JPH0669175A - Method of cleaning semiconductor base material - Google Patents

Abstract

PURPOSE:To provide a refining system which can efficiently regenerate organic solvent waste liquid inside a clean room by using anion exchange film as the separating film for selectively gasifying and separating one ingredient liquid from the liquid mixture. CONSTITUTION:Used cleaning waste liquid is extracted from a cleaner 1, and it is received in a waste liquid tank 3 from a line 2. The waste liquid is processed to remove water by the purvaparation method using anion exchange film as a separation film 5, and the processing liquid being gotten from dehydration method is distilled to obtain an organic solvent being refined as distilled liquid. That is, for a device which is divided into a processing liquid chamber 4 and a permeated steam chamber 6 by a separating film 5 is used. The organic solvent being refined this way is returned to a cleaner again by a circulation line 12, and is used again. This way, the mixing in of impurities from the outside can be reduced remarkably.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for cleaning a semiconductor substrate such as a silicon wafer. Specifically, it is a method for cleaning a semiconductor substrate, which enables efficient removal of impurities from the organic solvent waste liquid after cleaning the semiconductor substrate and reuse as a cleaning liquid.

[0002]

2. Description of the Related Art In the processing of semiconductor substrates such as silicon wafers, acids, moisture, ionic substances, etc. which adhere to the surface of the substrate by polishing treatment, etching treatment, washing treatment, etc.
Cleaning with an organic solvent is performed for the purpose of removing particles and the like. The organic solvent used for cleaning the semiconductor substrate, as the cleaning is repeated, the acid content, water,
The amount of impurities such as ionic substances and particles is increased, so that the cleaning effect is deteriorated, and the quality of the semiconductor substrate is deteriorated and the yield is decreased.

In order to solve the above problem, a method is conceivable in which a waste liquid of an organic solvent containing impurities such as an acid component, water, an ionic substance and particles is purified by distillation and reused.

[0004]

However, when the organic solvent is purified by the above method, the following problems occur. That is, in the above cleaning, the organic solvent is an isopropyl alcohol (hereinafter, also referred to as IPA) in order to efficiently remove water, acid, etc. adhering to the surface of the semiconductor substrate.
An organic solvent having a polarity such as is generally used. However, the organic solvent as described above becomes an azeotropic mixture with water contained as an impurity, and it becomes difficult to easily remove water by ordinary distillation. Therefore, in order to obtain a distillate in which the content of water is not more than the concentration that does not cause a problem in cleaning the semiconductor substrate, the distillation apparatus becomes complicated and large-scaled. For example, in the case of IPA, the IPA concentration is 88% (wt
%), It has an azeotropic composition with water, so that an IPA aqueous solution having a lower concentration than this cannot be concentrated to a concentration of 88% or more by a normal distillation operation. In this case, a commonly used concentration method is a method of performing azeotropic distillation by adding an entrainer such as benzene, but at least three columns of a dehydration tower by an entrainer, a recovered water removal tower of the entrainer, and an IPA purification tower are used. In order to obtain a distillate whose water content is required and whose concentration does not cause a problem in cleaning the semiconductor substrate, the height of the tower is usually 6 m or more, which makes it difficult to be compact. In particular, the cleaning operation of the semiconductor substrate is carried out in a small space such as a clean room with a small volume of solvent, so it is substantially difficult to perform a complicated distillation operation in the space of such a space. However, the equipment cost becomes expensive, and there is no merit of recycling.

Further, by utilizing the IPA-water azeotrope, water is removed from the top of the azeotropic dehydration tower in the form of an IPA-water azeotrope, and the IPA containing less water than the bottom of the tower. However, this method also requires an azeotropic dehydration tower with a tower height of about 5 m or more, and it depends on the IPA concentration of the treatment liquid.
The loss rate of A reaches several tens of percent, which is economically unusable. Moreover, since IPA is taken out from the bottom of the tower, almost no impurities particles can be removed.

To solve the above problems, a method of dehydrating with a dehydrating agent such as molecular sieve can be considered, but the application range of the treatment liquid is narrow and the dehydrating agent is usually regenerated (although the water content is about 1% or less). A method using a dehydrating agent which requires treatment and has a possibility that impurities are mixed into a clear cleaning agent is essentially unfavorable.

[0007] If the water concentration in the cleaning organic solvent changes, the quality and yield of the semiconductor base material are subtly affected, so it is important to stabilize the quality of the cleaning agent itself. Therefore, it is possible to frequently replace with new liquid, but there is a large economic loss, and when the used IPA is discarded and replaced with new liquid, impurities in the particle tower are mixed from the container and the surroundings, and new liquid Often polluted.

Therefore, in the cleaning of semiconductor substrates, a major problem is to establish a cleaning method having a purification system capable of efficiently recycling the organic solvent waste liquid even in a clean room or the like, with a low loss rate and without the inclusion of impurities. It had been.

[0009]

Means for Solving the Problems As a result of intensive studies to solve the above-mentioned problems, the present inventors have succeeded in selectively vaporizing and separating one liquid component in a liquid mixture through a separation membrane. In the vaporization method, by using an anion exchange membrane as a separation membrane, water, an acid content, an ionic substance, an organic solvent waste liquid treatment containing impurities such as particles, most of the contained water is separated, After removing
Then, by distilling to obtain a purified organic solvent as a distillate, it was found that the distillation apparatus can be made extremely compact and the impurities can be removed extremely efficiently, and the present invention has been completed.

That is, the present invention provides a cleaning step for cleaning a semiconductor substrate with water and an organic solvent having a reference point, and an organic solvent containing impurities such as water, an acid ionic substance and particles discharged from the cleaning step. Distillation to obtain a purified organic solvent as a distillate by performing a dehydration process in which the waste liquid is treated by a pervaporation method using an anion exchange membrane as a separation membrane to remove water and distilling the treatment liquid obtained from the dehydration process. A method of cleaning a semiconductor substrate, which comprises a circulation step of circulating the purified organic solvent obtained in the step and the distillation step in the step of cleaning the semiconductor substrate.

In the present invention, the step of washing the semiconductor substrate is not particularly limited, and a known washing method using an organic solvent can be adopted without particular limitation. For example, steam cleaning or a combination of spray cleaning and steam cleaning is common.

Further, the present invention is particularly suitable for an organic solvent having an azeotropic point with water in the above washing step. Examples of such organic solvents include IPA, ethanol, n-
Examples thereof include alcohols such as propanol, isobutanol and isoamyl alcohol, and chlorinated hydrocarbons such as methyl chloride, methylene chloride and carbon tetrachloride. Among them, IPA is most preferable in terms of cleaning effect.

When the semiconductor substrate is washed with the above organic solvent, the acid components such as nitric acid and hydrofluoric acid adhering to the substrate,
Since impurities such as water and particles accumulate in the organic solvent, it is usually discarded when used to some extent from the viewpoint of yield and quality deterioration of the base material, but from the viewpoint of economic efficiency and quality stability,
It is preferably purified and reused.

The organic solvent waste liquid to be purified in the present invention is not particularly limited as long as it is an organic solvent containing impurities such as water, acid components, ionic substances, particles, etc. It is particularly effective when treating an organic solvent waste liquid containing water at a ratio of -40%. The reason for this is that in an organic solvent waste liquid containing less water than the above range, the cleaning effect due to water is less likely to decrease, and in the distillation described below, it is possible to obtain an organic solvent from which impurities have been removed relatively easily. Because you can. Of course, even in such an organic solvent waste liquid, there is an advantage that the quality can be further improved by applying the method of the present invention. Usually, the water content of the organic solvent waste liquid discharged from the semiconductor cleaning step is around 10%, and the present invention can be applied very effectively.

In the present invention, the organic solvent waste liquid is first supplied to the dehydration step and treated by the pervaporation method to remove most of the contained water. That is, by removing most of the water by the pervaporation method, it is possible to obtain an organic solvent having a sufficiently low water content as a distillate in the distillation apparatus having a low tower height in the next distillation step. . Therefore, the refining system can be made compact and can be installed in the cleaning process arranged in the clean room. Further, by obtaining a purified organic solvent as a distillate, it is possible to leave particles, ionic substances, etc. in the bottom liquid for separation. Furthermore, as for the acid content, most of the water is removed at the same time when it is removed by the pervaporation method, so there is a problem of corrosion due to acid in the metal distillation apparatus of the latter stage such as stainless steel and contamination by elution of metal ions. Will be resolved. In the pervaporation method, known devices and conditions can be adopted without particular limitation as long as an anion exchange membrane that can selectively permeate water in an organic solvent-water system is used as a separation membrane. The separation membrane has a solution permeability coefficient of 0.01
It is suitable to use at least kg / m ² · Hr, preferably at least 0.05 kg / m ² · Hr, and having a separation coefficient of 10 or more, preferably 30 or more. The separation factor is It is represented by. Specifically, an anion exchange membrane having an exchange group such as a pyridinium base, an amine base, or a quaternary ammonium base is preferable because of high removal rate of the acid component. In addition, if the apparatus and conditions in which the pervaporation method is adopted are specifically shown, an apparatus that basically has two chambers, a treatment liquid chamber and a permeation vapor chamber, which are divided by the separation membrane, is generally used. To be done. Further, the apparatus is preferably a so-called filter press type apparatus in which a plurality of treatment liquid chambers and permeation vapor chambers are alternately arranged via a separation membrane. Further, a type having a heating device for replenishing the heat of vaporization can also be used. On the other hand, the operating conditions are that the temperature of the liquid to be treated existing in the treatment liquid chamber is 20 to 100 ° C., and the degree of vacuum of the permeation vapor chamber is 0 to 10.
It is preferable to perform it so that it becomes 0 Torr. In this way, water is removed from the water-containing IPA during the pervaporation treatment, but a small amount of IPA migrates to the permeation vapor chamber side according to the separation coefficient value, resulting in loss of IPA. However, even when dehydration treatment is performed from 10% water-containing IPA to 1% water-containing IPA using a separation membrane having the above-mentioned permeability coefficient and separation coefficient, IPA
In general, the loss is less than 5%, which is very economical compared with the case where the entire amount is regularly replaced with new liquid.

The amount of water removed by the above-mentioned pervaporation method may be most of the water in the organic solvent waste liquid, but in particular, in terms of the yield and quality of the semiconductor substrate,
It is desirable to remove water so that the water content is reduced to 3% or less, preferably 1% or less based on the organic solvent.

The organic solvent waste liquid from which water and acid components have been removed by the above-mentioned method is sent to a distillation step, and by distillation, the purified organic solvent is taken out as a distillate.

As the distillation apparatus used in the present invention, known structures such as an ordinary packed column bubble column, a perforated plate column and the like can be used without limitation, but a packed column is preferable from the viewpoint of easy size reduction. As a distillation method, either simple distillation or reflux distillation in which a part of generated vapor is condensed can be used. In the case of the reflux type distillation column, Japanese Patent Application No. 58-123154 and Japanese Patent Application No. 58-1
The model shown in No. 09008 is preferably used as a small and simple device. In any case, the distillation apparatus is provided with at least a distillation pot section equipped with a heating source, a rectification section (filling section) for performing a rectification action, and a condensation section, and impurities such as particles from the outside inside the distillation apparatus. Care must be taken to prevent contamination from entering. In particular, it is desirable that the inside of the distillation apparatus, the inside of the contact pipe and the like be subjected to a surface treatment such as buffing, acid and alkali washing treatment in advance so that fine particles are not generated by the distillation operation. or,
At the time of stopping the operation of the distillation apparatus, it is preferable that the apparatus is sealed with a sealing gas such as clear air or nitrogen gas so that gas such as air enters the apparatus and the inside of the apparatus is not contaminated by impurities and particles in the gas. . Particularly, as the sealing gas, it is desirable that the number of particles having a diameter of 0.5 μm or more is 350 particles / liter or less in terms of quality control of the processing liquid. The operating conditions of the distillation apparatus may be appropriately selected depending on the type and composition of the organic solvent dehydrated from the pervaporation method apparatus, the composition of the distillation column, etc., but if the distillation rate is too fast, particles or ionicity may occur due to entrainment of droplets. Care should be taken as substances may be mixed in the concentrated liquid (treatment liquid). Generally, the steam velocity is 5 to 50 cm / se
It is desirable to use c. By feeding the treatment liquid thus treated by the pervaporation method into the distillation apparatus and performing the distillation operation, particles, ionic substances, high boiling point components, etc. can be easily removed, and the treatment liquid is a new liquid. It becomes a high-quality organic solvent that is almost the same as, and can be reused. For example, as a result of sampling and analyzing the IPA processed by the pervaporation method, the IPA concentration is 99.1%, the number of particles (0.5 μm
m or more) Approx. 9500 pieces / 100 cc, ionic substance, Na ion 6 ppm, K ion 5 ppm, Fe ion 9 ppm, Cu
The ions were 8 ppm and the specific resistance was 2 MΩcm, but when the distillation operation was carried out while performing a partial reflux operation in a packed column connected to a pervaporation device, I
PA concentration 99.0%, 930 particles / 100c
c, Na ion 0.02ppm, K ion 0.03ppm,
The Fe ion content was 0.03 ppm, the Cu ion content was 0.01 ppm, and the specific resistance was 250 MΩcm. The number of particles and the ionic substance were very purified. As a result of analyzing commercially available IPA, the IPA concentration was 99.9% and the number of particles was 260.
0, Na ion 0.05ppm, K ion 0.01ppm
, Fe ion 0.01ppm, Cu ion 0.01ppm
The specific resistance was 90 MΩcm, and the treatment liquid which had been subjected to the pervaporation treatment and the distillation treatment was of a quality substantially equivalent to that of the new liquid.

The organic solvent purified by the above method may be recycled for reuse in the washing step. in this case,
To prevent particles from mixing in the air during circulation,
It is desirable to connect the distillation apparatus and the washing process with piping so that the circulation system does not come into contact with the atmosphere.

When the amount of the purified organic solvent is insufficient, a new organic solvent may be added.

A typical embodiment of the method of the present invention will be briefly described with reference to FIG. The used cleaning waste liquid is drawn from the cleaning device 1 and received by the waste liquid tank 3 from the line 2. A pump is supplied from the waste liquid tank 3 to the treatment liquid chamber 4 of the pervaporation apparatus to dehydrate most of the water. 5 is a separation membrane and 6 is a permeation vapor chamber, and the gas that has permeated the separation membrane is discharged as it is or after being condensed. Next, the dehydrated treatment liquid is sent from the line 7 to the distillation apparatus 8 using back pressure. 9 is a filler and 10 is a condenser. The purified IPA liquid from which ionic substances and particles have been removed as a distillate from the distillation apparatus is stored in the intermediate tank 11. The purified IPA from which impurities such as water, acid, ionic substance, and particles have been removed in this way is returned to the cleaning device 1 again by the circulation line 12 and reused. In the cleaning device, IPA for the loss is replenished from the new liquid supply line 13.

[0022]

As can be understood from the above description, the present invention is directed to water, acid components,
Ionic substances, organic solvent waste liquids containing impurities such as particles are treated by combining the pervaporation method using a specific separation membrane and distillation, so that a compact distillation apparatus can efficiently and highly purify It is possible to regenerate the organic solvent and circulate it in the washing step. Therefore, it has become possible to provide a closed system in which a purification process is added to the semiconductor substrate cleaning process, which has been difficult to achieve in the past, and these are connected by a pipe, and it is possible to significantly reduce the mixing of impurities from the outside and clean the semiconductor. It can be performed.

Example 1 The waste IPA solution discharged from the wafer cleaning apparatus was purified by using a pervaporation apparatus loaded with an ion exchange membrane and a packed column type distillation apparatus. The waste IPA
When the solution was sampled and analyzed, IPA
Concentration 91wt%, moisture 9wt%, acid content (as HF) 13pp
m, Na; 12 ppm, K; 7 ppm, Fe; 12 ppm, C
u; 13 ppm, specific resistance 0.3 MΩcm, number of fine particles (diameter 0.5 μm or more); 9700/100 cc. The waste IPA liquid was first sent to a pervaporation device and mainly dehydrated. The apparatus used had an effective membrane area of 1 m and was partitioned into a treatment liquid chamber and a permeation vapor chamber by pyridinium type anion exchange. In the pervaporation, the waste IPA solution is continuously supplied at a liquid amount of 1.5 kg / Hr, the treatment liquid chamber temperature is 60 ° C., and the permeation vapor chamber vacuum degree is 10
It was done while adjusting to Torr. The anion exchange membrane used was prepared as follows. 100 parts of 2 methyl-5 vinyl pyridine, divinyl benzene (purity 50%) 10
Part, benzoyl peroxide 2 parts, and polyvinyl chloride fine powder 50 parts to prepare a viscous paste-like mixture, which was applied to a polyvinyl chloride cloth and polymerized by heating to form a polymer film. . The polymer film was placed in a quaternization solution of methyl iodide: methanol = 1: 1 at room temperature 16
After soaking for an hour to obtain an anion exchange membrane, further soak in a mixed solution of water: acetone = 1: 2 (vol ratio) for about 20 hours, then soak in water to remove acetone, and then to obtain a film thickness of 1
A 20 μm pyridinium-type anion exchange membrane was obtained. The separation characteristics of this membrane by pervaporation were as follows: IPA concentration 95%, liquid temperature 60 ° C., vacuum degree 10 Torr, permeation coefficient 0.
35 kg / m · Hr, separation factor 160. However, the separation coefficient is represented by the ratio of the permeate water concentration / permeate IPA concentration and the treatment liquid water concentration / treatment liquid IPA concentration. From the vapor permeation chamber side of the pervaporation device, the IPA concentration was about 22.5.
% Aqueous solution was discharged in an amount of 0.16 kg / Hr, and the IPA loss rate was about 2.6%. The liquid treated by the pervaporation device was sampled at the outlet of the device and analyzed. IPA concentration was 99.2 wt% and water content was 0.8 wt.
%, Acid content; 1 ppm, Na; 6 ppm, K; 5 ppm, Fe;
9ppm, Cu; 8ppm Specific resistance 2MΩcm Fine particle coefficient 950
At 0/100 cc, the acid content was well removed along with the water content. Next, the liquid from which most of the water was removed by the pervaporation device was continuously supplied to a distillation device connected by a pipe to remove ionic substances and particles. The distillation device has an inner diameter of 60φ and the packing is magnetic 3/8.
The filling height is 100 cm and the total height of the distillation column is 180 cm using an in-flyer hilling. The material used was stainless steel. The reflux rate is 1: 1 and the distillation rate is 1.34 kg.
/ H, the distillation column and the processing liquid tank have a pore size of 0.1
It was sealed with N ₂ gas filtered through a μm filter so that impurities in the atmosphere were not mixed in. The result of sampling and analyzing the distillate (treatment liquid) from the distillation apparatus is I
PA concentration 99.1%, moisture 0.9%, acid content 1ppm or less,
Na; 0.02 ppm, K; 0.03 ppm, Fe; 0.0
3 ppm, Cu; 0.01 ppm, specific resistance of 250 MΩcm, fine particles of 930 particles / 100 cc, ionic substances and particles were well removed, and the product was purified to a quality that would cause no problem even if reused in the cleaning step. As a result of circulating the treated purified IPA through the pipe sealed from the outside air in the cleaning step, it was possible to perform cleaning with a stable cleaning effect without inclusion of impurities. The IPA for the loss was replenished with a new solution in the washing process. In the examples, IPA, water is a gas chromatographic method, acid is an alkali titration method, Na and K are atomic absorption methods, Fe and Cu are IPA methods, and specific resistance is a resistivity meter.
The number of fine particles was measured with an automatic fine particle counter.

Example 2 Except that as the separation membrane of the pervaporation apparatus of Example 1, Neocepta AM-1 (manufactured by Tokuyama Soda Co., Ltd.) was used as the quaternary ammonium salt type anion exchange membrane. The waste IPA liquid was purified in the same manner as in Example 1. Pervaporation device: 1.1 kg / Hr of liquid supply
The water was removed at an IPA concentration of 91% to 99.0 wt%. The numbers of Na, K, Fe and Cu fine particles were almost the same as in Example 1, but the acid content was 7 ppm. Also, IP
The A loss rate was 4.6%. Although the ionic substance and fine particles were removed from the pervaporation treatment liquid by the subsequent distillation apparatus in the same manner as in Example 1 and reused as a cleaning liquid, the cleaning effect was not deteriorated and stable cleaning could be performed.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing an exemplary embodiment of an apparatus for carrying out the method of the present invention.

[Explanation of symbols]

 1 Cleaning Device 2 Line 3 Waste Liquid Tank 4 Treatment Liquid Chamber 5 Separation Membrane 6 Permeation Vapor Chamber 7 Line 8 Distillation Device 9 Filler 10 Condenser 11 Intermediate Tank 12 Circulation Line 13 New Liquid Supply Line

Claims (1)

[Claims] 1. A washing step of washing a semiconductor substrate with water and an organic solvent having a reference point, and an organic solvent waste liquid containing water, an acid component, an ionic substance and impurities such as particles discharged from the washing step. A dehydration step of removing water by treatment by a pervaporation method using an anion exchange membrane as a separation membrane, a treatment step obtained by the dehydration step is distilled, and a distillation step of obtaining a purified organic solvent as a distillate solution, and A method of cleaning a semiconductor substrate, which comprises a circulation step of circulating a purified organic solvent obtained in the distillation step in the step of cleaning the semiconductor substrate.