Particle beam system with cooling system, method for operating the same and computer program product

Abstract

A particle beam system is disclosed, comprising an object holder for mounting an object under investigation, a particle beam source, a lens for focusing the particle beam, a detector, and a cooling system for cooling the object holder. The cooling system includes a coolant passage in the object holder, a supply port, an outlet, a two-pass heat exchanger, a first connecting line connected to the inlet of the coolant passage and the first passage of the heat exchanger, a second connecting line connected to the outlet of the coolant passage and the second passage of the heat exchanger, a third connecting line connected to the first passage of the heat exchanger and the supply port, a fourth connecting line connected to the second passage of the heat exchanger and the outlet, and a cooler for cooling a portion of the first connecting line.

Description

[0001] The present invention relates to a particle beam system with a cooling system, a method for operating the particle beam system and a computer program product.

[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. For acquiring the particle-optical image, particularly with biological and chemical objects, it is desirable to keep the object's temperature low. This is typically achieved using an object holder to keep the object within the particle beam system, which is connected to nitrogen cooling. 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] Typically, such nitrogen cooling systems use gaseous nitrogen as a coolant and liquid nitrogen to cool the gaseous nitrogen. When the nitrogen cooling system is operating to cool the object held by the object holder, the liquid nitrogen evaporates. Therefore, the user of the particle beam system with this type of nitrogen cooling must regularly refill the cooling system with liquid nitrogen, which is associated with increased costs and additional effort for the user. Accordingly, one objective of the present invention is to reduce the consumption of liquid nitrogen.

[0004] US patent 2022 / 0172921A1 discloses a combination system of a light microscope and a particle beam microscope, wherein a specimen holder incorporates an additional scintillator material.

[0005] The dissertation by T. Kohlberger 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 under investigation for the study of superconducting devices based on LaAlO3 / SrTiO3 heterostructures.

[0006] To achieve the aforementioned goal, a particle beam system is proposed comprising an object holder for holding an object under investigation, 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 includes a coolant passage in the object holder with an inlet port and an outlet port, a supply port for adding a gas, an outlet for removing the gas, a heat exchanger with a first passage and a second passage, each having an inlet port and an outlet port, and a first connecting line.the first end of which is connected to the inlet port of the coolant passage of the object holder and the second end of which is connected to the outlet port of the first passage of the heat exchanger, a second connecting line, the first end of which is connected to the outlet port of the coolant passage of the object holder and the second end of which is connected to the inlet port of the second passage of the heat exchanger, a third connecting line, wherein, in a cooling operation, the first end of which is connected to the inlet port of the first passage of the heat exchanger and the second end of which is connected to the supply port, a fourth connecting line, wherein, in a cooling operation, the first end of which is connected to the outlet port of the second passage of the heat exchanger and the second end of which is connected to the outlet, and comprising a cooler for cooling at least a first part of the first connecting line.

[0007] This means that the proposed particle beam system incorporates a cooling system in which, after passing through the coolant passage of the object holder and thus cooling the object holder, the still-cold gas flows through a heat exchanger. This allows the still-cold gas to absorb heat from newly supplied gas before being released into the environment, thereby pre-cooling the newly supplied gas. This reduces the amount of heat transferred from the newly supplied gas to the liquid nitrogen in the cooler, thus reducing the consumption of liquid nitrogen. Furthermore, the energy consumption of the cooling system is reduced because the energy used to cool the gas is utilized more efficiently.

[0008] It should be noted that a connection via connecting lines implies that further functional components may be arranged between the first and second ends of the respective connecting line. For example, valves, sensors, controllers, or similar devices may be arranged between the first and second ends of the first connecting line, or between the inlet port of the coolant passage and the outlet port of the first passage of the heat exchanger.

[0009] According to some embodiments, the cooling system further comprises a reducing valve arranged in the gas flow between the supply port and the outlet, providing variable resistance to the gas flow through the reducing valve; a temperature sensor for outputting a signal representing the temperature of the object holder; and a controller configured to control the reducing valve based on the temperature signal. For example, the reducing valve is a rotary valve, an electrically actuated valve, or the like, with which the gas flow can be adjusted.

[0010] The reducing valve is a valve capable of regulating the amount of gas flowing through the cooling system. The reducing valve can be an electrically controlled valve, such as a solenoid valve, which can be actuated by the controller to regulate the gas flow. The temperature sensor is a sensor capable of measuring the temperature of the object holder and transmitting this temperature to the controller via a corresponding signal. This can be advantageous for providing feedback control of the cooling system. In particular, with such an embodiment, a target temperature for the object holder can be set.The control system 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, during which the object holder has reached thermal equilibrium.

[0011] According to some embodiments, the reducing valve can be arranged at the supply connection, or in the gas flow between the supply connection and the first part of the first connecting line that is cooled by the cooler, whereby the gas pressure in the entire cooling system is defined by the degree of opening of the reducing valve. In particular, the pressure of the gas supplied to the cooling system in such a case is not dependent on the gas source used or on the quantity of gas contained in the source, which allows the cooling system to operate more reliably.

[0012] According to some embodiments, the first connecting line has an insulating layer surrounding it in a second section between the cooler and the object holder, which reduces heat transfer between the second section of the first connecting line and the environment. It is particularly advantageous that the first section of the first connecting line is free of an insulating layer surrounding it, so that heat transfer between the cooler and the gas can occur efficiently. Furthermore, the insulating layer is not present in the third and fourth connecting lines. The insulating layer is, for example, a sheathing of the connecting line in the second section with a material that has a low thermal conductivity. An insulating layer can also be achieved by enclosing the connecting line in a housing within which a vacuum is created.Furthermore, a vacuum prevents the connecting pipe from icing up, as the part of the connecting pipes surrounded by the insulating layer does not come into contact with water dissolved in the environment.

[0013] It can also be advantageous for the insulating layer to surround the second connecting line and the heat exchanger, thus reducing unwanted heating of the gas in these areas. Particularly when the insulating layer is created by a vacuum, the aforementioned vacuum housing can surround the first connecting line, the second connecting line, and the heat exchanger. Alternatively, the insulating layer can be created by connecting the aforementioned vacuum housing to a vacuum chamber within the particle beam system.

[0014] In some embodiments, the cooler includes a cooling chamber. The cooling chamber is a volume into which a cooling medium, such as liquid nitrogen, can be filled. Advantageously, the cooling medium is filled into the cooling chamber before the cooling operation begins. During cooling operation of the particle beam system, the first section of the first connecting line is immersed in this liquid nitrogen. Furthermore, it is advantageous to perform a defrost cycle after a certain period of cooling operation of the particle beam system to remove deposits from the first connecting line. These deposits form when impurities in the gas accumulate due to the low temperature in the cooling system and increasingly clog the first connecting line. For this purpose, during the defrost cycle, the gas is supplied to the cooling system in such a way that uncooled gas flows through the first connecting line.For defrosting, it is therefore advantageous to be able to deactivate the cooler so that the gas in the first section of the first connecting line is not cooled. To achieve this, the first section of the first connecting line can be immersed in liquid nitrogen before cooling and then removed from it without damage before defrosting. This allows the cooler to be deactivated.

[0015] According to some embodiments, the particle beam system further comprises a vacuum jacket that defines a vacuum chamber. The vacuum jacket is, for example, a metal housing for the particle beam system. A vacuum is generated in the vacuum chamber during operation of the particle beam system to reduce unwanted interactions of the particle beam with the atmosphere. It can be advantageous to arrange components outside the vacuum chamber that do not require a vacuum for their operation, as this reduces the expansion of the vacuum chamber and prevents an unnecessary increase in energy during vacuum generation. For example, the cooler can be located outside the vacuum chamber.Furthermore, as described above, the insulating layer can be connected to the vacuum space, so that a pump simultaneously generates the vacuum for scanning the object with the particle beam and the vacuum for insulating the second part of the first connecting line and other components.

[0016] According to some embodiments, the cooling system of the particle beam system further comprises a changeover valve for switching between cooling and defrosting modes. In defrosting mode, the first end of the third connecting line is connected to the inlet of the first passage of the heat exchanger, and the second end is connected to the outlet. In defrosting mode, the first end of the fourth connecting line is connected to the outlet of the second passage of the heat exchanger, and the second end is connected to the supply port. This means that in cooling mode, the gas is routed through the cooling system such that it first flows through the first passage of the heat exchanger, where it is pre-cooled. It is then cooled in the first part of the first connecting line and finally cools the object holder as the gas flows through the coolant passage in the object holder.After exiting the coolant passage of the object holder, the gas flows through the second passage of the heat exchanger to pre-cool newly supplied gas. Conversely, during defrosting, the gas is routed through the cooling system in such a way that it first flows through the second passage of the heat exchanger and the coolant passage of the object holder, thereby warming the object holder. The gas then flows through the first section of the first connecting line, removing deposits that accumulated there during the previous cooling operation, and is subsequently discharged into the environment after passing through the first passage of the heat exchanger.

[0017] It should be noted that the above designations of the inlet and outlet ports of the coolant passage are for illustrative purposes only and do not define the direction of gas flow. For example, the most common operating mode is that in which the changeover valve is in the first position. This operation is also referred to as cooling mode. Accordingly, the inlet port of the coolant passage is the port through which the gas enters the coolant passage during cooling mode, and the outlet port of the coolant passage is the port through which the gas exits the coolant passage during cooling mode. It should be emphasized that the assignment of the inlet and outlet ports is independent of the current operation of the changeover valve.

[0018] In some embodiments, the changeover valve is a 5 / 2-way valve. A 5 / 2-way valve is a valve with five ports and two positions. The five ports are divided into two inlet ports and three outlet ports, with one of the three outlet ports being connected to one of the inlet ports in both positions, and the other two outlet ports each being connected to one of the inlet ports only in one of the positions. Alternatively, a 4 / 2-way valve can be used, for example. A 4 / 2-way valve is a valve with four ports and two positions, with the four ports being divided into two inlet ports and two outlet ports, and the two outlet ports being connected in the second position to the inlet ports opposite to those in the first position.

[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 move the object held by the object holder across the stage relative to the lens for focusing the particle beam. The object holder is, for example, held at a distance from the stage by spacers to reduce heat transfer between the object holder, which is to be cooled, and the stage connected to the actuator. Fewer than ten, and in particular three, spacers are used to maintain the distance between the object holder and the stage. For example, the spacers are made of a material with a low coefficient of thermal conductivity and are spherical in shape to minimize heat transfer from the stage to the object holder.Alternatively, the object holder can, for example, not be supported by a stage, but instead be guided into the vacuum chamber via a connection through a vacuum lock. The vacuum lock is a feedthrough through the vacuum jacket with two seals that close sequentially when the object holder is removed from the vacuum chamber, thus maintaining the vacuum within the chamber during removal.

[0020] According to some embodiments, a method for operating the particle beam system comprises operating the particle beam system in a first operating mode, namely cooling mode. In cooling mode, the gas is first supplied to the supply port, whereupon the gas is pre-cooled as it flows through the first passage of the heat exchanger. The gas is then cooled in the second part of the first connecting line to the cooler, and the object holder and an object mounted on the object holder are cooled by the cooled gas flowing through the coolant passage in the object holder. After exiting the coolant passage in the object holder, the gas flows through the second passage of the heat exchanger to pre-cool newly supplied gas through heat exchange.The cooled object is scanned with the particle beam, and the signals generated by the object upon impact are captured by the detector, thus creating a particle-optical image. Since the cooling induced in the gas can be used more effectively, the consumption of liquid nitrogen is reduced.

[0021] In some embodiments, the supplied gas is nitrogen. It should be noted that gases typically contain impurities. Here, nitrogen refers 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] According to some embodiments, the method includes operating the particle beam system in a second operating mode, namely defrost mode. For defrost mode, the system is first switched from cooling mode to defrost mode using the changeover valve. Gas is then supplied to the supply connection, and the object holder is heated with the supplied gas. Switching back to cooling mode also requires switching the changeover valve.

[0023] Certain embodiments are explained in more detail below with reference to figures. These show: Fig. 1 a particle beam system with a cooling system according to one embodiment. Fig. 2. A flowchart to illustrate a procedure for operating the in Fig. 1 particle beam system shown.

[0024] Fig. Figure 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 control unit 9 via an electrical line 7. The control unit 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 control unit 9 via an electrical line 17. The control unit 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 control unit 9 supplies the particle beam source 5 with the first electrical potential, thereby releasing particles from the particle beam source 5.Furthermore, the control unit 9 supplies the beam tube 11 with a second electric potential different from the first electric 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.

[0025] It should be noted that in the example described herein, the upper end 13 of the jet tube 11 acts as an accelerating electrode. However, an additional accelerating electrode may be provided, which is located in the Fig. The particle beam system shown in 1 can, for example, be contained in the particle beam source 5.

[0026] 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 control unit 9 via an electrical line 27, enabling the control unit to supply an electric current to the coil 23 of the condenser lens 21, thereby generating a magnetic field. The magnetic field generated by the coil 23 of the condenser lens 21 enters the beam tube 11 at an opening in 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 in Fig. While 1 is represented as a magnetic lens, the condenser lens 21 can also be any other lens suitable for influencing the particle beam 19. For example, the condenser lens can be an electrostatic lens, such as a single lens.

[0027] 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 control unit 9 via an electrical line 37, enabling the control unit to supply an electric current to the coil 31 of the objective lens 29, thereby generating a magnetic field. The pole piece 33 of the objective lens 29 has a lower end 35, which is located 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, allowing the magnetic field generated by the coil 31 of the objective lens 29 to enter the path of the particle beam 19 and influence it.

[0028] The particle beam 19 is focused by the objective lens 29 onto 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 one described in the Fig. The magnetic lens shown in 1 could also be an electrostatic lens, such as a single lens.

[0029] The particle beam 19 further 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 control unit 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 mass potential in order to avoid an energy input by the control unit 9.

[0030] An electric field between the lower end 15 of the beam tube 11 and the object 39 is defined by the difference between the second electric potential supplied to the beam tube 11 and the third electric potential supplied to the object 39. When this electric field prevails between the lower end 15 of the beam tube 11 and the object 39, the particle beam 19 is affected. This electric field produces a focusing lens effect. Since the electric field of the electrostatic lens strongly overlaps with the magnetic field of the objective lens 29, this setup can also be called a combination lens.

[0031] The point of impact of the particle beam 19 on the object 39 is influenced by a deflection arrangement 45. In the case of the Fig. In the example shown, the deflection arrangement 45 comprises several pairs of electrodes which, when a voltage is applied between the electrodes of a pair by the control 9 via an electrical line 47, generate an electric field which deflects the particle beam 19 when passing through the electric field.

[0032] When the particle beam 19 strikes the object 39, electrons are emitted from the object 39. These electrons are accelerated into the beam tube 11 by the focusing electrostatic lens located between the object 39 and the lower end 15 of the beam tube 11. The beam tube 11 also has a chamber 49 for components, in which, as in Fig. Figure 1 shows, for example, a detector 51 arranged which is connected to the control unit 9 via an electrical line 53. The detector 51 comprises a detector area to detect the electrons entering the beam tube 11. The detector 51 generates a detector signal, which represents a number of electrons striking the detector 51, and transmits the detector signal to the control unit 9 via the electrical line 53.

[0033] The particle beam system 1 generates an image of object 39 by having the controller 9 set different voltage values ​​at the deflection arrangement 45 and assign each of these voltage values ​​to a detector signal. The detector signals and the voltage values ​​can be stored in a memory of the controller 9.

[0034] 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 control unit 9 via an electrical line 59. The actuator 57 can be used, for example, to change the 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.

[0035] The object stage 55 supports the object holder 43 at a distance defined by spacers 61 between the object stage 55 and the object holder 43. As shown in Fig. As shown in Figure 1, the spacers 61 can have a spherical shape to minimize the contact area between the object holder 43 and the spacers 61, or between the object stage 55 and the spacers 61. Reducing this contact area reduces heat transfer between the object stage 55 and the object holder 43 that needs to be cooled.

[0036] The particle beam system 1 further comprises a vacuum jacket 63, which surrounds a vacuum chamber 65 in which the components of the particle beam system 1 described above, with the exception of the control unit 9, are arranged. Air is extracted from the vacuum chamber 65 using a pump (not shown) connected to a pump nozzle 67, thus creating a vacuum.

[0037] The particle beam system 1 further comprises the cooling system 3. The cooling system 3 includes 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 during cooling operation, and an outlet port 73, from which the nitrogen 70 flows out of the coolant passage 69 during cooling operation.

[0038] The inlet port 71 of the coolant passage 69 is connected to a heat exchanger 74 via a first connecting line 75. For this purpose, a first end of the connecting line 75 is connected to the inlet port 71 of the coolant passage 69, the connecting line 75 is led through a vacuum seal 79 through the vacuum jacket 63 and out of the vacuum chamber 65, and a second end of the connecting line 75 is connected to a first passage 78 of the heat exchanger 74. The vacuum seal 79 is a seal that hermetically closes an opening in the vacuum jacket 63. For example, the vacuum seal 79 is a rubber seal or a metal seal. In particular, the one in Fig. Figure 1 shows a vacuum seal 79 with 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 one end to the outlet port 73 of the coolant passage 69 and at the other end to a second passage 76 of the heat exchanger 74.

[0039] The cooling system 3 further comprises an additional vacuum jacket 91, which surrounds part of the first connecting line 75, the second connecting line 81, and the heat exchanger 74. The vacuum jacket 91 has a pump port 92 to which another pump (not shown) is connected. When the pump is operated, it pumps air out of a vacuum chamber 94 surrounded by the vacuum jacket 91, thereby creating a vacuum in the vacuum chamber 94. The vacuum chamber 94 acts as a thermal insulation layer for part of the first connecting line 75, the second connecting line 81, and the heat exchanger 74. In particular, the vacuum prevailing in the vacuum chamber 94 reduces heat transfer between the components of the cooling system 3 surrounded by the vacuum jacket 91 and the environment.Furthermore, the vacuum prevailing in vacuum chamber 94 prevents icing of water dissolved in the environment at the first connecting line 75, the second connecting line 81, and the heat exchanger 74. It should be noted that vacuum chamber 94 can be connected to vacuum chamber 65, so that the vacuum in vacuum chamber 94 can be generated by the pump (not shown) at pump port 67. In such a case, pump port 92 is not required.

[0040] The cooling system 3 further comprises a cooler 83, which has a cooling chamber 85. Before the cooling system is put into operation, liquid nitrogen 87 is filled into the cooling chamber 85, and a first section 89 of the first connecting line 75 is immersed in the liquid nitrogen 87. For this purpose, the first section 89 of the first connecting line 75 is led out of the vacuum chamber 94 through the vacuum jacket 91 via vacuum seals 80. The nitrogen 70 flowing through the first section 89 of the first connecting line 75 is cooled by the liquid nitrogen 87 in the cooler 83.

[0041] The heat exchanger 74 comprises the first passage 76 and the second passage 78 and is a counterflow heat exchanger in which the nitrogen 70 flows through the first passage 78 and the second passage 76 in opposite directions. The first passage 78 and the second passage 76 of the heat exchanger 74 are each connected to a changeover valve 77 by means of a vacuum seal 82. The heat exchanger 74 enables efficient heat transfer between the nitrogen 70 in the first passage 78 of the heat exchanger 74 and the nitrogen 70 in the second passage of the heat exchanger 74. Although the heat exchanger 74 is in Fig. Although Figure 1 is depicted as a simple counterflow heat exchanger, any type of heat exchanger suitable for the aforementioned purpose can be used. For example, a heat exchanger can be used in which the first passage 78 and the second passage 78 are configured as two concentric tubes, such that the second passage 76 surrounds the first passage 78. The heat exchanger 74 ensures that the nitrogen 70 in the first passage 78 of the heat exchanger 74 is pre-cooled by the nitrogen 70 in the second passage 76 of the heat exchanger 74 before the nitrogen 70 is cooled in the first part 89 of the first connecting line 75. Pre-cooling the nitrogen 70 in the first passage 78 of the heat exchanger 74 reduces the consumption of liquid nitrogen 87 in the cooler 83, since the liquid nitrogen 87 absorbs less heat from the nitrogen 70 and thus evaporates in smaller quantities.Furthermore, for example, in a case where the object holder 43 has reached a target temperature and only needs to be maintained at that temperature, the nitrogen 70 is prevented from being cooled and released into the environment. This also reduces the energy consumption of the cooling system 3.

[0042] Cooling system 3 further comprises an outlet 93 from which the nitrogen 70 is discharged. The outlet 93 is connected to the changeover valve 77 via a fourth connecting line 98. Cooling system 3 also includes a supply port 95 for feeding the nitrogen 70 into cooling system 3. For this purpose, the supply port 95 is connected to a nitrogen reservoir 97, such as a nitrogen cylinder or a nitrogen tank. The supply port 95 is also connected to the changeover valve 77 via a third connecting line 96. To regulate the flow of nitrogen 70 from the nitrogen reservoir 97, the supply port 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 electrically controlled. For control purposes, the reducing valve 99 is connected to a control unit 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 nitrogen 70, and supplies the determined current to the reducing valve 99.

[0043] The diverter valve 77 is connected to the control unit 103 via an electrical line 105. The in Fig. The changeover valve 77 shown is a 4 / 2-way valve; however, the changeover valve 77 could be of a different type, such as a 5 / 2-way valve. For the sake of simplicity, the 4 / 2-way valve as it appears in the Fig. 1 is shown.

[0044] The changeover valve 77 comprises four ports connected to the third connecting line 96, the fourth connecting line 98, the first passage 78 of the heat exchanger 74, and the second passage 76 of the heat exchanger. The changeover valve 77 further comprises a first position and a second position. The first position is represented by the solid lines 107 and 108, and the second position is represented by the dashed lines 109 and 110. When the changeover valve 77 is in the first position, represented by the solid lines 107 and 108, the supply port 95 is connected to the first passage 78 of the heat exchanger 74, and the outlet 93 is connected to the second passage 76 of the heat exchanger 74. Accordingly, in the first position of the switching valve 77, the nitrogen 70 flows from the nitrogen reservoir 97 into the first passage 78 of the heat exchanger 74 and then into the first connecting line 75.The nitrogen 70 is cooled in the first section 89 of the first connecting line 75 and flows through the coolant passage 69 in the object holder 43, thereby cooling the object holder 43 and the object 39 located on the object holder 43. The nitrogen 70 then flows through the second connecting line 81 into the second passage 76 of the heat exchanger 74 and undergoes heat exchange with the nitrogen 70 in the first passage 78 of the heat exchanger 74. Subsequently, the nitrogen 70 flows from the second passage 76 of the heat exchanger 74 to the outlet 93 and is discharged there into the environment. The flow rate of the nitrogen 70 at the first position of the changeover valve 77 is given in... Fig. 1 with the solid arrow 112.

[0045] The switching valve 77 serves to enable switching between a cooling operation and a defrosting operation of the particle beam system 1. During defrosting operation, deposits in the first section 89 of the first connecting line 75 are removed, which arise, for example, from impurities contained in the nitrogen 70 freezing in the first section 89 of the first connecting line 75.

[0046] To remove the deposits during defrosting, the controller 103 is able to change the position of the changeover valve 77 via an electrical line 105, thus moving the changeover valve 77 to the second position. Additionally, the cooler 83 is removed by taking the first part 89 of the first connecting line 75 out of the liquid nitrogen 87. It should be noted that removing the cooler 83 is not strictly necessary. In a case where the cooler 83 is, for example, a Peltier cooler, it is sufficient if the cooler 83 has a lower cooling capacity, so that the nitrogen 70 is only slightly cooled when the changeover valve 77 is in the second position.

[0047] 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, warming it. The nitrogen 70 then flows through the first connecting line 75, warming the first section 89 of the first connecting line 75, thereby loosening the deposits. The loosened deposits are then expelled into 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 changeover valve 77 is in the Fig. 1 is shown with the dashed arrow 114. By reversing the flow direction of the nitrogen 70 in the first connecting line 75 and the second connecting line 81 at the second position of the changeover valve 77, the dissolved deposits cannot 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.

[0048] The cooling system 3 further includes a temperature sensor 116, which is attached to the object holder 43 to detect the 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 to switch to the second position or to the first position of the changeover valve 77, as will be described in more detail later.

[0049] The particle beam system 1 described above is capable of reducing the consumption of liquid nitrogen and achieving the aforementioned goal. It should be noted that the control unit 103 of the cooling system 3 does not necessarily have to be separate from the control unit 9, as shown in the Fig. Figure 1 is shown. In addition, several components of the cooling system 3, which are located in the Fig. 1 shown outside the vacuum space 65, may also be arranged inside the vacuum space 65.

[0050] Fig. Figure 2 shows a flowchart to explain a procedure for operating the in Fig. 1 particle beam system 1 shown. The method includes operating the particle beam system 1 in a first operating mode, which includes steps S1 to S8, operating the particle beam system 1 in a second operating mode, which includes steps S10 to S13, and steps S9 and S14 for switching between the first operating mode and the second operating mode.

[0051] In step S1, the control unit 103 moves the switching valve 77 into the first position, which is in Fig. 1 are represented by the solid paths 107 and 108. Subsequently, in step S2, the control unit 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.

[0052] After passing through the switching valve 77 in the first position, the nitrogen 70 flows through the first passage 78 of the heat exchanger 74 and is pre-cooled there by heat exchange with the nitrogen 70 in the second passage 76 of the heat exchanger 74 in step S3.

[0053] The nitrogen 70, pre-cooled in step S3, is then cooled by the cooler 83 as it flows through the first part 89 of the first connecting line 75 in step S4. In the case of the particle beam system 1, the nitrogen 70 is cooled particularly by the 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 S5 and cools the object holder 43 and the object 39 located on it.

[0054] In step S6, after exiting the coolant passage 69 in the object holder 43, the nitrogen 70 flows through the second passage 76 of the heat exchanger 74 and is used in the second passage 76 to pre-cool the nitrogen 70 flowing through the first passage 78 of the heat exchanger 74. This pre-cooling occurs through heat exchange between the nitrogen 70 in the second passage 76 and the nitrogen 70 in the first passage 78. After passing through the second passage 76 of the heat exchanger 74, the nitrogen 70 flows through the changeover valve 77 and is discharged into the environment. Pre-cooling the nitrogen 70 in the first passage 78 of the heat exchanger 74 reduces the consumption of liquid nitrogen 87 in the cooler 83 and the energy consumption of the cooling system 3, since the liquid nitrogen 87 absorbs less heat from the nitrogen 70 and therefore evaporates in smaller quantities.

[0055] The cooled object 39 can then be used to acquire a particle microscopic image with the particle beam system 1. In particular, in step S7, the controller 9 scans an area on the object 39 by applying several successive voltages to the electrodes of the deflection arrangement 45 and assigning each voltage to the detected detector signal.

[0056] 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. If the first section 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 adequately cooled. Consequently, the temperature of the object holder 43 rises, which is detected by the temperature sensor 116. Therefore, in step S8, the controller 103 evaluates the signal from the temperature sensor 116 and compares it to a predetermined threshold. For example, such a threshold is 5 °C higher than a target temperature for the object holder 43. If the measured temperature of the object holder 43 does not exceed the threshold, the first operating mode continues.More precisely, nitrogen 70 continues to be supplied, the nitrogen 70 is pre-cooled and cooled, the object holder 43 is cooled with the nitrogen 70 and the object 39 is scanned with the particle beam system 1, as described in steps S2 to S7 of the . Fig. 2 is described.

[0057] If the temperature of the object holder 43 exceeds the threshold, the system switches to the second operating mode. In step S9, the first section 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 removing the first section 89 of the first connecting line 75 from the liquid nitrogen 87 is necessary. After the user has removed the first section 89 of the first connecting line 75 from the liquid nitrogen 87, they can, for example, acknowledge the notification via the user interface, allowing the particle beam system 1 to continue the process.Alternatively, the first part 89 of the first connecting line 75 can be fixed in a guide that can be extended from the cooler 83 by means of an actuator. Such an actuator can be controlled by the controller 103.

[0058] After removing the first part 89 of the first connecting line 75 from the cooler 83, the control unit 103 proceeds to step S10, in which the control unit 103 moves the switching valve 77 to the second position, which is in Fig. 1 is represented by the dashed paths 109 and 110. Subsequently, in step S11, the controller 103 sets a flow of nitrogen 70 at the reducing valve 99, so that the nitrogen 70 is supplied via the supply port 95.

[0059] Since the flow direction of the nitrogen 70 is reversed by the second position of the changeover valve 77 with respect to the first position of the changeover valve 77, as indicated by the solid arrow 112 and in particular the dashed arrow 114 in Fig. As shown in Figure 1, the uncooled nitrogen 70 flows through the coolant passage 69 in the object holder 43, as described in step S12 of the Fig. 2 described. This heats the coolant passage 69 and the object holder 43. The uncooled nitrogen 70 also heats the first part 89 of the first connecting line 75 and removes deposits that are present in the first part 89 of the first connecting line 75.

[0060] The controller 103 monitors the duration of operation of the particle beam system 1 in the second operating mode. Specifically, in step S13, 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 precisely, the supply of nitrogen 70 and the heating of the coolant passage 69 of the object holder 43 in steps S11 and S12, as well as the checking of the duration of operation of the particle beam system 1 in the second operating mode in step S13, are repeated.

[0061] If, in step S13, the controller 103 determines that the predetermined operating time has elapsed since the start of operation of the particle beam system 1 in the second operating mode, it switches to the first operating mode. For this purpose, in step S14, 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, similar to the procedure described above with reference to step S9, 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 a guide may be provided by which step S14 can be carried out by the controller 103.It should be noted that the predetermined operating time of half an hour described above serves for illustrative purposes and any other value for the operating time can be selected. Furthermore, it should be noted that in step S13, similar to step S8, 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 room temperature, the temperature of the nitrogen 70 at the exit from the nitrogen reservoir 97, or similar values.

[0062] It should be noted that the cooling system may have three additional sensors that generate signals used by the controller 103 in step S8 and / or step S13. For example, another temperature sensor may be located 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 S8 and / or step S13, compare a temperature measured by this temperature sensor on the first part 89 of the first connecting line 75 with a predetermined threshold. The predetermined threshold is, for example, a value slightly above a typical liquid nitrogen temperature and may be -190 °C. If the temperature measured on the first part 89 of the first connecting line 75 exceeds the threshold in step S8, the process continues with step S9 as described above.Otherwise, proceed with steps S2 to S7 as described above.

[0063] 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 and represents, for example, room temperature. This allows the controller 103 to determine whether step S9 is necessary. For example, the controller 103 does not need to notify the user of the particle beam system 1 about the need to remove the first part 89 of the first connecting line 75 from the liquid nitrogen 87 and can instead skip step S9 if the temperature measured at the first part 89 of the first connecting line 75 is higher than the second threshold value, i.e., higher than room temperature.

[0064] If the temperature measured at the first section 89 of the first connecting line 75 falls below the threshold value in step S13, the process continues with step S14 as described above. Otherwise, it continues with steps S11 and S12 as described above. With such control of the cooling system 3, it is possible to automatically switch from cooling operation to defrosting operation when the first section 89 of the first refrigerant line 75 is removed from the liquid nitrogen 87, or when the liquid nitrogen 87 is consumed.

[0065] Several other embodiments are conceivable. For example, the controller 103 and the controller 9 can be implemented in a common controller, such as a general-purpose computer. Furthermore, the coolant is not limited to nitrogen. The detailed embodiment of the particle beam system 1 is advantageous with any coolant in which impurities are deposited due to the cooling process.

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); 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 heat exchanger (74) having a first passage (78) and a second passage (76), the first passage (78) and the second passage (76) each having an inlet opening and an outlet opening; a first connecting line (75) whose first end is connected to the inlet connection (71) of the coolant passage (69) of the object holder (43) and whose second end is connected to the outlet opening of the first passage (78) of the heat exchanger (74); a second connecting line (81) whose first end is connected to the outlet port (73) of the coolant passage (69) of the object holder (69) and whose second end is connected to the inlet opening of the second passage (76) of the heat exchanger (74); a third connecting line (96), the first end of which is connected to the inlet opening of the first passage (78) of the heat exchanger (74) and the second end of which is connected to the supply connection (95) in a cooling operation; a fourth connecting line (98), wherein in a cooling mode, its first end is connected to the outlet opening of the second passage (76) of the heat exchanger (74) and its second end is connected to the outlet (93); and a cooler (83) for cooling at least a first part (89) 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) between the supply connection (95) and the cooler (83). [4] Particle beam system (1) according to one of claims 1 to 3, wherein the first connecting line (75) has an insulating layer (94) surrounding the first connecting line (75) in a second part between the cooler (83) and the object holder (43). [5] Particle beam system (1) according to claim 4, wherein the insulating layer (94) further surrounds the second connecting line (81) and the heat exchanger (74). [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 connecting line (75) is free of an insulating layer surrounding it. [8] Particle beam system (1) according to one of claims 6 or 7, wherein the cooling chamber (85) is configured to receive liquid nitrogen (87). [9] Particle beam system (1) according to one of claims 6 to 8, wherein the first part (89) of the 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, 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 cooler (83) is arranged outside the vacuum space (65). [11] Particle beam system (1) according to one of claims 1 to 10, wherein the cooling system (3) further comprises a switching valve (77) for switching between the cooling operation and a defrosting operation; wherein in the defrosting mode, the first end of the third connecting line (98) is connected to the inlet opening of the first passage (78) of the heat exchanger (74) and the second end is connected to the outlet (93); and wherein in the defrosting operation, the first end of the fourth connecting line (96) is connected to the outlet opening of the second passage (76) of the heat exchanger (74) and the second end is connected to the supply connection (95). [12] Particle beam system (1) according to claim 11, wherein the switching valve (77) is a 5 / 2-way valve. [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 (43) and the main surface of the object table (55); 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, wherein the first operating mode comprises: Supplying gas (70) to the supply connection (95); Pre-cooling the gas (70) in the first passage (78) with the heat exchanger (74); Cooling the gas (70) in the second 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 cooled gas (70); Using the gas (70) in the second passage (76) of the heat exchanger (74) after cooling the object holder (43) for pre-cooling with the heat exchanger (74); and Scanning the particle beam (19) over the object (39) and detecting signals with the detector (51). [17] The method of claim 16, wherein the supplied gas (70) is nitrogen gas. [18] The method of claim 16 or 17, further comprising: Operating the particle beam system (1) in a second operating mode, wherein the second operating mode comprises: Switching the operation with the changeover valve (77); Supplying gas (70) to the supply connection (95), and Heating the object holder (43) with the supplied gas (70); wherein the first operating mode further comprises switching the operation with the switching valve (77). [19] The method of claim 18, wherein the cooler (83) is not operated in the second operating mode. [20] Method according to claim 19 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. [21] Method according to one of claims 16 to 20 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. [22] The method according to claim 21, 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. [23] A computer program product comprising instructions which, when executed by the particle beam system according to any one of claims 1 to 15, cause the particle beam system to perform the method according to claim 16 or 17.

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