JPH0680119B2 - Purification method of novolak resin - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for purifying a novolac resin, and more particularly to a method for reducing the metal content of a novolac resin for use in a resist or a planarizing agent.

2. Description of the Related Art In recent years, as the integration and speed of semiconductor devices have increased, the demand for miniaturization of devices has increased. To meet this requirement, resists used in lithography are
The conventional cyclized polyisoprene-bisazide-based negative resist is changing to a novolak resin-quinonediazide-based positive resist. The cyclized polyisoprene-bisazide-based resist utilizes the difference in solubility between a portion where cyclized polyisoprene is crosslinked by nitrene generated by the decomposition of bisazide by light and a portion where it is not crosslinked. Therefore, when attempting to remove (develop) the non-crosslinked portion with an organic solvent that is a good solvent for cyclized polyisoprene, it is unavoidable that the crosslinked portion swells with this solvent, limiting resolution improvement. There is. On the other hand, novolak resin-quinonediazide type resist has a quinonediazide structure part in the novolak resin or the compound mixed in it, and the structure of this part changes by light, and the alkaline aqueous solution that is a developer before and after exposure is used. It is based on the fact that the solubility with respect to is greatly changed. Since the developing solution is water, there is essentially no problem of swelling, and it is possible to easily obtain high resolution, cut lines, and highly accurate dimensions. Recently, a (negative) resist composed of a novolak resin and a bisazide compound has been reported, which utilizes this non-swelling property.

On the other hand, among the performance requirements for resists, one that has recently become more important is that the metal content is low.
This is because when a resist containing a large amount of metal is used, the metal remains in the drawn pattern, deteriorating the electrical characteristics of the semiconductor. The resist is applied by, for example, a spinner so as to have an appropriate film thickness, the remaining solvent is removed by prebaking, and then the resist is exposed through a mask having a desired pattern, and the formed latent image is treated with a developing solution. It becomes a visible image. A substrate made of silicon or the like is etched by using this visible image as a mask, and a desired pattern is transferred to the substrate. Regarding the etching of the substrate, the cyclized polyisoprene-bisazide-based resist was mainly wet etching with a hydrofluoric acid aqueous solution, but gradually, dry etching using active species generated during plasma discharge is used. In particular, for a resist using a novolac resin, dry etching is usually adopted because of the problem of adhesion to the substrate. Also, after etching the substrate, the unnecessary resist is peeled off,
Also in this process, plasma is often used.
When using a solution such as wet etching, some of the metal in the resist is removed by these solvents,
In dry etching or plasma stripping, most of the metal in the resist remains as it is on the substrate and becomes a source of contamination on the substrate.

Thus, it is one of the important characteristics of the resist that a fine pattern can be drawn and the metal content is small.

However, the metal content of the novolak resin-quinone diazide-based resists currently on the market is not at a level that satisfies semiconductor manufacturers, and is a major problem in terms of semiconductor structure.

The main components of a typical novolak resin-quinonediazide resist are a matrix resin such as a novolac resin, a dissolution inhibitor such as a quinonediazide compound, and a solvent.

A quinonediazide compound is generally obtained by reacting a compound having a quinonediazide structure such as naphthoquinonediazide-5-sulfonyl chloride with a compound having a hydroxy group such as 2,3,4-trihydroxybenzophenone in the presence of a weak alkali. To be It is easy to purify the reaction raw materials and products by a known method, and a quinonediazide compound having a low metal content can be obtained. Also,
Also for the solvent, it is easy to reduce the metal content by distillation or the like.

Novolak resins are phenol derivatives such as phenol, cresol and xylenol, aldehydes such as formaldehyde or ketones such as acetone, inorganic acids such as hydrochloric acid and sulfuric acid or organic acids such as oxalic acid, magnesium carbonate, zinc acetate, calcium hydroxide, etc. It is produced by dehydration condensation at a high temperature using a catalyst such as a metal compound. The product novolac resin contains various metals such as those derived from these catalysts, various raw materials such as iron and sodium, and those derived from manufacturing equipment.

Therefore, it can be said that most of the metal in the novolac resin-quinonediazide resist is due to the novolac resin. The same can be pointed out regarding the metal content of resists of other systems using novolac resin.

Further, recently, when lithography is applied to a stepped substrate, in order to reduce the influence of the step on the pattern width, a flattening agent is first applied on the stepped substrate, and a resist is further applied on this. After that, a so-called multilayer resist method of performing lithography such as exposure-development-dry etching has come to be used.

A resist may be used as the flattening agent, but it is not necessarily photosensitive and a novolac resin or the like is often used alone. Also in this case, as in the case of the above-mentioned resist, the metal content in the novolac resin becomes a big problem.

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention
It is possible to reduce the metal content in the novolak resin by purifying the novolac resin by a specific method.By using the novolac resin that has been purified as described above, the metal content in the resist or the planarizing agent can be significantly increased. The present invention has been completed based on this finding.

Means for Solving the Problems Thus, according to the present invention, the novolak resin is dissolved in a solvent having a solubility in water at 20 ° C. of 100 or less, and liquid-liquid extraction is performed from the resulting solution using water, Provided is a method for purifying a novolac resin, which is characterized by reducing a metal content in the resin.

The method for purifying the novolac resin will be described below. The solvent used in the present invention is a solvent of novolac resin,
Solubility in water at ℃ 100 or less, preferably 50
It is as follows. Specific examples thereof include ethyl acetate,
Acetic acid esters such as n-butyl acetate and isoamyl acetate,
Ketones such as methyl ethyl ketone, methyl isobutyl ketone and cyclohexanone, alcohols such as n-butanol, i-butanol and i-amyl alcohol, glycol ether acetates such as ethylene glycol monoethyl ether acetate and ethylene glycol monobutyl ether acetate, tetrachloride Carbon, chloroform,
Halogenated hydrocarbons such as tetrachloroethane, ethers, ligroin, solvent naphtha and the like can be mentioned. These solvents may be used alone or in combination of two or more. If the solubility of the solvent in water exceeds 100, the novolac resin will be precipitated during purification, or the separation of the novolac resin solution layer and the aqueous layer will be difficult or impossible.

The novolac resin is dissolved in the solvent. The preferred concentration is not specified, but at low concentration, there is a problem in operation because the total amount of liquid increases, and when the concentration is too high, the solution viscosity becomes high and the separation from the aqueous layer becomes poor. Occurs.
The preferred range is 3% to 50%.

Next, water is added to the solution of the novolac resin. Alternatively, the solution may be added to water. The water used preferably has a low metal content for the purposes of the present invention. The amount of water used is not an essential issue,
The volume ratio of the novolac resin solution is preferably 1/10 to 10 times. If it is less than 1/10, the number of extractions for metal removal will increase, and if it is more than 10 times, problems will occur in that a part of the novolac resin will be precipitated and the amount of liquid to be handled will increase. The water used for the extraction is preferably sulfuric acid, hydrochloric acid, acetic acid, or the like having a pH of 5 or less. Although the reason is not clear, a part of the metal contained in the novolak resin has a chelate structure and the like, and it is considered that it is more soluble in an organic solvent than water. It is thought that this is because it causes a structural change and becomes compatible with water.

Next, the water and the novolac resin solution are mixed well by stirring or shaking, and then allowed to stand. As a result, the novolac resin solution layer and the water layer are separated into two layers, and the novolac resin solution layer is separated by decantation or the like. With respect to this novolac resin solution layer, the above-mentioned operations of water addition, mixing by stirring or shaking, standing and separation are repeated several times.

The solvent is removed from the thus-obtained novolak resin solution by evaporation to dryness, or the solution is put in a non-solvent of the novolak resin to reprecipitate the novolak resin and then filtered to remove the novolak resin. Collect.

The thus-obtained novolac resin has a greatly reduced metal content (preferably 100 ppb or less) as compared with that before purification. By mixing and dissolving this novolak resin together with a quinonediazide compound in a solvent, a positive photoresist solution having a low metal content is prepared.

Known quinonediazide compounds are esters of hydroxybenzophenone or a derivative thereof, gallic acid or a derivative thereof, a polymer having a hydroxy group such as acetone-pyrogallol resin, and an ester of o-naphthoquinonediazide-5-sulfonyl chloride. However, the present invention is not limited to these. The amount of the quinonediazide compound is usually in the range of 1/1 to 1/6 with respect to the novolak resin.

As the solvent, alcohols such as propanol and butanol, ketones such as methyl ethyl ketone, methyl isobutyl ketone and cyclohexanone, acetic acid esters such as ethyl acetate, butyl acetate and isoamyl acetate, cyclic ethers such as tetrahydrofuran and dioxane, methyl cellosolve, Examples thereof include ethyl cellosolve and butyl cellosolve, as well as ethyl cellosolve acetate, butyl cellosolve acetate and γ-butyrolactone. Further, aromatic hydrocarbons such as xylene and toluene may be mixed.

The positive photoresist composition described above may further contain small amounts of additional resins, plasticizers, dyes and the like as additional additives.

In addition to the above positive photoresist composition, a negative resist having a low metal content can be obtained using the purified novolac resin of the present invention, for example, according to the method disclosed in Japanese Patent Laid-Open Publication No. 57-86831. it can. Further, the novolac resin of the present invention can be applied to a known resist composition or a leveling agent using a novolac resin.

EFFECTS OF THE INVENTION Thus, according to the present invention, it becomes possible to obtain a novolak resin having a reduced metal content as compared with the prior art,
By using this novolac resin, it is possible to obtain a resist composition or a flattening agent having a small metal content that does not deteriorate the electrical characteristics when used in the production of semiconductor integrated circuits.

EXAMPLES The present invention will be described more specifically with reference to examples. In the examples, comparative examples and reference examples,% is based on weight unless otherwise specified.

Reference example 1 Novolak resin (Suzuki Chemical Co., Ltd., SR-3020NZ)
As a solution of methylisobutylketone containing no metal, the metal content was measured by flameless atomic absorption spectrometry (measured value is expressed in ppb). Fe 1,770, Na 280, and Mn 63 were respectively added to the weight of the novolak resin. , Cu 5
4, Mg 12, K 55, Ca 20, Zn 110, Pb 320, Ni 1
64, Cr 240, Al and Sn were below the detection limit (each 100 ppb).

Example 1 10 g of the novolak resin of Reference Example 1 was dissolved in 90 g of methyl isobutyl ketone, and then transferred to a separating funnel of 1. To this was added 500 g of a 3% aqueous sulfuric acid solution prepared from ultrapure water containing substantially no metal and sulfuric acid. The mixture was shaken well and allowed to stand for 30 minutes. The novolak resin solution layer was separated into the upper layer, the aqueous layer was separated into the lower layer, and the aqueous layer was removed. The above-mentioned new 3% is added to the remaining novolac resin solution layer.
A sulfuric acid aqueous solution is added, and the mixture is shaken again and left to stand, and the separated aqueous layer is removed. After performing this extraction operation 5 times in combination, the metal content of this novolak resin solution was adjusted to Na, K, Mn, M
When g, Fe, Ca, Cu, Al, Sn, Zn, Pb, Ni and Cr were measured, all were below the detection limit. The detection limit is 2 ppb for Fe, 10 ppb for Al, Sn, Cr, 5 ppb for Pb, Ni,
It is 1 ppb for Na, Mn, Cu, Mg, K, Ca and Zn. This novolak resin solution was put into cyclohexane to obtain a novolac resin substantially free of metal.

Example 2 A cyclohexanone solution was obtained after performing the same operations as in Example 1 except that 8 g of the novolak resin was dissolved in 92 g of cyclohexanone. When the metal content of this material was measured for the same metal as in Example 1, all were below the detection limit.

Example 3 Five extraction operations were performed in the same manner as in Example 1 except that a 3% aqueous solution of acetic acid was used instead of the 3% aqueous solution of sulfuric acid. The Fe content in the novolak resin was determined from the Fe content of the obtained solution, and was below the detection limit.

Comparative Example 1 The same operation as in Example 1 was performed using acetone (solubility in water at 20 ° C. ∞) in place of methyl isobutyl ketone. After the first shaking, 480
It was allowed to stand for a minute, but remained in an emulsion state.

Examples 4 to 8 The same operation as in Example 1 was performed using the novolac resin of Reference Example 1 and changing the type of solvent, the concentration of the novolac resin solution, and the volume ratio of the solution / water. The results are shown in Table 1.

Comparative Example 2 Commercially available novolac resin-quinonediazide photoresist (metal content (ppb) of this is Fe 120, Pb 30
(8, Mn 68, K 14, Na 6) was coated on a silicon substrate to a thickness of 1 micron, and then oxygen 300c.c., 30
Detach with plasma of 0 W (13.56 MHz), 1 Torr, and then form a diode,
When g) was measured (measurement of CT), it was 30 to 100 microseconds. When a diode is formed on an untreated silicon substrate, it takes 300 to 500 microseconds.

Example 9 10 g of the novolak resin obtained in Example 1, 3 g of a compound obtained by reacting o-naphthoquinonediazide-5-sulfonyl chloride with 2,3,4-trihydroxybenzophenone at a molar ratio of 2: 1 Then, it was dissolved in 33 g of ethylene glycol monoethyl ether acetate and then filtered through a filter having a pore size of 0.2 μm to obtain a positive photoresist composition.

This resist composition was applied in the same manner as in Comparative Example 2, stripped under the same conditions, and the C-T was measured to be 200 to 400 microseconds, which was almost the same as that of an untreated silicon substrate. A significant improvement in device characteristics was observed compared to general resists.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Mikio Tanijima 1-2-1, Yokou, Kawasaki-ku, Kawasaki, Kanagawa Japan Zeon Co., Ltd. Technology Development Center (72) Katsuhiro Fujino, Ueda, Nakahara, Kawasaki, Kanagawa 1015 Address within Fujitsu Limited (72) Inventor Hiroshi Yano 1015 Kamiodanaka, Nakahara-ku, Kawasaki City, Kanagawa Prefecture Within 1015 Fujitsu Limited (72) Inventor: Shuzo Fujimura 1015, Uedotachu, Nakahara-ku, Kawasaki City, Kanagawa Prefecture

Claims (1)

[Claims] 1. A metal content in a novolak resin is reduced by dissolving the novolac resin in a solvent having a solubility in water at 20 ° C. of 100 or less and extracting the resulting solution with water. A method for purifying a novolak resin, comprising: