JPH08278270A - Device for measuring conductivity and specific resistance - Google Patents

Abstract

PURPOSE: To enable electrode surface to be non-dynamic, stabilize electrical characteristics, and achieve an accurate measurement by forming TiN film or TiC film on the electrode surface. CONSTITUTION: For example, the surface of both electrodes 1 and 2 in AC double-pole system is set to be non-dynamic by forming TiN layer or TiC layer by applying nitriding treatment or carbonizing treatment on the surface of Ti. The electrodes 1 and 2 are chemically stable by the nondynamic state and the TiN or TiC is a conductor, thus reducing potential drop due to a capacitance component at an electrode interface, achieving improved stability against disturbance when temperature changes, and reliably performing measurement. Also, the TiN film or TiC film has an extremely solid characteristic, a large wear resistance, an improved durability, and is inexpensive and hence is best suited for industrial applications.

Description

Detailed Description of the Invention

[0001]

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

[0002]

2. Description of the Related Art An apparatus for measuring the electric conductivity or the specific resistance in a sample liquid is an alternating current 2 as shown in FIG.
As materials for the electrodes 2 and 1 of the polar type, platinum, Ti, stainless steel, and those obtained by subjecting a Ti surface to TiO treatment (thickness 2 to 3 μm) have been used.

[0003]

However, when platinum is used as the material of the electrode, the material is stable and is preferable for so-called laboratories mainly used in laboratories, but for industrial use. In the application, the structure is required to be robust, and the electrode itself is expensive, which is not suitable for industrial use.

In the case of the Ti electrode, the surface is oxidized during use and TiO is formed on the surface layer. The thickness of TiO gradually changes, and electrode characteristics are likely to change due to external disturbances such as temperature changes, which causes a pointing effect and lowers reliability. This increase with time of the specific resistance value can be confirmed by the experimental data in the pure water device shown in FIG.

From the figure, the specific resistance value of pure water as the sample liquid was about 15 MΩ · cm at the initial stage of the measurement, but after 30 days or more, even if the sample liquid did not change, the theoretical Specific resistance of pure water (18.24 MΩ · cm)
Will exceed. It can be understood that this is 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 in the surface layer. The change in conductivity, which is the reciprocal of the specific resistance, is shown in FIG. By the way, the conductivity of theoretical pure water is 0.0548μ.
s · cm ⁻¹ .

In the case of the stainless steel electrode, the degree of change is lower than that of the Ti electrode, but the specific resistance value is gradually increased and there is a problem that the indicating effect occurs.

When a thick TiO treatment is applied to the Ti surface, the surface of the TiO layer does not change because the TiO layer itself is passivated. However, since the TiO layer is an insulator, the temperature does not change. It is easily affected by disturbances such as changes, and there is a problem 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 an apparatus for measuring conductivity or specific resistance which has stable electric characteristics and high reliability.

[0009]

The present invention has means for solving the above-mentioned problems as follows. That is, a TiN film or a Ti
It is characterized in that a C film is formed. As the material of the electrode, Ti is preferable, and stainless steel or the like may be used.

[0010]

[Function] 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 reliably obtained. .

[0011]

Embodiments of the present invention will be described below with reference to the drawings. For example, the alternating bipolar electrodes 1 and 2 as shown in FIG. 1 are subjected to a nitriding treatment or a carbonizing treatment on the surface of Ti to form a TiN layer or a TiC layer and passivate the electrode surface. Such electrodes 1 and 2 are chemically stable by passivation and, in addition, their TiN or T
Since iC is a conductor, there is little potential drop due to the capacitive component at the electrode interface portion, it is extremely stable against disturbances such as temperature changes, and high measurement accuracy can be reliably obtained. Moreover, since the TiN film or the TiC film has very strong characteristics, has great wear resistance, has good durability, and is inexpensive, it is suitable for industrial use. Becomes

The electrode interface generated on the surfaces of the electrodes 1 and 2 will be described. An equivalent circuit of the interface including the surfaces of the electrodes 1 and 2 at the time of measurement can be shown as shown in FIG. The composite impedance (R ') of the surface of is expressed by the equation. 1 / R ′ = 1 / R ₁ + 2πfc ₁ ... A constant and small value of 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 electrodes and the liquid, and c ₁ is the capacitance between the electrodes and the liquid.

In the above formula, since TiN or TiC is a conductor, R ₁ is small, and the capacitance of 2π
Since c of fc is large, as a result, R ′ has a very small value. This means that there are few factors that cause a measurement error with respect to a disturbance such as a change in temperature that may be a concern when used for industrial purposes, etc., and it is high without troublesome temperature compensation. The reliability can be obtained. The specific resistance value of TiN is 2.2 × 10 ⁻⁵ Ω · c.
m, and the specific resistance value of TiC is 6.8 × 10 ⁻⁵ Ω · cm
On the other hand, the specific resistance value of TiO is ≧ 10 ¹⁴ Ω · c
It is very high at m. Therefore, in the case of TiO, R ₁ becomes very large and is easily affected by disturbance.

Incidentally, in addition to the above TiN and TiC, as the electrode material satisfying the condition that the value of R ′ in the above formula is constant, Ti + TiO, Pt, Au.
There is plating etc. Further, Ti + TiO and Pt are 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.

The transition of the specific resistance value of the electrode treated with such TiN in the pure water apparatus is shown in the graph of FIG. As is clear from the graph, almost no change in specific resistance with time was observed, and it can be confirmed that TiN is very stable electrically and chemically. The graph is an average of the measured values, and the measured values are 16.
Floating is recognized between 5 and 17.7 MΩ · cm.

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

[0017]

As described above, according to the apparatus for measuring the electric conductivity or the specific resistance of the present invention, since the TiN film or the TiC film is formed on the surfaces of both electrodes of the AC bipolar type, the TiN film is formed. The film and TiC film are conductive and have a low specific resistance, and they are extremely hard and passivated to stabilize the electrical characteristics, high measurement accuracy can be obtained reliably, and they are inexpensive, and are most suitable for industrial use. Becomes

[Brief description of drawings]

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

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

FIG. 3 is a graph showing the transition of the resistance value of an electrode that has been treated with TiN according to the present invention.

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

FIG. 5 is a graph showing changes over time in the specific resistance value of a conventional Ti electrode.

FIG. 6 is a graph showing changes in the conductivity with time.

[Explanation of symbols]

 1, 2 ... Electrodes

Claims (1)

[Claims] 1. An apparatus for measuring conductivity or specific resistance, comprising a TiN film or a TiC film formed on both surfaces of an AC bipolar electrode.