WO2016096233A1

WO2016096233A1 - Pressure-reducing device, apparatus for mass spectrometric analysis of a gas and cleaning method

Info

Publication number: WO2016096233A1
Application number: PCT/EP2015/075589
Authority: WO
Inventors: Hin Yiu Anthony Chung; Michel Aliman; Gennady Fedosenko; Rüdiger Reuter; Leonid Gorkhover; Peter Awakowicz; Marc Böke; Achim von Keudell; Jörg Winter; Alexander Laue; Jan Benedikt
Original assignee: Carl Zeiss Smt Gmbh; Carl Zeiss Microscopy Gmbh
Priority date: 2014-12-16
Filing date: 2015-11-03
Publication date: 2016-06-23
Also published as: DE102014226038A1

Abstract

The invention relates to a pressure-reducing device (3), comprising: a vacuum housing (4), which has an inlet opening (5) for the inlet of a gas (2) to be tested at an ambient pressure (P_U) and an analysis chamber (7) for the mass spectrometric testing of the gas (2) to be tested at a working pressure (P_A), wherein the inlet opening (5) and an inlet opening (10) of the analysis chamber (7) are arranged along a common line of sight (11). The vacuum housing (4) comprises a plurality of vacuum components (21, 26) which can be connected to each other in modular manner and arranged one after another along the line of sight (11), and at least one pressure-reducing chamber (12) separated from the analysis chamber (7) in a gas-tight manner extends through at least one of the vacuum components (23, 27) through which the analysis chamber (7) extends. The invention also relates to an apparatus for testing by mass spectrometry of a gas (2), which has such a pressure-reducing device (3), and a method for cleaning such a pressure-reducing device (7).

Description

Pressure reducing device, device for

Mass spectrometric analysis of a gas and purification process

Reference to related application

This application claims the priority of the German patent application DE 10 2014 226 038.8 of 16 December 2014, the entire

The disclosure content is made by reference to the content of this application.

Background of the invention

The invention relates to a pressure reducing device, comprising: a vacuum housing, which has an inlet opening for the inlet of a gas to be examined at an ambient pressure and an analysis room for the mass spectrometric examination of the gas to be examined at a working pressure. The inlet opening and an inlet opening of the analysis chamber are arranged along a common line of sight. The invention also relates to a device for mass spectrometric analysis of a gas with such a pressure reducing device and a

Method for removing contaminants from such a pressure reducing device. For analysis of gases to be examined, ie of gaseous products or substances by means of mass spectrometers usually in the mass spectrometer, more precisely in the analysis room, working pressures of less than 10 ^"5 mbar, preferably less than 10 ^{" 6} mbar prevail to spectra with good resolution and good signal-to-background ratio. Often, the gas under investigation (the analyte) is included

Atmospheric pressure before. In this case, the ambient pressure prevailing in a chamber containing the gas under test must be reduced by intensive pumping until it enters the analysis room. But it is also possible that the ambient pressure is much smaller than

Atmospheric pressure.

For reducing the pressure, capillaries may be used in which the ambient pressure, e.g. Atmospheric pressure prevails. The capillary is fed into the vacuum vessel with the mass spectrometer, which is pumped intensively. The capillary is used to reduce the conductance in such a way that with a powerful pump the desired final pressure

(Working pressure) can be achieved. The transferred gas volumes are very low, typically in the range of 10 ^"4 mbars ^" so that effective

Suction capacities s ^"sufficient of typically 100 I ¹ for this purpose. However, a disadvantage is that no dynamic measurements can be carried out practically, because the analyte very slowly diffuses through the capillary and in this case carries many collisions with the wall of the capillary. In particular, reactive

Analytes can therefore be changed in their properties before entering the mass spectrometer or in the analyzer.

Another method for reducing pressure is based on the multiple differential pumps in different pressure levels or

Pressure reduction spaces. The pressure reduction chambers are each connected by diaphragms or apertures vacuum vessels, which are associated with autonomous pumping stages or pumping devices, the pressure of Reduce pressure reduction space accordingly to pressure reduction chamber. In the last pressure reduction space, which forms an analysis room, is the mass spectrometer or the analyzer of the mass spectrometer

arranged. Such a commercially available device is e.g. the high-pressure analyzer from HIDEN. Usually, three Pumpbzw. Pressure Reduction spaces to the pressure of the ambient pressure, e.g. Atmospheric pressure to bring to working pressure.

By means of a differentially pumped device a certain dynamics of the investigated processes can be detected when the so-called molecular beam mass spectrometry is applied, i. when typically neutral gas to be examined in the form of a molecular beam, i. a directed beam of atoms and / or molecules (typically without collisions between the particles of the beam) is guided into the analysis room. In this case, the inlet opening and the inlet opening are arranged in the analysis room in a line of sight ("line-of-sight"), so that the gas to be examined without collisions on the chamber walls

Reach analysis room and can be detected as a reactive species.

A disadvantage of such commercially available high-pressure analyzer devices is that the gas to be analyzed (the analyte) with its carrier gas flows continuously into the device and thus generates a high background pressure in the analysis chamber, which leads to a poor signal-to-background ratio and thus the sensitivity of the

Restricts device. Another disadvantage of devices for

Mass spectrometric analysis of gases by means of molecular beam mass spectrometry is that they are very unwieldy and

are bulky. Immersion in the recipient with simultaneous multi-stage pressure reduction is therefore virtually impossible in the rule. In particular, in the investigation of reactive gases in the pressure reducing device contaminating substances can be deposited, which in the worst case can cause the pressure reducing device to malfunction.

In the thesis "Reaction chemistry in oxygen or hexamethyldisiloxane containing noble gas microplasma jet: a quantitative molecular beam mass spectrometry study" by Dirk Eilerweg, Ruhr-University Bochum (2012), a mass spectrometer for the investigation of gases by molecular beam mass spectrometry using three To describe the signal-to-background ratio in such a device

improve, the supply of a pulsed gas stream can be done in the pressure stages. For this purpose, a chopper (possibly with embedded skimmer) may be mounted in the first compression stage and e.g. be rotated by means of a stepper motor. When the chopper is open, direct access from the environment, e.g. from a process chamber into the second pressure stage allows. A 3-stage pumped mass spectrometer described in the dissertation is also described in the article "Mass spectrometric detection of reactive neutral species: beam-to-background ratio" by H. Singh et al., Journal of Vacuum Science and Technology A 17, 2447 (1999).

From WO 02/00962 A1 an in-situ cleaning system for removing deposits has become known, which of process gases in a

Sample chamber of a process monitor a wafer manufacturing plant are generated. A test head of a gas analyzer is in the sample chamber

arranged to analyze a plasma-ionized gas sample. Deposits that occur in the course of one or more analyzes in the

Sample chamber or set on the probe head can be removed if necessary using a cleaning gas. The cleaning gas forms in the production of a plasma in the sample chamber with the deposits, a gaseous cleaning product, which is discharged from the sample chamber. Object of the invention

The object of the invention is a pressure reducing device for a gas to be examined, a device for mass spectrometry

Investigation of the gas to be examined with such

Pressure reducing device and a method for cleaning a

Specify pressure reducing device that overcome one or more of the problems described above, in particular improve the signal-to-background ratio.

Subject of the invention

This object is achieved by a pressure reducing device of the type mentioned, in which the vacuum housing has a plurality of modularly interconnected and along the line of sight arranged vacuum components, and in which at least one of the vacuum components through which the analysis space runs, at least one gas-tight separated from the analysis space pressure reduction space runs.

An above-mentioned disadvantage of existing devices for molecular beam mass spectrometry is that they are typically formed as a monolithic block and thus not flexible to the ambient pressure (suction pressure) are adaptable. If, as with many plasma processes, the suction pressure is well below atmospheric pressure, e.g. in the range of a few mbar, significantly more compact and less expensive trained pressure reducing devices can be used, which can be realized by the above-described modular construction of the vacuum housing.

In order to reduce the pressure within the vacuum housing from the ambient pressure to the working pressure, it depends on the ambient pressure, if necessary not sufficient to evacuate only the analysis room by means of a vacuum pump. If the ambient pressure corresponds to the atmospheric pressure, two further pressure stages or

Pressure reduction rooms required, which are differentially pumped and in each of which there is a pressure which is between the ambient pressure and the working pressure. The pressure reduction chambers are formed in conventional mass spectrometers between the inlet opening and the inlet opening and are pumped laterally. Such lateral pumping is unfavorable if the pressure reducing device is to submerge in the recipient.

To be at least partially immersed in a recipient

Pressure Reducing device to realize one or two pressure stages between the inlet opening and the inlet opening of the analysis space, a pressure reduction device is proposed, in which a respective pressure reduction space in at least one of the vacuum components is guided laterally past the analysis room. In this way, the

Pressure reduction space via a at the inlet opening facing away from the end of the vacuum housing mounted vacuum port, which is typically located outside of the recipient, are connected to a vacuum pump. In this way can be avoided, the

to arrange required vacuum connection within the recipient.

In one embodiment, the analysis space extends through at least two of the vacuum components arranged along the line of sight. It is advantageous if the distance traveled by the gas to be analyzed in the vacuum housing to the analysis room is as small as possible. When the vacuum housing with a partial region having the inlet opening enters the recipient, for example a process chamber, the analysis chamber is included

conventional mass spectrometers outside of the submerged into the recipient portion. In contrast, the extends Analytical space in the pressure reduction device described here by at least two, possibly by three or more adjacent, interconnected vacuum components. In this way, an analyzer and / or an ionization device can be arranged in the analysis chamber at or in the vicinity of the inlet opening and the analysis chamber can be connected to a vacuum component, which is arranged opposite the inlet opening, with a vacuum pump. to the working pressure (typically ^~ less than about 10 ^"6 mbar or 10 ⁷ mbar) to be generated in the analyzing space. the gas discharge or the connection with a vacuum pump can be effected for example by a mounting flange made of, where the vacuum Housing is connected to the housing of the recipient and / or from a connection flange, which is arranged outside the recipient.

In a further development, at least one of the vacuum components has a vacuum connection for connecting the at least one

Pressure reduction chamber with a vacuum pump on. Typically, such a vacuum connection is formed on a vacuum component in which, as described above, the analysis space and separately therefrom

Pressure reduction space run.

In a further development, the vacuum connections of a first pressure reduction space and a second pressure reduction space are formed on different vacuum components. Depending on

Ambient pressure may not be needed for both pressure reduction rooms. Due to the design of the vacuum connections on different vacuum components, it is possible, if necessary, to dispense with pumping a pressure reduction space and thus the vacuum component with the corresponding vacuum connection at a comparatively low ambient pressure.

In a further development, a portion of a first pressure reduction space is formed in one of the vacuum components, with the inlet opening in the Analyzer room communicates. As described above, the first pressure reduction space in at least one vacuum component in the direction of the line of sight is guided laterally past the analysis space and is not in communication therewith. To deal with the first pressure reduction room a

To realize pressure stage, it is necessary to connect this with the inlet opening in the analysis room, which can be done in a dedicated vacuum component. The section of the pressure reduction space provided in this vacuum component extends as far as the inlet opening or up to the line of sight between the inlet opening and the inlet opening. If the first pressure reduction space is not required, this vacuum component can optionally be omitted, so that the number of vacuum components forming the vacuum housing is correspondingly reduced.

If necessary, the analysis chamber or the inlet opening into the analysis chamber can be connected to the section of the first pressure reduction chamber

However, it is also possible that the inlet opening having end of the analysis space in the vacuum component with the portion of the first

Pressure reduction space is appropriate. Also in the field of

Inlet provided skimmer may optionally be attached to the vacuum component, which has the line extending to the line of sight.

In a further development is in one of the vacuum components

Section of a second pressure reduction space formed with the

Inlet opening is connected in the vacuum housing. The portion of the second pressure reduction space extends to the common line of sight between the inlet port and the inlet port. Along the line of sight between the inlet opening and the inlet opening, a further opening is typically provided in this case, the first

Pressure reduction chamber connects to the second pressure reduction space. in the For example, a chopper and / or a skimmer may be provided in the region of the further opening, which extends to just before the inlet opening

extend. If the second pressure reduction space is not needed, the vacuum component with the line of sight extending portion can be omitted, so that the number of the vacuum housing forming vacuum components is reduced accordingly.

In a further embodiment, the vacuum components are designed as pipe components. The formation of the vacuum components as pipe components is advantageous because this allows a compact design of the vacuum housing. Also can be formed as a pipe components vacuum components in a simple manner by means of flanges (by screwing) connect to each other, which can be realized in a particularly simple manner, the modular structure of the vacuum housing.

In a further development, the analysis chamber runs centrically through the pipe components along the line of sight. The analysis space preferably forms a cylindrical space within the pipe component (s) whose cylinder axis coincides with the line of sight. In this way, the required pump cross section for generating the working pressure can be realized in a particularly simple manner.

In a further development, the analysis space has a diameter of at least 70 mm. The diameter of the analysis chamber should not be too small to allow a sufficient pump cross-section for its evacuation. Also, a minimum diameter in the order of magnitude given here is required to use the analyzer in the

To accommodate analysis room.

In a further development, the pipe components have a

Pipe diameter of 150 mm or less, preferably 140 mm or less up. The pipe diameter of the pipe components should be as small as possible in order to keep the pressure reduction device compact, so that it can be introduced into the recipient, without disturbing the process possibly occurring there, for example a coating or etching process. On the other hand, a sufficient pump cross section must be available, in particular for the first pressure reduction space, so that the pipe diameter should typically be 120 mm or more.

In a further embodiment, at least one vacuum component has at least one electrical or mechanical connection for establishing an electrical or mechanical connection to a voltage source or to an actuator. Typically, electrical

Connections, usually in the form of electrical lines, as well as mechanical connections, typically in the form of cables, led through different connections in the vacuum housing. On the

Provision of mechanical connections may possibly be dispensed with, if the actuators e.g. be integrated in the vacuum housing in the form of stepper motors or piezo elements. The voltage generated by the voltage source or the potential differences generated by it are typically adjustable in order to control the provided in the vacuum housing, to be supplied with electrical power components suitable. The voltage source can be designed to generate a DC voltage and / or an AC voltage. If necessary, the

at least one electrical connection also for connection to a

Power source or the like may be formed. The voltage source or the voltage sources may also be connected to a control and / or regulating device which controls the entire pressure reduction device or the device for mass spectrometric examination.

In a further development, at least one vacuum component has at least one bore which can be connected to the electrical and / or mechanical connection for performing the mechanical and / or electrical connection to a further vacuum component. With the help of the holes, the electrical or mechanical connection can be made to a respective component to be connected to the actuator or to the voltage source. Optionally, one and the same bore both as a passage for an electrical connection and as

Implementation for a mechanical connection serve.

In a further development, at least one of the vacuum components for

Recording an ionization and / or an analyzer formed within the analysis room. The analyzer, i. the measuring cell, is used for mass spectrometric examination or analysis of the gas flowing into the analyzer. By way of example, the analyzer may be a quadrupole ion trap in which the gas to be analyzed can be accumulated before a spectrum of the gas to be analyzed is recorded. It is understood that other types of analyzers or of mass spectrometers can also be arranged in the analysis space in order to carry out the mass spectrometric analysis of the gas to be investigated, for example conventional quadrupole mass spectrometers.

In a further embodiment, the pressure reduction device has a chopper in the region of the inlet opening for the pulsed supply of the gas to be examined into the analysis space. The chopper can be arranged in the region of a further opening, which is the first

Pressure reduction chamber connects to the second pressure reduction space to close or open them selectively, so that the supply of the gas to be examined in the analysis room can be pulsed. Of the

Chopper gives the connection between the inlet opening and the

Analyzer room either free or blocked. In a further development of the chopper is designed to make the pulsed supply of the gas to be examined in the analysis room with pulse width independently adjustable pulse durations. The chopper can be activated, for example, by means of a trigger signal to the connection between the inlet opening and the analysis space for the supply of a single pulse of the gas to be examined in the analysis room

release. The open connection may remain open for a given period of time corresponding to the pulse duration of that pulse, or another trigger signal may be used to disconnect the inlet port and the analysis compartment at the end of the pulse. The pulse duration of an immediately following pulse can also be set individually, i. the pulse duration of the subsequent pulse does not depend on the pulse duration of the immediately preceding pulse. In contrast, in a chopper, which uses a rotating wheel for opening and closing the connection, by the

Changing the rotational frequency of the wheel does not set the pulse durations of the individual pulses independently.

In a development of the chopper is formed, given

(Typically constant) pulse rate to set the pulse durations in the pulsed supply of the gas to be examined in the analysis room. The opening and closing of the connection, for example, the inlet opening or the further opening by means of the chopper can be carried out at a constant pulse frequency, which typically corresponds to the measurement frequency in the mass spectrometric examination of the gas to be examined. The duration of the individual pulses can be changed at a constant pulse frequency if the duty cycle between the time period in which the chopper opens the inlet opening or the further opening and the time period in which the chopper closes the inlet opening or the further opening is changed , Such a procedure can be realized by means of a chopper, in which a change in the duty cycle, for example by a pulse width modulation is possible. For example, it may be a chopper, which is designed in the manner described below. By means of such a chopper, the amount of gas to be analyzed supplied to the analysis room can be changed from pulse to pulse at a constant pulse rate.

In another embodiment, the chopper acts on a skimmer, which is displaceable for pulsed delivery of the gas to be examined in a direction transverse to the inlet opening (and thus transversely to the line of sight). Due to the displacement of the skimmer, the opening provided in the skimmer, which is oriented concentrically in the open state to the line of sight, can be displaced laterally, so that it no longer lies on the line of sight between the inlet opening and the inlet opening and

Entry port (nearly), i. is closed except for a narrow gap formed between the inlet opening and the skimmer.

The skimmer is preferably spring-mounted in the direction transverse to the inlet opening and can be deflected by means of an actuator in a periodic movement from a rest position. The actuator may, for example, be a reversible magnet or a piezo actuator. The skimmer can be stored for the resilient mounting, for example, between two leaf springs, which can be offset by the actuator in the manner of a tuning fork in a harmonic vibration about a rest position. The oscillation frequency can be set so that it corresponds to the desired pulse or measurement frequency for the inlet of the gas to be examined into the analysis space or is adapted to it. The chopper may have a control and / or regulating device which transmits a control signal to the actuator of the skimmer. The control signal may be, for example, a digital signal, which may be

is pulse width modulated, so that with constant pulse or measurement frequency, the duration of the individual pulses can be selectively changed. In this way For example, the amount of gas that enters the analysis room with a single pulse can be set in a targeted manner and, if necessary, regulated.

In a further embodiment, the pressure reducing device additionally has a in the region of the inlet opening of the analysis space

arranged skimmer for guiding the gas to be examined in the analysis room. In particular, the skimmer may be removable so as to permit a direct supply of the gas to be analyzed into the analysis room in the event that a very low ambient pressure prevails in the recipient.

In a further embodiment, the pressure reduction device has an actuatable diaphragm for covering the inlet opening. The orifice is used to close the inlet opening when no analysis of a gas to be examined is to be made. The panel thereby protects the interior of the vacuum housing against contamination, which can occur in particular in coating processes carried out in the recipient. The visor may be designed to be removable and, for example, by means of a mechanical connection or execution, which acts eccentrically on the diaphragm, perform a rotational movement in order to open or close the inlet opening.

The invention also relates to an apparatus for the mass spectrometric analysis of a gas, comprising: a pressure reduction device as described above, and an analyzer arranged in the analysis space for the mass spectrometric analysis of the gas at the working pressure. As described above, the analyzer may be, for example, a conventional quadrupole mass spectrometer, a quadrupole ion trap, etc. Since the gas to be investigated typically in the form of neutral atoms and / or molecules in the Pressure Reducing device occurs, it is necessary to ionize this before the mass spectrometric examination in the analyzer.

In one embodiment, the device has an ionization device arranged in the analysis chamber and / or connected to the analyzer for ionizing the gas to be investigated. The ionization device may be located in the analysis room itself and in this case is typically arranged along the line of sight between the inlet opening into the analysis room and the analyzer. The ionization device can also be connected via a lateral connection, i. transverse to the line of sight, be connected to the analyzer to introduce ions and / or metastable particles of an ionizing gas in the analyzer, which the

examining gas e.g. by impact ionization and / or by

Ionize charge exchange ionization directly in the analyzer. The ionization device can in this case, for example, as

Plasma ionization be formed.

A further aspect of the invention relates to a method for removing contaminants from a pressure reduction device as described above, comprising the steps of introducing (cleaning) gas into the analysis space and / or into at least one pressure reduction space via at least one gas inlet, which is preferred is formed on at least one of the vacuum components, and removing the contaminants by generating a glow discharge between a first skimmer, which is arranged in the region of the inlet opening of the vacuum housing, and a second skimmer, which is arranged in the region of the inlet opening into the analysis space is.

The two skimmers are typically electrically isolated so that between them a voltage sufficient to produce a glow discharge is sufficient, if a gas with a suitable pressure is inserted between the skimmers serving as electrodes. The glow discharge or the plasma causes the contaminants, which have accumulated within the vacuum housing, are converted into the gas phase and can be pumped out of the vacuum housing. The removal of the contaminants can be automated, ie the cleaning process can from the

Pressure reduction device itself be activated, for example, when sensors for detecting the degree of contamination in the

Pressure reduction device are provided.

Further features and advantages of the invention will become apparent from the following description of embodiments of the invention, with reference to the figures of the drawing, which show details essential to the invention, and from the claims. The individual features can be realized individually for themselves or for several in any combination in a variant of the invention.

drawing

Embodiments are illustrated in the schematic drawing and will be explained in the following description. It shows

Fig. 1 is a schematic representation of an apparatus for

Mass spectrometric analysis of a gas with two pressure reduction chambers and an analysis chamber, which are differentially pumpable,

Fig. 2a, b are schematic representations of a pressure reduction unit in

Form of a vacuum housing for the device of Fig. 1 in a sectional view and in an exploded view, Fig. 3 is a side view and an exploded view of five about

Flanges interconnectable vacuum components of the pressure reducing device in a side view and in an exploded view,

Fig. 4 is a schematic representation of a detail of

Pressure reducing device in the area between a

Inlet opening in the vacuum housing and an inlet opening in the analysis room, and

Fig. 5 is a schematic representation of a vacuum component, in which the

Generation of a pulsed gas supply in the analysis room a chopper for lateral displacement of a skimmer is integrated.

In the following description of the drawings are for the same or

functionally identical components identical reference numerals used.

In Fig. 1 is a section through a device 1 for

mass spectrometric examination of a gas 2, which has a pressure reducing device 3 with a vacuum housing 4, which has an inlet opening 5, through which the gas to be examined 2 can enter the vacuum housing 4. The gas 2 to be examined is located in a recipient 6, for example a process chamber, a

Reaction chamber or a vacuum chamber of an EUV lithography system, which may in particular also be a surrounding at least one optical element chamber (so-called "mini-environment"), in which the proportion of contaminants is reduced from the environment.

In the recipient 6, an ambient pressure Pu prevails, in the example shown atmospheric pressure (Pu = 1 bar). The vacuum housing 4 has a Analysis room 7, in which a working pressure P _A of typically less than about 10 ^"6 mbar, preferably less than 1CT ⁷ mbar prevails

Working pressure P _A is required for a in the analysis space integrated analyzer 8, for example in the form of a quadrupole ion trap ( "quadrupole ion trap" QIT), can be used for mass spectrometric analysis. A low operating pressure P _A is in particular necessary to a

To obtain sufficient signal-to-background ratio in the recording of spectra of the gas to be examined 2.

The gas 2 to be examined is typically present in the recipient 6 in a neutral form. The gas 2 to be examined may be a reactive species, for example an intermediate of one in the

Recipients 6 running process, e.g. a plasma etching process or a coating process. In order to be able to examine the gas 2 to be investigated in the analyzer 8, it is necessary for it to be as small as possible during transport from the inlet opening 5 of the vacuum housing 4 into the analysis space 7, more precisely to an inlet opening 10 of the analysis space 7 Number of impacts with the walls of the vacuum housing 4 performs. In order to keep the number of shocks with the housing walls as small as possible, the inlet opening 5 and the inlet opening 10 are arranged along a common line of sight 11, so that the

examining gas 2 can be transported in the form of a molecular beam from the inlet opening 5 to the inlet opening 10, as will be described in more detail below.

In order to reduce the ambient pressure Pu to the operating pressure P _{A is} the pressure reducing device 3 is a so-called in the example shown

Triple-pressure stage formed, i. this has, in addition to the analysis chamber 7, a first pressure reduction chamber 12 and a second pressure reduction chamber 12

Pressure reduction space 13, each having a portion 12 a, 13 a, between the inlet opening 10 of the analysis space 7 and the Inlet opening 5 of the vacuum housing 4 extends. Both the analysis chamber 7 and the first and second pressure reduction chambers 12, 13 are differentially pumpable, ie each with its own vacuum pump connected, so that in the first pressure reduction chamber 12, a first pressure P _D1 can be generated, which is greater than the working pressure in the analysis room 7 and the

for example, in the order of about 10 ^"2 mbar can be.

Accordingly, in the second pressure reducing space 13, a pressure P _D 2 greater than the pressure P _D i in the first one may be generated

Pressure reduction chamber 12, but less than the ambient pressure P _y . The pressure P _D 2 in the second pressure reduction chamber 13 may be, for example, in the order of about 10 mbar. Between the two

Pressure reduction chambers 12, 13 along the line of sight 11, a further opening 14 is mounted in order to transport the gas to be examined 2 in the analysis room 7 can. The further opening 14 may for example have a diameter of about 1 mm or smaller.

As can also be seen in FIG. 1, the analyzer 8 is connected to an ionization device 9, in which ions and / or metastable particles of an ionizing gas are generated, which are introduced into the analyzer 8 via a lateral flange. The ionizing gas may, for example, be a noble gas, in particular helium, or

Oxygen, for example, which is ionized by a micro-plasma or converted into metastable particles. The ions and / or metastable particles of the ionizing gas ionize the gas 2 to be examined in the analyzer 8, for example by impact ionization and / or by

Ladungsaustauschionisation. It is understood that the ionization of the gas to be examined 2 can also be done in other ways. In particular, the ionization device 9 can also be integrated into the analysis chamber 7, so that the lateral flange is omitted, which is therefore shown in dashed lines in Fig. 1. Furthermore, it is also possible for the ionization device 9 in FIG the first pressure reduction chamber 12 or in the second

Integrate pressure reduction space 13 so that the ionization at higher pressure PD-I, PD2 can take place and the analyte ions are then passed into the analysis room 7. In this case, it is advantageous for optimal ion guidance of the analyte ions generated in the analysis chamber 7 at the higher pressure P _D i, PD 2, the first pressure reduction chamber 12 or the second

Pressure reduction space 13 nachzuschalten a suitable ion optics.

In the example shown in Fig. 1, the vacuum housing 4 is modular and has six vacuum components 21 to 26, which are successively arranged along the line of sight 1 and vacuum-tightly attached to each other. The vacuum components 21 to 26 are pipe components which are connected to each other via flanges. It has proven to be advantageous if the distance A between the inlet opening 5 and the

Inlet opening 10 is as low as possible. In the example shown, the distance A is approximately 70-80 mm. In order to arrange the inlet opening 5 at a desired location within the recipient 6 despite the small distance A, which can be at a considerable distance A '(eg of 50 cm) from the chamber wall of the recipient 6, the analysis space 7 runs in the example shown through the third to sixth of the vacuum components 23 to 26 therethrough. In this way, the analysis chamber 7 at the end facing away from the inlet opening 10 from an outside of the recipient. 6

arranged vacuum pump to be evacuated, as will be described in more detail below. The analyzer 8 is arranged in the third vacuum component 23, at whose inlet end 5 facing the end

Inlet opening 10 of the analysis chamber 7 is formed. The analyzer 8 is thus located near the inlet 10 so that the path of the molecular beam forming gas 2 to be analyzed into the analyzer 8 is small (typically not more than about 80 mm). As can also be seen in FIG. 1, in the event that the ionization device 9 is integrated in the vacuum housing 4, the first to third vacuum components 21 to 23 protrude into the recipient 6 inside. By selecting a suitable length of the respective vacuum components 21 to 23 or optionally by inserting a further vacuum component as an intermediate piece, the distance A ', the inlet opening 5 has to the wall of the recipient 6, be suitably adapted.

As can be seen in FIGS. 2 a, b, the pressure reduction device 3 has two further vacuum components 27, 28, which, like the six vacuum components 21 to 26 shown schematically in FIG. 1, are arranged along the line of sight 11 and gas-tight with one another are connected. The eighth and final vacuum component along the line of sight 11 has a vacuum port 28a for connection to a first vacuum pump VP1 to which s may be ^"formed or greater, for example, as a molecular drag pump with a suction capacity of for example 60 I. The first vacuum For example, pump VP1 can be connected to the cylindrical analysis chamber 7, which itself has a diameter d of 70 mm, by means of a flange with an inner diameter of approximately 70 mm

Analyzer room 7 is on the one hand enough space for the integration of the analyzer 8 available and on the other hand, a sufficiently large pump cross section is guaranteed.

The seventh vacuum component 27 has to pump out the first

Pressure Reduction space 12 a vacuum port 27a (vacuum flange) for connection to a second vacuum pump VP2, which may also be designed as a molecular support pump and typically a larger suction power (eg, about 300 I s ^"1 or larger / smaller The second vacuum pump VP2 is connected to the seventh vacuum component 27 via a larger diameter vacuum port 27a to pump off the first pressure reduction chamber 12, which is centered in the seventh vacuum Component 27

arranged analysis chamber 7 is substantially annular (in two annular Segments). The cylindrical analysis chamber 7 is in the seventh

Vacuum component 27 vacuum-tight from the first pressure reduction chamber 12 separated, i. There is no connection to the analysis chamber 7 within the seventh vacuum component 27. The first pressure reduction chamber 12 also extends through the third to sixth vacuum components 23 to 26 in a corresponding manner.

In the second vacuum component 22, in which the inlet opening 10 is formed in the analysis chamber 7, a portion 12a of the first extends

Pressure Reduction space 12 radially inwardly to the line of sight 1 1 and thus connects the first pressure reduction chamber 12 with the inlet opening 10. The first pressure reduction chamber 12 extends in the third to seventh

Vacuum component 23 to 27 past the central analysis chamber 7, whereby the suction with the aid of the second vacuum pump VP2 from the inlet opening 10 opposite end of the vacuum housing 4 can be made from. The required pump cross section is significant. With a diameter d of the analysis space which is about 70 mm, the first pressure reduction space should be

12 have an outer diameter of about 120 mm.

The second pressure reduction chamber 13 runs gas-tight from the analysis chamber 7 and from the first pressure reduction chamber 12 through the second to sixth vacuum component 13, in the form of a bore connected to the vacuum port 26 a, which is indicated in FIG. 3. To the

Pumping off the second pressure reduction chamber 13 has the sixth

Vacuum component 26 a vacuum port 26 a, the second

Pressure reduction chamber 13 with a third vacuum pump VP3 connects, which may be formed, for example, as a rotary vane pump. In the first vacuum component 21 is a section 13a of the second pressure reduction space

13, which extends radially inwardly to the line of sight and connects the second pressure reducing space 13 with the inlet opening 5. The

Realization of the second pressure reduction chamber 13 in the form of the bore possible because the pumping cross section required for pumping is low.

Accordingly, the required length of the first vacuum component 21 along the line of sight 1 is comparatively small.

In the example shown, the vacuum components 22 to 27 designed as pipe components, through which the first pressure reduction chamber 12 and the second pressure reduction chamber 13 extend, have a pipe diameter D of typically more than about 120 mm and not more than about 150 mm , As can also be seen in FIGS. 2 a, b, the second vacuum component 22 has a slightly larger pipe diameter (eg 150 mm) than the other vacuum components 21, 23 to 27. The larger pipe diameter serves for the pressure reduction device 3 to be attached or flanged to the protruding edge region on the recipient 6, ie In the example shown in FIGS. 2a, b, only the first and the second vacuum component 21, 22 protrude into the recipient 6, since the third vacuum component 23 has a lateral flange in which the ionization device 9 is arranged.

It is understood that in a miniaturization or in a complete integration of the ionization device 9 in the vacuum housing 4, the protruding CF flange may be formed on another vacuum component 24 to 26 or possibly another vacuum component to To fix the vacuum housing 4 to the recipient 6 and in this case to position the inlet opening 5 at a desired distance A 'from the wall of the recipient 6 and thus adjust the immersion depth suitable.

To the inlet opening 5 at a desired distance A 'of the

Chamber chamber to be able to arrange the recipient 6, it is not sufficient to make only the pumping past the central analysis room 7, but it is also usually required that mechanical and

electrical connections from the side facing away from the inlet opening 5 of the Vacuum housing 4, ie from outside the recipient 6, are passed through a plurality of vacuum components 21 to 24.

It has proved favorable if all mechanical connections 25a are integrated in a single vacuum component 25 and if all electrical connections 24a are integrated in a further vacuum component 24. The electrical connections 24a serve to produce an electrical

Contact with a voltage source 30 shown in Fig. 3, wherein at a respective terminal 24a, an electrical connection 30a in the form of one or two electrical lines to the voltage source 30 can be connected.

The mechanical connections 25a serve to establish a mechanical connection 31a with an actuator 31 (motor). At the mechanical

Ports 25a are holes with sufficient

Diameter, so that a mechanical connection 31a, for example in the form of a cable or Bowden cable can be introduced into the vacuum housing 4. As can be seen in Fig. 2a, takes place in the vacuum component 24, which has the mechanical connection 24a, a deflection of the mechanical connection 31a in the form of the Bowden cable by 90 °, as an exclusively coaxial bore or implementation of the mechanical

Compound 31a (and also the electrical connection 30a) due to space reasons difficult to realize.

In the vacuum components 22 to 25 and 26 bores 32 are introduced (see, for example, Fig. 2a), the implementation of the electrical connections 30a (see Fig. 3) and the mechanical connections 31a to the

Serve components that are shown with the respective in Fig. 3

Voltage source 30 and to be connected to the respective actuator 31 shown in FIG. 3. The serving as a passage bores 32 extend in the example shown coaxially to the line of sight 11. The mechanical Connections 31a in the form of cables serve to produce a

Rotary movement of mechanical components, which serve for closing openings formed in the vacuum housing 4. In the example shown, three mechanical connections 31a are provided for connection to three actuators 31.

A first port 25a serves to move a shutter 33 (see Fig. 3) disposed in front of the inlet port 5 to protect the pressure reducing device 3 from contamination, that is, to prevent the pressure reduction device 3 from being contaminated. Aperture 33 is opened only when a measurement is taken. The latter is particularly favorable if a coating process is carried out in the recipient 6. As can be seen in Fig. 2a, the mechanical connection 31 a in the form of the Bowden cable acts eccentrically on the diaphragm 33 and allows it in this way, the aperture 33 to rotate. It is not necessary that the shutter 33, the vacuum housing 4 closes vacuum-tight, since during maintenance or the like, the two pressure reduction chambers 12, 13 can be vented, while the analysis room 7 itself should not be ventilated. The orifice 33 is positioned on the inlet opening 5 of the first vacuum component 21 and is removable, i. the aperture 33 is modularly connectable to the first vacuum component 21 and is u.a. held by the mechanical connection 31a at this.

To prevent the ventilation of the analysis room 7 is a second

provided mechanical connection, which serves to close the inlet opening 10 in the analysis chamber 7 vacuum-tight. In the example shown, for this purpose a Viton ball (not shown) is displaced into the inlet opening 10, to be more precise in a skimmer 36 (see Fig. 3) provided at the inlet opening 10. This is possible because the inlet opening 10 in the analysis chamber 7 has a comparatively large diameter of, for example, about 2 mm. A third rotary leadthrough serves to move a further diaphragm 35 (see FIG. 1) ("flag") in the region of the opening of the analyzer 8. The further diaphragm 35 makes it possible for the diaphragm 4 to be moved through the vacuum housing 4

existing residual gas signal to distinguish from the signal, which is due to the gas to be examined 2 (the molecular beam). Aperture 35 is incorporated into the molecular beam for this purpose, i. moved into the area of the line of sight 11. It is understood that the mechanical connections need not necessarily be realized in the manner described here, but that they can also be realized in other ways, for example by integrated stepper motors.

Two of the electrical connections 30a are used for electrically contacting the skimmer 36 in the region of the inlet opening 10 in the analysis chamber 7 and another skimmer 34 in the region of the inlet opening 5 in the vacuum housing 4 (see Fig. 4) of the Skimmer 36th at the

Inlet opening 10 is electrically insulated in the analysis room 7. As usual, the skimmers 34, 36 serve as electrostatic lenses for beam shaping of the molecular beam forming gas 2 to be examined. A third electrical connection 30a serves for contacting a chopper 37, which acts on the skimmer 34 arranged in the region of the inlet opening 5, to produce a pulsed one To allow supply of the gas to be examined 2 in the analysis room 7.

To the inlet opening 5, which may for example have a diameter of about 100 prn or of about 50 pm, joins along the line of sight 11 at a small distance to the first skimmer 34, in which an opening is formed, which is the the line of sight 11 extending portion 12a of the first pressure reduction chamber 12 with the line of sight 11 extending portion 13a of the second pressure reduction chamber 13 connects. The chopper 37 acts on the first skimmer 34 and shifts it laterally, so that the first skimmer 34 in the region of the line of sight 11th is displaced and in this way closes the inlet opening 5 (nearly) gas-tight, so that the first vacuum pump VP1 can generate a sufficiently low base pressure. In the open state, the chopper 37 releases the inlet opening 5 in the short term, so that the gas 2 to be examined expands behind the inlet opening 5 and forms a molecular beam which enters the analyzer 8 with minimal background pressure. The pulsed supply by means of the chopper 37 (in the millisecond range) can significantly increase the signal-to-background ratio, for example by an order of magnitude (factor ten), compared to conventional devices. The diameter of the inlet opening 5 is selected such that, on the one hand, a representative quantity of the gas 2 to be examined can enter the vacuum housing 4 and, on the other hand, no return flow from the interior of the vacuum housing 4 into the recipient 6 takes place.

5 shows the second vacuum component 22 with the integrated therein chopper 37, which acts on the arranged in the region of the inlet opening 5 first skimmer 34 which extends along the line of sight 1 1 approximately to the inlet opening 5 to this (almost completely) to close and thereby cause the pulsed supply of the gas to be examined 2 in the analysis room 7. In the example shown, a chopper 37 is used to generate gas pulses, which works in the manner of a tuning fork. The first skimmer 34 is formed on a plate, which is mounted on its opposite sides on two lateral leaf springs 38a, b. The leaf springs 38a, b are at one end to a

Supported body 40 and are deflected laterally at its other end by means of a magnet 39, whereby the lateral position of the arranged between the two leaf springs 38a, b first skimmer 34 changed so that it either the inlet opening 5 either releases or blocks. Alternatively, the first skimmer 34 may be replaced by another actuator,

be deflected or moved for example by a piezo actuator. The first skimmer 34 projects into the so-called "zone of silence" of the Machkonus formed behind the inlet port 5 to avoid a change in the composition of the entering into the vacuum housing 4 gas 2 through the shock front. The resilient mounting of the first skimmer 34 makes it possible to deflect it in a harmonic oscillation from a rest position in which it is aligned concentrically with the line of sight 11. The oscillation or pulse frequency f _{P of} the first skimmer 34 can be adapted to the desired measurement frequency or coincides with it.

It is furthermore possible, by pulse width modulation of the opening times of the first skimmer 34, to regulate or adjust the amount of gas 2 to be analyzed which has been admitted into the analysis space 7 during a respective measurement. For this purpose, from the chopper 37 or from an integrated in this control and / or regulating device

pulse width modulated control signal to the acting as an actuator magnet 39 are applied, whereby the pulse durations At _{P of} the individual gas pulses and thus the amount of gas admitted can be selectively changed or adjusted from pulse to pulse.

Due to the modular design of the vacuum housing 4, individual maintenance and optimization of the pressure reduction device 3 or the device 1 for mass spectrometric analysis of the gas 2 to be examined can specifically exchange or manipulate individual vacuum components 21 to 26 without having to do so for this purpose the whole

Pressure reduction device 3 must be rebuilt. In addition, due to the modular construction of the pressure reduction device 3, different measurement scenarios can be realized as a function of the ambient pressure Pu, as will be described in more detail below.

If the ambient pressure Pu is between approximately 1 bar and approximately 100 mbar, the pressure reduction device 3 with all six vacuum components 21 to 26 shown in FIG. 1 is typically used in order to pass through differential pumping over three pressure levels to produce the working pressure P _A in the analysis room 7. If the ambient pressure Pu between about 100 mbar and 0 ^"2 mbar, the second vacuum part 22 may be omitted, that is, in this case by the second pressure reduction chamber 13 and analysis chamber 7 implements two pressure stages. If the

Ambient pressure Pu between about 10 ^"2 mbar and about 10 ^{" 5} mbar, is one

Pressure level sufficient, which is realized via the first vacuum pump VP1 and the analysis room 7. At this ambient pressure Pu is the

Skimmer 34 mounted in the region of the inlet opening 10 of the analysis chamber 7. Is the ambient pressure Pu even smaller and is for example about 10 ^"5 mbar or less, for example at ^{10" 8} mbar, the skimmer 34 that is, the analyzer 8 is additionally removed from the inlet opening 10 free and can directly the to be tested ( Residual) gas 2 record. Due to the modular construction of the vacuum housing 4, the pressure reduction device 3 can thus be optimized for the measurement at a respective ambient pressure Pu.

To clean the pressure reducing device 3, i. to possibly

4), it is advantageous if cleaning mechanisms are used which make it possible to clean the inside of the vacuum housing 4, without the vacuum housing 4 having to be dismantled for this purpose , The vacuum housing 4 can be baked for this purpose, which typically can take several hours or possibly several days and possibly lead to a standstill of the device in which the pressure reduction device 3 and the device 1 is used.

In addition to the cleaning by heating the vacuum housing 4, it is also possible to generate in the vacuum housing 4, a plasma (DC and / or HF), which removes impurities in the vacuum housing 4 by these converted into the gas phase and be transported by means of the vacuum pump VP1 to VP3. For the plasma cleaning can over at least one gas inlet 28b, 27b, 26b attached to the eighth, seventh and sixth vacuum components 28, 27, 26, respectively, includes a gas 43, eg an inert gas such as Ar, He, Kr or oxygen, in the analysis space 7, in the first

Pressure reduction space 12 and / or in the second pressure reduction chamber 13 are introduced. The introduced gas 43 can be used to generate a

Glow discharge or a plasma can be used if in the vacuum housing 4 at least one electrically contactable component is provided which can serve as a plasma electrode to ignite a plasma. As the plasma electrode may be an electrically insulated component of the vacuum housing 4 or possibly a specially for this purpose in the vacuum housing. 4

arranged electrode serve.

By varying the pressure generated during the introduction into the vacuum housing 4, the position at which the plasma is generated can optionally be set in a targeted manner, so that different regions of the vacuum housing 4 and the pressure reduction device 3 successively increased Plasma intensity can be charged and cleaned. This process can also be combined with a temperature increase to speed up the cleaning process and to particularly strong

Effective removal of contaminants. In the example shown, a plasma or a glow discharge in the region between the two electrically insulated skimmers 34, 36 is generated in the vacuum housing 4 by a between the two skimmers 34, 36 for generating the

Glow discharge sufficient voltage is applied.

As can be seen in FIG. 2 a, in the sixth vacuum component 26, the gas inlet 26 b and the gas connection 26 a for connection to the third vacuum pump VP 3 coincide, while the seventh and eighth vacuum components 27, 28 two separate gas inlets 27b, 28b are provided. In the area of the gas inlets 26b, 27b, 28b or elsewhere

Sensors are attached to the pressure reducing device 3, which Critical parameters such as the respective pressure P _A , PD _I , PD ₂ , the temperature and / or the degree of contamination in the vacuum housing 4 of

Measure pressure reduction device 3. A control and / or regulating device (not shown) can be used to compare the measured actual values with desired values and, if appropriate, the vacuum pumps VP1 to VP3 are suitable

to reach the target values. In particular, the self-cleaning mechanism can also be automated by the control or

Control device are triggered when using suitable sensors, the exceeding of a predetermined contamination value is detected, so that the pressure reduction device 3 can monitor and protect itself. The pressure reduction device 3 can also be controlled such that a defined lower limit of the mean free path length is established in the analyzer 8 already after a short pumping time, ideally less than 100 milliseconds after the inlet of the gas 2 to be investigated.

The sealing between the vacuum components 21 to 27 can be done by bake-Viton O-rings whose sealing surfaces only the

Seal the environment of the analyzer 8 and the analysis room 7 against the interior of the recipient 6 and against the environment. The tightness of the high vacuum prevailing in the analysis chamber 7 with respect to the environment is ensured by the vacuum connections 26a, 27a, 28a designed as CF flanges. The analyzer 8 is held in the analysis room 7 via insulated spacers (not shown) extending from the fourth vacuum component 24 having the electrical terminals 24a. In this way, the analyzer 8 can be electrically contacted in a simple manner and it can be checked during installation, whether the analyzer 8 is functional. As described above, laterally to the analyzer 8, the micro-plasma is supplied to the ionizer 9 to ionize the gas 2 to be analyzed directly in the analyzer 8. Alternatively, it is also possible to position the ionization device 9 along the line of sight 11 in front of the analyzer 8, for which purpose the spacers are shortened can. As already mentioned above, it is also possible to integrate the ionization device 9 in the first pressure reduction chamber 12 or in the second pressure reduction chamber 13, so that the ionization can take place at higher pressure and the ions are conducted into the analysis chamber 7. As mentioned above, in this case it is for optimal ion guidance of the analyte ions generated in the higher pressure in the

Analyzer room 7 advantageous to nachzuschalten a suitable ion optics.

As an alternative to the above-described electrical and / or mechanical contacting, which is passed through one or more of the vacuum components 21 to 25, optionally also a direct, lateral mechanical and / or electrical contacting individual components of the vacuum components 21 to 25 and the analyzer 8, even if they are disposed within the recipient 6.

Claims

claims

A pressure reducing device (3) comprising:

a vacuum housing (4) having an inlet opening (5) for the inlet of a gas to be examined (2) at an ambient pressure (Pu) and an analysis chamber (7) for the mass spectrometric examination of the gas to be examined (2) at a working pressure (P _A ), wherein the inlet opening (5) and an inlet opening (10) of the analysis chamber (7) are arranged along a common line of sight (11),

characterized,

that the vacuum housing (4) has a plurality of modularly connectable and along the line of sight (11) one behind the other can be arranged vacuum components (21, ..., 28), and

in that at least one pressure-reducing chamber (12, 13) separated from the analysis chamber (7) by at least one of the vacuum components (23, 27) through which the analysis chamber (7) extends runs.

2. Pressure reducing device according to claim, wherein the

Analysis space (7) through at least two of the line of sight (11) arranged vacuum components (23, ..., 28) extends.

3. Pressure reducing device according to claim 1 or 2, wherein

at least one of the vacuum components (26, 27) has a vacuum connection (26a, 27a) for connecting the at least one pressure reduction chamber (12, 13) to a vacuum pump (VP2, VP3).

4. Pressure reducing device according to claim 3, wherein the vacuum ports (26a, 27a) of a first pressure reduction chamber (12) and a second pressure reduction chamber (13) on different vacuum components (26, 27) are formed.

5. Pressure reducing device according to one of the preceding claims, wherein in one of the vacuum components (22) a portion (12a) of a first pressure reduction chamber (12) is formed, which communicates with the inlet opening (10) in the analysis space (7) ,

6. Pressure reducing device according to one of the preceding claims, wherein in one of the vacuum components (21) a portion (13 a) of a second pressure reduction space (13) is formed, which with the

Inlet opening (5) in the vacuum housing (4) is connected.

7. Pressure reducing device according to one of the preceding claims, wherein the vacuum components (21, 28) are designed as pipe components.

8. Pressure reducing device according to claim 7, wherein the

Analysis room (7) along the line of sight (11) centrally through the pipe components (21, 28) extends.

9. Pressure reducing device according to claim 8, wherein the

Analytical space (7) has a diameter (d) of at least 70 mm.

10. Pressure reducing device according to one of claims 7 to 9, at

which the pipe members (21, 28) have a pipe diameter (D) of 150 mm or less.

11. Pressure reducing device according to one of the preceding claims, wherein at least one vacuum component (24, 25) at least one electrical or mechanical connection (24a, 25a) for producing an electrical or mechanical connection (30a, 31a) with a

Voltage source (30) or with an actuator (31).

12. Pressure reducing device according to claim 11, wherein at least one vacuum component (22, 25) at least one connectable to the electrical and / or mechanical connection (24a, 25a) bore (32) for carrying out the electrical and / or mechanical connection (30a , 31a) to a further vacuum component (22, 25).

13. Pressure reducing device according to one of the preceding claims, wherein at least one of the vacuum components (23) for receiving an ionization device (9) and / or an analyzer (8) within the analysis space (7) is formed.

14. Pressure reducing device according to the preamble of claim 1,

more particularly according to one of the preceding claims

comprising: a chopper (37) in the region of the inlet opening (5) for the pulsed supply of the gas (2) to be examined into the analysis chamber (7).

15. Pressure reducing device according to claim 14, wherein the chopper (37) is designed to perform the pulsed supply of the gas to be examined (2) in the analysis space (7) with pulse-to-pulse independently adjustable pulse durations (ATP).

16. Pressure reducing device according to claim 14 or 15, wherein the chopper (37) is formed, the pulse durations (ATP) in the pulsed

Supply of the gas to be examined (2) in the analysis room (7) at a predetermined pulse frequency (f _P ) set.

17. Pressure reducing device according to one of claims 14 to 16, wherein the chopper (37) acting on a Skimmer (34) which is displaceable for pulsed supply of the gas to be examined (2) in a direction transverse to the inlet opening (5).

18. Pressure reducing device according to claim 1 7, wherein the skimmer (34) is resiliently mounted and deflected in a periodic movement from a rest position.

19. Pressure reducing device according to one of the preceding claims, further comprising: one in the region of the inlet opening (10) of the

Analysis room (7) arranged Skimmer (36) for guiding the gas to be examined (2) in the analysis space (7).

20. Pressure reducing device according to one of the preceding claims, further comprising: an actuatable diaphragm (33) for covering the

Inlet opening (5).

21. Device (1) for the mass spectrometric examination of a gas (2), comprising:

a pressure reducing device (3) according to one of the preceding claims, as well as

a in the analysis room (7) arranged analyzer (8) for

Mass spectrometric analysis of the gas (2) in the

Working pressure (PA).

22. The apparatus of claim 21, further comprising: one in the analysis room (7) arranged and / or connected to the analyzer (8)

Ionization device (9) for ionizing the gas to be examined (2).

23. A method for removing contaminants (42) from a pressure reducing device (3) according to the preamble of claim 1, in particular according to one of claims 1 to 20, comprising the steps of: introducing gas (43) into the analysis space (7) and / or in at least a pressure reduction space (12, 13) via at least one gas inlet (26b, 27b, 28b) which is preferably formed on at least one of the vacuum components (26, 27, 28),

such as

Removing the contaminants (42) by generating a

Glow discharge between a first skimmer (34), which is arranged in the region of the inlet opening (5) of the vacuum housing (4), and a second skimmer (36) arranged in the region of the inlet opening (10) in the analysis space (7) is.