Protective sheet

Abstract

A protective sheet according to the present invention comprises a protective layer which is used by being applied to a surface to be protected of an electronic component, or to a surface to be protected of an electronic component assembly in which multiple electronic components are connected, wherein the protective layer includes a water-soluble polymer compound, and the viscosity η of the protective layer is 500,000 Pa·s or less at 60°C.

Description

protective sheet CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority from Japanese Patent Application Nos. 2023-099188 and 2023-214696, which are incorporated herein by reference.

[0002] The present invention relates to a protective sheet. More specifically, the present invention relates to a protective sheet including a protective layer containing a water-soluble polymer compound, which is applied to a surface to be protected of an electronic component or a surface to be protected of an electronic component assembly formed by connecting a plurality of electronic components.

[0003] In the manufacture of electronic component devices such as semiconductor devices, it is known to use a protective sheet to protect at least a portion of the surface of an object to be protected. When the electronic component device is a semiconductor device, the object to be protected is, for example, a semiconductor wafer. The protective sheet is used by being attached to at least a portion of the surface of the semiconductor wafer, which is the object to be protected, during the manufacturing process of the semiconductor device.

[0004] Generally, a method for manufacturing a semiconductor device includes a front-end process of forming a highly integrated electronic circuit on one side of a disk-shaped bare wafer (wafer body) to obtain a semiconductor wafer, and a back-end process of dicing the semiconductor wafer obtained in the front-end process to separate (cut) it into a plurality of semiconductor chips, and then assembling a semiconductor device using at least one semiconductor chip (see, for example, Patent Document 1 listed below). Note that in a semiconductor wafer, the side (one side) on which the highly integrated electronic circuit is formed is also referred to as the circuit side or the circuit-forming side.

[0005] As the semiconductor wafer, one having a plurality of electrode portions on the circuit forming surface of the semiconductor wafer body is known.

[0006] In a later step of the manufacturing method of a semiconductor device, before the semiconductor wafer is diced as described above, the semiconductor wafer may be subjected to back-grinding so that the semiconductor wafer body has a predetermined thickness. More specifically, the semiconductor wafer body may be thinned to a predetermined thickness by back-grinding, which grinds the semiconductor wafer body from the other side (the side opposite the circuit-forming surface) of the semiconductor wafer body.

[0007] The above-described grinding of the semiconductor wafer body is typically performed by holding one side of the semiconductor wafer on an adsorption plate such as a vacuum chuck, and then using a polishing head or the like to grind the other side of the semiconductor wafer body. In this type of grinding of the semiconductor wafer, the pressing force from the polishing head presses the multiple electrodes against the surface of the adsorption plate. To prevent the multiple electrodes from being damaged by this force, the one side of the semiconductor wafer body is held on the adsorption plate with, for example, a protective layer containing a water-soluble polymer compound interposed therebetween (see, for example, Patent Document 2 listed below).

[0008] Japanese Patent Publication No. 2015-170754 Japanese Patent Publication No. 2021-161735

[0009] However, when multiple electrode portions protrude from one surface of the semiconductor wafer body, the protruding electrode portions may not be sufficiently embedded in the protective layer. That is, voids may form between the protective layer and the multiple electrode portions. If voids form between the protective layer and the multiple electrode portions, the area of ​​the semiconductor wafer body corresponding to the voids may be excessively ground during the back-grinding process. As a result, variations in the thickness of the semiconductor wafer body may occur after the semiconductor wafer is back-grinded. For example, when at least one of bump electrodes and pillar terminals is formed on one surface of the semiconductor wafer body, the multiple bump electrodes or pillar terminals are typically arranged at close intervals. In other words, the multiple bump electrodes or pillar terminals are arranged at high density on one surface of the semiconductor wafer body. High-density bump electrodes or pillar terminals may be more difficult to embed in the protective layer, raising concerns about the likelihood of thickness variations in the semiconductor wafer body after grinding.

[0010] If variations occur in the thickness of the semiconductor wafer body, it may be difficult to perform further processes after the back-grinding process, such as dicing, on the semiconductor wafer body.

[0011] However, it cannot be said that sufficient research has yet been done to prevent thickness variations from occurring in the semiconductor wafer body of the semiconductor wafer when backgrinding the semiconductor wafer using a protective sheet with a protective layer.

[0012] Therefore, an object of the present invention is to provide a protective sheet that can suppress variations in thickness of the semiconductor wafer body that a semiconductor wafer has when the semiconductor wafer is back-grinded.

[0013] The protective sheet according to the present invention comprises a protective layer that is adhered to a surface to be protected of an electronic component or a surface to be protected of an electronic component assembly in which a plurality of the electronic components are connected, the protective layer containing a water-soluble polymer compound, and the viscosity η of the protective layer at 60°C is 500,000 Pa s or less.

[0014] The protective sheet according to the present invention comprises a protective layer that is adhered to a surface to be protected of an electronic component or to a surface to be protected of an electronic component assembly in which a plurality of the electronic components are connected, and the protective layer contains, as water-soluble polymer compounds, at least one selected from the group consisting of polyvinyl alcohol, polyvinylpyrrolidone, and water-soluble polyester, and a polymer having a structural unit derived from ethylene oxide.

[0015] 1 is a schematic cross-sectional view showing one configuration of a protective sheet; 2 is a schematic cross-sectional view showing an example of a semiconductor wafer; 3 is a schematic cross-sectional view showing the configuration of a wafer-level package; 4 is a schematic cross-sectional view showing the configuration of an image sensor package; 5 is a schematic cross-sectional view showing the configuration of a laminate for an image sensor package; 6 is a schematic cross-sectional view showing another configuration of a protective sheet; 7 is a schematic cross-sectional view showing back-grinding of a semiconductor wafer; 8 is a schematic cross-sectional view showing the configuration of a semiconductor wafer with a protective layer; 9 is a schematic cross-sectional view showing a first state when a semiconductor wafer with a protective layer is diced; 10 is a schematic cross-sectional view showing a second state when a semiconductor wafer with a protective layer is diced.

[0016] DETAILED DESCRIPTION OF THE INVENTION One embodiment of the protective sheet of the present invention will now be described with reference to the drawings. A protective sheet according to one embodiment of the present invention may be simply referred to as a protective sheet according to this embodiment.

[0017] [Protective Sheet] The protective sheet according to this embodiment includes a protective layer that is attached to a surface to be protected of an electronic component or a surface to be protected of an electronic component assembly formed by connecting a plurality of electronic components. The protective layer contains a water-soluble polymer compound. In the protective sheet according to this embodiment, the viscosity η of the protective layer at 60°C is 500,000 Pa s or less.

[0018] Alternatively, the protective sheet according to this embodiment includes a protective layer that is adhered to the surface of an electronic component to be protected or the surface of an electronic component assembly in which a plurality of electronic components are connected to each other to be protected, and the protective layer contains, as water-soluble polymer compounds, at least one selected from the group consisting of polyvinyl alcohol, polyvinylpyrrolidone, and water-soluble polyester, and a polymer having a structural unit derived from ethylene oxide.

[0019] With the above-described configuration, the protective layer of the protective sheet according to this embodiment can suppress variations in thickness of the semiconductor wafer body included in the semiconductor wafer when the semiconductor wafer is back-grinded.

[0020] 1 , the protective sheet 10 according to this embodiment includes a protective layer 10a. The protective sheet 10 according to this embodiment further includes a base layer 10b disposed opposite one side of the protective layer 10a, and a pressure-sensitive adhesive layer 10c disposed between the protective layer 10a and the base layer 10b. In the protective sheet 10 according to this embodiment, one side of the pressure-sensitive adhesive layer 10c facing the protective layer 10a and the other side facing the base layer 10b are releasably adhered to the protective layer 10a and the base layer 10b, respectively.

[0021] Examples of the electronic components include semiconductor chips and circuit boards. These electronic components are adherends of the protective layer 10a. Examples of the electronic component assembly include a connected circuit board formed by connecting a plurality of semiconductor wafers or circuit boards to obtain semiconductor chips.

[0022] An example of an electronic component device including the electronic component is a semiconductor device including a semiconductor chip. The semiconductor chip may be a TSV type semiconductor chip described later, or a sensor chip such as a CMOS chip. A semiconductor device including a CMOS chip may be configured to include a system LSI. Furthermore, the electronic component device may be a device including mechanical elements, sensors, actuators, or devices (MEMS (Micro Electro Mechanical Systems)) in which electronic circuits are integrated by microfabrication technology on a single substrate (e.g., a silicon substrate, a glass substrate, an organic material substrate, etc.). The electronic component device may also be a device including a wiring substrate.

[0023] An example of a semiconductor wafer is one configured as shown in FIG. 2 . The semiconductor wafer 20 shown in FIG. 2 includes a semiconductor wafer main body 20a and a plurality of electrode portions 20b arranged on one surface of the semiconductor wafer main body 20a. In the semiconductor wafer 20, the one surface of the semiconductor wafer main body 20a on which the plurality of electrode portions 20b are arranged is the circuit formation surface. In each electrode portion 20b in the semiconductor wafer 20 shown in FIG. 2, a plurality of bump electrodes 20b1 are arranged at close intervals. That is, each electrode portion 20b is configured by a plurality of bump electrodes 20b1 arranged at high density. The bump electrodes 20b1 are typically formed by plating one surface of the semiconductor wafer main body 20a. Therefore, in the semiconductor wafer 20 as shown in FIG. 2 , the plurality of electrode portions 20b are arranged so as to protrude from one surface of the semiconductor wafer main body 20a. The semiconductor wafer 20 is then divided (cleaved) along the cleaving line L1 shown in FIG. 2 by dicing or other processing, and is then singulated (cut into small pieces) into semiconductor chips each having at least one electrode portion 20b. The cleaving line L1 for dividing (cleaving) the semiconductor wafer main body 20a into individual pieces (small pieces) each having one electrode portion 20b is shown in FIG. 2 . After being singulated (cleaved) into semiconductor chips, the electrode portion 20b is electrically connected to the electrode portion of another component. Examples of the other component include a circuit board or another semiconductor chip configured similarly to the semiconductor chip. As mentioned above, semiconductor chips are classified as electronic components. In the semiconductor wafer 20 described above, one surface of the semiconductor wafer main body 20a is the surface to be protected. Specifically, the surface of the semiconductor wafer main body 20a on which the multiple electrode portions 20b are arranged and which constitutes the circuit formation surface is the surface to be protected.

[0024] Furthermore, a semiconductor wafer 20 (see FIG. 2) having a plurality of electrode portions 20b in which a plurality of bump electrodes 20b1 are arranged at close intervals may be used by attaching each electrode portion 20b to a semiconductor chip, and then sealing each semiconductor chip with resin. That is, the semiconductor wafer 20 shown in FIG. 2 may be used as a substrate for a wafer-level package (WLP). The wafer-level package (WLP) is also classified as an electronic component assembly.

[0025] The semiconductor chip may be, for example, a TSV (Through Silicon Via) type semiconductor chip. A TSV type semiconductor chip includes electrode portions arranged on both sides of the semiconductor chip body, which form pairs and are electrically connected to other components, and a conductive portion that penetrates the semiconductor chip body in the thickness direction so as to electrically connect both electrode portions. In a TSV type semiconductor chip, only one side may be a circuit formation surface, or both sides may be circuit formation surfaces. When electrode portions are formed on both sides of the semiconductor chip body, both sides of the semiconductor chip body become surfaces to be protected.

[0026] The semiconductor chip also includes a sensor chip in which the circuit has a sensor element (for example, a light receiving element or a vibration element) as an element, such as a CMOS (Complementary Metal-Oxide Semiconductor) chip.

[0027] The electronic component assembly may also be a pseudo wafer including a support substrate and a package formed by collectively sealing a plurality of semiconductor chips with resin while the semiconductor chips are arranged on the support substrate. The pseudo wafer may be a package removed from the support substrate. A rewiring layer may be formed on at least one surface of the pseudo wafer. In such a case, the protective layer 10a of the protective sheet 10 may be used to protect the rewiring layer. Note that a pseudo wafer divided into constituent units each including at least one semiconductor chip is classified as an electronic component.

[0028] Another example of the wafer-level package (WLP) is one configured as shown in FIG. 3 . The wafer-level package 100 shown in FIG. 3 includes a circuit board 110 and multiple semiconductor packages 120 mounted on the circuit board 110. That is, in the wafer-level package 100, multiple semiconductor chips are individually resin-encapsulated on the circuit board 110. In the wafer-level package 100, the surfaces (the surfaces farthest from the circuit board 110) of the multiple semiconductor packages 120 may each be configured with one side of a glass piece 120a. That is, in the wafer-level package 100, each semiconductor package 120 may have the glass piece 120a at the portion farthest from the circuit board 110. When the wafer-level package 100 is configured in this manner, the protective layer 10a of the protective sheet 10 is used to protect one side of the glass piece 120a of each of the multiple semiconductor packages 120. The wafer-level package 100 is divided (cut) along a cutting line L2 as shown in Fig. 3 by a dicing process or the like, and separated into individual semiconductor packages. The individual semiconductor packages separated from the wafer-level package 100 are classified as electronic components. Note that when the area of ​​the circuit board 110 is several times (e.g., four times) larger than the area of ​​the semiconductor wafer 20 as shown in Fig. 2, the wafer-level package 100 shown in Fig. 3 is sometimes referred to as a panel-level package (PLP).

[0029] An example of the electronic component is an image sensor package 200 as shown in FIG. 4A . The image sensor package 200 includes a sensor chip body 210 having a circuit formed on one surface thereof, and a glass piece 230 (cover glass) laminated on one surface (the surface on which the circuit is formed) of the sensor chip body 210. The sensor chip body 210 and the glass piece 230 (cover glass) are laminated via an adhesive layer 220 formed of an adhesive, glass frit, or the like. The image sensor package 200 is used, for example, as an imaging element for a camera or the like. In the image sensor package 200 configured as described above, the protective layer 10a of the protective sheet 10 is used to protect the surface of the glass piece 230 (the surface opposite to the sensor chip body 210). Note that the image sensor package 200 is typically obtained by dividing an image sensor package laminate 200′ by a dicing process or the like to separate individual image sensor packages 200 each including at least one circuit, as shown in FIG. 4B . The image sensor package laminate 200' before separation includes a sensor wafer main body 210' having a plurality of circuits formed on one surface thereof, and a glass plate 230' having substantially the same dimensions as the sensor wafer main body 210' in a plan view and laminated on one surface (the surface on which the plurality of circuits are formed) of the sensor wafer main body 210' via an adhesive layer 220' made of an adhesive, glass frit, or the like. Specifically, the image sensor package 200 is separated by a dicing process along a cleavage line L3 as shown in FIG. 4B to be singulated into individual image sensor packages 200. As described above, the image sensor package laminate 200' is classified as an electronic component assembly because it is formed by connecting a plurality of image sensor packages 200.

[0030] The viscosity η of the protective layer 10a at 60°C is preferably 450,000 Pa·s or less, more preferably 400,000 Pa·s or less, even more preferably 300,000 Pa·s or less, particularly preferably 200,000 Pa·s or less, and even more particularly preferably 150,000 Pa·s or less. By having the viscosity η of the protective layer 10a at 60°C be 150,000 Pa·s or less, at least one of the bump electrodes and pillar terminals can be particularly suitably embedded in the protective layer 10a, even when the bump electrodes and / or pillar terminals are densely arranged on one side of the semiconductor wafer body. Furthermore, the viscosity η of the protective layer 10a at 60°C is preferably 2,000 Pa·s or more, more preferably 5,000 Pa·s or more, even more preferably 10,000 Pa·s or more, and particularly preferably 30,000 Pa·s or more. When the viscosity η of the protective layer 10a at 60°C is 30,000 Pa s or more and the protective layer 10a is attached to a surface to be protected, such as an electronic component, that has a periphery, the protective layer 10a is prevented from protruding beyond the periphery. Therefore, when a device including an electronic component is manufactured, the device can be prevented from being contaminated by a part of the protective layer 10a.

[0031] The viscosity η of the protective layer 10a at 60°C can be increased by, for example, increasing the molecular weight of the water-soluble polymer compound contained in the protective layer 10a, whereas the viscosity η of the protective layer 10a at 60°C can be decreased by decreasing the molecular weight of the water-soluble polymer compound contained in the protective layer 10a.

[0032] The viscosity η of the protective layer 10a can be measured using a measuring device under the trade name "Thermo Scientific HAAKE MARS III Rheometer" manufactured by Thermo Fisher Scientific. The following measurement conditions can be used. When measuring the viscosity using a protective layer with a thickness of less than 300 μm, the viscosity is measured using a measurement sample whose thickness has been adjusted to 300 μm by laminating a protective layer. Measurement sample: protective layer with a thickness of 300 μm Probe diameter: 8 mm Plate gap: 250 μm Frequency: 1 Hz Measurement temperature: 60° C.

[0033] Examples of the water-soluble polymer compound include polyvinyl alcohol (PVA), polyvinylpyrrolidone (PVP), water-soluble polyester (PES), and polymers having structural units derived from ethylene oxide. As the water-soluble polymer compound, polyvinyl alcohol, polyvinylpyrrolidone, water-soluble polyester, and polymers having structural units derived from ethylene oxide may be used alone or in combination. The water-soluble polymer compound preferably contains at least one selected from the group consisting of polyvinyl alcohol, polyvinylpyrrolidone, and water-soluble polyester, and a polymer having structural units derived from ethylene oxide. Furthermore, the water-soluble polymer compound more preferably contains at least one of polyvinyl alcohol and water-soluble polyester, and a polymer having structural units derived from ethylene oxide.

[0034] In the water-soluble polymer compound, the mass ratio of at least one selected from the group consisting of polyvinyl alcohol, polyvinylpyrrolidone, and water-soluble polyester is defined as W １ and the mass ratio of the polymer having a structural unit derived from ethylene oxide is W ２ When the mass ratio W １ The mass ratio W is preferably 50% by mass or more. １ The mass ratio W may be 60% by mass or more, 70% by mass or more, or 80% by mass or more. １may be 95% by mass or less, or may be 90% by mass or less. ２ The mass ratio W may be 5% by mass or more, or may be 10% by mass or more. ２ may be 50% by mass or less, 40% by mass or less, 30% by mass or less, or 20% by mass or less.

[0035] The saponification degree [mol %] of the polyvinyl alcohol is preferably 50 or more and 98 or less, more preferably 60 or more and 90 or less. When the saponification degree is within the above numerical range, the polyvinyl alcohol exhibits sufficient water solubility. Furthermore, when the protective layer forming composition for forming the protective layer 10a contains polyvinyl alcohol, the protective layer forming composition can be applied onto the release liner with good workability. The saponification degree of the polyvinyl alcohol can be determined by proton magnetic resonance spectroscopy ( １ The saponification degree of polyvinyl alcohol can be measured by H-NMR measurement. If the peak derived from the additive overlaps with the peak used to calculate the saponification degree due to the presence of an additive in the measurement sample, the additive is removed by subjecting the measurement sample to a methanol extraction treatment or the like, and then the saponification degree of polyvinyl alcohol is measured. The saponification degree of polyvinyl alcohol can be measured under the following conditions. <Measurement conditions> - Analytical device FT-NMR: Bruker Biospin, AVANCE III-400 - Observation frequency 400 MHz (1H) - Measurement solvent Deuterium oxide or deuterated dimethyl sulfoxide (deuterated DMSO) - Measurement temperature 80°C - Chemical shift standard External standard TSP-d4 (0.00 ppm) (when measuring deuterium oxide) Measurement solvent (2.50 ppm) (when measuring deuterium oxide) The saponification degree 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) (deuterium oxide: 2.0 to 1.0 ppm, deuterium oxide: 1.9 to 1.0 ppm) and the peaks derived from the acetyl groups of the vinyl acetate unit (VAc) (deuterium oxide: around 2.1 ppm, deuterium oxide: around 2.0 ppm). In the following formula, [VOH(-CH ２ )-] is -CH in the vinyl alcohol unit２ - means the intensity of the peak derived from [VAc(CH ３ CO-)] is the CH ３ It means the peak intensity derived from CO-.

[0036]

[0037] The weight-average molecular weight Mw of the polyvinyl alcohol is preferably 1,000 or more, more preferably 2,000 or more, even more preferably 3,000 or more, and particularly preferably 4,000 or more. Such a weight-average molecular weight Mw may be 15,000 or less, 10,000 or less, 8,000 or less, or 6,000 or less. By having the weight-average molecular weight Mw within the above numerical range, the protective layer 10a having good shape retention can be formed with a more uniform thickness. The average polymerization degree of the polyvinyl alcohol is preferably 50 or more, more preferably 70 or more, and even more preferably 90 or more. Such an average polymerization degree may be 1,000 or less, 800 or less, 600 or less, 400 or less, 200 or less, or 150 or less. By having the average polymerization degree within the above numerical range, the polyvinyl alcohol exhibits sufficient water solubility. Furthermore, when the protective layer-forming composition for forming the protective layer 10a contains polyvinyl alcohol, the protective layer-forming composition can be applied to the release liner with good workability. The weight-average molecular weight Mw and average degree of polymerization of the polyvinyl alcohol can be measured by aqueous gel permeation chromatography (aqueous GPC). The weight-average molecular weight Mw and average degree of polymerization of the polyvinyl alcohol can be measured under the following conditions. <Measurement Conditions> - Analytical Instrument: Agilent 1260Infinity - Columns: TSKgel G6000PWXL (manufactured by Tosoh Corporation) and TSKgel G3000PWXL (manufactured by Tosoh Corporation). The two columns are connected in series. - Column Temperature: 40°C - Eluent: 0.2 M aqueous sodium nitrate solution - Injection Volume: 100 μL - Detector: Differential Refractometer (RI) - Standard Samples: PEG standard sample and PVA standard sample. Specifically, the measurement is performed as follows. (1) The mass-average molecular weights Mw of the sample (PVA) and the PVA standard samples are calculated by GPC measurement using PEG standard samples. The average degree of polymerization of the PVA standard samples is known. (2) A calibration curve is created using the average degree of polymerization of the PVA standard samples and the calculated mass-average molecular weights Mw of the PVA standard samples.(3) Using the created calibration curve, the average degree of polymerization of the sample (PVA) is determined from the mass average molecular weight Mw of the sample (PVA).

[0038] 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.

[0039] 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 mixture containing the polycarboxylic acid and the polyol. Whether the water-soluble polyester has water solubility can be determined based on common general technical knowledge.

[0040] The water-soluble polyester preferably satisfies at least one of the following requirements (1) to (4): (1) When room temperature (23±2°C) water 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 thin film completely dissolves in water. (2) When 50°C water 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 completely dissolves in water. (3) When the water-soluble polyester powder and room temperature water are mixed in a mass ratio of water-soluble polyester powder:room temperature water = 1:5 to obtain a mixed solution, and the mixed solution is irradiated with ultrasound for 20 minutes, the water-soluble polyester completely dissolves in water. (4) When the water-soluble polyester powder and 50°C water are mixed in a mass ratio of water-soluble polyester powder:50°C water = 1:5 to obtain a mixed solution, and the mixed solution is irradiated with ultrasound for 10 minutes, the water-soluble polyester completely dissolves in water.

[0041] The water-soluble polyester preferably has a mass average molecular weight Mw of 40,000 (40,000) or less. When the protective layer-forming composition contains a water-soluble polyester having a mass average molecular weight Mw within the above range, the protective layer 10a can be easily formed into a film. The film-like protective layer 10a formed on the surface to be protected of an electronic component or an electronic component assembly can sufficiently prevent fine foreign matter from adhering to the surface to be protected. When the water-soluble polyester contains a water-soluble polyester having a mass average molecular weight Mw within the above range, the water solubility of the protective layer 10a is improved. The water-soluble polyester preferably has a mass average molecular weight Mw of 30,000 (30,000) or less, more preferably 20,000 (20,000) or less, and even more preferably 15,000 or less. The water-soluble polyester may also have a mass average molecular weight Mw of 5,000 or more, 7,000 or more, or 10,000 or more.

[0042] The mass average molecular weight of the water-soluble polyester is measured by the same method (GPC measurement method) as the method for measuring the mass average molecular weight of polyvinyl alcohol described above.

[0043] The polymer having a structural unit derived from ethylene oxide may be a homopolymer of ethylene oxide (EO), or a copolymer of ethylene oxide and an alkylene oxide other than ethylene oxide. The copolymer may be a random copolymer or a block copolymer. Examples of the alkylene oxide other than ethylene oxide include propylene oxide (PO) and butylene oxide (BO). When the protective layer 10a of the protective sheet 10 according to this embodiment contains a polymer having a structural unit derived from ethylene oxide, it becomes easier to adjust the viscosity η of the protective layer 10a to 500,000 Pa s or less.

[0044] Examples of the homopolymer of ethylene oxide (EO) include polyethylene glycol (PEG) having a mass average molecular weight of less than 20,000 and polyethylene oxide (PEO) having a mass average molecular weight of 20,000 or more. Polyethylene oxide (PEO) is preferred in terms of suppressing the protrusion of the protective layer 10a.

[0045] The mass average molecular weight of the polymer having a structural unit derived from ethylene oxide is measured by the same method (GPC measurement method) as the method for measuring the mass average molecular weight of polyvinyl alcohol described above, except that a PEG standard sample is used as the standard substance.

[0046] The polymer having a structural unit derived from ethylene oxide is preferably a copolymer, and among copolymers, a binary copolymer of ethylene oxide (EO) and propylene oxide (PO) is more preferable. In particular, when the protective layer 10a contains a binary copolymer of ethylene oxide (EO) and propylene oxide (PO) as a polymer having a structural unit derived from ethylene oxide, it becomes even easier to adjust the viscosity η of the protective layer 10a to 500,000 Pa s or less.

[0047] When the polymer having a structural unit derived from ethylene oxide is a binary copolymer of ethylene oxide (EO) and propylene oxide (PO), the molar ratio MR of the structural unit derived from ethylene oxide (EO) in the binary copolymer is ＥＯ is the molar ratio MR of the structural unit derived from propylene oxide (PO) ＰＯ In the binary copolymer, the molar ratio MR of the structural units derived from ethylene oxide (EO) is preferably higher than ＥＯ The molar ratio MR of the structural units derived from ethylene oxide (EO) in the binary copolymer is preferably 55 mol% or more, more preferably 60 mol% or more, even more preferably 70 mol% or more, and particularly preferably 80 mol% or more. ＥＯ In the binary copolymer, the upper limit of the molar ratio MR of the structural unit derived from propylene oxide (PO) is, for example, 90 mol %. ＰＯ The molar ratio MR of the structural units derived from propylene oxide (PO) in the binary copolymer is preferably 45 mol% or less, more preferably 40 mol% or less, even more preferably 30 mol% or less, and particularly preferably 20 mol% or less. ＰＯThe lower limit is, for example, 10 mol %.

[0048] The mass average molecular weight Mw of the polymer having structural units derived from ethylene oxide may be 100,000 or more, 200,000 or more, 300,000 or more, or 400,000 or more. Furthermore, the mass average molecular weight Mw of the polymer having structural units derived from ethylene oxide may be 1,000,000 or less, 900,000 or less, 800,000 or less, 700,000 or less, or 600,000 or less. The mass average molecular weight of the polymer having structural units derived from ethylene oxide can be measured in the same manner as the mass average molecular weight Mw of polyvinyl alcohol described above.

[0049] The viscosity of the aqueous solution containing the polymer having a structural unit derived from ethylene oxide is preferably 20 mPa·s or more, more preferably 30 mPa·s or more, and even more preferably 40 mPa·s or more, at a 2% by mass concentration at 25°C. Furthermore, the viscosity of the aqueous solution at a 2% by mass concentration at 25°C may be 500 mPa·s or less, 400 mPa·s or less, or even 300 mPa·s or less. The viscosity can be measured using a digital viscometer (product name "DV-1 Prime") manufactured by Eiko Instruments Co., Ltd. as the measuring device, using an LV-3 spindle, and at a rotation speed of 50 rpm.

[0050] In the protective sheet 10 according to this embodiment, the protective layer 10a may contain, as water-soluble polymer compounds, a first water-soluble polymer compound and a second water-soluble polymer compound having a mass-average molecular weight Mw greater than that of the first water-soluble polymer compound. In peak analysis of the mass-average molecular weight Mw based on gel permeation chromatography (GPC measurement), the first water-soluble polymer compound preferably has a peak top P1 of the mass-average molecular weight Mw in the range of 1,000 to 20,000. In peak analysis of the mass-average molecular weight Mw based on gel permeation chromatography (GPC measurement), the second water-soluble polymer compound preferably has a peak top P2 of the mass-average molecular weight Mw in the range of 100,000 to 1,000,000.

[0051] The peak top P1 is more preferably in the range of 2,000 to 15,000, even more preferably in the range of 3,000 to 8,000, and particularly preferably in the range of 4,000 to 6,000. When the peak top P1 of the mass-average molecular weight Mw of the first water-soluble polymer compound is within the above-mentioned range, the protective layer 10a can be particularly well adhered to the surface of the semiconductor wafer to be protected. Furthermore, the first water-soluble polymer compound can be particularly well dissolved in the protective layer-forming composition for forming the protective layer 10a. Examples of first water-soluble polymer compounds having a peak top P1 within the above-mentioned range include polyvinyl alcohol, polyvinylpyrrolidone, and water-soluble polyester.

[0052] The peak top P2 is more preferably in the range of 200,000 to 800,000, more preferably in the range of 300,000 to 700,000, and even more preferably in the range of 400,000 to 600,000. When the peak top P2 of the mass average molecular weight Mw of the second water-soluble polymer compound is within the above numerical range, the protective layer 10a can have a good balance of both mechanical strength and ductility. In other words, the protective layer 10a can have sufficient toughness. Examples of second water-soluble polymer compounds having a peak top P2 within the above numerical range include polymers having structural units derived from ethylene oxide.

[0053] In the protective layer 10a, the proportion of the first water-soluble polymer compound in the total amount of the first water-soluble polymer compound and the second water-soluble polymer compound is preferably less than 90% by mass, and more preferably 80% by mass or less. Furthermore, the proportion of the first water-soluble polymer compound is preferably 5% by mass or more, more preferably 10% by mass or more, and even more preferably 30% by mass or more. By ensuring that the proportion of the first water-soluble polymer compound in the total amount of the first water-soluble polymer compound and the second water-soluble polymer compound is within the above range, it is possible to achieve both good releasability of the release liner (first release liner 10d or second release liner 10e) from the protective layer 10a and good embeddability of the protective layer 10a.

[0054] The base layer 10b supports the pressure-sensitive adhesive layer 10c. The base layer 10b is made of a metal foil, a fiber sheet, a rubber sheet, a resin film, or the like.

[0055] The fiber sheet is made of, for example, paper, woven fabric, or nonwoven fabric.

[0056] Examples of materials for the resin film include polyolefins such as polyethylene, polypropylene, and ethylene-propylene copolymers; ethylene copolymers such as ethylene-vinyl acetate copolymers, ionomer resins, ethylene-(meth)acrylic acid copolymers, ethylene-(meth)acrylic acid ester random copolymers, and ethylene-(meth)acrylic acid ester alternating copolymers; polyesters such as polyethylene terephthalate, polyethylene naphthalate, and polybutylene terephthalate; polyacrylates; polyvinyl chloride (PVC); polyurethanes; polycarbonates; polyphenylene sulfide; polyamides such as aliphatic polyamides and wholly aromatic polyamides (aramids); polyether ether ketones; polyimides; polyetherimides; polyvinylidene chloride; ABS (acrylonitrile-butadiene-styrene copolymers); cellulose or cellulose derivatives; silicone-containing polymers; and fluorine-containing polymers. These may be used alone or in combination of two or more.

[0057] When the base layer 10b is made of a resin film, the base layer 10b may be obtained by non-stretch molding or by stretch molding, but is preferably obtained by stretch molding.

[0058] The surface of the base layer 10b on which the pressure-sensitive adhesive layer 10c is laminated (hereinafter simply referred to as the surface) may be subjected to a surface treatment in order to enhance adhesion to the pressure-sensitive adhesive layer 10c. The surface treatment may be a chemical method such as chromic acid treatment, ozone exposure, flame exposure, high-voltage shock exposure, or ionizing radiation treatment, or a physical method. Alternatively, the surface treatment may be a coating treatment using a coating agent such as an anchor coating agent, a primer, or an adhesive.

[0059] The surface of the base material layer 10b on which the adhesive layer 10c is not laminated (hereinafter simply referred to as the back surface) may be coated with a release agent (release agent) such as a silicone resin or a fluororesin to improve peelability.

[0060] The thickness of the base layer 10b is adjusted appropriately depending on the use mode of the protective sheet 10. For example, when the protective sheet 10 is used as a dicing tape used in a dicing process, the thickness of the base layer 10b may be 55 μm or more, or 60 μm or more. The thickness of the base layer 10b may be 195 μm or less, 190 μm or less, 170 μm or less, or 160 μm or less. When the thickness of the base layer 10b is within the above range, a laminated sheet body of the base layer 10b and the pressure-sensitive adhesive layer 10c can be efficiently produced. The thickness of the base layer 10b can be determined, for example, by measuring the thickness at five randomly selected locations using a dial gauge (manufactured by PEACOCK, Model R-205) and calculating the arithmetic average of these measured values.

[0061] In the protective sheet 10 according to this embodiment, the pressure-sensitive adhesive layer 10c has adhesiveness (pressure-sensitive adhesiveness) and can hold the protective layer 10a and the base layer 10b together by adhesive force. The pressure-sensitive adhesive layer 10c contains an adhesive to exhibit the above-described adhesiveness.

[0062] The adhesive may be, for example, one whose adhesive strength is reduced by an external action during use of the protection sheet 10 (hereinafter also referred to as a reduced-adhesion adhesive).

[0063] When a reduced-adhesion adhesive is used as the adhesive, the adhesive layer 10c can be in both a state exhibiting relatively high adhesive strength (hereinafter referred to as a high-adhesion state) and a state exhibiting relatively low adhesive strength (hereinafter referred to as a low-adhesion state) during use of the protective sheet 10. For example, when a semiconductor wafer attached to the protective layer 10a of the protective sheet 10 is cleaved, the adhesive layer 10c is in a high-adhesion state, which can prevent the multiple semiconductor chips separated by cleaving the semiconductor wafer from lifting up or peeling off from the adhesive layer 10c. In contrast, when the multiple semiconductor chips separated after cleaving the semiconductor wafer are picked up, the adhesive layer 10c is in a low-adhesion state, which makes it easier to pick up the multiple semiconductor chips from the adhesive layer 10c.

[0064] The tack-reducing adhesive is, for example, an adhesive (hereinafter also referred to as an active energy ray-curable adhesive) that can be cured by irradiation with active energy rays during use of the protective sheet 10. In this case, the tack-reducing adhesive contains a curing component that is cured by irradiation with active energy rays.

[0065] Examples of the active energy ray-curable adhesive include adhesives that are cured by irradiation with electron beams, ultraviolet rays, α rays, β rays, γ rays, or X-rays. Among these, adhesives that are cured by ultraviolet irradiation (ultraviolet-curable adhesives) are preferred.

[0066] The active energy ray-curable pressure-sensitive adhesive includes, for example, a base polymer as a main component and an active energy ray-polymerizable monomer component or an active energy ray-polymerizable oligomer component having a functional group such as an active energy ray-polymerizable carbon-carbon double bond. The base polymer is preferably an acrylic polymer. The base polymer may undergo a polymerization reaction upon irradiation with active energy rays, thereby curing the pressure-sensitive adhesive layer 10c and thereby reducing the adhesive strength of the pressure-sensitive adhesive layer 10c.

[0067] Examples of the acrylic polymer include those containing a monomer unit derived from a (meth)acrylic acid ester. Examples of (meth)acrylic acid esters include linear (meth)acrylic acid alkyl esters, branched (meth)acrylic acid alkyl esters, cyclic (meth)acrylic acid alkyl esters, and aryl (meth)acrylic acid esters. Examples of the monomer unit derived from a (meth)acrylic acid ester include 2-hydroxyethyl acrylate (HEA), ethyl acrylate (EA), butyl acrylate (BA), 2-ethylhexyl acrylate (2EHA), isononyl acrylate (iNA), lauryl acrylate (LA), 4-acryloylmorpholine (AMCO), and 2-isocyanatoethyl methacrylate (MOI). The monomer unit derived from a (meth)acrylic acid ester may be a single type, or a combination of two or more types. The acrylic polymer preferably contains 2-ethylhexyl acrylate (2EHA), 2-hydroxyethyl acrylate (HEA), and 2-isocyanatoethyl methacrylate (MOI) as monomer units derived from the (meth)acrylic acid ester. The 2-isocyanatoethyl methacrylate (MOI) may be bonded to the 2-hydroxyethyl acrylate (HEA) through a urethane reaction. The acrylic polymer may also contain lauryl acrylate (LA) and isononyl acrylate (iNA) as monomer units derived from the (meth)acrylic acid ester, in addition to 2EHA, HEA, and MOI.

[0068] The pressure-sensitive adhesive layer 10c may contain an external crosslinking agent. The external crosslinking agent is not particularly limited as long as it can react with the base polymer (e.g., an acrylic polymer) to form a crosslinked structure. Examples of such external crosslinking agents include polyisocyanate compounds, epoxy compounds, polyol compounds, aziridine compounds, and melamine-based crosslinking agents.

[0069] Examples of the active energy ray-polymerizable monomer component include urethane(meth)acrylate, trimethylolpropane tri(meth)acrylate, pentaerythritol tri(meth)acrylate, pentaerythritol tetra(meth)acrylate, dipentaerythritol monohydroxypenta(meth)acrylate, dipentaerythritol hexa(meth)acrylate, and 1,4-butanediol di(meth)acrylate. Examples of the active energy ray-polymerizable oligomer component include various oligomers such as urethane-based oligomers, polyether-based oligomers, polyester-based oligomers, polycarbonate-based oligomers, and polybutadiene-based oligomers. The content of the active energy ray-polymerizable monomer component or active energy ray-polymerizable oligomer component in the active energy ray-curable adhesive is selected within a range that appropriately reduces the adhesiveness of the adhesive layer 10c.

[0070] The active energy ray-curable adhesive preferably contains a photopolymerization initiator. Examples of the photopolymerization initiator include azo compounds, α-ketol compounds, acetophenone compounds, benzoin ether compounds, ketal compounds, aromatic sulfonyl chloride compounds, photoactive oxime compounds, benzophenone compounds, thioxanthone compounds, camphorquinone, halogenated ketones, acylphosphinoxides, and acylphosphonates. Examples of the azo compounds include azobisisobutyronitrile (AIBN).

[0071] When the pressure-sensitive adhesive layer 10c contains an external crosslinking agent, the pressure-sensitive adhesive layer 10c preferably contains the external crosslinking agent in an amount of 0.1% by mass to 3.0% by mass. When the pressure-sensitive adhesive layer 10c contains a photopolymerization initiator, the pressure-sensitive adhesive layer 10c preferably contains the photopolymerization initiator in an amount of 0.1% by mass to 10.0% by mass.

[0072] In addition to the above-mentioned components, the pressure-sensitive adhesive layer 10c may contain a crosslinking accelerator, a tackifier, an antioxidant, a colorant such as a pigment or a dye, and the like.

[0073] The thickness of the pressure-sensitive adhesive layer 10c is preferably 1 μm or more and 50 μm or less, more preferably 2 μm or more and 30 μm or less, and even more preferably 5 μm or more and 25 μm or less. The thickness of the pressure-sensitive adhesive layer 10c can be determined, for example, by measuring the thickness at five randomly selected locations using a dial gauge (manufactured by PEACOCK, Model R-205) and calculating the arithmetic average of these measured values.

[0074] The above description has been given of an adhesive whose adhesive strength can be reduced by external action during use of the protective sheet 10. An example of such an adhesive is an adhesive that can be cured by irradiation with active energy rays, but the adhesive is not limited to this. For example, the adhesive may be a pressure-sensitive adhesive that does not cure by irradiation with active energy rays.

[0075] The protective sheet 10 can be produced, for example, by bonding the protective layer 10a to a laminated sheet body in which the base layer 10b and the pressure-sensitive adhesive layer 10c are laminated together. Specifically, the protective sheet 10 can be produced by bonding the protective layer 10a to the pressure-sensitive adhesive layer 10c of the laminated sheet body.

[0076] The laminated sheet can be produced, for example, by applying a pressure-sensitive adhesive composition to the base layer 10b, in which the components for forming the pressure-sensitive adhesive layer 10c are dissolved or suspended in an organic solvent (e.g., toluene). Specifically, the pressure-sensitive adhesive composition is applied to one surface of the base layer 10b to a predetermined thickness (e.g., 10 μm) using an applicator or the like. The laminated sheet can then be produced by drying at a predetermined temperature for a predetermined time (e.g., 120°C for 2 minutes). The protective layer 10a can also be produced on one surface of a release liner. Specifically, a protective layer-forming composition is prepared by dissolving or suspending the components for forming the protective layer 10a in water. The protective layer-forming composition is applied to the release-treated surface of the release liner to a predetermined thickness (e.g., 40 μm) using an applicator or the like. The protective layer 10a can then be produced by drying at a predetermined temperature for a predetermined time (e.g., 115°C for 90 seconds). Then, protective layer 10a formed on the release-treated surface of the release liner is attached to pressure-sensitive adhesive layer 10c of the laminated sheet. Thereafter, by peeling the release liner from protective layer 10a, protective sheet 10 can be obtained, in which base layer 10b, pressure-sensitive adhesive layer 10c, and protective layer 10a are laminated in this order.

[0077] Although the specific example above shows protective sheet 10 formed by laminating substrate layer 10b, PSA layer 10c, and protective layer 10a in this order (see FIG. 1 ), protective sheet 10 is not limited to this example. Protective sheet 10 may also include protective layer 10a, a first release liner 10d overlying one side of protective layer 10a, and a second release liner 10e overlying the other side of protective layer 10a, as shown in FIG. 5 . That is, protective sheet 10 may be configured such that protective layer 10a is sandwiched between a pair of release liners (first release liner 10d and second release liner 10e) from both sides. Alternatively, protective sheet 10 may include only protective layer 10a, without including substrate layer 10b, PSA layer 10c, first release liner 10d, and second release liner 10e. In other words, the protective sheet 10 comprises at least a protective layer 10a. An example of the first release liner 10d is a base sheet made of a resin such as polyethylene terephthalate (PET) that has been subjected to a release treatment. Examples of the release treatment include silicone release treatment. The second release liner 10e may be the same as the first release liner 10d. An example of a release liner is "MRA50" manufactured by Mitsubishi Chemical Corporation.

[0078] The thickness of each of the first release liner 10d and the second release liner 10e 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 10d and the thickness of the second release liner 10e may be the same as or different from each other. The thickness of the first release liner 10d and the second release liner 10e can be determined in the same manner as the thickness of the protective layer 10a described above.

[0079] [Example of Use of Protective Sheet] The protective sheet 10 according to the present embodiment is used, for example, during back-grinding of the electronic component assembly to reduce its thickness. The protective sheet 10 according to the present embodiment is also used during dicing of the electronic component assembly to break it into individual electronic components. First, with reference to FIG. 6 , an example of using the protective sheet 10 according to the present embodiment during back-grinding will be described. Further, with reference to FIGS. 8A and 8B , an example of using the protective sheet 10 according to the present embodiment during dicing will be described. Also, an example of using a semiconductor wafer as the electronic component assembly will be described. Specifically, an example of using a semiconductor wafer 20 (see FIG. 2 ) including a semiconductor wafer main body 20 a and a plurality of electrode portions 20 b arranged on one surface of the semiconductor wafer main body 20 a will be described. As shown in FIG. 2 , each of the plurality of electrode portions 20 b is formed by a plurality of bump electrodes 20 b 1 arranged at close intervals. That is, each of the plurality of electrode portions 20b is configured by arranging a plurality of bump electrodes 20b1 at high density.

[0080] <Use in Back-Grinding> In this embodiment, back-grinding of the semiconductor wafer 20 is performed using a back-grinding device 300 as shown in Fig. 6. The back-grinding device 300 includes a suction plate 310 and a polishing head 320 disposed opposite the suction plate 310. The suction plate 310 is, for example, a vacuum chuck that suction-holds an object by reducing pressure.

[0081] In this embodiment, as shown in FIG. 6 , a semiconductor wafer 20, one side of which is protected by a protective layer 10a of a protective sheet 10, is suction-held on a suction plate 310. As shown in FIG. 6 , the other side of the semiconductor wafer main body 20a (the side opposite to the side on which the electrode portions 20b are arranged) serves as the grinding surface. Furthermore, the one side of the semiconductor wafer main body 20a, protected by the protective layer 10a, is protected by the protective layer 10a in a temperature environment of 60°C so as to embed the electrode portions 20b protruding from the one side of the semiconductor wafer main body 20a. As described above, in the protective sheet 10 according to this embodiment, the viscosity η of the protective layer 10a is a relatively low value of 500,000 Pa·s or less at 60°C. Therefore, even if multiple bump electrodes 20b1 are densely arranged on each of the multiple electrode portions 20b arranged on one side of the semiconductor wafer main body 20a, the multiple electrode portions 20b can be sufficiently embedded within the protective layer 10a.

[0082] 6, the polishing head 320 includes a polishing head body 320a and a plurality of abrasive grains 320b protruding from one surface of the polishing head body 320a. In the back-grinding process for the semiconductor wafer 20, the semiconductor wafer body 20a is ground by the abrasive grains 320b of the polishing head body 320a, and the semiconductor wafer body 20a is thinned to a predetermined thickness.

[0083] After grinding, the semiconductor wafer 20 is removed from the suction plate 310 with the protective sheet 10 attached to one side of the semiconductor wafer main body 20a. If the adhesive layer 10c is composed of an adhesive that can be cured by irradiation with active energy rays, active energy rays are irradiated from the base layer 10b side of the protective sheet 10. This irradiation causes the adhesive layer 10c to have a low adhesiveness. The protective layer 10a is peeled from the adhesive layer 10c to obtain the semiconductor wafer 20 with only the protective layer 10a attached, as shown in FIG. 7. Note that hereinafter, the semiconductor wafer 20 shown in FIG. 7 will be referred to as the semiconductor wafer 20 with the protective layer 10a attached.

[0084] <Example of Use in Dicing> In this embodiment, dicing of a semiconductor wafer 20 is performed using a blade dicing device 400 as shown in Fig. 8A. As shown in Fig. 8A, the blade dicing device 400 includes a stage ST, a liquid spray unit SP, and a dicing blade DB. Note that, below, an example of performing dicing using a semiconductor wafer 20 with a protective layer 10a as shown in Fig. 7 will be described.

[0085] In dicing the semiconductor wafer 20 with the protective layer 10a, as shown in Figure 8A, the semiconductor wafer 20 with the protective layer 10a is placed on the stage ST of the blade dicing device 400 so that the stage ST abuts the exposed surface of the semiconductor wafer 20 (the surface opposite to the surface coated with the protective layer 10a).

[0086] Next, as shown in FIG. 8B , in the blade dicing device 400, cooling water is sprayed from the liquid spray unit SP to wash the semiconductor wafer with the protective layer 10a with water, while the dicing blade DB divides the semiconductor wafer with the protective layer 10a. The semiconductor wafer with the protective layer 10a is divided so that each divided piece has at least one electrode portion 20b. Specifically, the dicing blade DB cleaves the semiconductor wafer 20 with the protective layer 10a along the cleavage line L″ shown in FIG. 8A to separate the semiconductor wafer 20 into individual pieces. In the example shown in FIG. 8B , the semiconductor wafer 20 is divided so that each divided piece has one electrode portion 20b. This results in multiple semiconductor chips 20′ each coated with a separated piece of the protective layer 10a. In other words, the dicing blade DB divides the protective layer 10a into pieces corresponding to the chip size along with the semiconductor wafer 20. As described above, by performing the blade dicing process while spraying cooling water, at least a portion of each separated piece of the protective layer 10a may be dissolved.

[0087] As described above, by dicing the semiconductor wafer 20 while protecting one surface (the surface on which the electrode portions 20b are arranged) of the semiconductor wafer main body 20a, it is possible to prevent minute foreign matter such as cutting chips generated by the dicing process from adhering to one surface of the semiconductor wafer main body 20a. After the semiconductor wafer 20 is diced into a plurality of semiconductor chips 20', the divided pieces of the protective layer 10a can be further washed with water (cold water washing or warm water washing) to remove the divided pieces of the protective layer 10a from the plurality of semiconductor chips 20'.

[0088] The matters disclosed by this specification include the following.

[0089] (1) A protective sheet comprising a protective layer that is attached to a surface to be protected of an electronic component or a surface to be protected of an electronic component assembly in which a plurality of the electronic components are connected, the protective layer containing a water-soluble polymer compound, and the viscosity η of the protective layer at 60°C is 500,000 Pa·s or less.

[0090] (2) The protective sheet according to (1), wherein the protective layer contains, as the water-soluble polymer compounds, a first water-soluble polymer compound and a second water-soluble polymer compound having a mass-average molecular weight greater than that of the first water-soluble polymer compound, and wherein, in peak analysis of the mass-average molecular weight distribution based on gel permeation chromatography measurement, the peak top of the mass-average molecular weight of the first water-soluble polymer compound is in the range of 1,000 to 20,000, and the peak top of the mass-average molecular weight of the second water-soluble polymer compound is in the range of 100,000 to 1,000,000.

[0091] (3) A protective sheet comprising a protective layer that is attached to a surface to be protected of an electronic component or a surface to be protected of an electronic component assembly in which a plurality of the electronic components are connected, the protective layer containing, as water-soluble polymer compounds, at least one of polyvinyl alcohol and a water-soluble polyester, and a polymer having a structural unit derived from ethylene oxide.

[0092] (4) The protective sheet according to any one of (1) to (3) above, comprising: a base layer disposed so as to face one side of the protective layer; and a pressure-sensitive adhesive layer disposed between the protective layer and the base layer, wherein both sides of the pressure-sensitive adhesive layer are releasably adhered to the protective layer and the base layer, respectively.

[0093] The protective sheet according to the present invention is not limited to the above-described embodiment, nor is it limited by the above-described effects. The protective sheet according to the present invention can be modified in various ways without departing from the spirit and scope of the present invention.

[0094] For example, in the above embodiment, the example of using the protective sheet 10 has been described in which the attachment target of the protective layer 10a is a semiconductor wafer 20, which is an electronic component assembly. However, the attachment target is not limited to this. The attachment target may be, for example, a wafer-level package 100 (see FIG. 3 ) as an electronic component assembly, or an image sensor package laminate 200′ (see FIG. 4B ). That is, the protective sheet 10 may be used when backgrinding the circuit board 110 of the wafer-level package 100 or when singulating the wafer-level package 100 into multiple semiconductor packages 120. The protective sheet 10 may also be used when backgrinding the sensor wafer main body 210′ ​​of the image sensor package laminate 200′ or when singulating the image sensor package laminate 200′ into multiple image sensor packages 200.

[0095] 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.

[0096] <Raw materials used> [PVA-1] Trade name "JMR-3M" manufactured by Japan Vinyl Acetate & Poval Co., Ltd. (mass average molecular weight Mw 5,000, degree of saponification 60 mol%, average degree of polymerization 100) [PVA-2] Trade name "JMR-8M" manufactured by Japan Vinyl Acetate & Poval Co., Ltd. (mass average molecular weight Mw 10,000, degree of saponification 60 mol%, average degree of polymerization 200) [PES] Water-soluble polyester Trade name "Z-221" manufactured by Goo Chemical Co., Ltd. (mass average molecular weight Mw 14,000) [EO / PO copolymer-1] Binary copolymer of ethylene oxide (EO) and propylene oxide (PO) (EO / PO binary copolymer) Trade name "ALKOX (registered trademark) EP1550H" manufactured by Meisei Chemical Industry Co., Ltd. (EO molar ratio: 85%, PO molar ratio: 15%, mass average molecular weight Mw 500,000) [EO / PO copolymer-2] A binary copolymer of ethylene oxide (EO) and propylene oxide (PO) (EO / PO binary copolymer) "ALKOX (registered trademark) EP1010N" (EO molar ratio: 85%, PO molar ratio: 15%, mass average molecular weight Mw 100,000) manufactured by Meisei Chemical Industry Co., Ltd. [PEO] Polyethylene oxide "ALKOX (registered trademark) R-150" (mass average molecular weight Mw 150,000) manufactured by Meisei Chemical Industry Co., Ltd. [PEG600] Polyethylene glycol (mass average molecular weight Mw 600) commercially available product [PEG2000] Polyethylene glycol (mass average molecular weight Mw 2,000) commercially available product

[0097] Example 1 Polyvinyl alcohol (PVA) and a binary copolymer of ethylene oxide (EO) and propylene oxide (PO) (EO / PO binary copolymer) were dispersed in water in a container to prepare an aqueous dispersion. The aqueous dispersion was prepared so that the mass ratio of PVA to EO / PO binary copolymer was 90:10. The polyvinyl alcohol used was the above-mentioned "PVA-1." The EO / PO binary copolymer used was the above-mentioned "EO / PO copolymer-1."

[0098] 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 polyvinyl alcohol in water, thereby obtaining a protective layer-forming composition. Subsequently, the protective layer-forming composition was applied using an applicator to the release-treated surface of a PET release liner (manufactured by Mitsubishi Chemical Corporation, product name "MRA50", thickness 50 μm) having a silicone release-treated surface, so that the dried thickness would be 30 μm. Furthermore, the protective layer-forming composition on the PET release liner was dried at 115°C for 90 seconds to form a 30 μm-thick protective layer on the PET release liner. Finally, the release-treated surface of another PET release liner (the same product as above) was bonded to the exposed surface of the protective layer. This produced a protective sheet having a 30 μm-thick protective layer. That is, this protective sheet was composed of a PET release liner, a 30 μm-thick protective layer, and a PET release liner laminated in this order.

[0099] Separately, a 300 μm thick protective layer was prepared by laminating three 100 μm thick protective layers. Specifically, the protective layer-forming composition was applied to the release-treated surface of a PET release liner (same as above) using an applicator in the same manner as described above, so that the dried thickness would be 100 μm. Next, a drying treatment was performed at 130°C for 300 seconds to form a 100 μm thick protective layer on the PET release liner. This operation was repeated three times in total to obtain three PET release liners with protective layers. Subsequently, a second PET release liner with protective layer was overlaid on the exposed surface of the protective layer of the first PET release liner with protective layer to obtain a laminate. In other words, a laminate with two protective layers was obtained. Furthermore, in this laminate, the PET release liner was peeled off from the second PET release liner with a protective layer to expose the protective layer, and then the protective layer of the third PET release liner with a protective layer was superimposed on the exposed surface to obtain a further laminate. That is, a laminate with three protective layers was obtained. Then, this laminate was heat-treated at a temperature of 90°C using a laminator. In this way, a protective sheet with a 300 μm-thick protective layer was produced. That is, this protective sheet was composed of a PET release liner, a 300 μm-thick protective layer, and a PET release liner laminated in this order.

[0100] The mass average molecular weight Mw, degree of saponification, and average degree of polymerization of the PVA were measured according to the methods described in the above embodiment section. The mass average molecular weight Mw of the EO / PO binary copolymer was also measured according to the methods described in the above embodiment section. In the EO / PO binary copolymer, the molar ratios of EO and PO are those at the start of polymerization. Furthermore, the viscosity η of the protective layer at 60°C was measured using a protective layer with a thickness of 300 μm. The viscosity η was measured according to the method described in the above embodiment section. The results are shown in Table 1.

[0101] Example 2 A protective layer-forming composition was obtained in the same manner as in Example 1, except that an aqueous dispersion was prepared by dispersing PVA and EO / PO binary copolymer in water so that the mass ratio of PVA to EO / PO binary copolymer was 50:50. Using this protective layer-forming composition, a protective sheet having a 30 μm-thick protective layer and a protective sheet having a 300 μm-thick protective layer were obtained in the same manner as in Example 1. That is, a protective sheet having a PET release liner, a 30 μm-thick protective layer, and a PET release liner laminated in this order, and a protective sheet having a PET release liner, a 300 μm-thick protective layer, and a PET release liner laminated in this order were produced. Furthermore, the viscosity η of the protective layer at 60°C was measured using a 300 μm-thick protective sheet. The viscosity η was measured in accordance with the method described in the embodiment section above. The results are shown in Table 1.

[0102] Example 3 A protective layer-forming composition was obtained in the same manner as in Example 2, except that a water-soluble polyester (PES) was used instead of PVA. The PES product described above was used. Furthermore, using this protective layer-forming composition, a protective sheet having a 30 μm-thick protective layer and a protective sheet having a 300 μm-thick protective layer were obtained in the same manner as in Example 1. That is, a protective sheet having a PET release liner, a 30 μm-thick protective layer, and a PET release liner laminated in this order was produced, and a protective sheet having a PET release liner, a 300 μm-thick protective layer, and a PET release liner laminated in this order was produced. Furthermore, the viscosity η of the protective layer at 60°C was measured using a 300 μm-thick protective layer. The viscosity η was measured in accordance with the method described in the embodiment section above. The results are shown in Table 1.

[0103] Example 4 A protective layer-forming composition was prepared using the same mass ratio of PVA to EO / PO binary copolymer as in Example 2. Next, using this protective layer-forming composition, a protective layer was formed on a PET release liner in the same manner as in Example 1, resulting in a thickness of 5 μm after drying, thereby obtaining a protective layer with a release liner. Separately, a protective layer was formed on a PET release liner in the same manner as in Example 1, resulting in a thickness of 60 μm after drying, thereby obtaining another protective layer with a release liner. Next, a dicing tape was prepared. Specifically, a dicing tape manufactured by Nitto Denko Corporation under the product name "UB-3200F" (substrate layer thickness: 100 μm, adhesive layer thickness: 100 μm) was prepared. Furthermore, the viscosity η of the protective layer at 60°C was measured using a protective layer (thickness: 60 μm) with a release liner. The viscosity η was measured in accordance with the method described in the above embodiment section. The results are shown in Table 1.

[0104] Next, the exposed surface of the pressure-sensitive adhesive layer of the dicing tape was superimposed on the exposed surface of the protective layer (5 μm thick) with a release liner to obtain a laminated sheet. The laminated sheet was then processed using a laminating roll at a temperature of 25°C and a speed of 10 mm / s to obtain a protective sheet with a 5 μm thick protective layer. That is, this protective sheet was composed of a substrate layer, a pressure-sensitive adhesive layer, a 5 μm thick protective layer, and a PET release liner laminated in this order. Separately, another laminated sheet was obtained by superimposing the exposed surface of the pressure-sensitive adhesive layer of the dicing tape on the exposed surface of a protective layer (60 μm thick) with a release liner. Then, another laminated sheet was processed using a laminating roll in the same manner as above to obtain a protective sheet with a 60 μm thick protective layer. That is, this protective sheet was composed of a substrate layer, a pressure-sensitive adhesive layer, a 60 μm thick protective layer, and a PET release liner laminated in this order.

[0105] Comparative Example 1 A protective layer-forming composition was obtained in the same manner as in Example 1, except that only PVA was dispersed in water. Furthermore, using this protective layer-forming composition, a protective sheet having a 30 μm-thick protective layer was obtained in the same manner as in Example 1. Separately, a protective sheet having a 300 μm-thick protective layer was obtained in the same manner. That is, a protective sheet having a 30 μm-thick protective layer with a PET release liner attached to one side thereof and a protective sheet having a 300 μm-thick protective layer with a PET release liner attached to one side thereof were produced. Furthermore, the viscosity η of the protective layer at 60°C was measured using a 300 μm-thick protective layer. The viscosity η was measured in accordance with the method described in the embodiment section above. The results are shown in Table 1.

[0106] Example 5 A protective layer-forming composition was obtained in the same manner as in Example 1, except that an aqueous dispersion was prepared by dispersing PVA and EO / PO binary copolymer in water so that the mass ratio of PVA:EO / PO binary copolymer was 75:25, that the above-mentioned "PVA-2" was used as the PVA, and that the above-mentioned "EO / PO copolymer-2" was used as the EO / PO binary copolymer. Furthermore, a protective sheet having a 30 μm-thick protective layer and a protective sheet having a 300 μm-thick protective layer were each obtained in the same manner as in Example 1. That is, a protective sheet in which a PET release liner, a 30 μm-thick protective layer, and a PET release liner were laminated in this order, and a protective sheet in which a PET release liner, a 300 μm-thick protective layer, and a PET release liner were laminated in this order were each produced. Furthermore, the viscosity η of the protective layer at 60°C was measured using a 300 μm-thick protective layer. The viscosity η was measured in accordance with the method described in the above embodiment section, and the results are shown in Table 2.

[0107] Example 6 A protective layer-forming composition was obtained in the same manner as in Example 1, except that an aqueous dispersion was prepared by dispersing PES and EO / PO binary copolymer in water so that the mass ratio of PES:EO / PO binary copolymer was 75:25, and that the above-mentioned "EO / PO copolymer-2" was used as the EO / PO binary copolymer. Furthermore, a protective sheet having a 30 μm-thick protective layer and a protective sheet having a 300 μm-thick protective layer were obtained in the same manner as in Example 1. That is, a protective sheet having a PET release liner, a 30 μm-thick protective layer, and a PET release liner laminated in this order, and a protective sheet having a PET release liner, a 300 μm-thick protective layer, and a PET release liner laminated in this order were produced. Furthermore, the viscosity η of the protective layer at 60°C was measured using a 300 μm-thick protective layer. The viscosity η was measured in accordance with the method described in the embodiment section above. The results are shown in Table 2.

[0108] Example 7 A protective layer-forming composition was obtained in the same manner as in Example 1, except that an aqueous dispersion was prepared by dispersing PES and polyethylene oxide in water so that the mass ratio of PES:polyethylene oxide was 75:25, and that the above-mentioned "PEO" was used as the polyethylene oxide. Furthermore, a protective sheet having a 30 μm-thick protective layer and a protective sheet having a 300 μm-thick protective layer were obtained in the same manner as in Example 1. That is, a protective sheet having a PET release liner, a 30 μm-thick protective layer, and a PET release liner laminated in this order, and a protective sheet having a PET release liner, a 300 μm-thick protective layer, and a PET release liner laminated in this order were produced. Furthermore, the viscosity η of the protective layer at 60°C was measured using a 300 μm-thick protective layer. The viscosity η was measured in accordance with the method described in the above embodiment section. The results are shown in Table 2.

[0109] Example 8 A protective layer-forming composition was obtained in the same manner as in Example 1, except that an aqueous dispersion was prepared by dispersing PVA and polyethylene glycol in water so that the mass ratio of PVA to polyethylene glycol was 75:25, that the above-mentioned "PVA-2" was used as the PVA, and that the above-mentioned "PEG600" was used as the polyethylene glycol. Furthermore, a protective sheet having a 30 μm-thick protective layer and a protective sheet having a 300 μm-thick protective layer were each obtained in the same manner as in Example 1. That is, a protective sheet having a PET release liner, a 30 μm-thick protective layer, and a PET release liner laminated in this order, and a protective sheet having a PET release liner, a 300 μm-thick protective layer, and a PET release liner laminated in this order were each produced. Furthermore, the viscosity η of the protective layer at 60°C was measured using a 300 μm-thick protective layer. The viscosity η was measured in accordance with the method described in the embodiment section above. The results are shown in Table 2.

[0110] Example 9 A protective layer-forming composition was obtained in the same manner as in Example 1, except that an aqueous dispersion was prepared by dispersing PES and polyethylene glycol in water at a mass ratio of PES:polyethylene glycol = 75:25, and that the above-mentioned "PEG2000" was used as the polyethylene glycol. Furthermore, a protective sheet having a 30 μm-thick protective layer and a 300 μm-thick protective layer were obtained in the same manner as in Example 1. That is, a protective sheet having a PET release liner, a 30 μm-thick protective layer, and a PET release liner laminated in this order, and a protective sheet having a PET release liner, a 300 μm-thick protective layer, and a PET release liner laminated in this order were produced, respectively. Furthermore, the viscosity η of the protective layer at 60°C was measured using a 300 μm-thick protective layer. The viscosity η was measured in accordance with the method described in the above embodiment section. The results are shown in Table 2.

[0111] Example 10 A protective layer-forming composition was obtained in the same manner as in Example 1, except that an aqueous dispersion was prepared by dispersing PES and polyethylene glycol in water to a mass ratio of PES:polyethylene glycol = 75:25, and that the above-mentioned "PEG 600" was used as the polyethylene glycol. Furthermore, a protective sheet having a 30 μm-thick protective layer and a 300 μm-thick protective layer were obtained in the same manner as in Example 1. That is, a protective sheet having a PET release liner, a 30 μm-thick protective layer, and a PET release liner laminated in this order, and a protective sheet having a PET release liner, a 300 μm-thick protective layer, and a PET release liner laminated in this order were produced. Furthermore, the viscosity η of the protective layer at 60°C was measured using a 300 μm-thick protective layer. The viscosity η was measured in accordance with the method described in the above embodiment section. The results are shown in Table 2.

[0112] (Evaluation of release liner releasability) For each of the above protective sheets, the releasability of the PET release liner from the protective layer was evaluated in an environment at a temperature of 25°C. The evaluation criteria for releasability are as follows. The evaluation results for releasability are shown in Table 1. Excellent: No adhesion of the protective layer was visually observed on the surface of the PET release liner after peeling. Poor: Adhesion of the protective layer, even if slight, was visually observed on the surface of the PET release liner after peeling.

[0113] (Evaluation 1 of Embeddability) For each of the protective sheets described above, the embeddability of a semiconductor chip having a plurality of bump electrodes on one surface (hereinafter referred to as a semiconductor chip with bump electrodes) was evaluated (Evaluation 1 of Embeddability). A semiconductor wafer (hereinafter also referred to as a semiconductor wafer with bump electrodes) was divided as follows to obtain a plurality of semiconductor chips with bump electrodes. Specifically, the semiconductor wafer with bump electrodes before division had a plurality of regions (3 mm × 3 mm regions) on one surface, in which a plurality of bump electrodes each having a diameter (bump diameter) of 45 μm in top view were arranged with a spacing (bump pitch) between adjacent bump electrodes of 150 μm. Each semiconductor chip with bump electrodes was cut from this semiconductor wafer with bump electrodes so as to include one of the plurality of regions and have planar dimensions of 5 mm × 5 mm. In Evaluation 1 of Embeddability, the protective layer after peeling off the PET release liner was used. Each bump electrode was provided so that the height from one surface of the semiconductor wafer body to the tip was 40 μm.

[0114] For embeddability evaluation 1, the protective layer of each of the above protective sheets was applied to one side of the semiconductor wafer body under conditions of a pressure (laminating pressure) of 0.4 MPa and a roller temperature of 60°C. Embeddability evaluation 1 was performed by observation with a digital microscope according to the following criteria. The evaluation results of embeddability evaluation 1 are shown in Table 1. Excellent: No optical interference was observed. That is, the entire bump electrode was sufficiently embedded inside the protective layer. Good: Some optical interference was observed in the outer periphery of each bump electrode. That is, the vicinity of the top of each bump electrode was sufficiently embedded inside the protective layer, but the outer periphery of each bump electrode was not sufficiently embedded. Poor: Clear voids were observed in the outer periphery of each bump electrode. That is, even the vicinity of the top of each bump electrode was not sufficiently embedded inside the protective layer.

[0115] (Evaluation of Embeddability 2) Two bare wafers with different planar dimensions and thicknesses were stacked in the thickness direction to prepare a test specimen having a step. Then, for each of the protective sheets described above, the embeddability of the test specimen having the step was evaluated (Evaluation of Embeddability 2). The test specimen having the step was prepared by stacking a first bare wafer having an outer diameter of 10 mm and a thickness of 700 μm and a second bare wafer having an outer diameter of 5 mm and a thickness of 300 μm, with a die bond film having a thickness of 10 μm interposed therebetween. That is, the test specimen having the step had a step height of 310 μm. In Evaluation of Embeddability 2, the protective layer after peeling off the PET release liner was also used.

[0116] For embeddability evaluation 2, the protective layer of each of the protective sheets described above was adhered to one surface (the surface having the step) of a test specimen having a step under conditions of a pressure (laminating pressure) of 0.4 MPa and a roller temperature of 60°C. In embeddability evaluation 2, the horizontal distance HD between the corner where the periphery of the second bare wafer contacts one surface of the first bare wafer and the protective layer facing the corner was measured using a digital microscope. Evaluation was performed according to the following evaluation criteria. The evaluation results of embeddability evaluation 2 are shown in Table 1. Excellent: The horizontal distance HD is 1.0 mm or less. Good: The horizontal distance HD is more than 1.0 mm and less than 2.0 mm. Poor: The horizontal distance HD is more than 2.0 mm, or the protective layer is damaged.

[0117]

[0118]

[0119] As can be seen from Tables 1 and 2, for each of the protective sheets of the Examples, the embeddability evaluation 1 result was "excellent" or "good." Furthermore, the embeddability evaluation 2 result was "excellent" or "good." In contrast, for the protective sheet of the Comparative Example, the embeddability evaluation 1 result and the embeddability evaluation 2 result were both "poor." As can be seen from the above results, by using the protective sheet of this embodiment, the electrode portion provided on one side of the semiconductor wafer can be sufficiently embedded inside the protective layer. Therefore, it is believed that when the protective sheet of this embodiment is used to back-grind the semiconductor wafer, thickness variations in the semiconductor wafer body provided on the semiconductor wafer can be suppressed. The evaluation results for the above-mentioned "evaluation of the release liner's releasability" were all "excellent." Furthermore, a protective layer was attached to the surface to be protected so that the edge of the adherend, the silicon wafer (surface to be protected), overlapped with the edge of the protective layer, and observations were made to determine whether the protective layer protruded beyond the edge. Protrusion was observed for each of the protective layers of Examples 8 to 10, but not for the other protective layers.

[0120] Reference Example An aqueous dispersion was prepared by dispersing PVA and EO / PO binary copolymer in water so that the mass ratio of PVA:EO / PO binary copolymer was 5:95. The above-mentioned "PVA-1" was used as the PVA, and the above-mentioned "EO / PO copolymer-1" was used as the EO / PO binary copolymer. Thereafter, a protective layer-forming composition was obtained in the same manner as in Example 1. Next, a 30 μm thick protective layer was formed on a PET release liner in the same manner as in Example 1. That is, a protective sheet was obtained in which a PET release liner, a 30 μm thick protective layer, and a PET release liner were laminated in this order. Separately, a 300 μm thick protective layer was formed on a PET release liner in the same manner as in Example 1. That is, a further protective sheet was obtained in which a PET release liner, a 300 μm thick protective layer, and a PET release liner were laminated in this order.

[0121] For the protective sheet of the reference example (protective layer thickness: 30 μm), evaluation 1 of embeddability was performed using the same method as above. The results are shown in Table 3. Furthermore, for the protective sheet of the reference example (protective layer thickness: 300 μm), evaluation 2 of embeddability was performed using the same method as above. The results are shown in Table 3.

[0122]

[0123] As can be seen from Table 3, the protective sheet according to the reference example received "excellent" results in both embeddability evaluation 1 and embeddability evaluation 2.

[0124] The protective sheet of the present invention is preferably used as an auxiliary tool when manufacturing electronic component devices such as semiconductor devices. The method for manufacturing an electronic component device of the present invention is preferably used when manufacturing electronic component devices such as semiconductor devices.

[0125] 10: Protective sheet, 10a: Protective layer, 10b: Base material layer, 10c: Adhesive layer, 10d: First release liner, 10e: Second release liner, 20: Semiconductor wafer, 20a: Semiconductor wafer main body, 20b: Electrode portion, 20b1: Bump electrode, 20': Semiconductor chip, 100: Wafer level package, 110: Circuit board, 120: Semiconductor package, 120a: Glass piece, 200: Image sensor package, 210: Sensor chip main body, 220: Adhesive layer, 230: Glass piece, 200': Laminate for image sensor package, 210': Sensor wafer main body, 220': Adhesive layer, 230': Glass plate, 300: Back grinding device, 310: Suction plate, 320: Polishing head, 320a: Polishing head main body, 320b: Abrasive grains, 400: Blade dicing device, DB: Dicing blade, SP: Liquid spraying unit, ST: Stage.

Claims

1. a protective layer attached to a surface to be protected of an electronic component or to a surface to be protected of an electronic component assembly in which a plurality of the electronic components are connected, the protective layer contains, as water-soluble polymer compounds, a first water-soluble polymer compound and a second water-soluble polymer compound having a mass-average molecular weight greater than that of the first water-soluble polymer compound; A protective sheet, wherein the viscosity η of the protective layer at 60°C is 2,000 Pa·s or more and 450,000 Pa·s or less.

2. A protective sheet as described in claim 1, wherein, in peak analysis of mass molecular weight distribution based on gel permeation chromatography measurement, the peak top of the mass average molecular weight of the first water-soluble polymer compound is in the range of 1,000 to 20,000, and the peak top of the mass average molecular weight of the second water-soluble polymer compound is in the range of 100,000 to 1,000,000.

3. A protective sheet according to claim 1 or 2, a protective layer comprising, as the water-soluble polymer compound, at least one of polyvinyl alcohol and a water-soluble polyester as the first water-soluble compound, and a polymer having a structural unit derived from ethylene oxide as the second water-soluble compound.

4. a base layer disposed opposite one surface of the protective layer; a pressure-sensitive adhesive layer disposed between the protective layer and the base layer, The protective sheet according to claim 1 or 2, wherein both sides of the pressure-sensitive adhesive layer are releasably adhered to the protective layer and the base layer, respectively.