JP2006003527A - Positive resist and pattern forming method using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To enhance the transparency of a resist and to provide a resist capable of forming a fine pattern by a high contrast resist, and to provide a resist pattern forming method using the same. <P>SOLUTION: Protective groups have been introduced into a chemically amplified resist resin so as to suppress its alkali solubility. By using the protective groups containing two or more functional moieties, capable of bonding to the resin per group, it is made possible for the resin to have a crosslinked structure, such as resin-protective group-resin. With this structure, the molecular weight of the resin increases, as compared with that of the conventional resin, accordingly though the protective groups are small, alkali dissolution suppressing effect can be increased, and dissolution contrast is enhanced. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a pattern forming method applied to a semiconductor manufacturing process such as an IC, a circuit board such as a liquid crystal or a thermal head, and other photo application processes, and is particularly suitable for microfabrication of a semiconductor element using an F2 excimer laser. The present invention relates to a pattern forming method used.

  High integration of semiconductor integrated circuits is progressing, and miniaturization of integrated circuits is rapidly progressing. In order to cope with miniaturization, the exposure light source has been shortened in the lithography process. The KrF excimer laser (248 nm) has already been put into practical use, and the short wavelength ArF excimer laser (193 nm) is also being put into practical use. The demand for further miniaturization is expected to continue in the future, and F2 excimer laser (157 nm) is considered promising as a method to meet this demand, and development is progressing rapidly today.

  Conventional i-line and KrF excimer lasers have used aromatic ring-containing resins such as novolac resins and polyvinylphenol resins as resists. In the ArF excimer laser, the light absorption of the aromatic ring has become a serious problem, so the alicyclic resin has been changed. However, in the F2 excimer laser, both the benzene ring-containing resin and the alicyclic resin have large light absorption and are not suitable for use. For this reason, examination and development of a fluorine-containing non-aromatic ring resin with low light absorption have been performed (see Non-Patent Document 1).

Fluorine-containing resins developed so far have good light absorption and good light absorption, but they have large light absorption by acid generators and protecting groups necessary for imparting photosensitivity. As a photosensitive composition (resist) The transparency of is not always sufficient.
S. Ishikawa et al., Proc.SPIE, vol.5039, 580 (2003)

  In order to improve the transparency of the resist, it is necessary to select a protecting group with little light absorption. However, since such a protecting group has a low molecular weight, the transparency is improved, but there is a problem that the ability to inhibit alkali dissolution is lowered.

  The present invention has been made in view of the problem of improving the ability to inhibit alkali dissolution, and its purpose is to improve the transparency of the resist and to form a resist capable of forming a fine pattern with a high contrast resist. It is to provide a resist pattern forming method used.

  As a result of earnestly examining the resist pattern formation method, the present inventor has found that the above object can be achieved by using a protecting group having two or more sites where a resin-protecting group bond is present in one protecting group. This has resulted in the present invention.

The first aspect of the present invention is a chemically amplified positive resist comprising an acid-sensitive fluorine-containing resin protected by a protecting group, and a photoacid generator that generates an acid by exposure light irradiation,
The positive resist is characterized in that the protective group has at least two binding sites with a fluorine-containing resin.

  In the first aspect of the present invention, the bond between the protective group and the fluorine-containing resin is preferably an acetal bond.

According to a second aspect of the present invention, there is provided a chemically amplified resist comprising a fluorine-containing resin as a base polymer, added with a photoacid generator that generates an acid upon irradiation with actinic light and cleaves a protective group of the fluorine-containing resin by the action of the acid. In the pattern forming method used,
In the pattern forming method, the protective group of the fluorine-containing resin is one having at least two binding sites with the fluorine-containing resin.

In the second aspect of the present invention, the bond between the protective group and the fluorine-containing resin is preferably an acetal bond.
In the second aspect of the present invention, the actinic ray for exposure is preferably F2 excimer laser light.

  By using the resin having a protective group of the present invention as a resist, it is possible to effectively suppress alkali solubility in the unexposed area. As a result, the difference in the developing speed between the exposed portion and the unexposed portion is increased, so that the resolution performance of the resist is improved and a fine pattern can be formed.

The principle of the present invention will be described below.
It is known that not only fluororesins but generally resins having a lower molecular weight have a higher ability to dissolve in a solvent or developer, and conversely become insoluble as the molecular weight increases.
For this reason, compared with the case where a single protecting group has a single site that performs resin-protecting group bonding, two or more sites that perform resin-protecting group bonding in a single protecting group. When the protecting group is used, the molecular weight of the protected resin increases because it can take the form of resin-protecting group-resin. Since the resin having such a protecting group has low alkali solubility even at a low protection rate, the developing speed of the unexposed area is lowered. As a result, the difference in development speed between the unexposed area and the exposed area is enlarged, and a resist having excellent contrast can be obtained.

  Further, in F2 (157 nm) lithography, since the protecting group itself is required to be transparent, it is effective to use an acetal type protecting group having a small light absorption at 157 nm.

Hereinafter, embodiments of the present invention will be described in detail.
[Resist]
The resist of the present embodiment is a positive chemically amplified resist in which an acid-sensitive fluorine-containing resin serving as a base polymer and a photoacid generator are dissolved in a solvent, and if necessary, a surfactant. An acid diffusion inhibitor or the like can also be added. Each of these components will be described below.

(Base polymer)
The base polymer that is a constituent component of the resist of the present embodiment, that is, the acid-sensitive fluorine-containing resin has a fluorine atom in the resin skeleton or side chain, and also has a hydroxyl group, carboxyl group, amide group, imide group, sulfonic acid group. These hydrophilic groups (polar groups) are contained in the resin skeleton or side chain, and these hydrophilic groups (polar groups) are bonded to protective groups. Acid sensitivity in this base polymer means that when the base polymer is formed on the substrate surface as a chemically amplified resist and exposed to light, the protecting group is formed by the action of an acid generated from the photoacid generator added to the resist. This means that the base polymer is released from the base polymer and becomes soluble in an alkali developer. The resist is dissolved and removed by developing the exposed substrate using such an acid-sensitive base polymer. Is formed.

  As the fluorine-containing resin constituting the base polymer, conventionally known resist fluororesins found in, for example, JP-A-2003-140349 can be used. Specifically, a fluorine-substituted alkylene group, a resin having a fluorine-substituted norbornene skeleton, a polymer or copolymer such as fluorine-substituted acrylic acid or methacrylic acid, a copolymer of tetrafluoroethylene and norbornene, and a perfluoroalkyl group or Examples include known resist resins in which a hydrophilic group (polar group) such as a hydroxyl group, a carboxyl group, or an amino group is introduced into a polymer skeleton such as a perfluoroalkylene group-containing resin.

  In the present invention, the hydrophilic group (polar group) of the base polymer is protected by a protecting group to prevent alkali solubility. It is characterized in that a compound having two or more sites bonded to the hydrophilic group (polar group) of the base polymer is used for one molecule constituting this protective group. By using such a protecting group, the protecting group cross-links between the two base polymer molecules, increasing the molecular weight of the base polymer, which is effective even with small molecular weight protecting groups. In addition, it is possible to improve the ability to inhibit dissolution of the alkaline developer in the exposed portion of only the resist.

Those having two or more sites (functional groups) that react with the hydrophilic group (polar group) of the base polymer, which is a protective group that can be used in this embodiment, should be groups as shown by the following chemical formula 1. Can do. In the following chemical formula 1, a compound in which R ₀ is a methylene group, R ₁ is a hydrogen atom, and R ₂ is a methyl group is called an acetal bond. In the present invention, all the bonds represented by the following chemical formula 1 are all acetal. This is called bonding. In particular, in the following chemical formula 1, the total number of carbon atoms contained in R ₀ , R ₁ , and R ₂ is 4 or less, thereby improving the alkali dissolution inhibiting ability while maintaining the transparency of the base polymer. It is preferable because it is possible.

式中、Ｒ_０は、メチレン基、エチレン基、などの直鎖アルキレン基であり、
Ｒ_１，Ｒ_２は、水素、メチル基、エチル基など直鎖アルキル基を表し、これらは同一であっても異なっていても良い。

In the formula, R ₀ is a linear alkylene group such as a methylene group or an ethylene group,
R ₁ and R ₂ represent a linear alkyl group such as hydrogen, a methyl group, and an ethyl group, and these may be the same or different.

  As a means for introducing the protecting group into the base polymer, a conventional method can be employed as a means for synthesizing a polymer substance. That is, the reaction between the hydrophilic group (polar group) of the base polymer and the acetal bond-forming molecule is an esterification reaction, an etherification reaction, an amidation reaction, etc., and well-known means are adopted for these reactions. can do.

  The hydrophilic group (polar group) protected by the protective group is preferably in the range of 5 to 35% of the hydrophilic group present in the base polymer skeleton. When this ratio is less than the above range, the solubility of the base polymer itself is high, and the dissolution contrast between the exposed and unexposed areas decreases. On the other hand, when the ratio exceeds the above, there is a problem that a residue (undissolved) due to a developer insoluble component is likely to be generated.

  The introduction of the protective group into the base polymer can be performed by reacting a base polymer having a hydrophilic group with a protective group-forming compound having two or more functional groups. As a result, one molecule of the protective group-forming compound reacts with the hydrophilic group (polar group) of a plurality of base polymers to crosslink the base polymer and increase the molecular weight.

(Photoacid generator)
As the photoacid generator used in the present embodiment, conventionally known photoacid generators can be used. Specifically, bissulfoniudiazomethanes, nitrobenzyl derivatives, polyhydroxy compounds and aliphatic or aromatic sulfonic acids. Examples include esters, onium salts, sulfonylcarbonylalkanes, sulfonylcarbonyldiazomethanes, halogen-containing triazine compounds, oxime sulfonate compounds, and phenylsulfonyloxyphthalimides.
This photo-acid generator can be added and used in the range of 2 to 10% by weight with respect to the solid content of the resist. When this amount is below the above range, there is a problem of sensitivity deterioration. On the other hand, when the amount of the photoacid generator is above the above range, there is a problem of transparency deterioration due to the acid generator.

(solvent)
As the solvent for dissolving the resist base polymer and the like, a commonly used solvent can be used. Specifically, ethylene chloride, cyclohexanone, cyclopentanone, 2-heptanone, γ-butyrolactone, methyl ethyl ketone. , Ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, 2-methoxyethyl acetate, ethylene glycol monoethyl ether acetate, propylene glycol monomethyl ether, propylene glycol monoethyl ether, propylene glycol monomethyl ether acetate, toluene, ethyl acetate, methyl lactate, Ethyl lactate, methyl methoxypropionate, ethyl ethoxypropionate, ethyl pyruvate, propyl pyruvate, N, N, -dimethyl Le formamide, dimethyl sulfoxide, N- methylpyrrolidone, or the like can be used tetrahydrofuran. Of these, propylene glycol monomethyl ether acetate (PGMEA) is particularly preferred.
The resist concentration in this embodiment can be in the range of 4 to 15% by weight.

(Acid diffusion inhibitor)
In chemically amplified resists, the acid generated from the photoacid generator upon exposure serves as a catalyst to promote the elimination reaction of the protective group of the base polymer and form a pattern. In the baking process after exposure, May move in the resist. In this case, the acid that has entered even in the unexposed portion of the resist causes a separation reaction of the protective group of the base polymer, and the accuracy of the pattern decreases. An acid diffusion inhibitor can be used to prevent this. Specifically, organic base compounds such as substituted amine compounds, nitrile compounds, and N-methylpyrrolidone can be used.

[process]
Hereinafter, the process of the pattern formation method which is this Embodiment is demonstrated.
This process mainly includes a step of applying a resist on a substrate, a pre-bake step for heating the resist layer, an exposure step for irradiating the pre-baked resist layer with far ultraviolet light, and a post-bake step for heating the exposed resist layer. It consists of a developing step for developing to form a pattern, and a rinsing / drying step.
The present embodiment will be described below in accordance with each process.

(Resist application process)
First, a substrate such as a silicon wafer, or a substrate on which a base layer such as a metal wiring, an interlayer insulating film, an oxide film, a nitride film, a polysilicon layer, or an aluminum wiring is formed, or a surface thereof. In addition, a resist dissolved in a known solvent on a surface of a substrate to be treated such as a substrate treated with a silane coupling agent for improving the adhesion between the resist and the substrate, or a substrate having an antireflection film formed on the surface of the substrate. The material is applied using a coating device such as a spin coater, dip coater, or roller coater. The coating thickness can be determined in the range of several tens of nm to several μm. As the antireflection film, a conventionally known organic antireflection film or inorganic antireflection film can be used. The circuit may be formed on the substrate.

(Pre-baking process)
Next, after drying the resist applied to the substrate to be processed, a pre-baking process is performed. This treatment can be performed by heat treatment at a temperature condition of 70 to 150 ° C. for 30 to 300 seconds using a hot plate or the like. Thereby, the solvent remaining in the applied resist layer is volatilized. After the heat treatment, the substrate provided with the resist layer is cooled to about room temperature.

(Exposure process)
Next, the resist layer is exposed using an excimer laser having a wavelength of 200 nm or less, preferably F2 excimer laser light, using a required mask. In the present embodiment, it is particularly preferable to use an F2 excimer laser in forming a fine pattern.
In this step, the amount of exposure by the excimer laser greatly depends on the exposure pattern and cannot be determined unconditionally, but can usually be set in the range of ^{2 to} 200 mJ / cm ² .

(Post-bake process (PEB))
Next, the substrate provided with the exposed resist layer is heated, and post-exposure baking (PEB) is performed. The heat treatment in this step is performed in the range of 70 to 150 ° C. for 30 to 300 seconds. This heat treatment promotes the desorption reaction of the dissolution inhibitor and facilitates the development process in the chemically amplified resist. When the heating temperature is lower than the above range, the sensitivity (required exposure amount) is remarkably deteriorated. On the other hand, when the heating temperature is higher than the above range, the resin and other components are decomposed. appear. Further, when the heating time is below the above range, there is a problem of sensitivity deterioration and line width uniformity deterioration. When the heating time is above the above range, there is a problem that throughput is deteriorated or incidental equipment is required. Depending on the type of resist, this step can be omitted. When the PEB process is performed, the substrate to be processed is cooled to approximately room temperature.

(Development process)
Next, after the exposure, development processing is performed using an alkali developer. As the alkali developer, various known alkali developers can be used. Examples of the developer constituting these developers include tetramethylammonium hydroxide, tetraethylammonium hydroxide, tetrapropylammonium hydroxide, and tetrabutylammonium hydroxide. These developers are dissolved in water or alcohol such as methanol or ethanol and used as a developer. The concentration of the developer is usually used in the range of 0.1 to 15% by weight. As such a developer, a 2.38% tetramethylammonium hydroxide aqueous solution is generally used as a standard developer. The developer temperature can be 21 to 25 ° C., and the development time can be 10 seconds to 20 minutes.

(Rinse and drying process)
In this step, the resist pattern formed by developing in the above step is washed with pure water, and the developer and the dissolved resist are removed. Then, this can be dried to obtain a substrate having a resist pattern formed on the surface.
Through the above steps, a pattern forming process using an F2 excimer laser can be performed. According to this process, the contrast of the fluororesin resist is improved by adopting a resist using a protecting group in which there are two or more sites that react with the base polymer in a single protecting group. Probability is greatly reduced.

  In the above embodiment, mainly a step of applying a resist on the substrate, a pre-baking step of heating the resist layer, an exposure step of exposing the pre-baked resist layer by irradiating far ultraviolet rays, and a post for heating the exposed resist layer A process comprising a baking process, a development process for developing to form a pattern, and a rinsing / drying process has been shown. However, as long as the present invention employs a base polymer having a protective group having two or more binding sites, Various modifications are possible without being limited to the above.

  Moreover, in the said embodiment, although the site | part which reacts with a base polymer in the single protective group was 2, the example which may be 3 or more may be sufficient as long as it can synthesize | combine chemically. Of course.

  EXAMPLES Hereinafter, although this invention is demonstrated concretely using an Example, this invention is not restrict | limited to the following Example.

(Comparative Example 1)
The process flow of Comparative Example 1 is shown in FIG. As is apparent from FIG. 1, in this process, a resist resin film 2 is formed on the surface of the silicon substrate 1 and then developed to form a pattern. Due to this development processing, the surface of the resist resin film 2 is reduced. In this comparative example, a resin having a protecting group in which one site for resin-protecting group bonding is present in one protecting group was used. Of the sites on the resin side where resin-protecting group bonding is possible, 10% is a protected resin. This resin was used as a 7 wt% PGMEA solution. Subsequently, the resin solution was spin-coated on the silicon substrate 1 and baked at 110 ° C./60 sec to form a resin film 2 having a thickness of 150 nm. The silicon substrate on which this resin film was formed was developed with a 2.38% tetramethylammonium hydroxide aqueous solution for 60 seconds, and when the amount of the remaining film was investigated with a film thickness measuring device, it was confirmed that a film thickness reduction of 50 nm occurred. .

(Example 1)
The process of the present invention was performed in the process flow shown in FIG. That is, as a resist, a resin having a protecting group with two sites for resin-protecting group bonding in one protecting group was used. Of the sites on the resin side where resin-protecting group bonding is possible, 10% is a protected resin. This resin was used as a 7 wt% PGMEA solution. Subsequently, the resin solution was spin-coated on the silicon substrate 1 and baked at 110 ° C./60 sec to form a resin film 2 having a thickness of 150 nm. The silicon substrate on which this resin film was formed was developed with a 2.38% tetramethylammonium hydroxide aqueous solution for 60 seconds, and when the amount of the remaining film was investigated with a film thickness measuring device, it was confirmed that the film thickness was reduced by 10 nm. .

(Comparative Example 2)
A process flow diagram of Comparative Example 2 is shown in FIG. In this comparative example, an antireflection film 3 is formed on the surface of a silicon substrate 1 and a resist film 4 is formed on the surface, followed by exposure and development processing. In this comparative example, as this resist material, a resin having a protecting group having one site for resin-protecting group bonding in one protecting group was used. Of the sites on the resin side where resin-protecting group bonding is possible, 10% is a protected resin. This resin was made into a 7 wt% PGMEA solution, and then 5 wt% acid generator (TPS-109, Midori Kagaku) was added to form a resist.

  Subsequently, an antireflection film material (trade name: DUV30) was spin-coated on the silicon substrate 1, and then a baking treatment at 205 ° C./60 sec was performed to form the antireflection film 3. The resist solution was spin-coated on the antireflection film 3 and then baked at 110 ° C./60 sec to form a resist film 4 having a thickness of 150 nm. The resist film 4 was exposed with an EXITTECH F2 exposure machine (NA 0.85, σ 0.3, LEVENSON reticle), and then baked at 110 ° C./60 sec. Subsequently, development was performed with a 2.38% tetramethylammonium hydroxide aqueous solution for 60 seconds, and the cross-sectional shape of the resist was confirmed. As a result, a large film reduction was observed at 80 nm LS as shown in FIG.

(Example 2)
As in Comparative Example 2, a resist pattern was formed by using a resin having a protecting group having two sites where a resin-protecting group is bonded in one protecting group by the process flow shown in FIG. That is, 10% of the resin-side sites capable of resin-protecting group bonding are protected. This resin was made into a 7 wt% PGMEA solution, and then 5 wt% acid generator (TPS-109, Midori Kagaku) was added to form a resist.

Subsequently, an antireflection film material (trade name: DUV30) was spin-coated on the silicon substrate 1, and then a baking process at 205 ° C./60 sec was performed to form the antireflection film 3. The resist solution was spin-coated on the antireflection film 3 and then baked at 110 ° C./60 sec to form a resist film 4 having a thickness of 150 nm. The resist film 4 was exposed using an F2 exposure machine manufactured by EXITETECH (NA 0.85, σ 0.3, LEVENSON reticle), and then baked at 110 ° C./60 sec. Subsequently, development was performed with a 2.38% tetramethylammonium hydroxide aqueous solution for 60 seconds, and the cross-sectional shape of the resist was confirmed. As a result, a pattern with less film loss was observed at 80 nm LS as shown in FIG.

The schematic sectional drawing which shows the process flow in the case of forming a resist film on a board | substrate. The schematic sectional drawing which shows the process flow in the case of forming a resist film after forming an antireflection film on a board | substrate. Sectional drawing for comparing the resist pattern obtained by the comparative example 2 and Example 2. FIG.

Explanation of symbols

1. 1. Silicon wafer 2. Resin film 3. Antireflection film Resist film

Claims (5)

A chemically amplified positive resist comprising an acid-sensitive fluorine-containing resin protected by a protecting group, and a photoacid generator that generates an acid by exposure light irradiation,
A positive resist, wherein the protective group has at least two binding sites with a fluorine-containing resin.   2. The positive resist according to claim 1, wherein the bond between the protective group and the fluorine-containing resin is an acetal bond. In a pattern formation method using a chemically amplified resist in which a fluorine-containing resin is used as a base polymer, an acid is generated by irradiation with actinic rays, and a photoacid generator is added to cleave the protective group of the fluorine-containing resin by the action of the acid.
A pattern forming method using a protective group for the fluorine-containing resin having at least two binding sites with the fluorine-containing resin.   The pattern forming method according to claim 3, wherein the bond between the protective group and the fluorine-containing resin is an acetal bond. 5. The pattern forming method according to claim 3, wherein the actinic ray for exposure is F2 excimer laser light.

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