U.S. patent application number 10/136589 was filed with the patent office on 2003-11-06 for annealing of cmp polishing pads.
Invention is credited to Moinpour, Mansour, Sorooshian, Jamshid, Tregub, Alexander.
Application Number | 20030207661 10/136589 |
Document ID | / |
Family ID | 29268972 |
Filed Date | 2003-11-06 |
United States Patent
Application |
20030207661 |
Kind Code |
A1 |
Tregub, Alexander ; et
al. |
November 6, 2003 |
Annealing of CMP polishing pads
Abstract
A manufactured chemical mechanical polishing pad is annealed
after manufacture to improve its operating characteristics.
Annealing can stabilize the operational properties of the pad, such
as coefficient of thermal expansion and compressibility. In one
embodiment, annealing partially or fully completes a curing process
that was incomplete after the pad was manufactured.
Inventors: |
Tregub, Alexander; (Oak
Park, CA) ; Sorooshian, Jamshid; (Tucson, AZ)
; Moinpour, Mansour; (San Jose, CA) |
Correspondence
Address: |
BLAKELY SOKOLOFF TAYLOR & ZAFMAN
12400 WILSHIRE BOULEVARD, SEVENTH FLOOR
LOS ANGELES
CA
90025
US
|
Family ID: |
29268972 |
Appl. No.: |
10/136589 |
Filed: |
May 1, 2002 |
Current U.S.
Class: |
451/550 |
Current CPC
Class: |
B24B 37/20 20130101;
B24D 18/00 20130101 |
Class at
Publication: |
451/550 |
International
Class: |
B24B 005/00 |
Claims
What is claimed is:
1. An article, comprising a chemical mechanical polishing pad which
has been annealed after manufacture of the chemical mechanical
polishing pad.
2. The article of claim 1, wherein said chemical mechanical
polishing pad includes a polymer-based material.
3. The article of claim 1, wherein said chemical mechanical
polishing pad includes polyurethane filled with at least one of
solid fibers and solid fillers.
4. The article of claim 1, wherein said chemical mechanical
polishing pad has been annealed at a temperature within a range of
about 100-120 degrees Celsius.
5. The article of claim 1, wherein said chemical mechanical
polishing pad has been annealed for a time within a range of about
7 to 9 hours.
6. A system, comprising: an oven; and a controller coupled to the
oven and including one or more parameters to control at least one
of temperature and time in the oven to anneal a manufactured
chemical mechanical polishing pad.
7. The system of claim 6, wherein: the oven is to anneal the
manufactured chemical mechanical polishing pad for a predetermined
time at a predetermined temperature to further cure a material in
the manufactured chemical mechanical polishing pad.
8. The system of claim 6, wherein: the controller is to control the
oven to anneal the manufactured chemical mechanical polishing pad
at a temperature between about 100 and 120 degrees Celsius.
9. The system of claim 6, wherein: the controller is to control the
oven to anneal the manufactured chemical mechanical polishing pad
for a time of between about 7 to 9 hours.
10. A method, comprising annealing a manufactured chemical
mechanical polishing pad to further cure a material in the
manufactured chemical mechanical polishing pad.
11. The method of claim 10, wherein said annealing includes
annealing for a predetermined time.
12. The method of claim 10, wherein said annealing includes
annealing for about 7 to 9 hours
13. The method of claim 10, wherein said annealing includes
annealing at a predetermined temperature.
14. The method of claim 10, wherein said annealing includes
annealing within a temperature range of about 100-120 degrees
Celsius.
15. The method of claim 10, wherein said annealing includes
annealing a polymer-based chemical mechanical polishing pad.
16. The method of claim 10, wherein said annealing includes
annealing a chemical mechanical polishing pad having polyurethane
filled with at least one of solid fibers and solid fillers.
17. The method of claim 10, wherein said annealing takes place
after preparing a polishing surface on the chemical mechanical
polishing pad.
18. The method of claim 10, wherein said annealing takes place
before preparing a polishing surface on the chemical mechanical
polishing pad.
19. A machine-readable medium that provides instructions, which
when executed by a set of one or more processors, cause said set of
processors to perform operations comprising: selecting a
predetermined temperature and predetermined time to heat a
previously-manufactured chemical mechanical polishing pad; and
heating the previously-manufactured chemical mechanical polishing
pad to the predetermined temperature for the predetermined time to
further cure a material in the chemical mechanical polishing
pad.
20. The medium of claim 19, wherein: said selecting includes
selecting the predetermined temperature and predetermined time to
further cure a polymer-based chemical mechanical polishing pad.
21. The medium of claim 19, wherein: said selecting includes
selecting the predetermined temperature and predetermined time to
further cure a polyurethane chemical mechanical polishing pad
having at least one of solid fibers and solid fillers.
22. The medium of claim 19, wherein: said selecting the
predetermined temperature includes selecting the predetermined
temperature within a temperature range of about 100-120 degrees
Celsius.
23. The medium of claim 19, wherein: said selecting the
predetermined time includes selecting the predetermined time within
a time range of about 7 to 9 hours.
24. An article produced by a process of: annealing a chemical
mechanical polishing pad after manufacture of the chemical
mechanical polishing pad.
25. The article of claim 24, wherein said annealing includes
annealing for a predetermined time.
26. The article of claim 24, wherein said annealing includes
annealing for about 7 to 9 hours
27. The article of claim 24, wherein said annealing includes
annealing at a predetermined temperature.
28. The article of claim 24, wherein said annealing includes
annealing within a temperature range of about 100-120 degrees
Celsius.
29. The article of claim 24, wherein said annealing includes
annealing a polymer-based chemical mechanical polishing pad.
30. The article of claim 24, wherein said annealing includes
annealing a chemical mechanical polishing pad having polyurethane
filled with at least one of solid fibers and solid fillers.
Description
BACKGROUND
[0001] 1. Technical Field
[0002] An embodiment of the invention relates generally to
integrated circuit manufacturing, and in particular relates to
devices used for polishing operations during integrated circuit
manufacturing.
[0003] 2. Description of the Related Art
[0004] During the fabrication of integrated circuits, chemical
mechanical polishing (CMP), sometimes also referred to as chemical
mechanical planarization, is used to remove controlled levels of
surface material from a semiconductor wafer (e.g., partially remove
a metal layer previously deposited on the semiconductor wafer)
while retaining the required levels of smoothness and flatness on
the wafer surface. CMP is typically performed by polishing the
wafer with a CMP pad and a chemical slurry. The chemical slurry
serves as both a polishing compound and a chemical agent that
reacts with the material being polished. To meet sub-micron
tolerances in the polishing operation, the pad must exert a certain
pressure on the wafer during the polishing. The stability of this
pressure is affected by the coefficient of thermal expansion (CTE)
of the pad, and by the pad compressibility. Pad compressibility is
related to the mechanical modulus of the pad material. (Mechanical
modulus is a measure of the stress/strain ratio in a material, a
characteristic sometimes loosely referred to as hardness.
Compressibility indicates how easily a material may be compressed
under pressure. The two are inversely related, i.e., a low
mechanical modulus indicates high compressibility, indicating that
a given amount of compression requires only a relatively small
amount of force.)
[0005] Many CMP pads are formed from a "cake" (a bulk quantity of
material with a predetermined size and/or shape) of a polymer-based
material, such as polyurethane filled with solid fibers and/or
fillers. The cake is sliced into individual pads after the material
has been cured. As used herein, "cure" refers to non-reversible
chemical and/or physical changes in the material. Unfortunately,
the curing process that takes place during manufacture is typically
incomplete when the bulk material is sliced into pads, when the
pads are sold, and when the pads are used. The degree of cure may
vary from one cake to another, and may even vary between pads from
the same cake, depending on where in the cake that a given pad was
produced. During operational use of the pads, the degree of cure
affects the stability of the relevant properties of CTE and
compressibility. This results in multiple quality control problems
for the pad users: 1) The pads can continue to slowly cure after
manufacture, so the relevant properties change while the pads are
still on the shelf, making the operational properties of any
particular pad unpredictable; and 2) the operating temperature of
the pad during use varies due to friction and other effects, and
the CTE and mechanical modulus of an uncured pad can vary
considerably with temperature, causing unpredictable variations in
the polishing operation (e.g., as the CTE changes with temperature,
if the rate of expansion/contraction of the pad changes by an
undetermined amount, the polishing pressure also changes by an
undetermined amount, and the frictional heating due to the
polishing pressure will cause undetermined temperature changes and
CTE changes, etc.); 3) as the mechanical modulus and
compressibility of the pad material vary with temperature, those
two parameters change by an undetermined amount, resulting in
further unpredictability in pressure and effectiveness; etc.
[0006] Conventional ways of addressing these problems are: 1) to
reduce the shelf life of the pads to reduce the range of
post-manufacturing curing, 2) to increase the frequency of pad
replacement (thereby reducing a pad's operational lifetime), and/or
3) to reduce the operating cycle time of each pad to minimize
operation-induced temperature effects. Each of these solutions is
wasteful and expensive.
BRIEF DESCRIPTION OF THE DRAWINGS
[0007] The invention may best be understood by referring to the
following description and accompanying drawings that are used to
illustrate embodiments of the invention. In the drawings:
[0008] FIG. 1 shows CMP pads at various stages of the manufacturing
and annealing process, according to one embodiment of the
invention.
[0009] FIG. 2 shows a flow chart of a method to produce CMP pads,
according to one embodiment of the invention.
[0010] FIG. 3 shows a graph of the affect of annealing temperature
on the width of the operational temperature range within which CTE
is low, according to one embodiment of the invention.
[0011] FIG. 4 shows a graph of the affect of annealing time on the
width of the operational temperature range within which CTE is low,
according to one embodiment of the invention.
[0012] FIG. 5 shows a graph of the affect of annealing temperature
on mechanical modulus, according to one embodiment of the
invention.
[0013] FIG. 6 shows a flow chart of a process to anneal CMP pads in
an oven, according to one embodiment of the invention.
DETAILED DESCRIPTION
[0014] In the following description, numerous specific details are
set forth. However, it is understood that embodiments of the
invention may be practiced without these specific details. In other
instances, well-known circuits, structures and techniques have not
been shown in detail in order not to obscure an understanding of
this description.
[0015] References to "one embodiment", "an embodiment", "example
embodiment", "various embodiments", etc., indicate that the
embodiment(s) of the invention so described may include a
particular feature, structure, or characteristic, but not every
embodiment necessarily includes the particular feature, structure,
or characteristic. Further, repeated use of the phrase "in one
embodiment" does not necessarily refer to the same embodiment,
although it may.
[0016] In various embodiments of the invention, CMP pads that have
already been manufactured are annealed to fully or more fully
complete the curing process, resulting in more stable operating
characteristics for the pads. The operating characteristics that
are more fully stabilized in this manner may include one or both of
CTE and compressibility.
[0017] FIG. 1 shows CMP pads at various stages of the manufacturing
and annealing process, according to one embodiment of the
invention. FIG. 1 shows a CMP cake 110, which is sliced into
manufactured CMP pads 120. Annealing is performed in an oven 130
under the control of controller 135, to produce annealed CMP pads
140. FIG. 2 shows a flow chart of a method to produce CMP pads,
according to one embodiment of the invention. In the following
text, FIGS. 1 and 2 are sometimes described in relation to each
other. However, it is understood that the embodiment of FIG. 1 may
be implemented without using the embodiment of FIG. 2, and the
embodiment of FIG. 2 may be implemented without using the
embodiment of FIG. 1.
[0018] In the exemplary embodiment described in flow chart 200 of
FIG. 2, a CMP cake is produced at block 210. In one operation, a
fluid form of the pad material is poured into a mold and processed
until the material solidifies. In the exemplary embodiment of FIG.
1 the cake is cylindrically shaped, but in other embodiments the
cakes may have other shapes. The cake may be made of various
materials, and may undergo various processes suited to those
materials. The cake formation process may use any number of
techniques to solidify the material, including one or more of time,
heat, and chemical reaction. While in one embodiment a basic
material in the cake is polyurethane, in alternate embodiments the
basic material may be something else (e.g., polycarbonate). In some
embodiments, additional substances are introduced into the basic
material to provide the necessary abrasive qualities. In one
embodiment solid polymer fibers and/or fillers (material in a
non-fiber shape) are added to the basic material while the basic
material is in a liquid state to provide an abrasive surface on the
finished pad. In another embodiment, gas micro bubbles are
introduced into the basic material when the basic material is in
the liquid state. The resulting cavities produce a rough surface
when the material is hardened and sliced into pads, exposing the
bubble cavities. Still other embodiments may use other
techniques.
[0019] Returning to FIG. 2, but with reference to FIG. 1, at block
220 the cake is sliced into individual pads 120. At block 230 the
polishing surfaces on each pad are prepared, to produce the
necessary roughness and other surface characteristics. In various
embodiments, preparation may include one or more of operations
including but not limited to sanding, grinding, embossing,
grooving, etc. to achieve the desired surface characteristics on
the pad's polishing surfaces. In a particular embodiment in which
only one surface of the pad is to be used for polishing, the
preparation may be limited to that one surface. If the method of
slicing produces a surface with the necessary qualities,
preparation of the polishing surfaces may be unnecessary and block
230 may be skipped.
[0020] While in one embodiment the pads are considered manufactured
after the slicing operation, in another embodiment the pads are
considered manufactured after the polishing surfaces are
prepared.
[0021] At block 240, the pads 120 are annealed by placing them into
an oven 130 and heating the pads 120 at a predetermined temperature
for a predetermined time. Controller 135 may be used to control the
temperature and/or time of heating in oven 130. Operation of
controller 135 may include, but is not limited to, one or more of
mechanical, electrical, electronic, and programmable means to
control the temperature and/or time of annealing. After annealing,
the annealed CMP pads 140 are provided for CMP usage at block
250.
[0022] FIG. 3 shows a graph of the affect of annealing temperature
on the width of the operational temperature range within which CTE
is low, according to one embodiment of the invention. The effect of
annealing on the CTE of manufactured pads is affected by the
annealing temperature and the time at which the pad is exposed to
that temperature. These parameters are further affected by the
material used in the pad and by the amount of cure that previously
took place when the cake was formed. The measurements shown for the
example embodiments of FIG. 3-5 are based on commercially available
polyurethane pads with solid non-organic fillers, but other
embodiments with other pad materials may produce different
characteristic curves. For example, other embodiments may include
organic fibers, organic fillers, and/or non-organic fibers. Fillers
may be considered material in which the length-to-width ratio of
individual particles is approximately `1`, while individual
particles of fiber may have a length-to-width ratio greater than
that value.
[0023] In the example embodiments of FIGS. 1 and 2, CTE is very
low, and may even approach zero, within a range (a `thermal
window`) of the operating temperatures that the pad will likely
experience during a polishing operation. Such operating
temperatures typically fall between about 25 and 75.degree. C. A
pad with a wider thermal window can operate over a wider portion of
these typical operating temperatures without experiencing the
detrimental effects caused by excessive expansion/contraction of
the pad. As shown in FIG. 3, the width of this thermal window for a
given pad varies with the amount of annealing. To provide a common
standard for pads of different sizes and manufacturing techniques,
FIGS. 3 and 4 show the percentage change in the width of the
thermal window (as compared with the width for a non-annealed pad)
rather than the measured width in .degree. C. In the exemplary
embodiment of FIG. 3, measurements were taken for pads that were
annealed for one hour at 70.degree. C., 110.degree. C., 150.degree.
C., and 190.degree. C., as well as for a non-annealed pad kept at
room temperature (RT). The remaining portion of the curve was
extrapolated from these data points.
[0024] In the example embodiment of FIG. 3, annealing the pads at a
temperature of approximately 110.degree. C. maximizes the range of
operating temperatures within which CTE remains low. In some
embodiments, annealing at approximately 110.degree. C. produces
pads having a low CTE across the entire operating range of
25.degree. C. -75.degree. C. Other embodiments may include pads
that have other optimum annealing temperatures.
[0025] FIG. 4 shows a graph of the affect of annealing time on CTE,
according to one embodiment of the invention. The annealing
temperature for these pads was 110 .degree. C. Like FIG. 3, the
vertical axis shows a percentage change in the width of the thermal
window of operating temperatures in which CTE is acceptably low. In
the example embodiment, the maximum thermal window is achieved with
an annealing time of about 8 hours, and annealing beyond that time
gradually decreases the width of the thermal window.
[0026] FIG. 5 shows a graph of the effect of annealing temperature
on mechanical modulus, according to one embodiment of the
invention. The vertical axis of the graph represents the maximum
variation in mechanical modulus as the operating temperature of the
pads varies across the range of normal operating temperatures.
Actual tests were conducted on pads that had been annealed for one
hour at 70.degree. C., 110.degree. C., 150.degree. C. and
190.degree. C., as well as a non-annealed pad kept at room
temperature (RT) until the test. Intermediate annealing
temperatures have been extrapolated from these points. As can be
seen from the graph, the lowest variation in mechanical modulus
occurred in pads that were annealed at a temperature of
approximately 80.degree. C., with pads annealed at temperatures
above that optimum temperature also showing lower variation than
non-annealed pads.
[0027] As seen from FIGS. 3, 4 and 5, a single combination of
annealing time/temperature may not optimize both CTE and
compressibility. But depending on the overall requirements for
polishing performance, an annealing time/temperature to produce
best overall results for each type of pad may be determined with
minimal testing. In the example embodiments of FIGS. 3, 4, and 5, a
variation of plus or minus 10.degree. C. in temperature and plus or
minus one hour in time does not produce significantly different
results, so one embodiment uses an annealing temperature of between
approximately 100-120 degrees .degree. C., and an annealing time of
between approximately 7-9 hours. Other embodiments may use other
times and/or temperatures.
[0028] The invention may be implemented in one or a combination of
hardware, firmware, and software. The invention may also be
implemented as instructions stored on a machine-readable medium,
which may be read and executed by at least one processor to perform
operations described herein. A machine-readable medium may include
any mechanism for storing or transmitting information in a form
readable by a machine (e.g., a computer). For example, a
machine-readable medium may include read only memory (ROM); random
access memory (RAM); magnetic disk storage media; optical storage
media; flash memory devices; electrical, optical, acoustical or
other form of propagated signals (e.g., carrier waves, infrared
signals, digital signals, etc.), and others.
[0029] FIG. 6 shows a flow chart of a process to anneal CMP pads in
an oven, according to one embodiment of the invention. The process
of flow chart 600 may be implemented through any number of
techniques, such as but not limited to one or more of: 1) manual
control of the oven, 2) automated control of the oven (e.g., with a
computerized oven controller), 3) a combination of manual and
automated controls, etc.
[0030] Different types of pads (e.g., different materials,
different manufacturing processes, different sizes, etc.) may
produce different characteristic curves than those shown in FIGS.
3, 4 and 5. Based on this information, the preferred parameters of
annealing time and annealing temperature for different pads may be
determined through testing and stored for reference. The correct
parameters may then be retrieved and used as needed. At block 610,
parameters are obtained that identify the annealing characteristics
for the particular CMP pads to be annealed. While in one embodiment
these time and temperature parameters are provided by a human
operator through a keyboard or other input device, in another
embodiment these time and temperature parameters are provided
through an input port from a device external to the oven
controller. Blocks 620, 622 and 624 pertain to three different
types of identifying parameters. In block 620, time and temperature
parameters for the oven are input directly.
[0031] In block 622, one or more `type` parameters are obtained,
identifying the type of pad to be annealed. This information may be
in the form of brand name, model number, or other parameter that
identifies a particular type of pad. At block 632, the type
parameter may be used to look up a corresponding entry in a table
that contains the time and temperature parameters for various types
of pads.
[0032] In block 624, indirect pad parameters are obtained. These
parameters may define such things as the material used in the pad,
the pad's dimensions, and other material characteristics that
affect the desired annealing parameters, regardless of the brand or
model of the pads. At block 634, these indirect parameters may be
used to look up a corresponding entry in a table that contains the
time and temperature parameters for pads with various
characteristics. Alternately, indirect parameters may also be used
to calculate time and temperature parameters using one or more
predetermined algorithms.
[0033] The approaches described in blocks 620, 622/632, and 624/634
represent three different ways of obtaining time/temperature
setting for the annealing process. While in one embodiment an oven
controller is designed to receive parameters in only one of these
methods, in another embodiment two or more of these may be
incorporated into a single oven controller that permits multiple
forms of input. At block 640, the temperature parameter derived
from the appropriate combination of blocks 620, 622/632, and
624/634 is applied to heat up the oven.
[0034] Although not shown in flow chart 600, the pads may be placed
in the oven at any time prior to block 650. While in one embodiment
this is done manually by a human operator, in another embodiment
the pads are placed into the oven through automated means.
[0035] At block 650 a timer is started to determine when the pads
have been annealed for the proper amount of time, with the
expiration of the annealing time determined at block 660. While in
one embodiment a mechanical timer is used, in another embodiment an
electronic or software timer is used. While in one embodiment the
annealing time includes predetermined heatup and cool down times,
in another embodiment the pads are placed into, and removed from,
the oven while the oven is at the indicated annealing temperature.
In still another embodiment, the annealing process includes
multiple sequential annealing stages, each with its own
predetermined time and temperature parameters. Each stage may
include predetermined heat up and cool down times. When multiple
stages are used, multiple timeouts may be experienced at block 660.
Regardless of whether one or multiple annealing stages are used,
when the final timeout occurs, the annealing process for the
current pads is ended at block 670.
[0036] In another embodiment not shown, instead of placing a fixed
number of pads into a stationary oven, a conveyer belt may move a
continuous supply of pads through a tunnel-shaped oven. The
conveyor speed may be set to control the annealing time by
controlling how long it takes a given pad to travel through the
oven. Different stages may be achieved by using thermal dividers to
segment the oven into different temperature zones having different
lengths.
[0037] The foregoing description is intended to be illustrative and
not limiting. Variations will occur to those of skill in the art.
Those variations are intended to be included in various embodiments
of the invention, which are limited only by the spirit and scope of
the appended claims.
* * * * *