U.S. patent application number 10/818081 was filed with the patent office on 2004-09-30 for wire-bond process flow for copper metal-six, structures achieved thereby, and testing method.
This patent application is currently assigned to Intel Corporation. Invention is credited to Seshan, Krishna, Singh, Kuljeet.
Application Number | 20040192019 10/818081 |
Document ID | / |
Family ID | 21975393 |
Filed Date | 2004-09-30 |
United States Patent
Application |
20040192019 |
Kind Code |
A1 |
Seshan, Krishna ; et
al. |
September 30, 2004 |
Wire-bond process flow for copper metal-six, structures achieved
thereby, and testing method
Abstract
The present invention relates to a device that includes a
low-ohmic test. The device includes a metallization copper pad such
as metal-six, a metal first film such as Ni that is disposed above
the metallization copper pad, and a metal second film such as Au
that is disposed above the metal first film. The present invention
also relates to a wire-bonding process, and to a method of pulling
a first wire bond and making a second wire bond.
Inventors: |
Seshan, Krishna; (San Jose,
CA) ; Singh, Kuljeet; (Folsom, CA) |
Correspondence
Address: |
SCHWEGMAN, LUNDBERG, WOESSNER & KLUTH, P.A.
P.O. BOX 2938
MINNEAPOLIS
MN
55402
US
|
Assignee: |
Intel Corporation
|
Family ID: |
21975393 |
Appl. No.: |
10/818081 |
Filed: |
April 5, 2004 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10818081 |
Apr 5, 2004 |
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10052089 |
Jan 16, 2002 |
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6715663 |
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Current U.S.
Class: |
438/617 ;
257/E21.509; 257/E23.02 |
Current CPC
Class: |
H01L 24/03 20130101;
H01L 2224/05655 20130101; H01L 2224/4807 20130101; H01L 2224/48463
20130101; H01L 2924/01006 20130101; H01L 24/85 20130101; H01L
2924/01014 20130101; H01L 2924/01043 20130101; H01L 2924/01019
20130101; H01L 2224/05166 20130101; H01L 2224/45124 20130101; H01L
2224/05147 20130101; H01L 2224/05644 20130101; H01L 2924/0104
20130101; H01L 2224/48453 20130101; H01L 2924/01078 20130101; H01L
24/45 20130101; H01L 2924/01015 20130101; H01L 2224/48644 20130101;
H01L 2924/01058 20130101; H01L 2224/48655 20130101; H01L 2924/01039
20130101; H01L 2224/0392 20130101; H01L 2224/48724 20130101; H01L
2224/48624 20130101; H01L 2924/00014 20130101; H01L 2224/05556
20130101; H01L 2224/05647 20130101; H01L 2224/48755 20130101; H01L
2224/85 20130101; H01L 2924/01038 20130101; H01L 2224/48669
20130101; H01L 2224/02166 20130101; H01L 2924/01011 20130101; H01L
2924/01047 20130101; H01L 2924/0103 20130101; H01L 2924/01025
20130101; H01L 2224/05558 20130101; H01L 2924/01027 20130101; H01L
24/05 20130101; H01L 2924/01013 20130101; H01L 2924/01029 20130101;
H01L 2924/01052 20130101; H01L 2224/48647 20130101; H01L 2924/01074
20130101; H01L 2924/01075 20130101; H01L 24/48 20130101; H01L
2224/0517 20130101; H01L 2924/01021 20130101; H01L 2924/01042
20130101; H01L 2224/05009 20130101; H01L 2924/01022 20130101; H01L
2924/01045 20130101; H01L 2224/04042 20130101; H01L 2924/01079
20130101; H01L 2224/05669 20130101; H01L 2924/01028 20130101; H01L
2224/05184 20130101; H01L 2924/01024 20130101; H01L 2224/05073
20130101; H01L 22/32 20130101; H01L 2224/05155 20130101; H01L
2924/01005 20130101; H01L 2224/45144 20130101; H01L 2924/01057
20130101; H01L 2924/01077 20130101; H01L 2924/01012 20130101; H01L
2924/01072 20130101; H01L 2224/05624 20130101; H01L 2224/48747
20130101; H01L 2224/48769 20130101; H01L 2224/45124 20130101; H01L
2924/00014 20130101; H01L 2224/45144 20130101; H01L 2924/00014
20130101; H01L 2224/48463 20130101; H01L 2924/00014 20130101; H01L
2224/05624 20130101; H01L 2924/00014 20130101; H01L 2924/00014
20130101; H01L 2224/78 20130101; H01L 2224/48624 20130101; H01L
2924/00 20130101; H01L 2224/48644 20130101; H01L 2924/00 20130101;
H01L 2224/48647 20130101; H01L 2924/00 20130101; H01L 2224/48655
20130101; H01L 2924/00 20130101; H01L 2224/48669 20130101; H01L
2924/00 20130101; H01L 2224/48724 20130101; H01L 2924/00 20130101;
H01L 2224/48744 20130101; H01L 2924/00 20130101; H01L 2224/48755
20130101; H01L 2924/00 20130101; H01L 2224/48769 20130101; H01L
2924/00 20130101; H01L 2224/48747 20130101; H01L 2924/00
20130101 |
Class at
Publication: |
438/617 |
International
Class: |
H01L 021/44; H01L
021/4763 |
Claims
What is claimed is.
1. A process of forming a wire bond comprising: forming a
protective structure over a metallization copper pad, wherein the
metallization copper pad makes contact with a device, and wherein
the protective structure includes a metal first film disposed above
and on the metallization copper pad and a metal second film
disposed above and on the metal first film; and at the second metal
film, wire bonding the device.
2. The process according to claim 1, further including: by probing
the metal second film, electrically testing the device.
3. The process according to claim 1, before forming a protective
structure, further including: forming a passivation structure that
exposes at least a portion of the metallization copper pad.
4. The process according to claim 1, wherein the metallization
copper pad is a metal-six copper (M6 Cu) pad.
5. The process according to claim 1, wherein forming a passivation
structure includes: forming a first passivation layer over the
metallization copper pad; forming a second passivation layer over
the metallization copper pad; and patterning the first and second
passivation layers to expose at least a portion of the
metallization copper pad.
6. The process according to claim 1, wherein forming a protective
structure includes: forming the metal first film by a process
selected from PVD, CVD, electroplating, and electroless plating;
and forming the metal second film by a process selected from PVD,
CVD, electroplating, and electroless plating.
7. The process according to claim 6, wherein forming the metal
first film results in a film selected from Ni, Pd, Pt, Co, Rh, Ir,
Sc, Yt, La, Ce, Re, Ir, Cu, Au, Ag, Cr, Mo, W, Mn, Tc, Ti, TiW, Zr,
Hr, NiB, NiP, NiBP, NiCrB, NiCrP, NiCrBP, NiMoB, NiMoP, NiMoBP,
NiWB, NiWP, NiWBP, NiMnB, NiMnP, NiMnBP, NiTcB, NiTcP, NiTcBP,
NiReB, NiReP, NiReBP, NiCoB, NiCoP, NiCoBP, NiCoCrB, NiCoCrP,
NiCoCrBP, NiCoMoB, NiCoMoP, NiCoMoBP, NiCoWB, NiCoWP, NiCoWBP,
NiCoMnB, NiCoMnP, NiCoMnBP, NiCoTcB, NiCoTcP, NiCoTcBP, NiCoReB,
NiCoReP, NiCoReBP, CoB, CoP, CoBP, CoCrB, CoCrP, CoCrBP, CoMoB,
CoMoP, CoMoBP, CoWB, CoWP, CoWBP, CoMnB, CoMnP, CoMnBP, CoTcB,
CoTcP, CoTcBP, CoReB, CoReP, and CoReBP, CoNiB, CoNiP, CoPdBP,
CoPdCrB, CoPdCrP, CoPdCrBP, CoPdMoB, CoPdMoP, CoPdMoBP, CoPdWB,
CoPdWP, CoPdWBP, CoPdMnB, CoPdMnP, CoPdMnBP, CoPdTcB, CoPdTcP,
CoPdTcBP, CoPdReB, CoPdReP, CoPdReBP, CuB, CuP, CuBP, CuCrB, CuCrP,
CuCrBP, CuMoB, CuMoP, CuMoBP, CuWB, CuWP, CuWBP, CuMnB, CuMnP,
CuMnBP, CuTcB, CuTcP, CuTcBP, CuReB, CuReP, CuReBP, CuNiB, CuNiP,
CuNiBP, CuNiCrB, CuNiCrP, CuNiCrBP, CuNiMoB, CuNiMoP, CuNiMoBP,
CuNiWB, CuNiWP, CuNiWBP, CuNiMnB, CuNiMnP, CuNiMnBP, CuNiTcB,
CuNiTcP, CuNiTcBP, CuNiReB, CuNiReP, CuNiReBP and combinations
thereof.
8. The process according to claim 6, wherein forming the metal
second film results in a film selected from gold, dor, platinum,
and aluminum.
9. The process according to claim 1, wherein metal first film is
electrolessly plated with a composition including: from zero to at
least one primary metal selected from cobalt, rhenium, iridium,
nickel, palladium, platinum, titanium, zirconium, hafnium, copper,
silver, gold, and combinations thereof; from zero to at least one
secondary metal selected from chromium, molybdenum, tungsten,
manganese, technetium, rhenium, and combinations thereof; from zero
to at least one primary reducing agent in a concentration range
from about 1 gram/liter to about 30 gram/liter; from zero to at
least one secondary reducing agent in a concentration range from
about 0 gram/liter to about 2 gram/liter; a complexing and
buffering agent; and at least one pH adjusting agent.
10. The process according to claim 1, after wire bonding the
device, further including: removing the wire bonding; and
replacement wire bonding the device.
11. A wire-bond configuration comprising: a metallization copper
pad disposed over a device; a protective structure disposed above
an on the metallization copper pad, wherein the protective
structure includes a metal first film disposed above and on the
metallization copper pad and a second metal film disposed above and
on the metal first film, and wherein the metal first film has at
least one of a hardness or a corrosion potential that is greater
than at least one of the hardness or corrosion potential of the
second metal film; and at least one of a test probe tip and a bond
wire in contact with the protective structure.
12. The wire-bond configuration according to claim 11, further
including: a passivation structure that exposes the metallization
copper pad, wherein the passivation structure includes an inorganic
first layer disposed on the metallization copper pad and an organic
second layer disposed on the inorganic first layer.
13. The wire-bond configuration according to claim 11, wherein the
passivation structure includes: a nitride first layer disposed
above and on the metallization copper pad; and a polyimide second
layer disposed above an on the nitride first layer.
14. The wire-bond configuration according to claim 11, wherein the
protective structure includes: a metal first film including at
least one primary metal selected from Ni, Pd, Pt, Co, Rh, Ir, Sc,
Yt, La, Ce, Re, Ir, Cu, Au, Ag, Cr, Mo, W, Mn, Tc, Ti, Zr, Hf, and
combinations thereof; and a metal second film selected from Au,
dor, Pt, and Al.
15. The wire-bond configuration according to claim 14, wherein the
metal first film is Ni has a hardness that is greater than the
hardness of the metal second film.
16. The wire-bond configuration according to claim 14, wherein the
metal second film is Au has a resistance to corrosion that is
greater than the resistance to corrosion of the metal first
film.
17. The wire-bond configuration according to claim 14, wherein the
metal first film is Ni has a hardness that is greater than the
hardness of the metal second film, and wherein the metal second
film has a resistance to corrosion that is greater than the
resistance to corrosion of the metal second film.
18. A method of testing a device, comprising: contacting a test
probe tip to a metallization, wherein the metallization has a
structure including a metal first film disposed above and on the
metallization, and a metal second film disposed above and on the
metal first film, wherein the metal first film has at least one of
a hardness or a corrosion potential that is greater than at least
one of the hardness or corrosion potential of the metal second
film; and passing a test current through the test probe, wherein
the test current experiences an ohmic resistance in a range from
about 0.5 .OMEGA. to about 4 .OMEGA..
19. The method according to claim 18, wherein the metal first film
includes Ni and the metal second film includes Au, or the metal
first film includes Ti and the metal second film includes Al.
20. The method according to claim 18, wherein the ohmic resistance
is in a range from about 1 .OMEGA. to about 3 .OMEGA..
21. The method according to claim 18, wherein the test probe tip
penetrates the metal second film and stops before penetrating the
metal first film.
22. The method according to claim 18, following passing a test
current, further including: first bonding a first bond wire to the
metal second film.
23. The method according to claim 18, following passing a test
current, further including: first bonding a first bond wire to the
metal second film; removing the first bond wire; and second bonding
a second bond wire to the metal second film.
Description
RELATED APPLICATIONS
[0001] The application is a divisional of U.S. patent application
Ser. No. 10/052,089, filed Jan. 16, 2002, which is incorporated
herein by reference.
FIELD OF THE INVENTION
[0002] The present invention relates generally to electrical
testing (e-test) and wire bonding for a metallization process flow.
More particularly, the present invention relates to an electroless
plating process flow that follows e-test, and for a wire bonding
process flow that follows a metal-six copper (M6 Cu)
metallization.
DESCRIPTION OF RELATED ART
[0003] Metallization process flows may be carried out near the
back-end of processing by electrical connections such as a metal
bump formation on a ball-limiting metallurgy (BLM) that surmounts
the metallization pad, or by a wire bonding process on the
metallization pad. During the wire bonding process, typically an
aluminum or gold wire is used to make contact with the
metallization pad. However, this process flow often causes
significant corrosion of the metallization pad, particularly if it
is copper, and the result is an unacceptable yield loss during the
wire-bonding process. FIG. 8 depicts a prior art wire bond on a
metallization pad that illustrates corrosion. A semiconductor
structure 10 includes a substrate 12 and an upper metallization 14
such as a trace or pad, that is electrically connected to a lower
metallization 16 through a contact 18. A wire bond 20 is depicted
in connection with upper metallization 14. It is noted that upper
metallization 14, if copper for example, has experienced corrosion
22 (depicted in an arbitrary size and shape).
[0004] The corrosion 22 has resulted from at least one of several
environments or other conditions. For example, an aluminum wire
bond 20 will corrode upper metallization 14, or processing
conditions including back-end-of-line (BEOL) testing such as a hot
ambient steam test (HAST) and/or bum-in, add to corrosion 22. Other
processing conditions add to corrosion including the galvanic
differential that is established between the two disparate metals
of upper metallization 14 and wire bond 20. Once corrosion begins,
a variable and unpredictable contact resistance (CRES) occurs
between the numerous probes and the upper metallization 14.
Additionally, a copper scumming of the probe tip requires frequent
and unpredictable cleaning.
BRIEF DESCRIPTION OF THE DRAWINGS
[0005] In order to illustrate the manner in which embodiments of
the invention are obtained, a more particular description of the
invention briefly described above will be rendered by reference to
specific embodiments thereof which are illustrated in the appended
drawings. Understanding that these drawings depict only typical
embodiments of the invention that are not necessarily drawn to
scale and are not therefore to be considered to be limiting of its
scope, the invention will be described and explained with
additional specificity and detail through the use of the
accompanying drawings in which:
[0006] FIG. 1 is a cross-section of a semiconductor structure
during processing according to an embodiment;
[0007] FIG. 2 is a cross-section of the semiconductor structure
depicted in FIG. 1 after further processing;
[0008] FIG. 3 is a cross-section of the semiconductor structure
depicted in FIG. 2 after further processing;
[0009] FIG. 4 is a cross-section of the semiconductor structure
depicted in FIG. 3 after further processing;
[0010] FIG. 5 is a cross-section of the semiconductor structure
depicted in FIG. 4 after further processing, and that also
illustrates an e-test embodiment;
[0011] FIG. 6 is a cross-section of the semiconductor structure
depicted in FIG. 4 after further processing, and that also
illustrates a wire-bond embodiment;
[0012] FIG. 7 illustrates a process flow according to an
embodiment; and
[0013] FIG. 8 is a cross-section of a known semiconductor
structure.
DETAILED DESCRIPTION OF THE INVENTION
[0014] The present invention relates to a wire-bond process flow
that minimizes copper corrosion in the copper pad or other
metallization that is wire bonded. In one embodiment, a structure
embodiment is disclosed that resists corrosion of the copper pad or
other metallization during processing, testing, and field use. In
another embodiment, the structure embodiment is used in an
electrical testing (e-test) during wafer sorting, that does not
damage the copper pad or the like, and that minimizes e-test error
but also lowers the e-test resistance. In one embodiment, an e-test
method is disclosed that uses the inventive structure
embodiment.
[0015] According to an embodiment, FIG. 1 is a cross-section of a
semiconductor structure 110 during fabrication that includes a
substrate 112 and metallization 114 such as copper pads that make
connection to what is commonly referred to as metal-six copper (M6
Cu) by way of non-limiting example. Metallization 114 may be
disposed with an upper surface 116 that is coplanar with substrate
112 where substrate 112 may be an interlayer dielectric (ILD)
composition. A nitride layer 118 and a passivation layer 120 are
formed over substrate 112 and metallization 114. It is noted that
metallization 114 is connected through a contact 122 to a lower
metallization 124.
[0016] Nitride layer 118 and passivation layer 120 act to protect
substrate 112 and to expose a portion of metallization 114
according to subsequent patterning. Passivation layer 120 may be a
polyimide material or it may be an inorganic material such as a
silicon oxide that is formed by the decomposition of tetraethyl
ortho silicate (TEOS). Patterning is accomplished by a mask (not
pictured) that exposes passivation layer 120.
[0017] FIG. 2 illustrates a patterned passivation structure, that
includes portions of nitride layer 118 and passivation layer 120,
and that exposes a portion of metallization 114. The process may be
carried out by blanket forming nitride layer 118 and passivation
layer 120, patterning, etching a recess 126, and curing passivation
layer 120 where passivation layer 120 is a polyimide or the like.
In one embodiment after the cure, passivation layer 120 has formed
a slope that has an angle 128, in a range from about 30.degree. to
about 60.degree.. In one embodiment after the cure, passivation
layer 120 has formed angle 128 that is about 45.degree..
[0018] FIG. 3 illustrates further processing according to
embodiments. A protective structure is formed that protects
metallization 114 during testing, but that also allows for a
lower-resistance test method. In a first process flow, a protective
structure is made that includes a metal first film 130 that is
disposed above and on the metallization 114. Metal first film 130
acts as a penetration barrier that may otherwise prevent damage by
a test probe tip during e-test according to an embodiment. The
thickness of metal first film 130 is in a range from about 1,000
.ANG.to about 1,500 .ANG.. In another embodiment, the thickness of
metal first film 130 is about 500 .ANG..
[0019] In one embodiment, metal first film 130 is a refractory
(hard) metal or alloy, and metallization 114 is a M6 Cu pad. Metal
first film 130 is formed by a deposition process flow that is
selected from vapor deposition, electroplating, and electroless
plating. The vapor deposition is selected from chemical vapor
deposition (CVD), including modified CVD such as plasma-enhanced
CVD (PECVD), and atomic layer CVD (ALCVD). In another embodiment,
physical vapor deposition (PVD) is used for form metal first film
130. The conditions of PVD may be selected in order to achieve a
desired morphology of metal first film 130. In the vapor depositing
embodiments, after a blanket deposition, a center-patterned masking
(not pictured) is carried out that blinds metal first film 130.
Thereafter, an etch is used to strip off unwanted refractory metal
material. The etch is a wet etch or a dry etch according to a
selected process integration plan.
[0020] Refractory metals for metal first film 130 include nickel
(Ni), palladium (Pd), platinum (Pt), and the like. In another
embodiment, refractory metals for metal first film 130 include
cobalt (Co), rhodium (Rh), iridium (Ir), and the like. In another
embodiment, refractory metals for metal first film 130 include
scandium (Sc), yttrium (Yt), lanthanum (La), cerium (Ce), and the
like. One property embodiment is that metal first film 130 exhibits
sufficient adhesion to the metallization that liftoff or spalling
thereof will not occur during fabrication, test, and ordinary field
use. In another embodiment, metal first film 130 is selected from
nickel, palladium, cobalt, tungsten, chromium, titanium,
ti-tungsten (TiW), zirconium, hafnium, and the like. Another
property embodiment is that metal first film 130 is hard enough
that an ordinary tungsten test probe or the like, will not
penetrate metal first film 130 during ordinary e-test
conditions.
[0021] Besides vapor depositing, liquid plating processing may be
done. Such liquid plating processing embodiments include spray
deposition, electroplating and electroless plating. One advantage
of electroless plating of the metal first film 130, is that due to
the chemically-induced oxidation-reduction reaction that is carried
out only at chemically enabled sites, no post-deposition patterning
and etching needs to be done. According to an embodiment,
semiconductor structure 110 is immersed in a bath that contains one
or more metal ions, and reduction of the ions occurs at the exposed
portion of metallization 114 to form metal first film 130.
[0022] As set forth herein, metal first film 130 is preferably a
refractory metal. In conjunction with a second metal film 132 (see
FIG. 4) and according to an embodiment, metal first film 130 is
less noble than the second metal film 132 (FIG. 4). The metal ion
or ions that are used to form metal first film 130 may be selected
from various metals or combinations thereof. In one embodiment, the
metal is selected from at least one primary metal and from zero to
at least one secondary metal. The at least one primary metal is
selected from the group of nickel (Ni), palladium (Pd), platinum
(Pt), and combinations thereof. In one embodiment, the at least one
primary metal is selected from the group of cobalt (Co), rhodium
(Rh), iridium (Ir), and combinations thereof. In one embodiment,
the at least one primary metal is selected from the group of copper
(Cu), silver (Ag), gold (Au), and combinations thereof. In another
embodiment, the at least one primary metal is selected from a
combination of at least two metals that combine metals from the
above-referenced groups. In one embodiment, the primary metal(s) is
supplied in a concentration range from about 2 gram/liter to about
50 gram/liter. In another embodiment, the primary metal(s) is
supplied in a concentration range from about 5 gram/liter to about
35 gram/liter.
[0023] In one embodiment, at least one secondary metal is added to
the primary metal(s) to form metal first film 130. In one
embodiment, the at least one secondary metal is selected from the
group of chromium (Cr), molybdenum (Mo), tungsten (W), and
combinations thereof. In another embodiment, the at least one
secondary metal is selected from the group of manganese (Mn),
technetium (Tc), rhenium (Re), and combinations thereof. In another
embodiment, the at least one secondary metal is selected from a
combination of at least two metals that combine metals from the
above-referenced groups. In one embodiment, the secondary metal(s)
is supplied in a concentration range from about 1 gram/liter to
about 40 gram/liter. In another embodiment, the secondary metal(s)
is supplied in a concentration range from about 2 gram/liter to
about 35 gram/liter.
[0024] Reducing agents are provided to assist in assuring metal
deposition if metal first film 130, as the chemical environment of
the substrate onto which the metal deposits continues to change.
Although initial deposition of a metal ion onto a substrate may be
autocatalytic, the changing chemical environment may interrupt the
autocatalytic environment. In one embodiment, where deposition is
upon a Cu M6 metallization pad 114 as known in the art, initial
deposition will be achieved in the presence of the Cu M6 pad 114.
Consequently, the Cu M6 pad 114 affects the initial, presumably
oxidation-reduction (REDOX) deposition chemistry. However, as the
Cu M6 pad 114 is covered by way of non-limiting example, by nickel,
the REDOX chemical environment changes from a nickel-onto-copper
plating, to a nickel-onto-nickel plating. Accordingly, a reducing
agent(s) is provided to assure continued nickel plating despite the
changed substrate environment.
[0025] In one embodiment, the electroless plating composition is
combined with from zero to at least one primary reducing agent in a
mixture of solvents. In one embodiment, a primary reducing agent
including boron (B) is provided. Primary reducing agents that can
be utilized for this application include ammonium, alkali metal,
alkaline earth metal borohydrides, and the like, and combinations
thereof. In one embodiment, inorganic primary reducing agent
embodiments include sodium borohydride, lithium borohydride, zinc
borohydride, and the like, and combinations thereof. In one
embodiment, an organic primary reducing agent is
dimethylaminoborane (DMAB). In another embodiment, other
aminoboranes are used such as diethylaminoborane, morpholine
borane, combinations thereof, and the like. In one embodiment, the
primary reducing agent(s) is supplied in a concentration range from
about 1 gram/liter to about 30 gram/liter. In another embodiment,
the primary reducing agent(s) is supplied in a concentration range
from about 2 gram/liter to about 20 gram/liter.
[0026] In one embodiment, a secondary reducing agent is provided to
assist the changing chemical environment during deposition of the
primary metal and optional secondary metal. However, the secondary
reducing agent may be used alone, without the primary reducing
agent. In one embodiment a phosphorus-containing compound is
selected as the secondary reducing agent. Phosphorus-containing
compounds may include hypophosphites. In one embodiment, the
hypophosphite is selected from organic hypophosphites such as
ammonium hypophosphite and the like.
[0027] In one embodiment, the hypophosphite is selected from
inorganic hypophosphites such as sodium hypophosphite and the like.
One embodiment includes an inorganic phosphorus-containing compound
such as hypophosphites of lithium, sodium, potassium, and mixtures
thereof. One embodiment includes an inorganic phosphorus-containing
compound such as hypophosphites of, magnesium, calcium, strontium,
and mixtures thereof. One embodiment includes an inorganic
phosphorus-containing compound such as nickel hypophosphite and the
like. One embodiment includes an inorganic phosphorus-containing
compound such as hypophosphorous acid and the like.
[0028] Other secondary reducing agents are selected from sulfites,
bisulfites, hydrosulfites, metabisulfites, and the like. Other
secondary reducing agents are selected from dithionates, and
tetrathionates, and the like. Other secondary reducing agents are
selected from thiosulfates, thioureas, and the like. Other
secondary reducing agents are selected from hydrazines,
hydroxylamines, aldehydes, glyoxylic acid, and reducing sugars. In
another embodiment, the secondary reducing agent is selected from
diisobutylaluminum hydride, sodium bis(2-methoxyethoxy)aluminum
hydride, and the like.
[0029] In one embodiment, the secondary reducing agent(s) is
supplied in a concentration range from about 0 gram/liter to about
5 gram/liter. In another embodiment, the secondary reducing
agent(s) is supplied in a concentration range from about 1
gram/liter to about 2 gram/liter.
[0030] In one embodiment, the primary reducing agent is DMAB in a
concentration range from about 1 gram/liter to about 30 gram/liter,
and the secondary reducing agent is ammonium hypophosphite in a
concentration range from about 0 gram/liter to about 2 gram/liter.
Other embodiments include primary and secondary reducing agents
that are substituted for DMAB and ammonium hypophosphite, or one of
them, as long as they approximate the gram equivalent amounts of
the primary and secondary reducing agents of the DMAB and the
ammonium hypophosphite. The gram equivalent amounts may be adjusted
by various means, such as according to the comparative dissociation
constants of the reducing agents.
[0031] In addition to the reducing agents, other agents may be
added such alkaline metal-free chelating agents. Embodiments of
chelating agents include citric acid, ammonium chloride, glycine,
acetic acid, malonic acid, and the like in concentration range from
about 5 gram/liter to about 70 gram/liter.
[0032] A complexing agent and a buffering agent are also used to
hold the metal ion(s) in solution until deposition is appropriate.
In one embodiment, an organic sulfate salt compound is used such as
ammonium sulfate, (NH).sub.2SO.sub.4 and the like. Other complexing
and buffering agents may be selected that have an effective gram
equivalent amount to the (NH).sub.2SO.sub.4 such as copper sulfate,
CUSO.sub.4. In one embodiment, the complexing/buffering agent is
supplied in a concentration range from about 50 gram/liter to about
1,000 gram/liter. In another embodiment, the complexing/buffering
agent is supplied in a concentration range from about 80 gram/liter
to about 600 gram/liter.
[0033] Various pH-adjusting compositions may be used including
organic and inorganic bases. That a compound is basic can be easily
confirmed by dipping pH test paper, measuring its aqueous solution
using a pH meter, observing the discoloration caused by an
indicator or measuring the adsorption of carbonic acid gas, and by
other methods.
[0034] In one embodiment, the organic base compounds which can be
used include organic amines such as pyridine, pyrrolidine,
combinations thereof, and the like. Other embodiments include
methylamine, dimethylamine, trimethylamine, combinations thereof,
and the like. Other embodiments include ethylamine, diethylamine,
triethylamine, combinations thereof, and the like. Other
embodiments include tetramethylammonium hydroxide (TMAH),
tetraethyl ammonium hydroxide (TEAH), tetrapropyl ammonium
hydroxide (TPAH), tetrabutyl ammonium hydroxide (TBAH),
combinations thereof, and the like. Other embodiments include
aniline, toluidine, and the like.
[0035] In one embodiment, the organic base includes TMAH in a
concentration range from about 30 mL to about 150 mL, added to a
100 mL volume of the other constituents of the inventive
electroless plating solution. Other embodiments include the gram
equivalent amounts of the organic base compounds set forth
herein.
[0036] In one embodiment, the inorganic base compounds which can be
used are salts of strong bases and weak acids. In one embodiment,
alkali metal acetates, alkaline earth metal acetates, and
combinations thereof are used. In one embodiment, alkali metal
propionates, alkaline earth metal propionates, and combinations
thereof are used. In one embodiment, alkali metal carbonates,
alkaline earth metal carbonates, and combinations thereof are used.
In one embodiment, alkali metal hydroxides, alkaline earth metal
hydroxides, and combinations thereof are used. In one embodiment,
combinations of at least two of the acetates, propionates,
carbonates, and hydroxides is used.
[0037] Inorganic base compounds may be provided in a concentration
such as a 25% sodium hydroxide, NaOH in a deionized (DI) water
solution, to make a volume of about 10 mL to about 50 mL. This
volume of solution is added to an about 100 mL volume of the other
inventive electroless plating composition constituents. Other
embodiments include the gram equivalent amounts of the inorganic
base compounds set forth herein.
[0038] Other compounds may be added to the inventive electroless
plating composition such as surface active agents. One commercial
surfactant is RHODAFAC RE 610, made by Aventis (formerly
Rhone-Poulenc Hoechst). Another commercial surfactant is Triton
x-100T.TM. made by Sigma-Aldrich. Other surfactants include
cystine, polyethylene glycols, polypropylene glycol
(PPG)/polyethylene glycol (PEG) (in a molecular range of
approximately 200 to 10,000) in a concentration range of about 0.01
to 5 gram/liter, and the like.
[0039] Several combinations of primary and secondary metals are
achievable according to various embodiments. The primary metal may
include, but is not limited to from zero to at least one metal,
selected from nickel, palladium, platinum, cobalt, rhodium,
iridium, copper, silver, and gold and combinations thereof,
although other refractory metals may be selected as set forth
herein. The secondary metal may include, but is not limited to from
zero to at least one metal selected from chromium, molybdenum,
tungsten, manganese, technetium, and rhenium. In one embodiment,
because of the presence of at least one of the primary and
secondary reducing agents, a metallic compound forms that
incorporates at least one of boron and phosphorus.
[0040] In one embodiment, nickel is a primary metal for an
electroless plating embodiment to form metal first film 130, the
composition includes a nickel solution to form a nickel plating
layer. According to an embodiment, where nickel is the primary
metal, because of the inventive electroless plating bath
environment, a metallic film forms that includes but is not limited
by such combinations as NiB, NiP, NiBP, NiCrB, NiCrP, NiCrBP,
NiMoB, NiMoP, NiMoBP, NiWB, NiWP, NiWBP, NiMnB, NiMnP, NiMnBP,
NiTcB, NiTcP, NiTcBP, NiReB, NiReP, and NiReBP. In these nickel
compounds, as in other embodiments set forth in this disclosure,
where a given element is listed first, second, third, etc., one
embodiment includes the largest presence in the first-listed
element, the second largest presence in the second listed element,
etc. Thus, where NiCrB is set forth, the concentrations may be
70Ni28Cr2B, by way of non-limiting example. Where two primary
metals are used in solution, the inventive electroless plating bath
environment may form metal first film 130 that includes but is not
limited by such combinations as to NiCoB, NiCoP, NiCoBP, NiCoCrB,
NiCoCrP, NiCoCrBP, NiCoMoB, NiCoMoP, NiCoMoBP, NiCoWB, NiCoWP,
NiCoWBP, NiCoMnB, NiCoMnP, NiCoMnBP, NiCoTcB, NiCoTcP, NiCoTcBP,
NiCoReB, NiCoReP, and NiCoReBP. It can be seen that at least
zero--to at least one primary metals and from zero to at least one
secondary metals are combinable according to various embodiments.
In similar embodiments, palladium can be used in place of--or in
addition to nickel. Similarly, platinum can be used in place of--or
in addition to nickel. Additionally, a blend of at least two of
nickel, palladium, and platinum can be used as set forth
herein.
[0041] In another embodiment, metal first film 130 uses cobalt is a
primary metal for an electroless plating embodiment, the
composition includes a cobalt solution to form a cobalt plating
layer. According to an embodiment, where cobalt is the primary
metal, because of the inventive electroless plating bath
environment, metallic films form that include but are not limited
by such combinations as CoB, CoP, CoBP, CoCrB, CoCrP, CoCrBP,
CoMoB, CoMoP, CoMoBP, CoWB, CoWP, CoWBP, CoMnB, CoMnP, CoMnBP,
CoTcB, CoTcP, CoTcBP, CoReB, CoReP, and CoReBP. Where two primary
metals are used in solution, the inventive electroless plating bath
environment may form metallic films that include but not are
limited by such combinations as to CoNiB, CoNiP, CoPdBP, CoPdCrB,
CoPdCrP, CoPdCrBP, CoPdMoB, CoPdMoP, CoPdMoBP, CoPdWB, CoPdWP,
CoPdWBP, CoPdMnB, CoPdMnP, CoPdMnBP, CoPdTcB, CoPdTcP, CoPdTcBP,
CoPdReB, CoPdReP, and CoPdReBP.
[0042] It can be seen that zero to at least one primary metal and
from zero to at least one secondary metal are combinable according
to various embodiments to form metal first film 130. In similar
embodiments, rhodium can be used in place of, or in addition to
cobalt. Similarly, iridium can be used in place of, or in addition
to cobalt. Additionally, a blend of at least two of cobalt,
rhodium, and iridium can be used as set forth herein.
[0043] By way of non-limiting example, copper is used to form metal
first film 130 as a primary metal for an electroless plating
embodiment. The composition includes a copper solution to form a
copper plating layer. According to an embodiment, where copper is
the primary metal, because of the inventive electroless plating
bath environment, metallic films form that include but are not
limited by such combinations as CuB, CuP, CuBP, CuCrB, CuCrP,
CuCrBP, CuMoB, CuMoP, CuMoBP, CuWB, CuWP, CuWBP, CuMnB, CuMnP,
CuMnBP, CuTcB, CuTcP, CuTcBP, CuReB, CuReP, and CuReBP. Where two
primary metals are used in solution, the inventive electroless
plating bath environment may form metallic films that include but
not are limited by such combinations as to CuNiB, CuNiP, CuNiBP,
CuNiCrB, CuNiCrP, CuNiCrBP, CuNiMoB, CuNiMoP, CuNiMoBP, CuNiWB,
CuNiWP, CuNiWBP, CuNiMnB, CuNiMnP, CuNiMnBP, CuNiTcB, CuNiTcP,
CuNiTcBP, CuNiReB, CuNiReP, and CuNiReBP. It can be seen that from
zero to at least one primary metal and from zero to at least one
secondary metal is combinable according to various embodiments. In
similar embodiments, silver can be used in place of, or in addition
to copper. Similarly, gold or silver can be used in place of--or in
addition to copper. Additionally, a blend of at least two of
copper, silver, and gold can be used as set forth herein.
[0044] FIG. 4 illustrates further processing after the formation of
metal first film 130. A metal second film 132 is formed that in one
embodiment is at least one of a more noble, or a softer (more
ductile) metal than metal first film 130. In one embodiment, metal
second film 132 is selected from gold, dor, platinum, and the like.
In another embodiment, metal second film 132 is aluminum, and metal
first film 130 is selected from titanium, tungsten, titungsten,
zirconium, hafnium, and other refractory metals and refractory
metal alloys as set forth herein.
[0045] One embodiment includes a metal second film 132 that resists
alloying with a bond wire (see FIG. 6) during ordinary wire-bonding
process flows. Typically, an aluminum bond wire is attached to
metal second film 132. In such embodiments, metal second film 132
is of a composition that is substantially immiscible with aluminum
under ordinary wire-bonding conditions.
[0046] The formation of metal second film 132 is carried out
according to vapor or liquid plating techniques as set forth
herein. In one embodiment, metal second film 132 is carried out by
electroless plating by using a gold-cyanide electroless plating
solution, and the Merrill-Crowe technique. In this embodiment, an
atom-thick layer of zinc (Zn, not pictured) is pre-plated onto
metal first film 130 by an electroless process that does not
substantially cover passivation layer 120, and the gold-cyanide
solution is contacted with the zinc which causes the reduction of
the gold out of the gold-cyanide complex.
[0047] In another electroless plating embodiment, semiconductor
structure 110 is contacted with a gold halide solution, and the
Eh-pH environment of the solution is manipulated according to the
technique pioneered by Pourbaix. In one embodiment, metal first
film 130 acts as an autocatalytic surface to assist the selective
precipitation of the gold of metal second film 132 as depicted in
FIG. 4.
[0048] In another embodiment, a CVD process is carried out during
which a organometallic gold vapor or a gold halide vapor is metered
toward semiconductor structure 110, blanket deposited, and
patterned with an etch. In another embodiment, a PVD process is
carried out in which a gold target is impinged under PVD conditions
to form a blanket layer of gold that is subsequently patterned into
metal second film 132.
[0049] In another embodiment, a metal second film 132 is aluminum
that is formed on a metal first film 130 of titanium. The formation
of metal second film 132 is by CVD or PVD.
[0050] In one embodiment, metal first film 130 has a thickness in a
range from about 500 .ANG. to about 2,000 .ANG.. In another
embodiment, metal first film 130 has a thickness of about 1,000
.ANG.. In one embodiment, metal second film 132 has a thickness in
a range from about 100 nm to about 1,000 nm. In one embodiment,
metal second film 132 has a thickness in a range from about 300 nm
to about 500 nm. In one embodiment, metal first film 130 is from
about 500 .ANG. to about 2,000 .ANG. and metal second film 132 is
from about 0.3 microns to about 0.5 microns.
[0051] Another embodiment of the present invention relates to an
e-test method according to the process embodiments. FIG. 5
illustrates semiconductor structure 110 during an e-test, before
wire bonding is carried out (FIG. 6). A tungsten test probe tip 134
or the like is depicted as penetrating into and through metal
second film 132, and making contact against metal first film 130
without penetrating it. Tip 134 under prior methods, experienced an
ohmic resistance in a range from about 5 ohms (.OMEGA.) or greater.
According to an embodiment, the ohmic resistance during an e-test
is in a range from about 0.5 .OMEGA. to about 4 .OMEGA.. In another
embodiment, the ohmic resistance during an e-test is in a range
from about 0.75 .OMEGA. to about 2 .OMEGA.. In another embodiment,
the ohmic resistance during an e-test is in a range from about 0.95
.OMEGA. to about 1.5 .OMEGA.. In another embodiment, the ohmic
resistance during an e-test is about 1 .OMEGA..
[0052] In a first example, a protective structure is formed by
plating nickel as a metal first film 130, and gold as a metal
second film 132. Patterning is done by a clear field mask to
center-pattern metal first film 130 and metal second film 132.
Etching is carried out, followed by testing. During the probe test,
the ohmic resistance is in a range from about 0.5 .OMEGA. to about
4 .OMEGA., and the first standard deviation of the ohmic resistance
is less than about 2 .OMEGA..
[0053] In a second example, a protective structure was formed by
depositing titanium as a metal first film 130, and depositing
aluminum as a metal second film 132. Patterning was done by a clear
field mask to center-pattern metal first film 130 and metal second
film 132. Etching was carried out, followed by testing. During the
probe test, the ohmic resistance had a mean value of about 1.5
.OMEGA., and the first standard deviation of the ohmic resistance
was about 0.1 .OMEGA..
[0054] In a comparative example, a tungsten test probe tip was
impinged on a copper metallization. The ohmic resistance had a mean
value of about 5 .OMEGA., and the first standard deviation of the
ohmic resistance was about 2 .OMEGA.. During this comparative
example, a deformation of the copper metallization was observed, as
well as a scumming of the tungsten test probe tip with some of the
copper.
[0055] Under previous process flows, and according to previous
architectures, corrosion of the upper metallization would be
significant enough to cause the rejection of several devices during
the probe for sort e-test. According to an embodiment of the
present invention, metal first film 130 protects copper
metallization 114 from physical stresses, and metal second film 132
protects copper metallization from corrosive stresses.
[0056] FIG. 6 illustrates an embodiment of the semiconductor
structure 110 after e-test, or after further processing. A bond
wire 136 is depicted as having been bonded to metal second film
132. As set forth herein, the metal of bond wire 136 is selected
from aluminum and the like according to known technique. Metal
second film 132 is a material that resists alloying with bond wire
136, and preferably is a gold, dor, or platinum material.
[0057] One feature of an embodiment is the ability of the metal
second film 132 to bond with bond wire 136, but not to alloy
therewith. In some applications, a bond wire article may be
rejected by pulling or cutting the bond wires and repeating the
bond wire process flow. According to an embodiment, because
metallization 114 is significantly protected from both physical and
corrosive stresses, the bond wire 136 is cut or pulled away from
metal second film 132, and wire bonding is repeated with no
significant change in the ohmic resistance through metal second
film 132 and metal first film 130. Accordingly, ohmic resistance in
a second bond wire process when compared to a first bond-wire
process changes, by a range from about 50% reduction to about 150%
improvement, and in another embodiment, from about 10% reduction to
about 110% improvement.
[0058] FIG. 7 is a process flow depiction according to an
embodiment. The process 700 commences by forming 710 a protective
structure above a metallization. In one particular exemplary
embodiment, the protective structure includes metal first film 130
and metal second film 132 as illustrated in FIGS. 4-6. Further, the
metallization is an M6 Cu pad 114. Next, the process of an e-test
is depicted by testing 720 the device by probing the metallization
with a probe tip. After an e-test, the process continues by wire
bonding 730 the device to the protective structure. In one
particular exemplary embodiment, the protective structure is the
metal second film 132 that is bonded to the bond wire. Finally,
where the rejection of a wire-bonding run is required, the wire
bond is pulled and a replacement wire bonding is done 740.
[0059] It will be readily understood to those skilled in the art
that various other changes in the details, material, and
arrangements of the parts and method stages which have been
described and illustrated in order to explain the nature of this
invention may be made without departing from the principles and
scope of the invention as expressed in the subjoined claims.
* * * * *