DE2225864A1 - HEATING CURRENT CONTROL ARRANGEMENT IN ELECTRON BEAM DEVICE - Google Patents

Description

, H.. ■ · i - f Schole PHN _n 5666 .

- N-Y-Philips-Gioeüampenfabriekea BOSS / WJM,

FilesNa .; PKtT- 5666
May 26, 1972

"Heating current control arrangement in electron beam device".

The invention relates to an electron beam device with a cathode for the thermal emission of a Electron beam 5 of a Wehnelt electrode and a heating current control arrangement.

In arrangements with a thermal cathode for generating an electron beam for electron-optical In applications it is important that the cathode is always in operation to emit such an electron beam has optimal temperature. An operating temperature lower than the optinuile temperature has a relatively low emission power result in the cathode. As a result, a through the

Cathode to be emitted electron beam at least the cathode surface is relatively small

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Current density. The. ··, has a new negative influence on the optical properties of the device. A very high operating temperature of the cathode leads to a shortened service life of the cathode, especially in the case of directly heatable Heizfudenkathoden.

A well-known pre-fall tin setting the

Cathode temperature is based on visual assessment an image of the emitting cathode to be formed on a fluorescent screen. Here the temperature becomes like this set that on the luminescent screen an acceptable A consistently illuminated image is created. This egg stand - procedure has the disadvantage that the setting criterion is determined by subjective perceptions and that a cathode deposition is always present for any subsequent memory Must be educated. It has been shown that the application of this criterion is usually too high Cathode tempera door leads.

An automatic heating system for an E Lok troneiis trah 1 device with a thermal cathode is known from Dutch patent application 6800 ^r ) 6 ⁽ ) . A change in the current emanating from the cathode is compared with a voi'c Inges t < tandardomitis Loriskur ve assumed emission μ curve derived.Differences in dan Emiss ioiiskurveii We different cathodes and toinpn ~ emanating from the cathode

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PHN. 5666.

Temperature-dependent leakage currents can cause deviations of the optimal tempo setting.

The invention aims to address these disadvantages

eliminate and a reliable, - if desired automatic To create the heating filament temperature regularly. A such electron emitting device is corresponding to the Invention characterized in that in the electron beam device an intercepting screen forming part of the heating control arrangement is located around part of the electron beam to be collected locally.

In an electron beam according to the invention device is the subjective criterion by one in the electron beam device replaces the objective measured value to be generated, with dom you do not need to use a reference value. In a preferred embodiment according to Invention becomes the ¥ elnielt resistance or the Wehnelt tension associated with a periodic change, and a resulting signal from the interceptor screen becomes the Setting the optimal cathodes! empex'atur 'is used.

The ErfiiKhmg is based on some of the Drawings of illustrated examples in more detail explained. Show it ·

Prop. 1 unites? his' schemnt 5 .srhc; depiction

one "with an inventive Uvi zstromregelanord- nüng koheneii El ekt roiir; microscopeK,

I'ig. 2 a Kai hodon-rVohnol t circuit to the g "ei mn * Ih: i /.si i'onuO, 'u>] arrangement with a self

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changing heat resistance, and

Fig. 3 shows a cathode Wehnelt circuit for Application of a Heizstromrogel arrangement with a changing Wehnelt tension.

In one illustrated in Figure 1 electron microscope 1 are located opposite to the advancing direction of a is to be produced, the electron beam 2, a phosphor screen 3 for collecting the electron beam, k is a projection lens, a Zw: Lschenlinse 5> is a diffractive lens 6, an objective lens 7 »a second condenser lens 8, a first condenser lens 9 »an acceleration anode 10, a Wehnelt electrode 11 and a cathode 12. The cathode is formed here by the heating filament 13, which is made up of two filaments which are united at one point. The filament 13 is connected via the filament feed lines lh to a flow control arrangement which is connected to an intercepting screen 17 via a coupling 16. During operation, the interception screen 17 intercepts at least 5 / ° from the electron beam 2. The interception screen is preferably made of a plate with a round opening with a diameter of approximately 300 microns. The protective screen can also be provided at another point in the electron microscope, with the diameter of the opening being able to be adapted to the position. The protective screen is preferably made of an electrically conductive material and it must then be used to derive an electrical signal in relation to the elec-

309807/0781

PUN, $ 666.

electron microscope electrically isolated arranged so-in. Diο coupling; \ 6 then orders from an ■ electrical conductor. In another embodiment, the Abi ^ uigschirin contains a phosphor to be activated by an electron beam. A case-to-use optical coupling 16 is a dependent on the beam current intensity signal will comply with the example \ v ^T else dui-ch a photosensitive member can be absorbed by the Heizstromregelanordnung 15th If the entire emitted electron beam does not reach the screen '_} , the arrangement can also be designed in such a way that the screen 3 rider when the entire emitted electron beam hits the screen. Screen hits, part of the screen is effective. An electrical or optical signal dependent on the beam flow density is then obtained from the screen. The detected signal is fed to the control system 15 so that it controls the heating current as a function of the received signal.

In a preferred embodiment of a ho iztronic arrangement shown in FIG. 2, a setting signal is received on the interception screen by changing the thermal resistance. For this purpose, the illustrated onthüLt Kfithoden-Wohne 11 ^ EHAL processing a series of -Wiclorständen 20 and a currency 1 .scha 1 tor 2 1 for setting a Be tr iobswor ts country for Wohne 1. twiders. With a switch 22, the possible inclusion of resistors of a series of resistors 2 '} in the circuit im

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-G-

Uehiio L twiders tand ciiip change from beispioLswoLst! K) hifi, '? 0'; u des Be LriebsuorLs made. Figure 2 ζ "IGT also don with two equal Ka Thode resis tändon 2h and ^r 2) before ;; ohonen filament 1'31 dor to the two s-I in oiiiotn point forward in igonden threads on Ls Landen is L, the; Wehnelt electrode 1T and cinuii on cathode point LiaL to switching switch point 2 (>.

Home Generate oinos signals on dom Abi'ong-

umbrella, by doing i'live 1 tu'lders tand between the Ilotdrive.s - word and oinoin slightly lower 1 iogf? iideii word poriodisch is changed, the fitäi ^ kej dos signal decreases when the speed of communication is low, and niiiiiiit zn if you · Ka thodeii tompora door · ^ n lioch set is. In both situations, the heating current κο It must be subsequently regulated that the signal returns to the output level, consequently the operating value of the living I twid'ors t aiid.-i belongs i Strengths; aiifwu'st. After that this process can be repeated until a Veline t tw Lders tandsänderr.g no longer affects the signal. Then the optimal one Ka thodeiitempera door reached. The Xachs fcel lon dos Heizstroms can simply be reached automatically when on the hot current regulator! arrangement has a circuit for generating it a difference signal between the signal at the operating value of the Wehiip 1. twidors tands and the signal with the Wolmeltwidorsfcand reduced. With this signal is then about with a servomechanism Gost-controlled heating current.

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A Kathodenwelmelt circuit for a more practical heating current control according to the invention is shown in FIG. The Wehnelt electrode 11, the cathode 13 with the cathode resistors Zh and 25 and a Wehnolt circuit 27 and a voltage source 28 are specified therein. The Wehnelt voltage, the magnitude of which depends on the geometry of the electron beam device, is generated by the Wehnelt circuit 27. The voltage source 28 superimposes a periodic, preferably sinusoidal, voltage change on the generated Wehnelt voltage. For example, an alternating voltage with a peak-to-peak value of 10 Y can be superimposed on a nominal alternating cathode voltage of 200 V.

Since the current density of the electron beam as a function of the Wehnelt voltage is precisely at the optimum Has a maximum cathode temperature, an alternating voltage superimposed on the Wehnelt voltage has a signal As a result, with one hour at the optimal temperature setting with regard to the frequency of the applied alternating voltage double frequency. In a preferred embodiment, this is used by doubling the frequency with the insertion of a frequency-sensitive detector used as an indicator for the optimum temperature An oscilloscope can be used as a detector - which makes the frequency doubling visually is perceptible. In certain cases, such as in an electron beam processing device in which a

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large part of the electron beam to be emitted by the cathode is effectively used, a phase-sensitive element can successfully regulate the heating current be used. In these cases, the measurement at the edge of the electron beam becomes too imprecise Impression of the brightness changes in the center of the Electron beam received.

BATH ORIGINAL

^Λ 309807/0701

Claims (1)

PIiN. ρ λ τ ε. \ ^Γ τ _ \ __> «_. ^ JLlLlLlLALiL- ·. ]. J Ι) 1 tbsp; troll · t ι lhl gei 'it mil i'hicr Killiodi-' iür the thermal emission oiiK!. ·; El.ekt ronens t rahl η, oilier VoImel toi oktrode and ο inor He i / ,: 5t rom control arrangement, characterized in that it is fjoräl in the electron beam a one foil, dor Ho i / ^ tromro ^ i} laiiordininfj bildon— the A)) TaHiJiJt hirm bofiiidcit, to part of the electron beam » locally aui'zufiJHf.Mi, Mt ELek troiKiiifi trahlf.ei-ät according to AiiBpi-uch 1, This fjokemizoi chiie t that the lloizHti'ormOtyolanoi'tlimng a changeable Wehnel tv resistance and an arrangement for changing a hasty «t hurried Wehnel tworesistor contains. '3. Klektroiieiiststrahlgorät according to claim 2, characterized gokeimzei planarized da.ss do Heissstroinrogelanordnung ( "iiKj Sclialtung to Hilden a :. difference ignal's of i be the äus.ser.s ton values of Woiinol twidor a tands recorded signals includes. hm Eleklronenstfahlgeiät according to claim 1, Due to the fact that the Ileizistj-omiegel arrangement contains a Spaimuiigygeiiorut or in order to superimpose the Kat liodenwohneit - voltage a Spuniiung change . thereby gekeiin / cichiict, il.iss (J ie He izs tromiegelanerdiiiung an i) haseneinpi'iiidl icheii Detfikcor contains uiul that a E iiii · -te 1 Ikri tei * ium by a pre-c ingested 11 e phase shift with regard to the offered. signal, or / ioj t wild. 30 9 807/0 781 BAD ORfGJNAL