JP4344212B2 - Copolymer, production method of copolymer and novel thiol compound - Google Patents

Description

  The present invention relates to a copolymer obtained by radical copolymerization using a thiol compound as a chain transfer agent, a method for producing the copolymer, and the novel thiol compound. More specifically, the present invention relates to a copolymer suitable as a film-forming polymer such as a resist polymer and an antireflection film polymer used in semiconductor lithography, a method for producing the copolymer, and a novel thiol compound.

In lithography used for manufacturing semiconductors, the formation of finer patterns is required as the degree of integration increases. Shortening the wavelength of the exposure light source is indispensable for pattern miniaturization, but now lithography using krypton fluoride (KrF) excimer laser light (wavelength 248 nm) is becoming the mainstream, and argon fluoride (ArF) excimer laser Lithography using light (wavelength 193 nm) with a line width of 100 nm or less is also being put into practical use. Furthermore, lithography technology using fluorine dimer (F ₂ ) excimer laser light (wavelength 157 nm), extreme ultraviolet light (EUV), X-rays, electron beams, etc. is in the development stage.

  The resist polymer used in these lithography techniques has a non-polar substituent and a repeating unit having a structure in which the non-polar substituent is decomposed by an acid and a polar group soluble in an alkali developer is expressed, A repeating unit having a polar group for improving adhesion to a semiconductor substrate is an essential component, and a repeating unit having a nonpolar substituent for adjusting the solubility in a resist solvent or an alkaline developer is included as necessary. Consists of. As these repeating units, for example, when using a KrF excimer laser as an exposure source, hydroxystyrenes and derivatives thereof are mainly used. When using an ArF excimer laser, hydroxystyrenes emit light having a wavelength of 193 nm. In order to absorb, (meth) acrylates and derivatives thereof have been studied.

  Specific examples of such a resist polymer include, for example, a copolymer using a (meth) acrylic acid monomer and a styrene monomer (for example, see Patent Documents 1 to 4) or hydroxystyrene in a system using a KrF excimer laser. Polymers partially protected with acetal (for example, see Patent Documents 5 to 8, etc.) are known, and in systems using ArF excimer laser, for example, copolymers of (meth) acrylic acid monomers having a lactone structure (For example, refer to Patent Documents 9 to 10).

  However, even a polymer containing a repeating unit having a polar group for enhancing the adhesion to a semiconductor substrate as described above has a terminal structure derived from a polymerization initiator or a chain transfer agent used during the polymerization reaction. Since the structure is not sufficient, there is a problem that it is impossible to cope with finer pattern formation.

  Also, in the formation of resist patterns, there is a problem that when the washing water volatilizes by drying after development and rinsing, the formed pattern collapses due to the surface tension of the water. Since the area of the contact substrate decreases, pattern collapse is likely to occur. In order to avoid this, it is necessary to keep the pattern aspect ratio (height ÷ width) low. On the other hand, to satisfy the dry etching resistance of the pattern, the coating film is thick, that is, the resist pattern has a high aspect ratio. There is a need to. Therefore, there has been a demand for a resist polymer that can increase the aspect ratio even in the formation of a fine pattern and has higher adhesion to the substrate so that pattern collapse does not occur.

  Therefore, a method has been studied in which a polar group is contained in a polymerization initiator or a chain transfer agent to enhance the substrate adhesion of a resist polymer. For example, as an example of incorporating a polar group into the polymerization initiator, a method using a polymerization initiator having an oxygen atom-containing group or a substituted or unsubstituted amino group in the molecule is known (see, for example, Patent Document 11). However, among the hydroxyl groups, carboxyl groups, substituted oxyl groups, substituted oxycarbonyl groups, acyl groups, substituted or unsubstituted carbamoyl groups, hydroxyimino groups, substituted or unsubstituted oxyimino groups mentioned as oxygen atom-containing groups, carboxyl groups In this method, even though the alkali solubility and the substrate adhesion can be improved, the water absorption of the polymer becomes too strong due to the introduction of the carboxyl group. In lithography, there was a problem that a stable pattern could not be obtained. In addition, hydroxyl groups, substituted oxyl groups, substituted oxycarbonyl groups, acyl groups, and the like have low polarity and are insufficient to enhance substrate adhesion. Further, oxygen atom-containing groups containing nitrogen atoms such as substituted or unsubstituted carbamoyl groups, hydroxyimino groups, substituted or unsubstituted oxyimino groups, and substituted or unsubstituted amino groups are generated by a photoacid generator when used as a resist. Since the trapped acid is trapped, there is a problem such as a decrease in sensitivity, which is not practical.

  On the other hand, as an example of using a chain transfer agent having a polar group, a method using a carboxyl group-containing thiol such as mercaptoacetic acid or mercaptopropionic acid as a chain transfer agent (see, for example, Patent Document 12), and ester compounds thereof Alternatively, a method using a hydroxyl group-containing thiol such as mercaptoethanol (for example, see Patent Documents 13 to 14) is known. However, also in these methods, as in the case of the above polymerization initiator, the method using a carboxyl group-containing thiol has a problem that swelling easily occurs during alkali development, and an ester compound or a hydroxyl group-containing thiol is used. The method had insufficient substrate adhesion, and none of them reached a practical level.

Further, in lithography using a substrate with high reflectivity, there is a problem that halation occurs in the resist pattern due to the influence of reflected light, and a fine resist pattern cannot be accurately reproduced. In order to solve this problem, it has been proposed to form an antireflection film having a property of absorbing radiation reflected from the substrate under the resist film to be formed on the substrate. In addition to this antireflection film, a polymer for forming a coating film such as a film to be etched having a resolution by dry etching, which is formed in a lower layer of a resist layer in a multilayer resist, etc. Adhesion is important, and a polymer having better adhesion has been demanded.
JP 59-45439 A JP-A-5-113667 JP-A-7-209868 JP 11-65120 A JP 62-115440 A JP-A-4-219757 JP-A-3-223860 JP-A-4-104251 JP-A-9-73173 Japanese Patent Laid-Open No. 10-239846 Japanese Patent Laid-Open No. 2002-20424 Japanese Patent Laid-Open No. 10-55069 JP 2000-19737 A JP 2001-117231 A

  The present invention has been made in view of the background described above, and its purpose is to form a coating film for obtaining a resist pattern having high adhesion to a substrate and less pattern collapse in the formation of an extremely fine pattern in the production of a semiconductor. Provided are a novel copolymer suitable as a polymer, a method for producing the copolymer, and a novel thiol compound useful as a chain transfer agent in the production of a copolymer suitable as a film-forming polymer. There is.

  As a result of intensive studies to solve the above problems, the present inventors have dramatically improved the adhesion of the obtained copolymer to the substrate by using a thiol compound having a specific structure as a chain transfer agent. As a result, the present invention has been completed.

That is, the present invention provides the following formula (1-b)

(In the formula, any one of R ^{1 to} R ⁶ is a thiol group, the other is independently a hydrogen atom, a methyl group or an ethyl group, Y is a methylene group, a dimethylene group or an oxygen atom, and n is Each represents an integer of 1 or 2, and the two Y's at n = 2 may be the same or different.)
A copolymer obtained by radically copolymerizing two or more polymerizable compounds having an ethylenic double bond using a thiol compound represented by the formula: It is to provide.

  Furthermore, the present invention provides the following formula (1-b)

(In the formula, any one of R ^{1 to} R ⁶ is a thiol group, the other is independently a hydrogen atom, a methyl group or an ethyl group, Y is a methylene group, a dimethylene group or an oxygen atom, and n is Each represents an integer of 1 or 2, and two Y's at n = 2 may be the same or different from each other.

  Since the copolymer of the present invention has a lactone structure at the end of the polymer chain, it has excellent adhesion to the substrate, and in particular, a resist pattern with little pattern collapse when performing extremely fine pattern formation in lithography of semiconductor manufacturing. It can be suitably used as a polymer for forming a coating film for forming. In addition, when the novel thiol compound of the present invention is used as a chain transfer agent, the effect of improving the adhesion of the resulting copolymer to the substrate is high, and the etching resistance is also improved by including an alicyclic structure. Since it can be expected, it can be used very suitably for the production of the above-mentioned copolymer.

The copolymer of the present invention is represented by the following formula (1-b) as described above.

Is used as a chain transfer agent.

In the above formula (1-b) , any one of R ^{1 to} R ⁶ is a thiol group, the other is independently a hydrogen atom, a methyl group or an ethyl group, and Y is a methylene group, a dimethylene group or oxygen. An atom represents n or an integer of 1 or 2, respectively. Note that the two Ys at n = 2 may be the same or different.

Specific examples of the thiol compound represented by n = 1 in the above formula (1-b) include compounds having the following structures, and the 5-position, 8-position and / or 9-position of these compounds: Mention may be made of compounds in which one or both of the methyl group and the ethyl group are substituted.

Further , specific examples of the thiol compound represented by n = 2 in the above formula (1-b) include compounds having the structures shown below, and either or both of a methyl group and an ethyl group are 1 One or more substituted compounds can be mentioned.

Of the thiol compounds having a polycyclic alicyclic structure of the formula (1-b) , a thiol compound represented by n = 1 that is easier to synthesize is more preferable.

  The thiol compound represented by the formula (1-b) is a novel compound, and its general synthesis method will be described. The thiol compound is synthesized using an unsaturated lactone having a corresponding alicyclic structure as a starting material. can do. The unsaturated lactone having an alicyclic structure as a raw material is, for example, one of the carbonyl groups of the unsaturated dicarboxylic acid anhydride having an alicyclic structure corresponding to the target unsaturated lactone and an alkali such as sodium borohydride. Method of selective reduction using metal borohydride or lithium aluminum hydride as a reducing agent [Ski (I) below]; Diels-Alder reaction of cyclic diene and unsaturated γ lactone having an ethylenic double bond [below It can be synthesized by scheme (II)] or the like.

(In the reaction formula, R ^{2 to} R ⁶ each independently represent a hydrogen atom, a methyl group or an ethyl group, n represents an integer of 1 or 2, Y represents a methylene group, a dimethylene group or an oxygen atom, and n represents 1 Or an integer of 2 and the two Y's at n = 2 may be the same or different.)

  In the reaction of Scheme (I), usually 0.5 to 5 mol, preferably 1 to 3 mol of a reducing agent (for example, an alkali) is used per 1 mol of the unsaturated dicarboxylic acid anhydride (Ia) and the compound. Metal borohydride, lithium aluminum hydride, etc .; in the scheme, sodium borohydride is exemplified) in a solvent (eg, tetrahydrofuran, methanol, ethanol, etc.) usually at −50 to 100 ° C., preferably −30 to 70 ° C. The compounds shown in (Ib) to (Ic) are usually obtained by reacting for 0.1 to 48 hours, preferably 0.5 to 24 hours.

Specific examples of the unsaturated dicarboxylic acid anhydride represented by (Ia) include 5-norbornene-2,3-dicarboxylic acid anhydride, methyl-5-norbornene-2,3-dicarboxylic acid anhydride, bicyclo [ 2,2,2] -5-octene-2,3-dicarboxylic acid anhydride, 7-oxabicyclo [2,2,1] -5-heptene-2,3-dicarboxylic acid anhydride, tetracyclo [4. 4.0.1 ^2,5 . 1 ^7,10 ] -3-dodecene-8,9-dicarboxylic anhydride, 11-oxatetracyclo [4.4.0.1 ^2,5 . 1 ^7,10 ] -8-dodecene-3,4-dicarboxylic anhydride and the like.

  In the reaction of scheme (II), the unsaturated γ-lactone having an ethylenic double bond represented by (II-b) and 1 mol of the compound (II-b) are usually 0.5 to 5 Mol, preferably 0.5 to 3 mol of the cyclic diene represented by (II-a) is usually 100 to 200 ° C., preferably 150 to 180 ° C. in a solvent (eg, benzene, toluene, etc.) By reacting for 1 to 24 hours, preferably 3 to 8 hours, the compound represented by (II-c) is obtained.

    Specific examples of the cyclic diene represented by (II-a) include dicyclopentadiene, methylcyclopentadiene dimer, 1,3-cyclohexadiene, furan, 3-methylfuran and the like. Specific examples of the unsaturated γ-lactone having an ethylenic double bond represented by (II-b) include crotonlactone and angelicalactone.

  The target thiol compound of the present invention is obtained by adding a thioacid such as thioacetic acid or thiopropionic acid according to, for example, scheme (III) using an unsaturated lactone having an alicyclic structure obtained by the above reaction as a reaction raw material. The obtained thioacetate can be synthesized by a method of decomposing by hydrolysis or alcoholysis.

(In the reaction formula, R ^{2 to} R ⁶ each independently represent a hydrogen atom, a methyl group or an ethyl group, n represents an integer of 1 or 2, Y represents a methylene group, a dimethylene group or an oxygen atom, and n represents 1 Or an integer of 2 and the two Y's at n = 2 may be the same or different.)

  In the reaction of Scheme (III), the unsaturated lactone (III-a) having an alicyclic structure and 1 mol of the compound are usually 1 to 10 mol, preferably 1 to 3 mol of thioacid (for example, thioacetic acid). Thiopropionic acid, etc .; thioacetic acid is exemplified in the scheme) in the presence of a radical initiator (eg, 2,2′-azobisisobutyronitrile, peroxide, etc.), usually 0-100 ° C., The thioacetic acid ester shown in (III-b) is preferably obtained by reacting at 10 to 80 ° C., usually 10 minutes to 12 hours, preferably 1 to 8 hours, and then purifying by distillation or the like. Further, the obtained thioacetic acid ester and 5 to 50 mol, preferably 10 to 30 mol of water or alcohol (for example, methanol, ethanol, etc.) with respect to 1 mol of the compound are combined with an acid (for example, hydrochloric acid, sulfuric acid). Sulfonic acids, etc.) or alkali (eg, NaOH, KOH, etc.), usually after reaction at 0-80 ° C., preferably 50-80 ° C., usually 1-20 hours, preferably 3-5 hours. The thiol compound shown in (III-c) can be obtained by column purification or distillation purification.

The copolymer of the present invention uses, for example, the thiol compound represented by the above formula (1-b) as a chain transfer agent, and radically copolymerizes two or more polymerizable compounds having an ethylenic double bond. Can be obtained. Therefore, the terminal of the polymer chain of the copolymer of the present invention contains a γ lactone ring structure as a chain transfer agent residue at the terminal of the polymer chain. For this reason, the copolymer of this invention is excellent in adhesiveness with the board | substrate used for semiconductor lithography, and can be conveniently used as coating-film formation polymers, such as a polymer for resists, and a polymer for antireflection films.

  When using the copolymer of this invention for the polymer for film formation in semiconductor lithography, if there is too little content of the said terminal structure, improvement effects, such as adhesiveness to a board | substrate, will become inadequate. Therefore, the content of the terminal structure is preferably 0.1 mol% or more, and more preferably 0.5 mol% or more with respect to the total number of monomer units contained in the copolymer.

  In order to make the content of the terminal structure within the above range, the amount of the thiol compound used as the chain transfer agent is preferably 0.1 mol or more with respect to 100 mol of the raw material monomer, More preferably. The amount of the terminal structure contained in the copolymer increases as the amount of the chain transfer agent used increases. On the other hand, the molecular weight of the obtained copolymer decreases, so that the desired average molecular weight is Select within the range that is obtained.

  If the weight average molecular weight of the copolymer of the present invention is too high, the solubility in a solvent or an alkali developer used at the time of coating film formation will be low, while if it is too low, the coating film performance will be poor. The range of 4,000 to 40,000 is preferable, and the range of 3,000 to 30,000 is more preferable.

  The raw material monomer used for radical copolymerization in the production of the copolymer of the present invention can be used without particular limitation as long as it is a polymerizable compound (monomer) having an ethylenic double bond. When a polymer is used as a coating film-forming polymer in semiconductor lithography, the structure required to exert its function varies depending on the specific application.

  First, when the obtained copolymer is used as a resist polymer, the copolymer of the present invention is at least a repeating unit having a structure that is decomposed by an acid and becomes soluble in an alkali developer. Includes a repeating unit (A) having a structure in which a non-polar substituent is decomposed by an acid and a polar group soluble in an alkali developer is expressed, and a repeating unit having a polar group for improving adhesion to a semiconductor substrate (B) is an essential component, and includes a repeating unit (C) having a nonpolar substituent for adjusting the solubility in a resist solvent or an alkaline developer as necessary.

  The repeating unit (A) which is decomposed by an acid and becomes alkali-soluble means a structure generally used as a resist from the past, and a monomer having a structure which is decomposed by an acid and becomes alkali-soluble is polymerized. Alternatively, after polymerizing a monomer having an alkali-soluble structure, a group having an alkali-soluble group (alkali-soluble group) in the alkali-soluble structure (an acid-decomposable group) that is not dissolved in an alkali but is decomposed by an acid (acid-decomposable group) It can obtain by protecting with.

  Examples of the monomer having a structure that is decomposed by an acid and becomes alkali-soluble can include a compound in which a protective group that is not dissolved in an alkali and decomposes by an acid is bonded to a polymerizable compound containing an alkali-soluble substituent. And a compound having a phenolic hydroxyl group protected with a nonpolar acid-dissociable group, a carboxyl group or a hydroxyfluoroalkyl group.

Accordingly, specific examples of the polymerizable compound containing an alkali-soluble group include hydroxystyrenes such as p-hydroxystyrene, m-hydroxystyrene, and p-hydroxy-α-methylstyrene; acrylic acid and methacrylic acid. , alpha-trifluoromethyl acrylate, 5-norbornene-2-carboxylic acid, 2-trifluoromethyl-5-norbornene-2-carboxylic acid, carboxymethyl tetracyclo [4.4.0.1 ^2,5 .1 ^{7 , 10} ] carboxylic acids having an ethylenic double bond such as dodecyl methacrylate; p- (2-hydroxy-1,1,1,3,3,3-hexafluoro-2-propyl) styrene, 2- (4- (2-Hydroxy-1,1,1,3,3,3-hexafluoro-2-propyl) cyclohexyl) -1,1,1,3,3,3-hexaph Fluoropropyl acrylate, 2- (4- (2-hydroxy-1,1,1,3,3,3-hexafluoro-2-propyl) cyclohexyl) -1,1,1,3,3,3-hexa Polymerizable compounds having a hydroxyfluoroalkyl group such as fluoropropyl trifluoromethyl acrylate and 5- (2-hydroxy-1,1,1,3,3,3-hexafluoro-2-propyl) methyl-2-norbornene Can be mentioned.

Examples of the protecting group that is decomposed by an acid include tert-butyl group, tert-amyl group, 1-methyl-1-cyclopentyl group, 1-ethyl-1-cyclopentyl group, 1-methyl-1-cyclohexyl group, 1-ethyl- 1-cyclohexyl group, 2-methyl-2-adamantyl group, 2-ethyl-2-adamantyl group, 2-propyl-2-adamantyl group, 2- (1-adamantyl) -2-propyl group, 8-methyl-8 -Tricyclo [5.2.1.0 ^2,6 ] decanyl group, 8-ethyl-8-tricyclo [5.2.1.0 ^2,6 ] decanyl group, 8-methyl-8-tetracyclo [4.4 .0.1 ^2,5 .1 ^7,10] dodecanyl group, 8-ethyl-8-tetracyclo [saturated hydrocarbon group such as 4.4.0.1 ^2,5 .1 ^7,10] dodecanyl group; 1 -Methoxyethyl group, 2-ethoxyethyl group, 1-iso- Ropokishiechiru group, 1-n-butoxyethyl group, 1-tert-butoxyethyl group, 1-cyclopentyloxy ethyl, 1-cyclohexyloxyethyl group, 1-tricyclo [5.2.1.0 ^{2, 6]} decanyl Oxyethyl group, 1-methoxymethyl group, 2-ethoxymethyl group, 1-iso-propoxymethyl group, 1-n-butoxymethyl group, 1-tert-butoxymethyl group, 1-cyclopentyloxymethyl group, 1-cyclohexyl Examples thereof include an oxygen-containing hydrocarbon group such as an oxymethyl group, 1-tricyclo [5.2.1.0 ^2,6 ] decanyloxymethyl group, and tert-butoxycarbonyl group.

  When a monomer having an alkali-soluble structure is polymerized and the alkali-soluble group in the alkali-soluble structure is protected with a substituent that is not dissolved in an alkali but decomposes with an acid, the compound having the alkali-soluble group is left as it is. A protective group that is decomposed by an acid can be introduced by reacting with a compound that gives a substituent that does not dissolve in an alkali, such as vinyl ether or halogenated alkyl ether, under an acid catalyst. Examples of the acid catalyst used in the reaction include p-toluenesulfonic acid, trifluoroacetic acid, and strongly acidic ion exchange resin.

  On the other hand, examples of the monomer that gives the repeating unit (B) having a polar group for improving the adhesion to the semiconductor substrate include compounds having a phenolic hydroxyl group, a carboxyl group, or a hydroxyfluoroalkyl group as the polar group. Specifically, for example, as a polymerizable compound containing an alkali-soluble group, the above-described hydroxystyrenes, carboxylic acids having an ethylenic double bond, a polymerizable compound having a hydroxyfluoroalkyl group, and more polar to these In addition to a monomer substituted with a group, a monomer having a polar group bonded to an alicyclic structure such as a norbornene ring or a tetracyclododecene ring can be used.

As the polar group introduced into the repeating unit (B) as a substituent, those having a lactone structure are particularly preferable. For example, γ-butyrolactone, γ-valerolactone, δ-valerolactone, and 1,3-cyclohexanecarbolactone. Examples include substituents containing a lactone structure such as 2,6-norbornanecarbolactone, 4-oxatricyclo [5.2.1.0 ^2,6 ] decan-3-one, and mevalonic acid δ-lactone. . Examples of polar groups other than the lactone structure include hydroxyalkyl groups such as a hydroxymethyl group, a hydroxyethyl group, a hydroxypropyl group, and a 3-hydroxy-1-adamantyl group.

Furthermore, as a monomer that contains a repeating unit (C) having a non-polar substituent for adjusting solubility in a resist solvent or an alkali developer, which is contained as necessary, specifically, for example, styrene, Styrenes such as α-methylstyrene and P-methylstyrene; acrylic acid, methacrylic acid, trifluoromethylacrylic acid, norbornene carboxylic acid, 2-trifluoromethyl norbornene carboxylic acid, carboxytetracyclo [4.4.0.1 ^{2,5.1 7,10} ] ester compounds in which an acid-stable nonpolar group is substituted for a carboxylic acid having an ethylenic double bond such as dodecyl methacrylate; having an ethylenic double bond such as norbornene or tetracyclododecene An alicyclic hydrocarbon compound etc. can be mentioned. Examples of acid-stable nonpolar substituents that are ester-substituted to the carboxylic acid include methyl group, ethyl group, cyclopentyl group, cyclohexyl group, isobornyl group, and tricyclo [5.2.1.0 ^2,6 ] decanyl. group, 2-adamantyl group, and a tetracyclo [4.4.0.1 ^2,5 .1 ^7,10] dodecyl group.

  These monomers can be used by mixing one type or two or more types for each of the repeating units (A), (B) and (C), and the composition ratio of each repeating unit in the resulting resist polymer is The basic performance as a resist can be selected within a range not impairing. That is, in general, the repeating unit (A) is preferably 10 to 70 mol%, and more preferably 10 to 60 mol%. The composition ratio of the repeating unit (B) is preferably 30 to 90 mol%, more preferably 40 to 90 mol%, but for monomer units having the same polar group, 70 mol% or less. It is preferable that Furthermore, the composition ratio of the repeating unit (C) is preferably 0 to 50 mol%, more preferably 0 to 40 mol%.

  In addition, when the copolymer obtained as described above is used as a polymer for a lower layer coating film or an antireflection film of a multilayer resist, it is decomposed with the acid from the resist polymer structure to be alkali-soluble. A polymer having a structure excluding the repeating unit (A) is used. Since the composition ratio of each repeating unit in the copolymer varies depending on the intended use of the coating film, it cannot be defined unconditionally, but in general, the composition ratio of the repeating unit (B) is selected from the range of 10 to 100 mol%, The composition ratio of the repeating unit (C) is selected from the range of 0 to 90 mol%.

  In addition, when using the copolymer of the present invention as an antireflection film, it is necessary to include a crosslinking point and a structure that absorbs radiation irradiated in photolithography. Examples of the crosslinking point include a hydroxyl group, an amino group, A reactive substituent that can be cross-linked by an ester bond, a urethane bond, or the like, such as an epoxy group, can be used. Examples of the monomer containing a reactive substituent as a crosslinking point include hydroxystyrenes such as p-hydroxystyrene and m-hydroxystyrene, and the above-described polymerizable compounds such as the hydroxyl group, amino group, and epoxy group. A monomer substituted with a reactive substituent can be used as appropriate.

  Although the structure which absorbs the said radiation changes with wavelengths of the radiation to be used, for example with respect to ArF excimer laser light, the structure containing a benzene ring and its analog is used suitably. Examples of the monomer having such a structure include styrenes such as styrene, α-methylstyrene, p-methylstyrene, p-hydroxystyrene, m-hydroxystyrene, and derivatives thereof; substituted or unsubstituted phenyl (meth) acrylate, Examples thereof include aromatic-containing esters having an ethylenic double bond such as substituted or unsubstituted naphthalene (meth) acrylate and substituted or unsubstituted anthracenemethyl (meth) acrylate. The monomer having a structure that absorbs radiation may be introduced as either the repeating unit (B) or (C) depending on the presence or absence of a polar group, but the composition ratio as a monomer having a structure that absorbs radiation is 10 It is preferably selected from the range of ˜100 mol%.

  The polymerization initiator used in the polymerization reaction for producing the copolymer of the present invention is not particularly limited as long as it is generally used as a radical generator. For example, 2,2′-azobisisobutyro Nitrile, 2,2′-azobis (2-methylbutyronitrile), dimethyl 2,2′-azobisisobutyrate, 1,1′-azobis (cyclohexane-1-carbonitrile), 4,4′-azobis (4- Azo compounds such as cyanovaleric acid), decanoyl peroxide, lauroyl peroxide, benzoyl peroxide, bis (3,5,5-trimethylhexanoyl) peroxide, succinic acid peroxide, tert-butylperoxy-2- An organic peroxide such as ethyl hexanoate can be used alone or in combination. The amount of the polymerization initiator used depends on the raw material monomer used in the polymerization reaction, the type and amount of the chain transfer agent, and the polymerization conditions such as the polymerization temperature and the polymerization solvent. It is selected from the range of 0.01 to 10 mol, preferably 0.1 to 5 mol, relative to 1 mol.

  As a polymerization method for producing the copolymer of the present invention, solution polymerization is preferable, and radical copolymerization is preferably performed in a state in which a raw material monomer, a polymerization initiator, and a chain transfer agent are dissolved in a polymerization solvent. Solution polymerization includes, for example, a so-called batch polymerization method in which all monomers, a polymerization initiator, and a chain transfer agent are dissolved in a polymerization solvent and heated to a polymerization temperature, or some or all of the monomers, polymerization initiator, and chain transfer agent are It can be carried out by a so-called drop polymerization method in which the solution is dropped into a polymerization system heated to the polymerization temperature.

  The solvent used in the polymerization reaction is not particularly limited as long as the solvent can stably dissolve the raw material monomer, the obtained copolymer, the polymerization initiator, and the chain transfer agent. Specific examples of the polymerization solvent include ketones such as acetone, methyl ethyl ketone and methyl amyl ketone; ethers such as tetrahydrofuran, dioxane, glyme and propylene glycol monomethyl ether; esters such as ethyl acetate and ethyl lactate; propylene glycol methyl Examples include ether esters such as ether acetate, and lactones such as γ-butyrolactone, and these can be used alone or in combination. Although there is no restriction | limiting in particular in the usage-amount of a polymerization solvent, Usually, it is 0.5-20 weight part with respect to 1 weight part of monomers, Preferably it is 1-10 weight part. If the amount of the solvent used is too small, the monomer or copolymer may be precipitated, and if it is too large, the rate of the polymerization reaction may be insufficient.

  The polymerization reaction conditions are not particularly limited, but in general, the reaction temperature is preferably about 60 ° C to 100 ° C, and the reaction time is preferably about 1 hour to 20 hours.

  The polymer obtained by the above polymerization reaction is prepared by dropping the polymerization reaction liquid into a poor solvent alone or a mixed solvent of a poor solvent and a good solvent, and further washing as necessary to obtain unreacted monomers and oligomers. In addition, unnecessary substances such as a polymerization initiator, a chain transfer agent, and a reaction residue thereof can be removed and purified. The poor solvent is not particularly limited as long as the obtained copolymer does not dissolve, but for example, water, alcohols such as methanol and isopropanol, saturated hydrocarbons such as hexane and heptane, etc. are used alone or in combination. Can be used. The good solvent is not particularly limited as long as it is a solvent in which a monomer, an oligomer, a polymerization initiator, a chain transfer agent, and these reaction residues are dissolved, but the same solvent as the polymerization solvent is preferable in terms of management of the production process.

  The use form of the copolymer of the present invention obtained as described above is not particularly limited, but when used as a film-forming polymer in semiconductor lithography, it is usually used by dissolving in a solvent for film-forming. Is done. Since the copolymer after purification contains the solvent used for purification, it can be dried under reduced pressure and then dissolved in a solvent for forming a coating film, or a good solvent such as a solvent for forming a coating film or a polymerization solvent as it is Then, the solvent for forming a coating film is supplied as necessary, and the other solvent can be distilled off under reduced pressure to finish the coating film forming solution.

  The solvent for forming the coating film is not particularly limited as long as it dissolves the copolymer. However, usually considering the boiling point, the influence on the semiconductor substrate and other coating films, and the absorption of radiation used in lithography. Selected. Examples of solvents generally used for forming a coating film include solvents such as propylene glycol methyl ether acetate, ethyl lactate, methyl amyl ketone, γ-butyrolactone, and cyclohexanone. Although the usage-amount of a solvent is not restrict | limited in particular, Usually, it is the range of 1 weight part-20 weight part with respect to 1 weight part of copolymers.

  When the copolymer of the present invention is used as a resist polymer, a radiation-sensitive acid generator and a nitrogen-containing compound for preventing acid diffusion to a portion not exposed to radiation are added to the coating film-forming solution. An acid diffusion control agent such as the above can be added to finish the resist composition. As the radiation-sensitive acid generator, those generally used as a resist raw material such as an onium salt compound, a sulfone compound, a sulfonic acid ester compound, a sulfonimide compound, and a disulfonyldiazomethane compound can be used. In addition, compounds that are commonly used as resist additives such as dissolution inhibitors, sensitizers, and dyes can be added to the resist composition as necessary.

  The compounding ratio of each component (excluding the resist solvent) in the resist composition is not particularly limited. Generally, the polymer concentration is 10 to 50% by mass, the radiation sensitive acid generator is 0.1 to 10% by mass, and the acid diffusion controller. It is selected from the range of 0.001 to 10% by mass.

  In addition, when the obtained copolymer of the present invention is used as an antireflection film, it is used alone or mixed with bifunctional or higher functional isocyanate, amine, epoxide or the like capable of crosslinking between polymers.

EXAMPLES Next, although an Example is given and this invention is further demonstrated, this invention is not limited to these Examples. In addition, the average copolymer composition of the obtained copolymer was calculated | required from the measurement result of ¹³ C-NMR. The weight average molecular weight Mw and the degree of dispersion Mw / Mn were determined from the measurement results of gel permeation chromatography (GPC).
Reference example 1

Synthesis of 5-methyl-4-oxa-tricyclo [5,2,1,0 ^2,6] dec-8-en-3-one (starting compound):
Into an autoclave with a stirring function, 392 g of α-angelica lactone, 397 g of dicyclopentadiene and 1.9 g of triethylamine were added and reacted at 155 to 160 ° C. for about 7 hours. After the reaction solution was simply distilled to remove heavy components, the obtained distillate was precisely distilled at a pressure of 0.3 Kpa and a bottom temperature of 130 ° C. or less using a glass packed tower having a length of 18 cm. raw material to become 5-methyl-4-oxa-tricyclo [5,2,1,0 ^2,6] to obtain 651g of dec-8-en-3-one. The gas chromatographic purity of the obtained raw material compound was 99% or more. The above reaction is represented by the following scheme.

8- or 9-mercapto-5-methyl-4-oxatricyclo [5,2,1,0 ^2,6] decan-3-one:
The title compound represented by the following formula was prepared as follows.

In a four-necked round bottom flask equipped with a stirrer, thermometer and condenser, under a nitrogen atmosphere, 20 g (122 mmol) of the raw material compound obtained in Reference Example 1, 11.1 g (146 mmol) of thioacetic acid, 1,4-dioxane 60 g and 2,2′-azobisisobutyronitrile 6 g (37 mmol) were added and heated at 70 ° C. for 8 hours. Further, 60 g of methanol and 7.0 g (37 mmol) of paratoluenesulfonic acid monohydrate were added to the reaction solution, and the mixture was stirred for 8 hours under reflux. Thereafter, the reaction solution was returned to room temperature, washed with a saturated aqueous sodium hydrocarbon solution, and extracted with ethyl acetate. The obtained organic phase was extracted and the solvent and light components were removed with an evaporator, followed by distillation under reduced pressure, and 8-mercapto-5-methyl-4-oxatricyclo [5,2,1 which is the target novel thiol compound. , ^{0 2,6]} decan-3-one and 9-mercapto-5-methyl-4-oxatricyclo [5,2,1,0 ^2,6] decane-3-mixture of one (hereinafter, "MAGL" Was obtained.) The reaction scheme is as follows.

The obtained MAGL was subjected to structural analysis by the following analysis, and it was confirmed that four kinds of isomers were contained. The gas chromatographic purity (total of 4 types) was 97%.
・ Mass spectrum (GC-MS)
m / z: 198 (M ⁺ ) · ¹³ C-NMR spectrum (CDCl ₃ solvent)
δ (ppm): 177.4 (C═O), 176.9 (C═O), 176.8 (C═O), 176.7 (C═O), 81.0 (CH), 80. 4 (CH), 76.4 (CH), 75.5 (CH), 51.5-30.4 (m), 23.0 (CH ₃ ), 22.9 (CH ₃ ), 22.4 ( CH ₃ ), 22.3 (CH ₃ )
-FT-IR (cm < ^-1 >): 3000-2900 (aliphatic CH, expansion-contraction), 2558 (SH, expansion-contraction), 1760 (lactone C = O, expansion-contraction)

Production of copolymer 1 represented by the following structural formula:
The title compound represented by the following formula was prepared as follows.

76 g of methyl ethyl ketone (hereinafter referred to as “MEK”) was charged into a flask equipped with a stirrer, a thermometer, and a condenser under a nitrogen atmosphere, and heated to about 80 ° C. while stirring. In a separate container, 29 g of γ-butyrolactone-2-yl methacrylate (hereinafter referred to as “GBLM”), 24 g of tert-butyl methacrylate (hereinafter referred to as “TBMA”), MEK 155 g, dimethyl-2,2′-azobisiso 0.82 g of butyrate and 3.3 g of MAGL obtained in Example 1 were added as a chain transfer agent to prepare a mixed solution, which was dropped into the previous flask and polymerized over 4 hours. The feed ratios of the raw material monomer and the chain transfer agent are shown in Table 1. After dropping the whole amount, the flask was aged for 2 hours while being kept at 80 ° C., and cooled to room temperature. The obtained polymerization liquid was put into methanol, and the deposited precipitate was filtered. Methanol washing and filtration were further repeated twice to remove unreacted simple substances, and the resulting precipitate was dried with a vacuum dryer to obtain 20 g of a white solid (Copolymer 1). When the content of the terminal structure derived from the thiol compound in the obtained copolymer was determined by ¹³ C-NMR measurement, it was 2.6 mol% based on the total number of monomer units contained in the copolymer. It was.

Further, the obtained copolymer 1 was dissolved in propylene glycol methyl ether acetate (hereinafter referred to as “PGMEA”) to form a 20% solution, and 1,1,1,3,3,3-hexamethyldisilazane in advance. The treated silicon wafer was spin coated and baked at 110 ° C. for 90 seconds to form a coating film having a thickness of 1.5 μm. About the obtained coating film, the peeling strength and peeling mode of the coating film were measured in the constant load mode using the Daipura-Wintes SAICAS CN-20 type | mold. Table 2 shows the physical properties of the obtained copolymer 1 and the measurement results of the peel strength and peel mode of the coating film.
Comparative Example 1

Production of copolymer 2 represented by the following structural formula:
The title compound represented by the following formula was prepared as follows.

In Example 2, 33 g of 5-methacryloyloxy-2,6-norbornanecarbolactone (hereinafter referred to as “NLM”) instead of GBLM as a monomer, and 2-methyl-2-adamantyl methacrylate (instead of TBMA) Hereinafter, 45 g of “MAM”) and α-mercapto-γ-butyrolactone (hereinafter referred to as “AMBL”) are used as a chain transfer agent instead of MAGL, and dimethyl-2,2′-azobisisobuty The rate charge was changed to 0.75 and the same operation as in Example 2 was performed to obtain 62 g of a white solid (copolymer 2). Table 1 shows the charging ratio of the raw material monomer and the chain transfer agent, and Table 2 shows the properties of the obtained copolymer 2, the peeling strength of the coating film, and the peeling mode.
Comparative Example 2

In Example 2, polymerization was carried out by the same procedure except that 1.06 g of 2-mercaptoethanol (hereinafter referred to as “MEO”) was used as a chain transfer agent to obtain a white solid (Copolymer 3). . Table 1 shows the charging ratio of the raw material monomer and the chain transfer agent, and Table 2 shows the properties of the obtained copolymer 3, the peeling strength of the coating film, and the peeling mode.
Comparative Example 3

In Comparative Example 1 , polymerization was carried out by the same procedure except that 0.53 g of MEO was used as a chain transfer agent to obtain a white solid (copolymer 4). The charge ratios of the raw material monomer and the chain transfer agent are shown in Table 1, and the properties of the obtained copolymer 4, the peel strength of the coating film, and the peel mode are shown in Table 2.

  As these results show, the copolymer of the present invention has a remarkably improved peel strength as compared with the prior art, and is found to be very excellent in substrate adhesion.

INDUSTRIAL APPLICABILITY According to the present invention, a novel copolymer suitable as a coating film-forming polymer for obtaining a resist pattern having high adhesion to a substrate and less pattern collapse in the formation of an extremely fine pattern in semiconductor production, and the copolymer Provided are novel thiol compounds useful as chain transfer agents in the production of copolymers and the production of copolymers suitable as these coating-forming polymers.

Claims (7)

The following formula (1-b)

(Wherein R ¹ ~ R ⁶ Any one of them represents a thiol group, the other each independently represents a hydrogen atom, a methyl group or an ethyl group, Y represents a methylene group, a dimethylene group or an oxygen atom, n represents an integer of 1 or 2, Two Y at n = 2 may be the same or different. )
A copolymer obtained by radically copolymerizing two or more polymerizable compounds having an ethylenic double bond, using a thiol compound represented by the formula:   The copolymer according to claim 1, which has a γ-lactone ring structure at a polymer chain terminal as a chain transfer agent residue.   The copolymer according to claim 1, which is used as a polymer for forming a coating film in semiconductor lithography. 4. The resist unit according to claim 3 , wherein the resist unit has at least a repeating unit having a structure that is decomposed by an acid and becomes soluble in an alkali developer, and a repeating unit having a polar group for enhancing adhesion to a semiconductor substrate. The copolymer described. The copolymer according to claim 3, which is used as an antireflection film for forming a lower layer of a resist layer. In a method for producing a copolymer by radical copolymerization of two or more polymerizable compounds having an ethylenic double bond, the following formula (1-b)

(Wherein R ¹ ~ R ⁶ Any one of them represents a thiol group, the other each independently represents a hydrogen atom, a methyl group or an ethyl group, Y represents a methylene group, a dimethylene group or an oxygen atom, n represents an integer of 1 or 2, Two Y at n = 2 may be the same or different. )
The manufacturing method of the copolymer characterized by using the thiol compound represented by these as a chain transfer agent. The following formula (1-b)

(In the formula, any one of R ^{1 to} R ⁶ is a thiol group, the other is independently a hydrogen atom, a methyl group or an ethyl group, Y is a methylene group, a dimethylene group or an oxygen atom, and n is Each represents an integer of 1 or 2, and the two Y's at n = 2 may be the same or different.)
A novel thiol compound represented by