U.S. patent application number 10/024689 was filed with the patent office on 2002-08-29 for method for enhancing the adhesion of copper deposited by chemical vapor deposition.
Invention is credited to Carl, Daniel, Chen, Liang, Cong, Dennis, Gandikota, Srinivas, Ramaswami, Sesh.
Application Number | 20020119657 10/024689 |
Document ID | / |
Family ID | 23009845 |
Filed Date | 2002-08-29 |
United States Patent
Application |
20020119657 |
Kind Code |
A1 |
Gandikota, Srinivas ; et
al. |
August 29, 2002 |
Method for enhancing the adhesion of copper deposited by chemical
vapor deposition
Abstract
The present invention provides a method for improving the
adhesion of copper and other metal-comprising conductive metals to
a barrier layer. A barrier is provided that has a first surface
that is substantially unoxidized, wherein at least a portion of the
surface is free from the presence of oxygen atoms. A conductive
layer is then deposited onto the first surface of the barrier
layer. The substantially unoxidized state of the first surface
enhances the adhesion of the metal-comprising layer to the barrier
layer. The method is particularly useful in obtaining excellent
adhesion of a copper nucleation layer to an underlying barrier
layer surface.
Inventors: |
Gandikota, Srinivas; (Santa
Clara, CA) ; Cong, Dennis; (Sunnyvale, CA) ;
Chen, Liang; (Foster City, CA) ; Ramaswami, Sesh;
(Saratoga, CA) ; Carl, Daniel; (Pleasanton,
CA) |
Correspondence
Address: |
Patent Counsel
Applied Materials, Inc.
P.O. Box 450 A
Santa Clara
CA
95052
US
|
Family ID: |
23009845 |
Appl. No.: |
10/024689 |
Filed: |
December 17, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10024689 |
Dec 17, 2001 |
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09265290 |
Mar 9, 1999 |
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6362099 |
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Current U.S.
Class: |
438/687 |
Current CPC
Class: |
H01L 23/53233 20130101;
H01L 2924/0002 20130101; H01L 23/53238 20130101; H01L 2924/0002
20130101; H01L 2924/00 20130101 |
Class at
Publication: |
438/687 |
International
Class: |
H01L 021/44 |
Claims
What is claimed is:
1. A method for depositing copper, comprising: (a) providing a
barrier layer having a first surface that is substantially
unoxidized; and (b) depositing a first copper layer onto the first
surface of the barrier layer.
2. The method of claim 1, wherein the barrier layer has an adhesion
promoting top layer on which the first surface is disposed.
3. The method of claim 1, wherein the first copper layer is
deposited by chemical vapor deposition (CVD).
4. The method of claim 1, wherein the first copper layer is
deposited by physical vapor deposition (PVD).
5. The method of claim 1, wherein the first copper layer is
deposited by electroless plating.
6. The method of claim 1, wherein the first copper layer is
deposited by electroplating.
7. The method of claim 1, wherein the first surface of the barrier
layer includes a noble metal, in a quantity sufficient to affect
the tendency of the first surface of the barrier layer to
oxidize.
8. The method of claim 7, wherein the first surface of the barrier
layer includes one or more metals selected from the group
consisting of gold (Au), silver (Ag), platinum (Pt), chromium (Cr),
nickel (Ni), and palladium (Pd), in a quantity sufficient to affect
the tendency of the first surface of the barrier layer to
oxidize.
9. The method of claim 8, wherein the first surface of the barrier
layer consists essentially of one or more metals selected from the
group consisting of gold (Au), silver (Ag), platinum (Pt), chromium
(Cr), nickel (Ni), and palladium (Pd), in a quantity sufficient to
affect the tendency of the first surface of the barrier layer to
oxidize.
10. The method of claim 9, wherein said barrier layer is
subsequently used as a seed layer for the electroless plating of
copper.
11. The method of claim 9, wherein the first surface of the barrier
layer consists essentially of gold (Au).
12. The method of claim 9, wherein the first surface of the barrier
layer consists essentially of silver (Ag).
13. The method of claim 9, wherein the first surface of the barrier
layer consists essentially of platinum (Pt).
14. The method of claim 9, wherein the first surface of the barrier
layer consists essentially of Nickel (Ni).
15. The method of claim 9, wherein the first surface of the barrier
layer consists essentially of palladium (Pd).
16. The method of claim 7, wherein the noble metal is added to the
barrier layer by ion implantation.
17. The method of claim 1, wherein the first surface of the barrier
layer includes a refractory metal that forms a volatile oxide, in a
quantity sufficient to affect the tendency of the first surface of
the barrier layer to oxidize.
18. The method of claim 17, wherein the first surface of the
barrier layer includes one or more metals selected from the group
consisting of tungsten (W) and molybdenum (Mo), in a quantity
sufficient to affect the tendency of the first surface of the
barrier layer to oxidize.
19. The method of claim 18, wherein the first surface of the
barrier layer consists essentially of one or more metals selected
from the group consisting of tungsten (W) and molybdenum (Mo), in a
quantity sufficient to affect the tendency of the first surface of
the barrier layer to oxidize.
20. The method of claim 19, wherein the first surface of the
barrier layer consists essentially of tungsten (W).
21. The method of claim 19, wherein the first surface of the
barrier layer consists essentially of molybdenum (Mo).
22. The method of claim 1, wherein the first copper layer is
deposited from a precursor containing less than about 2,000 ppm of
water.
23. The method of claim 1, wherein the first surface that is
substantially unoxidized is provided by removing oxide from the
surface of barrier layer.
24. The method of claim 23, wherein the oxide is removed using a
process selected from the group consisting of ion bombardment,
reactive cleaning by contact with a gas which reacts with the oxide
to produce a volatile reaction product, and reactive cleaning by
contact with a plasma species which reacts with the oxide to
produce a volatile reaction product.
25. The method of claim 1, wherein the environment to which the
first surface of the barrier layer is exposed, and the period of
time that is allowed to elapse, between the completion of step (a)
and the beginning of step (b), are controlled such that a
substantial amount of oxide does not form on the first surface of
the barrier layer.
26. The method of claim 1, wherein the deposition of Cu is started
while the deposition o the barrier layer is still proceeding, and
wherein the first surface refers to the part of the barrier layer
deposited just before the deposition of Cu is started.
27. The method of claim 1, wherein the copper layer is deposited by
CVD, and wherein a precursor used to deposit the first copper layer
is combined with a material of the barrier layer prior to
deposition during the period of time after step (b) is started and
before step (a) is completed.
28. The method of claim 1, further comprising the step of
depositing a second copper layer onto the first copper layer by
chemical vapor deposition (CVD) using process parameters different
than those used in step (b).
29. The method of claim 1, further comprising the step of
depositing a second copper layer onto the first copper layer by
physical vapor deposition (PVD) using process parameter different
than those used in step (b).
30. A method for depositing layers onto a substrate, comprising:
(a) depositing a barrier layer onto a substrate, wherein a first
surface of the barrier layer includes a noble metal in a quantity
sufficient to affect the tendency of the first surface of the
barrier layer to oxidize; (b) depositing a first copper layer by
chemical vapor deposition (CVD) onto the first surface of the
barrier layer.
31. A method for depositing layers onto a substrate, comprising:
(a) depositing a barrier layer onto a substrate, wherein a first
surface of the barrier layer includes refractory metals that form
volatile oxides, in a quantity sufficient to affect the tendency of
the first surface of the barrier layer to oxidize; (b) depositing a
first copper layer by chemical vapor deposition (CVD) onto a first
surface of the barrier layer.
32. A method for depositing layers onto a substrate, comprising:
(a) depositing a barrier layer onto a substrate; (b) depositing a
first copper layer by chemical vapor deposition (CVD) onto a first
surface of the barrier layer, wherein the first copper layer is
deposited from a precursor that contains less than about 2,000 ppm
of water.
33. A method for depositing layers onto a substrate, comprising:
(a) depositing a barrier layer onto a substrate; (b) removing oxide
from a surface of barrier layer;. (c) depositing a first copper
layer by chemical vapor deposition (CVD) onto the surface of the
barrier layer.
34. A method for depositing layers onto a substrate, comprising:
(a) depositing a barrier layer onto a substrate; and (c) depositing
a first copper layer by chemical vapor deposition (CVD) onto the
surface of the barrier layer; wherein the environment to which the
first surface of the barrier layer is exposed, and the period of
time that is allowed to elapse, between the completion of step (a)
and the beginning of step (b), are controlled such that a
substantial amount of oxide does not form on the first surface of
the barrier layer.
35. A method for depositing layers onto a substrate, comprising:
(a) depositing a barrier layer onto a substrate; (b) depositing a
first copper layer by chemical vapor deposition (CVD) onto the
surface of the barrier layer, wherein, wherein the deposition of Cu
is started while the deposition of the barrier layer is still
proceeding.
36. A semiconductor wafer comprising: a barrier layer; and a copper
layer deposited onto the barrier layer; wherein the interface
between the barrier layer and the copper layer is substantially
free of oxides.
37. A method of preventing particulate formation during processing
of a semiconductor substrate, wherein said processing includes
deposition of a copper layer either by CVD or by electroless
plating of copper, said method comprising depositing a
non-oxidizing layer of material upon process apparatus surfaces
prior to initiation of said deposition of said copper layer,
whereby excess copper which is not deposited upon said
semiconductor substrate is adhered to said non-oxidized layer of
material which is present upon said process apparatus surfaces.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates generally to a metallization
process for manufacturing semiconductor devices. More particularly,
the present invention relates to the use of barrier layers having
enhanced adhesion to overlying conductive films of copper and other
conductive materials.
[0003] 2. Background
[0004] Multilevel metal interconnects having a dimension smaller
than 0.20 microns are expected to play a key part in achieving
ultra large scale integration (ULSI), which is the next generation
of very large scale integration (VLSI). It is also expected that
the Damascene process, which involves the deposition of metal into
patterned dielectric openings, followed by subsequent
chemical-mechanical polishing (CMP) to provide planarization, will
also play a key part in achieving such multilevel metal
interconnects. As a result, there is a need for a method to
reliably deposit metal into patterned dielectric trenches, and to
do so in a way that leads to interconnects having desirable
properties. The Damascene process is described in Ryu, C.,
"Microstructure and Reliability of Copper Interconnects," doctoral
thesis, Stanford University (June 1998), which is hereby
incorporated by reference.
[0005] Aluminum (Al) has been widely used as an interconnect metal
because of its good electrical properties. Preferred, known
procedures for depositing Al interconnects include chemical vapor
deposition (CVD) and physical vapor deposition (PVD). CVD is a
preferred procedure for depositing Al into high aspect ratio
features of the kind found in Damascene processes, because it leads
to good conformal layers of Al, i.e., layers that have a uniform
thickness over the substrate surface even when the topography of
the surface includes a base and sidewalls requiring step coverage,
such as in a trench or contact via. It is known to fabricate Al
interconnects by depositing Al by CVD at relatively low
temperatures into apertures smaller than 0.5 microns.
[0006] However, as device sizes continue to shrink while device
densities, chip sizes, and maximum interconnect length increase,
the limitations of Al become increasingly apparent. In particular,
interconnects having a width smaller than about 0.18 microns are
desirable for the next generation of integrated circuits. However,
at this dimension, the electromigration of aluminum can cause
failures in the interconnect. The resistivity of Al also leads to
unacceptably high resistances for long interconnects, which can
lead to RC delay, i.e., a delay due to the time required for the
energy stored in an interconnect to dissipated. Accordingly, new
metals are needed to satisfy the requirements of the next
generation of integrated circuits.
[0007] Copper (Cu) is currently being investigated as a replacement
for aluminum in interconnects. Ryu, which was previously
incorporated by reference, provides a review of the current state
of the art with respect to copper interconnects. Cu has a bulk
resistivity of 1.67 .mu..OMEGA.-cm, which is approximately 40% less
than that of Al (2.66 .mu..OMEGA.-cm). Also, Cu exhibits resistance
to electromigration superior to that of Al under similar
circumstances, and lower RC delay. Thus, the lower resistivity of
Cu accommodates a higher line density, i.e., a smaller width, while
allowing for increased device speed.
[0008] Copper interconnects may be deposited by a variety of
conventional procedures, such as physical vapor deposition (PVD),
electroplating, and electroless plating. Chemical vapor deposition
(CVD) is a viable method due to its superior step coverage and
selective deposition capability. CVD involves the formation of a
reaction product, copper in this case, on a substrate by thermal
reaction or decomposition of gaseous compounds, referred to as
precursors. Metal-organic CVD (MOCVD), which uses one or more
organo-metallic precursors, is preferred for the CVD of copper
because they may be used at relatively low temperatures. Preferred
organo-metallic precursors include Cu.sup.+2(hfac).sub.2 and
Cu.sup.+2(fod).sub.2, where hfac is an abbreviation for the
hexafluoroacetylacetonate anion, and fod is an abbreviation for
heptafluoro dimethyl octanediene.
[0009] A preferred process uses the volatile liquid complex
copper.sup.+1(hfac)(tmvs) as a precursor, where tmvs is an
abbreviation for trimethylvinylsilane, with argon as a carrier gas.
Because this precursor is a liquid under ambient conditions, it can
be utilized in standard CVD bubbler precursor delivery systems
currently used in semiconductor fabrication. The deposition
reaction is believed to proceed on a heated substrate according to
the following mechanism, in which (s) denotes interaction with a
surface and (g) denotes the gas phase.
[0010] (1) 2Cu.sup.+1(hfac)(tmvs) (g).fwdarw.2Cu.sup.+1(hfac)(tmvs)
(s)
[0011] (2) 2Cu.sup.+1(hfac)(tmvs) (s).fwdarw.2Cu.sup.+1(hfac) (s)+2
(tmvs) (g)
[0012] (3) 2Cu.sup.+1hfac(s).fwdarw.Cu(hfac)
(s)+Cu.sup.+2(hfac).sub.2 (s)
[0013] (4) Cu(hfac) (s)+Cu.sup.+2(hfac)(s).fwdarw.Cu
(s)+Cu.sup.+2(hfac).sub.2(s)
[0014] In step 1, the precursor is adsorbed from the gas phase onto
a metallic surface. In step 2, the precursor is dissociated to
2Cu.sup.+1(hfac) and 2 (tmvs). (tmvs) leaves the surface by
desorption. In step 3, Cu(hfac) and Cu.sup.+2(hfac).sub.2 are
generated by electron exchange between surface Cu.sup.+1(hfac)
species. In step 4, copper metal and volatile Cu.sup.+2(hfac).sub.2
are formed by the migration of (hfac) groups.
Cut.sup.+2(hfac).sub.2 leaves the surface by desorption, leaving
copper metal. The overall disproportionation reaction is described
by the following equation:
2Cu.sup.+1(hfac)(tmvs) (g).fwdarw.Cu
(s)+Cu.sup.-2(hfac).sub.2(g)+2(tmvs) (g)
[0015] Both tmvs and Cu.sup.+2(hfac).sub.2 are volatile byproducts
of the deposition reaction that are exhausted from the chamber.
Cu.sup.+2(hfac).sub.2 does not contribute to further deposition
because the temperature is much lower than that required for
Cu.sup.+2(hfac).sub.2 decomposition.
[0016] Cu.sup.+1(hfac)(tmvs) can be used as a precursor to deposit
Cu through either a thermal process, or a plasma based process,
referred to as plasma enhanced CVD (PECVD). The substrate is
preferably held at a temperature between about 100 and 400.degree.
C. for PECVD of Cu from Cu.sup.+1(hfac)(tmvs). The substrate is
preferably held at a temperature between about 150 and 220.degree.
C., and more preferably at about 170.degree. C., for CVD of Cu from
Cu.sup.+1(hfac)(tmvs) that is not plasma enhanced. Lower
temperatures result in a very slow deposition rate, and higher
temperatures may adversely affect the resistivity of the resultant
interconnect. Thermal CVD is typically preferred over PECVD due to
the lower temperatures typically involved with thermal CVD.
[0017] However, copper may diffuse into surrounding dielectric or
insulating layers, as well as the underlying silicon substrate, and
interfere with the desirable properties of those layers. This
problem also exists with aluminum, and it is known to use a barrier
layer to separate such interconnects from other features. Barrier
layers for aluminum interconnects are commonly made from materials
that include tantalum (Ta), tantalum nitride (TaN), titanium (Ti),
and titanium nitride (TiN). It is also known to use a barrier layer
to separate copper interconnects from other features. Barrier
layers used to separate copper interconnects from other features
include those listed above for use with aluminum interconnects.
However, while the interaction between these barrier layers and
aluminum has been intensively studied, the interaction with Cu may
be different. In particular, there is often poor adhesion between
barrier layers and the copper interconnects deposited on the
barrier layers, which may lead to dewetting and device failures due
to high via resistance and poor electromigration resistance. This
problem is particularly pronounced with Cu interconnects deposited
by CVD, but may also exist to a lesser extent with Cu deposited by
other methods, such as PVD, electroplating, and electroless
plating. In addition, an improper selection of a barrier layer may
lead to problems with the growth of the copper interconnect,
interfacial contamination, and/or an undesirable microstructure in
the copper. With respect to CVD, efforts at solving these problems
have largely been directed to attempts to prevent chlorine and
fluorine present in the precursors from incorporating into the
copper films.
[0018] Layers of Cu deposited by PVD have typically demonstrated
better adhesion to conventional barrier layers than layers of Cu
deposited by CVD. However, CVD is preferred over PVD for other
reasons, such as superior trench and via fill. To take advantage of
the favorable properties of both CVD and PVD, it is known to
deposit a seed layer of Cu by PVD for good adhesion to the
underlying barrier layer, followed by the deposition of Cu by CVD
to achieve superior trench and via fill. However, using both CVD
and PVD requires extra process steps which increases manufacturing
time and cost. It is also known to anneal CVD deposited Cu after
deposition to enhance adhesion. See id.
SUMMARY OF THE INVENTION
[0019] The present invention provides a method for improving the
adhesion of copper and other conductive metals to a substrate, such
as a barrier layer. A barrier is provided that has a first surface
that is substantially unoxidized. A copper layer is then deposited
onto the first surface of the barrier layer. The substantially
unoxidized state of the first surface enhances the adhesion of the
copper layer to the barrier layer. The substantially unoxidized
first surface of the barrier layer may be provided by preventing
oxidation of the barrier layer subsequent to its deposition, or by
removing or displacing oxidation from at least a portion of the
barrier layer surface prior to deposition of the conductive metal.
Further, an adhesion promoting material may be added to the barrier
layer which ensures that at least a portion of the barrier surface
remains free from oxidation. In the case of copper, the copper may
be deposited by a variety of processes, including chemical vapor
deposition (CVD), physical vapor deposition (PVD), electroless
plating, and electroplating, for example.
[0020] The substantially unoxidized first surface of a barrier
layer may be provided by including a noble metal in the barrier
layer. This noble metal may be selected from the group consisting
of gold (Au), silver (Ag), platinum (Pt), chromium (Cr), nickel
(Ni), and palladium (Pd), for example. The barrier layer may
consist essentially of the noble metal, or may be doped with the
noble metal, so that at least a portion of the surface of the
barrier layer will not be oxidized. The barrier layer may include
an adhesion promotion layer of the noble metal. The noble metal may
be added to the barrier layer by ion implantation and other
techniques known in the art.
[0021] The substantially unoxidized first surface may also be
provided by including a refractory metal that forms a volatile
oxide at the barrier layer surface, using the techniques described
above with reference to noble metals. This refractory metal may be
selected from the group consisting of tungsten (W) and molybdenum
(Mo), for example, but not by way of limitation.
[0022] The environment to which the barrier layer is exposed may
also be controlled to minimize oxidation prior to application of
the metal-comprising interconnect material. For example, the
deposition of copper may be started while the deposition of the
barrier layer is still proceeding. When the copper is deposited by
CVD, the material of the barrier layer may be incorporated into the
precursor during at least the first portion of the CVD deposition.
Oxidation of the barrier layer during the deposition of copper by
chemical vapor deposition (CVD) may be avoided by using a precursor
that is substantially free of water.
[0023] The substantially unoxidized first surface may be provided
by removing oxide from the surface of barrier layer using
techniques such as ion bombardment, chemical reaction to produce a
volatile species, and contact with a displacing material, for
example, and not by way of limitation.
BRIEF DESCRIPTION OF THE DRAWINGS
[0024] FIG. 1 shows a metallization geometry useful for Cu
interconnects in accordance with the present invention.
[0025] FIG. 2 shows a diagram'of an exemplary integrated cluster
tool of the kind useful in controlling the ambient to which a
substrate surface is exposed during the PVD deposition of barrier
layers and the CVD deposition of metal-comprising interconnect
layers.
[0026] FIG. 3 shows an XPS peak for tantalum for a sample having a
Ta barrier layer onto which Cu was deposited using a Cupra 2500
precursor.
[0027] FIG. 4 shows an XPS peak for oxygen for the sample of FIG.
3.
[0028] FIG. 5 shows an XPS peak for tantalum in a sample similar to
that of FIG. 3, but where the Cu was deposited using a Cupra 2504
precursor.
[0029] FIG. 6 shows an XPS peak for oxygen for the sample of FIG.
5.
[0030] FIG. 7 shows a SIMS profile for a sample having a Ta barrier
layer.
[0031] FIG. 8 shows a SIMS profile for a sample having a Ni barrier
layer.
[0032] FIG. 9 shows a SIMS profile for a sample having a Pt barrier
layer.
DETAILED DESCRIPTION OF THE INVENTION
[0033] The present invention provides a copper interconnect having
excellent adhesion to an underlying barrier layer. While not
intending to be limited by the theory as to how the present
invention works, the inventors believe that poor adhesion between
metal-comprising interconnect depositions and barrier layers is
typically caused by oxidation present on the surface of
conventional barrier layers fabricated by conventional methods.
This oxidation appears to be especially harmful when copper is the
metal-comprising interconnect material.
[0034] 1. Definitions
[0035] 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, and reference to "copper" includes alloys
thereof.
[0036] Specific terminology of particular importance to the
description of the present invention is defined below.
[0037] The term "aspect ratio" refers to, but is not limited to,
the ratio of the height dimension to the width dimension of a
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.
[0038] The term "copper" refers to copper and alloys thereof,
wherein the copper content of the alloy is at least 80 atomic %.
The alloy may comprise more than two elemental components.
[0039] 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. The
substrate 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
plasma source power and bias power on one another.
[0040] 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.
[0041] The term "FWHM" refers to a conmnonly reported indication of
aluminum texture. The FWHM is obtained from an X-ray diffraction
"Rocking Curve", which is a measurement obtained by rotating
(rocking) a sample through the specified Bragg angles of its phases
while the X-ray detector is fixed at 2.theta.. The FWHM, expressed
in degrees, represents the number of degrees spanned by the width
of the curve at half its maximum height. A wider curve, spanning a
larger number of degrees, indicates that the crystallographic
orientation of interest is not highly textured. A narrow curve,
spanning a limited number of degrees is a strong signal, indicating
a larger quantity of the crystallographic orientation of interest
(a high texture). The FWHM measurement is preferred over the
diffraction intensity, since it is less sensitive to the
measurement variables and is a direct indicator of the degree of
texture for a given sample. The Rocking Curve has become a standard
indicator of electromigration resistance for a deposited aluminum
film, since electromigration is directly related to
crystallographic orientation of the aluminum.
[0042] The term "high density plasma sputter deposition" refers to,
but is not limited to a sputter deposition (preferably a magnetron
sputter deposition), where a high density, inductively coupled RF
plasma is created 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.
[0043] The term "SIMS" refers to a secondary ion mass
spectrometer.
[0044] 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.
[0045] The term "XPS" refers to X-ray photo electron
spectroscopy.
[0046] 2. An Apparatus for Practicing the Invention
[0047] A process system which can be used to carry out substrate
pre-cleaning steps (typically ion bombardment), the deposition of
barrier layers and the deposition of copper seed layers is the
ENDURA.RTM. Integrated Processing System available from Applied
Materials, Inc. (Santa Clara, Calif.) The system is shown and
described in U.S. Pat. Nos. 5,186,718 and 5,236,868, the
disclosures of which are incorporated by reference. FIG. 2 shows
one configuration of an ENDURA.RTM. Integrated Processing
System
[0048] 3. Preferred Embodiments of the Present Invention
[0049] With respect to Cu deposited by CVD using
copper.sup.+1(hfac)(tmvs) as a precursor in particular, the
inventors believe that a metallic or electrically conductive
barrier layer having a non-oxidized surface facilitates the
electron transfer that occurs in step (3) of the deposition
reaction described in the background section, while an oxidized
barrier layer surface inhibits this electron transfer. It is
believed that such oxidation similarly inhibits steps necessary for
good adhesion in other deposition processes for Cu, such as PVD,
electroplating, and electroless plating. The present invention
provides a barrier layer having a substantially unoxidized surface,
onto which Cu can be deposited such that there is goos adhesion
between the Cu and the barrier layer. "Substantially unoxidized"
means having a metallic surface that facilitates the deposition of
Cu, relative to an oxidized surface. Preferably, the substantially
unoxidized surface has less than a single monolayer of oxide. At a
minimum, at least portions of the barrier layer surface are free
from the presence of oxygen atoms.
[0050] There are several ways to provide a barrier layer having a
substantially unoxidized surface. A barrier layer material may be
chosen that does not oxidize under the conditions to which it will
be exposed, using thermodynamic, kinetic, or other criteria. The
barrier material may be a noble metal known to be resistant to
oxidation under many conditions, such as gold (Au), silver (Ag),
platinum (Pt), chromium (Cr), nickel (Ni), and palladium (Pd). The
barrier material may be a refractory metal, such as tungsten (W)
and molybdenum (Mo), that forms a volatile oxide, i.e., an oxide
that vaporizes under vacuum conditions,. The barrier may be made of
a material that is not necessarily resistant to oxidation, but is
doped with a material resistant to oxidation to improve the
oxidation resistance of the barrier layer and to ensure the
presence of non-oxidized surface areas on the barrier layer. A
material resistant to oxidation may also be incorporated into at
least the initial portion of the Cu deposition process to enhance
adhesion. For example, a noble metal may be incorporated into a
precursor used to deposit Cu by CVD.
[0051] The environment to which the barrier layer is exposed may
also be controlled to minimize oxidation. The preferred embodiment
of the present invention includes the use of materials that are not
necessarily resistant to oxidation, but where the environment can
be controlled to produce a surface substantially free of oxide at
the time of Cu deposition. Cu may be deposited shortly after
depositing a barrier material, such that there is not time for the
barrier material to oxidize. The deposition of Cu may be started
before the deposition of the barrier layer is complete, such that
the barrier layer has no time to form an oxide, and there is an
interface at which Cu is intimately mixed with the material of the
barrier layer. A vacuum or a controlled non-oxidizing environment
is preferably maintained over the barrier layer until the Cu is
deposited, for example by performing the deposition of the barrier
layer and the Cu in the same vacuum chamber or in connected vacuum
chambers, where the chamber ambients are non-oxidizing and may
include a flow-through nonreactive gas which sweeps across the
barrier layer surface to prevent oxidation of such surface.
[0052] The barrier layer may comprise multiple layers, where the
top layer is an adhesion promotion layer onto which the Cu is to be
deposited, such that the underlying layers may be fabricated of
materials to which Cu may not adhere as well, but which have other
desirable properties. Such an adhesion promotion top layer may be
fabricated by depositing layers of barrier material in sequence.
Alternatively, the barrier layer may include an adhesion-promoting
dopant that preferentially migrates to the surface of the barrier
layer. An annealing step may be performed to segregate such a
dopant to the surface.
[0053] The material and method of fabricating the barrier layer are
preferably chosen such that the barrier is a conformal layer that
prevents diffusion of Cu into surrounding materials, adheres well
to the underlying material, has good conductivity, and does not
adversely affect the properties of the underlying materials. As a
result, some barrier layers and methods that provide a surface
substantially free of oxide onto which Cu may be deposited may not
be suitable for use in some devices, yet may be suitable for use in
others.
Thermodynamic Selection of Suitable Barrier Materials
[0054] Some metals are known to be resistant to oxidation under a
variety of environments, including environments to which barrier
layers are typically exposed. These metals include gold (Au),
silver (Ag), platinum (Pt), chromium (Cr), nickel (Ni), and
palladium (Pd). Other metals are known to have oxides that are
volatile under the vacuum conditions to which barrier layers are
exposed, such as tungsten (W) and molybdenum (Mo). Depending upon
criteria unrelated to adhesion, such as compatibility with the rest
of the device and processing complexity and cost, any of these
metals may be preferred for use as a barrier layer, a dopant or
component in a barrier layer, and/or an adhesion promotion top
layer of a barrier layer.
[0055] Thermodynamic criteria may be used to select a material
resistant to oxidation for use as a barrier layer. For example,
Table 1 shows the Heat of oxide formation for various oxides of
materials used in semiconductor fabrication.
1TABLE 1 Heat of oxide formation Compound Heat of Formation
Al.sub.2O.sub.3 -399 K cal/mole Au.sub.2O.sub.3 11 K cal/mole CuO
-38.5 K cal/mole Cu.sub.2O -43 K cal/mole MgO -143.84 K cal/mole
NiO -58.4 K cal/mole PdO -20.4 K cal/mole SiO.sub.2 -202 K cal/mole
TiO.sub.2 -214 K cal/mole Ta.sub.2O.sub.5 -486 K cal/mole
[0056] In addition to resistance to oxidation, the conductivity of
the barrier layer material may also be considered. Proposed
materials and their resistivities include: Au (2.4 .mu..OMEGA.-cm),
Co (9 .mu..OMEGA.-cm), Ni (7 .mu..OMEGA.-cm), Pt (10.5
.mu..OMEGA.Q-cm), Pd (10.8 .mu..OMEGA.-cm). Typically an acceptable
material will have a resistivity of less than about 50
.mu..OMEGA.-cm.
Environmental Control to Reduce Oxidation of the Barrier Layer
[0057] Depending upon the barrier material used, the amount of
oxide that forms on the barrier layer may be sensitive to the
environment to which the barrier layer is exposed. Preferably, the
barrier material is selected such that significant amounts of oxide
do not form under a variety of environments, such that careful
control of the environment is not necessary. However, barrier
materials that do form oxides may be used within the present
invention by controlling the environment to which the barrier layer
is exposed: Relevant parameters include the partial pressure of
oxygen and/or amount of moisture to which the barrier layer is
exposed, the temperature during such exposure, the presence of a
non-oxidizing purge gas for removal of oxygen which may be
available within the process chamber from various sources, and the
duration of exposure prior to the deposition of Cu.
[0058] For Cu deposited by CVD, the precursor used to deposit the
Cu may affect the oxidation of the barrier material. For example,
the commonly used .beta.-diketonate ligand, hfac, is a potential
contamination source of oxygen and/or water (as well as fluorine
and carbon). Indeed, water is conventionally added to precursors
such as copper.sup.+1(hfac)(tmvs), for example by hydrating the
hfac, to increase the Cu deposition rate. The inventors' analysis
shows that addition of such water is detrimental to the adhesion of
Cu to the barrier layer, because the water oxidizes the surface of
the barrier layer onto which the Cu is to be deposited. A precursor
that contains only very low amounts of water and oxygen, and that
is preferably essentially free of those substances, may be used to
reduce oxidation.
[0059] The use of a precursor having a low amount of water is
contrary to the conventional use of water to enhance CVD deposition
rate. However, any oxidation of the barrier layer due to water in
the precursor happens before or during the deposition of the first
few atomic layers of Cu, i.e., during the first few seconds of the
Cu deposition. As a result, good adhesion may be obtained by using
a precursor having a reduced amount of water to deposit a
nucleation layer of Cu by CVD. Good deposition rates may be then
obtained by depositing Cu by CVD using a precursor having more
water, or adding water to the same precursor which is used to
deposit the nucleation layer of Cu. This process preferable to the
deposition of a nucleation layer by PVD, followed by CVD
deposition, because the deposition of Cu is by CVD only, which
reduces manufacturing complexity.
Use of Ion Bombardment for Removal of Oxidation from the Barrier
Layer Surface
[0060] Ion bombardment may be used for "plasma cleaning" or
"sputter cleaning" of a barrier layer surface just prior to
deposition of a copper nucleation layer. Techniques for ion
bombardment of a semiconductor substrate surface are well known in
the art and will not be discussed in detail herein. It is also
possible to use ion bombardment during the initial application of
the copper nucleation layer to further facilitate adhesion of this
nucleation layer to an underlying barrier layer surface.
Metallization Geometry
[0061] FIG. 1 shows a metallization geometry useful for Cu
interconnects in accordance with the present invention. The
metallization geometry of FIG. 1 is preferably fabricated in
accordance with a DRY FILL.TM. process provided by Applied
Material, Inc. of Santa Clara, Calif., which includes CVD followed
by PVD. A substrate 12, preferably made of a dielectric material,
has a via 14 with a high aspect ratio. However, the present
invention may be beneficial in cooperation with vias having any
aspect ratio. Via 14 has walls 18 and a floor 20. A thin barrier
layer 16 is deposited directly onto substrate 12 covering
substantially all surfaces, including walls 18 and floor 20 of via
14. The thin barrier layer 16 will generally have a thickness of
between about 150 .ANG. and about 1,000 .ANG.. However, because the
barrier layer contributes to the overall resistivity of the
interconnect, the preferred thickness is in a range of between
about 150 .ANG. and about 350 .ANG.. A conformal CVD Cu layer 22 is
deposited on the barrier layer 16 to a desired thickness not to
exceed the thickness which would seal the top of the contact or
via. Barrier layer 16 is fabricated using a material and/or process
such that the surface between barrier layer 16 and Cu layer 22 is
substantially free of oxide when Cu layer 22 is deposited. A PVD Cu
layer 23 is then deposited onto the CVD Cu layer 22. The interface
between CVD Cu layer 22 and PVD Cu layer 23 is shown as a dotted
line, because the interface should not be apparent after PVD Cu
layer 23 is deposited, i.e., CVD Cu layer 22 and PVD Cu layer 23
form a single integrated Cu layer. Top surface 26 of PVD Cu layer
23 may then planarized by known methods, such as chemical
mechanical polishing (CMP). The Mirra System available from Applied
Materials of Santa Clara, Calif. is one CMP apparatus which may be
used to advantage. PVD Cu layer 23 may be doped with dopants such
as tin (Sn) to alter the electrical properties of PVD Cu layer 23.
The process may be controlled such that these dopants disperse into
CVD Cu layer 22 as well, thereby altering the electrical properties
of the integrated Cu layer. In general, however, PVD Cu layer 23
does not need to be doped.
Preferred Embodiment-Fabrication Apparatus
[0062] The methods of the present invention are preferably carried
out in an integrated cluster tool that has been programmed to
process a substrate accordingly. For example, U.S. Pat. No.
5,186,718, entitled "Staged-Vacuum Wafer Processing System and
Method," Tepman et al., issued on Feb. 16, 1993, which is
incorporated herein by reference, discloses a one staged-vacuum
wafer processing system.
[0063] FIG. 2 shows a diagram of an exemplary integrated cluster
tool 60. Cluster tool 60 is preferably equipped with a
microprocessor controller programmed to carry out the processing
methods. Substrates may be introduced into cluster tool through a
cassette loadlock 62. A robot 64 having a blade 67 transfers the
substrate from cassette loadlock 62 through a buffer chamber 68 to
a degas wafer orientation chamber 70 and then to a preclean chamber
72. Degassing and precleaning may be performed in these chambers
using techniques known to the art.
[0064] Robot 64 then transfers the substrate to a robot 78 located
in a transfer chamber 80.
[0065] Robot 78 positions the substrate in chamber 82, where a
barrier layer is deposited in accordance with the present
invention. Robot 78 then positions the substrate in a CVD chamber
84, where a Cu layer such as Cu layer 22 of FIG. 1 is deposited by
CVD. Robot 78 then positions the substrate in a PVD chamber 86,
where a PVD Cu layer such as PVD Cu layer 23 of FIG. 1 is deposited
by PVD. The substrate is then passed back through the transfer
chamber 80, cooldown chamber 76 and buffer chamber 68 for removal
through loadlock 62. The substrate may then be polished in a
chemical mechanical polishing apparatus (not shown) for
planarization, using techniques known to the art.
[0066] During the above described fabrication steps, the substrate
may be processed or cooled in one or more chambers any number of
times in any order to accomplish fabrication of the desired
structure on the substrate. The exact arrangement and combination
of chambers may be altered for purposes of performing specific
steps of a fabrication process.
[0067] The foregoing is merely illustrative of a possible
processing sequence, other sequences may be preformed according to
the present invention. For example, for the fabrication of a
traditional barrier layer such as a Ta barrier layer, having an
adhesion promotion layer in accordance with the present invention,
the substrate may be delivered to an IMP chamber 88 for deposition
of Ta, then to PVD chamber 86 for deposition of an adhesion
promotion layer of Ni or Pt, for example, prior to the deposition
of Cu layers.
Cu Deposited by PVD, Electroless Plating, and Electroplating
[0068] The foregoing description has focused primarily on barrier
layers for use with CVD Cu. However, the barrier layers of the
present invention may be used to advantage with any method of
depositing Cu where the oxidation or conductivity of the surface
onto which the Cu is deposited affects the deposition or adhesion
of the Cu, or an electron transfer on a conductive surface occurs
in one of the reaction steps. These methods include PVD,
electroplating, and electroless plating. For example,
electroplating Cu fill and electroless plating of Cu both involve
electron transfer on a conducting surface.
[0069] In electroless Cu plating, Cu atoms are supplied to a film
surface by catalytic reduction of aqueous Cu ions. The electrons
for the Cu reduction are provided by the oxidation of a reducing
agent in the deposition bath. The oxidation of the reducing agent,
in turn, is catalyzed only on conductive surfaces. A typical Cu
electroless process is represented by the following equation:
Cu.sup.+2+2HCHO+4OH.sup.-.fwdarw.Cu.sup.0+H.sub.2+2HCOO.sup.-+2H.sub.2O
[0070] where Cu ions are supplied from a Cu sulfate pentahydrate
solution (CuS.sub.4O.5H.sub.2O). The conductive surface may be any
of the barrier layers of the present invention deposited by any
conventional method and as described above.
[0071] Cu electroplating affords a number of advantages over
electroless plating including superior trench and via fill because
the deposition parameters are easily controlled. Cu electroplating
typically involves a sulfuric acid plating bath and a Cu sulfate
solution. The reaction is a simple dissociation of Cu sulfate and a
reduction of Cu ions:
CuSO.sub.4.fwdarw.Cu.sup.2++SO.sub.4.sup.2-
[0072] As with CVD Cu and electroless Cu, the reduction of the Cu
ions in electroplating requires a conductive surface. The barrier
layers of the present invention are ideally suited for this purpose
and may be deposited by any known method and as described above.
High density plasma sputter deposition is a preferred method of
deposition.
EXAMPLES
Example 1
[0073] Oxidation of Ta
[0074] Several samples were prepared, each having a 200 .ANG.
barrier layer of Ta deposited on a substrate having a structured
SiO.sub.2 layer. The Ta was deposited using a high density plasma
sputtering process. Cu was then deposited onto the barrier layers
by CVD to a thickness of about 1000 .ANG.. Another Cu layer was
then deposited by PVD to a thickness of about 1 micron.
[0075] In particular, the Ta barrier layer was deposited using a
Vectra.TM. (Applied Materials, Inc. high density plasma source. The
CVD Cu was deposited using Cupra select (hfac), 2504 blend, Cu
(tmvs) precursor supplied by Schumacher, which was delivered to a
"shower head" distributor using a direct liquid injection system.
The substrate platen (cathode) heater temperature was maintained
between 180.degree. C. and about 200.degree. C. The CVD reactor
process pressure was maintained at about 1.5 Torr with helium as
the carrier gas. The PVD Cu deposition was carried out using a 280
mm target-substrate spacing Cu sputtering source (a long-throw or
.gamma. copper source) developed by Applied Materials, Inc.
[0076] The conditions to which the Ta barrier later was exposed
before the Cu was deposited by CVD were controlled. In particular,
the samples were not removed from the vacuum chamber in between
processes, and the time between processes and the amount of oxygen
in the chamber during that time were controlled as indicated in
Table 2. After the PVD Cu was deposited, the adhesion between the
CVD Cu and the Ta barrier layer was tested using the common tape
test method, using both the blank and scribe tape tests. "Blank"
indicates an undisturbed deposition layer, while "scribe" indicates
that the layer has been purposefully scarred in order to determine
the localized adhesion strength of the CVD Cu layer to the barrier
layer. Descriptions of the blank and scribe tape tests are
presented in the following articles: B. N. Chapman, J. Vac. Sci.
Technol 11 (1974), 106; and P. A. Steinmann and H. E. Hintermann,
J. Vac. Sci. Technol. A 7 (1989), 2267.
[0077] Table 2 summarizes the results of those tests.
2TABLE 2 Effect of Ta Exposure to Various Ambients Exposure Tape
Test Sample Ambient Time Blank Scribe 1. IMP Ta (200 .ANG.)/CVD Cu
1E-09 Torr 0 min Pass Pass (1 K.ANG.)/PVD Cu (1 .mu.m) 2. IMP Ta
(200 .ANG.)/CVD Cu 1E-09 Torr 5 min Pass Fail (1 K.ANG.)/PVD Cu (1
.mu.m) 3. IMP Ta (200 .ANG.)/CVD Cu 3E-08 Torr 5 min Pass Fail (1
K.ANG.)/PVD Cu (1 .mu.m) 4. IMP Ta (200 .ANG.)/CVD Cu 3E-07 Torr 5
min Pass Fail (1 K.ANG.)/PVD Cu (1 .mu.m) 5. IMP Ta (200 .ANG.)/CVD
Cu 1 m Torr 5 min Pass Fail (1 K.ANG.)/PVD Cu (1 .mu.m) 6. IMP Ta
(200 .ANG.)/CVD Cu 100 m 5 min Fail Fail (1 K.ANG.)/PVD Cu (1
.mu.m) Torr
[0078] Table 2 shows that increasing the amount of oxygen to which
the Ta barrier layer is exposed weakens the adhesion between the Ta
and the CVD Cu, and that oxidation on the surface of the barrier
layer decreases the adhesion of a subsequently deposited Cu layer.
Table 2 also shows that the adhesion of Cu to Ta may be improved by
controlling the conditions to which the Ta barrier layer is exposed
prior to the deposition of Cu to minimize the amount of oxide that
forms on the surface of the Ta layer. In particular, the adhesion
of Cu to Ta was particularly good in Sample 1. While replication of
the exact conditions used to fabricate Sample 1 may not be
practical in large scale production, the present invention
contemplates other, more practical ways of providing a surface of a
barrier layer substantially free of oxide onto which Cu may be
deposited.
Example 2
[0079] Barrier Layer Materials
[0080] Several samples were prepared, each having a barrier layer
deposited on a substrate having a structured SiO2 layer. The
barrier layers were deposited to a thickness of about 200 .ANG.,
and were made of various materials as shown in Table 3. The Ta and
TaN barrier layers were deposited in an ionized metal plasma
chamber (IMP). The TiN barrier layer was deposited by CVD. The Ni
and Pt were deposited using standard, traditional sputtering
technique on a DC magnetron Endura.RTM. platform of the kind known
in the art. The Ni and Pt substrates were exposed to ambient
atmospheric conditions for approximately 2 days prior to CVD Cu
deposition.
[0081] Cu was then deposited onto the barrier layers by CVD using
the same general process parameters and materials described with
respect to Example 1. The samples were then tested by the
conventional tape test method, as described with respect to Example
1.
3TABLE 3 Tape Test Results on Traditional Barrier Layers vs.
Barrier Layers of the Present Invention Sample Tape Test 1. IMP Ta
(200 .ANG.)/CVD Cu (1 K.ANG.) Fail Fail 2. IMP TaN (200 .ANG.)/CVD
Cu (1 K.ANG.) Fail Fail 3. CVD TiN (200 .ANG.)/CVD Cu (1 K.ANG.)
Fail Fail 4. Ni (200 .ANG.)/(CVD Cu (1 K.ANG.) Pass Pass 5. Ni (200
.ANG.)/(CVD Cu (4 K.ANG.) Pass Pass 6. Pt (200 .ANG.)/CVD Cu (1
K.ANG.) Pass Pass 7. Pt (200 .ANG.)/CVD Cu (4 K.ANG.) Pass Pass 8.
Pt (200 .ANG.)/CVD Cu (8 K.ANG.) Pass Pass 9. IMP Ta (200
.ANG.)/PVD Cu (200 .ANG.)/CVD Cu (1 K.ANG.) Pass Pass
[0082] As can be seen from Table 3, the samples in which Cu was
deposited by CVD onto barrier layers made of conventional materials
used with Al, such as Ta, TaN, and TiN, failed the tape test. The
inventors believe that this failure may be attributed to the
formation of an oxidation layer on the barrier layer. Conversely,
the samples having barrier layers made of materials that, according
to the inventor's analysis, are unlikely to form significant oxide
layers passed the tape test. In particular, samples having Ni and
Pt barrier layers passed the tape test.
[0083] Cu deposited by PVD is apparently less sensitive to
oxidation on the surface of the barrier layer to which the Cu is
deposited, as shown by Sample 9, in which a PVD Cu layer passed the
tape test. However, the inventor's analysis shows that the adhesion
of Cu deposited by PVD may also be enhanced by the present
invention.
Example 3
[0084] Adhesion of CVD Cu Using a Low Moisture Precursor
[0085] Several samples were prepared, each having a barrier layer
deposited on a substrate having a structured SiO.sub.2 layer. The
barrier layers were deposited to a thickness of about 200 .ANG.,
and were made of various materials as shown in Table 4. The Ta,
TaN, and TiN barrier layers were deposited in a manner similar to
that described for Example 2. The substrates were then exposed to
clean room ambient conditions for about 3 minutes while the
substrates were transferred from one chamber loadlock to another
chamber loadlock through ambient air.
[0086] Cu was then deposited onto the barrier layers by CVD from a
Cupra Select 2500 blend precursor, available from Schumacher,
Carlsbad, Calif. This precursor is formulated to have a low
moisture content (below about 2,500 ppm). The temperature during
the deposition of Cu was between about 200 and 260.degree. C. The
CVD apparatus and general process parameters used were the same as
that described with reference to the previous examples. The samples
were then tested by the conventional tape test method, as described
with respect to Example 1. The results of these tests are
summarized in Table 4. Note that when there is no mention of "air"
in Table 4, the substrates were moved under a controlled
environment at about 10.sup.-7 Torr, at room temperature, over a
time period of less than about one minute. Whenever there is a
mention of "air", the barrier layers were exposed to clean room
ambient for about e minutes during transfer from one chamber to
another.
4TABLE 4 Tape Test Results Cu Deposited from a Low Moisture
Precursor Sample Tape Test 1. IMP Ta (200 .ANG.)/CVD Cu (1 K.ANG.)
Pass Pass 2. IMP TaN (200 .ANG.)/CVD Cu (1 K.ANG.) Pass Pass 3. CVD
TiN (200 .ANG.)/air/CVD Cu (1 K.ANG.) Pass Pass 4. IMP TaN (200
.ANG.)/air/CVD Cu (1 K.ANG.) Pass Fail 5. IMP Ta (200
.ANG.)/air/CVD Cu (1 K.ANG.) Pass Fail 6. IMP Ta (200 .ANG.)/CVD Cu
(3 K.ANG.) Pass Pass 7. IMP TaN (200 .ANG.)/CVD Cu (3 K.ANG.) Pass
Pass 8. IMP Ta (200 .ANG.)/PVD Cu (200 .ANG.)/CVD Cu (8 K.ANG.)
Pass Pass
[0087] As can be seen from Table 4, CVD Cu deposited from a low
moisture precursor has adhesion to the barrier layer sufficient to
pass the tape test under most of the circumstances tested. The only
failures were for the scribe test, where the barrier layer had been
exposed to air prior to the deposition of Cu. This failure probably
occurred because the exposure to air formed enough oxide to inhibit
the adhesion of copper, regardless of how little oxide was formed
due to moisture in the precursor. It is believed that TiN forms
oxide at a lower rate than Ti and TaN, which explains why the TiN
sample exposed to air passed the scribe test, while the Ti and TaN
samples failed.
Example 4
[0088] XPS Analysis of Ta/CVD Cu Interfaces
[0089] Two samples were prepared, each having a Ta barrier layer
deposited on a substrate having a structured SiO.sub.2 layer. The
barrier layers were deposited to a thickness of about 250 .ANG..
The Ta barrier layers were deposited in a manner similar to that
described for Example 3. The substrates were then transferred to
the CVD deposition chamber by passing them through clean room
ambient on a wafer holder over a time period of less than about 3
minutes, as described with reference to Example 3. The CVD
apparatus and process parameters used for CVD Cu deposition were
the same as described with reference to previous examples.
[0090] Cu was then deposited onto the barrier layers by CVD using a
Cupra Select 2500 blend precursor for one sample, and a Cupra
Select 2504 blend for the other, both available from
Schumacher.
[0091] The primary difference between Cupra 2500 and Cupra 2504 is
that Cupra 2500 has a lower moisture content, i.e., Cupra 2504 is
basically Cupra 2500 which has been hydrated using a proprietary
method of Schumacher. The precise moisture content is not known,
but is greater than 2,500 ppm. The sample prepared using the Cupra
2500 precursor passed the both the scribe and blank adhesion tests.
The sample prepared using the Cupra 2504 precursor failed that
test, showing that the sample prepared with the low moisture
precursor had better adhesion between the barrier layer and the
Cu.
[0092] FIGS. 3, 4, 5 and 6 shows X-ray photoelectron spectroscopy
(XPS) plots for the two samples. FIG. 3 shows an XPS peak for
tantalum in the sample prepared using the Cupra 2500 precursor.
FIG. 4 shows an XPS peak for oxygen in the sample prepared using
the Cupra 2500 precursor. FIG. 5 shows an XPS peak for tantalum in
the sample prepared using the Cupra 2504 precursor. FIG. 6 shows an
XPS peak for oxygen in the sample prepared using the Cupra 2504
precursor. The "x" axis is the binding energy in eV; the "y" axis
is the counts per second; and, the "z" axis is the sputter time in
minutes. The plotted tantalum peaks of FIGS. 3 and 5 are Ta4d5
peaks, which are caused by Ta in contact with Cu. The plotted
oxygen peaks of FIGS. 4 and 6 are O1s peaks, caused by the presence
of oxygen.
[0093] A comparison of FIGS. 3 and 4 to FIGS. 5 and 6 show that
there is less oxidation at the interface between the copper and the
tantalum in the sample prepared with the low moisture precursor
Cupra 2500 (FIGS. 3 and 4) than in the sample prepared with the
higher moisture precursor Cupra 2504 (FIGS. 5 and 6). In
particular, the FWHM signal of FIG. 5 is broader than that of FIG.
3, the oxygen peak of FIG. 4 is shifted with respect to that of
FIG. 6. In particular, the FWHM for tantalum from the 50 minute
sputtering time to the 80 minute sputtering time for the 2500 Blend
is about 60.degree., where the FWHM for tantalum from the 25 minute
sputtering time to the 50 minute sputtering time for the 2504 Blend
is about 40.degree.. This broadening of the Ta signal FWHM for the
Ta surface in contact with the CVD Cu from the 2500 Blend indicates
that the Ta surface in contact with CVD Cu from the 2500 Blend is
less oxidized than the Ta surface in contact with the 2504 Blend.
The height of the oxygen peak for the corresponding time for the
2500 Blend shows the Oxygen counts per second (c/s) to be about
zero; much smaller than for the 2504 Blend which shows a c/s of
about 0.25 for the Oxygen signal, indicating less tantalum
oxidation for the 2500 Blend.
Example 5
[0094] SIMS Analysis of CVD Cu on Pt, Ni. and Ta Barrier Layers
[0095] Several samples were prepared, each having a barrier layer
deposited on a substrate having a structured SiO2 layer. The
barrier layers were deposited to a thickness of about 200 .ANG..
Three samples were prepared, having Pt, Ni, and Ta barrier layers,
respectively. The barrier layers were fabricated as described in
Example 2. The environment to which the barrier layers were exposed
prior to CVD Cu was the same as previously described (The samples
were placed in a box located in ambient atmospheric conditions at
room temperature for approximately 2 days prior to CVD Cu
deposition).
[0096] Cu was then deposited onto the barrier layers by CVD using
the apparatus and general process parameters described with respect
to previous examples and Cupra select 2504 Blend. The samples were
then tested using both the scribe and blank conventional tape test
methods, as described with respect to Example 1. The sample having
a Ta barrier layer failed the tape test, while the sample having a
Ni barrier layer and the sample having a Pt barrier layer passed
the tape test.
[0097] FIGS. 7, 8 and 9 show SIMS profiles for the samples having a
Ta, Ni, and Pt barrier layer, respectively. The x axis represents
position in a direction perpendicular to the plane of the barrier
layer. The y axis represents the concentration of various elements,
in atoms per cubic centimeter. Plots 710, 720, 730, 740, 750 and
760 of FIG. 7 show the concentration of Cu, fluorine, carbon,
oxygen, silicon and Ta, respectively, for the sample having a Ta
barrier layer. Plots 810, 820, 830, 840, 850 and 860 of FIG. 8 show
the concentration of Cu, fluorine, carbon, oxygen, silicon and Ni,
respectively, for the sample having a Ni barrier layer. Plots 910,
920, 930, 940, 950 and 960 of FIG. 9 show the concentration of Cu,
fluorine, carbon, oxygen, silicon and Pt, respectively, for the
sample having a Pt barrier layer.
[0098] The interface between the Cu and the barrier layer is
located approximately at the peak in the fluorine and carbon
concentrations, where the Cu concentration begins to drop off. The
similarity in the fluorine and carbon profiles, i.e., compare plots
720, 820 and 920, for fluorine and plots 730, 830 and 930 for
carbon, combined with the different tape test results, show that
differences due to fluorine and carbon, either at the interface
between the Cu and the barrier layer or in the Cu matrix, are
probably not responsible for the superior adhesion of the samples
having Pt and Ni barrier layers.
[0099] The sample having a Ta barrier layer shows an oxygen peak at
the interface between the Cu and the Ta barrier layer, see FIG. 7,
plot 740 of FIG. 7, suggesting that the Ta oxidized prior to or
during the deposition of Cu. The samples having Ni and Pt barrier
layers do not have a corresponding peak, see FIGS. 8 and 9, plots
840 and 940, respectively, suggesting that the Ni and Pt did not
significantly oxidize prior to or during the deposition of Cu.
According to the inventors'analysis, this difference in the
oxidation of the barrier layer is responsible for the superior
adhesion properties of the samples having Pt and Ni barrier layers,
relative to the sample having a Ta barrier layer.
Example 6
[0100] X-TEM Analysis of CVD Cu Deposited on Ex-Situ Pt and Ni
[0101] Two samples were prepared, each having a barrier layer
deposited on a substrate having a structured SiO.sub.2 layer. The
barrier layers were deposited to a thickness of about 200 .ANG..
One sample had a Pt barrier layer, and the other had a Ni barrier
layer. The barrier layers were fabricated as described in Example
2. The environment to which the barrier layers were exposed prior
to CVD Cu was the same as previously described (The samples were
placed in a box located in ambient atmospheric conditions at room
temperature for approximately 2 days prior to CVD Cu
deposition).
[0102] Cu was then deposited onto the barrier layers by CVD using
the apparatus and general process parameters described with respect
to previous examples and Cupra select 2504 Blend. The samples were
then tested using both the scribe and blank conventional tape test
methods, as described with respect to Example 1. All samples passed
the tape testing.
[0103] The samples were cross-sectioned and examined using X-ray
transmission electron microscopy (X-TEM). There was no visible
oxide layer on the Pt barrier layer, and the interface between the
Pt and Cu was well defined. Patches of oxide were observed on the
surface of the Ni barrier layer. In the regions where there was no
visible oxide, the interface between the Ni and Cu appeared sharp
and well defined. Evidently the small scattered portion of the
interface between Ni and Cu which exhibited visible oxide presence
was inadequate to cause failure during the tape testing of this
sample.
[0104] While the foregoing is directed to preferred embodiments of
the present invention, other and further embodiments of the
invention may be devised without departing from the basic scope
thereof. The scope of the invention is determined by the claims
which follow.
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