US3717785A

US3717785A - System of electrostatic quadrupole micro-lenses

Info

Publication number: US3717785A
Application number: US00107720A
Authority: US
Inventors: G Guernet
Original assignee: Commissariat a lEnergie Atomique CEA
Current assignee: Commissariat a lEnergie Atomique et aux Energies Alternatives CEA
Priority date: 1970-01-20
Filing date: 1971-01-19
Publication date: 1973-02-20
Anticipated expiration: 1990-02-20
Also published as: DE2102608A1; NL7100748A; FR2122684A6; GB1305523A; FR2076567A5

Abstract

The system comprises an array of parallel filiform electrodes and each micro-lens is made up of at least four adjacent electrodes which define a tunnel having a cross-section in the shape of a square. Each vertex of the square is intercepted by a quarter-circle of the cross-section of the adjacent one of said electrodes and the cross-section of said array in a plane at right angles to said electrodes forms a substantially square lattice. Means are also provided for electrically polarizing said electrodes.

Description

United States Patent 1 1 Guernet [451 Feb. 20, 1973 s41 SYSTEM OF ELECTROSTATIC 3,497,744 2 1970 Himmelbauer et a1. .313/78 QUADRUPOLE MICRO-LENSES 3,612,946 10 1971 Toyoda ..313 103 x [75] Inventor: Georges Guernet, Grenoble, France OTHER PUBLICATIONS 1 1 Assignee: com'lfissariat A LEmrgie IEE Transactions on Microwave Theory & Techniques 's Pam, France vol. MTT-l4, No. 12 Dec. 1966 pp. 657665 [22] Filed: Jan. 19, 1971 350-175GN A Light Beam Waveguide Using Hyperbolic-Type Gas Lenses by Suematsu et a1. [21] Appl. No.: 107,720

Primary ExaminerNathan Kaufman 30 Foreign Application Priority Data Attorney-Cameron, Kerkam & S n

Jan. 20, 1970 France ..7001862 [57] ABSTRACT [52] U.S. C1. ..3l3/23l, 313/78, 313/63, The system comprises an array of parallel filiform /495 electrodes and each micro-lens is made up of at least [51] Int. Cl. ..H01j 17/26, Holj 61/28 four adjacent electrodes which define a tunnel having 1 Field of Search a cross-section in the shape of a square. Each vertex 313/75, 105! 107-5, 103; M C, of the square is intercepted by a quarter-circle of the DS; 330/4-7 cross-section of the adjacent one of said electrodes and the cross-section of said array in a plane at right [56] References Cted angles to said electrodes forms a substantially square UNITED STATES PATENTS lattice. Means are also provided for electrically polarizing said electrodes. 2,919,381 12/1959 Glaser ..250/49.5 C X 2,941,114 6/1960 Cook ..3l3/83 X 11 Claims, 4 Drawing Figures M/C/PO-BEA/ s f [LECTF/CAILY INSULATING MATERIAL i PRINTED C/kCU/T INSULATING MATfR/AL MEANS TO POLARIZE THE ELECTRODES 1 ELECTRIC CONNECTIONS RINTED CIRCUITS \DC VOLTAGE SOURCE v CIRCUITS PmEmEnFwaoms 3,717, 785

SHEET 2 BF 3 I B MEANS TO POLARIZE THE ELECTRODES 1 ELECTRIC CONNE OF PRINTED v ELEC c CONNE 0 OF PRINTED CIRCUITS lllli PATENTEDFEBZOQH 5717. 7 85 sum 3 or 3 SYSTEM OF ELECTROSTATIC QUADRUPOLE MICRO-LENSES This invention is concerned with a system of electrostatic quadrupole micro-lenses, that is to say an assembly of electrostatic lenses of very small size, each lens being made up of four electric poles. This system makes it possible to obtain at the same time from a beam of electrically charged particles of large crosssectional area a plurality of micro-beams of small crosssectional area which are parallel to each other and convergent.

Quadrupole lenses are employed for the purpose of focusing a beam of charged particles and said particles can be either ions or electrons. Modification of the charged-particle paths is obtained by means of four electrodes which are usually placed symmetrically with respect to the axis of the incident beam. These electrodes are metallic and usually have a hyperbolic shape. Said electrodes are polarized by applying thereto an electric voltage having a value which depends on the nature and velocity of the particles as well as on the angle of convergence to be given to the particle beam. In some applications such as ion implantation of charged particles in semiconductor material, it is of interest to have available at the same time micro-beams of small cross-sectional area which are parallel to each other and focused, the distance between two adjacent microbeams being very small (a few millimeters, for example). The design concept of electrostatic lenses of the prior art is such that the electrodes are usually of large size. In order to obtain simultaneously a plurality of micro-beams from a beam of incident particles of substantial cross-sectional area, it would be necessary in the case of known devices to produce an incident beam having a much larger cross-sectional area than any beam which can be produced in the present state of knowledge. Moreover, the spacing between two microbeams would be relatively substantial.

The invention provides a device which meets practical requirements more effectively than any comparable devices of the prior art, particularly insofar as the disadvantages mentioned above no longer arise. The invention is primarily intended to provide a system of electrostatic quadrupole lenses which deliver from an incident beam of substantial cross-sectional area focused micro-beams which are parallel to each other and such that the distance between two adjacent microbeams is very small.

More specifically, the invention proposes a system of electrostatic quadrupole micro-lenses which essentially comprises an array of parallel filiform electrodes, each microlens being made up of at least four adjacent electrodes which delimit a tunnel having a cross-section substantially in the shape of a square which is truncated at each vertex by a quarter-circle of the cross-section of the one of said electrodes and the cross-section of said array in a plane at right angles to said electrodes being such as to form a substantially square lattice, and means for electrically polarizing said electrodes.

in a first embodiment, said system is such that each of said tunnels is delimited by four adjacent electrodes each constituted at the surface by two electrically conducting portions separated by an electrically insulating portion.

In a second embodiment, said system is such that each micro-lens is constituted by two groups each formed by four adjacent electrodes, each electrode of one of said two groups being located in the line of extension of an electrode of the other group.

A better understanding of the invention will be obtained by consideration of the following description of two modes of execution of the invention which are given by way of non-[imitative example, reference being made in the description to the accompanying drawings, in which FIG. 1 illustrates a first embodiment of the invention FIG. 2 illustrates a cross-section of the device taken in the direction of the arrow A of FIG. 1

FIG. 3 is a detail view of a micro-lens;

FIG. 4 is a partial view of the second embodiment.

The device which is illustrated in FIG. ll comprises a set of filiform electrodes 1 and three plates 2, 3 and 4 having flat parallel faces, the plates 2 and 3 being in juxtaposed relation. The ends of each electrode are inserted in cylindrical holes 5 and 6 which serve as recesses and are pierced in oppositely-facing relation in the plates 3 and 4 respectively. The filiform electrodes 1 which are at right angles to the plates 2, 3 and 4 are formed of electrically insulating material. The holes 5 and 6 form a square lattice on eachplate 3 and 4.

Bores

7 and 8 are pierced from one side to the other and parallel to the electrodes 1 in the plates 2, 3 and 4 respectively at an equal distance from the holes 5 and 6. Said bores are therefore located along the same axis which is parallel to the electrodes 1 and therefore form a square lattice in the plates 2, 3 and 4. The bores 7 have the shape of two cylinders which are joined to each other by a cone frustum and one of which therefore has a much smaller diameter than the other. The bores '7 have a very small cross-sectional area at that end which is located nearest the electrodes and within the plate 3. That portion of each bore 7 which is located within the plate 2 has the same diameter as the bores 8 of the plate 4. Two

bores

7 and 8 in oppositelyfacing relation and the four electrodes 1 which surround said two bores form a tunnel 9. A thin film 10 has been deposited at the surface and over a given length at each end of the electrodes 1 each electrode 1 is therefore constituted at the surface by two electrically conducting portions 10 separated by an electrically insulating portion 1 1.

Means illustrated in FIG. I serve to polarize the electrodes I. By way of example, said means can consist of a printed circuit formed by a film of electrically insulating material deposited on the opposite faces of the plates 3 and 4 of the electrodes 1 and by a metallic film which is deposited selectively on the electrically insulating layer. The construction of printed circuits of this type is known per se three successive layers are deposited on the two faces of the plates 3 and 4 which are located opposite to the electrodes the first layer is formed of electrically insulating material, the second layer is formed of electrically conducting material and the third layer is formed of photosensitive resin which is exposed through a screen representing the pattern of electric connections. The exposed resin is first removed by chemical etching and this is followed by removal of the metallic portion which is located beneath the exposed resin. Finally, the entire resin layer is completely dissolved.

In FIG. 2 which shows a cross-section of the device of FIG. 1 as taken in the direction'of the arrow A, it is observed that the electrodes 1 which are surrounded by their conductive layers as well as the tunnels 9 form a square lattice. Each tunnel is delimited by four identical electrodes which are positioned symmetrically with respect to the axis of said tunnel.

In FIG. 3, there are shown in perspective four adjacent electrodes which delimit a tunnel 9 and form a micro-lens. The electrodes are polarized as follows electricvoltages of equal value but of opposite sign are applied to the electrically conducting portions designated by the reference numerals l2 and 13 in FIG. 3 (for example V in the case of the portion 12 and V in the case of the portion 13). The quarter circle at each vertex of the square is shown in broken line.

The operation of the device is accordingly as follows the electrically charged particles enter the device in the direction of the arrows 14 of FIG.v l. The incident beam is then split up by the bores 7 which form charged-particle beams of very small cross-sectional area. Said beams are then focused as they pass through the tunnels 9. In the first portion of the tunnel, the initially circular cross-section of the micro-beams becomes elliptic and then again becomes circular but smaller in the second portion. The micro-beams which emerge from the bores 8 are then focused and have a very small cross-sectional area. By virtue of the system of micro-lenses formed by the electrodes 1, it is therefore possible to form a set of focused micro-beams from an incident beam of charged particles having a large cross-sectional area by making use of a device in accordance with the invention. In the case of identical charged particles having a given energy, the focal length of the lenses depends on the value of the electric voltage which is applied to the electrodes. The distance between two adjacent micro-beams is the distance between two adjacent bores 8.

The plates 2, 3 and 4 are indium or nickel plates having thicknesses respectively of 5 mm, 1.5 mm and 5 mm. The large diameter of the bores 7 is equal to 1 mm whereas the small diameter is only 200 microns. The bores 8 have a uniform diameter of 1 mm. The crosssection of four adjacent electrodes which define a tunnel and constitute a micro-lens forms a square lattice, the length of each side being equal to 2 mm. The electrodes are formed of alumina wires each having a length of 25 mm and a diameter of 1 mm. The metallic coatings formed at each end of the electrodes have a thickness of-lOOmicrons and are deposited over a distance of, 6 mm in the case of the portion which is located nearest the plate 3 and over a distance of 8 mm in the case of the other portion which is located nearest the plate 4;

However, in the first embodiment of the system of micro-lenses, the lenses are formed .of electrodes having an electrically insulating central portion, with the result that the distribution of the lines of electric force is not perfect. By improving this distribution, better focusing of the micro-beams can be obtained. Moreover, the electrically insulating portion of an electrode which is located between two electrically conducting portions stores charged particles during the course of time and becomes less and less insulating, with the result that the electric insulation between the two conducting portions deteriorates to a progressively greater extent. It then becomes necessary to dismantle the system of micro-lenses in order to perform a cleaning operation.

The present invention proposes a second vform of construction of the system of micro-lenses which is mechanically of more simple design and makes it possible to obtain better focusing of the micro-beams.

In the second embodiment which is illustrated in FIG. 4, the system comprises three flat

parallel plates

20, 22 and 24 having substantially parallel faces and of circular shape. Cylindrical bores 26 extend through the first plate 20 and are disposed on a square lattice. The axes 28 of said cylindrical bores are perpendicular to the plate 20. Cylindrical bores 30 and 32 extend through the

plates

22 and 24 respectively and are located in alignment with said axes 28. The diameter of each

cylindrical bore

30 and 32 is preferably very substantially smaller than the diameter of each bore 26. The

bores

30 and 32 form a square lattice which is identical with the lattice formed by the bores 26 in the plate 20 and have axes which are perpendicular to the

plates

22 and 24. Recesses which are disposed on a square lattice are pierced at right angles to the

plates

22 and 24 around each bore 30 and 32. An electrode 34 of cylindrical shape is fixed within each recess. SAid electrodes are located at the four corners of squares, the centers of which correspond to the axis 28 of the

bores

26, 30 and 32. The electrodes 34 of the

plates

22 and 24 are placed in opposite relation. This arrangement constitutes the most important part of the mechanical portion of a system of quadrupole microlenses which is constituted by an array of parallel filiform electrodes, each micro-lens being made up of two groups each formed of four adjacent electrodes. For example, a first group can comprise the

electrodes

36, 38, 40 and 42 and the second group corresponding to the first can comprise the

electrodes

44, 46, 48 and 50. Each electrode of one of these two groups is located in the line of extension of an electrode of the other group in fact, the electrode 36 is in the line of extension of the electrode 44, the electrode 38 is in the line of extension of the electrode 46 and so forth. In order to ensure that the distribution of potential should be strictly that of a quadrupole lens, the electrodes 34 have the shape of a quadric of revolution. As a first approximation and as shown in FIG. 1, said electrodes can be cylinders of revolution, the free ends thereof being half-spheres having the same radius. The

parallel plates

20, 22 and 24 are maintained in rigidly fixed relation by suitable means such as a rod 52 and two

spacer members

54 and 56. Means which are. not shown in the single figure serve to polarize the electrodes 34. By way of example, said means can be partly constituted by a printed circuit formed of a film layer of electrically insulating material deposited on those faces of the

plates

22 and 24 which are located opposite to the electrodes 34 and of a metallic film which is selectively deposited on said electrically insulating film layer.

All the electrodes 34 are brought to the same electric voltage at absolute value, said voltage being measured with respect to a reference potential which is the last stage of the ion source, said source being placed at the entrance of the micro-lens system. Moreover, the potentials of the electrodes 34 are of opposite sign when these latter are on the one hand adjacent to and on the other hand in the line of extension of each other by way of example, the

electrodes

36, 42, 46 and 48 are brought to a potential V while the

electrodes

38, 40, 44 and 50 are at a potential V.

This device operates in the same manner as the first embodiment which has already been described. A parallel ion beam of substantial width as shown by the arrows 58 arrives perpendicularly to the plate which constitutes the entrance of the micro-lens system. By passing through the bores 26, said wide beam is split up into a plurality of small parallel beams having small cross-sectional areas. Each of said small beams is reduced to a micro-beam which traverses the plate 22 through a small bore 30, is initially focused by a first group of four electrodes of a micro-lens and then focused a second time by the second group of four electrodes of said micro-lens. The micro-beams which pass through the bores 32 of the plate 24 are accordingly convergent. The focal length of the micro-lenses depends on the one hand on the energy of the incident ions and on the other hand on the electric voltage which is applied to the electrodes 34. By modifying the voltage of said electrodes, it is possible to vary the focal length in consequence, at a predetermined distance from the exit of the micro-lens system, it is possible to vary the dimensions of the zones in which the microbeams impinge on a target. When it is desired to maintain the focal points of the micro-lenses in the same plane, it is only necessary to vary the electrical voltages applied to the electrodes 34 in proportion to the energies of the incident ions (in other words, the electric voltages to be applied to the electrodes vary in the same proportion as the energy of the ions).

The

plates

20, 22 and 24 can advantageously be fabricated from alumina which has excellent mechanical strength and permits of machining to very accurate dimensions. The electrodes 34 can also be formed of alumina and in this case a metallic film is deposited on the surface of each electrode 34.

By way of example, the dimensions of the device which is illustrated in FIG. 4 can be the following length of electrodes 6 to 8 mm distance between oppositely-facing electrodes 8 mm diameter of bores 26 1 mm diameter of

bores

30 and 32 0.2 mm ;diameter offiliform electrodes 1 mm distance between the axes of two adjacent electrodes 2 mm. This device retains the advantage of the first embodiment while being 'more simple in mechanical design, thereby facilitating the alignment of the electrodes. Moreover, the distribution of the lines of electric force within the micro-lenses is improved and this has the effect ofreducing the dimensions of focal spots.

The embodiments which are illustrated in FIGS. 1 and 4 can be mounted in a rigid and permanent manner by fixing the

plates

2, 3 and 4 or 20, 22 and 24 within a sleeve formed of electrically insulating material such as alumina, for example. Another mode of procedure consists in fixing the

plates

2 and 3 or 20 and 22 and in mounting the plate 4 or 24 on a support which is capable on the one hand of undergoing a movement of translation in two directions at right angles to each other and on the other hand of undergoing a movement of rotation. These movements can advantageously be carried out by means of stepping motors. The advantage of the design solution which has just been mentioned lies in the possibility of obtaining excellent centering of the electrodes with respect to the different bores of the device and therefore of obtaining maximum intensity of the micro-beams as well as perfect focusing.

By way of example of industrial application, mention can be made of a device which is similar to that hereinabove described and illustrated in FIG. 1 or FIG. 4 and which has been employed in the collective formation of integrated micro-circuits by the method of ion implantation. It has thus been possible to fabricate l,000 or 2,000 identical integrated electric circuits both simultaneously and in a relatively short period of time. The use ofa device in accordance with the invention and in combination with other devices is described in copending U.S. Application Ser. No. 107,354, filed Jan. 18, 1971, by Philippe Glotin et al., for Method and Device for Obtaining Parallel and Focused Ionic Micro-Beams and Application of Said Method To The Collective Formation of Electric Circuits By Ion Implantation."

Moreover, the invention can be employed for obtaining a plurality of electron micro-beams which are capable of carrying out collectively a large number of operations such as machining, welding, cutting of thinfilm resistors and capacitors, irradiation of sensitive resins, cutting of screens and the like.

What we claim is 1. Apparatus for transforming a beam of charged particles of large cross-section into a plurality of microbeams of particles which micro-beams are substantially parallel and focused comprising a ring of filiform electrodes substantially parallel to the axis of the beam of particles of large cross-section, two plane spaced plates supporting said electrodes at the vertexes of a square, a plurality of openings in said plates dividing the beam, said openings being disposed at the verticies ofa square similar to the first square, four adjacent ones of said electrodes being symmetrically disposed around the axis of each of said openings, electric means for applying electric potential to said electrodes whereby the space between four adjacent ones of said electrodes has a quadrupolar electrostatic field, a group of said four electrodes forming an quadrupolar electrostatic microlens.

2. A system of electrostatic quadrupole micro-lenses as defined in claim 1, including .spaced flat plates supporting said electrodes and the diameter of said bores of one of said plates being very substantially smaller than the diameter of the bores of the other of said plates.

3. A system of electrostatic quadrupole micro-lenses as defined in claim 1, wherein said electrodes are wires of electrically insulating material, each of said electrically conducting portions being a metallic film which is deposited on said wires.

4. A system of electrostatic quadrupole micro-lenses as defined in claim 1, wherein said plates are each provided with a printed circuit constituted by a film of electrically insulating material covering that face of said plates which is located nearest said electrodes and an electrically conducting film which is deposited selectively on said insulating material, the function of said circuit being to polarize said electrodes.

5. A system of electrostatic quadrupole micro-lenses as defined in claim 1, wherein said plates are fixed within a sleeve formed of insulating material.

6. A system of electrostatic quadrupole micro-lenses as defined in claim 1, wherein one plate is stationary and the otherplate is rigidly fixed to a support which is capable of carrying out two movements of translation in two directions at right angles to each other and a movement of rotation.

7. Apparatus as described in claim 1, each of said quadrupolar micro-lenses being formed of two groups of electrodes, each of said groups being formed by four adjacent ones of said electrodes, each of said electrodes of one of said two groups being located in the line of extension of an electrode of the other of said groups.

8. A system of electrostatic quadrupole micro-lenses as defined in claim 7, wherein each electrode has the shape of a quadric.

9. A system of electrostatic quadrupole micro-lenses as defined in claim 7, wherein each electrode is a cylinder of revolution terminating in a half-sphere having the same radius.

10. A system of electrostatic quadrupole micro-lensees as defined in claim 7, wherein each electrode is constituted by a cylindrical rod which is formed of insulating material and the entire surface of which is coated with an electrically conducting layer.

11. Apparatus as described in claim 1, the diameter of said openings being substantially smaller than the spacing between two of said adjacent electrodes.

Claims

1. Apparatus for transforming a beam of charged particles of large cross-section into a plurality of micro-beams of particles which micro-beams are substantially parallel and focused comprising a ring of filiform electrodes substantially parallel to the axis of the beam of particles of large cross-section, two plane spaced plates supporting said electrodes at the vertexes of a square, a plurality of openings in said plates dividing the beam, said openings being disposed at the verticies of a square similar to the first square, four adjacent ones of said electrodes being symmetrically disposed around the axis of each of said openings, electric means for applying electric potential to said electrodes whereby the space between four adjacent ones of said electrodes has a quadrupolar electrostatic field, a group of said four electrodes forming an quadrupolar electrostatic micro-lens.

2. A system of electrostatic quadrupole micro-lenses as defined in claim 1, including spaced flat plates supporting said electrodes and the diameter of said bores of one of said plates being very substantially smaller than the diameter of the bores of the other of said plates.

6. A system of electrostatic quadrupole micro-lenses as defined in claim 1, wherein one plate is stationary and the other plate is rigidly fixed to a support which is capable of carrying out two movements of translation in two directions at right angles to each other and a movement of rotation.

10. A system of electrostatic quadrupole micro-lenses as defined in claim 7, wherein each electrode is constituted by a cylindrical rod which is formed of insulating material and the entire surface of which is coated with an electrically conducting layer.