U.S. patent application number 09/847292 was filed with the patent office on 2001-12-20 for polishing head of a chemical and mechanical polishing apparatus.
Invention is credited to Choy, Young-Man, Kim, Hee-Duk, Kim, Kyung-Dae, Lee, Sang-Yeoul.
Application Number | 20010053665 09/847292 |
Document ID | / |
Family ID | 19669053 |
Filed Date | 2001-12-20 |
United States Patent
Application |
20010053665 |
Kind Code |
A1 |
Lee, Sang-Yeoul ; et
al. |
December 20, 2001 |
Polishing head of a chemical and mechanical polishing apparatus
Abstract
A polishing head of a chemical and mechanical polishing
apparatus includes a retainer ring which adheres more uniformly to
a polishing pad. The retainer ring surrounds and protects a wafer
chucked to the polishing head. The bottom surface of the retainer
ring is inclined by a predetermined angle from the outer periphery
thereof towards the inner periphery thereof. A resilient fixing
plate disposed against the upper surface of the inner peripheral
portion of the retainer ring provides a seal between the retainer
ring and the carrier. Therefore, when the retainer ring is pressed
against a polishing pad and the inner peripheral portion of the
retainer ring is pushed downwardly due to the resiliency of the
fixing plate, the retainer ring flexes such that uniform pressure
is produced between the bottom surface of the retainer ring and the
polishing pad. Hence, the wafer will be polished uniformly.
Inventors: |
Lee, Sang-Yeoul; (Suwon-si,
KR) ; Kim, Kyung-Dae; (Suwon-si, KR) ; Kim,
Hee-Duk; (Suwon-si, KR) ; Choy, Young-Man;
(Suwon-si, KR) |
Correspondence
Address: |
JONES VOLENTINE, L.L.C.
SUITE 150
12200 SUNRISE VALLEY DRIVE
RESTON
VA
20191
US
|
Family ID: |
19669053 |
Appl. No.: |
09/847292 |
Filed: |
May 3, 2001 |
Current U.S.
Class: |
451/288 |
Current CPC
Class: |
B24B 37/32 20130101 |
Class at
Publication: |
451/288 |
International
Class: |
B24B 007/22 |
Foreign Application Data
Date |
Code |
Application Number |
May 18, 2000 |
KR |
2000-26646 |
Claims
What is claimed is:
1. A polishing head of a chemical and mechanical polishing
apparatus comprising: a housing defining at least one air passage
therein and through which air is introduced into and discharged
from the polishing head; a carrier connected to said housing so as
to be movable up and down relative to said housing; a wafer chuck
mounted to said carrier and communicating with a said air passage
defined in the housing so that a wafer can be chucked thereto by a
vacuum created when air is discharged through said air passage; a
flexible retainer ring mounted to said carrier, and extending along
an outer peripheral portion of the carrier around said wafer chuck
so as to guide the wafer chuck and protect a wafer chucked by the
wafer chuck, the retainer ring having a lowermost surface that
extends upwardly at a predetermined inclination relative to the
horizontal from the outer periphery thereof towards the inner
periphery thereof, in the absence of forces exerted on the retainer
ring; and a resilient member disposed in the polishing head so as
to exert a downward force that causes the inner peripheral portion
of said retainer ring to be pushed downwardly when the retainer
ring is pressed downwardly against a polishing pad, whereby the
retainer ring will flex to allow the lowermost surface of the
retainer ring to be pressed uniformly against the polishing
pad.
2. A polishing head according to claim 1, wherein an air chamber is
defined by and between said wafer chuck and said carrier, and said
resilient member is a fixing ring interposed between an upper
surface of the retainer ring, at the inner peripheral portion
thereof, and a lower surface of the carrier so as to seal the air
chamber defined between the wafer chuck and the carrier.
3. A polishing head according to claim 1, wherein the lowermost
surface of said retainer ring is inclined at an angle of 0.8 to 0.9
degrees relative to the horizontal.
4. A polishing head according to claim 1, wherein said retainer
ring is made of a material selected from the group consisting of
acethal resin, a polyphenylene sulfide resin, and a polyether
sulfone (PES) resin.
5. A polishing head of a chemical and mechanical polishing
apparatus comprising: a housing defining a plurality of air
passages therein and through which air is introduced into and
discharged from the polishing head; a carrier connected to said
housing so as to be movable up and down relative to said housing; a
wafer chuck including a chucking plate, and a connector connecting
the chucking plate to the carrier such that said chucking plate is
movable upwardly and downwardly relative to said carrier; a guide
member disposed between said carrier and said chucking plate, said
connector defining a first air chamber together with the carrier,
the chucking plate, and the guide member, said guide member and
said chucking plate defining a second chamber therebetween, said
guide member being engaged with said wafer chuck so as to guide
said wafer chuck during up and down movement of said chucking
plate, and said guide member having a through-hole that places one
of said air passages defined in the housing in communication with
the air chamber defined between the guide member and the chucking
plate; an air cushion disposed on the lower surface of said
carrier, exposed to said first air chamber and communicating with
one of said air passages defined in the housing, said air cushion
being inflatable and deflatable by air introduced into and
discharged from the polishing head via said one of the air passages
so as to change the pressure in said first air chamber and thereby
selectively move said chucking plate upwardly and downwardly; a
flexible retainer ring mounted to said carrier, and extending along
an outer peripheral portion of the carrier around said wafer chuck
so as to guide the wafer chuck and protect a wafer chucked by the
wafer chuck, the retainer ring having a lowermost surface that is
extends upwardly at a predetermined inclination relative to the
horizontal from the outer periphery thereof towards the inner
periphery thereof, in the absence of forces exerted on the retainer
ring; and a resilient member disposed in the polishing head so as
to exert a downward force that causes the inner peripheral portion
of said retainer ring to be pushed downwardly when the retainer
ring is pressed downwardly against a polishing pad, whereby the
retainer ring will flex to allow the lowermost surface of the
retainer ring to be pressed uniformly against the polishing
pad.
6. A polishing head according to claim 5, wherein said resilient
member is a fixing ring interposed between the inner peripheral
portion of the retainer ring and a lower surface of said carrier,
and sealing said first air chamber defined by said chucking plate
and said carrier.
7. A polishing head according to claim 5, wherein the lowermost
surface of said retainer ring is inclined at an angle of 0.8 to 0.9
degrees relative to the horizontal.
8. A polishing head according to claim 5, wherein said retainer
ring is made of a material selected from the group consisting of
acethal resin, a polyphenylene sulfide resin, and a polyether
sulfone (PES) resin.
9. A retainer ring for use in protecting a wafer chucked by a wafer
chuck of a polishing head of a chemical mechanical polishing
apparatus, said retainer ring comprising a flexible annular body
having an uppermost surface, a lowermost surface, an inner
peripheral surface, and an outer peripheral surface, an upper end
of said inner peripheral surface adjacent the uppermost surface
being stepped, a plurality of screw holes for allowing the annular
body to be fixed to a carrier extending into the annular body from
said uppermost surface thereof at respective locations adjacent
said outer peripheral surface, and said lowermost surface being
inclined upwardly at a predetermined inclination towards the
uppermost surface from the outer peripheral surface of the annular
body towards the inner peripheral surface thereof.
10. A polishing head according to claim 9, wherein the lowermost
surface of said retainer ring is inclined at an angle of 0.8 to 0.9
degrees relative to a plane that extends orthogonally to the
longitudinal axis of the annular body.
11. A polishing head according to claim 9, wherein said retainer
ring is made of a material selected from the group consisting of
acethal resin, a polyphenylene sulfide resin, and a polyether
sulfone (PES) resin.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a chemical and mechanical
polishing apparatus. More particularly, the present invention
relates to the polishing head of a chemical and mechanical
polishing apparatus.
[0003] 2. Description of the Related Art
[0004] A chemical and mechanical polishing process is used to
planarize the front surface or the rear surface of a semiconductor
wafer in the manufacturing of an integrated circuit on the wafer.
The planarizing technology associated with the chemical and
mechanical polishing process is becoming more important as the
degree to which semiconductor integrated circuits are integrated
becomes higher and the diameters of the semiconductor wafers become
larger.
[0005] The chemical and mechanical polishing (CMP) apparatus used
to planarize surfaces of a wafer comprises a device for mounting
and detaching a wafer cassette, a wafer moving device, a polishing
device, a wafer cleaning device, and a controlling device. The
polishing device, in turn, comprises a polishing head for
supporting and pressing a wafer, a polishing plate to which a
polishing pad is attached, a driving mechanism, a device for
dressing the polishing pad, a device for cleaning a wafer chuck,
and a slurry supplying device.
[0006] In the mechanical aspect of the polishing process, material
is removed at the surface of the wafer at a rate that is
proportional to the polishing pressure and the polishing speed. In
the chemical aspect of the polishing process, material is removed
by a chemical reaction between the wafer surface and the slurry. As
long as the polishing load, the polishing speed, the amount of
slurry supplied, the friction between the wafer surface and the
polishing pad, and the polishing temperature are uniform across the
wafer surface, the planarizing is carried out over a wide area on
the wafer and the residual layer will exhibit a uniform thickness.
However, in practice, the above-mentioned parameters and the
surface state of the polishing pad vary over time. Thus, the
residual layer often exhibits an irregular thickness. Furthermore,
the planarizing process can produce dishing and tinning phenomena,
which lower the yield of the semiconductor device manufacturing
process. Therefore, the above-mentioned parameters need to be
controlled precisely through experimentation and the scientific
process.
[0007] In addition, under 1 .mu.m of material is polished away in
the chemical and mechanical polishing process, and 0.01 .mu.m of
surface planarizing degree is needed. Therefore, the way in which
the wafer is supported is very important.
[0008] One of the problems of the conventional chemical and
mechanical polishing technology is that it can produce defects
which reduce the die yield and product reliability. For example, if
the pressure needed polishing a particular wafer is too high, the
wafer carrier ring of the CMP apparatus will become considerably
bent. Accordingly, the portion of the wafer carrier ring overlying
the wafer will not be flat with respect to the wafer. Consequently,
the flow of slurry flow becomes so bad that the wafer is polished
irregularly.
[0009] In addition, a rubber bladder of the conventional CMP
apparatus can leak. Therefore, preventative maintenance must be
carried out to check for such potential leakage. This maintenance
requires the apparatus to be down for some period of time.
[0010] Therefore, measures have been taken to reduce the bending of
the retainer ring and the leakage of the bladder of a chemical and
mechanical polishing head. For instance, U.S. Pat. No. 5,944,590
discloses a polishing device which includes a retainer ring rounded
along the lower outer peripheral surface thereof. The difference
between the lower surface of the retainer ring and the lower
surface of the semiconductor wafer is 50 .mu.m or less. U.S. Pat.
No. 5,948,204 discloses a ring assembly which is attached to a
rubber bladder. The ring assembly includes a plurality of rings.
The first ring is made of a soft material, and supports a backing
plate attached to the wafer while the wafer is being polished. The
second ring is made of a hard material, and reduces the bending of
the first ring while the wafer is being polished. The second ring
is attached to a wafer carrier plate for preventing the rubber
bladder from leaking.
[0011] U.S. Pat. No. 5,664,988 also discloses an apparatus for
polishing a semiconductor wafer, the apparatus including a wafer
carrier ring and a support ring. Japanese Patent Laid-Open
Publication No. Hei 8-339979 discloses a method for polishing a
polished substrate retaining device and a substrate. A guide member
of the polished substrate retaining device is annular, and includes
a passage which extends radially therethrough.
[0012] FIG. 1 is a cross-sectional view of a conventional polishing
head 10. As shown in FIG. 1, the polishing head 10 includes a
housing 12, a wafer carrier 14 that is mounted to the housing 12
and includes a wafer chucking plate 13, and a wafer retainer ring
16 that is mounted to the carrier 14 and maintains the wafer W in
proper position on the wafer chucking plate.
[0013] The wafer carrier 14 and the retainer ring 16 are mounted to
the housing 12 so as to be movable vertically relative to the
housing 12. A sealing ring 15 made of a synthetic resilient
material is disposed between the wafer carrier 14 and the retainer
ring 16 to establish a seal therebetween.
[0014] In the conventional polishing head 10, the wafer W is
pressed against a polishing pad P by a biasing force applied to the
wafer carrier 14, and the wafer W is polished while the retainer
ring 16 is biased against the polishing pad P by the wafer carrier
14. Therefore, the wafer W is pressed uniformly against the
polishing pad P so that the entire surface of the wafer W can be
uniformly polished.
[0015] However, in the polishing head 10, the outer edge of the
lower surface of the retainer ring 16 is separated from the
polishing pad P by the resilient force of the seal ring 15 that is
exerted on the inner peripheral portion of the retainer ring 16. As
a result, the pressure at which the wafer W supported by the
chucking plate 13 and the retainer ring 16 are adhered to the
polishing pad P becomes irregular during rotation of the polishing
head 10. Accordingly, the inner peripheral portion of the retainer
ring 16 is polished by the polishing pad P to form particles, and
scratches are formed on the polished surface of the wafer by these
particles of the retainer ring 16. The scratches constitute damage
to the polished surface of the wafer W.
[0016] Furthermore, the slurry supplied between the wafer W and the
polishing pad P is not uniformly distributed over the polishing pad
P because the retainer ring 16 and the wafer are pressed
non-uniformly against the polishing pad P. As a result, the surface
of the wafer W is not polished flat.
SUMMARY OF THE INVENTION
[0017] An object of the present invention is to solve the
above-described problem of the prior art. Accordingly, it is an
object of the present invention to provide a polishing head of a
chemical and mechanical polishing apparatus, which includes a
retainer ring that will adhere uniformly to a polishing pad even
when it is deflected by the resilient force of a sealing ring
during the course of polishing a wafer.
[0018] In order to achieve the above-mentioned object of the
present invention, the bottom surface of the retainer ring is
inclined upwardly by a predetermined angle as taken in the
direction extending radially from the outer periphery of the ring
towards the inner periphery thereof. The retainer ring is mounted
to a carrier. The carrier is in turn connected to a housing
defining air passages for guiding air into and out of the polishing
head. A wafer chuck is also mounted to the carrier for chucking a
wafer using suction. The retainer ring extends along the outer
peripheral portion of the carrier, guides the wafer chuck as it is
moved towards a polishing pad, and protects the wafer chucked by
the wafer chuck.
[0019] The bottom surface of the retainer ring is inclined so that
when the inner peripheral portion is pushed downwardly by a sealing
ring or the like, the bottom surface will be pressed uniformly
against the polishing pad.
[0020] Hence, the wafer will be polished uniformly. Moreover, the
bottom surface of the retainer ring will not require polishing,
thereby saving time and labor.
BRIEF DESCRIPTION OF THE DRAWINGS
[0021] The above and other objects, features and advantages of the
present invention will become more apparent by referring to the
following detailed description thereof made with reference to the
accompanying drawings, of which:
[0022] FIG. 1 is a cross-sectional view is a conventional polishing
head of a chemical and mechanical polishing apparatus;
[0023] FIG. 2 is a cross-sectional view of an embodiment of a
polishing head of a chemical and mechanical polishing apparatus
according to the present invention;
[0024] FIG. 3 is a perspective view of a retainer ring of the
polishing head according to the present invention; and
[0025] FIG. 4 is a cross-sectional view of the retainer ring.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0026] A polishing head of a chemical and mechanical polishing
apparatus according to the present invention will be described in
detail hereinafter with reference to the FIGS. 2-4.
[0027] Referring first to FIG. 2, the polishing head 100 of a
chemical and mechanical polishing apparatus according to the
present invention includes a housing 110, a carrier 120 connected
to the housing 110 for supporting a wafer W that is to be polished
by a polishing pad P, a wafer chuck 130 that is mounted to the
carrier 120 and chucks the wafer W using suction, and a retainer
ring 140 that is mounted to the carrier 120. The retainer ring 140
extends along the outer periphery of the carrier 120, contacts the
polishing pad P, guides the wafer chuck 130, and protects the wafer
W chucked by the wafer chuck 130.
[0028] The housing 110 has a body portion 110a for guiding the
carrier 120 so that the carrier 120 can move upwardly and
downwardly, and a flange portion 110b that extends radially from
the lower end of the body portion 110a. The carrier 120 is
connected to the housing 110 at the flange portion 110b.
[0029] The body portion 110a of the housing 110 has a circular
cross section. The housing 110 also includes a guide projection 112
integral with the body portion 110a and extending downwardly from
the central portion of the lower surface of the body portion 110a.
The body portion 110a also has a first through-hole 114a extending
longitudinally through the axial center thereof from the upper
surface to the lower surface thereof, and second and third
through-holes 114b and 114c that extend from the upper surface of
the body portion 110a to the lower surface thereof at locations
spaced radially outwardly of the first though-hole 114a. The second
and third through-holes 114b and 114c can be located symmetrically
about the first through-hole 114a. The first, second, and third
through-holes 114a, 114b, and 114c function as air passages through
which compressed air is introduced to and discharged from the
polishing head 100.
[0030] The guide projection 112 has a through-hole 112a. The
through-hole 112a is contiguous with the first through-hole 114a
extending through the center of the body portion 110a. The
through-hole 112a of the projection 112 has a diameter that is
larger than that of the first through-hole 114a of the body portion
110a.
[0031] The flange portion 110b of the housing 110 has a plurality
of through-holes spaced from one another along the outer periphery
of the flange portion 110b. The housing 110 is connected to the
carrier 120 by screws inserted into these through-holes.
[0032] The carrier 120 has a body portion 122 and a connector 124
for connecting the body portion 122 to the housing 110 so that the
body portion 122 can be moved upwardly and downwardly by compressed
air that is introduced and discharged through the second
through-hole 114b of the housing 110. The body portion 122 of the
carrier 120 defines a first axial through-hole 122a, a second axial
through-hole 122b, a first annular recess 126a in the upper surface
of the body portion 122 thereof, and a second annular recess 126b
in the lower surface of the body portion 122.
[0033] The first through-hole 122a has the same diameter as that of
the through-hole 112a formed in the projection 112 of the housing
110. The second through-hole 122b spaced radially from the first
through-hole 122a and is open to the lower surface of the body
portion 122 within the second annular recess 126b
[0034] The first annular recess 126a is concentric with respect to
the center of the body portion 122 and is spaced radially inwardly
from the outer periphery of the upper surface of the body portion
122. A plurality of through-holes extend through the outer
peripheral portion of the body portion 122. Screws extend through
these through-holes, respectively, and into tapped holes formed in
the retainer ring 140 to fix the retainer ring 140 to the carrier
120.
[0035] The second annular recess 126b is concentric with respect to
the center of the body portion 122 and is located mid-way between
the center of the body portion 122 and the outer periphery of the
lower surface of the body portion 122. The outer periphery of the
lower surface of the body portion 122 is stepped so as to define a
first outer annular surface concentric with respect to the center
of the lower surface of the body portion 122, and a second annular
surface extending radially inwardly from the first annular surface.
the second annular surface is also concentric with respect to the
center of the lower surface of the body portion 122. Furthermore,
the second annular surface is wider than the first outer annular
surface. The outer periphery of the lower surface of the body
portion 122 also includes a third annular surface that extends at
an inclination from the second annular surface to the second
annular recess 126b.
[0036] The central portion of the body portion 122 of the carrier
120 is thinner than any other portion of the body portion 122. The
body portion 122 also has a plurality of tapped openings in the
upper surface thereof between the central portion and the first
annular recess 126a. The tapped openings are disposed radially
about the central portion of the body portion 122. The connector
124 of the carrier 120 has an outer clamp 124a that is fixed to the
bottom surface of the housing 110 by nuts and bolts, an inner clamp
124b that is fixed to the upper surface of the carrier 120 by
screws extending into the tapped openings in the upper surface
thereof, and an annular resilient sheet 124c. The annular resilient
sheet 124c is made of rubber or a synthetic resin. The annular
resilient sheet 124c has a predetermined width, and the diameter of
the annular resilient sheet 124c is larger than that of the inner
clamp 124b, and is smaller than those of the carrier 120 and the
outer clamp 124a. The outer circumferential portion of the annular
resilient sheet 124c is fixed to the housing 110 by the outer clamp
124a, whereas the inner circumferential portion of the annular
resilient sheet 124a is fixed to the carrier 120 by the inner clamp
124b.
[0037] More specifically, the outer clamp 124a of the connector 124
comprises a body portion and a flange portion integral with the
body portion. The inner diameter of the outer clamp 124a is larger
than the outer diameter of the inner clamp 124b, and the outer
diameter of the outer clamp 124a is equal to the maximum diameter
of the housing 110. The flange portion of the outer clamp 124a has
a plurality of through-holes that correspond to the plurality of
through-holes formed in the flange 110b of the housing 110. The
outer circumferential portion of the resilient sheet 124c is
disposed between the bottom surface of the housing 110 and the
outer clamp 124a. The outer clamp 124a is fixed to the housing 110
by nuts and bolts inserted into the corresponding through-holes in
the flange portion of the outer clamp 124a and the flange 110b of
the housing 110 so as to sandwich the outer circumferential portion
of the resilient sheet 124c therebetween.
[0038] The inner clamp 124b of the connector 124 is disc-shaped.
The radius of the inner clamp 124b is equal to the distance from
the center of the carrier 120 to the first annular recess 126a. The
inner clamp 124b has a central through-hole of a diameter that is
equal to or greater than the outer diameter of the projection 112,
and a plurality of through-holes that correspond to the plurality
of tapped holes in the upper surface of the body portion 122 of the
carrier 120. The inner clamp 124b is fixed to the body portion 122
by screws inserted into the corresponding through-holes in the
inner clamp 124b and the tapped holes in the upper surface of the
body portion 122 of the carrier 120 so as to sandwich the inner
circumferential portion of the resilient sheet 124c
therebetween.
[0039] The inner clamp 124b also has a through-hole, corresponding
to the third through-hole 114c of the housing 110, and an elongate
groove having a width that is equal to the diameter of the
through-hole. The through-hole of the inner clamp 124b is spaced
radially outwardly of the center of the inner clamp 124b, and the
elongate groove extends radially in the lower surface of the inner
clamp 124b from the through-hole to a position corresponding to the
second through-hole 122b of the carrier 120. An air conduit 129 is
disposed in the elongate groove. The air conduit 129 has a first
end connected to the third through-hole 114c of the housing 110 and
a second end connected to an annular air cushion 128 to supply and
discharge air to and from the air cushion 128.
[0040] The annular air cushion 128 is disposed in the annular
recess 126 defined at the lower surface of the carrier 120. The air
cushion 128 is made of a flexible synthetic resin or rubber, and
has an opening therein that allows air to be introduced therein or
discharged therefrom. The air cushion 128 is inflated by the
pressure of compressed air that is supplied through the air conduit
129 to move the wafer chuck 130 downwardly. On the other hand, the
air conduit 129 is deflated when the compressed air is discharged
through the air conduit 129 to allow the wafer chuck 130 to move
upwardly.
[0041] The housing 110 is connected to the carrier 120 so as to
define an air chamber 120a therebetween. Compressed air introduced
through the second through-hole 114b of the housing 110 flows into
the air chamber 120a and forces the carrier 120 downwardly relative
tot he housing 100. When the compressed air is discharged through
the second through-hole 114b, a vacuum is created in the air
chamber 120a. As the result, the carrier 120 is moved upwardly
towards the housing 110.
[0042] The wafer chuck 130 comprises a resilient plate 132 that can
be extended and retracted by air pressure, a chucking plate 134 for
supporting and chucking the wafer W, a connector 136 for fixing the
resilient plate 132 to the chucking plate 134 and connecting the
chucking plate 134 to the carrier 120, and a guide member 138 for
guiding the connecting member 136 as the chucking plate 134 moves
upwardly or downwardly.
[0043] The resilient plate 132 comprises a disc of rubber or a
synthetic resin. The resilient plate also has a plurality of
through-holes disposed radially outwardly of the center of the
resilient plate 132 at the outer peripheral portion of the
resilient plate 132.
[0044] The chucking plate 134 is also disc-shaped. A plurality of
through-holes extend therethrough at locations spaced radially
outwardly of the center of the chucking plate 134. Air is sucked
through the through-holes to chuck the wafer W to the chucking
plate 134. The chucking plate 134 also has an annular recess in the
upper surface thereof. The annular recess is concentric with
respect to the center of the plate 134 and is located at the outer
periphery of the chucking plate 134. A plurality of screw holes are
disposed in the recess.
[0045] The connector 136 comprises an annular resilient sheet 136a
(of rubber or a synthetic resin) that connects the chucking plate
134 to the carrier 120 such that an air chamber 130a is defined
between the carrier 120 and the wafer chuck 130, a first connecting
ring 136b fixing the resilient plate 132 to the chucking plate 134,
a second connecting ring 136c fixing the inner peripheral portion
of the resilient sheet 136a to the chucking plate 134, and a
resilient fixing ring 136d fixing the outer peripheral portion of
the resilient sheet 136a to the carrier 120.
[0046] The outer diameter of the first connecting ring 136b is
significantly smaller than the outer diameter of the chucking plate
134. The first connecting ring 136b also has a plurality of
through-holes that correspond to the screw holes formed in the
chucking plate 134. A plurality of screw holes can be formed in the
upper surface of the annular sheet 136a in alignment with the
through-holes of the first connecting ring 136b.
[0047] The resilient plate 132 is fixed to the chucking plate 134
by the first connecting ring 136b. First, the resilient plate 132
is disposed over the lower surface of the chucking plate 134.
Subsequently, the outer peripheral portion of the chucking plate
132 is bent upwardly along the outer peripheral edge of the
chucking plate 134 and then is bent again into contact with the
upper surface of the chucking plate 134. Next, the first connecting
ring 136b is disposed on the outer peripheral portion of the
resilient plate 132 such that the though-holes formed in the first
connecting ring 136b are aligned with the through-holes formed in
the outer peripheral portion of the resilient plate 132. Finally,
screws are passed through the through-holes formed in the outer
peripheral portions of the first connecting ring 136b and the
resilient plate 132, and into engagement with the threads of the
screw holes formed in the upper surface of the chucking plate 134
to fix the resilient plate 132 to the chucking plate 134.
[0048] The second ring 136c of the connector 136 has an outer
diameter that is smaller than the outer diameter of the first
connecting ring 136b, and an inner diameter that is smaller than
the inner diameter of the first connecting ring 136b. The inner
peripheral surface of the second connecting ring 136c is machined
so that it is inclined at a predetermined angle from the upper end
thereof towards the lower end thereof. The diameter of the lower
end of the inner peripheral surface of the second connecting ring
136c is larger than the diameter of the upper end of the inner
peripheral surface. The second connecting ring 136c may also have a
plurality of through-holes that correspond to the screw holes
formed in the upper surface of the first connecting ring 136b.
[0049] The fixing ring 136d of the connector 136 is made of a
resilient synthetic resin or rubber. The fixing ring 136d has a
thickness of about 1 mm. The maximum diameter of the fixing ring
136d is significantly smaller than the diameter of the carrier 120.
The fixing ring 136d fixes the resilient sheet 136a to the carrier
120, and seals the space between the carrier 120 and the retainer
ring 140.
[0050] The resilient sheet 136a has the same outer diameter as the
resilient fixing ring 136d. The resilient sheet 136a may have a
plurality of through-holes in the inner peripheral portion thereof
that is interposed between the first connecting ring 136b and the
second connecting ring 136c. ln this case, the resilient sheet 136a
is disposed between the first connecting ring 136b and the second
connecting ring 136c such that the through-holes formed in the
inner peripheral portion of the resilient sheet 136a are aligned
with the screw holes formed in the first connecting ring 136b and
the second connecting ring 136c. Screws are passed through the
screw holes formed in the first connecting ring 136b and the
through-holes formed in the inner peripheral portion of the
resilient sheet 136a and into engagement with the threads of the
screw holes formed in the second connecting ring 136c. Accordingly,
the resilient sheet 136a is connected to the first and second
connecting rings 136b and 136c.
[0051] Alternatively, both surfaces of the inner peripheral portion
of the resilient sheet 136a may be coated with a binder, whereby
the inner peripheral portion is bonded to the first connecting ring
136b and the second connecting ring 136c.
[0052] The outer peripheral portion of the resilient sheet 136a may
also be coated with the binder, whereby the outer peripheral
portion is bonded to the lower surface of the carrier 120 and the
fixing ring 136d.
[0053] The guide member 138 comprises a disc-shaped member having a
stepped portion at the outer periphery thereof, and an extending
portion that extends upwardly from the center of the guide member
138. The guide member 138 has a through-hole that extends from the
upper end of the extending portion to the lower surface of the
guide member 138. The outer diameter of the extending portion of
the guide member 138 is equal to or smaller than the inner diameter
of the projection 112 of the housing 110 and the through-hole
formed at the center of the carrier 120.
[0054] As shown in FIG. 2, the extending portion of the guide
member 138 extends through the through-hole formed at the central
portion of the carrier 120 and into the through-hole formed in the
projection 112 of the housing 110. The inclined inner peripheral
surface of the second connecting ring 136c of the wafer chuck 130
is seated against the stepped portion of the guide member 138 such
that the second connecting ring 136c can slide along the stepped
portion and move upwardly or downwardly according to the pressure
in chamber 130a. The upper surface of the guide member 138 is
adhered to the lower surface of the carrier 120.
[0055] The through-hole formed in the guide member 138 communicates
with the first through-hole 114a formed in the housing 110, and
with the air chamber 130b defined by the guide member 138, the
chucking plate 134, the connector 136, and the resilient plate 132.
Therefore, when air is discharged from the air chamber 130b through
the through-hole formed in the guide member 138 and the first
through-hole 114a formed in the housing 110, a portion of the
resilient plate 132 disposed on the lower surface of the chucking
plate 134 is sucked into the through-holes formed in the chucking
plate 134. Consequently, a vacuum is created between the resilient
plate 132 and the wafer W, whereby the wafer W is adhered to the
resilient plate 132.
[0056] On the other hand, the connecting member 136 of the wafer
chuck 130 defines the air chamber 130a together with the carrier
120 and the guide member 138. The pressure in the air chamber 130a
is raised when the air cushion 128 is inflated. As a result, the
second connecting ring 136c of the connector 136, the first
connecting ring 136b, and the chucking plate 134 are moved
downwardly. Conversely, if the air cushion 128 is contracted by
discharging the air therefrom, the air pressure in the air chamber
130a is decreased. As a result, the second connecting ring 136c,
the first ring 136b, and the chucking plate 134 are moved upwardly
by a restoring force exerted by the resilient sheet 136a of the
connector 136.
[0057] Referring now to FIGS. 3 and 4, the retainer ring 140 of the
polishing head 100 is made of a resin such as a polyphenylene
sulfide PPS (resin). However, the retainer ring 140 can be made of
an acethal resin or a polyether sulfone (PES) resin.
[0058] In general, the retainer ring 140 is made by cutting a
section from a cylindrical body of PPS resin. Then, the section is
shaped using a lathe. The inner diameter of the retainer ring 140
is about 200 mm, the outer diameter thereof is about 240 to 250 mm,
and the width of the lower surface thereof is about 20 to 25
mm.
[0059] Furthermore, as shown in FIGS. 3 and 4, the retainer ring
has a first step 142 and a second step 144 at the upper portion of
the inner periphery thereof. The width and the height of the first
step 142 are typically the same as the width and the thickness of
the fixing ring 136d, respectively. However, the height of the
first step 142 may be smaller than the thickness of the fixing ring
136d. The second step 144 of the retainer ring 140 is engaged with
a jaw portion of the carrier 120. Therefore, the width and the
height of the second step are the same as the width and the height
of the jaw portion.
[0060] The lowermost surface 146 of the retainer ring 140 is
machined so that it is inclined with respect to a (horizontal)
plane orthogonal to the longitudinal axis of the ring by about 0.8
to 0.9 degrees, in the absence of any forces exerted on the ring.
Preferably, the angle of inclination is 0.85 degrees. The inclined
surface of the retainer ring 140 extends upwardly from the outer
periphery of the retainer ring 140 towards the inner periphery of
the retainer ring 140, when viewed from the bottom of the retainer
ring 140. The lowermost surface 146 of the retainer ring thus
subtends an angle 15 of about 89 degrees with respect to the
vertical. The outer peripheral surface of the retainer ring 140 is
0.35 mm longer than the inner peripheral surface of the retainer
ring 140.
[0061] A plurality of screw holes 148, preferably twelve screw
holes 148, are formed in the outer peripheral portion of the upper
surface of the retainer ring 140. The retainer ring 140 is fixed to
the carrier 120 by screws extending through the through-holes of
the carrier 120 and into engagement with the threads of the screw
holes 148 formed in the retainer ring 140.
[0062] On the other hand, twelve holes (not shown) are formed
between the screw holes 148 in the outer periphery of the retainer
ring 140. Three holes (not shown) are formed in the inner periphery
of the retainer ring 140 between each adjacent pair of screw holes
148, so that a total of thirty-six holes are formed in the inner
periphery of the retainer ring 148. Each hole in the outer
periphery of the retainer ring 140 communicates with a respective
set of three holes in the inner periphery of the retainer ring 140.
Slurry is supplied by a slurry supplying device to the holes in the
outer periphery of the retainer ring 140 so that the slurry flows
to the inner periphery of the retainer ring 140 through the holes
in the inner periphery of the retainer ring 140. The slurry is used
to polish the wafer W.
[0063] Next, the operation of the polishing head 100 according to
the present invention will be described in detail.
[0064] Referring again to FIG. 2, air is discharged from the air
chamber 120a through the second through-hole 114b of the housing
110 to vacuum the air chamber 120a. Accordingly, a vacuum is
created in the air chamber 120a and as a result, the carrier 120 is
adhered to the lower surface of the housing 110.
[0065] With the carrier 120 adhered to the lower surface of the
housing 110, the retainer ring 140 and the wafer chuck 130 are
disposed in an upper position. Then, air is supplied into the air
cushion 128 through the air conduit 129 extending through the inner
clamp 124b and the third through hole 114c of the housing 110. As
the air cushion 128 is thus inflated, pressure is produced in the
air chamber 130a defined by the carrier body 122 of the carrier
120, the guide member 138 of the wafer chuck 130 and the connector
136. The wafer chuck 130 is moved downwardly by the air pressure
produced the air chamber 130a. More specifically, the inclined
surface of the second connecting ring 136 slides along the stepped
portion of the guide member 138, and the resilient plate 132 is
moved downwardly until the lower surface thereof becomes coplanar
with the bottom surface 146 of the retainer ring 140. Thus, the
wafer chuck 130 is pressed against a wafer W fed to a location
below the polishing head 100 by a wafer feeding device (not
shown).
[0066] In the state in which the wafer chuck 130 is adhered to the
wafer, air is discharged from the air chamber 130b defined by the
guide member 138, the chucking plate 134, and the connecting member
136 through the air passage of the extending portion of the guide
member 138 and the first through-hole 114a formed in the housing
110. Consequently, a vacuum is produced in the air chamber 130b,
and the resilient plate 132 is sucked into the through-holes formed
in the chucking plate 134. Therefore, a vacuum is also produced
between the chucking plate 134 and the wafer W such that the wafer
W is firmly adhered to the chucking plate 134.
[0067] Subsequently, the air is discharged from the air cushion 128
to deflate the air cushion 128. Therefore, the pressure in the air
chamber 130a is lowered. Accordingly, the chucking plate 134 is
moved upwardly by the resilient sheet 136a of the connector 136.
Thus, the wafer W adhered to the chucking plate 134 is positioned
above the bottom surface 146 of the retainer ring 140.
[0068] Next, air is supplied into the air chamber 120a while a
vacuum is maintained in the air chamber 130b. As a result, the body
portion 122 of the carrier 120 is moved downwardly by the pressure
produced in the air chamber 120a. The retainer ring 140 and the
wafer chuck 130 connected to the carrier 120 are also moved
downwardly together with the carrier 120. As shown in FIG. 2, the
retainer ring 140 makes contact with the upper surface of the
polishing pad P. As this happens, the inner peripheral portion of
the retainer ring 140 is moved downwardly by the resilient force of
the fixing ring 136d such that the retainer ring 140 contacts the
upper surface of the polishing pad P uniformly. In this state, the
wafer W is spaced above the upper surface of the polishing pad
P.
[0069] However, the air continues to be supplied into the air
chamber 120a. Thus, the retainer ring 140 remains in contact with
the upper surface of the polishing pad P. In addition, a vacuum is
maintained in the air chamber 130b. Then, air is supplied into the
air cushion 128. As the air cushion 128 is thus inflated, the
pressure in the air chamber 130a is increased. As a result, the
wafer chuck 130 is moved downwardly. Hence, the lower surface of
the wafer W chucked by the wafer chuck 130 is brought into contact
with the upper surface of the polishing pad P. The pressure in the
air chamber 130a is increased until the wafer W is adhered firmly
to the polishing pad P.
[0070] In this state, the slurry is supplied between the wafer W
and the polishing pad P and the polishing head 100 are rotated in
opposite directions. Accordingly, the lower surface of the wafer W
is polished.
[0071] Because the bottom surface of the retainer ring 140 is
inclined as described above, the bottom surface of the retainer
ring is pressed uniformly against the polishing pad even though the
fixing ring 136d exerts a downward force on the inner peripheral
portion of the retainer ring 140.
[0072] Therefore, the retainer ring does not have to be polished.
In addition, the retainer ring and the wafer are pressed uniformly
against the polishing pad, thereby ensuring that the lower surface
of the wafer is polished uniformly.
[0073] Finally, although the present invention has been shown and
described with respect to the preferred embodiments thereof,
various changes thereto and modifications thereof will become
readily apparent to those of ordinary skill in the art.
Accordingly, all such changes and modifications are sen to be
within the true spirit and scope of the present invention as
hereinafter claimed.
* * * * *