Patent Publication Number: US-6214105-B1

Title: Alkane and polyamine solvent compositions for liquid delivery chemical vapor deposition

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This is a continuation-in-part of U.S. patent application Ser. No. 08/975,372 filed Nov. 20, 1997, now issued as U.S. Pat. No. 5,916,359, which is a continuation-in-part of U.S. patent application Ser. No. 08/484,654 filed Jun. 7, 1995, now U.S. Pat. No. 6,110,529, which is a continuation-in-part of U.S. patent application Ser. No. 08/414,504 filed Mar. 31, 1995, now issued as U.S. Pat. No. 5,820,664. This application also claims the priority of U.S. Provisional Patent Application No. 60/064,047 filed Nov. 3, 1997. This application also claims the priority of U.S. patent application Ser. No. 60/064,047 filed Nov. 3, 1997 in the name of Frank S. Hintermaier. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a solvent composition useful for liquid delivery chemical vapor deposition of metal organic precursors including metal (beta-diketonato) precursors. 
     2. Description of the Related Art 
     In the liquid delivery method of carrying out chemical vapor deposition (CVD) processes, a solid precursor is dissolved in an appropriate solvent medium or a liquid-phase precursor is vaporized and the resulting precursor vapor, typically mixed with a carrier gas (such as argon, helium or nitrogen) is transported to the chemical vapor deposition reactor. In the reactor, the precursor vapor stream is contacted with a heated substrate to effect decomposition and deposition of a desired component or components from the solution and/or vapor phase on the substrate surface. 
     In such liquid delivery CVD process, a wide variety of solvents have been employed for dissolution or suspension of precursor species, with the liquid solution or suspension being vaporized by various techniques, including flash vaporization on a heated element onto which the liquid containing the precursor is discharged, to volatilize the solvent and precursor species. 
     In many instances, where a variety of precursors are employed to form a multi-component deposited film in the CVD process, it is desirable to utilize a single solvent medium for the respective precursor species, for ease of operation and simplicity of the process system, thereby avoiding any deleterious solvent-solvent interactions which may occur if different solvent media are utilized for different precursor species. Further, it is desirable that solvent compositions when used for multiple species not interact with the precursor or metal-containing molecules to form unstable chemical solutions, since such instability renders the overall composition unsuitable for liquid delivery. 
     In a specific field in which the present invention has applicability, ferroelectric ceramic materials based on bismuth oxide are promising materials for use in non-volatile memories. Promising candidates derive from the group of Aurivillius phase compounds having the general formula: 
     (Bi 2 O 2 ) 2+ (A m−1 B m O 3m+1 ) 2− , wherein A=Bi 3+ , L 3+ , L 2+ , Ca 2+ , Sr 2+ , Ba 2+ , Pb 2+ , Na + , B=Fe 3+ , Al 3+ , Sc 3+ , Y 3+ , L 4+ , Ti 4+ , Nb 5+ , Ta 5+ , W 6+ , Mo 6+ , with L=metal from the lanthanide series, such as Ce 4+ , La 3+ , Pr 3+ , Ho 3+ , Eu 2+ , Yb 2+ , etc. and m=1,2,3,4,5. 
     Among materials of the foregoing type, SrBi 2 Ta 2 O 9  (SBT) and Bi 4 Ti 3 O 12  find widespread interest for integration in ferroelectric random access memories (FeRAMs) and in smart cards. 
     In chemical vapor deposition processes for SBT, the use of precursors such as Sr(thd) 2 (tetraglyme), Ta(OiPr) 4 (thd) and triphenyl bismuth, dissolved in a solvent mixture such as tetrahydrofuran: isopropanol: tetraglyme in a volumetric ratio of 8:2:1 produced the result that Bi 2 O 3  deposition was difficult to control. Efforts to resolve such difficulties included replacement of the triphenyl bismuth precursor with Bi(thd) 3  with the latter precursor showing a reliable and reproducible Bi 2 O 3  deposition rate. Unfortunately, however, in the vaporizer the Bi(thd) 3  precursor caused the formation of black bismuth-rich residues, indicating premature decomposition was taking place during vaporization and transport. Such premature decomposition allowed only ten operational runs to be conducted with the Bi(thd) 3  precursor until the vaporizer required maintenance to remove unwanted deposits. 
     Chemical considerations associated with the foregoing adverse decomposition indicated the solvent system was one source of the problem. It appeared that the isopropanol was reacting with the Bi(thd) 3  precursor in the elevated temperature conditions of the vaporizer (190° C.) and the precursor was resultingly reduced to Bi metal producing the black residue. Concurrently, it is expected that the IPA is oxidized during this decomposition (redox) reaction. 
     Accordingly, an improved solvent system is desired for such deposition process for the formation of SBT films. Such a solvent system faces a number of problems. The solubility of the precursors in the solvent medium must be sufficiently high to provide adequate precursor delivery rates in the vaporizer. Moreover, there should not be a precipitation of material over a period of time due to any slight oversaturation incurred during preparation of the source reagent compositions, or caused by a ligand exchange among the different precursor species. 
     It therefore is the object of the present invention to provide a novel solvent composition having broad utility for CVD precursors, such as those comprising metal organic compositions with β-diketonate ligands. 
     Other objects and advantages of the present invention will be more fully apparent from the ensuing disclosure and appended claims. 
     SUMMARY OF THE INVENTION 
     The present invention relates in one aspect to a solvent composition for liquid delivery chemical vapor deposition of metal organic precursors. 
     One composition of the invention comprises a mixture of solvent species A, B and C in the proportion A:B:C wherein A is from about 3 to about 7 parts by volume, B is from about 2 to about 6 parts by volume, and C is present up to about 3 parts by volume, wherein such parts by volume are based on the total volume of the mixture, and wherein A is a C 6 -C 8  alkane, B is a C 8 -C 12  alkane, A and B are different from one another, and C is a glyme-based solvent (glyme, diglyme, tetraglyme, etc.), a polyamine, and/or other suitable Lewis base ligand. 
     In one specific and preferred aspect, the solvent composition may comprise (A) octane, (B) decane, and (C) an amine, a diamine or a polyamine, in approximately 5:4:1 proportion (of A:B:C) by volume. 
     Concerning preferred amine, diamine and polyamine species for component C in the composition of the solvent composition, preferred amine species include trialkylamine, preferred diamines include tetralkyl ethylene diamine, and preferred polyamine species include N, N, N′, N′-tetramethylethylenediamine, N, N, N′, N″, N″-pentamethyldiethylenetriamine, and N, N, N′, N″, N′″, N′″-hexamethyltriethylenetetramine. 
     In another aspect, the present invention relates to a precursor composition for liquid delivery chemical vapor deposition, comprising at least one metal organic precursor component in a solvent mixture comprising a mixture of solvent species A, B and C in the proportion A:B:C wherein A is from about 1 to about 10 parts by volume, B is from about 0 to about 6 parts by volume, and C is present from 1 up to about 4 parts by volume, wherein such parts by volume are based on the total volume of the mixture, and wherein A is a C 6 -C 8  alkane, B is a C 8 -C 12  alkane, A and B are different from one another, and C is a glyme-based solvent (glyme, diglyme, tetraglyme, etc.) or an amine, a diamine or a polyamine. 
     The metal organic precursor in such composition may for example comprise one or more metal β-diketonate(s) and/or adduct(s) thereof. 
     Another aspect of the invention relates to a liquid delivery MOCVD method of forming a metal-containing film on a substrate including the steps of vaporizing a precursor solution to form a precursor vapor, and contacting the precursor vapor with the substrate to deposit said metal-containing film, wherein the precursor composition includes a solvent medium comprising one or more alkanes, having dissolved therein one or more compatible metal organic compound(s) selected from the group consisting of (i) β-diketonate compound(s), (ii) compound(s) including alkoxide ligands, and (iii) compound(s) including alkyl and/or aryl groups. 
     In a further aspect, the invention relates to a process for forming a film of SrBi 2 Ta 2 O 9  (SBT) on a substrate, in applications such as the formation of ferroelectric microelectronic device structures, wherein the precursors Sr(thd) 2 (tetraglyme), Ta(OiPr) 4 (thd) and Bi(thd) 3  are employed in a solvent medium comprising one or more alkanes. 
     A still further aspect of the invention relates to a precursor composition for MOCVD of a metal-containing film on a substrate, wherein the precursor composition includes a solvent medium comprising one or more alkanes, having dissolved therein one or more compatible metal organic compound(s). Such compound(s) may for example be β-diketonate compounds or complexes, compound(s) including alkoxide ligands, compound(s) including alkyl and/or aryl groups at their outer (molecular) surface, or compound(s) including other ligand coordination species (i.e., Lewis base ligands) and specific metal constituents. 
     In one embodiment, such compound(s) may be selected from the group consisting of Sr(thd) 2 (tetraglyme), Sr(thd) 2 (polyamine), Ba(thd) 2 (tetraglyme), Ba(thd) 2 (polyamine), Ta(OiPr) 4 (thd), Ti(OiPr) 2 (thd) 2 , Zr(OiPr) 2 (thd) 2 , [Zr(OiPr) 3 (thd) 2 ] 2 , Bi(thd) 3 , Pb(thd) 2 , Pb(thd) 2 (tmeda), Pb(thd) 2 (pmeda), Pt(thd) 2 , Pt(hfac) 2 , (methylcyclopentadienyl) Pt(Me) 3 , (MeCN) 2 PtMe 2 , Pd(allyl) 2 , Pd(hfac) 2 , Me 2 Au(hfac), MeAu(PMe 3 ), Cu(hfac) 2 , (COD)Cu(hfac), (DMCOD)Cu(hfac), (MHY)Cu(hfac), (Me 3 P)CuO t Bu, Ta(OR) 5 , and Ti(OR) 4 , wherein R=C 1 -C 8  alkyl (branched or straight chain). 
    
    
     Other aspects, features and embodiments of the invention will be more fully apparent from the ensuing disclosure and appended claims. 
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a plot of upstream pressure, in torr, as a function of time, in minutes, for a liquid delivery chemical vapor deposition system employed for vaporization of the precursor solution at 180° C. and deposition of strontium bismuth tantalate, utilizing β-diketonate precursors for strontium, bismuth and tantalum, in a 8:2:1 solvent composition of tetrahydrofuran:isopropanol:polyamine. 
     FIG. 2 is a plot of upstream pressure, in torr, as a function of time, in minutes, for a liquid delivery chemical vapor deposition system employed for deposition of strontium bismuth tantalate following precursor solution vaporization at 180° C., utilizing β-diketonate precursors for strontium, bismuth and tantalum, in a solvent composition according to the invention comprising 5:4:1 octane:decane:polyamine. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION, AND PREFERRED EMBODIMENTS THEREOF 
     The disclosures of the following U.S. patent applications are hereby incorporated herein in their entireties: U.S. patent application Ser. No. 08/975,372 filed Nov. 20, 1997, now U.S. Pat. No. 5,916,359; U.S. patent application Ser. No. 08/484,654 filed Jun. 7, 1995, now U.S. Pat. No. 6,110,529; U.S. patent application Ser. No. 08/414,504 filed Mar. 31, 1995, now U.S. Pat. No. 5,820,664; U.S. patent application Ser. No. 08/960,915 filed Oct. 30, 1997, now U.S. Pat. No. 5,859,274; and U.S. patent application Ser. No. 08/976,087 filed Nov. 20, 1997. 
     The present invention is based on the discovery of solvent compositions which are advantageously used for liquid delivery chemical vapor deposition of metal organic precursors such as metal β-diketonate precursors, e.g., of Group II and other metals. Such solvent compositions have been found highly advantageous in carrying out deposition of metals from such β-diketonate precursors, including β-diketonate-based complexes of metals such as strontium, bismuth, tantalum, and the like. 
     One class of compositions of the present invention comprises a mixture of solvent species A, B and C in the proportion A:B:C wherein A is from about 1 to about 10 parts by volume of the solution (A+B+C), B is from about 0 to about 6 parts by volume of the solution, and C is present in an amount greater than zero up to about 4 parts by volume, wherein such parts by volume are based on the total volume of the solution, and wherein A is a C 6 -C 8  alkane, B is a C 8 -C 12  alkane, A and B are different from one another, and C is a glyme-based solvent (glyme, diglyme, tetraglyme, etc.) or an amine, a diamine or a polyamine. A highly preferred composition according to the invention includes octane as the solvent species A and decane as the solvent species B, with C being either or a diamine or polyamine, in a 5:4:1 ratio of the respective solvent species A, B and C. 
     In a particularly preferred aspect of such compositions of the invention, a 5:4:1 solvent composition of octane: decane: polyamine is utilized as a solvent species for each of the strontium, bismuth and tantalum β-diketonate precursors for liquid delivery chemical vapor deposition of SrBi 2 Ta 2 O 9 . 
     The solvent compositions of the invention permit low pressure volatilization of the β-diketonate precursors, and afford good transport and minimal residue in the vaporization and chemical vapor deposition process. 
     When C in the A:B:C solvent composition is a polyamine, the polyamine component of the solvent composition may be any suitable polyamine. Examples include N, N, N′, N′-tetramethyl ethylenediamine, N, N, N′, N″, N″-pentamethyl diethylenetriamine, N, N, N′, N″, N′″, N′″-hexamethyltriethylenetetramine, etc. 
     The metal β-diketonate precursors with which the solvent composition of the invention may be employed include β-diketonato compositions whose metal constituent may be any suitable metal, as for example strontium, bismuth, tantalum, niobium, copper, gold, palladium, lead, calcium, barium, iron, aluminum, scandium, yttrium, titanium, tungsten, molybdenum and lanthanide metals such as Ce, La, Pr, Ho, Eu, Yb, etc. The β-diketonate ligand may be any suitable species, as for example a β-diketonate ligand selected from the group consisting of: 
     2,2,6,6-tetramethyl-3,5-heptanedionato; 
     1,1,1-trifluoro-2,4-pentanedionato; 
     1,1,1,5,5,5-hexafluoro-2,4-pentanedionato; 
     6,6,7,7,8,8,8-heptafluoro-2,2-dimethyl-3,5-octanedionato; 
     2,2,7-trimethyl-3,5-octanedionato; 
     1,1,1,5,5,6,6,7,7,7-decafluoro-2,4-heptanedionato; and 
     1,1,1-trifluoro-6-methyl-2,4-heptanedionato. 
     The solvent composition of the present invention has particular utility for the deposition of bismuth-containing thin films, using bismuth precursors such as anhydrous mononuclear tris(2,2,6,6-tetramethyl-3,5-heptanedionato) bismuth and polyamine-adducted Sr(thd) 2 . Such metal β-diketonate compounds may be readily employed in the solvent compositions of the invention to prepare superior bismuth-containing thin films, such as SrBi 2 Ta 2 O 9 . 
     In another class of solvent compositions, the solvent medium may comprise an alkane solvent medium, comprising one or more hydrocarbon solvent species. Such alkane solvent medium enables a process for forming a film of SrBi 2 Ta 2 O 9  (SBT) on a substrate, in applications such as the formation of ferroelectric microelectronic device structures, wherein the precursors Sr(thd) 2 (pmdeta), Ta(OiPr) 4 (thd) and Bi(thd) 3  are employed in a solvent medium comprising one or more alkanes. The alkanes may be of any suitable type and carbon number, e.g., the solvent medium may comprise one or more compatible solvent species selected from C 1 -C 10  alkanes. The metal organic compound(s) may be formulated in the solvent to form a precursor solution or suspension by simple mixing of the compound(s) with the solvent medium, followed by agitation, gentle heating, sonication dispersal, etc., as necessary or desirable in a specific end use application to place the compound(s) in the solvent medium employed. 
     The alkane solvent medium may for example comprise solvent species such as butane, pentane, hexane, heptane, octane, nonane, decane, etc., and solvent mixtures of different alkanes may be employed to adjust the boiling point of the overall solvent medium by appropriate proportion of the constituent solvents having different individual boiling points. The resulting precursor composition is storage stable at room temperature for at least several weeks, during which time it remains clear and shows no precipitation or discoloration. By selectively mixing alkane solvent components having different boiling points, it is possible to selectively adjust the overall boiling point of the solvent composition to accommodate boiling point as well as solubility requirements. 
     Thus, since different alkanes having different boiling points, the solvent of the desired boiling point can be selected. Furthermore, mixing two or more alkanes is also useful to achieve a desired boiling point. The capability of adjusting the boiling point is advantageous as it enables reliable operation, since the solvent can be adjusted to accommodate the evaporation characteristics of a specific precursor. 
     The alkane solvent compositions of the invention have the further advantage that degenerate ligand exchange reactions are typically slow in non-polar solvent media with the result that the precursor compositions including alkane solvent media will be very stable in high temperature vaporization conditions in MOCVD operations. Additionally, alkanes are relatively inert to the metal organic precursor compound(s), in contrast to solvent media such as alcohols, which can act in a reducing manner, delivering electrons to reduce the metal ion of the precursor compound(s) to the corresponding metal, as occurred with Bi(thd) 3  in alcoholic solvent media in the hot vaporization zone of the CVD process system (see discussion in the Background section hereof). 
     Alkane-based solvent compositions thus have the following advantages: 
     they show good stability and solubility for precursors containing β-diketonate ligands such as thd, as well as for precursor compound(s) containing alkoxide, aryl, and/or alkyl functionality; 
     their solutions are stable with time, enabling stable storage, handling and delivery of the precursor solutions to the reactor; 
     the boiling point of the solvent can readily be adjusted to a desired value by appropriate mixing of different alkane solvent species; and 
     the ligand exchange process is slow in such solvent media, and therefore the solutions will be stable in elevated temperature conditions such as are encountered in the vaporization zone of the MOCVD process system, with a corresponding decrease in premature decomposition of the precursors relative to other solvent media permitting faster and more extensive ligand reactions. 
     The solvent-based precursor compositions of the invention may be employed to form a wide variety of thin film articles and device structures, including microelectronic device structures such as memory structures (e.g., FeRAMs). 
     The invention therefore contemplates precursor compositions for MOCVD of a metal-containing film on a substrate, wherein the precursor composition includes a solvent medium comprising one or more alkanes, having dissolved therein one or more compatible metal organic compound(s). Such compound(s) may for example be β-diketonate compounds or complexes, compound(s) including alkoxide ligands, compound(s) including (non-polar) alkyl and/or aryl groups at their outer (molecular) surface, or compound(s) including other ligand coordination species and specific metal constituents. 
     In one embodiment, such compound(s) may be selected from the group consisting of Sr(thd) 2 (tetraglyme), Sr(thd) 2 (polyamine), Ba(thd) 2 (tetraglyme), Ba(thd) 2 (polyamine), Ta(OiPr) 4 (thd), Ti(OiPr) 2 (thd) 2 , Zr(OiPr) 2 (thd) 2 , [Zr(OiPr) 3 (thd) 2 ] 2 , Bi(thd) 3 , Pb(thd) 2 , Pb(thd) 2 (tmeda), Pb(thd) 2 (pmdeda), Pt(thd) 2 , Pt(hfac) 2 , (methylcyclopentadienyl) Pt(Me) 3 , (MeCN) 2 PtMe 2 , Pd(allyl) 2 , Pd(hfac) 2 , Me 2 Au(hfac), MeAu(PMe 3 ), Cu(hfac) 2 , (COD)Cu(hfac), (DMCOD)Cu(hfac), (MHY)Cu(hfac), (Me 3 P)CuO t Bu, Ta(OR) 5  and Ti(OR) 4 . In such formulae, Me=methyl, COD=cyclooctadiene, thd=2,2,6,6-tetramethyl-3,5-heptanedionato, hfac=1,1,1,5,5,5-hexafluoro-2,4-pentanedionato, R=C 1 -C 8  alkyl (branched or straight chain), and  t Bu=tert-butyl. Other compounds and coordinated complexes can be employed, e.g., other β-diketonate ligands including, without limitation, 1,1,1-trifluoro-2,4-pentanedionato, denoted tfac; 6,6,7,7,8,8,8-heptafluoro-2,2-dimethyl-3,5-octanedionato, denoted fod; 2,2,7-trimethyl-3,5-octanedionato, denoted tod; 1,1,1,5,5,6,6,7,7,7-decafluoro-2,4-heptanedionato, denoted dfhd; and 1,1,1-trifluoro-6-methyl-2,4-heptanedionato, denoted tfmhd. 
     The alkane solvent compositions of the invention may be usefully employed for a variety of metal organic compound(s) having the metal species coordinated with one or more alkoxide ligands, such as for example ethoxide groups, isopropoxide groups, etc., and/or metal organic compound(s) having unpolar alkyl and/or aryl groups at their outer molecular surface, including, without limitation, carboxylates, e.g., Bi pivalate, alkoxides, e.g., Bi pentoxide, Bi amides, e.g., Bi(NMe 2 ) 3 , alkyls, e.g., triethylaluminum and Al(OiPr) 3 , and aryls, e.g., triphenylbismuth. 
     Precursor solutions therefore are readily formed using the alkane solvent compositions of the invention. The resulting solution is then vaporized to form a precursor vapor, which can be introduced into a deposition chamber to deposit a metal-containing film on a substrate, e.g., a wafer, that is contacted with the precursor vapor. Multiple precursors may be utilized in a desired ratio and provided in a solution in a single reservoir for delivery to the liquid vaporizer and subsequently the reactor (deposition chamber). Alternatively, separate precursor solutions may be provided in separate reservoirs, and be subsequently mixed in an appropriate ratio to provide a combined precursor liquid solution for subsequent vaporization and deposition, or the separate precursor solutions may each be separately vaporized and the resulting vapors then mixed in a desired ratio to provide a combined precursor vapor which then is flowed to the deposition chamber for contacting with the substrate. 
     The present invention provides a solvent composition for precursors useful to produce CVD films. The solvent may comprise a compound selected from the group comprising alkanes. Alkanes in one embodiment comprise hexane, butane, octane or decane. In one embodiment, the solvent composition comprises hexane. A solvent composition comprising more than one alkane compound is also useful in the broad practice of the present invention. 
     In one embodiment of the invention, the solvent is used to dissolve a CVD precursor selected from the group comprising metal β-diketonates. CVD precursors comprising an alkoxide ligand or a thd ligand can also be used in the alkane solvent composition, e.g., metal β-diketonates including an alkoxide ligand or a thd ligand. A CVD precursor including an alkyl group or an aryl group at its outer molecular surface, e.g., a non-polar group of such type, can also be utilized in the alkane solvent composition. Other precursors such as Pt(thd) 2 , Pt(hfac) 2 , (MeCp)PtMe 3 , (MeCN) 2 PtMe 2 , Pd(allyl) 2 , Pd(hfac) 2 , Me 2 Au(hfac), MeAu(PMe 3 ), Cu(hfac) 2 , (COD)Cu(hfac), (Me 2 P)CuO t Bu are soluble in alkanes, and usefully employed in the practice of the invention. 
     In another embodiment, precursors with alkoxide ligands include Ta(thd)(OiPr) 4 , Ta(OEt) 5 , Ta(OiPr) 4 , Ti(OEt) 5 , Ti(OEt) 4 , Bi pentoxide, and Ti(OiPr) 4 . Other alkoxide precursors are also useful. 
     In yet another embodiment, the CVD precursors comprise precursors having non-polar alkyl groups at their outer molecular surface. Precursors with non-polar alkyl groups in their outer molecular surface include precursors comprising carboxylate compounds, amide compounds, alkoxide compounds, and aryl compounds. Amide-containing precursors include, for example, Bi(NMe 2 ) 3 . Alkyl-containing precursors include, for example, AlEt 3  and Al(OiPr) 3 . Aryl-containing precursors include for example BiPh 3 . Other precursors such as Pt(thd) 2 , Pt(hfac) 2 , (MeCp)PtMe 3 , (MeCN) 2 PtMe 2 , Pd(allyl) 2 , Pd(hfac) 2 , Me 2 Au(hfac), MeAu(PMe 3 ), Cu(hfac) 2 , (COD)Cu(hfac), (Me 3 P)CuO t Bu are also useful CVD precursors. 
     The CVD precursor compositions of the invention are useful in depositing metal-containing films. In one embodiment, the metal-containing film comprises metal oxide ceramics. In another embodiment, the metal oxide ceramic comprises or is capable of comprising ferroelectric properties. Non-ferroelectric metal oxide ceramics are also useful. In one embodiment, the metal oxide ceramic comprises paraelectric characteristics. Metal-containing films that comprise a high dielectric constant are also useful. 
     A ferroelectric metal oxide ceramic may be used for example in ferroelectric transistors or non-volatile ferroelectric memory cells for non-volatile ferroelectric memory ICs. Non-volatile ferroelectric memory cells and ferroelectric ICs are described for example in U.S. patent application Ser. No. 08/974,779, now U.S. Pat. No. 5,923,970, for “METHOD OF FABRICATING A FERROELECTRIC CAPACITOR WITH A GRADED BARRIER LAYER,” the disclosure of which is hereby incorporated herein by reference in its entirety. 
     The metal oxide ceramic may for example be deposited on a substrate by CVD, e.g., a low temperature CVD process, and/or with amorphous deposition of the metal oxide ceramic by CVD, as for example are described in U.S. patent application Ser. No. 08/975,087 for “LOW TEMPERATURE CHEMICAL VAPOR DEPOSITION PROCESS FOR FORMING BISMUTH-CONTAINING CERAMIC FILMS USEFUL IN FERROELECTRIC MEMORY DEVICES,” the disclosure of which is hereby incorporated herein by reference in its entirety. 
     The substrate may be processed to include, for example, a gate oxide of a ferroelectric transistor. In other cases, the substrate may be processed to include a bottom electrode of a ferroelectric capacitor. The bottom electrode is patterned on an interlevel dielectric. The substrate may also be processed to include other types of materials. Circuit components of an IC, such as transistors, may also be included on the substrate. 
     In one embodiment, the metal oxide ceramic comprises or is capable of comprising ferroelectric properties. The metal oxide ceramic comprises Bi-based oxide ceramics. The Bi based oxide is generally expressed by ABi 2 B 2 O 9 , where A comprises a 2-valent cation and B comprises a 5-valent cation. In one embodiment, B is equal to one or more elements selected from Sr, Ba, Pb, and Ca. A, in one embodiment, is equal to one or more elements selected from Ta and Nb. 
     In one embodiment, the Bi-based oxide ceramic comprises Sr. A Bi-based oxide comprising Sr and Ta is also useful. Preferably, the Bi-oxide comprises SrBi 2 Ta 2 O 9 . 
     Derivatives of SBT are also useful. In one embodiment, the SBT derivative comprises Bi and Ta. In another embodiment, the SBT derivative comprises Bi and Sr. In yet another embodiment, the SBT derivative comprises Bi, Sr, and Ta. SBT derivatives include, for example, SrBi 2 Ta 2−x Nb x O 9  (0&lt;x&lt;2), SrBi 2 Nb 2 O 9 , Sr 1−x Ba 2 Bi 2 Ta  2−y Nb y O 9  (0≦x≦1, 0≦y≦2), Sr 1−x Ca 2 Bi 2 Ta  2−y Nb y O 9  (0≦x≦1, 0≦y≦2), or Sr 1−x−y−z Ba x Ca y Pb z Bi 3 Ta  2−p Nb p O 9  (0≦x≦1, 0≦y≦1, 0≦z≦1, 0≦p≦2). 
     In yet another embodiment, substituting or doping at least one element of the Bi-based oxide with a metal of the lanthanide series is also useful. 
     In another embodiment, the Bi-based oxide ceramic comprises an Aurivillius phase expressed generally by (Bi 2 O 2 ) 2+ (A m−1 B m O 3m+1 ) 2− , wherein A=Bi 3+ , L 3+ , L 2+ , Ca 2+ , Sr 2+ , Ba 2+ , Pb 2+ , Na +, B=Fe   3+ , Al 3+ , Sc 3+ , Y 3+ , L 3+ , L 4+ , Ti 4+ ,Nb 5+ , Ta 5+ , W 6+  and Mo 6+ , wherein L is a lanthanide series metal (Ce 4+ , La 3+ , Pr 3+ , Ho 3+ , Eu 2+ , Yb 2+  etc.) and m=1,2,3,4 or 5. 
     In yet another embodiment, metal oxide ceramic including lead-based oxide ceramics, such as lead zirconium titanate (PZT), and lithium niobium oxide (LiNbO 2 ) are also useful. Also, non-ferroelectric metal oxide ceramics are useful. In one embodiment, a metal ceramic oxide comprises a superconductor material such as a Bi-based high temperature superconductor material. Bi-based high temperature superconductor layers are referred to, for example, as “BSCCO” or “bissco.” BSCCO are described in, for example, Rees, “CVD of Nonmetals” (1996) ISBN 3-527-29295-0, the disclosure of which is hereby incorporated herein by reference for all purposes. Typical compositions of BSCCO include, for example, Bi 2 Sr 2 CaCu 2 O x  or (Pb, Bi) 2 Sr 2 Ca 2 Cu 2 O x . Other compositions of BSCCO include, for example, Bi 2 Sr 2 CuO x  and Bi 2 Sr 2 Ca 2 Cu 2 O x . 
     Features and advantages of the present invention are more fully shown with respect to the following non-limiting example, wherein all parts and percentages are by weight, unless otherwise expressly stated. 
     EXAMPLE 
     A solution containing 7 atomic percent Sr(thd) 2 (pentamethyldiethylenetriamine), 55 atomic percent Bi(thd) 3  and 38 atomic percent Ta(OiPr) 4 (thd), wherein thd=2,2,6,6-tetramethyl-3,5-heptanedionato, in a solvent mixture of 5:4:1 octane:decane:pentamethyldiethylenetriamine is metered to the liquid delivery chemical vapor deposition system where the precursor solution is flash vaporized at 190° C. and then carried to the CVD chamber in 400 sccm argon. 
     The precursor vapor is mixed with 1100 sccm oxygen and then additional 100 sccm argon for a combined for a 7:3 oxygen:argon ratio, and is passed through a showerhead disperser to the chemical vapor deposition chamber which is maintained at 1 torr. Decomposition occurs on a substrate heated to a surface temperature of 385° C. The substrate is a 0.5 micron linewith SiO 2  (TEOS) structure covered with platinum. The SBT film produced on the substrate is highly conformal, exhibiting a minimum SBT thickness which is greater than 90% of the maximum thickness, consistent with the device requirements for microelectronic fabrication. The low temperature and amorphous character of the deposition contribute to the conformal coating of the deposited film. Under these conditions, the composition varies less than 0.5% relative (which is the precision of the x-ray fluorescence method employed). 
     FIG. 1 is a plot of upstream pressure, in torr, as a function of time, in minutes, for a liquid delivery system employed for deposition of strontium bismuth tantalate, with vaporization of the precursor solution at 180° C., and utilizing β-diketonate precursors for strontium, bismuth and tantalum, in a 8:2:1 solvent composition of tetrahydrofuran:isopropanol:polyamine. Such solvent composition is typical of the solvent compositions heretofore used in the art for precursors such as metal β-diketonates and adducts thereof. 
     FIG. 2 shows upstream pressure in a liquid delivery system employed for vaporization of metal organic precursors in a solvent composition of the present invention, 5:4:1 octane:decane:pentamethyldiethylenetriamine. The precursor components of such precursor solution are Sr(thd) 2 (pentamethyldiethylenetriamine), Bi(thd) 3  and Ta(OiPr) 4 (thd) where thd=2,2,6,6-tetramethyl-3,5-heptanedionato, wherein the bismuth reagent is of anhydrous mononuclear form. 
     The plot of FIG. 2 shows the upstream pressure in torr as a function of time in minutes for vaporization of the precursor solution at 180° C. As shown, the upstream pressure is highly uniform over the time frame of the process, indicating good vaporization and transport properties of the precursors in such solvent mixture with concomitant low levels of residue (significant levels of residue being indicative of clogging which significantly increases upstream pressure). 
     The steep increase in pressure shown in the curve for FIG. 1 is indicative of decomposition of the precursor resulting in clogging of the liquid delivery system. As a consequence of such clogging, the liquid delivery system fails to deliver the precursor in the desired amount and at the desired rate to the downstream chemical vapor deposition chamber, and thereby lowers the overall process efficiency. 
     The plots of FIGS. 1 and 2 therefore show the superior solvent efficiency of the solvent composition of the present invention. 
     While the invention has been illustratively described with respect to particular features, aspects and embodiments herein, it will be appreciated that the utility of the invention is not thus limited, and other variations, modifications and embodiments will readily suggest themselves to those skilled in the art. Accordingly, the invention is to be broadly construed, consistent with the claims hereafter set forth.