JP2012154720A - Reference minute gas flow rate introduction device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a device for introducing gas with known minute flow rate in a vacuum container.SOLUTION: A device is constituted of: a micropore filter; a gas reservoir; a gas introduction system; a vacuum pump; a vacuum gauge; a valve; and pipe arrangement, and gas with known minute flow rate can be introduced in the vacuum container in almost all kinds of gas with one device by introducing the gas in a vacuum device while maintaining a condition under which flow of gas passing through the micropore filter satisfies a molecular flow condition by using the micropore filter of which the conductance of the molecular flow and the pressure to be the molecular flow are preliminarily calibrated, since relation between primary pressure and flow rate is linear, different flow rate can be easily generated, the gas with the known flow rate can be introduced even by using mixed gas, temperature dependence can be theoretically corrected, gas, such as water vapor and ethanol vapor with condensability, adsorptivity in which it is difficult to introduce the gas with the known flow rate can be also similarly introduced.

Description

  The present invention relates to an apparatus for introducing a gas having a known minute flow rate into a vacuum vessel.

Conventionally, when a gas having a known flow rate is introduced into a vacuum vessel (in this application, it is assumed that the pressure is 1 Pa or less), a mass flow controller has been used in many cases, but the lower limit that can be introduced is 10 ⁻³ Pa · m ^3. / S (0.1 sccm).
From this, when introducing a gas with a low flow rate, a standard capillary or a standard leak has been used. However, in the case of a standard capillary, the gas flow becomes an intermediate flow in the middle, and the characteristics become complicated. ) It is difficult to correct the flow rate when the gas type changes, (2) The relationship between the primary pressure and the introduction flow rate is nonlinear, (3) The flow rate characteristics in the case of mixed gas are unknown, (4) Temperature dependence is an empirical rule There was a problem of being based.
On the other hand, when standard leaks are used, there is a problem that the number of standard leaks to be introduced has to be purchased, resulting in high costs. Furthermore, until now, it has been difficult to introduce a gas having a known flow rate with respect to a condensable and adsorptive gas such as water vapor or ethanol vapor.
In addition, the present inventors have previously filed an application for a calibration method and a calibration apparatus (Patent Document 1) for a standard mixed gas leak microporous filter.

Japanese Patent Application No. 2009-197894

C. D. Ehrlich, J .; A. Basford, “J. Vac. ScI. Techno!” A10 (1), p1-17, “Recommended practices for the calibration and use of leaks”.

Micropores calibrated with the calibration method and calibration apparatus (see Patent Document 1) of the standard mixed gas leak micropore filter previously filed by the present inventors for the above-mentioned problems when using a conventional standard capillary or standard leak A gas having a known minute flow rate in a vacuum vessel (1 Pa or less) using the micropore filter, which aims to solve the problem by using a gas introducing device using a filter, and the flowing gas is a molecular flow. It is in providing the apparatus for introduce | transducing.
By using this device, it is easy to correct the flow rate when the gas type is changed. Therefore, with a single device of the present invention, a known minute flow rate gas of almost any gas type can be introduced into the vacuum vessel. Since the relationship between the pressure and the flow rate is linear, different known flow rates can be easily introduced by changing the primary pressure, and each gas of the mixed gas can be handled independently. Gas can be introduced, and temperature correction of the introduced flow rate can be performed based on gas molecular kinetics.

Reference micro gas flow introduction device of the present invention, microporous filter, gas reservoir, a gas introduction system, the vacuum pump, the pressure P _R for measuring gauge in the gas reservoir is constituted by a valve and piping, vacuum container (1 Pa to be introducing a gas Connect to: The micropore filter previously calibrates the pressure at which the molecular flow is realized and the conductance of the molecular flow with a certain gas type (N ₂ or the like) (see Patent Document 1). When a mixed gas is used, it is necessary to use a positive displacement vacuum pump that does not depend on the gas type in the exhaust characteristics. A vacuum gauge that does not depend on the gas type, such as a diaphragm vacuum gauge, or that that is calibrated with respect to the introduced gas type is used.

A method for introducing a reference minute gas flow rate will be described. An arbitrary gas is introduced into the gas reservoir. Next, the pressure in the gas reservoir is adjusted to be equal to or lower than the pressure (for example, 10 kPa) at which the gas passing through the microporous filter realizes a molecular flow. At this time, through the microporous filter, the gas flow rate Q which is introduced into the vacuum _{vessel, Q = P R · C α} · (M α / M) becomes ^{_{1/2 · (T 0 / T)}} 1/2 . Here, P _R is the molecular weight of the conductance, M _alpha gas species alpha pressures, C _alpha gas species micropore filter calibrated alpha of the gas reservoir, M is the molecular weight of any gas to be introduced, T ₀ is C _alpha Is a temperature when calibrating, and T is a temperature when introducing an arbitrary gas.
When a mixed gas is introduced, the mixing ratio or concentration of the mixed gas needs to be known. In this case, the partial pressure P _Ri of gas species i in the gas reservoir is so represented by the product of the total pressure P _R and concentration, by using the partial pressure P _Ri of gas species i in the gas reservoir instead of P _R The flow rate Q _i of the gas species i introduced into the vacuum vessel can be obtained.
The gas to be introduced may be a substance that is liquid at atmospheric pressure, such as water or ethanol. In this case, the container filled with the liquid is connected to the gas reservoir, and after evacuating for a certain time with the vacuum pump, the valve before the vacuum pump is completely sealed. Thus, the pressure P _R in the gas reservoir is equal to the vapor pressure of the liquid, as well as other gases can introduce gas into the vacuum chamber.

  By using the reference minute gas flow rate introduction device of the present invention, it is possible to introduce almost all kinds of gases having known minute flow rates into the vacuum vessel with one device of the present invention and to change the primary pressure. , Different known flow rates can be easily introduced, and even with mixed gas, known flow rates can be introduced, the temperature dependence of the introduced flow rate can be theoretically corrected, and condensability / adsorption properties It was realized that gases such as water vapor and ethanol vapor could be introduced as well.

FIG. 1 is an explanatory view showing an embodiment of a reference minute gas flow rate introducing device of the present invention. FIG. 2 is a schematic view of an apparatus for calibrating a microporous filter previously filed by the present inventors.

FIG. 1 shows an apparatus, which is an embodiment of the reference micro gas introduction apparatus of the present invention, connected to a vacuum vessel into which gas is to be introduced. As shown, apparatus, microporous filter, gas reservoir, a gas introduction system, the vacuum pump, the pressure P _R for measuring gauge in the gas reservoir, and a valve and piping. The micropore filter calibrates the pressure realized by the molecular flow and the conductance of the molecular flow in advance. Here, it is assumed that the molecular flow conductance for a certain gas species α is C _α .
At this time, an arbitrary gas (molecular weight M) is introduced into the vacuum vessel at a fixed flow rate Q according to the following procedure.
1) An arbitrary gas is introduced into the gas reservoir.
2) Reduce the pressure in the gas reservoir to a pressure range where molecular flow is achieved.
3) At this time, the introduced gas flow rate Q is expressed by the following equation.

Here, the temperature at P _R is the pressure in the gas reservoir was measured by the gauge, T ₀ is the temperature at which the C _alpha is calibrated, T is the introduction of any gas.

The reference minute gas flow rate introduction apparatus of the present invention uses the apparatus of the present invention as shown in FIG. 1 as an embodiment, connected to a vacuum vessel into which gas is to be introduced. As shown, apparatus, microporous filter, gas reservoir, a gas introduction system, the vacuum pump, the pressure P _R for measuring gauge in the gas reservoir, and a valve and piping. The micropore filter calibrates the pressure realized by the molecular flow and the value of the molecular flow conductance in advance.
Here, as an example, when the gas flowing micropore filter is 10kPa or less, and becomes molecular flow, molecular flow conductance _{C N2} of _{N 2} is assumed to be ^{1 × 10 -9 m 3 / s} .

(1) Pure gas introduction method Arbitrary gas is introduced into the gas reservoir. Next, the pressure in the gas reservoir is adjusted to be equal to or lower than the pressure at which the gas passing through the microporous filter realizes the molecular flow (here, 10 kPa or lower). At this time, the gas flow rate Q introduced into the vacuum vessel through the micropore filter is expressed by the following equation based on the gas molecule kinetic theory.

Here, P _R is the pressure of the gas reservoir, M _N2 molecular weight of N _2, M is the molecular weight of any gas to be introduced, T ₀ is the temperature as measured, calibrated C _N2, T introduces any gas Is the temperature of the hour. For example, sealed Ar gas (molecular weight 40) to the pressure _{P R} of the gas reservoir, when kept at 10 kPa, Ar gas flow rate _{Q Ar} is introduced into the vacuum vessel,

Thus, a much lower flow rate gas can be introduced into the vacuum vessel than the mass flow controller. A lower flow rate can be easily generated by lowering the pressure of the gas reservoir. Even if the gas type is changed, a known minute flow rate can be similarly introduced.

(2) To introduce the method mixed gas of the mixed gas, the flow rate Q _i of the gas species i introduced into the vacuum vessel, instead of P _R, and the partial pressure P _Ri of gas species i in the gas reservoir Thus, similarly, it can be obtained using equation (1). For example, when a mixed gas of 95% nitrogen and 5% hydrogen is introduced to the gas reservoir up to 10 kPa, the partial pressures P _R-N2 and P _R-H2 in the gas reservoir are 10 kPa × 0.95, 10 kPa × 0. .05, the gas flow rates Q _N2 and Q _H2 are as follows.

(3) Method of introducing substances that are liquid in the atmosphere, such as water and ethanol, but become gas when the pressure is reduced Connect the container filled with the liquid to the gas reservoir, evacuate for a certain time with the vacuum pump, Seal the valve. Accordingly, the pressure P _R in the gas reservoir is equal to the vapor pressure of the liquid. The gas flow rate of the introduced gas can be calculated in the same manner by the above equation (1).
FIG. 3 shows the gas flow rate when water vapor is introduced. Since the vapor pressure of water is 2784 Pa at 23 ° C., the flow rate Q _H2O of the introduced water vapor is as follows.

FIG. 2 is a diagram for explaining a calibration device and a calibration method for a micropore filter calibrated in advance used in the present invention, and shows the calibration device. The calibration device of FIG. 2 is the same as the device of Patent Document 1 previously filed by the present inventors, and a standard mixed gas and pure gas introduction system, a positive displacement vacuum pump upstream of the microporous filter. vacuum pump etc., arranged vacuum gauge diaphragm gauge or the like of the upstream pressure P _u measurement, downstream of the micropore filter, a vacuum vessel is arranged, the vacuum in the chamber high vacuum pump for evacuation, downstream pressure P _d measuring total pressure vacuum gauge, the microporous filter calibration apparatus connected downstream pressure P _d for measuring partial pressure vacuum gauge, through a micropore filter, upon introduction of the gas into the vacuum vessel, the pressure inside the vacuum chamber In order to calibrate whether or not molecular flow is realized with a micropore filter by selecting the pumping speed of the high vacuum pump so that it is within the operating pressure range of the total pressure vacuum gauge and partial pressure vacuum gauge is there.

In the method of calibrating the micropore filter using the calibration device of FIG. 2, as described in Patent Document 1 above, (1) a pure gas is introduced upstream of the micropore filter and a vacuum disposed downstream. when evacuated at the vessel discharge rate C _P at the high vacuum pump, the upstream pressure P _u in a vacuum gauge such as diaphragm gauge to measure the downstream pressure P _d at full pressure vacuum gauge, wherein C _{F =} C _{P P d} / P _u is used to obtain C _F while changing the upstream pressure P _u , the pressure region where C _F is constant is calibrated as the region where the molecular flow is realized, and further, the gas type is changed to change C _F , And calibrate that the molecular flow is realized by the ratio being the 1/2 power of the mass number of the gas. (2) Introduce the standard mixed gas upstream of the micropore filter and downstream in the exhaust speed C _Pi of the gas species i and arranged vacuum chamber at a high vacuum pump When you care, the total pressure P _u of the upstream measured with a vacuum gauge, such as a diaphragm gauge, while changing the total pressure P _u upstream to measure the partial pressure P _di downstream of the gas species i in minutes, pressure vacuum gauge, The pressure region where the P _di / P _u ratio is constant is calibrated as the region where the molecular flow is realized, and the value of C _Pi · P _{di and} the value of C _Fi · P _u · m _i (here in, C _Fi conductance microporous filter of the gas species i, m _i is the concentration of a gas species i in a standard mixed gas), the pressure range to which both are equal by comparing the molecular flow is achieved (3) When the standard mixed gas is introduced upstream of the microporous filter and the vacuum vessel disposed downstream is exhausted at the exhaust speed _CPi by the high vacuum pump, the upstream total pressure P _u It was measured with a vacuum gauge such as diaphragm gauge, while changing the total pressure P _u in the upstream The total pressure _{P d} of the flow was measured in all pressure vacuum _gauge, C Fi of _· P u _{· m i} values _{(here, C Fi} conductance microporous filter of the gas species i, _{m i} is a gas at standard mixed gas is the concentration of species i), the calculated, the value obtained by dividing this calculated value the more C _Pi all sums are calculated for gas species i, the sum value is, downstream of which was measured at every pressure vacuum gauge The above three calibration methods can be considered in which the pressure range equal to the total pressure _Pd is calibrated as the pressure range in which the molecular flow is realized.
The reference micro gas flow rate introducing device of the present invention is characterized by using a micropore filter that has been calibrated in advance to realize a molecular flow by any of the calibration methods described above.

Claims (3)

(1) introducing a pure gas into the microporous filter upstream, when a vacuum vessel which is located downstream to the exhaust the exhaust rate C _P at the high vacuum pump, the upstream pressure P _u in the gauge, the downstream pressure P _d total Measured with a pressure gauge, and using the formula C _F = C _P P _d / P _u , C _F is obtained while changing the upstream pressure P _u , and the molecular flow realizes the pressure region where C _F is constant. Calibration method for calibrating that the molecular flow is realized by calibrating as a region in which the gas flow is changed, measuring _CF by changing the gas type, and the ratio being the 1/2 power of the mass number of the gas Or (2) When the standard mixed gas is introduced upstream of the micropore filter and the vacuum vessel disposed downstream is exhausted by the high vacuum pump at the exhaust speed _CPi of the gas species i, the upstream total pressure _Pu is measured with a vacuum gauge, the partial pressure of the downstream gas species i while changing the total pressure P _u in the upstream P The _i was measured in minutes pressure vacuum _gauge, a pressure region P di / _{P u} ratio becomes constant, calibrated as a region molecular flow is realized, _further, the value of _{C Pi · P di, C Fi} · P u of _· m _i values and (where, C _Fi conductance microporous filter of the gas species i, m _i is the concentration of a gas species i in the standard gas mixture), is equal both to compare Calibration method that calibrates the pressure range as the pressure range realized by the molecular flow, or (3) A standard mixed gas is introduced upstream of the microporous filter, and the vacuum vessel placed downstream is evacuated with a high vacuum pump When exhausted at the speed C _Pi , the upstream total pressure P _u is measured with a vacuum gauge, the downstream total pressure P _d is measured with a total pressure vacuum gauge while changing the upstream total pressure P _u , and C _Fi · P _u · _{m i} values _{(here, C Fi} Koh microporous filter gas species i Inductance, m _i is the concentration of a gas species i in a standard mixed gas), the calculated, a value obtained by dividing this calculated value further C _Pi sums asking for all gas species i, is the sum value , by the calibration method of calibrating a pressure range which is equal to the total pressure P _d of the downstream were measured in all pressure vacuum gauge as a pressure range in which molecular flow is realized, the calibration that molecular flow can be achieved by pre micropore filter A reference micro gas flow rate introduction device using a microporous filter,
A device comprising the micropore filter, a gas reservoir, a gas introduction system, a vacuum pump, and a vacuum gauge, and using the micropore filter in which the conductance of the molecular flow and the pressure to become the molecular flow are calibrated in advance, By introducing the gas into the vacuum apparatus while maintaining the condition that the gas flow through the molecular flow condition is satisfied, the gas having a known minute flow rate can be evacuated in almost all kinds of gas by one apparatus of the present invention. Since the relationship between the primary pressure and the flow rate can be introduced into the container and the relationship between the primary pressure and the flow rate is linear, it is possible to easily generate different flow rates. Gas that could not be introduced with known flow rates, such as water vapor and ethanol vapor, that can be corrected automatically and that is condensable and adsorbable Kill, reference micro gas flow introduction device, characterized in that. Using a gas species α having a molecular weight M _α and introducing a molecular flow conductance of the calibrated microporous filter C _α , a gas reservoir pressure P _R , and a molecular weight of the pure gas β to be introduced M _{β at} a temperature T _0. when the temperature at the time is T, the flow rate Q _beta pure gas beta _introduced, at _{P R · C α · (M} α / M β) 1/2 · (T 0 / T) 1/2, expressed The reference minute gas flow rate introduction device according to claim 1. Use gas species alpha molecular weight M _alpha, at a temperature T _0, the calibrated molecular flow conductance of the microporous filter was C _alpha, the pressure of the gas reservoir P _R, the concentration of gaseous species β in the mixed gas to be introduced m _beta, a molecular weight M _beta, when the temperature at the introduction is T, the flow rate Q _beta gas species beta in the mixed gas _{introduced, P R · m β · C} α · (M α / M The reference minute gas flow rate introduction device according to claim 1, wherein _β ) ^1/2 · (T ₀ / T) ^1/2 .