Electric lamp and discharge devices – With positive or negative ion acceleration – Plural apertured electrodes
Reexamination Certificate
1999-06-21
2001-06-12
Patel, Vip (Department: 2879)
Electric lamp and discharge devices
With positive or negative ion acceleration
Plural apertured electrodes
C313S268000, C060S202000
Reexamination Certificate
active
06246162
ABSTRACT:
FIELD OF INVENTION
This invention relates generally to gridded ion sources, and more particularly to the design of ion optics for such ion sources.
This invention can find application in a variety of thin film applications such as etching, sputter deposition, or the property modification of deposited films. It can also find application in space propulsion.
BACKGROUND ART
Gridded ion sources are described in an article by Kaufman, et al., in the AIAA Journal, Vol. 20 (1982), beginning on page 745, which is incorporated herein by reference. The ion sources described therein use a direct-current discharge to generate ions. It is also possible to use a radiofrequency discharge to generate ions, as shown by U.S. Pat. No. 5,274,306—Kaufman et al.
Typical ion optics for gridded ion sources are also described in the aforesaid article by Kaufman, et al. An improved ion optics design is described in U.S. Pat. No. 4,873,467—Kaufman, et al., which as incorporated herein by reference. The problems addressed in this patent are basic to ion optics: need to maintain the apertures in different grids in alignment while the grids and supporting members can vary in temperature, reach different equilibrium temperatures, and, at least for the grids, can have significant temperature variations within a part at equilibrium conditions.
Some specific grid temperatures are given in a chapter by Kaufman in a chapter beginning on page 265 of
Advances in Electronics and Electron Physics
, Vol. 36 (L. Marton, ed.), Academic Press, New York, 1974. The center of the screen grid is typically at 400 to 500° C. during operation, while the center of the accelerator grid is 50 to 100° C. cooler. The edges of the grids operate at 100 to 300° C. cooler than the centers of the grids. Starting operation from ambient temperatures thus involves large temperature differences and gradients.
The temperature differences and variations are aggravated by the poor heat transfer in a vacuum environment, i.e., the heat transfer between parts bolted or riveted together is usually close to the heat transfer that would occur due to radiation alone. For industrial applications of ion sources, it is particularly important that routine assembly not depend on careful hand-eye coordination or the use of expensive and complicated instrumentation.
While the use of a design described in the aforesaid U.S. Pat. No. 4,873,467 is a considerable improvement over prior art in regard to maintaining alignment with varying temperatures, there are still serious problems. Using supporting members of normal flatness tolerances, large clamping forces are required to assure proper contact of parts. These forces are sufficient to plastically deform grids in the contact regions upon which the alignment depends, thereby degrading the precision of that alignment.
In some cases, positive contact of the insulator with adjacent parts is lost at some point in the startup-cooldown thermal cycle, resulting in rotation of that insulator. With a sufficient number of such cycles, a portion of the insulator that is coated with sputtered material can be rotated enough to cause electrical shorting of the ion optics.
SUMMARY OF INVENTION
In light of the foregoing, it is an overall general object of the invention to provide an improved ion optics design that greatly reduces the forces on insulator seats incorporated into ion optics grids and thereby reduces the associated plastic deformation that degrades the alignment precision of apertures through which the ions are accelerated.
Another object of the present invention is to provide a design in which the elastic motion of parts is sufficient to maintain the positive contact of insulators with adjacent parts and thereby prevent the gradual rotation of insulators during repeated thermal cycles and the eventual shorting of the ion optics due to that rotation.
A further object of the present invention is to provide a design that is more adaptable to ion optics configurations having more than two grids.
In accordance with one specific embodiment of the present invention, the ion optics for use with an ion source have first and second electrically conductive grids having mutually aligned respective pluralities of apertures through which ions may be accelerated and wherein each has an integral peripheral portion. There is also a support member. There are first and second mutually aligned series of seats spaced around the respective peripheral portions of the first and second grids. A plurality of first spherical insulators are distributed between corresponding seats of the first and second series, thereby establishing a predetermined distance between the grids while still enabling radial movement between the peripheral portions of the grids relative to each other. There are third and fourth mutually aligned series of seats spaced around the support member and the peripheral portion of the second grid, respectively, with seats of the fourth series displaced from those of the second series in the same grid. A plurality of second spherical insulators are distributed between corresponding seats of the third and fourth series, thereby establishing a predetermined distance between the support member and the second grid while still enabling motion in at least the radial direction between the support member and the peripheral portion of the second grid. A clamping force between the support member and the peripheral portion of the first grid maintains contact between the first plurality of insulators and the first and second grids and between the second plurality of insulators and the support member and the second grid.
REFERENCES:
patent: 4873467 (1989-10-01), Kaufman et al.
patent: 5274306 (1993-12-01), Kaufman et al.
“Ion Source Design for Industrial Applications”, AIAA 81-0668R, Kaufman and Robinson, vol. 20, No. 6, Jun. 1982, p. 745 et seq.
Kahn James R.
Kaufman Harold R.
Robinson Raymond S.
Berck Ken A.
Edmundson Dean P.
Kaufman & Robinson, Inc.
Patel Vip
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