DE1807290C

DE1807290C - Electron or ion microscope with an image intensifier for the final image

Info

Publication number: DE1807290C
Authority: DE
Inventors: Ekkehard Dr 8012 Ottobrunn Engel Fritz 8011 Poing Fuchs
Original assignee: Siemens AG
Current assignee: Siemens AG

Description

i 807 290 -i 807 290 -

Die Erfindung betrifft ein Elektronen- oder Ionenmikroskop mit einer Endbildebene und einem Bildverstärker für das Endbild. Es sei an dieser Stelle eingefügt, daß unter einem Bildverstärker auch eine Anordnung zu verstehen ist, die eine Verstärkung eines Beugungsbildes eines Präparates, d.h. nicht nur des üblichen Durchstrahlungsbildes, vornimmt.The invention relates to an electron or ion microscope with a final image plane and an image intensifier for the final image. It should be added at this point that under an image intensifier there is also a Arrangement is to be understood that intensifies a diffraction image of a specimen, i.e. not only the usual radiographic image.

Bekanntlich ist das hochvergrößerte Endbild in Elektronenmikroskopen, das auf dem Endbildleuchtschirm unterhalb der Projektivlinse entworfen wird, so lichtschwach, daß eine Scharfstellung der Linsen des Mikroskops und die Korrektur von Abbildungsfehlern, insbesondere des Astigmatismus, durch visuelle Beobachtung ebenso wie die Betrachtung von Präparateinzelheiten außerordentlich schwierig und nur ungenau möglich ist. Die Strahlstromdichte des abbildenden Strahles läßt sich in aller Regel ohne Gefährdung des zu untersuchenden Präparates nicht ίο weit erhöhen, daß diese Schwierigkeit vermieden ist.As is well known, the highly magnified final image in electron microscopes is that on the final luminescent screen is designed below the projective lens, so faint that the lens can be focused of the microscope and the correction of aberrations, especially astigmatism, by visual Observation as well as consideration of specimen details is extremely difficult and is only possible imprecisely. The beam current density of the imaging beam can usually be without Do not increase the risk of the preparation to be examined ίο far that this difficulty is avoided is.

Die Auswertung des fotografierten Endbildes (Langzeitbelich«ung) ist insbesondere im Rahmen der Scharfstellung und der Korrektur von Abbildungsfehlern im Hinblick auf den großen Zeitaufwand nur ein Notbehelf.The evaluation of the final photographed image (long-term exposure) is particularly important within the framework of the Focusing and the correction of aberrations in view of the large amount of time only a stopgap.

Aus diesem und anderen Gründen (Vergrößerung der möglichen Zahl der Beobachter) hat man, wie beispielsweise aus der niederländischen Patentanmeldung 6 704 611 h 'vorgeht, an das eigentliche Elektronenmikroskop über Fiberplatten bereits einen Bildverstärker und eine nachgesclu'.^te Fernsehlamera angeschlossen, so daß das ^ndbild verstärkt auf einem Fernsehempfänger betracntet werden kann. Dabei erfolgt eine mehrfache Umwandlung des Bildes, nämlich zunächst im Endbildleuchtschirm eine Umwandlung der Elektronenstrahldichteverteilung in lichtbares Licht, das durch eine erste Fiberplattenanordnung beispielsweise auf eine Fotokathode geleitet wird, die die Eingangselektrode des Bildveritärkers bildet und eine zweite Umsetzung, diesmal von sichtbarer Strahlung in Elektronenstrahlung, bewirkt; diese Elektronenstrahlung wird mittels einer Schicht auf der Ausgangsfläche des Veistärkers wiederum in Licht umgesetzt, das durch eine zweite Fibcrplattenanordnung zur Eingangselektrode der Fernsehkamera gelangt. Auf diese Weise ist es in der TnI möglich, auch von empfindlichen Präparaten Bilder solcher Intensität zu erhalten, daß eine sofortige I3ildauswertung möglich ist.For this and other reasons (increasing the number of observers possible) one has how for example from the Dutch patent application 6 704 611 h 'proceeds to the actual electron microscope already an image intensifier and a downstream television camera via fiber plates connected so that the ^ ndbild can be observed more intensely on a television receiver. A multiple conversion of the image takes place, namely initially one in the final luminescent screen Conversion of the electron beam density distribution into light which can be emitted by a first fiber plate arrangement for example, is passed to a photocathode, which is the input electrode of the image verifier forms and causes a second conversion, this time from visible radiation to electron beams; this electron radiation is in turn by means of a layer on the output surface of the amplifier converted into light, which through a second fiber plate arrangement to the input electrode of the TV camera arrives. In this way it is possible in the TnI to also take pictures of sensitive specimens of such intensity that an immediate image evaluation is possible.

Der Erfindung liegt die Aufgabe zugrunde, das F.ndbild so zu verstärken, daß ohne mehrfache Umict/ung eines elektronischen in ein sichtbares Bild eine sofortige Bildauswertung /um Zwecke der Scharfstellung, der Bildfehlerkorrektur und der Br-ΙπκΙιΙιιιιμ von Präparatemzelhcitcn möglich ist.The invention is based on the object of strengthening the image in such a way that without repeated changes an electronic in a visible image an immediate image evaluation / for purposes of Focusing, the aberration correction and the Br-ΙπκΙιΙιιιιμ of preparation cells is possible.

/tir I oNiing dieser Aufgabe ist das Elektronen oder Ionenmikroskop dadurch gekennzeichnet, dall das Mikroskop mit einer !ils Bildverstärker dienen' den Elüklronenverviclfachungskanalpliitte unter Verzicht iiuf einen in Strnlilrichtung vor dieser liegenden Liulhildlcuchlschirm ausgerüstet ist, die quer zur Mikroskopachsc mit ihrer Strahlcintriltsfliiehc in der Ijulbiklubene liegend angeordnet ist. und daß in Stnihlriclitung hinter der F-Icktroncnvurviclfachungskiituilplalte eine Speicheranordnung für das verstärkte Kndbild vorgesehen ist./ tir I oNiing this task is the electrons or ion microscope, characterized in that the microscope is used with an image intensifier ' the Elüklronenviclfachungskanalpliitte with waiver On one lying in front of it in the direction of the flow Liulhildlcuchlschirm is equipped, which transversely to the microscope axis with its Strahlcintriltsfliiehc in the Ijulbiklubene is arranged lying down. and that in Directional line behind the transverse curvature of the compartment a memory arrangement is provided for the enhanced character image.

Während ulso bei dem beschriebenen bekannten r.lcktoneiitnikroskop unter Verwendung eines üblichen Endbildleuchtschirmes im Mikroskop eine mehrfache Umsetzung von einem Elektronenbild in ein Bild sichtbarer Strahlung vorgenommen wurde und hierbei ein Bildverstärker Verwendung f^nd, der ein abgeschlossenes Bauelement bildet, erfolgt bei der Erfindung eine direkte Verstärkung des durch die Stromdichteverteilung im Elektronenstrahl in der Endbildebene gegebenen Endbildes ohm mittels eines Bildschirmes vor dem Bildverstärker vorge-While ulso known in the case of the described r.lcktoneiitnikoskop using a conventional End screen in the microscope one multiple conversion of an electron image into an image of visible radiation has been carried out and here an image intensifier use f ^ nd, the forms a closed component, there is a direct reinforcement of the by the invention Current density distribution in the electron beam in the end image plane given end image ohm means a screen in front of the image intensifier

iQ nornmene Zwischenumwandlung und ohne Verwendung eines ein selbständiges Bauelement darstellenden Verstärkers. Daher ist es möglich, daß die Elektronenvervielfachungskanalplatte einen Teil des Vakuumgehäuses des Mikroskops bildet und ihre Aus-iQ nornmene intermediate conversion and without use an amplifier which is a stand-alone component. Therefore, it is possible that the electron multiplication channel plate forms part of the vacuum housing of the microscope and its design

trittsfläche luftdicht abgeschlossen ist. Damit wird der Bildverstärker konstruktiv nicht anders behandelt als eine übliche Fiberpiatte (ohne Verjtärkerwirkung) gemäß der Anordnung nach der britischen Patentschrift 841200.the step surface is hermetically sealed. So that will the image intensifier is structurally not treated differently than a normal fiber plate (without intensifying effect) according to the arrangement of British Patent 841200.

ao Die direkte Verstärkung der Stromdichteverteilung in der Endbildebene bietet ferner die Möglichkeit, die Stromdichte in jedem Punkt des Endbildes zu messen, ohne — wie bisher — hierfür einen Faraday-Käfig zusätzlich verwenden zu müssen.ao The direct amplification of the current density distribution in the final image plane also offers the possibility of increasing the current density in each point of the final image measure without - as before - additionally having to use a Faraday cage.

Die Erfindung läßt sich jedoch auch in der Weise ausbilden, daß die Multiplierkanalplatte von dem Vakuumgehäuse des Mikroskops aufgenommen ist. Verwendet man als Speicheranordnung eine solche, die das verstärkte Endbild als Ladungsverteilung speichert, und sieht man eine diese Ladungsverteilung in elektronische Signale umsetzende Abtasteinrichtung vor, so erreicht man mit erheblich geringerem Aufwand dasselbe wie die Anordnung nach der USA.-Patentschrift 894 160, bei der innerhalb des eigentlichen Mikroskops ein Mehrschicht-Schirm angeordnet ist, der ebenfalls eine Umsetzung von Elektronen in Photonen und umgekehrt vornimmt.However, the invention can also be trained in such a way that the multiplier channel plate of the Vacuum housing of the microscope is added. If one uses a storage arrangement such as which stores the amplified end image as a charge distribution, and one sees this charge distribution before scanning device converting electronic signals, it is achieved with considerably less The same effort as the arrangement according to US Pat. No. 894 160, in which within the actual microscope a multilayer screen is arranged, which also converts electrons in photons and vice versa.

Die Elektronenvervielfachungskanalplatten sind an sich bekannte Bauelemente. Es sei dies im Zusammenhang beispielsweise auf Aufsätze in »Electronic Engineering«, 1965, S. 180, sowie in »Philips Technische Rundschau«, 1967, 28. Jahrgang, Nr. 8/9/10, S. 256 bis 261, verwiesen. In der letztgenannten Litcraturstelle wird die Anwendung einer derartigen Platte als Röntgenbildvertärker vorgeschlagen.The electron multiplication channel plates are components known per se. Let it be in context for example on articles in "Electronic Engineering", 1965, p. 180, as well as in "Philips Technische Rundschau ”, 1967, Volume 28, No. 8/9/10, pp. 256 to 261, referenced. In the last-mentioned reference the use of such a plate as an X-ray image intensifier is proposed.

Auch dort erfolgt jedoch eine Umwandlung des Bildes, nämlich zunächst eine Umwandlung des Röntgenbildes ^;n eine Elektronendichteverteilung und dann eine L mwandlung dieses Elektronenbildes mittels eines phosphoreszierenden Schirmes in ein Lichtbild. Dieses Lichtbild wird anschließend mittels einer Plumbikonröhre elektronisch weiter verarbeitet. There, however, a conversion of the image also takes place, namely initially a conversion of the X-ray image ^; n an electron density distribution and then a conversion of this electron image into a light image by means of a phosphorescent screen. This photo is then electronically processed using a plumbicon tube.

In Abweichung davon werden bei der beschriebenen Ausfiihrungsform speziell eines Korpuskularstrahlmikroskops irgendwelche Biklumw -dlungen bewußt vermieden, vielmehr wird eine dir te elektronische Verstärkung und Umsetzung in elektronische Signale vorgenommen.In deviation from this, in the case of the Embodiment specifically of a particle beam microscope any bicycles deliberately avoided, rather a dir te electronic one is used Amplification and conversion into electronic signals made.

Eine Elektronenvcrviclfachungskanalplattc, die im folgenden auch als Kanalplatte bezeichnet wird, läßt sich als Elektronenvervielfacher mil kontinuierlich ■;. verteilten Dynoden beschreiben. Der einzelne Kanal besteht aus einer dünnen Glasrohre, deren Durch- :j messer etwa ein Fünfzigste! bis ein Hundertstel der ; Länge beträgt. Die innere Oberfläche dieser Glas- * röhre ist mit einer hochohmigen Schicht bedeckt, aus der von einfallenden Elektronen (des abbildendenAn electron multiplication channel plate, which is also referred to below as a channel plate, can be used as an electron multiplier with continuous. describe distributed dynodes. The individual channel consists of a thin glass pipes whose throughput: j diameter about one fiftieth up to a hundredth of; Length is. The inner surface of this glass tube is covered with a high-resistance layer from which the incident electrons (the imaging

Claims

Beam) secondary electrons are triggered. However, the figures are not used as a descriptive

Reinforcement by these secondary electrons is kung are to be understood.

are available at the end of the channel at today - As with a camera tube from the Super-ürthikon-

the multiplier channels a maximum of 3-10 ^s . The optimal type is in the embodiment according to FIG. 1

Sensitivity is in the energy range from 100 to 5 in front of the storage disk 6, the grid-like or net-like

400 keV, i.e. H. precisely in the energy range of the electrode 8, which when electrons strike. '

Electrons in an electron microscope. The Ka- the storage disk 6 from this triggered secondary

nalpiatte now consists of a large number of electrons so that the storage disk 6

individual channels assembled to form the plate, on their surface facing the electrode 8

whose axes parallel to the axis of the microscope to positively charge. This charge distribution transfers

or run inclined towards this. due to a directed conductivity of the storage

In this way, without converting the image, cherplatteo also overcomes those that are lower in the figure electronic signals can be applied to surface. In the direction of the beam behind the storage plate 6 evaluate different ways. For example, the scanning unit is located. It contains the Kanen any number of televisions 9, which scan the electron beam 10 dispensing devices are fed. However, you can emit its slow electrons in dependence - and possibly at the same time - a wedge of the charge distribution on the storage direction for automatic focusing of the end plate 6 reflected or recorded from the storage plate 6 or a device for autorrjitic astig- can be taken. Such a reflected electromatic correction are fed. The device is indicated with its path at 11; that automatic focus adjustment, d. H. to the fo-electron hits the anode 12, that of the secunkussing of imaging lenses of the microscope, the electron multiplier 13 is assigned. the can for example work in principle so that the collecting plate 14 of the secondary electron multiplied End image scanned line by line and the fachers 13 is with the output 15 for the elektroso obtained electronic signals connected to frequency analog signals.

be lysed. Certain frequency components could then, depending on their amplitude, under the influence of the deflection coil arrangement 16, line-by-line scanning of the amplified end image (in the case of electromagnetic lenses) stored on the Speimotoren readjustment e.g. It is estimated that with an ind; e amplitude of these frequency components a value determined by the desired focusing η: τ with high electron-optical magnification reaches 2.5 · ΙΟ " ¹¹ A / cm ^2. The device for automatic astig end image plane, a gain factor for the elimination of single matism, ie for automatic one multiplier channel of 10 ⁸ and a capacity setting of a stigmator, can with an evaluation of the individual element of the storage disk of certain, filtered out frequency components of the electrical 35 0.2 pF and at a sampling frequency of 50 Hz at troniscnen Signals work. Again, the storage disk will be given a voltage of about 10 ' ¹ V for a line-by-line scan of the stored image. The voltage on the storage disk, which is usually required for a super-orthicon, is done by means of the scanning device, but the line system with such a Ge is only in the order of magnitude of 10 V, so that it can rotate at the required speed A voltage excess of several larger scans of the stored image required orders when using the invention results. It takes time to complete one revolution. can therefore with several tens factors small-

As a memory arrangement, however, an imager can also generate current density in the imaging electron beam.

umbrella use. At within the work and accordingly the preparation to be examined

Channel plate arranged on the Kuuingehäuses can reproduce this * 5 without risk of damage. Vice versa

be the usual final screen of the microscope, which can be measured on the specimen with the same current density.

but is not now in the final image plane. Set the image- much higher magnifications as they do

screen can also be placed on the beam exit surface for higher releases.

the duct plate. If this is a stock, the electronic output signals can be

is part of the vacuum housing, the screen is then 50 evaluate in another way. For example

outside the case. you can use a program-controlled calculator

The figures show schematically two embodiments are supplied, for example a sol-

example of an electron microscope. dia, which with regard to automatic astigmatism

The program in the final image level 1 of the electron removal and focus adjustment

ray 2 below the last imaging lens, which is 55 mi: rt.

Projective lens3, designed final image falls on the according to FIG. 2 is behind

speaking arranged entry surface 4 of the channel plate 5 of the screen 20,

plate 5. So it does not take place, as is usually the case with electrical equipment. A screen in front of the amplifier is also missing here, Nemicroscopes common to an end screen in

der Endbildencne 1 an implementation of the electron- 60 patent claims: image into a photograph.

In the individual channels of the channel plate S is done I. Electron or ion microscope with a

by secondary emission an amplification of the Elek · Endbildebenc and an image intensifier for the

troncnbildes, which in the arrangement according to FIG. 1 as the end figure, characterized by the fact that «.

The charge image is stored on the storage device 6 by the microscope with an image intensifier

is chert. The entrance face 4 and the exit serving electron multiplication channel plate

surface 7 of the channel plate S are present in this embodiment, dispensing with one in the direction of the sirahl

RunRs examples at a voltage of 3000 volts. equipped with this lying end screen

is, which lies transversely to the microscope axis with its beam entrance surface in the final image plane is arranged, and that in the beam direction behind the electron multiplication channel plate one Storage arrangement is provided for the final enhanced image.

2. Microscope according to claim 1, characterized in that the electron multiplication channel plate forms part of the vacuum housing of the microscope and forms its electron exit surface is hermetically sealed.

3. Microscope according to claim 1, characterized in that the electron multiplication channel plate is arranged within the vacuum housing of the microscope. «5

4. Microscope according to one of claims 1 to 3, characterized in that in the beam direction behind the electron multiplication channel plate the amplified end image as A storage arrangement storing charge distribution as well as this charge distribution in scanning device converting electronic signals are provided.

5. Microscope according to claim 4, characterized in that the memory arrangement as and the scanning means are disposed within the vacuum housing.

6. Microscope according to claim 4 or 5, characterized in that the electronic Signals are fed to television display devices.

7. Microscope according to one of claims 4 to 6, characterized in that the electronic Signals fed to a device for automatic focusing of the final image will.

8. microscope according to one of claims 4 to 7, characterized in that the electronic Signals are fed to a device for automatic astigmatism correction.

9. Microscope according to one of claims 1 to 3, characterized in that the memory arrangement a screen is.

10. Microscope according to claim 9, characterized in that the screen is the usual End screen of the microscope is.

11. Microscope according to claim 9, characterized in that gc indicates that the screen uses the usual electron exit surface for electrons! Faci.ungskanalplatte is arranged.

1 sheet of drawings

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