DD143187A1 - PROTECTION OF A CATODE IN ELECTRON BEAM INSTRUMENTS - Google Patents

Description

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Title:

Protective device of a cathode in electron beam devices

Applicability of the invention:

The invention relates to a device for deflecting positive ions to electron beams, which serves to protect the cathode by reducing the ion bombardment.

This device can be used in electron beam devices in which stable precursor electron probes require a precise stationary position of the electron source, e.g. for electron beam and electron beam exposure apparatus.

Characteristic of the known technical solutions:

Are known asymmetric systems of ion traps in electron beams, using a bent by magnetic or electrical means electron beam is used (eg in E.Bas: Optics 12, (1955) 8, p.377-384 and Rint: manual for HP and electrical engineers) , On. such beam path deteriorates the focus and thus the image quality in electron probe devices because of asymmetric deflection and lens aberration.

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Furthermore, axial ion trap systems are known which do not disrupt the nighttime rush of the unbalanced systems. These systems operate e.g. with axialsy-mmetrischer guidance of the electron beam by electrostatic means which are arranged around an attached in the optical axis ion trap (eg US-PS 3,452,241) The wax part of this system is that it is very expensive in terms of electrodes and the corresponding supply voltages Especially when the demands on the quality of the electron beam are high.

In electron emitters without Ionenablankung an ablation of the cathode tip u.a, by Katodenbeschuß specified by the manufacturer, the adverse effect - decrease the directional beam v / er tes - the user of the radiator by readjusting the cathode, korrigier s must. For this purpose, the electron beam device must be taken out of service and the spotlight to be dismantled. This technique is expensive, can lead to the destruction of embrittled Katodenteile and reduced depending on the stability requirement of the electron beam device whose availability more or less. The original directional beam value can not be reliably adjusted by readjusting the cathode.

Aim of the invention; '

The aim of the invention is to reduce the technical complexity of devices of the type mentioned and Nachjustieraufwand or .. to eliminate the Nachjustieraufwand, and to increase the availability of radiators and the life of cathodes in radiators with reduced effort.

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Presentation of Article 3 of the Invention:

The invention has for its object to provide a way that the life of cathodes is increased by protecting the cathode tip from positive ions and thereby the orbits of the electrons are not interfered with.

In an apparatus for deflecting positive ions on an electron gun to protect the cathode from ion bombardment, the object according to the invention is therefor. solved by that the cathode is surrounded by a magnetic ring system and a * rotationally symmetrical PeId around the electron-optical axis, which diverges from the cathode to the anode of the electron gun. It is advantageous if the magnetic ring system consists of two permanent magnet rings, which are surrounded by a ring-shaped magnetic yoke and between which there is a variable air gap. Another favorable solution is to form the magnetic ring system as an axially magnetized permanent magnet ring, which is arranged in an annular pole shoe.

Furthermore, the rotationally symmetric field can be generated by the magnet system of an atomizer pump integrated in the electron gun. The effect of the device is based on the fact that the rotationally symmetric magnetic field line course diverging towards the anode causes a defocusing on the positive ions and reduces the ion current density on the cathode tip.

Embodiment ;

In the following the invention with reference to embodiments and the accompanying drawings, in the

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1 shows a device with a magnetic ring containing two magnet rings and

FIG. 2 shows a device with a magnetic ring tag containing only one magnetic ring and pole ring rings.

on average, will be explained in more detail.

The apparatus shown in Fig. 1 consists of two magnetic rings 1 and 2, which are arranged axially parallel to a fixed in a holder 3 cathode 4 of an electron gun. In the air gap of the magnetic rings 1 and 2, which are surrounded by a magnetic yoke 5, the discharge system 6 of an integrated Zerstäuberionenpumpe is arranged.

For the purpose of adjusting the electron emitter to the electron-optical axis 7 of the electron beam device, two adjusting screws 8 are provided, with the aid of which the magnetic rings 1 and 2 of the magnetic ring system can be moved radially.

The mode of operation of the device is based on the fact that a diverging magnetic field 11 existing in the space 9 between the cathode 4 and the anode 10, which is represented by its field line profile, is located on charge carriers close to the axis 12 due to the radial components of the magnetic field 11 compensating there On electrons of the carrier beams 12, which move relatively close to the axis 7, the magnetic field 11 thus has no negative influence. Near the anode 10, the electrons are accelerated so high that even the divergent negative parts of the carrier beams 12 by the transverse component of the there relatively weak magnetic field 11 are hardly affected. From the lying under the anode 10 space 13 of the radiator with higher pressure than in space 9 positive ions mch the known cosine distribution through the anode hole in the

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Spotlight space and are accelerated in the direction of the cathode 4. Due to their large mass, the relatively weak magnetic field hardly collects on ions close to the axis. Obliquely incident positive ions, which are represented as rays 14, are further scattered by the magnetic field 11 diverging outside Acsense 7, in particular just above the anode 10 in space 9, where the ions are not yet accelerated, so that at the location of the tip Katode 4 the total ion density is reduced. As a result, damage to the cathode are greatly reduced.

Figure 2 shows a device which consists of an arranged around the cathode 4, axially magnetized permanent magnet ring 15, which is surrounded by a Polschuhringsystem. The Polschuhringsystem consists of a fixed Polschuhring 16 and four adjustment screws 17, which serve for .Perschiebung of the magnetic ring 15 and for adjusting the electron beam to the axis of the electron beam device, and from an adjustable Polschuhring 18, with the help of the annular gap 19 and thus the stray field in Set area of the cathode 4. An axial adjustment of the magnetic ring 15 to the cathode 4 is possible by means of a collar 20. The mode of action of the device according to Pig. 2 is analogous to the standing Fig. 1; this is also due to the fact that due to the rotationally symmetric, diverging to the anode magnetic FeIdlinienverlaufs causes a defocusing on the positive ions and the ion current density is reduced on the cathode tip.

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'I.Erfindun & sanspruch

1. Device 2ium deflecting ν on positive ions at an electron gun to protect the cathode from ion bombardment, characterized in that the. Cathode is surrounded by a magnet system 'and a rotationally symmetrical Pond around the electron-optical axis, which diverges from the cathode to the anode of the electron beam.

2. Device according to item 1, characterized in that the magnetic system consists of two magnetic rings per manent, which are surrounded by a ring-shaped magnetic return and rule between which there is a variable air gap.

3. Device according to item 1, characterized gekennaeichnet,. the magnet ring system consists of an axially magnetized permanent magnet ring which is arranged in an annular pole shoe.

4. The device according to item 1, characterized in that the rotationally symmetrical PED is generated by the magnetic system of an integrated in the electron gun Zerstäuberionenpumpe.

5. The device according to item 1, characterized in that the magnetic ring system is adjustable to the electron-optical axis.

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Claims (5)

';., Erf indu'nÄsanspruch Anspruch [en] A device for deflecting positive ions on an electron gun to protect the cathode from ion bombardment, characterized in that. Cathode is surrounded by a magnet system and there is a rotationally symmetrical PeId to the electron-optical axis, which diverges from the cathode to the anode of the electron gun. 2 · Device according to item 1, characterized in that the magnet system consists of two permanent magnet rings, which are surrounded by a ring-shaped magnetic yoke and between which there is a variable air gap. Device according to item 1, characterized in that the magnetizing system consists of an axially magnetized permanent magnet ring arranged in an annular pole piece. 4 · Device according to item 1, characterized in that the rotationally symmetrical PED is generated by the magnet system of an atomizer pump integrated in the electron gun. 5. The device according to item 1, characterized in that the magnetic ring system is adjustable to the electron-optical axis. , 3460