Particle beam system with cooling system and method for operating it

Abstract

A particle beam system is disclosed, comprising a fixture for holding an object under investigation, a particle beam source, a lens for focusing the particle beam, a detector, and a cooling system for cooling the fixture. The cooling system includes a coolant passage in the fixture, a supply port, an outlet, a two-position changeover valve, a first connecting line linked to the coolant passage and the changeover valve, a second connecting line linked to the coolant passage and the changeover valve, and a cooler for cooling a portion of the first connecting line. In its first position, the changeover valve connects the supply port to the first connecting line and the outlet to the second connecting line; in its second position, it connects the supply port to the second connecting line and the outlet to the first connecting line.

Description

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

[0002] To examine the microscopic structures of an object, particle-optical images are sometimes acquired using a particle beam system that scans an area of ​​the object with a particle beam. When acquiring the particle-optical image, it is desirable to keep the object's temperature low, particularly for biological and chemical objects. For this purpose, a specimen holder is typically used to hold the object in the particle beam system, with the specimen holder connected to a nitrogen cooler. An object holder of this type is available, for example, under the product names "PP3006 CoolLok" or "PP3005 SEMCool" from Quorum Technologies Ltd, Laughton, United Kingdom.

[0003] Commercially available nitrogen contains impurities that, due to the low temperature, build up in the nitrogen cooling system when nitrogen is used to cool the specimen holder. Such deposits can clog the nitrogen lines, ultimately rendering the desired cooling impossible. Therefore, if necessary, the nitrogen cooling system's cooling operation is stopped and the uncooled nitrogen is passed through the nitrogen cooling system to remove the deposits.

[0004] However, removing the deposits typically takes several hours, during which the particle beam system cannot be used to acquire particle-optical images. Therefore, one goal of the present invention is to shorten the time required for removing the deposits.

[0005] US 2022 / 0 172 921 A1 discloses a combination system of a light microscope and a particle beam microscope, wherein an object holder has an additional scintillator material.

[0006] T. Kohlberger's dissertation on "Low-temperature scanning electron microscopy of superconducting devices and LaAlO3 / SrTiO3 interfaces" at the University of Tübingen, 2020, reveals a specific cooling of an object to be examined for the investigation of superconducting devices based on LaAlO3 / SrTiO3 heterostructures.

[0007] To achieve the above-mentioned objective, a particle beam system is proposed, which comprises an object holder for holding an object to be examined, a particle beam source for generating a particle beam, a lens for focusing the particle beam on the object, a detector for detecting signals generated by the particle beam on the object, and a cooling system for cooling the object holder.The cooling system comprises a coolant passage in the object holder with an inlet connection and an outlet connection, a supply connection for supplying a gas, an outlet for discharging the gas, a switching valve with a first position and a second position, a first connecting line whose first end is connected to the inlet connection of the coolant passage and whose second end is connected to the switching valve, a second connecting line whose first end is connected to the outlet connection of the coolant passage and whose second end is connected to the switching valve, and a cooler for cooling at least a first part of the first connecting line. In the first position, the switching valve connects the supply connection to the second end of the first connecting line and the outlet to the second end of the second connecting line.In addition, in the second position, the switching valve connects the supply port to the second end of the second connecting line and the output to the second end of the first connecting line.

[0008] This means that the particle beam system can be operated in two modes: cooling mode and defrosting mode. During cooling mode, the gas is cooled and thus cools the object holder as the cooled gas flows through it. The deposits mentioned above are caused, for example, by water contained in the gas, which freezes in the first cooled part of the cooling system, namely in the first part of the first connecting line. The water frozen there can be removed by nitrogen flowing uncooled through the connecting lines during defrosting mode, thus thawing the frozen water and expelling it through the connecting lines. Which operating mode is carried out is set by the particle beam system via the switching valve, which for this purpose has a first position and a second position.The switching valve is connected to the connecting lines of the cooling system in such a way that during defrosting mode, i.e. when the switching valve is in the second position, the gas flows through the connecting lines in a direction that is the opposite of the gas flow direction during cooling mode. This prevents the gas from first defrosting the frozen water during defrosting mode and then flowing through the still-cooled object holder, which would result in the defrosted water freezing in the coolant passage of the object holder during defrosting mode and having to be defrosted again there. By reversing the flow direction of the gas during defrosting mode through the switching valve, the gas first flows through the object holder, then flows through the first part of the first connecting line, thus removing the deposits, and is then expelled to the environment without flowing through a cooled area of ​​the cooling system again.This reduces the time required to remove deposits in the cooling system and achieves the above-mentioned goal.

[0009] It should be noted that the names used for the inlet port and outlet port of the coolant passage are for illustrative purposes only and do not specify the flow direction of the gas. For example, the most commonly used operation is cooling operation, in which the changeover valve is operated in the first position. Accordingly, the inlet port of the coolant passage is the port of the coolant passage through which the gas enters the coolant passage during cooling operation, and the outlet port of the coolant passage is the port through which the gas exits the coolant passage during cooling operation. In particular, it should be noted that the assignment of the inlet port and the outlet port does not depend on the operation of the changeover valve that is currently being performed.

[0010] It should also be noted that a connection through the first or second connecting line includes the possibility of further functional components being arranged between the first end and the second end of the respective connecting line. For example, valves, sensors, regulators, or the like can be arranged between the first end and the second end of the first connecting line, or between the inlet connection of the coolant passage and the switching valve.

[0011] According to some embodiments, the cooling system further comprises a reducing valve arranged in the flow of the gas between the supply port and the outlet and providing a variable resistance to the flow of the gas through the reducing valve, a temperature sensor for outputting a signal representing a temperature of the object holder, and a controller configured to control the reducing valve based on the signal representing the temperature of the object holder.

[0012] The reducing valve is a valve capable of adjusting the amount of gas flowing through the cooling system. The reducing valve can be an electrically controllable valve, such as a solenoid valve, which can be controlled by the controller to adjust the gas flow. The temperature sensor is a sensor capable of measuring the temperature of the object holder and communicating this temperature to the controller via a corresponding signal. This can be advantageous for providing feedback control of the cooling system. In particular, in such an embodiment, a target temperature for the object holder can be adjustable.The controller is then able to increase the gas flow to such an extent that the temperature sensor detects the target temperature at the object holder, or detects it over a longer period of time until the object holder has reached thermal equilibrium.

[0013] According to some embodiments, the reducing valve can be arranged at the supply port, or in the gas flow between the supply port and the switching valve, whereby a gas pressure in the entire cooling system is defined by the degree of opening of the reducing valve. In particular, in such a case, the pressure of the gas supplied to the cooling system is not dependent on the gas source used or on the amount of gas contained in the source, allowing the cooling system to operate more reliably.

[0014] According to some embodiments, the reducing valve in the first connecting line can be arranged such that, during cooling operation of the cooling system, the gas, after flowing through the switching valve, first flows through the reducing valve before flowing through the cooler. Consequently, during defrosting operation, namely the second position of the switching valve, the gas first flows through the object holder and the first part of the first connecting line before flowing through the reducing valve. This can be advantageous because, in such a case, during defrosting operation, the maximum pressure prevails in the cooling system from the gas source, which makes it easier to defrost frozen water in the connecting lines.

[0015] According to some embodiments, the first connecting line has, in a second part between the cooler and the object holder, an insulating layer surrounding the first connecting line, which reduces heat transfer between the second part of the first connecting line and the environment. In particular, the insulating layer is not present between the switching valve and the first part of the first connecting line. The insulating layer can also be absent from the second connecting line. It is also advantageous for the first part of the first connecting line to be free of an insulating layer surrounding it, so that heat transfer between the cooler and the gas can be carried out efficiently. The insulating layer is, for example, a sheathing of the connecting line in the second part with a material having a low thermal conductivity coefficient.An insulating layer can also be implemented by surrounding the connecting line in a housing within which a vacuum is created. A vacuum also prevents the connecting line from icing up, as the part of the connecting line surrounded by the insulating layer does not come into contact with water dissolved in the environment.

[0016] According to some embodiments, the cooler comprises a cooling chamber. The cooling chamber is a volume into which a cooling medium, such as liquid nitrogen, can be filled. The cooling medium is advantageously filled into the cooling chamber before the start of cooling operation. In particular, the first part of the first connecting line can be immersed in the liquid nitrogen before cooling operation and removed from it again without damage before defrosting operation. This allows the cooler to be deactivated, which is advantageous during defrosting operation because the nitrogen, which is intended to remove the deposits in the first connecting line, is not cooled in an undesired manner.

[0017] According to some embodiments, the switching valve is a 5 / 2-way valve. The 5 / 2-way valve is a valve with five ports and two positions. The five ports are divided into two input ports and three output ports, with one of the three output ports being connected to one of the input ports in both positions, and the other two output ports being connected to one of the input ports in only one of the positions. Alternatively, a 4 / 2-way valve can be used, for example. The 4 / 2-way valve is a valve with four ports and two positions, with the four ports being divided into two input ports and two output ports, and the two output ports in the second position being connected to the input ports opposite the first position.

[0018] According to some embodiments, the particle beam system further comprises a vacuum enclosure that defines a vacuum space. The vacuum enclosure is, for example, a metal housing of the particle beam system. A vacuum is generated in the vacuum space during operation of the particle beam system to reduce undesirable interactions of the particle beam with the atmosphere. It may be advantageous to arrange components outside the vacuum space that do not require a vacuum for operation, as this reduces the expansion of the vacuum space and prevents an unnecessary increase in energy during vacuum generation. For example, the switching valve and / or the cooler can be arranged outside the vacuum space.

[0019] According to some embodiments, the particle beam system further comprises a stage that holds the object holder and is connected, for example, to an actuator that can be driven to displace the object held by the object holder across the stage relative to the lens for focusing the particle beam. The object holder is held at a distance from the stage, for example, via spacers, to reduce heat transfer between the object holder to be cooled and the object stage connected to the actuator. To maintain the distance between the object holder and the stage, fewer than ten, and in particular three, spacers are used. For example, the spacers are made of a material with a low thermal conductivity coefficient and are spherical in shape to minimize heat transfer from the stage to the object holder.Alternatively, the specimen holder can be connected to the vacuum chamber via a vacuum lock instead of being supported by a specimen stage. The vacuum lock is a passage through the vacuum jacket with two seals that close at different times when the specimen holder is removed from the vacuum chamber, allowing the vacuum in the vacuum chamber to be maintained during removal.

[0020] According to one embodiment, a method for operating the particle beam system comprises operating the particle beam system in two operating modes, namely a cooling mode and a defrosting mode. In the cooling mode, the switching valve is first set to the first position. Gas is then supplied to the supply connection, and the first part of the first connecting line is cooled by the cooler, thereby cooling the gas flowing through the first part of the first connecting line. The cooled gas then cools the object holder and an object arranged on the object holder. The cooled object is scanned with the particle beam, and signals generated by the object upon impact of the particle beam are detected by the detector, allowing the generation of a particle-optical image. In the defrosting mode, the switching valve is first set to the second position.Gas is then supplied to the supply connection, and the specimen holder is heated with the supplied gas. Heating the specimen holder prevents deposits removed and absorbed by the gas from redepositing as they flow through the coolant passage in the specimen holder, thus shortening the time required to remove the deposits.

[0021] According to some embodiments, the supplied gas is nitrogen. It should be noted that gases typically contain impurities. Nitrogen refers herein to gases in which the proportion of impurities is small compared to the proportion of actual nitrogen. In particular, the nitrogen contains less than 1% by volume of impurities.

[0022] In the following, certain embodiments are explained in more detail with reference to figures. Herein: Fig. 1 a particle beam system with a cooling system according to an embodiment. Fig. 2 a flowchart for explaining a method for operating the Fig. 1 shown particle beam system.

[0023] Fig. 1 shows a particle beam system 1 with a cooling system 3 according to one embodiment. The particle beam system 1 comprises a particle beam source 5, which is connected to a controller 9 via an electrical line 7. The controller 9 is capable of supplying a first electrical potential to the particle beam source 5 via the electrical line 7. The particle beam system 1 further comprises a beam tube 11 with an upper end 13 and a lower end 15. The beam tube 11 is connected to the controller 9 via an electrical line 17. The controller 9 is capable of supplying a second electrical potential to the beam tube 11 via the electrical line 17. During operation of the particle beam system 1, the controller 9 supplies the first electrical potential to the particle beam source 5, whereby particles are released from the particle beam source 5.In addition, the controller 9 supplies the beam tube 11 with a second electrical potential different from the first electrical potential, so that the particles released from the particle beam source 5 are accelerated towards the upper end 13 of the beam tube 11 and form a particle beam 19.

[0024] It should be noted that in the example described herein, the upper end 13 of the beam tube 11 acts as an accelerating electrode. However, an additional accelerating electrode may be provided, which Fig. 1 shown particle beam system 1 can be included, for example, in the particle beam source 5.

[0025] The particle beam 19 passes through a condenser lens 21, which has a pole piece 25 and a coil 23. The coil 23 of the condenser lens 21 is connected to the controller 9 via an electrical line 27, so that the controller is able to supply an electrical current to the coil 23 of the condenser lens 21, whereby the coil 23 of the condenser lens 21 generates a magnetic field. The magnetic field generated by the coil 23 of the condenser lens 21 enters the beam tube 11 at an opening of the pole piece 25 and influences the particle beam 19 passing through the condenser lens 21. The condenser lens 21 is used to collimate the particle beam 19. However, the condenser lens 21 can also be used to focus the particle beam 19. Although the condenser lens 21 Fig. 1 as a magnetic lens, the condenser lens 21 may also be another lens suitable for influencing the particle beam 19. For example, the condenser lens may be an electrostatic lens, such as a single lens.

[0026] The particle beam 19 further passes through an objective lens 29, which comprises a coil 31 and a pole piece 33 with a lower end 35. The coil 31 of the objective lens 29 is connected to the controller 9 via an electrical line 37, so that the controller is able to supply an electrical current to the coil 31 of the objective lens 29, whereby the coil 31 of the objective lens 29 generates a magnetic field. The pole piece 33 of the objective lens 29 has a lower end 35, which is arranged below the lower end 15 of the beam tube 11. The pole piece 35 of the objective lens 29 is open towards the particle beam 19, so that the magnetic field generated by the coil 31 of the objective lens 29 can enter the path of the particle beam 19 and influence it.

[0027] The particle beam 19 is focused by the objective lens 29 on an object 39. It should be noted that the focusing of the particle beam 19 can also be performed by the condenser lens 21. Furthermore, the objective lens 29 can be used similarly to the condenser lens 21 instead of the Fig. The magnetic lens shown in Figure 1 can also be an electrostatic lens, such as a single lens.

[0028] The particle beam 19 also passes through an electrostatic lens formed by the lower end 15 of the beam tube 11 and the object 39. A third potential can be supplied to the object 39 by the controller 9 via an electrical line 41 and an object holder 43. In the particle beam system 1 described herein, it is advantageous if the third electrical potential supplied to the object 39 corresponds to a ground potential in order to avoid an energy supply by the controller 9.

[0029] An electric field between the lower end 15 of the beam tube 11 and the object 39 is defined by a difference between the second electric potential supplied to the beam tube 11 and the third electric potential supplied to the object 39. When the particle beam 19 passes through this electric field prevailing between the lower end 15 of the beam tube 11 and the object 39, it is influenced. This electric field creates a focusing lens effect. Since the electric field of the electrostatic lens strongly overlaps with the magnetic field of the objective lens 29, this design can also be referred to as a combination lens.

[0030] The point of impact of the particle beam 19 on the object 39 is influenced by a deflection arrangement 45. In the Fig. 1, the deflection arrangement 45 comprises a plurality of pairs of electrodes which, when a voltage is applied between the electrodes of a pair by the controller 9 via an electrical line 47, generate an electric field which deflects the particle beam 19 when it passes through the electric field.

[0031] When the particle beam 19 strikes the object 39, electrons are emitted from the object 39, which are accelerated into the beam tube 11 due to the focusing electrostatic lens between the object 39 and the lower end 15 of the beam tube 11. The beam tube 11 further comprises a space 49 for components, in which, as shown in Fig. 1, for example, a detector 51 is arranged, which is connected to the controller 9 via an electrical line 53. The detector 51 comprises a detector surface for detecting the electrons entering the beam tube 11. The detector 51 generates a detector signal representing a number of electrons impinging on the detector 51 and transmits the detector signal to the controller 9 via the electrical line 53.

[0032] The particle beam system 1 generates an image of the object 39 by the controller 9 setting various voltage values ​​on the deflection arrangement 45 and assigning each of these voltage values ​​to a detector signal. For this purpose, the detector signals and the voltage values ​​can be stored in a memory of the controller 9.

[0033] The particle beam system 1 further comprises an object stage 55. The object stage 55 can be moved by an actuator 57, which can be activated by the controller 9 via an electrical line 59. For example, the actuator 57 can be used to change a distance between the lower end 35 of the pole piece 33 of the objective lens 29 and the object 39, which can also be referred to as the working distance.

[0034] The object table 55 carries the object holder 43 at a distance defined by spacers 61 between the object table 55 and the object holder 43. As in Fig. As shown in Figure 1, the spacers 61 can have a spherical shape in order to minimize the contact area between the specimen holder 43 and the spacers 61, or between the specimen stage 55 and the spacers 61. Reducing this contact area reduces heat transfer between the specimen stage 55 and the specimen holder 43 to be cooled.

[0035] The particle beam system 1 further comprises a vacuum jacket 63 surrounding a vacuum chamber 65 in which the above-described components of the particle beam system 1 are arranged, with the exception of the controller 9. Air is sucked into the vacuum chamber 65 using a pump (not shown) connected to a pump nozzle 67, thus creating a vacuum.

[0036] The particle beam system 1 further comprises the cooling system 3. The cooling system 3 comprises a coolant passage 69 in the object holder 43. The object holder 43 can transfer heat to a coolant via the coolant passage 69. The coolant used for this purpose is a gas 70, such as nitrogen. For the purpose described above, the coolant passage 69 has an inlet port 71, into which the nitrogen 70 flows into the coolant passage 69 during cooling operation, and an outlet port 73, from which the nitrogen 70 flows out of the coolant passage 69 during cooling operation.

[0037] The inlet connection 71 of the coolant passage 69 is connected to a switching valve 77 via a first connecting line 75. For this purpose, a first end of the connecting line 75 is connected to the inlet connection 71 of the coolant passage 69, the connecting line 75 is led through a vacuum seal 79 through the vacuum jacket 63 out of the vacuum chamber 65, and a second end of the connecting line 75 is connected to the switching valve 77. The vacuum seal 79 is a seal that hermetically seals an opening of the vacuum jacket 63. For example, the vacuum seal 79 is a rubber seal or a metal seal. In particular, the Fig. The vacuum seal 79 shown in Figure 1 is a double feedthrough which, in addition to the first connecting line 75, also leads a second connecting line 81 through the vacuum jacket 63 out of the vacuum chamber 65. The second connecting line 81 is connected at a first end to the outlet connection 73 of the coolant passage 69 and at a second end to the switching valve 77.

[0038] The cooling system 3 further comprises a cooler 83 having a cooling chamber 85. For example, before the cooling system is put into operation, liquid nitrogen 87 is filled into the cooling chamber 85, and a first portion 89 of the first connecting line 75 is immersed in the liquid nitrogen 87. As a result, the nitrogen 70 flowing through the first portion 89 of the first connecting line 75 is cooled by the liquid nitrogen 87.

[0039] Furthermore, a second part of the first connecting line 75 and a part of the second connecting line 81 have an insulating layer 91. The insulating layer 91 reduces heat transfer from the environment to the second part of the first connecting line 75 and the part of the second connecting line 81 surrounded by the insulating layer 91. This reduces heating of the nitrogen 70 in the second part of the first connecting line 75. In particular, the insulating layer 91 can be a casing into which a vacuum is pumped, so that the second part of the first connecting line 75 and the part of the second connecting line 81 are surrounded by a vacuum and insulated.Such a structure also prevents external icing of the second part of the first connecting line 75 and the part of the second connecting line 81 which are surrounded by the insulating layer 91, since they are not in contact with water dissolved in the environment due to the vacuum separation.

[0040] In a case where the insulating layer 91 is implemented with the vacuum described above, the insulating layer 91 can be connected to the vacuum chamber 65 of the particle beam system 1 via an opening, so that the vacuum chamber is generated by operating the pump (not shown) via the pump nozzle 67. Alternatively, the insulating layer 91 can have additional pump nozzles to which a further pump is connected for generating the vacuum in the insulating layer 91.

[0041] The cooling system 3 further comprises an outlet 93 from which the nitrogen 70 is expelled. In addition, the cooling system 3 comprises a supply connection 95 for supplying the nitrogen 70 to the cooling system 3. For this purpose, the supply connection 95 is connected to a nitrogen reservoir 97, such as a nitrogen bottle or a nitrogen tank. In order to be able to adjust the inflow of the nitrogen 70 from the nitrogen reservoir 97, the supply connection 95 is connected to the changeover valve 77 via a reducing valve 99. The reducing valve 99 is, for example, a solenoid valve that can be controlled electrically. For control, the reducing valve 99 is connected to a controller 103 via an electrical line 101. For example, the controller 103 determines a current to be supplied to a solenoid valve in order to achieve a target flow of the nitrogen 70 and supplies the determined current to the reducing valve 99.

[0042] The switching valve 77 is connected to the control unit 103 via an electrical line 105. The Fig. The switching valve 77 shown in Figure 1 is a 4 / 2-way valve, but the switching valve 77 may be of a different type, such as a 5 / 2-way valve. For simplified illustration, the 4 / 2-way valve is described below as shown in Fig. 1 is shown.

[0043] The switching valve 77 includes four ports connected to the supply port 95, the outlet 93, the first connecting line 75, and the second connecting line 81. The switching valve 77 further has a first position and a second position. The first position is represented by the solid paths 107 and 108, and the second position is represented by the dashed paths 109 and 110. When the switching valve 77 is in the first position, represented by the solid paths 107 and 108, the supply port 95 is connected to the first connecting line 75, and the outlet 93 is connected to the second connecting line 81. Accordingly, in the first position of the switching valve 77, the nitrogen 70 flows from the nitrogen reservoir 97 into the first connecting line 75.The nitrogen 70 is then cooled in the first part 89 of the first connecting line 75 and flows through the coolant passage 69 in the specimen holder 43, thereby cooling the specimen holder 43 and the specimen 39 located on the specimen holder 43. The nitrogen 70 then flows through the second connecting line 81 to the outlet 93, where it is expelled to the environment. The flow of the nitrogen 70 in the first position of the switching valve 77 is shown in . Fig. 1 is represented by solid arrows 112.

[0044] Since, for example, water is present as a minor impurity in the nitrogen 70, the water freezes when the nitrogen 70 enters the first part 89 of the first connecting line 75 due to the low temperature caused by the liquid nitrogen 87. The frozen water thus accumulates in the first part 89 of the first connecting line 75. During prolonged operation of the particle beam system 1 with the switching valve 77 in the first position, an increasing amount of ice accumulates in the first connecting line 75, clogging the first connecting line 75 and impairing the cooling performance of the cooling system 3.

[0045] To remove the deposits, the controller 103 is able to change the position of the switching valve 77 via an electrical line 105, thus moving the switching valve 77 to the second position. Additionally, the cooler 83 is removed by removing the first part 89 of the first connecting line 75 from the liquid nitrogen 87. It should be noted that the cooler 83 does not necessarily have to be removed. In a case where the cooler 83 is a Peltier cooler, for example, it is sufficient if the cooler 83 has a lower cooling capacity, so that the nitrogen 70 is only slightly cooled when the switching valve 77 is operated in the second position.

[0046] In the second position of the switching valve 77, represented by the dashed paths 109 and 110, the supply port 95 is connected to the second connecting line 81, and the outlet 93 is connected to the first connecting line 75. Accordingly, in the second position of the switching valve 77, the nitrogen 70 flows from the nitrogen reservoir 97 into the second connecting line 81. The uncooled nitrogen 70 then flows through the coolant passage 69 in the specimen holder 43 and heats it. The nitrogen 70 then flows through the first connecting line 75 and heats the first part 89 of the first connecting line 75, thereby dissolving the deposits.

[0047] The dissolved deposits are then expelled to the environment by the nitrogen 70 flowing through the first connecting line 75 and the outlet 93. The flow of nitrogen 70 in the second position of the switching valve 77 is in the Fig. 1 by dashed arrows 114.

[0048] By reversing the flow direction of the nitrogen 70 in the first connecting line 75 and the second connecting line 81 in the second position of the switching valve 77, it is ensured in particular that the dissolved deposits do not redeposit in the cooling system 3, since the heating of the object holder 43 or the first connecting line 75 is carried out with the nitrogen 70, which does not yet contain any dissolved deposits. Since the dissolved deposits are removed directly from the cooling system 3 by the particle beam system 1, the deposits can be removed quickly and efficiently.

[0049] The cooling system 3 further includes a temperature sensor 116, which is attached to the object holder 43 to detect a temperature of the object holder 43. For example, the temperature sensor 116 is a resistance temperature sensor. The temperature sensor 116 generates a signal representing the temperature of the object holder 43 and transmits the signal to the controller 103 via an electrical line 118. The temperature sensor 116 serves, for example, to determine whether switching to the second position of the switching valve 77 or to the first position of the switching valve 77 should take place, as will be described in more detail later.

[0050] It should be noted that the control 103 does not necessarily have to be separated from the control 9, as in the Fig. 1. In addition, several components of the cooling system 3 shown in the Fig. 1 outside the vacuum space 65, can also be arranged inside the vacuum space 65.

[0051] Fig. 2 shows a flowchart for explaining a method for operating the Fig. 1. The method comprises operating the particle beam system 1 in a first operating mode, which comprises steps S1 to S6, operating the particle beam system 1 in a second operating mode, which comprises steps S8 to S11, and steps S7 and S12 for switching between the first operating mode and the second operating mode.

[0052] In step S1, the controller 103 sets the switching valve 77 to the first position, which is Fig. 1 are represented by the solid paths 107 and 108. Subsequently, in step S2, the controller 103 sets a flow of nitrogen 70 at the reducing valve 99, which then flows from the nitrogen reservoir 97 through the switching valve 77 into the first connecting line 75.

[0053] The nitrogen 70 flowing through the first connecting line 75 is cooled by the cooler 83 in step S3 as it flows through the first part 89 of the first connecting line 75. In the case of the particle beam system 1, the nitrogen 70 is cooled, in particular, by liquid nitrogen 87 as it flows through the first part 89 of the first connecting line 75. The nitrogen 70 then flows through the coolant passage 69 in the object holder 43 in step S4 and cools the object holder 43 and the object 39 located thereon. The nitrogen 70 is then expelled into the environment.

[0054] The cooled object 39 can then be used to acquire a particle microscopic image with the particle beam system 1. In particular, in step S5, the controller 9 scans an area on the object 39 with the particle beam 19 by applying several consecutive voltages to the electrodes of the deflection arrangement 45 and assigning each voltage to the detected detector signal.

[0055] During operation of the particle beam system 1 in the first operating mode, the controller 103 monitors the temperature of the object holder 43 using the temperature sensor 116. In a case where the first part 89 of the first connecting line 75 has a large amount of deposits, the cooling capacity of the cooling system 3 is limited, and the object holder 43 cannot be sufficiently cooled. Accordingly, the temperature of the object holder 43 rises, which is detected by the temperature sensor 116. For this reason, the controller 103 evaluates the signal from the temperature sensor 116 in step S6 and compares it with a predetermined threshold value. For example, if such a threshold value is 5°C higher than a target temperature of the object holder 43. If the measured temperature of the object holder 43 does not exceed the threshold value, the first operating mode continues to be executed.More specifically, nitrogen 70 continues to be supplied, the nitrogen 70 is cooled, the object holder 43 is cooled and the object 39 is scanned with the particle beam system 1, as described in steps S2 to S5 of the . Fig. 2 is described.

[0056] If the measured temperature of the object holder 43 exceeds the threshold value, the system switches to the second operating mode. For this purpose, in step S7, the first part 89 of the first connecting line 75 is removed from the liquid nitrogen 87. This can be done, for example, by a user of the particle beam system 1 after being notified via a user interface that the first part 89 of the first connecting line 75 needs to be removed from the liquid nitrogen 87. Alternatively, the first part 89 of the first connecting line 75 can be secured in a guide that can be extended from the cooler 83 via an actuator. Such an actuator can be controlled by the controller 103.

[0057] After removing the first part 89 of the first connecting line 75 from the cooler 83, the controller 103 proceeds to step S8, in which the controller 103 sets the switching valve 77 to the second position, which is shown in Fig. 1 is represented by the dashed paths 109 and 110. The controller 103 then adjusts a flow of nitrogen 70 at the reducing valve 99 in step S9.

[0058] Since the flow direction of the nitrogen 70 through the second position of the switching valve 77 is reversed with respect to the first position of the switching valve 77, as indicated by the solid arrows 112 and in particular the dashed arrows 114 in Fig. 1, the uncooled nitrogen 70 flows through the coolant passage 69 in the object holder 43, as in step S10 of the Fig.2. This heats the coolant passage 69 and the specimen holder 43. The uncooled nitrogen 70 also heats the first portion 89 of the first connecting line 75 and removes deposits present in the first portion 89 of the first connecting line 75.

[0059] The controller 103 monitors the duration of operation of the particle beam system 1 in the second operating mode. In particular, in step S11, the controller 103 checks whether a predetermined operating time has elapsed since the start of operation of the particle beam system 1 in the second operating mode. The predetermined operating time is, for example, half an hour. If the predetermined operating time has not elapsed since the start of operation of the particle beam system 1 in the second operating mode, the controller 103 continues the operation of the particle beam system 1 in the second operating mode. More specifically, the supply of the nitrogen 70 and the heating of the coolant passage 69 of the object holder 43 in steps S9 and S10, as well as the checking of the duration of operation of the particle beam system 1 in the second operating mode in step S11, are repeated.

[0060] If the controller 103 determines in step S11 that the predetermined operating time has elapsed since the start of operation of the particle beam system 1 in the second operating mode, the system switches to the first operating mode. To this end, in step S12, the first part 89 of the first connecting line 75 is immersed in the liquid nitrogen 87, and the controller 103 continues with step S1. The immersion of the first part 89 of the first connecting line 75 into the liquid nitrogen 87 can be carried out by a user in a manner similar to that described above with reference to step S7, after the user has been notified that the insertion of the first part 89 of the first connecting line 75 into the cooler 83 is necessary, or there may be guidance through which step S12 can be carried out by the controller 103.It should be noted that the predetermined operating time of half an hour described above is illustrative, and any other value for the operating time can be selected. Furthermore, it should be noted that in step S11, similar to step S6, the temperature of the object holder 43 can also be monitored using the temperature sensor 116. In such a case, the controller 103 can, for example, compare the temperature value measured by the temperature sensor 116 with a room temperature, a temperature of the nitrogen 70 upon exiting the nitrogen reservoir 97, or the like.

[0061] It should be noted that the cooling system 3 can have additional sensors that generate signals that are used by the controller 103 in step S6 and / or in step S11. For example, a further temperature sensor can be arranged on the first part 89 of the first connecting line 75 and connected to the controller 103 via an electrical line. The controller 103 can then, in step S6 and / or in step S11, compare a temperature measured by this temperature sensor on the first part 89 of the first connecting line 75 with a predetermined threshold value. The predetermined threshold value is, for example, a value that is slightly above a typical temperature of liquid nitrogen and can be -190°C. If the temperature measured on the first part 89 of the first connecting line 75 exceeds the threshold value in step S6, the process continues with step S7 as described above.Otherwise, continue with steps S2 to S5 as described above.

[0062] Furthermore, the controller 103 can compare the temperature measured at the first part 89 of the first connecting line 75 with a second threshold value that is higher than the aforementioned threshold value and that represents, for example, a room temperature. This allows the controller 103 to determine whether step S7 is necessary. For example, the controller 103 need not notify the user of the particle beam system 1 of the need to remove the first part 89 of the first connecting line 75 from the liquid nitrogen 87 and instead skip step S7 if the temperature measured at the first part 89 of the first connecting line 75 is greater than the second threshold value, i.e., for example, greater than room temperature.

[0063] If the temperature measured at the first part 89 of the first connecting line 75 falls below the threshold value in step S11, the process continues with step S12 as described above. Otherwise, the process continues with steps S9 and S10 as described above. With such a control of the cooling system 3, it is possible to automatically switch the cooling system 3 from cooling mode to defrost mode when the first part 89 of the first coolant line 75 is removed from the liquid nitrogen 87 or the liquid nitrogen 87 is used up.

[0064] Several further embodiments are conceivable. For example, controller 103 and controller 9 can be implemented in a common controller, such as a general-purpose computer. Furthermore, the coolant is not limited to nitrogen. The particle beam system 1 disclosed herein is advantageous for any coolant in which impurities are deposited in the coolant due to the cooling of the coolant.

Claims

[1] Particle beam system (1), comprising: an object holder (43) for holding an object (39) to be examined; a particle beam source (5) for generating a particle beam (19); a lens (29) for focusing the particle beam (19) on the object (39); a detector (51) for detecting signals generated by the particle beam (19) on the object (39); and a cooling system (3) for cooling the object holder (43); wherein the cooling system (3) comprises: a coolant passage (69) in the object holder (43) with an inlet connection (71) and an outlet connection (73); a supply connection (95) for supplying a gas (70); an outlet (93) for discharging the gas (70); a changeover valve (77) having a first position (107, 108) and a second position (109, 110); a first connecting line (75) whose first end is connected to the inlet port (71) of the coolant passage (69) and whose second end is connected to the changeover valve (77); a second connecting line (81) whose first end is connected to the outlet port (73) of the coolant passage (69) and whose second end is connected to the changeover valve (77); and a cooler (83) for cooling at least a first part (89) of the first connecting line (75); wherein the changeover valve (77) in the first position (107, 108) connects the supply connection (95) to the second end of the first connecting line (75) and connects the outlet (93) to the second end of the second connecting line (81); and wherein the changeover valve (77) in the second position (109, 110) connects the supply connection (95) to the second end of the second connecting line (81) and connects the outlet (93) to the second end of the first connecting line (75). [2] Particle beam system (1) according to claim 1, wherein the cooling system (3) further comprises: a reducing valve (99) arranged in the flow of the gas (70) between the supply port (95) and the outlet (93) and providing a variable resistance to the flow of the gas (70) through the reducing valve (99); a temperature sensor (116) for outputting a signal representing a temperature of the object holder (43); and a controller (103) configured to control the reducing valve (99) based on the signal representing the temperature of the object holder (43). [3] Particle beam system (1) according to claim 2, wherein the reducing valve (99) is arranged in the flow of the gas (70) at the first position (107, 108) of the switching valve (77) between the supply connection (95) and the switching valve (77) and upstream of the cooler (83). [4] Particle beam system (1) according to claim 2, wherein the reducing valve (99) is arranged in the flow of the gas (70) between the switching valve (70) and the cooler (83). [5] Particle beam system (1) according to one of claims 1 to 4, wherein the first connecting line (75) has an insulating layer (91) surrounding the first connecting line (75) in a second part between the cooler (83) and the object holder (43). [6] Particle beam system (1) according to one of claims 1 to 5, wherein the cooler (83) comprises a cooling chamber (85) through which the first part (89) of the first connecting line (75) passes. [7] Particle beam system (1) according to claim 6, wherein the first part (89) of the first connecting line (75) is free of an insulating layer surrounding it. [8] Particle beam system (1) according to claim 6 or 7, wherein the cooling chamber (85) is configured to accommodate liquid nitrogen (87). [9] Particle beam system (1) according to one of claims 6 to 8, wherein the first part (89) of the first connecting line (75) can be removed from the cooling chamber (85) without destruction and can then be reinserted therein. [10] Particle beam system (1) according to one of claims 1 to 9, wherein the switching valve (77) is a 5 / 2-way valve. [11] Particle beam system (1) according to one of claims 1 to 10, further comprising a vacuum jacket (63) defining a vacuum space (65); wherein the object holder (43) is arranged within the vacuum space (65); and wherein the changeover valve (77) is arranged outside the vacuum chamber (43). [12] Particle beam system (1) according to claim 11, wherein the cooler (83) is arranged outside the vacuum space (65). [13] Particle beam system (1) according to one of claims 1 to 12, further comprising an object table (55) which is displaceable relative to the lens (29) for focusing the particle beam (19) and which carries the object holder (43). [14] Particle beam system (1) according to claim 13, wherein the object holder (43) is thermally insulated from the object table (55). [15] Particle beam system (1) according to claim 14, wherein the object holder (43) has a main surface facing the object table (55); wherein the object table (55) has a main surface facing the object holder (43); wherein spacers (61) are provided between the object holder (43) and the object table (55) in order to maintain a distance between the main surface of the object holder and the main surface of the object table; wherein a number of spacers (61) is less than ten and in particular equal to three. [16] Method for operating the particle beam system (1) according to one of claims 1 to 15, comprising: Operating the particle beam system (1) in a first operating mode and in a second operating mode; where the first operating mode includes: Moving the changeover valve (77) to the first position (107, 108), Supplying gas (70) to the supply connection (95); Cooling the first part (89) of the first connecting line (75) with the cooler (83), Cooling the object holder (43) and an object (39) arranged on the object holder (43) with the gas (70) cooled in the first connecting line (75), and Scanning the particle beam (19) over the object (39) and detecting signals with the detector (51); and the second operating mode includes: Moving the changeover valve (77) to the second position (109, 110), supplying gas (70) to the supply connection (95), and Heating the object holder (43) with the supplied gas (70). [17] The method of claim 16, wherein the cooler (83) is not operated in the second operating mode. [18] Method according to claim 17 in conjunction with any one of claims 6 to 9, further comprising removing the first part (89) of the first connecting line (75) from the cooling chamber (85) after operating the particle beam system (1) in the first operating mode and before operating the particle beam system (1) in the second operating mode. [19] Method according to one of claims 16 to 18 in conjunction with claim 8 or 9, further comprising filling the cooling chamber (85) with liquid nitrogen (87) before operating the particle beam system (1) in the first operating mode. [20] The method according to claim 19, further comprising removing the first part (89) of the first connecting line (75) from the cooling chamber (85) after operating the particle beam system (1) in the first operating mode and before operating the particle beam system (1) in the second operating mode and inserting the first part (89) of the first connecting line (75) into the cooling chamber (85) after operating the particle beam system (1) in the second operating mode and before operating the particle beam system (1) in the first operating mode. [21] A method according to any one of claims 16 to 20, wherein the supplied gas (70) is nitrogen.

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