JP2014212179A - Composition for forming protection film, method of forming protection film, protection film, and method of removing protection film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a protection film that has an excellent adhesion property with a wafer and that can be easily removed while preventing generation of residues.SOLUTION: Provided is a protection film formation composition for forming a protection film protecting a surface of a wafer when rear face processing of the wafer or transportation of the wafer, that are to be performed after surface processing of the wafer in a process of manufacturing a semiconductor element, is performed. The protection film formation composition contains a thermoplastic resin whose glass-transition temperature is 200°C or more, and an organic solvent that can dissolve the thermoplastic resin. It is preferred that the protection film formation composition further contains a compound having at least one kind of polar functional group selected from a group consisting of a hydroxyl group, a thiol group, a carboxyl group, and an amino group.

Description

  The present invention relates to a protective film forming composition, a protective film forming method, a protective film, and a protective film removing method.

  In a process for manufacturing a power semiconductor element, a back surface process may be performed after a wafer surface process. As the back surface processing, for example, back grinding processing, electrode formation processing, or the like is performed. When performing wafer backside processing, the wafer is turned over, placed on the suction stage, and moved to a place where each processing is performed by moving the suction stage. When the wafer is turned over and the wafer is placed on the suction stage as it is, the surface of the wafer that has been processed first comes into contact with the surface of the suction stage. In such a case, there is a concern that the surface of the wafer is damaged or that foreign matter adheres to the surface of the wafer. Therefore, it is desired to protect the front surface of the wafer when performing backside processing and when transporting the wafer.

  As a method for protecting the surface of the wafer, a support is temporarily fixed to the surface of the wafer via a temporary fixing material (see JP 2011-225814 A), and the surface of the wafer is covered with a protective film of an ultraviolet curable resin. It has been proposed (see JP 2006-124354 A).

  In the method of temporarily fixing the support, the support is temporarily fixed to the wafer by bonding the wafer and the support after the temporary fixing layer (temporary fixing material) is formed on the surface of the support or the wafer. Therefore, in order to temporarily fix the support to the wafer, at least two steps of forming the temporary fixing layer and bonding the wafer and the support are necessary. A member is required. Therefore, it is difficult to say that it is advantageous in terms of manufacturing cost. If the adhesion between the temporarily fixed material and the wafer is too high, it is difficult to remove the temporarily fixed material from the wafer. In order to facilitate the removal of the temporarily fixing material from the wafer, the adhesion between the temporarily fixing material and the wafer may be lowered. In this case, there is a possibility that a positional deviation occurs between the support and the wafer. is there. In particular, when the back surface treatment includes a high temperature process, a positional deviation is likely to occur between the support and the wafer. If the wafer is positioned with reference to the support, if the positional deviation occurs between the support and the wafer, the wafer is displaced relative to the suction stage. When such a case occurs, there is a possibility that a process that requires positional accuracy such as an electrode forming process cannot be performed appropriately.

  On the other hand, the method of covering with an ultraviolet curable resin film is excellent in adhesion to the wafer because the protective film is an ultraviolet curable resin film. On the other hand, since the protective film is an ultraviolet curable resin film, it is not easy to remove the protective film from the surface of the wafer, and a residue may be generated when the protective film is removed. In order not to generate a residue, conditions (for example, temperature and the type of solvent used) required for removing the protective film become severe, so that the surface of the wafer may be damaged.

  In this way, the temporary fixing material, the protective film, etc. can be easily removed while preventing the occurrence of residues, and the adhesion between the wafer and the temporary fixing material, the protective film, etc., in order to suppress the occurrence of wafer misalignment. It is not easy to improve both of these.

JP 2011-225814 A JP 2006-124354 A

  The present invention has been made based on the above circumstances, and an object of the present invention is to provide a protective film that has excellent adhesion to a wafer and can be easily removed while preventing generation of residues.

The invention made to solve the above problems is
A protective film forming composition for forming a protective film that protects the surface of a wafer when the wafer is subjected to a back surface treatment or a wafer transfer after a wafer surface treatment in a semiconductor element manufacturing process. ,
A thermoplastic resin having a glass transition temperature of 200 ° C. or higher (hereinafter also referred to as “[A] thermoplastic resin”), and an organic solvent capable of dissolving the thermoplastic resin (hereinafter also referred to as “[B] organic solvent”). )
A composition for forming a protective film (hereinafter also referred to as “composition for forming a protective film (X)”).

The protective film forming method of the present invention comprises:
A step of applying the protective film-forming composition to a wafer, and a step of removing the organic solvent.

  The protective film of the present invention is formed by the protective film forming method.

  The protective film removing method of the present invention includes a step of dissolving and removing the protective film with an organic solvent or a step of mechanically peeling and removing.

  The protective film provided by the protective film forming composition and the protective film forming method of the present invention is excellent in adhesion to the wafer, and can be easily removed while preventing the generation of residues by the protective film removing method of the present invention. Therefore, it is possible to appropriately perform the back surface processing or the transport after the surface processing while protecting the front surface of the wafer advantageously in terms of manufacturing cost.

It is a typical perspective view for demonstrating the process of apply | coating the composition for protective film formation to a wafer. It is a typical sectional view for explaining back grinding processing. It is a typical perspective view for demonstrating the removal process of a protective film.

  Hereinafter, the composition for forming a protective film, the protective film forming method, the protective film, and the protective film removing method of the present invention will be described in detail.

  The protective film-forming composition (X) is for forming a protective film that protects the wafer surface when the wafer back surface treatment or wafer transfer is performed after the wafer surface treatment in the semiconductor element manufacturing process. It is.

  The semiconductor element here is an element that requires a wafer backside process in the manufacturing process. An example of such a semiconductor element is a power semiconductor element. Power semiconductor elements include, for example, inverter elements that mutually convert direct current and alternating current, frequency conversion elements, regulator elements that increase or decrease voltage, drive elements that drive motors, microcomputers, LSIs, etc., charging elements that charge batteries, etc. It is used as an element for controlling and supplying the power of the power source and an element used as a power source. Examples of the power semiconductor element include a diode, a transistor, an IC having a diode and a transistor, and the like.

  Wafer surface treatment and back surface treatment are steps necessary to form a power semiconductor element or the like. For example, when a semiconductor element is formed as a transistor, backside treatment, ion implantation treatment, annealing treatment is performed as the back surface treatment. , Including sputtering.

[Composition for forming protective film (X)]
The protective film-forming composition (X) contains [A] a thermoplastic resin and [B] an organic solvent as essential components, and is selected from the group consisting of a hydroxyl group, a thiol group, a carboxyl group, and an amino group as suitable components. And a compound having at least one polar functional group (hereinafter, also referred to as “[C] compound”). The protective film-forming composition (X) may contain other optional components as long as the effects of the present invention are not impaired.

<[A] Thermoplastic resin>
[A] The thermoplastic resin is a thermoplastic resin having a glass transition temperature of 200 ° C. or higher. [A] The thermoplastic resin is not particularly limited as long as the glass transition temperature is 200 ° C. or higher. [A] Examples of the thermoplastic resin include polyether resin, polyimide resin, polyester resin, polycarbonate resin, phenoxy resin, and novolac resin. Of these, polyether resins are preferred.

[Polyether resin]
The polyether resin has at least one structural unit selected from the group consisting of a structural unit represented by the following formula (1) and a structural unit represented by the following formula (2) (hereinafter referred to as “structural unit (i)”. "). This polyether resin may further contain at least one of a structural unit (ii) and a structural unit (iii) described later in addition to the structural unit (i).

(Structural unit i)
The structural unit (i) increases the glass transition temperature of the thermoplastic resin [A] and increases the solubility in the organic solvent [B].

In the above formula (1), R ^{1 to} R ⁴ are each independently a monovalent organic group having 1 to 12 carbon atoms. However, the organic groups of R ^{1 to} R ^{4 do not} include a chain hydrocarbon group or an alicyclic hydrocarbon group. b to e are each independently an integer of 0 to 4. R ⁵ is a monovalent organic group having 1 to 12 carbon atoms. f is an integer of 0-3. When R ¹ to R ⁵ is plural, respectively, a plurality of ^R 1 to R ^5, may each be the same or different. R ⁶ is a cyano group, a nitro group or a formyl group.

Here, the “organic group” refers to a group containing at least one carbon atom.
Further, the “chain hydrocarbon group” means a hydrocarbon group that does not include a cyclic structure but is composed only of a chain structure, and includes both a linear hydrocarbon group and a branched hydrocarbon group. .
On the other hand, the “alicyclic hydrocarbon group” means a hydrocarbon group that includes only an alicyclic hydrocarbon structure as a ring structure and does not include an aromatic ring structure. However, it is not necessary to be constituted only by the structure of the alicyclic hydrocarbon, and a part thereof may include a chain structure.

Examples of the monovalent organic group having 1 to 12 carbon atoms represented by R ⁵ include at least one selected from the group consisting of a monovalent hydrocarbon group having 1 to 12 carbon atoms, an oxygen atom, and a nitrogen atom. C1-C12 monovalent organic groups containing these atoms.

  Examples of the monovalent hydrocarbon group having 1 to 12 carbon atoms include a monovalent chain hydrocarbon group having 1 to 12 carbon atoms, a monovalent alicyclic hydrocarbon group having 3 to 12 carbon atoms, and carbon. Examples thereof include monovalent aromatic hydrocarbon groups of 6 to 12.

Examples of the monovalent chain hydrocarbon group having 1 to 12 carbon atoms include:
Alkyl groups such as methyl, ethyl, propyl, butyl, and pentyl groups;
Alkenyl groups such as ethenyl group, propenyl group, butenyl group, pentenyl group;
Examples thereof include alkynyl groups such as ethynyl group, propynyl group, butynyl group, and pentynyl group.

  As carbon number of the said chain hydrocarbon group, 1-8 are preferable and 1-5 are more preferable.

Examples of the monovalent alicyclic hydrocarbon group having 3 to 12 carbon atoms include:
A cycloalkyl group such as a cyclopropyl group, a cyclobutyl group, a cyclopentyl group, a cyclohexyl group, a norbornyl group, an adamantyl group;
And cycloalkenyl groups such as cyclopropenyl group, cyclobutenyl group, cyclopentenyl group and norbornenyl group.

  The alicyclic hydrocarbon group preferably has 3 to 8 carbon atoms, and more preferably 3 or 4 carbon atoms.

Examples of the divalent aromatic hydrocarbon group having 6 to 12 carbon atoms include:
Aryl groups such as phenyl group, tolyl group, xylyl group, naphthyl group;
Examples thereof include aralkyl groups such as benzyl group, phenethyl group, and naphthylmethyl group.

  Examples of the monovalent organic group having 1 to 12 carbon atoms containing an oxygen atom include an organic group composed of a hydrogen atom, a carbon atom and an oxygen atom, and an ether bond, a carbonyl group or an ester bond, and a hydrocarbon group. And a monovalent organic group having 1 to 12 carbon atoms.

  Examples of the monovalent organic group having 1 to 12 carbon atoms having an ether bond include alkoxy groups such as a methoxy group, an ethoxy group, a propoxy group, an isopropyloxy group, a butoxy group, and a cyclohexyloxy group; an ethenyloxy group and a propenyloxy group. An alkynyloxy group such as an ethynyloxy group; an aryloxy group such as a phenoxy group; an alkoxyalkyl group such as a methoxymethyl group.

  As said C1-C12 monovalent organic group which has the said carbonyl group, acyl groups, such as an acetyl group, a propionyl group, an isopropionyl group, a benzoyl group, etc. are mentioned, for example.

  Examples of the monovalent organic group having 1 to 12 carbon atoms having an ester bond include acyloxy groups such as acetyloxy group, propionyloxy group, isopropionyloxy group, and benzoyloxy group.

  Examples of the monovalent organic group having 1 to 12 carbon atoms containing a nitrogen atom include an organic group composed of a hydrogen atom, a carbon atom and a nitrogen atom, and an amino group, an imidazolyl group, a triazolyl group, a benzimidazole group, and the like. Examples include a ryl group and a benztriazolyl group.

  Examples of the monovalent organic group having 1 to 12 carbon atoms containing an oxygen atom and a nitrogen atom include an organic group composed of a hydrogen atom, a carbon atom, an oxygen atom and a nitrogen atom, and an oxazolyl group and an oxadiazolyl group. Group, benzoxazolyl group, benzoxadiazolyl and the like.

  Among these, a hydrocarbon group is preferable, a chain hydrocarbon group and an aromatic hydrocarbon group are more preferable, and a methyl group, an ethyl group, and a phenyl group are further preferable.

Examples of the monovalent organic group having 1 to 12 carbon atoms represented by R ^{1 to} R ⁴ include organic compounds including a chain hydrocarbon group or an alicyclic hydrocarbon group among those exemplified as R ⁵ above. Examples thereof include the same groups as the organic group excluding the group.
Among these, an aromatic hydrocarbon group is preferable, and a phenyl group is more preferable.

R ⁶ is preferably a cyano group or a nitro group, and more preferably a cyano group.

In said formula (2), R < ⁷ > -R < ¹⁰ > is respectively independently a C1-C12 monovalent organic group. However, the organic group of R < ⁷ > -R < ¹⁰ > does not contain a chain hydrocarbon group or an alicyclic hydrocarbon group. R ¹¹ and R ¹² are each independently a halogen atom, a nitro group, or a monovalent organic group having 1 to 12 carbon atoms. g to l are each independently an integer of 0 to 4; If R ⁷ to R ¹² are a plurality of each of a plurality of ^R 7 ^{to R 12} may each be the same or different. Y is a single bond, —SO ₂ — or —CO—. m is 0 or 1. However, when m is 0, R ¹² is neither a nitro group nor a cyano group.

Examples of the monovalent organic group having 1 to 12 carbon atoms represented by R ^{7 to} R ¹⁰ (excluding an organic group containing a chain hydrocarbon group or an alicyclic hydrocarbon group) include, for example, the above formula Examples thereof include the same groups as the organic groups exemplified as R ^{1 to} R ^{4 in} (1).

  Among these, an aromatic hydrocarbon group is preferable, and a phenyl group is more preferable.

Examples of the halogen atom represented by R ¹¹ and R ¹² include a fluorine atom, a chlorine atom, a bromine atom, and an iodine atom. Among these, a fluorine atom and a chlorine atom are preferable, and a fluorine atom is more preferable.

Examples of the monovalent organic group having 1 to 12 carbon atoms represented by R ¹¹ and R ^12, for example, like same groups as exemplified organic groups as R ⁵ in the formula (1).

R ¹¹ and R ¹² are preferably a halogen atom or an organic group, more preferably an organic group, still more preferably a chain hydrocarbon group, and particularly preferably a methyl group.

  As said g ~ l, the integer of 0-2 is preferable, 0 or 1 is more preferable, and 0 is further more preferable.

  Y is preferably a single bond or —CO—.

  As said m, 1 is preferable.

(Structural unit (ii))
[A] The thermoplastic resin may further include a structural unit (ii) represented by the following formula (3). [A] When the thermoplastic resin contains the structural unit (ii), the adhesion of the protective film to the wafer can be improved. [A] The reason why the adhesiveness is increased by including the structural unit (ii) in the thermoplastic resin is not necessarily clear, but the presence of the polysiloxane chain in the structural unit (i) gives flexibility to the molecular chain. It is thought that it is to be done. However, the structural unit (ii) is not necessarily required when sufficient adhesion can be realized by, for example, containing the [C] compound in the protective film-forming composition (X).

In the above formula ^{(3), R 13} and ^{R 14} are each independently an aryl group an alkyl group or a C6-15 having 1 to 4 carbon atoms. n is an integer of 5 to 100. The plurality of R ¹³ and R ¹⁴ may be the same or different. R ¹⁵ and R ¹⁶ are each independently a single bond or a divalent organic group having 1 to 12 carbon atoms. X is a divalent group represented by the following formula (3a) or (3b).

In the above formulas (3a) and (3b), R ¹⁷ is a monovalent organic group having 1 to 12 carbon atoms. a is an integer of 0-3. If R ¹⁷ is plural, plural ^{R 17} may be the same or different. R ¹⁸ is a cyano group, a nitro group, or a formyl group.

The alkyl group having 1 to 4 carbon atoms represented by ^{R 13} and ^{R 14,} for example, a methyl group, an ethyl group, a propyl group. Examples of the aryl group having 6 to 15 carbon atoms represented by R ¹³ and R ¹⁴ include a phenyl group, a benzyl group, a tolyl group, a xylyl group, and a naphthyl group. Among these, as R ¹³ and R ¹⁴ , an alkyl group is preferable and a methyl group is more preferable from the viewpoint of adhesion of the protective film to the wafer.

Examples of the group represented by —Si (R ¹³ ) (R ¹⁴ ) — in the above formula (3) include a dimethylsilanediyl group, a diphenylsilanediyl group, and a methylphenylsilanediyl group. Among these, from the viewpoint of adhesion of the protective film to the wafer, a dimethylsilanediyl group and a diphenylsilanediyl group are preferable, and a dimethylsilanediyl group is more preferable.

In the above formula (1), when groups represented by —Si (R ¹³ ) (R ¹⁴ ) — include different groups, each group may be arranged so as to form a block. However, from the viewpoint of the adhesion of the protective film to the wafer, it is preferably arranged randomly.

  The lower limit of n is, for example, 5, 10 is preferable, 25 is more preferable, and 50 is more preferable. On the other hand, the upper limit of n is, for example, 200, 150 is preferable, 80 is more preferable, and 70 is more preferable. If n is less than the above lower limit, there is a possibility that sufficient adhesion of the protective film to the wafer cannot be ensured. When n exceeds the upper limit, [A] the heat resistance of the thermoplastic resin may be reduced.

Examples of the divalent organic group having 1 to 12 carbon atoms represented by R ¹⁵ and R ^16, for example, a divalent hydrocarbon group having 1 to 12 carbon atoms, selected from the group consisting of oxygen atom and a nitrogen atom C1-C12 bivalent organic group etc. which contain at least 1 sort (s) of atom are mentioned.

  Examples of the divalent hydrocarbon group having 1 to 12 carbon atoms include a divalent chain hydrocarbon group having 1 to 12 carbon atoms, a divalent alicyclic hydrocarbon group having 3 to 12 carbon atoms, and carbon. Examples thereof include divalent aromatic hydrocarbon groups of 6 to 12.

Examples of the divalent chain hydrocarbon group having 1 to 12 carbon atoms include:
Alkanediyl groups such as methanediyl, ethanediyl, propanediyl, butanediyl, pentanediyl;
Alkenediyl groups such as ethenediyl group, propenediyl group, butenediyl group, pentenediyl group;
Examples include alkynediyl groups such as ethynediyl group, propynediyl group, butynediyl group, and pentynediyl group.

  As carbon number of the said chain hydrocarbon group, 1-8 are preferable and 1-5 are more preferable.

As said C3-C12 bivalent alicyclic hydrocarbon group, for example,
Cycloalkanediyl groups such as cyclopropanediyl group, cyclobutanediyl group, cyclopentanediyl group, cyclohexanediyl group, norbornanediyl group, adamantanediyl group;
And cycloalkenediyl groups such as cyclopropenediyl group, cyclobutenediyl group, cyclopentenediyl group and norbornenediyl group.

  The alicyclic hydrocarbon group preferably has 3 to 8 carbon atoms, and more preferably 3 or 4 carbon atoms.

Examples of the divalent aromatic hydrocarbon group having 6 to 12 carbon atoms include:
Arenediyl groups such as benzenediyl group, toluenediyl group, xylenediyl group, naphthalenediyl group;
Examples thereof include arenediylalkanediyl groups such as benzenediylmethanediyl group, benzenediylethanediyl group and naphthalenediylmethanediyl group.

  Examples of the C1-C12 divalent organic group containing an oxygen atom include an organic group consisting of a hydrogen atom, a carbon atom and an oxygen atom, and an ether bond, a carbonyl group or an ester bond, and a hydrocarbon group. And a divalent organic group having 1 to 12 carbon atoms.

  Examples of the C1-C12 divalent organic group having an ether bond include alkanediyloxy groups such as methanediyloxy group, ethanediyloxy group, propanediyloxy group, butanediyloxy group, and cyclohexanediyloxy group. Alkenediyloxy group such as ethenediyloxy group; alkynediyloxy group such as ethynediyloxy group; arenediyloxy group such as benzenediyloxy group; alkanediyloxy group such as methanediyloxymethanediyl group; Examples include alkanediyl groups.

  Examples of the divalent organic group having 1 to 12 carbon atoms having a carbonyl group include alkanediylcarbonyl groups such as methanediylcarbonyl group, propanediylcarbonyl group and butanediylcarbonyl group; arenediyl groups such as benzenediylcarbonyl group Carbonyl group; alkanediylcarbonylalkanediyl group such as methanediylcarbonylmethanediyl group and the like.

  Examples of the divalent organic group having 1 to 12 carbon atoms having an ester bond include alkanediylcarbonyloxy groups such as methanediylcarbonyloxy group, propanediylcarbonyloxy group and butanediylcarbonyloxy group; benzenediylcarbonyloxy An arenediylcarbonyloxy group such as a group; an alkanediylcarbonyloxyalkanediyl group such as a methanediylcarbonyloxymethanediyl group;

  Examples of the divalent organic group having 1 to 12 carbon atoms containing a nitrogen atom include an organic group composed of a hydrogen atom, a carbon atom and a nitrogen atom, and an imino group, an imidazole diyl group, a triazole diyl group, a benzine. Examples thereof include an imidazole diyl group and a benztriazole diyl group.

  As a C1-C12 bivalent organic group containing an oxygen atom and a nitrogen atom, the organic group which consists of a hydrogen atom, a carbon atom, an oxygen atom, and a nitrogen atom etc. are mentioned, for example, An oxazole diyl group, an oxadiazole Diyl group, benzoxazole diyl group, benzoxadiazole group diyl and the like can be mentioned.

R ¹⁵ and R ¹⁶ are preferably a single bond, a chain hydrocarbon group, or an aromatic hydrocarbon group from the viewpoint that the heat resistance of the thermoplastic resin [A] can be maintained higher, and the chain hydrocarbon group is preferably More preferably, a C1-C5 chain hydrocarbon group is more preferable, and a propanediyl group is particularly preferable.

Examples of the monovalent organic group having 1 to 12 carbon atoms represented by R ¹⁷ in the formula (3a) of X include the same groups as the organic groups exemplified as R ^{5 in the} formula (1). It is done.

The monovalent hydrocarbon groups of 1 to 12 carbon atoms, for example, such as the same groups as the hydrocarbon groups exemplified as R ⁵ in the formula (1).

R ¹⁷ is preferably a chain hydrocarbon group, more preferably a chain hydrocarbon group having 1 to 5 carbon atoms, and still more preferably a methyl group or an ethyl group.

  As said a, the integer of 0-2 is preferable, 0 or 1 is more preferable, and 0 is further more preferable.

R ¹⁸ in the above formula (3b) is preferably a cyano group or a nitro group, and more preferably a cyano group.

  X is preferably a divalent group represented by the above formula (3a) from the viewpoint of further improving the glass transition temperature.

(Structural unit (iii))
[A] The thermoplastic resin is at least one structural unit selected from the group consisting of a structural unit represented by the following formula (4) and a structural unit represented by the following formula (5) (hereinafter referred to as “structural unit”). (Iii) ").

  The structural unit (iii) increases rigidity by increasing the crystallinity of the thermoplastic resin [A].

In the formula ^{(4), R 19} is a monovalent organic group having 1 to 12 carbon atoms. However, the organic group of R ¹⁹ does not include a chain hydrocarbon group or an alicyclic hydrocarbon group. o is an integer of 0-3. When R ¹⁹ represents a plurality, the plurality of R ¹⁹ may be the same or different. Ar is a divalent group represented by at least one selected from the group consisting of the following formulas (4a), (4b) and (4c).

In the above formulas (4a), (4b) and (4c), R ^{20 to} R ²³ are each independently a monovalent organic group having 1 to 12 carbon atoms. However, the organic group of R ^{20 to} R ²³ does not include a chain hydrocarbon group or an alicyclic hydrocarbon group. p, q, and r are each independently an integer of 0-4. s is an integer of 0-6. R ²⁰ to R when ²³ is plural, respectively, a plurality of ^R 20 ^{to R 23} may each be the same or different.

Examples of the monovalent organic group having 1 to 12 carbon atoms represented by R ^{19 to} R ²³ (excluding an organic group containing a chain hydrocarbon group or an alicyclic hydrocarbon group) include, for example, the above formula exemplified organic group, and the like as ^R 1 to R ⁴ in (1). Among these, an aromatic hydrocarbon group is preferable, and a phenyl group is more preferable.

As said o, the integer of 0-2 is preferable, 0 or 1 is more preferable, and 0 is further more preferable.
As said p, q, and r, the integer of 0-2 is preferable, 0 or 1 is more preferable, and 0 is further more preferable.
s is preferably an integer of 0 to 2, more preferably 0 or 1, and still more preferably 0.

  Among the divalent groups represented by the above formulas (4a) to (4c), [A] 2 represented by the above formula (4c) from the viewpoint of improving the glass transition temperature and the thermal decomposition temperature of the thermoplastic resin. A valent group is preferred.

In Formula (5), R ²⁴ and R ²⁵ are each independently a monovalent organic group having 1 to 12 carbon atoms. However, the organic group of R ²⁴ and R ²⁵ does not include a chain hydrocarbon group or an alicyclic hydrocarbon group. t and u are each independently an integer of 0 to 4. If R ²⁴ and ^{R 25} are a plurality of each of the plurality of ^{R 24} and ^{R 25} may each be the same or different. Z is a single bond, —SO ₂ — or —CO—. w is 0 or 1.

Examples of the monovalent organic group having 1 to 12 carbon atoms (excluding those containing a chain hydrocarbon group or an alicyclic hydrocarbon group) represented by R ²⁴ and R ²⁵ include, for example, the above formula (1) Examples include the same groups as the organic groups exemplified as R ^{1 to} R ⁴ . Among these, an aromatic hydrocarbon group is preferable, and a phenyl group is more preferable.

  As said t and u, the integer of 0-2 is preferable, 0 or 1 is more preferable, and 0 is further more preferable.

  Z is preferably a single bond or —CO—.

  As said w, 1 is preferable.

(Other structural units)
[A] The thermoplastic resin may contain other structural units other than the structural units (i) to (iii).

[Content ratio of structural units]
As a content ratio of each structural unit,
[A] The thermoplastic resin preferably contains the structural unit (i) among the structural units (i) to (iii).
[A] When the thermoplastic resin includes the structural unit (i) and the structural unit (ii) and does not include the structural unit (iii), the total of the structural unit (i) and the structural unit (ii)
As a minimum of the content rate of structural unit (i), 50 mol% is preferable, 70 mol% is more preferable, 90 mol% is further more preferable, 93 mol% is especially preferable.
As an upper limit of the content rate of structural unit (i), 99.95 mol% is preferable, 99.5 mol% is more preferable, 99 mol% is further more preferable, 98 mol% is especially preferable, 97 mol% is especially especially 97 mol% preferable.
Moreover, as a minimum of the content rate of structural unit (ii), 0.05 mol% is preferable, 0.5 mol% is more preferable, 1 mol% is further more preferable, 2 mol% is especially preferable, 3 mol% is Further particularly preferred.
As an upper limit of the content rate of structural unit (ii), 50 mol% is preferable, 30 mol% is more preferable, 10 mol% is further more preferable, and 7 mol% is especially preferable.

[A] When the thermoplastic resin includes the structural unit (i) and the structural unit (iii) and does not include the structural unit (ii), the total of the structural unit (i) and the structural unit (iii)
Although it does not necessarily limit as a minimum of the content rate of structural unit (i), 50 mol% is preferable, 60 mol% is more preferable, 70 mol% is further more preferable, 75 mol% is especially preferable.
The upper limit of the content ratio of the structural unit (i) is not particularly limited, but is preferably 99 mol%, more preferably 90 mol%, still more preferably 85 mol%, and particularly preferably 8 mol%.
The lower limit of the content ratio of the structural unit (iii) is not particularly limited, but is preferably 1 mol%, more preferably 10 mol%, further preferably 15 mol%, and particularly preferably 20 mol%. .
The upper limit of the content ratio of the structural unit (iii) is not particularly limited, but is preferably 50 mol%, more preferably 40 mol%, still more preferably 30 mol%, and particularly preferably 25 mol%.

[A] When the thermoplastic resin includes the structural unit (i), the structural unit (ii), and the structural unit (iii), the total of the structural unit (i), the structural unit (ii), and the structural unit (iii) ,
The lower limit of the total content of the structural units (i) and (iii) is preferably 50 mol%, more preferably 70 mol%, further preferably 90 mol%, particularly preferably 93 mol%, and further preferably 50 mol%. Particularly preferred.
The upper limit of the total content of the structural units (i) and (iii) is preferably 99.95 mol%, more preferably 99.5 mol%, still more preferably 99 mol%, particularly preferably 98 mol%, 97 More particularly preferred is mol%.
Moreover, as a minimum of the content rate of structural unit (ii), 0.05 mol% is preferable, 0.5 mol% is more preferable, 1 mol% is further more preferable, 2 mol% is especially preferable, 3 mol% is Further particularly preferred.
As an upper limit of the content rate of structural unit (ii), 50 mol% is preferable, 30 mol% is more preferable, 10 mol% is further more preferable, and 7 mol% is especially preferable.

<[A] Method for synthesizing thermoplastic resin>
[A] The thermoplastic resin can be synthesized by a known method. [A] When the thermoplastic resin is a polyether resin, the polyether resin can be synthesized, for example, by reacting a bisphenol compound and an aromatic dihalide compound. Examples of the bisphenol compound include a compound represented by the following formula (u) (hereinafter also referred to as “compound (u)”), the following formulas (v-1), (v-2), and (v-3). (Hereinafter, also referred to as “compounds (v-1), (v-2), (v-3)”), and the like.

In the above formula (u), R ^{7 ′ to} R ^{10 ′} each independently represent a halogen atom or a monovalent organic group having 1 to 12 carbon atoms. However, the organic group of R ^{7 ′ to} R ^{10 ′} does not include a chain hydrocarbon group or an alicyclic hydrocarbon group. b'-e 'is an integer of 0-4 each independently. When there are a plurality of R ^{7 ′ to} R ^{11 ′} , the plurality of R ^{7 ′ to} R ^{18 ′} may be the same as or different from each other.

In the above formulas (v-1) to (v-3), R ^{20 to} R ²³ are each independently a monovalent organic group having 1 to 12 carbon atoms. However, the organic group of R ^{20 to} R ²³ does not include a chain hydrocarbon group or an alicyclic hydrocarbon group. p, q, and r are each independently an integer of 0-4. s is an integer of 0-6. R ²⁰ to R when ²³ is plural, respectively, a plurality of ^R 20 ^{to R 23} may each be the same or different.

  Examples of the compound (u) include 9,9-bis (4-hydroxyphenyl) fluorene, 9,9-bis (3-phenyl-4-hydroxyphenyl) fluorene, 9,9-bis (3,5- Diphenyl-4-hydroxyphenyl) fluorene, 9,9-bis (4-hydroxy-3-methylphenyl) fluorene, 9,9-bis (4-hydroxy-3,5-dimethylphenyl) fluorene, 9,9-bis (4-hydroxy-3-cyclohexylphenyl) fluorene, 9,9-bis (4-hydroxyphenyl) -2,7-dibromofluorene, and reactive derivatives thereof. Among these, 9,9-bis (4-hydroxyphenyl) fluorene, 9,9-bis (4-hydroxy-3-methylphenyl) fluorene, 9,9-bis (4-hydroxyphenyl) -2,7 -Dibromofluorene is preferably used.

Examples of the compound (v-1) include hydroquinone, resorcinol, 2-phenylhydroquinone, and the like. Of these, hydroquinone and resorcinol are preferred.
Examples of the compound (v-2) include 4,4′-biphenol, 3,3′-biphenol, and the like. Of these, 4,4′-biphenol is preferred.
Examples of the compound (v-3) include 2,6-dihydroxynaphthalene and 2,7-dihydroxynaphthalene. Of these, 2,7-dihydroxynaphthalene is preferred.

  Examples of the bisphenol compound include silicone compounds having a phenolic hydroxyl group at the terminal. Examples of the silicone compound include a compound represented by the following formula (z) (hereinafter also referred to as “compound (z)”).

In the above formula (z), R ¹ and R ² are each independently an alkyl group having 1 to 4 carbon atoms or an aryl group having 6 to 15 carbon atoms. n is an integer of 5 to 100. A plurality of R ¹ and R ² may be the same or different. R ³ and R ⁴ are each independently a single bond or a divalent organic group having 1 to 12 carbon atoms.

  Examples of the aromatic dihalide compound include at least one of aromatic ketone dihalides among cyano group, nitro group, or formyl group-substituted aromatic dihalides.

  Examples of the cyano group, nitro group, or formyl group-substituted aromatic dihalide include compounds represented by the following formula (x) (hereinafter also referred to as “compound (x)”), and the like. Examples of the halide include a compound represented by the following formula (y) (hereinafter also referred to as “compound (y)”).

In the above formulas (x) and (y), R ^{5 ′} is a monovalent organic group having 1 to 12 carbon atoms. a is an integer of 0-3. R ^{6 ′} is a cyano group, a nitro group or a formyl group. Q is each independently a halogen atom.

  Examples of the halogen atom represented by Q include a fluorine atom, a chlorine atom, a bromine atom, and an iodine atom. Among these, a fluorine atom is preferable from the viewpoint of the reactivity of the compounds (x) and (y).

  Examples of the compound (x) include 2,6-difluorobenzonitrile, 2,5-difluorobenzonitrile, 2,4-difluorobenzonitrile, 2,6-dichlorobenzonitrile, 2,5-dichlorobenzonitrile, Examples include 2,4-dichlorobenzonitrile and derivatives thereof. Among these, 2,6-difluorobenzonitrile and 2,6-dichloro are considered from the viewpoints of reactivity and economy, improvement in heat resistance of the obtained [A] thermoplastic resin, and adhesion of the protective film to the wafer. Benzonitrile is preferred, and 2,6-difluorobenzonitrile is more preferred.

  Examples of the compound (y) include 4,4′-difluorobenzophenone, 2,4′-difluorobenzophenone, 2,2′-difluorobenzophenone, 4,4′-dichlorobenzophenone, 2,4′-dichlorobenzophenone, 2,2′-dichlorobenzophenone and the like can be mentioned. Among these, 4,4-difluorobenzophenone and 4,4-dichlorobenzophenone are preferred from the viewpoints of reactivity and economy, and improvement in heat resistance of the obtained [A] thermoplastic resin and adhesion of the protective film to the wafer. Preferably, 4,4-difluorobenzophenone is more preferable.

  As said aromatic dihalide, the diphenylsulfone dihalide represented by a following formula (w) can also be added and made to react as needed.

  In the formula (w), each Q is independently a halogen atom.

  [A] The thermoplastic resin can be synthesized, for example, by reacting the above compound in an organic solvent in the presence of an alkali metal compound. In addition, the said compound may be made to react all kinds simultaneously, Among the said compounds, after making a bisphenol compound and an alkali metal compound react and obtaining an alkali metal salt, the obtained alkali metal salt and the remaining An aromatic halide compound or the like can also be reacted. In the reaction, one or more of the above compounds may be used.

Examples of the alkali metal compound include:
Alkali metals such as lithium, sodium and potassium;
Alkali metal hydrides such as lithium hydride, sodium hydride, potassium hydride;
Alkali metal hydroxides such as lithium hydroxide, sodium hydroxide and potassium hydroxide;
Alkali metal carbonates such as lithium carbonate, sodium carbonate, potassium carbonate;
Examples thereof include alkali metal hydrogen carbonates such as lithium hydrogen carbonate, sodium hydrogen carbonate, and potassium hydrogen carbonate. Of these, alkali metal carbonates are preferred, and potassium carbonate is more preferred.

  With respect to the amount of the alkali metal compound used, the amount of metal atoms in the alkali metal compound is usually 1 to 3 times equivalent, preferably 1.1 times equivalent to 2 times the phenolic hydroxyl group of the compound used in the reaction. The amount is equivalent, more preferably 1.2 times equivalent to 1.5 times equivalent.

  Examples of the organic solvent include N, N-dimethylacetamide (DMAc), N, N-dimethylformamide, N-methyl-2-pyrrolidone, 1,3-dimethyl-2-imidazolidinone, γ-butyrolactone, sulfolane. , Dimethyl sulfoxide, diethyl sulfoxide, dimethyl sulfone, diethyl sulfone, diisopropyl sulfone, diphenyl sulfone, diphenyl ether, benzophenone, dialkoxybenzene (1 to 4 carbon atoms of alkoxy group), trialkoxybenzene (1 to 4 carbon atoms of alkoxy group) Etc. Among these, N-methyl-2-pyrrolidone, N, N-dimethylacetamide, sulfolane, diphenylsulfone, and dimethyl sulfoxide are preferable because they are polar solvents having a high dielectric constant.

  Further, in the above reaction, a solvent azeotropic with water such as benzene, toluene, xylene, hexane, cyclohexane, octane, chlorobenzene, dioxane, tetrahydrofuran, anisole, and phenetole can be further used.

  As reaction temperature, 60 to 250 degreeC is preferable and 80 to 200 degreeC is more preferable. The reaction time is preferably 15 minutes to 100 hours, more preferably 1 hour to 24 hours.

[[A] Physical properties of thermoplastic resin]
(Glass-transition temperature)
[A] The lower limit of the glass transition temperature (Tg) of the thermoplastic resin is 200 ° C, preferably 230 ° C, more preferably 270 ° C, and further preferably 300 ° C.
The upper limit of Tg is more preferably 500 ° C. or 400 ° C.
Tg is a value measured by differential scanning calorimetry (DSC) under the condition of a heating rate of 20 ° C./min.

(Weight average molecular weight)
[A] The polystyrene-reduced weight average molecular weight (Mw) of the thermoplastic resin is preferably 5,000 to 500,000, more preferably 15,000 to 400,000, and still more preferably 30,000 to 300,000. .

(Molecular weight distribution)
[A] Polystyrene conversion molecular weight distribution (weight average molecular weight (Mw) / number average molecular weight (Mn)) of the thermoplastic resin is, for example, 1.0 to 5.0, preferably 2.0 to 3.5.

<[B] Organic solvent>
[B] The organic solvent is a solvent capable of dissolving [A] the thermoplastic resin. [B] Examples of the organic solvent include ether solvents, ketone solvents, ester solvents, amide solvents, and the like. [B] As an organic solvent, you may use 1 type, or 2 or more types.

  [B] By using an organic solvent, [A] composition (X) for forming a protective film in which a thermoplastic resin is appropriately dissolved can be obtained. This protective film-forming composition (X) is excellent in wettability when applied to a wafer, and can form a protective film having high heat resistance and excellent adhesion to the wafer. In addition, according to the protective film forming composition (X), by containing the organic solvent [B], the protective film forming composition (X) is formed with less burden on the human body and the environment. The deterioration of the quality of the protective film due to the decomposition of the solvent can be suppressed.

  Since the ether solvent is less decomposed than a ketone solvent, an ester solvent and an amide solvent, the composition for forming a protective film (X) containing an ether solvent is superior in film quality. It is suitable for forming a protective film having

  Examples of the ether solvent include mono- or dialkyl ethers such as ethylene glycol and diethylene glycol, cyclic ethers such as dioxane and tetrahydrofuran, and aromatic ethers such as anisole. Among these, ethers having 3 to 10 carbon atoms are preferable, ethers having 3 to 7 carbon atoms are more preferable, and among them, anisole and tetrahydrofuran are more preferable.

  Examples of the ketone solvent include methyl ethyl ketone, methyl-n-propyl ketone, methyl-iso-propyl ketone, diethyl ketone, methyl-n-butyl ketone, methyl-iso-butyl ketone, methyl-sec-butyl ketone, methyl-tert- And dialkyl ketones such as butyl ketone; and cyclic ketones such as cyclopentanone and cyclohexanone. Among these, ketones having 4 to 10 carbon atoms are preferable, and ketones having 4 to 6 carbon atoms are more preferable from the viewpoint of boiling point and cost, and among them, methyl ethyl ketone, cyclopentanone, and cyclohexanone are preferable. More preferred is cyclohexanone, particularly preferred.

  Examples of the ester solvent include alkyl esters such as ethyl acetate, n-propyl acetate, iso-propyl acetate, and butyl acetate; alkoxyalkyl esters such as 1-methoxy-2-propyl acetate; β-propiolactone , Lactones such as α-methyl-γ-butyrolactone, γ-butyrolactone, δ-caprolactone, and γ-butyrolactone. Among these, esters having 3 to 10 carbon atoms are preferable, and esters having 3 to 6 carbon atoms are more preferable. Among these, γ-butyrolactone is more preferable.

Examples of the amide solvent include alkyl amides such as N, N-dimethylformamide, N, N-dimethylacetamide, N, N-dipentylacetamide, N, N-di-tert-butylacetamide; N, N— Alkoxyalkylamides such as dimethoxypropylacetamide, 3-methoxy-N, N-dimethylpropionamide, 3-n-butoxy-N, N-dimethylpropionamide; 1,3-dimethyl-2-imidazolidinone, N- And cyclic amides such as methyl-2-pyrrolidone. Among these, amides having 3 to 10 carbon atoms are preferable, and amides having 3 to 6 carbon atoms are more preferable. Among these, N, N-dimethylacetamide and N-methyl-pyrrolidone are preferable from the viewpoints of coatability and economy.
[B] When the above amide solvent is used alone as the organic solvent, there is a merit that facilities related to solvent recovery and reuse and recovery can be simplified.

  [B] The organic solvent includes at least one organic solvent selected from the group consisting of a ketone solvent, an ester solvent, and an ether solvent from the viewpoint of reducing repellency during film formation and improving adhesion. A mixed solvent containing an amide solvent is preferable, a mixed solvent of a cyclic ketone and an amide solvent, or a mixed solvent of an ether solvent and an amide solvent is more preferable.

  [B] When a mixed solvent is used as the organic solvent, the content of the amide solvent with respect to 100 parts by mass of the total organic solvent is preferably 5 to 95 parts by mass, more preferably 10 to 90 parts by mass, and 30 to 70 parts by mass. Further preferred. By setting the content of the amide solvent in the above range, the homogeneity (smoothness) of the obtained protective film can be enhanced. The “total organic solvent” refers to all organic solvents contained in the resin composition.

  [B] When the above mixed solvent is used as the organic solvent, the total content of the ketone solvent, the ester solvent and the ether solvent is preferably 5 to 95 parts by mass with respect to 100 parts by mass of the total organic solvent. -90 mass parts is more preferable, and 30-70 mass parts is further more preferable.

  The content of the organic solvent [B] in the composition for forming a protective film (X) is usually preferably 100% by mass or more and 2000% by mass or less, and more preferably 150% by mass or more and 900% by mass with respect to 100% by mass of the solid content. % Or less is more preferable.

<[C] Compound>
[C] A compound is a suitable component in composition (X) for protective film formation. This [C] compound has a polar functional group. In the protective film-forming composition (X), the adhesion between the protective film and the wafer is enhanced by the polar functional group by further containing the [C] compound in addition to the [A] thermoplastic resin. For example, on the surface of the wafer after the surface treatment, for example, silicon that is the surface of the wafer, aluminum that forms wiring, polyimide that is a passivation film, silicon nitride that forms a buffer layer, and the like are exposed. The polar functional group acts on silicon, aluminum, polyimide, silicon nitride, and the like, and plays a role of improving the adhesion between the protective film and the wafer.

  The polar functional group is not particularly limited as long as it can properly adhere the thermoplastic resin to the surface of the wafer, and may be a low molecular weight compound or a polymer, but it is polymerized like an epoxy group or an acryloyl group. The functional group such as an alkoxysilane that is chemically bonded to the surface of the wafer or the like has a high adhesion to the wafer and tends to be inferior in the removability of the protective film.

  The polar functional group of the [C] compound is preferably at least one selected from the group consisting of, for example, a hydroxyl group, a thiol group, a carboxyl group, and an amino group. By having these polar functional groups, the adhesion between the wafer and the protective film can be enhanced. In particular, for aluminum, a polar functional group that is hydrogen bonded to an OH group formed by oxidation of the aluminum surface, such as a hydroxyl group, is preferable. Examples of the hydroxyl group include a phenolic hydroxyl group and an alcoholic hydroxyl group, and a phenolic hydroxyl group is preferable.

  As the [C] compound having a hydroxyl group, compounds represented by the following formulas (C-1) to (C-3) are preferable.

  As the [C] compound having a thiol group, compounds represented by the following formulas (C-4) and (C-5) are preferable.

  As the [C] compound having a carboxyl group, a compound represented by the following formula (C-6) is preferable.

  As the [C] compound having an amino group, a compound represented by the following formula (C-7) is preferable.

  The content of the [C] compound is, for example, preferably 1 part by mass or more and 50 parts by mass or less, 20 parts by mass or more and 40 parts by mass or less, and 25 parts by mass with respect to the total mass of the [A] thermoplastic resin and the [C] compound. More preferred is 35 parts by weight or more. By setting the content of the compound [C] within the above range, it is possible to form a protective film that hardly causes pinholes, has high adhesion to the wafer, and can be easily removed from the wafer.

<Method for Preparing Composition (X) for Protective Film Formation>
The protective film-forming composition (X) can be obtained, for example, by dissolving [A] a thermoplastic resin, and if necessary, a [C] compound and other optional components in [B] an organic solvent. [A] The thermoplastic resin may be obtained as a mixture containing the organic solvent used in the synthesis. In that case, after the (A) thermoplastic resin is isolated (purified) as a solid content, B] It is preferable to prepare by re-dissolving in an organic solvent. In the above method, when the same type of organic solvent as used in [B] organic solvent was used as the organic solvent used in the synthesis of [A] thermoplastic resin, the [A] thermoplastic resin obtained by the above method was used. A solution obtained by removing the by-produced salt from the mixture with the organic solvent used in the synthesis may be used as the protective film forming composition (X).

  The viscosity of the protective film-forming composition (X) is usually 2,000 to 100,000 mPa · s, depending on the molecular weight and concentration of the thermoplastic resin [A], and is 3,000 to 50,000 mPa · s. s is preferred. By setting the viscosity of the protective film-forming composition (X) in the above range, the protective film-forming composition (X) is excellent in retention during film formation, and the thickness can be easily adjusted.

[Protective film forming method and protective film]
The protective film forming method includes a coating step of applying the protective film forming composition (X) to the wafer, and [B] an organic solvent removing step of removing the organic solvent.

<Application process>
The application step is performed by applying the protective film forming composition (X) to the wafer.

  Examples of the method for applying the protective film-forming composition (X) include a spin coating method, a roll coating method, a gravure coating method, and a doctor blade method.

  An example of a case where the coating process is performed by a spin coating method will be described with reference to FIGS. 1 (A) and 1 (B). After discharging a predetermined amount of the protective film forming composition (X) from the dispenser 1 to the back surface of the wafer 2 as shown in FIG. 1 (A), the wafer 2 is rotated as shown in FIG. 1 (B). A coating liquid film 3 is formed on the back surface of the wafer 2.

<Organic solvent removal step>
In the organic solvent removing step, as shown in FIGS. 1B and 1C, the coating liquid film 3 is made the protective film 4 by removing the organic solvent [B] from the coating liquid film 3. Examples of the method for removing the [B] organic solvent from the coating liquid film 3 include a method of heating the coating liquid film 3, a method of placing the coating liquid film 3 under reduced pressure, and a method of using heating and decompression in combination. It is done. Among these, the method of heating the coating liquid film 3 is preferable.

  The heating conditions may be selected as appropriate according to the wafer and [A] thermoplastic resin as long as the [B] organic solvent evaporates. For example, the heating temperature is preferably 30 ° C to 300 ° C, more preferably 40 ° C to 250 ° C, and still more preferably 50 ° C to 230 ° C. The heating time is preferably 10 minutes to 5 hours.

  The heating may be performed in two or more stages. Specifically, a method of heating at 30 ° C. to 80 ° C. for 10 minutes to 2 hours, and further heating at 100 ° C. to 250 ° C. for 10 minutes to 2 hours can be exemplified.

  The atmosphere at the time of heating is not particularly limited, but is preferably in the air or in an inert gas atmosphere, and more preferably in an inert gas atmosphere. As the inert gas, nitrogen gas, argon gas, and helium gas are preferable, and nitrogen gas is more preferable.

  Although the thickness of a protective film is suitably selected according to a use, 0.05 micrometers-250 micrometers are preferable, 2 micrometers-150 micrometers are more preferable, 10 micrometers-125 micrometers are more preferable.

<Backside treatment>
The back surface treatment includes back grinding treatment, ion implantation treatment, annealing treatment, and sputtering treatment. However, all of these processes are not essential, some of the processes can be omitted, and processes other than the above processes may be included. Further, the wafer is conveyed while being adsorbed on the adsorption stage, and is moved to an apparatus in which each process is performed.

(Back grinding)
The back grinding process is performed to reduce the thickness of the wafer 2 as shown in FIG. The back grinding process is performed using, for example, a back grinding wheel in a state where the wafer 2 is placed on the suction stage 5 so that the back surface of the wafer 2 is on the upper side. This back grinding wheel scrapes a wafer using a diamond hole whose abrasive layer is diamond. However, the back grinding process is omitted when it is not necessary to reduce the thickness of the wafer.

(Ion implantation process)
The ion implantation process is performed to form an impurity region. In the ion implantation process, for example, when the wafer 2 is P-type, N-type impurity ions are implanted. When the semiconductor element is a transistor, the ion implantation process is performed, for example, to form a drain region.

(Annealing treatment)
The annealing process is performed in order to recover a crystal structure broken by ion implantation. This annealing process is performed by, for example, an electric furnace or a laser heating device. The heating temperature by the annealing treatment is, for example, 250 ° C. or higher and 350 ° C. or lower.

(Sputtering treatment)
Sputtering is performed to form an electrode. In this sputtering process, a conductor layer is formed on the impurity region. When the semiconductor element is a transistor, the sputtering process is performed, for example, to form a drain electrode on the drain region.

  By forming the protective film 4 on the surface of the wafer 2, damage to the surface of the wafer 2 and adhesion of foreign matters to the surface of the wafer can occur during back grinding, ion implantation, annealing, sputtering, and wafer transfer. Can be suppressed. In particular, since the protective film 4 is formed from the protective film forming composition (X), it has excellent adhesion to the wafer 2. Therefore, it is possible to appropriately maintain the state in which the surface of the wafer 2 is covered with the protective film 4 during the back surface processing and during the transfer, thereby further preventing damage to the surface of the wafer 2 and adhesion of foreign matter to the surface of the wafer 2. It can be suppressed appropriately.

[Protective film removal method]
As shown in FIG. 3, the protective film removal method is performed to remove the protective film 4 from the wafer 2. This protective film removal process has a dissolution removal process or a peeling removal process.

<Dissolution removal process>
The melt removal step is performed by dissolving and removing the protective film 4 with an organic solvent. As a method for removing the protective film with an organic solvent, for example, a method in which a wafer having a protective film formed in an organic solvent is immersed, a method in which an organic solvent is sprayed on the protective film, Examples include a method of applying ultrasonic waves in the immersed state.

  Examples of the organic solvent include those similar to the organic solvent [B] contained in the protective film-forming composition (X). That is, examples of the organic solvent include ether solvents, ketone solvents, ester solvents, amide solvents, and the like. Specific examples of the ether solvent, the ketone solvent, the ester solvent, and the amide solvent are the same as those in the [B] organic solvent.

  Although the temperature of an organic solvent is not specifically limited, Preferably it is 20 to 80 degreeC, More preferably, it is 20 to 50 degreeC.

<Peeling and removing process>
The peeling and removing process is performed by mechanically peeling and removing the protective film 4. This peeling and removing process is performed by turning off the protective film 4 in a state where the adhesion between the protective film 4 and the wafer 2 is lowered by room temperature or heat treatment, for example.

  The heat treatment may be determined by the thermoplastic resin [A] to be contained in the protective film forming composition (X), but is usually 100 ° C to 400 ° C, preferably 150 ° C to 350 ° C, and more preferably It is performed at about 200 ° C to 225 ° C.

  EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples, but the present invention is not limited to these examples. The evaluation method of each physical property in the examples is shown below.

[Evaluation method]
(1) Weight average molecular weight (Mw) and molecular weight distribution (Mw / number average molecular weight (Mn))
[A] Mw and Mn of a thermoplastic resin (hereinafter also referred to as “component (A)”) use a GPC apparatus (HLC-8220 type, manufactured by Tosoh Corporation), columns: SuperH2000 and SuperH4000, guard column: SuperH- L was concatenated, tetrahydrofuran was used as a developing solvent, and monodispersed polystyrene was used as a standard.

(2) Glass transition temperature (Tg)
The glass transition temperature of the component (A) was measured using a DSC apparatus (Thermo Plus DSC8230, manufactured by Rigaku) under a temperature increase rate of 20 ° C./min under nitrogen.

(3) Adhesion with substrate (Si and Al) A cross-cut peel test was performed on the protective film prepared on the silicon substrate or the aluminum substrate in accordance with JIS-K5400. Evaluation results were judged according to the following criteria.
○: Result on silicon substrate is remaining number / parameter is 90/100 or more, and result on aluminum substrate is 90/100 or more. Δ: One of results on silicon substrate and aluminum substrate is remaining number / The parameter is 90/100 or more, and the other result is less than 90/100. X: The results for the silicon substrate and the aluminum substrate are both the remaining number / parameter is less than 90/100.

(4) Heat resistance (high temperature adhesion)
After forming a protective film on the silicon substrate, another silicon substrate was placed on the protective film. In this state, when heated at 250 ° C. for 1 hour and then cooled to room temperature, when the two overlapping silicon substrates are peeled off, the case where the protective film is not transferred to the other silicon substrate is indicated as ◯, and the case where the transferred film is transferred as × It was.

(5) Film removability The film removability was evaluated by two kinds of methods: dissolution removal and mechanical peeling.
The dissolution and removal were performed by immersing the silicon substrate or aluminum substrate on which the protective film was formed in N-methyl-2-pyrrolidone (NMP) at room temperature for 20 minutes.
Mechanical peeling was performed by turning over the protective film by hand at room temperature.
The evaluation of film removability was judged according to the following criteria.
○: The protective film can be completely dissolved or removed mechanically on both the silicon substrate and the aluminum substrate. △: Either the silicon substrate or the aluminum substrate can be completely dissolved or removed or mechanically peeled off. One side cannot be removed ×: The protective film could not be completely removed from the silicon substrate and the aluminum substrate.

<Synthesis example>
(Synthesis of polyether (polymer 1))
In a 1 L four-necked flask, 9,9-bis (4-hydroxyphenyl) fluorene (116.750 g, 333.181 mmol) as a compound to be reacted, and 2,6-difluorobenzonitrile (46.577 g, 334. 847 mmol), potassium carbonate (92.098 g, 666.362 mmol) as an alkali metal compound, and 243.1 g of N, N-dimethylacetamide (DMAc) as a solvent and 60.8 g of toluene were charged. Subsequently, a thermometer, a stirrer, a nitrogen introducing tube, a Dean-Stark tube, and a cooling tube were attached to the four-necked flask, and then the reaction reagent charged was stirred to obtain a solution.
Next, after the atmosphere in the flask was replaced with nitrogen, the resulting solution was reacted at 128 ° C. for 6 hours while removing the generated water from the Dean-Stark tube as needed.
After the completion of the reaction, the reaction mixture was cooled to room temperature (25 ° C.), the generated salt was removed with filter paper, the obtained filtrate was poured into methanol for reprecipitation, and the filtrate (residue) was isolated by filtration. The obtained filtrate was vacuum dried at 60 ° C. overnight to obtain a white powder (Polymer 1) (yield 140 g, yield 93%).

(Synthesis of polyether (polymer 2))
In the synthesis of polymer 1, as the compound to be reacted, 9,9-bis (4-hydroxyphenyl) fluorene (83.634 g, 238.075 mmol), X22-1822 (29.462 g) manufactured by Shin-Etsu Chemical Co., Ltd., resorcinol (6 562 g, 59.593 mmol), and 2,6-difluorobenzonitrile (42.504 g, 305.565 mmol), except that potassium carbonate (84.044 g, 608.089 mmol) was used. Similarly, the polymer 2 was obtained (yield 140 g, yield 93%).

(Synthesis of polyimide (polymer 3))
In a three-necked flask equipped with a thermometer, a nitrogen introduction tube and a stirring blade at 25 ° C. under a nitrogen stream, 16.5656 g (0.005) of 4,4′-diamino-2,2′-bis (trifluoromethyl) biphenyl (TFMB). 0517mol), both terminal amino-modified side chain phenyl methyl type silicone X-21-1660B-3 (manufactured by Shin-Etsu Chemical Co., Ltd.) [2.2991 g (0.000523 mol)], and a polyimide precursor in the resin composition 184.286 g of N-methylpyrrolidone (NMP) was added so that the concentration of was 14%, and the mixture was stirred for 10 minutes until a completely homogeneous solution was obtained. Pyromellitic dianhydride (PMDA) (11.353 g, 0.0511 mol) was added thereto, and the reaction was terminated by stirring for 60 minutes. Then, using a polytetrafluoroethylene filter (pore size 1 μm), precision was obtained. By performing filtration, an NMP solution of polymer 3 was produced.
(PMDA moles / (TFMB moles + X-22-1660B-3 moles) = 0.977 equivalent)

[Example 1]
With the composition shown in Table 1, the protective film-forming composition (X) was prepared by dissolving the [A] thermoplastic resin and the [C] compound in the [B] organic solvent.
This composition for forming a protective film was applied to a silicon substrate and an aluminum substrate using a spin coater. The coating amount of the protective film-forming composition was such that the final thickness of the protective film was 10 μm. The substrate coated with the composition for forming a protective film is heated at 90 ° C. for 10 minutes at 120 ° C. for 10 minutes at 120 ° C., and further heated at 200 ° C. for 30 minutes in an oven to remove the organic solvent. A protective film was formed thereon.

[Examples 2 to 6, Examples 8 to 10 and Comparative Examples 1 and 2]
A protective film was formed on the substrate in the same manner as in Example 1 except that the protective film-forming composition having the composition shown in Table 2 including the component [A] shown in Table 1 was used.

[Example 7]
A protective film was formed by using the composition for forming a protective film shown in Table 2 containing the component [A] shown in Table 1 while changing the heating conditions during the formation of the protective film from those in Example 1. Heating conditions were 75 ° C. for 15 minutes on a hot plate, 120 ° C. for 15 minutes, 300 ° C. for 60 minutes, and 400 ° C. for 30 minutes in an oven.

[Evaluation]
For the substrates on which the protective films of Examples 1 to 10 and Comparative Examples 1 and 2 were formed, adhesion, heat resistance and film removability were evaluated according to the methods described above. The results are shown in Table 2.

  From the results of Table 1, the protective film-forming compositions of Examples 1 to 10 and the protective film obtained from this composition are excellent in adhesion, heat resistance, and film removability. On the other hand, it can be seen that the protective film-forming compositions of Comparative Examples 1 and 2 containing a thermoplastic resin having a low glass transition temperature and the protective film obtained from this composition are inferior in heat resistance or film removability.

  The protective film provided by the protective film forming composition and the protective film forming method of the present invention is excellent in adhesion to the wafer, and can be easily removed while preventing the generation of residues by the protective film removing method of the present invention. Therefore, it is possible to appropriately perform the back surface processing or the transport after the surface processing while protecting the front surface of the wafer advantageously in terms of manufacturing cost.

Claims (10)

A protective film forming composition for forming a protective film that protects the surface of a wafer when the wafer is subjected to a back surface treatment or a wafer transfer after a wafer surface treatment in a semiconductor element manufacturing process. ,
A protective film-forming composition comprising: a thermoplastic resin having a glass transition temperature of 200 ° C. or higher; and an organic solvent capable of dissolving the thermoplastic resin. The thermoplastic resin contains at least one structural unit (i) selected from the group consisting of a structural unit represented by the following formula (1) and a structural unit represented by the following formula (2). A composition for forming a protective film according to 1.

(In formula (1), R ^{1 to} R ⁴ are each independently a monovalent organic group having 1 to 12 carbon atoms, provided that the organic group of R ^{1 to} R ⁴ is a chain hydrocarbon group. Or, it does not contain an alicyclic hydrocarbon group, b to e are each independently an integer of 0 to 4. R ⁵ is a monovalent organic group having 1 to 12 carbon atoms. , when it ^.R 1 to R ⁵ are a plurality each an integer of 0 to 3, the plurality of ^R 1 to R ^5, good .R ⁶ also the same as or different from each other, a cyano group, a nitro group or a formyl Group.)

(In formula (2), R ^{7 to} R ¹⁰ are each independently a monovalent organic group having 1 to 12 carbon atoms, provided that the organic group of R ^{7 to} R ¹⁰ is a chain hydrocarbon group. Or R ¹¹ and R ¹² are each independently a halogen atom, a nitro group or a monovalent organic group having 1 to 12 carbon atoms, g to l are each independently if ^.R 7 ^{to R 12} are a plurality each an integer of 0 to 4, a plurality of ^R 7 ^{to R 12} may optionally be the same or different each .Y represents a single bond, -SO ₂ - or -CO- .m is 0 or 1 provided that when m is ^{0, R 12} is neither a nitro group and a cyano group).. The composition for forming a protective film according to claim 2, wherein the thermoplastic resin further comprises a structural unit (ii) represented by the following formula (3).

(In Formula (3), R <^13> and R < ¹⁴ > are respectively independently a C1-C4 alkyl group or a C6-C15 aryl group. N is an integer of 5-100. The plurality of R ¹³ and R ¹⁴ may be the same or different, and R ¹⁵ and R ¹⁶ are each independently a single bond or a divalent organic group having 1 to 12 carbon atoms. (It is a divalent group represented by the following formula (3a) or (3b).)

(In the formulas (3a) and (3b), R ¹⁷ is a monovalent organic group having 1 to 12 carbon atoms. A is an integer of 0 to 3. When R ¹⁷ is plural, a plurality of R ¹⁷ may be the same or different, and R ¹⁸ is a cyano group, a nitro group or a formyl group. The thermoplastic resin further includes at least one structural unit (iii) selected from the group consisting of a structural unit represented by the following formula (4) and a structural unit represented by the following formula (5). The protective film-forming composition according to claim 2 or claim 3.

(In Formula (4), R ¹⁹ is a monovalent organic group having 1 to 12 carbon atoms. However, the organic group of R ¹⁹ may not contain a chain hydrocarbon group or an alicyclic hydrocarbon group. .o, if ^{.R 19} is plural an integer of 0 to 3, the plurality of ^{R 19} .Ar good be the same or different, the following formulas (4a), (4b) and (4c) A divalent group represented by at least one selected from the group).

(In the formulas (4a), (4b) and (4c), R ^{20 to} R ²³ are each independently a monovalent organic group having 1 to 12 carbon atoms, provided that the organic group of R ^{20 to} R ²³ is used. The group does not include a chain hydrocarbon group or an alicyclic hydrocarbon group, p, q and r are each independently an integer of 0 to 4. s is an integer of 0 to 6 .R ²⁰ to R when ²³ is plural, respectively, a plurality of ^R 20 ^{to R 23} may each be the same or different.)

(In Formula (5), R ²⁴ and R ²⁵ are each independently a monovalent organic group having 1 to 12 carbon atoms, provided that the organic group of R ²⁴ and R ²⁵ is a chain hydrocarbon group or no .t and if u containing an alicyclic hydrocarbon group, when the integer a is ^{.R 24} and ^{R 25} each independently 0-4 is plural, respectively, a plurality of ^{R 24} and ^{R 25} are each And may be the same or different, Z is a single bond, —SO ₂ — or —CO—, and w is 0 or 1.)   5. The protective film-forming material according to claim 1, further comprising a compound having at least one polar functional group selected from the group consisting of a hydroxyl group, a thiol group, a carboxyl group, and an amino group. Composition.   The composition for forming a protective film according to claim 5, wherein the polar functional group is a phenolic hydroxyl group.   The protective film formation according to any one of claims 1 to 6, wherein the organic solvent is at least one selected from the group consisting of an ether solvent, a ketone solvent, an ester solvent, and an amide solvent. Composition. A method for forming a protective film, comprising: applying a composition for forming a protective film according to any one of claims 1 to 7 to a wafer; and removing the organic solvent.   A protective film formed by the protective film forming method according to claim 8. The protective film removal method which has the process of melt | dissolving and removing the protective film formed by the protective film formation method of Claim 8 with an organic solvent, or mechanically peeling and removing.

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