U.S. patent application number 11/507066 was filed with the patent office on 2008-02-21 for method and system for depositing alloy composition.
This patent application is currently assigned to Semitool, Inc.. Invention is credited to Marvin Bernt, Bioh Kim, Paul R. McHugh, Greg Wilson.
Application Number | 20080041727 11/507066 |
Document ID | / |
Family ID | 39083175 |
Filed Date | 2008-02-21 |
United States Patent
Application |
20080041727 |
Kind Code |
A1 |
Kim; Bioh ; et al. |
February 21, 2008 |
Method and system for depositing alloy composition
Abstract
Electric potential, current density, and deposition rate are
controlled to deposit metal alloys, such as tin based solder alloys
or magnetic alloys, with minimal variations in the weight ratios of
alloying metals at different locations within the deposited metal
alloy feature. Alternative embodiments include processes that form
metal alloy features wherein the variation in weight ratio of
alloying metals within the feature is not necessarily minimized,
but is controlled to provide a desired variation.
Inventors: |
Kim; Bioh; (Kalispell,
MT) ; Bernt; Marvin; (Kalispell, MT) ; Wilson;
Greg; (Kalispell, MT) ; McHugh; Paul R.;
(Kalispell, MT) |
Correspondence
Address: |
CHRISTENSEN, O'CONNOR, JOHNSON, KINDNESS, PLLC
1420 FIFTH AVENUE, SUITE 2800
SEATTLE
WA
98101-2347
US
|
Assignee: |
Semitool, Inc.
Kalispell
MT
|
Family ID: |
39083175 |
Appl. No.: |
11/507066 |
Filed: |
August 18, 2006 |
Current U.S.
Class: |
205/118 ;
204/242 |
Current CPC
Class: |
H01L 2224/05139
20130101; H01L 2224/05164 20130101; H01L 2224/05669 20130101; H01L
24/11 20130101; C25D 5/18 20130101; H01L 2924/01322 20130101; H01L
2224/05655 20130101; H01L 2224/05647 20130101; H01L 2224/05147
20130101; C25D 21/10 20130101; C25D 7/123 20130101; H01L 2924/01079
20130101; H01L 2924/01078 20130101; H01L 2224/05664 20130101; H01L
2224/05144 20130101; H01L 2224/05639 20130101; H01L 2224/05169
20130101; H01L 2224/05673 20130101; H01L 2224/05001 20130101; H01L
2224/05616 20130101; H01L 2924/3025 20130101; H01L 24/03 20130101;
C25D 3/56 20130101; H01L 2224/05155 20130101; H01L 2224/05173
20130101; H01L 2224/05111 20130101; H01L 21/2885 20130101; H01L
24/05 20130101; H01L 2224/05116 20130101; H01L 2224/05568 20130101;
H01L 2224/05611 20130101; C25D 5/02 20130101; H01L 2224/05023
20130101; H01L 2224/05644 20130101; H01L 2924/01327 20130101; H01L
2924/01322 20130101; H01L 2924/00 20130101; H01L 2224/05611
20130101; H01L 2924/00014 20130101; H01L 2224/05639 20130101; H01L
2924/00014 20130101; H01L 2224/05647 20130101; H01L 2924/00014
20130101; H01L 2224/05111 20130101; H01L 2924/00014 20130101; H01L
2224/05139 20130101; H01L 2924/00014 20130101; H01L 2224/05147
20130101; H01L 2924/00014 20130101; H01L 2224/05111 20130101; H01L
2924/01029 20130101; H01L 2224/05611 20130101; H01L 2924/01029
20130101; H01L 2224/05611 20130101; H01L 2924/01047 20130101; H01L
2924/01029 20130101; H01L 2224/05611 20130101; H01L 2924/01083
20130101; H01L 2224/05111 20130101; H01L 2924/01083 20130101; H01L
2224/05111 20130101; H01L 2924/01047 20130101; H01L 2924/01029
20130101; H01L 2224/05155 20130101; H01L 2924/013 20130101; H01L
2924/00014 20130101; H01L 2224/05655 20130101; H01L 2924/013
20130101; H01L 2924/00014 20130101; H01L 2224/05116 20130101; H01L
2924/0105 20130101; H01L 2224/05616 20130101; H01L 2924/0105
20130101; H01L 2224/05616 20130101; H01L 2924/013 20130101; H01L
2924/00014 20130101; H01L 2224/05116 20130101; H01L 2924/013
20130101; H01L 2924/00014 20130101; H01L 2224/05144 20130101; H01L
2924/00014 20130101; H01L 2224/05644 20130101; H01L 2924/00014
20130101; H01L 2224/05655 20130101; H01L 2924/00014 20130101; H01L
2224/05155 20130101; H01L 2924/00014 20130101; H01L 2224/05164
20130101; H01L 2924/00014 20130101; H01L 2224/05169 20130101; H01L
2924/00014 20130101; H01L 2224/05669 20130101; H01L 2924/00014
20130101; H01L 2224/05664 20130101; H01L 2924/00014 20130101; H01L
2224/05673 20130101; H01L 2924/00014 20130101; H01L 2224/05173
20130101; H01L 2924/00014 20130101 |
Class at
Publication: |
205/118 ;
204/242 |
International
Class: |
C25D 5/02 20060101
C25D005/02; C25B 9/00 20060101 C25B009/00 |
Claims
1. A method of forming a metal alloy feature comprising: providing
a microfeature workpiece that includes a metal feature within a
recess; providing an electroplating bath in contact with an
electrode; contacting the microfeature workpiece with the
electroplating bath; applying an electric potential between the
metal feature and the electrode and producing a first current
density; depositing metal alloy having a first weight ratio of
alloying metals within the recessed feature; adjusting the electric
potential to change the first current density to a second current
density; depositing metal alloy having a second weight ratio of
alloying metals within the recessed feature; adjusting the electric
potential to change the second current density to a third current
density; and depositing metal alloy having a third weight ratio of
alloying metals within the recessed feature.
2. The method of claim 1, wherein the second current density is
greater than the first current density.
3. The method of claim 1, wherein the third current density is
greater than the second current density.
4. The method of claim 1, wherein the weight ratio of alloying
metals in at least two of the first composition, the second
composition, and the third composition are substantially the
same.
5. The method of claim 1, wherein the weight ratio of alloying
metals in the first composition, the second composition and the
third composition are not substantially the same.
6. The method of claim 1, wherein the metal alloy is a solder
alloy.
7. The method of claim 6, wherein the solder alloy comprises metals
selected from lead, tin, silver, and copper.
8. The method of claim 1, wherein the metal alloy is a non-solder
alloy.
9. The method of claim 1, further comprising: filling the recessed
feature with the metal alloy; and depositing the metal alloy over
the filled recessed feature.
10. The method of claim 9, where the step of depositing metal alloy
over the filled recessed feature is carried out at a fourth current
density, the fourth current density being less than the third
current density.
11. The method of claim 10, wherein the step of depositing metal
alloy over the filled recessed feature is carried out at a fourth
current density, the fourth current density being greater than the
third current density.
12. A tool for forming a metal alloy feature comprising: a reactor
for receiving a microfeature workpiece that includes a metal
feature within a recess and contacting the microfeature workpiece
and an electrode with an electroplating bath; and a power source
for applying a first electric potential, second electric potential,
and third electric potential between the metal feature and the
electrode, the first electric potential producing a first current
density, the first current density causing a metal alloy having a
first weight ratio of alloying metals to be deposited within the
recessed feature, the second electric potential producing a second
current density, the second current density causing a metal alloy
having a second weight ratio of alloying metals to be deposited
within the recessed feature, and the third electric potential
producing a third current density, the third current density
causing a metal alloy having a third weight ratio of alloying
metals to be deposited within the recessed feature.
13. A method of forming a metal alloy feature comprising: providing
a microfeature workpiece that includes a metal feature within a
recess; providing an electroplating bath in contact with an
electrode; contacting the microfeature workpiece with the
electroplating bath; applying an electric potential between the
metal feature and the electrode and producing a first current
density; depositing metal alloy having a first weight ratio of
alloying metals; adjusting the first current density to a second
current density as the recessed feature is filled; and continuing
to deposit metal alloy having a weight ratio of alloying metals
that is substantially similar to the first weight ratio.
14. The method of claim 13, further comprising: adjusting the
second current density to a third current density as the recessed
feature is filled; and continuing to deposit metal alloy having a
weight ratio of alloying metals that is substantially similar to
the first weight ratio.
15. A method of forming a metal alloy feature comprising: providing
a microfeature workpiece that includes a metal feature within a
recess; providing an electroplating bath in contact with an
electrode; contacting the microfeature workpiece with the
electroplating bath; applying an electric potential between the
metal feature and the electrode and producing a first current
density; depositing metal alloy having a first weight ratio of
alloying metals; and controlling the variation of the weight ratio
of the alloying metals in the deposited metal alloy from the first
weight ratio by adjusting the current density as the recessed
feature is filled.
Description
BACKGROUND
[0001] The subject matter described herein relates to methods and
systems for forming metal alloy features on microfeature workpieces
and controlling composition gradients within the deposited metal
alloy features.
[0002] Metal alloys are utilized in numerous applications in the
microelectronic industry. For instance, Permalloy and other
magnetic alloys (which are based on nickel, cobalt and iron) are
used in giant magnoresistive heads and magnoresistive heads. Metal
alloys are also used as conductive features for interconnects and
vias. Noble metal alloys are used as electrodes for capacitors.
Other metal alloys, such as lead-tin alloys and lead-free alloys
are used as solders for mounting microelectronic devices to
substrates.
[0003] When metal ions in an electroplating solution have similar
reduction potentials, the weight ratio of the metals deposited as
an alloy tend to be similar to the ratio of concentrations of the
metal ions in the electroplating solution. This characteristic
lends itself to predictability and control the deposited alloy
composition within the deposited feature. In contrast, when the
alloying metals do not have similar reduction potentials,
prediction and control of the alloy composition within the
deposited feature becomes more challenging.
[0004] Lead-free solders and Permalloy are formed from alloying
metals that have substantially different reduction potentials. In
addition the baths used to electroplate lead-free solders and
Permalloy include the alloying metals in much different
compositions. For example for tin-silver solders, the silver
concentration in the electroplating bath is much less than the
concentration of the tin concentration. In electroplating baths
from which Permalloys are deposited, the non-nickel metal ion
concentration is generally much less than the concentration of
nickel ions. These factors can contribute to variations in the
ratio of metals at different locations within the deposited alloys.
Such variations can be undesirable for several reasons.
[0005] Near-eutectic tin alloy based solders are desirable due to
properties such as good melting, solderability, ability to cope
with lead contamination and reliability. To use these alloys as
general purpose solders, the silver and copper contents are limited
to near eutectic compositions on account of melting point
limitations for bumping applications. If the weight ratio of metals
at different locations within the formed feature varies too far
from the ratio needed to provide an alloy with the desired melting
properties, incomplete reflow may result at those locations and
some of the solder alloy may not melt at the reflow temperature.
Simply elevating the reflow temperature is often not an solution
because higher temperatures may damage surrounding architecture.
Incomplete reflow is undesirable because it can adversely effect
conductivity properties of the alloy and integrity of intermetallic
interfaces.
[0006] In magnetic head applications, variations in magnetic
properties of a magnetic head are undesirable because of their
impact on performance of the head. The magnetic properties of
Permalloy are effected by the composition of the alloy. If portions
of the deposited Permalloy differ in composition from other
portions, performance of the magnetic head may be adversely
effected.
[0007] In some applications it may be desirable to produce metal
alloy features where portions of the alloy feature differ in
composition from other portions of the alloy feature. For example,
when an alloy feature interfaces with two dissimilar materials, it
may be desirable for a portion of the alloy feature to have one
composition at the interface with one material and a different
composition at the interface with another material.
SUMMARY
[0008] In one aspect, the processes and systems described herein
provide techniques and tools that can be used to minimize
variations in composition within a formed metal alloy feature.
Minimizing variations in composition within formed metal alloy
features will reduce the likelihood that alloy features will not
function in the manner they were designed to function. For example,
minimizing compositional variations in solder alloys can reduce the
likelihood that incomplete reflow will occur at desired reflow
temperatures or that surrounding architecture will be damaged by
increasing the reflow temperature to achieve complete solder
reflow. For alloys used for magnetic head applications, minimizing
compositional variations in the alloy can reduce the likelihood
that the magnetic head will not perform as desired.
[0009] One method described below in more detail for forming a
metal alloy feature includes a step of providing a microfeature
workpiece that includes a metal feature within a recess. The
microfeature workpiece is contacted with an electroplating bath
that is also in contact with an electrode. Applying an electric
potential between the metal feature and the electrode produces a
first current density that promotes deposition of a metal alloy
having a first weight ratio of alloying metals within the recessed
feature. The electric potential is then adjusted to change the
first current density to a second current density which results in
deposition of a metal alloy having a second weight ratio of
alloying metals within the recessed feature. The electric potential
is then changed a third time to provide a third current density
that results in deposition of a metal alloy having a third weight
ratio of alloying metals within the recessed feature. As described
below in more detail, in some embodiments, the first, second, and
third current densities are different and in other embodiments, the
first, second, and third current densities are similar. In
addition, as described below in more detail, the resulting first
weight ratio of alloying metals, second weight ratio of alloying
metals, and third weight ratio of alloying metals in the deposited
metal alloy can be substantially the same or can be substantially
different.
[0010] Methods described herein can be used to form metal alloy
features wherein the weight ratio of alloying metals within the
deposited metal alloy feature is different at different locations
within the deposited feature or form metal alloy features wherein
the variance in the weight ratio of alloying metals within the
formed metal alloy feature is minimized. A method for producing
metal alloy features wherein variation of the weight ratio of
alloying metals throughout the deposited metal alloy feature is
minimized includes the step of providing a microfeature workpiece
that includes a metal feature within a recess. The microfeature
workpiece is contacted with an electroplating bath that is also in
contact with an electrode. An electric potential is applied between
the metal feature and the electrode which produces a first current
density and causes deposition of a metal alloy having a first
weight ratio of alloying metals onto the metal feature. In
accordance with this method, the first current density is then
adjusted to a second current density as the recessed feature is
filled with metal alloy and deposition of metal alloy having a
weight ratio of alloying metals that is substantially similar to
the first weight ratio is continued.
[0011] Methods described herein can be carried out in a tool for
forming a metal alloy feature that includes a reactor for receiving
a microfeature workpiece that includes a metal feature within a
recess. The reactor contains an electroplating bath that is in
contact with an electrode. The reactor contacts the microfeature
workpiece with the electroplating bath. The tool further includes a
power source for applying a first electric potential, a second
electric potential, and a third electric potential between the
metal feature and the electrode. The first electric potential
produces a first current density, which causes a metal alloy having
a first weight ratio of alloying metals to be deposited within the
recessed feature. The second electric potential produces a second
current density, which causes a metal alloy having a second weight
ratio of alloying metals to be deposited within the recessed
feature. The third electric potential produces a third current
density that causes a metal alloy having a third weight ratio of
alloying metals to be deposited within the recessed feature.
[0012] The methods and systems described herein include steps and
components to control the composition, e.g., weight ratio of
alloying metals in a deposited metal alloy feature. The control
provided by the methods and systems described herein will allow
microelectronic device manufacturers to produce metal alloy
features wherein variation of the metal alloy composition within
the metal alloy feature is minimized or wherein variation of the
metal alloy composition within the formed metal alloy feature is
controlled to vary in a desired manner.
[0013] This summary is provided to introduce a selection of
concepts in a simplified form that are further described below in
the Detailed Description. This summary is not intended to identify
key features of the claimed subject matter, nor is it intended to
be used as an aid in determining the scope of the claimed subject
matter.
DESCRIPTION OF THE DRAWINGS
[0014] The foregoing aspects and many of the attendant advantages
of the subject matter described herein will become more readily
appreciated as the same become better understood by reference to
the following detailed description, when taken in conjunction with
the accompanying drawings, wherein:
[0015] FIG. 1 is a schematic illustration of a tool for carrying
out processes for forming metal alloy features described
herein;
[0016] FIG. 2 is a schematic illustration of a reactor for carrying
out methods described herein and for use in the tool described with
reference to FIG. 1;
[0017] FIGS. 3A-3E schematically illustrate a sequence of steps
corresponding to a method for depositing metal alloys described
herein;
[0018] FIG. 4 is a graphical representation of a predicted
relationship between the silver content of a tin-silver alloy and
the deposition rate as a recessed feature is filled;
[0019] FIG. 5 graphically illustrates the silver content of a
tin-silver alloy that is deposited within a recessed feature using
a method described herein that employs four different plating rates
{circle around (A)}-{circle around (D)};
[0020] FIG. 6 graphically illustrates a predicted change in silver
content as a recessed feature is filled at a constant deposition
rate of 5 .mu.m/min.; and
[0021] FIG. 7 graphically illustrates how the predicted silver
content of a tin-silver alloy varies with the depth of the recessed
feature when the deposition is carried out at a constant deposition
rate of 5 .mu.m/min. depicted in FIG. 5.
DETAILED DESCRIPTION
[0022] While illustrative embodiments have been illustrated and
described below, it will be appreciated that various changes can be
made therein without departing from the spirit and scope of the
subject matter described.
[0023] As used herein, the terms "microfeature workpiece" or
"workpiece" refer to substrates on and/or in which micro devices
are formed. Such substrates include semiconductive substrates
(e.g., silicon wafers and gallium arsenide wafers), nonconductive
substrates (e.g., ceramic or glass substrates), and conductive
substrates (e.g., doped wafers). Examples of micro devices include
microelectronic circuits or components, micromechanical devices,
microelectromechanical devices, micro optics, thin film recording
heads, data storage elements, microfluidic devices, and other small
scale devices.
[0024] In the description that follows regarding forming a metal
alloy feature on a microfeature workpiece, specific reference is
made to an exemplary tin-silver solder system. The reference to
deposition of a tin-silver solder is for exemplary purposes, and it
should be understood that the methods and systems described herein
are not limited to tin and silver ions.
[0025] As used herein, the term "substrate" refers to a base layer
of material over which one or more metallization levels is
disposed. The substrate may be, for example, a semiconductor, a
ceramic, a dielectric, etc.
[0026] The formation of metal alloy features in accordance with
processes described herein can be carried out in a tool designed to
electrochemically deposit metals such as one available from
Semitool, Inc., of Kalispell, Mont., under the trademark
Raider.TM..
[0027] An integrated tool can be provided to carry out a number of
process steps involved in the formation of microfeatures on
microfeature workpieces. Below is described one possible
combination of processing stations that could be embodied in a
processing tool platform sold under the trademark Raider.TM. by
Semitool, Inc. of Kalispell, Mont. It should be understood that
other processing tool platforms could be configured in similar or
different manners to carry out metallization steps such as those
described below. Referring to FIG. 1, an exemplary integrated
processing tool 120 includes stations to carry out a pre-wet step
122, optional copper deposition step 124, under bump metallization
step 126, rinse step 128, alloy deposition step 130, and a
spin-rinse-dry step 132. The chambers for carrying out such steps
can be arranged in various configurations. Microelectronic
workpieces are transferred between the chambers through the use of
robotics (not shown). The robotics for the tool 120 are designed to
move along a linear track. Alternatively, the robotics can be
centrally mounted and designed to rotate to access the input
section 136 and the output section 138 of tool 120. Suitable
chambers for use in tool 120 include those available for the
modular configuration of an Equinox.RTM. brand processing tool from
Semitool, Inc. For example, one chamber useful for the alloy
deposition step 130 is the Raptor.TM. reactor available from
Semitool, Inc. Processing tool 120 is capable of being programmed
to implement user entered processing recipes and conditions.
[0028] The pre-wet chamber 122, rinse chamber 128 and
spin-rinse-dry chamber 132 can be of the type available from
numerous manufacturers for carrying out such process steps.
Examples of such chambers include spray processing modules and
immersion processing modules available in conjunction with the
Raider.TM. system described above. The optional copper deposition
chamber 122, under bump metallization chamber 126 and metal alloy
deposition chamber 130 can be provided by numerous electroplating
and electroless deposition chambers such as those available as
immersion processing modules and electroplating processing reactors
for the Raider.TM. model ECD tool. Specific examples of an
electroplating processing reactor include the types described in
U.S. Provisional Application No. 60/739,343 and International
Application Nos. WO 00/061498, WO 02/097165, WO 04/108353, WO
05/001896, and WO 05/060379, the portions of the descriptions of
these applications relating to the electroplating processing
reactors are expressly incorporated herein by reference.
[0029] In general, a chamber for electroplating metal alloys
includes a reactor, a bath supply, an electrode, e.g., an anode, a
power supply, and a controller. The reactor receives the surface of
the workpiece and exposes the surface to an electroplating bath.
The bath supply includes a source of metal ion(s) to be deposited
on the surface of the workpiece. The electrode is in electrical
contact with the electroplating bath. The power supply supplies
electroplating power between the surface of the workpiece and the
electrode which promotes the electroplating of electroplate metal
ions onto the surface. The controller controls the supply of
electroplating power so that the metal ions are deposited on the
workpiece surface.
[0030] FIG. 2 illustrates a simplified form of a reactor 60.
Reactor 60 includes a processing head 62 and an electroplating bowl
assembly 64. The electroplating bowl assembly includes a cup
assembly 70 that is disposed within a reservoir container 72. The
cup assembly 70 includes a fluid reactor 72 portion that holds the
electroplating bath fluid. The cup assembly also includes a
depending annular skirt 74 which extends below the cup bottom 76,
and which includes apertures opening therethrough for fluid
communication of the plating bath solution, and for release of any
gases that might collect as the reactor of the reservoir assembly
is filled with plating solution. The cup is preferably made from a
material that is inert to plating solutions, such as
polypropylene.
[0031] A lower opening in the bottom wall of the cup assembly 70 is
connected to a polypropylene (or other material) riser tube 78,
which preferably is adjusted in height relative to the cup assembly
by a threaded connection. A first end of the riser tube 78 is
secured to the rear portion of an anode shield 80, which supports
an anode 82. A fluid inlet line 84 is disposed within the riser
tube 78. Both the riser tube 78 and the fluid inlet line 84 are
secured to the processing bowl assembly 64 by a fitting 86. The
fitting 86 can accommodate height adjustment of both the riser tube
78 and the inlet line 84. As such, this connection provides for
vertical adjustment of the anode 82. The inlet line 84 is
preferably made from a conductive material, such as titanium, and
is used to conduct electrical current to the anode 82 from the
power supply, as well as to supply fluid to the cup assembly
70.
[0032] The metal or metals to be plated onto the workpiece in
accordance with the methods described herein are present in a
plating solution as species of metal ions to be deposited onto the
workpiece. Electroplating solution is provided to the cup assembly
70 through the fluid inlet line 84 and proceeds therefrom through a
plurality of fluid inlet openings 88. The plating solution then
fills the reactor 72 through openings 88, as supplied by a plating
fluid pump (not shown) or other suitable supply. As described below
in more detail, the metal ions are deposited under process
conditions that preferentially deposit metal ions into recessed
features as opposed to the surrounding field surfaces.
[0033] The upper edge of the cup sidewall 90 forms a weir, which
limits the level of electroplating solution within the cup. This
level is chosen so that only the bottom surface of a wafer W (or
other workpiece) is contacted by the electroplating solution.
Excess solution pours over this top edge into an overflow reactor
92.
[0034] The outflow liquid from the reactor 72 is preferably
returned to a suitable reservoir where it can be treated with
additional plating chemicals to adjust the levels of the
constituents and then recycled through the plating reactor 72.
[0035] The anode 82 can be an inert anode used in connection with
the plating of metals onto the workpiece. The specific anode may
alternatively be a consumable anode, with the anode used in reactor
60 varying depending upon the specifics of the plating liquid and
process being used.
[0036] The reactor illustrated in FIG. 2 also employs a diffuser
element 93 that is disposed above the anode 82, providing an even
distribution of the flow of fluid across the surface of wafer W.
Fluid passages are provided over all or a portion of the diffuser
plate 93, to allow fluid communication therethrough. The height of
the diffuser element within the cup assembly may be adjustable by
using a height adjustment mechanism 94.
[0037] The anode shield 80 is secured to the underside of the anode
82 using anode shield fasteners 96, to prevent direct impingement
by the plating solution as the solution passes into the processing
reactor 72. The anode shield 80 and anode shield fasteners 96 are
preferably made from a dielectric material, such as polyvinylidene
fluoride or polypropylene. The anode shield serves to electrically
isolate and physically protect the backside of the anode.
[0038] The processing head 62 holds a wafer W (or other workpiece)
within the upper region of the processing reactor 72. FIG. 2
illustrates in a simplified form that the head 62 is constructed to
rotate the wafer W within the reactor 72 about an axis R. To this
end, the processing head 62 includes a rotor assembly 98 having a
plurality of wafer W engaging contacts 200 that hold the wafer W
against features of the rotor. The rotor assembly 98 preferably
includes a ring contact as described in International Application
No. WO 00/40779, which is incorporated herein by reference. The
contacts 200 for a ring contact assembly are preferably adapted to
conduct current between the wafer W and an electrical power
supply.
[0039] The processing head 62 is supported by a head operator (not
shown) that is adjustable to adjust the height of the processing
head. The head operator also has a head connection shaft 202 that
is operable to pivot about a horizontal pivot axis. Pivotal action
of the processing head using the operator allows the processing
head to be placed in an open or face-up position (not shown) for
loading and unloading of the wafer W. FIG. 2 illustrates the
processing head pivoted into a face-down position in preparation
for processing.
[0040] Chambers useful for the optional copper deposition, under
bump metallization and metal alloy deposition may also include
components to improve the mass transfer of metal ions into recessed
features. Components for improving mass transfer of metal ions into
recesses by reducing diffusion layer thicknesses include providing
fluid jets to increase fluid flow velocities of the processing
fluid at the surface of the workpiece to be treated, reciprocating
elements to provide agitation and increase fluid flow, and
components designed to form vortices adjacent the surface of the
microfeature workpiece being treated.
[0041] The foregoing tools and chambers can be used to form metal
alloys within recessed features using methods described below in
more detail.
[0042] The following discussion references a specific alloy system
tin-silver; however, it should be understood that the reference to
tin-silver is for exemplary purposes and that the processes and
systems described herein are also applicable to other metal alloy
systems such as lead alloy systems and noble metal alloy
systems.
[0043] Referring to FIGS. 3A-3E, one method for forming a metal
alloy feature is described with reference to a tin-silver solder
alloy. Referring to FIG. 3A, substrate 204, e.g., a silicon wafer
carries a dielectric layer 206 that has been patterned to provide
recesses 208 within the dielectric material. Dielectric 206 can be
patterned using conventional techniques such as photolithography. A
metal feature 210, such as a seed layer, under bump metallization,
or barrier layer 210 is formed within recess 208. Metal feature 210
can be formed using conventional techniques such as electrolytic,
electroless, PVD, or CVD techniques.
[0044] In accordance with methods described herein, metal alloy
features having a ratio of alloying metals within the feature that
is relatively constant (or of minimal variance), e.g., from the
bottom to the top of the feature, are provided by adjusting the
current density and, accordingly, the deposition rate, as the
recessed feature is filled. The manner in which the current density
is adjusted and the timing of the adjustment in the current density
will depend at least in part upon the specific chemistry employed
as well as the cross section and depth dimensions of the recessed
feature to be filled. In certain situations, it may be desirable to
increase the deposition rate by increasing the current density as
the recessed feature is filled. In other situations, it may be
preferred to decrease the deposition rate by decreasing the current
density as the recessed feature is filled.
[0045] Continuing to refer to FIGS. 3A-3E using methods described
herein, a metal alloy feature is formed over metal feature 210
within recess 208. Processes described herein include steps that
result in the formation of metal alloy features wherein the
variation of the ratio of alloying metals within the formed metal
alloy features is minimal. In other words, processes described
herein produce metal alloy features wherein the weight ratio of
alloying metals in the formed metal alloy features is relatively
constant within the formed alloy feature, e.g., there is minimal
variance in the weight ratio of alloying metals from the bottom to
the top of the formed metal alloy feature. Acceptable variances in
the weight ratio of alloying metals in the deposited feature will
depend in part upon the composition of the alloy and the end use.
For example variations in alloying weight ratios acceptable for tin
solder alloys may not be acceptable for Permalloy and other
magnetic alloys. The ratio of alloying metals in a formed metal
alloy feature is considered to be substantially constant when the
variation in the ratio of alloying metals at locations within the
formed metal alloy feature differs by less than about .+-.1 weight
% from a target alloy composition for tin solder applications and
less than about .+-.5 weight % from a target alloy composition for
Permalloy and other magnetic alloy applications. Conversely, the
ratio of alloying metals in formed metal alloy features is
considered not to be substantially constant when the variation in
the weight ratio of alloying metals at locations within the formed
metal alloy feature falls outside these ranges for tin alloy
solders, Permalloy and other magnetic alloy systems.
[0046] Using tools and reactors described above, substrate 204 is
contacted with an electroplating bath that is also in contact with
an electrode. Conventional electroplating baths available from
numerous commercial sources can be employed. In accordance with
processes described herein, the electric potential that is applied
between the metal feature and the electrode is specifically
adjusted during the course of the electroplating process as the
recessed feature is filled and the feature formed. Increasing the
electric potential increases the current density within the
reaction chamber, which increases the deposition rate. Decreasing
the electric potential decreases the current density within the
reaction chamber, which decreases the deposition rate.
[0047] For near eutectic tin-silver alloy, silver has a higher
reduction potential with significantly less amount of silver
concentration than tin concentration in the plating solution. The
present inventors predict that as the depth of a recessed feature
decreases as a result of being filled by tin-silver alloy, mass
transfer limitations on silver diminish and, accordingly, a greater
amount of silver relative to the amount of tin is deposited into
the recessed feature. In order to balance out the increased
proportion of silver deposited into the recessed feature as it is
filled and continue to deposit an alloy of the same or similar
composition, the current density can be increased, which results in
an increase in the deposition rate of tin. In instances where it is
desired to reduce variances in the weight ratio of tin and silver
at different locations within the deposited metal alloy, the
increase in current density is controlled such that the increased
rate of tin deposition is proportional to the increased rate of
silver deposition as the recessed feature is filled. The foregoing
presumes that the current density is above the limiting current
density of silver and, thus, an increase in current density has
little impact on the deposition rate of silver. Controlling current
density as described above provides a means for reducing and
minimizing variances in the weight ratio of tin and-silver within
the deposited metal alloy. In some applications, it may be possible
to reduce the variances to a point where the weight ratio of tin to
silver is substantially the same throughout the entire deposited
feature.
[0048] Referring to FIG. 4, an exemplary sequence for increasing
deposition rates {circle around (A)}-{circle around (D)} as a
recessed feature is filled is illustrated. The illustrated
deposition rate increases can be achieved by adjusting the current
density within a reaction chamber. The recessed feature being
filled is a solder bump having a stud that is 108 microns in
diameter with a total solder bump height of 120 microns. The
sequence of deposition rate increases includes four step-ups that
are instituted at different times as the recessed feature is
filled. Table 1 below lists the thickness of the deposited metal
alloy for the different deposition rates.
TABLE-US-00001 TABLE 1 Step Plating Depth (.mu.m) Deposition Rate
(.mu.m/min.) A 0 20 3.5 B 20 40 4.5 C 40 70 5.5 D 70 120 6
[0049] The silver metal content of the deposited alloy feature just
prior to the deposition rate increase was determined using x-ray
fluorescence spectroscopy (XRF). These values are depicted in FIG.
5 as diamonds. XRF provides a meaningful measurement of the silver
content of the metal alloy that is being deposited at the
particular depth within the recessed feature indicated in FIG. 5.
The measured values for silver content range between 2-3 weight
%.
[0050] Referring back to FIGS. 3B-3E, during plating interval
{circle around (A)} in FIG. 5, a layer of metal alloy 212
characterized by a first ratio of alloying metals is deposited over
metal feature 210. Thereafter, the current density is increased to
provide an increased deposition rate during interval {circle around
(B)} that results in the deposition of metal alloy layer 214
characterized by a second ratio of alloying metals. Thereafter,
during interval {circle around (C)} a third layer 216 of metal
alloy having a third ratio of alloying metals present is deposited.
Thereafter, during interval {circle around (D)}, the balance of the
stud portion and a mushroom portion 218 of the solder bump is
deposited. Portion 218 is characterized by a fourth weight ratio of
alloying metals.
[0051] Continuing to refer to FIG. 3E, the mushroom portion of the
solder bump may continue to grow as indicated by the broken lines
220 and 222. For the mushroom portion of the solder bumps, the mass
transfer limits imposed by the requirements of depositing metal
alloys into recessed features are less predominant; however, the
concepts discussed herein for reducing the variance in composition
of the deposited metal alloy features may also be applied to
control the alloy composition of the mushroom portion of the solder
bump. With the mushroom portion, it may be more desirable to
decrease current density with increasing plateable area of the
mushroom portion. Alternatively, formation of the mushroom portion
of the solder bump could be carried out at as high a current
density as possible in order to minimize the effect of the limiting
current density of the more noble metal(s) used to form the metal
alloy. Use of pulse conditions with an optimized duty cycle that
provides an instantaneous current density that is elevated, may
reduce the effect of the more noble metal limiting current density
on the film composition.
[0052] As illustrated in FIG. 5 and noted above, the resulting
solder bump includes four locations wherein the silver content of
the solder bump ranges from 2% to 3%.
[0053] Referring to FIG. 6, the dotted line illustrates predicted
silver content based on a constant deposition rate of 5 microns per
minute. From FIG. 6, it can be seen that as the recessed feature
fills, the percent silver content of the deposited tin-silver alloy
increases. This increase is graphically illustrated more clearly in
FIG. 7. FIG. 6 and FIG. 7 illustrate that if the deposition rate is
held constant at 5 microns per minute, the predicted silver content
for the deposited metal feature increases from about 2.7% near the
bottom of the recessed feature to about 7.3% near the top of the
solder bump.
[0054] The method described above with respect to FIGS. 3A-3E and
FIG. 5 describes a four-step increase in the current
density/deposition rate. An alternative to a step-wise increase in
the current density/deposition rate would be a more continuous
increase in the current density/deposition rate. For example,
rather than the step-wise increase in deposition rate illustrated
in FIG. 5, a curvilinear profile for the deposition rate increase
could be employed. Using such a curvilinear continuous increase in
the current density/deposition rate may minimize variations in the
weight ratio of alloying metals within individual layers, e.g.,
within layer 212.
[0055] For some applications, it may be more desirable to deposit a
metal alloy feature under conditions that are controlled to produce
a desired variation in alloying metal weight ratio in the deposited
feature as opposed to minimizing variation in alloying metal weight
percent in the deposited feature. For example, there may be
applications where it is preferred that the composition near the
top of the deposited metal alloy feature varies significantly from
the composition of the metal alloy near the bottom of the deposited
feature. Such a feature can be produced using the method described
below. A method for forming metal alloy features in recessed
features that exhibit a controlled variance in weight ratio of
alloying metals within the feature can be carried out in a manner
similar to the method described above for producing metal alloy
features wherein variance in the weight ratio of alloying metals in
the formed feature is minimized. Unlike the processes described
above for minimizing the variation in the weight ratio of alloying
metals in the deposited feature, methods for controlling the weight
ratio variance as opposed to minimizing the variance involve
adjusting the current density/deposition rates so that the desired
variable weight ratio of alloying metals is achieved.
[0056] Referring to FIG. 6, in one method a metal alloy feature can
be formed wherein the weight ratio of alloying metals varies within
the formed feature as depicted by dotted line 600 in FIG. 6. As
noted above, dotted line 600 represents a process for forming a
metal alloy feature that is carried out at a constant deposition
rate of 5 microns per minute. When the deposition rate is held
constant at 5 microns per minute, FIG. 6 predicts the silver
content of the deposited alloy will increase as the recessed
feature is filled. This variation in silver content of the
deposited metal alloy feature is graphically illustrated in FIG. 7.
Alternatively, rather than holding the current density/deposition
rate constant, the current density and deposition rate can be
varied in a manner that results in the ratio of alloying metals in
the deposited metal feature varying to the desired degree.
* * * * *