JPH0260915A - Removal of oligo-nuclear component of novolak resin - Google Patents

Abstract

PURPOSE:To control the content of oligo-nuclear components in a novolak resin by adding a water-soluble alcohol and water to a soln. of the novolak resin in a specified solvent and transferring part of the oligo-nuclear components of the novolak to an ag. soln. layer. CONSTITUTION:A resin soln. is obtd. by dissolving 1-50wt.% novolak resin obtd. by performing the condensation polymn. of 1mol of a phenol and 0.7-1mol of an aldehyde in the presence of 1X10<-4>-5X10<-1>mol of an acid catalyst based on 1mol of the phenol in a solvent in which the solubility of water at 20 deg.C is 50 or lower (e.g., ethyl cellosolve acetate). 100 pts.wt. said resin soln. is mixed with 5-100 pts.wt. water-soluble alcohol (e.g., methanol) and, if necessary, 5-300 pts.wt. ion-exchanged water or distilled water contg. 0.01-10wt.% org. acid (e.g., oxalic acid) to extract oligo-nuclear components of the novolak resin to an ag. soln. layer, which is left to stand to separate a resin soln. layer therefrom.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a method for removing low-nucleate substances in novolak resin.

[Prior art] Conventionally, positive resists used in the production of integrated circuits are
It is usually composed of a novolac resin and a 1,2-quinonediazide compound, and is widely used because it can provide a high-resolution resist pattern.

However, in recent years, there has been a strong demand for higher integration of integrated circuits, and along with this, there has been a strong demand for improved resolution of positive resists.

Under these circumstances, one way to improve the resolution of positive resists is to optimize the composition of phenols and aldehydes, which are the monomers of novolak resin, which is the raw material for positive resists. .

However, in the polycondensation reaction between phenols and aldehydes, it is difficult to control the amount of low-nucleate substances produced in novolac resins, and when such novolac resins are used as raw materials for positive resists, resolution and developability However, there is a problem in that it is difficult to obtain a positive resist with excellent balance in heat resistance, etc., and excellent reproducibility.

[Problem to be solved by the invention]

The purpose of the present invention is to solve the above-mentioned problems, to provide a positive resist that can control the proportion of low-nucleate substances contained in the novolac resin, and has excellent balance in resolution, developability, heat resistance, etc., and reproducibility. The object of the present invention is to provide a method by which a novolak resin can be obtained.

[Means to solve the problem]

The method for removing low-nuclear elements in novolak resin of the present invention involves dissolving the novolak resin in a solvent whose solubility in water at 20°C is 50 or less, and then adding and mixing water-soluble alcohol and water to this resin solution. After that, the novolak resin is separated into a resin solution layer and an aqueous solution layer, and a part of the low-nuclear substances contained in the novolak resin is removed together with the aqueous solution layer.

The novolak resin used in the present invention uses phenols, which are aromatic compounds having a phenolic hydroxyl group, and aldehydes, preferably in a ratio of 0.7 to 1 mole of aldehydes to 1 mole of phenol, and uses an acid catalyst. This is a resin obtained by condensation polymerization as described below.

The phenols used at this time include, for example, phenol, 0-cresol, m-cresol, p-cresol, 0-ethylphenol, m-ethylphenol, p-cresol,
-Ethylphenol, 0-butylphenol, m-butylphenol, p-butylphenol, 2,3-xylenol, 2,4-xylenol, 2.5-xylenol, 26-xylenol, 3.4-xylenol, 3,5
-xylenol, 3.6-xylenol, 2.35-trimethylphenol, 3,4.5-1-limethylphenol, p-phenylphenol, resorcinol, hydroquinone, hydroquinone monomethyl ether, pyrogallol, phloroglucinol, hydroxydiphenyl, Bisphenol A1 Bisphenol C2 Bisphenol S
, gallic acid, gallic acid ester, α-naphthol, β-
Examples include naphthol. These phenols are
They may be used singly or in combination of two or more, taking into account the alkali solubility of the novolak resin produced.

Examples of aldehydes include formaldehyde,
Examples include paraformaldehyde, furfural, benzaldehyde, nitrobenzaldehyde, acetaldehyde, etc., and these aldehydes may be used singly or in combination.
Used as a mixture of more than one species.

Examples of acid catalysts include inorganic acids such as hydrochloric acid, nitric acid, and sulfuric acid;
Organic acids such as formic acid, oxalic acid, and acetic acid are used.

This acid catalyst is usually used for 1 mole of phenols.
X 10-' to 5X10-' moles are used.

Details of these novolak resins are given in JP-A-55-123.
No. 614, No. 57-101834, No. 57-
It is described in Japanese Patent No. 101833, Japanese Patent No. 58-17112, and US Pat. No. 4,404,357.

The solvent for dissolving the novolac resin used in the present invention is
The solvent has a water solubility of 50 or less at 20'C. In addition, the solubility of 50 or less means that the solvent used is 100c
It means that less than 50g of water at 20°C can be dissolved in c). When the solubility exceeds 50, it becomes difficult to separate the novolanque resin solution layer and the aqueous solution layer. The solvent may be used to remove the water-soluble alcohol and water from the resin solution layer separated from the aqueous solution layer and to use the resin solution layer as it is as a raw material for a positive resist.
．． From the viewpoint of solubility of the 2-quinonediazide compound, ethyl cellosolve acetate, propylene glycol monomethyl ether acetate, etc. are preferably used.

The concentration of novolak resin dissolved in the solvent is 10 to 50
It is preferably 10 to 40% by weight, more preferably 10 to 40% by weight. If the concentration of the novolac resin is less than 10% by weight, the production efficiency will be poor, and if it exceeds 50% by weight, the solution viscosity will increase, precipitates are likely to form, and the separation from the aqueous solution layer in the subsequent process will be poor. It may get worse.

The water-soluble alcohol used in the present invention is used in order to dissolve the low-nuclear substances contained in the novola-tsuku resin into the aqueous solution layer and to improve the separation from the resin solution layer. Further, depending on the amount of water-soluble alcohol used, the low-nucleate substances contained in the novolak resin can be removed at an arbitrary ratio. The amount of the water-soluble alcohol used is preferably 5 to 100 parts by weight, more preferably 10 to 80 parts by weight, per 100 parts by weight of the novolac resin solution. If the amount used is less than 5 parts by weight, low-nuclear elements cannot be removed sufficiently, and if it exceeds 100 parts by weight, the effect of removing low-nuclear elements becomes too large, resulting in a decrease in sensitivity when used in a positive resist. There is. The water-soluble alcohol may be one with a low boiling point that can be easily removed after separation (methanol, ethanol, isopropyl alcohol, etc. are preferably used).

As the water used in the present invention, ion exchange water or diluted water is preferably used. Furthermore, when a novolac resin with a high metal content is used as the novolak resin, it is preferable to use water containing an organic acid because it is possible to simultaneously remove the low-nucleus elements in the novolac resin and remove the metals in the novolak resin. In addition, acetic acid, propionic acid, and butyric acid, which have a low v1 ratio of carboxyl groups to the molecular weight of the organic acid, are easily soluble in the resin solution layer, so if this solution is used as a resist solution as it is, the coating properties on silicon wafers are poor. This may have an adverse effect on the rate of film reduction in a developing solution consisting of an alkaline aqueous solution. As the organic acid, oxalic acid is preferably used. When water containing an organic acid is used, the concentration of the organic acid is usually 0.01 to 10% by weight, or 0.1 to 8% by weight. The amount of water used is 100% of the novolac resin solution.
The amount is preferably 5 to 300 parts by weight, more preferably 20 to 200 parts by weight. If the amount used is less than 5 parts by weight, it will be difficult to separate the low-nucleated substances, and if it exceeds 300 parts by weight, the concentration of water-soluble alcohol in the aqueous solution layer will be too low, making it difficult for the low-nucleated substances to dissolve in the aqueous solution layer. Removal of the low-nuclear bodies may be difficult.

In the present invention, the low-nuclear elements contained in the novolac resin are removed by dissolving the novolac resin in a solvent whose solubility in water at 20°C is 50 or less, and then adding and mixing water-soluble alcohol and water to the resin solution. This is carried out by extracting the low-nuclear elements in the novolac resin into an aqueous solution layer, and separating the resin solution layer and the aqueous solution layer by, for example, static separation or centrifugation. Note that the amount of the solvent used is adjusted so that the resin content in the separated resin solution is usually 10 to 50% by weight.

In addition, the separated MFi solution layer contains water-soluble alcohol and water, so it remains as it is (regis)? If used as a liquid, it will adversely affect the applicability to wafers, the film thickness of the resist, and the storage stability, so it is preferable to heat the resin solution under normal pressure or reduced pressure to distill off the water-soluble alcohol and water.

In addition, if the resin solution contains water-soluble alcohol, water, and organic acids, either the water-soluble alcohol and water are distilled off from the resin solution layer, and then the organic acid is removed by washing with water and the water is distilled off. After washing with water to remove organic acids, it is preferable to distill off the water-soluble alcohol and water.

When a 1,2-quinonediazide compound is blended into the obtained novolak resin from which low-nucleus substances have been removed by the method of the present invention and used as a positive resist, the removal rate of low-nucleus substances from the novolak resin is 5 to 50% by weight. , particularly preferably 5 to 40% by weight. If the removal rate of low-nuclear elements is less than 5% by weight, the heat resistance of the resist will not improve, and if it exceeds 50% by weight, the solubility in an alkaline aqueous solution may decrease, resulting in poor developability and sensitivity.

The amount of the 1,2-quinonediazide compound used in the positive resist is preferably 5 to 100 parts by weight, more preferably 10 parts by weight, based on 100 parts by weight of the novolac resin.
~50 weight in heavy view section. If the blending amount is too small, I, 2-
Since the amount of carboxylic acid produced by the quinonediazide compound when it absorbs radiation is small, buttering becomes difficult when the resin composition is used as a positive resist. Ta1゜2
- Not all of the quinonediazide compound can be decomposed, and development with a developer consisting of an alkaline aqueous solution may become difficult.

As the 1,2-quinonediazide compound, for example, 1
, 2-benzoquinonediazide-4-sulfonic acid ester, 1,2-naphthoquinonediazide-4-sulfonic acid ester, 1,2-naphthoquinonediazide-5-sulfonic acid ester, and the like. Specifically, 1,2-benzoquinonediazide-4-sulfonic acid ester of (poly)hydroxybenzene such as p-cresol, resorcinol, pyrogallol, phloroglycitur, ■, 2-naphthoquinonediazide-4-sulfonic acid ester or 1 .2-
naphthoquinone diazide-5-sulfonic acid ester; 2,
4-dihydroxyphenyl-propyl ketone, 2.4-
Dihydroxyphenyl-n-hexylketone, 2,4-dihydroxybenzophenone, 2,3.4-)dihydroxyphenyl-n-hexylketone, 2,3.4-1-dihydroxybenzophenone, 2,4. 6-trihydroxybenzophenone, 2,3,4,4°-te[·dihydroxybenzophenone, 2,3,4.2'-tetrahydroxybenzophenone, 2.2',4°4'-tetrahydroxybenzophenone, 2,2'3,4.6'-pentahydroxybenzophenone, 2,3.3',4.4',
5'-hexahydroxybenzophenone, 2.3', 4
．． 4'.

1,2-benzoquinonediazide-4-sulfonic acid ester, 1,2-naphthoquinonediazide-4-sulfone of (poly)hydroxyphenylalkyl ketone or (poly)hydroxyphenylaryl ketone such as 5',6-hexahydroxybenzophenone acid ester or 1.2
-Naphthoquinone diazide-5-sulfonic acid ester; bis(p-hydroxyphenyl)methane, bis(2,4-dihydroxydiphenyl)methane, bis(2,3,4-trihydroxyphenyl)methane, 2,2-bis( p-hydroxyphenyl)propane, 2,2-bis(2,4-dihydroxyphenyl)propane, 2,2-bis(2,3
, 4-1-dihydroxyphenyl)propane, etc.
1,2-Benzoquinonediazide-4-sulfonic acid ester of (poly)hydroxyphenyl]alkane, 1,2-
naphthoquinonediazide-4-sulfonic acid ester or 1.゛2-Naphthoquinonediazide 5-sulfonic acid ester; 3,5-dihydroxybenzoic acid lauryl, 2,3
．． Phenyl 4-trihydroxybenzoate, 3,4.5-
(poly)hydroxybenzoic acid alkyl esters or (poly)hydroxybenzoic acid aryl esters such as lauryl 1-dihydroxybenzoate, propyl 3.4.5-trihydroxybenzoate, and phenyl 3,4.5-trihydroxybenzoate; 1,2-benzoquinonediazide-4 sulfonic acid ester, 1,2-naphthoquinonediazide-4
-Sulfonic acid ester or 1,2 naphthoquinonediazide-5-sulfonic acid ester: bis(2,5-dihydroxybenzoyl)methane, bis(2,3,4-1-dihydroxybenzoyl)methane, bis(2,4,6 -)dihydroxybenzoyl)methane, p-bis(2,5-dihydroxybenzoyl)benzene, p-bis(2゜3.
4-)Lihydroxybenzoyl)benzene, pbis(2,
Bis[(poly)hydroxybenzoyl coalkanes such as 4,6-1-dihydroxybenzoyl)benzene or 1,2 of bis[(poly)hydroxybenzoyl]benzene
-benzoquinonediazide-4-sulfonic acid ester, 1
, 2-naphthoquinonediazide-4-sulfonic acid ester or 1,2-naphthoquinonediazide-5-sulfonic acid ester; ethylene glycoluge (3,5-dihydroxybenzoate), polyethylene glin! - Rouge (
1,2-benzoquinonediazide-4 of (poly)ethyl glycoludi((poly)hydroxybenzoate) such as polyethylene glycoludi(3,5-dihydroxybenzoate), polyethylene glycoludi(3,4,5-1,dihydroxybenzoate) -sulfonic acid ester, 1,2-naphthoquinonediazide-4-sulfonic acid ester or 1.2-naphthoquinonediazide-5-sulfonic acid ester.
Author: “Light-3ensitivc System”
ms” 339-352 (1965), John
Wiley & 5ons (New York)
) and W.S. DeFores are also authors of “Photoresi
spi50. (19'75), McGraw-IIi 1
1. It is also possible to use 1,2-quinonediazide compounds published in J.D., Inc., New York.

Among the 1,2-quinonediazide compounds, 23.
4-1-lyhydroxybenzophenone-1,2-naphthoquinonediazide-4-sulfonic acid ester, 2.3. ．．
4-) Lyhydroxybenzophenone-1,2-naphthoquinonediazide-5-sulfonic acid ester, 2,4.6-
) -12- of trihydroni-1-sibenzophenone such as hydroxybenzophenone-1,2-naphthoquinonediazide 4-sulfonic acid ester-2,4,6-1-lyhydroxybenzophenone-12-naphthoquinonediazide-5-sulfonic acid ester Naphtho: F nondiazide sulfonic acid esters, 2.2', 4゜4'-tetrahydroxybenzophenone-1,2 naphthoquinonediazide-
4-sulfonic acid ester, 22° 4,4'-tetrahydroxybenzophenone-12-naphthoquinonediazide-5-sulfonic acid ester, 2,3,4.4'-tetrahydroxybenzophenone-1,2-naphthoquinonediazide-4- Sulfonic acid ester, 2,3゜4.4'-tetrahydroxybenzophenone-1゜2-naphthoquinonediazide-5-sulfonic acid ester, 2,3,4.2'
-tetrahydroxybenzophenone-1,2-naphthoquinonediazide-4-sulfonic acid ester, 2,3,4.
2'-tetrahydroxybenzophenone-1,2-naphthoquinonediazide-5-sulfonic acid ester, 31 me[
・Xy-2,3,4,4'-tetrahydroxybenzophenone-12-naphthoquinonediazide 4-sulfonic acid ester, 3'-methoxy-2°3.4.4"-tetrahydroxybenzophenone 1,2-naphthoquinonediazide- 1,2-naphthoquinonediazide sulfonic acid esters of tetrahydroxyhensiphenone such as 5-sulfonic acid ester are preferable. .5-3 trihydroxybenzophenone-1,2
- Naphthoquinone diazide sulfonic acid ester and tetrahydroxybenzophenone with an average condensation ratio of 2 to 4 -
1,2-naphthoquinonediazide sulfonic acid ester is preferred. These 1,2-quinonediazide compounds may be used alone or in combination of two or more.

The positive photoresist may also contain an aggravating agent in order to improve sensitivity. Examples of exacerbating agents include 2H-pyrido[32b)-1,4-oxazin-3(4H)ones, 10H-pyrido(3,2-b)
[1,4)-benzothiazines, urazoles, hydantoin α, barbituric acids, glycine hydrate fi,
] -Hydroxybenzotriazoles, alloxanes, maleimide rn, and the like. The amount of these sensitizers is usually 100 parts by weight or less per 100 parts by weight of the 1,2-quinonediazide compound.

Further, a surfactant may be added to the positive photoresist in order to improve coating properties, for example, striations and developability of the radiation irradiated area after forming a dry coating film.

Examples of the surfactant include polyoxyethylene alkyl ethers such as polyoxyethylene lauryl ether, polyoxyethylene stearyl ether, and polyoxyethylene oleyl ether, polyoxyethylene octylphenyl ether, and polyoxyethylene nonylphenyl ether. Nonionic surfactants such as polyoxyethylene alkyl phenyl ethers, polyethylene glycol dialkyl ethers such as polyethylene glycol phenyl dilaurate and polyethylene glycol distearate, Efthomp EF301, EF303
, EF352 (manufactured by Shinjuyo Kasei Co., Ltd.), Megafac F17
1, F172, F173 (Dainippon Ink Co., Ltd., Florado FC430, FC431 (manufactured by 3M Co., Ltd.)
, Asahi Guard AG710, Surflon 5382.5C
101, 5C102, 5C103, 5C104, 5C1
05,5C106 (manufactured by Asahi Glass Co., Ltd.), organosiloxane polymer KP-341 (manufactured by Shin-Etsu Chemical Co., Ltd.), acrylic acid-based or methacrylic acid-based (co)polymer Polyflow No., 75, No. , 95 (manufactured by Kyoeisha Yushi Kagaku Kogyo Co., Ltd.). The blending amount of these surfactants is usually 2% by weight or less based on the solid content of the positive resist.

Further, the positive photoresist may be blended with dyes and pigments to visualize the latent image of the radiation irradiated area and to reduce the effect of halide during radiation irradiation, and an adhesion aid to improve adhesiveness. You can also do it.

Furthermore, the positive photoresist may also contain a storage stabilizer, an antifoaming agent, etc., if necessary.

The positive photoresist includes the novolac resin, 1.
Predetermined products of the 2-quinonediazide compound and various compounding agents are dissolved in a solvent so that the solid content concentration is, for example, 20 to 40% by weight, and each time the solution is filtered through a filter with a pore size of 0.2 ttm. It is applied to a substrate such as a silicon wafer by spin coating, flow coating, roll coating, etc.

In addition to the solvent used to dissolve the novolak resin mentioned above, examples of the solvent used in this case include methyl cellosolve acetate, propylene glycol heptanoethyl ether acetate, methyl 2-hydroxypropionate, and ethyl 2-hydroxypropionate. Solvents such as can be used. Two or more of these solvents can also be used in combination.

Examples of the developer for the resin composition include inorganic alkalis such as sodium hydroxide, potassium hydroxide, sodium carbonate, sodium silicate, sodium metasilicate, aqueous ammonia, and primary amines such as ethylamine and n-propylamine. secondary amines such as diethylamine and di-n-propylamine, tertiary amines such as triethylamine and methyldiethylamine, dimethylethanolamine,
Alcohol amines such as triethanolamine, tetramethylammonium hydroxide, tetraethylammonium hydroxide, quaternary ammonium salts such as choline, pyrrole, piperidine, 1°8-diazabicyclo(5,4,0)-7-undecene, Cyclic amines such as 1,5-diazabicyclo(4,3,0)-5-nonane)
An alkaline aqueous solution is used.

Further, the developer may be used by adding an appropriate amount of a water-soluble organic solvent, such as the water-soluble alcohol or surfactant.

After developing with the developer, the film is rinsed with water and dried.

[Examples] Hereinafter, the present invention will be explained in detail with reference to Examples, but the present invention is not limited to these Examples in any way.

Example 1 400 g of novolak resin obtained from m-cresol, 3.5-dimethylphenol (molar ratio of m-cresol:3.5-dimethylphenol = 50:50) and formaldehyde (hereinafter referred to as "novolak resin a")
), ethyl cellosolve acetate 1600I
: to prepare a resin solution.

After adding 900 g of ion-exchanged water and 240 g of methanol to 600 g of the resin solution thus obtained and stirring, the mixture was allowed to stand and was separated into a +51 fat solution layer and an aqueous solution layer. No precipitate was formed.

Furthermore, methanol and water in the obtained resin solution layer were distilled off under reduced pressure, and ethyl cellosolve acetate was added to obtain a novolac resin solution A with a novolac resin content of 35% by weight and a water content of 0.05% by weight. . Note that the removal rate of low-nucleate substances in the obtained resin solution layer was 10%. The removal rate of low-nuclear bodies was determined as follows.

In addition, the molecular weight distribution (b/a) in terms of polystyrene before and after removing the low-nuclear elements of the Novolank resin was measured using GPC manufactured by Toyo Soda Co., Ltd.
Column (G3000T62, G3000TT6, (1
;4000H6) with a flow rate of 1°5mjl! /m1n
X? Ejection solvent tetrahydrofuran, column temperature 40°C
It was determined by the gel permeation chromatography (GPC) method using monodisperse polystyrene as a standard under the analytical conditions of
The maximum height values of the peaks in the range of 0 to 900 were taken as a and b, respectively, and b/a was calculated. The results are shown in Table 1.

Example 2 m-cresol, p-cresol (the molar ratio of m-
500 g of novolak resin obtained from cresol: p-cresol = 60:40) and formaldehyde,
A resin solution was prepared by dissolving it in 2000 g of ethyl cellosolve acetate.

After adding 750 g of ion-exchanged water and 200 g of methanol to 500 g of the resin solution thus obtained and stirring, the mixture was allowed to stand and was separated in the same manner as in Example 1, but no precipitate was formed. .

Furthermore, water and methanol in the resin solution obtained in the same manner as in Example 1 were removed, and ethyl cellosolve acetate was added to the solution, so that the novolak resin content was 35% by weight and the water content was 0.0%.
A 5% by weight novolak resin solution B was obtained. Note that the removal rate of low-nucleate substances in the obtained resin solution layer was 20% by weight.

In addition, the polystyrene equivalent molecular weight of the novolac resin before and after removing the low-nucleate substances was determined in the same manner as in Example 1, and b/
a was calculated. The results are shown in Table 1.

Example 3 m-cresol, 2,3.5-)dimethylphenol (
A resin solution was prepared by dissolving 300 g of a novolak resin obtained from m-cresol:2,3,51/dimethylphenol=55:45), phorol, and aldehyde in 450 g of ethyl cellosolve acetate.

After adding 500 g of ion-exchanged water and 230 g of methanol to 1,500 g of the resin solution thus obtained and stirring, the mixture was allowed to stand and was separated in the same manner as in Example 1, but no precipitate was formed. Ta. Furthermore, water and alcohol were removed from the resin solution obtained in the same manner as in Example 1, and ethyl cellosolve acetate was added to obtain a novolac resin solution C with a novolac resin content of 40% by weight and a water content of 0.03% by weight. Ta. Note that the removal rate of low-nucleate substances in the obtained resin solution layer was 22% by weight.

In addition, the polystyrene equivalent molecular weight of the novolac resin before and after removing the low-nucleate substances was determined in the same manner as in Example 1, and b/
a was calculated. The results are shown in Table 1.

Example 4 m-cresol, 2,3.5-trimethylphenol,
p-cresol (mole ratio of m-cresol nitrimethylphenol: p-1 to 7'-l = 46:31:
23) 500 g of novolac resin obtained from formaldehyde was mixed with 200 g of ethyl cellosolve acetate.
A resin solution was prepared by dissolving 0g of the resin.

After adding 750 g of ion-exchanged water and 200 g of methanol to 500 g of the resin solution thus obtained and stirring, the mixture was allowed to stand and was separated in the same manner as in Example 1. Furthermore, water and alcohol were removed from the resin solution obtained in the same manner as in Example 1, and ethyl cellosolve acetate was added to obtain a novolac resin solution with a novolac resin content of 40% by weight and a water content of 0.05% by weight. The removal rate of low-nucleate substances in the obtained resin solution layer was 11% by weight.

In addition, the polystyrene equivalent molecular weight of the novolac resin before and after removing the low-nucleate substances was determined in the same manner as in Example 1, and b/
a was calculated. The results are shown in Table 1.

Example 5 400 g of Novolanc resin obtained from m-cresol, 35-dimethylphenol (the molar ratio of m = cresol = 3,5-dimethylphenol = 65:35) and formaldehyde was dissolved in 1600 g of ethyl cellosolve acetate. A resin solution was prepared. The iron content of this resin solution was determined using PerkinElmer Zeeman 5100.
When measured using a mold, it was 0.217 ppm.

500 g of the thus obtained resin solution, 750 g of 1% by weight oxalic acid aqueous solution and 200 g of methanol were added and stirred, then allowed to stand and separated in the same manner as in Example 1, but no precipitate was formed. I hadn't.

Furthermore, methanol and water in the obtained resin solution were distilled off under reduced pressure while adding ethyl cellosolve acetate. Thereafter, washing with water was performed, and ethyl cellosolve acetate was added to obtain Novolank resin solution E with a resin content of 35% by weight. The iron content of the solution was 0.0025 ppm, and the oxalic acid content was 9 pprn. Note that the removal rate of low-nucleate substances in the obtained resin solution layer was 10% by weight.

In addition, the tristyrene-equivalent molecular weight before and after removing the low-nuclear substance of the novolak resin was determined in the same manner as in Example I, and b/
a was calculated. The results are shown in Table 1.

Comparative Example ■ In Example 1, a novolak resin solution was obtained in the same manner as in Example 1 except that methanol was not used, but the low-nucleate substances contained in the novolak resin were not removed at all.

Comparative Example 2 An attempt was made to separate the resin solution layer in the same manner as in Example 1 except that water was not used, but separation could not be achieved.

Comparative Example 3 The resin solution layer was separated to obtain a resin solution in the same manner as in Example 1, except that methanol was used instead of ethyl cellosolve acetate when preparing the resin solution before adding water and alcohol. Ta. When water was added to this solution, a precipitate formed.

Furthermore, the precipitate contained an aqueous solution, making complete separation difficult.

Test Example 1> 1,2-quinonediazide compound of the type and amount shown in Table 1 was added to the novolac resin solution A obtained in the example process, and ethyl cellosolve was further added so that π was as shown in Table 1. Acetate was added and dissolved, and the mixture was filtered through a membrane filter with a pore size of 0.2 μm.

The obtained positive resist is applied to a silicon wafer L using a conventional method.
The coating was applied by spinning using a spinner and prebaked for 2 minutes on a hot plate kept at 90°C.

Next, it was exposed to light using a Nikon N5R1505G4D reduction projection exposure machine with different exposure colors, developed at 25°C for 60 seconds using a 2.4% by weight aqueous solution of tetramethylammonium hydroxy as a developer, and rinsed with water. and dried. The obtained resist pattern was observed with a scanning electron microscope, and its developability and resolution were evaluated. Heat resistance was also evaluated by placing a wafer with a resist pattern formed in an oven and checking the temperature at which the pattern began to collapse.

The evaluation results are shown in Table 1.

<Test Examples 2 to 5> In Test Example 1, the novolac resin solutions B, C, D, and E obtained in Examples 2 to 5 were used instead of the novolac resin solution of Example 1, and the results shown in Table 1 were Otori shown in 2-
A resist pattern was obtained in the same manner as in Test Example 1, except that a quinonediazide compound and ethyl cellosolve acetate were used, and the same evaluation was performed. The evaluation results are shown in Table 1.

<Test Example 6> In Test Example 1, instead of the Novolank resin solution,
A resist pattern was obtained in the same manner as in Test Example I, except that novolak resin a was used, and a 1,2-quinonediazide compound and ethyl cellosolve acetate, which are not shown in Table 1, were used, and the same evaluation was performed. The evaluation results are shown in Table 1.

The following margins [Effects of the Invention] According to the method for removing low-nucleate substances in novolak resin of the present invention, it is possible to finely control the low-nucleate substances contained in novolac resin with good reproducibility, resulting in improved resolution, developability, and heat resistance. It is possible to obtain a novolac resin that has an excellent balance of properties such as ultraviolet rays, deep ultraviolet rays, X-rays, electron beams, molecular beams, gamma rays, synchrotron radiation, proton beams, and other radiation, and is suitable as a raw material for positive resists. can.

Agent: Patent Attorney Kawakita Takecho

Claims (1)

[Claims] (1) Novolac resin is dissolved in a solvent whose solubility in water at 20°C is 50 or less, and then water-soluble alcohol and water are added and mixed to this resin solution, and then separated into a resin solution layer and an aqueous solution layer. A method for removing low-nucleus substances from a novolak resin, comprising removing a part of the low-nucleus substances contained in the novolak resin together with an aqueous solution layer.