US3404255A - Source of vaporizable material for bombardment thereof by an electron bombarding means - Google Patents

Description

MTRO4- GR 314049255 QCL 1968 A R. HAMILTON 3,404,255

SOURCE OF VAPORIZLABLE MATERIAL FOR BOMBARDMENT THEREOF BY AN ELECTRON BOMBARDING MEANS Filed June 23, 1965 2 Sheets-Sheet 1 INVENTOR. /4Z/V 2 4414/4 70/1/ Oct. 1, 1968 A. R. HAMILTON 3,404,255

SOURCE OF VAPORIZABLE MATERIAL FOR BOMBARDMENI THEREOF BY AN ELECTRON BOMBARDING MEANS Filed June 23, 1965 2 Sheets-Sheet 2 INVENTOR fizz/v 1? AIM/z m/v United States Patent ABSTRACT OF THE DISCLOSURE A source of vaporizable material which employs either a rod of vaporizable material having a plurality of mutualv ly spaced annular grooves distributed therealong or a rod having a plurality of mutually spaced pellets of vaporizable material stacked on a supporting pin. The rod of vaporizable material may include a progressively increasing cross-sectional area as seen from a top surface to a bottom surface. An electron bombarding means is spaced from a free end of the vaporizable rod to cause vaporization of material from the free end of the rod. An adjustment means is provided for adjusting the position of the rod to control the spacing between the free end of the rod and the electron bombarding means.

The present invention relates to apparatus and equipment for vaporizing material and, more particularly, to a source of vaporizable material.

This application is a continuation in part of my prior patent application Ser. No. 387,407, filed Aug. 4, 1964, for Source of Vaporized Material, now abandoned.

Sources of vaporizable material are well known. They are, for example, used in vacuum pumps for providing getter material inside the pump housing, and in vacuum coating apparatus for depositing various materials on articles. Thus, the expression vaporizable material as used herein is meant to cover at least vaporizable getter material, as well as vaporizable materials of the type used in vacuum coating processes.

A proposed type of vaporizable material source comprises a rod made of the material to be vaporized and mounted to have a free end. This type of source includes means for heating the rod at its free end to vaporize material therefrom. In a preferred form of this type of source, the heating means include means, such as an electron gun or an electron-emitting filament, for bombarding the free end of the rod with electrons that bring about a vaporization of material from the rod. As the vaporization process progresses, the rod is successively consumed from the free end thereof.

One advantage of this type of vaporizable material source is that it is operative for several hours or days without having to be replenished with fresh material during that time and without requiring intricate material feeder mechanisms for its operation.

On the other hand, this type of source has been found to be subject to heat losses through conduction of heat along the rod and radiation of heat laterally from the rod. This not only leads to a waste of heating power, but requires the heating power to be repeatedly varied as the longitudinal and the lateral surface area dimensions of the rod are progressively diminished by the vaporization of material. In the absence of such repeated variation, the evaporation rate is non-uniform as the vaporization process proceeds.

It is the principal object of the invention to diminish these disadvantages.

According to one aspect of the invention, the rod ma- 3,404,255 Patented Oct. 1, 1968 terial to be vaporized defines a plurality of mutually spaced annular grooves distributed along the rod for impeding flow of heat therealong. Preferably, the grooves extend substantially perpendicularly to the general direction of heat flow along the rod.

In this manner, the power requirements of the means for heating the free end of the rod and the power rating of the equipment for energizing these means are significantly reduced. The life of these means is at the same time increased, and there is less heat dissipation from the source, so that the walls of the apparatus in which the source is used will operate at lower temperatures and can be located closer to the source than before. The reduction of heat conduction along the rod leads further to more equalized power requirements for vaporizing material as the dimensions of the rod are progressively diminished and to more equalized evaporation rates.

According to another aspect of the invention, the rod is tapered substantially along its entire length in the direction of its free end so that the area heated for the vaporization of material increases progressively as the length and the lateral surface area of the rod are successively decreased by the vaporization of material from the rod.

The feature of having the vaporization area increase as the latter dimensions decrease leads to a substantial equalization of the power requirement for vaporization over the useful life of the rod and to a corresponding equalization of the rate of evaporation of material from the rod, since the available heat energy is progressively distributed over a larger vaporization area as the heat dissipation from the overall surface of the rod decreases during the operation of the source. This will become more readily apparent as the description proceeds.

If desired, the two aspects of the invention so far described may be combined by providing the tapered rod just mentioned with the mutually spaced annular heat impedance grooves defined above. The result is a highly advantageous source of vaporizable material which is characterized by particularly moderate and equalized power requirements and a substantially constant evaporation rate.

The term rod of material to be vaporized as used herein is meant to refer not only to cylindrical but also to non-cylindrical bodies.

The invention will become more readily apparent from the following detailed description of preferred embodiments thereof, illustrated by way of example in the accompanying drawings, in which:

FIG. 1 is a longitudinal section of a getter-ion vacuum pump including a source of vaporizable material in accordance with a first embodiment of the invention;

FIG. 2 is an elevation on an enlarged scale of a source of vaporizable material in accordance with a second embodiment of the invention;

FIG. 3 is an elevation on a yet more enlarged scale of a source of vaporizable material in accordance with a third embodiment of the invention;

FIG. 4 is a top view on a still more enlarged scale along the line 4-4, of the source of vaporizable material illustrated in FIG. 3; and

FIG. 5 is a top view on the same scale as in FIG. 4 of a section, along the line 5--5, through the source of vaporizable material illustrated in FIG. 3.

The pump shown in the drawing comprises a housing 10 having a substantially cylindrical side wall 11, a bottom 12 with an aperture 13, and a flange 14 encompassing an inlet opening 15. A substantially cylindrical anode grid 18 is located inside the housing 10. A lead 19, which extends through an insulating bushing 20 in housing wall 11, connects 'anode 18 to the positive terminal of an ionizing high voltage supply 22. The negative terminal of supply 22 is connected to housing wall 11 by a lead 23.

A rod of getter material to be vaporized, such as titanium, is located in the lower region of housing 10. The rod 25 is mounted on a support 26 which, in turn, is mounted on an insulating strut 27. A shield disc 28 is interposed between support 26 and strut 27. The strut 27 is connected on the bottom 30 of a bellows 31, which has a flange 32 sealably attached to housing bottom 12 around the aperture 13 thereof. The bottom 30 of bellows 31 has a threaded bolt 34 attached thereto. The bolt 34 extends through an aperture (not shown) in a yoke 35 that is attached to housing bottom 12. A nut 36 is threaded on bolt 34 at the lower surface of yoke 35 and a spring 46 biases the bellows bottom 30 away from the lower part of yoke 35.

An electron-emitting filament 38 is located above the rod 25 and is connected to a heating current supply 39 by a lead 40 which extends through an insulating bushing 42 in housing wall 11, and a lead 41 which extends through housing wall 11 and is connected thereto at 42, so that the filament 38 is biased negatively with respect to the rod 25. A wire 47 connects the negative terminal of a high voltage supply to housing wall 11 and thus to point 43 and filament 38. A wire 54 extends through a bushing 55 in housing wall 11 and connects the support 26 and thus the rod 25 to the positive terminal of the high voltage of supply 45.

The pump shown in the drawing is connected at fiange 14 and inlet opening 15 to a space or vessel to be evacuated (not shown). This space or vessel may be preevacuated by a conventional roughing pump (not shown). Gas molecules entering the pump housing 10 are ionized by action of electrons traveling from the filament 38 to the anode 18 under the influence of the electric potential of the ionizing voltage supply 22. This ionization process is well known in the art. The ionized gas molecules are attracted by and deposit themselves on the inner surface 50 of housing wall 11 which thus serves as a molecule collector surface.

This pumping action is assisted and enhanced by operation of the getter maten'al source including the rod 25 and filament 38. To this effect, the nut 36 is first adjusted until the free end 51 of rod 25 has a desired initial spacing from filament 38. The supply 39 is then switched on to send a heating current through filament 38 and the high voltage supply 45 is switched on to bias filament 38 negatively with respect to the rod 25. In this manner, the free end 51 of rod 25 is bombarded with electrons which heat the free rod end and vaporize material therefrom. A hollow cylindrical shield 53 is mounted to encompass the rod 25 and to be electrically connected to the negative terminal of high voltage supply 45, so that shield 53 aids in the direction and focusing of electrons from filament 38 onto the free end 51 of rod 25. In addition, the shield 53 serves as a means for reducing heat dissipation from rod 25.

According to the invention, the getter rod 25 is provided with a plurality of mutually spaced annular grooves 55a which extend perpendicularly or transversely to the general direction of heat flow from the free rod end 51 through the rod. In this manner, the rod 25 is subdivided into a plurality of spaced cylindrical pellets 56 of getter material. The grooves 55a extend from the lateral surface of rod 25 to the vicinity of the longitudinal center axis of rod 25, so as to leave just sufficient material between adjacent pellets 56 to keep the pellets mechanically supported during the getter vaporization process. The grooves 55a impede the flow of heat along rod 25 or from getter pellet to getter pellet. The heat developed by electron bombardment of the free end 51 of rod 25 is thus largely retained at this free end, so that the vaporization of getter material takes place thereat most effectively. As the rod 25 wears down or as the getter pellets 56 are successively consumed due to getter vaporization therefrom, the desired distance between rod 25 and filament 38 is readjusted by turning the nut 36. During this wearing down of the rod, the grooves 55a, which impede heat dissipation along the rod, lead to more equalized power requirements for the vaporization of successive pellets.

The getter material that is vaporized from rod 25 enters the free space in pump housing 10 and deposits itself on the inner surface 50 of housing wall 11 where it aids in the entrapment of gas molecules. If desired, the anode 18 may be located from the rod 25 by a distance larger than as shown in the drawing, so that the vaporized getter material will primarily deposit itself on a portion of the inner surface 50 of housing wall 11 that is located below anode 18. In this case, the action of the vaporized getter material is separate from the action of the gas molecule ionizing system including anode 18. If desired, a filament (not shown) which is separate from the filament 38 may, in a conventional fashion, be provided for releasing ionizing electrons to the anode 18.

The rod 25 as shown in FIG. 1 may be prepared by machining the grooves 55a into a rod of getter material, so as to leave the getter pellets 56 and the short sections of material therebetween.

FIG. 2 shows the result of a different method. The rod shown in FIG. 2 has a pin 126 of a suitable material, such as tantalum, molybdenum or tungsten. A series of getter pellets 127 of a suitable material, such as titanium, are stacked on pin 126 and are maintained in mutually spaced relationship by washers 128, which may be of titanium, tantalum, molybdenum or another suitable material. The rod 125 may be used in lieu of the abovementioned rod 25.

In this case it is desirable to use for the filament 38 a conventional circular filament configuration (not shown) such that the pin 126 will pass through the center of the filament circle. By suitable sizing and positioning the filament with respect to the getter rod, the number of electrons bombarding the free end of the getter rod will not be appreciably diminished by the presence of the pin.

An alternate method is to allow the pin 126 to approach the filament 38 where it will be subjected to electron bombardment sufficiently intensive to cause the pin 126 to vaporize.

FIGS. 3, 4 and 5 illustrate a source of vaporizable material which is characterized by particularly equalized power requirements throughout the useful life of the source.

The source in accordance with these figures comprises a rod of a material to be vaporized. The rod has a top surface 151 at its free end 152, and a bottom 154 opposite the free end. The rod 150 is tapered from the bottom 154 to the free end 152. Because of this tapering, the rod increases progressively in cross-sectional area from the top surface 151 to the bottom 154. In the illustrated embodiment, the lateral tapering angle 156 is 5 /2 with respect to the vertical, which I found suitable for the subject purposes. Other angles may also be employed.

In the tapered rod illustrated in FIGS. 3 to 5, annular grooves 158 have been cut into the body of the rod 150, so as to divide this rod into a plurality of aligned and space pellets 160. The grooves 158 are cut so as to leave small supporting posts 162 of the material to be vaporized between the pellets 160.

The tapered and grooved rod 150 of FIGS. 3 to 5 may be substituted for the rod 25 in the pump shown in FIG. 1. In the illustrated embodiment, the rod 150 has a pin 165 for connection to the support 26 of FIG. 1.

With the rod 150 inserted in the apparatus of FIG. land the heating current supply 39 and high voltage supply 45 energized, electrons released by the filament 38 will predominantly bombard and heat the top surface 152 at the free end 151 of the rod. The rod 150 will gradually wear in the direction of the bottom 154 as material is vaporized from the top. Since the rod is tapered as shown, the area presented to electron bombardment increases as material is vaporized and the rod is worn down.

This is particularly well apparent from FIG. 5 which,

shows the surface 168 located below the top pellet shown in FIG. 3. This surface 168 is larger in area than the top surface 152. In FIG. 5, the surface 168 includes the crosssectional area of the post section 162 which is vaporized upon consumption of the top pellet shown in FIG. 3.

The area presented to electron bombardment will, of course continue to increase as further material is vaporized below the surface 168. As indicated above, the reason for this deliberate increase in vaporization area is to equalize the heat energy requirements of the source of vaporized material, and to provide more equalized vaporization rates with a given magnitude of heating power. Initially, the rod has an overall surface of a given area from which heat will be dissipated. These heat losses are reduced as the overall surface area of the rod decreases with the progressing vaporization of material from the rod. An uncompensated decrease of these heat losses leads to an increase in the evaporation rate which can reach undesirable proportions unless the heat source is checked.

By having the area which is subjected to heating increase as the vaporization of material proceeds, a substantial compensation is provided for the above mentioned decline in heat losses, since progressively increasing vaporization areas will tend to acquire gradually lower temperatures with a given source of heating power.

The principle inherent in the embodiment of FIGS. 3 to 5 can also be expressed as providing for a gradual spreading of the available heat energy over a larger evaporation area as a function of a progressive decline in heat losses. The result is a more constant rate of evaporation from the rod with a heat source of a given power.

The advantageous effect is enhanced by the grooves 158 illustrated in FIG. 3, since these grooves impede heat flow along the rod and thus tend to maintain the available heat energy at the location of vaporization. It will, however, be understood that the advantageous effect just mentioned i1s also present in the absence of the grooves 158. Accordingly, the invention extends also to tapered getter rods of the type shown in FIGS. 3 to 5 but having no grooves of the type of grooves 158.

If a grooved arrangement is desired, the tapered pellets 160 shown in FIG. 3 may be manufactured separately and may be arranged on the above mentioned pin 126 shown in FIG. 2 with intervening washers 128 to preserve the spacing, as illustrated in FIG. 2. When the pellets 160 are thus positioned on the pin 126, each pellet below the top pellet will have a mean diameter which is larger than the mean diameter of the next higher pellet, in the same manner as in the embodiment of FIGS. 3 to 5.

. Those skilled in the art will recognize that a good approximation is obtained with a string of cylindrical pellets arranged in the manner of the pellets 160 in FIG. 3, provided each cylindrical pellet below the top pellet has a diameter which is larger than the diameter of the next higher pellet. In other words, the pellets 160 in the embodiment of FIGS. 3 to 5 may be cylindrical instead of tapered, as long as each pellet below the top pellet has a larger crosssectional area than the next higher pellet. This approximation to a strictly tapered configuration is sometimes easier to manufacture and yields often sufliciently satisfactory results.

While specific embodiments of the invention have been shown, it will be recognized that many modifications within the scope of the invention are possible. Thus, the free end of the getter rod herein described may also be bombarded with electrons that emanate from an electron gun, rather than a heated filament. The subject invention may also be employed in getter-ion pumps of a different structure than that shown. Moreover, the invention and its various aspects may be employed in vacuum coating apparatus, as has been mentioned initially.

Other modifications within the scope of the invention will be apparent to those skilled in the art.

I claim:

1. A source of vaporizable material, comprising a rod being of material to be vaporized and having a free end,

and means for heating the rod at said free end to vaporize material therefrom, the rod defining a plurality of mm tually spaced annular grooves distributed along the rod for impeding flow of heat therealong.

2. A source of vaporizable material, comprising a sub stantially cylindrical rod being of material to be vaporized and having a free end, and means for heating the rod at said free end to vaporize material therefrom, the rod defining a plurality of mutually spaced annular grooves extending substantially at right angles to the longitudinal axis of the rod and extending from the outer lateral surface of the rod to the vicinity of said longitudinal axis to impede flow of heat along the rod.

3. A source of vaporizable material, comprising a rod being of material to be vaporized and having a free end, means for heating the rod at said free end to vaporize material therefrom, the rod defining a plurality of mutually spaced annular grooves distributed along the rod for impeding flow of heat therealong, and a heat shield being spaced from and laterally surrounding the rod.

4. A source of vaporizable material, comprising a substantially cylindrical rod being of material to be vaporized and having a free end, and means for heating the rod at said free end to vaporize material therefrom, the rod defining a plurality of mutually spaced annular grooves extending substantially at right angles to the longitudinal axis of the rod and extending from the outer lateral surface of the rod to the vicinity of said longitudinal axis to impede flow of heat along the rod, and a heat shield being spaced from and concentrically surrounding said rod at a region below said free end thereof.

5. A source of vaporizable material, comprising a rod being of material to be vaporized and having a free end, and means for bombarding the rod with electrons at said free end thereof to cause vaporization of material from the free end of the rod, the rod defining a plurality of mutually spaced annular grooves distributed along the rod for impeding flow of heat therealong.

6. A source of vaporizable material, comprising a rod being of material to be vaporized and having a free end, and means for bombarding the rod with electrons at said free end thereof to cause vaporization of material from the free end of the rod, the rod defining a plurality of mutually spaced annular grooves distributed along the rod for impeding flow of heat therealong, and a substantially hollow cylindrical, negatively biased shield of electrically conductive material being spaced from and laterally surrounding the rod for reducing heat dissipation from the rod and focusing electrons onto the rod.

7. A source of vaporizable material, comprising a rod being of a material to be vaporized and having a free end, means spaced from the free end of the rod for bombarding the rod with electrons at said free end thereof to cause vaporization of material from the free end of the rod, the rod defining a plurality of mutually spaced annular grooves distributed along the rod for impeding flow of heat therealong, and means for adjusting the position of the rod to control the spacing between the free end of the rod and said electron bombarding means.

8. A source of vaporizable material, comprising a supporting pin and a series of pellets of material to be vaporized stacked on the supporting pin in mutually spaced relationship.

9. A source of vapo-rizable material, comprising a supporting pin, a series of pellets of material to be vaporized stacked on the supporting pin, and a washer between each adjacent pair of pellets for spacing the pellets of said adjacent pair.

10. A source of vaporizable material, comprising a rod being of a material to be vaporized and having a free end, and means for heating an area of the rod at said free end to vaporize material therefrom, the rod defining a plurality of mutually spaced annular grooves distributed along the rod for impeding flow of heat therealong, and the rod being tapered toward said free end whereby the area heated by said means increases as material is vaporized from the rod.

11. A source of vaporizable material, comprising a rod being of a material to be vaporized and having a free end, and means for heating an area of the rod at said free end to vaporize material therefrom, the rod being tapered toward said free end substantially along its entire length whereby the area heated by said means increases as material is vaporized from the rod.

12. A source of vaporizable material, comprising a frustoconical rod of material to be vaporized having a top surface and a bottom opposite the top surface and increasing progressively in cross-sectional area from the top surface to the bottom, and means for bombarding the rod with electrons at the top surface to vaporize material therefrom, and for progressively bombarding the increasing cross-sectional areas as material is vaporized from the rod.

13. A source of vaporizable material, comprising a frustoconical rod of material to be vaporized having a top surface and a bottom opposite the top surface and increasing progressively in cross-sectional area from the top surface to the bottom, said rod defining a plurality of annular grooves extending parallel to said top surface and being spaced from each other between said top surface and said bottom to impede in the fiow of heat in the direction of said bottom, and means for bombarding the rod with electrons at the top surface to vaporize material therefrom, and for progressively bombarding the increasing cross-sectional areas as material is vaporized from the rod.

14. A source as claimed in claim 13, including means for adjusting the position of the rod relative to the electron bombarding means.

.15. A source of vaporizable material, comprising a series of aligned, interconnected and mutually spaced frustoconical pellets of material to be vaporized.

16. A source of vaporizable material, comprising a substantially cylindrical top pellet of material to be vaporized, and a plurality of substantially cylindrical additional pellets of material to be vaporized, said additional pellets being connected to and located below the top pellet, being aligned with the top pellet and being spaced from the top pellet and spaced from each other, and each of said additional pellets having a mean diameter which is larger than the mean diameter of the next higher pellet.

References Cited UNITED STATES PATENTS 2,423,729 7/1947 Riihle 219-121 2,746,420 5/ 1956 Steigerwald 219-121 2,771,568 11/1956 Steigerwald 219-121 2,793,282 5/1957 Steigerwald 219-121 3,162,767 12/1964 Di Curcio et a1. 118-491 3,205,087 9/1965 Allen 118-491 3,251,536 5/1966 Connor 118-495 3,267,015 8/1966 Morley 204-192 3,293,587 12/1966 Robinson 219-121 RICHARD M. WOOD, Primary Examiner.

W. D. BROOKS, Assistant Examiner.

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