JPH07138374A - Preparation of aqueous highly pure polymer compound solution for production of semiconductor element - Google Patents

Abstract

PURPOSE:To obtain a polymer compound solution by ultrafiltering an aqueous solution of a polymer compound. CONSTITUTION:An aqueous solution of a water-soluble polymer compound such as a partially saponified PVA having a viscosity of 3-10000cP (20 deg.C) and containing about 100-5000ppm of metallic ions such as Na, K, Mg, Ca, Cr, Mn, Fe, Co, Ni, Cu and Zn ions is caused to pass through an ultrafilter provided with several laid ultrafilter membranes having a separation capacity of a fractionation molecular weight of 1000-1000000 and excellent permeability and made of e.g. a polyether sulfone under a pressure of 0.5-2kg/cm<2> and is allowed to circulate. By repeating such ultrafiltration several times, an aqueous highly pure polymer compound solution having a specified concentration and a metallic ion concentration of as low as about 0.1ppm or below for each kind of metal can be obtained. This solution is diluted to a viscosity of 3-10000cP, and the diluted solution is applied to a semiconductor element base by spin coating and dried at about 20-100 deg.C to form a film of a thickness of about 0.05-10mum.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for preparing an aqueous solution of a high-purity polymer compound used for manufacturing a semiconductor device.

[0002]

2. Description of the Related Art Transistors, diodes, ICs, LSs
I, in a manufacturing process of a semiconductor element such as a thin film magnetic head, a film formed of a polymer compound is used for preventing a damage of a semiconductor substrate, a protective film, and a contact between a resist and a contrast enhancing layer. It is used as a barrier coat. As the above-mentioned polymer compound, water-soluble polymer compounds such as polyvinyl alcohol and polyvinylpyrrolidone are preferably used. Generally, the above-mentioned polymer compound film is formed by spin-coating a semiconductor substrate with an aqueous solution of the polymer compound. Therefore, in addition to having a viscosity suitable for spin coating, it is necessary to obtain a required film thickness by one spin coating. Therefore, when obtaining a thick film, it is necessary to prepare a high-concentration or high-viscosity polymer compound aqueous solution.

On the other hand, the characteristics of the semiconductor device are greatly changed by the adhesion of metal or metal ions. Therefore, if metal or the like adheres, the performance of the semiconductor device will be greatly reduced. In the process of manufacturing a semiconductor element, there is a problem that the semiconductor element may malfunction due to contamination of the semiconductor substrate by metal or the like contained in the material. Therefore, it is necessary to prepare a high-purity polymer compound aqueous solution containing no impurities such as metals. Specifically, water-soluble polymer compounds that are generally used as raw materials contain various metal ions, which are impurities, at 100 to 5,000 p
pm contains and needs to be removed before use.
In a polymer compound aqueous solution suitable for semiconductor device production, the concentration of metal ions needs to be 1 ppm or less per solid content. Especially Na, K, Mg, Ca, Cr, Mn, Fe, Co, N
In the case of ions of i, Cu and Zn, it is desired that the content be 0.1 ppm or less.

Generally, as a method for preparing a high-purity polymer compound aqueous solution having a viscosity suitable for spin coating and containing no metal or the like, (A) a polymer compound is washed with a solvent such as alcohol. After removing impurities by reprecipitation or the like and drying, the resulting polymer compound powder is dissolved in water, and (B) ion exchange is performed to remove impurities such as metals from a dilute polymer aqueous solution. To obtain a thick film, a method of further heating under reduced pressure and concentrating is known.

However, in the method (A), a large amount of solvent is used; the processing work requires a long time; the processing work is complicated; a considerable part of the polymer compound flows out into the solvent. The metal ion content is 1 ppm or less (relative to polymer solids) because a trace amount of metal ions remain in the solvent used for washing or reprecipitation, or new contamination occurs when transferring to a container. However, there is a drawback in that In addition, the method (B) has advantages such as no loss of polymer compound, but it is difficult to process a high viscosity liquid of 100 cP or more at the time of ion exchange, so that the high viscosity required for thick film production is high. There are drawbacks such as the inability to prepare an aqueous solution of a molecular compound, the inclusion of impurities in the apparatus or the like when the dilute solution is heated and concentrated, and the poor operability because bubbles are generated.

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to produce a semiconductor device for producing a semiconductor device, which is capable of easily preparing an aqueous solution of a high-purity polymer compound containing no metal ions without loss of the polymer compound and in a short time. It is intended to provide a method for preparing a polymer compound aqueous solution.

[0007]

Means for Solving the Problems As a result of intensive studies for solving the above-mentioned problems, the present inventor has found that the ultrafiltration method can be applied to the preparation of a high-purity polymer compound aqueous solution for semiconductor device production. This led to the present invention. That is, the present invention provides a method for preparing an aqueous solution of a high-purity polymer compound for producing a semiconductor device, which comprises ultrafiltration of an aqueous solution of a polymer compound.

The present invention will be described in detail below. Step of ultrafiltering aqueous solution of polymer compound The step of ultrafiltering aqueous solution of polymer compound, which is a feature of the present invention, will be described. This step is a step for removing metal ions from an aqueous solution of a polymer compound containing metal ions as impurities by an ultrafiltration method by utilizing the fact that the molecular weights of metal ions and water are extremely smaller than the molecular weight of polymer compounds. . Specifically, a polymer compound containing a metal ion as an impurity in an ultrafiltration membrane having pores of a size that does not allow a polymer compound having a molecular weight of a specific value or more to pass a metal ion as an impurity. Of water. That is, this step is a step of separating the aqueous solution into an aqueous solution containing metal ions that can pass through the ultrafiltration membrane and an aqueous solution containing a polymer compound that cannot pass through the ultrafiltration membrane.

Ultrafiltration In this step, an aqueous solution of a polymer compound prepared to have a viscosity of 3 to 10,000 cP (20 ° C., hereinafter the viscosity is shown at 20 ° C.) is usually subjected to ultrafiltration . . If the viscosity of the aqueous solution is too high, the filtration resistance becomes large, and a long time is required for filtration. Also, even if the concentration or viscosity of the aqueous solution is too low, the amount of the aqueous solution of the polymer compound to be filtered becomes large, so that it takes time to filter. Then, an aqueous solution of the polymer compound is added under pressure to
Perform ultrafiltration through an ultrafiltration membrane while maintaining the viscosity range of 10,000 cP. The pressure range at this time is preferably 0.5 to 2.0 kg / cm ² . Ultrafiltration may be repeated to obtain desired purity, viscosity, and the like. After removing some metal ions from the polymer compound by ion exchange, the resulting aqueous solution may be subjected to ultrafiltration to increase the purity of the aqueous solution of the polymer compound.

[0010] Materials of the ultrafiltration membrane wherein the ultrafiltration membrane is not particularly limited, for example, polyethersulfone compounds, cellulose-based compounds, ultrafiltration membrane of fluorine compounds. Among these, the ultrafiltration membrane of a polyethersulfone compound which is particularly resistant to organic solvents and has excellent separability and permeability is preferably used. Selection of the ultrafiltration membrane is usually carried out by the molecular weight cutoff. As the ultrafiltration membrane preferably used in the present invention, for example, one having a molecular weight cutoff of 1,000 to 1,000,000 and two or more having a different molecular weight cutoff can be appropriately selected depending on the purpose. When an ultrafiltration membrane having a too small molecular weight cutoff is used, the loss of the polymer is small, but it takes a long time for filtration and is likely to cause clogging. Further, if an ultrafiltration membrane having an excessively large molecular weight cutoff is used, most of the polymer compound in the aqueous solution will pass through the ultrafiltration membrane, and the desired aqueous solution cannot be obtained efficiently.

Polymer Compound The method of the present invention can be applied to any water-soluble polymer compound that is usually used in a semiconductor device manufacturing process. Examples of the water-soluble polymer compound, for example,
Completely saponified polyvinyl alcohol, partially saponified polyvinyl alcohol (saponification degree 70 mol% or more), vinyl alcohol-based polymers such as re-esterified products of polyvinyl alcohol; polyvinylpyrrolidone, vinylpyrrolidone-vinyl acetate copolymer, vinylpyrrolidone-acrylic acid copolymer Vinylpyrrolidone-based polymers such as coalesce and vinylpyrrolidone-styrene copolymers; cellulose derivatives such as methylcellulose, ethylcellulose, benzylcellulose, cyanoethylcellulose, carboxymethylcellulose, carboxyethylcellulose, and hydroxypropylcellulose.

Among the above water-soluble polymer compounds, polyvinyl alcohol is particularly excellent in film forming property and oxygen barrier property, is not easily attacked by organic solvent, and is easily removed from a semiconductor substrate by washing with water after use. The polyvinyl alcohol is suitable for use in the production of semiconductor devices in that it can be obtained. However, the polyvinyl alcohol can be easily highly purified by the method of the present invention.

Applications The high-purity polymer compound aqueous solution obtained by the method of the present invention is used for manufacturing semiconductor devices. Specifically, for example, it is used for forming a film on a semiconductor substrate by spin coating so as to form a film having a thickness of 0.05 to 10 μm and drying at a temperature of 20 to 100 ° C. At this time, the viscosity range of the aqueous solution suitable for spin coating is 3 to 1
It is 0,000 cP, more preferably 3 to 1,000 cP.
If the viscosity of the aqueous solution is too low, the film thickness becomes too thin to function as a protective film for preventing damage to the semiconductor substrate or as a barrier coat for preventing contact between the resist and the contrast enhancing layer. On the other hand, if the viscosity is too high, the film thickness becomes large and the film uniformity deteriorates. According to the method of the present invention, the high-purity polymer compound aqueous solution can be prepared as an aqueous solution having a suitable viscosity range of 3 to 10,000 cP required for the production of semiconductor devices.

[0014]

EXAMPLES Examples of the present invention will be described below, but the present invention is not limited to the following examples. Hereinafter, as the ultrafiltration device, Filtron miniset (trade name) manufactured by Fuji Filter Industry Co., Ltd. was used, and as the ultrafiltration membrane, a polyethersulfone membrane was used. The area of ultrafiltration membrane is 700 cm ² /
It was a sheet. Ultrafiltration was carried out at a liquid feeding pressure of 2.0 kg / cm ² G. The metal ion concentration was measured by the atomic absorption method (based on JIS K0121). The electric conductivity was measured using a conductivity meter manufactured by Horiba, Ltd. in a solution at 20 ° C.

Example 1 5% by weight aqueous solution of partially saponified polyvinyl alcohol having an average molecular weight of 18,000 (saponification degree: 80 mol%) (Na in the aqueous solution)
Ion concentration: 6ppm) 10 liters, molecular weight cut off 10,000
Continuous ultrafiltration was carried out by an ultrafiltration device equipped with two ultrafiltration membranes of No. 1 and ultrafiltration was performed until the ultrafiltration residual liquid reached 2 liters. The time required for ultrafiltration was 1 hour. The polyvinyl alcohol concentration in the obtained aqueous solution was 24.5% by weight. The obtained aqueous solution was diluted with ultrapure water until the polyvinyl alcohol concentration became 5% by weight, and the Na ion concentration in the solution was measured and found to be 1.2 ppm.

The polyvinyl alcohol concentration in the aqueous solution of the polymer compound after repeating the above ultrafiltration four times was 2
The content was 4.5% by weight and the viscosity was 600 cP. This aqueous solution was diluted with ultrapure water so that the concentration of the polyvinyl alcohol was 5% by weight, and the Na ion concentration in the solution was 15 ppb and the viscosity was 5 cP. When the semiconductor device substrate was spin-coated with the diluted aqueous solution (rotation speed: 3000 rpm, 10 seconds), a uniform coating film with a thickness of 0.1 μm was obtained.

Example 2 5 liters of a 5% by weight aqueous solution of hydroxypropylcellulose containing metal ions as shown in Table 1 was subjected to a molecular weight cut-off of 10,000.
The solution was sent to an ultrafiltration device having three ultrafiltration membranes of No. 3 attached. Ultrapure water was added to the filtration residue at 10 liters / hour, and the mixture was stirred and fed at 10 liters / hour for repeated ultrafiltration. After 4 hours from the start of liquid feeding, the concentration of the filtration residual liquid was 4.9% by weight and the viscosity was 10 cP. When the metal ion concentration and the electric conductivity were measured before and after the ultrafiltration of the aqueous cellulose solution, the results shown in Table 1 were obtained. Spin coating of the aqueous cellulose solution after ultrafiltration on a semiconductor substrate (rotation speed 4000 rpm, 10 seconds)
A uniform coating having a thickness of 0.2 μm was obtained.

[0018]

[Table 1]

Example 3 A 5% by weight aqueous solution of partially saponified polyvinyl alcohol having an average molecular weight of 18,000 (saponification degree: 80 mol%) (Na in the aqueous solution)
Ion concentration: 6 ppm) 60 liters were prepared and subjected to ion exchange to obtain a high-purity polyvinyl alcohol aqueous solution. The polyvinyl alcohol concentration of the aqueous solution after this ion exchange is
It was 4.9% by weight and the viscosity was 4.5 cP. Next, the aqueous solution 55
The liter was ultrafiltered by an ultrafiltration device equipped with three ultrafiltration membranes having a molecular weight cut off of 10,000 so that the aqueous solution reached 10 liters (required time: 4 hours). The viscosity of the aqueous solution after the above ultrafiltration was 650 cP and spin coating (rotation speed 2000 rpm, 20 seconds) on the semiconductor substrate gave 8 μm.
A uniform coating film was obtained.

Comparative Example 1 5 kg of methanol was added to 500 g of partially saponified polyvinyl alcohol (saponification degree: 88 mol%) powder having an average molecular weight of 25,000 and containing 120 ppm of Na ions. The obtained mixture was heated and stirred at 60 ° C. for 1 hour, and the polyvinyl alcohol powder was dissolved in methanol. After this aqueous solution was cooled to room temperature to precipitate polyvinyl alcohol, the precipitated polyvinyl alcohol and the aqueous solution were separated by suction filtration. The polyvinyl alcohol precipitate obtained was mixed again with 5 kg of methanol,
The resulting mixture was heated and stirred under the same conditions as above, and suction filtered. After repeating a series of operations from the above mixing to separation four times, the obtained polyvinyl alcohol was dried to give a powder. The amount of the polyvinyl alcohol powder was 325 g, and the Na ion content in the powder was 6 ppm. The time required to repeat the above-described series of operations four times was 35 hours, and the polyvinyl alcohol recovery rate was 65%.

Comparative Example 2 Partially saponified polyvinyl alcohol having an average molecular weight of 18,000 (saponification degree: 80 mol%) in a 15% by weight aqueous solution (viscosity: 65 cP,
Na ion concentration in the aqueous solution: 18 ppm) 10 liters were not pumped to ultrafiltration, but pressure fed to a column with an inner diameter of 6 cm filled with 2 liters of ion exchange resin (Amberlite MB-2, manufactured by Organo Japan) (2 kg / cm ² ) I did. The time required for ion exchange is 3
It was 0 hours. The polyvinyl alcohol concentration in the obtained aqueous solution was 15% by weight. Na in this deionized aqueous solution
When the ion concentration was measured, it was 0.3 ppm.

[0022]

EFFECTS OF THE INVENTION According to the method of the present invention, metal ions contained as impurities in an aqueous solution of a polymer compound can be easily removed. Therefore, metal ions-free high purity suitable for semiconductor device production can be obtained. A polymer compound aqueous solution can be obtained efficiently in a short time and easily. Further, the present invention provides a method for preparing a high-purity polymer compound aqueous solution for semiconductor device production, wherein the polymer compound is washed away by a cleaning solvent, the aqueous solution is altered by heating, and the inner wall material of the apparatus is mixed. There is no problem such as pollution. The method of the present invention can prepare an aqueous solution of a polymer compound with a viscosity suitable for spin coating used in the production of semiconductor devices. Therefore, the coating film prepared from the high-purity polymer compound aqueous solution obtained by the present invention is used as a protective film for preventing damage to the semiconductor element substrate, a barrier coat for preventing contact between the resist and the contrast enhancing layer, and the like. It is suitable.

Claims (1)

[Claims] 1. A method for preparing an aqueous solution of a high-purity polymer compound for producing a semiconductor device, which comprises ultrafiltration of an aqueous solution of a polymer compound.