Methods for preparing ruthenium metal films

The present invention provides methods for the preparation of ruthenium metal 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, derivatives thereof additionally containing heteroatoms such as halide, Si, S, Se, P, As, N, or 0, or combinations thereof.

FIELD OF THE INVENTION 
This invention relates to the preparation of ruthenium metal 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 metal films 
using chemical vapor deposition techniques. 
SUMMARY OF THE INVENTION 
The present invention provides methods for the preparation of ruthenium 
metal 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 toward the semiconductor substrate or 
substrate assembly to form a ruthenium metal 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, 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 150.degree. C. to about 
350.degree. C. (more preferably, at a temperature of about 200.degree. C. 
to about 250.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 toward the semiconductor 
substrate or substrate assembly to form a ruthenium metal 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 metal 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 metal 
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. 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. Ser. No. 09/141,431, dated Aug. 27, 1998, 
filed on even date herewith. 
Complexes of Formula I that are suitable for use in the present invention 
are neutral complexes and are liquids at room temperature or are 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/or one or more inert carrier gases to form a ruthenium 
metal film, if desired. Neither reaction gases nor carrier gases are 
required, however, as the precursor composition can be vaporized by 
heating a vessel containing the precursor connected to a deposition 
chamber and transported to a substrate by mass transport. 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 metal film. The reaction gas can be selected from a wide 
variety of reducing gases reactive with the complexes described herein, at 
least at a surface under the conditions of chemical vapor deposition. 
Examples of reducing gases include H.sub.2 and NH.sub.3. Various 
combinations of optional 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 metal 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 metal 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 metal 
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 metal 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 coverage). Examples of suitable CVD processes 
are generally discussed in Applicants' Assignees' copending patent 
application entitled "Precursor Chemistries for Chemical Vapor Deposition 
of Ruthenium and Ruthenium Oxide," having Ser. No. 09/141,236, dated Aug. 
27, 1998, and filed on even date herewith, 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 
150.degree. C. to about 350.degree. C. For optimum step coverage, 
deposition rate, and formation of a film, the most preferred substrate 
temperature is about 200.degree. C. to about 250.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. If desired, a reaction gas (preferably, a 
reducing gas) 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 density it if 
desired. This can be done in the CVD reaction chamber or not. To 
crystallize and/or density a film, preferably, the annealing process is 
carried out in an inert gas, as described above for the carrier 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 300.degree. C. to about 1000.degree. C., and 
more preferably, about 500.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 
(e.g., barriers for other metals or barriers to oxidation of Si, TiN, Ti, 
Al, and Cu). 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. 
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 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 200.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 nitrogen 
(plumbed separately to the precursor delivery line) at 50 sccm. The helium 
carrier flow was diverted through the precursor bubbler for 2.5 minutes 
yielding a film that was later measured by SEM micrographs to be 800 
Angstroms thick. This corresponds to a deposition rate of 320 
Angstroms/minute. The film was highly reflective and consisted of highly 
pure ruthenium (as determined by XPS on blanket films). X-ray diffraction 
proved the films to be polycrystalline ruthenium and SEM micrographs 
revealed better than 80% 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.