Protective film forming agent, protective film, protective film manufacturing method, and semiconductor chip manufacturing method

Abstract

Provided are a protective film forming agent, a protective film obtained using the protective film forming agent, a protective film manufacturing method, and a semiconductor chip manufacturing method, the protective film forming agent containing a metal salt of tin, a first resin having no aromatic ring, and a solvent.

Description

Protective film forming agent, protective film, method for manufacturing protective film, and method for manufacturing semiconductor chip

[0001] The present invention relates to a protective film-forming agent, a protective film, a method for manufacturing a protective film, and a method for manufacturing a semiconductor chip.

[0002] Wafers formed in the semiconductor device manufacturing process are stacks of insulating films and functional films on the surface of semiconductor substrates such as silicon substrates, which are then divided into sections by grid-like dividing lines called streets. Multiple semiconductor chips are obtained by cutting the wafer along these streets (chipping). In other words, each area divided by the streets becomes a semiconductor chip such as an IC or LCI.

[0003] By cutting the wafer along these streets, multiple semiconductor chips are obtained. For example, in the case of an optical device wafer, a stack of layers of gallium nitride compound semiconductors and the like is divided into multiple regions by the streets. By cutting along these streets, the optical device wafer is divided into optical devices such as light-emitting diodes and laser diodes. These optical devices are widely used in electrical equipment.

[0004] Such wafer cutting is performed by, for example, plasma dicing. Plasma dicing is a processing technique in which a wafer is cut into chips by dry etching under vacuum or reduced pressure. Plasma dicing uses, for example, the Bosch process, which can deeply dig into the wafer.

[0005] Patent Document 1 discloses a method for dicing a substrate containing a plurality of ICs, the method including the steps of: forming a mask on the substrate to cover and protect the ICs, the mask including a layer of water-soluble material in contact with the top surface of the ICs; patterning the mask by a laser scribing process to provide a patterned mask having gaps that expose areas of the substrate between the ICs; and plasma etching the substrate through the gaps in the patterned mask to singulate the ICs.

[0006] Special table 2014-523112 publication

[0007] When cutting a wafer by plasma dicing, a protective film is formed on the surface of the wafer to protect the wafer. The protective film prevents impurities such as cutting debris and other particles generated during dicing from adhering to the wafer surface, but there is still room for improvement in the performance of the protective film.

[0008] Typically, protective films are formed by applying a protective film-forming agent to a wafer and forming a film. However, if cracks occur in the protective film, impurities such as cutting debris and other particles adhere to the wafer, contaminating or damaging the wafer. Furthermore, when performing plasma dicing on a device with steps, the protective film may not be thick enough at the top of the steps, resulting in unintended thinning. For these reasons, protective film-forming agents are required to have excellent film-forming properties that can suppress the occurrence of cracks.

[0009] In plasma dicing, wafers are etched using etching gases such as fluorine-based gases. In this process, radicals generated from such etching gases (e.g., fluorine radicals generated from fluorine-based gases) can unnecessarily etch or damage the wafer. Such unintended etching can lead to increased thickness loss of the protective film. For this reason, protective film-forming agents are required to have a high selectivity between the protective film and the film to be etched.

[0010] The present invention has been made in consideration of the above circumstances, and its main object is to provide a protective film forming agent that has excellent film-forming properties and can produce a protective film having a high selectivity, as well as a protective film obtained using such a protective film forming agent, a method for manufacturing a protective film, and a method for manufacturing a semiconductor chip.

[0011] As a result of extensive research to achieve the above-mentioned objective, the inventors unexpectedly discovered that a protective film-forming agent containing a metal salt of tin, a first resin not having an aromatic ring, and a solvent could be obtained, and thus the present invention was completed.

[0012] That is, the present invention is as follows. <1> A protective film-forming agent containing a metal salt of tin, a first resin not having an aromatic ring, and a solvent. <2> The protective film-forming agent according to <1>, further containing a second resin having an aromatic ring. <3> The protective film-forming agent according to <1> or <2>, in which the tin content of the metal salt is 500 ppb by mass or more in the total amount of components of the protective film-forming agent excluding the solvent. <4> The protective film-forming agent according to any one of <1> to <3>, in which the metal salt includes at least one selected from the group consisting of sulfates, nitrates, nitrites, and hydrates thereof. <5> The protective film-forming agent according to any one of <1> to <4>, in which the first resin includes at least one selected from the group consisting of cellulose-based resins and vinyl-based resins. <6> The protective film-forming agent according to any one of <1> to <5>, wherein the first resin comprises at least one resin selected from the group consisting of a resin (1A) containing a repeating unit represented by the following formula (1a), a resin (1B) containing a repeating unit represented by the following formula (1b-1) and a repeating unit represented by the following formula (1b-2), a resin (1C) containing a repeating unit represented by the following formula (1c), and a resin (1D) containing a repeating unit represented by the following formula (1d):

[0013]

[0014] (In the formula, R １ , R ２ , and R ３ are each independently —H, —CH ３ , -CH ２ CH ３ , or -CH ２ CH(OH)CH ３ and all R １ , R ２ , and R ３ At least one of these is a substituent other than —H.

[0015]

[0016]

[0017]

[0018] <7> The protective film-forming agent according to any one of <2> to <6>, wherein the second resin comprises at least one selected from the group consisting of resin (2A) containing a repeating unit represented by the following formula (2a-1) and a repeating unit represented by the following formula (2a-2), resin (2B) containing a repeating unit represented by the following formula (2b-1) and a repeating unit represented by the following formula (2b-2), and resin (2C) containing a repeating unit represented by the following formula (2c):

[0019]

[0020] (In the formula, X ＋ is an alkali metal cation, a proton, or N ＋ R ４ ４ and R ４ is a hydrogen atom, an alkyl group, or a hydroxyalkyl group.

[0021]

[0022] (In the formula, M １＋ and M ２＋ are each independently an alkali metal cation, a proton, or N ＋ R ５ ４ and R ５ is a hydrogen atom, an alkyl group, or a hydroxyalkyl group.

[0023]

[0024] <8> A protective film containing a metal salt of tin and a first resin having no aromatic ring. <9> The protective film according to <8>, further containing a second resin having an aromatic ring. <10> The protective film according to <8> or <9>, wherein the tin content of the metal salt in the protective film is 500 ppb by mass or more. <11> The protective film according to any one of <8> to <10>, wherein the film thickness is 0.1 μm or more and 100 μm or less. <12> A method for producing a protective film, comprising the step of applying the protective film-forming agent according to any one of <1> to <7> onto a substrate to form a protective film. <13> A method for manufacturing semiconductor chips by cutting a semiconductor wafer by plasma dicing, the method comprising the steps of: applying the protective film-forming agent according to any one of <1> to <7> onto a semiconductor wafer to form a protective film; irradiating laser light onto predetermined positions of one or more layers on the semiconductor wafer, including the protective film, to expose the surface of the semiconductor wafer and form grooves in a pattern corresponding to the shape of the semiconductor chip; and irradiating plasma onto the semiconductor wafer with the grooves formed therein to cut the semiconductor wafer at the positions of the grooves, thereby obtaining semiconductor chips.

[0025] According to the present invention, it is possible to provide a protective film forming agent that has excellent film-forming properties and can produce a protective film having a high selectivity, as well as a protective film obtained using such a protective film forming agent, a method for manufacturing a protective film, and a method for manufacturing a semiconductor chip.

[0026] Hereinafter, a mode for carrying out the present invention (hereinafter simply referred to as "the present embodiment") will be described in detail. The following present embodiment is an example for explaining the present invention, and is not intended to limit the present invention to the following content. The present invention can be implemented by appropriately modifying it within the scope of its gist. Furthermore, unless otherwise specified, the configurations and parameters disclosed in this specification can be arbitrarily combined. Furthermore, unless otherwise specified, the upper and lower limits of the values ​​disclosed in this specification can be arbitrarily combined.

[0027] <Protective film forming agent>

[0028] The protective film forming agent according to the present embodiment is a protective film forming agent containing a metal salt of tin, a first resin having no aromatic ring, and a solvent. The protective film forming agent can be used, for example, to form a protective film on the surface of a semiconductor wafer when dicing the semiconductor wafer. As a result of extensive research, the inventors have unexpectedly found that by using a resin having no aromatic ring and a metal salt of tin in combination, a protective film having excellent film-forming properties and excellent selectivity can be obtained.

[0029] (metal salts of tin)

[0030] The protective film-forming agent according to this embodiment contains a metal salt of tin. The metal salt of tin may be present in the protective film-forming agent as a tin ion. The type of salt is not particularly limited, but from the viewpoint of film-forming properties and selectivity, it is preferable to include at least one selected from the group consisting of sulfates, nitrates, nitrites, and hydrates thereof. These salts tend to be highly water-soluble, which further increases their compatibility with other components in the protective film-forming agent, thereby further improving film-forming properties and selectivity.

[0031] The tin content is not particularly limited, but from the viewpoint of achieving an even higher selectivity while maintaining excellent film-forming properties, the tin content ratio of the metal salt relative to the total amount of components excluding the solvent from the protective film-forming agent ((tin) / (total amount of components excluding the solvent from the protective film-forming agent)) is preferably 500 mass ppb or more. The lower limit of this content ratio is more preferably 600 mass ppb or more, even more preferably 700 mass ppb or more, even more preferably 750 mass ppb or more, and even more preferably 800 mass ppb or more. The upper limit of this content ratio is more preferably 1000 mass ppb or less, even more preferably 950 mass ppb or less, and even more preferably 900 mass ppb or less. Note that, when tin is present as tin ions in the protective film-forming agent, the tin content also includes the tin ions.

[0032] Regarding the metal species of the metal salt, the protective film-forming agent according to this embodiment preferably contains a low content of metal ions other than tin, and preferably does not contain any metal ions at all, from the viewpoint of achieving both higher levels of film-forming ability and selectivity. For example, the content of metal ions of Li, Be, Na, Mg, Al, K, Ca, Mn, Fe, Co, Ni, Cu, Zn, Ga, Rb, Sr, Y, Zr, Ag, Cd, In, Cs, Ba, La, and Ce is preferably 100 ppb by mass or less, more preferably 50 ppb by mass or less, and even more preferably 0% by mass. Furthermore, it is even more preferable that these metal ions other than tin are not substantially contained. In this specification, "substantially does not contain" means that the component is not actively added or mixed, and does not exclude the inevitable inclusion or mixing of the component.

[0033] (First Resin)

[0034] The first resin is a resin that does not have an aromatic ring (sometimes referred to as a "non-aromatic resin"). The first resin is preferably water-soluble (sometimes referred to as a "water-soluble resin"). If the first resin is water-soluble, a protective film can be effectively formed by dissolving the resin in a solvent such as water or an aqueous medium, applying the solution, and drying it. Furthermore, after plasma etching, the protective film can be easily removed by rinsing with water. In this specification, "water-soluble" means that 0.5 g or more of the solute (the resin) dissolves in 100 g of water at 25°C.

[0035] In this regard, conventionally, when a protective film is formed using a water-soluble material, there is a problem that cracks are likely to occur. This tendency is particularly strong when the protective film is thick. Furthermore, the use of a water-soluble material tends to reduce the selectivity. However, according to the present embodiment, unexpectedly, the use of the metal salt and the first resin in combination effectively suppresses the occurrence of such problems.

[0036] The term "water-soluble resin" also includes resins that have been solubilized in water by hydrolysis or treatment with a base in an aqueous medium. For example, a resin that has been subjected to such a reaction or treatment and that can dissolve 0.5 g or more of the solute (the resin) in 100 g of water at 25° C. is also included in the "water-soluble resin" used in this specification.

[0037] The first resin preferably contains at least one selected from the group consisting of cellulose-based resins, vinyl-based resins, polyalkylene oxides (e.g., polyethylene oxides such as polyethylene glycol, polypropylene oxides such as polypropylene glycol), polyglycerin, and water-soluble nylon, and more preferably contains at least one selected from the group consisting of cellulose-based resins and vinyl-based resins. These are preferably water-soluble.

[0038] The weight average molecular weight of the first resin is not particularly limited, but is usually preferably 100 to 300,000. The lower limit of this weight average molecular weight is more preferably 1,000 or more, and even more preferably 10,000 or more. The upper limit of this weight average molecular weight is more preferably 200,000 or less, and even more preferably 150,000 or less.

[0039] Unless otherwise specified, the weight average molecular weight in this specification is the weight average molecular weight (M) in terms of polystyrene obtained by gel permeation chromatography (GPC) analysis. ｗ )

[0040] The cellulose-based resin is preferably cellulose or a cellulose derivative, and is water-soluble. Examples of the cellulose derivative include cellulose modified with an alkyl group (e.g., a methyl group, an ethyl group, etc.) and cellulose modified with a hydroxyalkyl group (e.g., a hydroxymethyl group, a hydroxyethyl group, a hydroxypropyl group, etc.). Specific examples of the cellulose derivative include at least one selected from the group consisting of methyl cellulose, ethyl cellulose, hydroxymethyl cellulose, hydroxyethyl cellulose, and hydroxypropyl cellulose.

[0041] The weight-average molecular weight of the cellulose-based resin is not particularly limited, but is preferably 1,000 to 300,000. The lower limit of this weight-average molecular weight is more preferably 10,000 or more. The upper limit of this weight-average molecular weight is more preferably 200,000 or less, and even more preferably 150,000 or less.

[0042] The vinyl resin is preferably a water-soluble homopolymer of a monomer having a vinyl group or a copolymer of a monomer having a vinyl group. Specific examples of the vinyl resin include at least one selected from the group consisting of polyvinyl alcohol resin, poly-N-vinylacetamide, polyvinylpyrrolidone, polyacrylamide, poly(N-alkylacrylamide), polyallylamine, poly(N-alkylallylamine), partially amidated polyallylamine, poly(diallylamine), allylamine-diallylamine copolymer, and polyacrylic acid.

[0043] Specific examples of polyvinyl alcohol-based resins include polyvinyl alcohol, polyvinyl acetal (including vinyl acetate copolymers), butenediol-vinyl alcohol copolymers, polyvinyl alcohol-polyacrylic acid block copolymers, polyvinyl alcohol-polyacrylic acid ester block copolymers, etc. Among these, polyvinyl alcohol is preferred.

[0044] The protective film formed on the surface of the semiconductor wafer is usually removed from the surface of the semiconductor wafer or semiconductor chip by washing with water at an appropriate time after the formation of the processing grooves. Therefore, from the viewpoint of the water washability of the protective film, a water-soluble resin with high affinity with water is preferred. Among the above-mentioned resins, preferred water-soluble resins with high affinity with water include resins having only hydroxyl groups, amide bonds, and / or ether bonds as polar groups, such as hydroxypropyl cellulose, polyvinyl alcohol, poly-N-vinylacetamide, polyvinylpyrrolidone, and polyethylene glycol.

[0045] Furthermore, from the viewpoint that deterioration of the shape of the processed groove due to heat sagging of the protective film can be expected to be more effectively suppressed, cellulose-based resins and vinyl-based resins are preferred, and hydroxypropyl cellulose, polyvinyl alcohol, poly-N-vinylacetamide, polyvinylpyrrolidone, etc. are more preferred.

[0046] These may be used alone or in combination of two or more.

[0047] More specific preferred examples of the first resin will be described. The first resin preferably contains at least one selected from the group consisting of resin (1A) containing a repeating unit represented by formula (1a) below, resin (1B) containing a repeating unit represented by formula (1b-1) below and a repeating unit represented by formula (1b-2) below, resin (1C) containing a repeating unit represented by formula (1c) below, and resin (1D) containing a repeating unit represented by formula (1d) below.

[0048]

[0049] (In the formula, R １ , R ２ , and R ３ are each independently —H, —CH ３ , -CH ２ CH ３ , or -CH ２ CH(OH)CH ３ and all R １ , R ２ , and R ３ At least one of these is a substituent other than —H.

[0050]

[0051]

[0052]

[0053] Resin (1A) may be any resin containing a repeating unit represented by formula (1a), and may also contain other repeating units. From the viewpoints of the film-forming properties of the protective film, selectivity, water washability, precision of the shape of the processed groove, etc., resin (1A) is preferably a resin containing only a repeating unit represented by formula (1a). Specific examples of resin (1A) include cellulose derivatives. Suitable examples of resin (1A) include the above-mentioned methyl cellulose, ethyl cellulose, and propylene cellulose.

[0054] R in formula (1a) １ , R ２ , and R ３ are each independently —H, —CH ３ , -CH ２ CH ３ , or -CH ２ CH(OH)CH ３ The substituent represented by formula (1a) may be any substituent represented by formula (1a). １ , R ２ , and R ３ are each independently —H or —CH ２ CH(OH)CH ３ and all R １ , R ２ , and R ３ At least one of the groups is —CH ２ CH(OH)CH ３ It is preferable that:

[0055] The weight average molecular weight of the resin (1A) is not particularly limited, but is preferably 10,000 or more and 300,000 or less. The lower limit of the weight average molecular weight is more preferably 15,000 or more, and even more preferably 20,000 or more. The upper limit of the weight average molecular weight is more preferably 200,000 or less, more preferably 100,000 or less, and even more preferably 50,000 or less.

[0056] Resin (1B) may be any resin containing a repeating unit represented by formula (1b-1) and a repeating unit represented by formula (1b-2) (see formula (1b)), and may also contain other repeating units. From the viewpoints of the film-forming properties of the protective film, selectivity, water washability, precision of the shape of the processed groove, etc., resin (1B) is preferably a resin containing only a repeating unit represented by formula (1b-1) and a repeating unit represented by formula (1b-2) (see formula (1b)).

[0057] The water solubility of the resin (1B) can be improved by, for example, adjusting the content of the repeating unit represented by formula (1b-1), the content of the repeating unit represented by formula (1b-2), and the molar ratio of the repeating unit represented by formula (1b-1) to the repeating unit represented by formula (1b-2).

[0058] The ratio of the repeating units represented by formula (1b-1) and the repeating units represented by formula (1b-2) is not particularly limited, but from the above-mentioned viewpoint, the upper limit of the molar ratio of the repeating units represented by formula (1b-1) in the total of the repeating units represented by formula (1b-1) and the repeating units represented by formula (1b-2) (formula (1b-1) / (formula (1b-1)+formula (1b-2))) is preferably 0.965 or less, and more preferably 0.890 or less. The lower limit of this molar ratio is not particularly limited, but is preferably 0.500 or more, and more preferably 0.695 or more.

[0059] Suitable examples of resin (1B) include the above-mentioned polyvinyl alcohol. Polyvinyl alcohol can be obtained, for example, by saponifying polyvinyl acetate obtained by polymerizing vinyl acetate monomer. In this case, a resin having both the repeating unit represented by formula (1b-1) and the repeating unit represented by formula (1b-2) can be obtained, as represented by formula (1b).

[0060] The degree of polymerization of the resin (1B) is not particularly limited, but is preferably 300 or more and 2500 or less. The lower limit of the degree of polymerization is more preferably 500 or more. The upper limit of the degree of polymerization is more preferably 2000 or less.

[0061] Resin (1C) may be any resin containing a repeating unit represented by formula (1c), and may also contain other repeating units. From the viewpoints of the film-forming properties of the protective film, selectivity, water washability, precision of the processed groove shape, etc., resin (1C) is preferably a resin containing only a repeating unit represented by formula (1c). Suitable examples of resin (1C) include the above-mentioned poly-N-vinylacetamide.

[0062] The weight average molecular weight of the resin (1C) is not particularly limited, but is preferably 200,000 or more and 1,500,000 or less. The lower limit of the weight average molecular weight is more preferably 250,000 or more, and even more preferably 500,000 or more. Furthermore, from the viewpoint of film-forming properties, etc., the upper limit of the weight average molecular weight is more preferably 1,000,000 or less.

[0063] Resin (1D) may be any resin containing a repeating unit represented by formula (1d), and may also contain other repeating units. From the viewpoints of the film-forming properties of the protective film, selectivity, water washability, precision of the groove shape, etc., resin (1D) is preferably a resin containing only a repeating unit represented by formula (1d). Suitable examples of resin (1D) include the above-mentioned polyvinylpyrrolidone.

[0064] The weight average molecular weight of the resin (1D) is not particularly limited, but is preferably 10,000 or more and 1,500,000 or less. The lower limit of the weight average molecular weight is more preferably 40,000 or more, even more preferably 50,000 or more, and even more preferably 100,000 or more. The upper limit of the weight average molecular weight is more preferably 1,200,000 or less.

[0065] (Second Resin)

[0066] The protective film-forming agent according to this embodiment preferably contains a second resin having an aromatic ring. The second resin may be a resin having an aromatic ring (sometimes referred to as an "aromatic resin"), and the aromatic ring may be a monocyclic aromatic ring or a polycyclic aromatic ring. Examples of aromatic rings having a cyclic structure include a benzene ring. Examples of aromatic rings having a polycyclic structure include a naphthalene ring, a biphenyl ring, an anthracene ring, and a phenanthrene ring.

[0067] The second resin is preferably water-soluble. When the second resin is a water-soluble resin, it is more preferably a water-soluble resin having an aromatic ring and a water-soluble group. As mentioned above, the water-soluble resin here also includes resins that have been solubilized in water by hydrolysis or treatment with a base in an aqueous medium. Examples of the water-soluble group include, for example, -SO ３ － A ＋ (A ＋ is an alkali metal cation, a proton, or N ＋ R ４ R is a hydrogen atom, an alkyl group, or a hydroxyalkyl group.), —COO － A ＋ (A ＋ is an alkali metal cation, a proton, or N ＋ R ４ R is a hydrogen atom, an alkyl group, or a hydroxyalkyl group. Examples of the alkyl group include a carboxylic anhydride group (—CO—O—CO—), a hydroxyl group, and an ether bond (—O—).

[0068] The alkali metal cations include, for example, sodium cations (Na ＋ ), potassium cation (K ＋ ), strontium cation (Sr ＋) and the like. Examples of the alkyl group include a methyl group, an ethyl group, and a propyl group (e.g., an n-propyl group, an isopropyl group). Examples of the hydroxyalkyl group include a hydroxymethyl group, a hydroxyethyl group, and a hydroxypropyl group. In addition, a carboxylic anhydride group (-CO-O-CO-) can be converted to -COO by hydrolysis or treatment with a base in water. － X ＋ It is a group that gives

[0069] Examples of the second resin include a resin containing a styrene-based unit and a resin containing a phenol-based unit. Examples of the styrene-based unit include a structural unit derived from styrene or a styrene derivative having a substituent at the α-position or on the benzene ring. Examples of the phenol-based unit include a resin containing a phenolic hydroxyl group.

[0070] Depending on the structure, resins having phenolic hydroxyl groups may be water-soluble or poorly soluble in water (water-insoluble). When a resin having phenolic hydroxyl groups is poorly soluble in water, the resin may be solubilized in water by treating the resin in a basic aqueous medium to convert the phenolic hydroxyl groups into salts.

[0071] The weight average molecular weight of the second resin is not particularly limited, but is usually preferably 100 to 300,000. The lower limit of this weight average molecular weight is more preferably 1,000 or more, and even more preferably 10,000 or more. The upper limit of this weight average molecular weight is more preferably 200,000 or less, and even more preferably 150,000 or less.

[0072] More specific preferred examples of the second resin will be described. The second resin preferably contains at least one selected from the group consisting of resin (2A) containing a repeating unit represented by the following formula (2a-1) and a repeating unit represented by the following formula (2a-2), resin (2B) containing a repeating unit represented by the following formula (2b-1) and a repeating unit represented by the following formula (2b-2), and resin (2C) containing a repeating unit represented by the following formula (2c). By using these resins in combination with the above-mentioned metal salt and first resin, it is possible to further improve at least the film-forming properties and the selectivity.

[0073]

[0074] (In the formula, X ＋ is an alkali metal cation, a proton, or N ＋ R ４ ４ and R ４ is a hydrogen atom, an alkyl group, or a hydroxyalkyl group.

[0075]

[0076] (In the formula, M １＋ and M ２＋ are each independently an alkali metal cation, a proton, or N ＋ R ５ ４ and R ５ is a hydrogen atom, an alkyl group, or a hydroxyalkyl group.

[0077]

[0078] Resin (2A) may be any resin containing a repeating unit represented by formula (2a-1) and a repeating unit represented by formula (2a-2) (see formula (2a)), and may also contain other repeating units. From the viewpoints of the film-forming properties of the protective film, the selectivity, water washability, and the precision of the shape of the processed groove, resin (2A) is preferably a resin containing only a repeating unit represented by formula (2a-1) and a repeating unit represented by formula (2a-2) (see formula (2a)).

[0079] In formula (2a-2), X ＋is an alkali metal cation, a proton, or N ＋ R ４ ４ and R ４ may be a hydrogen atom, an alkyl group, or a hydroxyalkyl group. The alkali metal cation may be, for example, a sodium cation (Na ＋ ), potassium cation (K ＋ ), strontium cation (Sr ＋ Examples of the alkyl group include a methyl group, an ethyl group, and a propyl group (e.g., an n-propyl group and an isopropyl group). Examples of the hydroxyalkyl group include a hydroxymethyl group, a hydroxyethyl group, and a hydroxypropyl group.

[0080] Among the above, X ＋ is N ＋ R ４ ４ Preferably, R ４ is more preferably a hydrogen atom. ＋ Specific examples of X ＋ is NH ４ ＋ It is preferable that:

[0081] The water solubility of the resin (2A) can be improved, for example, by increasing the content of the repeating unit represented by formula (2a-2), which has high hydrophilicity.

[0082] The ratio of the repeating unit represented by formula (2a-1) to the repeating unit represented by formula (2a-2) is not particularly limited, but from the viewpoint described above, the molar ratio of the repeating unit represented by formula (2a-1) to the repeating unit represented by formula (2a-2) (formula (2a-1) / (formula (2a-2)) is preferably 0.1 or more and 9 or less, from the viewpoint of ease of imparting water solubility. The lower limit of this molar ratio is more preferably 0.25 or more. The upper limit of this molar ratio is more preferably 7 or less, and even more preferably 4 or less.

[0083] Suitable examples of the resin (2A) include X in the formula (2a-2): ＋ NH ４＋ This resin may be, for example, a resin having a dihydroxydiphenylsulfone type repeating unit (see formula (2a-1)) and a phenol type repeating unit of sodium sulfonate (X in formula (2a-2)). ＋ Na ＋ The copolymer can be obtained by demetallizing a copolymer containing hydroxy groups (see the case where hydroxy groups are hydroxy groups) with hydrochloric acid treatment and then diluting it with aqueous ammonia.

[0084] The weight average molecular weight of the resin (2A) is not particularly limited, but is preferably 5,000 or more and 300,000 or less. The lower limit of the weight average molecular weight is more preferably 10,000 or more, even more preferably 15,000 or more, and even more preferably 20,000 or more. The upper limit of the weight average molecular weight is more preferably 200,000 or less, even more preferably 100,000 or less, even more preferably 50,000 or less, and even more preferably 25,000 or less.

[0085] Resin (2B) may be any resin containing a repeating unit represented by formula (2b-1) and a repeating unit represented by formula (2b-2) (see formula (2b)), and may also contain other repeating units. From the viewpoints of the film-forming properties of the protective film, selectivity, water washability, precision of the shape of the processed groove, etc., resin (2B) is preferably a resin containing only a repeating unit represented by formula (2b-1) and a repeating unit represented by formula (2b-2) (see formula (2b)).

[0086] In formula (2b-2), M １＋ and M ２＋ are, for example, monovalent cations, each independently an alkali metal cation, a proton, or N ＋ R ５ ４ and R ５ may be a hydrogen atom, an alkyl group, or a hydroxyalkyl group. The alkali metal cation may be, for example, a sodium cation (Na ＋ ), potassium cation (K ＋ ), strontium cation (Sr ＋Examples of the alkyl group include a methyl group, an ethyl group, and a propyl group (e.g., an n-propyl group and an isopropyl group). Examples of the hydroxyalkyl group include a hydroxymethyl group, a hydroxyethyl group, and a hydroxypropyl group.

[0087] Among the above, M １＋ and M ２＋ At least one of ＋ R ５ ４ Preferably, R ５ is more preferably a hydrogen atom. １＋ and M ２＋ It is more preferred that M １＋ and M ２＋ Specific examples of at least one of ４ ＋ Preferably, M １＋ and M ２＋ All of these are NH ４ ＋ It is preferable that:

[0088] The water solubility of the resin (2B) can be improved, for example, by increasing the content of the repeating unit represented by formula (2b-2), which has high hydrophilicity.

[0089] The ratio of the repeating unit represented by formula (2b-1) to the repeating unit represented by formula (2b-2) is not particularly limited, but from the above-mentioned viewpoint, the molar ratio of the repeating unit represented by formula (2b-1) to the repeating unit represented by formula (2b-2) (formula (2b-1) / (formula (2b-2)) is preferably 1 or more and 8 or less, from the viewpoint of ease of imparting water solubility. The lower limit of this molar ratio is more preferably 2 or more. The upper limit of this molar ratio is more preferably 6 or less, even more preferably 5 or less, and even more preferably 4 or less.

[0090] As described above, preferred examples of the resin (2B) include M １＋ and M ２＋ All of these are NH ４ ＋This resin can be obtained, for example, by diluting a styrene-maleic anhydride copolymer with aqueous ammonia.

[0091] The weight average molecular weight of the resin (2B) is not particularly limited, but is preferably 5,000 or more and 200,000 or less. The lower limit of the weight average molecular weight is more preferably 7,000 or more, and even more preferably 8,000 or more. The upper limit of the weight average molecular weight is more preferably 100,000 or less, even more preferably 50,000 or less, even more preferably 40,000 or less, and even more preferably 30,000 or less.

[0092] Resin (2C) may be any resin containing a repeating unit represented by formula (2c), and may also contain other repeating units. From the viewpoints of the film-forming properties of the protective film, selectivity, water washability, precision of the groove shape, etc., resin (2C) is preferably a resin containing only a repeating unit represented by formula (2c). A suitable example of resin (2C) is polystyrene sulfonic acid.

[0093] The weight average molecular weight of resin (2C) is not particularly limited, but is preferably 5,000 or more and 1,200,000 or less. The lower limit of the weight average molecular weight is more preferably 10,000 or more, even more preferably 15,000 or more, and even more preferably 20,000 or more. The upper limit of the weight average molecular weight is more preferably 500,000 or less, more preferably 300,000 or less, even more preferably 100,000 or less, even more preferably 50,000 or less, and even more preferably 30,000 or less.

[0094] The protective film forming agent according to the present embodiment preferably contains only a water-soluble resin as the resin. In this case, the protective film forming agent according to the present embodiment may further contain other resins in addition to the first resin and the second resin described above. For example, when the protective film forming agent according to the present embodiment contains only the first resin as the resin, it is preferable that the first resin is a water-soluble resin. When the protective film forming agent according to the present embodiment contains only the first resin and the second resin as the resin, it is preferable that the first resin and the second resin are water-soluble resins. When the protective film forming agent according to the present embodiment contains the first resin, the second resin, and other resins in addition to the first resin and the second resin as the resin, it is preferable that the first resin, the second resin, and other resins are all water-soluble resins.

[0095] In the protective film-forming agent according to this embodiment, the contents of the first resin and the second resin are not particularly limited, but the total content of the first resin and the second resin per 100 parts by mass of solids in the protective film-forming agent is preferably 99.8 parts by mass or less, and more preferably 99.6 parts by mass or less, and the total content of the first resin and the second resin per 100 parts by mass of solids in the protective film-forming agent is preferably 80.0 parts by mass or more, and more preferably 90.0 parts by mass or more.

[0096] (additives, etc.)

[0097] The protective film-forming agent according to this embodiment may contain other additives as needed, such as a light-absorbing agent, a basic compound, a dye, a pigment, a plasticizer, a preservative, and a surfactant.

[0098] (light absorbing agent)

[0099] The light-absorbing agent may be any of those commonly used in protective film-forming agents, including, for example, organic acids having a carboxyl group and / or a sulfo group, sodium salts, potassium salts, ammonium salts, and quaternary ammonium salts of these organic acids, and compounds having a hydroxy group.

[0100] Specific examples of the light absorbing agent include benzophenone compounds, cinnamic acid compounds, anthraquinone compounds, naphthalene compounds, biphenyl compounds, and water-soluble amines.

[0101] Specific examples of benzophenone compounds include benzophenone, 4,4'-dicarboxybenzophenone, benzophenone-4-carboxylic acid, tetrahydroxybenzophenone, 2-(4-diethylamino-2-hydroxybenzoyl)benzoic acid (DHBA), and 4,4'-bis(diethylamino)benzophenone.

[0102] Specific examples of cinnamic acid compounds include cinnamic acid, 4-aminocinnamic acid, 3-aminocinnamic acid, 2-aminocinnamic acid, sinapic acid (3,5-dimethoxy-4-hydroxycinnamic acid), ferulic acid, caffeic acid, etc. Among these, 4-aminocinnamic acid, 3-aminocinnamic acid, 2-aminocinnamic acid, and ferulic acid are preferred, 4-aminocinnamic acid and ferulic acid are more preferred, and 4-aminocinnamic acid is even more preferred.

[0103] Specific examples of the anthraquinone-based compound include anthraquinone, 2-carboxyanthraquinone, 2,6-anthraquinone disulfonic acid, and 2,7-anthraquinone disulfonic acid.

[0104] Specific examples of the naphthalene-based compound include naphthalene, 1,2-naphthalenedicarboxylic acid, 1,8-naphthalenedicarboxylic acid, 2,3-naphthalenedicarboxylic acid, 2,6-naphthalenedicarboxylic acid, and 2,7-naphthalenedicarboxylic acid.

[0105] Specific examples of biphenyl compounds include biphenyl, biphenyl-4-sulfonic acid, and the like.

[0106] Specific examples of water-soluble amines include curcumin.

[0107] Among the above, benzophenone compounds and cinnamic acid compounds are preferred, with tetrahydroxybenzophenone, 2-(4-diethylamino-2-hydroxybenzoyl)benzoic acid (DHBA), 4-aminocinnamic acid, and the like being more preferred.

[0108] The content of the light-absorbing agent in the protective film-forming agent according to this embodiment is not particularly limited as long as it is within a range that does not impair the object of this embodiment, but the content of the light-absorbing agent per 100 parts by mass of the solid content in the protective film-forming agent is preferably 1 part by mass or more and 10 parts by mass or less. The lower limit of the content of the light-absorbing agent per 100 parts by mass of the solid content in the protective film-forming agent is more preferably 1.5 parts by mass or more. Furthermore, the upper limit of the content of the light-absorbing agent per 100 parts by mass of the solid content in the protective film-forming agent is more preferably 7 parts by mass or less, even more preferably 5 parts by mass or less, and even more preferably 3 parts by mass or less.

[0109] (Basic Compound)

[0110] The protective film-forming agent according to this embodiment may contain a basic compound for the purpose of making the solid content more easily soluble. As the basic compound, either an inorganic compound or an organic compound can be used. As the basic compound, an organic compound is preferred.

[0111] Specific examples of the basic compound include basic inorganic compounds such as sodium hydroxide, potassium hydroxide, sodium carbonate, potassium carbonate, sodium silicate, sodium metasilicate, and ammonia; and basic organic compounds such as ethylamine, n-propylamine, monoethanolamine (MEA), diethylamine, di-n-propylamine, diethanolamine, triethylamine, methyldiethylamine, dimethylethanolamine, triethanolamine, tetramethylammonium hydroxide, tetraethylammonium hydroxide, pyrrole, piperidine, 1,8-diazabicyclo[5,4,0]-7-undecene, and 1,5-diazabicyclo[4,3,0]-5-nonane. Of these, monoethanolamine (MEA), ammonia, and the like are more preferred.

[0112] The content of the basic compound in the protective film-forming agent according to this embodiment is not particularly limited as long as it is within a range that does not impair the object of this embodiment, but the content of the basic compound per 100 parts by mass of the solid content in the protective film-forming agent is preferably 0.1 parts by mass or more and 3.0 parts by mass or less. The upper limit of the content of the basic compound per 100 parts by mass of the solid content in the protective film-forming agent is more preferably 1.5 parts by mass or less, and even more preferably 1.0 part by mass or less. Furthermore, the lower limit of the content of the basic compound per 100 parts by mass of the solid content in the protective film-forming agent is more preferably 0.3 parts by mass or more.

[0113] Furthermore, the molar ratio of the basic compound to the light-absorbing agent (basic compound / light-absorbing agent) is preferably 1 or more, and more preferably 1 or more and 20 or less. The lower limit of the molar ratio of the basic compound to the light-absorbing agent may be 1.5 or more, 2 or more, or even 3 or more. The upper limit of the molar ratio of the basic compound to the light-absorbing agent may be 15 or less, 10 or less, or 5 or less.

[0114] (dye)

[0115] The dye is preferably a water-soluble dye. Specific examples of the water-soluble dye include azo dyes (monoazo and polyazo dyes, metal complex azo dyes, pyrazolone azo dyes, stilbene azo dyes, and thiazole azo dyes), anthraquinone dyes (anthraquinone derivatives and anthrone derivatives), indigoid dyes (indigoid derivatives and thioindigoid derivatives), phthalocyanine dyes, carbonium dyes (diphenylmethane dyes, triphenylmethane dyes, xanthene dyes, and acridine dyes), quinoneimine dyes (azine dyes, oxazine dyes, and thiazine dyes), methine dyes (cyanine dyes and azomethine dyes), quinoline dyes, nitroso dyes, benzoquinone dyes, naphthoquinone dyes, naphthalimide dyes, perinone dyes, and other dyes.

[0116] (dye)

[0117] The dye is preferably a water-soluble dye. Specific examples of water-soluble dyes include food additive dyes such as Food Red No. 2, Food Red No. 40, Food Red No. 102, Food Red No. 104, Food Red No. 105, Food Red No. 106, Food Yellow NY, Food Yellow No. 4 Tartrazine, Food Yellow No. 5, Food Yellow No. 5 Sunset Yellow FCF, Food Orange AM, Food Vermilion No. 1, Food Vermilion No. 4, Food Vermilion No. 101, Food Blue No. 1, Food Blue No. 2, Food Green No. 3, Food Melon Color B, and Food Egg Color No. 3. Food additive dyes are preferred from the viewpoint of low environmental impact, etc.

[0118] (Plasticizer)

[0119] Use of a plasticizer can more effectively suppress the occurrence of cracks in the protective film and can also more effectively improve the flexibility, elasticity, laser processability, etc. of the protective film. Specific examples of plasticizers include monosaccharides and disaccharides.

[0120] Specific examples of monosaccharides include aldoses (monosaccharides having a formyl group), ketoses (monosaccharides having a carbonyl group), and derivatives thereof. Examples of derivatives include aldonic acids (carboxylic acids in which the formyl group at position 1 of an aldose is converted to a carboxyl group), uronic acids (carboxylic acids in which the hydroxymethyl groups at the terminals of the main chain of a monosaccharide are converted to a carboxyl group), and aldaric acids (dicarboxylic acids in which the formyl group at position 1 of an aldose and the hydroxymethyl groups at the terminals of the main chain are both converted to carboxyl groups).

[0121] Specific examples of aldoses include D-glyceraldehyde, D-erythrose, D-threose, D-ribose, D-arabinose, D-xylose, D-lyxose, D-glucose, D-galactose, D-allose, D-altrose, D-mannose, D-gulose, D-idose, and D-talose.

[0122] Specific examples of ketoses include dihydroxyacetone, D-erythrulose, D-xylulose, D-ribulose, D-fructose, D-psicose, D-sorbose, D-tagatose, and D-sedoheptulose.

[0123] Specific examples of derivatives include gluconic acid, glucuronic acid, glucaric acid, inositol, and the like.

[0124] Disaccharides include disaccharides composed of the monosaccharides described above as monosaccharides. Specific examples of disaccharides include maltose, sucrose, lactose, lactulose, trehalose, and cellobiose.

[0125] Among the above, D-ribose, D-xylose, D-glucose, D-galactose, D-fructose, inositol, and maltose are preferred, and D-ribose, D-glucose, D-galactose, D-fructose, inositol, and maltose are more preferred.

[0126] (preservatives)

[0127] From the viewpoint of further improving the antiseptic effect of the protective film-forming agent according to this embodiment and further reducing the burden on the treatment of wastewater after cleaning semiconductor wafers, it is preferable to use an antiseptic. Examples of antiseptics include benzoic acid, butylparaben, ethylparaben, methylparaben, propylparaben, sodium benzoate, sodium propionate, benzalkonium chloride, benzethonium chloride, benzyl alcohol, cetylpyridinium chloride, chlorobutanol, phenol, phenylethyl alcohol, 2-phenoxyethanol, phenylmercuric nitrate, thimerosal, metacresol, and lauryldimethylamine oxide. These may be used alone or in combination of two or more.

[0128] (Surfactant)

[0129] The surfactant is used, for example, to improve the defoaming property during production of the protective film-forming agent, the stability of the protective film-forming agent, the coatability of the protective film-forming agent, etc. From the viewpoint of the defoaming property during production of the protective film-forming agent, it is preferable to use a surfactant.

[0130] The protective film is formed, for example, by spin-coating a protective film-forming agent. However, when forming the protective film, unevenness due to air bubbles may occur. To prevent the occurrence of such unevenness, it is preferable to use an antifoaming agent such as a surfactant.

[0131] As the surfactant, a water-soluble surfactant can be preferably used. As the surfactant, any of a nonionic surfactant, a cationic surfactant, an anionic surfactant, and an amphoteric surfactant can be used. The surfactant may be a silicone surfactant. From the viewpoint of cleaning properties, a nonionic surfactant is preferred.

[0132] (solvent)

[0133] The protective film-forming agent according to this embodiment contains a solvent to dissolve the solid components. The solvent may be water (e.g., pure water, ultrapure water (DIW), ionized water, distilled water, purified water, etc.), an organic solvent, or both. It is preferable that the solvent contains water, because it reduces the risk of ignition during use and is cost-effective. Specifically, the solvent is preferably water or an aqueous solution of an organic solvent, and more preferably a combination of water and an organic solvent.

[0134] Specific examples of the organic solvent include, but are not limited to, methyl alcohol, ethyl alcohol, alkylene glycol, alkylene glycol monoalkyl ether, alkylene glycol monoalkyl ether acetate, and the like.

[0135] Examples of alkylene glycols include ethylene glycol and propylene glycol. Examples of alkylene glycol monoalkyl ethers include ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, propylene glycol monomethyl ether, and propylene glycol monoethyl ether. Examples of alkylene glycol monoalkyl ether acetates include ethylene glycol monomethyl ether acetate, ethylene glycol monoethyl ether acetate, propylene glycol monomethyl ether acetate, and propylene glycol monoethyl ether acetate.

[0136] The organic solvents may be used alone or in combination of two or more.

[0137] The protective film-forming agent according to this embodiment may contain a combination of water and an organic solvent. As a combination of water and an organic solvent, for example, a mixed solvent of water and an alkylene glycol monoalkyl ether is preferred, and a mixed solvent of water and propylene glycol monomethyl ether is more preferred.

[0138] When a mixed solvent containing water and an organic solvent is used, the content of the organic solvent in the mixed solvent (the content of the organic solvent relative to the total of water and organic solvent; (organic solvent / (water + organic solvent))) is not particularly limited. From the viewpoint of flammability, however, the upper limit of the content of the organic solvent in the mixed solvent is preferably less than 50% by mass, more preferably 30% by mass or less, even more preferably 20% by mass or less, and even more preferably 15% by mass or less.

[0139] Furthermore, from the viewpoint of flammability, it is desirable to reduce the content of the organic solvent in the mixed solvent, and according to the present embodiment, when only a water-soluble resin is used as the resin, the content of the organic solvent can be sufficiently reduced. From such a viewpoint, a preferred embodiment that can be achieved by the present embodiment is that the lower limit of the content of the organic solvent in the mixed solvent can be reduced to preferably 5% by mass (5% by mass or more), more preferably 3% by mass (3% by mass or more), and even more preferably 0% by mass (0% by mass or more).

[0140] In this embodiment, when only a water-soluble resin is used as the resin, it is preferable because the solid content in the protective film-forming agent can be effectively dissolved even if the content of the organic solvent is reduced to the above range.

[0141] The solvent is preferably selected so that the protective film-forming agent does not have a flash point at 1 atmosphere. Specifically, the flash point of the protective film or whether or not it has a flash point can be adjusted by adjusting the water content in the protective film-forming agent.

[0142] A protective film forming agent that does not have a flash point can ensure even higher safety. For example, the protective film forming agent can be placed in a non-explosion-proof environment. Specifically, the protective film forming agent can be stored, transported, used, and handled in a non-explosion-proof environment. For example, not only can the protective film forming agent be introduced into a semiconductor factory, but the formation of the protective film can also be carried out in a non-explosion-proof environment. Therefore, a protective film forming agent that does not have a flash point is extremely advantageous industrially in that it does not require an explosion-proof environment such as typically expensive explosion-proof equipment.

[0143] The flash point is measured under 1 atmosphere using a tag closed-cup tester at a liquid temperature of 80° C. or less, and using a Cleveland open-cup tester at a liquid temperature of more than 80° C. In this specification, if the flash point cannot be measured even when measured using a Cleveland open-cup tester, it is considered that there is no flash point.

[0144] <Protective Film Manufacturing Method, Protective Film>

[0145] According to this embodiment, a protective film can be obtained by applying the above-described protective film-forming agent onto a substrate or the like to be protected. Specifically, the method for producing a protective film according to this embodiment preferably includes a step of applying the above-described protective film-forming agent onto a substrate to form a protective film. The application method is not particularly limited, and spin coating, spray coating, die coating, roll coating, flow coating, curtain coating, or the like can be used depending on the shape and material of the object to be protected. Furthermore, after application, post-treatments such as a drying step such as natural drying or hot air drying, or a light irradiation step such as ultraviolet irradiation, may be performed.

[0146] Typically, spin coating or the like is used to form a protective film for a semiconductor wafer. Spin coating includes, for example, (i) a step (discharge step) of applying a protective film-forming agent to an object to be coated (such as a semiconductor wafer) fixed on the stage of a spin coater, (ii) a step (rotation process step) of removing excess protective film-forming agent by centrifugal force by rotating the stage to form a thin film, and (iii) a step (drying step) of removing the workpiece from the spin coater and forming a thin film by natural drying, hot air drying, or the like. Spin coating has the advantages of being able to form a film with little film thickness deviation and being able to be performed without a vacuum, resulting in excellent film formation costs and film formation speed, making it suitable for use as a protective film for semiconductor wafers and even as a protective film for plasma dicing.

[0147] The protective film obtained by this embodiment is a protective film containing a tin metal salt and a first resin that does not have an aromatic ring. Furthermore, the protective film preferably further contains a second resin that has an aromatic ring. The tin metal salt, the first resin, and the second resin can be those described above. Furthermore, if necessary, other components can be contained, and examples of such components can be those described above.

[0148] As described above, from the viewpoint of film-forming properties and selectivity, the tin metal salt preferably includes at least one selected from the group consisting of sulfates, nitrates, nitrites, and hydrates thereof. These salts tend to be highly water-soluble, which further increases the compatibility with other components in the protective film-forming agent, thereby further improving film-forming properties and selectivity.

[0149] The content of the tin metal salt in the protective film according to this embodiment is not particularly limited, but is preferably 500 mass ppb or more from the viewpoint of achieving an even higher selectivity while maintaining excellent film-forming properties. The lower limit of this content is more preferably 600 mass ppb or more, even more preferably 700 mass ppb or more, even more preferably 750 mass ppb or more, and even more preferably 800 mass ppb or more. The upper limit of this content is more preferably 1000 mass ppb or less, even more preferably 950 mass ppb or less, and even more preferably 900 mass ppb or less.

[0150] According to this embodiment, it is expected that a protective film having excellent film-forming properties and etching resistance can be formed over a wide range of film thicknesses, from thin to thick. In a preferred embodiment, the thickness of the protective film is preferably 0.1 μm or more and 100 μm or less. The lower limit of the film thickness is more preferably 1 μm or more, and even more preferably 3 μm or more. The upper limit of the film thickness is more preferably 50 μm or less, even more preferably 30 μm or less, even more preferably 20 μm or less, and even more preferably 10 μm or less. In this regard, for example, when the protective film is formed by spin coating, it is possible to more effectively form a film having excellent film-forming properties and selectivity within the above-mentioned film thickness range.

[0151] <Method of manufacturing semiconductor chips>

[0152] By using the protective film forming agent according to this embodiment, semiconductor wafers can be suitably manufactured by plasma dicing. Typically, the above-described semiconductor chip manufacturing method includes cutting the semiconductor wafer at the positions of the kerfs (positions corresponding to the positions of the streets). A suitable example of the semiconductor chip manufacturing method according to this embodiment is a semiconductor chip manufacturing method in which the semiconductor wafer is cut by plasma dicing, and includes the following steps: (1) applying the above-described protective film forming agent to the semiconductor wafer to form a protective film; (2) irradiating laser light to predetermined positions of one or more layers, including the protective film, on the semiconductor wafer to expose the surface of the semiconductor wafer and form kerfs in a pattern corresponding to the shape of the semiconductor chip; and (3) irradiating plasma to the semiconductor wafer with the kerfs formed therein to cut the semiconductor wafer at the positions of the kerfs to obtain semiconductor chips.

[0153] Hereinafter, the step of forming a protective film (see step (1)) will also be referred to as a "protective film forming step." The step of forming grooves (see step (2)) will also be referred to as a "groove forming step." The step of cutting the semiconductor wafer at the positions of the grooves (see step (3)) will also be referred to as a "cutting step."

[0154] (Protective film formation process)

[0155] In the protective film forming step, the protective film is formed by applying the protective film forming agent described above onto the semiconductor wafer. The protective film forming agent is preferably applied by spin coating.

[0156] The shape of the processing surface of a semiconductor wafer is not particularly limited as long as the semiconductor wafer can be processed as desired. Typically, the processing surface of a semiconductor wafer has numerous irregularities. In addition, recesses are formed in areas corresponding to the streets. On the processing surface of a semiconductor wafer, multiple areas corresponding to semiconductor chips are partitioned by the streets.

[0157] The thickness of the protective film is preferably 0.1 μm or more and 100 μm or less, because it allows for easy removal of the protective film by washing with water after processing and further improves the durability (e.g., selectivity) of the protective film against plasma irradiation when plasma irradiation is performed in the cutting step described below. The lower limit of the film thickness is more preferably 1 μm or more, and even more preferably 3 μm or more. The upper limit of the film thickness is more preferably 50 μm or less, even more preferably 30 μm or less, even more preferably 20 μm or less, and even more preferably 10 μm or less.

[0158] A preferred embodiment of the method for manufacturing semiconductor chips is described below, in which a semiconductor wafer having a plurality of semiconductor chips partitioned by grid-like streets is diced using a protective film-forming agent. The shape and size of the semiconductor chips are not particularly limited and can be set appropriately depending on the design of the semiconductor chips.

[0159] In a semiconductor wafer, a laminate is provided on the surface of a semiconductor substrate (silicon substrate, etc.) made of silicon or the like, in which insulating films and functional films that form circuits are stacked. A plurality of semiconductor chips such as ICs and LSIs are formed in a matrix on this laminate. Each semiconductor chip is partitioned by streets formed in a grid pattern. The insulating film is, for example, SiO ２ Alternatively, a low-k insulating film (Low-k film) made of an inorganic film such as SiOF or BSG (SiOB), or an organic film such as a polymer film of polyimide or parylene can be used.

[0160] Then, a protective film-forming agent is applied to the surface of the laminate on the semiconductor substrate to form a protective film. In the protective film forming step, the protective film-forming agent is applied to the surface of the semiconductor wafer using, for example, a spin coater. The method for applying the protective film-forming agent is not particularly limited as long as it can form a protective film of the desired thickness, and the various application methods described above can be used.

[0161] Subsequently, if necessary, the liquid protective film-forming agent that coats the surface is dried. This forms a protective film on the surface of the semiconductor wafer. As described above, the protective film according to this embodiment is a protective film that suppresses the occurrence of cracks, has no cracks or has few cracks, and has an excellent selectivity. Furthermore, a protective film that suppresses stickiness can be formed.

[0162] After the protective film is formed on the front surface of the semiconductor wafer in this manner, a protective tape may be attached to the rear surface of the semiconductor wafer, if necessary.

[0163] (Processed groove forming process)

[0164] In the groove formation process, laser light is irradiated onto a predetermined position of one or more layers, including a protective film, on a semiconductor wafer to expose the surface of the semiconductor substrate and form grooves in a pattern corresponding to the shape of the semiconductor chip. The protective film-forming agent and protective film according to this embodiment are expected to not only have excellent film-forming properties and selectivity, but also to improve the linearity of the grooves (the linearity of the sidewalls of the protective film that constitute the grooves) and the rectangularity of the cross-section of the grooves (the rectangularity of the cross-section of the protective film that constitutes the grooves). Excellent processability allows for accurate cutting without deviation from the desired position when cutting by plasma etching, thereby enabling cutting with higher positional accuracy.

[0165] Specifically, a laser beam is irradiated onto the surface (streets) of the semiconductor wafer through a protective film. From the viewpoint of laser intensity, an ultraviolet laser with a wavelength of 100 nm or more and 400 nm or less is preferred. A YVO4 laser or a YAG laser with a wavelength of 266 nm, 355 nm, or the like is also preferred.

[0166] The laser light irradiation in the groove forming step can be carried out under the following processing conditions, for example. The focused spot diameter can be appropriately selected taking into consideration the width of the groove. Laser light source: YVO4 laser or YAG laser Wavelength: 355 nm Repetition frequency: 50 kHz to 100 kHz Output: 0.1 W to 4.0 W Processing feed rate: 1 mm / sec to 800 mm / sec

[0167] By carrying out the above-described groove forming process, grooves are formed along the streets in a stack having streets in a semiconductor wafer. As described above, the protective film according to this embodiment can suppress the occurrence of cracks and has excellent durability (e.g., selectivity). As a result, by irradiating the protective film with laser light, grooves (grooves) with excellent linearity and cross-sectional rectangularity can be formed in the protective film.

[0168] After the laser beam has been irradiated along the predetermined street as described above, the semiconductor wafer held on the chuck table is indexed and moved by the distance of the street, and the laser beam is irradiated again.

[0169] After completing the laser beam irradiation and indexing movement for all the streets extending in the predetermined direction in this manner, the semiconductor wafer held on the chuck table is rotated 90 degrees, and the laser beam irradiation and indexing movement are repeated in the same manner as above along each street extending perpendicular to the predetermined direction. In this manner, grooves can be formed along all the streets formed in the stack on the semiconductor wafer.

[0170] (Cutting process)

[0171] In the cutting process, the semiconductor wafer with the grooves formed therein is irradiated with plasma to cut the semiconductor wafer at the groove locations, thereby obtaining semiconductor chips. Specifically, the semiconductor wafer with grooves at locations corresponding to the street locations is cut by plasma etching. The protective film according to this embodiment is also suitable as, for example, a protective film for plasma etching, and therefore can exhibit its advantages in semiconductor wafer manufacturing methods that use plasma etching for cutting.

[0172] When irradiating the plasma, the plasma is irradiated onto a part or the entire surface of the semiconductor wafer that has the protective film so that the surface of the processed groove is exposed to the plasma. An example of a cutting method using plasma irradiation will be described below.

[0173] First, a semiconductor wafer having a protective film and a kerf is irradiated with plasma. This cuts the semiconductor wafer at the positions of the kerfs. Specifically, after forming the kerfs in the semiconductor wafer covered with a protective film as described above, the protective film and the surface of the semiconductor substrate exposed through the kerfs are irradiated with plasma. This cuts the semiconductor wafer according to the shape of the semiconductor chips, and the semiconductor wafer is divided into individual semiconductor chips.

[0174] The plasma irradiation conditions are not particularly limited as long as they allow the semiconductor wafer to be well cut at the position of the groove. The plasma irradiation conditions can be selected to be suitable for plasma etching of a semiconductor substrate, taking into consideration the material of the semiconductor wafer, the type of plasma, etc.

[0175] The gas used for plasma generation in plasma irradiation (etching gas) can be appropriately selected depending on the material of the semiconductor wafer, etc., but for example, SF ６ Gases, etc. can be used. Also, by adopting the Bosch process, ４ F ６ Gas and C ４ F ８It is preferable to cut the semiconductor wafer by alternately supplying a fluorine-based gas such as a fluorine gas to protect the sidewall and etching the semiconductor wafer by plasma irradiation. The Bosch process has the advantage that etching at a high aspect ratio is possible and cutting of the semiconductor wafer is easy even when the semiconductor wafer is thick.

[0176] Furthermore, in the Bosch process, the above-mentioned fluorine-based gas is used as an etching gas under vacuum or reduced pressure, which generates fluorine radicals in the system. However, the protective film according to this embodiment contains a metal salt of tin, which effectively prevents the fluorine radicals from volatilizing in the system. As a result, there is also the advantage that problems such as unnecessary contamination, etching, or damage to the wafer caused by the volatilized fluorine radicals can be effectively prevented.

[0177] The protective film according to this embodiment has at least an excellent selectivity. It is expected that the use of such a protective film will result in a groove with excellent straightness and cross-sectional rectangularity. As a result, it will be possible to accurately cut the desired position by plasma irradiation, and to obtain a semiconductor chip with excellent straightness.

[0178] Furthermore, the protective film according to this embodiment at least suppresses the occurrence of cracks and has excellent film-forming properties. Therefore, it is possible to sufficiently protect areas other than the cutting position, and effectively prevent cutting of undesired positions (positions other than the cutting groove) due to plasma irradiation or the like. Furthermore, it is also possible to effectively suppress contamination and damage of the semiconductor substrate due to gases such as fluorine-based gases used in plasma irradiation.

[0179] Next, the protective film covering the surface of the semiconductor chip is removed. As described above, if the protective film contains a water-soluble resin, the protective film can be efficiently washed away with water.

[0180] The above describes an example of a method for manufacturing semiconductor chips by processing a semiconductor wafer. The semiconductor chip manufacturing method according to this embodiment includes forming a protective film on the surface of the semiconductor wafer, forming grooves in the surface of the semiconductor wafer that is provided with the protective film at positions corresponding to the streets, and cutting the surface by plasma irradiation. This method can be applied to various semiconductor chip manufacturing methods.

[0181] In recent years, streets have become narrower to increase the number of chips that can be extracted from a single wafer. Furthermore, for small-chip devices, which are in demand for mobile devices and IoT, further improvements in quality and productivity are desired. In semiconductor manufacturing processes for devices that require high quality and high productivity, the manufacturing method according to this embodiment is particularly suitable as it can solve the above-mentioned problems associated with plasma dicing.

[0182] The present invention will be described in more detail with reference to the following examples and comparative examples, but the present invention is not limited to these examples. Unless otherwise specified, the quantities are based on mass, and the experiments were carried out at 25°C and atmospheric pressure.

[0183] <Ingredients used>

[0184] Each component used in this example will be described below.

[0185] (1) First Water-Soluble Resin (Non-Aromatic Resin) Resin (1Aa): Hydroxypropyl cellulose (a resin having a repeating unit represented by the following formula (1Aa), a weight-average molecular weight of 25,000, manufactured by Nippon Soda Co., Ltd., trade name "HPC-SSL", HPC-SSL)

[0186]

[0187] (In the formula, R １ , R ２ , and R ３ are each independently —H or —CH ２ CH(OH)CH ３ and all R １ , R ２ , and R３ At least one of the groups is —CH ２ CH(OH)CH ３ It is.)

[0188] Resin (1Bb): Polyvinyl alcohol (formula (1b): a resin having a repeating unit represented by the following formula (1b-1) and a repeating unit represented by the following formula (1b-2), estimated degree of polymerization: 500, manufactured by Kuraray Co., Ltd., trade name "Kuraray Poval PVA-505C", PVA-505C)

[0189] Resin (1Cc): Poly-N-vinylacetamide (a resin having a repeating unit represented by the following formula (1c), weight average molecular weight 300,000, manufactured by Resonac Corporation, trade name "PNVA GE191-104", PNVA 104)

[0190]

[0191] Resin (1Dd): Polyvinylpyrrolidone (a resin having a repeating unit represented by the following formula (1d), weight-average molecular weight 1,200,000, manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd., trade name "Pitzcol K-90", PVP K-90)

[0192]

[0193] (2) Second Water-Soluble Resin (Aromatic Resin) Resin (2Aa): A resin having a repeating unit represented by formula (2a-1) and a repeating unit represented by formula (2a-2) (see formula (2Aa), weight average molecular weight 22,000) was prepared and used.

[0194]

[0195] Resin (2Aa) was obtained by treating raw material resin (2Aaa) (see formula (2Aaa) below; resin (2Aaa) having repeating units represented by formula (2aa-1) and repeating units represented by formula (2aa-2) in a molar ratio of 4:1, i.e., the molar ratio of repeating units represented by formula (2aa-1) to repeating units represented by formula (2aa-2) (formula (2a-1) / (formula (2a-2))) is 4, weight average molecular weight is 22,000, product name "WSR-SP82" manufactured by Konishi Chemical Industry Co., Ltd.) with hydrochloric acid, followed by dilution treatment with aqueous ammonia (WSR-SP82(NH ４ )).

[0196]

[0197] Resin (2Bb): A resin having a repeating unit represented by formula (2b-1) and a repeating unit represented by formula (2b-2) (see formula (2Bb), weight average molecular weight 10,000) was prepared and used.

[0198]

[0199] Resin (2Bb) was obtained by diluting a raw material styrene-maleic anhydride copolymer (see formula (2Bbb) below; resin (2Bbb) having repeating units represented by formula (2bb-1) and repeating units represented by formula (2bb-2) in a molar ratio of 3:1, i.e., a molar ratio of repeating units represented by formula (2bb-1) to repeating units represented by formula (2bb-2) of 3, a weight average molecular weight of 10,000, and a trade name "XIRAN 3000P" manufactured by POLYSCOPE) with an aqueous ammonia solution (ammonia concentration of 5% by mass) in a mixed solvent of ultrapure water (DIW) and propylene glycol monomethyl ether (PGME) (a mass ratio of DIW / PGME = 85 / 15) to a resin solids concentration of 14% by mass, thereby ring-opening maleic anhydride (XIRAN-3000P(NH ４ )).

[0200]

[0201] Resin (2Cc): Polystyrene sulfonic acid (resin having a repeating unit represented by the following formula (2c), weight average molecular weight 22,000, manufactured by Tosoh Finechem Co., Ltd., trade name "PS-1H", PS-1H)

[0202]

[0203] In addition, the first water-soluble resin (first resin) and the second water-soluble resin (second resin) described above were both soluble in an amount of 0.5 g or more in 100 g of water at 25°C.

[0204] (3) Additives: Light absorber: 2-(4-diethylamino-2-hydroxybenzoyl)benzoic acid (DHBA); Basic compound: monoethanolamine (MEA).

[0205] Example 1

[0206] First, 100 parts by mass of the components shown in Table 1 (a first resin (a cellulose derivative obtained by reacting cellulose with propylene oxide, manufactured by Nippon Soda Co., Ltd., trade name "NISSO HPC-SSL") and tin nitrate as a metal tin salt) were added to a mixed solvent of ultrapure water (DIW: de-ionized water) and propylene glycol monomethyl ether (PGME) (a mass ratio of DIW / PGME = 85 / 15, the content of the organic solvent in the mixed solvent being 15% by mass) and diluted to the Sn content and solids concentration shown in Table 1 (target solids concentration, solvent mass ratio = DIW / PGME = 85 / 15). The mixture was then stirred until the system became homogeneous, yielding a protective film-forming agent. This protective film-forming agent had 100 parts by mass of the first resin (non-aromatic resin) as solids, a tin content of 800 ppb by mass, and a solids concentration of 20% by mass.

[0207] Next, a protective film forming agent was applied to the surface of the silicon substrate using a spin coater, and then the applied agent was allowed to dry naturally at room temperature for 15 minutes to form a protective film having a thickness of 5 μm.

[0208] Next, the surface of the Si substrate on the protective film side was linearly irradiated with plasma, and etching was performed to form the dividing grooves. The plasma irradiation was performed by the Bosch process under the following laser irradiation conditions: Bosch process: fluorine-based gas (C ４ F ８ The sidewall protection process is performed by supplying fluorine-based gas (a process in which a fluorine-based gas is turned into plasma to deposit a CF-based protective film on the silicon substrate), and the etching process is performed by removing the film on the bottom surface by the ion-assisted effect and depositing SF ６ The silicon on the silicon substrate exposed by plasma irradiation reacts with the fluorine atoms generated by plasma generation to produce silicon tetrafluoride (SiF ４ The laser irradiation conditions were: wavelength: 355 nm, frequency: 100 kHz, output: 0.1 W, defocus: -0.1 mm, feed rate: 100 mm / s, and pass count: 2.

[0209] (Measurement of solid content concentration) First, the aluminum case was weighed (tare weight A (g)). Next, 1 g of the protective film forming agent was weighed and placed in the aluminum case (weighing value: B (g)). This was dried at 140°C for 120 minutes. After drying, it was cooled to room temperature and then weighed (weighing value: C (g)). The solid content concentration was then calculated based on the following formula. The electronic balance used for the weighing was capable of weighing to the nearest 0.0001 g. Solid content concentration (mass %) = (C - A) / (B - A) x 100 A: mass of the tare (g) B: total mass of the sample and the tare (g) C: total mass of the sample and the tare after drying (g)

[0210] (Measurement of Sn Content) The tin content ratio of the metal salt to the total amount of components excluding the solvent from the protective film-forming agent ((tin) / (total amount of components excluding the solvent from the protective film-forming agent)) was measured in accordance with the following method. The Sn content in the protective film-forming agent was quantified by inductively coupled plasma atomic emission spectroscopy. The measurement was performed by a calibration curve method, where a calibration curve was created at four or more concentration levels, and measurements were performed when the calibration curve had a correlation coefficient of 0.99 or more. The metal reagent used in the calibration curve method was a mixed solvent (metal element concentration 100 ppb by mass) of 1 part by mass of a multi-element mixed standard solution "XSTC-622" (metal element concentration 10 mg / L) manufactured by SPEX and 99 parts by mass of dimethylacetamide (DMAC).

[0211] (Evaluation of Film Formability (Cracks in Protective Film)) Under the conditions described above, the protective film forming agent was applied to a silicon substrate by spin coating to obtain a protective film with a film thickness of 5 μm. The obtained protective film was dried under reduced pressure to the measurement environment (6.0 Pa) of an SEM (scanning electron microscope). The coated film after reduced pressure drying was then observed with a 10x optical microscope, and the film formability (presence or absence of cracks in the protective film) was evaluated based on the following criteria. Note that if cracks were present (case "B"), the selectivity was not measured ("-" in each table). - "A": No cracks were observed. - "B": Cracks were observed. Note that for each example, the surface of the protective film was touched with a finger to check for stickiness (tack), and it was confirmed that there was no stickiness in any of the examples.

[0212] (Measurement of Selectivity Ratio) The selectivity ratio was calculated based on the following formula: Selectivity ratio = film loss amount of silicon substrate / film loss amount of protective film; film loss amount of silicon substrate = film thickness of silicon substrate before irradiation - film thickness of silicon substrate after irradiation; film loss amount of protective film = film thickness of protective film before irradiation - film thickness of protective film after irradiation.

[0213] <Examples 2 to 8>

[0214] Protective film-forming agents were prepared in accordance with Example 1, except that the components of the protective film-forming agent were changed to the components listed in Table 1. For example, the protective film-forming agent of Example 5 is a protective film-forming agent having a solids concentration of 20% by mass, which contains, as solid contents, 96.8 parts by mass of the first resin, as well as 2.5 parts by mass of 2-(4-diethylamino-2-hydroxybenzoyl)benzoic acid (DHBA) and 0.7 parts by mass of monoethanolamine (MEA). Furthermore, the protective film-forming agent of Example 5 had a molar ratio of MEA / DHBA of 1.1 (=(0.7÷61.08) / (2.5÷246.22).

[0215] <Examples 9 to 14>

[0216] Protective film-forming agents were prepared in accordance with Example 1, except that the components of the protective film-forming agent were changed to the components listed in Table 2. For example, the protective film-forming agent of Example 9 contains, as solid contents, 90 parts by mass of a first resin (non-aromatic resin) and 10 parts by mass of a second resin (aromatic resin), and has a solid content concentration of 18% by mass.

[0217] In addition, for Examples 1 to 14, straightness was also evaluated based on the following criteria. As a result, it was confirmed that all Examples were rated at least "B" or higher ("B" or "A"). - "A": The cross section of the protective film (side walls of the processed groove) was flat, and a straight groove (trench) without any wobble was formed. - "B": The cross section of the protective film was relatively flat, and a relatively straight groove (trench) was formed with some wobble. - "C": The cross section of the protective film was not flat, and a groove (trench) with significant wobble was formed. - "D": Processing failure (the pattern became soft due to the heat of the laser and could no longer maintain its shape, and a processed groove could not be formed.)

[0218] <Comparative Examples 1 to 12>

[0219] A protective film-forming agent was prepared in accordance with Example 1, except that the components of the protective film-forming agent were changed to the components shown in Table 3. For example, the protective film-forming agent of Comparative Example 1 contains 100 parts by mass of the first resin (non-aromatic resin) as a solid content, does not contain a tin metal salt, and has a solid content concentration of 18% by mass.

[0220] The formulations and evaluation results of Examples 1 to 8 are shown in Table 1, the formulations and evaluation results of Examples 9 to 14 are shown in Table 2, and the formulations and evaluation results of Comparative Examples 1 to 12 are shown in Table 3.

[0221]

[0222]

[0223]

[0224] From the above, it was at least confirmed that the protective film forming agent according to this example is excellent in film-forming properties and can form a protective film having a high selectivity.

[0225] This application is based on a Japanese patent application (Patent Application No. 2023-222517) filed with the Japan Patent Office on December 28, 2023, the contents of which are incorporated herein by reference.

Claims

1. A protective film forming agent containing a metal salt of tin, a first resin having no aromatic ring, and a solvent.

2. The protective film forming agent according to claim 1, further containing a second resin having an aromatic ring.

3. The protective film forming agent according to claim 1 or 2, wherein the content ratio of tin in the metal salt in the total amount of the components excluding the solvent from the protective film forming agent is 500 mass ppm or more.

4. The protective film forming agent according to claim 1 or 2, wherein the metal salt contains at least one selected from the group consisting of sulfates, nitrates, nitrites, and hydrates thereof.

5. The protective film forming agent according to claim 1 or 2, wherein the first resin contains at least one selected from the group consisting of cellulose-based resins and vinyl-based resins.

6. The first resin contains at least one selected from the group consisting of a resin (1A) containing a repeating unit represented by the following formula (1a), a resin (1B) containing a repeating unit represented by the following formula (1b-1) and a repeating unit represented by the following formula (1b-2), a resin (1C) containing a repeating unit represented by the following formula (1c), and a resin (1D) containing a repeating unit represented by the following formula (1d). The protective film forming agent according to claim 1 or 2. (In the formula, R １ , R ２ , and R ３ are each independently a substituent represented by -H, -CH ３ , -CH ２ CH ３ , or -CH ２ CH(OH)CH ３ , and at least one of all R １ , R ２ , and R ３ is a substituent other than -H.) 7. The protective film-forming agent according to claim 2, wherein the second resin contains at least one selected from the group consisting of a resin (2A) containing a repeating unit represented by the following formula (2a-1) and a repeating unit represented by the following formula (2a-2), a resin (2B) containing a repeating unit represented by the following formula (2b-1) and a repeating unit represented by the following formula (2b-2), and a resin (2C) containing a repeating unit represented by the following formula (2c). (In the formula, X ＋ is an alkali metal cation, a proton, or N ＋ R ４ ４ and R ４ is a hydrogen atom, an alkyl group, or a hydroxyalkyl group.) (In the formula, M １＋ and M ２＋ are each independently an alkali metal cation, a proton, or N ＋ R ５ ４ and R ５ is a hydrogen atom, an alkyl group, or a hydroxyalkyl group.) 8. A protective film containing a metal salt of tin and a first resin having no aromatic ring.

9. The protective film according to claim 8, further containing a second resin having an aromatic ring.

10. The protective film according to claim 8 or 9, wherein the content rate of tin in the metal salt in the protective film is 500 mass ppm or more.

11. The protective film according to claim 8 or 9, having a film thickness of 0.1 μm or more and 100 μm or less.

12. A method for manufacturing a protective film, including a step of applying the protective film forming agent according to claim 1 or 2 on a substrate to form a protective film.

13. A method for manufacturing a semiconductor chip, which is a method for cutting a semiconductor wafer by plasma dicing, including a step of applying the protective film forming agent according to claim 1 or 2 on the semiconductor wafer to form a protective film, a step of irradiating laser light at a predetermined position of one or more layers including the protective film on the semiconductor wafer to expose the surface of the semiconductor wafer and form a processing groove having a pattern corresponding to the shape of the semiconductor chip, and a step of irradiating the semiconductor wafer having the processing groove formed thereon with plasma to cut the position of the processing groove of the semiconductor wafer to obtain a semiconductor chip.

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