U.S. patent application number 10/835450 was filed with the patent office on 2005-11-03 for method for cleaning a reactor using electron attachment.
Invention is credited to Dong, Chun Christine, Ji, Bing.
Application Number | 20050241670 10/835450 |
Document ID | / |
Family ID | 35185844 |
Filed Date | 2005-11-03 |
United States Patent
Application |
20050241670 |
Kind Code |
A1 |
Dong, Chun Christine ; et
al. |
November 3, 2005 |
Method for cleaning a reactor using electron attachment
Abstract
A method for cleaning, and/or enhancing the cleaning of, a
reactor is disclosed herein. In one aspect, there is provided a
method comprising: providing the reactor wherein a surface of the
reactor is coated with a substance; providing a first and second
electrode in close proximity to the reactor wherein the first and
second electrode reside within a target area; passing a gas mixture
comprising a reactive gas into the target area; supplying energy to
at least one of the first or the second electrodes to generate
electrons within the target area wherein at least a portion of the
electrons attach to at least a portion of the reactive gas thereby
forming a negatively charged cleaning gas; contacting the substance
with the negatively charged cleaning gas wherein the negatively
charged cleaning gas reacts with the substance and forms a volatile
product; and removing the volatile product from the reactor.
Inventors: |
Dong, Chun Christine;
(Macungie, PA) ; Ji, Bing; (Allentown,
PA) |
Correspondence
Address: |
AIR PRODUCTS AND CHEMICALS, INC.
PATENT DEPARTMENT
7201 HAMILTON BOULEVARD
ALLENTOWN
PA
181951501
|
Family ID: |
35185844 |
Appl. No.: |
10/835450 |
Filed: |
April 29, 2004 |
Current U.S.
Class: |
134/1.1 ;
134/22.1 |
Current CPC
Class: |
C23C 16/4405 20130101;
B08B 7/0035 20130101 |
Class at
Publication: |
134/001.1 ;
134/022.1 |
International
Class: |
C25F 001/00 |
Claims
We claim:
1. A method for removing a substance from a reactor, the method
comprising: providing the reactor wherein at least a portion of a
surface of the reactor is coated with the substance; providing a
first and a second electrode that is in close proximity to the
reactor wherein the first and the second electrode resides within a
target area; passing a gas mixture comprising a reactive gas into
the target area wherein the reactive gas has an electron affinity
greater than 0; supplying energy to at least one of the first or
the second electrodes to generate electrons within the target area
wherein at least a portion of the electrons attach to at least a
portion of the reactive gas thereby forming a negatively charged
cleaning gas; contacting the substance with the negatively charged
cleaning gas wherein the negatively charged cleaning gas reacts
with the substance and forms at least one volatile product; and
removing the at least one volatile product from the reactor.
2. The method of claim 1 wherein the reactive gas comprises a
halogen.
3. The method of claim 2 wherein the reactive gas is at least one
member selected from NF.sub.3, ClF.sub.3, ClF, SF.sub.6, a
perfluorocarbon, a hydrofluorocarbon, an oxyfluorocarbon, a
hypofluorite, a fluoroperoxide, a fluorotrioxide, COF.sub.2, NOF,
F.sub.2, a compound having the formula NF.sub.nCl.sub.3-n, wherein
n is a number ranging from 1 to 2, BCl.sub.3, Cl.sub.2, and
combinations thereof.
4. The method of claim 3 wherein the reactive gas is NF.sub.3.
5. The method of claim 1 wherein the gas mixture comprises reactive
species that were activated within a remote chamber.
6. The method of claim 1 wherein the gas mixture further comprises
an inert diluent gas.
7. The method of claim 6 wherein the inert diluent gas comprises at
least one selected from nitrogen, helium, argon, neon, xenon,
krypton, radon, and mixtures thereof.
8. The method of claim 6 wherein the inert diluent gas has an
electron affinity that is less than the electron affinity of the
reactive gas.
9. The method of claim 1 wherein the energy in the supplying step
is at least one source selected from the group consisting of an
electric energy source, an electromagnetic energy source, a thermal
energy source, an electric energy source, a photo energy source, or
combinations thereof.
10. The method of claim 9 wherein the energy is an electric energy
source.
11. The method of claim 1 wherein the first electrode is
grounded.
12. The method of claim 1 wherein the second electrode is
grounded.
13. The method of claim 1 wherein the target area resides within
the reactor.
14. The method of claim 1 wherein the target area is outside of the
reactor.
15. The method of claim 1 wherein the electrons are generated in
the supplying step by at least one method selected from the group
consisting of cathode emission, gas discharge, and combinations
thereof.
16. The method of claim 15 wherein the electrons are generated by a
cathode emission method selected from the group consisting of field
emission, thermal emission, thermal-field emission, photoemission,
and electron beam emission.
17. The method of claim 1 wherein the substance is at least one
selected from a W, Ti, SiO.sub.2, TiO.sub.2, SiON, poly-silicon,
amorphous silicon, SiN, WN, Al.sub.2O.sub.3, HfO.sub.2, ZrO.sub.2,
HfSiO.sub.4, and mixtures thereof.
18. A method of removing a substance from at least a portion of a
surface of a reactor, the method comprising: providing the reactor
comprising at least one electrode and the surface wherein at least
a portion of the surface is grounded; introducing a gas mixture
comprising a reactive gas and optionally an inert diluent gas into
the reactor; supplying voltage to the at least one electrode and/or
the surface to generate electrons wherein at least a portion of the
electrons attach to at least a portion of the reactive gas thereby
forming a negatively charged cleaning gas; contacting the substance
with the negatively charged cleaning gas wherein the negatively
charged cleaning gas reacts with the substance and forms at least
one volatile product; and removing the at least one volatile
product from the reactor.
19. The method of claim 18 wherein the gas mixture further
comprises reactive species.
20. The method of claim 18 wherein the reactive gas is at least one
member selected from NF.sub.3, ClF.sub.3, ClF, SF.sub.6, a
perfluorocarbon, a hydrofluorocarbon, an oxyfluorocarbon, a
hypofluorite, a fluoroperoxide, a fluorotrioxide, COF.sub.2, NOF,
F.sub.2, a compound having the formula NF.sub.nCl.sub.3-n, wherein
n is a number ranging from 1 to 2, BCl.sub.3, Cl.sub.2, and
combinations thereof.
21. The method of claim 20 wherein the reactive gas is
NF.sub.3.
22. The method of claim 18 wherein the substance is at least one
selected from SiO.sub.2, TiO.sub.2, SiON, W, poly-silicon,
amorphous silicon, SiN, WN, Al.sub.2O.sub.3, HfO.sub.2, ZrO.sub.2,
HfSiO.sub.4, HfSiO.sub.4, and mixtures thereof.
23. The method of claim 18 wherein the voltage ranges from 0.01 to
50 kV.
24. The method of claim 23 wherein the voltage ranges from 0.1 to
30 kV.
25. The method of claim 18 wherein the voltage is pulsed.
26. The method of claim 18 wherein the gas mixture is at a pressure
ranging from 1 Torr to 20 psia.
27. The method of claim 18 wherein the gas mixture comprises the
inert diluent gas.
28. The method of claim 18 wherein the amount of inert diluent gas
ranges from 1 to 99% by volume.
29. A method of removing a substance from at least a portion of a
surface of a reactor, the method comprising: providing a reactive
gas into a remote chamber that is outside of the reactor,
activating the reactive gas in the remote chamber to form reactive
species; providing the reactor comprising at least one electrode
and the surface wherein at least a portion of the surface is
grounded; introducing a gas mixture comprising a reactive gas,
reactive species, and optionally an inert diluent gas into the
reactor; supplying voltage to the at least one electrode and/or the
surface to generate electrons wherein at least a portion of the
electrons attach to at least a portion of the reactive gas thereby
forming a negatively charged cleaning gas; contacting the substance
with the negatively charged cleaning gas wherein the negatively
charged cleaning gas reacts with the substance and forms at least
one volatile product; and removing the at least one volatile
product from the reactor.
30. The method of claim 29 wherein the activating step is conducted
using power that ranges from 100 to 14,000 Watts.
Description
BACKGROUND OF THE INVENTION
[0001] In the manufacture of semiconductor integrated circuits
(IC), opto-electronic devices, and microelectro-mechanical systems
(MEMS), multiple steps of thin film deposition are performed in
order to construct several complete circuits (chips) and devices on
monolithic substrate wafers. Each wafer is often deposited with a
variety of thin films such as, but not limited to, conductor films,
e.g., tungsten; semiconductor films, e.g., doped and undoped
poly-crystalline silicon (poly-Si), doped and undoped (intrinsic)
amorphous silicon (a-Si), etc.; dielectric films, e.g., silicon
dioxide (SiO.sub.2), undoped silicon glass (USG), boron doped
silicon glass (BSG), phosphorus doped silicon glass (PSG),
borophosphrosilicate glass (BPSG), silicon nitride
(Si.sub.3N.sub.4), silicon oxynitride (SiON) etc.; low-k dielectric
films, e.g., fluorine doped silicate glass (FSG), and carbon-doped
silicon glass, such as "Black Diamond".
[0002] In modern manufacturing, thin film deposition is
accomplished by placing a substrate or wafer into a reaction
chamber or reactor and introducing gases that undergo chemical
reactions to deposit solid materials onto the surface of a
substrate. Such a deposition process is called chemical vapor
deposition (CVD). These chemical reactions typically require
elevated temperatures (up to 600.degree. C.) to overcome reaction
activation energies. Alternatively, radio frequency (RF) energies
are coupled into the vacuum chamber to ignite the precursors into a
discharge state, i.e., plasma. In the latter method, higher quality
films can be deposited at lower process temperatures and more
efficiently using plasma energy. Such process is termed plasma
enhanced chemical vapor deposition (PECVD).
[0003] The deposition process not only facilitates the growth of
films onto a substrate surface but also leaves films and solid
residues on the internal surfaces of the reactors. These unwanted
solid residues could change the reactor surface characteristics as
well as RF power coupling efficiency. Such reactor changes can also
lead to deposition process performance drifts and a loss of
production yield. For example, accumulated solid residues can flake
off from the reactor's internal surface and deposit particles onto
the wafer surface during subsequent deposition cycles.
Consequently, periodic cleaning, or chamber cleaning, of the
internal surfaces of the deposition reactors may be necessary to
maintain production yield.
[0004] For CVD reactors, cleaning of the reactor, also referred to
as chamber cleaning, may be conducted using fluorine chemistry to
convert solid residues into volatile gaseous byproducts that can be
pumped out of the CVD reactor by vacuum pumps. In this connection,
reactive fluorine atoms (F.cndot.) are generated from
fluoro-compounds. Historically, perfluorocarbons (PFCs), such as
CF.sub.4 and C.sub.2F.sub.6, are used as the source of reactive
fluorine in plasma activated chamber cleaning. Unfortunately, using
perfluorocarbon gases for chamber cleaning has significant adverse
environmental impact. Perfluorocarbons, such as CF.sub.4 and
C.sub.2F.sub.6, strongly absorb infrared radiation and have very
long atmospheric lifetimes (more than 50,000 years for CF.sub.4,
and 10,000 years for C.sub.2F.sub.6). As a result, these
perfluorocarbon gases are the most potent greenhouse gases that
cause global warming. Since perfluorocarbon molecules are very
stable, they are difficult to breakdown in plasmas. In other words,
the PFC destruction efficiency (DE) tends to be very low. Typical
DE is only 5%-20% for CF.sub.4, and 20%-50% for C.sub.2F.sub.6. In
addition to undestroyed feed PFC gases, all perfluorocarbon-based
chamber cleaning emits significant amount of CF.sub.4 as explained
above. Though estimates vary somewhat, it is generally agreed that
up to 70% of the PFC emissions from a semiconductor fabrication
facility comes from CVD chamber cleaning processes. With the
exponential growth of the semiconductor industry, the PFC gas
emitted from semiconductor manufacturing processes could become a
significant source of global warming emissions.
[0005] Replacing perfluorocarbons with nitrogen trifluoride
(NF.sub.3) for CVD chamber cleaning offers dramatic improvement in
reducing greenhouse gas emissions. NF.sub.3 has a relatively
shorter atmospheric lifetime, 750 years, compared to
perfluorocarbon gases. When fully optimized, the destruction
efficiency for NF.sub.3 in an in situ chamber clean plasma can be
above 90%. Since NF.sub.3 does not contain carbon, no CF.sub.4 will
be emitted from NF.sub.3 plasmas. Plasma can be broadly defined as
a state of matter in which a significant number of the atoms and/or
molecules are electrically charged or ionized. The numbers of
negative and positive charges are equal, and thus the overall
charge of the plasma is neutral. No global warming byproducts can
be formed in NF.sub.3 plasmas. Therefore, significant reductions in
greenhouse gas emissions can be achieved by replacing
perfluorocarbon gases with NF.sub.3 in CVD chamber clean.
[0006] Currently, there are three technology platforms to utilize
NF.sub.3 for chamber cleaning: thermal, in situ plasma, and remote
plasma. Existing NF.sub.3-based CVD chamber cleaning technologies
typically use either thermal or plasma activation. Both thermal and
plasma activated NF.sub.3 chamber cleaning technologies present
challenges in NF.sub.3 usage, fluorine utilization, and energy
consumption. In a typical thermal chamber cleaning process using
NF.sub.3, NF.sub.3 may need to be heated to a temperature in excess
of 500.degree. C. to initiate thermal decomposition of the NF.sub.3
molecule. Unfortunately, certain non-thermal CVD reactors, such as
PECVD reactors, use temperature controllers to maintain the reactor
at temperatures below 400.degree. C., which is too low for
effective thermal NF.sub.3 cleaning. For in situ plasma cleaning,
RF plasma is generated inside the reactor and high-energy electrons
in the plasma dissociate NF.sub.3 by electron impact. In situ
plasmas, however, can become highly electronegative, such as, for
example, by the formation of negative ions. When negative ions
dominate over electrons as the charge carrier, the plasma becomes
unstable and/or collapses within the reactor thereby leading, inter
alia, to incomplete chamber cleaning, poor NF.sub.3 utilization,
and low NF.sub.3 dissociation efficiency. Further, highly energetic
ion bombardment that occurs during in situ cleaning may cause
hardware damage. While remote plasma cleaning alleviates the
drawbacks of in situ cleaning, fluorine utilization efficiency is
much lower, increasing the overall cost of ownership of the
process. These challenges may impede wider adoption of
NF.sub.3-based chamber cleaning in the industry.
BRIEF SUMMARY OF THE INVENTION
[0007] A method for removing a substance from at least a portion of
a surface within a reactor is disclosed herein. In one aspect,
there is provided a method for cleaning a reactor comprising:
providing the reactor wherein at least a portion of a surface of
the reactor is coated with a substance; providing a first and a
second electrode that is in close proximity to the reactor wherein
the first and the second electrode resides within a target area;
passing a gas mixture comprising a reactive gas into the target
area wherein the reactive gas has an electron affinity of greater
than zero; supplying energy to at least one of the first or the
second electrodes to generate electrons within the target area
wherein at least a portion of the electrons attach to at least a
portion of the reactive gas thereby forming a negatively charged
cleaning gas; contacting the substance with the negatively charged
cleaning gas wherein the negatively charged cleaning gas reacts
with the substance and forms at least one volatile product; and
removing the at least one volatile product from the reactor.
[0008] In another aspect of the invention, there is provided a
method for removing a substance from at least a portion of a
surface of a reactor comprising: providing the reactor comprising
at least one electrode and the surface wherein at least a portion
of the surface is grounded; introducing a gas mixture comprising a
reactive gas and optionally an inert diluent gas into the reactor;
supplying voltage to the at least one electrode and/or the surface
to generate electrons wherein at least a portion of the electrons
attach to at least a portion of the reactive gas thereby forming a
negatively charged cleaning gas; contacting the substance with the
negatively charged cleaning gas wherein the negatively charged
cleaning gas reacts with the substance and forms at least one
volatile product; and removing the at least one volatile product
from the reactor.
[0009] In a further aspect of the present invention, there is
provided a method removing a substance from at least a portion of a
surface of a reactor comprising: introducing a reactive gas into a
remote chamber that is outside of the reactor, activating the
reactive gas in the remote chamber to form reactive species;
providing the reactor comprising at least one electrode and the
surface wherein at least a portion of the surface is grounded;
introducing a gas mixture comprising a reactive gas, reactive
species, and optionally an inert diluent gas into the reactor;
supplying voltage to the at least one electrode and/or the surface
to generate electrons wherein at least a portion of the electrons
attach to at least a portion of the reactive gas thereby forming a
negatively charged cleaning gas; contacting the substance with the
negatively charged cleaning gas wherein the negatively charged
cleaning gas reacts with the substance and forms at least one
volatile product; and removing the at least one volatile product
from the reactor.
DETAILED DESCRIPTION OF THE INVENTION
[0010] A chamber cleaning process wherein a substance to be
removed, such as the residues that collect on the internal surfaces
and fixtures of a reactor, can be effectively removed by a
negatively charged cleaning gas formed by electron attachment is
disclosed herein. The process removes a non-volatile substance,
such as, but not limited to, W, Ti, SiO.sub.2, TiO.sub.2, SiON,
poly-silicon, amorphous silicon, SiN, WN, Al.sub.2O.sub.3,
HfO.sub.2, ZrO.sub.2, HfSiO.sub.4, and mixtures thereof, from at
least a portion of the surface within a reactor and any fixtures
contained therein. The substance to be removed is converted from a
non-volatile material into a volatile product that can be readily
removed by the reactor vacuum pump or other means. The term
"volatile product", as used herein, relates to reaction products
and by-products of the reaction between the substance to be removed
and the negatively charged cleaning gas. Thus, the substance may be
removed from a chamber and the surfaces of fixtures contained
therein by contacting it with the negatively charged cleaning gas
under conditions sufficient to react with the substance and form
volatile products.
[0011] The following demonstrates a particular embodiment wherein
the gas mixture comprises the reactive gas NF.sub.3 and the inert
diluent gas N.sub.2. In this embodiment, negatively charged
fluorine ions, F.sup.-, are formed through dissociative attachment
process of the NF.sub.3 molecules as illustrated in reaction
(1):
NF.sub.3(g)+e.sup.-.fwdarw.NF.sub.2(g)+F.sup.-(g) (1)
[0012] The negative F.sup.- ions then drift to the anode, which may
be, for example, grounded internal surfaces within the reactor. At
the anode, the negatively charged ions, such as F.sup.- in equation
(1), can act as active species which then react with the substance
to be removed, such as SiO.sub.2 in equation (2) below, to form one
or more volatile products, such as SiF.sub.4 and O.sub.2 in
equation (2):
4F.sup.-(g)+SiO.sub.2(s).fwdarw.SiF.sub.4(g)+O.sub.2(g)+4e.sup.-
(2)
[0013] As a by-product of reaction (2), the free electrons may be
neutralized at the grounded anode. During this process, the effect
of inert gases can be very small or negligible because of their
small or zero value of electron affinity (e.g. N.sub.2).
[0014] The method disclosed herein may be useful for a variety of
chamber cleaning processes. For example, in one embodiment, it can
be used as an alternative chamber cleaning method to conventional
in situ plasma or thermal chamber cleaning methods. In this
embodiment, a gas mixture comprising a reactive gas and optionally
an inert diluent gas can form a negatively charged cleaning gas by
electron attachment inside the reaction chamber. An
electron-emitting electrode inside a chamber may be used as a
cathode and the wall of the chamber may be grounded to act as an
anode. When an energy source such as, for example, DC voltage is
applied between the two electrodes, low-energy electrons that may
range, for example, from 0 to 10 eV, are emitted from the
electron-emitting electrode and drift to the grounded chamber walls
along the electric field. During this electron drift, some reactive
gas molecules can capture the electrons and form a negatively
charged cleaning gas containing ions, which then act as the active
species. The electron attachment processes for these gases are
exothermic reactions. The formed negatively charged cleaning gas
can be preferentially adsorbed on the internal surface of the
deposition reactor due to the electric field drifting and thus the
efficiency of the reactive gas and the cleaning rate may be
increased. Further, the electron attachment process, which uses a
relatively lower energy, negatively charged cleaning gas, may
minimize hardware damage typically caused by high-energy positive
ion bombardments.
[0015] In an alternative embodiment, the method can be used to
enhance remote plasma cleaning. The term remote plasma cleaning, as
used herein, relates to the generation of plasma outside of the
reactor, such as for example, in a remote chamber. In remote plasma
cleaning, an energy source such as, but not limited to, a RF or
microwave source at a relatively high power range (e.g., 100 to
14,000 W), is used to generate an intense plasma containing
reactive species using a reactive gas, such as any of the reactive
gases disclosed herein, in the remote chamber. In these
embodiments, the gas mixture may comprise the reactive species,
i.e., reactive ions or reactive atoms that were activated in a
remote chamber prior to electron attachment to form the negatively
charged cleaning gas. In these embodiments, the electron attachment
of the reactive species and/or the reactive gas molecules may
enhance the efficiency of the remotely generated plasma. For
example, by applying the electron attachment process downstream to
the remote plasma generator, neutral reactive species such as F
atoms and/or F.sub.2 molecules coming out of the remote plasma
generator will form negatively charged ions which can act as active
agents for cleaning deposition residues inside the deposition
chamber. Further, negatively charged reactive species such as
F.sup.- may not readily recombine to form neutral molecules such as
F.sub.2. Additionally, recombination byproducts such as F.sub.2 can
be converted into F.sub.2.sup.- which is more reactive than its
neutral counterpart (F.sub.2). Improved cleaning efficiency not
only reduces clean time and clean gas usage but also reduces the
scrubbing load of the effluent emission from chamber cleaning
process. Therefore, the overall cost of ownership (COO) of the
chamber cleaning process can be reduced.
[0016] In a still further embodiment, the method can be used as an
alternative to remote plasma cleaning. In this embodiment, the gas
mixture comprising the reactive gas is passed through a target area
and/or a remote negative ion generator, which contains a first and
second electrode that act as a cathode and an anode. An example of
a remote negative ion generator is illustrated in co-pending U.S.
patent application Ser. No. 10/819,277 which is currently assigned
to the assignee of the present invention and incorporated herein by
reference in its entirety. In embodiments wherein the gas mixture
is passed through the remote negative ion generator, the outlet of
the remote negative ion generator may be in fluid communication
with the reactor.
[0017] In certain embodiments, energy is supplied to at least one
of the electrodes, such as for example, the first electrode
sufficient to cause the first electrode to generate electrons. In
certain embodiments, the energy source can be an electric energy or
voltage source, such as an AC or DC source. Other energy sources,
such as an electromagnetic energy source, a thermal energy source,
or a photo energy source may also be used alone, or in combinations
with any of the aforementioned energy sources. The energy source
may be constant or alternatively pulsed. In certain embodiments of
the present invention, the first electrode, or cathode-acting
electrode, is connected to a first voltage level and the second
electrode, or anode-acting electrode, is connected to a second
voltage level. In alternatively embodiments, the first and second
electrode may alternate between acting like a cathode an acting
like an anode. The difference in the voltage levels creates a bias
in electrical potential. One of the first or the second voltage
levels may be zero indicating that either of the two electrodes can
be grounded. In this connection, the second electrode may not be an
actual electrode, but rather, the grounded walls and/or fixtures
within a reactor.
[0018] To produce negatively charged ions by electron attachment, a
large quantity of electrons needs to be generated. In this
connection, the electrons can be generated by a variety of ways
such as, but not limited to, cathode emission, gas discharge, or
combinations thereof. Among these electron generation methods, the
selection of the method depends mainly on the efficiency and the
energy level of the electrons generated.
[0019] As mentioned previously, for embodiments wherein the
fluorine containing gas is NF.sub.3, the most efficient ion
formation through electron attachment is accomplished by using free
electrons having an energy of .about.2 eV. In these embodiments,
such low energy level electrons can be generated by cathode
emission and/or gas discharge. For embodiments involving electron
generation through cathode emission, these embodiments may include:
field emission, thermal emission, thermal-field emission,
photoemission, and electron or ion beam emission.
[0020] Field emission involves applying an electric field with a
negative bias on the emission electrode relative to the base
electrode that is sufficiently high in intensity to overcome an
energy barrier for electrons to be generated from the surface of
the emission electrode. In certain embodiments, a DC voltage is
applied between the two electrodes that ranges from 0.1 to 50 kV,
or from 2 to 30 kV. In these embodiments, the distance between the
electrodes may range from 0.1 to 30 cm, or from 0.5 to 5 cm.
[0021] Thermal emission, on the other hand, involves using a high
temperature to energize electrons in the emission electrode and
separate the electrons from the metallic bond in the material of
the emission electrode. In certain preferred embodiments, the
temperature of the emission electrode may range from 800 to
3500.degree. C., or from 800 to 1500.degree. C. The emission
electrode may be brought to and/or maintained at a high temperature
by a variety of methods such as, but not limited to, directly
heating by passing AC or DC current through the electrode; indirect
heating such as contacting the cathode surface with an electrically
insulated hot surface heated by a heating element, IR radiation, or
combinations thereof.
[0022] For thermal-field emission, both an electric field and a
high temperature are applied. Therefore, thermal-field emission may
require a lesser electric field and a lower electrode temperature
for generating the same quantity of electrons as compared with pure
field emission and pure thermal emission. In embodiments wherein
the thermal-field emission is used for electron generation, the
temperature of the first electrode that acts as the cathode may
range from ambient to 3500.degree. C., or from 150 to 1500.degree.
C. In these embodiments, the electric voltage may range from 0.01
to 20 kV or from 0.1 to 10 kV.
[0023] In embodiments wherein the cathode emission mechanism is
used for generating electrons, the voltage applied between the two
electrodes can be constant or pulsed. The frequency of the voltage
pulse may range from 0 to 100 kHz. With applying a pulsed voltage,
the arcing tendency between two electrodes can be reduced, so that
the applied voltage can be increased and cathode emission can be
intensified.
[0024] As mentioned previously, electrons can be generated from a
first electrode that acts as a cathode when it has a negative bias
relative to a second electrode that acts as an anode. In certain
embodiments, the second electrode is the grounded chamber walls
and/or grounded fixtures contained within the reactor. In
embodiments wherein the cathode emission mechanism is used for
generating electrons, the electrode material may be comprised of a
conductive material with relatively low electron-emission energy or
work function and a high stability under processing conditions.
Examples of suitable materials include nickel, iridium, and iridium
oxide. In embodiments wherein field emission is involved, the
electrode is preferably made of geometries having a large surface
curvature, such as thin wires or sharp tips, to intensify the
electric field near the electrode surface. Further examples of
geometries are provided in co-pending U.S. patent application Ser.
No. 10/425,405 which is currently assigned to the assignee of the
present invention and incorporated herein by reference in its
entirety.
[0025] Low energy electrons may also be generated through gas phase
discharge wherein the energy level of the discharged electrons may
be adjusted by the pressure of the gas phase. These embodiments may
include thermal discharge, photo-discharge, and various avalanche
discharge, including glow discharge, arc discharge, spark
discharge, and corona discharge. In these embodiments, the gas
phase used for chamber cleaning may contain a reactive gas and an
inert diluent gas used for donating electrons wherein the electron
affinity of the inert diluent gas is significantly lower than that
of the reactive gas. In one particular embodiment involving gas
phase discharge, a high frequency pulsed voltage may be applied
between the first and second electrodes and electrons are generated
from the gas mixture between two electrodes that then drift toward
the anode. During the electron drift, some of these electrons may
attach on the reactive gas molecules and form negatively charged
ions by electron attachment. In addition, some positive ions are
also created by ionization of the inert gas, which then drift
toward the anode and are neutralized at the anode surface.
[0026] As mentioned previously, a gas mixture comprising a reactive
gas and optionally an inert gas is generally used as the feed gas
for chamber cleaning. For applying electron attachment in the
chamber cleaning, a reactive gas with a certain electron affinity
greater than 0 can be used and treated by electron attachment.
Examples of suitable gases include halogen-containing gases such
as, but not limited to, NF.sub.3, a compound having the formula
NF.sub.nCl.sub.3-n wherein n is a number ranging from 1 to 2,
F.sub.2, mixed halogen gases such as ClF and ClF.sub.3, HF,
SF.sub.6, BF.sub.3, fluorocarbons such as CF.sub.4, C.sub.2F.sub.6,
C.sub.3F.sub.8, C.sub.4F.sub.8, and oxyfluorocarbons such as
C.sub.4F.sub.8O, COF.sub.2 etc. Besides the aforementioned reactive
gas, any other gas that has certain electron affinity and is
intrinsically reactive or can form active species by electron
attachment to convert solid deposition residues into at least one
volatile product is potentially applicable for current
invention.
[0027] In certain embodiments, an inert diluent gas or a dilution
gas can be added to the gas mixture. In these embodiments, the
inert diluent gas has an electron affinity that is less than that
of the reactive gas contained within the gas mixture. Examples of
suitable inert diluent gases include, but are not limited to,
N.sub.2, Ar, He, Ne, Kr, Xe, and mixtures thereof. The
concentration of the inert diluent gas within the gas mixture can
range from 0 to 99.9% or from 1 to 99% by volume.
[0028] For a given quantity of free electrons, the efficiency of
the electron attachment can increase at increased gas pressure due
to a reduced acceleration of the free electrons and/or an increase
in collision probability between the molecules contained within the
gas mixture and the free electrons. The pressure range within the
reactor may range from 10 millitorr to 700 torr or from 1 torr to
700 torr. In certain embodiments, a sub-atmospheric pressure (such
as 700 Torr) may be used for safety concerns to minimize outbound
leak of reactive gases. When the potential hazard of outbound gas
leakage is mitigated, however, the pressure can be increased to
higher ranges, such as, for example above atmospheric pressure, to
further enhance the efficiency of electron attachment processes. In
alternative embodiments, the pressure within the reactor is higher
than that of the pressure within the target area, remote ion
generator, and/or remote plasma chamber, to encourage the flow of
the negatively charged cleaning gas into the reactor.
[0029] The method disclosed herein is useful for cleaning the
inside of reactors and the surfaces of various fixtures contained
therein such as, but not limited to, fluid inlets and outlets,
showerheads, work piece platforms, etc. In these embodiments, the
surface of the chamber and fixtures contained therein may be
comprised of a variety of different materials including metals,
such as titanium, aluminum, stainless steel, nickel, or alloys
comprising same, or insulating materials, such as a ceramic, e.g.,
quartz or Al.sub.2O.sub.3.
[0030] In certain embodiments, the method disclosed herein may be
used to enhance remote plasma cleaning. In these embodiments, a
remote plasma source, such as, but not limited to, a remote thermal
activation source, a remote catalytically activated source, or a
source which combines thermal and catalytic activation, may be used
rather than an in situ plasma to generate the volatile product. In
remote plasma cleaning, an intense discharge of cleaning gases is
generated outside of the deposition chamber, reactive species such
as reactive atoms and radicals then flow downstream into the
deposition chamber to volatize the deposition residues. Either an
RF or a microwave source can generate the remote plasma source.
Depending upon the energy source, power ranging from 100 to 14,000
Watts may be used to activate the plasma. In certain embodiments,
reactions between the negatively charged cleaning gas containing
remote plasma generated reactive species and the deposition
residues may be activated/enhanced by heating the reactor. In these
embodiments, the reaction between the negatively charged cleaning
gas containing the remote plasma generated reactive species and
substance to be removed can be activated and/or enhanced by heating
the reactor to a temperature sufficient to dissociate the one or
more reactive gas contained within the reactive gas. The specific
temperature required to activate the cleaning reaction with the
substance to be removed depends on the reactive gas(s) adopted.
[0031] In remote thermal activation, the reactive gas first flows
through a heated area such as a remote chamber outside of the
vessel to be cleaned. In the remote chamber, the gas dissociates by
contact with the high temperatures within a vessel outside of the
reactor to be cleaned. Alternative approaches include the use of a
catalytic converter to dissociate the reactive gas, or a
combination of thermal heating and catalytic cracking to facilitate
activation of the one or more reactive gases within the gas
mixture.
[0032] In alternative embodiments, the molecules of one or more
reactive gases within the gas mixture can be dissociated by intense
exposure to photons to form reactive radicals and atoms. For
example ultraviolet, deep ultraviolet and vacuum ultraviolet
radiation can assist breaking strong chemical bonds in deposition
residues as well as dissociating the one or more reactive gas
within the gas mixture thereby increasing the removal rates of the
deposition residues. Other means of activation and enhancement to
the cleaning processes can also be employed. For example, one can
use photon induced chemical reactions to generate reactive species
and enhance the negatively charged cleaning gas that is generated
by electron attachment.
[0033] In certain embodiments, the reactor can remain at
substantially similar operating conditions (pressure and
temperature) during the cleaning operation as during the deposition
operation. For example, in embodiments wherein the reactor is a CVD
reactor, the flow of deposition gas is stopped and purged from the
reactor and delivery lines. If needed, the temperature of the
reactor temperature may be changed to an optimum value; however in
the preferred mode the reactor temperature is maintained at the
deposition process conditions. A gas mixture, that may contain the
reactive gas, an inert diluent gas, and/or reactive species, is
flowed into the reactor. The reactive gas converts the substance,
i.e., debris on the reactor surfaces into volatile compounds that
are swept from the reactor. After a prescribed time, or after the
concentration of the formed volatile compounds detected in the
reactor effluent is below an acceptable level, the cleaning gas
flow is stopped and preferably purged from the reactor and delivery
lines. The flow of the deposition gas is then restarted and the CVD
deposition process resumed.
[0034] In a further embodiment, the method described herein may be
used in several areas of semiconductor manufacturing other than
chamber cleaning, such as etching silicon wafers and removing
post-etch or post-ion implantation photoresist materials and
sidewall passivations films. Traditionally wet stripping and/or
plasma etching are used in these wafer-manufacturing processes.
Comparing with the traditional methods, the use of a negatively
charged cleaning gas may provide at least one of the following
advantages: high etching rate; high anisotropy of etching;
feasibility for etching high aspect ratio features; low operation
cost; and low capital cost.
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