EP3510622A1

EP3510622A1 - Nap immersion lens

Info

Publication number: EP3510622A1
Application number: EP17755507.5A
Authority: EP
Inventors: Martin Breitschaft; Martin Johansson; Dietmar Funnemann; Kai Kunze; Sebastian Hagen; Oliver Schaff; Thorsten Kampen; Andreas Thissen
Original assignee: SPECS Surface Nano Analysis GmbH
Current assignee: SPECS Surface Nano Analysis GmbH
Priority date: 2016-09-07
Filing date: 2017-08-22
Publication date: 2019-07-17
Also published as: WO2018046293A1; DE102016116765B3

Abstract

A device for examining a non-gaseous sample interacting with gases in an electron- and/or ion-optical system is provided, wherein the sample is arranged in a sample chamber and the sample chamber furthermore has a diaphragm having a hole-like aperture, and wherein a potential can respectively be applied to the sample and the diaphragm, as a result of which an electric field forms between the sample and the diaphragm, such that the sample and the diaphragm together form an electrostatic immersion lens, and the electrical potentials are selectable in such a way that discharges and/or electron and/or ion scattering are/is counteracted.

Description

NAP-immersion lens

The invention relates to a device of an electron-optical system for examining a gas-interacting non-gaseous sample. Electric and magnetic fields act on charged particles much like optical media on a light beam. In electron-optical systems the charged particles are electrons, in ion-optical systems the charged particles are ions. Electron and ion optical systems are suitable for electrons or ions. This invention relates equally to electron and ion optical systems, although for simplicity in some instances only the term of an electron optical device or an electron optical system is used herein. The term of a particle-optical device or a particle-optical system can also be used. The charged particles, also referred to as charged particles, may accordingly be electrons or ions.

For examining a non-gaseous sample in an electron and / or ion-optical system, devices are known which have a sample chamber for arranging the sample in a gaseous environment (DE 38 78 838 T2, US 2008/0 035 861 A1, US 2009/0 230 304 A1, WO 2009/043 317 A1). The prior art devices are designed to scan a sample and image based thereon, but have no immediate optical function.

It is an object of the present invention to provide an advantageous arrangement for inspecting a non-gaseous sample in a gaseous environment. It is a further object of the present invention to provide a beneficial electron or ion optical method of inspecting a non-gaseous sample.

The first object is achieved by means of an electron and / or ion-optical device having the features of claim 1, the second object by a method having the features of claim 12. Further advantageous Embodiments and embodiments of the invention will become apparent from the dependent claims and subclaims, the figures and the embodiments.

A first aspect of the invention relates to a device for examining a non-gaseous sample in an electron and / or ion-optical system, the device comprising a sample chamber, which is designed to arrange the sample in a gaseous environment, the sample chamber having at least one first orifice comprising a hole-like opening in the region of the sample to be arranged, and to which a controllable sample potential V1 and to the first diaphragm a controllable diaphragm potential V2 can be applied so that a controllable electric field between the sample surface and diaphragm is mediated, and wherein the Device has an electron and / or ion-optical lens effect. The device is particularly characterized in that the electrical potentials are selectable such that discharges and / or electron and / or ion scattering is counteracted.

The first diaphragm is referred to below as the diaphragm. It is clear that the aperture is meant to be the first aperture, unless it is explicitly mentioned as a second or further aperture. The device according to the invention is advantageous because the diaphragm and the sample form an electrostatic immersion lens by the formation of the electric field. This immersion lens causes an electron-optical effect, and by the selectability of the voltage applied to diaphragm and sample voltage can advantageously counteract gas discharges and / or particle scattering and particle-optical properties can be used. The voltage can be adjusted with the device according to the invention so that sets a desired lens effect. In other words, with the device according to the invention, if appropriate in cooperation with further particle-optical components, an image can be generated, and a particle beam can be controlled or focused by adjusting the voltage such that a desired image effect occurs. In addition, works the image formation by the device even without external electron source, eg via electrons released by photoemission.

Furthermore, the invention is advantageous because the aperture, in combination with the formation of the electrostatic immersion lens, limits leakage of gas from the sample chamber to other parts of the system. Under gaseous environment in the sample chamber is to be understood that in the sample chamber, a gas is contained, with which the sample can interact, and there is no vacuum. The gas in the device preferably has approximately ambient pressure (near ambient pressure, NAP), that is, starting from the ultrahigh vacuum, a pressure that is orders of magnitude higher than ultra-high vacuum pressures.

Furthermore, the limitation of the gas flow from the device together with existing in the system vacuum pump advantageously causes a reduction of the gas pressure in other parts of the system, which, for example, advantageously a reduction of electron or ion scattering is achieved and / or discharges are avoided. The aperture can therefore also be referred to as a differential pumping stage. The invention thus makes it particularly advantageous to examine a sample under approximate ambient pressure using an electrostatic lens. It has surprisingly been found that an optical imaging without gas discharges is possible. The electrons in the sample chamber are accelerated in accordance with the potential difference between orifice and sample, whereby they only have to cover a limited distance in the gas at working pressure. The potential difference between aperture and sample is chosen to be sufficiently small, so that discharges are avoided. Outside the sample chamber, where due to the gas flow limitation through the aperture in cooperation with vacuum pumps, a significantly lower gas pressure prevails than within the sample chamber, the electrons can then be nachbeschleunigt with significantly higher voltage without causing discharges. In this case, an electric field which can be controlled via the potentials V1 and V2 can also prevail between the first diaphragm and further diaphragms outside the sample chamber, for example arranged between the diaphragm of the device and one of the diaphragms adjacent Objective lens of an electron and / or ion-optical system in which the device is integrated. This field is also relevant for the lens effect.

Preferably, the aperture of the aperture is formed such as to allow charged particles to pass from a means for generating a particle beam through the aperture to the sample surface and to direct charged particles from the sample surface to an area outside the sample chamber. In other words, the hole-like opening has a size and shape such that charged particles can be conducted to the sample and from the sample. Furthermore, the hole-like opening is preferably designed such that electrically neutral particles and / or light can be conducted from an area outside the sample chamber to the sample surface and / or from the sample surface into a region outside the sample chamber. In other words, the hole-like opening has a size and shape such that electrically neutral particles and / or light can be conducted to the sample and from the sample. The hole-like opening can furthermore advantageously be designed such that both charged and electrically neutral particles as well as light can be passed to the sample and from the sample. The potentials V1 and V2 have a significant influence on the particle-optical properties of the device according to the invention. The aperture and its hole-like opening are preferably designed such that the potentials V1 and V2 result in a particle-optically favorable field distribution. Furthermore, the sample chamber is preferably designed so that in addition to the aperture in other areas of the sample chamber at least a second opening with a visual access to the sample surface is present, can be passed through the light and / or particles to the sample surface. In other words, the second opening provides further access to the sample, through which the sample can be irradiated with particles and / or light. The second opening may be present both in the panel itself, but especially in a wall of the sample chamber. This allows light and / or particles to be conducted past the diaphragm to the sample. Thus, the sample surface can be more favorably irradiated from different angles with light and / or particles. A trained for light irradiation opening may be closed with a translucent disk. An aperture formed for particle irradiation may be closable with a flap, with the flap open providing visual access and access for particles to the sample, and closure of the flap limits gas flow through the aperture. In a preferred embodiment, the diaphragm is at least partially conical or cone-shaped. In other words, the diaphragm preferably has at least one region in which it is of conical or conical-like design. This design is advantageous because it favors lateral visual access to the sample in that the sample is not obscured by the aperture in a side view access. Cone-like here means that the diaphragm may have a modified form of a cone, for example, a curved shape. The design of the aperture also has effects on the electric field. Furthermore, the at least partially conical design of the diaphragm advantageously makes it possible to adjust the angle of inclination of the sample relative to the diaphragm while maintaining a sufficient distance between the diaphragm and the sample or sample holder, without the diaphragm and sample or sample holder approaching too closely or touch, which could lead to unwanted field overshoots, electrical short circuits or mechanical damage, for example. In addition to the conical or cone-like areas, the diaphragm may also have one or more areas in which it is not conical or cone-shaped, such as the immediate, with respect to the entire aperture close environment of the hole-like opening, or provided for the attachment of the panel areas.

Furthermore, it is preferred that in the device according to the invention, the electric field between diaphragm and sample surface can be superimposed with a magnetic field. In a further advantageous embodiment, the device according to the invention additionally comprises at least one second diaphragm. In a further embodiment of the device according to the invention, more than two diaphragms can also be arranged one behind the other in the device.

A second aspect of the invention relates to an electron and / or ion-optical system with a device according to the invention.

The system according to the invention preferably has additional electron-optical components in addition to the device according to the invention.

The system according to the invention is preferably a spectrometer. It is also preferred if the system according to the invention is an electron microscope.

A third aspect of the invention relates to a method for examining a non-gaseous sample in a system comprising a device according to the invention, comprising the steps of:

Placing a sample in the sample chamber,

Fill the sample chamber with a gas until the gas pressure

Ambient pressure is approximated

Applying a potential V1 to the sample

Applying a potential V2 to the first diaphragm

Selecting the potentials V1 and V2 such that discharges and / or electron and / or ion scattering is counteracted

Analyze charged particles released by the

Sample surface are emitted.

The advantages of the method according to the invention correspond to the advantages of the system according to the invention. The method is used especially for Examine a non-gaseous sample in a gaseous environment. In other words, the method is directed to examining a liquid or solid sample which interacts with gases.

Preferably, in an additional step of the method according to the invention, the sample surface is irradiated with charged particles and / or light. In this case, this step is optional because the method according to the invention also works without irradiation. In particular, it works independently of the source mechanism and origin of the imaged charged particles. Examples are electron imaging from an external source which irradiates the sample and which is imaged after interaction with the sample, and electron imaging which is released by photoemission from the sample, the latter usually with an excitation light source is irradiated. Alternatively or additionally, the sample is preferably heated in an additional step. This advantageously, for example, cleans the sample which reaches the temperature necessary for certain surface processes (e.g., film growth or catalysis), or excites electrons of the sample to thermal emission (annealing emission), which can then be imaged.

The invention will be explained in more detail with reference to FIGS. Show it

Figure 1 is a schematic representation of an embodiment of the device according to the invention.

FIG. 2 shows a schematic representation of the device according to FIG. 1. Figure 3 is a schematic representation of the apparatus of FIG. 1 and

Second

4 shows a system with a device according to one of FIGS. 1-3.

FIG. 5 is a flow chart of one embodiment of the invention

inventive method. In an embodiment according to FIG. 1, a device 1 of an electron and / or ion-optical system has a sample chamber 2, in which a sample 3 is arranged. It is clear that in the sample chamber 2, a device for storing the sample 3, possibly also rotatable, is present. Sample 3 is non-gaseous and may be solid or liquid. The sample has a sample surface 3a. The sample chamber is filled with a gas 4, so that the sample 3 can interact with the gas 4. The gas 4 can be any gas, for example air, water vapor, oxygen, hydrogen, nitrogen, methanol or ammonia, without being limited to this list. The gas 4 in the sample chamber 2 has preferably approximately ambient pressure (near ambient pressure, NAP), so the ultra high vacuum, starting a (compared to ultra-high vacuum pressures are orders of magnitude higher pressure, for example, 0.1 mbar in comparison with, for example, 10 ^"7 mbar ).

The sample chamber 2 has a first diaphragm 5 (hereinafter referred to as diaphragm 5). The orifice 5 is designed to limit the volume of the sample chamber 2 so that the gas 4 can, to a limited extent, escape from the sample chamber 2, as represented by the gas flow 4a. The diaphragm 5 has a hole-like opening 6 in a central region. The aperture 5 is formed substantially conically according to the embodiment shown in Fig. 1. In the area of the hole-like opening 6, it can also be different, e.g. plan, be educated.

Through the hole-like opening 6, particles and / or light, especially charged particles, such as electrons or ions, can pass into the sample chamber 2 to the sample 3 and from the sample 3 out of the sample chamber 2 (shown in FIG. 1 by the bidirectional arrow 7). , FIG. 2 shows with an exemplary trajectory how the sample 3 is irradiated with charged particles (lane 7a) and charged particles are emitted from the sample (lane 7b). In other words, particles pass from an external particle source (not shown) from outside the sample chamber 2 to the sample 3 (lane 7a) and corresponding particles emitted from the sample 3 from the sample Sample surface 3a from the sample chamber 2 addition to an analysis device (not shown), such as an analyzer of a spectrometer or an electron microscope. By means of the invention it is possible to process charged particles coming from the direction of the sample independently of their origin. For example, charged particles may be generated by field emission, thermal emission, photoemission, or atomization of the sample, or may be from the external particle source outside the sample chamber. Thus, the particle source is an optional component.

As shown in FIG. 1, a sample potential V1 can be applied to the sample 3 and an iris potential V2 can be applied to the diaphragm 5. When applying the potentials V1, V2, an electric field 8 is formed between the sample surface 3a and the diaphragm 5, a so-called extraction field 8. In this way, the sample 3 and the diaphragm 5 together form an electrostatic immersion lens. In this case, one of the two potentials V1, V2 can also be zero, i. 0V amount.

In an embodiment in which the device 1 has an additional diaphragm in addition to the first diaphragm 5, potentials can be applied to both diaphragms. The aperture potentials of the two diaphragms can be the same here, or alternatively also different from one another. It is also possible that one potential is applied to one diaphragm and not to the others. The second aperture can also be used for differential pumping. In a further embodiment, in which the device 1 has more than two diaphragms, it is possible to apply equal potentials to the individual diaphragms, or else different potentials or else no potentials.

In Fig. 3, the device 1 according to the invention is shown with further technical details. Shown is the sample chamber 2, in which the sample 3 is arranged. Furthermore, the aperture 5 is shown with the hole-like opening 6. Shown are also a fixed part of the device 1 1, a sample 3 with the movable part of the device 12, a window 13 for a visual access to the sample 3, for example for a Excitation light source, an insulator 14, a sample holder with seal 15 and a bellows 16th

The window 13 is closed in the illustration of Fig. 3 with a disc through which light can be passed to the sample surface. Alternatively, the window can also be closed with a flap so that particles can be conducted to the sample surface when the flap is open and gas flow through the opening is limited when the flap is closed. The window 13 or a similarly arranged optionally closable opening is thus a second opening of the sample chamber 2 provided in addition to the aperture 6, through which light and / or particles can be conducted to the sample surface. The window 13 is arranged in the wall of the sample chamber 2 in FIG. 3. It could also be arranged in eg in the aperture 5. Also, more than one additional opening of the sample chamber 2 could be present. In Fig. 4, a system 20 according to the invention is exemplified as a low energy electron microscope (LEEM) on which the device 1 is mounted. The LEEM / PEEM is an electron microscope and also an electron spectrometer. The illustrated LEEM / PEEM 20 comprises an electron source for producing a collimated and directed electron beam (also referred to as an electron gun) consisting of the electron emitter 21, the lens of the electron gun 22, the stigmator of the electron gun 23, a condenser lens disposed in the path of the electron beam 24, the first 25a and second deflector of the electron gun 25b. In the beam path from the electron emitter 21 to the sample 3, a prism 26 having a microdiffraction diaphragm 27, an entrance slit 28, a transfer lens 29, a lens stigmator 30 and an objective lens 31 are further arranged. The LEEM 20 further comprises a selection aperture 32 arranged in the region of the prism 26, a prism deflector 33, a contrast aperture 34, a first 35a and second projector reflector 35b, a group of projector lenses 36 with the lenses P1, P2, P3, P4A and P4B, and a detector 37 on, but without the named components to be limited or to include all named components.

In an embodiment of the method according to the representation of FIG. 5, in a first step S1 the sample 3 is arranged in the sample chamber 2 on a device provided for this purpose. In a second step S2, the sample chamber 2 is filled with a gas. In a third step, a potential V1 is applied to the sample 3, and in a fourth step to the diaphragm 5, a potential V2. The steps S3 and S4 can also be executed at the same time. In a fifth step S5, the potentials V1 and V2 are selected such that discharges and / or electron and / or ion scattering are counteracted. In a further, optional step, the sample surface 3a is filled with electrons or, alternatively, with other charged particles, e.g. Ions, and / or light irradiated. Alternatively or additionally, the sample is heated. From the sample surface 3a, electrons or ions emitted from the device 1 are emitted into an analyzer, e.g. an analyzer of a spectrometer or an electron microscope, are steered and analyzed there in a sixth step S6.

Alternatively, the sequence of steps in other embodiments of the method may also be different. For example, potentials may also first be applied to the sample 3 and the orifice 5, and then gas may be introduced into the sample chamber, so that the aforementioned steps S3 and S4 are performed before step S2. Further, the sample surface 3a may be irradiated with electrons or light while filling gas in the sample chamber. Furthermore, the potentials V1 and V2 can be switched on and / or off while the sample surface 3a is irradiated with electrons or light. It is also possible to operate the sample chamber without introduced gas. LIST OF REFERENCE NUMBERS

1 device

2 sample chamber

3 sample

3a sample surface

4 gas

4a gas flow

5 first aperture

6 opening of the first panel

7 arrow for the indication of charged particles

7a Path of charged particles into the sample chamber

7b Path of charged particles from the sample chamber

8 extraction field

1 1 fixed part of the device

12 moving part of the device

13 windows for light and visual access to the sample

14 insulator

15 sample holder with seal

16 bellows

20 electron or ion optical system

21 electron emitter

22 Lens of the electron gun

23 Stigmator of the electron gun

24 condenser lens

25a first deflector of the electron gun

25b second deflector of the electron gun

26 prism

27 microdiffraction aperture

28 entrance slit

29 transfer lens

30 lens stigmator

31 objective lens

32 selection aperture 33 prism deflector

34 contrast aperture

35a first projector reflector

35b second projector reflector

36 projector lens system P1 projector lens

P2 projector lens

P3 projector lens

P4A projector lens

P4B projector lens

37 detector

Claims

claims

1 . Apparatus (1) for inspecting a non-gaseous sample (3) in an electron and / or ion-optical system (20), the apparatus (1) comprising a sample chamber (2) arranged to place the sample (3) in gaseous form The sample chamber (2) comprises at least one first diaphragm (5) which has a hole-like opening (6) in the region of the sample (3) to be arranged, and wherein a controllable sample potential is applied to the sample (3) V1 and to the first diaphragm (5) a controllable diaphragm potential V2 can be applied so that a controllable electric field between the sample surface (3a) and the first diaphragm (5) is mediated and the device (1) has an electron and / or ion-optical lens effect , characterized in that the electrical potentials are selectable such that discharges and / or electron and / or ion scattering is counteracted.

2. Device (1) according to claim 1, wherein the hole-like opening of the diaphragm (6) is designed such that a guided charge of charged particles from a device for generating a particle beam through the opening (6) to the sample surface (3 a) and Passing charged particles from the sample surface (3a) into an area outside the sample chamber (2) is possible.

3. Device (1) according to claim 1 or 2, wherein the hole-like opening of the diaphragm (6) is designed such that a guiding of neutral particles and / or light from an area outside the sample chamber (2) to the sample surface (3a). and / or is possible (6) from the sample surface (3a) into an area outside the sample chamber (2) through the opening.

4. Device (1) according to one of the preceding claims, wherein in addition to the aperture (6) in other areas of the sample chamber (2) at least a second opening with a visual access to the sample surface (3 a) is present, can be passed through the light and / or particles to the sample surface (3a).

5. Device (1) according to one of the preceding claims, wherein the first diaphragm (5) is at least partially conical or cone-shaped.

6. Device (1) according to one of the preceding claims, wherein the electric field (8) between the first diaphragm (5) and the sample surface (3a) can be superimposed with a magnetic field.

7. Device (1) according to one of the preceding claims, which additionally comprises at least one second diaphragm.

8. electron and / or ion optical system (20) with a device according to one of claims 1-7.

9. System (20) according to claim 8, which additionally comprises further electron-optical components.

A system (20) according to any one of claims 8 or 9, which is a spectrometer.

1 1. A system (20) according to any one of claims 8 or 9, which is an electron microscope.

A method of inspecting a non-gaseous sample in a gaseous environment in a system comprising a device according to any one of claims 1-7, comprising the steps of:

Arranging a sample (3) in the sample chamber (2),

- filling the sample chamber (2) with a gas (4) until the gas pressure is approaching the ambient pressure,

Applying a potential V1 to the sample (3),

Applying a potential V2 to the first diaphragm (5),

Selecting the potentials V1 and V2 such that discharges and / or electron and / or ion scattering are counteracted, - Analyzing charged particles emitted from the sample surface (3a).

13. The method according to claim 12, wherein in an additional step, the sample surface is irradiated with charged particles and / or light.

14. The method of claim 12 or 13, wherein in an additional step, the sample is heated.