JP4558345B2 - Protective sheet and semiconductor wafer processing method - Google Patents

Description

  The present invention relates to a protective sheet, and more particularly, when a semiconductor wafer is subjected to a processing with an exothermic reaction under vacuum, it is attached to one side of the wafer in order to protect the front surface (circuit surface) or back surface of the wafer. It relates to a protective sheet to be worn.

  The present invention also relates to a semiconductor wafer processing method using this protective sheet.

  Various characteristics required for semiconductor devices have been diversified, and various processing processes for semiconductor wafers have been proposed. Some of the various semiconductor wafer processing processes include processing that involves an exothermic reaction of the wafer under vacuum.

  Specifically, for example, there is a plasma etching process on the back surface of the wafer.

  In a back grinding process for grinding a wafer thinly, a grinding device (grinder) having a rotating grindstone is usually used. By grinding using a grinder, a minute scratch layer called a crushed layer is formed on the back surface of the wafer. It is known that when such a crushed layer is present, the bending strength is lowered particularly in an extremely thin chip. For this reason, in order to remove the crushed layer, it has been studied to perform wet etching, CMP, dry polishing, plasma etching, or the like after the mechanical grinding by the grinder is completed. Among these, plasma etching is considered promising particularly from the viewpoint of cost and environmental load.

  By the way, in the above-described series of back surface grinding steps, in order to protect the circuit surface during back surface grinding, a releasable adhesive sheet called a surface protection sheet is attached to the circuit surface. At the time of back surface grinding using a grinder, the circuit surface is protected by a surface protection sheet, and the circuit surface side is fixed to a processing table by a vacuum chuck via the surface protection sheet, and back surface grinding is performed. Such surface protection is naturally required even in the plasma etching process.

  Since the plasma etching is performed under reduced pressure, the vacuum chuck as described above cannot generate an attracting force and is usually fixed by an electrostatic chuck. However, in the electrostatic chuck, there is no attracting electrode sheet inside the table corresponding to the outer peripheral edge portion of the wafer, and the insulating material is located. For this reason, the outer peripheral portion of the wafer is insufficiently fixed by the electrostatic chuck.

  On the other hand, in the plasma etching, the back surface of the wafer is exposed to plasma and generates heat and becomes high temperature. Therefore, the processing table is provided with a cooling device such as water cooling. That is, in order to prevent the wafer and the surface protection sheet from being deteriorated by this heat during etching, the circuit surface side (surface protection sheet side) is fixed to a processing table equipped with a cooling device. Will be.

  However, as described above, the fixing by the electrostatic chuck is insufficient to fix the outer peripheral portion of the circuit surface, that is, the outer peripheral portion of the surface protective sheet. As a result, the outer periphery of the surface protection sheet is partially lifted from the electrostatic chuck table, and the surface protection sheet away from the table accumulates the reaction heat that is etched by the plasma without being cooled, resulting in thermal deterioration. May end up. The heat-deteriorated surface protection sheet does not use the surface protection sheet because the adhesive remains on the circuit surface of the wafer or the peeling performance is lost.

  Such a problem occurs not only in the plasma etching process on the back surface of the wafer, but also in various processes in which processing with an exothermic reaction of the wafer is performed under reduced pressure. For example, when a circuit is formed on the wafer surface, a conductive film may be formed by sputtering or the like. At this time, a protective sheet for protecting and fixing the back side may be deteriorated.

  Therefore, when fixing a semiconductor wafer using an electrostatic chuck and performing processing with heat generation of the wafer, the outer peripheral portion of the wafer (that is, the outer peripheral portion of the protective sheet) is brought into close contact with a processing table provided with cooling means, Efficient heat dissipation is required.

  The present invention aims to keep the protective sheet in close contact with the processing table even under heating, so that heat can be reliably radiated from the outer periphery of the protective sheet. As a multilayer base material composed of two or more constituent layers having different rates, the constituent layers are laminated in a specific order.

Patent Document 1 states that “at least one of the layers constituting the substrate in the adhesive sheet for sticking a wafer in which a pressure-sensitive adhesive layer is applied on a substrate having at least two or more layers”. Is made of a heat-shrinkable film having a shrinkage rate of 0.5 to 20%, at least one layer is made of a non-shrinkable film, and an adhesive layer is coated on the non-shrinkable film. An “adhesive adhesive sheet” is disclosed. However, the pressure-sensitive adhesive sheet described in Patent Document 1 mainly relates to a dicing tape, can prevent the sheet from being stretched and wrinkled due to ultraviolet irradiation after the dicing process, and the dicing line becomes non-uniform, or the pressure-sensitive adhesive. The purpose of the present invention is to provide an adhesive sheet for sticking to a wafer in which the adhesion between the substrate and the substrate does not decrease. Not.
Japanese Patent No. 3073239

  In the present invention, when a semiconductor wafer is fixed using an electrostatic chuck and the processing accompanied by heat generation of the wafer is performed, the outer peripheral portion of the wafer is kept in close contact with the processing table provided with a cooling means to efficiently dissipate heat. It aims at providing the protective sheet which can be performed. Another object of the present invention is to provide a method for processing a semiconductor wafer, wherein the protective sheet is used to protect one side of the wafer while processing the other side under vacuum with an exothermic reaction.

The protective sheet according to the present invention is a protective sheet that is provided with an adhesive layer on a multilayer base material, and is applied to one surface of a wafer when processing a semiconductor wafer with an exothermic reaction under vacuum. There,
The multilayer substrate has two or more constituent layers having different shrinkage rates,
The shrinkage rate at 100 ° C. of the constituent layer close to the adhesive layer is −5 to + 5%,
The shrinkage rate at 100 ° C. of the constituent layer far from the pressure-sensitive adhesive layer is 10 to 30%.

In the method for processing a semiconductor wafer according to the present invention, the protective sheet is attached to one side of the semiconductor wafer,
The semiconductor wafer is characterized by being subjected to processing with an exothermic reaction under vacuum.

In one preferred embodiment of the method for processing a semiconductor wafer of the present invention, a protective sheet is attached to the semiconductor wafer, and the processing with an exothermic reaction under vacuum is either plasma etching or sputtering on the backside of the semiconductor wafer. is there.

  According to the present invention as described above, when performing processing with heat generation of a wafer in a vacuum, the outer peripheral portion of the wafer can be kept in close contact with the processing table provided with a cooling means to efficiently dissipate heat. Protective sheet is provided. The present invention also provides a method for processing a semiconductor wafer, wherein the protective sheet is used to protect one side of the wafer while processing the other side with a heat generation reaction under vacuum.

  Hereinafter, the present invention will be described more specifically with reference to the drawings.

As shown in FIG. 1, the protective sheet 10 according to the present invention is provided with a pressure-sensitive adhesive layer 2 on a multilayer substrate 1,
The multilayer substrate 1 has two or more constituent layers having different shrinkage rates,
The shrinkage rate at 100 ° C. of the constituent layer 3 close to the pressure-sensitive adhesive layer 2 is −5 to + 5%, preferably −3 to + 3% (hereinafter, the constituent layer 3 is described as “low-shrinkage film 3”. Is)
The shrinkage rate at 100 ° C. of the constituent layer 4 far from the pressure-sensitive adhesive layer 2 is 10 to 30%, preferably 15 to 25% (hereinafter, the constituent layer 4 may be referred to as “highly shrinkable film 4”. ).

  Here, the shrinkage rate is a value measured as follows. That is, the film is heated at 100 ° C. for 1 minute, and is calculated based on the following formula 1 from the dimensions before heating and the dimensions after heating.

  Various types of low-shrinkage films 3 are conventionally known, but in the present invention, any film that does not adversely influence ion contamination or the like on the wafer as an adherend is generally used. Can do. Specifically, polyolefin films such as polyethylene film, polypropylene film, polybutene film, polymethylpentene film; polyvinyl chloride film, polyethylene terephthalate film, polybutylene terephthalate film, polybutadiene film, polyurethane film, ethylene vinegar Bifilm or the like is used. Moreover, the polymer film containing the compound which has a carboxyl group as a polymer structural unit, or the laminated body of this and a general purpose polymer film can also be used.

  The thickness of the low shrinkable film 3 is preferably 10 to 200 μm, more preferably 20 to 100 μm.

As the high-shrinkage film 4, the same material as the low-shrinkage film described above can be used as the material. Among the aforementioned films, a film such as a polyethylene film, a polypropylene film, or a polyethylene terephthalate film is preferably used.

  The thickness of the highly shrinkable film 4 is preferably 10 to 100 μm, more preferably 20 to 70 μm.

  The difference in shrinkage between the low shrinkage film 3 and the high shrinkage film 4 is preferably in the range of 5 to 35%, more preferably 10 to 30%.

  The difference between the high shrinkage film and the low shrinkage film used in the present invention is that the shrinkage rate is different. For example, when producing a polyethylene film, it is possible to produce two types of polyethylene films having different shrinkage rates by appropriately setting the production conditions and the like.

  The multilayer substrate 1 is formed by laminating the low-shrinkage film 3 and the high-shrinkage film 4 described above. The low-shrinkage film 3 and the high-shrinkage film 4 may be directly laminated by dry lamination, coextrusion, or the like, or may be laminated via another resin layer such as an adhesive layer.

  The pressure-sensitive adhesive layer 2 can be formed of various conventionally known pressure-sensitive pressure-sensitive adhesives. Such an adhesive is not limited at all, but an adhesive such as rubber-based, acrylic-based, silicone-based, or polyvinyl ether is used. In addition, an energy ray curable adhesive, a heat-foaming adhesive, or a water swelling adhesive can be used.

  As the energy ray curable (energy ray curable, ultraviolet ray curable, electron beam curable) pressure-sensitive adhesive, it is particularly preferable to use an ultraviolet ray curable pressure-sensitive adhesive. Moreover, as a water swelling type adhesive, what is described, for example in Japanese Patent Publication No. 5-77284, Japanese Patent Publication No. 6-101455, etc. is used preferably.

  The energy beam curable pressure-sensitive adhesive generally comprises an acrylic pressure-sensitive adhesive and an energy beam polymerizable compound as main components.

  Examples of the energy ray-polymerizable compound used in the energy ray-curable pressure-sensitive adhesive can be three-dimensionally reticulated by light irradiation as disclosed in, for example, JP-A-60-196956 and JP-A-60-223139. Low molecular weight compounds having at least two photopolymerizable carbon-carbon double bonds in the molecule are widely used. Specifically, trimethylolpropane triacrylate, tetramethylolmethane tetraacrylate, pentaerythritol triacrylate, pentaerythritol Tetraacrylate, dipentaerythritol monohydroxypentaacrylate, dipentaerythritol hexaacrylate or 1,4-butylene glycol diacrylate, 1,6-hexanediol diacrylate, polyethylene glycol Diacrylates, such as the commercially available oligoester acrylates are used.

In addition to the acrylate compounds as described above, urethane acrylate oligomers can also be used as the energy beam polymerizable compound. 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, and 1,3-xylylene diisocyanate. 1, 4-xylylene diisocyanate, diphenylmethane 4,4-diisocyanate, and the like, a terminal isocyanate urethane prepolymer obtained by reacting with an acrylate or methacrylate having a hydroxyl group such as 2-hydroxyethyl acrylate or 2-hydroxy Ethyl methacrylate, 2-hydroxypropyl acrylate, 2-hydroxypropyl methacrylate, polyethylene glycol acrylate, polyethylene glycol methacrylate, etc. Obtained by.

  The blending ratio of the acrylic pressure-sensitive adhesive and the energy beam polymerizable compound in the energy ray curable pressure sensitive adhesive is 10 to 500 parts by weight, preferably 20 to 20 parts by weight of the energy ray polymerizable compound with respect to 100 parts by weight of the acrylic pressure sensitive adhesive. It is desirable to use it in an amount in the range of 300 parts by weight, particularly preferably 50 to 250 parts by weight. In this case, the protective sheet obtained has a large initial adhesive strength, and the adhesive strength is greatly reduced after irradiation with energy rays. Therefore, at the time of peeling of the protective sheet, peeling at the interface between the wafer and the energy ray curable pressure-sensitive adhesive layer becomes easy.

  The energy beam curable pressure-sensitive adhesive may be formed of an energy beam curable copolymer having an energy beam polymerizable group in the side chain. Such an energy beam curable copolymer has the property of having both adhesiveness and energy beam curable properties. Details of the energy beam curable copolymer having an energy beam polymerizable group in the side chain are described in, for example, JP-A Nos. 5-32946 and 8-27239.

  By mixing a photopolymerization initiator in the energy ray curable pressure-sensitive adhesive, it is possible to reduce the polymerization curing time and light irradiation amount by light irradiation.

  Examples of such photopolymerization initiators include photoinitiators such as benzoin compounds, acetophenone compounds, acylphosphine oxide compounds, titanocene compounds, thioxanthone compounds, and peroxide compounds, and photosensitizers such as amines and quinones. Specifically, 1-hydroxycyclohexyl phenyl ketone, benzoin, benzoin methyl ether, benzoin ethyl ether, benzoin isopropyl ether, benzyl diphenyl sulfide, tetramethyl thiuram monosulfide, azobisisobutyronitrile, dibenzyl, diacetyl, β- Examples include crawl anthraquinone.

  The amount of the photopolymerization initiator used is preferably 0.05 to 15 parts by weight, more preferably 0.1 to 10 parts by weight, particularly preferably 0.5 to 5 parts by weight, based on 100 parts by weight of the total pressure-sensitive adhesive. Part.

  The acrylic energy ray-curable pressure-sensitive adhesive as described above has a sufficient adhesion force to an adherend such as a wafer before irradiation with energy rays, and the adhesion force significantly decreases after irradiation with energy rays. That is, before the energy beam irradiation, the pressure-sensitive adhesive sheet and the adherend such as a wafer are brought into close contact with each other with sufficient adhesive force to enable surface protection, and after the energy beam irradiation, the adherend such as a wafer is easily peeled off. be able to.

  The thickness of the pressure-sensitive adhesive layer in the protective sheet 10 of the present invention is preferably 5 to 100 μm, more preferably 10 to 70 μm.

  In FIG. 1, as an example of the protective sheet 10 of the present invention, a protective sheet composed of the pressure-sensitive adhesive layer 2, the low-shrinkage film 3 and the high-shrinkage film 4 is shown, but the present invention is not limited to this configuration and will be described later. Various modifications may be made as long as the shrinkage behavior is not impaired. For example, another resin layer may be interposed between the pressure-sensitive adhesive layer 2 and the low-shrinkage film 3, and another resin layer or adhesive between the low-shrinkage film 3 and the high-shrinkage film 4. May be interposed. Further, the highly shrinkable film 4 may be further subjected to a treatment such as a heat resistant coating.

The protective sheet 10 of the present invention has the above-described configuration, and is adhered to the other surface of the wafer when a processing process involving an exothermic reaction is performed on one surface of the semiconductor wafer under vacuum. A specific example of such processing will be described later.

  As described above, the protective sheet 10 of the present invention, the pressure-sensitive adhesive layer 2, the low-shrinkage film 3 having a shrinkage rate of -5 to + 5% at 100 ° C, and the high shrinkage of 10 to 30% shrinkage at 100 ° C. The conductive film 4 is laminated in this order. Due to the difference in shrinkage between the adjacent low-shrinkage film 3 and the high-shrinkage film 4, a force to curl convexly on the pressure-sensitive adhesive layer 2 side as shown in FIG. .

  Therefore, as shown in FIG. 3, the adhesive layer 2 of the surface protection sheet 10 is adhered to the semiconductor wafer 11, the multilayer substrate 1 side is fixed on the processing table 12 made of an electrostatic chuck, and the back surface of the semiconductor wafer Etching with plasma causes the following phenomenon.

  Since the electrostatic chuck table corresponding to the outer peripheral portion of the wafer has no attracting force, the surface protection sheet 10 tends to float on the outer peripheral portion of the wafer. When the lifting occurs, the heat is not exhausted into the table and the surface protection sheet 10 is heated. However, when the temperature of the surface protection sheet 10 is increased, the surface protection sheet 10 is curled in the direction shown in FIG. 2, and the surface protection sheet 10 is again in close contact with the table so that heat can be exhausted and the temperature increase stops. Actually, when the temperature of the surface protection sheet 10 exceeds a certain level, a force as shown in FIG. As a result, the heat generated by etching the back surface of the wafer by the plasma is dissipated through the processing table 12 without accumulating in the surface protection sheet, so that thermal degradation of the surface protection sheet 10 is avoided.

  For this reason, the protective sheet 10 according to the present invention is used as a sheet for protecting the other surface of the wafer when a processing process involving an exothermic reaction of the wafer is performed on one surface of the semiconductor wafer under vacuum.

  An example of processing that involves an exothermic reaction of the wafer under vacuum is plasma etching on the back surface of the wafer.

  Plasma etching is a process of removing a crushed layer generated by mechanical grinding of the back surface of the wafer. This process is performed in a vacuum, and the wafer generates heat because it is exposed to plasma. At this time, the circuit surface of the wafer is protected by the protective sheet 10, and the wafer is fixed to the processing table 12 via the protective sheet 10. Since this step is performed in a vacuum, the wafer is fixed using an electrostatic chuck. In the electrostatic chuck, since the end of the fixing portion needs to be insulated, the outer peripheral portion of the protective sheet adhered to the wafer circuit surface is insufficiently fixed by the electrostatic chuck, and is processed. Adhesion with the table 12 is reduced.

  However, by using the protective sheet 10 of the present invention, a shrinkage force is generated in the protective sheet 10 due to heat during the plasma etching process, and this force presses the outer periphery of the protective sheet 10 against the processing table 12 (FIG. 3). The protective sheet 10 comes into close contact with the processing table 12. Since the processing table 12 is equipped with cooling means such as a water-cooled pipe, heat dissipation from the protective sheet 10 is efficiently performed, and thermal deterioration of the protective sheet 10 is prevented. As a result, the adhesive layer or the base material is not melted by the deterioration of the protective sheet, and the resin component does not remain on the back surface of the wafer or the processing table.

  The protective sheet 10 of the present invention is used for processing that involves an exothermic reaction of the wafer under vacuum, and is not limited to the above-described plasma etching on the back surface of the wafer, but can be employed in various processes such as film formation by sputtering.

  According to the present invention, when performing processing with heat generation of the wafer in vacuum, such as plasma etching of the wafer, the wafer outer peripheral portion is kept in close contact with the processing table provided with a cooling means, A protective sheet capable of efficiently performing heat dissipation is provided.

EXAMPLES Hereinafter, although an Example demonstrates this invention, this invention is not limited to these Examples.
(Example)
As a low-shrinkage film 3, a highly adhesive acrylic pressure-sensitive adhesive (PK, manufactured by Lintec Co., Ltd.) is applied to a polyethylene terephthalate film (thickness 50 μm) having a thermal shrinkage rate of 0.1% at 100 ° C. to a thickness of 10 μm. After drying, a polyethylene terephthalate film (thickness: 25 μm) having a heat shrinkage rate of 25% at 100 ° C. was laminated as a highly shrinkable film 4 on the pressure-sensitive adhesive surface to obtain a multilayer substrate 1.

Subsequently, 100 parts by weight of an acrylic polymer (butyl acrylate / methyl methacrylate / hydroxyethyl acrylate (65/30/5) copolymer), 200 parts by weight of urethane acrylate having a molecular weight of about 3,000, and an isocyanate-based crosslinking agent 2 parts by weight of a pressure-sensitive adhesive is blended, and this is coated and dried on the release surface of a release sheet (SP-PET3811, manufactured by Lintec Corporation) to a thickness of 20 μm. The surface protective sheet 10 was prepared by sticking to 3.

This surface protective sheet 10 was affixed to the mirror surface of a dummy silicon wafer (200 mm, thickness 720 μm), and the back side of the wafer was ground to a thickness of 100 μm. Subsequently, the surface protection sheet 10 was fixed to a plasma etching apparatus having an electrostatic chuck table so as to face the wafer, and the back surface (on the grinding surface) of the wafer was subjected to plasma treatment under reduced pressure. After the predetermined treatment, the surface protective sheet was irradiated with ultraviolet rays to cure the pressure-sensitive adhesive layer and peeled from the silicon wafer. No adhesive residue was observed on the outer and inner surfaces of the wafer.
(Comparative example)
An experiment was conducted in the same manner as in the example except that the base material of the surface protection sheet was a single layer film of a polyethylene terephthalate film (thickness 125 μm) having a thermal shrinkage rate at 100 ° C. of 0.1%.

  The surface protective sheet after plasma etching had a thin outer periphery and browned. When the surface protective sheet was peeled off from the silicon wafer after the predetermined treatment, the thermally deteriorated adhesive marks were adhered to the outer peripheral portion of the wafer.

Sectional drawing of the protection sheet which concerns on this invention is shown. The shrinkage | contraction behavior of the protection sheet which concerns on this invention is shown. The usage aspect of the protection sheet which concerns on this invention is shown.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Multilayer base material 2 ... Adhesive layer 3 ... Low-shrinkage film 4 ... High-shrinkage film 11 ... Semiconductor wafer 12 ... Processing table

Claims (3)

A pressure-sensitive adhesive layer is provided on a multi-layer substrate, and when a semiconductor wafer is fixed using an electrostatic chuck and a semiconductor wafer is subjected to processing with an exothermic reaction under vacuum, it is adhered to one side of the wafer. A protective sheet,
The multilayer substrate has two or more constituent layers having different shrinkage rates,
The shrinkage rate at 100 ° C. of the constituent layer close to the adhesive layer is −5 to + 5%,
The protective sheet whose shrinkage | contraction rate in 100 degreeC of the structural layer far from an adhesive layer is 10 to 30%. A pressure-sensitive adhesive layer is provided on a multilayer substrate having two or more constituent layers having different shrinkage ratios on one surface of a semiconductor wafer, and the shrinkage ratio at 100 ° C. of the constituent layers close to the pressure-sensitive adhesive layer is -5. + 5%, a protective layer with a shrinkage rate of 10 to 30% at 100 ° C. of the constituent layer far from the adhesive layer is attached,
A method of processing a semiconductor wafer, wherein the semiconductor wafer is fixed using an electrostatic chuck, and the semiconductor wafer is subjected to processing with an exothermic reaction under vacuum. The method for processing a semiconductor wafer according to claim 2, wherein a protective sheet is attached to the semiconductor wafer, and the processing with an exothermic reaction under vacuum is either plasma etching or sputtering on the back surface of the semiconductor wafer.

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