JPH0737486B2 - Method for purifying polymer for semiconductor substrate coating material - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for purifying a polymer, and more specifically,
The present invention relates to a method for reducing the metal content of a polymer used as a semiconductor substrate coating material.

2. Description of the Related Art In recent years, as the integration and speed of semiconductor devices have increased, the demand for miniaturization of the devices has increased. To meet this requirement, resists used in lithography are
Conventional cyclized polyisoprene-bisazide negative resist is changing to novolak resin-quinonediazide positive resist, and when a finer pattern is required, chloromethylstyrene-styrene copolymer, methacrylic acid is used. -Electron beam resists such as methacrylic acid ester copolymers are also used.

Further, as the structure of the semiconductor element becomes complicated, it becomes necessary to form a pattern on a substrate having a step. In this case, a so-called multilayer resist system may be used. First, various polymers are applied as a flattening agent, and a resist layer is formed thereon.

To form a pattern on a semiconductor substrate using a resist, first, the resist is applied by a spinner or the like to form a resist layer having an appropriate film thickness, and then the remaining resist solvent is removed by prebaking. In a multi-layer resist system, a leveling agent layer is similarly formed on a semiconductor substrate, and then a resist layer is further formed thereon by the above method. Next, a desired pattern is drawn (exposure) by a method according to each resist, and the generated latent image is processed by a developing solution to become 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-etched with an aqueous solution of hydrofluoric acid, but gradually dry etching that uses active species generated in plasma discharge is frequently used. Has become.

Then, the resist and the flattening agent which have become unnecessary are stripped off. In this step, plasma is often used instead of the conventional wet method.

As described above, the process of forming a pattern on a semiconductor substrate is shifting from a conventional wet process using a solvent to a dry process not using a solvent, but a new problem occurs in this process.

That is, when the resist and the flattening agent are removed by dry etching or plasma, most of the metal contained in the resist and the flattening agent remains on the substrate, so that the electrical characteristics of the semiconductor formed from these substrates are increased. Will be lowered. Similar problems can be pointed out for other polymers applied to semiconductor substrates.

Therefore, it is becoming important as a characteristic of a material such as a resist or a flattening agent to be applied to a semiconductor substrate that a fine pattern can be drawn and a metal content is small.

However, the metal content of semiconductor substrate coating materials such as resists and planarizing agents that are currently on the market is not at a level that can satisfy semiconductor manufacturers, and has become a major problem in semiconductor manufacturing.

Various causes can be considered for the origin of the metal contained in the semiconductor substrate coating material such as the resist and the flattening agent. A semiconductor substrate coating material such as a resist or a planarizing agent is one in which various polymers are dissolved as a main component in a solvent. In addition to this, a photosensitizer, a dissolution inhibitor, a sensitizer, a storage stabilizer, a plasticizer Contains various surfactants and other compounding agents. Therefore, these compounds are all conceivable as sources of metal contamination. The solvent has the highest blending ratio among these various blends, but grades for electronic materials purified by various methods are commercially available, and the metal content due to the solvent is low. .

On the other hand, there are many polymers used as coating materials for semiconductor substrates such as resists and planarizing agents.
These polymers are those that are touched by the raw material monomers and the solvent of the reaction, those that are caused by various solvents and cocatalysts used in the polymerization or condensation of the monomers or the polymer modification reaction, or those that are caused by the manufacturing equipment. Various metals are included. Although other formulations also contain metals, when considering their contents and blending amounts, the major cause of metals contained in coating materials for semiconductor substrates such as resists or planarizing agents is the large amount of polymer. That is to include the metal.

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention As a result of intensive studies to solve the above-mentioned drawbacks, the present inventors have found that if a polymer used as a material for coating a semiconductor substrate is purified by a specific method, the metal in the polymer is It was found that it is possible to reduce the content, and by using the above-mentioned purified polymer, the metal content in the semiconductor substrate coating material such as resist or flattening agent can be significantly reduced. Based on this, the present invention has been completed.

According to the present invention, a polymer used as a coating material for semiconductor substrates has a solubility in water at 20 ° C. of 10 or less.
A method for purifying a polymer for semiconductor substrate coating material, which comprises dissolving in a solvent of 0 or less, performing liquid-liquid extraction of the resulting solution with water, and centrifuging to reduce the metal content in the polymer. Will be provided.

Polymers used as coating materials for semiconductor substrates (hereinafter,
The method for purifying the material polymer) will be described below. Examples of the polymer include novolac resin, polymethylmethacrylate, methylmethacrylate-methacrylic acid copolymer, methylmethacrylate-acrylonitrile copolymer,
Acrylate polymers such as methyl methacrylate-isobutylene copolymer, hexafluorobutyl polymethacrylate, tetrafluoropropyl polymethacrylate, epoxidized polyisoprene, polyglycidyl methacrylate, glycidyl methacrylate-ethyl acrylate copolymer, methacrylic acid Epoxy-based polymers such as glycidyl-styrene copolymers, silicone-based polymers such as methylvinylsiloxane, poly (butene-1-sulfone),
Olefin-sulfone polymers such as poly (styrene sulfone), polystyrene, styrene polymers such as poly-α-methylstyrene, polychloromethylstyrene, styrene-chloromethylstyrene copolymers, polymethylisopropenyl ketone, orisoisobutylene, Examples thereof include polydiallyl phthalate.

The solvent used in the present invention is a solvent for the material polymer and has a solubility in water at 20 ° C. of 100 or less, preferably 50 or less. Specific examples thereof include aromatic hydrocarbons such as benzene, toluene and xylene, aliphatic hydrocarbons such as hexane and heptane, cyclohexane,
Alicyclic hydrocarbons such as tetralin, ethyl acetate, acetic acid n
-Butyl, acetic acid esters such as isoamyl acetate, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone and other ketones, n-butanol, i-butanol, i
-Alcohols such as amyl alcohol, glycol ether acetates such as ethylene glycol monoethyl ether acetate and ethylene glycol monobutyl ether acetate, halogenated hydrocarbons such as carbon tetrachloride, chloroform and tetrachloroethane, and other ethers, ligroins and solvents. Examples include naphtha. These solvents may be used alone or in combination of two or more. The solubility of the solvent in water
When it exceeds 100, the material polymer is precipitated during the purification, or the separation of the material polymer solution layer and the aqueous layer becomes difficult or impossible.

The material polymer is dissolved in the solvent. The preferred concentration is not specified, but if the concentration is too low, there is a problem in operation because the total amount of liquid is large, and if the concentration is too high, the solution viscosity becomes high and the separation from the aqueous layer becomes poor. . The preferred range is 3% to 50%.

Next, water is added to the solution of the material polymer. Alternatively, the solution may be added to water. The water used is
For the purpose of the present invention, those having a low metal content are desirable. The amount of water used is not an essential problem, but it is preferably 1/10 to 10 times the volume of the solution of the material polymer by volume. If it is less than 1/10, the number of extractions for removing metals will be too small, and if it is more than 10 times, problems will occur in that a part of the material polymer 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, some of the metals contained in the various polymer materials have a chelate structure and are more suitable for organic solvents than water.
It is more easily dissolved, but it is thought that this is because the structure changes due to the acid and it has an affinity for water.
Further, most of the metals are contained in the material in the form of oxides, but it is possible that these become salts in the form of acid and become more soluble in water.

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

In the present invention, the efficiency of purification can be further improved by combining the above-mentioned operation with a centrifugation operation. This centrifugation operation may be carried out after repeating the above-mentioned water addition, mixing, standing and separation several times, or may be repeated several times in the cycle of water addition, mixing, standing, separation and centrifugation. Good. Further, a centrifugation operation may be added before the first-time addition of water to the material polymer solution. The effects of these centrifugations are considered as follows. That is, first of all, metal oxides and the like which are present in a solvent-insoluble form are removed by centrifugation. Secondly, a considerable amount of the metal that has become soluble in water in the form of a salt exists because the water used for liquid-liquid extraction is suspended (or emulsified) in the solvent.
This is because the suspended water is present in the solvent in the form of being contained in the water, but the suspended water is removed from the solvent by centrifugation, and therefore the metal dissolved therein is also removed. .

Furthermore, in addition to the operations of the liquid-liquid extraction and the centrifugal separation, the addition of filtration and operation with a filter also has the effect of removing the metal present in a form insoluble in the solvent.

The solvent is removed from the material polymer solution thus obtained by evaporation to dryness, or the solution is put in a non-solvent of the material polymer to reprecipitate the material polymer and then filtered. Collect the polymer. The purified solution can be used as it is for preparation of a resist, a planarizing agent, or the like.

In the material polymer thus obtained, the amount of metal contained is greatly reduced (preferably 50 ppb or less, more preferably the detection limit or less) as compared with that before purification.

By blending and preparing the material polymer thus obtained according to each purpose, a semiconductor substrate coating material such as a resist having a low metal content, a flattening agent and the like is prepared.

EFFECTS OF THE INVENTION Thus, according to the present invention, it becomes possible to obtain a polymer for a coating material for a semiconductor substrate having a metal content reduced as compared with the prior art, and by using this polymer, it was used in a semiconductor integrated circuit structure. At this time, it is possible to obtain a semiconductor substrate coating material such as a resist or a flattening agent having a small metal content without deteriorating the electrical characteristics. Therefore, the present invention is particularly useful when a fine pattern is required and a dry etching process is performed.

Examples The present invention will be described in more detail below with reference to examples. The parts and% in Examples, Comparative Examples and Reference Examples are based on weight unless otherwise specified.

Reference Example Commercially available novolac resin was used as a solution of metal-free methyl isobutyl ketone, and the metal content was measured by flameless atomic absorption spectrometry (measurement value is displayed in ppb),
Fe 1,770, Na 28 for novolak resin weight respectively
0, Mn 63, Cu 54, Mg 12, K 55, Ca 20, Zn 110, Pb 32
0, Ni 164, Cr 240, Al and Sn were below the detection limit (each 100 ppb).

Example 1 10 g of the novolak resin of Reference Example was dissolved in 90 g of methyl isobutyl ketone, and then transferred to a separating funnel of 1ι. This was added to 500 g of 3% sulfuric acid aqueous solution (pH 0.7) prepared from ultrapure water containing substantially no metal and sulfuric acid. The mixture was shaken and shaken, and then allowed to stand for 30 minutes. Since the novolac resin solution layer was separated into the upper layer, the aqueous layer into the lower layer, and the two layers were separated, the aqueous layer was removed. The remaining novolac resin solution layer was 5,000 rpm by an H-251 type centrifugal separator manufactured by Domestic Centrifuge Co., Ltd.
Centrifuged at 10 ° C for 15 minutes. Take out the novolac resin solution layer, transfer it to a 1 separation funnel, and add the new 3%
An aqueous solution of sulfuric acid was added, and the mixture was shaken again and allowed to stand, the separated aqueous layer was removed, and the mixture was centrifuged again. After repeating this series of operations three times, the metal content of this novolak resin solution was measured for Na, K, Mn, Mg, Fe, Ca, Cu, Al, Sn, Zn, Pb, Ni, Cr. However, all were below the detection limit.

Example 2 When a commercially available polymethylmethacrylate resin was used as a solution of metal-free methyl ethyl ketone and the Fe and Na contents were measured, they were 90 and 30 ppb per polymer weight, respectively.

After dissolving 8 g of this polymethylmethacrylate resin in 92 g of diisobutyl ketone, the same operation as in Example 1 was performed. When the metal content of this polymethylmethacrylate resin solution was measured for Fe and Na, both were below the detection limit.

Example 3 A polymer having 4-chloromethylstyrene unit of 36 mol%, 4-chlorostyrene unit of 64%, weight average molecular weight of 24,000 and dispersity of 1.70 was dissolved in toluene containing no metal to obtain a metal. When the contents were measured for Fe and Na, they were 200 ppb and 40 ppb, respectively, relative to the polymer weight. The same operation as in Example 1 was carried out except that 15 g of this polymer was dissolved in 85 g of toluene, and sulfuric acid was changed to hydrochloric acid (aqueous solution pH 0.3). However, each operation was repeated twice. When the metal content of this solution was measured for Fe and Na, both were below the detection limit.

Example 4 Weight average molecular weight 190,000, methyl methacrylate unit 94.5
%, Methacrylic acid unit 5.5% polymer was dissolved in metal-free 2-ethoxyethyl acetate, and the metal content was measured. Na 790, K 95, Mg 190, Fe 250, Ca 520, Cu 11
It was 0 ppb. Mn, Li and Al were not detected. 5 g of this polymer was dissolved in 95 g of 2-ethoxyethyl acetate and the same operation as in Example 1 was performed. When the metal content of the obtained polymer solution was measured for Na, K, Mg, Fe, Ca, Cu,
All metals were below the detection limit.

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

This resist composition was applied on a silicon substrate to a thickness of 1 micron, and then oxygen 300c.c., 300W (13.56MHz), 1To
Peeling off with rr plasma, then forming diode,
Generation lifetime (γg) was measured (C
-T measurement), but it was 30 to 100 microseconds. If the diode is formed on an untreated silicon substrate, 30
0 to 500 microseconds.

Example 5 The same experiment as in Comparative Example 1 was carried out except that the novolak resin obtained in Example 1 was used in place of the novolak resin used in Comparative Example 1, and the CT was measured. ~ 450
The time is microsecond, which is almost the same as that of an untreated silicon substrate, and a significant improvement in device characteristics was seen as compared with the conventional general resist.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Shinichi Takahashi 1-2-1, Yokou, Kawasaki-ku, Kawasaki-shi, Kanagawa, Japan Zeon Corporation Technology Development Center (72) Hiroshi Yano, Nakahara-ku, Kawasaki-shi, Kanagawa 1015 Odanaka, Fujitsu Limited (72) Inventor Shuzo Fujimura 1015, Kamiodanaka, Nakahara-ku, Kawasaki-shi, Kanagawa Within Fujitsu Limited

Claims (1)

[Claims] 1. A polymer used as a material for coating a semiconductor substrate is dissolved in a solvent having a solubility in water at 20 ° C. of 100 or less, and the resulting solution is subjected to liquid-liquid extraction with water and centrifugation to obtain the polymer. A method for purifying a polymer for a semiconductor substrate coating material, which comprises reducing a metal content in the polymer.