U.S. patent application number 10/146416 was filed with the patent office on 2002-11-07 for methods of producing ultra -low resistivity tantalum films..
This patent application is currently assigned to Applied Materials, Inc.. Invention is credited to Chiang, Tony, Chin, Barry, Ding, Peijun.
Application Number | 20020162738 10/146416 |
Document ID | / |
Family ID | 22577743 |
Filed Date | 2002-11-07 |
United States Patent
Application |
20020162738 |
Kind Code |
A1 |
Chiang, Tony ; et
al. |
November 7, 2002 |
METHODS OF PRODUCING ULTRA -LOW RESISTIVITY TANTALUM FILMS.
Abstract
We have discovered that, by depositing a tantalum layer upon a
substrate at a temperature of at least 325.degree. C., it is
possible to obtain an ultra low resistivity which is lower than
that previously published in the literature. In addition, it is
possible deposit a Ta.sub.xN.sub.y film having an ultra low
resistivity by depositing the Ta.sub.xN.sub.y film upon a substrate
at a temperature of at least 275.degree. C., wherein x is 1 and y
ranges from about 0.05 to about 0.18. These films having an ultra
low resistivity are obtained at temperatures far below the
previously published temperatures for obtaining higher resistivity
films. A combination of elevated substrate temperature and ion
bombardment of the film surface during deposition enables the use
of lower substrate temperatures while maintaining optimum film
properties. In another development, we have discovered that the
ultra low resistivity tantalum and Ta.sub.xN.sub.y films produced
by the method of the present invention also exhibit particularly
low residual stress, so that they are more stable and less likely
to delaminate from adjacent layers in a multilayered semiconductor
structure. Further, these films can be chemical mechanical polished
at significantly higher rates (at least 40% higher rates) than the
higher resistivity tantalum and Ta.sub.xN.sub.y films previously
known in the industry. This is particularly useful in damascene
processes when copper is used as the interconnect metal, since it
reduces the possibility of copper dishing during a polishing
step.
Inventors: |
Chiang, Tony; (Mountain
View, CA) ; Ding, Peijun; (San Jose, CA) ;
Chin, Barry; (Saratoga, CA) |
Correspondence
Address: |
Patent Counsel
Applied Materials, Inc.
P.O. Box 450 A
Santa Clara
CA
95052
US
|
Assignee: |
Applied Materials, Inc.
Santa Clara
CA
|
Family ID: |
22577743 |
Appl. No.: |
10/146416 |
Filed: |
May 14, 2002 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10146416 |
May 14, 2002 |
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09770934 |
Jan 25, 2001 |
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09770934 |
Jan 25, 2001 |
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09160638 |
Sep 24, 1998 |
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Current U.S.
Class: |
204/192.15 ;
204/192.22; 257/E21.17; 257/E21.292 |
Current CPC
Class: |
C23C 14/165 20130101;
H01L 21/76864 20130101; H01L 21/28556 20130101; H01L 21/76843
20130101; C23C 14/541 20130101; C23C 14/0641 20130101; H01L
21/02266 20130101; Y10T 428/31678 20150401; H01L 21/02183 20130101;
H01L 21/318 20130101; C23C 14/5806 20130101 |
Class at
Publication: |
204/192.15 ;
204/192.22 |
International
Class: |
C23C 014/34 |
Claims
We claim:
1. A tantalum film having a resistivity of less than 25
.mu..OMEGA.-cm.
2. A tantalum film according to claim 1, wherein said film has a
residual stress ranging between about 5.0.times.10.sup.9 and
-5.0.times.10.sup.9 dynes/cm.sup.2.
3. A tantalum film according to claim 1, having a
chemical-mechanical polishing rate which is at least 40% increased
over the polishing rate of a tantalum film having a resistivity of
at least 100 .mu..OMEGA.-cm.
4. A method of producing the tantalum film according to claim 1, or
claim 2, or claim 3, wherein said film is produced by sputter
deposition upon a substrate at a temperature of about 325.degree.
C. or greater.
5. The method according to claim 4, wherein said sputter deposition
is high density plasma sputter deposition, and the surface of said
tantalum film is ion bombarded during deposition, whereby said
substrate temperature is reduced by as much as about 40% during
said deposition without an increase in the resistivity of said
deposited tantalum film.
6. The method according to claim 4, wherein said tantalum film is
produced by sputter deposition upon a substrate at a temperature
within the range of about 350.degree. C. to about 550.degree.
C.
7. The method according to claim 6, wherein said sputter deposition
is high density plasma sputter deposition, and the surface of said
tantalum film is ion bombarded during deposition, whereby said
substrate temperature is reduced by as much as about 40% during
said deposition without an increase in the resistivity of said
deposited tantalum film.
8. A method of producing the tantalum film according to claim 1,
wherein said film is produced by sputter deposition upon a
substrate at a temperature of less than about 325.degree. C. and
wherein said film is subsequently annealed at a temperature greater
than about 325.degree. C.
9. A Ta.sub.xN.sub.y film having a resistivity of less than 25
.mu..OMEGA.-cm, wherein x is 1 and y ranges from about 0.05 to
about 0.18.
10. A Ta.sub.xN.sub.y film according to claim 9, wherein said film
has a residual stress ranging between about 5.0.times.10.sup.9 and
-5.0.times.10.sup.9 dynes/cm.sup.2.
11. A Ta.sub.xN.sub.y film according to claim 9, having a
chemical-mechanical polishing rate which is at least 40% increased
over the polishing rate of a Ta.sub.xN.sub.y film having a
resistivity of at least 100 .mu..OMEGA.-cm.
12. A method of producing the Ta.sub.xN.sub.y film of claim 9,
wherein said film is produced by sputter deposition upon a
substrate at a temperature of about 275.degree. C. or greater.
13. A method of producing the Ta.sub.xN.sub.y film according to
claim 9, wherein said film is produced by sputter deposition upon a
substrate at a temperature of less than about 275.degree. C. and
wherein said film is subsequently annealed at a temperature of
about 275.degree. C. or greater.
14. A tantalum film according to claim 1, wherein said film has a
chemical-mechanical polishing rate of at least 270 .ANG. per
minute.
15. A Ta.sub.xN.sub.y film according to claim 9, wherein said film
has a chemical-mechanical polishing rate of at least 270 .ANG. per
minute.
16. A method of producing a sputtered tantalum film having a
resistivity of less than 25 .mu..OMEGA.-cm, said method comprising:
placing a substrate on a temperature-controlled support platen in a
physical vapor deposition process chamber; and controlling the
temperature of said support platen during the sputtering of said
tantalum film upon said substrate, in a manner such that said
substrate temperature is about 325.degree. C. or higher during
deposition of said sputtered tantalum film.
17. The method according to claim 16, wherein said support platen
temperature is controlled to be at an individual temperature
between about 350.degree. C. and about 550.degree. C. or is
controlled over a temperature ranging between about 350.degree. C.
and about 550.degree. C.
18. A method of producing a sputtered Ta.sub.xN.sub.y film, said
method comprising: placing a substrate on a temperature-controlled
support platen in a physical vapor deposition process chamber; and
controlling the temperature of said support platen during the
sputtering of said Ta.sub.xN.sub.y film upon said substrate, in a
manner such that said substrate temperature is about 275.degree. C.
or greater during deposition of said sputtered Ta.sub.xN.sub.y
film.
19. The method according to claim 18, wherein said support platen
temperature is controlled to be at an individual temperature
between about 275.degree. C. and about 550.degree. C. or is
controlled over a temperature ranging between about 275.degree. C.
and about 550.degree. C.
20. The method according to claim 16, wherein said sputter
deposition is high density plasma sputter deposition, and the
surface of said tantalum film is ion bombarded during deposition,
whereby said substrate temperature is reduced by as much as about
40% during said deposition without an increase in the resistivity
of said deposited tantalum film.
21. The method according to claim 18, wherein said sputter
deposition is high density plasma sputter deposition, and the
surface of said Ta.sub.xN.sub.y film is ion bombarded during
deposition, whereby said substrate temperature is reduced by as
much as about 40% during said deposition without an increase in the
resistivity of said deposited Ta.sub.xN.sub.y film.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention pertains to tantalum films having
ultra-low resistivity, in the range of about 10 .mu..OMEGA.-cm, as
well as methods for depositing ultra-low resistivity tantalum
films. Tantalum films deposited according to the method of the
invention can be removed from a semiconductor substrate surface
using chemical mechanical polishing (CMP) techniques far more
rapidly than previously known tantalum films.
[0003] 2. Brief Description of the Background Art
[0004] As microelectronics continue to miniaturize, interconnection
performance, reliability, and power consumption has become
increasingly important, and interest has grown in replacing
aluminum alloys with lower resistivity and higher reliability
metals. Copper offers a significant improvement over aluminum as a
contact and interconnect material. For example, the resistivity of
copper is about 1.67 .mu..OMEGA.-cm, which is only about half of
the resistivity of aluminum.
[0005] One of the preferred technologies which enables the use of
copper interconnects is the damascene process. This process for
producing a multi-level structure having feature sizes in the range
of 0.5 micron (.mu.m) or less typically includes the following
steps: blanket deposition of a dielectric material over a
substrate; patterning of the dielectric material to form openings;
deposition of a diffusion barrier layer and, optionally, a wetting
layer to line the openings; deposition of a copper layer onto the
substrate in sufficient thickness to fill the openings; and removal
of excessive conductive material from the substrate surface using
chemical-mechanical polishing (CMP) techniques. The damascene
process is described in detail by C. Steinbruchel in "Patterning of
copper for multilevel metallization: reactive ion etching and
chemical-mechanical polishing", Applied Surface Science 91 (1995)
139-146.
[0006] The preferred barrier layer/wetting layer for use with
copper comprises a tantalum nitride--tantalum barrier/wetting layer
having a decreasing nitrogen content toward the upper surface of
the layer. This structure, which provides excellent barrier
properties while increasing the <111> content of an overlying
copper layer, provides a copper layer having improved
electromigration resistance, as described in applicants' copending
application Ser. No. 08/995,108. A barrier layer having a surface
which is essentially pure tantalum or tantalum including only a
small amount of nitrogen (typically less than about 15 atomic
percent) performs well as a barrier layer and also as a wetting
layer to enhance the subsequent application of an overlying copper
layer.
[0007] Philip Catania et al. in "Low resistivity body-centered
cubic tantalum thin films as diffusion barriers between copper and
silicon", J. Vac. Sci. Technol. A 10(5), September/October 1992,
describes the resistivity of thin bcc-tantalum films and
.beta.-tantalum films. The resistivity for bcc-tantalum
(.alpha.-tantalum) films is said to be on the order of 30
.mu..OMEGA.-cm, while the resistivity of the .beta.-tantalum films
ranges from about 160-180 .mu..OMEGA.-cm. A comparison of the
effectiveness of thin bcc-Ta and .beta.-Ta layers as diffusion
barrier to copper penetration into silicon shows that the bcc-Ta
which exhibits low resistivity also performs well as a barrier
layer up to 650.degree. C.
[0008] Kyung-Hoon Min et al. in "Comparative study of tantalum and
tantalum nitrides (Ta.sub.2N and TaN) as a diffusion barrier for Cu
metallization", J. Vac. Sci. Technol. B 14(5), September/October
1996, discuss tantalum and tantalum nitride films of about 50 nm
thickness deposited by reactive sputtering onto a silicon
substrate. The performance of these films as a diffusion barrier
between copper and silicon is also discussed. The diffusion barrier
layer performance is said to be enhanced as nitrogen concentration
in the film is increased.
[0009] U.S. Pat. No. 3,607,384 to Frank D. Banks, issued Sep. 21,
1971, describes thin film resistors which utilize layers of
tantalum or tantalum nitride. FIG. 1 in the '385 patent shows the
resistivity for a particular tantalum nitride film as a function of
the sputtering voltage and FIG. 2 shows the resistivity as a
function of the nitrogen content of the film. The lowest
resistivity obtained under any conditions was about 179
.mu..OMEGA.-cm.
[0010] U.S. Pat. No. 3,819,976 to Chilton et al., issued Jun. 25,
1974, describes a tantalum-aluminum alloy attenuator for traveling
wave tubes. In the background art section of this patent, there is
a reference to tantalum film undergoing a phase transition from
beta-tantalum to body-centered-cubic (alpha) tantalum at about
700.degree. C.
[0011] U.S. Pat. No. 3,878,079 to Alois Schauer, issued Apr. 15,
1975, describes and claims a method of producing thin tantalum
films which are body-centered cubic lattices. The films are
deposited upon a glass substrate, and FIG. 2 of the '079 patent
shows resistivity for tantalum nitride films as a function of
nitrogen content. U.S. Pat. No. 4,000,055 to Kumagai et al., issued
Dec. 28, 1976, discloses a method of depositing nitrogen-doped
beta-tantalum thin films. FIG. 2 of the '055 patent also shows the
resistivity of the film as a function of the nitrogen content of
the film.
[0012] U.S. Pat. No. 4,364,099 to Koyama et al., issued Dec. 14,
1982, discloses a tantalum film capacitor having an
.alpha.-tantalum as a lower electrode, a chemical conversion layer
of .alpha.-tantalum as a dielectric, and an upper electrode. This
references also discusses a phase transition of the tantalum film
depending on the nitrogen concentration of the film. When the
nitrogen content ranges from about 6 to about 12 percent, the
resistivity of the tantalum thin film is said to be advantageously
low, although no particular resistivity data is provided.
[0013] U.S. Pat. No. 5,221,449 to Colgan et al., issued Jun. 22,
1993, describes a method of making alpha-tantalum thin films. In
particular, a seed layer of Ta(N) is grown upon a substrate by
reactive sputtering of tantalum in a nitrogen-containing
environment. A thin film of .alpha.-tantalum is then formed over
the Ta(N) seed layer. In the Background Art section of the patent,
reference is made to the "Handbook of Thin Film Technology",
McGraw-Hill, page 18-12 (1970), where it is reported that if the
substrate temperature exceeds 600.degree. C., alpha phase tantalum
film is formed. Further reference is made to an article by G.
Feinstein and R. D. Huttemann, "Factors Controlling the Structure
of Sputtered Tantalum Films", Thin Solid Films, Vol. 16, pages
129-145 (1973). The authors are said to divide substrates into
three groups: Group I, containing substrates onto which only
beta-tantalum can be formed (including glass, quartz, sapphire, and
metals such as copper and nickel); Group II, containing substrates
onto which only alpha (bcc) tantalum can be grown (including
substrates coated with 5000 .ANG. thick metal films such as gold,
platinum, or tungsten); and Group III, containing substrates which
normally produce alpha-tantalum, but which can be induced to yield
beta-tantalum or mixtures of alpha and beta by suitable treatment
of the surface (i e., substrates coated with 5,000 .ANG. of
molybdenum, silicon nitride, or stoichiometric tantalum nitride,
Ta.sub.2N).
[0014] As the feature size of semiconductor devices becomes ever
smaller, the barrier/wetting layer becomes a larger portion of the
interconnect structure. In order to maximize the benefit of
copper's low resistivity, the diffusion barrier/adhesion layer must
be made very thin and/or must have low resistivity itself (so that
it does not impact the effective line resistance of the resulting
metal interconnect structure). As is readily apparent, depending on
the device to be fabricated, various methods have been used in an
attempt to develop a tantalum film which is .alpha. phase when
lower resistivity is desired. Typically, small additions of
nitrogen have been made to tantalum films to lower the resistivity
of the tantalum. This method is difficult to control, as any
deviation in the nitrogen content (even .+-.1 sccm of nitrogen
flow) may lead to a significant increase in resistivity. Another
proposed sputter deposition method for lowering resistivity
involves control of the ion energy striking the substrate (via
grounding of the substrate). However, this method does not always
produce reproducible results, is sensitive to substrate cleaning
and preparation, and affects the film stress. Care must be taken to
avoid high film stress so that the barrier/wetting layer does not
tend to separate or pop off the substrate upon which it is
deposited.
[0015] After deposition of the tantalum-comprising barrier/wetting
layer, any of the tantalum-comprising material deposited on the
substrate in areas other than the conductive interconnect
structures must be removed. Whether the tantalum-comprising
material is removed by ion bombardment techniques (e.g., reactive
ion etching) or by CMP, the difference in hardness between the
tantalum-comprising material and copper causes problems. Residual
material from the copper deposition is rapidly removed, leaving
residual material from the tantalum-comprising barrier layer.
Continued ion bombardment or CMP to remove the tantalum-comprising
material can result in the undesired removal of adjacent copper
which is intended to make up the interconnect structure.
[0016] It would be highly desirable to have an ultra-low
resistivity tantalum film which exhibits low stress (tends to stay
bonded to underlying layers), and which is more easily polished
using CMP, so that its polishing rate is closer to that of
copper.
SUMMARY OF THE INVENTION
[0017] We have discovered that, by depositing a tantalum layer at
particular substrate temperatures, it is possible to obtain a lower
resistivity than has previously been known in the literature. The
low resistivity material has been obtained by sputter deposition at
an elevated substrate temperature ranging from about 325.degree. C.
to about 550.degree. C., or by sputter deposition at a substrate
temperature of less than about 325.degree. C. followed by annealing
at a temperature of about 325.degree. C. or greater. High density
plasma sputtering techniques which provide for ion bombardment of
the film surface can be used in combination with the elevated
substrate temperature, to add momentum energy to the film surface,
thereby reducing the substrate temperature required, while still
providing the ultra-low resistivity tantalum film. A reduction of
about 40% in the required substrate temperature can be obtained by
this means, while maintaining a reasonable film stress and a
reasonable film deposition time period.
[0018] In a less preferred, alternative method, a small amount
(less than about 15 atomic %) of nitrogen may be added to the
tantalum film (while depositing the film at an elevated
temperature) to obtain the lower resistivity at a slightly lower
substrate temperature, in the range of about 275.degree. C. This
provides a lower resistivity than previously known for nitrogen
addition, while reducing the process temperature necessary to
obtain the lower resistivity.
[0019] In another development, we have discovered that the tantalum
layer produced by the method of the present invention can be more
readily removed by the CMP polishing techniques used for removal of
excess, residual metal in the damascene process. The low
resistivity tantalum is more flexible, more easily cleaved, and
more easily polished--an advantage in the damascene process when it
is desired to remove excess metal from the field surface of a
device structure. This is particularly helpful when copper is used
as the interconnect metal, since copper polishes easily and it
previously took 4 times longer to remove tantalum barrier layer
then to remove excess copper from a field surface. The low
resistivity tantalum deposited using the present method exhibits an
increase in CMP polishing rate of nearly 50% over the previously
known CMP polishing rate for tantalum films.
BRIEF DESCRIPTION OF THE DRAWINGS
[0020] FIG. 1 shows a schematic cross-sectional view of a
sputtering chamber of the kind which can be used to deposit the
tantalum film of the present invention. This illustration shows the
critical elements of a high density plasma (ion-deposition)
sputtering chamber (or reactive-ion-deposition sputtering chamber).
The critical elements include a sputtering target to with DC power
is applied, an RF powered coil for creating and maintaining ionized
species within a plasma over the surface of the semiconductor
substrate being processed, and a means for application of RF power
to the support platen on which the substrate sets, enabling the
creation of a bias on the substrate. The combination of the RF
powered coil with the RF powered support platen enables the ion
bombardment of a film surface as the tantalum film is
deposited.
[0021] FIG. 2 is a graph showing the resistivity of a
sputter-deposited tantalum film (deposited using long-throw or high
density plasma techniques) as a function of the substrate platen
heater temperature during deposition of the film. The substrate
surface temperature is estimated to have been between 50.degree. C.
to 75.degree. C. colder than the substrate platen heater
temperature illustrated.
[0022] FIG. 3 is a graph showing the resistivity of a
sputter-deposited tantalum film (deposited using long-throw or high
density plasma techniques), where the tantalum was deposited at
room temperature, then annealed for 15 minutes at 400.degree. C. or
600.degree. C.
[0023] FIG. 4 is a graph showing the resistivity of a
sputter-deposited Ta.sub.xN.sub.y film (deposited using long-throw
or high density plasma techniques) as a function of the substrate
platen heater temperature during deposition of the film, wherein x
is 1 and y ranges from about 0.05 to about 0.18.
[0024] FIG. 5 is a graph showing the stress (in dynes/cm.sup.2) of
a sputter-deposited tantalum film (deposited using long-throw or
high density plasma techniques) as a function of the substrate
platen heater temperature during deposition of the film.
[0025] FIG. 6 is a graph showing the chemical-mechanical polishing
(CMP) removal rate (in .ANG./min) of a sputter-deposited tantalum
film (deposited using long throw or high density plasma techniques)
as a function of the substrate platen heater temperature. FIG. 6
also shows the CMP polishing rate for two Ta.sub.xN.sub.y films
which were deposited at a substrate platen heater temperature of
about 50.degree. C.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0026] We have discovered a surprising and simple method for
depositing ultra-low resistivity (about 10 .mu..OMEGA.-cm) tantalum
films. These films can be obtained by either sputter deposition
upon a substrate which is at an elevated temperature or by a
combination of deposition upon a substrate at such elevated
temperature with simultaneous ion bombardment of the film surface
during deposition.
[0027] Tantalum films having a slightly higher resistivity (about
20 .mu..OMEGA.-cm) can be obtained by deposition at low temperature
(e.g. room temperature), followed by thermal annealing. Deposition
at an elevated temperature is preferred for process throughput
reasons and because a lower resistivity is obtained.
[0028] Deposition of a 1,000 .ANG. thick tantalum film using high
density plasma or long-throw sputtering upon a silicon dioxide
substrate, at a substrate support platen temperature of about
400.degree. C. or higher (a substrate temperature of about
325.degree. C. or higher) results in a tantalum film resistivity of
about 10 .mu..OMEGA.-cm. (Deposition of thinner films under the
same conditions provides the same low resistivity.) This is
compared with a film resistivity of about 165 .mu..OMEGA.-cm
obtained for a tantalum film sputtered upon a room temperature
substrate. In addition, deposition of the tantalum film at room
temperature, followed by a 15 minute anneal at a substrate
temperature of either 350.degree. C. or 550.degree. C., produces a
tantalum film having a resistivity of about 20 .mu..OMEGA.-cm.
[0029] We have also discovered that by adding a small amount of
nitrogen to the sputtering chamber, to produce a Ta.sub.xN.sub.y
film where x is 1 and y ranges from about 0.5 to about 0.18, a
Ta.sub.xN.sub.y film having a resistivity of about 20
.mu..OMEGA.-cm can be obtained at even lower temperatures,
particularly at a substrate temperature of about 275.degree. C. or
greater.
[0030] Although tantalum and tantalum nitride are quickly gaining
industry acceptance as the barrier layer of choice for copper
metallization, the difference in CMP polishing rate between copper
and these materials causes problems in the damascene process for
preparation of copper interconnect structures. The softer copper,
which polishes more rapidly tends to "dish", i.e. to be removed
from an intended deposition area during the polishing period
necessary for removal of excess barrier layer materials. We have
discovered that the low resistivity .alpha. phase tantalum produced
by the method of the present invention (described above) shows a
CMP rate superior to standard .beta. phase tantalum and more
similar to that of tantalum nitride. This makes it possible to use
tantalum as the barrier layer and to use thicker tantalum barrier
layers.
[0031] A more detailed description of the ultra-low resistivity
tantalum films and methods for their deposition is presented
below.
[0032] I. Definitions
[0033] As a preface to the detailed description, it should be noted
that, as used in this specification and the appended claims, the
singular forms "a", "an", and "the" include plural referents,
unless the context clearly dictates otherwise. Thus, for example,
the term "a semiconductor" includes a variety of different
materials which are known to have the behavioral characteristics of
a semiconductor.
[0034] Specific terminology of particular importance to the
description of the present invention is defined below.
[0035] The term "aspect ratio" refers to, but is not limited to,
the ratio of the height dimension to the width dimension of
particular feature. When the feature has more than one width
dimension, the aspect ratio is typically calculated using the
smallest width dimension of the feature. For example, a contact via
opening which typically extends in a tubular form through multiple
layers has a height and a diameter, and the aspect ratio would be
the height of the tubular divided by the diameter. The aspect ratio
of a trench would be the height of the trench divided by the
minimal width of the trench, which typically occurs at its
base.
[0036] The term "collimated sputtering" refers to, but is not
limited to, collimated sputtering where a spatial filter or
`collimator`, comprising a plurality of transmissive cells, is
positioned between the sputtering target and the substrate to
prevent sputtered particles from reaching the substrate surface at
low angles of incidence. The spatial filter controls the location
at which sputtered emissions are deposited upon the substrate
surface. This serves to create a more directional flux to the
substrate.
[0037] The term "copper" includes, but is not limited to alloys of
copper of the kind typically used in the semiconductor industry.
The preferred embodiments described herein are with reference to a
copper alloy comprising about 98% by weight copper, but the
invention can be used in combination with other conductive
materials which exhibit a substantially smaller copper content. For
example, the invention can be used where the metallization layer
comprises aluminum-copper alloys, where the copper content is
typically less than about 4 weight %, and aluminum-copper-silicon
alloys, where the copper content is typically about 0.5 weight
%.
[0038] The term "decoupled plasma source" refers to a plasma
generation apparatus which has separate controls for power input to
a plasma source generator and to a substrate bias device. Typically
the plasma source controller controls the supply of inductively
coupled RF power which determines plasma density (source power) and
the bias controller controls the supply of RF power or DC power
which is used to generate a DC bias voltage on the semiconductor
substrate surface (bias power). The bias voltage affects the ion
bombardment energy on the substrate surface. This decoupled plasma
source typically incorporates measures to separate (decouple) the
influence of the source power and bias power on one another. The
ENDURA.RTM. metal deposition system and CENTURA.RTM. metal etch
system available from Applied Materials, Inc. of Santa Clara,
Calif. which includes decoupled plasma source power and bias power
control are referred to as "DPS" systems. Similar equipment
available from other manufacturers may be referred to by different
nomenclature.
[0039] The term "feature" refers to, but is not limited to,
contacts, vias, trenches, and other structures which make up the
topography of the substrate surface.
[0040] The term "high density plasma sputter deposition" or "ion
plasma deposition" or "IMP sputter deposition" refers to, but is
not limited to, sputter deposition, preferably magnetron sputter
deposition (where a magnet array is placed behind the target),
where a high density plasma is created using the application of
inductively coupled RF power which is typically applied to a coil
which is positioned between the sputtering cathode and the
substrate support electrode. This arrangement provides an increased
portion of the sputtered emission is in the form of ions at the
time it reaches the substrate surface. In high density plasma
deposition, the electron density is typically at least 10.sup.11
e.sup.-/cm.sup.3. A preferred apparatus for high density plasma
sputter deposition is the ENDURA.RTM. "IMP" metal deposition
system.
[0041] The term "ion deposited copper" or "IMP deposited copper"
refers to a copper deposition which was sputtered using a high
density plasma sputter deposition process.
[0042] The term "ion deposited Ta or Ta.sub.xN.sub.y" or "IMP
deposited Ta or Ta.sub.xN.sub.y" refers to a Ta or Ta.sub.xN.sub.y
deposition which was sputtered using a high density plasma sputter
deposition process.
[0043] The term "long-throw sputter deposition" refer to a sputter
deposition technique which utilizes conventional, non-collimated
magnetron sputtering at low pressures, where the distance between
the target and the substrate is equal to or greater than the
diameter of the substrate. Long-throw (gamma) sputter deposition
enables control of the degree of directionality in the deposition
of film layers, resulting in improved step coverage as compared
with conventional magnetron sputtering.
[0044] The term "reactive ion deposition" or "reactive ion metal
plasma" refers to ion-deposition sputtering wherein a reactive gas
is supplied during the sputtering to react with the ionized
material being sputtered, producing an ion-deposition sputtered
compound containing the reactive gas element.
[0045] The term "SEM" refers to a scanning electron microscope.
[0046] The term "standard copper deposition" or "traditional
sputtering" refers to a method of forming a film layer on a
substrate wherein a target is sputtered and the material sputtered
from the target passes between the target and the substrate to form
a film layer on the substrate, and no means is provided to ionize a
substantial portion of the target material sputtered from the
target before it reaches the substrate. One apparatus configured to
provide traditional sputtering is disclosed in U.S. Pat. No.
5,320,728, the disclosure of which is incorporated herein by
reference. In such a traditional sputtering configuration, the
percentage of ionized target material which reaches the substrate
is less than 10%, more typically less than 1%, of that sputtered
from the target.
[0047] The term "tantalum film" refers to a film wherein at least
98 atomic % of the film is tantalum.
[0048] The term "Ta.sub.xN.sub.y" refers to a material wherein x
represents the number of tantalum atoms and y represents the
relative number of nitrogen atoms.
[0049] II. An Apparatus for Practicing the Invention
[0050] A process system in which the method of the present
invention may be carried out is the Applied Materials, Inc. (Santa
Clara, Calif.) Endura.RTM. Integrated Processing System. This
process system is not specifically shown in the Figures. However,
the system is generally known in the semiconductor processing
industry and is shown and described in U.S. Pat. Nos. 5,186,718 and
5,236,868, the disclosures of which are incorporated by reference.
The critical elements of a reactive ion metal plasma sputter
deposition system are shown in a schematic format in FIG. 1.
Process chamber 100 is used for the high density plasma deposition
of a barrier layer such as a Ta or a Ta.sub.xN.sub.y layer.
[0051] Process chamber 100 is typically a magnetron chamber which
employs a standard sputter magnet (not shown) to confine the
sputtering plasma, enabling an increased sputtering rate. In
addition, the process chamber includes an inductively coupled RF
source 110, typically in the form of a single, flat coil 108,
positioned between a sputtering cathode (target) 102 and the
substrate support electrode 104, whereby a larger portion of the
sputtered emission is in the form of ions at the time it reaches
the substrate surface. An RF power source 106 is used to apply a
bias to substrate support electrode 104, enabling formation of a DC
bias on semiconductor substrate 105. Typically a shield 113
surrounds the area in which plasma 107 is created from gases which
enter through channels 103. Shield 113 is surrounded by a vacuum
chamber 112 which enables the evacuation of gases from the
substrate processing area through evacuation channels (not shown).
In the preferred embodiment of the present invention where the
barrier layer to be formed is Ta.sub.xN.sub.y, the tantalum nitride
is formed by sputtering a tantalum target using techniques known in
the art, where argon is gas used to create sputtering ions, and by
adding nitrogen to the process chamber 100 through channels 103. At
least a portion of the nitrogen is ionized as it passes by
ionization coil 108. The reactive nitrogen is free to react with
reactive tantalum to form tantalum nitride which is then attracted
toward the surface of semiconductor substrate 105 by the bias
placed on that substrate.
[0052] III. The Ultra-Low Resistivity Tantalum Films
[0053] The tantalum films of the invention have a resistivity of
less than 25 .mu..OMEGA.-cm; more preferably, less than 20
.mu..OMEGA.-cm; most preferably, less than 15 .mu..OMEGA.-cm.
Resistivities as low as 10 .mu..OMEGA.-cm or less have been
achieved using the deposition methods of the invention.
[0054] Curve 200, FIG. 2, shows the resistivity (on vertical axis
202) of sputter-deposited tantalum films (deposited via collimated,
or long-throw, or high density plasma techniques) as a function of
the substrate platen heater temperature (on vertical axis 204)
during deposition of the film. (The substrate surface temperature
is estimated to have been about 50.degree. C. to about 75.degree.
C. colder than the substrate platen heater temperature
illustrated.) The tantalum films represented by portion 206 of
curve 200, where the tantalum resistivity is greater than 100
.mu..OMEGA.-cm, were determined to be .beta.-tantalum. The tantalum
films represented by portion 208 of curve 200, where the
resistivity is less than 25 .mu..OMEGA.-cm, were determined to be
.alpha.-tantalum (body-centered cubic tantalum). The ultra low
resistivity films were obtained when the substrate platen heater
temperature was about 400.degree. C. (representing a substrate
temperature of about 325.degree. C.-350.degree. C.) or higher.
[0055] FIG. 3, at point 306, shows the resistivity of a
sputter-deposited tantalum film (deposited via collimated, or
long-throw, or high density plasma techniques) deposited at room
temperature (about 25.degree. C.). Once again, the resistivity is
shown on vertical axis 302 and the substrate platen heater
temperature is shown on horizontal axis 304. This sputter deposited
tantalum film, when annealed on the substrate support platen for a
time period of about 15 minutes at a heater temperature of about
400.degree. C. or higher, exhibits a resistivity of less than about
20 .mu..OMEGA.-cm, as illustrated by curve 308.
[0056] FIG. 4 shows the resistivity of collimated, or long-throw,
or high density plasma deposited films having a Ta.sub.x N.sub.y
composition, where x is 1 and y ranges from about 0.05 to about
0.18. The resistivity is shown as a function of the substrate
platen heater temperature during sputtering. Once again, the
resistivity is shown on vertical axis 402 and the substrate platen
heater temperature is shown on horizontal axis 404. The substrate
temperature is typically about 50.degree. C. to about 75.degree. C.
lower than the substrate platen heater temperature. With the
nitrogen present in the sputtered film, it is possible to obtain
the ultra low resistivity Ta.sub.x N.sub.y film at even lower
deposition temperatures. Ta.sub.x N.sub.y films having a
resistivity of about 20 .mu..OMEGA.-cm were obtained at substrate
heater temperatures of about 340.degree. C. or higher (substrate
temperatures of about 275.degree. C. or higher).
[0057] The ultra-low resistivity films of the present invention
tend to be low stress films as well. FIG. 5 is a graph showing the
stress (in dynes/cm.sup.2 on vertical axis 502) of a
sputter-deposited tantalum film as a function of the substrate
platen heater temperature (in .degree. C. on horizontal axis 504)
during deposition of the film. As can be seen from the graph in
FIG. 5, tantalum films deposited at heater temperatures within the
range of about 365.degree. C. to about 500.degree. C. had low
tensile stresses ranging from about -2.5.times.10.sup.9 to about
5.times.10.sup.9 dynes/cm.sup.2. The negative stress values,
represented by area 510 under line 507 represent tantalum films in
compression. The positive stress values, represented by area 508
over line 507 represent tantalum films in tension. By maintaining
the heater temperature at about 365.degree. C. or higher during
deposition of the film, the stability of the deposited film and its
adhesion to adjacent substrates is improved.
[0058] Unexpectedly, we discovered that the tantalum films of the
present invention can be polished more rapidly using CMP techniques
and are more flexible when cleaved than the prior art tantalum
films. FIG. 6 shows the chemical-mechanical polishing (CMP) removal
rate (in .ANG./min on vertical axis 602) of a sputter-deposited
tantalum film (deposited via collimated, or long-throw, or high
density plasma techniques, with or without nitrogen) as a function
of the substrate platen heater temperature (in .degree. C. on
horizontal axis 604). The CMP removal rate of Ta.sub.xN.sub.y (in
.ANG./min on vertical axis 602) as a function of nitrogen content
(in atomic % of the film on horizontal axis 605), when deposited at
a heater temperature of about 50.degree. C. Tantalum films
deposited at a heater temperature of 50.degree. C. had a CMP
removal rate of about 230 .ANG. per minute; Ta films deposited at a
heater temperature of 350.degree. C. had a CMP removal rate of
about 280 .ANG. per minute; and, Ta films deposited at a heater
temperature of 500.degree. C. had a CMP removal rate of about 340
.ANG. per minute. Extrapolating from the graph in FIG. 6, tantalum
films deposited at a heater temperature within the range of about
375.degree. C. to about 500.degree. C. (representing a substrate
temperature within the range of about 300-450.degree. C.) would
have a CMP removal rate in the range of about 300 to about 340
.ANG. per minute, which is significantly better than the CMP
removal rate of 230 .ANG. per minute obtained for Ta films
deposited at a heater temperature of 50.degree. C.
[0059] Referring again to the graph in FIG. 6, tantalum films
containing about 18 atomic percent nitrogen had a CMP removal rate
of about 250 .ANG. per minute. Tantalum films containing about 37
atomic percent nitrogen had a CMP removal rate of about 350 .ANG.
per minute. However, these films do not offer the low resistivity
of the Ta films of the present invention.
[0060] The ultra-low resistivity tantalum films of the invention
are particularly suited for use as barrier/adhesion layers for use
in copper metallization, in high stability conductive films for
integrated circuit devices (e.g., gate material to DRAMs, etc.), in
thin film resistors, and in ink jet heads, by way of example and
not by way of limitation.
[0061] IV. Methods for Depositing the Ultra-low Resistivity
Tantalum Films
[0062] A preferred embodiment method of the invention comprises
sputter depositing a tantalum film on a substrate at a substrate
temperature of about 325.degree. C. or greater; preferably, at a
substrate temperature within the range of about 350.degree. C. to
about 450.degree. C.
[0063] In a second preferred embodiment method, in addition to
sputter depositing a tantalum film on a substrate at an elevated
temperature, the surface of the film is ion bombarded during
deposition to transfer momentum energy to the film surface. This
permits deposition of the film at a temperature which is about 40%
lower than when ion bombardment is not used.
[0064] In a first, less preferred alternative method, the tantalum
film is sputter deposited at room temperature (about 25.degree.
C.), and the film is subsequently annealed at a temperature ranging
from about 325.degree. C. to about 550.degree. C. for a time period
of about 1 minute to about 15 minutes (longer periods will also
work).
[0065] In a second, less preferred alternative method, a
Ta.sub.xN.sub.y film is sputter deposited on a substrate at an
elevated temperature, where x is 1 and y ranges from about 0.05 to
about 0.18 (nitrogen is present in the sputtering chamber in an
amount which produces a Ta.sub.xN.sub.y film containing between
about 5 and about 15 atomic percent nitrogen). The elevated
substrate temperature is about 275.degree. C. or greater;
preferably, at a substrate temperature within the range of about
300.degree. C. to about 400.degree. C. It is expected that ion
bombardment of the Ta.sub.xN.sub.y film surface during sputter
deposition would permit deposition of the film at a temperature
which is about 40% lower, as described with respect to
tantalum.
[0066] In a third, less preferred alternative method, a
Ta.sub.xN.sub.y film was sputter deposited on the substrate at
approximately room temperature (i.e., at a substrate temperature
within the range of about 15.degree. C. to about 50.degree. C.),
and then annealed by heating the film (and substrate) to a
temperature within the range of about 325.degree. C. to about
550.degree. C. for a period of about 1 minute to about 15 minutes
(longer time periods will work also).
[0067] The method of the present invention is not limited to a
particular sputtering technique. In addition to the sputtering
techniques described above, it is possible to use an
externally-generated plasma (typically generated by microwave)
which is supplied to the film deposition chamber, or to use a
hallow cathode technique of the kind known in the art. However, we
have found that when the feature size is small (less than about 0.5
.mu.m) and the aspect ratio is high (about 2:1 or higher), it is
advantageous to use collimated, long-throw, or high density plasma
sputter deposition in the apparatus which is described in detail
herein.
[0068] Typical process parameters for high density plasma sputter
deposition, collimated sputter deposition, and long-throw sputter
deposition of the ultra-low resistivity tantalum films are set
forth in Table 1, below.
1TABLE 1 Typical Process Conditions for Sputter Deposition of
Ultra-low Resistivity Tantalum Films in ENDURA .RTM. Process
Chamber High Denisty Long-throw Process Parameter Plasma Collimated
(Gamma) Process Chamber 10-40 3-5 1-3 Pressure (mT) DC Power to
Target (kW) 1 4 4 RF Power to Coil (kW) 1.5 None None Bias Power
(W) 350 None None
[0069] An example of a high density plasma sputtering method is
provided by S. M. Rossnagel and J. Hopwood in their papers "Metal
ion deposition from ionized magnetron sputtering discharge", J.
Vac. Sci. Technol. B, Vol. 12, No. 1 (January/February 1994) and
"Thin, high atomic weight refractory film deposition for diffusion
barrier, adhesion layer, and seed layer applications", J. Vac. Sci.
Technol. B, Vol. 14, No. 3 (May/June 1996)
[0070] The technique for long throw sputtering is described by S.
M. Rossnagel and J. Hopwood in their paper entitled "Thin, high
atomic weight refractory film deposition for diffusion barrier,
adhesion layer, and seed layer applications", J. Vac. Sci.
Technol., B 14(3), May/June 1996. The method uses conventional,
non-collimated magnetron sputtering at low pressures, with improved
directionality of the depositing atoms. The improved directionality
is achieved by increasing the distance between the workpiece
surface (the throw), such that the distance between the target and
the substrate is equal to or greater than the diameter of the
substrate, and by reducing the argon pressure during sputtering.
For a film deposited with commercial cathodes (Applied Materials
Endura.RTM. class; circular planar cathode with a diameter of 30
cm) and rotating magnet defined erosion paths, a throw distance of
25 cm is said to be approximately equal to an interposed collimator
of aspect ratio near 1.0, to enable the aluminum to reach the
bottom and sidewalls of the contact via structure without causing a
bridge-over effect of the structure experienced in some sputter
deposition configurations. In the present disclosure, use of this
long-throw technique with traditional, non-collimated magnetron
sputtering at low pressures is sometimes referred to as "gamma
sputtering".
[0071] A description of collimated sputtering is provided in U.S.
Pat. No. 5,330,628 of Demaray et al., issued Jul. 19, 1994, and a
method of controlling a collimated sputtering source is described
in U.S. Pat. No. 5,478,455 to Actor et al. issued Dec. 26,
1995.
[0072] The method of the present invention is easily practiced in
view of the present disclosure, and does not require alteration of
existing physical vapor deposition (PVD) equipment presently
available within the industry. However, when it is desired to lower
the substrate temperature below about 325.degree. C. during
deposition of the tantalum film, it is necessary to use high
density plasma sputtering techniques which provide for ion
bombardment of the film surface, to add momentum energy to the
depositing film surface. This enables lowering of the substrate
surface temperature by as much as about 40%, while providing a
reasonable film deposition time period.
[0073] The method of the invention results in the production of
tantalum films and Ta.sub.xN.sub.y films having ultra-low bulk
resistivities and minimal residual film stress. The method of the
invention also provides tantalum films which can be more rapidly
polished using CMP techniques. The CMP rate of the tantalum films
of the present invention is more compatible with the CMP rate of
copper, resulting in a reduction of copper dishing.
[0074] The above described preferred embodiments are not intended
to limit the scope of the present invention, as one skilled in the
art can, in view of the present disclosure expand such embodiments
to correspond with the subject matter of the invention as claimed
below.
* * * * *