JP3616840B2 - Conductivity meter - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a conductivity meter used for purity control of pure water used in a semiconductor wafer cleaning process.
[0002]
[Prior art]
For example, in the manufacturing process of a semiconductor wafer, the presence of fine dust or slight dirt is not allowed, and therefore a cleaning process such as cleaning with pure water is provided. This pure water for cleaning also has an influence on the surface of the wafer depending on its components, so it is necessary to appropriately manage the purity of the pure water. When performing such conventional purity control, monitoring is performed using a conductivity meter in order to utilize the fact that the conductivity changes when impurities are present in pure water.
[0003]
In such a conductivity meter, an AC voltage is applied to the electrodes provided facing each other, and a change in current is detected to measure the conductivity and specific resistance of the liquid to be inspected. The material of the electrode used at that time is titanium, stainless steel, platinum, or a titanium surface treated with titanium oxide, and the like, and a material with a TiN film or TiC film formed on the electrode surface is proposed. Has been.
[0004]
[Problems to be solved by the invention]
In the case of using titanium as an electrode material as described above, the surface is oxidized during use, titanium oxide is formed on the surface layer, its thickness gradually changes, and the electrode characteristics are affected by disturbances such as temperature changes. There was a drawback that it was easy to change, the instructions were affected, and reliability was lowered. Further, in the case of using stainless steel, although the degree of change is lower than that of the titanium electrode, the specific resistance value gradually increases, and there is a drawback that the instruction is affected. Further, when a platinum electrode is used, although it is stable in terms of material, there is a drawback that structurally robustness is required for its use, and the electrode itself is expensive. In addition, when the titanium surface is treated with titanium oxide, since the titanium oxide layer itself is passivated, there is no change in the surface, but since the titanium oxide layer is an insulator, the temperature change, etc. There is a drawback that is susceptible to disturbances.
[0005]
Furthermore, in the case where the electrode surface is subjected to a coating treatment of TiN, it has been confirmed that the TiN layer is transformed into TiO ₂ in high-temperature water. That is,
2TiN + 4H ₂ O → 2TiO ₂ + 2NH ₃ + H ₂
2TiN + 2O ₂ → 2TiO ₂ + N ₂
The chemical changes of both are considered, and all produce TiO ₂ . In addition, in the case where a TiC film is formed on the electrode surface, the specific resistance of the TiC film is as large as 193 × 10 ⁻⁶ Ω · cm, which is not suitable as an electrode coating material.
[0006]
Accordingly, an object of the present invention is to provide a highly reliable conductivity meter that can stabilize the electrical characteristics of the electrode by stabilizing the electrode surface, maintain high measurement accuracy in the long term. .
[0007]
[Means for Solving the Problems]
In the present invention, a titanium boride film is formed on the electrode surface of a conductivity meter in order to solve the above problems.
[0008]
[Means for Solving the Problems]
In order to solve the above-mentioned problems, the present invention has a central electrode of a purity meter for conductivity control of pure water and a concentric cylindrical peripheral electrode around the center electrode, and an alternating current through which an alternating voltage is passed. In both bipolar electrodes, the electrode material is made of titanium, and a titanium boride film is formed on the surface thereof .
[0009]
DETAILED DESCRIPTION OF THE INVENTION
As shown in the figure, the electrode part of the electrometer to which the present invention is applied has a central electrode 1 and a cylindrical peripheral electrode 2 which is concentric with a space around the center electrode 1, and an AC voltage is energized there. . The material of each electrode is made of titanium, and a titanium boride (titanium B, titanium B ₂ ) layer is formed on the surface of the electrode in the present invention.
[0010]
The titanium boride layer can be formed by a solid method, a molten salt bath immersion method, a paste method, or a molten salt bath electrolysis method. For example, a molten salt bath method can be used. In this method, a mixed salt such as boric acid, boric acid borate, carbonic acid carbonate, or magnesium is melted, and the material is immersed in a molten salt bath covered with an inert gas such as argon in order to prevent oxidation of the material or molten salt. Processing is performed at a temperature of 1023 to 1323K. The titanium B ₂ layer can also be formed by a paste method. According to this method, a mixture of drugs such as B ₄ C, Na ₂ B ₄ O ₇ , NaBF ₄ , NH ₄ Cl and the like is pasted with ethyl alcohol, applied to the surface of the material, dried, and then contains B ₄ C It can also be obtained by being embedded in alumina powder and heat-treated in the atmosphere at a temperature of 1123 to 1238K.
[0011]
Furthermore, it can also be based on a molten salt bath electrolysis method. In order to form a titanium boride layer by this method, a commercially available pure titanium rolled plate having a thickness of 3 mm is polished with emery paper, washed with trichlorethane, degreased, and then with an aqueous solution of 10% nitric acid and 3% hydrofluoric acid. Pickle. As a molten salt bath electrolytic boration treatment apparatus, a graphite crucible is used as an electrolytic cell, and a molten salt electrolyte obtained by melting anhydrous borax (Na ₂ B ₄ O ₇ ) is used. Then, the sample is immersed in a molten salt bath with the cathode, the electrolytic layer is the anode, the treatment temperature is 1123 to 1223 K, the treatment time is 10.8 to 54 ks, and the current density is 200 to 600 A / m ^2. Process. Since titanium is easily oxidized, the sample is immersed in an argon atmosphere inside the apparatus. Thus, a titanium boride layer can be formed with respect to titanium by various methods.
[0012]
The formed titanium boride layer as described above specific resistance is smaller compared to 193 × ^{10 -6} Ω · cm of 6.4 × ^{10 -6} Ω · cm and above TiC, suitable as a coating material of the electrode It is clear that
[0013]
【The invention's effect】
In the conductivity meter of the present invention, since the titanium boride layer is formed on the electrode, the very hard conductive film is excellent in oxidation resistance and heat resistance and has stable electrical characteristics. And long-term high measurement accuracy can be obtained with high reliability.
[Brief description of the drawings]
FIG. 1 is a schematic view showing an electrode portion of a conductivity meter according to an embodiment of the present invention.
[Explanation of symbols]
1 Center electrode 2 Peripheral electrode

Claims (1)

In the AC bipolar bipolar electrode having a central electrode and a concentric cylindrical peripheral electrode with an interval around the center electrode, and an AC voltage is applied, the material of the electrode is made of titanium, and its surface Further, a conductivity meter for purity control of pure water, wherein a titanium boride layer is formed .

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