JP2018106062A - Resist pattern forming method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To form a clear resist pattern with high sensitivity.SOLUTION: A resist pattern forming method has a step for forming a resist film using a positive resist composition containing a polymer having a monomer unit (A) represented by a specific formula, and a monomer unit (B) represented by formula (II), with the total number of fluorine atoms included in both monomer units of 1 or more, an exposure step, and a developing step for developing using a developer containing a linear alcohol having 4 or less carbon atoms.SELECTED DRAWING: None

Description

  The present invention relates to a resist pattern forming method, and more particularly to a resist pattern forming method using a positive resist.

  Conventionally, in the field of semiconductor manufacturing and the like, ionizing radiation such as an electron beam and short wavelength light such as ultraviolet rays (hereinafter, ionizing radiation and short wavelength light may be collectively referred to as “ionizing radiation or the like”). A polymer whose main chain is cleaved by irradiation and has increased solubility in a developing solution is used as a main chain-cutting positive resist.

  As a high-sensitivity main-chain-breaking positive resist, a positive resist comprising an α-methylstyrene / α-methyl chloroacrylate copolymer containing α-methylstyrene (AMS) units and methyl α-chloroacrylate units. A type resist has been proposed (see, for example, Patent Document 1). Patent Document 1 discloses a method of developing a positive resist using xylene to obtain a resist pattern.

  In addition, the formation of a resist pattern using a resist film formed using a positive resist made of α-methylstyrene / α-methyl chloroacrylate copolymer includes an exposed portion irradiated with ionizing radiation, ionizing radiation, etc. This is carried out by utilizing the difference in the dissolution rate with respect to the developer with the unexposed portion that has not been irradiated. As the developer, for example, a carboxylic acid ester solvent having an alkyl group such as amyl acetate or hexyl acetate, a mixed solution of isopropanol and fluorocarbon (for example, Vertrel XF (registered trademark)), fluorocarbon (for example, Vertrel XF) (Registered trademark) etc.) are used (see, for example, Patent Documents 2 to 6).

Japanese Patent Publication No. 8-3636 International Publication No. 2013/145695 JP 2011-215243 A JP 2011-215244 A JP 2012-150443 A International Publication No. 2013/018569

  In the resist pattern forming method using the main chain cutting type positive resist, the resist pattern is subjected to an exposure process of irradiating the resist film with ionizing radiation or the like, and a development process of developing the resist film exposed using the developer. Form. If strong light is irradiated in the exposure step, the solubility of the exposed portion in the developer can be easily improved, and a resist pattern with high clarity can be easily obtained. Here, in recent years, it has been required to form a resist pattern with high clarity while reducing the intensity of light irradiated in the exposure process. However, in the resist pattern forming method according to the conventional technique as described above, the sensitivity is improved by reducing the irradiation intensity of ionizing radiation or the like in the exposure process, and the clarity of the resist pattern obtained through the development process is improved. There was room for improvement. In other words, the conventional resist pattern forming method has room for improvement in terms of achieving both high sensitivity and high clarity.

  When forming a resist pattern using the difference in dissolution rate in the developer between the exposed area and the unexposed area, the solubility of the exposed area in the developer is required to form a clear resist pattern. It is required to suppress dissolution of the unexposed portion in the developer while increasing the thickness. However, in the formation of a resist pattern using a main-chain-breaking positive resist, the solubility of the exposed and unexposed areas in the developer depends on the properties of the polymer used as the positive resist and the type of developer. Changes under the influence of.

  Therefore, a clear resist pattern can be enhanced by appropriately combining a polymer contained in a main chain-breaking positive resist composition and a developer used for developing a resist formed using the resist composition. Development of a method that can be formed with sensitivity has been demanded.

  The inventor has intensively studied to achieve the above object. And this inventor forms a resist film using the positive resist composition containing the polymer containing the monomer unit which has 1 or more and 4 or less fluorine atoms, and carbon number is 4 for this resist film. The present invention was completed by newly finding that a clear resist pattern can be formed with high sensitivity when developed using a developer containing the following linear alcohol.

〔式（Ｉ）中、Ｒ^１は、非置換の有機基またはフッ素原子で置換された有機基（但し、フッ素原子の数は１以上４以下である。）である。〕で表される単量体単位（Ａ）と、下記一般式（ＩＩ）：

〔式（ＩＩ）中、Ｒ^２は、水素原子、フッ素原子、非置換のアルキル基またはフッ素原子で置換されたアルキル基であり、Ｒ^３は、水素原子、非置換のアルキル基またはフッ素原子で置換されたアルキル基であり、ｐ及びｑは、０以上５以下の整数であり、ｐ＋ｑ＝５である。〕で表される単量体単位（Ｂ）とを有し、且つ、前記Ｒ^１〜Ｒ^３に含まれるフッ素原子の合計数が１以上であり、前記現像を、炭素数が４以下の直鎖アルコールを含む現像液を用いて行うことを特徴とするものである。重合体にフッ素原子を有する単量体単位を含有させるとともに、当該重合体を含むポジ型レジストを炭素数が４以下の直鎖アルコールを含む現像液を用いて現像すれば、明瞭なレジストパターンを高感度で形成可能である。
なお、本発明において、式（ＩＩ）中のｐが２以上の場合には、複数あるＲ^２は互いに同一でも異なっていてもよく、また、式（ＩＩ）中のｑが２以上の場合には、複数あるＲ^３は互いに同一でも異なっていてもよい。 That is, the present invention aims to advantageously solve the above-mentioned problems, and the resist pattern forming method of the present invention forms a resist film using a positive resist composition containing a polymer and a solvent. A resist pattern forming method including a step (A) of performing, a step (B) of exposing the resist film, and a step (C) of developing the exposed resist film, wherein the polymer has the following general structure: Formula (I):

[In the formula (I), R ¹ represents an unsubstituted organic group or an organic group substituted with a fluorine atom (provided that the number of fluorine atoms is 1 or more and 4 or less). And a monomer unit (A) represented by the following general formula (II):

[In Formula (II), R ² is a hydrogen atom, a fluorine atom, an unsubstituted alkyl group or an alkyl group substituted with a fluorine atom, and R ³ is a hydrogen atom, an unsubstituted alkyl group or a fluorine atom. It is a substituted alkyl group, p and q are integers of 0 or more and 5 or less, and p + q = 5. And the total number of fluorine atoms contained in R ^{1 to} R ³ is 1 or more, and the development is carried out directly with 4 or less carbon atoms. It is characterized by using a developer containing a chain alcohol. A clear resist pattern can be obtained by adding a monomer unit having a fluorine atom to a polymer and developing a positive resist containing the polymer with a developer containing a linear alcohol having 4 or less carbon atoms. It can be formed with high sensitivity.
In the present invention, when p in the formula (II) is 2 or more, a plurality of R ² may be the same or different from each other, and when q in the formula (II) is 2 or more The plurality of R ³ may be the same as or different from each other.

Here, the resist pattern forming method of the present invention, it is preferred that the total number of fluorine atoms contained in the R ¹ to R ³ is 4 or less. By using a positive resist composition containing a polymer in which the total number of fluorine atoms contained in R ^{1 to} R ³ is 4 or less, the clarity of the resulting resist pattern can be further improved.

Furthermore, a resist pattern forming method of the present invention preferably has a surface free energy of the polymer is 26 mJ / ^{m 2} or more 35 mJ / ^{m 2} or less. If the surface free energy of the polymer contained in the positive resist composition is within the specific range, the clarity of the resulting resist pattern can be further improved.
Here, in the present specification, the “surface free energy” of a polymer is known for the surface tension, polarity term and dispersion force term of a film (film) formed using the polymer, using a contact angle meter. The contact angles of the two types of solvents (water and diiodomethane) can be measured and calculated based on the evaluation of surface free energy by the method of Owens-Wendt (expanded Fowkes equation).

  Furthermore, in the resist pattern formation method of this invention, it is preferable that the said linear alcohol is at least 1 sort (s) selected from the group which consists of methanol, ethanol, and 1-propanol. If a resist film containing the specific polymer is developed using any of the above groups as a developer, a clearer resist pattern can be obtained with higher sensitivity.

Further, in the resist pattern forming method of the present invention, the R ¹ is a 2,2,2-trifluoroethyl group, p is 5 and q is 0, and the R ² is a hydrogen atom or a fluorine atom. Is preferred. If a resist film containing such a specific polymer is used, it becomes possible to obtain a clearer resist pattern with higher sensitivity.

  Furthermore, in the resist pattern formation method of this invention, it is preferable that the development time in the said process (C) is 1 minute or more and 4 minutes or less. By setting the development time within the predetermined range, a resist pattern can be efficiently formed and the clarity of the obtained resist pattern can be further improved.

  According to the resist pattern forming method of the present invention, a clear resist pattern can be formed with high sensitivity.

Hereinafter, embodiments of the present invention will be described in detail.
The resist pattern forming method of the present invention includes a step (A) of forming a resist film using a positive resist composition containing a polymer and a solvent, a step (B) of exposing the resist film, and an exposed resist. And (C) developing the film. The resist pattern forming method of the present invention can be used, for example, when forming a resist pattern in a manufacturing process of a printed board such as a build-up board. Hereinafter, each process is explained in full detail.

(Process (A): Resist film formation process)
In the resist film forming step, a positive resist composition is applied onto a workpiece such as a substrate processed using a resist pattern, and the applied positive resist composition is dried to form a resist film. . Here, the substrate is not particularly limited, and a substrate having an insulating layer and a copper foil provided on the insulating layer, which is used for manufacturing a printed circuit board, and the like can be used. Further, the method for applying and drying the positive resist composition is not particularly limited, and a method generally used for forming a resist film can be used. And in the pattern formation method of this invention, the following positive resist compositions are used.

<Positive resist composition>
The positive resist composition contains a polymer containing a specific monomer unit described in detail below and a solvent, and optionally further contains known additives that can be generally blended into the resist composition. Yes.

〔式（Ｉ）中、Ｒ^１は、非置換の有機基またはフッ素原子で置換された有機基（但し、フッ素原子の数は１以上４以下である。）である。〕
で表される単量体単位（Ａ）と、
下記一般式（ＩＩ）：

〔式（ＩＩ）中、Ｒ^２は、水素原子、フッ素原子、非置換のアルキル基またはフッ素原子で置換されたアルキル基であり、Ｒ^３は、水素原子、非置換のアルキル基またはフッ素原子で置換されたアルキル基であり、ｐ及びｑは、０以上５以下の整数であり、ｐ＋ｑ＝５である。〕で表される単量体単位（Ｂ）とを有し、且つ、前記Ｒ^１〜Ｒ^３に含まれるフッ素原子の合計数が１以上であることを必要とする。 << Polymer >>
The polymer used in the resist pattern forming method of the present invention is a main-chain-cut positive resist in which the main chain is cut and the molecular weight is reduced by irradiation with ionizing radiation such as an electron beam or short-wavelength light such as ultraviolet rays. As a polymer that can be used satisfactorily. The polymer has the following general formula (I):

[In the formula (I), R ¹ represents an unsubstituted organic group or an organic group substituted with a fluorine atom (provided that the number of fluorine atoms is 1 or more and 4 or less). ]
A monomer unit (A) represented by:
The following general formula (II):

[In Formula (II), R ² is a hydrogen atom, a fluorine atom, an unsubstituted alkyl group or an alkyl group substituted with a fluorine atom, and R ³ is a hydrogen atom, an unsubstituted alkyl group or a fluorine atom. It is a substituted alkyl group, p and q are integers of 0 or more and 5 or less, and p + q = 5. And the total number of fluorine atoms contained in R ^{1 to} R ³ is 1 or more.

  In addition, although the polymer mentioned above may contain arbitrary monomer units other than a monomer unit (A) and a monomer unit (B), in all the monomer units which comprise a polymer. The ratio of the monomer unit (A) and the monomer unit (B) is preferably 90 mol% or more in total, more preferably 100 mol%, and more preferably 100 mol% (that is, More preferably, the polymer contains only the monomer unit (A) and the monomer unit (B).

Moreover, as long as the polymer mentioned above has a monomer unit (A) and a monomer unit (B), for example, a random polymer, a block polymer, an alternating polymer (ABAB ...), etc. Although it may be either, it is preferable that it is a polymer containing 90 mass% or more (upper limit is 100 mass%) of an alternating polymer. Here, it is preferable that the alternating polymers do not form a crosslinked body. When a fluorine atom is contained in R ¹ of the monomer unit (A), a crosslinked product is not formed.

  Here, since the above-described polymer contains predetermined monomer units (A) and monomer units (B), ionizing radiation or the like (for example, electron beam, KrF laser, ArF laser, EUV laser, etc.) ) Is irradiated, the main chain is cleaved to lower the molecular weight.

  Since the above-mentioned polymer has at least one fluorine atom, when used as a resist, the sensitivity of the resist can be improved and the occurrence of resist pattern collapse can be suppressed. doing. The reason why the resist film can be prevented from falling by containing a polymer having fluorine atoms in the resist film is not clear, but fluorine atoms improve the liquid repellency of the polymer. This is presumably because it is possible to suppress the occurrence of tension between the patterns when the developer is removed in the process of forming the resist pattern.

〔式（ＩＩＩ）中、Ｒ^１は、式（Ｉ）と同様である。〕で表される単量体（ａ）に由来する構造単位である。 [Monomer unit (A)]
Here, the monomer unit (A) has the following general formula (III):

[In formula (III), R ¹ is the same as in formula (I). ] Is a structural unit derived from the monomer (a) represented by

  And the ratio of the monomer unit (A) in all the monomer units which comprise a polymer is not specifically limited, For example, it can be 30 mol% or more and 70 mol% or less.

Here, the unsubstituted organic group that can constitute R ¹ in the formulas (I) and (III) is not particularly limited, and examples thereof include an unsubstituted alkyl group having 1 to 10 carbon atoms. It is done. Among them, as the unsubstituted organic group capable of constituting the R ^1, a methyl group or an ethyl group is preferred.
Further, the organic group substituted with a fluorine atom that can constitute R ¹ in the formulas (I) and (III) is not particularly limited, and fluorine contained in the substituted organic group Examples include groups having a structure in which part or all of the hydrogen atoms in the organic group are substituted with fluorine atoms so that the total number of atoms is 1 or more and 4 or less.

From the viewpoint of increasing the solubility in a developer containing a linear alcohol having 4 or less carbon atoms to increase the sensitivity of the resist and the clarity of the resulting resist pattern, R ¹ is a fluoroalkyl group, a fluoroalkoxyalkyl group, Alternatively, it is preferably a fluoroalkoxyalkenyl group, more preferably a fluoroalkyl group. The number of carbon atoms of the organic group as R ¹ is preferably 1 or more, 10 or less, more preferably 2 or more and 4 or less, and even more preferably 2.
In addition, the number of fluorine atoms contained in the fluoroalkyl group as R ¹ in the formulas (I) and (III) is preferably 1 or more and 3 or less, and more preferably 3.

Specifically, the fluoroalkyl group as R ¹ in the formulas (I) and (III) includes a trifluoromethyl group (3 fluorine atoms and 1 carbon atom), 2,2,2- Examples include trifluoroethyl groups (3 fluorine atoms and 2 carbon atoms), 1H, 1H, 3H-tetrafluoropropyl groups (4 fluorine atoms and 3 carbon atoms). , 2-trifluoroethyl group is preferable.

  The monomer (a) represented by the above formula (III) that can form the monomer unit (A) represented by the above formula (I) is not particularly limited, For example, α-chloroacrylic acid fluoroalkyl ester such as α-chloroacrylic acid trifluoromethyl, α-chloroacrylic acid 2,2,2-trifluoroethyl, α-chloroacrylic acid 1H, 1H, 3H-tetrafluoropropyl Is mentioned.

（式（ＩＶ）中、Ｒ^２、Ｒ^３、並びに、ｐ及びｑは、式（ＩＩ）と同様である。）で表される単量体（ｂ）に由来する構造単位である。 [Monomer unit (B)]
The monomer unit (B) has the following general formula (IV):

(In formula (IV), R ² , R ³ , and p and q are the same as those in formula (II).) Are structural units derived from the monomer (b).

  And the ratio of the monomer unit (B) in all the monomer units which comprise a polymer is not specifically limited, For example, it can be 30 mol% or more and 70 mol% or less.

Here, the unsubstituted alkyl group that can constitute R ² and R ³ in formula (II) and formula (IV) is not particularly limited, and is an unsubstituted alkyl having 1 to 5 carbon atoms. Groups. Especially, as an unsubstituted alkyl group which can comprise R < ² >, R < ³ >, a methyl group or an ethyl group is preferable.
In addition, the alkyl group substituted with a fluorine atom that can constitute R ² and R ³ in formula (II) and formula (IV) is not particularly limited, and a part of hydrogen atoms in the alkyl group Or the group which has the structure which substituted all by the fluorine atom is mentioned.

Here, in the resist pattern forming method of the present invention, the total number of fluorine atoms contained in R ^{1 to} R ³ in formulas (I) to (IV) is preferably 4 or less. By using a positive resist composition containing a polymer in which the total number of fluorine atoms contained in R ^{1 to} R ³ is 4 or less, the clarity of the resulting resist pattern can be further improved.

Furthermore, from the viewpoint of improving the ease of preparation of the polymer, R ² and / or R ³ present in plural in Formula (II) and Formula (IV) are all hydrogen atoms or unsubstituted alkyl groups. It is preferably a hydrogen atom or an unsubstituted alkyl group having 1 to 5 carbon atoms, and more preferably a hydrogen atom. That is, when emphasizing ease of preparation of the polymer, the monomer unit (B) does not contain a fluorine atom, and the number of fluorine atoms contained in R ¹ in the formulas (I) and (III) Is preferably 1 or more and 4 or less.

When R ^{1 in} formulas (I) and (III) is a 2,2,2-trifluoroethyl group, p in formula (II) and formula (IV) is 5, and q is 0, all R ² are A hydrogen atom is preferred. According to such a polymer, the solubility of the exposed portion of the resist film in the developer can be increased, and thereby a clearer resist pattern can be obtained with higher sensitivity.
In addition, when R ¹ in the formulas (I) and (III) is a 2,2,2-trifluoroethyl group, p in the formula (II) and the formula (IV) is 5 and q is 0, R ² It is preferable that at least one of these is a fluorine atom, and other R ² are all hydrogen atoms, one R ² is a fluorine atom, and the other four R ² are all hydrogen atoms. preferable. This is because, in addition to achieving both the clarity of the resist pattern obtained and the sensitivity of the resist film, the effect of preventing pattern collapse can be obtained.

And as a monomer (b) represented by the above-mentioned formula (IV) which can form the monomer unit (B) represented by the above-mentioned formula (II), it is not limited in particular, Examples thereof include α-methylstyrene (AMS) and derivatives thereof such as the following (b-1) to (b-11).

Among these, the monomer unit (B) includes α-methylstyrene (AMS) represented by the above formulas (b-1) to (b-6) having 3 or less fluorine atoms and its A structural unit derived from the monomer (b) which is a derivative is preferable. Further, as described above, when R ^{1 in} formulas (I) and (III) is a 2,2,2-trifluoroethyl group, p in formula (II) and formula (IV) is 5, q Is 0, α-methylstyrene (the above formula (b-1)) in which all R ² are hydrogen atoms, or one R ² is a fluorine atom and the other four R ² are all hydrogen atoms. 4-fluoro-α-methylstyrene (formula (b-2)) or 3-fluoro-α-methylstyrene (formula (b-3)) is preferred. In particular, from the viewpoint of solubility in a developer, the monomer unit (B) is preferably a structural unit derived from the monomer represented by the formula (b-2) or (b-3). .

[Weight average molecular weight (Mw)]
Here, the weight average molecular weight (Mw) of the polymer is preferably 100,000 or less, and preferably 10,000 or more. If the weight average molecular weight (Mw) of the polymer is not more than the above upper limit, when used as a positive resist, the solubility in a developing solution can be increased with a relatively low irradiation amount. Sensitivity when used can be improved moderately. On the other hand, if the weight average molecular weight (Mw) of the polymer is not less than the above lower limit value, it is possible to suppress the solubility of the resist film in the developing solution with an excessively low irradiation amount, and the clarity is excessively lowered. Can be suppressed.

[Number average molecular weight]
The number average molecular weight (Mn) of the polymer is preferably 75,000 or less. If the number average molecular weight (Mn) of the polymer is not more than the above upper limit, the sensitivity when a resist formed using a positive resist composition containing such a polymer is used as a positive resist can be further increased. it can.

[Molecular weight distribution]
The molecular weight distribution (Mw / Mn) of the polymer is preferably 1.15 or more, more preferably 1.20 or more, and preferably 1.70 or less, and 1.65 or less. More preferably. When the molecular weight distribution (Mw / Mn) of the polymer is not less than the above lower limit, the ease of production of the polymer can be enhanced. On the other hand, when the molecular weight distribution (Mw / Mn) of the polymer is not more than the above upper limit, the clarity of the resulting resist pattern can be enhanced when used as a positive resist.

[Surface free energy]
Here, the film (film) produced using the polymer preferably has a surface free energy of 26.0 mJ / m ² or more, and preferably 35.0 mJ / m ² or less. If the surface free energy is within the above range, the solubility of the resist film in the exposed portion of the developer containing a linear alcohol having 4 or less carbon atoms can be further increased, and a clearer resist pattern is more highly sensitive. Can be formed.
The surface free energy is obtained by using the contact angle meter to determine the contact angles of two types of solvents (water and diiodomethane) whose surface tension, polarity term (p) and dispersion force term (d) are known. And can be calculated according to the method of Owens-Wendt (extended Fowkes equation).

[Method for preparing polymer]
And the polymer which has the monomer unit (A) and monomer unit (B) mentioned above polymerizes the monomer composition containing a monomer (a) and a monomer (b), for example. Then, it can be prepared by purifying the polymer obtained arbitrarily.
The composition, molecular weight distribution, weight average molecular weight and number average molecular weight of the polymer can be adjusted by changing the polymerization conditions and the purification conditions. Specifically, for example, the composition of the polymer can be adjusted by changing the content ratio of each monomer in the monomer composition used for polymerization. Further, the weight average molecular weight and the number average molecular weight can be reduced by increasing the polymerization temperature. Furthermore, the weight average molecular weight and the number average molecular weight can be reduced by shortening the polymerization time.

-Polymerization of monomer composition-
Here, as a monomer composition used for the preparation of the polymer, a monomer component including the monomer (a) and the monomer (b), an optionally usable solvent, a polymerization initiator, Mixtures with optional additives can be used. The polymerization of the monomer composition can be performed using a known method. Among these, when a solvent is used, it is preferable to use cyclopentanone or the like as the solvent. Moreover, it is preferable to use radical polymerization initiators, such as azobisisobutyronitrile, as a polymerization initiator. In addition, the weight average molecular weight and number average molecular weight of a polymer can also be adjusted by changing the compounding quantity of a polymerization initiator. Specifically, the weight average molecular weight and the number average molecular weight can be increased by decreasing the blending amount of the polymerization initiator, and conversely, can be decreased by increasing the blending amount of the polymerization initiator. .

  The polymer obtained by polymerizing the monomer composition may be used as a polymer as it is, but is not particularly limited, and a good solvent such as tetrahydrofuran is added to the solution containing the polymer. Thereafter, the solution to which the good solvent is added is dropped into a poor solvent such as methanol to solidify the polymer, and the solution can be purified as follows.

-Purification of polymer-
The purification method used for purifying the obtained polymer is not particularly limited, and known purification methods such as a reprecipitation method and a column chromatography method can be mentioned. Among them, it is preferable to use a reprecipitation method as a purification method.
The purification of the polymer may be repeated a plurality of times.

  The purification of the polymer by the reprecipitation method is performed, for example, by dissolving the obtained polymer in a good solvent such as tetrahydrofuran, and then mixing the obtained solution with a good solvent such as tetrahydrofuran and a poor solvent such as methanol. It is preferable to carry out by dropping into a solvent and precipitating a part of the polymer. In this way, if the polymer solution is purified by dropping the polymer solution into the mixed solvent of the good solvent and the poor solvent, the weight obtained by changing the type and mixing ratio of the good solvent and the poor solvent can be obtained. The molecular weight distribution, weight average molecular weight and number average molecular weight of the coalesced can be easily adjusted. Specifically, for example, the molecular weight of the polymer precipitated in the mixed solvent can be increased as the proportion of the good solvent in the mixed solvent is increased.

  In addition, when purifying a polymer by a reprecipitation method, as the polymer, a polymer precipitated in a mixed solvent of a good solvent and a poor solvent may be used, or a polymer not precipitated in the mixed solvent. (That is, a polymer dissolved in a mixed solvent) may be used. Here, the polymer which did not precipitate in the mixed solvent can be recovered from the mixed solvent by using a known method such as concentration to dryness.

<< Solvent >>
In addition, as a solvent, if it is a solvent which can dissolve the polymer mentioned above, a known solvent can be used. Among them, from the viewpoint of obtaining a positive resist composition having an appropriate viscosity and improving the coating property of the positive resist composition, the solvent includes propylene glycol methyl ether acetate (PGMEA); n-pentyl acetate, N-pentyl esters of organic acids; n-hexyl esters of organic acids, such as n-hexyl acetate. These may be used individually by 1 type and may be used in mixture of multiple types.

(Process (B): Exposure process)
In the exposure step, the resist film formed in the resist film formation step is irradiated with ionizing radiation or light to draw a desired pattern. For irradiation with ionizing radiation or light, a known drawing apparatus such as an electron beam drawing apparatus or a laser drawing apparatus can be used.

(Process (C): Development process)
In the development process, the resist film exposed in the exposure process is brought into contact with the developer to develop the resist film, thereby forming a resist pattern on the workpiece.
Here, the method of bringing the resist film into contact with the developer is not particularly limited, and a known technique such as immersion of the resist film in the developer or application of the developer to the resist film can be used. .

<Developer>
The developer needs to contain a linear alcohol having 4 or less carbon atoms, and 90% by volume or more of the whole developer is preferably a linear alcohol having 4 or less carbon atoms, and the developer is inevitable. A straight-chain alcohol having 4 or less carbon atoms containing only impurities is particularly preferred. Examples of the linear alcohol having 4 or less carbon atoms include methanol, ethanol, 1-propanol, and 1-butanol, and methanol, ethanol, or 1-propanol is preferable, and methanol or ethanol is more preferable. As the developer, two or more kinds of solutions can be mixed and used, but one kind of solution is preferably used alone. When one type of solution is used as the developer, compared to the case where a plurality of developers are mixed and used, processing such as mixing and filtration is unnecessary, and a resist pattern can be formed efficiently. Furthermore, if one type of solution is used as the developer, the solution has a single boiling point compared to the case of the mixed solution, so that the properties of the developer are stabilized and the quality of the resist pattern obtained varies. It is possible to suppress the occurrence. Furthermore, if one type of solution is used as the developer, the developer can be easily recovered.

<Development conditions>
The development conditions can be appropriately set so as to obtain a resist pattern having a desired quality. The temperature of the developer described above can be, for example, 21 ° C. or more and 25 ° C. or less. Further, the development time is preferably 1 minute or more and 4 minutes or less, and more preferably 2 minutes or more and 3 minutes or less. By setting the development time within such a range, the resist pattern can be formed efficiently and the clarity of the resulting resist pattern can be further improved.

In addition, the resist pattern formation method of this invention may include the process of performing the rinse process using a rinse liquid after a image development process. As the rinsing liquid, it is preferable to select a rinsing liquid that is less likely to dissolve the unexposed resist than the developing solution to be used and is easily mixed with the developing solution. For example, as the rinse liquid, a fluorocarbon solvent such as CF ₃ CFHCFHCF ₂ CF ₃ which is one of fluorine-based solvents can be used.

EXAMPLES Hereinafter, although this invention is demonstrated concretely based on an Example, this invention is not limited to these Examples.
In Examples and Comparative Examples, the weight average molecular weight, number average molecular weight and molecular weight distribution of the polymer, surface free energy of the film (film) produced using the polymer, Eth (sensitivity), and γ value (clarity) The remaining film ratio (Examples 1, 2, 5 to 9) was measured and evaluated by the following methods.

<Weight average molecular weight, number average molecular weight and molecular weight distribution>
The weight average molecular weight (Mw) and the number average molecular weight (Mn) of the polymers obtained in Examples and Comparative Examples were measured using gel permeation chromatography, and the molecular weight distribution (Mw / Mn) was calculated. Specifically, gel permeation chromatograph (manufactured by Tosoh Corporation, HLC-8220) is used, tetrahydrofuran is used as a developing solvent, and the weight average molecular weight (Mw) and number average molecular weight (Mn) of the polymer are converted into standard polystyrene values. As sought. And molecular weight distribution (Mw / Mn) was computed.

<Surface free energy>
In the evaluation of the γ value described later, the surface tension, the polar term (p) and the dispersion force of the films (membranes) produced in Examples and Comparative Examples were measured using a contact angle meter (manufactured by Kyowa Interface Science, Drop Master 700). The contact angle of two types of solvents (water and diiodomethane) whose term (d) is known is measured under the following conditions, the surface free energy is evaluated by the method of Owens-Wendt (extended Fowkes equation), and the surface of the polymer Free energy was calculated. The measurement conditions for contact angle measurement were as follows.
<< Measurement conditions for contact angle measurement >>
Needle: Metal needle 22G (water), Teflon (registered trademark) coating 22G (diiodomethane)
Standby time: 1000ms
Liquid volume: 1.8 μL
Recognized liquid: water 50dat, diiodomethane 100dat
Temperature: 23 ° C

γ値の値が大きいほど、感度曲線の傾きが大きく、明瞭性の高いパターンを良好に形成し得ることを示す。
＜Ｅｔｈ（感度）＞
「γ値（明瞭性）」の評価方法と同様にしてシリコンウェハ上にレジスト膜を形成した。得られたレジスト膜の初期厚みＴ_０を光学式膜厚計（大日本スクリーン製、ラムダエース）で測定した。また、γ値の算出の際に得られた直線（感度曲線の傾きの近似線）の残膜率が０となる際の、電子線の総照射量Ｅｔｈ（μＣ／ｃｍ^２）を求めた。なお、Ｅｔｈの値が小さいほど、レジスト膜の感度が高く、レジストパターンの形成効率が高いことを意味する。 Example 1
As a polymerization initiator, 3.0 g of α-chloroacrylic acid 2,2,2-trifluoroethyl (ACATFE) as monomer (a) and 4.40 g of α-methylstyrene as monomer (b) A monomer composition containing 0.006975 g of azobisisobutyronitrile and 1.85 g of cyclopentanone as a solvent was placed in a glass container, and the glass container was sealed and purged with nitrogen, and was heated at 78 ° C. in a nitrogen atmosphere. The mixture was stirred for 6 hours in a constant temperature bath. Then, after returning to room temperature and releasing the inside of the glass container to the atmosphere, 10 g of tetrahydrofuran (THF) was added to the resulting solution. And the solution which added THF was dripped in 300 g of methanol, and the polymer was deposited. Thereafter, the solution containing the precipitated polymer was filtered through a Kiriyama funnel to obtain a white coagulated product (polymer). This polymer was directly used as a polymer. The weight average molecular weight (Mw), number average molecular weight (Mn), and molecular weight distribution (Mw / Mn) of the obtained polymer were measured. In addition, the surface free energy of a film (film) produced using the obtained polymer was measured. The results are shown in Table 1. Further, the obtained polymer contained 50 mol% of α-chloroacrylic acid 2,2,2-trifluoroethyl units and 50 mol% of α-methylstyrene units.
<Preparation of positive resist composition>
The obtained polymer was dissolved in propylene glycol monomethyl ether acetate as a solvent to prepare a resist solution (positive resist composition) having a polymer concentration of 11% by mass. And γ value (clarity) and Eth (sensitivity) were evaluated according to the following. The results are shown in Table 1.
<Γ value (clarity)>
Using a spin coater (manufactured by Mikasa, MS-A150), the positive resist composition was applied on a silicon wafer having a diameter of 4 inches to a thickness of 500 nm. The applied positive resist composition was heated on a hot plate at a temperature of 180 ° C. for 3 minutes to form a resist film on the silicon wafer (resist film forming step). Then, using an electron beam drawing apparatus (ELS-S50, manufactured by Elionix Co., Ltd.), a plurality of patterns (dimensions 500 μm × 500 μm) with different electron beam irradiation amounts are drawn on the resist film (exposure process) as a developer. Then, development processing was performed for 1 minute at a temperature of 23 ° C. using methanol (carbon number: 1) (development process). Thereafter, rinsing was performed for 10 seconds with a fluorocarbon solvent (Mitsui DuPont Fluorochemical Co., Ltd., Bertrell XF (registered trademark), CF ₃ CFHCHFCF ₂ CF ₃ ). The irradiation amount of the electron beam was varied in the range of 4μC / cm ² of 200μC / cm ² by 4μC / cm ^2. Next, the thickness of the resist film in the drawn portion is measured with an optical film thickness meter (Dainippon Screen, Lambda Ace), the common logarithm of the total irradiation amount of the electron beam, and the remaining film ratio of the resist film after development (= (Film thickness of developed resist film / film thickness of resist film formed on a silicon wafer)) was created, and a sensitivity curve (horizontal axis: total electron beam) was obtained. With respect to the common logarithm of the irradiation amount, the vertical axis: the remaining film ratio of the resist film (0 ≦ remaining film ratio ≦ 1.00)), the γ value was determined using the following formula, where E ₀ Fits the sensitivity curve to a quadratic function in the range of the residual film ratio of 0.20 to 0.80, and the residual function is obtained with respect to the obtained quadratic function (function of the residual film ratio and the common logarithm of the total irradiation amount) a total dose of log obtained when substituting film ratio 0. Moreover, E ₁ is the residual film rate on the resulting quadratic function A straight line (approximate line of the slope of the sensitivity curve) connecting the point and the remaining film rate of 0.50 is created, and for the obtained straight line (a function of the remaining film rate and the common logarithm of the total irradiation amount) This is the logarithm of the total irradiation amount obtained when substituting the remaining film ratio of 1.00, and the following equation represents the slope of the straight line between the remaining film ratios of 0 and 1.00.

The larger the γ value, the larger the slope of the sensitivity curve, indicating that a clear pattern can be formed better.
<Eth (sensitivity)>
A resist film was formed on a silicon wafer in the same manner as the “γ value (clarity)” evaluation method. The initial thickness T ₀ of the obtained resist film was measured with an optical film thickness meter (manufactured by Dainippon Screen, Lambda Ace). Further, the total electron beam dose Eth (μC / cm ² ) when the remaining film rate of the straight line (approximate line of the slope of the sensitivity curve) obtained at the time of calculating the γ value was 0 was obtained. Note that the smaller the value of Eth, the higher the sensitivity of the resist film and the higher the resist pattern formation efficiency.

(Example 2)
In the development step, a resist pattern was formed and evaluated in the same manner as in Example 1, except that ethanol (carbon number: 2) was used instead of methanol as a developer. The results are shown in Table 1.

(Example 3)
In the development process, a resist pattern was formed and evaluated in the same manner as in Example 1 except that 1-propanol (carbon number: 3, linear) was used instead of methanol as the developer. . The results are shown in Table 1.

Example 4
In the development step, a resist pattern was formed and evaluated in the same manner as in Example 1 except that 1-butanol (carbon number: 4, linear) was used instead of methanol as the developer. . The results are shown in Table 1.

(Comparative Example 1)
A positive resist composition was prepared using the polymer prepared as follows, and a resist film forming step and an exposure step similar to those in Example 1 were performed using the positive resist composition. In the development step, amyl acetate (manufactured by Zeon Corporation, ZED-N50, including impurities inevitably mixed in production) was used as a developer. Each evaluation was performed in the same manner as in Example 1. The results are shown in Table 1.
<Preparation of polymer>
Α-methyl chloroacrylate (ACAM) 3.0 g and α-methylstyrene (AMS) 6.88 g as monomers, 2.47 g of cyclopentanone as a solvent, and azobisisobutyrate as a polymerization initiator A monomer composition containing 0.01091 g of nitrile was placed in a glass container, the glass container was sealed and purged with nitrogen, and stirred in a thermostat at 78 ° C. for 6.5 hours under a nitrogen atmosphere. Then, after returning to room temperature and releasing the inside of the glass container to the atmosphere, 30 g of tetrahydrofuran (THF) was added to the resulting solution. And the solution which added THF was dripped in 300 g of methanol, and the polymer was deposited. Thereafter, the solution containing the precipitated polymer was filtered through a Kiriyama funnel to obtain a white coagulated product (polymer). This polymer was directly used as a polymer. Various measurements were performed on the obtained polymer. Moreover, the obtained polymer contained 50 mol% of α-methylstyrene units and α-methyl chloroacrylate units.
<Preparation of positive resist composition>
The obtained polymer was dissolved in anisole as a solvent to prepare a resist solution (positive resist composition) having a polymer concentration of 11% by mass.

(Comparative Example 2)
Comparative Example 1 except that in the development step, a fluorocarbon solvent (Mitsui DuPont Fluorochemical Co., Ltd., Vertrel XF (registered trademark), CF ₃ CFHCCFHCF ₂ CF ₃ ) was used as a developer instead of amyl acetate. Similarly, a resist pattern was formed and each evaluation was performed. The results are shown in Table 1.

(Comparative Examples 3-6)
A resist pattern was formed in the same manner as in Comparative Example 1 except that the developer used in the development step was changed as shown in Table 1, and each evaluation was performed. The results are shown in Table 1.

From Table 1, a resist film made of a polymer containing predetermined monomer units (A) and (B) having a total number of fluorine atoms of 3 is a developer containing a linear alcohol having 4 or less carbon atoms. It can be seen that in the examples developed using these, the value of Eth is sufficiently low and the γ value is sufficiently high. In other words, according to the resist pattern forming method according to the example, it can be seen that a resist pattern with high clarity was obtained with high sensitivity.
On the other hand, in Comparative Examples 1 and 2 in which a resist film made of a polymer containing no fluorine atom and a developer containing no linear alcohol having 4 or less carbon atoms is used, the value of Eth is sufficiently lowered, It can be seen that it was not possible to achieve a sufficiently high γ value. In other words, it can be seen that Comparative Examples 1 and 2 could not achieve both high clarity and good sensitivity. Furthermore, in Comparative Examples 3 to 6 in which a resist film made of a polymer containing no fluorine atom was developed with a developer containing a linear alcohol having 4 or less carbon atoms, the resist film after the exposure process was developed. When trying to develop in the process, the exposed portion in the resist film was not sufficiently dissolved in the developer. For this reason, the resist film could not be developed and a resist pattern could not be formed.

  Next, Examples 5 to 9 show the results of performing the resist pattern forming method with different development times. About these Examples 5-9 and Example 1 and 2 mentioned above, the remaining film rate was also evaluated according to the following.

<Determination of remaining film ratio>
Was used when the sensitivity curve creation, the dose of the electron beam having different portions 4μC / cm ² in a range of 4μC / cm ² of 200μC / cm ² (i.e., 4,8,12,16 ··· 196,200μC / cm ² ) was divided by the Eth determined as described above.
If there is an electron beam irradiation amount at which the obtained value (electron beam irradiation amount / Eth) is 0.95, the remaining film rate at the electron beam irradiation amount is expressed as a residual film rate (0.95 Eth). did.
When there is no electron beam irradiation amount at which the obtained value (electron beam irradiation amount / Eth) is 0.95, among these values, two values closest to 0.95 are specified. The electron beam doses at the two points were P (μC / cm ² ) and P + 4 (μC / cm ² ), respectively. And the remaining film rate (0.95 Eth) was determined by the following formula. The results are shown in Table 1.
Residual film ratio (0.95 Eth) = S − {(ST) / (V−U)} × (0.95−U)
In this formula,
S represents the remaining film rate at the electron beam irradiation dose P;
T represents the remaining film rate at the electron beam irradiation dose P + 4,
U represents P / Eth and
V represents (P + 4) / Eth.
Similarly, the remaining film ratio (0.97 Eth) at the electron beam irradiation amount at which the obtained value (electron beam irradiation amount / Eth) becomes 0.97, and the obtained value (electron beam irradiation amount / Eth). The residual film ratio (0.93Eth) was determined at the electron beam irradiation dose with which Eth) was 0.93.
The higher the remaining film rate at 0.97Eth, 0.95Eth, and 0.93Eth as calculated here, the lower the irradiation amount than the total irradiation amount of the electron beam that can make the remaining film rate substantially 0, This means that the resist film is difficult to dissolve in the developer. In other words, the solubility of the resist film in the developing solution is low in the non-exposed area which is the peripheral area of the resist pattern. Therefore, the fact that the remaining film ratio calculated as described above is high means that the boundary between the area that should be dissolved on the resist film to form the pattern and the area that should remain without being dissolved is clear. Means high clarity.

(Examples 5-6)
A resist pattern was formed in the same manner as in Example 1 except that the development time in the development process was changed to 2 minutes (Example 5) and 3 minutes (Example 6), respectively. And Eth and (gamma) value were evaluated similarly to Example 1, and the remaining film rate was evaluated according to the above. The results are shown in Table 2.

(Examples 7 to 9)
A resist pattern was formed in the same manner as in Example 1 except that the development time in the development process was 2 minutes (Example 7), 3 minutes (Example 8), and 4 minutes (Example 9). And Eth and (gamma) value were evaluated similarly to Example 1, and the remaining film rate was evaluated according to the above. The results are shown in Table 2.

  From Table 2, when the development time is 1 minute or more and 4 minutes or less, the value of Eth is sufficiently low, and the values of the γ value and the remaining film ratio are sufficiently high. In particular, the development time is 2 minutes or more and 3 minutes or less. It can be seen that when the time is less than or equal to the minute, the value of Eth is sufficiently lower, and the values of the γ value and the remaining film ratio are much higher. In other words, in the resist pattern forming method according to the example, it can be seen that a resist pattern with high clarity was obtained with high sensitivity by setting the development time within the above-mentioned preferable range.

  According to the resist pattern forming method of the present invention, a clear resist pattern can be formed with high sensitivity.

Claims (6)

A step (A) of forming a resist film using a positive resist composition containing a polymer and a solvent, a step (B) of exposing the resist film, and a step of developing the exposed resist film (C And a resist pattern forming method comprising:
The polymer is
The following general formula (I):

[In the formula (I), R ¹ represents an unsubstituted organic group or an organic group substituted with a fluorine atom (provided that the number of fluorine atoms is 1 or more and 4 or less). ]
A monomer unit (A) represented by:
The following general formula (II):

[In Formula (II), R ² is a hydrogen atom, a fluorine atom, an unsubstituted alkyl group or an alkyl group substituted with a fluorine atom, and R ³ is a hydrogen atom, an unsubstituted alkyl group or a fluorine atom. It is a substituted alkyl group, p and q are integers of 0 or more and 5 or less, and p + q = 5. ]
And the total number of fluorine atoms contained in R ^{1 to} R ³ is 1 or more, and the monomer unit (B) represented by
The resist pattern forming method, wherein the development is performed using a developer containing a linear alcohol having 4 or less carbon atoms. The resist pattern forming method according to claim 1, wherein the total number of fluorine atoms contained in R ^{1 to} R ³ is 4 or less. The surface free energy of the polymer is 26 mJ / ^{m 2} or more 35 mJ / ^{m 2} or less, a resist pattern forming method according to claim 1 or 2.   The resist pattern formation method in any one of Claims 1-3 whose said linear alcohol is at least 1 sort (s) selected from the group which consists of methanol, ethanol, and 1-propanol. The resist according to claim 1, wherein R ¹ is a 2,2,2-trifluoroethyl group, p is 5, and q is 0, and R ² is a hydrogen atom or a fluorine atom. Pattern formation method.   The method for forming a resist pattern according to claim 1, wherein the development time in the step (C) is from 1 minute to 4 minutes.