JP7173481B2 - Photosensitive resin composition, pattern forming method, and electronic device manufacturing method - Google Patents

Description

The present invention relates to a photosensitive resin composition, a pattern forming method, and an electronic device manufacturing method.

Various photosensitive resin compositions are known in the manufacture of electronic devices. For example, "photoresist compositions" used for etching electronic substrates, ion implantation, metal sputtering, metal plating and the like are known.
Photoresist compositions can be non-chemically amplified or chemically amplified. In advanced fields where high performance (such as high resolution) is required, there is a tendency to use chemically amplified ones.
A chemically amplified photoresist composition typically contains a resin whose alkali-soluble group is protected by an acid-decomposable protective group, and a photoacid generator.
Various resins have been investigated, and for example, novolak resins (phenolic resins) have been actively investigated.

For example, Patent Document 1 discloses a photoresist composition containing a novolak resin (A1) introduced with a protective group cleavable by the action of an acid (A1), an acid generator (B), an anticorrosive agent (G) and a solvent (D). things are described.
Further, in Patent Document 2, (A) a novolak resin containing 20 mol% or more of m-cresol-based repeating units and having some hydrogen atoms of phenolic hydroxyl groups substituted with 1-ethoxyethyl groups, (B ) a quinone diazide ester and (C) 1,1-bis(4-hydroxyphenyl)cyclohexane are described.

JP-A-2017-9999 JP-A-2003-149816

As described above, a photoresist composition containing a resin in which the phenolic hydroxyl group of a novolak resin is protected with an acid-decomposable protecting group is known.
Since the photoresist composition is used for forming fine structures of semiconductors, it is necessary to balance various performances to a high degree. However, according to the findings of the present inventors, conventional photoresist compositions containing resins in which the phenolic hydroxyl groups of novolac resins are protected with acid-decomposable protective groups are difficult to achieve in terms of both sensitivity and film retention. , there was room for improvement. For sensitivity, it is important that the novolac resin "dissolves well" in the alkaline developer, while for the residual film ratio, it is important that the novolac resin "does not dissolve too much" in the alkaline developer. Balancing was difficult.

The present invention has been made in view of such circumstances. An object of the present invention is to obtain a photosensitive resin composition having both sensitivity and film retention by using a resin in which the phenolic hydroxyl group of a novolak resin is protected with an acid-decomposable protective group.

As a result of various investigations, the present inventors have found that the structure of the novolak resin, the type of acid-decomposable group, and the weight average molecular weight of the resin are important for solving the problem. Based on this finding, the inventors have made the invention provided below and have found that the above objects can be achieved.

According to the invention,
A photosensitive resin composition containing an acid-decomposable resin, a photoacid generator and a solvent,
The acid-decomposable resin is a novolac resin in which at least part of the phenolic hydroxy groups are protected with acid-decomposable groups,
The novolak resin contains a structural unit derived from o-cresol and a structural unit derived from an aldehyde,
The acid-decomposable group is at least one selected from the group consisting of a 1-ethoxyethyl group and a 1-propoxyethyl group,
A photosensitive resin composition is provided in which the acid-decomposable resin has a weight average molecular weight of 3,000 to 7,000.

Moreover, according to the present invention,
A film forming step of forming a photosensitive resin film from the photosensitive resin composition;
an exposure step of exposing the photosensitive resin film;
and a developing step of developing the photosensitive resin film.

Moreover, according to the present invention,
A method for manufacturing an electronic device is provided, which includes the pattern forming method.

According to the present invention, it is possible to obtain a photosensitive resin composition containing a resin in which the phenolic hydroxyl group of a novolac resin is protected with an acid-decomposable protective group, and which has both sensitivity and film retention.

Hereinafter, embodiments of the present invention will be described in detail.

In this specification, the notation "a to b" in the description of numerical ranges means from a to b, unless otherwise specified. For example, "1 to 5% by mass" means "1% by mass or more and 5% by mass or less".
In the description of a group (atomic group) in the present specification, a description without indicating whether it is substituted or unsubstituted includes both those having no substituent and those having a substituent. For example, the term “alkyl group” includes not only alkyl groups without substituents (unsubstituted alkyl groups) but also alkyl groups with substituents (substituted alkyl groups).
The term "electronic device" in this specification refers to elements to which electronic engineering technology is applied, such as semiconductor chips, semiconductor elements, printed wiring boards, electric circuit display devices, information communication terminals, light emitting diodes, physical batteries, chemical batteries, etc. , devices, final products, etc.

<Photosensitive resin composition>
The photosensitive resin composition of this embodiment contains an acid-decomposable resin, a photoacid generator and a solvent.
The acid-decomposable resin is a novolak resin in which at least part of the phenolic hydroxy groups is protected with an acid-decomposable group.
The above novolak resins contain structural units derived from o-cresol and structural units derived from aldehyde.
The above acid-decomposable group is at least one selected from the group consisting of 1-ethoxyethyl group and 1-propoxyethyl group.
The weight average molecular weight of the acid-decomposable resin is 3,000-7,000.

The reason why such a photosensitive resin composition achieves both sensitivity and film retention can be explained as follows. It should be noted that the following description includes speculation, and the present invention is not limited by the following description.

It is believed that the acid-decomposable resin contains a structural unit derived from o-cresol, thereby appropriately controlling the structure of the novolac resin as compared with conventional novolak resins (m/p-cresol, etc.). As a result, the alkali-soluble group (phenolic hydroxyl group) is more likely to come into contact with the alkaline developer, and the solubility in the alkaline developer is increased (that is, the sensitivity is improved).
In addition, the 1-ethoxyethyl group or 1-propoxyethyl group, which is an acid-decomposable group, requires very little energy for deprotection. It is considered that the "difference" in dissolution rate between the portion (the portion where the protective group has been removed) and the unexposed portion (the portion where the protective group remains protected) is appropriate. In other words, it is considered that the portions that should be dissolved are dissolved and the portions that should not be dissolved are not dissolved, thereby achieving a good residual film rate.

Components contained in the photosensitive resin composition, physical properties of the photosensitive resin composition, and the like will be specifically described.

(Acid-decomposable resin)
The acid-decomposable resin is obtained by protecting at least part of the phenolic hydroxy groups of the original novolak resin with an acid-decomposable group.

It is preferred that the novolac resin, which is the base of the acid-decomposable resin, does not substantially contain structural units other than structural units derived from o-cresol as structural units having a phenolic hydroxyl group. For example, the novolac resin that is the base of the acid-decomposable resin preferably does not contain a structural unit derived from m-cresol or p-cresol. As a result, the "structural control of the novolac resin" described above can be performed more appropriately, and it is believed that both higher sensitivity and higher residual film ratio can be achieved, and an ideal rectangular cross section can be achieved.

The term "substantially free" as used herein means that in the novolak resin that is the source of the acid-decomposable resin, the structure other than the structural unit derived from o-cresol is used for the entire structural unit having a phenolic hydroxy group. It represents that the proportion of units is, for example, less than 5 mol %, preferably less than 3 mol %, more preferably less than 1 mol %, particularly preferably 0.
In other words, the ratio of structural units derived from o-cresol to the total structural units having phenolic hydroxy groups in the novolak resin, which is the base of the acid-decomposable resin, is, for example, 95 mol% or more, preferably 97 mol%. Above, more preferably 99 mol % or more, particularly preferably 100 mol %.

The novolak resin, which is the base of the acid-decomposable resin, contains structural units derived from aldehyde in addition to structural units derived from o-cresol. The ratio of these structural units is not particularly limited. 9 to 1.1.

The acid-decomposable resin is protected by at least one acid-decomposable group selected from the group consisting of 1-ethoxyethyl group and 1-propoxyethyl group. That is, at least some of the hydrogen atoms of the phenolic hydroxy groups of the original novolak resin are substituted with 1-ethoxyethyl groups and/or 1-propoxyethyl groups.
The acid-decomposable resin may have only a 1-ethoxyethyl group or only a 1-propoxyethyl group as an acid-decomposable group. - You may have both propoxyethyl groups.

The degree of protection of the acid-decomposable resin, that is, the extent to which the phenolic hydroxyl groups of the original novolac resin are protected by the acid-decomposable groups is not particularly limited.
However, from the viewpoint of optimizing the dissolution rate (that is, sensitivity) of the resin to the alkaline developer and the residual film rate, the phenolic hydroxy group of the novolak resin is preferably 20 to 60 mol%, more preferably 25 to 60 mol. %, more preferably 30 to 55 mol %, are protected with at least one acid-labile group selected from the group consisting of 1-ethoxyethyl group and 1-propoxyethyl group.
The protection rate can be obtained from the peak areas of ¹ H-NMR before and after protection of the resin.

The weight average molecular weight of the acid-decomposable resin is 3,000-7,000, preferably 4,000-7,000, more preferably 4,500-6,500. By appropriately adjusting the weight-average molecular weight, the dissolution rate in an alkaline developer can be made more appropriate, which is preferable from the viewpoint of sensitivity and film retention rate.
Further, the degree of dispersion of the acid-decomposable resin (the value obtained by dividing the weight average molecular weight by the number average molecular weight) is preferably 1.6 to 2.3, more preferably 1.7 to 2.3, still more preferably 1.7 to 2.3. 8 to 2.2. Compared to m/p-cresol, etc., the o-cresol novolac resin structure can be appropriately controlled, and thus the degree of dispersion can be made relatively small. Resolution can be further improved by reducing the degree of dispersion of the acid-decomposable resin.
The weight average molecular weight and degree of dispersion can be obtained by gel permeation chromatography (GPC) measurement using polystyrene as a standard substance.

The acid-decomposable resin may be produced by any method, and known synthetic methods can be applied as appropriate.
Typically, first, a novolak resin is synthesized from phenols (mainly o-cresol) and aldehydes by addition condensation (synthesis of novolac resin), and then a protecting group is introduced into the novolak resin (protection group introduction).

Phenols (mainly o-cresol) and aldehydes can be used as starting monomers for synthesizing novolak resins. As the aldehydes, formaldehyde is preferable in terms of industrial availability, cost, and the like.

Synthesis may be carried out according to a conventional method using an acid catalyst or the like. For example, it can be carried out at 60 to 150° C. for 2 to 30 hours.
A reaction solvent may be used in the synthesis. Examples of solvents include ketones such as acetone and methyl ethyl ketone, alcohols such as ethanol and butanol, esters such as ethyl acetate and butyl acetate, and ether alcohols such as ethoxyethyl alcohol. , ether ester of propylene glycol monomethyl ether acetate, and the like.
After completion of the reaction, a basic compound may be added for neutralization to remove the acid catalyst, and the neutralized salt may be removed by washing with water.

Catalysts that can be used in the synthesis include inorganic acids such as hydrochloric acid, sulfuric acid, perchloric acid and phosphoric acid, organic acids such as formic acid, acetic acid, oxalic acid, trichloroacetic acid and p-toluenesulfonic acid, zinc acetate, zinc chloride. and divalent metal salts such as magnesium acetate. These may be used alone or in combination of two or more.
After synthesis, it is preferable to remove unreacted components, oligomers, impurities, and the like.

The method for introducing the protecting group is not particularly limited. For example, when protecting the phenolic hydroxy group of the novolac resin synthesized above with a 1-ethoxyethyl group, a predetermined amount of ethyl vinyl ether is added to the novolak resin at room temperature and reacted for a predetermined time under an acid catalyst. can be obtained with When protecting with a 1-propoxyethyl group, propyl vinyl ether is added.
After introduction of the protective group, the resin may be washed with water to remove impurities and unreacted components.

The photosensitive resin composition of the present embodiment may contain two or more acid-decomposable resins as long as it exhibits good sensitivity and film retention rate. When two or more acid-decomposable resins are contained, (i) all of the acid-decomposable resins contain the above resins (that is, o-cresol-derived structural units, specific acid-decomposable groups, weight-average molecular weights is 3000 to 7000), or (ii) a part of the resin may be a resin that does not correspond to the above. However, from the viewpoint of good sensitivity and film retention rate, the photosensitive resin composition of the present embodiment preferably does not fall under (ii) above. Further, from the viewpoint of better sensitivity and film retention rate, the photosensitive resin composition of the present embodiment preferably contains only one type of acid-decomposable resin.

The content of the acid-decomposable resin in the photosensitive resin composition is not particularly limited. % by mass.

(Photoacid generator)
The photosensitive resin composition of the present embodiment contains a photoacid generator, that is, a compound that generates acid when irradiated with light.
Any photoacid generator can be used. For example, organic halides, sulfonate esters (e.g. 2-nitrobenzyl esters, aromatic sulfonates, oxime sulfonates, N-sulfonyloxyimides, sulfonyloxyketones, diazonaphthoquinone 4-sulfonates) and sulfones (e.g. disulfones, ketosulfones, sulfonyldiazomethane) can be used. Also, ionic photoacid generators such as onium salts containing onium cations (eg, diazonium salts, phosphonium salts, sulfonium salts, iodonium salts) can be used. The anions of the onium salts include sulfonate anions, sulfonylimide anions, sulfonylmethide anions, and the like.

The photoacid generator preferably contains a compound that generates a fluorine-containing acid upon irradiation with light.
A 1-ethoxyethyl group and a 1-propoxyethyl group are inherently easy to deprotect, and are considered to be sufficiently deprotected even with a relatively weak acid. However, by using an acid substituted with an atom having a strong electron-withdrawing property such as fluorine, it is believed that the effect of further improving the sensitivity can be obtained.

More preferably, the photoacid generator comprises a fluorinated alkyl phosphate sulfonium salt. More specific examples of the fluorinated alkyl sulfonium phosphate include compounds represented by the following general formulas.

In the above general formula,
R1, R2 and R3 each independently represent a hydrogen atom or a monovalent substituent,
Rf represents a fluorinated alkyl group, and n represents an integer of 1-6.

Examples of monovalent substituents for R1, R2 and R3 include alkyl groups, cycloalkyl groups, alkenyl groups, aryl groups, aralkyl groups, hydroxy groups, carboxy groups, alkoxy groups, aryloxy groups, and arylthio groups. can.
At least one of R1, R2 and R3 is preferably a phenylthio group (C ₆ H ₅ --S--). Further, when at least one of R1, R2 and R3 is a phenylthio group (C ₆ H ₅ --S--), the rest of R1, R2 and R3 are preferably hydrogen atoms.
A perfluoroalkyl group is preferable as the fluorinated alkyl group for Rf. The carbon number of Rf is between 1 and 10, for example.

The photosensitive resin composition may contain only one type of photoacid generator, or may contain two or more types.
The content of the photoacid generator in the photosensitive resin composition is not particularly limited. is 0.5 to 6% by mass.

(solvent)
The photosensitive resin composition of this embodiment contains a solvent.
Any solvent can be used. The solvent is typically an organic solvent.
Examples of organic solvents include glycol ether esters (e.g., ethyl cellosolve acetate, methyl cellosolve acetate, propylene glycol monomethyl ether acetate, etc.), glycol ethers (propylene glycol monomethyl ether, etc.), esters (ethyl lactate, butyl acetate, amyl acetate and ethyl pyruvate, etc.), ketones (acetone, methyl isobutyl ketone, 2-heptanone, cyclohexanone, etc.), lactones (γ-butyrolactone, etc.), and mixed solvents thereof.

In particular, the solvent preferably contains a cyclic ketone. The cyclic ketone is more preferably 90% by mass or more in the total amount of the solvent, still more preferably 95% by mass or more in the total amount of the solvent, and particularly preferably the total amount of the solvent.
By using a cyclic ketone as the solvent, it is possible to suppress the deterioration of the photosensitive resin composition over time during storage. More specifically, even after the photosensitive resin composition is stored for a long period of time of about 6 months or more, it is possible to suppress the decrease in the residual film ratio. In addition, according to the findings of the present inventors, the cyclic ketone solvent is more effective in forming a film from a photosensitive resin composition than other solvents (for example, commonly used propylene glycol monomethyl ether acetate). It is difficult to remain inside. As a result, the alkali solubility of the film as a whole can be made more uniform, and as a result, the rectangularity of the pattern can be improved and the aspect ratio can be further improved. Examples of cyclic ketones include cyclohexanone and cyclopentanone.
The effect of improving the rectangularity of the pattern and further improving the aspect ratio can be obtained not only with the cyclic ketone, but also with a solvent such as alkyl lactate (ethyl lactate, etc.).

(Other ingredients)
The photosensitive resin composition of the present embodiment may contain optional components other than the acid-decomposable resin, photoacid generator and solvent. For example, a compound (quencher) that has the action of capturing the acid generated from the acid generator by exposure, a substrate corrosion inhibitor, a surfactant, a sensitizer, a dissolution inhibitor, a stabilizer, an antioxidant, and other photo Additives known in the field of resists may also be included.

Examples of quenchers include amines and ammonium salts. Amines include aliphatic amines and aromatic amines. Aliphatic amines include primary, secondary and tertiary amines. More specific examples of aliphatic amines include monoalkylamines, dialkylamines, and trialkylamines. Moreover, aniline, an aniline derivative, etc. can be mentioned more specifically as an aromatic amine.

Specific examples of aliphatic or aromatic amines include 1-naphthylamine, 2-naphthylamine, aniline, diisopropylaniline, 2-, 3- or 4-methylaniline, 4-nitroaniline, N-methylaniline, N,N - dimethylaniline, diphenylamine, hexylamine, heptylamine, octylamine, nonylamine, decylamine, dibutylamine, dipentylamine, dihexylamine, diheptylamine, dioctylamine, dinonylamine, didecylamine, triethylamine, trimethylamine, tripropylamine, tributylamine, tripentylamine, trihexylamine, triheptylamine, trioctylamine, trinonylamine, tridecylamine, dibutylmethylamine, methyldipentylamine, dihexylmethylamine, dicyclohexylmethylamine, diheptylmethylamine, methyldioctylamine, methyl dinonylamine, didecylmethylamine, ethyldibutylamine, ethyldipentylamine, ethyldihexylamine, ethyldiheptylamine, ethyldioctylamine, ethyldinonylamine, ethyldidecylamine, tris[2-(2-methoxyethoxy) ethyl]amine, triisopropanolamine, ethylenediamine, tetramethylenediamine, hexamethylenediamine, 4,4'-diamino-1,2-diphenylethane, 4,4'-diamino-3,3'-dimethyldiphenylmethane, 4,4 '-diamino-3,3'-diethyldiphenylmethane and the like.

As the quencher, among nitrogen-containing heterocyclic compounds, those showing basicity can be used.

(concentration/viscosity)
It is preferable that the concentration and viscosity of the photosensitive resin composition of the present embodiment be appropriately adjusted, for example, by changing the amount or type of the solvent described above.
For example, the concentration of the non-volatile components (components other than the solvent) of the photosensitive resin composition is adjusted to 30 to 60% by mass in consideration of uniform coating with a relatively thick film by a spin coater. Preferably, it is more preferably adjusted to 45 to 60% by mass.

The photosensitive resin composition of the present embodiment exhibits good performance in relatively thick film pattern formation. More specifically, in forming a pattern with a high aspect ratio (the aspect ratio is the value of "height/line width" of the pattern), the shape of the pattern is likely to be rectangular.
The reason for this is considered as follows. The o-cresol novolac resin has a properly controlled novolak resin structure compared to conventional novolak resins (m/p-cresol, etc.). Therefore, once the protective group is deprotected, it will dissolve in the alkaline developer at a uniform speed, and the dissolution speed in the alkaline developer before and after deprotection is digitally 0 or 1, so to speak. It can be controlled. It is presumed that this makes it easier to form a rectangular pattern in the patterning of a thick film.
The effects of high aspect ratio and rectangularity of pattern shape can be obtained more reliably by appropriately selecting the solvent. For example, by using the aforementioned cyclic ketone, alkyl lactate, or the like as a solvent, a high aspect ratio and a rectangular pattern shape can be obtained.

By increasing the concentration of the non-volatile components (components other than the solvent) of the photosensitive resin composition as described above, it becomes easier to form a thick resin film, and by patterning the thick resin film, a high aspect ratio is obtained. A ratio pattern can be obtained.

From another point of view, the viscosity of the photosensitive resin composition at 25° C. is preferably 50 to 10,000 mPa s, more preferably 300 to 10,000 mPa s, and more preferably 500 to 4,000 mPa s. s is more preferred. When the viscosity of the photosensitive resin composition is relatively high, it becomes easy to form a thick resin film, and by patterning the thick resin film, a pattern with a high aspect ratio can be obtained.
Viscosity can be measured by, for example, a rotational viscometer, a Canon Fenske viscometer using a capillary tube, or a tuning fork vibrating viscometer (equipment by A&D, model number: SV-10, etc.).

<Pattern Forming Method and Electronic Device Manufacturing Method>
A pattern (typically positive pattern) can be obtained.
Further, electronic devices can be manufactured by using the obtained pattern as a mask for dry etching, ion implantation, metal sputtering or metal plating.

The film formation process, exposure process and development process described above will be briefly described.

(Film forming process)
The substrate on which the photosensitive resin film is formed is not particularly limited. Examples include glass substrates, silicon wafers, ceramic substrates, aluminum substrates, SiC wafers, GaN wafers, copper substrates, and copper-plated substrates.
The substrate may be an unprocessed substrate or a substrate having electrodes or elements formed thereon.

A method for forming the photosensitive resin film is not particularly limited. In the field of manufacturing electronic devices, spin coating using a spinner is common, but other methods may be used. For example, spray coating using a spray coater, dipping, printing, roll coating, ink jet method, and the like may be used.

Drying of the photosensitive resin composition applied on the substrate is typically performed by heat treatment. The heating temperature is usually 80-140°C, preferably 90-120°C. In addition, the heating time varies depending on the heating device, but when using a hot plate, it is usually 30 to 300 seconds, preferably about 60 to 180 seconds, and when using a hot air oven, it is usually 5 to 60 minutes, preferably It takes about 10 to 30 minutes.

The film thickness of the photosensitive resin film is not particularly limited, and may be appropriately adjusted according to the application to be applied, the pattern to be finally obtained, and the like. For example, when aiming to form copper bumps, the thickness is usually 5 to 100 μm, preferably 10 to 100 μm, more preferably 15 to 100 μm. The film thickness can be adjusted by adjusting the non-volatile component concentration in the photosensitive resin composition, changing the coating method, or the like.

(Exposure process)
The exposure process is usually performed by exposing the photosensitive resin film to actinic rays through a suitable photomask.
Actinic rays include, for example, X-rays, electron beams, ultraviolet rays, and visible rays. Light with a wavelength of 200 to 500 nm is preferable. From the viewpoint of pattern resolution and handleability, the light source is preferably g-line, h-line or i-line of a mercury lamp, and particularly preferably i-line. Also, two or more rays may be mixed and used. Exposure devices include contact aligners, mirror projection, steppers, and the like.
The amount of light for exposure may be appropriately adjusted depending on the amount of the photosensitive agent in the photosensitive resin film, and is, for example, about 100 to 500 mJ/cm ² .

If necessary, the photosensitive resin film can be heated after exposure and before the development step (post-exposure heating: Post Exposure Bake). The temperature is, for example, 70-150°C, preferably 70-120°C. Also, the time is usually 30 to 300 seconds, preferably 60 to 180 seconds when using a hot plate, for example. By heating after exposure, the deprotection reaction can be accelerated, so further enhancement of sensitivity can be expected.
However, since the 1-ethoxyethyl group and 1-propoxyethyl group are relatively easily deprotected, sufficient deprotection is possible without post-exposure heating (that is, sufficiently high deprotection is possible without post-exposure heating). sensitivity). This will also be shown in Examples described later. This "sufficiently high sensitivity can be obtained without performing post-exposure heating" has great merits in terms of production efficiency in terms of process omission/reduction of equipment.

(Development process)
A pattern can be obtained by developing the exposed photosensitive resin film with a developer. Development can be carried out using, for example, an immersion method, a paddle method, a rotary spray method, or the like. By development, the exposed portion of the photosensitive resin film is usually eluted and removed to obtain a positive pattern.

As the developer, an alkaline aqueous solution is usually used. Specific examples of alkaline aqueous solutions include (i) inorganic alkaline aqueous solutions such as sodium hydroxide, sodium carbonate, sodium silicate and ammonia, (ii) organic amine aqueous solutions such as ethylamine, diethylamine, triethylamine and triethanolamine, and (iii) Examples include aqueous solutions of quaternary ammonium salts such as tetramethylammonium hydroxide and tetrabutylammonium hydroxide.
As the developer, an aqueous tetramethylammonium hydroxide solution is particularly preferred. The concentration of tetramethylammonium hydroxide is preferably 0.1-10% by mass, more preferably 0.5-5% by mass.

A pattern can be obtained by the above steps, and it is preferable to wash the pattern and the substrate with a rinse after development. Ultrapure water is suitable as the rinse liquid.

The resulting pattern can be used, for example, as a mask for dry etching, a mask for ion implantation processes, or a mask for metal sputtering or metal plating in the manufacture of electronic devices.

Although the embodiments of the present invention have been described above, these are examples of the present invention, and various configurations other than those described above can be adopted. Moreover, the present invention is not limited to the above-described embodiments, and includes modifications, improvements, etc. within the scope of achieving the object of the present invention.
Examples of reference forms are added below.
1.
A photosensitive resin composition containing an acid-decomposable resin, a photoacid generator and a solvent,
The acid-decomposable resin is a novolac resin in which at least part of the phenolic hydroxy groups are protected with acid-decomposable groups,
The novolak resin contains a structural unit derived from o-cresol and a structural unit derived from an aldehyde,
The acid-decomposable group is at least one selected from the group consisting of a 1-ethoxyethyl group and a 1-propoxyethyl group,
The photosensitive resin composition, wherein the acid-decomposable resin has a weight average molecular weight of 3,000 to 7,000.
2.
1. A photosensitive resin composition according to
The novolac resin is a photosensitive resin composition in which substantially no structural units other than structural units derived from o-cresol are included as structural units having a phenolic hydroxy group.
3.
1. or 2. A photosensitive resin composition according to
A photosensitive resin in which 20 to 60 mol% of the phenolic hydroxy groups of the novolak resin are protected with at least one acid-decomposable group selected from the group consisting of 1-ethoxyethyl group and 1-propoxyethyl group. Composition.
4.
1. ~3. A photosensitive resin composition according to any one of
The photosensitive resin composition, wherein the photoacid generator contains a compound that generates a fluorine-containing acid upon irradiation with light.
5.
1. ~ 4. A photosensitive resin composition according to any one of
A photosensitive resin composition, wherein the solvent contains a cyclic ketone.
6.
1. ~ 5. A photosensitive resin composition according to any one of
A photosensitive resin composition having a concentration of non-volatile components in the composition of 30 to 60% by mass.
7.
1. ~6. A photosensitive resin composition according to any one of
A photosensitive resin composition having a viscosity of 50 to 10,000 mPa·s at 25°C.
8.
1. ~7. A film forming step of forming a photosensitive resin film from the photosensitive resin composition according to any one of
an exposure step of exposing the photosensitive resin film;
a developing step of developing the photosensitive resin film;
A method of forming a pattern, comprising:
9.
8. A method of manufacturing an electronic device, comprising a method of forming a pattern of

Embodiments of the present invention will be described in detail based on examples and comparative examples. In addition, the present invention is not limited to the examples.

<Synthesis of novolac resin before protection with a protecting group>
[Synthesis Example A (production of o-cresol novolak resin)]
A separable flask equipped with a thermometer, a stirrer and a reflux condenser was charged with 100 parts of o-cresol, 32.5 parts of 92% paraformaldehyde and 1.0 part of oxalic acid, and reacted for 4 hours while refluxing. 50.0 parts of propylene glycol monomethyl ether acetate was added and the temperature was raised to 120°C. The distilled water was removed. Furthermore, after reacting at 120° C. for 5 hours, the mixture was heated to 180° C. and the pressure was reduced to remove propylene glycol monomethyl ether acetate. The resin melted at 180° C. was extracted and cooled to obtain a solid o-cresol novolak resin.
The weight average molecular weight of this resin was 5,690 by gel permeation chromatography (converted to polystyrene).

[Synthesis Example B (production of o-cresol novolak resin)]
A novolak resin was obtained in the same manner as in Synthesis Example 1, except that the amount of 92% paraformaldehyde added was changed to 33.5 parts.
The weight average molecular weight of this resin was 7,980 by gel permeation chromatography (polystyrene conversion).

[Synthesis Example C (production of o-cresol novolak resin)]
A novolak resin was obtained in the same manner as in Synthesis Example 1, except that the amount of 92% paraformaldehyde added was changed to 30.5 parts.
The weight average molecular weight of this resin was 2,410 by gel permeation chromatography (polystyrene conversion).

[Synthesis Example D (manufacture of m-cresol novolak resin)]
100 parts of m-cresol, 60 parts of 37% formalin, and 0.2 parts of oxalic acid were charged into a 3 L four-necked flask equipped with a stirrer, thermometer, and heat exchanger, and refluxed at 97 to 103° C. for 4 hours. After that, dehydration was carried out under normal pressure and the internal temperature was raised to 140°C, followed by dehydration and demonomerization to an internal temperature of 200°C under a reduced pressure of 70 Torr to obtain 90 parts of a novolak type phenolic resin.
The weight average molecular weight of the obtained resin was 3000 by gel permeation chromatography (converted to polystyrene).

[Synthesis Example E (manufacture of m/p-cresol novolac resin)]
60 parts of m-cresol, 40 parts of p-cresol, 52.5 parts of 37% formalin, and 0.2 part of oxalic acid were charged in a 3 L four-necked flask equipped with a stirrer, thermometer, and heat exchanger, and the temperature was 97 to 103°C. After carrying out a reflux reaction for 4 hours, dehydration was carried out under normal pressure and the internal temperature was raised to 140°C, followed by dehydration and demonomerization to an internal temperature of 200°C under a reduced pressure of 70 Torr, resulting in 77.2 parts of a novolac-type phenolic resin. got
The weight average molecular weight of the obtained resin was 7000 by gel permeation chromatography (converted to polystyrene).

[Synthesis Example F (manufacture of m/p-cresol + 3,5-xylenol novolac resin)]
45 parts of meta-cresol, 25 parts of para-cresol, 30 parts of 3,5-xylenol, 37.5 parts of 37% formalin, and 0.2 part of oxalic acid were placed in a 3 L four-necked flask equipped with a stirrer, thermometer, and heat exchanger. and subjected to a reflux reaction at 97 to 103° C. for 4 hours, followed by dehydration under normal pressure and raising the internal temperature to 140° C., followed by dehydration and demonomerization up to an internal temperature of 200° C. under a reduced pressure of 70 Torr. 90 parts of a mold phenolic resin were obtained.
The weight average molecular weight of the obtained resin was 5000 by gel permeation chromatography (converted to polystyrene).

<Synthesis of acid-decomposable resin (protection of phenolic hydroxyl group)>
[Synthesis Example 1 (protection with an alkoxyalkyl group)]
First, the novolak resin obtained in Synthesis Example A was dissolved in cyclopentanone so that the resin content concentration was 15%.
Next, 130 g of the above resin solution and 3.6 mg of p-toluenesulfonic acid monohydrate were charged in a flask. After 7.8 g of ethyl vinyl ether was added dropwise to this resin solution, the mixture was allowed to react at room temperature for 3 hours. After that, in order to remove the acid catalyst, a washing process of adding ion-exchanged water to the reaction solution, stirring the reaction solution, allowing it to stand, and extracting the organic layer by liquid separation was repeated five times. The organic layer finally taken out was concentrated while also removing moisture. A resin solution having a resin concentration of 59% was obtained.
Analysis of the resulting resin by ¹ H-NMR revealed that 46.5% of the phenolic hydroxyl groups in the novolac resin were protected with 1-ethoxyethyl groups.

[Synthesis Example 2 (protection with an alkoxyalkyl group)]
The reaction and concentration were carried out in the same manner as in Synthesis Example 1, except that ethyl vinyl ether was changed to NPVE (propyl vinyl ether) as the starting material for the protective group. A resin solution having a resin concentration of 56% was obtained.
Analysis of the resulting resin by ¹ H-NMR revealed that 55.7% of the phenolic hydroxyl groups in the novolac resin were protected with 1-propoxyethyl groups.

[Synthesis Example 3 (protection with alkoxyalkyl group)] (for comparison)
The novolak resin used was the m-cresol novolak resin synthesized in Synthesis Example D dissolved in cyclopentanone so that the content concentration was 15%. rice field. A resin solution having a resin concentration of 55% was obtained.
Analysis of the resulting resin by ¹ H-NMR revealed that 43.4% of the phenolic hydroxyl groups in the novolak resin were protected with 1-ethoxyethyl groups.

[Synthesis Example 4 (protection with alkoxyalkyl group)] (for comparison)
React and concentrate in the same manner as in Synthesis Example 2 except that the m/p-cresol novolac resin synthesized in Synthesis Example E was dissolved in cyclopentanone so that the content concentration was 15%. I went to A resin solution having a resin concentration of 57% was obtained.
Analysis of the resulting resin by ¹ H-NMR revealed that 39.8% of the phenolic hydroxyl groups in the novolak resin were protected with 1-propoxyethyl groups.

[Synthesis Example 5 (protection with alkoxyalkyl group)] (for comparison)
Same as Synthesis Example 2 except that the m/p-cresol + 3,5-xylenol novolac resin synthesized in Synthesis Example F was dissolved in cyclopentanone so that the content concentration was 15%. and concentrated. A resin solution having a resin concentration of 56% was obtained.
Analysis of the resulting resin by ¹ H-NMR revealed that 38.6% of the phenolic hydroxyl groups in the novolac resin were protected with 1-propoxyethyl groups.

[Synthesis Example 6 (protection with t-BOC group)] (for comparison)
The reaction and concentration were carried out in the same manner as in Synthesis Example 1, except that di-tert-butyl dicarbonate was used instead of ethyl vinyl ether as the starting material for the protective group. A resin solution having a resin concentration of 53% was obtained.
Analysis of the resulting resin by ¹ H-NMR revealed that 53.4% of the phenolic hydroxyl groups in the novolak resin were protected with t-butoxycarbonyl groups (t-BOC).

[Synthesis Example 7 (protection with THP group)] (for comparison)
The reaction and concentration were carried out in the same manner as in Synthesis Example 1, except that ethyl vinyl ether was changed to dihydropyran as the starting material for the protective group. Then, a resin solution having a resin concentration of 52% was obtained.
Analysis of the resulting resin by ¹ H-NMR revealed that 50.8% of the phenolic hydroxyl groups in the novolac resin were protected with tetrahydropyranyl groups (THP).

[Synthesis Example 8 (protection with an alkoxyalkyl group)]
The reaction was carried out in the same manner as in Synthesis Example 1 except that the novolak resin used was Synthesis Example B, and the reaction was carried out up to the concentration. A resin solution having a resin concentration of 57% was obtained.
Analysis of the resulting resin by ¹ H-NMR revealed that 48.3% of the phenolic hydroxyl groups in the novolac resin were protected with 1-ethoxyethyl groups.

[Synthesis Example 9 (protection with an alkoxyalkyl group)]
The reaction was carried out in the same manner as in Synthesis Example 1, except that the novolac resin used was Synthesis Example C, and the concentration was carried out. A resin solution having a resin concentration of 59% was obtained.
Analysis of the resulting resin by ¹ H-NMR revealed that 47.7% of the phenolic hydroxyl groups in the novolak resin were protected with 1-ethoxyethyl groups.

[Synthesis Example 10 (protection with an alkoxyalkyl group)]
Synthesis was carried out in the same manner as in Synthesis Example 1 except that methyl isobutyl ketone (MIBK) was used as the solvent, and the washing process was repeated five times. While removing, it was replaced with a propylene glycol monomethyl ether acetate (PGMEA) solvent. At this time, the reaction was carried out at 100° C. or lower in order to prevent removal of the protective group.
The solid content of the PGMEA solution of the obtained resin was 54%. ¹ H-NMR analysis of the obtained resin revealed that 42.5% of the phenolic hydroxyl groups of the novolac resin were protected with ethoxyethyl.

[Synthesis Example 11 (protection with an alkoxyalkyl group)]
Synthesis was carried out in the same manner as in Synthesis Example 2 except that methyl isobutyl ketone (MIBK) was used as the solvent, and the washing process was repeated five times. While removing, it was replaced with ethyl lactate (EL) solvent. At this time, the reaction was carried out at 100° C. or lower in order to prevent removal of the protective group.
The solid content of the EL solution of the obtained resin was 53%. ¹ H-NMR analysis of the obtained resin revealed that 41.8% of the phenolic hydroxyl groups of the novolak resin were protected with ethoxyethyl.

<Preparation of photosensitive resin composition>
In a room under yellow light, each of the protected novolak resin solutions obtained in Synthesis Examples 1 to 11 was charged with a predetermined amount of the photoacid generator and other materials shown in Table 1, and stirred at room temperature for 3 hours. and dissolved. The dissolved solution was filtered under nitrogen pressure through a polypropylene membrane capsule filter having a pore size of 1.0 μm to obtain a photosensitive resin composition.
Table 1 summarizes the constituent components of the photosensitive resin composition, the amount of each component, the concentration of non-volatile components, the viscosity, and the like.
Although not shown in Table 1, the degree of dispersion (based on GPC measurement) of the acid-decomposable resins used in Examples 1 to 4 was about 1.9 to 2.1.

In Table 1, CPI-210S is a photoacid generator manufactured by San-Apro (fluorinated alkyl phosphate sulfonium salt, structure corresponding to the above general formula).
The quencher "TEA" stands for triethylamine.
The solvent "PGMEA" represents propylene glycol monomethyl ether acetate, and "EL" represents ethyl lactate.
Viscosity is a value measured by a tuning fork type vibration viscometer (equipment of A&D Co., model number: SV-10) (viscosity was measured only for the photosensitive resin compositions of Examples 1 to 4. ).

<Evaluation>
Each of the compositions listed in Table 1 was dropped onto a 4-inch silicon wafer, applied using a spin coater, and then prebaked on a hot plate at 100° C. for 60 seconds. The film thickness of the sample after pre-baking was measured with an optical film thickness meter (F-20, manufactured by FILMMETRICS). The target film thickness was set to 15 μm, and the coating-baking process was repeated several times while adjusting the spin speed to obtain a coated sample with a film thickness of 15 μm±0.5 μm.
After that, an exposure apparatus (Mask Aligner MA-20 manufactured by Mikasa Co., Ltd.) using an ultra-high pressure mercury lamp (g-line, h-line, i-line mixed wavelength) as a light source was used to obtain various patterns with a line and space width of 1:1. It was exposed through a test pattern mask with uniform line width. After exposure, the film was developed by being immersed in a 2.38% aqueous tetramethylammonium hydroxide solution, and then rinsed with ultrapure water to obtain a resist pattern. A post-exposure bake (PEB) step was not performed. Each performance was evaluated as follows.

[sensitivity]
During the exposure, the wafer was partially masked so that only a part of the wafer was exposed to the exposure light, and the exposure was repeated by changing the exposure amount while appropriately shifting the masked area. As a result, exposed wafers were obtained in which the exposure amount was increased stepwise from 100 to 300 mJ/cm ² in steps of 50 mJ/cm ² .
After developing and rinsing this wafer, the pattern was observed with an optical microscope. The minimum exposure dose (50 mJ/cm ² steps) was taken as the sensitivity. And it evaluated in the following three steps.
High: Sensitivity 150 mJ/cm ² or less Medium: Sensitivity 200 mJ/cm ² or more, 250 mJ/cm ² or less Low: Sensitivity 300 mJ/cm ² or more

[Remaining film rate]
The film thickness of the unexposed portion after development and rinsing was measured and divided by the initial film thickness (15 μm) to obtain the residual film ratio. And it evaluated in the following three steps.
High: 90% or more Medium: 80% or more, less than 90% Low: Less than 80%

[Pattern profile]
The cross-sectional shape of the 10 μm line resist was observed with an electron microscope (SEM) at a location (+50 mJ/cm ² ) where the exposure dose for one step was larger than the minimum exposure dose on the substrate subjected to the sensitivity measurement, and the profile shape was determined.
The reason for observation at a place where the exposure amount is one step higher than the minimum exposure amount is as follows.
Observed with an optical microscope, the bottom portion of the resist pattern is usually not completely removed at the minimum exposure dose, and the resist line width is often slightly thicker than the mask line width. Therefore, it is reasonable to consider that the optimum exposure amount is about 1.1 to 2.0 times the minimum exposure amount, so the observation position of this profile is set to the exposure amount that is one step higher, that is, the point of the optimum exposure amount.

[Resolution and Aspect Ratio]
As with the pattern profile described above, a portion thinner than the 10 μm line and space is observed at an exposure location that is one step higher than the minimum exposure dose, that is, at the location of the optimum exposure dose, and the minimum line where the space portion is open The width is the resolution. The mask used has a line & space pattern with a step size of 1 μm for 10 μm or less and a minimum of 1 μm.
Further, like the resolution, the aspect ratio is also an index for judging the quality of the registration performance. The aspect ratio is the ratio of resist profile height (film thickness)/line width. The aspect ratio in the table is the value obtained by dividing the initial film thickness (15 μm) by the minimum line width, which is the resolution.

[Stability over time (remaining film rate)]
The prepared photosensitive resin composition was stored at 25°C for 6 months. Using this composition, the same evaluation as the above [Remaining film rate] was performed. It was compared with the residual film rate immediately after preparation, and was evaluated in the following two stages.
Good: Decrease of less than 10 points Poor: Decrease of 10 points or more

Table 2 summarizes the evaluation results.

As shown in Table 2, an acid-decomposable resin having a weight average molecular weight of 3000 to 7000, in which at least part of the phenolic hydroxyl groups of the o-cresol novolac resin is protected with a 1-ethoxyethyl group or a 1-propoxyethyl group. When patterns were formed using the photosensitive resin compositions (Examples 1 to 4) containing the above, good results were obtained in terms of both sensitivity and residual film ratio.
In particular, in Examples 1, 2 and 4 using cyclic ketone (cyclopentanone or cyclohexanone) or alkyl lactate (ethyl lactate) as the solvent, the pattern profile and aspect ratio were also good.
In particular, in Examples 1 and 2 using a cyclic ketone (cyclopentanone or cyclohexanone) as a solvent, the stability over time was also good.

On the other hand, Comparative Examples 1 to 3 using a resin in which the phenolic hydroxyl group of a phenolic resin that is not an o-cresol novolac resin is protected, the phenolic hydroxyl group is protected with a protecting group that is neither a 1-ethoxyethyl group nor a 1-propoxyethyl group. In the photosensitive resin compositions of Comparative Examples 4 and 5 using an o-cresol novolak resin, and Comparative Examples 6 and 7 in which the weight-average molecular weight of the resin was outside the range of 3000 to 7000, both sensitivity and residual film ratio were achieved. No effect was obtained.

It should be noted that the photosensitive resin compositions of Examples 1 to 4 exhibit sufficiently high sensitivity without post-exposure heating. This is thought to be related to the ease of deprotection of the 1-ethoxyethyl group and 1-propoxyethyl group. This property that "sufficiently high sensitivity can be obtained without performing post-exposure heating" is very favorable from the standpoint of production efficiency, such as the reduction of equipment and shortening of takt time.

Claims (9)

A photosensitive resin composition containing an acid-decomposable resin, a photoacid generator and a solvent,
The acid-decomposable resin is a novolac resin in which at least part of the phenolic hydroxy groups are protected with acid-decomposable groups,
The novolak resin contains a structural unit derived from o-cresol and a structural unit derived from an aldehyde,
The novolak resin substantially does not contain structural units other than structural units derived from o-cresol as structural units having a phenolic hydroxy group,
The acid-decomposable group is at least one selected from the group consisting of a 1-ethoxyethyl group and a 1-propoxyethyl group,
The acid-decomposable resin has a weight average molecular weight of 3000 to 7000 ,
The photosensitive resin composition, wherein the photoacid generator contains a compound that generates a fluorine-containing acid upon irradiation with light . A photosensitive resin composition containing an acid-decomposable resin, a photoacid generator and a solvent,
The acid-decomposable resin is a novolac resin in which at least part of the phenolic hydroxy groups are protected with acid-decomposable groups,
The novolak resin contains a structural unit derived from o-cresol and a structural unit derived from an aldehyde,
The novolak resin substantially does not contain structural units other than structural units derived from o-cresol as structural units having a phenolic hydroxy group,
The acid-decomposable group is at least one selected from the group consisting of a 1-ethoxyethyl group and a 1-propoxyethyl group,
The acid-decomposable resin has a weight average molecular weight of 3000 to 7000,
A photosensitive resin composition in which the concentration of nonvolatile components in the photosensitive resin composition is 30 to 60% by mass. The photosensitive resin composition according to claim 1 or 2,
A photosensitive resin in which 20 to 60 mol% of the phenolic hydroxy groups of the novolak resin are protected with at least one acid-decomposable group selected from the group consisting of 1-ethoxyethyl group and 1-propoxyethyl group. Composition. The photosensitive resin composition according to claim 2 ,
The photosensitive resin composition, wherein the photoacid generator contains a compound that generates a fluorine-containing acid upon irradiation with light. The photosensitive resin composition according to any one of claims 1 to 4,
A photosensitive resin composition, wherein the solvent contains a cyclic ketone. The photosensitive resin composition according to claim 1 ,
A photosensitive resin composition having a concentration of non-volatile components in the composition of 30 to 60% by mass. The photosensitive resin composition according to any one of claims 1 to 6,
A photosensitive resin composition having a viscosity of 50 to 10,000 mPa·s at 25°C. A film forming step of forming a photosensitive resin film from the photosensitive resin composition according to any one of claims 1 to 7;
an exposure step of exposing the photosensitive resin film;
and a developing step of developing the photosensitive resin film. A method of manufacturing an electronic device, comprising the pattern forming method of claim 8 .