JP2001054767A - Cleaning method - Google Patents

Abstract

(57) [Summary] An electronic material such as a silicon substrate for a semiconductor and a glass substrate for a liquid crystal,
Provided is a cleaning method capable of effectively removing organic contaminants adhering to a machine part or the like requiring a highly clean surface by wet cleaning. A cleaning method includes contacting ozone-bubble-containing water with an object to be cleaned in the presence of a reducing substance.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a cleaning method. More specifically, the present invention utilizes the strong oxidizing power of ozone to apply organic substances adhering to electronic materials such as silicon substrates for semiconductors and glass substrates for liquid crystals, and mechanical parts that require highly clean surfaces. The present invention relates to a cleaning method capable of effectively removing contamination by wet cleaning.

[0002]

2. Description of the Related Art Conventionally, wet cleaning has been widely performed to remove impurities on the surface of an object to be cleaned. The impurities to be removed include fine particles, metals, organic substances, and the like, and an appropriate cleaning solution and cleaning method are adopted according to the purpose. Among them, in order to remove airborne organic matter and organic matter contamination such as resist residue, a chemical solution having a high ability to reduce the molecular weight of the organic matter, dissolve the organic matter, and take it into the solution has been used. A mixture of sulfuric acid and hydrogen peroxide (S
PM) is a typical example. When such a chemical is used at a high temperature, an organic substance adhered to the surface of the object to be cleaned is oxidized to obtain an excellent cleaning effect, but more recently, the cost of the chemical has been reduced, and a rinsing step after the cleaning has been required. For the purpose of simplification, reduction of the burden of wastewater treatment, and the like, wet cleaning technology using ozone that has a strong oxidizing power and is converted into harmless oxygen by decomposition has been developed and put into practical use. Ozone-dissolved water can certainly remove organic matter contamination on the surface of the object to be cleaned, but its detergency is one step further than conventional cleaning with a mixed solution of sulfuric acid and hydrogen peroxide. When high-concentration ozone-dissolved water such as tens of mg / L is used, high detergency equivalent to a mixed solution of sulfuric acid and hydrogen peroxide can be obtained, but such high-concentration ozone-dissolved water can be produced and concentrated. Maintenance was not easy and there was a need for improvement in practicality.

[0003]

SUMMARY OF THE INVENTION The present invention utilizes the strong oxidizing power of ozone to provide electronic materials such as silicon substrates for semiconductors and glass substrates for liquid crystals, and mechanical parts that require highly clean surfaces. An object of the present invention is to provide a cleaning method capable of effectively removing organic contaminants adhering to, for example, by wet cleaning.

[0004]

Means for Solving the Problems The inventors of the present invention have made intensive studies to solve the above-mentioned problems, and as a result, by bringing ozone-bubble-containing water into contact with an object to be cleaned in the presence of a reducing substance. It has been found that ozone is continuously dissolved in water from bubbles to maintain a strong oxidation state and an excellent cleaning effect can be obtained, and the present invention has been completed based on this finding. That is, the present invention provides (1) a cleaning method characterized by bringing ozone bubble-containing water into contact with an object to be cleaned in the presence of a reducing substance. further,
As a preferred embodiment of the present invention, (2) the cleaning method according to (1), wherein the reducing substance is hydrogen peroxide, and (3) cleaning filled with water in which the reducing substance is dissolved or overflowed. The object to be cleaned is immersed in the tank, and the ozone-containing gas is bubbled from the lower part of the cleaning tank, whereby the ozone-bubble-containing water is brought into contact with the object to be cleaned in the presence of the reducing substance.
(1) The cleaning method described in (1), (4) by immersing the object to be cleaned while bubbling an ozone-containing gas from below into a cleaning tank filled with water in which a reducing substance is dissolved or overflowed. The cleaning method according to (1), wherein the object to be cleaned is brought into contact with the ozone-bubble-containing water in the presence of a reducing substance, (5) a cleaning tank filled or overflowed with water in which the reducing substance is dissolved. Immerse the object to be cleaned in
The cleaning method according to (1), wherein the emulsion liquid containing fine bubbles of the ozone-containing gas is injected into the cleaning tank, whereby the ozone-bubble-containing water is brought into contact with the object to be cleaned in the presence of a reducing substance. (6) An emulsion liquid containing fine bubbles of an ozone-containing gas is injected into a washing tank filled with water in which a reducing substance is dissolved or overflowed, and stirred,
By immersing the object to be cleaned in the cleaning tank, the ozone bubble-containing water is brought into contact with the object to be cleaned in the presence of the reducing substance.
(7) The washing method described in (1), (7) The water in which the reducing substance is dissolved and the milky fluid containing the fine bubbles of the ozone-containing gas are simultaneously poured onto the object to be cleaned, thereby reducing the reducing substance. The cleaning method according to (1), wherein the object to be cleaned is brought into contact with the ozone-bubble-containing water in the presence thereof, and (8) water containing a reducing substance dissolved therein and ozone-containing gas or fine bubbles of ozone-containing gas. The ozone-bubble-containing water is brought into contact with the object to be cleaned in the presence of a reducing substance by merging the flow paths of the emulsion-containing fluid and pouring the mixture immediately after mixing the two. The washing method described above can be used.

[0005]

BEST MODE FOR CARRYING OUT THE INVENTION The cleaning method of the present invention involves contacting water to be cleaned with ozone-bubble-containing water in the presence of a reducing substance. The method of the present invention comprises a silicon substrate for a semiconductor,
Applicable to cleaning electronic materials such as glass substrates for liquid crystal and quartz substrates for photomasks, and mechanical parts that require highly clean surfaces, and effectively removes organic contaminants adhering to the surface. . The reducing substance used in the method of the present invention is not particularly limited. For example, in addition to hydrogen peroxide and the like, reducing gases such as hydrogen gas, organic reducing substances such as formic acid, aldehyde, and alcohol, hydrazine, and inorganic substances such as hydrogen sulfide. Reducing substances, sulfites such as sodium hyposulfite and ammonium hyposulfite, sulfites such as sodium sulfite and ammonium sulfite, bisulfites such as sodium bisulfite and ammonium bisulfite, nitrites such as sodium nitrite and ammonium nitrite And the like. Hydrogen peroxide is generally used as an oxidizing agent. When an oxidizing agent such as ozone having a strong oxidizing power is present, it acts as a reducing agent and also has an action as an ozone decomposition catalyst. Hydrogen peroxide is generally used in a wet cleaning step of an electronic material or the like, and can be used particularly preferably because a high-purity product can be easily obtained and there is no possibility of becoming a contamination source of the electronic material. Also, hydrogen gas can be suitably used because there is no risk of secondary contamination and the load on the rinse after cleaning is small.

In the method of the present invention, when hydrogen peroxide is used as a reducing substance, it is preferable to use water as a solution in which hydrogen peroxide is dissolved. There is no particular limitation on the concentration of dissolved hydrogen peroxide, but it is preferably 0.1 to 50 mg / L, more preferably 1 to 10 mg / L. When hydrogen gas is used as the reducing substance, it is preferably used as hydrogen gas dissolved water. There is no particular limitation on the concentration of the hydrogen gas-dissolved water.
It is preferably at least 1 mg / L, more preferably at least 0.1 mg / L. The method for preparing hydrogen gas-dissolved water is not particularly limited, and examples thereof include bubbling of hydrogen gas into ultrapure water and use of a module having a gas permeable membrane. In the method of the present invention, the method for preparing ozone-bubble-containing water is not particularly limited. For example, ozone-bubble-containing water can be directly obtained by bubbling an ozone-containing gas through a diffuser or the like into water in which a reducing substance is dissolved. Alternatively, by using a pump having a high stirring effect for the purpose of accelerating the dissolution of gas, and supplying the ozone-containing gas with water to the suction side thereof, an emulsion liquid containing fine bubbles of the ozone-containing gas is obtained. You can also. The ozone content of the emulsion fluid containing fine bubbles of the ozone-containing gas is not particularly limited, but the ozone content is preferably 0.1 to 30 mg / L, and 1 to 20 m / L.
More preferably, it is g / L.

In the method of the present invention, there is no particular limitation on the method of contacting the object to be cleaned with ozone-bubble-containing water in the presence of a reducing substance. For example, the method is filled with water in which the reducing substance is dissolved or overflowed. The object to be cleaned is immersed in the cleaning tank, and the ozone-containing gas can be bubbled from the lower part, or the ozone-containing gas can be bubbled from the lower part into the cleaning tank filled with water in which the reducing substance is dissolved or overflowed. The object to be cleaned can be immersed while bubbling. In the method of the present invention, when an emulsion liquid containing fine bubbles of an ozone-containing gas is used, the object to be cleaned is immersed in a cleaning tank filled with water in which a reducing substance is dissolved, or overflowed, By injecting the emulsion liquid containing fine bubbles of the contained gas into the washing tank and spreading the whole, the water containing ozone bubbles can be brought into contact with the object to be washed in the presence of the reducing substance, or Injecting a milky fluid containing fine bubbles of ozone-containing gas into the washing tank filled with water or overflowing with water in which the active substance is dissolved, and washing the washing tank with stirring. By immersing the object, the ozone bubble-containing water can be brought into contact with the object to be cleaned in the presence of the reducing substance. When a washing tank is used in the method of the present invention, it is preferable to overflow water in which a reducing substance is dissolved. By overflowing the water in which the reducing substance is dissolved, the oxidized and decomposed products of the organic matter removed from the surface of the object to be cleaned can be eliminated outside the cleaning tank, and the cleaning can be continued in a clean state.

[0008] The method of the present invention can also be applied to single wafer cleaning. In other words, in a single-wafer cleaning apparatus, water in which a reducing substance is dissolved and an emulsion liquid containing fine bubbles of an ozone-containing gas are simultaneously poured on the object to be cleaned, thereby reducing the presence of the reducing substance. The ozone-bubble-containing water can be brought into contact with the object to be cleaned, or the flow path of the water in which the reducing substance is dissolved and the emulsion liquid containing the ozone-containing gas or the fine bubbles of the ozone-containing gas can be passed through a nozzle or the like. It is also possible to bring the ozone-bubble-containing water into contact with the object to be cleaned in the presence of a reducing substance by allowing them to join and pouring the mixture immediately after mixing. In single-wafer cleaning, a high cleaning effect can be obtained by rapidly dissolving ozone in water, which is the rate-determining step,
The bubbles of the ozone-containing gas are preferably small. For this reason, a method using an emulsion liquid containing fine bubbles of an ozone-containing gas prepared using a pump is particularly preferable. According to the method of the present invention, the ozone-bubble-containing water is brought into contact with the object to be cleaned in the presence of the reducing substance, so that ozone dissolves in the water from the bubbles and the reducing substance is present on the surface of the object to be cleaned or in the vicinity thereof. Reacts with to generate active substances such as hydroxy radicals and exerts a strong oxidizing power. Therefore, the decomposition of ozone can be used for cleaning without waste. If ozone-dissolved water is used instead of the ozone-bubble-containing water, the decomposition of ozone proceeds very rapidly, so that the active substance generated by the decomposition of ozone and the object to be cleaned cannot be effectively contacted. If bubbles of the ozone-containing gas are present in the water in which the reducing substance is dissolved, the dissolution of ozone into the water at the bubble interface becomes the rate-determining step of the generation of the active substance derived from ozone. Ozone can be decomposed in the vicinity thereof to generate an active substance.

In the method of the present invention, when hydrogen peroxide is used as the reducing substance, the amount of hydrogen peroxide required to promote the decomposition of ozone may be very small.
In order to quickly decompose ozone eluted into water from ozone bubble-containing water containing mg / L ozone, a concentration of 5 mg / L
Hydrogen peroxide solution of L or less is sufficient. Although this amount is equal to or less than the equivalent to ozone, such a small amount is sufficient because hydrogen peroxide functions not only as a reducing agent but also as a decomposition catalyst for ozone. When the minimum required amount of hydrogen peroxide is used, the amount of ozone and hydrogen peroxide remaining in the wastewater discharged from the cleaning system by the method of the present invention is small, and the amount of impurities removed from the object to be cleaned is reduced. Since it is pure water in which only oxygen gas is dissolved abundantly, the same collection and reuse can be performed very easily. In the method of the present invention, a chemical such as an acid or an alkali may be injected to enhance the cleaning effect. According to the method of the present invention, ozone is dissolved in washing water in a place where a clean substance that promotes the decomposition of ozone and an object to be cleaned coexist, so that a strong oxidation state due to an active substance generated immediately after dissolution of ozone is generated. Is continued, and the surface of the object to be cleaned is efficiently cleaned, so that organic matter contamination can be effectively removed.

[0010]

EXAMPLES The present invention will be described in more detail with reference to the following Examples, which should not be construed as limiting the present invention. In Examples and Comparative Examples, an amorphous silicon (a-Si) film cut into a size of 100 mm × 100 mm, which was left in a clean room for 10 days and caused organic contamination by clean room air, was applied as an object to be cleaned. A glass substrate was used. The cleaning effect was evaluated by measuring the contact angle of ultrapure water dropped on the glass substrate using a contact angle meter. After leaving for 10 days, the contact angle of the glass substrate that caused organic contamination was
It was 51 degrees. A small contact angle means that the glass substrate surface is clean, and a large contact angle means that the glass substrate surface is contaminated with organic matter. Example 1 Ultrapure water in which 5 mg / L of hydrogen peroxide was dissolved overflowed at a rate of 10 L / min.
An ozone-containing gas was bubbled using an air diffuser so that the supply amount of ozone was 100 mg / min. The three glass substrates with organic contamination were stored in a cassette, and immersed in a portion of the cleaning tank where bubbles of the ozone-containing gas existed.
Removed after seconds. After the glass substrate was dried, the contact angle of ultrapure water was measured. The average value of the three glass substrates was 18 degrees. When the immersion time was set to 90 seconds and 180 seconds for the same cleaning and the contact angle was measured, the average value was 5 degrees or less in all cases. Example 2 An ozone-containing gas was injected into 1 L of ultrapure water so that the supply amount of ozone became 10 mg, and emulsion-type ozone-bubble-containing water was continuously prepared. 5 L / min of ultrapure water in which 5 mg / L of hydrogen peroxide was dissolved and 5 L / min of the above water containing ozone bubbles were supplied to a 30 L washing tank so as to be mixed, and overflowed. Three glass substrates with organic contaminants were stored in a cassette, and immersed in a cleaning tank in the same manner as in Example 1 to perform cleaning for 30 seconds, 90 seconds, and 180 seconds. The average value of the contact angle is 1 when the immersion time is 30 seconds.
At 3 degrees, 90 seconds and 180 seconds, all were 5 degrees or less. Comparative Example 1 Ozone-dissolved water having a dissolved ozone concentration of 5 mg / L was supplied at a rate of 10 L / min to a washing tank having a capacity of 30 L to overflow. Each of the three glass substrates with organic contamination was stored in a cassette and immersed in a cleaning tank in the same manner as in Example 1.
Washing was performed for 30, 90, and 180 seconds. The average value of the contact angle was 30 degrees when the immersion time was 30 seconds, 23 degrees when the immersion time was 90 seconds, and 18 degrees when the immersion time was 180 seconds. Comparative Example 2 Instead of the ozone-dissolved water, ultrapure water in which 5 mg / L of hydrogen peroxide was dissolved was supplied at a rate of 10 L / min. The average value of the contact angle was 47 degrees when the immersion time was 30 seconds, 41 degrees when the immersion time was 90 seconds, and 35 degrees when the immersion time was 180 seconds. Comparative Example 3 Ozone-bubble-containing water prepared in the same manner as in Example 2 was supplied at 10 L / min instead of the ozone-dissolved water, and washing was performed in the same manner as in Comparative Example 1. The average value of the contact angle was 32 degrees when the immersion time was 30 seconds, 26 degrees when the immersion time was 90 seconds, and 21 degrees when the immersion time was 180 seconds. Table 1 shows the results of Examples 1 and 2 and Comparative Examples 1 to 3.

[0011]

[Table 1]

As can be seen from Table 1, Example 1 in which an ozone-containing gas was washed by bubbling ultrapure water in which hydrogen peroxide was dissolved, ultrapure water in which hydrogen peroxide was dissolved, and water containing ozone bubbles. In Example 2 in which was mixed and washed, the contact angle became 5 degrees or less after 90 seconds, and organic contamination of the glass substrate was effectively removed. In contrast, in Comparative Example 1 using only ozone-dissolved water, Comparative Example 2 using only ultrapure water in which hydrogen peroxide was dissolved, and Comparative Example 3 using only ozone-bubble-containing water, even after 180 seconds. The contact angle is 18 to 35 degrees, and the removal of organic contamination is slower than in the example. Example 3 A glass substrate having organic contamination was attached to a single-wafer spin washer, and 500 mL / min of ultrapure water in which 5 mg / L of hydrogen peroxide was dissolved while rotating at a rotation speed of 500 rpm. Ozone bubble-containing water 500 mL /
The mixture was mixed in a nozzle, poured into the center of the glass substrate for 20 seconds, dried, and then the contact angle of ultrapure water was measured. Three
The average of the measurements was 7 degrees. 60 cleaning times
When the contact angle was measured in the same manner for 120 seconds and 120 seconds,
The average value was 5 degrees or less in all cases. Comparative Example 4 In the same manner as in Example 3, except that 1 L / min of ozone-dissolved water having a dissolved ozone concentration of 5 mg / L was poured as washing water,
The glass substrate that caused organic contamination was washed. The average value of the contact angle was 24 degrees for a cleaning time of 20 seconds, 18 degrees for 60 seconds, and 14 degrees for 120 seconds. Comparative Example 5 Ultrapure water 1 in which 5 mg / L of hydrogen peroxide was dissolved as washing water
The glass substrate that caused organic contamination was washed in the same manner as in Example 3 except that L / min was poured. The average value of the contact angle was 42 degrees for a cleaning time of 20 seconds, 35 degrees for 60 seconds, and 29 degrees for 120 seconds. Comparative Example 6 The same procedure as in Example 3 was carried out except that the ozone-bubble-containing water 1 L / min prepared in the same manner as in Example 2 was poured as the wash water, to clean the glass substrate having organic contamination. . The average value of the contact angle is 26 degrees when the cleaning time is 20 seconds,
It was 20 degrees at 60 seconds and 17 degrees at 120 seconds.
Table 2 shows the results of Example 3 and Comparative Examples 4 to 6.

[0013]

[Table 2]

As can be seen from Table 2, in Example 3 in which ultrapure water in which hydrogen peroxide was dissolved and water containing ozone bubbles were poured into the glass substrate immediately after mixing in the nozzle, after 60 seconds, The contact angle becomes 5 degrees or less, and organic contamination of the glass substrate is effectively removed. In contrast, in Comparative Example 4 using only ozone-dissolved water, Comparative Example 5 using only ultrapure water in which hydrogen peroxide was dissolved, and Comparative Example 6 using only ozone-bubble-containing water, even after 120 seconds. Contact angle 14-29
, And the removal of organic contaminants is slower than in the examples.

[0015]

According to the cleaning method of the present invention, by contacting water to be cleaned with ozone-bubble-containing water in the presence of a reducing substance, ozone is continuously dissolved from the bubbles into the water, resulting in strong oxidation. The state is continued, an excellent cleaning effect can be obtained, and organic contamination of the object to be cleaned can be effectively removed.

Claims (1)

[Claims] 1. A cleaning method comprising bringing ozone bubble-containing water into contact with an object to be cleaned in the presence of a reducing substance.