U.S. patent application number 12/971744 was filed with the patent office on 2012-06-21 for seed layer deposition in microscale features.
This patent application is currently assigned to Nexx Systems, Inc.. Invention is credited to Johannes Chiu, Daniel Goodman, Arthur Keigler, Zhenqiu Liu.
Application Number | 20120152752 12/971744 |
Document ID | / |
Family ID | 46232956 |
Filed Date | 2012-06-21 |
United States Patent
Application |
20120152752 |
Kind Code |
A1 |
Keigler; Arthur ; et
al. |
June 21, 2012 |
SEED LAYER DEPOSITION IN MICROSCALE FEATURES
Abstract
A method of forming a metal feature on a workpiece with
deposition is provided. The method includes providing an under bump
metal layer for solder of an electronic device on the workpiece,
depositing a substantially pure tin layer directly to the under
bump metal layer, and depositing a tin silver alloy layer onto the
substantially pure tin layer.
Inventors: |
Keigler; Arthur; (Wellesley,
MA) ; Chiu; Johannes; (Bedford, MA) ; Liu;
Zhenqiu; (Northboro, MA) ; Goodman; Daniel;
(Lexington, MA) |
Assignee: |
Nexx Systems, Inc.
Billerica
MA
|
Family ID: |
46232956 |
Appl. No.: |
12/971744 |
Filed: |
December 17, 2010 |
Current U.S.
Class: |
205/118 ;
204/267; 205/176 |
Current CPC
Class: |
H01L 2924/01322
20130101; C25D 5/50 20130101; H01L 24/11 20130101; H01L 2224/11462
20130101; C25D 5/10 20130101; H01L 2224/11502 20130101; H01L
2924/00 20130101; H01L 2924/00 20130101; C25D 5/02 20130101; H01L
2924/01322 20130101; H01L 2224/11901 20130101; H01L 2924/14
20130101; H01L 2924/14 20130101; H01L 2224/11849 20130101 |
Class at
Publication: |
205/118 ;
205/176; 204/267 |
International
Class: |
C25D 5/00 20060101
C25D005/00; C25D 5/48 20060101 C25D005/48; C25D 5/02 20060101
C25D005/02 |
Claims
1. A method of forming a metal feature on a workpiece with
deposition, the method comprising: providing an under bump metal
layer for solder of an electronic device on the workpiece;
depositing a substantially pure tin layer directly to the under
bump metal layer; and depositing a tin silver alloy layer onto the
substantially pure tin layer.
2. The method of claim 1, wherein substantially all of the
substantially pure tin plating chemistry from the workpiece is
rinsed.
3. The method of claim 1, wherein the deposition is accomplished by
electrodeposition.
4. The method of claim 1, wherein the under bump metal comprises
either copper or nickel.
5. The method of claim 1, wherein the workpiece is thermally
treated.
6. An apparatus for forming a substantially lead free solder bump
on a workpiece having an electrically conducting seed layer, the
electrically conducting seed layer being covered by a patterned
resist mask layer having a plurality of feature openings is
provided, the apparatus comprising: a first plating bath with a
metal ion content configured to deposit a substantially pure tin
layer in the resist pattern features; a second plating bath with a
metal ion content configured to deposit a tin-silver alloy layer in
the resist pattern features.
7. The apparatus of claim 6, further comprising a rinse tank
configured to rinse substantially all of the substantially pure tin
plating chemistry from the workpiece; and.
8. The apparatus of claim 6, further comprising a copper
electrodeposition module.
9. The apparatus of claim 6, further comprising a copper
electrodeposition module and a nickel electrodeposition module.
10. The apparatus of claim 6, further comprising a cleaning
module.
11. A method for forming an electronic device having a lead free
solder feature, the method comprising: depositing a substantially
pure tin layer directly to a layer of under bump metal for solder
of the electronic device; and depositing a tin silver alloy layer
onto the pure tin layer.
12. The method of claim 11, wherein the deposition is accomplished
by electrodeposition.
13. The method of claim 11, wherein the under bump metal comprises
either copper or nickel.
14. The method of claim 11, further comprising rinsing
substantially all of the substantially pure tin plating chemistry
from the electronic device.
15. A method for forming a lead free solder bump on a workpiece,
the method comprising: providing the workpiece with an electrically
conducting seed layer, the electrically conducting seed layer being
covered by a patterned resist mask layer having a plurality of
feature openings; immersing the workpiece in a first plating bath,
the first plating bath having a metal ion content; providing
electrical contact to the seed layer and providing an electrical
potential through the metal ion content of the first plating bath
to cause between about 2 and about 150 microns of substantially
pure tin to deposit in the resist pattern features; immersing the
workpiece in a second plating bath with a metal ion content; and
forming electrical contact to the seed layer to form an electrical
potential through the metal ion content of the second plating bath
to cause between about 2 and about 150 microns of a tin-silver
alloy to deposit in the resist pattern features.
16. The method of claim 15, further comprising removing the
photoresist patterning layer.
17. The method of claim 15, wherein substantially all of the seed
layer not covered by the plated tin and tin-silver alloy is
removed.
18. The method of claim 15, further comprising thermally treating
the workpiece at between about 210 to about 230 degrees centigrade
to cause the substantially pure tin and tin-silver layers to
intermix and form a substantially uniform tin-silver alloy
feature.
19. The method of claim 15, wherein the substantially pure tin
layer is about 30 microns and the tin-silver alloy layer is about
30 microns, and wherein the tin-silver alloy composition is between
about 1% and about 7% silver by weight before thermal treatment and
about 0.5% to about 3.5% silver by weight after thermal
treatment.
20. The method of claim 15, wherein the substantially pure tin
layer is about 10 microns and the tin-silver alloy layer is about
10 microns, and wherein the tin-silver alloy composition is between
about 1% and about 7% silver by weight before thermal treatment and
about 0.5% to about 3.5% silver by weight after thermal
treatment.
21. The method of claim 15, wherein the substantially pure tin
layer is about 1 micron or about 10 microns and the tin-silver
alloy layer is between about 20 microns to about 120 microns.
22. The method of claim 15, wherein the substantially pure tin
layer is about one-fourth the thickness of the tin-silver
layer.
23. The method of claim 15, further comprising moving the workpiece
to a rinse tank, rinsing substantially all of the substantially
pure tin plating chemistry from the workpiece, and removing the
workpiece from the rinse tank.
24. An apparatus for forming a lead free solder bump on a workpiece
having an electrically conducting seed layer, the electrically
conducting seed layer being covered by a patterned resist mask
layer having a plurality of feature openings, the apparatus
comprising: a first process module disposed to support a first
plating bath having a metal ion content adapted to deposit a
substantially pure tin layer on the workpiece; a second process
module disposed to support a second plating bath with a metal ion
content adapted to deposit a tin and silver layer on the workpiece;
and a controller programmable to plate the workpiece with the
substantially pure tin layer in the first process module and to
plate the workpiece with the tin and silver layer in the second
process module.
25. The apparatus of claim 24, further comprising a rinse tank
disposed to support rinsing substantially all of the pure tin
plating chemistry from the workpiece, wherein the controller is
further programmable to rinse the workpiece in the rinse tank.
26. The apparatus of claim 24, further comprising a copper
electrodeposition module, wherein the controller is further
programmable to deposit copper on the workpiece with the copper
electrodeposition module.
27. The apparatus of claim 24, further comprising a nickel
electrodeposition module, wherein the controller is further
programmable to deposit nickel on the workpiece with the nickel
electrodeposition module.
28. The apparatus of claim 24, further comprising a cleaning
module, wherein the controller is further programmable to clean the
workpiece with the cleaning module.
Description
BACKGROUND
[0001] 1. Field
[0002] The disclosed embodiments relate generally to a method and
apparatus for applying metal structures to a workpiece, and more
particularly to a method and apparatus for depositing a lead-free
solder into micro-scale patterns in the surface of a workpiece
coated with a photo-resist patterning film, and more particularly
to a method and apparatus for electroplating tin-silver alloy
solder bumps.
[0003] 2. Brief Description of Related Developments
[0004] The semiconductor industry has been working towards
eliminating lead in electronics, as required under the European
Union's Restriction of Hazardous Substances (RoHS) Directive. The
industry is moving faster than the regulation to offer "green"
consumer's electronics with lead-free packaging. Electrodepositon
of lead-free solder such as using through mask patterned
deposition, is a technology capable of providing tight pitch
bumping (connection pitch less than approximately 300 microns) or
microbumping for advanced electronic packaging. An alloy of tin
(Sn) and silver (Ag) is the leading candidate metal for these
applications. Substantially pure tin has many desirable properties
of a solder metal, for example fatigue, resistance, thermal cycling
and ductile mechanical properties, however the industry has found
that tin whisker growth in substantially pure tin solder makes it
an unreliable joining solder for advanced packaging applications.
It has been found that a small addition of silver, between
approximately 1% and 4% Ag by weight, may significantly reduce the
likelihood of Sn whisker formation in the solder joint. Tin-silver
alloy (SnAg) solder plating in a conventional manner is more
difficult than substantially pure tin electroplating or lead-tin
(PbSn) electroplating because of the large difference in
electrochemical reduction potential between tin (-0.13 volts SHE)
and silver (+0.799 volts SHE). This reduction potential difference
causes Ag.sup.+ ions in the solution to spontaneously react with
metallic Sn and or the stannous ion (Sn.sup.+2) oxidizing the Sn or
Sn.sup.+2 to Sn.sup.+2 or Sn.sup.+4 and thereby immersion
depositing metallic Ag on the Sn surface. Similarly the Ag.sup.+
ion in the plating solution can immersion deposit on other metals
such as nickel or copper. Chemical suppliers have developed organic
molecules that are to complex the Ag.sup.+ ion to bring its
reduction potential close to that of Sn.sup.+2 and thereby
stabilize the Ag.sup.+ ion in the plating solution. The organic
Ag.sup.+ ion complex in the plating solution does not eliminate the
likelihood of unwanted Ag immersion deposition on the Under Bump
Metal (UBM), which is typically Nickel or Copper, when
electroplating SnAg lead free solder on such UBM structures. This
unwanted immersion deposition may cause void defects at the
UBM/SnAg interface, said voids are observable after reflowing the
solder, and such voids can cause mechanical and electrical failures
of the chip to package joint. There is therefore a need for an
alternate method of electroplating SnAg solder to form reliable
lead-free bump attachment to the underlying metal to solve the
problem facing the electronics industry as it moves toward
eliminating all lead from integrated circuit products. Further, the
industry also needs to develop economical methods of replacing the
lead-tin (PbSn) plated bump structures with a lead-free (SnAg)
plated bump structures. Due to the high cost of the Ag-complexor
and other components in commercial SnAg plating chemistries, the
typical cost of SnAg plated bumps is several multiples of the PbSn
bumps. Existing methods of electrodepositing SnAg bumps involve
expensive control systems in the manufacturing equipment, for
example as described in U.S. patent application Ser. No.
11/840,748, which is hereby incorporated by reference in its
entirety discloses a commercial plating equipment with a control
system to ensure that a constant alloy composition is provided in
the solder metal throughout the deposition. There is therefore a
need for a method of SnAg electroplating that minimizes the use of
expensive chemistry while providing a reliable interface between
the SnAg and the underlying metal.
BRIEF DESCRIPTION OF THE DRAWINGS
[0005] The foregoing aspects and other features of the embodiments
are explained in the following description, taken in connection
with the accompanying drawings. The technology described above may
be better understood by referring to the following description
taken in conjunction with the accompanying drawings. In the
drawings, like reference characters generally refer to the same
parts throughout the different views. The drawings are not
necessarily to scale, emphasis instead generally being placed upon
illustrating the principles of the technology.
[0006] FIG. 1 shows a cross sectional view of prior art after the
deposition step;
[0007] FIG. 2 shows a cross sectional view of prior art after the
deposition step;
[0008] FIG. 3 shows a cross sectional view of solder bump after
thermal treatment;
[0009] FIG. 4 shows a top-down section of prior art showing the
presence of voids at the UBM to SnAg interface;
[0010] FIG. 5 shows a top-down section of the present disclosed
embodiments showing absence of voids at the UBM to SnAg
interface;
[0011] FIG. 6 shows a cross sectional view of the present disclosed
embodiments after the second deposition step;
[0012] FIG. 7 shows a commercial wafer electro-deposition machine
suitable for a manufacturing process using the present disclosed
embodiments;
[0013] FIG. 8 shows a electro-deposition module; and
[0014] FIG. 9 shows a process flow diagram.
DETAILED DESCRIPTION OF THE EMBODIMENTS
[0015] Although the present embodiments will be described with
reference to the embodiments shown in the drawings, it should be
understood that the embodiments can be embodied in many alternate
forms of embodiments. In addition, any suitable size, shape or type
of elements or materials could be used. The present disclosed
embodiments provide a method of providing a reliable interface
between an electrodeposited lead-free solder bump and an underlying
bump metal (UBM).
[0016] Referring now to FIG. 1, there is shown a cross section of a
single bump at the workpiece surface where the workpiece has been
prepared for electrodeposition. An electrical contact element 101
is substantially surrounded by an insulating film 100, these type
of features are disposed in a semi-periodic array over the
integrated circuit workpiece, for example a 300 millimeter silicon
wafer may have 1,000 to 100,000 of such electrical contact elements
distributed across the surface. It is noted that any suitable
workpiece or substrate may be provided, for example, gallium
arsenide or otherwise. The workpiece is coated with a seed layer
102 and then coated with photoresist 104 which is photo patterned
to provide openings into which an under bump metal 106, such as
nickel (Ni) or copper (Cu) or a series of Ni and Cu layers, is
electrodeposited. Solder metal 120 is electrodeposited onto the
under bump metal 106 using the same resist pattern mask layer 104.
For example, U.S. Pat. No. 7,012,333 which is hereby incorporated
by reference herein in its entirety teaches deposition of a SnAg
solder alloy with the alloy being deposited at lower than the SnAg
eutectic point which is about 3.5% by weight.
[0017] Referring now to FIG. 2, there is shown another prior art
method of providing lead-free bump, for example a SnAg or SnAgCu
alloy where more noble substantially pure metal layer(s) 131 are
deposited on the under bump metal prior to the deposition of a
substantially pure tin layer 130. U.S. Pat. No. 6,596,621, which is
hereby incorporated by reference in its entirety, teaches forming a
lead-free SnAgCu bump by using a under bump metal layer 106
comprised of about 2 micron thick Ni and then coating layer 106
with Ag/Cu 131 in proportions to the substantially pure Sn 130
necessary to form a SnAgCu alloy bump with proportions of about
3.5% Ag and about 0.6% Cu and with the balance Sn.
[0018] Referring now to FIG. 3, the potential drawbacks of these
prior art approaches will be discussed where FIG. 3 shows a cross
section of the solder bump after the thermal reflow process. A
thermal reflow process is advantageous to stabilize the solder bump
structure prior to subsequent processing. After the
electrodeposition step, the photoresist 104 (not shown) is removed
and the seed layer 102 is etched away everywhere except where it is
protected by the under bump metal 106. Subsequently the wafer is
thermally treated in a so-called reflow process step. Briefly
described, reflow involves heating the workpiece in a controlled
atmosphere so that the tin-oxides are substantially removed before
the solder melts, which may occur between about 221.degree. C. and
about 232.degree. C. for SnAg alloy; about 221.degree. C. being the
SnAg eutectic at composition of about 3.5% Ag and about 232.degree.
C. being the substantially pure Sn melting point, when the solder
changes phase from solid to liquid the surface tension causes the
metal volume to change shape, transforming into a substantially
spherical shape 126 as the liquid surface tension minimizes the
surface area. Also occurring at the elevated temperature is the
formation of a layer of intermetallic compounds (IMCs) 128 which
are a mixture of several alloy phases, for example at a Cu/Sn
interface the IMCs will be a combination of Cu.sub.5Sn.sub.6 and
Cu.sub.3Sn alloy phases. Also occurring at the elevated temperature
is the vaporization and outgassing of various organic molecules
that may be incorporated into the solder during the deposition
process. These elevated temperature processes are halted by cooling
down the wafer or substrate, causing the solder to solidify,
wherein the solid solder is composed of many sub-micron sized
grains which can have different sizes and compositions. For
example, U.S. Pat. No. 6,805,974, which is hereby incorporated by
reference herein in its entirety, teaches the importance of
controlling the alloy composition and the cool-down rate to avoid
the unwanted formation of large Ag.sub.3Sn plate shaped grains and
instead form a fine grained dispersion of Sn grains and Ag.sub.3Sn
small grains.
[0019] The importance of providing a repeatable and well controlled
intermetallic structure (IMC) between the underbump metal (UBM) and
the solder, along with a well controlled grain structure within the
solder, may influence both the mechanical and electromigration
reliability of the solder bump. In addition, during cooldown the
nucleation and growth of the solder grain structure is strongly
influenced by the IMCs that were formed. Prohibiting the presence
of Ag away at the underbump metal interface during the initial
phase of reflow is advantageous as is demonstrated by comparing
FIGS. 4 and 5 which show optical microscope images 230, 240 of
bumps that have been lapped and polished to the interface region
232, 242 between the underbump metal and the solder, where light
and dark colors correspond to the different materials of solder,
UBM, and IMC, where the very dark spots are voids. Using a nickel
UBM layer and about a 2.5% Ag alloy single step electrodeposition
of SnAg shown in FIG. 4 for example, frequent occurrence of
interface voids 234, 236, 238 in the region between the UBM and
SnAg may occur. By contrast, the disclosed embodiments using a
first layer of substantially pure tin and a second layer of
tin-silver repeatedly as shown in FIG. 5, no such occurrence of
interface voids occur. The substantially pure Sn layer/bath may be
referred to as, for example, a commercially available substantially
pure Sn material or bath such as available from Dow Chemical.
[0020] Referring now to FIG. 6, there is shown a single bump
structure in cross section. Workpiece 250 is prepared with a
structure 252 having electrical contact element 101 that is
substantially surrounded by an insulating film 100, where these
type of features are disposed in a semi-periodic array where the
workpiece is coated with a seed layer 102 and then coated with
photoresist 104 which is photopatterned to provide openings into
which an underbump metal 106, such as nickel (Ni) or copper (Cu) or
a series of Ni and Cu layers, is electrodeposited. It is noted that
any suitable underbump metal may be provided. A substantially pure
tin layer 121 is electrodeposited using an electroplating bath with
a metal ion content containing no other metal ion besides tin. It
is noted that the workpiece 250 may be rinsed to remove the
electroplating bath. A tin-silver layer 122 is then
electrodeposited using the same resist pattern mask layer 104 in
another plating bath having a metal ion content including tin and
silver ions. The thicknesses of the substantially pure Sn layer,
T.sub.Sn, and of the SnAg layer, T.sub.SnAg, and the % Ag in the
SnAg layer, C.sub.SnAg, are adjusted to provide a final composition
% Ag according to the following equation:
% Ag=CSnAg.times.TSnAg/(TSnAg+TSn).
[0021] For example, to achieve a final composition % Ag equal to
1.5% Ag the T.sub.Sn=T.sub.SnAg and C.sub.SnAg=3.0% .
[0022] It has been considered to apply substantially pure silver
(Ag) and substantially pure tin (Sn) to facilitate fabrication of
the SnAg alloy, or even to apply Ag, then Cu, then Sn which would
then be reflowed to form a SnAgCu alloy, this method could have
particular cost advantages since substantially pure Ag and
substantially pure Sn plating materials are less expensive then
SnAg alloy plating. When using a combination of substantially pure
metal layers it is necessary to apply the more noble metals prior
to applying the substantially pure tin for two reasons: (1)
electrodeposition of Ag onto a Sn surface is difficult to control
because of the problem of uncontrolled Ag immersion deposition on
Sn, thereby producing an unstable Sn/Ag interface which will cause
production control problems between the deposition step and the
thermal treatment reflow step; (2) during the thermal reflow
process the substantially pure Ag doesn't melt, instead it
dissolves into the Sn, and therefore a Ag metal layer would be
unstable on the melted tin solder ball, drifting around during the
period between Sn melting and Ag fully dissolving into the Sn.
However, to apply the Ag directly on top of the UBM material during
the reflow process where the intermetallic layer is formed, the
presence of Ag between the Sn and the UBM causes the formation of
voids in the intermetallic layer, and these voids reduce the
reliability of the solder joint. Because the SnAg materials are
several times more expensive than Sn materials the present
disclosed embodiments provide some of the economic benefit of the
substantially pure Ag and substantially pure Sn method, for example
reducing the solder deposition cost by approximately 50% or more,
without the associated disadvantage of worsening the solder joint
reliability.
[0023] Referring now to FIG. 7, there is shown a commercial wafer
electro-deposition machine suitable for a manufacturing process
using the present disclosed embodiments. The disclosed embodiments
may be implemented in a commercially available electrodeposition
machine such as the Stratus from NEXX Systems in Billerica MA.
System 200 may incorporate features as disclosed in the
International Application WO 2005/042804 A2 published under the
Patent Cooperation Treaty and having publication date May 12, 2005
which is hereby incorporated by reference herein in its entirety.
System 200 is shown in block diagram form as an exemplary system.
It is noted that more or less modules may be provided having
different configurations and locations. The industrial
electrodeposition machine 200 may contain load ports 206 by which
substrates previously patterned with photoresist as described above
are inserted and withdrawn from the system. Loading station 204 may
have a robotic arm which transfers substrates 278 into
substrate-holders 270, 272, 274 which are then transferred by
transport 280 to modules 210, 212, 214, 216, 260, 262, 264, 266 and
processed in succession, The succession may include a copper (Cu)
electrodeposition module 216, a nickel (Ni) electrodeposition
module 214, a tin (Sn) electrodeposition module 212, a tin-silver
(SnAg) electrodeposition module 210. The substrates may then be
returned to the loading station 204 which unloads the substrates
and passes them through a substrate cleaning module 202 from which
they are returned to the load ports 206. Cleaning steps, using
de-ionized water for example, may be disposed before and after the
electrodeposition steps, for example, cleaning modules 260, 262,
264, 266 may be provided. Alternately, modules 260, 262, 264 and
266 may be rinse or thermal treatment modules as well as clean
modules. Controller(s) 220 may be provided within each station or
module to sequence the process and/or transport within the station
or module. A system controller(s) 222 may be provided within the
system 200 to sequence substrates between the stations or process
modules and to coordinate system actions, such as, host
communication, lot loading and unloading or otherwise those actions
that are required to control the system 200. Controller 222 may be
programmable to plate the workpiece with substantially pure tin in
process module 212 disposed to support a plating bath having a
suitable metal ion content (e.g. such as that described above). It
is noted that the process module 212 may include either a pure tin
anode or an insoluble platinum-titanium (Pt--Ti) anode. Controller
222 may be further programmable to rinse the workpiece in a rinse
tank disposed to support rinsing substantially all of the
substantially pure tin plating chemistry from the workpiece.
Controller 222 may further be programmable to plate the workpiece
with tin and silver in process module 210 disposed to support a
plating bath with a suitable metal ion content (e.g. such as that
described above). It is noted that the process module may include,
for example, an insoluble Pt--Ti anode or any other suitable anode.
Controller 222 or any other suitable controller may further be
programmable to thermally treat the workpiece in a thermal
treatment module disposed to thermally treat the workpiece to cause
the tin and tin-silver layers to intermix and form a substantially
uniform tin-silver alloy feature. Controller 222 may be further
programmable to deposit copper on the workpiece with copper
electrodeposition module 216. Controller 222 may further be
programmable to deposit nickel on the workpiece with nickel
electrodeposition module 214. Controller 222 may further be
programmable to clean the workpiece with clean module 260. In the
embodiment shown, four electrodeposition modules 210, 212, 214, 216
and four cleaning modules 260, 262, 264, 266 are shown. It is
noted, however, that more or less modules may be provided. By way
of example, only tin (Sn) electrodeposition module(s) and
tin-silver (SnAg) electrodeposition module(s) may be provided. As a
further example, separate tools having tin (Sn) electrodeposition
module(s) and tin-silver (SnAg) electrodeposition module(s) may be
provided. As a further example, multiple duplicate
electrodeposition modules may be provided to allow multiple
workpieces to be processed in parallel to increase the throughput
of the system. As such, all such variations, alternatives and
modifications of system configurations are embraced.
[0024] Referring now to FIG. 8, there is shown a block diagram of
an exemplary electrodeposition process module 210.
Electrodeposition module 210 may incorporate features as do modules
found in Stratus tools from NEXX Systems in Billerica MA and may
incorporate features as disclosed in the International Application
WO 2005/042804 A2 published under the Patent Cooperation Treaty and
having publication date May 12, 2005 which is hereby incorporated
by reference herein in its entirety. Exemplary electrodeposition
module has housing 300 which contains fluid 302 where fluid 302 may
flow through housing 300 and where fluid 302 may be a circulated
electrolyte. Workpiece holder 272 may be removable from housing 300
by handler 280 and may hold substrates 278. Although two substrates
are shown, holder may hold more or less substrate(s). Anodes 310,
312 are provided with shield plates 314, 316 and paddle or fluid
agitation assemblies 318 and 320. It is noted that more or less
assemblies may be provided. For example, a single anode may be
provided. By way of further example, the anode may be part of
housing 300 or shield plates 314, 316 and paddle or fluid agitation
assemblies 318 and 320 may not be provided.
[0025] The illustrated process may be performed, such as will be
described further below with apparatus 200 for example. As may be
realized, controller(s) 220 may be suitably programmed to effect
the process at least in part in an automatic manner.
[0026] Referring now to FIG. 9, there is shown an exemplary process
flow diagram 400 showing a method for forming a lead free solder
bump on a workpiece. In accordance with the exemplary embodiment,
for example, a workpiece with an electrically conducting seed layer
covered by a patterned resist mask layer having a plurality of
openings may be provided, block 402, for instance in the apparatus.
The workpiece may be immersed, block 404, in a tin plating bath
containing, for example, a substantially pure tin anode or an
insoluble platinum-titanium anode. In block 404, electrical contact
to the seed layer may be formed and electrical potential applied
between the workpiece and the anode to cause substantially pure tin
to be deposited, for example, between about 2 and about 150 microns
of tin to deposit in the resist pattern features. In block 408, the
workpiece may be moved to a rinse tank. In block 410, substantially
all of the substantially pure tin plating chemistry from the
workpiece may be rinsed. The workpiece may be removed from the
rinse tank, block 412, and immersed in a plating bath containing
tin and silver ions and an anode (e.g. such as, for example, an
insoluble platinum-titanium anode), block 414. Electrical contact
to the seed layer may be formed as per block 416, and electrical
potential applied between the workpiece and the anode to cause
tin-silver alloy to deposit. For example, between about 2 and about
150 microns of a tin-silver alloy may be deposited in the resist
pattern features. In block 418, the photoresist patterning layer
may be removed, and substantially all of the seed layer not covered
by the plated tin and tin-silver alloy may be removed, per block
420. Thermally treating the workpiece such as in block 422, for
example, at between about 210.degree. C. to about 230.degree. C.
(degrees centigrade) may cause the tin and tin-silver layers to
intermix and form a substantially uniform tin-silver alloy feature
as desired. In the exemplary process 400, the tin and tin-silver
layers may have any suitable thickness or composition, for example,
the tin layer may be about 30 microns and the tin-silver alloy
layer is about 30 microns and the tin-silver alloy composition may
be between about 1% and about 7% silver by weight before thermal
treatment and about 0.5% to about 3.5% silver by weight after
thermal treatment. By way of further example, the tin layer may be
about 10 microns and the tin-silver alloy layer may be about 10
microns and the tin-silver alloy composition may be between about
1% and about 7% silver by weight before thermal treatment and about
0.5% to about 3.5% silver by weight after thermal treatment. By way
of further example, the tin layer may be about one-fourth the
thickness of the tin-silver layer. Further, in the embodiments,
process 400 may provide more or less steps or one or more steps may
be combined in one or more step or process. By way of further
example, the tin layer may be about 1 micron or 10 microns and the
tin-silver layer may be between about 20 microns to about 120
microns.
[0027] In accordance with an embodiment, a method of forming a
metal feature on a workpiece with deposition is provided. The
workpiece is provided with an under bump metal layer for solder of
an electronic device. A substantially pure tin layer is deposited
directly to the under bump metal layer. A tin silver alloy layer is
deposited onto the substantially pure tin layer.
[0028] In the embodiment, substantially all of the substantially
pure tin plating chemistry from the workpiece may be rinsed.
[0029] In the embodiment, the deposition is accomplished by
electrodeposition.
[0030] In the embodiment, the under bump metal comprises either
copper or nickel.
[0031] In the embodiment, an apparatus for forming a lead free
solder bump on a workpiece having an electrically conducting seed
layer, the electrically conducting seed layer covered by a
patterned resist mask layer having a plurality of feature openings
is provided. The apparatus has a first plating bath with a metal
ion content adapted to deposit a substantially pure tin layer in
the resist pattern features. A rinse tank may be provided and
adapted to rinse substantially all of the substantially pure tin
plating chemistry from the workpiece. A second plating bath is
provided with a metal ion content adapted to deposit a tin-silver
alloy layer in the resist pattern features.
[0032] In the embodiment, a copper electrodeposition module is
provided.
[0033] In the embodiment, a copper electrodeposition module and a
nickel electrodeposition module are provided.
[0034] In the embodiment, a cleaning module is provided.
[0035] In the embodiment, an electronic device having a lead free
solder feature is prepared by a process having a step of depositing
a substantially pure tin layer directly to a layer of under bump
metal for solder of the electronic device. A step of depositing a
tin silver alloy layer onto the substantially pure tin layer is
provided.
[0036] In the embodiment, a step of rinsing substantially all of
the substantially pure tin plating chemistry from the electronic
device may be provided.
[0037] In the embodiment, the deposition is accomplished by
electrodeposition.
[0038] In the embodiment, the under bump metal comprises either
copper or nickel.
[0039] In the embodiment, a method for forming a lead free solder
bump on a workpiece is provided, the method comprising providing a
step of providing the workpiece with an electrically conducting
seed layer, the electrically conducting seed layer covered by a
patterned resist mask layer having a plurality of feature openings.
The workpiece is immersed in a first plating bath with a metal ion
content. The method comprises providing electrical contact to the
seed layer and providing an electrical potential through the metal
ion content of the first plating bath to cause between about 2 and
about 150 microns of substantially pure tin to deposit in the
resist pattern features. The workpiece is immersed in a second
plating bath with a metal ion content. Electrical contact to the
seed layer is formed and an electrical potential between through
the metal ion content in the second plating bath is provided to
cause between about 2 and about 150 microns of a tin-silver alloy
to deposit in the resist pattern features is provided.
[0040] In the embodiment, the method may include moving the
workpiece to a rinse tank, rinsing substantially all of the
substantially pure tin plating chemistry from the workpiece is
provided, and removing the workpiece from the rinse tank is
provided.
[0041] In the embodiment, removal of the photoresist patterning
layer is provided.
[0042] In the embodiment, substantially all of the seed layer not
covered by the plated tin and tin-silver alloy is removed.
[0043] In the embodiment, thermally treating the workpiece at
between about 210 to about 230 degrees centigrade to cause the tin
and tin-silver layers to intermix and form a substantially uniform
tin-silver alloy feature is provided.
[0044] In the embodiment, the tin layer is about 30 microns and the
tin-silver alloy layer is about 30 microns, and wherein the
tin-silver alloy composition is between about 1% and about 7%
silver by weight before thermal treatment and about 0.5% to about
3.5% silver by weight after thermal treatment.
[0045] In the embodiment, the tin layer is about 1 micron or about
10 microns and the tin-silver alloy layer is between about 20
microns to about 120 microns.
[0046] In the embodiment, the tin layer is 10 microns and the
tin-silver alloy layer is about 10 microns, and wherein the
tin-silver alloy composition is between about 1% and about 7%
silver by weight before thermal treatment and about 0.5% to about
3.5% silver by weight after thermal treatment.
[0047] In the embodiment, the tin layer is about one-fourth the
thickness of the tin-silver layer.
[0048] In the embodiment, an apparatus for forming a lead free
solder bump on a workpiece having an electrically conducting seed
layer, the electrically conducting seed layer covered by a
patterned resist mask layer having a plurality of feature openings
is provided. The apparatus has a controller programmable to plate
the workpiece with substantially pure tin in a first process module
disposed to support a first plating bath having a metal ion content
adapted to deposit a substantially pure tin layer on the workpiece.
The controller is further programmable to plate the workpiece with
tin and silver in a second process module disposed to support a
second plating bath with a metal ion content adapted to deposit a
tin and silver layer on the workpiece.
[0049] In the embodiment, the controller is further programmable to
rinse the workpiece in a rinse tank disposed to support rinsing
substantially all of the substantially pure tin plating chemistry
from the workpiece.
[0050] In the embodiment, the controller is further programmable to
deposit copper on the workpiece with a copper electrodeposition
module.
[0051] In the embodiment, the controller is further programmable to
deposit nickel on the workpiece with a nickel electrodeposition
module.
[0052] In the embodiment, the controller is further programmable to
clean the workpiece with a clean module.
[0053] In the exemplary embodiment, a method for processing one or
more workpieces to electrochemically form a pattern of lead-free
bumps on a workpiece is provided. In one embodiment the lead-free
bump is formed by a substantially two step deposition process, the
first step being through mask deposition of substantially pure tin
from an electroplating solution containing tin-ions (e.g. a metal
ion content), and a second step being through mask deposition of
tin-silver alloy from an electroplating solution containing a
controlled mixture of tin-ions and silver ions (e.g. a metal ion
content), the two steps being controlled to provide target layer 1
and layer 2 thicknesses, T1 and T2, along with the second step
being controlled to provide X% alloy composition, such that after a
subsequent thermal treatment the two layers intermix and form a
substantially uniform alloy of tin-silver (SnAg), said alloy having
a concentration intermediate between the deposited X% Ag in the
alloy deposition step and the 0% Ag in the substantially pure tin
deposition step. The disclosed embodiments prevent the immersion
deposition of noble metal ion, such as Ag, and organic complexor on
the Under Bump Material (UBM) surface to eliminate the potential
forming of voids between the UBM and solder interface. A less noble
metal layer, such as substantially pure Tin, is electrodeposited on
the UBM before the lead-free solder alloy of Sn and more noble
metal such as Ag and/or Cu is co-deposited with Sn as a SnAg or
SnAgCu alloy to form a bump for electronic packaging.
[0054] It should be understood that the foregoing description is
only illustrative of the invention. Various alternatives and
modifications can be devised by those skilled in the art without
departing from the invention. Accordingly, the present invention is
intended to embrace all such alternatives, modifications and
variances which fall within the scope of the appended claims.
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