U.S. patent application number 10/974736 was filed with the patent office on 2005-05-26 for polishing apparatus.
Invention is credited to Ishikawa, Akira, Matsuo, Hisanori.
Application Number | 20050112998 10/974736 |
Document ID | / |
Family ID | 34587204 |
Filed Date | 2005-05-26 |
United States Patent
Application |
20050112998 |
Kind Code |
A1 |
Matsuo, Hisanori ; et
al. |
May 26, 2005 |
Polishing apparatus
Abstract
A polishing apparatus is used for polishing a substrate such as
a semiconductor wafer to a flat finish. The polishing apparatus
includes a polishing tool having a polishing surface, a substrate
holder configured to hold a substrate, a monitoring device
configured to monitor a polishing state of the surface of the
substrate being polished, and a controlling device configured to
change a polishing condition on the basis of the polishing state of
the surface of the substrate being polished detected by the
monitoring device.
Inventors: |
Matsuo, Hisanori; (Tokyo,
JP) ; Ishikawa, Akira; (Tokyo, JP) |
Correspondence
Address: |
WENDEROTH, LIND & PONACK, L.L.P.
2033 K STREET N. W.
SUITE 800
WASHINGTON
DC
20006-1021
US
|
Family ID: |
34587204 |
Appl. No.: |
10/974736 |
Filed: |
October 28, 2004 |
Current U.S.
Class: |
451/5 ; 451/7;
451/8 |
Current CPC
Class: |
B24B 37/013 20130101;
B24B 49/12 20130101 |
Class at
Publication: |
451/005 ;
451/008; 451/007 |
International
Class: |
B24B 049/00 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 30, 2003 |
JP |
2003-370100 |
Claims
What is claimed is:
1. A polishing apparatus for polishing a substrate, comprising; a
polishing tool having a polishing surface; a substrate holder
configured to hold a substrate, the substrate held by said
substrate holder being brought into sliding contact with said
polishing surface; a monitoring device configured to monitor a
polishing state of the surface of the substrate being polished; and
a controlling device configured to change a polishing condition on
the basis of said polishing state of the surface of the substrate
being polished detected by said monitoring device.
2. A polishing apparatus according to claim 1, wherein said
controlling device changes said polishing condition when said
polishing state of the surface of the substrate being polished
detected by said monitoring device becomes a preset condition
related to peeling-off of a film formed on the substrate.
3. A polishing apparatus according to claim 2, wherein said film
comprises a low-k film.
4. A polishing apparatus according to claim 1, wherein said
monitoring device monitors at least one of a load torque of a motor
for rotating said polishing tool and a load torque of motor for
rotating said substrate holder.
5. A polishing apparatus according to claim 1, wherein said
monitoring device monitors a force acting on said substrate holder
in a sliding direction of said substrate holder.
6. A polishing apparatus according to claim 1, wherein said
monitoring device monitors the state of the surface of the
substrate being polished optically.
7. A polishing apparatus according to claim 1, wherein said
monitoring device monitors whether acoustic emission is generated
or not.
8. A polishing apparatus according to claim 1, wherein said
polishing condition is a polishing load.
9. A polishing apparatus according to claim 1, wherein said
polishing condition is at least one of a rotational speed of said
polishing tool and a rotational speed of said substrate holder.
10. A polishing apparatus according to claim 1, wherein said
polishing condition is a swing speed of said substrate holder.
11. A polishing apparatus according to claim 1, wherein said
polishing condition is a supply amount of a polishing liquid
supplied to said polishing surface.
12. A polishing apparatus according to claim 1, wherein said
polishing condition is a type of polishing liquid.
13. A polishing apparatus according to claim 1, wherein said
polishing condition is in-situ dressing condition.
14. A polishing apparatus according to claim 1, wherein said
polishing condition is a temperature of a polishing liquid supplied
to said polishing surface.
15. A polishing apparatus according to claim 1, wherein said
polishing condition is a temperature of said polishing surface.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a polishing apparatus for
polishing a substrate such as a semiconductor wafer to a flat
finish.
[0003] 2. Description of the Related Art
[0004] As telecommunication means such as Internet and high-speed
large-capacity communication network have been remarkably
developed, there has been an increasing demand for miniaturization
and high integration in a semiconductor integrated circuit
technology which supports the telecommunication means.
[0005] However, as a semiconductor device has become smaller in
size and more highly integrated, an electric signal delay in the
semiconductor device, i.e., RC delay has become a large problem.
The RC delay is determined by the product of interconnect
resistance R and interconnect capacitance C. Therefore, a
countermeasure for preventing such RC delay is to use a combination
of an interconnect metal having a low electric resistance and an
interlayer dielectric/intermetal dielectric having a low dielectric
constant.
[0006] Accordingly, instead of using tungsten (W), aluminum (Al),
or aluminum alloys as a material for interconnects, there is a
growing movement towards using copper (Cu) or copper alloys which
have a lower electric resistance. Further, instead of Sio.sub.2, a
low dielectric constant (i.e., low-k) material has been developed
as a material for the interlayer dielectric/intermetal dielectric.
In addition to the development of the low dielectric constant
material, attempts have been made to lower a density of the film by
introducing a porous structure into the material so that the
dielectric constant of the interlayer dielectric/intermetal
dielectric is further lowered.
[0007] Further, as a semiconductor device has become smaller in
size and more highly integrated, structures of semiconductor
elements have become more complicated. In addition, the number of
layers in multilayer interconnects has been increased. Accordingly,
irregularities on a surface of a semiconductor device become
increased, and hence step heights on the surface of the
semiconductor device tend to be larger. This is because, in a
manufacturing process of a semiconductor device, a thin film is
formed on a semiconductor device, then micromachining processes,
such as patterning or forming holes, are performed on the
semiconductor device, and these processes are repeated many times
to form subsequent thin films on the semiconductor device.
[0008] When the number of irregularities on a surface of a
semiconductor device is increased, a thickness of a thin film
formed on a portion having a step tends to be small. Further, an
open circuit is caused by disconnection of interconnects, or a
short circuit is caused by insufficient insulation between
interconnect layers. As a result, good products cannot be obtained,
and the yield tends to be reduced. Furthermore, even if a
semiconductor device initially works normally, reliability of the
semiconductor device is lowered after a long-term use. At the time
of exposure in a lithography process, if a surface to be irradiated
has irregularities, then a lens unit in an exposure system cannot
focus on such irregularities. Therefore, if the irregularities of
the surface of the semiconductor device are increased, then it
becomes difficult to form a fine pattern on the semiconductor
device.
[0009] Accordingly, in a manufacturing process of a semiconductor
device, it becomes increasingly important to planarize a surface of
a semiconductor device. The most important one of the planarizing
technologies is CMP (Chemical Mechanical Polishing). The chemical
mechanical polishing is performed with use of a polishing
apparatus. Specifically, a substrate such as a semiconductor wafer
is brought into sliding contact with a polishing surface such as a
polishing pad while a polishing liquid containing abrasive
particles such as silica (SiO.sub.2) is supplied onto the polishing
surface, so that the substrate is polished.
[0010] This type of polishing apparatus comprises a polishing table
having a polishing surface constituted by a polishing pad or a
fixed abrasive, and a substrate holder, called a top ring or a
carrier head, for holding a substrate such as a semiconductor
wafer. A substrate such as a semiconductor wafer is polished by the
polishing apparatus in the following manner: The substrate is held
by the substrate holder and then pressed against the polishing
surface under a predetermined pressure. At this time, the polishing
table and the substrate holder are moved relative to each other for
thereby bringing the substrate into sliding contact with the
polishing surface. Accordingly, the surface of the substrate is
polished under a predetermined polishing pressure.
[0011] Generally, a low dielectric constant material has a low film
adhesion strength. Therefore, in a case where the low dielectric
constant material is used for the interlayer dielectric/intermetal
dielectric, the following problems may arise in a polishing
process:
[0012] (1) Separation (peeling-off) occurs at an interface between
the interlayer dielectric/intermetal dielectric and a metal film or
other films, resulting in failure of a fabrication process of a
semiconductor device.
[0013] (2) In order to prevent such separation of the interlayer
dielectric/intermetal dielectric, an excessively low polishing
pressure is required in the polishing process, thus increasing a
process time in a polishing process.
SUMMARY OF THE INVENTION
[0014] The present invention has been made in view of the above
drawbacks. It is therefore an object of the present invention to
provide a polishing apparatus which can prevent a film formed on a
substrate from being separated during a polishing process and can
eliminate a need for selecting a process condition which may
increase a process time in a polishing process.
[0015] In order to achieve the above object, according to the
present invention, there is provided a polishing apparatus for
polishing a substrate, comprising; a polishing tool having a
polishing surface; a substrate holder configured to hold a
substrate, the substrate held by the substrate holder being brought
into sliding contact with the polishing surface; a monitoring
device configured to monitor a polishing state of the surface of
the substrate being polished; and a controlling device configured
to change a polishing condition on the basis of the polishing state
of the surface of the substrate being polished detected by the
monitoring device.
[0016] According to the present invention, during polishing of the
substrate, the polishing state of the surface of the substrate
being polished is monitored by the monitoring device, and the
polishing condition can be changed on the basis of the polishing
state of the surface being polished which has been detected by the
monitoring device. Therefore, even if a film composed of a material
having a weak adhesion such as a low dielectric constant material
is formed on the substrate, the polishing condition is changed by
detecting the polishing state having a possibility of peeling-off
of the film during polishing of the substrate, thus preventing the
film from being peeled off.
[0017] According to one aspect of the present invention, the
controlling device changes the polishing condition when the
polishing state of the surface of the substrate being polished
detected by the monitoring device becomes a preset condition
related to peeling-off of a film formed on the substrate.
[0018] According to the present invention, as a preset condition
related to peeling-off of a film, for example, a threshold value of
a frictional force acting on the polishing interface is set, and
when the frictional force which is being monitored during the
polishing process exceeds the threshold value, operational commands
are sent from the monitoring device to the controlling device, and
then the process condition is controlled so that the frictional
force is lowered by the controlling device. Thus, the film formed
on the substrate can be prevented from being peeled off. Further,
since the threshold value at which peeling-off of the film does not
occur is determined in advance, and polishing of the substrate can
be performed in such a condition that the frictional force
approaches the threshold value as close as possible, the
excessively safe process which takes long time to polish the
substrate in order to prevent the film from being peeled off is not
required to be selected.
[0019] According to one aspect of the present invention, the film
comprises a low-k film.
[0020] According to one aspect of the present invention, the
monitoring device monitors at least one of a load torque of a motor
for rotating the polishing tool and a load torque of motor for
rotating the substrate holder.
[0021] According to one aspect of the present invention, the
monitoring device monitors a force acting on the substrate holder
in a sliding direction of the substrate holder.
[0022] According to one aspect of the present invention, the
monitoring device monitors the state of the surface of the
substrate being polished optically.
[0023] According to one aspect of the present invention, the
monitoring device monitors whether acoustic emission is generated
or not.
[0024] According to one aspect of the present invention, the
polishing condition is a polishing load.
[0025] According to one aspect of the present invention, the
polishing condition is at least one of a rotational speed of the
polishing tool and a rotational speed of the substrate holder.
[0026] According to one aspect of the present invention, the
polishing condition is a swing speed of the substrate holder.
[0027] According to one aspect of the present invention, the
polishing condition is a supply amount of a polishing liquid
supplied to the polishing surface.
[0028] According to one aspect of the present invention, the
polishing condition is a type of polishing liquid.
[0029] According to one aspect of the present invention, the
polishing condition is in-situ dressing condition.
[0030] According to one aspect of the present invention, the
polishing condition is a temperature of a polishing liquid supplied
to the polishing surface.
[0031] According to one aspect of the present invention, the
polishing condition is a temperature of the polishing surface.
[0032] According to the present invention, even if a material
having a weak adhesion such as a low dielectric constant material
is used for a film of a semiconductor device, the film formed on
the substrate can be prevented from being peeled off during
polishing of the substrate. Further, it is not necessary to select
the excessively safe process which takes long time to polish the
substrate in order to prevent the film from being peeled off. Thus,
the process margin can be broadened.
BRIEF DESCRIPTION OF THE DRAWINGS
[0033] FIG. 1 is a schematic view showing an overall structure of a
polishing apparatus according to an embodiment of the present
invention;
[0034] FIG. 2 is a schematic view showing the polishing apparatus
shown in FIG. 1, various sensors provided in the polishing
apparatus, and a polishing-state monitoring and controlling
apparatus;
[0035] FIG. 3 is a graph showing the pre-obtained data regarding
the relationship between a load torque of a motor and a frictional
force acting on a polishing interface;
[0036] FIG. 4 is a graph showing the pre-obtained data regarding
the relationship between reflectivity of light and a surface of a
substrate being polished;
[0037] FIG. 5 is a graph showing the relationship between a supply
amount of a polishing liquid and a frictional force; and
[0038] FIG. 6 is a graph showing the relationship between types of
polishing liquid and frictional coefficients.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0039] A polishing apparatus according to embodiments of the
present invention will be described below with reference to
drawings.
[0040] FIG. 1 is a schematic view showing an overall structure of a
polishing apparatus according to an embodiment of the present
invention. As shown in FIG. 1, the polishing apparatus according to
the present invention comprises a polishing table 1 having a
polishing surface, a substrate holder 5 for holding a substrate 4
such as a semiconductor wafer to be polished and pressing the
substrate 4 against the polishing surface of the polishing table 1,
and a dresser 25 for dressing the polishing surface of the
polishing table 1. The substrate 4 to be polished has a lower
surface comprising a low-k film which is an object to be polished.
A material for forming the low-k film includes SiOC, F doped
SiO.sub.2, HSQ, MSQ, BCB (Benzo Cyclo Butene), PAE (Poly Arylene
Ethers), SiO.sub.2, SiOF, Polyimide, PSI (Polyimide siloxane),
CVD-PI (CVD polyimide), PTFE (Polytetrafluoroethylene), PNT
(Polynaphthalene), BCB (Benzo cyclo butane), a-C:F (fluorinated
amorphous carbon), Palylene-N, Palylene-F, SOG-Siloxan, or a porous
structural member made of one of these materials.
[0041] The polishing table 1 has an upper surface to which a
polishing pad 2 is attached, and the upper surface of the polishing
pad 2 constitutes the polishing surface. The polishing table 1 is
rotatable by a polishing table drive motor 9. A polishing liquid
supply nozzle 8 is provided above the polishing table 1, and a
polishing liquid Q (slurry) is supplied onto the polishing pad 2 on
the polishing table 1 from the polishing liquid supply nozzle
8.
[0042] Various types of polishing pads are available on the market.
For example, some of these are SUBA800, IC-1000, and
IC-1000/SUBA400 (two-layer cloth) manufactured by Rodel, Inc., and
Surfin xxx-5 and Surfin 000 manufactured by Fujimi Inc. SUBA800,
Surfin xxx-5, and Surfin 000 are non-woven fabrics bound by
urethane resin, and IC-1000 is made of rigid foam polyurethane
(single-layer). Foam polyurethane is porous and has a large number
of fine recesses or holes formed in its surface.
[0043] Although the polishing pad serves as the polishing surface,
the present invention is not limited to the above structure. For
example, the polishing surface may be constituted by a fixed
abrasive. The fixed abrasive is formed into a flat plate comprising
abrasive particles fixed by a binder. With the fixed abrasive for
polishing, the polishing process is performed by abrasive particles
that are self-generated from the fixed abrasive. The fixed abrasive
comprises abrasive particles, a binder, and pores. For example,
cerium dioxide (CeO.sub.2) or silicon oxide (SiO.sub.2) or alumina
(Al.sub.2O.sub.3) having an average particle diameter of 0.5 .mu.m
or less is used as an abrasive particle, and thermosetting resin
such as epoxy resin or phenol resin or thermoplastic resin such as
MBS resin or ABS resin is used as a binder. Such a fixed abrasive
forms a harder polishing surface. The fixed abrasive includes not
only the above plate-like fixed abrasive but also a fixed abrasive
pad having a two-layer structure formed by a thin layer of a fixed
abrasive and an elastic polishing pad attached to a lower surface
of the thin layer of the fixed abrasive.
[0044] The above polishing table and the polishing pad constitute a
polishing tool. Further, the above polishing table and the fixed
abrasive constitute a polishing tool. Here, the polishing table
comprises SuS (metal), Al.sub.2O.sub.2, SiC, or the like.
[0045] The substrate holder 5 comprises a holder body 6 for holding
the upper surface of the substrate, and an annular retainer ring 7
fixed to the lower end of the holder body 6 for retaining an outer
circumferential edge of the substrate. The holder body 6 is made of
a material having high strength and rigidity, such as metal or
ceramics. The retainer ring 7 is made of highly rigid synthetic
resin, ceramics, or the like. The substrate holder 5 is connected
to a substrate holder drive shaft 11 by a universal joint 10, and
the substrate holder drive shaft 11 is coupled to a substrate
holder air cylinder 13 fixed to a substrate holder head 12. The
substrate holder air cylinder 13 operates to move the substrate
holder drive shaft 11 vertically to thereby lift and lower the
substrate holder 5 as a whole and to press the substrate holder 5
against the polishing table 1.
[0046] The substrate holder air cylinder 13 is connected to a
compressed air source 22 via a fluid passage 21 and a regulator R.
The regulator R can regulate a pressure of compressed air or the
like which is supplied to the substrate holder air cylinder 13.
Thus, it is possible to adjust a pressing force to press the
polishing pad 2 with the substrate holder 5, and hence a polishing
pressure applied to the substrate can be adjusted to a desired
value.
[0047] The substrate holder drive shaft 11 is connected to a rotary
sleeve 15 by a key (not shown). The rotary sleeve 15 has a timing
pulley 16 fixedly disposed at a peripheral portion thereof. A
substrate holder drive motor 17 is fixed to the substrate holder
head 12, and the timing pulley 16 is coupled to a timing pulley 19
mounted on the substrate holder drive motor 17 via a timing belt
18. Therefore, when the substrate holder drive motor 17 is
energized for rotation, the rotary sleeve 15 and the substrate
holder drive shaft 11 are rotated in unison with each other via the
timing pulley 19, the timing belt 18, and the timing pulley 16 to
thereby rotate the substrate holder 5. The substrate holder head 12
is supported on a substrate holder head shaft 20 rotatably
supported on a frame (not shown). The substrate holder head 12 is
swingable by rotating the substrate holder head shaft 20 so that
the substrate holder 5 is movable between a substrate transfer
position for transferring the substrate and a polishing position on
the polishing surface of the polishing table 1. The substrate
holder 5 is swingable on the polishing surface of the polishing
table 1 by rotating the substrate holder head shaft 20 in normal
and reverse directions. Further, the swing speed of the substrate
holder 5 is adjustable by the rotational speed of the substrate
holder head shaft 20.
[0048] The dresser 25 comprises a diamond dresser having diamond
particles electrodeposited thereon, for example. The dresser 25 is
supported from a dresser head 27 by a dresser drive shaft 26. The
dresser drive shaft 26 is coupled to a dresser drive motor 28, and
the dresser 25 is rotated by a dresser drive motor 28. The dresser
head 27 is supported on a dresser head shaft 29 rotatably supported
on a frame (not shown). The dresser head 27 is swingable by
rotating the dresser head shaft 29 so that the dresser 25 is
movable between a standby position and a dressing position on the
polishing surface of the polishing table.
[0049] Overall operation of the polishing apparatus shown in FIG. 1
will be described below.
[0050] In the polishing apparatus having the above structure, when
the substrate 4 such as a semiconductor wafer is to be supplied to
the top ring 1, the substrate holder 5 is placed in its entirety
into the substrate transfer position. Then, the substrate 4 is
transferred to the substrate holder 5 by a substrate transfer
apparatus (pusher) provided at the substrate transfer position, and
the substrate 4 is held on the lower end surface of the substrate
holder 5 under vacuum. Next, the substrate holder 5 holding the
substrate 4 under vacuum is moved in its entirety to a position
above the polishing table 1. The outer circumferential edge of the
substrate 4 is retained by the retainer ring 7 so that the
substrate 4 will not be dislodged from the substrate holder 5.
[0051] Then, the attraction of the substrate 4 is released. At the
same time, the substrate holder air cylinder 13 connected to the
substrate holder drive shaft 11 is operated to press the substrate
4 held by the lower end surface of the substrate holder 5 against
the polishing pad 2 of the polishing table 1. At this time, the
polishing table 1 and the substrate holder 5 are being rotated by
the polishing table drive motor 9 and the substrate holder drive
motor 17 at respective desired rotational speeds. The polishing
liquid Q which has been supplied from the polishing liquid supply
nozzle 8 is retained on the polishing pad 2. The substrate 4 is now
polished with the polishing liquid Q being present between the
surface (lower surface) of the substrate 4 and the polishing pad 2.
By regulating a pressure of air supplied to the substrate holder
air cylinder 13, a polishing pressure applied to the substrate can
be adjusted to a desired value. During polishing of the substrate
4, a polishing state of the surface of the substrate 4 being
polished is monitored, and is controlled. At the same time that the
substrate is polished, the dresser 25 is rotated at a predetermined
rotational speed while the dresser 25 is pressed against the
polishing pad 2 and the dressing liquid is supplied to the
polishing pad 2. Thus, in-situ dressing of the polishing pad 2 is
performed.
[0052] Next, a polishing state monitoring and controlling apparatus
for monitoring a polishing state of the substrate and controlling
the polishing state of the substrate during a polishing process
will be described with reference to FIGS. 2 through 6.
[0053] FIG. 2 is a schematic view showing the polishing apparatus
shown in FIG. 1, various sensors provided in the polishing
apparatus, and a polishing state monitoring and controlling
apparatus. As shown in FIG. 2, the polishing apparatus has a
polishing state monitoring and controlling apparatus 30, and the
polishing state monitoring and controlling apparatus 30 comprises a
polishing state monitoring unit 31 and a polishing state
controlling unit 32. The polishing state monitoring unit 31
constitutes a monitoring device configured to monitor a polishing
state of the surface of the substrate being polished, and the
polishing state controlling unit 32 constitutes a controlling
device configured to change a polishing condition on the basis of
the polishing state of the surface of the substrate being polished
detected by the monitoring device (described later). A motor torque
of the polishing table drive motor 9 for rotating the polishing
table 1 is detected on the basis of a motor current value, and the
detected motor torque is inputted into the polishing state
monitoring unit 31 of the polishing state monitoring and
controlling apparatus 30. A motor torque of the substrate holder
drive motor 17 for rotating the substrate holder 5 is detected on
the basis of a motor current value, and the detected motor torque
is inputted into the polishing state monitoring unit 31 of the
polishing state monitoring and controlling apparatus 30.
[0054] A force sensor 33 for detecting an acting force is provided
on the substrate holder 5, and a force acting on the substrate
holder 5 in the sliding direction of the substrate holder 5 is
detected by the force sensor 33. Then, the detected acting force is
inputted into the polishing state monitoring unit 31 of the
polishing state monitoring and controlling apparatus 30. Further,
an acoustic emission sensor (AE sensor) 35 is provided on the
substrate holder 5, and elastic wave (described later on) detected
by the acoustic emission sensor 35 is inputted into the polishing
state monitoring unit 31 of the polishing state monitoring and
controlling apparatus 30.
[0055] On the other hand, an optical sensor 34 is provided in the
polishing table 1, and reflected light from the substrate 4
detected by the optical sensor 34 is inputted into the polishing
state monitoring unit 31 of the polishing state monitoring and
controlling apparatus 30. The optical sensor 34 comprises a
light-emitting element and a light-receiving element. Light for
measurement from the light-emitting element is applied to the
substrate 4, and reflected light from the substrate 4 is received
by the light-receiving element. This received reflected light is
inputted into the polishing state monitoring unit 31, as described
above.
[0056] Next, operation of the various sensors and the polishing
state monitoring and controlling apparatus constructed as shown in
FIG. 2 will be described below.
[0057] The respective torque values of the polishing table drive
motor 9 and the substrate holder drive motor 17 are inputted into
the polishing state monitoring unit 31 of the polishing state
monitoring and controlling apparatus 30. In the polishing state
monitoring unit 31, a frictional force acting between the surface
of the substrate 4 and the polishing surface of the polishing pad 2
on the polishing table 1 is detected from the torque of the
polishing table drive motor 9 and/or the torque of the substrate
holder drive motor 17. In this case, the relationship between the
frictional force acting on the polishing interface between the
surface of the substrate 4 and the polishing surface of the
polishing pad 2 on the polishing table 1, and the load torque
(torque of the motor) are determined in advance.
[0058] FIG. 3 is a graph showing the pre-obtained data regarding
the relationship between a load torque of a motor and a frictional
force acting on a polishing interface. In FIG. 3, the horizontal
axis represents a load torque of the motor, and the vertical axis
represents a frictional force acting on the polishing interface. As
shown in FIG. 3, there is linear correlation between the load
torque of the motor and the frictional force.
[0059] As shown in FIG. 3, the frictional force acting between the
surface of the substrate 4 being polished and the polishing surface
of the polishing pad 2 on the polishing table 1 is detected from a
torque of the polishing table drive motor 9 and/or a torque of the
substrate holder drive motor 17 on the basis of the pre-obtained
data regarding the relationship between the load torque of the
motor and the frictional force acting on the polishing interface.
In this manner, the detected frictional force acting on the
polishing interface between the surface of the substrate 4 being
polished and the polishing surface of the polishing pad 2 on the
polishing table 1 is monitored at all times during a polishing
process by the polishing state monitoring unit 31.
[0060] The force sensor 33 provided on the substrate holder 5
comprises an acceleration sensor, and the frictional force acting
on the polishing interface between the surface of the substrate 4
being polished and the polishing surface of the polishing pad 2 can
be detected on the basis of an acceleration (vibration) detected by
the force sensor 33. In this case, in the polishing state
monitoring unit 31, frequency components having a strong
correlation with the polishing process are extracted from signals
inputted from the force sensor 33 into the polishing state
monitoring unit 31 of the polishing state monitoring and
controlling apparatus 30, and the time variation of the extracted
frequency components is monitored. The relationship between a
vibration strength and a frictional force acting on the polishing
interface between the surface of the substrate 4 being polished and
the polishing surface of the polishing pad 2 is determined in
advance.
[0061] Further, in the optical sensor 34, visible light is applied
to the surface of the substrate 4 being polished by the
light-emitting element, and reflected light from the surface of the
substrate 4 being polished is received by the light-receiving
element. Then, the reflected light is inputted into the polishing
state monitoring unit 31 of the polishing state monitoring and
controlling apparatus 30, and reflectivity of light can be
detected. In the polishing state monitoring unit 31, during the
polishing process, the state of the surface of the substrate 4
being polished can be optically monitored by monitoring the
reflectivity of light.
[0062] FIG. 4 is a graph showing the pre-obtained data regarding
the relationship between reflectivity of light and a surface of a
substrate being polished. In FIG. 4, the horizontal axis represents
time (seconds), and the vertical axis represents reflectivity of
light (%) of a surface of a substrate being polished. As shown in
FIG. 4, the reflectivity (%) varies rapidly after a lapse of about
30 seconds, and thereafter the reflectivity is rapidly lowered. In
this case, this is because peeling-off of a film occurs after a
lapse of about 30 seconds. By monitoring the reflectivity of light
of the surface of the substrate 4 being polished, generation of
peeling-off of the film formed on the substrate 4 can be
detected.
[0063] When the film of the surface of the substrate 4 being
polished is peeled off, elastic wave in an ultrasonic band is
emitted, and this phenomenon is called acoustic emission.
Therefore, the acoustic emission sensor 35 provided on the
substrate holder 5 detects this elastic wave to detect peeling-off
of the film. In the polishing state monitoring unit 31, during the
polishing process, whether the acoustic emission (AE) is generated
or not is monitored, whereby peeling-off of the film generated in
the surface of the substrate 4 being polished is monitored.
[0064] In this manner, various values including the torque of the
motor, the vibration strength, the reflectivity of light, the AE,
and the like are monitored at all times during the polishing
process in the polishing state monitoring unit 31 of the polishing
state monitoring and controlling apparatus 30. In this case, in the
polishing state monitoring unit 31, measured values such as
torques, vibration strength, reflectivity of light, and the like
are compared with predetermined threshold values at all times
during the polishing process.
[0065] The above threshold values are determined in the following
procedure, for example.
[0066] (1) A critical frictional force at which peeling-off of a
film of a substrate to be polished occurs is determined in
advance.
[0067] (2) A threshold value of the frictional force which can be
applied to the substrate during the polishing process is determined
in consideration of safety factor.
[0068] The above determined threshold value is used, and when the
frictional force of the polishing interface which is being
monitored exceeds the determined threshold value, operational
commands are sent from the polishing state monitoring unit 31 to
the polishing state controlling unit 32, and the process condition
is controlled so that the frictional force is lowered by the
polishing state controlling unit 32. Specifically, the polishing
load is lowered, the flow rate of the polishing liquid (slurry) is
reduced, the rotational speed of the substrate holder 5 and/or the
polishing table 1 is lowered, the type of polishing liquid (slurry)
is changed, or other controls may be performed.
[0069] As described above, when the measured value which is being
monitored exceeds the threshold value, the operational commands are
sent form the polishing state monitoring unit 31 to the polishing
state controlling unit 32. Then, as shown in FIG. 2, control of the
polishing load, control of the rotational speed of the polishing
table 1 and/or the substrate holder 5, control of the supply amount
of the polishing liquid, control of the in-situ dressing condition,
control of the temperature of the polishing liquid, control of the
temperature of the polishing surface, and change of the type of
polishing liquid are performed. In this case, of these kinds of
control, one or more kinds of control are suitably combined to
prevent the film formed on the substrate 4 from being peeled off.
The control of the temperature of the polishing liquid is performed
by a temperature adjustment device such as a heater or a chiller
for heating or cooling the polishing liquid. Further, a control
method of controlling the temperature of the polishing surface
includes a method of allowing a temperature regulating fluid to
flow from the backside surface of the polishing table, a method of
warming the polishing surface by applying light to the polishing
surface, and a method of cooling the polishing surface by
ventilation.
[0070] FIG. 5 is a graph showing the relationship between a supply
amount of a polishing liquid and a frictional force, and the
horizontal axis represent a flow rate of the polishing liquid
(ml/min) and the vertical axis represents a frictional force of a
polishing interface (N).
[0071] As shown in FIG. 5, the frictional force of the polishing
interface can be lowered by reducing the supply amount of the
polishing liquid. Therefore, when the frictional force which is
being monitored exceeds a threshold value, the frictional force is
lowered by reducing the supply amount of the polishing liquid.
Thus, the film formed on the substrate 4 can be prevented from
being peeled off.
[0072] FIG. 6 is a graph showing the relationship between types of
polishing liquid and frictional coefficients, and the horizontal
axis represents types of polishing liquid and the vertical axis
represents frictional coefficients. In FIG. 6, Ox-1 is
silicon-dioxide-film polishing slurry SS-25 manufactured by Cabot
Corporation, Cu-1 is copper-film polishing slurry PL7101
manufactured by Fujimi Incorporated, Cu-2 is copper-film polishing
slurry CMS7303/7304 manufactured by JSR Corporation, Cu-3 is
copper-film polishing slurry PL7102/DCM-G2 manufactured by Fujimi
Incorporated, Cu-4 is abrasive particle-free copper-film polishing
slurry l, and Cu-5 is abrasive particle-free copper-film polishing
slurry 2. Further, Ta-1 is barrier-metal polishing slurry B-12
manufactured by Fujimi Incorporated, and Ta-2 is barrier-metal
polishing slurry CMS8301 manufactured by JSR Corporation.
[0073] As is apparent from FIG. 6, the frictional force of the
polishing interface can be lowered by changing the type of
polishing liquid. Therefore, when the frictional force of the
polishing interface which is being monitored exceeds the threshold
value, the frictional force is lowered by changing the type of
polishing liquid. Thus, the film formed on the substrate 4 can be
prevented from being peeled off.
[0074] A plurality of threshold values can be determined, and the
optimum process can be maintained by determining a lower limit and
an upper limit of the threshold values. The optimum process
condition means that the frictional force of the polishing
interface is as small as possible and the polishing rate is as
large as possible. However, it is necessary to consider within
wafer non-uniformity of the surface of the substrate to be polished
or the pattern characteristics. Basically, the larger the
frictional force is, the higher the polishing rate is. Therefore,
the optimum process condition may be such a condition that the
frictional force approaches the above threshold value as close as
possible. Specifically, while the frictional force of the polishing
interface is monitored by the polishing state monitoring unit 31,
if the frictional force is lowered excessively, then the polishing
apparatus is operated such that parameters are controlled so as to
increase the frictional force.
[0075] Although certain preferred embodiments of the present
invention have been shown and described in detail, it should be
understood that various changes and modifications may be made
therein without departing from the scope of the appended
claims.
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