JPH1151890A - Conductivity meter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To stabilize the electrical characteristics of an electrode by forming a titanium boride on the surface of the electrode and to enhance the reliability by sustaining high measurement accuracy over a long term. SOLUTION: An AC voltage is applied between a central electrode 1 and a tubular peripheral electrode 2 arranged concentrically thereto through an interval. Each electrode is made of titanium and a titanium boride layer (titanium B, titanium B2 ) is formed thereon. The titanium boride layer can be formed by various methods. In case of molten salt bath method, a mixed salt of borate, potassium borate, potassium carbide, magnesium, or the like, is melted and a material is immersed into the molten salt covered with an inert gas, e.g. argon, in order to protect the material and the molten salt against oxidation before being treated at a temperature of 1023-1323 K, for example. A titanium boride layer thus formed has specific resistivity on the order of 6.4×10<-6> Ω.cm which is lower than the specific resistivity 193×10<-6> Ω.cm of a conventional TiC film and it is evident that the titanium boride layer is suitable as the coating material for the electrode.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a conductivity meter used for controlling the purity of pure water used in a semiconductor wafer cleaning step.

[0002]

2. Description of the Related Art For example, in the manufacturing process of a semiconductor wafer, since fine dust or slight dirt is not allowed, a cleaning process such as cleaning with pure water is provided.
This pure water for cleaning also affects the surface of the wafer depending on its components, so that it is necessary to appropriately control the purity of the pure water. When such conventional purity control is performed, monitoring is performed using a conductivity meter to utilize the fact that the conductivity changes when impurities are present in pure water.

In such a conductivity meter, an AC voltage is applied to electrodes provided opposite to each other, and a change in current is detected to measure the conductivity and specific resistance of the liquid to be inspected. As the material of the electrode used at this time, titanium, stainless steel, platinum, or other materials obtained by performing titanium oxide treatment on the titanium surface are used, and a TiN film,
Alternatively, a device having a TiC film formed has been proposed.

[0004]

As described above, in the case of using titanium as the material of the electrode, the surface oxidizes during use, titanium oxide is formed on the surface layer, and the thickness gradually changes. The electrode characteristics are liable to change due to disturbances such as a temperature change, which affects the indication and lowers the reliability. In the case of using stainless steel,
Although the degree of change is lower than that of the above-mentioned titanium electrode, there still exists a drawback that the specific resistance value gradually increases and the indication is affected. Further, when a platinum electrode is used, although it is stable in material, it requires structural rigidity when used, and has the disadvantage that the electrode itself is expensive. In the case where titanium surface is subjected to a titanium oxide treatment, the surface of the titanium oxide layer itself is not passivated because the titanium oxide layer itself is passivated. However, since the titanium oxide layer is an insulator, temperature change and the like are prevented. There is a disadvantage that it is easily affected by disturbance.

[0005] Further, it has been confirmed that in the case where the electrode surface is subjected to a TiN coating treatment, the TiN layer is transformed in high-temperature water to become TiO ₂ . _{That, 2TiN + 4H 2 O → 2TiO} 2 + 2NH 3 + H 2 2TiN + 2O 2 → 2TiO 2 + chemical changes N ₂ is considered, both resulting in TiO _2. In the case where a TiC film is formed on the electrode surface, Ti
The specific resistance of the C film is as large as 193 × 10 ⁻⁶ Ω · cm, which is not suitable as a coating material for an electrode.

Accordingly, the present invention is to provide a highly reliable conductivity meter which can stabilize the electrical characteristics of the electrode by stabilizing the electrode surface, maintain high measurement accuracy over a long period of time, and provide a highly reliable conductivity meter. Aim.

[0007]

According to the present invention, a titanium boride film is formed on an electrode surface of a conductivity meter in order to solve the above problems.

In the present invention, since the titanium boride film is formed on the surface of the electrode of the conductivity meter as described above, the surface of the electrode is stabilized, and the specific resistance thereof is small, so that it is most suitable as a coating material for the electrode.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The electrode section of a conductivity meter to which the present invention is applied has a central electrode 1 and a concentric cylindrical peripheral electrode 2 with a space around the central electrode 1 as shown in FIG. Is supplied with an AC voltage. The material of each of these electrodes is made of titanium, and a titanium boride (titanium B, titanium B ₂ ) layer is formed on the surface thereof 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 electrolytic method. For example, a molten salt bath method can be used. In this method, a mixed salt of boric acid, calcium borate, calcium carbonate, magnesium, etc. is melted, and the material is immersed in a molten salt bath covered with an inert gas such as argon to prevent oxidation of the material and the molten salt. The treatment is performed at a temperature of 1023 to 1323K. Titanium B can also be prepared by the paste method.
_Two layers can be formed. According to this method, B ₄ C
, Na ₂ B ₄ O ₇ , NaBF ₄ , NH ₄ Cl, etc., a mixture of chemicals is pasted with ethyl alcohol, applied to the surface of the material, dried, and embedded in alumina powder containing B ₄ C. It can also be obtained by performing a heat treatment in the atmosphere at the temperature described above.

Further, it is also possible to employ a molten salt bath electrolysis method. 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 and degreased with trichlorethane, then nitric acid 10%,
Pickling is performed with an aqueous solution of 3% hydrofluoric acid. As a molten salt bath electrolytic bo oxidation treatment apparatus, a graphite crucible is used as an electrolytic tank, and as a molten salt electrolyte, a substance obtained by melting anhydrous borax (Na ₂ B ₄ O ₇ ) is used. After the sample was sufficiently treated, the sample was immersed in a molten salt bath at the cathode, and the electrolytic layer was used as the anode, at a processing temperature of 1123 to 1223 K, a processing time of 10.8 to 54 ks, and a current density of 200 to 60.
The boring treatment is performed under the condition of 0 A / m ² . Since titanium is easily oxidized, the sample is immersed in an argon atmosphere in the apparatus. As described above, a titanium boride layer can be formed on titanium by various methods.

The titanium boride layer formed as described above has a specific resistance of 6.4 × 10 ⁻⁶ Ω · cm, which is 1% of the above-mentioned TiC.
It is apparently smaller than 93 × 10 ⁻⁶ Ω · cm and suitable as a coating material for the electrode.

[0013]

According to the conductivity meter of the present invention, since a titanium boride layer is formed on its electrode, an extremely hard conductive film has excellent oxidation resistance and heat resistance, and has stable electric characteristics. Then, high measurement accuracy can be reliably obtained over a long period of time.

[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 (5)

[Claims] 1. A conductivity meter having a titanium boride film formed on both electrode surfaces. 2. The conductivity meter according to claim 1, wherein the titanium boride film is formed by a solid-state method. 3. The conductivity meter according to claim 1, wherein the titanium boride film is formed by a molten salt bath method. 4. The conductivity meter according to claim 1, wherein the titanium boride film is formed by a paste method. 5. The conductivity meter according to claim 1, wherein the titanium boride film is formed by a molten salt bath electrolysis method.