Residual gas analysis method and residual gas analysis system

Abstract

The invention relates to a residual gas analysis method and system, wherein a high vacuum is generated in a vacuum chamber (40). In a first phase (T1), a first residual gas composition contained in the vacuum chamber (40) is mass spectrometrically examined and a first measured pressure value (M1) relating to the total pressure (P1) of the first residual gas composition is recorded by means of a pressure sensor (45). In a second phase (T3), an auxiliary gas is introduced into the vacuum chamber (40) and a second residual gas composition resulting from the introduction of the auxiliary gas is mass spectrometrically examined, and a second measured pressure value (M2) relating to the total pressure (P2) of the second residual gas composition is recorded by means of the pressure sensor (45). The difference between the second measured pressure value (M2) and the first measured pressure value (M1) is put into a relationship with an ion current change (Δauxiliary gas), which is mass spectrometrically determined and corresponds to the auxiliary gas, in order to obtain a sensitivity factor (S), and a mass spectrometrically determined ion current (Ii) of another residual gas component (i) is multiplied by the sensitivity factor (S) in order to obtain a standardized partial pressure (pi) for the residual gas component (i).

Description

27.11.2024 / PH Residual gas analysis method and residual gas analysis system

[0001] The invention relates to a residual gas analysis method and a residual gas analysis system.

[0002] This patent application claims priority from German patent application DE 10 2024 201 766.3, filed on February 27, 2024, to which reference is made and the contents of which are incorporated herein in their entirety (“incorporation by reference”).

[0003] Restgasanalysen werden durchgeführt, um die Zusammen-composition of a residual gas contained in a vacuum chamber. A mass spectrometric measurement can be performed to determine an ion current for various residual gas components, which represents the number of corresponding particles in the residual gas composition. Assuming that the mass spectrometer is suitably calibrated, the recorded mass spectra can be used to determine the ratios of the various residual gas components to one another in the residual gas. In order to deduce the partial pressure of a residual gas component from the ion current, it is necessary to establish a relationship between the total pressure in the vacuum chamber and the measured ion current. Without proper normalization between the total pressure and the ion current, the determined partial pressures are subject to systematic error.In general, it has proven to be not easy to correctly calibrate and standardize mass spectrometric measurement values, DE 102016 209 878 A1, DE 102020 209 482 A1, DE 102007 057 252 A1.

[0004] The invention is based on the object of presenting a residual gas analysis method and a residual gas analysis system that mitigates the aforementioned disadvantages. This object is achieved by the features of the independent claims. Advantageous embodiments are specified in the subclaims.

[0005] In the residual gas analysis method according to the invention, a high vacuum is created in a vacuum chamber. In a first phase, a first residual gas composition contained in the vacuum chamber is analyzed by mass spectrometry, and a pressure sensor records a first pressure measurement based on the total pressure of the first residual gas composition. In a second phase, an auxiliary gas is introduced into the vacuum chamber, and a second residual gas composition resulting from the introduction of the auxiliary gas is analyzed by mass spectrometry, and a second pressure measurement based on the total pressure of the second residual gas composition is recorded by the pressure sensor. The difference between the second pressure measurement and the first pressure measurement is related to an ion current change corresponding to the auxiliary gas, determined by mass spectrometry, in order to obtain a sensitivity factor for the mass spectrometric measurement.An ion current of another residual gas component determined by mass spectrometry is multiplied by the sensitivity factor to obtain a standardized partial pressure for the residual gas component. The partial pressure of the other residual gas component can be determined in a single process using the sensitivity factor or in a separate process from the determination of the sensitivity factor. The terms "first phase" and "second phase" do not imply any restriction regarding the temporal sequence of the phases. The method can be carried out such that the first phase occurs before or after the second phase.

[0006] The invention is based on the realization that a measured value for the total pressure of a residual gas does not always provide a suitable reference point by which partial pressures can be correctly standardized. The pressure sensor used to measure the total pressure can be an ionization vacuum gauge, for example a hot-cathode vacuum gauge, in particular a Bayard-Alpert vacuum gauge. With such a pressure sensor, in which the number of particles in the residual gas is determined from electrical quantities, not all components of the residual gas contribute equally to the measured pressure. Ionization vacuum gauges are usually calibrated to the components of the natural atmosphere, so that an accurate pressure reading is obtained if the composition of the residual gas is similar to that of the natural atmosphere. If the residual gas contains a high proportion of other substances, such as hydrocarbons, the resulting pressure readings are distorted.Partial pressures that are standardized to falsified pressure measurements are also falsified.

[0007] The invention proposes normalizing the partial pressures of residual gas components based on a difference between two measured total pressure values. The two measured pressure values ​​are obtained by changing the composition of a residual gas by supplying an auxiliary gas. The auxiliary gas changes the total pressure, which is reflected in a change in the measured pressure value. In addition, the distribution of the ion currents determined with the mass spectrometer changes. The two changes correspond to each other, as they are due to the same change in the composition of the residual gas. A sensitivity factor for the mass spectrometric measurement can be determined, with which the measured ion current change is related to the corresponding change in the total pressure. This sensitivity factor can be applied to other residual gas components to calculate a standardized partial pressure from the ion current of the residual gas component. A side effect of this procedure is that the sum of the partial pressures calculated according to the invention generally does not agree with the measured total pressure.

[0008] The method is preferably carried out in such a way that the first pressure measurement and the second pressure measurement are obtained using a pressure sensor calibrated to the auxiliary gas. This means that, for a residual gas whose composition matches the composition of the auxiliary gas, either the pressure sensor directly provides accurate information about the total pressure or accurate information about the total pressure can be obtained by applying a known correction factor to the measured value. If the addition of the auxiliary gas is the only change in the composition of the residual gas, a direct relationship arises between the change in the auxiliary gas partial pressure and the difference between the two pressure measurements.

[0009] The auxiliary gas can be introduced into the vacuum chamber at a constant flow rate. This creates a constant total pressure, which forms an equilibrium between the flow rate of the auxiliary gas and the suction rate of the vacuum system. A total pressure is referred to as constant within the meaning of the invention if unavoidable pressure changes are small in relation to the total pressure and to pressure changes between the first phase and the second phase. After the introduction of the auxiliary gas begins, it may take some time for a new equilibrium to be established. The second pressure measurement value across the total pressure of the second residual gas composition is preferably recorded after a constant total pressure of the second residual gas composition has been established.

[0010] Since the method according to the invention relates relative quantities to one another, the method can be carried out without calibrating the flow rate of the auxiliary gas to an absolute value. If, in one possible embodiment of the method, the flow rate is calibrated to an absolute value, this opens up the additional possibility of monitoring the sensitivity of the total pressure measurement.

[0011] The introduction of auxiliary gas can be stopped after the second pressure measurement has been recorded. It can then take some time after the auxiliary gas supply has been stopped until a new equilibrium has been established in which the residual gas composition in the vacuum chamber is no longer enriched with the auxiliary gas. The residual gas composition that is established after the auxiliary gas introduction has been stopped can correspond to the first residual gas composition that existed in the vacuum chamber before the auxiliary gas was supplied. By switching the auxiliary gas introduction on and off, a repeated change between the first residual gas composition and the second residual gas composition can be made. The first pressure measurement value corresponding to the first residual gas composition and the second pressure measurement value corresponding to the second residual gas composition can each be recorded after the switching on or offSwitching off the auxiliary gas supply has caused the resulting unsteady transition conditions to subside.

[0012] The method can be carried out by determining the sensitivity factor in a pre-measurement and applying the pre-determined sensitivity factor to mass spectra acquired at a later time. Alternatively, determining the sensitivity factor and acquiring the mass spectra can be to which the sensitivity factor is applied, must be carried out within a single process. By switching repeatedly between the first residual gas composition and the second residual gas composition, current sensitivity factors can be continuously obtained. This increases the probability that the sensitivity factor closely matches the actual conditions within the residual gas analysis system.

[0013] Das Hilfsgas kann aus einer Hilfsgasquelle in Form ei-An auxiliary gas supply can be supplied. The auxiliary gas supply can be connected to the vacuum chamber via a connecting line. A switchable valve can be formed between the auxiliary gas supply, in which the pressure can be higher than in the vacuum chamber, and the vacuum chamber. The switchable valve can have a first switching state in which the connection between the auxiliary gas supply and the vacuum chamber is interrupted, so that no auxiliary gas can pass from the auxiliary gas supply into the vacuum chamber. The switchable valve can have a second switching state in which the connection between the auxiliary gas supply and the vacuum chamber is open. A throttle can be arranged between the auxiliary gas supply and the vacuum chamber so that the auxiliary gas flows into the vacuum chamber at a constant flow rate in the second switching state. The throttle can be an adjustable throttle.

[0014] The auxiliary gas can be a pure gas. The atomic mass unit (amu) of the auxiliary gas can, for example, be between 10 and 70, preferably between 20 and 50. The pressure measurements recorded with a pressure sensor calibrated for atmospheric gas can then often be used directly without the need for additional calibration. In one embodiment, the auxiliary gas is nitrogen, in particular N2.

[0015] Allgemein ist es von Vorteil, wenn das Hilfsgas einehas a low tendency to fragmentation. There is then a high probability that the molecular structure will survive the ionization process in the mass spectrometer unchanged, and there is no need to identify both the auxiliary gas itself and the fragments in the mass spectrometric measurement. In this context, a noble gas, particularly argon, can be used as the auxiliary gas. Noble gases sometimes have mass numbers that differ significantly from the mass numbers of the predominant components of the atmospheric gas. To nevertheless be able to use measured values ​​recorded with a pressure sensor calibrated for atmospheric gas, a correction factor can be applied, which relates the change in the partial pressure of the auxiliary gas to the change in the total pressure. Isotopes of a noble gas can be taken into account by applying a compensation factor. The same applies to molecular fragments of an auxiliary gas.

[0016] The vacuum chamber can be heated to a total pressure between 10- 5 mbar and 10 -9 mbar, preferably to a total pressure between 10 -6 mbar and 10 -8 mbar. The pressure difference between the total pressure of the first residual gas composition and the total pressure of the second residual gas composition can, for example, be between 10-8 mbar and 10-4 mbar, preferably between 10-8 mbar and 10-6 mbar.

[0017] To create and / or maintain the vacuum, a vacuum pump can be connected to the vacuum chamber. If the vacuum pump has a calibrated suction power, the determined partial pressure can be used to determine the corresponding outgassing rate of a component arranged in the vacuum chamber.

[0018] For the mass spectrometric investigation of the residual gas compositions in the vacuum chamber, a quadrupole A mass spectrometer can be used. In one embodiment, the range of mass-to-charge ratios detected by the mass spectrometer extends from 0 to 200.

[0019] In the method according to the invention, at least the ion current determined for a mass-to-charge ratio is multiplied by the sensitivity factor to obtain a standardized partial pressure for the respective residual gas component. The method can be carried out such that, for several mass-to-charge ratios, the determined ion currents are multiplied by the sensitivity factor to obtain a standardized partial pressure for a plurality of residual gas components. In one embodiment, the mass-spectrometrically detected range of mass-to-charge ratios is divided into a plurality of bins, for example, bins of integer mass numbers, with an ion current being determined for each of the bins. By applying the sensitivity factor to the ion current, a standardized partial pressure can be determined for each of the bins.

[0020] If a partial pressure calculated according to the invention is available for all determined residual gas components, a calculated total pressure can be obtained by summing the calculated partial pressures. The calculated total pressure can be compared with a measured total pressure. Assuming that the measured pressure is calibrated to the natural atmosphere, the deviation between the calculated total pressure and the measured total pressure can be used to determine whether the composition of the residual gas is similar to the natural atmosphere or deviates significantly from it.

[0021] The method according to the invention can be carried out for the purpose of qualifying a component, in particular for determining the outgassing rate of a component. The component can a component of a microlithographic projection exposure system. Microlithographic projection exposure systems are often operated under vacuum. This is especially true when the wavelength of the radiation used is in the extreme ultraviolet spectral range, specifically between 5 nm and 30 nm. For image quality, it is important that the composition of the residual gas inside the projection exposure system is within the specified specifications. This requires that the components used there do not emit excessive outgassing.

[0022] To determine whether the outgassing of a component intended for a microlithographic projection exposure system is within the specified limits, the component can be placed in the vacuum chamber according to the invention and exposed to a high vacuum. The composition of the residual gas in the vacuum chamber is largely determined by the component's outgassing. From the composition of the residual gas, a conclusion can be drawn as to whether the component meets the specification with regard to its outgassing rate.

[0023] It is also possible for the method according to the invention to be carried out for the purpose of process monitoring. The vacuum chamber can be a component of a microlithographic projection exposure system operated with EUV radiation. The optical components of the projection exposure system that guide or shape the EUV beam path can be arranged within the vacuum chamber. The method according to the invention can be used to determine whether the composition of the residual gas in the vacuum chamber meets the specifications.

[0024] The invention also relates to a residual gas analysis system comprising a vacuum chamber, a vacuum pump, an auxiliary gas source, a pressure sensor, a mass spectrometer and a Control unit. The vacuum pump is designed to create a high vacuum in the vacuum chamber. The control unit is designed to control the components of the residual gas analysis system such that, in a first phase, a first residual gas composition contained in the vacuum chamber is analyzed with the mass spectrometer, and a first pressure measurement value for the total pressure of the first residual gas composition is recorded with the pressure sensor. In a second phase, an auxiliary gas is introduced into the vacuum chamber from the auxiliary gas source, and a second residual gas composition created by the introduction of the auxiliary gas is analyzed with the mass spectrometer, wherein a second pressure measurement value for the total pressure of the second residual gas composition is recorded with the pressure sensor.The control unit is further designed to relate the difference between the second pressure measurement value and the first pressure measurement value to a mass spectrometrically determined ion current change corresponding to the auxiliary gas in order to obtain a sensitivity factor, and to multiply a mass spectrometrically determined ion current of another residual gas component by the sensitivity factor in order to obtain a standardized partial pressure for the residual gas component.

[0025] The disclosure includes further developments of the method with features described in the context of the system according to the invention. The disclosure includes further developments of the system with features described in the context of the method according to the invention.

[0026] The invention is described below by way of example with reference to the accompanying drawings using advantageous embodiments. They show: Fig. 1: an embodiment of a microlithographic projection exposure system; Fig. 2: an embodiment of a residual gas analysis system according to the invention; Fig. 3: a schematic representation of a quadrupole mass spectrometer; Fig. 4: a schematic representation of the pressure curve when carrying out the method according to the invention; Fig. 5: an alternative embodiment of a residual gas analysis system according to the invention.

[0027] Fig. 1 schematically illustrates a microlithographic EUV projection exposure system. The projection exposure system comprises an exposure beam source 14, an illumination system 10, and a projection lens 22, which are operated together in a vacuum housing 23.

[0028] The exposure beam source 14 generates electromagnetic radiation in the EUV range, i.e., in particular, with a wavelength between 5 nm and 30 nm. The exposure radiation emanating from the exposure beam source 14 is focused into an intermediate focal plane 16 by a collector 15. Exposure radiation passing from the intermediate focal plane 16 is guided into an object plane 12 by the illumination system 10, so that an object field in the object plane 12 is illuminated with uniform radiation intensity.

[0029] The illumination system 10 comprises a deflecting mirror 17, with which the exposure radiation is deflected onto a first facet mirror 18. A second facet mirror 19 is arranged downstream of the first facet mirror 18. The second facet mirror 19 images the facets of the first facet mirror 18 onto the object plane 12.

[0030] A photomask 13 is arranged in the object plane 12 and is imaged into an image plane 21 via a plurality of mirrors 11 of the projection lens 22. A structure formed on the photomask 13 is transferred to a radiation-sensitive layer of a wafer 20 arranged in the image plane 21. The photomask 13 is suspended from a first scanning device 24, and the wafer 20 rests on a second scanning device 25, so that the wafer 20 can be exposed in a scanning process in which the photomask 13 and the wafer 20 are moved synchronously with one another.

[0031] The various mirrors of the projection exposure system, which reflect the illumination radiation, are designed as EUV mirrors. The EUV mirrors are provided with highly reflective coatings. These can be multilayer coatings, particularly multilayer coatings with alternating layers of molybdenum and silicon.

[0032] Components arranged in the vacuum housing 23 of the projection exposure system are subject to strict outgassing specifications. Excessive outgassing can lead to an undesirable change in the composition of the residual gas in the vacuum housing 23, which in turn can adversely affect the operation of the projection exposure system. Therefore, before using a component in the projection exposure system, an examination can be conducted to determine the level of outgassing of the component.

[0033] As shown schematically in Fig. 2, the examination can be carried out in a vacuum chamber 40. A vacuum pump 47 is connected to the vacuum chamber 40 and is designed to create a high vacuum in the interior of the vacuum chamber 40 with a pressure in the order of magnitude of, for example, 10 -7 mbar. A connection 46 is connected to a A pressure sensor 45 in the form of an ionization vacuum gauge is connected to the vacuum chamber 40. A quadrupole mass spectrometer 43 is connected to the interior of the vacuum chamber 40 via a connecting tube 44. A support surface 41 is formed in the vacuum chamber 40, on which a component 42 to be examined rests.

[0034] The component 42 may have undergone one or more manufacturing steps, which may, for example, have taken place in a process chamber under vacuum. After completion of the manufacturing steps, the component 42 may have been transported from the process chamber to the vacuum chamber 40. It is also possible that one or more manufacturing steps took place directly in the vacuum chamber 40. In one embodiment, the vacuum is applied during the manufacturing step and maintained until the examination.

[0035] After undergoing such manufacturing steps, the component 42 generally has an outgassing rate that is higher than permissible for use in the projection exposure system. The method according to the invention can be used to investigate the outgassing rate of the component 42 and to qualify whether the outgassing rate of the component 42 meets the relevant specifications. When the vacuum pump 43 is in operation, an equilibrium is established that depends, among other things, on the outgassing rate of the component 42 and the suction rate of the vacuum pump 43. This equilibrium leads to a constant total pressure being established in the interior of the vacuum chamber 40 over time.

[0036] The ionization vacuum gauge 45 provides a measured value of the total pressure in the vacuum chamber 40. The pressure measurement with the ionization vacuum gauge 45 is indirect, in that the number of particles in the residual gas composition is deduced from electrical quantities. In this type of Measurement, it cannot be assumed that the ionization vacuum gauge 45 has a uniform sensitivity for different types of particles. For example, it has been observed that the sensitivity decreases with increasing mass number of the particles. An erroneous pressure measurement is provided, which is usually lower than the actual total pressure. The ionization vacuum gauge 45 could provide a pressure measurement that corresponds to the actual total pressure if it were calibrated to a gas composition that corresponds to the residual gas composition. In practice, ionization vacuum gauges 45 are usually calibrated to the composition of the atmospheric gas, i.e., air. Due to the outgassing of component 42, however, the residual gas composition in the vacuum chamber 40 has a significantly different composition than air and, in particular, a significantly higher proportion of particles with a high mass number.

[0037] Das zu dem Quadrupol-Massenspektrometer 43 führendeConnecting tube 44 is connected to the vacuum chamber 40. Through free gas exchange, which can optionally be supported by the influence of a pressure gradient acting in the direction of the quadrupole mass spectrometer 43, the residual gas spreads toward the quadrupole mass spectrometer 43, so that the composition of the residual gas can be investigated with the quadrupole mass spectrometer 43.

[0038] Gemäß Fig. 3 hat das Quadrupol-Massenspektrometer 43 an inlet opening 34 through which the residual gas enters the interior of the quadrupole mass spectrometer 43. An ion source 32 and a mass analyzer 27 are arranged one behind the other in the quadrupole mass spectrometer 43. The mass analyzer 27 comprises a quadrupole 31 and a detector 37. The components of the residual gas, which are mostly still neutral upon entering the quadrupole mass spectrometer 43, are ionized in the ion source 32. Ionized by the ion source 32 Species continue their journey through the quadrupole 31 and enter the detector region of the mass analyzer 27, where they are analyzed based on their mass-to-charge ratio.

[0039] Der Massenanalysator 27 umfasst den Detektor 37, der extends in a radial direction relative to the direction of motion of the particles. The ionic species change their direction of motion under the influence of an electric field before being detected by detector 37. For this purpose, an electrical voltage is applied, with which the ionic species are accelerated as electrically charged particles toward detector 37. The voltage can, for example, be on the order of a few kilovolts.

[0040] Der Detektor 37 ist in der beispielhaften Ausführungs-It is designed as a secondary electron multiplier, which determines the number of charge carriers flowing when the ionic species strike the detector 37. By applying a suitable combination of DC and AC voltage to the rods of the quadrupole 31, the quadrupole 31 can be adjusted so that only species with a specific mass-to-charge ratio can pass through the quadrupole 31. The number of charge carriers counted by the detector 37 corresponds to the number of ionic species that have passed through the quadrupole, all of which have the same mass-to-charge ratio due to filtering by the quadrupole 31. Over time, the quadrupole 31 is tuned through various mass-to-charge ratios, so that, based on a temporal correlation between the charge carriers counted by the detector 37 and the state of the quadrupole 31, a number of charge carriers can be assigned to each mass-to-charge ratio.

[0041] Jeder massenspektrometrisch gemessene Ionenstrom ent-corresponds to a partial pressure in the residual gas composition. In order to convert the ion current into a partial pressure, it is necessary to relate the ion current to the total pressure in the vacuum chamber 40. If standardization is performed based on an incorrectly determined measured value for the total pressure, the partial pressure will also be incorrectly determined. According to the invention, it is proposed to bring about a change in the total pressure and to standardize the partial pressure based on the pressure change.

[0042] According to Fig. 2, an auxiliary gas source is connected to the vacuum chamber 40 in the form of a reservoir 48 filled with a gas of defined composition. In the present embodiment, the gas is nitrogen (N2). However, other gases, such as noble gases, are also possible in the reservoir 48. A switchable valve 49 and an adjustable throttle 50 are connected in series between the reservoir 48 and the vacuum chamber 40. The series configuration of the valve 49 and the throttle 50 can also be reversed from that shown in Fig. 2.

[0043] In the method according to the invention, the system is initially in a state in which the switchable valve 49 is closed. The vacuum pump 47 is in operation, so that an equilibrium state is established in which the total pressure P1 of a first residual gas composition in the vacuum chamber 40 is constant. At a time T1, which lies within a first phase of the method according to the invention, a pressure measurement value M1 is recorded with the ionization vacuum gauge 45, see Fig. 4. The pressure measurement value M1 correlates with the total pressure P1 in the vacuum chamber 40, but is subject to a systematic error, as explained. At a subsequent time T2, the switchable valve 49 is opened. The adjustable throttle 50 results in a constant leak rate, with which the gas flows from the storage container 48 into the vacuum chamber 40 as auxiliary gas. This results in a rapid pressure increase, after which it takes a short time until equilibrium is established with the new total pressure P2 of a second residual gas composition. At a time T3, which lies within a second phase of the method according to the invention, a second pressure measurement value M2 is recorded, which correlates with the higher total pressure P2, but is also subject to a systematic error. At a subsequent time T4, the switchable valve 49 is closed again, so that the flow of auxiliary gas is interrupted. It takes a certain time until the vacuum pump 47 has again established an equilibrium corresponding to the lower total pressure P1.

[0044] In parallel, mass spectra are continuously recorded with the mass spectrometer 43, which range from, for example, 1 to 200. The addition of the auxiliary gas changes the mass spectrum by detecting a large number of particles of the auxiliary gas. For the mass-charge ratio associated with the auxiliary gas, a difference results between a first mass spectrum, recorded at time T1 without the auxiliary gas, and a second mass spectrum, recorded at time T2 with the auxiliary gas.

[0045] Since the conditions have otherwise remained unchanged, the difference ΔI in the auxiliary gas ion current corresponds to the difference Δp Hilfsgas between the pressure readings M2 and M1. A sensitivity factor S can be determined by calculating the difference Δp caused by the auxiliary gas Hilfsgasbetween the second pressure measurement value M2 and the first pressure measurement value M1 is set in relation to the difference ΔIauxiliary gas in the ion current of the auxiliary gas.

[0046] With each mass spectrum, an ion current Ii is also determined for each of the other components i of the residual gas composition. By multiplying the ion currents Ii by the sensitivity factor S, a partial pressure P can be determined for each of the components i of the residual gas composition. i be determined. ^^ = ^ ∙ ^^

[0047] A partial pressure p determined in this way i requires no further standardization if the ionization vacuum gauge 45 is calibrated to the auxiliary gas, which is usually the case when nitrogen is used as the auxiliary gas.

[0048] If an auxiliary gas is used for which the ionization vacuum gauge 45 is not calibrated, a correction factor k can be applied to obtain the correct relationship between the measured pressure difference Δp Hilfsgas , gemessen and the actual pressure difference Δpauxiliary gas,real. ∆^^^^^^^^^^,^^^^ = ^ ∙ ∆^^^^^^^^^^,^^^^^^^^

[0049] The application of such a correction factor k is often necessary when, for example, a noble gas is used as the auxiliary gas. The sensitivity factor then applies

[0050] If, without further compensation, the ion current change ΔI determined for the mass-to-charge ratio of the auxiliary gas Hilfsgas used to determine the sensitivity factor S, it is not taken into account that individual particles of the auxiliary gas may have changed their state before they are the detector 37 of the mass spectrometer 43. For example, if the gas is nitrogen, some of the N2 molecules may have split into individual N atoms. This results in them being detected not with the mass-to-charge ratio of the auxiliary gas, but with a different mass-to-charge ratio. This effect can be corrected with a compensation factor R.

[0051] Compensation factors R can be applied accordingly to correctly account for different isotopes of a noble gas. The compensation factors R applicable to the respective application are available because the behavior of the gas species in question under the influence of the ionization unit of a mass spectrometer has been well studied.

[0052] The residual gas analysis system in Fig. 2 comprises a control unit 51, which communicates with the quadrupole mass spectrometer 43, the ionization vacuum gauge 45, the switchable valve 49, and the adjustable throttle 50. The quadrupole mass spectrometer 43 and the switchable valve 49 are controlled in such a way that the pressure measurement values ​​M1, M2 required for the inventive method, as well as the associated mass spectra, can be recorded. The data are combined and evaluated in the control unit 51 to obtain standardized partial pressures for the various mass-to-charge ratios of the mass spectra.

[0053] Fig. 5 shows an alternative embodiment in which the method according to the invention is applied to a microlithographic projection exposure system for the purpose of process monitoring. In the interior of the vacuum housing An inner housing 28 is formed within this housing 23, which surrounds the exposure beam path. In Fig. 1, only a section of the inner housing 28 arranged between the deflection mirror 17 and the first facet mirror 18 is indicated. In fact, the inner housing 28 surrounds further sections of the beam path. The inner housing 28 is designed such that the exposure beam path can take its path over the various optical elements 17, 18, 19, M1-M6, without the inner housing 28 getting in the way.

[0054] Through interaction between the EUV radiation and the hydrogen, a plasma is generated, which includes ionic plasma species (H +) or radical plasma species (H) are formed. The hydrogen plasma has the effect of removing contamination, which can arise, for example, from outgassing from components of the projection exposure system, from the surfaces of the optical elements arranged in the inner housing 28. This creates compounds, for example, of hydrogen and carbon or of hydrogen and nitrogen, which are distributed in the residual gas atmosphere in the interior of the inner housing 28.

[0055] The projection exposure system is equipped with a mass spectrometer 43 designed to analyze the composition of the residual gas. Figure 1 shows a single mass spectrometer 43 connected to the inner housing 28 in the region between the deflection mirror 17 and the first facet mirror 18. The projection exposure system can comprise a plurality of mass spectrometers 43 in order to be able to analyze the composition of the residual gas in different regions of the inner housing 28. The projection exposure system with the mass spectrometer 43 forms a residual gas analysis system according to the invention, which is operated under the control of a controller (not shown) such that the method according to the invention is carried out.

Claims

Patent claims1. Residual gas analysis method, in which a high vacuum is created in a vacuum chamber (40), in which, in a first phase (T1), a first residual gas composition contained in the vacuum chamber (40) is analyzed by mass spectrometry, and a first pressure measurement value (M1) is recorded with a pressure sensor (45) over the total pressure (P1) of the first residual gas composition, in which, in a second phase (T3), an auxiliary gas is introduced into the vacuum chamber (40), and a second residual gas composition resulting from the introduction of the auxiliary gas is analyzed by mass spectrometry, wherein, with the pressure sensor (45), a second pressure measurement value (M2) is recorded over the total pressure (P2) of the second residual gas composition, in which the difference between the second pressure measurement value (M2) and the first pressure measurement value (M1) is set in a ratio to an ion current change corresponding to the auxiliary gas, determined by mass spectrometry (∆Iauxiliary gas),to obtain a sensitivity factor (S), and in which a mass spectrometrically determined ion current (Ii) of another residual gas component (i) is multiplied by the sensitivity factor (S) to obtain a standardized partial pressure (pi) for the residual gas component (i).

2. The method according to claim 1, wherein the first pressure measurement value (M1) and the second pressure measurement value (M2) are recorded with an ionization vacuum gauge (45).

3. The method according to claim 1 or 2, wherein the first pressure measurement value (M1) and the second pressure measurement value (M2) are obtained with a pressure sensor (45) that is calibrated to the auxiliary gas.

4. The method according to any one of claims 1 to 3, wherein the auxiliary gas is introduced into the vacuum chamber (40) at a constant flow rate.

5. The method according to claim 4, wherein the flow rate is calibrated to an absolute value.

6. The method according to claim 4 or 5, wherein the second pressure measurement (M2) is recorded after a constant total pressure (P2) has been established in the vacuum chamber (40).

7. The method according to any one of claims 1 to 6, wherein the introduction of auxiliary gas is terminated after the second pressure measurement (M2) has been recorded.

8. The method according to any one of claims 1 to 7, wherein a repeated change between the first residual gas composition and the second residual gas composition is carried out by switching the auxiliary gas supply on and off.

9. The method according to any one of claims 1 to 8, wherein the auxiliary gas is nitrogen, argon, or another noble gas. 10.Method according to one of claims 1 to 9, wherein the vacuum is applied with a vacuum pump (47) and wherein the vacuum pump (47) has a calibrated suction power.

11. Method according to one of claims 1 to 10, wherein the method is carried out to determine the outgassing rate of a component (42) arranged in the vacuum chamber (40).

12. Method according to claim 11, wherein the component (42) is intended for use in a microlithographic projection exposure system.

13. The method according to any one of claims 1 to 10, wherein the method is carried out for process monitoring during operation of a microlithographic projection exposure system.

14. A residual gas analysis system comprising a vacuum chamber (40), a vacuum pump (47), an auxiliary gas source (48), a pressure sensor (45), a mass spectrometer (43), and a control unit (51), wherein the vacuum pump (47) is designed to create a high vacuum in the vacuum chamber (40), and wherein the control unit is designed to control the components of the residual gas analysis system such that, in a first phase (T1), a first residual gas composition contained in the vacuum chamber (40) is analyzed with the mass spectrometer (43), and a first pressure measurement value (M1) is recorded via the total pressure (P1) of the first residual gas composition with the pressure sensor (45).that in a second phase (T3) an auxiliary gas is introduced into the vacuum chamber (40) from the auxiliary gas source (48), and a second residual gas composition resulting from the introduction of the auxiliary gas is examined with the mass spectrometer (43), wherein a second pressure measurement value (M2) is recorded via the total pressure (P2) of the second residual gas composition with the pressure sensor (45), wherein the control unit (51) is further designed to relate the difference between the second pressure measurement value (M2) and the first pressure measurement value (M1) to a mass spectrometrically determined ion current change (∆Iauxiliary gas) corresponding to the auxiliary gas in order to obtain a sensitivity factor (S), and to multiply a mass spectrometrically determined ion current (Ii) of another residual gas component (i) by the sensitivity factor (S) in order to obtain a standardized partial pressure (pi) for the residual gas component (i)to win.,

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