JP6844549B2 - Method of forming resist pattern and method of determining development conditions - Google Patents

Description

The present invention relates to a method for forming a resist pattern and a method for determining development conditions.

Conventionally, in fields such as semiconductor manufacturing, ionizing radiation such as electron beams and short-wavelength light such as ultraviolet rays (hereinafter, ionizing radiation and short-wavelength light may be collectively referred to as "ionizing radiation and the like"). A polymer in which the main chain is cleaved by irradiation and the solubility in a developing solution is increased is used as a main chain cleaving type positive type resist.

Then, for example, in Patent Document 1, methyl α-methylstyrene / α-chloroacrylate containing α-methylstyrene unit and methyl α-chloroacrylate unit as a highly sensitive main chain cleavage type positive resist. A positive resist made of a copolymer is disclosed.

Special Fair 8-3636 Gazette

Here, in the main chain cutting type positive resist, the efficiency at the time of patterning is improved and the obtained resist pattern is clear, that is, the portion where the resist film remains (residual film) and the portion. It is required that the boundary with the melted part is clear. Specifically, from the viewpoint of enabling the formation of a more clear resist pattern, the resist does not dissolve in the developing solution unless the irradiation amount reaches a specific amount, and when the irradiation amount reaches a specific amount, the resist is promptly dissolved. It shows the property that the main chain is cut and dissolved in the developer, that is, the magnitude of the inclination of the sensitivity curve showing the relationship between the common logarithm of the irradiation amount such as ionizing radiation and the residual film thickness of the resist after development. It is required to increase the γ value. Further, due to the demand for high integration, it is also required to make the resist pattern finer to improve the resolution. For this purpose, the resist is required to be less susceptible to irradiation noise such as blurring of the irradiation region, which may occur when the obtained pattern is irradiated with ionizing radiation or the like.

However, for example, in the formation of a resist pattern using a main chain cutting type positive resist as described in Patent Document 1, the clarity of the obtained pattern can be obtained by changing the type of developer and the development time. Could not be raised sufficiently. Further, although the positive type resist as described in Patent Document 1 has good patterning efficiency, the resist dissolves in the developing solution even when the irradiation amount is relatively low, and the obtained pattern is formed by ionizing radiation. The resolution of the pattern could not be sufficiently increased because the influence of noise that could occur during the irradiation of the pattern was reflected. Therefore, in the formation of a resist pattern using a main chain cutting type positive resist, it has been required to develop a method capable of forming a resist pattern having high resolution and clarity.

The present inventor has conducted diligent studies for the purpose of forming a resist pattern having high resolution and clarity. Then, the present inventor appropriately determines the properties of the α-methylstyrene / α-methylchloroacrylate copolymer and the type of developer in the formation of a resist pattern using a main-chain cut-type positive resist. We have found that there are development conditions for polymers and resist patterns that can be used as positive resists that can improve the clarity and resolution of the obtained pattern while maintaining or improving the γ value by combining them. The present invention has been completed.

That is, the present invention aims to advantageously solve the above problems, and the resist pattern forming method of the present invention contains a weight containing α-methylstyrene units and α-methylchloroacrylate units. A step of forming a resist film using a positive resist composition containing a coalescence and a solvent, a step of exposing the resist film, and a step of developing the exposed resist film are included, and the molecular weight of the polymer exceeds 100,000. Is characterized in that the ratio of the components of is 13% or less, and the development is carried out under the condition that the residual film ratio is 0.250 or more at an irradiation amount of 0.95 Eth. In the formation of a resist pattern using a positive resist composed of a polymer containing α-methylstyrene unit and methyl α-chloroacrylate unit and having a molecular weight of more than 100,000 and a proportion of 13% or less, the above-mentioned conditions If the resist pattern is developed with, a resist pattern having high resolution and clarity can be formed.
In the present invention, the proportion of the component whose molecular weight is in the predetermined range uses the chromatogram obtained by gel permeation chromatography, and the molecular weight in the chromatogram is in the predetermined range with respect to the total area (A) of the peaks in the chromatogram. It can be obtained by calculating the ratio (= (X / A) × 100%) of the total (X) of the peak areas of the components.
Further, in the present invention, "Eth" is an index indicating the sensitivity of the resist, and the residual film ratio of the resist dissolved in the developing solution by irradiating the resist with ionizing radiation or the like can be made substantially 0. It is a guideline for the total irradiation amount. The "residual film rate when the irradiation amount is 0.95 Eth" is the irradiation amount obtained by multiplying Eth by 0.95, that is, the residual film rate of the resist film at an irradiation amount of 95% of Eth (0 ≤ residual film rate ≤). It means 1.00). Then, "Eth" and "residual film ratio at an irradiation amount of 0.95Eth" are both calculated by using the method described in the examples of the present specification.

Further, in the resist pattern forming method of the present invention, the proportion of components having a molecular weight of less than 10,000 is preferably more than 0% and 1% or less. This is because the resolution and clarity of the resist pattern can be further improved by using the positive resist composition containing such a polymer.

Further, in the resist pattern forming method of the present invention, it is preferable that the proportion of the component having a molecular weight of more than 40,000 is 75% or more and 90% or less. This is because the resolution and clarity of the resist pattern can be further improved by using the positive resist composition containing such a polymer.

Further, in the resist pattern forming method of the present invention, it is preferable to carry out the development using a developing solution containing 90% by mass or more of hexyl acetate. This is because if development is carried out using such a developing solution, the γ value can be further increased and the clarity of the resist pattern can be further improved. Moreover, the resolution of the resist pattern can be further improved.

The present invention also aims to advantageously solve the above problems, and the method for determining the development conditions of the present invention is a polymer containing an α-methylstyrene unit and an α-methylchloroacrylate unit. A method for determining development conditions in forming a resist pattern using a positive resist composition containing coalescence, wherein the proportion of components having a molecular weight of more than 100,000 of the polymer is 13% or less, and a sensitivity curve is created. Therefore, it is characterized in that a condition is obtained in which the residual film ratio is 0.250 or more when the irradiation amount is 0.95 Eth. If development is performed under the condition that the residual film ratio is 0.250 or more at an irradiation amount of 0.95 Eth, a resist pattern having high resolution and clarity can be formed.

According to the resist pattern forming method of the present invention, a resist pattern having high resolution and clarity can be formed.
Further, according to the method for determining the developing conditions of the present invention, it is possible to determine the developing conditions capable of forming a resist pattern having high resolution and clarity.

Hereinafter, embodiments of the present invention will be described in detail.
Here, the resist pattern forming method of the present invention uses a main chain cutting type positive resist in which the main chain is cut to reduce the molecular weight by irradiation with ionizing radiation such as an electron beam or short wavelength light such as ultraviolet rays. This is a method for forming a resist pattern, and can be suitably used when manufacturing a printed circuit board such as a build-up substrate. Further, the method for determining the developing conditions of the present invention can be used when determining the developing conditions in the resist pattern forming method of the present invention.

(Method of forming resist pattern)
In the resist pattern forming method of the present invention, a step of forming a resist film (film forming step), a step of exposing the resist film formed in the film forming step (exposure step), and a step of developing the resist film exposed in the exposure step are developed. The process (development process) is included. The resist pattern forming method of the present invention comprises a polymer containing α-methylstyrene units and methyl α-chloroacrylate units in a film forming step and having a molecular weight of more than 100,000 and a proportion of 13% or less. A resist film is formed using the positive resist composition containing the mixture, and the developing step is carried out under the condition that the residual film ratio is 0.250 or more at an irradiation amount of 0.95 Eth.

Since the above-mentioned polymer contains a structural unit (methyl unit of α-chloroacrylate) derived from methyl α-chloroacrylate having a chloro group (-Cl) at the α-position, it contains ionizing radiation and the like (for example, electron). When irradiated with a line, KrF laser, ArF laser, EUV (Extreme ultraviolet) laser, etc.), the main chain is easily cleaved to reduce the molecular weight. Then, in the resist pattern forming method of the present invention, the residual film ratio at an irradiation amount of 95% of Eth is as high as 0.250 or more. This means that the dissolution of the resist is suppressed at an irradiation amount almost equal to that of Eth. Therefore, according to the method for forming a resist pattern of the present invention, the clarity of the obtained pattern can be sufficiently improved by sufficiently increasing the γ value. In addition, due to such a high residual film ratio, the influence of irradiation noise in the non-irradiated region can be further reduced, and the resolution of the obtained resist pattern can be sufficiently increased. Therefore, by using the pattern forming method of the present invention, a resist pattern having excellent resolution and clarity can be formed.

<Film formation process>
In the film forming step, a positive resist composition is applied onto a work piece to be processed using a resist pattern such as a substrate, and the applied positive resist composition is dried to form a resist film. ..
Here, the substrate is not particularly limited, and a semiconductor substrate, a mask blank, a substrate having a copper foil provided on an insulating layer and an insulating layer used for manufacturing a printed circuit board, or the like is used. Can be done. 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. Here, in the film forming step, the film thickness of the resist film is preferably 1000 nm or less, more preferably 500 nm or less, and particularly preferably 200 nm or less. This is because if a resist film having a film thickness within the above range is used in the resist pattern forming method of the present invention, a resist pattern having high clarity and high resolution can be formed.
Then, in the pattern forming method of the present invention, the following positive resist composition is used.

[Positive resist composition]
The positive resist composition is a polymer (α-methylstyrene / α-) containing α-methylstyrene units and α-methylchloroacrylate units and having a molecular weight of more than 100,000 in a proportion of 13% or less. It contains a methyl chloroacrylate copolymer) and a solvent, and optionally further contains known additives that can be incorporated into the resist composition.

[[Polymer]]
-Α-Methylstyrene unit-
Here, the α-methylstyrene unit is a structural unit derived from α-methylstyrene. Since the polymer has α-methylstyrene units, it exhibits excellent dry etching resistance due to the protective stability of the benzene ring when used as a positive resist.
The polymer preferably contains α-methylstyrene units in a proportion of 30 mol% or more and 70 mol% or less.

-Α-Methyl chloroacrylate unit-
The methyl α-chloroacrylate unit is a structural unit derived from methyl α-chloroacrylate. Since the polymer has a methyl unit of α-chloroacrylate, the chlorine atom is desorbed when irradiated with ionizing radiation or the like, and the main chain is easily cleaved by the β cleavage reaction. Therefore, the positive resist made of this polymer exhibits high sensitivity.
The polymer preferably contains methyl α-chloroacrylate in a proportion of 30 mol% or more and 70 mol% or less.

-Weight average molecular weight-
Here, the weight average molecular weight (Mw) of the polymer is preferably 57,000 or more, and preferably 90,000 or less. When the weight average molecular weight (Mw) of the polymer is 57,000 or more, the residual film in the region not irradiated with ionizing radiation or the like used for patterning (hereinafter, also referred to as non-irradiated region) when used as a positive resist. The rate can be increased, the γ value can be further improved, and the clarity of the obtained resist pattern can be further enhanced. Further, when the weight average molecular weight (Mw) of the polymer is 57,000 or more, the resist is not easily affected by irradiation noise when used as a positive resist, so that the obtained resist pattern can have a high resolution. Further, when the weight average molecular weight (Mw) of the polymer is 90,000 or less, the ease of producing the polymer can be improved. When the weight average molecular weight (Mw) of the polymer is within the above range, the γ value when used as a positive resist can be further increased, and the clarity of the obtained pattern can be further enhanced.

-Molecular weight distribution-
The molecular weight distribution (Mw / Mn) of the polymer is preferably less than 1.40, more preferably 1.35 or less, and preferably 1.20 or more. When the molecular weight distribution (Mw / Mn) of the polymer is 1.40 or more, the γ value when used as a positive resist cannot be sufficiently increased. Further, when the molecular weight distribution (Mw / Mn) of the polymer is 1.20 or more, the ease of producing the polymer can be improved. In the present invention, the "molecular weight distribution (Mw / Mn)" refers to the ratio of the weight average molecular weight (Mw) to the number average molecular weight (Mn). Then, in the present invention, the "number average molecular weight (Mn)" and the "weight average molecular weight (Mw)" can be measured by using gel permeation chromatography.

-Percentage of components with a molecular weight over 100,000-
The polymer needs to have a component having a molecular weight of more than 100,000 in an amount of 13% or less, preferably 12% or less, and preferably 10% or more. When the proportion of the component having a molecular weight of more than 100,000 is not more than the above upper limit value, the polymer can be easily produced, and a resist formed by using a positive resist composition containing such a polymer is used as a positive resist. The γ value at the time of use can be increased, and the clarity of the obtained resist pattern can be further enhanced. Further, when the proportion of the component having a molecular weight of more than 100,000 is equal to or higher than the above lower limit value, the residual film ratio in the non-irradiated region can be increased and the top can be suppressed from collapsing when used as a positive resist. The clarity of the resist pattern to be obtained can be further enhanced. In the present specification, the “top” refers to a portion on the resist on the non-irradiated region side that is in contact with the boundary between the non-irradiated region and the irradiated region and that forms an edge of the resist pattern.

-Percentage of components with a molecular weight over 80,000-
Further, the proportion of the component having a molecular weight of more than 80,000 is preferably 20% or less, and preferably 15% or more in the polymer. When the proportion of the component having a molecular weight of more than 80,000 is not more than the above upper limit value, the γ value when used as a positive resist can be further increased, and the clarity of the obtained resist pattern can be further enhanced. When the proportion of components having a molecular weight of more than 80,000 is equal to or higher than the above lower limit, the residual film ratio in the non-irradiated region when a resist formed by using a positive resist composition containing such a polymer is used as a positive resist. It is possible to suppress the collapse of the top, and it is possible to further enhance the clarity of the obtained resist pattern.

-Percentage of components with a molecular weight over 50,000-
Further, the polymer has a component having a molecular weight of more than 50,000, preferably 45% or more, more preferably 50% or more, preferably 80% or less, and 55% or less. Is more preferable. When the proportion of the component having a molecular weight of more than 50,000 is within the above range, the resolution and clarity of the pattern when the resist formed by using the positive resist composition containing such a polymer is used as the positive resist is further enhanced. Can be improved.

-Percentage of components with a molecular weight over 40,000-
Further, the polymer has a component having a molecular weight of more than 40,000, preferably 75% or more, more preferably 80% or more, preferably 90% or less, and 85% or less. Is more preferable. When the proportion of the component having a molecular weight of more than 40,000 is within the above range, the resolution and clarity of the pattern when the resist formed by using the positive resist composition containing such a polymer is used as the positive resist is further enhanced. Can be improved.

-Percentage of components with a molecular weight of less than 10,000-
The proportion of the component having a molecular weight of less than 10,000 is preferably more than 0% and 1% or less, more preferably 0.5% or less, and further preferably 0.1% or less. When the proportion of components having a molecular weight of less than 10,000 is more than 1%, when a resist formed by using a positive resist composition containing such a polymer is used as a positive resist, the amount of irradiation such as ionizing radiation is small. Even so, the film is excessively thinned, and the resolution and clarity of the obtained pattern cannot be sufficiently improved.

[[Method for preparing polymer]]
Then, the polymer having the above-mentioned properties is obtained by polymerizing, for example, a monomer composition containing α-methylstyrene and methyl α-chloroacrylate, and then purifying the obtained polymer as necessary. Can be prepared by.
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 weight average molecular weight and the number average molecular weight can be reduced by increasing the polymerization temperature. Further, the weight average molecular weight and the number average molecular weight can be reduced by shortening the polymerization time.

-Polymerization of monomeric composition-
Here, as the monomer composition used for preparing the polymer, a monomer containing α-methylstyrene, a monomer containing methyl α-chloroacrylate, a solvent, a polymerization initiator, and optionally. A mixture with the added additive can be used. Then, the polymerization of the monomer composition can be carried out by using a known method. Among them, it is preferable to use cyclopentanone or the like as the solvent, and it is preferable to use a radical polymerization initiator such as azobisisobutyronitrile as the polymerization initiator.

The composition of the polymer can be adjusted by changing the content ratio of each monomer in the monomer composition used for the polymerization.

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

-Purification of polymer-
The purification method used when purifying the obtained polymer to obtain a polymer is not particularly limited, and a known purification method such as a reprecipitation method or a column chromatography method can be used. Above all, it is preferable to use the reprecipitation method as the purification method.
The purification of the polymer may be repeated a plurality of times.

Then, in the purification of the polymer by the reprecipitation method, for example, the obtained polymer is dissolved in a good solvent such as tetrahydrofuran, and then the obtained solution is mixed 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 dropped into the mixed solvent of the good solvent and the poor solvent to purify the polymer, the weight obtained by changing the types and mixing ratios 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 coalescence can be easily adjusted. Specifically, for example, the higher the proportion of the good solvent in the mixed solvent, the larger the molecular weight of the polymer precipitated in the mixed solvent.

When the polymer is purified by the reprecipitation method, 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 mixed solvent). A polymer dissolved in the solvent) may be used. Here, the polymer that did not precipitate in the mixed solvent can be recovered from the mixed solvent by using a known method such as concentrated dryness.

[[solvent]]
As the solvent, a known solvent can be used as long as it is a solvent capable of dissolving the above-mentioned polymer. Above all, from the viewpoint of obtaining a positive resist composition having an appropriate viscosity and improving the coatability of the positive resist composition, it is preferable to use anisole as the solvent.

<Exposure process>
In the exposure step, the resist film formed in the film forming step is irradiated with ionizing radiation or light to draw a desired pattern.
A known drawing device such as an electron beam drawing device or a laser drawing device can be used for ionizing radiation or light irradiation.

<Development process>
In the developing step, the resist film exposed in the exposure step and the developing solution are brought into contact with each other to develop the resist film, and a resist pattern is formed on the workpiece.
Here, the method of bringing the resist film into contact with the developing solution is not particularly limited, and known methods such as immersing the resist film in the developing solution and applying the developing solution to the resist film can be used. ..
In the developing step of the present invention, it is necessary to satisfy "a condition that the residual film ratio is 0.250 or more when the irradiation amount is 0.95 Eth" (hereinafter, also referred to as condition (i)).

[Method of determining development conditions]
The development conditions in which the irradiation amount satisfies the above condition (i) can be determined by using the method for determining the development conditions of the present invention, which can specify the type of developer, the development time, and the like.

Specifically, first, in forming a resist pattern using a positive resist composition containing an α-methylstyrene / α-methylchloroacrylate copolymer, conditions such as the type of developer and the development time are tentatively set. The sensitivity curve under the provisional development conditions is set and created by using the method described in the examples of the present specification. Next, the value of Eth in this sensitivity curve and the value of the residual film ratio at an irradiation dose of 0.95 Eth are derived using the method also described in the examples of the present specification. Then, as long as the above condition (i) is satisfied, the provisional development condition can be a development condition that can be adopted in the resist pattern forming method of the present invention. If the provisional development condition does not satisfy the above condition (i), the provisional development condition is set again and a sensitivity curve is created to derive a value of the residual film ratio when the irradiation amount is 0.95Eth. In setting the conditions again, for example, if a developing solution having a lower dissolving ability in the resist is used, the residual film ratio at an irradiation amount of 0.95 Eth can be increased. Further, if the developing time is shortened, the residual film ratio at an irradiation amount of 0.95 Eth can be improved. By repeating this operation, it is possible to determine the developing conditions capable of forming a resist pattern having high resolution and clarity when a positive resist composition containing a specific polymer is used.

[[Eth]]
Then, in determining the developing conditions, it is preferable to adopt the developing conditions in which Eth is 70 μC / cm ² or more and 130 μC / cm ^{2 or less.} By adopting the development conditions in which Eth is within the above range, the influence of irradiation noise in the non-irradiation region can be reduced, and the resolution of the obtained resist pattern can be sufficiently increased.

[[Remaining film rate when the irradiation dose is 0.95Eth]]
Further, in determining the developing conditions, it is necessary to adopt the developing conditions in which the residual film ratio at an irradiation amount of 0.95 Eth is 0.250 or more as described above. The residual film ratio at an irradiation amount of 0.95Eth is preferably 0.250 or more, more preferably 0.275 or more, and further preferably 0.290 or more. When the residual film ratio at an irradiation amount of 0.95 Eth is 0.250 or more, the γ value can be increased to enhance the clarity, and a high-resolution resist pattern can be formed.

[[Remaining film rate when the irradiation dose is 0.90Eth]]
Furthermore, in determining the development conditions, it is preferable to adopt the development conditions in which the residual film ratio is 0.500 or more when the irradiation amount is 0.90 Eth, and it is more preferable to adopt the development conditions in which the residual film ratio is 0.506 or more. It is preferable to adopt development conditions of 0.520 or more, and it is more preferable to adopt the development conditions. By adopting development conditions in which the residual film ratio at an irradiation amount of 0.90Eth is 0.500 or more, the γ value can be further increased to further improve the clarity of the resist pattern, and further, in the non-irradiated region. By further increasing the residual film ratio of the resist, the clarity of the resist pattern can be further improved. In addition, the influence of irradiation noise in the non-irradiated region can be further reduced, and the resolution of the obtained resist pattern can be sufficiently increased.

[[Remaining film rate when the irradiation dose is 0.85Eth]]
Further, in determining the developing conditions, it is preferable to adopt the developing conditions in which the residual film ratio at an irradiation amount of 0.85 Eth is 0.670 or more, and it is more preferable to adopt the developing conditions in which the residual film ratio is 0.679 or more. It is more preferable to adopt development conditions of 0.700 or more. By adopting development conditions in which the residual film ratio at an irradiation amount of 0.85Eth is 0.670 or more, the γ value can be further increased to further improve the clarity of the resist pattern, and further, in the non-irradiated region. By further increasing the residual film ratio of the resist, the clarity of the resist pattern can be further improved. In addition, the influence of irradiation noise in the non-irradiated region can be further reduced, and the resolution of the obtained resist pattern can be sufficiently increased.

[[Developer]]
The developer may be appropriately selected from known developers according to the method for determining development conditions described above. Examples of the components of the developer that can be used include butyl acetate, amyl acetate, and hexyl acetate, and a developer containing at least one of these components in an amount of 90% by mass or more is preferable. A developer containing 90% by mass or more of hexyl acetate is more preferable. It is more preferable that the developer is one of the above-mentioned components containing only impurities unavoidably mixed in the production.
The temperature of the developing solution is not particularly limited, but can be, for example, 21 ° C. or higher and 25 ° C. or lower.

[[Development time]]
The developing time may also be appropriately determined by the above-mentioned method for determining the developing conditions. The specific development time depends on other development conditions such as the properties of the polymer and the type of developer, but for example, 1 minute or more and 30 minutes or less, 1 minute or more and 20 minutes or less, 1 minute or more and 10 minutes or less, 1 minute. 5 minutes or less, 2 minutes or more and 30 minutes or less, 2 minutes or more and 20 minutes or less, 2 minutes or more and 10 minutes or less, 2 minutes or more and 5 minutes or less, 3 minutes or more and 30 minutes or less, 3 minutes or more and 20 minutes or less, 3 minutes or more It can be 10 minutes or less, 3 minutes or more and 5 minutes or less, and 3 minutes or more and 4 minutes or less. The development time determined by the method for determining the development conditions of the present invention is not limited to these illustrated ranges. In particular, in the resist pattern forming method of the present invention, since a resist composition containing a polymer having a molecular weight of more than 100,000 and a proportion of components having a molecular weight of more than 100,000 is 13% or less is used, the development time is preferably relatively short. This is because the polymer contained in the resist composition contains a relatively small amount of high molecular weight components having a molecular weight of more than 100,000, so that the resist film may be excessively dissolved and the γ value may decrease due to long-term development.

Hereinafter, the present invention will be specifically described based on examples, but the present invention is not limited to these examples. In the following description, "%" and "part" representing quantities are based on mass unless otherwise specified.
Then, in Examples and Comparative Examples, the weight average molecular weight of the polymer, the molecular weight distribution, and the ratio of the components of each molecular weight in the polymer were measured by the following methods.

<Weight average molecular weight and molecular weight distribution>
The weight average molecular weight (Mw) of the obtained polymer was measured by gel permeation chromatography, and the number average molecular weight (Mn) was measured to calculate the molecular weight distribution (Mw / Mn). The results are shown in Tables 1 and 2.
Specifically, a gel permeation chromatograph (manufactured by Tosoh Corporation, HLC-8220) is used, and tetrahydrofuran is used as the developing solvent, and the weight average molecular weight (Mw) and the number average molecular weight (Mn) of the polymer are converted into standard polystyrene equivalent values. Asked as. Then, the molecular weight distribution (Mw / Mn) was calculated. The results are shown in Tables 1 and 2.

<Ratio of components of each molecular weight in the polymer>
Using a gel permeation chromatograph (manufactured by Tosoh Corporation, HLC-8220) and using tetrahydrofuran as a developing solvent, chromatographs of polymers A and B prepared in Examples and Comparative Examples were obtained. Then, from the obtained chromatogram, the total area of the peaks (A) and the total area of the peaks of the components having a molecular weight within a predetermined range (X) were obtained. Specifically, the ratios were calculated for _{the components (X 1 to} X ₁₀ ) having a molecular weight within a predetermined range, which are each determined by the following plurality of threshold values. The results are shown in Table 3.
_{Percentage of components (X 1} ) with a molecular weight of less than 10,000 (%) = (X ₁ / A) x 100
Percentage of components (X ₄ ) with a molecular weight over 40,000 (%) = (X ₄ / A) x 100
_{Percentage of components (X 5} ) with a molecular weight of more than 50,000 (%) = (X ₅ / A) x 100
Percentage of components (X ₈ ) with a molecular weight over 80,000 (%) = (X ₈ / A) x 100
Percentage of components (X ₁₀ ) with a molecular weight over 100,000 (%) = (X ₁₀ / A) x 100

(Example 1-1)
<Preparation of polymer A>
[Polymerization of monomeric composition]
3.0 g of methyl α-chloroacrylate and 6.88 g of α-methylstyrene as monomers, 2.47 g of cyclopentanone as a solvent, and 0.01091 g of azobisisobutyronitrile as a polymerization initiator. The monomer composition containing the above was placed in a glass container, the glass container was sealed and replaced with nitrogen, and the mixture was stirred in a constant temperature bath at 78 ° C. for 6 hours under a nitrogen atmosphere. Then, the temperature was returned to room temperature, the inside of the glass container was released to the atmosphere, and then 30 g of tetrahydrofuran (THF) was added to the obtained solution. Then, a solution to which THF was added was added dropwise to 300 g of methanol to precipitate a polymer. Then, the solution containing the precipitated polymer was filtered through a Kiriyama funnel to obtain a white coagulated product (polymer). The weight average molecular weight (Mw) of the obtained polymer was 45,000, and the molecular weight distribution (Mw / Mn) was 1.68. The obtained polymer contained 46 mol% of α-methylstyrene units and 54 mol% of α-methylchloroacrylate units.
[Purification of polymer]
Then, the obtained polymer was dissolved in 100 g of THF, and the obtained solution was added dropwise to a mixed solvent of 600 g of THF and 400 g of methanol (Methanol), and a white coagulated product (α-methylstyrene unit and α-chloroacrylic unit) was added. Polymer A) containing a methyl acid unit was precipitated. Then, the solution containing the precipitated polymer A was filtered through a Kiriyama funnel to obtain a white polymer A. Then, the weight average molecular weight and the molecular weight distribution of the obtained polymer A were measured and evaluated. The results are shown in Table 1. Table 3 shows the results of measuring the ratio of the components of each molecular weight in the polymer according to the above method for the polymer A.
<Preparation of positive resist composition>
The obtained polymer A was dissolved in anisole as a solvent to prepare a resist solution (positive resist composition) having a concentration of the polymer A of 11% by mass.

＜Ｅｔｈの決定＞
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。
＜残膜率の決定＞
感度曲線作成時に使用した、４μＣ／ｃｍ^２から２００μＣ／ｃｍ^２の範囲内で４μＣ／ｃｍ^２ずつ異ならせた電子線の照射量（すなわち、４、８、１２、１６・・・１９６、２００μＣ／ｃｍ^２）を、それぞれ上述のように決定したＥｔｈで除した。
得られた値（電子線の照射量／Ｅｔｈ）が０．９５となる電子線の照射量が存在すれば、その電子線の照射量における残膜率を、残膜率（０．９５Ｅｔｈ）とした。
得られた値（電子線の照射量／Ｅｔｈ）が０．９５となる電子線の照射量が存在しない場合、これらの値のうち、０．９５に最も近接する２つの値を特定し、この２点における電子線の照射量を、それぞれＰ（μＣ／ｃｍ^２）、Ｐ＋４（μＣ／ｃｍ^２）とした。そして、下記式により、残膜率（０．９５Ｅｔｈ）を決定した。結果を表１に示す。
残膜率（０．９５Ｅｔｈ）＝Ｓ−｛(Ｓ−Ｔ)/(Ｖ−Ｕ)｝×(０．９５−Ｕ)
この式中、
Ｓは電子線の照射量Ｐにおける残膜率を示し、
Ｔは電子線の照射量Ｐ＋４における残膜率を示し、
ＵはＰ／Ｅｔｈを示し、そして、
Ｖは（Ｐ＋４）／Ｅｔｈを示す。
同様にして、得られた値（電子線の照射量／Ｅｔｈ）が０．８５となる電子線の照射量における残膜率（０．８５Ｅｔｈ）、及び得られた値（電子線の照射量／Ｅｔｈ）が０．９０となる電子線の照射量における残膜率（０．９０Ｅｔｈ）を決定した。
ここで算出したような０．８５Ｅｔｈ、０．９０Ｅｔｈ、及び０．９５Ｅｔｈにおける残膜率が高いほど、残膜率を概ね０とすることができる電子線の総照射量よりも低い照射量では、レジスト膜が現像液に対して溶解しにくいということである。換言すれば、照射量の比較的少ない領域である、レジスト膜上におけるパターン形成領域の周辺領域では、レジスト膜の現像液に対する溶解性が低いということである。したがって、上述のようにして算出した残膜率が高いということは、レジスト膜上で溶解されてパターンを形成すべき領域と、溶解せずに残るべき領域との境界が明瞭であり、パターンの明瞭性が高いということを意味する。
さらに、上記残膜率が高いということは、非照射領域においてレジストが照射ノイズの影響を受けにくく、得られるレジストパターンの解像度を十分に高めることができることを意味する。<Creation of sensitivity curve>
Using a spin coater (MS-A150 manufactured by Mikasa), the positive resist composition was applied onto a silicon wafer having a diameter of 4 inches to a thickness of 500 nm. Then, 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 a silicon wafer. Using an electron beam drawing device (ELS-S50 manufactured by Elionix Inc.), a plurality of patterns (dimensions 500 μm × 500 μm) having different electron beam irradiation amounts are drawn on the resist film, and the resist developer is made of hexyl acetate. A developing solution (hexyl acetate containing only impurities unavoidably mixed in production, ZED-N60 manufactured by Nippon Zeon Co., Ltd.) was used for 1 minute of development treatment at a temperature of 23 ° C., and then rinsed with isopropyl alcohol for 10 seconds. .. 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 part was measured with an optical film thickness meter (Lambda Ace, manufactured by Dainippon Screen), and the common logarithm of the total irradiation amount of the electron beam and the residual film ratio of the resist film after development were measured. A sensitivity curve showing the relationship with (= film thickness of the resist film after development / film thickness of the resist film formed on the silicon wafer) was created.
<Determination of gamma value>
About the obtained sensitivity curve (horizontal axis: common logarithm of total irradiation amount of electron beam, vertical axis: residual film ratio of resist film (0 ≤ residual film ratio ≤ 1.00)), γ value using the following formula Asked. In the following formula, E ₀ is a quadratic function obtained by fitting the sensitivity curve to a quadratic function in the range of 0.20 to 0.80 residual film ratio (regular use of residual film ratio and total irradiation amount). It is the logarithm of the total irradiation dose obtained when 0 is substituted for the residual film ratio (function with the logarithm). Further, E ₁ creates a straight line (approximate line of the slope of the sensitivity curve) connecting the point with the residual film ratio of 0 and the point with the residual film ratio of 0.50 on the obtained quadratic function, and the obtained straight line. It is the logarithm of the total irradiation amount obtained when the residual film ratio 1.00 is substituted for (the function of the residual film ratio and the common logarithm of the total irradiation amount). The following equation represents the slope of the straight line between the residual film ratio of 0 and 1.00. The larger the γ value, the larger the slope of the sensitivity curve, indicating that a pattern with high clarity can be formed. The results are shown in Table 1.

<Decision of Eth>
^{The total irradiation amount Eth (μC / cm 2} ) of the electron beam when the residual film ratio of the straight line (approximate line of the slope of the sensitivity curve) obtained in the calculation of the γ value became 0 was obtained.
<Determination of residual 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 residual film ratio in the electron beam irradiation amount is defined as the residual film ratio (0.95Eth). did.
When there is no electron beam irradiation amount at which the obtained value (electron beam irradiation amount / Eth) is 0.95, two values closest to 0.95 are specified among these values, and this value is specified. The irradiation amounts of the electron beams at the two points were P (μC / cm ² ) and P + 4 (μC / cm ² ), respectively. Then, the residual film ratio (0.95Eth) was determined by the following formula. The results are shown in Table 1.
Residual film ratio (0.95Eth) = S-{(ST) / (VU)} × (0.95-U)
In this formula,
S indicates the residual film ratio at the irradiation amount P of the electron beam.
T indicates the residual film ratio at the electron beam irradiation amount P + 4.
U indicates P / Eth, and
V indicates (P + 4) / Eth.
Similarly, the residual film ratio (0.85 Eth) at the electron beam irradiation amount at which the obtained value (electron beam irradiation amount / Eth) is 0.85, and the obtained value (electron beam irradiation amount / Eth). The residual film ratio (0.90Eth) at the irradiation amount of the electron beam at which Eth) was 0.90 was determined.
The higher the residual film ratio at 0.85Eth, 0.90Eth, and 0.95Eth as calculated here, the lower the irradiation amount than the total irradiation amount of the electron beam, which can make the residual film ratio approximately 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 region around the pattern forming region on the resist film, which is a region where the irradiation amount is relatively small. Therefore, the fact that the residual film ratio calculated as described above is high means that the boundary between the region that should be dissolved on the resist film to form a pattern and the region that should remain undissolved is clear, and the pattern It means that the clarity is high.
Further, the high residual film ratio means that the resist is not easily affected by irradiation noise in the non-irradiated region, and the resolution of the obtained resist pattern can be sufficiently increased.

(Examples 1-2 to 1-5)
Polymer A and a positive resist composition were prepared in the same manner as in Example 1-1. Then, the measurement and evaluation were carried out in the same manner as in Example 1-1 except that the development time was changed as shown in Table 1. The results are shown in Table 1.

(Comparative Example 1-1)
Polymer A and a positive resist composition were prepared in the same manner as in Example 1-1. Then, the measurement and evaluation were carried out in the same manner as in Example 1-1 except that the development time was changed as shown in Table 1. The results are shown in Table 1.

(Comparative Examples 2-1 to 2-6)
A positive resist composition in which the polymerization time is changed to 6.5 hours and the polymer recovered by filtration when the monomer composition is polymerized is used as it is as the polymer B without purifying the polymer. Was prepared. Then, the measurement and evaluation were carried out in the same manner as in Example 1-1 except that the development time was changed as shown in Table 2. The results are shown in Table 2. Table 3 shows the results of measuring the ratio of the components of each molecular weight in the polymer according to the above method for the polymer B.

From Tables 1 to 3 above, when a positive resist composition containing an α-methylstyrene / α-methylchloroacrylate copolymer having a proportion of more than 100,000 components of 13% or less is used, the irradiation dose By adopting development conditions in which the residual film ratio at 0.95 Eth is 0.250 or more, it is possible to maintain a relatively high residual film ratio at an irradiation dose near Eth while ensuring a high γ value. It can be seen that a resist pattern with high clarity and resolution can be formed.

According to the resist pattern forming method of the present invention, a resist pattern having high resolution and clarity can be formed.
Further, according to the method for determining the developing conditions of the present invention, it is possible to determine the developing conditions capable of forming a resist pattern having high resolution and clarity.

Claims (5)

A step of forming a resist film using a positive resist composition containing a polymer and a solvent containing an α-methylstyrene unit and an α-methylchloroacrylate unit, and a step of forming a resist film.
The step of exposing the resist film and
The step of developing the exposed resist film and
Including
The proportion of components having a molecular weight of more than 100,000 in the polymer is 13% or less.
The weight average molecular weight of the polymer is 57,000 or more and 90,000 or less, and the molecular weight distribution of the polymer is 1.20 or more and less than 1.40.
A resist pattern forming method in which the development is carried out under the condition that the irradiation amount is 0.95 Eth and the residual film ratio is 0.250 or more. The resist pattern forming method according to claim 1, wherein the proportion of components having a molecular weight of less than 10,000 is more than 0% and 1% or less. The resist pattern forming method according to claim 1 or 2, wherein the proportion of the component having a molecular weight of more than 40,000 of the polymer is 75% or more and 90% or less. The resist pattern forming method according to any one of claims 1 to 3, wherein the development is carried out using a developing solution containing 90% by mass or more of hexyl acetate. A method for determining development conditions in resist pattern formation using a positive resist composition containing a polymer containing an α-methylstyrene unit and a methyl chloroacrylate unit.
The proportion of components having a molecular weight of more than 100,000 in the polymer is 13% or less.
The weight average molecular weight of the polymer is 57,000 or more and 90,000 or less, and the molecular weight distribution of the polymer is 1.20 or more and less than 1.40.
A method for determining development conditions, in which a sensitivity curve is created to obtain a condition in which the residual film ratio is 0.250 or more when the irradiation amount is 0.95 Eth.