JP3229771B2 - Equipment for measuring conductivity or resistivity - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement in an apparatus for measuring the electrical conductivity or specific resistance of a sample liquid, and is used particularly in the field of monitoring purity of pure water in a semiconductor manufacturing process.

[0002]

2. Description of the Related Art In an apparatus for measuring the electrical conductivity or specific resistance in a sample solution, for example, as shown in FIG.
Platinum, Ti, stainless steel, Ti surface-treated TiO (2 to 3 μm in thickness), or the like has been used as a material for the polar electrodes 1 and 2.

[0003]

However, when platinum is used as a material for an electrode, it is stable in terms of material and is preferable for a so-called laboratory used mainly in a laboratory or the like, but is preferable for an industrial use. In these applications, structural rigidity is required, and the electrodes themselves are expensive and unsuitable for industrial use.

In the case of a Ti electrode, the surface is oxidized during use, and TiO is formed on the surface layer. The thickness of TiO changes gradually, and the electrode characteristics are liable to change due to disturbances such as temperature change, and there is a problem in that the indication effect occurs and the reliability is reduced. This increase in the specific resistance value over time can be confirmed by the experimental data of the pure water apparatus shown in FIG.

[0005] As shown in the figure, at the beginning of the measurement, the specific resistance of pure water as a sample solution was about 15 MΩ · cm. Specific resistance of pure water (18.24 MΩ · cm)
Will be exceeded. This is understood to be due to the surface change of the Ti electrode itself, that is, the potential drop caused by the electric double layer at the electrode interface including the generation of TiO on the surface layer. FIG. 6 shows the change in the conductivity, which is the reciprocal of the specific resistance. By the way, the conductivity of theoretical pure water is 0.0548μ
s · cm ⁻¹ .

In the case of a stainless steel electrode, the degree of change is lower than that of a Ti electrode.

When a thick TiO treatment is applied to the Ti surface, the TiO layer itself is passivated and there is no change in the surface. However, since the TiO layer is an insulator, the temperature is low. It is susceptible to disturbances such as changes and there is a defect due to the insulator.

The present invention has been made in view of such circumstances,
It is an object of the present invention to provide a highly reliable device for measuring conductivity or resistivity with stable and stable electric characteristics.

[0009]

According to the present invention, means for solving the above-mentioned problems are constituted as follows. That is, a TiN film or Ti
It is characterized by forming a C film. In addition, as a material of the electrode, Ti is preferable, and stainless steel or the like can be used.

[0010]

By forming a very hard conductive TiN film or TiC film on the electrode surface, the electrode surface is passivated, the electrical characteristics are stabilized, and high measurement accuracy can be obtained with high reliability. .

[0011]

Embodiments of the present invention will be described below with reference to the drawings. For example, both electrodes 1 and 2 of the AC bipolar type as shown in FIG. 1 are subjected to nitriding or carbonizing on the surface of Ti to form a TiN layer or a TiC layer, and the electrode surface is passivated. Such electrodes 1 and 2 are chemically stable due to passivation and have a TiN or T
Since iC is a conductor, the potential drop due to the capacitance component at the electrode interface is small, and extremely stable against disturbances such as temperature changes, and high measurement accuracy can be obtained with high reliability. In addition, the TiN film or TiC film has very strong characteristics, has high abrasion resistance, has good durability, and is low in cost, so that it meets the conditions for industrial use. Becomes

The electrode interface generated on the surfaces of the electrodes 1 and 2 will be described. FIG. 2 shows an equivalent circuit of the interface including the surfaces of the electrodes 1 and 2 at the time of measurement. The combined impedance (R ′) of the surface of the is represented by the following equation. 1 / R ′ = 1 / R ₁ + 2πfc ₁ ... This constant R ′ is a requirement for maintaining and improving the measurement accuracy. Note that R is the resistance of the sample liquid (measurement target), R _{1 is} the resistance between the electrode and the liquid, and c ₁ is the capacity between the electrode and the liquid.

In the above formula, since TiN or TiC is a conductor, R ₁ is small, and 2π
Since c of fc is large, R ′ has a very small value as a result. This means that there are few factors that cause measurement errors with respect to disturbances such as temperature changes that are a concern when used for industrial purposes, for example, and are high even without performing troublesome temperature compensation. Reliability can be obtained. The specific resistance of TiN is 2.2 × 10 ⁻⁵ Ω · c.
m, and the specific resistance of TiC is 6.8 × 10 ⁻⁵ Ω · cm.
Whereas the specific resistance of TiO is ≧ 10 ¹⁴ Ω · c
m and very high. Thus, in the case of TiO, R ₁ is subject to very large, and the effect of disturbance.

Incidentally, in addition to the above-described TiN and TiC, electrode materials satisfying the condition that the value of R 'in the above equation is constant include Ti + TiO, Pt, and Au.
There are plating and the like. In addition, there are Ti + TiO and Pt as being stable in strength, and Pt has a particularly small value of R ′. However, these cannot satisfy all the industrial adoption conditions that the value of R ′ is constant, the value is small, the strength is stable, and the cost is low. TiN and T can satisfy all of these conditions.
iC.

FIG. 3 is a graph showing the transition of the specific resistance value of the electrode subjected to the TiN treatment in the pure water apparatus. As is clear from the graph, there is almost no change in the specific resistance value over time, and it can be confirmed that TiN is very stable electrically and chemically. The graph is obtained by averaging the measured values.
Floating has been observed between 5 and 17.7 MΩ · cm.

Also, it has been confirmed that the electrode subjected to the TiC treatment is also electrically and chemically stable. Needless to say, the alternating current bipolar electrode that has been subjected to such TiN treatment or TiC treatment can measure not only the specific resistance but also the conductivity depending on the configuration of the detection circuit.

[0017]

As described above, according to the apparatus for measuring electric conductivity or specific resistance of the present invention, a TiN film or a TiC film is formed on both surfaces of an AC bipolar electrode. The film and TiC film are conductive, have low specific resistance, are very hard and passivated, stabilize their electrical characteristics, can reliably obtain high measurement accuracy, are inexpensive, and are optimal for industrial use. Becomes

[Brief description of the drawings]

FIG. 1 is a sectional view showing one embodiment of an apparatus for measuring electric conductivity or specific resistance of the present invention.

FIG. 2 is a schematic diagram of an equivalent circuit for describing an electrode interface.

FIG. 3 is a graph showing a change in resistance value of an electrode subjected to a TiN treatment of the present invention.

FIG. 4 is a schematic view of an AC bipolar electrode.

FIG. 5 is a graph showing a change with time of a specific resistance value of a conventional Ti electrode.

FIG. 6 is a graph showing a change over time in the electrical conductivity.

[Explanation of symbols]

 1,2 ... electrode

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) G01N 27/00-27/10 G01R 27/22

Claims (1)

(57) [Claims] 1. An apparatus for measuring electrical conductivity or resistivity, wherein a TiN film or a TiC film is formed on both surfaces of an AC bipolar electrode.