U.S. patent application number 12/906530 was filed with the patent office on 2011-02-10 for in-situ profile measurement in an electroplating process.
Invention is credited to MANOOCHER BIRANG, Bernardo Donoso, Nicolay Y. Kovarsky.
Application Number | 20110031112 12/906530 |
Document ID | / |
Family ID | 36829852 |
Filed Date | 2011-02-10 |
United States Patent
Application |
20110031112 |
Kind Code |
A1 |
BIRANG; MANOOCHER ; et
al. |
February 10, 2011 |
IN-SITU PROFILE MEASUREMENT IN AN ELECTROPLATING PROCESS
Abstract
A method and apparatus for measuring differential voltages in an
electrolyte of an electrochemical plating cell. Current densities
are calculated from the measured differential voltages and
correlated to thickness values of plated materials. A real time
thickness profile may be generated from the thickness values.
Inventors: |
BIRANG; MANOOCHER; (Los
Gatos, CA) ; Kovarsky; Nicolay Y.; (Sunnyvale,
CA) ; Donoso; Bernardo; (San Jose, CA) |
Correspondence
Address: |
PATTERSON & SHERIDAN, LLP - - APPM/TX
3040 POST OAK BOULEVARD, SUITE 1500
HOUSTON
TX
77056
US
|
Family ID: |
36829852 |
Appl. No.: |
12/906530 |
Filed: |
October 18, 2010 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
11137711 |
May 25, 2005 |
7837851 |
|
|
12906530 |
|
|
|
|
Current U.S.
Class: |
204/229.8 ;
428/195.1 |
Current CPC
Class: |
C25D 21/12 20130101;
G01B 7/287 20130101; G01B 7/06 20130101; H01L 21/67253 20130101;
C25D 7/123 20130101; C25D 17/001 20130101; Y10T 428/24802
20150115 |
Class at
Publication: |
204/229.8 ;
428/195.1 |
International
Class: |
C25D 17/00 20060101
C25D017/00; C25D 21/12 20060101 C25D021/12; B32B 3/00 20060101
B32B003/00 |
Claims
1. An electrochemical plating system, comprising, a fluid basin
assembly having a fluid volume configured to retain an electrolyte
therein; a contact ring is configured to position a substrate in a
plane across an upper portion of the fluid basin assembly and
electrically contact the substrate for electrochemical plating; an
anode disposed in a lower portion of the fluid basin assembly; and
a sensor assembly disposed in the fluid volume, wherein the sensor
assembly comprises at least a first sensor and a second sensor
configured to measure local voltage levels in the fluid volume.
2. The electrochemical plating system of claim 1, wherein the first
and second sensors are positioned in a line substantially
perpendicular to the plane where the substrate is positioned, and
the first sensor is closer to the plane than the second sensor.
3. The electrochemical plating system of claim 2, wherein the
sensor assembly further comprises a third sensor, and the first
sensor and the third sensor are positioned in a line substantially
parallel to the plane.
4. The electrochemical plating system of claim 1, wherein the first
sensor and second sensor are wires electrically floating in the
fluid volume.
5. The electrochemical plating system of claim 4, wherein the wires
are made of copper, copper plated over a novel metal, or a noble
metal.
6. The electrochemical plating system of claim 1, wherein the
sensor assembly comprises an array of sensors distributed from near
a center of the fluid basin assembly to near an edge region of the
fluid basin assembly.
7. The electrochemical plating system of claim 6, wherein the array
of sensors comprise: a first row of sensors disposed on a printed
circuit board; and a second row of sensors disposed on the printed
circuit board, wherein the first row of sensors are positioned in a
distance closer to the plane than the second row of sensors.
8. The electrochemical plating system of claim 6, wherein the array
of sensors are disposed in a spiral pattern.
9. The electrochemical plating system of claim 1 further comprising
a diffusion plate disposed in the fluid volume above the anode,
wherein the sensor assembly is integrated in the diffusion
plate.
10. The electrochemical plating system of claim 1, further
comprising a control unit connected to the sensor assembly and
configured to determine a voltage difference between the first
sensor and the second sensor, wherein the control unit comprises:
an electric circuit connected to the sensor assembly, wherein the
electric circuit is configured to sample and process input of the
sensor assembly.
11. An electrochemical plating system, comprising, a fluid basin
assembly having a fluid volume configured to retain an electrolyte
therein; a contact ring having one or more electric contacting
elements configured electrically contact a perimeter of a substrate
being processed, wherein the contact ring is configured to support
the substrate and position the substrate across an upper portion of
the fluid volume; an anode disposed in a lower portion of the fluid
basin assembly; a power supply coupled to connected to the contact
ring and the anode to apply a bias between the contact ring and the
anode; and a sensor assembly comprising at least a first sensor and
a second sensor, wherein the first and second sensors are
conductors electronically floating in the fluid volume; and a
signal sampling and processing circuit connected to the sensor
assembly, wherein the signal sampling and processing circuit is
configured to obtain a voltage difference between the first sensor
and the second sensor.
12. The system of claim 10, wherein the sensors assembly comprise:
a first row of sensors disposed in the fluid volume; and a second
row of sensors disposed directly underneath the first row of
sensors, wherein the signal sampling and processing circuit is
connected to obtain voltage differences between each sensor in the
first row of sensors and a perspective sensor in on the second row
of the sensors.
13. The system of claim 12, wherein the first row and second row of
sensors are conductors on a printed circuit board disposed in the
fluid volume.
14. The system of claim 12, wherein the first rows and the second
rows of sensors are distributed across a radius of the fluid
volume.
15. The system of claim 12, wherein the first rows and the second
rows of sensors are disposed in a spiral pattern.
16. The system of claim 10, further comprising a diffusion plate
disposed in the fluid volume above the anode, wherein the sensor
assembly is integrated in the diffusion plate.
17. A patterned substrate for calibrating a sensor assembly in an
electrochemical plating cell, wherein the electroplating cell
comprises a fluid basin assembly having a fluid volume, a contact
ring is configured to position a substrate in a plane across an
upper portion of the fluid basin assembly, an anode disposed in a
lower portion of the fluid basin assembly, and the sensor assembly
disposed in the fluid volume, comprising: a first conductive patch;
and a first contact point positioned in an edge of the patterned
substrate and configured to connect the contact ring of the
electroplating cell, wherein the first conductive patch is in
electric communication with the first contact point through a
protected trace.
18. The patterned substrate of claim 17, further comprising: a
plurality of conductive patches insulated from one another; and a
plurality of contact points insulated from one another positioned
in the edge of the patterned substrate, wherein each of the
plurality of the contact points is adapted to align with an
individual contact pin of the contact ring of the electroplating
cell, and each of the plurality of the conductive patches is in
electric communication with a corresponding contact point of the
plurality of the contact points.
19. The patterned substrate of claim 18, wherein the plurality of
patches are distributed across a radius of the patterned
substrate.
20. The patterned substrate of claim 18, wherein the plurality of
patches are distributed in a straight line across a radius of the
patterned substrate.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is a divisional application of copending
U.S. patent application Ser. No. 11/137,711 (Attorney Docket No.
010217), filed Sep. May 25, 2005, which is incorporated herein by
reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] Embodiments of the invention generally relate to measuring
spatial plating cell current distribution represented by measuring
the differential voltages inside an electrochemical plating cell
in-Situ.
[0004] 2. Description of the Related Art
[0005] In semiconductor processing, electrochemical plating (ECP)
is generally the preferred technique for filling features formed
onto substrates with a conductive material. A typical ECP process
generally includes immersing a substrate into an electrolyte
solution that is rich in ions of the conductive material (generally
copper), and then applying an electrical bias between a conductive
seed layer formed on the surface of the substrate and an anode
positioned in the electrolyte solution. The application of the
electrical bias between the seed layer and the anode facilitates an
electrochemical reaction that causes the ions of the conductive
material to plate onto the seed layer.
[0006] However, with conventional ECP processes and systems, the
conductive seed layer formed on the substrate is generally very
thin, and as such, is highly resistive. The resistive
characteristics of the seed layer causes the electric field
traveling between the anode and the seed layer in a plating process
to be much more dense near the perimeter of the substrate where
electrical contact with the seed layer is generally made. This
increased electric field density near the perimeter of the
substrate causes the plating rate near the perimeter of the
substrate to increase proportionally. This phenomenon is generally
known as the "terminal effect", and is an undesirable
characteristic associated with conventional plating systems.
[0007] The terminal effect is of particular concern to
semiconductor processing, because as the size of features continues
to decrease and aspect ratios continue to increase, the seed layer
thickness will inherently continue to decrease. This decrease in
the thickness of the seed layer will further increase the terminal
effect, as the decreased thickness of the seed layer further
increases the resistivity of the layer.
[0008] Another challenge in an electrochemical process is that
features on some portions of a substrate may be undesirably filled
or even filled up while immersing the substrate into a plating
bath. During the immersion process, a forward or plating bias is
generally applied to counteract etching of the seed layer on the
substrate by the plating solution, which is generally an acidic
solution. During this time period, which may be as little as 0.25
seconds, some features in certain region on the substrate may be
filled which may result in poor uniformity and variable device
yield performance.
[0009] Therefore, there is a need for an electrochemical plating
cell and methods for plating onto conductive materials
semiconductor substrates, wherein the plating thickness profile is
monitored and controlled in real time.
SUMMARY OF THE INVENTION
[0010] Embodiments of the invention generally provide an
electrochemical plating system having a sensor assembly disposed in
an electrolyte and a control unit connected to the sensors.
[0011] Embodiments of the invention may further provide a method
for measuring plating thickness profile in-situ during an
electrochemical plating process. Spatial differential voltages in
the plating bath are measured through an array of sensors disposed
in the plating bath. A real time plating profile is then generated
by integrating current values associated with the differential
voltage values.
[0012] Embodiments of the invention may further provide a method
and an apparatus for generating plating thickness profile in-situ
during an electrochemical plating process. The method comprises
measuring plating cell current distribution represented by
differential voltages in the electrolyte and generating real time
thickness profiles by integrating the electrical current values
over time. Since the copper thickness is directly proportional to
the integral electrical values over time.
[0013] Embodiments of the invention may further provide a method
for producing a uniform profile on a substrate by electrochemical
plating. The method generally comprises starting an electroplating
on the wherein the substrate is in contact with an electrolyte;
measuring a set of cell current distributions in the electrolyte;
generating a real time thickness profile from the set of cell
current distributions; and adjusting one or more process parameters
according to the real time thickness profile.
[0014] Embodiments of the invention may further provide a method
for producing a desired profile on a substrate by electroplating.
The method generally comprises starting an electroplating on the
wherein the substrate is in contact with an electrolyte; measuring
a set of cell current distributions in the electrolyte; generating
a real time thickness profile from the set of cell current
distributions; comparing the real time thickness profile to the
desired thickness profile to obtain an error profile; adjusting one
or more process parameters according to the real time thickness
profile; and terminating the electroplating process when the error
profile is within a predetermined tolerance profile.
[0015] Embodiments of the invention may further provide a method
for monitoring immersing a substrate into an electrolyte for
electrochemical plating. The method generally comprises applying a
bias voltage between the substrate and an anode assembly disposed
in the electrolyte; immersing the substrate into the electrolyte;
during immersing, monitoring cell current distributions of the
electrolyte; determining immersing status from the cell current
distributions; and adjusting the bias voltage corresponding to the
immersing status.
[0016] The details of one or more implementations are set forth in
the accompanying drawings and the description below. Other features
and advantages of the invention will be apparent from the
description and drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0017] So that the manner in which the above recited features of
the present invention can be understood in detail, a more
particular description of the invention, briefly summarized above,
may be had by reference to embodiments, some of which are
illustrated in the appended drawings. It is to be noted, however,
that the appended drawings illustrate only typical embodiments of
this invention and are therefore not to be considered limiting of
its scope, for the invention may admit to other equally effective
embodiments.
[0018] FIG. 1 illustrates a schematic view of an exemplary plating
cell.
[0019] FIG. 2 illustrates a schematic sectional view of an
exemplary plating cell and the electric field lines generated
therein.
[0020] FIG. 3 illustrates a schematic sectional view of an
exemplary plating cell of the present invention.
[0021] FIG. 3A illustrates an exemplary sensor assembly of the
plating cell shown in FIG. 3.
[0022] FIG. 3B illustrates an exemplary sensor assembly of the
plating cell shown in FIG. 3.
[0023] FIG. 3C illustrates a top view of an exemplary arrangement
of a sensor assembly of the present invention.
[0024] FIG. 3D illustrates a top view of an exemplary arrangement
of a sensor assembly of the present invention.
[0025] FIG. 3E illustrates a top view of an exemplary arrangement
of a sensor assembly of the present invention.
[0026] FIG. 4A illustrates a sectional view of an exemplary plating
cell with uniform electric field.
[0027] FIG. 4B illustrates a sectional view of an exemplary plating
cell with non-uniform electric field.
[0028] FIG. 4C illustrates a set of exemplary geometry factors.
[0029] FIG. 4D illustrates an exemplary embodiment of generating a
thickness profile from cell current distributions.
[0030] FIG. 5 illustrates an exemplary embodiment of data sampling
and processing circuit for the array of sensors in the present
invention.
[0031] FIG. 6 illustrates an exemplary embodiment of identifying
geometry factors.
[0032] FIG. 7 illustrates an exemplary embodiment of generating
real time thickness profiles.
[0033] FIG. 8 illustrates an exemplary embodiment of achieving
uniform thickness during an electrochemical plating process.
[0034] FIG. 9 illustrates an exemplary embodiment of achieving a
desired thickness profile during an electrochemical plating
process.
[0035] FIG. 10 illustrates an exemplary embodiment of monitoring
immersing a substrate into a plating solution.
[0036] FIG. 11 illustrates an exemplary embodiment of an
electrochemical plating system of the present invention.
[0037] FIG. 11A illustrates an exemplary embodiment of the process
optimization software of the electrochemical plating system shown
in FIG. 11.
[0038] FIG. 12 illustrates an exemplary embodiment of a
characterization tool of the present invention.
[0039] FIG. 13 illustrates a schematic sectional view of one
embodiment of an electroplating cell.
[0040] FIG. 14 illustrates a schematic sectional and partial
perspective view of one embodiment of an electroplating cell.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0041] The present invention generally provides an electrochemical
plating cell configured to plate a metal onto a semiconductor
substrate. The plating cell of the invention generally includes a
fluid volume cell, a contact ring, an anode and array of sensors
disposed in the fluid volume. The array of sensors positioned in
the fluid volume are configured to measure cell current
distributions during plating. A thickness profile of plated metal
can be generated from the cell current distributions using a method
provided by the present invention.
[0042] FIG. 1 illustrates a schematic view of an exemplary plating
cell 100. The plating cell 100 generally includes an outer basin
101 and an inner basin 102 positioned within the outer basin 101.
The inner basin 102 is generally configured to contain a plating
solution that is used to plate a metal, e.g., copper, onto a
substrate during an electrochemical plating process. During the
plating process, the plating solution is generally continuously
supplied to the inner basin 102 (e.g. 1 gallon per minute), and
therefore, the plating solution continually overflows the uppermost
point of the inner basin 102 (generally termed as "weir") and is
collected by the outer basin 101. The solution collected by the
outer basin 101 is then drained therefrom for recirculation and/or
chemical management.
[0043] As illustrated in FIG. 1, plating cell 100 is generally
positioned at a tilt angle, i.e., the frame portion 103 of plating
cell 100 is generally elevated on one side such that components of
the plating cell 100 are tilted between about 3.degree. and about
30.degree.. Therefore, in order to contain an adequate depth of
plating solution within the inner basin 102 during plating
operations, the uppermost portion of the inner basin 102 may be
extended upward on one side of the plating cell 100, such that the
uppermost point of the inner basin 102 is generally horizontal and
allows contiguous overflow of the plating solution supplied thereto
around the perimeter of the inner basin 102. However, embodiment of
the present invention are not limited to tilted plating cells, as
positioning the plating cell 100 at any angle with respect to
horizontal, including 0.degree., for example, is contemplated
within the scope of the invention.
[0044] The frame member 103 of the plating cell 100 generally
includes an annular base member 104 secured to the frame member
103. Since the frame member 103 is elevated on one side, the upper
surface of base member 104 is generally tilted from the horizontal
at an angle that corresponds to the angle of the frame member 103
relative to a horizontal position. The base member 104 includes an
annular or disk shaped recess formed therein, the annular recess
being configured to receive a disk shaped anode member 105. The
base member 104 further includes a plurality of fluid inlets/drains
109 positioned on a lower surface thereof. Each of the fluid
inlets/drains 109 are generally configured to individually supply
or drain a fluid to or from either the anode compartment or the
cathode compartment of the plating cell 100. The anode member 105
generally includes a plurality of slots 107 formed therethrough,
wherein the slots 107 are generally positioned in parallel
orientation with each other across the surface of the anode 105.
The parallel orientation allows for dense fluids generated at the
anode surface to flow downwardly across the anode surface and into
one of the slots 107.
[0045] The plating cell 100 further includes a membrane support
assembly 106. Membrane support assembly 106 is generally secured at
an outer periphery thereof to the base member 104, and includes an
interior region configured to allow fluids to pass therethrough. A
membrane 108 is stretched across the support 106 and generally
operates to fluidly separate a catholyte chamber (positioned
adjacent the substrate being plated) and an anolyte chamber
(positioned adjacent the anode electrode in the cell). The membrane
support assembly 106 may include an o-ring type seal positioned
near a perimeter of the membrane 108, wherein the seal is
configured to prevent fluids from traveling from one side of the
membrane 108 secured on the membrane support 106 to the other side
of the membrane 108. As such, the membrane 108 generally provides
fluid isolation between the anode and cathode portions of the
plating cell 100. Exemplary membranes that may be used to fluidly
isolate an anolyte from a catholyte are illustrated in commonly
assigned U.S. patent application Ser. No. 10/627,336 filed on Jul.
24, 2003 entitled "Electrochemical Processing Cell", which is
hereby incorporated by reference in its entirety. Alternatively,
the membrane 108 may be a fluid permeable filter-type membrane that
allows fluid to pass therethrough. In one aspect, no membrane or
filter type membrane is used in the plating cell to reduce the
plating cell cost and complexity.
[0046] A diffusion plate 110, which is generally a porous ceramic
disk member or other fluid permeable electrically resistive member
is positioned above the membrane 108. Once the plating solution is
introduced into the cathode chamber, the plating solution travels
upward through the diffusion plate 110. The diffusion plate 110,
which is generally a ceramic or other porous disk shaped member,
generally operates as a fluid flow restrictor to even out the flow
pattern across the surface of the substrate. Further, the diffusion
plate 110 operates to resistively damp electrical variations in the
electrochemically active area of the anode 105 or surface of the
membrane 108, which is known to reduce plating uniformities.
[0047] Additional embodiments of the exemplary plating cell
illustrated in FIG. 1 are illustrated in commonly assigned U.S.
patent application Ser. No. 10/268,284 which was filed on Oct. 9,
2002 under the title "Electrochemical Processing Cell", claiming
priority to U.S. Provisional Application Ser. No. 60/398,345 which
was filed on Jul. 24, 2002, both of which are incorporated herein
by reference in their entireties. Additional embodiments of the
plating cell are also illustrated in commonly assigned U.S. patent
application Ser. No. 10/627,336 filed on Jul. 24, 2003 entitled
"Electrochemical Processing Cell", which is also incorporated by
reference herein in its entirety.
[0048] FIG. 2 illustrates a schematic view of an electrochemical
plating cell 200, which is similar to the electrochemical plating
cell 100 shown in FIG. 1, and the electric field lines generated
therein when a plating process is being performed on the substrate
215. The plating cell 200 generally includes a fluid basin assembly
201 configured to contain a fluid volume 216, which is generally an
electrolyte plating solution. An anode 205 is positioned in a lower
portion of the fluid basin assembly 201 and a substrate 215 that is
to be plated is generally positioned across an upper open portion
of the cell 200. The substrate 215 is supported by a contact ring
214 that is configured to electrically contact a plating surface
215A of the substrate 215 near the perimeter of the substrate 215
via one or more electric contact elements 213. The substrate
plating surface 215A has a conductive seed layer deposited thereon.
The electric contact elements 213 are in electrical communication
with a first terminal 221A of a power supply 221, while a second
terminal 221B of the power supply 221 is in electrical
communication with the anode 205. A collimator 212 having an
annular shape is generally disposed above the diffusion plate 210
and below the contact ring 214. The collimator generally 212 has a
diameter smaller than that of the substrate 215 and is configured
to channel electric field in the fluid volume 216.
[0049] FIG. 2 also illustrates electric field lines 220 generated
during a plating process in the plating cell 200. As noted above,
the plating surface 215A has a conductive layer deposited thereon.
The conductive layer formed on the plating surface 215A may in some
cases be a conductive seed layer is generally very thin, and as
such, is highly resistive. The resistive characteristics of the
seed layer causes the electric field lines formed between the anode
205 and the plating surface 215A during a plating process to be
much more dense near the perimeter of the plating surface 215A
where electrical contact with the plating surface 215A is generally
made. The electric field lines 220 inherently converge toward the
electrical contact elements 213 as a result of the voltage drop
formed in the conductive layer, where the higher voltage (cathodic
bias) being proximate the contact elements 213. This higher voltage
near the contact elements 213 then forms a path of least
resistance. Several manufacturers of plating cells have attempted
to solve the convergence problem by substantially increasing the
resistivity of the electrolyte, however, it has been shown that
this causes an unacceptable decrease in plating rates and does not
sufficiently reduce the electric field convergence effect.
[0050] FIG. 3 illustrates a schematic sectional view of an
exemplary plating cell 300 of the present invention. The plating
cell 300 generally includes a fluid basin assembly 301 configured
to contain a fluid volume 316, which is generally an electrolyte
plating solution. An anode 305 is positioned in a lower portion of
the fluid basin assembly 301 and a substrate 315 that is to be
plated is generally positioned across an upper open portion of the
cell 300. The substrate 315 is supported by a contact ring 314 that
is configured to electrically contact a plating surface 315A of the
substrate 315 near the perimeter of the substrate 315 via one or
more electric contact elements 313. The electric contact elements
313 are in electrical communication with a first terminal 321A of a
power supply 321, while a second terminal 321B of the power supply
321 is in electrical communication with the anode 305. A diffusion
plate 310 is generally positioned between the substrate 315 and the
anode 305. A collimator 312 having an annular shape is generally
disposed above the diffusion plate 310 and below the contact ring
314. The collimator generally 312 has a diameter smaller than that
of the substrate 315 and is configured to channel electric field in
the fluid volume 316. In one aspect, the diffusion plate 310 may be
placed close to the substrate 315, for example within 2-3 mm and a
collimator may not be necessary.
[0051] Referring to FIG. 3, a sensor assembly 330 having an array
of sensors 331 is generally disposed in the plating cell 300. The
sensors 331 are floating in the plating cell 300 since they are not
connected to a reference electrode. The sensors 331 may be wires
made of copper, or a noble metal, for example, platinum, gold,
palladium, Iridium, ruthenium, or copper plated over a noble metal.
Two or more sensor 331 may be configured to sense the local voltage
level between the sensors 331 positioned in the plating volume 316.
The sensor assembly 330 is adapted to a signal sampling and
processing circuit 332 configured to obtain local cell current
distributions in the fluid volume 316 where the sensor assembly 330
is disposed. FIG. 3 illustrates a schematic configuration of one
embodiment of a processing circuit 332 comprising a plurality of
high input impedance differential amplifiers 333, one or more
multiplexers 334, and an A/D converter 335. The plurality of high
input impedance differential amplifiers are generally connected to
the array of sensors 331 such that the two input pin of each high
input impedance differential amplifier 333 are in electrical
communication with two different sensors 331. Thus, each of the
high input impedance differential amplifiers 333 outputs a
differential voltage between two sensors 331. The high input
impedance differential amplifiers 333 may be connected to the one
or more multiplexers 334, which perform the function of selecting
any one of multiple input lines and feeding the selected input to
an output line 334A. The output line 334A of the multiplexer 334
may be connected to the A/D converter 335 which converts the analog
signals into digital signals. The A/D converter 335 may be
connected to a computer 336 having a program to process the
differential voltage data and provide information of the electric
field in the fluid volume 316. In one aspect, a real time thickness
profile can be generated by integrating current values associated
with the differential voltages. The computer 336 may be configured
to calculate the current values from the measured differential
voltage data and knowledge of properties of the plating solution,
integrate the current values relative to plating time to get a
thickness profile, then plot and/or display the thickness profile.
Upon receiving and processing the differential voltages in the
fluid volume 316, the computer 336 may further output a control
signal to the power supply 321 and/or other controllable components
in the plating cell 300 to adjust the localized intensity of the
electric field, thus, performs a closed-loop control of plating
processes.
[0052] Referring to FIG. 3, in one embodiment, the sensor assembly
330 is generally a rectangular printed circuit board with the array
of sensors 331 distributed across length. The sensor assembly 330
may be positioned perpendicular to the plating surface 315A. One
end of the sensor assembly 330 is positioned near the center of the
plating surface 315A and the other end of the sensor assembly 330
is positioned near the perimeter of the plating surface 315A. In
one aspect, the sensors 331 are distributed across the radius of
the plating surface 315A such that the electric field corresponding
to plating thickness across a radii of the substrate 315 can be
monitored. In one embodiment, as shown in FIG. 3, the sensor
assembly 330 may be positioned above the diffusion plate 310 and
below the plating surface 315A. In one aspect, the sensor assembly
331 may be disposed in a position such that the sensors 331 are
between about 1 mm to about 15 mm away from the plating surface
315A.
[0053] In one embodiment, not shown, the sensor assembly 330 may be
integrated into the diffusion plate 310 rather than formed in a
printed circuit board. In another embodiment, the sensors are
positioned a known distance apart but not attached to a rigid
element of the plating cell. In one embodiment, the sensors may be
disposed anywhere in the entire plating cell including both
catholyte chamber and anolyte chamber. In one aspect, the sensors
may include an anode or a cathode (i.e. a contact pin) in a plating
cell.
[0054] FIG. 3A illustrates a front view of an exemplary sensor
assembly 330A of the plating cell 300 shown in FIG. 3. The sensor
assembly 330A is generally a printed circuit board with an
elongated portion of a different height. A taller portion of the
sensor assembly 330A has two rows of sensors 331A. In one aspect,
the sensors 331A in each row are distributed evenly along the
length of the taller portion of the sensor assembly 330A and have a
distance D1 from one another. In this configuration, the sensors
331A of a first row are positioned close to a top edge of the
taller portion of the sensor assembly which enables the sensors
331A to measure the areas very close to the plating surface. Each
sensor 331A of a second row is positioned directly underneath a
respective sensor 331A of the first row and has a distance D2 from
the respective sensor 331A of the first row. In one aspect, the
distance D1 may be about 7.5 mm and the distance D2 may be about
7.5 mm. In another embodiment, not shown, the sensors 331A of each
row may be unevenly distributed along the length of the sensor
assembly 330A. In one aspect, a plurality of contacts 341A may be
disposed in a shorter portion of the sensor assembly 330A. Each
contact 341A is in electrical communication with one sensor 331A
and is configured to connect the corresponding sensor with other
circuits, such as the signal sampling and processing circuit 332 in
FIG. 3.
[0055] In one aspect, the sensors 331A and 331B may be positioned
in other arrangements such as at angels (not vertically or
horizontally) relative to each other or any combination of
vertical, horizontal and angular arrangements depending on their
locations relative to the substrate or other elements of the
plating cell. In one aspect, a sensor assembly may be formed in a
coordinate system, such as a 3D coordinate system, a polar
coordinate system, and an elliptical coordinate system, that can
describe an electric field in a plating cell.
[0056] FIG. 3B illustrates a front view of an exemplary sensor
assembly 330B of the plating cell 300 shown in FIG. 3. The sensor
assembly 330B is generally a printed circuit board with an
elongated portion of a different height. A taller portion of the
sensor assembly 330B has three rows of sensors 331B. In one aspect,
the sensors 331B in each row are distributed evenly along the
length of the taller portion of the sensor assembly 330B and are
spaced a distance D3 from one another. In one aspect, the sensors
331B of a first row are positioned close to a top edge of the
taller portion of the sensor assembly which enables the sensors
331A to measure the areas very close to the plating surface. Each
sensor 331B of a second row and of a third row is positioned
directly underneath a respective sensor 331B of the first row and
are spaced a distance D4 from the respective sensor 331B in the row
above. In one aspect, the distance D3 may be about 3.75 mm and the
distance D4 may be about 3.75 mm. In another embodiment, not shown,
the sensors 331B of each row may be unevenly distributed along the
length of the sensor assembly 330B. In one aspect, a plurality of
contacts 341B are generally disposed in a shorter portion of the
sensor assembly 330A. Each contact 341B is in electrical
communication with one sensor 331B and is configured to connect the
corresponding sensor with other circuits, such as the signal
sampling and processing circuit 332 in FIG. 3.
[0057] Other arrangements for the locations of individual sensors
and/or groups of sensors can also be used.
[0058] FIG. 3C illustrates a top view of an exemplary arrangement
of a sensor assembly 330C relative to a substrate 315C being
plated. In one embodiment, one end of the sensor assembly 330C is
positioned near the center of the substrate 315C and the other end
of the sensor assembly 330C is positioned near the perimeter of the
substrate 315C. Sensors in the sensor assembly 331C are distributed
in a straight line across the radius of the substrate 315C such
that the electric field corresponding to a plating thickness across
the substrate 315C can be monitored. In another embodiment, as
shown in FIG. 3D, a plurality of sensor assemblies 330D are
distributed in a spiral pattern across a substrate 315D. This
arrangement enables monitoring both an electric field across the
radius of the substrate 315D and an electric field in different
segments of the plating fluid. Comparing to the arrangement shown
in FIG. 3C, this arrangement also enables a higher sensor density,
especially near the perimeter of the substrate 315D. FIG. 3E
illustrates a top view of another exemplary arrangement of sensor
assemblies 330E of the present invention. A plurality of sensor
assemblies 330E, five as shown in FIG. 3E, are distributed radially
from the center of a substrate 315E. This arrangement enables
monitoring both an electric field across the radius of the
substrate 315E and an electric field in different segments of the
plating solution.
[0059] FIG. 4A illustrates a schematic view of a plating cell 400A
with a uniform electric field. The plating cell 400A generally
comprises an anode 405, a substrate 415 having a conductive seed
layer 425, an electrolyte volume 416, a power supply 421, and an
array of sensors 431.sub.1-4 configured to measure local voltage
levels in the electrolyte volume 416. The power supply 421 is
coupled to the conductive seed layer 425 and the anode 405. Both
the anode 405 and the conductive layer 425 are in contact with a
plating solution retained in the electrolyte volume 416. A uniform
electric field is generated in the electrolyte volume 416 when the
power supply 421 provides a voltage between the conductive layer
425 and the anode 405. The electric field strength is represented
by iso-voltage lines V1, V2, V3 and electric field lines 420. The
iso-voltage lines V1, V2 and V3 are indicative of voltage levels in
the electrolyte volume 416 and are parallel to the seed layer 425.
The electric field lines travel perpendicularly to the voltages
lines indicating an ion flux or currents in the electrolyte volume
416. As shown in FIG. 4A, the sensors 431.sub.1 and 431.sub.3 are
positioned in the same voltage line V2, thus, generally the voltage
measured between 431.sub.1 and 431.sub.3 will equal zero since the
difference voltage values .DELTA.V will be V2-V2. Sensors 431.sub.1
and 431.sub.2, on the other hand, are positioned in the iso-voltage
lines V2 and V3 respectively, thus, will generally output voltage
values reflecting V2 minus V3 respectively. Since sensors 431.sub.1
and 431.sub.2 are positioned in the same electric field line
420.sub.1, the differential voltage between voltage values at
431.sub.1 and at 431.sub.2 is associated with the current value of
the electric field line 420A in the form of,
local current density = differential voltage between sensors (
geometry constant ) .times. ( electrolyte resistance ) .times. (
distance between sensors ) ( equation 1 ) ##EQU00001##
In this case, when the plating cell 400A has a uniform electric
field, measuring voltage drop between sensors by positioning two
sensors in the electrolyte volume 416 allows estimating the local
current density. The local current density can then be correlated
to a total charge and a local plating thickness.
[0060] As described in relation to FIG. 2, the electric field in
the plating cell may be a non-uniform field, especially near the
perimeter of a plating surface. FIG. 4B illustrates a schematic
view of a plating cell 400B with a non-uniform electric field. The
plating cell 400B generally comprises an anode 405B, a substrate
415B having a conductive seed layer 425B, an electrolyte volume
416B, a power supply 421B, and an array of sensors 431.sub.5-12
configured to measure local voltage levels in the electrolyte
volume 416B. The power supply 421B is coupled to the conductive
seed layer 425B and the anode 405B. Both the anode 405B and the
conductive layer 425B are in contact with a plating solution
retained in the electrolyte volume 416B. A electric field which in
some cases may be non-uniform is generated in the electrolyte
volume 416B when the power supply 421 provides a voltage between
the conductive layer 425B and the anode 405B. The electric field is
represented by iso-voltage lines V1B-V6B and electric field lines
420B. In this example, the electric field lines 420B a distance
away from the surface of the substrate are not perpendicular to the
conductive layer 425B. Thus, local current densities may not be
easily predicted from voltage measurements of sensors perpendicular
to the conductive layer 425B. An additional horizontal component of
a differential voltage may be measured to calculate the current
density. As shown in FIG. 4B, the sensors 431.sub.5, 431.sub.7,
431.sub.9 and 431.sub.11 are positioned in one horizontal line
parallel to the plating surface 425B, the voltage levels measured
between these positions are different due to the non-uniformity of
the electric field. Thus, the horizontal component of a
differential voltage can be obtained by measuring the voltage
difference between two sensors. For example, the voltage levels
measured between sensors 431.sub.5 and 431.sub.7, and between
431.sub.8 and 431.sub.7 can be used to calculate the magnitude and
direction of current density in this region. The horizontal
component dVh can be calculated from dVh=voltage level at
431.sub.5-voltage level at 431.sub.7. The vertical component dVn
can be calculated from dVn=voltage level at 431.sub.8-voltage level
at 431.sub.7. Then the differential voltage dV at 431.sub.7 can be
calculated by a vector summation of dVn and dVh, as shown in FIG.
3C. Then the local current density can be calculated using equation
1.
[0061] However, as shown in FIG. 4C, the differential voltage dV
calculated from dVn and dVh may vary compared to the actual
differential voltage .SIGMA.dV in a non-uniform electric field
partially because the finite distances between the sensors. In one
aspect, this deviation can be compensated by introducing a set of
geometry coefficients, for example, a horizontal geometry
coefficient C1 and a vertically geometry coefficient C2. The
horizontal component dVh and the vertical component dVn are first
multiplied by C1 and C2 respectively, then summed together to
obtain the actual differential voltage .SIGMA.dV. Equation 2
provides a scalar form of this calculation: .SIGMA.dV= {square root
over ((C.sub.1dVh).sup.2+(C.sub.2dVn).sup.2)}{square root over
((C.sub.1dVh).sup.2+(C.sub.2dVn).sup.2)} (equation 2). Applying
geometry coefficients in obtaining differential voltage of a
non-uniform electric field has been proven to be effective and
methods of identifying geometry coefficients will be described
below.
[0062] Referring to FIG. 4B, local current density in the middle of
the electrolyte volume 416B may be significantly different from the
local current density near the conductive layer 425B. Thus, it is
desirable to position the sensors 431 close to the conductive layer
425B to calculate plating thickness from differential voltages
measured by the sensors 431.
[0063] FIG. 4D illustrates an exemplary embodiment of method of
generating a thickness profile measurement from measured
differential voltages. A thickness profile measurement can be
depicted by use of a 2D curve with an x-axis indicates the distance
to the center or edge of a substrate and a y-axis indicates a
thickness of plated material. In step 454, current across the
x-axis is calculated from measured differential voltages. This step
may be contacted in two parts. First, for each sample point, an
actual differential voltage is calculated from measured horizontal
and vertical voltages between two or more sensors and a set of
geometry coefficients is calculated by using an mathematical model,
such as, for example, equation 2. Then a local current density is
calculated using equation 1. The voltage levels at each sample
point may be periodically sampled during the course of a plating
process. Thus, a set of local current density values may be
obtained for each sample point.
[0064] In step 456 of FIG. 4D, for each sample point, a total
charge is obtained by integrating the local current over plating
time. The integral may be approximated by a summation,
Total charge (t)=.SIGMA.(1(t).DELTA.A (Equation 3)
where .DELTA.A indicates a corresponding area on the substrate or a
distance along the radius for each sample point and i is local
current density at each sample point.
[0065] In step 458, the total charge at each sample point is
correlated to a thickness of plated material by calculation or
through an empirical look up table. For example, in a process that
Cu.sup.2+ ions are being plated on the substrate. It is known that
for a copper crystal: a=b=c=361.49 pm=3.6149 .ANG.. Thus, the
volume of a unit cell is 47.23 .ANG..sup.3. Since there are four
(4) atoms in a unit cell and two (2) charges per atom, the total
charge required to deposit a unit cell is: 4 atoms*2 charges*1.6
e.sup.-19 Coulombs. The total charge required to deposit a
thickness of 3.6149 .ANG. (i.e. a layer of unit cells) on a sample
area is 4 atoms*2 charges*1.6 e.sup.-19*sample area/3.6149
.ANG./3.6149 .ANG. Coulombs.
[0066] In step 460, a thickness profile is generated from
calculated thickness of plated material from step 458. In one
aspect, the thickness profile may be calculated by adding the
plated thickness to an initial thickness, as shown in equation
4.
Thickness=Initial Thickness+Thickness of plated Material (Equation
4)
[0067] A thickness profile may be generated by integrating current
in the electrolyte over plating time. Current values may be
calculated from differential voltages in the electrolyte.
Differential voltages can be obtained by measuring voltage
differences between sensors using a differential voltage device.
One implementation of a differential voltage measuring device,
shown in FIG. 5, senses and amplifies voltage differences between
sensors, then converts amplified differential voltages to a digital
signal. In this implementation, a plurality of high input impedance
differential amplifiers 503 are used to measure and amplify voltage
differences between sensors. For each high input impedance
differential amplifier 503, each of the two input pins is connected
to a resistor 501 which connects to a sensor 331; a resistor
502.sub.1 connects the negative input pin of 503 to the output pin
of 503; the positive input pin of 503 connects to the ground
through a resistor 502.sub.2. The voltage differences between the
sensors 331 corresponding to the input pins is amplified by
R.sub.502/R.sub.501 times. For example, the resistors 502 may have
a resistance of 100 k ohms and the resistors 501 may have a
resistance of 1 k ohms. The voltage difference between the input
pins may be amplified by 100 times. As shown in FIG. 5, the high
input impedance differential amplifiers 503 may be used to sense
and amplify horizontal and vertical components of differential
voltages. The outputs of the high input impedance differential
amplifiers 503 are then connected to input pins of one or more
multiplexers 504 and be sequenced and input to an A/D converter
505. In one aspect, the A/D converter 505 may be a 12-bit A/D
converter. The output of the A/D converter 506 is then connected to
a computer 506 through a data bus. The computer 506 may have a
program that can use the measured differential voltages to generate
a real time thickness profile, identify a set of geometry
coefficients, control a plating process, optimize a plating
process, and more. Embodiments of methods and apparatus of
utilizing the differential voltages in an electrochemical process
are given in FIGS. 6-11.
[0068] FIG. 6 illustrates an exemplary embodiment of identifying a
set of geometry coefficient. In this embodiment, an original
thickness (of a seed layer) may be measured using a thickness
measuring device, for example, through surface resistivity or x-ray
reflectivity measurements. Then start a plating process in a
plating cell with an array of sensors disposed in the electrolyte.
Differential voltages are measured periodically using the sensors
and data collecting devices discussed above in conjunction with
FIGS. 3-5 till the end of the plating process. A final thickness
profile can then be measured using the thickness measuring device.
Initial values can then be chosen for a set of geometry
coefficients. Next, in step 620, a generated thickness profile can
be obtained from the measured differential voltages, the geometry
coefficients and the original thickness profile, as described in
FIG. 4D. In step 622, the generated thickness profile is compared
to the measured thickness profile obtained in step 616. An error
profile or a parameter indicating the difference between the
generated and measured thickness profiles is evaluated in step 624.
If the error or the difference exceeds a limit of a predetermined
tolerance, for example, a maximum error, step 626 is executed and
new values geometry coefficients are given. Steps 620, 622, 624,
and 626 will be run iteratively until the error or the difference
is within a limit of a predetermined tolerance. Then the process
will stop and the geometry coefficients are identified. Empirical
results have shown that geometry coefficients mainly depend on
electrolyte conductivity. Initial resistivity of a substrate may
have a small influence on the geometry coefficients too. Thus, once
identified, a set of geometry coefficient can be applied to
generate thickness profile for plating processes having the same
electrolyte conductivity and similar substrate initial
resistivity.
[0069] FIG. 7 illustrates an embodiment of the present invention
for generating real time thickness profiles during a plating
process. An original thickness profile may be measured by a probe
before the plating process, as described in step 710. In one
aspect, step 710 may be done only once for a batch of substrates
where incoming layer thickness may not vary that much. In step 720,
an electrochemical plating process is stated in a plating cell
having an array of sensors disposed in the electrolyte. After the
plating process has started, steps 730-780 may be performed
periodically or in variable frequencies depending on process
parameters. Step 730 involves sampling differential voltage data,
for example, horizontal differential voltages (dVh) and vertical
differential voltages (dVn). Step 740 may comprise calculating
actual differential voltages from the differential voltage data
using a set of geometry coefficients, and calculating current
densities form the actual differential voltages. Step 750 generally
includes integrating the current densities over the sample time to
obtain total charge values. Step 760 generally includes correlating
the total charge values to plated thickness values. Step 770
generally includes updating the thickness profile by adding the
plated thickness values. In step 780, the updated thickness profile
may be plotted or presented in other manners, thus enables
automatic or interactive adjust the plating process.
[0070] FIG. 8 illustrates an embodiment of the present invention
for achieving uniform thickness during an electrochemical plating
process. In step 810, an electrochemical plating process is
performed in a plating cell having an array of sensors disposed
therein. After the plating process has started, steps 820-850 may
be performed periodically or in variable frequencies depending on
process parameters. Step 820 involves sampling differential voltage
data, for example, horizontal differential voltages and vertical
differential voltages. In step 830, a real time thickness profile
is generated. In one aspect, this step can be implemented as
described in steps 740 to 770 in FIG. 7. Step 840 generally
includes analyzing the real-time thickness profile and determining
uniformity of the plated surface. In determining uniformity,
geometry features of the thickness profile, such as flatness, may
be calculated, and high and low points in profile may be marked. In
step 850, one or more process parameters may be adjusted according
to the surface uniformity. It is to be noted, if uniformity is
satisfactory, process parameters not need to be adjusted. Process
parameters that may be adjusted include, but are not limited to one
or more of current set point, anode timing, thief current, head
spacing, current and timing of anode elements. Detailed information
of anode elements are described in the U.S. Provisional Patent
Application Ser. No. 60/684,444, filed on May 25, 2005 under the
title "Electroplating apparatus based on an array of anodes" which
is incorporated herein by reference of its entirety.
[0071] FIG. 9 illustrates an embodiment of the present invention
for achieving a desired thickness profile during an electrochemical
plating process. In step 910, an electrochemical plating process is
performed in a plating cell having an array of sensors disposed
therein. After the plating process has started, steps 920-960 may
be performed periodically or in variable frequencies depending on
process parameters. Step 920 involves sampling differential voltage
data, for example, horizontal differential voltages and vertical
differential voltages. In step 930, a real time thickness profile
is generated. In one aspect, this step can be implemented as
described in steps 740 to 770 in FIG. 7. In step 940, the real time
thickness profile is compared to a desired thickness profile
obtained and an error profile or a parameter indicating the
difference between the real time thickness profile and the desired
thickness profiles is obtained. If the error or the difference
exceeds a limit of a predetermined tolerance, for example, a
critical error, step 960 is performed. When the error or the
difference is within a limit of a predetermined tolerance, the
plating process will stop. Step 960 determines if the process
parameters that need to adjusted. In one aspect, determining
process may include analyzing the error profile. In step 970, one
or more process parameters may be adjusted according to the error
profile. Adjusting process parameters may be one or more of current
set point, anode timing, thief current, head spacing, current and
timing of anode elements.
[0072] FIG. 10 illustrates an embodiment of the present invention
for monitoring the process of immersing a substrate into a plating
solution of a plating cell. During step 1010, a cathodic voltage
bias is generally applied between the substrate and an anodically
biased electrode (anode). During step 1020, the substrate is being
immersed into the plating cell having an array of sensors disposed
therein. In step 1030, differential voltages of the plating
solution is monitored by sampling and processing signals from the
sensors. Step 1040 generally includes determining the immersing
status of the substrate and/or generating a thickness profile. As a
substrate is immersed in the plating solution, thus electrical
communication is established, the one or more sensors in the array
of sensors is noted so that difference between various regions of
the substrate can be compensated for during the process. A real
time thickness profile can also be generated, for example, by a
process described in steps 740-770. In step 1050, the bias may be
adjusted according to the immersing status. When the anode is
segmented, bias of each segment of anode may be adjusted
independently. The process described in FIG. 10 may be added to the
processes described in FIGS. 7-9.
[0073] FIG. 11 illustrates an exemplary embodiment of an
electrochemical plating system 1100 of the present invention. The
system 1100 generally comprises an electrochemical plating cell
1110 and a control unit 1120 coupled to the plating cell 1110 such
that various process variables can be monitored by the control unit
1120 and the control unit 1120 can send control signals to the
plating cell 1110 to adjust process variables to control the
plating results. The control unit 1120 generally comprises a data
sampling and processing device 1130, a real time thickness profile
generator 1122, and a process optimization module 1124. The plating
cell 1110 may have a plurality of sensors the data sampling and
processing device 1130 of the control unit 1120. The plurality of
sensors may include an array of sensors disposed in an electrolyte
of the plating cell 1110 and configured to measure differential
voltages in the electrolyte. The data sampling and processing
device 1130 is configured to sample and process the signals from
the plurality of sensors and output processed process variables to
the process optimization module 1124. The processing variables may
comprise, for example, but are not limited to differential
voltages, bath temperature, wafer height, acidity, head rotation,
tilt angle, and anode condition. In one aspect, the data sampling
and processing device 1130 may output differential voltage
measurements to the real time thickness profile generator 1122
which is configured to generate real time thickness profiles and
output to the process optimization module 1124. The real time
thickness profile generator 1122 may comprise software and/or
hardware to implement processes described in FIGS. 7 to 10. The
process optimization module 1124 may include software and/or
hardware to optimize the plating process conducted in the plating
cell 1110 by sending a plurality of control signals which may
include, for example, current set point, anode timing, anode
segment control signal, thief current, head spacing. FIG. 11A
illustrates an exemplary embodiment of the process optimization
module of the electrochemical plating system shown in FIG. 11. The
process optimization module 1124A may have a plurality of input
variables and a plurality of output variables. The input variables
may include, for example, real time thickness profile, bath
temperature, wafer height, acidity, head rotation, tilt angle, and
anode condition. The output variables may include, for example,
current set point, anode timing, anode segment control signal,
thief current, head spacing. In one embodiment, the process
optimization module 1124A may be a multi input multi output
software model that uses a predictive algorithm which determines a
plurality of output variables required to converge to a desired
plating result according to a plurality of input variables.
[0074] FIG. 12 illustrates an exemplary embodiment of a
characterization tool 1200 of the present invention. The
characterization tool 1200 is a special wafer that has metal
patches 1201 at different radius of the wafer 1200. Each patch 1201
is connected to a connection point 1203 on a perimeter of the wafer
1200 by a metal trace 1202 on the wafer. The metal trace 1202 are
covered by a dielectric material such that when the wafer 1200 is
in contact with an electrolyte, the metal trace 1202 does not make
contact with the electrolyte. In one aspect, the wafer 1200 may be
disposed to be plated in an electroplating cell with the connection
points 1203 aligned with contact pins on an contact ring of the
electroplating cell. A current on each metal patch 1201 may be
measured down stream from a corresponding contact ring. In one
aspect, the current value measured from a contact ring can be
compared with a current value measured by corresponding sensors of
along the same radius. In one aspect, the sensors accuracy may be
characterized. In another aspect, the comparison results may be
used to calibrate and "correct" the sensor readings. The wafer 1200
may also be used to characterize a plating cell or an anode
assembly. In one embodiment, the patches 1201, the trace 1202 and
the connection point 1203 are made of copper. In one aspect, the
patches 1201 may have a size of 2 mm.sup.2. The patches 1201 and
the connection points 1203 may be arranged in different ways.
[0075] FIG. 13 illustrates a schematic sectional view of an
exemplary plating cell of the present invention. The
electrochemical plating cell 2100 generally includes a basin
assembly 2101 configured to contain a plating solution that is used
to plate a metal, e.g., copper, onto a substrate 2107 during an
electrochemical plating process. During the plating process, the
plating solution is generally continuously supplied to the basin
assembly 2101, and therefore, the plating solution continually
overflows out of the basin assembly 2101 and is collected and
drained for chemical management and/or recirculation.
[0076] The basin assembly 2101 generally includes basin walls 2134,
a basin base 2135 and a base member 2133, configured to contain an
electrolyte and direct a flow circulation for the electrolyte
contained therein. The basin walls 2134 may define a cylindrical
volume. The basin base 2135 is generally an annular disk attached
to the basin walls 2134 near an end of the basin walls 2134. The
basin base 2135 may have a central aperture and may have a
plurality of fluid inlets/drains 2137 connected thereto and
configured to individually supply or drain the fluid in the basin
assembly 2101. The base member 2133 is generally disposed in the
central aperture of the basin base 2135 and generally includes a
disk shaped recess formed into a central portion configured to
receive an anode assembly 2120. The base member 2133 may include
trenches and slots which may form fluid conduits connected in fluid
communication with the plurality of inlets/drains 2137. The anode
assembly 2120 is generally disposed in the recess of the basin base
2133.
[0077] A membrane support assembly 2114 is generally disposed above
the anode assembly 2120 in the basin assembly 2101. The basin
assembly 2101 defines a volume which may be divided into an anolyte
chamber 2102 and a catholyte chamber 2103 by a membrane 2116
stretched on top of the membrane support assembly 2114. A diffusion
plate 2113 may be disposed above the membrane 2116 and a collimator
2111 may be disposed above the diffusion plate 2113. A contact ring
2105 having a plurality of contact pins 2109 is positioned near the
top of the catholyte chamber 2103 and is vertically movable
relative to the cell body 2101. The contact pins 2109, configured
to apply a bias near the perimeter of a substrate 2107 to be
plated, are in electrical communication with a first terminal 2106
of a power supply 2104. A second terminal 2108 of the power supply
2104 is in electrical communication with the anode assembly 2120.
The power supply 2104 may be a single power source with multiple
output channels or single power source with multiple switches or
may be multiple power sources.
[0078] The membrane support assembly 2114 generally includes an
interior region configured to allow fluids to pass therethrough and
may comprise an upper support 2115 and a lower support 2117. The
lower support 2117 generally secured at an outer periphery of the
base member 2133 may be constructed by a series of parallel bars
configured to support the upper support 2115 and the membrane 2116
and to direct the flow in the anolyte chamber 2102. The membrane
2116 is stretched across the upper support 2115 disposed on top of
the lower support 2117. The membrane 2116 generally operates to
fluidly separate the catholyte chamber 2103 (positioned adjacent
the substrate 2107 being plated) and the anolyte chamber 2102
(positioned adjacent the anode assembly 2120). The upper support
2115 may include an o-ring type seal positioned near a perimeter of
the membrane 2116, wherein the seal is configured to prevent fluids
from traveling from one side of the membrane 2116 secured on the
upper support 2115 to the other side of the membrane 2116. As such,
membrane 2116 generally provides fluid isolation between the
anolyte chamber 2102 and the catholyte chamber 2103 of the plating
cell 2100, i.e., via use of a cationic membrane. Exemplary
membranes that may be used to fluidly isolate an anolyte from a
catholyte. Alternatively, membrane 2116 may be a fluid permeable,
filter-type membrane that allows fluids to pass therethrough. In
one embodiment, the electroplating cell 2100 may be a single
chamber plating cell without the membrane assembly 2114.
[0079] The diffusion plate 2113, which is generally a ceramic or
other porous disk shaped member or other fluid permeable
electrically resistive member, generally operates as a fluid flow
restrictor to even out the flow pattern across the surface of the
substrate. Once the plating solution is introduced into the
catholyte chamber 2103, the plating solution travels upward through
the diffusion plate 2113. Further, the diffusion plate 2113
operates to resistively damp electrical variations in the
electrochemically active area of the anode assembly 2120 or surface
of the membrane 2116, which is known to reduce plating
uniformities.
[0080] The collimator 2111 having an annular shape is generally
disposed above the diffusion plate 2113 and below the contact ring
2105. The collimator generally 2111 has a diameter smaller than
that of the substrate 2107 and is configured to constrain the
electric field in the catholyte chamber 2103.
[0081] In one embodiment of the present invention, the anode
assembly 2120 may include a plurality of anode elements 2127 which
are arranged in the form of an array which can be biased
independently. The anode elements 2127 are generally conductive
metal plates which may be made of copper, titanium, platinum,
platinum coated titanium, or any other metal or conductor. The
anode elements 2127 have an anode surface and can be a variety of
shapes, including the shape of a triangle, a rectangle, a square, a
circle, or a hexagon and may be arranged in hexagonal, rectangular,
square, and circular arrangements. Hexagonal arrangements may have
particular advantages as described below.
[0082] In one aspect, an anode frame 2119 having a disk shape with
a plurality of openings 2128 that define a pattern of an
arrangement may be used to secure the arrangement of the anode
elements 2127. In one embodiment, the anode element 2127 may have a
rod extending from an opposite side of the anode surface. The rod
being smaller in size than the anode plate enables each of the
anode elements 2127 to be supported and held in place by one of the
openings 2128. Each of the anode elements 2127 may further be
secured by a nut 2131 from an opposite side of the anode frame
2119. A seal 2129 may be used in each of the openings 2128 to
prevent the fluid in the anolyte chamber 2102 from leaking through
the openings 2128. An anode base 2135 having a central aperture is
attached to the anode frame 2119 near the perimeter of the anode
frame 2119. The anode frame 2119 and the anode base 2125 may form a
chamber 2110 configured to house the nuts 2131 and wirings to power
the anode elements 2127. A printed circuit board 2123 with the same
pattern of openings as the anode frame 2119 may be used to connect
each of the anode elements 2127 to a respective power source in the
power supply 2104. In one aspect, a foil 2121 having the same
arrangement but larger openings may be used to detect leakage of
the fluid in the anolyte chamber 2102. The anode base 2119, the
foil 2121 and the printed circuit board 2123 are generally stacked
together with their openings in alignment so that the anode
elements are isolated from each other and are connected to the
power supply 2104 independently.
[0083] In one aspect, the printed circuit board 2123 may have
different designs to connect different anode elements 2127 in
certain geometric patterns. For example, the anode elements 2127
may be divided into a plurality of zones by the printed circuit
board 2123 and the anode elements 2127 in each zone may be biased
by the same power source. In one aspect, each zone may be a
discrete circle or a discrete ring formed by multiple anode
elements 2127. This concentric ring arrangement is advantageous in
implementing a symmetrical patterned bias with limited power
sources without producing small rings of unbiased areas in a
plating surface as do concentric anode rings. In one aspect, the
zones may be a series of parallel strips formed by multiple anode
elements. This stripped zone arrangement is advantageous in
implementing non-symmetrical patterned bias particularly during an
immersing process.
[0084] In one aspect, the printed circuit board 2123 may be used to
mount power chips to control switching of individual anode element
2127. The power chips may be used to simplify requirements for the
power supply 2104, or implement various bias patterns, or enables
speedy switching functions.
[0085] In one embodiment, not shown, individual anode element 2127
may be connected to the power source 2104 by insulated wire
conductors in stead of the printed circuit board 2123.
[0086] FIG. 14 illustrates a schematic sectional and partial
perspective view of one embodiment of an anode assembly 3220. Only
the anode assembly 3220 and a partial basin assembly 3201 of an
electrochemical plating cell are shown in FIG. 14. The anode
assembly 3220 is generally disposed in the partial basin assembly
3201. An array of anode elements 3227 is generally disposed in an
anode frame 3219. Each of the anode elements 3227 is secured to the
stack of the anode frame 3219, a foil 3221, and a printed circuit
board 3223 by a conductive nut 3233. In one embodiment, the anode
elements 3227 have a shape of a bolt with a hexagonal head. The
heads of the anode elements 3227 serve as individual anodes with a
hexagonal plate. The anode elements 3227 are packed in a hexagonal
arrangement. In one embodiment, the anode elements 3227 may be M12
bolts plated with platinum.
[0087] While the foregoing is directed to embodiments of the
present invention, other and further embodiments of the invention
may be devised without departing from the basic scope thereof, and
the scope thereof is determined by the claims that follow.
* * * * *