JP2000325902A - Cleaning method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce wastewater treatment cost and to remove organic substances on a substrate efficiently even at low temperatures by preparing a cleaning solution by dissolving ozone gas in pure or ultrapure water and adding hydrogen peroxide and cleaning an object while ultrasonic vibration is applied to the solution. SOLUTION: A cleaning solution is prepared by dissolving ozone gas in pure or ultrapure water and adding hydrogen peroxide, and an object is cleaned while ultrasonic vibration is applied to the solution. The molar concentration ratio of hydrogen peroxide to ozone is preferably 0.1-10. A substrate is preferably cleaned while ultrasonic waves are applied to the solution. Moreover, in order to dissolve ozone gas in pure water and others, a method in which, for example, ozone gas is supplied to the surface of hollow fibers of a material having ozone gas permeability and ozone resistance, pure water and others are supplied into the hollow fibers, and the ozone gas is dissolved by gas-liquid contact and others can be used.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cleaning method performed in a manufacturing process of a semiconductor device, a liquid crystal display device or an electronic component, and particularly to a method of cleaning and removing an organic substance attached to a substrate such as a semiconductor wafer or a liquid crystal glass substrate. To a cleaning method.

[0002]

2. Description of the Related Art In recent years, the pattern interval of semiconductor devices formed on a semiconductor substrate such as a silicon wafer has been increased in density and miniaturized to a submicron level.

In order to achieve such a high density,
The surface of the substrate must be kept highly purified. That is, organic substances, metals, fine particles, and the like must be substantially completely removed from the substrate surface.

In particular, organic molecules adhering to the surface of the substrate significantly deteriorate the reliability of the semiconductor device. In particular, the organic molecules adhere to the substrate surface in the form of a film, and metal impurities are present inside the film. If fine particles or fine particles are present, it is not possible to carry out a sufficient cleaning treatment on metal impurities and fine particles inside the film unless the film of organic molecules is removed. Becomes

For this reason, conventionally, in a substrate cleaning step,
It is common to remove organic matter first. In order to prevent the deterioration of the semiconductor device as described above, it is necessary to remove as much as possible organic substances on the surface of the substrate on which the semiconductor device is to be formed. For this reason, a cleaning agent is generally used for cleaning the substrate surface. Have been done. Conventional methods for removing organic substances on the substrate surface include:
A method in which concentrated sulfuric acid and hydrogen peroxide are mixed in a volume ratio of about 4: 1 and the substrate is immersed and washed in a solution heated to about 130 ° C., and then rinsed with ultrapure water is used. According to this method, organic substances are oxidized and decomposed, and most of them are removed from the substrate surface.

However, in the above method, a large amount of concentrated sulfuric acid and hydrogen peroxide of several tens% is used, and a large amount of ultrapure water is required for rinsing after washing.
There is a problem that these cleaning components are discharged into the waste liquid, and a large amount of expense is required for wastewater treatment. In addition, since this method includes a high-temperature step, the chemical solution has a high vapor pressure, and there is a problem that the clean room environment is inevitably contaminated. On the other hand, recently, a method of washing a substrate with pure water or ultrapure water in which ozone gas is dissolved to remove organic substances has also been put into practical use.
A method of using pure water or ultrapure water in which about 0 ppm of ozone gas is dissolved for about 10 minutes at room temperature has also been proposed.

[0007] However, the method of simply dissolving ozone gas in pure water or ultrapure water and cleaning at room temperature conditions lacks the ability to remove organic substances on the substrate surface. There is a problem that it is difficult to sufficiently remove from the surface.

[0008]

As described above, in the conventional method of cleaning a substrate using concentrated sulfuric acid and hydrogen peroxide, these components are discharged into a waste liquid, and many wastewater treatments are required. In addition to the expense, there is a problem that these steams are generated and contaminate the clean room environment.

In the method of cleaning a substrate using pure water or ultrapure water in which ozone gas is dissolved, the ability to remove organic substances is insufficient, and the organic substances are sufficiently removed from the surface depending on the type and amount of organic substances. There was a problem that it was difficult to do.

The present invention has been made to solve such a conventional problem, and does not require much cost for wastewater treatment, and provides a cleaning method capable of effectively removing organic substances on a substrate surface even at a low temperature. The purpose is to do.

[0011]

According to a method of cleaning a substrate of the present invention, an ozone gas is dissolved in pure water or ultrapure water and hydrogen peroxide is added to prepare a cleaning liquid, and ultrasonic vibration is applied to the cleaning liquid. The object to be cleaned is washed while cleaning.

It is preferable that the molar concentration ratio of the hydrogen peroxide to the ozone is 0.1 or more and less than 10. In the cleaning, it is preferable that the substrate is cleaned with the cleaning liquid while irradiating the cleaning liquid with ultrasonic waves.

In this specification, “pure water” refers to 2
5 ° C conversion electric resistivity is 15.0 MΩ · cm or more, TO
Number of fine particles with C concentration of 50 ppb or less and 0.2 μm or more 10
Water having a high degree of cleanliness of particles / ml or less. “Ultra pure water” means 10 particles having an electrical resistivity of 25 ° C. or more of 18.0 MΩ · cm or more, a TOC concentration of 5 ppb or less, and 0.05 μm or more. / Extremely clean water of less than / ml.

In order to dissolve ozone gas in pure water or ultrapure water, for example, ozone gas is applied to the surface of a hollow fiber made of a material having ozone gas permeability and having ozone resistance (for example, fluorine resin). On the other hand, a method of supplying pure water or ultrapure water inside the hollow fiber and dissolving ozone gas in the pure water or ultrapure water by gas-liquid contact, on the upstream side of the pure water or ultrapure water supply pump A method in which ozone gas is supplied and dissolved by stirring in a pump, a method in which ozone gas is dissolved in pure water or ultrapure water via an ejector, a method in which ozone gas is dissolved in pure water or ultrapure water by bubbling, and the like are adopted. be able to.

The concentration of dissolved ozone in pure water or ultrapure water to be dissolved in the cleaning liquid is appropriately adjusted depending on the properties of the surface of the object to be cleaned, but is preferably 0.1 ppm or more. More preferably 2 ppm or more, further preferably 5 ppm
That is all. When the concentration of dissolved ozone dissolved in pure water or ultrapure water is lower than 0.1 ppm, it is difficult to sufficiently obtain the effect of removing organic substances adhering to the surface of the object to be cleaned.

In the present invention, even if coexisting gas other than ozone is present in pure water or ultrapure water, the effect is not affected.
In particular, the oxygen gas and the nitrogen gas may be saturated. As the ozone gas used in the present invention, ozone gas generated by electrolysis of water, ozone gas generated from oxygen gas by silent discharge, ozone gas generated from oxygen gas by ultraviolet irradiation, and the like can be used.
Ozone gas generated by electrolysis of water can be preferably used. By using the ozone gas generated by the electrolysis of water as described above, it is possible to prevent contamination and contamination of impurities such as anode electrolyzed water in which the ozone gas obtained by directly electrolyzing the water is dissolved. Can be.

When dissolving ozone gas in pure water or ultrapure water, for example, a dissolved ozone concentration detector of a diaphragm type is installed in a pure water or ultrapure water supply line. The concentration of dissolved ozone in pure water or ultrapure water may be controlled by detecting the concentration of dissolved ozone in the water and feeding it back to the ozone generator. Hydrogen peroxide is added to the cleaning solution after the ozone gas is dissolved. The molar concentration ratio of hydrogen peroxide added to the cleaning liquid is preferably 0.1 or more and less than 10 with respect to the molar concentration of ozone dissolved in pure water or ultrapure water, more preferably 0.5 or more. Less than 5, more preferably 0.5
It is adjusted to a range of not less than 3 and less.

When the molar concentration ratio of the added hydrogen peroxide to ozone gas is less than 0.1, a predetermined organic substance decomposing ability cannot be obtained. The organic matter decomposition ability corresponding to the above cannot be obtained.

In the present invention, the hydrogen peroxide acts not only as an organic matter decomposition aid but also as an ozone decomposer, and is therefore preferably added immediately before washing.

In the present invention, the effect is further improved by using ultrasonic irradiation at the time of cleaning.

The ultrasonic wave applied to the cleaning liquid preferably has a frequency of 30 kHz or more, more preferably 100 kHz.
Hz or more and 2000 kHz or less, more preferably 70 kHz or less.
It is 0 kHz or more and 1500 kHz or less.

In order to carry out cleaning while applying ultrasonic vibration to the cleaning liquid, for example, a method of irradiating an ultrasonic wave with the object to be cleaned immersed in the cleaning liquid supplied to a cleaning tank provided with a vibrator is used. For example, a method of applying ultrasonic vibration to a supply liquid while supplying the cleaning liquid to the object to be cleaned from a nozzle or the like and performing cleaning is used. In the case of the latter method in which the cleaning liquid is applied to the object to be cleaned from a nozzle or the like while applying the ultrasonic vibration to the supply liquid to perform cleaning, a method of irradiating ultrasonic waves with a cleaning liquid injection nozzle incorporating a vibrator, or A method of irradiating ultrasonic waves from a bar-type sound wave transmitter having a built-in vibrator or a sound wave transmitter having a vibrator mounted on a quartz rod is employed.

[0023]

In the present invention, even organic substances having poor decomposability with ozone alone are easily decomposed by using hydrogen peroxide in combination, and further decomposed by applying ultrasonic vibration.

When decomposing an organic substance, the key point is how much OH radicals are generated in the vicinity of the organic substance. However, in general, the life of the OH radical is short, and the OH radical which does not contribute to the decomposition of the organic substance due to self-decomposition or the like. It is said that there are many.

It is considered that the effect of the ultrasonic vibration according to the present invention contributes to increasing the proportion of OH radicals that contribute to the decomposition of organic substances.

[0026]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in more detail with reference to examples.

(Examples 1 to 4, Comparative Examples 1 to 3) Ozone water of 5 ppm was generated by a method described later, and a 6-inch silicon wafer (CZn-100) was prepared while overflowing the ozone water. After immersion for 1 minute, it was rinsed with ultrapure water for 1 minute.

After the wafer was dried in a clean bench, it was left in a laboratory other than a clean room for 72 hours to obtain a forced contamination sample.

The degree of reduction of the organic substances adhering to the wafer was measured by a water drop contact angle method in which water drops of ultrapure water were dropped.

The water contact angle of the compulsory contaminated sample is 72-7.
6 °, and the water droplet contact angle of the wafer before forced contamination was 2 °.
4 to 28 °.

Prior to the experiment, 3.6 liters of sulfuric acid (98%, special grade, manufactured by Kanto Chemical) and hydrogen peroxide (30%) were used.
%, Special grade, manufactured by Mitsubishi Gas Chemical)
At the time when the temperature was raised to 130 ° C., the above-mentioned forcedly contaminated sample was charged and washed for 10 minutes, and the contact angle of a water droplet of a wafer rinsed with ultrapure water for 10 minutes by an overrinsing method was measured as a reference.

As a result of the measurement, the water droplet contact angle of the reference wafer was 22 to 27 °.

Therefore, if the contact angle of the water droplet after washing is about 25 °, it can be determined that the organic matter has been removed to a level at which there is no problem at present.

A dissolved ozone meter (MOCA3600, manufactured by Orbis Sphere) was used for measuring the dissolved ozone concentration of the cleaning solution, and a hydrogen peroxide concentration test paper (manufactured by Nomura Micro Science) was used for measuring the hydrogen peroxide of the cleaning solution. did.

(Examples 1 to 4) A gas-permeable membrane module (GORE) made of PTFE (tetrafluoroethylene resin) was added to ultrapure water.
Ozone gas generated from an ozonizer (OR-3Z, manufactured by Onoda Cement) via a TEX) was dissolved to generate ozone water.

The generated ozone water is stored in a 3 mm-thick quartz bath, and hydrogen peroxide (30%, special grade,
(Mitsubishi Gas Chemical) was added to prepare a cleaning solution.

A quartz bath filled with 5 liters of this cleaning solution was placed in an ultrasonic cleaner (950 kHz, HI MEGAON).
IC 600, manufactured by KAIJO), set in a SUS bath filled with water at the bottom and equipped with an ultrasonic oscillator at the bottom, and placed the forcedly contaminated sample (wafer) in a wafer holder with an open bottom to allow ultrasonic waves to pass. The wafer was held, set in the quartz bath, and washed with an ultrasonic output of 200 W for 10 minutes.

After the washing, it is dried in a clean bench,
Drop contact angle measurement with ultrapure water was performed. Table 1 shows the composition of the cleaning solution and the contact angle of the water droplet after the cleaning.

[0039]

[Table 1]

(Comparative Example 1) Wafer cleaning was performed under the same conditions as in Example 1 except that hydrogen peroxide was not added to the cleaning liquid. Table 2 shows the composition of the cleaning solution and the contact angle of the water droplet after cleaning.
Shown in

(Comparative Example 2) Wafer cleaning was performed under the same conditions as in Example 1 except that ozone was not dissolved in the cleaning liquid. Table 2 shows the composition of the cleaning solution and the contact angle of the water droplet after the cleaning.

(Comparative Example 3) Wafer cleaning was performed under the same conditions as in Example 1 except that the substrate was immersed for 10 minutes without applying ultrasonic vibration during cleaning with the cleaning liquid. Table 2 shows the composition of the cleaning solution and the contact angle of the water droplet after the cleaning.

[0043]

[Table 2]

[0044]

As described in detail above, according to the present invention, a cleaning liquid is prepared by dissolving ozone gas in pure water or ultrapure water and adding hydrogen peroxide, and ultrasonic vibration is applied to the cleaning liquid. By washing the object to be washed while applying it, there is no need to use a cleaning agent that requires a lot of wastewater treatment, and since cleaning is performed at room temperature, there is no generation of dissolved component vapors. Organic substances can be removed up to.

[0045]

Claims (3)

[Claims] 1. A cleaning liquid is prepared by dissolving ozone gas in pure water or ultrapure water and adding hydrogen peroxide thereto, and cleaning an object to be cleaned while applying ultrasonic vibration to the cleaning liquid. Cleaning method. 2. The cleaning method according to claim 1, wherein a molar concentration ratio of the hydrogen peroxide to the ozone is 0.1 or more and less than 10. 3. The cleaning method according to claim 1, wherein the object to be cleaned is cleaned with the cleaning liquid while irradiating the cleaning liquid with ultrasonic waves.