Methods for preparing ruthenium oxide films

The present invention provides methods for the preparation of ruthenium oxide films from liquid ruthenium complexes of the formula (diene)Ru(CO).sub.3 wherein "diene" refers to linear, branched, or cyclic dienes, bicyclic dienes, tricyclic dienes, fluorinated derivatives thereof, combinations thereof, or derivatives thereof additionally containing heteroatoms such as halide, Si, S, Se, P, As, N, or O.

FIELD OF THE INVENTION
 This invention relates to the preparation of ruthenium oxide films using
 chemical vapor deposition and liquid ruthenium precursors.
 BACKGROUND OF THE INVENTION
 Films of metals and metal oxides, particularly ruthenium films and oxides
 thereof, are becoming important for a variety of electronic and
 electrochemical applications. For example, high quality RuO.sub.2 thin
 films deposited on silicon wafers have recently gained interest for use in
 ferroelectric memories. Ruthenium films are generally unreactive to
 silicon and metal oxides, resistant to diffusion of oxygen and silicon,
 and are good conductors. Oxides of ruthenium also possess these
 properties, although perhaps to a different extent.
 Thus, films of ruthenium and oxides thereof have suitable properties for a
 variety of uses in integrated circuits. For example, they can be used in
 integrated circuits for electrical contacts. They are particularly
 suitable for use as barrier layers between the dielectric material and the
 silicon substrate in memory devices, such as ferroelectric memories.
 Furthermore, they may even be suitable as the plate (i.e., electrode)
 itself in capacitors.
 There are a wide variety of ruthenium compounds that can be used as
 precursors for the preparation of such films. Many are particularly well
 suited for use in chemical vapor deposition techniques. See, for example,
 U.S. Pat. No. 5,372,849 (McCormick et al.), which discloses the use of
 ruthenium compounds containing carbonyl ligands and other ligands.
 However, such compounds typically form dimers, which are less volatile and
 not as easily used in chemical vapor deposition techniques. Thus, there is
 a continuing need for methods for the preparation of ruthenium oxide films
 using chemical vapor deposition techniques.
 SUMMARY OF THE INVENTION
 The present invention provides methods for the preparation of ruthenium
 oxide films. In one embodiment, the method includes the steps of:
 providing a liquid precursor composition comprising one or more compounds
 of the formula (Formula I):
EQU (diene)Ru(CO).sub.3
 wherein: "diene" refers to linear, branched, or cyclic dienes, bicyclic
 dienes, tricyclic dienes, fluorinated derivatives thereof, derivatives
 thereof additionally containing heteroatoms such as halide, Si, S, Se, P,
 As, N, or O, or combinations thereof; vaporizing the liquid precursor
 composition to form vaporized precursor composition; and directing the
 vaporized precursor composition in combination with an oxidizing gas
 toward the semiconductor substrate or substrate assembly to form a
 ruthenium oxide film on a surface of the semiconductor substrate or
 substrate assembly. This method is particularly useful on complex
 structures, such as those containing one or more small high aspect ratio
 openings, which typically require excellent step coverage.
 Complexes of Formula I suitable for use in the methods of the present
 invention are neutral complexes and are liquids at a temperature within a
 range of about 20.degree. C. to about 50.degree. C. They can be used in
 flash vaporization, bubbling, microdroplet formation techniques, etc. As
 used herein, "liquid" refers to a neat liquid (a liquid at room
 temperature or a solid at room temperature that melts at an elevated
 temperature up to about 50.degree. C.).
 Methods of the present invention are particularly well suited for forming
 films on a surface of a semiconductor substrate or substrate assembly,
 such as a silicon wafer, having high surface area topology, such as high
 aspect ratio openings formed therein, but such gaps are not required, used
 in forming integrated circuits. It is to be understood that methods of the
 present invention are not limited to deposition on silicon wafers; rather,
 other types of wafers (e.g., gallium arsenide wafer, etc.) can be used as
 well. Also, the methods of the present invention can be used in
 silicon-on-insulator technology. Furthermore, substrates other than
 semiconductor substrates or substrate assemblies can be used in methods of
 the present invention. These include, for example, fibers, wires, etc. If
 the substrate is a semiconductor substrate or substrate assembly, the
 films can be formed directly on the lowest semiconductor surface of the
 substrate, or they can be formed on any of a variety of the layers (i.e.,
 surfaces) as in a patterned wafer, for example. Thus, the term
 "semiconductor substrate" refers to the base semiconductor layer, e.g.,
 the lowest layer of silicon material in a wafer or a silicon layer
 deposited on another material such as silicon on sapphire. The term
 "semiconductor substrate assembly" refers to the semiconductor substrate
 having one or more layers or structures formed thereon.
 In one embodiment of the invention, a method of manufacturing a
 semiconductor structure, preferably having a surface with one or more
 small high aspect ratio openings therein is provided. The method includes
 the steps of: providing a semiconductor substrate or substrate assembly,
 which is preferably at a temperature of about 130.degree. C. to about
 300.degree. C. (more preferably, at a temperature of about 140.degree. C.
 to about 180.degree. C.), and contained within a reaction chamber
 preferably having a pressure of about 10.sup.-3 torr to about 1 atmosphere
 (more preferably, having a pressure of about 0.1 torr to about 10 torr);
 providing a liquid precursor composition preferably at a temperature of
 about 20.degree. C. to about 50.degree. C. (more preferably, at a
 temperature of about 40.degree. C. to about 50.degree. C.), the precursor
 composition comprising one or more compounds of Formula I; vaporizing the
 liquid precursor composition to form vaporized precursor composition; and
 directing the vaporized precursor composition in combination with an
 oxidizing gas toward the semiconductor substrate or substrate assembly to
 form a ruthenium oxide film on the surface of the semiconductor substrate
 or substrate assembly having the one or more small high aspect ratio
 openings.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
 The present invention provides methods of forming a ruthenium oxide film
 using a chemical vapor deposition technique and one or more liquid
 ruthenium complexes. Specifically, the present invention is directed to
 methods of manufacturing a semiconductor device having a ruthenium oxide
 film thereon.
 The liquid ruthenium complexes are of the following formula (Formula I):
EQU (diene)Ru(CO).sub.3
 wherein: "diene" refers to linear, branched, or cyclic dienes, bicyclic
 dienes, tricyclic dienes, fluorinated derivatives thereof, derivatives
 thereof additionally containing heteroatoms such as halide, Si, S, Se, P,
 As, N, or O, or combinations thereof. Preferably, the diene ligands
 include about 5 to about 8 carbon atoms, and more preferably, about 6 to
 about 7 carbon atoms. These precursor complexes are described in
 Applicants' Assignees' copending patent application entitled "Precursor
 Chemistries for Chemical Vapor Deposition of Ruthenium and Ruthenium
 Oxide" having U.S. Ser. No. 09/141,236, dated Aug. 27, 1998, and filed on
 even date herewith now U.S. Pat. No. 6,063,705. They can be prepared
 according to methods described therein or according to methods described
 in Applicants' Assignees' copending patent application entitled "Methods
 for Preparing Ruthenium and Osmium Compounds" having U.S. Serial No.
 09/141,431, dated Aug. 27, 1998, filed on even date herewith now U.S. Pat.
 No. 5,962,716.
 Complexes of Formula I that are suitable for use in the present invention
 are neutral complexes and are liquids at room temperature or solids at
 room temperature that melt at an elevated temperature up to about
 50.degree. C. These complexes are suitable for use in chemical vapor
 deposition (CVD) techniques, such as flash vaporization techniques,
 bubbler techniques, and/or microdroplet techniques. Preferred embodiments
 of the complexes described herein are particularly suitable for low
 temperature CVD, e.g., deposition techniques involving substrate
 temperatures of about 100.degree. C. to about 400.degree. C.
 A preferred class of complexes include those that have a vapor pressure of
 greater than 0.1 torr at 50.degree. C. Examples of such compounds include
 (cyclohexadiene)Ru(CO).sub.3 and (cycloheptadiene)Ru(CO).sub.3.
 The precursor composition can be vaporized in the presence of one or more
 reaction gases and optionally one or more inert carrier gases to form a
 ruthenium oxide film. The inert carrier gas is typically selected from the
 group consisting of nitrogen, helium, argon, and mixtures thereof. In the
 context of the present invention, an inert carrier gas is one that is
 generally unreactive with the complexes described herein and does not
 interfere with the formation of a ruthenium oxide film. The reaction gas
 can be selected from a wide variety of oxidizing gases reactive with the
 complexes described herein, at least at a surface under the conditions of
 chemical vapor deposition. Examples of oxidizing gases include O.sub.2,
 N.sub.2 O, O.sub.3, NO, NO.sub.2, H.sub.2 O.sub.2, and H.sub.2 O. Various
 combinations of reaction gases and optional carrier gases can be used in
 the methods of the present invention to form films.
 Methods of the present invention are particularly well suited for forming
 highly pure ruthenium oxide films (preferably, at least about 95 atom-%
 pure, based on X-ray Photoelectron Spectroscopy (XPS), Auger Spectroscopy,
 or other methods) on a variety of substrates, such as a semiconductor
 wafer (e.g., silicon wafer, gallium arsenide wafer, etc.), glass plate,
 etc., and on a variety of surfaces of the substrates, whether it be
 directly on the substrate itself or on a layer of material deposited on
 the substrate as in a semiconductor substrate assembly. Methods of the
 present invention are particularly useful for depositing highly pure
 ruthenium oxide films on the surface of a semiconductor substrate or
 substrate assembly, such as a silicon wafer, having a high surface area
 topology, such as a surface (e.g., of an insulation layer) having high
 aspect ratio openings (i.e., gaps) formed therein. Small high aspect ratio
 openings typically have feature sizes or critical dimensions below about 1
 micron (e.g., the diameter or width of an opening is less than about 1
 micron), and more typically, about 0.3 micron to about 1 micron, and
 aspect ratios greater than about 1. Such aspect ratios are applicable to
 contact holes, vias, trenches, and a variety of other configurations. For
 example, a trench having an opening of 1 micron and a depth of 3 microns
 has an aspect ratio of 3. The present invention is particularly beneficial
 for forming diffusion barrier layers in small high aspect ratio features
 due to the use of CVD processes for forming conformal ruthenium oxide
 diffusion barrier layers over step structures. Typically, using methods of
 the present invention greater than about 80% step coverage can be
 achieved. This refers to the ratio of the thickness of the layer deposited
 on the bottom surface to that on the top surface.
 The ruthenium oxide film is deposited upon decomposition (typically,
 thermal decomposition) of one or more complexes of Formula I. Methods of
 the present invention can utilize various vapor deposition techniques,
 such as flash vaporization, bubbling, etc., optionally photo- or
 plasma-assisted (although photo- and plasma-assisted depositions do not
 typically provide good step overage). Examples of suitable CVD processes
 are generally discussed in Applicants' Assignees' copending patent
 application entitled "Precursor Chemistries or Chemical Vapor Deposition
 of Ruthenium and Ruthenium Oxide," having Ser. No. 09/141,236, dated Aug.
 27, 1998, and filed on even date herewith now U.S. Pat. No. 6,063,705, as
 well as in U.S. Pat. No. 5,372,849 (McCormick et al.), for example.
 A typical chemical vapor deposition (CVD) system that can be used to
 perform a process of the present invention is shown in FIG. 1. The system
 includes an enclosed chemical vapor deposition chamber 10, which may be a
 cold wall-type CVD reactor. Reduced pressure may be created in chamber 10
 using turbo pump 12 and backing pump 14. Preferably, the chamber pressure
 during deposition is about 10.sup.-3 torr to about atmospheric pressure,
 and most preferably, it is about 0.1 torr to about 10 torr. The pressure
 is chosen such that it produces good step coverage and deposition rates.
 One or more substrates 16 (e.g., semiconductor substrates or substrate
 assemblies) are positioned in chamber 10. A constant nominal temperature
 is established for the substrate, preferably at a temperature of about
 130.degree. C. to about 300.degree. C. For optimum step coverage,
 deposition rate, and formation of a film, the most preferred substrate
 temperature is about 140.degree. C. to about 180.degree. C. Substrate 16
 may be heated, for example, by an electrical resistance heater 18 on which
 substrate 16 is mounted. Other known methods of heating the substrate may
 also be utilized. For plasma- and photo-assisted CVD processes, however,
 the temperature of the substrate may be significantly lower.
 In this process, the precursor composition 40, which contains one or more
 complexes of Formula I, is stored in liquid form (a neat liquid at room
 temperature or at an elevated temperature if solid at room temperature) in
 vessel 42. The temperature of the liquid precursor composition is
 preferably about 20.degree. C. to about 50.degree. C., and more
 preferably, about 40.degree. C. to about 50.degree. C. The pressure within
 vessel 42 is typically similar to that within chamber 10. A source 44 of a
 suitable inert gas is pumped into vessel 42 and bubbled through the neat
 liquid (i.e., without solvent) picking up the precursor composition and
 carrying it into chamber 10 through line 45 and gas distributor 46.
 Additional inert carrier gas or reaction gas may be supplied from source
 48 as needed to provide the desired concentration of precursor composition
 and regulate the uniformity of the deposition across the surface of
 substrate 16. As shown, valves 50-55 are opened and closed as required.
 The reaction and optional carrier gases can be preheated if desired.
 Generally, the precursor composition is carried into the CVD chamber 10 at
 a flow rate of the carrier gas of about 10 sccm (standard cubic
 centimeters) to about 500 sccm, and preferably, at a flow rate of about
 100 sccm to about 400 sccm. A reaction gas (preferably, an oxidizing gas
 such as O.sub.2) is typically introduced into the CVD chamber 10 at a flow
 rate of about 10 sccm to about 1000 sccm, and preferably, at a flow rate
 of about 50 sccm to about 500 sccm. The semiconductor substrate is exposed
 to the precursor composition at a pressure of about 0.1 torr to about 10
 torr for a time of about 10 seconds to about 30 minutes depending on the
 desired thickness. In chamber 10, the precursor composition will form an
 adsorbed layer on the surface of the substrate 16. As the deposition rate
 is temperature dependent, increasing the temperature of the substrate will
 typically increase the rate of deposition. However, if step coverage is
 required, higher temperatures may become detrimental. Thus a substrate
 temperature is chosen to balance these two properties. Typically,
 desirable deposition rates are about 100 Angstroms/minute to about 1000
 Angstroms/minute. The carrier gas containing the precursor composition is
 terminated by closing valve 53.
 Alternatives to such methods include an approach wherein the precursor
 composition is heated and vapors are drawn off and controlled by a vapor
 mass flow controller, and a pulsed liquid injection method as described in
 "Metalorganic Chemical Vapor Deposition By Pulsed Liquid Injection Using
 An Ultrasonic Nozzle: Titanium Dioxide on Sapphire from Titanium (IV)
 Isopropoxide," by Versteeg, et al., Journal of the American Ceramic
 Society, 78, 2763-2768 (1995). The complexes of Formula I are also
 particularly well suited for use with vapor deposition systems, as
 described in copending application U.S. Ser. No. 08/720,710 entitled
 "Method and Apparatus for Vaporizing Liquid Precursor compositions and
 System for Using Same," filed on Oct. 2, 1996. Generally, one method
 described therein involves the vaporization of a precursor composition in
 liquid form. In a first stage, the precursor composition is atomized or
 nebulized generating high surface area microdroplets or mist. In a second
 stage, the constituents of the microdroplets or mist are vaporized by
 intimate mixture of the heated carrier gas. This two stage vaporization
 approach provides a reproducible delivery for precursor compositions
 (either in the form of a neat liquid or solid dissolved in a liquid
 medium) and provides reasonable deposition rates, particularly in device
 applications with small dimensions.
 Various combinations of carrier gases and/or reaction gases can be used in
 certain methods of the present invention. They can be introduced into the
 chemical vapor deposition chamber in a variety of manners, such as
 directly into the vaporization chamber or in combination with the
 precursor composition.
 Although specific vapor deposition processes are described by reference to
 FIG. 1, methods of the present invention are not limited to being used
 with the specific vapor deposition systems shown. Various CVD process
 chambers or reaction chambers can be used, including hot wall or cold wall
 reactors, atmospheric or reduced pressure reactors, as well as plasma
 enhanced reactors. Furthermore, methods of the present invention are not
 limited to any specific vapor deposition techniques.
 After deposition, the film can be further annealed to crystallize and/or
 further oxidize it if desired. This can be done in the CVD reaction
 chamber or not. To crystallize and/or densify a film, preferably, the
 annealing process is carried out in an inert gas, as described above for
 the carrier gases. To further oxidize a film, preferably, the annealing
 process is carried out in an oxidizing gas, as described above for the
 reaction gases. Preferably, the pressure of this post annealing process is
 about 0.5 torr to about 5 atmospheres. Preferably, the substrate
 temperature of this post annealing process is about 100.degree. C. to
 about 1000.degree. C., and more preferably, about 300.degree. C. to about
 800.degree. C.
 The use of the complexes and methods of forming films of the present
 invention are beneficial for a wide variety of thin film applications in
 semiconductor structures, particularly those requiring diffusion barriers.
 For example, such applications include capacitors and metallization
 layers, such as multilevel interconnects in an integrated circuit
 structure. Such structures are described, for example, in Applicants'
 Assignees' copending patent application entitled "Ruthenium Silicide
 Diffusion Barrier Layers and Methods of Forming Same," having Ser. No.
 09/141,240, dated Aug. 27, 1998, and filed on even date herewith now U.S.
 Pat. No. 6,197,628.
 The following examples are offered to further illustrate the various
 specific and preferred embodiments and techniques. It should be
 understood, however, that many variations and modifications may be made
 while remaining within the scope of the present invention.
 EXAMPLES
 Ruthenium Oxide Film Deposition Using (C.sub.6 H.sub.8)Ru(CO).sub.3
 The pale yellow precursor, (C.sub.6 H.sub.8)Ru(CO).sub.3, was added to a
 bubbler equipped with a dip tube and exit valve. The bubbler was connected
 to a CVD reactor. The bubbler was further connected to helium carrier gas
 introduced through a mass flow controller into the dip tube port of the
 bubbler. The bubbler was heated to about 40.degree. C. and all downstream
 connections to the chamber were heated to about 50.degree. C. to about
 60.degree. C. A silicon wafer having a layer of BPSG thereon (into which
 was etched various sizes of contact holes) was placed on a heated chuck
 inside the CVD reactor. Ruthenium deposition was carried out by heating
 the wafer to 150.degree. C. (as measured by a thermocouple placed on the
 surface of the wafer) and establishing a chamber pressure of 3 torr using
 a helium carrier flow of 25 sccm and an additional flow of oxygen (plumbed
 separately to the precursor delivery line) at 50 sccm. The helium carrier
 flow was diverted through the precursor bubbler for 4.0 minutes yielding a
 film that was later measured by SEM micrographs to be 8950 Angstroms
 thick. This corresponds to a deposition rate of 237 Angstroms/minute. The
 film was highly reflective and consisted of highly pure ruthenium oxide
 (as determined by XPS on blanket films). X-ray diffraction proved the
 films to be amorphous ruthenium oxide and SEM micrographs revealed better
 than 85% step coverage in holes nominally 0.3 micron to 1.0 micron in
 diameter and 2.5 microns deep.
 All patents, patent applications, and publications are herein incorporated
 by reference in their entirety, as if each were individually incorporated.
 The foregoing detailed description and examples have been given for
 clarity of understanding only. No unnecessary limitations are to be
 understood therefrom. The invention is not limited to the exact details
 shown and described, for variations obvious to one skilled in the art will
 be included within the invention defined by the claims.