JPH057168B2 - - Google Patents

Description

[Detailed description of the invention]

TECHNICAL FIELD OF THE INVENTION The present invention relates to a wafer cutting method, and more particularly to a method for effectively preventing dust, cutting debris, etc. from adhering to the circuit surface of the wafer surface when cutting a semiconductor wafer. 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 placed on a dicing sheet (adhesive tape) in advance.
Dicing, washing, drying,
Expanding, picking up, and mounting processes are added. Since a semiconductor wafer has a circuit surface formed on its surface, it is necessary to prevent dirt and dust from adhering to it. However, in each of the above steps,
Since only the back side of the semiconductor wafer is attached to the dicing sheet and the front side of the wafer is exposed, there is a risk that dirt, dust, etc. may adhere to the front side of the wafer. Particularly in the dicing process, there was a risk that cutting debris would adhere to the surface of the wafer. In order to eliminate such inconveniences, a protective film made of adhesive tape is attached to the surface of the wafer before it is cut and separated, and the processes following the dicing process are performed in this state, and at least before using the wafer chip, the protective film is By tearing off the
It is possible to prevent dust, cutting chips, etc. from adhering to the wafer surface during wafer chip manufacturing. According to such a method, it is certainly possible to prevent cutting debris from adhering to the surface of the wafer during the dicing process. However, it is difficult to peel off the protective film from the surface of a wafer that has been cut into small element pieces, and if this work is done with tweezers or the like, there is a risk of damaging circuits on the wafer surface. Further, even if the protective film could be peeled off conveniently, there was a risk that adhesive components would remain on the wafer surface. In this way, if there are foreign substances such as adhesive components on the wafer surface, even if they are minute, when the adherend is a device using an optical-related semiconductor wafer, etc. However, there was a risk that the device would be acutely recognized and the device would become unusable. Purpose of the Invention The present invention has been made in order to eliminate such inconveniences, and is capable of dicing wafers without causing foreign matter such as dirt, dust, cutting chips, or adhesive components to adhere to the wafer surface. It is possible to carry out the process and subsequent steps, and
The purpose of the present invention is to provide a wafer cutting method that has an easy work process and is suitable for automation. Summary of the Invention In order to achieve the above object, the method of the present invention includes the following steps:
A dicing sheet is attached to the back surface of the wafer before it is cut and separated into small pieces of elements, and a protective film made of a heat-shrinkable plastic film is attached to the front surface of the wafer using a radiation-crosslinkable adhesive. The method is characterized in that the wafer is cut into chips along with the protective film, and then the protective film is irradiated with radiation, and the protective film is heated to shrink and peeled off from the wafer surface. According to the wafer cutting method according to the present invention, since a protective film is attached to the wafer surface, dust and dirt are removed from the wafer surface during the wafer cutting (dicing) process and subsequent processes. , cutting debris, etc. will not adhere.
In addition, as a means of attaching the protective film to the surface of the wafer, a radiation-crosslinkable adhesive is used, and the protective film is peeled off after being irradiated with radiation. Almost no components remain. Furthermore, since the protective film is made of a heat-shrinkable plastic film, it shrinks when heated and becomes easily peeled off from the wafer surface, making the work easier and automating the work. It becomes possible. DETAILED DESCRIPTION OF THE INVENTION Hereinafter, the present invention will be described in detail based on embodiments shown in the drawings. 1 to 3 are cross-sectional views showing each process of the wafer cutting method according to the present invention. As shown in FIG. 1, in the present invention, first, a dicing sheet 4 is attached to the back surface of a wafer 2 before being cut into element pieces, and a protective film 6 is attached to the front surface of the wafer 2. In this state, the wafer 2 is held by the dicing sheet 4 and transferred to each process. In the wafer cutting (dicing) step, the wafer 2 is cut into element shapes by a dicer 8 to obtain wafer chips 2a. During this dicing process, the protective film 6 attached to the surface of the wafer 2 is also cut. The protective film 6 used in the present invention includes the base material 1
A heat-shrinkable plastic film is used as the heat-shrinkable plastic film, and an adhesive film coated with the adhesive 12 on one side is preferable from the viewpoint of workability. good. When the protective film 6 is the base material 10 itself, the adhesive 1 is applied to the surface of the wafer.
2, a protective tape 6 made of a base material 10 is attached. When the protective film 6 is an adhesive film in which the adhesive 12 is coated on one side of the base material 10, the protective film 6 can be easily attached to the surface of the wafer 2. The heat-shrinkable plastic film constituting the base material 10 may include polyethylene, polypropylene,
A transparent and well-stretched film made of polyolefin such as polymethylpentene, polyvinyl chloride, polyester, etc. is preferable. In particular, film thickness
Films with good transmittance between 10 and 100 μm are preferred. This is because, in the present invention, as will be described later, the protective film 6 is irradiated with radiation such as ultraviolet (UV) light, and the UV light needs to pass through to the adhesive 12. Note that when an electron beam (EB) is used as the radiation, the base material 10 does not necessarily need to be transparent. As the adhesive 12,
In the present invention, a radiation crosslinkable adhesive is used. As the radiation-crosslinkable adhesive, an ordinary adhesive containing a radiation-polymerized compound is used. Conventionally known adhesives can be widely used as ordinary adhesives, but acrylic adhesives are preferred, and specifically, from homopolymers and copolymers containing acrylic acid ester as the main monomer unit. Copolymers of selected acrylic polymers and other functional monomers, and mixtures of these polymers. For example, monomer acrylic esters include ethyl methacrylate, butyl methacrylate, 2-ethylhexyl methacrylate, glycidyl methacrylate, 2-hydroxyethyl acrylate methacrylate, and the above-mentioned methacrylic acids. For example, those in place of acrylic acid can also be preferably used. Furthermore, in order to improve compatibility with oligomers described later, monomers such as acrylic acid, methacrylic acid, acrylonitrile, and vinyl acetate may be copolymerized. The molecular weight of the acrylic polymer obtained by polymerizing these monomers is 2.0×10 ⁵ ~
10.0×10 ⁵ , preferably 4.0×10 ⁵ to 8.0×
10 ⁵ . In addition, examples of radiation polymerizable compounds include:
JP-A-60-196956 and JP-A-60-223139
Low molecular weight compounds having at least two or more photopolymerizable carbon-carbon double bonds in the molecule that can be formed into a three-dimensional network by light irradiation as disclosed in the above publication are widely used, and 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 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. are reacted. 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 the adhesive will not adhere to the chip surface when the protective film 6 is peeled off even if the semiconductor wafer surface is rough. In addition, when using a urethane acrylate oligomer as a radiation polymerizable compound, a compound having at least two photopolymerizable carbon-carbon double bonds in the molecule as disclosed in JP-A-60-196956 is used. An extremely superior protective film can be obtained compared to the case where a molecular weight compound is used. That is, the adhesive strength of the protective film 6 before irradiation is sufficiently large, and the adhesive strength is sufficiently reduced after the irradiation, so that almost no adhesive remains on the surface of the wafer tip 2a when the protective film is peeled off. The blending ratio of the acrylic adhesive and urethane acrylate oligomer in the adhesive in the present invention is as follows:
The urethane acrylate oligomer is preferably used in an amount ranging from 50 to 900 parts by weight based on 100 parts by weight of the acrylic pressure-sensitive adhesive. In this case, the resulting protective film has a high initial adhesive strength, but the adhesive strength decreases significantly after radiation irradiation, and the protective film 6 is easily attached to the wafer chip 2a.
It can be peeled off from. Further, if necessary, the adhesive 12 may contain, in addition to the above-mentioned ordinary adhesive and radiation polymerizable compound, a compound that is colored by radiation irradiation. By incorporating a coloring compound into the adhesive 12 by such radiation irradiation, the protective film 6 is colored after being irradiated with radiation, and therefore the wafer chip 2a is colored by the optical sensor. Detection accuracy is improved when detecting, and malfunction does not occur when the protective film 6 is peeled off. Further, it is possible to immediately determine by visual inspection whether or not the protective film has been irradiated with radiation. 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, 4,4′,4″−
trisdimethylaminotriphenylmethanol,
Examples include 4,4',4''-trisdimethylaminotriphenylmethane. Color developers that are preferably used with these leuco dyes include prepolymers of phenol-formalin resins and aromatic carboxylic acids, which are conventionally used. Examples include electron acceptors such as derivatives and activated clay.Furthermore, when changing the color tone, various known coloring agents can be used in combination.Compounds that are colored by radiation irradiation are Adhesive 1 after being dissolved such as
2, or may be made into a fine powder and included in the adhesive. This compound is desirably used in the adhesive in an amount of 0.01 to 10% by weight, preferably 0.5 to 5% by weight. If the compound is used in an amount exceeding 10% by weight, the radiation irradiated to the protective film will be absorbed too much by the compound, resulting in insufficient curing of the adhesive 12, which is undesirable. If it is used in an amount less than % by weight, sufficient coloring may not occur during radiation irradiation, and malfunctions may easily occur when the protective film is peeled off, which is not preferable. In some cases, the adhesive 12 may contain a light-scattering inorganic compound powder in addition to the above-mentioned ordinary adhesive and radiation polymerizable compound. Such light scattering inorganic compound powder is used as adhesive 1.
2, even if the surface of the semiconductor wafer becomes gray or black for some reason, when the protective film is irradiated with radiation such as ultraviolet rays, the adhesive corresponding to the gray or black part will be removed. The adhesive strength of the adhesive 12 is sufficiently reduced, so that the adhesive component does not remain on the surface of the wafer tip when the protective film is peeled off, and it has sufficient adhesive strength before irradiation with radiation. You can get the effect of doing so. This light-scattering inorganic compound is a compound that can diffusely reflect radiation such as ultraviolet rays (UV) or electron beams (EB) when it is irradiated with it. ,
Examples include alumina powder, silica alumina powder, and mica powder. This light scattering inorganic compound is
It is preferable to use a material that almost completely reflects radiation as described above, but it is also possible to use a material that absorbs radiation to some extent. The light-scattering inorganic compound is preferably in powder form, and its particle size is 1 to 100 μm, preferably 1 to 20 μm.
It is desirable that it be about m. This light-scattering inorganic compound is desirably used in the adhesive in an amount of 0.1 to 10% by weight, preferably 1 to 4% by weight.
If this compound is used in an adhesive in an amount exceeding 10% by weight, the adhesive strength of the adhesive may decrease, which is undesirable.On the other hand, if it is less than 0.1% by weight, the semiconductor wafer surface may turn gray. Alternatively, in the case of blackening, even if the area is irradiated with radiation, the adhesive strength will not be sufficiently reduced and adhesive components will remain on the wafer surface when the protective film is peeled off, which is not preferable. Even if a light-scattering inorganic compound powder is added to the adhesive 12 and the surface of the semiconductor wafer becomes gray or black for some reason, radiation will not be applied to the gray or black part. It is thought that the reason why the adhesion force is sufficiently reduced even in this part when it is irradiated is as follows. That is, when the adhesive 12 is irradiated with radiation, the radiation-polymerizable compound contained in the adhesive 12 is cured and its adhesive strength is reduced. However, gray or black portions may appear on the surface of a semiconductor wafer for some reason. In such a case, when the adhesive 12 is irradiated with radiation, the radiation passes through the adhesive 12 and reaches the wafer surface, but if there is a gray or black area on the wafer surface, the radiation will be absorbed by this area. Then, there will be no more reflection. For this reason, the radiation that should normally be used to cure the adhesive 12 is absorbed by the gray or blackened areas, resulting in insufficient curing of the adhesive 12 and insufficient reduction in adhesive strength. . Therefore, it is thought that the adhesive component may adhere to the surface of the wafer tip when the protective film is peeled off. However, when a light-scattering inorganic compound powder is added to the adhesive 12, the irradiated radiation collides with the compound and changes its direction before reaching the wafer surface. Therefore, even if there is a gray or black part on the wafer chip surface, the diffusely reflected radiation will penetrate into the area above this part, and therefore this gray or black part will also be absorbed. harden. Therefore, by adding light-scattering inorganic compound powder to the adhesive 12, even if there are gray or black areas on the semiconductor wafer surface for some reason,
The adhesive 12 will not be insufficiently cured in this area, and the adhesive component will not adhere to the chip surface when the protective film 6 is peeled off. Further, by mixing an isocyanate curing agent into the above-mentioned pressure-sensitive adhesive, the initial adhesive strength can be set to an arbitrary value. Specifically, such curing agents include polyvalent isocyanate compounds,
For example, 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 and the like 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. Next, the dicing sheet 4 will be explained.
As the dicing sheet 4, an adhesive sheet consisting of a base material 14 and an adhesive 16 is used. The shape of this pressure-sensitive adhesive sheet can be any shape such as a tape shape or a label shape. The material of the base material 14 is as follows:
Although not particularly limited, a polymer film containing a compound having a carboxyl group as a polymer constituent unit is preferably used. Examples of such a polymer film containing a compound having a carboxyl group as a polymer constituent unit include a monomer having a carboxyl group such as an ethylene-methacrylic acid copolymer film and an ethylene-vinyl acetate-methacrylic acid copolymer film. Polymer films obtained by polymerizing ethylene-vinyl acetate copolymers or ethylene-vinyl acetate copolymers are modified with dibasic acids to introduce carboxyl groups into the copolymers. used. Further, as the base material 14, a film obtained by laminating a general-purpose polymer film and a polymer film containing a compound having a carboxyl group as a polymer constituent unit as described above can also be used. By laminating a polymer film containing a compound having a carboxyl group as a polymer constituent unit and a general-purpose polymer film, the elongation or strength of the base film can be set as desired. Examples of the above-mentioned general-purpose polymer films include polyethylene or polyethylene copolymers such as ethylene-vinyl acetate copolymers, polypropylene,
polybutylene, ionomer, polybutadiene,
Polyethylene terephthalate, polybutylene terephthalate, polymethylpentene, polyurethane, polyvinyl chloride, polyvinyl chloride copolymers, or crosslinked products of these copolymers are used. When using a laminate like the one above,
The adhesive layer made of the adhesive 16 may be provided on a polymer film containing a compound having a carboxyl group as a polymer constituent unit, or may be provided on a general-purpose polymer film, but It is preferable to provide it on a polymer film containing a compound having a carboxyl group. This is because general-purpose polymer films generally have better slipperiness than the above-mentioned polymer films, and for this reason, the wafer 2 is pasted on the dicing sheet 4, and this is fixed on a jig to dice the wafer. This is because slipperiness is provided between the jig and the dicing sheet 4 at this time. Further, in the base film 14 of the dicing sheet, a lubricant may be added to the side of the base film that comes into contact with the jig to improve the slipperiness. Note that the thickness of the base film 14 in the dicing sheet 4 is preferably 80 to 100 μm.
The adhesive 16 constituting the adhesive layer in the dicing sheet 4 is not particularly limited, but like the adhesive 12 in the protective film 6, a radiation-crosslinkable adhesive is preferable. This is to prevent the adhesive component from adhering to the wafer chip 2a when the wafer chip 2a is picked up in a subsequent process. In the present invention, as shown in FIG. 1, after cutting (dicing) the wafer 2 together with a protective film 6 into small pieces of elements, as shown in FIG. film 6
Radiation is applied to the side. By this, adhesive 1
The radiation polymerizable compound contained in 2 is polymerized and cured,
The adhesive strength of the adhesive 12 will be greatly reduced. Moreover, the same can be said when the adhesive 16 contains a radiation-polymerizable compound. However, in this case, it is preferable to irradiate the radiation also from the dicing sheet 4 side. Examples of radiation include ultraviolet rays (UV) and electron beams (EB). When using UV as radiation, the base materials 10 and 14 need to be light-transmissive. Next, in the present invention, the protective film 6 is heated from the surroundings. As a heating means, a dicing sheet 4 is used.
One possibility would be to put the whole thing into a heating furnace. The heating temperature is determined by the material of the base material 10, and may be at least the temperature at which the base material 10 thermally shrinks. However, the heating should be done within a range that does not adversely affect the wafer tip 2a. Specifically, heating at 100° C. or higher for 30 seconds or longer is preferable. Due to such heating, the protective film 6 attached to the surface of each wafer chip 2a is thermally shrunk into a roll shape or a dumpling shape, as shown in FIG. This makes it very easy to peel off the protective film 6 from the surface of the wafer chip 2a, making it possible to peel off the protective film 6 without coming into contact with the circuit surface formed on the surface, and the process can be automated. Note that the heating step described above can be omitted if a material that shrinks only by radiation irradiation is selected as the material of the base material 10. Moreover, the heating process of the protective film 6 mentioned above is
During the process of mounting the wafer tip (during the process of gluing the wafer tip 2a to the lead frame, etc.)
It can also be done at the same time as the heating. In that case, since an epoxy adhesive is used as the adhesive, heating is performed at 150° C. for about 2 to 3 hours. Further, the above-described peeling operation of the protective film 6 may be performed after any step in the manufacturing process of the wafer tip 2a, but it is preferably performed as close to the final step as possible. This is because it prevents dirt and dust from adhering to the surface of the wafer tip 2a until the final step is reached. According to the wafer cutting method according to the present invention, since the protective film 6 is attached to the surface of the wafer 2, the surface of the wafer 2 is not covered during the cutting (dicing) process of the wafer 2 and subsequent processes. ,
No dirt, dust, cutting chips, etc. will stick to it. In addition, a protective film 6 is placed on the surface of the wafer 2.
A radiation crosslinkable adhesive 1 is used as a means for attaching the
Since the protective film 6 is peeled off after the protective film 6 side is irradiated with radiation using the protective film 2, almost no adhesive component remains on the surface of the film 2. Furthermore, since the protective film 6 is made of a heat-shrinkable plastic film, it shrinks when heated and becomes easily peeled off from the surface of the wafer 2, making the work easier and easier. Automation becomes possible. Next, the present invention will be explained based on further embodiments. Examples One side of a stretched polypropylene film having a film thickness of 40 μm is subjected to a corona treatment, and an adhesive is applied to the treated surface so as to have a thickness of 10 μm to obtain a protective film according to the present invention. This was pasted on the mirror surface of a silicon wafer, left for one day, irradiated with an 80W/cm high-pressure mercury UV lamp for 2 seconds, and then heated at 100°C. In 30 seconds, it peeled off into a roll or dumpling shape, separating the film from the wafer. The contact area is 0-3%, and in most cases the film will fall when the wafer is turned over. Even if it does not fall, it can be removed by lifting it with extremely weak force using tweezers, etc. At this time, it is extremely easy to prevent the tweezers from coming into contact with the wafer surface. In addition, all of the above experiments were conducted in a clean room, and after the protective film was peeled off, the surface of the adhesive was inspected for foreign matter using a surface defect inspection/laser inspection device. Table 1 shows the results.

【table】

[Table] As mentioned above, after the film is peeled off, only the same number of foreign substances as the reference or less than that of the reference is found. Comparative Example A tape was created in the same manner as in the example. However, the adhesive does not contain a radiation curing component. Therefore, no UV irradiation is performed. Heat shrinkage is performed in the same manner, and the surface of the wafer is checked. Even without using a surface defect inspection/laser inspection device, adhesive residue was visually confirmed in spots. Effects of the Invention As explained above, according to the present invention, a dicing sheet is attached to the back surface of the wafer before it is cut and separated into small element pieces, and a radiation-crosslinkable adhesive is applied to the surface of the wafer. After attaching a protective film made of a heat-shrinkable plastic film, the wafer is cut into chips along with the protective film, and then the protective film is irradiated with radiation and the protective film is heated. , dirt and dust on the wafer surface.
Although it is possible to perform the wafer dicing process and subsequent processes without adhering foreign matter such as cutting chips or adhesive components, it has the excellent effect of not complicating the work process. play.

[Brief explanation of the drawing]

1 to 3 are cross-sectional views showing each process of the wafer cutting method according to the present invention. 2... Wafer, 2a... Wafer tip, 4...
dicing sheet, 6...protective film, 10,
14... Base material, 12, 16... Adhesive.

Claims (1)

[Claims] 1. A dicing sheet is attached to the back surface of the wafer before it is cut and separated into small pieces of elements, and the surface of the wafer is protected by a radiation-crosslinkable adhesive and a heat-shrinkable plastic film. After the film has been attached, the wafer is cut into chips along with the protective film, and then the protective film is irradiated with radiation, and the protective film is heated to shrink and peeled off from the wafer surface. Wafer cutting method. 2. The wafer cutting method according to claim 1, wherein the protective film is also heated at the same time as the radiation irradiation. 3. The wafer cutting method according to claim 1 or 2, wherein a dicing sheet is attached to the back surface of the wafer using a radiation-crosslinkable adhesive. 4. Claim 1, wherein the protective film is an adhesive sheet having an adhesive layer made of the radiation-crosslinkable adhesive formed on one side.
The wafer cutting method according to any one of Items 1 to 3.