Device For Recording With Electron Rays

Abstract

A device is disclosed for recording image elements, by exposing recording material, at constant current density with the aid of a focused electron beam provided with means before the last focusing device for varying the shape and/or size, in the recording plane, the cross section of the electron beam in conformity with image signals.

Description

The invention relates to a device for binary recording with the aid of an electron beam provided with an electron source for producing the beam, a means for focusing the beam, electron optical means for shaping the beam and for exposing the recording material with the beam at virtually constant current density and means for displacing the recording material and the beam relatively to each other.

Similar devices are known. On the one hand devices are known for exposing a photographic emulsion or a photolacquer for making a mask. On the other hand arrangements are known for exposing a photographic emulsion or photolacquer for carrying out direct processes on circuits.

In the case of the device for making a mask, the mask to be made is a reduced image of a material mask previously placed between the condenser lens and the intermediate lens. If, therefore, it is desired to make masks of a different shape, the material mask must be replaced by a material mask of that shape. In the case of the device for carrying out processes on circuits, the processes are guided by a computer control tape. During exposure the beam is focused on the workpiece and then always has practically the same shape and cross section. The required pattern is produced by deflecting the focused beam.

It is the object of the invention to provide a different method of making a pattern, which has proved to have many additional advantages.

For this purpose, the invention is characterized by means of varying the shape and/or size of the cross section of the electron beam in the recording plane, forming the exposing part in an image element.

The required pattern is produced by dividing this pattern into image elements and by making exposures in these elements with the beam, with a beam cross section varying locally in size and shape, the beam being controlled for this by a programmed computer or by a scanned model.

In one embodiment the electron beam cross section is controlled by a biprism placed between the electron source and the focusing device, the biprism being an electrostatic prism across which the voltage differential can be modulated.

Application of this control system results in two point focuses of the source at each side of the original focus, each having half the intensity and the distance between them being proportional to the modulation. By applying two quadrupole lenses in succession in the direction of the beam, the point focuses are changed into line focuses. Such a system with line focuses and a diaphragm located before the recording plane is particularly suitable for use in binary recording.

In another embodiment the electron beam cross section is controlled by modulation of a deflecting device located between a diaphragm and a focusing device with a second diaphragm aligned with the first diaphragm and located in the image plane of this focusing device.

The means used in this embodiment are applied instead of and in the place of the biprism mentioned in the first embodiment.

The invention will be further elucidated by reference to a drawing with nine figures for these and other embodiments and details.

FIG. 1 shows the path of the beam when imaging with two quadrupole lenses.

FIG. 2 shows a quadrupole lens diagrammatically.

FIG. 3 shows a circuit for feeding a quadrupole lens.

FIG. 4 shows a biprism.

FIG. 5 is a sketch showing the principle of the path of the beam in an exposure apparatus with a biprism and quadrupole lenses.

FIG. 6 shows a slightly different beam path diagrammatically in a single plane and with means added for inverting the exposed image.

FIG. 7 shows the beam path for an apparatus in which the means comprise two half diaphragms, a deflector and a focusing device.

FIGS. 7a and 7b show the operation of the regulated deflecting system P in FIG. 7.

FIG. 8 shows three embodiments of diaphragms applicable in apparatus with a beam as in FIG. 7.

FIG. 9 shows an exposure apparatus in perspective.

In the figures, identical numbers and letters relate to identical elements.

FIG. 1 shows three rays, 1, 2 and 3 of a diverging beam transmitted by source B and converging at point C.

Rays 1 and 3 and rays 2 and 3 are in planes which are at an angle of 90.degree..

Lines A.sub.1 and A.sub.2 show diagrammatically the strength of the quadrupole lenses and the quadrupole lenses themselves, which provide the image C of source B.

The arrows 4, 5, 6 and 7 in lines A.sub. 1 and A.sub.2 indicate the direction of focusing and defocusing of the beam.

Arrow 4, for instance, indicates that the beam in the plane of rays 2 and 3 is further diverged by the first lens and arrow 5 indicates that the beam in the plane of rays 1 and 3 is converged by the first lens.

The quadrupole lenses A.sub.1 and A.sub.2 therefore focus in one plane and hence defocus in the plane practically perpendicular thereto.

Each quadrupole lens A.sub.1 and A.sub.2 consists of four coils 8, 9, 10 and 11, see FIG. 2, designed separately.

The strength of the lens is calculated from the imaging and enlarging requirements and is determined by the column dimensions.

The current through a coil 8, 9, 10 and 11 of the lens is determined with the aid of the formulae:

in which f.sub.x and f.sub.y are the focal lengths in the focusing and defocusing direction and in which .beta..sup.2 is given as a parameter of the lens by

in which

ni = the number of ampere windings per coil.

u = the accelerating potential of the electrons in volts.

1 = the length of the coil parallel to the system axis.

r = the distance from the coil to the axis.

The circuit for the coils of a lens is shown in FIG. 3.

In order to correct the first order deflection fault, both north and south poles are included in a simple balanced circuit. The location of the two lenses follows from the imaging and enlarging requirements.

In the embodiment of an exposure installation shown in FIG. 5 a biprism as shown in FIG. 4 is connected before the quadrupole lenses A.sub.1 and A.sub.2.

The biprism consists of a hollow cylinder 15 and a tungsten wire 16.

The cylinder 15 is provided with an opening 17 to let through beam 19 and an opening 18 to let through beams 19.sub.1 and 19.sub.2.

Beams 19.sub.1 and 19.sub.2 are obtained by applying a voltage differential across the biprism.

In this way, two virtual sources arise and, depending upon the voltage differential, these virtual sources will either overlap or not.

Owing to a slit diaphragm being applied as a Wehnelt opening in the electron source of FIG. 5, an elliptical crossover of the source is obtained.

The ratio between the two main axes is then about 1:3, which is an improvement on the customary case with a round Wehnelt opening, in which the ratio may be as high as 2:3.

The line source B so obtained forms, with the aid of the biprism of which only wire 16 is shown, two virtual line sources B.sub.1 and B.sub.2 for the quadrupole lenses A.sub.1 and A.sub.2 which image the sources B.sub.1 and B.sub.2 at C.sub.1 and C.sub.2 on coated roll 20.

Images C.sub.1 and C.sub.2 consist of line images about 100 microns long and only a few microns wide.

Owing to the position and the energizing of the two quadrupole lenses A.sub.1 and A.sub.2, the enlargement can be varied within wide limits in both main axis directions.

For this purpose the quadripole lenses are rotatable about and axially movable along a tube.

By regulating the voltage differential across the biprism, the distance d between images C.sub.1 and C.sub.2 is regulated and thereby the Kodak Photo Resist or some other exposable material applied as a thin coating on roll 20 is exposed.

Coated roll 20 rotates at a constant speed under images C.sub.1 and C.sub.2, moving axially at the rate of 0.14 mm. per rotation.

Because of the 0.14-mm. pitch of coated roll 20 and the track thereby described on roll 20 of the line images C.sub.1 and C.sub.2, a 0.15-mm. diaphragm D.sub.2 is applied immediately above roll 20 to prevent the tracks overlapping.

Owing to the presence of diaphragm D.sub.2, the cross section of the electron beam in the recording plane is varied owing to modulation on roll 20 as shown (See exposed tracks E).

To limit the margin of error in imaging due to lens aberrations, especially owing to spherical aberration, the beam is diaphragmed through diaphragm D.sub.1.

The exposed coated roll 20 can if desired be gravured by etching, the unexposed parts being etched after development of the K.P.R. coating, each image element of a form thus containing for instance one or more ink cells with different surface areas and/or different depths.

FIG. 6 shows diagrammatically the path of the beam for a device with inverted line imaging.

In this device the biprism 16 is located after the first quadrupole lens A, in order to increase sensitivity. In the absence of modulation of biprism 16, images C.sub.1 and C.sub.2 coincide on mask F. There is then no exposure on the coated roll 20.

Upon modulation, images C.sub.1 and C.sub.2 fall partly or entirely outside mask F.

The second biprism G and the rotational-symmetric lens H combine these images C.sub.1 and C.sub.2 again to a line image I, whose length is determined by modulation and with which coated roll 20 is exposed.

FIG. 7 shows the path of the beam, again in a different arrangement.

Source B is imaged by the rotational-symmetric lens K in the plane of the rotational-symmetric lens N.

A diaphragm L, embodiments of which are drawn in FIG. 8, intercepts part of the beam.

A deflection system M, to which a modulating signal can be connected is located before lens N.

Behind lens N, there is a diaphragm O.

In the absence of modulation of system M, the image in the plane of lens N will be imaged unimpeded through diaphragm O on roll 20, with the aid of the rotational-symmetric lens H.

The continuous lines converging in image element R show the path of the beam in this situation.

If the system M is modulated, however, part of the beam will be intercepted by diaphragm O.

The broken lines converging in image element R' show the path of the beam for this.

Deflection system P is coupled to system M and is applied to ensure that the centers of gravity of the image elements are aligned on the cylinder.

FIG. 7a gives an example of this for line image elements in the absence of deflection system P.

FIG. 7b gives an example of image elements in the form of squares, in which, with the regulated system P for example, the centers of gravity are shown on a straight line z.

Upon application in FIG. 7 of a diaphragm L, O of the type shown in FIG. 8a, image elements R are obtained in the form of a line whose length varies with modulation.

Upon application of a diaphragm of the type shown in FIG. 8b, these become squares whose size varies with modulation. And upon application of a diaphragm of the type shown in FIG. 8c the image elements form a squared pattern with a constant number of squares varying in size with modulation.

FIG. 9 shows diagrammatically and in perspective an arrangement according to the invention with a beam path corresponding to that of FIG. 6 using slit lenses S and T instead of the quadrupole lenses A.sub.1 and A.sub.2.

The modulating signal can, of course, be adapted electronically to the standards required for good reproduction of the halftones in the resulting print.

This is very important because the signal of the device scanning the original will not be linear with the quantity of ink which must be transferred per ink cell from the printing cylinder to the copy.

With this system, local corrections are of course also possible.

Claims

We claim:

1. A device for binary recording with the aid of an electron beam comprising an electron source for producing said electron beam, a recording medium, a means for focusing the central axis of said beam on said recording medium, electron optical means for shaping said beam and for exposing said recording medium with said beam, means for displacing said recording medium and said beam relatively to each other, and means for varying the cross section of said electron beam on said recording medium with respect to said central axis to form an image thereon at substantially constant current density.

2. A device as claimed in claim 1 further comprising two electrostatic slit lenses located in succession in the direction of said beam from said electron source to said recording medium.

3. A device as claimed in claim 1 wherein said electron source includes a slit diaphragm.

4. A device as claimed in claim 1 further comprising a diaphragm located in front of said recording medium.

5. A device as claimed in claim 1, wherein said means for varying the cross section of the beam comprises a biprism located to intersect said beam and a modulator for controlling said biprism to deflect said beam.

6. A device as claimed in claim 5, wherein said means for varying furthermore includes in succession from said electron source to said recording image a mask located in the image plane of said means for focusing, a second biprism, and a second focusing means.

7. A device as claimed in claim 5, wherein said biprism is an electrostatic prism in the form of a cylindrical condenser with an inner conductor, and said modulator modulates the voltage differential across said inner conductor.

8. A device as claimed in claim 1 further comprising two quadrupole lenses located in succession in the direction of said beam from said electron source to said recording medium.

9. A device as claimed in claim 8, wherein said quadrupole lenses are magnetic lenses and further comprising means for rotating and axially displacing said quadrupole lenses with respect to the central axis of said beam.

10. A device as claimed in claim 8 further comprising a diaphragm located in the principal plane of one of said quadrupole lenses.

11. A device as claimed in claim 1, wherein said means for varying the cross section of said beam are located between said electron source and said means for focusing and comprise in succession from said electron source to said recording medium a first diaphragm, a deflector, a second focusing means and a second diaphragm in alignment with said first diaphragm in the image plane of said second focusing means.

12. A device as claimed in claim 11, wherein the diaphragms are segments of a circle.

13. A device as claimed in claim 11, wherein the diaphragms are gauzes.