JP2500732B2 - Adsorbent for chemical liquid purification and method for preparing the same - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an adsorbent used for refining a chemical used in a semiconductor device manufacturing process, particularly a hydrofluoric acid-containing chemical, and a method for preparing the same.

[0002]

2. Description of the Related Art With the high integration of VLSI, the requirement for cleaning the surface of a silicon wafer has become strict. The contaminants on the surface of the silicon wafer include fine particles, metals, organic substances, oxide films and the like.

The oxide film is removed by etching with a chemical solution containing hydrofluoric acid. Although the oxide film can be removed by this treatment, if harmful metal ions are contained in the hydrofluoric acid-containing chemical solution, they adhere to the wafer and affect the electrical characteristics. Therefore, the hydrofluoric acid-containing chemical solution in which harmful metal ions are accumulated as the wafer is charged must be recycled or replaced by purification.

Conventionally, the distillation method, the ion exchange resin method, and the silicon particle adsorption method have been used as a method for removing harmful metal ions.

The distillation method is not suitable for refining a mixed solution such as a hydrofluoric acid-containing chemical solution because the composition ratio of the solution after distillation changes. The ion exchange resin 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.

A conventional silicon particle adsorption method (Japanese Patent Laid-Open No. 3-1
No. 02827) discloses a method for purifying a hydrofluoric acid-containing chemical solution.
The hydrofluoric acid-containing chemical liquid is passed through a silicon particle-containing filter provided in the hydrofluoric acid-containing chemical liquid supply system, and harmful metal ions such as Cu ions in the hydrofluoric acid-containing chemical liquid are adsorbed and removed by the silicon particles.

[0007]

In the above-described conventional method for purifying a hydrofluoric acid-containing chemical solution using silicon particles, harmful metal ions are required because the adsorption efficiency (adsorption rate) of the adsorbent is low (slow). There was a problem that it could not be removed to a low concentration level (0.1 ppb or less), and that if the flow rate of the chemical solution flowing through the silicon particle-containing filter was increased, the outflow concentration of harmful metal ions would be high and the flow rate could not be increased.

An object of the present invention is to provide an adsorbent which can be used for refining a hydrofluoric acid-containing chemical liquid to a purity that can be used in a semiconductor device manufacturing process, and a method for preparing the adsorbent.

[0009]

In order to achieve the above-mentioned object, the adsorbent for chemical liquid purification of the first invention uses silicon particles as a base material, and a metal having an ionization tendency smaller than that of silicon is partially deposited on the surface. It is an adsorbent. The metal to be deposited is in particular silver or gold.

In the method for preparing an adsorbent for chemical liquid purification of the second invention, silicon particles are dipped in a hydrofluoric acid-containing chemical liquid containing a metal to be deposited in a predetermined concentration, and after stirring for a predetermined time, the silicon is washed with pure water. It is a thing.

[0011]

In the adsorbent of the present invention, silicon particles having a large surface area are selected, and a metal having an ionization tendency smaller than that of silicon is partially deposited on the surface to increase the adsorption rate of harmful metal ions. The harmful metal ions are deposited by the reduction that occurs on the surface of the silicon particles. The metal deposited on the surface of the silicon particles acts as a deposition nucleus that promotes the deposition of harmful metal ions.

[0012]

EXAMPLES Next, examples of the present invention will be described. FIG.
FIG. 3 is a cross-sectional view of a reaction container for explaining the first embodiment in which the metal deposited on the surface of silicon particles is gold.

Reaction vessel 2 on magnetic stirrer 1
First, several kinds of 4.9% dilute hydrofluoric acid solutions 3 containing 0 to 50 ppm of gold are prepared. The concentration of hydrofluoric acid may be 0.1% or more. Next, 2 g of each silicon particle 4 having a particle size of 0.1 to 1 mm was added to these solutions, and the mixture was stirred for 15 minutes with a stirrer 5 to deposit gold on the surface of the silicon particle 4,
It was thoroughly washed with pure water.

In each of the silicon particles thus prepared, 0 to 1.25 mg of gold is deposited per 1 g of gold.
2 g of these silicon particles were added to a 4.9% dilute hydrofluoric acid solution containing 50 ppb of copper and stirred. FIG. 2 shows the change with time of the copper concentration in the hydrofluoric acid solution at this time. As is clear from FIG. 2, 0.10 mg per 1 g of silicon particles
Using the above-mentioned silicon particles in which gold is deposited, 4.9%
It was found that copper in the dilute hydrofluoric acid solution can be removed up to the detection limit (0.02 ppb) or less. On the other hand, it can be seen that 50 ppb of copper cannot be removed with silicon particles without gold deposition.

Next, 2 g of silicon particles prepared by depositing plural kinds of gold prepared in the first embodiment were added to a mixed solution of ammonium fluoride containing 50 ppb of copper and hydrofluoric acid and stirred. FIG. 3 shows the change with time of the copper concentration in the hydrofluoric acid-containing solution at this time. When silicon particles in which 0.25 mg or more of gold is deposited per 1 g of silicon particles are used, copper in a solution containing hydrofluoric acid and ammonium fluoride can be detected at a lower limit (0.02).
It was found that up to ppb) can be removed.

Next, the case where the metal to be deposited is silver will be described as a second embodiment. The reactor shown in FIG. 1 was used.

Reaction vessel 2 on magnetic stirrer 1
First, several kinds of 4.9% dilute hydrofluoric acid solutions 3 containing 0 to 50 ppm of silver are prepared. Next, 2 g of each silicon particle 4 was added to these solutions, and the mixture was stirred for 15 minutes with a stirrer 5 to deposit silver on the surface of the silicon particles 4, and then thoroughly washed with pure water.

In each of the silicon particles thus prepared, 0 to 1.25 mg of silver is deposited per 1 g of silver particles. 2 g of these silicon particles were added to a 4.9% dilute hydrofluoric acid solution containing 50 ppb of copper and stirred. FIG. 4 shows the change over time in the copper concentration in the hydrofluoric acid solution at this time. As is clear from FIG. 4, 0.025 m per 1 g of silicon particles
If silicon particles in which g or more of silver is deposited are used, 4.9
% Of copper in dilute hydrofluoric acid solution (0.02 pp
b) It was found that up to the following can be removed.

Next, 2 g of silicon particles prepared by depositing plural kinds of silver prepared in the second embodiment were added to a mixed solution of ammonium fluoride containing 50 ppb of copper and hydrofluoric acid and stirred. FIG. 5 shows the change with time of the copper concentration in the hydrofluoric acid-containing solution at this time. When silicon particles in which 0.025 mg or more of silver is deposited per 1 g of silicon particles are used, copper in a solution containing hydrofluoric acid and ammonium fluoride can be detected at a lower limit (0.0
It was found that up to 2 ppb) or less can be removed.

In the above examples, the case was explained in which gold or silver was deposited at a maximum of 1.25 mg on 1 g of silicon particles to adjust the adsorbent. However, the amount of gold or silver deposited was up to 5 to 10 mg. It is possible.

[0021]

As described above, the use of the adsorbent of the present invention makes it possible to purify a hydrofluoric acid-containing solution at a high purity level (metal impurities of 0.1 ppb or less), which has been difficult to purify. By purifying the hydrofluoric acid-containing chemical liquid using the adsorbent of the present invention, the chemical liquid can be reused,
We were able to reduce the cost of semiconductor devices and the environmental load.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a reaction container used for preparing an adsorbent of an example.

FIG. 2 is a diagram showing a relationship between a stirring time and a Cu concentration in a dilute hydrofluoric acid solution when the adsorbent of the first embodiment is used.

FIG. 3 is a diagram showing a relationship between a stirring time and a Cu concentration in a mixed solution of ammonium fluoride and hydrofluoric acid when the adsorbent of the first embodiment is used.

FIG. 4 is a diagram showing the relationship between the stirring time and the concentration of Cu in the dilute hydrofluoric acid solution when the adsorbent of the second embodiment is used.

FIG. 5 is a diagram showing a relationship between a stirring time and a Cu concentration in a mixed solution of ammonium fluoride and hydrofluoric acid when the adsorbent of the second embodiment is used.

[Explanation of symbols]

 1 magnetic stirrer 2 reaction vessel 3 dilute hydrofluoric acid solution 4 silicon particles 5 stirrer

Claims (5)

(57) [Claims] 1. An adsorbent for chemical liquid purification, comprising silicon particles and a metal partially deposited on the surface of the silicon particles and having an ionization tendency smaller than that of silicon. 2. The adsorbent for chemical liquid purification according to claim 1, wherein the metal having a low ionization tendency is gold or silver. 3. The adsorbent for chemical liquid purification according to claim 2, wherein the amount of gold deposited is 0.1 mg or more per 1 g of silicon particles. 4. The adsorbent for chemical liquid purification according to claim 2, wherein the amount of precipitated silver is 0.02 mg or more per 1 g of silicon particles. 5. A method comprising immersing silicon particles in a hydrofluoric acid-containing chemical solution containing a predetermined concentration of a metal to be precipitated and stirring the solution for a predetermined time to precipitate the metal on the surface of the silicon particle and washing the silicon particle with pure water. A method for preparing an adsorbent for chemical liquid purification.