Apparatus and method for mass-spectrometric high-vacuum leak detection

Abstract

In a mass-spectrometric high-vacuum leak detector (10) with a mass spectrometer (12) acting as a gas detector, a high-vacuum pump (16) evacuating the mass spectrometer (12), and a test connection (22) serving for connecting a test object to the gas detector, wherein, for its evacuation, the test connection (22) is connected to the high-vacuum pump (16) and / or a further vacuum pump (26), it is provided that the mass spectrometer (12) is connected directly to the test connection (22), in order for gas from the test connection (22) or a vacuum line evacuating the test connection to be let into the mass spectrometer (12) directly, and that the test connection (22) and / or the inlet line (28, 30, 32) connecting the test connection (22) to the mass spectrometer (12) is / are connected to an atmospheric line open to the atmosphere.

Description

[0001] Device and method for mass spectrometric high-vacuum leak detection

[0002] The invention relates to a mass spectrometric high-vacuum leak detector and a method for mass spectrometric high-vacuum leak detection.

[0003] High-vacuum leak detectors are gas detectors that operate in a high vacuum. These are typically mass spectrometers that are pumped to a high vacuum pressure of approximately 1 xlO' by a high-vacuum pump. 4 mbar. The high-vacuum pump, in turn, can typically be evacuated by a backing pump. Such a mass spectrometric gas detector can be, for example, a quadrupole mass spectrometer (QMS). The test sample is connected to a test port. The gas drawn from the test port is fed to the mass spectrometer for gas analysis.

[0004] In such high vacuum leak detectors, it is known that the gas sucked in from the test port is fed to the mass spectrometer according to the countercurrent principle. The test port is evacuated via a side inlet of the high vacuum pump of the mass spectrometer. Beforehand, the test port and the test sample are evacuated to the necessary pre-vacuum pressure by the backing pump. If the pressure in the mass spectrometer is sufficiently low, the test gas enters the mass spectrometer in countercurrent through the high vacuum pump. Light gas components, such as hydrogen or helium, enter the mass spectrometer particularly easily and can therefore be easily detected using the countercurrent principle. For heavier gas components, such as argon, which are heavier than helium, the countercurrent principle is less suitable. The turbomolecular pump (TMP) therefore has no capacity for gas compositions admitted via the side inlet (e.g.Air with test gas) has an enriching effect on lighter gas components on the high-vacuum side of the TMP. Thus, the concentration ratio of light to heavy gas components on the high-vacuum side of the TMP is higher compared to the ratio of gas concentrations at the side inlet of the TMP.

[0005] To detect the tracer gases helium and hydrogen, the tracer gas is typically detected using countercurrent mass spectrometry for vacuum leak detection. This means that the gas to be detected is not introduced directly into the detection volume containing the mass spectrometer, but rather into a side inlet of the turbomolecular pump (TMP), which pumps the volume with the mass spectrometer. The light gases helium and hydrogen flow against the pumping direction of the TMP, allowing them to enter the detection volume in the opposite direction. Thus, the TMP achieves an additional selective effect between the light, fast tracer gases helium and hydrogen and the other gases in the atmosphere.

[0006] For other alternative test gases, inlet via the TMP's side inlet is not practical. For example, argon, CO2, or other heavy molecules such as solvents, DMC, and thus "slow" test gases do not flow sufficiently against the TMP's pumping direction. Furthermore, the concentration of the heavier and slower gas components is lower than that of lighter gas components. Such test gases are therefore admitted directly into the detection volume, the so-called mainstream inlet.

[0007] As much gas as possible is admitted from the test chamber; the more gas, the more test gas can be detected. However, the pressure in the ion source and the separation system must not exceed a maximum pressure. If the pressure is too high, space charge effects and losses due to particle collisions occur, which negatively impact the detection. For a given test gas concentration, this detection optimum occurs at a total pressure of approximately 1 / 100 CT. 4mbar in the detection volume or ion source. Higher pressure results in an even lower detection signal. At lower total pressures, the signal is approximately proportional to the total pressure for a given test gas concentration. A pressure transducer lowers the total pressure from the leak detector inlet via an inlet capillary to the permissible working pressure in the mass spectrometer volume.

[0008] The inlet pressure at the vacuum leak detector is not constant. As the test volume is pumped, the total pressure drops from an initial atmospheric pressure (approx. 1000 mbar) to continuously decreasing working pressures, so that with a constant pressure transducer conductance, the working pressure in the mass spectrometer (QMS) volume also drops. Due in particular to the slow and steadily decreasing water vapor desorption from the chamber's interior wall surfaces, the total pressure drops steadily over a very long period during the pumping process and is therefore unstable.

[0009] Sensitivity depends on the amount of gas entering the high vacuum of the gas detection system via the pressure transducer inlet. In a capillary, the flow rate is quadratically dependent on the pressure on the high-pressure side of the capillary. With continuous pumping of the test specimen or test chamber, the inlet pressure drops continuously over time. This significantly reduces the sensitivity of the leak detection system.

[0010] Against this background, the invention is based on the object of creating a mass spectrometric high-vacuum leak detector which enables stabilization of the pressure at the inlet, as well as providing a corresponding mass spectrometric high-vacuum leak detection method.

[0011] The mass spectrometric high vacuum leak detector according to the invention is defined by the features of patent claim 1.

[0012] Accordingly, a high-vacuum leak detector uses a mass spectrometer as a gas detector. A high-vacuum pump evacuates the mass spectrometer. A test port is provided for connecting a test sample to the gas detector. The test port is connected to the high-vacuum pump and / or another vacuum pump, such as a backing pump that evacuates the high-vacuum pump, to evacuate the test port. The mass spectrometer is directly connected to the test port to allow gas from the test port to be drawn directly into the mass spectrometer.

[0013] The special feature of the invention is that a vacuum line evacuating the test connection and / or an inlet line connecting the test connection or the vacuum line to the mass spectrometer are connected to an atmosphere line open to the atmosphere. The pressure at the test connection can be stabilized via the partial flow supplied to the mass spectrometer from the vacuum line by changing the amount of the supplied partial flow, or by the supplied partial flow dominating the resulting inlet pressure. In particular, this enables a sufficient gas flow in the vacuum line and in the section of the inlet line facing the mass spectrometer, in order to enable a sufficient gas flow even at low pressure at the test connection, i.e. when the test object is largely evacuated.

[0014] The invention offers the advantage that the test port is directly connected to the mass spectrometer, allowing gas components from the test port to enter the mass spectrometer directly, without having to pass through the counterflow through the mass spectrometer's high-vacuum pump. This allows even gas components heavier than helium, such as argon, to enter the mass spectrometer directly and be detected.

[0015] In principle, a gas stream can also be fed countercurrently to the mass spectrometer via a side inlet of the TMP. It is therefore conceivable that the gas could also be fed countercurrently to the mass spectrometer through a portion of the high-vacuum pump. However, this proportion would be negligible compared to the gas stream fed directly to the mass spectrometer because gases with high molecular mass only enter the mass spectrometer volume via the countercurrent path to a small extent. Alternatively, it is also conceivable that the gas could not be fed countercurrently to the mass spectrometer through a portion of the high-vacuum pump. To ensure a sufficiently low high-vacuum pressure in the inlet line connecting the test port to the mass spectrometer, the inlet line can be equipped with a pressure transducer.The pressure transducer can be an orifice plate, a capillary, a throttling control valve, a gas-permeable membrane, a thin layer of gas-permeable material, or a porous gas-permeable body. It is particularly important that the pressure transducer allows for high vacuum pressure on the side facing the mass spectrometer, while the pressure at the test port or the pressure in the vacuum line connecting the test port to a vacuum pump is applied on the side of the pressure transducer facing the test port.

[0016] The inlet line can be opened or closed using a separately switchable valve.

[0017] Preferably, the atmosphere line opens into the vacuum line or into the inlet line in the area between the test connection and the mass spectrometer and preferably in the area between the test connection and a pressure transducer contained in the inlet line.

[0018] During gas leak detection, the test port is typically continuously evacuated. To ensure sufficient gas flow in the vacuum line and in the section of the inlet line facing the test port, even at low pressure at the test port—i.e., when the test object is largely evacuated—the test port and / or the inlet line can be connected to a separate atmosphere line open to the atmosphere, through which additional gas can be drawn in. The gas supplied via the atmosphere line should not contain any test gas.

[0019] Furthermore, the invention provides a method for mass spectrometric high-vacuum leak detection, in which a partial flow is selectively fed directly to the mass spectrometer from the vacuum line through which the test port is evacuated, in such a way that the partial flow is not fed countercurrently to the mass spectrometer by part of the high-vacuum pump. While the partial flow is being fed, the test port is preferably continuously evacuated. The pressure can be monitored via a pressure measurement in the mass spectrometer, and the inlet pressure of the mass spectrometer can be stabilized by controlling the feed of the partial flow. Gas analysis is performed in the mass spectrometer.

[0020] Gas from the surrounding atmosphere can be supplied to the vacuum line, the inlet line and / or the test connection.

[0021] The invention is based on the principle of stabilizing the inlet pressure of the mass spectrometer by selectively introducing a gas stream into the inlet. A partial flow is introduced into the detection volume of the mass spectrometer from the vacuum line connecting the test port to the vacuum pump, or from the test port via the inlet line. The test port is continuously evacuated by the backing pump or an intermediate inlet of the mass spectrometer's high-vacuum pump, or continuously evacuated via a separate vacuum pump. A test specimen or a test chamber can be connected to the test port.

[0022] Two exemplary embodiments of the invention are explained in more detail below with reference to the figures. They show:

[0023] Fig. 1 is a schematic representation of a first embodiment and

[0024] Fig. 2 is a schematic representation of a second embodiment.

[0025] The mass spectrometer 12 of the illustrated high vacuum leak detector 10 is a quadrupole mass spectrometer. The mass spectrometer 12 is connected to a

[0026] High vacuum pump 16 in the form of a turbomolecular pump. The high vacuum pump 16 is connected via a forevacuum line 18 to a

[0027] Backing pump 20 connected.

[0028] The test connection 22, which can be connected to a test object to be tested for leaks, is connected to a vacuum pump via a vacuum line 24. This can be the backing pump 20, as in the exemplary embodiment shown in Fig. 1. The vacuum line 24 is then connected to the backing line 18 and can also be connected, as shown in Fig. 1, or alternatively, to an intermediate gas inlet 25 of the high vacuum pump. Alternatively, as shown in Fig. 2, it is conceivable that the vacuum line 24 is connected to a separate vacuum pump 26.

[0029] The high vacuum pump can be connected to a backing pump for evacuating the high vacuum pump. The vacuum line connecting the test port to the vacuum pump evacuating the test port can be connected to an intermediate gas inlet of the high vacuum pump. Additionally or alternatively, the vacuum line can be connected to a backing line connecting the high vacuum pump to its backing pump. Furthermore, it is conceivable for the vacuum line to be connected to a separate vacuum pump, distinct from the high vacuum pump and its backing pump.

[0030] In all embodiments, the vacuum line is directly connected to the mass spectrometer 12 via at least one inlet line 28. In Fig. 1, this is precisely one inlet line 28. In the embodiment in Fig. 2, in addition to a first inlet line 28, a second inlet line 30 and a third inlet line 32 are further provided, wherein the test port 22 is connected to the mass spectrometer 12 via each of the inlet lines 28, 30, 32. Each inlet line 28 or 28, 30, 32 is provided with a separate valve 34 or 34a, 34b, 34c for selectively blocking and opening the inlet line 28 or 28, 30, 32. In addition, each inlet line is provided with a pressure transducer 36 or 36a, 36b, 36c.

[0031] In the embodiment in Fig. 1, the pressure transducer 36 is an aperture with a suitably selected hole opening, which on its side facing the mass spectrometer 12 has a high vacuum pressure of approximately 10'4Millibar, while on the side facing the test connection, the pressure present in the vacuum line 24 is applied. In the embodiment shown in Fig. 2, the pressure transducers 36a, 36b, 36c are each capillaries with different conductances. The conductances of the capillaries are designed such that an inlet pressure of approximately 100 millibar is applied on the side of the pressure transducer 36a facing the test connection 22, while an inlet pressure of approximately 10 millibar is applied on the side of the second pressure transducer 36b facing the test connection 22, and an inlet pressure of approximately 1 millibar is applied on the side of the pressure transducer 36c facing the test connection 22. Other pressure ranges are conceivable. In particular, fewer or more inlet lines connecting the vacuum line 24 to the mass spectrometer 12, each with its own pressure transducer and selectively operable valve, are conceivable in order to cover a larger or smaller pressure range.In the embodiment of Fig. 2, it is thus possible to open a suitable inlet line 28, 30, 32 for different pressure ranges within the vacuum line 24 and at the test connection 22 and to supply gas to the mass spectrometer 12 via the respective pressure transducer 36a, 36b, 36c.

[0032] In both exemplary embodiments, it is also conceivable to connect the test connection 22 and the respective inlet line 28, 30, 32, as shown in Fig. 1, to an atmosphere line 38 that is open to the atmosphere. In the exemplary embodiment in Fig. 2, the atmosphere line 38 is shown in dashed lines to indicate that the atmosphere line 38 is not absolutely necessary. The atmosphere line 38 is provided with a suitable throttle 40 to enable a suitable gas flow or to limit the gas flow through the atmosphere line 38 in a suitable manner. Furthermore, the atmosphere line can be selectively opened or closed with a separately actuated valve 42.

[0033] As soon as the pressure at test connection 22 falls below a certain value and, as a result, a lower gas flow through vacuum line 24 is present, from which a partial flow is supplied to mass spectrometer 12, additional gas from the atmosphere can be supplied to vacuum line 24 and inlet line 28 or inlet lines 28, 30, 32 via atmosphere line 38. This gas supplied via atmosphere line 38 should not contain any test gas. The invention thus offers the decisive advantage of creating a mass spectrometric high-vacuum leak detector that enables the detection of even heavier gas components that are heavier than helium, such as argon, with stabilized sensitivity.

Claims

Claims 1. Mass spectrometric high-vacuum leak detector (10) with a mass spectrometer (12) as a gas detector, a high-vacuum pump (16) evacuating the mass spectrometer (12), and a test connection (22) for connecting a test object to the gas detector, wherein the test connection (22) is connected to the high-vacuum pump (16) and / or a further vacuum pump (26) for evacuating the test object, characterized in that the mass spectrometer (12) is directly connected to the test connection (22) in order to admit gas from the test connection (22) or a vacuum line evacuating the test connection directly into the mass spectrometer (12), and in that the test connection (22) and / or the inlet line (28, 30, 32) connecting the test connection (22) to the mass spectrometer (12) are connected to an atmosphere line open to the atmosphere.

2. Mass spectrometric high-vacuum leak detector (10) according to claim 1, characterized in that an inlet line (28, 30, 32) directly connecting the test connection (22) to the mass spectrometer (12) is provided with a pressure transducer (36, 36a, 36b, 36c) which is designed to maintain a high vacuum pressure on the side of the pressure transducer (36, 36a, 36b, 36c) facing the mass spectrometer (12), while a higher pressure is applied on the opposite side of the pressure transducer (36, 36a, 36b, 36c) facing the test connection (22).

3. Mass spectrometric high-vacuum leak detector (10) according to claim 1 or 2, characterized in that the atmosphere line (38) is provided with a separately closable valve (42) and a throttle (40) with a predetermined conductance.

4. Mass spectrometric high-vacuum leak detector (10) according to one of the preceding claims, characterized in that preferably the atmosphere line opens into the vacuum line or into the inlet line in the region between the test connection and the mass spectrometer and preferably in the region between the test connection and a pressure transducer or the pressure transducer contained in the inlet line.

5. Mass spectrometric high vacuum leak detector (10) according to one of the preceding claims, characterized in that the inlet line (28, 30, 32) is provided with a separately closable valve (34, 34a, 34b, 34c).

6. Mass spectrometric high vacuum leak detector (10) according to one of the preceding claims, characterized in that the test connection (22) is connected to the mass spectrometer (12) via a plurality of parallel inlet lines (28, 30, 32), each having a capillary pressure transducer (36, 36a, 36b, 36c) and a separately closable valve (34, 34a, 34b, 34c), wherein the pressure transducers (36, 36a, 36b, 36c) of the different inlet lines (28, 30, 32) have different conductances, so that a first of the inlet lines (28, 30, 32) is used for a first pressure range of the pressure at the test connection (22) and at least a second of the inlet lines (28, 30, 32) is used for a second pressure range of the pressure at the test connection, which is different from the first pressure range. test connection (22) can be used.

7. Mass spectrometric high vacuum leak detector (10) according to claim 6, characterized in that the pressure transducer (36, 36a, 36b, 36c) is an orifice plate, a capillary, a throttling control valve, a gas-permeable membrane, a thin layer of a gas-permeable material or a porous gas-permeable body.

8. Mass spectrometric high vacuum leak detector (10) according to one of the preceding claims, characterized in that the test connection (22) is connected by a vacuum line (24) to the Test connection (22) evacuating vacuum pump (16, 20, 26), wherein at least one inlet line (28, 30, 32) connecting the test connection (22) to the mass spectrometer branches off from the vacuum line (24).

9. A method for mass spectrometric high-vacuum leak detection with a mass spectrometer (12) as a gas detector, a high-vacuum pump (16) evacuating the mass spectrometer (12) and a test connection (22) for connecting a test object to the gas detector, wherein the test connection (22) is connected to the high-vacuum pump and / or another vacuum pump for evacuating the test object, characterized by the steps: Evacuating the test connection via a vacuum line (24) connected to the test connection (22), selectively admitting a partial flow from the test connection or the vacuum line directly into the mass spectrometer (12), wherein air from the surrounding atmosphere is supplied to the vacuum line, an inlet line connecting the vacuum line to the mass spectrometer and / or the test connection (22).

10. The method according to claim 9, characterized in that the pressure of the partial gas stream supplied to the mass spectrometer is converted so that the pressure in the vacuum line is greater than that in the mass spectrometer.

11. Method according to one of the preceding claims, characterized in that the pressure in the mass spectrometer is measured during the introduction of the partial stream and the amount of gas admitted is changed as a function of the pressure in order to stabilize the pressure.

12. Method according to one of the preceding claims, characterized in that the partial stream is fed to the mass spectrometer in such a way that the pressure of the fed partial stream at the inlet of the mass spectrometer is at least about 0.01 mbar, preferably at least 0.1 mbar and in particular about 1 mbar.

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