JPH06142501A - Production of washing water - Google Patents

Abstract

PURPOSE:To provide a method for producing washing water which is capable of washing fine pore parts of water repellent material such as a silicon wafer. CONSTITUTION:Deaerated high-purity water 9 is supplied to a sealed vessel 5. The sealed vessel 5 is immersed in deaerated water 4 supplied to a water tank 3. The inside of the sealed vessel 5 is exhausted and vaccumized. When an ultrasonic vibrator 2 is actuated and the deaerated water 4 is radiated with ultrasonic wave, the ultrasonic wave acts on high-purity water 9 being a state wherein it is not brought into contact with air through the sealed vessel 5. A cluster is decomposed by cavitation generated in high-purity water 9. Washing water 9 wherein surface tension is decreased is obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing cleaning water used for cleaning a water repellent material such as a silicon wafer.

[0002]

2. Description of the Related Art Conventionally, materials such as silicon wafers have been used as wiring boards for mounting semiconductor components such as ICs and LSIs. The wiring board made of the silicon wafer is
It is manufactured by pressing and solidifying silicon resin or stacking silicon wafers in multiple layers, and it has a hole for mounting the semiconductor component, and a copper foil is stuck or a conductor paste is printed on the surface. By doing so, the wiring pattern is formed. In addition, fine holes are formed on the surface of the wiring board for various purposes other than the above. After manufacturing, the wiring board is cleaned to remove material scraps, foreign matters, etc. adhering to the surface, but the cleaning does not reduce the conductivity by oxidizing the wiring pattern formed on the surface. , Using ultrapure water.

However, since the silicon wafer is excellent in insulating property, heat resistance and the like, and is also excellent in water repellency, if washed with the ultrapure water, the ultrapure water has a surface tension. In addition, there is a disadvantage that the micropores, especially the small corners such as the corners thereof, cannot enter, and such micropores are difficult to clean.

[0004]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a method for producing cleaning water which eliminates such inconveniences and can also clean micropores of a water repellent material such as a silicon wafer.

[0005]

The ultrapure water used for cleaning the above-mentioned silicon wafer or the like is usually prepared by replacing the raw material water by ion exchange with cations and anions to H ⁺ and OH ⁻ , respectively. Is extremely low.

By the way, water is chemically represented by the general formula C _n H
_In alcohols represented by _{2n + 1} OH, carbon number n =
It is considered to correspond to 0 compounds. And in general,
It is known that physical properties such as boiling point and surface tension of organic compounds represented by a single general formula, for example, C _n H _{2n + 1} OH, change according to molecular weight. As shown in Table 1, as the carbon number n decreases and the molecular weight decreases, the boiling point decreases. However, the boiling point of water corresponding to the compound having carbon number n = 0 in the above general formula is 100.
C., which violates the general rule.

[0007]

[Table 1]

The anomaly of the water is the same with respect to the surface tension. The surface tension of ethyl alcohol at 20 ° C. is 22.27 dyn / cm and that of methyl alcohol is 22.5.
Although it is 5 dyn / cm and gradually increases with a decrease in the molecular weight, it shows an extreme increase of 72.75 dyn / cm in water.

The anomaly of water is not a structure represented by a molecular formula of H ₂ O when water exists as a liquid, but H ₂ O molecules are associated with each other to form a molecular group (cluster). It is explained by the theory. According to the theory, the cluster is the H atom and the O atom of each H ₂ O molecule.
It is said that they are bound to each other by a hydrogen bond formed with the atom. Therefore, water having a small surface tension can be obtained by decomposing the clusters and converting the associated H ₂ O molecules into smaller molecular clusters or individual H ₂ O molecules. Therefore, it is considered that the micropores of the water repellent material such as the silicon wafer can be advantageously cleaned.

As a result of extensive studies on the method for decomposing the water clusters, the present inventor found that not only the hydrogen bonds but also oxygen molecules and nitrogen in the air dissolved in the water were formed in the formation of the water clusters. It was found that molecules are also involved, and therefore, in order to decompose the clusters to obtain water having a small surface tension, ultrasonic waves are applied to the raw material water in a state where the dissolved gas is degassed from the raw material water. Proved to be effective.

Therefore, the method for producing cleaning water of the present invention is characterized by comprising the step of radiating ultrasonic waves to deaerated water in a state where the water does not come into contact with air.

In order to keep the water out of contact with air, ultrasonic waves are radiated to the water contained in the sealed container under a reduced pressure. Alternatively, ultrasonic waves may be radiated to the water while circulating the water in a conduit that does not come into contact with air.

The method for producing washing water of the present invention can be advantageously applied when the water is ultrapure water.

[0014]

According to such means, since the degassed water of the dissolved gas is further blocked from the air, the air is not newly dissolved and the water molecules are in a state where it is difficult to form the clusters. There is. And, in this state, because ultrasonic waves are radiated to the water, hydrogen bonds that bond the water molecules to each other are broken by cavitation generated in the water upon receiving the ultrasonic waves, and the clusters are formed. Is decomposed to obtain washing water with reduced surface tension.

Since the water is contained in a hermetically sealed container under reduced pressure or is circulated in a conduit that does not come into contact with air, the water is shielded from the air and new air is not dissolved. Also, by irradiating the water with ultrasonic waves while circulating the water in a conduit that does not come into contact with air, cleaning water with reduced surface tension can be continuously obtained.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The method for producing wash water of the present invention will be described in more detail with reference to the accompanying drawings. FIG. 1 is an explanatory view showing a method for producing cleaning water according to a first embodiment of the present invention, FIG. 2 is an explanatory view showing a wet state of a silicon wafer, and FIG. 3 is a cleaning water according to the second embodiment. It is explanatory drawing which shows a manufacturing method.

In the first embodiment of the present invention, wash water is produced by the wash water producing apparatus 1 shown in FIG.

The washing water producing apparatus 1 includes a water tank 3 having an ultrasonic vibrator 2 at the bottom, and deaerated water 4 supplied to the water tank 3.
And a sealed container 5 immersed in The deaerated water 4 is deaerated so that the amount of dissolved oxygen is 2 ppm or less so that the ultrasonic waves emitted from the ultrasonic oscillator 2 can be easily transmitted to the sealed container 5.

The gas dissolved in the liquid such as degassed water 4 is usually air, and other gases such as nitrogen are also dissolved in addition to oxygen. However, since the composition of dissolved air is almost constant, the total dissolved gas amount is represented by the dissolved oxygen amount.

A round bottom flask sealed with a rubber stopper 6 can be used as the sealed container 5, and the inside of the sealed container 5 is a conduit connected to an L-shaped glass tube 7 through which the rubber stopper 6 is passed. A vacuum pump (not shown) can be used to reduce the pressure via 8. The sealed container 5 is supported by a stand (not shown) or the like, and at least a part thereof is immersed in the degassed water 4 supplied to the water tank 3.

In the manufacturing method of this embodiment, first, the rubber stopper 6 sealing the sealed container 5 is removed, and ultrapure water 9 is supplied to the sealed container 5. The ultrapure water 9 has an electric conductivity of 17.5 μΩ, and the amount of dissolved oxygen is reduced to about 0.1 ppm by a known method. Since the amount of dissolved oxygen in the ultrapure water 9 is reduced as described above, cavitation easily occurs due to the ultrasonic waves emitted from the ultrasonic vibrator 2.

When ultrasonic waves are radiated from the ultrasonic oscillator 2, the energy of the ultrasonic waves is converted into heat, so that the degassed water 4 and the ultrapure water 9 are heated, and the cavitation tends not to occur easily. There is. Therefore, the degassed water 4 and the ultrapure water 9 are preferably cooled in advance.

The cooling may be performed so long as the water temperatures of the degassed water 4 and the ultrapure water 9 are maintained at room temperature when the ultrasonic waves are radiated, and the degassed water 4 and ultrasonic waves before the ultrasonic waves are radiated. It is preferable that the water temperature of the ultrapure water 9 is adjusted to 10 ° C. or lower.

Next, the sealed container 5 is sealed again with the rubber stopper 6, and the sealed container 5 is immersed in the deaerated water 4 supplied to the water tank 3. Then, a vacuum pump (not shown) is operated to evacuate the inside of the sealed container 5 to reduce the pressure to 5 to 10 Torr.

When the ultrapure water 9 comes into contact with the air when it is supplied to the sealed container 5, the air is dissolved, but the dissolved air is subsequently reduced by depressurizing the sealed container 5 as described above. Since it is discharged to the upper space in 5, it is degassed again, and thereafter it does not come into contact with air until the work is completed.

Next, by activating the ultrasonic oscillator 2 to radiate ultrasonic waves to the degassed water 4, the ultrapure water 9 which is not in contact with air as described above is passed through the sealed container 5 through the sealed container 5. And apply ultrasonic waves.

The ultrasonic wave has a fundamental frequency of, for example, 28k.
Although the ultrasonic wave of Hz may be radiated alone, the ultrasonic wave of the fundamental frequency of 28 MHz has a frequency of 100 MHz and 200M.
It is preferable to superimpose and emit ultrasonic waves such as Hz. It is considered that the cavitation occurs at a place where the change of the sound pressure density of the ultrasonic wave changes drastically, that is, at the peak portion of the ultrasonic wave, but as described above, it is larger than that of the ultrasonic wave of the fundamental frequency. By superposing and radiating ultrasonic waves of a frequency, cavitation is uniformly generated not only in the peak portion of the ultrasonic wave of the fundamental frequency but also in each portion.

In this embodiment, the washing water producing apparatus 1 is used to generate ultrasonic waves having a fundamental frequency of 28 MHz and a frequency of 100 M.
By irradiating the ultrapure water 9 with supersonic waves of Hz and 200 MHz for 1 hour, the cavitation generated in the ultrapure water 9 decomposes the clusters to obtain the ultrapure water 9 with reduced surface tension. It was

Next, the ultrapure water 9 whose surface tension has been reduced
Was used to clean the silicon wafer 10 shown in FIG. As shown in FIGS. 2A and 2B, generally, when the liquid 22 comes into contact with the solid 21, the liquid 22 becomes water drops due to its surface tension. At this time, the angle θ formed by the tangent line of the liquid droplet 22 and the surface of the solid 21 is defined as the solid 2 of the liquid 22.
As shown in FIG. 2 (a), the larger the surface tension of the liquid 22, the larger the contact angle θ as shown in FIG. 2 (a), and the larger the water droplets, and the smaller the surface tension of the liquid 22, as shown in FIG. 2 (b). The contact angle θ is small and the water droplets are flat.

Therefore, when normal ultrapure water 9 is used, since the surface tension is large, the silicon wafer 10 is hard to wet as shown in FIG. 2C, and the silicon wafer 10 has a depth of about 0.1 μm. When the holes 11 are formed, the corners 12 that do not come into contact with the ultrapure water 9 are provided inside the minute holes 11.
Can not be washed sufficiently. On the other hand, when the ultrapure water 9 having a reduced surface tension is used, the silicon wafer 10 is easily wetted, so that the micropores 11 of the silicon wafer 10 do not come into contact with the ultrapure water 9 as shown in FIG. 2D. The parts are eliminated and the cleaning efficiency is improved.

Next, when the state of the micropores 11 of the silicon wafer 10 cleaned as described above is observed with a microscope, the micropores 11 are sufficiently cleaned and no material scraps, foreign matters, etc. are observed. It was

Next, a second embodiment of the present invention will be shown. Second
In this embodiment, the wash water is produced by the wash water producing apparatus 31 shown in FIG.

The washing water producing apparatus 31 comprises a water tank 33 having an ultrasonic transducer 32 at the bottom and a conduit 35 immersed in deaerated water 34 supplied to the water tank 33. Aquarium 33
An outlet 36a for taking out the degassed water 34 and a supply port 36b for supplying the degassed water 34 are provided to face each other on the side wall of the degassing water 34.
6a is circulated to the supply port 36b.
The degassed water 34 is used for the same reason as in the first embodiment.
The dissolved oxygen amount is 2 ppm or less, and the water temperature is adjusted to 10 to 20 ° C.

The conduit 35 is made of SUS, Teflon, glass or the like, and the portion 35a formed in a serpentine shape has degassed water 34.
The ultrapure water 38 that has been degassed by the degassing means 37 connected to the upstream side is circulated, and the ultrapure water 38 is disposed downstream.
Is connected to a silicon wafer cleaning tank 39. The ultrapure water 38 has an electric conductivity of 17.5 μΩ,
For the same reason as in the above example, the water temperature is adjusted to 10 ° C. or lower.

In the manufacturing method of this embodiment, first, ultrapure water 38 is supplied to the degassing means 37 so that the amount of dissolved oxygen is 0.1 ppm.
Degas to the extent. The ultrapure water 38 is degassed as described above for the same reason as in the first embodiment.

The deaerating means 37 includes a sealed tank 40 and a sealed tank 40.
It consists of a vacuum pump 41 that sucks and exhausts the inside to reduce the pressure,
By introducing the ultrapure water 38 into the sealed tank 40 and bringing it into contact with the space inside the sealed tank 40 that is decompressed by the vacuum pump 41, the gas dissolved in the ultrapure water 38 is transferred into the space inside the sealed tank 40. Release and degas.

Next, while the degassed ultrapure water 38 is flowing through the conduit 35, the ultrasonic vibrator 32 is operated to operate the degassed water 3
By radiating the ultrasonic wave to the ultrasonic wave 4, the ultrasonic wave is caused to act on the ultrapure water 38 which is in the state of not being in contact with the air, which is circulated in the conduit 35 as described above, via the serpentine tubular portion 35a.
In the present embodiment, ultrasonic waves having a frequency of 28 MHz are converted into ultrasonic waves having a frequency of 100 MHz and 200 by using the cleaning water manufacturing apparatus 31.
Ultrasonic waves of MHz were superposed and emitted to the ultrapure water 38 flowing through the conduit 35. As a result, clusters were decomposed by cavitation generated in the ultrapure water 38, and the ultrapure water 38 with reduced surface tension was continuously obtained.

Next, while the ultrapure water 38 whose surface tension has been reduced as described above is continuously supplied to the silicon wafer cleaning tank 39, the silicon wafer 10 shown in FIG. It was washed. After the cleaning, the state of the micropores 11 of the silicon wafer 10 was observed with a microscope. As a result, the micropores 11 were sufficiently cleaned and no material scraps, foreign matters, etc. were observed.

As the degassing means 37, there are other known degassing modules such as a degassing module for sucking and exhausting the outer peripheral portion of the hollow fiber-shaped or spiral gas separation membrane while circulating ultrapure water 38 therein. Means may be used.

The ultrapure water 38 may be supplied from a storage tank (not shown) or the like to the silicon wafer cleaning tank 39 via the deaeration means 37 and the manufacturing apparatus 31, and may be discharged as it is after the cleaning. After that, it may be circulated to the deaeration means 37 again and reused. Ultra pure water after cleaning 38
When reusing, the physical properties of the ultrapure water 38 as ultrapure water have deteriorated, such as an increase in electric conductivity, so that it should be recycled through a degassing means 37 after being regenerated through a filter, an ion exchange resin or the like. Is preferred.

Further, an ultrasonic vibrator 42 may be provided in the silicon wafer cleaning tank 39 to carry out ultrasonic cleaning.

[0042]

As is clear from the above, according to the method for producing cleaning water of the present invention, it is possible to obtain cleaning water with reduced surface tension. The micropores of the water-repellent material can also be sufficiently washed.

[Brief description of drawings]

FIG. 1 is an explanatory view showing a method of manufacturing wash water according to a first embodiment of the present invention.

FIG. 2 is an explanatory view showing a wet state of a silicon wafer.

FIG. 3 is an explanatory view showing a method of manufacturing wash water according to a second embodiment of the present invention.

[Explanation of symbols]

1, 31 ... Washing water production apparatus, 2, 32 ... Ultrasonic transducer, 5 ... Sealed container, 9, 38 ... Degassed water, 35 ...
conduit.

Claims (4)

[Claims] 1. A method for producing cleaning water, comprising the step of radiating ultrasonic waves to deaerated water in a state where the water does not come into contact with air. 2. The method for producing wash water according to claim 1, wherein ultrasonic waves are emitted while the water is contained in a hermetically sealed container under a reduced pressure. 3. The method for producing wash water according to claim 1, wherein ultrasonic waves are radiated while the water is being circulated in a conduit that does not come into contact with air. 4. The method for producing wash water according to claim 1, wherein the water is ultrapure water.