JP2002001243A - How to clean electronic materials - Google Patents

Abstract

[PROBLEMS] To clean electronic materials such as a silicon substrate for a semiconductor and a glass substrate for a liquid crystal, which require a highly clean surface, to a degree of cleanliness comparable to high-concentration chemical solution cleaning such as RCA cleaning. Provided is a simple and easy method for cleaning electronic materials. An electronic material cleaning method includes an acidic ozone water cleaning step of cleaning with ozone water to which an acid has been added and an alkaline ozone water cleaning step of cleaning with ozone water to which an alkali has been added.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for cleaning electronic materials. More specifically, the present invention can clean electronic materials such as silicon substrates for semiconductors and glass substrates for liquid crystals, which require a highly clean surface, to a degree of cleanliness comparable to high-concentration chemical solution cleaning such as RCA cleaning. The present invention relates to a simple method for cleaning electronic materials.

[0002]

2. Description of the Related Art For cleaning electronic materials, high-temperature cleaning technology using high-concentration chemicals called RCA cleaning has been used in many factories. In the RCA cleaning, a mixed solution of sulfuric acid and hydrogen peroxide (SPM) is heated to 120 to 150 ° C., or a mixed solution of ammonia and hydrogen peroxide (AP) is used.
This is a cleaning method in which M) is heated to 60 to 80 ° C. and used, or a mixed solution of hydrochloric acid and hydrogen peroxide (HPM) is heated to 60 to 80 ° C. and used. With RCA cleaning, a clean surface is indeed obtained. However, there are problems such as the chemical solution used, the time required for switching the chemical solution, the cost pressure due to ultrapure water required between switching and the rinsing performed in the final process, the environmental load due to the large amount of discharged chemical-containing wastewater and the exhaust of the chemical solution, etc. Therefore, a shift to resource-saving cleaning that does not use chemicals as much as possible is required. On the other hand, the present inventors have developed a room temperature cleaning technique using ozone water, hydrogen water, or the like in which only a specific gas is slightly dissolved in ultrapure water. It is known that ozone water has a very high oxidizing power and is effective in removing organic substances and noble metals on a substrate. In particular, when an acid is added, the effect of removing organic substances and precious metals in ozone water is further enhanced.
If ultrasonic irradiation is used here, the effect of removing organic substances can be further enhanced. On the other hand, the inventors of the present invention have found that washing with hydrogen water, oxygen water, rare gas water, and the like and using ultrasonic irradiation in combination is highly effective in removing fine particles. When an alkali is added to the cleaning water, an effect of making the zeta potential on the surface of the substrate the same as that of the foreign substance is obtained, and the adhesion of the foreign substance is prevented, and the cleaning effect is further enhanced. Further, various cleaning processes combining these methods have been studied. For example, the present inventors have proposed a method of using a combination of ozone water for removing organic substances and metals and hydrogen water for removing fine particles. Thus, while the wet cleaning technology has been undergoing drastic improvement, there is still a need for the development of a simpler cleaning method with a high cleaning effect.

[0003]

SUMMARY OF THE INVENTION The present invention is intended to clean electronic materials such as silicon substrates for semiconductors and glass substrates for liquid crystals, which require a highly clean surface, with a cleanliness level comparable to high-concentration chemical cleaning such as RCA cleaning. An object of the present invention is to provide a simple method for cleaning an electronic material that can be cleaned.

[0004]

Means for Solving the Problems As a result of intensive studies to solve the above problems, the present inventor has found that an acidic ozone water washing step of washing with acid-added ozone water, an ozone water addition of alkali, It has been found that the combination of the alkaline ozone water cleaning step of cleaning with an organic solvent can effectively remove all of the organic substances, metals and fine particles attached to the surface of the electronic material, and based on this finding, the present invention has been completed. Was. That is, the present invention provides a method for cleaning an electronic material, comprising: (1) an acidic ozone water cleaning step of cleaning with ozone water to which an acid is added, and an alkaline ozone water cleaning step of cleaning with ozone water to which an alkali is added. ,
(2) The method for cleaning electronic materials according to the above (1) to which a hydrofluoric acid cleaning step for cleaning with a hydrofluoric acid-based chemical solution is added, and (3) a non-chemically injected ozone water cleaning step for cleaning with non-chemically injected ozone water. 3. A method for cleaning an electronic material according to item 1 or 2. Further, as a preferred embodiment of the present invention, (4) the first acid, wherein the acid is hydrochloric acid, sulfuric acid, nitric acid or carbonic acid
(5) The method for cleaning an electronic material according to (1), wherein the alkali is ammonia, tetramethylammonium hydroxide, sodium hydroxide or potassium hydroxide, (6) the ultrasonic oscillation function. 3. The method for cleaning an electronic material according to claim 1, wherein the cleaning is performed using a single-wafer cleaning machine having a nozzle having: (7) ozone water is continuously passed through, and acid injection, alkali injection and ozone water piping are performed. 4. The method for cleaning an electronic material according to claim 3, wherein the injection of the chemical solution is controlled in the order of non-chemical injection, wherein the hydrofluoric acid cleaning step is performed between the alkaline ozone water cleaning step and the non-chemical injection ozone water cleaning step. 4. The method for cleaning an electronic material according to claim 3, wherein (9) the hydrofluoric acid-based chemical solution is a mixed aqueous solution of hydrofluoric acid and hydrogen peroxide, hydrochloric acid or nitric acid. Method.

[0005]

BEST MODE FOR CARRYING OUT THE INVENTION A method for cleaning an electronic material according to the present invention comprises:
It has an acidic ozone water washing step of washing with ozone water to which an acid has been added and an alkaline ozone water washing step of washing with ozone water to which an alkali has been added. The method of the present invention can be suitably applied to the cleaning of electronic materials such as silicon substrates for semiconductors, glass substrates for liquid crystals, and quartz substrates for photomasks, which require extremely highly clean surfaces. Although the concentration of ozone water used in the method of the present invention is not particularly limited, the concentration of ozone is preferably 0.1 mg / L or more, preferably 1 mg / L.
More preferably, it is the above. Ozone concentration of 0.1mg
If it is less than / L, the cleaning effect may be insufficient. The method for producing ozone water used in the method of the present invention is not particularly limited, and for example, it can be produced using an ejector, a suction-type gas dissolution pump, a bubbling device, a gas permeable membrane device, or the like. Among them, the ejector and the suction-type gas dissolving pump can be suitably used because it is not necessary to pressurize and supply the ozone-containing gas, and the ejector has a simple device configuration using a member excellent in ozone resistance. Therefore, it can be particularly preferably used. Members such as the ozone water producing apparatus and the ozone water supply pipe are preferably made of a material having sufficient ozone resistance because they come into contact with ozone gas or ozone water having strong oxidizing power.
Examples of such a material include polytetrafluoroethylene, a fluororesin such as a tetrafluoroethylene-perfluoroalkylvinyl ether copolymer, a tetrafluoroethylene-hexafluoropropylene copolymer, a metal having a passivated surface, and quartz. And the like, and a material coated with an inert material.

In the method of the present invention, the acid used for preparing the acidic ozone water is not particularly limited, but inorganic acids such as hydrochloric acid, sulfuric acid, nitric acid and carbonic acid can be suitably used. When the acid is hydrochloric acid, the concentration of hydrogen chloride in the acidic ozone water is 0.1%.
The concentration is preferably 1 to 5,000 mg / L, and when the object to be cleaned is a silicon wafer, the concentration of hydrogen chloride is preferably 0.1 to 10 mg / L. If the concentration of hydrogen chloride is less than 0.1 mg / L, the cleaning effect may be insufficient. The concentration of hydrogen chloride is 5,000mg / L
Although the cleaning effect does not have any problem when the pressure exceeds the above, the cleaning effect does not increase further with the concentration of hydrogen chloride. In the method of the present invention, the alkali used for the preparation of the alkaline ozone water is not particularly limited, but ammonia, tetramethylammonium hydroxide, sodium hydroxide, potassium hydroxide and the like can be suitably used.
When the alkali is ammonia, the concentration of ammonia in the alkaline ozone water is preferably from 0.1 to 5,000 mg / L, and when the object to be cleaned is a silicon wafer, the concentration of ammonia is from 0.1 to 5,000 mg / L. Preferably it is 10 mg / L. If the concentration of ammonia is less than 0.1 mg / L, the cleaning effect may be insufficient. Generally, if the concentration of ammonia exceeds 5,000 mg / L, there is no problem with the cleaning effect, but the cleaning effect does not increase further with the concentration of ammonia.

In the method of the present invention, by performing acidic ozone water cleaning, organic substances and noble metals adhering to the object to be cleaned are effectively removed by the high oxidizing power of the acidic ozone water. Further, by performing the alkaline ozone water cleaning, the fine particles adhering to the object to be cleaned are effectively removed. Although the effect of removing the fine particles by the alkaline ozone water is slightly inferior to that of hydrogen water, it is slightly better than that of rare gas water, and is almost equivalent to oxygen water. The mechanism by which the alkaline ozone water removes the fine particles is not clear, but when made alkaline, the decomposition of ozone dissolved in the water is promoted and oxygen is generated. It is considered to be transformed into water. In the method of the present invention, the order of the acidic ozone water cleaning step and the alkaline ozone water cleaning step is not particularly limited, but it is preferable to perform the cleaning with the acidic ozone water first. By cleaning with acidic ozone water to remove organic substances adhering to the object to be cleaned, and by making the surface of the object to be cleaned hydrophilic, the cleaning water can be easily applied to the object to be cleaned in the subsequent cleaning process, and the cleaning effect Can be increased. In the method of the present invention, a hydrofluoric acid cleaning step of cleaning with a hydrofluoric acid-based chemical can be added to the acidic ozone water cleaning step and the alkaline ozone water cleaning step. By adding the hydrofluoric acid cleaning step, metals other than the noble metal adhered to the surface of the object to be cleaned can be effectively removed. There is no particular limitation on the hydrofluoric acid chemical used. For example, dilute hydrofluoric acid having a concentration of 2% by weight or less, dilute hydrofluoric acid having a concentration of 2% by weight or less, hydrogen peroxide having a concentration of 10% by weight or less, nitric acid, hydrogen chloride, and the like are used. Mixed liquid, or
Ozone water to which dilute hydrofluoric acid having a concentration of 2% by weight or less is added. When adding a hydrofluoric acid cleaning step,
There is no particular limitation on the method of introducing the hydrofluoric acid-based chemical solution into the washing machine,
For example, there can be mentioned a method of sending a liquid by a chemical-resistant pump or a method of sending a liquid by pressurizing a sealed chemical solution tank with an inert gas such as clean nitrogen. It is preferable to provide a dedicated supply pipe for the hydrofluoric acid-based chemical supply pipe separately from the ozone water supply pipe.

In the method of the present invention, a chemical-free ozone water washing step of washing with chemical-free ozone water to which no acid or alkali is added can be added. By washing with non-chemically injected ozone water, an oxide film is formed on the surface of the substrate to make it hydrophilic, and the washed surface is protected when stored after washing. When a gate oxide film forming step is included in the post-cleaning step, it is preferable to make the surface of the substrate hydrophobic. Since the non-chemically injected ozone water does not leave foreign matter on the surface of the object to be cleaned, the non-chemically injected ozone water cleaning step can be the final rinsing step. The final rinsing can be performed using ultrapure water, hydrogen water, or the like. However, by using ozone water, members such as pipes and valves can be reduced, and the cleaning equipment can be simplified. In the method of the present invention, cleaning can be performed while irradiating ultrasonic waves in each cleaning step. In the alkaline ozone water cleaning step, it is particularly preferable to use ultrasonic waves together, since the use of ultrasonic waves can significantly increase the efficiency of removing fine particles. Also in the acidic ozone water cleaning step and the hydrofluoric acid cleaning step, the cleaning effect can be enhanced by using ultrasonic waves together. The frequency of the irradiated ultrasonic wave is 20kHz-3M
Hz is preferable, and in order to prevent damage to the substrate surface due to cavitation effect caused by ultrasonic waves and obtain a high cleaning effect, the frequency is more preferably 200 kHz to 3 MHz. There is no particular limitation on the method of irradiating the ultrasonic waves. For example, a single-wafer cleaning machine having a nozzle having an ultrasonic oscillation function can be used. After washing the electronic material by the method of the present invention, it is preferable to immediately proceed to the drying step. There is no particular limitation on the drying method. For example, when the cleaning process is a single wafer spin method, the process can be directly shifted to spin drying. In the case of a cleaning step other than the spin method, drying using isopropanol vapor, drying using substitution with isopropanol, drying using the Marangoni effect, or the like can be applied.

FIG. 1 is a process flow chart of one embodiment of an apparatus for carrying out the method for cleaning an electronic material according to the present invention. Pure water and an ozone-containing gas are supplied to a gas dissolver 1 to produce ozone water, which is sent to an ozone water supply pipe 2. The ozone water supply pipe is provided with an acid injection section 3 and an alkali injection section 4. The acid is injected from the acid tank 5 to the acid injection section by the pump 6. The alkali is injected into the alkali injection section from the alkali tank 7 by the pump 8.
The ozone water into which the acid or alkali has been injected is uniformly mixed in the mixer 9 to be turned into acidic ozone water or alkaline ozone water and supplied to the washing machine. In a state where neither acid nor alkali is injected, ozone water is supplied to the washing machine as chemical-free ozone water. Separately from the ozone water supply pipe, a hydrofluoric acid-based chemical solution is supplied from a hydrofluoric acid-based chemical solution tank 10 to a washing machine by a pump 11. The washing machine is provided with a washing nozzle 12 having an ultrasonic oscillator, and acidic ozone water, alkaline ozone water, hydrofluoric acid-based chemical solution or non-chemically injected ozone water is held by a wafer chuck 13 and rotated by a drive motor 14. Irradiating the object to be cleaned 15. In the apparatus of the present embodiment, an acid and alkali chemical liquid injection section is provided in one ozone water supply pipe, and only acidic ozone water, alkaline ozone water and non-chemically injected ozone water are controlled by chemical injection control from the chemical liquid injection section. Can be divided. In order to effectively separate the respective ozone waters, it is preferable that the chemical solution injection part is close to the cleaning nozzle, and more specifically, the cleaning liquid nozzle is connected to the cleaning nozzle by 5 mm.
m is preferable in order to secure a prompt switching response. Further, a filter can be mounted on the downstream side of the chemical solution injection section.

According to the method of the present invention, an organic substance, an organic ozone water cleaning step, an alkaline ozone water cleaning step, and a chemical-free ozone water cleaning step can be used.
Along with the fine particles, it is possible to efficiently remove a noble metal which is particularly difficult and troublesome in metal contamination.
Furthermore, by adding cleaning with a hydrofluoric acid-based chemical solution, a cleaning recipe of an acidic ozone water cleaning step, an alkaline ozone water cleaning step, a hydrofluoric acid cleaning step, and a chemical-free ozone water cleaning step is used to remove metals other than noble metals. It can be completely removed, and organic matter, fine particles and all metals are highly removed. When the object to be cleaned is a silicon wafer,
By providing a chemical-free ozone water cleaning step, cleaning is completed with a clean oxide film that is less likely to be contaminated by foreign substances. According to the method of the present invention, a much simpler cleaning recipe is constructed by assembling a cleaning process based on a foreign matter removing mechanism based on ozone water, which has already been recognized as having a very high cleaning power.

[0011]

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 the examples and comparative examples, the alumina abrasive particles having an average particle diameter of 0.3 μm and copper (II) were used.
Forcibly contaminated by immersion in ion-containing water, and left in a clean room for 4 days to contaminate organic matter.
An inch silicon wafer was used as an object to be cleaned. The initial contaminated state of the object to be cleaned is as follows.
The amount was 00 to 9,000 / wafer, copper was 1 to 2 × 10 ¹² atoms / cm ² , and organic matter was 1 × 10 ¹³ atoms / cm ² in terms of carbon atoms. Further, ozone water having a dissolved ozone concentration of 8 mg / L was used as the non-chemically injected ozone water. The acidic ozone water was adjusted to pH 4.0 by adding hydrochloric acid to the ozone water. The pH of alkaline ozone water is adjusted by adding ammonia water.
Adjusted to 9.4. At the time of washing with alkaline ozone water, an ultrasonic wave having a frequency of 1 MHz was irradiated from a megasonic nozzle (Honda Electronics, Pulse Jet). As the fluorine-based chemical, an aqueous solution containing 0.5% by weight of hydrogen fluoride and 0.5% by weight of hydrogen peroxide was used. Using a single-wafer spin cleaning apparatus, the cleaning liquid nozzle was swung at a pace of one reciprocating 10 seconds between the center of the wafer and the edge while rotating the wafer at 500 rpm, and each cleaning liquid was poured at a flow rate of 25 mL / second for cleaning. . No rinsing was performed between the changes of the washing liquid. Finally, the spin speed of the wafer was increased to 1,500 rpm, and spin drying was performed for 20 seconds. Example 1 Cleaning with acidic ozone water, cleaning with alkaline ozone water, cleaning with hydrofluoric acid, and cleaning with ozone water without chemical injection were performed in this order. The number of fine particles on the wafer surface after drying is less than 100 / wafer, copper is less than 3 × 10 ⁹ atoms / cm ² , and organic matter is 1 in terms of carbon atoms.
Less than × 10 ¹⁰ atoms / cm ² , the surface finish was hydrophilic. Example 2 Cleaning with acidic ozone water, cleaning with alkaline ozone water and cleaning with ozone water without chemical injection were performed in this order. Example 3 Cleaning with acidic ozone water, cleaning with alkaline ozone water and cleaning with hydrofluoric acid were performed in this order. Comparative Example 1 Cleaning with acidic ozone water, cleaning with hydrofluoric acid, and cleaning with ozone water without chemical injection were performed in this order. Comparative Example 2 Alkaline ozone water cleaning, hydrofluoric acid cleaning, and chemical-free ozone water cleaning were performed in this order. Examples 1-3 and Comparative Examples 1
Table 1 shows the cleaning process No. 2 and the evaluation results. However, the symbols in the table represent the following evaluation results. Fine particles: 未 満 Less than 100 / wafer △ 100 / wafer or more to less than 1,000 / wafer NG 1,000 / wafer or more Copper: 未 満 Less than 3 × 10 ⁹ atoms / cm ² △ 3 × 10 ⁹ atoms / cm ² or more to less than 1 × 10 ¹⁰ atoms / cm ² Organic matter (in terms of carbon atoms): ◎ Less than 1 × 10 ¹⁰ atoms / cm ² Surface finish: hydrophilic Water contact angle less than 5 degrees Hydrophobic water contact angle 5 degrees or more

[0012]

[Table 1]

As can be seen from Table 1, in Examples 1 and 3 in which acidic ozone water cleaning, alkaline ozone water cleaning and hydrofluoric acid cleaning were performed, the removal rates of fine particles, copper and organic substances were all high, and Surface is obtained. Further, in Example 1 in which chemical-free ozone water cleaning was performed last, the surface became hydrophilic, and in Example 3, in which chemical-free ozone water cleaning was not performed, the surface was hydrophobic. In Example 2 in which the acidic ozone water cleaning and the alkaline ozone water cleaning were performed and the hydrofluoric acid cleaning was not performed, the removal rate of copper was slightly low, but the removal rates of fine particles and organic substances were high. On the other hand, in Comparative Example 1 in which the alkaline ozone water cleaning was not performed, the removal rate of the fine particles was low, and in Comparative Example 2 in which the acidic ozone water cleaning was not performed, both the removal rates of the fine particles and copper were slightly low, and the cleaning rate was low. Is inadequate.

[0014]

According to the method for cleaning an electronic material of the present invention,
With a very simple cleaning recipe composed of only ozone water and a small amount of a chemical solution, a cleaning effect comparable to the conventional RCA method can be obtained. Further, since a chemical solution to be used is simple, a cleaning apparatus for realizing this cleaning method can be assembled very simply.

[Brief description of the drawings]

FIG. 1 is a process flow diagram of one embodiment of an apparatus for carrying out the method of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Gas dissolver 2 Ozone water supply pipe 3 Acid injection part 4 Alkali injection part 5 Acid tank 6 Pump 7 Alkaline tank 8 Pump 9 Mixer 10 Hydrofluoric acid chemical liquid tank 11 Pump 12 Cleaning nozzle 13 Wafer chuck 14 Drive motor 15 Cleaning object

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Claims (3)

[Claims] An electronic material cleaning method comprising: an acidic ozone water cleaning step of cleaning with ozone water to which an acid has been added; and an alkaline ozone water cleaning step of cleaning with ozone water to which an alkali has been added. 2. The electronic material cleaning method according to claim 1, further comprising a hydrofluoric acid cleaning step of cleaning with a hydrofluoric acid-based chemical. 3. The method for cleaning an electronic material according to claim 1, further comprising a non-chemically injected ozone water cleaning step of cleaning with non-chemically injected ozone water.