U.S. patent application number 10/812562 was filed with the patent office on 2005-10-06 for wafer polishing control system for chemical mechanical planarization machines.
This patent application is currently assigned to NIKON CORPORATION. Invention is credited to Arai, Hiroshi, Hsin, Yi-Ping, Smith, Christopher B., Soma, Takeshi, Szoboszlay, Gabor D., Uda, Yutaka, Yuan, Bausan.
Application Number | 20050221736 10/812562 |
Document ID | / |
Family ID | 35054996 |
Filed Date | 2005-10-06 |
United States Patent
Application |
20050221736 |
Kind Code |
A1 |
Hsin, Yi-Ping ; et
al. |
October 6, 2005 |
Wafer polishing control system for chemical mechanical
planarization machines
Abstract
Methods and apparatus for applying a uniform polishing pressure
on a wafer are disclosed. According to one aspect of the present
invention, a chemical mechanical planarization polishing apparatus
includes a polishing pad, a wafer holder, and a force control
system. The wafer holder supports a wafer to be polished using the
polishing pad. The polishing pad is arranged to move relative to
the wafer holder such that an area of contact between the wafer
holder and the polishing pad varies. The force control system
including a controller and a plurality of actuators that apply
forces to the polishing pad. The controller controls the forces as
the area of contact varies to substantially maintain a first
polishing pressure on the wafer arranged to be supported by the
wafer holder.
Inventors: |
Hsin, Yi-Ping; (Dublin,
CA) ; Uda, Yutaka; (Tokyo, JP) ; Smith,
Christopher B.; (San Jose, CA) ; Yuan, Bausan;
(San Jose, CA) ; Soma, Takeshi; (Saitama, JP)
; Szoboszlay, Gabor D.; (Santa Clara, CA) ; Arai,
Hiroshi; (Kanagawa, JP) |
Correspondence
Address: |
AKA CHAN LLP
900 LAFAYETE STREET
SUITE 710
SANTA CLARA
CA
95050
US
|
Assignee: |
NIKON CORPORATION
Tokyo
JP
|
Family ID: |
35054996 |
Appl. No.: |
10/812562 |
Filed: |
March 30, 2004 |
Current U.S.
Class: |
451/357 |
Current CPC
Class: |
B24B 49/16 20130101;
B24B 37/042 20130101 |
Class at
Publication: |
451/357 |
International
Class: |
B24B 023/00 |
Claims
What is claimed is:
1. A chemical mechanical planarization polishing apparatus
comprising: a polishing pad; a wafer holder, the wafer holder being
arranged to support a wafer to be polished using the polishing pad,
wherein the polishing pad is arranged to move relative to the wafer
holder such that an area of contact between the wafer holder and
the polishing pad varies; and a force control system, the force
control system including a controller and a plurality of actuators
arranged to apply forces to the polishing pad, the controller being
arranged to control the forces as the area of contact varies to
substantially maintain a first polishing pressure on the wafer
arranged to be supported by the wafer holder.
2. The chemical mechanical planarization polishing apparatus of
claim 1 wherein the controller is arranged to vary the forces as
the area of contact varies to substantially maintain the first
polishing pressure on the wafer arranged to be supported by the
wafer holder.
3. The chemical mechanical planarization apparatus of claim 1
wherein the plurality of actuators are electromechanical actuators,
and controlling the forces applied by the plurality of actuators
includes controlling currents provided to the actuators.
4. The chemical mechanical planarization apparatus of claim 1
wherein the controller is further arranged to determine the forces,
the forces being determined based upon a position associated with
the polishing pad, the first polishing pressure, an air pressure
load on the polishing pad, and a distance between a center of the
polishing pad and a center of gravity associated with the chemical
mechanical planarization apparatus.
5. The chemical mechanical planarization apparatus of claim 4
wherein the area of contact varies with the position associated
with the polishing pad.
6. The chemical mechanical planarization apparatus of claim 4
wherein the position associated with the polishing pad is a
distance between the center of the polishing pad and a center of
the wafer arranged to be supported on the wafer holder.
7. The chemical mechanical planarization apparatus of claim 1
wherein the plurality of actuators includes a first actuator, a
second actuator, and a third actuator, the second actuator and the
third actuator being arranged to each apply a first force to the
polishing pad while the first actuator is arranged to apply a
second force to the polishing pad.
8. The chemical mechanical planarization apparatus of claim 1
wherein the first polishing pressure is a substantially uniform
polishing contact pressure.
9. A wafer planarized using the chemical mechanical planarization
apparatus of claim 1.
10. A method for planarizing a surface of a wafer using a chemical
mechanical planarization apparatus, the chemical mechanical
planarization apparatus including a force system, a polishing pad,
and a chuck arranged to support the wafer substantially in contact
with the polishing pad, the force system including a plurality of
actuators which are arranged to apply forces to the polishing pad,
the method comprising: polishing the wafer using the polishing pad,
wherein polishing the wafer using the polishing pad includes
rotating the wafer while the wafer is in contact with the polishing
pad; determining a current area of contact between the polishing
pad and the wafer; and adjusting the forces applied by each of the
plurality of actuators to substantially maintain a first polishing
pressure on the wafer, wherein the forces are adjusted based upon
the current area of contact.
11. The method of claim 10 further including: determining the
forces to be applied by each of the plurality of actuators to
substantially maintain the first polishing pressure on the wafer,
wherein determining the forces includes determining a current
position associated with the polishing pad, identifying the first
polishing pressure, identifying an air pressure load on the
polishing pad, and determining a current distance between a center
of the polishing pad and a center of gravity associated with the
chemical mechanical planarization apparatus.
12. The method of claim 11 wherein the current area of contact
varies with the current position associated with the polishing
pad.
13. The method of claim 10 wherein the plurality of actuators are a
plurality of electromechanical actuators, and the forces applied by
each of the plurality of actuators are arranged to substantially
pull up on edge areas of the polishing pad.
14. The method of claim 13 wherein the forces applied by each of
the plurality of actuators are varied by altering currents provided
to each of the plurality of actuators.
15. The method of claim 10 wherein the plurality of actuators
includes a first actuator, a second actuator, and a third
actuators, the first actuator and the second actuator being
arranged to be controlled substantially together to apply forces of
substantially the same magnitude.
16. The method of claim 10 further including: setting parameters
associated with the chemical mechanical planarization
apparatus.
17. The method of claim 16 wherein the chemical mechanical
planarization apparatus further includes an arm, the arm being
arranged to position the polishing pad, and wherein the parameters
include at least one of the first polishing pressure, a polishing
time, a chuck rotating speed, a polishing pad rotating speed, and
an arm moving trajectory.
18. A force control system suitable for maintaining approximately a
first polishing pressure on a wafer being polished using a
polishing pad of a chemical mechanical planarization apparatus, the
force control system comprising: a controller, the controller being
arranged to determine a first suction force and a second suction
force that are suitable for enabling a first polishing pressure to
be applied to the wafer while the wafer is being polished; a first
actuator, the first actuator being arranged to apply the first
suction force at a first area approximately near an edge of the
polishing pad to substantially pull up on the edge of the polishing
pad; and a second actuator, the second actuator being arranged to
apply the second suction force at a second area approximately near
the edge of the polishing pad to substantially pull up on the edge
of the polishing pad.
19. The force control system of claim 18 wherein the controller is
arranged to determine the first suction force and the second
suction force based on a contact area between the wafer being
polished and the polishing pad.
20. The force control system of claim 19 wherein the controller is
further arranged to determine the first suction force and the
second suction force based on the first polishing pressure, a
location of a center of gravity of the chemical mechanical
planarization apparatus, an air pressure load applied on the
polishing pad, and at least one location associated with the
polishing pad.
21. The force control system of claim 18 further including a third
actuator, the third actuator being arrange to apply the second
suction force at a third area approximately near the edge of the
polishing pad to substantially pull up on the edge of the polishing
pad.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of Invention
[0002] The present invention relates generally to semiconductor
processing equipment. More particularly, the present invention
relates to a relatively compact wafer polishing apparatus which is
capable of maintaining substantially uniform contact pressure on a
wafer polishing area during operation.
[0003] 2. Description of the Related Art
[0004] Chemical mechanical planarization apparatuses are generally
used during semiconductor fabrication processes to polish wafer
surfaces. As will be appreciated by those skilled in the art,
chemical mechanical planarization is an abrasive process that
polishes a wafer to create a smooth surface through the use of a
chemical slurry and circular motions of a polishing pad and a
wafer. A smooth or even surface on a wafer is critical to ensure
the integrity of a semiconductor formed using the wafer, e.g., to
ensure that interconnects between layers of the wafer are not
deformed and to ensure that desired photolithographic depths of
focus are maintained.
[0005] FIG. 1a is a diagrammatic top-view representation of one
conventional chemical mechanical planarization apparatus used for
wafer polishing. An apparatus 102 includes a polishing pad 104
which has a significantly larger diameter than the diameter of a
wafer 108. Apparatus 102 also includes a swinging arm 106 that
allows polishing pad 104 to be moved relative to wafer 108, which
is typically held in a wafer chuck (not shown) that, like polishing
pad 104, spins while apparatus 102 is in use.
[0006] The use of polishing pad 104 that is larger than wafer 108
generally ensures that substantially even polishing of wafer 108
occurs, as a relatively even contact pressure may be readily
maintained between polishing pad 104 and wafer 108. Hence, a
surface of wafer 108 may be relatively evenly polished. However,
when polishing pad 104 is significantly larger than wafer 108,
apparatus 102 may be inconvenient and, hence, impractical to use.
For example, the overall footprint of apparatus 102 may be larger
than desired, and power requirements associated with rotating
polishing pad 104 relatively to wafer 108 may be higher than
desired. In addition, the cost of a polishing pad 104 that is
larger than a wafer 108 may be relatively high.
[0007] Some systems use a polishing pad that has a smaller diameter
than a wafer being polished. FIG. 1b is a diagrammatic top-view
representation of a wafer polishing apparatus which includes a
polishing pad which is smaller than a wafer being polished. An
apparatus 112 includes a polishing pad 114 which is arranged to
polish a surface of a wafer 118. When substantially all of a
polishing surface of polishing pad 114 is in contact with a surface
of wafer 118, as shown, a first contact pressure may be maintained
between polishing pad 114 and wafer 118. However, when at least a
part of a polishing pad 114 is not in contact with a surface of
wafer 118, as shown in FIG. 1c, a contact pressure between
polishing pad 114 and wafer 118 is not the same as the first
contact pressure which may be maintained when substantially all of
a polishing surface of polishing pad 114 is in contact with wafer
118. Specifically, when polishing pad 114 has a smaller diameter
than the diameter of wafer 118, the application of a constant force
to polishing pad 114 does not enable a uniform contact pressure to
be maintained irregardless of the position of polishing pad 114
relative to wafer 118, as the contact pressure varies depending
upon how much of polishing pad 114 is in contact with wafer 118. As
a result, a polishing process which involves apparatus 118
generally does not allow for a surface of wafer 118 to be evenly
polished.
[0008] The inability to enable relatively even polishing of a
surface of a wafer to occur unless a wafer-polishing pad has a
diameter that is significantly larger than the diameter is often
problematic. Often, trade-offs may have to be made between the
higher costs associated with an apparatus which enables relatively
even polishing of a surface and the lower costs associated with an
apparatus which provides for less even polishing.
[0009] Therefore, what is needed is a relatively compact and
cost-efficient apparatus which allows for relatively even polishing
of a wafer surface. That is, what is desired is a chemical
mechanical planarization polishing apparatus which enables a
wafer-polishing pad that is not significantly larger than a wafer
to provide relatively even polishing of a surface of the wafer.
SUMMARY OF THE INVENTION
[0010] The present invention relates to a chemical mechanical
planarization polishing apparatus which allows a substantially
uniform polishing pressure to be maintained on the wafer. According
to one aspect of the present invention, a chemical mechanical
planarization polishing apparatus includes a polishing pad, a wafer
holder, and a force control system. The wafer holder supports a
wafer to be polished using the polishing pad. The polishing pad is
arranged to move relative to the wafer holder such that an area of
contact between the wafer holder and the polishing pad varies. The
force control system including a controller and a plurality of
actuators that apply forces to the polishing pad. The controller
controls the forces as the area of contact varies to substantially
maintain a first polishing pressure on the wafer arranged to be
supported by the wafer holder.
[0011] In one embodiment, the controller is arranged to vary the
forces as the area of contact varies to substantially maintain the
first polishing pressure on the wafer arranged to be supported by
the wafer holder. In another embodiment, the controller determines
the forces based upon a position associated with the polishing pad,
the first polishing pressure, an air pressure load on the polishing
pad, and a distance between a center of the polishing pad and a
center of gravity associated with the chemical mechanical
planarization apparatus.
[0012] A chemical mechanical planarization polishing apparatus
which includes a force control system that allows the magnitude of
forces applied on a polishing pad to be adjusted as needed enables
a substantially uniform polishing pressure to be maintained on a
wafer that is being polished using the apparatus. By allowing a
desired polishing pressure to be maintained regardless of how large
a contact area between the polishing pad and the wafer is, i.e., by
adjusting forces applied by actuators of the force control system
based upon the size of a contact area between the polishing surface
of the polishing pad and the polishing surface of the wafer, the
likelihood that the integrity of the polished wafer is compromised
during the polishing process may be reduced.
[0013] According to another aspect of the present invention, a
method for planarizing a surface of a wafer using an apparatus
which includes a force system with a plurality of actuators, a
polishing pad, and a chuck arranged to support the wafer
substantially in contact with the polishing pad involves polishing
the wafer using the polishing pad. Polishing the wafer using the
polishing pad includes rotating the wafer while the wafer is in
contact with the polishing pad. The method also includes
determining a current area of contact between the polishing pad and
the wafer, and adjusting the forces applied by each of the
plurality of actuators to substantially maintain a first polishing
pressure on the wafer. The magnitudes of the forces are adjusted
based upon the current area of contact.
[0014] In one embodiment, the method also includes determining the
forces to be applied by each of the plurality of actuators to
substantially maintain the first polishing pressure on the wafer.
Determining the forces includes determining a current position
associated with the polishing pad, identifying the first polishing
pressure, identifying an air pressure load on the polishing pad,
and determining a current distance between a center of the
polishing pad and a center of gravity associated with the chemical
mechanical planarization apparatus.
[0015] These and other advantages of the present invention will
become apparent upon reading the following detailed descriptions
and studying the various figures of the drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] The invention may best be understood by reference to the
following description taken in conjunction with the accompanying
drawings in which:
[0017] FIG. 1a is a diagrammatic top-view representation of one
conventional chemical mechanical planarization apparatus used for
wafer polishing.
[0018] FIG. 1b is a diagrammatic top-view representation of a wafer
polishing apparatus which includes a polishing pad which is smaller
than a wafer being polished.
[0019] FIG. 1c is a diagrammatic top-view representation of a wafer
polishing apparatus which includes a polishing pad which is smaller
than a wafer being polished and is not completely in contact with
the wafer.
[0020] FIG. 2 is a diagrammatic top-view representation of a
chemical mechanical planarization polishing apparatus in accordance
with an embodiment of the present invention.
[0021] FIG. 3 is a block diagram representation of a polishing
apparatus with a non-contact force system in accordance with an
embodiment of the present invention.
[0022] FIG. 4 is a diagrammatic representation of an orientation of
actuators of a force system in accordance with an embodiment of the
present invention.
[0023] FIG. 5 is a block diagram representation of a wafer
polishing control system which is suitable for controlling a wafer
polishing apparatus in accordance with an embodiment of the present
invention.
[0024] FIGS. 6a and 6b are a process flow diagram which illustrates
a method of performing chemical mechanical planarization polishing
on a wafer in accordance with an embodiment of the present
invention.
[0025] FIG. 7 is a diagrammatic representation of a wafer polishing
force distribution in accordance with an embodiment of the present
invention.
[0026] FIG. 8 is a signal flow chart for a force control system
module in accordance with an embodiment of the present
invention.
[0027] FIG. 9 is a diagrammatic representation of a
photolithography apparatus in accordance with an embodiment of the
present invention.
[0028] FIG. 10 is a process flow diagram which illustrates the
steps associated with fabricating a semiconductor device in
accordance with an embodiment of the present invention.
[0029] FIG. 11 is a process flow diagram which illustrates the
steps associated with processing a wafer, i.e., step 1304 of FIG.
10, in accordance with an embodiment of the present invention.
DETAILED DESCRIPTION OF THE EMBODIMENTS
[0030] The careful control of chemical mechanical planarization
machines used for wafer polishing is crucial in ensuring that the
integrity of a wafer polished using a chemical mechanical
planarization machine is not significantly compromised. When a
chemical mechanical planarization machine includes a polishing pad
which has a smaller diameter than a wafer that is to be polished,
when the polishing pressure applied by the polishing pad on the
wafer is not accurately controlled, the polished surface of the
wafer may be relatively uneven, which often compromises the
integrity of semiconductor devices formed using the wafer.
[0031] A force control system which includes a plurality of
actuators that are arranged to apply different magnitudes of forces
to sections of a polishing pad may be included as a part of a
chemical mechanical planarization apparatus. Such a force control
system allows the magnitude of forces applied on a polishing pad to
be adjusted as needed to maintain a substantially uniform polishing
pressure. The ability to adjust forces applied to different
sections or areas of a polishing pad enables a substantially
uniform polishing pressure to be effectively maintained
irregardless of whether substantially all of the polishing surface
of the polishing pad or only part of the polishing surface of the
polishing pad are in contact with the polishing surface of a wafer.
That is, the polishing pressure may be maintained at a desired
level by adjusting forces applied by actuators of the force control
system based upon the size of a contact area between the polishing
surface of the polishing pad and the polishing surface of the
wafer.
[0032] FIG. 2 is a diagrammatic top-view representation of a
chemical mechanical planarization polishing apparatus which
includes a force control system in accordance with an embodiment of
the present invention. A polishing apparatus 200 includes a
polishing pad 204 and a wafer chuck 214 which holds a wafer 208
such that wafer 208 may come into contact with polishing pad 204
during a wafer polishing or planarization process. Apparatus 200
also includes an arm 218 which is coupled to an air pressure load
system 226 and a force control system or a force system 224, e.g.,
an electromagnetic force system, that is arranged to control the
amount of force applied to polishing pad 204 based on instructions
provided by a controller 222. The forces applied to polishing pad
204 using force system 224 may be suction forces which allows
portions of polishing pad 204 to effectively be pulled up.
[0033] During wafer polishing, polishing pad 204 is moving and
wafer 208 is spinning or rotating, and polishing pad 204 contacts
wafer 208 with a desired polishing pressure that is provided by a
head base weight associated with a polishing head (not shown) which
supports polishing pad 204 and air pressure load system 226. Force
system 224 is arranged to substantially cooperate with air-pressure
load system 226 to balance the polishing head (not shown) and to
maintain a substantially uniform contact pressure on a polishing
surface of wafer 208. In one embodiment, forces associated with
actuators in force system 224 are controlled to effectively
compensate for the air pressure load provided by air pressure load
system 226.
[0034] In general, actuators which are a part of force system 224
may be substantially any suitable actuators. Suitable actuators
include, but are not limited to, EI-core actuators, CI-core
actuators, and various other electromagnetic actuators. Actuators
which are a part of force system 224 may be individually controlled
to effectively dynamically compensate for an air load such that
relatively even polishing may occur on a surface of wafer 208
irregardless of how polishing pad 204 is positioned relative to
wafer 208. By way of example, force system 224 may be controlled by
controller 222 such that a surface of wafer 208 may be evenly
polished whether a part of a polishing surface of polishing pad 204
is not in contact with the surface of wafer 208 or whether
substantially all of the polishing surface of polishing pad 204 is
in contact with the surface of wafer 208.
[0035] Force system 224 is generally a non-contact force system. By
way of example, when force system 224 includes actuators that are
EI-core actuators, E-cores of the actuators may be coupled to force
system 224 while I-cores of the actuators are coupled to polishing
pad 204 or an arrangement which supports polishing pad 204. Force
system 224 operates by providing an attraction force to a polishing
pad arrangement which includes polishing pad 204, e.g., such that
an E-core attracts an I-core. The attraction force pulls up on,
e.g., effectively applies suction to, polishing pad 204 as
appropriate to compensate for the air load. FIG. 3 is a block
diagram representation of a polishing apparatus with a non-contact
force system in accordance with an embodiment of the present
invention. A polishing apparatus 300 includes a rotating wafer 308
which is arranged substantially beneath a moving polishing pad
arrangement 305 which is suitable for polishing, e.g., abrading, a
top surface of the rotating wafer. A fixed, non-contact force
system 324 is arranged over rotating polishing pad arrangement 305
such that force system 324 may apply magnetic forces that
effectively pull up on portions of a polishing pad of rotating
polishing pad arrangement 305. By pulling up portions of the
polishing pad, the overall polishing pressure associated with
polishing a surface of rotating wafer 308 may be maintained at a
constant level such that even polishing may occur irregardless of
whether all of or only a portion of a polishing surface of a
rotating polishing pad comes into contact with rotating wafer
308.
[0036] When force system 324 includes E-cores of EI-core actuators,
and rotating polishing pad arrangement 305 includes I-cores of the
EI-core actuators, gap distances between each E-core and each
I-core may be changed to substantially directly affect the amount
of attraction force effectively applied to portions of a polishing
pad. Hence, E-cores of force system 324 may be used to control the
overall polishing force associated with rotating polishing pad
arrangement 305. As will be appreciated by those skilled in the
art, varying the current provided to a coil of an E-core allows the
attraction force between the E-core and a corresponding I-core to
be changed or otherwise controlled. In one embodiment, multiple
E-cores may essentially be associated with a single I-core of a
ring-shaped configuration, as described in co-pending U.S. patent
application Ser. No. 10/430,598, filed May 5, 2003, which is
incorporated herein by its entirety.
[0037] A force system such as force system 324 may include any
number of actuators. For example, a force system may include three
actuators that are positioned such that a first actuator is located
substantially over the inner part of a polishing pad which is the
closest point to the wafer center, and second and third actuators
are located substantially opposite from the first actuator, i.e.,
at slight offsets from approximately 180 degrees away from the
first actuator. As shown in FIG. 4, a first actuator 424a of a
force system 422 may be located substantially opposite, i.e., 180
degrees from, a center point 430 between a second actuator 424b and
a third actuator 424c. Second actuator 424b and third actuator 424c
are generally positioned at a slight offset from a centerline 434
of force system 422 which passes through first actuator 424a.
[0038] In the described embodiment, actuators 424b, 424c are
effectively controlled together to apply sufficient force to pull
up an edge of a polishing pad when the polishing surface associated
with the edge of the polishing pad is not in contact with a wafer
being polished. It should be appreciated, however, that actuators
424b, 424c may also be controlled separately. In addition, the
location of actuators 424b, 424c may vary.
[0039] The amount of force applied using actuators 424 is dependent
upon the overall location of a polishing pad which is subjected to
the force applied using actuators 424. Hence, given a desired
polishing pressure, a controller, e.g., controller 222 of FIG. 2,
may determine forces to be applied using actuators 424 as a
function of a location of the polishing pad.
[0040] FIG. 5 is a block diagram representation of a wafer
polishing control system which is suitable for controlling a wafer
polishing apparatus such as polishing apparatus 200 of FIG. 2 in
accordance with an embodiment of the present invention. A chemical
mechanical planarization host computer 502, which may be
substantially any suitable computing system which includes a
processor for processing command instructions, is arranged to
provide arm movement control 506 for a swinging arm. Controlling
arm movement allows a current polishing pad position to be
determined, and provided to an electromagnetic force control system
510 or, more generally, a force system which is used to effectively
control a polishing pressure between the polishing pad and a wafer
being polished. The amount of force generated by each actuator
included in electromagnetic force control system 510 is dependent
upon a current polishing pad position.
[0041] In addition to a current pad position, electromagnetic force
control system 510 also receives information relating to a fixed
air load force and a desired polishing pressure from host computer
502. During wafer polishing, the rotating polishing pad touches the
surface of the wafer to be polished at a desired polishing
pressure, which may be determined by a head base weight and air
air-pressure load system. Electromagnetic force control system 510
is arranged to substantially compensate for an overloaded
air-pressure force to balance the polishing head which supports the
polishing pad, and to maintain substantially uniform contact
pressure on the polishing surface of the wafer.
[0042] Host computer 502 is also arranged to provide an air
pressure load control system 514 with instructions, and to provide
instructions to a pad and chuck rotation controller 518. That is,
host computer 502 allows an air-pressure load to be controlled, and
also allows rotation of both a polishing pad and a wafer chuck
which supports a wafer to be controlled.
[0043] With reference to FIGS. 6a and 6b, the steps associated with
one method of performing chemical mechanical planarization
polishing on a wafer will be described in accordance with an
embodiment of the present invention. A process 600 of performing
chemical mechanical planarization polishing begins at step 604 in
which a wafer that is to be polished is moved to, or otherwise
positioned in, a wafer chuck of a polishing apparatus. Then, in
step 608, various parameters associated with a polishing process
are set. By way of example, a polishing pressure, a polishing time,
a polishing pad rotation speed, a wafer chuck rotation speed, and
an arm moving trajectory may be set.
[0044] Once parameters associated with the polishing process are
set, an air-pressure load is set in step 612. After a predetermined
amount of time, during which air may effectively be pumped to the
polishing pad, a determination is then made in step 616 as to
whether an air-load set point has been reached. If it is determined
that the air-load set point has not been reached, then process flow
returns to step 612 in which an air-pressure load is set.
[0045] Alternatively, if it is determined in step 616 that the
air-load set point has been reached, then process flow proceeds to
step 620 in which the polishing pad and the wafer chuck begin
spinning. In step 624, the polishing head or, more specifically,
the polishing pad, is effectively lowered to come into contact with
the wafer supported on the wafer chuck. After lowering the
polishing pad, actuators of a force system are turned on in step
628. In the described embodiment, the actuators are electromagnetic
actuators, and turning on the actuators may include providing
current to coils associated with the electromagnetic actuators.
[0046] Upon turning on the actuators, the actuators begin to ramp
up to set forces in step 632 which are appropriate to achieve the
polishing pressure set in step 608. A determination is made in step
636 regarding whether the set forces have been reached. It should
be appreciated that such a determination may be made after a
predetermined amount of time has elapsed. If it is determined that
the set forces have not been reached, process flow returns to step
632 in which the actuators continue to ramp up to set forces.
Alternatively, if it is determined that set forces have been
reached, the arm moves, and polishing occurs while actuator forces
change 640. As previously mentioned, the actuator forces change to
provide a uniform polishing pressure irregardless of whether
substantially all of a polishing surface of a polishing pad is in
contact with a wafer, or only a portion of the polishing surface of
the polishing pad is in contact with the wafer.
[0047] In step 644, it is determined if there is an unbalanced
force associated with the polishing apparatus. If it is determined
that there is an unbalanced force, then the polishing process is
aborted. If it is determined that there is no unbalanced force, a
determination is made in step 648 as to whether the polishing time
set in step 608 has been reached. When it is determined that the
polishing time has not been reached, process flow returns to step
640 in which polishing continues to occur while actuator forces
change as appropriate.
[0048] If the determination in step 648 is that the polishing time
has been reached, then the actuators are turned off in step 652,
and the polishing head is lifted in step 656. Once the polishing
head is lifted, the spinning of the polishing pad and the wafer
chuck is stopped in step 660. Finally, the wafer is removed from
the chuck in step 664, and the process of performing chemical
mechanical planarization polishing is completed.
[0049] In order to determine actuator output forces needed to
maintain a desired polishing pressure irregardless of a polishing
pad location, the force distribution associated with a polishing
apparatus that includes a force system with actuators may be
studied. A command force vector F, which includes output forces for
actuators, may be determined to be a function of an air pressure
load and base weight, a resistant force from a wafer, and the
contact area between a polishing pad and the wafer.
[0050] FIG. 7 is a diagrammatic representation of a wafer polishing
force distribution in accordance with an embodiment of the present
invention. A polishing pad 704 and a wafer 708 have a contact area
`A` 746 which is a function of a position of a center of pressure
722 of polishing pad 704 relative to a center of wafer 748. That
is, contact area `A` 746 is a function of a distance `x` 750
between center of pressure 722 and center of wafer 748, i.e.,
contact area `A` 746 is effectively contact area `A(x)` 746. It
should be appreciated that contact area `A(x)` 746 may be
calculated such that for every distance `x` 750, or pad position,
the corresponding contact area `A(x)` 746 is known before a
polishing apparatus which includes polishing pad 704 and wafer 708
is put into use.
[0051] An air load `L` 760 is effectively applied to polishing pad
704 through center of pressure 722. Air load `L` 760 is an air
pressure load, which is a passive load. Actuators 718 which are
part of a force system apply forces `F.sub.2` 758 at a distance
`r.sub.2` 764 from center of pressure 722. An actuator 714 applies
a force `F.sub.1` 754 at a distance `r.sub.1` 762 from center of
pressure 722. Force `F.sub.1` 754 and forces `F.sub.2` 758 are
arranged to enable a substantially uniform or desired polishing
contact pressure `P` to be maintained on wafer 708. Hence, force
`F.sub.1` 754 and forces `F.sub.2` 758 are adjusted depending upon
contact area `A(x)` 746. In the described embodiment, actuator 718a
and actuator 718b are arranged to provide forces `F.sub.2` 758 of
substantially the same magnitude and are, hence, effectively
controlled together.
[0052] A resistant force `R` 774 is a function of distance `x` 750,
and is a resistant force from wafer 708. A gravity center distance
`g` 770 varies depending on distance `x` 750, and expresses a
distance between a point where resistant force `R` 774 acts and
center of pressure 722. That is, gravity center distance `g` 770 at
a point in time is a distance between center of pressure 722 and a
center of gravity associated with pad 704 and wafer 708 at the
point in time. Gravity center distance `g` 770 may be calculated in
real-time as a function of distance `x` 750, i.e., while a
polishing apparatus which includes polishing pad 704 is in use,
using geometric relationships, or may be determined while the
polishing apparatus is in use through the use of a pre-calculated
look-up table which lists gravity center distances relative to pad
positions.
[0053] Resistant force `R` 774 is generally dependent upon a
desired polishing pressure `P` and contact area `A` 746, as well as
distance `x` 750. Hence, resistant force `R` 774 may be expressed
as follows:
R(x)=P.multidot.A(x)
[0054] As previously mentioned, contact area `A` 746 may be
predetermined, or calculated prior to using polishing pad 704, as a
function of pad position or distance `x` 750. It should be
appreciated by those skilled in the art that geometric
relationships may be used to calculate contact area `A` 746 as a
function of distance `x` 750. Polishing pressure `P` is a desired
polishing pressure which is to be maintained while wafer 708 is
being polished using polishing pad 704.
[0055] Balancing forces and moments on pad 704 and wafer 770 yields
the following equations:
F.sub.1+2.multidot.F.sub.2+R(x)=L
F.sub.1.multidot.r.sub.1+R(x).multidot.g(x)=2.multidot.F.sub.2.multidot.r.-
sub.2
[0056] Rewritten in matrix form, the above equations may be
expressed as: 1 [ 1 2 r 1 - 2 r 2 ] [ F 1 F 2 ] = [ L - R ( x ) - R
( x ) g ( x ) ]
[0057] Substituting for resistant force `R` 774 yields: 2 [ 1 2 r 1
- 2 r 2 ] [ F 1 F 2 ] = [ L - P A ( x ) - P A ( x ) g ( x ) ]
[0058] A force command vector {circumflex over (F)} which expresses
desired forces F.sub.1 754 and F.sub.2 758, to be produced by
actuators 714, 718, respectively, may be given as: 3 F ) = [ F 1 F
2 ] = [ 1 2 r 1 - 2 r 2 ] - 1 [ L - P A ( x ) - P A ( x ) g ( x )
]
[0059] Since distance `r.sub.1` 762, distance `r.sub.2` 764,
air-pressure load force and base weight `L` 760, and desired
pressure `P` are known, e.g., given by a user or operator of an
overall chemical mechanical planarization polishing apparatus,
force command vector {circumflex over (F)} may be determined given
distance `x` 750, as contact area `A` 746 and gravity center
distance `g` 770 are effectively known if distance `x` 750 is
given.
[0060] Referring next to FIG. 8, a signal flow chart for a force
control system module will be described in accordance with an
embodiment of the present invention. Within a force control system
800, a pad position 850, which is a function of time since a
polishing pad moves relative to a wafer during polishing, is
provided to geometric equations 890. Through the use of geometric
equations or relationships 890, pad position 850 may be used to
determine a contact area and a gravity center distance 872 as
functions of pad position 850 and, hence, time. Contact area and
gravity center distance 872 are then provided to a transform matrix
892, along with an air-pressure load 860 and a desired polishing
pressure 866, to enable a force command vector {circumflex over
(F)} 856, or desired forces, to be determined. That is, given
desired polishing pressure 866, preset air-pressure load 860, pad
position 850 or a pad position trajectory from an arm encoder
signal, force command vector {circumflex over (F)} 856 may be
determined for all actuators associated with force control system
800. In the described embodiment, force control system 800 has
three associated electromagnetic actuators, so force command vector
{circumflex over (F)} 856 may include three forces. When at least
two of the electromagnetic actuators are controlled together, then
force command vector {circumflex over (F)} 856 may include a force
to be produced by a first electromagnetic actuator and a force to
be produced by each of the electromagnetic actuators that are
controlled together.
[0061] Force command vector {circumflex over (F)} 856 is provided
as input to a feedback control system 894 which, through the use of
sensors, as for example load cell force sensors, provides an actual
force output 896 for each actuator that is sent as a feedback
signal to feedback control system 894. It should be appreciated
that actual force output 896 for each actuator is the force
generated by each actuator, and is ideally substantially equal to
forces specified in force command vector {circumflex over (F)}
856.
[0062] In one embodiment, when force control system 800 reads
encoder counts and converts the encoder counts to pad position 850
at substantially every servo sampling time, force control system
800 may update a desired compensation force trajectory, i.e., by
updating force command vector {circumflex over (F)} 856. The new
computed compensation force trajectory may be provided to each
actuator associated with force control system 800 in order for each
actuator to generate a substantially desired actual output force
896.
[0063] Generally, the configuration of feedback control system 894
may vary widely. Typically, feedback control system 894 includes an
adaptive gain adjustment servomechanism which uses a real-time
force gain estimate scheme and an extra adaptive gain adjustment
block in a servo loop. One suitable feedback control system is
described in co-pending U.S. patent application Ser. No.
10/430,598, which has been incorporated by reference in its
entirety.
[0064] With reference to FIG. 9, a photolithography apparatus which
be used to as a part of an overall semiconductor fabrication
apparatus that also includes a chemical mechanical planarization
polishing apparatus. A photolithography apparatus (exposure
apparatus) 40 includes a wafer positioning stage 52 that may be
driven by a planar motor (not shown), as well as a wafer table 51
that is magnetically coupled to wafer positioning stage 52 by
utilizing an EI-core actuator, e.g., an EI-core actuator with a top
coil and a bottom coil which are substantially independently
controlled. The planar motor which drives wafer positioning stage
52 generally uses an electromagnetic force generated by magnets and
corresponding armature coils arranged in two dimensions. A wafer 64
is held in place on a wafer holder or chuck 74 which is coupled to
wafer table 51. Wafer positioning stage 52 is arranged to move in
multiple degrees of freedom, e.g., in up to six degrees of freedom,
under the control of a control unit 60 and a system controller 62.
The movement of wafer positioning stage 52 allows wafer 64 to be
positioned at a desired position and orientation relative to a
projection optical system 46.
[0065] Wafer table 51 may be levitated in a z-direction 10b by any
number of voice coil motors (not shown), e.g., three voice coil
motors. In one described embodiment, at least three magnetic
bearings (not shown) couple and move wafer table 51 along a y-axis
10a. The motor array of wafer positioning stage 52 is typically
supported by a base 70. Base 70 is supported to a ground via
isolators 54. Reaction forces generated by motion of wafer stage 52
may be mechanically released to a ground surface through a frame
66. One suitable frame 66 is described in JP Hei 8-166475 and U.S.
Pat. No. 5,528,118, which are each herein incorporated by reference
in their entireties.
[0066] An illumination system 42 is supported by a frame 72. Frame
72 is supported to the ground via isolators 54. Illumination system
42 includes an illumination source, which may provide a beam of EUV
light that may be reflected off of a reticle. In one embodiment,
illumination system 42 may be arranged to project a radiant energy,
e.g., light, through a mask pattern on a reticle 68 that is
supported by and scanned using a reticle stage 44 which includes a
coarse stage and a fine stage. It should be appreciated that for
such an embodiment, photolithography apparatus 40 may be a part of
a system other than an EUV lithography system. In general, a stage
with isolated actuators may be used as a part of substantially any
suitable photolithography apparatus, and is not limited to being
used as a part of an EUV lithography system. The radiant energy is
focused through projection optical system 46, which is supported on
a projection optics frame 50 and may be supported the ground
through isolators 54. Suitable isolators 54 include those described
in JP Hei 8-330224 and U.S. Pat. No. 5,874,820, which are each
incorporated herein by reference in their entireties.
[0067] A first interferometer 56 is supported on projection optics
frame 50, and functions to detect the position of wafer table 51.
Interferometer 56 outputs information on the position of wafer
table 51 to system controller 62. In one embodiment, wafer table 51
has a force damper which reduces vibrations associated with wafer
table 51 such that interferometer 56 may accurately detect the
position of wafer table 51. A second interferometer 58 is supported
on projection optical system 46, and detects the position of
reticle stage 44 which supports a reticle 68. Interferometer 58
also outputs position information to system controller 62.
[0068] It should be appreciated that there are a number of
different types of photolithographic apparatuses or devices. For
example, photolithography apparatus 40, or an exposure apparatus,
may be used as a scanning type photolithography system which
exposes the pattern from reticle 68 onto wafer 64 with reticle 68
and wafer 64 moving substantially synchronously. In a scanning type
lithographic device, reticle 68 is moved perpendicularly with
respect to an optical axis of a lens assembly (projection optical
system 46) or illumination system 42 by reticle stage 44. Wafer 64
is moved perpendicularly to the optical axis of projection optical
system 46 by a wafer stage 52. Scanning of reticle 68 and wafer 64
generally occurs while reticle 68 and wafer 64 are moving
substantially synchronously.
[0069] Alternatively, photolithography apparatus or exposure
apparatus 40 may be a step-and-repeat type photolithography system
that exposes reticle 68 while reticle 68 and wafer 64 are
stationary, i.e., at a substantially constant velocity of
approximately zero meters per second. In one step and repeat
process, wafer 64 is in a substantially constant position relative
to reticle 68 and projection optical system 46 during the exposure
of an individual field. Subsequently, between consecutive exposure
steps, wafer 64 is consecutively moved by wafer positioning stage
52 perpendicularly to the optical axis of projection optical system
46 and reticle 68 for exposure. Following this process, the images
on reticle 68 may be sequentially exposed onto the fields of wafer
64 so that the next field of semiconductor wafer 64 is brought into
position relative to illumination system 42, reticle 68, and
projection optical system 46.
[0070] It should be understood that the use of photolithography
apparatus or exposure apparatus 40, as described above, is not
limited to being used in a photolithography system for
semiconductor manufacturing. For example, photolithography
apparatus 40 may be used as a part of a liquid crystal display
(LCD) photolithography system that exposes an LCD device pattern
onto a rectangular glass plate or a photolithography system for
manufacturing a thin film magnetic head.
[0071] The illumination source of illumination system 42 may be
g-line (436 nanometers (nm)), i-line (365 nm), a KrF excimer laser
(248 nm), an ArF excimer laser (193 nm), and an F.sub.2-type laser
(157 nm). Alternatively, illumination system 42 may also use
charged particle beams such as x-ray and electron beams. For
instance, in the case where an electron beam is used, thermionic
emission type lanthanum hexaboride (LaB.sub.6) or tantalum (Ta) may
be used as an electron gun. Furthermore, in the case where an
electron beam is used, the structure may be such that either a mask
is used or a pattern may be directly formed on a substrate without
the use of a mask.
[0072] With respect to projection optical system 46, when far
ultra-violet rays such as an excimer laser is used, glass materials
such as quartz and fluorite that transmit far ultra-violet rays is
preferably used. When either an F.sub.2-type laser or an x-ray is
used, projection optical system 46 may be either catadioptric or
refractive (a reticle may be of a corresponding reflective type),
and when an electron beam is used, electron optics may comprise
electron lenses and deflectors. As will be appreciated by those
skilled in the art, the optical path for the electron beams is
generally in a vacuum.
[0073] In addition, with an exposure device that employs vacuum
ultra-violet (VUV) radiation of a wavelength that is approximately
200 nm or lower, use of a catadioptric type optical system may be
considered. Examples of a catadioptric type of optical system
include, but are not limited to, those described in Japan Patent
Application Disclosure No. 8-171054 published in the Official
gazette for Laid-Open Patent Applications and its counterpart U.S.
Pat. No. 5,668,672, as well as in Japan Patent Application
Disclosure No. 10-20195 and its counterpart U.S. Pat. No.
5,835,275, which are all incorporated herein by reference in their
entireties. In these examples, the reflecting optical device may be
a catadioptric optical system incorporating a beam splitter and a
concave mirror. Japan Patent Application Disclosure (Hei) No.
8-334695 published in the Official gazette for Laid-Open Patent
Applications and its counterpart U.S. Pat. No. 5,689,377, as well
as Japan Patent Application Disclosure No. 10-3039 and its
counterpart U.S. Pat. No. 5,892,117, which are all incorporated
herein by reference in their entireties. These examples describe a
reflecting-refracting type of optical system that incorporates a
concave mirror, but without a beam splitter, and may also be
suitable for use with the present invention.
[0074] Further, in photolithography systems, when linear motors
(see U.S. Pat. No. 5,623,853 or 5,528,118, which are each
incorporated herein by reference in their entireties) are used in a
wafer stage or a reticle stage, the linear motors may be either an
air levitation type that employs air bearings or a magnetic
levitation type that uses Lorentz forces or reactance forces.
Additionally, the stage may also move along a guide, or may be a
guideless type stage which uses no guide.
[0075] Alternatively, a wafer stage or a reticle stage may be
driven by a planar motor which drives a stage through the use of
electromagnetic forces generated by a magnet unit that has magnets
arranged in two dimensions and an armature coil unit that has coil
in facing positions in two dimensions. With this type of drive
system, one of the magnet unit or the armature coil unit is
connected to the stage, while the other is mounted on the moving
plane side of the stage.
[0076] Movement of the stages as described above generates reaction
forces which may affect performance of an overall photolithography
system. Reaction forces generated by the wafer (substrate) stage
motion may be mechanically released to the floor or ground by use
of a frame member as described above, as well as in U.S. Pat. No.
5,528,118 and published Japanese Patent Application Disclosure No.
8-166475. Additionally, reaction forces generated by the reticle
(mask) stage motion may be mechanically released to the floor
(ground) by use of a frame member as described in U.S. Pat. No.
5,874,820 and published Japanese Patent Application Disclosure No.
8-330224, which are each incorporated herein by reference in their
entireties.
[0077] Isolaters such as isolators 54 may generally be associated
with an active vibration isolation system (AVIS). An AVIS generally
controls vibrations associated with forces 112, i.e., vibrational
forces, which are experienced by a stage assembly or, more
generally, by a photolithography machine such as photolithography
apparatus 40 which includes a stage assembly.
[0078] A photolithography system according to the above-described
embodiments, e.g., a photolithography apparatus which may include
one or more dual force actuators, may be built by assembling
various subsystems in such a manner that prescribed mechanical
accuracy, electrical accuracy, and optical accuracy are maintained.
In order to maintain the various accuracies, prior to and following
assembly, substantially every optical system may be adjusted to
achieve its optical accuracy. Similarly, substantially every
mechanical system and substantially every electrical system may be
adjusted to achieve their respective desired mechanical and
electrical accuracies. The process of assembling each subsystem
into a photolithography system includes, but is not limited to,
developing mechanical interfaces, electrical circuit wiring
connections, and air pressure plumbing connections between each
subsystem. There is also a process where each subsystem is
assembled prior to assembling a photolithography system from the
various subsystems. Once a photolithography system is assembled
using the various subsystems, an overall adjustment is generally
performed to ensure that substantially every desired accuracy is
maintained within the overall photolithography system.
Additionally, it may be desirable to manufacture an exposure system
in a clean room where the temperature and humidity are
controlled.
[0079] Further, semiconductor devices may be fabricated using
systems described above, as will be discussed with reference to
FIG. 10. The process begins at step 1301 in which the function and
performance characteristics of a semiconductor device are designed
or otherwise determined. Next, in step 1302, a reticle (mask) in
which has a pattern is designed based upon the design of the
semiconductor device. It should be appreciated that in a parallel
step 1303, a wafer is made from a silicon material. Making a wafer
may include subjecting the wafer to a chemical mechanical
planarization process that allows a surface of the wafer to be
polished. The mask pattern designed in step 1302 is exposed onto
the wafer fabricated in step 1303 in step 1304 by a
photolithography system. One process of exposing a mask pattern
onto a wafer will be described below with respect to FIG. 11. In
step 1305, the semiconductor device is assembled. The assembly of
the semiconductor device generally includes, but is not limited to,
wafer dicing processes, bonding processes, and packaging processes.
Finally, the completed device is inspected in step 1306.
[0080] FIG. 11 is a process flow diagram which illustrates the
steps associated with wafer processing in the case of fabricating
semiconductor devices in accordance with an embodiment of the
present invention. In step 1311, the surface of a wafer is
oxidized. Then, in step 1312 which is a chemical vapor deposition
(CVD) step, an insulation film may be formed on the wafer surface.
Once the insulation film is formed, in step 1313, electrodes are
formed on the wafer by vapor deposition. Then, ions may be
implanted in the wafer using substantially any suitable method in
step 1314. As will be appreciated by those skilled in the art,
steps 1311-1314 are generally considered to be preprocessing steps
for wafers during wafer processing. Further, it should be
understood that selections made in each step, e.g., the
concentration of various chemicals to use in forming an insulation
film in step 1312, may be made based upon processing
requirements.
[0081] At each stage of wafer processing, when preprocessing steps
have been completed, post-processing steps may be implemented.
During post-processing, initially, in step 1315, photoresist is
applied to a wafer. Then, in step 1316, an exposure device may be
used to transfer the circuit pattern of a reticle to a wafer.
Transferring the circuit pattern of the reticle of the wafer
generally includes scanning a reticle scanning stage which may, in
one embodiment, include a force damper to dampen vibrations.
[0082] After the circuit pattern on a reticle is transferred to a
wafer, the exposed wafer is developed in step 1317. Once the
exposed wafer is developed, parts other than residual photoresist,
e.g., the exposed material surface, may be removed by etching.
Finally, in step 1319, any unnecessary photoresist that remains
after etching may be removed. As will be appreciated by those
skilled in the art, multiple circuit patterns may be formed through
the repetition of the preprocessing and post-processing steps.
[0083] Although only a few embodiments of the present invention
have been described, it should be understood that the present
invention may be embodied in many other specific forms without
departing from the spirit or the scope of the present invention. By
way of example, a force control system has generally been described
as having three actuators, two of which are arranged to provide
substantially the same force when the force control system is in
use. In general, however, a force control system may include any
number of actuators. Additionally, the actuators of a force control
system may all be substantially individually controlled, and the
spacing of the actuators may also vary.
[0084] Geometric equations or relationships used to determine the
size of a contact area between a polishing pad and a wafer as a
function of a location of the center of pressure of the polishing
pad may vary. That is, any suitable geometric relationships may be
used to determine the contact area.
[0085] Electromagnetic actuators have generally been described as
being suitable for use as actuators in a force control system.
Electromagnetic actuators may include, but are not limited to,
EI-core and CI-core actuators. It should be appreciated, however,
that substantially any suitable actuators, electromagnetic or
otherwise, may be used as a part of a force control system for a
chemical mechanical planarization polishing apparatus.
[0086] The steps associated with a wafer polishing operation may
vary depending, for example, on the overall requirements of a
semiconductor fabrication process. Steps may be added, removed,
reordered, and changed without departing from the spirit or the
scope of the present invention. Therefore, the present examples are
to be considered as illustrative and not restrictive, and the
invention is not to be limited to the details given herein, but may
be modified within the scope of the appended claims.
* * * * *