Protective sheet and how to use the protective sheet

Abstract

To provide a protective sheet that allows easy positioning of a protective layer with respect to a transfer device, an adherend and the like.SOLUTION: A protective sheet according to the present invention comprises a protective layer attached to an adherend, and a release liner provided on a surface of the protective layer. The protective layer contains a water-soluble polymer. The release liner is provided with an inner surface that faces the protective layer, and an outer surface that serves as an opposite surface from the inner surface. An optical transmittance of transmission from the outer surface of the release liner through the protective layer is at least 15% lower than an optical transmittance of the release liner at least at one wavelength.SELECTED DRAWING: Figure 1A

Description

[Technical Field]

[0001] The present invention relates to a protective sheet. [Background technology]

[0002] Conventionally, in the manufacture of electronic components such as semiconductor elements such as semiconductor chips and liquid crystal display devices, it has been known to use adhesive protective sheets to prevent foreign matter from adhering to the electronic components (for example, Patent Document 1 below). Patent Document 1 below discloses a protective sheet comprising a protective layer formed from a resin composition containing an oxyalkylene group-containing polyvinyl alcohol-based resin, and two release sheets disposed on both sides of the protective layer.

[0003] Among the manufacturing methods of the above electronic components, the manufacturing of semiconductor chips is usually carried out by dividing (cutting) one semiconductor wafer (for example, Patent Document 2 below). For example, Patent Document 2 below discloses that semiconductor chips are manufactured as follows. (1) A plurality of dividing lines are formed in a grid pattern on one surface of a silicon wafer. (2) A circuit pattern is formed and electrodes are arranged in each of the areas partitioned in a grid pattern by the plurality of planned division lines (hereinafter also referred to as grid-shaped partitioned areas), thereby producing a semiconductor wafer for obtaining semiconductor chips. (3) The semiconductor wafer is divided (cut) along the plurality of planned dividing lines, in other words, the semiconductor wafer is divided (cut) into the grid-shaped partitioned regions to obtain a plurality of semiconductor chips. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent Publication No. 2021-161735 [Patent Document 2] Japanese Patent Application Laid-Open No. 2012-119670 Summary of the Invention [Problem to be solved by the invention]

[0005] As described above, when a single semiconductor wafer is divided (cleaved) to obtain multiple semiconductor chips, a small amount of dust may be generated due to the powdering of a portion of the semiconductor wafer near the division (cleavage) portion. If such dust adheres to one surface side of the semiconductor chip (the side on which the circuit pattern is formed), this is undesirable because it may reduce the operational reliability of the circuit contained in the circuit pattern formed on the one surface side. Therefore, when manufacturing semiconductor chips, it is conceivable to protect the semiconductor chips by attaching the protective sheet to one surface side (the side on which the circuit pattern is formed) of one semiconductor wafer. It is believed that such a protective sheet would be useful if it had a water-soluble protective layer that can be easily removed from the adherend, such as a semiconductor wafer, after use.

[0006] When applying a protective sheet to an adherend such as a semiconductor wafer, possible methods include cutting the protective sheet to a predetermined shape, placing it in a laminating device, and applying it to the adherend, or directly applying the protective sheet cut to a predetermined shape to the adherend. Furthermore, it is believed that providing a gripping area on the release liner is effective in facilitating alignment of the protective layer and peeling the release liner from the protective layer when setting it in a laminating device or when directly attaching it to an adherend. However, doing so would cause the release liner to extend beyond the outer edge of the protective layer, and the outer edge of the release liner would no longer coincide with the outer edge of the protective layer, making it difficult to accurately determine the position of the protective layer from the release liner side and potentially making it difficult to align the protective layer. Therefore, an object of the present invention is to provide a protective sheet that allows easy alignment of the protective layer with respect to a transfer device, an adherend, or the like. [Means for solving the problem]

[0007] That is, the protective sheet according to the present invention is a protective layer attached to the adherend; a release liner disposed on the surface of the protective layer, the protective layer contains a water-soluble polymer, the release liner has an inner surface facing the protective layer and an outer surface opposite the inner surface, The light transmittance from the outer surface of the release liner through the protective layer is at least 15% lower than the light transmittance of the release liner at least at one wavelength.

[0008] The protective sheet according to the present invention also comprises: a protective layer attached to the adherend; a first release liner disposed on one surface of the protective layer; a second release liner disposed on the other surface of the protective layer; the protective layer contains a water-soluble polymer compound, each of the first release liner and the second release liner has an inner surface facing the protective layer and an outer surface opposite the inner surface; The light transmittance from the outer surface of the second release liner to the outer surface of the first release liner is at least 15% less than the light transmittance of the second release liner at at least one wavelength. [Effects of the Invention]

[0009] According to the present invention, it is possible to provide a protective sheet that allows easy alignment of the protective layer with respect to a transfer device, an adherend, or the like. [Brief explanation of the drawings]

[0010] [Figure 1A] 1 is a schematic cross-sectional view showing the configuration of a protective sheet according to one embodiment of the present invention. [Figure 1B]FIG. 4 is a schematic cross-sectional view showing the configuration of a protection sheet according to another embodiment of the present invention. [Figure 2A] FIG. 3 is a schematic cross-sectional view showing one embodiment of cutting the protective layer in the protective sheet according to one embodiment of the present invention. [Figure 2B] FIG. 4 is a schematic cross-sectional view showing one embodiment of cutting the protective layer to obtain a protective sheet according to another embodiment of the present invention. [Figure 2C] FIG. 10 is a schematic cross-sectional view showing an example of obtaining a protective sheet according to another embodiment by laminating a first release liner to the exposed surface of a protective layer. [Figure 3A] FIG. 10 is a schematic cross-sectional view showing how the position of the protective layer obtained by post-precutting is detected using a sensing device. [Figure 3B] 10 is a schematic cross-sectional view showing how a protective layer obtained by post-precutting is bonded to a surface of a semiconductor wafer to be protected using a mounting device. FIG. [Figure 3C] 1 is a schematic cross-sectional view showing a state in which a protective layer is bonded to a surface to be protected of a semiconductor wafer. [Figure 4A] FIG. 10 is a schematic cross-sectional view showing how the position of the protective layer obtained by pre-cutting is detected using a sensing device. [Figure 4B] 1 is a schematic cross-sectional view showing how a protective layer obtained by pre-cutting is bonded to a surface of a semiconductor wafer to be protected using a laminating device. [Figure 4C] 1 is a schematic cross-sectional view showing a state in which a protective layer is bonded to a surface to be protected of a semiconductor wafer. DETAILED DESCRIPTION OF THE INVENTION

[0011] An embodiment of the present invention will be described below.

[0012] [Protective sheet according to the first embodiment] As shown in Figures 1A and 1B, the protective sheet 10 according to the first embodiment of the present invention comprises a protective layer 1, a first release liner 2 disposed on one surface of the protective layer 1, and a second release liner 3 disposed on the other surface of the protective layer 1. In the protective sheet 10 according to the first embodiment, the protective layer 1 contains a water-soluble polymer compound. That is, the protective layer 1 is water-soluble. On the other hand, the first release liner 2 and the second release liner 3 are water-insoluble.

[0013] The protective layer 1 of this embodiment has adhesiveness sufficient to allow it to be attached to an adherend. The protective layer 1 of this embodiment preferably has tackiness (pressure-sensitive adhesiveness). The protective sheet 10 of this embodiment is used to prevent foreign matter from adhering to the surface of an adherend (in this embodiment, a "semiconductor wafer") while various treatments are being performed on the adherend by adhering the protective layer 1 to the adherend.

[0014] The first release liner 2 and the second release liner 3 are each attached to the protective layer 1 to prevent foreign matter from adhering to the protective layer 1 before it is attached to the semiconductor wafer. Each of the first release liner 2 and the second release liner 3 has an inner surface facing the protective layer 1 and an outer surface opposite the inner surface. Protective sheet 10 of this embodiment is used by peeling off second release liner 3 and adhering the other surface of protective layer 1 to a semiconductor wafer.

[0015] In this embodiment, as will be described later, the surface to be protected of the adherend and the protective layer 1 are accurately positioned, and then the protective layer 1 is attached to the surface to be protected. Positioning may be indirect rather than direct. For example, when the protective layer 1 is set in a laminating device where the adherend is expected to be placed at a predetermined position and the protective layer 1 is bonded to the adherend using the laminating device, the protective layer 1 can be positioned on the adherend by positioning the protective layer 1 in the laminating device.

[0016] In this embodiment, at the time of positioning, the protective layer 1 is not stuck to the entire surface of the second release liner 3, but is provided so as to partially cover the inner surface of the second release liner 3. In this embodiment, when positioned, the protective sheet 10 has a laminated region where the second release liner 3 and the protective layer 1 are laminated, and a single-layer region where the second release liner 3 is the only liner, with no protective layer 1 laminated thereon, and the single-layer region is arranged to surround the laminated region.

[0017] In the protective sheet 10 according to the first embodiment, the light transmittance of the second release liner 3 is higher than the light transmittance of either the protective layer 1, the first release liner 2, or the laminate of the protective layer 1 and the first release liner 2. More specifically, in this embodiment, the light transmittance from the outer surface of the second release liner until it passes through the protective layer 1 is at least 15% lower than the light transmittance of the second release liner 3 at at least one wavelength, or the light transmittance from the outer surface of the second release liner 3 to the outer surface of the first release liner 2 is at least 15% lower than the light transmittance of the second release liner 3 at at least one wavelength.

[0018] In the protective sheet 10 according to the first embodiment, the transmittance T of the second release liner 3 measured at a wavelength included in the near-infrared region is A and the transmittance T of the protective layer 1 measured at the one wavelength. B The difference between AB and the transmittance T A and the transmittance T of the first release liner 2 measured at the one wavelength C The difference between AC and the transmittance T A and the transmittance T of the laminate of the protective layer 1 and the first release liner 2 measured at the one wavelength. D The difference between AD When the above ΔT AB , the ΔT AC , or the ΔT AD However, it is more than 15%.

[0019] In this specification, the near-infrared region refers to a region with wavelengths of 800 nm or more and 2500 nm or less. In the first embodiment of the present invention, it is preferable to use a wavelength of 1060 nm as one wavelength included in the near-infrared region.

[0020] The protective layer 1 is used by being attached to the surface of an electronic component to be protected. The electronic component may be, for example, a semiconductor wafer. The semiconductor wafer may be a semiconductor wafer having grid-shaped partitioned areas (hereinafter also referred to as grid-shaped partitioned areas) formed on one surface side, in which a circuit pattern is formed in each of the grid-shaped partitioned areas and an electrode portion is arranged. When the electronic component is a semiconductor wafer as described above, the protective layer 1 is used by being attached to one surface of the semiconductor wafer. In this way, by bonding the protective layer 1 to one surface of the semiconductor wafer, it is possible to prevent minute foreign matter that is generated when the semiconductor wafer is divided (fractured) to obtain multiple semiconductor chips and a part of the semiconductor wafer near the dividing portion (fractured portion) is powdered from adhering to each circuit pattern formed on the one surface (circuit pattern formed for each of the grid-shaped divided areas) and each electrode portion arranged on the one surface (electrode portion arranged for each of the grid-shaped divided areas).

[0021] In protective sheet 10 shown in FIG. 1A, protective layer 1, first release liner 2, and second release liner 3 have approximately the same dimensions in plan view. The protective layer 1 usually has a size larger than the surface of the electronic component to be protected in a plan view.

[0022] The protective sheet 10 of this embodiment is used to protect a semiconductor wafer, for example, in the following manner. (a) After one and the other release liners (2, 3) are laminated on both sides of the protective layer 1 to obtain the protective sheet, the laminate is cut so that the planar dimensions of the laminate of one release liner (first release liner 2) and the protective layer 1 are approximately the same as the planar dimensions of one semiconductor wafer (post-precutting method). That is, in the post-precut method, the protective sheet 10 is configured such that the protective layer 1 is sandwiched between another release liner (second release liner 3) having planar dimensions larger than the protective layer 1 and one release liner (first release liner 2) having planar dimensions approximately the same as those of the protective layer 1.

[0023] The protective sheet 10 of this embodiment can also be used to protect a semiconductor wafer in the following manner. (b) After one release liner (first release liner 2) is laminated on one surface of the protective layer 1, only the protective layer 1 is cut so that its planar dimensions are approximately the same as those of the semiconductor wafer (first pre-cutting method). Then, on the other surface of the cut protective layer 1, another release liner having planar dimensions larger than those of the protective layer 1 (for example, a release liner (second release liner 3) having planar dimensions approximately the same as those of the one release liner) is laminated. That is, in the pre-cut method, the protective sheet 10 is configured such that the protective layer 1 is sandwiched between two release liners (one and the other release liner) having planar dimensions larger than that of the protective layer 1.

[0024] As explained in (a) above, in one aspect of this embodiment, when the protective layer 1 is bonded to the surface of the electronic component to be protected, the protective layer 1, while in a laminated state with the first release liner 2, is cut from the first release liner 2 side so that it has approximately the same planar dimensions as the surface of the electronic component to be protected (see Figure 2A). That is, in the protective sheet 10 shown in FIG. 1A, the protective layer 1 is made to have substantially the same dimensions as the surface of the electronic component to be protected by a post-precutting method.

[0025] In protective sheet 10 shown in FIG. 1A, first release liner 2 and second release liner 3 have approximately the same dimensions in plan view, and these plan dimensions are larger than the surface of the electronic component to be protected. In contrast, in protective sheet 10 shown in FIG. 1B, protective layer 1 has substantially the same dimensions as the surface of the electronic component to be protected in plan view. Specifically, the protective layer 1 is laminated with one of the release liners, for example, the first release liner 2, and then cut (see Figure 2B) to have planar dimensions approximately the same as the surface of the electronic component to be protected. That is, in protective sheet 10 shown in FIG. 1B, protective layer 1 is pre-cut to have approximately the same dimensions as the surface of the electronic component to be protected. The other release liner, for example, second release liner 3, is attached to the exposed surface of protective layer 1 after protective layer 1 has been cut (see FIG. 2C).

[0026] The second release liner 3 may be in the form of a long strip having a longitudinal direction and a lateral direction. The protective sheet 10 comprises a strip-shaped second release liner 3 and multiple protective layers 1 having the same shape as the surface to be protected, and the multiple protective layers 1 may be arranged in a line in the longitudinal direction of the second release liner 3, or a fixed distance may be provided between adjacent protective layers 1 in the longitudinal direction. In this case, the first release liner 2 may be strip-shaped like the second release liner 3, or may have the same shape as the surface to be protected like the protective layer 1.

[0027] The second release liner 3 may be larger than the protective layer 1 not only in the longitudinal direction but also in the lateral direction. That is, in protective sheet 10 , second release liner 3 may extend outward beyond the outer peripheral edge of protective layer 1 , and the extension of second release liner 3 may occur along the entire periphery of protective layer 1 .

[0028] The protective sheet 10 can be produced, for example, as follows. (1) Using an applicator or the like, a water-soluble resin composition containing a water-soluble polymer compound and an excess liquid component is applied to the first release liner 2 in a predetermined thickness (for example, 10 μm). (2) The applied water-soluble resin composition is dried at a predetermined temperature for a predetermined time (for example, 2 minutes at 110° C.), thereby forming a protective layer 1 containing a water-soluble polymer compound on the first release liner 2. (3) A second release liner 3 is attached to the surface of the protective layer 1 opposite to the surface on which the first release liner 2 is disposed (the exposed surface of the protective layer 1). In the production of the protective sheet 10 shown in Figure 1B, between the above steps (2) and (3), a step (step (2'), see Figure 2B) is carried out in which the protective layer 1 is cut so that it has approximately the same planar dimensions as the surface of the electronic component to be protected.

[0029] In the protective sheet 10 according to the first embodiment, the protective layer 1 is preferably prepared using a water-soluble resin composition containing a water-soluble polymer compound and an excess liquid content, the water-soluble polymer compound being dispersed in water (hereinafter referred to as the protective layer-forming composition). The protective layer-forming composition preferably contains 5 to 80 parts by weight of the water-soluble polymer compound per 100 parts by weight of water, more preferably 10 to 70 parts by weight, and even more preferably 15 to 60 parts by weight. In addition, in the protective layer-forming composition, the water-soluble polymer compound is preferably dissolved in water. In the protective layer-forming composition, the water-soluble polymer compound can be dissolved in water by treating at a temperature of 20 to 90°C. Furthermore, the protective layer-forming composition preferably has a viscosity at 25° C. of 0.03 Pa·s or more, more preferably 0.05 Pa·s or more, and even more preferably 0.1 Pa·s or more. By ensuring that the viscosity at 25°C is equal to or greater than the above-mentioned lower limit, when the protective layer-forming composition is applied to a first release liner 2 to form a protective layer 1 on the first release liner 2, the thickness of the protective layer 1 can be prevented from easily fluctuating. The protective layer-forming composition preferably has a viscosity at 25° C. of 15 Pa·s or less, more preferably 10 Pa·s or less, and even more preferably 5 Pa·s or less. When the viscosity at 25° C. is equal to or greater than the above upper limit, the coating properties of the protective layer-forming composition when it is applied onto the first release liner 2 can be improved. The viscosity of the protective layer-forming composition at 25°C can be measured using a digital viscometer (product name "DV-I Prime") manufactured by Eiko Seiki Co., Ltd. as the measuring device, using an LV-3 spindle and adopting conditions of a rotation speed of 50 rpm.

[0030] Examples of the water-soluble polymer compound include polyvinyl alcohol (PVA), polyvinylpyrrolidone (PVP), water-soluble polyester (PES), and polyethylene oxide (PEO). The water-soluble polymer compound may be polyvinyl alcohol, polyvinylpyrrolidone, water-soluble polyester, polyethylene oxide, or the like, which may be used alone or in combination of two or more thereof. As the water-soluble polymer compound, it is preferable to use at least one selected from the group consisting of polyvinyl alcohol, water-soluble polyester, and polyethylene oxide, and it is more preferable to use polyvinyl alcohol.

[0031] The polyvinyl alcohol preferably has a degree of saponification of 50 or more and 98 or less, more preferably 60 or more and 90 or less. By having a degree of saponification within the above numerical range, the polyvinyl alcohol can exhibit sufficient water solubility, and when the polyvinyl alcohol is contained in the protective layer-forming composition, the protective layer-forming composition can be applied to the first release liner 2 with good workability. The degree of saponification of the polyvinyl alcohol was determined by proton magnetic resonance spectroscopy ( 1 It can be measured by H-NMR measurement. In addition, when the measurement sample contains an additive and the peak derived from the additive overlaps with the peak used for calculating the degree of saponification, the measurement sample is subjected to methanol extraction or the like to separate the additive, and then the degree of saponification of the polyvinyl alcohol is measured. The degree of saponification of the polyvinyl alcohol can be measured under the following conditions. <Measurement conditions> ·Analyzer FT-NMR: Bruker Biospin, AVANCE III-400 Observation frequency: 400MHz (1H) Measurement solvent: deuterated water or deuterated dimethyl sulfoxide (deuterated DMSO) ·Measurement temperature 80℃ ·Chemical shift standard External standard TSP-d4 (0.00ppm) (when measuring heavy water) Measurement solvent (2.50 ppm) (when measuring deuterated DMSO) The degree of saponification of the polyvinyl alcohol is calculated based on the following formula using the peaks derived from the methylene groups of the vinyl alcohol unit (VOH) (heavy water: 2.0 to 1.0 ppm, deuterated DMSO: 1.9 to 1.0 ppm) and the peaks derived from the acetyl groups of the vinyl acetate unit (VAc) (heavy water: around 2.1 ppm, deuterated DMSO: around 2.0 ppm). In the following formula, [VOH(-CH2)-] means the intensity of the peak derived from -CH2- in the vinyl alcohol unit, and [VAc(CH3CO-)] means the intensity of the peak derived from CH3CO- in the vinyl acetate unit.

[0032]

number

[0033] The polyvinyl alcohol preferably has an average degree of polymerization of 100 or more and 1,000 or less, and more preferably 100 or more and 800 or less. By having an average degree of polymerization within the above numerical range, the polyvinyl alcohol can exhibit sufficient water solubility, and when the polyvinyl alcohol is contained in the protective layer-forming composition, the protective layer-forming composition can be applied to the first release liner 2 with good workability. The average degree of polymerization of the polyvinyl alcohol can be measured by aqueous GPC. The average degree of polymerization of the polyvinyl alcohol can be measured under the following conditions. <Measurement conditions> ·Analyzer Agilent, 1260Infinity Columns: TSKgel G6000PWXL (Tosoh Corporation) and TSKgel G3000PWXL (Tosoh Corporation) The two columns are connected in series. Column temperature: 40℃ Eluent: 0.2M aqueous sodium nitrate solution ·Injection volume 100μL Detector: Differential refractometer (RI) Standard samples: PEG standard sample and PVA standard sample The specific measurement is carried out as follows. (1) The mass-average molecular weights Mw of the sample (PVA) and the PVA standard sample are calculated by GPC measurement using a PEG standard sample. The PVA standard sample has a known average degree of polymerization. (2) A calibration curve is prepared using the average degree of polymerization of the PVA standard sample and the calculated mass average molecular weight Mw of the PVA standard sample. (3) Using the created calibration curve, the average degree of polymerization of the sample (PVA) to be measured is determined from the mass average molecular weight Mw of the sample (PVA).

[0034] When polyvinyl alcohol is used as the water-soluble polymer, a plurality of polyvinyl alcohols having different degrees of saponification may be used in combination, or a plurality of polyvinyl alcohols having different average degrees of polymerization may be used in combination.

[0035] The water-soluble polyester has a residue of a polycarboxylic acid and a residue of a polyol. The water-soluble polyester is, for example, a polymerization product of a monomer component including a polycarboxylic acid component and a polyol component. Whether the water-soluble polyester has water solubility can be determined based on common technical knowledge.

[0036] The water-soluble polyester preferably satisfies at least one of the following (1) to (4). (1) When water at room temperature (23±2°C) is sprayed onto the entire surface of a 20 μm-thick thin film formed from the water-soluble polyester at a spray pressure of 0.005 MPa for 20 minutes, the entire thin film dissolves in water. (2) When water at 50° C. is sprayed onto the entire surface of a 20 μm-thick thin film formed from the water-soluble polyester at a spray pressure of 0.005 MPa for 10 minutes, the thin film dissolves completely in water. (3) The water-soluble polyester and room temperature water are mixed in a mass ratio of water-soluble polyester:room temperature water=1:5 to obtain a mixed solution, and when the mixed solution is irradiated with ultrasound for 20 minutes, the water-soluble polyester is completely dissolved in the water. (4) The water-soluble polyester and 50°C water are mixed in a mass ratio of water-soluble polyester:50°C water=1:5 to obtain a mixed solution, and when the mixed solution is irradiated with ultrasound for 10 minutes, the water-soluble polyester is completely dissolved in the water.

[0037] The thickness of the protective layer 1 is preferably 2 μm or more and 70 μm or less, more preferably 3 μm or more and 50 μm or less, and even more preferably 5 μm or more and 40 μm or less. The thickness of the protective layer 1 can be determined, for example, by measuring the thickness at five randomly selected points using a dial gauge (manufactured by PEACOCK, model R-205) and calculating the arithmetic mean of these thicknesses.

[0038] The first release liner 2 may be, for example, a resin sheet made from a resin such as polyethylene terephthalate (PET). At least the surface of the resin sheet to be bonded to the protective layer 1 may be subjected to a release treatment. The release treatment may be silicone release treatment. The second release liner 3 may be the same as the first release liner 2 .

[0039] The thickness of the first release liner 2 and the second release liner 3 is preferably 15 μm or more and 75 μm or less, and more preferably 20 μm or more and 60 μm or less. The thickness of the first release liner 2 and the second release liner 3 may be the same or different. The thicknesses of the first release liner 2 and the second release liner 3 can be determined in the same manner as the thickness of the protective layer 1 .

[0040] As explained above, in the protective sheet 10 according to the first embodiment, the transmittance of the second release liner 3 is higher than the transmittance of either the protective layer 1, the first release liner 2, or the laminate of the protective layer 1 and the first release liner 2. Furthermore, in the protective sheet 10 according to the first embodiment, the transmittance T of the second release liner 3 measured at a wavelength included in the near-infrared region is A and the transmittance T of the protective layer 1 measured at the one wavelength. B The difference between AB and the transmittance T Aand the transmittance T of the first release liner 2 measured at the one wavelength C The difference between AC and the transmittance T A and the transmittance T of the laminate of the protective layer 1 and the first release liner 2 measured at the one wavelength. D The difference between AD When the above ΔT AB , the ΔT AC , or the ΔT AD However, it is more than 15%. In addition, the transmittance T A means the ratio when light of the one wavelength is transmitted through the second release liner 3 in the thickness direction, and the transmittance T B means the ratio when light of the one wavelength is transmitted through the protective layer 1 in the direction parallel to the thickness direction, and the transmittance T C means the ratio of light of one wavelength transmitted through the first release liner 2 in the thickness direction, and transmittance T D means the ratio at which light of one wavelength passes through the laminate of the protective layer 1 and the first release liner 2 in the direction parallel to the thickness direction. That is, the transmittance T A ~T D means the parallel ray transmittance.

[0041] Light included in the near-infrared region, that is, near-infrared light, has an extremely long wavelength, and therefore when irradiated onto an object, it easily passes through the object in a direction parallel to the thickness direction. Therefore, the above ΔT AB In order to make ΔT 15% or more, it is necessary to prevent light of one wavelength included in the near-infrared region from passing through the protective layer 1 in a direction parallel to the thickness direction. AC In order to make ΔT 15% or more, it is necessary to prevent the light of one wavelength from passing through the first release liner 2 in a direction parallel to the thickness direction. AD In order to make the transmittance 15% or more, it is necessary to prevent the light of the one wavelength from passing through the laminate of protective layer 1 and first release liner 2 in a direction parallel to the thickness direction. Specifically, it is necessary to absorb a portion of the light of one wavelength that passes through the protective layer 1 or the first release liner 2 parallel to the thickness direction, or to diffusely reflect a portion of the light of one wavelength that passes through the protective layer 1 or the first release liner 2 parallel to the thickness direction.

[0042] An example of the treatment for preventing light of one wavelength from passing through the protective layer 1 in a direction parallel to the thickness direction is to include a pigment in the protective layer-forming composition for forming the protective layer 1. By including a pigment in the protective layer 1, even if the light is near-infrared light such as the light of the one wavelength, the pigment can absorb a part of the light of the one wavelength. Furthermore, the pigment can cause a portion of the light of the one wavelength to be diffusely reflected.

[0043] As the pigment, any known pigment can be used. Examples of the pigment include inorganic pigments such as zinc carbonate, zinc oxide, zinc sulfide, talc, kaolin, calcium carbonate, titanium oxide, silica, lithium fluoride, calcium fluoride, barium sulfate, alumina, zirconia, iron oxide, iron hydroxide, chromium oxide, fired spinel, chromate, chrome vermilion, iron blue, aluminum powder, bronze powder, and calcium phosphate; and organic pigments such as phthalocyanine, azo, condensed azo, azo lake, anthraquinone, perylene-perinone, indigo-thioindigo, isoindolinone, azomethane, and carbon black.

[0044] The protective layer 1 preferably contains 0.1 parts by mass or more of the pigment per 100 parts by mass of the water-soluble polymer compound, more preferably 0.5 parts by mass or more, and even more preferably 1.0 part by mass or more. Furthermore, the protective layer 1 preferably contains 30 parts by mass or less of the pigment per 100 parts by mass of the water-soluble polymer compound, more preferably 20 parts by mass or less, and even more preferably 10 parts by mass or less. The pigment means a colorant that does not dissolve in organic solvents such as water or alcohol.

[0045] Another example of a treatment that prevents light of one wavelength from passing through the protective layer 1 in a direction parallel to the thickness direction is to subject the protective layer-forming composition used to form the protective layer 1 to a foaming treatment. The protective layer 1 formed from the protective layer-forming composition that has been subjected to such foaming treatment will contain a plurality of bubbles. This allows diffuse reflection to occur in the multiple bubbles contained in the protective layer 1, thereby reducing the proportion of near-infrared light, such as the light of one wavelength, that passes through the protective layer 1 parallel to the thickness direction.

[0046] As explained above, when the first release liner 2 is a resin sheet made using a resin such as polyethylene terephthalate (PET), a treatment that prevents the light of one wavelength from passing through the first release liner 2 parallel to the thickness direction can be performed by subjecting the resin composition used to make the resin sheet to a foaming treatment. The resin sheet (resin foam sheet) obtained by subjecting the resin composition to foaming treatment contains a plurality of bubbles, and the bubbles can cause diffused reflection. This makes it possible to reduce the proportion of near-infrared light, such as the light of one wavelength, that is transmitted through the first release liner 2 in the direction parallel to the thickness direction. Furthermore, when the first release liner 2 is a resin sheet made using a resin such as polyethylene terephthalate (PET), the resin sheet may be subjected to a foaming treatment. For example, the resin sheet may be stretched and subjected to a foaming treatment to generate voids during the stretching.

[0047] Furthermore, an example of a treatment that prevents the light of one wavelength from passing through the first release liner 2 parallel to the thickness direction is to coat at least one surface of the first release liner 2 with ink containing a pigment such as titanium oxide. By forming a coating layer containing a pigment on at least one surface (inner surface, outer surface, or both surfaces) of the first release liner 2, even if the light is near-infrared light such as the light of the one wavelength, the pigment contained in the coating layer can absorb a portion of the light of the one wavelength. Furthermore, the pigment can cause a portion of the light of the one wavelength to be diffusely reflected.

[0048] Furthermore, the first release liner 2 may be constructed using a resin containing a pigment, and the proportion of light of said wavelength that passes through the first release liner 2 parallel to the thickness direction may be reduced by having the pigment absorb part of the light of said wavelength or by having the pigment diffusely reflect part of the light of said wavelength.

[0049] Furthermore, examples of treatments that prevent light of one wavelength from passing through the first release liner 2 parallel to the thickness direction include matting or embossing at least one surface of the first release liner 2. By subjecting at least one surface of the first release liner 2 to a matte finish or embossing, it is possible to generate diffused reflection at the irregularities on the surface of the first release liner 2 . This makes it possible to reduce the proportion of near-infrared light, such as the light of one wavelength, that is transmitted through the first release liner 2 in the direction parallel to the thickness direction.

[0050] The first release liner 2 may be a laminate film having a light-blocking layer, a laminate film having a resin layer and a metal vapor deposition layer, or an aluminum laminate film.

[0051] The light of the one wavelength is prevented from passing through the laminate of the protective layer 1 and the first release liner 2 in the thickness direction, and the transmittance T A and the transmittance T of the laminate of the protective layer 1 and the first release liner 2 D The difference between AD In order to make the transmittance T Aand the transmittance T of protective layer 1 B The difference between AB , and the transmittance T of the second release liner 3 A and the transmittance T of the first release liner 2 C The difference between AC The total value of these must be 15% or more. For example, ΔT AB is set to 5% or more, and ΔT AC or 10% or more, ΔT AB is set to 10% or more, and ΔT AC can be set to 5% or more. Transmittance T of protective layer 1 B and the transmittance T of the first release liner C can be adjusted in the same manner as described above. Naturally, as explained above, ΔT AB and ΔT AC By setting at least one of the above to 15% or more, the above ΔT AD can be set to 15% or more.

[0052] The difference in transmittance for detecting the presence of protective layer 1 and first release liner 2 through second release liner 3 is preferably 20% or more, and more preferably 25% or more. The difference in transmittance may be 30% or more, 40% or more, or 50% or more. Incidentally, it is also preferable that such a difference in transmittance exists in other embodiments described later.

[0053] The transmittance T of the protective layer 1 measured at the one wavelength B , the transmittance T of the first release liner 2 measured at the one wavelength C , and the transmittance T of the laminate of the protective layer 1 and the first release liner 2 measured at the one wavelength. D From the viewpoint of making the difference as large as possible, the transmittance T A It is preferable that the transmittance of the light of the one wavelength is high. The transmittance T of the second release liner 3 measured at the one wavelength A is preferably 65% ​​or more, more preferably 75% or more, and even more preferably 85% or more. The transmittance T of the second release liner 3 measured at the one wavelength A may be 100% or less, or may be 95% or less.

[0054] The transmittance T of the second release liner 3 at the one wavelength A , the transmittance T of the protective layer 1 at the one wavelength B , the transmittance T of the first release liner 2 at the one wavelength C , and the transmittance T of the laminate of the protective layer 1 and the first release liner 2 at the one wavelength. D can be determined by measuring the parallel ray transmittance at the one wavelength using a spectrophotometer (manufactured by JASCO Corporation, trade name "V-670"). When measuring parallel ray transmittance using a spectrophotometer, the measurement wavelength can be in the range of 190 nm to 3000 nm. Furthermore, the measurement sample for the second release liner 3 can be approximately 50 μm thick, the measurement sample for the protective layer 1 can be approximately 10 μm thick, and the measurement sample for the first release liner 2 can be approximately 40 μm thick. The parallel ray transmittance is measured using a spectrophotometer without using an integrating sphere.

[0055] [Protective sheet according to the second embodiment] The protective sheet 10 according to the second embodiment of the present invention has a transmittance T A’ and the transmittance T of the protective layer 1 measured at the one wavelength. B’ The difference between A’B’ and the transmittance T A’ and the transmittance T of the first release liner 2 measured at the one wavelength C’ The difference between A’C’ and the transmittance T A’and the transmittance T of the laminate of the protective layer 1 and the first release liner 2 measured at the one wavelength. D’ The difference between A’D’ When the above ΔT A’B’ , the ΔT A’C’ , or the ΔT A’D’ The protective sheet 10 has the same structure as the protective sheet 10 according to the first embodiment described above, except that the thickness is 15% or more.

[0056] In this specification, the ultraviolet region refers to a region with wavelengths of 200 nm or more and less than 380 nm. In the second embodiment of the present invention, it is preferable to use a wavelength of 330 nm as the wavelength included in the ultraviolet region.

[0057] The transmittance T A’ ~T D’ is the transmittance T A ~T D Similarly, it means the parallel ray transmittance. In addition, the transmittance T of the second release liner 3 at a wavelength included in the ultraviolet region A’ , the transmittance T of the protective layer 1 at the one wavelength B’ , the transmittance T of the first release liner 2 at the one wavelength C’ , and the transmittance T of the laminate of the protective layer 1 and the first release liner 2 at the one wavelength. D’ can be measured in the same manner as described above.

[0058] Light in the ultraviolet region, i.e., ultraviolet light (ultraviolet rays), has an extremely short wavelength, and therefore when irradiated onto an object, it is more difficult for the light to pass through the object than light with an extremely long wavelength, i.e., near-infrared light, as described above. Therefore, by subjecting the protective layer 1 to the same treatment as described in the first embodiment, the ΔT A’B’ can be made 15% or more, and by subjecting the first release liner 2 to the same treatment as described in the first embodiment above, the ΔT A’C’can be 15% or more, and by subjecting the laminate of the protective layer 1 and the first release liner 2 to the same treatment as described in the first embodiment above, the ΔT A’D’ can be set to 15% or more.

[0059] In addition, by carrying out treatment other than the above, the above ΔT A’B’ , ΔT A’C’ , and ΔT A’D’ can be set to 15% or more. For example, the protective layer 1 may be formed from the protective layer-forming composition containing an ultraviolet absorber, or the first release liner 2 may be formed from a resin containing an ultraviolet absorber, thereby reducing the ΔT A’B’ , the ΔT A’C’ , and ΔT A’D’ can be set to 15% or more.

[0060] Examples of the ultraviolet absorber include triazine-based ultraviolet absorbers, benzotriazole-based ultraviolet absorbers, benzophenone-based ultraviolet absorbers, oxybenzophenone-based ultraviolet absorbers, salicylic acid ester-based ultraviolet absorbers, and cyanoacrylate-based ultraviolet absorbers. These various ultraviolet absorbents may be used alone or in combination of two or more.

[0061] When the protective layer 1 contains the ultraviolet absorber, the protective layer 1 preferably contains 0.1 parts by mass or more of the ultraviolet absorber per 100 parts by mass of the water-soluble polymer compound, more preferably 0.5 parts by mass or more, and even more preferably 1.0 part by mass or more. Furthermore, when the protective layer 1 contains the ultraviolet absorber, the protective layer 1 preferably contains 20 parts by mass or less of the ultraviolet absorber per 100 parts by mass of the water-soluble polymer compound, more preferably 15 parts by mass or less, and even more preferably 10 parts by mass or less.

[0062] Furthermore, the protective layer 1 may be formed from the protective layer-forming composition containing an azo dye, which will be described later, instead of the ultraviolet absorber, or the first release liner 2 may be formed from a resin containing the azo dye, which will be described later. A’B’ , the ΔT A’C’ , and ΔT A’D’ can be set to 15% or more. Examples of the azo dye include yellow dyes that exhibit a yellow color.

[0063] When the protective layer 1 contains the azo dye, the content thereof can be the same as the content of the ultraviolet absorber described above.

[0064] Furthermore, the ΔT can also be reduced by forming the protective layer 1 using the protective layer-forming composition containing the azo dye in addition to the ultraviolet absorber, or by forming the first release liner 2 using a resin containing the azo dye in addition to the ultraviolet absorber. A’B’ , the ΔT A’C’ , and ΔT A’D’ can be set to 15% or more.

[0065] [Protective sheet according to the third embodiment] The protective sheet 10 according to the third embodiment of the present invention has a transmittance T A’’ and the transmittance T of the protective layer 1 measured at the one wavelength. B’’ The difference between A’’B’’ and the transmittance T A’’ and the transmittance T of the first release liner 2 measured at the one wavelength C’’ The difference between A’’C’’ and the transmittance T A’’ and the transmittance T of the laminate of the protective layer 1 and the first release liner 2 measured at the one wavelength. D’’ The difference between A’’D’’ When the above ΔT A’’B’’ , the ΔT A’’C’’ , or the ΔT A’’D’’The protective sheet 10 has the same structure as the protective sheet 10 according to the first embodiment described above, except that the thickness is 15% or more.

[0066] In this specification, the visible region refers to a region of wavelengths equal to or greater than 380 nm and less than 800 nm. In the third embodiment of the present invention, it is preferable to use a wavelength in the range of 550 nm to 650 nm as the wavelength included in the visible region.

[0067] Transmittance T A’’ ~T D’’ is the transmittance T A ~T D Similarly, it means the parallel ray transmittance. The transmittance T of the second release liner 3 at one wavelength included in the visible region is A’’ , the transmittance T of the protective layer 1 at the one wavelength B’’ , the transmittance T of the first release liner 2 at the one wavelength C’’ , and the transmittance T of the laminate of the protective layer 1 and the first release liner 2 at the one wavelength. D’’ can be measured in the same manner as described above.

[0068] Light included in the visible region, i.e., visible light (visible rays), has a shorter wavelength than near-infrared light, and therefore when irradiated onto an object, it is more difficult for the light to pass through the object than near-infrared light. Therefore, by subjecting the protective layer 1 to the same treatment as described in the first embodiment, the ΔT A’’B’’ can be made 15% or more, and by subjecting the first release liner 2 to the same treatment as described in the first embodiment above, the ΔT A’’C’’ can be 15% or more, and by subjecting the laminate of the protective layer 1 and the first release liner 2 to the same treatment as described in the first embodiment above, the ΔT A’’D’’ can be set to 15% or more.

[0069] In addition, the ΔT can also be reduced by forming the protective layer 1 using the protective layer-forming composition containing a component that absorbs visible light, or by forming the first release liner 2 using a resin containing a component that absorbs visible light. A’’B’’ , the ΔT A’’C’’ , and ΔT A’’D’’ can be set to 15% or more. An example of a component that absorbs visible light is a dye. The dye refers to a colorant that is soluble in water, organic solvents, or the like.

[0070] Examples of the dye include azo dyes, anthraquinone, quinonephthalone, styryl, diphenylmethane, triphenylmethane, oxazine, triazine, xanthan, methane, azomethine, acridine, and diazine.

[0071] When the dye is contained in the protective layer 1, the protective layer 1 preferably contains 0.1 parts by mass or more of the dye per 100 parts by mass of the water-soluble polymer compound, more preferably 0.5 parts by mass or more, and even more preferably 1.0 part by mass or more. When the protective layer 1 contains the dye, the protective layer 1 preferably contains 30 parts by weight or less of the dye per 100 parts by weight of the water-soluble polymer compound, more preferably 20 parts by weight or less, and even more preferably 10 parts by weight or less.

[0072] In the protective sheets 10 according to the first to third embodiments described above, examples have been described in which the difference in transmittance is used to distinguish between the second release liner 3 and the protective layer 1, between the second release liner 3 and the first release liner 2, or between the second release liner 3 and the laminate of the protective layer 1 and the first release liner 2. On the other hand, the second release liner 3 may be distinguished from the protective layer 1, the second release liner 3 from the first release liner 2, and the second release liner 3 from the laminate of the protective layer 1 and the first release liner 2 by differences in haze (cloudiness) and brightness (L value) in addition to differences in transmittance.

[0073] When distinguishing between the first release liner 2 and the second release liner 3 based on the difference in haze (cloudiness), it is preferable that the haze of the first release liner 2 be as high as possible, and that the haze of the second release liner 3 be as low as possible. The lower limit of the haze of the first release liner 2 is preferably 70% or more, more preferably 80% or more, even more preferably 90% or more, even more preferably 93% or more, and particularly preferably 98% or more. Furthermore, the upper limit of the haze of the second release liner 3 is preferably 10% or less, more preferably 7% or less, even more preferably 5% or less, and particularly preferably 3% or less. The haze of the first release liner 2 and the haze of the second release liner 3 refer to the haze in the thickness direction, and the haze in the thickness direction is a value measured in accordance with JIS K 7136. The haze in the thickness direction can be measured using a turbidity meter (manufactured by Nippon Denshoku Industries Co., Ltd., trade name "NDH2000").

[0074] Furthermore, when distinguishing between the protective layer 1 and the second release liner 3 based on the difference in haze (cloudiness), it is preferable that the haze of the protective layer 1 be as high as possible, and that the haze of the second release liner 3 be as low as possible. The lower limit of the haze of the protective layer 1 is preferably 15% or more, more preferably 25% or more, and even more preferably 35% or more. The upper limit of the haze of the second release liner 3 is preferably set as described above. The haze of the protective layer 1 also refers to the haze in the thickness direction, and the haze in the thickness direction can be measured in the same manner as for the first release liner 2 and the second release liner 3.

[0075] When distinguishing between the first release liner 2 and the second release liner 3 based on the difference in lightness (L value), it is preferable that the lightness (L value) of the first release liner 2 be as low as possible, and it is preferable that the lightness (L value) of the second release liner 3 be as high as possible. The upper limit of the lightness (L value) of the first release liner 2 is preferably 10 or less, more preferably 7 or less, and even more preferably 5 or less. The lower limit of the lightness (L value) of the second release liner 3 is preferably 70 or greater, more preferably 80 or greater, and even more preferably 90 or greater. The lightness (L value) of the first release liner 2 and the lightness (L value) of the second release liner 3 can be measured using a color meter (manufactured by Suga Test Instruments Co., Ltd., product name "SM-T"). In the measurement using the color meter, the chromaticity (a value and b value) of the first release liner 2 and the chromaticity (a value and b value) of the second release liner 3 can also be measured simultaneously.

[0076] Furthermore, when distinguishing between the protective layer 1 and the second release liner 3 based on the difference in lightness (L value), it is preferable that the lightness (L value) of the protective layer 1 be as low as possible, and that the lightness (L value) of the second release liner 3 be as high as possible. The upper limit of the lightness (L value) of the protective layer 1 is preferably 70 or less, and more preferably 65 or less. The lower limit of the lightness (L value) of the second release liner 3 is preferably 80 or greater, and more preferably 90 or greater. The lightness (L value) of the protective layer 1 can also be measured using the color meter in the same manner as the lightness (L value) of the first release liner 2 and the lightness (L value) of the second release liner 3. In the measurement using the color meter, the chromaticity (a value and b value) of the protective layer 1 can also be measured at the same time.

[0077] The protective layer 1 can also be distinguished from the first release liner 2 and the second release liner 3 by the difference in gloss (hereinafter also referred to as gloss difference). For example, the gloss difference can be determined by measuring the gloss (gloss at an incident angle of 60°) when light is incident at an angle of 60° on a laminate in which a first release liner 2 is laminated on one side of a protective layer 1 and a second release liner 3 is laminated on the other side of the protective layer 1. The light incident at an angle of 60° can be white light. The gloss at an incident angle of 60° can be measured using a spectrophotometer CM-26dG manufactured by Konica Minolta. The gloss difference of the laminate is preferably 20 GU or more, more preferably 30 GU or more, even more preferably 50 GU or more, and even more preferably 90 GU or more. When the gloss difference of the laminate is within the above range, the protective layer 1 can be sufficiently distinguished from the first release liner 2 and the second release liner 3.

[0078] Next, using a semiconductor wafer as an example of an electronic component, we will explain an example in which a protective layer 1 (see Figure 2A) obtained by the post-precut method is bonded to the surface of the semiconductor wafer to be protected, and we will also explain an example in which a protective layer 1 (see 2B) obtained by the pre-precut method is bonded to the surface of the semiconductor wafer to be protected. First, an example will be described below in which protective sheet 10 having protective layer 1 obtained by the post-precut method is used to attach protective layer 1 to the surface of a semiconductor wafer to be protected.

[0079] The bonding of the protective layer 1 to the surface of the semiconductor wafer to be protected using the protective sheet 10 having the protective layer 1 obtained by the post-precut method is carried out using a sensing device 100 that detects the position of the protective layer 1 on the protective sheet 10, and a mounting device 200 that bonds the protective layer 1 to the surface of the semiconductor wafer to be protected based on the position of the protective layer 1 detected by the sensing device 100.

[0080] As shown in Figure 3A, the sensing device 100 includes a holding table 101 having a holding surface 1011 that holds the protective sheet 10 from the side of the first release liner 2, and a position detection unit 102 that is arranged at a distance opposite to the holding surface 1011 of the holding table 101 and detects the position of the protective layer 1 on the protective sheet 10. The position detection unit 102 includes a camera 1021 for capturing an image of the protective sheet 10 from the side of the second release liner 3, and a lens 1022 for widening the imaging field of the camera 1021. That is, sensing device 100 detects the position of protective layer 1 on protective sheet 10 using an image captured by camera 1021 from the second release liner 3 side. As shown by the dashed line in FIG. 3A, the imaging field of view of camera 1021 is expanded by lens 1022 to cover the entire protection sheet 10. That is, in the sensing device 100, the camera 1021 is capable of capturing an image of the entire protective sheet 10 from the second release liner 3 side.

[0081] As explained above, in the protective sheet 10 according to the first embodiment, the transmittance T A and the transmittance T of the protective layer 1 at the one wavelength. B The difference between AB is 15% or more, or the transmittance T A and the transmittance T of the first release liner 2 at the one wavelength. C The difference between AC is 15% or more, or the transmittance T A and the transmittance T of the laminate of the protective layer 1 and the first release liner 2 at the one wavelength. D The difference between AD is more than 15%. The protective sheet 10 according to the first embodiment has a region (single-layer region) with a single-layer structure of only the second release liner 3, and a region (laminated region) with a laminated structure of the first release liner 2 and the protective layer 1. The intensity of light transmitted through protective sheet 10 from the side where protective layer 1 is provided differs between the light transmitted through the single-layer region and the light transmitted through the laminated region. In this embodiment, the light transmittance from the outer surface of the second release liner to the protective layer 1, i.e., the transmittance in the laminated region, is 15% or more lower than the light transmittance of the second release liner 3 alone (transmittance in the single layer region). Therefore, in this embodiment, by photographing the protective sheet 10 with a camera 1021 (near-infrared camera) from the outer surface side of the second release liner 3, the single-layer region can be identified as a bright area, and the laminated region can be identified as a dark area that is darker than the bright area. In this embodiment, a difference in transmittance of 15% or more creates sufficient contrast between the dark and bright areas, allowing the outer periphery of the laminated region to be detected with high accuracy. Therefore, in the protective sheet 10 according to the first embodiment, the position of the protective layer 1 can be identified. This makes it possible to detect the position of the protective layer 1 on the protective sheet 10 according to the first embodiment, and also to detect the position on the holding surface 1011 of the holding table 101 at which the protective layer 1 is arranged.

[0082] Furthermore, as explained above, in the protective sheet 10 according to the second embodiment, the transmittance T A’ and the transmittance T of the protective layer 1 at the one wavelength. B’ The difference between A’B’ is 15% or more, or the transmittance T A’ and the transmittance T of the first release liner 2 at the one wavelength. C’ The difference between A’C’ is 15% or more, or the transmittance T A’ and the transmittance T of the laminate of the protective layer 1 and the first release liner 2 at the one wavelength. D’ The difference between A’D’ is more than 15%. That is, in the protective sheet 10 according to the second embodiment, the intensity of ultraviolet light transmitted through the laminated region and the single-layer region differs. Therefore, as in the first embodiment, by photographing the protective sheet 10 with a camera 1021 (ultraviolet camera) from the outer surface side of the second release liner 3, the single-layer region can be seen as a bright area, and the laminated region can be seen as a dark area that is darker than the bright area. Therefore, by identifying the light and dark areas in the image, it is possible to identify the position of the protective layer 1 in the protective sheet 10 according to the second embodiment as well. This makes it possible to detect the position of the protective layer 1 on the protective sheet 10 according to the second embodiment, and also to detect at which position on the holding surface 1011 of the holding table 101 the protective layer 1 is arranged.

[0083] Furthermore, as explained above, in the protective sheet 10 according to the third embodiment, the transmittance T A’’ and the transmittance T of the protective layer 1 at the one wavelength. B’’ The difference between A’’B’’ is 15% or more, or the transmittance T A’’ and the transmittance T of the first release liner 2 at the one wavelength. C’’ The difference between A’’C’’ is 15% or more, or the transmittance T A’’ and the transmittance T of the laminate of the protective layer 1 and the first release liner 2 at the one wavelength. D’’ The difference between A’’D’’ is more than 15%. That is, in the protective sheet 10 according to the third embodiment, the intensity of visible light transmitted through the laminated region differs from that transmitted through the single-layer region. Therefore, as in the first embodiment, by photographing the protective sheet 10 with a camera 1021 (visible light camera) from the outer surface side of the second release liner 3, the single-layer region can be seen as a bright area, and the laminated region can be seen as a dark area that is darker than the bright area. Therefore, by identifying the light and dark areas, the position of the protective layer 1 can also be identified in the protective sheet 10 according to the third embodiment. This makes it possible to detect the position of the protective layer 1 on the protective sheet 10 according to the third embodiment, and also to detect at which position on the holding surface 1011 of the holding table 101 the protective layer 1 is arranged.

[0084] In this embodiment, a backlight may be provided to improve the detectability of the camera 1021, and light containing any of near-infrared rays, ultraviolet rays, and visible rays may be irradiated from the inner surface side of the second release liner 3. After detecting the position of the protective layer 1 on the protective sheet 10 and determining where the protective layer 1 is located on the holding surface 1011 of the holding table 101, the second release liner 3 is peeled off, exposing one side of the protective layer 1.

[0085] As shown in FIG. 3B, the mounting device 200 includes a chamber 201, an electrostatic chuck table 202 disposed at the bottom of the chamber 201, a head unit 203 disposed within the chamber 201 above the electrostatic chuck table 202, and a pump P for reducing the pressure inside the chamber 201. In the following description, the up-down direction (vertical direction) is referred to as the Z-axis direction, the horizontal direction along the cut surface when the electrostatic chuck table 202 and the head unit 203 are cut along a plane parallel to the Z-axis (the horizontal direction along the paper surface in FIG. 3B) is referred to as the X-axis direction, and the direction perpendicular to both the Z-axis and the X-axis (the direction perpendicular to the paper surface in FIG. 3B) is referred to as the Y-axis direction.

[0086] As shown in FIG. 3B, in the mounting apparatus 200, an electrostatic chuck table 202 holds the dicing die bond film D, to which the semiconductor wafer W is attached, by electrostatic force. The dicing die bond film D includes a die bond film in which a pressure-sensitive adhesive layer is laminated on a base material, and a die bond layer disposed on the pressure-sensitive adhesive layer of the die bond film. The semiconductor wafer W is bonded to the die bond layer of the dicing die bond film D. In addition, a dicing ring R is attached to the edge side of the dicing die bond film D. Furthermore, as shown in FIG. 3B, in the mounting device 200, the head portion 203 holds the holding table 101, which holds the laminate of the protective layer 1 and the first release liner 2 from the first release liner 2 side, by suction or the like. In addition, in the mounting device 200, the head part 203 is configured to be movable within the chamber 201 along the X-axis direction, the Y-axis direction, and the Z-axis direction.

[0087] In the mounting device 200, the inside of the chamber 201 is maintained at atmospheric pressure before the head unit 203 holds the holding table 101, and is depressurized by the pump P after the head unit 203 holds the holding table 101. That is, the holding table 101 is held by the head unit 203 under atmospheric pressure, and the protective layer 1 is bonded to the surface of the semiconductor wafer W to be protected under reduced pressure.

[0088] In the mounting device 200 configured as described above, the protective layer 1 is bonded to the surface to be protected of the semiconductor wafer W based on information on the position of the protective layer 1 detected by the sensing device 100, more specifically, information on the position of the protective layer 1 on the holding surface 1011 of the holding table 101 (hereinafter simply referred to as the position information of the protective layer on the holding table).

[0089] Specifically, based on the position information of the protective layer on the holding table, the head unit 203 is moved in the X-axis direction or the Y-axis direction to roughly align the outer periphery of the semiconductor wafer W with the outer periphery of the protective layer 1, and then the head unit 203 is moved downward in the Z-axis direction to bond the exposed surface of the protective layer 1 to the surface of the semiconductor wafer W to be protected. The exposed surface of the protective layer 1 is preferably attached while applying a pressure of about 0.3 MPa. This allows the exposed surface of the protective layer 1 to be sufficiently bonded to the surface of the semiconductor wafer W to be protected. Then, after the exposed surface of the protective layer 1 has been fully bonded to the surface of the semiconductor wafer W to be protected, the head part 203 is moved upward in the Z-axis direction to release the first release liner 2 from the protective layer 1. This allows the surface of the semiconductor wafer W to be provided with a protective layer 1 as shown in FIG. 3C. When bonding the exposed surface of the protective layer 1 to the surface of the semiconductor wafer W to be protected, at least one of the holding table 101 and the electrostatic chuck table 202 may be kept in a heated state.

[0090] Next, an example will be described in which a protective sheet having a protective layer 1 obtained by the pre-cut method is used to attach the protective layer 1 to the surface of a semiconductor wafer to be protected.

[0091] When a protective sheet 10 having a protective layer 1 obtained by the pre-cut method as shown in Figure 1B is bonded to the surface of a semiconductor wafer to be protected, either the first release liner 2 or the second release liner 3 is peeled off to expose the surface of protective layer 1, and the position of protective layer 1 relative to the bonded release liner is detected. Therefore, in this embodiment, it is necessary that a difference in transmittance occurs between the release liner attached to one surface of the protective layer 1 and the protective layer 1.

[0092] For example, when the first release liner 2 is peeled off from the protective layer 1 and the second release liner 3 is bonded to the protective layer 1, the transmittance T A and the transmittance T of the protective layer 1 at the one wavelength. B The difference between AB The transmittance T of the second release liner 3 at one wavelength in the ultraviolet region must be 15% or more. A’ and the transmittance T of the protective layer 1 at the one wavelength. B’ The difference between A’B’ The transmittance T of the second release liner 3 at one wavelength included in the visible region must be 15% or more. A’’ and the transmittance T of the protective layer 1 at the one wavelength.B’’ The difference between A’’B’’ must be 15% or more. Below, we will explain an example in which the first release liner 2 is peeled off from the protective layer 1, the second release liner 3 is bonded to the protective layer 1, the position of the protective layer 1 relative to the second release liner 3 is detected, and then the protective layer 1 is bonded to the surface of the semiconductor wafer to be protected.

[0093] The bonding of the protective layer 1 to the surface of the semiconductor wafer to be protected using the protective sheet 10 having the protective layer 1 obtained by the pre-cut method is carried out using a sensing device 300 that detects the position of the protective layer 1 relative to the second release liner 3 and the position of the semiconductor wafer, and a laminating device 400 that bonds the protective layer 1 to the surface of the semiconductor wafer to be protected based on the position of the protective layer 1 relative to the second release liner 3 and the position of the semiconductor wafer detected by the sensing device 300.

[0094] As shown in FIG. 4A, the sensing device 300 includes a wafer holding table 301 having a holding surface 3011 for holding a semiconductor wafer W, a gripping tool 302 arranged above the wafer holding table 301 for gripping the laminate of the protective layer 1 and the second release liner 3 from both end edge sides of the laminate, and a position detection unit 303 arranged above the gripping tool 302 for detecting the position of the protective layer 1 relative to the second release liner 3 and the position of the semiconductor wafer W. In the following description, the up-down direction (vertical direction) is defined as the Z-axis direction, the horizontal direction along the cut surface when wafer holding table 301 or the like is cut along a plane parallel to the Z-axis (the horizontal direction along the paper surface in FIG. 4A) is defined as the X-axis direction, and the direction perpendicular to both the Z-axis and the X-axis (the direction perpendicular to the paper surface in FIG. 4A) is defined as the Y-axis. In addition, in the following FIG. 4B, the X-axis direction, the Y-axis direction, and the Z-axis direction refer to the same directions as the X-axis direction, the Y-axis direction, and the Z-axis direction in FIG. 4A.

[0095] The position detection unit 303 is equipped with a camera 3031 for capturing images of the laminate of the protective layer 1 and the second release liner 3, as well as the semiconductor wafer W, from the second release liner 3 side, and a lens 3032 for widening the imaging field of view of the camera. That is, the sensing device 300 detects the position of the protective layer 1 and the position of the semiconductor wafer W relative to the second release liner 3 using an image taken by the camera 3031 from the second release liner 3 side. As shown by the dashed line in FIG. 4A, the imaging field of view of camera 3031 is expanded by lens 3032 to the vicinity of the area grasped by grasper 302. That is, in the sensing device 300, the camera 3031 is capable of capturing an image of the laminate of the protective layer 1 and the first release liner 2 from the second release liner 3 side to the vicinity of the area gripped by the gripping tool 302, as well as capturing an image of the semiconductor wafer W.

[0096] The gripping tool 302 is attached to an arm (not shown) and is movable in the X-axis, Y-axis, and Z-axis directions by the arm.

[0097] Here, as described above, the semiconductor wafer W has a circuit pattern formed on one surface side and an electrode portion disposed thereon. Furthermore, the semiconductor wafer W usually has a thickness of about several tens of μm (for example, 50 μm). Therefore, even near-infrared rays having extremely long wavelengths are difficult to transmit through the semiconductor wafer W. Therefore, whether a near-infrared camera, an ultraviolet camera, or a visible light camera is used as camera 3031 to image the laminate of protective layer 1 and second release liner 3, and the semiconductor wafer W, from the side of second release liner 3, in any of the images captured, protective layer 1 and semiconductor wafer W will be shown as shaded areas (dark areas). This makes it possible to detect the position of the protective layer 1 relative to the second release liner 3 and the position of the semiconductor wafer W by identifying the shaded portions (dark portions) in the image. Then, based on information on the position of the protective layer 1 relative to the second release liner 3 and information on the position of the semiconductor wafer W, the gripping tool 302 is moved in the X-axis direction, Y-axis direction, Z-axis direction, etc., until the outer periphery of the semiconductor wafer W and the outer periphery of the protective layer 1 are approximately aligned. Next, the gripping tool 302 is moved downward in the Z-axis direction, and the protective layer 1 of the laminate of the protective layer 1 and the second release liner 3 is bonded to the surface of the semiconductor wafer W to be protected.

[0098] As shown in FIG. 4B, laminating device 400 includes roller 401 that rotates and presses the laminate of protective layer 1 and second release liner 3 while being in contact with second release liner 3 of the laminate. In the laminating device 400, the roller 401 rotates and moves in the X-axis direction, as shown in FIG. 4B, while pressing the laminate of the protective layer 1 and the second release liner 3, thereby bonding the protective layer 1 to the surface to be protected of the semiconductor wafer W. The pressing is preferably carried out while applying a pressure of about 0.3 MPa. This allows the exposed surface of the protective layer 1 to be sufficiently bonded to the surface of the semiconductor wafer W to be protected.

[0099] Then, after the exposed surface of the protective layer 1 has been fully bonded to the surface of the semiconductor wafer W to be protected, the second release liner 3 is peeled off from the protective layer 1 by moving the gripping tool 302 upward in the Z-axis direction. This allows the surface of the semiconductor wafer W to be provided with a protective layer 1 as shown in FIG. 4C.

[0100] The protective layer 1 may be bonded to the surface of the semiconductor wafer W to be protected using a vacuum diaphragm laminator that bonds the protective layer 1 to the surface of the semiconductor wafer W to be protected under vacuum. Furthermore, the bonding of the protective layer 1 to the surface of the semiconductor wafer W to be protected may be performed by a differential pressure press in a pressure-adjustable chamber.

[0101] The matters disclosed by this specification include the following.

[0102] (1) a protective layer attached to the adherend; a release liner disposed on the surface of the protective layer, the protective layer contains a water-soluble polymer, the release liner has an inner surface facing the protective layer and an outer surface opposite the inner surface, The light transmittance of the release liner from the outer surface through the protective layer is at least 15% lower than the light transmittance of the release liner at at least one wavelength. Protective sheet.

[0103] With this configuration, the position of the protective layer can be accurately grasped from the release liner side. This makes it possible to easily align the protective layer with the transfer device, the adherend, and the like.

[0104] (2) a protective layer attached to the adherend; a first release liner disposed on one surface of the protective layer; a second release liner disposed on the other surface of the protective layer; the protective layer contains a water-soluble polymer compound, each of the first release liner and the second release liner has an inner surface facing the protective layer and an outer surface opposite the inner surface; the light transmittance from the outer surface of the second release liner to the outer surface of the first release liner is at least 15% lower than the light transmittance of the second release liner at at least one wavelength; Protective sheet.

[0105] According to this configuration, the positions of the protective layer and the first release liner can be accurately grasped from the second release liner side. Therefore, particularly when the protective layer and the first release liner are pre-cut so that they have approximately the same dimensions in a planar view, the position of the protective layer can be accurately determined based on the position of the first release liner. This makes it possible to easily align the protective layer with the transfer device, the adherend, and the like.

[0106] (3) The protective sheet according to (1) or (2) above, wherein the one wavelength is a wavelength in the ultraviolet region, the visible region, or the near-infrared region.

[0107] The protective sheet of the present invention is not limited to the above-described embodiment, nor is it limited by the above-described effects. The protective sheet of the present invention can be modified in various ways without departing from the spirit and scope of the present invention.

[0108] For example, the protective sheet according to the present invention is not limited to being used with semiconductor wafers, but can also be used with other objects to be protected than semiconductors. Furthermore, although the present embodiment exemplifies an embodiment in which a protective layer is provided between two release liners, the first release liner and the second release liner, the protective sheet of the present invention may also have a two-layer structure consisting of one release liner and a protective layer. Furthermore, the protective sheet of the present invention is not limited to the above examples. [Example]

[0109] The present invention will now be described in more detail with reference to examples. The following examples are intended to explain the present invention in more detail, but are not intended to limit the scope of the present invention.

[0110] [Example 1] In a container, polyvinyl alcohol (saponification degree 65, average polymerization degree 240) was dispersed in water to prepare an aqueous dispersion. In the following, polyvinyl alcohol will also be referred to as PVA. Next, the container containing the aqueous dispersion was placed in a water bath at 90°C, and the aqueous dispersion was stirred to dissolve the PVA in water, thereby obtaining a PVA dissolved composition. Next, the PVA solution composition was applied to a thickness of 10 μm using an applicator onto the release-treated surface of a second release liner (manufactured by Mitsubishi Chemical Corporation, product name MRA50, thickness 50 μm) having a surface treated with silicone release. Next, the second release liner coated with the PVA solution composition was dried at 110°C for 2 minutes to form a protective layer on the second release liner, thereby obtaining a laminate of the second release liner and the protective layer. Next, a foamed first release liner (manufactured by Toyobo Co., Ltd., product name "Crisper (registered trademark) K1211", thickness 38 μm) was attached to the protective layer to obtain the protective sheet of Example 1. The first release sheet was foamed by generating voids during stretching, and no release treatment was applied to the surface. The protective sheet according to Example 1 described above was produced so as to reduce the permeability of the first release liner.

[0111] The saponification degree and average polymerization degree of the polyvinyl alcohol were measured in accordance with the method described in the above embodiment section.

[0112] [Example 2] A protective sheet according to Example 2 was obtained in the same manner as in Example 1, except that a PET film (manufactured by Fujiko Co., Ltd., product name "PET38-SCA1", thickness 38 μm) having a coating layer containing titanium oxide on one side was used as the first release liner. The first release liner had the other surface (the surface opposite to the surface having the coating layer) subjected to release treatment. The protective sheet of Example 2 was produced by forming a protective layer on a second release liner and then bonding the release-treated surface of the first release liner (the surface without the coating layer) to the protective layer. The protective sheet according to Example 2 above was also produced so as to reduce the permeability of the first release liner.

[0113] [ reference Example 3] The same procedures as in Example 1 were carried out except that a protective layer containing silica was used and a release liner having a surface treated with silicone release (manufactured by Mitsubishi Chemical Corporation, product name MRA38, thickness 38 μm) was used as the first release liner. reference A protective sheet according to Example 3 was obtained. reference In the protective sheet of Example 3, the protective layer was formed by applying a silica-containing composition, in which silica was added to the PVA dissolved composition, to the release-treated surface of the second release liner using an applicator to a thickness of 10 μm, and then drying the second release liner to which the silica-containing composition had been applied at 110°C for 2 minutes. As the silica, "Snowtec (registered trademark) MP-2040" manufactured by Nissan Chemical Industries, Ltd. was used. The concentration of the silica in the silica-containing composition was 30% by mass. Furthermore, the first release liner was attached to the protective layer by attaching the release-treated surface to the protective layer. As above reference The protective sheet of Example 3 was produced so as to reduce the transmittance of the protective layer.

[0114] [Reference example 1] The protective layer contained a dye, but reference In the same manner as in Example 3, a protective sheet according to Reference Example 1 was obtained. In the protective sheet of Reference Example 1, the protective layer was formed by applying a dye-containing composition, in which a dye was dissolved in the PVA solution composition, to a thickness of 10 μm on the release-treated surface of the second release liner using an applicator, and then drying the second release liner to which the dye-containing composition had been applied at 110°C for 2 minutes. As the dye, "Linablue (registered trademark)" (blue pigment) manufactured by DIC Corporation was used. The concentration of the dye in the dye-containing composition was 5%. The protective sheet according to Reference Example 1 as described above was also produced so as to reduce the transmittance of the protective layer.

[0115] [Comparative Example 1] The first release liner is a release liner having a surface treated with silicone release agent. The same as in Example 1 except that a 38 μm thick film (Mitsubishi Chemical Corporation product name MRA38) was used. In this manner, a protective sheet according to Comparative Example 1 was obtained. In Comparative Example 1, the first release sheet was attached to the protective layer as follows: reference Same as Example 3 The test was carried out by bonding the release-treated surface of the substrate to the other substrate. In the protective sheet according to Comparative Example 1, both the protective layer and the first release liner are transparent. It was produced without reducing the transmittance.

[0116] <Transmittance> For the protective sheet according to each example, the transmittance of the first release liner, the protective layer, and the second release liner was measured. The transmittance was measured using light with a wavelength of 1060 nm (near infrared light), light with a wavelength of 330 nm (ultraviolet light), light with a wavelength of 550 nm (visible light), and light with a wavelength of 650 nm (visible light). The transmittance of the protective layer was measured using a protective layer obtained by obtaining a laminate of the second release liner and the protective layer and then peeling the second release liner from the laminate. The transmittance was measured by the method described in the above embodiment section. The results are shown in Table 1 below.

[0117] In Table 1 below, the transmittance of the second release liner measured using light with a wavelength of 1060 nm is T A and the transmittance of the protective layer measured using light of wavelength 1060n is expressed as T B The transmittance of the first release liner measured using light with a wavelength of 1060 nm is expressed as T C It is written as follows. The transmittance of the second release liner measured using light with a wavelength of 330 nm was T A’ The transmittance of the protective layer measured using light with a wavelength of 330 nm is expressed as T B’ The transmittance of the first release liner measured using light with a wavelength of 330 nm is expressed as T C’ It is written as follows. Furthermore, the transmittance of the second release liner measured using light with a wavelength of 550 nm was T A’’1 The transmittance of the protective layer measured using light with a wavelength of 550 nm is expressed as T B’’1 The transmittance of the first release liner measured using light with a wavelength of 500 nm is expressed as T C’’1 It is written as follows. The transmittance of the second release liner measured using light with a wavelength of 650 nm was T A’’2 The transmittance of the protective layer measured using light with a wavelength of 650 nm is expressed as T B’’2 The transmittance of the first release liner measured using light with a wavelength of 650 nm is expressed as T C’’2 It is written as follows. Furthermore, the transmittance T A and transmittance T B The difference between (T A -T B ) to ΔT AB and transmittance T A and transmittance T C The difference between (T A -T C ) to ΔT AC and transmittance T A’ and transmittance T B’ The difference between (T A’ -TB’ ) to ΔT A’B’ and transmittance T A’ and transmittance T C’ The difference between (T A’ -T C’ ) to ΔT A’C’ and transmittance T A’’1 and transmittance T B’’1 The difference between (T A’’1 -T B’’1 ) to ΔT A’’1B’’1 and transmittance T A’’1 and transmittance T C’’1 The difference between (T A’’1 -T C’’1 ) to ΔT A’’1C’’1 and transmittance T A’’2 and transmittance T B’’2 The difference between (T A’’2 -T B’’2 ) to ΔT A’’2B’’2 and transmittance T A’’2 and transmittance T C’’2 The difference between (T A’’2 -T C’’2 ) to ΔT A’’2C’’2 It is written as follows.

[0118] <Haze> For the protective sheet according to each example, the haze of the first release liner, the protective layer, and the second release liner was measured. The haze was measured by the method described in the above embodiment section. The results are shown in Table 1 below.

[0119] <Gloss at an incident angle of 60°> For the protective sheet of each example, the gloss was measured when light was incident on the first release liner, protective layer, and second release liner at an angle of 60° (gloss at an incident angle of 60°). White light was used as the light incident at an angle of 60°. The gloss at an incident angle of 60° was measured using a spectrophotometer CM-26dG manufactured by Konica Minolta. The results are shown in Table 1 below. In Table 1, the "GU" (Gloss Unit) in parentheses is a unit of gloss.

[0120] <Lightness (L value)> For the protective sheet according to each example, the lightness (L value) of the first release liner, protective layer, and second release liner was measured. The lightness (L value) was measured using a color meter as described in the above embodiment section. The results are shown in Table 1 below. When measuring lightness (L value) using a color meter, chromaticity (a value and b value) is also measured at the same time. Therefore, Table 1 below also shows the measurement results of the chromaticity (a value and b value) of the first release liner, protective layer, and second release liner for the protective sheet according to each example. Table 1 below shows the lightness (L value) and chromaticity (a value and b value) of the first release liner, protective layer, and second release liner for each example of the protective sheet. 2 +a 2 +b 2 ) 1 / 2 The value was calculated. The results are also shown in Table 1 below.

[0121] <Distinguishing ability> For the protective sheet according to each example, the distinguishability of the protective layer or first release liner was evaluated. In the evaluation of discriminability, the protective layer and the first release liner were pre-cut and used as test specimens. The evaluation of the discrimination ability was carried out using a transmission type photoelectric sensor (manufactured by KEYENCE Corporation, product name "PR-G51N") equipped with a light projecting part and a light receiving part. Specifically, for the protective sheet of each example, a light-emitting section was positioned outside the second release sheet and a light-receiving section was positioned outside the first release sheet, and then laser light was irradiated from the light-emitting section to evaluate whether the protective layer or the first release liner was identified as a shaded area (dark area) in the light-receiving section. If the protective layer or the first release liner was discernible as a shaded area (dark area), it was rated as "excellent," and if it was not discernible as a shaded area, it was rated as "poor." The laser light emitted from the light projecting unit was a laser light with a wavelength of 550 nm and a laser light with a wavelength of 650 nm. The distinguishability of the protective layer or the first release liner was evaluated using a 550 nm laser beam and a 650 nm laser beam, and the results are shown in Table 1 below.

[0122] [Table 1]

[0123] From Table 1, ΔT A’’2C’’2 In Examples 1 and 2, where the difference is 15% or more, the evaluation of the discriminability when irradiated with a laser beam having a wavelength of 650 nm is "excellent," and ΔT A’’2B’’2 is more than 15% reference It can be seen that in Example 3 and Reference Example 1, the evaluation of the distinguishability when irradiated with a laser beam having a wavelength of 650 nm was "excellent." In contrast, ΔT A’’2C’’2 and ΔT A’’2B’’2 However, in Comparative Example 1, where both values ​​are less than 15%, the evaluation of the distinguishability when irradiated with laser light having a wavelength of 650 nm is "fail." Also, ΔT A’’1C’’1 In Examples 1 and 2, where the difference is 15% or more, the evaluation of the discrimination ability when irradiated with a laser beam having a wavelength of 550 nm is "excellent," and ΔT A’’1B’’1 is more than 15% reference In Example 3, it can be seen that the evaluation of distinguishability when irradiated with laser light having a wavelength of 550 nm was "excellent." In contrast, in Reference Example 1 and Comparative Example 1, ΔT A’’1B’’1 is less than 15%, which indicates that the evaluation of distinguishability when irradiated with laser light of a wavelength of 550 nm is "unacceptable." From these results, it can be seen that when visible light is irradiated as laser light, if the difference in transmittance between the second release liner and the protective layer is 15% or more, the second release liner and the protective layer can be sufficiently distinguished, and if the difference in transmittance between the second release liner and the first release liner is 15% or more, the second release liner and the first release liner can be sufficiently distinguished. Furthermore, even when near-infrared light or ultraviolet light is used as the laser light instead of visible light, if the difference in transmittance between the second release liner and the protective layer is 15% or more, the second release liner and the protective layer can be sufficiently distinguished, just as in the case of visible light, and if the difference in transmittance between the second release liner and the first release liner is 15% or more, the second release liner and the first release liner can be sufficiently distinguished, just as in the case of visible light. [Explanation of symbols]

[0124] 1 protective layer, 2 first release liner, 3 second release liner, 10 protective sheet.

Claims

1. a protective layer attached to the adherend; a first release liner disposed on one surface of the protective layer; a second release liner disposed on the other surface of the protective layer; the first release liner is laminated to the protective layer with their outer peripheral edges aligned, the second release liner protrudes outward from the outer peripheral edge of the protective layer, the protective layer contains a water-soluble polymer compound, each of the first release liner and the second release liner has an inner surface facing the protective layer and an outer surface opposite the inner surface; the second release liner has a higher light transmittance than the first release liner; the light transmittance from the outer surface of the second release liner to the outer surface of the first release liner is at least 15% lower than the light transmittance of the second release liner at at least one wavelength; Protective sheet.

2. The protective sheet according to claim 1 , wherein the one wavelength is a wavelength in any of the ultraviolet region, the visible region, and the near-infrared region.

3. A method for using the protective sheet according to claim 1 or 2, comprising: a step of photographing the protective sheet with a camera from the outer surface side of the second release liner to detect the outer periphery of the protective layer and identify the position of the protective sheet; peeling the second release liner from the other surface of the protective layer; and attaching the other surface of the protective layer, the position of which has been identified, to the adherend. How to use the protective sheet.

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