U.S. patent application number 09/863689 was filed with the patent office on 2001-12-27 for control of cmp removal rate uniformity by selective control of slurry temperature.
Invention is credited to Swanson, Leland.
Application Number | 20010055940 09/863689 |
Document ID | / |
Family ID | 26906354 |
Filed Date | 2001-12-27 |
United States Patent
Application |
20010055940 |
Kind Code |
A1 |
Swanson, Leland |
December 27, 2001 |
Control of CMP removal rate uniformity by selective control of
slurry temperature
Abstract
A CMP machine (100, 200, 300) and/or process that uses selective
heating of the slurry (160) to improve uniformity. A temperature
control mechanism (110) is used to heat and/or cool slurry (160)
applied to a selected area of the pad or belt (120, 220, 320).
Heating in the selected area improves the removal rate in that
area, whereas cooling decreases the removal rate in that area. For
example, heating along the perimeter of the pad (120, 220) improves
the removal rate at the perimeter of the semiconductor wafer
(150).
Inventors: |
Swanson, Leland; (McKinney,
TX) |
Correspondence
Address: |
TEXAS INSTRUMENTS INCORPORATED
P O BOX 655474, M/S 3999
DALLAS
TX
75265
|
Family ID: |
26906354 |
Appl. No.: |
09/863689 |
Filed: |
May 23, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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60211671 |
Jun 15, 2000 |
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Current U.S.
Class: |
451/53 |
Current CPC
Class: |
B24B 37/015
20130101 |
Class at
Publication: |
451/53 |
International
Class: |
B24B 001/00 |
Claims
In the claims:
1. A method of fabricating an integrated circuit, comprising the
steps of: placing a wafer against a moving polishing pad while
adding a first slurry to a first location and a second slurry to a
second location wherein a temperature of said first slurry is
higher than a temperature of said second slurry.
2. The method of claim 1, wherein said polishing pad is a polishing
belt.
3. The method of claim 1, wherein said temperature of said first
slurry is between room temperature and 40.degree. C.
4. The method of claim 1, wherein said temperature of said second
slurry is between 5.degree. C. and room temperature.
5. The method of claim 1, wherein said second slurry spends a
higher percentage of time near a center said wafer than said first
slurry.
6. The method of claim 1, wherein said second slurry penetrates
further under said wafer than said first slurry.
7. A method of fabricating an integrated circuit, comprising the
steps of: providing a partially fabricated wafer to a wafer carrier
of a chemical-mechanical polish (CMP) machine; moving a polishing
pad of said CMP machine; adding slurry to a surface of said
polishing pad from at least two dispense points, wherein there is a
slurry temperature gradient between said at least two dispense
points; and placing said wafer against said surface while said
polishing pad is moving.
8. The method of claim 7, wherein said polishing pad is a polishing
belt.
9. The method of claim 7, wherein a first of said at least two
dispense points is located near a center of said polishing piece
and a second of said at least two dispense points is located near
an edge of said polishing piece.
10. The method of claim 9, wherein a temperature of said slurry
from said first dispense point is less than a temperature of said
slurry from said second dispense point.
11. The method of claim 7, wherein slurry from a first of said at
least two dispense points penetrates further under the wafer than
slurry from a second of said at least two dispense points.
12. The method of claim 7, wherein slurry from a first of said at
least two dispense points has a lower temperature than slurry from
a second of said at least two dispense points.
13. A chemical-mechanical polish (CMP) machine comprising: a
platen; a polishing pad located over said platen; a wafer carrier
for holding a wafer against said polishing pad; and at least two
slurry dispense outlets, wherein at least one of said slurry
dispense outlets contains a temperature control mechanism for
establishing a slurry temperature gradient between said at least
two slurry dispense outlets.
14. The CMP machine of claim 13, wherein said a first of said at
least two slurry dispense outlets is located nearer a center of
said polishing piece and a second of said at least two slurry
dispense outlet is located nearer an edge of said polishing piece.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] The following co-pending application is related and hereby
incorporated by reference:
[0002] Serial No. TI-29332
[0003] Filing Date
[0004] Inventor(s) Swanson
FIELD OF THE INVENTION
[0005] The invention is generally related to the field of
semiconductor processing and more specifically to
chemical-mechanical polishing semiconductor wafers.
BACKGROUND OF THE INVENTION
[0006] Chemical-mechanical polishing (CMP) for planarizing
semiconductor wafers during fabrication is becoming more and more
common. A CMP system generally consists of a polishing pad, wafer
carrier, and slurry. As a wafer carrier positions a semiconductor
wafer against the polishing pad, slurry is added between the
polishing pad and the wafer. The wafer, the pad, or, more
typically, both are moved to planarize the surface of the wafer.
CMP employs both a mechanical removal of material (due to the
physical abrasion of the polishing pad and slurry particles against
the surface of the wafer) and a chemical removal (etch) of material
(due to the chemical components of the slurry).
[0007] Three basic types of architecture are currently being
manufactured. The first type is a rotary polisher. In a rotary
polisher, the platen (and the polishing pad it holds) has a radius
that is slightly larger than the diameter of the semiconductor
wafer. Both the platen and the wafer are typically rotated. The
second type of CMP machine is an orbital polisher. In an orbital
polisher, the platen diameter is slightly larger than the wafer
diameter. The wafer is rotated, but the pad is not. The wafer's
center orbits around an axis of rotation offset slightly from the
pad center. The third type of CMP machine is a linear belt
polisher. In a linear belt polisher, a continuously fed belt is
moved over the platen. The wafer is rotated during polishing.
[0008] The planarization uniformity on many polishing machines is
difficult to control. This can be due to such process
irregularities as pad conditioning, down force, and slurry
delivery. Hence, achieving good planarization across a wafer is
difficult. This is especially true for copper CMP, which is
currently under development.
SUMMARY OF THE INVENTION
[0009] The invention is an improved CMP machine and/or process that
uses selective control of the slurry temperature to improve
uniformity. Slurry is applied to the polishing pad/belt at several
locations. At least one slurry location includes a temperature
adjustment mechanism to adjust the slurry temperature for a more
uniform removal rate. For example, heating slurry applied along the
perimeter of the pad and/or cooling slurry applied near the center
of the pad may improve the removal rate uniformity by increasing
the removal rate at the perimeter of the semiconductor wafer and/or
decreasing the removal rate near the center of the wafer.
[0010] An advantage of the invention is a CMP machine and/or
process having improved planarization uniformity.
[0011] This and other advantages will be apparent to those of
ordinary skill in the art having reference to the specification in
conjunction with the drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] In the drawings:
[0013] FIG. 1 is a top view of a rotary polisher modified to
include a selective control of the slurry temperature according to
the invention;
[0014] FIG. 2 is a top view of an orbital polisher modified to
include selective control of the slurry temperature according to
the invention; and
[0015] FIG. 3 is a top view of a belt polisher modified to include
a selective control of the slurry temperature according to the
invention.
DETAILED DESCRIPTION OF THE EMBODIMENTS
[0016] The invention will now be described in conjunction with
three separate CMP machine architectures. It will be apparent to
those of ordinary skill in the art that the invention may be
applied to other machine architectures as well.
[0017] It is known that the copper removal rate during polish
increases as the pad and slurry temperature rises. This is due to
the fact that the chemical component of the CMP process is
thermally activated. In the invention, the temperature of the
slurry applied to selective areas of the pad is adjusted to improve
the uniformity across a wafer during CMP. For example, heated
slurry may be applied to selective areas of the pad that correspond
to areas of the wafer having a low removal rate. Alternatively, or
additionally, cooled slurry may be applied to selective areas of
the pad that correspond to areas of the wafer having high removal
rate. By balancing out the removal rate across a wafer, uniformity
is improved.
[0018] In copper CMP, the removal rate is lower near the edges of a
wafer (.about.2-5 cm inset from the edge of the wafer by a few mm)
than near the center of the wafer. In order to improve the removal
rate uniformity across the wafer, heated slurry may be applied to
the area of the polishing pad that polishes more of the edge of the
wafer than the center. The heated slurry, in turn, increases the
removal rate in that area making it more uniform across the
wafer.
[0019] New slurries specifically for shallow trench isolation and
copper CMP are currently under development. An important feature of
these new slurries is that they have a highly non-linear removal
rate vs. down force relation. The result is that high features on a
wafer are polished down significantly faster than low areas. The
higher the differential between the high and low site removal rate
(RR), the better. This way dishing of wide features, such as Cu
bond pads is minimized. The conventional way that this is achieved
through slurry design is to build in two competing mechanisms:
passivation, and chemical etch, each with there own reaction rates.
The sequence of events during CMP is basically the following:
[0020] 1. The surface is passivated after immersion into the
fluid
[0021] 2. The pad, along with the slurry abrasive, removes the
passivation layer. Since the pad pressure on the low or recessed
sites is less than that on the high areas, the passivation RR is
less there.
[0022] 3. Chemical attack by the etchant component of areas lacking
passivation. Since passivation RR is less on low areas, the etch
rate will also be less, and the overall material RR is also less.
The etchant component may be a chemical, which merely converts the
surface to a softer material that is very easily removed by the
pad/abrasive combination, effectively increasing the material RR in
that manner.
[0023] 4. The overall surface tends toward a planar topography, as
desired.
[0024] The idea behind using an increased or decreased slurry
temperature is to increase the reaction rate of the etchant in step
3 above. Since all chemical reactions are thermally activated,
changing the temperature should vary the rates in step 3.
[0025] It should be noted that since the slurry heats the pad, the
pad may be softened. Such softening may increase dishing on those
areas of the wafer. This is an effect to be balanced against the
need to achieve uniform removal across the wafer.
[0026] FIG. 1 shows a rotary polisher 100 modified to include
selective control of the temperature of the slurry applied to
selective areas of the polishing pad 120. In a rotary polisher 100,
the platen 140 has a radius that is slightly larger than the wafer
150 diameter. Platen 140 is used to hold pad 120. Wafer 150 is held
against polishing pad 120 and rotated by a wafer carrier (not
shown).
[0027] Slurry 160 is applied to the polishing pad 120 at several
sites. Two such sites are shown in FIG. 1. Temperature control
mechanism 110 is located at one or more of the slurry application
sites. Temperature control mechanism 110 heats or cools the slurry
immediately before the slurry is applied to the polishing pad 120.
The volume of temperature control mechanism 110 depends on the rate
slurry is applied to the wafer and the length of time required to
change the temperature of the slurry. It is expected that a 100 ml
volume is sufficient. The slurry may be heated for selective areas
of the polishing pad 120 where an increased removal rate is
desired. Alternatively, or additionally, the slurry 160 may be
cooled for selective areas of the polishing pad where a decreased
removal rate is desired. For example, in copper CMP the removal
rate is lower near the edge of the wafer. Therefore, to improve
this non-uniformity, the slurry 160a applied to a peripheral area
of the polishing pad 120 may be heated since this area contacts the
outer portions of the wafer 150. The slurry 160b, applied to a more
central site, may alternatively or additionally be cooled to
decrease the removal rate in that area.
[0028] In operation, slurry 160 is applied to the pad 120 from
several locations. FIG. 1 shows two slurry dispense locations.
Additional slurry dispense locations may be included. Wafer 150 is
pressed against pad 120 with the desired downforce and both the pad
and wafer are rotated. The arrows on the pad and wafer indicated
rotation direction. The slurry 160a at selected locations may be
heated using temperature control mechanism 110 to improve the
removal rate in those areas. The slurry is heated above room
temperature to a temperature as high as 30-40.degree. C.
Alternatively, or additionally, the slurry 160b at other selected
locations may be chilled using temperature control mechanism 110 to
decrease the removal rate in those areas. The slurry may be chilled
below room temperature to a temperature as low as 5.degree. C. For
copper CMP, the slurry 160a applied to the periphery of the
polishing pad 120 is heated and/or the slurry 160b applied near the
center of the polishing pad 120 is chilled. The slurry 160b is
intended to reach the center of wafer 150 and the slurry 160a
affects only the wafer edge. Lines with arrows extending from the
dispense points show the approximate path of the slurry. Slurry
160b spends more time circulating around the wafer carrier, hence
penetrating more deeply under the wafer 150. The slurry 160a is
expected to have a greater impact on the outer edge as slurry 160a
is in contact with the wafer carrier for far less time. The pad
under the outer edge may be warmed up due to the slurry and further
contribute to an increased removal rate. The result is a more
uniform removal rate across the wafer 150.
[0029] A number of different slurries are used in CMP. The
stability of the slurry at various temperatures should be
considered when setting the temperature. One danger is that
particulates may congeal out of suspension and collect on the inner
surfaces of the heater. It is known that the abrasive material of
the slurry will collect on the surface of a container where an
ultrasonic transducer is mounted outside to measure fluid column
height. Apparently, the ultrasonic energy induces agglomeration. So
heater construction and operation is important in avoiding
agglomeration. Any thermal spiking of the heater would raise the
heater surface temp much higher than the set temp, causing a high
thermal gradient through the slurry.
[0030] FIG. 2 shows an orbital polisher 200 modified to include
selective temperature control of the slurry applied to the
polishing pad 220. In an orbital polisher 200, the platen 240 has a
diameter that is slightly larger than the wafer 150 diameter.
Platen 240 is used to hold pad 220. Wafer 150 is held against
polishing pad 220 and rotated by a wafer carrier (not shown).
[0031] As with the rotary polisher, temperature control mechanism
110 selectively controls the temperature of slurry 160 applied at
various locations of the polishing pad 220. Temperature control
mechanism 110 is not shown in FIG. 2, but would be placed below
polishing pad 220. Slurry 160 is applied through holes in the
polishing pad 220 and may be heated or chilled in selected areas
just prior to application to the polishing pad. For example, in
copper CMP the removal rate is lower near the edge of the wafer.
Therefore, to improve this non-uniformity, the slurry 160a applied
to the periphery 230 of the polishing pad 220 may be heated since
this area contacts the outer portions of the wafer 150.
Alternatively or additionally, the slurry 160b applied to a more
central location 232 of the polishing pad 220 may be chilled to
decrease the removal rate nearer the center of wafer 150. Although
only one slurry dispense point is shown in each zone for
simplicity, each zone actually contains multiple slurry dispense
holes.
[0032] Temperature control mechanism 110 should be located as close
to the point of application to polishing pad 220 as possible.
Temperature control mechanism 110 could include an array of heaters
112 to heat the slurry or an array of chillers. Chillers generally
operate by circulating cooled H.sub.2O-ethylene glycol mixtures.
Alternative heating and cooling mechanisms will be apparent to
those of ordinary skill in the art.
[0033] In operation, slurry 160 is applied to the pad 220 through
holes in the pad 220. Wafer 150 is pressed against pad 220 with the
desired downforce and the wafer 150 is rotated. The pad 220 does
not rotate, but the center orbits around an axis of rotation. The
slurry applied to selected areas of the pad 120 are heated using
temperature control mechanism 110 to improve the removal rate in
those areas and/or slurry applied to other areas may be chilled to
decrease the removal rate in those areas. FIG. 2 shows three
temperature zones (230, 232, and 234). At least two zones are
required, but additional zones may be included. For copper CMP, the
slurry 160a applied to the periphery 230 of the pad 220 is heated
and/or the slurry 160b applied to a more central location 232 of
the pad 220 is chilled. The slurry 160c applied to an intermediate
zone 234 may have a temperature between the temperature of slurry
160b and 160a. This results in a more uniform removal rate across
the wafer 150.
[0034] A linear belt polisher 300 modified to include slurry
temperature control mechanism 110 is shown in FIG. 3. Linear belt
polisher 300 comprises a continuously fed belt 320. Wafer 150 is
held against polishing belt 320 and rotated by a wafer carrier (not
shown).
[0035] Slurry temperature control mechanism 110 may be used to
selectively heat slurry 160 applied to selected areas of the
polishing belt 320 where an increased removal rate is desired. For
example, in copper CMP the removal rate is lower near the edge of
the wafer 150. Therefore, to improve this non-uniformity, the
slurry 160a is heated and applied to a portion of the polishing
belt 320 where the slurry is in contact with the wafer carrier for
a short time since this area contacts the outer portions of the
wafer 150. Alternatively, (or additionally) slurry temperature
control mechanism 110 may be used to selectively cool slurry 160b
applied to selected areas of polishing belt 320 where there is a
longer contact with the wafer carrier. This results in the slurry
penetrating more deeply under the wafer.
[0036] Temperature control mechanism 110 may be located as close to
the point of slurry application as possible. For heating, either an
electrically operated heat exchanger, or a hot water heat exchanger
may be used. A chiller may be used to cool the slurry, by using a
heat exchanger very similar to the hot water system. The
semiconductor industry commonly uses chillers or heaters that
operate by circulating H.sub.2O-ethylene glycol mixtures, which are
at the desired temperature. In fact, the same unit may be used to
heat or chill on demand.
[0037] In operation, slurry 160 is applied to the pad 320 at
multiple locations. Wafer 150 is pressed against pad 320 with the
desired downforce, the wafer is rotated and the continuously fed
belt 320 is moved. The direction of rotation and belt feed are
indicated in FIG. 3. The slurry applied to selected areas of the
pad 320 may be heated using heating mechanism 110 to improve the
removal rate in those areas. For copper CMP, the slurry 160a is
heated and applied to the pad 320 so that minimal contact with the
wafer 150 occurs (i.e., the right edge of the belt). Thus, the
heated slurry 160a affects the removal rate near the edge of wafer
150. Alternatively, or additionally, the slurry 160a is chilled and
applied to the polishing belt such that the slurry is in contact
with the wafer edge for a longer period of time (i.e., the left
side of the belt). Thus, the slurry 160b penetrates more deeply
under the wafer 150 to affect the removal rate nearer the center of
wafer 150. This results in a more uniform removal rate across the
wafer 150.
[0038] While this invention has been described with reference to
illustrative embodiments, this description is not intended to be
construed in a limiting sense. Various modifications and
combinations of the illustrative embodiments, as well as other
embodiments of the invention, will be apparent to persons skilled
in the art upon reference to the description. It is therefore
intended that the appended claims encompass any such modifications
or embodiments.
* * * * *