U.S. patent application number 14/067648 was filed with the patent office on 2014-02-27 for plasma clean method for deposition chamber.
This patent application is currently assigned to Novellus Systems, Inc.. The applicant listed for this patent is Novellus Systems, Inc.. Invention is credited to Zhiyuan Fang, Keith Fox, Jon Henri, Pramod Subramonium.
Application Number | 20140053867 14/067648 |
Document ID | / |
Family ID | 49596597 |
Filed Date | 2014-02-27 |
United States Patent
Application |
20140053867 |
Kind Code |
A1 |
Fang; Zhiyuan ; et
al. |
February 27, 2014 |
PLASMA CLEAN METHOD FOR DEPOSITION CHAMBER
Abstract
Improved methods and apparatuses for removing residue from the
interior surfaces of the deposition reactor are provided. The
methods involve increasing availability of cleaning reagent
radicals inside the deposition chamber by generating cleaning
reagent radicals in a remote plasma generator and then further
delivering in-situ plasma energy while the cleaning reagent mixture
is introduced into the deposition chamber. Certain embodiments
involve a multi-stage process including a stage in which the
cleaning reagent mixture is introduced at a high pressure (e.g.,
about 0.6 Torr or more) and a stage the cleaning reagent mixture is
introduced at a low pressure (e.g., about 0.6 Torr or less).
Inventors: |
Fang; Zhiyuan; (West Linn,
OR) ; Subramonium; Pramod; (Beaverton, OR) ;
Henri; Jon; (West Linn, OR) ; Fox; Keith;
(Tigard, OR) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Novellus Systems, Inc. |
Fremont |
CA |
US |
|
|
Assignee: |
Novellus Systems, Inc.
Fremont
CA
|
Family ID: |
49596597 |
Appl. No.: |
14/067648 |
Filed: |
October 30, 2013 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
12355601 |
Jan 16, 2009 |
8591659 |
|
|
14067648 |
|
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Current U.S.
Class: |
134/1.1 ;
134/57R |
Current CPC
Class: |
B08B 7/0035 20130101;
H01J 37/32862 20130101; B08B 9/00 20130101; C23C 16/4405 20130101;
H01J 37/32357 20130101 |
Class at
Publication: |
134/1.1 ;
134/57.R |
International
Class: |
B08B 7/00 20060101
B08B007/00; B08B 9/00 20060101 B08B009/00 |
Claims
1. A method of cleaning a residue from interior surfaces of a
semiconductor deposition chamber, the method comprising: a first
stage performed at a chamber pressure of at least about 0.6 Torr,
the first stage comprising: (a) introducing one or more cleaning
reagents into a remote plasma generator; (b) generating activated
species from the cleaning reagents in the remote plasma generator
by delivering a first plasma energy to the cleaning reagents; (c)
introducing a cleaning mixture into the deposition chamber, wherein
the cleaning mixture comprises the activated species; (d) exposing
the interior surfaces of the deposition chamber to the cleaning
mixture while delivering a second plasma energy to the cleaning
reagents from an in-situ plasma generator, wherein delivering the
second plasma energy comprises applying a power to the deposition
chamber; and (e) reacting the residue with the cleaning mixture to
form volatile products to be removed from the deposition chamber; a
second stage performed at a chamber pressure of no more than 0.6
Torr, the second stage comprising repeating operations (a) through
(e), wherein the applied power during the first stage is less than
the applied power during the second stage.
2. The method of claim 1, wherein the first stage is performed
prior to the second stage.
3. The method of claim 1, wherein the second stage is performed
prior to the first stage.
4. The method of claim 1, wherein the cleaning reagents comprise an
oxygen containing compound and a fluorine containing compound and a
flow rate of the oxygen containing compound is at least ten times
greater than a flow rate of the fluorine containing compound during
the first stage and at least three times greater during the second
stage.
5. The method of claim 1, wherein the second plasma energy is
delivered at between about 1,000 W and 2,000 W during the first
stage and at between about 2,000 W and 3,000 W during the second
stage.
6. The method of claim 1, wherein the first and second set of
reagents comprise an oxygen containing compound and fluorine
containing compound.
7. The method of claim 6, further comprising: introducing a third
set of one or more cleaning reagents into the remote plasma
generator, the third set of one or more cleaning reagents
comprising a third amount of a fluorine containing compound and
substantially no oxygen containing compound; and repeating
operations (b)-(d) using the third set of one or more cleaning
reagents.
8. A semiconductor apparatus configured to clean a residue from
interior surfaces after deposition process, comprising: a
semiconductor process chamber; a first plasma generator configured
to generate an in-situ plasma within the process chamber; a remote
plasma generator; and a controller comprising program instructions
for performing first and second cleaning stages, wherein the
instructions for the first cleaning stage comprise: instructions
for introducing a first set of one or more cleaning reagents into
the remote plasma generator; instructions for powering the remote
plasma generator to generate activated species from the first set
of cleaning reagents; instructions for introducing the first set of
activated species to the process chamber; instructions for applying
a first power to the first plasma generator while the first set of
activated species are in the process chamber; and instructions for
maintaining a first deposition chamber pressure; further wherein
the instructions for the second cleaning stage comprise:
instructions for introducing a second set of one or more cleaning
reagents into the remote plasma generator; instructions for
powering the remote plasma generator to generate activated species
from the second set of cleaning reagents; instructions for
introducing the second set of activated species to process chamber;
instructions for applying a second power to the first plasma
generator while the second set of activated species are in the
process chamber; and instructions for maintaining a second
deposition chamber pressure, wherein the first deposition chamber
pressure is at least about 0.6 Torr, and the first applied power is
less than the second applied power.
9. The apparatus of claim 8, wherein the instructions further
comprise instructions for performing the first cleaning stage
performed prior to the second cleaning stage.
10. The apparatus of claim 8, wherein the instructions further
comprise instructions for performing the second cleaning stage
performed prior to the first cleaning stage.
11. The apparatus of claim 8, wherein the instructions for
introducing the first set of cleaning reagents comprise
instructions for introducing an oxygen containing compound and a
fluorine containing compound, the instruction further comprise
instruction for introducing the oxygen containing compound at a
flow rate of at least ten times the flow rate of the fluorine
containing compound.
12. The apparatus of claim 11, wherein the instructions for
introducing the second set of cleaning reagents comprise
instructions for introducing an oxygen containing compound and a
fluorine containing compound, the instruction further comprise
instruction for introducing the oxygen containing compound at a
flow rate of at least three times the flow rate of the fluorine
containing compound.
13. A semiconductor apparatus configured to clean a residue from
interior surfaces after deposition process, comprising: a
semiconductor process chamber; a first plasma generator configured
to generate an in-situ plasma within the process chamber; a remote
plasma generator; and a controller comprising program instructions
for performing first and second cleaning stages, wherein the
instructions for the first cleaning stage comprise: instructions
for introducing a first set of one or more cleaning reagents into
the remote plasma generator, the first set of one or more cleaning
reagents comprising a first amount of an oxygen containing compound
and a first amount of a fluorine containing compound; instructions
for powering the remote plasma generator to generate activated
species from the first set of cleaning reagents; instructions for
introducing the first set of activated species to process chamber;
instructions for applying a first power to the first plasma
generator while the first set of activated species are in the
process chamber; and instructions for maintaining a first
deposition chamber pressure; further wherein the instructions for
the second cleaning stage comprise: instructions for introducing a
second set of one or more cleaning reagents into the remote plasma
generator, the second set of one or more cleaning reagents
comprising a second amount of an oxygen containing compound and a
second amount of a fluorine containing compound; instructions for
powering the remote plasma generator to generate activated species
from the second set of cleaning reagents; instructions for
introducing the second set of activated species to process chamber;
instructions for applying a second power to the first plasma
generator while the second set of activated species are in the
process chamber; an instructions for maintaining a second
deposition chamber pressure, wherein a ratio of the first amount of
the fluorine containing compound to the first amount of the oxygen
containing compound is less than a ratio of the second amount of
the fluorine containing compound to the second amount of the oxygen
containing compound, the first applied power is less than the
second applied power, and the first deposition chamber pressure is
greater than the second deposition chamber pressure.
14. The apparatus of claim 13, wherein the first deposition
pressure is at least about 0.6 Torr.
15. The apparatus of claim 13, wherein the second deposition
chamber pressure is no more than about 0.6 Torr.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] The application is a divisional of and claims priority to
U.S. patent application Ser. No. 12/355,601, titled "PLASMA CLEAN
METHOD FOR DEPOSITION CHAMBER," filed Jan. 16, 2009, all of which
is incorporated herein by this reference for all purposes.
FIELD OF THE INVENTION
[0002] The present invention relates generally to methods and
apparatuses for cleaning deposition chambers and more specifically
to methods and apparatuses for cleaning residues from interior
surfaces of deposition chambers using plasmas.
BACKGROUND OF THE INVENTION
[0003] Deposition of thin films is one of the key processes in
semiconductor manufacturing. A typical wafer goes through
deposition of several thin films, some of which may completely or
partially remain in the final electronic device, while others may
only temporarily remain on the wafer and serve some intermediate
processing needs. For example, an ashable hard mask film may be
used as an etch hardmask layer. Such film is first deposited on a
wafer and then partially removed to define circuit line patterns.
An etchant is then applied to remove some of the underlying
dielectric forming trenches and vias for the future circuit lines.
Eventually, all remaining ashable hard mask film is removed from
the wafer.
[0004] Various deposition processes are used to deposit thin films.
For example, an ashable hard mask film may be deposited using
chemical vapor deposition (CVD), or more specifically plasma
enhanced chemical vapor deposition (PECVD), processes. One
consequence of almost any deposition process is that the film
material is not only deposited onto the wafer but also on the
interior surfaces of the deposition chambers, thereby forming
residues. These residues can build up over time and dissolve,
detach or otherwise disperse through the deposition chamber causing
contamination. The built-up residues are periodically removed to
avoid such contamination.
SUMMARY
[0005] Provided are plasma cleaning methods for removing residues
that have accumulated on the interior surfaces of deposition
chambers. Provided also are apparatuses for executing the presented
cleaning methods. The plasma cleaning methods involve generating
cleaning reagent activated species in a remote plasma generator to
form a cleaning reagent mixture and then introducing the mixture
into a deposition chamber. Activated species within the mixture
etch the deposition residue, forming removable etch byproducts that
can be pumped away from the chamber. At the same time, in-situ RF
plasma is provided by applying RF power to the clean mixture from a
plasma RF generator. The in-situ RF plasma dissociates and
activates cleaning reagent molecules that have not dissociated or
activated while passing through the remote plasma generator or that
have recombined from the activated species along the distribution
path from the remote plasma generator to the deposition chamber.
The additional activated species supplied by the in-situ RF plasma
from this cleaning method provide improved cleaning efficiency.
[0006] In certain embodiments, the method of cleaning residues from
the interior surfaces of a chamber includes introducing one or more
cleaning reagents into a remote plasma generator and generating
activated species from the cleaning reagents in the remote plasma
generator by delivering first plasma energy to the cleaning
reagents. The activated species become a part of a cleaning mixture
that is introduced into the deposition chamber. The interior
surfaces of the deposition chamber are exposed to the cleaning
mixture while an in-situ plasma generator delivers second plasma
energy to the cleaning reagents for at least one period of time. In
certain embodiments, the second plasma energy generates additional
activated species inside the deposition chamber. In the same or
other embodiments, the second plasma energy re-dissociates
recombined molecules to form radicals. The residue reacts with the
cleaning mixture to form volatile products to be removed from the
deposition chamber. The residue may include carbon, silicon oxide,
or other components. In certain embodiments, the residue is formed
during deposition of an ashable hard mask film.
[0007] Generation of the activated species may include forming
radicals. In certain embodiments, the cleaning reagents include an
oxygen containing compound and a fluorine containing compound. For
example, the cleaning reagents may include oxygen and nitrogen
trifluoride. The pedestal of the deposition chamber may be kept
between about 250 and 550 degrees Centigrade while the residue is
reacting with the cleaning mixture.
[0008] The cleaning method may include two stages. For example,
introducing the cleaning mixture into the deposition chamber,
exposing the interior surfaces of the deposition chamber to the
cleaning mixture and reacting the residue with the cleaning mixture
may be performed at a chamber pressure of at least about 0.6 Torr
during the first stages and no more than about 0.6 Torr during the
second stage. In certain embodiments, the first stage is performed
prior to the second stage. The second plasma energy during the
first stage may be less than the second plasma energy during the
second stage. In certain embodiments, the second plasma energy is
delivered at between about 1,000 W and 2,000 W during the first
stage and at between about 2,000 W and 3,000 W during the second
stage. In the embodiments where the cleaning reagents comprise an
oxygen containing compound and a fluorine containing compound, the
oxygen containing compound has a flow rate of at least ten times
greater than a flow rate of the fluorine containing compound during
the first stage and at least three times greater during the second
stage. The etch rate of the carbon containing residue around on a
pedestal surface kept at least 150 degrees Centigrade is at least 1
micron per minute during the first stage.
[0009] The cleaning method may also include a third stage that
involves introducing one or more cleaning reagents into the remote
plasma generator, generating the activated species from the
cleaning reagents in the remote plasma generator by delivering the
first plasma energy to the cleaning reagents, introducing the
cleaning mixture comprising the activated species into the
deposition chamber, exposing the interior surfaces of the
deposition chamber to the cleaning mixture, and reacting the
residue with the cleaning mixture to form volatile products to be
removed from the deposition chamber. The cleaning reagents during
the third stage may include a fluorine containing compound. The
third stage may be shorter than the second stage. In certain
embodiments, the in-situ plasma generator is turned off during the
third stage.
[0010] In certain embodiments, cleaning of the residue is performed
by semiconductor apparatus that includes a semiconductor process
chamber configured to generate an in-situ plasma within the
chamber, a remote plasma generator, and a controller with program
instructions for introducing one or more cleaning reagents into the
remote plasma generator, generating activated species from the
cleaning reagents in the remote plasma generator by delivering a
first plasma energy to the cleaning reagents, introducing a
cleaning mixture into the deposition chamber, wherein the cleaning
mixture comprises the activated species, exposing the interior
surfaces of the deposition chamber to the cleaning mixture while
delivering a second plasma energy in-situ; and reacting the residue
with the cleaning mixture to form volatile products to be removed
from the deposition chamber.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] FIGS. 1A-1C illustrate distribution of remaining residues
inside the deposition chambers after the chambers have been cleaned
using three different cleaning methods.
[0012] FIG. 2 illustrates a process flowchart of a plasma cleaning
method for removal of residues from the inside surfaces of
deposition chambers in accordance with one embodiment of the
present invention.
[0013] FIG. 3 illustrates various stages in a plasma cleaning
method for removal of residues from the inside surfaces of
deposition chambers in accordance with one embodiment of the
present invention.
[0014] FIG. 4 presents a general block diagram depicting various
hardware elements of a deposition chamber and a corresponding
cleaning apparatus for implementing the plasma cleaning method in
accordance with one embodiment of the present invention.
[0015] FIG. 5 is a plot illustrating experimental data of the
etched thicknesses of ashable hard mask films from the surfaces of
300 mm wafers that were subjected to different cleaning conditions
of four cleaning methods for about 30 seconds.
DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT
[0016] In the following description, numerous specific details are
set forth in order to provide a thorough understanding of the
present invention. The present invention may be practiced without
some or all of these specific details. In other instances, well
known process operations have not been described in detail to not
unnecessarily obscure the present invention. While the invention
will be described in conjunction with the specific embodiments, it
will be understood that it is not intended to limit the invention
to the embodiments.
Introduction
[0017] Thin film deposition usually causes some residue to
accumulate on the inside surfaces of deposition chambers. For
example, a typical chemical vapor deposition (CVD) process involves
distributing precursor gases through a shower head and directing
the gases towards the wafer's surface. The wafer normally is
positioned on a heated pedestal to stimulate the deposition
process. An in-situ plasma may be used to energize and dissociate
precursor molecules making them more reactive. However, not all
precursor materials react and end up being deposited on wafer. Some
are pumped out of the chamber, while other may be deposited on the
inside surfaces, including a showerhead, a top plate, chamber
walls, and other remote areas and surfaces of the chambers. Over
time these residues need to be removed to avoid contamination.
[0018] Cleaning methods involve introducing cleaning reagents into
the deposition chamber that react with residue and form volatile
products, which are then pumped out of the chamber. To expedite the
cleaning process, the reagents may be activated in a plasma
generator to form a more reactive cleaning mixture. Activating
chemical species may include energizing them bringing them to a
higher energy state, dissociating them into radicals and forming
reactive atoms and ions. Cleaning efficiency may also be improved
by heating up the cleaning mixture and surfaces containing residues
because many residue materials do not readily react at low
temperatures or may form non-volatile substances that must be later
mechanically removed in a slow and laborious process. For example,
high carbon content ashable hard mask materials may be etched with
activated oxygen and fluorine species. However, when temperature
drops below 100.degree. C., carbon is essentially non-reactive with
oxygen, while it may form non-volatile polymer substances with
fluorine. While the cleaning reagent mixture may include high
energy molecules, activated atoms and ions are primarily
responsible for etching the residue.
[0019] According to various embodiments, cleaning reagents may be
dissociated or otherwise activated both externally in a remote
plasma generator, such as a Remote Plasma Cleaning (RPC) unit, and
inside the deposition chamber using an in-situ plasma generator.
Cleaning methods using a remote plasma generator are less damaging
to the deposition equipment but may not provide adequate cleaning
by leaving substantial amounts of residue 108 as shown in FIGS. 1A
and B in comparison with a substantially clean chamber shown in
FIG. 1C. FIG. 1A illustrates a chamber including a shower head 104
and a pedestal 106 after remote plasma cleaning using fluorine
containing cleaning reagents in the absence of oxygen radicals.
FIG. 1B shows a similar chamber after remote plasma cleaning using
cleaning reagents that only contain oxygen radicals. The remote
plasma generator provides high degree of activation of cleaning
reagents, but many of theses activated species then go back to
their neutral state before reaching the residue on the internal
surfaces of the chamber. For example, oxygen radicals are
particularly prone to recombination along the distribution path and
easily form oxygen molecules that are not sufficiently reactive to
remove carbon residues. As a result, the amount of residue 108 left
after cleaning is typically greater in a chamber cleaned with
cleaning reagents including only oxygen radicals as shown in FIG.
1B than in the chamber cleaned with fluorine containing cleaning
reagents as shown in FIG. 1A. Usually, the wafer pedestal 106 and
the shower head 104 are cleaned more effectively with fluorine
containing cleaning reagents. However, fluorine may be also
damaging to the chamber at high concentration. In the absence of
oxygen radicals, fluorine radicals can react with carbon residue on
cold interior surfaces and form non volatile etch products which
are difficult to remove. Combining oxygen and fluorine containing
cleaning reagents together in a remote plasma unit improves the
etch efficiency by generating more reactive etch species inside the
remote plasma unit itself, and reduces recombination loss of
reactive species during the transportation from the unit to the
chamber. However, in many cases, the improvement is still not
sufficient to remove the entire residue from the chamber. For
example, the reactive oxygen radicals may recombine before reaching
the chamber.
[0020] An in-situ plasma cleaning method is another method to
remove residues from the deposition chamber as shown in FIG. 1C.
The activation of cleaning reagents happens inside the deposition
chamber and is provided by in-situ plasma. While the degree of
activation for the in-situ plasma method, for example measured by
dissociation, is much less than for remote plasma cleaning
(approximately 50% for in-situ plasma as compared to more than 90%
for remote plasma cleaning), in-situ dissociation occurs near
residue surfaces and recombination effect is minimal if any.
Additionally, the in-situ plasma helps to heat up chamber surfaces
leading to higher etch rate of removing process. As a result,
residue removal is complete, or much higher than for the remotely
generated plasma cleans described above with respect to FIGS. 1A
and 1B.
[0021] Increasing energy delivered by in-situ plasma generators
improves cleaning effectiveness; however, there is a trade off
between the amount of energy and damage to the components directly
exposed to the in-situ plasma. The internal components experience
continuous ion bombardment that increases with the level of plasma
energy used and may result in rapid deterioration of these
components. In particular, the shower head 104 may be damaged due
to fast aluminum fluoride layer growth at elevated temperature and
RF power levels, which may be required for high etching rates
during cleaning. Aluminum fluoride layer can delaminate from
showerhead surface and cause particle contamination.
[0022] The methods described herein provide effective cleaning
without damaging the internal components. These methods involve
generating activated species from the cleaning reagents in a remote
plasma generator to form a cleaning mixture and introducing the
mixture into a deposition chamber that generates in-situ plasma.
The plasma cleaning method takes advantage of high degree of
dissociation of the remote plasma generator and localized
activation of the clean species in the mixture near residue
surfaces by in-situ plasma. As described below, experimental
results indicate more effective cleaning (higher etch rates) for
the new methods.
Process
[0023] FIG. 2 illustrates a process flowchart of a plasma cleaning
method in accordance with the present invention. Usually, a chamber
having residues from thin film depositions on its interior surfaces
is provided. For example, the provided chamber may have residue
formed from depositing ashable hard mask films having a thickness
of between about 2,000 and 10,000 Angstroms on 30-150 wafers. Any
chamber having in-situ cleaning capabilities, i.e. in which plasma
can be struck, can be cleaned using the described cleaning method.
In one embodiment, a deposition chamber may be a PECVD chamber. In
more specific embodiment, the chamber may be a Vector PECVD
chamber, or a Vector Extreme PECVD chamber, both manufactured by
Novellus Systems in San Jose, Calif. A Remote Plasma Cleaning (RPC)
unit is connected to the deposition chamber so that clean species
can be transported into the chamber. A chamber may have a dedicated
cleaning apparatus or may share the same cleaning apparatus among
several other deposition chambers. Additional details of the
deposition chamber and the cleaning apparatus are provided in the
context of FIG. 4.
[0024] The process continues with introducing cleaning reagents
into the remote plasma generator unit (block 202). Selection of the
cleaning reagents normally depends on residue composition, which
typically corresponds to composition of deposited films. For
example, deposition of ashable hard mask film may lead to formation
of residue comprising carbon, hydrogen, nitrogen and other
components. In a specific embodiment, the residue may contain more
than 60% and even more than 80% of carbon. The cleaning reagents
for this example may include oxygen containing compounds, such as
oxygen, ozone, nitrous oxide, carbon oxide, carbon dioxide, and
other oxidizers, and fluorine containing compounds, such as
nitrogen trifluoride, fluorine, tetrafluoromethane,
tetrafluoroethylene, hexafluoroethane, octafluoropropane and
others. Ashable hard mask residue may also have underlying residues
comprising silicon oxide formed during dielectric deposition.
Fluorine containing cleaning reagents are effective to remove
silicon containing residues because etch product, i.e., silicon
fluoride, is volatile and can be easily pumped out of the chamber.
Thus, a combination of oxygen and fluorine containing clean
reagents not only works for etching of ashable hard mask films, but
also can be used for cleaning residues left after depositing
silicon containing dielectric films, such as silicon oxide, low-K
films, silicon nitride, silicon oxynitride, and others. Cleaning of
many residues may be substantially improved by having higher
relative concentration of activated cleaning species near the
surface of residues. Residues may be cleaned individually or in
combination with other residues.
[0025] Flow rates of the cleaning reagents typically depend on the
size of the deposition chamber. For example, the overall flow rate
may vary between about 1,000 and 20,000 sccm for a 195-liter Vector
PECVD chamber. Generally, flow rates are scalable with a volume of
the process chamber. Several different cleaning reagents may be
simultaneously introduced into a remote plasma generator unit for
at least a part of the entire processing time. For example, the
overall cleaning process may involve several stages with varying
flow rates, different cleaning reagents and inert gases introduced
and discontinued at different times, varying pressure and plasma
generation power levels, and stage durations. Additional details on
cleaning stages used in the plasma cleaning method are provided in
the context of FIG. 3.
[0026] In a remote plasma generator some cleaning reagent molecules
are activated to form cleaning reagent radicals, ions, high energy
atom and molecules, which are collectively referred to as
"activated species" (block 204). Activated species are more
reactive with residues than the original cleaning reagents
containing stable cleaning reagent molecules. Remote plasma
generators provide high degree of dissociation of reagent molecules
into activated species, usually 90% and higher. Still some
molecules may pass through a remote plasma generator without being
activated. Many activated species may return to their stable form,
such as recombination of radicals back into the molecules before
reaching the deposition chamber. A combination of cleaning reagent
molecules and activated species is generally referred to as a
cleaning reagent mixture, a cleaning mixture, or simply a mixture.
It should be readily understood that the cleaning mixture has
varying relative concentrations of activated species and stable
cleaning reagent molecules in different locations of the overall
cleaning system. The concentration of activated species (radicals,
ions, and high energy atoms and molecules) may be as high as 90% at
exit of the remote plasma generator, and then may gradually
decrease before reaching the deposition chamber and the residue
surfaces inside the chamber. The concentration of activated species
is then increased inside the deposition chamber with the help from
in-situ plasma generation, as described below.
[0027] After passing through the remote plasma generator the
cleaning reagent mixture is then introduced into the deposition
chamber (block 206), which involves flowing the mixture through the
line connecting the remote plasma generator and the deposition
chamber and then coming into the deposition chamber through a
shower head or other chamber opening areas. The concentration of
activated species continues to drop. For example, recombination of
cleaning reagent radicals in the mixture may rapidly occur while
the mixture is being delivered. Recombination depends on the
delivery pressure, materials of the delivery line, length,
diameter, curvature, surface area and temperature of the delivery
line, and deposition chamber conditions. Moreover, various cleaning
reagents may exhibit different recombination behaviors. For
example, oxygen cleaning reagents tend to show poor performance in
remote plasma cleaning methods due to rapid recombination of oxygen
radicals despite a high degree of initial dissociation
externally.
[0028] Once the cleaning reagent mixture is introduced into the
deposition chamber, it reaches the exposed interior surfaces of the
deposition chamber (block 208), and an in-situ plasma is struck
simultaneously to increase the concentration of reactive etch
radicals. While most of the mixture is directed towards the wafer
pedestal by the shower head, some of it reaches other surfaces as
well. The overall process may include several cleaning stages
designed to target different parts of the deposition chamber and
have varying chamber pressure, cleaning reagent compositions, power
levels of in-situ plasma generation, and durations.
[0029] In-situ plasma generation may serve several purposes during
introduction of the cleaning reagent mixture. First, the molecules
that have not dissociated in the remote plasma generator or ones
that has already recombined or generally "de-activated" upon
entering the deposition chamber may be activated and "re-activated"
by the in-situ plasma. In certain embodiments, the in-situ plasma
generator used in the methods describes herein may be set to lower
power levels than in conventional in-situ cleaning methods because
of the enhanced etch resulting from the synergy effect of in-situ
and remote clean methods. The composition of the cleaning reagents
may also be adjusted to include more cleaning reagents that are
prone to recombine, such as oxygen, and less aggressing cleaning
reagents that are damaging to the equipment, such as fluorine.
Second, in-situ plasma increases ionized species concentration and
provides additional ion bombardment energy to assist in the
breakdown and dissociation of deposited residues. Furthermore,
in-situ plasma heats up the inside surfaces of the deposition
chamber including the areas with residues leading to faster etch
rates and more desirable volatile reaction products. A wafer
pedestal may be separately heated using its internal heater and
kept at between about 100.degree. C. and 650.degree. C. during the
entire cleaning process. In a more specific embodiment, the
pedestal may be kept between about 250.degree. C. and 550.degree.
C.
[0030] As indicated above, in certain embodiments, the in-situ
plasma generator may be set to lower power levels than required in
conventional in-situ plasma cleaning methods. In certain
embodiments, this is true even when some or most of the radical
species generated remotely have recombined prior to introduction
into the deposition chamber. One mechanism that permits this is
radicals recombining into high energy molecules prior to
introduction into the deposition chamber. Although the radicals are
recombined, the energy necessary to dissociate them is less than
what it would be if entering the chamber without previously passing
through the remote plasma generator.
[0031] The cleaning reagent mixture then reacts with the residues
(block 210) to form volatile compounds that are evacuated from the
chamber (block 212). For example, high carbon content ashable hard
mask residues may form volatile carbon oxides (CO and CO.sub.2),
carbon fluorides (CF.sub.4, C.sub.2F.sub.4, C.sub.2F.sub.6 and
others) and etch products. The underlying SiO.sub.2 film is also
etched away by fluorine radicals. The remaining un-reacted mixture,
inert gases, and volatile compounds are pumped out of the
chamber.
[0032] The overall cleaning process may include multiple stages,
each stage designed to clean different parts of the chamber and/or
different residues. One embodiment having three cleaning stages is
illustrated in FIG. 3. The method includes: a high pressure (HP)
cleaning stage (block 302), a low pressure (LP) cleaning stage
(block 304), and fluorine RPC cleaning stage (block 306). The HP
cleaning stage is typically performed at higher pressure levels and
uses more oxygen containing compound. Such combination allows for
faster but non-destructive cleaning of the showerhead and the
pedestal. Aluminum is a common material for showerheads and tends
to form aluminum fluoride during long and aggressive cleaning at
high temperature and high fluorine containing compounds' flow
rates. During the HP stage the oxygen containing compounds
effectively dilute the fluorine containing compounds and diminish
destructive effect of the fluorine containing compounds. Because of
the high pressure and high flow rates, the HP stage may be
substantially shorter than the LP stage, which is typically
performed at lower pressure and lower overall flow rate. During the
LP stage, the flow rate of the oxygen containing cleaning reagents
is reduced, thereby, increasing the concentration of the fluorine
containing cleaning reagents. The power level of in-situ plasma
generation can be raised to increase the etch rate, while the
pressure is decreased. The LP stage is usually the longest duration
stage to allow for cleaning reagents to reach remote areas of the
chamber, such as under the pedestal, around the chamber top plate,
and the chamber walls. In addition to removing carbon containing
residues, some silicon oxide residues on the showerhead and
pedestal may be also removed by fluorine radicals. Finally, the
pure fluorine RPC clean stage may be performed using only the
fluorine containing cleaning reagents and requires no in-situ power
generation. The focus is on removing the remaining silicon oxide
residue and, thus, oxygen containing cleaning compounds may not be
needed. Additionally, fluorine radicals do not recombine as rapidly
as oxygen radicals, and in-situ plasma generation may be
discontinued to prevent damage to the exposed aluminum chamber
components after most of the deposition residues have been removed.
The stage can be performed at a pressure higher than the LP stage
and may be close to the pressure level of the HP stage. Note that
an RPC unit is used in all three stages. In certain embodiments,
the unit automatically adjusts the power settings depending on the
flow rate and pressure of the cleaning gases. However, the in-situ
plasma is only used during the HP cleaning and the LP cleaning
stages so that the damage to chamber hardware parts is minimized.
According to various embodiments, the HP, LP and fluorine RPC
cleaning stages may be performed in different orders than that
presented in FIG. 3.
[0033] The following parameters may be used in a cleaning method
according to the embodiment presented in FIG. 3 for removal of high
carbon content residues. However, it should be readily understood
that the described stages and some parameters may be also
applicable to clean other residue materials. The HP cleaning stage
(302) is performed for between about 100 seconds and 1,000 seconds,
while the chamber pressure of between about 0.25 Torr and 4 Torr.
It should be understood that the duration of the stages may depend
on the amount of residue present in the chamber. The in-situ
generator may be set to provide between about 500-4,000 W. The
cleaning reagent mixture is primarily composed (and may consist
essentially) of oxygen containing compounds during this stage. The
flow rate may vary between about 1,000 sccm and 15,000 sccm, or in
more specific embodiment between about 3,000 sccm and 10,000 sccm,
for a Vector deposition chamber with four deposition stations.
Because of high level of activation of the cleaning reagents in a
remote plasma generator with further activation inside the
deposition chamber, oxygen containing cleaning compounds may
provide effective initial cleaning of the shower head and the wafer
pedestal. The flow rate of fluorine containing cleaning compounds
may be at least ten times less than that of oxygen containing
cleaning compounds. In other embodiments, the ratio may be between
about 2 and 5. In one specific embodiment, the flow rate of the
fluorine containing cleaning compounds is between about 100 and 500
sccm for a Vector deposition chamber.
[0034] During the LP cleaning stage the pressure is reduced to
between about 0.05 Torr and 1 Torr, while the RF power is increased
to between about 1,000 W and 5,000 W. The flow rate of the oxygen
containing cleaning compounds may be also reduced for this stage.
For example, a flow rate of between about 200 sccm and 5,000 sccm
may be used for oxygen containing cleaning compounds in a Vector
deposition chamber. The flow rate of the fluorine containing
compounds may be kept the same. The goal of this cleaning stage is
to reach the remote areas of the deposit chamber, such as the side
walls and a top plate above the showerhead and the surfaces under
the wafer pedestal. It usually requires a longer period, so that
the LP cleaning stage may proceed for between about 200 seconds and
2,000 seconds. Additionally, some of the silicon dioxide residues
may be etched away during this stage because high concentration of
fluorine radicals is present in the chamber. Usually, ashable hard
mask residues are completely removed from the deposition chamber at
the end of the LP stage.
[0035] Finally, the fluorine RPC cleaning stage may be used to
remove any silicon dioxide under the ashable hard mask residues.
This stage involves a high flow rate of fluorine containing
compounds, for example between about 1,000 sccm and 8,000 sccm for
a Vector deposition chamber, while no or relatively small amount of
the oxygen containing compounds are used. The in-situ plasma
generation is usually turned off or set to a very low power level.
In-situ plasma generation is less critical during this stage
because fluoride containing compounds are primarily used and
fluorine radicals are less prone to recombine than oxygen radicals.
Furthermore, the inside surfaces of the deposition chamber may have
already been pre-heated by two prior stages. The chamber pressure
may be between about 0.25 Torr and 4 Torr, while the duration of
this stage may be between about 50 seconds and 500 seconds. The
table below summarizes various parameter ranges for different
stages of the cleaning process described above.
TABLE-US-00001 TABLE 1 HP Cleaning LP Cleaning Fluorine RPC
Fluorine Containing 100-500 100-500 1,000-8,000 Compound Flow Rate
(sccm) Oxygen Containing 1,000-15,000 200-5,000 0-500 Compound Flow
Rate (sccm) Inert Gas (sccm) 200-5,000 200-5,000 3,000-20,0000 RF
Power Level (W) 500-4,000 1,000-5,000 0-1,000 Pressure (Torr)
0.25-4 0.05-1 0.25-4 Time (sec) 100-1,000 200-2,000 50-500
[0036] The process parameters for a more specific embodiment are
presented in the table below.
TABLE-US-00002 TABLE 2 HP Cleaning LP Cleaning Fluorine RPC
Fluorine Containing 200-400 300-400 3,000-5,000 Compound Flow Rate
(sccm) Oxygen Containing 4,000-8,000 1,000-2,000 0-100 Compound
Flow Rate (sccm) Inert Gas (sccm) 750-1,250 750-1,250 6,000-12,0000
RF Power Level (W) 1,000-2,000 2,000-3,000 0-500 Pressure (Torr)
0.75-1.25 0.1-0.5 0.75-1.25 Time (sec) 200-500 300-800 60-200
Apparatus
[0037] Any suitable deposition chamber may be cleaned using the
plasma cleaning method. Examples of deposition apparatuses include
Novellus's Sequel PECVD system, Vector PECVD system, Vector Extreme
PECVD system, which are all available from Novellus Systems, Inc.
of San Jose, Calif., or any of a variety of other commercially
available processing systems. In some cases, depositions performed
on multiple deposition stations sequentially. Each station may be
cleaned by the methods described above.
[0038] FIG. 4 illustrates an overall system that may be
conceptually divided into a deposition chamber 418 and a cleaning
apparatus including a remote plasma generator 406. The deposition
chamber 418 includes a wafer pedestal 420, a shower head 414, an RF
generator 416, a control system 422 and other components described
below.
[0039] The cleaning reagents and inert gases, such as argon, helium
and others, are supplied to the remote plasma generator 406 from
various cleaning reagent sources, such as source 402. A cleaning
reagent source may be a storage tank containing one or a mixture of
reagents. Moreover, a facility wide source of the cleaning reagents
may be used.
[0040] Any suitable remote plasma generator may be used for initial
processing of the cleaning reagents. For example, a Remote Plasma
Cleaning (RPC) units, such as ASTRON.RTM. i Type AX7670,
ASTRON.RTM. e Type AX7680, ASTRON.RTM. ex Type AX7685, ASTRON.RTM.
hf-s Type AX7645, all available from MKS Instruments of Andover,
Mass., may be used An RPC unit is typically a self-contained device
generating weakly ionized plasma using the supplied cleaning
reagents. Imbedded into the RPC unit a high power RF generator
provides energy to the electrons in the plasma. This energy is then
transferred to the neutral cleaning reagent molecules leading to
temperature in the order of 2000K resulting in thermal dissociation
of the cleaning reagents. An RPC unit may dissociate more than 90%
of incoming cleaning reagent molecules because of its high RF
energy and special channel geometry causing the cleaning reagents
to adsorb most of this energy.
[0041] The cleaning reagent mixture is then flown through a
connecting line 408 into the deposition chamber 418, where the
mixture is distributed through the shower head 414. The shower head
414 or the pedestal 420 typically has an internal RF generator 416
attached to it. In one example, it is a High Frequency (HF)
generator capable of providing between about 0 W to 10,000 W at
frequencies 1 MHz to 100 MHz. In a more specific embodiment, the HF
generator may deliver 0 W to 5,000 W at 13.56 MHz. The RF generator
416 generates in-situ plasma that is used to further dissociate
cleaning reagent molecules in the mixture and to supply ion
bombardment energy to enhance the cleaning process. The methods of
the invention are not limited to RF-generated plasmas, but may
employ microwave and other types of plasmas.
[0042] The chamber 418 may include sensors 424 for sensing various
materials and their respective concentrations, pressure,
temperature, and other process parameters and providing information
on reactor conditions during the clean to the system controller
422. Examples of chamber sensors that may be monitored during the
clean include mass flow controllers, pressure sensors such as
manometers, thermocouples located in pedestal. Sensors 424 may also
include an infra-red detector or optical detector to monitor
presence of gases in the chamber and control measures.
[0043] Cleaning of residue generates various volatile species that
must be removed from the chamber 418. Moreover, the chamber 418
needs to operate at certain pressure levels, which may different
from one cleaning stage to another. The volatile etching products
and other excess gases are removed from the reactor 418 via an
outlet 426 that may be include a vacuum pump and a valve.
[0044] In certain embodiments, a system controller 422 is employed
to control process conditions during the clean. The system
controller 422 will typically include one or more memory devices
and one or more processors. The processor may include a CPU or
computer, analog and/or digital input/output connections, stepper
motor controller boards, etc. Typically there will be a user
interface associated with system controller 422. The user interface
may include a display screen, graphical software displays of the
apparatus and/or process conditions, and user input devices such as
pointing devices, keyboards, touch screens, microphones, etc.
[0045] In certain embodiments, the system controller 422 controls
the pressure in the reactor. The system controller 422 may also
control all of the activities during the cleaning process,
including gas flow rate and RF generator process parameters. The
system controller 422 executes system control software including
sets of instructions for controlling the timing, mixture of gases,
chamber pressure, chamber temperature, and other parameters of a
particular process. Other computer programs stored on memory
devices associated with the controller may be employed in some
embodiments.
[0046] The computer program code for controlling the processes in a
process sequence can be written in any conventional computer
readable programming language: for example, assembly language, C,
C++, Pascal, Fortran or others. Compiled object code or script is
executed by the processor to perform the tasks identified in the
program. The system software may be designed or configured in many
different ways. For example, various chamber component subroutines
or control objects may be written to control operation of the
chamber components necessary to carry out the inventive deposition
processes. Examples of programs or sections of programs for this
purpose include process gas control code, pressure control code,
and plasma control code.
[0047] The controller parameters relate to process conditions such
as, for example, timing during each stage, chamber pressure during
each stage, process gas composition and flow rates, plasma
conditions such as RF power levels and RF frequency, and chamber
temperature. These parameters are provided to the user in the form
of a recipe, and may be entered utilizing the user interface.
Signals for monitoring the process may be provided by analog and/or
digital input connections of the system controller 422. The signals
for controlling the process are output on the analog and digital
output connections of the deposition apparatus.
[0048] A chamber pressure profile program may include program code
for controlling the chamber pressure during each stage of the
cleaning process by regulating, e.g., a throttle valve in the
exhaust system of the chamber 426. A stage timing program may
include a code for changing pressure based on the amount of carbon
oxides in the chamber and/or user input and/or predetermined timing
sequences. A process gas control program may include code for
controlling gas composition and flow rates. A plasma control
program may include code for setting RF (or other plasma source
power) power levels applied to the RF plasma generator.
Example 1
[0049] An experiment was conducted to compare effectiveness of
etching an ashable hard mask film from the wafer surface using a
cleaning method versus an in-situ cleaning method. Standard 300-mm
wafers with 5,500 .ANG. ashable hard mask film were divided into
four separate groups. Each group was etched for about 30 seconds in
a Vector PECVD deposition chamber using four different clean
conditions. To evaluate effect of certain process parameters, the
same temperature of about 350.degree. C., the same pressure of
about 0.45 Torr, and the same cleaning reagents were used for all
groups. Nitrogen trifluoride was flown at 300 sccm and oxygen was
flown at 6,000 sccm in all tests. The two cleaning reagents were
flown simultaneously at the constant flow rates indicated above
during the entire cleaning test. The process conditions were
selected for comparison purposes only and were not representative
of the optimal process parameters evaluated in the experiments
below.
[0050] FIG. 5 is a plot illustrating experimental data of the
etched thicknesses of ashable hard mask films according to each of
the processes: The top solid line 502 represents the etched
thickness of the ashable hard-mask deposit across the entire wafer
width of 300 mm using an embodiment of the clean method described
above with reference to FIG. 2. The cleaning reagents were first
flown through the ASTRON.RTM. hf-s Type unit and then into the
PECVD chamber. The HF generator was set to deliver about 300 W at
13.56 MHz. The entire ashable hard mask deposit was essentially
removed from the wafer surface exposing the under-laying silicon.
The etch rate was estimated to be at least 1.1 .mu.m/min and
possibly much higher.
[0051] For comparison, lines 504, 506 and 508 show results from
different in-situ only clean processes. The bottom dashed line 508
represents the etch thickness using an in-situ only clean method
with the HF generator set at 300 W to match the settings of the
cleaning method described above with reference to the results shown
in line 502. It was estimated that the etched thickness for this
second group was only 1,400 .ANG., which corresponds to an etch
rate of about 0.28 .mu.m/min. Therefore, the cleaning performance
of the in-situ cleaning method was determined to be approximately
four times worse than that of the inventive cleaning method. Adding
an RPC unit to dissociate cleaning reagents before introducing into
the deposition chamber for an in-situ like clean indicates
substantial improvement in cleaning.
[0052] Higher power levels of the HF generator were used for the
next two in-situ cleaning groups. The second dashed line from the
bottom 506 corresponds to the etched thickness for the in-situ
cleaning where the HF generator was set to about 500 W. The average
etched thickness was estimated at about 1,500 .ANG., i.e. 0.30
.mu.m/min etched rate. Even further increasing power of the HF
generator did not provide cleaning efficiency that is comparable to
that of the new method. The next dashed line 504 corresponds to the
etched thickness of about 2,200 .ANG., i.e. 0.44 .mu.m/min etch
rate, where the RF generator was set to deliver about 1500 W. Still
the cleaning method with the 300 W setting was almost three times
more effective than any of the in-situ cleaning conditions tested.
Note that higher RF power is not desirable because of the
destructive effects on the internal components of the deposition
chamber.
Example 2
[0053] Yet another experiment was conducted to using a Vector PECVD
chamber. First, a set of ashable hard mask depositions was
conducted to build up the film accumulation inside the chamber.
Fifty wafers were deposited with approximately 5,500 .ANG. thick
ashable hard mask film at 350.degree. C. The chamber was then
cleaned using one of several proposed cleaning methods. An in-situ
cleaning method with the clean parameters listed in the table
below. A total of 26 min cleaning time to achieve adequate
cleanness of the chamber, i.e. lack of any visible residues.
TABLE-US-00003 TABLE 3 HP Clean HP Clean 2 LP Clean NF.sub.3 Flow
Rate (sccm) 600 1000 400 O.sub.2 Flow Rate (sccm) 6000 1500 1500 He
Flow Rate (sccm) 0 3000 0 HF Power Level (W) 4000 3000 3250
Pressure (Torr) 1.0 1.5 0.25
[0054] The results of the in-situ cleaning were compared to results
of several runs using a cleaning method. Three different settings
were tested for the HF generator during the low pressure cleaning
stage. The process parameters for the cleaning method are
summarized in table below.
TABLE-US-00004 TABLE 4 HP Clean LP Clean Fluorine RPC NF.sub.3 Flow
Rate (sccm) 300 300 4000 O.sub.2 Flow Rate (sccm) 6000 1500 0 Argon
Flow Rate (sccm) 1000 1000 9000 HF Power Level (W) 1500
1000/1500/2000 0 Pressure (Torr) 1 0.25 1
[0055] With 1.0 kW setting during the LP cleaning stage the chamber
was effectively cleaned in about 20 min achieving approximately 6
min saving over the in-situ cleaning. Increase the power to 1.5 kW
saved additional 2 min. Finally, setting the HF generator to 2.5 kW
led to the overall cleaning time of about 16 min or about 10
minutes (.about.38%) of total savings over the in-situ cleaning
method. Further increasing the power level may have allowed even
shorter cleaning time.
CONCLUSION
[0056] Although the foregoing invention has been described in some
detail for purposes of clarity of understanding, it will be
apparent that certain changes and modifications may be practiced
within the scope of the appended claims. It should be noted that
there are many alternative ways of implementing both the process
and compositions of the present invention. Accordingly, the present
embodiments are to be considered as illustrative and not
restrictive, and the invention is not to be limited to the details
given herein.
[0057] All references cited herein are incorporated by reference
for all purposes.
* * * * *