U.S. patent application number 11/106307 was filed with the patent office on 2005-08-11 for ultra low dielectric constant thin film.
This patent application is currently assigned to LSI Logic Corporation, Inc.. Invention is credited to Burke, Peter A., Catabay, Wilbur G., Cui, Hao.
Application Number | 20050176216 11/106307 |
Document ID | / |
Family ID | 34521871 |
Filed Date | 2005-08-11 |
United States Patent
Application |
20050176216 |
Kind Code |
A1 |
Cui, Hao ; et al. |
August 11, 2005 |
Ultra low dielectric constant thin film
Abstract
A method for forming a substantially oxygen-free silicon carbide
layer on a substrate, where the silicon carbide layer has a
dielectric constant of less than about four. The substrate is held
at a deposition temperature of between about zero centigrade and
about one hundred centigrade, and a gas flow of tetramethylsilane
is introduced at a rate of no more than about one thousand
scientific cubic centimeters per minute. The deposition pressure is
held between about one milli Torr and about one hundred Torr, and a
radio frequency plasma discharge is produced with a power of no
more than about two kilowatts. The plasma discharge is halted when
a desired thickness of the silicon carbide layer has been
formed.
Inventors: |
Cui, Hao; (West Linn,
OR) ; Burke, Peter A.; (Portland, OR) ;
Catabay, Wilbur G.; (Saratoga, CA) |
Correspondence
Address: |
LSI LOGIC CORPORATION
1621 BARBER LANE
MS: D-106
MILPITAS
CA
95035
US
|
Assignee: |
LSI Logic Corporation, Inc.
|
Family ID: |
34521871 |
Appl. No.: |
11/106307 |
Filed: |
April 14, 2005 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11106307 |
Apr 14, 2005 |
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10691400 |
Oct 22, 2003 |
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6905909 |
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Current U.S.
Class: |
438/459 ;
257/E21.576; 257/E21.579 |
Current CPC
Class: |
H01L 21/76828 20130101;
C23C 16/325 20130101; H01L 21/022 20130101; H01L 21/02167 20130101;
H01L 21/3148 20130101; H01L 21/76801 20130101; H01L 21/76826
20130101; H01L 21/02274 20130101; H01L 21/76807 20130101 |
Class at
Publication: |
438/459 |
International
Class: |
H01L 021/46 |
Claims
What is claimed is:
1. A substantially oxygen-free silicon carbide layer having a
dielectric constant of less than about four.
2. The silicon carbide layer of claim 1, wherein the dielectric
constant is less than about three.
3. The silicon carbide layer of claim 1, wherein the silicon
carbide layer is a hydrogenated silicon carbide layer.
4. The silicon carbide layer of claim 1, wherein the silicon
carbide layer is a nitrogen doped hydrogenated silicon carbide
layer.
5. An integrated circuit including the silicon carbide layer of
claim 1.
6. A method for forming on a substrate a substantially oxygen-free
silicon carbide layer having a dielectric constant of less than
about four, the method comprising the steps of: holding the
substrate at a deposition temperature of between about zero
centigrade and about one hundred centigrade, introducing a gas flow
of tetramethylsilane at a rate of no more than about one thousand
scientific cubic centimeters per minute, holding a deposition
pressure of between about one milli Torr and about one hundred
Torr, producing a radio frequency plasma discharge with a power of
no more than about two kilowatts, and halting the plasma discharge
when a desired thickness of the silicon carbide layer has been
formed.
7. The method of claim 6, wherein the method is accomplished in a
plasma enhanced chemical vapor deposition reactor.
8. The method of claim 6, wherein the deposition temperature is
held at about twenty-five centigrade.
9. The method of claim 6, wherein the deposition pressure is held
between about five hundred milli Torr and about seven hundred and
fifty milli Torr.
10. The method of claim 6, wherein the gas flow is introduced at a
rate of between about twenty-five scientific cubic centimeters per
minute and about seventy-five scientific cubic centimeters per
minute.
11. The method of claim 6, wherein the plasma discharge is produced
with a power of between about five hundred watts and about seven
hundred and fifty watts.
12. The method of claim 6, further comprising the step of
introducing at least one of helium, nitrogen, argon, methane, and
ammonia gas during the plasma discharge.
13. The method of claim 6, wherein the deposition temperature is
held at about twenty-five centigrade, the tetramethylsilane is
introduced at a rate of about seventy-five scientific cubic
centimeters per minute, helium gas is introduced during the plasma
discharge at a rate of about two hundred scientific cubic
centimeters per minute, the deposition pressure is held at about
five hundred milli Torr, and the plasma discharge is produced with
a power of about eight hundred watts.
14. The method of claim 6, wherein the deposition temperature is
held at about twenty-five centigrade, the tetramethylsilane is
introduced at a rate of about twenty-five scientific cubic
centimeters per minute, nitrogen gas is introduced during the
plasma discharge at a rate of about four hundred scientific cubic
centimeters per minute, the deposition pressure is held at about
seven hundred and fifty milli Torr, and the plasma discharge is
produced with a power of about six hundred watts.
15. The method of claim 6, wherein the deposition temperature is
held at about twenty-five centigrade, the tetramethylsilane is
introduced at a rate of about twenty-five scientific cubic
centimeters per minute, methane gas is introduced during the plasma
discharge at a rate of about two hundred scientific cubic
centimeters per minute, the deposition pressure is held at about
seven hundred and fifty milli Torr, and the plasma discharge is
produced with a power of about seven hundred and fifty hundred
watts.
16. The method of claim 6, further comprising the step of treating
the silicon carbide layer with at least one of a helium plasma and
a hydrogen plasma at a temperature of no more than about four
hundred centigrade.
17. The method of claim 6, further comprising the step of treating
the silicon carbide layer with a thermal anneal at a temperature of
between about one hundred centigrade and about four hundred
centigrade under one of a vacuum environment and an inert gas
ambient environment.
18. An inter layer dielectric stack, comprising: a bottom layer of
a substantially oxygen-free silicon carbide material having a
dielectric constant of less than about four, a middle layer of a
low k material, and a top layer of a substantially oxygen-free
silicon carbide material having a dielectric constant of less than
about four.
19. The inter layer dielectric stack of claim 18, wherein the
middle layer of the low k material comprises a first layer and a
second layer of the low k material, with an intervening layer of a
substantially oxygen-free silicon carbide material having a
dielectric constant of less than about four.
20. An integrated circuit including the inter layer dielectric
stack of claim 18.
Description
FIELD
[0001] This invention relates to the field of integrated circuit
fabrication. More particularly, this invention relates to advanced
materials for use as non electrically conducting layers.
BACKGROUND
[0002] As integrated circuits have become increasingly smaller,
electrically conductive structures within the integrated circuits
are placed increasingly closer together. This situation tends to
enhance the inherent problem of parasitic capacitance between
adjacent electrically conductive structures. Thus, new electrically
insulating materials have been devised for use between electrically
conductive structures, to reduce such capacitance problems. The new
electrically insulating materials typically have lower dielectric
constants, and thus are generally referred to as low k materials.
While low k materials help to resolve the capacitance problems
described above, they unfortunately tend to introduce new
challenges.
[0003] Low k materials are typically filled with small voids that
help reduce the material's effective dielectric constant. Thus,
there is less of the material itself within a given volume, which
tends to reduce the structural strength of the material. The
resulting porous and brittle nature of such low k materials
presents new challenges in both the fabrication and packaging
processes. Unless special precautions are taken, the robustness and
reliability of an integrated circuit that is fabricated with low k
materials may be reduced from that of an integrated circuit that is
fabricated with traditional materials, because low k materials
differ from traditional materials in properties such as thermal
coefficient of expansion, moisture absorption, adhesion to adjacent
layers, mechanical strength, and thermal conductivity.
[0004] For example, when forming back end of line dual damascene
copper interconnect structures, dielectric barrier films, and often
a middle etch stop film, is formed between the low k inter layer
dielectric layers. The dielectric barrier films perform valuable
functions, including forming a diffusion barrier to prevent copper
diffusion into the low k inter layer dielectrics, acting as an etch
stop layer on top of the copper during the dual damascene via etch
process, and acting as a passivation layer to prevent damage, such
as exposure to an oxidizing environment and moisture, to the copper
during subsequent processing. The middle etch stop layer acts as an
etch stop during dual damascene trench etch and enhances the
control of the trench depth and the via profile. High etch
selectivity between the inter layer dielectric and the middle etch
stop layer is generally desired.
[0005] It is desirable to have dielectric barrier films and the
etch stop films that also have a low dielectric constant, so as to
achieve a low overall effective k of the overall dielectric film
stack. However, the properties of tradition low k dielectric films
have made them inadequate to fulfill the purposes of the barrier
and etch stop films. Dielectric barrier and etch stop materials
typically include silicon nitride with a k of about seven, silicon
carbide with a k of about five, and silicon carbon nitride with a k
of about five, deposited using plasma enhanced chemical vapor
deposition. These materials have properties that enable them to
function well as barriers and etch stops, but they all have
relatively high k values.
[0006] With the drive toward smaller integrated circuit feature
sizes, as mentioned above, and with the use of inter layer
dielectrics with lower k values, the dielectric barrier and middle
etch stop films tend to have a more significant contribution to the
overall effective k value of the dielectric stack in which they are
used. When integrated circuit feature sizes become smaller, inter
layer dielectric thicknesses tend to become thinner. But the
barrier layer and etch stop layer thicknesses do not scale down as
much as inter layer dielectric thickness does, due to the
requirements on the barrier layers. For example, as the inter layer
dielectric thickness decreases from about 7,700 angstroms to about
6,000 to 6,500 angstroms, the dielectric barrier deposition
thickness remains substantially constant at about five hundred
angstroms. Thus, to reduce the overall dielectric constant of the
barrier and middle etch stop films, films with lower k values need
to be found.
[0007] Plasma enhanced chemical vapor deposition silicon carbide
films are very good dielectric barrier and middle etch stop due to
their excellent properties, such as good diffusion barrier for
copper and moisture, high etch selectivity to carbon doped oxide
inter layer dielectric, and industry-friendly plasma enhanced
chemical vapor deposition methods. These films are usually
deposited at elevated temperatures of between about three hundred
centigrade and about four hundred centigrade using
trimethylsilane-based chemistry.
[0008] One approach to achieve lower k plasma enhanced chemical
vapor deposition silicon carbide is to introduce oxygen into the
film as it is formed, to reduce the density of the film. This can
be accomplished by using precursor gases that include some form of
oxygen, such as those with oxygen in their molecular structure, or
the introduction of oxygen gas or oxygen-containing gases during
the deposition process. Incorporation of oxygen tends to reduce the
k value. However, there are problems with oxygenated silicon
carbide films. Other approaches to achieving lower k silicon
carbide films include the use of novel precursors or
post-deposition treatment to increase the porosity of the deposited
film. However, these processes are in an early development stage,
and as of yet there has been no report of a plasma enhanced
chemical vapor deposition oxygen-free silicon carbide material with
a k value of less than about four.
[0009] What is needed, therefore, is a method of depositing a
plasma enhanced chemical vapor deposition silicon carbide based
thin film that is substantially oxygen free and which has a
dielectric constant of less than about four.
SUMMARY
[0010] The above and other needs are met by a substantially
oxygen-free silicon carbide layer having a dielectric constant of
less than about four. The dielectric constant is preferably less
than about three. In various embodiments, the silicon carbide layer
is a hydrogenated silicon carbide layer, and in some embodiments
the silicon carbide layer is a nitrogen doped hydrogenated silicon
carbide layer. Also described is an integrated circuit including
the silicon carbide layer.
[0011] Also described is a method for forming a substantially
oxygen-free silicon carbide layer on a substrate, where the silicon
carbide layer has a dielectric constant of less than about four.
The substrate is held at a deposition temperature of between about
zero centigrade and about one hundred centigrade, and a gas flow of
tetramethylsilane is introduced at a rate of no more than about one
thousand scientific cubic centimeters per minute. The deposition
pressure is held between about one milli Torr and about one hundred
Torr, and a radio frequency plasma discharge is produced with a
power of no more than about two kilowatts. The plasma discharge is
halted when a desired thickness of the silicon carbide layer has
been formed.
[0012] In this manner, there is provided a silicon carbide film
having a dielectric constant of less than about four, which has
excellent properties for use in an inter layer dielectric stack.
For example, because the silicon carbide film described is
substantially oxygen-free, it does not oxidize the underlying
copper film when used in such a system. Further, the silicon
carbide film tends to exhibit a good etch selectivity with the
inter layer dielectric. In addition, the ability of the silicon
carbide film to act as a barrier against copper diffusion tends to
be quite good, because of the lack of oxygen in the film.
[0013] In various embodiments, the method is accomplished in a
plasma enhanced chemical vapor deposition reactor. The deposition
temperature is preferably held at about twenty-five centigrade, the
deposition pressure is preferably held between about five hundred
milli Torr and about seven hundred and fifty milli Torr, the gas
flow is preferably introduced at a rate of between about
twenty-five scientific cubic centimeters per minute and about
seventy-five scientific cubic centimeters per minute, and the
plasma discharge is preferably produced with a power of between
about five hundred watts and about seven hundred and fifty watts.
In some embodiments, at least one of helium, nitrogen, argon,
methane, and ammonia gas is introduced during the plasma
discharge.
[0014] In a first specific embodiment, the deposition temperature
is held at about twenty-five centigrade, the tetramethylsilane is
introduced at a rate of about seventy-five scientific cubic
centimeters per minute, helium gas is introduced during the plasma
discharge at a rate of about two hundred scientific cubic
centimeters per minute, the deposition pressure is held at about
five hundred milli Torr, and the plasma discharge is produced with
a power of about eight hundred watts.
[0015] In a second specific embodiment, the deposition temperature
is held at about twenty-five centigrade, the tetramethylsilane is
introduced at a rate of about twenty-five scientific cubic
centimeters per minute, nitrogen gas is introduced during the
plasma discharge at a rate of about four hundred scientific cubic
centimeters per minute, the deposition pressure is held at about
seven hundred and fifty milli Torr, and the plasma discharge is
produced with a power of about six hundred watts.
[0016] In a third specific embodiment, the deposition temperature
is held at about twenty-five centigrade, the tetramethylsilane is
introduced at a rate of about twenty-five scientific cubic
centimeters per minute, methane gas is introduced during the plasma
discharge at a rate of about two hundred scientific cubic
centimeters per minute, the deposition pressure is held at about
seven hundred and fifty milli Torr, and the plasma discharge is
produced with a power of about seven hundred and fifty hundred
watts.
[0017] In various embodiments there is an additional step of
treating the silicon carbide layer with at least one of a helium
plasma and a hydrogen plasma at a temperature of no more than about
four hundred centigrade. In other embodiments there is an
additional step of treating the silicon carbide layer with a
thermal anneal at a temperature of between about one hundred
centigrade and about four hundred centigrade under one of a vacuum
environment and an inert gas ambient environment.
[0018] Further described is an inter layer dielectric stack, with a
bottom layer of a substantially oxygen-free silicon carbide
material having a dielectric constant of less than about four, a
middle layer of a low k material, and a top layer of a
substantially oxygen-free silicon carbide material having a
dielectric constant of less than about four. In one embodiment, the
middle layer of the low k material includes a first layer and a
second layer of the low k material, with an intervening layer of a
substantially oxygen-free silicon carbide material having a
dielectric constant of less than about four. An integrated circuit
including the inter layer dielectric stack is also described.
BRIEF DESCRIPTION OF THE DRAWINGS
[0019] Further advantages of the invention are apparent by
reference to the detailed description when considered in
conjunction with the figures, which are not to scale so as to more
clearly show the details, wherein like reference numbers indicate
like elements throughout the several views, and wherein:
[0020] FIG. 1 is a flow chart depicting the process steps for a
first preferred embodiment of a method for depositing an ultra low
dielectric constant oxygen-free silicon carbide film according to
the present invention.
[0021] FIG. 2 is a flow chart depicting the process steps for a
second preferred embodiment of the method for depositing an ultra
low dielectric constant oxygen-free silicon carbide film according
to the present invention.
[0022] FIG. 3 is a flow chart depicting the process steps for a
third preferred embodiment of the method for depositing an ultra
low dielectric constant oxygen-free silicon carbide film according
to the present invention.
[0023] FIG. 4 is a chart depicting the Fourier transform infrared
spectroscopy absorbance spectrum for the first preferred embodiment
of the method for depositing an ultra low dielectric constant
oxygen-free silicon carbide film according to the present
invention.
[0024] FIG. 5 is a chart depicting the Fourier transform infrared
spectroscopy absorbance spectrum for a more traditional silicon
carbide film having a higher dielectric constant.
[0025] FIG. 6 is a chart depicting the current-voltage leakage
characteristics for two embodiments of an ultra low dielectric
constant oxygen-free silicon carbide film according to the present
invention and two more traditional silicon carbide films having
higher dielectric constants.
[0026] FIG. 7 is a cross sectional depiction of a portion of an
integrated circuit with an inter layer dielectric stack including
ultra low dielectric constant oxygen-free silicon carbide films
according to the present invention.
DETAILED DESCRIPTION
[0027] This invention includes methods to deposit an oxygen-free
silicon carbide film with a dielectric constant as low as 2.92
using plasma enhanced chemical vapor deposition techniques and
reactors, with tetramethylsilane-based precursors. Currently there
has no public report of the deposition of plasma enhanced chemical
vapor deposition oxygen-free silicon carbide material with a
dielectric constant of less than about four. A distinct feature of
this invention is that the deposition is carried out at a
substantially lower temperature compared to the conventional
silicon carbide deposition temperature. In the embodiments
presented herein, the deposition temperature is between about zero
centigrade and about one hundred centigrade, whereas typical
silicon carbide films are deposited at a temperature of between
about three hundred centigrade and about four hundred
centigrade.
[0028] Different reaction chemistries are described herein, and
preferred embodiments of invention are presented. Properties of the
ultra low dielectric constant silicon carbide films deposited using
some preferred embodiments of this invention are also presented. A
mechanism for the reduction of the dielectric constant in ultra low
dielectric constant silicon carbide films is proposed.
[0029] The present invention is directed to a method for forming a
silicon carbide film on a substrate comprising the steps of: (a)
keeping the substrate at a deposition temperature of between about
zero centigrade and about one hundred centigrade; (b) providing
tetramethylsilane in a gas flow amount up to about one thousand
scientific cubic centimeters per minute; (c) reaching a pressure
between about one milli Torr and one hundred Torr; (d) plasma
discharge with radio frequency power up to about two kilowatts, and
(e) depositing the silicon carbide film on the substrate. The
deposition can be carried out in any plasma enhanced chemical vapor
deposition system available.
[0030] In the preferred embodiments of this invention, the
deposition is carried out at a temperature of about twenty-five
centigrade, where the pressure of step (c) is between about five
hundred milli Torr and about seven hundred and fifty milli Torr.
The tetramethylsilane is preferably provided in a gas flow of
between about twenty-five scientific cubic centimeters per minute
and about seventy-five scientific cubic centimeters per minute, in
a plasma discharge with a radio frequency power in a preferred
range of between about five hundred watts and about seven hundred
and fifty watts. In preferred embodiments, the tetramethylsilane in
step (b) is the primary silicon-containing precursor, and the
plasma discharge of step (b) includes one or more of gases such as
helium, nitrogen, argon, methane, and ammonia.
[0031] FIG. 1 is a flow chart of the deposition sequence 10 of
preferred embodiment 1 of this disclosure. In this embodiment, the
temperature is twenty-five centigrade as given in block 12. A
mixture of seventy-five scientific cubic centimeters per minute of
tetramethylsilane and two hundred scientific cubic centimeters per
minute of inert gases is used in the plasma discharge as given in
block 14, with a pressure of five hundred milli Torr as given in
block 16. Helium is used as an example of the inert gas of this
embodiment. Other candidates for the inert gas are argon or mixture
of helium and argon. The inert gases are preferably used as the
carrier gas for the tetramethylsilane, and help to strike and
maintain a uniform and stable plasma discharge. The inert gases are
preferably not actively involved in the reaction during the
deposition of the silicon carbide film. The power is about eight
hundred watts as given in block 18 The silicon carbide film
deposited using this embodiment as given in block 20 is a
substantially pure hydrogenated silicon carbide (SiC.sub.xH.sub.y)
without any dopants, and is substantially oxygen-free.
[0032] The final post-deposition treatment as given in block 22 is
optional and can be used to preferably stabilize and control the
deposited silicon carbide film properties. Examples of such
post-deposition treatments include helium plasma treatment at a
temperature of no more than about four hundred and fifty
centigrade, a hydrogen plasma treatment at a temperature of no more
than about four hundred and fifty centigrade, and a thermal anneal
at a temperature of between about one hundred centigrade and about
four hundred and fifty centigrade in a vacuum environment or in an
inert gas ambient environment.
[0033] FIG. 2 is a flow chart of the deposition sequence 30 of
preferred embodiment 2 of this disclosure. The deposition
temperature is twenty-five centigrade as given in block 32. The
main difference between this embodiment and embodiment 1 is that a
mixture of twenty-five scientific cubic centimeters per minute of
tetramethylsilane and four hundred scientific cubic centimeters per
minute of nitrogen-containing gases is used during the film
deposition. In this embodiment, a mixture of tetramethylsilane and
ammonia gases or a mixture of tetramethylsilane, nitrogen and
ammonia is used to deposit the silicon carbide film. Inert carrier
gases such helium and argon can optionally be used during the
deposition without affecting the silicon carbide film properties.
The deposition pressure is seven hundred and fifty milli Torr as
given in block 36, and the power as given in block 38 is six
hundred watts.
[0034] The deposition reaction as given in block 40 of this
embodiment is different as compared to that of embodiment 1,
because the nitrogen-containing gases are actively involved in the
deposition reaction, due to the presence of active nitrogen and
hydrogen radicals in the plasma. As a result, an ultra low
dielectric constant hydrogenated silicon carbide film with nitrogen
dopants (silicon carbon nitride, or SiC.sub.xN.sub.yH.sub.z) is
produced using this embodiment. Basic chemistry and physics teach
that this film should retain good dielectric barrier and etch stop
properties. The post processing as given in block 42 is optional,
as described above.
[0035] FIG. 3 is a flow chart of the deposition sequence 50 of
preferred embodiment 3 of this disclosure. In this embodiment, the
deposition temperature is twenty-five centigrade, and a mixture of
twenty-five scientific cubic centimeters per minute of
tetramethylsilane and two hundred scientific cubic centimeters per
minute of methane gases is used in the film deposition. Other
hydrocarbon gases, such as ethane or a mixture of methane and
ethane, can be used to replace the methane in this embodiment. The
hydrocarbon gases are actively involved in the deposition reaction
with tetramethylsilane, to deposit a hydrogenated silicon carbide
film (SiC.sub.xH.sub.y).
[0036] Inert carrier gases such helium and argon are optionally
used during the deposition as given in block 60 without affecting
the silicon carbide film properties. The tetramethylsilane to
methane flow ratio is preferably tuned to adjust the carbon content
of the silicon carbide film, which affects the etch selectivity
between the low k inter layer dielectric and the hydrogenated
silicon carbide film during a dual damascene via etch. The
deposition pressure as given in block 56 is seven hundred and fifty
milli Torr, and the power as given in block 58 is seven hundred and
fifty watts. As before, the post-processing as given in block 62
and described above is optional.
[0037] Some basic film properties of the ultra low dielectric
constant silicon carbide films deposited using preferred
embodiments 1 and 2 of this invention are presented in the
following portion of the disclosure. The films were all deposited
in an F.times.P deposition system manufactured by Trikon
Technologies, Inc. of Fountain Valley, Calif.
[0038] The dielectric constants of the films were determined by
capacitance-voltage measurement and analysis of fabricated
metal-insulator-semiconductor capacitors. To fabricate a
metal-insulator-semiconductor capacitor, approximately one thousand
angstroms of the ultra low dielectric constant silicon carbide film
is deposited onto a low resistivity silicon substrate. Aluminum or
copper dots are then sputtered onto the film using a shadow mask.
The capacitance-voltage measurements are performed at a frequency
of about one megahertz. The refractive indices are measured using
an Opti-Probe refractometer manufactured by Therma-Wave, Inc. of
Fremont, Calif.
[0039] Tables 1 and 2 below provide the dielectric constant and
refractive index of the ultra low dielectric constant silicon
carbide films described herein. Also included are a dielectric
constant and refractive index of more traditional silicon carbide
films. These data show that the ultra low dielectric constant
silicon carbide films deposited using the preferred embodiments
according to this invention have very low dielectric constants and
refractive indices.
1TABLE 1 Dielectric constant of ultra low-k silicon carbide films
Ultra low-k SiC.sub.xH.sub.y Ultra low-k SiC.sub.xN.sub.yH.sub.z
Traditional Traditional Embodiment 1 Embodiment 2 SiC.sub.xH.sub.y
SiC.sub.xN.sub.yH.sub.z 2.92 3.38 4.8 5.1
[0040]
2TABLE 2 Refractive index of ultra low-k silicon carbide films
Ultra low-k SiC.sub.xH.sub.y Ultra low-k SiC.sub.xN.sub.yH.sub.z
Traditional Traditional Embodiment 1 Embodiment 2 SiC.sub.xH.sub.y
SiC.sub.xN.sub.yH.sub.z 1.6 1.59 2 1.93
[0041] The chemical compositions of the films described herein have
been determined by Rutherford backscattering spectrometry and
hydrogen forward scattering. Fourier transform infrared
spectroscopy analysis is used to study the film's chemical bonding
structure. Films of about three thousand angstroms in thickness
were used in these analyses.
[0042] Table 3 below shows the chemical composition of ultra low
dielectric constant silicon carbide films. Also included are the
chemical compositions of more traditional silicon carbide films. It
is apparent that the ultra low dielectric constant pure
hydrogenated silicon carbide (SiC.sub.xH.sub.y) film is
successfully produced using preferred embodiment 1. It is further
apparent that nitrogen atoms are incorporated into the ultra low
dielectric constant silicon carbide film deposited using preferred
embodiment 2, to form the ultra low-k silicon carbon nitride
(SiC.sub.xN.sub.yH.sub.z) film. It can also be seen that the atomic
ratios of carbon to silicon for the ultra low dielectric constant
silicon carbide films are significantly higher than the more
traditional films that exhibit a higher dielectric constant.
3TABLE 3 Atomic chemical composition of ultra low-k silicon carbide
films Films Si (%) C (%) H (%) N (%) Ultra low-k SiC.sub.xH.sub.y
16 28 56 0 Embodiment 1 Ultra low-k SiC.sub.xN.sub.yH.sub.z 11.9
22.3 56 8.8 Embodiment 2 Traditional SiC.sub.xH.sub.y 25.3 24.7 50
0 Traditional SiC.sub.xN.sub.yH.sub.z 24.5 17.5 46 12
[0043] FIG. 4 depicts the Fourier transform infrared spectroscopy
spectrum of the ultra low dielectric constant silicon carbide film
(SiC.sub.xH.sub.y) that is deposited using preferred embodiment 1,
and a more traditional silicon carbide film (SiC.sub.xH.sub.y). The
ultra low dielectric constant silicon carbide film has a similar
spectrum pattern as compared to a silicon carbide film with a
dielectric constant of 4.8. The major difference is that the ultra
low dielectric constant silicon carbide film has a much higher
Si--CH3 bending absorbance peak intensity (.about.1,250 cm.sup.-1)
and C--H.sub.n (n=1, 2, 3) stretching absorbance peak intensity
(2,900-2,960 cm.sup.-1) as normalized to the main peak around wave
number 800 cm.sup.-1. The Si--CH.sub.3/Si--C and C--H.sub.n/Si--C
peak intensity ratios of the ultra low dielectric constant
SiC.sub.xH.sub.y film in FIG. 4 is more than twice that of the more
traditional SiC.sub.xH.sub.y film as depicted in FIG. 5.
[0044] This analysis suggests that more methyl-related groups
(CH.sub.3, CH.sub.2) are attached to the silicon atoms and less
Si--C network is formed in the ultra low dielectric constant
silicon carbide film. The Si--C network is a very dense network.
Without being bound by theory, it is proposed that the
incorporation of more large methyl-related groups and disordering
of the Si--C network make the present silicon carbide film more
porous and cause the reduction in the dielectric constant. This
proposal tends to also be confirmed by the change in the C/Si
atomic ratio, as compared to traditional films with higher
dielectric constants, as shown in Table 3 above. The pure Si--C
network has a C/Si ratio of close to one, while the ultra low
dielectric constant silicon carbide films described herein have
C/Si ratios of close to two. The higher C/Si atomic ratio of the
ultra low dielectric constant silicon carbide film suggests that
more methyl-related groups are attached to the silicon atoms.
[0045] Low leakage current is highly desirable for dielectric
barrier and etch stop films that are to be used for back end of
line interconnects. FIG. 6 shows the current-voltage
characteristics of the ultra low dielectric constant silicon
carbide films 94 and 96 at room temperature. Current-voltage
characteristics of traditional silicon carbide films 90 and 92 are
also included as references. Current-voltage tests were done on
metal-insulator-semiconductor capacitors with copper as the gate
contact. All films tested have thicknesses of about one thousand
angstroms. FIG. 6 shows that the ultra low dielectric constant
silicon carbide films 94 and 96 have low leakage current, and
breakdown fields that are higher than about four millivolts per
centimeter. In particular, the ultra low dielectric constant
SiC.sub.xH.sub.y 96 with a dielectric constant of 2.92 has a
significantly lower leakage current than traditional silicon
carbide films 90 and 92 with a higher dielectric constant.
[0046] With reference now to FIG. 7, there is depicted a portion of
an integrated circuit 70. The integrated circuit 70 includes a
substrate 72, which is preferably formed of a semiconducting
material, such as at least one of silicon, germanium, and a III-V
compound such as gallium arsenide. The substrate 72 also preferably
includes circuitry formed therein, which circuitry is not depicted
in the figure. The integrated circuit 70 also includes a dielectric
stack of materials 74, 78, and 80. The layers 74 are preferably
formed of a low k material, as described above. The layers 78 and
option layer 80 are preferably etch stop and barrier layers formed
of the ultra low dielectric constant substantially oxygen-free
silicon carbide material formed by the processes as described
above. As introduced above, such layers are useful in combination
with copper dual damascene structures 76.
[0047] In summary, this invention presents methods to deposit ultra
low dielectric constant plasma enhanced chemical vapor deposition
silicon carbide films that are substantially oxygen-free. Three
preferred embodiments are proposed. Basic properties of the ultra
low dielectric constant silicon carbide films deposited using the
preferred embodiments are presented. A mechanism for the dielectric
constant reduction is proposed.
[0048] The foregoing description of preferred embodiments for this
invention has been presented for purposes of illustration and
description. It is not intended to be exhaustive or to limit the
invention to the precise form disclosed. Obvious modifications or
variations are possible in light of the above teachings. The
embodiments are chosen and described in an effort to provide the
best illustrations of the principles of the invention and its
practical application, and to thereby enable one of ordinary skill
in the art to utilize the invention in various embodiments and with
various modifications as are suited to the particular use
contemplated. All such modifications and variations are within the
scope of the invention as determined by the appended claims when
interpreted in accordance with the breadth to which they are
fairly, legally, and equitably entitled.
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