U.S. patent application number 10/657069 was filed with the patent office on 2004-03-11 for rhodium film and method of formation.
Invention is credited to Marsh, Eugene P., Uhlenbrock, Stefan.
Application Number | 20040048451 10/657069 |
Document ID | / |
Family ID | 25385902 |
Filed Date | 2004-03-11 |
United States Patent
Application |
20040048451 |
Kind Code |
A1 |
Marsh, Eugene P. ; et
al. |
March 11, 2004 |
Rhodium film and method of formation
Abstract
A method for the formation of rhodium films with good step
coverage is disclosed. Rhodium films are formed by a low
temperature atomic layer deposition technique using a first gas of
rhodium group metal precursor followed by an oxygen exposure. The
invention provides, therefore, a method for forming smooth and
continuous rhodium films which also have good step coverage and a
reduced carbon content.
Inventors: |
Marsh, Eugene P.; (Boise,
ID) ; Uhlenbrock, Stefan; (Boise, ID) |
Correspondence
Address: |
DICKSTEIN SHAPIRO MORIN & OSHINSKY LLP
2101 L STREET NW
WASHINGTON
DC
20037-1526
US
|
Family ID: |
25385902 |
Appl. No.: |
10/657069 |
Filed: |
September 9, 2003 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
10657069 |
Sep 9, 2003 |
|
|
|
10283316 |
Oct 30, 2002 |
|
|
|
10283316 |
Oct 30, 2002 |
|
|
|
09884997 |
Jun 21, 2001 |
|
|
|
6656835 |
|
|
|
|
Current U.S.
Class: |
438/478 ;
257/E21.009; 257/E21.011; 257/E27.087 |
Current CPC
Class: |
C23C 16/18 20130101;
H01L 28/65 20130101; C23C 16/045 20130101; C23C 16/16 20130101;
H01L 27/10811 20130101; H01L 27/10852 20130101; C23C 16/45553
20130101; H01L 28/60 20130101; H01L 28/55 20130101; C23C 16/4401
20130101 |
Class at
Publication: |
438/478 |
International
Class: |
C30B 001/00; H01L
021/20; H01L 021/36 |
Claims
What is claimed as new and desired to be protected by Letters
Patent of the United States is:
1. A method for conducting atomic layer deposition of rhodium on a
substrate comprising the steps of: positioning said substrate in a
deposition region of a reactor chamber; introducing a rhodium group
metal precursor into said reactor chamber to deposit a rhodium
monolayer on said substrate; and introducing oxygen into said
deposition region to remove carbon from said rhodium monolayer.
2. The method of claim 1, wherein said rhodium group metal
precursor comprises an organic rhodium group metal precursor having
the formula Ly[Rh]Yz, wherein L is independently selected from the
group consisting of neutral and anionic ligands; y is one of {1, 2,
3, 4}; Y is independently a pi-orbital bonding ligand selected from
the group consisting of CO, NO, CN, CS, N.sub.2, PX.sub.3,
PR.sub.3, P(OR).sub.3, AsX.sub.3, AsR.sub.3, As(OR).sub.3,
SbX.sub.3, SbR.sub.3, Sb(OR).sub.3, NH.sub.xR.sub.3-x, CNR, and
RCN, wherein R is an organic group, X is a halide and x is one of
{0, 1, 2, 3}; and z is one of {0, 1, 2, 3, 4}.
3. The method of claim 2, wherein said rhodium group metal
precursor is dicarbonyl cyclopentadienyl rhodium.
4. The method of claim 1, wherein said atomic layer deposition is
performed at a temperature of about 100.degree. C. to about
200.degree. C.
5. The method of claim 4, wherein said atomic layer deposition is
performed at a temperature of about 100.degree. C. to about
150.degree. C.
6. The method of claim 1, wherein said rhodium group metal
precursor is introduced into said reactor chamber at a rate of
about 0.1 to about 500 sccm.
7. The method of claim 1, wherein said rhodium group metal
precursor is introduced into said reactor chamber at a rate of
about 0.1 to about 5 sccm.
8. The method of claim 1, wherein said oxygen is introduced into
said reactor chamber at a rate of about 1 to about 500 sccm.
9. The method of claim 8, wherein said oxygen is introduced into
said reactor chamber at a rate of about 10 to about 200 sccm.
10. The method of claim 1 further comprising introducing a first
gas into said reactor chamber after said step of introducing said
rhodium group metal precursor and before said step of introducing
oxygen.
11. The method of claim 10, wherein said first gas is selected from
the group consisting of helium, argon and nitrogen.
12. The method of claim 10 further comprising introducing a second
gas into said reactor chamber after said step of introducing
oxygen.
13. The method of claim 12, wherein said second gas is selected
from the group consisting of helium, argon and nitrogen.
14. A method for conducting atomic layer deposition of rhodium on
an integrated circuit material layer, said method comprising the
steps of: positioning said material layer in a deposition region of
a reactor chamber; introducing dicarbonyl cyclopentadienyl rhodium
into said deposition region of said reactor chamber to deposit a
rhodium monolayer on said material layer at a temperature of about
100.degree. C. to about 200.degree. C.; and introducing oxygen into
said deposition region of said reactor chamber to remove carbon
atoms from said rhodium monolayer.
15. The method of claim 14, wherein said atomic layer deposition is
performed at a temperature of about 100.degree. C. to about
150.degree. C.
16. The method of claim 15, wherein said atomic layer deposition is
performed at a temperature of about 100.degree. C.
17. The method of claim 14, wherein said dicarbonyl
cyclopentadienyl rhodium is introduced into said reactor chamber at
a rate of about 0.1 to about 500 sccm.
18. The method of claim 17, wherein said dicarbonyl
cyclopentadienyl rhodium is introduced into said reactor chamber at
a rate of about 5 sccm.
19. The method of claim 14, wherein said oxygen is introduced into
said reactor chamber at a rate of about 10 to about 500 sccm.
20. The method of claim 19, wherein said oxygen is introduced into
said reactor chamber at a rate of about 50 sccm.
21. The method of claim 14 further comprising introducing helium
into said reactor chamber after said step of introducing said
dicarbonyl cyclopentadienyl rhodium and before said step of
introducing oxygen, at a rate of about 50 sccm and for about 5
seconds.
22. The method of claim 14 further comprising introducing helium
into said reactor chamber after said step of introducing oxygen, at
a rate of about 50 sccm and for about 5 seconds.
23. A method for conducting atomic layer deposition of rhodium on
an integrated circuit material layer at a temperature of about
100.degree. C. to about 200.degree. C., comprising the steps of:
positioning said material layer in a deposition region of a reactor
chamber; introducing dicarbonyl cyclopentadienyl rhodium into said
reactor chamber at a rate of about 0.1 to about 500 sccm and for
about 0.1 to about 30 seconds to deposit a rhodium monolayer on
said material layer; introducing a first purge gas at a rate of
about 10 to about 200 sccm and for about 0.1 to about 10 seconds;
introducing oxygen into said deposition region at a rate of about
10 to about 200 sccm and for about 0.1 to about 10 seconds, and
removing carbon atoms from said rhodium monolayer; and introducing
a second purge gas at a rate of about 10 to about 200 sccm and for
about 0.1 to about 10 seconds.
24. The method of claim 23, wherein said atomic layer deposition of
rhodium is conducted at a temperature of about 100.degree. C.
25. The method of claim 23, wherein said dicarbonyl
cyclopentadienyl rhodium is introduced into said reactor chamber at
a rate of about 5 sccm and for about 5 seconds.
26. The method of claim 23, wherein said oxygen is introduced into
said reactor chamber at a rate of about 50 sccm and for about 5
seconds.
27. The method of claim 23, wherein said first and said second
purge gases are each introduced into said reactor chamber at a rate
of about 50 sccm and for about 5 seconds.
28. A method of forming a capacitor comprising the steps of:
forming a first and second electrode; forming a dielectric layer
between said first and second electrode; and wherein at least one
of said first and second electrode is formed by conducting atomic
layer deposition of a rhodium group metal precursor.
29. The method of claim 28, wherein said rhodium group metal
precursor comprises an organic rhodium group metal precursor having
the formula Ly[Rh]Yz, wherein L is independently selected from the
group consisting of neutral and anionic ligands; y is one of {1, 2,
3, 4}; Y is independently a pi-orbital bonding ligand selected from
the group consisting of CO, NO, CN, CS, N.sub.2, PX.sub.3,
PR.sub.3, P(OR).sub.3, AsX.sub.3, AsR.sub.3, As(OR).sub.3,
SbX.sub.3, SbR.sub.3, Sb(OR).sub.3, NH.sub.xR.sub.3-x, CNR, and
RCN, wherein R is an organic group, X is a halide and x is one of
{0, 1, 2, 3}; and z is one of {0, 1, 2, 3, 4}.
30. The method of claim 29, wherein said rhodium group metal
precursor is dicarbonyl cyclopentadienyl rhodium.
31. The method of claim 28, wherein said atomic layer deposition is
performed at a temperature of about 100.degree. C. to about
200.degree. C.
32. The method of claim 28, wherein said rhodium group metal
precursor is introduced into a reactor chamber at a rate of about
0.1 to about 500 sccm.
33. The method of claim 28, wherein said rhodium group metal
precursor is introduced into said reactor chamber at a rate of
about 0.1 to about 5 sccm.
34. The method of claim 32 further comprising the step of
introducing oxygen into said reactor chamber at a rate of about 10
to about 500 sccm.
35. The method of claim 34, wherein said oxygen is introduced into
said reactor chamber at a rate of about 10 to about 200 sccm.
36. The method of claim 34 further comprising introducing a first
gas into said reactor chamber after said step of introducing said
rhodium group metal precursor and before said step of introducing
oxygen.
37. The method of claim 36, wherein said first gas is selected from
the group consisting of helium, argon and nitrogen.
38. The method of claim 36 further comprising introducing a second
gas into said reactor chamber after said step of introducing
oxygen.
39. The method of claim 38, wherein said second gas is selected
from the group consisting of helium, argon and nitrogen.
40. A method of forming a rhodium upper electrode of a capacitor in
an insulating layer of a substrate, comprising the steps of:
forming a conductive layer; forming a dielectric layer over said
conductive layer; and forming a rhodium layer by atomic layer
deposition at a temperature of about 100.degree. C. to about
200.degree. C. over said dielectric layer.
41. The method of claim 40, wherein said step of forming said
rhodium layer by atomic layer deposition comprises introducing said
substrate in a deposition region of a reactor chamber, and
introducing dicarbonyl cyclopentadienyl rhodium into said reactor
chamber.
42. The method of claim 41, wherein said dicarbonyl
cyclopentadienyl rhodium is introduced at a rate of about 0.1 sccm
to about 500 sccm.
43. The method of claim 41, wherein said dicarbonyl
cyclopentadienyl rhodium is introduced into said reactor chamber at
a rate of about 0.1 sccm to about 5 sccm.
44. The method of claim 41, wherein said step of forming said
rhodium layer by atomic layer deposition further comprises
introducing oxygen into said reactor chamber.
45. The method of claim 44, wherein said oxygen is introduced into
said reactor chamber at a rate of about 10 to about 500 sccm.
46. The method of claim 44, wherein said oxygen is introduced into
said reactor chamber at a rate of about 10 to about 200 sccm.
47. A method of forming a rhodium lower electrode of a capacitor in
an insulating layer of a substrate, comprising the steps of:
forming a rhodium layer by atomic layer deposition at a temperature
of about 100.degree. C. to about 200.degree. C.; forming a
dielectric layer over said rhodium layer; and forming a conductive
layer over said dielectric layer.
48. The method of claim 47, wherein said step of forming said
rhodium layer by atomic layer deposition comprises introducing said
substrate in a deposition region of a reactor chamber, and
introducing dicarbonyl cyclopentadienyl rhodium into said reactor
chamber.
49. The method of claim 48, wherein said dicarbonyl
cyclopentadienyl rhodium is introduced at a rate of about 0.1 sccm
to about 500 sccm.
50. The method of claim 49, wherein said dicarbonyl
cyclopentadienyl rhodium is introduced into said reactor chamber at
a rate of about 0.1 sccm to about 5 sccm.
51. The method of claim 48, wherein said step of forming said
rhodium layer by atomic layer deposition further comprises
introducing introducing oxygen into said reactor chamber.
52. The method of claim 51, wherein said oxygen is introduced into
said reactor chamber at a rate of about 10 to about 500 sccm.
53. The method of claim 52, wherein said oxygen is introduced into
said reactor chamber at a rate of about 10 to about 200 sccm.
54. A method of fabricating a DRAM cell container capacitor
comprising the steps of: forming a first and second conductive
layer; and forming a dielectric between said first and second
conductive layer, at least one of said first and second conductive
layer being a rhodium layer formed by atomic layer deposition of
dicarbonyl cyclopentadienyl rhodium at a temperature of about
100.degree. C. to about 200.degree. C. and for about 5 seconds.
55. A capacitor comprising: a first electrode and a second
electrode; a dielectric provided between said first electrode and
said second electrode; and at least one of said first and second
electrode comprising a continuous ALD deposited rhodium film with
reduced carbon content.
56. A capacitor comprising: a first electrode and a second
electrode; a dielectric provided between said first electrode and
said second electrode; and at least one of said first and second
electrode comprising a reduced-carbon rhodium film formed by
rhodium atomic layer deposition at a temperature of about
100.degree. C. to about 200.degree. C.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to the field of semiconductor
integrated circuits and, in particular, to a novel method for
forming high quality rhodium (Rh) films.
BACKGROUND OF THE INVENTION
[0002] Thin film technology in the semiconductor industry requires
thin deposition layers, increased step coverage, large production
yields, and high productivity, as well as sophisticated technology
and equipment for coating substrates used in the fabrication of
various devices. For example, process control and uniform film
deposition directly affect packing densities for memories that are
available on a single chip or device. Thus, the decreasing
dimensions of devices and the increasing density of integration in
microelectronics circuits require greater uniformity and process
control with respect to layer thickness.
[0003] Various methods for depositing thin films of complex
compounds, such as metal oxides, ferroelectrics or superconductors,
are known in the art. Current technologies include mainly RF
sputtering, spin coating processes, and chemical vapor deposition
(CVD), with its well-known variation called rapid thermal chemical
vapor deposition (RTCVD). These technologies, however, have some
disadvantages. For example, the RF sputtering process yields poor
conformality, while the spin deposition of thin films is a complex
process, which generally involves two steps: an initial step of
spinning a stabilized liquid source on a substrate usually
performed in an open environment, which undesirably allows the
liquid to absorb impurities and moisture from the environment; and
a second drying step, during which evaporation of organic
precursors from the liquid may leave damaging pores or holes in the
thin film. Further, both CVD and RTCVD are flux-dependent processes
requiring uniform substrate temperatures and uniform distribution
of the chemical species in the process chamber.
[0004] Promising candidates for materials for capacitor electrodes
in IC memory structures include noble metals, such as platinum
(Pt), palladium (Pd), iridium (Ir), ruthenium (Ru), rhodium (Rh)
and osmium (Os), as wells as their conductive oxides (for example,
ruthenium oxide (RuO.sub.2), iridium oxide (IrO.sub.2) or osmium
oxide (OsO.sub.2), among others). Although the above-mentioned
noble metals are all physically and chemically similar, platinum
(Pt) is most commonly used because platinum has a very low
reactivity and a high work function that reduces the leakage
current in a capacitor. Platinum is also inert to oxidation, thus
preventing oxidation of electrodes which would further decrease the
capacitance of storage capacitors. The use of platinum as the
material of choice for capacitor electrodes poses, however,
problems. One of them arises from the difficulty of etching and/or
polishing platinum.
[0005] Recently, particular attention has been accorded to rhodium
(Rh) as an alternative material to platinum because rhodium has
excellent electrical properties which are the result of good
electrical conductivity, good conductivity, good heat-transfer
properties and high work function. Rhodium films are currently
deposited by sputtering, CVD or RTCVD, among others. Although the
CVD processing technologies afford good step coverage, as the
geometries of the future generations of semiconductors become
extremely aggressive, these processing technologies will not be
able to afford better step coverage, that is a high degree of
thickness and/or uniformity control over a complex topology for
thin films of such future generation of semiconductors.
[0006] Accordingly, there is a need for an improved carbon-free
rhodium film with good step coverage and improved electrical
properties, as well as a new and improved method for forming such
continuous and smooth rhodium films with good step coverage.
BRIEF SUMMARY OF THE INVENTION
[0007] The present invention provides a novel method for the
formation of rhodium films with good step coverage which may be
used as top and/or lower plate electrodes for a capacitor. Rhodium
films are formed by a low temperature atomic layer deposition
technique using a rhodium gas precursor followed by an oxygen
exposure. The invention provides, therefore, a method for forming
smooth and continuous rhodium films which also have good step
coverage.
BRIEF DESCRIPTION OF THE DRAWINGS
[0008] FIG. 1 is a conventional time diagram for atomic layer
deposition gas pulsing.
[0009] FIG. 2 is an elevation view of an atomic layer deposition
(ALD) apparatus used for the formation of a rhodium film according
to the present invention.
[0010] FIG. 3 illustrates a schematic cross-sectional view of a
DRAM device on which an upper capacitor rhodium plate will be
formed according to a method of the present invention.
[0011] FIG. 4 illustrates a schematic cross-sectional view of the
DRAM device of FIG. 4 at a stage of processing subsequent to that
shown in FIG. 4.
[0012] FIG. 5 is an ink copy of a scanning electron microscopic
(SEM) micrograph of a rhodium film deposited by a method of the
present invention.
[0013] FIG. 6 is an illustration of a computer system having a
memory device including a rhodium film formed according to a method
of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
[0014] In the following detailed description, reference is made to
various specific embodiments in which the invention may be
practiced. These embodiments are described with sufficient detail
to enable those skilled in the art to practice the invention, and
it is to be understood that other embodiments may be employed, and
that structural, logical, and electrical changes may be made.
[0015] The term "substrate" used in the following description may
include any semiconductor-based structure. Structure must be
understood to include silicon, silicon-on insulator (SOI),
silicon-on sapphire (SOS), doped and undoped semiconductors,
epitaxial layers of silicon supported by a base semiconductor
foundation, and other semiconductor structures. The semiconductor
also need not be silicon-based. The semiconductor could be
silicon-germanium, germanium, or gallium arsenide. When reference
is made to a substrate in the following description, previous
process steps may have been utilized to form regions or junctions
in or on the base semiconductor or foundation.
[0016] The term "rhodium" is intended to include not only elemental
rhodium, but rhodium with other trace metals or in various alloyed
combinations with other metals as known in the semiconductor art,
as long as such rhodium alloy is conductive.
[0017] The present invention provides a novel method for the
formation of carbon-free rhodium films with good step coverage
which could be used, for example, as top and/or lower plate
electrodes for capacitors, as fuse elements or as seed layers for
electroplating. According to an exemplary embodiment of the
invention, rhodium films are formed by a low temperature atomic
layer deposition technique using a gas precursor of dicarbonyl
cyclopentadienyl rhodium (I) [CpRh(CO.sub.2)] in an oxygen
exposure. The invention provides, therefore, a method for forming
smooth and continuous rhodium films which also have good step
coverage and reduced carbon content.
[0018] Continuous and smooth rhodium films formed according to
embodiments of the present invention employ atomic layer deposition
(ALD) processes for achieving good step coverage. For a better
understanding of the formation of the ultra-uniform thin rhodium
layers according to the present invention, the ALD technique will
be outlined below.
[0019] Generally, the ALD technique proceeds by chemisorption at
the deposition surface of the substrate. The ALD process is based
on a unique mechanism for film formation, that is the formation of
a saturated monolayer of a reactive precursor molecules by
chemisorption, in which reactive precursors are alternately pulsed
into a deposition chamber. Each injection of a reactive precursor
is separated by an inert gas purge or a pump cycle. Each injection
also provides a new atomic layer on top of the previously deposited
layers to form a uniform layer of solid film. This cycle is
repeated according to the desired thickness of the film.
[0020] This unique ALD mechanism for film formation has several
advantages over the current CVD technology mentioned above. First,
because of the flux-independent nature of ALD, the design of the
reactor is simple because the thickness of the deposited layer is
independent of the amount of precursor delivered after the
formation of the saturated monolayer. Second, interaction and high
reactivity of precursor gases in the gas phase above the wafer is
avoided since chemical species are introduced independently, rather
than together, into the reactor chamber. Third, ALD allows almost a
perfect step coverage over complex topography as a result of the
self-limiting surface reaction.
[0021] To illustrate the general concepts of ALD, which will be
further used in describing the method of the present invention,
reference is now made to the drawings, where like elements are
designated by like reference numerals. FIG. 1 illustrates one
complete cycle in the formation of an AB solid material by atomic
layer deposition. A first species Ax is deposited over an initial
surface of a substrate as a first monolayer. A second species By is
next applied over the Ax monolayer. The By species reacts with Ax
to form compound AB. The Ax, By layers are provided on the
substrate surface by first pulsing the first species (also called
first precursor gas) Ax and then the second species (also called
second precursor gas) By into the region of the surface. If thicker
material layers are desired, the sequence of depositing Ax and By
layers can be repeated as often as needed until a desired thickness
is reached. Between each of the precursor gas pulses, the process
region is purged with an inert gas or evacuated.
[0022] As illustrated in FIG. 1, a first pulse of precursor Ax is
initially generated and followed by a transition time of no gas
input. Subsequently, an intermediate pulse of a purge gas takes
place, followed by another transition time. Precursor gas By is
then pulsed, another transition time follows, and then a purge gas
is pulsed again. Thus, a full complete cycle incorporates one pulse
of precursor Ax and one pulse of precursor By, each precursor pulse
being separated by a purge gas pulse.
[0023] The cycle described above for the formation of an AB solid
material by atomic layer deposition is employed in the formation of
a rhodium film in a deposition apparatus, which is illustrated in
FIG. 2. Such an apparatus includes a reactor chamber 10, which may
be constructed as a quartz container, and a suscepter 14 which
holds one or a plurality of semiconductor substrates, for example,
semiconductor substrate 20, and which is mounted on the upper end
of a shaft 28. Mounted on one of the chamber defining walls, for
example on upper wall 30 of the reactor chamber 10, are reactive
gas supply inlets 16a and 16b, which are further connected with
reactive gas supply sources 17a, 17b supplying first and second gas
precursors, respectively. An exhaust outlet 18, connected with an
exhaust system 19, is situated on an opposite lower wall 32 of the
reactor chamber 10. A purge gas inlet 26, connected to a purge gas
system, is also provided on the upper wall 30 and in between the
reactive gas supply inlets 16a and 16b.
[0024] According to an embodiment of the present invention, a first
reactive gas precursor 23 (FIG. 2) of an organic rhodium group
metal precursor is supplied into the reactor chamber 10 through the
reactive gas inlet 16a. The first reactive gas precursor 23 flows
at a right angle to the semiconductor 20 and reacts with its
surface portion to form a rhodium monolayer. The first reactive gas
precursor 23 (FIG. 2) of an organic rhodium group metal precursor
may be any suitable organic compound which allows rhodium to
deposit from the gas onto the surface of the semiconductor
substrate 20. Thus, the organic rhodium group metal precursor may
be, for example, an organic rhodium (I) group metal precursor and
having at least one rhodium source compound selected from the group
consisting of compounds of the formula (1):
Ly[Rh]Yz (1)
[0025] wherein:
[0026] L is independently selected from the group consisting of
neutral and anionic ligands;
[0027] y is one of {1, 2, 3, 4} and more preferably 1;
[0028] Y is independently a pi-orbital bonding ligand selected from
the group consisting of CO, NO, CN, CS, N.sub.2, PX.sub.3,
PR.sub.3, P(OR).sub.3, AsX.sub.3, AsR.sub.3, As(OR).sub.3,
SbX.sub.3, SbR.sub.3, Sb(OR).sub.3, NH.sub.xR.sub.3-x, CNR, and
RCN, wherein R is an organic group, X is a halide and x is one of
(0, 1, 2, 3 ; and
[0029] z is one of {0, 1, 2, 3, 4}, preferably one of {1, 2, 3, 4},
more preferably one of {2, 3} and most preferably 2.
[0030] Thus, and in accordance with formula (1) outlined above, the
first reactive gas precursor 23 (FIG. 2) of an organic rhodium
group metal precursor may include, for example, rhodium
beta-diketonates, rhodium acetylacetonate, alkyl rhodium dienes, or
compounds including a carbon ring, for example, rhodium
cyclopentadienyl derivatives such as dicarbonyl cyclopentadienyl
rhodium [CpRh(CO).sub.2], among many others.
[0031] In an exemplary embodiment, vapors of dicarbonyl
cyclopentadienyl rhodium [CpRh(CO).sub.2] are used as the first
pulse of precursor 23 at a temperature of about 100.degree. C. to
about 200.degree. C., more preferably of about 100.degree. C. to
about 150.degree. C., at a rate of about 0.1 to 500 standard cubic
centimeters per minute ("sccm"), more preferably of about 0.1 to 5
sccm, and for a duration of about 0.1 second to about 30 seconds,
more preferably of about 0.2 second to about 10 seconds.
[0032] Although the reactions for the atomic layer deposition of
rhodium are not known in the art, it is believed that
organo-metallic rhodium precursor molecules chemisorb to the
semiconductor substrate 20 forming an organorhodium monolayer. The
surface is dosed long enough to ensure surface saturation. Thus,
the organo-metallic rhodium precursor molecules attach to the
initial surface of the semiconductor substrate 20 to form a
complete and saturated organorhodium monolayer. Any excess rhodium
gas precursor 23 in the reactor chamber 10 is then removed by
either purging or evacuating the reactor chamber 10.
[0033] In an exemplary embodiment, after the first saturated
organorhodium monolayer is formed and any of the remaining
unreacted gas precursor 23 is completely exhausted through the
exhaust inlet 18, a first purge gas 36 (FIG. 2) is then introduced
into the reactor chamber 10 through the inlet 26. Although the
present invention will be described with reference to the use of a
purge gas, such as the first purge gas 36, it must be understood
that the invention also contemplates the complete evacuation of the
remaining unreacted gas precursor 23, by using a vacuum pump, for
example, and without employing a purge gas.
[0034] The first purge gas 36 may be introduced into the reactor
chamber 10 after about 1 second from the complete exhaustion of the
unreacted rhodium precursor 23, and for a purge duration of about
0.1 second to about 10 seconds. The first purge gas 36 is fed into
the reactor chamber 10 at a rate of about 0 to about 1,000 sccm,
more preferably of about 10 to 500 sccm, most preferably of about
10 to 200 sccm. The flow rate of the first purge gas 36 into the
reactor chamber 10 is determined based on the rhodium group metal
to be deposited, as well as on the substrate on which rhodium is
deposited and the temperature and pressure at which the atomic
layer deposition takes place. Preferable gases for the first purge
gas 36 are helium (He), argon (Ar), or nitrogen (N) among others,
with helium most preferred.
[0035] The substrate 20, with the deposited saturated
organo-rhodium monolayer, is then exposed to a second reactive gas
precursor 25, shown in FIG. 2. The second reactive gas precursor 25
is supplied into the reactor chamber 10 through the reactive gas
inlet 16a and also flows at a right angle onto the semiconductor 20
and the saturated organo-rhodium monolayer.
[0036] According to the present invention, the second reactive gas
precursor 25 is oxygen (O.sub.2) which is fed into the reactor
chamber 10 at a rate of about 1 to 500 sccm, most preferably of
about 10 to 200 sccm, and for a duration of about 0.1 second to
about 30 seconds, more preferably of about 1 second to about 10
seconds, which is carefully tailored according to the other ALD
parameters so that saturation of the available surface sites is
reached, and the organic component of the organo-rhodium monolayer
is completely converted to a metallic rhodium film. The flow rate
of oxygen is also determined based on the rhodium group metal to be
deposited, as well as on the substrate on which rhodium is
deposited and the temperature and pressure at which the atomic
layer deposition takes place.
[0037] Although the precise details of the formation of the rhodium
monolayer are unknown, it is believed that oxygen facilitates
removal of the cyclopentadienyl (Cp) ring of the dicarbonyl
cyclopentadienyl rhodium [CpRh(CO).sub.2] gas precursor as well as
the removal or the oxidation of carbonyl groups, such as (CO)
groups, to (CO.sub.2) groups. Thus, along with the (CO.sub.2)
groups, the carbon from the deposited saturated organo-rhodium
monolayer is removed and a pure metallic rhodium layer forms on the
surface of the substrate 20. This way, carbon contamination is
greatly reduced as carbon is removed with the use of oxygen.
Accordingly, the rhodium layer formed by ALD at low temperatures
has a pure metallic composition, improved smoothness and uniformity
and an extremely high step coverage.
[0038] Any remaining reactive oxygen precursor 25 in the reactive
chamber 10 is exhausted through the exhaust inlet 18. An
intermediate pulse of a second purge gas 37 is then introduced into
the reactor chamber 10 through the inlet 26. The second purge gas
37 may be introduced into the reactor chamber 10 for a purge
duration of about 0.1 second to about 10 seconds. The second purge
gas 37 is fed into the reactor chamber 10 at a rate of about 0 to
about 1,000 sccm, more preferably of about 10 to 500 sccm, most
preferably of about 10 to 200 sccm. The flow rate of the second
purge gas 37 into the reactor chamber 10 is determined based on
rhodium group metal to be deposited, as well as on the substrate on
which rhodium is deposited and the temperature and pressure at
which the atomic layer deposition takes place. Preferable gases for
the second purge gas 37 are helium (He), argon (Ar), or nitrogen
(N) among others, with helium most preferred. As noted above, the
invention is not limited to the use of a purge gas, such as the
second purge gas 37, and the invention also contemplates the
complete evacuation of the reactive oxygen precursor 25 instead of
employing a purge gas.
[0039] As explained above, this cycle could be repeated for a
number of times, according to the desired thickness of the
deposited rhodium film. Assuming that 1 Angstrom of rhodium film is
deposited per one ALD cycle, then the formation of a rhodium film
with a thickness of about 300 Angstroms, for example, will require
about 300 ALD cycles.
[0040] The low temperature atomic layer rhodium deposition of the
present invention is useful for forming rhodium seed layers for
electroplating, catalyst beds in industrial chemical processes, for
example in coating applications requiring catalytic converters, or
in forming rhodium bond pads, among others. Further, the low
temperature atomic layer rhodium deposition forms rhodium films
with good step coverage onto the surface of any substrate. While
the method is useful for rhodium deposition onto any surface, the
method has particular importance for rhodium films formed on
surfaces used in integrated circuits. For example, rhodium films
with good step coverage may be formed according to the present
invention onto borophosphosilicate (BPSG), silicon, polysilica
glass (PSG), titanium, oxides, polysilicon or suicides, among
others. The invention is further explained with reference to the
formation of a rhodium electrode, for example an upper capacitor
plate or upper electrode, of a metal-insulator-metal (MIM)
capacitor.
[0041] Although the present invention will be described below with
reference to a metal-insulator-metal (MIM) capacitor (FIGS. 3-4)
that has an upper capacitor plate 77 (FIG. 4) formed of rhodium
deposited by low temperature ALD, it must be understood that the
present invention is not limited to MIM capacitors having a rhodium
upper capacitor plate, but it also covers other capacitor
structures, such as, for example, conventional capacitors or
metal-insulator-semiconductor (MIS) capacitors used in the
fabrication of various IC memory cells, as long as one or both of
the capacitor plates are formed of rhodium deposited by low
temperature ALD.
[0042] Referring now to the drawings, FIG. 3 shows a portion 100 of
a conventional DRAM memory at an intermediate stage of the
fabrication. A pair of memory cells having respective access
transistors are formed on a substrate 50 having a doped well 52,
which is typically doped to a predetermined conductivity, e.g.
P-type or N-type depending on whether NMOS or PMOS transistors will
be formed. The structure further includes field oxide regions 53,
conventional doped active areas 54, and a pair of gate stacks 55,
all formed according to well-known semiconductor processing
techniques. The gate stacks 55 include an oxide layer 56, a
conductive gate layer 57, spacers 59 formed of an oxide or a
nitride, and a cap 58 which can be formed of an oxide, an
oxide/nitride, or a nitride. The conductive gate layer 57 could be
formed, for example, of a layer of doped polysilicon, or a
multi-layer structure of polysilicon/WSi.sub.x,
polysilicon/WN.sub.x/W or polysilicon/TiSi.sub.2.
[0043] Further illustrated in FIG. 3 are two MIM capacitors 70, at
an intermediate stage of fabrication and formed in an insulating
layer 69, which are connected to active areas 54 by two respective
conductive plugs 60. The DRAM memory cells also include a bit line
contact 62, which is further connected to the common active area 54
of the access transistors by another conductive plug 61. The access
transistors respectively write charge into and read charge from
capacitors 70, to and from the bit line contact 62.
[0044] The processing steps for the fabrication of the MIM
capacitor 70 (FIG. 3) provided in the insulating layer 69 include a
first-level metallization 71, a dielectric film 72 deposition, and
a second-level metallization. For example, FIG. 3 illustrates the
MIM capacitor 70 after formation of the dielectric film 72. As
such, a lower capacitor plate 71, also called a bottom or lower
electrode, has already been formed during the first-level
metallization. The material for the lower capacitor plate 71 is
typically selected from the group of metals, or metal compositions
and alloys, including but not limited to osmium (Os), platinum
(Pt), rhodium (Rh), ruthenium (Ru), palladium (Pd), iridium (Ir),
and their alloys.
[0045] Following the first-level deposition, the first level
metallization is removed from the top surface regions typically by
resist coat and CMP or dry etch. A high dielectric film 72 (FIG. 3)
is formed over the lower capacitor plate 71. The most common high
dielectric material used in MIM capacitors is tantalum oxide
(Ta.sub.2O.sub.5), but other materials such as strontium titanate
(SrTiO.sub.3), alumina (Al.sub.2O.sub.3), barium strontium titanate
(BaSrTiO.sub.3), or zirconium oxide (ZrO.sub.2) may also be used.
Further, perovskite oxide dielectric films of the paraelectric
type, such as lead titanate (PbTiO.sub.3) or lead zirconite
(PbZrO.sub.3), are also good candidates for high dielectric film
materials even if their dielectric constant is slightly lower than
that of the above mentioned dielectrics. As known in the art, the
thickness of the high dielectric film 72 determines the capacitance
per unit area of the MIM capacitor 70.
[0046] After the formation of the dielectric film 72 (FIG. 3), a
second-level metallization is performed during which a rhodium film
77 (FIG. 4) is formed by the low temperature ALD method described
in detail above, to complete the formation of the MIM capacitor 70.
Thus, the substrate 50 is introduced in the reactor chamber 10 of
the apparatus of FIG. 2 so that a first reactive gas precursor 23
(FIG. 2) of an organic rhodium metal group precursor is pulsed over
the substrate 50. According to the present invention, the first
reactive gas precursor 23 (FIG. 2) of an organic rhodium group
metal precursor may be, for example, any suitable organic compound
with formula Ly[Rh]Yz, which allows rhodium to deposit from the gas
onto the surface of the semiconductor substrate 50 and having at
least one rhodium source compound selected from the group
consisting of compounds of the formula (1) outlined above. In a
preferred embodiment, vapors of dicarbonyl cyclopentadienyl rhodium
[CpRh(CO.sub.2)] are used as the first pulse of precursor 23 at a
temperature of about 100.degree. C. and for about 5 seconds. The
surface of the substrate 50 is dosed long enough to ensure
saturation and to form an organ-rhodium monolayer that is
saturated.
[0047] After any of the remaining unreacted [CpRh(CO.sub.2)] is
completely exhausted through the exhaust inlet 18 (FIG. 2), a first
purge gas 36 is then introduced into the reactor chamber 10 through
the inlet 26. In an exemplary embodiment, the first purge gas 36 is
helium which is introduced into the reactor chamber 10 after the
complete exhaustion of the uncreated [CpRh(CO.sub.2)] and for a
purge duration of about 0.1 second to about 10 seconds. The helium
is fed into the reactor chamber 10 at a rate of about 50 sccm.
[0048] The semiconductor 50 is then exposed to a second reactive
gas precursor 25, shown in FIG. 2. The second reactive gas
precursor 25 is supplied into the reactor chamber 10 through the
reactive gas inlet 16a and also flows at a right angle onto the
semiconductor 50 and the organo-rhodium monolayer. In an exemplary
embodiment, the second reactive gas precursor 25 is oxygen
(O.sub.2) which is fed into the reactor chamber 10 at a rate of
about 50 sccm, and for a duration of about 1 second. Any remaining
reactive oxygen in the reactive chamber 10 is exhausted through the
exhaust inlet 18. An intermediate pulse of a second purge gas 37 is
then introduced into the reactor chamber 10 through the inlet 26.
In a preferred embodiment, the second purge gas 37 is helium which
is introduced into the reactor chamber 10 after about 1 second from
the complete exhaustion of the unreacted oxygen and for a purge
duration of about 0.1 second to about 10 seconds. The helium is fed
into the reactor chamber 10 at a rate of about 50 sccm. The cycle
is repeated until a metallic pure rhodium film 77 is formed to a
desired thickness as an upper capacitor plate or upper electrode,
which is shown in FIG. 4. Although FIG. 4 shows the rhodium film 77
as a patterned upper capacitor plate, those skilled in the art will
realize that the rhodium film formed by the ALD method of the
present invention is initially formed as a blanket-deposited layer
over the dielectric film 72 and then both the rhodium layer and the
dielectric film 72 are patterned and etched according to known
methods of the art to obtain the capacitor structure of FIG. 4.
[0049] The low temperature atomic layer rhodium film 77 (FIG. 4)
formed according to the present invention has good step coverage
and enhanced uniformity and purity due to the complete reaction
during ALD steps.
[0050] To illustrate the enhanced properties of the rhodium films
formed at low temperature ALD processing, reference in now made to
FIG. 5 which illustrates an ink copy of a scanning electron
microscopic (SEM) micrograph of a pure metallic rhodium film 102
deposited by low temperature ALD method of the present invention
(FIG. 5). As shown in FIG. 5, the ALD-deposited rhodium film 102
formed in test structure 112 of FIG. 5 has improved step coverage
without poor film nucleation. The test structure 112, which may be
for example a contact hole between a capacitor and a transistor,
has a very narrow width W (FIG. 5) of about 0.15 microns and a
large length D (FIG. 5) of about 1 micron.
[0051] The rhodium film 102 of FIG. 5 shows extremely good step
coverage and enhanced physical properties, such as smoothness and
purity. The rhodium film 102 of FIG. 6 was deposited at about
100.degree. C. by atomic layer deposition under the following
conditions:
[0052] Example:
[0053] first precursor: 5 sccm dicarbonyl cyclopentadienyl
rhodium
[0054] [CpRh(CO.sub.2)] at about 100.degree. C. and for about 5
seconds
[0055] first purge gas: 50 sccm He for about 5 seconds
[0056] second precursor: 50 sccm O.sub.2 for about 5 seconds
[0057] second purge gas: 50 sccm He for about 5 seconds
[0058] Although the invention has been described with reference to
the formation of an upper rhodium plate of an MIM capacitor, the
invention is not limited to the above embodiments. Thus, the
invention contemplates the formation of high quality rhodium films
with good step coverage that can be used in a variety of IC
structures, for example as seed layers for electroplating
processes, as fuse elements or as bond pads, among many others.
[0059] The MIM capacitor 70 of FIG. 4 including the rhodium film 77
formed according to a method of the present invention could further
be part of a memory device of a typical processor based system,
which is illustrated generally at 400 in FIG. 6. A processor
system, such as a computer system, generally comprises a central
processing unit (CPU) 444, such as a microprocessor, which
communicates with an input/output (I/O) device 446 over a bus 452.
A memory 448, for example a DRAM memory, a SRAM memory, or a Multi
Chip Module (MCM), also communicates with the CPU 444 over bus 452.
Either the processor and/or memory or other circuit elements
fabricated as an integrated circuit may use a conductor, for
example, a conductor used in a capacitor 70 including a rhodium
film 77 fabricated as described above with reference to FIGS.
3-4.
[0060] In the case of a computer system, the processor system may
include additional peripheral devices such as a floppy disk drive
454, and a compact disk (CD) ROM drive 456 which also communicate
with CPU 444 over the bus 452. The memory 448 may be combined with
a processor, such as a CPU, digital signal processor or
microprocessor, with or without memory storage, in a single
integrated circuit chip.
[0061] The above description illustrates preferred embodiments that
achieve the features and advantages of the present invention. It is
not intended that the present invention be limited to the
illustrated embodiments. Modifications and substitutions to
specific process conditions and structures can be made without
departing from the spirit and scope of the present invention.
Accordingly, the invention is not to be considered as being limited
by the foregoing description and drawings, but is only limited by
the scope of the appended claims.
* * * * *