U.S. patent application number 11/280540 was filed with the patent office on 2006-05-11 for apparatus for monitoring and controlling force applied on workpiece surface during electrochemical mechanical processing.
Invention is credited to Bulent M. Basol, Jeffrey A. Bogart, Efrain Velazquez.
Application Number | 20060096702 11/280540 |
Document ID | / |
Family ID | 28790588 |
Filed Date | 2006-05-11 |
United States Patent
Application |
20060096702 |
Kind Code |
A1 |
Basol; Bulent M. ; et
al. |
May 11, 2006 |
Apparatus for monitoring and controlling force applied on workpiece
surface during electrochemical mechanical processing
Abstract
In one aspect, the present invention monitors a signal
corresponding to a torque value of a motor that is used to maintain
relative motion between a conductive top surface of a workpiece and
a workpiece surface influencing device in the presence of physical
contact between the conductive top surface of the workpiece and the
workpiece surface influencing device. In another aspect, the
present invention uses the signal to control a force applied to a
top conductive surface of a workpiece during electrotreatment.
Inventors: |
Basol; Bulent M.; (Manhattan
Beach, CA) ; Bogart; Jeffrey A.; (Los Gatos, CA)
; Velazquez; Efrain; (San Jose, CA) |
Correspondence
Address: |
KNOBBE MARTENS OLSON & BEAR LLP
2040 MAIN STREET
FOURTEENTH FLOOR
IRVINE
CA
92614
US
|
Family ID: |
28790588 |
Appl. No.: |
11/280540 |
Filed: |
November 15, 2005 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10122646 |
Apr 12, 2002 |
6967166 |
|
|
11280540 |
Nov 15, 2005 |
|
|
|
Current U.S.
Class: |
156/345.13 ;
204/194; 257/E21.304; 257/E21.309 |
Current CPC
Class: |
H01L 21/32134 20130101;
B24B 49/16 20130101; C25D 5/22 20130101; C25D 7/12 20130101; H01L
21/3212 20130101; B24B 37/005 20130101; B24B 37/046 20130101; C25D
17/001 20130101 |
Class at
Publication: |
156/345.13 ;
204/194 |
International
Class: |
C23F 1/00 20060101
C23F001/00 |
Claims
1. An apparatus for monitoring force applied on a top conductive
surface of a wafer during an electrotreatment process that uses an
electrotreatment solution, comprising: an electrode; an
electrotreatment dispenser for dispensing the electrotreatment
solution; a workpiece surface influencing device disposed between
the top conductive surface and the electrode; means for creating a
potential difference between the electrode and the top conductive
surface in the presence of the electrotreatment solution; a device
adapted to provide for relative movement of the wafer with respect
to the workpiece surface influencing device in the presence of
physical contact between the top conductive surface and the
workpiece surface influencing device while the electrotreatment
solution is disposed between the top conductive surface and the
workpiece surface influencing device and while the potential
difference between the electrode and the top conductive surface is
maintained; and a monitoring system adapted to monitor a frictional
force occurring between the top conductive surface and the
workpiece surface influencing device.
2. The apparatus according to claim 1, further including: a control
system adapted to input a monitoring signal from the monitoring
system and create an output signal that will control the frictional
force occurring between the top conductive surface and the
workpiece surface influencing device.
3. The apparatus according to claim 2, wherein: the device adapted
to provide for relative movement is a wafer holding device that
includes a spindle motor for rotating the wafer holder, the spindle
motor maintaining the relative movement between the top conductive
surface and the workpiece surface influencing device; and the
monitoring system monitors a signal that corresponds to a torque
value of the spindle motor, such that the torque value of the
spindle motor corresponds to the frictional force.
4. The apparatus of claim 3, wherein the wafer holding device
further includes a lateral drive motor to create lateral movement
between the conductive surface and the workpiece surface
influencing device.
5. The apparatus according to claim 4, wherein the signal monitored
by the monitoring system further includes a torque value of the
lateral drive motor.
6. The apparatus of claim 3, wherein the wafer holding device
further includes a a vertical drive motor that is used to fix a
displacement between the conductive surface and the workpiece
surface influencing device.
7. The apparatus of claim 1, wherein the electrotreatment dispenser
is adapted to dispense an electrolyte containing a conductive
material therein and wherein the means for creating a potential
difference create a depositing potential difference.
8. The apparatus of claim 1, wherein the electrotreatment dispenser
is adapted to dispense an etching or polishing solution and wherein
the means for creating a potential difference create a polishing
potential difference.
9. The apparatus of claim 1, wherein the monitoring system is
adapted to monitor the frictional force periodically during the
processing of the wafer.
10. The apparatus of claim 2, the device contains a wafer support
to which pressure is applied on a backside in order to control the
frictional force occurring between the top conductive surface and
the workpiece surface influencing device.
11. The apparatus of claim 2, the device moves vertically in order
to control the frictional force occurring between the top
conductive surface and the workpiece surface influencing
device.
12. The apparatus of claim 2, wherein the device is further adapted
to provide for full-face plating of the wafer during a period of
time with the relative motion.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application is a divisional application of and claims
priority to co-pending U.S. patent application Ser. No. 10/122,646,
filed Apr. 12, 2002, the disclosure of which is hereby incorporated
by reference in its entirety.
BACKGROUND
[0002] 1. Field of the Invention
[0003] The present invention relates to manufacture of
semiconductor integrated circuits and, more particularly to a
method for planar deposition or etching of conductive layers.
[0004] 2. Description of the Related Art
[0005] Conventional semiconductor devices generally include a
semiconductor substrate, such as a silicon substrate, and a
plurality of sequentially formed dielectric interlayers such as
silicon dioxide and conductive paths or interconnects made of
conductive materials. Copper and copper alloys have recently
received considerable attention as interconnect materials because
of their superior electro-migration and low resistivity
characteristics. The interconnects are usually formed by filling
copper in features or cavities etched into the dielectric layers by
a metallization process. The preferred method of copper
metallization is electroplating. In an integrated circuit, multiple
levels of interconnect networks laterally extend with respect to
the substrate surface. Interconnects formed in sequential layers
can be electrically connected using vias or contacts.
[0006] In a typical process, first an insulating layer is formed on
the semiconductor substrate. Patterning and etching processes are
performed to form features such as trenches and vias in the
insulating layer. Then, a conductor such as copper is electroplated
to fill all the features. However, the plating process results in a
thick copper layer on the substrate, some of which need to be
removed before the subsequent step. Conventionally, after the
copper plating, CMP process is employed to globally planarize and
then reduce the thickness of the copper layer down to the level of
the surface of the barrier layer, which is later also removed. CMP
is a costly and time consuming process that reduces production
efficiency. High pressures used in the CMP processes also damage
low-k dielectrics that are mechanically weaker than the silicon
oxide.
[0007] The adverse effects of conventional material removal
technologies may be minimized or overcome by employing an
Electrochemical Mechanical Processing (ECMPR) approach that has the
ability to provide thin layers of planar conductive material on the
workpiece surface, or even provide a workpiece surface with no or
little excess conductive material. This way, CMP process can be
minimized or even eliminated. The term of Electrochemical
Mechanical Processing (ECMPR) is used to include both
Electrochemical Mechanical Deposition (ECMD) processes as well as
Electrochemical Mechanical Etching (ECME), which is also called
Electrochemical Mechanical Polishing (ECMP). It should be noted
that in general both ECMD and ECME (or ECMP) processes are referred
to as electrochemical mechanical processing (ECMPR) since both
involve electrochemical processes and mechanical action on the
workpiece surface.
[0008] Descriptions of various planar deposition and planar etching
methods i.e. ECMPR approaches and apparatus, can be found in the
following patents and pending applications, all commonly owned by
the assignee of the present invention: U.S. Pat. No. 6,126,992
entitled "Method and Apparatus for Electrochemical Mechanical
Deposition," U.S. application Ser. No. 09/740,701 entitled "Plating
Method and Apparatus that Creates a Differential Between Additive
Disposed on a Top Surface and a Cavity Surface of a Workpiece Using
an External Influence," filed on Dec. 18, 2001, and U.S.
application filed on Sep. 20, 2001 with Ser. No. 09/961,193
entitled "Plating Method and Apparatus for Controlling Deposition
on Predetermined Portions of a Workpiece". U.S. application with
Ser. No. 09/960,236 filed on Sep. 20, 2001, entitled "Mask Plate
Design," and U.S. Provisional Application with Ser. No. 60/326,087
filed on Sep. 28, 2001, entitled "Low Force Electrochemical
Mechanical Processing Method and Apparatus," both assigned to the
same assignee as the present invention. These methods can deposit
metals in and over cavity sections on a workpiece in a planar
manner.
[0009] FIG. 1 shows an exemplary ECMPR system 10, which includes a
workpiece-surface-influencing device (WSID) 12 such as a mask, pad
or a sweeper, a carrier head 14 holding a workpiece 16 such as a
wafer, and an electrode 18. The wafer can be a silicon wafer to be
plated with copper using the ECMPR system or it can be a copper
plated wafer to be electro-etched using the ECMPR approach. The
WSID 12 is used during at least a portion of the ECMPR when there
is physical contact and relative motion between a surface 20 of the
wafer 16 and the top surface 22 of the WSID 12. During ECMPR, A top
surface 22 of the WSID sweeps the surface 20 of the wafer 16 while
an electrical potential is established between the electrode 18 and
the surface of the wafer. Alternately, in some cases potential is
established right after WSID surface 22 sweeps the surface 20 of
the wafer. In other words establishment of the potential and
sweeping of the substrate surface by the WSID do not have to be
simultaneous or continuous as described in detail in previous
applications cited above. Channels 24 of the WSID allow a process
solution 26 such as a copper plating electrolyte to flow to the
surface of the wafer. The WSID is basically composed of a top layer
28, which is preferably made of a flexible film, and a compressible
layer 30 that is made of a spongy or otherwise compressible
material. The top layer 28 and the compressible layer 30 may
themselves be composite layers, i.e. they may consist of one or
more layers of different materials. The top layer 28 may be an
abrasive film. The WSID is supported by a rigid support plate 32
which is porous, or otherwise has set of openings to direct the
process solution towards the surface of the workpiece surface
through the WSID structure.
[0010] If the ECMD process is carried out to plate a conductor such
as copper onto the wafer in the ECMPR system of FIG. 1, the surface
of the wafer is wetted by a deposition electrolyte which is also in
fluid contact with an electrode (in this case an anode), such as
electrode 18 shown in FIG. 1, and a potential is applied between
the surface of the wafer and the electrode rendering the wafer
surface cathodic. If the ECME process is carried out, the surface
of the wafer is wetted by the deposition electrolyte or a special
etching electrolyte, which is also in fluid contact with an
electrode (this time the cathode) and a potential is applied
between the surface of the wafer and the electrode rendering the
wafer surface anodic. Thus etching takes place from the wafer
surface.
[0011] The ECMPR systems are capable of performing planar or
non-planar plating as well as planar or non-planar electro-etching.
If non-planar process approach is chosen, the front surface of a
wafer is brought near the top flexible layer of the WSID, but it
does not touch it, so that non-planar metal deposition can be
performed. Further, if planar process approach is chosen, the front
surface of the wafer contacts the top flexible layer, at least
during a portion of the process period, as a relative motion is
established between the top layer and the wafer surface. As an
electrolyte solution is delivered through the channels of the WSID,
the wafer is moved, i.e., rotated and preferably also laterally
moved, while the front surface contacts the flexible layer. Under
an applied potential between the wafer and an electrode, and in the
presence of the process solution, the metal such as copper, is
plated on or etched off the front surface of the wafer depending on
the polarity of the voltage applied between the wafer surface and
the electrode. During the process, the wafer surface is pushed
against the surface of the WSID or vice versa at a pressure range
of about 0.1-2 psi, preferably at a range of 0.1-1 psi, at least
part of the time when the surface of the workpiece is swept by the
WSID. Planar deposition is achieved due to this sweeping action as
described in the above-cited patent applications. It should be
noted that even higher pressures may be applied to the substrate
surface by the WSID in applications where high stress does not
cause damage on the surface of the substrate. It should also be
noted that although the invention is described as it is applied to
manufacturing of interconnects on wafers, it is applicable to all
cases where cavities on a substrate is filled with a planar
conductor material. Although a specific WSID structure is given to
describe the invention, the invention is applicable to any WSID
design or structure as long as the WSID is used to contact the
workpiece surface during at least some portion of the deposition or
etching process.
[0012] The amount of force that is applied on the wafer during
ECMPR affects the characteristics of the deposited layer. This
physical contact needs to be uniform and repeatable for best
results. For example, during planar deposition of copper layers, if
the wafer is pushed against the top flexible layer, the force on
the wafer is increased as the compressible layer is compressed more
and more toward the support layer. For many compressible layer
materials, the force exerted onto the wafer surface increases
roughly linearly as the wafer is pushed into the WSID from a
`zero-touch` position in which the wafer surface just touches the
WSID surface. For example, for a selected compressible layer
material with certain spring constant, pushing the wafer into the
WSID by 0.5 mm may apply an average force of 0.3 psi onto the wafer
surface. Increasing the pushing distance to 1 mm may increase the
force to approximately 0.6 psi. For other materials this
relationship may not be linear but it may show a sub-linear or
super-linear behavior. In any case, it can be appreciated from the
above discussion that the stability of the ECMPR over hundreds or
thousands of wafers may require a knowledge of the "zero-touch"
position, the amount of push or displacement by the wafer surface
into the WSID, or the force applied onto the wafer surface.
[0013] Conventionally, the touch position is determined during the
set-up of the ECMPR equipment after installation of a new WSID or
any time a change is made in the set-up that may have affected the
zero-touch position. The touch position can be determined, for
example, by placing a thin (typically 2-4 mils thick) sheet between
the wafer surface and the WSID. The gap between the wafer surface
and the WSID is then gradually reduced through commands to the
z-motion controller and z-motion motor typically at 0.1 mm
increments. As the wafer surface is brought closer and closer to
the WSID surface the thin sheet in between the two surfaces is
continually moved. When the zero-touch position is reached the
sheet cannot be easily moved any more indicating that the WSID
surface is pushed against the wafer surface. This procedure is time
consuming and not necessarily accurate.
[0014] Once the zero-touch position is determined and recorded, the
ECMPR recipe then commands a vertical, or z-motion, controller of
the wafer holder 14 to push the wafer into the WSID during the
process, by a fixed amount relative to this recorded zero-touch
value, the amount of displacement corresponding to the desired
level of force on the wafer surface. For example, zero-touch
position may correspond to a reading of 30.55 mm (a position that
is measured with respect to a surface under the WSID of FIG. 2, for
example with respect to the top of the layer 125c) on the
z-position indicator. If during ECMPR, z-position controller asks
the z-position motor to bring the wafer surface down to a z
displacement position of 30.05 mm, this will mean that the wafer
surface is pushed into the WSID by an amount of 0.5 mm which may
correspond to a force of 0.5 psi depending upon the characteristics
such as the spring constant of the compressible layer.
[0015] There are, however, drawbacks in this approach. For example,
during processing of plurality of wafers with the same WSID, the
compressible layer of the WSID may swell or shrink due to exposure
to the process solutions, and this may cause the "z" position of
the WSID surface to change in time from the value set during the
initial set up, which in turn may result in wafer to wafer
variations in zero touch position. Soaking of the compressible
layer 30 in process solution for long periods of time may also
change the spring constant of this layer. In other words the force
applied to the wafer surface may not be the same for the same
displacement or push value after the WSID is soaked in the process
solution. Also, if the WSID is replaced, the height of the WSID or
the distance between the WSID and the wafer surface may change due
to the possible thickness variation from batch to batch of the
compressible layer of the WSID. This may result in variations in
zero touch positions for the wafers processed before and after the
replacement. As explained above, variations in the zero touch
position may result in changes in the force that is exerted on the
wafers during the process. It may also cause changes in the
distance between the WSID surface and the wafer surface during
no-touch deposition. Furthermore, changes in the properties of the
compressible layer or the top layer of the WSID may result in
changes in the force applied to the wafer surface even for the same
displacement of the wafer surface into the WSID structure. Such
process non-uniformity is not desirable in the semiconductor
industry.
[0016] To this end, there is need for an improved method and
apparatus for monitoring and controlling the force applied to the
surface of substrates during planar metal electrochemical
mechanical deposition or electro-etching.
SUMMARY
[0017] It is an advantage of the present invention to obtain a more
uniform electrotreatment process.
[0018] It is a further advantage of the present invention to
provide a more uniform electrotreatment process when sequentially
processing a plurality of workpieces using the same
electrotreatment apparatus.
[0019] It is a further advantage of the present invention to
provide a desired force between a conductive top surface of a
workpiece and a workpiece surface influencing device during
electrotreatment of the workpiece.
[0020] It is a further advantage of the present invention to
monitor a torque of a motor that is used to maintain relative
motion between a conductive top surface of a workpiece and a
workpiece surface influencing device in the presence of physical
contact between the conductive top surface of the workpiece and the
workpiece surface influencing device.
[0021] It is a further advantage of the present invention to
control a force applied to a top conductive surface of a workpiece
during electrotreatment.
[0022] Certain of the above advantages, either singly or in
combination, are achieved by the present invention. In one aspect,
the present invention monitors a signal corresponding to a torque
value of a motor that is used to maintain relative motion between a
conductive top surface of a workpiece and a workpiece surface
influencing device in the presence of physical contact between the
conductive top surface of the workpiece and the workpiece surface
influencing device.
[0023] In another aspect, the present invention uses the signal to
control a force applied to a top conductive surface of a workpiece
during electrotreatment.
BRIEF DESCRIPTION OF THE DRAWINGS
[0024] The above and other aspects, features, and advantages of the
present invention are further described in the detailed description
which follows, with reference to the drawings by way of
non-limiting exemplary embodiments of the present invention,
wherein like reference numerals represent similar parts of the
present invention throughout several views and wherein:
[0025] FIG. 1 shows an exemplary ECMPR system;
[0026] FIG. 2 illustrates an ECMPR system with a force monitoring
and control system according to the present invention.
[0027] FIG. 3 shows a portion of the ECMPR system with a wafer
being operated upon in close proximity to a workpiece surface
influencing device.
[0028] FIG. 4 shows an electrotreatment process stage when a
workpiece is brought into an initial touch position according to
the present invention.
[0029] FIG. 5 shows a touch stage of the electrotreatment process
according to the present invention.
[0030] FIG. 6 illustrates an exemplary graph of torque readings
versus time during a process having stages of no-touch, zero-touch,
and touch according to the present invention.
[0031] FIG. 7 illustrates another illustrative embodiment of a
portion of an ECMPR system according to the present invention.
[0032] FIG. 8 illustrates another embodiment of the present
invention that alters pressure on a backside support within a wafer
carrier head to change the applied force.
DETAILED DESCRIPTION
[0033] As will be described below, the present invention provides a
force monitoring system and method for ECMPR techniques that use a
WSID for processing wafers. The force monitoring system of the
present invention monitors variations in the motor current or
torque of the carrier head to monitor and, if desired, control the
force on the wafers. By processing wafers at the same torque level,
without regard to zero-touch position or displacement values, each
wafer is processed with the same amount of force applied to its
surface irrespective of possible changes that may take place in the
material characteristics of the WSID. The present invention can be
used in the initial set up of the ECMPR equipment. The invention
also measures, monitors and if desired, controls, the force applied
on wafers to ensure uniform processing of each wafer at the same
force level, regardless of changes in zero touch position or
materials properties of the WSID.
[0034] FIG. 2 illustrates an ECMPR system 100 having an exemplary
force monitoring station 102. The system 100 comprises a carrier
head 104, a WSID 106 having channels 108 and a surface 109. One
carrier head design which is especially suited for use to practice
the present invention is disclosed in US provisional application
with Ser. No. 60/326,087 filed on Sep. 28, 2001, entitled "Low
Force Electrochemical Mechanical Processing Method and Apparatus,"
assigned to the assignee of the present invention. The system also
comprises an electrode 110 immersed in a process solution 112
(typically an electrolyte in the case of ECMD or an electrolyte or
an electropolishing etching solution containing no slurry in the
case of ECME) which is contained in a container 114. A wafer 118
with a front surface 116, typically a conductive front surface, to
be processed is held by the carrier head 104. Electrode 110 and the
front side of the wafer are electrically connected to the opposite
terminals of power supply 120 during processing. The wafer 118 may
be a preprocessed silicon wafer having features or cavities such as
vias or trenches lined with a barrier layer and a copper seed
layer. The carrier head 104 can be rotated by a shaft 121 that is
connected to a spindle motor 122A (preferably using a servo motor),
moved in a z-direction using a z-drive or vertical drive motor 122B
(preferably using a stepper motor), and also, preferably can be
moved in a lateral or y-direction using a y-drive or lateral drive
motor 122C (preferably using a stepper motor). It is noted that the
specific location of each of the motors 122A, 122B and 122C is not
illustrated in FIG. 2, but these motors are shown in block form to
illustrate each of their inclusion in the system 100. Power from
power supply 20, which will be at the appropriate level for each
respective motor 122, is supplied to a respective one of drivers
124A-C, which drivers 124A-C are used to determine the power
supplied to each motor 122 based upon signals supplied from the
force monitoring unit 102. Signals are provided from each of the
respective drivers 124 that provide feedback information relating
to the torque of the resspective motor. These signals are used by
the force monitoring unit 102 as described hereinafter along lines
132.
[0035] The WSID is comprised of a top layer 125a, an intermediate
layer 125b and a support plate 125c. The top layer is made of a
flexible material and preferably has an abrasive hard surface. The
intermediate layer is a compressible layer made of a material such
as polyurethane foam. Examples of various WSID designs which are
suited for use to practice the present invention are also disclosed
in above cited U.S. provisional application with Ser. No.
60/326,087 filed on Sep. 28, 2001, entitled "Low Force
Electrochemical Mechanical Processing Method and Apparatus,"
assigned to the assignee of the present invention.
[0036] As illustrated in FIG. 2, the force monitoring unit 102 may
comprise a computer 126 with a CPU (not shown) and a memory unit
(not shown), a monitor 128 and input devices such as a keyboard 130
or a pointing device (not shown). The force monitoring unit 102
shown in FIG. 2 is simplified for the purpose of clarification, its
components and the location and other features may vary and such
variations are within the scope of this invention. The computer may
run a suitable process monitoring and control software. The
computer 126 may receive input signals along signal lines 132 from
the drivers 124A-C (in the preferred embodiment from motor 122A as
described hereinafter) relating to the torque value of the various
motors 122A-C, which signals typically correspond to the current
drawn from respective motor. The output signal lines 134 may carry
control signals indicating the direction of movement (clockwise or
counterclockwise in the case of a stepper motor used for spindle
motor 122A, or up or down counts in the case of a stepper motor
used for motors 122B and 122C) and the amount of electrical current
or power (typically amount of torque in the case of a servo motor
used for spindle motor 122A or acceleration in the case of a
stepper motor used for motors 122B and 122C) that is used by each
of the drivers 124A-C to determine the appropriate power that gets
supplied to each of the motors 122.
[0037] In addition to using the output signals along signal lines
134 during actual processing, the output signals along signal lines
134 may contain commands that will result in the various motors 122
performing a a test to check the current zero touch position and
adjust the amount the wafer 118 is pushed into the WSID. As during
other processing, signals provided along lines 132 that can then be
monitored by the force monitoring unit 102, including current data
that can be transformed into torque values to observe changes in,
for example, carrier head motor torque, throughout the test
process. This test may be conducted at the beginning of the process
and may be repeated at intervals during the process. The input
signals along lines 132 including current data to computer 126 may
be transformed into torque values or may alternatively already
represent the torque values, to observe changes in carrier head
motor torque throughout the process time.
[0038] FIGS. 3-5 describe the process of the present invention with
help of an exemplary graph 202 in FIG. 6 which shows torque
readings versus time during a process having stages of no-touch
(I), zero-touch (II) and a touch (III).
[0039] FIG. 3 shows a portion of the system 100, shown in FIG. 2,
in which the wafer 118 is in close proximity of the WSID. At this
stage the vertical distance between the wafer and the WSID may be
approximately 0.5-5 millimeters. Since there is no physical contact
between the wafer and the WSID, the torque reading shown with graph
200 in FIG. 6 is assumed zero through out the no-touch stage (I).
It should be noted that in actual practice there will be a torque
reading. However, this reading will be taken as the reference
reading which will be assumed as zero for calibration purposes.
[0040] FIG. 4 shows the stage when the wafer is brought to the
initial touch position or zero-touch position on the WSID surface
109. At this stage, the gap between the wafer surface 116 and the
surface of the WSID is zeroed, while the wafer is rotated or
otherwise moved. In response to contact and resulting frictional
force between the surface 116 of the wafer and the surface 109 of
the WSID, the torque value is suddenly increased. This is shown in
FIG. 6 in graph 200 in zero-touch stage (II) as a short steep climb
followed by a plateau in torque value. The z position of the
carrier head when torque changes in stage II is registered by the
computer 126 of the force monitoring unit 102 as the zero touch
position.
[0041] FIG. 5, shows the touch stage of the process where the wafer
118 is pressed onto the WSID while the wafer is being rotated and
possibly translated at the same time. At this stage, the wafer is
pushed or pressed down by a predetermined depth into the WSID,
which is denoted with `d`. FIG. 6 shows the abrupt change in torque
value in the touch stage (III), as the wafer is pressed down to the
depth `d`. Once the depth `d` is reached, the force applied on the
wafer reaches its predetermined value for that depth d.
Alternately, the torque value may be pre-determined and the wafer
is pressed down slowly to get the pre-determined value of the
torque. Once the required torque value is reached the carrier head
z motion is stopped. In any case both the `d` value and the
corresponding torque value may be registered by the computer 126 of
the monitoring unit 102. If a plurality of wafers is to be
processed, wafers following the first wafer may be processed using
the same registered torque value that was obtained for the first
wafer. This provides repeatability for the process. However, as
explained above in the background section, during the process,
zero-touch position of the wafer may also change. This, in turn,
may change the spacing between the wafer surface and the WSID
surface during the non-touch plating step. It is, therefore,
preferable to at least occasionally adjust the zero-touch position
during processing.
[0042] In one embodiment the system of FIG. 2 may be used to
initially setup the ECMPR system. In other words the zero-touch
position can be determined during, the initial set-up. This can be
achieved in two ways. In manual approach the wafer, preferably a
set-up wafer, may be moved (preferably rotated) as the torque value
is monitored. Then wafer may be incrementally lowered towards the
WSID by manually controlling the z-motion motor, through for
example a switch. When the torque value shows a sudden increase
indicating contact between the wafer surface and the WSID surface,
z motion is stopped, or switched off, and the z reading is taken as
the zero-touch position. Alternately, in the automatic mode, the
sudden change in the torque is sensed by the electronics and z
motion is automatically stopped and the z value for zero-touch
position is registered by the computer. Once the zero touch
position is determined process can be run by placing the wafer
surface above the WSID by a pre-determined amount (e.g. 2 mm) for
no-touch plating or by pushing the wafer surface into the WSID by a
pre-determined amount (e.g. 1 mm) for ECMPR. The system in FIG. 2
may also be used to automatically determine the zero touch position
at constant intervals throughout processing several wafers.
[0043] In the case of position-based control described above, the
system is used to periodically monitor and adjust the zero-touch
position and place the wafer surface by pre-determined distance
(dictated by the process recipe) above or below this zero-touch
position. It is understood that during the set up stage, the
present invention is used to determine where the zero-touch
position is. After the initial determination, the carrier head is
moved up or down by a predetermined (by the process recipe)
distance to carry out either no-touch or touch ECMD or ECME
process. As described above, the force monitoring unit 102
periodically determines the zero-touch position.
[0044] In another embodiment, the present invention performs
torque-based control. In this embodiment, the process recipe
contains the desired torque values for the electrochemical
mechanical processing, and also the desired distance from the WSID
surface the workpiece is to be processed during a possible
non-contact or no-touch processing step. In this case, the
zero-touch position is determined as before. Then the wafer may be
placed by the z-motor control by the predetermined amount (dictated
by the process recipe) above the WSID surface and non-contact
processing can be carried out. For processing in contact mode or
touch mode, the wafer is moved towards the WSID and then pushed
into the WSID structure as the force monitoring unit 102 monitors
the torque. When the desired torque value dictated by the process
recipe is reached, the force monitoring unit 102 stops the z motion
and wafer processing is carried out at this desired torque value.
It should be noted that the torque value is related to the
frictional force between the wafer surface and the WSID surface,
which in turn is related to the force applied by the WSID structure
onto the wafer surface. Throughout the process, this frictional
force value can be kept relatively constant on the wafers by
automatic adjustment of the vertical displacement `d` by the force
monitoring unit 102. This way a plurality wafers can be processed
under similar conditions despite any changes that may be taking
place in the properties of the WSID. As the discussion above shows,
the present invention may be used for just monitoring zero-touch
position and frictional force on the wafer surface. It may also be
used for actively controlling the frictional force on the
wafers.
[0045] It should be noted that this invention is also useful in
evaluating different WSID surfaces in terms of frictional force
that they apply to the wafer surface. Depending on the friction
coefficient of the material of the top layer 125a of the WSID, even
for the same `d` value, the frictional force on the wafer surface
may change. For example, for the same displacement value or `d`
value, materials with low friction coefficients may yield lower
torque values than the materials with higher friction
coefficients.
[0046] As an example let us assume that plurality of wafers such as
500 wafers will be processed by an ECMD system using a process
recipe that calls for a first process period t1 of no-touch copper
plating on the wafer surface with wafer surface 1 mm above the
surface of the WSID. This step may be, for example, used to fill
substantially all the features with at least one dimension less
than about 0.5 um with copper. The process recipe may then call for
a second process period t2 during which time planar deposition of
copper may take place on the wafer surface. Let us assume that this
planar deposition step requires the surface of the wafer to be
pushed into the WSID structure by 0.5 mm, which may correspond to a
force of 0.5 psi being applied to the wafer surface for that
specific WSID structure. Let us also assume that a brand new WSID
is installed in the system for processing this plurality of wafers.
It would be beneficial to process all the wafers under
substantially the same conditions, i.e. first at a distance 1 mm
away from the WSID surface, then during planar deposition at a
relatively constant force applied to the wafer surface. There are
two approaches to be taken as will be described below:
[0047] If the WSID structure is stable for a predetermined period
of time necessary to process the plurality of wafers, the initial
zero-touch position preferably should be determined after
installing the WSID. The predetermined time period may be the time
required to process certain number of wafers without replacing the
WSID or re-determining its zero-touch position. Initially, a setup
wafer is held in close proximity of the WSID (see FIG. 3). During
this initial stage the wafer is being rotated and the torque value
is registered as zero. Then, the wafer is lowered on the WSID and
the z position when the torque suddenly changes is recorded as the
zero-touch position. From this point on the set up is considered
complete and the plurality of wafers can be processed by placing
their surface by 1 mm above this pre-determined zero-touch position
and then 0.5 mm below it.
[0048] In practice, even if the spring constant of the compressible
layer in the WSID structure may not change with time, there may be
some swelling of it in the process solution. This may change the
zero-touch position in time. Therefore, the zero-touch position may
be periodically checked by the system of FIG. 2. This can be
achieved by inserting a set-up wafer into the process periodically,
for example after every 50 wafer processing, and determining the
zero-touch position as described above.
[0049] Alternately during the process the nth wafer, such as the
50th, that is already processed may be used to check the zero-touch
position as follows. Consider the case the wafer is processed by
first a non-touch plating step followed by a touch plating step.
After the touch plating step, the z position of the wafer surface
may be slowly changed, for example reducing "d" at 0.05 or 0.1 mm
intervals while rotating the wafer and monitoring the torque value.
The torque value is expected to decrease towards zero. The z value
when the torque reaches zero or near-zero is the zero-touch
position which may be recorded as the new zero-touch position to be
used for the next 50 wafer processing.
[0050] If the WSID structure is unstable (both the spring constant
and thickness of the compressible layer changing) for the period of
time necessary to process a plurality of wafers, force-based or
torque-based control is necessary. As an example let us assume that
a plurality of wafers, such as 500 wafers, will be processed by an
ECMD system using a process recipe that calls for a first process
period t1 of no-touch copper plating on the wafer surface with
wafer surface 1 mm above the surface of the WSID. This step may be,
for example, used to fill substantially all the features with at
least one dimension less than about 0.5 um with copper. The process
recipe may then call for a second process period t2 during which
time planar deposition of copper may take place on the wafer
surface. Let us assume that this planar deposition step requires
the WSID structure to apply a pressure of 0.5 psi on the wafer
surface, which may correspond to a pre-determined torque value of
"Q" for that specific WSID structure. Let us also assume that a
brand new WSID is installed in the system for processing this
plurality of wafers. It would again be beneficial to process all
the wafers under substantially the same conditions, i.e. first at a
distance 1 mm away from the WSID surface, then during planar
deposition at a constant torque value "Q" which corresponds to a
relatively constant pressure of 0.5 psi applied to the wafer
surface.
[0051] Initially, a setup wafer is held in close proximity of the
WSID (see FIG. 3). During this initial stage the wafer is being
rotated and the torque value is registered as zero. Then, the wafer
is lowered on the WSID using the z-drive motor 122B and the z
position when the torque suddenly changes is recorded as the
zero-touch position. From this point on the set up is considered
complete and the plurality of wafers can be processed by placing
their surface by 1 mm above this pre-determined zero-touch position
to carry out the non-touch process step. For the touch process
step, the wafer surface is slowly pushed into the WSID structure by
the z-motor 122B and z-motor control as the torque value is
monitored by system 102 of FIG. 2. When the torque value reaches
"Q" z motion is stopped and process commences. During process, the
torque value "Q" is kept constant through continuous monitoring and
feedback loop that adjusts the z-position to keep the torque value
constant. In this approach the zero-touch position should also be
continually or periodically monitored and adjusted as explained
before. The torque value is monitored and controlled for each wafer
assuring process stability and repeatability.
[0052] While the torque value for the spindle motor 122A that
rotates the carrier head 104 is discussed above as being used for
purposes of monitoring torque, it should be understood that the
lateral or y-drive motor 122C can also be for monitoring torque,
although monitoring from such motors will typically not provide as
sensitive a measurement as from the spindle motor 122A.
[0053] It should be noted that the invention is described by giving
as an example the WSID structure which is especially suited for a
low-force ECMPR approach as disclosed in U.S. Provisional
Application with Ser. No. 60/326,087 filed on Sep. 28, 2001,
entitled "Low Force Electrochemical Mechanical Processing Method
and Apparatus," assigned to the same assignee as the present
invention. However, it should be appreciated that the invention is
applicable to any ECMPR approach that uses a workpiece and a WSID.
For example, processes using rigid WSID structures can also be
monitored and controlled by the present invention. In this case the
workpiece holder may be, for example, a gimballing type as
disclosed in patent application U.S. application Ser. No.
09/472,523 filed Dec. 27, 1999 entitled "Work Piece Carrier Head
For Plating or Polishing" or as described in Ser. No. 09/910,686
filed Jul. 20, 2001 entitled "Method of Sealing a Wafer Backside
for Full-Face Electrochemical Plating and the force between the
workpiece surface and the WSID surface is determined by the
pressure exerted by the workpiece holder onto the back surface of
the wafer pushing it against the WSID surface. In this case the
invention may be used to determine and control the zero-touch
position. It also can monitor the torque from the workpiece holder
motor and adjust the pressure exerted by the workpiece holder
against the WSID structure to keep this torque value constant.
[0054] Similarly the invention is described in terms of a
stationary WSID and moving workpiece where the monitoring of torque
is done from the motor that moves (rotates) the workpiece. It is,
however, possible to carry out ECMPR using stationary workpiece and
moving WSID or even using moving workpiece and moving WSID. As an
example refer to FIG. 7 where a workpiece holder 72 holds the
workpiece 70 in contact with a process solution 73. The WSID 71 is
smaller than the workpiece 70 and it has the capability to rotate.
Zero-touch position and the frictional force monitoring and control
in this case may be done monitoring the torque value of the motor
(not shown) rotating the WSID 71. It should also be noted that
ECMPR does not necessarily need rotation. It just needs relative
motion between the workpiece surface and a WSID (see e.g. U.S.
application Ser. No. 09/740,701 entitled "Plating Method and
Apparatus that Creates a Differential Between Additive Disposed on
a Top Surface and a Cavity Surface of a Workpiece Using an External
Influence," filed on Dec. 18, 2001, and U.S. application filed on
Sep. 20, 2001 with Ser. No. 09/961,193 entitled "Plating Method and
Apparatus for Controlling Deposition on Predetermined Portions of a
Workpiece"). In any case, torque can be monitored and used as
described in this application from any motor providing any motion
to the WSID and/or to the wafer surface.
[0055] FIG. 8 illustrates another embodiment of the present
invention that, instead of moving the entire wafer carrier 104 when
changing the vertical displacement between the conductive surface
and the workpiece surface influencing device, pressure, through
using a fluid or a spring of some type, on a backside surface of a
workpiece support is changed. As shown, the pressure can be applied
using a pressure unit 160 that contains necessary mechanism for
changing the applied pressure, as well as contains sensors for
providing pressure information to the force monitoring unit 102.
Control signals to the pressure unit 160 from the force monitoring
unit 102 and pressure sensor signals from the pressure unit 150 to
the force monitoring unit 102 are shown as being transmitted along
signal lins 162. Signals from the pressure unit and/or the drivers
can be used by the force monitoring unit to sense the change in
pressure and/or displacment.
[0056] The workpiece support will move up or down vertically within
an otherwise stationery (at that time) housing of the wafer carrier
104, depending upon whether pressure is applied or removed, in
order to effect the vertical displacement. U.S. patent application
Ser. No. 09/472,523 filed on Dec. 27, 1999 entitled "Workpiece
Carrier Head for Plating or Polishing" and assigned to the same
assignee as the present invention further describes a pressure
mechanism that can be used with such a wafer carrier 140 that can
be used. Further, full face plating can be obtained applying the
teachings provided in U.S. application Ser. No. 09/910,686 filed
Jul. 20, 2001 entitled "Method of Sealing Wafer Backside for
Full-Face Electrochemical Plating" and assigned to the same
assignee as the present invention.
[0057] Although various preferred embodiments have been described
in detail above, those skilled in the art will readily appreciate
that many modifications of the exemplary embodiment are possible
without materially departing from the novel teachings and
advantages of this invention.
* * * * *