the base film, wherein the pressure-sensitive adhesive layer has a thickness of 20 to 50 μm. The adhesive sheet for adhering a wafer according to claim 1, wherein the base film has a Young's modulus of 130 MPa or less. The pressure-sensitive adhesive sheet for sticking a wafer according to claim 1 or 2, wherein the base film has at least one layer containing an ionomer resin. The pressure-sensitive adhesive sheet for sticking a wafer according to any one of claims 1 to 3, wherein the pressure-sensitive adhesive sheet is used for dicing a wafer. The wafer is bonded to the adhesive sheet for adhering a wafer according to any one of claims 1 to 4, and when the wafer is diced, the wafer is not cut to the base material of the adhesive sheet. Processing method.

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