U.S. patent application number 10/302223 was filed with the patent office on 2003-04-24 for front-reference carrier on orbital solid platen.
This patent application is currently assigned to SpeedFam-IPEC Corporation. Invention is credited to Herb, John D., Korovin, Nikolay, Schultz, Stephen C..
Application Number | 20030077986 10/302223 |
Document ID | / |
Family ID | 24361775 |
Filed Date | 2003-04-24 |
United States Patent
Application |
20030077986 |
Kind Code |
A1 |
Schultz, Stephen C. ; et
al. |
April 24, 2003 |
Front-reference carrier on orbital solid platen
Abstract
The present invention is an apparatus and method for planarizing
a front surface of a wafer. The present invention may include a
rigid platen, for supporting a polishing pad, connected to a
supporting base that has means, or is connected to means, for
orbiting the platen. A carrier, preferably a front-reference
carrier with a plurality of individually controllable pressure
areas, may be used to hold and press the wafer against the
polishing pad while the supporting base orbits the rigid platen.
The planarization process may be further optimized by orbiting the
polishing pad in a radius smaller than 4 mm, orbiting the polishing
pad faster than 400 orbits per minute or both.
Inventors: |
Schultz, Stephen C.;
(Gilbert, AZ) ; Herb, John D.; (Phoenix, AZ)
; Korovin, Nikolay; (Phoenix, AZ) |
Correspondence
Address: |
SPEEDFAM-IPEC CORPORATION
305 NORTH 54TH STREET
CHANDLER
AZ
85226
US
|
Assignee: |
SpeedFam-IPEC Corporation
Chandler
AZ
|
Family ID: |
24361775 |
Appl. No.: |
10/302223 |
Filed: |
November 22, 2002 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10302223 |
Nov 22, 2002 |
|
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|
09590319 |
Jun 8, 2000 |
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Current U.S.
Class: |
451/41 ; 451/288;
451/63 |
Current CPC
Class: |
B24B 37/30 20130101;
B24B 37/12 20130101 |
Class at
Publication: |
451/41 ; 451/63;
451/288 |
International
Class: |
B24B 001/00; B24B
007/19 |
Claims
We claim:
1. An apparatus for planarizing a wafer comprising: a) a rigid
platen; b) a supporting base connected to the platen for moving the
platen in an orbital motion; c) a polishing pad mounted on the
platen; and d) a carrier adapted for holding and pressing a wafer
against the polishing pad.
2. The apparatus of claim 1 further comprising: a) a shaft
connected to the carrier; and b) a motor connected to the shaft
adapted for rotating the shaft and the carrier.
3. The apparatus of claim 1 wherein the carrier is a
front-reference carrier.
4. The apparatus of claim 1 wherein the carrier is a back-reference
carrier.
5. The apparatus of claim 3 wherein the carrier may be adjusted to
provide a plurality of individually controllable pressure areas on
the back surface of the wafer.
6. The apparatus of claim 1 wherein the supporting base is adapted
to orbit the polishing pad at an orbital radius of less than about
four mm.
7. The apparatus of claim 1 wherein the supporting base is adapted
to orbit the polishing pad at an orbital rate faster than about 400
orbits per minute.
8. A method of planarizing a wafer comprising the steps of: a)
loading a wafer into a carrier; b) positioning the wafer adjacent a
polishing pad mounted to a solid platen; c) pressing the wafer
against the polishing pad; d) orbiting the polishing pad; and e)
removing the wafer from the polishing pad.
9. The method of claim 8 further comprising the step of: a)
rotating the wafer prior to removing the wafer from the polishing
pad.
10. The method of claim 8 further comprising the step of: a)
alternately rotating the wafer in a clock-wise direction and a
counterclockwise direction prior to removing the wafer from the
polishing pad.
11. The method of claim 8 wherein the pressing step further
comprises the steps of: applying a first pressure against a central
area on a back surface of the wafer; and applying a second pressure
against a concentric peripheral area in relation to the central
region, wherein the second pressure is different than the first
pressure.
12. The method of claim 8 wherein the polishing pad is orbited
faster than about 400 orbits per minute.
13. The method of claim 8 wherein the polishing pad is orbited in a
radius smaller than about four mm.
14. The method of claim 8 wherein the polishing pad is orbited
faster than about 400 orbits per minute in an orbital radius
smaller than about four mm.
15. The method of claim 8 wherein the carrier is a front-reference
carrier.
Description
TECHNICAL FIELD
[0001] The present invention relates generally to semiconductor
manufacturing, and more specifically to the field of
chemical-mechanical polishing methods and apparatus for the
planarization and removal of thin films used in semiconductor
manufacturing.
BACKGROUND OF THE INVENTION
[0002] A flat disk or "wafer" of single crystal silicon is the
basic substrate material in the semiconductor industry for the
manufacture of integrated circuits. Semiconductor wafers are
typically created by growing an elongated cylinder or boule of
single crystal silicon and then slicing individual wafers from the
cylinder. The slicing causes both faces of the wafer to be
extremely rough. The front face of the wafer on which integrated
circuitry is to be constructed must be extremely flat in order to
facilitate reliable semiconductor junctions with subsequent layers
of material applied to the wafer. Also, the material layers
(deposited thin film layers usually made of metals for conductors
or oxides for insulators) applied to the wafer while building
interconnects for the integrated circuitry must also be made a
uniform thickness.
[0003] Integrated circuits manufactured today are made up of
literally millions of active devices such as transistors and
capacitors formed in a semiconductor substrate. Integrated circuits
rely upon an elaborate system of metalization in order to connect
the active devices into functional circuits. A typical multilevel
interconnect 100 is shown in FIG. 1. Active devices such as MOS
transistors 107 are formed in and on a silicon substrate or well
102. An interlayer dielectric (ILD) 104, such as SiO.sub.2, is
formed over silicon substrate 102. ILD 104 is used to electrically
isolate a first level of metalization which is typically aluminum
from the active devices formed in substrate 102. Metalized contacts
106 electrically couple active devices formed in substrate 102 to
interconnections 108 of the first level of metalization. In a
similar manner metal vias 112 electrically couple interconnections
114 of a second level of metalization to interconnections 108 of
the first level of metalization. Contacts and vias 106 and 112
typically comprise a metal 116 such as tungsten (W) surrounded by a
barrier metal 118 such as titanium-nitride (TiN). Additional
ILD/contact and metalization layers can be stacked one upon the
other to achieve the desired interconnections.
[0004] Planarization is the process of removing projections and
other imperfections to create a flat planar surface, both locally
and globally, and/or the removal of material to create a uniform
thickness for a deposited thin film layer on a wafer. Semiconductor
wafers are planarized or polished to achieve a smooth, flat finish
before performing process steps that create integrated circuitry or
interconnects on the wafer. A considerable amount of effort in the
manufacturing of modem complex, high density multilevel
interconnects is devoted to the planarization of the individual
layers of the interconnect structure. Nonplanar surfaces create
poor optical resolution of subsequent photolithographic processing
steps. Poor optical resolution prohibits the printing of high
density lines. Another problem with nonplanar surface topography is
the step coverage of subsequent metalization layers. If a step
height is too large there is a serious danger that open circuits
will be created. Planar interconnect surface layers are required in
the fabrication of modem high density integrated circuits. To this
end, CMP tools have been developed to provide controlled
planarization of both structured and unstructured wafers.
[0005] In a conventional CMP tool for planarizing a wafer, a wafer
is secured in a carrier connected to a shaft. The shaft is
typically connected to mechanical means for transporting the wafer
between a load or unload station and a position adjacent a
polishing pad mounted on a platen. A pressure is exerted on the
back surface of the wafer via the carrier in order to press the
wafer against the polishing pad, usually in the presence of slurry.
The wafer and/or polishing pad are then moved in relation to each
other via motor(s) connected to the shaft and/or platen in order to
remove material in a planar manner from the front surface of the
wafer.
[0006] The motion of the carrier and polishing pad in relation to
each other is an important factor in the planarization process. The
search for improved motions for the carrier and the polishing pad
continues as new requirements and materials are used in the
manufacturing process of semiconductors. One of the goals of the
planarization process is to remove material at a uniform rate
across the front surface of the wafer. One method for trying to
remove material at a uniform rate is to have every point on the
front surface of the wafer experience the same relative motion
against the polishing pad as every other point. An orbital tool,
which orbits the polishing pad around an axis offset from the
center of the polishing pad while continually maintaining the
rotational orientation of the polishing pad throughout the orbit,
is one possible way to achieve this goal. Orbital tools are
desirable since they allow every point on the front surface of the
wafer to experience the same circular motion against the polishing
pad as every other point.
[0007] Conventional orbital tools use a polishing pad that is
supported by a diaphragm. Front-reference carriers are known in the
art for supporting a wafer with a fluid or flexible
diaphragm/membrane. Front-reference carriers are able to uniformly
press on the back surface of a wafer regardless of the back
surface's contour. Applicant has discovered that when a
front-reference carrier is used with a conventional orbital tool,
i.e. one with a polishing pad supported by a diaphragm, the
resulting planarization process lacks stability. The reasons for
the lack of stability are not entirely understood, but Applicant
believes they may be caused by the lack of a fixed reference
plane.
[0008] Another problem with conventional orbital tools is that they
tend to leave a band on the periphery of the front surface of the
wafer where material is removed at an accelerated rate. Applicant
noticed that the width of the band is typically the same as the
diameter of the orbit of the polishing platen. Applicant believes
the band may be due to the loading of the center of the polishing
pad with residue from the planarization process while the periphery
of the polishing pad is slightly conditioned by the retaining ring.
This results in the center of the wafer polishing slower against
the loaded polishing pad while the periphery of the wafer polishes
faster against the conditioned periphery of the polishing pad.
[0009] What is needed is a system for planarizing the front surface
of a wafer to a very fine degree that provides a stable process
while minimizing the band of nonuniform material removal at the
periphery of the wafer.
SUMMARY OF THE INVENTION
[0010] The present invention is an apparatus and method for
planarizing a front surface of a wafer. The present invention
includes a rigid platen, i.e. does not use a membrane or diaphragm
as in the prior art, for supporting a polishing pad. The platen is
connected to a supporting base that has means, or is connected to
means, for orbiting the platen. A carrier, preferably a
front-reference carrier, holds and presses the wafer against the
polishing pad while the supporting base orbits the platen.
[0011] Optionally, the carrier may be connected to a motor via a
shaft for rotating or otherwise moving the wafer during the
planarization process. Additional flexibility for the planarization
process may be obtained by using a carrier that is able to apply a
plurality of different pressure zones to the back surface of the
wafer. The planarization process may be optimized for various
wafers and thin films deposited on the wafer by adjusting the
orbital radius and/or orbital speed. Applicant has discovered that
improved planarization results may be obtained by orbiting the
polishing pad in a radius smaller than conventional orbital radii,
orbiting the polishing pad at a rate faster than conventional
orbital rates and, preferably, both in combination.
[0012] The present invention may be practiced by loading a wafer in
a carrier, preferably a front-reference carrier, and positioning
the wafer adjacent a polishing pad mounted to a substantially rigid
platen. The wafer is planarized by pressing the wafer against the
polishing pad as the polishing pad is orbited, preferably with a
radius smaller than a four mm and at a speed faster than 400 orbits
per minute. Optionally, the carrier may be rotated to smooth out
patterns that tend to form on the front surface of the wafer. As a
further option, the carrier may be alternately rotated clockwise
and counterclockwise, preferably with each rotation less than 360
degrees, to simplify the communication of fluids to the
carrier.
[0013] If a front-reference carrier with a plurality of
individually controllable pressure zones is used, further
improvements to the planarization process may be obtained. Higher
or lower pressures may be applied adjacent the back surface of the
wafer corresponding to areas on the front surface of the wafer with
greater or lesser amounts of material to remove. The wafer
planarization process may be terminated by removing the wafer from
the polishing pad or stopping relative motion between the wafer and
the polishing pad.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] The present invention will hereinafter be described in
conjunction with the appended drawing figures, wherein like
numerals denote like elements, and:
[0015] FIG. 1 is a cross sectional illustration of a standard
multilayer interconnect structure used in semiconductor integrated
circuits;
[0016] FIG. 2 is a cross section view of a front-reference carrier
holding a wafer against a polishing pad mounted on a solid
platen;
[0017] FIG. 3 is a plan view of a wafer adjacent an orbiting
polishing pad;
[0018] FIG. 4a is a plan view of a stationary wafer with an
orbiting polishing pad shown at four different times during the
orbit of the polishing pad;
[0019] FIG. 4b is a view of the front face of the wafer
illustrating the motion experienced by every point on the front
face of the wafer due solely to an orbital motion;
[0020] FIG. 5 is a cross section view of one possible mechanism for
producing an orbital motion for a polishing pad; and
[0021] FIG. 6 is a flow chart illustrating one possible method of
practicing the present invention.
DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS
[0022] An improved polishing apparatus and method utilized in the
polishing of semiconductor substrates and thin films formed thereon
will now be described. In the following description, numerous
specific details are set forth illustrating Applicants' best mode
for practicing the present invention and enabling one of ordinary
skill in the art to make and use the present invention. It will be
obvious, however, to one skilled in the art that the present
invention may be practiced without these specific details. In other
instances, well-known machines and process steps have not been
described in particular detail in order to avoid unnecessarily
obscuring the present invention.
[0023] Referring to FIG. 2, an apparatus for practicing the present
invention will now be discussed. A front-reference carrier 215 may
be used to hold and press the wafer 216 against the polishing pad
207 during a planarization process. Front-reference carriers
provide a substantially uniform pressure on the back surface of the
wafer 216 despite protrusions on the back surface of the wafer 216.
Thus, problems associated with protrusions for back-reference
carriers are avoided, i.e. creating localized high pressure spots
on the front surface of the wafer opposite the protrusions.
Front-reference carriers typically use a pressurized fluid, e.g.
filtered air, deionized water, etc., and/or a flexible
membrane/diaphragm 203 to press uniformly against the back surface
of the wafer 216. A few examples of front-reference carriers that
may be used to practice the present invention are disclosed in U.S.
Pat. No. 5,423,716 Strasbaugh, U.S. Pat. No. 5,449,316 Strasbaugh,
U.S. Pat. No. 5,635,083 Breivogel et al., U.S. Pat. No. 5,851,140
Barns et al., U.S. Pat. No. 6,012,964 Arai et al. and U.S. Pat. No.
6,024,630 Shendon et al. and are hereby incorporated by
reference.
[0024] The carrier 215 may have a plurality of areas 204, 228 or
zones, typically concentric to each other, that may be individually
pressurized to create a plurality of uniform pressure areas. In
other words, while each area may have a pressure different from
every other area, the pressure is substantially uniform within each
area. These multizone carriers 215 may be advantageously used for
removing excess material faster from the front face of the wafers
216 at concentric areas having bulges. Specifically, the multizone
carrier 215 may exert a higher uniform pressure against the back
surface of the wafer 216 opposite a bulge. At the same time, other
areas on the back surface of the wafer, for example areas between
bulges, may have a lower uniform pressure applied to them. Examples
of multizone front-reference carriers that may be used to practice
the present invention are disclosed in U.S. Pat. No. 5,941,758
Mack, U.S. patent application Ser. No. 09/540,476 and U.S. patent
application Ser. No. 08/504,686 and are all hereby incorporated by
reference.
[0025] FIG. 2 illustrates one possible embodiment of a
front-reference carrier 215 having two individually controllable
uniform pressure areas 204, 228 with equipment for practicing the
present invention. A pressure source 227 may be used to feed two
pressure regulators 223, 224 via a manifold 229. The pressure
regulators 223, 224 are preferably computer controlled and may be
connected to a control system 230. The pressure regulators 223, 224
may communicate pressurized fluids to corresponding rotary couplers
(not shown) in the carrier shaft 201. The rotary couplers may then
communicate the pressurized fluids through tubes or channels 225,
226 in the shaft 201 to corresponding tubes or channels in the
carrier 215. The tubes or channels in the carrier 215 may then
direct the pressurized fluid to plenums 204, 228 in the carrier 215
for controlling the pressure exerted on a corresponding area on the
back surface of the wafer 216. The plenums 204, 228 may be
separated by one or more ring shaped barriers 205 so that each
plenum may have a separate internal pressure. Thus, the control
system 230 is able to individually control the pressure exerted by
two areas 204, 228 on the back surface of the wafer 216 with this
particular embodiment of the present invention. It is to be
appreciated that a variety of other carriers may be employed to
facilitate a desired application of pressure on the back surface of
the wafer. While a particular front-reference carrier 215 has been
described in detail and the invention is preferably practiced with
a front-reference carrier, the invention may be practiced using a
variety of front and back-reference carriers.
[0026] The carrier 215 may be held stationary or moved in a variety
of motion, e.g. moved linearly, orbited, vibrated or rotated on the
polishing pad. For example, the carrier 215 may be rotated by motor
222 via shaft 201. If the carrier 215 is rotated, it is preferably
rotated at about 10-20 rpm. Rotating the carrier 215 has been shown
to smooth-out or eliminate patterns that tend to develop on the
front face of the wafer due to the periodic nature of the orbital
motion of the polishing pad 207. As an alternative, the carrier 215
may be alternately rotated clock-wise and counterclockwise. This is
particularly beneficial if a front-reference carrier with multiple
chambers is being used. Every chamber requires additional fluid
communication paths to operate. If the carrier 215 rotates only in
one direction, complicated fluid communication means, such as
rotary couples, will be needed. However, if the carrier 215
alternately rotates clock-wise and counterclock-wise, preferably
less than 360 degrees, then less complicated fluid communication
means, such as conventional tubing, may be used.
[0027] During the planarization process, the front face of the
wafer 216 is pressed against a polishing pad 207 fixed to a rigid
platen 221, typically in the presence of a slurry. The polishing
pad 207 may be, for example, an IC1000 or an IC1000 supported by a
Suba IV polishing pad, both manufactured and made commercially
available by Rodel Inc. headquartered in Phoenix, Ariz. The
particular polishing pad 207 used may be varied depending on the
characteristics of the wafer 216, but typically comprises a
urethane based material. As shown in FIG. 3, the polishing pad 207
may have holes 322 for delivering slurry to the surface of the
polishing pad 207. Slurries are generally silica-based solutions
that have different additives depending upon the type of material
being polished. In addition, the polishing pad 207 may have grooves
(not shown) for assisting in the distribution of slurry over the
face of the polishing pad 207.
[0028] Referring back to FIG. 2, the platen 221 may be made from a
rigid material with a substantially planar surface for mounting a
polishing pad 207 thereto. The platen 221 for the present invention
should be stiffer than conventional platens in prior art orbital
tools that use pressurized diaphragms or membranes to support the
polishing pad. For example, the platen 221 may comprise aluminum,
stainless steel, ceramic, titanium, polymer or other such materials
that are rigid and preferably noncorrosive.
[0029] During the planarization process, the platen 221 may be
orbited by a supporting base 220. Referring to FIG. 4a, the orbital
motion of the polishing pad will be further described. The
polishing pad moves through positions 207a, 207b, 207c and 207d at
time 1, time 2, time 3 and time 4 respectively resulting in the "X"
on the polishing pad traveling in a circle 400a. It should be
observed that the polishing pad does not rotate when orbited. The
radius of the orbit is the same as the radius of the circle 400a or
any other circle generated by an orbited point on the polishing
pad. The size of the orbital motion shown by circle 400a is larger
than typically desired to aid in the description of the orbital
motion.
[0030] Referring to FIG. 4b, a wafer 216 is shown with multiple
circular motions 400b. The circular motions 400b represent the
motion each point on the front surface of the wafer 216 experiences
during an orbit. The radius of the orbit creating the circular
motion 400b is much smaller than the radius of the orbit creating
the circular motion 400a. The radius of the orbit may be controlled
by the mechanisms used to create the orbital motion, several
examples of which will now be discussed.
[0031] U.S. Pat. No. 5,582,534 Shendon et al. and U.S. Pat. No.
5,938,884 Hoshizaki et al. disclose several mechanisms for creating
an orbital motion for a carrier. The principles for the mechanisms
disclosed for creating an orbital motion may be applied by one of
ordinary skill in the art to create a supporting base 220 capable
of orbiting the platen 221 and are hereby incorporated by
reference.
[0032] FIG. 5 is a cross-sectional view of an exemplary supporting
base 220 that may be used to generate an orbital motion for the
platen 211. The supporting base is generally disclosed in U.S. Pat.
No. 5,554,064 Breivogel et al. and is hereby incorporated by
reference. Supporting base 220 may have a rigid frame 502 that can
be securely fixed to the ground. Stationary frame 502 is used to
support and balance motion generator 500. The outside ring 504 of a
lower bearing 506 is rigidly fixed by clamps to stationary frame
502. Stationary frame 502 prevents outside ring 504 of lower
bearing 506 from rotating. Wave generator 508 formed of a circular,
hollow rigid stainless steel body is clamped to the inside ring 510
of lower bearing 506. Wave generator 508 is also clamped to outside
ring 512 of an upper bearing 514. Waver generator 508 positions
upper bearing 514 parallel to lower bearing 506. Wave generator 508
offsets the center axis 515 of upper bearing 514 from the center
axis 517 of lower bearing 506. A circular aluminum platen 211 is
symmetrically positioned and securely fastened to the inner ring
519 of upper bearing 514. A polishing pad or pad assembly can be
securely fastened to ridge 525 formed around the outside edge of
the upper surface of platen 211. A universal joint 518 having two
pivot points 520a and 520b is securely fastened to stationary frame
502 and to the bottom surface of platen 211. The lower portion of
wave generator 508 is rigidly connected to a hollow and cylindrical
drive spool 522 that in turn is connected to a hollow and
cylindrical drive pulley 523. Drive pulley 523 is coupled by a belt
524 to a motor 526. Motor 526 may be a variable speed, three phase,
two horsepower AC motor.
[0033] The orbital motion of platen 211 is generated by spinning
wave generator 508. Wave generator 508 is rotated by variable speed
motor 526. As wave generator 508 rotates, the center axis 515 of
upper bearing 514 orbits about the center axis 517 of lower bearing
506. The radius of the orbit of the upper bearing 517 is equal to
the offset (R) 526 between the center axis 515 of upper bearing 514
and the center axis 517 of the lower bearing 506. Upper bearing 514
orbits about the center axis 517 of lower bearing 506 at a rate
equal to the rotation of wave generator 508. It is to be noted that
the outer ring 512 of upper bearing 514 not only orbits but also
rotates (spins) as wave generator 508 rotates. The function of
universal joint 518 is to prevent torque from rotating or spinning
platen 211. The dual pivot points 520a and 520b of universal joint
518 allow the platen 211 to move in all directions except a
rotational direction. By connecting platen 211 to the inner ring
519 of upper bearing 514 and by connecting universal joint 518 to
platen 211 and stationary frame 502 the rotational movement of
inner ring 519 and platen 211 is prevented and platen 211 only
orbits as desired. The orbit rate of platen 211 is equal to the
rotation rate of wave generator 508 and the orbit radius of platen
211 is equal to the offset of the center 515 of upper bearing 514
from the center 517 of lower bearing 506. It is to be appreciated
that a variety of other well-known means may be employed to
facilitate the orbital motion of the polishing pad. While a
particular method for producing an orbital motion has been given in
detail, the present invention may be practiced using a variety of
techniques for orbiting the polishing pad on the platen 211.
[0034] With reference to FIG. 2 and FIG. 6, an exemplary method of
operation for the present invention will now be disclosed. The
first step is to load a wafer 216 into a carrier 215 (step 600).
While a back-reference carrier 215 may be used, exceptional results
have been obtained using a front-reference carrier 215 with the
invention. If the wafer 216 has one or more concentric bulges of
excess material on its front surface, a front-reference carrier 215
with a plurality of individually controllable pressure areas may be
advantageously used. The individually controllable pressure areas
may apply a higher pressure on the back surface of the wafer
adjacent bulges as compared to the pressure applied adjacent
troughs or low points on the wafer. The number and placement of
bulges may be determined, for example, by taking in situ
measurements or by knowing the typical wafer contour created by the
previous processing step.
[0035] The wafer 216 may then be positioned adjacent a polishing
pad 207 fixed to a rigid platen 221 (step 601). Mechanical means
for moving the wafer 216 adjacent the polishing pad 207 are well
known in the art and will not be discussed to avoid unnecessarily
obscuring the invention. The pressure applied to the back surface
of the wafer 216 urges the wafer against the polishing pad 207
(step 604). The optimum pressure or pressures applied to the back
surface of the wafer 216 will vary depending on the characteristics
of the wafer 216, polishing pad 207, slurry, desired removal rate
and other factors. However, pressures between about three (3) and
about seven (7) psi have yielded excellent results. However, the
present invention may easily be used with lower or higher
pressures.
[0036] At about the same time as the wafer 216 is being pressed
against the polishing pad 207 (step 604), the polishing pad 207 may
start to orbit (step 602) and the carrier may start to rotate (step
603). The polishing pad 207 is preferably orbited faster than 400
orbits per minute and the Applicant has obtained excellent
planarization results at about 600 orbits per minute with a 16 mm
orbit radius. In addition, the orbital radius of the polishing pad
may be less than six mm and Applicant has obtained excellent
planarization results with an orbital radius of about 1.5 mm with
an orbital frequency of about 6400 orbits per minute. A smaller
orbit radius will generally require a higher orbital frequency to
maintain a given removal rate of material from the front surface of
the wafer. The carrier may be rotated slower than 30 rpm and is
preferably rotated between about 10 and about 20 rpm. The fluid
communication paths 225, 226 may be simplified if the carrier 215
is alternately rotated clockwise and counterclockwise less than 360
degrees.
[0037] The wafer 216 may be removed from the polishing pad 207
thereby terminating the planarization process based on input from
an end-point detection system or based on an empirically found time
required by the particular planarization process.
[0038] While the invention has been described with regard to
specific embodiments, those skilled in the art will recognize that
changes can be made in form and detail without departing from the
spirit and scope of the invention.
* * * * *