U.S. patent number RE34,425 [Application Number 07/876,588] was granted by the patent office on 1993-11-02 for method and apparatus for mechanical planarization and endpoint detection of a semiconductor wafer.
This patent grant is currently assigned to Micron Technology, Inc.. Invention is credited to Laurence D. Schultz.
United States Patent |
RE34,425 |
Schultz |
November 2, 1993 |
Method and apparatus for mechanical planarization and endpoint
detection of a semiconductor wafer
Abstract
A method and apparatus for mechanical planarization and endpoint
detection of a semiconductor wafer or the like. The apparatus
includes a polishing head for rotating the wafer under a controlled
pressure against a rotating polishing platen. The polishing head is
mounted such that the wafer can be moved across the polishing
platen to overhang a peripheral edge of the polishing platen and
expose the surface of the wafer. Endpoint detection apparatus in
the form of a laser interferometer measuring device is directed at
an unpatterned die on the exposed surface of the wafer to detect
oxide thickness at that point. The laser light beam is enclosed in
a column of liquid to clean the wafer surface at the point of
detection and to provide a uniform reference medium for the laser
light beam.
Inventors: |
Schultz; Laurence D. (Boise,
ID) |
Assignee: |
Micron Technology, Inc. (Boise,
ID)
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Family
ID: |
27073157 |
Appl.
No.: |
07/876,588 |
Filed: |
April 30, 1992 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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Reissue of: |
563054 |
Aug 6, 1990 |
05081796 |
Jan 21, 1992 |
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Current U.S.
Class: |
451/41; 451/63;
451/8; 700/164 |
Current CPC
Class: |
B24B
49/12 (20130101); B24B 37/013 (20130101) |
Current International
Class: |
B24B
37/04 (20060101); B24B 49/12 (20060101); B24B
049/00 () |
Field of
Search: |
;51/281SF,281R,283R,131.1,131.3,55,57,165R,165.71,165.74,165.72,165.75,54
;356/358,359,363,355 ;364/474.06,563 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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164773 |
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Jul 1986 |
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JP |
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256342 |
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Oct 1988 |
|
JP |
|
3121773 |
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May 1991 |
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JP |
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Primary Examiner: Rachuba; M.
Attorney, Agent or Firm: Wells, St. John, Roberts, Gregory
& Matkin
Claims
I claim:
1. A process for polishing a flat wafer comprising:
a. holding the wafer in a rotatable polishing head mounted for
movement across and over a peripheral edge of a polishing
platen;
b. rotating a surface of the wafer in a polishing slurry across the
polishing platen;
c. overhanging a portion of the wafer across a peripheral edge of
the polishing platen to expose a surface of the wafer; and
d. detecting using endpoint detection means an endpoint of the
wafer.
2. A process as claimed in claim 1 and wherein the endpoint
detection means comprises a laser interferometer measuring
device.
3. A process as claimed in claim 2 and wherein the laser
interferometer measuring device is situated to detect the thickness
of an oxide on the wafer located on an unpatterned die on the
wafer.
4. A process as claimed in claim 3 and wherein the polishing platen
is also rotatably mounted for rotation in the same direction
.[.a.]..Iadd.as .Iaddend.the polishing head.
5. A process as claimed in claim 3 and further comprising:
directing a column of liquid on the wafer for cleaning the wafer
and for providing a reference medium for the laser.
6. A process for polishing a thin flat semiconductor wafer having
an oxide surface comprising:
a. holding the semiconductor wafer in a rotatable polishing head
mounted for movement across and over a peripheral edge of a
polishing platen;
b. rotating the wafer in a polishing slurry across the polishing
platen;
c. overhanging a portion of the wafer across a peripheral edge of
the polishing platen to expose a surface of the wafer; and
d. detecting a thickness of the oxide coating of the wafer
utilizing a laser detection apparatus having a detecting laser beam
enclosed in a column of water and directed at an unpatterned die on
the wafer surface.
7. The process as claimed in claim 6 and further comprising:
rotating the polishing platen in the same direction as the
polishing head.
8. The process as claimed in claim 6 and further comprising:
moving the polishing head across the peripheral edge of the
polishing platen to compensate for a velocity differential between
different portions of the rotating wafer.
9. The process as claimed in claim 8 and wherein:
the wafer, polishing head, and polishing platen are each generally
circular in shape.
10. The process as claimed in claim 8 and wherein: the unpatterned
die includes a metallic film having an oxide coating thereon.
11. A process for polishing a thin flat generally circular shaped
semiconductor wafer having an oxide coating and for detecting the
thickness of the oxide coating, comprising:
a. holding the semiconductor wafer in a rotatable polishing
head;
b. rotating the semiconductor wafer over a rotating polishing
platen under pressure from the polishing head in a polishing
slurry;
c. overhanging a portion of a surface of the semiconductor wafer
over the polishing platen to expose the surface for endpoint
detection of an oxide on the semiconductor wafer;
d. directing a laser beam enclosed in a column of liquid at an
unpatterned die on the wafer, for detecting using laser
interferometry a thickness of an oxide coating on the wafer;
and
e. moving the wafer across the peripheral edge of the polishing
platen for overhanging the wafer and for compensating for velocity
differentials on different portions of the generally circular
shaped wafer.
12. The process as claimed in claim 11 and wherein:
the semiconductor wafer is formed of silicon having a silicide
surface and the unpatterned die includes a tungsten film with an
oxide coating.
13. Apparatus for mechanically planarizing a thin flat wafer
comprising:
a. polishing means including a polishing platen and an abrasive
slurry;
b. a polishing head for holding the wafer and mounted for rotating
and for moving the wafer across the polishing platen and past a
peripheral edge of the polishing platen under a controlled
pressure; and
c. endpoint detection means including a laser interferometer with a
laser beam contained in a column of liquid for detecting an
endpoint on an exposed surface of the wafer.
14. Apparatus as claimed in claim 13 and wherein:
the polishing platen is rotated in the same direction as said
polishing head.
15. Apparatus as claimed in claim 14 and wherein:
the laser interferometer detection device includes a laser light
beam, a return light conduit, and a liquid conduit which is
arranged to direct a liquid at the exposed surface of the wafer to
surround the laser light beam and clean a surface of the wafer and
to provide a uniform reference medium for the laser light beam.
16. Apparatus as claimed in claim 15 and wherein:
the laser light beam is directed at an unpatterned die on the
wafer.
17. Apparatus as claimed in claim 16 and wherein:
the unpatterned die includes a metallic film having an oxide
coating formed thereon.
18. Apparatus as claimed in claim 17 and wherein:
said metallic film is tungsten and said oxide film is a
silicide.
19. Apparatus for mechanically planarizing a thin flat
semiconductor wafer comprising:
a. polishing means including a rotating generally circular shaped
polishing platen and an abrasive slurry;
b. a polishing head for holding the semiconductor wafer and mounted
for rotation and for moving the wafer across a peripheral
circumferential edge of the polishing platen under a controlled
pressure to expose a surface of the wafer; and
c. endpoint detection means including a laser interferometer
measuring device having a laser light beam directed at an
unpatterned die on the surface of the wafer and including a control
unit, a light return conduit, and a liquid conduit circumjacent to
the laser light beam for directing a liquid at the wafer surface to
clean the surface and provide a reference medium for the laser
light beam.
20. Apparatus as claimed in claim 19 and wherein:
said unpatterned die includes a metallic film coated with an
oxide.
21. Apparatus as claimed in claim 19 and wherein:
said polishing platen is rotated in the same direction as the
polishing head.
22. Apparatus as claimed in claim 21 and wherein:
said liquid for surrounding the laser light beam is water.
.Iadd.
23. A process for polishing a flat wafer comprising:
a. holding a wafer in a rotatable polishing head mounted for
movement across and over a peripheral edge of a polishing
platen;
b. rotating a surface of the wafer in a polishing slurry across the
polishing platen; and
c. overhanging a portion of the wafer across a peripheral edge of
the polishing platen to expose a surface of the wafer. .Iaddend.
.Iadd.24. A process as claimed in claim 23 wherein the polishing
platen is also rotatably mounted for rotation in the same direction
as the polishing head. .Iaddend. .Iadd.25. A process as claimed in
claim 23 further comprising:
moving the polishing head across the peripheral edge of the
polishing platen to compensate for a velocity differential between
different portions of the rotating wafer. .Iaddend. .Iadd.26. A
process as claimed in claim 23 further comprising overhanging
approximately one-half of the wafer across the peripheral edge of
the polishing platen. .Iaddend.
.Iadd. 7. A process as claimed in claim 23 wherein:
the wafer, polishing head, and polishing platen are each generally
circular in shape. .Iaddend. .Iadd.28. A process for polishing a
thin flat generally circular shaped semiconductor wafer having an
oxide coating comprising:
a. holding a semiconductor wafer in a rotatable polishing head;
b. rotating the semiconductor wafer over a rotating polishing
platen under pressure from the polishing head in a polishing
slurry; and
c. moving the wafer across a peripheral edge of the polishing
platen for overhanging the wafer and for compensating for velocity
differentials on different portions of the generally circular
shaped wafer. .Iaddend. .Iadd.29. A process as claimed in claim 28
further comprising moving approximately one-half of the wafer
across the peripheral edge of the polishing platen. .Iaddend.
Description
FIELD OF THE INVENTION
This invention relates to the fabrication of integrated circuits
and more particularly to a novel method and apparatus for
mechanical planarization and endpoint detection of a semiconductor
wafer.
BACKGROUND OF THE INVENTION
In the fabrication of integrated circuits (ICs), it is often
necessary to polish a side of a part such as a thin flat wafer of a
semiconductor material.Iadd.. .Iaddend.In general, a semiconductor
wafer can be polished to remove topography, surface defects such as
crystal lattice damage, scratches, roughness, or embedded particles
of dirt or dust. This polishing process is often referred to as
mechanical planarization and is utilized to improve the quality and
reliability of semiconductor devices. This process is usually
performed during the formation of various devices and integrated
circuits on the wafer.
In general, the mechanical planarization process involves holding
or rotating a thin flat wafer of semiconductor material against a
wetted polishing surface under a controlled pressure or
temperature. A polishing slurry such as a solution of alumina or
silica is utilized as the abrasive medium. A rotating polishing
head is typically utilized to hold the wafer under controlled
pressure against a rotating polishing platen. The polishing platen
is typically covered with a relatively soft wetted material such as
blown polyurethane.
Such apparatus for polishing thin flat semiconductor wafers are
well known in the art. U.S. Pat. Nos. 4,193,226 and 4,811,522 to
Gill, Jr. and U.S. Pat. No. 3,841,031 to Walsh, for instance,
disclose such apparatus.
A particular problem encountered in the use of such polishing
apparatus is in the determination that a part has been planed to a
desired flatness or relative thickness. In the past, this typically
has been accomplished by control of the rotational speed, downward
pressure, and polishing time of the planarization process. As a
final step, however, the part typically must be mechanically
removed from the polishing apparatus and physically measured by
techniques known in the art to ascertain dimensional and planar
characteristics of the polished part. If the part does not meet
specification, it must be loaded back into the polishing apparatus
and planarized a second time. Alternately, the part may have been
subjected to too much polishing and an excess of material may have
been removed, rendering the part as substandard.
Additionally, the semiconductor wafer may be subjected to spacially
non-uniform planarization due to the relative velocity differential
between the outer peripheral portions and the interior portions of
the rotating semiconductor wafer. The faster moving peripheral
portions of the semiconductor wafer may, for instance, experience a
relatively larger rate of material removal than the relatively
slower moving interior portions. In the past, this problem has been
approached by the use of a polishing head having a generally convex
shape to impart a greater force on the interior portions of the
semiconductor disc and a lesser force along the outer peripheral
portions.
These planarization problems are compounded because the
semiconductor wafer is held face down against the polishing platen:
and, absent removing the semiconductor disc, there is no provision
for monitoring the polishing process.
In general, there is a need in the mechanical planarization of
semiconductor wafers to be able to detect or monitor the endpoint
of the planarized wafer while the planarization process is in
operation. The present invention is directed to a novel method and
apparatus for endpoint detection of a semiconductor wafer which can
be accomplished during the planarization process.
SUMMARY OF THE INVENTION
In accordance with the present invention, a novel method and
apparatus for mechanical planarization and endpoint detection of a
thin flat semiconductor wafer is provided. The apparatus of the
invention generally stated comprises: polishing means in the form
of a rotatable polishing platen and a polishing slurry; a rotatable
polishing head adapted for carrying a semiconductor wafer and
mounted for movement across and past the outer circumference of the
polishing platen for overhanging or supporting a portion less than
the entire semiconductor wafer on the polishing platen; and
endpoint detection means in the form of a laser interferometer
measuring device for detecting the thickness of a material to be
planarized, such as an oxide formed on the semiconductor wafer.
The apparatus is adapted to detect the endpoint of a semiconductor
wafer or portion thereof by a method which generally comprises the
steps of: rotating the semiconductor wafer through a polishing
slurry on a polishing platen; overhanging a portion of the
semiconductor wafer over the peripheral edge of the polishing
platen; and detecting, using laser interferometry and a laser beam
contained in a column of liquid, the thickness of a portion of the
semiconductor wafer such as an oxide coating of the wafer.
In use of the method and apparatus of the invention, a part to be
mechanically planarized, such as a semiconductor wafer, is placed
in a polishing head. The polishing head is mounted for rotation in
a polishing slurry and for movement across a generally circular
polishing platen. The polishing platen may also be rotated
preferably in the same direction as the polishing head. The
polishing head is adapted to be moved across and past the outer
circumferential edge of the polishing platen and overhang the
peripheral edge of the polishing platen.
Overhanging the semiconductor wafer across the edge of the
polishing platen exposes the polished surface of the wafer and
permits endpoint detection means, such as a laser interferometer
measuring device, to be directed at the wafer surface to determine
the endpoint. The endpoint detection may detect the thickness of a
portion of the wafer such as an oxide (i.e. silicide) surface of
the wafer or an edge thickness of the wafer.
The laser detection means is preferably pulsed in synchronization
with a marker on the wafer such as an unpatterned die. As an
example, the unpatterned die may include a metallic film having a
silicide coating. The laser can be directed at the unpatterned die
to detect the thickness of the silicide at the point. Other
reference points at other locations on the disc can also be
utilized to obtain an average thickness across the wafer.
The laser detection means of the invention is preferably contained
within a column of liquid to clean the wafer of polishing slurry or
the like at the point of measurement and to provide a uniform
liquid reference medium for the laser beam.
Other objects, advantages, and capabilities of the present
invention will become more apparent as the description
proceeds.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a plan view of a thin flat semiconductor wafer suitable
for mechanical planarization by the method and apparatus of the
invention;
FIG. 2 is a side elevation view of a mechanical planarization
apparatus with endpoint detection constructed in accordance with
the invention;
FIG. 3 is a schematic plan view showing relative rotation movement
and positioning of a polishing head constructed in accordance with
the invention with respect to a rotating polishing platen;
FIG. 4 is a cross-sectional view taken along section line 4--4 of
FIG. 2;
FIG. 5 is a cross-sectional view taken along section line 5--5 of
FIG. 1; and
FIG. 6 is a schematic flow diagram of the method of the
invention.
DETAILED DESCRIPTION OF THE INVENTION
Referring now to FIG. 1, a semiconductor wafer 10 suitable for
mechanical planarization in accordance with the method and
apparatus of the invention is shown. The semiconductor wafer 10 is
thin and flat, generally circular in shape, and is formed with a
micro topography. The semiconductor wafer may include a substrate
such as silicon or oxidized silicon on which a plurality of
individual integrated circuit dies are formed. These individual
dies are represented schematically by the criss-cross pattern in
FIG. 1.
The formation of integrated circuits requires the deposition of
various films such as metal film contacts and resistive and
dielectric films on the wafer substrate. During fabrication of the
wafer 10, it may be necessary to mechanically planarize the surface
of the wafer in order, for instance, to provide a planarized
topography for definition of these films. This planarization
process helps to minimize barriers to multilayer formation and
metallization. Additionally, the planarization process smooths,
flattens, and cleans the surface of the wafer.
As shown in cross-section in FIG. 5, the wafer 10, in a certain
area, may include a silicon substrate 12 on which a layer of
silicon dioxide (SiO.sub.2) 14 (hereinafter referred to as oxide)
is formed thereon. In general, mechanical planarization of the
wafer 10 involves planarization of the oxide layer 14 of the wafer
10. The wafer 10 may also include one or more unpatterned dies 16
of a metallic film such as tungsten formed on the silicon substrate
12 and covered with the oxide coating 14.
Referring now to FIG. 2, a mechanical planarization and endpoint
detection apparatus constructed in accordance with the invention is
shown and generally designated as 20. The apparatus 20 of the
invention in general comprises:
polishing means in the form of a rotating polishing platen 22 to
which an abrasive slurry 24 such as alumina is applied:
a rotatable polishing head 26 adapted for supporting the
semiconductor wafer 10 and mounted as shown in FIG. 3, for movement
across and past the peripheral edge of the rotating polishing
platen 22 for overhanging a portion less than the entire
semiconductor wafer 10 on the rotating polishing platen 22; and
endpoint detection means in the form of a laser interferometer
measuring device 28 for detecting the thickness of an oxide coating
14 or the like formed on the semiconductor wafer 10.
With reference to FIG. 6, the apparatus 20 of the invention is
adapted to detect the thickness of the oxide coating 14 or the like
on the wafer 10 by a process which includes the steps of:
rotating the wafer 10 in a polishing slurry 24 on a polishing
platen 22, step 30;
overhanging a portion of the wafer 10 over a peripheral edge of the
polishing platen 22, step 32; and
detecting, using a laser interferometer measuring device 28 having
a laser beam contained in a column of liquid, the thickness of the
oxide coating 14 on a blank die 16 of the wafer 10, step 34.
With reference to FIGS. 2 and 3, the polishing means may include
the polishing head 26 which is mounted to a rotational drive means
such as a drive motor 36. As shown in FIG. 3, the drive motor 36
imparts a rotary motion indicated by arrow 38 to the polishing head
26. The polishing head 26 is constructed, as is known in the art,
to hold and rotate the wafer 10 face down over the polishing platen
22, without damaging the wafer 10. Moreover, the polishing head 26
is constructed to impart a controlled downward force as indicated
by arrow 39 (FIG. 2) to the wafer 10.
In addition to rotary and up-and-down movement, the polishing head
26 is also mounted for transverse movement in either direction
across the polishing platen 22 as indicated by arrows 40,42 in FIG.
3 and arrow 41 in FIG. 2. Further, the polishing head 26 is mounted
with respect to the polishing platen 22 such that the wafer 10 can
be moved across the polishing platen 22 and held in an overhanging
position with respect to the outer circumferential peripheral edge
of the polishing platen 22. This is clearly shown in FIG. 2. With
this arrangement and as is critical to the practice of the
invention, the wafer 10 can be moved past the edge of the polishing
platen 22 to overhang the outer circumferential or peripheral edge
of the polishing platen 22 during the mechanical planarization
process.
This overhanging arrangement permits the wafer 10 to be moved on
and off the polishing platen 22 to compensate for polishing
irregularities caused by the relative velocity differential between
the faster moving outer portions and the slower moving inner
portions of the generally circular shaped wafer 10. Additionally,
with this arrangement, a portion of the face of the wafer 10, as
shown in FIG. 2, is exposed to the laser interferonmeter measuring
device 28 for endpoint detection as will hereinafter be more fully
explained.
As shown in FIG. 3, the polishing platen 22 is also mounted for
rotational motion in the same direction as the polishing head 26.
This motion is denoted by arrows 44,46 in FIG. 3. The surface of
the polishing platen may be formed of a relatively soft material
such as blown polyurethane. Additionally, this surface may be
wetted with a lubricant such as water.
As shown in FIG. 2, the abrasive slurry 24 is directed onto the
surface of the polishing platen 22 to provide an abrasive medium
for polishing the wafer 10. The slurry 24 may be formed of a
solution of an abrasive material such as alumina or silica.
With reference to FIGS. 2 and 4, the endpoint detection means of
the invention is clearly shown. In the illustrative embodiment of
the invention, the endpoint detection means comprises a laser
interferometer measuring device 28. The interferometer measuring
device 28 employs the interference of light waves for purposes of
measurement. In the illustrative embodiment of the invention, the
interferometer measuring device 28 is mounted to detect the
thickness of the oxide layer 14 of the wafer 10 in the area of an
unpatterned die 16 on the wafer 10. Alternately, the laser
interferometer measuring device may also be arranged to detect the
edge thickness of the wafer 10 or other features of the wafer
10.
As shown in FIG. 3, the laser interferometer measuring device 28
includes a laser light beam 48 and a light return conduit 50 which
extend from a laser control unit 54 to a suitable mount (not shown
) located in close proximity to the exposed surface of the wafer
10. As is apparent in the illustrative embodiment of the invention,
the interferometer measuring device 28 functions to direct and
return a beam of laser light 48 or radiation against the oxide 14
located on the unpatterned die 16 of the wafer 10 to accurately
measure the thickness of the oxide coating 14 at that point. This
can be done by laser techniques known to those skilled in the
art.
Further, and as shown in FIG. 4, a liquid conduit 52 directs a
liquid such as water onto the oxide surface 14 at the point of
measurement by the laser beam 48 on the wafer 10. As shown in FIG.
4, the liquid medium completely surrounds or encloses the laser
light beam 48. This liquid .[.54.]. functions to clean the surface
of the wafer 10 at the point of laser measurement and to provide a
constant liquid reference background or medium for obtaining the
laser measurement.
The apparatus and method of the invention thus provide for
mechanical planarization of a semiconductor wafer with means for
accurately detecting the endpoint of the surface or oxide thickness
of the semiconductor wafer during the planarization operation. As
is apparent from the foregoing description, this is accomplished by
detecting an oxide thickness at a predetermined reference point
(i.e unpatterned die). Other reference points on the wafer may also
be utilized. Additionally, other types of measuring devices or
multiple laser measuring devices and/or multiple reference points
can also be utilized to obtain an average thickness.
While the process of the invention has been described with
reference to a preferred embodiment, as will be apparent to those
skilled in the art, certain changes and modifications can be made
without departing from the scope of the invention as defined by the
following claims.
* * * * *