U.S. patent application number 09/796300 was filed with the patent office on 2001-07-19 for removal of polishing residue from substrate using supercritical fluid process.
This patent application is currently assigned to Supercritical Systems Inc.. Invention is credited to Koch, Robert.
Application Number | 20010008800 09/796300 |
Document ID | / |
Family ID | 26798867 |
Filed Date | 2001-07-19 |
United States Patent
Application |
20010008800 |
Kind Code |
A1 |
Koch, Robert |
July 19, 2001 |
Removal of polishing residue from substrate using supercritical
fluid process
Abstract
A method of removing polishing residue from a substrate includes
placing the substrate in a pressure chamber, pressurizing the
pressure chamber, and maintaining the supercritical fluid in
contact with the substrate until the polishing residue is removed
from the substrate. Following removal of the polishing residue from
the substrate, the pressure chamber is flushed and vented.
Inventors: |
Koch, Robert; (Fremont,
CA) |
Correspondence
Address: |
Thomas B. Haverstock
HAVERSTOCK & OWENS LLP
Suite 420
260 Sheridan Avenue
Palo Alto
CA
94306
US
|
Assignee: |
Supercritical Systems Inc.
|
Family ID: |
26798867 |
Appl. No.: |
09/796300 |
Filed: |
February 27, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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09796300 |
Feb 27, 2001 |
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09407628 |
Sep 28, 1999 |
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60101988 |
Sep 28, 1998 |
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Current U.S.
Class: |
438/690 ;
257/E21.228; 438/689; 438/691; 438/692 |
Current CPC
Class: |
B08B 7/0021 20130101;
H01L 21/02052 20130101 |
Class at
Publication: |
438/690 ;
438/691; 438/692; 438/689 |
International
Class: |
H01L 021/302 |
Claims
We claim:
1. A method of removing a polishing residue from a surface of a
substrate comprising the step of maintaining a supercritical fluid
in contact with the substrate until the polishing residue is
removed from the substrate.
2. A method of removing a polishing residue from a surface of a
substrate comprising the step of maintaining supercritical carbon
dioxide in contact with the substrate until the polishing residue
is removed from the substrate.
3. A method of removing a polishing residue from a surface of a
substrate comprising the step of maintaining supercritical carbon
dioxide and a solvent in contact with the substrate until the
polishing residue is removed from the substrate.
Description
RELATED APPLICATIONS
[0001] This application is a continuation of U.S. patent
application No. 09/407,628, filed on Sep. 28, 1999, which claims
priority from U.S. Provisional Application No. 60/101,988, filed on
Sep. 28, 1998, both of which are incorporated by reference.
FIELD OF THE INVENTION
[0002] The present invention relates to the field of removing
polishing residue from a substrate. More particularly, the present
invention relates to the field of removing polishing residue from a
substrate using a supercritical fluid.
BACKGROUND OF THE INVENTION
[0003] Manufacture of semiconductor devices commonly employ a
Chemical Mechanical Polishing (CMP) process to planarize a wafer
surface. The CMP process removes top surface layers from a
semiconductor wafer. The CMP process leaves a CMP residue of CMP
chemicals and particles that is difficult and problematic to remove
by current post-CMP cleaning methods. It is well known that the CMP
residue predominantly remains in surface features on the wafer
surface.
[0004] The current post-CMP cleaning methods require that the wafer
surface be mechanically washed or brushed by a commercially
available machine called a scrubber. The scrubber may employ heat
or ultrasonic augmentation and typically requires immersion times
of two to twenty minutes to achieve complete removal of the CMP
residue from the wafer surface. Because the wafer surface is
mechanically washed or brushed by the scrubber, the scrubber leaves
defects or scratches in the wafer surface.
[0005] It is well known that, if some of the CMP residue remains in
the surface features, performance of the semiconductor devices will
be degraded. Additionally, it is well known that the cost of
manufacturing a wafer of the semiconductor devices is proportional
to the time employed for each processing step.
[0006] It would be advantageous to be able to remove the CMP
residue without using the mechanical washing or brushing employed
by the scrubber in order to reduce an amount of the defects and the
scratches. Further, it would be advantageous to more effectively
remove the CMP residue from the surface features on the wafer
surface.
[0007] What is needed is a method of removing polishing residue
that does not use the mechanical washing or brushing.
[0008] What is further needed is a method of removing polishing
residue that is more effective than the mechanical washing or
brushing in removing the polishing residue from the surface
features.
[0009] What is additionally needed is a method of removing the
polishing residue that is more efficient than the scrubber.
SUMMARY OF THE INVENTION
[0010] The present invention is a method of removing polishing
residue from a surface of a semiconductor substrate. The
semiconductor substrate, including the polishing residue on the
surface, is placed within a pressure chamber. The pressure chamber
is then pressurized. Supercritical carbon dioxide and a solvent are
introduced into the pressure chamber. The supercritical carbon
dioxide and the solvent are maintained in contact with the
semiconductor substrate until the polishing residue is removed from
the semiconductor substrate. The pressure chamber is then flushed
and vented.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] FIG. 1 is a flow chart illustrating the steps of a method of
the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0012] The present invention utilizes high solvency and cleaning
characteristics of supercritical carbon dioxide to assist in a
post-CMP cleaning process. In the preferred embodiment, a small
amount of a chemical, i.e., a solvent or a solvent mixture, is
added to affect the post-CMP cleaning process as compared to the
prior art. In the present invention, the supercritical carbon
dioxide carries a small amount of the chemical to a wafer surface
to be cleaned and is then recycled back to a carbon dioxide
compressor for reuse.
[0013] The chemical is soluble or insoluble in carbon dioxide and
is not damaging to semiconductor device materials. The high
solvency and solubilizing ability of the supercritical carbon
dioxide makes this method fast, safe, and very quick. High
turbulence at wafer surface features in conjunction with
hyper-efficient mass transport of a chemical co-solvent package can
clean the wafer surface in less than five minutes. CMP residue of
CMP chemicals and abrasive particles is effectively removed without
direct mechanical contact, in contrast to current methods. Another
advantage of the present invention is that the wafer surface
contains fewer defects as compared to mechanical scrubber
methods.
[0014] The solvency of supercritical carbon dioxide increases with
pressure. Diffusivity and viscosity at or above a critical point of
carbon dioxide remains similar to that of a gas phase. Because
density above the critical point of the carbon dioxide is nearly
equal to that of a liquid state, the supercritical carbon dioxide
carries the chemical onto the wafer surface and cleans sub-micron
surface features of a modern semiconductor device. In the presert
invention, the supercritical carbon dioxide also functions to carry
away the CMP residue, including the CMP chemicals and abrasive
particles, from the sub-micron surface features of the modern
semiconductor device. Thus, a small amount of the chemical mixed
with the supercritical carbon dioxide performs the post-CMP
cleaning process and also cleans away any remaining unwanted
chemicals and the CMP residue.
[0015] The preferred embodiment of the post-CMP cleaning process of
the present invention is illustrated in FIG. 1. The semiconductor
wafer including the CMP residue is placed in a pressure chamber in
a first process step 20. The pressure chamber is then sealed and
pressurized with the carbon dioxide, in a second process step 22.
As the pressure inside the pressure chamber builds, the carbon
dioxide becomes liquid and then reaches supercritical temperature
and pressure. Typical conditions for this process range from 20 to
70.degree. C. and 1050 and 6000 psig. When the desired conditions
are reached, a small amount of the chemical is introduced into a
supercritical carbon dioxide stream and thus added into the
pressure chamber to begin cleaning, in a third process step 24.
Typical types and amounts of chemicals are:
[0016] a. 0.1-15.0 v/v % of isopropyl alcohol and related
alcohols;
[0017] b. 0.1-15.0 v/v % of propylene carbonate and related
carbonates;
[0018] c. 0.1-15.0 v/v % of ethylene glycol and related
glycols;
[0019] d. 0.001-5.0 v/v % of ozone;
[0020] e. 0.1-15.0 v/v % of hydrogen fluoride and related
fluorides;
[0021] f. 0.1-15.0 v/v % of ammonium hydroxide and related
hydroxides;
[0022] g. 0.1-15.0 v/v % of citric acid and related acids; and
[0023] h. 0.1-15.0 v/v % of a mixture of any of the above
chemicals.
[0024] The chemical is preferably selected from a preferred group
including the isopropyl alcohol, the propylene carbonate, the
ethylene glycol, the ozone, the hydrogen fluoride, the ammonium
hydroxide, and the citric acid, or a mixture thereof.
[0025] The chemical is alternatively selected from an alternative
group including the alcohols related to the isopropyl alcohol, the
carbonates related to the propylene carbonate, the glycols related
to the ethylene glycol, the fluorides related to the hydrogen
fluoride, the hydroxides related to the ammonium hydroxide, and the
acids related to the citric acid, or a mixture selected from these
chemicals and the preferred group.
[0026] The post-CMP cleaning process continues with recirculation
of the supercritical carbon dioxide and with mixing, i.e.,
agitating, thereof inside the pressure chamber until the CMP
residue is removed, typically from one-half to five minutes, in a
fourth process step 26. The pressure chamber is then flushed with
pure supercritical carbon dioxide or liquid carbon dioxide to
remove all traces of any remaining chemicals, in a fifth process
step 28. Finally, the chamber is vented to atmosphere and the wafer
is removed, in a sixth process step 30. At this point, an optional
rinse in DI (deionized) or ultra pure water may be performed to
finish the cleaning process.
[0027] The present invention uses the supercritical carbon dioxide
in combination with the small amount of a chemical admixture to
remove the CMP residue from the surfaces of the semiconductor
devices in a post-CMP cleaning system. The post-CMP cleaning system
includes a wafer process chamber, a pump, a sensor system, a
pressure and flow regulating system, and a recovery chamber. The
wafer process chamber holds the semiconductor wafer or
semiconductor wafers. The pump is capable of compressing liquid
carbon dioxide beyond the critical point. The sensor system
measures temperature, pressure and flows. The pressure and flow
regulating system connects a carbon dioxide source to the wafer
chamber at the desired conditions. The recovery chamber collects
solid and liquid material exhausted from the wafer chamber.
[0028] The post-CMP cleaning system preferably includes a
temperature control system for heating the wafer process
chamber.
[0029] The post-CMP cleaning system preferably includes a chemical
introduction system for adding precise amounts of the chemical into
the supercritical carbon dioxide process stream.
[0030] The post-CMP cleaning process of the present invention
includes the following steps. The wafer is placed in the wafer
process chamber. The post-CMP cleaning system is preferably purged
with inert gas or the carbon dioxide. Alternatively, the post-CMP
cleaning system is not purged. Next, the post-CMP cleaning system
is pressurized with the carbon dioxide to achieve supercritical
conditions. A desired amount of the chemical is added into the
carbon dioxide, which forms chemical laden supercritical carbon
dioxide. The chemical-laden supercritical carbon dioxide is
contacted with the wafer. The wafer process chamber is preferably
flushed using the supercritical carbon dioxide to remove
contaminants. Alternatively, the wafer process chamber is flushed
using the liquid carbon dioxide. The post CMP cleaning system is
then depressurized to allow removal of the wafer.
[0031] The post-CMP cleaning process results in the wafer surface
having a defect level that is much lower than current cleaning
methods, which utilize mechanical contact of the wafer with roller
or brush equipment.
[0032] The post-CMP cleaning process removes the CMP residue from
semiconductors, bare silicon wafers, metallic covered wafers, and
memory storage devices. It will be readily apparent to one of
ordinary skill in the art that the post-CMP cleaning process
removes the CMP residue from other substrates, including other
semiconductor substrates, that have been polished or planarized in
the CMP process.
[0033] It will be readily apparent to one skilled in the art that
other various modifications may be made to the preferred embodiment
without departing from the spirit and scope of the invention as
defined by the appended claims.
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