TREA

Patterning thin film superconductors using focused beam techniques

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Information

  • Patent Grant
  • 4952556
  • Patent Number
    4,952,556
  • Date Filed
    Friday, July 29, 1988
    36 years ago
  • Date Issued
    Tuesday, August 28, 1990
    34 years ago
Information
Abstract
Patterned films of superconducting materials are formed using focused beam techniques, such as electron beam, ion beam, and laser beam techniques. A solution comprising the neodecanoates of yttrium, barium, and copper is formed which is soluble in an organic solvent. The solution is spun onto an appropriate substrate. The solution is dried and subsequently selectively exposed using focused beam techniques, so that the exposed regions are no longer soluble in the organic solvent. The solution is immersed in the organic solvent, so that the only the exposed, insoluble regions remain on the substrate. The solution is then heated at a temperature sufficient to decompose the neodecanoates, about 500.degree. C., and then heated again, preferably using rapid thermal annealing techniques, to promote recrystallization and grain growth of the remaining metal oxides. The resulting patterned film exhibits superconductive characteristics.
Description
Claims
  • 1. A method for producing patterned films of superconductor materials comprising the steps of:
  • preparing a solution from the neodecanoates of yttrium, barium, and copper, said metals form an oxide mixture exhibiting superconductive properties characterized by a ratio of yttrium to barium to copper of approximately 1:2:4, said solution comprising up to approximately 25 volume percent pyridine in xylene;
  • depositing a film of said solution onto a substrate;
  • exposing selective regions of said film to an electron beam in a substantially vacuum environment so that said exposed regions of said film become insoluble in a second organic solvent, said electron beam being focused to a beam diameter ranging between about 5 to 500 nanometers and an energy level ranging between about 20-50 keV, said electron beam emitting a dose of about 1200 micro-Coulombs per square centimeter;
  • immersing said film into said second organic solvent so that said insoluble, exposed regions of said film remain on said substrate, said second organic solvent comprising primarily xylene;
  • heating said film to a temperature of approximately 500.degree. C. for a duration of approximately 5 minutes sufficient to thermally decompose said metal neodecanoates into a film containing metal oxides, but insufficient to significantly recrystallize said oxides; and
  • heating said oxide film at a second temperature ranging between about 850.degree. C. to about 1000.degree. C. for a duration of up to about 60 minutes that is sufficient to promote recrystallization and grain growth of said metal oxides within said film and induce a change therein by which said film exhibits superconducting properties.
  • 2. A method for producing patterned films of superconductor materials as recited in claim 1 wherein:
  • said heating at said second temperature is at a temperature of approximately 850.degree. C. for a duration of about 60 seconds sufficient to promote rapid recrystallization within said film and followed by a cooling of said film to room temperature; and
  • further comprising heating said oxide film at a third temperature of about 920.degree. C. for a duration of of about 30 seconds sufficient to promote rapid grain growth within said oxide film.
  • 3. A method for producing patterned films of superconductor materials comprising the steps of:
  • preparing a solution from the neodecanoates of yttrium, barium, and copper, said metals form an oxide mixture exhibiting superconductive properties characterized by a ratio of yttrium to barium to copper of approximately 1:2:4, said solution comprising up to approximately 25 volume percent pyridine in xylene;
  • depositing a film of said solution onto a substrate;
  • exposing selective regions of said film to an ion beam in a substantially vacuum environment so that said exposed regions of said film become insoluble in a second organic solvent, said ion beam being generated from the group consisting of the elements oxygen, gallium, boron, phosphorus and silicon and having a beam diameter ranging from about 5 to about 1000 nanometers, an energy value ranging between about 10 to about 400 keV, and an ion dosage of about 10.sup.13 to about 10.sup.16 ions per square centimeter;
  • immersing said film into said second organic solvent so that said insoluble, exposed regions of said film remain on said substrate, said second organic solvent comprising essentially xylene;
  • heating said film at a temperature of about 500.degree. C. for a duration of approximately five minutes sufficient to thermally decompose said metal neodecanoates into a film containing metal oxides, but insufficient to significantly recrystallize said oxides; and
  • heating said oxide film at a second temperature ranging between about 850.degree. C. to about 1000.degree. C. for a duration of up to about 60 minutes sufficient to promote recrystallization and grain growth of said metal oxides within said film and induce a change therein by which said film exhibits superconducting properties.
  • 4. A method for producing patterned films of superconductor materials as recited in claim 3 wherein:
  • said heating at said second temperature is at a temperature of about 850.degree. C. for a duration of about 60 seconds sufficient to promote rapid recrystallization within said film followed by cooling of said film to room temperature; and
  • further comprising heating said oxide film at a third temperature of about 920.degree. C. for a duration of about 30 seconds sufficient to promote rapid grain growth within said oxide film.
  • 5. A method for producing patterned films of superconductor materials comprising the steps of:
  • preparing a solution from the neodecanoates of yttrium, barium, and copper, said metals form an oxide mixture exhibiting superconductive properties and characterized by a ratio of yttrium to barium to copper of 1:2;4, said solution comprising up to approximately 25 volume percent pyridine in xylene;
  • depositing a film of said solution onto a substrate;
  • exposing selective regions of said film to a laser beam in an oxygen-rich environment so that said exposed regions of said film become insoluble in a second organic solvent, said laser beam being having a beam diameter of approximately 6000 nanometers and emitted at approximately 515 nonometers wavelength from an argon laser source and an energy value ranging between about 0.1 to about 100 Watts;
  • immersing said film into said second organic solvent so that said insoluble, exposed regions of said film remain on said substrate, said second organic solvent comprises essentially xylene;
  • heating said film at a temperature of about 500.degree. C. for a duration of approximately 5 minutes sufficient to thermally decompose said metal neodecanoates into a film containing metal oxides, but insufficient to significantly recrystallize said oxides; and
  • heating said oxide film at a second temperature ranging between about 850.degree. C. to about 1000.degree. C. for a duration of up to about 60 minutes sufficient to promote recrystallization and grain growth of said metal oxides within said film and induce a change therein by which said film exhibits superconducting properties.
  • 6. A method for producing patterned films of superconductor materials as recited in claim 5 wherein:
  • said heating at said second temperature is at approximately 850.degree. C. for a duration of about 60 seconds sufficient to promote rapid recrystallization within said film followed by cooling of said film to room temperature; and
  • further comprising heating said oxide film at a third temperature of approximately 920.degree. C. for a duration of about 30 seconds sufficient to promote rapid grain growth within said oxide film.
  • 7. A method for producing patterned films of superconductor materials comprising the steps of:
  • preparing a solution from the neodecanoates of yttrium, barium, and copper, said metals form an oxide mixture exhibiting superconductive properties characterized by a ratio of yttrium to barium to copper of 1:2:4, said solution comprising up to approximately 25 volume percent pyridine in xylene;
  • depositing a film of said solution onto a substrate;
  • exposing selective regions of said film to a laser beam in an oxygen-rich environment, said laser beam operating at a temperature above approximately 450.degree. C. but less than approximately 850.degree. C. for a duration sufficient to thermally decompose said metal neodecanoates into a film containing metal oxides, so that said exposed regions of said film become insoluble in a second organic solvent, said laser beam being focused to a beam diameter of about 6000 nanometers and emitted at approximately 515 nanometers wavelength from an argon laser source and an energy value ranging between about 0.1 to about 100 watts;
  • immersing said film into said second organic solvent so that said insoluble, exposed regions of said film remain on said substrate, said second organic solvent comprising essentially xylene; and
  • heating said oxide film at a second temperature ranging between about 850.degree. C. to about 1000.degree. C. for a duration of up to approximately 60 minutes sufficient to promote recrystallization and grain growth of said metal oxides within said film and induce a change therein by which said film exhibits superconducting properties.
  • 8. A method for producing patterned films of superconductor materials as recited in claim 7 wherein:
  • said heating at said second temperature is at approximately 850.degree. C. for a duration of about 60 seconds sufficient to promote rapid recrystallization within said film and followed by cooling said film to room temperature; and
  • further comprising heating said oxide film at a third temperature of about 920.degree.C. for a duration of about 30 seconds sufficient to promote rapid grain growth within said oxide film.
BACKGROUND OF THE INVENTION

This application is a continuation-in-part of U.S. Ser. No. 130,135, filed in the U.S. on Dec. 8, 1987, now abandoned and entitled "Patterning Thin Film Superconductors Using Focused Beam Techniques." This invention relates to superconducting materials. More particularly, this invention relates to methods for forming patterned films of superconducting materials. Films of superconducting materials have been formed using metallo-organic deposition techniques. Superconducting films formed by metallo-organic deposition offer many advantages over standard methods for film preparation and deposition. A significant advantage is that the metallo-organic deposition process does not require vacuum processing. In addition, the chemical constituents of the films may be altered with ease. Examples of such superconducting materials prepared using metallo-organic deposition techniques are disclosed in the previously filed U.S. Ser. No. 186,627, entitled "Formation of Film Superconductors by Metallo-Organic Deposition," assigned to the same assignee of the present application and herein incorporated by reference. Metallo-organic deposition of the thin film superconductors generally involves a three step process. First, an organic liquid, such as the composition comprising yttrium, barium, and copper neodecanoates disclosed in the previously filed U.S. Ser. No. 186,627, is spin-coated onto a suitable substrate so as to form a film of the metal neodecanoates. The organic film is then heated in air at about 500.degree. C. for about five minutes so as to decompose the neodecanoates to their metal oxides. Lastly, the metal oxide film is annealed so as to promote recrystallization and grain growth within the metal oxides. Preferably a rapid thermal annealing two-step process is used; a first exposure at approximately 850.degree. C. for approximately 60 seconds, followed by a second exposure at approximately 920.degree. C. for approximately 30 seconds. The resulting empirical composition for the superconducting thin films prepared in accordance with this metallo-organic deposition technique is Y.sub.1 Ba.sub.2 Cu.sub.4 O.sub.z, with z ranging between about 6-8. Electrical measurements indicate a superconducting transition temperature of about 90K for these superconducting materials, with the temperature of zero state resistance as high as about 86K. It is desirable to provide a method for forming patterned films of superconductive material It is an object of the present invention to provide patterned films of superconductive material. It is a further object of this invention to provide a method for forming patterned films of superconductive material. It is still a further object of this invention that these patterned superconductive films be formed using focused beam techniques. In accordance with a preferred embodiment of this invention, these and other objects and advantages are accomplished as follows. We are the first to produce patterned superconductive films using focused beam techniques. For the first time a method is disclosed for forming patterned superconductive films by first patterning metal neodecanoate organic films which subsequently reduce to superconducting films of YBaCuO, and, second, exposing the neodecanoates comprised within the metallo-organic films to focused beams. Initially a yttrium, barium, copper neodecanoate solution is spin-coated onto a suitable substrate, much like conventional photoresist is spun onto a silicon wafer. In a preferred embodiment, the solvent within the neodecanoate solution is driven from the organic film by prebaking the film and substrate at a temperature below the decomposition temperature for the metal neodecanoates, about 25-450.degree. C. preferably about 250.degree. C., for a short period of time, about five minutes. The metal neodecanoate organic film is still soluble in a xylene-pyridine solvent solution after this prebaking step. The prebaked metal neodecanoate organic film is then patterned by exposing selected areas of the organic film to focused beams of electrons, ions, or laser light. This exposure renders the metal neodecanoate material insoluble in the xylene-pyridine mixture where the focused beams have impinged upon the metallo-organic film. The prebaked organic film and substrate is then rinsed in xylene which acts as a developer to remove the unexposed regions of the organic film, so that only those regions of the metal neodecanoate film which have been exposed to the focused beams remain on the substrate. The substrate and patterned metallo-organic film is then heated to approximately 500.degree. C. for about five minutes, so as to fully decompose the metal neodecanoates and leave only the metal oxides on the substrate surface. The metal oxide film is then preferably rapid thermal annealed in an oxygen atmosphere at a first temperature of approximately 850.degree. C. for about 60 seconds and then at a second temperature of approximately 920.degree. C. for about 30 seconds. The resulting patterned material is superconductive. Other objects and advantages of this invention will be better appreciated from a detailed description thereof, which follows.

US Referenced Citations (3)
Number Name Date Kind
4239816 Breininger et al. Dec 1980
4401474 Donley Aug 1983
4485094 Pebler et al. Nov 1984
Foreign Referenced Citations (1)
Number Date Country
0292387A2 Nov 1988 EPX
Non-Patent Literature Citations (21)
Entry
Cody et al., "Rapid Thermal Anneal of Sprayed Y.sub.1 Ba.sub.2 Cu.sub.3 O.sub.7-x Slurry", Appl. Phys. Lett., 52(18), May 1988, pp. 1531-1533.
Venkatesan, "Laser Deposited High Tc Superconducting Thin Films", Solid State Technology, Dec. 1987, pp. 39-41.
Gross et al. (I), "A Versatile New Metallo-organic Spin-on Process for Preparing Superconducting Thin Films", MRS, vol. 99, Nov. 1987, pp. 731-734.
Gross et al. (II), "Laser Direct-write Metallization in Thin Palladium Acetate Films", J. Appl. Phys., vol. 61(4), Feb. 1987, pp. 1628-1632.
Davison et al., "High Tc Superconducting Films from Metallo-organic Precursors", MRS, vol. 99, Nov. 1987, pp. 289-292.
Gurvitch et al., "Preparation and Substrate Reaction of Superconducting Y--Ba--Cu--O Films", Appl. Phys. Lett. 51(13), Sep. 1987, pp. 1027-1029.
Koch et al., "Thin Films and Squids made from YBa.sub.2 Cu.sub.3 O.sub.y ", MRS ed., Gubser et al., Apr. 1987, (Anaheim, Calif.), pp. 81-84.
Gross, "Laser Direct-write Metallization in Metallo-organic Films", MRS ed., von Gutfeld et al., Dec. 1985, (Boston, Mass.), pp. 21-23.
A. Gupta et al., "Direct Laser Writing of Superconducting Patterns of Y.sub.1 Ba.sub.2 Cu.sub.3 O.sub.7-y ", Applied Physics Letters, vol. 52, No. 8, Feb. 22, 1988, pp. 665-666.
M. K. Wu et al., "Superconductivity at 93K in a New Mixed Phase Y--Ba--Cu--O Compound System at Ambient Pressure", Physical Review Letters, vol. 58, No. 9, Mar. 2, 1987, pp. 908-910.
H. Adachi et al., "Preparation and Characterization of Superconducting Y--Ba--Cu--O Thin Film", Japanese Journal of Applied Physics, vol. 26, No. 5, May 1987, pp. L709-L710.
D. Dijkkamp et al., "Preparation of Y--Ba--Cu Oxide Superconductor Thin Films Using Pulsed Laser Evaporation from High T.sub.c Bulk Material", Applied Physics Letters, vol. 51, No. 8, Aug. 24, 1987, pp. 619-621.
M. E. Gross et al., "Versatile New Metalorganic Process for Preparing Superconducting Thin Films", Applied Physics Letters, vol. 52, No. 2, Jan. 11, 1988, pp. 160-162.
C. E. Rice et al., "Preparation of Superconducting Thin Films of Ba.sub.2 YCu.sub.3 O.sub.7 by a Novel Spin-on Pyrolysis Technique", Applied Physics Letters, vol. 51, No. 22, Nov. 30, 1987, pp. 1842-1844.
D. K. Lathrop et al., "Production of YBa.sub.2 Cu.sub.3 O.sub.7--y Superconducting Thin Films in situ by High Pressure Reactive Evaporation and Rapid Thermal Annealing", Applied Physics Letters, vol. 51, No. 19, Nov. 9, 1987, pp. 1554-1556.
H. G. Craighead et al., "Metal Deposition by Electron Beam Exposure of an Organometallic Film", Applied Physics Letters, vol. 48, No. 25, Jun. 23, 1986, pp. 1748-1750.
L. R. Harriott et al., "Decomposition of Palladium Acetate Films with a Microfocused Ion Beam", Applied Physics Letters, vol. 49, No. 24, Dec. 15, 1986, pp. 1661-1662.
S. Matsui et al., "Ion Species Dependence of Focused-Ion-Beam Lithography", Journal Vacuum Science Technology, vol. B5, No. 4, Jul./Aug. 1987, pp. 853-857.
S. S. Eskildesn et al., "Inorganic Ion Beam Resist for Additive Plating of Metallic Interconnects", Applied Physics Letters, vol. 46, No. 11, Jun. 1, 1985, pp. 1101-1102.
Y. Ohmura et al., "Focused Ion Beam Induced Fine Patterns of Organogold Films", Applied Physics Letters, vol. 51, No. 19, Nov. 9, 1987, pp. 1500-1502.
A. Gupta et al., "Laser Writing of Copper Lines from Metalorganic Films", Applied Physics Letters, vol. 51, No. 26, Dec. 28, 1987, pp. 2254-2256.
Continuation in Parts (1)
Number Date Country
Parent 130135 Dec 1987