Workpiece machining method

Abstract

To provide a workpiece machining method that can suppress warping of a workpiece having residual stress.SOLUTION: A workpiece machining method includes a step of attaching a surface protection sheet to a workpiece having a surface and a back surface opposite the surface, in which residual stress has occurred, and a step of grinding the back surface of the workpiece with the surface protection sheet attached, in which a convex pattern is formed on the surface before the surface protection sheet is attached to the surface.SELECTED DRAWING: Figure 6

Description

[Technical field]

[0001] The present invention relates to a method for machining a workpiece, and more particularly to a method for machining a workpiece that is suitable for suppressing warpage of the workpiece. [Background technology]

[0002] Chips on which circuits such as semiconductor chips are formed are obtained as workpieces by dividing a workpiece such as a wafer on which a plurality of circuits are formed. With the rapid progress of miniaturization and multi-functionalization of electronic devices on which such chips are mounted, there is a demand for chips to be smaller, thinner, and more dense. In order to reduce the size and height of a chip, it is common to form a circuit on the front surface of a workpiece, and then grind the back surface of the workpiece to reduce the thickness of the chip.

[0003] On the surface of the workpiece, a passivation film for protecting the circuit, or a protective film for protecting the vicinity of the connection between the circuit and a convex electrode (such as a bump electrode) that electrically connects the chip and an electrode on the circuit may be formed. An example of the former method of forming the protective film is a method of forming the protective film by applying a composition for forming a passivation film on the surface of the workpiece and thermally curing the composition, and an example of the latter method of forming the protective film is a method of attaching a film for forming a protective film to the surface of the workpiece.

[0004] However, for example, since the passivation film is formed by shrinking the composition for forming the passivation film by thermal curing, residual stress due to this shrinkage occurs in the passivation film. In addition, since the film for forming the protective film is attached while applying tension to the film, residual stress due to the tension occurs in the protective film after attachment. Furthermore, a difference in attachment pressure occurs between the area where the convex electrode is formed and the area where it is not formed, and residual stress due to the pressure difference also occurs in the protective film.

[0005] In addition, when grinding the backside of a workpiece, a protective sheet called a backgrind tape is applied to the surface of the workpiece to temporarily protect the circuits on the surface of the workpiece and to hold the workpiece in place. When this backgrind tape is applied, residual stress due to the above-mentioned tension is also generated in the backgrind tape.

[0006] Since the workpiece before back grinding is thick and has high rigidity, the residual stress generated is canceled by the rigidity of the workpiece, and no warping occurs in the laminate of the workpiece including the protective film, etc. and the back grinding tape. However, when the workpiece becomes thinner by back grinding, the rigidity of the workpiece decreases, so the residual stress becomes apparent and the laminate, i.e., the workpiece including the protective film, etc., warps. When the workpiece warps, problems occur such as the workpiece becoming more susceptible to breakage and being difficult to transport to the next process.

[0007] To address such problems, for example, Patent Document 1 discloses a surface protection sheet in which high stress relaxation properties are imparted to the substrate in order to suppress warping of semiconductor wafers. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] International Publication No. 2016 / 063827 Summary of the Invention [Problem to be solved by the invention]

[0009] In Patent Document 1, the warpage of the semiconductor wafer is suppressed by imparting stress relaxation properties to the substrate and eliminating the residual stress generated in the substrate. However, the protective sheet described in Patent Document 1 cannot eliminate the residual stress generated in the protective film, etc., as in the case of a semiconductor wafer on which a protective film, etc. is formed. As a result, there is a problem that the warpage of the semiconductor wafer cannot be suppressed when residual stress is generated in the semiconductor wafer itself. In addition, there is a problem that Patent Document 1 does not take into account the residual stress caused by the difference in the attachment pressure.

[0010] The present invention has been made in consideration of the above circumstances, and has an object to provide a method for machining a workpiece that can suppress warping of a workpiece in which residual stress occurs. [Means for solving the problem]

[0011] The aspects of the present invention are as follows.

[0012] [1] A process for attaching a surface protective sheet to a workpiece having a surface and a back surface opposite to the surface, in which residual stress has occurred; A step of grinding the back surface of the workpiece to which the surface protection sheet is attached, This is a method for processing a workpiece having a convex pattern formed on its surface before a surface protection sheet is applied to the surface.

[0013] [2] A method for machining a workpiece as described in [1], wherein the surface has an inner circumference and an outer circumference surrounding the inner circumference, and the convex pattern is formed on the outer circumference.

[0014] [3] A method for processing a workpiece according to [1] or [2], wherein the workpiece in which residual stress has occurred is a workpiece having a functional film formed on at least a portion of its surface.

[0015] [4] A method for machining a workpiece described in any one of [1] to [3], wherein the surface has a difference in height.

[0016] [5] A method for machining a workpiece as described in [4], wherein the surface has an inner circumference and an outer circumference surrounding the inner circumference, the height of the outer circumference is lower than the height of the inner circumference, and a convex pattern is formed on the outer circumference.

[0017] [6] A method for machining a workpiece according to either [4] or [5], wherein the workpiece has a convex electrode formed on its surface.

[0018] [7] A method for processing a workpiece according to any one of [1] to [6], wherein the convex pattern is made of a resin composition.

[0019] [8] A method for processing a workpiece according to any one of [1] to [7], wherein the surface protection sheet has a substrate and an adhesive layer.

[0020] [9] A process for forming a groove on the surface of the workpiece before the process for attaching a surface protective sheet to the surface of the workpiece, A method for processing a workpiece according to any one of [1] to [8], wherein in a process of grinding the back surface of the workpiece, the workpiece is diced into a plurality of workpiece pieces starting from the grooves.

[0021]

[10] A process for forming a modified region inside the workpiece before the process for grinding the back surface of the workpiece, A method for processing a workpiece according to any one of [1] to [8], wherein in a step of grinding the back surface of the workpiece, the workpiece is diced into a plurality of workpiece pieces starting from the modified region. Effect of the Invention

[0022] According to the present invention, it is possible to provide a method for machining a workpiece that can suppress warping of a workpiece in which residual stress occurs. [Brief description of the drawings]

[0023] [Figure 1] FIG. 1 is a schematic cross-sectional view of a workpiece having a height difference on its surface, in which a convex electrode is formed on the surface of the workpiece. [Figure 2A] FIG. 2A is a schematic cross-sectional view showing a workpiece after backside grinding with no surface protection sheet attached. [Figure 2B] FIG. 2B is a schematic cross-sectional view showing the workpiece to which a surface protection sheet has been attached after backside grinding. [Figure 3A] FIG. 3A is a schematic plan view of a workpiece having a flat surface on which a convex pattern is formed on the outer periphery in the workpiece machining method according to the present embodiment. [Figure 3B] FIG. 3B is a schematic cross-sectional view taken along line IIIA-IIIA in FIG. 3A. [Figure 4A]FIG. 4A is a schematic plan view of a convex pattern formed on the outer periphery of a workpiece on which a convex electrode is formed, in the workpiece machining method according to this embodiment. [Figure 4B] FIG. 4B is a schematic cross-sectional view taken along line IVA-IVA in FIG. 4A. [Figure 4C] FIG. 4C is a schematic cross-sectional view showing another example of the location where a convex pattern is formed on a workpiece. [Figure 5A] FIG. 5A is a schematic cross-sectional view of a surface protection sheet that is preferably used in the workpiece processing method according to this embodiment. [Figure 5B] FIG. 5B is a schematic cross-sectional view showing another example of a surface protection sheet that is preferably used in the workpiece processing method according to this embodiment. [Figure 5C] FIG. 5C is a schematic cross-sectional view showing another example of a surface protection sheet that is preferably used in the workpiece processing method according to this embodiment. [Figure 6] 6(A) to 6(C) are schematic cross-sectional views for explaining how warpage of a workpiece is reduced when the workpiece is machined by the method according to this embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0024] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will now be described in detail with reference to the accompanying drawings based on specific embodiments. First, the main terms used in this specification will be explained.

[0025] The work refers to a plate-like body to which a surface protection sheet is attached and then cut into individual pieces. In addition, when a functional film described later is formed on the work, the work includes the functional film. Examples of the work include a circular wafer (including a case having an orientation flat), a rectangular panel level package, and a strip (rectangular substrate) sealed with molded resin. Among them, a wafer is preferable from the viewpoint of easily obtaining the effect of the present invention. The wafer may be, for example, a semiconductor wafer such as a silicon wafer, a gallium arsenide wafer, a silicon carbide wafer, a gallium nitride wafer, or an indium phosphide wafer, or an insulator wafer such as a glass wafer, a lithium tantalate wafer, or a lithium niobate wafer, or may be a reconstructed wafer made of a resin and a semiconductor used for producing a fan-out package or the like. From the viewpoint of easily obtaining the effect of the present invention, a semiconductor wafer or an insulator wafer is preferable, and a semiconductor wafer is more preferable.

[0026] Singulation of a work refers to dividing the work into individual circuits to obtain individual work pieces. For example, if the work is a wafer, the individual work pieces are chips, and if the work is a panel level package or a strip (rectangular substrate) sealed with molded resin, the individual work pieces are semiconductor packages.

[0027] The "front surface" of a workpiece refers to the side on which a circuit or the like is formed or on which the formation of a circuit or the like is planned, and the "back surface" of a workpiece refers to the side on which a circuit or the like is not formed or on which the formation of a circuit or the like is not planned.

[0028] DBG is a method in which a groove of a specified depth is formed on the front side of a workpiece, and then the workpiece is ground from the back side to separate the workpiece by grinding. The grooves formed on the front side of the workpiece are formed by methods such as blade dicing, laser dicing, and plasma dicing.

[0029] LDBG is a modified version of DBG, in which a modified region is created inside the workpiece using a laser, and the workpiece is divided into individual pieces by the stress generated when grinding the back surface of the workpiece.

[0030] The term "group of individual workpieces" refers to a plurality of individual workpieces held on the surface protection sheet of the present invention after the workpiece is singulated. These individual workpieces, as a whole, form a shape similar to that of the workpiece. The term "group of chips" refers to a plurality of chips held on the surface protection sheet of the present invention after the wafer as the workpiece is singulated. These chips, as a whole, form a shape similar to that of the wafer.

[0031] "(Meth)acrylate" is used as the term to refer to both "acrylate" and "methacrylate," and similar terms.

[0032] The term "energy rays" refers to ultraviolet rays, electron beams, etc., and is preferably ultraviolet rays.

[0033] Unless otherwise specified, "weight average molecular weight" is a polystyrene equivalent value measured by gel permeation chromatography (GPC). Measurements using this method are performed, for example, using a high-speed GPC device "HLC-8120GPC" manufactured by Tosoh Corporation, connected in this order to high-speed columns "TSK guard column HXL-H", "TSK Gel GMHXL", and "TSK Gel G2000 HXL" (all manufactured by Tosoh Corporation), under the following conditions: column temperature: 40°C, flow rate: 1.0 mL / min, and a differential refractometer as the detector.

[0034] The mass ratios in the explanations 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.

[0035] (1. Workpiece machining method) The workpiece machined by the method according to the present embodiment is a workpiece in which residual stress occurs. An example of such a workpiece is a workpiece that includes an element having residual stress on the workpiece. Specifically, the workpiece is a workpiece in which a functional film is formed on at least a part of the surface of the workpiece. The functional film is a film formed to protect, insulate, etc., circuits, convex electrodes, etc. formed on the surface of the workpiece.

[0036] In this embodiment, the functional film is formed on the workpiece in such a manner that residual stress is generated. Specifically, examples of the functional film include a form in which a dimensional change occurs during the formation of the functional film, and a form in which a film-like functional film is attached to the workpiece by applying tension.

[0037] Examples of the functional film include a passivation film and a protective film, which are preferably organic films made of organic components. Examples of the passivation film include a polyimide film and a polybenzoxazole film. Examples of the protective film include a resin film made of a curable organic component such as a thermosetting component or an energy ray curable component.

[0038] The surface of the workpiece on which the residual stress occurs may be a flat surface or a surface having height differences. Examples of the surface of the workpiece having height differences include a workpiece on which a convex electrode (bump electrode, pillar electrode, etc.) is formed, a chip-on-wafer (CoW) on which a chip is disposed on the surface of the workpiece, and a half-trim wafer in which a part of the edge of the workpiece is removed.

[0039] As shown in Fig. 1, the workpiece with the convex electrode is a workpiece having a convex electrode 2a formed on the surface 1a of the workpiece 1 for electrically connecting a circuit formed on the surface 1a of the workpiece 1 to a substrate or the like, and a functional film 5 for protecting the vicinity of the connection between the convex electrode 2a and the circuit formed on the surface. The convex electrode 2a is formed to protrude in the thickness direction of the workpiece. Therefore, there is a height difference D between the tip of the convex electrode and the area on the workpiece where the convex electrode is not formed.

[0040] 1, the height difference D of the surface 1a corresponds to the height difference between the inner peripheral part and the outer peripheral part of the work (wafer) 1, and the inner peripheral part is surrounded by the outer peripheral part. Therefore, in this embodiment, the height difference of the surface is formed by the inner peripheral part and the outer peripheral part surrounding the inner peripheral part, and it is preferable that the height of the outer peripheral part is lower than the height of the inner peripheral part.

[0041] In the case of a workpiece having a convex electrode, the 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 is the height of the inner peripheral portion.

[0042] In the following, a workpiece having a functional film formed on the surface thereof will be described as an example of a workpiece having residual stress.

[0043] When a passivation film is formed on the work surface as a circuit protection layer, residual stress occurs in the passivation film due to shrinkage during the formation of the passivation film. Furthermore, when a curable film for forming a protective film for protecting a convex electrode is attached to a work surface on which a convex electrode is formed, residual stress due to the tension of the film occurs in the curable film for forming a protective film. Furthermore, a difference in attachment pressure occurs due to the difference in height between an area where the convex electrode is formed and an area where it is not formed, and residual stress due to the pressure difference occurs in the curable film for forming a protective film. Furthermore, residual stress occurs in the protective film due to shrinkage during curing of the curable film for forming a protective film.

[0044] However, when forming the passivation film and the protective film, the workpiece usually has high rigidity, and therefore the residual stress is counteracted by the rigidity of the workpiece.

[0045] On the other hand, back grinding of the workpiece is an example of processing the workpiece. By back grinding the workpiece, it is possible to realize a thinning of the workpiece obtained by dividing the workpiece. When the back grinding of the workpiece is performed, the thickness of the workpiece becomes thin, so the rigidity of the workpiece decreases and residual stress becomes apparent. As a result, as shown in FIG. 2A, the residual stress causes a warp W in the workpiece 1 so that the functional film faces inward.

[0046] Here, when grinding the back surface of a workpiece, there is a possibility that abrasives, cooling water, etc. may get into the workpiece surface, causing contamination of the circuits, etc., and that the circuits, etc. may be damaged by the force applied during back grinding, so it is useful to attach a surface protection sheet to protect the workpiece surface.

[0047] However, when the surface protective sheet is applied, residual stress is generated in the surface protective sheet, similar to when the protective film-forming curable film is applied.

[0048] Therefore, if a surface protection sheet is attached to a workpiece with residual stress and the backside of the workpiece is ground, the warp W of the workpiece 1 becomes even larger, as shown in Fig. 2B. If the warp of the workpiece is large, problems such as a high possibility of the workpiece being damaged, poor handling of the workpiece, and poor transportability to the next process occur.

[0049] The present inventors have found that warping of a workpiece in which residual stress occurs can be suppressed by employing the following technique. The workpiece machining method according to this embodiment will be described in detail below.

[0050] The method for machining a workpiece according to this embodiment includes at least the following steps 1 and 2. Step 1: A step of attaching a surface protection sheet to a workpiece having a surface and a back surface opposite to the surface, in which residual stress has occurred. Process 2: Grinding the back surface of the workpiece with the surface protection sheet attached

[0051] In the following, a description will be given of a workpiece processing method including the above-mentioned steps 1 and 2, in which the workpiece is a wafer and the workpiece in which residual stress has occurred is a workpiece having a functional film formed on its surface.

[0052] In this embodiment, step A described below is performed before step 1. That is, step A is performed before a surface protection sheet is attached to the surface of the wafer. In step A, a functional film and a convex pattern are formed on the surface of the wafer. The formation of a functional film is an aspect in which residual stress often occurs, and examples of this include an aspect in which a functional film is formed by curing and shrinking a functional film-forming composition, and an aspect in which a functional film-forming sheet including a functional film-forming film is attached to a wafer while applying tension.

[0053] Next, a convex pattern is formed on the surface of the wafer or on the functional film. In this embodiment, the convex pattern is preferably formed on the outer periphery of the wafer in order to intentionally generate stress that counteracts the residual stress. When the wafer surface 1a is a flat surface, the convex pattern 3 is formed as shown in Figures 3A and 3B. When the wafer surface 1a has a height difference, the convex pattern 3 is formed as shown in Figures 4A and 4B.

[0054] (1.1.Process 1) In step 1, a surface protection sheet is attached to the surface of the wafer on which the functional film and the convex pattern are formed. Usually, when a surface protection sheet is attached, stress that promotes warping of the wafer is generated, as described above.

[0055] However, in this embodiment, a convex pattern is formed on the surface of the wafer. When a surface protection sheet is attached to the wafer surface under such circumstances, the pressure during attachment tends to concentrate on the convex pattern, and the pressure during attachment becomes smaller in the region where the convex pattern is not formed. As a result, stress caused by the pressure difference during attachment tends to be generated so as to cancel out the residual stress generated in the functional film. Therefore, even if residual stress is generated in the functional film, by attaching the surface protection sheet, the influence of the residual stress can be reduced, and the warpage of the wafer manifested by back grinding of the wafer can be reduced. That is, by forming the convex pattern, the stress generated by attaching the surface protection sheet is not made to act so as to increase the influence of the residual stress generated in the functional film, but rather can be made to act so as to reduce the influence of the residual stress.

[0056] (1.2. Convex Pattern) The height of the convex pattern may be set so as to reduce the residual stress generated in the functional film. For example, when the wafer surface is a flat surface, the height Ha of the convex pattern is preferably in the range of 1 μm or more and 2000 μm or less, and more preferably in the range of 5 μm or more and 500 μm or less.

[0057] Also, when the wafer surface has height differences, when the height of the convex pattern is Hb and the difference between the height of the inner peripheral portion and the height of the outer peripheral portion is Hd, it is preferable to satisfy the relationship of Hd / 1.2 < Hb < Hd / 0.5, and more preferably to satisfy the relationship of Hd / 1.1 < Hb < Hd / 0.6. Note that Hd is preferably in the range of 5 μm or more and 2000 μm or less, and more preferably in the range of 30 μm or more and 1000 μm or less.

[0058] The convex pattern may have various shapes. For example, as shown in Fig. 3A and Fig. 4A, the convex pattern 3 may be formed in a ring shape including the outer edge of the wafer 1. Such a convex pattern is easy to form, and the stress caused by the pressure difference during attachment can reliably cancel the residual stress generated in the functional film. In addition, the convex pattern 3 shown in Fig. 3A and Fig. 4A is a continuous pattern, but it may be an intermittently formed pattern.

[0059] 4C, the convex pattern 3 may be formed at a distance radially inward from the outer edge of the wafer 1. Such a convex pattern has the advantage that the entire surface of the convex pattern can be covered with a pick-up tape in the step of peeling off the surface protection sheet, which will be described later, making it easy to peel off the convex pattern together with the surface protection sheet.

[0060] Although the convex pattern can be formed over the entire outer periphery (for example, outside the area where the convex electrode is formed), it is preferable to form it apart from the convex electrode from the viewpoints of the amount of material required for its formation being large and the material of the convex pattern adhering to the convex electrode and the circuit, etc. In other words, it is preferable for the outer periphery to include an area where the convex pattern is not formed.

[0061] The means for forming the convex pattern may be determined according to the material for forming the convex pattern. For example, when forming the convex pattern using a curable resin composition described later, a means for applying a 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.

[0062] The material constituting the convex pattern may be any material that can provide the above-mentioned effects. In this embodiment, from the viewpoint of facilitating the formation of the convex pattern, the material constituting the convex pattern is preferably a resin composition. The resin composition is preferably an adhesive composition that adheres closely to the wafer surface. Examples of the adhesive composition include an acrylic adhesive composition, a silicone adhesive composition, a urethane adhesive composition, an epoxy adhesive composition, a phenolic adhesive composition, a urea adhesive composition, an alkyd adhesive composition, a vinyl acetate adhesive composition, a vinyl chloride adhesive composition, an amide adhesive composition, an imide adhesive composition, a chloroprene rubber, a nitrile rubber, and a styrene butadiene rubber.

[0063] In addition, the resin composition is preferably curable. By the resin composition being curable, it is easy to form a predetermined shape before curing, and after curing, it is easy to make a material hard enough to prevent abrasives, cooling water, etc. from penetrating into the circuitry of the wafer during back grinding. Examples of the curable resin composition include a thermosetting resin composition and an energy ray curable resin composition.

[0064] In this embodiment, from the viewpoint of removing the convex pattern from the wafer surface after back grinding, an energy ray curable resin composition is preferred, and an energy ray curable acrylic adhesive composition is more preferred. The energy ray curable acrylic 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.

[0065] The shear storage modulus of the convex pattern at 23° C. is preferably 50 MPa or more. By having the shear storage modulus at 23° C. within the above range, the convex pattern becomes relatively hard, and even during back grinding, the height difference between the outer periphery and the inner periphery of the wafer is easily suppressed. When the convex pattern is formed from a curable resin, the shear storage modulus is a value measured for the resin after curing.

[0066] (1.3. Surface protection sheet) The surface protection sheet attached to the surface may be configured to protect the circuits and the like on the wafer surface. In this embodiment, as shown in FIG. 5A, the surface protection sheet 10 preferably has a base material 11 and an adhesive layer 12. The adhesive layer is attached to the wafer surface, so that the wafer surface is reliably protected. When the wafer surface has a height difference, the adhesive layer may or may not follow the height difference of the wafer surface.

[0067] In this embodiment, when a convex electrode is formed on the wafer surface, it is preferable that the adhesive layer follows the height difference to embed the convex electrode. The convex pattern may be embedded in the surface protection sheet, or a part of the convex pattern may not be embedded in the surface protection sheet and may be exposed to the outside.

[0068] 5B, in the surface protection sheet 10, an intermediate layer 13 may be disposed between the substrate 11 and the adhesive layer 12. In particular, when a convex electrode is formed on the wafer surface and the wafer surface has a height difference, the intermediate layer makes it possible to reliably embed the convex electrode.

[0069] The surface protection sheet 10 shown in Fig. 5B will be described in detail below. Fig. 5B shows a surface protection sheet 10 having a configuration in which an intermediate layer 13 and a pressure-sensitive adhesive layer 12 are laminated in this order on a substrate 11.

[0070] The surface protective sheet 10 may have other layers. For example, another layer may be formed between the substrate 11 and the intermediate layer 13, or another layer may be formed between the intermediate layer 13 and the pressure-sensitive adhesive layer 12.

[0071] The components of surface protection sheet 10 shown in FIG. 5B will be described in detail below.

[0072] (1.3.1. Base material) The substrate is a member that is responsible for the rigidity of the surface protection sheet. The substrate is not limited as long as it is made of a material that can support the workpiece. For example, various resin films used as substrates for backgrinding tapes are exemplified. By using such a resin film, the workpiece can be held without being damaged even if the thickness of the workpiece becomes thin due to grinding. 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.

[0073] In this embodiment, examples of the material of the substrate include polyesters such as polyethylene terephthalate, polyethylene naphthalate, polybutylene terephthalate, wholly aromatic polyesters, polyamides, polycarbonates, polyacetals, modified polyphenylene oxides, polyphenylene sulfides, polysulfones, polyether ketones, biaxially oriented polypropylenes, etc. Among these, polyesters are preferred, and polyethylene terephthalate is more preferred.

[0074] The thickness of the substrate affects the rigidity of the surface protection sheet, and may be set according to the material of the substrate. In this embodiment, the thickness of the substrate is preferably 25 μm or more and 200 μm or less, more preferably 35 μm or more and 150 μm or less, and even more preferably 40 μm or more and 150 μm or less.

[0075] At least one of the main surfaces of the substrate may be subjected to an adhesion treatment such as a corona treatment in order to improve adhesion with a layer formed on the main surface. Also, at least one of the main surfaces of the substrate may be provided with an easy-adhesion layer in order to improve adhesion with a layer formed on the main surface.

[0076] (1.3.2. Adhesive Layer) The adhesive layer is attached to the surface of the wafer, and protects the surface and supports the wafer until it is peeled off from the surface. In this embodiment, the adhesive layer is closely attached to the surface of the wafer and fixed thereto. As a result, even if cooling water or the like is used during back grinding, the surface protection sheet can prevent the cooling water from penetrating into the wafer surface, and can adequately protect the wafer surface. Furthermore, even if the wafer is divided into individual pieces, contact between chips can be suppressed. The adhesive layer may be composed of one layer (single layer), or may be composed of two or more layers.

[0077] The thickness of the adhesive layer is not particularly limited as long as it is thick enough to support the wafer. In this embodiment, the thickness of the adhesive layer is preferably 1 μm or more and 100 μm or less, more preferably 5 μm or more and 50 μm or less. The thickness of the adhesive layer means the thickness of the entire adhesive layer. For example, the thickness of an adhesive layer composed of multiple layers means the total thickness of all layers constituting the adhesive layer.

[0078] 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 composed of, for example, an acrylic adhesive, a urethane adhesive, a rubber adhesive, a silicone adhesive, or the like.

[0079] In addition, the adhesive layer is preferably formed from an energy ray curable adhesive. By forming the adhesive layer of the surface protection sheet from an energy ray curable adhesive, the adhesive layer adheres to the wafer with high adhesive strength when attached to the wafer, and the adhesive strength can be reduced by irradiating energy rays when peeled off from the wafer. Therefore, while appropriately protecting the circuits of the wafer, the destruction of the circuits on the wafer surface and the transfer of the adhesive onto the wafer can be prevented when peeling off the surface protection sheet.

[0080] In this embodiment, the energy ray curable adhesive is preferably composed of an adhesive composition containing an acrylic adhesive. As the acrylic adhesive, it is preferable to use an acrylic polymer. As the energy ray curable acrylic adhesive, it 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 preferable.

[0081] The acrylic polymer having energy ray curability may be any known acrylic polymer, but in this embodiment, an acrylic polymer having an energy curable group introduced into a functional group-containing acrylic polymer is preferred. The functional group-containing acrylic polymer may be a homopolymer formed from one type of acrylic monomer, a copolymer formed from multiple types of acrylic monomers, or a copolymer formed from one or multiple types of acrylic monomers and a monomer other than the acrylic monomer.

[0082] In this embodiment, the functional group-containing acrylic polymer is preferably an acrylic copolymer obtained by copolymerizing an alkyl (meth)acrylate with a functional group-containing monomer.

[0083] Examples of the alkyl (meth)acrylate include methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, t-butyl (meth)acrylate, n-pentyl (meth)acrylate, n-hexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, isooctyl (meth)acrylate, and n-octyl (meth)acrylate.

[0084] The functional group-containing monomer is a monomer containing a reactive functional group. The reactive functional group is a functional group capable of reacting with other compounds such as a crosslinking agent described later. Examples of the functional group in the functional group-containing monomer include a hydroxyl group, a carboxyl group, and an epoxy group, and a hydroxyl group is preferred.

[0085] Examples of hydroxyl group-containing monomers include hydroxyalkyl (meth)acrylates such as hydroxymethyl (meth)acrylate, 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, 3-hydroxybutyl (meth)acrylate, and 4-hydroxybutyl (meth)acrylate; and non-(meth)acrylic unsaturated alcohols (unsaturated alcohols not having a (meth)acryloyl skeleton) such as vinyl alcohol and allyl alcohol.

[0086] Examples of the energy ray curable group include a (meth)acryloyl group and a vinyl group, and a (meth)acryloyl group is preferred. The energy ray curable group is introduced into the acrylic polymer by, for example, adding an energy ray curable compound described later to the functional group-containing acrylic polymer.

[0087] The energy ray-curable compound having an energy ray-curable group is preferably a compound having one or more groups selected from an isocyanate group, an epoxy group, and a carboxy group, and more preferably a compound having an isocyanate group.

[0088] Examples of compounds having an isocyanate group include 2-methacryloyloxyethyl isocyanate, meta-isopropenyl-α,α-dimethylbenzyl isocyanate, methacryloyl isocyanate, allyl isocyanate, 1,1-(bisacryloyloxymethyl)ethyl isocyanate; acryloyl monoisocyanate compounds obtained by reacting a diisocyanate compound or a polyisocyanate compound with hydroxyethyl (meth)acrylate; and acryloyl monoisocyanate compounds obtained by reacting a diisocyanate compound or a polyisocyanate compound with a polyol compound and hydroxyethyl (meth)acrylate. The isocyanate group undergoes an addition reaction with the hydroxyl group of the functional group-containing acrylic polymer.

[0089] The pressure-sensitive adhesive composition preferably further contains a crosslinking agent, which reacts with functional groups, for example, to crosslink resins contained in the functional-group-containing acrylic polymer.

[0090] Examples of the crosslinking agent include isocyanate-based crosslinking agents (crosslinking agents having an isocyanate group) such as tolylene diisocyanate, hexamethylene diisocyanate, xylylene diisocyanate, and adducts of these diisocyanates; epoxy-based crosslinking agents (crosslinking agents having a glycidyl group) such as ethylene glycol glycidyl ether; aziridine-based crosslinking agents (crosslinking agents having an aziridinyl group) such as hexa[1-(2-methyl)-aziridinyl]triphosphatriazine; metal chelate-based crosslinking agents (crosslinking agents having a metal chelate structure) such as aluminum chelate; and isocyanurate-based crosslinking agents (crosslinking agents having an isocyanuric acid skeleton).

[0091] The crosslinking agent is preferably an isocyanate-based crosslinking agent from the viewpoints of improving the cohesive strength of the pressure-sensitive adhesive and thereby improving the adhesive strength of the pressure-sensitive adhesive layer, and of easy availability.

[0092] The pressure-sensitive adhesive composition may further contain a photopolymerization initiator. When the pressure-sensitive adhesive composition contains a photopolymerization initiator, the curing reaction proceeds sufficiently even when irradiated with relatively low-energy energy rays such as ultraviolet rays.

[0093] Examples of the photopolymerization initiator 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.Specific examples include α-hydroxycyclohexyl phenyl ketone, benzoin, benzoin methyl ether, benzoin ethyl ether, benzoin isopropyl ether, benzyl diphenyl sulfide, benzyl dimethyl ketal, tetramethylthiuram monosulfide, azobisisobutyronitrile, dibenzyl, diacetyl, β-chloroanthraquinone, and 2,4,6-trimethylbenzoyldiphenylphosphine oxide.

[0094] (1.3.3. Middle Layer) The intermediate layer is a layer disposed between the substrate and the pressure-sensitive adhesive layer. In this embodiment, the intermediate layer may be composed of one layer (single layer) or may be composed of two or more layers.

[0095] The thickness of the intermediate layer may be set in consideration of the height difference on the wafer surface. In this embodiment, the thickness of the intermediate layer is preferably 50 μm or more and 600 μm or less, and more preferably 150 μm or more and 500 μm or less. The thickness of the intermediate layer means the thickness of the entire intermediate layer. For example, the thickness of the intermediate layer composed of multiple layers means the total thickness of all layers that compose the intermediate layer.

[0096] In this embodiment, when the surface protective sheet has an intermediate layer, the intermediate layer preferably has the following physical properties.

[0097] (1.3.3.1. Shear storage modulus at 65°C) In this embodiment, the shear storage modulus (G') of the intermediate layer at 65°C is preferably 0.5 MPa or less. The shear storage modulus (G') is one of the indicators of the ease of deformation (hardness) of the intermediate layer. When the shear storage modulus (G') of the intermediate layer at 65°C is within the above range, damage to the wafer or the like during back grinding can be suppressed.

[0098] The shear storage modulus of the intermediate layer at 65° C. is more preferably 0.4 MPa or less, and even more preferably 0.2 MPa or less. Furthermore, from the viewpoint of suppressing exudation of intermediate layer components during storage of the surface protection sheet, the shear storage modulus of the intermediate layer at 65° C. is preferably 0.005 MPa or more.

[0099] The shear storage modulus of the intermediate layer at 65° C. may be measured by a known method. For example, the intermediate layer may be used as a sample of a predetermined size, and the sample may be strained at a predetermined frequency within a predetermined temperature range using a dynamic viscoelasticity measuring device to measure the elastic modulus, and the shear storage modulus may be calculated from the measured elastic modulus.

[0100] (1.3.3.2.Loss tangent at 65°C) In this embodiment, the loss tangent (tan δ) of the intermediate layer at 65° C. is preferably greater than 0.5. The loss tangent is defined as "loss modulus / storage modulus" and is a value measured by the response to stress applied to an object using a dynamic viscoelasticity measuring device. When the loss tangent of the intermediate layer at 65° C. is within the above range, damage to wafers and the like during back grinding can be suppressed.

[0101] The loss tangent of the intermediate layer at 65° C. is more preferably 0.7 or more, and even more preferably 1.0 or more. Also, the loss tangent of the intermediate layer at 65° C. is preferably 2.0 or less.

[0102] The loss tangent of the intermediate layer at 65° C. may be measured by a known method, similar to the shear storage modulus. For example, the intermediate layer is prepared as a sample of a predetermined size, and a dynamic viscoelasticity measuring device is used to apply a strain to the sample at a predetermined frequency within a predetermined temperature range to measure the elastic modulus, and the loss tangent can be calculated from the measured elastic modulus.

[0103] (1.3.4. Composition for intermediate layer) Although the composition of the intermediate layer is not particularly limited, in this embodiment, the intermediate layer is preferably composed of a composition having a resin (intermediate layer composition). The intermediate layer composition preferably contains the following components.

[0104] (1.3.4.1. Urethane (meth)acrylates) The urethane (meth)acrylate is a compound having at least a (meth)acryloyl group and a urethane bond, and has the property of being polymerized by energy ray irradiation. In this embodiment, the urethane (meth)acrylate is a component for imparting flexibility to the intermediate layer.

[0105] The urethane (meth)acrylate may be a monofunctional type or a multifunctional type. In this embodiment, a multifunctional urethane (meth)acrylate is preferred, and a bifunctional urethane (meth)acrylate is preferred.

[0106] The urethane (meth)acrylate may be an oligomer, a polymer, or a mixture thereof. In this embodiment, a urethane (meth)acrylate oligomer is preferred.

[0107] The urethane (meth)acrylate can be obtained, for example, by reacting a polyol compound with a polyisocyanate compound to obtain a terminal isocyanate urethane prepolymer, and then reacting the resulting prepolymer with a hydroxyl group-containing (meth)acrylate. The urethane (meth)acrylate may be used alone or in combination of two or more kinds.

[0108] The content of the urethane (meth)acrylate in the intermediate layer composition is preferably 20% by mass or more, more preferably 25% by mass or more, and even more preferably 30% by mass or more. The content of the urethane (meth)acrylate in the intermediate layer composition is preferably 70% by mass or less, more preferably 65% ​​by mass or less, and even more preferably 50% by mass or less.

[0109] (1.3.4.2. Polymerizable Monomers) The polymerizable monomer is preferably a polymerizable compound other than the above-mentioned urethane (meth)acrylate, and is a compound that can be polymerized with other components by irradiation with energy rays. In this embodiment, the polymerizable monomer is a compound having one reactive unsaturated double bond group.

[0110] 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-vinyl formamide, N-vinyl pyrrolidone, and N-vinyl caprolactam.

[0111] Examples of the (meth)acrylate having an alkyl group having 1 to 30 carbon atoms include methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, t-butyl (meth)acrylate, n-pentyl (meth)acrylate, n-hexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, n-octyl (meth)acrylate, nonyl (meth)acrylate, decyl (meth)acrylate, undecyl (meth)acrylate, dodecyl (meth)acrylate, tridecyl (meth)acrylate, tetradecyl (meth)acrylate, hexadecyl (meth)acrylate, octadecyl (meth)acrylate, and eicosyl (meth)acrylate.

[0112] Examples of the (meth)acrylate having a functional group include hydroxyl group-containing (meth)acrylates such as 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, 3-hydroxybutyl (meth)acrylate, and 4-hydroxybutyl (meth)acrylate; (meth)acrylamide, N,N-dimethyl (meth)acrylamide, N-butyl (meth)acrylamide, and N-methylol (meth)acrylamide. Examples of the amide group-containing compounds include acrylamide, N-methylolpropane (meth)acrylamide, N-methoxymethyl (meth)acrylamide, and N-butoxymethyl (meth)acrylamide; amino group-containing (meth)acrylates such as primary amino group-containing (meth)acrylates, secondary amino group-containing (meth)acrylates, and tertiary amino group-containing (meth)acrylates; and epoxy group-containing (meth)acrylates such as glycidyl (meth)acrylate, methyl glycidyl (meth)acrylate, and allyl glycidyl ether.

[0113] Examples of (meth)acrylates having an alicyclic structure include isobornyl (meth)acrylate, dicyclopentenyl (meth)acrylate, dicyclopentanyl (meth)acrylate, dicyclopentenyloxy (meth)acrylate, cyclohexyl (meth)acrylate, trimethylcyclohexyl (meth)acrylate, and adamantane (meth)acrylate.

[0114] Examples of the (meth)acrylate having an aromatic structure include phenylhydroxypropyl (meth)acrylate, benzyl (meth)acrylate, and 2-hydroxy-3-phenoxypropyl (meth)acrylate.

[0115] Examples of the (meth)acrylate having a heterocyclic structure include tetrahydrofurfuryl (meth)acrylate and morpholine (meth)acrylate.

[0116] In this embodiment, the polymerizable monomer preferably includes a (meth)acrylate having an alkyl group with 1 to 30 carbon atoms and a (meth)acrylate having an alicyclic structure. Among (meth)acrylates having an alkyl group with 1 to 30 carbon atoms, (meth)acrylates having an alkyl group with 4 to 14 carbon atoms are preferred, and as (meth)acrylates having an alicyclic structure, isobornyl (meth)acrylate and trimethylcyclohexyl (meth)acrylate are preferred.

[0117] In addition, when the intermediate layer composition contains a crosslinking agent, a (meth)acrylate having a functional group capable of reacting with the crosslinking agent is not preferred. This is because the crosslinked structure formed by the crosslinking reaction may increase the shear storage modulus of the intermediate layer. For example, a composition for the intermediate layer containing a polyisocyanate-based crosslinking agent and a (meth)acrylate having a hydroxyl group is not preferred.

[0118] The content of the polymerizable monomer in the intermediate layer composition is preferably 20% by mass or more, more preferably 30% by mass or more, and is preferably 80% by mass or less, more preferably 70% by mass or less.

[0119] In addition, the mass ratio of the urethane (meth)acrylate to the polymerizable monomer (urethane (meth)acrylate / polymerizable monomer) in a total of 100 parts by mass of the urethane (meth)acrylate and the polymerizable monomer is preferably from 20 / 80 to 80 / 20, and more preferably from 30 / 70 to 70 / 30.

[0120] (1.3.4.3. Photopolymerization initiator) When the intermediate layer composition contains the above-mentioned urethane (meth)acrylate and polymerizable monomer, the intermediate layer composition preferably contains a photopolymerization initiator. By containing the photopolymerization initiator, polymerization proceeds reliably, and an intermediate layer having the above-mentioned characteristics can be easily obtained.

[0121] 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. Specific examples include 1-hydroxycyclohexyl phenyl ketone, 2-hydroxy-2-methyl-1-phenyl-propan-1-one, benzoin, benzoin methyl ether, benzoin ethyl ether, benzoin isopropyl ether, and 2,2-dimethoxy-1,2-diphenylethan-1-one. These photopolymerization initiators may be used alone or in combination of two or more.

[0122] The amount of the photopolymerization initiator is preferably 0.05 to 15 parts by mass, and more preferably 0.5 to 10 parts by mass, per 100 parts by mass of the total of the urethane (meth)acrylate and the polymerizable monomer.

[0123] (1.3.4.4. Chain transfer agents) The intermediate layer composition preferably contains a chain transfer agent. The chain transfer agent can cause a chain transfer reaction and adjust the progress of the curing reaction of the intermediate layer composition. By containing the chain transfer agent, it becomes possible for components with short molecular chains to remain relatively even after curing, so that the cured polymer has a crosslinked structure with relatively high flexibility. As a result, it becomes easy to set the shear storage modulus of the intermediate layer within the above range.

[0124] Examples of the chain transfer agent include thiol group-containing compounds. Examples of the thiol group-containing compounds include nonyl mercaptan, 1-dodecanethiol, 1,2-ethanedithiol, 1,3-propanedithiol, triazine thiol, triazine dithiol, triazine trithiol, 1,2,3-propane trithiol, tetraethylene glycol-bis(3-mercaptopropionate), trimethylolpropane tris(3-mercaptopropionate), pentaerythritol tetraki ... Examples of the chain transfer agent include erythritol tetrakis thioglucolate, dipentaerythritol hexakis (3-mercaptopropionate), tris [(3-mercaptopropionyloxy)-ethyl]-isocyanurate, 1,4-bis (3-mercaptobutyryloxy) butane, pentaerythritol tetrakis (3-mercaptobutyrate), and 1,3,5-tris (3-mercaptobutyloxyethyl)-1,3,5-triazine-2,4,6- (1H,3H,5H)-trione. The chain transfer agent may be used alone or in combination of two or more.

[0125] The amount of the chain transfer agent is preferably 0.1 to 10 parts by mass, more preferably 0.3 to 5 parts by mass, based on 100 parts by mass of the total of the urethane (meth)acrylate and the polymerizable monomer.

[0126] (1.3.5. Manufacturing of Surface Protection Sheets) The surface protection sheet can be manufactured by a known method. For example, first, the above-mentioned adhesive layer composition (if necessary, intermediate layer composition) is prepared. Next, the prepared composition is applied to the surface of a release sheet, a substrate, etc., using a known coating method, and then dried and cured to obtain a surface protection sheet having a predetermined structure.

[0127] (1.4.Process 2) As shown in FIG. 6(A), a convex pattern is formed on the surface 1a of the wafer, and a surface protection sheet 10 is attached onto the surface of the wafer.

[0128] 6(B), the front surface side of the wafer 1 with the surface protection sheet 10 attached thereto is placed on the chuck table 100. The chuck table 100 has, for example, a porous holding surface, and the surface protection sheet 10 is adsorbed and fixed to the chuck table 100 by suction from the side opposite to the side on which the wafer 1 is placed.

[0129] After the wafer 1 is fixed to the chuck table 100, the back surface 1b of the wafer 1 is ground, for example, by a grinding wheel or the like. The thickness of the wafer after the back surface grinding is, for example, about 25 μm or more and 600 μm or less.

[0130] After grinding, the suction is released and the wafer 1 and surface protection sheet 10 are released from the chuck table 100. In this embodiment, since step A is adopted before step 1, the residual stress of the functional film 5 is cancelled and warping of the wafer 1 after grinding is suppressed as shown in Fig. 6(C).

[0131] (1.5.Step 3) In this embodiment, it is preferable to peel off the surface protection sheet from the wafer after the backside grinding. That is, the method for processing a workpiece according to this embodiment preferably includes a step (step 3) of peeling off the surface protection sheet from the wafer after the backside grinding. By peeling off the surface protection sheet, the wafer can be transported to the next step. Step 3 is performed, for example, as follows.

[0132] When the adhesive layer of the surface protection sheet is formed from an energy ray curable adhesive, the adhesive layer is cured and shrunk by irradiating it with energy rays, and the adhesive strength to the adherend (wafer) is reduced. Next, a pick-up tape is attached to the back side of the wafer after the back grinding, and the position and direction are adjusted so that the wafer can be picked up. At this time, a ring frame arranged on the outer periphery of the wafer is also attached to the pick-up tape, and the outer periphery of the pick-up tape is fixed to the ring frame. The wafer and the ring frame may be attached to the pick-up tape at the same time, or may be attached at different times. Next, the surface protection sheet is peeled off from the wafer held on the pick-up tape.

[0133] In this embodiment, when the surface protection sheet is peeled off, it is preferable that at least a portion of the convex pattern formed on the surface of the wafer is peeled off together with the surface protection sheet, and it is particularly preferable that the entire convex pattern is peeled off.

[0134] By peeling off at least a portion of the convex pattern together with the surface protection sheet, the convex pattern can be easily removed from the wafer surface.

[0135] (1.6. Steps 4A and 4B) The method for processing a workpiece according to this embodiment is also applicable to DBG or LDBG. In this case, it is preferable to use a surface protection sheet 10 shown in FIG. 5C as the surface protection sheet. In the surface protection sheet 10 shown in FIG. 5C, a buffer layer 14 is formed on a main surface 11b of a substrate 11 opposite to a main surface on which an intermediate layer 12 and an adhesive layer 13 are formed.

[0136] The buffer layer is a layer that is softer than the base material and relieves stress during back grinding of the wafer to prevent cracks and chips from occurring in the wafer. Also, the presence of the buffer layer makes it easier for the wafer to be properly held on the chuck table.

[0137] The thickness of the buffer layer is preferably 1 to 200 μm, more preferably 10 to 100 μm, and further preferably 20 to 80 μm. By setting the thickness of the buffer layer within the above range, the buffer layer can appropriately relieve stress during back grinding.

[0138] The buffer layer may be a layer formed from a buffer layer composition containing an energy ray-polymerizable compound, or may be a film such as a polypropylene film, an ethylene-vinyl acetate copolymer film, an ionomer resin film, an ethylene-(meth)acrylic acid copolymer film, an ethylene-(meth)acrylic acid ester copolymer film, an LDPE film, or an LLDPE film.

[0139] When the workpiece processing method according to this embodiment is applied to DBG or LDBG, in addition to the above steps 1 to 3, a step of forming a groove on the surface of the wafer (step 4A: DBG) or a step of forming a modified region inside the wafer (step 4B: LDBG) is included. The groove and modified region are formed so as to follow the parting line when the wafer is divided into individual workpieces (chips) in the above step 2.

[0140] When grooves are formed on the surface of the wafer by dicing or the like, step 1 (and step A) is performed after step 4A. That is, in step 1, a surface protection sheet is attached to the surface of the wafer having the grooves formed in step 4A described below.

[0141] The grooves formed in step 4A are shallower than the thickness of the wafer. The grooves can be formed by dicing using a conventionally known dicing device or the like. In step 2 described above, the wafer is divided into a plurality of chips along the grooves by the stress applied during back grinding.

[0142] On the other hand, when forming a modified region on the wafer, step 1 (and step A) may be performed before or after step 4 B. In this embodiment, when forming a modified region on the wafer, it is preferable to perform step 1 (and step A) before step 4 B.

[0143] In addition, the modified region is a brittle portion of the wafer, and is the starting point for the wafer to be destroyed and diced into chips when the wafer becomes thinner due to grinding in the grinding process or when stress is applied during backside grinding.

[0144] The modified region is formed inside the wafer by irradiating the laser focused on the inside of the wafer. The laser may be irradiated from the front side or the back side of the wafer. In the embodiment in which the modified region is formed, when step 4B is performed after step 1 and the laser is irradiated from the front side of the wafer, the laser is irradiated to the wafer through the surface protection sheet.

[0145] In DBG, the back grinding in step 2 is performed to thin the wafer at least to the bottom of the grooves. This back grinding turns the grooves into cuts that penetrate the wafer, and the wafer is divided by the cuts into individual chips.

[0146] In LDBG, the grinding surface (wafer back surface) may reach the modified region by grinding, but it does not have to reach the modified region strictly. In other words, it is sufficient to grind to a position close to the modified region so that the wafer is broken and singulated into chips starting from the modified region. For example, the actual singulation of the chips may be performed by attaching a pick-up tape (described later) and then stretching the pick-up tape.

[0147] After the back surface grinding is completed, dry polishing may be performed prior to picking up the chips.

[0148] Step 3 may be performed as described above, but the surface protection sheet is peeled off from the individual wafers. Even in this case, the convex patterns can be easily peeled off.

[0149] The shape of the individualized chips (workpiece individualized products) obtained through step 3 may be square or elongated, such as rectangular. The thickness of the individualized chips is not particularly limited, but is preferably about 5 to 100 μm, and more preferably 10 to 45 μm. LDBG makes it easy to make the thickness of the individualized chips 50 μm or less, and more preferably 10 to 45 μm. The size of the individualized chips is not particularly limited, but the chip size is preferably 600 mm or less. 2 Less than 400mm, more preferably 2 Less than 120mm, more preferably 2 is less than.

[0150] Although the embodiment of the present invention has been described above, the present invention is not limited to the above embodiment, and may be modified in various aspects within the scope of the present invention. EXAMPLES

[0151] The present invention will be described in more detail below using examples, but the present invention is not limited to these examples.

[0152] Example 1 (1) Resin composition for forming a convex pattern As materials for forming a convex pattern, 40 parts by mass of bifunctional polyol-modified urethane acrylate (molecular weight 7300), 60 parts by mass of isobornyl acrylate, and 0.5 parts by mass of a photopolymerization initiator (Omnirad1173, manufactured by IGM Resin) were mixed to obtain an energy ray-curable acrylic adhesive composition.

[0153] (2) Surface protection sheet As the surface protection sheet, surface protection sheet A shown below was used.

[0154] A composition for an intermediate layer was obtained by blending 48 parts by mass of a urethane acrylate oligomer (CN9021 NS, manufactured by Arkema Co., Ltd.), 26 parts by mass of isobornyl acrylate, 16 parts by mass of trimethylcyclohexyl acrylate, and 10 parts by mass of lauryl acrylate, for a total of 100 parts by mass, with 3.4 parts by mass of a photopolymerization initiator (Omnirad1173, manufactured by IGM Resin Co., Ltd.) and 1.0 part by mass of a chain transfer agent (Karenz MT PE1, manufactured by Showa Denko K.K.).

[0155] The obtained intermediate layer composition was applied by knife coating onto a substrate PET film (manufactured by Toray Industries, Inc., thickness 75 μm) to a thickness of 400 μm to form an intermediate layer composition layer. Immediately after application, a PET-based release film (manufactured by Lintec Corporation, SP-PET752150, thickness 75 μm) was further laminated onto the intermediate layer composition layer. Thereafter, a high-pressure mercury lamp was used to illuminate the intermediate layer composition layer at an illumination intensity of 120 mW / cm. 2 , light intensity 240mJ / cm 2 The intermediate layer composition layer was irradiated with ultraviolet light under the conditions of 330 mW / cm illuminance using a metal halide lamp. 2 , light intensity 1260mJ / cm 2 The intermediate layer composition layer was cured by irradiating ultraviolet light under the above conditions, thereby forming an intermediate layer having a thickness of 400 μm on the PET film substrate.

[0156] Next, 80 parts by mass of 2-ethylhexyl acrylate (2EHA) and 20 parts by mass of 2-hydroxyethyl acrylate (HEA) were copolymerized to obtain an acrylic copolymer, to which 2-isocyanatoethyl methacrylate (MOI) was added so that the addition ratio was 80 equivalents relative to the hydroxyl group (100 equivalents) derived from HEA. To the energy ray curable acrylic copolymer (weight average molecular weight: 800,000) obtained by adding 1.5 parts by mass of trimethylolpropane adduct tolylene diisocyanate (manufactured by Tosoh, Coronate L) as a crosslinking agent and 2.2 parts by mass of 2,2-dimethoxy-2-phenylacetophenone (manufactured by IGM Resin, Omnirad651) as a photopolymerization initiator, toluene was further added to adjust the solid content concentration to 30%, and the mixture was stirred for 30 minutes to prepare a pressure-sensitive adhesive composition.

[0157] Next, the prepared solution of the adhesive composition was applied to a PET-based release film (manufactured by Lintec Corporation, SP-PET382150, thickness 38 μm) and dried to form an adhesive layer with a thickness of 10 μm, thereby producing an adhesive sheet.

[0158] The release film on the intermediate layer obtained above was removed, and the intermediate layer was laminated with the adhesive layer of the adhesive sheet to produce surface protection sheet A having a substrate / intermediate layer / adhesive layer configuration.

[0159] (Wafer warpage evaluation) A silicon wafer (760 μm thick) with bump electrodes, each with a bump electrode height of 200 μm and a pitch of 400 μm, was prepared. A functional film-forming composition was applied to the surface of this silicon wafer with bump electrodes by spin coating, and the functional film-forming composition was heat-cured to form a functional film by heating at 350° C. for 2 hours, and then cooled. The functional film formed was a polyimide film with a thickness of 4 μm. It is assumed that residual stress was generated in this polyimide film due to the heat curing and cooling during film formation.

[0160] The energy ray curable resin obtained above was applied to the outer periphery (on the polyimide film) of this silicon wafer with bump electrodes, where no bump electrodes were formed, using a dispenser (Musashi Engineering, Shotmaster350DS), to a thickness of 70 μm and a width of 2 mm, so that no gap was formed between the outer edge of the wafer. The applied energy ray curable resin was irradiated with ultraviolet light (illuminance 230 mW / cm 2 , light intensity 200mJ / cm 2 ) and curing to form a convex pattern.

[0161] A surface protection sheet was attached to the silicon wafer with bump electrodes after the convex pattern was formed using a tape laminator (manufactured by Lintec Corporation, RAD-3510F / 12) under the condition that the temperature of the lamination table was 65°C. The wafer after the surface protection sheet was attached was placed on the chuck table so that the surface protection sheet was in contact with the chuck table, and the wafer was fixed to the chuck table by suction. Next, the back surface of the wafer was ground with a grinding wheel, and the grinding was terminated when the thickness of the wafer became 250 μm. Thereafter, the wafer was placed on a flat plate with the ground surface (wafer back surface) facing down, and the maximum distance between the ground surface and the flat plate was measured to evaluate the amount of warping of the wafer. In this example, the amount of warping of the wafer was judged to be good when it was 2.0 mm or less. The results are shown in Table 1.

[0162] (Transportability evaluation) The ground wafer obtained above was placed at a predetermined position in a peeling device (manufactured by Lintec Corporation, RAD-3010F / 12) and transported to a peeling operation position. At the peeling operation position, the adhesive layer of the surface protection sheet attached to the ground wafer was irradiated with ultraviolet light (illuminance 230 mW / cm 2 , irradiation amount 1200mJ / cm 2 The above-mentioned operation was carried out in a fully automated manner, and the conveyability was evaluated according to the following criteria. ○: The wafer was transported to the peeling operation position and peeling was also possible with full automation. ×: The wafer was not sufficiently adsorbed during full-automatic operation, and it was not possible to transport it to the peeling operation position.

[0163] Comparative Example 1 Except for not forming a convex pattern, the amount of wafer warpage and transportability were evaluated in the same manner as in Example 1. The results are shown in Table 1.

[0164] [Table 1]

[0165] From Table 1, it was confirmed that by forming a convex pattern, the warpage of the wafer after back grinding was reduced and the wafer transportability was improved. [Explanation of symbols]

[0166] 1...Work (wafer) 2a...Convex electrode 3…Convex pattern 5...Functional membrane 10...Surface protection sheet 11...Base material 12...Adhesive layer 13. Middle class 14...Buffer layer

Claims

1. A surface protective sheet is attached to a workpiece having a surface and a back surface opposite to the surface, in which residual stress is generated; and grinding the back surface of the workpiece to which the surface protection sheet is attached. A method for processing a workpiece having a convex pattern formed on its surface before the surface protective sheet is attached to the surface.

2. The method for machining a workpiece according to claim 1 , wherein the surface has an inner periphery and an outer periphery surrounding the inner periphery, and the convex pattern is formed on the outer periphery.

3. 3. The method for machining a workpiece according to claim 1, wherein the workpiece in which the residual stress occurs has a functional film formed on at least a portion of the surface of the workpiece.

4. The method for machining a workpiece according to claim 1 , wherein the surface has a height difference.

5. A method for machining a workpiece as described in claim 4, wherein the surface has an inner circumference and an outer circumference surrounding the inner circumference, the height of the outer circumference is lower than the height of the inner circumference, and the convex pattern is formed on the outer circumference.

6. 6. The method for machining a workpiece according to claim 4, wherein the workpiece has a convex electrode formed on the surface thereof.

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

8. The method for processing a workpiece according to claim 1 or 2, wherein the surface protection sheet has a base material and an adhesive layer.

9. A step of forming a groove on the surface of the workpiece before the step of attaching a surface protection sheet to the surface of the workpiece, 3. The method for machining a workpiece according to claim 1, wherein in the step of grinding the rear surface of the workpiece, the workpiece is diced into a plurality of workpiece pieces starting from grooves.

10. A process for forming a modified region inside the workpiece before the process for grinding the back surface of the workpiece, 3. The method for machining a workpiece according to claim 1, wherein in the step of grinding the rear surface of the workpiece, the workpiece is diced into a plurality of workpiece pieces starting from modified regions.

Images