Workpiece processing method

Abstract

To provide a workpiece processing method capable of suppressing generation of a residue of a protective sheet on a surface to be protected of a workpiece while suppressing contamination of the workpiece caused by cooling water during grinding.SOLUTION: A method of processing a workpiece having a front surface and a back surface opposite to the front surface, in which the front surface has an inner peripheral portion including a circuit surface and an outer peripheral portion surrounding the inner peripheral portion, a first convex pattern which is hardly soluble in water is formed on the outer peripheral portion so as to protrude from the front surface and have a closed shape in a plan view, and a second convex pattern which is easily soluble in water is formed on the inner peripheral portion so as to be in contact with at least the circuit surface, the method comprising: The workpiece processing method includes a step of attaching the protective sheet to the front surface side of the workpiece so as to cover at least a part of the first convex pattern and at least a part of the second convex pattern, a step of grinding the back surface of the workpiece to which the protective sheet is attached, and a step of dissolving the second convex pattern in water after grinding the back surface.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present invention relates to a method for processing a workpiece, and more particularly to a method for processing a workpiece that suppresses contamination of the workpiece caused by cooling water during grinding, while minimizing the generation of residues of a protective sheet placed on the surface side of the workpiece on the surface of the workpiece. [Background technology]

[0002] A workpiece such as a wafer on which multiple circuits are formed is divided into individual circuits, resulting in multiple individual workpieces (chips). These chips are mounted on substrates as electronic components and installed in electronic devices.

[0003] In recent years, with the rapid progress in miniaturization and multi-functionality of electronic devices, there has been a demand for chips to be smaller, thinner, and more dense. To achieve this, a common method is to form circuits on the front surface of a wafer, then grind the back surface of the wafer to reduce the thickness of the chip.

[0004] During back grinding of the wafer, a protective sheet called back grind tape is applied to the wafer surface to protect the circuits and chips arranged on the wafer surface and to hold the wafer in place.

[0005] Patent Document 1 discloses an adhesive tape for semiconductor wafer processing that has good conformability to the surface of semiconductor wafers having steps or protrusions and can be peeled off without damaging the semiconductor wafer or leaving adhesive residue. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2017-171896 Summary of the Invention [Problem to be solved by the invention]

[0007] However, when the adhesive tape described in Patent Document 1 is applied to the surface of a semiconductor wafer and then peeled off, even if the components of the adhesive tape are configured to prevent adhesive residue, there are problems such as adhesive residue remaining during peeling depending on the size and shape of the steps or protrusions, the area to be applied, the application conditions, the peeling conditions, etc., or cooling water seeping into the wafer during grinding, causing wafer contamination.

[0008] The present invention has been made in consideration of the above-described situation, and aims to provide a method for processing a workpiece that suppresses contamination of the workpiece caused by cooling water during grinding while suppressing the generation of protective sheet residue on the surface of the workpiece that should be protected. [Means for solving the problem]

[0009] The aspects of the present invention are as follows.

[0010] [1] A method for machining a workpiece having a front surface and a back surface opposite to the front surface, the surface has an inner periphery including a circuit surface and an outer periphery surrounding the inner periphery; a first convex pattern which is poorly soluble in water is formed on the outer periphery so as to protrude from the surface and have a closed shape in plan view, and a second convex pattern which is readily soluble in water is formed on the inner periphery so as to be in contact with at least the circuit surface; A step of attaching a protective sheet to the front surface side of the workpiece so as to cover at least a portion of the first convex pattern and at least a portion of the second convex pattern; A step of grinding the back surface of the workpiece to which the protective sheet is attached; and after grinding the back surface, dissolving the second convex pattern in water.

[0011] [2] A method for processing a workpiece according to [1], wherein the second convex pattern contains polyvinyl alcohol resin.

[0012] [3] A method for processing a workpiece according to [1] or [2], wherein the first convex pattern is made of a resin composition.

[0013] [4] A method for processing a workpiece according to any one of [1] to [3], in which a difference in height is formed on the circuit surface.

[0014] [5] The method for processing a workpiece according to [4], wherein the second convex pattern is formed so as to completely fill in the height difference. [Effects of the Invention]

[0015] According to the present invention, it is possible to provide a method for processing a workpiece in which the generation of residue of a protective sheet on the surface of the workpiece to be protected is suppressed. [Brief explanation of the drawings]

[0016] [Figure 1A] FIG. 1A is a schematic cross-sectional view showing an example of a workpiece to be machined by the workpiece machining method according to the first embodiment. [Figure 1B] FIG. 1B is a schematic plan view of FIG. 1A as viewed from the direction IB. [Figure 2A] FIG. 2A is a schematic cross-sectional view of a workpiece having a first convex pattern and a second convex pattern formed on the surface thereof in the method for processing a workpiece according to the first embodiment. [Figure 2B] FIG. 2B is a schematic plan view of FIG. 2A as viewed from the direction IIB. [Figure 3] FIG. 3 is a cross-sectional schematic diagram showing a protective sheet attached to the front surface of a workpiece on which a first convex pattern and a second convex pattern are formed. [Figure 4] 4(A) and 4(B) are cross-sectional views showing a process of grinding the back surface of a workpiece to which a protective sheet is attached. [Figure 5A] FIG. 5A is a schematic cross-sectional view of a workpiece having a convex electrode formed on the surface thereof, as an example of a workpiece to be machined by the method for machining a workpiece according to the second embodiment. [Figure 5B] FIG. 5B is a schematic cross-sectional view of a chip-on-wafer as an example of a workpiece to be processed by the method for processing a workpiece according to the second embodiment. [Figure 5C] FIG. 5C is a schematic cross-sectional view of a half-trim wafer as an example of a workpiece to be processed by the method for processing a workpiece according to the second embodiment. [Figure 6A] FIG. 6A is a cross-sectional view schematically illustrating a state in which a second convex pattern is formed in the second embodiment. [Figure 6B] FIG. 6B is a cross-sectional view schematically illustrating a state in which the second convex pattern is formed in the second embodiment. [Figure 7] 7(A) to 7(E) are cross-sectional schematic diagrams for explaining that the TTV of a workpiece increases when the workpiece is machined by a conventional method. [Figure 8] FIG. 8 is a schematic cross-sectional view for explaining that the TTV of a workpiece is reduced when the workpiece is machined by the method according to this embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0017] The present invention will be described in detail below based on specific embodiments with reference to the accompanying drawings. First, the main terms used in this specification will be explained.

[0018] The term "workpiece" refers to a plate-like body to which a protective sheet is attached and then singulated. Examples of workpieces include circular wafers (including those with an orientation flat), rectangular panel-level packages, and strips (rectangular substrates) sealed with molded resin. Among these, wafers are preferred because they facilitate the attainment of the effects of the present invention. Examples of wafers include semiconductor wafers such as silicon wafers, gallium arsenide wafers, silicon carbide wafers, gallium nitride wafers, and indium phosphide wafers, as well as insulator wafers such as glass wafers, lithium tantalate wafers, and lithium niobate wafers. They may also be reconstructed wafers made of resin and semiconductors used in the manufacture of fan-out packages, etc. Because the effects of the present invention are readily attainable, semiconductor wafers or insulator wafers are preferred.

[0019] Singulation of a workpiece refers to dividing the workpiece into individual circuits to obtain individual workpieces. For example, if the workpiece is a wafer, the individual workpieces are chips, and if the workpiece is a panel-level package or a strip (rectangular substrate) sealed with molded resin, the individual workpieces are semiconductor packages.

[0020] The "front surface" of a workpiece refers to the side on which a circuit or the like is formed or on which a circuit or the like is planned to be formed, and the "back surface" of a workpiece refers to the side on which a circuit or the like is not formed or on which a circuit or the like is not planned to be formed.

[0021] The term "(meth)acrylate" is used to refer to both "acrylate" and "methacrylate," and similar terms.

[0022] "Energy rays" refers to ultraviolet rays, electron beams, etc., and is preferably ultraviolet rays.

[0023] The release sheet is a sheet that supports the pressure-sensitive adhesive layer in a releasable manner. The term "sheet" is not limited to a specific thickness, and is used to include films.

[0024] The mass ratios in the descriptions of compositions such as the pressure-sensitive adhesive layer composition are based on the active ingredient (solid content), and do not include the solvent unless otherwise specified.

[0025] (1. Workpiece processing method) One example of processing a workpiece having a circuit or the like formed on one surface (front surface) and no circuit or the like formed on the other surface (back surface) is back grinding of the workpiece. Grinding the back surface can reduce the thickness of the individual workpieces obtained by dividing the workpiece.

[0026] Backside grinding is usually performed by rotating the workpiece while a rotating grinding wheel is brought into contact with the backside of the workpiece. At this time, heat generated by friction between the backside and the grinding wheel is removed by cooling water.

[0027] Therefore, in order to prevent contamination of circuits, etc. due to the intrusion of abrasives, cooling water, etc. onto the workpiece surface during back grinding, and damage to circuits, etc. due to the force applied during back grinding, a protective sheet is attached to the surface of the workpiece in advance before back grinding is performed.

[0028] After backgrinding, the protective sheet attached to the surface is peeled off, but the components that make up the protective sheet may remain on the surface as adhesive residue during peeling. The occurrence of such adhesive residue can cause contamination of the circuit surface, necessitating a cleaning process to remove the adhesive residue, which reduces productivity. The occurrence of adhesive residue is thought to be influenced by various factors, including the components that make up the protective sheet, the attachment conditions, and the peeling conditions, and it has been difficult to prevent it.

[0029] The inventors have discovered that the occurrence of adhesive residue can be suppressed by interposing a member between the surface of the workpiece and the protective sheet during backgrinding to suppress contact between them, and then removing the member after backgrinding. Below, an example of a workpiece processing method according to this embodiment will be described in two parts: a first embodiment and a second embodiment. The first embodiment differs in that the surface of the workpiece to be processed is flat, while the second embodiment differs in that the surface of the workpiece to be processed has elevation differences.

[0030] (2. First Embodiment) 1A and 1B show a workpiece to be machined by the method according to this embodiment. As shown in FIG. 1A, workpiece 1 has a front surface 1a and a back surface 1b opposite to the front surface. Front surface 1a and back surface 1b are flat surfaces. As shown in FIG. 1B, front surface 1a has an inner periphery 5 and an outer periphery 7, and inner periphery 5 is surrounded by outer periphery 7. Furthermore, inner periphery 5 has a circuit surface 2a formed thereon that includes multiple circuits.

[0031] The workpiece machining method according to this embodiment includes at least the following steps 1 to 3. Step 1: A step of attaching a protective sheet to the surface side of the workpiece so as to cover at least a portion of the first convex pattern formed on the outer periphery and at least a portion of the second convex pattern formed on the inner periphery. Process 2: Grinding the backside of the workpiece with the protective sheet attached Step 3: After grinding the back surface, dissolving the second convex pattern in water

[0032] In the following, a description will be given of a method for processing a workpiece including the above steps 1 to 3, in which the workpiece is a wafer.

[0033] In step 1, a protective sheet is attached to the front surface of the wafer, and in this embodiment, a first convex pattern is formed on the outer periphery of the front surface, and a second convex pattern is formed on the inner periphery of the front surface, and the protective sheet is attached so as to cover the first and second convex patterns. Therefore, before step 1, the first convex pattern is formed on the outer periphery, and the second convex pattern is formed on the inner periphery.

[0034] (2.1. First Convex Pattern) As shown in Fig. 2A, the first convex pattern 31 is formed on the outer periphery 7 of the surface 1a of the wafer 1 so as to protrude from the surface. Also, as shown in Fig. 2B, the shape of the first convex pattern 31 in plan view is a closed shape (ring shape).

[0035] In this embodiment, the first convex pattern is poorly soluble in water. As a result, even if the first convex pattern comes into contact with cooling water during back grinding in step 2 described below, penetration of cooling water into the inner periphery can be suppressed. "Poorly soluble" is a concept that includes "insolubility." In this embodiment, a substance is defined as being poorly soluble in water if, when 1 g of the convex pattern is added to water at 20°C ± 5°C and the water is vigorously shaken every 5 minutes, the amount of water required to dissolve the substance within 30 minutes is 10,000 mL or more.

[0036] The first convex pattern may be made of a material that is poorly soluble in water, or may be made of a member that is poorly soluble in water, as long as it is fixed on the outer periphery of the wafer surface.

[0037] An example of the poorly water-soluble material is a poorly water-soluble resin composition. In this embodiment, from the viewpoint of facilitating the formation of the first convex pattern, a poorly water-soluble resin composition is preferred. The resin composition is preferably an adhesive composition that adheres to the wafer surface. Examples of adhesive compositions include acrylic adhesive compositions, silicone adhesive compositions, urethane adhesive compositions, epoxy adhesive compositions, phenolic adhesive compositions, urea adhesive compositions, alkyd adhesive compositions, vinyl acetate adhesive compositions, vinyl chloride adhesive compositions, amide adhesive compositions, imide adhesive compositions, chloroprene rubber, nitrile rubber, and styrene butadiene rubber.

[0038] In addition, the resin composition is preferably curable. Since the resin composition is curable, it can be easily formed into a predetermined shape before curing, and after curing, it can be easily made into a material hard enough to prevent abrasives, cooling water, etc. from penetrating into the circuits of the wafer during back grinding. Examples of curable resin compositions include thermosetting resin compositions and energy ray curable resin compositions.

[0039] In this embodiment, from the viewpoint of easily removing the first convex pattern from the wafer surface after backgrinding, an energy ray-curable resin composition is preferred, and an energy ray-curable acrylic pressure-sensitive adhesive composition is more preferred. The energy ray-curable acrylic pressure-sensitive adhesive composition preferably contains, for example, an energy ray-curable compound such as a monomer or oligomer having an unsaturated group in the molecule and capable of being polymerized and cured by energy ray irradiation, a polymerizable monomer having one reactive unsaturated double bond group, and a photopolymerization initiator.

[0040] Examples of the energy ray-curable compound include polyvalent (meth)acrylate monomers such as trimethylolpropane tri(meth)acrylate, pentaerythritol (meth)acrylate, pentaerythritol tetra(meth)acrylate, dipentaerythritol hexa(meth)acrylate, 1,4-butylene glycol di(meth)acrylate, and 1,6-hexanediol (meth)acrylate, and oligomers such as urethane (meth)acrylate, polyester (meth)acrylate, polyether (meth)acrylate, and epoxy (meth)acrylate.

[0041] Among these, urethane (meth)acrylate and dipentaerythritol hexa(meth)acrylate are preferred from the viewpoint of ease of removal from the wafer surface after curing.

[0042] The urethane (meth)acrylate may be an oligomer, a polymer, or a mixture thereof. In this embodiment, a urethane (meth)acrylate oligomer is preferred.

[0043] The urethane (meth)acrylate can be obtained, for example, by reacting a polyol compound with a polyvalent isocyanate compound to obtain a terminal isocyanate urethane prepolymer, and then reacting the resulting prepolymer with a (meth)acrylate having a hydroxyl group. The urethane (meth)acrylate may be used alone or in combination of two or more.

[0044] Examples of the polymerizable monomer include (meth)acrylates having an alkyl group having 1 to 30 carbon atoms; (meth)acrylates having a functional group such as a hydroxyl group, an amide group, an amino group, or an epoxy group; (meth)acrylates having an alicyclic structure; (meth)acrylates having an aromatic structure; (meth)acrylates having a heterocyclic structure; and vinyl compounds such as styrene, hydroxyethyl vinyl ether, hydroxybutyl vinyl ether, N-vinylformamide, N-vinylpyrrolidone, and N-vinylcaprolactam.

[0045] Examples of the photopolymerization initiator include photopolymerization initiators such as benzoin compounds, acetophenone compounds, acylphosphinoxide compounds, titanocene compounds, thioxanthone compounds and peroxide compounds, and photosensitizers such as amines and quinones.

[0046] When forming the first convex pattern using the curable resin composition, any means for applying the liquid resin before curing can be used. Specifically, a coating device such as a die coater, curtain coater, spray coater, slit coater, or knife coater; a printing device such as a screen printer or inkjet printer; or a dropping device such as a dispenser can be used.

[0047] An example of a poorly water-soluble member is an adhesive tape having a poorly water-soluble substrate and a poorly water-soluble adhesive layer.

[0048] Examples of poorly water-soluble substrates include various resin films used as substrates for backgrinding tapes. The substrate may be a single-layer film made of one resin film, or a multi-layer film made of a plurality of resin films laminated together. Examples of substrate materials include polyesters such as polyethylene terephthalate, polyethylene naphthalate, polybutylene terephthalate, wholly aromatic polyesters, polyamides, polycarbonates, polyacetals, modified polyphenylene oxides, polyphenylene sulfides, polysulfones, polyether ketones, and biaxially oriented polypropylenes.

[0049] Examples of the poorly water-soluble adhesive layer include the above-mentioned poorly water-soluble adhesive compositions.

[0050] By using such an adhesive tape, the first convex pattern can be easily formed.

[0051] The height H1 of the first convex pattern from the wafer surface may be any height that can prevent the intrusion of cooling water during backgrinding, but in this embodiment, H1 is preferably the same as or higher than the height H2 of the second convex pattern from the wafer surface, which will be described later. Also, H1 is preferably 1 to 2000 μm.

[0052] As long as the first convex pattern is formed in a closed shape on the outer periphery, it may be formed so as to cover the entire outer periphery or a part of the outer periphery. Furthermore, a plurality of first convex patterns may be formed. Furthermore, a convex pattern different from the first convex pattern and the second convex pattern may be formed inside the first convex pattern. The convex pattern may be either poorly soluble or readily soluble in water.

[0053] (2.2. Second Convex Pattern) 2A, the second convex pattern 32 is formed on the inner peripheral portion 5 of the surface 1a of the wafer 1, protruding from the surface, and is in contact with the circuit surface 2a included in the inner peripheral portion 5. The first convex pattern and the second convex pattern may be formed apart from each other without contacting each other, but in this embodiment, it is preferable that the first convex pattern and the second convex pattern are formed in contact with each other.

[0054] In this embodiment, the second convex pattern is easily soluble in water. Therefore, after backgrinding, the second convex pattern can be easily and quickly removed from the inner periphery by contacting water with the second convex pattern. In other words, rather than peeling the second convex pattern from the wafer as a solid, the water in which the second convex pattern has dissolved is washed away from the wafer, so no adhesive residue from the second convex pattern is left on the wafer. Furthermore, due to the presence of the second convex pattern, even if a protective sheet is attached to the front side of the wafer, the protective sheet does not come into contact with the inner periphery of the wafer, preventing adhesive residue caused by the protective sheet.

[0055] "Readily soluble" refers to the property of the components constituting the second raised pattern being soluble in water to the extent that no adhesive residue is left behind. In this embodiment, a substance is defined as being readily soluble in water if, when 1 g of the raised pattern is added to water at 20°C ± 5°C and the water required to dissolve the substance within 30 minutes is less than 10,000 mL, preferably less than 1,000 mL, and the water is vigorously shaken every 5 minutes.

[0056] The second convex pattern may be made of a material that is easily soluble in water, or may be made of a member that is easily soluble in water, as long as it is in contact with at least the circuit surface.

[0057] An example of a material that is easily soluble in water is a resin composition that is easily soluble in water. In this embodiment, from the viewpoint of facilitating the formation of the second convex pattern, a resin composition is preferred. Examples of resin compositions include a polyvinyl alcohol-based resin composition, a polyvinylpyrrolidone-based resin composition, a water-soluble polyester-based resin composition, a polyethylene oxide-based resin composition, a polyacrylic acid-based resin composition, a copolymer-based resin composition of polyvinyl alcohol and polyvinylpyrrolidone, a copolymer-based resin composition of polyvinyl alcohol and vinyl acetate, and a copolymer-based resin composition of polyvinylpyrrolidone and vinyl acetate. In this embodiment, a polyvinyl alcohol-based resin composition is preferred. Furthermore, from the viewpoint of adhesion to the wafer surface, the resin composition is preferably an adhesive composition.

[0058] When forming the second convex pattern using the resin composition, an aqueous solution of the resin composition may be prepared and poured into the inside of the first convex pattern. The water is then removed from the aqueous solution by drying or other methods to form the second convex pattern. That is, the first convex pattern may be formed beforehand, and then the second convex pattern may be formed. This ensures that the second convex pattern is in contact with the circuit surface while preventing water from coming into contact with the second convex pattern during grinding.

[0059] An example of a water-soluble member is an adhesive tape comprising a substrate and a water-soluble adhesive layer. The substrate may be either water-soluble or poorly soluble. When the substrate is poorly soluble in water, the adhesive tape may be attached to the inner periphery including the circuit surface, and then the substrate may be peeled off.

[0060] As described above, the height H2 of the second convex pattern from the wafer surface is preferably lower than the height H1 of the first convex pattern from the wafer surface. In particular, when the second convex pattern is formed using an aqueous solution of an adhesive composition, the height H2 of the second convex pattern is set lower than the height H1 of the first convex pattern so that the aqueous solution does not overflow outside the first convex pattern. Furthermore, H2 is preferably 1 to 2000 μm.

[0061] The second convex pattern may be formed so as to contact the entire inner periphery, or may be formed so as to contact only a portion of the inner periphery, as long as it is formed so as to contact at least the circuit surface.

[0062] (2.3.Process 1) In step 1, a protective sheet is attached to the front surface of the wafer. At this time, a first convex pattern and a second convex pattern are formed on the front surface of the wafer. That is, the step of forming the first convex pattern and the second convex pattern (step A) is performed before step 1.

[0063] (2.4. Protective Sheet) The protective sheet is attached to protect the wafer surface during backgrinding. In this embodiment, a first convex pattern and a second convex pattern are formed on the wafer surface (outer and inner peripheral portions). Therefore, as shown in FIG. 3 , the protective sheet 10 is attached so as to cover at least a portion of the first convex pattern 31 and the second convex pattern 32. That is, the protective sheet 10 is attached without contacting the surface 1a of the wafer 1. As a result, the inner peripheral portion 5 of the wafer and the second convex pattern 32 are surrounded by the first convex pattern 31 and the protective sheet 10, and therefore do not come into contact with abrasives, cooling water, etc., even during backgrinding, as described below. Therefore, contamination of the circuit surface is suppressed. Furthermore, even if the protective sheet is subsequently peeled off, no residue of the protective sheet due to peeling is left on the wafer surface.

[0064] The protective sheet may be configured to protect the wafer surface during backgrinding. As long as it has good adhesion to the first and second convex patterns, it may be a so-called adhesive sheet having a substrate and an adhesive layer, or it may be a resin film. The resin film is a thin-layered resin molded product without an adhesive layer, and may be a single layer or a laminate. While such a resin film generally does not have adhesive properties, if it has high affinity with the materials of the first and second convex patterns, it can be attached to the first and second convex patterns by applying appropriate pressure and, if necessary, heating. When the protective sheet is a resin film, it may be composed of a single-layer film made of a single resin film, or a multilayer film made of multiple resin films laminated together. When the protective sheet is an adhesive sheet, a separate layer, such as an intermediate layer, may be formed between the substrate and the adhesive layer. However, in this embodiment, the second convex pattern can fulfill the role of the intermediate layer, thereby omitting the intermediate layer, etc., and thereby reducing the thickness of the protective sheet. Below, the substrate and pressure-sensitive adhesive layer will be described as components of the protective sheet.

[0065] (2.4.1. Base material) The substrate is a member that provides the rigidity of the protective sheet. The substrate is not limited as long as it is made of a material that can support a workpiece (wafer). For example, various resin films used as substrates for backgrinding tapes are exemplified. The substrate may be made of a single-layer film made of one resin film, or may be made of a multi-layer film in which multiple resin films are laminated.

[0066] In this embodiment, examples of the material for the substrate include polyesters such as polyethylene terephthalate, polyethylene naphthalate, polybutylene terephthalate, wholly aromatic polyester, polyamide, polycarbonate, polyacetal, modified polyphenylene oxide, polyphenylene sulfide, polysulfone, polyether ketone, biaxially oriented polypropylene, etc. Among these, polyester is preferred, and polyethylene terephthalate is more preferred.

[0067] (2.4.2. Adhesive Layer) The adhesive layer is attached to the first and second convex patterns formed on the surface of the wafer, and protects the surface of the wafer and supports the wafer until it is peeled off from the convex patterns.

[0068] The composition of the adhesive layer is not limited as long as it has enough adhesiveness to protect the surface of the wafer. In this embodiment, the adhesive layer is preferably made of, for example, an acrylic adhesive, a urethane adhesive, a rubber adhesive, a silicone adhesive, or the like.

[0069] The adhesive layer is preferably formed from an energy ray-curable adhesive, which exhibits high adhesive strength when attached and can be reduced by irradiation with energy rays when peeled off.

[0070] In this embodiment, the energy ray-curable adhesive is preferably composed of an adhesive composition containing an acrylic adhesive. As the acrylic adhesive, an acrylic polymer is preferably used. The energy ray-curable acrylic adhesive may be an acrylic adhesive composed of an acrylic polymer having energy ray curability, or an acrylic adhesive containing an acrylic polymer having energy ray curability and / or an acrylic polymer not having energy ray curability, and an energy ray-curable compound such as an oligomer having an energy ray-curable group. In this embodiment, an acrylic adhesive composed of an acrylic polymer having energy ray curability is preferred.

[0071] The pressure-sensitive adhesive composition may further contain a crosslinking agent, preferably an isocyanate-based crosslinking agent, and a photopolymerization initiator.

[0072] (2.5.Process 2) In step 2, the back surface of the wafer with the protective sheet attached is ground.

[0073] 4(A), the wafer 1 with the protective sheet 10 attached thereto is placed with the front surface 1a side on a chuck table 100. The chuck table 100 has, for example, a porous holding surface, and the protective sheet 10 is adsorbed and fixed to the chuck table 100 by applying suction from the side opposite to the side on which the wafer 1 is placed.

[0074] After the wafer 1 is fixed to the chuck table 100, the back surface 1b of the wafer 1 is ground, for example, using a grinding wheel (not shown). During this process, the abrasives and cooling water used in the grinding process spread all around the wafer, but due to the presence of the first convex pattern 31 and the protective sheet 10, they do not penetrate onto the front surface 1a of the wafer 1. This prevents contamination of the front surface 1a of the wafer 1. Furthermore, dissolution of the second convex pattern 32 by the cooling water is also prevented. After back surface grinding, the wafer is thinned as shown in FIG. 4(B). The thickness of the wafer after back surface grinding is, for example, approximately 15 μm or more and 600 μm or less.

[0075] (2.6.Step 3) After step 2, in step 3, the second convex pattern is dissolved in water. Any method can be used to dissolve the second convex pattern. For example, the second convex pattern may be dissolved by spraying water onto it, or by immersing the second convex pattern in water. The dissolved second convex pattern forms an aqueous solution together with water, and by removing the aqueous solution from the wafer, the second convex pattern is successfully removed from the wafer surface. Furthermore, because the second convex pattern is dissolved in water, no residue (adhesive residue) resulting from the second convex pattern is left on the wafer surface. Therefore, problems caused by adhesive residue do not occur.

[0076] The temperature of the water used for dissolution may be within a temperature range in which the second convex patterns dissolve well, and is preferably, for example, 1°C or higher and 80°C or lower.

[0077] The second convex pattern may be dissolved in water after partially peeling off the protective sheet, or the entire protective sheet may be peeled off before dissolving the second convex pattern in water. In either case, no residue (adhesive residue) resulting from the protective sheet is left on the wafer surface.

[0078] The first convex pattern may be peeled off before the second convex pattern is dissolved in water, or may be peeled off from the wafer surface after the second convex pattern is dissolved in water, or may be peeled off together with the protective sheet.

[0079] (2.7.Step 4) The workpiece processing method according to this embodiment may include a step of obtaining individual workpieces (chips) by dicing the workpiece (wafer) in addition to the above steps 1 to 3. Examples of methods for dicing the wafer include blade dicing, laser grooving, laser full dicing, DBG (Dicing Before Grinding), LDBG (Laser Dicing Before Grinding), etc.

[0080] When dividing a wafer into individual pieces by laser grooving, the workpiece processing method according to this embodiment includes a step (step 4A) of forming a groove shallower than the thickness of the wafer on the front side of the wafer using a laser, and then cutting the wafer along the groove using a blade so that the groove reaches the back side of the wafer.

[0081] When the wafer is divided into individual pieces by laser full dicing, the method for processing a workpiece according to this embodiment includes a step of completely cutting the wafer with a laser (step 4B).

[0082] When the wafer is divided into individual pieces by DBG, the method for processing a workpiece according to this embodiment includes a step (step 4C) of forming grooves shallower than the thickness of the wafer on the front surface of the wafer. The grooves may be formed by a blade, a laser, or plasma.

[0083] When the wafer is divided into individual pieces by LDBG, a step (step 4D) of forming a modified region inside the wafer with a laser is included.

[0084] Steps 4A and 4B may be performed before step 3 or after step 3, provided that they are performed after step 2. Step 4C is performed before step 2, in which backgrinding is performed to a position that reaches the bottom of the groove. This backgrinding turns the groove into a cut that penetrates the wafer, and the wafer is divided along the cut and singulated into individual chips. Step 4D is performed before step 2, in which backgrinding may be performed to a position that reaches the formed modified region in step 2, but does not necessarily have to reach the modified region strictly. In other words, backgrinding may be performed to a position close to the modified region to apply stress so that the wafer is broken starting from the modified region and singulated into chips.

[0085] (3. Second Embodiment) In the second embodiment, the description common to the first embodiment will be omitted. In the second embodiment, the surface of the workpiece to be machined has a difference in height. Examples of such a workpiece include a workpiece having a convex electrode (bump electrode, pillar electrode, etc.) formed on its surface, a chip-on-wafer (CoW) having a chip disposed on the surface of the workpiece, and a half-trim wafer having a part of the edge of the workpiece removed.

[0086] As shown in Fig. 5A, the workpiece having a convex electrode formed thereon has a convex electrode 2b formed thereon for electrically connecting a circuit surface 2a formed on the inner peripheral portion 5 of the surface 1a of the workpiece 1 to a substrate or the like. The convex electrode 2b is formed to protrude in the thickness direction of the workpiece. Therefore, there is a height difference D between the tip (top) of the convex electrode and the area on the workpiece where the convex electrode is not formed.

[0087] Chip-on-wafer technology is used to improve the performance and density of electronic devices. As shown in Figure 5B, a chip-on-wafer is a wafer in which a plurality of chips 2c, each smaller than wafer 1, are arranged on an inner periphery 5 of a plate-like body such as wafer 1. The chip-on-wafer is then diced to form multiple high-density stacked packages. The chips 2c are stacked on the surface 1a of the workpiece. Therefore, there is a height difference D between the top surface of the chip and the area on the wafer where no chips are arranged.

[0088] Half-trim wafers are used to prevent wafer breakage. Specifically, a half-trim wafer is a wafer in which a portion of the front side of the edge of the wafer is trimmed to prevent chipping, which can lead to wafer breakage, from occurring at the edge of the wafer during backside grinding. Therefore, as shown in Figure 5C, there is a height difference D between the removed area (edge) and the unremoved area of ​​wafer 1.

[0089] 5A to 5C, the height difference D of the surface 1a corresponds to the height difference between the inner peripheral portion 5 and the outer peripheral portion 7 of the workpiece (wafer) 1. As in the first embodiment, the inner peripheral portion is surrounded by the outer peripheral portion. Therefore, in this embodiment, the height difference of the surface is formed by the inner peripheral portion and the outer peripheral portion surrounding the inner peripheral portion, and it is preferable that the height of the outer peripheral portion is lower than the height of the inner peripheral portion.

[0090] In the case of a workpiece having a convex electrode, multiple convex electrodes are formed at a predetermined interval. Therefore, even in the inner peripheral portion, there is a region between the convex electrodes that is approximately the same height as the region (outer peripheral portion) where no convex electrode is formed. However, the height of this region is not the height of the inner peripheral portion, but the height to the tip of the convex electrode.

[0091] Furthermore, in the case of chip-on-wafer, chips are usually arranged at a predetermined interval. Therefore, even in the inner periphery, there are areas (usually lattice-shaped areas) between chips where no chips are arranged, and the height of this area is almost the same as the height of the outer periphery. However, the height of this area is not the height of the inner periphery, but the height of the chip is the height of the inner periphery.

[0092] In the case of a half-trim wafer, as shown in Figure 5C, a portion of the outer periphery (edge) on the surface side is removed by trimming, and the inner periphery is the area that is not removed by trimming. Typically, the inner periphery has a uniform height, so this height is the height of the inner periphery.

[0093] As in the first embodiment, the method for processing a workpiece having a surface with height differences includes at least steps 1 to 3. In the following, a case where the workpiece is a wafer on which a convex electrode is formed will be described.

[0094] In the second embodiment, a first convex pattern is formed on the outer periphery of the wafer surface, and a second convex pattern is formed on the inner periphery. Furthermore, a convex electrode is formed on the circuit surface of the inner periphery, and the second convex pattern covers the circuit surface. As shown in FIG. 6A, the second convex pattern 32 may cover the circuit surface 2a and partially embed the convex electrode 2b (the top of the convex electrode 2b may penetrate the second convex pattern 32), or as shown in FIG. 6B, the second convex pattern 32 may cover the circuit surface 2a and completely embed the convex electrode 2b. In this embodiment, it is preferable that the second convex pattern 32 cover the circuit surface 2a and completely embed the convex electrode 2b, as shown in FIG. 6B. In other words, in Figure 6A, by forming the second convex pattern 32, the height difference D is reduced to the height difference D1, and in Figure 6B, by forming the second convex pattern 32, the height difference D is almost eliminated (the height difference D becomes almost 0).

[0095] Then, as in the first embodiment, a protective sheet is attached so as to cover at least a portion of the first convex pattern and the second convex pattern in step 1. If the protective sheet is attached to the surface when the first convex pattern and the second convex pattern are not formed on the surface, as shown in Fig. 7(A), the protective sheet 20 follows the shapes of the surface 1a and the convex electrode 2b, and therefore the height difference D is reflected in the protective sheet 20, resulting in a height difference D' in the protective sheet 20 after attachment.

[0096] 7(B), when a wafer is subjected to backside grinding while the protective sheet has a height difference, the front side of the wafer, i.e., the protective sheet 20, is placed in contact with the chuck table 100, and the wafer 1 and protective sheet 20 are fixed to the chuck table 100, for example, by suction. At this time, the protective sheet 20 on the convex electrode 2b is in contact with the chuck table 100 when placed on the chuck table 100. However, the protective sheet 20 on the area where the convex electrode 2b is not formed, i.e., on the outer periphery of the wafer 1, may not be in sufficient contact with the chuck table 100 due to the height difference, or a gap C may be generated between the chuck table 100 and the protective sheet 20 when placed on the chuck table 100.

[0097] When suction is performed in this state, as shown in Fig. 7(C), the protective sheet 20 on the outer periphery of the wafer 1 is deformed by suction and drops toward the chuck table 100, where it is fixed. Because the outer periphery of the wafer 1 is in close contact with the protective sheet 20, the outer periphery of the wafer 1 also deforms as the protective sheet 20 deforms. In other words, the outer periphery of the wafer 1 is fixed at a position closer to the chuck table 100 than the inner periphery of the wafer 1 (the region where the convex electrode 2b is formed).

[0098] After the wafer 1 and protective sheet 20 are fixed to the chuck table 100, the back surface 1b of the wafer 1 is ground. The wafer after grinding is shown in FIG. 7(D). Because the back surfaces of the wafers are ground to approximately the same height, as shown in FIG. 7(D), the thickness of the outer periphery of the wafer 1 is thicker than the thickness of the inner periphery of the wafer 1 because the outer periphery of the wafer 1 was fixed closer to the chuck table 100. As a result, when the suction is released, the deformation of the protective sheet 20 is released, and the height difference between the inner periphery of the wafer 1 and the outer periphery of the wafer 1 becomes apparent, as shown in FIG. 7(E). Therefore, in this case, the thickness of the outer periphery of the wafer 1 tends to be the maximum value, and the thickness of the inner periphery of the wafer 1 tends to be the minimum value.

[0099] The difference between the maximum and minimum thicknesses of a wafer is called TTV (Total Thickness Variation), and the TTV increases due to the height difference. A large TTV can lead to problems such as the wafer being more susceptible to cracks and problems occurring during wafer singulation. That is, the height difference D on the wafer surface when the protective sheet is attached can affect the TTV of the wafer after backside grinding via the height difference D' of the protective sheet 20 after attachment.

[0100] In contrast, in this embodiment, as shown in Figures 6A and 6B, a first convex pattern 31 and a second convex pattern 32 are formed on the front surface 1a of the wafer. This reduces the height difference D to a height difference D1 or almost eliminates it. Therefore, even if backgrinding is performed, the state shown in Figure 7(E) does not occur. Instead, as shown in Figure 8, the thickness of the outer periphery of the wafer 1 after backgrinding approaches the thickness of the inner periphery of the wafer. As a result, the TTV can be reduced. Furthermore, backgrinding can be performed without problems even with protective sheets that are thinner than conventional ones, thereby expanding the options for protective sheets.

[0101] Furthermore, when the convex electrodes are completely embedded in the second convex pattern, the protective sheet attached to the second convex pattern does not come into contact with the convex electrodes, which prevents residue (adhesive residue) from being left behind when the protective sheet is peeled off, as in the first embodiment.

[0102] Furthermore, if the second convex pattern does not completely embed the convex electrodes, when a protective sheet having an adhesive layer is attached to the front side of the wafer, the adhesive layer of the protective sheet is likely to come into contact with the tips of the convex electrodes that penetrate the second convex pattern. Here, a release sheet is usually provided on the adhesive layer to protect the adhesive layer until the protective sheet is used. When in use, the release sheet is peeled off from the adhesive layer, and the adhesive layer is attached to an adherend. A release component may be formed on the release surface of the release sheet that contacts the adhesive layer to impart release properties to the release surface. When the release sheet is placed on the adhesive layer, such a release component may transfer from the release surface to the adhesive layer. Furthermore, the release component transferred to the adhesive layer may also transfer from the adhesive layer to the adherend when the protective sheet is attached to the adherend. If the adherend is a circuit surface having a convex electrode, and the convex electrode penetrates the second convex pattern, the adhesive layer is likely to come into contact with the tip of the convex electrode, and the convex electrode may be contaminated by the transfer of the peeling component.

[0103] However, if the convex electrode is completely embedded in the second convex pattern, the protective sheet adheres to the second convex pattern, and the protective sheet does not come into contact with the convex electrode, thereby preventing the transfer of peeling components to the convex electrode.

[0104] Steps 2 and 3 are performed in the same manner as in the first embodiment. Furthermore, if the method for processing a workpiece further includes any of steps 4A to 4D, steps 4A to 4D can also be performed in the same manner as in the first embodiment.

[0105] Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments and may be modified in various ways within the scope of the present invention. [Explanation of symbols]

[0106] 1...Workpiece (wafer) 1a...Front side, 1b...Back side 2a...circuit surface, 2b...convex electrode, 2c...chip 31...First convex pattern 32...Second convex pattern 10...Protective sheet

Claims

1. A method for machining a workpiece having a front surface and a back surface opposite to the front surface, comprising: the surface has an inner periphery including a circuit surface and an outer periphery surrounding the inner periphery, a first convex pattern that is poorly soluble in water is formed on the outer circumferential portion so as to protrude from the surface and have a closed shape in a plan view, and a second convex pattern that is easily soluble in water is formed on the inner circumferential portion so as to contact at least the circuit surface, A step of attaching a protective sheet to the front surface side of the workpiece so as to cover at least a portion of the first convex pattern and at least a portion of the second convex pattern; A step of grinding the back surface of the workpiece to which the protective sheet is attached; a step of dissolving the second convex pattern in water after grinding the back surface.

2. The method for machining a workpiece according to claim 1 , wherein the second convex pattern contains polyvinyl alcohol resin.

3. 3. The method for processing a workpiece according to claim 1, wherein the first convex pattern is made of a resin composition.

4. 3. The method for machining a workpiece according to claim 1, wherein a difference in height is formed on the circuit surface.

5. The method for machining a workpiece according to claim 4 , wherein the second convex pattern is formed so as to completely fill the height difference.

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