JPH05289331A - Positive photoresist composition - Google Patents

Abstract

PURPOSE:To provide a positive photoresist composition excellent in heat resistance without deteriorating sensitivity and resolution by making it contain a specific photosensitive compound. CONSTITUTION:An alkali soluble resin is a polycondensation material of at least one kind of a phenolic compound expressed by a formula I with at least one kind of ketons or aldehydes expressed by a formula II and the weight average molecular weight of the polycondensation material by gel permeation chromatography is 2500-30000 expressed in terms of polystyrene. And a quinone diazide photosensitive compound mainly contains a quinone azide sulfonic esterified material which is a polycondensation compound of at least one kind of the phenolic compound expressed by the formula I and at least one kind of a hydroxy aromatic aldehyde expressed by a formula III and the weight average molecular weight of the polycondensation compound is 600-2000 expressed in terms of polystyrene. In the formula I-III, R<1> is a 1-4C alkyl group or the like, each of R<2> and R<3> is hydrogen atom, an allyl group or the like and R<4> is hydrogen atom or the like.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a positive photoresist composition. More specifically, the present invention relates to a positive photoresist composition containing an alkali-soluble resin, a quinonediazide-based photosensitive compound and a solvent as main components and sensitive to radiation such as ultraviolet rays, far ultraviolet rays, electron beams and X-rays.

[0002]

2. Description of the Prior Art Positive photoresist compositions are usually composed mainly of an alkali-soluble resin, a photosensitive compound and a solvent. Currently, as a generally used positive photoresist composition for semiconductors, a novolak resin is used as an alkali-soluble resin, and a condensate (esterified product) of naphthoquinonediazide sulfonic acid chloride and hydroxybenzophenone is used as a photosensitizer. And these are dissolved in a solvent such as ethyl cellosolve acetate (see, for example, JP-A-58-17112 and JP-A-62-136637).

Various processes for forming a pattern of such a positive photoresist are known, and the general principle is as follows. That is, in the irradiation part, the quinonediazide type photosensitive compound (hereinafter referred to as "photosensitizer") is decomposed to generate indenecarboxylic acid, which is easily dissolved in the alkaline aqueous solution. On the other hand, in the non-irradiated area, the solubility of the alkali-soluble novolac resin in the alkali developing solution is inhibited by the photosensitizer (hereinafter, this inhibiting effect is referred to as “masking effect”), so that it becomes difficult to dissolve in the alkali developing solution and a high residual film thickness is obtained. Hold the rate. As a result, a high resolution resist pattern can be obtained.

[0004]

In recent years, the miniaturization of integrated circuits has advanced along with higher integration, and nowadays, submicron pattern formation is required, resulting in excellent resolution and high sensitivity. A positive photoresist is desired. With the miniaturization, dry etching has become the mainstream instead of the conventional wet etching. Due to this dry etching, the heat resistance of the resist has been required more than ever. Generally, the improvement of heat resistance is achieved by increasing the molecular weight of the alkali-soluble novolac resin used for the positive photoresist, but this method causes a significant decrease in sensitivity. It causes a very serious inconvenience that the performance of is worse. In view of the background described above, an object of the present invention is to provide a positive photoresist composition having excellent heat resistance without deteriorating the sensitivity and resolution as compared with conventional products.

[0005]

In order to solve such a problem, the inventors of the present invention have conducted extensive studies, and as a result, as a photosensitive compound, a naphthoquinonediazide compound which is a photosensitive component is used as an alkali resin which is a binder resin. Soluble resin is combined with another low molecular weight novolak resin, and by selecting a compound in which this novolak resin is a polycondensate of a specific phenolic compound and hydroxyaromatic aldehydes, We have found that the photoresist containing this photosensitive compound has high heat resistance without deteriorating the sensitivity and resolution as compared with the conventional products, and arrived at the present invention.

That is, the gist of the present invention is a positive photoresist composition comprising an alkali-soluble resin, a quinonediazide photosensitive compound, and a solvent, wherein the alkali-soluble resin is at least one of the following general formula [A]. A polycondensation product [C-1] of a phenolic compound and at least one ketone or aldehyde represented by the following general formula [B-1], and gel permeation chromatography of the polycondensation product [C-1]. Has a polystyrene-reduced weight average molecular weight of 2,500 to 30,000, and a quinonediazide-based photosensitive compound is at least one phenolic compound represented by the following general formula [A] and at least one represented by the following general formula [B-2]. Polycondensate with one kind of hydroxyaromatic aldehyde [C-2]
And a polystyrene-reduced weight average molecular weight of the polycondensate [C-2] is 600 to 2000, which is a positive photoresist composition.

[0007]

[Chemical 4]

[0008]

[Chemical 5]

[0009]

[Chemical 6]

(In the formula, R ¹ represents an alkyl group having 1 to 4 carbon atoms, an alkoxy group having 1 to 4 carbon atoms, or a hydroxyl group, and R ² and R ³ each represent a hydrogen atom or an alkyl group having 1 to 4 carbon atoms. A group, an aryl group or an aralkyl group, R ⁴
Is a hydrogen atom, an alkyl group having 1 to 4 carbon atoms or 1 to 4 carbon atoms
4 is an alkoxy group, 1 is an integer of 0 to 3, m and n are integers of 1 to 5, respectively, and the sum of m and n is 5. However, when 1 or m is an integer of 2 or more, a plurality of R
¹ or R ⁴ may be the same or different. )

The present invention will be described in detail below. In the positive photoresist composition of the present invention, the alkali-soluble resin as the binder resin is at least one phenolic compound represented by the general formula [A] and at least one phenolic compound represented by the general formula [B-1]. It is a polycondensate with a ketone or an aldehyde (hereinafter sometimes referred to as a novolac resin). 1 carbon atom in the general formula [A]
As the alkyl group of ~ 4, methyl group, ethyl group, n-
Examples of the alkoxy group having 1 to 4 carbon atoms such as propyl group include methoxy group, ethoxy group, n-propoxy group and the like.

Specific examples of the phenolic compound represented by the above formula [A] include phenol; o-cresol, m-cresol, p-cresol, 3,5-
Dimethylphenol, 2,5-dimethylphenol,
2,3-dimethylphenol, 3,4-dimethylphenol, 2,3,5-trimethylphenol, 3,4,5
-Trimethylphenol, 2-t-butylphenol,
3-t-butylphenol, 4-t-butylphenol, resorcinol, 2-methylresorcinol, 4-
Methylresorcinol, 5-methylresorcinol, catechol, 4-t-butylcatechol, pyrogallol,
2-methoxyphenol, 3-methoxyphenol, 4
-Methoxyphenol, 2-methoxyresorcinol,
2,3-dimethoxyphenol, 2,5-dimethoxyphenol, 3,5 dimethoxyphenol, 2-ethylphenol, 3-ethylphenol, 4-ethylphenol, 2,3,5-triethylphenol, 3,4,5-
Triethylphenol, 2,3-diethylphenol,
3,5-diethylphenol, 2-isopropylphenol, 3-isopropylphenol, 4-isopropylphenol, 2-propylphenol, 3-propylphenol, 4-propylphenol, 2-methoxy-5
Examples thereof include monohydric or polyhydric phenols which may be substituted with an alkyl group, an alkoxy group or the like such as -methylphenol and 2-t-butyl-5-methylphenol.

In the above general formula [A], R ¹ is preferably a methyl group or a hydroxyl group. In particular,
o-cresol, m-cresol, p-cresol,
3,5-dimethylphenol, 2,5-dimethylphenol, 2,3-dimethylphenol, 3,4-dimethylphenol, 2,3,5-trimethylphenol, 3,
4,5-Trimethylphenol, resorcinol, 2-
Methylresorcinol and pyrogallol are preferred. These compounds may be used alone or in combination of two or more.

In the general formula [B-1], the alkyl groups represented by R ² and R ³ are the same as those of R ^1, and the aryl group includes phenyl group, naphthyl group and the like aralkyl group. Examples thereof include a benzyl group. Examples of the ketone or aldehyde represented by the general formula [B-1] include aldehydes such as formaldehyde, acetaldehyde, propionaldehyde, benzaldehyde, acetone, methyl ethyl ketone, acetophenone,
Examples thereof include ketones such as benzophenone. Of these, formaldehyde, alkyl aldehydes having 2 to 4 carbon atoms, benzaldehyde, and acetone are preferable. More preferred are formaldehyde, acetaldehyde and acetone. These compounds may be used alone or in combination of two or more.

A method for producing the above-mentioned alkali-soluble resin is according to a conventional method, for example, in the presence of an acid catalyst,
A method of mixing and heating to cause polycondensation can be mentioned. Examples of the acid catalyst include inorganic acids such as hydrochloric acid, nitric acid and sulfuric acid, and organic acids such as formic acid, oxalic acid and acetic acid, which may be used alone or in combination. In the polycondensation reaction of the present invention, a reaction solvent is not usually used, but a solvent can also be used. Examples of these solvents include methanol,
Examples thereof include alcohols such as ethanol and propanol, and ethers such as ethylene glycol dimethyl ether and diethylene glycol dimethyl ether. The reaction temperature varies depending on the phenolic compound represented by the general formula [A], but is usually about 10 to 200 ° C, preferably about 20 to 150 ° C. After completion of the reaction, generally, the internal temperature is raised to about 150 ° C to 250 ° C, the unreacted raw materials, the acid catalyst and water are distilled off under reduced pressure, and then the molten alkali-soluble resin is taken out. Alternatively, the product using a reaction solvent can be obtained by adding the reaction mixture to a solvent such as water after the reaction is completed to cause the alkali-soluble resin to break out, and filtering the dried product to dryness. These alkali-soluble resins may be used alone or in combination of two or more. The alkali-soluble resin of the present invention has a polystyrene-reduced weight average molecular weight (hereinafter referred to as “MW”) of 2500 to 3000 by gel permeation chromatography.
It is 0. When the MW is less than 2500, the heat resistance of the positive photoresist is deteriorated, and when it exceeds 30,000, the sensitivity is remarkably deteriorated, and it is difficult to obtain a good alkali-soluble resin.

On the other hand, as the quinonediazide photosensitive compound used in the present invention, at least one phenolic compound represented by the general formula [A] and the general formula [B-
It is essential to use a quinonediazide sulfonic acid esterified product of a polycondensation product [C-2] with at least one hydroxyaromatic aldehyde represented by 2].
Examples of the phenolic compound represented by the general formula [A] that is a raw material of the quinonediazide-based photosensitive compound include the same compounds as those exemplified as the phenolic compound that is a raw material of the alkali-soluble resin that is the binder resin. Can be done. These compounds may be used alone or in combination of two or more.

On the other hand, examples of the alkyl group and the alkoxy group in the general formula [B-2] include the same ones as R ¹ . Examples of the hydroxyaromatic aldehydes represented by the general formula [B-2] include o-hydroxybenzaldehyde, m-hydroxybenzaldehyde, p-hydroxybenzaldehyde, vanillin, orthovanillin, 4
-Hydroxy-3-methylbenzaldehyde, 2,6-
Dimethyl-4-hydroxybenzaldehyde, 3,6-
Dimethyl-4-hydroxybenzaldehyde, 3,5-
Dimethyl-4-hydroxybenzaldehyde, 2,3-
Dihydroxybenzaldehyde, 2,4-dihydroxybenzaldehyde, 2,5-dihydroxybenzaldehyde, 3,4-dihydroxybenzaldehyde, 2-hydroxy-4-methoxybenzaldehyde, 2-hydroxy-5-methoxybenzaldehyde, 3-hydroxy-4-methoxybenzaldehyde , 5-hydroxy-4
-Methoxybenzaldehyde and the like can be mentioned.
These compounds may be used alone or in combination of two or more.

As the method for producing the polycondensate [C-2] from the phenolic compound represented by the general formula [A] and the hydroxyaromatic aldehyde represented by the general formula [B-2], the alkali is used. The same method as for the soluble resin [C-1] is adopted. However, the polycondensate [C-2] has a polyethylene equivalent weight average molecular weight of 600 to 200.
It should be 0, preferably 700-1800. When the molecular weight of the polycondensate [C-2] is too small, a satisfactory masking effect cannot be obtained and a good pattern profile cannot be obtained. Conversely, if the molecular weight is too high,
Significant deterioration of sensitivity.

The quinonediazidesulfonyl group for esterifying the hydroxyl group of the polycondensate [C-2] is 1,2
-Benzoquinonediazide-4-sulfonyl group, 1,2-
Examples thereof include a naphthoquinonediazide-4-sulfonyl group and a 1,2-naphthoquinonediazide-5-sulfonyl group. Esterification rate of quinonediazide sulfonic acid ester of polycondensate [C-2], that is, polycondensate [C-2]
Substitution ratio of quinonediazidesulfonyl group to hydrogen of hydroxyl group of [(quinonediazidesulfonyl group per molecule of quinonediazide sulfonic acid ester of polycondensate [C-2]) / (hydroxyl group per molecule of polycondensate [C-2] Number). ] Is about 30 to 100%, preferably about 35 to 80%.

The esterification reaction of the polycondensate [C-2] is usually carried out by reacting the polycondensate [C-2] with a predetermined amount of quinonediazidesulfonic acid chloride in an organic solvent at room temperature. can do. In the present invention, a polycondensate [C-2] synthesized from the above-mentioned specific raw material is used.
A compound having a quinonediazide-based photosensitive component bonded to is used as a photosensitive compound. At this time, two or more kinds of the photosensitive compounds may be used in combination. Furthermore, 1,2-naphthoquinonediamide-5-of polyhydroxybenzophenone is used within a range that does not significantly impair the effects of the above photosensitive compound.
You may mix and use some conventionally well-known some photosensitive compounds, such as a sulfonic acid ester compound.

The solvent used in the present invention may be any solvent as long as it can dissolve the above-mentioned quinonediazide type photosensitive compound and alkali-soluble resin.
From the viewpoint of operability during use, those having a boiling point of 100 to 180 ° C. are preferable. These solvents include ether esters such as ethyl cellosolve acetoate, methyl cellosolve acetoate, and propylene glycol monomethyl ether acetate, ether alcohols such as ethyl cellosolve, methyl cellosolve, and propylene glycol monomethyl ether, and carvone such as ethyl acetate and butyl acetate. Acid esters, kents such as γ-butyrolactone, cyclic ketones such as cyclohexanone, carboxylic acid esters of dibasic acids such as dier oxalate and dityl malonate, and glycols such as ethylene glycol diacetate and propylene glycol diacetate. Examples include oxycarboxylic acid esters such as dicarboxylic acid esters, ethyl 2-oxypropionate, methyl 3-methoxypropionate, and ethyl 3-ethoxypropionate. . These solvents can be used alone or in combination of two or more.

The concentration of the alkali-soluble resin in the photoresist composition of the present invention is usually 1 to 30% by weight. Further, the concentration of the quinonediazide photosensitive compound is
It is 0.1 to 15% by weight. Furthermore, the ratio of the quinonediazide photosensitive compound to the alkali-soluble resin is usually 0.1 to 0.5 times by weight. If necessary, a surfactant such as polyoxyethylene ethers and fluoroalkyl esters may be added to the photoresist composition of the present invention in order to improve coating properties such as striation. The addition amount of these is usually 2% by weight or less, preferably 1% by weight or less. Further, a dye or the like may be added to reduce the influence of diffused light reflected from the substrate during image transfer, and a sensitizer or the like may be added to improve sensitivity.

The photoresist composition of the present invention is used after undergoing the steps of coating, exposing and developing on a substrate according to known methods. The substrate on which the photoresist composition is applied is a semiconductor substrate such as a silicon wafer. A spin coater is usually used to apply the photoresist composition to such a substrate, and the film thickness of the photoresist composition is usually about 0.3 to 5 μm. Usually, after coating the photoresist composition, the substrate is heated on a hot plate or the like to remove the solvent, and then exposed through a mask to print a desired pattern on the substrate. For exposure, g-line (436 nm), i
Light having a wavelength of 330 to 450 nm such as a line (365 nm) is preferably used. After exposure, the substrate may be 90-
After heating at about 120 ° C. for about 60 to 120 seconds, development is performed with an alkaline aqueous solution. Examples of the alkaline aqueous solution include inorganic alkalis such as potassium hydroxide, sodium carbonate, sodium silicate, sodium metasilicate and aqueous ammonia, primary amines such as ethylamine and n-propylamine, diethylamine and di-n-propylamine. An alkaline aqueous solution consisting of an aqueous solution of a secondary amine such as triethylamine, a tertiary amine such as trimethylamine, or a quaternary ammonium base such as tetramethylammonium hydroxide or trimethylhydroxyethylammonium hydroxide is preferably used. .. Incidentally, alcohol, a surfactant and the like may be added to the developing solution, if necessary.

[0024]

EXAMPLES Hereinafter, the specific embodiments of the present invention will be described in more detail with reference to Examples, but the present invention is not limited to the following Examples unless it exceeds the gist. still,
In the following examples, the molecular weight is the polystyrene-equivalent weight average molecular weight as a result of analysis by gel permeation chromatography, and the esterification rate is the esterification rate obtained from the charged molar ratio.

Novolak Resin Synthesis Example 1 m-cresol 237.9 was added to a 1 liter separable flask.
g, p-cresol 190.3 g, 2,5-xylenol 53.7 g, oxalic acid 15 g, and 35% hydrochloric acid 1 ml were charged, and 90% acetaldehyde 30.
1 g is added dropwise. After that, the internal temperature was raised to 95 ° C, and 37%
200.0 g of formalin aqueous solution was dropped, and the reaction was carried out for 5 hours while maintaining the temperature. Then the internal temperature is 180 ℃
Water was distilled out of the system while heating the temperature over 1.5 hours, and after the distillation, the internal temperature was further raised to 195 ° C. and the unreacted monomer was distilled off under reduced pressure of 20 torr. Resin (a) was obtained. The molecular weight of this resin was 4,500. Novolac resin synthesis example 2 m-cresol 190.3 was added to a 1 l separable flask.
g, p-cresol 237.9 g, 2,5-xylenol 53.7 g, and oxalic acid 15 g were charged, and the internal temperature was adjusted to 9 while stirring.
The temperature was raised to 5 ° C, and 246.0 g of 37% formalin aqueous solution was added.
The mixture was added dropwise and the reaction was carried out for 5 hours while maintaining the temperature. Then, water was distilled out of the system while raising the inner temperature to 180 ° C over 1.5 hours, and after the distillation, the inner temperature was further raised to 195 ° C and the unreacted monomer was reduced under a reduced pressure of 20 torr. Was distilled off to obtain a novolak resin (b). The molecular weight of this resin is 6
It was 500.

Novolak Resin Synthesis Example 3 A novolak resin (c) was obtained in the same manner as in Novolak Resin Synthesis Example 2 except that 475.2 g of m-cresol, 15 g of oxalic acid and 196.4 g of a 37% aqueous formalin solution were used.
The molecular weight of this resin was 986. Novolac resin synthesis example 4 m-cresol 21.6 in a 200 ml four neck flask
g, 2-hydroxybenzaldehyde 18.3 g, 35
% Hydrochloric acid 0.5 ml and ethanol 50 ml were charged, the oil bath temperature was maintained at 100 ° C., and the mixture was heated under reflux for 7 hours to carry out the reaction. After completion of the reaction, the reaction solution was dropped into 1 liter of water with stirring to crystallize. The obtained crystallized product was filtered, washed 3 times with 1 l of water and then dried to obtain a novolak resin (d). The molecular weight of this resin was 950.

Novolak Resin Synthesis Example 5 A novolak resin (e) was prepared in the same manner as in Novolak Resin Synthesis Example 4 except that 18.3 g of 4-hydroxybenzaldehyde was used instead of 2-hydroxybenzaldehyde.
Got The molecular weight of this resin was 720. Photosensitizer Synthesis Example 1 18.92 g of novolak resin (d) and 24.12 g of 1,2-naphthoquinone diad-5-sulfonyl chloride.
100 ml of acetone, 30 m of N-methylpyrrolidone
dissolved in a mixed solvent of 1 and triethylamine 9.85 g
Was added dropwise and the mixture was reacted at room temperature for 2 hours, then the reaction solution was filtered to remove triethylamine hydrochloride. The filtrate was added to 1 liter of water with stirring, and the precipitated crystal product was filtered, washed with water, and dried to obtain a photosensitizer (P-1). The esterification rate of the photosensitizer (P-1) is 50%.

Photosensitizer Synthesis Example 2 21.60 g of novolak resin (e) and 27.77 g of 1,2-naphthoquinone diad-5-sulfonyl chloride.
130 ml of acetone, 36 m of N-methylpyrrolidone
1 of the mixed solvent, triethylamine 11.30
A photosensitizer (P-2) was obtained in the same manner as in Photosensitizer Synthesis Example 1 except that g was dropped. The esterification rate of the photosensitizer (P-2) is 50%. Photosensitizer Synthesis Example 3 Novolak resin (c) 39.40 g and 1,2-naphthoquinone diad-5-sulfonyl chloride 58.00 g
240 ml of acetone and 65 m of N-methylpyrrolidone
1 of a mixed solvent of triethylamine 22.10
A photosensitizer (P-3) was obtained in the same manner as in Photosensitizer Synthesis Example 1 except that g was dropped. The esterification rate of the photosensitizer (P-3) is 65%. Photosensitizer Synthesis Example 4 29.58 g of novolak resin (c) and 33.45 g of 1,2-naphthoquinone diad-5-sulfonyl chloride
160 ml of acetone, 43 m of N-methylpyrrolidone
1 of a mixed solvent of triethylamine 12.73
A photosensitizer (P-4) was obtained in the same manner as in Photosensitizer Synthesis Example 1 except that g was dropped. The esterification rate of the photosensitizer (P-4) is 50%.

Preparation Example 1 of Photoresist Composition Novolak Resin (a) as Alkali-Soluble Resin
730 g and 2.030 g of the photosensitizer (P-1) were dissolved in 22.20 g of methyl 3-methoxypropionate to give a pore size of 0.
A photoresist composition (PR-1) was obtained by filtering with a 2 μm membrane filter. Photoresist Composition Preparation Examples 2-5 A photoresist composition was prepared in the same manner as in Photoresist Composition Preparation Example 1 except that the alkali-soluble resin and the photosensitizer shown in Table 1 below were combined in the proportions shown in Table 1. (PR
-2-PR-5) was obtained.

[0030]

[Table 1]

Examples 1 to 3 and Comparative Examples 1 to 2 Photoresist compositions (PR-1) to (PR-5) were prepared.
Patterning was performed by the following patterning method, and the sensitivity, limiting resolution and heat resistance were evaluated, and the results are shown in Table-2.
In Table 2, the following symbols and terms have the following meanings.

[0032]

[Table 2] E ₀ : When the line & space pattern is 1: 1 on a mask of 0.6 μm, the line width of the exposed portion and the unexposed portion is reduced to 0.6 μm by developing with an alkaline developer after exposure. Shows the exposure amount that is finished at 1: 1 by the exposure time Limiting resolution: The minimum line & space pattern that can be resolved at the exposure amount E ₀ Heat resistance: When the wafer is heated on the hot plate for 5 minutes Maximum temperature at which space pattern does not deform (however, at 5 ° C intervals)

<Patterning Method> A photoresist composition was applied to a silicon wafer by a spin coater, and then heated on a hot plate at 80 ° C. for 90 seconds to remove the solvent to form a photoresist applied film having a thickness of 1.01 μm. did. This is a Nikon i-line stepper (NA =
After exposure to 0.5), it was heated on a 120 ° C. hot plate for 90 seconds, and then immersed in a 2.38% tetramethylammonium hydroxide aqueous solution at 23 ° C. for 60 seconds to develop.

[0034]

[Table 3]

[0035]

EFFECT OF THE INVENTION The photoresist composition of the present invention has good sensitivity and resolution and high heat resistance.

Claims (1)

[Claims] 1. A positive photoresist composition comprising an alkali-soluble resin, a quinonediazide photosensitive compound and a solvent, wherein the alkali-soluble resin is at least one phenolic compound represented by the following general formula [A] and the following general formula: It is a polycondensation product [C-1] with at least one ketone or aldehyde represented by [B-1], and the polycondensation product [C-1] has a polystyrene-reduced weight average molecular weight measured by gel permeation chromatography. , 2500 to 30000, and the quinonediazide-based photosensitive compound is at least one phenolic compound represented by the following general formula [A] and the following general formula [B-
[2]] containing as a main component a quinonediazide sulfonic acid ester of a polycondensate [C-2] with at least one hydroxyaromatic aldehyde,
2] has a polystyrene-reduced weight average molecular weight of 600 to 2
Positive photoresist composition. [Chemical 1] [Chemical 2] [Chemical 3] (In the formula, R ¹ is an alkyl group having 1 to 4 carbon atoms, and 1 to 1 carbon atoms.
4 is an alkoxy group or a hydroxyl group, R ² and R ³ are each a hydrogen atom, an alkyl group having 1 to 4 carbon atoms,
An aryl group or an aralkyl group, R ⁴ is a hydrogen atom,
Represents an alkyl group having 1 to 4 carbon atoms or an alkoxy group having 1 to 4 carbon atoms, l represents an integer of 0 to 3, m and n each represent an integer of 1 to 5, and the sum of m and n is 5. is there. However,
When 1 or m is an integer of 2 or more, a plurality of R ¹ or R ⁴ may be the same or different. )