JPH047558Y2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] This invention relates to an analysis device that analyzes impurities in gas using a mass spectrometer.

[Conventional technology]

Analyzers that use mass spectrometers to analyze impurities in gas include devices that directly introduce sample gas into the analysis chamber and measure the partial pressure of impurities to analyze impurities, and mass spectrometers and gas chromatographs. There is a device (hereinafter referred to as "GCMS") that combines this and analyzes impurities using the separation and concentration effects of a gas chromatography column.

The former is further divided into those that combine a turbomolecular pump and an oil rotary pump, and those that combine an oil diffusion pump and an oil rotary pump, depending on the vacuum evacuation system of the analysis room. ^{According to}
It is not possible to completely exhaust the degassing from the components of the analysis chamber, and the degassing components H ₂ , O ₂ ,
_N2 , CO, CO2 _, etc. remain. Therefore, during sample gas analysis, the above-mentioned H ₂ , O ₂ , N ₂ , CO, CO ₂ , etc. are present as a background in the analysis chamber, and the impurity components to be measured in the sample gas are When detecting a component of the same type as a ground component, the impurity component must have a concentration that has a partial pressure greater than the background partial pressure, so the minimum analysis concentration is limited to several ppm.

On the other hand, even with GCMS, which is generally said to have a lower minimum analysis concentration (higher analysis accuracy) than the former, it is not possible to completely prevent leaks from gas chromatography columns and degassing from column members and packing materials. When analyzing certain O ₂ , N _2, etc., it is impossible to perform accurate analysis for concentrations below 0.1 ppm, and quantification on the ppm order or lower requires several tens to several digits.
Since it is estimated and quantified from a calibration curve prepared on the order of 100 ppm, there are limitations such as poor reliability.

[Problem that the invention attempts to solve]

On the other hand, in recent years, gases used in the semiconductor industry, such as H ₂ gas, have a purity of 6 nines (purity
99.9999%), 7 nines, and even 8 nines are now required.
In order to meet this demand, impurity components in the gas are
There is now a need for an analytical device that can detect individual substances down to a level of 1 ppb, and that can also analyze all impurity components.

However, conventional analytical devices, such as devices that directly introduce sample gas into the analysis chamber, use a combination of an oil diffusion pump and an oil rotary pump to evacuate the analysis chamber, or a combination of a turbomolecular pump and an oil rotary pump. In either type of evacuation, as mentioned above, the degree of vacuum in the analysis chamber is limited to 10 ^-8 to _{10 -9} Torr.
The minimum analytical concentration of impurities is limited to ppm order. In addition, in GCMS, as already mentioned, there are limits to preventing leaks and degassing in gas chromatography columns, etc., and calibration curves on the ppm order or lower are based on estimation, so it is not possible to accurately measure ppb orders. It is difficult to give analytical values.

As described above, none of the conventional analyzers can accurately analyze impurities in a sample gas on the order of ppb, and cannot fully meet the above-mentioned demands of the industrial world.

This idea was made in view of these circumstances, and the impurity components in the gas were individually reduced to 1 ppb.
The purpose of the present invention is to provide an analyzer that can detect up to the level of impurities and analyze all impurity components.

[Means for solving problems]

In order to achieve the above object, the gas impurity analyzer of this invention has an oil-less turbo molecule that connects the exhaust part of the analysis chamber to which the analysis tube of the mass spectrometer is connected and the intake part of the oil rotary pump. An oil-less pump such as a soap pump or diaphragm pump is connected by a flow path that includes a pump, a gate bubble, a cooling trap, and an oil diffusion pump in this order.
It is connected to the above flow path by a branch flow path equipped with a switching means, and is configured such that the degree of vacuum in the analysis chamber can be set to 10 ^-11 Torr or less.

Next, this invention will be explained in detail based on examples.

FIG. 1 shows the configuration of an embodiment of this invention. 1 is the analysis room, where the minimum detectable partial pressure is 10 ^-13 to 10 ^-14
An analysis tube 2 of a mass spectrometer (not shown) having a resolution of approximately M/ΔM=2000 and a nude gauge 3 of an ionization vacuum gauge are connected. The analysis chamber 1 is covered with a casing 4, and liquid nitrogen is introduced into the space between the casing 4 and the analysis chamber 1. This is provided to cool the inside of the analysis chamber 1 to an ultra-low temperature with liquid nitrogen and to achieve a high vacuum state that cannot be achieved at room temperature. Reference numeral 5 denotes a baking heater, which heats the analysis chamber 1 before introducing liquid nitrogen into the casing 4 and expels occluded gas such as O ₂ stored in the constituent members of the analysis chamber. It acts to increase the degree of vacuum. The exhaust port 6 of the analysis chamber 1 is connected to the intake port 8 of the oilless turbo molecular pump 7,
The exhaust port 9 of this oil-less turbomolecular pump 7 is connected to the inlet port 13 of the oil diffusion pump 12 via a flow path A equipped with a gate valve 10 and a cooling trap 11 to prevent back diffusion of oil. .
The oil diffusion pump 12 is used to efficiently exhaust H ₂ in view of the fact that in a vacuum of 10 ⁻⁸ Torr or less, most of the residual gas in the analysis chamber 1 becomes H ₂ . A Pirani vacuum gauge 17 and a stop valve 18 are provided in a flow path B extending from the exhaust port 14 of the oil diffusion pump 12 to the oil rotary pump 15.
19 is a leak valve; a leak passage C extends from passage A connecting gate valve 10 and cooling trap 11;
It is opened when the vacuum state of the oil diffusion pump 12 is released. The leak path C is connected to an inert gas cylinder (not shown), and when the leak valve 19 is opened, Ar
An inert gas such as N ₂ flows into the oil diffusion pump 12 so that the vacuum state can be released without causing deterioration due to oxidation of the oil, contamination of moisture, etc.

A leak passage D extends from the passage connecting the stop valve 18 and the oil rotary pump 15 and is open to the air. When the leak valve 20 is opened, air flows into the oil rotary pump 15 and the vacuum state is released.

A stop valve 2 is provided in the flow path connecting the exhaust port 9 of the oilless turbo molecular pump 7 and the gate valve 10.
2. A soap pump 21 is connected via a branch channel E equipped with a Pirani vacuum gauge 16;
Analysis room 1 and oil-less turbo molecular pump 7
Used for roughing. On the other hand, an inlet 23 for introducing sample gas into the analysis chamber 1 is connected to the analysis chamber 1 through a flow path F that includes a stop valve 24, a filter 25, a variable leak valve 26, and a gate valve 27 in this order. . This flow path F includes branch flow paths G and H, and the flow path G
high purity for purging via stop valve 28
It is connected to the Ar inlet 29. The flow path H has a purge valve 30, and the purge valve 30
When opened, it becomes an exhaust port.

In this configuration, the sample gas is, for example,
When N ₂ gas is introduced and its impurity components are analyzed, the following operation is performed. In this case, in order to make it easier to understand, the following three operations will be performed: (a) adjusting the degree of vacuum, (b) creating a calibration curve, and (c) analyzing the sample gas.
I will explain it in stages.

(a) Adjustment of the degree of vacuum First, the stop valve 28 is opened, and the high purity Ar for purging is sufficiently flowed to purge the entire channel, and then the stop valve 28 is closed. At this time, the bake heater 5 is turned on to heat the inside of the analysis chamber 1 so that the occluded gas stored in the members constituting the analysis chamber is expelled during the next evacuation.

Next, evacuation consisting of rough evacuation and main evacuation is performed to bring the inside of the analysis chamber 1 into a high vacuum state. The rough evacuation is performed using the flow path E by opening the stop valve 22 and operating the soap pump 21 with the gate valve 10 closed. When the Pirani vacuum gauge 16 reaches about 1 Torr, the oilless turbo molecular pump 7 is started and waits until the rotation speed reaches a sufficient number. Meanwhile, cooling trap 11,
The exhaust line of the oil-less turbo molecular pump 7 consisting of the oil diffusion pump 12 and the oil rotary pump 15 is prepared for operation. First, fill the cooling trap 11 with liquid nitrogen, open the stop valve 18, and oil rotary pump 1.
Activate 5. When the Pirani vacuum gauge 17 reaches approximately 1 Torr, the oil diffusion pump 12 is started, and the system waits until the oil diffusion pump 12 has sufficient exhaust capacity.

When the oil diffusion pump 12 has sufficient exhaust capacity and the oilless turbo molecular pump 7, which has already started, reaches a sufficient rotation speed, the stop valve 22 is closed, the gate valve 22 is closed, and the gate valve is closed. Open 10. This completes the rough evacuation of the analysis chamber 1 and the oilless turbomolecular pump 7 using the flow path E, and at the same time moves on to the main evacuation using the flow paths A and B.

By performing rough evacuation by changing the flow path, backflow of oil into the analysis chamber 1 is prevented. That is, after rough evacuation to about 1 Torr using the oil-less soap pump 21, the oil-less turbo molecular pump 7, which exhibits its performance in a vacuum state, is started and reaches a sufficient rotation speed to prevent oil from flowing back. When the condition is reached, soap pump 21
By switching from the flow path to the oil diffusion pump 12 and oil rotary pump 15, backflow of oil from the oil diffusion pump 12 and oil rotary pump 15 to the analysis chamber 1 can be completely prevented. As a result, inside analysis room 1,
Accurate analysis results can be obtained even under ultra-high vacuum for long periods of time without being contaminated by vaporized backflow oil.

In order to prevent oil from entering the analysis chamber 1, an oil-less magnetic levitation turbo molecular pump is used, and this is combined with an oil rotary pump to drive both of them to prevent oil from entering the analysis chamber 1. Oil infiltration cannot be completely prevented. In other words, the above-mentioned magnetic levitation type turbomolecular pump does not exhibit sufficient performance unless it is in a high rotation and high vacuum state.
Until then, the backflow of oil from the oil rotary pump to the analysis chamber 1 cannot be blocked.

Next, from the above state, proceed with evacuation using the exhaust channels A and B consisting of the oil diffusion pump 12 and the oil rotary pump 15, and once the inside of the analysis chamber 1 has become a vacuum of about 10 ^-9 Torr, proceed to The bake heater 5 that has been put in is turned off, liquid nitrogen is introduced into the casing 4, and the inside of the analysis chamber 1 is cooled to an ultra-low temperature to bring the inside of the analysis chamber 1 to a degree of vacuum of 10 ^-11 Torr or less. The pressure inside the analysis chamber 1 is read by the nude gauge 3 of the ionization vacuum gauge.

(b) Creating a calibration curve Before starting the analysis of _N2 gas, create a calibration curve for the predicted target impurity components. First, high-purity Ar gas containing 0.1% of the target impurity component, for example CO ₂ , is prepared and used as a standard gas.
In this case, CO ₂ is 1 c.c. per 1 standard gas, which is an amount that can be handled accurately, so it can be produced with high precision. Next, this standard gas is introduced from the sample gas inlet 23 into the analysis chamber, which has been adjusted to 10 ^-11 Torr by adjusting the vacuum level, at a pressure in the range of 10 ^-10 to ^{10 -7} Torr.
Then, within this pressure range, the output current value of the mass spectrometer is read, and a relationship diagram between pressure and output current value is created.

Here, since the CO ₂ concentration in the standard gas is 0.1%,
The partial pressure of CO ₂ is also 1/1000 of the pressure of standard gas.
Therefore, the relationship diagram between pressure and output current value above is as follows:
It can be converted into a relationship diagram between the partial pressure of CO ₂ and the output current value. This relationship diagram becomes the calibration curve used to quantify impurities during analysis. Similarly, if there are impurity components other than CO ₂ to be analyzed, a calibration curve for them is created. The calibration curve may be created for each impurity component to be measured, or it may be created for a mixed gas with a defined molar ratio.

(c) Analysis of sample gas Before starting the analysis, the analysis room 1
After adjusting the vacuum level in the analysis chamber and confirming that it is below 10 ^-11 Torr, close the stop valve 2.
8 and introduce high-purity Ar for purging, adjust the variable leak valve 26 and release the inside of the analysis chamber.
Set to 10 ^-8 Torr. When a sample gas is introduced into the analysis chamber 1, which is evacuated to an ultra-vacuum level of 10 ^-11 Torr or less, the background partial pressure near the analysis tube in the analysis chamber 1 is reduced by the degassed components due to the flow of the introduced sample gas. By suppressing the diffusion of Ar, the pressure becomes about an order of magnitude lower than before introduction, so when Ar is introduced at 10 ^-8 Torr, the background partial pressure is 10 ^-12
Torr or less, and only H ₂ is difficult to exhaust. If you measure the gas in the analysis chamber in this state, even if there is an impurity component of about 1 ppm in high-purity Ar, the partial pressure will be 10 ^-14 Torr and it will not be detected, and background components other than Ar will be detected. only will be detected. i.e. _H2 below 10 ^-12 Torr
only detected. If this state is confirmed, preparation for analysis of the sample gas is completed. Next, close the stop valve 28 and open the stop valve 24 to switch from high-purity Ar for purging to the sample gas, introduce the sample gas N ₂ into the analysis chamber 1, and adjust the pressure with the variable leak valve 26 to 10 ^-4 Torr. Analyze with. When the target impurity component in the sample gas is H ₂ , analysis accuracy is poor below 10 ^-12 Torr;
As for other impurity components, it can be said that sufficient analytical accuracy is achieved even at 10 ^-12 Torr or less. If the output power value of the mass spectrometer at this time is read and converted to the partial pressure of the impurity by comparing it with the calibration curve prepared earlier, the concentration of the impurity can be determined using the following calculation formula.

(Calculation formula) Impurity concentration _(ppb) = impurity partial pressure (Torr)
×10 ⁹ /Analysis chamber pressure (Torr) If we apply this equation, we can calculate that the impurity components are
It can accurately analyze concentrations down to 10 ppb for H ₂ and about 1 ppb when the impurity component is other than H ₂ .

In the above embodiment, the soap pump 21 that performs initial roughing is connected to the flow path connecting the exhaust port 9 of the oilless turbo molecular pump 7 and the gate valve 10 via the flow path E. As shown in FIG. 2, the soap pump 21 may be connected to a flow path connecting the exhaust port 14 of the oil diffusion pump 12 and the stop valve 18 via a flow path E'. Even in this case, the same effects as in the embodiment described above can be obtained.

Furthermore, in both of the above two embodiments, a soap pump is used as the initial roughing pump, but an oilless diaphragm pump may be used instead.

[Effect of idea]

As described above, the gas impurity analyzer of this invention connects the exhaust part of the analysis chamber and the intake part of the oil rotary pump to a flow system equipped with an oil-less turbo molecular pump, a gate valve, a cooling trap, and an oil diffusion pump. Since the soap pump (or oilless diaphragm pump) is connected to the above flow path by a branch flow path equipped with a switching means, it is possible to create a high vacuum of 10 ^-11 Torr in the analysis chamber. , can analyze impurities in gases down to the 1ppb level. Furthermore, with this device, it is easy to create a diagram of the relationship between the partial pressure of impurities used for quantitative analysis and the output current value of the mass spectrometer, and even in ultra-trace analysis, it is possible to perform quantitative analysis within the range of standard gases. This enables much more reliable analysis than conventional GCMS. In addition, by operating the switching means, the soap pump is used when roughing the analysis chamber, so even if it is started and stopped repeatedly, there is no backflow of oil to the oilless turbomolecular pump and the analysis chamber, and it can be used for a long period of time. Therefore, the accuracy of analysis is not compromised. In this way, the gas impurity analyzer of this invention can accurately analyze impurity components in gas down to 10 ppb for H ₂ and 1 ppb for other components, and can analyze all impurity components. Therefore, it is extremely useful for analyzing high purity gases such as 6 nines, 7 nines, and even 8 nines used in the semiconductor industry.

[Brief explanation of drawings]

FIG. 1 is a configuration diagram showing an embodiment of this invention.
FIG. 2 is a configuration diagram of an embodiment in which the connection position of the soap pump is changed. 1...Analysis room, 2...Analysis tube of mass spectrometer, 7
...Oilless turbo molecular pump, 10...Gate valve, 11...Cooling trap, 12...Oil diffusion pump, 15...Oil rotary pump, 21...Sorption pump, E, E'...Branch flow path .

Claims (1)

[Scope of utility model registration request] The exhaust part of the analysis chamber to which the analysis tube of the mass spectrometer is connected and the intake part of the oil rotary pump form a flow path equipped with an oil-less turbo molecular pump, a gate valve, a cooling trap, and an oil diffusion pump in this order. An oil-less pump such as a soap pump or a diaphragm pump is connected to the above flow path by a branch flow path equipped with a switching means, and the vacuum level of the analysis chamber is set to 10 ^-11 Torr or less. An apparatus for analyzing ultra-trace impurities in gas using a mass spectrometer, which is characterized by being able to analyze trace impurities in gas.