Process and system for the control of the focusing of a beam of monopolar charged particles

A process and a system are disclosed for controlling the focusing of a beam of monopolar charged particles which is used, for example, to vaporize substances in vacuum coating systems. The beam (S) has a cross-sectional area (Q) in a plane (E.sub.1) transverse to the axis of the beam. Perpendicular to plane (E.sub.1) there is a plane (E.sub.2), the surface normal (R) to which indicates the direction in which the change in the cross-sectional area (Q) is to occur. According to the invention, flux density fields (B.sub.1, B.sub.2) are applied, which are parallel on opposite sides to plane (E.sub.2) but have opposing directions. As a result, the change in the focusing of the beam has essentially no effect on any deflection of the beam; that is, it is possible to control the focusing without exerting any significant effect on the deflection.

FIELD OF THE INVENTION 
The present invention pertains to a process and to a system for controlling 
the focusing of a beam of monopolar charged particles, especially 
electrons, in accordance with the preambles of claim 1 and claim 15, 
respectively. 
BACKGROUND OF THE INVENTION 
It is known that the focusing of a beam of monopolar charged particles can 
be controlled by means of the action of a magnetic flux density field. 
Beams of this type, especially electron beams, are used, for example, to 
vaporize substances in vacuum coating systems. It is important in this 
case to be able to change, in a controlled manner, the cross-sectional 
area of the beam striking the material to be vaporized as well as its 
shape or extent and position; that is, it is important to be able not only 
to focus the beam in a controlled manner but also to deflect it in a 
controlled manner. The goal of controlled focusing, that is, of 
controlling the shape or size of the cross-sectional area striking the 
material to be vaporized, is, for example, to bring about the uniform 
removal of the material to be vaporized and/or to make allowances for the 
many different thermal characteristics of the various materials being 
vaporized. 
When focusing is controlled by means of magnetic flux density fields, 
advantage is taken of the fact that moving charged particles such as 
electrons or ions are subjected in such a field to a force which is 
proportional to the charge of the particle being considered but also 
proportional to the cross-product of the particle velocity v times the 
magnetic flux density B. 
A process of this type is known from U.S. Pat. No. 4,064,352. 
According to that document, pole shoes extend along both sides of the 
electron beam, between which a largely homogeneous magnetic field is 
generated by means of a magnet. 
The field is nonhomogeneous in the narrow air gaps between the 
inward-projecting magnetic cores. 
In addition, W. German Patent No. 2,719,725 discloses an electromagnetic 
beam focusing technique for an essentially flat beam in which, based 
largely on a quadrupole system, an encompassing rectangular frame core is 
provided in a plane perpendicular to the direction of beam propagation; 
winding arrays are provided on the shanks of this core. The fields 
controlling the focusing, which are antiparallel, extend for a certain 
distance in a way which corresponds to the extension of the flat beam. No 
provision is made for shifting the beam, as in the case of an adjustable 
beam deflecting system. 
The present invention has the goal of creating a process and a system of 
the type indicated above by means of which the focusing can be adjusted in 
one direction within certain limits, independently of the position of the 
beam in the direction transverse thereto or in which the adjusted focusing 
remains unaffected when the beam is shifted in the transverse direction 
indicated. 
In connection with the present invention, additional windings are of 
particular interest. 
It can be seen in particular from this that the components of the field 
vectors directed toward the opposing magnetic cores exert a deflecting 
effect on the electron beam in the direction transverse thereto and that, 
even temporarily without consideration of the electromagnets, the 
transverse components of the magnetic field vectors in question, of the 
fields between the opposing pairs of cores, act in opposition to each 
other. 
If now, by means of the system of electromagnets, the field in the air gap 
between one pair of cores is intensified and the one in the air gap 
between the other pair is weakened to the same extent, the deflecting 
field component in the direction from one core to the other remains 
constant precisely on one coordinate, such as on a plane of symmetry 
between the two air gaps of the pairs of cores, and then, in spite of the 
change in the field intensities, the electron beam remains unaffected by 
the deflecting field components in the direction from core to core, that 
is, by the pairs of cores, when, which is true only in the ideal case, the 
transverse extent of the electron beam is negligible. Otherwise, the 
deflecting forces acting on the electrons are different on the left from 
those on the right, and thus the point of greatest electron density shifts 
across the beam, which is equivalent to a change in beam deflection in the 
transverse direction and to a change in the way it is focused in this 
direction. 
This effect is ignored in the document mentioned. It is assumed that, when 
the field change mentioned occurs, the change in the components in the 
direction of the pairs of cores does not affect the beam. Advantage is 
taken of the change in the field vector components in the transverse 
direction. If, as explained by way of example, the field is intensified in 
the air gap of one of the pairs of cores but weakened in the other air gap 
of the other pair, the transverse vector components in the first air gap 
will now be dominant. 
This results in vector components in the transverse direction on both sides 
of the electron beam; these vector components are by definition parallel 
to each other and have opposing directions. This is how the focusing of 
the electron beam is influenced in the core pair direction. 
By means of the system just described, it is impossible to adjust the 
focusing of the beam without simultaneously changing how it is deflected. 
Nor is it possible to change the position of the beam transversely to the 
focusing effect without readjusting the focusing control fields. 
BRIEF DESCRIPTION OF THE INVENTION 
The present invention also has the goal of creating a process for 
controlling the focusing which itself has essentially no effect on the 
deflection of the beam. With such a process, it is possible to modulate 
the focusing in an electron-optic system essentially independently of the 
deflection. The control is intended to act directly and thus highly 
efficiently on the focusing, which also means that the focusing can be 
adjusted quickly and over a wide range of settings. 
This is achieved in accordance with the text of the characterizing portion 
of claim 1.

DETAILED DESCRIPTION OF THE INVENTION AND THE PREFERRED EMBODIMENT THEREOF 
FIG. 2 shows the spatial arrangement of the beam of monopolar charged 
particles S and the plane E.sub.1 transverse thereto, with the 
cross-sectional area Q through which the beam passes. The figure also 
shows the direction R, along which the extent of the beam cross-sectional 
surface Q is to be varied in a controlled manner, and the plane E.sub.2, 
which is perpendicular to plane E.sub.1 and to direction R, corresponding 
to the Y-axis in the xyz-coordinate system. According to the invention, a 
flux density field B is now applied on opposite sides of plane E.sub.2, 
the courses of these fields being essentially parallel to each other; on 
the one side of plane E.sub.2, the flux density field has one polarity, 
whereas on the other side the field has the other polarity. As a result of 
the two flux density fields B.sub.1 and B.sub.2 applied in accordance with 
the invention, a force F.sub.y is applied to the surface charge in the 
beam cross section Q on one side of plane E.sub.2, whereas on the other 
side of this plane a force -F.sub.y is exerted, so that, depending on the 
polarities of the two flux density fields B.sub.1 and B.sub.2, the forces 
have a compressive or expansive effect on cross-sectional area Q 
indicated. 
To the extent that fields B.sub.1 and B.sub.2 have essentially no curvature 
at least along the x-extent of area Q, the charge carriers at least in 
area Q experience essentially no forces in the x-direction; and when the 
field strength is modulated, that is, when the values of vectors B.sub.1 
and B.sub.2 and their polarity are adjusted, the extent of the surface 
charge Q is controlled in the y-direction. Under the assumption that the 
extent in the x-direction is held constant in that, as already mentioned, 
at least in this region the field curvature is negligible, the net effect 
is that the charge density (surface charge) is reduced by the expansion of 
area Q in the y-direction. 
But if, as entered in broken line, the flux density fields B.sub.1 and 
B.sub.2 applied in accordance with the invention are curved in the area of 
the extent of cross sectional area Q, the result is that components 
B.sub.y and -B.sub.y perpendicular to plane E.sub.2 are produced, as 
entered in the figure, from which it can be seen that, in this case, too, 
simple relationships develop, in that, whenever cross-sectional area Q is 
expanded in the y-direction, it is simultaneously compressed in the 
x-direction and vice versa. 
Nevertheless, so that changes in the extent of the surface in one direction 
(y) can be made independently of such changes in the other direction (x), 
in a preferred variant according to the text of claim 2 the condition of 
the parallelism of the two flux density fields B.sub.1 and B.sub.2 is 
satisfied at least over a region which corresponds to the extent of the 
cross-sectional area Q. In this way, a controlled change in flux density 
fields B.sub.1 and B.sub.2 does not lead to the formation of transverse 
components in the y-direction in these fields, as a result of which the 
charges in surface Q are also subjected to force only in the y-direction. 
In the evaluation of whether, during the control of the focusing the beam 
undergoes a deflection or not, it must first be defined when a change in 
the focusing is to be described as a beam deflection. A charge within the 
beam cross-sectional area Q experiences no force--the path of such a 
charge or of the corresponding particle thus remaining 
unaffected--wherever the flux density fields B.sub.1 and B.sub.2 applied 
according to the invention cancel each other out. Conversely, it is 
possible to describe as deflection the simple situation in which the 
position of the center of the charge intensity of all charges occurring 
instantaneously in plane E.sub.1 shifts. The position of the center of 
charge intensity of the charges in surface Q, considered at a single 
instant, does not change when the two flux density fields B.sub.1 and 
B.sub.2 on opposite sides of the second plane E.sub.2 are applied 
symmetrically in accordance with the text of claim 3 and this symmetry is 
preserved during the controlled change of the fields. 
This can be explained on the basis of FIG. 3. In FIG. 3, the effective 
values B.sub.1, B.sub.2 of the two flux density fields B.sub.1 and B.sub.2 
are plotted against the y-axis, on which the extent of the cross-sectional 
area Q is plotted. The course of these values is shown in a purely 
qualitative fashion and corresponds approximately to a curve which 
decreases with increasing distance from a magnetic dipole being generated. 
If plane E.sub.2 is laid through the center of charge intensity P of the 
surface charge on area Q, and if this center of charge intensity P is not 
to be changed when the surface extent in direction y is to be changed by 
the flux density fields applied in accordance with the invention, these 
two fields B.sub.1 and B.sub.2 are applied in such a way that they cancel 
each other out in plane E.sub.2. The resulting course is shown 
qualitatively as a dot-dash line. If now, furthermore, the two flux 
density fields B.sub.1 and B.sub.2 are laid out in such a way that their 
values .vertline.B.sub.1 .vertline., .vertline.B.sub.2 .vertline. are 
symmetric to plane E.sub.2, as shown in broken line, and if this condition 
is preserved even when there is a change in the fields, the net result is 
that the fields continue to cancel each other out one side, considered 
locally, at location P, and that forces of equal value act on the surface 
charge on opposite sides of plane E.sub.2, as a result of which the 
charges in area Q travel along paths which have been modified 
symmetrically with respect to plane E.sub.2. Thus the center of charge 
intensity remains at location P, and there is no deflection of the beam. 
The trough-like distribution of the resulting forces F.sub.y is shown 
qualitatively in FIG. 3 and in broken line for the opposite polarity. 
It is known from, for example, U.S. Pat. No. 4,064,352, already mentioned, 
that electron beams, as beams of charged particles, can be directed in 
vacuum systems along a curved path from the beam generator onto the 
material to be vaporized. In some cases, this can be done by a good deal 
more than 180.degree. and even by as much as 270.degree. or more. To be 
able to realize this, it is necessary, in principle again by means of a 
magnetic flux density field, to apply force along extended sections of the 
beam path. This frequently means that flux density fields with the 
deflecting function indicated must be applied at a very early point, that 
is, very close to the beam generator, to achieve the large amount of 
deflection ultimately desired. For the sake of the type of deflection 
indicated and for the type of focusing control being discussed here, it is 
therefore impossible in many cases--including cases in which it is a goal 
to reduce the size of the electron optics to a desirable compactness--to 
shift the point at which the deflecting force is exerted to a location far 
enough away from where the focusing of the beam is controlled that, as a 
result of the deflection and its adjustment to change the position of the 
impact area of the beam on the material to be vaporized, the focusing of 
the beam is not also changed. 
As can be seen from FIG. 3, when, as a result of these deflection measures 
the position of surface Q is changed, the corresponding surface charges 
enter into the changing relationships of the field applied according to 
the invention, as a result of which changes in the focusing occur in 
concert with the deflection. In view of these requirements, it is also 
frequently essential to be able to deflect the beam at least in one 
direction, without at the same time changing the focusing relationships. 
It is clear from FIG. 2 that this can be done easily by the use of a 
procedure according to the present invention: 
Under the conditions shown in FIG. 2 for the two flux density fields 
B.sub.1 and B.sub.2 applied according to the invention, it is possible to 
shift the beam and thus its cross-sectional area Q in the x-direction 
without at the same time affecting the changes in the focusing which have 
been controlled in accordance with the invention in the y-direction. From 
this it can be seen that another preferred embodiment of the process 
according to the invention in accordance with the text of claim 4 consists 
in that the fields on either side of the second plane are applied in a 
constant manner over a region which is considerably longer than the extent 
of the cross-sectional area Q in such a way that the field relationships 
remain unchanged in the area in question and proceeding from that area in 
the x or -x direction. When, for example, the beam is now to be deflected 
over a large angle and this deflection is to be carried out in plane 
E.sub.2, this can be accomplished even before the focusing is adjusted in 
accordance with the invention and can also be modified so as to change the 
position of the impact area without in this way having any effect on the 
focusing adjustment in accordance with the invention. 
When we consider the course of the values .vertline.B.sub.1 .vertline., 
.vertline.B.sub.2 .vertline. of the applied flux density fields according 
to FIG. 3, it can be seen that in this way a three-dimensional surface is 
bracketed, with a valley extending in the x-direction, the sides of which 
rise up. 
In many cases it can be desirable to be able to control the focusing of the 
beam in several directions, such as in two directions perpendicular to 
each other, either independently of each other or with one being 
controlled as a function of the other, that is, in principle and in 
accordance with FIG. 2, both in the y-direction and in the x-direction. 
For this purpose, it is proposed in accordance with claim 5 that, with 
respect to a third plane, namely E.sub.3 in FIG. 2, which is perpendicular 
to the first plane E.sub.1 and to the second plane E.sub.2 and which is 
aligned in direction R, a second flux density field is applied with 
parallel vector components of opposite polarity on the two sides and 
preferably with values which are symmetrical to the third plane. A second 
flux density field of this type corresponds to the fields already entered 
in FIG. 2, indicated in broken line as B.sub.y and -B.sub.y, which are 
produced when, as explained above, the first flux density field B.sub.1, 
B.sub.2, as also entered in solid line in FIG. 2, is curved. 
The first magnetic flux density field with its components B.sub.1, B.sub.2 
according to FIG. 2 are entered in FIG. 4 in the form of a top view onto a 
diagram analogous to FIG. 2. The second flux density field with its 
components B.sub.3, B.sub.4 is also shown. In the constellation according 
to FIG. 4, the polarities of the flux density fields B alternate as one 
travels around cross-sectional surface Q. In this way, the force 
relationships, also shown in FIG. 4, are produced; that is, when the 
polarity relationships are preserved, surface Q is compressed or stretched 
in the one direction x or y while it is stretched or compressed in the 
other direction y or x. This field polarity constellation can be realized 
easily by the provision of two magnetic dipoles, as can be seen from the 
distribution of the poles around surface Q. 
A design of the flux density fields corresponding to claim 5 is shown in 
FIG. 5. The diagram is analogous to FIG. 4. In this case, as one travels 
around cross-sectional surface Q, the polarities of the flux density field 
components B.sub.1 to B.sub.4 do not alternate. In this constellation of 
the polarities, all forces brought about by the field components act, as 
shown, either outward or inward, as a result of which a centro-symmetric 
expansion or contraction of cross-sectional surface Q is made possible. 
This polarity constellation cannot, as is readily evident from the 
illustration of the magnetic poles, be realized by means of two magnetic 
dipoles. Additional measures must be taken for this purpose, such as those 
to be explained in connection with FIG. 7. 
If as a result of the applied second flux density field with its components 
B.sub.3 and B.sub.4 in the two polarity distributions according to FIGS. 4 
and 5, only the focusing of the beam corresponding to a change in its 
cross-sectional surface Q in the x or -x-direction is to be effected, this 
second flux density field is applied in a parallel manner at least over a 
distance corresponding to the extent of surface Q in the y-direction, 
according to the text of claim 6. With respect to the preferred symmetric 
pattern of the values of the second applied flux density field specified 
in claim 5, the considerations presented on the basis of FIG. 3 for the 
first applied flux density field apply: This is a requirement as long as 
the goal is to preserve the original location of the center of charge 
intensity of the surface charges situated at that moment in surface Q. 
If according to claim 7 the second applied flux density field is also 
applied in such a way that the fields on either side of the third plane 
are constant over an area which is considerably longer than the extent of 
cross-sectional surface Q, then according to FIGS. 4 and 5 the change in 
the focusing in the x-direction by the second flux density field with its 
components B.sub.3, B.sub.4 is not affected by a deflection of the beam in 
the y direction, which brings about a local displacement of 
cross-sectional surface Q. The combination that, namely, the focusing in 
the y-direction caused by the first flux density field B.sub.1, B.sub.2 is 
not affected by a shift in surface Q or of the beam in the x-direction and 
that the focusing in the x-direction brought about by the second flux 
density field with its components B.sub.3, B.sub.4 is not affected by a 
shift in cross-sectional surface Q and thus of the beam in the y-direction 
is desirable in many cases, so that in particular the focusing control 
fields can be balanced more easily at a working point of the beam, around 
which it is deflected again in the x- and y-directions during operation. 
The polarity distribution according to FIG. 4 can offer considerable 
advantages in certain applications. In many applications of electron 
beams, as already mentioned, it is frequent practice to bring about a 
significant deflection of the beam in one plane. With the design of the 
first flux density field according to the invention with components 
B.sub.1, B.sub.2 according to FIG. 2, it is advisable, as shown in the top 
view of FIG. 6a, to achieve this deflection of beam S in the second plane 
E.sub.2. FIG. 6b shows a side view of the course of beam S in plane 
E.sub.2. With a deflection like this, an area K, in which the beam is 
constricted, is usually formed, as is also known from U.S. Pat. No. 
4,064,352 and as shown in the side view of FIG. 6b. A constriction of this 
type does not occur in many cases when seen from the top, that is, in 
deflection plane E.sub.2. 
Optimum advantage can be taken of these relationships only when one 
proceeds in accordance with FIG. 4 and in correspondence with claim 8. 
When according to FIG. 4 the flux density field B.sub.1, B.sub.2 is used 
to expand cross-sectional surface Q and thus to expand the beam in the 
y-direction, the relationships shown in broken line in FIG. 6a are 
produced. At the same time, it is possible to use the second applied flux 
density field with the components B.sub.3, B.sub.4 --coupled directly to 
the first flux density field--to compress cross-sectional surface Q. The 
cross-sectional surfaces Q' shown in broken line in FIG. 6a are the 
result. 
Looking at FIG. 6b, however, we see that, when cross-sectional area Q is 
reduced in the x-direction, constricted region K is shifted, for example, 
to region K', that is, closer to the source of the beam. This is analogous 
to the shift of a focal point closer to a source of the beam. In this way, 
the inverse effect is produced on the target, e.g., the material M to be 
vaporized, as seen in the x-direction, i.e., in plane E.sub.2 ; that is, 
when cross-sectional surface Q is compressed in this direction, the impact 
surface on material M is enlarged because of the shift of constricted 
region K'. Thus the advantage of the polarity selection shown in FIG. 4, 
in particular in the case of a large deflection of electron beam S in 
question by more than 90.degree., especially by more than 180.degree., 
becomes evident: Precisely through this choice of polarity, impact surface 
Z in FIG. 6 is expanded or compressed radially in all directions. The 
resulting qualitative distribution of the beam is also shown in FIG. 6b in 
broken line. The position of the constricted region, in the sense of a 
working point around which this position is changed by adjusting the 
focus, is determined essentially by the beam generator and by the 
electron-optic measures used to shape the beam. 
Whereas--as will be explained further below--in the choice of a polarity 
configuration according to FIG. 5, this is realized preferably in that the 
first flux density field B.sub.1, B.sub.2 and the second flux density 
field B.sub.3, B.sub.4 are applied with an offset along the axis of the 
beam, in the embodiment according to FIG. 4 the two flux density fields 
are applied in essentially the same plane, i.e., in the first plane 
E.sub.1, according to claim 9. 
If in the polarity configuration according to FIG. 4 or FIG. 5 the goal is 
to be able to modulate the first flux density field B.sub.1, B.sub.2 
independently of the second B.sub.3, B.sub.4, then, according to FIG. 7 
and the text of claim 10, the first flux density field B.sub.1, B.sub.2 is 
applied with an offset in the direction of propagation of beam S with 
respect to the second flux density field B.sub.3, B.sub.4. It is 
preferable to provide magnetic shielding Sch between the two flux density 
fields, so that the two fields cannot affect each other. This procedure is 
indicated in any case in the polarity selection according to FIG. 5. 
Nevertheless, this configuration can also be implemented by the 
time-staggered generation of field B.sub.1, B.sub.2 on the one hand and 
field B.sub.3, B.sub.4 on the other in plane E.sub.1. 
FIG. 8 is a schematic diagram showing by way of example a system according 
to the invention for controlling the focusing. It comprises an array of 
magnets, which is designed in principle so that the vector components of 
the flux density field generated by the magnet array, as explained on the 
basis of FIGS. 2 and 3, are produced. Preferably the array of magnets is 
formed by a pair of dipoles 3, 5, which are preferably formed by 
electromagnetic systems, each one supplied via power sources 7, 9, which 
are controlled by a control unit 11. Dipoles 3, 5 can also, however, for 
the sake of adjusting the focusing for different working points, for 
example, be formed by permanent magnets or include permanent magnets. In 
the system, a region 13 is defined, through which beam S of monopolar 
charged particles, electrons in particular, is sent. For this purpose, the 
position of a beam generator 15, illustrated schematically in FIG. 8, is 
fixed or fixable with respect to the dipole array consisting of dipoles 3, 
5, such as by means of an adjustable mounting device for beam generator 
15, so that the generator can be held in a defined position with respect 
to dipoles 3, 5. A corresponding fixed installation of dipoles 3, 5 and of 
beam generator 15 is shown schematically at 16. As can be seen from FIG. 
8, the two dipoles 3, 5 generate in principle the components B.sub.1, 
B.sub.2 of the flux density field explained in FIG. 2, laid out with 
respect to region 13 for beam S as already explained on the basis of FIG. 
2 with respect to beam S. According to the text of claim 14, the goal of a 
preferred embodiment of the invention is to shape the course of flux 
density field B.sub.1, B.sub.2 on opposite sides of plane E.sub.2, also 
entered in FIG. 8, in such a way that the components are essentially 
parallel in a region which is at least the same as the diameter of beam 
cross-sectional surface Q, formed by the beam S passing through region 13. 
As can be easily seen from FIG. 8, in this simple way the goal is achieved 
that the length of dipole 3 or 5, considered in the x-direction, is much 
larger than the extent, considered in the x-direction, of cross-sectional 
surface Q of beam S passing through the intended region 13. 
By means of control unit 11, flux density components B.sub.1, B.sub.2 on 
either side of region 13 where beam S passes through, that is, on either 
side of plane E.sub.2, are controlled in such a way that the values of the 
flux density fields on either side of this plane E.sub.2 are symmetric 
with respect to each other. In this way, according to the explanation of 
FIG. 3, it is achieved that, when beam cross-sectional area Q is changed 
in the y-direction by the controlling flux density fields B.sub.1, 
B.sub.2, the center of charge intensity of the surface charge present at 
that moment in area Q remains unchanged. The control of flux density 
fields B.sub.1, B.sub.2 such that this condition is fulfilled is carried 
out as a function of the geometric alignment of the two magnetic dipoles 
3, 5 with respect to plane E.sub.1, wherein cross-sectional area Q of beam 
S is to be effectively adjusted, by means of the appropriate choice or 
control of the currents generated by power sources 7, 9. 
To achieve, furthermore, that the control in the y-direction of beam 
cross-sectional area Q of the beam passing through region 13 by means of 
magnet systems 3, 5 remains independent over a relatively long distance, 
considered in the x-direction, of the position of beam S in the 
x-direction, the magnetic field arrangement, preferably consisting of the 
two dipoles 3, 5, is designed in such a way that the course of flux 
density field B.sub.1, B.sub.2 is constant on either side of the indicated 
second plane E.sub.2 over an area which is considerably longer than the 
extent of cross-sectional surface Q of beam S. This is in turn 
accomplished by the correspondingly long extent of magnetic dipoles 3, 5, 
seen in the x-direction. 
Although it is quite possible to generate the course of the flux density 
field according to FIG. 2 by the 3-dimensional superimposition of several 
flux density fields, it is preferable, as shown in FIG. 8, to produce this 
field by means of an array of magnets with two magnetic dipoles, namely, 
dipoles 3, 5, which are essentially parallel to the second plane. These 
two dipoles do not initially need to be in plane E.sub.1, nor do they need 
to be symmetric with respect to plane E.sub.2. That is, the relative 
geometric position of dipoles 3, 5 with respect to their effective range, 
namely, the area of the intersection between planes E.sub.1 and E.sub.2, 
can be freely selected within wide limits while still ensuring that the 
flux density fields assume the desired configuration according to the 
invention in the effective area by means of the corresponding electrical 
modulation of the array of magnets. 
Nevertheless, it may be necessary to take into account complicated spatial 
field superimpositions in some cases. If not necessary for other reasons, 
such as construction-related boundary conditions, one will therefore set 
up the two magnetic dipoles, as shown in FIG. 8, essentially in the first 
plane E.sub.1, according to the text of claim 18. Then the field 
relationships are clear and logical. Even in this case, however, the two 
dipoles 3, 5 do not necessarily have to be symmetric to the second plane 
E.sub.2, and it is obvious that an asymmetry can be compensated by the 
appropriate asymmetric modulation or asymmetric windings of power sources 
7, 9 or of the electromagnets. Furthermore, unless there are no other 
boundary conditions such as design-related ones with respect to beam 
generator 15, one will preferably set up the magnetic dipoles lying in the 
first plane symmetrically with respect to the second plane as illustrated 
in FIG. 8 and as stated in claim 19. 
FIG. 9 shows essentially a diagram of certain parts of the system according 
to FIG. 8 again. As explained previously, the control of the beam in the 
y-direction achieved in accordance with the invention by the two dipoles 
3, 5 is, depending on the design of the dipoles and depending in 
particular on their length in the x-direction, almost completely 
independent of the position of the beam in the x-direction. If now, as is 
known, for example, from U.S. Pat. Nos. 4,064,352 and 3,420,977, the beam 
is subjected to a strong deflection, namely, to such an extent that 
deflecting forces must be exerted on the beam shortly after it leaves the 
beam generator, corresponding to 15 in FIG. 9, to bring the beam to its 
goal within a reasonably short distance, it is proposed that a deflection 
of this sort can be undertaken in accordance with the text of claim 20 
essentially in the second plane. 
This is illustrated in FIG. 9, wherein the deflecting device, such as that 
according to U.S. Pat. No. 3,420,977, generates a deflecting flux density 
field B.sub.U, which extends essentially in the y-direction as shown in 
FIG. 9. In this way, as shown in broken line, beam S is deflected to an 
ever-increasing extent and can undergo a deflection up to 270.degree. or 
even more. Because a deflection device of this type generating deflecting 
field B.sub.U must be effective very soon after the beam leaves generator 
15 so that the beam can be deflected within the shortest possible 
distance, as required, it will be necessary to anticipate shifts of beam S 
in the x-direction even when the focusing control according to the 
invention is used, specifically when the deflection is modulated to shift 
the beam over the target. 
Because the control of the focusing in the x-direction brought about 
according to the invention is essentially independent of the position of 
the beam in this direction, the deflection is therefore carried out 
preferably in plane E.sub.2. 
On the basis of FIGS. 4, 5, and 6 we have discussed the effects which occur 
when, in addition to the indicated first flux density field B.sub.1, 
B.sub.2, a second flux density field B.sub.3, B.sub.4 is applied 
perpendicular to the first. 
FIG. 10 is a schematic diagram of the system of two dipoles 3, 5, seen from 
the top, according to FIGS. 8 and 9. Depending on the distance between the 
two dipoles 3, 5 in the y-direction and their length in the x-direction, 
flux density fields B.sub.3, B.sub.4, which also act on the intended 
pass-through region 13 for beam S with its cross-sectional surface Q, are 
created, as shown schematically in FIG. 4. Thus, as a result of the 
appropriate dimensioning of the system with dipoles 3, 5, the flux density 
field configuration according to FIG. 4 with the field polarities shown 
there is achieved directly; therefore, the advantages pertaining to the 
inversion of target surface size changes with respect to cross-sectional 
surface size changes of Q are also obtained. 
In principle, therefore, when the system includes a device for generating a 
beam such as an electron-optical system (depending on the type of 
particles constituting the beam) which generates at least one constricted 
area in the direction in which the beam propagates, as already explained 
on the basis of FIG. 6, the goal is to coordinate the array of magnets, as 
already explained on the basis of FIGS. 8, 9, and 10; the device such as 
the deflecting device shown in FIG. 9; and a beam generator of a known 
design in such a way that a change in the cross-sectional surface near the 
area of influence of the magnetic flux densities B.sub.1 -B.sub.4 brought 
about by the array of magnets with dipoles 3, 5 has an inverse effect on a 
change in the diameter of a beam target surface, at least in one 
direction, as explained in detail on the basis of FIG. 6. This is achieved 
by means of the system according to FIG. 10 in the case of a deflecting 
device and a beam generator, which produce a constricted area according to 
FIG. 6b. 
FIG. 11 shows in the form of a schematic diagram an array of magnets which 
makes it possible to modulate the flux density B.sub.1, B.sub.2 and the 
additional flux density B.sub.3, B.sub.4 perpendicular thereto 
independently of each other. For this purpose, the two dipoles 3, 5 are 
provided first in the direction of propagation of beam S; and then, with a 
certain offset in the direction of beam propagation, additional dipoles 
23, 25 are provided, perpendicular to dipoles 3, 5. These additional 
dipoles modulate the flux density field B.sub.3, B.sub.4 according to FIG. 
5 or FIG. 4. Through the provision of a magnetic shield 27 with a 
through-opening 29 for the beam, the two flux density fields B.sub.1, 
B.sub.2 and B.sub.3, B.sub.4 to be modulated independently of each other 
are almost completely decoupled from each other. In this way, it is 
possible to control the beam in terms of its focusing independently of 
each other both in the x-direction and in the y-direction. As shown 
schematically at 16, the two pairs of dipoles 3, 5 and 23, 25 are fixed in 
place with respect to the region intended for the beam. 
FIG. 12 is a schematic diagram of a preferred design of a system according 
to the invention. Two electromagnets 33, 35, corresponding to dipoles 3, 5 
of FIG. 8, 9, or 10, are parallel to each other, each embedded in its own 
cheek-like holder 37, 39. Holders 37, 39 are made of nonferromagnetic 
material, at least in the area of electromagnets 33, 35, but, so that they 
can also be cooled efficiently, they are preferably composed of portions 
of different metals, especially of portions of copper and stainless steel. 
In a schematic manner, a holding system for a beam generator 41 is shown, 
which emits beam S, in particular an electron beam, centrally between 
holders 37, 39. The field configuration with flux density field B.sub.1, 
B.sub.2 is shown by way of example in FIG. 12, as is the effect of the 
transverse field B.sub.3. 
By means of the system according to the invention and the process according 
to the invention, it was possible to adjust the cross-sectional extent of 
the beam on the target over a range of 1:10, e.g., from a focal point 
diameter of 5 mm to one of 50 mm, even when the beam was deflected by as 
much as about 270.degree.. This could be accomplished dynamically at 
adjusting frequencies of up to 1 kHz. Thus it is also possible to pulse 
the focusing of the beam if desired. A latitude of modification, change 
and substitution is intended in the foregoing disclosure, and in some 
instances, some features of the invention will be employed without a 
corresponding use of other features. Accordingly, it is appropriate that 
the appended claims be construed broadly and in a manner consistent with 
the spirit and scope of the invention therein.