JPH05142202A - Method and apparatus for analyzing gas - Google Patents

Abstract

PURPOSE:To obtain a method and an apparatus for analyzing a minute amount of gaseous-phase moisture contained in monosilane gas. CONSTITUTION:A gas pipe for introducing monosilane gas and a pipe for introducing the gas containing the constant concentration of gaseous-phase moisture are connected. The two kinds of the gases are mixed and introduced into an analyzer 15. In the introducing pipe of the monosilane gas 1, the part, wherein a moisture removing means such as adsorbent 6 is provided, and a bypass pipe 7, which does not pass the moisture removing means, are provided. When a calibration curve is measured, the monosilane gas 1 is supplied through the moisture removing means. When an atmospheric-pressure ionization mass spectrometer 15 is used, the cluster ions of monosilane water (the raio between the mass number and the electric charge is 49 and the like) is used for the reference of the calibration curve. Therefore, when the atmospheric-pressure ionization mass spectrometer is used, the concentration of the gaseous phase moisture can be analyzed quickly and highly sensitively.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a purity analysis of monosilane gas which is indispensable as a silicon semiconductor device material, and in particular, provides an analysis method of a trace amount of gas phase water contained in monosilane gas.

[0002]

2. Description of the Related Art Gases such as nitrogen and argon that are used as a carrier gas for purging manufacturing equipment or as a material gas component are gas phase ionization mass spectrometers and trace amounts of water at controlled concentrations. By combining with a water generating means to be generated inside, it is possible to quantify a minute amount of gas phase water up to 1 ppb or less. In this regard, the Proceedings of Microcontamination Conference and Exposition, 1991, pp. 168-180 (Proc. Of mic
rocontamination Conf. & Expo. 1991, pp.168-180).

[0003]

In the above-mentioned conventional examples, the mass spectrum of monosilane gas is not known, and the ion serving as the reference of the calibration curve of the vapor phase water concentration has not been determined. Therefore, naturally, there was no measurement example of the calibration curve. Also, the monosilane gas simultaneously generates a solid reaction product when it is ionized by corona discharge in the ion source of the atmospheric pressure ionization mass spectrometer. When this is deposited inside the ion source, the discharge becomes unstable, and there is a problem that continuous measurement for a long time is difficult. Further, when measuring the calibration curve, it is necessary to mix a small amount of vapor-phase water, the concentration of which has been determined, into the monosilane gas. However, in the above conventional moisture generation technology, since the sump is installed in the gas stream, monosilane reacts with the water in the sump, which is not only dangerous but also difficult to generate accurate moisture. There was a problem that there was.

[0004]

The inventor has found that when an atmospheric pressure ionization mass spectrometer is used, cluster ions of monosilane and water are detected and the ionic strength thereof is determined by the water concentration in the monosilane gas. It was The above problem can be solved by using this ion as the reference ion of the calibration curve of the vapor phase water concentration. Further, when measuring a calibration curve, a gas that does not react with water is used as a carrier gas, and gas phase water is contained by flowing it through a water generating means, and the gas is mixed with monosilane gas, so that the monosilane gas is directly supplied. You don't have to touch the sump. Therefore, a small amount of vapor phase water can be added to the monosilane gas stably and accurately. In addition, since the monosilane gas is diluted with the carrier gas, the deposition of reaction products in the ion source is reduced, and the stable measurable time can be extended.

[0005]

According to the present invention, the vapor phase water content contained in monosilane gas is analyzed as follows. Below, <A +>
Promises to represent the positive ion of the atom A.
Pass the monosilane gas through a means to remove water,
Remove contained gas phase water. Then, the monosilane gas from which the water was removed was mixed with a gas containing a certain concentration of water in the gas phase and introduced into the atmospheric pressure ionization mass spectrometer,
Measure the mass spectrum. The inventors have found that when hydrogen gas is used as the gas containing vapor phase water, <SiH ₃ H ₂ O +
>, <SiH ₃ (H ₂ O) ₂ +> was found. These ions are cluster ions of monosilane and water. In particular, since <SiH ₃ H ₂ O +> has a structure containing one molecule of water, it is theoretically expected that its strength will increase in proportion to the vapor phase water concentration.
As shown in, the proportional relationship was confirmed experimentally. <S
Not only iH ₃ H ₂ O +>, but the cluster ion intensities of monosilane and water change in correlation with the gas-phase water concentration, so that they can be used as reference ions for the calibration curve.

At the time of preparing a calibration curve, a carrier gas that does not react with water is introduced into the water generating means, and a small amount of vapor phase water is mixed, and then mixed with monosilane gas. This method avoids the problem of water and monosilane reacting in the water generator to generate silicon dioxide. Furthermore, since the atmospheric pressure ionization mass spectrometer has high sensitivity, trace impurities can be detected even when diluted, and rapid analysis is possible, so the amount of monosilane gas used is small and economical. Is. Hereinafter, the analysis method will be specifically described in Examples.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described with reference to FIG.
The monosilane gas 1 to be analyzed is taken out from the cylinder 2, and the pressure is adjusted by the pressure regulator 3 to the flow controller 4
After the flow rate is adjusted by, the flow path switching valve 5 allows the adsorbent 6 to flow through either the pipe or the bypass pipe 7. On the other hand, gas 1 containing a certain concentration of vapor phase water
3 is prepared by using the gas 11 obtained by purifying the unpurified diluting gas 8 with the purifier 9, adjusting the flow rate with the flow rate controller 10, and then allowing the water to pass through the water generator 12. The gas 1 and the gas 13 are mixed to form a mixed gas 14, which is introduced into the analyzer 15. The gas that has passed through the analyzer 15 is exhausted (exhaust gas 16).

As the moisture generator 12, for example, the device shown in the conventional example (FIG. 4) can be used. The temperature from the moisture generator 12 to the analyzer 15 is maintained at about 120 ° C. to 150 ° C. by the temperature maintaining means 17 such as a heater. This is to prevent the deterioration of the accuracy of the vapor phase moisture concentration due to the vapor phase moisture being adsorbed on the inner surface of the pipe.

According to this example, the gas phase water concentration in monosilane is analyzed as follows.

The flow path switching valve 5 is adjusted to allow the monosilane gas 1 (flow rate L ₁ ) to flow through the pipe passing through the adsorbent 6. The adsorbent 6 reduces the vapor phase water content contained in the monosilane gas. A gas (flow rate L ₂ ) containing a constant concentration of vapor-phase water is mixed with this gas in the water generator 12 and measured by the analyzer 15. When an atmospheric pressure ionization mass spectrometer is used as the analyzer and hydrogen gas is used as the gas containing water, the water concentration and m / z (mass number) can be measured by changing the water concentration by adjusting the water generator 12. And the ion intensity of the charge ratio) 49 has a proportional relationship as shown in FIG. The inventor says that this ion is SiH
It was confirmed to be a cluster ion of monosilane and water having a structure of ₃ H ₂ O +. Since it has an ionic structure containing one water molecule, it is theoretically expected that it will be a linear function of the gas phase water concentration. Experimentally, a linear relationship was established at a gas phase water concentration of about 200 ppb or less. Therefore, in this vapor-phase moisture concentration region, analysis can be performed by using FIG. 2 as a calibration curve of vapor-phase moisture.

The quantification of the vapor phase water content contained in the original monosilane gas 1 is carried out as follows. Adjust the flow path switching valve 5 so that monosilane gas 1 is bypassed 7
To flow. In the moisture generator 12, the generation of moisture is stopped, and the purified gas 11 is adjusted to flow out as it is to become the gas 13. The flow rates of gas 1 and gas 13 are kept at L ₁ and L ₂ . M / z4 observed at this time
When the ionic strength of 9 is I shown in FIG. 2, the gas phase water concentration obtained from the calibration curve is C. To convert this to the vapor phase water concentration C ₀ contained in the original monosilane gas 1, it is sufficient to set C ₀ = C × (L ₁ + L ₂ ) / L ₁ .

The ionic strength I at a water concentration of 0 in FIG.
B is water adsorbed on the inner surface of the gas pipe of this experimental device,
This is the background caused by the vapor-phase moisture contained in the gas 11, the vapor-phase moisture remaining without being removed by the adsorbent 6, and the like. The background concentration is determined by the absolute value CB of the water concentration indicated by the point where the straight line in FIG. 2 intersects the water concentration axis. Since the background is almost constant when the flow rate is kept constant, this background concentration determines the lower limit of detection (Climit) of the water concentration in the original monosilane gas. It is Climit = CB × (L ₁ + L ₂ ) / L ₁
Becomes Background moisture must be lowered to lower the lower limit of detection. For this reason, it is important to use a welded structure in which a stainless steel pipe having an inner surface electropolished is used as the pipe and the joint valve and the like are eliminated as much as possible.

FIG. 3 shows another embodiment of the present invention.

When the gas phase moisture concentration contained in the monosilane gas 1 is high beyond the linear region shown in FIG. 2, the purified gas 11 is branched through the purifier 9 as shown in FIG. A method of diluting the gas 1 by mixing the gas 1 with the gas 1 on the upstream side of the flow path switching valve 5 after controlling the flow rate by the flow rate controller 19 is effective. The sum of the gas 1 (flow rate L ₁₁ ) and the gas 18 (flow rate L ₁₂ ) is set to be the flow rate L ₁ , and the gas is passed through the adsorbent 6. Then, as in the case of Example 1, the gas 13 containing a constant concentration of vapor-phase water is used.
Mix with (flow rate L ₂ ) and measure the calibration curve. Next, the mixed gas of the gas 1 and the gas 18 is caused to flow through the bypass pipe 7, and the moisture generation device 12 is made to stop the moisture generation, and the vapor phase moisture concentration is measured. It is assumed that the gas phase moisture concentration in the mixed gas of the gas 1 and the gas 18 measured at this time is C ₂ . Since this C ₂ contains the vapor phase water content contained in the gas 18, it must be corrected.
Therefore, the gas 1 is stopped and the gas 18 alone is used as the flow rate L ₁ (that is, L ₁₁ = 0, L ₁₂ = L ₁ ) to measure the calibration curve, and then the gas phase water concentration is analyzed. In this case, for example, when the gas 18 is hydrogen, it is known in the atmospheric pressure ionization mass spectrometer that m / z 19 or <H ₃ O +> is an ion that increases in proportion to the gas phase water concentration. This is used as the reference ion of the calibration curve. When the gas phase water concentration of the gas 18 alone is C ₃ , the gas phase water concentration C of the original monosilane gas 1 is C = (L ₁ × C ₂ −L ₁₂ × C
₃ ) / L ₁₁ can also be stopped.

[0015]

EFFECTS OF THE INVENTION According to the present invention, there is a great effect that a trace amount of gas phase water, which is an impurity, can be measured for monosilane gas, which is important as a material gas for semiconductors. Also,
Since rapid analysis can be performed by the atmospheric pressure ionization mass spectrometer, the amount of monosilane gas used is small, which is economical.

[Brief description of drawings]

FIG. 1 is a device configuration diagram showing an embodiment of the present invention.

FIG. 2 is a diagram showing an example of a calibration curve of vapor phase moisture in a gas containing monosilane gas.

FIG. 3 is a device configuration diagram showing another embodiment of the present invention.

FIG. 4 is a device configuration diagram showing a conventional example.

[Explanation of Codes] 1 ... Monosilane gas, 2 ... Cylinder, 3 ... Pressure regulator,
4, 10, 19 ... Flow rate controller, 5 ... Flow path switching means, 6 ... Adsorbent, 7 ... Bypass pipe, 8 ... Unpurified dilution gas, 9 ... Purifier, 11 ... Purified gas, 12 ...
Moisture generator, 13 ... Gas containing a constant concentration of vapor phase moisture, 1
4 ... Mixed gas of gas 1 and gas 13, 15 ... Analyzer, 16
... Exhaust gas, 17 ... Temperature maintaining means, 18 ... Gas branched from gas 11.

Claims (5)

[Claims] 1. An apparatus comprising an ion source for generating ions, a mass spectrometer for separating the ions by mass and individually measuring the intensities, a monosilane gas and a means for supplying the monosilane gas, which are contained in the monosilane gas. A gas analyzer characterized by quantifying a small amount of gas phase water content from the intensity of water and cluster ions of monosilane observed by a mass spectrometer. 2. The monosilane gas supply means of the gas analyzer comprises two gas flow paths which are switched by a flow path switching means, and one of which is provided with a vapor phase water removing means. Item 1. The gas analyzer according to item 1. 3. Immediately before the ion source of the gas analyzer, a means for introducing a gas containing a constant concentration of vapor-phase moisture supplied from a means for generating moisture in the vapor phase is added. 1. The gas analyzer according to 1. 4. The gas analyzer according to claim 1, wherein a means for introducing a gas from which vapor-phase water has been removed is added upstream of the flow path switching means according to claim 2. 5. The gas analyzer according to claim 1, wherein the gas containing vapor-phase moisture according to claim 3 and the gas from which vapor-phase moisture is removed according to claim 4 are particularly hydrogen gas. ..