JPH0798296A - Measuring method for concentration of additive in electroless copper plating liquid - Google Patents

Abstract

PURPOSE:To obtain the concentration of the additive in plating liquid by measuring the electrochemical characteristic value on an electrode by dipping the metallic electrode after a material for removing formaldehyde in electroless copper plating liquid is added into the electroless copper plating liquid. CONSTITUTION:Formaldehyde in electroless copper plating liquid is removed. The electrochemical characteristic value on a metallic electrode is measured under the state wherein the plating reaction of the electroless copper plating liquid does not occur and the effect of the formaldehyde itself is removed. Thus, the behavior of additive is adequately obtained. As the material for removing the formaldehyde in the electroless copper plating liquid, one or more kinds of sodium sulfite, sodium hydrogensulfite, hydrogen peroxide and iodine can be used. As the electrode, gold, platinum and palladium are suitable. As the configurations, the substances in the shapes of a plate (box), and a disk (rotary electrode) are suitable. It is preferable that the electrochemical characteristic value as the index of the additive concentration is measured by a potential- current curve method and the like.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a method for measuring the concentration of an additive in an electroless copper plating solution.

[0002]

2. Description of the Related Art When an electroless copper plating bath is industrially operated, it is important to maintain its component concentration at a constant level, operate the plating bath stably, and control the thickness and physical properties of the deposited plating film. is there. Therefore, the copper ion concentration in the plating bath,
2. Description of the Related Art A bath management device that measures an alkali concentration, a reducing agent concentration, and a complexing agent concentration and manages them so as to maintain them at a constant concentration is becoming widespread.

On the other hand, the electroless copper plating bath contains various trace additives for the purpose of stabilizing the bath, controlling the plating rate, and improving the physical properties of the deposited film. These additives have such a large influence that they affect the characteristics of the plating bath, even though they are in very small amounts, and maintaining the concentration of the additives appropriately is as important as controlling the concentration of the main component of the plating bath. However, since the concentration of the additive is very low, a usual analysis method can hardly be used, and conventionally, the method of empirically being generally used is to mix the additive with the main component replenisher of the plating solution to replenish it.

[0004]

However, it is difficult to keep the additive concentration constant by such an indirect method, and it is not possible to directly know the actual concentration in the plating solution. There is also an attempt to control the additive concentration by measuring the plating rate, but there is no unique correspondence between the plating rate and the additive concentration, and it must be said that this is an indirect method. Further, focusing on the fact that the electroless copper plating reaction is an electrochemical hybrid reaction consisting of a combination of a cathodic reduction reaction of metal ions and an anodic oxidation reaction of a reducing agent, electrochemical measurement (for example, mixed potential measurement, Linear polarization method, AC impedance method, coulostat method, chronopotentiometry, cyclic voltammetry, polarization curve measurement)
Various attempts have been made to obtain knowledge about the characteristics of the electroless copper plating solution (including the behavior of additives).

However, in all of these conventional methods, since the electrode in which the electroless copper plating reaction is progressing is measured as the working electrode, the information about the plating reaction itself having a low impedance is the main, and the behavior of the additive is Only indirect information is available as to the effect of additives on the plating reaction. In particular, when formaldehyde is present and the plating reaction is in progress, even if an electrochemical measurement method is used, the concentration of the additive should be accurately measured due to the influence of reducing agent formaldehyde and dissolved oxygen. Is difficult

It is an object of the present invention to provide a method for quickly and accurately measuring the concentration of a trace amount of additive in a plating solution.

[0007]

[Means for Solving the Problems] The method for measuring the concentration of an additive in an electroless copper plating solution according to the present invention is as follows: It is characterized in that the concentration of the additive in the plating solution is obtained by immersing the metal electrode and measuring the electrochemical characteristic value on the metal electrode.

As a result of earnest studies, the inventors of the present invention removed formaldehyde in the electroless copper plating solution, removed the influence of formaldehyde itself while the plating reaction of the electroless copper plating solution did not occur. The inventors of the present invention discovered that the behavior of the additive can be properly and sensitively measured by measuring the electrochemical characteristic value on the metal electrode. .

In the present invention, if the electroless copper plating solution to be measured is of a high temperature type, it is desirable to cool it to about room temperature in advance. It may be diluted with water.

The substances that remove the formaldehyde in the electroless copper plating solution added to the electroless copper plating solution include sodium sulfite, sodium hydrogen sulfite, hydrogen peroxide, iodine, ammonium chloride, mercuric iodide potassium, hydroxylamine hydrochloride, At least one of primary amines, potassium permanganate, potassium bromate, cerium sulfate, and potassium cyanide may be used. The state of the added substance is preferably a solution state.
Further, the amount to be added may be an amount sufficient to remove formaldehyde in the plating solution.

Gold, platinum and palladium are suitable for the electrode used in the present invention, but other platinum group elements can also be used. It is also possible to use copper as the electrode. The shape of the electrode is not limited, but generally, a plate (foil) shape, a linear shape or a disk shape (rotating electrode) is suitable. It is particularly preferable to use a rotating platinum electrode.

In the present invention, the electrochemical characteristic value as an index of the additive concentration is preferably measured by a potential-current curve method (cyclic voltammetry, potential sweep method) or the like. The electrochemical characteristic values include peak current value, peak potential, equilibrium potential, oxidation potential,
A reduction potential, a half-wave potential, and a limiting current value can be used. Particularly preferably, it is desirable to use a peak current value which is a dissolution current value of the plated copper deposited on the metal electrode, which has a good quantitative correspondence with the additive concentration.

[0013]

【Example】

Example 1 An electroless copper plating solution having the following composition was prepared, and mercaptosuccinic acid as an additive was added thereto in the range of 0 to 10 mg / l to prepare a calibration curve as a plating solution for preparation. -Copper sulfate: 5 g / l-EDTA-4Na: 40 g / l-37% formaldehyde: 4 ml / l-PEG1000: 2 g / l-NaOH: 2 g / l Platinum rotating electrode HR-103 as a metal electrode (working electrode)
A (trade name, manufactured by Hokuto Denko Co., Ltd.) was used. A silver / silver chloride electrode was used as the reference electrode, and a platinum mesh was used as the counter electrode. This electroless copper plating solution is returned to room temperature and 50 ml sampled,
After adjusting the pH to 10 with concentrated sulfuric acid, 25 ml of a 1 mol / 1 aqueous Na ₂ SO ₃ solution was added, and water was added to this to 200 ml, and then the rotary electrode was immersed and potentiostat / galvanostat HA-501 ( Hokuto Denko Co., Ltd., trade name) and function generator HB-
Using 104 (manufactured by Hokuto Denko Co., Ltd., trade name), a potential-current curve was measured at a measurement temperature of 25 ° C. The rotation speed of the rotating electrode is 2500 RPM, and the scanning potential is -100 to -150.
The scanning speed was 0 mV and the scanning speed was 5 mV / sec. The obtained potential-current curve has a peak current value near -300 mV. A calibration curve created based on this current value is shown in FIG. Next, the electroless copper plating solution shown below was prepared for measurement.・ Copper sulfate: 5 g / l ・ EDTA ・ 4Na: 40 g / l ・ 37% formaldehyde: 4 ml / l ・ NaOH: 2 g / l ・ PEG1000: 2 g / l ・ Mercaptosuccinic acid 5 mg / l This electroless copper plating solution With respect to the plating solution which was heated to 70 ° C., plated on the substrate, and appropriately sampled, the current-potential curve was measured in the same manner as above, and the peak current value was obtained for each. The mercaptosuccinic acid concentration in the plating solution was calculated from the current value at this time and the calibration curve previously obtained. The change over time is shown in FIG. As a result, the consumption of the additive (mercaptosuccinic acid) in the plating solution was clearly understood.

[0014]

As described in detail above, according to the present invention, the concentration of the additive in the electroless copper plating solution, which has been difficult to analyze up to now, can be determined by a relatively simple operation.

[Brief description of drawings]

FIG. 1 is a diagram showing a relationship between an additive concentration and an electrochemical characteristic for explaining an example of the present invention.

FIG. 2 is a diagram showing the relationship between the additive concentration in the plating solution calculated based on FIG. 1 and the elapsed time of the plating solution.

Claims (3)

[Claims] 1. By adding a substance for removing formaldehyde in an electroless copper plating solution to an electroless copper plating solution, immersing the metal electrode, and measuring an electrochemical characteristic value on the metal electrode. A method for measuring the concentration of an additive in an electroless copper plating solution, which comprises determining the concentration of an additive in a plating solution. 2. A substance that removes formaldehyde in an electroless copper plating solution is sodium zincate, sodium hydrogen sulfite, hydrogen peroxide, iodine, ammonium chloride, potassium iodide potassium, hydroxylamine hydrochloride, primary amines. 2. The method for measuring the concentration of an additive in an electroless copper plating solution according to claim 1, wherein at least one or more of potassium permanganate, potassium bromate, cerium sulfate, and potassium cyanide is used. 3. The concentration measurement of the additive in the electroless copper plating solution according to claim 1, wherein a dissolution current value of plated copper deposited on a metal electrode is used as the electrochemical characteristic value. Law.