U.S. patent application number 10/988646 was filed with the patent office on 2006-05-18 for current collimation for thin seed and direct plating.
Invention is credited to John O. Dukovic, Harald Herchen, Lily Pang.
Application Number | 20060102467 10/988646 |
Document ID | / |
Family ID | 36051497 |
Filed Date | 2006-05-18 |
United States Patent
Application |
20060102467 |
Kind Code |
A1 |
Herchen; Harald ; et
al. |
May 18, 2006 |
Current collimation for thin seed and direct plating
Abstract
A method and apparatus for plating a conductive material onto a
substrate is provided. The apparatus includes a fluid processing
cell having a fluid basin configured to contain an electrolyte
solution and having an opening configured to receive a substrate
for processing, an anode assembly positioned in the fluid basin,
and a collimator positioned in the fluid basin between the anode
assembly and the opening.
Inventors: |
Herchen; Harald; (Los Altos,
CA) ; Dukovic; John O.; (Palo Alto, CA) ;
Pang; Lily; (Fremont, CA) |
Correspondence
Address: |
PATTERSON & SHERIDAN, LLP
3040 POST OAK BOULEVARD, SUITE 1500
HOUSTON
TX
77056
US
|
Family ID: |
36051497 |
Appl. No.: |
10/988646 |
Filed: |
November 15, 2004 |
Current U.S.
Class: |
204/230.2 |
Current CPC
Class: |
C25D 17/007 20130101;
C25D 17/001 20130101; C25D 7/123 20130101; C25D 17/008
20130101 |
Class at
Publication: |
204/230.2 |
International
Class: |
C25C 3/16 20060101
C25C003/16; C25B 9/00 20060101 C25B009/00; C25D 17/00 20060101
C25D017/00 |
Claims
1. A fluid processing cell, comprising: a fluid basin configured to
contain an electrolyte solution and having an opening configured to
receive a substrate for processing; an anode assembly positioned in
the fluid basin; and a collimator positioned in the fluid basin
between the anode and the opening.
2. The fluid processing cell of claim 1, wherein the collimator
comprises a plurality of electrically insulative fluid
conduits.
3. The fluid processing cell of claim 2, wherein the fluid conduits
are positioned such that a longitudinal axis of each of the
conduits is parallel to each of the other longitudinal axes of the
conduits.
4. The fluid processing cell of claim 1, wherein the collimator
comprises a plurality of fluid conduits positioned such that a
longitudinal axis of each of the conduits is generally
perpendicular to an upper surface of the anode assembly.
5. The fluid processing cell of claim 3, wherein an upper
terminating end of the conduits is positioned between about 0.5 mm
and about 15 mm from a substrate processing position.
6. The fluid processing cell of claim 5, wherein a lower
terminating end of the conduits is positioned between about 0.5 mm
and about 15 mm from at least one of the anode assembly and a
membrane positioned across the fluid basin between the anode
assembly and the opening.
7. The fluid processing cell of claim 6, wherein a horizontal cross
section of an individual conduit is at least one of a circle,
square, triangle, hexagon, pentagon, or other polygon.
8. The fluid processing cell of claim 2, wherein the fluid conduits
are circular and have an interior diameter of between about 1 mm
and about 10 mm.
9. The fluid processing cell of claim 1, wherein the anode assembly
comprises a plurality of individually powered polygon shaped anode
members that cooperatively form a substantially planar upper anode
surface.
10. An electrochemical plating cell, comprising: a cell body
configured to contain a plating solution therein and having an
opening configured to receive a substrate for plating; an anode
assembly positioned in the cell body such that the anode assembly
is in electrical communication with the plating solution; and an
electric field collimator positioned in the cell body between the
anode assembly and the opening, the collimator comprising a
plurality of electrically insulative fluid conduits having
substantially parallel longitudinal axes.
11. The electrochemical plating cell of claim 10, wherein each of
the plurality of electrically insulative fluid conduits has an
inner diameter of less than about 20 mm.
12. The electrochemical plating cell of claim 10, wherein each of
the plurality of electrically insulative fluid conduits has an
inner diameter of between about 1 mm and about 10 mm.
13. The electrochemical plating cell of claim 10, wherein an upper
surface of the electric field collimator is positioned between
about 0.5 mm and about 20 mm from a substrate processing
position.
14. The electrochemical plating cell of claim 10, wherein a lower
surface of the electric field collimator is positioned between
about 2 mm and about 20 mm from at least one of an upper surface of
the anode assembly and a membrane positioned across the cell body
between the anode assembly and the opening.
15. The electrochemical plating cell of claim 10, wherein the
electric field collimator comprises more than about 500
electrically insulative fluid conduits.
16. The electrochemical plating cell of claim 15, wherein the
diameter of the collimator is between about 275 mm and about 325
mm.
17. The electrochemical plating cell of claim 16, wherein the
opening is sized to receive a substrate having a diameter greater
than about 275 mm.
18. The electrochemical plating cell of claim 10, wherein the
electric field collimator occupies between about 50% and about 99%
of vertical space between the anode assembly and the substrate.
19. The electrochemical plating cell of claim 10, wherein the
electric field collimator comprises a disk shaped insulative
material having a plurality of bores formed therethrough which
define the fluid conduits.
20. The electrochemical plating system of claim 10, wherein the
anode assembly comprises a plurality of individually powered square
shaped anode members, each of the square shaped anode members
having an electrically insulating spacer positioned around the
perimeter thereof.
21. A method for plating a conductive material onto a substrate,
comprising: generating an electric field between an anode
positioned in a plating cell and a substrate being plated in the
plating cell; collimating the electric field in a substantially
linear direction between the anode and the substrate; and plating
the conductive material onto the substrate.
22. The method of claim 21, wherein collimating further comprises:
receiving the electric field into a first opening of an
electrically insulating collimator; transmitting the electric field
to a second opening of the collimator via a substantially linear
fluid conduit connecting the first and second openings; and
transmitting the electric field toward the substrate from the
second opening.
23. The method of claim 22, wherein the second opening is
positioned between about 0.5 mm and about 20 mm from the
substrate.
24. The method of claim 22, wherein the first opening is positioned
between about 1 mm and about 20 mm from the anode.
25. The method of claim 22, wherein the substantially linear fluid
conduit connecting the first and second openings has a longitudinal
axis that is generally perpendicular to an upper surface of the
anode.
26. The method of claim 22, wherein the electrically insulating
collimator occupies between about 50% and about 99% of vertical
space between the anode and the substrate.
27. The method of claim 21, generating the electric field comprises
individually powering a plurality of polygon shaped anode
members.
28. The method of claim 27, further comprising controlling plating
uniformity by controlling power application to the individual anode
members.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] Embodiments of the invention generally relate to an
electrochemical plating cell having an electric field collimator
positioned between the anode and the substrate being plated.
[0003] 2. Description of the Related Art
[0004] 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.
[0005] 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.
[0006] 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 heighten the terminal
effect, as the decreased thickness of the seed layer further
increases the resistivity of the layer.
[0007] Therefore, there is a need for an electrochemical plating
cell and method for plating onto semiconductor substrates, wherein
the plating cell and method are configured to eliminate the
terminal effect.
SUMMARY OF THE INVENTION
[0008] Embodiments of the invention generally provide an
electrochemical plating cell having a collimator positioned between
the anode of the cell and a substrate positioned in the cell for
plating. The collimator operates to channel the electric field
traveling from the anode to the substrate, such that the electric
field travels in a substantially linear path. The plating cell of
the invention further provides for a zoned anode, wherein each of
the zones comprises a non-concentrically shaped anode element.
[0009] Embodiments of the invention may further provide a method
and apparatus for plating a conductive material onto a substrate.
The apparatus includes a fluid processing cell having a fluid basin
configured to contain an electrolyte solution and having an opening
configured to receive a substrate for processing, an anode assembly
positioned in the fluid basin, and a collimator positioned in the
fluid basin between the anode and the opening.
[0010] Embodiments of the invention may further provide an
electrochemical plating cell having a cell body configured to
contain a plating solution therein and having an opening configured
to receive a substrate for plating. The cell further includes an
anode assembly positioned in the cell body such that the anode
assembly is in electrical communication with the plating solution,
and an electric field collimator positioned in the cell body
between the anode assembly and the opening, the collimator
comprising a plurality of electrically insulative fluid conduits
having substantially parallel longitudinal axes.
[0011] Embodiments of the invention may further provide a method
for plating a conductive material onto a substrate, wherein the
method includes generating an electric field between an anode
positioned in a plating cell and a substrate being plated in the
plating cell, collimating the electric field in a substantially
linear direction between the anode and the substrate, and plating
the conductive material onto the substrate.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] 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.
[0013] FIG. 1 illustrates a schematic view of a conventional
plating cell and the electric field lines generated therein.
[0014] FIG. 2 illustrates a schematic sectional view of a plating
cell of the invention having a collimator positioned therein.
[0015] FIG. 3A illustrates a plan view of an exemplary collimator
of the invention using circular conduits
[0016] FIG. 3B illustrates a plan view of an exemplary collimator
of the invention using octagonal conduits.
[0017] FIG. 3C illustrates a plan view of an exemplary collimator
of the invention using hexagonal conduits.
[0018] FIG. 3D illustrates a plan view of an exemplary collimator
of the invention using square conduits.
[0019] FIG. 3E illustrates a plan view of an exemplary collimator
of the invention using triangular conduits.
[0020] FIG. 4 illustrates a sectional view of an exemplary plating
cell of the invention having a collimator in the cell.
[0021] FIG. 5A illustrates a top perspective view of an exemplary
anode assembly in the plating cell of the invention.
[0022] FIG. 5B illustrates a sectional view of the exemplary anode
assembly of the plating cell of the invention.
[0023] FIG. 5C illustrates a sectional/schematic view of the anode
assembly of the invention with schematic representation of the
power supply connections to the individual anode members.
[0024] FIG. 5d illustrates an electrical resistance schematic view
of an exemplary plating cell of the invention.
[0025] FIG. 6 illustrates partial sectional view of the exemplary
anode assembly of the invention including an anode adjustment
member.
[0026] FIG. 7 illustrates a plating thickness plot for a plating
cell incorporating the collimator of the invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0027] FIG. 1 illustrates a schematic view of a conventional
plating cell 100 and the electric field lines generated therein.
The conventional plating cell 100 generally includes a fluid basin
101 configured to contain a fluid volume 102, which is generally an
electrolyte plating solution. An anode 104 is positioned in a lower
portion of the fluid basin 101 and a substrate 106 that is to be
plated is generally positioned across an upper open portion of the
cell 100. The substrate 106 is supported by a contact ring that is
configured to electrically contact the plating surface 108 of the
substrate 106 near the perimeter of the substrate 106 via one or
more electric contact elements 110. The electric contact elements
110 are in electrical communication with a cathodic terminal of a
power supply 114, while the anodic terminal of the power supply is
in electrical communication with the anode 104. Further details of
the conventional plating cell 100 may be found in commonly assigned
U.S. Pat. No. 6,271,433, which is hereby incorporated by reference
in its entirety to the extent not inconsistent with the present
invention.
[0028] FIG. 1 also illustrates the electric field lines 112
generated during a plating process in the conventional plating cell
100. As noted above, the substrate plating surface 108 has a thin
conductive seed layer deposited thereon and the electric field
lines 112 inherently converge toward the electrical contact
elements 110 as a result of the least resistive path between the
anode and the cathode being toward the perimeter of the substrate
proximate the contact elements 110. 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.
[0029] FIG. 2 illustrates a schematic sectional view of a fluid
processing or plating cell 200 of the invention having a collimator
202 positioned therein. The plating cell 200 generally includes a
fluid basin 206 that defines a fluid volume therein and has an open
upper portion that is configured to receive a substrate 212 for
plating. The basin 206 includes at least one fluid inlet/outlet 208
and an uppermost weir 210 that defines the opening that receives
the substrate 212. The fluid inlets/outlets 208 may be configured
to supply plating solutions, e.g., anolyte and/or catholyte
solutions, to various regions or volumes within the fluid basin
206. The electrolyte (anolyte and/or catholyte solutions) supplied
to the fluid basin generally overflows the uppermost weir 210,
which is positioned above a processing position of the substrate
212 (so that the substrate plating surface 214 is immersed in the
electrolyte contained in the fluid basin 206).
[0030] The lower portion of basin 206 includes an anode assembly
204. The anode electrode assembly 204, which may include several
independently powered electrode elements, as will be further
discussed herein, in electrical communication with an anodic
terminal of a power supply 220. The cathodic terminal of the power
supply 220 is in electrical communication with a substrate contact
ring 222 that is configured to support and electrically contact the
plating surface 214 of the substrate 212. Exemplary contact rings
may be found in commonly assigned U.S. patent application Ser. No.
10/355,479, filed Jan. 31, 2003, entitled "Contact Ring with
Embedded Flexible Contacts", U.S. patent application Ser. No.
10/278,527, filed Oct. 22, 2002, entitled "Plating Uniformity
Control by Contact Ring Shaping" and U.S. Pat. No. 6,251,236, all
of which are hereby incorporated by reference in their entirety to
the extent not inconsistent with the present invention. The plating
cell 200 may optionally include a membrane 216, such as a cationic
membrane, for example, positioned across the interior volume of the
fluid basin 206 between the anode 204 and the substrate 212. When
membrane 216 is implemented, the fluid basin inlet/outlets 208 may
be configured to supply different electrolytes to the volumes above
and below the membrane 216, i.e., a catholyte solution to the
volume above the membrane and an anolyte solution to the volume
below the membrane, for example. An exemplary plating cell
incorporating the membrane separation noted above may be found in
commonly assigned U.S. patent application Ser. No. 10/627,336,
filed Jul. 24, 2003, entitled "Electrochemical Processing Cell",
which is hereby incorporated by reference in its entirety to the
extend not inconsistent with the present invention.
[0031] The collimator 202 may be a single unit when no membrane 216
is implemented, or alternatively, when a membrane 216 is
implemented, a first collimator may be positioned above the
membrane 216 and a second collimator may be positioned below the
membrane 216. Similarly, in embodiments where a membrane 216 is
implemented, a single collimator may be positioned above the
membrane 216, however, in this embodiment, it is desirable to have
the membrane 216 positioned as close to the anode assembly 204 as
possible to prevent electric field divergence (horizontal movement)
from the center of the cell prior to the electric field entering
the collimator 202, as will be further discussed herein.
[0032] The collimator 202, which is illustrated in plan view in
FIG. 3A, generally includes a plurality of elongated conduits
positioned adjacent to each other and having substantially parallel
axes. The plurality of conduits 304 are generally manufactured from
a dielectric material, such as ceramics, PVDF, plastic materials,
Teflon.RTM., or other electrically resistive or insulating
materials that are non-reactive with electrochemical plating
solutions. Each of the conduits 304 forms an elongated hollow
interior region 302 that fluidly communicates one terminating end
of the conduit 304 with an opposing terminating end of the conduit.
The plurality of conduits 304 are affixed together such that the
longitudinal axis of each of the conduits is generally parallel to
each of the other axes of the conduits 304, and further, the axes
of the conduits 304 are generally positioned orthogonal to the
plating surface 214 of the substrate 212 being plated in the
plating cell 200. As such, the longitudinal axes of conduits 304
are generally positioned orthogonal to both the upper surface of
the anode assembly 204 and to the substrate plating surface 214.
The conduits 304 may be affixed together via glue or epoxy process,
via a heat treatment process, a sintering process, or other process
suitable to affix the conduits 304 together such that the assembled
collimator 202 is rigid and capable of supporting its own weight
without substantial deflection or bowing.
[0033] Assembly of the collimator 202 in a manner that prevents
substantial deflection or bowing in a plating process is important
to the operation of the invention. More particularly, as noted
herein, the upper surface 230 of the collimator 202 is preferably
positioned between about 0.5 mm and about 20 mm, or more
particularly, between about 1 mm and about 10 mm, or about 15 mm
away from the plating surface 214 of the substrate 212. This
spacing operates to prevent excessive lateral or horizontal
divergence of the electric field exiting from the conduits 304
before the electric field contacts the plating surface 214. If the
collimator 202 is manufactured in a manner that allows for bowing
or vertical deflection, then the spacing between the collimator 202
and the plating surface 214 will be increased near the middle of
the plating cell, and as a result thereof, horizontal or lateral
movement of the electric filed will be more likely near the center
of the cell as a result of the increased spacing. Allowing the
electric field to diverge away from the center of the cell furthers
the terminal effect, and as such, is undesirable in the present
invention. Thus, vertical rigidity of the collimator 202, i.e., the
ability to retain shape/remain planar under its own weight, and
additionally, under processing conditions that include fluid flow,
is an important aspect of the invention.
[0034] Further, the conduits 304 are generally affixed together in
a manner such that the space 306 between the outer surfaces of the
conduits 304 may also form a conduit from one side of the
collimator 202 to the other side thereof. The space 306 shares a
parallel axis with the other conduits 304, and as such, further
facilitates the electric field channeling of the invention. In
other embodiments of the invention, the collimator 202 may be
manufactured from various shapes of conduits 304 that may or may
not form space 306. For example, conduits 304 may be triangular,
square, pentagonal, hexagonal, heptagonal, octagonal, nonagons,
decagons, or other polygon shapes. For example, FIG. 3B illustrates
a plan view of a collimator 202 of the invention manufactured from
octagonal conduits; FIG. 3C illustrates a plan view of a collimator
202 of the invention manufactured from hexagonal conduits; FIG. 3D
illustrates a plan view of a collimator 202 of the invention
manufactured from square conduits; and FIG. 3E illustrates a plan
view of an exemplary collimator of the invention using triangular
shaped conduits.
[0035] Additionally, other embodiments of the invention contemplate
that the collimator 202 may be formed by boring conduits of varying
cross sectional shapes out of a solid disk of material. For
example, a plurality of circular or other polygon shaped bores may
be formed into a solid disk of material to generate a collimator
202.
[0036] FIGS. 3C, 3D, and 3E include polygon shaped conduits 302
that do not generate any vertical space 306 between the respective
conduits, i.e., these embodiments eliminate the space 306
illustrated in FIGS. 3A and 3B by having the respective conduits
abut directly against each other, and therefore, these embodiments
of collimator 202 do not include the additional conduits formed by
the spaces 306. As such, these embodiments of the collimator 202
provide conduits that are all symmetric and identically shaped,
which may operate to provide a more uniform electric field at the
substrate surface during plating operations as a result of the
elimination of the spaces 306 that are not shaped identically to
the shape of the conduits 302.
[0037] Collimator 202 is generally positioned such that an upper
terminating surface 230 of the collimator 202 is positioned
proximate to and in a generally parallel relationship with the
plating surface 214, and such that a lower terminating surface 240
is positioned proximate to and generally parallel to an upper
surface 235 of the anode assembly 204. The positioning of the upper
and lower surfaces 230, 240 proximate the plating surface 214 and
the upper surface 235 of the anode assembly 204 operates to
restrict horizontal flow or dispersion of the electric field
traveling from the anode 204 to the plating surface 214. The
spacing of the lower surface 240 may be generally the same as the
upper surface, e.g., the spacing between the anode 204 and the
lower surface 204 may be as recited herein with respect to the
spacing between the plating surface 214 and the upper surface 230.
Arrows 222 in FIG. 2 illustrate the electric field flow in a
plating cell 200 of the invention incorporating the collimator 202.
The electric field flow 222 is substantially vertical and has
minimal horizontal movement or dispersion, as the conduits of the
collimator 202 prevent the electric field from traveling
horizontally or dispersing while traveling therethrough. During the
time period when the electric field is entering and exiting the
collimator 202, e.g., when the electric field is traveling from the
anode assembly 204 to the collimator 202 and when the electric
field is traveling from the collimator 202 to the plating surface
214, the electric field is not prevented from dispersing. As such,
it is desirable to minimize the vertical distance 208 between the
collimator and the plating surface 214 and between the collimator
202 and the anode assembly 204, as these distances directly impact
the dispersion ability of the electric field.
[0038] More particularly, in order to minimize horizontal electric
field movement in the plating cell of the invention, the upper and
lower terminating ends 230, 240 are positioned proximate the
plating surface 214 and the upper surface 235 of the anode 204,
respectively. More particularly, the inventors have found that when
the upper terminating end 230 of the collimator 202 is positioned
less than about 15 mm from the plating surface 214, and more
particularly, within about 7 mm, or within about 3 mm from the
plating surface 214, that horizontal electric field movement is
essentially eliminated, i.e., the only area where the electric
field can travel horizontally is in the space 209 between the upper
terminating end 230 of the collimator 202 and the plating surface
214. Since the space 209 is very small as a result of the spacing
between the collimator 202 and the substrate being in the range of
about a 0.5 mm to about a 5 mm gap, there is little area for the
electric field to travel or disperse horizontally. Further,
although the inventors have determined that the closer the upper
terminating end 230 of the collimator 202 is to the plating
surface, the greater the reduction in the horizontal electric field
movement, embodiments of the invention are not limited to
configurations where the collimator 202 is positioned less than
about 15 mm from the plating surface 214. Different processing
conditions and plating requirements may allow for placement of the
collimator 202 farther from the plating surface 214, e.g., between
about 5 mm and about 25 mm away, for example, while still
maintaining acceptable processing results for particular processing
applications.
[0039] Similarly, the positioning of the lower surface 240 of the
collimator 202 close to the membrane 402 also operates to minimize
horizontal electric field movement. For example, in the plating
cell of the invention, membrane 402 operates to transmit the
electric field emitted from the anode 204 therethrough so that the
electric field can travel to the substrate to facilitate the
electrochemical plating process. Positioning the lower surface 240
of the collimator 202 within about 15 mm from the membrane 402
operates to capture the electric field being traveling through the
membrane 402 before the electric field is able to travel
horizontally. Once the electric field is captured by the conduits
of the collimator 202, the electric field is vertically channeled
toward the substrate plating surface. Positioning the collimator
202 closer, i.e., within about 10 mm, for example, from the anode
204 further assists with minimizing electric field divergence in
the plating cell of the invention.
[0040] Another factor that impacts the ability of the invention to
prevent horizontal dispersion of the electric field is the size,
and in particular, the cross sectional width or diameter of the
conduits 302. More particularly, when circular conduits 302 are
implemented, for example, it is desirable to have the cross
sectional diameter of each of the conduits 302 to be less than
about 10 mm, and more particularly, between about 2 mm and about 10
mm, or between about 1 mm and about 5 mm, for example. Smaller
diameters of conduits 302, i.e., less than about 10 mm, have been
experimentally shown to provide improved electric field collimation
and reduced electric field dispersion over larger diameter conduits
302, i.e., greater than about 15 mm for semiconductor processing.
In embodiments of the invention where measurements of diameter are
inapplicable, i.e., where some polygon or triangular shapes are
implemented, then the cross sectional area of the conduit 302
should be minimized. For example, it is desirable to have the cross
sectional area of the conduits to be between about 2 mm.sup.2 and
about 30 mm.sup.2. Additionally, for a 300 mm substrate processing
cell, for example, there will generally be more than about 250 of
the fluid conduits 302 that are used to form the collimator 202. In
embodiments where the inner diameter of the conduits 302 is smaller
and the conduits 302 are closely packed, the number of conduits
used for a 300 mm plating cell may be more than about 500, or more
than about 1000, for example.
[0041] In another embodiment of the invention, the terminating ends
of the conduits 302 may increase or decrease in diameter. For
example, the lower end of the conduits, i.e., the end proximate the
anode, may be funnel shaped in order to gather the electric field.
Both the upper and lower ends may be sized in accordance with the
plating characteristics desired. In this embodiment of the
invention, the upper and lower portions of the conduits may be
larger or smaller than the respective other end.
[0042] In another embodiment of the invention, the collimator 202
is sized and positioned such that the vertical size or height of
the collimator 202 occupies between about 50% and about 99% of the
vertical space between the anode 204 and the substrate 212 being
plated. More particularly, embodiments of the invention contemplate
that the collimator 202 will occupy between about 75% and about 95%
of the vertical space between the anode 204 and the substrate 212,
or between about 80% and about 99% of the space between the anode
and the substrate being plated. These proportions of occupied space
have been shown to substantially reduce terminal effect
plating.
[0043] FIG. 4 illustrates a sectional view of an exemplary plating
cell 400 of the invention having a collimator 202 in the cell 400.
A general description of the components of plating cell 400 may be
found in commonly assigned U.S. patent application Ser. No.
10/268,284, filed Oct. 9, 2002, entitled "Electrochemical
Processing Cell", which is hereby incorporated by reference in its
entirety to the extent not inconsistent with the present invention.
Plating cell 400 generally includes a catholyte volume and an
anolyte volume, where the catholyte volume is generally defined as
the fluid volume in the plating cell 400 that is above the ionic
membrane 402, and where the anolyte volume is generally defined as
the fluid volume in the plating cell 400 that is below the membrane
402 adjacent the anode assembly 404 positioned in the anode base
member 406. However, plating cell 400 differs from the application
cited above in that plating cell 400 does not include a diffusion
member (illustrated as element 210 in the commonly assigned
application). Rather, the diffusion member of the incorporated case
is replaced in the present invention with the collimator 202, as
described above.
[0044] Collimator 202 is generally positioned above the membrane
402 and below the substrate being plated in the catholyte volume
(the fluid volume above the membrane 402) of the plating cell 400,
i.e., between the substrate being plated and the membrane 402. The
lower surface of the collimator 202 is generally positioned between
about 0.1 mm and about 10 mm from the upper surface of the membrane
402. Preferably, the lower surface of the collimator 202 is
positioned between about 0.1 mm and about 5 mm from the upper
surface of the membrane 402, so that the electric field traveling
from the anode toward the substrate being plated does not have
sufficient vertical space to disperse horizontally or radially
outward toward the perimeter or outer wall of the plating cell.
Similarly, as discussed above, the upper surface of the collimator
202 is generally positioned as close as possible to the plating
surface of a substrate positioned in the cell for plating. More
particularly, the upper surface of the collimator 202 may be
positioned between about 0.5 mm and about 10 mm, or between about
0.5 mm and about 5 mm from the plating surface of the substrate.
This narrow spacing prevents the electric field exiting from the
collimator 202 from traveling horizontally (dispersing) toward the
edge of the substrate before contacting the plating surface of the
substrate, i.e., prevents the electric field effects that are known
to cause the terminal effect. Research has shown that placement of
the collimator 202 within about 2 mm and about 10 mm from the
plating surface is sufficient to substantially eliminate the
terminal effect in semiconductor plating processes.
[0045] FIG. 5A illustrates a top perspective view of an exemplary
anode assembly 404 of the plating cell 400 of the invention. The
anode assembly 404, as noted above, is positioned in an anode base
assembly 406 and is configured to work with the collimator 202 to
control electric field density in the plating cell. The anode base
assembly 406 is generally manufactured from an electrically
insulative material that is not reactive with electrochemical
plating solutions. Further details of the construction and
operation of the anode base assembly 406 and surrounding components
may be found in commonly assigned U.S. patent application Ser. No.
10/627,336, filed Jul. 24, 2003, entitled "Electrochemical
Processing Cell", which is incorporated by reference in its
entirety to the extent not inconsistent with the present
invention.
[0046] The anode assembly 404 of the invention generally includes a
plurality of individual anode members 405 that cooperatively form
the anode assembly 404. For example, embodiments of the invention
may include between about 20 and about 200 individual anode members
405 that collectively form the anode assembly 404. The individual
anode members 405 may be manufactured from a soluble conductive
material, such as copper for a copper electrochemical plating
system, or from another material that is soluble in an
electrochemical plating solution. Alternatively, the individual
anode members 405 may be manufactured from an insoluble conductive
material, such as platinum, titanium, or other insoluble metals
amenable to electrochemical plating solutions. Further, the
conductive material of anode members 405 may be coated with another
conductive material, such as platinum, for example. The individual
anode members 405 may be manufactured as square shaped (in plan
view) conductive members, wherein an electrically insulative spacer
408 may be positioned between the respective square shaped anode
members 405 to electrically isolate the anode members 405 from each
other, as illustrated in the sectional view of the anode member in
FIG. 5B. The spacers 408 generally have a thickness of less than
about 3 mm, and more particularly, less than about 1 mm, so that
the surface area on the anode surface that is not electrically
active is minimized, as inactive surface area on the anode has been
shown to facilitate plating uniformity problems, such as the
problems associated with concentric anode configurations where
there is a small non-active space between the concentric rings of
the anode member. The spacers 408 used in the present anode
assembly 404 may be made from any insulative or dielectric material
that is not reactive with electrochemical plating solutions, such
as, PVDF, Teflon.RTM.-type materials, plastics, insulative oxides,
anodized materials, the same material as the anode, etc.
Additionally, the central portion of the anode assembly 404 may
include a collection of anode members 405 that do not have
insulative spacers 408 positioned therebetween, as the inventors
have found that the spacers tend to create low plating areas on the
substrate when positioned proximate the center of the anode
assembly 404.
[0047] The upper surface of each of the respective anode members
405 are generally positioned in a substantially parallel
orientation with each other such that a unitary planar upper anode
surface is generated. Further, each of the respective anode members
405 is also generally in electrical communication with an anodic
terminal of a power supply (as illustrated in FIG. 2). The
electrical power or current applied to each of the respective anode
members 405 may be individually controlled or regulated by a
controller (not shown). The controller may be used to adjust the
resistance of a variable resistor (not shown), for example,
positioned in series electrical connection between each individual
anode member 405 and the power supply. The controller may be a
microprocessor type controller configured to control a processing
sequence, as is generally known in the art. The controller may be
modified, however, to allow for control of the individual anode
members 405. The anode members 405 may further be controlled in
groups or banks, e.g., regions of the anode assembly 404, such as a
group of anode members 405 in the central portion of the anode
assembly 404 and a surrounding group of anode members 405 near the
perimeter of the anode assembly 404. The controlled banks or groups
of anode members 405 may be in any shape, size, or number. For
example, concentric or symmetrically shaped regions or banks may be
used. In one embodiment of the invention, the anode assembly 404 is
divided into at least two concentric regions, wherein a first
region covers the center of the anode assembly 404 and at least one
second region covers an annularly shaped region surrounding the
center region. In this embodiment, the center region may be powered
to generate a greater plating rate near the center of the
substrate, which further minimizes the terminal effect.
[0048] FIG. 5C illustrates a sectional/schematic view of the anode
assembly 404 of the invention with schematic representation of the
power supply connections to the individual anode members 405. In
this embodiment, each of the respective anode members 405 is in
series electrical connection with a variable resistor 502. The
plurality of variable resistors 502 (one resistor 502 for each
anode member 405) are in parallel electrical connection with each
other. The parallel relationship of variable resistors 502 is in
series electrical communication with an anodic terminal of a power
supply 503. The variable resistors 502 are generally controllable
by a system controller configured to control the operation of the
plating system of the invention. One advantage of this
configuration is that only one power supply is needed to drive a
plurality of anode members 405. For an anode member 405 that is
square and has a side length of 10 mm, for example, a typical
resistance value for the variable resistor is about 10
k.OMEGA..
[0049] FIG. 5d illustrates an electrical resistance schematic view
of the plating cell of the invention. The power supply 503 is in
parallel connection with each of the anode member circuits 506, as
illustrated by the dashed line. Each anode member circuit 506
includes the variable resistor 502, resistance 506 (which
represents the resistance of the anode member 405 and the
electrolyte solution between the anode member 405 and the substrate
being plated), and a horizontal resistance 505 that represents the
resistance of the seed layer on the substrate. As noted above,
typical resistance values for the 10 mm wide anode members 405 are
10 k.OMEGA., and around 10 ohms for the seed resistors 505.
However, note that the drawing does not illustrate a horizontal
resistance for the electrolyte, as this resistance is in parallel
with the seed resistance 505, and generally has a value of between
about 5 and 10.OMEGA. when the anode members 405 are spaced from
the substrate at a distance of about 2 mm. As such, the resistance
for the electrolyte may be combined with resistance 505 or
generally ignored.
[0050] By having the impedance of the variable resistor 502 be
about 1000 times greater than the seed layer resistance 505, the
anode resistors predominate in controlling the current distribution
across the surface of the substrate being plated. Thus, as the
copper thickness increases during plating, the seed layer
resistance will decrease in value, and the anode resistors become
more dominant in controlling the current distribution. In the
present embodiment of the invention, the value of the variable
resistors 502 will generally be inversely proportional to the top
surface area of the corresponding anode member 405. For example,
for the previously noted resistance value about 10 k.OMEGA., the
top surface area of the anode member 405 would be around 1
cm.sup.2. In this configuration, the current passing through the
resistors 502 would be substantial, and as such, the resistors 502
would inherently become heated. As such, the inventors contemplate
that cooling (air, fluid, etc.) of the circuits 506 may be
required.
[0051] FIG. 6 illustrates a partial sectional view of the exemplary
anode assembly of the invention including an anode adjustment
mechanism 610. The anode adjustment mechanism 610 is positioned
below each of the respective anode segments 405 and above the anode
base 406. The anode adjustment member 610 generally includes a
mechanism that is configured to vertically move the anode segment
405 positioned thereon. The movement of the anode segment by the
adjustment member 610 is calculated to maintain the upper surface
of the anode assembly 204 in a substantially planar orientation
with respect to the upper surface of the other anode segments 405.
The adjustment member 610 may be configured to vertically move the
associated anode segment 405 vertically in response to the changing
weight of the anode segment 405, such as through a weight
responsive spring mechanism that will raise the anode segment 405
in proportion to the quantity of material eroded from the segment.
This particular embodiment of the invention is configured for use
in plating systems incorporating soluble anodes, as soluble anodes
are known to erode at varying rates, thus generating a non-planar
upper anode surface. Use of the adjustment member 610 allows for
individual vertical adjustment of the respective anode segments 405
such that the upper surfaces of the anode segments 405 continually
remain coplanar, despite the varying erosion rates of the
respective anode elements 405.
[0052] In operation, embodiments of the invention may be used to
plate a conductive material onto a semiconductor substrate in a
substantially uniform manner, i.e., substantially eliminating
increased plating accumulation near the perimeter of the substrate
as a result of the electrical contact being made near the perimeter
of the substrate, e.g., the terminal effect. A plating process
using embodiments of the invention generally begins with a
substrate to be plated being immersed into a plating solution
contained in a plating cell of the invention, such as plating cell
200 or 400 illustrated in FIGS. 2 and 4 respectively. The substrate
may be electrically biased during the immersion process to prevent
etching of any conductive material already deposited on the
substrate prior to initiation of the plating process. Once
immersed, the substrate may be positioned in a plating position,
i.e., generally an orientation where the plating surface 214 of the
substrate is positioned substantially parallel to an anode assembly
204 of the plating cell, as generally illustrated in FIG. 2.
[0053] Once the substrate is in the plating position, an electrical
plating bias is applied between the anode assembly 204 (connected
to an anodic terminal of the power supply) and the substrate
plating surface 214 (connected to a cathodic terminal of the power
supply) to drive the electrolytic reaction that causes copper ions
in the plating solution to deposit onto the plating surface 214.
The plating bias may be a constant current, constant voltage, a
pulsed current or voltage, a ramped current or voltage, and may
include reverse current or voltage step(s) and/or relaxation
intervals between application of plating or deplating electrical
bias steps. A more detailed description of the application of the
plating bias may be found in commonly assigned U.S. Pat. No.
6,261,433, which is hereby incorporated by reference in its
entirety, to the extent not inconsistent with the present
invention.
[0054] The application of the plating bias generates a current flow
between the anode 204 and the plating surface 214. The current flow
inherently generates an electric field between the anode 204 and
the plating surface. This electric field in a conventional plating
cell, as shown in FIG. 2, tends to diverge toward the perimeter of
the substrate where the electrical contact is generally made. This
divergence of the electric field causes the deposition rate near
the perimeter of the substrate to be greater than the deposition
rate near the center of the substrate, as the electric field flux
is known to be proportional to the deposition rate.
[0055] The present invention solves the challenges associated with
diverging electric field in electrochemical plating cells by
positioning the collimator 202 between the anode 204 and the
plating surface 214. The electric field 222 is received by the
lower surface of the collimator 202 just above the anode 204. The
electric field 222 is then transmitted via the conduits 302 (shown
in FIG. 3) of the collimator 202 toward the substrate plating
surface 214. The conduits 302 channel the electric field 222 such
that the electric field travels directly toward the plating surface
214, i.e., in a vertical direction, without horizontal divergence.
The electric field is then emitted from the upper surface 230 of
the collimator 202 proximate the substrate plating surface 214.
More particularly, the upper surface 230 is generally. positioned
less than about 20 mm from the plating surface, and as such, when
the electric field is emitted from the conduits 302 of the
collimator 202, the field has minimal opportunity to travel
horizontally prior to intersecting with the plating surface. Since
the inventors have found that the vertical spacing between the
upper surface 230 and the plating surface 214 is controlling of the
divergence (smaller spacing between the upper surface 230 and the
plating surface 214 provides proportional reduction in horizontal
field divergence), embodiments of the invention contemplate that
the spacing between the upper surface 230 and the plating surface
214 may be less than about 25 mm, and more particularly, between
about 0.5 mm and about 15 mm, as these spacing dimensions provide
minimal vertical spacing for horizontal field dispersion.
[0056] FIG. 7 illustrates a plating thickness plot 700 for a
plating cell incorporating the collimator of the invention. The
plot was obtained in a plating cell having a plurality of anodes
with the collimator positioned less than about 10 mm away from the
plating surface of the substrate. The anodes were independently
powered with the center anodes receiving more power than the
surrounding anodes, and the outer anodes receiving more power than
either of the inner anodes. The substrate plated had a diameter of
300 mm and had a 1000 .ANG. thick seed layer formed thereon. A
total of 7000 .ANG. was plated onto the seed layer using an acidic
copper sulfate based plating solution. The plot 700 illustrates
that the collimator may be used to control the plating uniformity,
i.e., the edge of the substrate has reduced plating thickness, as
illustrated by 702. Additionally, the center of the substrate has
reduced plating thickness 706, while the middle portion of the
substrate between the center and edge has increased plating rate
704. This data illustrates that the collimator of the invention may
be used to overcome edge high plating characteristics associated
with the terminal effect.
[0057] 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.
* * * * *