U.S. patent application number 09/785636 was filed with the patent office on 2002-10-10 for method of manufacturing a polishing pad using a beam.
Invention is credited to Crevasse, Annette M., Easter, William G., Miceli, Frank.
Application Number | 20020144985 09/785636 |
Document ID | / |
Family ID | 25136130 |
Filed Date | 2002-10-10 |
United States Patent
Application |
20020144985 |
Kind Code |
A1 |
Crevasse, Annette M. ; et
al. |
October 10, 2002 |
METHOD OF MANUFACTURING A POLISHING PAD USING A BEAM
Abstract
The present invention provides a method of manufacturing a
polishing pad using a beam, and a system incorporating the method.
In one embodiment, the method includes providing a cake that is
susceptible to beam ablation, and skiving a polishing pad from the
cake using a beam apparatus configured to produce a beam.
Inventors: |
Crevasse, Annette M.;
(Orlando, FL) ; Easter, William G.; (Orlando,
FL) ; Miceli, Frank; (Orlando, FL) |
Correspondence
Address: |
HITT GAINES & BOISBRUN P.C.
P.O. BOX 832570
RICHARDSON
TX
75083
US
|
Family ID: |
25136130 |
Appl. No.: |
09/785636 |
Filed: |
February 16, 2001 |
Current U.S.
Class: |
219/121.68 ;
219/121.69 |
Current CPC
Class: |
B24B 37/20 20130101;
B24D 18/00 20130101; B23K 26/38 20130101 |
Class at
Publication: |
219/121.68 ;
219/121.69 |
International
Class: |
B23K 026/36 |
Claims
What is claimed is:
1. A method of manufacturing a polishing pad, including: providing
a polishing pad cake susceptible to beam ablation; and skiving a
polishing pad from the cake using a beam.
2. The method recited in claim 1 wherein providing a cake includes
providing a cake comprising a polymer.
3. The method recited in claim 2 wherein providing a cake
comprising a polymer includes providing a cake comprising
polyurethane.
4. The method recited in claim 1 wherein skiving a polishing pad
with a beam includes using a laser.
5. The method recited in claim 4 wherein using a laser includes
pulsing the laser to skive the polishing pad.
6. The method recited in claim 5 wherein pulsing the laser includes
pulsing for a period of time ranging from about 10 ns to about 50
ns.
7. The method recited in claim 1 wherein skiving a polishing pad
using a beam includes skiving a polishing pad using a beam having a
beam intensity of about 400 mJ.
8. The method recited in claim 1 wherein skiving a polishing pad
using a beam includes skiving a polishing pad using a beam having a
frequency ranging from about 250 Hz to about 800 Hz.
9. The method recited in claim 1 wherein skiving a polishing pad
using a beam includes skiving a polishing pad using a beam having a
wavelength ranging from about 193 nm to about 308 nm.
10. A system for manufacturing a polishing pad, comprising: a cake
susceptible to beam ablation; and a beam apparatus configured to
produce a beam capable of skiving the cake to produce a polishing
pad.
11. The system recited in claim 10 wherein the cake comprises a
polymer.
12. The system recited in claim 11 wherein the cake comprises
polyurethane.
13. The system recited in claim 10 wherein the beam apparatus is a
laser generator, and the beam is a laser.
14. The system recited in claim 10 wherein the beam apparatus is
configured to be pulsed.
15. The system recited in claim 14 wherein the beam apparatus is
configured to pulse for a period of time ranging from about 10 ns
to about 50 ns.
16. The system recited in claim 10 wherein the beam apparatus is
configured to produce a beam having a beam intensity of 400 mJ.
17. The system recited in claim 10 wherein the beam apparatus is
configured to produce a beam having a frequency ranging from about
250 Hz to about 800 Hz.
18. The system recited in claim 10 wherein the beam apparatus is
configured to produce a beam having a wavelength ranging from about
193 nm to about 308 nm.
19. A method of manufacturing an integrated circuit, comprising:
forming devices on a semiconductor wafer; polishing a material
deposited over the devices with a polishing pad skived from a cake
using a beam; and interconnecting the devices to form an operative
integrated circuit.
20. The method recited in claim 19 further including providing a
polishing pad skived from a polymer cake.
21. The method recited in claim 1 wherein polishing includes
polishing with a polishing pad skived from a cake using a
laser.
22. The method recited in claim 23 wherein polishing with a
polishing pad skived from a cake includes polishing with a
polishing pad skived using a laser pulsed for a period of time
ranging from about 10 ns to 50 ns and at an intensity of about 400
mJ, and at a frequency ranging from about 250 Hz to about 800
Hz.
23. The method recited in claim 1 wherein forming devices includes
forming devices wherein the devices are transistors, inductors,
resistors, capacitors, optical devices or optoelectronic devices.
Description
TECHNICAL FIELD OF THE INVENTION
[0001] The present invention is directed, in general, to polishing
pads and, more specifically, to a method of manufacturing a
polishing pad using a focused beam.
BACKGROUND OF THE INVENTION
[0002] In the fabrication of semiconductor components, the various
devices are formed in layers upon an underlying substrate, such as
silicon. In such semiconductor components, it is desirable that all
layers, including insulating layers, have a smooth surface
topography, since it is difficult to lithographically image and
pattern layers applied to nonuniform surfaces. To this end,
conventional chemical/mechanical polishing (CMP) has been developed
for providing planar semiconductor topographies. Typically, a given
semiconductor wafer may be planarized several times, such as upon
completion of each metal layer.
[0003] The CMP process involves holding, and optionally rotating, a
thin, reasonably flat, semiconductor wafer against a rotating
polishing pad. The wafer may be repositioned radially within a set
range as the polishing pad is rotated across the surface of the
wafer. The polishing surface, which conventionally includes a
polyurethane material affixed to a platen, is wetted by a chemical
slurry, under controlled chemical, pressure, and temperature
conditions. The chemical slurry contains selected chemicals which
etch or oxidize selected surfaces of the wafer during the CMP
process in preparation for their removal.
[0004] The more uniformly the chemical and mechanical agents remove
the material during the polishing process, the better planarization
of the polished surface of the semiconductor wafer. However, in
this process it is important to remove a sufficient amount of
material to provide a planar surface, without removing an excessive
amount of underlying materials. As a result, uniform material
removal is particularly important in today's submicron technologies
where the layers between device and metal levels are constantly
getting thinner.
[0005] Because of the importance of the uniform removal of
material, the manufacture of semiconductor wafer polishing pads has
become a critical part of the overall manufacturing process.
Conventional polishing pads for use in the CMP process are
typically formed by adhering a polyurethane polishing surface, or
other suitable polymer material, to a foam or felt pad impregnated
with the same or similar polymer material. However, before the
gluing may take place, an initial step in the manufacture of such
polishing pads is cutting the polishing pad from a large cylinder,
called a "cake," composed of that material. This step of the
manufacturing process is typically referred to as "skiving."
Unfortunately, conventional techniques used to skive the polishing
pad from the cake are believed to be problematic.
[0006] Accordingly, what is needed in the art is a method of
manufacturing a polishing pad that does not suffer from the
numerous deficiencies of the methods found in the prior art.
SUMMARY OF THE INVENTION
[0007] To address the above-discussed deficiencies of the prior
art, the present invention provides a method of manufacturing a
semiconductor wafer polishing pad using a beam, and a system
incorporating the method. In one embodiment, the method includes
providing a cake that is susceptible to beam ablation, and skiving
a polishing pad from the cake using the beam. In an advantageous
embodiment, the cake is comprised of polyurethane.
[0008] In exemplary embodiments of the present invention the beam
may be a laser, for example an excimer laser, and may be pulsed
along the cutting line where the cake will be skived. In these
embodiments, the beam may have an intensity of about 400 mJ, a
wavelength ranging from about 193 nm to about 308 nm, and a
frequency ranging from about 250 Hz to about 800 Hz. In addition,
if the beam is pulsed, the duration of each pulse ranges from about
10 ns to about 50 ns.
[0009] The foregoing has outlined, rather broadly, preferred and
alternative features of the present invention so that those skilled
in the art may better understand the detailed description of the
invention that follows. Additional features of the invention will
be described hereinafter that form the subject of the claims of the
invention. Those skilled in the art should appreciate that they can
readily use the disclosed conception and specific embodiment as a
basis for designing or modifying other structures for carrying out
the same purposes of the present invention. Those skilled in the
art should also realize that such equivalent constructions do not
depart from the spirit and scope of the invention in its broadest
form.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] For a more complete understanding of the present invention,
reference is now made to the following description taken in
conjunction with the accompanying drawing, in which,
[0011] FIG. 1 illustrates a system for skiving a polishing pad
using a beam, such as that generated from a beam apparatus,
according to the principles of the present invention.
DETAILED DESCRIPTION
[0012] Most conventional techniques require skiving the polishing
pad from the cake with a large, optionally rotated, metal blade. It
has been recently discovered, however, that skiving with such a
blade negatively impacts the physical characteristics of the pad
removed from the cake and used to form the polishing surface of the
polishing pad. It is believed that the primary physical
characteristic is the change in the viscoelastic properties of the
polyurethane across its diameter and throughout its thickness.
[0013] Ultrasonic mapping of the type described in co-pending
patent application Ser. No. 09/340,779, filed Jun. 28, 1999 and
entitled "Non-Destructive System And Method For Measuring Bond
Completion On Urethane Polishing Pads," has been used to reveal
this nonuniformity. Through such mapping, the nonuniform density of
the polyurethane is revealed to be a bulk phenomenon, and the
distortion is not simply limited to the surface of the polishing
pad. The details of performing such an ultrasonic mapping technique
are described in the aforementioned application, which is commonly
assigned with the present invention and is incorporated herein by
reference in its entirety.
[0014] It is believed that among the causes of this nonuniformity
is the mechanical distortion of the polyurethane caused by the
pressure of the blade during the skiving process. It is further
hypothesized that the thermal distortion caused by the heat
generated from the friction between the blade and the cake causes
further nonuniformity in the physical characteristics of the
polishing pads. In addition to non-uniformity, device damaging
defects are generated. Moreover, the damage to the polishing
surface is believed to be exacerbated when the polymer material
comprising the cake is particularly soft or heat sensitive. In
addition, as metal blades dull, these disadvantages become even
more prominent until the blade is replaced, often at significant
cost.
[0015] The combination of these disadvantages typically results in
a costly skiving process that produces a polishing pad having
nonuniform physical characteristics across the diameter of the
polishing pad. Consequently, without uniform physical properties
across the entire polishing pad, and throughout its thickness, the
uniformity, as well as the overall quality, of the polishing
performed on semiconductor wafers is also lost. In turn, such loss
of uniformity in polishing is routinely the source of defects found
on the surface of wafers. As device size continues to shrink,
defect reduction becomes critical to maintain quality. With the
intense competition in today's semiconductor industry, and the high
cost of semiconductor materials, manufacturers are understandably
eager to reduce or eliminate the production of defective
wafers.
[0016] In light of these newly recognized problems, the present
invention, in an exemplary embodiment, as illustrated in FIG. 1,
provides a system 100 for skiving a polishing pad using a beam. The
system 100 includes a cake 110 from which semiconductor wafer
polishing pads are skived.
[0017] In an exemplary embodiment, the cake 110 is comprised of
conventional materials, such as a polymer, and in an advantageous
embodiment, is comprised of polyurethane. Those skilled in the art
understand the advantages of forming semiconductor wafer polishing
pads from polyurethane, as well as the benefits of using
polyurethane polishing pads to polish semiconductor wafers. A
polyurethane polishing pad 120, which has been skived from the cake
110, is also illustrated in FIG. 1.
[0018] The system 100 further includes a beam apparatus 130. The
beam apparatus 130 is used to generate a beam 140, which is
directed towards the cake 110. The beam 140 is used to skive the
cake 110 in accordance with the principles of the present
invention. The use of a beam on a polymer material is discussed at
length in co-pending patent application Ser. No. 09/686,028, filed
Oct. 10, 2000, and entitled "A Method of Manufacturing a Slurry
Distribution System on a Semiconductor Wafer Polishing Pad," which
is commonly assigned with the present invention and is also
incorporated by reference herein in its entirety.
[0019] In advantageous embodiments, the beam apparatus 130 may be
any device capable of producing a beam capable of cutting, such as
a focused beam, examples of which includes a laser or a focused ion
beam apparatus. Other beams that may be generated to skive the cake
110 include an energy beam, or a particle beam. In an advantageous
embodiment, a laser is used that generates a focused laser beam
that falls within the laser spectrum. The laser spectrum as used
herein includes frequencies between about 1.00.times.10.sup.12 Hz
and about 1.00.times.10.sup.15 Hz. In a particularly advantageous
embodiment, the beam apparatus 130 is an excimer laser generator.
Additionally, depending on the gas supplied to the beam apparatus,
if any, radiation may be obtained on varying wavelengths. (See
Table 1)
1 TABLE 1 Gas Wavelength XeF 351 nm XeCl 308 nm KrF 248 nm ArF 193
nm F.sub.2 157 nm
[0020] In order to skive the polishing pad 120 from the cake 110,
the beam 140 is projected against the cake 110. Once in contact
with the cake 110, the beam 140 is used to cut through the material
comprising the cake 110. It must be noted that the present
invention is not limited to a single beam 140. In other
embodiments, the cake 110 may be skived by multiple beams produced
from the single beam apparatus 130 illustrated in FIG. 1 using beam
splitters, or even generated from more than one beam apparatus
130.
[0021] When the beam 140 is focused and concentrated onto the cake
110, thermal energy generated by the beam apparatus 130 and carried
by the beam 140 cuts, or skives, the material of the cake 110 at a
desired location. By ablating the cake 110 material with a narrowly
beam 140, rather than cutting the material using the crude
mechanical methods found in the prior art, semiconductor wafer
polishing pads are created with greater speed and precision.
Moreover, it is believed that mechanical and thermal distortion of
the polyurethane caused by the pressure of the blade during the
skiving process is substantially reduced with the use of the
pulsed, beam apparatus. This is so since organic polymers have poor
thermal conductivity and strong absorption at these
wavelengths.
[0022] The beam 140 may also be pulsed against the cake 110 during
the skiving process. In a more specific embodiment, the beam 140 is
pulsed for a period of time ranging from about 10 ns to about 50
ns. In an advantageous embodiment, by pulsing the beam 140 for a
duration less than 50 ns most of the thermal energy carried by the
beam 140 is carried off by the polymer material ejected during the
ablation of the cake 110. More precisely, the polymer material of
the cake 110 is heated during the pulse duration of the beam
apparatus 130, which is set to a particular intensity, so as to
sublimate the polymer material. By dissipating most of the thermal
energy along with the ejected material in this manner, little or no
thermal damage to the remaining cake 110 material occurs. Those
skilled in the art recognize one embodiment of this method of
operating a beam apparatus to cut material as "pulsed laser
evaporation," a form of ablation, and is commonly employed in other
fields of micro-machining.
[0023] The further dissipate thermal energy, the beam 140 may also
be focused on varying locations of the cake 110, all along the line
of cutting. Specifically, in an exemplary embodiment of the present
invention, a conventional computer system 150 conventionally
programmed with the varying pattern may be employed to maneuver the
beam 140 to different locations along the line of cutting in any of
a number of desired movements. In an alternative embodiment, the
computer system 150 may move the cake 110 itself while holding the
beam 140 in a stationary position, or may even maneuver both the
beam 140 and the cake 110 simultaneously during the skiving
process. In a further embodiment, mirrors may be employed to
redirect the beam 140 across the cutting line on the cake 110. Of
course, such maneuvering may also be accomplished manually, rather
than with the assistance of the computer system 150. Regardless of
the method used, it should be understood that such maneuvering of
the beam 140 along the cutting line allows the polishing pad 120 to
be skived from the cake 110 without concentrating a great deal of
thermal energy in a single location for an extended period of
time.
[0024] In another exemplary embodiment, the beam 140 used to skive
the polishing pad 120 has a frequency ranging from about 250 Hz to
about 800 Hz. In an advantageous embodiment, the beam 140 has a
specific frequency of about 300 Hz. It has been found that
operating the beam apparatus 130 at about 300 Hz, such as with an
excimer laser, is most advantageous when skiving semiconductor
wafer polishing pads comprised of polyurethane. Of course, other
frequencies are well within the broad scope of the present
invention.
[0025] The beam apparatus 130 in this advantageous embodiment is
also operated at an intensity of about 400 mJ/cm.sup.2. By focusing
the beam 140 on the cake 110 with an intensity of about 400
mJ/cm.sup.2, the polishing pad 120 may be skived with high
efficiency. Moreover, efficiency may be maximized by applying the
beam 140 with the minimum intensity necessary to skive the
polishing pad 120, so that the least amount of damaging thermal
energy is generated by the beam apparatus 130. By operating the
beam apparatus 130 at this advantageous point, thermal damage to
the material remaining on the cake 110 is curtailed or eliminated.
When combined with one of the maneuvering technique described
above, the possibility of thermal damage to the remaining material
on the cake 110 is even further minimized. Moreover, with the use
of a beam, such as a excimer laser beam, polishing pads having
substantially uniform physical characteristics throughout may be
consistently manufactured with greater ease and less expense due to
the pulse-to-pulse energy stability, as well as the wavelength
stability and reproducibility, achievable with laser beams. In
addition, a XeCl excimer laser has the advantage of using HCl gas
rather than the F.sub.2 gas required for a KrF (308 nm) laser in a
manufacturing environment.
[0026] Similarly, the beam apparatus 130 may be operated to
generate a beam 140 within the ultraviolet wavelength, for example,
ranging from about 248 nm to about 308 nm. In an exemplary
embodiment, the beam 140 has a wavelength of about 248 nm, which
results in the removal (and sublimation) of only about 1000 nm of
polymer material from the cake 110 during one pulse. By removing
such small amounts of material at a time, in addition to the
sublimate effect discussed above, the thermal damage caused to the
remaining material is even further curtailed, resulting in the
manufacture of a more precise and uniform polishing pad 120.
[0027] The computer system 150 discussed above is coupled to the
beam apparatus 130 in order to regulate the parameters of the beam
140 mentioned above. With the computer system 150, the numerous
parameters of the beam 140 may be established such that the
polishing pad 120 may be skived from the cake 110 with little or no
variation in physical characteristics. By producing a polishing pad
120 having substantially uniform physical characteristics across
its entire diameter, as well as throughout its thickness, the
polishing of semiconductor wafers becomes much more precise than
with polishing pads manufactured using techniques found in the
prior art. This uniformity may be seen by performing ultrasonic
mapping of the polishing pads skived in accordance with the present
invention, in accordance with the technique described above.
[0028] In addition, a feedback sensor (not illustrated) may also be
coupled to the computer system 150 in order to send information
regarding those physical characteristics to the computer system 150
during the skiving process. In response to such information from
the feedback sensor, the computer system 150 may then alter the
settings of the beam apparatus 130, and thus the parameters of the
beam 140 generated therefrom. Thus, whether the physical
characteristics of the polishing pad 120 are uniform may be
monitored, and if necessary corrected, throughout the skiving
process. In addition, this level of precision may be repeated from
one polishing pad to the next, with little or no variation between
them.
[0029] In conclusion, a method and system have been described that
uses a beam apparatus generating a beam to skive a cake in order to
manufacture semiconductor wafer polishing pads. By employing a beam
to skive the cake, the present invention overcomes the
disadvantages found in the prior art methods. Specifically,
inaccuracies between new and used blades is eliminated, since a
beam, such as a pulsed excimer laser beam, produces higher accuracy
and precision. Additionally, thermal damage to the areas
surrounding the cutting line is reduced or eliminated by adjusting
the intensity and duration of the beam, based on the material
comprising the cake. With the proper adjustment of the beam, the
thermal energy generated by the beam is dispersed along with the
material ejected and sublimated during the skiving process. As a
result, semiconductor wafer polishing pads having substantially
uniform physical characteristics across their diameters may be
manufactured quickly, accurately and repeatedly. Additionally, by
conducting the skiving process with a computer system, the
repeatability of these uniform physical characteristics from one
polishing pad to the next may be assured, as evidenced through
ultrasonic mapping of polishing pads manufactured using the system
or method of the present invention.
[0030] Although the present invention has been described in detail,
those skilled in the art should understand that they can make
various changes, substitutions and alterations herein without
departing from the spirit and scope of the invention in its
broadest form.
* * * * *