U.S. patent application number 09/932764 was filed with the patent office on 2002-04-04 for temperature endpointing of chemical mechanical polishing.
Invention is credited to Ashihara, Masayuki, Hecker, Philip E. JR., Korthuis, Vencent C..
Application Number | 20020039874 09/932764 |
Document ID | / |
Family ID | 26920175 |
Filed Date | 2002-04-04 |
United States Patent
Application |
20020039874 |
Kind Code |
A1 |
Hecker, Philip E. JR. ; et
al. |
April 4, 2002 |
Temperature endpointing of chemical mechanical polishing
Abstract
A method is described for temperature endpointing of a CMP
process. A temperature sensor (110) detects temperature changes
when the CMP polishing process transitions between different
materials.
Inventors: |
Hecker, Philip E. JR.;
(Dallas, TX) ; Ashihara, Masayuki; (Tsuchiura,
JP) ; Korthuis, Vencent C.; (Plano, TX) |
Correspondence
Address: |
TEXAS INSTRUMENTS INCORPORATED
P O BOX 655474, M/S 3999
DALLAS
TX
75265
|
Family ID: |
26920175 |
Appl. No.: |
09/932764 |
Filed: |
August 16, 2001 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
60226065 |
Aug 17, 2000 |
|
|
|
Current U.S.
Class: |
451/7 ; 451/41;
451/53; 451/63 |
Current CPC
Class: |
B24B 37/013 20130101;
B24B 37/042 20130101; B24B 49/14 20130101 |
Class at
Publication: |
451/7 ; 451/41;
451/53; 451/63 |
International
Class: |
B24B 049/00 |
Claims
We claim:
1. A method for detecting the end point of a chemical mechanical
polishing process comprising: providing a semiconductor substrate
with a top film of a first material overlying a second film of a
second material; monitoring temperature of a polishing pad during a
chemical mechanical polishing of said top film of said first
material; and stopping said chemical mechanical polishing upon
detecting a non random change in temperature of said polishing pad
as said chemical mechanical polishing transitions from said top
film of said first material to said second film of said second
material.
2. The method of claim 1 wherein said top film is a metal.
3. The method of claim 1 wherein said second film is a
dielectric.
4. The method of claim 1 wherein said monitoring temperature of
said polishing pad is performed using an infrared detector.
5. The method of claim 1 wherein said top film is a metal selected
from the group consisting of tungsten and copper.
6. The method of claim 5 wherein said second film is silicon
dioxide.
7. The method of claim 1 wherein said top film is silicon
oxide.
8. The method of claim 7 wherein said second film is silicon
nitride.
9. A method for detecting the end point of a chemical mechanical
polishing process comprising: providing a semiconductor substrate
with a top film of a first material overlying a second film of a
second material; monitoring temperature of a slurry during a
chemical mechanical polishing of said top film of said first
material; and stopping said chemical mechanical polishing upon
detecting a non random change in temperature of said slurry as said
chemical mechanical polishing transitions from said top film of
said first material to said second film of said second
material.
10. The method of claim 9 wherein said top film is a metal.
11. The method of claim 10 wherein said second film is a
dielectric.
12. The method of claim 9 wherein said monitoring temperature of
said polishing pad is performed using an infrared detector.
13. The method of claim 9 wherein said top film is selected from
the group consisting of tungsten and copper.
14. The method of claim 13 wherein said second film is selected
from the group consisting of silicon dioxide and silicon
nitride.
15. A method for detecting the end point of a chemical mechanical
polishing process comprising: providing a semiconductor substrate
with a plurality of films; monitoring temperature of a polishing
pad during a chemical mechanical polishing of said plurality of
films; and stopping said chemical mechanical polishing upon
detecting a non random change in temperature of said polishing pad
as said chemical mechanical polishing transitions from a first
material film of said plurality of films to a second material film
of said plurality of films.
16. The method of claim 15 wherein said plurality of films is
formed from material from the group consisting of tungsten, silicon
dioxide, copper, silicon nitride, and silicon.
17. The method of claim 15 wherein said monitoring temperature of
said polishing pad is performed using an infrared detector.
Description
CROSS-REFERENCE TO RELATED PATENT/PATENT APPLICATIONS
[0001] The following commonly assigned patent/patent applications
are hereby incorporated herein by reference:
1 U.S. Pat. No./Ser. No. Filing Date TI Case No. 09/034,514
03/04/98 TI-23590AA
FIELD OF THE INVENTION
[0002] The present invention relates to a method of detecting the
endpoint of a chemical mechanical polishing method. The endpoint
method involves the real time monitoring of the temperature change
of the polishing pad as the polisher transitions from one material
to another.
BACKGROUND OF THE INVENTION
[0003] Integrated circuits are comprised of semiconductor devices
which are fabricated on silicon wafers and/or substrates. These
semiconductor devices are interconnected on the wafer by forming
conducting lines or interconnects that contact the various
terminals of the device. Currently, these interconnects are formed
using aluminum, copper, doped polycrystalline silicon and other
electrically conducting metals and alloys. The complexity of
integrated circuits requires a number of different layers or levels
of interconnects. The various layers of interconnect are separated
from each other by dielectric insulator layers. In most cases these
insulator layers are formed using silicon dioxide, silicon nitride
or some combination of these materials. The semiconductor devices
on the wafer are electrically connected to the interconnects
through the use of contacts. In forming these contacts, an
insulating layer is first formed on the wafer completely covering
the semiconductor device. Using standard photolithography, contact
windows are opened in the insulating layer to expose the device
terminals to which electrical contact is to be made. A barrier
layer is first formed in the contact window to reduce unwanted
diffusion between the device terminal and the conducting material
that will subsequently be used to fill the contact window. This
barrier layer is sometimes formed using titanium nitride or
materials with similar properties. Following the formation of this
barrier layer, a metal layer is formed which completely fills the
window and covers the surface of the insulating layer. This metal
layer typically comprises tungsten, aluminum, titanium, or a metal
with similar properties. To complete the formation of the contact,
the portion of the metal layer that is above the insulating layer
is removed. In addition to the formation of contacts, the above
described process is used to electrically connect the various
layers of interconnect by forming structures usually referred to as
vias. In the case of both contact and via formation, the metal used
to fill the contact window openings must be removed from all areas
of the underlying insulating layer. Typically this process is
performed using a selective plasma etch process. Given the very
small feature size of current integrated circuits, selective plasma
etching will not produce satisfactory results and chemical
mechanical polishing (CMP) is now used to perform this metal
removal.
[0004] In the chemical mechanical polishing (CMP) process, a
rotating polishing head or wafer carrier, is typically utilized to
hold the wafer under controlled pressure against a rotating
polishing platen. A chemical slurry is controllably introduced
between the polishing head and the wafer to facilitate the
polishing. The polishing process is a combination of mechanical
abrasion and a chemical reaction. A particular problem encountered
during the CMP process is the control of the various process
parameters to achieve the desired wafer characteristics. In using
the CMP process to remove the metal from the underlying insulating
layer, it is crucial that the polishing process is stopped as soon
as all the metal is removed and a planar surface is formed. Over
polishing will lead to erosion of the dielectric layer particularly
in dense contact or via arrays while under polishing will result in
remaining metal. In both cases, the presence of these defects will
often lead to circuit failure or unreliable circuit performance. It
is therefore important to be able to precisely detect the endpoint
of the polishing process. Current methods of endpoint detection
involve using a timed process, monitoring the current of the
polishing motor, and monitoring the temperature of the wafer. These
methods often lead to unsatisfactory results. Thus there is a need
for an accurate endpoint detection method that is easily
implementable on existing CMP equipment. The present invention is
directed to a novel method for controlling a CMP process in real
time by monitoring the temperature changes of the polishing pad.
This process is especially useful for the tungsten CMP processes
used in the formation of contacts and vias and for copper metal
processes.
SUMMARY OF INVENTION
[0005] The instant invention described (CMP end point method) is
independent of the pattern density of the contacts and vias being
formed. It is also independent of film thickness and most other
processing conditions. It is easily adaptable into existing CMP
equipment and is non invasive. The instant invention can also be
applied to the removal of multiple films or layers. Other technical
advantages will be readily apparent to one skilled in the art from
the following FIGUREs, description, and claims. In particular an
embodiment of the method comprises: providing a semiconductor
substrate with a top film of a first material overlying a second
film of a second material; monitoring temperature of a polishing
pad during a chemical mechanical polishing of said top film of said
first material; and stopping said chemical mechanical polishing
upon detecting a non random change in temperature of said polishing
pad as said chemical mechanical polishing transitions from said top
film of said first material to said second film of said second
material.
BRIEF DESCRIPTION OF THE DRAWINGS
[0006] For a more complete understanding of the present invention
and the advantages thereof, reference is now made to the following
description taken in conjunction with the accompanying drawings,
wherein like reference numerals represent like features, in
which:
[0007] FIG. 1 is an schematic diagram of a CMP polishing
apparatus.
[0008] FIG. 2 is a cross-section diagram of the wafer surface
topography, polishing pad, slurry, and the wafer carrier.
[0009] FIG. 3 is a cross-section diagram showing the end of the CMP
process.
[0010] FIG. 4 is a cross-section diagram showing the instant
invention applied to a plurality of films.
DETAILED DESCRIPTION OF THE INVENTION
[0011] Illustrated in FIG. 1 is a schematic diagram of a CMP system
for use with the end point detection method of the instant
invention. The system comprises a table (platen) 10 that rotates
around the axis 30 in the direction shown 40. In an embodiment of
the instant invention, the platen 10 rotation is in a counter
clockwise direction. A polishing pad 20 is affixed to the platen
and is used to polish the surface of the semiconductor wafer or
semiconductor substrate 90. In some instances the polishing pad 20
will be formed using polyurethane or other similar materials. The
semiconductor wafer 80 is attached face down to a wafer carrier 50
that rotates around an axis 70. The wafer carrier 50 rotates in the
same direction as the platen 10. The slurry 105 used in the
polishing process is delivered to the polishing pad through a
slurry delivery system 100. In an embodiment of the instant
invention, additives 106 can be added to the main slurry using a
separate delivery system 112. The chemicals in this case will
combine on the polishing surface. In another embodiment of the
instant invention, the chemicals can be combined above the surface
of the table by mixing the slurry and the additives before delivery
to the platen surface or polishing pad 20. The centrifugal force on
the slurry due to the platen rotation causes mixing of the
chemicals and their delivery to the wafer or substrate surface 90.
In an embodiment of the invention, during the polishing process,
the wafer carrier periodically lifts the wafer off the surface of
the platen (and polishing pad) to allowing mixing of the chemicals
(interpolish lift off). For example in a particular process this
might occur about every 30 seconds for about 3 seconds. The
frequency and duration of this interpolish lift off process is not
confined to these times but will be a function of the process where
CMP of different materials will require different times or
frequencies. In most CMP systems the pad temperature is monitored
using a temperature sensor 110. In an embodiment of the instant
invention this temperature sensor comprises an infra red sensor.
Such a temperature sensor provides an electrical signal that is
proportional to the temperature of the pad 20 and the slurry
105.
[0012] Shown in FIG. 2 is a cross section of the wafer carrier 50,
the semiconductor wafer or semiconductor substrate 80 and the
polishing pad 20. The wafer or substrate 80 comprises silicon
devices (not shown for clarity), dielectric layers 120, 130,
interconnects 140, and a metal film 150 which will be used to form
the vias for contacting the interconnects 140. In an embodiment of
the instant invention, the metal film 150 will be tungsten and or a
tungsten alloy or copper, and the dielectric layers 120 and 130
will be silicon dioxide or silicon nitride. As shown in FIG. 2, the
portion of the metal film 150 underlying the dielectric film 130
will be removed during the CMP process. During polishing, the wafer
50 is affixed to the wafer carrier 50 with the wafer surface to be
polished 155 facing the polishing pad 20. In an embodiment of the
invention, a tungsten layer 150 will be in contact with the slurry
105 and the polishing pad 20. Typically, the slurry 105 used during
the process will comprise alumina or another abrasive silica and
hydrogen peroxide or a suitable metal oxidizing agent. A suitable
slurry is a colloidal silicia formulation. Suitable slurries
include, but are not limited to, Cabot (El Dorado Hills, Calif.
USA)SS-W2000. This slurry represent the mainstream slurry used in
metal polish operations by most major US semiconductor
manufacturers. In the preferred embodiment of the present
invention, the slurry is SS-W2000 from Cabot. During the CMP
process, the slurry will first oxidize the surface of the metal
film 155 and the resulting metal oxide will be removed by the
mechanical polishing action of the pad 20 and the abrasive agents
in the slurry. During this polishing process, the temperature
sensor 110 will monitor the slurry 105 and the pad 20 whose
temperature will remain constant within the tolerances of the CMP
equipment. As stated above, during the polishing process both the
polishing pad 20 and the wafer carrier 50 will rotate in the same
direction. This rotation produces friction between the oxidized
metal surface 155 and the pad 20 which aids the polishing process.
The polishing process ends when the metal film 150 underlying the
dielectric layer 130 has been removed and a planar dielectric
surface exists.
[0013] The end point of the CMP process and the resulting planar
surface 160 is illustrated in FIG. 3. The removal of the underlying
metal film 150 results in the formation of vias 157 which will
provide electrical contact to the interconnects 140. Typically,
additional processing will be performed following the CMP process
to produce the completed integrated circuit. As shown in FIG. 3, at
the end point of the metal film removal CMP process, the surface
160 that is in contact with the slurry 105 and the polishing pad 20
will have changed from metal 150 and/or metal oxide to a dielectric
130. This change in surface type changes the interaction between
the slurry 105 and the wafer surface 160 at the end point of the
process. Compared to the oxidization and polish of the metal film
(150 in FIG. 2), the dielectric film 130 undergoes a purely
mechanical polish with a resulting decrease in pad and slurry
temperature. This temperature decrease is detected by the
temperature sensor 110 and the resulting change in the electrical
signal provided by the temperature sensor 110 is used to end point
the CMP process. If the metal film 150 is tungsten and the
dielectric film 130 is silicon dioxide, the resulting decrease in
temperature of the pad 20 and slurry 105 is approximately 5 degrees
centigrade.
[0014] An advantage of the above described CMP end point method is
that it is independent of the pattern density of the contacts and
vias being formed. It is also independent of film thickness and
most other processing conditions. It is easily adaptable into
existing CMP equipment and is non invasive. The instant invention
can also be applied to the removal of multiple films or layers. In
such an embodiment, any number of films could be removed and the
CMP process would end point on the material transition that
produced the desired polishing pad temperature change. A multiple
film CMP process is illustrated in FIG. 4. Here, the wafer or
substrate 80 is attached to the wafer carrier 50 which rotates
during polishing. The multiple films 170, 175, 180, and 185 can
comprise any combination of metal, dielectric, semiconductor, and
insulator films. In particular the films 170, 180, and 185 could
comprise silicon oxide and silicon nitride layers. During the CMP
polishing process, the temperature of the pad 20 and the slurry 105
will be monitored using a temperature sensor 110. As the CMP
polishing process transitions from one layer to the next, the
temperature of the pad 20 and the slurry 105 will change in a non
random manner. This non random change in temperature can be used to
end point the CMP process after the desired number of layers have
been removed. The idea of a non random temperature change in the
context of the instant invention is a temperature change that can
be differentiated from the normal random temperature variations of
the pad 20 and slurry 105 that occurs during the CMP polishing of
any single layer or film.
[0015] Although the instant invention has been described with
respect to a metal-dielectric CMP process, it can be used for any
CMP process that results in a transition between two different
materials. Some of these processes include the formation of
contacts, vias, pre-metal 1 dielectric (PMD) layer, interlevel
dielectric (ILD) layer, formation of metal trenches in damascene
and dual damascene CMP processes, and shallow trench isolation
(STI) CMP processes. 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.
* * * * *