NL2027307B1 - A charged particle lens assembly and a charged particle beam apparatus provided with such charged particle lens assembly. - Google Patents
A charged particle lens assembly and a charged particle beam apparatus provided with such charged particle lens assembly. Download PDFInfo
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- NL2027307B1 NL2027307B1 NL2027307A NL2027307A NL2027307B1 NL 2027307 B1 NL2027307 B1 NL 2027307B1 NL 2027307 A NL2027307 A NL 2027307A NL 2027307 A NL2027307 A NL 2027307A NL 2027307 B1 NL2027307 B1 NL 2027307B1
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- Prior art keywords
- charged particle
- lens assembly
- permanent magnet
- temperature
- magnet system
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
- H01J37/00—Discharge tubes with provision for introducing objects or material to be exposed to the discharge, e.g. for the purpose of examination or processing thereof
- H01J37/02—Details
- H01J37/04—Arrangements of electrodes and associated parts for generating or controlling the discharge, e.g. electron-optical arrangement, ion-optical arrangement
- H01J37/10—Lenses
- H01J37/14—Lenses magnetic
- H01J37/143—Permanent magnetic lenses
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
- H01J2237/00—Discharge tubes exposing object to beam, e.g. for analysis treatment, etching, imaging
- H01J2237/10—Lenses
- H01J2237/14—Lenses magnetic
- H01J2237/1405—Constructional details
- H01J2237/1415—Bores or yokes, i.e. magnetic circuit in general
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- Chemical & Material Sciences (AREA)
- Analytical Chemistry (AREA)
- Electron Beam Exposure (AREA)
Abstract
It is an object to provide a charged particle lens assembly as well as a charged particle beam apparatus provided with such charged particle lens assembly of limited constructional dimensions and a stable magnet field, as required to ensure beam quality and beam position, comprising at least one magnet system positioned around the beam path and structured to generate the magnetic field for focusing the charged particle beam; wherein the at least one magnet system is a permanent magnet system, and the charged particle lens assembly further comprising a temperature control system being in heat exchanging contact with the at least one permanent magnet system for controlling the temperature of the at least one permanent magnet system during focusing of the charged particle beam propagating along the beam path. Figure 1
Description
TITLE A charged particle lens assembly and a charged particle beam apparatus provided with such charged particle lens assembly.
TECHNICAL FIELD The invention relates to a charged particle lens assembly and a charged particle beam apparatus provided with such charged particle lens assembly. In particular, such charged particle lens assembly and charged particle beam apparatus are used in the field of projecting a charged particle beam, such as an ion beam or an electron beam, in mass spectrometry applications or in charged particle beam optics, for example charged particle beam lithography applications for lithographing a mask pattern on a sample by moving and focussing such a charged particle beam.
BACKGROUND OF THE INVENTION In several technical fields implementing a charged particle beam, such as in mass spectrometry applications or in charged particle beam optics, for example charged particle beam lithography applications, focussing systems are implemented for moving (deflecting) or focusing a charged particle beam. For focusing a charged particle beam a strong magnetic field is needed in order to focus the beam of positively charged ions or negatively charged electrons on a microscopic point. Such electromagnetic fields are created by an electromagnetic lens, an electrostatic lens, etc., and the focussing and/or deflection is effected by controlling a (non-}symmetry in the electromagnetic field.
To generate a stable magnetic field, the common practise is to use electromagnets. Hereby the strength of the magnetic field is only dependent on the amount of coil windings and the electric current being applied through the coil. As such, any possible variation in the magnetic field can be compensated by changing the electric current.
The downside of focussing systems for charged particle beams, which equip electromagnets is its volume. Compared to permanent magnets, electromagnets take much more volume at similar magnetic field levels. The downside of using permanent magnets is the stability of the magnetic field. From permanent magnets it is known that the magnetic field changes with the operational temperature and will decrease over time as well, due to aging of the magnetic materials used.
It is thus an object of the invention to provide a charged particle lens assembly as well as a charged particle beam apparatus provided with such charged particle lens assembly of limited constructional dimensions and a stable magnet field, as required to ensure beam quality and beam position.
According to a first aspect of the disclosure, a charged particle lens assembly for focusing a charged particle beam propagating along a beam path in a magnetic field is proposed, with the charged particle lens assembly comprising at least one magnet system positioned around the beam path and structured to generate the magnetic field for focusing the charged particle beam; wherein the at least one magnet system is a permanent magnet system, and the charged particle lens assembly further comprising a temperature control system being in heat exchanging contact with the at least one permanent magnet system for controlling the temperature of the at least one permanent magnet system during focusing of the charged particle beam propagating along the beam path.
This guarantees to keep the permanent magnet at a constant temperature to minimize thermal effects on the magnetic field. This temperature control mechanism not only allows to compensate for short term thermal behaviour {- hours) such as a charged particle lens assembly that is heating up. It also allows for calibrating the lens assembly for long term behaviour such as aging (~years) of the permanent magnet, for which the operational temperature of the magnet also needs to be controlled.
In a particular example of the disclosure, the temperature control system comprises a heat exchanging device and optionally at least one temperature sensor. The optional temperature sensor can be structured for sensing the temperature of the at least one permanent magnet system, wherein the temperature control system is structured to control the heat exchanging device in responsive to the temperature being sensed.
Thus with such temperature control both the short term as well as the long term stability of the magnetic field is maintained.
In particular, the heat exchanging device comprises a thermal cooling sink being in heat exchanging contact with the at least one permanent magnet system, thus guaranteeing a beneficial heat exchange with the permanent magnet.
In a further example, the heat exchanging device comprises a thermal heating sink being in heat exchanging contact with the at least one permanent magnet system, thus allowing proper temperature control of the permanent magnet.
Additionally, the temperature control system is structured to control the heat exchanging device, such that the temperature of at least one permanent magnet system conforms to a pre-set temperature level. By maintaining the permanent magnet at a pre-set desired operational temperature, a short term as well as a long term stability of the magnetic field is achieved.
In a specific example of the disclosure, the permanent magnet system comprises an inner yoke and an outer yoke arranged concentric with each other, with at least one ring shaped magnet element arranged concentric between both inner and outer yokes. Herewith a compact construction is achieved with minimal dimensions allowing implementation of such permanent magnet systems in mass spectrometry applications or in charged particle beam optics, such as charged particle beam lithography applications, where constructional constraints are often upheld.
Preferably in an example, the at least one temperature sensor is provided at a first side of the at least one ring shaped magnet element and wherein the heat exchanging device is provided at a further, opposite side of the at least one ring shaped magnet element. Herewith an overall temperature assessment of the ring shaped magnet element is acquired, allowing for a more accurate temperature control and hence an improved long term stability of the magnetic field.
In yet another advantageous example of the disclosure, which provides a more compact construction with limited dimensions, the permanent magnet system comprises a further ring shaped magnet element spaced apart from the one ring shaped magnet element and concentric between both inner and outer yokes, with the heat exchanging device being provided between both ring shaped magnet elements and a temperature sensor each provided at the first sides of a ring shaped magnet element.
Preferably, the heat exchanging device is mounted against the inner yoke.
Additionally, a shielding sleeve can be provided coaxially around the permanent magnet system, thus avoiding any external influence or leakage of the magnetic field towards the environment.
In a further example, the disclosure also pertains to a charged particle beam apparatus comprising a charged particle generator for generating charged particles and for emitting the charged particles as a charged particles beam along a beam path towards a target location as well as at least one charged particle lens assembly for focusing the charged particle beam propagating along the beam path in a magnetic field according to the disclosure.
BRIEF DESCRIPTION OF THE DRAWINGS The invention will now be discussed with reference to the drawings, which show in: Figure 1 a first example of a charged particle lens assembly for focusing a charged particle beam according to the invention; Figure 2 a further example of a charged particle lens assembly for focusing a charged particle beam according to the invention;
DETAILED DESCRIPTION OF THE DRAWINGS For a proper understanding of the invention, in the detailed description below corresponding elements or parts of the invention will be denoted with identical reference numerals in the drawings.
It is known in several technical fields implementing a charged particle beam, such as in mass spectrometry applications or in charged particle beam optics, for example charged particle beam lithography applications, to implement focussing systems for moving (deflecting) or focusing a charged particle beam. For focusing a charged particle beam a strong magnetic field is needed in order to focus the beam of positively charged ions or negatively charged electrons on a microscopic point. Such electromagnetic fields are created by an electromagnetic lens, an electrostatic lens, etc., and the focussing and/or deflection is effected by controlling a (non-}symmetry in the electromagnetic field.
To generate a stable magnetic field, the common practise is to use electomagnets. Hereby the strength of the magnetic field is only dependent on the amount of coil windings and the electric current being applied through the coil. As such, any possible variation in the magnetic field can be compensated by changing the electric current.
The downside of focussing systems for charged particle beams, which equip electromagnets is its volume. Compared to permanent magnets, electromagnets take much more volume at similar magnetic field levels. The downside of using permanent magnets is the stability of the magnetic field. From permanent magnets it is known that the magnetic field changes with the operational temperature and will decrease over time as well, due to aging of the magnetic materials used.
In Figures 1 and 2 examples are shown of charged particle lens assemblies according to the disclosure, exhibiting limited constructional dimensions as well as a stable magnet field, as required to ensure beam quality and beam position.
In Figures 1 and 2, the two example of a charged particle lens assembly for focusing a charged particle beam propagating along a beam path in a magnetic field 5 according to the disclosure are denoted with reference numerals 10 and 100, respectively. Their construction is of a concentric nature as both example exhibit a symmetrical axis 10a and 100a, respectively. The symmetrical concentric axis 10a and 100a, respectively, for the beam path for a charged particle beam, which has been generated by generated using a charged particle emitter, such as an electron gun (not shown).
The charged particle beam can consist of positively charged particles, such as ions or protons, or negatively charged particles, such as electrons. In Figures 1 and 2 the charged particle beam is indicated as an electron beam using the reference e. In Figure 1 and 2, the charged particle beam e enters the charged particle lens assembly 10 (100) via the entrance side 10° (100%), passes through the magnetic systems of both charged particle lens assemblies 10 (100) and leaves via the entrance side 10” (1007), thereof.
Returning to Figure 1, the charged particle lens assembly 10 is composed of one magnet system indicated with 10-1, which is concentrically positioned around the beam path 10a and structured to generate a magnetic field for focusing the charged particle beam e'. In Figure 1 one magnet system 10-1 is implemented, whereas in the example of Figure 2 the charged particle lens assembly 100 uses two magnet systems 100-1 and 100-2, which are positioned spaced apart from each other along the beam path 100a.
The magnet systems 10-1 (100-1 and 100-2) are permanent magnet systems.
In Figure 1 the permanent magnet system 10-1 comprises an inner yoke 11b and an outer yoke 11a, which are arranged concentric with each other with respect to the concentric axis 10a. In addition, a ring shaped magnet element 12 is similarly arranged concentric between both inner and outer yokes 11b and 11a, respectively. Herewith a compact construction is achieved with minimal dimensions allowing implementation of such permanent magnet systems in mass spectrometry applications or in charged particle beam optics, such as charged particle beam lithography applications, where constructional constraints are often upheld. Both yokes 11a-11b are manufactured from a soft magnetic material. Any ferro-metal can be used as the magnetic material for th yokes 11a-11b, in particular steel, electric steel, nickel iron, cobalt iron.
The later material cobalt iron has a very high saturation level and therefore highly suitable.
In order to maintain the permanent magnet system 10-1 (100-1; 100-2) at a constant temperature to minimize thermal effects on the magnetic field thus generated, a temperature control system is implemented, which is in heat exchanging contact with the permanent magnet system 10-1 (100-1; 100-2). The temperature control system controls the operational temperature of the permanent magnet system 10-1 (100-1; 100-2) during focusing of the charged particle beam e propagating along the beam path 10a (100a). In both examples of Figures 1 and 2, the temperature control system comprises a heat exchanging device 14. Optionally, the temperature control system may also comprise at least one temperature sensor 13a.
The at least one temperature sensor 13a is structured for sensing the local temperature of the permanent magnet system 10-1 (100-1; 100-2), and to generate a signal representative for the temperature being sensed.
Said signal being representative for the temperature of the permanent magnet system being sensed is forwarded to the temperature control system, which in turn is structured to control the heat exchanging device 14 in responsive to the temperature being sensed, in particular in response to the signal being generated by the at least one temperature sensor 13a.
A temperature sensor is optional for a correct operation of the temperature control system, for example in case the materials of the several parts of both embodiments of the charged particle lens assemblies 10-100, and thus their temperature behavior is known.
In such example, the temperature control system implements a feedforward control, wherein the heating exchanging device 14 is controlled as function of exposure time of the permanent magnet system.
Thus with both temperature control systems outlined above, the short term as well as the long term stability of the magnetic field is maintained.
In the example of Figure 1, two temperature sensors 13a and 13b are implemented and each mounted at a first side 12’ of the ring shaped magnet element 12 arranged concentric between both inner and outer yokes 11b and 11a.
The first side 12° of the ring shaped magnet element 12 can be arbitrarily chosen, but in this embodiment the first side 12’ is located at the entrance side 10’ of the charged particle beam e entering the charged particle lens assembly 10. Similarly, the heat exchanging device 14 is provided at a further, opposite side 12” of the ring shaped magnet element 12, close to the exit side 10” of the charged particle lens assembly 10. Herewith an overall temperature assessment of the ring shaped magnet element 12 is acquired, allowing for a more accurate temperature control and hence an improved long term stability of the magnetic field.
As shown in Figure 1, the heat exchanging device 14 is in direct heat exchanging contact with the ring shaped magnet element 12. Alternatively, the heat exchanging device 14 can also be in direct heat exchanging contact with the inner yoke 11b and/or the outer yoke 11a.
In particular, the heat exchanging device 14 may comprise a thermal cooling sink being in heat exchanging contact with the permanent magnet system 10-1, in particular with the ring shaped magnet element 12 and/or the inner yoke 11b and/or the outer yoke 11a, thus guaranteeing a beneficial heat exchange with the permanent magnet system.
In another example, the heat exchanging device 14 may comprise a thermal heating sink being in heat exchanging contact with the permanent magnet system 10-1, in particular with the ring shaped magnet element 12 and/or the inner yoke 11b and/or the outer yoke 11a, thus guaranteeing a beneficial heat exchange with the permanent magnet, thus allowing proper temperature control of the permanent magnet system.
As stipulated above, two temperature sensors 13a and 13b generate signals being representative for the local temperature of the ring-shaped permanent magnet element 12 being sensed, which signals are used by the temperature control system to control the heat exchanging device 14 (either a thermal cooling sink and/or a thermal heating sink), based on said signals, such that the temperature of the permanent magnet system 10-1 (the ring-shaped magnet element 12) conforms to a pre-set temperature level. By maintaining the permanent magnet 12 at a pre-set desired operational temperature, a long term stability of the magnetic field is achieved.
In the example of the disclosure of Figure 2, the charged particle lens assembly 100 implements two magnet systems 100-1 and 100-2, which are positioned spaced apart from each other along the beam path 100a. The two magnet systems 100-1 and 100-2 both use — similar as in Figure 1 - the concentric configuration of an inner yoke 11b and an outer yoke 11a arranged around the concentric axis 100a. Both yokes 11a- 11b are manufactured from a soft magnetic material, similar as outlined with respect to the embodiment of Figure 1.
Here, however, next to the first ring shaped magnet element 12a placed concentric between both inner and outer yokes 11b and 11a, respectively, a further ring shaped magnet element 12b spaced apart from the first ring shaped magnet element 12a is implemented. Also the further ring shaped magnet element 12b is mounted concentric between both inner and outer yokes.
Similarly as in Figure 1, each ring shaped magnet element 12a-12b is provided with a first side 12’ and a second, opposite side 12”. In Figure 2, the first sides 12’ of each ring shaped magnet element 12a and 12b, respectively, are located closed to either entrance side 100" and exit side 100” of the beam path 100a and the second, opposite sides 12” of the ring shaped magnet elements 12a and 12b are facing each other, albeit at some distance from each other.
For each of the ring shaped magnet elements 12a and 12b at least one, but preferably two temperature sensors 13a-13b and 13c-13d are provided at each first side 12° of a corresponding ring shaped magnet element 12a-12b. Hence, the temperature sensors 13a-13b and 13c-13d are positioned to either entrance side 100’ and exit side 100” of the beam path 100a. The heat exchanging device 14 is provided between the space 16 formed between both ring shaped magnet elements 12a-12b. With only one heating device 14 mounted between the ring shaped magnet elements 12a-12b a further more compact construction is achieved.
Preferably, the heat exchanging device 14 is mounted in heat exchanging contact against the inner yoke 11b, but alternatively the heat exchanging device 14 is in heat exchanging contact with either second, opposite sides 12” of the ring shaped magnet elements 12a and 12b are facing each other. A more compact construction with limited dimensions is obtained, allowing the magnet elements 12a-12b to be positioned closer to each other.
Also in this example, the heat exchanging device 14 may comprise a thermal cooling sink being in heat exchanging contact with the two permanent magnet systems 100-1 and 100-2, in particular with the inner yoke 11b and/or both the ring shaped magnet elements 12a-12b. Alternatively, it may be in heat exchanging contact with the outer yoke 11a as well.
In another example, the heat exchanging device 14 in Figure 2 may comprise a thermal heating sink being in heat exchanging contact with the two permanent magnet systems 100-1 and 100-2, in particular with the inner yoke 11b and/or both the ring shaped magnet elements 12a-12b. Alternatively, it may be in heat exchanging contact with the outer yoke 11a as well. In both examples, a proper temperature control of the permanent magnet systems 100-1 and 100-2 is achieved.
Similarly as above, the temperature sensors 13a-13b and 13c-13d generate signals being representative for the local temperature of the ring-shaped permanent magnet elements 12a and 12b, respectively. These signals are used by the temperature control system to control the heat exchanging device 14 (either a thermal cooling sink and/or a thermal heating sink), based on said signals, such that the temperature of the permanent magnet systems 100-1 and 100-2 (the ring-shaped magnet elements 12a-12b) conforms to a pre-set temperature level. By maintaining the permanent magnets 12a-12b at a pre-set desired operational temperature, a long term stability of the magnetic field is achieved.
In both examples of Figures 1 and 2, by maintaining the permanent magnets 12a-12b at a pre-set desired operational temperature, a long term stability of the magnetic field is achieved, thus guaranteeing desired, stable beam characteristics of the charged particle beam, such as kinetic energy, direction and focus.
Additionally, in both examples, a shielding sleeve 15 can be provided coaxially around the permanent magnet system, thus avoiding any external influence or leakage of the magnetic field towards the environment. The sleeve 15 may not be in contact with the outer yokes 11a, thus avoiding any magnetic shortening, which would hamper the operational functionality of the charged particle lens assembly 10-100.
With both examples shown in Figure 1 and Figure 2, the magnetic field generated by the permeant magnet systems 10-1 (100-1; 100-2) can be fine tuned, by changing the temperature of the permanent magnet 12 (12a-12b) using the heat exchanging devices 14.
It is noted, that the absolute temperature of the permanent magnets 12 (12a-12b) is not critical except for the magnetic field generated by the permanent magnet. So by changing the set point of the temperature control system, the absolute temperature can be changed and thus also the magnetic field can be changed and tuned. With these examples, the adjustment range of the magnetic field strength is larger than when using only electrostatic lenses. This allows for a relaxation of the tolerance budget of the permanent magnet and thus a cost reduction for the complete set up.
Furthermore, magnets made of a magnetic material having a low temperature coefficient are rare and thus more difficult to find. Likewise, magnet systems implementing such magnets of rare magnetic materials are more expensive and prone to failure and standstill, as the supply chain of such rare magnetic materials is more risky.
In addition, both examples of the disclosure exploit the temperature dependence of the permanent magnet for controlling and focussing a charged particle beam, which obviated the need for high end low thermal coefficient permanent magnet grades.
Claims (11)
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| NL2027307A NL2027307B1 (en) | 2021-01-13 | 2021-01-13 | A charged particle lens assembly and a charged particle beam apparatus provided with such charged particle lens assembly. |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| NL2027307A NL2027307B1 (en) | 2021-01-13 | 2021-01-13 | A charged particle lens assembly and a charged particle beam apparatus provided with such charged particle lens assembly. |
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| Publication Number | Publication Date |
|---|---|
| NL2027307B1 true NL2027307B1 (en) | 2022-07-25 |
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| NL2027307A NL2027307B1 (en) | 2021-01-13 | 2021-01-13 | A charged particle lens assembly and a charged particle beam apparatus provided with such charged particle lens assembly. |
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Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP4318542A3 (en) * | 2022-07-15 | 2024-04-10 | IMS Nanofabrication GmbH | Adjustable permanent magnetic lens having thermal control device |
Citations (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS60221933A (en) * | 1985-03-27 | 1985-11-06 | Hitachi Ltd | Braun tube |
| GB2341448A (en) * | 1998-09-11 | 2000-03-15 | Oxford Magnet Tech | Temperature dependent magnetic field control system |
| US20130134322A1 (en) * | 2010-10-27 | 2013-05-30 | Param Corporation | Electron lens and the electron beam device |
-
2021
- 2021-01-13 NL NL2027307A patent/NL2027307B1/en active
Patent Citations (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS60221933A (en) * | 1985-03-27 | 1985-11-06 | Hitachi Ltd | Braun tube |
| GB2341448A (en) * | 1998-09-11 | 2000-03-15 | Oxford Magnet Tech | Temperature dependent magnetic field control system |
| US20130134322A1 (en) * | 2010-10-27 | 2013-05-30 | Param Corporation | Electron lens and the electron beam device |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP4318542A3 (en) * | 2022-07-15 | 2024-04-10 | IMS Nanofabrication GmbH | Adjustable permanent magnetic lens having thermal control device |
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