US3382388A - Ion pump and scrubbing gun for high vacuum apparatus - Google Patents

Description

May 7, 1968 W. G, HENDERSON ETAL 3,382,388

ION PUMP AND SCRUBBING GUN FOR HIGH VACUUM APPARATUS Filed June l5, 1966 @7.1. H mw@ United States Patent O 3,382,388 ION PUMP AND SCRUBBING GUN FOR HIGH VACUUM APPARATUS William G. Henderson and John T. Mark, Lancaster, Pa.,

assignors to Radio Corporation of America, a corporation of Delaware Filed .lune 15, 1966, Ser. No. 557,755 7 Claims. (Cl. 313-7) ABSTRACT F THE DISCLOSURE A sputter ion pump has an electron scrubbing gun disposed within the pump housing for dislodging adsorbed and absorbed gases from the housing walls. To shield the flat gas absorbing electrodes of the sputter ion pump from the electron scrubbing gun, such electrodes have their edges oriented toward the scrubbing gun.

This invention relates to apparatus for producing a n relatively high vacuum, and particularly to such apparatus comprising a sputter ion pump and an electron scrubbing Igun within a common enclosure.

While a sputter ion pump is capable theoretically of producing relatively high vacuums of the order of 1()-13 torr, it is limited in its evacuating function by the continuous release of what are believed to be adsorbed and absorbed gases from the walls defining the pump.

The technique for leasing adsorbed and absorbed gases from Walls of a chamber to be evacuated is available in the form of electron scrubbing. However, it has not been suggested heretofore to employ this technique for releasing such gases from the walls of a sputter ion pump. It is believed that the absence heretofore of a suggestion for electron scrubbing of the interior walls of a sputter ion pump is due to an appreciation of the fact that the pump is intendedl to entra-p gas molecules and not to release such molecules as by electron scrubbing. Indeed, such release of gases from the gettering material of a sputter ion pump in which gases are entrapped, would defeat the very purpose of the pump. Because of this limitation with respect to release of gases from the pump envelope walls during outgassing of sputter ion pumps, situations have arisen wherein an electron scrubbed envelope to be evacuated was capable of sustaining a lower pressure than that obtainable with a non-scrubbed sputter ion pump.

Accordingly, it is an object of the invention to provide a sputter ion pump capable of evacuating a chamber to appreciably lower pressures than feasible heretofore.

Another object is to provide an evacuating apparatus comprising a novel combination of a sputter ion pump and an electron scrubbing `gun housed in a common envelope.

In one example to -be described herein, there is provided a multiple pump modular type of sputter ion pump for increased speed of evacuation. This type of pump includes a relatively large envelope, thus resulting in a relatively large release during operation of what are believed to be absorbed and absorbed gases. A portion of the space within the envelope is free of pump structure and provides a path for gases to the several pumps of the modular structure. This space also provides a convenient centralized accommodation for an electron scrubbing gun.

Further objects and features will become apparent as the description continues.

In the drawing to which reference is now made for an exemplary embodiment of the invention:

FIG. 1 is a longitudinal sectional view of an evacuating apparatus comprising a modular sputter ion pump associated with a scrubbing gun;

3,382,388 Patented May 7, 1968 ICC FIG. 2 is a transverse sectional view taken along the line 2-2 of FIG. l; and

FIG. 3 shows a graph in which curves depict pressures attainable heretofore and in accordance with the present disclosure.

The evacuating apparatus shown in FIGS. l and 2 comprises a novel combination of a sputter ion pump and an electron scrubbing gun 12. The sputter ion pump 10 is of modular type and may include four pump modules 14, 16, 18 and 20` disposed in recesses extending radially outward from a chamber 22. Each module is a self-contained sputter ion pump. The provision of a plurality of modules contributes to increased pumping speed. The chamber 22 has an opening 24 which may be connected hermetically to an envelope to be evacuated and to a suitable forepump for initially reducing the pressure in the chamber 22 and in the envelope to be evacuated, to a value such as about 10-4 torr, at which sputter ion pumps become reasonably eliicient.

Within the chamber 22 is disposed the electron scrubbing gun 12. The scrubbing gun 12 comprises a lament 216 made of tungsten for example and supported on conducting rods 28, 30. The conducting rods 28, 30 are sealed through insulating tubes 32, 34 made of ceramic for example. The insulating tubes 32, 34 are hermetically sealed through a metal cap 36 made of stainless steel for example. The cap 36 is hermetically sealed across an open end of an insulating tube 38 made of ceramic for example. The other end of the tube 38 is sealed hermetically to a metal tube 40 which may be made of stainless steel. The metal tube 40 is fixed as by welding t0 the wall of an opening through a metal disc 42 which also may be made of stainless steel. The disc 42 is hermetically and removably attached to a ange 44 by suitable means such as bolts 46. The shield 47 serves to isolate the insulating tube 38 from material sputtered from elements of the ion pump modules during operation.

In operation, the leads 28, 30 are connected to the secondary winding of a transformer 49 which develops a current for suitably energizing the iilament 26 and a voltage of from 2O to -40 kilovolts for creating an electric field between the filament and walls of the pump to thereby cause high velocity electrons from the emissive filament to strike the walls for electron scrubbing.

The electrodes of the sputter ion pump modules 14, 16, 18 and 20 are edge oriented in relation to the filament 26 of the electron scrubbing gun, so that the function of the electrodes of absorbing gas molecules is not affected adversely by the scrubbing gun. Thus, as more clearly seen in FIG. 2, each sputter ion pump module includes two oppositely disposed parallel plates 48, 50 made of titanium for example, and electrically and mechanically attached to the adjacent walls of a module. The plates 48, 50 serve as cathodes of a pump module. Between the plates 48, 50 and in spaced relation therewith, is supported an anode 52 of at cellular structure and comprising a plurality of tubes 54 made for example of stainless steel. The tubes 54 are mutually parallel and extend axially in normal relation to the plates 48, 50. The tubes 54 may be combined within a metal frame 56 and supported by one or more brackets 58. The brackets S8 are supported by electrically insulating standoffs 60 iixed to the inner wall of the chamber 22. Each anode 52 is connected to a suitably positive voltage source by a lead 62 and an external contact pin 65 passing through an electrically insulating bushing 64.

Only the edges of the cathode plates 48, 50 and the cellular anode 52 are exposed to the chamber 22 and to the scrubbing gun filament 26 therein. Therefore, high velocity electrons from the filament 26 do not strike the flat surfaces of the ion pump electrodes and consequently do not release gas molecules trapped in such electrodes during pumping.

To the external surfaces of each ion pump module is attached a plurality of permanent magnets 66 for causing the electrons from the cathodes 48, 50 to travel in spiral paths. The attachment may be effected by causing the magnets to embrace the modules in a friction fit. In FIG. 1 only two magnets are shown in the interests of simplicity. Actually, seven magnets are associated with each pump module. The field intensity of the magnets 66 is related to the diameter of the anode tubes 54 for efficient pumping action. Thus, when the diameter of the anode tu'bes is one-half inch, the magnetic eld intensity of the magnets should be about 1000 gauss for desirable pumping speed. In the interests of drawing simplicity, magnets are shown only in connection with ion pump module 16. However, in operation such magnets are also provided in respect of modules 14, 18 and 20.

In operation, a variable positive potential of from about 0.5 kv. to about 7 kv. is applied to the contact pins 65 for energizing the anodes 52. The envelope of the modular ion pump structure may be grounded, as shown in FIG. l, thereby grounding the cathode plates 48, 50 in the several modular units and reducing hazard to operating personnel. These potentials produce an electric field between the circular anodes 52 and the cathode plates 48, 50. This electric field causes a breakdown of gas within the pump modules resulting in a glow discharge within the anode tubes 54 and the spaces between the anodes 52 and the cathode plates 48, 50. The glow discharge in combination with the electric and magnetic eld results in the formation of positive ions which are driven into the cathode plates 48, 50, with sufficient energy to produce dislodgement such as by sputtering, of reactive titanium cathode material. The dislodged material is sputtered onto a nearby anode 52 to produce a gettering of molecules in the gaseous state coming in contact therewith.

While this pumping or gettering action is going on, the electron scrubbing filament is energized by from -20 kv. to -40 kv. from the transformer 49. This causes emission of high velocity electrons which strike the inner walls of the chamber 22 thereby dislodging adsorbed and absorbed gas molecules. Such dislodged gas molecules are absorbed by the ion pump modules in the manner aforedescribed.

The combination of a sputter ion pump with an electron scrubbing gun, as described herein, has resulted in appreciably increasing the pumping ability of the pump at relatively low pressures, beyond that feasible heretofore. In PIG. 3, curve 68 denotes the speed of evacuation and the lowest pressure obtainable heretofore with a prior art ion pump under conditions wherein no attempt is made to remove adsorbed and absorbed gases from the envelope of the ion pump. After initial evacuation by conventional pumps, such as mechanical and diffusion type pumps, to a pressure of about -4 torr, the evacuation effected by the ion pump results in a gradually decreasing pressure to a value of about 10-a torr after about 100 hours. Curve 70 indicates the pumping action when the ion pump is outgassed by heating to a temperature of about 400 C. during pumping. This temperature is provided by a suitable heating means such as an oven. It will be noted that the pressure is gradually reduced to about 10-6 torr and then as adsorbed gases are released by the outgassing temperature, the pressure rises to about 10-5 torr after on hour. After the application of the outgassing temperature is terminated, the pressure drops to about 10-9 torr after 100 hours of pump operation.

Curve 72 shows the pumping action of an evacuating apparatus herein described in which one or more ion pumps are combined with an electron scrubbing gun in a common envelope. With this novel combination the pressure is initially reduced from 10-4 torr to about 10-5 torr and then increased to a pressure slightly greater than 4 10-4 torr due to the efficient dislodgement of both adsorbed and absorbed gas molecules. During about the rst ten hours of pump operation, the pressure is steeply reduced to a value of about 10-9 torr. The scrubbing action may then be terminated. After the rst 100 hours of pump operation the pressure is reduced to a value appreciably below 10'10 torr. This pressure is more than two orders of magnitude below that achieved when both temperature outgassing and scrubbing are omitted. This pressure is over one order of magnitude below the lowest pressure heretofore attainable by temperature outgassing of the pump. When an envelope or chamber to be evacuated is also scrubbed by an electron gun, the pressure in such envelope or chamber can be reduced by the combined ion pump and electron scrubbing gun herein described to a value heretofore unattainable by ion pumps.

After an appreciable period of operation, the anodes 52 of the ion pump modules and the electron scrubbing gun may have to be replaced. Such replacement of the anode 52 may be effected by separating parts of the modular ion pump structure at regions 74, 76, 68, (FIG. 2) by releasing bolts 82 at such regions. The separation effected by loosing the bolts 82 exposes the interior of the ion pump modules and facilitates removal and replacement of anode 52. Removal of the scrubbing gun 12 for replacement of the filament 26 is effected by loosening bolts 46 and pulling the gun from the chamber 52. After replacement of the anode 52 and scrubbing gun 12, the chamber 22 may be hermetically sealed by tightening bolts 82 and 86.

What is claimed is:

1. An evacuating apparatus comprising:

(a) an envelope,

(b) an electron scrubbing gun in said envelope and adapted to dislodge gas molecules from walls of said envelope, and

(c) a sputter ion pump in said envelope for absorbing gas molecules in said envelope including said dislodged gas molecules.

2. An evacuating apparatus according to claim 1 and wherein said envelope includes a chamber having an outwardly extending recess therein, said scrubbing gun being located in said chamber and said sputter ion pump being located in said recess.

3. An evacuating apparatus according to claim 7 and wherein said anode comprises a plurality of parallel metal tubes extending normal to the flatness dimension of said anode, said tubes being adapted to receive sputtered gettering material on the inner surface thereof from said cathode, whereby said sputtered -gettering material is shielded from electrons produced by said electron scrubbing gun.

4. An evacuating yapparatus comprising:

(a) an envelope,

(b) a plurality of sputter ion pumps in said envelope, each of said pumps comprising a plurality of tlat electrodes,

(c) an electron scrubbing gun having an electron emitter in said envelope,

(d) said at electrodes being positioned to expose edges only thereof to said emitter,

(e) whereby the flat surfaces of said electrodes are substantially shielded from said emitter.

5. An evacuating apparatus according to claim 5 and wherein said envelope has a plurality of recesses extending radially outward from a central region of said envelope, said plurality of ion pumps being disposed in said recesses and said electron emitter being located in said central region.

6. An evacuating apparatus according to claim 6 and wherein external surfaces of each of said outwardly extending recesses are embraced by at least one permanent magnet.

7. An evacuating apparatus comprising:

(a) an envelope,

5 6 (b) an electron scrubbing gun within said envelope of said electrodes are substantially preserved having an electron emitter oriented to direct electrons from electron impingement.

in a given path, (c) electrodes of a sputter ion pump in said envelope, (1) said electrodes comprising a flat cathode and References Cited UNITED STATES PATENTS a flat lcellular anode parallel to and substantially 3,042,8M 7 /1962 Lloyd et a1 313 7 coextensive with said cathode, said electrodes 3,117,247 1/1964 Jepsen 230-69 X having flat surfaces parallel to said electron path 3,152,689 10/1964 Connor 313--7 X and relatively narrow edge surfaces normal to said electron path whereby said at surfaces 10 DAVID J. GALVIN, Primary Examine"-

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