JP2001116724A - Method and apparatus for measuring concentration of moisture in gas - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method and an apparatus for measuring a concentration of a water content in a gas whereby a time for measuring the water content can be shortened, the apparatus can be made small, and an extremely small quantity of the water content can be measured highly accurately. SOLUTION: In the method and apparatus for measuring a concentration of a water content in a gas are carried out a process of desorbing and removing a water content adsorbed to a sampling piping, a process of introducing a gas to be measured into the sampling piping cooled to a predetermined temperature and adsorbing a water content in the gas to an inner surface of the sampling piping, a process of vacuumizing the interior of the sampling piping and discharging the gas to be measured, a process of heating the sampling piping to a predetermined temperature and desorbing the water content of a bilayer and afterwards adsorbed to the inner surface of the piping, and a process of introducing the desorbed water content to a mass spectrometer to measure the water content.

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 the concentration of water in a gas, and more particularly to a method and an apparatus for measuring the concentration (content) of a trace amount of water contained in a semiconductor material gas. .

[0002]

2. Description of the Related Art The applicant of the present invention has proposed a method and an apparatus for measuring a trace amount of water in a semiconductor material gas by using a water analysis method utilizing the adsorption and desorption of water on the inner surface of a pipe. See JP-A-11-83806).

According to this method, when a gas containing moisture (gas to be measured) is allowed to flow through a pipe from which water has been removed to a bimolecular layer, the inner surface of the pipe is in equilibrium with the moisture concentration in the gas phase. Continue to adsorb moisture in the gas phase until equilibrium is reached,
It utilizes the property that it is no longer adsorbed.

For example, while heating a pipe (sampling pipe) for absorbing and desorbing water to 100 to 170 ° C., a carrier gas containing substantially no water is introduced to thereby introduce two molecules adsorbed on the inner surface of the pipe. The water after the layer is desorbed and removed, and then a predetermined gas to be measured is introduced and circulated into the sampling pipe cooled to 20 to 25 ° C., and only the water in the gas to be measured is adsorbed on the inner surface of the pipe. The sampling pipe is heated to 100 to 170 ° C. to desorb the adsorbed water to the bimolecular layer, and the desorbed water is introduced into the mass spectrometer together with the carrier gas to measure the desorbed water amount ( Quantitative).

[0005]

However, in the above-described method, when measuring the desorbed moisture, most of the gas introduced into the mass spectrometry unit is introduced into the mass spectrometer because the moisture is accompanied by the carrier gas. In addition, since the sample system is at atmospheric pressure or pressurized state, and the mass spectrometer is in a vacuum state, a sampling pipe and a mass spectrometer are provided by providing parts such as a jet separator for controlling the gas introduction amount. It is necessary to appropriately maintain the pressure difference, and the device becomes large and complicated. A 6-way valve is used to switch between the carrier gas and the sample gas,
Resin is used in the seat portion of the six-way valve, and the absorption and desorption of moisture in the resin portion exists as a background, so that the measurement accuracy was not sufficiently high. Furthermore, since the sampling pipe is in the atmospheric pressure or the pressurized state at the time of measurement, there is a problem that a substantial desorption speed of water is slow and a measurement time is long.

Accordingly, the present invention is intended to shorten the time for measuring moisture and reduce the size of the apparatus, to reduce the background of moisture in the sampling system, and to measure a trace amount of moisture with high accuracy. An object of the present invention is to provide a method and an apparatus for measuring a water concentration.

[0007]

In order to achieve the above object, a method for measuring the water concentration in a gas according to the present invention measures the water concentration in a gas to be measured by utilizing the adsorption and desorption of water on the inner surface of a pipe. A method for removing and removing water from the second and subsequent molecular layers adsorbed on a sampling pipe, and introducing a gas to be measured into the sampling pipe cooled to a predetermined temperature to sample water in the gas. A water adsorption step of adsorbing on the inner surface of the sample, an evacuation step of evacuating the sampling pipe to discharge the gas to be measured, and a two molecule adsorbing on the inner surface of the sampling pipe by heating the sampling pipe to a predetermined temperature. It is characterized by including a water desorption step of desorbing water after the layer, and an analysis step of introducing the desorbed water into a mass spectrometer and measuring it.

Further, the apparatus for measuring the concentration of water in a gas according to the present invention is an apparatus for measuring the concentration of water in a gas to be measured by utilizing the absorption and desorption of water on the inner surface of a pipe. Piping, heating means for heating the sampling pipe to a predetermined temperature and cooling means for cooling the sampling pipe to a predetermined temperature, means for introducing a gas to be measured into the sampling pipe, means for evacuating the sampling pipe, and sampling. A mass spectrometer for measuring the moisture in the gas derived from the pipe.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a system diagram showing one embodiment of a moisture concentration measuring apparatus according to the present invention. This moisture concentration measuring device comprises a sampling pipe 1 for absorbing and desorbing moisture,
A thermostat 2 having a heating means for heating the sampling pipe 1 to a predetermined temperature and a cooling means for cooling to a predetermined temperature;
A mass spectrometer for measuring the moisture in the gas derived from the sampling pipe 1 by connecting the measured gas introduction path 3 as a means for introducing the measured gas into the sampling pipe 1 and the analysis pipe 4 to the sampling pipe 1. A first exhaust path 8 including a turbo-molecular pump 6 and a rotary pump 7 as means for evacuating the sampling pipe 1, and a flow controller for controlling the flow rate of the gas to be measured passing through the sampling pipe 1. (Mass flow controller: MFC) 9
A second exhaust path 10 having a flow path, a third exhaust path 12 branched from the middle of the exhaust path 8 and connected to a primary side of the rotary pump 7 via a flow control valve 11, and a second exhaust path 10 for introducing a purge gas. Switching means 15, 16, provided with a purge gas introduction path 13, a vent path 14 for flowing the gas to be measured introduced from the measurement gas introduction path 3 to the exhaust path 10, and a valve for switching the gas path; 17,1
8 and 19.

In general, the measured gas introduction path 3 is
A gas container filled with the gas to be measured is mounted via a pressure regulating valve, and a purge gas introduction path 13 is usually provided with a gas source which does not affect the measurement of moisture by the mass spectrometer 5 if necessary. It is installed via a regulating valve or a water removal device (purification device). Further, an electric heater can be used as a heating means of the constant temperature bath 2, and a low-temperature refrigerant such as liquefied nitrogen can be used as a cooling means.

Since the sampling pipe 1 only needs to desorb water from the second molecular layer adsorbing and desorbing on the inner surface of the pipe 1, it is not necessary to perform special treatment such as oxidation passivation on the inner peripheral surface. Ordinary stainless steel piping material can be used as it is. Further, by using a relatively thin pipe to spirally wind, the thermostat 2 can be reduced in size, the heating efficiency and the cooling efficiency can be improved, and the temperature can be stabilized.

The switching means 15, 16, 17, 18, 1
9, one valve or a plurality of valves can be used according to the connection status of each path. In particular, a block valve in which a plurality of valves are combined into one block is used, and a valve seat or the like of each valve is used. By forming it entirely of metal, the background of moisture can be greatly reduced as compared with the case of a conventional switching valve using a resin sheet. Further, as each valve, an appropriate valve can be used according to conditions such as conductance and flow rate of the path.

Next, a procedure for measuring the moisture in the gas to be measured by the method of the present invention using the above-described apparatus will be described. First,
While the turbo molecular pump 6 and the rotary pump 7 are started, the constant temperature bath 2 is heated to a predetermined heating temperature, for example, 100 to
By heating to 170 ° C., the valves 17 a of the switching means 17 and the valves 19 a and 19 b of the switching means 19 are opened, and the sampling pipe 1 is evacuated while being heated, so that the second and subsequent molecular layers adsorbed on the inner surface of the pipe are obtained. A moisture removing step of desorbing and removing the moisture from the first exhaust path 8 is performed. The valve 15a of the switching means 15 is opened, and the introduction of the gas to be measured into the gas introduction path 3 is started with the valve 16a of the switching means 16 closed. The measured gas is adjusted to a predetermined flow rate. Further, if necessary, the valve 16b of the switching means 16 is opened, and a purge gas, for example, purified helium is introduced from the purge gas introduction path 13 into each path in the system, or the gas to be measured is caused to flow through each path to purge each path. be able to.

The constant temperature bath 2 is cooled with the gas to be measured flowing through the vent path 14 and, for example, liquefied nitrogen is injected to -50
After cooling to a predetermined cooling temperature of the sampling pipe 1, the valves 15a, 16b, 17a and 18
b is closed, and the valves 16a, 17b and 18a are opened to introduce the gas to be measured from the gas introduction path 3 into the sampling pipe 1, and the moisture in the gas to be measured is adsorbed on the inner surface of the sampling pipe 1. Perform a moisture adsorption step. The gas to be measured exiting the sampling pipe 1 is supplied to the second exhaust path 1
0, exhausted through the flow controller 9. This moisture adsorption step is performed for a predetermined time according to the amount of moisture in the gas to be measured,
The measured gas amount is calculated based on the set flow rate of the flow controller 9 and the time.

When the moisture adsorption step is completed, the valve 16a is closed, the valve 15a is opened, and the gas to be measured from the gas introduction path 3 is discharged to the vent path 14. If necessary, the valve 16a is opened.
b is opened and a purge gas is passed through the sampling pipe 1 to purge the gas to be measured from inside the sampling pipe 1.
Subsequently, with the valves 16a and 16b closed, the switching means 1
8, the valve 18a is closed, the valve 18b is opened, and the third exhaust path 1
A preliminary evacuation process is performed in which the inside of the sampling pipe 1 is evacuated to an appropriate pressure by the rotary pump 7 via the pump 2. At this time, a rapid pressure change can be avoided by adjusting the exhaust amount by the flow control valve 11 including a needle valve or the like.

When the pressure in the sampling pipe 1 drops to an appropriate pressure, the valve 17b is closed, the valve 17a and the valves 19a and 19b of the switching means 19 are opened, and the gas in the sampling pipe 1 is supplied to the mass spectrometer by the turbo molecular pump 6. 5, for example, 0.05332 Pa (4 × 10
A main evacuation process is performed in which the evacuation is performed to about ⁻⁴ Torr) and the evacuation is performed from the first evacuation path 8. At this time, a flow control valve such as an orifice is used as the valve 19c.
It is preferable that the valve 19c is opened while the valve a is closed, and the valve 19a is opened after the degree of vacuum is increased.

When the inside of the sampling pipe 1 reaches a predetermined degree of vacuum, the valve 17a is closed, the constant temperature bath 2 is heated to a predetermined temperature, for example, about 120 ° C., and the two molecules adsorbed on the inner surface of the sampling pipe 1 A water desorption step of desorbing water after the layer is performed, and the desorbed water is sealed in the sampling pipe 1 between the switching means 16 and the switching means 17. At this time, the desorption of moisture can be performed only by heating operation, since the inside of the sampling pipe 1 is in a vacuum state, and can be performed in a short time.

Finally, the valves 19b and 19c are closed and the valve 19b is closed.
By opening the valve 17a with the a opened, the water sealed in the sampling pipe 1 is introduced into the mass spectrometer 5 which is in a standby state in advance, and the analysis process is performed, and the water content is measured. Is done. The amount of water (concentration) in the gas to be measured is calculated based on the measured amount of water and the amount of the gas to be measured flowing through the sampling pipe 1 in the moisture adsorption step. Thus, a clear peak can be obtained by introducing the desorbed water into the mass spectrometer 5 after sealing it in the sampling pipe 1.

The heating temperature and the cooling temperature can be arbitrarily set according to the type of the gas to be measured and the amount of water. Also, the purge gas has a strong adsorption property of the gas to be measured,
The main purpose is to introduce a purge gas into the sampling pipe 1 and discharge the gas to be measured from the sampling pipe 1 when it is difficult to evacuate the gas to be measured from the sampling pipe 1 easily. In the case where the adsorptivity is weak, or when there is no problem in the moisture measurement by the mass spectrometer 5 even when the gas to be measured remains in the sampling pipe 1, the purge gas introduction path 13 can be omitted.

Further, as described above, the vent path 14 is provided to continuously flow the gas to be measured in the path upstream of the sampling pipe 1, thereby purging the inside of the upstream path and retaining moisture. Can be prevented, and the analysis accuracy in the case of measuring a trace amount of water can be improved. However, this can be omitted depending on the amount of water to be measured. In addition, when an appropriate valve is used as each valve of the switching means 19 and the exhaust process of the sampling pipe 1 can be performed from the beginning in the first exhaust route 8, the third exhaust route 12 for performing the preliminary exhaust process can be omitted. it can. If these paths are omitted, the associated switching means is of course unnecessary.

In the above description, the procedure for once measuring the moisture content after sealing the desorbed moisture in the sampling pipe 1 has been described. However, the valve 17a and the valve 19a are kept open.
That is, the sampling pipe 1 is heated to a predetermined temperature while being evacuated through the analysis system path 4 to desorb water, and the desorbed water is introduced into the mass spectrometer 5 so that the water desorption step and the analysis step are performed. May be performed simultaneously.

As described above, the inside of the sampling pipe 1 is evacuated to a predetermined degree of vacuum and then heated to desorb moisture, compared to the case of heating at atmospheric pressure or a pressurized state to desorb moisture. As a result, the desorption rate of water can be increased, and the measurement time can be shortened. In addition, the mass spectrometer 5
Since gas (moisture) flows through the apparatus, components such as a conventional jet separator are not required, and the apparatus can be simplified and downsized. Further, depending on the properties of the gas to be measured and the amount of water to be measured, the purge gas can be omitted, so that the cost of the apparatus and the cost of operation can be reduced.

[0023]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In an apparatus having the structure shown in FIG.
2m long stainless steel 1/16 inch
Using piping, set the heating temperature to 150 ° C and the cooling temperature (
Ring temperature) at -50 ° C
2.666 Pa (2 × 10 ^-2Torr).
The gas to be measured must be an atmospheric pressure ionization mass spectrometer
Contains 10 ppb of moisture by measurement with a moisture meter calibrated in
Helium, and the flow rate is 500sccm (standard condition)
0.5L / min in conversion), supply pressure 58840Pa
(0.6kgf / cm²).

FIG. 2 shows the respective peak areas obtained from the mass spectrometer when the sampling time (moisture adsorption step time) is 2, 3, 4, and 5 minutes, and the adsorbed moisture at each sampling time. The relationship with the amount (theoretical value when the water concentration is assumed to be 10 ppb), that is, a calibration curve is shown. The total time required for evacuation was 2 minutes and 20 seconds.
The time required from water desorption to analysis was 3 minutes.

Here, the concentration of water in the gas to be measured [pp
b] can be represented by the following equation.

C = A × F / (rt / RT) A: Δ peak area of gas to be measured F: factor (gradient of calibration curve) r: gas flow rate [liter / min] t: sampling time [min] R: Gas constant T: Sampling temperature [K]

The flow rate of the gas to be measured is set to 0.5 L / m
When fixed to "in", the required sampling time when flowing the gas to be measured having a water concentration of 1 ppb is calculated by the above equation to be 4.2 minutes, which is within the condition range of the calibration curve shown in FIG. This indicates that an analysis sensitivity of 1 ppb has been achieved.

The lower limit of detection can be calculated from the number of moles adsorbed on a representative peak, which indicates S / N = 2. For example, FIG. 3 shows that the number of moles adsorbed is 8.9 × 10
The peak at ^-10 mol is shown, from which the lower limit of detection can be known by using the following formula. (2N / H) × M = MDL M: number of moles adsorbed MDL: lower limit of detection H: peak height N: noise width By substituting each numerical value, (2 × 0.3 × 10 ⁻¹¹ ) / (5. 7 × 10 ⁻¹¹ =
Since it is 9.4 × 10 ⁻¹¹ , the lower limit of detection is 9.4 × 10 ⁻¹¹ [mo
l].

[0029]

As described above, according to the present invention,
Since the sampling pipe is evacuated when the adsorbed water is desorbed and introduced into the mass spectrometer, the desorption speed is increased and the measurement time can be shortened. In addition, since a large-sized component such as a jet separator for increasing the differential pressure is not required, the size of the apparatus can be reduced.

[Brief description of the drawings]

FIG. 1 is a system diagram showing one embodiment of a device for measuring the concentration of water in a gas according to the present invention.

FIG. 2 is a diagram showing an example of a calibration curve.

FIG. 3 is a diagram showing an example of a peak.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Sampling piping, 2 ... Constant temperature chamber, 3 ... Gas introduction path to be measured, 4 ... Analysis path, 5 ... Mass spectrometer, 6 ... Turbo molecular pump, 7 ... Rotary pump, 8 ... First exhaust path,
9: flow controller, 10: second exhaust path, 11: flow control valve, 12: third exhaust path, 13: purge gas introduction path,
14 vent path, 15, 16, 17, 18, 19 switching means

Claims (2)

[Claims] 1. A method for measuring the concentration of water in a gas to be measured using the adsorption and desorption of water on the inner surface of a pipe, the method comprising desorbing and removing water after the second molecular layer adsorbed on a sampling pipe. A removing step, a moisture adsorption step of introducing a gas to be measured into the sampling pipe cooled to a predetermined temperature and adsorbing moisture in the gas to an inner surface of the sampling pipe, and evacuating the sampling pipe to remove the gas to be measured. An evacuation step of discharging, a moisture desorption step of heating the sampling pipe to a predetermined temperature to desorb water after the second molecular layer adsorbed on the inner surface of the pipe, and introducing the desorbed water into the mass spectrometer. A method for measuring the concentration of water in a gas, comprising: 2. An apparatus for measuring the water concentration in a gas to be measured by utilizing the adsorption and desorption of water on the inner surface of a pipe,
A sampling pipe for absorbing and desorbing moisture, a heating means for heating the sampling pipe to a predetermined temperature and a cooling means for cooling the sampling pipe to a predetermined temperature, a means for introducing a gas to be measured into the sampling pipe, and the sampling pipe being evacuated And a mass spectrometer for measuring the moisture in the gas derived from the sampling pipe.