U.S. patent application number 09/886157 was filed with the patent office on 2001-10-25 for apparatus, backing plate, backing film and method for chemical mechanical polishing.
Invention is credited to Kato, Nobuhiro, Watanabe, Tomoharu.
Application Number | 20010034192 09/886157 |
Document ID | / |
Family ID | 17693714 |
Filed Date | 2001-10-25 |
United States Patent
Application |
20010034192 |
Kind Code |
A1 |
Watanabe, Tomoharu ; et
al. |
October 25, 2001 |
Apparatus, backing plate, backing film and method for chemical
mechanical polishing
Abstract
A polishing apparatus has a guide (5) to be pressed against a
polishing cloth (7) when polishing an object (1). Within the guide,
a ring (3) is arranged between a backing plate (4) and a backing
film (2). When the guide and polishing cloth are rotated to rub
with each other, force of the periphery of the object of pressing
the polishing cloth drops. The ring prevents such a force drop,
thereby equalizing polishing rates over a surface of the object.
Also provided is a polishing method applied to the polishing
apparatus.
Inventors: |
Watanabe, Tomoharu;
(Mie-ken, JP) ; Kato, Nobuhiro; (Mie-ken,
JP) |
Correspondence
Address: |
FINNEGAN, HENDERSON, FARABOW, GARRETT &
DUNNER LLP
1300 I STREET, NW
WASHINGTON
DC
20005
US
|
Family ID: |
17693714 |
Appl. No.: |
09/886157 |
Filed: |
June 22, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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09886157 |
Jun 22, 2001 |
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09392749 |
Sep 9, 1999 |
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6276999 |
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Current U.S.
Class: |
451/41 ; 451/36;
451/533 |
Current CPC
Class: |
B24B 37/30 20130101 |
Class at
Publication: |
451/41 ; 451/36;
451/533 |
International
Class: |
B24B 001/00 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 7, 1998 |
JP |
P10-285606 |
Claims
What is claimed is:
1. A polishing apparatus for polishing an object, comprising: a
polishing cloth having a flat bottom face that is moved in a plane
containing the bottom face and a top face that is in parallel with
the bottom face, a part of the top face being pressed against a
face of the object to be polished; a guide for surrounding the
periphery of the object, the guide being pressed against the top
face of said polishing cloth; and a backing structure for pressing
an area of the object that is within a predetermined distance from
said guide stronger than a remaining area of the object against
said polishing cloth.
2. The polishing apparatus of claim 1, wherein the predetermined
distance is in the range of 5 mm to 30 mm.
3. The polishing apparatus of claim 1, wherein said backing
structure comprises: a backing plate that is a flat disk having top
and bottom faces that are in parallel with each other; a
cylindrical ring having top and bottom faces that are in parallel
with each other and are defined by concentric outer and inner
circles, a diameter of the outer circle being equal to a diameter
of said backing plate, a center of the top face of said ring
agreeing with a center of the bottom face of said backing plate;
and a backing film whose hardness is lower than that of said
backing plate, having a flat disk shape having the same diameter as
said backing plate and top and bottom faces that are in parallel
with each other, a center of the top face of said backing film
agreeing with a center of the bottom face of said ring.
4. The polishing apparatus of claim 3, wherein: a height of said
ring is in the range of 30 .mu.m to 60 .mu.m; and a difference
between the diameters of the outer and inner circles of said ring
is within the range of 10 mm to 60 mm.
5. The polishing apparatus of claim 1, wherein said backing
structure comprises: a backing plate composed of a disk and a
cylindrical ring, the disk having top and bottom faces that are in
parallel with each other, the ring having top and bottom faces that
are in parallel with each other and are defined by concentric outer
and inner circles, a diameter of the outer circle being equal to a
diameter of the disk, a center of the top face of the ring agreeing
with a center of the bottom face of the disk; and a backing film
whose hardness is lower than that of said backing plate, having a
flat disk shape having the same diameter as the outer circle of the
ring and top and bottom faces that are in parallel with each other,
a center of the top face of said backing film agreeing with a
center of the bottom face of the ring.
6. The polishing apparatus of claim 5, wherein: a height of the
ring is in the range of 30 .mu.m to 60 .mu.m; and a difference
between the diameters of the outer and inner circles of the ring is
within the range of 10 mm to 60 mm.
7. The polishing apparatus of claim 1, wherein said backing
structure comprises: a backing plate that is a disk having top and
bottom faces that are in parallel with each other; and a backing
film whose hardness is lower than that of said backing plate,
composed of a disk film and a ring film, the disk film having top
and bottom faces that are in parallel with each other, the ring
film having top and bottom faces that are in parallel with each
other and are defined by concentric outer and inner circles, a
diameter of the outer circle being equal to a diameter of the disk
film, a center of the bottom face of the ring film agreeing with a
center of the top face of the disk film, the top face of the ring
film being in contact with said backing plate.
8. The polishing apparatus of claim 7, wherein: a thickness of the
ring film is in the range of 30 .mu.m to 60 .mu.m; and a difference
between the diameters of the outer and inner circles of the ring
film is within the range of 10 mm to 60 mm.
9. The polishing apparatus of claim 7, wherein a hardness of the
ring film is equal to that of the disk film.
10. A backing plate comprising: a flat disk having top and bottom
faces that are in parallel with each other; and a cylindrical ring
having top and bottom faces that are in parallel with each other
and are defined by concentric outer and inner circles, a diameter
of the outer circle being equal to a diameter of said disk, a
center of the top face of said ring agreeing with a center of the
bottom face of said disk.
11. The backing plate of claim 10, wherein: a height of said ring
is in the range of 30 .mu.m to 60 .mu.m; and difference between the
diameters of the outer and inner circles of said ring is with the
range of 10 mm to 60 mm.
12. A backing film comprising: a flat disk film having top and
bottom faces that are in parallel with each other; and a ring film
having top and bottom faces that are in parallel with each other
and are defined by concentric outer and inner circles, a diameter
of the outer circle being equal to a diameter of said disk film, a
center of the bottom face of said ring film agreeing with a center
of the top face of said disk film.
13. The backing film of claim 12, wherein: a thickness of said ring
film is in the range of 30 .mu.m to 60 .mu.m; and a difference
between the diameters of the outer and inner circles of said ring
film is with the range of 10 mm to 60 mm.
14. The backing film of claim 12, wherein a hardness of said ring
film is equal to that of said disk film.
15. A method of polishing an object, comprising steps of: (a)
making the object come in contact with a backing structure and a
polishing cloth while a guide being away from the polishing cloth
by a gap; (b) pressing the object with the backing structure and
the polishing cloth so that a peripheral area of the object is
pressed stronger than a remaining area thereof, and at the same
time pressing the guide against the polishing cloth; and (c) moving
the polishing cloth with respect to the object.
16. The method of claim 15, wherein the gap is in the range of 0.07
mm to 0.28 mm.
17. The method of claim 15, wherein a boundary between the
peripheral area of the object and the remaining area thereof is
away from the guide by a constant distance that is within the range
of 5 mm to 30 mm.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a polishing apparatus and a
polishing method, and particularly, to the apparatus and the method
for polishing semiconductor wafers based on a chemical mechanical
polishing (CMP) technique. The present invention also relates to a
backing plate and a backing film used by the polishing
apparatus.
[0003] 2. Description of the Related Art
[0004] FIG. 1A is a top view showing a polishing apparatus
according to a related art and FIG. 1B is a side view showing the
same. The polishing apparatus is used for semiconductor device
manufacturing for polishing and planarizing the steps in the
surface of a semiconductor wafer due to devices and
interconnections formed thereon. A disk-like surface plate 8 has a
shaft 10 rotated by a driver (not shown). A polishing cloth 7 made
of, for example, polyurethane foam is attached to the top of the
surface plate 8. A port 11 supplies abrasive 12 onto the polishing
cloth 7. A wafer base 13 is arranged above the surface plate 8. The
bottom of the wafer base 13 holds a wafer. The wafer base 13 has a
shaft 9, which is connected to a pressing unit (not shown) and a
rotating unit (not shown). The pressing unit presses the wafer
against the polishing cloth 7. The rotating unit rotates the wafer
in the same direction as the rotating direction of the surface
plate 8.
[0005] FIG. 2 is a sectional view showing the wafer base 13 and the
vicinity thereof. The wafer base 13 is made of a head 6, backing
plate 4, a backing film 2, and a guide 5. The head 6 is driven by
the shaft 9 and rotates above the surface plate 8. The head 6 is
pushed down by the pressing unit through the shaft 9. The head 6
uniformly presses the wafer 1 against the polishing cloth 7 through
the backing plate 4. To flatly polish the wafer 1, an interface of
the backing plate 4 with the backing film 2 is processed flat. The
backing film 2 is resilient so that the backing plate 4 may evenly
press the wafer 1 against the polishing cloth 7. Even if dust is
present between the wafer 1 and the backing film 2, the backing
film 2 is flexible to contain the dust so that a surface of the
wafer 1 to be polished may evenly be pushed against the polishing
cloth 7. The guide 5 prevents the wafer 1 from moving away from the
backing film 2. An end face of the guide 5 tat faces the polishing
cloth 7 is higher than the polished surface of the wafer 1 with
respect to the polishing cloth 7. When the wafer 1 is set on the
polishing cloth 7, the end face of the guide 5 is away from the
polishing cloth 7. When the wafer 1 is pressed against the
polishing cloth 7, the backing film 2 and polishing cloth 7 are
compressed and the end face of the guide 5 comes in contact with
and presses the polishing cloth 7.
[0006] With this arrangement, the port 11 feeds the abrasive 12
onto the polishing cloth 7 that is rotated. The wafer 1 set under
the backing film 2 is rotated and pushed by the wafer base 13
toward the polishing cloth 7 so that the surface of the wafer 1
contacting with tie polishing cloth 7 is polished.
[0007] Polishing rates and their uniformity on a thermal oxidation
film formed on the surface of an 8-inch silicon wafer will be
explained. The wafer has LSIs formed on the surface thereof. The
size of each LSI is dependent on a step-and-repeat technique used
to form the LSIs and is usually 1-cm square. To improve the yield
and quality of LSIs on each wafer, polishing rates within the wafer
must be as uniform as possible.
[0008] FIG. 3 shows polishing rates measured at different
measurement points on a wafer. The wafer is a silicon wafer of 200
mm in diameter and has a thermal oxidation film to be polished with
the wafer being pressed against the polishing cloth 7 and the guide
5 being away from the polishing cloth 7. The measurement points 1
to 7 are set along a straight line passing through the notch and
center of the wafer and are away from the center of the wafer by 96
mm, 80 mm, 40 mm, 0 mm, 40 mm, 80 mm, and 96 mm, respectively.
Namely, the measurement points 1 and 7 are at the periphery of the
wafer, and the measurement point 4 is at the center thereof.
Polishing rates measured at the points 1 and 7 are each about 1.7
times greater than that measured at the point 4.
[0009] FIG. 4 shows polishing rates measured at different
measurement points with the guide 5 being pressed against the
polishing cloth 7 when polishing a thermal oxidation film formed on
a silicon; wafer of 200 mm in diameter. The measurement points 1 to
7 are the same as those of FIG. 3. Polishing rates at the
peripheral measurement points 1 and 7 are about 20% smaller than
those at the other measurement points. Compared with FIG. 3, FIG. 4
shows an improvement in the uniformity of polishing rates on the
wafer, and therefore, it can be said that pressing the guide 5
against the polishing cloth 7 is advantageous. This, however, may
deteriorate the quality of LSIs formed at the periphery of the
wafer below criteria because the peripheral polishing rates are
about 20% smaller than the others.
SUMMARY OF THE INVENTION
[0010] The reason why the peripheral polishing rates are lower than
the others will be examined.
[0011] FIG. 5 is a partly see-through top view showing essential
parts of a polishing apparatus. A polishing cloth 7 is circular,
600 mm in diameter, and about 4 mm in thickness. When polishing a
wafer 1, the polishing cloth 7 is rotated counterclockwise at about
30 rpm. A guide 5 is a cylinder having an inner diameter of about
202 mm. When polishing the wafer 1, the guide 5 is rotated
counterclockwise at about 30 rpm. The wafer 1 is circular, 200 mm
in diameter, and about 0.8 mm in thickness. When being polished,
the wafer 1 is pushed against a backing film 2 (not shown) that
revolves with the guide 5. At this time, the wafer 1 slightly
slides on the backing film 2 and rotates counterclockwise at a
speed slower than 30 rpm. Under this situation, the wafer 1 is
shifted toward a right part of the ring 5, and a gap 16 of about 2
mm is formed between the guide 5 and the left edge of the wafer 1.
In connection with this, two cases will be examined.
[0012] (1) A first case is that the guide 5 is away from the
polishing cloth 7 even after the wafer 1 is pressed against the
polishing cloth 7. FIGS. 6A, 6B, and 6C are sectional views taken
along a line I-I of FIG. 5. In FIG. 6A, the wafer 1 is not pressed
against the polishing cloth 7, and the polishing cloth 7 and a
wafer base 13 are not rotated yet. A gap 15 between the guide 5 and
the polishing cloth 7 is set to be in the range of 0.3 mm to 0.5 mm
so that the guide 5 is away from the polishing cloth 7 after the
wafer 1 is pressed against the polishing cloth 7 and so that the
wafer 1 may not escape from the guide 5 even when the polishing
cloth 7 and wafer base 13 are rotated.
[0013] In FIG. 6B, a shaft 9 is thrust to press the wafer 1 against
the polishing cloth 7. The wafer 1 compresses the polishing cloth
7, and the backing film 2 on the wafer 1 is also compressed
evenly.
[0014] In FIG. 6C, the polishing cloth 7 and wafer base 13 are
rotated from the condition of FIG. 6B. The polishing cloth 7 moves
rightward in FIG. 6C, and therefore, the wafer 1 is shifted toward
the right part of the guide 5 and the polishing cloth 7 at the edge
of the wafer 1 is deformed due to rotation. In particular, the
polishing cloth 7 at the left edge of the wafer 1 rises and is
compressed further than FIG. 6B. At this time, the left edge of the
wafer 1 is pushed more strongly than the remaining part thereof by
the polishing cloth 7, to increase a polishing rate at tie left
edge.
[0015] The reason why polishing rates at the periphery of a wafer
is about 1.7 times greater than those at the other parts in FIG. 3
is because the periphery of the wafer is pushed more strongly than
the other parts by the polishing cloth 7 and because the wafer 1 is
rotated by the wafer base 13.
[0016] (2) A second case is that the guide 5 is pressed against the
polishing cloth 7 when the wafer 1 is pushed to the polishing cloth
7. FIGS. 7A, 7B, and 7C are sectional views taken along the line
I-I of FIG. 5. In FIG. 7A, the wafer 1 is not pressed against the
polishing cloth 7, and the polishing cloth 7 and wafer base 13 are
not rotated yet. A gap 15 between the guide 5 and the polishing
cloth 7 is set to be in the range of 0.21 mm to 0.28 mm so that the
guide 5 may be pressed against the polishing cloth 7 when the wafer
1 is pressed against the polishing clot 7 and so that the wafer 1
may not escape from the guide 5 when the polishing cloth 7 and
wafer base 13 are rotated.
[0017] In FIG. 7B, the shaft 9 is thrust to press the wafer 1
against the polishing cloth 7. The polishing cloth 7 is compressed
by the wafer 1, and tie backing film 2 on the wafer 1 is also
compressed. The guide 5 is pressed against the polishing cloth 7.
If the thrust on the shaft 9 is the same as that of FIG. 6B, force
of the wafer 1 of pushing the polishing cloth 7 becomes smaller
than that of FIG. 6B when the guide 5 is pressed against the
polishing cloth 7. The uniformity of the force of the wafer 1 of
pushing the polishing cloth 7 of FIG. 7B is substantially the same
as that of FIG. 6B because the gap 15 between the guide 5 and the
polishing cloth 7 of FIG. 7A is so set. If the gap 15 is narrower,
the force of the guide 5 of pressing the polishing cloth 7 will be
stronger so that a deformation of the polishing cloth 7 may reach
the wafer 1 to deteriorate the uniformity of the force of the wafer
1 of pressing the polishing cloth 7.
[0018] In FIG. 7C, the polishing cloth 7 and wafer base 13 are
rotated from the state of FIG. 7B. The polishing cloth 7 moves
rightward, and therefore, the wafer 1 is shifted toward the right
part of the guide 5. At this time, the polishing cloth 7 at the
edge of the wafer 1 is deformed by rotation. The polishing cloth 7
at the left edge of a left part of the guide 5 rises and is
compressed further than FIG. 7B. On the other hand, the polishing
cloth 7 at the right edge of the left part of the guide 5 is
stretched. The stretched area of the polishing cloth 7 reaches the
wafer 1. Force of the polishing cloth 7 of pushing the wafer 1 in
the stretched area is weaker than that in the remaining area, and
polishing rates in the stretched area are smaller than the
others.
[0019] The reason why polishing rates at the periphery of a wafer
are about 20% smaller than the others in FIG. 4 is because the
force of the polishing cloth 7 of pushing the wafer is small at the
periphery of the wafer and because the wafer is rotated by the
wafer base 13.
[0020] The two cases mentioned above show that force applied to the
surface of a wafer is uniform when the wafer is simply pressed
against the polishing cloth 7 and becomes uneven when the wafer is
rubbed with the polishing cloth 7.
[0021] An object of the present invention is to equally distribute
force, which is not present when the wafer 1 is pressed against the
polishing cloth 7 and is produced when the pressed wafer 1 is
rubbed with the polishing cloth 7, over the surface of the wafer
1.
[0022] Another object of the present invention is to equalize force
on the surface of the wafer 1, thereby equalizing polishing rates
on the wafer 1.
[0023] Still another object of the present invention is to
uniformly polish LSIs formed on a wafer, equalize the quality of
the LSIs, and improve the yield of the LSIs.
[0024] To accomplish the objects, three ideas are studied:
[0025] (1) A first idea is to use harder material for the polishing
cloth 7 so that the polishing cloth 7 may not be deformed due to
pressing force and friction. If the polishing cloth 7 is hard, it
may unevenly contact and polish a wafer. Accordingly, the first
idea is inadequate. The polishing cloth 7 must be soft to some
extent.
[0026] (2) A second idea is that there will be an optimum value for
the gap 15 between the guide 5 and the polishing cloth 7 in FIGS.
6A and 7A and that the optimum value will be between the gap 15 of
FIG. 6A and that of FIG. 7A. If there is such an optimum gap, force
with which the guide 5 pushes the polishing cloth 7 will be smaller
than that of FIG. 7C. This force will vary, and therefore, a
strongly compressed area of the polishing cloth 7 will move between
under the wafer 1 and under the guide 5. This fluctuates polishing
rates at the periphery of the wafer 1. Accordingly, the second idea
is inadequate.
[0027] (3) A third idea is to enlarge the wafer base 13 with
respect to the size of the wafer 1 so that the stretched area of
the polishing cloth 7 of FIG. 7C may not reach the wafer 1. This,
however, produces a highly compressed area not only under the guide
5 but also under the wafer 1. There will be an idea to adjust the
edge of the stretched area of the polishing cloth 7 to the edge of
the wafer 1. Adjusting the whole edge of the wafer 1 to the edge of
the stretched area of the polishing cloth 7 is very difficult. In
addition, a play between the guide 5 and the wafer 1 will increase.
Accordingly, the third idea is inadequate.
[0028] In order to accomplish the objects, the present invention
is, first, characterized by that a polishing apparatus for
polishing an object, comprises a polishing cloth having a flat
bottom face that is moved in a plane containing the bottom face and
a top face that is in parallel with the bottom face, a part of the
top face being pressed against a face of the object to be polished
and, a guide for surrounding the periphery of the object, the guide
being pressed against the top face of the polishing cloth and, a
backing structure for pressing an area of the object that is within
a predetermined distance from the guide stronger than the remaining
area of the object against the polishing cloth. Here, the backing
structure consists of a backing plate and a backing film.
[0029] A pressing unit thrusts the backing structure to press the
object against the polishing cloth. A distribution of force with
which the object pushes the polishing cloth is dependent on a
distribution of the distance from the guide. The polishing rate is
dependent on the force with which the object pushes the polishing
cloth. Namely, when the polishing rate is dependent on the
distribution of the distance from the guide, changing the
distribution of the force equalizes polishing rates on the object.
Generally, the guide is pressed against the polishing cloth and the
guide and polishing cloth are rotated, force at the periphery of
the object of pressing the polishing cloth drops. This force drop
is supplemented by the backing structure of the present invention
to equalize force of the object on the polishing cloth.
[0030] Moreover, preferably, the predetermined distance according
to the first feature of the present invention is in the range of 5
mm to 30 mm. The polishing rates on the object become uniform.
[0031] Moreover, preferably, the backing structure according to the
first feature of the present invention comprises a backing plate
that is a flat disk having top and bottom faces that are in
parallel with each other and, a cylindrical ring having top and
bottom faces that are in parallel with each other and are defined
by concentric outer and inner circles, the diameter of the outer
circle being equal to the diameter of the backing plate, the center
of the top face of the ring agreeing with the center of the bottom
face of the backing plate and, a backing film whose hardness is
lower than that of the backing plate, having a flat disk shape
having the same diameter as the backing plate and top and bottom
faces that are in parallel with each other, the center of the top
face of the backing film agreeing with the center of the bottom
face of the ring.
[0032] Since the backing structure has a changing thickness
depending on distances from the guide, a distribution of force with
which the object pushes the polishing cloth is dependent on a
distribution of the thickness of the backing structure. Namely, the
distribution of the thickness of the backing structure determines a
distribution of polishing rates on the object. Generally, polishing
rates on the object are dependent on distances from the guide, and
therefore, the changing thickness of the backing structure that are
dependent on distances from the guide equalizes polishing rates on
the object. The ring provides the same effect as the thickness
change of the backing structure. The thickness and width of the
ring are determined based on the type of an object to polish.
Objects to be polished by the apparatus of the present invention
need different abrasives and polishing rates and have different
coefficients of friction with respect to the polishing cloth.
Therefore, force on the polishing cloth and torque to rotate the
polishing cloth depend on an object to polish. Namely, a force drop
at the periphery of an object and an area where the force drop
occurs are dependent on the object. This is the reason why the
thickness and width of the ring must be determined based on the
properties of an object to polish.
[0033] The present invention is capable of equalizing force, which
is not present when a wafer is set on the polishing cloth and is
produced when the wafer is rubbed with the polishing cloth, on the
surface of the wafer, thereby equalizing polishing rates over the
wafer. The present invention is capable of uniformly polishing LSIs
formed on a wafer, thereby equaling the quality of the LSIs and
improving the yield thereof. The present invention is capable of
improving the polishing speed of each wafer, thereby shortening a
polishing time of wafers, improving the productivity of LSIs cut
from the wafers, and reducing the production cost of the LSIs.
[0034] Moreover, preferably, the height of the ring according to
the first feature of the present invention is in the range of 30
.mu.m to 60 .mu.m. And the difference between the diameters of the
outer and inner circles of the ring is within the range of 10 mm to
60 mm. The polishing rates of the object become uniform.
[0035] Moreover, preferably, the backing structure according to the
first feature of the present invention comprises a backing plate
composed of a disk and a cylindrical ring, the disk having top and
bottom faces that are in parallel with each other, the ring having
top and bottom faces that are in parallel with each other and are
defined by concentric outer and inner circles, the diameter of the
outer circle being equal to the diameter of the disk, the center of
the top face of the ring agreeing with the center of the bottom
face of the disk, and a backing film whose hardness is lower than
that of the backing plate, having a flat disk shape having the same
diameter as the outer circle of the ring and top and bottom faces
that are in parallel with each other, the center of the top face of
the backing film agreeing with the center of the bottom face of the
ring. Namely, partly changing the thickness of the backing plate
provides the effect of partly changing the thickness of the backing
structure.
[0036] Moreover, preferably, the backing structure according to the
first feature of the present invention comprises a backing plate
that is a disk having top and bottom faces that are in parallel
with each other, and a backing film whose hardness is lower than
that of the backing plate, composed of a disk film and a ring film,
the disk film having top and bottom faces that are in parallel with
each other, the ring film having top and bottom faces that are in
parallel with each other and are defined by concentric outer and
inner circles, the diameter of the outer circle being equal to the
diameter of the disk film, the center of the bottom face of the
ring film agreeing with the center of the top face of the disk
film, the top face of the ring film being in contact with the
backing plate. Namely, partly changing the thickness of the backing
film provides the effect of partly changing the thickness of the
backing structure. Preferably, the hardness of the ring film
according to the first feature of the present invention is equal to
that of the disk film. The backing film is capable of
monolithically forming.
[0037] The second feature of the present invention is characterized
by that a backing plate comprises a flat disk having top and bottom
faces that are in parallel with each other, and a cylindrical ring
having top and bottom faces that are in parallel with each other
and are defined by concentric outer and inner circles, the diameter
of the outer circle being equal to the diameter of the disk, the
center of the top face of the ring agreeing with the center of the
bottom face of the disk. When the guide is pressed against the
polishing cloth and the guide and polishing cloth are rotated,
force at the periphery of the object of pressing the polishing
cloth drops. This force drop is supplemented by the backing plate
of the present invention to equalize force of the object on the
polishing cloth.
[0038] Moreover, preferably, the height of the ring according to
the second feature of the present invention is in the range of 30
.mu.m to 60 .mu.m. And the difference between the diameters of the
outer and inner circles of the ring is within the range of 10 mm to
60 mm. The polishing rates on the object become uniform.
[0039] The third feature of the present invention is characterized
by that a backing film comprises a flat disk film having top and
bottom faces that are in parallel with each other, and a ring film
having top and bottom faces that are in parallel with each other
and are defined by concentric outer and inner circles, the diameter
of the outer circle being equal to the diameter of the disk film,
the center of the bottom face of the ring film agreeing with the
center of the top face of the disk film. When the guide is pressed
against the polishing cloth and the guide and polishing cloth are
rotated, force at the periphery of the object of pressing the
polishing cloth drops. This force drop is supplemented by the
backing film of the present invention to equalize force of the
object on the polishing cloth.
[0040] Moreover, preferably, the thickness, of the ring film
according to the third feature of the present invention is in the
range of 30 .mu.m to 60 .mu.m. And the difference between the
diameters of the outer and inner circles of the ring film is within
the range of 10 mm to 60 mm. The polishing rates on the object
become uniform.
[0041] Moreover, preferably, the hardness of the ring film
according to the third feature of the present invention is equal to
that of the disk film. The force at the periphery of the object of
pressing the polishing cloth easily becomes greater.
[0042] The fourth feature of the present invention is characterized
by that a method of polishing an object, comprises the steps of (a)
making the object come in contact with a backing structure and a
polishing cloth while a guide being away from the polishing cloth
by a gap, and (b) pressing the object with the backing structure
and polishing cloth so that a peripheral area of the object is
pressed stronger than the remaining area thereof, and at the same
time, pressing the guide against the polishing cloth, and (c)
moving the polishing cloth with respect to the object. The guide is
properly pressed against the polishing cloth. When the guide and
polishing cloth are rotated, a drop of the force at the periphery
of the object of pressing the polishing cloth is supplemented by
the step of pressing the object of the present invention to
equalize force of the object on the polishing cloth.
[0043] Moreover, preferably, the gap film according to the fourth
feature of the present invention is in the range of 0.07 mm to 0.28
mm. The guide is properly pressed against the polishing cloth.
[0044] Moreover, preferably, a boundary between the peripheral area
of the object and the remaining area thereof according to the
fourth feature of the present invention is away from the guide by a
constant distance that is within the range of 5 mm to 30 mm. When
the guide and polishing cloth are rotated, a drop of the force at
the only periphery of the object of pressing the polishing cloth is
supplemented.
[0045] Other and further objects and features of the present
invention will become obvious upon an understanding of illustrative
embodiments about to be described in connection with the
accompanying drawings or will be indicated in the appended claims,
and various advantages not referred to herein will occur to one
skilled in the art upon employing of the invention in practice.
BRIEF DESCRIPTION OF THE DRAWINGS
[0046] FIGS. 1A and 1B are top and side views showing a polishing
apparatus according to a related art;
[0047] FIG. 2 is a sectional view showing the polishing apparatus
of the related art;
[0048] FIGS. 3 and 4 are graphs showing polishing rates measured at
different measurement points on a thermal oxidation film of a wafer
polished with the polishing apparatus of the related art;
[0049] FIG. 5 is a partly see-through top view showing essential
parts of a polishing apparatus;
[0050] FIGS. 6A and 7A are sectional views showing no-press,
no-rotation states of the polishing apparatus of the related
art;
[0051] FIGS. 6B and 7B are sectional views showing pressed
no-rotation states of the polishing apparatus of the related
art;
[0052] FIGS. 6C and 7C are sectional views showing pressed rotating
states of the polishing apparatus of the related art;
[0053] FIG. 8A is a sectional view showing a polishing apparatus
according to an embodiment of the present invention;
[0054] FIGS. 8B and 8C are sectional and top views showing a ring
of the polishing apparatus of FIG. 8A;
[0055] FIG. 9A is a sectional view showing a no-press, no-rotation
state of the polishing apparatus of the present invention;
[0056] FIG. 9B is a sectional view showing a pressed no-rotation
state of the polishing apparatus of the present invention;
[0057] FIG. 9C is a sectional view showing a pressed rotating state
of the polishing apparatus of the present invention;
[0058] FIG. 10A is a sectional view showing the vicinity of a wafer
base of a polishing apparatus according to a first modification of
the present invention;
[0059] FIGS. 10B and 10C are sectional and bottom views showing a
backing plate of the polishing apparatus of FIG. 10A;
[0060] FIG. 11A is a sectional view showing the vicinity of a wafer
base of a polishing apparatus according to a second modification of
the present invention;
[0061] FIGS. 11B and 11C are sectional and top views showing a
backing film of the polishing apparatus of FIG. 11A;
[0062] FIG. 12A is a sectional view showing the vicinity of a wafer
base of a polishing apparatus according to a third modification of
the present invention;
[0063] FIGS. 12B and 12C are sectional and bottom views showing a
backing plate of the polishing apparatus of FIG. 12A;
[0064] FIG. 13A is a sectional view showing the vicinity of a wafer
base of a polishing apparatus according to a fourth modification of
the present invention;
[0065] FIGS. 13B and 13C are sectional and top views showing a
backing film of the polishing apparatus of FIG. 13A;
[0066] FIG. 14 is a graph showing polishing rates measured at
different measurement points on a thermal oxidation film of a wafer
polished with the polishing apparatus of the present invention;
[0067] FIG. 15A is a sectional view showing a wafer with patterns
covered with a thermal oxidation film on which polishing rates are
measured;
[0068] FIG. 15B is a graph showing polishing rates measured at
different measurement points on the wafer of FIG. 15A polished with
the polishing apparatus of the present invention;
[0069] FIGS. 16 to 18 are graphs showing polishing rates measured
at different measurement points on polysilicon films of wafers
polished with the polishing apparatus of the present invention;
and
[0070] FIG. 19 is a graph showing relationships among the shapes of
rings, polishing rates on a tungsten film of a wafer, and the
uniformity of the polishing rates on the tungsten film of the wafer
polished with the polishing apparatus of the present invention.
DETAILED DESCRIPTION OF THE EMBODIMENTS
[0071] Various embodiments of the present invention will be
described with reference to the accompanying drawings. It is to be
noted that the same or similar reference numerals are applied to
the same or similar parts and elements throughout the drawings, and
the description of the same or similar parts and elements will be
omitted or simplified.
[0072] The drawings show only models of the embodiments, and the
thicknesses, dimensions, and the proportion of thicknesses of
layers of elements shown differ from actual ones. The actual
thicknesses and dimensions of the elements must be judged from the
following description. The dimensions and proportions of the
elements may differ from one drawing to another.
[0073] FIG. 8A is a sectional view showing the vicinity of a wafer
base 13 of a polishing apparatus according to an embodiment of the
present invention. The polishing apparatus has at least a polishing
cloth 7, a guide 5 surrounding an object (e.g., a silicon wafer) 1
to polish, and a backing structure to support the wafer 1 between
the polishing cloth 7 and the backing structure. The thickness of
the backing structure changes depending on distances from the guide
5. The backing structure consists of a backing plate 4, a backing
film 2, and a ring 3. The wafer base 13 consists of a head 6, the
backing plate 4, the backing film 2, the guide 5, and the ring 3.
The guide 5 is cylindrical. The ring 3 is arranged between the
backing plate 4 and the backing film 2. The head 6, backing plate
4, and backing film 2 have holes, which pass compressed air 14 to
pressurize the wafer 1. The polishing cloth 7 is attached to a
surface plate 8 having a shaft 10. The shaft 10 is connected to a
motor (not shown) to rotate the surface plate 8 through the shaft
10. The polishing cloth 7 rotates with the surface plate 8.
Abrasive is supplied onto the polishing cloth 7. The wafer 1 is set
under the backing film 2. The wafer base 13 is rotated and thrust
to press the wafer 1 against the polishing cloth 7. The compressed
air 14 pressurizes a central part of the top of the wafer 1 so that
a surface of the wafer 1 contacting the polishing cloth 7 is
polished. FIGS. 8B and 8C are sectional and top views showing the
ring 3. The ring 3 is made of, preferably, polyethylene
terephthalate (PET). The ring 3 may be made of other material such
as stainless steel, fluorine-contained polymers,
polytetrafluoroethylene (PTFE), polyethylene, polypropylene,
polystyrene, polyimide, and polyvinyl chloride (PVC). The head 6
may be made of polycarbonate and Vespel of Du Pont. The backing
plate 4 may be made of stainless steel and ceramics such as alumina
(Al.sub.2O.sub.3). The backing film 2 may be made of polyurethane.
The polishing cloth 7 may be made of polyurethane and rayon.
[0074] To clarify the effect of the ring 3 of the present
invention, a mechanism of equalizing polishing rates on a wafer
will be examined.
[0075] FIGS. 9A, 9B, and 9C are sectional views showing the
polishing apparatus of the present invention and corresponding to a
sectional view taken along the line I-I of FIG. 5. In FIG. 9A, the
wafer 1 is not pressed against the polishing cloth 7, and the
polishing cloth 7 and wafer base 13 are not rotated. In this
situation, a gap 15 between the guide 5 and the polishing cloth 7
is in the range of 0.07 mm to 0.28 mm. With the gap 15 being within
this range, the guide 5 can be pressed against the polishing cloth
7 when the wafer 1 is pressed against the polishing cloth 7. The
wafer 1 will not move out of the guide 5 when the polishing cloth 7
and wafer base 13 are rotated. The ring 3 forms a space 31 between
the backing plate 4 and the backing film 2.
[0076] In FIG. 9B, the shaft 9 is thrust to press the wafer 1
against the polishing cloth 7. The polishing cloth 7 is compressed
by the wafer 1, and the backing film 2 on the wafer 1 is also
compressed. A part of the backing film 2 that is in contact with
the ring 3 is compressed and a part of the backing film 2 that is
under the space 31 is not compressed. This phenomenon continues
even if large force is applied to close the space 31. As a result,
the backing film 2 applies larger force to the wafer 1 under the
ring 3 and smaller force thereto under the space 31, thereby
curving the wafer 1 into a concave on the polishing cloth 7.
Namely, the wafer 1 strongly compresses the polishing cloth 7 under
the ring 3 and weakly compresses the same under the space 31. In
other words, the wafer 1 receives larger force from the polishing
cloth 7 under the ring 3 and smaller force from the same under the
space 31. Namely, the surface of the wafer 1 receives uneven force
from the polishing cloth 7. Changing the thickness and width of the
ring 3 changes the magnitude and distribution of force applied to
the wafer 1. The thickness of the ring 3 may be uniform, or changed
in steps, or changed continuously.
[0077] In FIG. 9C, the polishing cloth 7 and wafer base 13 are
rotated from the state of FIG. 9B. The polishing cloth 7 moves
rightward, and therefore, the wafer 1 is shifted toward a right
part of the guide 5 as explained with reference to FIG. 5. The
polishing cloth 7 at the edge of the wafer 1 deforms due to
rotation. The polishing cloth 7 at the left edge of a left part of
the guide 5 rises and is compressed greater than FIG. 9B. An area
of the polishing cloth 7 from the right edge of the left part of
the guide 5 to the wafer 1 is stretched. In the stretched area,
force of the polishing cloth 7 of pressing the wafer 1 is weaker
than that of the remaining part. As shown in FIG. 9B, force of the
polishing cloth 7 of pressing the wafer 1 under the ring 3 is
stronger. As a result, force of the polishing cloth 7 of pressing
the wafer 1 is equalized over the wafer 1 in FIG. 9C. This,
however, is not a complete equalization because force of the
polishing cloth 7 of pushing the wafer 1 under the right part of
the ring 3 is stronger than that under the space 31. The wafer 1 is
rotated, and therefore, the periphery of the wafer 1 alternately
passes under the right and left parts of the ring 3. This means
that polishing rates on the wafer 1 will be equalized if settings
are made to equalize an average of polishing rates under the right
and left parts of the ring 3 with a polishing rate under the space
31. In consequence, the ring 3 increases force of pressing the
periphery of the wafer 1 against the polishing cloth 7 to dissolve
an unevenness of force on the wafer 1 that is not present when the
wafer 1 is simply pressed against the polishing cloth 7 and is
created when the pressed wafer 1 and polishing cloth 7 are
rotated.
[0078] FIGS. 10A, 10B, and 10C show a backing plate 41 according to
the first modification of the present invention. The backing plate
41 is a combination of a ring 3 and a backing plate 4 that are
solidified together with, for example, adhesives. The ring 3 and
backing plate 4 are made of different materials. In FIG. 10A, the
backing plate 41 is installed on a wafer base 13. FIGS. 10B and 10C
are sectional and bottom views showing the backing plate 41. The
backing plate 41 and a backing film 2 form a backing structure of
the present invention.
[0079] FIGS. 11A, 11B, and 11C show a backing film 21 according to
the second modification of the present invention. The backing film
21 is a combination of a backing film 2 and a ring 3 that are
solidified together with, for example, adhesives. The backing film
2 and ring 3 are made of different materials. In FIG. 11A, the
backing film 21 is installed on a wafer base 13. FIGS. 11B and 11C
are sectional and top views showing the backing film 21. The
backing film 21 and a backing plate 4 form a backing structure of
the present invention.
[0080] FIGS. 12A, 12B, and 12C show a backing plate 42 according to
the third modification of the present invention. The backing plate
42 has a recess to realize the function of the ring 3 of FIG. 8A.
In FIG. 12A, the backing plate 42 is installed on a wafer base 13.
FIGS. 12B and 12C are sectional and bottom views showing the
backing plate 42. The backing plate 42 and a backing film 2 form a
backing structure of the present invention.
[0081] FIGS. 13A, 13B, and 13C show a backing film 22 according to
the fourth modification of the present invention. The backing film
22 has a recess to realize the function of the ring 3 of FIG. 8A.
In FIG. 13A, the backing film 22 is installed on a wafer base 13.
FIGS. 13B and 13C are sectional and top views showing the backing
film 22. The backing film 22 and a backing plate 4 form a backing
structure of the present invention.
First Embodiment
[0082] The first embodiment polishes a thermal oxidation film
formed on an 8-inch silicon wafer 1.
[0083] The first embodiment employs the: polishing apparatus of
FIG. 8A. The backing plate 4 is a disk having a diameter of about
201 mm and a thickness of about 9.1 mm. The backing film 2 is a
circular film having a diameter of about 201 mm and a thickness of
about 0.5 mm and made of urethane. The guide 5 is a cylinder having
an inner diameter of 202 mm, an external diameter of about 220 mm,
and a height of about 10 mm. The ring 3 has an inner diameter of
181 mm, an external diameter of 201 mm, a width of 10 mm, and a
thickness of 30 .mu.m. The surface plate 8 has a diameter of 600
mm. The surface plate 8 and the polishing cloth 7 attached thereto
are rotated at 50 rpm. The thickness of the polishing cloth 7 is
about 4 mm. The abrasive 12 is supplied onto the polishing cloth 7
at 200 cc/min. The wafer 1 is set under the backing film 2 of the
wafer base 13. The wafer base 13 is rotated at 50 rpm and is
pressed against the polishing cloth 7 under 500 g/cm.sup.2. The air
14 is pressurized to 400 g/cm.sup.2 to press a central part of the
top of the wafer 1. As a result, the thermal oxidation film of the
wafer 1 is polished.
[0084] FIG. 14 is a graph showing polishing rates at various
measurement points on the thermal oxidation film of the silicon
wafer 1 of 200 mm in diameter with both the wafer 1 and guide 5
pressed against the polishing cloth 7. The measurement points 1 to
7 are set along a straight line passing through the notch and
center of the wafer 1 and are away from the center of the wafer 1
by 96 mm, 80 mm, 40 mm, 0 mm, 40 mm, 80 mm, and 96 mm,
respectively. The graph shows that polishing rates at the periphery
of the wafer 1 are substantially the same as those at the remaining
part of the wafer 1. Compared with FIG. 4, it is understood that
the ring 3 of the present invention improves the uniformity of
polishing rates over the wafer 1. Since the polishing rates at the
periphery of the wafer 1 are substantially equal to those at the
other parts, LSIs formed at the periphery of the wafer 1 keep
criteria. When the dimensions of the ring 3 are changed to 151 mm
in inner diameter, 201 mm in outer diameter, 25 mm in width, and 30
.mu.m in thickness with the other conditions unchanged, polishing
rates on the wafer 1 are also equalized like FIG. 14.
[0085] FIG. 15A shows a wafer 51 having patterns and covered with a
thermal oxidation film to be polished according to the present
invention. The wafer 51 is an 8-inch silicon wafer. Each pattern on
the wafer 51 is made of a polysilicon layer 53 and a silicon
nitride (Si.sub.3N.sub.4) layer 54. The thermal oxidation film 52
that covers these patterns is a silicon oxide (SiO.sub.2) film
formed by CVD method. The silicon oxide film 52 rises on the
patterns. These rises cause breakage in LSI wiring, and therefore,
must be removed by polishing. Compared with polishing a wafer
having no patterns, polishing a wafer having patterns resembles a
polishing work carried out during a multilayer wiring process of
LSIs. When the wafer 51 having rises is pressed against the
polishing cloth 7, valleys between the rises hardly get in contact
with the polishing cloth 7. As a result, the rises of the wafer 51
are strongly pressed against the polishing cloth 7 to increase
unevenness in pressing force on the wafer 51.
[0086] FIG. 15B is a graph showing polishing rates at various
measurement points on a wafer having patterns polished by the
polishing apparatus of the present invention. The measurement
points 1 to 7 are the same as those of FIG. 14. Triangular marks
represent a case with the ring 3 having 181 mm in inner diameter,
201 mm in outer diameter, 10 mm in width, and 30 .mu.m in
thickness. Square marks represent a case with the ring 3 having 151
mm in inner diameter, 201 mm in outer diameter, 25 mm in width, and
30 .mu.m in thickness. Other polishing conditions are the same as
those used for the wafer having no patterns. The 10-mm-width ring 3
represented with the triangular marks provides polishing rates
about 2.5 times larger than those of the wafer having no patterns.
Like the case of FIG. 14, polishing rates at the measurement points
1 and 7 are smaller than those at the measurement points 2, 3, 5,
and 6. This tendency is also observed in FIG. 4 and is common when
the guide 5 is pressed against the polishing cloth 7 when polishing
a wafer. The 25-mm-width ring 3 represented with the square marks
provides polishing rates about 3 times larger than those of the
wafer having no patterns. Polishing rates at the measurement points
1 and 7 are larger than those at the measurement points 2, 3, 5,
and 6. In this way, changing the width of the ring 3 changes
polishing rates at the periphery of a wafer relative to polishing
rates at the other part of the wafer.
Second Embodiment
[0087] The second embodiment polishes a polysilicon film formed on
an 8-inch silicon wafer.
[0088] The second embodiment employs the polishing apparatus of
FIG. 8A with different rings. A first ring 3 has an inner diameter
of 181 mm, an outer diameter of 201 mm, and a thickness of 50
.mu.m. A second ring 3 has an inner diameter of 191 mm, an outer
diameter of 201 mm, and a sickness of 30 .mu.m. The surface plate 8
and polishing cloth 7 are rotated at 100 rpm. The abrasive 12 is
supplied onto the polishing cloth 7 at 250 cc/min. The wafer 1 is
set on the wafer base 13, which is rotated at 100 rpm and is
pressed against the polishing cloth 7 under 300 g/cm.sup.2. The air
14 is pressurized to 150 g/cm.sup.2 to press a central part of the
top of the wafer 1.
[0089] FIG. 16 is a graph showing polishing rates at various
measurement points on the polysilicon film formed on the silicon
wafer 1 of 200 mm in diameter polished with the first ring 3 and
with both the wafer 1 and guide 5 pressed against the polishing
cloth 7. FIG. 17 is a graph showing polishing rates with the second
ring 3 under the same conditions as those of FIG. 16. FIG. 18 is a
graph showing polishing rates without the ring 3 under the same
conditions as those of FIG. 16. The measurement points 1 to 7 are
the same as those of FIG. 14.
[0090] In FIG. 16, polishing rates at the peripheral measurement
points 1 and 7 are substantially equal to polishing rates at the
other measurement points, and a proper uniformity of polishing
rates is observed. In FIG. 17, polishing rates at the peripheral
measurement points 1 and 7 are relatively lower than polishing
rates at the other measurement points but they are not so low as
those of FIG. 18. It is understood that the first ring provides an
effect of sufficiently equalizing polishing rates over the surface
of a wafer and that the second ring provides a similar effect. In
FIG. 16, the polishing rates at the periphery of the wafer are
substantially the same as those at the other parts thereof, and
therefore, LSIs formed at the periphery of the wafer will keep
criteria.
Third Embodiment
[0091] The third embodiment polishes a tungsten (W) film formed on
an 8-inch silicon wafer.
[0092] The third embodiment employs the polishing apparatus of FIG.
8A with different rings. A first ring 3 has an inner diameter of
181 mm, an outer diameter of 201 mm, a width of 10 mm, and a
thickness of 30 .mu.m. A second ring 3 has an inner diameter of 151
.mu.mm, an outer diameter of 201 mm, a width of 25 mm, and a
thickness of 30 .mu.m. A third ring 3 has an inner diameter of 151
mm, an outer diameter of 201 mm, a width of 25 mm, and a thickness
of 35 .mu.m. A fourth ring 3 has an inner diameter of 191 mm, an
outer diameter of 201 mm, a width of 5 mm, and a thickness of 60
.mu.m. The surface plate 8 and polishing cloth 7 are rotated at 100
rpm. The abrasive 12 is supplied onto the polishing cloth 7 at 200
cc/min. The wafer 1 is set on the wafer base 13, which is rotated
at 50 rpm and is pressed against the polishing cloth 7 under 200
g/cm.sup.2. The air 14 is pressurized to 130 g/cm.sup.2 to press a
central part of the top of the wafer 1.
[0093] FIG. 19 is a graph showing relationships between the
uniformity of polishing rates on silicon wafers each of 200 mm in
diameter and the polishing rates when polishing tungsten films
formed on the wafers with the four types of rings. An abscissa of
the graph indicates a case with no ring (0 mm wide, 0 .mu.m thick),
a case with the first ring (10 mm wide, 30 .mu.m thick), a case
with the second ring (25 mm wide, 30 .mu.m thick), a case with the
third ring (25 mm wide, 35 .mu.m thick), and a case with the fourth
ring (5 mm wide, 60 .mu.m thick). Each white dot in the graph
indicates a polishing rate and a black dot a uniformity of
polishing rates on a wafer. Compared with the case using no ring,
the first ring improves the polishing rate uniformity and increases
polishing rates, the second and third rings further improve the
polishing rate uniformity and increase polishing rates, and the
fourth ring shows no change in the polishing rate uniformity and
increases polishing rates to the levels of the second and third
rings. Consequently, it is understood that the second and third
rings sufficiently improve polishing rates and the uniformity
thereof and that the first ring provides a proper effect. The rings
improve not only the uniformity of polishing rates but also
polishing rates themselves. Accordingly, the rings are capable of
maintaining the quality of LSIs formed at the periphery of a wafer
within criteria and shortening a polishing time to improve
productivity and reduce production cost. The fourth ring provides
an effect of improving polishing rates.
[0094] Although the present invention has been explained based on
the embodiments, the present invention is not limited to these
embodiments and accompanying drawings. It is apparent for persons
skilled in the art that many modifications, alterations, and
applications are possible based on the disclosure of the present
invention.
[0095] For example, the present invention is applicable to
polishing 6-inch wafers, 12-inch wafers, VLSIs, etc. Semiconductor
materials to which the present invention is applicable include not
only silicon but also compound semiconductor such as gallium
arsenide (GaAs).
[0096] In the above explanation, the guide 5 is pressed against the
polishing cloth 7. The present invention is Applicable when the
guide 5 is away from the polishing cloth 7. In this case, the
backing structure is curved into a convex toward an object, e.g., a
wafer.
[0097] Various modifications will become possible for those skilled
in the art after receiving the teachings of the present disclosure
without departing from the scope thereof.
* * * * *