JP2500568B2 - Method for purifying chemical solution containing hydrofluoric acid - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for purifying a hydrofluoric acid-containing chemical liquid for removing harmful metal ions in the hydrofluoric acid-containing chemical liquid.

[0002]

2. Description of the Related Art The demand for cleaning the surface of a silicon wafer has become more and more strict with the high integration of VLSI. A hydrofluoric acid-containing chemical is used to remove the thermal oxide film and natural oxide film on the surface of the silicon wafer by etching.
When the hydrofluoric acid-containing chemical contains metal ions (Cu, Au, etc.) having a smaller ionization tendency than Si, they adhere to the wafer surface and affect the electrical characteristics. Therefore, it is indispensable to remove these harmful metal ions from the hydrofluoric acid-containing chemical liquid to make it highly purified.

Recently, high purification has been advanced, but due to problems such as variations in purity between lots and contamination from storage containers, chemical supply systems, etc., high purification at the point of use is required. Further, along with the introduction of the wafer into the hydrofluoric acid-containing chemical solution tank, the harmful liquid metal carried by the input wafer contaminates the hydrofluoric acid-containing chemical solution. Therefore, in order to extend the life of the chemical solution, it is necessary to circulate and purify the chemical solution to remove harmful metal ions.

Conventionally, an ion exchange method and a silicon particle adsorption method have been used as a method for removing harmful metal ions. The ion exchange method can be applied only to dilute hydrofluoric acid, and cannot be applied to a chemical solution in which high-concentration hydrofluoric acid (several 10%) and ammonium fluoride coexist. Further, the elution of organic substances from the ion exchange resin has been a problem. A silicon particle adsorption method has been developed as a method for solving these problems.

In the hydrofluoric acid-containing chemical solution, the oxide film on the silicon surface is removed and the active metal silicon surface is exposed, so that metals (Cu, Au) having a smaller ionization tendency than Si are exposed.
And the like), for example, when Cu is present, Cu is deposited on the surface of the metal silicon by the reaction of the following equation and removed from the liquid.

2Cu ²⁺ + Si → 2Cu + Si ⁴⁺ Therefore, the metal ions that can be removed by the silicon particle adsorption method are limited to those having a smaller ionization tendency than Si. However, the harmful metal ions that contaminate the silicon wafer in the chemical liquid are these elements, and there is no practical problem.

A conventional silicon particle adsorption method (Japanese Patent Laid-Open No. 3-1
A method for purifying a hydrofluoric acid-containing chemical solution according to JP-A-02827) will be described with reference to FIG. A silicon particle-containing filter 22 provided with a hydrofluoric acid-containing chemical liquid 21 in a hydrofluoric acid-containing chemical liquid supply system
To remove harmful metal ions such as Cu ions in the hydrofluoric acid-containing chemical liquid 21 by adsorbing them to the silicon particles 23.

[0008]

In the above-mentioned conventional method for purifying a hydrofluoric acid-containing chemical solution using silicon particles, since the adsorption efficiency (adsorption rate) is low (slow), harmful metal ions required at a low concentration level are required. However, there is a problem in that the flow rate cannot be increased because the toxic metal ion outflow concentration becomes high if the flow rate of the chemical liquid flowing through the silicon particle-containing filter is increased.

An object of the present invention is to provide a method for purifying a hydrofluoric acid-containing chemical solution which solves these problems.

[0010]

In order to achieve the above object, in the method for purifying a hydrofluoric acid-containing chemical solution of the present invention, the hydrofluoric acid-containing chemical solution is brought into contact with metal-deposited silicon particles having metal ions deposited on the surface, The harmful metal ions (Cu ions, etc.) in the chemical solution are adsorbed to the metal-deposited silicon particles and removed. A column is packed with metal-deposited silicon particles, and a hydrofluoric acid-containing chemical solution is flown through the packed column to remove harmful metal ions in the chemical solution. The metal-deposited silicon particles are prepared by immersing the silicon particles in a hydrofluoric acid-containing chemical solution containing metal ions. The metal-precipitated silicon particles having a reduced purification effect are washed with a washing liquid to clean the surface and regenerated before use.

[0011]

FIG. 7 is a sectional view showing the mechanism of adsorption of harmful metal ions on the surface of silicon particles. Cu ions are shown as an example of harmful metal ions. If Cu ions are present in the hydrofluoric acid-containing chemical liquid, the silicon particles 1 in the chemical liquid 1
On the surface, a local battery is formed in which the portion of the Cu precipitation nucleus (or Cu precipitate) is the local cathode 2 and the surrounding exposed metal silicon portion is the local anode 3. Cu ions (Cu ²⁺ ) are adsorbed by the silicon particles 1 in the form of depositing on the local cathode 2 and removed from the hydrofluoric acid-containing chemical solution. Since the adsorption rate depends on the surface area of the local cathode 2, the adsorption does not proceed effectively until the local cathode 2 is generated and the surface area increases in the initial stage of adsorption, and the adsorption rate is slow.
In order to increase the adsorption rate, silicon particles 1 (metal-deposited silicon particles) in which a metal to be the local cathode 2 is deposited and the surface area thereof is increased is effective.

[0012]

Next, the present invention will be described with reference to the drawings. 1 is a cross-sectional view of a reaction container for explaining a first embodiment of the present invention, showing a purification method by a batch method.

In this example, Cu ions were used as harmful metal ions, 5% hydrofluoric acid was used as the hydrofluoric acid-containing chemical solution, and Au-precipitated silicon particles (particle diameter: about 1 mm) were used as the metal-precipitated silicon particles.

5% containing Cu ions (50 ppb)
The Au ion-concentrated silicon particles 6 (50 g) were added to the reaction vessel 5 containing hydrofluoric acid 4 (500 ml), and the mixture was stirred by the stirrer 7 to change the Cu ion concentration in 5% hydrofluoric acid 4 with time when reacted. Is shown in FIG. The temperature at this time was 23 ° C. The horizontal axis represents the reaction time, and the vertical axis represents the Cu ion concentration in 5% hydrofluoric acid 4. For comparison, the results of using untreated silicon particles that are conventionally used are also shown. Figure 2
As shown in, the Cu ion concentration in the liquid decreased sharply and became almost constant after 30 minutes. The concentration at that time was 0.5 ppb, and it was possible to remove to a concentration of 1/100 of the initial concentration. After 20 minutes, no difference was observed between the Au-precipitated silicon particles and the untreated silicon particles, but the removal rate was faster in the former case at the initial stage of the reaction, and the Cu ion concentration in the solution after 5 minutes was higher. It was 1/2 or less of the latter case.

When the silicon particles in which Au was deposited as the local cathode of the present example (Au-deposited silicon particles) were used, the adsorption rate was twice or more (5 minutes later) than the untreated silicon particles. The metal to be deposited as the local cathode may be any metal as long as it deposits on the surface of silicon particles in a hydrofluoric acid-containing chemical solution, is chemically stable, and does not elute into the chemical solution.

FIG. 3 is a sectional view of an apparatus for explaining the second embodiment of the present invention, showing a purification method by a column method.
In this embodiment, Cu ions are used as harmful metal ions, and Au-deposited silicon particles (particle diameter;
1 mm), and 5% hydrofluoric acid was used as a hydrofluoric acid-containing chemical solution.

A column 9 was filled with Au-precipitated silicon particles 8, and 5% hydrofluoric acid 10 containing Cu ions was fed from above the column 9 by a pump 11. Column size; 10m
mφ × 25 cm (volume: 19.5 cm 3), Cu ion concentration: 1000 ppb, temperature: 23 ° C., flow rate: 4 ml /
FIG. 4 shows changes in the Cu concentration in the outflow liquid 12 when the chemical liquid (containing Cu) was sent under the condition of min.

The horizontal axis represents the outflow amount of the effluent 12, and the vertical axis represents the Cu ion concentration in the effluent 12. For comparison, the results when using conventional untreated silicon particles are also shown.
When the Au precipitated silicon particles 8 were used, the Cu ion concentration in the 5% hydrofluoric acid 4 could not be reduced to below the detection limit (0.02 ppb) by the batch method of Example 1, but by the column method of this Example. According to this, the Cu ion concentration in the effluent 12 could be immediately reduced to below the detection limit (0.02 ppb). When the conventional untreated silicon particles were used, the Cu ion concentration in the effluent 12 was very high at the beginning and gradually decreased to a constant value (1 ppb) after the effluent amount of 120 ml. As described above, the method for purifying the hydrofluoric acid-containing chemical solution using the Au-precipitated silicon particles 8 of the example was much superior in adsorption ability to the conventional method using untreated silicon particles.

Table 1 shows changes in the concentration of Cu ions in the effluent 12 when the flow rate of the 5% hydrofluoric acid 10 containing Cu ions flowing in the column 9 is changed. 5% of this time
The Cu ion concentration in hydrofluoric acid 10 is 10 ppm. For comparison, Table 1 also shows the results when conventional untreated silicon particles were used.

[0020]

[Table 1]

When untreated silicon particles were used, 1 ppb of Cu ions had already flowed out at 4 ml / min.
When using Au-deposited silicon particles 8, 12 ml / mi
Even with n, the outflow concentration was 0.1 ppb or less. Therefore,
According to the method for purifying the hydrofluoric acid-containing chemical liquid of the present embodiment, the hydrofluoric acid-containing chemical liquid can be treated at a flow rate three times or more that of the conventional method.

FIG. 5 is a sectional view of a reaction vessel for explaining a method for preparing metal-deposited silicon particles of Example 3 of the present invention. In this example, Au ions were used as the deposited metal ions,
5% hydrofluoric acid was used as the hydrofluoric acid-containing chemical solution.

Silicon particles 15 (particle size: about 1 mm, 50 g) were added to a reaction vessel 14 containing 5% hydrofluoric acid 13 (500 ml) containing Au ions (1 ppm), and stirred with a stirrer 16 at room temperature for 10 minutes. By stirring, Au ions were deposited on the surface of the silicon particles 15. After stirring, filtering, washing with water,
Au precipitated silicon particles were obtained. Au in 5% hydrofluoric acid 13
About 95% of the ions were deposited on the surface of the silicon particles 15.
The precipitation mechanism is the same mechanism as the adsorption of harmful metal ions on the surface of silicon particles described in the section [Action],
Au deposited on the surface of the silicon particles 15 acts as a local cathode. The Au-precipitated silicon particles prepared in this Example 3 were applied to the purification of the hydrofluoric acid-containing chemical liquid in Examples 1 and 2.

If the concentration of Au ions in the 5% hydrofluoric acid 13 is too high, the concentration of precipitation on the surface of the silicon particles 15 becomes too high, which not only lowers the adsorption capacity of harmful metal ions but also causes a cost increase. Become. Therefore, the Au ion concentration may be a concentration sufficient to prepare Au-precipitated silicon particles having the required adsorption capacity.

In the case of Cu-precipitated silicon prepared by using Cu ions as the precipitating metal ions, when the Cu-precipitated silicon comes into contact with the atmosphere, the precipitated Cu is oxidized and dissolved in the hydrofluoric acid-containing chemical solution. Therefore, when the chemical solution is purified by the column method using Cu-deposited silicon particles, Cu ions flow out and conversely contaminate the chemical solution. Therefore, the metal ions used to prepare the metal-deposited silicon particles must be such that the deposit is chemically stable.

FIG. 6 is a sectional view of an apparatus for explaining a method for purifying a hydrofluoric acid-containing chemical solution incorporating a function of regenerating metal-deposited silicon particles according to Example 4 of the present invention. The metal-deposited silicon particles that have reached the adsorption saturation have no ability to adsorb harmful metal ions, but can be recycled by dissolving and removing the harmful metal deposited on the surface of the metal-deposited silicon particles with an acidic solution.

In this example, a method of regenerating the column 17 packed with Au-precipitated silicon particles used in Example 2 will be described.
When the adsorption capacity of column 17 decreased, 5N nitric acid 1
8 (200 ml, 60 ° C.) was fed and further washed with pure water 19. By this treatment, only the harmful metal (Cu) adsorbed on the surface was almost completely removed, and the Au-deposited silicon particles 20 could be regenerated to the state before use.

The acidic solution for regenerating the metal-precipitated silicon particles may be one that does not dissolve the silicon and the precipitated metal but can dissolve only the harmful metal, and the operating temperature may be within the range where the purpose can be achieved.

[0029]

As described above, according to the method for purifying a hydrofluoric acid-containing chemical solution of the present invention, the metal-deposited silicon particles have a higher ability to adsorb harmful metal ions than the conventional untreated silicon particles. It is possible to reduce harmful metal ions in the contained chemical liquid to a concentration level (0.1 ppb or less) required in the future. Further, since the treatment can be performed at a flow rate three times or more that of the conventional technique, the treatment capacity can be improved, and particularly the treatment time can be shortened.

[Brief description of drawings]

FIG. 1 is a sectional view of a reaction container for explaining a first embodiment of the present invention.

FIG. 2 is a diagram showing a change over time in Cu ion concentration in Example 1.

FIG. 3 is a sectional view of an apparatus for explaining a second embodiment of the present invention.

FIG. 4 is a diagram showing a relationship between an outflow amount and a Cu ion concentration in Example 2.

FIG. 5 is a sectional view of a reaction container for explaining a third embodiment of the present invention.

FIG. 6 is a sectional view of an apparatus for explaining a fourth embodiment of the present invention.

FIG. 7 is a cross-sectional view of silicon particles for explaining the basic principle of the present invention.

FIG. 8 is a diagram showing an internal structure of a filter for explaining a conventional technique.

[Explanation of symbols]

 1,15,23 Silicon particles 2 Local cathode 3 Local anode 4,10,13 5% Hydrofluoric acid 5,14 Reaction vessel 6,8,20 Au precipitated silicon particles 7,16 Stirrer 9,17 Column 11 Pump 12 Effluent 18 5N nitric acid 19 Pure water 21 Chemical solution containing hydrofluoric acid 22 Silicon particle mixed filter

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Office reference number FI technical display location B01J 39/08 B01J 39/08 49/00 49/00 E

Claims (4)

(57) [Claims] 1. A hydrofluoric acid-containing chemical solution is brought into contact with metal-deposited silicon particles in which metal ions are deposited on the surface of silicon particles, and harmful metal ions (Cu ions, etc.) in the chemical solution are adsorbed on the metal-deposited silicon particles. A method for purifying a hydrofluoric acid-containing chemical solution, which comprises removing the chemical solution. 2. A method for purifying a hydrofluoric acid-containing chemical liquid, which comprises passing a hydrofluoric acid-containing chemical liquid through a column packed with metal-deposited silicon particles to remove harmful metal ions in the chemical liquid. 3. A method for removing harmful metal ions from a hydrofluoric acid-containing chemical solution by contacting the hydrofluoric acid-containing chemical solution containing metal ions with silicon particles to deposit metal ions on the surface of the silicon particles. A method for purifying a hydrofluoric acid-containing chemical solution, which is used. 4. A method for purifying a hydrofluoric acid-containing chemical solution, which comprises cleaning metal-deposited silicon particles having a reduced refining effect with a cleaning solution to clean the surface and reusing the particles for reuse.