JPH0761431B2 - Polymer semipermeable membrane for high-level gas drying and its manufacturing method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial application] The present invention relates to a gas for manufacturing a semiconductor material such as a silicon wafer, a gas for manufacturing a semiconductor device, and a manufacturing process for a new material such as fine ceramics, a solar cell, and an optical fiber. The present invention relates to an improved fluoropolymer semipermeable membrane suitable for high-level drying of a working gas.

[Prior Art] For example, semiconductor devices called LSIs and VLSIs are currently playing a leading role in the remarkable development of the electronic field. In addition to general-purpose gas,
Noble gases such as argon and helium, corrosive gases such as hydrogen chloride and chlorine, and special gases such as silane, arsine, and borane gas are used. Further, at present, the semiconductor device manufacturing process is rapidly progressing toward higher integration (ultra-miniaturization).

As the degree of integration of LSIs increases and the current 256K bits increases to 1 megabit to 4 megabits, the line width of minute patterns becomes smaller and smaller, so that even fine particles, which have not been a problem until now, will affect the yield. It came out.

Therefore, the above-mentioned gas for semiconductor production is also used, for example, for a silicon wafer to be an LSI substrate, for epitaxial in device manufacturing process, for doping, for etching,
Gases for cleaning and the like are also required to have a purity of 4 to 5 nines or more, and in addition to them, those having a water content of 1 ppm or less and a degree of dryness and no suspended dust are required. Moisture in these gases causes various obstacles as described below, and therefore must be strictly controlled.

Corrosion of a metal part such as a pipe valve flow meter in semiconductor manufacturing occurs, and fine metal impurities and fine powder are generated (for example, corrosive gas such as HCl gas).

H ₂ and O ₂ are generated due to the decomposition of water in the manufacturing furnace, and especially O ₂ causes unexpected oxide impurities.

A chemical reaction occurs between the gas itself and water, producing duplicate impurities.

Currently, for example, an adsorption method using a molecular sieve is partially used for drying gas in a semiconductor device manufacturing process. Molecular sieves are desiccants that have the ability to adsorb phosphorus pentoxide, and it is relatively easy to dry ordinary gases to a water content of 1 ppm or less.

This desiccant is widely used because it has an advantage as a physical desiccant which does not cause troubles such as disintegration and swelling. However, the drawback is that the heating regeneration that is generally performed is 200 to 400
High temperature of ℃ is required, and suspended dust is generated by repeated use of heating and regeneration.

Further, the acidic gas such as hydrochloric acid gas also causes crushing of the molecular sieve.

There are acid-resistant grades, but the generation of suspended dust cannot be ignored, and a dust filter must be installed. It is also impossible to regenerate the molecular sieve.

On the other hand, a method of using a polymer film as a gas drying method is described in US Pat. No. 3,735,558 and JP-A-53-60563. Unlike the adsorption method using molecular sieves, these membrane permeation methods do not require regeneration and can be used continuously for a long time, which is an excellent method.

For the former, a polymer having a fluorinated sulfonic acid group is used, and it can also be used for corrosive gases.
However, neither of them has a high degree of dryness with a water content of 1 ppm or less, which is used for a semiconductor manufacturing process.

[Problems to be Solved by the Invention] The disposable molecular sieve adsorption method has a high running cost, so the running cost is low, and there is no suspended dust, and a gas with a high degree of dryness of 1 ppm or less of water content is easily obtained. Finding ways to gain is an important issue that must be resolved.

[Means and Actions for Solving Problems] The present invention has been earnestly studied to develop a novel method for solving the above-mentioned problems, and as a result, a polymer semi-polymer composed of a specific fluorocopolymer described below. The inventors have found that the permeable membrane is suitable for the above purpose and completed the present invention.

That is, according to the present invention, firstly, the general formula (In the formula, m = 0 or 1; n = integer of 2 to 5) which is made of a hollow fiber-shaped fluorine-containing copolymer and has a water absorption rate W and an ion exchange capacity Q.
The relation of A polymeric semipermeable membrane having is provided.

According to the present invention, secondly, (In the formula, m = 0 or 1; n = integer of 2 to 5) A hollow fiber-shaped fluorine-based copolymer containing a repeating unit represented by the following formula is heated to obtain the water absorption W and the ion exchange capacity Q. The relation is There is provided a method for producing a polymer semipermeable membrane, which comprises obtaining the polymer semipermeable membrane.

Examples of the fluorine-based copolymer include fluorinated olefins such as tetrafluoroethylene, trifluoroethylene, perfluorovinyl ether, vinylidene fluoride and vinyl fluoride. Those obtained by copolymerizing a perfluorovinyl ether monomer represented by (m = 0 or 1, n = integer of 2 to 5) are preferable. These copolymers are described in USP 4329434, USP 4329435, USP 3909378.

The present inventors have found that the relationship between the water absorption rate and the ion exchange capacity among the membranes of the fluoropolymer containing the repeating unit represented by the above general formula is as follows. It was discovered that the polymer semipermeable membrane, which is, is excellent in highly drying gas.

The sulfonic acid group of the fluorine-based copolymer is preferably introduced as an ion exchange capacity in an amount of 0.5 to 2.5 meq / g H-type dry resin in the copolymer. By setting the ion exchange capacity of the fluorine-based copolymer within the range of 0.5 to 2.5 meq / g H-type dry resin, the permeation rate of water vapor is not significantly reduced, and the melting point of the copolymer is high. The polymer thin film can be easily manufactured, and the physical strength of the polymer thin film can be maintained without lowering the physical strength.

Especially, the ion exchange capacity is 0.8 to 1.8 meq / g H
It is preferably a mold dry resin.

As the salt type of the sulfonic acid group of the fluorocopolymer used in the present invention, it is possible to use a metal salt or an ammonia salt type, but the SO ₃ H type has the highest water content, and the water vapor transmission rate is large. It is also preferable because it has sufficient thermal stability.

In the present invention, the shape of the fluorocopolymer is a hollow fiber membrane having a large membrane area per unit volume and a high treatment capacity.

In particular, the airtightness of the device is important for achieving a high degree of dryness, and the hollow fiber membrane is preferably used also from this point.

Regarding the thickness of the hollow fiber, the thinner the hollow fiber, the higher the water vapor permeability and the improved performance, which is preferable, but the hollow fiber is limited in terms of moldability and pressure resistance. Inner diameter 400 to 5 depending on hollow fiber diameter
A film having a thickness of 00 μm preferably has a film thickness of 40 to 60 μm.

In order to produce the film of the present invention, the above fluorine-based copolymer is formed into a thin film, which is then hydrolyzed with alkali and treated with a strong acid to convert the terminal group SO ₂ F into SO ₃ H, and then the copolymer. Is a heat treatment.

The heat treatment can be carried out, if necessary, while purging a dry gas, for example, nitrogen gas having a water content of 2.5 ppm or less, or under reduced pressure. A heat treatment temperature of 70 to 250 ° C is suitable. If the temperature is too high, the ion-exchange group may be eliminated and the performance may be deteriorated. The heat treatment temperature is particularly preferably 70 to 200 ° C.

The heat treatment causes the copolymer to shrink by several tens of percent, and the water absorption rate is also reduced. As a result, the relationship between the water absorption rate and the exchange capacity is 1.20Q-1.964 <logW <1.20Q-1.742.

By using the above heat-treated film, the gas has a moisture content of 5 p
A high degree of dehumidification with a water content of 1 ppm or less at room temperature of pm or less becomes possible. In this sense, it can be said that the above-mentioned copolymer film has a property of dehumidifying to a limit value which cannot be considered by the conventional common sense of the film.

The gas to be dried may be supplied to either side of the thin film of the fluorocopolymer. A dry purge gas having a low water content is passed through the membrane to the water permeation side, or a partial pressure difference, which is a driving force for membrane permeation, is generated by reducing the pressure with a vacuum pump or the like to achieve the purpose of dehumidification.

A dry purge gas with a low water content is a gas that is supplied to remove the water contained in the gas to be dried by removing the film, and is a gas that is inert and difficult to react even if the temperature rises. preferable. The reduced pressure means a pressure lower than the atmospheric pressure, although it depends on the pressure of the supplied source gas.

The membrane of the present invention is produced by heat treatment. In the case of a flat membrane, whether or not it is produced by heat treatment can be easily determined by measuring the water absorption.

However, if the membrane is a thin hollow fiber, the water absorption rate is difficult to measure, so that the determination can be made by measuring the heat shrinkage start temperature described below.

Attach a light weight (sufficient to straighten the thread but not enough to stretch it) to the hollow fiber membrane and hang it in the air tank. In that state, the temperature of the air tank is gradually raised, and the change in the yarn length is read and measured with a telescope. An example of the measurement results is shown in the graph when the horizontal axis is temperature and the vertical axis is length. L ₂₅ is a length of 25 ° C. and L _t is a length at a temperature of t ° C. In FIG. 4, the temperature indicated by the arrow, that is, the maximum temperature at which there is no dimensional change due to temperature rise is defined as the "maximum temperature at which there is no heat shrinkage." Several hollow fibers having different heat treatment temperatures (t) were prepared, the "maximum temperature (T) without heat shrinkage" was measured, and the results were plotted on a graph, as shown in FIG. That is, T = t (1), and the heat treatment temperature (t) of the hollow fiber membrane can be known by measuring the maximum temperature (T) without heat shrinkage.

In the method of the present invention, the gas to be dried is usually a gas filled in a cylinder, which is generally obtained on the market, and a gas whose water vapor concentration is not so high. The gas filled in the cylinder is usually about several ppm to several tens of ppm, but in some cases, 100 ppm or more. It is possible to obtain the target dehumidification level by changing the film area of the gas drying device according to the concentration of the target gas or by making it in multiple stages.

The method of the present invention is particularly suitable for highly drying gas for semiconductor material manufacturing process, gas for semiconductor device manufacturing and gas for new material manufacturing process such as solar cell and amorphous silicon.

ASH ₄ , H ₂ S, GeH ₄ , SeH ₂ , SbH ₃ , AsC as a typical example of semiconductor process gas as a gas for new material manufacturing process
l ₃ , (C ₂ H ₅ ) ₂ Te, (CH ₃ ) ₂ Cd, (C ₂ H ₅ ) ₂ Cd, AsF ₃ , PH ₃ ,
Doping gases such as PCl ₃ , B ₂ H ₅ , BF ₃ , BCl ₃ , (CH ₃ ) ₂ Te; SiH ₄ , SiH ₂ Cl ₂ , SiHCl ₂ , SiCl ₄ , B ₂ H ₅ , BBr ₃ , B
_{I 3, AsH 3, PH 3} , GeH 3, TeH 2, (CH 3) 3 As, (C 2 H 5) 3 Al,
(CH ₃ ) ₃ Sb, (C ₂ H ₅ ) ₃ Sb, (CH ₃ ) ₃ Ga, (C ₂ H ₅ ) ₃ Ga, (CH
₃ ) ₃ As, (C ₂ H ₅ ) ₃ As, (CH ₃ ) ₂ Hg, (C ₂ H ₅ ) ₂ Hg, (CH ₃ ) ₃
Epitaxial gases such as P, (C ₂ H ₅ ) ₃ P, SnCl ₄ , GeCl ₄ , SbCl ₅ , AlCl ₃ ; AsF ₅ , PF ₅ , PH ₃ , BF ₃ , BCl ₃ , SiF ₄ , SF ₆
Ion implantation gas such as AsH ₃ , PH ₃ , HCl, SeH ₂ , (CH ₃ ) ₂
Te, (C ₂ H ₅ ) ₂ Te and other gases for light-emitting diodes; Cl ₂ , HCl, H
Etching gas such as F, HBr, SF ₆ ; SiF ₄ , CF ₄ , C ₃ F ₈ , C
Plasma etching gas such as ₂ F ₆ , CHF ₃ , CClF ₃ , O ₂ ; C _{3
F 8, CHF 3, CClF 3} , ion beam etching gas such as CF _4; Ar, such as reactive sputtering gas O _2; SiH _4, SiH ₂
Chemical vapor deposition (CVD) gases such as Cl ₂ , SiCl ₄ , NO, O ₂ ; N ₂ , Ar, H
Balanced gases such as e, H ₂ , CO ₂ and N ₂ O can be cited.

[Examples] The present invention will be described in more detail below with reference to experimental examples, but the present invention is not limited to the examples.

The moisture content of the gas in the examples and comparative examples was measured by a dew point meter or a moisture meter, and depending on the gas, the Karl Fischer method.

Example 1 With tetrafluoroethylene And ion-exchange capacity of 0.94 meq / g H
A mold dry resin was obtained. The resin obtained is molded at a molding temperature of 250 ° C.
A film having a thickness of μm was prepared, and after hydrolyzing this film with an alkaline alcohol solution, ion exchange was performed with a hydrochloric acid aqueous solution to make the end of the side chain a sulfonic acid type (H type) and air-dried. The obtained film was subjected to dry temperature treatment in vacuum, and the equilibrium water absorption was determined at 25 ° C (Fig. 1).

As shown in Fig. 1, the water absorption rate decreased significantly when the dry heat treatment temperature was about 70 ° C or higher. The water absorption was almost constant even at higher temperatures.

Similarly, the monomer species were changed as shown in Table-A to prepare a polymer film having an ion exchange capacity of 0.8 to 1.1 meq / g, and a polymer film having the water absorption rate shown in Table-A was prepared. Table-A
From the results, the relation between the ion exchange capacity and the water absorption rate of the membrane of the present invention is shown by the shaded area in FIG.

Example 2 With tetrafluoroethylene Was copolymerized to obtain an H type dry resin having an ion exchange capacity of 0.9 meq / g. The obtained resin was melt-spun at a spinning temperature of 250 ° C. and a spinning speed of 88 mm using a molding machine equipped with a hollow fiber manufacturing die to obtain a hollow fiber membrane having an inner diameter of 500 μm and a film thickness of 60 μm.

After the hollow fiber was hydrolyzed with an alkaline alcohol solution, ion exchange was performed with a hydrochloric acid aqueous solution to make the end of the side chain a sulfonic acid type (H type) and air dried. 40 cm length of the obtained thread
Bunched 400 pieces of the above, and fixing them to a separator made of SUS with epoxy resin at both ends to make a gas drying device as shown in FIG. N ₂ gas adjusted to a moisture content of 1 ppm (dew point −76 ° C.) or less was pressurized to 5 kg / cm ² G in the drying device, and was hollow at a flow rate of 0.5 l / min (flow rate converted to atmospheric pressure; the same below). I shed it inside the thread.

Similarly, N ₂ gas adjusted to have a water content of 1 ppm (dew point −76 ° C.) or less was flowed at 0.75 l / min. This is placed in a constant temperature bath at 70 ° C. and heat-treated for 3 hours, and then the drying device is returned to room temperature,
N ₂ gas (sample gas) adjusted to a water content rate of 31 ppm (dew point −52 ° C.) and a pressure of 5 kg / cm ² G is flown inside the hollow fiber at 0.5 l / min, and a water content rate of 1 ppm (outside the hollow fiber). Dew point -76 ° C)
The N ₂ gas adjusted below was flowed at 0.75 l / min. When the dew point of the sample gas outlet of the drying device was measured, the water content was 1 ppm
It was below (dew point -76 ° C). Continuous operation as it is, 24
Sample gas outlet water content 1ppm (dew point -76
C) remained below.

On the other hand, also for the purge gas on the outside of the hollow fiber, the moisture content was 4.6 ppm when the drying device outlet dew point was measured after 24 hours.
It was (dew point -66 ° C). After that, the outlet water content of the sample gas remains 1ppm (dew point -76 ° C) or less after continuous operation for about 1000 hours under the same conditions, and the amount of water reduced by the sampling gas dryer and increased by the purge gas dryer The water content ratio was 1.2: 1, which was in good agreement within the measurement error.

As for the other films of the present invention, the same results as in Example 2 were obtained as shown in Table-A.

Comparative Example 1 When the sample gas and the purge gas were measured by the same apparatus as in Example 2 without the heating pretreatment under the same conditions as in Example 2, the moisture content of the sample gas was 10.6 ppm after 44 hours.
It did not reach the (dew point -60 ° C). Similarly, Table-A
As shown in FIG. 5, the films other than the present invention showed the same results as in Comparative Example 1.

Example 3,4,5,6 Using the same drying apparatus as in Example 2, the sample gas was changed to HCl.
(However, the pressure was kept at 5 kg / cm ² G) and the outlet water content of the sample gas was measured in the same manner as in Example 2 to obtain the results shown in Table 1. However, the purge side was performed by flowing dry N ₂ having a water content of 1 ppm or less or by reducing the pressure.

[Effects of the Invention] The effects of the semi-permeable polymer membrane for highly drying gas and the drying method using the membrane according to the present invention are summarized as follows.

The gas can be highly dried and its drying performance can be maintained for a long time.

 No airborne dust is generated during gas drying.

Even if an acidic gas such as hydrochloric acid gas contacts the thin film, it does not attack the thin film.

Unlike the adsorption method using molecular sieves, no regeneration is required and continuous use for a long time is possible.

Further, since the gas drying apparatus using the membrane of the present invention is a polymer semipermeable membrane having excellent performance in highly drying gas and is inserted into a large number of hollow fiber-shaped casings, The film area is large and the processing capacity is high and compact.

Further, in the method for producing the membrane of the present invention, by heating a specific fluorine-based copolymer, a membrane excellent in highly drying the above gas can be easily produced.

[Brief description of drawings]

FIG. 1 is a graph showing the relationship between the dry heat treatment temperature and the equilibrium water absorption of the polymer semipermeable membrane obtained in Example 1, and FIG. 2 is the ion produced in Example 1 by drying at 70 ° C. or higher. Exchange capacity 0.
Graph showing the relationship between the polymer water absorption rate (W) and the ion exchange capacity (Q) of the polymer semipermeable membrane of 8 to 1.1, FIG. 3 is a schematic explanatory view showing a gas drying apparatus according to the present invention, and FIG. The figure is a graph for obtaining the maximum temperature without heat shrinkage of the hollow fiber membrane, where the horizontal axis is temperature and the vertical axis is the length (L _t ) of the hollow fiber membrane at t ° C and the length at temperature 25 ° C (L ₂₅ ) And the ratio.
FIG. 5 is a graph showing the relationship between the heat treatment degree (t) of the hollow fiber membrane and the maximum temperature at which heat shrinkage does not occur, and the heat treatment temperature can be determined from this graph. 1 ... Hollow fiber membrane, 2 ... Sample gas inlet, 3 ... Sample gas outlet, 4 ... Purge gas inlet, 5 ... Purge gas outlet, 6
... cell, 7 ... diaphragm.

Claims (4)

[Claims] 1. A general formula (In the formula, m = 0 or 1; n = integer of 2 to 5) which is made of a hollow fiber-shaped fluorine-containing copolymer and has a water absorption rate W and an ion exchange capacity Q.
The relation of A semi-permeable membrane having a polymer. 2. The polymer semipermeable membrane according to claim 1, wherein m = 1 and n = 3. 3. General formula (In the formula, m = 0 or 1; n = integer of 2 to 5) A hollow fiber-shaped fluorine-based copolymer containing repeating units is heated to absorb water W and ion-exchange capacity Q.
The relation of A method for producing a polymer semipermeable membrane, comprising: 4. The method for producing a polymer semipermeable membrane according to claim 3, wherein heating is performed at a temperature of 70 to 200 ° C.