US3662154A - Spherical titanium sublimator - Google Patents

Spherical titanium sublimator Download PDF

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Publication number
US3662154A
US3662154A US81982A US3662154DA US3662154A US 3662154 A US3662154 A US 3662154A US 81982 A US81982 A US 81982A US 3662154D A US3662154D A US 3662154DA US 3662154 A US3662154 A US 3662154A
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source
heat
sublimed
heat energy
wall
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Expired - Lifetime
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US81982A
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English (en)
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David J Harra
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Varian Medical Systems Inc
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Varian Associates Inc
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N25/00—Investigating or analyzing materials by the use of thermal means
    • G01N25/02—Investigating or analyzing materials by the use of thermal means by investigating changes of state or changes of phase; by investigating sintering
    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
    • H05B3/00—Ohmic-resistance heating

Definitions

  • the sublimator comprises a generally spherical hollow body of the material to be sublimated enclosing a source of heating energy.
  • the wall of the hollow body is uniformly thick over its full extent, and the configuration of the heat source is correlated to the inner surface of the spherical body to provide a generally uniform rate of total heat energy absorption at substantially all portions of the body.
  • the body sublimates uniformly from its full outer surface, and at the time in which any one portion of the body is fully dissipated, i.e., when an aperture appears through the body, the remaining portion of the body is also substantially dissipated.
  • This invention relates to sublimation devices and, more particularly, to such a device making increased utilization of the heat energy provided to cause the desired sublimation of a material, and which is so designed that the amount of available material which is actually sublimated is maximized.
  • a controlled atmosphere of a material in gaseous form It is often desirable to be able to provide in an initially evacuated environment a controlled atmosphere of a material in gaseous form.
  • thin film devices such as microelectronic components and circuits, are commonly made by depositing a thin film of a desired material onto a substrate from a gaseous atmosphere formed from the material to be deposited.
  • condensation of a gettering material from an atmosphere of thematerial onto a gettering surface is used to constantly renew the gettering surface as well as provide mechanical burial of pumped particles.
  • the gaseous atmosphere of the material is quite often provided by sublimating the material. That is, a surface of a'body of a desired material is heated to the sublimation temperature of the material'to cause the solid material at the surface to pass directly to the gas phase without going through the liquid phase. Sublimation is preferred over evaporation from the liquid phase since it is much easier to support a solid in a vacuum chamber rather than a liquid, and sublimation is not limited to formation of the gas from only its upper surface as is evaporation from a liquid.
  • sublimation devices, or sublimators as devices of this nature are often called, suffer from certain disadvantages. For example, it is difficult to provide adequate rates of material sublimation without requiring complex apparatus.
  • the present invention provides a sublimation device which makes efficient use of all of the heat energy from a heat source, as well as assures that most of the material has been sublimated before the device becomes inoperative.
  • the sublimator of the invention comprises a hollow body of a material to be sublimed having a source of heat energy located within its hollow portion.
  • the hollow body is substantially closed about the heat source so that heat energy flowing directly from the source as well as all heat energy reflected from the inner surface of the body, cannot escape from the body but rather must be absorbed by the material.
  • the inner surface of the body has a configuration assuring that heat energy reflected from any one portion of this surface is ultimately directed to another portion of the surfaceforabsorption by the material to be sublimed, thereby assuring full utilization of the heat energy.
  • the wall of the body is of a generally uniform thickness and the configurations of the inner surface thereof and of the heat source are correlated to provide a generally uniform rate of total heat energy absorption at all portions of the body. This results in a uniform sublimation rate over substantially all portions of the outer surface of the body and simplifies the control of the total sublimation rate. It has been found that the simplest structure for providing the substantially closed hollow body and inner surface configuration relationship is a generally spherical hollow body having a uniformly thick wall.
  • the inner surface of the body is also generally spherical in configuration and it has been found that the predominant amount of the total heat absorbed by any portion of such a configuration is heat energy which has been reflected from another portion of the surface, rather than heat energy which is directly radiated from the heat source.
  • the particular configuration of the heat source becomes less critical than it is with other configurations.
  • FIG. 1 illustrates a preferred embodiment of the sublimator of the invention which is especially designed to sublimate a getter material and is incorporated into a vacuum system for high vacuum pumping;
  • FIG. 2 is an enlarged, mostly broken away view of the preferred embodiment of the sublimator illustrated in FIG. 1;
  • FIG. 3 is a partial and broken away embodiment of an alternate embodiment of the invention.
  • the sublimation device of the instant invention is most useful in providing an atmosphere of a gettering material for condensation on surfaces within a vacuum system to aid in high vacuum pumping. For this reason, the sublimator of the invention will be described with respect to a preferred embodiment especially adapted for this purpose.
  • the sublimator generally referred to by the reference numeral 11, is shown appropriately mounted within a vacuum system 12.
  • System 12 includes an enclosure in the form of the bell jar 13 defining a high vacuum work environment. Bell jar 13 is mounted upon a base sump 14 to which a conventional diffusion pump system 16, including a roughing pump, is communicably connected.
  • the sublimator ll of the invention is mounted within sump 14 with an electrical lead portion 17 thereof passing hermetically through the wall of the sump to the exterior.
  • gettering material sublimated therefrom forms a gaseous atmosphere within the sump 14 from which material condenses on the inner wall surfaces of the sump to thereby form gettering surfaces to aid in the high vacuum pumping.
  • a suitable baffle or valve can be provided between the sump 14 and the bell jar portion 13 to prevent any appreciable amount of the sublimated material from contaminating the bell jar environment.
  • the sublimator 11 includes a substantially closed, hollow body 18 made from the material to be sublimated.
  • the material to be sublimated and from which body 18 is made is desirably titanium.
  • body 18 is generally spherical. That is, the body is made up of two, generally hemispherical body portions 19 and 21 which are suitably joined at their open ends such as by welding. It is to be noted that each of the body portions 19 and 21 is not a perfect hemisphere, but rather includes a short cylindrical or tubular section at its open end.
  • the body is slightly elongated in the direction perpendicular to the hemispherical joining plane.
  • the body including the relatively short tubular section joining the two perfect hemispherical sections is referred to as generally spherical.
  • a source of heat energy is located within the hollow portion of body 18 to direct heat energy at the bodys inner surface 22 for conduction through the wall of the body to sublime material from the bodys exterior surface 23.
  • a helical filament 24 is supported within the body at one end by a molybdenum sleeve 26 which extends through the apex end of generally hemispherical member 19.
  • the other end of filament 24 extends through a cylindrical aperture 27 in the apex end of generally hemispherical member 21 and is suitably connected to a electrical conductor rod 28.
  • the diameter of cylindrical aperture 27 should be sufficiently larger than the diameter of the filament end wire 29 passing therethrough that electrical breakdown between the wire and the aperture wall is prevented.
  • the aperture should not be any larger than is necessary so that the loss of heat from the filament 24 through the aperture is minimized.
  • Support means are provided to facilitate mounting the body 18 within the sump 14.
  • Such support means includes a support sleeve 32 which tightly receives in one end thereof a short cylindrical extension 33 projecting from the apex of hemispherical body portion 21.
  • the other end of the sleeve 32 fits over a thicker walled tubular post 34 which is, in turn, received within a tubular acceptor rod 35.
  • tubular acceptor rod 35 is secured to a flange 36 which is hermetically sealed to another flange 37 welded to sump wall 38.
  • any suitable hermetic sealing arrangement such as the sealing flange configuration known by the registered trademark Conflat can be used to provide the desired hermetic seal.
  • the support means also includes means for mechanically supporting heater filament 24 in position, as well as delivering electrical power thereto. That is, end wire 29 of the heater filament extends coaxially into sleeve 32 where it is received into one end of connector rod 28.
  • Conductor rod 28 has a necked-down portion 39 which is received within a cylindrical insulating plug 41 within post 34. It will be appreciated that plug 41 acts to mechanically support the full electrical lead structure for the filament as described to this point from the remainder of the support structure, while yet insulating the same therefrom.
  • the free end of rod 39 is received within a female electrical connector 42 of the acceptor rod 35.
  • the tubular post 34 and lead portion 39 are removably received within the acceptor collar 35 and connector lead 42, respectively.
  • the amount of heat loss because of the support structure should be minimized.
  • the sleeve 32 is made as thin as it is practical to do so and yet assure that such sleeve has sufficient strength to support the body 18 at its high temperatures of operation.
  • a heat shield cup 43 coaxially surrounds the sleeve to minimize loss by radiation of heat from such sleeve.
  • a plurality of radiation shield discs 44 are held by an inner cylinder 46 secured to the end of post 34 at a location at which such discs minimize radiation losses from cylindrical section 33 of body 18.
  • a suitable material for the various members of the support structure, except for the insulating plug 37, is molybenum.
  • the insulating plug can be of any suitable ceramic.
  • the time interval is substantially the same for all portions of the body, the result is that all portions of the body are substantially dissipated at the time at which any one portion becomes dissipated.
  • the material is also substantially dissipated from all other portions of the body. It will be appreciated by those skilled in the art that this correlation of the inner surface configuration and the configuration of the heat source to the wall thickness cannot be so critically determined to provide full dissipation of all of the material at the end of the predetermined time.
  • the wall thickness of the body is generally uniform over its full extent.
  • This feature has several advantages. For example, it simplifies the correlation of the bodys inner surface configuration to the configuration of the heater. That is, to provide the desired substantial sublimation of all portions of the body at the end of a predetermined time interval, it is only necessary to see that all portions receive the same rate of heating when the body is uniformly thick.
  • the provision of the uniform thickness has the added advantage of assuring that the rate of sublimation of material is the same over the full area of the outer surface of the body. That is, there is no one portion of the outer surface of the body from which more material is being sublimated than at other portions. This is particularly helpful in use of the sublimator in high vacuum pumping since it means that gaseous material will be evolved from the body uniformly in all directions, thereby enabling renewal of various gettering surfaces within a vacuum system at generally the same rate.
  • the heater configuration of the I heat energy source With respect to the correlation of the configuration of the I heat energy source with that of the inner surface of the body, one would tend to think that in order to assure uniform heating of all portions of this surface, that the heater configuration would have to generally conform to that of the surface. That is, it would appear most reasonable that the outer envelope configuration of the heat source be also generally spherical or, in other words, have an outer configuration providing equal spacing of the heater from theinner surface of the body at all points.
  • the greater proportion of the heat energy actually absorbed by the material is not heat energy which comes directly from the heat source, but rather heat energy which has been reflected from the walls at some other portion of the body.
  • the emissivity of titanium is about 0.35.
  • the body includes means to compensate for the heat loss caused by the support means.
  • the inner surface 22 of the body is roughened, such as by way of serrations, at 51, adjacent the location at which the support means is secured to the body. This roughening increases the absorption of heat at such portion. That is, because of the irregular surface, some of the heat energy which is reflected upon striking the body at this roughened portion will be directed toward another portion of the roughened surface, rather than away from the roughened portion such as to another location along the inner surface configuration.
  • the total heat absorption rate of the body portion adjacent the roughened inner surface is greater than the other portions of the body surface.
  • An experimental embodiment of the invention which was the same as the embodiment described above insofar as the body shape and heater configuration are concerned, had a 1.3 inch diameter at the plane joining the generally hemispherical sections 19 and 21.
  • the body had a uniformly thick wall of 0.150 inches, thereby making the diameter of the body between the hemispherical apexes l.5 inches.
  • the aperture 27 through which the heater wire 29 extended was 0.188 inches in diameter, and the total weight of getter material equaled 50.3 grams before sublimation,
  • the filament heater 24 was made from about 17 inches of 0.032 diameter tungsten wire. The wire was wound in a helix having both a length and an outer diameter of about 0.65 inches.
  • the rate of sublimation of the life of the body did not vary to any appreciable extent. This was attributed to the fact that during the life of the body the total surface area from which sublimation occurred did not appreciably vary. That is, the spherical geometry is the optimum closed geometry assuring that the decrease in size over the life of the body of the area of the surface from which material is sublimated is minimized.
  • FIG. 3 schematically depicts such another configuration.
  • the inner surface configuration 61 of the body of sublimable material 62 is generally cylindrical with conical end portions.
  • a helical heater filament providing an open cylindrical radiating surface as illustrated, a greater proportion of the heat energy from the filament will be absorbed by the gettering material adjacent its midportion than at its end portions.
  • the body of gettering material is thicker at such location to compensate for the greater rate of sublimation thereat, so that all portions of the body will be fully sublimated at substantially the same interval of time as described above.
  • a source for providing sublimed material comprising a hollow body of a material to be sublimed, said hollow body having inner and outer surfaces, a source of heat energy located within said hollow body for directing heat energy at the inner surface of said hollow body for conduction through said body to sublime said material from said bodys outer surface, said hollow body being substantially closed to prevent escape therefrom of both the heat energy flowing directly from said source and the heat energy reflected from said inner surface of said body, the inner surface of said body having a configuration such that heat energy reflected from any one portion of said surface is ultimately directed to another portion of said surface for absorption by said material to be sublimated, said inner surface configuration and the configuration of said heat source being related to correlate the rate of total heat energy absorption at each portion of said body with the wall thickness at said portion so that substantially all of the material of said portion is sublimed at the end of a predetermined time interval which is generally the same for all portions of said body, whereby all portions of said body are substantially dissipated at the end of said interval to maximize the amount of material which is already sublimated
  • the source of sublimed material of claim 7 wherein the outer surface of said body also has a configuration which is generally spherical and the wall thickness of said hollow body is generally uniform over its full extent, and the configuration of said heat source is correlated to said spherical inner surface to provide a generally uniform rate of total heat energy absorption at substantially all portions of said body and a consequent uniform sublimation rate over substantially all portions of the outer surface of said body.
  • a source of sublimed material for high vacuum pumping comprising a body of a material to be sublimated having a wall defining two opposite surfaces, a first surface for receiving heat energy and a second one for the sublimation of material therefrom due to the conduction of heat through said body from said first surface, and a source of heat energy for directing heat energy at said first surface, said first surface including a portion which is rougher than other portions to increase absorption of heat at said roughened portion for conduction through said body.
  • a source for providing sublimed material comprising an electrical heater, a wall made of said material to be sublimed, said wall having inner and outer surfaces and being shaped to provide a hollow body substantially enclosing said heater, said heater being spaced from contact with said inner surface of said wall, said wall having an aperture therein, a lead for said heater passing through said aperture, and said heater within said hollow body having a size substantially larger than said aperture.
  • the source of sublimed material of claim 14 further comprising a support structure connected to said hollow body, an electrical connector attached to said heater lead, and said support structure being mechanically connected to said electrical connector by an electrical insulator.

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  • Physics & Mathematics (AREA)
  • Health & Medical Sciences (AREA)
  • Life Sciences & Earth Sciences (AREA)
  • Chemical & Material Sciences (AREA)
  • Analytical Chemistry (AREA)
  • Biochemistry (AREA)
  • General Health & Medical Sciences (AREA)
  • General Physics & Mathematics (AREA)
  • Immunology (AREA)
  • Pathology (AREA)
  • Vaporization, Distillation, Condensation, Sublimation, And Cold Traps (AREA)
  • Compressors, Vaccum Pumps And Other Relevant Systems (AREA)
US81982A 1970-10-19 1970-10-19 Spherical titanium sublimator Expired - Lifetime US3662154A (en)

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US8198270A 1970-10-19 1970-10-19

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US (1) US3662154A (de)
JP (1) JPS5615922B1 (de)
CA (1) CA930030A (de)
DE (1) DE2151030C2 (de)
FR (1) FR2111480A5 (de)

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4748313A (en) * 1985-08-23 1988-05-31 Elektroschmelzwerk Kempten Gmbh Apparatus by the continuous vaporization of inorganic compositions by means of a photon-generating thermal source of radiation heat
US5034604A (en) * 1989-08-29 1991-07-23 Board Of Regents, The University Of Texas System Refractory effusion cell to generate a reproducible, uniform and ultra-pure molecular beam of elemental molecules, utilizing reduced thermal gradient filament construction
US5080870A (en) * 1988-09-08 1992-01-14 Board Of Regents, The University Of Texas System Sublimating and cracking apparatus
US5156815A (en) * 1988-09-08 1992-10-20 Board Of Regents, The University Of Texas System Sublimating and cracking apparatus

Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3241740A (en) * 1963-10-16 1966-03-22 Cons Vacuum Corp Vacuum pumping methods and apparatus

Family Cites Families (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3427432A (en) * 1966-06-10 1969-02-11 Granville Phillips Co Sublimation device

Patent Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3241740A (en) * 1963-10-16 1966-03-22 Cons Vacuum Corp Vacuum pumping methods and apparatus

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4748313A (en) * 1985-08-23 1988-05-31 Elektroschmelzwerk Kempten Gmbh Apparatus by the continuous vaporization of inorganic compositions by means of a photon-generating thermal source of radiation heat
US5080870A (en) * 1988-09-08 1992-01-14 Board Of Regents, The University Of Texas System Sublimating and cracking apparatus
US5156815A (en) * 1988-09-08 1992-10-20 Board Of Regents, The University Of Texas System Sublimating and cracking apparatus
US5034604A (en) * 1989-08-29 1991-07-23 Board Of Regents, The University Of Texas System Refractory effusion cell to generate a reproducible, uniform and ultra-pure molecular beam of elemental molecules, utilizing reduced thermal gradient filament construction

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DE2151030A1 (de) 1972-04-20
JPS5615922B1 (de) 1981-04-13
CA930030A (en) 1973-07-10
FR2111480A5 (de) 1972-06-02
DE2151030C2 (de) 1982-09-23

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