JP2512347B2 - Method and apparatus for measuring impurity concentration in gas - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for measuring the concentration of impurities in a gas and a measuring apparatus therefor, and more particularly to a technique effectively applied to the measurement of trace impurities in a high-purity gas used in semiconductor manufacturing. is there.

[0002]

2. Description of the Related Art Recently, in the semiconductor manufacturing process, LS
With the miniaturization and thinning of I devices, the impurities in the process gas used for semiconductor manufacturing have a bad influence on the device, so that the measurement of impurities in the process gas has become important. Moisture, which is apt to be mixed in from the atmosphere, has a strong adsorptive property, so it is difficult to remove it once it is mixed in the gas line. In addition, water is the most harmful of the impurities, so monitoring is required. There is.

As a conventional measuring instrument for measuring a small amount of water in a gas, a dew point meter for measuring the water concentration by the temperature at which the water in the gas is condensed, that is, the dew point is used.

[0004]

However, since the dew point meter determines that dew condensation has occurred by detecting the temperature at which cloudiness has occurred on the detection surface, it can be detected when the water concentration in the gas is extremely low. The detector does not operate unless a small amount of water droplets are accumulated on the surface and accumulated to a value where minute water droplets are accumulated.Therefore, it takes several hours to several tens of hours to detect condensation in the extremely low concentration range of ppm or less. However, the response time was extremely slow.

The present invention has been made in view of the above problems of the prior art, and an object of the present invention is to measure a very small amount of impurities in a gas, particularly a very small amount of water at a high speed. A method and apparatus therefor.

[0006]

To this end, the present invention is directed to a discharge meter in a discharge chamber in which a measurement gas applied by a high-voltage constant-current power supply is arranged so that the discharge current of corona discharge is constant. The impurity concentration in the gas is measured by changing the potential difference between the counter electrode and the counter electrode. In addition, depending on the type of measurement gas, the relationship between the potential difference between the discharge needle and the counter electrode and the concentration of impurities in the gas may not be 1: 1.
By adding a standard gas containing a known concentration of impurities to the measurement gas, the concentration of the measurement gas is forcibly changed, and the concentration of impurities in the gas increases or decreases depending on whether the potential difference between the discharge needle and the counter electrode increases or decreases. Is to determine whether the concentration is higher or lower than the minimum value.

In the measuring device used for carrying out the above-mentioned measuring method, a discharge chamber in which a measuring gas flows, and a high-voltage constant current provided in the discharge chamber and having a constant discharge current for corona discharge. It has a discharge needle applied by a power source, a counter electrode provided so as to face the discharge needle, and a measuring means for measuring the potential difference between the discharge needle and the counter electrode. A variable resistor is provided between the high-voltage constant-current power supply and the discharge needle, and a temperature controller capable of adjusting the temperature of the discharge chamber to 100 ° C. or higher is provided in the discharge chamber.
Furthermore, a standard gas generator was added to add a standard gas containing a known concentration of impurities to the measurement gas flowing through the discharge chamber, and it was confirmed that the concentration of impurities in the measurement gas was 1 ppm or less. It is equipped with a moisture concentration meter.

[0008]

In the measuring device constructed as described above, a high-pressure constant-current power supply is provided in which the measuring gas is introduced into the discharge chamber through its gas inlet to make the discharge current of the corona discharge constant at the discharge needle inside the discharge chamber. When a high voltage is applied by, the corona discharge occurs between the discharge needle and the counter electrode, and the discharge current of the corona discharge is constant. Since the applied voltage applied between the electrodes decreases with the increase, the impurity concentration in the gas can be measured by measuring the potential difference between the electrodes by the measuring means.

Correction of the variation and deviation of the absolute value of the potential difference due to wear of the discharge needle, and the correction of the optimum value of the discharge voltage corresponding to the type of measurement gas are provided between the high-voltage constant current power supply and the discharge needle. If the measurement gas contains impurities with strong adsorptive properties, especially water, the adsorption / desorption time will be longer if the wall of the discharge chamber is cold. When the impurity concentration of the gas changes, the high-speed response deteriorates, causing a measurement error.In addition, the ionization of the measurement gas caused by corona discharge causes a measurement error due to a temperature change. Is adjusted to a temperature above the boiling point (100 ° C.) of water by a temperature controller or adjusted to a constant temperature. In addition, the relationship between the potential difference between the discharge needle and the counter electrode and the impurity concentration in the gas may not be 1: 1 depending on the type of the measurement gas. In this case, the known concentration from the standard gas generator is The impurity concentration in the gas is higher than the minimum value by measuring whether the potential difference between the electrodes increases or decreases when the standard gas is added to the measurement gas and the concentration of the measurement gas is forcibly changed. It is determined whether the concentration is low but low. Also, if it is confirmed by a moisture concentration meter such as a dew point meter that the concentration of impurities in the measurement gas is 1 ppm or less, the relationship between the potential difference between the electrodes and the concentration is 1: 1.
The concentration can be easily determined.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described with reference to the drawings. In FIG. 1, a block 10 made of metal such as stainless steel has a space 12 for forming a discharge chamber 11 in the central longitudinal direction thereof and an upper part thereof. On the side surface, an inlet 1 for introducing a measurement gas (argon, civolane, hydrogen, helium, nitrogen, nitric oxide, dinitrogen monoxide, neon, oxygen, phosphorus trifluoride, phosphine, monosilane, disilane, etc.)
3 and an outlet 14 at the bottom.

On the upper end surface of the block 10, the space 1 is formed.
The upper end of 2 is closed and the flange 15 is sealed by the metal packing 16 and hermetically fixed, the block 10 and the flange 15 are grounded, and the discharge chamber 11 is formed by the flange 15 and the space 12. There is. A counter electrode 17 is provided in the discharge chamber 11 so as to extend integrally from the lower surface of the flange 15 in an L shape. The counter electrode 17 is slightly above the counter electrode 17 via an insulating terminal 19. 1
A discharge needle 18 attached to the No. 5 is provided.

The discharge needle 18 is applied by the high-voltage constant current power source 21 through which the constant-current circuit keeps the discharge current of the corona discharge constant via the variable resistor 20, and the high-voltage constant current power source 21. Generated discharge needle 18 and counter electrode 1
Measuring means (voltage monitor) 2 capable of measuring the potential difference between 7 and outputting the value to a computer.
2 is connected in parallel with Further, a heater 23 and a thermocouple 24 are attached to the block 10, and these are connected to a temperature controller 25, and the temperature inside the discharge chamber 11 is adjusted to 100 ° C. or higher, preferably 120 ° C. by the temperature controller 25. Is available.

The block 10 and the flange 15 are sealed by the metal packing 16 because if there is a gas leak in the discharge chamber 11, atmospheric components are mixed and the impurity concentration of the measurement gas is changed. The metal backing is used for the grounding and the block 10
Is high temperature (about 200 ° C.). Further, the block 10 and the flange 15 are grounded so that the circuit is connected by the grounding of the high voltage constant current power source 21 and the grounding of the block 10 so that a current flows and the constant current circuit operates normally.

In the above structure, the measurement gas is introduced into the discharge chamber 11, and a high pressure is applied between the discharge needle 18 and the counter electrode 17 while the discharge chamber 11 is adjusted to a predetermined temperature by the temperature controller 25. When a high voltage of about 1 KV to 3 KV is applied by the constant current power source, corona discharge occurs around the discharge needle 18 and a current of about 1 to 10 μA flows, and this discharge current is controlled to be constant by the constant current circuit. Therefore, when the discharge state changes, the potential difference between the electrodes also changes. More specifically, when the impurity concentration in the measurement gas is less than or equal to ppm, as is clear from FIG. 4, which shows the relationship between the water concentration in nitrogen gas and the potential difference between the electrodes,
Since the applied voltage between the electrodes decreases with the increase of the impurity concentration, the impurity concentration in the gas can be measured by measuring the potential difference between the electrodes by the measuring means 22.

In the embodiment of FIG. 2, a standard gas generator 26 is attached to the inlet 13 of the measuring gas. Depending on the type of the measuring gas, as shown in FIG. 4, the potential difference between the electrodes and the impurity concentration are 1 or less. Since there is a region that does not correspond to the pair 1, a standard gas having a known concentration from the standard gas generator 26, preferably, a high-purity gas having a concentration of 10 ppb or less and the same component as the measurement gas is supplied from the conduit 28 via the valve 27. The concentration of the measurement gas is forcibly changed by being added to the measurement gas, and the increase or decrease direction of the change in the discharge voltage measured thereby determines which of the two possible impurity concentrations.

For example, in FIG. 5, the measured potential difference is 2
In case of 000V, the concentration is 600ppb and 10000pp
There are solutions at two points of b, and it is not possible to specify either of them from only one measured value. Therefore, the impurity concentration is 1p
The standard gas of pb is added to the measurement gas. However, if the impurity concentration of the measurement gas is 600 ppb, the potential difference between the electrodes increases, as shown in FIG. The discharge voltage once drops, but when the addition amount is further increased, the decrease of the discharge potential difference stops, and on the contrary, it starts to increase. By observing this change, it is possible to specify which of the two solutions the impurity concentration of the measurement gas has.

In the embodiment shown in FIG. 3, a moisture concentration meter 29 such as a dew point meter is attached to the inlet 13 of the measurement gas. It is possible to output a signal that is smaller or larger than (ppm order), and even if the measurement gas has an impurity concentration such that the relationship between the potential difference and the impurity concentration is not in a one-to-one relationship, The signal of the densitometer 29 can be used to determine the concentration of the measurement gas. Moisture concentration meter 29
Is a relatively high water concentration in the ppm order, the water concentration can be measured with a response time of a few seconds to a few minutes, so the water concentration of the measurement gas can be determined relatively quickly, and the discharge voltage can be either high or low. It gives enough information to determine if it is compatible.

Further, as an embodiment, although not particularly shown,
There is a method in which the discharge current of corona discharge generated between a discharge needle applied to a constant high voltage and a counter electrode is measured by a measuring means to measure the impurity concentration in the gas.

[0019]

As described above, according to the present invention, it is possible to rapidly measure the concentration of impurities, particularly the water content, in the measurement gas in the extremely low concentration range of ppm or less.

[Brief description of drawings]

FIG. 1 is a cross-sectional explanatory view showing an example of a measuring apparatus according to the present invention.

FIG. 2 is a cross-sectional explanatory view showing another example of the measuring apparatus according to the present invention.

FIG. 3 is a cross-sectional explanatory view showing still another example of the measuring apparatus according to the present invention.

FIG. 4 is an explanatory diagram showing the relationship between the water concentration in nitrogen gas and the potential difference between electrodes.

FIG. 5 is an explanatory diagram showing the relationship between the water concentration in nitrogen gas and the potential difference between electrodes, which is different from that of FIG. 4 in its exemplified range.

FIG. 6 is an explanatory diagram showing the relationship between the water concentration in nitrogen gas and the potential difference between electrodes, which is different from that of FIG. 4 in its exemplified range.

[Explanation of symbols]

 10 Block 11 Discharge Chamber 13 Measurement Gas Inlet 14 Measurement Gas Outlet 15 Flange 16 Counter Electrode 18 Discharge Needle 20 Variable Resistor 21 High Voltage Constant Current Power Supply 22 Measuring Means (Voltage Monitor) 25 Temperature Controller 26 Standard Gas Generator 29 Moisture Concentration Meter

Claims (6)

(57) [Claims] 1. The impurities in the gas are removed by the change in the potential difference between the discharge needle and the counter electrode in the discharge chamber, through which the measurement gas applied by the high-voltage constant-current power supply in which the discharge current of the corona discharge is kept constant. A method for measuring the concentration of impurities in a gas, which comprises measuring. 2. A method of forcibly changing the concentration of the measuring gas by adding a standard gas containing impurities of a known concentration to the measuring gas so that the direction in which the potential difference between the discharge needle and the counter electrode changes can be known. The method for measuring the concentration of impurities in a gas according to claim 1. 3. A measurement gas introduced from the introduction port is disposed in the discharge chamber and the discharge chamber flowing, and high by a high voltage constant current power supply discharge current to a constant corona discharge
And a counter electrode to which a voltage is disposed opposite to the discharge needle and said discharge needle is applied, the impurity concentration in the gas, characterized in configuration having a measuring means for measuring the potential difference between the discharge needles and a counter electrode measuring device. 4. An apparatus for measuring the concentration of impurities in a gas according to claim 3, wherein a variable resistor is interposed between the high-voltage constant current power supply and the discharge needle. Wherein the standard gas generator for adding a standard gas containing an impurity of the known concentration to the measurement gas to the discharge chamber a flows is attached to the measuring gas inlet of the discharge chamber
The device for measuring the concentration of impurities in a gas according to claim 3 or 4 . 6. The water concentration meter impurity concentration in the measurement gas can be confirmed that the following concentrations 1ppm said discharge chamber
The measuring device for measuring the impurity concentration in the gas according to claim 3 or 4 , wherein the measuring gas introducing port is attached .