U.S. patent application number 11/069800 was filed with the patent office on 2006-08-31 for methods and systems for electroplating wafers.
This patent application is currently assigned to Hitachi Global Storage Technologies. Invention is credited to Robert William Hitzfeld, Jennifer Ai-Ming Loo, Murali Ramasubramanian.
Application Number | 20060191784 11/069800 |
Document ID | / |
Family ID | 36931054 |
Filed Date | 2006-08-31 |
United States Patent
Application |
20060191784 |
Kind Code |
A1 |
Hitzfeld; Robert William ;
et al. |
August 31, 2006 |
Methods and systems for electroplating wafers
Abstract
Improved methods and systems for electroplating wafers are
described herein. The method includes the acts of introducing a
wafer which is coupled to an electrode into an electroplating cell
having a counter electrode; maintaining a flow of a plating
solution through the cell for electroplating the wafer; removing
the wafer from the cell; stopping the flow of the plating solution
through the cell; maintaining a volume of plating solution within
the cell sufficient to keep the counter electrode submerged during
stoppage of flow; removing the plating solution within the cell;
and repeating the above steps for a subsequent wafer. By stopping
the flow of plating solution after completion of plating one or
more wafers, a consumption rate of additives enhancing
electroplating properties is reduced, a production rate of
breakdown products produced during electroplating is reduced,
plating solution useable life is increased, and a need for plating
solution analysis is reduced.
Inventors: |
Hitzfeld; Robert William;
(San Jose, CA) ; Loo; Jennifer Ai-Ming; (Gilroy,
CA) ; Ramasubramanian; Murali; (Fremont, CA) |
Correspondence
Address: |
JOHN J. OSKOREP, ESQ.;ONE MAGNIFICENT MILE CENTER
980 N. MICHIGAN AVE.
SUITE 1400
CHICAGO
IL
60611
US
|
Assignee: |
Hitachi Global Storage
Technologies
|
Family ID: |
36931054 |
Appl. No.: |
11/069800 |
Filed: |
February 28, 2005 |
Current U.S.
Class: |
204/198 ;
205/118; 205/148; 257/E21.175 |
Current CPC
Class: |
C25D 3/38 20130101; C25D
17/001 20130101; H01L 21/2885 20130101; C25D 21/12 20130101; C25D
5/08 20130101 |
Class at
Publication: |
204/198 ;
205/148; 205/118 |
International
Class: |
C25D 17/00 20060101
C25D017/00; C25D 5/20 20060101 C25D005/20; C25D 5/02 20060101
C25D005/02 |
Claims
1. A method of electroplating wafers, comprising: a. introducing a
wafer coupled to an electrode into an electroplating cell having a
counter electrode; b. maintaining a flow of a plating solution
through the cell for electroplating the wafer; c. removing the
wafer from the cell; d. stopping the flow of the plating solution
through the cell; e. maintaining a volume of plating solution
within the cell sufficient to keep the counter electrode submerged
during stoppage of flow; f. removing the plating solution within
the cell; and g. repeating steps a to c for electroplating a
subsequent wafer.
2. The method of claim 1, wherein the act of maintaining the flow
comprises engaging a pump for a predetermined plating flow
rate.
3. The method of claim 1, wherein the act of stopping the flow
comprises the further act of disengaging a pump.
4. The method of claim 1, wherein the act of stopping the flow
comprises closing a valve.
5. The method of claim 1, wherein the act of removing the plating
solution comprises releasing the plating solution into a tank.
6. The method of claim 1, wherein the counter electrode comprises
one of titanium coated with one of platinum, platinized titanium,
platinized niobium, iridium oxide and ruthenium oxide.
7. The method of claim 1, wherein the plating solution is an
electrolytic solution comprising copper ions and additives for
enhancing electroplating properties.
8. The method of claim 1, wherein the plating solution is an
electrolytic solution comprising copper ions and additives for
enhancing electroplating properties, and wherein the additives
comprise at least one of aromatic quaternary amines, aliphatic
quaternary amines, polysulfide compounds, polyimines, polyethers,
selenium, tellurium and sulfur compounds.
9. The method of claim 1, further comprising: wherein the plating
solution is an electrolytic solution comprising copper ions and
additives for enhancing electroplating properties; wherein stoppage
of flow reduces a consumption rate of the additives; wherein
stoppage of flow reduces a production rate of breakdown products
produced during electroplating; wherein stoppage of flow increases
plating solution useable life; and wherein stoppage of flow reduces
a need for analysis of the plating solution.
10. A method of electroplating wafers, comprising: for a first set
of wafers to be electroplated: a. introducing a wafer coupled to an
electrode into an electroplating cell having a counter electrode;
b. maintaining a flow of a plating solution through the cell for
electroplating the wafer; c. removing the wafer from the cell; d.
repeating steps a to c for electroplating additional wafers of the
first set; e. stopping the flow of the plating solution through the
cell after electroplating the first set of wafers; f. maintaining a
volume of plating solution within the cell sufficient to keep the
counter electrode submerged during stoppage of flow; for a
subsequent set of wafers: g. removing the plating solution within
the cell; and h. performing steps a to d for electroplating the
subsequent set of wafers.
11. The method of claim 10, wherein the act of maintaining the flow
comprises activating a pump.
12. The method of claim 10, wherein the act of stopping the flow
comprises the further act of deactivating a pump.
13. The method of claim 10, wherein the act of stopping the flow
comprises closing a valve.
14. The method of claim 10, wherein the act of removing the plating
solution comprises releasing the plating solution into a holding
tank.
15. The method of claim 10, wherein the counter electrode comprises
one of titanium coated with one of platinum, platinized titanium,
platinized niobium, iridium oxide and ruthenium oxide.
16. The method of claim 10, wherein the plating solution is an
electrolytic solution comprising copper ions and additives for
enhancing electroplating properties.
17. The method of claim 10, wherein the plating solution is an
electrolytic solution comprising copper ions and additives for
enhancing electroplating properties, and wherein the additives
comprise at lease one of aromatic quaternary amines, aliphatic
quaternary amines, polysulfide compounds, polyimines, polyethers,
selenium, tellurium and sulfur compounds.
18. The method of claim 10, further comprising: wherein the plating
solution is an electrolytic solution comprising copper ions and
additives for enhancing electroplating properties; wherein stoppage
of flow reduces a consumption rate of the additives; wherein
stoppage of flow reduces a production rate of breakdown products
produced during electroplating; wherein stoppage of flow increases
plating solution useable life; and wherein stoppage of flow reduces
a need for analysis of the plating solution.
19. A system comprising: an electroplating cell for electroplating
a wafer; a positioning mechanism to introduce and remove the wafer
from the cell; a flow control mechanism to maintain a flow of
plating solution through the cell for electroplating the wafer and
to stop the flow thereafter; the flow control mechanism to further
maintain a volume of plating solution within the cell sufficient to
keep an electrode of the cell submerged during stoppage of flow;
and the flow control mechanism to further remove the volume of
plating solution from the cell prior to electroplating a subsequent
wafer.
20. The system of claim 19, wherein the positioning mechanism
comprises a rotor.
21. The system of claim 19 wherein the flow control mechanism
comprises a pump.
22. The system of claim 19, wherein the flow control mechanism
comprises a plating solution inlet valve to maintain and stop the
flow.
23. The system of claim 19 wherein the flow control mechanism
comprises a plating solution outlet valve to maintain and stop the
flow.
24. The system of claim 19, wherein the flow control mechanism
comprises a plating solution drain valve.
25. The system of claim 19, wherein the flow control mechanism
comprises: a pump; a plating solution inlet valve; and a plating
solution outlet valve.
26. The system of claim 19, wherein the flow control mechanism
comprises: a pump; a plating solution inlet valve; a plating
solution outlet valve; and a plating solution drain valve.
27. The system of claim 19, further comprising: a power supply
having an anode and a cathode for coupling to the wafer, the anode
comprising the electrode of the cell; a plating solution holding
tank from which the plating solution is drawn; a plating solution
inlet transport line connected to the holding tank which
facilitates flow of the plating solution from the holding tank to
the cell through an inlet valve of the flow control mechanism; a
pump of the flow control mechanism connected to the inlet transport
line; and a plating solution outlet transport line connected to the
cell which facilitates flow of the plating solution from the cell
to the holding tank through an outlet valve of the flow control
mechanism.
28. The system of claim 19, further comprising: a power supply
having an anode and a cathode for coupling to the wafer, the anode
comprising the electrode of the cell; a plating solution holding
tank from which the plating solution is drawn; a plating solution
inlet transport line connected to the holding tank which
facilitates flow of the plating solution from the holding tank to
the cell through an inlet valve of the flow control mechanism; a
pump of the flow control mechanism connected to the inlet transport
line; a plating solution outlet transport line connected to the
cell which facilitates flow of the plating solution from the cell
to the holding tank through an outlet valve of the flow control
mechanism; and a plating solution drain transport line connected to
the cell which facilitates removal of the volume of plating
solution within the cell sufficient to keep the electrode of the
cell submerged during stoppage of flow to a plating solution drain
tank through a drain valve to remove the volume of plating solution
from the cell.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] This invention relates generally to methods and systems for
electroplating substrates, such as those utilized for damascene
electroplating of write coils in magnetic heads.
[0003] 2. Description of the Related Art
[0004] The demand for manufacturing semiconductor integrated
circuit (IC) devices, such as computer chips with high circuit
speed, high-packing density, and low power dissipation, requires
the downward scaling of feature sizes in ultra-large-scale
integration (ULSI) and very-large-scale integration (VLSI)
structures. The trend to smaller chip sizes and increased circuit
density requires the miniaturization of interconnect features which
severely penalizes the overall performance of the structure because
of increasing interconnect resistance and reliability concerns such
as fabrication of the interconnects and electromigration. Magnetic
heads with inductive write coils also feature miniaturization
requirements to increase areal storage densities on magnetic disks
and reduction of coil resistance.
[0005] Historically, such structures have utilized aluminum and
aluminum alloys as the metallization on silicon wafers, with
silicon dioxide being the dielectric material. In general, openings
were formed in the silicon dioxide dielectric layer in the shape of
vias and trenches which were then metallized to form the
interconnects. Increased miniaturization, however, has required
these openings to be at submicron sizes (e.g., 0.5.mu. and lower).
To achieve such miniaturization, industries have moved to the use
of copper instead of aluminum as the metal to form the connection
lines and interconnects in the chip. Copper has a lower resistivity
than aluminum and the thickness of a copper line for the same
resistance can be thinner than that of an aluminum line.
Copper-based interconnects therefore represent the most foreseeable
future trend in the fabrication of such devices. Copper can be
deposited on substrates by plating (such as electroless and
electrolytic), sputtering, plasma vapor deposition (PVD), and
chemical vapor deposition (CVD). It is generally recognized that a
plating-based deposition is the best method to apply copper to the
device since it can provide high deposition rates and low system
costs.
[0006] Referring to FIG. 1, a plating system 100 of the prior art
is shown. Plating system 100 is used for electroplating copper onto
a wafer 112 which is coupled to a cathode. Plating system 100 may
be of the type provided by Semitool, Inc. of Kalispell, Mont.,
U.S.A., for example, the EQUINOX.RTM. system platform (EQUINOX is a
registered trademark of Semitool, Inc.). System 100 includes an
electroplating cell 110 which holds a plating solution 127. Cell
110 is made of a suitable material, such as plastic or other
material inert to plating solution 127. Cell 110 is preferably
cylindrical in shape, but alternatively may be square or
rectangular in shape. Wafer 112 is horizontally disposed at the
upper part of cell 110 and may be any type substrate, such as a
silicon, ceramic or other material having openings including
trenches and vias to be plated. A wafer surface 112a of wafer 112
is typically coated with a seed layer of copper or other metal to
initiate plating thereon. A copper seed layer may be applied by
sputtering, plasma vapor deposition (PVD), chemical vapor
deposition (CVD), or the like. An anode 113 is preferably circular
for wafer plating and is horizontally disposed at the lower part of
cell 110, forming a space therein between wafer 112 and anode 113.
Anode 113 is a soluble electrode which is consumed during
processing. Suitable soluble anodes include copper and other copper
alloys such as copper phosphate. The anode and cathode are
electrically connected by wiring 114 and 115, respectively, to a
power supply 116. In electroplating system 100, wafer 112 has a
negative charge so that copper ions in the solution are reduced to
form plated copper metal on wafer surface 112a. An oxidation
reaction takes place at anode 113 causing copper metal to go into
solution.
[0007] Plating system 100 further includes a plating solution
holding tank 119 from which a plating solution 127 is drawn via a
pump 122 through a plating solution inlet transport line 117, a
flow measurement device 151, and an inlet valve 140 to an inlet
110a of cell 110. Plating solution 127 flows through cell 110 and
thereby contacts wafer 112 and anode 113, filling the space therein
between them with the solution. A rotor 130 holds wafer 112 in
position and a rotor 131 holds anode 113 in place. Rotors 130 and
131 alternatively may be a flange, plate, or other similar device.
Plating solution 127 exits cell 110 through an overflow weir 125
into outlet 110b and is recycled into tank 119 through a plating
solution transport line 118. During operation of plating system 100
to plate wafer 112, plating solution 127 continuously flows through
the system at a predetermined plating flow rate. The plating flow
rate may be, for example, between 2 to 6 gallons per minute (g/m).
This forms a substantially uniform electrolyte composition in the
system and contributes to the overall effectiveness of the wafer
plating. Flow of plating solution 127 through plating system 100 is
controlled by a flow control mechanism which includes pump 122 and
inlet valve 140. Additionally, the flow control mechanism includes
a flow measurement device 151, such as a flow meter, and a closed
feedback loop 150 for more precise control over the flow of plating
solution 127.
[0008] During operation of plating system 100, copper metal is
plated on wafer surface 112a when power supply 116 is energized. A
pulse current, direct current (DC), reverse periodic current, or
other suitable current may be employed. The electroplating process
results in depletion of the copper concentration of plating
solution 127. Copper deposits must be uniform and capable of
filling the extremely small trenches and vias of the device. These
important properties are typically achieved using multi-component
plating solutions, which include organic and inorganic components.
Typical plating solution 127 formulations use highly stable
electrolytes containing copper sulfate and sulfuric acid. As an
example, copper concentration in these electrolytes may be between
12-60 grams/liter (g/l) and sulfuric acid 1-240 g/l.
[0009] Other components added to the plating solution are present
in relatively small amounts. These components are organic additives
and chloride ions. The organic additives, depending on the
concentration and chemical composition, affect the properties of
the electrodeposited copper including uniformity, hardness,
ductility, tensile strength, grain size, etc. These additives for
enhancing electroplating properties, which react at the wafer
surface during electroplating, fall into three major categories.
Accelerators are compounds that contain pendant sulfur atoms that
locally accelerate deposition where they are adsorbed. Suppressors
are polymers, such as polyethylene glycols, which have the ability
to form a current-suppressing film on the entire wafer surface. The
third category of organic additives are levelers, which are
secondary suppressors and work only on the protruding surfaces
where mass transfer is most effective.
[0010] After completing the electroplating of one or more wafers,
the flow through pump 122 is set and maintained at a reduced "idle
flow" rate. This reduced idle flow rate may be, for example,
between 1 to 1.5 g/m. During this time period, no wafers are being
electroplated. At some point in time, however, subsequent wafers
will be electroplated where pump 122 is once again set and
maintained at the higher plating flow rate.
[0011] In addition to reacting at the surface of the wafer during
electroplating, the additives of the plating solution undesirably
react at the surface of anode 113 within cell 110 during
electroplating and idle flow during non-plating periods. Further,
there are other interactions between the additives and inorganic
compounds which cause decomposition and modification of initial
organic compounds. These breakdown products ideally need to be kept
below a threshold level in order to provide the most uniform of
copper deposition and highest capability of filling the extremely
small trenches and vias of the device. Thus, monitoring these
breakdown products must be performed at least once every four to
six hours by analyzing the composition of the bath during idle
flow. Also, replacement of up to 20% may be done daily to maintain
the plating solution in steady state. Both of these requirements
result in a large amount of time and labor for plating solution
analysis and control. This is especially true when system
utilization is less than 100%.
[0012] Accordingly, what are needed are improved methods for
electroplating wafers as well as improved systems for performing
such methods.
SUMMARY
[0013] Improved methods and systems for electroplating wafers are
described herein. The method includes the acts of introducing a
wafer which is coupled to an electrode (e.g. a cathode) into an
electroplating cell having a counter electrode (e.g. an anode);
maintaining a flow of a plating solution through the cell for
electroplating the wafer; removing the wafer from the cell;
stopping the flow of the plating solution through the cell;
maintaining a volume of plating solution within the cell sufficient
to keep the counter electrode submerged during stoppage of flow;
removing the plating solution within the cell; and repeating the
above steps for a subsequent wafer.
[0014] By stopping the flow of plating solution after completion of
plating one or more wafers, a consumption rate of additives
enhancing electroplating properties is reduced, a production rate
of breakdown products produced during electroplating is reduced,
plating solution useable life is increased, and a need for plating
solution analysis is reduced.
BRIEF DESCRIPTION OF THE DRAWINGS
[0015] For a fuller understanding of the nature and advantages of
the present invention, as well as the preferred mode of use,
reference should be made to the following detailed description read
in conjunction with the accompanying drawings:
[0016] FIG. 1 is a system for electroplating wafers of the prior
art;
[0017] FIG. 2 is a flowchart which describes an improved method for
electroplating wafers in accordance with the present invention;
[0018] FIG. 3 is a system for electroplating wafers in accordance
with the present invention; and
[0019] FIG. 4 is a system for electroplating wafers according to a
preferred embodiment of the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0020] In describing the preferred embodiment of the present
invention, reference will be made herein to FIGS. 1-4 of the
drawings in which like numerals refer to like features of the
invention. Features of the invention are not necessarily shown to
scale in the drawings.
[0021] FIG. 2 is a flowchart which describes an improved method for
electroplating wafers in accordance with the present invention.
FIGS. 3-4 are process flow diagrams of plating systems 300 and 400
of the present invention within which the steps in the flowchart of
FIG. 2 may be employed. While the systems and methods are described
primarily with reference to plating a silicon wafer, it will be
appreciated by those skilled in the art that other substrates may
be plated. Although any suitable system platform may be utilized,
the plating system may be based on the type provided by Semitool,
Inc. of Kalispell, Mont., U.S.A., for example, the EQUINOX.RTM.
system platform (EQUINOX is a registered trademark of Semitool,
Inc.).
[0022] Referring first to FIG. 3, plating system 300 includes an
electroplating cell 110 which holds a plating solution 127. Cell
110 may be made of a suitable material, such as plastic or other
material inert to plating solution 127, which forms a reservoir for
holding the solution. Cell 110 is preferably cylindrical, but may
alternatively be different shapes, such as square or rectangular. A
wafer 112, which is coupled to an electrode (e.g. a cathode), is
inverted and horizontally disposed at the upper part of
electroplating cell 110 and may be any type of substrate, such as a
silicon wafer having openings including trenches and vias to be
plated. Wafer 112 may be introduced within and removed from cell
110 via a positioning mechanism (e.g. rotor 131). A wafer surface
112a of wafer 112 is typically coated with a seed layer of copper
or other metal to initiate plating thereon. A copper seed layer may
be applied by sputtering, plasma vapor deposition (PVD), chemical
vapor deposition (CVD) and the like. A counter electrode 113 (e.g.
an anode) is preferably circular, but may alternatively be
different shapes such as square or rectangular, for wafer plating
and is horizontally disposed at the lower part of cell 110, forming
a space therein between wafer 112 and counter electrode 113.
Counter electrode 113 is a soluble electrode which is consumed
during processing. Suitable soluble anodes include copper and other
copper alloys such as copper phosphate. Wafer 112 and counter
electrode 113 are electrically connected by wiring 114 and 115,
respectively, to a power supply 116. In plating system 300, wafer
112 has a negative charge so that copper ions in the solution are
reduced thereby forming plated copper metal on wafer surface 12a.
An oxidation reaction takes place at counter electrode 113 causing
copper metal to go into solution. Wafer 112 and counter electrode
113 are shown horizontally disposed but may alternatively be
vertically disposed in cell 110. Furthermore, wafer 112 and counter
electrode 113 may alternatively be disposed in opposite
positions.
[0023] Plating system 300 further includes a plating solution
holding tank 119 from which a plating solution 127 is drawn via a
pump 122 through a plating solution inlet transport line 117 and a
plating solution inlet valve 140 into an inlet 110a of cell 110.
Plating solution 127 flows through cell 110 and thereby contacts
wafer 112 and counter electrode 113, filling the space between them
with the solution. Rotor 130 holds wafer 112 in position and rotor
131 holds counter electrode 113 in place. Rotors 130 and 131
alternatively may be a flange, plate, or other similar device.
Plating solution 127 exits cell 110 through overflow weir 125 into
outlet 110b, flows through an adjacent plating solution outlet
valve 341, and is recycled into tank 119 through plating solution
transport line 118. During operation of plating system 100, plating
solution 127 continuously flows through the system at a
predetermined plating flow rate. The plating flow rate may be, for
example, between 2 to 6 gallons per minute (g/m). Such flow forms a
substantially uniform electrolyte composition in the system and
contributes to the overall effectiveness of the wafer plating. Flow
of plating solution 127 through plating system 300 is controlled by
a flow control mechanism which includes pump 122, inlet valve 140,
and outlet valve 341. Additionally, the flow control mechanism
includes a flow measurement device 151, such as a flow meter, and a
closed feedback loop 150 for more precise control over the flow of
plating solution 127. Note that plating system 300 is similar to
plating system 100 of FIG. 1 except that outlet valve 341 has been
added to plating solution transport line 118 positioned adjacent
outlet 110b of cell 110.
[0024] The composition of plating solution 127 may vary widely
depending on the substrate to be electroplated and the type of
copper deposition desired. Exemplary plating solutions include
copper fluoborate, copper pyrophosphate, copper cyanide, copper
phosphonate, and other copper metal chelates such as methane
sulfonic acid. One preferred plating solution is copper sulfate in
an acid solution. The concentration of copper and acid may vary
over wide limits. For copper or copper ions, compositions generally
vary up to 25 grams/liter (g/l) or more preferably 15 to 20 g/l.
The acidic composition is typically sulfuric acid in an amount up
to about 300 g/l or more, preferably 150 to 200 g/l. Chloride ions
may be used in the plating solution at levels up to about 90 mg/l.
Other components added to the plating solution are present in
relatively small amounts. These components are organic additives
and chloride ions. The additives for enhancing electroplating
properties, depending on the concentration and chemical
composition, affect the properties of the electrodeposited copper
including uniformity, hardness, ductility, tensile strength, etc. A
particularly desirable additive composition uses a mixture of
aromatic or aliphatic quaternary amines, polysulfide compounds,
polyimines and polyethers. Other additives include metaloids such
as selenium, tellurium and sulfur compounds.
[0025] A method of electroplating wafer 112 of FIG. 2 which may
utilize system 300 of FIG. 3 is now described. Beginning at a
starting point 202 in FIG. 2, wafer 112 is introduced into
electroplating cell 110 having counter electrode 113 with use of
the positioning mechanism (step 204 of FIG. 2). During operation of
system 300, a flow of plating solution 127 is maintained through
cell 110 at a predetermined plating flow rate (step 206 of FIG. 2).
The flow is controlled by the flow control mechanism which may
include pump 122, inlet valve 140 and outlet valve 341; pump 122 is
engaged and valves 140 and 341 are opened. Additionally, the flow
control mechanism includes a flow measurement device 151, such as a
flow meter, and a closed feedback loop 150 for more precise control
over the flow of plating solution 127. Over some period of time,
wafer 112 is electroplated within cell 110. Upon completion of
electroplating wafer 112, the wafer is removed from cell 110 with
use of the positioning mechanism (step 208 of FIG. 2). Additional
wafers of the same set or batch may thereafter be plated by
repeating these steps (step 210 of FIG. 2). Preferably, the wafer
includes a plurality of magnetic head structures for which
damascene copper electroplating is needed. Typically, the time
period between electroplating wafers of the same set is relatively
short. The time period may be, for example, between 0 and 60
minutes.
[0026] Once the electroplating of the wafer(s) is completed as
identified at step 210, flow of the solution through cell 110 is
stopped by turning off or disengaging pump 122 as well as closing
inlet valve 140 and outlet valve 341 (step 212 of FIG. 2). During
stoppage of flow, the volume of plating solution 127 is maintained
within cell 110 (step 214 of FIG. 2). This volume is sufficient to
keep counter electrode 113 submerged between electroplating runs.
An indefinite time period lapses until the next wafer or wafer set
is electroplated (step 216 of FIG. 2). This time period may
typically be, for example, between 1 and 24 hours.
[0027] For the next set of wafers to be electroplated, the volume
of the plating solution maintained within cell 110 is removed just
prior to electroplating the next wafer (step 218 of FIG. 2). To do
this, the plating solution may be recycled into solution holding
tank 119 by opening inlet valve 140 and outlet valve 341. The flow
of plating solution 127 is then started again by initializing and
operating pump 122 at the plating flow rate (step 220 of FIG.
2).
[0028] As indicated, the above method is applicable when
electroplating different sets or batches of wafers. For a first set
of wafers, steps 204, 206, 208 and 210 of FIG. 2 are repeated. Upon
completion of the first set, steps 212, 214 and 216 of FIG. 2 are
performed until a next set of wafers is to be plated. Steps 218 and
220 of FIG. 2 are then performed to initiate the electroplating of
the next set of wafers by again repeating steps 204-210.
[0029] During operation of plating system 300 (e.g. step 206 of
FIG. 2), copper metal is plated on wafer surface 112a when power
supply 116 is energized. A pulse current, direct current (DC),
reverse periodic current or other suitable current may be employed.
The electroplating process results in depletion of a copper
concentration of plating solution 127. Note that the additives for
enhancing electroplating properties typically undesirably react at
the surface of counter electrode 113 within the cell during
electroplating as well as during idle flow of the plating solution
during non-production periods. Further, there are other
interactions between the additives and inorganic compounds which
cause decomposition and modification of initial organic compounds.
These breakdown products ideally need to be kept below a threshold
level in order to provide the most uniform of copper deposition and
highest capability of filling the extremely small trenches and vias
of the device. As such, analysis of these breakdown products is
performed at least once every four to six hours by analyzing the
composition of the plating solution during idle flow under methods
and systems of the prior art. Also, replacement of up to 20% may be
done daily to maintain the plating solution in steady state during
operation of plating systems of the prior art.
[0030] In accordance with the present techniques, the flow of
plating solution 127 is stopped but a volume of plating solution
127 is maintained within cell 110 sufficient to keep counter
electrode 113 submerged between electroplating runs (see steps 212
and 214 of FIG. 2). These steps preserve an organic film which
grows on counter electrode 113. Further, this stoppage of flow
reduces a consumption rate of the additives; reduces a production
rate of breakdown products produced during electroplating;
increases plating solution useable life; and reduces a need for
analysis of the plating solution from once every four to six hours
to once every eight hours. Upon identifying the need to
electroplate subsequent wafers, the volume of plating solution 127
within the cell is removed (e.g. recycled into the plating solution
holding tank) by opening outlet valve 341.
[0031] Removing the plating solution from the system is performed
and new plating solution is added to the system either
simultaneously or after the recycling in substantially the same
amount. The new solution is preferably a single liquid containing
all the materials needed to maintain the electroplating system. The
addition/removal mechanism maintains the plating solution in
steady-state during operation of the plating system.
[0032] Referring now to FIG. 4, plating system 400 is similar to
plating system 300 of FIG. 3 except that a plating solution drain
transport line 420 positioned adjacent an outlet 110c of cell 110,
a plating solution drain valve 442, and a plating solution drain
tank 421 have also been provided. All previous descriptions
relating to the method of FIG. 3 hold true with the following
difference. In preparation for subsequent wafers after the
maintenance of the volume within the cell (step 214 of FIG. 2),
plating solution in cell 110 is removed through plating solution
drain transport line 420 into plating solution drain tank 421 by
opening drain valve 442. This step corresponds to step 218 of FIG.
2. Flow of the plating solution through plating system 400 is
thereafter controlled by the flow control mechanism which includes
pump 122, inlet valve 140, outlet valve 341, and drain valve 442.
In particular, after the plating solution is removed to drain tank
421, drain valve 442 is closed, valves 140 and 341 are opened, and
pump 122 is activated to facilitate the plating flow rate.
[0033] Note that the techniques for engaging/disengaging the pump,
opening/closing of the valves, and identifying various conditions
for change (e.g. wafer electroplating completed, new wafer set
introduced, etc.), may be implemented in whole or in part manually
by an end user(s) of the system or by computer control. If done by
computer control, software instructions may be written in
accordance with the described logic, stored in memory, and executed
by a computer processor for performing the method.
[0034] Thus, a method of electroplating wafers of the present
invention includes the steps of: for a first set of wafers: (a)
introducing a wafer coupled to an electrode into an electroplating
cell having a counter electrode; (b) maintaining a flow of a
plating solution through the cell for electroplating the wafer; (c)
removing the wafer from the cell; and (d) repeating steps a to c
for electroplating additional wafers of the first set. The method
continues with the steps of (e) stopping the flow of the plating
solution through the cell after electroplating the first set of
wafers; and (f) maintaining a volume of plating solution within the
cell sufficient to keep the counter electrode submerged during
stoppage of flow. For a subsequent set of wafers, the method
continues with the steps of (g) removing the plating solution
within the cell; and (h) reperforming steps a to d for
electroplating the subsequent set of wafers.
[0035] A system of the present invention includes an electroplating
cell for electroplating a wafer; a positioning mechanism to
introduce and remove the wafer from the cell; and a flow control
mechanism to maintain a flow of plating solution through the cell
for electroplating the wafer and to stop the flow thereafter. The
flow control mechanism also maintains a volume of plating solution
within the cell sufficient to keep an electrode of the cell
submerged during stoppage of flow, and removes the volume of
plating solution from the cell prior to electroplating a subsequent
wafer. The removal of plating solution may be done by draining the
cell for recycling within a holding tank or for disposal via a
drain/waste tank.
[0036] It is to be understood that the above is merely a
description of preferred embodiments of the invention and that
various changes, alterations, and variations may be made without
departing from the true spirit and scope of the invention as set
for in the appended claims. Few if any of the terms or phrases in
the specification and claims have been given any special meaning
different from their plain language meaning, and therefore the
specification is not to be used to define terms in an unduly narrow
sense.
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