DE2102616A1 - Electron beam device - Google Patents

Description

El ectr on beam device

The invention relates to an El ektronens traniger ät * in particular electron microscope, with a lens arrangement a fine electron beam along an electron-optical Acb.se brings about, which on the Surface of a test object hits, and also a Deflection arrangement for angular or rotary movement of the beam provided around the Asif meeting point on the breakfast surface is, and finally one to one with the .A deflection arrangement synchronized display device connected s-ener detector is available.

This can be the secondary electrons or thrown back Primary electrons or the current from the test item itself to be used * an image on the display device, for example the screen of a cathode ray tube, which is scanned synchronously with the beam or test object will. However, instead of electrons, electromagnetic radiation, such as X-raying ”or, for example, can also be used ! rays of light ,. from the. Detector was recorded and analyzed

the, which radiation by the hit on the electron beam is produced.

In the case of conventional electron beam devices, the specified Art is a beam of electrons, coming from an electron gun, formed by a Samniell lens arrangement, which usually comprises two electromagnetic lenses. The image created on the electron-optical axis of the electron source is converted by a last electromagnetic lens, the so-called objective lens, which has a short focal length, to a reduced image on the Surface of the test specimen reduced »Deflection coils are arranged within the rear bore of the objective lens, which deflect the beam in two mutually perpendicular directions which run transversely to the beam axis. Are there already two sets of deflection coils, axially at a distance of— arranged one above the other, provided for each deflection direction, to move the beam away from the axis and then back towards it to direct so that the beam, st & ts through the proportionately small last opening ^

When using a device of this type, ElektronenkanalisierungSreffekt been 1st in conjunction with Einkristallprüflingen observed ,, similar to that caused by crystallographic electron diffraction Eikuchi effect (Scanning Electron Microscopy 1969 "Proceedings of the Second Annual Scanning Electron fücroscope Symposium ,. April 1969) · This electron channeling effect is called the "pseudo-Eikuchi effect" »The contrast _r d-en; the sexton evokes in the picture is the result of the variation of the wrap of the incident ray with respect to the iris * allsi: structure as the ray travels back and forth. With such a. Arrangement is an angular deflection or scanning: an essential

rather part of the process, and the pattern produced is therefore necessarily that of a substantial area of the test object, for example of the order of magnitude

of two or three mm. The resolution is due to the angular spread of the beam, which is in the sub-bundled state.

In another proposed arrangement, the deflection is switched off so that the beam remains on a fixed axis while the test specimen is tilted about two orthogonal axes which run through the point of impact. Mechanical conditions limit the accuracy and angular resolution of the patterns. m

Another "proposal is to vary the relative currents in the upper and lower sets of deflection coils until the intersection is actually in the specimen surface, rather than just above the last opening in the front pole piece area of the last lens. The deflection coils move the beam to the point of impingement on the specimen. in practice, this point is not a geometric focal point, but a Verwaschungsscheibe whose area is determined by the electron optical aberrations, that is deviations of the deflection coils. These aberrations usually have a Verwaschungs- M disc with a diameter in the Of the order of 50 m

result. The last lens is either switched off or operated in the subdivision area.

The object of the invention is to create an electron beam device of the type specified at the outset, with which pseudo-Kikuchi pattern obtained from small surface areas can be.

109831 / 1S

Accordingly, the electron beam device of the present invention is characterized in that the lens arrangement is arranged and designed so that an image is in the plane A deflection coil arrangement comes about, which scans or scans the beam in an opening of a last lens. sweeping deflects which lens acts as a further deflecting element and the beam onto the electron-optical axis steers back.

The invention can be applied to known electron beam devices en can be realized simply by the fact that the last or objective lens of the normal beam bundling arrangement is used as the deflecting lens is used. If there are two sets of deflection coils in the device, the first deflection will be caused in the deflection of the first coil set alone, and the second coil set is removed or at least switched off.

As with known devices, the deflection usually takes place in two orthogonal directions, perpendicular to the electron optical axis.

Information about the crystal structure should basically be obtained at a single point, i. H. in as small an area of the test object as possible. The inevitable spherical aberration of the lens has variations of the point of impact in the deflection result, so that the painted area larger than is desirable. This can be avoided by entering a correction signal that changes synchronously with the deflection signal. For correction, the apparent position of the image of the electron source, which forms the object of the last lens, synchronously

109831/1531

with the scanning deflection along the electron-optical axis be shifted rhythmically. For this purpose, the two sets of deflection coils arranged axially at a distance from one another can be retained , if necessary with the addition of a third set of coils, the current in these coils then being adjusted to suitable Way is changed.

Instead, the spherical aberration of the last lens can also be corrected by that immediately the current therein changes in synchronism with the scanning deflection will. However, the high inductance of an iron-core electromagnetic lens limits the speed the change of such a correction signal is considerable, so that the overall scanning speed is very slow is. This significantly limits the usefulness of the device. This is why it is preferred as the last lens a so-called "mini lens" without an iron core, d. H. used with an air core, or a solenoid-type lens. However, it can even a last main lens with an iron core can be retained if the correction current of an auxiliary lens is abandoned is, preferably without an iron core, d. H. with air core. Instead of this or in addition, instead of a normal orthogonal grid, a Series of lines to build up an image are deflected or scanned in polar coordinates, with a relatively fast turning or angular deflection and a slow radial deflection. That way, a given area of the reproduced image, which represents a given fixed angle range when the beam hits, be swept over in a relatively short time, the radius vector thereafter only proportionally slowly changes, so that the correction signal, which only changes according to the change in the radius vector

109831/1531

must, can be given.

Accordingly, the electron beam device according to the invention is when it has an electromagnetic final lens, characterized in that the deflection coil arrangement is applied by a generator with such signals, that the beam is deflected like a pole and moves along a conical path with a slowly changing tip angle emotional. The display device is advantageously acted upon by the generator in such a way that a spirally scanned, image synchronized with the polar deflection of the beam is generated.

109831/1531

In the following, the invention is attached with reference to the " Drawings described, for example, in which show:

Pig. 1 shows the structure of an electron beam device in schematic representation;

Fig. 2 shows an orthodox deflection arrangement for painting an area of a test object surface, also in a schematic representation;

3 IUID 4 each one of the corresponding to Figure 2 showing an arrangement for obtaining electron channeling effects (pseudo-Kikuchi) by M using the existing doppeltablenkenden coil or the arrangement of the invention with a single set of deflection coils and a deflection lens.

Pig. 5 is a diagram to illustrate the advantages a spiral scan versus a straight scan.

According to Pig. 1 there is a conventional electron microscope for scanning or observing a specific area of a test object surface from an electron source or gun G, the electrons of which are bundled into a beam by two converging lenses L1 and M L2. The converging lenses L1 and L2 generate a reduced image of the source or cannon G, which is further reduced by a last beam-shaping lens L3, so that the diameter of the point of impact of the beam on the surface of the test object S, through which point of impact the electron-optical axis A runs, on the order of 50 angstroms or less

109831/1531

Two pairs of deflection coils D1 and D2 (Fig. 2) cause that the electron beam does not strike a single point, but rather a surface area of the test object S scans, with an Easter similar a television scanning grid. From still to Descriptive reasons is not just one set of deflection coils for each of the two mutually perpendicular deflection or scanning directions intended. Rather, they are two sets of coils arranged at a distance from one another in the direction of the axis A is present so that the electron beam is first directed away from axis A and then back towards it.

The secondary electrons or reflected primary electrons, which emanate from the point of impact on the surface of the test specimen, are captured in order to generate a signal which is amplified and used to control the brightness of the leak of a cathode ray tube T whose beam emits synchronously with the primary electron is deflected, namely by means of a common sampling generator ο B. Εε a two ld j reri; * lonal image is generated on the screen of the tube T, which the spatial ^{ver -:} -jj'uir £ o;. <· ] ■ '' -. R hiiriomene in the scanned area of the Pr -'- ifl ^ ag: .- '"Clnolie reproduces which variations of the zu-L'ücl>: gev; r- ( ^; η otrah ^ -ung cause so that the surface shape Oer .'ier electric or magnetic state is ersicrrii ch.

In a typical device, the two reel sets in the back hole are the last. -. recorded, which is almost invariable elektroms:,. To keep the pleck size small, the: - ' ^: ^ before aberration must be limited, which is why the last in / jr ,; / Jy according to i \ - _:. ':'. ■; ■ iu.fi small exit oXf'nunr Al "uofwe-s ¹ -. In .F'it ·:; ..

1 0 9 in 1 ' ^! “AD

2, the lower part of the column of the device is shown schematically according to FIG. This explains the purpose of the two axially spaced sets of deflection coils D1 and D2, which is to be ensured should that the beam always runs through the opening A1, which is in close proximity to the main plane, despite lateral deflection the lens L3 lies.

In order to use a scanning electron microscope with an electron channeling effect (pseudo-Kikuchi effect) To work, the angle of incidence of the electron beam on the test object surface is varied cyclically or periodically. Although the said effect can often be observed when there is a considerable surface area of a specimen is scanned when only the scanned area is a single crystal, the effect will be on a single crystal Location preferred examined. To do this, one has to refrain from deflecting the beam and instead use the test object tilted about two orthogonal axes which run perpendicular to axis A and through the point of impact. The result was reproduced as a two-dimensional image on the screen of a cathode ray tube with the X and Y deflections are synchronized with the two angular deflections of the test object.

According to FIG. 3, it has also been proposed to enlarge the opening A1 of the last lens L3 and to enlarge the To move the focal point of the lens arrangement formed by the two lenses L1 and L2 downwards, so that it is with the specimen surface collapses. At the same time, the relative strength of the coils D1 and D2 was adjusted so that the coils when deflecting the beam back to axis A on the test object surface instead of in opening A1.

109831/1531

to lead. The information obtained was again in the form of a two-dimensional image on the screen of a Cathode ray tube T reproduces, with the angular deflection of the primary electron beam in two directions in the image by linear displacement of the spot on the Screen is displayed in two linear directions. The picture shows a series of intersecting bright and dark bands, from which information about the crystal structure at the point of impact can be obtained.

In KLg. 4 shows the arrangement according to the invention. The second set of deflection coils D2 is not needed, at least not for deflection. Behind the second Lens L2, an opening A2 is provided which is very much smaller than that which is known to be present at this point Opening and, for example, a diameter of only 10 mm to reduce the divergence of the beam. The current in the lenses L1 and L2 is adjusted so that an image of the source or cannon G at a point I the Axis A is caused in the plane of the deflection coils D1. These coils D1 are used to deflect the beam with a sawtooth voltage applied. The beam is deflected in each of two perpendicular planes, but be here for the sake of better understanding, only one level has been considered. The current of the last lens L3 is set in such a way that that it bundles the image in the plane of the coils D1 in such a way that there is a reduced image on the surface of the test object Picture is given. The plane of the deflection coils D1 and the point of impact on the surface of the test object are thus conjugate Represent points with respect to the lens L3. The lens L3 acts not only as a converging lens, but also represents part of the deflection arrangement. Due to the normal lens action, the lens L3 bends each beam towards

109831/1531

Axis A back, which is offset from axis A and passes through lens LJ.

If the deflection coils D1 deflect the beam back and forth in the opening A1 of the last lens LJ, which opening has a size diameter of for example 2 mm, then the lens LJ directs the beam to the axis · ':. in such a Extent back, which depends on its distance from the axis A, so that the beam on the specimen surface in focussed on a focal point and is also always held incidentally at a fixed spot on the surface of the test specimen.

So when the deflection coils D1 deflect the beam back and forth, the beam travels around a fixed point of impact on the specimen surface. For example, the total angular deflection can in each case be δ degrees and the area of impact can be approximately 10 .mu. in diameter. The xreal diameter of the beam at this point is only 1 / U, but the lens is LJ in terms of deflection; and subject to the collecting effect of the spherical aberration ::, εο that the "ray crosses the axis A at a point, wr-L ^ Lr?" is closer to greater deflection of the lens than at:. " ^: i: * .-; -r; - deflection so that the point of impact actually moves.:.!:!. ^v ii - <~. ^k 'ver.c. for deflection or scanning. Jj Die: .r; elliiii; ^ "■ _-r test object surface is therefore chosen at a srlelisn point:,. Θ :: ¹ axis A, where a" circle of least ter-wascliTLiic "is given, but not at the theoretical focal point. Animal said circle has a specified diameter et-? i'a 10 ai on.

In the arrangement according to FIG. J, the coils DI can cause the beam to reach the fixed point on the specimen surface scans at a fixed angle, namely

SAD ORIGINAL

by means of a so-called "angle raster", ie by applying a fast sawtooth voltage similar to the line deflection in a television-like grid, while in the other plane the coils are subjected to a slower sawtooth voltage, which is similar to the television image scanning. The image on the screen of the cathode ray tube T is in the form of a two-dimensional grid, which is obtained from the same two sawtooth-shaped voltages, just like a television grid

The smallest area that is scanned in the impact region on the test object surface, can be made by correcting the spherical aberration of lens L3 be reduced. This can basically be done in two ways. As is well known, the spherical aberration causes that those electrons which pass through the lens at a considerable radial distance from the axis, converge at a focal point on the axis which is closer to the lens than that which is to those electrons which pass through the lens near the axis. This can be compensated for by the Image point I, which is formed by the lenses L1 and L2, rhythmically along the axis during the scanning or deflection is reciprocated so that it is further away from the lens L3 at large deflection angles than at small ones Deflection angles. Then the image or focal point is always on the same during the entire scanning or deflection cycle Location of the axis, d. H. exactly on the specimen surface.

To move the image point 1, the current in the lens L2 and, if necessary, in the lens L1 is varied. At the same time, the primary deflection arrangement must be modified,

1 0 9 8 3 1/1 F? 1

so that the pixel I can be shifted axially. Additional loan In addition to the coil pair D1, the coils D2 are used, and possibly also a third coil pair E. By suitably setting the current in these three pairs of coils, the apparent origin of the primary deflection, seen from the last lens L3, move along the axis as required, this origin always coinciding with the Pixel I coincides. In practice, the electricity is in the second converging lens L2 changed in order to move the image point I along the axis A in synchronism with the deflection. For example the point I in Fig. 3 moves in synchronism with the deflection amplitude, and a signal from the current in the Lens L2 derived and used to control the ratios of the currents in the coils D1 and D2 and possibly E, so that the apparent origin of the lateral deflection caused by these coils is with the pixel I. coincides.

The spherical aberration can also be corrected in other ways, namely by direct Change of the current in the last lens L3 in synchronism with the deflection, so that the effective focal length of the Lens L3 simultaneously, i.e. H. concurrent with the radial distance is changed by the axis A with which the electron beam passes through the lens. In this case it remains the pixel I is stationary, so that the primary deflection can take place solely through the single coil set D1, that is the coils D2 and E may be missing.

The iron core electromagnetic lens L3 has such dimensions and performance that it can with a considerable Is affected by inductance. It is therefore basically impossible to keep the current in sync with the

10983 1 / 1S31

to vary the deflection of a typical scanning grid, at which the total time for an image deflection is on the order of magnitude a few seconds, the time for a single line deflection (or a single angular deflection due to the coils D1 and the line direction) is only 1/100 see.

In order to make the desired correction, instead of the two angular deflections in mutually perpendicular directions made a deflection with polar coordinates, with the angle signal varying rapidly and the radial signal slowly changing. The beam then describes a conical path with a slowly changing tip angle. In Pig. FIG. 5 shows a two-dimensional image as it appears on the screen of a cathode ray tube which is shown in FIG consists of a series of straight lines, like a television grid. This is drawn in as a square in Pig · 5, but this is not essential. Linear distances from the center of the square image correspond to angular deviations of the primary electron beam it from axis A. The angular deviation thus fluctuates widely during each line, for example in the middle line within a line through zero of one Value equal to 1/2 y2 times the maximum value in one direction up to a value equal to 1/2 ^ 2 times the Maximum value in the other direction. A variation of the current in lens L3 in synchronism with it for correction would only be possible if the line frequency and thus the entire deflection cycle were as slow as basically not acceptable.

However, it is scanned or deflected along a circular path, the primary electron beam being the Generating a cone with the tip on the test object upper

109831/1

surface forms and runs along the surface of the cone quickly, while the apex angle of the cone slowly increases from zero to a maximum value, so that the spot on the screen of the cathode ray tube describes a corresponding spiral path, as shown in Fig. 5, then the same image area , i.e. the same fixed angle are covered with the same definition, but the angular deflection of the beam with respect to the axis A changes only with the image frequency instead of the line frequency.Since the correction signal to be sent to the winding of the lens L3 only depends on this angular deflection, it only needs to be accordingly use to change the frame rate. Accordingly%, the correction with acceptable image periods in the order of a few seconds or less. For a given maximum speed of the change or the change of the correction signal a predetermined solid angle that time be covered with a polar deflection in the half which is in law ⁿ ediglich a row of a Cartesian grid-like or Aülenkung required.

No special coils DI need to be used for polar deflection. The existing perpendicular coil pairs can be used. Suitable sine and cosine deflection signals are applied to them, so that M the spiral deflection occurs.

The special arrangement of the converging lenses and the openings can be modified, as can the position the primary deflection coils. For example, the opening A2 can be arranged above the lens L2, and it less or more than two lenses can make up the collective lens arrangement. It is only essential that a picture occurs on axis A at a point which

109831 / 1F

conjugated to the specimen surface in addition to the last lens LJ5 is, and that a primary deflection arrangement the The beam deflects at an angle from the axis with this point as the origin, with the last lens L3 itself being the secondary ab-1 Forms a deflection arrangement which directs the beam back to the axis on the surface of the test object

According to the invention, the last lens L3 is preferred with an air core, d. h · without a core, thus designed as a so-called "mini lens", its self-inductance is much lower than that of a conventional iron core lens. Instead, a main lens with a Iron core are used, which is supplied with a constant current, then the correction signal is a Auxiliary lens without iron core is abandoned

If spiral deflection or scanning is used, then the deflection speeds are adjusted so that the spot on the screen of the cathode ray tube with a constant Speed is running, that is, the angular deflection speed is opposite to or vice versa as the radial deflection changes. This ensures constant brightness throughout the image. It can also be used for a given maximum speed the change in the correction signal a predetermined fixed angle in only a quarter of that time are covered, which is required for a single line of a Cartesian deflection or scanning. Preferably the radial deflection also runs through the zero point from one limit to the other and back, since then there is no return which must necessarily be fast.

The invention can be realized both by modifying known relevant devices, as well as by the

109831

corresponding construction of completely new devices. Instead of the dar- " Provided converging lens arrangement can also find another use, which, for example, only a lens instead of two. Likewise, it is not essential that the image be created from reflected electrons. For example, it can be generated from the device under test stream. If the test item is made of photoluminescent material, a light signal can be evaluated.

109831 MS31

Claims (3)

Expectations M./Electron beam device, especially electron microscope, wherein a lens array creates a fine electron beam along an electron optical axis leaves, which impinges on the surface of a test object, furthermore a deflection arrangement for Winkeloder Rotational movement of the beam is provided around the point of impact on the test specimen surface, and wherein finally, a detector connected to a display device synchronized with the deflection arrangement is present is, characterized in that the lens arrangement (L1, L2) is arranged and designed so that a Image in the plane of a deflection coil arrangement (D 1) comes about, which the beam in an opening (A 1) a last lens (L 3) this scanning or sweeping deflects, which lens (L 3) as a further deflection organ acts and the beam on the electron-optical axis (A) steers back. 2. Electron beam device according to claim 1 with electromagnetic last lens, characterized in that the deflection coil arrangement (D 1) from a generator (B) with such signals is applied that the beam is deflected like a pole and along a conical Path moves with slowly changing tip angle. 3. Electron beam device according to claim 2, characterized in that the display device (T) from the generator (B) is applied so that a spirally scanned, synchronized with the polar deflection of the beam Image is generated. 109831/1531 Blank page Λ.:. SkK