U.S. patent application number 09/754429 was filed with the patent office on 2001-09-13 for method and apparatus for detecting a planarized outer layer of a semiconductor wafer with a confocal optical system.
Invention is credited to Allman, Derryl D.J., Daniel, David W., Gregory, John W..
Application Number | 20010021622 09/754429 |
Document ID | / |
Family ID | 22648210 |
Filed Date | 2001-09-13 |
United States Patent
Application |
20010021622 |
Kind Code |
A1 |
Allman, Derryl D.J. ; et
al. |
September 13, 2001 |
Method and apparatus for detecting a planarized outer layer of a
semiconductor wafer with a confocal optical system
Abstract
A method of planarizing a first side of a semiconductor wafer
with a polishing system includes the step of polishing the first
side of the wafer in order to remove material from the wafer. The
method also includes the step of moving a lens of a confocal
optical system between a number of lens positions so as to maintain
focus on the first side of the wafer during the polishing step. The
method further includes the step of determining a rate-of-movement
value based on movement of the lens during the moving step.
Moreover, the method includes the step of stopping the polishing
step if the rate-of-movement value has a predetermined relationship
with a movement threshold value. An apparatus for polishing a first
side of a semiconductor wafer is also disclosed.
Inventors: |
Allman, Derryl D.J.;
(Colorado Springs, CO) ; Daniel, David W.;
(Divide, CO) ; Gregory, John W.; (Colorado
Springs, CO) |
Correspondence
Address: |
Ralph R. Veseli
LSI Logic Corporation
Intellectual Property Department, M/S D-106
1551 McCarthy Boulevard
Milptas
CA
95035
US
|
Family ID: |
22648210 |
Appl. No.: |
09/754429 |
Filed: |
January 4, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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09754429 |
Jan 4, 2001 |
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09177335 |
Oct 22, 1998 |
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6201253 |
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Current U.S.
Class: |
451/6 |
Current CPC
Class: |
B24B 49/04 20130101;
B24B 37/013 20130101; H01L 21/67253 20130101; B24B 49/12
20130101 |
Class at
Publication: |
451/6 |
International
Class: |
B24B 049/00; B24B
051/00 |
Claims
What is claimed is:
1. A method of planarizing a first side of a semiconductor wafer
with a polishing system, comprising the steps of: polishing said
first side of said wafer in order to remove material from said
wafer; moving a lens of a confocal optical system between a number
of lens positions so as to maintain focus on said first side of
said wafer during said polishing step; determining a
rate-of-movement value based on movement of said lens during said
moving step; and stopping said polishing step if said
rate-of-movement value has a predetermined relationship with a
movement threshold value.
2. The method of claim 1, wherein said stopping step includes the
step of stopping said polishing step if said rate-of-movement value
is less than said movement threshold value.
3. The method of claim 1, wherein: said polishing step includes the
step of rotating said wafer with a wafer motor, and said stopping
step includes the step of idling said wafer motor if said
rate-of-movement value has said predetermined relationship with
said movement threshold.
4. The method of claim 1, wherein: said polishing step includes the
step of rotating a wafer carrier so as to urge said wafer into
contact with a polishing platen, and said confocal optical system
is positioned such that an incident light beam emitting therefrom
is directed through an opening defined in said polishing platen so
as to impinge upon said first side of said wafer.
5. The method of claim 1, wherein said moving step includes the
step of moving an objective lens of said confocal optical system
between said number of lens positions so as to maintain focus on
said first side of said wafer during said polishing step.
6. A method of planarizing a first side of a semiconductor wafer,
comprising the steps of: polishing said first side of said wafer in
order to remove material from said wafer; transmitting a first
incident light beam from a confocal optical system during a first
time period, wherein said first incident light beam impinges on
said first side of said wafer during said polishing step so as to
form a first reflected light beam which is reflected from said
first side of said wafer; analyzing said first reflected light beam
so as to determine if said confocal optical system is focused on
said first side of said wafer during said first time period;
transmitting a second incident light beam from said confocal
optical system during a second time period, wherein said second
incident light beam impinges on said first side of said wafer
during said polishing step so as to form a second reflected light
beam which is reflected from said first side of said wafer;
analyzing said second reflected light beam so as to determine if
said confocal optical system is focused on said first side of said
wafer during said second time period; and stopping said polishing
step if said confocal optical system is focused on said first side
of said wafer during both said first time period and said second
time period.
7. The method of claim 6, wherein: said polishing step includes the
step of rotating said wafer with a wafer motor, and said stopping
step includes the step of idling said wafer motor if said confocal
optical system is focused on said first side of said wafer during
both said first time period and said second time period.
8. The method of claim 6, wherein: said polishing step includes the
step of rotating a wafer carrier so as to urge said wafer into
contact with a polishing platen, and said confocal optical system
is positioned such that both said first and said second incident
light beams are directed through an opening defined in said
polishing platen.
9. The method of claim 8, wherein: said first incident light beam
includes a first incident laser beam, said second incident light
beam includes a second incident laser beam, said step of
transmitting said first incident light beam includes the step of
generating said first incident laser beam with a laser source unit,
said step of transmitting said second incident light beam includes
the step of generating said second incident laser beam with said
laser source unit, and said laser source unit is positioned such
that both said first and second incident laser beams are directed
through said opening defined in said polishing platen so as to
impinge on said first side of said wafer during said polishing
step.
10. An apparatus for polishing a first side of a semiconductor
wafer, comprising: a polishing system which operates to polish said
wafer, said polishing system having (i) a polishing platen which
includes a polishing surface, and (ii) a wafer carrier which is
configured to (a) engage said wafer by a second side of said wafer,
and (b) apply pressure to said wafer in order to press said wafer
against said polishing surface of said polishing platen; a confocal
optical system having a movable objective lens, said confocal
optical system being configured to move said objective lens between
a number of lens positions so as to maintain focus on said first
side of said wafer during polishing of said wafer; and a controller
electrically coupled to said confocal optical system, wherein said
controller is configured to (i) determine a rate-of-movement value
based on movement of said objective lens during polishing of said
wafer, and (ii) terminate operation of said polishing system so as
to cease polishing of said wafer in response to determination that
said rate-of-movement value has a predetermined relationship with a
movement threshold value.
11. The apparatus of claim 10, further comprising a wafer motor,
wherein: said wafer motor is operable in (i) a polishing mode of
operation in which said wafer motor rotates said wafer carrier, and
(ii) an idle mode of operation in which said wafer motor is idle,
and said wafer motor is positioned in said idle mode of operation
if said rate-of-movement value has said predetermined relationship
with said movement threshold.
12. The apparatus of claim 10, wherein: said polishing platen has
an opening defined therein, and said confocal optical system is
positioned such that an incident light beam emitting therefrom is
directed through said opening defined in said polishing platen so
as to be impinged upon said first side of said wafer.
13. The apparatus of claim 12, wherein: said confocal optical
system includes a confocal laser system, said incident light beam
includes an incident laser beam generated by said confocal laser
system, and said confocal laser system is positioned such that said
incident laser beam is directed through said opening defined in
said polishing platen so as to impinge said incident laser beam on
said first side of said wafer.
14. The apparatus of claim 10, wherein said controller is further
configured to terminate operation of said polishing system so as to
cease polishing of said wafer in response to determination that
said rate-of-movement value is less than said movement threshold
value.
15. An apparatus for polishing a first side of a semiconductor
wafer, comprising: a polishing system which operates to polish said
wafer, said polishing system having (i) a polishing platen which
includes a polishing surface, and (ii) a wafer carrier which is
configured to (a) engage said wafer by a second side of said wafer,
and (b) apply pressure to said wafer in order to press said wafer
against said polishing surface of said polishing platen; a confocal
optical system positioned such that (i) a first incident light beam
transmitted by said confocal optical system is impinged upon said
first side of said wafer during a first period of time so as to
form a first reflected light beam which is reflected from said
first side of said wafer, (ii) a second incident light beam
transmitted by said confocal optical system is impinged upon said
first side of said wafer during a second period of time so as to
form a second reflected light beam which is reflected from said
first side of said wafer, and (iii) said first and second reflected
light beams are received with said confocal optical system; and a
controller electrically coupled to said confocal optical system,
wherein said controller is configured to (i) analyze said first
reflected light beam so as to determine if said confocal optical
system is focused on said first side of said wafer during said
first time period, (ii) analyze said second reflected light beam so
as to determine if said confocal optical system is focused on said
first side of said wafer during said second time period, and (iii)
terminate operation of said polishing system so as to cease
polishing of said wafer in response to determination that said
confocal optical system is focused on said first side of said wafer
during both said first time period and said second time period.
16. The apparatus of claim 15, further comprising a wafer motor,
wherein: said wafer motor is operable in (i) a polishing mode of
operation in which said wafer motor rotates said wafer carrier, and
(ii) an idle mode of operation in which said wafer motor is idle,
and said wafer motor is positioned in said idle mode of operation
in response to determination that said confocal optical system is
focused on said first side of said wafer during both said first
time period and said second time period.
17. The apparatus of claim 15, wherein: said polishing platen has
an opening defined therein, and said confocal optical system is
positioned such that (i) said first and second incident light beams
are directed through said opening defined in said polishing platen
so as to be impinged upon said first side of said wafer, and (ii)
said first and second reflected light beams are directed through
said opening so as to be received with said confocal optical
system.
18. The apparatus of claim 17, wherein: said confocal optical
system includes a confocal laser system, said first and second
incident light beams include first and second incident laser beams
generated by said confocal laser system, said first and second
reflected light beams include first and second reflected laser
beams reflected from said first side of said wafer, and said
confocal laser system is positioned such that (i) said first and
second incident laser beams are directed through said opening
defined in said polishing platen so as to impinge said first and
second incident laser beams on said first side of said wafer, and
(ii) said first and second reflected laser beams are received by
said confocal laser system.
Description
TECHNICAL FIELD OF THE INVENTION
[0001] The present invention relates generally to a method and
apparatus for detecting a planarized outer layer of a semiconductor
wafer, and more particularly to a method and apparatus for
detecting a planarized outer layer of a semiconductor wafer by
monitoring movement of an objective lens associated with a confocal
optical system during polishing of the semiconductor wafer.
BACKGROUND OF THE INVENTION
[0002] Semiconductor integrated circuits are typically fabricated
by a layering process in which several layers of material are
fabricated on or in a surface of a wafer, or alternatively, on a
surface of a previous layer. This fabrication process typically
requires subsequent layers to be fabricated upon a smooth, planar
surface of a previous layer. However, the surface topography of
layers may be uneven due to an uneven topography associated with an
underlying layer. As a result, a layer may need to be polished in
order to present a smooth, planar surface for a subsequent
processing step. For example, a layer may need to be polished prior
to formation of a conductor layer or pattern on an outer surface of
the layer.
[0003] In general, a semiconductor wafer may be polished to remove
high topography and surface defects such as scratches, roughness,
or embedded particles of dirt or dust. The polishing process
typically is accomplished with a polishing system that includes top
and bottom platens (e.g. a polishing table and a wafer carrier or
holder), between which the semiconductor wafer is positioned. The
platens are moved relative to each other thereby causing material
to be removed from the surface of the wafer. This polishing process
is often referred to as mechanical planarization (MP) and is
utilized to improve the quality and reliability of semiconductor
devices. The polishing process may also involve the introduction of
a chemical slurry to facilitate higher removal rates, along with
the selective removal of materials fabricated on the semiconductor
wafer. This polishing process is often referred to as chemical
mechanical planarization or chemical mechanical polishing
(CMP).
[0004] In these polishing processes, it is often important to
determine when an outer layer or film has been polished to a
desired planarity level. In particular, it is desirable to know
when the outer layer of the semiconductor wafer has been polished
to a planarity level which is acceptable for presentation of the
wafer to a subsequent fabrication process.
[0005] In order to determine when a wafer has been polished to a
desired planarity level, systems and techniques have heretofore
been utilized which polish the wafer down to a predetermined
thickness. For example, a typical method employed for determining
when the wafer has been polished down to a predetermined thickness
is to measure the amount of time needed to planarize a first wafer
to the desired thickness, and thereafter polishing the remaining
wafers for a similar amount of time. In practice this method is
extremely time consuming since machine operators must inspect each
wafer (e.g. measure the thickness thereof) after polishing. In
particular, it is extremely difficult to precisely control the
removal rate of material since the removal rate may vary during the
polishing of an individual wafer. Moreover, the removal rate may be
diminished in the process of polishing a number of wafers in
sequence. Yet further, such methods do not actually measure the
planarity of the outer layer, but rather simply make an assumption
that the outer layer has been polished to an acceptable planarity
level when the wafer is polished to the desired thickness.
[0006] Another method employed for determining if the wafer has
reached the desired thickness is to impinge a light beam, such as a
laser light beam, onto the semiconductor wafer in order to
determine the thickness of the wafer. Various techniques have been
used to detect when an outer film associated with the semiconductor
wafer reaches the desired thickness. For example, the apparatus
disclosed in U.S. Pat. No. 5,151,584 issued to Ebbing et al directs
an incident laser beam onto the surface of a semi-transparent thin
film (e.g. silicon dioxide) of a semiconductor wafer during etching
thereof. A first portion of the incident beam is reflected from the
top surface of the film, and a second portion of the incident beam
is reflected from the bottom surface of the film. Since the film
has a finite thickness, the two reflections will either
constructively or destructively interfere with one another. As the
layer is etched, its thickness is changed thereby cycling intensity
of the reflected beam through constructive and destructive
interference patterns which may be utilized to determine when the
wafer has been etched to the desired thickness. Such a technique
has a number of drawbacks associated therewith. For example, such a
technique may only be utilized after certain steps in the
fabrication process. For example, such a technique may be useful
for measuring thickness of a blank wafer, but has been found to
perform unsatisfactorily when utilized to measure thickness of a
patterned wafer. Moreover, similarly to the manual inspection
method discussed above, such a technique does not actually measure
the planarity of the outer layer, but rather simply makes an
assumption that the outer layer has been polished to an acceptable
planarity level when the wafer is etched down to the desired
thickness.
[0007] In order to overcome the above-mentioned drawbacks
associated with wafer thickness-based polishing endpoint
techniques, a number of techniques have heretofore been utilized in
an attempt to measure the actual planarity of the outer layer of
the wafer. For example, a method which has heretofore been employed
for determining when the wafer has been polished to a desired
planarity level is to periodically remove the wafer from the
polishing system, and thereafter measure the planarity of the wafer
with an instrument such as an atomic force microscope or a
profilometer. If the wafer has been polished to the desired
planarity level, the wafer is released to a subsequent fabrication
step. However, if the wafer has not been polished to the desired
planarity level, the wafer must be placed back into the polishing
system for further polishing thereof. It should be appreciated that
numerous measurements may be required to reach the desired
planarity level. Hence, in practice this method is extremely time
consuming since machine operators must measure each wafer (i.e.
measure the planarity thereof) a number of times during the
polishing process.
[0008] Thus, a continuing need exists for a method and an apparatus
for in situ measurement of the planarity of the outer layer of a
semiconductor wafer during polishing thereof.
SUMMARY OF THE INVENTION
[0009] In accordance with a first embodiment of the present
invention, there is provided a method of planarizing a first side
of a semiconductor wafer with a polishing system. The method
includes the step of polishing the first side of the wafer in order
to remove material from the wafer. The method also includes the
step of moving a lens of a confocal optical system between a number
of lens positions so as to maintain focus on the first side of the
wafer during the polishing step. The method further includes the
step of determining a rate-of-movement value based on movement of
the lens during the moving step. Moreover, the method includes the
step of stopping the polishing step if the rate-of-movement value
has a predetermined relationship with a movement threshold
value.
[0010] Pursuant to a second embodiment of the present invention,
there is provided a method of planarizing a first side of a
semiconductor wafer. The method includes the step of polishing the
first side of the wafer in order to remove material from the wafer.
The method also includes the step of transmitting a first incident
light beam from a confocal optical system during a first time
period. The first incident light beam impinges on the first side of
the wafer during the polishing step so as to form a first reflected
light beam which is reflected from the first side of the wafer. The
method further includes the step of analyzing the first reflected
light beam so as to determine if the confocal optical system is
focused on the first side of the wafer during the first time
period. The method yet further includes the step of transmitting a
second incident light beam from the confocal optical system during
a second time period. The second incident light beam impinges on
the first side of the wafer during the polishing step so as to form
a second reflected light beam which is reflected from the first
side of the wafer. The method moreover includes the step of
analyzing the second reflected light beam so as to determine if the
confocal optical system is focused on the first side of the wafer
during the second time period. Finally, the method includes the
step of stopping the polishing step if the confocal optical system
is focused on the first side of the wafer during both the first
time period and the second time period.
[0011] Pursuant to a third embodiment of the present invention,
there is provided an apparatus for polishing a first side of a
semiconductor wafer. The apparatus includes a polishing system
which operates to polish the wafer. The polishing system has a
polishing platen which includes a polishing surface, and a wafer
carrier which is configured to engage the wafer by a second side of
the wafer, and apply pressure to the wafer in order to press the
wafer against the polishing surface of the polishing platen. The
apparatus also includes a confocal optical system having a movable
objective lens. The confocal optical system is configured to move
the objective lens between a number of lens positions so as to
maintain focus on the first side of the wafer during polishing of
the wafer. The apparatus further includes a controller electrically
coupled to the confocal optical system. The controller is
configured to determine a rate-of-movement value based on movement
of the objective lens during polishing of the wafer, and terminate
operation of the polishing system so as to cease polishing of the
wafer in response to determination that the rate-of-movement value
has a predetermined relationship with a movement threshold
value.
[0012] Pursuant to a fourth embodiment of the present invention,
there is provided an apparatus for polishing a first side of a
semiconductor wafer. The apparatus includes a polishing system
which operates to polish the wafer. The polishing system has a
polishing platen which includes a polishing surface. The polishing
system also includes a wafer carrier which is configured to engage
the wafer by a second side of the wafer and apply pressure to the
wafer in order to press the wafer against the polishing surface of
the polishing platen. The apparatus also includes a confocal
optical system positioned such that a first incident light beam
transmitted by the confocal optical system is impinged upon the
first side of the wafer during a first period of time so as to form
a first reflected light beam which is reflected from the first side
of the wafer. The confocal optical system is also positioned such
that a second incident light beam transmitted by the confocal
optical system is impinged upon the first side of the wafer during
a second period of time so as to form a second reflected light beam
which is reflected from the first side of the wafer. Yet further,
the confocal optical system is positioned such that the first and
second reflected light beams are received with the confocal optical
system. The apparatus also includes a controller electrically
coupled to the confocal optical system. The controller is
configured to analyze the first reflected light beam so as to
determine if the confocal optical system is focused on the first
side of the wafer during the first time period, analyze the second
reflected light beam so as to determine if the confocal optical
system is focused on the first side of the wafer during the second
time period, and terminate operation of the polishing system so as
to cease polishing of the wafer in response to determination that
the confocal optical system is focused on the first side of the
wafer during both the first time period and the second time
period.
[0013] It is an object of the present invention to provide a new
and useful method and apparatus for determining when a
semiconductor wafer has been polished to a desired planarity
level.
[0014] It is also an object of the present invention to provide an
improved method and apparatus for determining when a semiconductor
wafer has been polished to a desired planarity level.
[0015] It is yet further an object of the present invention to
provide a method and apparatus for determining when a semiconductor
wafer has been polished to a desired planarity level that is less
mechanically complex relative to polishing systems which have
heretofore been designed.
[0016] It is moreover an object of the present invention to provide
a method and apparatus for determining when a semiconductor wafer
has been polished to a desired planarity level that is less
mechanically complex relative to polishing systems which have
heretofore been designed, yet detects the planarity level of the
semiconductor wafer during polishing thereof.
[0017] It is also an object of the present invention to provide a
method and apparatus for determining when a semiconductor wafer has
been polished to a desired planarity level which does not require
chemical analysis of the slurry associated with the polishing
system.
[0018] The above and other objects, features, and advantages of the
present invention will become apparent from the following
description and the attached drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0019] FIGS. 1A-1F show sectional views of a semiconductor wafer
during various steps of a fabrication process;
[0020] FIG. 2 is a diagrammatic view of a polishing system which
incorporates various features of the present invention therein;
[0021] FIG. 3 is a top elevational view of the platen assembly of
the polishing system of FIG. 2;
[0022] FIG. 4 is a diagrammatic view of a first embodiment of the
confocal optical system associated with the polishing system of
FIG. 2;
[0023] FIG. 5 is a view similar to FIG. 4, but showing a second
embodiment of the confocal optical system; and
[0024] FIG. 6 shows a flowchart of a polishing procedure used by
the polishing system of FIGS. 2.
DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT
[0025] While the invention is susceptible to various modifications
and alternative forms, specific embodiments thereof have been shown
by way of example in the drawings and will herein be described in
detail. It should be understood, however, that there is no intent
to limit the invention to the particular forms disclosed, but on
the contrary, the intention is to cover all modifications,
equivalents, and alternatives falling within the spirit and scope
of the invention as defined by the appended claims.
[0026] Referring now to FIGS. 1A-1F, there is shown a semiconductor
wafer 10 after various steps of a fabrication process of the
present invention. In particular, as shown in FIGS. 1A and 1B, the
semiconductor wafer 10 includes a semiconductor substrate 12, such
as silicon. A first insulating layer 14 and a first metal layer 16
are deposited or otherwise disposed on the semiconductor substrate
12. More specifically, the fabrication process deposits the first
insulating layer 14 on the semiconductor substrate 12 such that a
contact hole 20 is formed in the first insulating layer 14 at a
location above a transistor portion of the semiconductor substrate
12. Moreover, the fabrication process patterns the first metal
layer 16 (e.g. aluminum) over the first insulating layer 14 and the
contact hole 20. As a result, the first metal layer 16 fills the
contact hole 20 thereby forming an electrical contact with the
transistor portion of the semiconductor substrate 12. Moreover, the
filling of the contact hole 20 forms a pit 22 in the portion of the
first metal layer 16 disposed above the contact hole 20.
[0027] As shown in FIG. 1C, a second insulating layer 24 is
deposited on the outer surface of the first insulating layer 14 and
the first metal layer 16. The second insulating layer 24 has an
uneven surface topography as a result of the varying topography
associated with the first insulating layer 14 and a first metal
layer 16. The uneven surface topography of the second insulating
layer 24 may cause accuracy problems in fabricating additional
layers associated with the semiconductor wafer 10. For example, the
uneven surface topography may cause accuracy problems for a
lithography process which is utilized to pattern a second metal
layer 26 (FIG. 1 F) on the second insulating layer 24. As shall be
discussed below in more detail, in order to avoid such accuracy
problems associated with the uneven topography of the second
insulating layer 24, a polishing system, such as a polishing system
30 of FIG. 2, polishes the second insulating layer 24 so as to
produce a planar surface 28 (see FIG. 1 D) having a desired
planarity level.
[0028] As alluded to above, once the semiconductor wafer 10 has
been polished to the desired planarity level, additional layers may
be deposited or otherwise fabricated thereon. For example, as shown
in FIGS. 1E and 1F, a via hole 36 may be etched through the second
insulating layer 24. Thereafter, the second metal layer 26 may be
deposited on the second insulating layer 24. It should be
appreciated that numerous additional layers may be deposited on the
semiconductor wafer 10 in the manner previously described.
[0029] Referring now to FIG. 2, there is shown a preferred
embodiment of the polishing system 30 which is used to planarize a
front side or surface 38 of the semiconductor wafer 10. The
polishing system 30 includes a platen motor or other drive
mechanism 40 and a platen assembly 42. The platen motor 40 rotates
the platen assembly 42 about a center axis 44. The platen motor 40
may rotate the platen assembly 42 in a clockwise direction (as
shown by arrow 46 of FIG. 2) or in the counterclockwise
direction.
[0030] The platen assembly 42 includes a polishing platen 48 and a
polishing pad 50 mounted on the polishing platen 48. Both the
polishing platen 48 and the polishing pad 50 are preferably
circular and collectively define a polishing surface against which
the front side 38 of the semiconductor wafer 10 may be polished.
Moreover, the polishing pad 50 is typically made of blown
polyurethane which protects the polishing platen 48 from chemical
slurry and other chemicals introduced during the polishing
process.
[0031] The polishing system 30 also includes a polishing head
assembly 52. The polishing head assembly 52 includes a wafer
carrier 54, a cooling mechanism 56, a wafer carrier motor or other
drive mechanism 58, and a wafer carrier displacement mechanism 60.
The wafer carrier 54 applies a controlled, adjustable force in the
general direction of arrow 62 in order to press the front side 38
of the semiconductor wafer 10 into contact with the polishing pad
50 so as to facilitate polishing of the front side 38 of the
semiconductor wafer 10.
[0032] The wafer carrier motor 58 rotates the wafer carrier 54 and
the semiconductor wafer 10 about a center axis 64. The wafer
carrier motor 58 may rotate the wafer carrier 54 in a clockwise
direction (as shown by arrow 66 of FIG. 2) or in the
counterclockwise direction. However, the wafer carrier motor 58
preferably rotates the wafer carrier 54 in the same rotational
direction as the platen motor 40 rotates the platen assembly 42
(although the wafer carrier motor 58 may rotate the semiconductor
wafer 10 in the rotational direction opposite the rotational
direction of the platen assembly 42 as desired).
[0033] The wafer carrier 54 also includes mechanisms (not shown)
for holding the semiconductor wafer 10. For example, the wafer
carrier 54 may include a vacuum-type mechanism which generates a
vacuum force that draws the semiconductor wafer 10 against the
wafer carrier 54. Once the semiconductor wafer 10 is positioned on
the wafer carrier 54 and held in contact with the platen assembly
42 for polishing, the vacuum force may be removed. In such an
arrangement, the wafer carrier 54 may be designed with a friction
surface or a carrier pad which engages a back side 70 of the
semiconductor wafer 10 with a carrier ring (not shown). Such a
carrier pad, along with the force being applied in the general
direction of arrow 62, creates a frictional force between the wafer
carrier 54 and the semiconductor wafer 10 that effectively holds
the semiconductor wafer 10 against the wafer carrier 54 thereby
causing the semiconductor wafer 10 to rotate at the same velocity
as the wafer carrier 54. It should be appreciated that such wafer
carriers and carrier pads are of conventional design and are
commercially available.
[0034] The cooling mechanism 56 counteracts heat generated during
the polishing process in order to maintain the wafer carrier 54 at
a substantially constant temperature. In particular, the cooling
mechanism 56 neutralizes the heat generated due to friction and a
chemical slurry reacting with the front side 38 of the
semiconductor wafer 10. Moreover, it should be appreciated that the
polishing system 30 may also include an additional cooling
mechanism (not shown) for cooling the components of the polishing
assembly 42 (e.g. the polishing platen 48) during polishing of the
semiconductor wafer 10.
[0035] The displacement mechanism 60 selectively moves the wafer
carrier 54 and hence the semiconductor wafer 10 across the platen
assembly 42 in the general direction of arrows 68 and 98. Such
movement defines a polishing path which may be linear, sinusoidal,
or a variety of other patterns. The displacement mechanism 60 is
also capable of moving the semiconductor wafer 10 along a polishing
path to a location beyond the edge of the polishing pad 50 so that
the semiconductor wafer 10 "overhangs" the edge. Such an
overhanging arrangement permits the semiconductor wafer 10 to be
moved partially on and partially off the polishing pad 50 to
compensate for polishing irregularities caused by a relative
velocity differential between the faster moving outer portions and
the slower moving inner portions of the platen assembly 42.
[0036] The polishing system 30 also includes a chemical slurry
system 72. The slurry system 72 includes a slurry storage reservoir
74, a slurry flow control mechanism 76, and a slurry conduit 78.
The slurry storage reservoir 74 includes one or more containers for
storing slurry. In particular, the slurry storage reservoir 74
contains a chemical slurry that includes abrasive material which
facilitates polishing of the front side 38 of the semiconductor
wafer 10. Chemical slurries having such properties are well known
and commercially available.
[0037] The slurry flow control mechanism 76 controls the flow of
slurry from the slurry storage 74, through the slurry conduit 78,
and onto the polishing area atop the platen assembly 42. Hence, the
slurry flow control mechanism 76 and the slurry conduit 78
selectively introduce a flow of slurry (as indicated by arrow 80)
atop the polishing pad 50.
[0038] In order to determine when the polishing system 30 has
polished the semiconductor wafer to the desired planarity level,
there is provided an endpoint detection system 150. As shown in
FIGS. 2 and 4, the endpoint detection system 150 includes an
confocal optical system 152. The confocal optical system 152
includes a light source such as a laser light source 154, a beam
splitter 156, an objective lens 158, a lens positioning device 160,
a photodetector 162, and an optics controller 164. Preferably, the
confocal optical system 152 is embodied as a confocal laser system.
One such confocal laser system which is suitable for use as the
confocal optical system 152 of the present invention is disclosed
in U.S. Pat. No. 4,689,491 issued to Lindow et al, the disclosure
of which is hereby incorporated by reference. Moreover, numerous
types of commercially available confocal laser systems may also be
utilized as the confocal optical system 152 of the present
invention. One such commercially available confocal laser system
which is particularly useful as the confocal optical system 152 of
the present invention is a Model Number 1010 confocal laser system
which is commercially available from KLA-Tencor Corporation of San
Jose, Calif.
[0039] The confocal optical system 152 is provided to monitor
polishing of the semiconductor wafer 10 in order to determine when
the first side 38 thereof has been planarized to a desired level
(i.e. when the planar surface 28 has been produced). In particular,
during polishing of the semiconductor wafer 10, the confocal
optical system generates incident laser beams which are directed
through an opening 166 defined in the platen assembly 42 (see FIG.
3) and are impinged on the front side 38 of the semiconductor wafer
10. Reflected laser beams are reflected back to the confocal
optical system 152 based on the degree of planarity of the front
side of the semiconductor wafer 10. It should be appreciated that,
as shall be discussed below in greater detail, the direction or
directions in which incident laser beams is/are reflected or
otherwise redirected is dependent on the surface topography of the
front side 38 of the semiconductor wafer 10.
[0040] The optics controller 164 analyzes reflected laser beams in
order to determine when the front side 38 of the semiconductor
wafer 10 has been polished down to a desired planarity level. In
particular, during polishing of the semiconductor wafer 10, the
laser source 154 generates a laser beam which is directed into the
beam splitter 156 so as to be directed through the objective lens
158, the opening 166 defined in the platen assembly 42 (see FIG.
3), and thereafter impinged on the front side 38 of the
semiconductor wafer 10. Reflected laser beams are reflected back
from a planar feature (if one is present) at the focal plane,
through the opening 166, the objective lens 158, the beam splitter
156, and are thereafter detected by the photodetector 162. The
output of the photodetector 162 is indicative of the intensity
level of the reflected laser beam from the front side 38 of the
wafer 10 and is transmitted to the optics controller 164 via a
signal line 168. The optics controller 164 then adjusts the
position of the objective lens 158 in order to focus the confocal
optical system 152 on the front side 38 of the semiconductor wafer
10. In particular, the optics controller 164 determines if the
intensity level of the reflected laser beam is within a
predetermined light intensity range. The predetermined light
intensity range is generally indicative of a maximum intensity
level associated with reflected laser beams from a planar surface
located at the focal plane of the confocal optical system 152.
Hence, as used herein, the confocal optical system 152 is "focused"
or "maintains focus" on the front side 38 of the semiconductor
wafer 10 when the intensity level of reflected laser beams (as
reflected from the front side 38 of the wafer 10) is within the
predetermined light intensity range.
[0041] The optics controller 164 provides closed-loop control of
the position of the objective lens 158 in order to maintain focus
on the front side 38 of the semiconductor wafer 10. In particular,
if the intensity level of a given reflected laser beam is not
within the predetermined light intensity range thereby indicating
that the confocal optical system 152 is not focused on the front
side 38 of the semiconductor wafer 10, the optics controller 164
communicates with the lens positioning device 160 so as to move the
objective lens 158 upwardly or downwardly (i.e. in the general
directions of arrows 170 or 172 of FIG. 4, respectively) in order
to focus the confocal optical system 152 onto the front side 38 of
the semiconductor wafer 10. More specifically, the optics
controller 164 generates an output signal on a signal line 174
thereby causing the lens positioning device 160 to move the
objective lens 158 either upwardly or downwardly (as required).
Thereafter, the optics controller 164 communicates with the laser
source 154 via a signal line 176 in order to generate another
incident laser beam which is impinged on the front side 38 of the
semiconductor wafer 10 in the manner previously described. The
intensity level of the reflected laser beam (as detected by the
photodetector 162) is then compared to the predetermined light
intensity range in order to determine if the confocal optical
system 158 is focused on the front side 38 of the wafer 10.
Thereafter, the position of the objective lens 158 may again be
adjusted if the confocal optical system 152 is not focused on the
front side of the semiconductor wafer 10.
[0042] It should be appreciated that such closed-loop control of
the position of the objective lens 58 continues throughout
operation of the polishing system 30. In particular, as the
semiconductor wafer 10 continues to be polished, the optics
controller 164 continuously adjusts the position of the objective
lens 158 so as to maintain focus on the front side 38 of the wafer
10. During such a time, the movement of the objective lens 58 may
be monitored in order to determine if the semiconductor wafer 10
has been polished to the desired planarity level. In particular,
the intensity level of laser beams reflected from the front side 38
of the semiconductor wafer 10 changes as the wafer 10 is further
polished by the polishing system 30. More specifically, when the
front side 38 of the semiconductor wafer 10 has been polished down
to the desired planarity level, incident laser beams impinged
thereon are reflected directly back into the confocal optical
system 152. It should be appreciated that such directly reflected
laser beams have intensity levels associated therewith which are
generally within the predetermined light intensity range.
[0043] In contrast, when the front side 38 of the semiconductor
wafer 10 has not yet been polished down to the desired planarity
level and therefore possesses an uneven or varying surface
topography, such as shown in FIG. 1 C, incident laser beams
impinging thereon are scattered or otherwise reflected in numerous
different directions thereby preventing detection thereof with the
photodetector 162. As described above, if the optics controller 164
determines that the confocal optical system 152 is not focused on
the front side 38 of the semiconductor wafer 10 (i.e. the reflected
laser beam is either not detected at all by the photodetector 162
or the intensity level of the detected light is not within the
predetermined light intensity range), the optics controller 164
causes the position of the objective lens 158 to be changed. Hence,
during a given period of time, the objective lens 158 is
repositioned a fewer number of times when the confocal optical
system 152 is impinging laser beams on a relatively planar
semiconductor wafer 10 in contrast to a wafer 10 which possesses an
uneven or varying surface topography. This is true since the
intensity level of laser beams reflected from a planar front side
38 of the wafer 10 will generally be within the predetermined light
intensity range thereby eliminating the need to reposition of the
objective lens 158. Conversely, during a similar period of time,
the objective lens 158 is repositioned a large number of times when
the confocal optical system 152 is impinging laser beams on a
semiconductor wafer 10 which possesses an uneven or varying surface
topography relative to a planar wafer 10. This is true since the
intensity level of the laser beams reflected from an uneven front
side 38 of the wafer 10 will generally not be within the
predetermined light intensity range (if detected at all) thereby
necessitating repositioning of the objective lens 158 a large
number of times within the given period of time.
[0044] As can be seen from the above-discussion, the objective lens
158 has a rate-of-movement value which is dependent on the
topography of the front side 38 of the semiconductor wafer 10. What
is meant herein by the term "rate-of-movement value" is the number
of occurrences during a given time period in which the objective
lens 158 is repositioned or otherwise physically moved in order to
focus the confocal optical system 152 on the front side 38 of the
semiconductor wafer 10. Hence, the rate-of-movement value of the
objective lens 158 decreases as the front side 38 of the
semiconductor wafer 10 becomes more planar. In particular, the
rate-of-movement value of the objective lens 158 will be relatively
large when a given semiconductor wafer 10 is initially polished
since the wafer 10 possesses a relatively uneven or varying
topography, such as shown in FIG. 1C, during initial polishing
thereof. However, as the semiconductor wafer 10 is further polished
so as to approach the desired planarity level, the rate-of-movement
value of the objective lens 158 will decrease.
[0045] In order to determine when the semiconductor wafer 10 has
been polished to the desired planarity level, a movement threshold
value may be established. The movement threshold value is
indicative of the rate-of-movement value of the objective lens 158
when the confocal optical system 152 is focused on a semiconductor
wafer 10 which has been polished to the desired planarity level
(i.e. when the planar surface 28 has been produced). Hence, during
polishing of a given semiconductor wafer 10, if the
rate-of-movement value of the objective lens 158 has a
predetermined relationship with the movement threshold value, the
optics controller 164 determines that the wafer 10 has been
polished to the desired planarity level. More specifically, during
polishing of the given semiconductor wafer 10, if the
rate-of-movement value of the objective lens 158 is equal to or
less than the movement threshold value, the optics controller 164
generates a wafer-planarized control signal which indicates that
the wafer 10 has been polished to the desired planarity level (i.e.
when the planar surface 28 has been produced).
[0046] Referring now to FIG. 5, there is shown a second embodiment
of a confocal optical system 252 which incorporates the features of
the present invention therein. The confocal optical system 252 is
somewhat similar to the confocal optical system 152. Thus, the same
reference numerals are used in FIG. 5 to designate common
components which were previously discussed in regard to FIG. 4.
[0047] The confocal optical system 252 does not include a lens
positioning device (i.e. the lens positioning device 160 of FIG.
4). Hence, the objective lens 158 is held stationary during
operation of the confocal optical system 252 thereby preventing
monitoring of the rate-of-movement value associated with the
objective lens 158 during polishing of the semiconductor wafer 10.
Therefore, the optics controller 164 monitors the number of
occurrences during a given time period in which the confocal
optical system 252 is focused on the front side 38 of the
semiconductor wafer 10 in order to determine when the wafer 10 has
been polished to the desired planarity level (i.e. when the planar
surface 28 has been produced). In particular, during polishing of
the semiconductor wafer 10, the confocal optical system 252
generates incident laser beams which are impinged upon the front
side 38 of the semiconductor wafer 10 so as to produce reflected
laser beams which are reflected from the front side 38 of the wafer
10. The photodetector 162 detects the intensity level of the
reflected laser beams (if such beams are reflected back to the
confocal optical system 252). The optics controller 164 then
determines if the intensity level of the reflected laser beam is
within the predetermined light intensity range. As described above,
the predetermined light intensity range is generally indicative of
a maximum intensity level associated with laser beams reflected
from a planar surface of the front side 38 semiconductor wafer 10
which is located at the focal plane of the confocal optical system
252.
[0048] Hence, during polishing of the semiconductor wafer 10, if
the optics controller 164 determines that during a predetermined
period of time, the confocal optical system 252 is continuously
focused on the front side 38 of the wafer 10, the optics controller
164 concludes that the wafer 10 has been polished to the desired
planarity level (i.e. the planar surface 28 has been produced).
More specifically, if during a predetermined period of time, the
optics controller 164 determines that the intensity level of each
of the laser beams reflected from the front side 38 of the wafer 10
is within the predetermined light intensity range, the optics
controller 164 generates a wafer-planarized control signal which
indicates that the wafer 10 has been polished to the desired
planarity level (i.e. the planar surface 28 has been produced).
[0049] However, if during the predetermined period of time, the
optics controller 164 determines that the intensity level of a
number of the laser beams reflected from the front side 38 of the
wafer 10 is not within the predetermined light intensity range, the
optics controller 164 does not generate a wafer-planarized control
signal. As shall be discussed below in more detail, absence of the
wafer-planarized control signal causes the polishing system 30 to
continue polishing the semiconductor wafer 10.
[0050] Referring back to FIG. 2, the polishing system 30 also
includes a polishing controller 82 for controlling the polishing
system 30 in order to effectuate the is desired polishing results
for the semiconductor wafer 10. In particular, the polishing
controller 82 is electrically coupled to the displacement mechanism
60 via a signal line 84 to monitor and controllably adjust the
polishing path of the semiconductor wafer 10 and the speed at which
the semiconductor wafer 10 is moved across the platen assembly
42.
[0051] Moreover, the polishing controller 82 is electrically
coupled to the platen motor 40 via a signal line 86 in order to
monitor the output speed of the platen motor 40 and hence the
rotational velocity of the platen assembly 42. The polishing
controller 82 adjusts the output speed of the platen motor 40 and
hence the rotational velocity of the platen assembly 42 as required
by predetermined operating parameters.
[0052] The polishing controller 82 is electrically coupled to the
slurry flow control mechanism 76 via a signal line 88 in order to
monitor the flow rate of the chemical slurry onto the polishing pad
50 of the platen assembly 42. The polishing controller 82 adjusts
the flow rate of the chemical slurry onto the polishing pad 50 of
the platen assembly 42 as required by predetermined operating
parameters.
[0053] The polishing controller 82 is further electrically coupled
to the wafer carrier motor 58 via a signal line 90 in order to
monitor the output speed of the wafer carrier motor 58 and hence
the rotational velocity of the wafer carrier 54. The polishing
controller 82 adjusts the output speed of the wafer carrier motor
58 and hence the rotational velocity of the wafer carrier 54 as
required by predetermined operating parameters. It should be
appreciated that upon polishing the semiconductor wafer 10 to the
desired planarity level, the wafer carrier motor 58 may be idled so
as to cease polishing of the semiconductor wafer 10. What is meant
herein by the term "idled" is that power is cutoff to the wafer
carrier motor 58 thereby preventing the wafer carrier motor 58 from
driving or otherwise contributing mechanical work to the rotation
of the wafer carrier 54.
[0054] The polishing controller 82 is also electrically coupled to
the confocal optical system 152, 252 via a signal line 92 in order
to determine when the semiconductor wafer 10 has been polished to
the desired planarity level (i.e. the planar surface 28 has been
produced). In particular regard to when the endpoint detection
system 150 is embodied to include the confocal optical system 152
(as opposed to the confocal optical system 252), the polishing
controller 82 is configured to determine the rate-of-movement value
of the objective lens 158 and thereafter determine if the
rate-of-movement value of the objective lens 158 has a
predetermined relationship (e.g. is less than or equal to) the
movement threshold value. More specifically, the polishing
controller 82 is configured to scan or otherwise read the signal
line 92 in order to determine if the confocal optical system 152
has generated a wafer-planarized control signal which, as described
above, is indicative of the rate-of-movement value of the objective
lens 158 having a predetermined relationship (e.g. is less than or
equal to) the movement threshold value.
[0055] In particular regard to when the endpoint detection system
150 includes the confocal optical system 252, the polishing
controller 82 is configured to analyze laser beams reflected from
the front side 38 of the semiconductor wafer 10 in order to
determine if the confocal optical system 252 is continuously
focused on the front side 38 of the wafer 10 for a predetermined
period of time. More specifically, the polishing controller 82 is
configured to scan or otherwise read the signal line 92 in order to
determine if the confocal optical system 252 has generated a
wafer-planarized control signal which, as described above, is
indicative of the confocal optical system 252 being continuously
focused on the front side 38 of the wafer 10 for a predetermined
period of time.
[0056] In operation, the polishing system 30 polishes the
semiconductor wafer 10 in order to planarize the front side 38
thereof. In particular, the polishing system 30 removes material
from the front side 38 of the semiconductor wafer 10 until the
wafer 10 is polished to the desired planarity level (i.e. the
planar surface 28 has been formed). More specifically, the wafer
carrier 54 engages the back side 70 of the semiconductor wafer 10
and presses the front side 38 of the semiconductor wafer 10 against
the polishing pad 50. The polishing controller 82 then causes the
platen motor 40 to rotate the platen assembly 42 and the wafer
carrier motor 58 to rotate the wafer carrier 54. The polishing
controller 82 may also begin to control the displacement mechanism
60 so as to move the wafer carrier 54 along a predetermined
polishing path. The slurry flow control mechanism 76 is also
controlled by the polishing controller 82 in order to apply
chemical slurry to the polishing pad 50 at a predetermined flow
rate. The resulting complex movement of the wafer carrier 54
relative to the polishing pad 50, the downward force being applied
to the semiconductor wafer 10 in the general direction of arrow 62
of FIG. 2, and the chemical slurry all cooperate to selectively
remove material from the front side 38 of the semiconductor wafer
10.
[0057] In addition, the polishing controller 82 communicates with
the confocal optical system 152, 252 in order to determine if the
semiconductor wafer 10 has been polished the desired planarity
level. In particular, the confocal optical system 152, 252
generates incident laser beams which are impinged on the front side
38 of the wafer 10 during polishing thereof thereby forming
reflected laser beams which are reflected from the front side 38 of
the wafer 10. The reflected laser beams are then analyzed (if
detected at all by the photodetector 162) by the confocal optical
system 152, 252.
[0058] In particular regard to the confocal optical system 152, the
intensity level of the reflected laser beams causes repositioning
of the objective lens 158 in the manner discussed above. If the
rate-of-movement value of the objective lens 158 is less than or
equal to a movement threshold, the confocal optical system 152
generates a wafer-planarized control signal which is sent to the
polishing controller 82. In response to receiving the
wafer-planarized control signal, the polishing controller 82 ceases
polishing the semiconductor wafer 10.
[0059] In regard to the confocal optical system 252, the intensity
level of the reflected laser beams is utilized to determine if the
confocal optical system 252 is continuously focused on the front
side 38 of the semiconductor wafer 10. In particular, if during a
predetermined period of time, the confocal optical system 252
determines that the intensity level of each of the laser beams
reflected from the front side 38 of the wafer 10 is within the
predetermined light intensity range, the confocal optical system
252 generates a wafer-planarized control signal which is sent to
the polishing controller 82. In response to receiving the
wafer-planarized control signal, the polishing controller 82 ceases
polishing the semiconductor wafer 10.
[0060] A polishing procedure 300 utilized by the polishing system
30 to polish the semiconductor wafer 10 according to the present
invention is shown in FIG. 6. The polishing procedure 300 begins
with step 302 in which the polishing controller 82 causes the
polishing system 30 to begin polishing the front side 38 of the
semiconductor wafer 10 in order to remove material therefrom. In
particular, the polishing controller 82 actuates the platen motor
40 in order to cause the platen assembly 42 to be rotated.
Thereafter, the polishing controller 82 actuates the wafer carrier
motor 58 thereby causing the wafer carrier 54 and hence the
semiconductor wafer 10 to be rotated so as to polish the front side
38 of the semiconductor wafer 10 against the rotating platen
assembly 42. The polishing controller 82 also actuates the
displacement mechanism 60 in order to cause the displacement
mechanism 60 to selectively move the wafer carrier 54 and hence the
wafer 10 along a predetermined polishing path. Moreover, the
polishing controller 82 causes the chemical slurry supply system 72
to apply chemical slurry to the polishing pad 50 of the platen
assembly 42 in order to facilitate the removal of material from the
front side 38 of the semiconductor wafer 10. The procedure 300 then
advances to step 304.
[0061] In step 304, the polishing controller 82 communicates with
the confocal optical system 152, 252 in order to detect the
planarity level of the semiconductor wafer 10 during polishing
thereof. In particular, the optics controller 164 generates an
output signal on the signal line 176 (see FIGS. 4 and 5) thereby
causing the laser source 154 to generate incident laser beams which
are impinged upon the front side 38 of the semiconductor wafer 10.
Reflected laser beams which are reflected from the front side 38 of
the semiconductor wafer 10 are directed through the objective lens
158 (if reflected in a direction toward the confocal optical system
152, 252), the beam splitter 156, and thereafter detected by the
photodetector 162. The reflected laser beams are then analyzed by
the confocal optical system 152, 252.
[0062] In particular regard to the confocal optical system 152, the
intensity level of the reflected laser beams causes repositioning
of the objective lens 158 in the manner discussed above in regard
to FIG. 4. If the rate-of-movement value of the objective lens 158
is less than or equal to a movement threshold value, the confocal
optical system 152 generates a wafer-planarized control signal
which is sent to the polishing controller 82. If the
rate-of-movement value of the objective lens 158 is greater than
the movement threshold value, a wafer-planarized control signal is
not generated by the confocal optical system 152.
[0063] In regard to the confocal optical system 252, the intensity
level of the reflected laser beams is utilized to determine if the
confocal optical system 252 is continuously focused on the front
side 38 of the semiconductor wafer 10. In particular, if during a
predetermined period of time, the confocal optical system 252
determines that the intensity level of each of the laser beams
reflected from the front side 38 of the wafer 10 is within the
predetermined light intensity range, the confocal optical system
252 generates a wafer-planarized control signal which is sent to
the polishing controller 82. However, if during the predetermined
period of time, the optics controller 164 determines that the
intensity level of a number of the laser beams reflected from the
front side 38 of the wafer 10 is not within the predetermined light
intensity range, the optics controller 164 does not generate a
wafer-planarized control signal.
[0064] The procedure then advances to step 306 in which the
polishing controller 82 determines if the front side 38 of the
semiconductor wafer 10 has been polished to the desired planarity
level. In particular, the polishing controller 82 scans or
otherwise reads the signal line 92 in order to determine if the
confocal optical system 152, 252 has generated a wafer-planarized
control signal. As described above, presence of a wafer-planarized
control signal on the signal line 92 indicates that the
semiconductor wafer 10 has been polished to the desired planarity
level (i.e. the planar surface 28 has been formed). Hence, in step
306, if the polishing controller 82 does not detect presence of a
wafer-planarized control signal on the signal line 92, the
polishing controller 82 concludes that the front side 38 of the
semiconductor wafer 10 has not been polished to the desired
planarity level, and the procedure 300 advances to step 308.
However, if the polishing controller 82 does detect generation of a
wafer-planarized control signal on the signal line 92, the
polishing controller 82 concludes that the front side 38 of the
semiconductor wafer 10 has been polished to the desired planarity
level, and the procedure 300 advances to step 310.
[0065] In step 308, the polishing controller 82 communicates with
the platen motor 40, the wafer carrier motor 58, the displacement
mechanism 60, and the slurry flow control 76 in order to continue
polishing the semiconductor wafer 10 in the manner previously
discussed. The procedure 300 then loops back to step 304 in order
to further monitor the planarization of the semiconductor wafer 10
during subsequent polishing thereof.
[0066] Returning now to step 306, if the front side 38 of the
semiconductor wafer 10 has been polished to the desired planarity
level, the procedure 300 advances to step 310. In step 310, the
polishing controller 82 ceases polishing of the semiconductor wafer
10. In particular, the polishing controller 82 communicates with
the platen motor 40, the wafer carrier motor 58, the displacement
mechanism 60, and the slurry flow control 76 in order to cease
polishing of the semiconductor wafer 10. However, it should be
appreciated that the polishing controller 82 may allow the
polishing system 30 to continue polishing the semiconductor wafer
10 for a short, predetermined amount of time in order to further
remove material from the semiconductor wafer 10. This further
removal of material or overpolishing may be desirable after certain
steps of a fabrication process. The procedure 300 then ends thereby
placing the polishing system 30 in an idle state until actuated to
polish a subsequent semiconductor wafer.
[0067] While the invention has been illustrated and described in
detail in the drawings and foregoing description, such illustration
and description is to be considered as exemplary and not
restrictive in character, it being understood that only preferred
embodiments have been shown and described and that all changes and
modifications that come within the spirit of the invention are
desired to be protected.
[0068] For example, although the confocal optical system 152 is
herein described as monitoring the rate-of-movement value of the
objective lens 158, and thereby producing numerous advantages in
the present invention, certain of such advantages may be achieved
by monitoring other values in order to determine when the
semiconductor wafer 10 has been polished down to the desired
planarity level. For example, the confocal optical system 152 may
be configured to monitor a range-of-movement value associated with
the objective lens 158. What is meant herein by the term
"range-of-movement value" is the physical distance in which the
objective lens 158 is repositioned or otherwise physically moved
during a given time period in order to focus the confocal optical
system 152 on the front side 38 of the semiconductor wafer 10. It
should be appreciated that during a given period of time, the
objective lens 158 is repositioned a fewer number of times (and
therefore traverses a relatively small distance) when the confocal
optical system 152 is impinging laser beams on a relatively planar
semiconductor wafer 10 in contrast to a wafer 10 which possesses an
uneven or varying surface topography. This is true since the
intensity level of laser beams reflected from a planar front side
38 of the wafer 10 will generally be within the predetermined light
intensity range thereby eliminating the need to reposition of the
objective lens 158. Conversely, during a similar period of time,
the objective lens 158 is repositioned a large number of times (and
therefore traverses a relatively large distance) when the confocal
optical system 152 is impinging laser beams on a semiconductor
wafer 10 which possesses an uneven or varying surface topography
relative to a planar wafer 10. This is true since the intensity
level of the laser beams reflected from an uneven front side 38 of
the wafer 10 will generally not be within the predetermined light
intensity range (if detected at all) thereby necessitating
repositioning of the objective lens 158 a large number of times
within the given period of time.
[0069] For further example, it should be appreciated that although
the polishing system 30 and the confocal optical system 152, 252
are herein described as having separate controllers (i.e. the
polishing controller 82 and the optics controller 164,
respectively), it should be appreciated that a single controller
may be provided to control both the polishing system 30 and the
confocal optical system 152, 252.
* * * * *