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US3281265A - Method and apparatus for controlling coating thickness by electron beam evaporation - Google Patents

Method and apparatus for controlling coating thickness by electron beam evaporation Download PDF

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US3281265A
US3281265A US309487A US30948763A US3281265A US 3281265 A US3281265 A US 3281265A US 309487 A US309487 A US 309487A US 30948763 A US30948763 A US 30948763A US 3281265 A US3281265 A US 3281265A
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strip
coating
supply
thickness
width
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US309487A
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Thomas K Cauley
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United States Steel Corp
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United States Steel Corp
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Priority to US309487A priority Critical patent/US3281265A/en
Priority to GB35565/64A priority patent/GB1062820A/en
Priority to BE652778A priority patent/BE652778A/xx
Priority to DE19641521555 priority patent/DE1521555A1/en
Priority to FR988152A priority patent/FR1411331A/en
Priority to NL6410796A priority patent/NL6410796A/xx
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N23/00—Investigating or analysing materials by the use of wave or particle radiation, e.g. X-rays or neutrons, not covered by groups G01N3/00 – G01N17/00, G01N21/00 or G01N22/00
    • G01N23/02—Investigating or analysing materials by the use of wave or particle radiation, e.g. X-rays or neutrons, not covered by groups G01N3/00 – G01N17/00, G01N21/00 or G01N22/00 by transmitting the radiation through the material
    • G01N23/06—Investigating or analysing materials by the use of wave or particle radiation, e.g. X-rays or neutrons, not covered by groups G01N3/00 – G01N17/00, G01N21/00 or G01N22/00 by transmitting the radiation through the material and measuring the absorption
    • G01N23/083—Investigating or analysing materials by the use of wave or particle radiation, e.g. X-rays or neutrons, not covered by groups G01N3/00 – G01N17/00, G01N21/00 or G01N22/00 by transmitting the radiation through the material and measuring the absorption the radiation being X-rays
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C14/00—Coating by vacuum evaporation, by sputtering or by ion implantation of the coating forming material
    • C23C14/22—Coating by vacuum evaporation, by sputtering or by ion implantation of the coating forming material characterised by the process of coating
    • C23C14/24—Vacuum evaporation
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C14/00—Coating by vacuum evaporation, by sputtering or by ion implantation of the coating forming material
    • C23C14/22—Coating by vacuum evaporation, by sputtering or by ion implantation of the coating forming material characterised by the process of coating
    • C23C14/24—Vacuum evaporation
    • C23C14/28—Vacuum evaporation by wave energy or particle radiation
    • C23C14/30—Vacuum evaporation by wave energy or particle radiation by electron bombardment
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C14/00—Coating by vacuum evaporation, by sputtering or by ion implantation of the coating forming material
    • C23C14/22—Coating by vacuum evaporation, by sputtering or by ion implantation of the coating forming material characterised by the process of coating
    • C23C14/54—Controlling or regulating the coating process
    • C23C14/542—Controlling the film thickness or evaporation rate
    • C23C14/545—Controlling the film thickness or evaporation rate using measurement on deposited material
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C14/00—Coating by vacuum evaporation, by sputtering or by ion implantation of the coating forming material
    • C23C14/22—Coating by vacuum evaporation, by sputtering or by ion implantation of the coating forming material characterised by the process of coating
    • C23C14/56—Apparatus specially adapted for continuous coating; Arrangements for maintaining the vacuum, e.g. vacuum locks
    • C23C14/562—Apparatus specially adapted for continuous coating; Arrangements for maintaining the vacuum, e.g. vacuum locks for coating elongated substrates
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N23/00—Investigating or analysing materials by the use of wave or particle radiation, e.g. X-rays or neutrons, not covered by groups G01N3/00 – G01N17/00, G01N21/00 or G01N22/00
    • G01N23/02—Investigating or analysing materials by the use of wave or particle radiation, e.g. X-rays or neutrons, not covered by groups G01N3/00 – G01N17/00, G01N21/00 or G01N22/00 by transmitting the radiation through the material
    • G01N23/06—Investigating or analysing materials by the use of wave or particle radiation, e.g. X-rays or neutrons, not covered by groups G01N3/00 – G01N17/00, G01N21/00 or G01N22/00 by transmitting the radiation through the material and measuring the absorption
    • G01N23/16—Investigating or analysing materials by the use of wave or particle radiation, e.g. X-rays or neutrons, not covered by groups G01N3/00 – G01N17/00, G01N21/00 or G01N22/00 by transmitting the radiation through the material and measuring the absorption the material being a moving sheet or film
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J37/00—Discharge tubes with provision for introducing objects or material to be exposed to the discharge, e.g. for the purpose of examination or processing thereof
    • H01J37/30—Electron-beam or ion-beam tubes for localised treatment of objects
    • H01J37/304—Controlling tubes by information coming from the objects or from the beam, e.g. correction signals
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J37/00—Discharge tubes with provision for introducing objects or material to be exposed to the discharge, e.g. for the purpose of examination or processing thereof
    • H01J37/32—Gas-filled discharge tubes
    • H01J37/34—Gas-filled discharge tubes operating with cathodic sputtering
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L21/00—Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof
    • H01L21/02—Manufacture or treatment of semiconductor devices or of parts thereof
    • H01L21/02104—Forming layers
    • H01L21/02107—Forming insulating materials on a substrate
    • H01L21/02225—Forming insulating materials on a substrate characterised by the process for the formation of the insulating layer
    • H01L21/02227—Forming insulating materials on a substrate characterised by the process for the formation of the insulating layer formation by a process other than a deposition process
    • H01L21/0223—Forming insulating materials on a substrate characterised by the process for the formation of the insulating layer formation by a process other than a deposition process formation by oxidation, e.g. oxidation of the substrate
    • H01L21/02233—Forming insulating materials on a substrate characterised by the process for the formation of the insulating layer formation by a process other than a deposition process formation by oxidation, e.g. oxidation of the substrate of the semiconductor substrate or a semiconductor layer
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L21/00—Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof
    • H01L21/02—Manufacture or treatment of semiconductor devices or of parts thereof
    • H01L21/04—Manufacture or treatment of semiconductor devices or of parts thereof the devices having potential barriers, e.g. a PN junction, depletion layer or carrier concentration layer
    • H01L21/18—Manufacture or treatment of semiconductor devices or of parts thereof the devices having potential barriers, e.g. a PN junction, depletion layer or carrier concentration layer the devices having semiconductor bodies comprising elements of Group IV of the Periodic Table or AIIIBV compounds with or without impurities, e.g. doping materials
    • H01L21/30—Treatment of semiconductor bodies using processes or apparatus not provided for in groups H01L21/20 - H01L21/26
    • H01L21/31—Treatment of semiconductor bodies using processes or apparatus not provided for in groups H01L21/20 - H01L21/26 to form insulating layers thereon, e.g. for masking or by using photolithographic techniques; After treatment of these layers; Selection of materials for these layers
    • H01L21/314—Inorganic layers
    • H01L21/316—Inorganic layers composed of oxides or glassy oxides or oxide based glass
    • H01L21/3165—Inorganic layers composed of oxides or glassy oxides or oxide based glass formed by oxidation
    • H01L21/31654—Inorganic layers composed of oxides or glassy oxides or oxide based glass formed by oxidation of semiconductor materials, e.g. the body itself

Definitions

  • the strip passes over a crucible which is housed in a vacuum chamber.
  • the crucible contains coating material, which is heated to a temperature sufiicient to vaporize it.
  • the vapors condense on the strip surface and form a continuous coating thereon.
  • Such processes can be used, for example, to coat steel strip with aluminum.
  • Various techniques are known for heating the coating material, one of which is to direct a stream of electrons from an electron gun against the surface thereof. Reference can be made to Ruhle Patent No. 2,423,729 or Simons Patent No. 3,046,936 for showings of exemplary arrangements in which electron guns are thus used.
  • An object of my invention is to provide an improved method and apparatus, applicable to an electron-gun vapor-deposition process for coating strip material, in which the coating thickness is controlled automatically to a predetermined value.
  • a further object is to provide an improved method and apparatus which alfords the foregoing advantage and in which the thickness is controlled individually at different locations across the width of a strip, whereby coatings of uniform thickness or of controlled variations in thickness can be obtained.
  • a more specific object is to provide an improved method and apparatus for controlling coating thickness in which individual grids are interposed between different portions of the cathode of an electron gun and the surface of a coating material, and the potentials on these grids are varied to regulate the intensity of the electron beam reaching diiferent portions of the surface.
  • FIGURE 1 is a schematic diagram of a vapor-deposition apparatus equipped with one form of control apparatus constructed in accordance with my invention.
  • FIGURE 2 is a similar view showing a modification.
  • FIGURE 1 shows schematically a vapor-deposition apparatus which includes a crucible and an electron gun 12 housed in a vacuum chamber 13.
  • a strip S for example of steel, travels through the chamber to be coated.
  • the crucible is spaced a few inches below the strip path, and contains a supply of coating material, for example aluminum.
  • the apparatus also includes conventional means (not shown) for feeding coating material to the crucible to replace what is consumed.
  • the electron gun has a cathode 14 and a transformer 15. Both the crucible and cathode are of a length approximately equal to the strip width. The gun directs an electron beam against the surface of the coating material in the crucible and heats the surface to at least 1200 C.
  • the coating material vaporizes and the vapors condense on the strip surface. Since the foregoing parts and their operation are conventional, no more detailed showing is deemed necessary. In the absence of any control, the central portion of the strip is exposed to vapor of greater density than the edge portions and hence receives a thicker coating.
  • the electron gun 12 includes a grid 16 interposed between the central portion of cathode 14 and the surface of the coating material in crucible 10, and grids 17 and 17a interposed between the edge portions of the cathode and the coating material.
  • Each grid is formed of a plurality of parallel wires which lie in a plane perpendicular to the path of electron travel.
  • I connect grid 16 to a conventional adjustable power supply 18, and grids 17 and 17a to a separate adjustable power supply 19.
  • a suitable power supply is available commercially from NJE Corporation of Kenilw-orth, New Jersey, as the Model ELA--50 RM and is described in a printed publication by the manufacturer NJE Power Suppliers, Spring 1959.
  • the power supplies 18 and 19 transmit controlled negative potentials to the grids to retard diiferent portions of the electron beam by different degrees.
  • the wires of grid 16 are spaced more closely than the wires of grids 17 and 17a, whereby at equal potentials grid 16 offers a greater electrostatic gradient then grids 17 and 17a. Consequently the edge portions of the electron beam are retarded less than the central portion and tend to vaporize greater quantities of coating material, whereby the coating thickness tends to be more nearly uniform across the strip width.
  • the technique for measuring coating thickness with an X-ray gage is known, as explained, for example, in Friedman Patent No. 2,926,257.
  • this mechanism includes a motor 21, an eccentric 22 and a connecting rod 23.
  • Gage 20 carries a cam 24, which closes a normally open double-pole switch 25 when the gage is over the central portion of the strip and closes a similar switch 26 when the gage is over the edge portion.
  • the control circuit includes two self-balancing potentiometers 31 and 32, the arms of which are electrically connected to the power supplies 18 and 19 respectively.
  • a reversible motor 33 is mechanically connected to the arm of potentiometer 31 through a magnetic clutch 34 and to the arm of potentiometer 32 through another magnetic clutch 35.
  • I connect one contact 25a of switch 25 in series with the winding of clutch 34 and an energizing source 36.
  • I connect one contact 26a of switch 26 in series with the winding of clutch 35 and an energizing source 37.
  • the circuit also includes a set-point potentiometer 38 and a conventional amplifier 39.
  • I connect the slide wire of the set-point potentiometer 38 and the output of X-ray gage 20 in series to one input terminal of the amplifier.
  • I connect the arm of the set-point potentiometer to the slide wire of the self-balancing potentiometer 31, and connect the arm of potentiometer 31 in series with the other contact 25b of switch 25 and the other input terminal of amplifier 39.
  • I connect the output terminals of amplifier 39 with motor 33.
  • I arrange the connections so that the sum of the voltages from the X-ray gage 20 and the self-balancing potentiometer 31 or 32 oppose the voltage from the set-point potentiometer 38. Hence motor 33 is energized only when the opposing voltages are unequal.
  • I manually adjust the arm of the setpoint potentiometer 38 in accordance with the thickness of coating I wish to maintain on the strip.
  • I operate motor 21 to move the X-ray gage 29 periodically between its two positions. When the gage is in its first position overlying the central portion of the strip, both contacts 25a and 25b of switch 25 close. If the coating is not of proper thickness, the combined voltage transmitted by the X-ray gage and self-balancing potentiometer 31 differs from the voltage transmitted by the set-point potentiometer 38.
  • Motor 33 runs in a direction to adjust potentiometer 31 to overcome this voltage difference. The adjustment of potentiometer 31 also changes the potential on grid 16 in a direction to correct the coating thickness.
  • the gage next moves to its second position and in like manner corrects the coating thickness at the edge of the strip.
  • the magnitude of each adjustment signal is in accordance with the measured error in coating thickness, but the gage soon moves away from its measurement position and opens the contacts of switch 25 or 26 before completion of the adjustment. I time the gage movement in relation to the strip speed so that th region of the strip on which a thickness correction has been made reaches the gage before there is another correction. In this manner I avoid hunting.
  • FIGURE 2 shows a modification in which I use two X-ray gages 44 and 45 and avoid continually shifting the gage.
  • the mechanism includes a motor 46 and three double contact rotary switches 47, 48 and 49, the arms of which are mechanically connected to said motor. The remainder of the circuit is similar to that already described.
  • Motor 46 periodically moves the arm of switch 47 to a first position in which it establishes a connection between the X-ray gage 44 and amplifier 39 and a second position in which it establishes a connection between the X-ray gage 45 and the amplifier.
  • switch 48 establishes connections between the self-balancing potentiometers 31 and 32 and the amplifier, and switch 49 between clutches 34 and 35 and a source of energy 50.
  • my invention affords a simple method and apparatus for controlling the thickness of a vapor-deposited coating.
  • I illustrate arrangements in which the coating thickness is measured at only two locations on the strip, it apparent the thickness could be measured at a larger number of locations and that a larger number of grids could be used. I can also use a similar apparatus to control the profile of the coating so that different portions of the strip intentionally have coatings of different thickness.
  • a method of controlling the coating thickness comprising measuring the coating thickness at a plurality of locations across the width of the strip, interposing electrostatic potentials between the source of said beam and the surface of the supply of coating material, and individually varying the intensity of said potentials in different portions of said beam across its width in accordance with the measured thickness of the coating, thereby varying the quantity of material vaporized at different portions of the surface of said supply.
  • a vapor-deposition apparatus for applying a coating to the surface of a strip
  • which apparatus includes a crucible adapted to contain a supply of coating material, an electron gun having a cathode for directing an electron beam at the surface of said supply, a vaccum chamber housing said crucible and said gun, and means for moving a strip over said crucible, the widths of said crucible and said beam being approximately equal to the strip width, the combination therewith of an apparatus for controlling the coating thickness comprising a plurality of grids interposed between said cathode and said crucible, means connected to said grids for applying electrostatic potentials thereto to modify the heating effect of said beam, and means for individually varying the degree to which the heating effect is modified at different grids across the width of said beam, thereby varying the quantity of material vaporized at different portions of said crucible.
  • each of said grids is formed of a plurality of parallel wires which lie in a plane perpendicular to the direction of travel of said beam, the wires of the grid opposite the central portion of said beam being spaced more closely than the wires of the grids opposite the edge portions.
  • a vapor-deposition apparatus for applying a coating to the surface of a strip
  • which apparatus includes a crucible adapted to contain a supply of coating material, an electron gun having a cathode for directing an electron beam at the surface of said supply, a vacuum chamber housing said crucible and said gun, and means for moving a strip over said crucible, the widths of said crucible and said beam being approximately equal to the strip width
  • an apparatus for controlling the coating thickness comprising means for measuring the coating thickness at a plurality of locations across the width of the strip, a plurality of grids interposed between said cathode and said crucible, individually adjustable power supplies connected with said grids for applying negative potentials thereto to retard said beam in varying degrees across its width, and an electric circuit connecting said measuring means and said power supplies to adjust said power supplies in accordance with the measured thickness of the coating to maintain the thickness in a predetermined pattern.
  • a vapor-deposition apparatus for applying a coating to the surface of a strip
  • which apparatus includes a crucible adapted to contain a supply of coating material, an electron gun having a cathode for directing an electron beam at the surface of said supply, a vacuum chamber housing said crucible and said gun, and means for moving a strip over said crucible, the widths of said crucible and said beam being approximately equal to the strip width
  • an apparatus for controlling the coating thickness comprising means for producing electric signals proportional to the coating thickness at a plurality of locations across the width of the strip, a plurality of grids interposed between said cathode and said crucible, individually adjustable power supplies connected with said grids for applying negative potentials thereto to retard said beam to a relatively greater degree in its central portion than in its edge portions, and an electric circuit connecting said signal-producing means and said power supplies to adjust said power supplies in accordance with the signals, thereby vaporizing greater quantities of coating material opposite the edge portions than opposite the central portion as required to deposit
  • said signal-producing means includes an X-ray gage mounted outside said chamber, and means for periodically shifting said gage between a first position in which it acts on the central portion of the strip and a second position in which it acts on one of the edge portions.
  • said circuit includes a set point potentiometer connected with said gage, and self-balancing potentiometers connected between said gage and the. respective power suppliers for making adjustments in the output of the latter when the coating thickness varies :from that set on said first-named potentiometer.
  • said signal-producing means includes a pair of X-ray gagw mounted outside said chamber, one of said gages being located to act on the central portion of the strip, the other gage being located to act on one of the edge portions.
  • said circuit includes a set-point potentiometer and self-balancing potentiometers connecting said gages and the respective power supplies for making adjustments in the latter when the coating thickness varies from that set on the set point potentiometer, and switch means for periodically completing current paths to each gage in turn.

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Description

Oct. 25, 1966 T. K. CAULEY METHOD AND APPARA TUS FOR CONTROLLING COATING THICKNESS BY ELECTRON BEAM EVAPORATION Filed Sept. 17, 1963 126 FIG: 1.
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lNVE/VTOR. THOMAS K. CAULE) y J Mfflfi;
Attorney man:
United tates Patent METHOD AND APPARATUS FOR CONTROLLING COATING THiCl-KNESS BY ELECTRON BEAM EVAPORATION Thomas K. Cauley, West Mifiiin, Pa., assignor to United States Steel Corporation, a corporation of New Jersey Filed Sept. 17, 1963, Ser. No. 309,487 14 Claims. (Cl. 117-106) This invention relates to an improved method and apparatus for controlling the thickness and profile of vapordeposited coatings.
In a conventional vapor-deposition process for coating strip material, the strip passes over a crucible which is housed in a vacuum chamber. The crucible contains coating material, which is heated to a temperature sufiicient to vaporize it. The vapors condense on the strip surface and form a continuous coating thereon. Such processes can be used, for example, to coat steel strip with aluminum. Various techniques are known for heating the coating material, one of which is to direct a stream of electrons from an electron gun against the surface thereof. Reference can be made to Ruhle Patent No. 2,423,729 or Simons Patent No. 3,046,936 for showings of exemplary arrangements in which electron guns are thus used. In these processes there is a problem in controlling the coating thickness and in obtaining a coating of uniform thickness across the width of a strip. The coating tends to be thickest in the central portion of the strip, which passes over the region of the crucible where the vapors are most dense, and to thin out near each edge.
An object of my invention is to provide an improved method and apparatus, applicable to an electron-gun vapor-deposition process for coating strip material, in which the coating thickness is controlled automatically to a predetermined value.
A further object is to provide an improved method and apparatus which alfords the foregoing advantage and in which the thickness is controlled individually at different locations across the width of a strip, whereby coatings of uniform thickness or of controlled variations in thickness can be obtained.
A more specific object is to provide an improved method and apparatus for controlling coating thickness in which individual grids are interposed between different portions of the cathode of an electron gun and the surface of a coating material, and the potentials on these grids are varied to regulate the intensity of the electron beam reaching diiferent portions of the surface.
In the drawing:
FIGURE 1 is a schematic diagram of a vapor-deposition apparatus equipped with one form of control apparatus constructed in accordance with my invention; and
FIGURE 2 is a similar view showing a modification.
FIGURE 1 shows schematically a vapor-deposition apparatus which includes a crucible and an electron gun 12 housed in a vacuum chamber 13. A strip S, for example of steel, travels through the chamber to be coated. The crucible is spaced a few inches below the strip path, and contains a supply of coating material, for example aluminum. The apparatus also includes conventional means (not shown) for feeding coating material to the crucible to replace what is consumed. The electron gun has a cathode 14 and a transformer 15. Both the crucible and cathode are of a length approximately equal to the strip width. The gun directs an electron beam against the surface of the coating material in the crucible and heats the surface to at least 1200 C. The coating material vaporizes and the vapors condense on the strip surface. Since the foregoing parts and their operation are conventional, no more detailed showing is deemed necessary. In the absence of any control, the central portion of the strip is exposed to vapor of greater density than the edge portions and hence receives a thicker coating.
In accordance with my invention, the electron gun 12 includes a grid 16 interposed between the central portion of cathode 14 and the surface of the coating material in crucible 10, and grids 17 and 17a interposed between the edge portions of the cathode and the coating material. Each grid is formed of a plurality of parallel wires which lie in a plane perpendicular to the path of electron travel. I connect grid 16 to a conventional adjustable power supply 18, and grids 17 and 17a to a separate adjustable power supply 19. One example of a suitable power supply is available commercially from NJE Corporation of Kenilw-orth, New Jersey, as the Model ELA--50 RM and is described in a printed publication by the manufacturer NJE Power Suppliers, Spring 1959. The power supplies 18 and 19 transmit controlled negative potentials to the grids to retard diiferent portions of the electron beam by different degrees. In the illustration the wires of grid 16 are spaced more closely than the wires of grids 17 and 17a, whereby at equal potentials grid 16 offers a greater electrostatic gradient then grids 17 and 17a. Consequently the edge portions of the electron beam are retarded less than the central portion and tend to vaporize greater quantities of coating material, whereby the coating thickness tends to be more nearly uniform across the strip width.
To control the coating thickness more precisely, I adjust the two power supplies 18 and 19 to vary the poten tials applied to grids 16, 17 and 17a in accordance with the measured thickness of the coating on different portions of the strip S. I measure the coating thickness with a conventional X-ray thickness gage 20, which is located outside chamber 13 and produces an electric output signal proportional to the coating thickness. The technique for measuring coating thickness with an X-ray gage is known, as explained, for example, in Friedman Patent No. 2,926,257. I connect gage 20 to a mechanism which periodically shifts it back and forth between a first position where it measures the coating thickness at the central portion of the strip and a second position where it measures the coating thickness at one edge portion. As illustrated, this mechanism includes a motor 21, an eccentric 22 and a connecting rod 23. Gage 20 carries a cam 24, which closes a normally open double-pole switch 25 when the gage is over the central portion of the strip and closes a similar switch 26 when the gage is over the edge portion.
The control circuit includes two self- balancing potentiometers 31 and 32, the arms of which are electrically connected to the power supplies 18 and 19 respectively. A reversible motor 33 is mechanically connected to the arm of potentiometer 31 through a magnetic clutch 34 and to the arm of potentiometer 32 through another magnetic clutch 35. I connect one contact 25a of switch 25 in series with the winding of clutch 34 and an energizing source 36. Similarly I connect one contact 26a of switch 26 in series with the winding of clutch 35 and an energizing source 37. Thus when either switch closes, the corresponding clutch is engaged. If motor 33 runs when clutch 34 is engaged, it moves the arm of potentiometer 31 to change the control voltage transmitted to the power supply 18. The output of the power supply 18 and the potential on grid 16 change correspondingly. Likewise if the motor runs when clutch 35 is engaged, the potential on grids 17 and 17a changes.
The circuit also includes a set-point potentiometer 38 and a conventional amplifier 39. I connect the slide wire of the set-point potentiometer 38 and the output of X-ray gage 20 in series to one input terminal of the amplifier. I connect the arm of the set-point potentiometer to the slide wire of the self-balancing potentiometer 31, and connect the arm of potentiometer 31 in series with the other contact 25b of switch 25 and the other input terminal of amplifier 39. I connect the other self-balancing potentiometer 32 and the other contact 26b of switch 26 in a similar manner. I connect the output terminals of amplifier 39 with motor 33. I arrange the connections so that the sum of the voltages from the X-ray gage 20 and the self- balancing potentiometer 31 or 32 oppose the voltage from the set-point potentiometer 38. Hence motor 33 is energized only when the opposing voltages are unequal.
In operation, I manually adjust the arm of the setpoint potentiometer 38 in accordance with the thickness of coating I wish to maintain on the strip. I operate motor 21 to move the X-ray gage 29 periodically between its two positions. When the gage is in its first position overlying the central portion of the strip, both contacts 25a and 25b of switch 25 close. If the coating is not of proper thickness, the combined voltage transmitted by the X-ray gage and self-balancing potentiometer 31 differs from the voltage transmitted by the set-point potentiometer 38. Motor 33 runs in a direction to adjust potentiometer 31 to overcome this voltage difference. The adjustment of potentiometer 31 also changes the potential on grid 16 in a direction to correct the coating thickness. The gage next moves to its second position and in like manner corrects the coating thickness at the edge of the strip. The magnitude of each adjustment signal is in accordance with the measured error in coating thickness, but the gage soon moves away from its measurement position and opens the contacts of switch 25 or 26 before completion of the adjustment. I time the gage movement in relation to the strip speed so that th region of the strip on which a thickness correction has been made reaches the gage before there is another correction. In this manner I avoid hunting.
FIGURE 2 shows a modification in which I use two X-ray gages 44 and 45 and avoid continually shifting the gage. The mechanism includes a motor 46 and three double contact rotary switches 47, 48 and 49, the arms of which are mechanically connected to said motor. The remainder of the circuit is similar to that already described. Motor 46 periodically moves the arm of switch 47 to a first position in which it establishes a connection between the X-ray gage 44 and amplifier 39 and a second position in which it establishes a connection between the X-ray gage 45 and the amplifier. In like manner switch 48 establishes connections between the self-balancing potentiometers 31 and 32 and the amplifier, and switch 49 between clutches 34 and 35 and a source of energy 50.
From the foregoing description it is seen that my invention affords a simple method and apparatus for controlling the thickness of a vapor-deposited coating. Although I illustrate arrangements in which the coating thickness is measured at only two locations on the strip, it apparent the thickness could be measured at a larger number of locations and that a larger number of grids could be used. I can also use a similar apparatus to control the profile of the coating so that different portions of the strip intentionally have coatings of different thickness.
While I have shown and described certain preferred embodiments of my invention, it is apparent that other modifications may arise. Therefore, I do not wish to be limited to the disclosure set forth but only by the scope of the appended claims.
I claim:
1. In a vapor-deposition process for applying a coating to the surface of a strip in which the strip passes over a supply of the coating material housed in a vacuum chamber, an electron beam is directed against the surface of the supply and heats the coating material to a temperature sufficient to vaporize it, and the vapors condense on the strip surface, the width of said supply and of said beam being approximately equal to the strip width, the combination therewith of a method of controlling the coating thickness comprising interposing electrostatic potentials between the source of said beam and the surface of the supply of coating material to modify the heating effect of said beam, and individually varying the degree to which the heating effect is modified in different portions of said beam across its width, thereby varying the quantity of material vaporized at different portions of said supply.
2. A method as defined in claim 1 in which said potentials are negative to retard said beam.
3. A method as defined in claim 1 in which the strip is steel and the coating material is aluminum.
4. A method as defined in claim 1 in which said beam is modified to vaporize relatively greater quantities of coating material opposite the edge portions of the strip than in the central portion to produce a coating of substantially uniform thickness.
5. In a vapor-deposition process for applying a coating to the surface of a strip in which the strip passes over a supply of the coating material housed in a vacuum chamber, an electron beam is directed against the surface of the supply and heats the coating material to a temperature sufiicient to vaporize it, and the vapors condense on the strip surface, the widths of said supply and of said beam being approximately equal to the strip width, the combination therewith of a method of controlling the coating thickness comprising measuring the coating thickness at a plurality of locations across the width of the strip, interposing electrostatic potentials between the source of said beam and the surface of the supply of coating material, and individually varying the intensity of said potentials in different portions of said beam across its width in accordance with the measured thickness of the coating, thereby varying the quantity of material vaporized at different portions of the surface of said supply.
6. In a vapor-deposition apparatus for applying a coating to the surface of a strip, which apparatus includes a crucible adapted to contain a supply of coating material, an electron gun having a cathode for directing an electron beam at the surface of said supply, a vaccum chamber housing said crucible and said gun, and means for moving a strip over said crucible, the widths of said crucible and said beam being approximately equal to the strip width, the combination therewith of an apparatus for controlling the coating thickness comprising a plurality of grids interposed between said cathode and said crucible, means connected to said grids for applying electrostatic potentials thereto to modify the heating effect of said beam, and means for individually varying the degree to which the heating effect is modified at different grids across the width of said beam, thereby varying the quantity of material vaporized at different portions of said crucible.
7. A combination as defined in claim 6 in which said potentials are of negative polarity to retard said beam and produce a greater retarding effect in the central portion of said beam than at the edge portions.
8. A combination as defined in claim 7 in which each of said grids is formed of a plurality of parallel wires which lie in a plane perpendicular to the direction of travel of said beam, the wires of the grid opposite the central portion of said beam being spaced more closely than the wires of the grids opposite the edge portions.
9. In a vapor-deposition apparatus for applying a coating to the surface of a strip, which apparatus includes a crucible adapted to contain a supply of coating material, an electron gun having a cathode for directing an electron beam at the surface of said supply, a vacuum chamber housing said crucible and said gun, and means for moving a strip over said crucible, the widths of said crucible and said beam being approximately equal to the strip width, the combination therewith of an apparatus for controlling the coating thickness comprising means for measuring the coating thickness at a plurality of locations across the width of the strip, a plurality of grids interposed between said cathode and said crucible, individually adjustable power supplies connected with said grids for applying negative potentials thereto to retard said beam in varying degrees across its width, and an electric circuit connecting said measuring means and said power supplies to adjust said power supplies in accordance with the measured thickness of the coating to maintain the thickness in a predetermined pattern.
10. In a vapor-deposition apparatus for applying a coating to the surface of a strip, which apparatus includes a crucible adapted to contain a supply of coating material, an electron gun having a cathode for directing an electron beam at the surface of said supply, a vacuum chamber housing said crucible and said gun, and means for moving a strip over said crucible, the widths of said crucible and said beam being approximately equal to the strip width, the combination therewith of an apparatus for controlling the coating thickness comprising means for producing electric signals proportional to the coating thickness at a plurality of locations across the width of the strip, a plurality of grids interposed between said cathode and said crucible, individually adjustable power supplies connected with said grids for applying negative potentials thereto to retard said beam to a relatively greater degree in its central portion than in its edge portions, and an electric circuit connecting said signal-producing means and said power supplies to adjust said power supplies in accordance with the signals, thereby vaporizing greater quantities of coating material opposite the edge portions than opposite the central portion as required to deposit a coating of substantially uniform thickness.
11. A combination as defined in claim in which said signal-producing means includes an X-ray gage mounted outside said chamber, and means for periodically shifting said gage between a first position in which it acts on the central portion of the strip and a second position in which it acts on one of the edge portions.
12. A combination as defined in claim 11 in which said circuit includes a set point potentiometer connected with said gage, and self-balancing potentiometers connected between said gage and the. respective power suppliers for making adjustments in the output of the latter when the coating thickness varies :from that set on said first-named potentiometer.
13. A combination as defined in claim 10 in which said signal-producing means includes a pair of X-ray gagw mounted outside said chamber, one of said gages being located to act on the central portion of the strip, the other gage being located to act on one of the edge portions.
14. A combination as defined in claim 13 in which said circuit includes a set-point potentiometer and self-balancing potentiometers connecting said gages and the respective power supplies for making adjustments in the latter when the coating thickness varies from that set on the set point potentiometer, and switch means for periodically completing current paths to each gage in turn.
References Cited by the Examiner UNITED STATES PATENTS 2,711,480 6/ 1955 Friedman 250-51.5 2,926,257 2/ 1960 Friedman 2505 1.5 3,046,936 7/1962 .Simons 11793.3 X 3,086,889 4/1963 Strong 1l8-8 X 3,168,418 2/1965 Payne 1l849.1
ALFRED L. LEAVITT, Primary Examiner.
A. GOLIAN, Assistant Examiner.

Claims (1)

1. IN A VOPOR-DEPOSITION PROCESS FOR APPLYING A COATING TO THE SURFACE OF A STRIP IN WHICH THE STRIP PASSES OVER A SUPPLY OF THE COATING MATERIAL HOUSED IN A VACUUM CHAMBER, AN ELECTRON BEAM IS DIRECTED AGAINST THE SURFACE OF THE SUPPLY AND HEATS THE COATING MATERIAL TO A TEMPERATURE SUFFICIENT TO VAPORIZE IT, AND THE VAPORS CONDENSE ON THE STRIP SURFACE, THE WIDTH OF SAID SUPPLY AND OF SAID BEAM BEING APPROXIMATELY EQUAL TO THE STRIP WIDTH, THE COMBINATION THEREWITH OF A METHOD OF CONTROLLING THE COATING THICKNESS COMPRISING INTERPOSING ELECTROSTATIC POTENTIALS BETWEEN THE SOURCE OF SAID BEAM AND THE SURFACE OF THE SUPPLY OF COATING MATERIAL TO MODIFY THE HEATING EFFECT OF SAID BEAM, AND INDIVIDUALLY VARYING THE DEGREE TO WHICH THE HEATING EFFECT IS MODIFIED IN DIFFERENT PORTIONS OF SAID BEAM ACROSS ITS WIDTH, THEREBY VARYING THE QUANTITY OF MATERIAL VAPORIZED AT DIFFERENT PORTIONS OF SAID SUPPLY.
US309487A 1963-09-17 1963-09-17 Method and apparatus for controlling coating thickness by electron beam evaporation Expired - Lifetime US3281265A (en)

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GB35565/64A GB1062820A (en) 1963-09-17 1964-08-31 Method and apparatus for controlling coating thickness
BE652778A BE652778A (en) 1963-09-17 1964-09-07
DE19641521555 DE1521555A1 (en) 1963-09-17 1964-09-14 Method and device for controlling coating thicknesses
FR988152A FR1411331A (en) 1963-09-17 1964-09-15 Method and apparatus for controlling the thickness of a coating
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US3397672A (en) * 1965-11-10 1968-08-20 United States Steel Corp Control system for vapor-deposition coating apparatus
US3432335A (en) * 1966-03-15 1969-03-11 Lokomotivbau Elektrotech Cyclically moving electron beam for uniform vapor deposited coating
US3455730A (en) * 1966-08-17 1969-07-15 Jones & Laughlin Steel Corp Vacuum vapor deposition-control of coating profile
US3602190A (en) * 1968-10-30 1971-08-31 Western Electric Co Multiple vaporizing system
US3709192A (en) * 1970-06-01 1973-01-09 Sierracin Corp Coating control system
US3928657A (en) * 1971-04-15 1975-12-23 British Steel Corp Strip shape correction on galvanising line
US4587134A (en) * 1984-05-28 1986-05-06 Nisshin Steel Company, Ltd. Method of rapidly changing deposition amount in a continuous vacuum deposition process
US4627989A (en) * 1983-08-20 1986-12-09 Leybold Heraeus Gmbh Method and system for a vacuum evaporative deposition process
US20230003675A1 (en) * 2021-07-01 2023-01-05 Fei Company Method and system for determining sample composition from spectral data

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US4943446A (en) * 1985-09-12 1990-07-24 Dennison Manufacturing Company Metallization of substrates
US7666490B1 (en) * 1999-02-10 2010-02-23 Toyo Boseki Kabushiki Kaisha Functional roll film and vacuum evaporation apparatus capable of producing the functional roll film

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US2711480A (en) * 1948-06-29 1955-06-21 Friedman Herbert Method of measuring thickness of thin layers
US2926257A (en) * 1955-05-16 1960-02-23 Friedman Herbert Method of measuring the thickness of thin coatings
US3046936A (en) * 1958-06-04 1962-07-31 Nat Res Corp Improvement in vacuum coating apparatus comprising an ion trap for the electron gun thereof
US3086899A (en) * 1956-05-04 1963-04-23 Dow Chemical Co Constructional lamina
US3168418A (en) * 1962-03-27 1965-02-02 Alloyd Electronics Device for monitoring and controlling evaporation rate in vacuum deposition

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Publication number Priority date Publication date Assignee Title
US2711480A (en) * 1948-06-29 1955-06-21 Friedman Herbert Method of measuring thickness of thin layers
US2926257A (en) * 1955-05-16 1960-02-23 Friedman Herbert Method of measuring the thickness of thin coatings
US3086899A (en) * 1956-05-04 1963-04-23 Dow Chemical Co Constructional lamina
US3046936A (en) * 1958-06-04 1962-07-31 Nat Res Corp Improvement in vacuum coating apparatus comprising an ion trap for the electron gun thereof
US3168418A (en) * 1962-03-27 1965-02-02 Alloyd Electronics Device for monitoring and controlling evaporation rate in vacuum deposition

Cited By (10)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3397672A (en) * 1965-11-10 1968-08-20 United States Steel Corp Control system for vapor-deposition coating apparatus
US3432335A (en) * 1966-03-15 1969-03-11 Lokomotivbau Elektrotech Cyclically moving electron beam for uniform vapor deposited coating
US3455730A (en) * 1966-08-17 1969-07-15 Jones & Laughlin Steel Corp Vacuum vapor deposition-control of coating profile
US3602190A (en) * 1968-10-30 1971-08-31 Western Electric Co Multiple vaporizing system
US3709192A (en) * 1970-06-01 1973-01-09 Sierracin Corp Coating control system
US3928657A (en) * 1971-04-15 1975-12-23 British Steel Corp Strip shape correction on galvanising line
US4627989A (en) * 1983-08-20 1986-12-09 Leybold Heraeus Gmbh Method and system for a vacuum evaporative deposition process
US4587134A (en) * 1984-05-28 1986-05-06 Nisshin Steel Company, Ltd. Method of rapidly changing deposition amount in a continuous vacuum deposition process
US20230003675A1 (en) * 2021-07-01 2023-01-05 Fei Company Method and system for determining sample composition from spectral data
US11703468B2 (en) * 2021-07-01 2023-07-18 Fei Company Method and system for determining sample composition from spectral data

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GB1062820A (en) 1967-03-22

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