CN1199506A - Integrated circuit comprising substrate and wiring layer with buffer layer between substrate and wiring layer - Google Patents

Integrated circuit comprising substrate and wiring layer with buffer layer between substrate and wiring layer Download PDF

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CN1199506A
CN1199506A CN96194607A CN96194607A CN1199506A CN 1199506 A CN1199506 A CN 1199506A CN 96194607 A CN96194607 A CN 96194607A CN 96194607 A CN96194607 A CN 96194607A CN 1199506 A CN1199506 A CN 1199506A
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layer
metal
substrate
precursor
layered superlattice
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吾妻正道
卡洛斯·A·帕斯·德·阿劳约
约瑟夫·D·库奇阿罗
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Panasonic Holdings Corp
Symetrix Corp
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Matsushita Electronics Corp
Symetrix Corp
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L23/00—Details of semiconductor or other solid state devices
    • H01L23/52—Arrangements for conducting electric current within the device in operation from one component to another, i.e. interconnections, e.g. wires, lead frames
    • H01L23/522—Arrangements for conducting electric current within the device in operation from one component to another, i.e. interconnections, e.g. wires, lead frames including external interconnections consisting of a multilayer structure of conductive and insulating layers inseparably formed on the semiconductor body
    • H01L23/532—Arrangements for conducting electric current within the device in operation from one component to another, i.e. interconnections, e.g. wires, lead frames including external interconnections consisting of a multilayer structure of conductive and insulating layers inseparably formed on the semiconductor body characterised by the materials
    • H01L23/53204—Conductive materials
    • H01L23/53209—Conductive materials based on metals, e.g. alloys, metal silicides
    • H01L23/53242—Conductive materials based on metals, e.g. alloys, metal silicides the principal metal being a noble metal, e.g. gold
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L23/00—Details of semiconductor or other solid state devices
    • H01L23/52—Arrangements for conducting electric current within the device in operation from one component to another, i.e. interconnections, e.g. wires, lead frames
    • H01L23/522—Arrangements for conducting electric current within the device in operation from one component to another, i.e. interconnections, e.g. wires, lead frames including external interconnections consisting of a multilayer structure of conductive and insulating layers inseparably formed on the semiconductor body
    • H01L23/532—Arrangements for conducting electric current within the device in operation from one component to another, i.e. interconnections, e.g. wires, lead frames including external interconnections consisting of a multilayer structure of conductive and insulating layers inseparably formed on the semiconductor body characterised by the materials
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L23/00—Details of semiconductor or other solid state devices
    • H01L23/52—Arrangements for conducting electric current within the device in operation from one component to another, i.e. interconnections, e.g. wires, lead frames
    • H01L23/522—Arrangements for conducting electric current within the device in operation from one component to another, i.e. interconnections, e.g. wires, lead frames including external interconnections consisting of a multilayer structure of conductive and insulating layers inseparably formed on the semiconductor body
    • H01L23/532—Arrangements for conducting electric current within the device in operation from one component to another, i.e. interconnections, e.g. wires, lead frames including external interconnections consisting of a multilayer structure of conductive and insulating layers inseparably formed on the semiconductor body characterised by the materials
    • H01L23/53204—Conductive materials
    • H01L23/53209—Conductive materials based on metals, e.g. alloys, metal silicides
    • H01L23/53242—Conductive materials based on metals, e.g. alloys, metal silicides the principal metal being a noble metal, e.g. gold
    • H01L23/53252—Additional layers associated with noble-metal layers, e.g. adhesion, barrier, cladding layers
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L28/00—Passive two-terminal components without a potential-jump or surface barrier for integrated circuits; Details thereof; Multistep manufacturing processes therefor
    • H01L28/40—Capacitors
    • H01L28/60—Electrodes
    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10B—ELECTRONIC MEMORY DEVICES
    • H10B53/00—Ferroelectric RAM [FeRAM] devices comprising ferroelectric memory capacitors
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L28/00—Passive two-terminal components without a potential-jump or surface barrier for integrated circuits; Details thereof; Multistep manufacturing processes therefor
    • H01L28/40—Capacitors
    • H01L28/55—Capacitors with a dielectric comprising a perovskite structure material
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L2924/00—Indexing scheme for arrangements or methods for connecting or disconnecting semiconductor or solid-state bodies as covered by H01L24/00
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    • H01L2924/0002—Not covered by any one of groups H01L24/00, H01L24/00 and H01L2224/00

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  • Physics & Mathematics (AREA)
  • Condensed Matter Physics & Semiconductors (AREA)
  • General Physics & Mathematics (AREA)
  • Inorganic Compounds Of Heavy Metals (AREA)
  • Semiconductor Integrated Circuits (AREA)
  • Internal Circuitry In Semiconductor Integrated Circuit Devices (AREA)
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Abstract

A thin-film ferroelectric capacitor (20) includes a bottom electrode structure (26) having an adhesion metal layer (36) and a noble metal portion (38). The electrode (26) is deposited over a thin-film buffer layer (24), which contains a layered superlattice material. The buffer layer is interposed between a substrate (22) and the bottom electrode (26). A process of manufacture includes deposition of a liquid precursor on the substrate (22) prior to formation of the bottom electrode (26).

Description

Integrated circuit comprising a substrate and a wiring layer with a buffer layer between the substrate and the wiring layer
Background
1. Field of the invention
The present invention relates to the field of wiring layers for integrated circuit devices, and more particularly to electrodes comprising buffer layers for compensating for inter-layer incompatibility problems, and methods for preparing such buffer layers. More specifically, the buffer layer is preferably used for an electrode of a ferroelectric capacitor.
2. Description of the prior art
Integrated circuit devices may fail or degrade performance due to material incompatibility issues. Surface irregularity problems can lead to defects in the sequentially deposited layers. The thin film layers may be doped due to diffusion from adjacent layers. Cracking, delamination, and surface irregularity problems can result from different coefficients of thermal expansion in the various layers or other causes, and thus, it is often necessary to heat the devices during the manufacturing process. These problems are exacerbated by the very thin nature of the circuit layers, since it is not possible to predict the thermal performance of a given layer without having to consider the substrate on which the layer is formed. Thus, the circuit designer must carefully select the materials used to form each thin film layer.
Common circuit failure mechanisms include: a crack due to poor connection between adjacent layers or a short circuit caused by one film layer being detached from another. In silicon technology devices, the platinum wiring layer or electrode may have a poor connection to the silicon dioxide or titanium dioxide barrier layer separating the platinum electrode and the silicon wafer. Researchers have successfully reduced the incidence of cracking by applying a titanium metal bond coat to the barrier layer prior to sputtering the platinum electrode; however, coating titanium metal has proven to be problematic. The additional titanium acts to dope the other layers by diffusion of titanium. The doping of diffused titanium is particularly problematic in integrated circuits, since titanium ions are usually present in many valence states, namely +2, +3 and +4, which lead to corresponding lattice defects. To isolate the bond line metals, metal nitride diffusion barriers have been constructed. See, for example, U.S. Pat. No. 5,5,005,102 (Larson) and Garceau et al, "Tin As A Diffusion Barrier In The Ti-Pt-Au Beam Less Metal systems", 60Thin Solid Films, 237-. Annealing of metal nitrides can create surface irregularities, such as hillocks, which can result in short circuits in dielectric or ferroelectric capacitors.
The magnitude of the polarization obtained by the thin film ferroelectric material is a limiting factor in controlling the storage density at a given voltage. Greater polarization can be used for denser storage. But in any event, good adhesion of the ferroelectric to the substrate is also required. Thus, in selecting materials, a conflicting conflict arises between the need for cohesiveness and the need for high polarization.
Means for solving the problems
The present invention overcomes the above-described problems by providing a buffer layer and an electrode comprising a bonding metal that are substantially free of surfaceirregularities. The additional buffer layer provides the ferroelectric capacitor with a substantial improvement in polarization performance of up to 100% or more when compared to a similarly processed ferroelectric capacitor without the buffer layer.
Generally, an electrode structure comprises an integrated circuit device comprising a substrate, a metal electrode or wiring layer, and a layer sequence (layer sequence) composed of a material sandwiched between the substrate and the wiring layer. The layer sequence comprises at least one buffer layer made of a layered superlattice material and is substantially free of an additional line layer.
A particularly preferred form of electrode structure comprises a layered superlattice material which is strontium bismuth tantalate. Other preferred layered superlattice materials include strontium bismuth niobate and strontium bismuth niobium tantalate. The substrate preferably comprises: the outermost silicon substrate adjacent to the sequence, for example silicon dioxide. Most preferred substrates include silicon wafers. The wiring layer preferably includes a bonding metal portion such as titanium or tantalum. The binder metal is preferably used in combination with a noble metal, the most preferred noble metal being platinum.
A ferroelectric capacitor may be formed by forming a ferroelectric layer on top of the electrode structure. The ferroelectric layer preferably comprises a layered superlattice material such as strontium bismuth tantalate, strontium bismuth niobate, or mixtures thereof. The capacitor is preferably completed by forming a second electrode on the ferroelectric layer.
The preferred method is used to prepare an integrated circuit device having the electrode structure described above. The method comprises the following steps: providing a substrate having a non-metallic outermost surface; forming a layeredsuperlattice material atop the substrate; and depositing an electrode on the layered superlattice material.
Particularly preferred methods are: those methods in which the forming step comprises applying a liquid precursor to the substrate to form a precursor film. The precursor preferably includes an effective amount of polyoxyalkylated metal moieties to obtain a layered superlattice material upon heat treatment of the precursor. The precursor is heat treated to obtain a layered superlattice material.
The treating step preferably comprises annealing the precursor at a temperature of at least 450 c, more preferably at least about 600 c. Additionally, the treating step may further comprise drying the precursor at a temperature of up to about 450 ℃ for a time sufficient to remove substantially all of the volatile organic components from the precursor film.
The method can be used to form a capacitor device by forming a second layered superlattice material on top of the electrode. In addition, the layers are preferably deposited using liquid deposition techniques. Upon heating of the precursor solution, the layered superlattice material is automatically generated from the liquid precursor solution of the superlattice forming portion.
As described above, the ferroelectric material is preferably a perovskite-like superlattice material. The term "perovskite-like" refers to a lattice consisting of individual layers of oxygen octahedra separated by a superlattice-generating layer comprising a trivalent metal, such as bismuth. These materials are considered a wide range of ferroelectric materials, but have not been successfully applied to integrated circuit devices to date due to device reliability issues. The perovskite-like portion of the layered superlattice material is formed as a discontinuous layer separated by a bismuth oxide layer. The perovskite-like layerincludes a host lattice having oxygen octahedra positioned within cubes defined by large a-plane metals at the corners. The oxygen atom occupies the center of the face of the cube, while the small B-plane element occupies the center of the cube. In some instances, the oxygen octahedral structure may be maintained without the a-plane elements.
The most preferred layered superlattice material is one having an average composition formula of SrBi2Ta2O9Strontium bismuth tantalate. Most preferably (Bi)2O2 2+) The superlattice generation layer is composed, but thallium (III) may also be contained as the metal. Therefore, the most preferred average composition formula of the oxygen octahedral structure layer is (SrTa)2O7)2-. Upon heating of the metal organic precursor solution, the layers automatically produce a layered superlattice. The oxygen octahedral layer is ferroelectric and has an average composition with ionic charges that are offset by the superlattice generating layer to balance the overall crystal charge. The buffer layer plays a role in keeping the layered superlattice material basically free of point defects; the point defects can reduce polarization.
Other features, objects, and advantages of the invention will be apparent to those skilled in the art upon a reading of the following specification and drawings.
Drawings
FIG. 1 depicts a thin film ferroelectric capacitor device comprising a buffer layer of layered superlattice material sandwiched between a bottom electrode and an underlying substrate;
FIG. 2 depicts a flow diagram for preparing the capacitor of FIG. 1;
FIG. 3 depicts a flow diagram for preparing a liquid precursorsolution for use in the method of FIG. 2;
FIG. 4 depicts a failed bottom electrode structure having a larger mound structure on its outermost surface;
fig. 5 is a bar graph comparing average polarization values obtained from capacitors treated under different conditions.
Description of The Preferred Embodiment
Fig. 1 depicts a capacitor 20 that includes a substrate 22, a buffer layer 24, a bottom electrode 26, a metal oxide layer 28, and a top electrode 30. Substrate 22 preferably includes a conventional silicon layer 32, which is capped by a spacer layer 34. Silicon layer 32 may be single crystal or polycrystalline silicon and may be derived from a number of silicon wafer sources. Layer 32 may also be formed from other known substrates such as gallium arsenide, indium antimonide, magnesium oxide, strontium tantalate, sapphire, quartz, and mixtures of the foregoing, as well as other materials. Spacer layer 34 is preferably comprised of a thick silicon dioxide that is formed on layer 32 by well-known methods such as spin-on glass ("SOG") deposition or baking of layer 32 in the presence of oxygen in a diffusion furnace. The term "substrate" as used herein refers specifically to a layer that provides support to other layers. The substrate 22 serves to support all other layers, but the term substrate can also refer to the substrate 22 in combination with other layers. Thus, the combination of the substrate 22, the buffer layer 24, and the bottom electrode 26 provides a substrate or support for the metal oxide layer 28, which in turn provides a support for the top electrode 30.
A buffer layer 24 is superimposed on the substrate 22. Layer 24 is preferably a perovskite-like, layered superlattice material. Particularly preferred layered superlattice materials include: strontium bismuth tantalate, strontium bismuth niobate, and strontium bismuth niobium tantalate. The most preferred strontium bismuth tantalate has the average compositional formula SrBi2Ta2O9. In addition, many perovskite-like layered superlattice materials are also highly dielectric.
The use of the buffer layer 24 provides significant polarization improvement for ferroelectric capacitors, particularly for capacitors using layered superlattice ferroelectrics. The layered superlattice material at least comprises layered superlattice materials of all three Smolenskii-type ferroelectrics, namely, materials respectively having the following average composition formulas:
(1)Am-1S2BmO3m+3
(2)Am+1BmO3m+1
(3)AmBmO3m+2where A is the A-plane metal of the perovskite superlattice, B is the B-plane metal of the perovskite superlattice, S is a trivalent superlattice-producing metal such as bismuth or tantalum, and m is a number sufficient to balance the overall compositional charge. When m is a fraction of the total composition, the composition typically provides a number of different or mixed perovskite-like layers, each having a different integer value. The a-side metal and the B-side metal can comprise a mixture of cations having similar ionic radii.
In the layered superlattice material according to formula (1), the formation of an oxygen octahedral structure layer having an m-octahedral thickness of the following structural formula (4) is thermodynamically favored.
(Am-1BmO3m+1)2-Wherein m is an integer greater than 1 and other variables as defined above. These layers are separated by a layer of bismuth oxide of formula (5).
(Bi2O2)2+Wherein Bi is S in the structural formula (1).
The superlattice generation layer S preferably comprises an oxide of bismuth (III) and may also comprise other trivalent metal cations of similar size, such as tantalum (III). Bismuth also functions as the A-plane metal in the perovskite-like lattice if it is present in excess of the stoichiometric amount required to produce the layered superlattice material of formula (1).
The bottom electrode 26 includes a bond metal portion 36 and a noble metal portion 38. The bond metal portion 36 is preferably comprised of sputtering titanium or tantalum, most preferably tantalum. The bond metal portion 36 is preferably sprayed to a thickness preferably in the range of about 50 angstroms to 250 angstroms, most preferably 200 angstroms. The first noble metal portion 38 is preferably platinum, but may be other noble metals such as gold, silver, palladium, iridium, rhenium, ruthenium, and osmium, as well as conductive oxides of these metals. The first noble metal portion 38 is preferably deposited by vacuum sputtering platinum onto the top of the bond metal portion 36, the thickness of the portion 38 being 3-15 times the thickness of the bond metal portion 36, and most preferably about 2000 angstroms when the bond metal portion is 100 to 200 angstroms thick. Thicknesses outside the preferred range are still possible, but a thinner first noble metal portion 38 will make the bond metal portion more readily diffuse to the layer 38 described above. The thicker noble metal portion would be a significant waste of noble metal material.
Layer 28 is preferably a ferroelectric perovskite layered superlattice material. Particularly preferred layered superlattice materials include strontium bismuth tantalate, strontium bismuth niobate, and strontium bismuth niobium tantalate. The most preferred strontium bismuth tantalate has the average compositional formula SrBi2Ta2O9。
The top wiring layer or electrode 30 is preferably a noble metal that is cathodically sputtered onto the metal oxide layer 30. The top electrode 28 is typically about 1000 angstroms to about 2000 angstroms thick, but may be a thickness outside of this range. The electrode 30 is preferably made of platinum.
Fig. 2 depicts a flow chart of a method of making capacitor 20. The method will be described with respect to the embodiment of fig. 1, but it will be apparent to those skilled in the art that the method may be used with other embodiments.
In step P40, a silicon wafer is made into a substrate 22 having a silicon layer 32 and a silicon dioxide layer 34. The silicon layer 32 may be baked in a diffusion furnace in the presence of oxygen at about 500 c to about 1100 c. This baking step serves to eliminate surface impurities and water and form the oxidized coating 34. In addition, a silicon wafer or layer 32 may also be coated using a conventional spin-on glass process to form an oxide layer 34. Step P40 may also include conventional steps for transistors or memory circuits, such as etching of contact holes (not shown) and coating of layer 32 (typically substrate 22), typically depending on the nature of the device desired to be formed.
Step P42 includes a method of preparing one or more liquid precursor solutions containing a plurality of metal portions in an amount effective to produce buffer layer 24 and/or ferroelectric layer 28 upon drying and annealing of the precursor solutions. Additional details of the preparation of the precursor solution will be described below.
In step P44, the precursor solution of step P42 is coated onto the substrate of step P42, which will produce the outermost surface of the oxide layer 34 for receiving the liquid precursor. The coating is preferably carried out by dropping the liquid precursor solution at room temperature and pressing it onto the outermost surface of oxide layer 34 (typically substrate 22) and then spinning the substrate at about 1500RPM to 2000RPM for about 30 seconds to remove excess solution, thus leaving a thin film of liquid residue. The most preferred rotational speed is 1500 RPM. In addition, liquid precursors may also be applied by spray deposition techniques as described in US5,456,945. The most preferred precursor solutions are those that yield layered superlattice materials such as strontium bismuth tantalate.
In step P46, the liquid precursor film of step P44 is dried on a hot plate, preferably under a dry atmosphere, at a temperature of about 200 ℃ to 500 ℃. The drying time and temperature must be sufficient to remove substantially all of the organic material from the liquid film and leave a dried metal oxide residue. Preferably, the drying time is from about one minute to about thirty minutes. For single stage drying, it is most preferred to dry in air at 400 ℃ for about 2 to 10 minutes. More preferably, however, the liquid film is dried at segmented intervals. For example, the film may be dried at 260 ℃ for 5 minutes and then at 400 ℃ for 5 minutes. In addition, it is preferred to include drying cycles at temperatures in excess of 700 ℃ with very rapid processing intervals, such as by heating the substrate to 725 ℃ for 30 seconds using a tungsten nickel lamp. This drying step P46 is critical in order to obtain the desired or reproducible electrical properties of the final metal oxide crystalline composition.
Steps P44 and P46 may be repeated if it is desired to increase the thickness of the entire buffer layer 24, however, it is often necessary or desirable to increase the thickness of the layer 24 beyond that which would be obtained with a single precursor liquid coating.
Optional step P48 includes sputtering titanium adhesion metal layer 36 atop buffer layer 24, preferably to a thickness of from about 50 angstroms to 250 angstroms, according to conventional conventions known in the art. The sputtered layer 36 is preferably formed to provide better adhesion to layer 24. This sputtering prevents delamination and cracking of adjacent layers that would result in shorting of the capacitor 20, however, the bonding metal can contaminate other layers by diffusion. Step P50 includes sputtering noble metal portion 38 atop portion 36, preferably to a thickness of from about 1000 to 2000 angstroms. Examples of preferred atomic sputtering conventions include: radio frequency sputtering and DC magnetron sputtering.
In step P52, the substrate 22 of step P50 is annealed to form the metal oxide of the buffer layer 24. Step P52 is referred to as a "first anneal" to distinguish it from other annealing steps; however, it should be understood that other annealing steps may be performed prior to this "first annealing" step. In step P52, the substrate comprising layers 36 and 38 is preferably heated to 450-1000 ℃ in a diffusion furnace under an oxygen atmosphere for 30 minutes to 2 hours. More preferably, step P52 is performed at 600 deg.C to 800 deg.C, and most preferably at about 600 deg.C for 8 minutes. The first annealing step of step P52 is preferably carried out with a push/pull method comprising "pushing" into the furnace for 5 minutes and "pulling" out of the furnace for 5 minutes. The annealing time includes the time required to establish a hot runner into and out of the furnace. This annealing step is referred to as a first annealing step to distinguish it from the other annealing steps.
Step P54 includes depositing the layered superlattice precursor of step P42 atop the noble metal layer 38. Preferably the precursor is a liquid precursor, but may also be sprayed from a solid target. The coating is preferably carried out by dropping the liquid precursor solution at room temperature and pressing it onto the outermost surface of the bottom electrode 26, and then rotating the substrate at a speed of about 1500RPM to 2000RPM for about 30 seconds and leaving a liquid residue in the form of a thin film. The most preferred rotational speed is 1500 RPM. Preferred precursor solutions include those materials having an effective amount of metal moieties capable of producing layered superlattice materials. The most preferred layered superlattice material is strontium bismuth tantalate.
In step P56, the liquid precursor film of step P54 is dried, preferably under a dry atmosphere, on a hot plate at about 200 deg.C to 500 deg.C. The drying time and temperature must be sufficient to remove substantially all of the organic material from the liquid film and leave a dried metal oxide residue. Preferably, the drying time is from about one minute to about thirty minutes. For single stage drying, it is most preferred to dry in air at 400 ℃ for about 2 to 10 minutes. More preferably, however, the liquid film is dried at segmented intervals. For example, the film may be dried at 260 ℃ for 5 minutes and then at 400 ℃ for 5 minutes. In addition, it is preferred to include drying cycles at temperatures in excess of 700 ℃ with very rapid processing intervals, such as by heating the substrate to 725 ℃ for 30 seconds using a tungsten nickel lamp. This drying step P56 is critical in order to obtain the desired or reproducible electrical properties of the final metal oxide crystalline composition.
In step P58, if the final dried film from P56 does not have the desired thickness, then P54, P56, and P58 should be repeated until the desired thickness is obtained. Thicknesses of about 1800 to 2000 angstroms typically require two coats with 0.130 to 0.200M precursor solution under the parameters described in this invention.
In step P60, the dried precursor residues of steps P56 and P54 are annealed to form the layered superlattice material of layer 26. This annealing step is referred to as a second annealing step to distinguish it from the other annealing steps. Preferably, this second annealing step is carried out under the same conditions as the first annealing step P52.
In step P62, the top electrode 28 is preferably deposited by vacuum sputtering platinum onto the top of the layered superlattice material layer 26. At this time, the capacitor 20 may also be annealed, and the annealing conditions are preferably the same as in step P52.
The device is then patterned in step P64 by conventional photolithography, including, for example, application of photoresist followed by ion etch lithography. This patterning is preferably performed prior to the third annealing step so that the third annealing relieves the patterning stress from the capacitor 20 and corrects any defects created by the patterning step.
The third annealing (step P66) is preferably performed in the same manner as the first annealing step (step P52).
Finally, the device is completed and evaluated in step P68. The completing step includes: deposition of supplemental layers, ion etching of contact holes, and other steps will be apparent to those skilled in the art. The substrate or silicon wafer 22 may be sawed into individual components to separate many integrated circuit devices simultaneously produced thereon.
A preferred process for preparing the polyoxyalkylated metal precursor of step P42 is described in US5,514,822. The method preferably comprises: reacting a metal with an alkoxide (e.g., 2-methoxyethanol) to form a metal alkoxide, and reacting the metal alkoxide with a carboxylate (e.g., 2-ethylhexanoate) to form a metal alkoxycarboxylate of one of the following general formulae:
(6) (R’-COO-)aM(-O-R)n’or
(7) (R’-C-O-)aM(-O-M’(-O-C-R”)b-1)n’Wherein M is a metal cation having an outer layer valence of (a + n), M 'is a metal cation having an outer layer valence of b, and M' are preferably independently selected from: tantalum, calcium, bismuth, lead, yttrium, scandium, lanthanum, antimony, chromium, thallium, hafnium, tungsten, niobium, vanadium, zirconium, manganese, iron, cobalt, nickel, magnesium, molybdenum, strontium, barium, titanium, and zinc; r and R 'are each an alkyl group preferably having 4 to 9 carbon atoms, and R' is an alkyl group preferably having 3 to 8 carbon atoms. The latter formula, having the structure-O-M-O-M' -O-is particularly preferred because it will form a solution having at least 50% metal-oxygen bonds present in the final solid metal oxide product.
The liquid precursor is preferably a metal alkoxide or metal carboxylate, more preferably a metal alkoxycarboxylate diluted to a desired concentration with a xylene or octane solvent. The use of substantially anhydrous metal alkoxycarboxylates is particularly preferred, since water-induced polymerization or gelation, which would significantly reduce the shelf life of solutions containing alkoxide coordination bonds, can be correspondingly avoided. It is preferred to avoid or minimize the presence of any hydrolysis-initiating moieties in the solution. Although hydrolyzed precursors such as conventional sol-gels can also be used, increased solution viscosity tends to disrupt the thickness uniformity obtained by the preferred spin-coating process, and the quality of the hydrolyzed solution tends to decrease rapidly over time. Thus, ready hydrolyzed gels tend to produce poor qualitymetal oxide films that do not have uniform quality over time. Preferred methods produce them well before the precursor solutions are needed.
The precursor solution is used to obtain the corresponding layered superlattice material, wherein it is understood that the oxygen octahedral structure that may be formed is favorable for thermodynamics. In general, for a perovskite-like octahedral structure or a perovskite octahedral structure, equivalent substitutions may be made between metal cations having substantially the same ionic radius (i.e., the radius does not change by more than about 20% at each lattice site). These substitutions may be made by adding additional metal moieties to the precursor solution.
Preferred formulations of the precursor solution include: preferred metals for the desired layered superlattice materials are stoichiometrically balanced in combination according to the compositional formula. Preferably reacting at least one a-plane element with an alcohol or a carboxylic acid to form an a-plane moiety; the A-surface element is selected from the following components: ba, Bi, Sr, Pb, La, Ca, and mixtures thereof. Preferably, the B-face moiety is formed by reacting an alcohol or carboxylic acid with at least one B-face element selected from the group consisting of: zr, Ta, Mo, W, V, Nb, and mixtures thereof. Although titanium can be used as a significant radius B-plane element, in practice it is not preferred because of the problems that occur with titanium diffusion into other integrated circuit components and point charge defects (point charge defects) created by different valence states in the titanium ion. In the case of layered superlattice materials, there is also an additional trivalent superlattice-producing metal, preferably bismuth. Upon heating, bismuth will spontaneously generate a bismuth oxide layer in the layered superlattice material, but the excess bismuth fraction can also provide a-surface elements to the perovskite-like lattice.
Fig. 3 depicts a flow diagram of the general method of the present invention for providing the liquid precursor solution prepared in step P42. The word "precursor" is often used ambiguously in the art. It may refer to: a solution containing one metal to be mixed with other materials to form a final solution, or a solution containing several, ready-made metals for the substrate. In the present discussion, we will refer to the precursor as "precursor" unless a different meaning is evident from the context. In the intermediate stages, this solution may be referred to as a "pre-precursor".
The preferred chemical reaction formulas for forming the liquid solutions of metal alkoxide, metal carboxylate, and metal alkoxycarboxylate to produce the starting metal precursor moiety are as follows: (8) (9) (10) wherein M is a metal cation with n charge; b is the number of moles of carboxylic acid in the range of 0-n; r' is preferably an alkyl group having 4 to 15 carbon atoms, and R is preferably an alkyl group having 3 to 9 carbon atoms.
In step P70, a first metal, represented by M in the above equation, is reacted with an alcohol and a carboxylic acid to form a metal-alkoxy carboxylate pre-precursor. The method preferably comprises: the metal is reacted with an alcohol (e.g., 2-methoxyethanol) to form a metal alkoxide of equation (8), and the metal alkoxide is reacted with a carboxylic acid (e.g., 2-ethylhexanoic acid) to form a metal alkoxycarboxylate of equation (10). The reaction of equation (9) can also be observed when the unreacted metal is mixed with both the alcohol and the carboxylic acid. The simultaneous reaction is preferably carried out in a reflux condenser for one to two days so that the alkoxide moiety is replaced by the carboxylate complex bond. The reflux condenser is heated by a heating plate at about 120 ℃ to about 200 ℃. At the end of the initial one to two day reaction cycle, the reflux condenser is preferably vented to atmosphere and the temperature of the solution is monitored to observe a fractionation plateau, i.e., a plateau at least above about 100 ℃, which indicates that all of the water and alcohol moieties are substantially removed from the solution, at which time the solution is removed from the heat source. More preferably, atmospheric distillation is carried out at least 115 deg.C, and most preferably at about 123 deg.C to 127 deg.C.
In the above equation, the metal is preferably selected from: tantalum, calcium, bismuth, lead, yttrium, scandium, lanthanum, antimony, chromium, thallium, hafnium, tungsten, niobium, vanadium, zirconium, manganese, iron, cobalt, nickel, magnesium, molybdenum, strontium, barium, titanium, and zinc. Alcohols which may be used preferably include: 2-methoxyethanol, 1-butanol, 1-pentanol, 2-pentanol, 1-hexanol, 2-hexanol, 3-hexanol, 2-ethyl-1-butanol, 2-ethoxyethanol, and 2-methyl-1-pentanol, with 2-methoxyethanol being preferred. The carboxylic acids which may be used preferably include: 2-ethylhexanoic acid, octanoic acid, and neodecanoic acid, among which 2-ethylhexanoic acid is preferred.
The reaction of step P70 and subsequent steps are preferably facilitated by the use of compatible solvents. Solvents that may be used include: xylene, 2-methoxyethanol, n-butyl acetate, n-dimethylformamide, 2-methoxyethyl acetate, methyl isobutyl ketone, methyl isoamyl ketone, isoamyl alcohol, cyclohexanone, 2-ethoxyethanol, 2-methoxyethyl ether, methyl butyl ketone, ethanol, 2-pentanol, ethyl butyrate, nitroethane, pyrimidine, 1, 3, 5-trioxane, isobutyl isobutyrate, isobutyl propionate, propyl propionate, ethyl lactate, n-butanol, n-pentanol, 3-pentanol, toluene, ethylbenzene, and octane, and other solvents. Preferably, the boiling point of these solvents is higher than the boiling point of water, so that the precursor is distilled to remove water therefrom prior to application of the precursor to the substrate. When it is desired to fully dissolve the precursor formulation, the co-solvents must be miscible with each other and have miscibility in different proportions, especially between polar and non-polar solvents. Xylene and octane are particularly preferred non-polar solvents, and n-butyl acetate is a particularly preferred polar co-solvent.
Where the intermediary metal reagent is obtained in analytical purity, part of step P70 may be omitted. For example, when tantalum isobutanol is used, it is only preferred that the iso-butoxide moiety be replaced by an acceptable carboxylate ligand by reacting the metal alkoxide with a carboxylic acid such as 2-ethylhexanoic acid in accordance with equation (10).
In a typical second step, step P72, an effective amount of a metal carboxylate, a metal alkoxide, or both, is added to the metal alkoxycarboxylate to provide an intermediate precursor having a mixture of superlattice-forming metal moieties that results in a stoichiometric balance of the solid metal oxide of layer 26. Since the bismuth compound is thermally unstable, the mixture does not take into account the bismuth compound at this point and can be added later if desired. Any of the metals listed above may be reacted with any of the carboxylic acids listed above to form a metal carboxylate, while any of the metals listed above may also be reacted with an alcohol to form an alkoxide. It is particularly preferred to carry out the reaction in the presence of a slight excess of carboxylic acid in order to partially replace the alkoxide ligand with a carboxylate ligand.
In step P74, the mixture of metal alkoxycarboxylates, metal carboxylates and/or metal alkoxides is heated and stirred, if necessary, to form metal-oxygen-metal bonds and to boil off any low-boiling organics produced by the reaction. According to general reaction theory, if a metal alkoxide is added to a metal alkoxycarboxylate and the solution is heated, the following reaction will occur: (11) (12) wherein M and M' are metals; r and R' are as defined above; r "is an alkyl group preferably having zero to sixteen carbon atoms; a, b and x are integers representing the relative amounts of the corresponding substituents corresponding to each valence of M and M'. Generally, since metal alkoxides react more readily than metal carboxylates, the reaction of equation (11) will occur first. Thus, theLow boiling ethers are often formed. These ethers are boiled out of the pre-precursor, leaving the final product with a reduced amount of organics and eventually the metal-oxygen-metal bonds of the desired metal oxide have partially formed. If the heating is sufficient, some reaction of equation (12) will also occur,resulting in metal-oxygen-metal bonds and esters. The esters generally have a higher boiling point and remain in solution. These high boiling point organics will slow the drying process after the final precursor is applied to the substrate, which tends to reduce cracks and defects; thus, in either case, a metal-oxygen-metal bond will be formed and the properties of the final precursor improved.
In practice, step P74 is a distillation step to remove the volatile fraction from the solution according to the reactions of equations (11) and (12). Removal of the volatile fraction from the solution forces these reactions to completion, i.e., high efficiency. The removal of the volatile moieties from the solution also serves to prevent cracking of the film and other defects associated with the presence of the volatile moieties in the solution. Thus, the progress of reactions (11) and (12) can be monitored by the rate of solution heating and the volume of liquid removed from the solution. Preferably the solution is heated to a boiling point plateau of at least 115 deg.C, more preferably to 120 deg.C, most preferably from 123 deg.C and 127 deg.C.
If the metal carboxylate is added to the metal alkoxycarboxylate and the mixture is heated, the following reaction will occur: (13) wherein R-COOOC-R' is an anhydride and the other items are as defined above. Performing this reaction requires much more heat than performing reactions (11) and (12) and the reaction rate is much slower. In addition to the above-described reaction to produce metal alkoxycarboxylates, the following reaction will occur: (14) the terms in the formula are as defined above. The reaction, heated in the presence of excess carboxylic acid, displaces the alkoxide portion of the intermediate metal alkoxycarboxylate to form a substantially complete carboxylate; however, it is believed that with the parameters disclosed herein, complete substitution of the alkoxide by the carboxylate does not proceed. Complete substitution of the carboxylic acid saltsA large amount of heat is required and even then complete replacement is difficult.
At the end of step P74, it is preferred that a solution of at least 50% metal-oxygen bonds of metal oxide layer 26 be formed. These reactions are preferably carried out in a vessel vented to atmospheric pressure and heated through a heating plate, preferably at about 120 c to about 200 c, until a fractionation plateau, meaning a plateau of at least greater than 100 c, is observed when the solution is monitored, which indicates substantial removal of water, alcohols, ethers, and other reactionbyproducts from the solution. Extended reflux at this point can produce potentially undesirable amounts of ester or anhydride by-products that are often difficult to remove from solution by fractional distillation. The potential complications of excessive anhydride concentrations can be completely avoided simply by adding the metal carboxylate in step P72, thereby eliminating the possible need for refluxing the solution.
Step P76 is an optional solvent exchange step. The use of common solvents in many precursor solutions is advantageous because, after application to a substrate, it is possible to ascertain fluid parameters, such as viscosity and bond tension, that affect the thickness of the liquid precursor film. The parameters of these fluids also affect the quality and electrical properties of the corresponding metal oxide thin film after annealing of the dried precursor residue. In step P76, a standard solvent, preferably xylene or n-octane, is added in an amount to adjust the intermediate precursor to the desired molar concentration of the superlattice formulation. The molar concentration is preferably from about 0.100M to about 0.400M in terms of the compositional formula of the metal oxide material, and most preferably from about 0.130M to about 0.200M in terms of the molar concentration of the metal oxide material that can be formed from one liter of solution. After the addition of the standard solvent is complete, the solution is heated to a temperature sufficient to evaporate off any non-standard solvent, thus providing a solution having the desired molarity.
Step P78 is preferably used only where a precursor is used for the layered superlattice material including bismuth. Bismuth (Bi)3+) Is the most preferred superlattice generating element and the most preferred bismuth pre-precursor is bismuth tri-2-ethylhexanoate. Due to these pre-prepsThe relative instability of the body, i.e., large amounts of heat will destroy the coordinate bonds, which will create potential for the solution's ability to achieve excellent thin film metal oxidesA deleterious effect; therefore, the bismuth pre-precursor is preferably added after the heating of step P74. It will be appreciated that, in this sense, step P78 is optional, and that the bismuth pre-precursor can often be added without any problems in either of steps P70 and P74.
These particular problems are considered to be the potential volatilization of bismuth during the high temperature annealing of dried precursor residues during heating of the precursor solution, especially in the formation of the desired stoichiometric layered superlattice material. Therefore, an excess of bismuth of about 5% to about 15% is preferably added in step 78 to compensate for the expected loss of bismuth in the precursor solution. The excess bismuth fraction in the precursor solution is typically 5% -15% when annealed at temperatures from about 600 c to about 850 c for about one hour, which is required for a stoichiometrically balanced layered superlattice product. Where excess bismuth is not sufficiently volatilized during the formation of the metal oxide, the remaining excess bismuth portion functions as an A-plane material, and thus, point defects are generated in the final layered superlattice crystal.
In step P80, the solution is thoroughly mixed and if the final solution is not used for several days or weeks, it is preferably stored under a dry nitrogen or argon inert atmosphere. The storage protection measures function as follows: ensuring that the solution remains substantially anhydrous and avoiding the deleterious effects of water-induced polymerization, viscous gelation, and precipitation of metal moieties in the alkoxide ligand. Even so, when the precursor preferably consists essentially of the metal bonded to the carboxylate ligand and the alkoxycarboxylate, the dry inert storage means is not necessarily required.
Exemplary discussions of reaction processes have been summarized above, and thus they are not limiting. The specific reaction that will occur depends on the metal, alcohol, and carboxylic acid used and the heat applied. A detailed example will be given below.
The following non-limiting examples set forth preferred materials and methods for practicing the present invention.
Example 1
Preparation of layered superlattice precursor solution
The precursor formulations of Table 1 were obtained from the indicated industrial sources and subdivided to give the parts shown.
TABLE 1
Ingredients Molecular weight (FW) (g/mol) Keke (Chinese character of 'Keke') Millimole Molar equivalent Vendors
Tantalum pentabutanol Ta (OC)4H9)5 546.52 43.72 2 80.00 1 2.000 0 Vnipim
2-ethyl hexanoic acid 144.21 72.68 4 504.0 1 12.60 0 Aldrich
Strontium salt 87.62 3.504 8 40.00 0 1.000 0 Strem
Bismuth tris-2-ethylhexanoate (in borneol) In oil) Bi (O)2C6H11)5 (765.50) 66.75 2 87.20 1 2.180 0 Strem
In table 1, "FW" represents the molecular weight, "g" represents grams, "mmoles" represents millimoles, and "equiv" represents the number of molar equivalents of the solution.
Tantalum pentabutanol and 252.85 millimoles of 2-ethylhexanoic acid were placed in a 250 flask containing 40ml of xylene, i.e., about 50ml of xylene per 100mmol of tantalum. The flask was covered with a 50ml beaker to facilitate reflux and separation of the components from atmospheric water. The mixture was refluxed for 48 hours with magnetic stirring on a hot plate at 160 ℃ to form a substantially homogeneous solution comprising butanol and tantalum 2-ethylhexanoate. It will be appreciated that although the butoxide moieties in the solution are almost completely substituted by 2-ethylhexanoic acid, complete substitution does not occur within the heating parameters of the present example. At the end of 48 hours, a 50ml beaker was removed and the temperature of the hot plate was raised to 200 ℃ to effect distillation of the butanol fraction and water to remove these components from the solution. The flask was removed from the hot plate when the solution first reached a temperature of 124 c, which was just the temperature at which substantially all of the butanol and water had been removed from the solution. The flask and its contents were cooled to room temperature.
Strontium and 50ml of 2-methoxyethanol solvent were added to the cooled mixture to react to form strontium di-2-ethylhexanoate. 100ml of xylene was added to the strontium mixture and the beaker and its contents were placed on a hot plate at 200 ℃ and again placed in a 50ml beaker for a reflux reaction for 5 hours to form the predominant tantalum-strontium alkoxycarboxylate product of formula (6). The beaker was removed and the temperature of the solution was raised to 125 ℃ to remove the 2-methoxyethanol solvent from the solution, as well as the ether, alcohol, or water in the solution. After removal from the heat source, the flask was cooled to room temperature. Bismuth tris-2-ethylhexanoate was added to the cooled solution and further diluted to 2000ml with xylene to form a precursor solution that formed 0.200 molar SrBi without volatilization of bismuth2.18Ta2O9.27。
Thus, this example shows that step P70, i.e., the reaction of strontium metal, alcohol, and carboxylic acid can be carried out in solution, resulting in the derivation of tantalum alkoxycarboxylates from tantalum pentabutanol and 2-ethylhexanoic acid. Thus, steps P70 and P72 may be performed in a single solution and in the opposite direction of fig. 3.
The precursor formulation is designed to compensate for the volatilization of bismuth during the preparation of the solid metal oxide from the liquid precursor. Specifically, Bi2.18The fraction included approximately a 9% excess (0.18) of bismuth moieties. This precursor solution is expected to yield a stoichiometric amount of the material of formula (3) with m-2, i.e., 0.2 moles of SrBi per liter of solution, after accounting for the expected volatilization of bismuth during the upcoming annealing step2Ta2O9。
EXAMPLE 2 formation of ferroelectric capacitor with layered superlattice Material buffer layer without adhesion Metal layer
According to the method of fig. 2, a wafer comprising a plurality of square ferroelectric capacitors, typically in a layered sequence as shown in fig. 1, is prepared. Step P48 is not performed, and therefore, these capacitors do not have gold bondingThe metal layer 36 (FIG. 1). A conventional four inch diameter multi-wafer or substrate 32 is prepared to receive the SrBi of example 12Ta2O9And (3) solution. The preparation method comprises the following steps: according to conventional convention for obtaining thick layers of silicon oxide 34 (see fig. 1), the baking is carried out in a diffusion furnace at 1100 c under an oxygen atmosphere.
0.2M SrBi prepared according to example 1 was filtered through a 0.2 micron filter by adding 1.08ml of n-butyl acetate2Ta2O9The precursor (2ml) was adjusted to a concentration of 0.13M. 2ml of precursor was applied to the substrate with a dropper and the substrate was then spun on a conventional spin coater at 1500 rpm. The precursor coated substrate was dried in air at 400 ℃ on a hot plate for 30 minutes.
The substrate including buffer layer 24 was cooled to room temperature and placed in a vacuum chamber for conventional DC magnetron sputtering. A 2000 angstrom thickness of platinum was sputtered on top of the titanium metal using a discharge voltage of 130 volts and a current of 0.53 amps. The sputtering completes step P52 of FIG. 2, optional step P48 is skipped.
The substrate including the liquid film was annealed in a diffusion furnace under an oxygen atmosphere at 600 c for 30 minutes. These 30 minutes include 5 minutes of pushing into the furnace and 5 minutes of removing from the furnace. The resulting structure includes a buffer layer as shown in fig. 1. These actions complete the process of fig. 2 to step P52.
0.2M SrBi prepared according to example 2 was filtered through a 0.2 micron filter by adding 1.08ml of n-butyl acetate2Ta2O9The precursor (2ml) was adjusted to a concentration of 0.13M. 2ml of precursor was applied to the substrate with a dropper and the substrate was then spun on a conventional spin coater at 1500rpm as previously described. Substrates coated with the precursor in air on a hot plate at 140 ℃Drying for 2 minutes. The substrate was then dried on a second hot plate at 260 ℃ for 4 minutes. The substrate was dried for a further 30 seconds at 725 ℃ under an oxygen atmosphere using a 1200W tungsten-halogen lamp (visible spectrum; Heatpulse 410 from Union, Inc., using bulb J208V from Ushio, Japan). The spin coating and drying steps are repeated again to increase the thickness of layer 28 toAbout 1800 angstroms.
The substrate 22 comprising two layers of dried precursor remains was annealed at 800 ℃ for 70 minutes in a diffusion furnace under an oxygen atmosphere, which included 5 minutes of pushing into the furnace and 5 minutes of removing from the furnace. These operations complete the process of fig. 2 to step P58.
Platinum metal as a top electrode 28 was sputtered onto layer 26 to a thickness of 2000 angstroms. A photoresist is applied and ion etched according to conventional conventions including removal of resist. The patterning device was annealed at 800 ℃ for 30 minutes in a diffusion furnace under an oxygen atmosphere, which included 5 minutes of pushing into the furnace and 5 minutes of removing from the furnace. These operations complete the process of fig. 2 up to step P68 and provide the ferroelectric capacitor 20 shown in fig. 1 with strontium bismuth tantalate (layer 26). Buffer layer 24 is 500 angstroms thick and is covered by a 2000 angstroms thick layer 38 of platinum.
EXAMPLE 3 formation of ferroelectric capacitor with layered superlattice Material buffer layer and adhesion Metal layer
Wafers having the layered sequence shown in fig. 1, including strontium bismuth tantalate capacitors, were produced according to the method including step P48 of fig. 2. The procedure was the same as in example 2 except that the procedure of step P50 was carried out in accordance with the capacitor including the adhesion metal layer 36. A titanium metal as the bond metal portion 36 was sputtered to a thickness of 2000 angstroms onto the buffer layer 24 at a sputtering pressure of 0.0081 torr using a discharge voltage of 95 volts and a current of 0.53 amps. The metallization of the bond metal portion should be performed just prior to the metallization of the platinum layer at step P52. Buffer layer 24 is 500 angstroms thick and is covered by a titanium adhesion metal layer 36(200 angstroms) and a platinum layer 38(2000 angstroms).
EXAMPLE 4 formation of ferroelectric capacitor with a binding metal layer and without a buffer layer of layered superlattice material
A wafer including a ferroelectric capacitor without buffer layer 24 (fig. 1) is produced according to the general method of fig. 2. The procedure was as in example 3 except that steps P44 and P46 were not performed. The resulting capacitor 20 has no layer 24 but includes a 200 angstrom layer of adhesion metal 36 and a 2000 angstrom layer of platinum 38. In this wafer, the bottom electrode 26 is subjected to a first anneal in step P52.
Example 5
Forming a ferroelectric capacitor with a bonding metal layer and without a buffer layer of layered superlattice material without annealing the bottom electrode
A wafer including a ferroelectric capacitor without buffer layer 24 (fig. 1) was produced according to the method of example 4. Except that step P52 is not performed. The sequence of the layers of the resulting capacitor 20 is identical to that of the device of example 4, but before carrying out step P54, the electrode is not subjected to the first annealing step of step P52. The resulting capacitor 20 has no layer 24 but includes a 200 angstrom layer of adhesion metal 36 and a 2000 angstrom layer of platinum 38.
Example 6
Forming a ferroelectric capacitor with a bonding metal layer and without a buffer layer of layered superlattice material without annealing the bottom electrode
A wafer including a ferroelectric capacitor without buffer layer 24 (fig. 1) was produced according to the method of example 5. Except that only 100 angstroms (rather than 200 angstroms) of bond metal was sputtered in step P48. The resulting capacitor 20 has no layer 24 but includes a 200 angstrom layer of adhesion metal 36 and a 2000 angstrom layer of platinum 38.
Example 7
Scanning electron microscopy contrast of bottom electrode surface irregularities
Some shorts were observed in the square capacitor blocksof the wafer of example 4. Therefore, according to embodiment 4, up to step P52, steps P44 and P46 are omitted, and a second device is constituted. The electrode structure was studied under a Scanning Electron Microscope (SEM) at a magnification of 40,000. Fig. 4 depicts the observation of SEM. The electrode 24 includes a titanium bond metal layer 36 and a platinum layer 38. The electrode 26 is provided with an outermost surface 82 covered by sharp, irregular, spaced apart, pointed hillocks, such as hillocks 84 and 86. This will raise surface 82 a distance of about 900 angstroms. These hillocks are due to the different relative rates of thermal shrinkage between the bottom electrode 26 and the underlying substrate comprising layers 32 and 34. The layers expand upon heating. Upon cooling, the silicon substrates 32 and 34 shrink more than the metallization layers 36 and 38. Layer 36 is bonded to layer 34. The resulting interlayer stress forms hillocks.
The thin film ferroelectric layer is defined as a liquid deposited on surface 82 (as layer 24). The thickness of these films is preferably from 500-3000 angstroms. The hillock 82 and 84 have the effect of reducing the yield due to shorting of layer 28 and will also cause problems with the long term reliability of the device.
Similar SEM observations were made for other device samples produced according to examples 2 and 3, through the first annealing step of step P52. No sharp hillocks were observed in the electrodes of the other samples. Some surface irregularities are observed, i.e., small, rough surfaces, but it is estimated that these surfaces will raise the surface 82 by no more than about 50-80 angstroms. These smaller mounds, i.e., the electrodes of examples 2 and 3, were essentially free of hillocks, were negligible because they did not adversely affect the performance of the device.
Example 8
Comparative evaluation of capacitor devices
The wafers of examples 2, 3, 4, 5, and 6, each comprising ferroelectric SrBi about 1800 angstroms thick2Ta2O9A material. Uncompensated Sawyer-Tower circuits including a Hewlitt Packard 3314A signal generator and a Hewlitt Packard 54502A digital oscilloscopeThe machine performs a polarization hysteresis measurement. The respective measurement values were obtained at 20 ℃ using sine wave signals having a frequency of 10,000Hz, voltage amplitudes of 0.25, 0.5, 1.0, 1.5, 2.0, 2.5, 3.0, 4.0, 5.0, and 7.0V.
FIG. 5 depicts the 2Pr polarization value (. mu.c/cm) measured from the 3V start2) Bar graph of (2). Three each representing data obtained from selected capacitors on a given waferAverage of the points. For ease of identification of the test specimens, each is labeled with the letters A, B, C, D, and E, as well as with descriptive information.
The difference between bars a and B indicates that the addition of 200 angstroms of titanium adhesion metal layer 36 to buffered bottom electrode 24 reduced the measured 2Pr polarization by 5.6% relative to bar B. The measured 2Pr polarization will be 30% lower for the un-shorted capacitor producing bar C (no buffer layer) relative to bar B. Thus, the addition of buffer layer 26 is responsible for the observed increase in polarization relative to strip C.
The addition of titanium bonding metal will reduce the corresponding polarization. Bars D and E represent polarization measurements taken from the same capacitor, except that the capacitor of bar D contains 200 angstroms thick of bonding metal, while the capacitor of bar E contains 100 angstroms thick of bonding metal. Increasing the 100 angstrom thickness of the titanium bond metal (bar D) will decrease the polarization measured relative to bar E by 43%. The deleterious effects of titanium are overcome using buffer layer 26 (strips a and B).
Using the foregoing discussion, less preferred variations of the present invention may be provided. For example, the bond metal may include titanium oxide, tantalum oxide, or other known bond metals. In practice, the layer 26 is composed of many different layers, and not all layers need necessarily be the same type of layered superlattice material. Furthermore, the geometries and relative thicknesses depicted in fig. 1 and 4 are illustrative only. These figures are not intended to reflect models of actual material proportions, and their composition and thickness may vary considerably.
It will be apparent to those skilled in the art that modifications may be made to the preferred embodiments described above without departing from the scope and spirit of the invention. Therefore, to the full extent possible, the inventors reiterate that the scope of the invention is to be accorded the broadest permissible interpretation of the following claims.

Claims (13)

1. An integrated circuit device (20) comprising:
a base material (22) and a metal wiring layer (26),
said integrated circuit device is characterized in that the layer sequence (24) is composed of a material sandwiched between said substrate and said metal wiring layer, said layer sequence comprising at least one buffer layer made of a layered superlattice material, said layer sequence being substantially free of additional wiring layers.
2. The device of claim 1 wherein said layered superlattice material comprises strontium bismuth tantalate.
3. The device according to claim 2, wherein said substrate comprises a silicon-based layer (34) adjacent to the outermost layer of said sequence.
4. The device of claim 1, wherein said wiring layer comprises a bonding metal (36).
5. The device of claim 4, wherein said metal line layer comprises a noble metal (38).
6. A device according to claim 1, comprising a ferroelectric layer (28) on top of the line layer.
7. The device of claim 6 wherein said ferroelectric layer comprises a layered superlattice material.
8. A method of making an integrated circuit device (20), said method comprising the steps of providing (P40) a substrate (22) having a non-metallized outermost surface (34); the method is characterized in that it consists in,
depositing (P44, P46) a layered superlattice material precursor (36) on top of the substrate; and
depositing (P50) an electrode (38) on said layered superlattice material.
9. The method of claim 8, wherein said depositing step comprises: applying (P44) a liquid precursor to said substrate to form a precursor film, said liquid precursor comprising a metal in an amount effective to provide said layered superlattice material upon heat treatment of said precursor; drying (P46) the precursor film to obtain a layered superlattice material (36).
10. The method according to claim 8, characterized in that after said step of depositing said electrodes, said integrated circuit device is annealed (P52) at a temperature of at least 450 ℃.
11. The method of claim 10 wherein said temperature is at least about 600 ℃.
12. The method of claim 9, wherein said drying step comprises: drying said precursor at a temperature of up to about 450 ℃ for a time sufficient to remove substantially all of the volatile organic components from said film.
13. The method according to claim 8, characterized in that a second layered superlattice material (28) is structured (P54) on top of said electrodes.
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US11412504B2 (en) 2007-09-27 2022-08-09 Interdigital Patent Holdings, Inc. Method and apparatus to allocate radio resources for transmitting a message part in an enhanced RACH
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KR19990022075A (en) 1999-03-25
TW347577B (en) 1998-12-11
CA2223106A1 (en) 1996-12-19
JPH11511293A (en) 1999-09-28
WO1996041375A1 (en) 1996-12-19
EP0834196A1 (en) 1998-04-08

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