JP5379377B2 - Surface protection sheet and semiconductor wafer grinding method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a surface protection sheet for a semiconductor wafer which protects a bump surface using a surface protection sheet consisting of a base material sheet and a ring-shaped adhesive agent layer formed in an outer periphery of one side of the base material sheet, and prevents from occurring that a bump is pressed to the base material sheet and crushed when grinding the other surface of the semiconductor wafer, and from generating dimples or cracks on the other surface of the wafer. <P>SOLUTION: In a surface protection sheet 10, an opening 3 which has a smaller diameter than an outer diameter of the semiconductor wafer 4 to be adhered and on which an adhesive agent layer is not formed, and an adhesive agent layer 2 surrounding the opening 3 are formed on one side of a base material sheet 1. A stress relaxation rate after one minute from extension outage of the base material sheet 1 is equal to or more than 18%, and a tension elasticity rate at a temperature of 23&deg;C is equal to or more than 180 MPa and equal to or less than 4,200 MPa. <P>COPYRIGHT: (C)2009,JPO&amp;INPIT

Description

  The present invention relates to a surface protection sheet and a semiconductor wafer grinding method, and more particularly, to a surface protection sheet suitably used for a back grinding process of a semiconductor wafer in which high height bumps are arranged at high density on a circuit surface. The present invention relates to a method for grinding a semiconductor wafer on which such bumps are formed.

  With the high density mounting of semiconductor devices, protruding electrodes (also called bumps) such as spherical solder are used for bonding the IC chip and the substrate. In particular, when an IC chip is directly bonded to a substrate, bumps having a diameter of about several hundreds of micrometers are often used. Such bumps are previously bonded to the circuit surface of the semiconductor wafer with high density.

  On the other hand, with the spread of IC cards, IC chips are being made thinner. For this reason, it has been required to grind the back surface of the wafer and reduce the thickness of the wafer to 50 to 100 μm or less. As the wafer that is a brittle member becomes thinner, the risk of breakage increases during processing and transportation. In addition, the circuit surface may be damaged or contaminated by cutting waste generated during back grinding. For this reason, when grinding a wafer to an extremely thin thickness or transporting an extremely thin wafer, the work is carried out by protecting the circuit surface side of the wafer with a surface protection sheet such as an adhesive sheet.

  However, when the back surface of the wafer with bumps as described above formed on the circuit surface is ground, the pressure difference due to bump bumps directly affects the back surface of the wafer, creating dimples and cracks called dimples on the back surface of the wafer. This will damage the semiconductor wafer. For this reason, by increasing the thickness of the pressure-sensitive adhesive layer of the surface protection sheet and further increasing the flowability of the pressure-sensitive adhesive, the pressure-sensitive adhesive layer and the wafer are brought into close contact with each other, and the pressure caused by bump bumps due to the cushioning property of the pressure-sensitive adhesive layer We deal with it by eliminating the difference. However, if the thickness of the pressure-sensitive adhesive layer is increased and the fluidity thereof is increased, the pressure-sensitive adhesive easily wraps around the base portion of the bump. For this reason, the adhesive adhered to the base portion of the bump by the peeling operation of the surface protection sheet may cause in-layer destruction, and a part thereof may remain on the circuit surface. This is a problem that may occur even when a surface protection sheet using an energy ray curable adhesive is used. If the adhesive remaining on the circuit surface is not removed by solvent cleaning or the like, it remains as a foreign substance of the device and impairs the reliability of the completed device.

  In order to solve such a problem, as shown in FIG. 3 attached to the present specification, Patent Document 1 discloses a surface protection sheet 10 used when grinding a back surface of a semiconductor wafer, which is a base material sheet. 1 is formed with an opening 3 in which a pressure-sensitive adhesive layer having a diameter smaller than the outer diameter of the semiconductor wafer 4 to be attached is formed, and a pressure-sensitive adhesive layer 2 (such as a double-sided pressure-sensitive adhesive sheet) formed on the outer periphery thereof. And a method for grinding a wafer using the surface protecting sheet. This surface protection sheet 10 has a structure in which a double-sided pressure-sensitive adhesive sheet 2 punched into a ring shape is formed on one side of the base material sheet 1, and since no adhesive is provided on the portion that contacts the bump 5, The adhesive does not adhere to the base portion of the bump 5, so that the reliability of the device cannot be insufficient. Moreover, since the edge part of the semiconductor wafer 4 can usually be closely fixed by the pressure-sensitive adhesive layer of the double-sided pressure-sensitive adhesive sheet 2, the intrusion of cleaning water into the circuit surface is prevented, and the contamination of the wafer can be reduced.

Further, Patent Document 2 discloses a similar method: “a semiconductor element forming step of forming a plurality of pad electrodes at predetermined positions on an active surface of an IC wafer; and a bump forming step of forming bumps on the pads. In a method of manufacturing a semiconductor device, including a back grinding process for grinding the inactive surface of the IC wafer to a predetermined thickness,
In the bump forming step, a bump is formed leaving a peripheral portion of the IC wafer,
Between the bump forming step and the back grinding step, a support member forming step for forming or sticking a support member on the peripheral portion is provided,
In the back grinding process, there is disclosed a method for manufacturing a semiconductor device, wherein the inactive surface is ground in a state where a peripheral portion of the IC wafer is supported by the support member.

In Patent Document 3, as a similar surface protection sheet, “a protective member for protecting the back surface of a semiconductor wafer having bumps formed on the surface,
Peripheral adhesive part that is attached to the outer peripheral area of the semiconductor wafer on which no bumps are formed, a bump protection part that is surrounded by the outer peripheral adhesive part to support and protect the bump, the outer peripheral adhesive part, and the bump protection And a recess for accommodating the bump, and a bump protecting member for grinding ”is disclosed.
JP 2005-123382 A JP 2004-288725 A JP 2005-109433 A

  In the wafer grinding method described in the above document, the outer peripheral part of the bump forming surface of the wafer is surrounded by an adhesive layer, and a substantially wafer-shaped substrate sheet (resin film) bonded on the adhesive layer is used to form bumps. The bump formation surface is protected by covering the formation surface.

  When the back surface of the wafer is ground in this protective form, the bumps are pressed against the resin film by the pressure of the grinder used for grinding. Therefore, bumps on the circuit surface may be crushed or dimples or cracks may be formed on the back surface of the wafer when grinding the back surface of the wafer. In particular, when the hardness of the resin film is too high, such a problem appears remarkably. On the other hand, if the hardness of the resin film is too low, the shape retainability becomes insufficient, and the risk of damaging the wafer increases during transportation to the next process following grinding.

  Therefore, an object of the present invention is to prevent the bumps on the circuit surface from being crushed and the occurrence of dimples and cracks on the back surface of the wafer when the semiconductor wafer is ground using the surface protecting sheet as described above.

  The gist of the present invention aimed at solving such problems is as follows.

(1) A surface protection sheet used when grinding a back surface of a semiconductor wafer,
On one side of the base sheet, an opening in which an adhesive layer having a diameter smaller than the outer diameter of the semiconductor wafer to be attached is formed, and an adhesive layer surrounding the opening,
A surface protecting sheet having a stress relaxation rate of 18% or more 1 minute after extension stop of the base material sheet and a tensile elastic modulus at 23 ° C. of 180 MPa or more and 4200 MPa or less.

(2) In the pressure-sensitive adhesive layer of the surface protective sheet according to (1) above,
A semiconductor wafer having a circuit surface on which bumps are formed is affixed so that the bump forming portion of the semiconductor wafer corresponds to the opening of the surface protection sheet, and the bump forming portion of the semiconductor wafer is protected,
A method for grinding a semiconductor wafer, comprising grinding a back surface of a wafer to which a surface protection sheet is not attached.

  Since the surface protective sheet of the present invention uses a resin film having specific stress relaxation properties and tensile elastic modulus as the base sheet, the bumps are pressed against the base sheet by the pressure of the grinder during the back surface grinding of the wafer. Even so, the pressure is relieved by the base sheet. For this reason, deformation and crushing of the bump due to pressure are reduced. Further, no dimples or cracks occur on the back surface of the wafer.

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

  FIG. 1 shows a perspective view of a surface protecting sheet 10 according to the present invention, and FIG. 2 shows a sectional view taken along line XX of FIG.

  As shown in FIGS. 1 to 3, the surface protection sheet 10 includes an opening 3 in which an adhesive layer having a smaller diameter than the outer diameter of the semiconductor wafer 4 to be attached is not formed on one surface of the base sheet 1. And an adhesive layer 2 surrounding the opening.

(Substrate sheet 1)
The base sheet 1 used for the surface protecting sheet 10 has a stress relaxation rate of 18% or more, preferably 60% or more, more preferably 60 to 100%, and a tensile elastic modulus at 23 ° C. after 1 minute of stretching stop. Is 180 MPa to 4200 MPa, preferably 180 MPa to 1200 MPa.

  For the stress relaxation rate, a test piece prepared by cutting the base sheet 1 into a predetermined size is pulled at a speed of 200 mm / min at room temperature (23 ° C.), a stress A at 10% elongation, and 1 for stretching stop. It is calculated from the stress B after minutes by (A−B) / A × 100 (%).

  The tensile modulus is measured according to JIS K7127.

  The stress relaxation rate is an index indicating the absorbability of the pressure applied to the bump. If the stress relaxation rate is too small, the pressure absorption performance is lowered, and dimples and cracks are generated on the back surface of the wafer after grinding. On the other hand, if the tensile elastic modulus is too large, the bumps are crushed when the surface protection sheet is laminated on the bump wafer or when the back surface of the wafer is ground. On the other hand, if the tensile elastic modulus is too small, the supportability to the wafer is lost, the operability is deteriorated, and the risk of damaging the wafer increases especially during transportation to the next process following grinding.

  As such a base sheet, various resin sheets can be used as long as the above physical properties are satisfied. Examples of the resin sheet include polyolefins such as low-density polyethylene, linear low-density polyethylene, polypropylene, and polybutene, ethylene / vinyl acetate copolymers, ethylene / (meth) acrylic acid copolymers, and ethylene / (meth) acrylic acids. Examples thereof include ethylene copolymers such as ester copolymers, polyesters such as polyethylene terephthalate and polyethylene naphthalate, resin sheets such as polyvinyl chloride, acrylic rubber, polyamide, polyurethane, and polyimide. The base sheet 1 may be a single layer or a laminate. Moreover, the sheet | seat which gave the process of bridge | crosslinking etc. may be used.

  Moreover, as the base sheet 1, a sheet obtained by forming a thermoplastic resin by extrusion molding may be used, or a sheet obtained by thinning and curing a curable resin by a predetermined means may be used. . Examples of the curable resin include a resin composition in which an energy ray-curable urethane acrylate oligomer is a main component, an acrylate monomer having a relatively bulky group is a diluent, and a photopolymerization initiator is blended as necessary. A polyurethane acrylate sheet used by curing such a resin composition is also preferably used.

  What is necessary is just to select suitably the base material sheet used by this invention which has a predetermined stress relaxation rate and a tensile elasticity modulus from the said resin sheet.

  For example, in the case of polyurethane acrylate, a polyurethane acrylate sheet having the above properties can be obtained by reacting the urethane acrylate oligomer and acrylate monomer using a urethane acrylate oligomer having a weight average molecular weight of 500 to 50,000 as the main agent. . In the case of polyurethane, as a commercial product, Rezamin P-2298 manufactured by Dainichi Seika Co., Ltd. may be mentioned.

  In the case of polyethylene terephthalate, examples of the polyethylene terephthalate having the above properties include Lumirror # 100 manufactured by Toray Industries, Inc.

  The thickness of the base sheet 1 is preferably 30 to 1000 μm, more preferably 50 to 500 μm, and particularly preferably 100 to 300 μm.

  Moreover, as shown in FIGS. 1 to 3, the base material sheet 1 may be pre-punched to a size substantially equal to the outer diameter of the semiconductor wafer 4 to be pasted, and via the adhesive layer 2. After affixing the surface protection sheet 10 to the semiconductor wafer 4, the base sheet 1 may be cut according to the outer diameter of the semiconductor wafer.

(Adhesive layer 2)
The type of the pressure-sensitive adhesive layer 2 of the surface protecting sheet 10 is not specified as long as it has an appropriate re-peelability to the wafer. From a general-purpose pressure-sensitive adhesive such as rubber, acrylic, silicone, urethane, and vinyl ether. It may be formed. Moreover, the energy ray hardening-type adhesive which hardens | cures by irradiation of an energy ray and becomes removability may be sufficient.

  The pressure-sensitive adhesive layer 2 may be formed of a single layer of pressure-sensitive adhesive, or double-sided pressure-sensitive adhesive in which pressure-sensitive adhesive layers 21 and 23 are provided on both sides of the core film 22 as shown in the cross-sectional view of FIG. It may be a sheet.

  When the pressure-sensitive adhesive layer is formed of a double-sided pressure-sensitive adhesive sheet, if a relatively rigid film such as a polyethylene terephthalate film is used as the core material film 22, dimensional stability at the time of manufacturing the surface protection sheet 10 or attaching the wafer is performed. Is preferable because The pressure-sensitive adhesive provided on the core material film 22 may be the same on both sides, but the pressure-sensitive adhesive layer 23 on the side facing the base material sheet 1 is a pressure-sensitive adhesive having a strong adhesion, and the side facing the wafer. The thing of the structure which consists of an adhesive in which the adhesive layer 21 of this shows removability is preferable.

  The preferred thickness of the pressure-sensitive adhesive layer 2 is determined by the height of the bumps 5 formed on the wafer 4 to be attached. When the thickness (At) of the adhesive layer and the height (Bh) of the bump are used, the difference (Bh-At) is preferably −5 to +50 μm, more preferably ± 0 to +40 μm, and particularly preferably +10 to +30 μm. is there. For example, when the height (Bh) of the bump 5 is 100 μm, the preferable thickness (At) of the pressure-sensitive adhesive layer 2 is 50 to 105 μm, preferably 60 to 100 μm, and particularly preferably 70 to 90 μm. With such a thickness relationship, the bumps 5 of the wafer and the base sheet 1 are in contact with each other with an appropriate pressure, and the surface protection sheet 10 is less likely to be peeled off or displaced during grinding. Even if the difference (Bh-At) value is negative and the adhesive layer is thicker than the bump height and the gap is open, if the value is small, due to the deflection of the semiconductor wafer due to the pressing pressure during grinding, Appropriate pressure is generated, and the entire wafer can be fixed. In addition, when forming an adhesive layer with a double-sided adhesive sheet, the thickness of an adhesive layer means the full thickness of a double-sided adhesive sheet.

  Since the pressure-sensitive adhesive layer 2 is usually processed such as punching before being laminated with the base material sheet, a release sheet treated with a silicone-based release agent or the like is laminated on both sides thereof. Provided. The release sheet plays a role of protecting the pressure-sensitive adhesive layer and providing support. If the release sheets laminated on both sides are configured to have a difference in peel force as in the light release type and the heavy release type, the workability at the time of creating the surface protection sheet is preferably improved. That is, as a release sheet, a light release type release sheet and a heavy release type release sheet are used to sandwich the pressure-sensitive adhesive layer 2, and a light release type release sheet side is used to remove a light release type release sheet. The sheet and the pressure-sensitive adhesive layer are punched to form the opening 3. Thereafter, the light release type release sheet on the adhesive layer surrounding the opening 3 is removed to expose the adhesive layer, the base sheet 1 is laminated on the exposed surface, and the remaining heavy release type release sheet Covers the opening 3.

  At this time, even if the light release type release sheet side pressure-sensitive adhesive layer 23 is a strong pressure-sensitive adhesive and the heavy release type release sheet side pressure-sensitive adhesive layer 21 is a re-peeling type adhesive, the light release type release sheet Since the sheet can be peeled first, the pressure-sensitive adhesive surface facing this is the surface to be laminated on the base sheet 1.

  The heavy release type release sheet is left to protect the pressure-sensitive adhesive layer 2. After that, when the surface protection sheet 10 is used, the adhesive surface that is exposed by removing the heavy release type release sheet becomes the surface to be attached to the wafer 4.

  The opening 3 formed by punching the pressure-sensitive adhesive layer 2 is formed to have a smaller diameter than the outer diameter of the semiconductor wafer 4 to be stuck. Further, the opening 3 is formed so as to have a larger diameter than the existing area of the bump formed on the semiconductor wafer 4. As a result, when the surface protection sheet 10 is affixed to the semiconductor wafer, the bump existing region is accommodated in the opening 3 as shown in FIG. On the other hand, the outer portion of the semiconductor wafer is fixed by the adhesive layer 2 surrounding the opening 3.

  In the semiconductor wafer 4 with bumps that is normally used, bumps are formed on the inner peripheral portion of the semiconductor wafer, and no bumps are formed on the outer portion. The width of the outer portion where the bumps are not formed is not constant, but usually an area of about 0.7 to 30 mm from the end of the semiconductor wafer is an area where there is no bump.

  An opening 3 is formed in the pressure-sensitive adhesive layer 2 by punching so as to have a larger diameter than the area where the bumps exist. And since a semiconductor wafer is fixed via the adhesive layer 2, the outer diameter of the opening part 3 is smaller than the outer diameter of a semiconductor wafer. The outer diameter of the pressure-sensitive adhesive layer 2 is preferably equal to or larger than the outer diameter of the semiconductor wafer to be attached. The pressure-sensitive adhesive layer 2 is preferably formed in an annular shape having a width of about 0.5 to 20 mm so as to surround the opening 3.

  As shown in FIGS. 1 to 3, the pressure-sensitive adhesive layer 2 may be punched in advance so that the outer diameter thereof is approximately equal to the outer diameter of the semiconductor wafer to be attached. After affixing to a semiconductor wafer, you may cut | disconnect the adhesive layer 2 according to the outer diameter of a semiconductor wafer.

(Preparation of surface protection sheet 10)
As shown in FIG. 3, the surface protection sheet 10 is a base sheet surface (opening) in which the adhesive layer 2 is not formed on the circuit forming portion provided with the bumps 5 of the wafer 4 to be stuck, as shown in FIG. 3. The outer portion of the wafer 4 where the part 3) faces and the circuit is not formed is configured so that the adhesive layer 2 faces.

  Before the pressure-sensitive adhesive layer 2 is laminated on the base sheet 1, a part of the pressure-sensitive adhesive layer 2 is cut and removed in a substantially circular shape by means of punching or the like to form an opening 3 where no pressure-sensitive adhesive layer is formed. When the pressure-sensitive adhesive layer is punched and the opening 3 is formed, in order to support the pressure-sensitive adhesive layer, a release sheet treated with a silicone-based release agent is laminated on both sides of the pressure-sensitive adhesive layer. Provided. If the release sheets laminated on both sides are configured to have a difference in peel force as in the light release type and the heavy release type, the workability at the time of creating the surface protection sheet is preferably improved. That is, as a release sheet, a light release type release sheet and a heavy release type release sheet are used to sandwich the pressure-sensitive adhesive layer 2, and a light release type release sheet side is used to remove a light release type release sheet. The sheet and the pressure-sensitive adhesive layer are punched to form the opening 3. Thereafter, the light release type release sheet on the adhesive layer surrounding the opening 3 is removed to expose the adhesive layer, the base sheet 1 is laminated on the exposed surface, and the heavy release type release sheet is opened. Cover part 3. In this case, the heavy release type release sheet is preferably left without being peeled to protect the pressure-sensitive adhesive layer 2 until the surface protecting sheet 10 is used.

  In the production of the surface protection sheet, it is preferable to punch the outer periphery of the pressure-sensitive adhesive layer 2 after forming the opening 3 so as to be substantially concentric with the opening 3 and in accordance with the diameter of the wafer to be attached. That is, it is preferable to punch out the pressure-sensitive adhesive layer so that the ring-shaped pressure-sensitive adhesive layer 2 remains on the heavy release type release sheet.

  In addition, the base material sheet 1 may be preliminarily cut into the same shape as the outer diameter of the wafer, and then the adhesive layer 2 may be laminated, or the adhesive layer is applied to the base material sheet 1 having a size larger than the outer diameter of the wafer. After laminating 2, the base sheet may be punched out in the same shape as the wafer outer diameter. Further, the base sheet 1 and the pressure-sensitive adhesive layer 2 may be simultaneously punched into the same shape as the wafer outer diameter.

  Therefore, as shown in FIGS. 1 to 3, it is preferable to cut and remove the base material sheet 1 and the pressure-sensitive adhesive layer 2 in advance according to the outer diameter of the wafer 4. By cutting the wafer in the same shape as the wafer in advance, it is not necessary to perform a step of cutting off an unnecessary portion (a portion protruding from the wafer) of the surface protection sheet with a cutter after the surface protection sheet 10 is attached to the wafer. In this way, the edge of the wafer is scratched by the cutter blade, and subsequent processing does not induce damage to the wafer.

(Backside grinding of wafer)
When a release sheet (heavy release type) is laminated on the pressure-sensitive adhesive layer 2, after removing the release sheet, the pressure-sensitive adhesive layer 2 of the surface protection sheet 10 becomes a bump of the wafer 4 as shown in FIG. 3. By sticking while accurately aligning so as not to face 5, a surface protection form for grinding a semiconductor wafer is obtained. The surface protection sheet 10 is applied with a low tension so as not to be deformed by a tension as much as possible.

  In addition, when the base material sheet 1 and the adhesive layer 2 are not cut in the same shape as the wafer in advance, after attaching the surface protection sheet 10 to the wafer, an unnecessary portion of the surface protection sheet (from the wafer) Cut out the protruding part.

  The wafer used in the semiconductor wafer grinding method of the present invention may be any wafer as long as bumps are formed on the circuit surface, but the bump height is 50 μm or more, preferably The wafer having a bump position of 100 μm or more and the outermost bump located 0.7 to 30 mm inside from the outer periphery of the wafer has been difficult to apply in the conventional surface protective adhesive sheet. More preferably used.

  The wafer 4 having the above surface protection configuration is ground by a normal grinding method using a grinder 6 or the like by placing the surface protection sheet 10 side on a wafer fixing base (not shown) of a wafer grinding apparatus. Do.

  Since the adhesive layer 2 is securely bonded to the outer portion of the wafer 4 so as to surround the entire periphery, the cleaning water or the like does not enter during the grinding process and the circuit surface of the wafer is not contaminated. Further, since the apexes of the bumps are in contact with the substrate sheet with an appropriate pressure with respect to the wafer circuit surface, the surface protection sheet is less likely to be peeled off or displaced during grinding.

  Thereafter, the wafer 4 is separated from the surface protection sheet 10. As illustrated, the wafer 4 is fixed to the surface protection sheet 10 via the ring-shaped pressure-sensitive adhesive layer 2. Since the width of the ring-shaped pressure-sensitive adhesive layer 2 is narrow and the adhesive force is weak, the wafer 4 can be easily peeled off. Further, when the pressure-sensitive adhesive layer 2 is formed of an energy ray-curable pressure-sensitive adhesive, or when the pressure-sensitive adhesive layer 2 is formed as a double-sided pressure-sensitive adhesive sheet and the pressure-sensitive adhesive layer 21 on the wafer side is formed of an energy ray-curable pressure-sensitive adhesive, By irradiating the energy ray curable pressure-sensitive adhesive layer with energy rays, the adhesive strength is reduced, and therefore the wafer 4 can be more easily separated.

(Example)
EXAMPLES Hereinafter, although an Example demonstrates this invention, this invention is not limited to these Examples.

  The stress relaxation rate and tensile modulus of the base sheet were measured as follows.

(Stress relaxation rate)
The base material sheet used in the Examples is cut into a width of 15 mm and a length of 100 mm to obtain a test piece. The test piece was pulled at a speed of 200 mm / min at room temperature (23 ° C.) using a TENSILON RTA-100 manufactured by Orientec Co., and the stress A at 10% extension and the stress B after 1 min from the extension stop. Calculated by (A−B) / A × 100 (%).

(Tensile modulus)
It measured based on JIS K7127 using Orientec Corporation TENSILON RTA-100.

  The surface protection sheet was evaluated as follows.

(Bump collapse)
After grinding the wafer, the shape of the bump was observed with an optical digital microscope (magnification 100 times) through the surface protection sheet to confirm whether the bump was crushed or not.

(Dimple and crack)
After grinding the wafer, the back surface of the wafer was visually observed to confirm that dimples were not generated in the portions corresponding to the bumps on the back surface of the wafer. The case where no dimples were generated was designated as A, the case where slight dimples were confirmed to be produced but B which was not practically problematic was designated as C, and the case where obvious dimples were produced was designated as C.

  Also, the presence or absence of wafer cracks (wafer cracks) was visually confirmed.

(Infiltration of grinding water)
After grinding the wafer, the surface protecting sheet was peeled off from the wafer, and the presence or absence of intrusion of grinding water was confirmed with an optical digital microscope (magnification 100 times).

Example 1
(1) 40 parts by weight of urethane acrylate oligomer (manufactured by Arakawa Chemical Co., Ltd.) having a weight average molecular weight of 3800, 40 parts by weight of isobornyl acrylate, 20 parts by weight of phenylhydroxypropyl acrylate, a photopolymerization initiator (manufactured by Ciba Geigy, Darocur D-1173) 0.5 part by weight was blended to obtain a photocurable resin composition (A) for casting a base sheet.

The obtained resin composition (A) was applied on a polyethylene terephthalate (PET) film (manufactured by Toray Industries, Inc., thickness 38 μm) to a thickness of 110 μm by a fountain die method, and the same PET film was further applied on the coating film. Then, using a high pressure mercury lamp (160 W / cm, height 10 cm), UV irradiation was performed under the condition of a light amount of 250 mJ / cm ² to crosslink and cure the coating film. Thereafter, a laminate of the PET film and the coating film was punched into a circle having a diameter of 200 mm, and the PET films on both sides were peeled off to obtain a base sheet (polyurethane acrylate film (A)) having a thickness of 110 μm and a diameter of 200 mm.

(2) A 70 μm thick PET film (manufactured by Toray Industries, Inc.) is coated with a strong adhesive acrylic adhesive (manufactured by Lintec, PA-T1) so that the dry film thickness is 5 μm, and is lightly peeled. The release-treated surface of the release sheet (trade name SP-PET3801, manufactured by Lintec Co., Ltd., thickness 38 μm) was laminated on the adhesive-coated surface to obtain a single-sided adhesive sheet.

  Subsequently, an energy ray-curable pressure-sensitive adhesive (n-butyl acrylate / acrylic acid = 91/9 (parts by weight)) was applied to the release-treated surface of a heavy release type release sheet (product name SP-P1001031, manufactured by Lintec Corporation, thickness 100 μm). 100 parts by weight of a copolymer (weight average molecular weight of about 600,000), 120 parts by weight of urethane acrylate (weight average molecular weight of about 7000), and 2 parts by weight of a crosslinking agent (isocyanate)) so that the dry film thickness is 20 μm. It was coated and dried, and an application surface of the energy ray curable pressure-sensitive adhesive was laminated on the non-coated surface (PET film side) of the previously prepared single-sided pressure-sensitive adhesive sheet. The double-sided PSA sheet is sandwiched between a light release type release sheet and a heavy release type release sheet.

  The layer from the light release type release sheet side of the double-sided PSA sheet to the energy ray curable adhesive layer is punched into a circle with a diameter of 195 mm so as to leave only the heavy release type release sheet, and this circular portion is removed to form an opening. Formed.

  Subsequently, all the layers from the light release type release sheet side to the heavy release type release sheet are punched into a circle having a diameter of 200 mm so as to be concentric with the previously punched opening, and the outer peripheral portion thereof is removed. On the heavy release type release sheet, a ring-shaped double-sided adhesive sheet having a width of 5 mm having an opening was left. A ring-shaped light release type release sheet is laminated on the acrylic pressure-sensitive adhesive layer surface of the double-sided pressure-sensitive adhesive sheet.

  The light release type release sheet on the acrylic pressure-sensitive adhesive layer was peeled off to expose the acrylic pressure-sensitive adhesive surface.

(3) The exposed acrylic pressure-sensitive adhesive layer was laminated on the base material sheet prepared in (1) to obtain a surface protecting sheet.

(4) On a mirror surface of a silicon wafer having a diameter of 200 mm and a thickness of 750 μm, bumps having a height of 100 μm were formed at a pitch (center distance between adjacent bumps) of 200 μm.

  The above-mentioned surface protection sheet was laminated on the bump forming surface side of the silicon wafer so that the respective outlines coincided. That is, the silicon wafer was affixed via the energy ray curable adhesive layer so that the bump forming part of the silicon wafer corresponded to the opening of the surface protecting sheet. Since the bump height was set to 100 μm, the difference between the bump height and the thickness of the double-sided pressure-sensitive adhesive sheet was 5 μm while the thickness of the double-sided pressure-sensitive adhesive sheet was 95 μm.

  The surface protection sheet side was fixed to the polishing table surface of the wafer polishing apparatus, and the silicon wafer was ground so that the finished thickness was 100 μm.

(5) Subsequently, ultraviolet rays were irradiated from the surface protection sheet side to reduce the adhesive force of the energy ray curable pressure-sensitive adhesive layer fixing the silicon wafer, and then the silicon wafer was separated from the surface protection sheet.

  The ground surface of the obtained silicon wafer was observed to observe the presence or absence of dimples (recesses) and cracks. Further, the circuit surface (bump forming surface) of the silicon wafer was observed, and the presence / absence of deformation, crushing of the bumps and intrusion of grinding water was observed.

  The results are shown in Table 2.

(Example 2)
60 parts by weight of urethane acrylate oligomer having a weight average molecular weight of 1500 (Arakawa Chemical Co., Ltd.), 40 parts by weight of isobornyl acrylate, and 0.5 parts by weight of a photopolymerization initiator (Darocur D-1173, manufactured by Ciba Geigy) And the resin composition (B) which has the photocurable property for cast film-forming a base material sheet was obtained.

  In Example 1, it replaced with the resin composition (A) and the resin composition (B) was used, and the polyurethane acrylate film (B) was obtained. The same operation as in Example 1 was performed except that the polyurethane acrylate film (B) was used instead of the polyurethane acrylate film (A) in Example 1. The results are shown in Table 2.

(Example 3)
The same operation as in Example 1 was performed except that a polyurethane film (manufactured by Dainichi Seika Co., Ltd., Rezamin P-2298, thickness 100 μm) was used instead of the polyurethane acrylate film (A) of Example 1. The results are shown in Table 2.

Example 4
The same operation as in Example 1 was performed except that a polyethylene terephthalate film (Lumirror # 100, thickness 100 μm, manufactured by Toray Industries, Inc.) was used instead of the polyurethane acrylate film (A) of Example 1. The results are shown in Table 2.

(Comparative Example 1)
The same operation as in Example 1 was performed except that a polyurethane film (manufactured by Dainichi Seika Co., Ltd., Rezamin P-2275, thickness 100 μm) was used instead of the polyurethane acrylate film (A) of Example 1. The results are shown in Table 2.

(Comparative Example 2)
The same operation as in Example 1 was performed except that polyimide (Ube Industries, Upilex 75S, thickness 75 μm) was used instead of the polyurethane acrylate film (A) of Example 1. The results are shown in Table 2.

Table 1 shows the stress relaxation rate and tensile elastic modulus of the base sheet used in Examples and Comparative Examples, and Table 2 shows the back grinding result of the bump wafer.

The perspective view of the sheet for surface protection concerning the present invention. XX sectional drawing of FIG. A state in which a surface protection sheet is attached to a bump surface of a wafer and the wafer back surface is ground is shown.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Base material sheet 2 ... Adhesive layer (double-sided adhesive sheet)
21, 23 ... Adhesive layer 22 ... Core material film 3 ... Opening 4 ... Semiconductor wafer 5 ... Bump 6 ... Grinder 10 ... Surface protection sheet

Claims (3)

A surface protection sheet for use in performing back surface grinding of a semiconductor wafer, wherein an opening in which an adhesive layer having a diameter smaller than the outer diameter of a semiconductor wafer to be attached is not formed on one side of a base sheet, and the opening A base material sheet is stretched at a rate of 200 mm / min at 23 ° C., a stress A at 10% elongation, and a stress B after one minute of extension stop (A− B) A sheet for surface protection having a stress relaxation rate calculated by: A × 100 (%) of 18% or more and 100% or less and a tensile elastic modulus at 23 ° C. of 180 MPa or more and 4200 MPa or less. In the pressure-sensitive adhesive layer of the surface protecting sheet according to claim 1,
A semiconductor wafer having a circuit surface on which bumps are formed is affixed so that the bump forming portion of the semiconductor wafer corresponds to the opening of the surface protection sheet, and the bump forming portion of the semiconductor wafer is protected,
A method for grinding a semiconductor wafer, comprising grinding a back surface of a wafer to which a surface protection sheet is not attached. The sheet for surface protection according to claim 1, wherein the stress relaxation rate is 20% or more and 90% or less, and the tensile elastic modulus is 200 MPa or more and 4000 MPa or less.

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