JP2000331973A - Cleaning method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To effectively remove metal impurities form the surface of a substrate, even at a low temperature without incuring a high cost for wastewater treatment. SOLUTION: In a cleaning method, a first cleaning solution 1 is prepared by dissolving >=5 ppm oxygen gas and an acid substantially containing no fluorine ion in pure water or ultrapure water and an object to be cleaned is cleaned with the first cleaning solution while ultrasonic vibrations are applied to the solution. Then a second cleaning solution is prepared by dissolving >=5 ppm oxygen gas and hydrofluoric acid in pure water or ultrapure water and the object cleaned with the first cleaning solution is cleaned with the second cleaning solution.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cleaning method for a semiconductor device, a liquid crystal display device or an electronic component manufacturing process, and more particularly to a metal impurity such as copper adhering to a substrate such as a semiconductor wafer or a liquid crystal glass substrate. The present invention relates to a cleaning method for cleaning and removing the resin.

[0002]

2. Description of the Related Art In recent years, semiconductor devices formed on a semiconductor substrate have 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 in a highly clean state. That is, organic substances, metals, fine particles, and the like must be substantially completely removed from the substrate surface.

In particular, metal impurities degrade the electrical characteristics of a semiconductor device. To prevent such deterioration, it is necessary to reduce the metal impurity concentration on the surface of the substrate on which the semiconductor device is formed as much as possible. Therefore, a cleaning agent is generally used for cleaning the substrate surface.

In order to remove metal impurities on the substrate surface, concentrated hydrochloric acid, hydrogen peroxide and ultrapure water are mixed at a ratio of about 1: 1: 6 to 1: 1: 4 by volume, and the mixture is mixed at 80 to 90 ° C. After immersion in a moderately heated solution, rinsing with ultrapure water is performed. According to this method, for example, even if metal impurities such as iron and copper adhere to the surface of the semiconductor substrate before cleaning, the surface concentration of 10 ¹⁰ atoms / cm ² or less, which is considered to have almost no adverse effect on device performance. It is said that it can be removed up to.

However, in the above-mentioned method, chemicals which are difficult to recover and reuse, such as hydrogen peroxide, and high-concentration acids are used in large amounts, so that these are discharged into waste liquid,
There has been a problem that wastewater treatment requires a lot of expense. 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.

Further, in the above-mentioned conventional cleaning method, there is also a problem of reverse contamination in which metal impurities once separated from the substrate surface are mixed into the cleaning agent, and the metal impurities are reattached to the substrate from the contaminated cleaning agent. Was.

[0008]

As described above, in the conventional cleaning method using concentrated hydrochloric acid or hydrogen peroxide for removing metal impurities, these components are discharged into waste liquid,
There is a problem that wastewater treatment requires a lot of expense and that the generation of these steams pollutes the clean room environment.

Further, this method has a problem that reverse contamination occurs in which the removed metal impurities are re-adhered.

The present invention has been made in order to solve the above-mentioned conventional problems. Since a concentrated chemical is not used, it is possible to reduce the processing cost of cleaning wastewater, and even at a lower temperature than copper or the like on the surface of an object to be cleaned. It is an object of the present invention to provide a cleaning method that can effectively remove metal impurities and that does not cause reverse contamination of metal impurities from a cleaning agent to a substrate.

[0011]

According to the cleaning method of the present invention, a first cleaning liquid is prepared by dissolving oxygen gas of 5 ppm or more and an acid substantially free of fluorine ions in pure water or ultrapure water, The object to be cleaned is cleaned while applying ultrasonic vibration to the cleaning liquid, and a second cleaning liquid in which 5 ppm or more of oxygen gas and hydrofluoric acid is dissolved in pure water or ultrapure water is prepared. The object to be cleaned which has been cleaned with the cleaning liquid is washed.

Further, in the above-mentioned cleaning method, the second cleaning liquid can be cleaned while applying ultrasonic vibration to the second cleaning liquid also in the second cleaning operation.

Note that another cleaning step may be inserted between the first cleaning step using the first cleaning liquid and the second cleaning step using the second cleaning liquid.

It is preferable that the pH of the first cleaning liquid is 1 or more and less than 7.

The concentration of hydrofluoric acid dissolved in the second cleaning solution is preferably 0.005 wt% or more and less than 10 wt%, and more preferably 0.03 wt% or more and less than 3 wt%.

Further, it is preferable that the ultrasonic vibration is applied to the first cleaning liquid by irradiating ultrasonic waves.

In the second cleaning step using the second cleaning liquid, it is preferable to perform the cleaning while applying ultrasonic vibration to the second cleaning liquid. In this case, the ultrasonic vibration is preferably applied by irradiating ultrasonic waves. Is more preferred.

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 oxygen gas in pure water or ultrapure water, for example, oxygen gas is supplied to the surface of a hollow fiber made of a material having oxygen gas permeability, while pure water or ultrapure water is supplied inside the hollow fiber. A method of supplying pure water and dissolving oxygen gas in the pure water or ultrapure water by gas-liquid contact, supplying oxygen gas to the upstream side of the pure water or ultrapure water supply pump, and dissolving by stirring in the pump A method of dissolving oxygen gas in pure water or ultrapure water through an ejector, a method of dissolving oxygen gas in pure water or ultrapure water by bubbling, and the like can be employed.

The concentration of dissolved oxygen in pure water or ultrapure water to be dissolved in the first and second cleaning solutions is appropriately adjusted depending on the properties of the surface of the object to be cleaned, but is preferably 5 ppm or more. It is more preferably at least 15 ppm, further preferably at least 20 ppm. When the concentration of dissolved oxygen dissolved in the pure water or ultrapure water is lower than 5 ppm, it is difficult to sufficiently obtain the effect of removing metal impurities attached to the surface of the object to be cleaned.

In the present invention, even if coexisting gas other than oxygen is present in pure water or ultrapure water, the effect is not affected. In particular, nitrogen gas may be saturated.

As the oxygen gas used in the present invention, oxygen gas generated by electrolysis of water can be preferably used. The use of oxygen gas produced by electrolysis of water in this way makes it possible to replace cylinders, such as when dissolving oxygen gas from an oxygen cylinder, or to install an economical place for stocking cylinders. And the contamination of impurities such as anode electrolyzed water in which oxygen gas obtained by directly electrolyzing water is dissolved and contamination from electrodes can be prevented. Of course, if there is an oxygen gas supply line in the immediate vicinity, it is more economical to use the oxygen gas than to use the oxygen gas generated by electrolysis of water.

In dissolving oxygen gas in pure water or ultrapure water, for example, a dissolved oxygen concentration detector of a diaphragm type is installed in a pure water or ultrapure water supply line, and pressure is adjusted in an oxygen gas supply path. A valve is provided, and the dissolved oxygen concentration in pure water or ultrapure water is detected by the detector, and the dissolved oxygen concentration in the pure water or ultrapure water is controlled by feeding back the dissolved oxygen concentration to the pressure control valve. It may be.

The pH of the first cleaning solution is adjusted by adding an acid substantially free of fluorine ions to pure water or ultrapure water before and after dissolution of oxygen gas. Cleaning solution p
H is appropriately adjusted depending on the properties of the surface to be cleaned.
It is preferably adjusted to at least 7 and less than 7, more preferably at least 1 and less than 6, more preferably at least 1 and less than 5.

It is important that the first cleaning liquid does not contain fluorine ions. When the first cleaning solution contains fluorine ions, metal impurities detached from the surface of the object to be cleaned are re-adhered, and reverse contamination occurs.

The acid which does not substantially contain fluorine ions used in the present invention includes hydrochloric acid, nitric acid, sulfuric acid, carbonic acid, formic acid, acetic acid, peracetic acid, bromic acid, perbronic acid, iodic acid, periodic acid and the like. And aqueous gases of hydrochloric acid, and gases such as hydrochloric acid gas and carbon dioxide gas. Since metal ions and organic ions do not exist as counter ions of hydrogen ions and the counter ions are volatile,
Hydrochloric acid, hydrochloric acid gas, and carbon dioxide gas, which do not cause impurities to adhere to the surface of the object to be cleaned, are more preferable.

In dissolving an acid substantially free of fluorine ions in pure water or ultrapure water, a pH meter is installed in a pure water or ultrapure water supply line to control the amount of acid to be added. It is preferable to configure as follows.

In the second cleaning solution, hydrofluoric acid is added to pure water or ultrapure water before and after dissolution of the oxygen gas. The concentration of the hydrofluoric acid to be added is appropriately adjusted depending on the properties of the surface of the object to be cleaned, but is preferably adjusted to 0.005% by weight or more and less than 10% by weight, more preferably 0.03% by weight.
Or more, less than 3 wt%, more preferably 0.03 wt%
Above, it is less than 1 wt%. If the concentration of the added hydrofluoric acid is less than 0.005 wt%, the effect of removing metal impurities from the surface of the object to be cleaned cannot be sufficiently obtained. Further, even when the hydrofluoric acid concentration is 10 wt% or more, the effect of removing metal impurities corresponding to the amount of addition cannot be obtained.

In the present invention, it is more effective to use 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 or more and 2000 kHz or less,
More preferably, it is 700 kHz or more and 1500 kHz or less.

In order to perform 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.

[0031]

In general, conditions for removing metal impurities are set based on the pH of the cleaning solution and the oxidation-reduction potential. However, according to the experiments of the present inventor, when hydrofluoric acid, which is a component for removing the silicon oxide film (SiO ₂ ), was added to the cleaning solution, the metal impurities (copper) on the wafer surface were found to have a pH and oxidation-reduction potential. It was found that it could hardly be removed even under conditions that should be able to be removed, and that it could be removed by using another acid without adding hydrofluoric acid.

The present invention has been made based on this finding. In the present invention, metal impurities are removed by a first cleaning solution in which 5 ppm or more of oxygen gas and an acid substantially free of fluorine ions are dissolved. Next, the thin silicon oxide film formed at this time is
Is removed by the washing liquid.

When the silicon oxide film grows, if metal impurities such as aluminum and nickel are present in the cleaning solution, the silicon oxide film grows while taking in these metal impurities. By removing the silicon oxide film, the second cleaning liquid also functions to remove these metal impurities taken into the silicon oxide film.

[0034]

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

(Examples 1 to 5, Comparative Examples 1 to 3) A 6-inch silicon wafer (CZn-100) was rinsed with ultrapure water for 1 minute by an overflow rinse method, and then the wafer was reduced to 0.5 wt%. Hydrofluoric acid (50%,
EL grade, manufactured by Morita Chemical Industries) and copper ion concentration of 10
ppm for analysis copper standard solution (Cu 1000,
(Kanto Chemical Co., Ltd.) was added to ultrapure water and immersed in a contaminated liquid for 2 minutes, rinsed with ultrapure water for 1 minute by the overflow rinse method, and dried in a clean bench to obtain a forced contamination sample. And

To measure the amount of copper contamination adhering to the wafer,
Hydrofluoric acid gas phase decomposition-atomic absorption method was used. The amount of copper contamination on the surface of the forcibly contaminated sample wafer was 4.5 × 10 ¹²
Atoms / cm ² . The dissolved oxygen concentration of the cleaning solution was measured by a dissolved oxygen test kit (K-7512, manufactured by Kemet), and the pH of the cleaning solution was measured by a glass electrode type pH meter (E).
L-9001, manufactured by Aplix).

(Examples 1 to 3) Ultra-high purity oxygen gas (N60 Ultraox, manufactured by Teisan) was dissolved in ultrapure water via a gas permeable membrane module (SEPAREL, manufactured by Dainippon Ink and Chemicals, Inc.). Stored in a 3 mm quartz bath, hydrochloric acid water (35%, for atomic absorption analysis, manufactured by Kanto Chemical)
Was added to prepare a first washing solution.

A quartz bath filled with 5 liters of the first cleaning solution was placed in an ultrasonic cleaner (950 kHz, HI MEGA).
(ONIC 600, manufactured by KAIJO) is set in a SUS bath filled with water and an ultrasonic oscillator is installed on the bottom, and the forcibly contaminated sample (wafer) is placed in a wafer holder having an open bottom for transmitting ultrasonic waves. The wafer was held, set in the quartz bath, and washed with an ultrasonic output of 200 W for 10 minutes. Furthermore, a gas permeable membrane module (SE
After ultra-high purity oxygen gas (N60 Ultraox, manufactured by Teisan) is dissolved through PAREL (manufactured by Dainippon Ink and Chemicals, Inc.), the solution is stored in another 3 mm thick quartz bath, and hydrofluoric acid (50%, EL grade) , Manufactured by Morita Chemical Industry Co., Ltd.). The quartz bath filled with 5 liters of the second cleaning solution is placed in an ultrasonic cleaner (9).
50kHz, HI MEGAONIC 600, KAI
SU made of JO) filled with water and equipped with an ultrasonic oscillator at the bottom
The sample was set in an S bath, and the sample washed with the first washing liquid was washed with an ultrasonic output of 200 W for 10 minutes.

After the washing, it is dried in a clean bench,
The surface copper contamination concentration remaining on the wafer was measured. Table 1 shows the composition of the cleaning solution and the removal rate of copper contamination on the surface.

[0040]

[Table 1]

(Examples 4 and 5) Ultrapure oxygen gas (N60 Ultraox, manufactured by Teisan) was dissolved in ultrapure water via a gas permeable membrane module (SEPAREL, manufactured by Dainippon Ink and Chemicals, Inc.). Stored in a 3 mm quartz bath, hydrochloric acid water (35%, for atomic absorption analysis, manufactured by Kanto Chemical)
Was added to prepare a first washing solution. A quartz bath filled with 5 liters of the first cleaning liquid is placed in an ultrasonic cleaning machine (950 kHz, HI MEGAONIC 60).
0, made by KAIJO) and set in a SUS bath with an ultrasonic oscillator installed at the bottom, and the forcedly contaminated sample (wafer) is placed in a wafer holder with an open bottom to pass ultrasonic waves. The wafer was held, set in the quartz bath, and washed with an ultrasonic output of 200 W for 10 minutes. Furthermore, a gas permeable membrane module (SEPAREL,
Ultra-high-purity oxygen gas (N60 Ultraox, manufactured by Teisan) was dissolved through Dainippon Ink and Chemicals, and then stored in another 3 mm-thick quartz bath, and hydrofluoric acid (50
%, EL grade, manufactured by Morita Chemical Industry Co., Ltd.) to prepare a second cleaning solution.

The sample washed with the first cleaning solution was immersed in a quartz bath filled with 5 liters of the second cleaning solution for 10 minutes without irradiating ultrasonic waves. After the cleaning, the wafer was dried in a clean bench, and the surface copper concentration remaining on the wafer was measured. Table 2 shows the composition of the cleaning solution and the removal rate of copper contamination adhering to the surface.

[0043]

[Table 2]

Comparative Example 1 Wafer cleaning was performed under the same conditions as in Example 1 except that ammonia water was added to the first cleaning liquid. Table 3 shows the composition of the cleaning solution and the removal rate of copper contamination adhering to the surface.

Comparative Example 2 Wafer cleaning was performed under the same conditions as in Example 1 except that hydrofluoric acid was added to the first cleaning liquid. Table 3 shows the composition of the cleaning solution and the removal rate of copper contamination on the surface
Shown in

(Comparative Example 3) Wafer cleaning was performed under the same conditions as in Example 1 except that the substrate was immersed in the first cleaning liquid for 10 minutes without applying ultrasonic vibration. Table 3 shows the composition of the cleaning solution and the removal rate of copper contamination adhering to the surface.

[0047]

[Table 3]

[0048]

As described above, according to the present invention, according to the present invention, the first cleaning liquid obtained by dissolving oxygen gas of 5 ppm or more and acid substantially free from fluorine ions in pure water or ultrapure water is used. The cleaning object is cleaned while applying ultrasonic vibration to the cleaning liquid, and a second cleaning liquid in which oxygen gas and hydrofluoric acid of 5 ppm or more are dissolved in pure water or ultrapure water is prepared. By cleaning the object to be cleaned which has been cleaned with the first cleaning liquid, it is possible to use a cleaning agent which requires a large amount of cost for wastewater treatment,
Further, since cleaning is performed at room temperature, vapor of dissolved components is not generated, and moreover, adhered metal impurities can be removed to a sufficient level.

[0049]

Claims (6)

[Claims] 1. A first cleaning liquid in which 5 ppm or more of oxygen gas and an acid substantially free of fluorine ions are dissolved in pure water or ultrapure water, a first cleaning liquid is prepared, and the cleaning liquid is coated while being subjected to ultrasonic vibration. Wash the object, and add 5p to pure water or ultrapure water.
A method for cleaning a substrate, comprising: preparing a second cleaning solution in which oxygen gas of not less than pm and hydrofluoric acid are dissolved, and cleaning an object to be cleaned which has been cleaned with the first cleaning solution. 2. A first cleaning liquid is prepared by dissolving 5 ppm or more of oxygen gas and an acid substantially free of fluorine ions in pure water or ultrapure water, and the first cleaning liquid is subjected to ultrasonic vibration while being subjected to ultrasonic vibration. Wash the object, and add 5p to pure water or ultrapure water.
a second cleaning solution prepared by dissolving an oxygen gas of at least pm or more and hydrofluoric acid therein, and cleaning the object to be cleaned which has been cleaned with the first cleaning solution while applying ultrasonic vibration to the cleaning solution. Method. 3. The method according to claim 1, wherein the pH of the first cleaning solution is 1 or more and 7 or more.
The cleaning method according to claim 1, wherein the cleaning method is less than. 4. The cleaning method according to claim 1, wherein the concentration of hydrofluoric acid dissolved in the second cleaning liquid is 0.005% by weight or more and less than 10% by weight. . 5. The apparatus according to claim 1, wherein the object to be cleaned is cleaned while irradiating the first cleaning liquid with ultrasonic waves.
The cleaning method according to any one of claims 1 to 4. 6. The object to be cleaned is cleaned while irradiating the second cleaning liquid with ultrasonic waves.
The cleaning method according to any one of claims 1 to 5.