TWI664320B - Method for recovering Au from iodine-based etching waste liquid and remaking etching solution - Google Patents

Abstract

The present invention is a method for electrolytically recovering Au from a used iodine-based etching solution containing Au and remaking the etching solution, characterized in that the potential of the cathode is set to -0.75V ~ -0.95V (reference electrode: Ag / AgCl), the ratio of the current density of the anode to the current density of the cathode is set to 3 to 50 (but excluding 3). An object of the present invention is to provide a method for treating used iodine-based etching solution stably and efficiently without performing strict pH control (a method for recovering Au and remaking the iodine-based etching solution).

Description

   Method for recovering Au from iodine-based etching waste liquid and remaking etching solution   

The present invention relates to the treatment of used iodine-based etching solutions discharged during the microfabrication of Au films in various semiconductor parts, and to the stable and efficient recovery of Au and etching solutions from this iodine-based etching waste liquid. Method of reproduction.

Wiring of various semiconductor parts uses highly conductive materials such as Au. The Au wiring is formed by forming a film using a PVD method or the like, and then is formed by microfabrication using wet etching. At this time, the used etching solution contains expensive Au. At this time, an iodine-based etching solution is often used as an etching solution. The industry uses chemical reduction using various reducing agents, replacement precipitation using metal powder, electrolytic refining, and the like to recover Au from the iodine-based etching solution.

On the other hand, the iodine-based etching solution after recovery of Au, having a capacity of triiodide ion etching (I ₃ ^-) is reduced to iodide ion (I ^-), result of the etching capability is reduced, the recovery of the iodine-based etching Au The solution becomes difficult to reuse.

For this situation, Patent Document 1 performs a process: By using a diaphragm of an electrolytic be addressed through the use of an etching solution, whereby the recovery of Au, and by iodide ion (I ^-) of reducing oxidized to triiodide ion (I ₃ ^-), the ability to recover so that it is etched (etching solution of reproduction).

However, the method of Patent Document 1 has the following problems: the current density changes with the passage of processing time, and on the cathode side, the pH value increases due to the electrolysis of water accompanied by the increase in current density, and the etching ability decreases. On the anode side, the pH is lowered due to the electrolytic decomposition of water accompanied by an increase in current density, and the etching ability becomes excessive. Further, precipitated on the anode side, iodine (I ₂₎ to the upper electrode, an iodide ion (I ^-) of reducing the concentration of the solution, and it becomes difficult to conduct stably and efficiently manufactured by weight of the etching solution.

Prior art literature

Patent literature

Patent Document 1: Japanese Patent Laid-Open No. 3-202484

Patent Document 2: Japanese Patent No. 5669995

In the case of recovering Au and etching solution from a used etching solution containing Au, it is difficult to perform electrolysis stably and efficiently due to changes in electrolytic conditions as described above. On the other hand, the following technique is cited in Reference 2 to maintain the cathode potential and anode potential in the electrolysis to a certain range, thereby improving the recovery rate of Au and restoring the ability of the etchant. However, in the case of this method, in order to strictly control the pH value of the solution before and after the treatment to within ± 0.5, complicated control tubes are required. In addition, the cathode potential is as low as -0.7V or more, so there is a processing time. Increased problems.

The problem of the present invention is to solve these problems, and it relates to a method for recovering Au from a used iodine-based etching solution containing Au and remaking the iodine-based etching solution, and particularly to provide a method which is stable without strict pH control. A method for efficiently reusing used iodine-based etching solution.

In order to solve the above-mentioned problems, the inventors have made intensive studies and obtained the following insights: By appropriately adjusting the current density of the cathode and the current density of the anode, water can be suppressed even without strict pH adjustment. The electrolytic solution and the precipitation of iodine can recover the Au, and the etching solution can be reproduced stably and efficiently. The present inventors have provided the following invention based on this knowledge.

1) A method for electrolytically recovering Au from a used iodine-based etching solution containing Au and remaking the etching solution, characterized in that the potential of the cathode is set to -0.75V to -0.95V (reference electrode: Ag / AgCl ), The ratio of the current density of the anode to the current density of the cathode is set to 3 to 50 (but excluding 3).

According to the present invention, it has the following excellent effects: In a method of electrolytically recovering Au from a used iodine-based etching solution containing Au and reusing the used etching solution, by appropriately adjusting the current density of the cathode and the anode, On the other hand, it is possible to suppress the electrolysis of water and the precipitation of iodine, thereby enabling the recovery of Au and the stable and efficient reproduction of the etching solution.

FIG. 1 is a schematic view of a reaction process of a used etching solution containing Au.

FIG. 2 is a schematic diagram of a processing flow of a used etching solution containing Au.

Fig. 3 is a photograph of iodine deposited on the anode after electrolysis (Comparative Example 1).

A schematic diagram of the treatment (reaction process) of the used etching solution containing Au of the present invention is shown in FIG. 1. As shown in FIG. 1, the electrolytic cell is separated into an anode chamber and a cathode chamber by a diaphragm (cation exchange membrane). The cathode chamber is supplied with an iodine-based etching solution containing Au (a used etching solution containing Au), and the anode chamber is supplied with after the (mobile) recovering iodine Au was reduced (from I ₃ ^- reduced to I ^-) in the etching solution. Then, Au is recovered in the cathode chamber, and the etching solution is reconstituted in the anode chamber.

A schematic diagram of a processing flow of a used etching solution containing Au is shown in FIG. 2. As shown in FIG. 2, the used etching solution containing Au supplied to the cathode chamber was deposited on the cathode by electrolytic treatment and recovered. On the other hand, by the reduction of iodine (from I ₃ ^- reduced to I ^-) etching solution is supplied (moved) after the recovery of Au used to the anode chamber, subjected to electrolytic oxidation treatment to have a capability of etching triiodo of ions (I ₃ ^-), whereby the user can be re-formed as the etching solution.

However, in the above-mentioned electrolytic treatment, if the current density is increased, electrolysis of water occurs, and on the cathode side, the pH value rises, and there is a problem that the etching ability of the reprocessed etching solution is reduced. In addition, in the anode chamber, the following problems occurred: the pH value decreased, and the etching ability of the reprocessed etching solution became excessive. Furthermore, the following problems occurred in the anode chamber: as the pH value decreased, iodine was precipitated on the electrode, and the concentration of iodide ions in the reprocessed etching solution decreased.

Therefore, the present inventors have obtained the insight that the current density on the cathode side is controlled by the potential of the cathode, and the current density on the anode side is controlled by the ratio of the current density to the cathode, thereby making it possible not to manage the pH value as closely as before The above-mentioned side reactions (electrolysis of water and precipitation of iodine) are effectively suppressed. Based on this knowledge, the present invention is characterized in that the potential of the cathode is set to -0.75V ~ -0.95V (reference electrode: Ag / AgCl), and the ratio of the current density of the anode to the current density of the cathode is set to 3 ~ 50 (except 3).

In the present invention, the potential of the cathode is preferably set to be -0.95V or more and -0.75V or less (reference electrode: Ag / AgCl). The reason is that if the potential of the cathode exceeds -0.75V, the treatment time for electrolysis will be longer and the production efficiency will decrease. On the other hand, if it is less than -0.95V, the electrolysis of water will be apparent on the cathode side. In addition, there are methods to control the cathode potential: measure the potential difference between the reference electrode and the cathode at any time, and reflect it to the output voltage of the rectifier through feedback control.

In addition, it is preferable that the current density of the anode relative to the current density of the cathode is within a range of 3 to 50 (except 3). If it exceeds this range, electrolysis of water will occur due to an increase in current density, causing a problem of excessive etching capacity of the re-etching solution accompanied by a decrease in pH, and a problem of iodine precipitation on the anode. The adjustment of the current density ratio can be adjusted by the area ratio of each electrode (the ratio of the area immersed in the electrolytic solution) as described later.

In addition, the pH of the cathode chamber and the anode chamber immediately before the electrolytic treatment is preferably adjusted to 4-6. If the pH value immediately before the electrolytic treatment is outside the range of 4 to 6, the reprocessing ability of the etchant will be reduced or become excessive. By setting the pH value before the electrolysis to the above range, Au can be recovered and the etching solution can be reconstituted stably and efficiently. In addition, in order to suppress the change in pH, an acid solution such as sulfuric acid may be added to the cathode chamber, and an alkali solution such as caustic soda may be added to the anode chamber to adjust the pH.

Examples

Next, examples and comparative examples of the present invention will be described. In addition, the following examples are merely representative examples, and the present invention is not limited to these examples, and should be interpreted within the scope of the technical ideas described in the specification.

(Example 1)

In an electrolytic cell in which the cathode chamber and the anode chamber were separated by a cation exchange membrane, 500 mL of an etching solution containing Au was supplied to the cathode chamber.

The Au-containing etching solution is composed of the following components. KI (0.25mol / L) + I ₂ (0.14mol / L) + Au (0.03mol / L)

On the other hand, 500 mL of a solution (after iodine reduction) after the recovery of Au was supplied to the anode chamber.

The solution after recovering Au (after iodine reduction) is composed of the following components.

KI (0.25mol / L)

Ti was used for the cathode (counter electrode), and those coated with IrO ₂ on Ti were used for the anode (working electrode), and the reference electrode was Ag / AgCl. In this case, the Ti electrodes immersed area to 20cm ^2, the immersed area of the IrO ₂ electrode is set to 62cm ^2, the cathode and the anode area ratio (ratio of current density) is set to 3.1. Then, the cathode potential was set to -0.75 V, and the solution was maintained at 20 ° C for electrolytic treatment. Then, the electrolysis was terminated when the current value became 5 mA or less.

With the above electrolytic treatment, the recovery rate of Au in the cathode chamber was 95.9%. In addition, investigating the change in pH before and after electrolysis, it was found that the pH in the anode room was 5.16 before electrolysis, 4.95 after electrolysis, and the pH in the cathode room was 5.61 before electrolysis, and 4.88 after electrolysis, which successfully suppressed the electrolysis of water. . As a result of investigating the etching performance of the etching solution after re-formation, 12.22 g of Au was dissolved with respect to the etching solution having a liquid amount of 2.10 L (Au concentration was 5.82 g / L), and it was confirmed that it could be reused as an Au etching solution.

(Example 2)

The immersion area of the Ti electrode was set to 2 cm ² , the immersion area of the IrO ₂ electrode was set to 100 cm ² , and the area ratio (current density ratio) of the cathode to the anode was set to 50. The rest were the same as in Example 1. Electrolytic treatment was performed under the same conditions.

With the above electrolytic treatment, the recovery rate of Au in the cathode chamber was 96.3%. In addition, the pH changes before and after the electrolysis were investigated. As a result, the pH in the anode room was 5.01 before electrolysis, 4.98 after electrolysis, and the pH in the cathode room was 5.11 before electrolysis, and 5.13 after electrolysis. The electrolysis of water was successfully suppressed. . As a result of investigating the etching performance of the re-etched etching solution, Au was dissolved in 12.31 g (Au concentration was 5.73 g / L) with respect to the etching solution having a liquid volume of 2.15 L, and it was confirmed that the etching solution could be reused as the Au etching solution.

(Example 3)

Except that the cathode potential was set to -0.95V, the rest were subjected to electrolytic treatment under the same conditions as in Example 1.

With the above electrolytic treatment, the recovery rate of Au in the cathode chamber was 96.1%. In addition, investigating the change in pH before and after electrolysis, it was found that the pH in the anode room was 4.99 before electrolysis, 4.31 after electrolysis, and the pH in the cathode room was 4.99 before electrolysis, and 5.88 after electrolysis. The electrolysis of water was successfully suppressed. . As a result of investigating the etching performance of the re-etched etching solution, 11.99 g of Au was dissolved in the etching solution having a liquid volume of 2.08 L (Au concentration was 5.76 g / L), and it was confirmed that the etching solution could be reused as the Au etching solution.

(Comparative example 1)

The immersion area of the Ti electrode was set to 40 cm ² , the immersion area of the IrO ₂ electrode was set to 80 cm ² , and the area ratio of the immersion area of the anode to the immersion area of the cathode was set to 2; An electrolytic treatment was performed in the same manner as in Example 1.

Investigated the change of pH value before and after electrolysis. As a result, the pH value in the anode room was 4.55 before electrolysis and 1.71 after electrolysis. In the cathode room, the pH value was 5.14 before electrolysis and 1.69 after electrolysis. The pH value increased due to the electrolysis of water. . In addition, hydrogen ions also move to the cathode chamber, and similarly, the pH value rises. Furthermore, as shown in FIG. 3, iodine was deposited on the anode after electrolysis.

[Industrial availability]

The method for recovering Au from the used iodine-based etching solution containing Au produced by the diaphragm electrolytic treatment method and the method for remaking the etching solution have the following excellent effects: they can be performed stably and efficiently, and Can greatly reduce the electrolysis time and improve production efficiency. The method of the present invention is useful in the field of recycling materials such as electronic equipment, electronic parts, substrates, and semiconductors.

Claims (1)

A method for electrolytically recovering Au from a used iodine-based etching solution containing Au and remaking the etching solution, characterized in that the potential of the cathode is set to -0.75V to -0.95V (reference electrode: Ag / AgCl), The ratio of the current density of the anode to the current density of the cathode is set to 3 to 50 (but excluding 3).