U.S. patent application number 10/828011 was filed with the patent office on 2005-10-20 for electrochemical methods for the formation of protective features on metallized features.
This patent application is currently assigned to Semitool, Inc.. Invention is credited to Chen, Linlin.
Application Number | 20050230262 10/828011 |
Document ID | / |
Family ID | 35095165 |
Filed Date | 2005-10-20 |
United States Patent
Application |
20050230262 |
Kind Code |
A1 |
Chen, Linlin |
October 20, 2005 |
Electrochemical methods for the formation of protective features on
metallized features
Abstract
Electrochemical processes and apparatus are described for
forming a protective feature on the exposed surface of a metallized
feature. The protective feature provides a diffusion barrier and
protects the metallized feature from corrosion and contamination.
Protective features formed from nickel, cobalt, and alloys of these
metals are described.
Inventors: |
Chen, Linlin; (Plano,
TX) |
Correspondence
Address: |
CHRISTENSEN, O'CONNOR, JOHNSON, KINDNESS, PLLC
1420 FIFTH AVENUE
SUITE 2800
SEATTLE
WA
98101-2347
US
|
Assignee: |
Semitool, Inc.
|
Family ID: |
35095165 |
Appl. No.: |
10/828011 |
Filed: |
April 20, 2004 |
Current U.S.
Class: |
205/122 ;
204/224R; 205/255; 205/271; 257/E21.174; 257/E21.589 |
Current CPC
Class: |
C23C 18/165 20130101;
C25D 17/001 20130101; H01L 21/76885 20130101; H01L 21/288 20130101;
H01L 21/76843 20130101; H01L 21/76852 20130101; C23C 18/50
20130101; C25D 5/10 20130101; C25D 7/123 20130101 |
Class at
Publication: |
205/122 ;
204/224.00R; 205/255; 205/271 |
International
Class: |
C25D 005/02; C25D
017/00 |
Claims
1. A method of forming a protective feature on a metallized feature
formed on a microelectronic workpiece, the method comprising:
forming the metallized feature on the microelectronic workpiece,
the metallized feature having an exposed surface; and
electrolytically depositing a conductive protective feature on the
exposed surface of the metallized feature.
2. The method of claim 1 wherein the exposed surface is a top
surface.
3. The method of claim 2, wherein the metallized feature has at
least one exposed sidewall.
4. The method of claim 3, wherein the metallized feature has at
least two exposed sidewalls.
5. The method of claim 4, wherein the electrolytically depositing
step further comprises depositing the conductive protective feature
on the exposed top surface and the at least two exposed
sidewalls.
6. The method of claim 1, wherein the conductive protective feature
comprises nickel, nickel alloys, cobalt, or cobalt alloys.
7. The method of claim 1, wherein the metallized feature includes
metals selected from the group comprising copper, copper alloys,
aluminum, aluminum alloys, gold, silver, platinum, platinum alloys,
and combinations thereof.
8. The method of claim 7, wherein the metallized feature comprises
copper.
9. The method of claim 1, wherein the step of forming the
metallized feature further comprises forming the metallized feature
on a barrier layer comprising tantalum or titanium.
10. The method of claim 9, wherein the step of forming the
metallized feature further comprises depositing a seed layer on the
barrier layer prior to formation of the metallized feature.
11. The method of claim 10, wherein after formation of the
metallized feature, a portion of the seed layer is removed prior to
electrolytically depositing the conductive protective feature.
12. A conductive feature on a microelectronic workpiece made by the
method of claim 1.
13. A method of forming a conductive protective feature on a
metallized feature formed on a microelectronic workpiece having a
front side and a backside, the method comprising: forming a barrier
layer on the front side of the microelectronic workpiece; forming a
seed layer exterior to the barrier layer formed on the front side
of the microelectronic workpiece; forming the metallized feature on
the front side of the microelectronic workpiece exterior to the
seed layer, the metallized feature having an exposed surface;
removing exposed portions of the seed layer; activating the exposed
surface of the metallized feature; and electrolessly depositing a
conductive protective feature on the exposed surface of the
metallized feature.
14. The method of claim 13, wherein the exposed surface is a top
surface.
15. The method of claim 13, wherein the metallized feature has at
least one exposed sidewall.
16. The method of claim 15, wherein the metallized feature has at
least two exposed sidewalls.
17. The method of claim 16, wherein the electrolessly depositing
step further comprises depositing the conductive protective feature
on an exposed top surface and the at least two exposed
sidewalls.
18. The method of claim 13, wherein the conductive protective
feature comprises nickel, nickel alloys, cobalt, or cobalt
alloys.
19. The method of claim 18, wherein the conductive protective
feature comprises the alloys of nickel-tungsten-phosphorus,
nickel-tungsten-boron, cobalt-tungsten-phosphorus,
cobalt-tungsten-boron, nickel-molybdenum-phosphorous,
cobalt-molybdenum-phosphorous, nickel-molybdenum-boron and
cobalt-molybdenum-boron.
20. The method of claim 13, wherein the metallized feature
comprises copper, copper alloys, aluminum, aluminum alloys, gold,
silver, platinum, platinum alloys, and combinations thereof.
21. The method of claim 20, wherein the metallized feature
comprises copper.
22. The method of claim 13, wherein the barrier layer comprises
tantalum or titanium.
23. A microelectronic workpiece including a conductive feature
formed by the method of claim 13.
24. A conductive feature on a microelectronic workpiece formed over
a titanium or tantalum barrier layer comprising: an
electrochemically deposited metallized feature having an exposed
surface; and a conductive protective feature electrochemically
deposited on the metallized feature exterior to the exposed
surface.
25. The conductive feature of claim 21, wherein the conductive
protective feature comprises nickel, nickel alloys, cobalt, or
cobalt alloys.
26. An apparatus for use in a manufacturing line for providing
conductive features on a microelectronic workpiece, the apparatus
comprising: an input section for receiving a microelectronic
workpiece, a surface of the microelectronic workpiece comprising a
barrier feature, a seed layer formed exterior to the barrier
feature, and a photoresist feature; a bulk metallization station
for electrochemically forming a metallized feature exterior to the
seed layer; a photoresist removal station for removing at least a
portion of the photoresist feature resulting in a raised metallized
feature with an exposed surface; a seed layer removal station for
removing at least a portion of the seed layer; an electrochemical
deposition station for electrochemically depositing a conductive
protective feature on the exposed surface of the metallized
feature; and a barrier layer etching station for removing at least
a portion of the barrier layer.
27. The apparatus of claim 26, where the electrochemical deposition
station comprises an electrolytic deposition chamber.
28. The apparatus of claim 26, wherein the electrochemical
deposition station comprises an electroless deposition chamber.
29. The apparatus of claim 26, further comprising a photoresist
developing station.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to electrochemical methods for
the formation of protective features on metallized features formed
on microelectronic workpieces.
BACKGROUND OF THE INVENTION
[0002] A microelectronic workpiece can have repeating layers of
insulating regions and conducting regions bonded to one another. An
inherent problem when joining two dissimilar materials is a
tendency of one or both materials to migrate or diffuse across the
common interface into the other material. Thus, in order to be
effective, the materials chosen to form the insulating regions and
the conducting regions must be properly isolated from each other so
that one material does not diffuse into the adjacent dissimilar
material.
[0003] Typically, metals have been used as materials for conducting
regions. Metals can be used to form interconnections between
differing layers or regions, or they can be used to form
intraconnections in the same layer. The newest generation of
microelectronic devices relies more and more heavily upon
copper-based interconnections.
[0004] While copper exhibits desirable conductivity and resistivity
characteristics, it has been found to have a high tendency to
diffuse into surrounding dielectric materials or corrode, which
degrades the integrity of the interconnection features as well as
the surrounding devices or dielectric structures. Typically, a
copper feature will be formed on a "barrier layer," which is
interposed between the underlying structure and the copper feature.
Such barrier layers are typically applied to the underlying
structure prior to deposition of the copper. In situations where
the copper is to be deposited into a trench or via the barrier
layer serves to isolate the bottom and sidewalls of the copper from
the dielectric. The resulting top surface of the copper feature can
then be "capped" by a barrier material to isolate the top surface
of the copper feature from subsequently applied layers of
dielectric.
[0005] Conventional materials for applying barrier layers include
sputter deposited or low-pressure chemical vapor deposited titanium
or tantalum metals or alloys thereof. For example, in U.S. Pat. No.
5,256,274 to Poris, a diffusion barrier is applied to a
silicone-based dielectric region before proceeding with an
electrodeposition step. Poris also describes a thin, nonconductive
silicon nitride layer which is applied to an exposed deposited
metal feature to act as a diffusion barrier. Such nonconductive
barrier layer must be removed prior to the deposition of a via or
line onto the underlying metal feature.
[0006] Sputter deposition and physical or chemical vapor
deposition, however, are costly because they involve time-consuming
processing steps when compared to electrochemical deposition
processes. Furthermore, such processes are nonselective and are
less than desirable when it comes to deposition on vertically
oriented features or features with high aspect ratios.
[0007] In Electrolessly Deposited Diffusion Barriers for
Microelectronics, J. Research & Development, by E. J.
O'Sullivan et al., electrolessly deposited capping layers for the
top surface of copper interconnects are described as protecting the
top surface of the copper feature from corrosion, preventing
diffusion and to ensure adhesion to subsequent polyimide
layers.
[0008] In certain process architectures, the top and/or sidewalls
of a metallized feature such as copper lines or vias are exposed.
When dielectric is deposited over these sidewalls, the possibility
for diffusion of the copper into the dielectric and corrosion of
the copper exists. Accordingly, there is a need for processes for
providing protective features on exposed surfaces of conductive
features, such as control top surface and/or sidewalls that have
been deposited and are to come in contact with dielectric materials
deposited after formation of the conductive feature.
SUMMARY OF THE INVENTION
[0009] The present invention provides electrochemical methods for
encapsulating conductive features, such as copper features, to
prevent diffusion of copper into surrounding structures such as
dielectrics deposited over the conductive features and to prevent
diffusion of undesired materials into the conductive features
themselves. The present invention achieves this goal by
encapsulating a metallized feature formed on a microelectronic
workpiece with a conductive protective feature, wherein a surface
of the metallized feature is covered by the conductive protective
feature prior to deposition of a dielectric material over the
metallized feature.
[0010] In one embodiment, the method involves forming a metallized
feature on a microelectronic workpiece wherein the metallized
feature has an exposed surface, such as a top surface or sidewalls.
The conductive protective feature is provided by electrolytically
depositing a metal such as nickel, cobalt, or alloys thereof on the
exposed surface of the metallized feature.
[0011] In another embodiment, the conductive protective feature is
provided by first forming a metallized feature on the front side of
a microelectronic workpiece wherein the metallized feature has an
exposed surface. The microelectronic workpiece carrying the
metallized feature is then cleaned. Thereafter, at least the
exposed surface of the metallized feature is activated, followed by
the electroless deposition of the conductive protective feature on
the exposed surface.
[0012] In the embodiments described above, the methods can also
include deposition of a protective feature on at least an exposed
sidewall.
[0013] A method carried out in accordance with the present
invention provides a conductive feature on a microelectronic
workpiece that comprises an electrochemically deposited metallized
feature having an exposed surface and a conductive protective
feature electrochemically deposited exterior to the top surface and
optionally on at least one sidewall.
[0014] The present invention also provides an apparatus for
carrying out processes in accordance with the present invention.
Such an apparatus is suitable for use in a manufacturing line for
providing conductive features on a microelectronic workpiece. The
apparatus includes an input section for receiving a microelectronic
workpiece which carries a barrier feature, a seed layer formed
exterior to the barrier feature and a photoresist feature.
Typically such microelectronic workpiece is processed in a tool
separate from a tool formed in accordance with the present
invention. The apparatus of the present invention also includes a
bulk metallization station for electrochemically forming a
metallized feature exterior to the seed layer. A photoresist
removal station is provided for removing at least a portion of the
photoresist feature. The removal of the photoresist results in a
metallized feature on the workpiece with an exposed surface, e.g.,
a top surface and/or at least one exposed sidewall. A seed layer
removal station removes those portions of the seed layer that are
not covered by the metallized feature. In order to deposit a
protective feature of the present invention, an electrochemical
deposition station is included in the apparatus for
electrochemically depositing a conductive protective feature on the
exposed surface of the metallized feature. Finally, a barrier layer
etching station is provided for removing at least a portion of the
exposed barrier layer. The electrochemical deposition station for
use in an apparatus formed in accordance with the present invention
can be either an electrolytic deposition chamber or an electroless
deposition chamber.
[0015] The methods and apparatuses of the present invention provide
for the selective and controllable deposition of a conductive
protective feature onto an exposed metallized feature that isolates
the exposed top surface(s) from a layer of dielectric deposited
after the metallized feature is formed. In a preferred embodiment,
the metallized feature is encapsulated by the protective feature.
The method of the present invention provides a protective feature
on the metallized feature and does not suffer from the nonselective
nature of prior processes for depositing diffusion barrier layers
and is a more controllable and less costly alternative to sputter
deposition, and physical or chemical vapor deposition
techniques.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] The foregoing aspects and many of the attendant advantages
of this invention will become more readily appreciated as the same
become better understood by reference to the following detailed
description, when taken in conjunction with the accompanying
drawings, wherein:
[0017] FIGS. 1-5 schematically illustrate a process architecture
for forming a raised exposed metallized feature suitable for
processing in accordance with the present invention;
[0018] FIGS. 6-8 schematically illustrate an alternative process
architecture for providing a raised exposed metallized feature for
processing in accordance with the present invention;
[0019] FIGS. 9-13 schematically illustrate another alternative
process architecture for providing a raised metallized feature with
exposed surfaces which can be processed in accordance with the
present invention;
[0020] FIGS. 14-16 schematically illustrate a process carried out
in accordance with the present invention;
[0021] FIG. 17 schematically illustrates a metallized feature which
has a protective feature provided in accordance with the present
invention; and
[0022] FIG. 18 schematically illustrates a manufacturing sequence
including a tool for carrying out the formation of a protective
feature in accordance with the present invention; and
[0023] FIG. 19 is a cross-section view of a reactor for carrying
out electrochemical deposition of metals in accordance with the
present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0024] Prior to undertaking the description of the present
invention, it is advantageous to describe the various terms used
herein to signify deposition methods and other terms used in the
present specification.
[0025] Electroplating, plating, or electrolytically depositing is a
process for deposition of a conductive material using an applied
current between a workpiece and an anode.
[0026] Electroless or electroless deposition is the autocatalytic
deposition of a conductive material without the use of an applied
current.
[0027] Electrochemical deposition as used herein refers to both
methods of electroplating and electroless deposition.
[0028] Layer is any region of substantially similar composition,
although it is not required to be constant throughout.
[0029] Microelectronic workpiece refers to workpieces having
generally planar first and second surfaces that are relatively
thin, including semiconductor wafers, ceramic workpieces, and other
workpieces upon which microelectronic circuits or components, data
storage elements, or layers, and/or micromechanical elements are
formed.
[0030] The methods of the present invention are applicable to
metallized features formed on a microelectronic workpiece,
typically by an additive or through plating process architecture,
such as photoresist pattern plating, template plating, or planar
subtractive metallization techniques. These techniques result in a
raised metallized feature such as the one described below having an
exposed surface(s) such as its top surface, its top surface and at
least one sidewall, and its top surface and two sidewalls.
[0031] An exemplary process architecture is illustrated and
described below with reference to FIGS. 1-5. Referring to FIG. 1, a
trench 100 is formed in a substrate 102 using conventional
photolithographic and etching techniques. A barrier layer 104 is
deposited onto the substrate and into trench 100 using physical
vapor deposition, such as sputtering, or by chemical vapor
deposition. Materials suitable for use as barrier layer 104 include
tantalum, tantalum nitride, titanium, and titanium nitride.
Suitable thicknesses for barrier layer 104 range from about 100 to
300 angstroms; however, the thickness may vary depending upon the
particular architecture. A metal seed layer 106 is provided
exterior to barrier layer 104 using known techniques, such as
sputter or vapor deposition. Suitable metals for use as a seed
layer 100 include, in addition to copper, metals such as chromium,
cobalt, silver, tin, lead, cadmium, platinum, palladium, iridium,
ruthenium, zinc, gold, nickel, alloys thereof, or any combination
thereof. Referring to FIG. 2, a patterned and developed photoresist
layer 108 is formed exterior to seed layer 106 providing a trench
109 centered over trench 100.
[0032] Referring to FIG. 3, a metallized feature 110 is deposited
into trench 100 and trench 109 using known techniques such as
electrochemical deposition. Suitable metals for use in the bulk
metallization include, in addition to copper, metals such as
chromium, cobalt, silver, tin, lead, cadmium, platinum, palladium,
iridium, ruthenium, zinc, gold, nickel, alloys thereof or any
combination thereof. Referring to FIG. 4, after metallized feature
110 is deposited, photoresist 108 is removed to provide raised
metallized feature 110 with its top surface 101 and opposing
sidewalls 103 and 105 exposed. As can be seen in FIG. 4, the term
exposed refers to the top 101 and sidewall surfaces 103 and 105
that are exposed after removal of photoresist 108. In contrast, the
sidewalls of the metallized feature formed in trench 100 are not
exposed as such term is used herein. Subsequent to the removal of
the photoresist 108, the portion of seed layer 106 not covered by
metallized feature 105 is removed by etching or a similar technique
to provide the structure illustrated in FIG. 5. A protective
feature formed in accordance with the present invention can be
applied to the structure illustrated in FIG. 5. Alternatively, the
exposed portion of the barrier layer 104 can be removed before a
protective feature formed in accordance with the present invention
is formed.
[0033] Alternatively, a raised exposed metallized feature which can
be treated in accordance with the present invention can be provided
by an alternative process architecture described below with
reference to FIGS. 6, 7, and 8.
[0034] Referring to FIG. 6, a trench 100 and trench 109 are
provided with a barrier layer 104 as described above with respect
to FIGS. 1-5; however, seed layer 106 has been omitted. In this
process architecture, seed layer 106 is deposited onto the portion
of barrier layer 104 which are not covered by the patterned
photoresist layer 108. After deposition of seed layer 106, bulk
metallization is carried out to deposit metallized feature 110 in
trenches 100 and 109 as illustrated in FIG. 8. Thereafter,
photoresist 108 can be removed to provide a metallized feature with
an exposed top surface and sidewalls identical to that described
above with reference to FIG. 5.
[0035] Finally, a raised metallized feature with exposed top
surface and sidewalls can be provided by a process architecture
described below with reference to FIGS. 9-13. In such a process
architecture, a barrier feature 104 and seed layer 106 are
sequentially deposited onto a substrate 102 to provide the
structure as illustrated in FIG. 9. Thereafter, a photoresist layer
108 is deposited and patterned to provide a trench 100 as
illustrated in FIG. 10. Subsequent to the formation of trench 100,
bulk metallization is carried out to fill trench 100 to provide
metallized feature 110 as illustrated in FIG. 11. Thereafter,
photoresist 108 is removed, exposing sidewalls 103 and 105 of
metallized feature 110. Thereafter, the portions of seed layer 106
and barrier feature 104 that are not covered by metal feature 110
can be removed by etching or other similar technique to provide the
metallized feature illustrated in FIG. 13 with an exposed top
surface and sidewalls.
[0036] It should be understood that while three different process
architectures have been described above for providing raised
metallized features with exposed top surface and sidewalls that can
benefit from the present invention, it should be understood that
the advantages of the present invention may be applicable to other
process architectures not specifically described herein that
provide similar structure. Examples of such alternative process
architectures may include damascene and dual damascene
processes.
[0037] The foregoing process architectures provide a metallized
feature which is raised and exposed on its top surface as well as
both sidewalls. In order to provide multilayer architectures, a
dielectric will eventually be deposited over the raised metallized
feature in order to form additional layers. In order to minimize
the possibility of diffusion of the metal of the metallized feature
into such dielectric layer, corrosion of the metallized feature,
and diffusion of undesirable materials into the metallized
features, a protective feature formed in accordance with the
present invention is advantageously provided.
[0038] For purposes of the present specification, and for a better
understanding of the present invention, a distinction is drawn
between those barrier layers described above that are applied to a
substrate prior to deposition of a metallized feature thereon and
the protective features of the present invention. Such barrier
layers serve to isolate the underlying substrate from the overlying
metallized feature. In contrast, the protective features of the
present invention are applied onto the exposed surfaces of an
already deposited metallized feature, thus isolating the metallized
feature from a subsequently deposited dielectric layer. For
convenience and ease of understanding, "protective feature" will be
used herein to refer to the layers of protective materials that are
applied after deposition of a metallized feature and before
deposition of a dielectric over the metallized feature.
[0039] Referring to FIG. 14, a conductive feature 120 formed in
accordance with the present invention from the raised exposed
metallized features described above with reference to FIGS. 1-8
includes a protective feature 112 which in the illustrated
embodiment has been deposited on the top surface 101 of metallized
feature 110 and the exposed sidewalls 103 and 105. The structure
illustrated in FIG. 14 can be prepared for subsequent planarization
by etching the exposed portions of barrier layer 104 to provide the
structure illustrated in FIG. 15. Thereafter, a planarizing
dielectric layer 114 can be deposited to provide the structure
illustrated in FIG. 16.
[0040] With respect to the raised metallized feature described
above with respect to FIGS. 9-13, a protective feature 112 can be
provided on the exposed top surface 101 and exposed sidewalls 105
to provide the structure illustrated in FIG. 17. In view of the
electrical isolation of metallized feature 110 in FIGS. 13 and 17,
it is understood that in order to provide a protective feature 112
in accordance with the present invention, such protective feature
112 will need to be provided by an electroless process as described
below in more detail. Since conductive feature 110 in FIG. 13 is
electrically isolated, it would not be possible to electrolytically
deposit a protective feature onto the exposed top and exposed
sidewalls because no applied current can be established between
conductive feature 110 and an anode. With respect to the raised and
exposed metallized features described above with reference to FIGS.
1-5 and 6-8, current can be carried to metallized feature 110
through barrier layer 104 and therefore a protective feature 112
can be deposited onto metallized feature 110 in FIGS. 1-5 and 6-8
either electrolytically or electrolessly.
[0041] A protective feature formed in accordance with the present
invention comprises metals such as nickel, its alloys, cobalt, and
its alloys. Specific examples of nickel alloys include
nickel-tungsten-phosphorus, nickel-molybdenum-phosphorus,
nickel-molybdenum-boron, nickel-tungsten-boron, nickel-boron and
nickel-phosphorus. Suitable alloys of cobalt include
cobalt-phosphorus, cobalt-boron nickel-cobalt-phosphorus,
nickel-cobalt-boron, cobalt-tungsten-phosphorus,
cobalt-molybdenum-phosphorous, cobalt-molybdenum-boron, and
cobalt-tungsten-boron. A protective feature can range in thickness
from about 500 angstroms to about 2,500 angstroms. It should be
understood that protective features that are less thick or more
thick than the recited range fall within the scope of the present
invention. Protective features that are thinner can be deposited
more quickly; however, their ability to isolate the metallized
feature from the overlying dielectric material may be less compared
to protective features that are thicker. In contrast, thicker
protective features will require longer extended processing
times.
[0042] The composition of the protective feature can vary depending
upon the particular architecture involved. The composition should
be chosen so that adequate isolation between the underlying
metallized feature and the overlying dielectric material is
provided while at the same time providing satisfactory adhesion
between the underlying metallized feature and overlying dielectric
material. In addition, the particular metal or its alloy chosen for
the protective feature should not have an undesirable effect on the
resistivity of the underlying metallized feature.
[0043] In accordance with the present invention, the protective
features of the present invention can be provided by
electrochemical deposition processes such as an electrolytic or
electroless process.
[0044] In an electrolytic process, the workpiece carrying the
metallized feature with its exposed surfaces is contacted with an
electroplating bath of a composition suitable for deposition of the
desired metal for the protective feature when a current is applied
between the workpiece and an anode in the bath. Specific metals
suitable for the electrolytically deposited protective features
have been described above, but it should be understood that other
metals which can be electrolytically deposited and are conductive
that provide the necessary diffusion barrier properties can also be
used in accordance with the present invention.
[0045] The metal or metals that are to be deposited as a protective
feature onto the exposed surfaces of the metallized features on the
workpiece in accordance with the present invention are present in a
solution as species of metal ions or complexed ions. The metal ions
are deposited under alkaline or acidic process conditions that
result in their preferential deposition on the raised and exposed
surfaces of the metallized features as opposed to the surrounding
field regions. Such electrolytic solutions advantageously include
organic additives that encourage deposition onto the raised exposed
features (i.e., accelerators) or that suppress deposition of metal
ions onto the surrounding field surface areas (i.e., suppressors).
In addition, the baths may include organic additives such as
brighteners or levelers.
[0046] Examples of accelerators for use in electrolytic baths
useful for carrying out the present invention include water-soluble
salts of organic acids including mercapto or thiol functional
groups, as well as other compounds that include the chemical
structure S--R.sub.1--S, wherein R.sub.1 is an alkyl or aryl
moiety. Examples of suitable suppressors include polyethylene
glycols and polyoxyethylene glycols having molecular weights of
approximately 3,000 to 8,000. Such suppressor agents are available
commercially from sources such as Shipley Company, Inc., Newton,
Mass., and Enthone-OMI, New Haven, Conn.
[0047] Complexing agents that are suitable for use in electrolytic
baths for depositing protective features in accordance with the
present invention include ethylene diamine tetracetic acid (EDTA),
ethylene diamine (ED), citric acid, and their salts. Such
complexing agents can be used alone, in combination with one
another, or in combination with one or more other complexing
agents. The specific amount of complexing agent employed will be
dependent upon the specific process conditions and composition of
the electrolytic processing bath. It should be understood that
other complexing agents may be employed depending upon the specific
chemistry of the electrolytic bath.
[0048] The electrolytic deposition of a protective feature in
accordance with the present invention can be carried out in an
alkaline bath. An exemplary alkaline bath for depositing a nickel
based protective feature includes a source of metal ions in the
form of nickel, such as nickel sulfate, nickel chloride, nickel
acetate or nickel sulfamate. Concentrations of 5-50 gm per liter of
the nickel salt in the plating bath are useful. If the metal or
alloy to be deposited is cobalt, the alkaline bath includes a
source of metal ions in the form of cobalt such as cobalt sulfate,
cobalt chloride, or cobalt acetate. Concentrations ranging from
about 5-50 gm per liter of the cobalt salt in the plating bath are
useful in accordance with the present invention. Other components
of an alkaline plating bath useful in accordance with the present
invention for depositing protective features of nickel or cobalt or
its alloys include complexing agents such as citrate salt,
ethylenediamine, glycine, oxalate salt, salicylate salt. As
alternatives to these salts, their acids, such as citric acid,
oxalic acid, salicylic acid, and bases, such as sodium hydroxide,
potassium hydroxide, ammonium hydroxide, and tetramethylammonium
hydroxide can be used. The complexing agents when used should be
present in a stoichiometric excess with respect to the nickel or
cobalt concentration in the bath. An exemplary range of
concentration is about 5-50 gm per liter. The bath may also include
a pH buffer such as boric acid in an amount ranging from about
10-30 gm per liter and a nonionic surfactant, such as Triton X-100
available from the Dow Chemical Company in an amount ranging from
about 0.01-1 gm per liter.
[0049] When the protective feature is formed from an alloy of
nickel or cobalt, the alloying metal is provided by including a
source of metal ions in the form of the alloying material in the
plating bath. When phosphorous is the alloying material, the bath
can include a source of phosphorous ions. When boron is the
alloying material, the bath can include a source of boron ions.
When tungsten is the alloying material, a tungsten salt, such as
sodium tungstate or ammonium tungstate can be present in the
plating bath in an amount ranging from about 2-10 gm per liter.
When molybdenum is the alloying material, the bath can include
sodium molybdate or ammonium molybdate in an amount ranging from
about 2-10 gm per liter.
[0050] The electrolytic deposition of a protective feature in
accordance with the present invention can also be carried out in an
acidic bath. An exemplary acidic bath for depositing a nickel based
protective feature includes a source of metal ions in the form of
nickel sulfate, an acid in the form of boric acid, and a citrate
complexing agent. A suitable nonlimiting composition and range of
concentrations for the various components of an electrolytic bath
for depositing nickel boron on an exposed metallized feature on a
workpiece according to the present invention include the
following:
[0051] 1. 0.25 M NiSO.sub.4;
[0052] 2. 0.5 M H.sub.3BO.sub.3;
[0053] 3. 0.33 M Na.sub.3C.sub.3H.sub.5O.sub.7; and
[0054] 4. pH of about 6.2.
[0055] The above-mentioned bath can also be used to plate nickel
tungsten (20%) or nickel phosphorus (25%) alloys if tungstate
(H.sub.2WO.sub.4) or H.sub.2PHO.sub.3 is present in the bath. In
addition, in view of the similar electroplating properties of
nickel and cobalt, cobalt can be used in place of nickel and
provided in the bath in the form of cobalt sulfate.
[0056] Other nickel or cobalt alloys can be selectively deposited
through the selection of the specific components present within the
electroplating bath. It should be understood that the
aforementioned solutions are not intended to limit the use of the
present invention to the specific baths. Solutions useful in
accordance with the method of the present invention can include one
or a plurality of metal ion source or sources, depending on whether
the protective feature to be deposited is a binary or ternary
alloy. Other sources of nickel ions or cobalt ions are also within
the scope of the present invention.
[0057] The electrolytic deposition of the protective features of
the present invention can be carried out in a tool designed to
electrochemically deposit metals such as one available from
Semitool, Inc., of Kalispell, Mont., under the trademark LT210.TM.
ECD system. Other commercially available systems for the
electrochemical deposition of metals include the Equinox.TM. model
tool available from Semitool, Inc. as well.
[0058] An integrated tool can be provided to carry out a number of
process steps carried out in accordance with the present invention.
Below is described one possible combination of processing stations
that could be embodied in a processing tool platform sold under the
trademark EquinoX.TM. by Semitool, Inc. of Kalispell, Mont. It
should be understood that other processing tool platforms could be
configured in similar or different manners to carry out the
metallization steps of the present invention. Referring to FIG. 18,
an exemplary integrated processing tool includes various stations
to carry out an optional seed layer deposition 122, a photoresist
developing step 124, a bulk metallization step 126, a seed layer
etch step 128, a barrier layer etch step 130, and a protective
feature deposition step 132. The tool may also include a
photoresist removal chamber 127 for removing developed photoresist.
The chambers for carrying out such steps can be arranged in various
configurations. Microelectronic workpieces are transferred between
the stations through the use of robotics (not shown). In addition,
other processing stations such as a rinse station identified by
reference 134 can be provided in the processing tool 120.
Processing tool 120 is capable of being programmed to implement
user entered processing recipes and conditions.
[0059] The robotics for the tool 120 are designed to move along a
linear track. Alternatively, the robotics can be centrally mounted
and designed to rotate to access the input section 136 and the
output section 138 of tool 120. Suitable chambers for use in tool
120 include those available for the modular configuration of an
Equinox.RTM. brand processing tool from Semitool, Inc.
[0060] For example, the photoresist developing chamber 124, seed
layer etch chamber 128, barrier layer etch chamber 130, can be of
the type available from numerous manufacturers for carrying out
such process steps. Examples of such chambers include spray
processing modules and immersion processing modules available in
conjunction with the Equinox.TM. system described above. The
optional seed layer deposition chamber 122, bulk metallization
chamber 126 and protective feature deposition chamber 132 can be
provided by numerous electroplating and electroless deposition
reactors such as those available as immersion processing modules
and electroplating processing reactors for the Equinox.TM.
processor specific examples of an electroplating processing reactor
include the types described in International Application No.
WO98/02911 (PCT/US97/12332) and International Application No.
WO00/03067, the portions of the descriptions of these applications
relating to the electroplating processing reactors are expressly
incorporated herein by reference.
[0061] In general, a chamber for electroplating bulk metal or
protective features in accordance with the present invention
includes a reactor, a bath supply, an anode, a power supply, and a
controller. The reactor receives the surface of the workpiece and
exposes the surface to an electroplating bath. The bath supply
includes a source of metal ions to be deposited on the surface of
the workpiece. The anode is in electrical contact with the
electroplating bath. The power supply supplies electroplating power
between the surface of the workpiece and the anode to electroplate
metal ions onto the surface. The controller controls the supply of
electroplating power so that the metal ions are deposited on the
workpiece surface. Referring to FIG. 19, the seed layer deposition
chamber 122, bulk metallization chamber 126 and/or protective
feature deposition chamber 132 can include a reactor vessel in
which the electroplating bath is held and which receives at least
one surface of the workpiece on which the metal to be deposited is
contained.
[0062] Referring to FIG. 20, a suitable reactor 60 includes a
processing head 62 and an electroplating bowl assembly 64. The
electroplating bowl assembly includes a cup assembly 70 that is
disposed within a reservoir container 72. The cup assembly 70
includes a fluid reactor 72 portion that holds the electroplating
bath fluid. The cup assembly also includes a depending annular
skirt 74 which extends below the cup bottom 76, and which includes
apertures opening therethrough for fluid communication of the
plating bath solution, and for release of any gases that might
collect as the reactor of the reservoir assembly is filled with
plating solution. The cup is preferably made from a material that
is inert to plating solutions, such as polypropylene.
[0063] A lower opening in the bottom wall of the cup assembly 70 is
connected to a polypropylene (or other material) riser tube 78,
which preferably is adjusted in height relative to the cup assembly
by a threaded connection. A first end of the riser tube 78 is
secured to the rear portion of an anode shield 80, which supports
an anode 82. A fluid inlet line 84 is disposed within the riser
tube 78. Both the riser tube 78 and the fluid inlet line 84 are
secured to the processing bowl assembly 64 by a fitting 86. The
fitting 86 can accommodate height adjustment of both the riser tube
78 and the inlet line 84. As such, this connection provides for
vertical adjustment of the anode 82. The inlet line 84 is
preferably made from a conductive material, such as titanium, and
is used to conduct electrical current to the anode 82 from the
power supply, as well as to supply fluid to the cup assembly
70.
[0064] The metal that is to be plated onto the workpiece in
accordance with the present invention is present in a plating
solution as species of metal ions to be deposited onto the
workpiece. Electroplating solution is provided to the cup assembly
70 through the fluid inlet line 84 and proceeds therefrom through a
plurality of fluid inlet openings 88. The plating solution then
fills the reactor 72 through openings 88, as supplied by a plating
fluid pump (not shown) or other suitable supply. The metal ions are
deposited under process conditions that preferentially deposit
metal ions onto the metallized features as opposed to the
surrounding field surfaces.
[0065] The upper edge of the cup sidewall 90 forms a weir, which
limits the level of electroplating solution within the cup. This
level is chosen so that only the bottom surface of a wafer W (or
other workpiece) is contacted by the electroplating solution.
Excess solution pours over this top edge into an overflow reactor
92.
[0066] The outflow liquid from the reactor 72 is preferably
returned to a suitable reservoir where it can be treated with
additional plating chemicals to adjust the levels of the
constituents and then recycled through the plating reactor 72.
[0067] In one embodiment of the apparatus for electroplating
metals, the anode 82 is an inert anode used in connection with the
plating of metals onto the workpiece. The specific anode may
alternatively be a consumable anode, with the anode used in reactor
60 varying depending upon the specifics of the plating liquid and
process being used.
[0068] The reactor illustrated in FIG. 19 also employs a diffuser
plate 93 that is disposed above the anode 82, providing an even
distribution of the flow of fluid across the surface of wafer W.
Fluid passages are provided over all or a portion of the diffuser
plate 93, to allow fluid communication therethrough. The height of
the diffuser plate within the cup assembly may be adjustable by
using a height adjustment mechanism 94.
[0069] The anode shield 80 is secured to the underside of the anode
82 using anode shield fasteners 96, to prevent direct impingement
by the plating solution as the solution passes into the processing
reactor 72. The anode shield 80 and anode shield fasteners 96 are
preferably made from a dielectric material, such as polyvinylidene
fluoride or polypropylene. The anode shield serves to electrically
isolate and physically protect the backside of the anode.
[0070] The processing head 62 holds a wafer W (or other workpiece)
within the upper region of the processing reactor 72. In a
preferred embodiment, the head 62 is constructed to rotate the
wafer W within the reactor 72 about an axis R. To this end, the
processing head 62 includes a rotor assembly 98 having a plurality
of wafer W engaging contact fingers 200 that hold the wafer W
against features of the rotor. Alternatively, the rotor assembly 98
includes a ring contact as described in International Application
No. PCT/US99/15850 (WO 00/40779), which is incorporated herein by
reference. The fingers 200 are for a ring contact assembly is
preferably adapted to conduct current between the wafer W and an
electrical power supply.
[0071] The processing head 62 is supported by a head operator (not
shown) that is adjustable to adjust the height of the processing
head. The head operator also has a head connection shaft 202 that
is operable to pivot about a horizontal pivot axis. Pivotal action
of the processing head using the operator allows the processing
head to be placed in an open or face-up position (not shown) for
loading and unloading of the wafer W. FIG. 19 illustrates the
processing head pivoted into a face-down position in preparation
for processing. The foregoing reactor can be readily adapted to
carry out an electroless deposition which does not require the
anode or a power supply for providing plating current.
[0072] Tool 120 can be incorporated into a manufacturing line that
includes other tools for producing raised metallized features
having an exposed top surface and exposed sidewalls. The additional
tools will be capable of carrying out operations on the substrate
that are not capable of being carried out in tool 120. For example,
the manufacturing line can include a tool or tools for patterning a
substrate and/or for depositing and exposing a dielectric layer
deposited on the substrate. Referring to FIG. 18, a tool for
patterning a substrate is schematically illustrated by block 140
and is arranged to receive the substrates and to provide a pattern
in the surface of the substrate, for example through a series of
photoresist deposition, photoresist patterning and etching steps.
Upon formation of a pattern in the microelectronic workpiece
substrate, the workpiece can be delivered to another tool 150
suitable for the deposition of a barrier layer within the features
formed in tool 140. In addition, tool 150 can include chambers that
can be used to deposit a seed layer onto the barrier layer. Typical
chambers present in tool 150 will be those capable of physical
vapor deposition techniques or chemical vapor deposition
techniques. The patterned microelectronic workpiece with the
deposited barrier layer and seed layer can be delivered to tool 160
where photoresist and dielectric can be deposited and exposed.
[0073] In tool 120, as an alternative to the vapor deposition of a
seed layer in tool 150, a chamber 122 is provided which allows for
the electrochemical deposition of the seed layer in tool 120. In an
exemplary process architecture, after a seed layer has been
deposited, the workpiece is removed from tool 120 and delivered to
tool 160 designed to deposit photoresist or dielectric and to
expose the photoresist. After deposition of the photoresist and its
exposure, the microelectronic workpiece can be returned to tool 120
for development and patterning of the photoresist in chamber 124.
Following the patterning of the photoresist in chamber 124, the
microelectronic workpiece is delivered to reactor 126 where bulk
metallization is carried out electrochemically. Subsequent to the
bulk metallization, the microelectronic workpiece is delivered to
reactor 127 where etching of the developed remaining photoresist is
carried out. Subsequent to the removal of the remaining
photoresist, the microelectronic workpiece is delivered to chamber
128 where the portion of the seed layer which is not covered by the
bulk metallized feature is removed. Subsequent to the removal of
seed layer in reactor 128, the microelectronic workpiece is
delivered either to chamber 130 for removal of the exposed barrier
layer or to chamber 132 where conductive protective features formed
in accordance with the present invention is electrochemically
deposited.
[0074] Tool 120 can also include a clean/rinse station 134 which
can be used between the respective processing steps.
[0075] Tool 120 can be configured to include chambers capable of
electrolytic deposition of metals or the electroless deposition of
metals. The specific configuration of tool 120 will be dependent
upon the specific process steps that the manufacturer chooses to
carry out. The present invention is not limited to the particular
sequence of process steps described above or the particular
sequence of chambers described above.
[0076] The particular conditions for carrying out the electrolytic
deposition of the protective feature will vary depending upon the
composition of the electrolytic bath, the rate of deposition
desired, and the thickness desired. Variables which can be
controlled in the electrolytic deposition process include the
temperature of the bath, its pH, concentration of the components in
the bath, agitation of the bath or workpiece, time of deposition,
and the current density.
[0077] The electrolytic plating of a protective feature on the
exposed surfaces of a metallized feature in accordance with the
present invention is carried out selectively on the metallized
feature because the surrounding field surfaces are nonconductive
and therefore are not suitable for electrolytic deposition of
metals thereon. As a result thereof, the method of the present
invention carried out using an electrolytic process results in the
selective deposition of a protective feature on the exposed
surfaces of a raised metallized feature.
[0078] In another embodiment, a protective feature can be
selectively deposited on the exposed surfaces of the metallized
feature without the application of an applied current, using an
electroless deposition process. Electroless deposition is
particularly useful when the metallized feature is electrically
isolated prior to deposition of a protective feature. In accordance
with this aspect of the present invention, the electroless
deposition of a protective feature on the exposed surfaces of a
metallized feature is carried out by first depositing a catalyst,
such as palladium, onto the exposed surfaces of the metallized
feature. The deposition of the palladium can be achieved by
immersing the metallized feature in a dilute aqueous, acidic
solution of palladium ions. Thereafter, the palladium "seeded"
surfaces of the metallized feature are contacted with a bath
containing nickel and/or cobalt, and alternatively including
nonmetallic elements such as phosphorus or boron and a reducing
agent. The reducing agent converts the metal ions to a zero valent
metal on the seeded surface of the metallized feature to form a
continuous metal film. Baths used for the electroless deposition of
protective features formed in accordance with the present invention
include those components described above with respect to the
electrolytic baths and in addition, include a reducing agent such
as a hypophosphite salt, e.g., sodium hypophosphite, potassium
hypophosphite, or ammonium hypophosphite or dimethylamine borane.
Two exemplary baths for the electroless deposition of a protective
feature in accordance with the present invention are as
follows:
Bath for Electroless Deposition of Cobalt-Tungsten-Phosphorus
Protective
[0079]
1 Ammonium tungstate 10 g/l Cobalt chloride 30 g/l Sodium citrate
80 g/l Sodium hypophosphate 20 g/l Surfactant 0.05 g/l
Bath for Electroless Deposition of Nickel-Tungsten-Phosphorus
Protective Feature
[0080]
2 Nickel sulfate 30 g/l Sodium hypophosphate 10 g/l Sodium citrate
40 g/l Ammonium chloride 40 g/l Sodium tungstate 2-10 g/l
[0081] The bath compositions described herein are exemplary of
baths suitable for electrolytically and electrolessly depositing
protective features of the present invention. Bath compositions for
other protective features can be readily formulated by one skilled
in the art without undue experimentation. It should be understood
that the present invention is not limited to the specific baths set
forth above.
[0082] The electroless deposition of the metallized feature can be
controlled through the manipulation of the temperature of the bath,
the concentration of the respective components, and the pH. The
thickness of the deposited protective feature can be controlled by
adjusting the time of contact of the metallized feature with the
metal-containing bath.
[0083] In certain situations, it is desirable to employ an
electrolytic deposition process to provide protective features in
accordance with the present invention. With an electrolytic bath,
it is easier to control the composition of the bath, the bath is
more stable, and electrolytic baths have fewer selectivity problems
as compared to electroless plating processes.
[0084] While the present invention has been described above with
reference to a dielectric/barrier/seed/metal layer structure, it
should be understood that the present invention is not specifically
limited to such structure. Fewer or a greater number of layers may
form the structure to which a protective feature formed in
accordance with the present invention is applied.
[0085] While the preferred embodiment of the invention has been
illustrated and described, it will be appreciated that various
changes can be made therein without departing from the spirit and
scope of the invention.
* * * * *