U.S. patent application number 10/780409 was filed with the patent office on 2005-08-18 for removal of embedded particles during chemical mechanical polishing.
This patent application is currently assigned to Infineon Technologies Richmond, LP.. Invention is credited to Hagl, Franz, Turner, Kyle.
Application Number | 20050181708 10/780409 |
Document ID | / |
Family ID | 34838583 |
Filed Date | 2005-08-18 |
United States Patent
Application |
20050181708 |
Kind Code |
A1 |
Turner, Kyle ; et
al. |
August 18, 2005 |
Removal of embedded particles during chemical mechanical
polishing
Abstract
A chemical mechanical polishing method and apparatus are
introduced that reduce embedded particles during CMP processing.
Throughout the CMP process, the wafer-carrier and the polish platen
turn or rotate in the same direction. This enables particles to
become embedded in the oxide or other film surface. In the
disclosed process, during a final polish step, the wafer carrier or
polish platen is turned or rotated in the opposite direction.
Embedded particles are then pulled out of the oxide or film,
creating a much cleaner wafer. This increases manufacturing yield
and decreases manufacturing cost while introducing one additional
step and a minor modification to conventional equipment.
Inventors: |
Turner, Kyle; (Frisco,
TX) ; Hagl, Franz; (Ilmendorf, DE) |
Correspondence
Address: |
BRINKS HOFER GILSON & LIONE
INFINEON
PO BOX 10395
CHICAGO
IL
60610
US
|
Assignee: |
Infineon Technologies Richmond,
LP.
|
Family ID: |
34838583 |
Appl. No.: |
10/780409 |
Filed: |
February 17, 2004 |
Current U.S.
Class: |
451/41 |
Current CPC
Class: |
B24B 37/042
20130101 |
Class at
Publication: |
451/041 |
International
Class: |
B24B 001/00 |
Claims
1. A chemical mechanical polishing method comprising: loading a
semiconductor wafer in a wafer carrier; rotating the semiconductor
wafer in the wafer carrier in a first direction while a polished
surface of the semiconductor wafer is maintained against a
polishing pad which is rotating in a second direction, the second
direction being opposite to the first direction; and reversing the
direction of rotation of one of the wafer carrier and the polishing
pad during a final polishing operation to remove embedded particles
from the polished surface of the semiconductor wafer.
2. The method of claim 1 further comprising: while reversing the
direction of rotation, spraying the polishing pad with a liquid to
remove the particles from the polishing pad.
3. The method of claim 1 further comprising: during a first
processing phase, rotating the semiconductor wafer in the wafer
carrier in a clockwise direction and rotating the polishing pad in
a counter-clockwise direction for a predetermined period of time;
and during a second processing phase, rotating the semiconductor
wafer in the wafer carrier in a counter-clockwise direction for a
final polish duration.
4. The method of claim 1 further comprising: during a first
processing phase, rotating the semiconductor wafer in the wafer
carrier in a counter-clockwise direction and rotating the polishing
pad in a clockwise direction for a predetermined period of time;
and during a second processing phase, rotating the semiconductor
wafer in the wafer carrier in a counter-clockwise direction for a
final polish duration.
5. A chemical mechanical wafer polishing system comprising: a wafer
carrier configured to retain a semiconductor wafer during a
chemical mechanical polishing process; a first drive system coupled
with the wafer carrier to rotate the wafer carrier with the
semiconductor wafer in one of a first rotational direction and a
second, opposite, rotational direction; a platen configured for
mounting a polishing pad, the polishing pad polishing a surface of
the semiconductor wafer when the wafer carrier and the platen are
brought into proximity; a second drive system coupled with the
platen to rotate the platen and the polishing pad in one of the
first rotational direction and the second rotational direction; and
a control system coupled with the first drive system and the second
system to rotate the semiconductor wafer and the polishing pads in
opposite directions during a first polishing interval and to
reverse rotation of the semiconductor wafer relative to the
polishing pad during a second polishing interval to remove embedded
particles from the surface of the semiconductor wafer.
6. The chemical mechanical wafer polishing system of claim 5
further comprising: a high pressure liquid spray system adjacent
the polishing pad and positioned to spray liquid on the polishing
pad to remove particles from the polishing pad.
7. A chemical mechanical wafer polishing (CMP) system comprising:
wafer rotation means for rotating a semiconductor wafer in one of a
first direction and a second direction in the CMP system; a
polishing pad to polish a surface of the semiconductor wafer; pad
rotation means for rotating the polishing pad relative to the
rotation of the semiconductor wafer to produce chemical mechanical
polishing of the surface of the semiconductor wafer; and control
means for controlling at least one of the wafer rotation means and
the pad rotation means, the control means producing a first
relative rotation during a first polishing duration and producing
an opposite relative rotation during a second polishing duration.
Description
BACKGROUND
[0001] The present application relates generally to chemical
mechanical polishing processes. More specifically, the present
application relates to removal of embedded particles during
chemical mechanical polishing.
[0002] Chemical mechanical polishing (CMP) is a commonly used
technique for polishing semiconductor wafers. Semiconductor wafers
are processed by a variety of chemical and thermal processes to
define electronic circuits on or near the surface of the wafers.
Some processes such as deposition of oxide or other layers form
conformal layers across substantially the entire wafer surface. CMP
is employed to convert the conformal oxide layer into a planar
oxide surface. After deposition of the oxide but prior to the CMP
process, the conformal oxide layer has a varied surface that
matches the topography of the underlying layer, including steps and
trenches in the underlying layer. The CMP process removes a portion
of the oxide layer above the metal step, producing a substantially
planar oxide layer. Subsequent layers deposited on the oxide layer
will have a planar surface for deposition.
[0003] Conventional CMP processing involves polishing a wafer
supported in a wafer-carrier head with a polishing pad mounted on a
polishing platen. The wafer-carrier head is mounted on a polish arm
or spindle. The wafer is held by the wafer-carrier head by a vacuum
or other means during loading and unloading. During polishing, the
polish arm moves to press the wafer surface against the polish pad
with a predetermined force. Typically, both the wafer-carrier head
and the polish table or polish platen rotate during polish. During
CMP, a chemical slurry is maintained on the polishing pad. The
slurry may include abrasive particles to modify the polishing
characteristics of the polishing pad or to enhance polishing.
[0004] While conventional CMP processes result in excellent
planarity and uniformity of the finished surface, contamination may
result from the CMP process. Contaminants such as the abrasive
particles from the slurry, air bubbles in the oxide or particles of
oxide itself may contaminate the surface of the wafer, becoming
embedded in the surface. The result is a localized lack of
planarity and non-uniform surface texture. The defects may be
characterized as particle scratching, chatter marks or surface
particles. When subsequent layers are deposited on the contaminated
surface, the result is imperfections and reduced yield, which
increases manufacturing cost.
[0005] One technique to reduce this sort of contamination has
involved a final polish step with slurry or water to remove the
contaminants. Alternatively, a brush cleaner has been used. A brush
cleaner uses a porous sponge or brush made of material such as
polyvinyl alcohol as the brushing element. The PVA material is soft
and scrubs particles from the surface of the wafer without further
damage to the surface material.
[0006] However, some sticky particles have remained, even after
cleaning with a brush cleaner. This has caused reduced yields, the
need for re-work, processing delays and increased manufacturing
cost. Accordingly there is a need for an improved method for
removal of embedded particles during chemical mechanical
polishing.
BRIEF SUMMARY
[0007] By way of introduction only, a chemical mechanical polishing
method and apparatus are introduced that reduce embedded particles
during CMP processing. Throughout the CMP process, the
wafer-carrier and the polish platen turn or rotate in the same
direction. This enables particles to become embedded in the oxide
or other film surface. In the disclosed process, during a final
polish step, the wafer carrier or polish platen is turned or
rotated in the opposite direction. Embedded particles are then
pulled out of the oxide or film, creating a much cleaner wafer.
[0008] The foregoing summary has been provided only by way of
introduction. Nothing in this section should be taken as a
limitation on the following claims, which define the scope of the
invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] FIG. 1 is a top view of a chemical mechanical polishing
(CMP) system;
[0010] FIG. 2 is a front elevation view of the CMP system of FIG.
1; and
[0011] FIG. 3 is a flow diagram illustrating a method for operating
the CMP system of FIGS. 1 and 2.
DETAILED DESCRIPTION OF THE DRAWINGS AND THE PRESENTLY PREFERRED
EMBODIMENTS
[0012] Referring now to the drawing, FIG. 1 shows a top view of a
chemical mechanical polishing (CMP) system and FIG. 2 shows a front
elevation view of the CMP system 100 of FIG. 1. The CMP system 100
is exemplary only and in the drawing is greatly simplified in order
to emphasize certain operational aspects of the system 100. It is
to be appreciated that in other embodiments, many modifications,
additions, deletions and rearrangements may be made while still
providing the benefits described herein.
[0013] The CMP system 100 includes a platen 102, a wafer carrier
104, a platen drive system 106, a wafer carrier drive system 108
and a control unit 110. The platen 102 is configured for mounting a
polishing pad 112. The wafer carrier 104 is configured to retain a
semiconductor wafer 114 during a chemical mechanical polishing
process. During the CMP process, the polishing pad 112 polishes a
surface 116 of the semiconductor wafer 114 when the wafer carrier
104 and the platen 102 are brought into proximity.
[0014] The platen drive system 106 is mechanically coupled with the
platen 102 to rotate the platen 102 and the polishing pad 112 in
one of a first rotational direction and a second rotational
direction. In the top view of FIG. 1, the first rotational
direction may be referred to as clockwise and the second rotational
direction may be referred to as counter-clockwise. Some embodiments
may not permit two-way rotation of the platen 102 and the polishing
pad 112 in both the clockwise and counter-clockwise directions. In
this regard, FIGS. 1 and 2 present the most general case. For
embodiments with more limited rotational functionality, the
principles described generally herein may be readily adopted to
accommodate the limitations.
[0015] The platen drive system 106 is coupled through a drive shaft
118 that rotates with the platen 102 about a center line 120. The
platen drive system 106 generally includes a motor such as an
electric motor for rotating drive shaft 118, the platen 102 and the
attached polishing pad 112. The platen drive system 106 thus forms
pad rotation means for rotating the polishing pad 112 relative to
the rotation of the semiconductor wafer 114 to produce chemical
mechanical polishing of the surface 116 of the semiconductor wafer
114. The pad rotation means may equivalently include a motor,
transmission system with gears for varying the rotational speed of
the platen 102 and a feedback control system for control of the
rotational speed. In the illustrated embodiment, the platen drive
system 106 is under control of the control unit 110.
[0016] The wafer carrier drive system 108 is mechanically coupled
with the wafer carrier 104 to rotate the wafer carrier 104 and the
semiconductor wafer 114 in one of the first rotational direction
and the second rotational direction. As shown in FIG. 1, the
semiconductor wafer 114 may be rotated in a clockwise direction or
a counterclockwise direction. Some embodiments may not permit
two-way rotation of the wafer carrier 104 and the semiconductor
wafer 114. Thus, FIGS. 1 and 2 present the most general case. For
embodiments with more limited functionality, the principles
described generally herein may be readily adopted to accommodate
the limitations.
[0017] The wafer carrier drive system 108 is coupled through a
drive shaft 112 that rotates with the wafer carrier 104 about a
center line 122. The wafer carrier drive system 108 generally
includes a motor such as an electric motor for rotating the drive
shaft 112, the wafer carrier 104 and the attached semiconductor
wafer 114. The wafer carrier drive system 108 thus forms wafer
rotation means for rotating the semiconductor wafer 114 in one of
the first direction and the second direction in the CMP system 100.
The wafer rotation means may equivalently include a motor,
transmission system with gears for varying the rotational speed of
the wafer carrier 14 and a feedback control system for control of
the rotational speed. In the illustrated embodiment, the wafer
carrier drive system 108 is under control of the control unit
110.
[0018] The control unit 110 in one embodiment includes a
microcontroller for monitoring and controlling operation of the CMP
system 100. The microcontroller of the control unit 110 operates in
response to data and instructions stored in a memory of the control
unit 110 and in response to conditions sensed about operation of
the CMP system 100. The control unit 110 may further include a user
interface for providing direct user control of portions of the CMP
system 100. The control unit 110 may further include a system
interface for providing automated control of the CMP system 100 by
remote data processing systems and for data logging.
[0019] The control unit 110 is electrically coupled to the platen
drive system 106 and the wafer carrier drive system 108 for
controlling these respective systems. By providing appropriate
digital or analog control signals to the platen drive system 106
and the wafer carrier drive system 108, the control unit 110 may
control the direction of rotation and the speed of rotation of the
platen 102 and the wafer carrier 104 over time, including the time
duration of CMP processing steps. In alternative embodiments, the
control unit 110 may communicate with either the platen drive
system 106 or the wafer carrier drive system 108 or both over a
data communication bus, sending and receiving data and commands to
the remote units.
[0020] The control unit 110 thus forms control means for
controlling at least one of the wafer carrier drive system or other
wafer rotation means and the platen drive system or other pad
rotation means. Operating as a control means, the control unit
generates the necessary control signals or data command to produce
a first relative rotation during a first polishing duration and
producing an opposite relative rotation during a second polishing
duration. In the illustrated embodiment, the first relative
rotation is rotation between the wafer carrier and the polishing
pad in opposite directions, and the opposite relative rotation is
rotation between the wafer carrier and the polishing pad in the
same direction.
[0021] It is to be noted that other embodiments may include more
than a single wafer carrier such as wafer carrier 104. The multiple
wafer carriers are positioned generally around the perimeter of the
polishing platen 102 so that multiple semiconductor wafers may be
processed simultaneously. This improves system throughput. Other
modifications or extensions may be made as well.
[0022] The embodiment of FIGS. 1 and 2 and similar embodiments may
be used to remove embedded particles introduced in the surface of
the semiconductor wafer 114 during a CMP process. By removing such
particles during a final polish process reduces the need for rework
of wafers in process and reduces defectivity which causes yield
loss.
[0023] It has been noticed that, due to the wafer carriers and
polish platens in CMP systems turning consistently in the same
direction during the primary CMP polish process, particles become
embedded in the film which forms the surface of the semiconductor
wafer being polished. In accordance with the presently disclosed
embodiments, during a final polish process, the polishing platen or
the wafer carrier is turned or rotated in the opposite direction
relative to rotating during the primary CMP polish process.
Particles embedded in the film of the surface are pulled out of the
film by the reverse-polishing process. This results in a cleaner
wafer with less defectivity caused by particle scratching or other
CMP processes.
[0024] In the embodiment illustrated in FIGS. 1 and 2, the primary
polish process and the final, reverse polish process are performed
using the same CMP system 100. Initially, a semiconductor wafer
such as the wafer 114 is loaded in a wafer carrier such as wafer
carrier 104. During a first processing phase, the semiconductor
wafer in the wafer carrier is rotated in a clockwise direction and
the polishing pad is rotated in a counter-clockwise direction for a
predetermined period of time. During a second processing phase, the
semiconductor wafer in the wafer carrier is rotated in a
counter-clockwise direction during a final polish duration.
[0025] In alternative embodiments, the respective rotation
directions may be varied. If the primary polishing process turns
the polishing pad counter-clockwise and turns the wafer carrier
clockwise, during the reverse polishing process, the polishing pad
will be turned clockwise and the wafer carrier will be turned
clockwise. Other possibilities are equivalent. For example, in some
CMP systems, the polishing pad and the wafer and wafer carrier are
conventionally rotated in the same direction, rather than in
opposing directions as described above in connection with FIGS. 1
and 2. During the final polish process, one of the platen and the
wafer carrier is reversed in rotation direction so that the reverse
polishing process will pull contaminant particles from the surface
of the semiconductor wafer.
[0026] The predetermined period of time for the primary polish
process and the final polish duration for the reverse polishing
process are preferably controlled by the control unit 110 so that
the processes may be automated. Alternatively, either phase may be
manually controlled. The predetermined period of time for the
primary polish process may be any suitable amount of time, such as
in the range of ten minutes. The final polish duration is generally
shorter, such as less than a minute, since this processing phase is
intended primarily to remove embedded particles rather than to
polish or planarize the wafer.
[0027] The direction of rotation of either the platen or the wafer
carrier may be reversed by any suitable technique. A transmission
system of either the wafer carrier drive system 108 or the platen
drive system 106 may be adjusted to reverse the rotation direction,
such as selecting a reverse gear. Alternatively, the motor of
either the wafer carrier drive system 108 or the platen drive
system 106 may be adjusted to reverse motor rotation. Any suitable
rotation speeds may be used.
[0028] The CMP system 100 of FIG. 1 further includes a spray nozzle
126 for introducing liquid onto the polishing pad 112 to remove
particles from the polishing pad. The liquid may be deionized (DI)
water, slurry or other pad conditioning material. Preferably, the
spray nozzle 126 directs a high pressure spray at the polishing pad
to dislodge and remove the particles from the pad surface so that
the particles are not re-introduced to the surface of the
semiconductor wafer 114.
[0029] FIG. 3 is a flow diagram illustrating one embodiment of a
method for removing embedded particles introduced during chemical
mechanical polishing in a CMP system. The method of FIG. 3 begins
at block 300.
[0030] At block 302, one or more semiconductor wafers are loaded on
wafer carriers at a load station of the CMP system. As noted, a
single wafer may be processed or, to increase system throughput,
multiple wafers may be loaded and processed substantially
simultaneously.
[0031] At block 304, the CMP polishing process begins. During a
primary polish phase, the wafer in the wafer carrier is rotated in
a first direction and brought in contact with the polishing pad
which is rotating in a first direction. The wafer rotation
direction and the polishing pad direction may be the same direction
or may be different. Speed of rotation and duration of the primary
polish phase may be set suitably to accomplish the goals of the CMP
process for the film being polished. For example, if a relatively
hard film is being planarized, a longer primary polish duration
will be required.
[0032] At block 306, the relative direction of rotation between the
semiconductor wafer and the polishing pad are reversed. This is
done, for example, by reversing the drive system for either the
wafer carrier or the polishing platen in any suitable manner. The
result is that the relative direction in which the surface of the
semiconductor wafer is moving past the surface of the polishing pad
is reversed, so that a reverse polishing action is imparted on the
surface of the wafer, tending to pull embedded particles from the
wafer surface. Because the relative sizes and rotation directions
of the polishing pad and the wafer may vary from embodiment to
embodiment, a key goal for any embodiment is implementation of a
reverse polishing process when the relative direction of the two
moving surfaces are reversed. This tends to counter the bias
introduced by the continuous forward polishing process and to
dislodge and remove any particles including sticky particles
introduced in the wafer surface.
[0033] In some embodiments, while the reverse polishing process
occurs at block 306, a high pressure nozzle is activated to spray
liquid on the polishing pad. This liquid may be DI water or other
material. The liquid serves to dislodge and wash away from the
polishing pad contaminant particles which have been removed from
the surface of the wafer so that the particles can not
recontaminate the wafer surface.
[0034] The duration of the reverse polishing process may be any
suitable time, but generally only a short time such as under a
minute is required. At block 310, the wafer or wafers are unloaded
from the CMP system. The method ends at block 312.
[0035] From the foregoing, it can be seen that the present
embodiments provide method and apparatus for reducing surface
particle contamination of semiconductor wafers during CMP
processes. After a primary polishing operation, a relatively brief
reverse polishing process is introduced to remove contaminants
including even sticky particles from the surface of the
semiconductor wafers. This process can dramatically reduce
defectivity and particle damage caused during CMP processes. This
substantially reduces manufacturing cost as the manufacturing yield
increases. The cost is minor, only a single additional step which
can be readily automated with modifications to existing equipment.
The process may even reduce the time necessary to clean CMP
equipment and the wafers themselves due to cleaner wafers coming
from the CMP tools.
[0036] It is therefore intended that the foregoing detailed
description be regarded as illustrative rather than limiting, and
that it be understood that it is the following claims, including
all equivalents, that are intended to define the spirit and scope
of this invention.
* * * * *