CHEMICAL VAPOR DEPOSITION FABRICATION OF HYBRID ELECTRODES FOR FERROELECTRIC DEVICE STRUCTURES

Abstract: A method of fabricating an electrode structure (200) on a ferroelectric film (202), involving chemical vapor deposition formation of a hybrid electrode (222, 224) constituted by a multilayer electrode structure (200) or an alloyed electrode structure (218) using either bubbler delivery or liquid delivery chemical vapor deposition.

Description: CHEMICAL VAPOR DEPOSITION FABRICATION OF HYBRID ELECTRODES FOR FERROELECTRIC DEVICE STRUCTURES BACKGROUND OF THE INVENTION Field of the Invention This invention relates generally to a chemical vapor deposition (CVD) process for the fabrication of hybrid electrodes in microelectronic device structures such as ferroelectric random access memory (FRAM) device structures, and to ferroelectric device structures comprising such hybrid electrodes. Description of the Related Art Ferroelectric random access memories (FRAMs) depend on the use of high integrity ferroelectric materials as a critical component of cell architecture. Although a wide variety of ferroelectric materials has been developed, having actual demonstrated and potential utility in device applications, the practical utilization of such materials in device architectures requires that such ferroelectric materials can be readily fabricated in an efficient and cost-effective manner with respect to their integration in conformations including barrier regions, isolation structures, interconnects, vias and electrodes. The electrical properties of ferroelectric materials in many instances are highly influenced by the materials used to fabricate electrodes for the ferroelectric material structure. For example, ferroelectric 1 mateπals such as Pb(Zr.Tι)0 3 (PZT) show a strong dependence on the type of electrode used as the contact for the device structure Noble metals such as platinum that have a high work function may be used to fabπcate electrodes that produce device structures with low electπcal leakage characteristics, but the rate of loss of remanent polarization in the structure with repeated switching cycles (ferroelectric fatigue) is unacceptably high Conversely, conductive oxide electrodes improve fatigue behavior, but usually at the cost of unacceptably large increase in electπcal leakage Kingon, et al , (US Patent 5,555,486) and Al-Shareef, et al (J Appl Phys 77 (5), 1 March 1995 2146), the disclosures of which are hereby incorporated herein by reference in their entirety, have demonstrated a hybπd electrode, compπsed of dual layers of Pt and conductive oxide, either with the Pt layers on the exteπor or the conductive oxide layers on the exteπor, and the other electrode mateπal on the inteπor in contact with the ferroelectπc mateπal When used with such hybπd electrodes, PZT displays both good fatigue endurance and low electπcal leakage The layered structures of the above-descπbed art represent one approach to concurrently achieving the benefits of conductive oxides and Pt electrodes An alternative approach utilizes alloyed electrodes, also demonstrated by Kingon, et al , (US Patent 5,555,486) and Al-Shareef, et al (J Appl Phys 77 (5), 1 March 1995 2146) Alloyed electrodes of Pt and Ruθ2 are formed by co-deposition of metals using ion-beam sputteπng In the preferred embodiment the noble metal is alloyed with an element (non-noble metal) that is relatively immiscible, and that has a tendency to oxidize to an electπcally conductive oxide Examples of such a combination include Pt and Ir where Ir can be oxidized to Irθ2 Other examples of alloy systems with a high degree of lmmiscibihty include Pd-Ir, Rh-Ir and Pd-Ru In the latter example, Ru oxidizes to Ruθ2 Still further examples include mixtures of noble metals (e g , Pt, Pd, Rh) and complex conductive oxides (LaSrCoθ3, SrRuθ3, indium tin oxide, and yttπum banum copper oxide) The bi-phasic microstructure consists ideally of noble metal and oxidizable metal grains uniformly distπbuted The oxidizable phase may be oxidized duπng the co-deposition process as taught by Kingon, et al , and Al-Shareef, et al , by a separate anneal in an oxidizing ambient (e , 0 2 , N2O, ozone) before deposition of the ferroelectπc, or alternatively, duπng the deposition process for the ferroelectπc which is usually earned out in an oxidizing ambient As device density increases, a need aπses for conformal coatings to cover sidewalls and to fill small features with electrodes Wet methods of deposition have poor conformality, as do line of sight processes such as evaporation Sputter deposition offers a higher 3 degree of conformality, but composition control of complex oxides is difficult with sputter techniques. Accordingly, there is a need in the art for improved electrode fabrication techniques to maximize the benefits achievable with composite electrode structures. SUMMARY OF THE INVENTION The present invention relates to a method of fabricating a hybrid electrode structure on a ferroelectric material, including the steps of: vaporizing a first organometallic precursor for a first electrode metal component to form a first electrode component precursor vapor; vaporizing a second organometallic precursor for a second electrode metal component to form a second electrode component precursor vapor; and depositing the first electrode component precursor vapor and the second electrode component precursor vapor on the ferroelectric material, by chemical vapor deposition for formation of said hybrid electrode structure, in a deposition mode selected from the group consisting of: (I) simultaneous chemical vapor deposition on the ferroelectπc mateπal of the first electrode metal component from the first electrode component precursor vapor and the second electrode metal component from the second electrode component precursor vapor, to yield an alloy hybπd electrode structure on the ferroelectπc mateπal; and (II) sequential chemical vapor deposition on the ferroelectπc mateπal of the first electrode metal component from the first electrode component precursor vapor and the second electrode metal component from the second electrode component precursor vapor, to yield a layered hybπd electrode structure on the ferroelectπc mateπal including a first layer containing the first electrode metal component and a second layer containing the second electrode metal component. The ferroelectπc mateπal utilized in the broad practice of the invention may compπse any suitable ferroelectπc mateπal, such as for example PbZrTιθ3, PbLaTiθ3, PbLaZrTιθ3, PbSrZrTιθ3 and SrBi2T 2θ9 In one aspect of the method of the invention, the first organometallic and second organometallic precursors are different from one another and are selected from the group of precursors consisting of : Platinum precursors: trimethyl (cyclopentadienyl) Pt (IV), trimethyl (β-diketonate) Pt (IV), bis (β-diketonate) Pt (II), tetrakis (trifluorophosphine) Pt (0); Indium precursors: Lewis base-stabilized β-diketonate indium compositions or Lewis base-stabilized β-ketoiminate compositions, of the formulae: Lewis base stabilized Ir(I) β-diketonates of formula I: R 0- L - Ir CH 0- R" wherein R and R' are the same or different and may be H, aryl, perfluoroaryl, Ci - C6 alkyl, or C \ - C perfluoroalkyl, and L is a coordinating Lewis base, preferably selected from the group consisting of alkene, diene, cycloalkene. cyclodiene. cyclooctatetraene, alkyne, substituted alkyne (symmetrical or asymmetrical), amine, diamine, triamine, tetraamine, ether, diglyme, triglyme, tetraglyme, phosphine, carbonyl, dialkyl sulfide, vinyltrimethylsilane, or allyltrimethylsilane. 6 Lewis base stabilized Ir(I) β-ketoiminates of formula II: R" R N L Ir. CH > . O- R' II wherein R, R', and R" are the same or different, and are 10 independently selected from the group consisting of H, aryl, perfluoroaryl, Ci - C6 alkyl, or C [ - C6 perfluoroalkyl, and L is a coordinating Lewis base, preferably selected from the group consisting of alkene, diene, cycloalkene, cyclodiene. cyclooctatetraene, alkyne, substituted alkyne (symmetrical or 15 asymmetrical), amine, diamine, triamine, tetraamine, ether, diglyme, triglyme, tetraglyme, phosphine, carbonyl, dialkyl sulfide, vinyltrimethylsilane, and allyltrimethylsilane; 20 Ruthenium precursors: bis(cyclopentadienyl) Ru and tris(tetramethyl-3,5-heptanedionate) Ru; Lanthanum precursors: β-diketonates, cyclopentadienyl compounds, β-ketoiminates and β-diiminates of La(III); SUBSTΓΠΠΈ SHEET (RULE 26) Strontium precursors: β-diketonates, cyclopentadienyl compounds, β-ketoiminates and β-diiminates of Sr (II); Cobalt precursors: β-diketonates, cyclopentadienyl compounds, β- ketoiminates and β-diiminates of Co (II); Rhodium precursors: Rhodium(I) β-diketonates. In one preferred embodiment, the first electrode metal component and the second electrode metal component are selected from the group consisting of the following first and second metal pairs: (i) Pt and Ir, (ii) Pt and Ru, (iii) Pd and Ir, (iv) Pd and Ru, (v) Rh and Ir, and (vi) Rh and Ru. In another aspect, the present invention relates to a ferroelectric device structure, comprising a ferroelectric material, having conformally deposited thereon by chemical vapor deposition a hybrid electrode structure, which may be a layered hybrid electrode structure or an alloy hybrid electrode structure. Other aspects, features and embodiments of the invention will be more fully apparent from the ensuing disclosure and appended claims. 8 BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a schematic representation of a bubbler volatilization and chemical vapor deposition system for forming the hybnd electrodes of the invention, according to one embodiment of the invention Figure 2 is a schematic representation of a liquid delivery volatilization and chemical vapor deposition system for forming the hybnd electrodes of the invention, according to another embodiment of the invention Figure 3 is a schematic representation of a fenoelectπc device structure according to one embodiment of the present invention, including a hybπd layered electrode on each of the top and bottom faces of the ferroelectπc mateπal Figure 4 is a schematic representation of a fenoelectnc device structure according to one embodiment of the present invention, including a hybπd alloy electrode on each of the top and bottom faces of the ferroelectπc mateπal DETAILED DESCRIPTION OF THE INVENTION. AND PREFERRED EMBODIMENTS THEREOF The present invention is based on the use of chemical vapor deposition (CVD), the thin film deposition method which has the highest degree of conformahty, as a technique for forming composite electrodes for ferroelectπc device structures Mateπals such as PbZrTιθ3, PbLaTιθ3, PbLaZrTιθ3, PbSrZrTιθ3 and SrBi2Ta2θ9 may be used as the ferroelectπc mateπal, although the invention is not limited in such respect, and may utilize any suitable ferroelectπc matenal The chemical vapor deposition method of the invention may be utilized for depositing layered hybπd electrodes, as well as for producing alloyed hybnd electrodes, compπsed of two relatively immiscible metals, as for example from the metal pairs of (l) Pt and Ir, (u) Pt and Ru, (in) Pd and Ir, (IV) Pd and Ru, (v) Rh and Ir, and (vi) Rh and Ru Chemical vapor deposition in the practice of the invention provides a fabπcation method affording supeπor control ot electrode composition As discussed in the Background of the Invention section hereof, the pπor art has proposed the use of composite electrodes for ferroelectπc matenals, but the art has purposely avoided the utilization of chemical vapor deposition as a fabπcation technique for such electrodes The reason for this is that the art has viewed the temperatures at which chemical vapor deposition is earned out to be inimical to the 10 achievement of useful ferroelectnc device structures Surpπsingly, however, we have tound that chemical vapor deposition may be utilized with bubbler delivery or liquid delivery of precursor vapor, to form electrodes on the fenoelectnc mateπal, and provide a highly efficient rerroelectnc device structure In some instances, it may be desirable to oxidize one or more non- noble metal components of the electrode structure of the present invention, to form a conesponding metal oxide The oxide may be present as a surface oxide layer or it may be present as a fully oxidized metal throughout the bulk of the oxidizable metal film, as may for example be achieved by canying out the deposition of the oxidizable metal in an oxidizing ambient environment As used herein, the term "oxidizing ambient environment" means an environment including oxygen-containing gas, such as oxygen, ozone, air, nitrogen oxide (NO), or the like Such oxidizing atmosphere may be provided in a deposition chamber or reaction vessel in which the deposition is earned out, and enables the formation of a metal oxide on the substrate from an oxidizable metal component of the overall electrode structure For example, the oxidizing ambient environment may be an ambient air environment, thereby simplifying the formation of the metal-containing electrode film on the substrate Alternatively, the metal oxide electrode film may be formed in a post-deposition process from the CVD-deposited metal, by treatment in an oxidizing environment 1 1 The bubbler delivery metalorganic chemical vapor deposition (MOCVD) process of forming the electrode structure on the ferroelectnc material may be earned out at varying appropπate temperature, pressure, flow rate and other process conditions, as are readily determinable without undue expenmentation by those skilled in the art of MOCVD thin film deposition. The liquid delivery MOCVD process of forming the electrode structure on the ferroelectπc mateπal may be vaπously carried out in accordance with the teachings of U.S. Patent 5,536,323 issued July 16. 1996 in the names of Peter S. Kirlin, et al., and U.S. Patent 5,71 1,816 issued January 27, 1998 in the names of Peter S. Kirlin, et al., the disclosures of which are hereby incorporated herein by reference in their entirety. The invention is descπbed more fully hereinafter with reference to the formation of specific illustrative layered conductive oxide / Pt electrode structures, and with respect to the formation of specific illustrative alloyed electrode structures. Multi-layered Electrodes To form layered conductive electrode / Pt structures, a two step CVD process is utilized. First, either Pt or the conductive oxide is deposited followed by the remaining metal component layer in the pair. After deposition of the fercoelectnc mateπal (e.g., PZT) layer, the process is 12 reversed to make a symmetπcal electrode In some instances, an asymmetπcal electrode is desired Here, the same order used to make the lower electrode would be used for the upper electrode It will therefore be understood that it may be possible to form the hybπd electrode structure first, and then to deposit the ferroelectπc mateπal on the electrode As used herein, reference to deposition of the electrode on the ferroelectπc mateπal will therefore be understood to likewise comprehend the initial deposition of the electrode, folowed by the deposition of the ferroelectnc mateπal The control of composition of complex oxides is facilitated by the use of a liquid delivery approach for MOCVD, in the fabπcation of electrode structures in the practice of the present invention Several examples of liquid delivery MOCVD processes to produce layered electrodes are descπbed below Pi A wide vaπety of CVD precursors currently exist for Pt CVD In general terms, the use of tπmethyl (cyclopentadienyl) Pt (IV), tπmethyl (β-diketonate) Pt (IV), bis (β-diketonate) Pt (II), and tetrakis (tnfluorophosphine) Pt (0) are prefened sources for both bubbler and liquid delivery approaches For fast growth rates in bubbler-based MOCVD systems, the tnfluorophosphine complex is strongly prefened and exhibits a vapor pressure of >12 Torr at room temperature High punty platinum can be deposited, however 13 trifluorophosphme is a toxic hemoglobin binder and its use therefore requires certain safety precautions. The other chemical precursors are viable candidates for low pressure CVD applications for forming the electrode structure The thermal decomposition and deposition of Pt films using oxidizing co-reactants and environments is more fully descπbed in copending application no. 08/673,372 filed June 28, 1996 in the names of Thomas H. Baum et al., the disclosure of which hereby is incorporated herein by reference in its entirety. Ir The indium precursors are more fully as descnbed in copending application no. 08/966,797 filed November 10, 1997, the disclosure of which is hereby incorporated herein in its entirety, and may for example comprise a Lewis base-stabilized β-diketonate indium composition or a Lewis base-stabilized β-ketoimmate composition, of the formulae: Lewis base stabilized Ir(I) β-diketonates of formula P R 0-" y x L Ir- J,CH R' wherein R and R' are the same or different and may be H, aryl, perfluoroaryl, C \ - C alkyl, or C j - C perfluoroalkyl, and L is a 14 coordinating Lewis base, preferably selected from the group consisting of alkene, diene, cycloalkene, cyclodiene. cyclooctatetraene, alkyne, substituted alkyne (symmetπcal or asymmetπcal), amine, diamine, tπamine, tetraamine, ether, diglyme, tπglyme, tetraglyme, phosphine, carbonyl, dialkyl sulfide, vinyltπmethylsilane. and allyltπmethylsilane, Lewis base stabilized Ir(I) β-ketoiminates of formula II R" R I , V Ir 1 .CH » 0- R' II wherein R, R', and R" are the same or different, and are independently selected from the group consisting of H, aryl, perfluoroaryl, C j - C alkyl, or C l - C6 perfluoroalkyl, and L is a coordinating Lewis base, preferably selected from the group consisting of alkene, diene. cycloalkene, cyclodiene, cyclooctatetraene, alkyne, substituted alkyne (symmetncal or asymmetπcal), amine, diamine, tπamine, tetraamine, ether, diglyme, tπglyme, tetraglyme, phosphine, carbonyl, dialkyl sulfide, vinyltnmethylsilane, and allyltπmethylsilane For the Lewis base in the above precursors of formulae I and II. one or more Lewis base molecules may be preferred, especially for ether, alkene. alkyne, carbonyl and phosphine ligands In some embodiments of precursors of formula II, R and R' may be identical and R" will be independently selected from the substituents listed above In the practice of the present invention, either a bubbler or organic solution liquid delivery can be utilized for the chemical vapor deposition of the Ir/Irθ2 thin film The specific precursor may be suitably optimized for the delivery and transport of the precursor to the CVD reactor The precursor is decomposed in the presence of an oxidant (e g , θ2, O3, or N2O) to preferentially deposit the metal Ir (< 500 °C) or the oxide, Irθ2 (>550 °C) In some applications, the formation of a bi-layered Ir/Irθ2 film may be preferred RuOo Ruthenium compounds can be used to deposit both Ru and Ruθ2 in the practice of the present invention in which ruthenium is used as a non-noble metal component in the hybπd electrode structure Bιs(cyclopentadιenyl) Ru and tπs(tetramethyl-3,5-heptanedιonate) Ru are useful precursors for formation of Ru- and Ru0 2 -contaimng electrode structures LaSrCoQj 16 The liquid delivery CVD of LaSrCoO may be earned out using β- diketonates of La(III), Sr (II), Co (II) in an oxidizing environment The concentrations in solution are selected to provide the conect film stoichiometry upon deposition The use of Lewis base adducts, specifically polyamine adducts, are usefully employed for improved transport and delivery of each constituent (La, Co and Sr), this same chemical approach may be realized by modification of the solution mixtures by solvent selection Other precursors may also be used for these particular elements, such as cyclopentadienyls, β-ketoiminates and β-duminates SrRuOj Liquid delivery MOCVD of Sr Ru 0 films can be readily accomplished via the use of Sr(thd) 2 and Ru(thd) 3 mixtures Modifications of the solution and/or precursor molecular structure can be utlized, as long as the modifications do not result in deleteπous ligand exchange in solution or duπng vapoπzation The use of oxidizing co-reactants, such as oxygen, ozone or nitrous oxide, may be employed to facilitate the formation of oxides duπng thermal decomposition In order to efficiently deposit multilayer electrodes, either multiple deposition chambers or multiple liquid delivery systems may be employed In the former method, a wafer is transfened between deposition chambers, preferably under vacuum, for deposition of each 17 conductive layer. In the latter method, the precursor gas stream is toggled between vaponzation systems and the deposition chamber Alloyed electrodes Examples of CVD processes to deposit alloyed electrodes within the broad practice of the present invention are given below The oxidizable non-noble metals descnbed below can be deposited as elemental metals and the oxidizable metal may be transformed to conductive oxide subsequently, or the elemental metal can be deposited in an oxidizing ambient to provie the metal oxide in situ Pt/Ir Combinations of Pt and Ir complexes are applicable to the formation of alloys with controlled stoichiometπes, as descnbed in copending U.S. patent application no. 08/966,797 filed November 10, 1997 in the names of Thomas H Baum and Chong-Ying Xu, the disclosure of which is hereby incorporated herein by reference in its entirety. Pd/Ir Palladium bιs(β-dιketonates) are a prefened precursor form for Pd alloys and such precursors can be used in tandem with Ir tns(β- diketonates) and Lewis base stabilized Ir(I) (β-diketonates). The use of forming gas is not required for metal film formation, but may be useful for extremely high-puπty alloy formation 18 Rh/Ir Lewis base stabilized Rhodιum(I) β-diketonates may be employed as Rh metal sources for CVD film growth The Lewis base complex can be matched to the Ir(I) complex for simultaneous delivery (via bubbling, liquid delivery and direct liquid injection) Pd/Ru Combinations of the above-descπbed mateπals may be usefully employed simultaneously, sequentially, or in independent steps to form the desired alloys The following electrode components can be deposited as metal and oxide using an oxidizing ambient Pt/LSCO A direct approach may be utilized by the combined or sequential deposition of each element using Pt(II) β-diketonates and β - diketonates of La, Sr and Co with oxidizing co-reactants Pt / SrRuO3 A direct approach for the deposition of this electrode composition involves the use of β-diketonates of Pt, Sr and Ru as descnbed heremabove The hybnd electrode structures of the invention thus may employ one or more compatible metals, e g , noble and non-noble metals, that are 19 alloyed, or sequentially deposited. Preferably, the non-noble metal element is relatively immiscible in the noble metal(s). Suitable non- noble metals include those having a tendency to oxidize to an electrically conductive oxides, such as Ir and Ru. Complex conductive oxides such as LaSrCoθ3, SrRuθ3, indium tin oxide, and yttrium barium copper oxide may also be utilized in the broad practice of the invention. Oxidation of the oxidizable metal forming the conductive oxide may be carried out during the deposition process, or subsequent thereto, in an oxidizing ambient. Figure I is a schematic representation of a bubbler volatilization and chemical vapor deposition system 10 with which the hybrid electrodes of the invention can be formed, according to one embodiment of the invention. The Figure 1 system 10 includes a deposition chamber 12 that contains a first chemical vapor deposition chamber 14 and a second chemical vapor deposition chamber 16. Chamber 14 contains a susceptor 18 supporting wafer 28 thereon. The susceptor is heated by electrical resistance heating element 20. Alternatively, the susceptor may be heated by IR radiant energy, a heat exchange fluid passed through interior heat exchange passages in the susceptor, or in any other suitable manner. 20 The wafer 28 receives a flux of precursor vapor from the showerhead disperser 30 as shown The showerhead disperser 30 is fed by precursor vapor supply line 32, which is joined to bubbler 34 In the bubbler, a vapor stream is passed through the bubbler vessel in a conventional manner to provide a stream of the metalorganic source reagent vapor, for deposition of the metal component of such vapor on the substrate wafer Subsequent to formation of the metal component on the substrate wafer in chemical vapor deposition chamber 14, the wafer 30 may be translated in the nght-hand direction of the bi-directional arrow A, to the second chemical vapor deposition chamber 16 In the second vapor deposition chamber 16, a second metal component is deposited over the first metal component previously deposited on the wafer (in chemical vapor deposition chamber 14) A second heated susceptor 46 is shown in the second CVD chamber 16, heated by electπcal resistance heating element 48 The wafer 50 on the susceptor 46 receives a flux of precursor vapor from showerhead disperser 44, which is supplied by precursor feed line 42 The precursor feed line 42 in turn is joined to the bubbler 40 holding the second metalorganic precursor, for volatilization thereof Figure 1 shows the respective CVD chambers holding different wafers The wafers may be disposed on a carousel or other translation means (not shown), serving to motively transport a wafer from the 21 first CVD chamber 14 to the second CVD chamber 16, with the wafer initially in CVD chamber 16 concurrently being transported to the chamber 14 In this manner the wafer receives in first CVD chamber 14 a coating of a first electrode metal on the wafer, followed in the second CVD chamber 16 with a coating of a second electrode metal, and vice versa (that is, the wafer initially in chamber 16 receives a first electrode metal coating on the wafer, followed by a second metal coating in the chamber 14) Alternatively, only a single wafer may be processed in a first one of the two CVD chambers 14 and 16, and thereafter in a second one of such chambers As a further alternative, a wafer may receive repeated metal layer coatings thereon, by shuttling back and forth between the chambers 14 and 16, in the direction indicated by the bidirectional arrow A, to provide a build-up of a seπes of alternating layers of the respective different metals In such manner, a layered hybπd electrode structure can be fabncated The Figure 1 system is also configured to permit the fabπcation of hybnd alloy electrodes As shown, the precursor feed lines 32 and 42 are interconnected by a manifold feed line 36 having flow control valve 38 therein By such expedient, the flow control valve can be modulated from a closed position, permitting only separate flow of the respective metalorganic precursors through the respective lines 32 and 42, for layered hybnd electrode formation However, if it is desired to produce an alloy hybπd electrode, viz , an electrode structure compnsmg an alloy of the metal components supplied by the respective bubblers 34 and 40, then the flow control valve 38 can be opened, to permit flow of metalorganic precursor from one of the bubblers to the feed line receiving the precursor vapor from the other bubbler For such purpose, the valve 38 is preferably a directional flow valve which permits flow from only one of the bubbler feed lines to the other feed line, at any given time The valve may be switchable to allow flow in either direction, as part of a system arrangement having maximum process flexibility Figure 2 is a schematic representation of a liquid delivery volatilization and chemical vapor deposition system 100 with which the hybπd electrodes of the invention can be formed, according to another embodiment of the invention In the Figure 2 system, the chemical vapor deposition chamber 102 contains a heated susceptor 104 therein, which is heated by heating element 106 A wafer 108 is mounted on the susceptor and heated to appropπate temperature to cause deposition on the wafer of the 23 desired composite metal alloy components, which form the alloy on the substrate wafer surface. The CVD chamber 102 receives a first precursor vapor containing a first metal component, by flow of metalorganic liquid source reagent from the supply vessel 1 10 therefor, in line 1 14, to the liquid delivery vaporizer unit 1 18. In the vaporizer unit 118, the liquid reagent from supply vessel 1 10 is flash vaporized to form the first precursor vapor. Concunently, a second metalorganic liquid source reagent vapor is flowed from supply vessel 1 12 in line 1 16 to the liquid delivery flash vaporization unit 120, where the liquid is flash vaporized to provide the second precursor vapor. The first precursor vapor flows in line 122 to the mixing valve 130, where it is blended in an appropriate stoichiometric proportion with the second precursor vapor from line 124. The mixing valve 130 may for the purpose of selectively varying the proportions of the first and second precursor vapors, be of a selectively adjustable character. Valve adjustment actuator 134 is operated to transmit a control signal in signal transmission line 132 to the mixing valve 130 for adjustment of the valve to provide the proper proportions desired for the first and second precursor vapors. The combined precursor vapor then is discharged from the mixing valve 130 as shown, and flowed into the chemical vapor deposition 24 chamber 102, for deposition of the alloy metal components on the substrate wafer in the desired stoichiometπc proportions The system shown in Figure 2 may also be selectively operated to provide graded electrode layers, wherein the alloy composition is vaned along the thickness of the electrode film, by corresponding adjustment of the mixing valve 130 duπng the deposition operation Figure 3 is a schematic representation of a fenoelectπc device structure 200 according to one embodiment of the present invention, including a hybπd layered electrode on each of the top and bottom faces of the ferroelectnc matenal 202 The electrode structure may by way of example include a layer 204 of a conductive oxide mateπal on the top face of the ferroelectnc mateπal, and a layer 208 of a same or different conductive oxide mateπal on the bottom face of the ferroelectπc mateπal The outermost layers 206 and 210 of the electrode structure may for example be composed of platinum or other noble metal Figure 4 is a schematic representation of a ferroelectnc device structure 218 according to one embodiment of the present invention, including hybπd alloy electrodes 222, 224 on the top and bottom faces of the ferroelectπc mateπal 220, respectively The electrode alloy composition may be homogeneous and isotropic throughout the electrode thickness, or the electrode may alternatively be graded or in 25 other manner compositionally heterogeneous, depending on the method of CVD formation of the electrodes. The MOCVD method of formation of hybrid electrode structures on ferroelectric materials in the practice of the present invention achieves a substantial advantage over the ion-beam sputtering methodology of the prior art, in obtaining a superior extent of conformal deposition of the electrode structure, with a low rate of loss of remanent polarization in the structure after repeated switching cycles, and low rates of electrical leakage. Accordingly, while the invention has been described herein with reference to specific features, aspects and embodiments, it will be recognized that the invention may be widely varied, and that numerous other variations, modifications and other embodiments will readily suggest themselves to those of ordinary skill in the art. Accordingly, the ensuing claims are to be broadly construed, as encompassing all such other variations, modifications and other embodiments, within their spirit and scope. INDUSTRIAL APPLICABILITY The method of fabricating a hybrid electrode structure on a ferroelectric material of the present invention permit the formation of a hybrid electrode in microelectronic device structures including, without limitation, ferroelectric random access memory (FRAM) 26 device structures. The method of fabricating the hybrid electrodes of the invention may be utilized to maximize the benefits achievable with composite electrode structures. 27

Claims: THE CLAIMS What is claimed is; 1. A method of fabricating a hybrid electrode structure on a ferroelectric material, comprising the steps of: vaporizing a first organometallic precursor for a first electrode metal component to form a first electrode component precursor vapor; vaporizing a second organometallic precursor for a second electrode metal component to form a second electrode component precursor vapor; and depositing the first electrode component precursor vapor and the second electrode component precursor vapor on the ferroelectric material, by chemical vapor deposition for formation of said hybrid electrode structure, in a deposition mode selected from the group consisting of: (I) simultaneous chemical vapor deposition on the ferroelectric material of the first electrode metal component from the first electrode component precursor vapor and the second electrode metal component from the second electrode component 28 precursor vapor, to yield an alloy hybrid electrode structure on the ferroelectric material; and (II) sequential chemical vapor deposition on the ferroelectric material of the first electrode metal component from the first electrode component precursor vapor and the second electrode metal component from the second electrode component precursor vapor, to yield a layered hybrid electrode structure on the ferroelectric material including a first layer containing the first electrode metal component and a second layer containing the second electrode metal component. 2. A method according to claim 1, wherein the hybrid electrode is formed by mode (I). 3. A method according to claim I, wherein the hybrid electrode is formed by mode (II). 4. A method according to claim 1, wherein the ferroelectric material comprises a material selected from the group consisting of PbZrTiθ3, PbLaTiθ3, PbLaZrTiθ3, PbSrZrTiθ3 and SrBi2T 2θ9. 29 5. A method according to claim 1, wherein the ferroelectric material comprises PbZrTiθ3. 6. A method according to claim 1 , wherein the first organometallic and second organometallic precursors are different from but compatible with one another and are selected from the group consisting of : Platinum precursors: trimethyl (cyclopentadienyl) Pt (IV), trimethyl (β-diketonate) Pt (IV), bis (β-diketonate) Pt (II), tetrakis (trifluorophosphine) Pt (0); Iridium precursors: a Lewis base-stabilized β-diketonate iridium composition or a Lewis base-stabilized β-ketoiminate composition, of the formulae: Lewis base stabilized Ir(I) β-diketonates of formula I: R 0- .*** L Ir ' , CH » 0- R' wherein R and R' are the same or different and may be H, aryl, perfluoroaryl, C\ - C alkyl, or Cj - C6 perfluoroalkyl, and L is a coordinating Lewis base, 30 Lewis base stabilized Ir(I) β-ketoiminates of formula II: R" R . v ,N Ir', CH 0- R' II 10 wherein R, R', and R" are the same or different, and are independently selected from the group consisting of H, aryl, perfluoroaryl, C[ - C6 alkyl, or Cl - C6 perfluoroalkyl, and L is a coordinating Lewis base, 15 Ruthenium precursors: bis(cyclopentadienyl) Ru and tris(tetramethyl-3,5-heptanedionate) Ru; Lanthanum precursors: β-diketonates, cyclopentadienyl 20 compounds, β-ketoiminates and β-diiminates of La(III); Strontium precursors: β-diketonates, cyclopentadienyl compounds, β-ketoiminates and β-diiminates of Sr (II); 31 Cobalt precursors: β-diketonates, cyclopentadienyl compounds, β- ketoiminates and β-diiminates of Co (II); Rhodium precursors: Rhodium(I) β-diketonates. 7. A method according to claim 1, wherein the first electrode metal component and the second electrode metal component comprise a metal pair selected from the group consisting of the following first metal and second metal pairs: (i) Pt and Ir, (ii) Pt and Ru, (iii) Pd and Ir (iv) Pd and Ru (v) Rh and Ir, and (vii) Rh and Ru. 8. A method according to claim 1, wherein one of the first and second electrode metal components comprises a noble metal and the other of said first and second electrode metal components comprises a non-noble metal that is relatively immiscible in the noble metal. 9. A method according to claim 8, wherein the noble metal is selected from the group consisting of Pt, Pd, and Rh. 32 10. A method according to claim 8, wherein the non-noble metal is selected from the group consisting of Ir, Ru, La, Sr, Co, In, Sn, Y, Ba, and Cu. 11. A method according to claim 8, wherein the non-noble metal in the hybrid electrode is present in an oxide selected from the group consisting of LaSrCoθ3, SrRuθ3, indium tin oxide, and yttrium barium copper oxide. 12. A method according to claim 8, wherein the non-noble metal is oxidized in an oxidizing ambient during or subsequent to its deposition. 13. A method according to claim 1 , wherein a hybrid electrode structure is fabricated on each of different surfaces of the ferroelectric material. 14. A ferroelectric device structure, comprising a ferroelectric material, having conformally deposited thereon by chemical vapor deposition a hybrid electrode structure. 15. A ferroelectric device structure according to claim 14, wherein the hybrid electrode structure is a layered hybrid electrode structure. 33 16. A ferroelectric device structure according to claim 14, wherein the hybrid electrode structure is an alloy electrode structure. 17. A ferroelectric device structure according to claim 14, wherein the ferroelectric material comprises a material selected from the group consisting of PbZrTiθ3, PbLaTiθ3, PbLaZrTiθ3, PbSrZrTiθ3 and SrBi2Ta2θ9. 18. A ferroelectric device structure according to claim 14, wherein the ferroelectric material comprises PbZrTiθ3. 19. A ferroelectric device structure according to claim 14, wherein the first and second metal electrode components are selected from the group consisting of: Platinum; Cobalt; Iridium: Ruthenium; Lanthanum; Indium; Tin; Copper; 34 Yttrium; Barium; Strontium; and Rhodium. 20. A ferroelectric device structure according to claim 14, wherein the hydbrid electrode comprises a first electrode metal component and a second electrode metal component, constituting a metal pair selected from the group consisting of the following first metal and second metal pairs: (i) Pt and Ir, (ii) Pt and Ru, (iϋ) Pd and Ir (iv) Pd and Ru (v) Rh and Ir, and (vi) Rh and Ru. 21. A ferroelectric device structure according to claim 14, wherein the hybrid electrode comprises first and second electrode metal components including a noble metal and a non-noble metal that is relatively immiscible in the noble metal. 22. A ferroelectric device structure according to claim 21, wherein the noble metal is selected from the group consisting of Pt, Pd, and Rh. 35 23. A ferroelectric device structure according to claim 21 , wherein the non-noble metal is selected from the group consisting of Ir, Ru, La, Sr, Co, In, Sn, Y, Ba, and Cu. 24. A ferroelectric device structure according to claim 21 , wherein the non-noble metal is present in the form of an oxide selected from the group consisting of LaSrCoθ3, SrRuθ3, indium tin oxide, and yttrium barium copper oxide. 25. A ferroelectric device structure according to claim 14, wherein a hybrid electrode structure is fabricated on each of different surfaces of the ferroelectric material. 36

Inventors: BAUM THOMAS H, ROEDER JEFFREY R, BAUM, THOMAS, H., ROEDER, JEFFREY, R.
Applicants: ADVANCED TECH MATERIALS, ADVANCED TECHNOLOGY MATERIALS, INC.
Application year: 1999
Main classification: H01L21
IPC codes: C23C16, H01L21, H01L27