U.S. patent application number 09/412542 was filed with the patent office on 2002-05-09 for semiconductor copper bond pad surface protection.
Invention is credited to ELLIS, TIMOTHY W., ESHELMAN, MARK A., MURDESHWAR, NIKHIL, RHEAULT, CHRISTIAN.
Application Number | 20020054955 09/412542 |
Document ID | / |
Family ID | 27493311 |
Filed Date | 2002-05-09 |
United States Patent
Application |
20020054955 |
Kind Code |
A1 |
ELLIS, TIMOTHY W. ; et
al. |
May 9, 2002 |
SEMICONDUCTOR COPPER BOND PAD SURFACE PROTECTION
Abstract
Methods for protecting the surface of an uninsulated portion of
a copper circuit from environmental contamination detrimental to
joining the surface to another metal surface, said method
comprising the step of coating the surface with a layer of a
ceramic material having a thickness that is suitable for soldering
without fluxing and that is sufficiently frangible when the
surfaces are being joined to obtain metal-to-metal contact between
the surfaces. Coated electronic packages including semiconductor
wafers are also disclosed.
Inventors: |
ELLIS, TIMOTHY W.;
(DOYLESTOWN, PA) ; MURDESHWAR, NIKHIL; (ABINGTON,
PA) ; ESHELMAN, MARK A.; (LANDSDALE, PA) ;
RHEAULT, CHRISTIAN; (WILLOW GROVE, PA) |
Correspondence
Address: |
PETER J BUTCH III
SYNNESTVEDT & LECHNER LLP
2600 ARAMARK TOWER
1101 MARKET STREET
PHILADELPHIA
PA
19107
|
Family ID: |
27493311 |
Appl. No.: |
09/412542 |
Filed: |
October 5, 1999 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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09412542 |
Oct 5, 1999 |
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09330906 |
Jun 11, 1999 |
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60103032 |
Oct 5, 1998 |
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60127249 |
Mar 31, 1999 |
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60146674 |
Aug 2, 1999 |
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Current U.S.
Class: |
174/256 ;
205/124; 205/125; 257/E21.508; 257/E23.02; 257/E23.077; 427/96.4;
427/96.8; 427/99.2 |
Current CPC
Class: |
H01L 2224/45015
20130101; H01L 2224/45015 20130101; H01L 2224/45015 20130101; Y10T
428/24917 20150115; H01L 24/45 20130101; H01L 2224/04042 20130101;
H01L 2924/04941 20130101; H01L 2924/01029 20130101; H01L 2924/01012
20130101; H01L 2224/45015 20130101; H01L 2224/45015 20130101; H01L
2924/01023 20130101; Y10T 29/4913 20150115; H01L 2224/45144
20130101; H01L 21/4846 20130101; H01L 2224/48699 20130101; H01L
2924/3025 20130101; H01L 2924/01013 20130101; H01L 2224/05647
20130101; H01L 2924/15787 20130101; H05K 3/282 20130101; H01L
2224/45124 20130101; H01L 2924/014 20130101; H01L 2224/45147
20130101; H01L 24/11 20130101; H01L 2224/13099 20130101; H01L
2224/45015 20130101; H01L 2224/45147 20130101; H01L 2224/48647
20130101; H01L 2924/01041 20130101; H01L 2924/09701 20130101; H01L
2924/20757 20130101; H01L 2924/00014 20130101; H01L 2924/00
20130101; H01L 2924/20757 20130101; H01L 2924/00014 20130101; H01L
2924/00014 20130101; H01L 2924/00014 20130101; H01L 2924/00014
20130101; H01L 2924/20754 20130101; H01L 2924/00014 20130101; H01L
2924/00 20130101; H01L 2924/00 20130101; H01L 2924/20756 20130101;
H01L 2924/00 20130101; H01L 2924/20755 20130101; H01L 2924/20754
20130101; H01L 2924/20753 20130101; H01L 2924/00 20130101; H01L
2924/20756 20130101; H01L 2924/00014 20130101; H01L 2924/00014
20130101; H01L 2924/20755 20130101; H01L 2924/2075 20130101; H01L
2924/20753 20130101; H01L 2924/00 20130101; H01L 2924/05042
20130101; H01L 2924/00 20130101; H01L 24/48 20130101; H01L
2924/01105 20130101; H01L 2924/15787 20130101; H01L 2924/04953
20130101; H01L 2224/45015 20130101; H01L 2924/01058 20130101; H01L
2224/48647 20130101; H01L 2924/01019 20130101; H01L 2924/01027
20130101; H01L 2924/01074 20130101; H01L 23/49894 20130101; H01L
2924/0104 20130101; H01L 24/05 20130101; H01L 2924/01327 20130101;
H01L 2224/48847 20130101; H01L 2224/48699 20130101; H01L 2224/45015
20130101; H01L 2224/48747 20130101; H01L 2224/48747 20130101; H01L
2924/01014 20130101; H01L 2924/01039 20130101; H01L 2924/01078
20130101; H01L 2924/01057 20130101; H01L 2924/01006 20130101; H01L
2224/48847 20130101; H01L 2224/45015 20130101; H01L 2224/0401
20130101; H01L 2224/45015 20130101; H01L 2924/01005 20130101; H01L
2924/01022 20130101; H01L 2224/45144 20130101; H01L 2924/01079
20130101; H01L 2224/45015 20130101; H01L 2224/05647 20130101; H01L
2224/04042 20130101; H01L 2224/45124 20130101; H01L 2924/01073
20130101; H01L 2224/45015 20130101; H01L 2224/05073 20130101 |
Class at
Publication: |
427/96 |
International
Class: |
B05D 005/12 |
Claims
What is claimed is:
1. A method for protecting the surface of an uninsulated portion of
a copper circuit from environmental contamination detrimental to
joining the surface to another metal surface, said method
comprising the step of coating the surface with a layer of a
ceramic material having a thickness that is suitable for soldering
without fluxing and that is sufficiently frangible when the
surfaces are being joined to obtain metal-to-metal contact between
the surfaces.
2. The method of claim 1, wherein said surface is the bonding
surface of a copper semiconductor bond pad and said ceramic
material has a thickness that is sufficiently frangible during ball
or wedge wire bonding to obtain metal-to-metal contact between the
bonding surface and the wire bonded thereto.
3. The method of claim 1, wherein the thickness of said coating
layer provides said layer with a Rockwell Hardness (N-45) greater
than about 38.
4. The method of claim 1, wherein said coating layer has a
thickness between about 10 and about 1,000 angstroms.
5. The method of claim 1, wherein said ceramic material is selected
from the group consisting of silicon nitride, silicon carbide,
titanium nitride, tantalum nitride, aluminum oxide, magnesium
oxide, silicon dioxide, titanium dioxide, zirconium oxide, tantalum
carbide, tungsten carbide, titanium carbide, boron carbide, cubic
boron nitride and diamond.
6. The method of claim 1, comprising first coating said uninsulated
copper surface with a layer of a material selected from the group
consisting of rare earth-copper complexes and copper-immiscible
metals that form metal hydride compounds and then exposing said
coated surface to a hydrogen-containing reducing environment.
7. The method of claim 6, wherein said coating is formed
immediately before exposure of said surface to said reducing
environment.
8. The method of claim 6, wherein said step of exposing said coated
surface to said reducing environment comprises the step of heating
said coated surface in a reducing atmo-sphere comprising hydrogen
or contacting said coated surface with a hydrogen-containing
plasma.
9. The method of claim 6, wherein said layer is coated on said
surface by vapor deposition, electrodeposition or chemical
deposition.
10. The method of claim 1, wherein said layer is coated on said
surface by vapor deposition.
11. The method of claim 9, wherein said layer comprises a
copper-rare earth metal complex formed by vapor deposition,
electrodeposition or chemical deposition on said surface of a rare
earth metal that forms a copper complex.
12. The method of claim 11, further comprising the step of heating
said deposited rare earth metal surface layer to form said copper
complex.
13. The method of claim 11, wherein said surface layer consists
essentially of said copper-rare earth metal complex.
14. The method of claim 6, wherein said surface layer comprises a
copper-immiscible metal.
15. The method of claim 14, wherein said copper-immiscible metal
layer is formed by co-deposition of copper with said
copper-immiscible metal followed by heating so that said
copper-immiscible metal migrates to the surface of said layer.
16. The method of claim 14, wherein said surface layer has a
thickness substantially less than 20% of the combined total
thickness of said uninsulated copper circuit and said surface
layer.
17. An electronic package comprising an uninsulated portion of a
copper circuit coated with a surface layer of a ceramic material
having a thickness that is suitable for soldering without fluxing
and that is sufficiently frangible when the surfaces are being
joined to obtain metal-to-metal contact between the surfaces.
18. The package of claim 17, wherein said ceramic material is
selected from the group consisting of hydrides of rare earth-copper
complexes, hydrides of hydride-forming copper-immiscible metals,
silicon nitride, silicon carbide, titanium nitride, tantalum
nitride, aluminum oxide, magnesium oxide, silicon dioxide,
titanium, dioxide, zirconium oxide, tantalum carbide, tungsten
carbide, titanium carbide, boron carbide, cubic boron nitride and
diamond.
19. The package of claim 17, wherein said thickness of said layer
of ceramic material provides said layer with a Rockwell Hardness
(N-45) value greater than about 38.
20. The package of claim 17, wherein said layer has a thickness
between about 10 and about 1,000 angstroms.
21. The package of claim 17, comprising a semiconductor wafer
including at least one device having an uninsulated copper bond pad
coated with a surface layer that is sufficiently frangible during
ball or wedge wire bonding to obtain metal-to-metal contact between
each bonding surface and the wire bonded thereto.
22. The wafer of claim 21, further comprising at least one wire
that is ball or wedge bonded to said bond pad of said wafer
device.
23. The wafer of claim 21, wherein said device is a flip chip in
which at least one wire lead is soldered to said metal
hydride-coated bond pad.
24. The package of claim 17, wherein said package comprises aan
organic substrate package, a metal substrate package or a ceramic
substrate package
25. An electronic package comprising an uninsulated portion of a
copper circuit coated with a surface layer of a material selected
from the group consisting of copper-rare earth metal complexes and
copper-immiscible metals that form metal hydride compounds, said
surface layer having a thickness that, upon exposure to a reducing
environment containing hydrogen, forms a hydride layer having a
thickness that is suitable for soldering without fluxing and that
provides the layer with a hardness that is sufficiently frangible
when the surfaces are being joined to obtain metal-to-metal contact
between the surfaces.
26. The package of claim 25, wherein said surface layer comprises a
copper-immiscible metal.
27. The package of claim 26, wherein said surface layer is formed
by co-deposition of said copper-immiscible metal and copper to form
said bond pad during wafer fabrication, followed by heating of said
wafer so that said copper-immiscible metal migrates to said bond
pad surface, thereby forming said surface layer.
28. The package of claim 27, wherein said surface layer is formed
by vapor, electro-chemical deposition of said copper-immiscible
metal onto said bond surface.
29. The package of claim 25, wherein said surface layer consists
essentially of a copper-rare earth metal complex.
30. The package of claim 29, wherein said copper complex is formed
by vapor deposition, electrodeposition or chemical deposition of
said rare earth metal in a layer onto said bond pad surface.
31. The package of claim 30, wherein said copper complex forms by
heating said deposited rare earth metal layer.
32. The package of claim 29, wherein said rare earth metal is
selected from the group consisting of La, Y and Ce.
33. The package of claim 25, wherein said copper-immiscible metal
is selected from the group consisting of Ta, V and Nb.
34. The package of claim 25, wherein said package comprises aan
organic substrate package, a metal substrate package or a ceramic
substrate package
35. The package of claim 25, comprising a semiconductor wafer
including at least one device having an uninsulated copper bond
pad.
36. An electronic package comprising an uninsulated portion of a
copper circuit coated with a surface layer of a rare earth metal
that forms a copper complex, said surface layer having a thickness
that, upon formation of said copper complex and exposure to a
reducing environment comprising hydrogen, forms a hydride layer
having a thickness that is suitable for soldering without fluxing
and that is sufficiently frangible when the surfaces are being
joined to obtain metal-to-metal contact between the surfaces.
37. The package of claim 36, wherein said surface layer is formed
by vapor deposition, electrodeposition or chemical deposition of
said rare earth metal in a layer on said bond pad surface.
38. The package of claim 36, wherein said rare earth metal is
selected from the group consisting of La, Y and Ce.
39. The package of claim 36, wherein said package comprises aan
organic substrate package, a metal substrate package or a ceramic
substrate package
40. The package of claim 36, comprising a semiconductor wafer
including at least one device having an uninsulated copper bond
pad.
41. An electronic package comprising an uninsulated portion of a
copper circuit coated with a surface layer of a metal hydride
compound selected from the group consisting of metal hydrides of
copper-rare earth metal complexes and metal hydrides of
copper-immiscible metals that form metal hydrides, said surface
layer having a thickness that is suitable for soldering without
fluxing and that is sufficiently frangible when the surfaces are
being joined to obtain metal-to-metal contact between the
surfaces.
42. The package of claim 41, wherein said surface layer comprises a
hydride of a copper-immiscible metal.
43. The package of claim 42, wherein said copper-immiscible metal
is selected from the group consisting of Ta, V and Nb.
44. The package of claim 41, wherein said surface layer consists
essentially of a hydride of a copper-rare earth metal complex.
45. The package of claim 41, wherein said rare earth metal is
selected from the group consisting of La, Y and Ce.
46. The package of claim 41, wherein said package comprises aan
organic substrate package, a metal substrate package or a ceramic
substrate package
47. The package of claim 41, comprising a semiconductor wafer
including at least one device having an uninsulated copper bond pad
coated with a surface layer that is sufficiently frangible during
ball or wedge wire bonding to obtain metal-to-metal contact between
each bonding surface and the wire bonded thereto.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application claims priority from U.S. Provisional
Patent Application No. 60/103,032 filed Oct. 5, 1998, No.
60/127,249 filed Mar. 31, 1999, and No. 60/146,674 filed Aug. 2,
1999, and is a Continuation-In-Part of U.S. patent application Ser.
No. 09/330,906 filed Jun. 11, 1999. The disclosures of all four
applications are incorporated herein by reference.
BACKGROUND OF THE INVENTION
[0002] The present invention relates to methods for protecting
semiconductor copper bond pad surfaces with ceramic coatings that
are sufficiently frangible during ball, wedge or flip chip bonding
to obtain metal-to-metal contact between the bonding surfaces and
the wires bonded thereto. The method protects the copper bond pads
during extended exposure to water and water solutions such as are
experienced during sawing.
[0003] The use of copper bond pads on semiconductor devices would
be an attractive alternative to that of aluminum, were it not for
atmospheric contamination of the copper surface, which oxidizes
readily to form a coating that is not removable by standard methods
of wire bonding machines, and requires the use of fluxes in
solder-type interconnects, e.g., flip chip bonding. Present
attempts to overcome this problem involve the use of a cover gas
that is unavoidably expensive and complex and restricts bond head
and work holder movement, or the use of a noble metal or
overplating with inert metals which are more costly and can lead to
the formation of unwanted intermetallic compounds at the bond pad
interface.
[0004] U.S. Pat. No. 5,771,157 encapsulates a wedge bond of an
aluminum wire to a copper pad with the resin, after the bond is
formed. No protection against oxidation is provided to the copper
pad prior to wedge bonding.
[0005] U.S. Pat. No. 5,785,236 protects a copper bond pad from
oxidation with a surface layer of aluminum. This detracts from the
advantages sought to be obtained by replacing aluminum bond pads
with copper bond pads.
[0006] There remains a need for methods by which copper bond pad
surfaces may be protected from oxidation prior to wire bonding or
flip chip soldering.
SUMMARY OF THE INVENTION
[0007] This need is met by the present invention. Ceramic coatings
have now been developed for the bonding surfaces of copper bond
pads that are sufficiently frangible to obtain metal-to-metal
contact between the bonding surface and the wire bonded thereto
during ball or wedge wire bonding, and to obtain a surface suitable
for soldering without fluxing.
[0008] It has also been discovered that the same ceramic coatings
can be generally used to protect the copper surfaces of electronic
packages. That is, the present invention provides ceramic coatings
for the protection of the copper surfaces of organic substrate
packages, metal substrate packages ceramic substrate packages, and
the like.
[0009] According to one aspect of the present invention, a method
is provided for protecting the surface of an uninsulated portion of
a copper circuit from environmental contamination detrimental to
joining the surface to another metal surface, wherein the method
includes the step of coating the surface with a layer of a ceramic
material having a thickness that is suitable for soldering without
fluxing and that is sufficiently frangible when the surfaces are
being joined to obtain metal-to-metal contact between the
surfaces.
[0010] The invention is particularly suited to protecting the
bonding surfaces of copper bond pads. Therefore, in a preferred
embodiment of the present invention, the uninsulated portion of the
copper circuit is the bonding surface of a copper semiconductor
bond pad.
[0011] The present invention thus provides electronic packages
having uninsulated copper circuit surfaces with coating layers that
are capable of being removed at bonding or soldering. Therefore,
according to another aspect of the present invention, an electronic
package is provided containing at least one uninsulated copper
surface coated with a layer of a ceramic material having a
thickness that is suitable for soldering without fluxing and which
provides the layer with the aforementioned hardness. In a preferred
embodiment, the electronic package is a semiconductor with
uninsulated copper bond pads.
[0012] This aspect of the present invention includes electronic
packages having uninsulated portions of copper circuits coated with
a layer of rare earth metals that form complexes with copper. The
layer has a thickness that, upon formation of the copper complex
and exposure to a reducing environment containing hydrogen, forms a
ceramic hydride layer having a thickness that is suitable for
soldering without fluxing and which provides the layer with the
aforementioned hardness.
[0013] This aspect of the present invention thus also includes
electronic packages having uninsulated portions of copper circuits
with protective ceramic metal hydride coatings. Therefore,
according to another aspect of the present invention, an electronic
package is provided containing an uninsulated portion of a copper
circuit coated with a surface layer of a metal hydride compound
selected from metal hydrides of copper-rare earth metal complexes
and metal hydrides of copper-immiscible metals that form metal
hydrides, in which the surface layer has a thickness that is
suitable for soldering without fluxing and which provides the layer
with the aforementioned hardness. Again the preferred electronic
package is a semiconductor having at least one copper bond pad.
[0014] The inventive method provides the ability to bond wires to
copper circuits using existing equipment without modification of
the wire bonder, and without additional costs and limitations of
cover gas technology and hardware. The foregoing and other objects,
features, and advantages of the present invention are more readily
apparent from the detailed description of the preferred embodiments
set forth below, taken in conjunction with the accompanying
drawing.
BRIEF DESCRIPTION OF THE DRAWING
[0015] The sole drawing FIGURE is a schematic diagram of one method
according to the present invention, in which semiconductor devices
according to the present invention having copper bond pads with
bonding surfaces coated with hydride-forming materials and metal
hydrides are also depicted.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0016] The present invention forms protective ceramic coating
layers on copper circuit bonding surfaces of electronic packages,
with thicknesses that are suitable for soldering without fluxing.
The ceramic layer thickness is selected to provide at least the
minimum hardness required for the layer to be sufficiently
frangible during ball or wedge wire bonding to obtain
metal-to-metal contact between each bonding surface and the wire
bonded thereto.
[0017] Ceramic, rather than metallic, coatings are employed because
metallic layers would be ductile and would plastically deform under
impact. Because ceramic materials cannot be deformed in the plastic
region, impact shatters the layer and allows it to be pushed aside
during wire bonding.
[0018] Essentially all commonly used ceramic materials have a
hardness suitable for use with the present invention. One measure
of ceramic hardness is the Rockwell Superficial Hardness Scale
(45-N) which is defined in Somiya, Advanced Technical Ceramics
(Prentice Hall, Englewood Cliffs, N.J. 1996). Ceramic materials
suitable for use with the present invention have a Rockwell
Hardness (N-45) greater than about 38.
[0019] For purposes of the present invention, the meaning of the
term ceramic materials is adopted as it is defined in Callister,
Materials Science and Engineering, An Introduction (3rd Ed., John
Wiley & Sons, New York 1994), page 4. Callister defines ceramic
materials as compounds between metallic and nonmetallic elements
that are most frequently oxides, nitrides and carbides. Ceramic
materials within this classification include materials composed of
clay minerals, cement and glass. Ceramic materials are insulative
to the passage of electricity and heat, and are more resistant to
high temperatures and harsh environments than metals and polymers.
As for mechanical behavior, ceramic materials are hard but very
brittle.
[0020] One method and apparatus of the present invention is
depicted in the sole drawing figure, in which bonding surface 12 of
copper bond pad 10 of a semiconductor device (not shown) is cleaned
(Stage I). If the copper surface is fresh and has not been exposed
to a contaminating atmosphere, Stage I cleaning is not required. In
the depicted embodiment, the bonding surface 12 is coated with a
layer 14 of a hydride-forming copper-immiscible metal or
copper-complexing rare earth metal (Stage II). For proper coating
of surface layer 14, it is necessary to reduce the oxides,
hydroxides and sulfides that form on the surface 12 of pad 10. Only
after this reduction is complete can proper surface coating be
performed. The surface 12 can be reduced by exposure to a reducing
atmosphere, such as an atmosphere containing hydrogen, or by
essentially any other conventional surface reducing techniques,
including cleaning techniques such as plasma cleaning.
[0021] Examples of metals that are completely immiscible in copper
include, but are not limited to, Ta, V and Nb. Examples of rare
earth metals that complex with copper include, but are not limited
to, La, Y, and Ce.
[0022] The surface 12 of copper pad 10 is coated with metal layer
14 by conventional vapor deposition or analogous techniques. The
rare earth metals may require a heating step after deposition for
the copper complex to form.
[0023] Surface layers of copper-immiscible hydride-forming metals
can be formed by an alternative route. The copper-immiscible metal
may be co-deposited with the copper as the copper bond pads are
formed during wafer fabrication. By heating the wafers after
fabrication, the co-deposited immiscible metal will migrate to the
surface of the copper bond pad, forming an oxidation-protective
layer. Electroless or electrodeposition techniques may also be
employed.
[0024] The deposited layer 14 should be of a thickness capable of
forming a frangible hydride layer. That is, the resulting ceramic
layer should have a thickness sufficient to provide the layer with
a Rockwell Hardness (N-45) greater than about 38. Suitable ceramic
layers have a thickness between about 10 and about 1,000 angstroms,
with a thickness between about 25 and about 500 angstroms being
preferred.
[0025] When a rare earth metal is employed, it is preferably
deposited in a layer thin enough to form an essentially pure copper
complex. This can be accomplished using rare earth metal layers
with thickness from about 10 to about 1,000 Angstroms.
[0026] Copper-immiscible metal layers are preferably thin enough to
be cost competitive and permit ease of fabrication. For these
purposes, the layer 12 should be no thicker than {fraction (1/10)}
the total combined thickness of the pad 10 and layer 14. A
thickness from about 10 to about 1,000 Angstroms is preferred.
[0027] Layer 14 is then converted to a hydride layer (Stage III) by
reduction with hydrogen, either by heating the bond pad in an
atmosphere containing hydrogen, or by exposing the bond pad to a
hydrogen-containing plasma, e.g, plasma-cleaning operations. Once
formed, the hydride layer 16 is stable at room temperature. It is
not necessary for deposition or hydride conversion of the layer 14
to be performed at the time of wafer fabrication. Both processes
can be done at a later time. As noted above, for proper deposition
of the layer 14, the surface 12 of bond pad 10 must be cleaned
prior to deposition.
[0028] The hydride-formation step can take place at any stage prior
to wire bonding or flip chip bonding, so long as the reducing
environment is sufficiently aggressive enough to reduce the layer
14 to remove any atmospheric contamination. Suitable reducing
conditions can be readily determined by those of ordinary skill in
the art without undue experimentation.
[0029] The hydride layer 16 provides the surface 12 of bond pad 10
with oxidation resistance. Yet, because the hydride layer is
frangible, conventional ball or wedge wire bonding can be performed
to obtain metal-to-metal contact between surface 12 and the wire
bonded thereto (not shown), which also provides a surface prepared
for soldering operations.
[0030] The hydride compound rapidly disintegrates during wire
bonding or soldering by two mechanisms. One mechanism is
mechanical, and derives from the frangibility of the hydride layer.
The hydride will also thermally de-hydride during bonding, forming
a hydrogen cover over the bond pad itself, which also prevents
oxidation.
[0031] It is not necessary for the hydride process to be performed
at the time of wafer fabrication. The hydride process can take
place at any stage prior to wire bonding or soldering, so long as
the hydrogen-containing atmosphere is sufficiently aggressive
enough to reduce any contaminants from the surface layer, and then
subsequently hydride the surface layer.
[0032] The present invention also includes a single-step process in
which the frangible ceramic coating is not a metal hydride.
Instead, a clean copper bond pad is coated with a layer of a
ceramic material having a thickness that is suitable for soldering
without fluxing and that provides the layer with a Rcokwell
Hardness (N-45) greater than about 38, so that the layer is
sufficiently frangible during ball or wedge wire bonding to obtain
metal-to-metal contact between each bonding surface and the wire
bonded thereto.
[0033] Examples of suitable ceramic materials include nitrides and
carbides of silicon, titanium and tantalium; oxides of aluminum,
magnesium and zirconium; silicon and titanium dioxide; tungsten and
boron carbide; and cubic boron nitride and diamond.
[0034] These coating layers are also formed by conventional vapor
deposition or analogous techniques.
[0035] The present invention can also be employed to coat the
uninsulated surfaces of copper circuits other than the bond pads of
semiconductors, using the same materials and method steps. Thus,
the same ceramic coatings can be used to protect prior to bonding
the uninsulated copper circuit surfaces of organic substrate
packages such as Polymer Ball Grid Arrays (PBGA), Enhanced Polymer
Ball Grid Arrays (EPBGA), Tape Ball Grid Arrays (TBGA), and the
like; metal substrate packages such as Metal Quad Flat Packs
(MQFP), is Metal Leaded Chip Carriers (MLCC), Thin Small Outline
Packages (TSOP), and the like; and ceramic substrate packages such
as Ceramic Quad Flat Packs (CQFP), Ceramic Dual In-line Packages
(CDIP), Leaderless Ceramic Chip Carriers (LCCC), and the like.
[0036] The present invention provides the uninsulated copper
circuit portions of electronic packages with oxidation-resistant
surfaces that can be ball or wedge wire bonded using conventional
techniques without changes or additions to current ball and wedge
wire bonding or flip chip bonding processes and equipment.
[0037] The following non-limiting example set forth hereinbelow
illustrates certain aspects of the invention, but is not meant in
any way to restrict the effective scope of the invention. All parts
and percentages are by weight unless otherwise noted, and all
temperatures are in degree Celsius.
EXAMPLE
[0038] Copper wafers having a copper thickness of at least 2,000
angstroms were made via vapor deposition. Frangible ceramic
coatings of silicon nitride with thicknesses between 10 and 1,000
angstroms were formed via sputtering techniques.
[0039] Wire ball bonding was performed using various gold wires and
a K&S Model 8020 wire bonder. The following wire bond process
conditions were employed:
[0040] Constant velocity=0.25-1.0 mil/msec.
[0041] Ultra sonic level=35-250 mAmp or equivalent power or voltage
setting
[0042] Bond time=5-50 msec.
[0043] Bond force=10-40 g
[0044] Free air ball diameter=1.4-3.0 mil
[0045] A variety of gold wire types were attempted and all were
found to be readily bondable: AFW-8, AFW-14, AFW-88, AFW-FP and
AFW-FP2. The harder wires, AFW-FP and AFW-FP2, performed the
best.
[0046] A variety of bonding tools (capillaries) were used and all
were found to yield bondability in the bonded ball regions for
which the capillaries were designed. The best performing
capillaries were part numbers 414FA-2146-335 and
484FD-2053-335.
[0047] Copper wire was also bonded to the ceramic-coated bond pads.
An inert cover gas was employed for ball formation. The bond
parameters were not identical for those of gold for the same bonded
ball size, but the bond parameter range was not widely different
for the range for gold ball bonding onto copper substrates.
[0048] The foregoing description of the preferred embodiments
should be taken as illustrating, rather than as limiting, the
present invention as defined by the claims. Numerous variations and
combinations of the features set forth above can be utilized
without departing from the presently-claimed invention. Such
variations should not be regarded as a departure from the spirit
and scope of the invention, and are intended to be included within
the scope of the following claims.
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