Precursors and processes for making metal oxides

• US 5,514,822 A
• Filed: 10/06/1993
• Issued: 05/07/1996
• Est. Priority Date: 12/13/1991
• Status: Expired due to Term

• Current Assignee: Symetrix Corporation
• Original Assignee: Symetrix Corporation
• Inventors: Paz de Araujo, Carlos A., Scott, Michael C., McMillan, Larry D.
• Primary Examiner(s): NAZARIO GONZALEZ, PORFIRIO
• Application Number:
  US08/132,744
• Time in Patent Office: 944 Days
• Field of Search: 556/28, 556/31, 534/16
• US Class Current: 556/28
• CPC Class Codes: C04B 2235/3213 Strontium oxides or oxide-forming salts thereof
• CPC Class Codes: C04B 2235/3224 Rare earth oxide or oxide forming salts thereof, e.g. scandium oxide
• CPC Class Codes: C04B 2235/3227 Lanthanum oxide or oxide-forming salts thereof
• CPC Class Codes: C04B 2235/3229 Cerium oxides or oxide-forming salts thereof
• CPC Class Codes: C04B 2235/3243 Chromates or chromites, e.g. aluminum chromate, lanthanum strontium chromite
• CPC Class Codes: C04B 2235/3268 Manganates, manganites, rhenates or rhenites, e.g. lithium manganite, barium manganate, rhenium oxide
• CPC Class Codes: C04B 2235/441 Alkoxides, e.g. methoxide, tert-butoxide
• CPC Class Codes: C04B 2235/449 Organic acids, e.g. EDTA, citrate, acetate, oxalate
• CPC Class Codes: C04B 2235/72 Products characterised by the absence or the low content of specific components, e.g. alkali metal free alumina ceramics
• CPC Class Codes: C04B 35/4682 based on BaTiO3 perovskite phase
• CPC Class Codes: C04B 35/6264 Mixing media, e.g. organic solvents
• CPC Class Codes: C23C 16/4412 Details relating to the exhausts, e.g. pumps, filters, scrubbers, particle traps
• CPC Class Codes: C23C 16/448 characterised by the method used for generating reactive gas streams, e.g. by evaporation or sublimation of precursor materials
• CPC Class Codes: C23C 16/4486 by producing an aerosol and subsequent evaporation of the droplets or particles
• CPC Class Codes: C23C 16/45561 Gas plumbing upstream of the reaction chamber
• CPC Class Codes: C23C 16/4558 Perforated rings
• CPC Class Codes: C23C 16/46 characterised by the method used for heating the substrate C23C16/48, C23C16/50 take precedence
• CPC Class Codes: C23C 16/482 using incoherent light, UV to IR, e.g. lamps
• CPC Class Codes: C23C 16/52 Controlling or regulating the coating process C23C16/45557, C23C16/279 take precedence
• CPC Class Codes: C23C 18/1216 Metal oxides C23C18/1212 takes precedence
• CPC Class Codes: C23C 18/1275 : performed under inert atmosphere
• CPC Class Codes: C30B 29/68 : Crystals with laminate structure, e.g. "superlattices"
• CPC Class Codes: C30B 7/00 : Single-crystal growth from solutions using solvents which are liquid at normal temperature, e.g. aqueous solutions from molten solvents C30B9/00; by normal or gradient freezing C30B11/00; under a protective fluid C30B27/00
• CPC Class Codes: H01C 7/1013 : Thin film varistors
• CPC Class Codes: H01L 21/02197 : the material having a perovskite structure, e.g. BaTiO3
• CPC Class Codes: H01L 21/02205 : the layer being characterised by the precursor material for deposition
• CPC Class Codes: H01L 21/02282 : liquid deposition, e.g. spin-coating, sol-gel techniques, spray coating
• CPC Class Codes: H01L 21/314 : Inorganic layers H01L21/3105, H01L21/32 take precedence
• CPC Class Codes: H01L 21/31691 : with perovskite structure
• CPC Class Codes: H01L 28/55 : with a dielectric comprising a perovskite structure material
• CPC Class Codes: H01L 28/56 : the dielectric comprising two or more layers, e.g. comprising buffer layers, seed layers, gradient layers
• CPC Class Codes: H01L 28/60 : Electrodes
• CPC Class Codes: H10B 12/30 : DRAM devices comprising one-transistor - one-capacitor [1T-1C] memory cells
• CPC Class Codes: H10B 53/00 : Ferroelectric RAM [FeRAM] devices comprising ferroelectric memory capacitors

Abstract

A first metal, an alcohol, and a carboxylic acid are reacted to form a metal alkoxycarboxylate which is then reacted with an alkoxide and/or a carboxylate of a second metal to form a precursor. Alternatively, a metal carboxylate and a metal alkoxide are combined and heated to form a precursor. In either alternative, the precursor includes all or most of the metal-oxygen-metal bonds of a desired metal oxide and a carboxylate ligand. The precursor is applied to a substrate, dried and annealed to form the metal oxide, such as BST. The metal-oxygen-metal bonds in the precursor permit the desired metal oxide to be formed from the precursor in one step, providing excellent thin films suitable for integrated circuits. The carboxylate ligand provides stability to the precursor allowing it to be stored for periods common in large scale manufacturing.

Claims

1. A liquid precursor for use in making a solid metal oxide, said precursor comprising:

a polyoxyalkylated metal portion having a molecular formula including a metal-oxygen-metal structure; and

a solvent portion forming an essentially liquid solution with said polyoxyalkylated metal portion,

said polyoxyalkylated metal portion being present in an effective amount for yielding a corresponding portion of an electronically competent thin-film metal oxide upon liquid deposition of said precursor followed by thermal treatment at effective metal-oxide forming temperatures,

said precursor being essentially free of distillable portions having a boiling point of less than about 115°

C.

2. The precursor as set forth in claim 1, said solvent portion being selected from a solvent group consisting of n-butyl acetate, and 2-methoxyethanol.

3. The precursor as set forth in claim 1, including metals of said metal-oxygen-metal structure being selected from a metal group consisting of barium, strontium, tantalum, calcium, bismuth, lead, yttrium, scandium, lanthanum, antimony, chromium, thallium, titanium, hafnium, tungsten, niobium, zirconium, manganese, iron, cobalt, nickel, magnesium, zinc, and mixtures thereof.

4. The precursor as set forth in claim 3, including said molecular formula selected from a formula group consisting of:

X_x M₁ --O--M₂ A_b-a,

A_a M₁ --O--M₂ X_y-x,

A_a M₁ --O--M₂ A_b-x and mixtures thereof,

wherein M₁ and M₂ are metals of said metal group, X is a carboxylate ligand;

A is an alkoxide ligand, O is oxygen; and

the subscripts x, a, (b-a), (b-x), and (y-x) indicate a respective number of units of X and A ligand required to satisfy valence requirements of the corresponding metal M₁ and M₂.

5. The precursor as set forth in claim 1, wherein said carboxylate ligands are selected from a carboxylate group consisting of octanoates and neodecanoates.

6. The precursor as set forth in claim 1, wherein said carboxylate ligands are 2-ethylhexanoates.

7. The precursor as set forth in claim 1, wherein said electronically competent metal oxide includes a ferroelectric material having a polarization-state switching endurance exceeding 10⁹ cycles.

8. The precursor as set forth in claim 1, wherein said electronically competent metal oxide includes a dielectric material having a dielectric constant of at least about 166 in combination with a leakage current of at most about 10^-8 amps/cm2 at 1-10 V.

9. A precursor for use in making a solid metal oxide, comprising;

a polyoxyalkylated metal portion having a molecular formula including a metal-oxygen-metal structure wherein at least one metal of said structure is bonded to a 2-ethylhexanoate ligand.

10. A method of making a precursor for fabricating a metal oxide, said method comprising the steps of:

mixing a metal alkoxycarboxylate-containing liquid with a carboxylic acid in an effective amount for shelf-stabilizing said liquid by substituting carboxylate ligands from said carboxylic acid in place of alkoxide ligands of said metal alkoxycarboxylate-containing liquid, thereby forming a mixture; and

heating said mixture to so substitute said carboxylate ligands in place of said alkoxide ligands.

12. The method as set forth in claim 10, including a step of providing said metal alkoxycarboxylate to at least two metals selected from a metal group consisting of barium, strontium, tantalum, calcium, bismuth, lead, yttrium, scandium, lanthanum, antimony, chromium, thallium, titanium, hafnium, tungsten, niobium, zirconium, manganese, iron, cobalt, nickel, magnesium, zinc, and mixtures thereof.

13. The method as set forth in claim 12, said metals being provided in effective amounts for forming strontium bismuth tantalate upon drying and calcining of said precursor.

14. The method as set forth in claim 12, said metals being provided in effective amounts for forming barium strontium tantalate upon drying and calcining of said precursor.

11. A precursor produced according to a method comprising the steps of:

mixing a metal alkoxycarboxylate-containing liquid with a carboxylic acid in an effective amount for shelf-stabilizing said liquid by substituting carboxylate ligands from said carboxylic acid in place of alkoxide ligands of said metal alkoxycarboxylate-containing liquid, thereby forming a mixture; and

heating said mixture to substitute said carboxylate ligands in place of said alkoxide ligands, said precursor having a shelf life exceeding at least two months.

15. A method of making a barium strontium titanate precursor, said method comprising the steps of:

combining a polyoxyalkylated barium moiety, a polyoxyalkylated strontium moiety, and a polyoxyalkylated titanium moiety to form a liquid solution,

each of said respective moieties having a formula in which corresponding barium, strontium, and titanium atoms bond with an oxygen atom in a ligand selected from a ligand group consisting of alkoxides and carboxylates; and

heating said liquid solution to a temperature of at least about 115°

C.

16. The method as set forth in claim 15, wherein said formula defines a member selected from a moiety group consisting of barium carboxylates, barium alkoxides, barium alkoxycarboxylates, strontium carboxylates, strontium alkoxides, strontium alkoxycarboxylates, titanium carboxylates, titanium alkoxides, and titanium alkoxycarboxylates.

17. The method as set forth in claim 16, wherein said heating step includes reacting two members of said moiety group to form a reaction product having a molecular formula including a central oxygen atom connecting two metal atoms, said two members including a single-metal alkoxycarboxylate and a metal alkoxide.

18. The method as set forth in claim 17, said two members including said barium alkoxycarboxylate and said titanium alkoxide.

19. The method as set forth in claim 18, said titanium alkoxide being titanium isopropoxide.

20. A method of making a strontium bismuth tantalate precursor, said method comprising the steps of:

combining a polyoxyalkylated strontium moiety, a polyoxyalkylated bismuth moiety, and a polyoxyalkylated tantalum moiety to form a liquid solution,

each of said respective moieties having a formula in which corresponding strontium, bismuth, and tantalum atoms bond with an oxygen atom in a ligand selected from a ligand group consisting of alkoxides and carboxylates; and

heating said liquid solution to a temperature of at least about 115°

C.

21. The method as set forth in claim 20, wherein said formula defines a member selected from a moiety group consisting of bismuth carboxylates, bismuth alkoxides, bismuth alkoxycarboxylates, strontium carboxylates, strontium alkoxides, strontium alkoxycarboxylates, tantalum carboxylates, tantalum alkoxides, and tantalum alkoxycarboxylates.

22. The method as set forth in claim 21, wherein said heating step includes reacting two members of said moiety group to form a reaction product having a molecular formula including a central oxygen atom connecting two metal atoms, said two members including a single-metal alkoxycarboxylate and a metal alkoxide.