U.S. patent application number 10/060827 was filed with the patent office on 2002-06-13 for stress tunable tantalum and tantalum nitride films.
Invention is credited to Chiang, Tony, Chin, Barry L., Ding, Peijun.
Application Number | 20020070375 10/060827 |
Document ID | / |
Family ID | 25341126 |
Filed Date | 2002-06-13 |
United States Patent
Application |
20020070375 |
Kind Code |
A1 |
Chiang, Tony ; et
al. |
June 13, 2002 |
Stress tunable tantalum and tantalum nitride films
Abstract
The present disclosure pertains to our discovery that the
residual stress residing in a tantalum (Ta) film or a tantalum
nitride (TaN.sub.x, where 0<x.ltoreq.1.5) film can be controlled
(tuned) by controlling particular process variables during
deposition of the film. Process variables of particular interest
during film deposition, for sputter applied Ta and TaN.sub.x films,
include the following. The power to the sputtering target; the
process chamber pressure (i.e. the concentration of various gases
and ions present in the chamber); the substrate DC offset bias
voltage (typically an increase in the AC applied substrate bias
power); and, the temperature of the substrate upon which the film
is being deposited. When the Ta or TaN.sub.x film is deposited
using IMP sputtering, the power to the ionization coil can be used
for stress tuning of the film. Of these variables, the process
chamber pressure and the substrate offset bias most significantly
affect the tensile and compressive stress components, respectively.
The most advantageous tuning of a sputtered film is achieved using
Ion Metal Plasma (IMP) as the film deposition method. This
sputtering method provides for particular control over the ion
bombardment of the depositing film surface. Tantalum (Ta) films
deposited using the IMP method typically exhibit a residual stress
ranging from about +1.times.10.sup.+10 dynes/cm.sup.2 (tensile
stress) to about -2.times.10.sup.+10 dynes/cm.sup.2 (compressive
stress), depending on the process variables described above.
Tantalum nitride (TaN.sub.x) films deposited using the IMP method
typically can be tuned to exhibit a residual stress within the same
range as that specified above with reference to Ta films. We have
been able to reduce the residual stress in either the Ta or
TaN.sub.x films to range between about 6.times.10.sup.+9 and about
-6.times.10.sup.+9 dynes/cm.sup.2 using tuning techniques described
herein. The Ta and TaN.sub.x films can also be tuned subsequent to
deposition using ion bombardment of the film surface and annealing
of the deposited film.
Inventors: |
Chiang, Tony; (Mountain
View, CA) ; Ding, Peijun; (San Jose, CA) ;
Chin, Barry L.; (Saratoga, CA) |
Correspondence
Address: |
Patent Counsel
Applied Materials, Inc.
P.O. Box 450 A
Santa Clara
CA
65052
US
|
Family ID: |
25341126 |
Appl. No.: |
10/060827 |
Filed: |
January 29, 2002 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10060827 |
Jan 29, 2002 |
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09611624 |
Jul 7, 2000 |
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09611624 |
Jul 7, 2000 |
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08863451 |
May 27, 1997 |
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Current U.S.
Class: |
252/512 ;
204/192.15; 204/192.17; 204/192.21; 252/518.1; 257/E21.169;
257/E21.582 |
Current CPC
Class: |
C23C 14/358 20130101;
H01L 21/76843 20130101; H01L 21/76841 20130101; C23C 14/5833
20130101; H01L 21/76864 20130101; H01L 2924/0002 20130101; C23C
14/16 20130101; H01L 23/53238 20130101; C23C 14/345 20130101; H01L
21/2855 20130101; C23C 14/3492 20130101; H01L 21/76838 20130101;
H01L 23/53233 20130101; C23C 14/0036 20130101; C23C 14/0641
20130101; H01L 21/76862 20130101; H01L 2924/0002 20130101; H01L
2924/00 20130101 |
Class at
Publication: |
252/512 ;
204/192.15; 204/192.17; 204/192.21; 252/518.1 |
International
Class: |
C23C 014/32; H01B
001/08 |
Claims
We claim:
1. A Ta film tuned to have a residual film stress ranging between
about 1.0.times.10.sup.+10 and about -2.times.10.sup.+10
dynes/cm.sup.2.
2. The Ta film of claim 1, wherein said Ta film was sputter
deposited.
3. The Ta film of claim 2, wherein said Ta film was IMP sputter
deposited.
4. The Ta film of claim 1, wherein said film residual stress ranges
between about 6.times.10.sup.+9 and about -6.times.10.sup.+9
dynes/cm.sup.2.
5. The Ta film of claim 1, wherein a crystalline structure of said
tantalum film is bcc Ta.
6. The Ta film of claim 1, wherein a crystalline structure of said
tantalum film is S Ta.
7. A TaN.sub.x film, where 0<x.ltoreq.1.5, tuned to have a
residual film stress ranging between about 1.0.times.10.sup.+10 and
about -2.times.10.sup.+10 dynes/cm.sup.2.
8. The TaN.sub.x film of claim 7, wherein said TaN.sub.x film was
sputter deposited.
9. The TaN.sub.x film of claim 8, wherein said TaN.sub.x film was
reactive IMP sputter deposited.
10. The TaN.sub.x film of claim 7, wherein said film residual
stress ranges between about 6.times.10.sup.+9 and about
-6.times.10.sup.+9 dynes/cm.sup.2.
11. The TaN.sub.x film of claim 7, wherein said film resistivity is
less than about 1,000 .mu..OMEGA.-cm and said film stress ranges
between about 6.times.10.sup.+9 and about -6.times.10.sup.+9
dynes/cm.sup.2.
12. The TaN.sub.x film of claim 11, wherein said film comprises
more than about 30 atomic % nitrogen.
13. The TaN.sub.x film of claim 12, wherein said film comprises and
less than about 60% nitrogen.
14. A method of tuning the residual film stress of a Ta film,
wherein said residual stress is tuned by controlling the amount of
ion bombardment of the depositing film surface.
15. The method of claim 14, wherein said Ta film is deposited using
a sputtering technique.
16. The method of claim 15, wherein said Ta film is deposited using
IMP sputtering.
17. The method of claim 15, wherein said tantalum film comprises
bcc Ta.
18. The method of claim 15, wherein a crystalline structure of said
tantalum film is .beta. Ta.
19. A method of tuning tile residual film stress of a Ta film by
adjustment of a film deposition process variable selected from the
group consisting of process chamber pressure, substrate DC offset
bias voltage, power to a sputtering target, power to an ionization
coil, substrate temperature, or a combination thereof.
20. The method of claim 19, wherein said residual film stress is
tuned to range between about 1.times.10.sup.+10 and about
-2.times.10.sup.+10 dynes/cm.sup.2.
21. A method of tuning the residual film stress of a Ta film
subsequent to deposition, wherein said treatment is selected from
the group consisting of ion bombardment, annealing, and
combinations thereof.
22. The method of claim 21, wherein said residual film stress is
tuned to range between about 1.times.10.sup.+10 and about
-2.times.10.sup.+10 dynes/cm.sub.2.
23. The method of claim 21, wherein said method of tuning is ion
bombardment.
24. The method of claim 21, wherein said method of tuning is
annealing, and wherein said annealing is carried out at a
temperature of at least about 25.degree. C.
25. The method of claim 24, wherein said temperature is at least
about 250.degree. C.
26. The method of claim 25, wherein said temperature is at least
about 350.degree. C.
27. A method of tuning the residual film stress of a TaN.sub.x,
film, wherein said residual stress is tuned by controlling the
amount of ion bombardment of the depositing film surface and where
0<x.ltoreq.1.5.
28. The method of claim 27, wherein said TaN.sub.x film is
deposited using a sputtering technique.
29. The method of claim 28, wherein said TaN film is deposited
using reactive IMP sputtering.
30. The method of claim 29, wherein said TaN.sub.x film comprises
at least about 30 atomic % nitrogen.
31. The method of claim 30, wherein said nitrogen content is less
than about 60 atomic % nitrogen.
32 A method of tuning the residual film stress of a TaN.sub.x film
by adjustment of a film deposition process variable selected from
the group consisting of process chamber pressure, substrate DC
offset bias voltage, power to a sputtering target, power to an
ionization coil, substrate temperature, or a combination
thereof.
33. The method of claim 32, wherein said residual film stress is
tuned to range between about 1.times.10.sup.+10 and about
-2.times.10.sup.+10 dynes/cm.sup.2.
34. A method of tuning the residual film stress of a TaN.sub.x film
subsequent to deposition, wherein said treatment is selected from
the group consisting of ion bombardment, annealing, and
combinations thereof.
35. The method of claim 34, wherein said residual film stress is
tuned to range between about 1.times.10.sup.+10 and about
-2.times.10.sup.+10 dynes/cm.sub.2.
36. The method of claim 34, wherein said method of tuning is ion
bombardment.
37. The method of claim 34, wherein said method of tuning is
annealing, and wherein said annealing is carried out at a
temperature of at least about 25.degree. C.
38. The method of claim 37, wherein said temperature is at least
about 250.degree. C.
39. The method of claim 38, wherein said temperature is at least
about 350.degree. C.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention pertains to tantalum and tantalum
nitride films which can be stress tuned to be in tension or in
compression or to have a particularly low stress, and to a method
of producing such films. These stress tuned films are particularly
useful in semiconductor interconnect structures where they can be
used to balance the stress within a stack of layers which includes
a combination of barrier layers, wetting layers, and conductive
layers, for example. Tge low stress tantalum and tantalum nitride
films are particularly suited for the lining of vias and trenches
having a high 1:1 aspect ratio.
[0003] 2. Brief Description of the Background Art
[0004] A typical process for producing a multilevel structure
having feature sizes in the range of 0.5 micron (.mu.m) or less
would include: blanket deposition of a dielectric material;
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 conductive material onto the
substrate in sufficient thickness to fill the openings; and removal
of excessive conductive material from the substrate surface using a
chemical, mechanical, or combined chemical-mechanical polishing
techniques. Future technological requirements have placed a focus
on the replacement of aluminium (and aluminum alloys) by copper as
the conductive material. As a result, there is an increased
interest in tantalum nitride barrier layers and in tantalum
barrier/wetting layers which are preferred for use in combination
with copper.
[0005] Tantalum nitride barrier films, Ta.sub.2N and TaN.sub.x have
been shown to function up to 700.degree. C. and 750.degree. C.,
respectively, without the diffusion of copper into an underlying
silicon (Si) substrate. Tantalum barrier/wetting films have been
shown to function at temperatures of approximately 500.degree. C.
It is advantageous in terms of processing simplicity to sputter the
barrier and or wetting layers underlaying the copper. Tantalum
nitride barrier layers are most commonly prepared using reactive
physical sputtering, typically with magnetron cathodes, where the
sputtering target is tantalum and nitrogen is introduced into the
reaction chamber.
[0006] S. M. Rossnagel and J. Hopwood describe a technique which
enables control of the degree of directionality in the deposition
of diffusion barriers in their paper titled "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. In particular, the paper describes a method of
depositing tantalum (Ta) which permits the deposition of the
tantalum atoms on steep sidewalls of interconnect vias and
trenches. 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 cathode and the workpiece
surface (the throw) 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. In the present
disclosure, use of this "long throw" technique with traditional,
non-collimated magnetron sputtering at low pressures is referred to
as "Gamma sputtering".
[0007] Gamma sputtering enables the deposition of thin, conformal
coatings on sidewalls of a trench having an aspect ratio of 2.8:1
for 0.5 .mu.m-wide trench features. However, we have determined
that Gamma sputtered TaN films exhibit a relatively high film
residual compressive stress, in the range of about
-1.0.times.10.sup.+10 to about -5.0.times.10.sup.+10
dynes/cm.sup.2. High film residual compressive stress, in the range
described above can cause a Ta film or a tantalum nitride (e.g.
Ta.sub.2N or TaN) film to peel off from the underlying substrate
(typically silicon oxide dielectric). In the alternative, the film
stress can cause feature distortion on the substrate (typically a
silicon wafer) surface or even deformation of a thin wafer.
[0008] A method of reducing the residual stress in a Ta
barrier/wetting film or a Ta.sub.2N or TaN barrier film would be
beneficial in enabling the execution of subsequent process steps
without delamination of such films from trench and via sidewalls or
other interconnect features. This reduces the number of particles
generated, increasing device yield during production. In addition,
a film having a near zero stress condition improves the reliability
of the device itself.
SUMMARY OF THE INVENTION
[0009] We have discovered that the residual stress residing in a
tantalum (Ta) film or a tantalum nitride (TaN.sub.x, where
0<x.ltoreq.1.5) film can be controlled (tuned) by controlling
particular process variables during deposition of the film. Process
variables of particular interest for sputter applied Ta and
TaN.sub.x films include the following. An increase in the power to
the sputtering target (typically DC) increases the compressive
stress component in the film. An increase in the process chamber
pressure (i.e. the concentration of various gases and ions present
in the chamber) increases the tensile stress component in the film.
An increase in the substrate DC offset bias voltage (typically an
increase in the applied AC as substrate bias power) stress
component in the film. The substrate temperature during deposition
of the film also affects the film residual stress. Of these
variables, an increase in the process chamber pressure-and an
increase in the substrate offset bias most significantly affect the
tensile and compressive stress components, respectively. The most
advantageous tuning of a sputtered film is achieved using Ion Metal
Plasma (IMP) as the film deposition method. This sputtering method
provides for particular control over the ion bombardment of the
depositing film surface. When it is desired to produce a film
having minimal residual stress, particular care must be taken to
control the amount of ion bombardment of the depositing film
surface, as an excess of such ion bombardment can result in an
increase in the residual compressive stress component in the
deposited film.
[0010] Tantalum (Ta) films deposited using the IMP method typically
exhibit a residual stress ranging from about +1.times.10.sup.+10
dynes/cm.sup.2 (tensile stress) to about -2.times.10.sup.+10
dynes/cm.sup.2 (compressive stress), depending on the process
variables described above. Tantalum nitride (TaN.sub.x) films
deposited using the IMP method typically can be tuned to exhibit a
residual stress within the same range as that specified above with
reference to Ta films. We have been able to reduce the residual
stress in either the Ta or TaN.sub.x films to low values ranging
from about +1.times.10.sup.+9 to about -2.times.10.sup.+9
dynes/cm.sup.2 using tuning techniques described herein. These film
residual stress values are significantly less than observed for
traditionally sputtered films and for Gamma-sputtered films. This
reduction in film residual compressive stress is particularly
attributed to bombardment of the film surface by IMP-generated ions
during the film deposition process. Heavy bombardment of the film
surface by IMP-generated ions can increase the film residual
compressive stress, so when it is desired to minimize the film
compressive stress, the ion bombardment should be optimized for
this purpose.
[0011] Other process variables which may be used in tuning the film
stress include the spacing between the sputter target and the
substrate surface to be sputter deposited; ion bombardment
subsequent to film deposition; and annealing of the film during or
after deposition.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] FIG. 1 is a graph showing the residual stress in an IMP
deposited Ta film as a function of DC power to the Ta target, RF
power to the IMP ionization coil, and the pressure in the process
chamber.
[0013] FIG. 2A is a contour plot showing the IMP deposited Ta film
residual stress in dynes/cm.sup.2 as a function of the DC power to
the Ta target and the process chamber pressure, when the RF power
to the ionization coil is 1 kW.
[0014] FIG. 2B is a contour plot showing the residual stress in an
IMP deposited Ta film as a function of the same variables
illustrated in FIG. 2A, when the RF power to the ionization coil is
3 kW.
[0015] FIG. 3 is a graph showing the residual stress in an IMP
deposited Ta film as a function of the substrate offset bias, and
in particular as a function of the AC bias power (typically the AC
power is coupled to the substrate through the substrate heater
which is in electrical contact with the substrate).
[0016] FIG. 4 is a graph showing the chemical composition of a
Gamma-sputtered tantalum nitride film, as a function of the
nitrogen gas flow rate to the sputtering process chamber. In
addition, FIG. 4 shows the resistivity and the structure of the
tantalum nitride compound, which is in conformance with the
nitrogen content of the compound.
[0017] FIG. 5 is a graph showing the film composition of a reactive
IMP-deposited tantalum nitride film, as a function of the nitrogen
gas flow rate to the process chamber. Again, the resistivity of the
film is indicative of the various film structures created as the
nitrogen content of the film is increased.
[0018] FIG. 6 is a graph showing the residual film stress for
Gamma-sputtered tantalum nitride film as a function of the nitrogen
gas flow rate to the sputtering process chamber and as a function
of the temperature at which the film is deposited.
[0019] FIG. 7 is a graph showing the residual film stress for
reactive IMP sputtered tantalum nitride film as a function of the
nitrogen gas flow rate to the sputtering process chamber.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0020] The present invention pertains to stress tunable tantalum
and tantalum nitride films and to a method of producing such films.
In particular, applicants have discovered that residual film stress
can be tuned by controlling particular process variables such as
process chamber pressure, DC offset bias voltage, power to the
sputtering target and substrate temperature during film deposition.
When IMP sputtering is used, a variation in the power to the
ionization coil can be used for tuning. Ion bombardment of the
depositing film surface is particularly useful in controlling
residual film stress.
I. Definitions
[0021] 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, reference to a "plasma" includes a gas or gas
reactants activated by an RF glow discharge, and reference to
"copper" includes alloys thereof.
[0022] Film stress values were measured using a Tencor.RTM. Flexus
FLX 3200 machine available from Tencor Corporation, Mountain View,
Calif.
[0023] Specific terminology of particular importance to the
description of the present invention is defined below.
[0024] The term "aspect ratio" refers to the ratio of the height
dimension to the width dimension of particular openings into which
an electrical contact is to be placed. For example, a 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
travel width of the trench at its base.
[0025] The term "completely filled" refers to the characteristic af
a feature such as a trench or via which is filled with a conductive
material, wherein there is essentially no void space present within
the portion of the feature filled with conductive material.
[0026] The term "copper" refers to copper and alloys thereof,
wherein the copper content of the alloy is at least 80 atomic %
copper. The alloy may comprise more than two elemental
components.
[0027] The term "feature" refers to contacts, vias, trenches, and
other structures which make up the topography of the substrate
surface.
[0028] The term "Gamma or (.gamma.) sputtered copper" refers to the
"long throw" sputtering technique described in the paper by S. M.
Rossnagel and J. Hopwood, which was discussed previously herein.
Typically the distance between the substrate and the target is
about the diameter of the substrate or greater; and, preferably,
the process gas pressure is sufficiently low that the mean free
path for collision within the process gas is greater than the
distance between the target and the substrate.
[0029] The term "ion metal plasma" or "IMP" refer to sputter
deposition, preferably magnetron sputter deposition (where a magnet
array is placed behind the target). A high density, inductively
coupled RF plasma is positioned between the sputtering cathode and
the substrate support electrode, whereby at least a portion of the
sputtered emission is in the form of ions at the time it reaches
the substrate surface.
[0030] The term "IMP sputtered tantalum" refers to tantalum which
was sputtered using the IMP sputter deposition method.
[0031] The term "IMP sputtered tantalum nitride" refers to tantalum
nitride which was sputtered using the IMP sputter deposition
method.
[0032] The term "reactive IMP sputtered tantalum nitride" refers to
ion-deposition sputtering wherein nitrogen gas is supplied during
the sputtering of tantalum, to react with the ionized tantalum,
producing an ion-deposition sputtered tantalum nitride-comprising
compound.
[0033] The term "stress tuned" refers to a TaN.sub.x or Ta film
which has been treated during processing to adjust the residual
stress within the deposited film to fall within a particular
desired range. For example, at times it is desired to use the
TaN.sub.x or Ta film to balance the overall stress within a stack
of layers, so the film may be tuned to be in compression or
tension. At other times it may be desired to reduce the stress in
the film to be as near to zero as possible.
[0034] The term "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 target material which is ionized
is less than 10 %, more typically less than 1%, of that sputtered
from the target.
II. An Apparatus for Practicing the Invention
[0035] 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. The system
is shown and described in U.S. Pat. No. 5,186,718, the disclosure
of which is hereby incorporated by reference.
[0036] The traditional sputtering process is well known in the art.
The Gamma sputtering method is described in detail by S. M.
Rossnagel and J. Hopwood in their paper titled "Thin, high atomic
weight refractory film deposition for diffusion barrier, adhesion
layer, and seed layer applications", as referenced above. The IMP
sputtering method is also described by S. M. Rossnagel and J.
Hopwood in their paper "Metal ion deposition from ionized magnetron
sputtering discharge, J. Vac. Sci. Technol. B, Vol. 12, No. 1
(January/February 1994).
III. The Structure of the Tantalum and Tantalum Nitride Films
[0037] We have been able to create a copper filled trench or via,
which is completely filled, at a feature size of about 0.4.mu. and
an aspect ratio of greater than 1:1 (up to about 3:1 presently). To
facilitate the use of a copper fill, the trench or via (constructed
in a silicon oxide surface layer) was lined with a reactive IMP
sputtered TaN.sub.x barrier layer, followed by a Ta barrier/wetting
layer, to create a bilayer over the oxide surface layer. The copper
fill layer was applied using a sputtering technique in the manner
described in applicants' co-pending application, Attorney Docket
No. 1811, filed May 13, 1997, which is hereby incorporated by
reference.
[0038] To ensure the overall dimensional stability of the
structure, we investigated various factors which affect the
residual film stress in a TaN.sub.x barrier layer and in a Ta layer
(which can serve as a barrier layer, a wetting layer, or both,
depending on the application).
[0039] One skilled in the art can division a combination of a
number of different layers underlaying the copper fill material.
Whatever the combination of layers, they provide a stack of layers;
and tuning the stress of individual layers within the stack can
provide a more stress balanced and dimensionally stable stack.
Although the preferred embodiment described above is for the lining
of trenches and vias, one skilled in the art will appreciate that
the stress tuned TaN.sub.x and Ta films described herein have
general application in semiconductor interconnect structures. The
method of controlling and reducing the residual film stress in
tantalum nitride and tantalum films can be used to advantage in any
structure in which a layer of such a film is present. The concept
of tuning the residual stress in a sputter-deposited film
comprising at least one metal element has broad applicability.
IV. The Method of Tuning Residual Stress in Tantalum and Tantalum
Nitride Films
[0040] The preferred embodiments described herein were produced in
an Endura.RTM. Integrated Processing System available from Applied
Materials of Santa Clara, Calif. The physical vapor deposition
(sputtering in this case) process chamber is capable of processing
an 8 inch (200 mm) diameter silicon wafer. The substrate was a
silicon wafer having a silicon oxide surface coating with trenches
in the surface of the silicon oxide. Sputtering was carried out
using a tantalum target cathode having approximately a 35.3 cm (14
in.) diameter, and DC power was applied to this cathode over a
range from about 1 kW to about 18 kW. The substrate was placed at a
distance of about 25 cm (9.8 in.) from the tantalum target cathode
in the case of gamma sputtering, and at a distance of about 14 cm
(5.5 in.) from the cathode in the case of IMP sputtering. During
IMP sputtering, an AC bias power ranging from about 0 W to about
400 W was applied to the substrate, to produce a substrate offset
bias ranging from about 0 V to about -100 V. The substrate offset
bias attracts ions from the plasma to the substrate.
EXAMPLE ONE
[0041] When Gamma-sputtered tantalum film was produced, the film
was sputtered using conventional (traditional) magnetron
sputtering, with rotating magnet-defined erosion paths (for better
uniformity and cathode utilization). Two hundred (200) mm sample
surfaces were sputter-deposited at a sample surface temperature of
about 25.degree. C., in argon, at pressures of about 1.5 mT or
less. The cathode to sample or "throw" distance was typically about
25 cm. The DC power to the tantalum target was approximately 4 kW.
No substrate offset bias was used. Under these conditions, the
residual film stress of the tantalum film was about
-1.5.times.10.sup.+10 dynes/cm.sup.2.
EXAMPLE TWO
[0042] When IMP-sputtered tantalum film was produced, a high
density, inductively coupled RF plasma was generated in the region
between the target cathode and the substrate by applying RF power
to a coil (having from 1 to 3 turns) over a range from about 400
kHz to about 13.56 MHz (preferably about 2 MHz). Two hundred (200)
mm sample surfaces were IMP sputter-deposited at a sample surface
temperature of about 25.degree. C., in argon, at pressures ranging
from about 10 mT to about 60 mT. The distance from the cathode to
the sample was typically about 14 cm. The DC power to the tantalum
target was adjusted over a range from about 1 kW to about 8 kW
(preferably about 1 kW to about 3 kW). The wattage to the RF power
coil was adjusted over a range from about 1.0 kW to about 5 kW
(preferably about 1.0 kW to about 3 kW). An AC bias power ranging
from about 0 W to about 500 W was used. FIG. 1 shows a graph 100 of
the residual film stress 101 of the tantalum film in
Dynes/cm.sup.2, as a function of the RF power 108 to the ionization
coil, as illustrated by the curve numbered 102; the pressure 110 in
the sputtering chamber, as illustrated by the curve numbered 104;
and the DC power 112 to the sputtering target (cathode), as
illustrated by the curve numbered 106.
[0043] As indicated in graph 100, the residual stress in the
deposited Ta film can be tuned over a wide range, for example (but
not by way of limitation), from about 1.0.times.10.sup.+10 to about
-2.times.10.sup.+10, and can be set at a low stress nominal value,
for example, between about 6.times.10.sup.+10 and about
-6.times.10.sup.+9, a range over which the residual stress can
approach zero. At a residual stress of about -6.times.10.sup.+9, by
way of example, the IMP sputtered film residual compressive stress
is a factor of three lower than the residual compressive stress of
a typical gamma-sputtered Ta film. The process variables which
affect film residual stress can be optimized to produce the desired
residual film stress in Ta films.
[0044] FIGS. 2A and 2B show the effect of an increase in the RF
power to the IMP ionization coil, which is directly related to the
amount of ion bombardment at the tantalum film surface. FIG. 2A,
graph 200, shows the Ta residual film stress in curves 201 through
206, when the power to the ionization coil is 1 kW, as a function
of process chamber argon pressure 207 and the DC power to the
tantalum target 208. FIG. 2B, graph 220, shows the Ta residual film
stress interior of ellipses 221 and 222, when the power to the
ionization coil is 3 kW, as a function of process chamber argon
pressure 227 and the DC power to the tantalum target 228.
[0045] These curves show that, with the other process values held
constant, an increase in RF power to the ionization coil from 1 kW
to 3 kW results in an increase in the film residual compressive
stress. Even so, under all of the process conditions shown, the
residual film stress for the IMP-sputtered tantalum is less than
that of a Gamma-sputtered tantalum film. We have concluded, then,
that there is an optimum amount of ion bombardment of a tantalum
film surface to produce a Ta film having only minor residual stress
(whether compressive or in tension). Process pressure appears to
have the greatest effect of the variables tested. It is believed
that an increase in the process pressure leads to an increase in
ionization within the process chamber, which leads to increased ion
bombardment of the depositing film surface.
EXAMPLE THREE
[0046] The effect of the increase in ion bombardment of a
depositing film surface, which can be achieved by increasing the DC
offset bias voltage of the substrate onto which the film is
deposited, is illustrated in FIG. 3. Graph 300 shows the residual
stress 311 in dynes/cm.sup.2 310 as a function of the AC bias power
320 in Watts The corresponding substrate DC offset bias voltage
ranges from about 0 V to about -150 V.
EXAMPLE FOUR
[0047] When tantalum nitride films are produced, the structure of
the tantalum nitride depends on the amount of nitrogen in the
tantalum nitride compound (film). FIGS. 4 and 5 show the chemical
composition and resistivity of tantalum nitride films produced
using Gamma sputtering and IMP sputtering techniques, respectively.
The chemical composition (atomic nitrogen content) of the film is
shown as a function of the nitrogen gas flow rate to the process
chamber in which the TaN.sub.x film is produced.
[0048] FIG. 4, graph 400, shows the nitrogen content 410 of the
Gamma-sputtered tantalum nitride film in atomic % 413, as a
function of the nitrogen flow rate 416 in sccm to the process
vessel. A two hundred (200) mm diameter sample surface was Gamma
sputter-deposited at a sample surface temperature of about
25.degree. C., in an argon/nitrogen atmosphere, at a pressure of
about 1.5 mT, where the Argon gas feed was about 15 sccm and the
nitrogen flow rate 416 was as shown on graph 400. The "throw"
distance between the tantalum target and the sample surface was
approximately 250 mm. The DC power to the tantalum target was about
4 kW.
[0049] In addition, graph 400 shows the resistivity 412 in
.mu..OMEGA.-cm 414 of the tantalum nitride film as the nitrogen
content 413 increases. The resistivity corresponds with the change
in the tantalum nitride structure, as indicated on Graph 400, where
402 represents .beta.-Ta; 404 represents bcc-Ta(N); 406 represents
amorphous TaN.sub.x; and 408 represents nanocrystalline
fcc-TaN.sub.x (x.apprxeq.1).
[0050] FIG. 4 shows that when the atomic nitrogen content exceeds
about 45% to about 50%, the resistivity of the TaN.sub.x film
increases drastically (to above 1,000 .mu..OMEGA.-cm).
[0051] FIG. 6, graph 600, shows the residual film stress in
dynes/cm.sup.2 602 of a Gamma sputtered TaN.sub.x film, as a
function of the nitrogen flow rate to the process chamber in sccm
604, and as a function of the substrate temperature at the time of
film deposition, when the other process variables are held at the
values described with reference to FIG. 4.
[0052] Curve 610 represents the TaN.sub.x film Gamma sputtered at a
substrate temperature of about 25.degree. C.; Curve 612 represents
the TaN.sub.x film Gamma sputtered at a substrate temperature of
about 250.degree. C., and Curve 614 represents the TaN.sub.x film
Gamma sputtered at a substrate temperature of about 450.degree.
C.
[0053] Line 606 constructed at a nitrogen flow rate 604 of about 16
scm, represents the atomic nitrogen content in excess of which the
resistivity of the TaN.sub.x film increases drastically (as
illustrated in FIG. 4 for a nitrogen flow rate of 16 sccm). Thus,
the gamma-sputtered TaN.sub.x films having reduced residual
compressive stress (in the direction of arrow 608) occur at
nitrogen contents at which the resistivity of the film is
unacceptably high (greater than about 1,000 .mu..OMEGA.-cm).
Looking at the residual film stress of TaN.sub.x films having a
resistivity lower than about 1,000 .mu..OMEGA.-cm, it is evident
that residual film stress can be reduced by increasing the
substrate temperature at the time of film deposition. This is in
contrast with TaN.sub.x films having a resistivity higher than
about 1,000 .mu..OMEGA.-cm, where the residual film stress
increases when the substrate temperature is higher during film
deposition. Considering this unexpected result, for Gamma sputtered
films having a nitrogen content below about 45%-50 %, it is
preferable to deposit the TaN.sub.x film at a substrate temperature
of at least about 250.degree. C., and more preferably at a
substrate temperature of at least about 350.degree.C.
EXAMPLE FIVE
[0054] FIG. 5 graph 500 shows the nitrogen content 510 of the
reactive IMP-sputtered TaN film in atomic % 513, as a function of
the nitrogen flow rate in sccm 516 to the process chamber. A two
hundred (200) mm diameter sample (substrate) surface was reactive
IMP sputter-deposited at a sample surface temperature of about
25.degree. C., in an argon/nitrogen atmosphere, at a pressure of
about 40 mT, where Argon gas feed was about 95 sccm (80 sccm to the
process chamber feed and 15 sccm to the heat exchange surface) and
the nitrogen flow rate 516 was as shown on graph 500. The DC power
to the tantalum target was about 2 kW. The RF power to the IMP
induction coil was about 1.5 kW. No offset bias of the substrate
was used.
[0055] In addition, graph 500 shows the resistivity 512 in
.mu..OMEGA.-cm 514 of the IMP sputtered TaN.sub.x film as the
atomic nitrogen content 513 increases. The resistivity corresponds
with the change in the tantalum nitride structure, as indicated on
Graph 500, where 502 represents .beta.-Ta; 504 represents
bcc-Ta(N); 506 represents amorphous TaN.sub.x; and 508 represents
nanocrystalline fcc-TaN.sub.x (x=I).
[0056] FIG. 5 also shows that when the atomic nitrogen content
exceeds about 45%, the resistivity of the TaN.sub.x film increases
drastically (to above 1,000 .mu..OMEGA.-cm).
[0057] FIG. 7, graph 700, shows the residual film stress in
dynes/cm.sup.2 702 of an IMP sputtered TaN.sub.x film, as a
function of the nitrogen flow rate to the process chamber in sccm
704, for deposition on a substrate at a temperature of about
25.degree. C., when the other process variables are held at the
values described with reference to FIG. 5.
[0058] Line 706, constructed at a nitrogen flow rate 704 of about
14- 16 sccm, represents the atomic nitrogen content in excess of
which the resistivity of the TaN.sub.x film increases drastically
(as illustrated in FIG. 5). We discovered that for IMP sputtered
TaN.sub.x films, in contrast with the gamma sputtered films, it is
possible to produce a film having reduced residual stress at the
lower nitrogen contents, where an acceptable resistivity can be
obtained. Further, the IMP sputtered TaN.sub.x film residual stress
appears to remain relatively unaffected by an increase in the
nitrogen content over the nitrogen content range represented by the
nitrogen flow rates illustrated in FIG. 7 (up to about 60 atomic %
nitrogen, based on FIG. 5).
[0059] By depositing the tantalum nitride film using the IMP
sputtering method which provides increased bombardment of the
depositing film surface (over that obtained by the Gamma sputtering
method), it is possible to produce a TaN.sub.x film having both an
acceptable resistivity and reduced residual film stress. This is
because the IMP sputtered TaN.sub.x film stress remains relatively
unchanged with increasing nitrogen content (in comparison with
gamma sputtered TaN.sub.x film stress which is strongly dependent
on the nitrogen content of the film in the region where the film
resistivity is acceptable).
[0060] 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 claimed
below.
* * * * *