JPH07103861A - Method and equipment for measuring moisture in sample gas - Google Patents

Abstract

PURPOSE:To determine the concentration of moisture contained in a volatile inorganic hydrogen compound or other special gas accurately by mixing a zero gas and a moisture standard gas at a predetermined ratio immediately before introduction into a moisture gauge thereby calibrating the moisture gauge. CONSTITUTION:A switching valve 22 inserted into a dry gas introduction passage 6 is turned to the moisture gauge 4 side and a sample gas of zero moisture is introduced for a predetermined time before the switching valve 22 is turned to the discharge side. At the same time, a switching valve 21 in a calibration gas introduction passage 5 is turned to the moisture gauge 4 side thus introducing a moisture standard gas for a predetermined time. The switching valves 21, 22 are switched alternately to introduce the dry sample gas (zero gas) and the moisture standard gas alternately and when the difference of oscillation frequency is settled at the moisture gauge 4, the frequency difference is read out and made to correspond with the concentration of moisture. Subsequently, the switching valve 22 and the switching valve 23 of a sample gas introduction passage 7 are switched to introduce the zero gas and the sample gas alternately to the moisture gauge 4 where the differential oscillation frequency is read out thus determining the concentration of moisture in the sample gas. This method allows to neglect reaction between a special gas and moisture.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and an apparatus for measuring water content in a sample gas, which is contained in a trace amount in volatile inorganic hydrides such as arsine, phosphine and silane, and other special gases. The present invention relates to a method and a device suitable for measuring water content.

[0002]

2. Description of the Related Art Generally, water in a gas is a crystal oscillation type,
It is measured by a phosphorus pentoxide electrolytic type or capacitance type moisture meter, but in the measurement by these moisture meters, it is necessary to calibrate the moisture meter itself before the measurement. Therefore, the moisture meter is usually calibrated using a gas containing a predetermined amount of moisture, that is, a moisture standard gas. As the moisture standard gas, those based on general gases such as nitrogen, hydrogen and argon are distributed in the general market.

On the other hand, a specific moisture meter is equipped with a calibrator in which a moisture meter sensor and a gas inlet are connected by a Teflon (registered trademark) tube and the Teflon tube is placed in water. In this case, moisture-removed gas is introduced from the gas inlet, a calibration gas containing predetermined moisture is created by utilizing moisture permeation through the Teflon tube, and the moisture meter is calibrated using the calibration gas. .

[0004]

However, in the moisture standard gas (normal moisture standard gas) distributed in the market,
There is no one based on various special gases such as volatile inorganic hydrides such as arsine, phosphine and silane, which are widely used in the semiconductor field. This is because in the normal moisture standard gas, the base gas does not react with moisture and the moisture concentration does not change even after long-term storage,
In the case of volatile inorganic hydrides such as arsine, phosphine, and silane, and chlorine gas, there is a high possibility that they will react with water. This is because there is a possibility that the price will change, and that there is little demand and it will not be viable commercially.

For this reason, conventionally, even in the measurement of moisture in a special gas, the moisture meter is calibrated with a normal moisture standard gas, but this method ignores the influence of the special gas on the moisture sensor. However, it cannot be said that the water content was accurately quantified.

Further, it was confirmed as a result of an experiment that the calibration method using the Teflon tube does not allow normal water permeation into the Teflon tube. Therefore, even the calibration method using a Teflon tube cannot accurately measure the water content in the special gas.

As described above, in the conventional measurement of moisture in a special gas, there is the above-described inconvenience in the calibration before measurement, and it is the actual situation that accurate moisture measurement cannot be performed.

Therefore, the present invention provides arsine, phosphine,
An object of the present invention is to provide a method and apparatus for measuring water content, which can accurately quantify the water content contained in a special gas such as volatile inorganic hydride such as silane.

[0009]

In order to achieve the above-mentioned object, the method for measuring water content of the present invention is such that the sample gas from which water has been removed is mixed with a normal water standard gas at a predetermined ratio to form a sample gas. It is characterized in that a calibration gas having a predetermined moisture concentration as a base is temporarily generated, and then the moisture meter is calibrated using this calibration gas, and then the sample gas is introduced into the moisture meter to measure moisture. .

Further, the moisture measuring apparatus of the present invention has a sample gas supply source, a normal moisture standard gas supply source, a dryer for removing moisture in the sample gas, and the dryer. A calibration gas introduction path for introducing a dry sample gas and the moisture standard gas into a moisture meter by mixing them at a predetermined ratio, a dry gas introduction path for introducing the dry sample gas into a moisture meter, and a sample from the supply source. A sample gas introduction path for introducing a gas into the moisture meter is provided, and a switching means for selectively introducing each gas into the moisture meter is provided in each of the introduction paths.

[0011]

[Operation] According to the above configuration, since the calibration of the moisture meter uses the calibration gas in which the dry sample gas from which moisture has been removed and the normal moisture standard gas are mixed at a predetermined ratio, the calibration of the moisture meter can be performed accurately. It can be carried out. That is, since the calibration gas is generated by mixing both gases immediately before introduction into the moisture meter, the reaction between the special gas and moisture can be almost ignored, and a calibration gas having an accurate moisture content can be obtained. Can be introduced to. Also, the amount of water in the calibration gas can be set arbitrarily by changing the mixing ratio of the sample gas from which water has been removed and the water standard gas, and a calibration gas corresponding to the expected amount of water can be obtained. it can.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will now be described in more detail based on an embodiment shown in the drawings. FIG. 1 is a system diagram showing the basic configuration of the device of the present invention.
A sample gas container 1 which is a source of a special gas such as a volatile inorganic hydride such as arsine, phosphine and silane; a moisture standard gas container 2 which is a source of a normal moisture standard gas; A dryer 3 for removing water in the sample gas, a calibration gas introduction path 5 for mixing the dry sample gas discharged from the dryer 3 and a moisture standard gas at a predetermined ratio and introducing the mixture into a moisture meter 4. Dry gas introduction path 6 for introducing the dry sample gas into the moisture meter 4 and sample gas introduction path 7 for introducing the sample gas from the sample gas container 1 directly into the moisture meter 4.
And a flow rate controller (MF for controlling the flow rate of each gas
C) 11, 12, 13, 14 and switching valves (three-way solenoid valves) 21, 22, 23 for switching the flow path of each gas, and pressure adjustment for adjusting the introduction pressure of the sample gas and the moisture standard gas. It comprises valves 31, 32, a purge gas introducing pipe 8 and a valve 9 for introducing a dry inert gas into the system.

An embodiment of the method of the present invention will be described below based on the measuring procedure of the above apparatus. As the moisture meter 4, a crystal oscillation type moisture meter using a crystal oscillation type sensor was used. This crystal oscillation type moisture meter introduces the sample gas (zero gas) from which moisture has been removed and the sample gas containing moisture alternately into the sensor for a certain period of time to obtain the difference in oscillation frequency, and the amount of moisture is calculated from the difference in oscillation frequency. Is quantified.

First, as a preparatory step, the valve 9 is opened and a dry inert gas, for example, nitrogen gas passed through a dryer is introduced from the purge gas introduction pipe 8 to purge the inside of the piping system and the moisture meter 4. At the same time, the desiccant filled in the drier 3, for example, the molecular sieve is sufficiently activated.

Next, the valve 9 is closed and the switching valve 2
After switching 1, 22, 23 to the exhaust side, sample gas container 1
The container valve 1a is opened to start the introduction of the sample gas, and the pressure control valve 32 adjusts the pressure to about ² to 3 kg / cm ² G to send the sample gas to the dryer 3 and the flow rate controller 14. The dried sample gas from which moisture has been removed by the dryer 3 is branched into two directions and sent to the flow rate controllers 12 and 13, respectively.

On the other hand, the container valve 2a of the moisture standard gas container 2 is opened to start the introduction of a moisture standard gas, for example, a gas containing a predetermined amount of moisture in nitrogen gas, and the pressure is adjusted by the pressure control valve 31 to the sample. Same as gas, adjusted to about ^{2 to 3} kg / cm ² G and sent to the flow rate controller 11.

The flow rate of each gas in the flow rate controller 11 and the flow rate controller 12 is set to an appropriate flow rate according to the expected water content contained in the sample gas and the water content of the water standard gas. Normally, the amount of water in the calibration gas obtained by mixing the dry sample gas and the moisture standard gas may be set to a value close to the expected amount of water in the sample gas. Generally, since the amount of water in the sample gas is extremely small, the mixing ratio of the dry sample gas and the water standard gas is set to about 99: 1,
It is preferable to use a small amount of water standard gas for accurate measurement.

Further, in order to keep the amount of gas introduced into the moisture meter 4 constant, the total flow rate of the flow rate controllers 11 and 12 (calibration gas flow rate) and the flow rate of the dry sample gas from the flow rate controller 13 are set. , And the flow rate of the sample gas from the flow rate controller 14 are adjusted to be the same.

The moisture meter 4 is calibrated by first switching the switching valve 22 of the dry gas introduction path 6 to the moisture meter side to introduce a dry sample gas with zero moisture into the moisture meter for a certain period of time, and then switching the switching valve 22 to the exhaust side. At the same time, the switching valve 21 of the calibration gas introduction path 5 is switched to the moisture meter side, and the calibration gas containing a predetermined moisture is introduced into the moisture meter 4 for a certain period of time. By switching the switching valves 21 and 22, the dry sample gas and the calibration gas are alternately introduced into the moisture meter 4 for a fixed period of time, and when the difference between the oscillation frequencies of the sensors of the moisture meter 4 becomes constant, the frequency difference is read, The frequency difference is made to correspond to the known water concentration contained in the calibration gas.

Next, the switching valve 22 and the switching valve 23 of the sample gas introduction path 7 are alternately switched to the moisture meter side, and the dry sample gas and the sample gas are alternately introduced into the moisture meter 4 for a fixed time. Then, when the difference between the oscillation frequencies of the sensors of the moisture meter 4 becomes constant, the frequency difference is read, and the water concentration in the sample gas is obtained from the relationship between the frequency difference and the frequency difference when the calibration gas is introduced.

Here, a concrete example of measuring the water concentration in the silane gas using the above apparatus will be described. As the moisture standard gas, nitrogen gas containing 83.9 ppm of moisture was used. As the calibration gas, the flow rate thereof was set to a constant amount of 2.2 ml / min, and the flow rate controllers 11 and 12 were adjusted to prepare each of the water concentrations shown in Table 1.

[0022]

[Table 1]

Then, the moisture meter 4 was calibrated for each calibration gas. The result is shown in FIG. As is clear from FIG. 2, the indicated value of the moisture meter for each calibration gas substantially matches the theoretical moisture concentration of each, and it can be seen that accurate calibration was performed. Therefore, by introducing the silane gas as the sample gas into the moisture meter 4 through the sample gas introduction path 7 after performing this calibration operation, it is possible to accurately measure even a trace amount of moisture of about 5 ppm.

In the above embodiment, the gas was alternately introduced according to the characteristics of the crystal oscillation type moisture meter. However, in the case of the moisture meter which can perform the calibration by simply introducing the zero gas and the calibration gas, the gas is alternated. It is not necessary to introduce it, and each gas may be introduced according to the characteristics of various moisture meters.

The components of the sample gas to which the present invention is applied are not particularly limited, and include gases that cannot react with moisture to form a moisture standard gas,
It is also possible to target gases that cannot produce a moisture standard gas in terms of cost. Furthermore, even in the case of a gas in which the moisture standard gas is in circulation, the moisture standard gas can be measured using other types of moisture standard gas. It is possible to perform the above, and it is possible to measure the moisture content of many kinds of gas only by preparing one kind of moisture standard gas.

[0026]

As described above, according to the present invention,
Since the sample gas for measuring the water content can be used as the zero gas and the calibration gas, the influence of the special gas on the sensor of the water content meter can be almost eliminated, and it is possible to eliminate the effects of volatile inorganic hydrides such as arsine, phosphine and silane The water content in the special gas can be measured accurately.

[Brief description of drawings]

FIG. 1 is a system diagram of a measuring apparatus showing an embodiment of the present invention.

FIG. 2 is a diagram showing a relationship between an indicated value of a moisture meter and a theoretical moisture concentration.

[Explanation of symbols]

1 ... Sample gas container, 2 ... Moisture standard gas container, 3 ... Dryer, 4 ... Moisture meter, 5 ... Calibration gas introduction path, 6 ... Dry gas introduction path, 7 ... Sample gas introduction path, 11, 12, 13,
14 ... Flow rate controller 21, 22, 23 ... Switching valve

Claims (2)

[Claims] 1. When measuring the water content in a sample gas,
The sample gas from which water has been removed is mixed with normal moisture standard gas at a predetermined ratio to temporarily generate a calibration gas having a predetermined moisture concentration based on the sample gas, and then the calibration gas is used to remove moisture. A method for measuring water content in a sample gas, comprising calibrating the meter and introducing the sample gas into a water content meter to measure the water content. 2. An apparatus for measuring water content in a sample gas, comprising a supply source of the sample gas, a normal water content standard gas supply source, and a drier for removing water content in the sample gas, A calibration gas introduction path for introducing a dry sample gas derived from a dryer and the moisture standard gas into a moisture meter at a predetermined ratio, a dry gas introduction path for introducing the dry sample gas into a moisture meter, and A sample gas introduction path for introducing the sample gas from the supply source into the moisture meter is provided, and in each of the introduction paths, a switching means for selectively introducing each gas into the moisture meter is provided. Moisture measuring device.