U.S. patent application number 10/674373 was filed with the patent office on 2004-10-28 for apparatus and method for controlling film thickness in a chemical mechanical planarization system.
This patent application is currently assigned to LAM RESEARCH CORPORATION. Invention is credited to Gotkis, Yehiel.
Application Number | 20040214508 10/674373 |
Document ID | / |
Family ID | 46300040 |
Filed Date | 2004-10-28 |
United States Patent
Application |
20040214508 |
Kind Code |
A1 |
Gotkis, Yehiel |
October 28, 2004 |
Apparatus and method for controlling film thickness in a chemical
mechanical planarization system
Abstract
An apparatus for use in a chemical mechanical planarization
(CMP) system is provided. A head capable of being positioned at a
proximate location over a polishing pad includes an input and an
output defined in the head. The input is capable of delivering a
fluid at the proximate location on the surface of a polishing pad.
The output being oriented adjacent to the input is capable of
removing at least part of the fluid delivered onto the surface of
the polishing pad. A method for controlling properties of a film
over a polishing pad surface is also provided.
Inventors: |
Gotkis, Yehiel; (Fremont,
CA) |
Correspondence
Address: |
MARTINE & PENILLA, LLP
710 LAKEWAY DRIVE
SUITE 170
SUNNYVALE
CA
94085
US
|
Assignee: |
LAM RESEARCH CORPORATION
Fremont
CA
|
Family ID: |
46300040 |
Appl. No.: |
10/674373 |
Filed: |
September 29, 2003 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10674373 |
Sep 29, 2003 |
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10463525 |
Jun 18, 2003 |
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10463525 |
Jun 18, 2003 |
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10186472 |
Jun 28, 2002 |
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Current U.S.
Class: |
451/5 ;
451/41 |
Current CPC
Class: |
B24B 49/105 20130101;
B24B 1/005 20130101; B24B 37/013 20130101; H01L 21/67253 20130101;
B24B 57/02 20130101 |
Class at
Publication: |
451/005 ;
451/041 |
International
Class: |
B24B 049/00; B24B
051/00; B24B 001/00 |
Claims
What is claimed is:
1. An apparatus for use in a chemical mechanical planarization
(CMP) system, comprising; a head capable of being positioned at a
proximate location over a polishing pad, the head including, an
input defined in the head, the input capable of delivering a fluid
at the proximate location and onto the surface of a polishing pad;
and an output in the head, the output being oriented adjacent to
the input, the output capable of removing at least part of the
fluid delivered onto the surface of the polishing pad.
2. The apparatus of claim 1, wherein the head is moveable.
3. The apparatus of claim 1, wherein the head may contain a
plurality of additional inputs and outputs.
4. The apparatus of claim 1, wherein a plurality of the heads may
be configured to span an application area.
5. The apparatus of claim 1, wherein the proximate location of the
head over the polishing pad is between about 0.1 mm and about 1
mm.
6. The apparatus of claim 1, wherein the input is formed in the
head by one of milling, drilling, boring, and casting.
7. The apparatus of claim 6, wherein the input formed in the head
may include at least one conduit.
8. The apparatus of claim 1, wherein the fluid may be one of an
abrasive-free chemically inert liquid, deionized water and a
process indifferent fluid.
9. The apparatus of claim 1, wherein the output is capable of
removing materials present on the polishing pad.
10. The apparatus of claim 10, wherein the materials on the
polishing pad capable of being removed by the output may be one or
a combination of slurry, de-ionized water, isopropyl alcohol,
particulates, abrasives, material residues, and pad residues.
11. The apparatus of claim 10, wherein removal of slurry adjusts a
degree of planarization by the CMP system.
12. The apparatus of the claim 1, further comprising a
computer.
13. The apparatus of the claim 12, wherein the computer is capable
of communication with a sensor located on the CMP system.
14. The apparatus of the claim 13, wherein the sensor is capable of
detecting material properties of a substrate including film
thickness, conductivity, surface roughness, and topography height
variations.
15. The apparatus of the claim 12, wherein the computer is capable
of providing control over operation of the head.
16. A method for controlling properties of a film over a--polishing
pad surface, comprising: delivering a fluid over the polishing pad,
the delivery being at a proximate location over the polishing pad
surface; and removing at least part of the fluid from over the
polishing pad surface, the removing configured to occur at a
proximate location over the polishing pad surface and adjacent to
the delivery of the fluid.
17. The method for controlling properties of a film over a
polishing pad surface as recited in claim 16, wherein the
delivering and removing is configured to assist in controlling
properties of the film over the polishing pad surface.
18. The method for controlling properties of a film over a
polishing pad surface as recited in claim 17, wherein the film
includes one or more of a slurry, an amount of de-ionized water, an
amount of chemicals, isopropyl alcohol, particulates, abrasives,
material residues, and pad residues.
19. The method of claim 16, wherein the removing of slurry from the
film adjusts a degree of planarization capable of being imparted by
the polishing pad surface.
20. An apparatus capable of controlling a chemical mechanical
polishing (CMP) system, comprising; a sensor; a computer; and a
head capable of being positioned at a proximate location over a
polishing pad, the head including, an input defined in the head,
the input capable of delivering a fluid at the proximate location
and onto the surface of a polishing pad; and an output in the head,
the output being oriented adjacent to the input, the output capable
of removing at least part of the fluid delivered onto the surface
of the polishing pad.
21. The apparatus of the claim 20, wherein the computer is capable
of communication with the sensor located on the CMP system.
22. The apparatus of the claim 20, wherein the sensor is capable of
detecting material properties of a wafer surface being
processed.
23. The apparatus of the claim 22, wherein material properties
includes film thickness, conductivity, surface roughness, and
topography height variations.
24. The system of claim 20, wherein the sensor is an inductive
sensor.
25. The apparatus of the claim 20, wherein the computer is capable
of providing control over operation of the head.
26. The apparatus of claim 20, wherein the head is connected to a
movable arm.
27. The apparatus of claim 20, wherein the head contains a
plurality of additional inputs and outputs.
28. The apparatus of claim 20, wherein a plurality of heads defined
by two or more of the heads is configured to span an application
area.
29. The apparatus of claim 20, wherein the proximate location of
the head over the polishing pad is between about 0.1 mm and about 1
mm.
30. The apparatus of 20, wherein the input formed in the head may
include at least one conduit.
31. The apparatus of claim 20, wherein the fluid may be one or a
combination of an abrasive-free chemically inert liquid and
deionized water.
32. The apparatus of claim 20, wherein the output is capable of
removing materials present on the polishing pad.
33. The apparatus of claim 32, wherein the materials on the
polishing pad capable of being removed by the output may be one or
a combination of slurry, de-ionized water, isopropyl alcohol,
particulates, abrasives, material residues, and pad residues.
34. The apparatus of claim 32, wherein removal of slurry adjusts a
degree of planarization by the CMP system.
35. An apparatus for use in a chemical mechanical planarization
(CMP) system, comprising; a head capable of being positioned at a
proximate location over a polishing pad, the head including, an
output defined in the head and capable of being positioned at the
proximate location over the polishing pad, the output being
configured to enable removal of a material present on the surface
of the polishing pad; and an input defined in the head and capable
of being positioned at the proximate location over the polishing
head, the input capable of delivering a fluid to the surface of the
polishing pad to at least partially replace the material that is
configured to be removed by the output, the output being positioned
on the head adjacent to the input.
36. The apparatus of claim 35, wherein the head is moveable.
37. The apparatus of claim 34, wherein the proximate location of
the head over the polishing pad is between about 0.1 mm and about 1
mm.
38. The apparatus of claim 35, wherein the material present on the
surface of the polishing pad may be one or a combination of slurry,
de-ionized water, isopropyl alcohol, particulates, abrasives,
material residues, and pad residues.
39. The apparatus of claim 35, wherein the fluid may be one of an
abrasive-free chemically inert liquid, deionized water and a
process indifferent fluid.
40. The apparatus of the claim 35, further comprising a computer
capable of communication with a sensor located on the CMP
system.
41. The apparatus of the claim 40, wherein the sensor is capable of
detecting material properties of a substrate including film
thickness, conductivity, surface roughness, and topography height
variations.
42. The apparatus of the claim 40, wherein the computer is capable
of providing control over operation of the head.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is continuation-in-part of U.S. patent
application Ser. No. 10/463,525, entitled "METHOD AND APPARATUS FOR
APPLYING DIFFERENTIAL REMOVAL RATES TO A SURFACE OF A SUBSTRATE,"
filed on Jun. 30, 2003 which is a continuation in part of U.S.
patent application Ser. No. 10/186,472, entitled "INTEGRATION OF
EDDY CURRENT SENSOR BASED METROLOGY WITH SEMICONDUCTOR FABRICATION
TOOLS," filed on Jun. 28, 2002. The disclosure of these patent
applications are incorporated herein by reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The invention relates generally to semiconductor fabrication
and more specifically to process control during chemical mechanical
planarization (CMP) wafer processing.
[0004] 2. Description of the Related Art
[0005] In the fabrication of semiconductor devices, there is a need
to perform Chemical Mechanical Planarization (CMP) operations,
including removal of the excessive material, buffing and post-CMP
wafer cleaning and drying. Typically, integrated circuit devices
are manufactured in the form of multi-level structures. At the
substrate level, transistor devices having positively and
negatively doped regions are formed. In subsequent levels,
interconnect metallization lines are patterned and electrically
connected to the transistor devices to define the desired
functional device. Patterned conductive features are insulated by
dielectric materials, such as silicon dioxide. As more
metallization levels and associated dielectric layers are formed,
the need to planarize the dielectric material increases. Without
planarization, fabrication of additional metallization layers
becomes substantially impossible due to variations in the surface
topography. In other applications, metallization line patterns are
formed in the dielectric material, and then metal CMP operations
are performed to remove excess metallization. Further applications
include planarization of dielectric films deposited prior to the
metallization process, such as dielectrics used for shallow trench
isolation of for poly-metal insulation.
[0006] Typically CMP systems implement a rotary table, belt,
orbital or brush operation in which belts, pads, or brushes are
used to scrub, buff, and polish one or both sides of wafer. The pad
itself is typically made of polyurethane material or other suitable
material and may be backed by a rigid table, supporting belt, for
example a stainless steel belt. In operation a slurry material is
applied to and spread across the surface of the polishing pad or
belt. As the belt or pad covered in slurry rotates, a wafer is
lowered to the surface of the pad and is planarized.
[0007] The desired result of successful CMP operations is a uniform
planar surface remaining on the processed wafer. Typically the
removal rate of films on the wafer is carefully tracked or
monitored. Various attempts have been made to control the operation
of chemical mechanical planarization systems in order to provide
uniform removal rates. One common attempt is to manipulate down
force applied by the wafer carrier or other workpiece holding
device, delivering variable pressure to an abrasive polishing
surface. Unfortunately down force variation can lead to local
degradation of so-called dishing and erosion performance at the
sections of the wafer where high compensative down force was
applied. Excessive down force may cause other quality problems like
film delamination, scratching, or inter-grain boundary damage. The
focus on uniformity of removal rates is misguided for current
applications. That is, from the end user's perspective, it is
desired to have a uniform end layer on the surface of the
semiconductor wafer which is not necessarily the result from a
uniform removal rate. For example, if the surface of the wafer
prior to planarization is not uniformly thick, the non-uniformities
are maintained when a uniform removal rate is applied to the
processed wafer. A uniform removal rate applied to substrate with
greater edge thickness will result in a wafer with a lower center
thickness, a condition similar to the wafer prior to the
planarization application. Additionally, in the example related
above, over-polishing of the center of the wafer can result in lost
die and lower wafer yield.
[0008] During the CMP operation there are many opportunities for
measuring device features on wafers. Many of the features can be
determined by capturing a signal indicating the feature. As
features continue to decrease in size, especially the thickness of
films employed in the manufacture of semiconductors, the signals
that are indicative of the feature become undetectable in certain
situations. Inductive sensors may be used for displacement,
proximity and film thickness measurements. The sensors rely on the
induction of current in a sample by the fluctuating electromagnetic
field of a test coil proximate to the object being measured.
Fluctuating electromagnetic fields are created as a result of
passing an alternating current through the coil. The fluctuating
electromagnetic fields induce eddy currents which superimpose with
the primary field and change the coils inductance. Feedback from
sensors such as inductive sensors during planarization can allow
for real-time monitoring and correction if needed during the CMP
operation.
[0009] In view of the foregoing, there is a need to provide a
method and apparatus that may deliver a uniform thickness rather
than a uniform removal rate in order to provide control over the
uniformity of the targeted remaining layer thickness for the
wafer.
SUMMARY OF THE INVENTION
[0010] Broadly speaking, the present invention is an apparatus that
provides control over planarization resulting in a specified
remaining film thickness on a semiconductor wafer. It should be
appreciated that the present invention can be implemented in
numerous ways, including as an apparatus, a system, a device, or a
method. Several inventive embodiments of the present invention are
described below.
[0011] In accordance with one embodiment of the present invention,
an apparatus for use in a chemical mechanical planarization (CMP)
system is provided. A head capable of being positioned at a
proximate location over a polishing pad includes an input and an
output defined in the head. The input is capable of delivering a
fluid at the proximate location on the surface of a polishing pad.
The output being oriented adjacent to the input is capable of
removing at least part of the fluid delivered onto the surface of
the polishing pad.
[0012] In another embodiment, a method for controlling properties
of a film over a polishing pad surface is provided. The method
includes delivering a fluid over the polishing pad and removing at
least part of the fluid from over the polishing pad surface. The
fluid is delivered at a proximate location over the polishing pad
surface. The removing of at least part of the fluid is configured
to occur at a proximate location over the polishing pad surface and
adjacent to the delivery of the fluid.
[0013] In another embodiment, an apparatus capable of controlling a
chemical mechanical polishing (CMP) system is provided. The
apparatus includes a sensor, a computer, and a head. The head is
capable of being positioned at a proximate location over a
polishing pad. The head includes an input defined in the head, the
input capable of delivering a fluid at the proximate location and
onto the surface of a polishing pad, and an output in the head, the
output being oriented adjacent to the input. The output is capable
of removing at least part of the fluid delivered onto the surface
of the polishing pad.
[0014] In accordance with another embodiment, an apparatus for use
in a chemical mechanical planarization (CMP) system is provided.
The apparatus includes a head capable of being positioned at a
proximate location over a polishing pad. An output defined in the
head is capable of being positioned at the proximate location over
the polishing pad and is configured to enable removal of a material
present on the surface of the polishing pad. An input defined in
the head is capable of being positioned at the proximate location
over the polishing head, is capable of delivering a fluid to the
surface of the polishing pad to at least partially replace the
material that is configured to be removed by the output, the output
being positioned on the head adjacent to the input.
[0015] It is to be understood that the foregoing general
description and the following detailed description are exemplary
and explanatory only and are not restrictive of the invention, as
claimed.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] The accompanying drawings, which are incorporated in and
constitute part of this specification, illustrate exemplary
embodiments of the invention and together with the description
serve to explain the principles of the invention.
[0017] FIG. 1 is a cross-sectional diagram of a chemical mechanical
planarization (CMP) system used for the differential closed loop
planarization control, in accordance with one embodiment of the
present invention.
[0018] FIG. 2 is a top view diagram of a differential control loop
chemical mechanical planarization (CMP) system showing a single
head with several inputs and outputs, in accordance with one
embodiment of the present invention.
[0019] FIG. 3 is a top view diagram of a differential control loop
chemical mechanical planarization (CMP) system showing a head that
can slide on an arm, in accordance with one embodiment of the
present invention.
[0020] FIG. 4 is a top view diagram of a differential control loop
chemical mechanical planarization (CMP) system showing a head that
can be moved by an extending arm, in accordance with one embodiment
of the present invention.
[0021] FIG. 5A is side view of an alternate configuration, in
accordance with one embodiment of the present invention.
[0022] FIG. 5B is top view of the present invention employed in a
rotary type system, in accordance with one embodiment of the
present invention.
[0023] FIG. 6 is a flow chart of a method for controlling
properties of a film over a polishing pad surface, in accordance
with one embodiment of the present invention.
[0024] FIG. 7 is a flow chart of a method for providing
differential control for removal rates applied to a substrate
surface through a removal of slurry from the polishing pad, in
accordance with one embodiment of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
[0025] Several exemplary embodiments of the invention will now be
described in detail with reference to the accompanying drawings. In
the following description, numerous specific details are set forth
in order to provide a thorough understanding of the present
invention. It will be understood, however, to one skilled in the
art, that the present invention may be practiced without some or
all of these specific details. In other instances, well known
process operations have not been described in detail in order not
to unnecessarily obscure the present invention.
[0026] FIG. 1 is a schematic diagram of a chemical mechanical
planarization system capable of providing real time differential
closed loop control in accordance with one embodiment of the
invention. A wafer 130 held by a wafer carrier 135 is rotated
against polishing pad 101. A fluid delivery device 103 delivers a
first fluid 102 to polishing pad 101. The first fluid 102 typically
contains a slurry intended for chemical mechanical planarization of
a wafer 130 that consists of both chemical and physical abrasives
which affect removal of material on the surface of a wafer. Slurry
on the polishing pad 101 may be joined by other particulates,
abrasives, material residues, pad residues, de-ionized water, and
isopropyl alcohol already resident on the polishing pad 101 all of
which combine to form a film across the surface of the polishing
pad 101. Grooves 106 and micropores 108 in the polishing pad 101
transport the first fluid 102 in the direction 120 of the wafer
carrier 135. It should be appreciated that any suitable technique
may be used to deliver fluid to the polishing pad 101 such as pump,
air pressure, etc.
[0027] A fluid restraining device 104, also referred to as a dam,
located downstream from the delivery device, is forced against
polishing pad 101 to evenly distribute the first fluid 102 over the
surface of the polishing pad 101. Even distribution entails uniform
disbursement of slurry across the width of the polishing pad 101,
creating a uniform film that proceeds in the direction of the
wafer. The delivery device 103, therefore does not have to be an
instrument requiring precise distribution of the first fluid 102 to
the polishing pad 101. The fluid flow restraining device 104
presses against polishing pad 101 creating a pool of the first
fluid 102 upstream from the fluid restraining device 104. It will
be apparent to one skilled in the art that fluid restraining device
104 may be clipped or affixed by other suitable technique to an arm
extending over polishing pad 101. The arm extending over polishing
pad 101 may be manipulated in a vertical as well as a horizontal
direction in order to control the angle and gap, relative to
polishing pad 101. In one embodiment, fluid restraining device 104
is composed of the same material of polishing pad 101, i.e.,
polyurethane. It should be appreciated, however, that fluid
restraining device 104 may be constructed from any material which
is compatible with the CMP operation and is capable of creating a
pool of the first fluid 102 while providing for the even
distribution downstream.
[0028] Still referring to FIG. 1, a head 115 is located between the
fluid restraining device 104 and the wafer carrier 135. The
location of the head 115 over the polishing pad 101 may be between
about 0.1 mm and about 1 mm and will be optimized to provide best
execution response. The exact optimal position will depend on the
first fluid 102 dispensing rate, its viscosity, wetting
coefficient, and other parameters defining the efficiency of the
head 155 in replacing the first fluid 102 with a second fluid 118.
The head 115 has at least one input 117 capable of delivering a
second fluid 118 and at least one output 119 capable of removing
the first fluid 102 and a portion of the second fluid 118 by way of
vacuum and other pressurized techniques. Delivery of the second
fluid 118 includes even distribution at the desired location on the
surface of the polishing pad 101. The second fluid 118 may be one
of an abrasive-free chemically inert liquid, deionized water and
other process indifferent fluids. A gap 116 adjacent to the surface
of the polishing pad 101 between one of the inputs 117 and one of
the outputs 119 of the head 115 allows for the second fluid 118 to
dilute and remove the first fluid 102 via the output 119. Dilution
of the first fluid 102 slows, and in the limit removal of the first
fluid 102, prevents planarization of the wafer 130 by the CMP
system. During removal of the first fluid 102, primarily slurry
along with other constituents of the film such as particulates,
material residues and pad residues, a portion of the second fluid
118, namely de-ionized water, proceeds in the direction 120 of the
wafer carrier 135. There is effectively reduced or no planarization
of a surface of the wafer 130 when the second fluid 118 is applied
to the polishing pad 101.
[0029] As described above, when the polishing pad 101 moves in the
direction 120 toward the application area it carries with it a
first fluid 102, which may be a film containing material such as
slurry, particulates, material residues, and pad residues. In one
embodiment a portion of the material remaining on the polishing pad
101, the first fluid 102, is removed prior to the addition of the
second fluid 118, which may be one of an abrasive-free chemically
inert liquid, deionized water and other process indifferent fluids.
Some portion of the second fluid 118 may be removed along with the
first fluid 102 through the gap 116 and the output 119 in the head
115. In this manner, the second fluid 118 may assist in the removal
of the first fluid 102 by providing a diluting and lifting effect
of the first fluid 102 from the surface of the polishing pad 101.
In another embodiment, all of the material remaining on the
polishing pad 101, the first fluid 102, is removed by the output
119 in the head 115 prior to the application of the second fluid
118 through the input 117. In the case of complete removal or near
complete of the first fluid 102 and replacement with the second
fluid 118, the second fluid 118, a process indifferent fluid,
proceeds in the direction 120 of the application area providing
effectively reduced or no material removal in the specified portion
of the wafer 130.
[0030] The wafer carrier 135 is capable of incorporating at least
one sensor 140 configured to detect material properties of the
wafer and the progress of the CMP operation. In one embodiment, the
sensor may detect a signal indicating a film thickness. In the case
of conductive films, the plurality of sensors 140 may be inductive
sensors configured to detect a signal produced by a magnetic field
emitted by the induced current. Frequently, the signal indicating
the thickness of the film includes third body effects. Inductive
sensors allow for the contactless measuring of a thin conductive
(eg. metal) film thickness in the full range of thicknesses
normally utilized in semiconductor manufacturing, typically varying
from about 0-15,000 Angstroms. It has been determined that
inductive sensors are capable of providing a fast enough response
for a wafer moving under typical loading robotics velocity.
Therefore, it is possible to perform thickness measurements during
processing without impacting process throughput. Moreover, the
movement of the wafer can be taken advantage of to produce a film
thickness profile from a limited number of sensors in a cluster
configuration. For example, wafer aligners provide movement in a
rotational direction and a linear radial direction to position
wafers in a consistent manner. Accordingly in the present
invention, a cluster of sensors can capture a film thickness
profile of a wafer while the wafer is undergoing common automated
wafer handling schemes, or while being rotated during CMP. As the
wafer 130 is rotated, a film thickness profile can be generated for
the wafer 130 so that the head 115 can optimize slurry displacement
for the desired thickness profile.
[0031] Still referring to FIG. 1, a computer 150, also referred to
as a controller, coordinates the various control activities for the
CMP system 100. The computer 150 is capable of communication 142
with the plurality of sensors 140, the head 115, the fluid
restraining device 104 and the fluid delivery device 103. The
computer 150 may be configured to adjust the signal indicating the
thickness of the film from the sensors 140 to substantially remove
both third body effects introduced by the CMP system and a
substrate thickness component. According to the value of the
adjusted signal, control signals for second fluid 118, the fluid
restraining device 104, and fluid delivery device 103 may be
generated. Film thickness feedback from the sensors 140 provides
the computer 150 information necessary to regulate removal rates
via commands issued to the head 115. If the signal generated by any
one of sensors 140 indicates that the removal rate is too high,
i.e., the thickness is lower in a particular region of wafer 130
corresponding to one of the sensors 140, then the second fluid 118,
being either deionized water or some other suitable displacement
chemistry may be distributed through the one of the inputs 117 on
the head 115 in order adjust the degree of planarization and reduce
the removal rate experienced at the corresponding point on wafer
130. Similarly, when a desired thickness on a portion of the wafer
130 has been obtained, the head 115, operating as an execution and
correction system, replaces the first fluid 102 with second fluid
118 preventing further planarization in the affected area. As used
herein, an execution and correction system receives commands from
the computer 150 and performs an operation such as fluid delivery
and removal in the present invention. Correction and adjustment of
the processing application is provided by the head 115 when slurry
is removed at specified locations on the surface of the polishing
pad 101.
[0032] FIG. 2 provides a top view of the CMP system described
above. It should be appreciated that the rotational velocity of
wafer 130, along with the linear velocity of polishing pad 101,
creates a situation where fluid directed at the center of wafer 130
is pushed off to the side due to the rotational velocity of the
wafer 130. In that situation, e.g., where slurry is present on the
polishing pad 101, the center of wafer 130 experiences a lower
removal rate due to a lesser amount of slurry being available at
the center. The head 115 downstream from the fluid restraining
device 104 applies differential removal rates to portions of a
surface of wafer 130 by removal of slurry and replacement with
water at a plurality of locations designated by the sensors 140.
Additionally the rotation of the wafer provides for an alternative
path 122 for fluids directed under the wafer carrier 135. The path
of fluids delivered on a linear belt will affect a circular
application when applied to the wafer in rotation. The inputs 117
capable of providing the second fluid are also capable of being
placed in a position according to the anticipated rotation of the
wafer 130 in a direction 121.
[0033] In the case of linear belt CMP systems, it should be
appreciated that the belt is capable of moving in a linear
direction 120 towards the wafer 130 while the wafer 130 is spinning
about its axis. Thus, the relative velocity experienced by top
section 130a of wafer 130 is greater than the relative velocity
experienced by bottom section 130b during a rotation cycle of wafer
130. As a result, the polishing pad 101 tends to stain in the
region experiencing the higher relative velocity, due to the
greater amount of debris accumulated at the upper half of belt.
Thus, one function of the fluid restraining device 104 and the pool
of the first fluid 102 is to collect and distribute the debris more
uniformly rather than having the debris recycle in the same general
area of polishing pad 101. Uniform distribution of the debris may
extend the life of the polishing pad 101 by promoting a more
uniform wearing pattern.
[0034] As shown in FIG. 2, it should be appreciated by those
skilled in the art that the fluid may be removed by outputs 119 and
a second fluid 118 may be delivered and at one or multiple
locations. The locations of the inputs 117 and outputs 119 can be
configured on the head 115 enabling isolation of specific regions
on the surface of the polishing pad 101 in order to manipulate the
removal rate applied to wafer 130. Because a gap 116 adjacent to
the surface of the polishing pad 101 between one of the inputs 117
and one of the outputs 119 of the head 115 allows for the second
fluid 118 to dilute and remove the first fluid 102 via the output
119, it can be said that the inputs 117 and the outputs 119 are
coupled together in pairs. The activation of pairs of the inputs
117 and outputs 119 can be independently controlled by the computer
150 as described in FIG. 1 above, so that the computer 150 can
isolate removal of the first fluid 102 in designated sections of
the polishing pad 101. The head 115 could contain a plurality of
inputs 117 and outputs 119 as shown spanning the width of the
polishing pad 101. The head 115 could be held by an arm 114 that
extends across the width of polishing pad 101 that operate in the
fashion described in FIG. 1 above. The arm 114 could be supported
by an apparatus above the polishing pad 101 or could be supported
by other structures on the system by extending beyond the polishing
pad 101.
[0035] FIG. 3 provides an alternative arrangement of the head 115
configured on the arm 114. The head 115 could move linearly along
an arm 114 that extends across the width of polishing pad 101 as
illustrated in FIG. 3. The location of the head 115 can enable
isolation of specific regions on the surface of the polishing pad
101 under the inputs 117 and outputs 119 in order to manipulate the
removal rate applied to wafer 130. A plurality of heads 115' may be
optional for improved coverage of the application area, the area of
the polishing pad 101 that will pass below the surface of the wafer
130. The head 115 and the heads 115' could move linearly in concert
or independently along an arm 114 that extends across the width of
polishing pad 101. The computer 150, described in FIG. 1 above, is
capable of providing orchestration of the movement of head 115 or
heads 115' in order to properly prepare the polishing pad 101 for
the differentially controlled planarization operation.
[0036] Alternatively, as shown in FIG. 4, the arm 114 could move
the head 115 to locations designated by the sensors 140. The arm
114 may have several joints 113 and may be controlled by any
suitable technique such as a step motor, servo motor, etc., in
order to direct slurry, deionized water, or some other suitable
fluid on the surface of polishing pad 101 downstream from fluid
restraining device 104, in order to manipulate the removal rate
applied to wafer 130. Additionally a plurality of arms 114' could
move a plurality of heads 115' to locations designated by the
computer 150 as described in FIG. 1 for polishing pad 101
preparation.
[0037] FIG. 6 is a flow chart of a method for controlling
properties of a film over a polishing pad in accordance with one
embodiment of the invention. The method begins by delivering a
fluid over the polishing pad at a proximate location over the
polishing pad surface in operation 404. In operation 408, at least
part of the fluid from over the polishing pad surface is removed at
a proximate location over the polishing pad surface adjacent to the
delivery of the fluid. The removal of fluid from the film over the
polishing pad surface can assist in controlling properties of the
film. The film may include slurry, an amount of de-ionized water,
an amount of chemicals, isopropyl alcohol, particulates, abrasives,
material residues, and pad residues. The composition of the film on
the polishing pad has a direct effect on the planarization
performed on the surface of the wafer. Removing slurry from the
film prevents planarization at a proximate location on the
polishing pad surface.
[0038] FIG. 7 is a flow chart diagram illustrating an operational
method for providing differential control of removal rates applied
to the surface of a wafer in accordance with one embodiment of the
invention. The method begins when a wafer is provided for the
purpose of having a film or films removed in operation 504. A
thickness map of the substrate could be generated prior to a
processing operation. The thickness map may be generated as the
surface of a wafer is scanned to obtain thickness data in the
absence of third bodies. Here, an aligner and other transfer
stations may be used to scan the surface of the wafer in order to
create a thickness map as described above. Third bodies, i.e.,
conductive objects are not present here as only the wafer and the
scanning mechanism is used to create the thickness map. A substrate
component of the thickness data and a film component of the
thickness data is identified. Here, the signal generated by
scanning the surface of the wafer is subdivided into the substrate
component and a film component. For example, an inductive signal
may be broken down into the two components. It should be
appreciated that from this component data, calibration coefficients
may be generated which may be subsequently applied to a downstream
measurement of the thickness, i.e., a sensor embedded in a wafer
carrier, in order to more precisely determine the thickness.
[0039] The method then proceeds to operation 506 where the wafer is
transferred to a processing station. In one embodiment, the
processing station is a CMP system. Of course, any suitable
robotic, mechanical, or manual technique may be used to transfer
the wafer to the processing station. The method then moves to
operation 508 where sensors on the wafer carrier determine film
thickness corresponding to discrete points on the wafer and the
presence of third bodies is detected. Here, one or more sensors
embedded in the wafer carrier as described above with reference to
FIGS. 1-4 may be used to detect the thickness data. In one
embodiment, an inductive sensor is used for this detection, however
scatterometers, spectral reflectometry, thermal monitoring, stress
monitoring, and other sensors could be employed.
[0040] Next in operation 510, thickness data corresponding to the
point on the wafer is adjusted to substantially eliminate both the
substrate component and the third body effects. That is, the
calibration coefficient determined in the absence of third bodies
is used to isolate the thickness data related to the film on the
wafer described above. A coordinate of the thickness map is
associated with a sensor (eg. inductive sensor described above)
utilized in the processing operation. A point on the thickness map
may be associated with a sensor embedded in the wafer carrier so
that the planarization process may be controlled in the region
associated with the sensor embedded in the wafer carrier. A
computer, also known as a controller, as described in FIG. 1 above
may provide the calculations necessary to make this association.
When slurry is applied to the pad in operation 512, planarization
of the wafer surface begins in operation 514. Film thickness at
discrete locations is calculated by the computer based on feedback
from the sensors 516 as describe above. Until desired thickness is
obtained at a particular location in operation 518, the
planarization process continues per operation 521. If the desired
thickness is obtained a particular location a query of all sensor
locations is made in operation 522. If desired thickness is
obtained at some but not all locations, a head removes slurry from
regions having desired thickness or excessive removal rates and
substitutes a second chemically inert non-abrasive fluid in
operation 525 as described in FIGS. 1-4 above. The method then
continues to apply slurry to the polishing pad in operation 512
while areas designated by the computer as having obtained the
desired thickness have the second fluid substituted for slurry.
Operation 512 continues until sensors at all locations indicate
that the desired thickness has been obtained in operation 522. When
desired thickness has been obtained at all positions on the wafer,
the planarization process is complete and the wafer is removed from
the polishing pad in operation 530.
[0041] In summary, the present invention provides for a CMP system
that capable of being configured to differentially control removal
rates being applied to regions of a wafer. Differential control
enables for a uniform thickness to be obtained as opposed to a
uniform removal rate. Through the use of a fluid restraining device
that creates a pool, a uniform slurry layer is defined downstream
of the restraining device. A head, operating as an execution and
control system provides process control by removing abrasives at
designated locations in order to arrive at a substrate having a
uniform film thickness. The uniform slurry layer provided by the
fluid restraining device is removed in areas where a desired film
thickness has been obtained as described above. After a desired
thickness is detected uniformly about the wafer, the planarization
operation is complete and a signal may be issued to stop the
operation. The plurality of sensors described above allow for the
determination of the endpoint and associated removal rates by
initially determining a thickness of a film on the wafer under
non-process conditions and also during the planarization process.
The determined thickness may be provided to sensors associated with
the process operation in order to calibrate the sensor so that
variables from processing conditions that cause error in the
thickness measurement (third body effects) are substantially
eliminated. For example, a calibration coefficient determined under
non-process conditions, i.e., without third bodies in the detection
region, may be applied to the signal of the second sensor in order
to substantially eliminate the third body effects introduced by the
processing module. In addition, a thickness map of the wafer is
generated where the thickness map breaks down the data into a film
thickness component and a substrate component, in order to isolate
the film thickness component. As mentioned above, the thickness map
is determined under non process conditions. Furthermore, the above
described embodiments may be applied to rotary or orbital type CMP
systems as well as linear CMP systems that rely upon belt type
polishing media.
[0042] The invention has been described herein in terms of several
exemplary embodiments. Other embodiments of the invention will be
apparent to those skilled in the art from consideration of the
specification and practice of the invention. The embodiments and
preferred features described above should be considered exemplary,
with the invention being defined by the appended claims.
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