Methods for operating a particle beam system and particle beam system

Abstract

A method for operating a particle beam system comprises a first operating mode and a second operating mode. The first operating mode involves evacuating gas from a vacuum chamber of the particle beam system into a buffer chamber of the particle beam system using a turbomolecular pump of the particle beam system, and evacuating the gas in the buffer chamber using a backing pump of the particle beam system. The second operating mode involves evacuating gas from the vacuum chamber into the buffer chamber using the turbomolecular pump, while the evacuation of the gas in the buffer chamber using the backing pump is stopped, and acquiring values ​​of a quantity characterizing the supply of electrical operating current to the turbomolecular pump while the evacuation of the gas in the buffer chamber using the backing pump is stopped, and switching to the first operating mode when the acquired quantity satisfies a predetermined first criterion.

Description

[0001] The present invention relates to a method for operating a particle beam system and a particle beam system.

[0002] In a particle beam system, such as an electron beam microscope, a particle beam generated by a particle beam source is directed onto a sample for examination. To prevent particles of the particle beam from interacting with gases in the particle beam system on their way from the source to the sample, a vacuum system is provided. This system uses multiple pumps to create a vacuum in a vacuum chamber within the particle beam system, which is permeated by the particle beam. The multiple pumps typically include a backing pump to create a forevacuum in the vacuum chamber, and a second pump, such as a turbomolecular pump, which further enhances the forevacuum created by the backing pump.

[0003] Operating a turbomolecular pump typically requires a pre-existing forevacuum, meaning the pump must continuously maintain this forevacuum. However, operating the forevacuum generates vibrations in the particle beam system, reducing the quality of particle optical images and incurring operating costs. Therefore, a method is known in which the forevacuum is temporarily switched off, during which time gas is pumped from the turbomolecular pump into an evacuated buffer chamber to mitigate forevacuum degradation. The duration of the forevacuum switch-off is controlled by the gas pressure at the buffer chamber, which is detected by a pressure sensor.

[0004] In general, the vacuum system of the particle beam system is a complex system that includes a large number of expensive components that need to be procured, assembled, are prone to failure, and require maintenance.

[0005] Accordingly, one objective of the present invention is to propose a particle beam system with a simplified vacuum system.

[0006] The particle beam system used in the method proposed below comprises a particle beam source for generating a particle beam, a sample holder on which a sample to be irradiated with the particle beam can be arranged, an evacuable vacuum space in which the sample holder is arranged, a turbomolecular pump, a buffer chamber and a backing pump.

[0007] It should be noted that an evacuable space is one in which removing gas from the space reduces the gas pressure within the space. Furthermore, the terms "connection" and "connected" refer to the fact that gas can flow through the connection. For example, connections between vacuum spaces refer to a gas flow from one vacuum space to another. Specifically, a vacuum space is separated from another if no gas, or very little compared to the volume of the vacuum space, can flow into the other vacuum space. Two vacuum spaces are connected by an opening if gas can flow through the opening from one vacuum space to the other. Signal and power lines are referred to here as electrical connections.

[0008] The method proposed to solve the aforementioned problem comprises a first operating mode and a second operating mode. The first operating mode involves evacuating gas from the vacuum chamber into the buffer chamber using the turbomolecular pump and evacuating the gas in the buffer chamber using the backing pump. The second operating mode involves evacuating gas from the vacuum chamber into the buffer chamber using the turbomolecular pump, while the evacuation of the gas in the buffer chamber using the backing pump is stopped, and acquiring values ​​of a quantity characterizing the supply of electrical operating current to the turbomolecular pump while the evacuation of the gas in the buffer chamber using the backing pump is stopped, and switching to the first operating mode when the acquired quantity meets a predetermined first criterion.According to some embodiments, the first criterion is met if the measured quantity represents a power of the electrical operating current supplied to the turbomolecular pump that is above a first threshold value, and is not met if the measured quantity represents a power of the electrical operating current supplied to the turbomolecular pump that is below the first threshold value. According to some embodiments, the backing pump is switched off in the second operating mode.

[0009] For example, the particle beam system is operated in a standby mode and a standard mode. In standby mode, the backing pump is switched off, while in standard mode, both the turbomolecular pump and the backing pump are operated. In standby mode, the operating current supplied to the turbomolecular pump is measured. This operating current depends on the gas pressure at one of the pump's outlets. If the gas pressure at the outlet is high, the load on the pump increases due to backflow, thus increasing the operating current. Therefore, by measuring the operating current supplied to the turbomolecular pump, it is possible to infer the gas pressure at the pump's outlet and, consequently, the need to operate the backing pump to evacuate the buffer chamber.By monitoring the operating current of the turbomolecular pump, a pressure sensor located in the buffer chamber is no longer required. Consequently, the pressure sensor and related components of the vacuum system can be eliminated, simplifying the vacuum system's assembly and maintenance. It should be noted that the load on the turbomolecular pump also depends on the gas pressure at one of its inlets. However, the method described above is particularly advantageous when the gas pressure at the turbomolecular pump inlet is not elevated or only slightly elevated. For example, according to some embodiments, the method described above can be suspended when the gas pressure at the turbomolecular pump inlet is elevated, and the backing pump can be operated until the gas pressure at the turbomolecular pump inlet has normalized.

[0010] According to some embodiments, the particle beam system includes a vacuum valve located between the buffer chamber and the backing pump, wherein the vacuum valve is open in the first operating mode and closed in the second operating mode. This valve is hereinafter also referred to as the standby valve and, in particular, prevents substances from being drawn into the backing pump by the backing pump when the backing pump is not operating.

[0011] A buffer chamber is a physical volume into which the turbomolecular pump pumps gas when the particle beam system is operating in standby mode. The buffer chamber can be provided by a connecting line between the turbomolecular pump and the backing pump, the volume of which is typically defined by its length and cross-sectional area. The volume of the connecting line can be extended and / or widened to increase the buffer chamber, and may include bulges, branch lines, and / or adjoining chambers. The buffer chamber need not be provided by the entire connecting line between the turbomolecular pump and the backing pump, but can also be provided only by the connecting line from an outlet of the turbomolecular pump to the standby valve.For example, a valve located directly at the outlet of the turbomolecular pump can also serve as the standby valve, so that the buffer space is provided by the turbomolecular pump outlet. Various embodiments are conceivable; however, the following description primarily focuses on a case in which a space is connected to the connecting line between the turbomolecular pump outlet and the pump outlet to increase the buffer space. Since the volume of the connecting line may be small compared to the space connected for expansion, the buffer space can be referred to as the buffer space in the following; however, this should not be understood as a limitation of the subject matter described above.

[0012] The vacuum valve described above can also be integrated as a component in the backing pump, or the vacuum valve can be omitted if the backing pump design ensures a seal between the backing pump and the environment when the backing pump is switched off. As described, the vacuum valve can be located at the outlet of the turbomolecular pump.

[0013] According to some embodiments, the particle beam system comprises a gas space that includes an outlet port of the turbomolecular pump, the buffer space, and an inlet port of the backing pump, wherein the particle beam system is free of a gas pressure sensor configured to detect a gas pressure in this gas space. The gas space here is, for example, the entire duct connecting the outlet of the turbomolecular pump to the backing pump, together with the buffer space. The buffer space may, for example, be located within the aforementioned duct or be connected to it, allowing gas from the duct to flow into the buffer space.

[0014] According to some embodiments, the first operating mode further includes switching to the second operating mode after a predetermined period of time from the start of the first operating mode. The predetermined period of time may, for example, be five minutes.

[0015] According to some embodiments, the buffer space has a volume of at least 500 cm³. 3 , in particular at least 1000 cm 3 and / or a volume of no more than 5000 cm³ 3 , in particular a maximum of 50000 cm 3 According to advantageous embodiments, the buffer space has a volume of 2000 cm³. 3 on.

[0016] According to some embodiments, the method includes directing the particle beam generated by the particle beam source onto the sample during the first operating mode and / or during the second operating mode. According to some embodiments, the method further includes detecting signals generated by the particle beam at the sample using a detector. For example, during the first and / or during the second operating mode, the sample can be scanned with the particle beam and a particle-optical image can be generated from the detected signals.

[0017] According to some embodiments, the first operating mode further comprises sensing the value of the quantity that characterizes the supply of electrical operating current to the turbomolecular pump and switching to the second operating mode when the sensed quantity satisfies a predetermined second criterion. According to some embodiments, the second criterion is satisfied if the sensed quantity represents a power of the electrical operating current supplied to the turbomolecular pump that is below a second threshold, and not satisfied if the sensed quantity represents a power of the electrical operating current supplied to the turbomolecular pump that is above the second threshold. For example, in a case where the particle beam system is operated in standard mode for an extended period, the operating current of the turbomolecular pump may be higher than the second threshold, which is therefore a lower threshold for the operating current.If the pre-pump is switched on after standby mode, it is possible to check when this lower threshold for the operating current is reached, and then switch back to standby mode.

[0018] According to some embodiments, the particle beam system includes a controller configured to cause the particle beam system to perform the above procedure.

[0019] According to certain embodiments, several particle beam systems can form a larger overall system. For example, an electron beam microscope can be combined with an ion beam system. Such an overall system includes at least one turbomolecular pump and at least one backing pump; that is, it can also include several turbomolecular pumps and / or several backing pumps.

[0020] The above embodiments are explained in more detail below with reference to figures. Fig. Figure 1 shows a first electron beam microscope suitable for carrying out the procedure. Fig. Figure 2 shows a second electron beam microscope suitable for carrying out the procedure. Fig. Figure 3 shows a flowchart illustrating the procedure according to a first embodiment. Fig. Figure 4 shows a flowchart illustrating the procedure according to a second embodiment. Fig. Figure 5 shows a diagram depicting the time course of an operating current supplied to a turbomolecular pump.

[0021] The Fig. Figure 1 shows an electron beam microscope 1 comprising a source chamber 3, a first intermediate vacuum chamber 5, a second intermediate vacuum chamber 7, and a sample chamber 9. An electron beam source 11 is arranged within the source chamber 3. The electron beam source 11 is electrically connected to a control unit 15 via a signal line 13, so that the control unit 15 can supply an electrical potential to the electron beam source 11 to cause the electron beam source 11 to generate an electron beam 17.

[0022] Source chamber 3 is separated from the first intermediate vacuum chamber 5 by an aperture 19. The aperture 19 has an opening 21 through which the electron beam 17 passes when the electron beam 17 is directed at a sample 23. The first intermediate vacuum chamber 5 is separated from the second intermediate vacuum chamber 7 by a protective valve 25 and an aperture 27. The aperture 27 has an opening 29 through which the electron beam 17 passes when the electron beam 17 is directed at the sample 23. The protective valve 25 comprises a sealing plate 31 and an actuator 33. The actuator 33 is electrically connected to the control unit 15 via a signal line 35.When the actuator 33 is operated by the control unit 15 via the signal line 35, it moves the sealing plate 31 into or out of the beam path of the electron beam 17, thereby completely opening or closing the connection between the first intermediate vacuum chamber 5 and the second intermediate vacuum chamber 7. When the protective valve 25 is open and the electron beam 17 is directed at the sample 23, the electron beam 17 passes through the protective valve 25.

[0023] The electron beam microscope 1 further comprises a condenser lens 37 and an objective lens 39. The condenser lens 37 includes a pole piece 41 with an aperture 43, as well as a coil 45. The coil 45 is electrically connected to the control unit 15 via a signal line 47. The control unit 15 controls the condenser lens 37 by supplying an electric current to the coil 45, which generates a magnetic field. This field exits the pole piece 41 at the aperture 43 and enters the beam path of the electron beam 17, thus focusing the electron beam 17. The electron beam 17 passes through the condenser lens 37 in the first intermediate vacuum chamber 5.

[0024] The objective lens 39 comprises a pole piece 49 with an opening 51, and a coil 53. The coil 53 is electrically connected to the control unit 15 via a signal line 55. The control unit 15 controls the objective lens 39 by supplying an electric current to the coil 53, which generates a magnetic field. This field exits the pole piece 49 at the opening 51 and enters the beam path of the electron beam 17, thus focusing the electron beam 17. The electron beam 17 passes through the objective lens 39 in the second intermediate vacuum chamber 7.

[0025] The second intermediate vacuum chamber 7 is separated from the sample chamber 9 by an aperture assembly 57. The aperture assembly 57 comprises a holder 59 with openings 61, and an interchangeable aperture body 63, which is supported by the holder 59. The aperture body 63 has a hole 65 whose cross-sectional area differs from the cross-sectional area of ​​the openings 61 of the holder 59. The aperture body 63 can be replaced by a user of the electron beam microscope 1 by removing the aperture body 63 with a guide mechanism 67 through a vacuum lock 69 and inserting another aperture body into the holder 59 with the guide mechanism 67. It should be noted that the Fig. 1 shows the guide mechanism 67, but in some embodiments this is removed from the sample chamber 9 or swung laterally out of an image field of the electron beam microscope 1 during the direction of the electron beam 17 onto the sample 23.

[0026] The electron beam 17 passes through the openings 61 of the holder 59 and the hole 65 of the aperture body 63. The electron beam 17 then strikes the sample 23.

[0027] Sample 23 is mounted on a sample holder 73 using a sample guide 71. The sample guide 71 comprises a guide rod 75 and a support 77. The user positions sample 23 on the support 77 outside the sample chamber 9 and then moves the sample 23 through a port 79 to the position of the sample holder 73 by moving the guide rod 75. The guide rod 75 can be detached from the support 77 and removed from the sample chamber 9. Alternatively, or in addition to the port 79, the electron beam microscope 1 can have an openable door on the sample chamber 9 through which sample 23 can be mounted on the sample holder 73. For example, if both the port 79 and the door are provided on the sample chamber 9, samples that are too large for the port 79 can be moved into the sample chamber 9 through the door.

[0028] The electron beam microscope 1 further comprises an actuator 81, with which the relative position of the sample holder 73 can be changed from the aperture assembly 57. For this purpose, the actuator 81 is electrically connected to the control unit 15 via a signal line 83.

[0029] The electron beam microscope 1 also includes a deflection arrangement 85. In the Fig. Figure 1 shows the deflection arrangement 85 as pairs of electrodes; however, the deflection arrangement 85 can also be implemented using electromagnetic coils. The deflection arrangement 85 is electrically connected to the control unit 15 via a signal line 87. The control unit 15 can thus supply electrical potentials to the deflection arrangement 85, causing the deflection arrangement 85 to generate an electric field in the beam path of the electron beam 17 and deflect the electron beam 17. This allows the electron beam 17 to be directed to different points on the sample 23.

[0030] When the electron beam 17 strikes the sample 23, various signals are generated at the sample 23, such as secondary electrons and backscattered electrons. The electron beam microscope 1 also includes a detector 89 arranged in the sample chamber 9, which can detect such signals and generate corresponding electrical signals. The electrical signals generated by the detector 89 are transmitted to the control unit 15 via a signal line 91.

[0031] To acquire a particle-optical image with the electron beam microscope 1, the control unit 15 sequentially applies different potentials to the deflection arrangement 85, thereby directing the electron beam to different impact locations on the sample 23 and storing the signals generated by the detector 89 along with the impact locations on the sample 23. This process is subsequently referred to as scanning the sample 23.

[0032] During operation of the electron beam microscope 1, vacuums of varying qualities are generated in the source chamber 3, the first intermediate vacuum chamber 5, the second intermediate vacuum chamber 7, and the sample chamber 9. A high vacuum is generated in the source chamber 3, whereas a significantly lower vacuum is maintained in the sample chamber 9. To generate the vacuums within the source chamber 3, the first intermediate vacuum chamber 5, the second intermediate vacuum chamber 7, and the sample chamber 9, the electron beam microscope 1 also includes a pumping system 93. The pumping system 93 comprises a backing pump 95, a turbomolecular pump 97, a first ion getter pump 99, and a second ion getter pump 101. The backing pump 95, for example, is a positive displacement pump that generates a backing vacuum of 10 -2The turbomolecular pump 97 can reach a vacuum of 10 mbar. It operates when at least a forevacuum is reached, as otherwise the turbomolecular pump 97 may be damaged. The turbomolecular pump 97 reaches a vacuum of 10 -5 mbar. The first ion getter pump 99 and the second ion getter pump 101 require a vacuum generated by the turbomolecular pump 97 and achieve a high vacuum of 10 -6 up to 10 -10 mbar.

[0033] Since the backing pump 95 must first generate the forevacuum in the source chamber 3, the first intermediate vacuum chamber 5, the second intermediate vacuum chamber 7, and the sample chamber 9, the backing pump 95 is connected to sample chamber 9 via a backing pump line 103, a transition line 105, and a sample chamber line 107, so that the backing pump 95 can evacuate sample chamber 9. Furthermore, the backing pump 95 is connected to the second intermediate vacuum chamber 7 via the backing pump line 103, the transition line 105, the sample chamber line 107, and a turbopump line 109, so that the backing pump 95 can evacuate the second intermediate vacuum chamber 7. The backing pump 95 is further connected to the source chamber 3 and to the first intermediate vacuum chamber 5 via the backing pump line 103, the transition line 105, the sample chamber line 107, the turbopump line 109 and ion getter pump lines 111 and 113, respectively, in order to be able to evacuate them.The backing pump 95 includes an outlet 114 that expels gas pumped from the vacuum chambers to the outside. Operation of the backing pump 95 is controlled by the control unit 15 via a signal line 116.

[0034] A shut-off valve 115 is provided in the transition line 105, which allows the backing pump 95 and the backing pump line 103 to be isolated from the sample chamber line 107 and thus from all vacuum chambers. The shut-off valve 115 is electrically connected to the control unit 15 via a signal line 117, enabling the control unit 15 to initiate the isolation of the backing pump 95 from the vacuum chambers. The transition line 105 and the valve 115 do not need to be located within the electron beam microscope 1, as the vacuums can also be generated by the backing pump 95 through the outlet 131 and the deactivated turbomolecular pump 97. Furthermore, a standby mode valve 119, electrically connected to the control unit 15 via a signal line 118, a buffer chamber 121, and a shut-off valve 123, electrically connected to the control unit 15 via a signal line 122, are provided in the backing pump line 103.The standby valve 119 and the buffer chamber 121 serve to allow the backing pump 95 to be temporarily switched off to reduce vibrations, noise, and electrical disturbances. Specifically, when the standby valve 119 is closed and the backing pump 95 is switched off, the turbomolecular pump 97 pumps gas into the buffer chamber 121, causing the gas pressure in the buffer chamber 121, and consequently also at the outlet 131 of the turbomolecular pump 97, to slowly increase. During this process, the buffer chamber 121 can, as in the... Fig. 1 shown, a space connected to the pre-pump line 103 so that gas from the pre-pump line 103 can flow into the buffer space 121, or the buffer space is provided by the pre-pump line 103 itself.

[0035] The isolation valve 123 is closed via the signal line 122 by the control unit 15 to protect the turbomolecular pump 97 if the forevacuum has not yet been reached.

[0036] The turbomolecular pump 97 comprises a rotor 125, a stator 127, impeller blades 129, and an outlet 131. The stator 127 is electrically connected to the controller 15 via a signal line 133. To operate the turbomolecular pump 97, the controller 15 supplies an electric current to the stator 127 via the signal line 133, causing the rotor 125 to rotate along with the impeller blades 129. The impeller blades 129, through collisions with gas particles, accelerate these particles towards the outlet 131. A current sensor 135 is arranged in the signal line 133, which detects the current supplied to the stator 127. Although the stator 127 is shown here without impeller blades, it should be noted that the stator 127 can also have impeller blades, which are arranged, for example, between pairs of the impeller blades 129 shown.

[0037] The turbomolecular pump 97 is connected to the second intermediate vacuum chamber 7 via the turbopump line 109, to the sample chamber 9 via the turbopump line 109 and the sample chamber line 107, and to the source chamber 3 and the first intermediate vacuum chamber 5, respectively, via the turbopump line 109 and the ion getter pump line 111 and the ion getter pump line 113. A shut-off valve 137 can also be provided in the turbopump line 109, which is electrically connected to the control unit 15 via a signal line 139. The control unit 15 can, for example, close the shut-off valve 137 while the backing pump 95 generates the forevacuum in the vacuum chambers via the transition line 105.

[0038] The sample chamber line 107 also includes a shut-off valve 141, which is electrically connected to the control unit 15 via a signal line 143. The shut-off valve 141 can be closed by the control unit 15 to isolate the sample chamber line 107 from the turbopump line 109. For example, the shut-off valve 141 is closed when gas is supplied to the transition line 105 through a leakage valve 151 to increase the gas pressure in the entire sample chamber 9. The shut-off valve 141 can then be closed as needed to prevent the gas pressure in the sample chamber 9 from decreasing due to the operation of the turbomolecular pump 97.

[0039] Furthermore, a vent 145 with a valve 147 is provided on the sample chamber line 107. The valve 147 can be controlled by the control unit 15 via a signal line 149. When the valve 147 is opened, the vent 145 connects the interior of the electron beam microscope 1 to the outside air, so that the electron beam microscope 1 is flooded with air. This can be done, for example, when damage to the electron beam microscope 1 is detected, when the user places a new sample 23 in sample chamber 9 through the aforementioned alternative or additional door on sample chamber 9, or when the electron beam microscope 1 is switched off for maintenance.

[0040] The transition line 105 is equipped with a leakage valve 151, which can be controlled by the controller 15 via a signal line 153. The controller 15 can adjust the flow of a process gas at the leakage valve 151, which flows into the transition line from a storage container 155 or from the ambient air. The transition line 105 also has a pressure sensor 157, which detects the gas pressure prevailing in the transition line 105 and thus the gas pressure prevailing in the sample chamber 9, and generates a signal that is transmitted to the controller 15 via a signal line 159.

[0041] Ion getter pump lines 111 and 113 each include ion getter pump 99 and ion getter pump 101, respectively, as well as isolation valves 161 and 163. Isolation valve 161 can be controlled by controller 15 via a signal line 165. Controller 167 communicates with controller 15 via a signal line 169. Isolation valve 163 can be controlled by controller 15 via a signal line 171. The control unit 167 controls the operation of the ion getter pumps 99 and 101. Once the vacuum achievable by the turbomolecular pump 97 is reached in the source chamber 3 and in the first intermediate vacuum chamber 5, the control unit 15 closes the valves 161 and 163 and the control unit 167 supplies a high voltage to the ion getter pumps 99 and 101 via signal lines 173 and 175 in order to generate the high vacuum in the source chamber 3 and in the first intermediate vacuum chamber 5.The controller 15 and the controller 167 can also be configured as a single controller that controls both the valves 161 and 163 and the high-voltage supply. The control of the respective components of the electron beam microscope 1 can be divided between the controller 15 and the controller 167 in any desired manner.

[0042] The one in Fig. The valves 115, 119, 123, 137, 141, 147, 151, 161 and 163 shown in Figure 1 can, for example, be solenoid valves. Valves 115, 119, 123, 137, 141, 147, 151, 161 and 163 can also be other types of valves, as long as they can be controlled by the controllers 15 and 167.

[0043] The Fig. Figure 2 shows a second electron beam microscope 1' suitable for carrying out the procedure. In the Fig. 2. Components and functions are provided with corresponding reference symbols. Components and functions whose reference symbols are in the Fig. 2 of the in the Fig. If the component used is the same as the one used, reference is made to the above description of the component or function.

[0044] The one in Fig. The electron beam microscope shown in section 1' differs from the one in the Fig. The difference in the electron beam microscope 1 shown in Figure 1 is that the process gas flow is not fed to the transition line 105, but is supplied directly to the sample 23 by means of a needle 177. The needle 177 is connected to the reservoir 155 via a gas supply line 179 and the leakage valve 151, so that the process gas from the reservoir 155 and / or the ambient air is supplied directly to the sample 23. In the electron beam microscope 1', a pressure sensor 181 is attached to the sample holder 73 and electrically connected to the control unit 15 via a signal line 183. This arrangement of the pressure sensor 181 has the advantage that the pressure is detected near the needle 177 and is not distorted by a large distance to the local supply of the process gas. It should also be noted that with a local supply of the process gas via the needle 177, the isolation valve 141 can be open during the measurement procedure.

[0045] It should be noted that the particle beam system is not limited to the electron beam microscope 1. For example, the particle beam system can also be an ion beam system that generates a particle beam from ionized atoms. The particle beam system can also be integrated into a larger system, such as a FIB-SEM, which generates both an ion beam and an electron beam.

[0046] The proposed method is described in detail below according to various embodiments. Fig. Figure 3 shows a flowchart illustrating the method according to a first embodiment. The method according to the first embodiment comprises steps S1 to S10, wherein steps S2 to S4 constitute the standard mode and steps S7 to S9 constitute the idle mode.

[0047] In step S1, the control unit 15 opens the standby mode valve 119, so that the pre-pump 95 can evacuate the pre-pump line 103 or the buffer chamber 121.

[0048] In step S2, the controller 15 operates the turbomolecular pump 97 to evacuate gas from the vacuum chamber of the electron beam microscope 1, in particular from the sample chamber 9 and the second intermediate vacuum chamber 7. The gas evacuated from the sample chamber 9 and the second intermediate vacuum chamber 7 is then expelled from the outlet 131 of the turbomolecular pump 97 into the fore-pump line 103.

[0049] In step S3, the controller 15 also operates the pre-pump 95 in standard mode to evacuate the pre-pump line 103 and the buffer chamber 121. The gas evacuated from the pre-pump line 103 and the buffer chamber 121 is then expelled to the outside through the outlet 114 of the pre-pump 95. It should be noted that step S3 can be interchanged with step S2 or performed simultaneously with step S2.

[0050] In step S4, the controller 15 checks whether five minutes have passed since the start of standard mode. If not, the controller 15 continues in standard mode and returns to step S2. If five minutes have passed since the start of standard mode, the controller 15 continues with step S5.

[0051] In step S5, the controller 15 closes the standby valve 119 and in step S6 switches off the pre-pump 95. Accordingly, from step S5 onwards, the pre-pump line 103 and the buffer chamber 121 are no longer evacuated.

[0052] In step S7, the controller 15 continues to operate the turbomolecular pump 97 to evacuate gas from the sample chamber 9 and the second intermediate vacuum chamber 7. The gas evacuated from the sample chamber 9 and the second intermediate vacuum chamber 7 is expelled from the outlet 131 of the turbomolecular pump 97 and enters the fore-pump line 103 and the buffer chamber 121, where it gradually accumulates and the gas pressure increases.

[0053] In step S8, the controller 15 also detects the operating current supplied to the turbomolecular pump 97 using the current sensor 135. In step S9, the controller 15 then checks whether the detected operating current is greater than a predetermined threshold. The predetermined threshold could, for example, be an operating current corresponding to an electrical power consumption of 50 watts for the turbomolecular pump 97. If the operating current of the turbomolecular pump 97 is less than or equal to the predetermined threshold, the controller 15 remains in standby mode and returns to step S7. If, however, the operating current of the turbomolecular pump 97 is greater than the predetermined threshold, the controller 15 proceeds to step S10 and thus returns to standard mode.

[0054] In particular, in step S10, the controller 15 switches the pre-pump 95 back on and then, in step S1, opens the standby mode valve 119. This allows the gas that accumulated in the pre-pump line 103 and the buffer chamber 121 during standby mode to be evacuated by the pre-pump 95 and expelled to the outside. As a result, the operating flow supplied to the turbomolecular pump 97 decreases again, since the gas pressure at the outlet 131 of the turbomolecular pump 97 also decreases.

[0055] It should be noted that the Fig. Figure 3 shows an embodiment of the method in which the switch from standard mode to standby mode is performed after a predetermined time, and the switch back from standby mode to standard mode is performed when the operating current of the turbomolecular pump 97 exceeds the predetermined threshold. However, any combination and criteria for switching between the operating modes are conceivable. An exemplary alternative embodiment is shown in the Fig. 4 shown.

[0056] The Fig. Figure 4 shows a flowchart illustrating the procedure according to a second embodiment. The diagram in the Fig. The procedure shown comprises steps S11 to S20, with steps S12 to S15 forming the standard mode and steps S18 and S19 forming the quiet mode.

[0057] Steps S11 to S13, S16 to S18 and S20 are related to those in the Fig. The three steps shown, S1 to S3, S5 to S7, and S10, are identical. Therefore, for steps S11 to S13, S16 to S18, and S20, please refer to the descriptions above for steps S1 to S3, S5 to S7, and S10.

[0058] In the standard mode of the second embodiment, the controller 15 detects the operating current supplied to the turbomolecular pump 97 in step S14 using the current sensor 135. This allows the controller 15 to monitor how much the operating current of the turbomolecular pump 97 has already decreased when gas is evacuated from the upstream pump line 103 and the buffer chamber 121 by the upstream pump 95.

[0059] In step S15, the controller 15 compares the measured operating current of the turbomolecular pump 97 with a predetermined threshold. The predetermined threshold is, for example, an operating current of the turbomolecular pump 97 that corresponds to an electrical power consumption of 20 watts. Specifically, the predetermined threshold for step S15 can be determined by operating the electron beam microscope 1 in standard mode and, after a certain period, measuring the operating current of the turbomolecular pump 97, which then corresponds to a minimum operating current of the turbomolecular pump 97. If, in step S15, it is determined that the operating current of the turbomolecular pump 97 is greater than or equal to the predetermined threshold, the controller remains in standard mode and returns to step S12.

[0060] If, however, step S15 determines that the detected operating current of the turbomolecular pump 97 is smaller than the predetermined threshold, the controller 15 continues with step S16 and thus switches to standby mode.

[0061] During the Fig. In the second embodiment shown in Figure 4, the operating current of the turbomolecular pump 97 is not detected in standby mode. Instead, in this second embodiment, the controller 15 checks whether the standby mode has been in operation for five minutes. If five minutes have not elapsed since the start of standby mode, the controller 15 remains in standby mode and returns to step S18. However, if the controller 15 determines that five minutes have elapsed since the start of standby mode, it proceeds to step S20 and thus switches to standard mode. It should be noted that in alternative embodiments, the operating current of the turbomolecular pump 97 can be detected in both operating modes and compared to a respective threshold value to trigger the switch.

[0062] The Fig. Figure 5 shows a diagram depicting the time course of the operating current supplied to the turbomolecular pump 97. The diagram shows a curve 185, where the x-axis represents time and the y-axis represents the operating current supplied to the turbomolecular pump 97. The graph in the Fig. Diagram 5 shown begins on the time axis with the standby mode, in which the turbomolecular pump 97 is operating and the backing pump 95 is switched off or disconnected by the standby mode valve 119. During this time, the gas expelled by the turbomolecular pump 97 accumulates in the backing pump line 103 and the buffer chamber 121, increasing the gas pressure at the outlet 131 of the turbomolecular pump 97 and gradually increasing the operating flow supplied to the turbomolecular pump 97. The standby mode continues until, at a first line 191, the operating flow of the turbomolecular pump 97 reaches a threshold value 187, whereupon the controller 15 switches to standard mode, operates the backing pump 95, and opens the standby mode valve 119.

[0063] The standard mode is then carried out until a second line 191 is located, for example, five minutes after the first line 191. During this time, the backing pump 95 evacuates the backing pump line 103 and the buffer chamber 121, thereby reducing the operating current of the turbomolecular pump 97 in the diagram of the Fig. 5 drops sharply. On the second line 191, the control 15 switches back to standby mode.

[0064] The Fig. Figure 5 also shows a lower threshold value 189, which can alternatively be used to switch to standby mode. For example, from the moment the first line 191 is reached, the controller 15 can operate in standard mode until the operating current of the turbomolecular pump 97, and thus curve 185, has dropped to the lower threshold value 189.

[0065] The above method for operating the particle beam system 1, 1' allows switching between a standby mode and a standard mode even without a pressure sensor provided at the buffer chamber 121. Accordingly, the pressure sensor and related components of the vacuum system can be omitted, thus simplifying the vacuum system and making it easier to assemble and maintain.

Claims

Method for operating a particle beam system (1, 1'), wherein the method comprises a first operating mode and a second operating mode; wherein the particle beam system (1, 1') comprises: a particle beam source (11) for generating a particle beam (17); a sample holder (73) on which a sample (23) can be arranged for irradiation with the particle beam (17); an evacuable vacuum chamber (3, 5, 7, 9) in which the sample holder (73) is arranged; a turbomolecular pump (97); a buffer chamber (121); and a backing pump (95); wherein the first operating mode comprises: evacuating gas from the vacuum chamber (3, 5, 7, 9) into the buffer chamber (121) with the turbomolecular pump (97) and evacuating the gas in the buffer chamber (121) with the backing pump (95);wherein the second operating mode comprises: evacuating gas from the vacuum chamber (3, 5, 7, 9) into the buffer chamber (121) using the turbomolecular pump (97), while the evacuation of the gas in the buffer chamber (121) using the backing pump (95) is stopped; and sensing values ​​of a quantity characterizing the supply of electrical operating current to the turbomolecular pump (97), while the evacuation of the gas in the buffer chamber (121) using the backing pump (95) is stopped, and switching to the first operating mode when the sensed quantity meets a predetermined first criterion. Method according to claim 1, wherein in the second operating mode the pre-pump (95) is switched off. Method according to claim 1 or 2, wherein the particle beam system (1, 1') comprises a vacuum valve (119; 123) provided between the buffer chamber (121; 131) and the backing pump (95); wherein in the first operating mode the vacuum valve (119) is open; wherein in the second operating mode the vacuum valve (119) is closed. Method according to any one of claims 1 to 3, wherein the particle beam system (1, 1') comprises a gas space comprising an outlet opening (131) of the turbomolecular pump (97), the buffer space (121) and an inlet opening of the backing pump (95); wherein the particle beam system (1, 1') is free of a gas pressure sensor configured to detect a gas pressure in this gas space. Method according to any one of claims 1 to 4, wherein the detected quantity characterizes a power of the electrical operating current supplied to the turbomolecular pump (97); wherein the first criterion is met if the detected quantity represents a power that is above a first threshold; and wherein the first criterion is not met if the detected quantity represents a power that is below the first threshold. Method according to any one of claims 1 to 5, wherein the first operating mode further comprises: switching to the second operating mode after a predetermined period of time from the start of the first operating mode. Method according to any one of claims 1 to 6, wherein the buffer space (121) has a volume of at least 500 cm3, in particular at least 1000 cm3; and / or wherein the buffer space (121) has a volume of at most 5000 cm3, in particular at most 50000 cm3. Method according to any one of claims 1 to 7, further comprising directing the particle beam (17) generated by the particle beam source (11) onto the sample (23) during the first operating mode and / or during the second operating mode. Method according to one of claim 8, further comprising detecting signals generated by the particle beam (17) at the sample (23) with a detector (89). Method according to any one of claims 1 to 9, wherein the first operating mode further comprises: detecting the values ​​of the quantity that characterizes the supply of the electrical operating current to the turbomolecular pump (97) and switching to the second operating mode when the detected quantity meets a predetermined second criterion. Method according to claim 10, wherein the detected quantity characterizes a power of the electrical operating current supplied to the turbomolecular pump (97); wherein the second criterion is met if the detected quantity represents a power that is below a second threshold; and wherein the second criterion is not met if the detected quantity represents a power that is above the second threshold. Particle beam system (1, 1') comprising: a particle beam source (11) for generating a particle beam (17); a sample holder (73) on which a sample (23) can be arranged for irradiation with the particle beam (17); an evacuable vacuum chamber (3, 5, 7, 9) in which the sample holder (73) is arranged; a turbomolecular pump (97); a buffer chamber (121); a backing pump (95); and a control system (15) configured to cause the particle beam system (1, 1') to carry out the method according to any one of claims 1 to 11.

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