U.S. patent application number 10/269250 was filed with the patent office on 2003-02-27 for method and apparatus for removal of unwanted electroplating deposits.
This patent application is currently assigned to Applied Materials, Inc.. Invention is credited to Dordi, Yezdi, Hey, Peter, Nayak, Radha, Stevens, Joseph.
Application Number | 20030038107 10/269250 |
Document ID | / |
Family ID | 26887010 |
Filed Date | 2003-02-27 |
United States Patent
Application |
20030038107 |
Kind Code |
A1 |
Nayak, Radha ; et
al. |
February 27, 2003 |
Method and apparatus for removal of unwanted electroplating
deposits
Abstract
An apparatus and associated method for removing deposits from a
substrate. In one aspect, a system is provided which supplies
etchant to an edge bead removal chamber. The apparatus includes an
etchant delivery system, an etchant tank, a sensor, and a mixing
tank.
Inventors: |
Nayak, Radha; (Redwood City,
CA) ; Dordi, Yezdi; (Palo Alto, CA) ; Stevens,
Joseph; (San Jose, CA) ; Hey, Peter;
(Sunnyvale, CA) |
Correspondence
Address: |
APPLIED MATERIALS, INC.
P.O. Box 450A
Santa Clara
CA
95052
US
|
Assignee: |
Applied Materials, Inc.
|
Family ID: |
26887010 |
Appl. No.: |
10/269250 |
Filed: |
October 11, 2002 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10269250 |
Oct 11, 2002 |
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09614406 |
Jul 12, 2000 |
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6494219 |
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60191387 |
Mar 22, 2000 |
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Current U.S.
Class: |
216/2 ; 134/56R;
156/345.11; 156/345.15; 156/345.18; 156/345.29; 216/83;
257/E21.175; 257/E21.309 |
Current CPC
Class: |
H01L 21/67051 20130101;
C23F 1/08 20130101; H01L 21/6708 20130101; H01L 21/02087 20130101;
H01L 21/67207 20130101; Y10S 134/902 20130101; H01L 21/2885
20130101; H01L 21/32134 20130101 |
Class at
Publication: |
216/2 ;
134/56.00R; 156/345.11; 156/345.15; 156/345.18; 156/345.29;
216/83 |
International
Class: |
C23F 001/00; B08B
003/00; H01L 021/306; C03C 015/00; B44C 001/22 |
Claims
1. A point-of-use etchant preparation and delivery apparatus,
comprising: a chemical source; a mixing module in fluid
communication with the chemical source and configured for mixing
two or more chemical received from the chemical source into an
etchant; and an edge bead removal chamber supply line coupled at
one end to the mixing module.
2. The apparatus of claim 1, wherein the chemical source comprises
an acid storage member.
3. The apparatus of claim 1, wherein the chemical source comprises
a nitric acid storage member.
4. The apparatus of claim 1, wherein the chemical source comprises
a citric acid storage member.
5. The apparatus of claim 1, wherein the chemical source comprises
a sulfuric acid storage member.
6. The apparatus of claim 1, wherein the chemical source comprises
an oxidizer storage member.
7. The apparatus of claim 1, wherein the mixing module further
comprises a fluid-level sensor.
8. The apparatus of claim 7, further comprising a controller
communicably connected to the fluid-level sensor and configured to
initiate an etchant mixing process within the mixing module in
response to information received from the fluid-level sensor.
9. The apparatus of claim 1, wherein the chemical source comprises
an acid storage member and an oxidizer storage member.
10. The apparatus of claim 9, wherein the acid storage member is a
sulfuric acid storage member and the oxidizer storage member is a
hydrogen peroxide storage member.
11. A point-of-use etchant preparation and delivery apparatus,
comprising: a chemical source comprising an acid source and an
oxidizer source; a mixing module in fluid communication with the
chemical source and configured for mixing an acid from the acid
source and an oxidizer from the oxidizer source into an etchant; a
supply line coupled at one end to the mixing module; and an edge
bead removal chamber connected at another end of the supply line
and comprising: a substrate support member; and a plurality of
etchant delivery nozzles.
12. The apparatus of claim 11, wherein the acid is citric acid.
13. The apparatus of claim 11, wherein the acid is one of citric
acid and sulfuric acid.
14. The apparatus of claim 11, wherein the oxidizer is hydrogen
peroxide and the acid is sulfuric acid.
15. The apparatus of claim 11, wherein plurality of nozzles are
circumferentially spaced around a periphery of the substrate
support member.
16. The apparatus of claim 11, further comprising a heating tank
disposed inline with the supply line.
17. The apparatus of claim 11, wherein the mixing module further
comprises a fluid-level sensor.
18. The apparatus of claim 17, further comprising a controller
communicably connected to the fluid-level sensor and configured to
initiate an etchant mixing process within the mixing module in
response to information received from the fluid-level sensor.
19. A method of preparing and delivering an etchant at a point of
use, comprising: flowing an acid from an acid source to a mixing
module; flowing an oxidizer from an oxidizer source to the mixing
module; mixing the oxidizer and acid in the mixing module to form
an etchant; flowing the etchant from the mixing module to an edge
bead removal chamber; wherein the acid source, oxidizer source and
edge bead removal chamber are each connected to the mixing module
during each of the flowing and mixing steps.
20. The method of claim 19, further comprising sensing a fluid
level in the mixing module.
21. The method of claim 19, wherein flowing the acid and flowing
the oxidizer occur in response to sensing a fluid level in the
mixing module.
22. The method of claim 19, wherein the oxidizer is hydrogen
peroxide and the acid is sulfuric acid.
23. The method of claim 19, wherein the oxidizer is hydrogen
peroxide and the acid is citric acid.
24. The method of claim 19, further comprising heating the
etchant.
25. The method of claim 19, further comprising applying the etchant
only to a peripherary of a substrate disposed in the edge bead
removal chamber to remove material therefrom.
26. The method of claim 25, further comprising, after applying the
etchant only to the peripherary of the substrate: spinning the
substrate; rinsing the substrate; and drying the substrate.
27. A method of processing a substrate having an electroplated
material deposited thereon to remove unwanted deposits of
electroplated material, the method comprising: mixing an oxidizer
and an acid in a mixing module to form an etchant; flowing the
etchant from the mixing module to an edge bead removal chamber;
applying the etchant only to a periphery of the substrate while
rotatating the substrate in the edge bead removal chamber;
28. The method of claim 27, further comprising, prior to mixing:
flowing the acid and flowing the oxidizer to the mixing module in
response to sensing a fluid level in the mixing module.
29. The method of claim 27, wherein the oxidizer is hydrogen
peroxide and the acid is sulfuric acid.
30. The method of claim 27, wherein the oxidizer is hydrogen
peroxide and the acid is citric acid.
31. The method of claim 27, further comprising heating the etchant.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation of co-pending U.S. patent
application Ser. No. 09/614,406, filed Jul. 12, 2000, which claims
benefit of U.S. Provisional Application No. 60/191,387 filed Mar.
22, 2000, both of which are herein incorporated by reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The invention relates to electrochemical deposition or
electroplating methods, and systems for removal of unwanted
deposits resulting from electrochemical deposition or
electroplating processes.
[0004] 2. Description of the Background Art
[0005] In semiconductor processes, multiple processes such a
chemical vapor deposition (CVD), physical vapor deposition (PVD),
and electroplating are performed in series on a substrate such as a
semiconductor wafer. After electroplating is performed, edge bead
removal (EBR) systems remove edge beads and other layers remaining
on the substrates.
[0006] Modern metal electroplating can be can be accomplished by a
variety of methods. Relatively high electrical conductivity, high
electromagnetic resistance, good thermal conductivity, and
availability in a highly pure form make copper and its alloys a
choice electroplating metal. Typically, electroplating copper or
other metals and alloys involves initially depositing a thin seed
layer (having an approximate thickness of 2000 Angstroms) of a
conductive material over the surface of the substrate including the
features formed on the substrate. A layer is then plated onto the
seed layer by applying an electric charge applied across the seed
layer. The seed layer having an electric charge applied thereto
attracts metal ions. The deposited layers and the dielectric layers
can then be planarized to define a conductive interconnect feature,
such as by chemical mechanical polishing (CMP).
[0007] During electroplating, metal ions contained in the
electrolyte solution deposit on those substrate locations that
electrolyte solution contacts that are covered by the seed layer.
The seed layer is usually deposited on the front side of the
substrate, however the seed layer may extend to the edge or the
backside of the substrate. As such, metal may deposit on certain
front side, edge, or backside locations that such metal depositions
are not desired, as now described.
[0008] FIGS. 2A shows a cross sectional view of one embodiment of
an edge of a substrate 22 including a bevel edge 33, a seed layer
34 deposited on the substrate, and an electroplated conductive
metal layer 38 deposited on the substrate. During processing of the
substrate, the seed layer 34 is formed on a plating surface of the
substrate (the plating surface faces downward in FIG. 2A). The seed
layer stops a short distance from the bevel edge 33. A conductive
metal layer is then deposited on the seed layer by an
electroplating process. The conductive metal layer in FIG. 2A does
not form on any portion of the substrate that does not have a seed
layer. In the embodiment shown in FIG. 2A, an excess deposit
buildup, known as an edge bead 36, forms at the edge of the
electroplated layer. The edge bead typically results from locally
higher current densities at the edge of the seed layer 34 and
usually forms within 2-5 mm from the edge of the substrate. Removal
of the edge bead from the substrate is desired to ensure uniform
thickness of the conductive metal layer on the substrate 22.
[0009] FIGS. 2B shows a cross sectional view of another embodiment
of an edge of a substrate 22 including the bevel edge 33, the seed
layer 34 deposited on the substrate, and the electroplated
conductive metal layer 38 in FIG. 2A. In this embodiment, the seed
layer 34 covers the front side 35 of the substrate, both bevels 33
on the edge, and for a small distance on the backside 42 of the
substrate. This type of seed layer is known as a full coverage seed
layer. Metal deposits form on those seed layer surfaces that are
exposed to electrolyte solution during electroplating. When a
full-coverage seed layer is applied to a substrate, removing the
edge bead 36 following the electroplating process is often desired.
Removing the deposited layers on the seed layer that occur on the
backside and/or edge of the substrate on the full coverage seed
layers limit contamination from these layers deposited on the
backside of the substrate.
[0010] FIG. 3 shows a cross sectional view of yet another
embodiment of an edge of a substrate 22 including the bevel edge
33, the seed layer 34 deposited on the substrate, and the
electroplated conductive metal layer 38 deposited on the substrate.
The electroplated conductive metal layer 38 includes a separated
edge deposit 39. Such a separated edge deposit 39 may form on a
substrate following electroplating. The separated edge deposit 39
of the seed layer typically forms within 2-5 mm from the deposited
edge material. The separated edge deposit often separates from the
substrate 22 since the separated edge deposit is not secured to the
seed layer that would attach the separated edge deposit to the
substrate. A separated edge deposit 39 often tears off during
subsequent processing such as chemical mechanical planarization
(CMP). The CMP pads that contain material of the separated edge
deposit 39 may abrade and damage the substrate during CMP. CMP pads
that contain embedded particles may severely damage (by scratching)
any wafer to which they contact.
[0011] Therefore, during electroplating copper contamination can
form on the front, the backside, or the edge of the substrate. Such
metal deposition at undesired locations occur from full coverage
seed layer wrapping around to the backside, small deposits of
electroplated copper on the backside of the substrate, or the
copper from the wet electrolyte solution drying on the backside of
the substrate. The existence of copper contamination on the
backside of the substrate can degrade the performance of an
electronic device that uses a portion of the wafer because of
altered properties of the substrate. Providing a system by which
the copper contamination can be removed from the backside or the
edge of the substrate following the metal deposition is
desirable.
[0012] Edge bead removal (EBR) systems remove the aforementioned
edge bead, the separated deposited layer, or certain other
undesired deposited layers on the substrate. Nozzles in the EBR
systems can be adjusted to direct etchant (that removes the
deposits) and/or rinse water at desired locations on the substrate.
EBR systems therefore can apply a variety of chemicals at an
electroplated substrate where the undesired deposits are located.
The chemicals used in EBR systems comprise, for example, a mixture
including a prescribed ratio of acid mixed with an oxidizer and
de-ionized water.
[0013] Chemicals used in prior EBR systems are mixed in a batch to
form an etchant. To limit the effort required to mix a large number
of batches frequently, the individual batch sizes are large. The
batch is maintained until the etchant is used or until the etchant
becomes unusable. The usable lifetime of the etchant in EBR systems
varies depending on such parameters as the specific chemicals and
amounts of each chemical mixed to form the etchant, the temperature
at which the etchant is stored, and the pressure applied to the
etchant. However, once the etchant becomes unusable, the etchant
must be disposed of and a new batch of etchant must be prepared.
One embodiment of etchant used for copper electroplating processes
becomes increasingly unstable at higher EBR system temperatures.
Unfortunately, etch rates of the chemicals used in EBR systems
typically increase with higher temperatures. When operators
increase the temperature of the EBR system to increase throughput
based on the higher etch rates, the time until each batch of
etchant becomes altered or unstable diminishes.
[0014] It is desired to maximize throughput in EBR systems since
the EBR system represents only one of a large number of expensive
processes that are utilized in expensive semiconductor processing
systems. The EBR system cannot be used for deposition removal
purposes when a new batch of chemicals is being mixed therein to
form etchant. Presently, batches of chemicals in EBR systems are
mixed by diffusion, so some time is necessary after a large batch
is mixed for the chemicals to properly mix into etchant. In an
effort to limit down time on an EBR system, the batches of etchant
are mixed in a large volume (1 to 4 liters). Such large batches of
etchant are difficult to dispose of after the etchant becomes
unstable. In addition, some time is necessary to clean the unstable
etchant from that equipment used to store, and/or dispense the
chemicals.
[0015] Therefore, there is a need to provide an EBR device
including a mixing tank, where the EBR device mixes chemicals into
etchant at or near where the etchant is being used in an amount
that can be used by the EBR device.
SUMMARY OF THE INVENTION
[0016] The invention generally relates to edge bead removal systems
and associated methods that remove unwanted deposited metal from a
substrate. An apparatus and associated method supplies etchant to
an edge bead removal chamber. The apparatus includes an etchant
tank that is capable of storing etchant, a sensor that senses the
sensed level of etchant that is contained in the etchant tank, and
a mixing tank that mixes one or more chemical components into
etchant that is supplied to the etchant tank in response to the
sensed level. The present invention is especially applicable to
edge bead removal systems, including for example, spin-rinse-dry
systems.
BRIEF DESCRIPTION OF THE DRAWINGS
[0017] The teachings of the present invention can be readily
understood by considering the following detailed description in
conjunction with the accompanying drawings, in which:
[0018] FIG. 1 is an elevational view, partially in cross section
view of an embodiment of an edge bevel removal module in accordance
with one embodiment of the invention;
[0019] FIG. 2, comprising FIGS. 2A and 2B are cross sectional views
of two embodiments of excessive edge beads forming on a deposition
layer adjacent the periphery of a substrate;
[0020] FIG. 3 is a cross sectional view of another substrate in
which a deposition layer adjacent to the periphery of the substrate
is peeling;
[0021] FIG. 4 is an elevational view, partially in cross section
view of another embodiment of an edge bevel removal module from
that shown in FIG. 1;
[0022] FIG. 5 is a vertical sectional view of an EBR chamber as
shown in FIG. 1 with the substrate positioned for rinsing;
[0023] FIG. 6 is a vertical sectional view of the EBR chamber of
FIG. 5 with the substrate positioned for processing;
[0024] FIG. 7 is a bottom block diagram view of an EBR chamber
illustrating one embodiment of the nozzle positions;
[0025] FIG. 8 is a side view of a nozzle disposed in relation to a
substrate in the EBR chamber shown in FIG. 7; and
[0026] FIG. 9 is a side cross sectional view of one embodiment of
etchant tank including a plurality of level sensors.
[0027] To facilitate understanding, identical reference numerals
have been used, where possible, to designate identical elements
that are common to the figures.
DETAILED DESCRIPTION
[0028] After considering the following description, those skilled
in the art will clearly realize that the teachings of the present
invention can be readily utilized in edge bead removal (EBR)
modules including, or separate from, spin-rinse-dry (SRD) systems.
In this disclosure, the term "etchant" refers to any mixture of
chemicals used in an EBR module. The term "edge bead" refers to any
unwanted deposit on a substrate. The terms wafer, substrate, or
object refers to any object, such as a semiconductor wafer, from
which an EBR module is used to remove an unwanted deposition
layer.
[0029] FIG. 1 is a side cross sectional view of one embodiment of
an EBR module 412. The EBR module 412 generally includes an EBR
chamber 502, an etchant/chemical delivery assembly 106, a mixing
module 173, and a controller 506. The EBR chamber 502 includes a
slit valve 512 disposed therein through which a substrate 22 is
inserted into, or removed from, the EBR chamber using a robot arm.
Nozzles 150 and rinse water nozzles 532 and 534 are located in the
EBR chamber 502. Nozzles 150 can be selectively connected to one or
more etchant/chemical sources, including de-ionized water and
various etchants. Controller 506 controls the flow rate from the
one or more etchant/chemical sources to the nozzles 150.
[0030] The plurality of rinse water nozzles 532 and 534 extend
through the sidewall 522 of the EBR chamber 502. The rinse water
nozzles 532 and 534 are each in fluid communication with the
de-ionized water source 160 via valve 161. The rinse water nozzles
532 and 534 are each positioned to dispense water over an adjacent
surface of the substrate 22 when the substrate is positioned
adjacent to the rinse water nozzles. In one embodiment, one valve
161 controls the rinse water flow to all rinse water nozzles 532
and 534. Alternatively, a separate valve 161 is connected to each
one of the rinse water nozzles 532, 534. The valves 161 therefore
control the rinse water flow to each rinse water nozzle 532, 534
separately. Nozzles 150 are in fluid communication with the etchant
tank 162 via valve 199. Nozzles 150 can thus be used to
controllably apply etchant to the edge of the substrate.
[0031] One embodiment of a mixing module 173 generally includes a
mixing tank 168, an etchant tank 162, a heating tank 195, a
plurality of valves 172, 179, and 199, a plurality of metering
valves 161, 178, 180, a pressure source 170, a deionized water
source 160, an acid supply 175, and an oxidizer supply 176. The
acid supply 175, the de-ionized water source 160, and the oxidizer
supply 176 are all applied under pressure to force the components
thereof into the desired mixing module 173. The mixing module 173
mixes a liquid etchant that is capable of etching metal deposited
on a substrate (such as a seed layer). The metering valves 161,
178, and 180 are each configured to dispense a controlled, measured
quantity of the component chemicals and de-ionized wafer that
combine to form the etchant.
[0032] A controller 506 comprises a central processor unit (CPU)
190, a memory 192, related circuits 194, an input/output circuit
(I/O) 196, and a bus (not shown). The controller 506 controls the
operation of the EBR module 412 as described below. A vacuum chuck
516 may engage the substrate 22. A spindle 518 supports a vacuum
chuck 516. The vacuum chuck 516 is generally cylindrical in shape
and has vacuum grooves 517 formed in the lower surface. An O-ring
(not shown) circumscribes the lower face of the vacuum chuck and
engages the top of a chucked substrate in some embodiments. The
O-ring assists in forming a seal that enhances a vacuum created by
vacuum pump 529.
[0033] The vacuum source 529 is connected to the vacuum groves 517
in the vacuum chuck 516 by one or more conduits 531. In FIG. 1, the
vacuum source 529 is located outside of the EBR chamber 502 with
the conduits 531 extending from the vacuum source 529 to the
grooves 517. The vacuum applied from the vacuum pump 529 to the
grooves 517 supports the substrate adequately to lift the substrate
from the platform 514. The upper surface of the platform 514 has an
upwardly facing, centrally disposed depression dimensioned to
receive the largest substrate to be processed. The depression
limits the substrate sliding off the platform 514. A rotary
actuator 520 that is supported by a support 519 vertically supports
the spindle. Vertical actuation of the rotary actuator 520 causes
rotary vertical lifting of the vacuum chuck 516 and the substrate
22. The rotary actuator 520 is also preferably capable of rotating
the spindle at a desired controllable angular velocity of, for
example, up to about 2000 RPM.
[0034] The etchant/chemical delivery assembly 106 comprises one or
more nozzles 150 disposed on one or more dispenser arms 152 for
dispensing etchant during the EBR operation. The dispenser arm 152
is structurally and fluidly coupled to a post 521 that passes
through a container ceiling 523 of the EBR chamber 502. An actuator
527 can angularly displace each post 521 about the axis of the post
to extend or retract the dispenser arm 152 as indicated by the
arrow 155 in FIG. 7. Rotary actuator 154 extends or retracts the
dispenser arm by rotating the post 521 that is rigidly connected to
the dispenser arm. Extending or retracting the dispenser arm 152
acts to change the distance between each nozzle 150 and the nearest
point on the container sidewall 522. When the dispenser arm 152 is
extended, each nozzle 150 is positioned underneath and in close
proximity to a substrate being processed. When the nozzles 150 are
positioned under a substrate, the nozzles block vertical motion of
the substrate 22 past the nozzles 150. When the actuator displaces
the dispenser arm 152 into the retracted position, the nozzles 150
are positioned proximate the container sidewall 522. In the
retracted position, the nozzles permit vertical movement of the
substrate past the nozzles 150. The nozzles 150 are also adjustable
so that the nozzles can direct fluid at different angles to contact
the edge of a substrate, and so substrates having different
diameters are accommodated. Such adjustability of the positioning
of the nozzles 150 provides a great deal of flexibility in the use
of the nozzles 150 within the EBR chamber 502.
[0035] Conduit 153 fluidly connects the nozzles 150 to the heating
tank 195. The etchant is thus fluidly supplied through the conduit
153 to one of the nozzles 150. The conduit 153 is within, or spaced
in close proximity to, the dispenser arm 152. FIGS. 7 and 8 depict
respective bottom and side views of one embodiment of the nozzles
150 positioned within the EBR chamber 502 with a substrate 22 in a
processed position. In FIG. 7, each nozzle 150 directs the etchant
at a horizontal angle .beta. relative to a tangent line 702. The
tangent line 702 is tangent to the periphery of the substrate. The
angle .beta. is selected to minimize the splashing of the fluid
being applied on other surfaces of the substrate (at direct contact
area 706). Preferably, the angle .beta. is between 0 degrees and
about 45 degrees, and more preferably between about 20 degrees and
about 40 degrees. Three nozzles 150 substantially equally spaced
are disposed about the interior of the container sidewall 522. Each
nozzle 150 can direct etchant at an edge bead 36 of the substrate
33 (shown in FIGS. 2A or 2B) when the nozzle 150 is positioned in
the extended position depicted in FIG. 6. Alternatively, each
nozzle 150 can direct etchant at a separated edge deposit 39 that
is separated from the substrate (shown in FIG. 3) when the nozzle
150 is positioned in the extended position depicted in FIG. 6.
[0036] Each one of the nozzles 150 is also angled from the
horizontal by an angle of incidence ax (shown in FIG. 8). The angle
of incidence a preferably is between about 20 and about 80 degrees,
and most preferably about 45 degrees from horizontal. The fluid
being sprayed from nozzles 150 is initially directed with an
outward component toward the edge bead proximate the periphery of
the substrate, as shown in FIG. 7. This sprayed fluid, after
contacting the substrate 22 at direct contact area 706, wraps
around to the backside (that faces upward) of the substrate. This
wrap around results from surface tension between the fluid and the
substrate and effectively redirects the direction of the fluid
(towards the center of the substrate) as indicated by arrow 710.
The distance that the fluid travels toward the center of the
substrate along the upper surface varies based on a variety of
factors. These factors include, but are not limited to, angular
velocity of the substrate 22, diameter of the substrate, velocity
at which the etchant supplied from the nozzles 150 contacts the
substrate 22, volumetric flow rate of the etchant from the nozzles
150, and the angular position of the nozzles.
[0037] The mixing module supplies chemicals that are mixed to a
prescribed ratio and delivered to the nozzles 150 via conduits 153.
The mixing module 173 performs online metering, mixing, and
dilution of etching and cleaning chemicals. Metering valves 161,
178, and 180 permit the respective de-ionized water, acid, and
oxidizer contained in the respective de-ionized water source 160,
acid supply 175, and oxidizer supply 176 to be dispensed at a
prescribed rate. The dispensed de-ionized water, acid, and oxidizer
pass into the mixing tank 168. The metering valves 161, 178, and
180 typically dispense fluid based on the weights of the respective
fluids (a prescribed weight of de-ionized wafer, an acid, and an
oxidizer are combined). Thus, if the operator wishes to produce a
specific chemical combination, the respective weights of water from
the de-ionized water source 160, acid from the acid supply 175, and
oxidizer from the oxidizer supply 176 are calculated based on the
desired etchant chemistry. These weights are input to the
controller 506. Alternately, the controller 506 can store the
weights of water, certain acids, and certain oxidizers contained in
the respective supplies 160, 175, and 176 that are commonly
utilized by the EBR module 412.
[0038] The mixing tank 168, the etchant tank 162, and the heating
tank 195 interact to mix the combination of water from the
de-ionized water source 160, the acid from the acid supply 175, and
the oxidizer from the oxidizer supply 176 as now described. The
mixing tank 168 acts to mix the chemicals inserted therein. The
mixing tank 168 is usually empty until more etchant is desired. The
etchant tank 162 acts as a holding tank that contains the mixed
etchant in a form that is ready for application. The heating tank
195 is provided with heating elements (not shown) that heat the
contents thereof to some prescribed temperature (e.g., 55.degree.
C.). The heating tank 195 is provided in close proximity (e.g.
three feet or less) to the nozzles 150 to ensure that the
temperature of the etchant is not altered significantly after
leaving the heating tank and prior to being applied to the
substrate. The mixing tank 168, the etchant tank 162, and the
heating tank 195 are all of a suitable size to respectively mix,
dispense, and heat a suitable amount of etchant to be dispensed
that could be used within a reasonable time frame by the user of
the EBR module 412 without excessive etchant spoilage. For example,
a distinct two-liter tank has been found suitable for the mixing
tank 168, the etchant tank 162, and the heating tank 195.
[0039] Pressure from the pressure source 170 is selectively applied
to either the mixing tank 168, the etchant tank 162, and/or the
heating tank 195 under the control of the controller 506 to assist
in the flow of the chemical components. Typically, the pressure
source 170 applies nitrogen gas having a pressure ranging from 5-15
psi.
[0040] The individual chemical components can be supplied to the
mixing module using a number of alternative supply configurations
including:
[0041] 1) distinct oxidizer, acid, and water pressurized house
facility lines are each fluidly connected to the mixing module;
[0042] 2) distinct drums containing oxidizer, acid, and water are
each fluidly connected to the mixing module;
[0043] 3) an online hydrogen peroxide generation unit fluidly
connects to the mixing module. Additionally, distinct house
facility acid and water lines fluidly connect to the mixing module.
The acid line dispenses a solution including, for example, sulfuric
acid or citric acid. The online peroxide generator eliminates the
need for storage of large quantities of hydrogen peroxide or other
unstable oxidizers; and
[0044] 4) a combination of the above three alternative supply
configurations.
[0045] FIG. 9 shows one embodiment of the etchant tank 162 having a
low level sensor 902 and a high level sensor 904. The low level
sensor 902 senses the minimum etchant level to be contained in the
etchant tank. The high level sensor 904 senses the maximum etchant
level to be contained in the etchant tank. The low level sensor 902
and the high level sensor 904 are both optical sensors in the FIG.
9 embodiment. Float sensors, electric or magnetic based sensors, or
any known suitable sensors that sense level of a fluid may
alternatively be used.
[0046] The controller 506 receives the output from low level sensor
902 and high level sensor 904. If the controller 506 receives
indication from the low level sensor that the etchant in the
etchant tank is below low level sensor 902, more chemical
components from sources 160,175, and 176 are mixed in the mixing
tank 168. The mixed chemicals in the mixing tank are then dispensed
into the etchant tank until the high level sensor 904 indicates to
the controller that the etchant in the etchant tank is at or above
the level of the high level sensor. These level sensors may also be
applied to the heating tank 195 and/or the mixing tank.
[0047] The controller 506 individually controls the supply of acid
from the acid supply 175, the oxidizer from the oxidizer supply
176, and the flow of de-ionized water from the de-ionized water
source 160. The controller 506 also controls the overall operation
of the mixing module 173 including the fluids and their respective
flow rates, the pressure, timing of any associated valves, and the
spin cycle(s) of the substrates. The controller could be remotely
located, for instance, in a control panel or control room and the
plumbing associated with the EBR module 412 controlled with remote
actuators. The controller 506 is fashioned as a microcontroller, a
microprocessor, a general-purpose computer, or any other known
applicable type of computer.
[0048] The CPU 190 communicates with the memory 192, the related
circuits 194 and the I/O 196 over the bus in a known manner. The
CPU 190 controls the contents of the tanks 160, 162, and 168 by
controlling the operation of valves 161, 172, 178, 180, and 199 by
issuing commands via the I/O circuit 196, as described below. The
CPU 190 also senses various operating parameters and outputs from
sensors (not shown) that are located at different locations
throughout the EBR module 412, e.g. temperature, RPM of the spindle
518, etc. to monitor the operation of the system as well as the
mixing of the chemicals. The CPU 190 also receives operating
commands and set-limits from the related circuit, e.g. by use of a
user input (using a keyboard and/or a mouse, for example), as well
as a display (using a cathode-ray display or LCD display, for
example). The integration of the above elements associated with the
controller 506 is well known, and will not be further detailed
herein.
[0049] In operation, the vacuum chuck 516 is raised slightly from
the position shown in FIG. 1 to permit insertion of a substrate 22
through the slit valve 512 onto the platform 514. The substrate is
positioned electroplated side down on the platform 514 by a robot
device (not shown). The rotary actuator 520 then displaces the
spindle 518 and the attached vacuum chuck 516 downwardly until the
vacuum chuck 516 contacts the substrate 22. The vacuum chuck is
then actuated such that the substrate 22 is attached to the vacuum
chuck 516.
[0050] The vacuum chuck 516 and a substrate 22 are shown in
different raised positions in FIG. 5 and FIG. 6. After the vacuum
chuck 516 picks the substrate off the platform 514, the chucked
substrate is displaced into a pre process position, shown in FIG.
5. When the substrate is in the pre-process position, the actuator
rotates the spindle 518, the vacuum chuck 516, and the substrate 22
at approximately 200 RPM as rinse water is applied through rinse
water nozzles 532 and/or 534 over the respective upper and lower
surface of the substrate. The rotation of the substrate through the
spray of the rinse water nozzle 532 ensures that the spray from the
rinse water nozzle 532 covers the entire upper surface of the
substrate 22. The rotation of the substrate through the spray of
the rinse water nozzle 534 ensures that the spray from the rinse
water nozzle 534 covers the entire lower surface of the substrate
22. The rinsing of the upper and lower surfaces through the rinse
water nozzles 532 and 534 rinse certain chemicals and other
impurities from the surfaces of the substrate prior to the etchant
is applied to the substrate from nozzles 150.
[0051] After a substrate is rinsed in the pre-process position, the
vacuum chamber 516 raises the substrate 22 into the processing
position shown in FIG. 6. When the substrate is in its process
position, each nozzle 150 is displaced (under the action of
actuator 527 as described above) to be adjacent to, and directed
at, the lower surface (electroplated side 23) of the substrate 22.
The rotary actuator 520 then accelerates the combined spindle 518,
vacuum chuck 516, and substrate 22 to, for example, 1000 RPM.
Etchant is then applied from the etchant tank 162 via the heating
tank 195 to the outer periphery of the substrate 22 to remove the
edge bead 36 (shown in FIG. 2) or the loose edge 306 (shown in FIG.
3). The positioning of the etchant stream from nozzles 150 has to
be precisely positioned depending on intended function and size of
the substrate. If removing material closer to the center of the
substrate is desired (such as the separated edge deposit 39 shown
in FIG. 3), then rotary actuator 154 rotates nozzles 150 in FIG. 1
toward the center of the substrate. If horizontally displacing the
nozzles to position the nozzles closer or further from the
container sidewall 522 is desired, then the rotary actuator 154 is
actuated.
[0052] After the substrate 22 has been processed, the vacuum chuck
516 preferably is lowered to a post-process position also shown in
FIG. 5. When the substrate is in the post-process position, the
rotary actuator 520 rotates the spindle 518, the vacuum chuck 516,
and the substrate 22 at approximately 200 RPM as rinse water is
applied through rinse water nozzles 532 and/or 534 over the
respective upper and lower surfaces of the substrate. Applying
spray from the rinse water nozzles 532 and 534 to the surface of
the substrate as the substrate rotates rinses the etchant,
chemicals and other impurities from the respective upper and lower
surfaces of the substrate.
[0053] An alternate embodiment of EBR module 412, shown in FIG. 4,
also includes a valve 179, a conduit 193, and a flow device 181 in
addition to those components of the embodiment shown in FIG. 1. The
conduit 193 extends from the heating tank 195 to the rinse water
nozzle 532 to provide a diluted etchant solution applied from the
rinse water nozzle 532 to the substrate. The valve 179 controls the
fluid flow through the conduit 173. The controller 506 controls
operation of valve 179. When the valve 179 is open, a prescribed
amount of etchant from the heating tank 195 is applied with
de-ionized water supplied from the de-ionized water source 160 to
form a diluted etchant solution. The etchant applied from the
heating tank 195 to via conduit 193 to the rinse water nozzle 532
is chemically identical to the etchant applied from the heating
tank 195 to the nozzles 150, as described elsewhere in this
application. The rinse water nozzle 532 applies the diluted etchant
solution over that portion of the backside of the wafer that is not
covered by the vacuum chuck 516. The diluted etchant solution is
applied at sufficient strength to be capable of removing deposited
materials and undesired contaminants from the backside (that is
facing up in FIG. 5) of the substrate 22.
[0054] When the valve 179 is closed, the etchant from the heating
tank 195 is not combined with the de-ionized water source 160 to
form a diluted etchant solution. The rinse water nozzle 532
therefore applies de-ionized water over the backside of the wafer.
The position of the valve 179 therefor controls the concentration
of (or the complete lack of) etchant to be mixed with the
de-ionized water to form the dilute etchant solution. The flow
device 181 limits backflow of diluted etchant from the conduit
leading to the rinse water nozzle 532 from flowing into the rinse
water nozzle 534 and the de-ionized water source 160.
[0055] Following the application of the diluted etchant to the
backside of the substrate, the valve 179 can be shut off causing
the diluted etchant to be rinsed from the rinse water nozzle 534.
The rinse water is then applied to the backside of the substrate 22
to rinse the backside of the diluted etchant. Although the diluted
etchant is described as being applied through the same rinse water
nozzle 532 to the backside of the substrate that applies de-ionized
water, a separate nozzle than rinse water nozzle 532 can apply the
diluted etchant. An operation that is often performed by a
spin-rinse-dry (SRD) chamber is providing selected application of
diluted etchant to large sections of the backside of a wafer.
Applied Materials, Inc. of Santa Clara Calif. produces SRD
chambers. One embodiment of SRD system is described in U.S. patent
application Ser. No. 09/289,074, filed Apr. 8, 1999 and entitled:
"ELECTRO-CHEMICAL DEPOSITION SYSTEM" (incorporated herein by
reference).
[0056] To combine the components to form the etchant within the
mixing module 173, de-ionized water, acid, and oxidizer are
sequentially supplied respectively from the de-ionized water source
160, the acid supply 175, and the oxidizer supply 176. Small
percentages of the total components from supplies 160, 175, and 176
can alternately be introduced into the mixing tank 168 to enhance
the mixing procedure since small volumes of different chemical
components mix more easily by diffusion than large volumes of
different chemical components. The mixing of the chemical
components is provided primarily because of diffusion of the
different chemical components together to form an etchant.
Expelling etchant from the mixing tank 168 into the etchant tank
162 causes further fluid turbulence of the chemical components that
ensure that the etchant is mixed.
[0057] Pressure from source 170 is initially applied to the mixing
tank 168 (but not etchant tank 162) to provide force to flow the
etchant from the mixing tank 168 into the etchant tank 162. The
controller 506 opens valve 172 to allow the etchant flow from the
mixing tank to the etchant tank. The combined chemicals from the
mixing tank 168 fills the etchant tank 162 to a desired level. The
controller 506 then closes valve 172 and applies pressure from
pressure source 170 to the etchant tank 162; the pressure is no
longer applied from the pressure source 170 to the mixing tank 168.
Pressure from the pressure source 170 expels the etchant from the
etchant tank 162 into conduit 153 when valve 199 is opened.
[0058] During operation, mixing tank 168 and etchant tank 162
interact to provide a constant and fresh supply of etchant to the
EBR chamber 502. Etchant tank 162 is maintained at a nearly filled
position during operation. The level of etchant in the etchant tank
is determined by the low level sensor 904 integrated in the etchant
tank 162 as described above relative to the embodiment shown in
FIG. 9. When the level of etchant in etchant tank 162 falls below a
predetermined threshold, then the controller 506 actuates the
monitoring valves 161, 178, and 180 as described above to combine
more chemicals into the mixing tank 168. During a brief diffusion
period (whose duration varies based on the system and chemical
configuration) the combined chemicals diffuse into etchant. The
etchant is then dispensed from the mixing tank into the etchant
tank 162. The controller 506 can therefore mix a selected amount of
etchant in the mixing tank 168 that corresponds to the amount that
is required to fill the etchant tank 162.
[0059] The above-described mixing tank 168 and etchant tank 162
interaction minimizes the etchant that must be pre-mixed and
stored, while still providing an adequate supply of fresh etchant
to supply the nozzles 150 in the EBR chamber 502. Typically, 30
ml/wafer of etchant is used for edge bead removal for each wafer
for a 200 mm wafer. The copper etchant to be used comprises a
mixture of an acid (either sulfuric or citric acid) and an oxidizer
(hydrogen peroxide). This mixture is an effective copper etchant,
but is chemically unstable thus deteriorating due to the
accelerated decomposition of hydrogen peroxide in the presence of
acid, to form water and oxygen. Deterioration may take as long as
four days.
[0060] The etchant is particularly chemically unstable at the same
time elevated temperatures that increases etch rates and increase
throughput. The current invention eliminates these considerations
by mixing the two component chemicals online in a point of use
mixing process. This point of use mixing keeps the required
duration between when the chemicals are mixed to when they are used
as short as possible. Such point of use mixing in the mixing tank
replenishes a limited supply of chemicals as the chemicals are
being used. The etchant contained in the mixing tank 168 can be
diluted to the desired concentration of 6 percent by weight of
hydrogen peroxide as the oxidizer, 2 percent by weight of sulfuric
acid, and 92 percent by weight of de-ionized water. House
de-ionized water can be supplied from the de-ionized water source
160. Chemical ratios and dilution rates can be changed to meet the
specific needs of the process.
[0061] The etchant is then pumped into the conduit 153 that is in
fluid communication with the nozzles 150. Heating elements in the
heating tank 195 heat the etchant contained in the heating tank to
between 25-65 degrees, depending on the chemical make-up of the
etchant. The etchant is then dispensed onto the substrate for bevel
copper removal and backside cleaning. The mixing time is recorded
for each etchant mixed. If the total idle time that a mixture of
etchant remains mixed in the etchant tank or the heating tank prior
to use exceeds a predetermined value (such as 3 to 4 days) the
etchant in the etchant tank 162 will be discarded through a module
drain and the EBR module 412 is cleaned. Operators of the EBR
module 412 can therefore maintain a potent and sufficient supply of
etchant without the excessive expense associated with discarding
large amounts of etchant that have gone bad. These expenses result
because the chemicals that produce etchant are expensive, and
considerable time is required to clean the etching chamber. Since
only a small amount of chemical etchant is stored in the etchant
tank 162 or the heating tank 195 is at any given time, chemical
wastage is minimized.
[0062] In one embodiment, rotary actuator 520 rotates the substrate
22 during the EBR process to provide substantially equal exposure
to the etchant at the peripheral portion of the substrate.
Preferably, the substrate 22 is rotated in the same direction as
the direction of the etchant spray pattern to facilitate controlled
edge bead removal adjacent the bevel edge 33. For example, as shown
in FIG. 7, the substrate is rotated in a counter-clockwise
direction (arrow A) that corresponds to the counter-clockwise spray
pattern. The substrate is preferably rotated at an angular velocity
between about 100 rpm to 1000 rpm, more preferably between about
500 rpm and 1000 rpm. The effective etch rate (i.e., the amount of
copper removed divided by the time required for removal) is a
function of the etch rate of the etchant, the velocity of the
etchant contacting the substrate edge, the temperature of the
etchant, the number of nozzles, and the velocity of the substrate
rotation. These parameters can be varied to achieve particular
desired results.
[0063] The number of nozzles 150 directed at a substrate factors
into the etch rate since etchant applied from a single nozzle
remains in contact with the etchant for only a portion of the
rotation of the substrate. Providing multiple radially spaced
nozzles 150 around the substrate increase the radial angle of
travel (and the amount of time) that the substrate is covered by
etchant during each substrate rotation. In another embodiment, the
substrate is maintained stationary during processing. The mixture
of etchant including 2% sulfuric acid by weight, 6% hydrogen
peroxide by weight, and 92% water by weight can etch a 1 .mu.m
thick film of copper in 15 seconds. The etching by the EBR module
described above produces a clean division (of 1/2 to 3/4 mm)
between the etched and the non-etched portions. With this etching
rate, throughput of the EBR module 502 can reach 72 wafers per
hour.
[0064] The etching process is performed for a pre-determined time
period sufficient to remove the edge bead 36 shown in FIG. 2 or the
separated edge deposit 39 that is separated from the substrate
shown in FIG. 3. The substrate is then preferably cleaned with
de-ionized water that supplied from the rinse water nozzles 532,
534. This application of water from the rinse water nozzle 532 and
534 occurs while the substrate 22 is in the post processing
position has been referred to above as a spin-rinse-dry (SRD)
process. The SRD process typically involves delivering de-ionized
water to the substrate to rinse residual etchant and other
chemicals from the substrate and spinning the substrate at a high
speed to dry the substrate. The substrate is then transferred out
of the EBR chamber 502 after the EBR and SRD processes, and the
substrate is ready for subsequent processing.
[0065] Although various embodiments that incorporate the teachings
of the present invention have been shown and described in detail
herein, those skilled in the art can readily devise many other
varied embodiments that still incorporate these teachings.
* * * * *