U.S. patent application number 14/292837 was filed with the patent office on 2014-12-04 for center flex single side polishing head.
The applicant listed for this patent is SunEdison Semiconductor Limited. Invention is credited to Peter Albrecht, Sumeet Bhagavat, Alex Chu, Roland Vandamme, Yunbiao Xin, Ichiro Yoshimura.
Application Number | 20140357161 14/292837 |
Document ID | / |
Family ID | 51985635 |
Filed Date | 2014-12-04 |
United States Patent
Application |
20140357161 |
Kind Code |
A1 |
Bhagavat; Sumeet ; et
al. |
December 4, 2014 |
CENTER FLEX SINGLE SIDE POLISHING HEAD
Abstract
A polishing head assembly for single side polishing of silicon
wafers includes a polishing head and a cap. The polishing head
includes a top surface and a bottom surface and defines a
longitudinal axis extending therethrough. The cap is positioned
coaxially with the polishing head and includes an upper surface and
a lower surface. The upper surface is spaced from the bottom
surface of the polishing head to form a chamber that allows the cap
to deflect toward the polishing head.
Inventors: |
Bhagavat; Sumeet; (St.
Charles, MO) ; Albrecht; Peter; (O'Fallon, MO)
; Chu; Alex; (Hsinchu, TW) ; Yoshimura;
Ichiro; (Shimotsuke City, JP) ; Xin; Yunbiao;
(Palo Alto, CA) ; Vandamme; Roland; (Wentzville,
MO) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
SunEdison Semiconductor Limited |
St. Peters |
MO |
US |
|
|
Family ID: |
51985635 |
Appl. No.: |
14/292837 |
Filed: |
May 31, 2014 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61829685 |
May 31, 2013 |
|
|
|
Current U.S.
Class: |
451/41 ; 451/288;
451/398 |
Current CPC
Class: |
B24B 37/30 20130101;
B24B 37/10 20130101 |
Class at
Publication: |
451/41 ; 451/398;
451/288 |
International
Class: |
B24B 37/10 20060101
B24B037/10; B24B 41/00 20060101 B24B041/00; B24B 37/30 20060101
B24B037/30 |
Claims
1. A polishing head assembly for single side polishing of silicon
wafers, the polishing head assembly comprising: a polishing head
having a top surface and a bottom surface and defining a
longitudinal axis extending therethrough; and a cap positioned
coaxially with the polishing head, the cap having an upper surface
and a lower surface, the upper surface being spaced from the bottom
surface of the polishing head to form a chamber therebetween to
allow the cap to deflect toward the polishing head.
2. The polishing head assembly of claim 1, further comprising a
source of pressurized fluid connected with the chamber to increase
a pressure within the chamber and to deflect the cap.
3. The polishing head assembly of claim 1, further comprising a
controller connected with the source of pressurized fluid to
control the pressure within the chamber.
4. The polishing head assembly of claim 1, further comprising a
liquid on the lower surface of the cap to retain a wafer by surface
tension.
5. The polishing head assembly of claim 4, further comprising a
wafer connected with the cap, the wafer being retained against the
lower surface of the cap by surface tension.
6. The polishing head assembly of claim 1, wherein the polishing
head assembly is configured to cause movement of the polishing head
along the longitudinal axis to increase and decrease a polishing
pressure.
7. The polishing head assembly of claim 1, further comprising a
first stopper located within the chamber, between the polishing
head and cap to limit deflection of the cap at a first location,
the first stopper having a first height.
8. The polishing head assembly of claim 7, further comprising a
second stopper located within the chamber, between the polishing
head and cap to limit deflection of the cap at a first location,
the first stopper having a second height.
9. The polishing head assembly of claim 8, wherein the second
stopper is a ring coaxially located about the first stopper.
10. The polishing head assembly of claim 8, wherein the first
height is one of less than and greater than the second height.
11. The polishing head assembly of claim 8, wherein the chamber has
a chamber height, the chamber height is greater than at least one
of the first height and the second height.
12. A single side polishing apparatus for single side polishing of
silicon wafers, the single side polishing apparatus comprising: a
polishing pad; a polishing head for forcing the wafer toward the
polishing pad, the polishing head having a polishing side facing a
location of the wafer; a cap mounted in spaced relation from the
polishing side of the polishing head, the cap being capable of
deflecting toward the polishing head under a polishing pressure and
away from the polishing head by an increase of pressure in the
chamber. a movable stopper located between the polishing head and
the cap to limit deflection of the cap along a direction that is
perpendicular to the polishing side of the polishing head.
13. The single side polishing apparatus of claim 12, further
comprising a source of pressurized fluid connected with the chamber
to increase pressure within the chamber and to deform the cap.
14. The single side polishing apparatus of claim 12, further
comprising a second stopper located between the polishing head and
the cap at a position radially outward from the movable stopper to
limit deflection of the cap.
15. The single side polishing apparatus of claim 12, wherein the
cap is attached to the polishing head with an adhesive.
16. The single side polishing apparatus of claim 14, wherein the
floor is flat in an undeflected state.
17. The single side polishing apparatus of claim 12, further
comprising a movable stopper located between the polishing head and
the cap to limit deflection of the cap along a direction that is
perpendicular to the polishing side of the polishing head.
18. The single side polishing apparatus of claim 17, further
comprising a source of pressurized fluid connected with the stopper
to adjust pressure within the stopper and to regulate a height of
the stopper.
19. A method for polishing of silicon wafers; the method
comprising: providing a polishing apparatus including a polishing
pad, a wafer carrier for retaining a wafer placed therein, and a
polishing head assembly having a polishing head and a cap attached
to a polishing side of the polishing head; forcing the polishing
head toward the polishing pad to cause the wafer to contact the
polishing pad at a polishing pressure; polishing a surface of the
wafer by causing rotational movement of the polishing pad with
respect to the wafer; deflecting the cap with respect to the
polishing head; and adjusting the polishing pressure to regulate
the deflection of the cap for improving flatness of the polished
surface.
20. The method of claim 19, further comprising adjusting an
internal pressure within a chamber formed between the polishing
head and the cap to deflect the cap for improving flatness of the
polished surface.
21. The method of claim 19, further comprising placing the wafer
adjacent to the cap and retaining the wafer with surface tension to
the cap.
22. The method of claim 19, wherein the polishing head includes a
stopper to limit the deflection of the cap.
23. The method of claim 22, further comprising adjusting the height
of the stopper to regulate the deflection of the cap.
24. The method of claim 23, wherein adjusting the height of the
stopper includes the step of adjusting pressure within the stopper.
Description
CROSS REFERENCE
[0001] This application claims priority to U.S. Provisional
Application No. 61/829,685 filed May 31, 2013, the disclosure of
which is hereby incorporated by reference in its entirety.
FIELD
[0002] This disclosure relates generally to polishing of
semiconductor or solar wafers and more particularly to single side
polishing apparatus and methods for controlling flatness of the
wafer.
BACKGROUND
[0003] Semiconductor wafers are commonly used in the production of
integrated circuit (IC) chips on which circuitry are printed. The
circuitry is first printed in miniaturized form onto surfaces of
the wafers. The wafers are then broken into circuit chips. This
miniaturized circuitry requires that front and back surfaces of
each wafer be extremely flat and parallel to ensure that the
circuitry can be properly printed over the entire surface of the
wafer. To accomplish this, grinding and polishing processes are
commonly used to improve flatness and parallelism of the front and
back surfaces of the wafer after the wafer is cut from an ingot. A
particularly good finish is required when polishing the wafer in
preparation for printing the miniaturized circuits on the wafer by
an electron beam-lithographic or photolithographic process
(hereinafter "lithography"). The wafer surface on which the
miniaturized circuits are to be printed must be flat. Similarly,
flatness and finish are also important for solar applications.
[0004] The construction and operation of conventional polishing
machines contribute to the unacceptable flatness parameters.
Polishing machines typically include a circular or annular
polishing pad mounted on a turntable or platen for driven rotation
about a vertical axis passing through the center of the pad and a
mechanism for holding the wafer and forcing it into the polishing
pad. The wafer is typically mounted to the polishing head using for
example, liquid surface tension or a vacuum/suction. A polishing
slurry, typically including chemical polishing agents and abrasive
particles, is applied to the pad for greater polishing interaction
between the polishing pad and the surface of the wafer. This type
of polishing operation is typically referred to as
chemical-mechanical polishing (CMP).
[0005] During operation, the pad is rotated and the wafer is
brought into contact with and forced against the pad by the
polishing head. As the pad wears, e.g., after a few hundred wafers,
wafer flatness parameters degrade because the pad is no longer
flat, but instead has a worn annular band forming a depression
along the polishing surface of the pad. Such pad wear impacts wafer
flatness, and may cause "dishing" or "doming" or a combination
thereof resulting in a "w-shape".
[0006] When the flatness of the wafers becomes unacceptable, the
worn polishing pad has to be replaced with a new one. Frequent pad
replacement adds significant costs to the operation of the
polishing apparatus not only because of the number of pads that
need to be purchased, stored, and disposed of, but also because of
the substantial amount of down time required to change the
polishing pad.
[0007] Accordingly, there is a need for a polishing apparatus that
has the ability to optimize flatness parameters by modulating the
wafer thickness shape in the polishing process for doming, dishing,
and +/-w-shape.
[0008] This Background section is intended to introduce the reader
to various aspects of art that may be related to various aspects of
the present disclosure, which are described and/or claimed below.
This discussion is believed to be helpful in providing the reader
with background information to facilitate a better understanding of
the various aspects of the present disclosure. Accordingly, it
should be understood that these statements are to be read in this
light, and not as admissions of prior art.
SUMMARY
[0009] A first aspect is a polishing head assembly for single side
polishing of silicon wafers. The polishing head assembly includes a
polishing head and a cap. The polishing head includes a top surface
and a bottom surface and defines a longitudinal axis extending
therethrough. The cap is positioned coaxially with the polishing
head and includes an upper surface and a lower surface. The upper
surface is spaced from the bottom surface of the polishing head to
form a chamber that allows the cap to deflect toward the polishing
head. The wafer carrier is disposed adjacent to the cap.
[0010] Another aspect is a single side polishing apparatus for
single side polishing of silicon wafers. The single side polishing
apparatus includes a polishing head for rotating the wafer in
relation to a polishing pad, a cap, and a movable stopper. The
polishing head has a polishing side facing a location of the wafer.
The cap is mounted in spaced relation from the polishing side of
the polishing head and is capable of deflecting under a polishing
pressure. The movable stopper is located between the polishing head
and the cap to limit movement of the cap with respect to the
polishing head along a direction that is perpendicular to the
polishing side of the polishing head.
[0011] Another aspect is a method for the polishing of silicon
wafers. The method includes providing a polishing apparatus that
includes a wafer carrier for retaining a wafer placed therein and a
polishing head assembly. The polishing head assembly has a
polishing head and a cap attached to a polishing side of the
polishing head for rotating the wafer in relation to a polishing
pad. The polishing head is moved with respect to the wafer carrier
to cause the cap to react against the wafer resulting in a
polishing pressure. The cap is deflected with respect to the
polishing head. A surface of the wafer is polished by causing
rotational movement between the wafer and the polishing pad to form
a polished surface on the wafer. The polishing pressure is adjusted
to regulate the deflection of the cap for improving flatness of the
polished surface.
[0012] Various refinements exist of the features noted in relation
to the above-mentioned aspects. Further features may also be
incorporated in the above-mentioned aspects as well. These
refinements and additional features may exist individually or in
any combination. For instance, various features discussed below in
relation to any of the illustrated embodiments may be incorporated
into any of the above-described aspects, alone or in any
combination.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] FIG. 1 is a partially schematic elevation of a single side
polisher;
[0014] FIG. 2 is a cross section of a single side polishing head
with a domed plate in accordance with one embodiment, the shape of
the domed plated being exaggerated for illustration purposes;
[0015] FIG. 3 is a cross section of the single side polishing head
of FIG. 3 under polishing pressure;
[0016] FIG. 4 is a cross section of the single side polishing head
of FIG. 3 under polishing pressure 0.9 P;
[0017] FIG. 5 is a cross section of the single side polishing head
of FIG. 3 under polishing pressure 1.1 P;
[0018] FIG. 6 is a pressure profile graph plotting the correlation
of the contact pressure and wafer radius;
[0019] FIG. 7 is a cross section of a single side polishing head
with a flat plate in accordance with another embodiment;
[0020] FIG. 8 is a cross section of the single side polishing head
of FIG. 7 with a pressurized section under no polishing
pressure;
[0021] FIG. 9 is a cross section of the single side polishing head
of FIG. 7 with a pressurized section under polishing pressure;
[0022] FIG. 10 is a cross section of the single side polishing head
of FIG. 7 with a pressurized section under polishing pressure 0.9
P;
[0023] FIG. 11 is a cross section of the single side polishing head
of FIG. 7 with a pressurized section under polishing pressure 1.1
P;
[0024] FIG. 12 is a cross section of a single side polishing head
with a flat plate and two adjustable stoppers in accordance with
another embodiment;
[0025] FIG. 13 is a cross section of the single side polishing head
of FIG. 12 with a pressurized section under no polishing
pressure;
[0026] FIG. 14 is a cross section of the single side polishing head
of FIG. 12 with a pressurized section under polishing pressure;
[0027] FIG. 15 is a cross section of the single side polishing head
of FIG. 12 with a pressurized section under polishing pressure 0.9
P;
[0028] FIG. 16 is a cross section of the single side polishing head
of FIG. 12 with a center stopper retracted and a pressurized
section under polishing pressure 1.3 P;
[0029] FIG. 17 is a cross section of the single side polishing head
of FIG. 12 with stopper ring retracted and a pressurized section
under polishing pressure 1.3 P;
[0030] FIG. 18 is a cross section of the single side polishing head
of FIG. 12 with both stoppers retracted and a pressurized section
under polishing pressure 1.1 P;
[0031] FIG. 19 is a Doming Correction graph plotting the
correlation of the contact pressure and the radius;
[0032] FIG. 20 is a Negative W-factor Correction graph plotting the
correlation of the contact pressure and the radius; and
[0033] FIG. 21 is a cross section of a single side polishing head
with a flat plate and an inflatable bellow attached to a center
stopper in accordance with another embodiment.
[0034] Like reference symbols in the various drawings indicate like
elements.
DETAILED DESCRIPTION
[0035] Generally, and in one embodiment of the present disclosure,
a wafer that has previously been rough polished so that it has
rough front and back surfaces is first subjected to an intermediate
polishing operation in which the front surface of the wafer, but
not the back surface, is polished to improve flatness parameters or
to smooth the front surface and remove handling scratches. To carry
out this operation, the wafer is placed against the polishing head.
In this embodiment, the wafer is retained in position against the
polishing head by surface tension. The wafer also is placed on a
turntable of a machine with the front surface of the wafer
contacting the polishing surface of a polishing pad.
[0036] A polishing head mounted on the machine is capable of
vertical movement along an axis extending through the wafer. While
the turntable rotates, the polishing head is moved against the
wafer to urge the wafer toward the turntable, thereby pressing the
front surface of the wafer into polishing engagement with the
polishing surface of the polishing pad.
[0037] A conventional polishing slurry containing abrasive
particles and a chemical etchant is applied to the polishing pad.
The polishing pad works the slurry against the surface of the wafer
to remove material from the front surface of the wafer, resulting
in a surface of improved smoothness. As an example, the
intermediate polishing operation preferably removes less than about
1 micron of material from the front side of the wafer.
[0038] The wafer is then subjected to a finish polishing operation
in which the front surface of the wafer is finish polished to
remove fine or "micro" scratches caused by large size colloidal
silica, such as Syton.RTM. from DuPont Air Products Nanomaterials,
LLC, in the intermediate step and to produce a highly reflective,
damage-free front surface of the wafer. The intermediate polishing
operation generally removes more of the wafer than the finishing
polishing operation. The wafer may be finish polished in the same
single-side polishing machine used to intermediate polish the wafer
as described above. However, a separate single-side polishing
machine may also be used for the finish polishing operation. A
finish polishing slurry typically has an ammonia base and a reduced
concentration of colloidal silica is injected between the polishing
pad and the wafer. The polishing pad works the finish polishing
slurry against the front surface of the wafer to remove any
remaining scratches and haze so that the front surface of the wafer
is generally highly-reflective and damage free.
[0039] Referring to FIG. 1, a portion of a single side polishing
apparatus is shown schematically and indicated generally at 100.
The single side polisher 100 may be used to polish a front surface
of semiconductor wafers W. It is contemplated that other types of
single side polishing apparatus may be used.
[0040] The polishing apparatus 100 includes a wafer holding
mechanism, e.g., a backing film 110, a retaining ring 120, a
polishing head assembly 130, and a turntable 140 having a polishing
pad 150. The backing film 110 is located between a polishing head
assembly 130 and the retaining ring 120, which receives a wafer W.
The retaining ring 120 has at least one circular opening to receive
the wafer W to be polished therein. The wafer W of this embodiment
is retained against the polishing head assembly 130 by surface
tension.
[0041] The polishing apparatus 100 applies a force to the polishing
head assembly 130 to move the polishing head assembly vertically to
raise and lower the polishing head assembly 130 with respect to the
wafer W and the turntable 140. An upward force raises the polishing
head assembly 130, and a downward force lowers the polishing head
assembly. As discussed above, the downward vertical movement of the
polishing head assembly 130 against the wafer W provides the
polishing pressure to the wafer to urge the wafer into the
polishing pad 150 of the turntable 140. As the polishing apparatus
100 increases the downward force, the polishing head assembly 130
moves vertically lower to increase the polishing pressure.
[0042] A portion of the polishing head assembly 130 and polishing
pad 150 and turntable 140 are rotated at selected rotation speeds
by a suitable drive mechanism (not shown) as is known in the art.
The rotational speeds of the polishing pad and the turntable may be
the same or different. In some embodiments, the apparatus 100
includes a controller (not shown) that allows the operator to
select rotation speeds for both the polishing head assembly 130 and
the turntable 140, and the downward force applied to the polishing
head assembly.
[0043] With reference to FIG. 2, the polishing head assembly 130
includes a polishing head 160 and a cap 170. The cap is suitably
made of plastic, aluminum, steel, ceramic, such as alumina or
silicon carbide, or any suitable material with sufficient
stiffness, including coated silicon.
[0044] The cap 170 includes a plate or floor 172 surrounded by an
annular wall 174 extending upward therefrom. In a natural or
un-deflected state, the floor 172 has a concave shape (relative to
the chamber), such that the center of the floor is lower than the
perimeter. The floor 172 is capable of temporarily deflecting
without permanently deforming. The floor 172 is about 0.118 to
about 0.275 inches (3-7 mm) thick, or about 0.625 inches (16 mm)
thick for plastic, and has a diameter of about 5.905 to about 6.496
inches (150-165 mm).
[0045] The annular wall 174 is rigidly attached to and extends
downward from an edge 162 of the polishing head 160. Together the
polishing head 160 and the cap 170 form a downwardly domed
structure. The cap 170 may be attached to the polishing head 160
with bolts or other suitable fasteners. In other embodiments, an
adhesive, such as an epoxy, is used to attach the cap 170 to the
edge 162 of the polishing head 160.
[0046] Downward movement of the polishing head assembly 130 causes
the cap 170 to contact the wafer W, and deflects the floor 172
upward toward the polishing head 160. The direction of deflection
is perpendicular to the top surface of the wafer W.
[0047] As the polishing pressure of the cap 170 against the wafer W
increases, the magnitude of deflection also increases. Regulation
of the polishing pressure allows the deflection of the floor 172 to
be increased or decreased. As the deflection of the floor 172 is
changed, the shape of the floor is also changed.
[0048] Changing the shape of the floor 172 causes a resulting
change in the force distribution of the polishing pressure across
the wafer W and thereby causes the wafer to bend in response. The
change in force distribution also causes a change in the rate of
removal of material from the wafer W. Generally, the rate of
removal is increased at portions of the wafer W that transfer
relatively greater force to the polishing pad 150.
[0049] As a result, the downward force of the polishing head
assembly 130 may be controlled to increase or decrease the
deflection of the floor 172 of the cap 170 and thereby adjust the
amount of doming or dishing of the wafer. As the polishing pressure
is increased, the floor 172 transitions from a natural,
un-deflected or downwardly curved shape to a flat shape that is
substantially parallel with a bottom surface of the polishing head
160, and finally to an upwardly curved or convex shape.
[0050] As shown in FIG. 3, under a given or predetermined polishing
pressure P the floor 172 is deflected to be substantially flat,
resulting in a removal profile that is also substantially flat. As
shown in FIG. 4, lowering the polishing pressure 0.9 P causes both
the floor 172 and the removal profile to become downwardly curved.
As shown in FIG. 5, increasing the polishing pressure 1.1 P causes
both the shape of the floor 172 and the removal profile to become
dished. Suitably, the change in polishing pressure may range from
about 0.7 P to about 1.3 P. Thus, a change in polishing pressure P
provides an operator with a control variable and the ability to
adjust the polished shape of the wafer W. In some embodiments, the
predetermined polishing pressure may range from 1.0 psi to 4.0 psi.
In other embodiments, the predetermined polishing pressure may be
less than 6.0 psi.
[0051] In some embodiments, the domed shaped plate may be attached
to an existing polishing head so as to change the polishing
properties of the polisher without extensively reworking the
machine or buying a new machine.
[0052] With reference to FIG. 6, a plot of a finite element
simulation showing the correlation between the contact pressure and
the radius are shown. This plot illustrates the ability of this
embodiment to modulate the contact pressure profile by increasing
or decreasing the standard polishing pressure P resulting in an
adjustment of the removal profile.
[0053] With reference to FIG. 7, another embodiment of the
polishing head assembly 230 has a polishing head 260 and a cap 270.
The cap 270 includes a floor 272 surrounded by an annular wall 274.
The floor 272 is substantially flat in an initial or un-deflected
state. The annular wall 274 is rigidly attached to and extends
downward from an edge 262 of the polishing head 260 to form a
chamber 232 between the floor 272 and the polishing head 260. The
chamber 232 may be connected with a pressurizing source (not shown)
to provide a pressurizing media or fluid to the chamber 232.
[0054] As shown in FIG. 8, the chamber 232 may be pressurized
causing the floor 272 to deflect into a downward dome shape,
similar to floor 172. The pressure within the chamber 232 does not
need to be changed frequently. Therefore, it may be adjusted
manually when the polishing head assembly 230 is mounted on the
polishing apparatus 100. In some embodiments, the cap 270 may be
used to retrofit an existing polishing head without the need to
drill holes through the existing head or spindle for passage of air
or fluid through the spindle and rotary unions.
[0055] Similar to the floor 172, the floor 272 of the cap 270 is
adapted to temporarily deflect in a direction that is perpendicular
to the polishing surface as the polishing pressure is increased.
The cap is not permanently deflected or deformed by the pressure.
The floor 272 transitions from a pressurized deflected or
downwardly curved shape to a flat shape that is substantially
parallel with a bottom surface of the polishing head 260, and
finally to a upwardly curved or convex shape as the polishing
pressure is increased.
[0056] As shown in FIG. 9, under a given or predetermined polishing
pressure P the floor 272 is deflected to be substantially flat,
resulting in a removal profile that is also substantially flat. As
shown in FIG. 10, lowering the polishing pressure 0.9 P causes both
the floor 272 and the removal profile to become downwardly curved.
As shown in FIG. 11, increasing the polishing pressure 1.1 P causes
both the shape of the floor 272 and the removal profile to become
dished. Thus, a change in polishing pressure P provides an operator
the ability to adjust the polished shape of the wafer W.
[0057] As described above, the polishing system is capable of
adjusting pressure distribution to control the shape of a polished
wafer, e.g., for minimizing doming and dishing of the wafer after
polishing.
[0058] With reference to FIG. 12, another embodiment of the
polishing head assembly 330 is adapted to adjust pressure
distribution to a wafer during the polishing process for
controlling or minimizing doming, dishing, and w-shape cross
section of the wafer.
[0059] The polishing head assembly 330 has a polishing head 360, a
cap 370, a stopper ring 380, and a center stopper 382. The cap 370
includes a floor 372 surrounded by an annular wall 374. The floor
372 is substantially flat in an initial or un-deflected state. The
annular wall 374 is rigidly attached to and extends downward from
an edge 362 of the polishing head 360 to form a chamber 332 between
the floor 372 and the polishing head 360. The chamber 332 may be
connected with a pressurizing source (not shown) to provide a
pressurizing fluid to the chamber 332.
[0060] As shown in FIG. 13, the chamber 332 may be pressurized
causing the floor 372 to deflect into a downward dome shape,
similar to floors 172 and 272. The pressure within the chamber 332
does not need to be changed frequently. Therefore, it may be
adjusted manually when the polishing head assembly 330 is mounted
on the polishing apparatus 100. In some embodiments, the cap 370
may be used to retrofit an existing polishing head without the need
to drill holes through the existing head for passage of air or
fluid through the spindle and rotary unions.
[0061] Similar to the floors 172 and 272, the floor 372 of the cap
370 is adapted to temporarily deflect in a direction that is
perpendicular to the polishing surface as the polishing pressure P
is increased. The cap is not permanently deflected or deformed by
the pressure. The floor 372 transitions from a pressurized
deflected or downwardly curved shape to a flat shape that is
substantially parallel with a bottom surface of the polishing head
360, and finally to a upwardly curved or convex shape.
[0062] As shown in FIG. 14, under a given or predetermined
polishing pressure P, the floor 372 is deflected to be
substantially flat, resulting in a removal profile that is also
substantially flat. As shown in FIG. 15, reducing the polishing
pressure 0.9 P causes both the floor 372 and the removal profile to
become downwardly curved.
[0063] Stopper ring 380 and center stopper 382 limit the upward
deflection of the floor 372. The stopper ring 380 is spaced inward
from the outer circumference and is annular in shape. The center
stopper 382 is co-axially aligned with the polishing head 360, the
cap 370, and the stopper ring 380. With additional reference to
FIG. 12, the stopper ring 380 and the center stopper 382 extends
from the bottom surface of the polishing head 360 to an inner or
top surface of the floor 372. The height of the stopper ring 380
and the center stopper 382 are substantially equivalent to the
between the polishing head 360 and the floor 372.
[0064] With reference to FIGS. 15-18, the height of each the
stopper ring 380 and the center stopper 382 may be adjusted to vary
the deflection shape of the floor 372.
[0065] As shown in FIG. 16, reducing the height of the center
stopper 382 and increasing the polishing pressure 1.3 P causes both
the shape of the floor 372 and the removal profile to become
w-shaped. As shown in FIG. 17, reducing the height of the stopper
ring 380 and increasing the polishing pressure 1.3 P causes both
the shape of the floor 372 and the removal profile to become
m-shaped. As shown in FIG. 18, reducing the height of both the
stopper ring 380 and the center stopper 382, and increasing the
polishing pressure 1.1 P causes both the shape of the floor 372 and
the removal profile to become domed. Thus, a change in polishing
pressure provides the operator with the ability to adjust the
polished shape of the wafer W.
[0066] Finite element simulation results illustrating this
embodiment's ability to modulate contact pressure profiles for
adjusting doming and w-shape wafer profiles are shown in FIGS. 19
and 20. FIG. 19 is a doming correction graph that plots the
correlation of the contact pressure and the radius in accordance
with the embodiment above is shown. FIG. 20 is a negative w-factor
correction graph that plots the correlation of contact pressure and
the radius in accordance with the embodiment above is shown.
[0067] With reference to FIG. 21, another embodiment of the
polishing head assembly 430 is adapted to adjust pressure
distribution to a wafer during the polishing process for
controlling or minimizing doming, dishing, and w-shape cross
section of the wafer.
[0068] The polishing head assembly 430 has a polishing head 460, a
cap 470, and a center stopper 480. The cap 470 includes a floor 472
that is rigidly attached to edges 462 of the polishing head 460
with screws 464 and extends across the edges to form a chamber 432
between the floor and the polishing head. In other embodiments, an
adhesive is used to attach the floor 472 to the edges 462 of the
polishing head 460, instead of screws 464. The floor 472 is
substantially flat in an initial or un-deflected state. The chamber
432 is connected with a first pressurizing source FS through a
chamber passageway 466 and connector 486 to provide a pressurizing
fluid to the chamber 432 that may cause the floor 472 to deflect
into a downward dome shape, similar to floors 172, 272, and
372.
[0069] Similar to the floors 172, 272, and 372, the floor 472 of
the cap 470 is adapted to temporarily deflect in a direction that
is perpendicular to the polishing surface as the polishing pressure
is increased. The cap 470 is not permanently deflected or deformed
by the pressure. The floor 472 has the ability to transition from a
pressurized deflected or downwardly curved shape to a flat shape
that is substantially parallel with a bottom surface of the
polishing head 460, and finally to an upwardly curved or convex
shape based on the amount of pressurizing fluid supplied to the
chamber 432.
[0070] Under a given or predetermined polishing pressure P, the
floor 472 is deflected to be substantially flat, resulting in a
removal profile that is also substantially flat. Reducing the
polishing pressure 0.9 P causes both the floor 472 and the removal
profile to become downwardly curved.
[0071] The center stopper 480 includes a stop 482 connected with
inflatable bellows 484. The bellow 484 is connected with and
extends into the chamber 432 from the polishing head 460. The
height of the stop 482 is adjusted by increasing or decreasing the
pressure within the bellows 484, which is connected with a second
pressurizing source SS through a center passageway 468 and a
connector 488. Adjustment of the pressure within the bellows 484
may either limit the upward deflection of the floor 472 or to
deflect the floor 472 outward. The first and second pressurizing
sources FS and SS may be connected through a controller 490 to
respective connectors 486 and 488. In some embodiments, first and
second pressurizing sources FS and SS are the same pressurizing
source and are connected with the respective connectors 486 and 488
through the controller 490, which may include a divider and control
valves (not shown). In some embodiments, the polishing head
assembly 430 does not include a center stopper 480. In these
embodiments, the first pressurizing source FS may be supplied to
the chamber 432 through the center of the polishing head 460.
[0072] The center stopper 480 is co-axially aligned with both the
polishing head 460 and the cap 470. During operation, the center
stopper 482 may extend from the bottom surface of the polishing
head 460 to an inner or top surface of the floor 472, such that the
height of the center stopper 480 is substantially equivalent to the
chamber between the polishing head 460 and the floor 472.
[0073] In a method of one embodiment, a polishing process of a
wafer is controlled by adjustment of the polishing pressure used in
the polishing apparatus 100 to change the shape of a polishing head
assembly to regulate the polished shape of a wafer W. In some
embodiments, the polishing apparatus is a single side polisher. In
another embodiment, the polishing pressure is regulated by a
controller before or during the polishing process.
[0074] The method includes providing a polishing apparatus with a
turntable for rotating a polishing pad in relation to the wafer and
a polishing head assembly with a cap attached to a polishing side
of a polishing head. The cap is moved with respect to the wafer to
cause a polishing pressure from the wafer to react against the cap.
The cap is deflected with respect to the polishing head. A liquid
may be applied to the cap to wet it, such that the wafer is held in
place, against the cap, by surface tension when the wafer is placed
against it. The liquid on the lower surface of the cap can be
squeezed to almost zero film thickness to retain the wafer by
surface tension.
[0075] The polishing pressure reacting against the cap is adjusted
to regulate the deflection of the cap for improving flatness of the
polished surface. A surface of the wafer is polished by causing
movement between the wafer and the polishing pad to form a polished
surface on the wafer. An internal pressure within a chamber between
the polishing head and the cap may be adjusted to regulate
deflection of the cap with respect to the wafer for improving
flatness of the polished surface.
[0076] Changing the shape of the cap from dish to dome or vice
versa changes the material removal profile of the wafer and thus,
changes the shape of the polished wafer. A domed head will cause
more material removal in the center and thus make the wafer
thickness profile dished relative to its thickness profile before
polishing. While a dished head will remove more material on the
edges of the wafer making the wafer domed relative to its thickness
profile before polishing. In some embodiments, the shape of the
polishing head may be changed by adding a low stiffness cap to the
bottom of the existing head and then regulating the polishing
pressure to deflect the cap to change its shape.
[0077] The embodiments described herein provide the ability to
modulate the polishing head for doming, dishing, and +/-w-shape to
enable an efficient and economical polishing method of processing
semiconductor wafers. The method improves wafer yield and process
capability, while reducing product tolerances and the time needed
for maintenance associated with the replacement of the polishing
pads and templates mounted on the single side polishing head.
[0078] When introducing elements of the present invention or the
embodiment(s) thereof, the articles "a", "an", "the" and "said" are
intended to mean that there are one or more of the elements. The
terms "comprising", "including" and "having" are intended to be
inclusive and mean that there may be additional elements other than
the listed elements. The use of terms indicating a particular
orientation (e.g., "top", "bottom", "side", "down", "up", etc.) is
for convenience of description and does not require any particular
orientation of the item described.
[0079] As various changes could be made in the above constructions
and methods without departing from the scope of the invention, it
is intended that all matter contained in the above description and
shown in the accompanying drawing[s] shall be interpreted as
illustrative and not in a limiting sense.
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