JP2005070742A - Positive resist composition and method for forming resist pattern - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a positive resist composition having solubility contrast sufficient for practical use and suppressing pattern collapse, and to provide a method for forming a pattern. <P>SOLUTION: The positive resist composition contains: (A1) a resin component which contains a star branched polymer having polymer chains extending in three or more directions from a lower alkyl molecule, and which shows the solubility with an alkali increased by the effect of an acid, or (A2) a resin component which contains a star branched polymer obtained by polymerization of monomers containing a (meth)acrylic acid ester in the presence of a polyfunctional chain transfer agent having three or more functional groups and which shows the solubility with an alkali increased by the effect of an acid; (B) an acid generating component which generates an acid by exposure; and (C) an organic solvent. The method for forming a resist pattern is carried out by forming a layer comprising the above positive resist composition on a substrate, preliminarily baking the layer, selectively exposing, heating after exposure and developing with an alkali. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a positive resist composition.

Recently, the miniaturization of semiconductor elements has been further advanced, and for example, development of a process using an ArF excimer laser (193 nm) has been vigorously advanced.
In a process using an ArF excimer laser as a light source, a resin having a benzene ring such as polyhydroxystyrene has insufficient transparency with respect to an ArF excimer laser (193 nm).
In order to solve such drawbacks, a chemically amplified resist using a resin that does not have a benzene ring and instead has a unit derived from a (meth) acrylic acid ester containing an adamantane ring in the main chain, for example. It is getting attention.
The reaction mechanism of the chemically amplified resist is that an acid is generated by irradiating light to an acid generator blended in the resist. On the other hand, by attaching a protecting group to the resist resin that is eliminated by the generated acid, the protecting group is eliminated only at the exposed portion, and the solubility in the developer is greatly changed.
As such a chemically amplified resist, many proposals have been made so far (Japanese Patent No. 2881969, Japanese Patent Laid-Open No. 5-346668, Japanese Patent Laid-Open No. 7-234511, Japanese Patent Laid-Open No. 9-73173). JP-A-9-90637, JP-A-10-161313, JP-A-10-319595, JP-A-11-12326, JP-A-2001-002735, etc.).
All of the resist resins described therein are only examples of linear polymers.
In addition, in JP 2001-002735 A, it is proposed to produce a resin having the above unit in the main chain in the presence of a polyfunctional chain transfer agent comprising an alkyl thiol. In the case of having one mercapto group therein and using such a multifunctional chain transfer agent, the polymer produced by chain transfer is a linear polymer having a thiol residue at one end.

Japanese Patent No. 2881969 JP-A-5-346668 JP-A-7-234511 JP-A-9-73173 JP-A-9-90637 JP-A-10-161313 JP 10-319595 A Japanese Patent Laid-Open No. 11-12326 JP 2001-002735 A

In the resist for ArF excimer laser, which is required to be further miniaturized, it is necessary to improve the resolution. However, when conventional polymers such as the above-mentioned polymers are used, the resist dissolution contrast is high. In many cases, it is difficult to obtain a resist pattern having a satisfactory shape with respect to mask linearity characteristics, depth of focus, and the like. Further, when a resist having a practically sufficient dissolution contrast is used, pattern collapse tends to occur, and it is often difficult to suppress this.
SUMMARY OF THE INVENTION In view of such circumstances, an object of the present invention is to provide a positive resist composition and a pattern forming method that have a sufficiently practical dissolution contrast and can suppress pattern collapse.

The positive resist composition of the present invention comprises a star-shaped branched polymer in which a polymer chain extends from a lower alkyl molecule in three or more directions, and is a resin component (A1 having increased solubility in alkali by the action of an acid. ), Or a star-shaped branched polymer obtained by polymerization of a monomer containing a (meth) acrylic acid ester in the presence of a trifunctional or higher-functional polyfunctional chain transfer agent. It contains a resin component (A2) that increases solubility in water, an acid generator component (B) that generates acid upon exposure, and an organic solvent (C).
In the resist pattern forming method of the present invention, a layer composed of the positive resist composition is provided on a substrate, pre-baked, selectively exposed, then subjected to PEB (post-exposure heating), and alkali development. It is characterized by doing.

  According to the present invention, there can be obtained a positive resist composition and a pattern forming method that have a sufficiently practical dissolution contrast and can suppress pattern collapse.

Hereinafter, embodiments according to the present invention will be described in detail.
<Resin component (A1) or (A2)>
The resin component (A1) in the present invention is a resin containing a star-shaped branched polymer having a polymer chain extending in three or more directions from a lower alkyl molecule and having increased solubility in alkali due to the action of an acid.
A star-shaped branched polymer refers to a polymer having a shape in which polymer chains extend from a lower alkyl molecule in three or more directions, and each polymer chain may be linear or branched. Here, the lower alkyl molecule means methane, ethane, propane, etc., and methane, ie, a polymer chain extending from one carbon atom in 3 or 4 directions, ethane, ie, 3 to 6 directions from two adjacent carbon atoms. In this case, propane, that is, a polymer chain extending in the 3 to 8 direction from three adjacent carbon atoms can be exemplified.
Each polymer chain may be linear or branched. The polymer chain in the present invention extends from one carbon atom in three or four directions from the viewpoint of easy preparation of a star-shaped branched polymer and solubility in a solvent when preparing a positive resist composition. It is preferable.
Since the star-shaped branched polymer has polymer chains extending in three or more directions in the resist, it is considered that in the unexposed area, the star-shaped branched polymer is entangled with other star-shaped branched polymers and other polymers to form a resist pattern. Therefore, this resist pattern can take a firm three-dimensional structure. Since it can form this solid structure more firmly when it extends in 4 directions from one carbon atom, it is preferable to extend in 4 directions. On the other hand, compared to the case where the polymer chain extends in 5 directions or more, the periphery of the lower alkyl molecule is not excessively dense, and therefore, the entanglement with other molecules is considered to be better.
The resin component (A1) in the present invention is a star-shaped branch obtained by polymerization of a monomer containing a (meth) acrylic acid ester in the presence of a trifunctional or higher functional chain transfer agent from the production method described later. It can also be specified as a resin component (A2) characterized by containing a polymer and having increased solubility in alkali by the action of an acid.

The molecular weight of the star-shaped branched polymer is preferably 3,000 to 20,000, and more preferably 5,000 to 15,000. By making the mass average molecular weight equal to or more than the above lower limit, the resist shape maintainability in the unexposed portion can be improved. By making it below the above upper limit, the solubility in the exposed area can be improved.
The resin component (A1) or (A2) in the present invention may further contain a linear polymer as long as it does not substantially adversely affect the pattern forming property other than the star-shaped branched polymer.

Method for producing star-shaped branched polymer The star-shaped branched polymer can be produced by various methods. For example, in the presence of a trifunctional or higher functional chain transfer agent, preferably a trifunctional or higher functional mercaptan compound, A method for polymerizing a monomer for forming a constituent unit of a star-shaped branched polymer, preferably a monomer containing a (meth) acrylic acid ester as described later can be employed. That is, the method of radical polymerization of the monomer mixture using a polymerization initiator in the presence of a tri- or higher functional mercaptan compound is preferable because of good chain transferability.
The mercaptan compound is not particularly limited as long as it is trifunctional or higher, but pentaerythritol tetrakis (2-mercaptoacetate), pentaerythritol tetrakis (3-mercaptopropionate), trimethylol methanetris (2 -Mercaptoacetate), trimethylol methanetris (3-mercaptopropionate), trimethylolpropane tris (3-mercaptopropionate) and the like. Among these, the tetra-functional pentaerythritol tetrakis (2-mercaptoacetate) and pentaerythritol are excellent because they are excellent in maintaining the three-dimensional structure of the unexposed portion of the resist pattern formed using the resin component containing the star-shaped branched polymer. Tetrakis (3-mercaptopropionate) is preferred, and pentaerythritol tetrakis (2-mercaptoacetate) is particularly preferred. By making these mercaptan compounds exist in the polymerization system, the growing radicals easily extract hydrogen from the mercaptan compounds, and the radicals generated by this chain transfer reaction are added to the monomers and restarted. Therefore, if a polyfunctional chain transfer agent having three or more functions is used, a tri-branched or 4-branched polymer is produced.
In the star-branched polymer, the molar ratio of the multifunctional chain transfer agent to the monomer constituting the polymer chain is 100 mol% of the total amount of the monomer and the multifunctional chain transfer agent. Is preferably 1 to 5 mol%, more preferably 2 to 3 mol%.

The polymerization initiator is not particularly limited as long as it can efficiently generate radicals by heat and polymerize the monomer.
Specifically, ketone peroxides such as methyl ethyl ketone peroxide, methyl isobutyl ketone peroxide, and cyclohexanone peroxide; diacyl peroxides such as isobutyryl peroxide and bis (3,5,5-trimethylhexanoyl) peroxide Hydroperoxides such as p-menthane hydroperoxide and 1,1,3,3-tetramethylbutyl hydroperoxide; 2,5-dimethyl-2,5-bis (t-butylperoxy) hexane and the like Dialkyl peroxides; peroxyketals such as 1,1-bis (t-butylperoxy) -3,3,5-trimethylcyclohexane; t-butylperoxyneodecanoate, 1,1,3,3 -Tetramethylperoxyneodeca Peroxyesters such as diate; peroxydicarbonates such as di-n-propyl peroxydicarbonate and diisopropyl peroxydicarbonate; azobisisobutyronitrile, 2,2′-azobis (2,4-dimethylvalero) Nitrile) and azo compounds such as 2,2′-azobisisobutyrate.

The resin of the present invention is produced by mass polymerization, suspension, and solution polymerization of (meth) acrylic acid ester having the above structural unit in the presence of a polymerization initiator and a polyfunctional chain transfer agent. Legal is preferred. The polymerization may be either batch type or continuous type, but the batch type is preferable because of excellent quality stability.
As the solvent used for this polymerization, a solvent capable of dissolving any of a monomer, a polymerization initiator, a polyfunctional chain transfer agent and a polymer to be produced is preferable, for example, 1,4-dioxane, isopropyl alcohol, acetone, Tetrahydrofuran, methyl ethyl ketone, methyl isobutyl ketone and the like can be mentioned.
50-150 degreeC is preferable and, as for the polymerization temperature in superposition | polymerization, 60-120 degreeC is more preferable.
The molecular weight of the star-shaped branched polymer can be adjusted by the amount of polymerization initiator and the amount of polyfunctional chain transfer agent relative to the amount of monomer used. Increasing the polymerization initiator amount and the polyfunctional chain transfer agent amount decreases the molecular weight.

  The star-shaped branched polymer solution thus obtained is diluted with a good solvent such as tetrahydrofuran so as to have an appropriate solution viscosity, and then dropped into a poor solvent such as water or methanol to be precipitated. The precipitate can be filtered, washed, and dried to obtain a star-shaped branched polymer as a product. Although this reprecipitation step may be unnecessary, after the reprecipitation step, unreacted monomers, polymerization initiators and the like can be removed, and the resist performance can be improved.

  It can be confirmed as follows that the resin of the present invention is a star-shaped branched polymer. It is known that polymer molecules have different structures in dilute solutions of polymers dissolved in a good solvent at different temperatures (BHZimm, WHStockmayer, J. Chem. Phys., 17, 1301 (1949)). For example, when comparing a linear polymer having the same molecular weight with a star-shaped branched polymer, the spread of the polymer molecule having a branched structure is smaller than that of the linear polymer molecule. As a result, the mean square turning radius representing the intrinsic viscosity and molecular size of the star-shaped branched polymer is observed to be smaller than that of the linear polymer. From this, the intrinsic viscosity of the polymer of the present invention was measured by the gel permeation chromatogram (GPC) method under the same conditions, and the intrinsic viscosity of the linear polymer synthesized in the absence of the polyfunctional chain transfer agent. The ratio g = [η] branch / [η] linear can be used as a branching parameter. That is, g <1 when comparing polymers having the same weight average molecular weight.

The resin component (A1) or (A2) in the present invention is a resin whose solubility in alkali is increased by the action of an acid, and the star-shaped branched polymer and / or linear polymer contains a dissociable dissolution inhibiting group. In particular, the star-shaped branched polymer preferably contains a dissociable, dissolution inhibiting group.
The acid dissociable, dissolution inhibiting group has an alkali dissolution inhibiting property that renders the resin component alkali-insoluble in the absence of an acid, and in the presence of an acid, it dissociates by the action of the acid to make the entire resist resin alkaline. It is a protecting group that changes the solubility.

Hereinafter, the example of the structural unit of the resin component in this invention is demonstrated.
・ Structural unit (a1)
The resin component in the present invention preferably has a structural unit (a1) derived from a (meth) acrylic acid ester containing an acid dissociable, dissolution inhibiting group, from the viewpoint of ArF excimer laser absorption and the like.
Here, (meth) acrylic acid ester refers to one or both of acrylic acid ester and methacrylic acid ester.
In particular, the star-shaped branched polymer preferably contains a structural unit (a1) derived from a (meth) acrylic acid ester containing an acid dissociable, dissolution inhibiting group.
As the acid dissociable, dissolution inhibiting group, any group can be used as long as it has the above-mentioned characteristics. However, a carboxyl group of (meth) acrylic acid and a cyclic or chain-like tertiary alkyl ester can be used. Those formed are preferred, and those containing an aliphatic polycyclic group are more preferably used. Such an acid dissociable, dissolution inhibiting group containing a polycyclic group is suitable as a positive resist for an ArF excimer laser because it has little light absorption in the wavelength band of ArF excimer laser and has good acid dissociability. It is.

Examples of the polycyclic group include groups in which one hydrogen atom has been removed from bicycloalkane, tricycloalkane, tetracycloalkane and the like.
Specific examples include groups in which one hydrogen atom has been removed from a polycycloalkane such as adamantane, norbornane, isobornane, tricyclodecane, and tetracyclododecane.
Such polycyclic groups can be appropriately selected from those proposed in large numbers in ArF resists. Of these, an adamantyl group, norbornyl group, and tetracyclododecyl group are preferred from the viewpoint of industrial applicability.

  The structural unit (a1) is preferably at least one selected from the group consisting of the following general formulas (I), (II) and (III).

（式中、Ｒは水素原子またはメチル基、Ｒ^１は炭素数１以上の低級アルキル基である）

(Wherein R is a hydrogen atom or a methyl group, and R ¹ is a lower alkyl group having 1 or more carbon atoms)

(Wherein R is a hydrogen atom or a methyl group, and R ² and R ³ are each independently a lower alkyl group)

（式中、Ｒは水素原子またはメチル基、Ｒ^４は第３級アルキル基である。）

(In the formula, R is a hydrogen atom or a methyl group, and R ⁴ is a tertiary alkyl group.)

  The structural unit represented by the general formula (I) is a structural unit in which a hydrocarbon group is ester-bonded to a structural unit of (meth) acrylic acid, and an oxygen atom (—O) in the ester part of the (meth) acrylate structural unit. -) Is bonded to a linear or branched alkyl group so that the carbon atom of the adamantyl group adjacent to the oxygen atom (the carbon atom at the 2-position of the adamantyl group) is a tertiary carbon atom. A tertiary alkyl ester is formed.

In the general formula (I), R ¹ is preferably a lower linear or branched alkyl group having 1 to 5 carbon atoms, specifically a methyl group, an ethyl group, a propyl group, an isopropyl group, n -Butyl group, isobutyl group, tert-butyl group, pentyl group, isopentyl group, neopentyl group and the like can be mentioned. In view of industrial availability, a methyl group is preferred. In addition, since an alkyl group having 2 or more carbon atoms, preferably 2 to 5 carbon atoms tends to have higher acid dissociability than that of a methyl group, when a higher acid dissociation property is required, the alkyl group has 2 to 2 carbon atoms. It is preferably 5, and an ethyl group is preferable from the viewpoints of industrial availability, prevention of steric hindrance, and efficient dissolution-dissociation group dissociation.

As in the general formula (I), the structural unit represented by the general formula (II) is a (meth) acrylic acid structural unit in which a hydrocarbon group is ester-bonded. The carbon atom adjacent to the oxygen atom (—O—) of the ester part of the acrylate structural unit is a tertiary carbon atom, and the tertiary carbon atom further has a ring skeleton such as an adamantyl group in the alkyl group. It exists.
R ² and R ³ are each independently preferably a lower alkyl group having 1 to 5 carbon atoms. Specific examples include a methyl group, an ethyl group, a propyl group, an isopropyl group, an n-butyl group, an isobutyl group, a tert-butyl group, a pentyl group, an isopentyl group, and a neopentyl group.
Such a group tends to have higher acid dissociability than the 2-methyl-2-adamantyl group in which R ^{1 in the} general formula (I) is a methyl group.
Among these, mention may be made of R ^2, R ³ are both a methyl group 2- (1-adamantyl) -2-propyl (meth) structural units derived from acrylate as preferred industrially.

The structural unit represented by the general formula (III) is a group of another ester on the ring skeleton of the tetracyclododecyl group of the (meth) acrylate structural unit composed of an ester of (meth) acrylic acid and a tetracyclododecyl group. —COOR ⁴ ) is bonded, and the group R ⁴ adjacent to the oxygen atom (—O—) of another ester (—COOR ⁴ ) is a tertiary alkyl group.
R ⁴ is a tertiary alkyl group such as a tert-butyl group or a tert-amyl group, and the case where it is a tert-butyl group is industrially preferred.
The group —COOR ⁴ may be bonded to the 3 or 4 position of the tetracyclododecyl group shown in the formula, but cannot be specified any more because it is included as an isomer. In addition, the carboxyl group residue of the (meth) acrylate structural unit may be bonded to the 8 or 9 position of the tetracyclododecanyl group, but cannot be specified because it is included together as an isomer as described above.

  The structural unit (a1) is preferably contained in an amount of 20 to 70 mol%, more preferably 30 to 50 mol%, based on the resin component. By setting the value to the lower limit or higher, the resolution of the resist and the verticality of the resist pattern shape are improved. By setting the value to the upper limit or lower, the dimensional dependence on the pattern density, the depth of focus, and the verticality of the resist pattern shape are improved. To do.

・ Structural unit (a2)
In the resin component, it is preferable that the star-shaped branched polymer and / or linear polymer contains a structural unit (a2) derived from a (meth) acrylic acid ester containing a lactone-containing monocyclic or polycyclic group.
When used as a positive resist composition, the lactone functional group is effective for enhancing the adhesion between the resist film and the substrate and enhancing the hydrophilicity with the developer.
Examples of the lactone-containing monocyclic or polycyclic group include a monocyclic group obtained by removing one hydrogen atom from γ-butyrolactone, and a polycyclic group obtained by removing one hydrogen atom from a lactone-containing bicycloalkane. It is done.
Specifically, for example, structural units represented by the following structural formulas (IV) to (VI) are preferable.

（式中、Ｒは水素原子又はメチル基である。）

(In the formula, R is a hydrogen atom or a methyl group.)

（式中、Ｒは水素原子又はメチル基である。）

(In the formula, R is a hydrogen atom or a methyl group.)

（式中、Ｒは水素原子又はメチル基である。）

(In the formula, R is a hydrogen atom or a methyl group.)

  Among the above formulas, norbornane lactone and γ-butyrolactone (meth) acrylate units represented by formula (IV) and formula (VI) are particularly preferred from the viewpoint of dry etching resistance and adhesion.

  The structural unit (a2) is preferably contained in an amount of 20 to 60 mol%, more preferably 30 to 50 mol%, based on the resin component. By setting it to the lower limit or more, the verticality of the resist pattern shape and the adhesion to the inorganic substrate are improved, and by setting the upper limit or less, the pattern collapse and resolution are improved.

・ Structural unit (a3)
Moreover, in the said resin component, it is preferable that the said star-shaped branched polymer and / or linear polymer contain the structural unit (a3) derived from the (meth) acrylic acid ester which has a hydroxyl group.
Since the hydroxyl group is a polar group, when the resin component contains the structural unit (a3), the affinity between the entire resin component and the alkali developer used when forming the resist pattern is increased. For this reason, when used as a positive resist composition, the alkali solubility in the exposed area is improved, which contributes to the improvement of resolution.
As the structural unit (a3), for example, a resin for resist composition of ArF excimer laser can be appropriately selected from among many proposed ones, and includes, for example, a hydroxyl group-containing aliphatic polycyclic group. Is preferred.
The polycyclic group can be appropriately selected from a large number of polycyclic groups similar to those exemplified in the description of the structural unit (a1).
Specifically, as the structural unit (a3), those having a hydroxyl group-containing adamantyl group (the number of hydroxyl groups is preferably 1 to 3, more preferably 1) are preferably used.
More specifically, a structural unit represented by the following general formula (VII) can be given.

（式中、Ｒは水素原子又はメチル基である。）

(In the formula, R is a hydrogen atom or a methyl group.)

  When the structural unit represented by the general formula (VII) is used, it is preferable because when it is used as a positive resist composition, it has an effect of increasing dry etching resistance and increasing the perpendicularity of the pattern cross-sectional shape.

  The structural unit (a3) is contained in an amount of 10 to 50 mol%, preferably 20 to 30 mol%, based on the resin component. By setting it to the lower limit value or more, the effect of improving the resolution becomes good, and when the upper limit value is exceeded, there is a possibility that it becomes inconvenient in terms of the balance of other structural units.

The resin component may include a structural unit (a4) other than the structural units (a1) to (a3).
The structural unit (a4) is not particularly limited as long as it is another structural unit that is not classified into the structural units (a1) to (a3). In other words, any acid dissociable, dissolution inhibiting group, lactone, or hydroxyl group may be used. For example, a structural unit containing an aliphatic polycyclic group and derived from a (meth) acrylic acid ester is preferable. When such a structural unit is used, when used as a positive resist composition, a resolution from an isolated pattern to a semi-dense pattern (line and space pattern having a space width of 1.2 to 2 with respect to a line width of 1) Since it is excellent in property, it is preferable.
Examples of the polycyclic group include those similar to those exemplified in the case of the structural unit (a1), and are conventionally known as ArF positive resist materials and KrF positive resist materials. Many can be used.
In particular, at least one selected from a tricyclodecanyl group, an adamantyl group, and a tetracyclododecanyl group is preferable in terms of industrial availability.
Specific examples of the structural unit (a4) include those having the following structures (VIII) to (X).

（式中、Ｒは水素原子又はメチル基である）

(Wherein R is a hydrogen atom or a methyl group)

（式中、Ｒは水素原子又はメチル基である）

(Wherein R is a hydrogen atom or a methyl group)

（式中、Ｒは水素原子又はメチル基である）

(Wherein R is a hydrogen atom or a methyl group)

  The structural unit (a4) is not essential for the resin component, but when it is contained in an amount of 1 to 25 mol%, preferably 10 to 20 mol%, the resolution of the semi-dense pattern from the isolated pattern is included. Is preferable.

As described above, in the resin component, the polymer chain of the star-shaped branched polymer preferably contains the structural unit (a1). This star-shaped branched polymer preferably further contains the structural unit (a2). The structural unit (a3) is also preferably a structural unit of a star-shaped branched polymer.
That is, the star-shaped branched polymer preferably contains the structural units (a1), (a2) and (a3) in one star-shaped branched polymer. Alternatively, the star-shaped branched polymer is preferably a mixture of a star-shaped branched polymer containing the structural units (a1) and (a2) and a star-shaped branched polymer containing the structural units (a1) and (a3).
Moreover, when containing a structural unit (a4), it should just be contained in either the said star-shaped branched polymer or a linear polymer. This linear polymer also preferably contains the structural unit (a1), the structural unit (a2) and / or the structural unit (a3).

  The molecular weight of the resin is preferably 3,000 to 20,000, more preferably 5,000 to 15,000. By making the mass average molecular weight equal to or more than the above lower limit, the resist shape maintainability in the unexposed portion can be improved. By making it below the upper limit, the solubility in the exposed area can be improved.

<Positive resist composition>
Next, the positive resist composition will be described.
The positive resist composition of the present invention contains the resin component (A), an acid generator component (B) that generates an acid upon exposure, and an organic solvent (C).

Component (B) As the component (B), an arbitrary one can be appropriately selected from those known as acid generators in conventional chemically amplified resists.
Examples of the acid generator include diphenyliodonium trifluoromethanesulfonate, (4-methoxyphenyl) phenyliodonium trifluoromethanesulfonate, bis (p-tert-butylphenyl) iodonium trifluoromethanesulfonate, triphenylsulfonium trifluoromethanesulfonate, (4 -Methoxyphenyl) diphenylsulfonium trifluoromethanesulfonate, (4-methylphenyl) diphenylsulfonium nonafluorobutanesulfonate, (p-tert-butylphenyl) diphenylsulfonium trifluoromethanesulfonate, diphenyliodonium nonafluorobutanesulfonate, bis (p-tert- Butylphenyl) iodonium nonafluorobutanesulfonate, And the like onium salts, such as Li-phenyl nonafluorobutanesulfonate. Among these, a sulfonium salt having a fluorinated alkyl sulfonate ion as an anion is preferable.

This (B) component may be used independently and may be used in combination of 2 or more type.
The compounding quantity is 0.5-30 mass parts with respect to 100 mass parts of (A) component, Preferably it is 1-10 mass parts. When the amount is 0.5 parts by mass or more, pattern formation is sufficiently performed. When the amount is 30 parts by mass or less, a uniform solution is obtained, and the storage stability tends to be improved.

Component (C) The positive resist composition can be produced by dissolving the component (A), the component (B), and the optional component (D) described below, preferably in the component (C). The amount of the component (C) in the positive resist composition is not particularly limited, and is, for example, a concentration at which a positive resist composition that can be applied onto a substrate or the like is obtained.
As the component (C), any component can be used as long as it can dissolve the component (A) and the component (B) to form a uniform solution. One or two or more can be appropriately selected and used.
For example, ketones such as acetone, methyl ethyl ketone, cyclohexanone, methyl isoamyl ketone, 2-heptanone, ethylene glycol, ethylene glycol monoacetate, diethylene glycol, diethylene glycol monoacetate, propylene glycol, propylene glycol monoacetate, dipropylene glycol, or dipropylene Polyhydric alcohols such as glycol monoacetate monomethyl ether, monoethyl ether, monopropyl ether, monobutyl ether or monophenyl ether and derivatives thereof, cyclic ethers such as dioxane, methyl lactate, ethyl lactate, methyl acetate , Ethyl acetate, butyl acetate, methyl pyruvate, ethyl pyruvate, methyl methoxypropionate, ethoxypropionate Esters such as phosphate ethyl and the like. These organic solvents may be used independently and may be used as 2 or more types of mixed solvents.

In particular, a mixed solvent of propylene glycol monomethyl ether acetate (PGMEA) and a polar solvent having a hydroxy group or a lactone functional group such as propylene glycol monomethyl ether (PGME), ethyl lactate (EL), or γ-butyrolactone is a positive resist. This is preferable because the storage stability of the composition is improved.
A mixed solvent of PGMEA and EL is particularly preferable.
As a mixed solvent of PGMEA / EL, the mass ratio of PGMEA: EL is preferably 6: 4 to 4: 6.

Component (D) In the positive resist composition, for the purpose of improving the resist pattern shape, stability of placement, etc., an optional component (D) is an amine, particularly a secondary lower aliphatic amine or tertiary. Lower aliphatic amines can be included.
Here, the lower aliphatic amine means an alkyl or alkyl alcohol amine having 5 or less carbon atoms. Examples of the secondary and tertiary amines include trimethylamine, diethylamine, triethylamine, di-n-propylamine, -N-propylamine, tripentylamine, diethanolamine, triethanolamine and the like can be mentioned, and alkanolamines such as triethanolamine are particularly preferable.
These may be used alone or in combination of two or more.
These amines are generally used in the range of 0.01 to 2 parts by mass with respect to 100 parts by mass of component (A).

(E) Organic carboxylic acid or phosphorous oxo acid or derivative thereof The positive resist composition is further optional for the purpose of improving the resist pattern shape, retention stability, etc., and adjusting the sensitivity, similar to the component (D). As the component (E), an organic carboxylic acid, an oxo acid of phosphorus, or a derivative thereof can be contained. In addition, (D) component and (E) component can also be used together, and any 1 type can also be used.
As the organic carboxylic acid, for example, malonic acid, citric acid, malic acid, succinic acid, benzoic acid, salicylic acid and the like are suitable.
Phosphorus oxoacids or derivatives thereof include phosphoric acid, phosphoric acid di-n-butyl ester, phosphoric acid diphenyl ester and other phosphoric acid or derivatives thereof such as phosphonic acid, phosphonic acid dimethyl ester, phosphonic acid- Like phosphonic acids such as di-n-butyl ester, phenylphosphonic acid, phosphonic acid diphenyl ester, phosphonic acid dibenzyl ester and derivatives thereof, phosphinic acids such as phosphinic acid, phenylphosphinic acid and their esters Among these, phosphonic acid is particularly preferable.
(E) A component is used in the ratio of 0.01-1.0 mass part per 100 mass parts of (A) component.

  The positive resist composition further contains miscible additives as desired, for example, additional resins for improving the performance of the resist film, surfactants for improving coatability, dissolution inhibitors, plasticizers, Stabilizers, colorants, antihalation agents and the like can be added.

Although this positive resist composition is particularly useful as a positive resist composition for ArF excimer laser, it has a shorter wavelength F ₂ laser, EUV (extreme ultraviolet), VUV (vacuum ultraviolet), electron beam. It is also effective for radiation such as X-rays and soft X-rays.

By the way, the above-mentioned pattern collapse is a particular problem when a fine resist pattern is formed with a light source having a shorter wavelength than that of an ArF excimer laser. In order to improve the resolution, it is preferable that the pattern cross-sectional shape is rectangular. For this purpose, it is necessary to increase the dissolution contrast of the ArF resist composition. However, when the dissolution contrast is high, in the conventional ArF resist composition, the side wall portion of the pattern may be partially dissolved, and the side wall portion may have a rough shape. As this tendency further progresses, the pattern width is partially narrowed, and it is assumed that pattern collapse occurs. In addition, if the resist pattern is weak, it is presumed that pattern collapse occurs.
On the other hand, when the positive resist composition of the present invention is used, the pattern collapse hardly occurs although the dissolution contrast is good (sensitivity is good).
The reason is presumed as follows.
In the positive resist composition of the present invention, since the resin component contains a star-shaped branched polymer, when a resist is applied to a substrate or the like and exposed, heated, and developed through a mask pattern, It is presumed that the star-shaped branched polymer maintains a three-dimensional shape. That is, the star-shaped branched polymers or the star-shaped branched polymer and other linear polymers can be entangled with each other to maintain a strong three-dimensional shape.
On the other hand, since the solubility of the resin component in the alkali is improved in the exposed portion, the acid acts by heating and is easily dissolved in the developer. In particular, this tendency becomes remarkable when the star-shaped branched polymer has an acid dissociable, dissolution inhibiting group. Therefore, it is considered that the dissolution contrast between the exposed portion and the unexposed portion of the resist can be increased.
On the other hand, regarding pattern collapse, since the resin component in the present invention contains a star-shaped branched polymer, in the unexposed part, the polymer is firmly entangled with each other, or the solid shape is firmly maintained and unexposed. The polymer does not fall off at the area, and the resist side wall is less rough. Therefore, the resist pattern has a rectangular cross-sectional shape and the exposed area is firmly dissolved to the bottom. Has an effect.

In addition, resin components using star-shaped branched polymers are difficult to dissolve in the unexposed areas even if the molecular weight is small. On the other hand, alkali solubility is increased by acid in the exposed areas. It becomes. Therefore, a high dissolution contrast can be achieved by reducing the molecular weight.
In addition, a polymer having a star-shaped branched polymer using a polyfunctional chain transfer agent can control the molecular weight, and has an effect that the molecular weight can be made smaller than that of a conventional one.
In addition, as described above, the fact that the resist cross-sectional shape is a clean rectangle is thought to lead to improved resolution and increased depth of focus (DOF). Therefore, it is possible to improve the resolution, mask linearity, DOF, and the effect of suppressing pattern collapse.
At present, the ArF resist, which is required to have a higher degree of miniaturization, must be thinned. However, with conventional resists, for example, a thin film such as 100 to 150 nm results in insufficient resist dissolution contrast, which is satisfactory. It may be difficult to obtain a pattern having the obtained shape. On the other hand, when the positive resist composition of the present invention is used, a satisfactory pattern can be obtained because it has a sufficient dissolution contrast.

<Resist pattern formation method>
The resist pattern forming method of the present invention can be performed, for example, as follows.
That is, first, the positive resist composition is applied onto a substrate such as a silicon wafer with a spinner and prebaked for 40 to 120 seconds, preferably 60 to 90 seconds under a temperature condition of 80 to 150 ° C. Then, for example, ArF excimer laser light is selectively exposed through a desired mask pattern by an ArF exposure apparatus or the like, and then subjected to PEB (post-exposure heating).
Thereafter, this is developed using an alkali developer, for example, an aqueous solution of 0.1 to 10% by mass of tetramethylammonium hydroxide to obtain a resist pattern to which the shape of the mask pattern has been transferred.
An organic or inorganic antireflection film can be provided between the substrate and the coating layer of the resist composition.
The thickness of the resist layer is not particularly limited, but is preferably 200 to 400 nm from the viewpoint of development contrast and etching resistance.

Hereinafter, the present invention will be described in more detail with reference to examples.
(Example 1)
100 parts by mass of tetrahydrofuran, 45 parts by mass of 2-methyl-2-adamantyl methacrylate, 30 parts by mass of γ-butyrolactonyl methacrylate and 3- 25 parts by mass of hydroxy-1-adamantyl methacrylate and 5 parts by mass of pentaerythritol tetrakis (2-mercaptoacetate) were added as a chain transfer agent, and the temperature was raised to 70 ° C. with stirring. While maintaining the temperature, a polymerization initiator solution in which 0.2 parts by mass of 2,2′-azobis (2,4-dimethylvaleronitrile) was dissolved in 1 part by mass of tetrahydrofuran was dropped over 10 minutes. After completion of dropping, stirring was continued for 5 hours while maintaining the temperature to complete the polymerization.
The obtained polymer solution was diluted about 1.5 times with tetrahydrofuran and then dropped into water to obtain a precipitate. This precipitate was filtered, washed and dried to obtain a star-shaped branched random copolymer (GPC weight average molecular weight 7,500, dispersity 1.7).
It was confirmed from the fact that the obtained polymer was a star-shaped branched copolymer because the branching parameter g was about 0.7.

Component A: 100 parts by mass of the star-shaped branched random copolymer obtained above,
Component B: triphenylsulfonium nonafluorobutane sulfonate
3.6 parts by mass,
Component C: PGMEA / EL mixed solvent (mixing ratio 6/4) 900 parts by mass D component: Triethanolamine 0.3 parts by mass was mixed and dissolved to produce a positive resist composition.

Next, a silicon wafer provided with a film thickness of 82 nm by heating the organic antireflection film AR-19 (trade name, manufactured by Shipley) for 90 seconds at 215 ° C. using the positive resist composition as a base film using a spinner. The resist layer having a thickness of 350 nm was formed by applying the coating on the substrate, prebaking (PAB treatment) at 115 ° C. for 90 seconds on a hot plate, and drying.
Subsequently, ArF excimer laser (193 nm) was selectively irradiated through the mask pattern by an ArF exposure apparatus NSR-S302 (NA (numerical aperture) = 0.60, 2/3 annular illumination manufactured by Nikon Corporation).
Then, PEB treatment was performed at 110 ° C. for 90 seconds, paddle development was performed with 2.38 mass% NMD-3 (tetramethylammonium hydroxide aqueous solution) at 23 ° C. for 60 seconds, and then washed with water for 20 seconds. And dried to form a resist pattern.

The resist pattern shape was a dense type with a pattern interval of 1: 1, and two widths and intervals of 110 nm and 120 nm were formed.
The sensitivity (minimum exposure amount at which the pattern was normally formed) was 20.0 mJ / cm ² , and the limit resolution was 110 nm. Moreover, the focal depth (DOF) of the 120 nm pattern was 900 nm. The cross-sectional shape of the pattern was a rectangular shape with the side walls rising perpendicular to the substrate.

(Example 2)
The following A to D components were mixed and dissolved to produce a positive resist composition.
As component A, in the presence of 5 parts by mass of pentaerythritol tetrakis (2-mercaptoacetate), 45 parts by mass of 2-methyl-2-adamantyl methacrylate, a single amount of methacrylate that gives a structural unit in which R is a methyl group in formula (IV) Example, except that 100 parts by mass of a star-shaped branched random copolymer (mass average molecular weight 7500, dispersity 1.7) obtained by dropwise polymerization of 30 parts by mass of the product and 25 parts by mass of 3-hydroxy-1-adamantyl methacrylate was used. A positive resist composition was obtained in the same manner as in Example 1, and then a resist pattern was formed in the same manner as in Example 1 to form a pattern having a width of 120 nm and a pattern interval of 1: 1.
The limiting resolution of the obtained pattern was 120 nm. The cross-sectional shape of the pattern was a rectangular shape with the sidewalls rising perpendicular to the substrate, and no pattern collapse was observed in any of the patterns obtained at the limit resolution or higher.

(Examples 3 to 5)
In Example 2, instead of pentaerythritol tetrakis (2-mercaptoacetate), trimethylolmethanetris (2-mercaptoacetate) (Example 3), trimethylolmethanetris (3-mercapto) was used instead of pentaerythritol tetrakis (2-mercaptoacetate). Propionate) (Example 4) and 1,2,3-trihydroxypropanetris (2-mercaptoacetate) (Example 5) were used in the same manner as in Example 2 except that the same amount was used.
The limit resolution of the obtained pattern was 130 nm in all cases. In addition, the cross-sectional shapes of the patterns were all rectangular with the side walls rising perpendicular to the substrate, and no pattern collapse was observed in any of the patterns obtained at the limit resolution or higher.

(Example 6)
The following A to D components were mixed and dissolved to produce a positive resist composition.
As an A component, in the presence of 5 parts by mass of pentaerythritol tetrakis (2-mercaptoacetate), 45 parts by mass of 2-methyl-2-adamantyl acrylate, and an acrylate monomer that gives a structural unit in which R is a hydrogen atom in formula (IV) 30 parts by mass of a star-shaped branched random copolymer (weight average molecular weight of 7000) obtained by dropwise polymerization of 30 parts by mass and 25 parts by mass of 3-hydroxy-1-adamantyl acrylate (in the general formula (VII), R corresponds to a monomer having a hydrogen atom) Dispersion 1.8) A positive resist composition was obtained in the same manner as in Example 1 except that 100 parts by mass was used. Then, in Example 1, except that both PAB and PEB were changed to 85 ° C. Then, a resist pattern was formed, and a pattern having a width of 160 nm and a pattern interval of 1: 1 was formed.
The limiting resolution of the obtained pattern was 160 nm. The cross-sectional shape of the pattern was a rectangular shape with the sidewalls rising perpendicular to the substrate, and no pattern collapse was observed in any of the patterns obtained at the limit resolution or higher.

(Comparative Example 1)
The following A to D components were mixed and dissolved to produce a positive resist composition. Component A: In Component A of Example 1, pentaerythritol tetrakis (2-mercaptoacetate) was not used, and 3.5 parts by mass of 2,2′-azobis (2,4-dimethylvaleronitrile) was added as a polymerization initiator. Polymerization was started, and the temperature was maintained for 5 hours. 45 parts by mass of 2-methyl-2-adamantyl methacrylate
30 parts by mass of γ-butyrolactonyl methacrylate (corresponding to a monomer in which R is a methyl group in the general formula (VI))
3-hydroxy-1-adamantyl methacrylate (in the general formula (VII), R corresponds to a monomer having a methyl group) 20 parts by mass 1-adamantyl methacrylate (in the general formula (IX), R corresponds to a monomer having a methyl group) 5 parts by mass Random copolymer obtained by copolymerization (weight average molecular weight about 10,000, dispersity 1.8)
100 parts by mass,
Component B: triphenylsulfonium nonafluorobutane sulfonate
3.6 parts by mass,
Component C: PGMEA / EL mixed solvent (mixing ratio 6/4) 900 parts by mass Component D: Triethanolamine 0.3 parts by mass

Next, using this positive resist composition, a resist pattern was formed in the same manner as in Example 1 except that the PAB treatment temperature and the PEB treatment temperature were 125 ° C., respectively.
The sensitivity was 17.0 mJ / cm ² and the limiting resolution was 120 nm. The depth of focus (DOF) was 500 nm.
The cross-sectional shape of the pattern was a tapered shape in which the upper side of the side wall was thin and the lower side was thick.
In addition, the pattern collapsed noticeably when the focus was shifted, and the pattern collapsed when overexposed.

The resists of Examples 1 to 6 each have a DOF of 600 nm or more. Moreover, it turns out that the pattern of a rectangular cross section is obtained in any case. Further, even when these are formed as thin films of 100 to 150 nm, the dissolution contrast between the exposed and unexposed portions of the resist is clear and a good pattern is obtained.
On the other hand, the resist of Comparative Example 1 has a shallow DOF of 500 nm and has a tapered cross-sectional shape. When the thickness is 150 nm, a good contrast pattern cannot be obtained.

Claims (12)

  A resin component (A1) that increases the solubility in alkali by the action of an acid, and an acid that generates an acid upon exposure, comprising a star-shaped branched polymer having a polymer chain extending in three or more directions from a lower alkyl molecule A positive resist composition comprising a generator component (B) and an organic solvent (C).   Solubility in alkali by the action of an acid, characterized by containing a star-shaped branched polymer obtained by polymerization of a monomer containing a (meth) acrylic acid ester in the presence of a trifunctional or higher polyfunctional chain transfer agent A positive resist composition comprising: a resin component (A2) that increases the amount of acid; an acid generator component (B) that generates acid upon exposure; and an organic solvent (C).   3. The positive resist composition according to claim 2, wherein the trifunctional or higher functional chain transfer agent is a trifunctional or higher functional mercaptan compound.   4. The positive resist composition according to claim 3, wherein the trifunctional or higher functional mercaptan compound is pentaerythritol tetrakis (2-mercaptoacetate).   The resin component (A1) or (A2) contains a structural unit (a1) derived from a (meth) acrylic acid ester containing an acid dissociable, dissolution inhibiting group. 2. The positive resist composition according to item 1. 6. The positive resist composition according to claim 5, wherein the structural unit (a1) is at least one selected from the group consisting of the following general formulas (I), (II) and (III).

(Wherein R is a hydrogen atom or a methyl group, and R ¹ is a lower alkyl group having 1 or more carbon atoms)

(Wherein R is a hydrogen atom or a methyl group, and R ² and R ³ are each independently a lower alkyl group)

(In the formula, R is a hydrogen atom or a methyl group, and R ⁴ is a tertiary alkyl group.)   The resin component (A1) or (A2) further contains a structural unit (a2) derived from a (meth) acrylic acid ester containing a lactone-containing monocyclic or polycyclic group. 6. The positive resist composition according to 6. The positive resist composition according to claim 7, wherein the structural unit (a2) is at least one selected from structural units consisting of the following structural formulas (IV) to (VI).

(In the formula, R is a hydrogen atom or a methyl group.)

(In the formula, R is a hydrogen atom or a methyl group.)

(In the formula, R is a hydrogen atom or a methyl group.)   The said resin component (A1) or (A2) contains the structural unit (a3) derived from the (meth) acrylic acid ester which has a hydroxyl group further, The any one of Claims 5-8 characterized by the above-mentioned. A positive resist composition. The positive resist composition according to claim 9, wherein the structural unit (a3) is a structural unit represented by the following general formula (VII).

(In the formula, R is a hydrogen atom or a methyl group.)   The positive resist composition according to claim 1, further comprising an amine (D). A layer made of the positive resist composition according to any one of claims 1 to 11 is provided on a substrate, pre-baked on the layer, selectively exposed, then subjected to PEB (post-exposure heating), and alkali A resist pattern forming method comprising developing the resist pattern.