Method for forming a protective film, and method for manufacturing a chip

Abstract

We propose a novel technology for forming a protective film to protect the surface of a wafer. [Solution] A method for forming a protective film to protect the surface of a wafer, comprising: a first protective film forming step of applying a first liquid resin to the surface of the wafer and curing it by external stimuli to form a first protective film; and a second protective film forming step of applying a second liquid resin that hardens by external stimuli to the surface of the first protective film and curing it by external stimuli to form a second protective film on the first protective film, wherein the first liquid resin neutralizes the acid generated when the second liquid resin is exposed to external stimuli.

Description

Technical Field

[0001] The present invention relates to a method for forming a protective film on a workpiece such as a wafer.

Background Art

[0002] Conventionally, in the manufacturing process of device chips used in electronic devices such as mobile phones and personal computers, first, a plurality of planned division lines (streets) intersecting each other are set on the surface of a wafer made of a material such as a semiconductor. Then, devices such as ICs (Integrated Circuits) and LSIs (Large-scale Integration) are formed in each region partitioned by the planned division lines. Thereafter, the wafer is divided along the planned division lines to form individual device chips.

[0003] When the wafer is cut by a cutting blade, there are problems that cutting chips adhere to bonding pads such as ICs and LSIs, hindering wiring such as wire bonding, and cutting chips enter into a fine device structure, significantly deteriorating the quality.

[0004] Therefore, a method for processing a wafer has been proposed in which a protective film is formed on the device surface of the wafer, and the wafer is cut together with the protective film to be divided into individual chips (Patent Document 1, Patent Document 2). In this case, since cutting water and cutting chips do not come into contact with the device surface of the wafer, it is possible to prevent quality deterioration due to contamination of the device surface.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0006] As materials used to form the aforementioned protective film, for example, tapes, waxes, and liquid epoxy resins that harden when exposed to external stimuli such as ultraviolet light are used. However, if the protective film formed by these materials is soft, it can cause clogging of the cutting blade during cutting. As a result, the cutting ability of the cutting blade decreases, and the quality of the cutting process deteriorates significantly.

[0007] To prevent a decrease in the cutting ability of such cutting blades, protective films are generally required to be highly hard. However, liquid epoxy resins with such properties, for example, generate acid during polymerization, which can lead to acidic corrosion of the device surface to be protected, making their use difficult.

[0008] The present invention has been made in view of the above, and proposes a novel technique for forming a protective film for protecting the surface of a wafer. [Means for solving the problem]

[0009] The problems that this invention aims to solve are as described above, and the means for solving these problems will now be explained.

[0010] According to one aspect of the present invention, a method for forming a protective film to protect the surface of a wafer comprises: a first protective film forming step of applying a first liquid resin to the surface of the wafer and curing it by external stimuli to form a first protective film; and a second protective film forming step of applying a second liquid resin that hardens by external stimuli to the surface of the first protective film and curing it by external stimuli to form a second protective film on the first protective film, wherein the first liquid resin neutralizes the acid generated when the second liquid resin is exposed to external stimuli.

[0011] Furthermore, according to one aspect of the present invention, the first liquid resin is a resin composition containing (meth)acrylate, a polymerization initiator, and a base generator.

[0012] Furthermore, according to one aspect of the present invention, the polymerization initiator comprises at least one of a photopolymerization initiator or a thermal polymerization initiator, and the base generator comprises at least one of a photobase generator or a thermal base generator.

[0013] Furthermore, according to one aspect of the present invention, the second liquid resin is a resin composition containing an epoxy resin and a polymerization initiator.

[0014] Furthermore, according to one aspect of the present invention, the polymerization initiator of the second liquid resin contains at least one of a photoacid generator or a thermoacid generator.

[0015] Furthermore, according to one aspect of the present invention, the first protective film and / or the second protective film are formed by spin coating and / or pressing.

[0016] Furthermore, according to one aspect of the present invention, the external stimulus is light or heat.

[0017] Furthermore, according to one aspect of the present invention, a chip manufacturing method comprising: a first protective film forming step of applying a first liquid resin to the surface of the wafer and curing it by external stimuli to form a first protective film; a second protective film forming step of applying a second liquid resin that hardens by external stimuli to the surface of the first protective film and curing it by external stimuli to form a second protective film on the first protective film; and a division step of dividing the wafer along a planned division line and dividing it into individual chips, wherein the first liquid resin neutralizes the acid generated when the second liquid resin is exposed to external stimuli.

[0018] Furthermore, according to one aspect of the present invention, the process includes a protective film removal step, which involves removing the first protective film and / or the second protective film, after the dividing step. [Effects of the Invention]

[0019] The present invention provides the following effects: That is, according to one aspect of the present invention, even when an epoxy resin that exhibits a high altitude after curing is used as the second protective resin and an acid is generated when the second protective resin polymerizes and cures, the first protective film exhibits basicity, so that the acid is neutralized, and the device can be prevented from being corroded by the acid. In addition, since the second protective film exhibits a high altitude, clogging of the cutting blade can be prevented, and improvement in processing quality and improvement in maintainability (reduction in the number of maintenance times) can be achieved.

Brief Description of the Drawings

[0020] [Figure 1] It is a schematic diagram of a wafer to be processed. [Figure 2] It is a flowchart regarding the method for forming a protective film of the present invention. [Figure 3] (A) is a diagram showing how the first protective resin is supplied. (B) is a diagram showing how the first protective resin is spread. [Figure 4] (A) is a diagram showing how the first protective resin is cured to form the first protective film. (B) is a diagram showing how the second protective resin is supplied. [Figure 5] (A) is a diagram showing how the first protective resin is spread. (B) is a diagram showing how the second protective resin is cured to form the second protective film. [Figure 6] (A) is a diagram showing how a cutting groove is formed with a cutting blade. (B) is a diagram showing how it is divided into chips. [Figure 7] (A) is a diagram showing how the protective film is removed. (B) is a diagram showing the chip from which the protective film has been removed. [Figure 8] (A) is a diagram showing how the first protective resin is spread by pressing. (B) is a diagram showing how the first protective resin is cured to form the first protective film. [Figure 9] (A) is a diagram showing how the wafer is peeled off from the peeling member. (B) is a diagram showing how the first protective resin is spread by pressing. [Figure 10] (A) is a diagram showing the curing of the second protective resin to form the second protective film. (B) is a diagram showing the wafer being peeled off the release member. [Modes for carrying out the invention]

[0021] Embodiments of the present invention will be described below with reference to the drawings. Figure 1 is a schematic diagram of a wafer W that is the workpiece to be processed in the protective film formation method according to the present invention. Multiple devices D are formed on the surface Wa, which is one side of the wafer W. The devices D are arranged in areas demarcated by, for example, grid-like division lines S (streets), and are later divided along the division lines S to form individual chips.

[0022] The material of the wafer W is not particularly limited, but examples include silicon, glass, sapphire, and resin. The shape of the wafer W is also not particularly limited, but examples include disc-shaped and rectangular-shaped wafers.

[0023] In this invention, a protective film is formed on the surface Wa of the wafer W in order to prevent damage to the device D when the wafer W is separated into chips. Figure 2 shows each step of the protective film formation method, and each step will be described below.

[0024] <First protective film formation step> As shown in Figures 3(A)(B) and 4(A), the first protective resin J1 is applied to the entire surface Wa of the wafer W and cured by external stimuli to form the first protective film H1.

[0025] Specifically, as shown in Figure 3(A), first, the back surface Wb of the wafer W is placed on the turntable 21, exposing the front surface Wa of the wafer W upwards. Next, as shown in Figure 3(B), a liquid first protective resin J1 is supplied to the center of the front surface Wa of the wafer W, and the turntable 21 is rotated to spread the first protective resin J1 over the entire surface Wa, thereby performing a so-called spin coating process that covers the surface Wa with the first protective resin J1.

[0026] Next, as shown in Figure 4(A), a UV irradiation unit 40 (ultraviolet irradiation unit) is used as a means of applying external stimuli, and a predetermined amount of ultraviolet light is irradiated onto the first protective resin J1 that covers the surface Wa for a predetermined time to cure the first protective resin J1 by polymerization, thereby forming the first protective film H1.

[0027] Furthermore, in addition to using ultraviolet light as an external stimulus, heat may also be used as an external stimulus to cure the first protective resin J1. In other words, the first protective resin J1 is cured by applying heat to it using a heater or the like.

[0028] The first protective resin J1 contains acrylic resin and can be cured by UV (ultraviolet) light. In addition, when heat is used as an external stimulus, a heat-curing material is used. Furthermore, the first protective resin J1 exhibits basicity due to a base-generating agent, and as will be described later, the acid (cation) generated when the second protective film hardens prevents corrosion of device D and the surface Wa on which device D is formed. Furthermore, by using a water-soluble material for the first protective resin J1, it can be removed later by washing with water.

[0029] (Meth)acrylate is used as the acrylic resin contained in the first protective resin J1. In addition to (meth)acrylate, the first protective resin J1 may also contain a polymerization initiator and a base generator.

[0030] (Meth)acrylates include, for example, Light Acrylate IAA, AT-600, UA-306H, UA-306T, UA-306I, UA-510H, UF-8001G, DAUA-167, UF-07DF (all manufactured by Kyoeisha Chemical Co., Ltd.), R-1235, R-1220, RST-201, RST-402, R-1301, R-1304, R-1214, R-1302XT, GX-8801A, R-1603, R-1150D, DOCR-102, DOCR-206 (all manufactured by Daiichi Kogyo Seiyaku Co., Ltd.), UX-3204, UX-4101, UXT-610. You can use 0, UX-6101, UX-7101, UX-8101, UX-0937, UXF-4001-M35, UXF-4002, DPHA-40H, UX-5000, UX-5102D-M20, UX-5103D, UX-5005, UX-3204, UX-4101, UX-6101, UX-7101, UX-8101, UX-0937, UXF-4001-M35, UXF-4002, UXT-6100, DPHA-40H, UX-5000, UX-5102D-M20, UX-5103, and UX-5005 (all manufactured by Nippon Kayaku Co., Ltd.). Furthermore, examples of (meth)acrylates include tetrahydrofurfuryl acrylate, isobornyl acrylate, phenylglycidyl ether acrylate, and 1,9-nonanediol diacrylate. Specifically, tetrahydrofurfuryl acrylate or isobornyl acrylate can be used.

[0031] The polymerization initiator contains at least one of a photopolymerization initiator or a thermal polymerization initiator, or both, and can be appropriately selected depending on the type of external stimulus applied when curing the first liquid resin.

[0032] Examples of photopolymerization initiators include those activated by irradiation with light of a wavelength of 250 to 800 nm, and specifically include acetophenone derivative compounds such as methoxyacetophenone; benzoin ether compounds such as benzoin propyl ether and benzioin isobutyl ether; ketal derivative compounds such as benzyldimethyl ketal and acetophenone diethyl ketal; phosphine oxide derivative compounds; bis(η5-cyclopentadienyl) titanocene derivative compounds, benzophenone, Michler ketone, chlorothioxanthone, todecylthioxanthone, dimethylthioxanthone, diethylthioxanthone, α-hydroxycyclohexylphenyl ketone, and 2-hydroxymethylphenylpropane, which are photoradical polymerization initiators.

[0033] Thermal polymerization initiators include those that decompose upon heat and generate active radicals that initiate polymerization curing. Specifically, examples include dicumyl peroxide, di-t-butyl peroxide, t-butyl peroxybenzoyl, t-butyl hydroperoxide, benzoyl peroxide, cumene hydroperoxide, diisopropylbenzene hydroperoxide, paramentane hydroperoxide, and di-t-butyl peroxide. Among these, cumene hydroperoxide, paramentane hydroperoxide, and di-t-butyl peroxide are preferred due to their high thermal decomposition temperatures.

[0034] The base generator contains at least one of a photobase generator or a thermal base generator, or both, and can be appropriately selected depending on the type of external stimulus applied when curing the first liquid resin.

[0035] Photobase generators are compounds that generate bases (anions) upon irradiation with ultraviolet light, and specifically include, for example, transition metal complexes, compounds having a benzylcarbamate structure, compounds having an ortho-substituted nitrobenzene structure, oximes, imidazole derivatives, benzoin compounds, compounds having an N-formylated aromatic amino group, compounds having an N-acylated aromatic amino group, compounds having an alkoxybenzylcarbamate group, compounds having a 1,4-dihydropyridine skeleton, oxime esters, quaternary ammonium salts, and the like.

[0036] Thermal base generators are compounds that generate bases (anions) upon heating. Specifically, examples include carbamate derivatives such as 2-(4-biphenyl)-2-propylcarbamate and 1,1-dimethyl-2-cyanoethylcarbamate, urea derivatives such as urea and N,N,N'-trimethylurea, dihydropyridine derivatives such as 1,4-dihydronicotinamide, dicyandiamides, and salts composed of acids and bases such as organic salts and inorganic salts.

[0037] As one example of the first protective resin J1, the following formulation is used. (Meth)acrylate:isobornyl acrylate:(98% by weight (wt%)) Polymerization initiator: omnirad184: (1 wt%) Base-generating agent: 1,2-dicyclohexyl-4,4,5,5-tetramethylbiguanidium-n-butyltriphenyl borate: (1 wt%)

[0038] <Second protective film formation step> As shown in Figures 4(B) and 5(A)(B), the second protective resin J2, which hardens upon external stimuli, is applied to the entire surface Ha of the first protective film H1 and hardened by external stimuli, thereby forming the second protective film H2 on top of the first protective film H1.

[0039] Specifically, as shown in Figure 4(B), first, liquid second protective resin J2 is supplied to the center of the wafer W surface (surface Ha of the first protective film H1) on which the first protective film H1 is formed. Next, as shown in Figure 5(A), the second protective resin J2 is spread over the entire surface Ha of the first protective film H1 by rotating the turntable 31, and so-called spin coating is performed to cover the first protective film H1 with the second protective resin J2.

[0040] Next, as shown in Figure 5(B), a UV irradiation unit 50 (ultraviolet irradiation unit) is used as a means of applying external stimuli, and the second protective resin J2 is irradiated with a predetermined amount of ultraviolet light for a predetermined time to cure the second protective resin J2 by ​​polymerization, thereby forming the first protective film H2.

[0041] Furthermore, in addition to using ultraviolet light as an external stimulus, heat may also be used as an external stimulus to cure the second protective resin J2. In other words, the second protective resin J2 is cured by applying heat to it using a heater or the like.

[0042] Here, the second protective resin J2 contains an epoxy resin and a polymerization initiator. Epoxy resins can be cured by UV (ultraviolet) light, or, when heat is used as an external stimulus, those that cure by heat are used. Furthermore, the second protective resin J2 is acidic due to the presence of epoxy resin. As will be described later, the acid (cation) generated when the second protective film hardens is neutralized by the alkali (anion) generated by the base generating agent contained in the first protective resin J1 (first protective film H1). Furthermore, by using a water-soluble second protective resin J2, it can be removed later by washing with water.

[0043] Examples of epoxy resins contained in the second protective resin J2 include bisphenol A type liquid epoxy resin, jER828 (manufactured by Mitsubishi Chemical Corporation).

[0044] The polymerization initiator contained in the second protective resin J2 contains at least one of a photopolymerization initiator or a thermal polymerization initiator, or both, and can be appropriately selected depending on the type of external stimulus applied when curing the second liquid resin.

[0045] Examples of photopolymerization initiators include those activated by irradiation with light of a wavelength of 250 to 800 nm, and specifically include acetophenone derivative compounds such as methoxyacetophenone; benzoin ether compounds such as benzoin propyl ether and benzioin isobutyl ether; ketal derivative compounds such as benzyldimethyl ketal and acetophenone diethyl ketal; phosphine oxide derivative compounds; bis(η5-cyclopentadienyl) titanocene derivative compounds, benzophenone, Michler ketone, chlorothioxanthone, todecylthioxanthone, dimethylthioxanthone, diethylthioxanthone, α-hydroxycyclohexylphenyl ketone, and 2-hydroxymethylphenylpropane, which are photoradical polymerization initiators.

[0046] Thermal polymerization initiators include those that decompose upon heat and generate active radicals that initiate polymerization curing. Specifically, examples include dicumyl peroxide, di-t-butyl peroxide, t-butyl peroxybenzoyl, t-butyl hydroperoxide, benzoyl peroxide, cumene hydroperoxide, diisopropylbenzene hydroperoxide, paramentane hydroperoxide, and di-t-butyl peroxide. Among these, cumene hydroperoxide, paramentane hydroperoxide, and di-t-butyl peroxide are preferred due to their high thermal decomposition temperatures.

[0047] As one example of the second protective resin J2, the following formulation is used. Epoxy resin: Polycondensate of 4,4'-isopropylidenediphenol and 1-chloro-2,3-epoxypropane (99% by weight (wt%)) Polymerization initiator: CPI-100P: (1 wt%)

[0048] <Splitting Steps> As shown in Figures 6(A) and 6(B), this step involves dividing the wafer W along the planned division line S and separating it into individual chips C.

[0049] In this embodiment, the wafer W is held by suction on the holding table 12 with the second protective resin J2 exposed, and a high-speed rotating cutting blade 14 is used to cut into the wafer W along the planned division line S, thereby forming a cutting groove.

[0050] During this cutting process, the surface Wa of the wafer W is protected by the first protective resin J1 and the second protective resin J2, thereby preventing damage to the device D.

[0051] In addition to performing cutting using the cutting blade 14, laser processing using a laser processing device may be used to form dividing grooves along the planned dividing lines or to form a modified layer.

[0052] <Protective film removal step> As shown in Figures 7(A) and 7(B), this is the step of removing the first protective film H1 and the second protective film H2.

[0053] These protective films can be removed, for example, by washing with water if the first protective film H1 and the second protective film H2 are formed by water-soluble first protective resin J1 and second protective resin J2. Alternatively, for example, the first protective film H1 and the second protective film H2 may be removed from the surface Wa of the wafer W by peeling, and then the surface Wa may be washed with a cleaning solution such as water.

[0054] Alternatively, the second protective film H2 may be removed while the first protective film H1 remains, and another process may be performed.

[0055] In addition to the embodiments described above, in the first protective film formation step, as shown in Figures 8(A)(B) and 9(A), the first protective resin J1 may be expanded by pressing and the first protective film H1 may be formed by applying external stimuli.

[0056] Specifically, as shown in Figure 8(A), a release member 82 is laid on the holding table 81, and the first protective resin J1 is supplied to the release surface 82a formed on the upper side of the release member 82. The release member 82 has a flat surface, and after the first protective resin J1 has hardened and formed, the first protective film H1 can be easily peeled off.

[0057] The release member 82 is composed of, for example, a translucent resin film that has release properties, or a translucent plate-shaped member (made of glass or resin) that has been treated to exhibit release properties.

[0058] Next, with the surface Wa of the wafer W facing downwards, the first protective resin J1 is spread out by the surface Wa so that the gap between the wafer W and the release member 82 is filled with the first protective resin J1.

[0059] Next, as shown in Figure 8(B), the first protective film H1 is formed by curing the first protective resin J1 by irradiating it with a predetermined amount of ultraviolet light for a predetermined time through the release member 82 using the UV irradiation unit 84 (ultraviolet irradiation unit) as shown in Figure 8(B). In the case of using heat as an external stimulus, the first protective resin J1 may be cured by applying heat to it using a heater or the like.

[0060] Next, as shown in Figure 9(A), the wafer W is moved upward to peel off the first protective film H1 from the peeling member 82.

[0061] Similarly, in the second protective film formation step, as shown in Figures 9(B) and 10(A)(B), the second protective resin J2 may be expanded by pressing, and the second protective film H2 may be formed by applying external stimuli.

[0062] Specifically, as shown in Figure 9(B), a release member 92 is laid on the holding table 91, and a second protective resin J2 is supplied to the release surface 92a formed on the upper side of the release member 92. The release member 92 has a flat surface, and after the second protective resin J2 has hardened and formed, the second protective film H2 can be easily peeled off.

[0063] The release member 92 is composed of, for example, a translucent resin film that has release properties, or a translucent plate-shaped member (made of glass or resin) that has been treated to exhibit release properties.

[0064] Next, with the first protective film H1 formed on the wafer W facing downwards, the second protective resin J2 is pushed and spread out by the first protective film H1 so that the gap between the first protective film H1 and the release member 92 is filled with the second protective resin J2.

[0065] Next, as shown in Figure 10(A), the second protective film H2 is formed by curing the second protective resin J2 by ​​irradiating it with a predetermined amount of ultraviolet light for a predetermined time through the release member 92 using the UV irradiation unit 94 (ultraviolet irradiation unit) as shown in Figure 10(A). In the case of using heat as an external stimulus, the second protective resin J2 may be cured by applying heat to it using a heater or the like.

[0066] Next, as shown in Figure 10(B), the wafer W is moved to peel off the second protective film H2 from the peeling member 92.

[0067] The present invention can be implemented as described above. Furthermore, according to the embodiment of the present invention, when an epoxy resin that exhibits high hardness after curing is used as the second protective resin, even if acid is generated when the second protective resin polymerizes and hardens, the acid is neutralized by the first protective film exhibiting basicity, thereby preventing the device from being corroded by the acid. In addition, because the second protective film exhibits high hardness, clogging of the cutting blade can be prevented, leading to improved processing quality and improved maintainability (reduction in the number of maintenance cycles). [Explanation of Symbols]

[0068] 12 Holding Table 14 Cutting Blades 21 Rotating Platform 31 Rotating Platform 40 Irradiation Units 50 irradiation units 81 Retention Table 82 Release Member 82a Peeling surface 84 Irradiation Units 91 Holding Table 92 Release Member 92a Peeling surface 94 Irradiation Unit C Chip D Device H1 1st protective film H2 2nd protective film Ha surface J1 First protective resin J2 Second protective resin S division planned line W wafer Wa surface Wb back side

Claims

1. A method for forming a protective film to protect the surface of a wafer, A first protective film forming step involves applying a first liquid resin to the surface of the wafer and curing it by external stimuli to form a first protective film, A second protective film forming step is to apply a second liquid resin that hardens upon external stimuli to the surface of the first protective film and harden it upon external stimuli to form a second protective film on the first protective film, It has, A method for forming a protective film, wherein the first liquid resin neutralizes the acid generated when the second liquid resin is exposed to external stimuli.

2. The first liquid resin is, This is a resin composition containing (meth)acrylate, a polymerization initiator, and a base generator. The method for forming a protective film according to feature 1.

3. The polymerization initiator comprises at least one of a photopolymerization initiator or a thermal polymerization initiator. The base generator contains at least one of a photobase generator or a thermal base generator. The method for forming a protective film according to feature 2.

4. The second liquid resin is, This is a resin composition containing epoxy resin and a polymerization initiator. A method for forming a protective film according to any one of claims 1 to 3.

5. The polymerization initiator of the second liquid resin contains at least one of a photoacid generator or a thermoacid generator. The method for forming a protective film according to feature 4.

6. The first protective film and / or the second protective film are Formed by spin coating and / or pressing, A method for forming a protective film according to any one of claims 1 to 3.

7. The first protective film and / or the second protective film are Formed by spin coating and / or pressing, The method for forming a protective film according to feature 4.

8. The first protective film and / or the second protective film are Formed by spin coating and / or pressing, The method for forming a protective film according to feature 5.

9. The method for forming a protective film according to any one of claims 1 to 3, characterized in that the external stimulus is light or heat.

10. The method for forming a protective film according to claim 4, characterized in that the external stimulus is light or heat.

11. The method for forming a protective film according to claim 5, characterized in that the external stimulus is light or heat.

12. The method for forming a protective film according to claim 6, characterized in that the external stimulus is light or heat.

13. The method for forming a protective film according to claim 7, characterized in that the external stimulus is light or heat.

14. The method for forming a protective film according to claim 8, characterized in that the external stimulus is light or heat.

15. A first protective film forming step involves applying a first liquid resin to the surface of the wafer and curing it by external stimuli to form a first protective film, A second protective film forming step is to apply a second liquid resin that hardens upon external stimuli to the surface of the first protective film and harden it upon external stimuli to form a second protective film on the first protective film, The process includes a splitting step of dividing the wafer along a planned splitting line and separating it into individual chips, A method for manufacturing a chip, characterized in that the first liquid resin neutralizes the acid generated when the second liquid resin is exposed to external stimuli.

16. After the division step, A protective film removal step is included, which involves removing the first protective film and / or the second protective film. The method for manufacturing a chip according to claim 15, characterized in that it is a chip manufacturing method.

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