US3024965A

US3024965A - Apparatus for vacuum deposition of metals

Info

Publication number: US3024965A
Application number: US689022A
Authority: US
Inventors: Milleron Norman
Original assignee: Individual
Current assignee: Individual
Priority date: 1957-10-08
Filing date: 1957-10-08
Publication date: 1962-03-13
Anticipated expiration: 1979-03-13

Description

March 13, 1962 N. MILLERON 3,024,965

APPARATUS FOR VACUUM DEPOSITION OF METALS Filed Oct. 8, 1957 3 Sheets-Sheet 1 WATER SUPPLY 5O INVENTOR.

NORMAN MILL ERON ATTORNEX POWER SUPPLY March 13, 1962 Filed Oct. 8, 1957 N. MILLERON APPARATUS FOR VACUUM DEPOSITION OF METALS 3 Sheets-Sheet 2 D.C. POWER SUPPLY SUPPLY INVENTOR. 3/ NORMAN M/LLERON BY 5 ,(4 WW ATTORNEY.

March 13, 1962 N. MILLERON 3,024,965

APPARATUS FOR VACUUM DEPOSITION OF METALS Filed Oct. 8, 1957 3 Sheets-Sheet 3 POWER I03 SUPPLY INVENTOR. NORMAN M/LLERON BY ATTORNEY.

charge of the electron gun.

Unite This invention relates in general to the vacuum deposition of metals, and particularly to an apparatus and process for the vacuum deposition of metals wherein the deposition is continuous. The invention may be specifically applied wherever a metal coating is desired, and because of the continuous deposition of metal characteristic of the invention there are particular advantages to be gained when used in high vacuum pumping equipment, including such embodiments as gettering pumps and ion pumps, in a manner which will be explained in detail. With minor structural modifications and a different operational procedure the vacuum apparatus is additionally adaptable to a high current electron source.

In the past the vaporization of metals for the purpose of plating or coating the metal upon a metallic surface has been largely confined to batch or intermittent operations. Usually a grounded strip of the desired plating metal is vaporized by bombarding the strip with an electron beam supplied by an electron gun. The strip is heated by virtue of the electron current and subsequently melts and vaporizes. The vaporized metal then radiates radially outward toward the metallic surface to be coated, which surface is frequently cooled to ensure attachment of the metal film. The entire operation is carried out in a closed vessel and a fore pump is commonly used to reduce the partial atmospheric pressure within the vessel to the order of lmm. Hg in order to avoid direct dis- Many different structural embodiments have been previously utilized to accomplish the foregoing. However, in all such embodiments the metal to be vaporized is either held within a refractory supporting piece or is self-supported, in which latter case the bombardment is intermittent. When self-supported, the metal to be bombarded is generally a Wire or ribbon which is automatically fed into the electron gun for bombrardment from a separate chamber. The metal is bombarded until such time as it begins to melt severely and ceases to support itself resulting in attendant dripping or clogging of the mechanism. The bombardment must consequently be stopped until the temperature of the wire is reduced to a point where the operation may be resumed.

In the refractory supporting method of the prior art the duration of the coating operation is dependent upon the amount of metal which can be held in a refractory or metal container and upon the temperature at which severe chemical reaction or melting of the container material transpires. In addition, the process cannot be used where extremely pure coatings are desired since the retlractory supporting material tends to diffuse into the coating metal and is radiated with same. The metal film being deposited also becomes contaminated with the entrapped gases held in the refractory material. Consequently, vapor coating with highly chemically reactive, or refractory, pure metal is not feasible and the method is furthermore relatively rigid and unadaptable. A process for continuously coating over an extended period has heretofore been impossible to attain.

A novel apparatus and method for vapor plating metals continuously without contamination from entrapped gases or other sources has now been discovered which accord- States Patent ice ingly overcomes the above-noted inadequacies of the prior art. A suitable plating wire or strip is fed through an externally cooled feeder tube adapted to thermally, or electrically, shield the wire or strip, the tube being constructed of a material having a high enough coefiicient of thermal conductivity that heat contained or generated in the tube surfaces is removed. Upon emerging from the tip of the cooled tube the wire is subjected to electron beam bombardment or other heating means causing the wire outside the feeder tube to be heated and to melt. The emerging Wire is preferably disposed in a vertical position to ensure symmetrical distribution of metal by gravitational force and is further disposed generally perpendicular to the plane of the electron gun or heat source in order to facilitate melting primarily in the outermost tip of the wire. The molten metal tends to form a molten ball held together by surface forces (i.e., surface tension), when the coolant, wire feed, and heating means are properly regulated. Heat contained in the wire behind the molten ball is conducted to the feeder tip or tube primarily by radiation rather than conduction. The molten metal in the ball being evaporated is radiated outward, while additional metal from the feeder wire melts. The wire may be continuously degassed prior to introduction into the feeder tube if pure coatings are desired. Close tolerance between the wire and tube is necessary if vacuum integrity is to be maintained.

The subject invention is accordingly useful in vaporizing pure metals, particularly in instances where continuous vaporization is desired, e.g., in the vacuum plating of metals, as mentioned hereinbefore, to obtain a metallic coat exhibiting corrosion resistance, decorative effect, specific surface characteristics, etc. The invention has additional, equally important applications in the high vacuum pumping art where a metal having the characteristic of being able to chemically or physically absorb large volumes of gases is required to continuously vaporize and coat surfaces to entrap gaseous molecules thereon. A simple application is a gettering pump in which the gettering or gaseous adsorption action of the continuous application of a metal coat is used to create a very high vacuum, usually after the vacuum cavity has initially been evacuated to a pressure of about 10* mm. Hg with a force pump. During operation, the gaseous particles remaining in the cavity randomly impinge upon the walls of a container communicably connected to the cavity being evacuated and are held thereon by the continuously increasing coat of adsorbent metal. A further application of the present invention is in ion pumps in which gaseous particles to be evacuated randomly enter an area between two cathode plates. A stream of electrons passing between the cathode plates ionizes the gaseous molecules and the resulting ions are attracted to the cathode plates. Ordinarily the ions are free to leave the plates upon contact therewith since they lose their charge and become neutral molecules. However, by placing the vaporized metal source of the present invention within the line of sight of the collecting surfaces of the cathode plates, during operation the vaporized metal is coated thereon and as the ions become electrically neutral upon striking the collecting plates, they are adsorbed by the continuously deposited metal. A greater pumping volume can thereby be achieved with the improved ion p-ump than could be obtained otherwise.

By the adaptation of the present invention to the vacuum pumping art, as indicated above, vacuum pressures and pumping speeds are attainable which were impossible previously. A limiting factor in all large scale vacuum pumps is the use of organic seals, lubricants and other materials employed in their construction. Such materials have rather high vapor pressures or slowly decompose such that pressures lower than 10- mm. Hg are extremely difiicult to attain. Under the present invention suitably baked and degassed gettering metals such as titanium, tantalum, tungsten, molybdenum, zirconium, niobium, rhenium, thorium, and uranium are used which have negligible vapor pressures, and accordingly vacuum pressures as low or lower than 10- mm. Hg can be attained while pumping at rates as high as hundreds of thousands of liters per second.

For gettering pumps the actual capacity per unit time or output of a given vaporized metal source is in large part determined by the surface area of the chamber walls that must be coated with metal and the amount of metal deposited per unit time. In principle, the pump relies upon the random or thermal motion of the gaseous molecules to cause them to enter the pumping chamber and to strike a wall surface. Once the molecule strikes a wall surface it has a tendency to stick for a finite period of time. When the surface consists of an adsorbent metal that is not already saturated with adsorbed gases, each molecule which strikes is adsorbed. As the adsorbtive capacity is reached, larger and larger numbers of the gaseous molecules will also tend to be desorbed, according to the equilibria for each individual metal employed with a particular gas. Fresh degassed metal must be deposited upon the wall surfaces with a frequency which will ensure that the gas molecules will be adsorbed substantially faster than they are desorbed.

In general with simple gettering pumps A n molecules of the gas to be pumped will impinge upon a square centimeter of wall surface per second, where n is the number of gaseous molecules per cubic centimeter in the space immediately adjacent the wall surface in question, and E is the root mean square velocity of the gas molecules. Under nominal pressures this will mean about impingements per second per square centimeter. Similar calculations can be carried out for ion pumps, although the above figure represents about the maximum number of impingements that can be adsorbed by any pump employing a single vaporized metal source without electrical discharge.

In order to ensure that most of the impinging gaseous molecules will stick to the surface an estimated C n5 metal atoms must also strike each square centimeter of surface per second, where C is variously estimated at from 3 to 10. This means approximately 10 to 10 atoms of gettering metal must occupy each cubic centimeter adjacent to the wall areas While the gettering pump is operating. Rates of vaporization beyond about 3 1O atoms per second cannot be achieved because at this point the vaporizing beam of electrons from the electron gun breaks down into an electrical discharge, thereby limiting the actual physical volume of a pump employing a single vaporizing metal source. In the present model a gettering pump using 30 mil molybdenum coating wire and a vaporizing electron current voltage of 5 kv. attains pumping speeds of 10 liters per second at pressures as low as l0 mm. Hg with a single vaporized metal source. Such pressures and volumes are necessary to meet the demands of modern vacuum work in thermonuclear machines, particle bombardments and other nuclear applications, mass spectroscopy, etc. It is only with the advent of a truly continuous vaporization source as provided by the instant invention that these pressures and volumes are possible.

As a further application of the present invention, the continuously supported molten ball thereby provided may be also utilized as a high current density electron source merely by utilizing alternating current voltage instead of direct current voltage between the molten ball and the electron source filament. High currents are derived from the molten ball during the positive excursion of the alternating voltage while during the negative excursion thereof the ball is heated and evaporated. Outputs as high as 200-300 amps for a 860-1000 watt input voltage may be obtained from the molten mass because of its high temperature emission characteristics. Ordinary tungsten filaments, operating at lower temperatures, require 4600 watts or more for the same amperage, and in addition would be at least 26 in. long and have other disadvantages. In the present applications the identical amount of current could be obtained from a molten ball 0.2 in. in diameter. Unlike the regular tungsten filament the molten ball is not subject to poisoning by the surrounding atmosphere because it is always evaporating slowly. The vaporizing molten ball also provides its own vacuum, since there is an automatic gettering action on adjacent surfaces due to adsorption and ion burying in the cvaporative coating portion of the voltage cycle. With slight structural additions or modifications, the high current electron source may be used as a means for heating metals to a very high temperature in vacuum, for positive ion space charge neutralization (creation of ionized plasmas), for high current vacuum tubes, or for numerous other applications where large currents in high vacuum are needed.

Accordingly, it is an object of this present invention to provide a novel method and apparatus for continuously producing and supporting a molten ball of vaporizing metal.

A further object of this invention is to provide a method and apparatus for continuously producing a selfsupporting molten ball of vaporizing metal on the tip of a wire.

Another object of the invention is to provide a novel method and apparatus for continuously vaporizing metals.

A further object of this invention is to provide a novel method and apparatus for the continuous vacuum plating of pure degassed metals.

Another object of this invention is to provide a method and apparatus for continuously feeding a metal wire or strip into a vacuum tight metallic vaporization zone without contamination of the resulting molten metal through contact with other materials.

Another object of this invention is to provide a water cooled feed mechanism for continuously feeding a degassed metal strip or wire into an electron gun chamber for electron bombardment where by regulation of the coolant, feed rate, and electron current, a molten ball of vaporizing metal is self-supported on said wire or strip.

A still further object of this invention is to provide a gettering pump in which the gettering metal is continuously fed into a vaporization chamber and is therein vaporized.

A still further object of this invention is to provide a gettering pump in which a wire or strip of gas adsorbing metal is continuously fed through a fluid cooled feed mechanism into an electron gun chamber for electron bombardment where by regulation of the coolant, feed rate, and electron current a ball of molten vaporizing metal is continuously self-supported on said wire or strip.

Another object of this invention is to provide an ion pump in which a cathode plate for attracting gaseous ions is continuously coated with a layer of metal.

An additional object of this invention is to provide an ion pump in which a metal wire or strip is continuously fed through a fluid cooled feed mechanism into an electron gun chamber for electron bombardment where by regulation of the coolant, feed rate and electron current a ball of molten metal is self-supported on said wire or strip and is vaporized to continuously coat a cathode plate for attracting ions.

One more object of this invention is to provide an apparatus and method for producing and discharging a high current of electrons from a continuously produced and supported molten ball of vaporizing metal.

One final object of this invention is to provide an apparatus and method. for..producing and discharging a current of electrons from a continuously produced and supported molten ball of vaporizing metal which creates vacuum conditions by the gettering action of the evaporating metal vapors.

Additional objects and advantages of the present invention will become apparent from the ensuing description taken in conjunction with the accompanying drawings, of which:

FIGURE 1 is a cross sectional elevation view partially in schematic of a preferred embodiment of an apparatus for the vaporization and vacuum deposition of metals, the apparatus also being adaptable for use as a getters p p;

FIGURE 2 is a longitudinal cross section of the fluid cooled feed unit of FIG. 1;

FIGURE 3 is a partially schematic cross sectional view illustrating the invention as embodied in an improved ion pump having apparatus for the continuous vaporization and plating of metals upon the cathode plates; and

FIGURE 4 is a cross section of an alternate embodiment of the invention for producing and discharging a current of electrons from a continuously produced and supported molten ball of vaporizing metal.

Referring now to FIG. 1, there is shown a preferred embodiment of the invention which is adapted for emment as a gettering pump and which is provided with a generally elongated cylinder 11 defining a vacuum chamber 12 opening at the upper end into a vacuum tank (not shown) formed by walls 13. The bottom of chamber 12 is closed by removable base plate 14 which also serves as an end wall to a second vacuum chamber 16 defined by cylinder 17. A pressure fit is provided between cylinders 11, and 17 as by means of bolts 18 acting upon

flanges

19, and 21 of such cylinders 11, and 17, respectively, upon either side of base plate 14 and upon deformable metal gaskets 22 interposed therebetween. The second chamber 16 is suitably closed at the lower end by a removable backing plate 23, and is preferably connected with a fore pump 24 through exit pipe 26.

A vertically disposed water cooled feed unit,27 is coaxially mounted within chamber 12 as by threadable engagement with base plate 14. The feed unit 27 is shown in cross section in FIG. 2 and consists of a threaded massive plug member 28 adapted to engage base plate 14 and through which member extends a bore 29 generally perpendicular to the plane of the exterior threads. A central elongated metal feed tube 31 in close fitting relation to bore 29 extends the length thereof and for a distance into vacuum chamber 12.

Suitable tubes

32 and 33 are respectively disposed outwardly concentric with respect to feed tube 31 each being countersunk for a distance into the top of plug member 28, which provides support therefor, outermost tube 33 being countersunk to a lesser depth than intermediate tube 32. Inlet and outlet ports 34- and 36 below base plate 14 in plug member 28 provide coolant entrance and exit means into

tubes

32 and 33, respectively. A suitably shaped tip 37 is joined to outer tube 33 as shown generally at 38 by any appropriate means of rigid. attachment and extends the tube structure to form a union with feed wire tube 31. Coolant water or equivalent cooling fluid introduced to inlet port 34 flows upward between

tubes

32 and 33, is deflected by tip 37 and flows downward between

tubes

32 and 31 and out exit port 36. Pipes 39 and 41 (see FIG. 1) are preferably connected to exit and

inlet ports

36 and 34 respectively and led exteriorly through chamber wall 17 as shown generally at 4-2 and 53, respectively, to facilitate connection to an external water supply 4-4.

A feed wire 46 (FIG. 1) fabricated from any desired metal to be deposited, and wound on a rotatable metal spool 47, passes between conventional externally

powered feeder rollers

48 and 19 to facilitate continuous introduction of the feed wire into feed wire tube 31.

While numerous conventional means may be used to maintain the vacuum around

rotatable drive shafts

57 and 58 extending through wall 17 for connection to

rollers

48 and 49, respectively, the use of liquid metal seals has been found particularly convenient and leak proof; for example, a metal having a composition of 62.5% gallium, 21.5% indium, and 16% tin, and which melts at approximately 10 C., has been utilized to great advantage in practice.

Reasonable vacuum integrity is maintained between

vacuum chambers

12 and 16 communicably connected through feed. wire tube 31 by incorporation of a feed wire size having a tolerance of 5 mils or less with respect to the feed Wire tube 31. Degassing of the wire 46 prior to feeding into the water cooled feed unit 27 is accomplished, as by resistance heating by means of a conductor 50 connected to a power supply 51 and led through backing plate 23 at a vacuum insulated point 52 to be connected to a spool holder 53 for supporting spool 47. Holder 53 is made of a conducting metal and is insulated from the backing plate as shown generally at 54. Power supply 51 is grounded to the backing plate by contact wire 56 to complete a circuit to ground through a current conduction path including wire 46. The wire is thus resistance heated by virtue of the current flowing therethrough. It will be appreciated feed wire 46 may be of any composition depending upon its purpose. For adsorption and pumping purposes highly adsorptive metals, i.e., particularly titanium, tantalum, tungsten and molybdenum, as well as zirconium, niobium, rhenium, thorium and uranium, have been found superior.

In order to heat the feed wire 46 emerging from the tip end of feed tube 31 to a high temperature, means are provided for bombarding the emerging feed wire with an electron beam. The means may be provided, for example, in the form of an electron gun 59 having a heated cathode filament 66 mounted above tip 37 as by means of cathode posts 61 embedded in and insulated from base plate 14. Energization of filament 59 to supply electrons is facilitated by conductors 62 connected to posts 61 at the under side of base plate 14. Such conductors lead through insulated hermetically sealed bushings 63 mounted in backing plate 23 for connection to a suitable D.C. power supply 64 operating above ground potential. The electrons emitted by filament 60 are roughly focused onto the molten ball 72 by a bias screen 66 supported coaxially about tip 37 by electrically conducting supports 67 attached to posts 61. Screen 66 is thereby maintained at least as negative as the potential of power supply 64 and therefore of filament 64). Moreover, feed wire 46 is grounded through base plate 14 as shown gen erally at 68 whereby the potential gradient thus established between filament 6t) and the emerging tip of feed wire 46 is effective in accelerating the beam of electrons thereto. The impinging electron beam vaporizes the tip of feed wire 46 as hereinafter described. with respect to the operation of the invention. To prevent the metal vapors thus evolved from contaminating vacuum areas outside of the main pumping cavity 12 a circular plate 69 is best disposed in spaced relation to wall 13 by means of supports 71 anchored thereto.

The process or method of operation is as follows: The vaporization chamber 12 is first pumped down by conventional means such as a fore pump (not shown) to a pressure of 18 mm. Hg or less to avoid direct discharge when the electron gun 59 is energized. The cooling water is next circulated through feed unit 27, water of room temperature or even higher being suflicient as long as the flow within chamber 12 is sufficient to remove heat rapidly.

Feeder rollers

48 and 49 are started and filament 60 is energized. Once the filament 60 has been energized the stream of electrons arriving at the emerging feed wire 46 heat the tip of the wire and cause it to become molten. A self-supported molten ball 72 forms at the tip of the wire, which ball is held together by surface tension. The molten ball 72 shields the feeder tip 37 from electron bombardment. Sufiicient energy is rained (concentrated) on the surface of the molten ball 72 to cause it to evaporate at a rate that is matched by the rate of feed of the wire. The feed wire immediately behind the ball is thermally and electrically protected by the water cooled tip 37 without which the ball 72 has a strong tendency to burn off because the wire becomes thin and is unable to support the molten ball.

When the vaporization apparatus of the present invention is operated merely as a means of vapor coating objects with a metal, such vaporization apparatus may be modified or simplified as desired to additionally include means for supporting the objects to be coated within the chamber in receiving relationship to the vaporized metal evolved from molten ball 72. The pumping means 24 for evacuating vacuum chamber 16 and the means for resistance heating of the feed wire 46 are necessary to hold air and adsorbed vapors to a minimum when extremely pure coatings are desired, e.g., coatings on foils for nuclear bombardments and other nuclear energy applications.

Operation as a pumping means at extremely low pressures, i.e., below 10* mm. Hg, is accomplished by first pumping out the upper and

lower vacuum chambers

12 and 16 for extensive periods of time at pressures of mm. Hg or less to degass the gases normally entrapped on the walls thereof. During this preliminary pumping period, or during later operation, power supply 51 provides means for heating the feed wire 46 to a temperature of the order of 2000 C. by resistance heating, the exact temperature depending upon the melting point of the particular wire material being used. All gaseous impurities are normally degassed at this temperature and the feed wire 46 than has a purity commensurate with that of the original metal. The entire vaporization unit is next brought into operation as detailed previously and vaporized metal continuously travels in a line of sight from the molten ball to the walls and any other surfaces disposed within the chamber 12. The clean pure metal coats the walls continuously and adsorbs and covers gaseous molecules thereon by chemisorption and physical adsorption mechanisms. With radiation rates of the order indicated above and with cylindrical pumps having on the order of 10 square centimeters wall area, pumping rates as high as 10 l./sec. may be obtained at 10* mm. Hg. These quantities operate as an upper limit for a single vaporization unit, although several such units may be arranged within the same pump housing to increase the pumping action.

While the pumping capacity as developed above is related to pump internal surface area and volume of vaporized metal radiated per unit time from feed unit 27, there must be sufiiciently large passageways into the gettering cavity 12 from the vessel to be evacuated for large numbers of gaseous molecules to enter because of their random or thermal motion. During deposition, the metal coat builds up in an irregular manner with many ridges and valleys caused by initial uneven deposition to thus increase the effective collecting surface area.

The gettering or vaporizing metal source of the present invention, viz., feed unit 27, may be additionally employed as a continuous gettering source in an ion pump, as shown in FIG. 3, to enhance the pumping action thereof. More particularly, there is provided a vacuum cavity 73 defined by container walls 74 connected to a cavity to be evacuated (not shown) through passageway 76 defined by an inlet conduit 77. Disposed within the cavity 73 in generally opposing positions and preferably on either side of passageway 76 are a pair of cathode electrodes 78. The electrodes 73 are insulated from wall 74 and energized with alternating voltage supplied by means of leads 79 connected to a tap of an AC. power supply 81. A magnetic field having a direction as indicated by arrow 82 normal to the cathode surfaces is created between the two electrodes 78 by a magnet (not shown) exterior to the wall 74. Two grids 83, respectively located proximate the facing sides of electrodes 82, are insulated therefrom and operated at a slightly higher alternating potential than the electrodes 78 by connection with a suitable tap of power supply 81 as by means of leads 84. A filament 86 is spaced between one of the grids 83 and corresponding electrodes 78 and is connected by means of insulated wire $57 to an appropriate tap of power supply 81 for operating the filament at a potential intermediate the potentials of the grids and electrodes. The chamber wall 74- operates at ground potential as indicated at 88.

All of the foregoing elements are conventional in various known ion pumps and are presented herein merely for purposes of illustration. In such conventional ion pumps an electron stream emitted from filament 86 oscillates between electrodes 7h due to the action of magnetic field 82 and the alternating electric field established by the potentials applied to electrodes 78 and grids 83. The oscillating electron stream ionizes gas molecules entering cavity 73 by random motion from a vessel to be evacuated. The ions thus produced are attracted to electrodes 78 and collected thereon to produce a pumping action. The ions upon impinging upon the electrodes, however, are neutralized and are free to migrate away from the plates. The accumulation of neutral molecules so formed in the region of electrodes 78 are then commonly evacuated by means of a mechanical vacuum pump (not shown).

In accordance with the salient features of the present invention, the pumping capacity of a conventional ion pump, for example of the type described above, is materially increased by the incorporation therein of a water cooled feed unit 27 as previously described. Such feed unit 27 is best disposed with the water cooled tip 37 thereof in a vertical position within ion pump cavity 73. The molten ball 72, when formed by the feed unit, is preferably in a line-of-sight distance from all parts of the opposing surfaces of electrodes 78. The electron source and other accessory means of the metal vaporizing source of the instant invention (not shown in detail in FIG. 3) may be the same as those shown in the gettering pump of FIG. 1, or may vary structurally as long as the same function (namely, production of a bombarding electron beam) is performed.

The process of operation is as follows: The vacuum cavity 73 and chambers to be evacuated are first pumped down to a pressure of the order of 10" mm. Hg as by means of a standard fore pump 89 connected to passage 76 by piping M. The components of the vacuum feed unit 27 are similarly pumped down and degassed, as in the gettering pump embodiment of FIG. 1 previously described. Operation of the metal vaporization means in the manner hereinbefore described provides a continuous stream of metal vapors which travel in a line of sight radially away from the molten ball 72 formed by feed unit 27. Electrodes 78, not yet energized, are continuously coated with metal vaporized from molten ball 72, and a gettering action is thus provided which traps a portion of the gaseous molecules entering cavity 73 through passageway 76 upon all surfaces where the metal coats. Upon activation of power supply 81 an oscillating electron stream is established in cavity 73 which then ionizes gaseous molecules in the conventional ion pumping manner, the ions being attracted to electrodes 78 and neutralized thereat. The neutral gas molecules which are commonw 1y free to migrate away from the electrodes are now trapped upon such electrodes by virtue of the concurrently deposited adsorptive metallic molecules emanating from feed unit 27 which establish a matrix for chemically inert gas molecules shot into the electrodes by the action of the electric field. The acceleration of ions caused by the potential dilferential between grids 83 and electrodes 78 causes the gaseous and metal ions to both stick very tightly to the electrodes. The gettering action produced by the present invention thus eifectively increases the pumpmg capacity of the ion pump by holding the gaseous particles onto the ion pump electrodes 78.

Operation of the present inventive structure as a means for maintaining a vacuum while at the same time acting as a source of a high current of electrons is illustrated in the embodiment of FIG. 4 where there is shown a vacuum cavity 92 defined by walls 93. A water cooled feed unit 27, similar in structure and design to the mechanism of the same number in FIGS. 1 and 2, is disposed vertically through the top wall 94 of cavity 92 together with feed Wire and Wire feed mechanism, coolant and coolant feed means, secondary vacuum pumping means and other components of the metal vaporization apparatus described in connection with FIGS. 1 and 2 and accordingly not shown in detail in the present figure. A cathode filament 96 is disposed beneath the feed unit 27 and is maintained at a higher potential than the electrically grounded feed unit 27 by connection to an A.C. power supply 97 through insulated lead wires 98. An extraction grid 99 may in addition be optionally disposed between the molten ball 72 formed by feed unit 27 and the filament 96, in which case the grid is connected through insulated conductor 1% to a tap of power supply 97 for producing a voltage of the same phase as applied to filament 96 but of smaller amplitude. The grid serves to lessen the distance between the two conductors and thereby increases the transmission amperage of the electron stream originating at filament 96.

A metallic collector block 101 to be heated or melted is disposed beneath the filament 96 and is maintained at a higher potential than the filament by means of an insulated lead wire 102 connecting the block 101 with a suitable tap of AC. power supply 97. Obviously other receiving means may be substituted for the block 101 when the high density electron current is to be used for other purposes. A pump 103 connected to the vacuum cavity 92 by outlet 164 is used to pre-evacuate the cavity to a pressure of about mm. Hg.

With the cavity 92 pre-evacuated and feed unit 27 together with its accessory equipment degassed as previously described in relation to the embodiment of FIGS. 1 and 2, the feed unit and accessories are next placed into operation and AC. power supply 97 energized. Initially a stream of electrons is produced by filament 96 and the electrons are alternated between the feed wire tip and plate 101 due to the alternating electric field established therebetween with the frequency of alternation being determined by the frequency of output voltage supplied by power supply 97. The alternating electron stream is in itially of small amperage. As the feed wire heats up due to bombardment by the electrons and forms molten ball 72, however the electron constituent of the vaporized metal emanating from the ball is extracted during the positive alternations of the applied electric field and attracted toward plate 191 to materially increase the amperage of the alternating electron stream. During the negative alternations of the applied field, the electrons (including both the electrons emitted by filament 96 as well as a portion of the electrons previously extracted from the vaporized metal) are attracted to molten ball 72 formed at feed unit 27 resulting in the continued heating and evaporation of the ball by electron bombardment. It is to be appreciated that in the present embodiment, the molten ball 72 not only functions to produce an intense electron stream but in addition the process of vaporization keeps the molten ball emitter free from contamination and the coating formed eifectively adsorbs substantially all gaseous particles in cavity 92 to produce an extremely high vacuum therein.

While the invention has been disclosed with respect to but several preferred embodiments, it will be apparent to those skilled in the art that numerous variations and modifications may be made Within the spirit and scope of the invention and thus it is not intended to limit the invention except as defined in the following claims.

What is claimed is:

1. In an apparatus for continuous deposition of metal vapors, the combination comprising a metal feed wire of vapor plating material, a cooled feed wire tube disposed coaxially about said feed wire in close tolerance therewith and terminating at the feed end in a generally vertical position to maintain the wire in a vertical position as it emerges from said tube, means coupled to said feed wire for continuously feeding same through said tube at a uniform rate, and means for rapidly heating said wire emerging from said tube to form from said wire a ball of molten metal self-supported on the emerging end thereof whereby said wire is continuously heated to form said molten ball and said molten ball is continuously vaporized.

2. In an apparatus for the continuous vacuum deposition of metal, the combination comprising a vacuum tight container, means coupled to said container for initially evacuating same to a pressure of at least about 10* mm. Hg, a coolant-jacketed feed wire tube disposed to terminate at the feed end in a generally vertical position within said container to discharge feed wire in a vertical position, a metal wire of material suitable for vapor plating extending through said tube, means coupled to said wire for continuously feeding the wire through said tube at a uniform rate, an electron source carried by said container and disposed to produce an electron beam for bombarding the tip of the wire emerging from said tube, and a ball of molten vaporizing metal formed from and self-supported on the end of said emerging wire, whereby said wire is continuously heated to form said molten ball and said ball is continuously vaporized.

3. Apparatus as defined by claim 2 further defined by said coolant-jacketed feed wire tube comprising a central elongated metallic tube having a bore diameter for establishing a close fitting relationship with respect to the feed wire, an outer metallic tube disposed concentrically about said central tube, an intermediate metallic tube concentrically interposed between said outer and central tubes and terminating at an axial position rearwardly from one end of said central tube, a metallic tip extending between the opposite end of said central tube and the corresponding end of said outer tube, means attached between said outer and intermediate tubes at the distal ends thereof with respect to said tip for terminally closing the intervening space between said outer and intermediate tubes, structure defining an inlet port communicating with said intervening space between said outer and intermediate tubes at said distal end thereof with respect to said tip to admit coolant thereinto, and structure defining an outlet port communicating with the intervening space be tween said intermediate and central tubes at said distal end thereof with respect to said tip for removing coolant therefrom.

4. In an apparatus for the continuous'vacuum deposition of metal, the combination comprising a vacuum-tight container, means communicably connected to said container for initially evacuating same to standard fore vac dimensions, a vertically disposed jacketed feed wire tube communicating through one wall of said container, means connected to said tube for circulating coolant through the jacket thereof, a rotatably supported spool, metal feed wire wound upon said spool and extending through said feed wire tube and emerging in a vertical position, rotatably driven feeder rollers engaging said wire intermediate said spool and feed tube for continuously feeding said wire through said tube at a uniform rate, heat generating means for heating and degassing said wire prior to entry into said tube, an electron emissive filament internally supported within said container vertically proximal the end of said feed tube from which said feed wire emerges, and a focusing grid disposed coaxially about the end of said feed tube for concentrating electrons emitted from said filament upon the tip of said feed wire emerging from said tube, said electrons uniformly heating the emerging tip of said feed wire, and a continuously evaporated molten ball self-supported thereon.

5. Apparatus as defined in claim 4 but wherein the feed wire metal is selected from the group consisting of tungsten, tantalum, molybdenum, titanium, zirconium, niobium, rhenium, thorium and uranium to produce a gettering action.

6. Apparatus for the continuous vacuum deposition of metal comprising a vacuum tight container adapted to stand upright, a second vacuum tight container, a pressure sealed base plate common to said first and second containers, a massive plug member mounted in said base plate and having a central axial bore communicably connecting said first and second containers, said plug member partially projecting into said second container, an elongated metal feed tube extend-ing the length of said bore in close fitting relation therewith and projecting vertically into the interior of said first container, an outer metal tube disposed outwardly concentric of said feed tube and countersunk into said plug member, an intermediate metal tube concentrically interposed between said outer tube and said feed tube, said intermediate tube countersunk into said plug member to a greater depth than said outer tube and extending to an axial position spaced rearwardly from the projecting end of said feed tube, a metal tip extending from the projecting end of said outer tube to the corresponding end of said feed tube, an inlet port mounted in the portion of said plug member projecting into said second container and communicably connected to the intervening space between said outer and intermediate tubes, an outlet port mounted in the portion of said plug member projecting into said second container and communicably connected to the intervening space between said intermediate tube and said feed tube, a coolant supply connected between said inlet and outlet ports for circulating coolant therethrough, a spool rotatably mounted within said second container and electrically insulated therefrom, metal feed wire of a material to be vacuum deposited wound upon said spool and extending through said vertical feed tube in close tolerance therewith, and thereby emerging in a vertical position, rotatably driven feeder rollers mounted within said second container and engaging said feed wire intermediate said spool and said feed tube for continuously feeding said wire into the feed tube at a constant rate, means connecting said feed tube to ground, a power supply connected between said spool and ground for resistance heating said feed wire, and an electron gun carried by said first container and disposed proximal said tip for electron bombarding in the axial direction thereof feed wire emerging from said feed tube to uniformly heat and form a continuously evaporated molten ball from the emerging feed wire and self-supported thereon whereby metallic surfaces to be coated may be disposed within said first container and the evaporated metal continuously deposited thereon.

7. In an apparatus for continuously pumping gases by adsorption onto freshly deposited metal, the combination comprising a vacuum tight container opening into a cavity to be evacuated, a coolant-jacketed feed Wire tube terminating at the feed end in a generally vertical position disposed through a wall of said container to discharge feed wire in a vertical position, means for connecting the coolant jacket of said feed wire tube with an exterior pressurized coolant supply, a metal wire having good gettering properties extending through said tube and in close tolerance therewith, a second vacuum tight container having said wall through which said tube is disposed in common with said first container, means communicating with said vacuum tight container and said second container for evacuating same to a pressure of about mm. Hg, a spool rotatably mounted in said second container and having said wire wound thereon, means carried by said container for continuously feeding said wire from said spool through said tube at a uniform rate, heating means carried by said second container for initially heating and degassing said wire prior to entrance into said tube, an internally supported electron emission filament in said first container vertically proximal and perpendicular to the wire emerging from said tube, a focusing grid supported around the emerging tip of said wire, an exterior power source connected in energizing relation to said filament, and a ball of molten vaporizing metal formed from and supported on the emerging tip of said wire, whereby said wire is degassed prior to being continuously heated by electron bombardment to form said molten ball and said ball is continuously vaporized and deposited on said vacuum tight container walls to produce a gettering action.

8. In an apparatus for continuously removing ionized gases, the combination comprising an ion pump including at least one electrode upon which ions are collected and neutralized to form gaseous molecules, a feed tube terminating at the feed end in a generally vertical position and extending interiorly of said pump and adapted for a vertical feed within line-of-sight of said electrode, jacket means for cooling said tube, a gettering wire extending through said tube and emerging therefrom, means carried by said pump for continuously feeding said wire through said tube at a uniform rate, means for rapidly and uniformly heating said wire emerging from said tube, and a ball of molten metal formed from and self-supported on the end of said emerging wire whereby said wire is continuously heated to form said molten ball and said ball is continuously vaporized to deposit said gettering metal upon said electrode.

9. In an ion pump in which the metal surfaces of the cathode electrodes are continuously coated with an adsorptive metal, the combination comprising a vacuum tight container opening into a cavity to be evacuated, means for initially evacuating said container to a pressure of at least about 10* mm. Hg, means including a pair of spaced cathodeelectrodes carried within the container for ionizing gas entering said container from said cavity, said cathode electrodes collecting and neutralizing ionized gases, a feed wire tube terminating at the feed end in a generally vertical position extending through a wall of said container and adapted to feed wire vertically within line of sight of said electrodes, means coupled with said tube for cooling same, a gettering wire extending through said tube and in close tolerance therewith and emerging in a vertical position, means engaging said wire for continuously feeding the wire through said tube at a uniform rate, means disposed within said container for rapidly heating the tip of the Wire emerging from said tube, and a ball of molten metal formed from and self-supported on the emerging end of said wire, whereby said wire during operation of said pump is continuously heated to form said molten ball and said ball is continuously vaporized to deposit said gettering metal upon said electrodes.

10. An ion pump comprising a vacuum tight container opening into a cavity to be evacuated, fore pump means communicating with said container, means including a pair of spaced electrodes disposed within said container for establishing an oscillating electron discharge between said electrodes, said electron discharge ionizing gas entering said container to establish an ionized gaseous discharge between said electrodes with the ions being collected and neutralized thereon, a jacketed feed tube mounted in a Wall of said container and having the feed tip projecting generally vertically and interiorly of said container in line of sight relationship with said electrodes, coolant means connected to said feed tube for circulating coolant through the jacket thereof, a rotatably mounted spool, gettering wire wound upon said spool and extending through said feed tube to emerge in a vertical position, means engaging said wire for continuously feeding same 13 through said tube at a uniform rate, an electron gun disposed within said container vertically proximal the tip of said feed tube for bombarding the gettering wire emerging from said tube with electrons, and a continuously evaporated molten ball of gettering wire material selfsupported on the emerging end of said wire whereby said electrodes during operation of said pump are continuously coated with the gettering wire material to trap the neutralized ions upon the electrodes by adsorption.

11. In an apparatus for continuously producing a high density electron current in a vacuum, the combination comprising a vacuum tight container, means coupled to said container for initially evacuating same to a pressure of about mm. Hg, a feed wire tube disposed within said container to terminate at the feed end in a generally vertical position and connected to ground, jacket means for cooling said tube, a gettering wire extending through said tube and emerging therefrom, means carried by said container for continuously feeding said wire through said tube at a uniform rate, an alternating current electron source deposed proximal and perpendicular to the axis of said wire emerging from said tube to heat the wire by AC. electron bombardment, a ball of molten metal formed from and supported on the end of the emerging wire, and electron receiving means disposed coaxial with said emerging wire and on the opposite side of said electron source from said tube, said means in phase with said electron source and of a greater electrical potential than said source whereby said molten ball is heated and vaporized by a stream of electrons during the negative alternation of said source and a high density electron current is discharged to said receiving means during the positive alternation of said source.

12. A high current electron source comprising a vacuum tight container, vacuum pump means connected to said container for evacuating same to a pressure of about 10' mm. Hg, a jacketed feed tube mounted in a Wall of said container and having a tip projecting interiorly thereof, said tip terminating in a generally vertical position, coolant means connected to said feed tube for circulating coolant through the jacket thereof, a rotatably mounted spool having gettering wire wound thereon, said gettering wire extending through said feed tube in close tolerance therewith and emerging from the tube in a vertical position, feed means engaging said wire for continuously feeding same through said tube at a uniform rate, a filament vertically disposed in coaxial alignment with the axis of the emerging gettering wire, an extraction grid coaxially interposed between said filament and said emerging wire, electron receiving means coaxially disposed on the opposite side of said filament from said grid, an AC. power supply coupled to said grid, filament, and receiving means to apply respective in phase alternating voltages of increasing amplitudes thereto, and means connecting said feed tube to ground.

13. In a method for the continuous vacuum deposition of metal, the steps comprising evacuating a vaporization and deposition chamber to a pressure of at least about 10' mm. Hg, feeding a metal wire continuously through a coolant-jacketed feed wire tube disposed for vertical wire feed in said chamber, said wire being in close tolerance with said tube, bombarding the tip of said wire emerging from said tube with a beam of electrons, whereby said tip heats and melts, and regulating the wire feed, coolant feed, and electron beam to cause the formation of molten vaporizing metal self-supported on said tip by surface tension in which additional wire is continuously melted to replace metal lost by vaporization.

14. In a process for the continuous vacuum deposition of a metal, the steps comprising evacuating a vaporization and deposition chamber to a pressure of at least about 16* mm. Hg, continuously evacuating a second adjacent chamber containing a metal wire on a spool, heating and degassing said wire, feeding said wire from said spool lid continuously through a coolant jacketed feed wire tube disposed to have said wire in a vertical position in said vaporization chamber as it emerges, said wire being in close tolerance with said tube, bombarding the tip of said wire emerging from said tube with a beam of electrons, whereby said tip heats and melts, and regulating the wire feed, coolant feed, and electron beam intensity to cause formation of a ball of molten vaporizing metal self-supported on said tip by surface tension in which additional wire is continuously melted to replace metal lost by vaporization.

15'. In a process for the continuous adsorption of gases onto freshly deposited metal, the steps comprising vertically feeding a degassed gettering wire continuously through an exteriorly cooled feed wire tube into a vacuum tight container evacuated to a pressure of at least about 10 mm. Hg, said container opening into a cavity to be evacuated, heating the tip of said wire emerging from said tube, and regulating the wire feed, coolant feed and electron beam intensity to form a vaporizing molten ball self-supported on said tip by surface tension whereby said vaporizing metal coats surface areas within said container to produce a gettering action.

16. In a process for the pumping of gases by adsorption onto a gettering metal continually being deposited on a surface, the steps comprising evacuating a vacuum tight container to a pressure of at least about 10" mm. Hg, said container opening into a cavity to be evacuated, degassing a gettering wire, feeding said gettering metal wire continuously through a coolant jacketed feed wire tube disposed to maintain said wire in a vertical position in said chamber as it emerges, said wire being in close tolerance with said tube, bombarding the tip of said wire emerging from said tube with a beam of electrons to heat and melt said tip, and regulating wire feed, coolant feed, and electron beam intensity to cause the formation of a ball of molten metal self-supported on said tip by surface tension in which additional wire is continuously melted to replace metal lost by vaporization, whereby said vaporizing metal coats surface areas within said container to produce a gettering action.

17. In a process for continually evacuating gases, the steps comprising operating an ion pump having a charged cathode electrode to ionize said gases and collect and neutralize the resulting ions at said electrode, feeding a degassed gettering wire continuously through an exteriorly cooled feed wire tube into said pump within line of sight of said electrode, said wire being in close tolerance with said tube, said tube terminating at the feed end in a generally vertical direction uniformly heating the tip of said wire emerging from said tube, and regulating the wire feed, coolant feed and electron beam density to form a vaporizing molten ball self-supported on said tip by surface tension whereby said vaporizing metal continuously coats said electrode.

18. In a process for continuously evacuating gases, the steps comprising operating an ion pump having a charged cathode electrode to ionize said gases and collect and neutralize the resulting ions at said electrode, degassing a gettering wire, feeding said gettering wire continuously through a coolant jacketed feed wire tube terminating at the feed end in a generally vertical direction being disposed to maintain said wire in a vertical position as it emerges in said ion pump within line of sight of said cathode electrode, said wire being in close tolerance with said tube, bombarding the tip of said wire emerging from said tube with a beam of electrons to heat and melt said tip and regulating wire feed, coolant feed, and electron beam intensity to cause the formation of a ball of molten metal self-supported on said tip by surface tension in which additional wire is continuously melted to replace metal lost by vaporization and said vaporizing metal coats said cathode electrode to produce a gettering action.

19. In a process for continuously evacuating gases, the

aeeasee steps comprising operating an ion pump having a charged cathode electrode to ionize said gases and collect and neutralize the resulting ions at said electrode, continuously evacuating a second adjacent chamber containing a gettering metal wire on a spool, feeding said wire from said spool continuously through a coolant jacketed feed wire tube terminating at the feed end in a generally vertical direction and being disposed to maintain said wire in a vertical position as it emerges in said ion pump within line of sight of said cathode electrode, said wire being in close tolerance with said plate, bombarding the tip of said wire emerging from said tube with a beam of electrons to heat and melt said tip, and regulating the wire feed, coolant feed, and electron beam intensity to cause formation of a ball of molten vaporizing metal self-supported on said tip by surface tension in which additional wire is continuously melted to replace metal lost by vaporization, whereby said vaporizing metal coats said cathode electrode to produce a gettering action.

20. In a process for producing a high density electron current in a vacuum, the steps comprising evacuating a vacuum tight container to a pressure of at least about mm. Hg, feeding a degassed gettering wire continuously through an eXteriorly cooled feed wire tube into said container, said tube terminating at the feed end in a generally vertical direction, said wire being in close tolerance with said tube to maintain the wire in a vertical position as it emerges from said tube, producing a stream of electrons from a source within said container, establishing an alternating electric field between said source and the emerging tip of said wire to alternately focus the electron stream thereon, and regulating the wire feed, coolant feed and electron beam density to form a self-supported evaporating molten ball of the wire material and extract electrons from said ball, and collecting said electrons at a receiver disposed within said electric field whereby a high density electron current is emitted from said molten ball.

21. In an apparatus adaptable to the continuous vacuum deposition of metals and to the continuous gettering of gases by metals as well as the production of high density electron currents in vacuum, the combination comprising a vacuum-tight container, means coupled to said container for initially evacuating same to a pressure of at least about 10" mm. Hg, a coolant-jacketed feed wire tube vertically deposed within said container, a metal Wire of material suitable for vapor plating and gettering gases extending through said tube, means coupled to said wire for continuously feeding the Wire through said tube at a uniform rate, an electron source carried by said container in vertical spaced relation to said metal Wire extending through said vertical feeder tube to produce an electron beam for bombarding said wire emerging from said tube, and a ball of molten vaporizing metal formed from and self supported on the end of said emerging wire, whereby said wire is continuously heated to form said molten ball, and said ball is continuously vaporized.

22. in an apparatus for continuously pumping gases by adsorption onto freshly deposited metal, the combination comprising a vacuum tight container opening into a cavity to be evacuated, means communicating with said container for initially evacuating said container to a pressure of about 10 mm. Hg, a coolant jacketed feed wire tube terminating in a generally vertically upward position disposed to feed gettering wire into said container, means for connecting the coolant jacket of said feed wire tube with an exterior pressurized coolant supply, a degassed metal Wire having good gettering properties extending through said tube and in close tolerances therewith, means carried by said container for feeding said degassed metal wire continuously through said feed tube from a spool at a uniform rate, an internally supported electron source vertically spaced from said discharge end of said jacketed feeder tube, an exterior power supply connected in energizing relation with said electron source, whereby during operation said wire is continuously heatedby electron bombardment, and a ball of molten vaporizing metal formed from and self-supported on the emerging tip of said wire.

References Cited in the file of this patent UNITED STATES PATENTS 2,103,623 Kott Dec. 28, 1937 2,293,186 Wydler Aug. 18, 1942 2,469,006 Shelby May 3, 1949 2,527,747 Lewis Oct. 31, 1950 2,746,831 Chapman May 22, 1956 2,754,259 Robinson et al July 10, 1956 2,825,619 Miller Mar. 4, 1958 2,850,225 Herb Sept. 2, 1958 FOREIGN PATENTS 754,102 Great Britain Aug. 1, 1956