US3623197A - Electrostatic deflection electrode system for electron beam device having an array of lenses - Google Patents

Abstract

ACCURATELY SPACED, PARALLEL CONDUCTORS FORMING AN ARRAY OF DEFLECTION ELECTRODES ARE PROVIDED TO RESPECTIVELY DEFLECT AN ELECTRON BEAM EMANATING FROM ONE OR MORE OF ANY ARRAY OF LENSES. THE ARRAY OF ELECTRODES ARE CONSTRUCTED BY FIRST FORMING A STACK OF PLANAR SHEETS COMPRISING ALTERNATE LAYERS OF THE ELECTRODE MATERIAL AND A SECOND REMOVABLE MATERIAL WHICH ACTS AS AN ACCURATE SPACER DURING FABRICATION OF THE ARRAY.

Description

Nov. 30, 1971 w. L. JONES 3,623,197

ELECTROSTATIC DEFLECTION ELECTRODE SYSTEM FOR ELECTRON BEAM DEVICE HAVING AN ARRAY OF LENSES Filed March 27, 1970 2 Sheets-Sheet 1 "mm" F|vG.2.

FORMING AN ASSEMBLY OF F I6, I, [1'4 PLANAR LAYERS cou msme ALTERNATE LAYERS 0F DISS/MILAR MATERIALS.

SLICING THE ASSEMBLY IN A PLANE NORMAL TO THE LAYERS.

SELECTIVELY REMOVING THE OTHER MATERIAL.

INVENTORZ WILLIAM L. JONES,

Nov. 30, 1971 w. L. JONES 3,623,197

' ELI'J'C'IROS'IATIC DEFLEC'I'ION ELECTRODE SYSTEM FOR ELECTRON BEAM DEVICE HAVING AN ARRAY 0F LENSES Filed March 27. 1970 2 Sheets-Sheet 8 INVENTOR:

WILLIAM L. JONES M BY kl g HIS ATTORN Y.

United States Patent US. Cl. 2925.14 4 Claims ABSTRACT OF THE DISCLOSURE Accurately spaced, parallel conductors forming an array of deflection electrodes are provided to respectively deflect an electron beam emanating from one or more of an array of lenses. The array of electrodes are constructed by first forming a stack of planar sheets comprising alternate layers of the electrode material and a second removable material which acts as an accurate spacer during fabrication of the array.

BACKGROUND OF THE INVENTION This invention relates to an electron beam tube having a compound lens system comprising a plurality of focusing and deflecting electrodes in a matrix for precise control of the electron beam. More particularly, the invention relates to a method of making an array of deflection electrodes for a compound lens system.

A system for precise control of an electron beam is described in a paper by S. P. Newberry entitled Problems of Microspace Information Storage, appearing in the Fourth Electron Beam Symposium (Mar. 29-30, 1962') published by Alloyd Electronics Corporation, Boston, Mass., and again in The Flys Eye Lens-A Novel Electron Optical Component for Use With Large Capacity Random Access Memories by S. P. Newberry in volume 29 of the American Federation of Information Processing Societies, Conference Proceedings, published by Spartan Books, Washington, DC. (November 1966). The system therein described comprises an ultrahigh density memory wherein impingement of an electron beam on a storage medium is controlled by an objective lens made up of a matrix of minute electron optical lenses, herein referred to as lenslets. This matrix of lenslets is superficially similar in appearance to the compound eye of an ordinary housefly and therefore is designated a Flys Eye Lens. By utilizing coarse deflection of the electron beam so as to strike only a desired lenslet of the matrix, the lenslet, thus struck, positions the beam to ultimately impinge upon the storage medium at the desired point. Although the coarsely deflected beam may not strike the desired lenslet at dead center, the accuracy with which the beam strikes the storage medium remains unimpaired so long as even a portion of the beam strikes the desired lenslet.

Briefly, the planar array of lenslets comprises three parallel plates with a plurality of axially aligned openings therein to form an array of Einzel lenses for fine focusing and, immediately following each lens, a set of X and Y deflection plates for fine deflection. The resultant ultrahigh resolution electron beam tube can be used, for example, in apparatus for the fabrication of integrated circuits such as described and claimed in US. Patent No. 3,491,236-Newberry, issued J an. 20, 1970 and assigned to the assignee of this invention.

The X-Y deflection array comprises two sets of parallel deflection bars orthogonal to one another and electrically coupled respectively to horizontal and vertical control circuitry. Alternate bars in each set are electrically coupled respectively to the positive and negative of the particular deflection circuit. Thus, the electron beam emanating from any one or more of the Einzel lens passes through a pair of horzontal deflection bars and a pair of vertical deflection bars.

It has been proposed to construct such a deflection electrode array by individually attaching accurately machined bars individually to an insulating substrate. Problems such as inaccurate spacing, warpage due to uneven heating, and overall time and expense have made this solution undesirable.

SUMMARY OF THE INVENTION It is therefore an object of this invention to provide a method of making an accurately spaced deflection electrode array. It is another object of this invention to provide a method of making an array of parallel bars. Other objects of the invention will become apparent from the description.

Briefly considered, in accordance with the invention a deflection electrode array is constructed by forming an assembly of planar layers comprising parallel alternate layers of at least two dissimilar materials. The layers are secured together and the assembly is then sliced in a plane normal to the planes of the layers while maintaining securement of the layers to one another. Selected end portions of one of the materials are secured to an insulating substrate and then the other material is selectively removed to provide an assembly of equidistant and parallel spaced elements. A second assembly is similarly constructed and the two assemblies are mounted in parallel planes with the axis of the bars or elements of one assembly orthogonal to the axis of the bars of the other assembly to provide an array of X-Y deflection electrodes.

:BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an illustration showing apparatus embodying the deflection electrode array produced by the invention.

FIG. 2 is a flow sheet of the invention.

FIG. 3 is an isometric view of the multilayered intermediate product formed by the process of the invention. 3 FIG. 4 is an isometric view of a sliced portion of FIG.

FIG. 5 is an isometric view of a portion of FIG. 4 after partial etching.

FIG. 6 is a top view of the sliced portion of FIG. 4 mounted to a support.

FIG. 7 is an exploded view of a deflection electrode array formed by the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to FIG. 1, a device is generally illustrated in which the deflection electrode array formed by the invention may be used. A vacuum enclosure is generally indicated at 2 wherein a beam 4 of charged particles such as an electron beam produced by an electron emitting source 6 is controllably deflected thru a compound lens system onto a target 20 such as a semiconductor wafer.

Beam 4 produced by electron source 6 passes through a beam limiting aperture 8 and is collimated by an electrostatic condenser lens 10. The beam is then coarsely deflected in the X and Y planes respectively, by deflection plates 12a, 12b and 14a, 14b. The particular electron optics used to direct the beam to each lenslet may, of course, be varied and optimized using various structures and techniques forming no part of the present invention.

The compound lens structure is generally indicated at 30 in FIG. 1. The electrostatic focusing lens structure generally comprises three parallel plates 32, 34, and 36, each having an array of openings therethrough in axial alignment to form an array of electrostatic lenses.

Immediately following the focusing lens array is the fine deflection system toward which this invention is directed. Briefly, the deflection system comprises a first set of parallel bars 60 immediately followed by a second set of parallel bars 90 at right angles to the first set of bars. The bars thus form a criss-cross array of lattice conforming spacially to the openings in the lens plates to provide a fine X-Y deflection system for each lens. Thus maintenance of even and parallel spacing of the deflection bars is desirable.

In accordance with the invention an array of parallel and evenly spaced deflection bars is constructed following the steps outlined in the flow sheet of FIG. 2 by first forming an assembly such as illustrated in FIG. 3 comprising alternate layers of at least two dissimilar materials. The sheets or layers comprising one of the materials are indicated by the numeral 66. This material is chosen for its removability at a later stage of the fabrication as will be explained below. Its function is to act as a temporary thickness gauge and alignment device for correct spacing and parallel alignment of the adjacent layers which will eventually become the deflection electrodes. The thickness of the layers 66 is therefore carefully selected to correspond to the desired eventual spacing between the electrodes of the desired deflection electrode array.

Alternating with layers 66 are layers of the desired electrode materials 62a, 64a, 62b, 64b, 62c, and 64c. It will be noted that the layers indicated by the numeral prefix 62 extend from one side of the stack while the layers indicated by the numeral prefix 64 extend out on the opposite side of the stack and also that these layers are staggered. This construction, as will be explained in more detail presently, is preferred as an aid to eventual electrical interconnection of the electrodes to provide alternate positive and negative deflection plates for either the X or Y axis.

The thickness of the plates 62 and 64, i.e. the width of the bars, is chosen to correspond with the desired spacing between the electrodes and the spacing of the lenslets in the Einzel lens array with which the eventual deflection electrode assembly is to operate. Other than for such design limitations the thickness of the plates 62 and 64 need only exceed the minimum necessary for mechanical stability of the particular electrode material chosen.

In the preferred embodiment the electrode material comprising plates 62 and 64 is titanium metal of about -30 mils thickness. Titanium electrode material is desirable because of its non-magnetic properties, its bondability to ceramic insulating materials, its low emission, and gettering properties.

Nickel-plated molybdenum is a preferred material for layer 66 when titanium electrode material is chosen. With this choice of materials the initial assembly can be brazed together, followed by a second, lower temperature braze of the titanium electrodes to a ceramic substrate such as fosterite without disturbing the titanium-nickelmolybdenum braze. When other electrode materials are used or other securement of the electrodes to a substrate utilized, the second material can of course be other than molybdenum.

The assembly of titanium and nickel coated molybdenum plate is secured together by vacuum brazing at about 1000 C. for about ten minutes. The length of brazing time will vary somewhat depending upon the thickness of the nickel coating forming the Ti-Ni braze. A thickness of nickel of about /2 mil has been found to be satisfactory.

After the brazed assembly has been cooled, it is sliced normal to the planes of the layers into portions 50 such as shown in FIG. 4 of about 30 mils thickness. The sliced surfaces, if necessary, are ground flat to assure uniformity of thickness.

The sliced portion 50 (with all layers still brazed together) is then mounted on a suitable support. In accordance with a preferred embodiment of the invention, portion 50 is mounted to a ceramic disk 100 which is preferably fosterite ceramic. When the conducting layers are made of titanium and the ceramic is fosterite, a very satisfactory bond can be eflected following the bonding method described and claimed in Beggs US. Patent 2,857,663, issued Oct. 28, 1958 and assigned to the assignee of this invention. Briefly, this patent teaches and claims the bonding of titanium to fosterite by a titanium-nickel-active-alloy seal.

When the above bonding technique is used, the molybdenum layers are preferably etched back from the ends of slice 50 as illustrated in FIG. 5. The selective partial etching can be done by suitably masking the central portion of the slice to maintain the slice in one piece thus preserving the alignment of the titanium layers. The etching can be done using an etching solution comprising 3 parts by weight water, 1 part by weight 12. N nitric acid, and 1 part by weight 12 N sulfuric acid. After this etching step is done, the protruding titanium portions are nickel plated to provide a satisfactory amount of nickel to effect the nickel-titanium-fosterite bond taught by the above Beggs patent.

As best seen in FIG. 6, sliced portion 50 is bonded to a ceramic support having a central cutaway portion of suflicient dimension to allow the short ends 62d, 62e, 62f, and 64d, Me, and 64f to rest on disk 100. Subsequent bonding of the titanium bars 62 and 64 to disc 100' provides bonding of both ends of each bar to disc 100.

Still referring to FIG. 5, strips and 82 are illustrated as mounted on disc in respective electrical contact with the longer ends 62a, 62b, 62c and 64a, 64b, and 64c. Strips 80 and 82 comprise thin nickel-titanium foil strips which are laid down on disc 100 before the slice comprising bars 62 and 64 is bonded to disc 100. In this way, the subsequent bonding provides simultaneous mechanical adhesion of bars 62 and 64 to disc 100 and electrical interconnection of alternate titanium electrode bars.

It should be noted here that the etching back of the molybdenum layers adjacent the ends of the bars is done to inhibit undesired interconnection of adjacent bars which could occur if the slice was not separated into discrete portions at the area of the bond.

After the subassembly or slice is brazed to the ceramic support, the remainder of the removable spacer layers illustrated herein as molybdenum can be removed. In the case of molybdenum, this can be done using an etching solution comprising 3 parts by weight water, 1 part by Weight 12 N nitric acid, and 1 part by weight 12 N sulfuric acid. This solution will effectively remove the molybdenum without affecting either the titanium layers or the titanium-nickel-fosterite seal.

The sealing technique described above provides the additional advantage of electrically interconnecting the protruding portions on each end of the subassembly. As mentioned above, these protruding layers are alternately spaced in the subassembly. Electrical interconnection of the protruding portions then permits, after removal of the spacing layers, electrical connection of the bars to a power source to provide alternate polarity on adjacent bars.

The deflection electrode assembly is completed .by the production of a second subassembly 112 mounted to a similar ceramic substrate 110. As shown in FIG. 7, the two mounted subassemblies 102 and 112 are mounted together with the respective bars orthogonal. A ceramic spacer insulates subassembly 102 from subassembly 112. Electrical connection of the respective electrodes to X and Y deflection power sources provides an array or lattice work of X+, X, Y+, and Y deflection electrodes to deflect the electron beam emanating from the corresponding lens in the preceding lens array.

Alternatively, the array may be formed by mounting one of the sliced portions to one side of a ceramic spacer and mounting the other sliced portion to the opposite side of the spacer with the bars of one subassembly orthogonal to the bars of the other subassembly. If closer spacing of the X-axis bars to the Y-axis bars is desired,

both sets of bars could be mounted on the same side of a ceramic spacer in a pair of grooves in the spacer machined at 90 to one another, one of which would be deeper than the other groove by slightly more than the height of the bars.

Thus the invention provides a method of making an array of deflection electrodes for a compound lens system wherein the individual electrodes are accurately spaced apart. The electrode array of the invention, it should be noted, is useful not only in a compound lens system but in other applications as well, such as a grid system Where accurate spacing is required. While a particular embodiment has been described minor modifications will be apparent to those skilled in the art and should be deemed to be within the scope of the invention defined in the appended claims.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. A method of making a deflection electrode array for a matrix of electron lenses comprising:

(a) forming an assembly of planar layers comprising alternate layers of at least two dissimilar materials, one of which comprises a conducting material,

(b) securing said layers together,

() slicing said assembly in a plane normal to the planes of the layers while maintaining securement of said layers to one another,

(d) securing together selected layer portions of said conducting material at each end of said slice to a support, and

6 (e) thereafter selecting material other than said conductive material to provide an array of equidistant and parallel spaced elements.

2. The method of claim 1 wherein said assembly comprises alternate layers of titanium and molybdenum brazed together.

3. The method of claim 2 wherein said conducting material comprises said titanium layers, and said layers are secured by brazing said titanium to a ceramic support.

4. The method of claim 3 wherein the molybdenum layers at the end portions of said sliced assembly are selectively removed by chemical etching before said titanium layers are brazed to said ceramic support and the remainder of said molybdenum is removed by chemical etching after said titanium layers are brazed to said ceramic to insure alignment of said titanium layers.

References Cited UNITED STATES PATENTS 2,791,710 5/1957 Dressler 29-25.14 X 2,857,663 10/1958 Beggs 29503 X 3,491,236 1/1970 Newberry 29-580 X JOHN F. CAMPBELL, Primary Examiner R. B. LAZARUS, Assistant Examiner US. Cl. X.R.

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