JPH0251948B2 - - Google Patents

Description

[Detailed description of the invention]

TECHNICAL FIELD OF THE INVENTION The present invention relates to an adhesive sheet for wafer attachment, and more particularly to an adhesive sheet for wafer attachment used when cutting and separating a semiconductor wafer into small pieces. Technical background of the invention and its problems Semiconductor wafers of silicon, gallium arsenide, etc. are manufactured in a large diameter state, and after this wafer is cut and separated into small element pieces (dicing), it is transferred to the next process, a mounting process. ing. At this time, the semiconductor wafer is previously attached to an adhesive sheet and subjected to the following steps: dicing, cleaning, drying, expanding, picking up, and mounting. Adhesive sheets used in the dicing process of semiconductor wafers have traditionally been made of a base material made of a general-purpose polymer film such as polyvinyl chloride or polypropylene, with an acrylic or other adhesive layer provided on the surface of the base material. things have been used. By the way, when the adhesive sheet is subjected to an expanding process after cutting and separating semiconductor wafers using the adhesive sheet as described above, the base sheet is relatively easily stretched, but the adhesive layer is not fully stretched. Without stretching, it is not possible to provide sufficient spacing between the chips to be picked up, which may cause adjacent chips to touch or be misaligned, resulting in malfunctions when picking up the chips. There was a problem that there was. Such problems also occur when rubber-based adhesives or acrylic adhesives are used as the adhesive layer, but in particular, photopolymerization occurs in molecules that can form a three-dimensional network when the adhesive layer is irradiated with radiation. A radioactive polymerizable compound having at least one carbon double bond is allowed to coexist, and after dicing the semiconductor wafer,
This occurred when the adhesive sheet was subjected to an expanding process after the adhesive layer was cured by irradiating the adhesive layer with radiation such as ultraviolet rays. This is because the adhesive layer is hardened and hardened by radiation irradiation, making it extremely difficult to stretch. The inventors of the present invention have made extensive studies to solve the problems associated with such conventional techniques, and have found that in a pressure-sensitive adhesive sheet formed by coating a pressure-sensitive adhesive layer on a base material surface,
The present invention was completed by discovering that it is sufficient to add an expanding agent such as oleic acid to the adhesive layer. Purpose of the Invention The present invention aims to solve all of the problems associated with the prior art as described above. When subjected to an expanding process, the adhesive layer is sufficiently expanded together with the base material such as a polymer film to provide sufficient spacing between the chips to be picked up, so that malfunctions do not occur when the chips are picked up. The purpose of this invention is to provide an adhesive sheet for wafer attachment. Summary of the Invention The adhesive sheet for attaching wafers according to the present invention is an adhesive sheet formed by coating an adhesive layer on a base material surface, in which the adhesive layer contains a higher fatty acid or a derivative thereof, a silicone compound, an epoxy compound, It is characterized by the addition of an expanding agent selected from polyol compounds, β-diketo compounds, and phosphites. The adhesive sheet for attaching wafers according to the present invention has an adhesive layer coated on the base material surface containing an adhesive and an expanding agent, so that the wafer attached on the adhesive sheet is subjected to the dicing process. After application, when the sheet is subjected to an expanding process, the adhesive layer is sufficiently expanded along with the sheet substrate to provide sufficient spacing between the chips to be picked up, so that adjacent chips do not come into contact with each other. There is no possibility of chipping or misalignment, and there is no malfunction when picking up the chip. In addition, the adhesive sheet for wafer attachment according to the present invention may further include a radiation-polymerizable compound in the adhesive layer, and in this case, in order to reduce the adhesive strength of the adhesive, the adhesive is Even when the adhesive layer is cured by irradiating the layer with radiation such as ultraviolet rays, it is possible to sufficiently extend the adhesive layer together with the base material in the expanding step. DETAILED DESCRIPTION OF THE INVENTION The adhesive sheet for attaching wafers according to the present invention will be specifically described below. The adhesive sheet 1 for attaching wafers according to the present invention, as its cross-sectional view is shown in FIG. In order to protect this adhesive layer 3,
As shown in FIG. 2, it is preferable to temporarily adhere a releasable sheet 4 to the upper surface of the adhesive 3. The shape of the adhesive sheet for wafer adhesion according to the present invention can be any shape such as a tape shape or a label shape. As the base material 2, a material having excellent heat resistance is suitable, and a synthetic resin film is particularly suitable. In the present invention, a radiation polymerizable compound may be included in the adhesive layer 3, and in this case, radiation such as EB or UV is performed when using the wafer pasting sheet. The base material 2 does not need to be transparent, but when used with UV irradiation, the material needs to be transparent. Specific examples of such a base material 2 include polyethylene film, polypropylene film, polyvinyl chloride film, polyethylene terephthalate film, polybutylene terephthalate film, polybutene film, polybutadiene film, polyurethane film, polymethylpentene film, and ethylene vinyl acetate film. etc. are used. Furthermore, if a polymer film containing a compound having a carboxyl group as a polymer constituent unit, such as a crosslinked polyolefin or an ethylene-methacrylic acid copolymer film, is used as the base material 2, the base material sheet will be sufficiently stretched during expansion. preferable. As the adhesive, conventionally known adhesives such as rubber-based or acrylic-based adhesives can be widely used.
Acrylic adhesives are preferred, and specifically, acrylic polymers selected from homopolymers and copolymers containing acrylic acid ester as the main constituent monomer unit and copolymers with other functional monomers. and mixtures of these polymers. For example, as monomer acrylic esters, ethyl methacrylate, butyl methacrylate, methacrylic acid-2-
Ethylhexyl, glycidyl methacrylate, 2-hydroxyethyl methacrylate, etc., and those in which the above-mentioned methacrylic acid is replaced with acrylic acid, for example, can also be preferably used. Furthermore, in order to improve compatibility with oligomers described later, monomers such as methacrylic acid, acrylic acid, acrylonitrile, and vinyl acetate may be copolymerized. The molecular weight of the acrylic polymer obtained by polymerizing these monomers is 2.0X10 ⁵ ~
^10.0X105 , preferably ^4.0X105 to ^8.0X105
It is. By including a radiation-polymerizable compound in the adhesive layer as described above, the adhesive force can be reduced by irradiating the adhesive layer with radiation after cutting and separating the wafer. By using the radiation-polymerizable compound, when the wafer tip is picked up from the adhesive sheet, no adhesive is attached to the wafer tip. In this way, as radiation polymerizable compounds, for example,
60-196956 and Japanese Patent Application Laid-Open No. 60-223139, which have at least two photopolymerizable carbon-carbon double bonds in the molecule that can be formed into a three-dimensional network by light irradiation. Molecular weight compounds are widely used, specifically trimethylolpropane triacrylate, tetramethylolmethanetetraacrylate, 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 the radiation polymerizable compound, in addition to the above-mentioned acrylate compounds, urethane acrylate oligomers can also be used. The urethane acrylate oligomer is composed of a polyol compound such as a polyester type or a polyether type, and a polyvalent isocyanate compound such as 2,4
- Terminal isocyanate obtained by reacting tolylene diisocyanate, 2,6-tolylene diisocyanate, 1,3-xylylene diisocyanate, 1,4-xylylene diisocyanate, diphenylmethane 4,4-diisocyanate, etc. An acrylate or methacrylate having a hydroxyl group, such as 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, 2-hydroxypropyl acrylate, 2-hydroxypropyl methacrylate, polyethylene glycol acrylate, polyethylene glycol methacrylate, etc., is reacted with the nertourethane prepolymer. can be obtained. This urethane acrylate oligomer is a radiation polymerizable compound having at least one carbon-carbon double bond. Such urethane acrylate oligomers preferably have a molecular weight of 3,000 to 10,000.
It is preferable to use a material having a molecular weight of 4,000 to 8,000 because even if the surface of the semiconductor wafer is rough, the adhesive will not adhere to the chip surface when the wafer chip is picked up. In addition, when using a urethane acrylate oligomer as a radiation polymerizable compound, a low molecular weight compound having at least two photopolymerizable carbon-carbon double bonds in the molecule as disclosed in JP-A-60-196956 is used. Compared to the case where a compound is used, an extremely superior pressure-sensitive adhesive sheet can be obtained. The blending ratio of the acrylic adhesive and the radiation polymerizable compound, preferably the urethane acrylate oligomer, in the adhesive in the present invention is 50 to 50 parts by weight of the radiation polymerizable compound per 100 parts by weight of the acrylic adhesive.
Preferably, an amount in the range of 900 parts by weight is used. In this case, the adhesive sheet obtained has a high initial adhesive strength, but the adhesive strength is greatly reduced after irradiation with radiation, and the pick-up can be easily picked up from the adhesive sheet. In the present invention, an expanding agent is added to the adhesive layer 3 in addition to the above-mentioned adhesive, but this expanding agent may be allowed to coexist with the radiation-polymerizable compound. As such an expanding agent, the following compounds are specifically used. (a) Higher fatty acids or their derivatives stearic acid, lauric acid, ricinoleic acid,
Esters of the acids mentioned above, such as naphthenic acid, 2-ethylhexoic acid, oleic acid, linoleic acid, myristic acid, palmitic acid, isostearic acid, hydroxystearic acid, behenic acid. Metal salts of the above acids such as Li, Mg, Ca,
Sr, Ba, Cd, Zn, Pb, Sn, K, Na salts, or composite metal salts containing two or more of the above metals. (b) Compounds with Si or siloxane structures. silicone oil etc. (c) Compounds containing fluorine. (d) Epoxy compounds. Methyl epoxy stearate, butyl epoxy stearate, epoxidized butyl linseed oil fatty acid, epoxidized tetrahydronatalate, bisphenol A diglycidyl ether, epoxidized butadiene. (e) Polyol compounds or derivatives thereof Glycerin, diglycerin, sorbitol,
Mannitol, xylitol, pentaerythritol, dipentaerythritol, trimethylolpropane, polyethylene glycol, polyvinyl alcohol, etc. Nitrogen-containing or sulfur-containing or metal complexes of the above compounds. (f) β-diketo compounds or derivatives thereof Acetoacetate, dehydroacetic acid, acetylacetone, benzoylacetone, trifluoroacetylacetone, stearoylbenzoylmethane, dibenzylmethane. Metal complexes of the above compounds. (g) Phosphites triphenylphosphine, diphenylphosphine, acid phenyl, hydrogenated bisphenol A phosphite polymer,

[Formula] (In the formula, R is C _o H _2o+1 .)

[Formula] (In the formula, R is C _o H _2o+1 .) Such an expanding agent is applied to the adhesive layer 3.
When mixed into the base sheet, sufficient spacing can be provided between the chips provided on the base sheet, so that adjacent chips do not come into contact or misalignment of the chips occurs, and therefore the pick-up of the chips is prevented. Occasional malfunctions do not occur. In particular, remarkable effects are observed when a radiation polymerizable compound is coexisting in the adhesive layer. The above-mentioned expanding agent is used in the adhesive layer 3 in an amount of 0.1 to 10% by weight, preferably 0.5 to 6% by weight. Expanding agent
If it is used in an amount less than 0.1% by weight, the adhesive layer will not stretch sufficiently during expansion, which is undesirable. On the other hand, if it is used in an amount exceeding 10% by weight, the initial adhesive strength of the adhesive will decrease. With,
This is not preferable because there is a risk that this expanding agent may adhere to the wafer surface. In the present invention, when a radiation-polymerizable compound is present in the adhesive layer, a compound that is colored by radiation irradiation may also be added to the adhesive layer 3. A compound that is colored by radiation irradiation is a compound that is colorless or light-colored before radiation irradiation, but becomes colored by radiation irradiation, and a preferred specific example of this compound is a leuco dye. As the leuco dye, commonly used triphenylmethane-based, fluoran-based, phenothiazine-based, auramine-based, and spiropyran-based dyes are preferably used. Specifically, 3-[N-(p
-tolylamino)]-7-anilinofluorane, 3
-[N-(p-tolyl)-N-methylamino]-7-
Anilinofluorane, 3-[N-(p-tolyl)-
N-ethylamino]-7-anilinofluorane,
3-diethylamino-6-methyl-7-anilinofluorane, crystal violet lactone,
Examples include 4,4',4''-trisdimethylaminotriphenylmethanol and 4,4',4''-trisdimethylaminotriphenylmethane. Color developers that are preferably used with these leuco dyes include electron acceptors such as conventionally used initial polymers of phenol-formalin resin, aromatic carboxylic acid derivatives, and activated clay. In some cases, various known coloring agents may be used in combination. Once the compound that is colored by radiation irradiation is dissolved in an organic solvent, etc., and the resulting solution is applied to either or both of the front and back surfaces of the base material 2, the surface of the base material 2 can be colored. A radiation irradiation colored layer containing a compound that is colored by radiation irradiation can be formed on at least one of the back surfaces. Further, a radiation-irradiated colored layer is formed by including a compound that is colored by radiation irradiation in an undercoat composition and applying this undercoat composition to at least one of the front and back surfaces of the base material 2. It's okay.
As such an undercoat composition, one containing a vinyl acetate-vinyl chloride copolymer as a main component, a polyurethane resin, a polyester resin, a polyamide resin, an epoxy resin, an acrylic resin, and the like are used. These undercoat compositions are appropriately selected and used depending on the type of the base material 2. On the other hand, a solution obtained by dissolving the above-mentioned compound that is colored by radiation in an organic solvent, etc.
Used when forming the base material 2 into a sheet shape, the base material 2
A compound that is colored by radiation irradiation may be added therein. In some cases, a compound that is colored by radiation irradiation may be added to the base material 2 in the form of a fine powder. In this way, the adhesive sheet 1 according to the present invention is exposed to radiation by applying a compound that is colored by radiation irradiation onto at least one of the front and back surfaces of the base material 2, or by including it in the base material 2. When the wafer chip is irradiated, the wafer chip is sufficiently colored, and the detection accuracy when detecting the wafer chip by the optical sensor is increased, thereby preventing malfunctions when picking up the wafer chip. Further, when a radiation-polymerizable compound is coexisting in the adhesive layer, the initial adhesive strength can be set to an arbitrary value by mixing an isocyanate curing agent into the above-mentioned adhesive. 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-xylylene diisocyanate, diphenylmethane-4,
4'-diisocyanate, diphenylmethane-2,
4'-diisocyanate, 3-methyldiphenylmethane diisocyanate, hexamethylene diisocyanate, isophorone diisocyanate, dicycloxylmethane-4,4'-diisocyanate,
Dicyclohexylmethane-2,4'-diisocyanate, lysine isocyanate, etc. are used. Furthermore, in the case of UV irradiation, a UV initiator may be mixed into the above-mentioned adhesive to reduce the polymerization and curing time due to UV irradiation as well as the amount of UV irradiation. Specifically, such UV initiators include:
Benzoin, benzoin methyl ether, benzoin ethyl ether, benzoin isopropyl ether, benzyl diphenyl sulfide, tetramethylthiuram monosulfide, azobisisobutyronitrile, dibenzyl, diacetyl, β
- Examples include chloranthraquinone. The method of using the pressure-sensitive adhesive sheet according to the present invention will be described below in the case where a radiation-polymerizable compound is coexisting in the pressure-sensitive adhesive layer. When a releasable sheet is provided on the top surface of the adhesive sheet 1 according to the present invention, remove the sheet, then turn the adhesive layer 3 of the adhesive sheet 1 upward, as shown in FIG. A semiconductor wafer A to be diced is attached to the upper surface of this adhesive layer 3. Dicing wafer A in this attached state,
Washing, drying, and expanding steps are added. At this time, the wafer tip is sufficiently adhered to the adhesive sheet by the adhesive layer 3, so
The wafer tip does not fall off during each of the above steps. Next, each wafer chip is picked up from the adhesive sheet and mounted on a lead frame. At this time, prior to or at the time of picking up, ultraviolet (UV) or electron beam (EB) radiation is applied as shown in Figure 4. The adhesive layer 3 of the adhesive sheet 1 is irradiated with ionizing radiation B such as the following. When the radiation-polymerizable compound is polymerized and cured by irradiating the adhesive layer 3 with radiation in this manner, the adhesive strength of the adhesive is greatly reduced, and only a small amount of adhesive strength remains. The adhesive sheet 1 is preferably irradiated with radiation from the side of the base material 2 on which the adhesive layer is not provided. Therefore, as mentioned above, as radiation
When using UV, the base material 2 needs to be light-transmissive, but when using EB as radiation, the base material 2 does not necessarily have to be light-transparent. After irradiating the adhesive layer 3 in the areas where the wafer tips A ₁ , A ₂ , . As shown in FIG. 5, the chip A ₁ ... to be picked up is pushed up from the lower surface of the base material 2 by the push-up needle 5 using the push-up needle rod 5, as shown in _FIG . ... is picked up using air tweezers 6, for example, and mounted on a predetermined base. In this way, the wafer tip
When picking up A ₁ , A _{2 .} . . , the chips can be easily picked up without any adhesive adhering to the surface of the wafer chips, and chips of good quality without contamination can be obtained. Note that radiation irradiation can also be performed at a pick-up station. The radiation irradiation does not necessarily need to be applied to the entire surface of the wafer A to be adhered at once, and some parts may be irradiated several times.
For example, the wafer tip A ₁ to be picked up,
A ₂ ... After irradiating each piece with a radiation tube that irradiates only the corresponding back side to reduce the adhesive strength of only the adhesive on that part, the wafers are attached using the lifting needle rod 5 A ₁ , A ₂ You can also pick up one by one by pushing up. 6th
The figure shows a modification of the above-mentioned radiation irradiation method. In this case, the push-up needle rod 5 is made hollow, and a radiation source 7 is provided in the hollow part to perform radiation irradiation and pick-up at the same time. In this way, the device can be simplified and at the same time the pick-up operation time can be shortened. In the above semiconductor wafer processing, it is also possible to perform a pick-up process on the wafer chips A ₁ , A _{2 .} . . immediately after dicing, cleaning, and drying without performing the expanding process. Effects of the Invention The adhesive sheet for attaching wafers according to the present invention has an adhesive layer coated on the base material surface that contains an adhesive, a higher fatty acid or a derivative thereof, a silicone compound, an epoxy compound, a polyol compound, a β-diketo compound. It also contains an expanding agent selected from phosphites, so after the wafer pasted on the adhesive sheet is subjected to the dicing process,
When subjecting the sheet to the expanding process,
The adhesive layer also extends sufficiently along with the sheet base material to provide sufficient spacing between the chips to be picked up, so that adjacent chips do not come into contact or become misaligned, thereby preventing malfunctions when picking up the chips. Never. In addition, the adhesive sheet for wafer attachment according to the present invention may further include a radiation-polymerizable compound in the adhesive layer, and in this case, in order to reduce the adhesive strength of the adhesive, the adhesive is Even when the adhesive layer is cured by irradiating the layer with radiation such as ultraviolet rays, it is possible to sufficiently extend the adhesive layer together with the base material in the expanding step. EXAMPLES The present invention will be explained below with reference to Examples, but the present invention is not limited to these Examples. Example 1 100 parts by weight of an acrylic adhesive (a copolymer of n-butyl acrylate and vinyl acetate) and a urethane acrylate oligomer with a molecular weight of approximately 7000 (trade name: Seikabeam PU-4, manufactured by Dainichiseika Chemical Industry Co., Ltd.)
50 parts by weight, 5 parts by weight of a curing agent (ethyleneimine type), and 2 parts by weight of a UV curing initiator (benzophenone type), and further adding 3 parts by weight of oleic acid as an expanding agent. A composition for forming an adhesive layer was prepared. This composition was applied to one side of an 80 μm thick ethylene-methacrylic acid copolymer film as a base material so that the adhesive layer had a thickness of 10 μm.
The mixture was heated for a minute to form an adhesive sheet for adhering to a wafer. A 6-inch diameter silicon wafer was attached to the obtained adhesive sheet for wafer attachment, and the wafer was cut and separated into 6 mm x 6 mm pieces using a dicing saw. Next, the adhesive layer of this adhesive sheet was irradiated with ultraviolet rays (UV) for 1 second using an air-cooled high-pressure mercury lamp (80 W/cm, irradiation distance 10 cm). Next, this pressure-sensitive adhesive sheet was expanded by 5% in all directions. When the pressure-sensitive adhesive sheet was stretched in this manner, the distance between each chip was 120 μm on average, and the minimum distance was 100 μm or more. Even in the pick-up process that was carried out after this, the chip spacing was sufficiently wide as described above, so
The chips are easily positioned by the sensor, and the chips are not in contact with each other when they are picked up, and each chip is taken out smoothly. Nakatsuta. Furthermore, when visually observed, no adhesive was attached to the surface of the peeled silicon wafer (the side to which the adhesive sheet had been applied). Example 2 A pressure-sensitive adhesive sheet for wafer attachment was formed in the same manner as in Example 1, except that 1 part by weight of a silicone compound was used instead of the oleic acid as an expanding agent. When this wafer adhesive sheet was stretched in the same manner as in Example 1, the average distance between each chip was 110 μm. Comparative Example 1 A silicon wafer was pasted, diced, and UV irradiated in the same manner as in Example 1, except that no lubricant was used, and it was stretched by 5% in all directions. At this time, the average distance between each chip was 30 μm. In the subsequent pick-up process, a chip came into contact with other chips during the pick-up process, resulting in part of the chip being damaged or scratched.

[Brief explanation of the drawing]

1 and 2 are cross-sectional views of the adhesive sheet according to the present invention, and FIGS. 3 to 6 are explanatory views when the adhesive sheet is used from the dicing process to the pick-up process of semiconductor wafers. . DESCRIPTION OF SYMBOLS 1... Adhesive sheet, 2... Base material, 3... Adhesive layer, A... Wafer, B... Radiation.

Claims (1)

[Scope of Claims] 1. A pressure-sensitive adhesive sheet comprising a pressure-sensitive adhesive layer coated on a base material surface, wherein the pressure-sensitive adhesive layer contains a higher fatty acid or a derivative thereof, a silicone compound, an epoxy compound, a polyol compound, a β-diketo compound. An adhesive sheet for pasting wafers, characterized in that it contains an expanding agent selected from phosphites. 2. The pressure-sensitive adhesive sheet according to claim 1, wherein the pressure-sensitive adhesive layer contains a radiation-polymerizable compound together with the expanding agent.