U.S. patent application number 11/435065 was filed with the patent office on 2007-11-22 for in situ cleaning of cvd system exhaust.
This patent application is currently assigned to Applied Materials, Inc.. Invention is credited to David K. Carlson.
Application Number | 20070267143 11/435065 |
Document ID | / |
Family ID | 38659696 |
Filed Date | 2007-11-22 |
United States Patent
Application |
20070267143 |
Kind Code |
A1 |
Carlson; David K. |
November 22, 2007 |
In situ cleaning of CVD system exhaust
Abstract
Embodiments of the invention relate to methods and apparatus are
disclosed for forming films using CVD. One or more method and
apparatus embodiments include preventing the formation of bonds
and/or breaking bonds that permit polymers to form in an exhaust
line of a CVD apparatus.
Inventors: |
Carlson; David K.; (San
Jose, CA) |
Correspondence
Address: |
DIEHL SERVILLA, LLC
77 BRANT AVENUE, SUITE 210
CLARK
NJ
07066
US
|
Assignee: |
Applied Materials, Inc.
|
Family ID: |
38659696 |
Appl. No.: |
11/435065 |
Filed: |
May 16, 2006 |
Current U.S.
Class: |
156/345.48 ;
216/58; 216/66 |
Current CPC
Class: |
C23C 16/4412
20130101 |
Class at
Publication: |
156/345.48 ;
216/58; 216/66 |
International
Class: |
C23F 1/00 20060101
C23F001/00; C03C 25/68 20060101 C03C025/68 |
Claims
1. A method of preventing the formation of polymers in the exhaust
line of a CVD reaction chamber comprising: flowing gases exhausted
from the CVD reaction chamber through a downstream chamber which
generates energy to break bonds and/or prevent bonds that form
polymers, to prevent the formation of polymeric species in the
exhaust line.
2. The method of claim 1, wherein the downstream chamber includes a
low frequency RF chamber.
3. The method of claim 2, wherein the low frequency RF chamber
generates temperatures between about 1000.degree. C. and
1200.degree. C.
4. The method of claim 3, wherein the low frequency RF chamber
operates at a frequency of less than about 10 KHz.
5. The method of claim 3, further comprising generating a low
pressure plasma.
6. The method of claim 5, wherein the pressure of the plasma is
less than about 10 Torr.
7. The method of claim 2, further comprising introducing an etchant
into the chamber.
8. The method of claim 7, wherein the etchant is selected from the
group consisting of HCl and Cl.sub.2.
9. The method of claim 1, wherein the downstream chamber includes a
UV light source.
10. The method of claim 1, wherein the UV light source operates at
a wavelength of about 172 nm.
11. The method of claim 9, wherein an etchant is introduced into
the downstream chamber.
12. The method of claim 11, wherein the etchant is selected from
the group consisting of HCl and Cl.sub.2.
13. A CVD apparatus comprising: a CVD reaction chamber including a
substrate support and a gas distribution system for introducing
gases into reaction chamber; an exhaust line connected to the
reaction chamber for removing gases from the process chamber; and a
device coupled to the exhaust line for preventing the formation of
polymers in the exhaust line.
14. The apparatus of claim 13, wherein the device comprises a
thermal chamber adapted to produce temperatures between about
1000.degree. C. and 1200.degree. C.
15. The apparatus of claim 14, wherein the thermal chamber
comprises a low frequency RF chamber.
16. The apparatus of claim 15, wherein the low frequency RF chamber
operates a frequency of less than about 10 KHz.
17. The apparatus of claim 14, further comprising an etchant gas
input in communication with the exhaust line.
18. The apparatus of claim 13, wherein the device comprises a UV
light source coupled to the exhaust line.
19. The apparatus of claim 18, wherein the UV light source operates
at a wavelength of 172 nm.
20. A CVD apparatus comprising: a CVD reaction chamber including a
substrate support and a gas distribution system for introducing
gases into reaction chamber; an exhaust line connected to the
reaction chamber for removing gases from the process chamber; and
means for preventing the formation of polymers in the exhaust
line.
21. The apparatus of claim 20, wherein the means for preventing the
formation of polymers comprises heated downstream chamber for
producing temperatures between about 1000.degree. C. and
1200.degree. C.
22. The apparatus of claim 20, wherein the means for preventing the
formation of polymers comprises a UV light source.
Description
TECHNICAL FIELD
[0001] Embodiments of the present invention generally pertain to
cleaning of chemical vapor deposition (CVD) exhaust systems and
more specifically to in situ cleaning of polymeric contaminants in
CVD systems.
[0002] During CVD processing, deposition gases are released inside
a processing chamber to form a thin film layer on the surface of a
substrate being processed. Unwanted deposition on areas such as the
walls of the processing chamber also occurs during such CVD
processes. Because the residence time in the chamber of individual
molecules in these deposition gases is relatively short, however,
only a small portion of the molecules released into the chamber are
consumed in the deposition process and deposited on either the
wafer or chamber walls.
[0003] During semiconductor manufacturing processes in which CVD is
utilized to form layers on wafers, it would be ideal if the
injected process gas would deposit only on the wafer substrate
surface, however, in reality, some gas molecules miss the substrate
surface and deposit on the process chamber surfaces. Some of the
unconsumed gas molecules are pumped out of the chamber along with
partially reacted compounds and reaction byproducts through an
exhaust line under vacuum. Many of the compounds in this exhausted
gas are still in highly reactive states and/or contain residues or
particulate matter that can form unwanted deposits in the exhaust
line. In a processing chamber such as an Epi Centura.RTM. chamber
manufactured by Applied Materials, the temperature of process gases
falls dramatically upon exit from the processing chamber as the
process gases enter the exhaust line, resulting in coating of the
exhaust inserts, exhaust cap, and at least the first four feet of
the exhaust line. In addition to the materials described above, the
coating has been observed to be generally a translucent viscous
liquid, with a honey-like consistency. The condensed exhaust
byproduct can also appear opaque white to opaque yellow to opaque
reddish brown, depending upon the process conditions and location
in the exhaust line. When the condensed exhaust byproduct is
opaque, it appears to be in a solid phase. It is believed that the
translucent liquid reacts immediately on exposure to the ambient to
form an opaque white material.
[0004] Thus the buildup of liquid and solid material in the exhaust
lines poses several problems. First, the build-up poses a safety
threat in that the matter is often a pyrophoric substance that may
ignite when the vacuum seal is broken and the exhaust line is
exposed to ambient conditions during standard, periodic cleaning
operations. Second, if enough of the deposition material builds-up
in the exhaust line, the exhaust line and/or its associated vacuum
pump may clog if it is not appropriately cleaned. Even when
periodically cleaned, matter build-up interferes with normal
operation of the vacuum pump and can drastically shorten the useful
life of the pump. Also, the solid matter may backwash from the
exhaust line into the processing chamber and contaminate the
processing chamber. If the translucent liquid is rapidly exposed to
air, an explosive reaction can occur.
[0005] To avoid these problems, the inside surface of the exhaust
line is regularly cleaned to remove the deposited material. This
procedure is performed during a standard chamber clean operation
that is employed to remove unwanted deposition material from the
chamber walls and similar areas of the processing chamber. Common
chamber cleaning techniques include the use of an etching gas, such
as fluorine, to remove the deposited material from the chamber
walls and other areas. The etching gas is introduced into the
chamber and a plasma is formed so that the etching gas reacts with
and removes the deposited material from the chamber walls. Such
cleaning procedures are commonly performed between deposition steps
for every wafer or a number of wafers.
[0006] Removal of deposition material from chamber walls is
relatively straight forward in that the plasma is created within
the chamber in an area proximate to the deposited material. Removal
of deposition material from the exhaust line is more difficult
because the exhaust line is downstream from the processing chamber.
In a fixed time period, most points within the processing chamber
come in contact with more of the etchant fluorine atoms than do
points within the exhaust line. Thus, in a fixed time period, the
chamber may be adequately cleaned by the clean process while
residue and similar deposits remain in the exhaust line.
[0007] To attempt to adequately clean the exhaust line, the
duration of the clean operation must be increased. Increasing the
length of the clean operation, however, is undesirable because it
results in equipment downtime, which adversely affects wafer
throughput. Also, such residue build-up can be cleaned only to the
extent that reactants from the cleaning process are exhausted into
the exhaust line in a state that they may react with the residue in
the exhaust line. In some systems and applications, the residence
time of the exhausted reactants is not sufficient to reach the end
or even middle portions of the exhaust line. In these systems and
applications, residue build-up is even more of a concern.
[0008] Several different devices have been designed to facilitate
the cleaning of such exhaust lines. One approach that has been
employed to clean the exhaust line is to trap the particulate
matter present in the exhaust stream before it reaches the vacuum
pump by diverting gas flow into a collection chamber from which
particulate matter cannot easily escape. Devices that rely on this
technique provide a removable door or similar access to the
collection chamber so that once a sufficient amount of material has
built up within the chamber it can be easily removed. Typically,
the substrate deposition system is temporarily shut off during the
period in which the collection chamber is cleaned, thereby limiting
or reducing wafer throughput of the system.
[0009] One approach that has been employed to clean the exhaust
line relies on a scrubbing system that uses plasma enhanced CVD
techniques to extract reactive components in the exhaust gas as
film deposits on electrode surfaces. The scrubbing system is
designed to maximize the removal of reactants as a solid film and
uses large surface area spiral electrodes. The spiral electrodes
are contained within a removable canister that is positioned near
the end of the exhaust line between the blower pump and mechanical
pump. After a sufficient amount of solid waste has built up on the
electrodes, the canisters may be removed for disposal and
replacement.
[0010] Problems exist in this prior art method in that the system
relies on the large surface area of the electrodes to provide an
area for deposited solid matter to collect. To accommodate the
large surface area of the electrodes, the system is necessarily
large and bulky. Furthermore, extra expenses are incurred in the
operation of this prior art scrubber system since the removable
canister is a disposable product that must be replaced and properly
disposed. Also, the scrubbing system is located downstream from a
beginning portion of the vacuum exhaust line and thus does not
ensure removal of powdery material or particulate matter that
builds-up in this portion of the line.
[0011] Another approach to cleaning the exhaust lines utilizes what
is sometimes referred to as a point of use reactor. The point of
use reactor uses a heater cartridge to react excess gas from the
process chamber. The maximum temperature of the point of use
reactor is about 500.degree. C., and reaction byproducts remain in
the exhaust line. The point of use reactor is not effective for
reduced pressure deposition since the polysilicon formation causes
significant particle formation.
[0012] Still another method and apparatus for cleaning the exhaust
line involves trapping powder residue and other particulate matter
in a collection chamber and removing the same with a plasma formed
downstream of the reaction chamber. Constituents from the plasma
react to form gaseous products that are readily pumped through and
out the exhaust line. The conversion process relies on forming a
plasma from an etchant gas in the area where the particles are
trapped, and this type of apparatus is sometimes referred to as a
Downstream Plasma Apparatus or "DPA" for short. Several examples of
such an apparatus and method are described in commonly assigned
U.S. Pat. No. 6,194,628, which is incorporated herein by reference
in its entirety. One embodiment of the apparatus described in U.S.
Pat. No. 6,194,628 includes a coil surrounding a gas passageway
defined by a vessel chamber. The coil is connected to an RF power
supply that is used to excite molecules from particulate matter and
residue within the passageway into a plasma state. The RF power in
a commercial version of such an apparatus utilizes high frequency
RF power with a fluorine-containing gas such as nitrogen
trifluoride to chemically etch the exhaust deposit. The upper limit
of the frequency range of the power supply described in U.S. Pat.
No. 6,194,628 is listed as 200 MHz, and the frequency used in
experimental setup in U.S. Pat. No. 6,194,628 is 13.56 MHz. A
potential problem with the use of a fluoride-containing gas is
compatibility with materials in the reactor, disposal of hazardous
waste generated by the cleaning process, and damage to the
equipment if proper controls are not employed.
[0013] Accordingly, it would be desirable to provide methods and
apparatus for efficiently and thoroughly cleaning the exhaust line
in a semiconductor processing systems.
DISCLOSURE OF THE INVENTION
[0014] Embodiments of the invention relate to methods and apparatus
for cleaning the exhaust line of a CVD processing chamber, for
example, a semiconductor processing chamber. Other embodiments
pertain to CVD processing apparatus and methods that include a
cleaning device.
[0015] In one embodiment, a CVD apparatus is provided which
comprises a CVD reaction chamber including a substrate support and
a gas distribution system for introducing gases into reaction
chamber; an exhaust line connected to the reaction chamber for
removing gases from the process chamber; and a device for
preventing the formation of polymers in the exhaust line. In one or
more embodiments, the device comprises an RF chamber. The RF
chamber may be adapted to produce temperatures sufficient to break
or prevent bonds that form polymers. The device may further include
a source of etchant gas and an etchant gas input into the RF
chamber. In other embodiments, the device for preventing the
formation of polymers in the exhaust line includes a UV light
source.
[0016] Other embodiments of the invention pertain to methods of
preventing the formation of polymers in the exhaust line of a CVD
reaction chamber comprising flowing gases exhausted from the CVD
reaction chamber through a downstream chamber which generates
energy to break bonds and/or prevent bonds that form polymers,
thereby preventing the formation of polymeric species in the
exhaust line. The device may include a low frequency RF chamber
which is adapted to generate temperatures sufficient to break
and/or prevent bonds that form polymeric species in the exhaust
line. Alternatively, the device may include a UV light source.
BRIEF DESCRIPTION OF THE DRAWINGS
[0017] FIG. 1 illustrates an embodiment of the present invention
including an exhaust line cleaning apparatus;
[0018] FIG. 2 illustrates an embodiment of an exhaust line cleaning
apparatus utilizing a heating system;
[0019] FIG. 3 is a side cross-sectional view of the exhaust
cleaning apparatus shown in FIG. 2;
[0020] FIG. 4 is a top cross-sectional view of the exhaust cleaning
apparatus shown in FIG. 2;
[0021] FIG. 5 is a side-view of the apparatus shown in FIG. 2;
[0022] FIG. 6 is a side cross-sectional view of another embodiment
of an exhaust cleaning apparatus utilizing a UV energy; and
[0023] FIG. 7 illustrates an embodiment of a UV system that can be
utilized with the apparatus shown in FIG. 6.
BEST MODE FOR CARRYING OUT THE INVENTION
[0024] Before describing several exemplary embodiments of the
invention, it is to be understood that the invention is not limited
to the details of construction or process steps set forth in the
following description. The invention is capable of other
embodiments and of being practiced or being carried out in various
ways.
[0025] Aspects of the present invention provide methods and
apparatus for chemical vapor deposition. Certain embodiments relate
to semiconductor processing apparatus and methods. Specific
embodiments pertain to methods and apparatus for cleaning an
exhaust line of a chemical vapor deposition apparatus, for example
a CVD reaction chamber of a semiconductor processing apparatus. In
one or more embodiments, an apparatus for breaking and/or
preventing the formation of bonds of exhaust components to prevent
the polymerization of exhaust components is provided downstream
from the reaction chamber. In a first embodiment, a low frequency
RF chamber is located adjacent the exhaust cap of the deposition
system and downstream from the reaction chamber. The downstream RF
chamber prevents the formation of polymeric species in the exhaust
line using heat alone or in combination with etchant species. In
certain embodiments, a low pressure plasma can be generated to
assist in the cleaning of the exhaust line. In another embodiment,
UV energy can be utilized adjacent the exhaust cap of the
deposition system and downstream of the reaction chamber to prevent
the polymerization of chemicals in the exhaust line. The UV energy
can be used alone or together with etchant species. In certain
embodiments, a low pressure plasma can be utilized with the UV
energy to assist in cleaning of the exhaust line.
[0026] A typical semiconductor processing chamber and operations
that can be utilized with the cleaning apparatus and methods
described herein will now be described. It will be understood that
the processing chamber and operations described herein are
exemplary only, and other types of processing chambers and
operations can be used with the cleaning methods and apparatus
described herein. The apparatus and methods of the present
invention can be used in conjunction with a variety of different
semiconductor processing apparatus.
[0027] One suitable device, a single wafer processor in which one
wafer at a time is processed in a processing chamber, is shown in
FIG. 1. A susceptor 120 divides a chamber 100 into one portion
which is below the susceptor (the lower portion) 124, and a second
portion which is above the susceptor (the upper portion) 122. The
susceptor 120 is generally mounted on a shaft 126 which rotates the
susceptor about its center to achieve a more uniform processing of
the wafer. A flow of a processing gas, such as a deposition gas
115, is provided in the upper portion 122 of the chamber. The
chamber generally has a gas inlet passage 178 at one side thereof,
and a gas exhaust passage 113 at an opposite side to achieve a flow
of the processing gas across the wafer. The susceptor 120 is heated
in order to heat the wafer to a desired processing temperature.
According to certain embodiments, one method used to heat the
susceptor is by the use of lamps 134 provided around the chamber
and directing their light into the chamber and onto the susceptor
120. In order to control the temperature to which the wafer is
being heated, the temperature of the susceptor is constantly
measured. This is often achieved by an infrared temperature sensor
136 which detects the infra-red radiation emitted from the heated
susceptor. Reflectors 135 may also be provided to reflect light
into the chamber.
[0028] A flow of an inert gas 121, such as hydrogen, may be
provided into the lower portion of the chamber at a pressure
slightly greater than that of the deposition gas in the upper
portion of the chamber to prevent deposits of material on the back
surface of the susceptor. One apparatus for achieving this is
described in the application for U.S. Pat. No. 5,916,369 of Roger
N. Anderson et al., entitled "Gas Inlets For Wafer Processing
Chamber". Since the inert gas in the lower portion of the chamber
is at a higher pressure, it will flow around the edge of the
susceptor from the lower portion of the chamber and into the upper
portion of the chamber. This flow of the inert gas prevents the
flow of the deposition gas 115 into the lower portion of the
chamber.
[0029] The above reactor description is mainly for illustrative
purposes, and the present invention may be used with other CVD
equipment such as electron cyclotron resonance (ECR) plasma CVD
devices, induction coupled RF high density plasma CVD devices, or
the like. The present invention may also be used with thermal CVD
devices, plasma etching devices and physical vapor deposition
devices. The apparatus of the present invention and the methods for
preventing deposition build-up within an exhaust line is not
limited to any specific semiconductor processing apparatus or to
any specific deposition or etching process or method.
[0030] During semiconductor processing operations such as chemical
vapor deposition processes carried out by CVD reactor 100, a
variety of gaseous waste products and contaminants are exhausted
from chamber 100 into exhaust line 131. As noted above, as
deposition gas 115 exits the chamber through exhaust passage 113,
the deposition gas cools and condenses to form exhaust products 111
within the exhaust passage 113. These exhaust products 111 are also
deposited in the exhaust cap 130 and exhaust line 131. Depending on
the particular operation being performed, these exhaust products
111 may include polymeric material and particulate matter such as
partially reacted products and byproducts that leaves a residue or
similar powdery material within the exhaust line 131 as it is
exhausted through the exhaust line. For example, during the
deposition of a silicon nitride film using silane (SiH.sub.4),
nitrogen (N.sub.2) and ammonia (NH.sub.3) as precursors, residue in
the form of a brown powder composed of Si.sub.xN.sub.yH.sub.z,
Si.sub.xH.sub.y, SiO.sub.x and elemental silicon has been observed
in the exhaust line. It is believed that this residue build-up is
from half-reacted byproducts of the reaction of
SiH.sub.4+N.sub.2+NH.sub.3. Similar residues are also formed during
the deposition of silicon nitride layers using other precursor
gases or liquids such as disilane (Si.sub.2H.sub.6) or organic
sources. Residue build-up may also occur during the deposition of
oxynitride films and silicon oxide films among other layers and may
also occur during plasma etching and other process steps. Viscous
material that has not been exposed to air has been observed to be
composed of chlorosilane polymers when they are not exposed to air.
These polymers react with water to form siloxane polymers. When
exposed to air, the viscous liquid condenses into solid residue,
examples of which are described above.
[0031] Embodiments of the present invention prevents build-up of
such residues and particulate matter by breaking and/or preventing
bonds and prevent polymerization of the components in the reactant
gases exhausted through the vacuum exhaust line. Embodiments of the
invention can be utilized with a low pressure plasma to assist in
cleaning of the exhaust line.
[0032] Still referring to FIG. 1 CVD reactor 100 is fitted with a
bond breaking or bond prevention apparatus 140 according to one or
more embodiments of present invention. The bond breaking or bond
prevention apparatus 140, which reduces and/or prevents
polymerization of species that form polymers in the exhaust line,
is positioned downstream from the exhaust gas source, the
processing chamber 100. The apparatus 140 may either connect to or
replace a portion of the exhaust line 131.
[0033] In FIG. 1, a bond breaking or bond prevention apparatus 140
(hereinafter referred to as "polymer prevention apparatus") for
breaking preventing the formation of polymers in the exhaust line
131 is fitted between vacuum pump system and vacuum manifold along
a portion of exhaust line 131. Because of its position, gases
exhausted from vacuum chamber 100 necessarily pass through polymer
prevention apparatus 140. Polymer prevention apparatus 140 may be
positioned at any location along exhaust line 131, but preferably,
polymer prevention apparatus 140 is positioned as close as possible
to exhaust cap 130 so that gases exhausted from chamber 100 pass
through polymer prevention apparatus 140 before passing through any
portion of exhaust line 131.
[0034] In operation, as deposition gases are exhausted from vacuum
chamber through exhaust line 131, polymer prevention apparatus 140
operates to break bonds or prevent formation bonds that would allow
the formation of polymeric species in the exhaust line, thereby
preventing the formation of such polymeric species in the exhaust
line 131. To prevent polymer formation, polymer prevention
apparatus 140 may be turned ON during both deposition and clean
operations or may be activated only during the clean procedure.
[0035] Specific embodiments of the polymer prevention apparatus
will now be described. Referring first to FIGS. 2-5, polymer
prevention apparatus may include a downstream high temperature
chamber 101 attached to exhaust cap 130. In the embodiment shown,
the downstream high temperature chamber 101 may be a low frequency
RF chamber. As used herein, low frequency means an RF frequency of
less than about 20 KHz, and typically less than about 10 KHz. The
RF chamber is capable of generating temperatures sufficient to
break or prevent bonds that form polymers in the exhaust line.
Temperatures sufficient to break or prevent bonds that form
polymers exceed about 1000.degree. C., typically exceed
1050.degree. C., and more typically are in the rage of about
1100.degree. C. to about 1200.degree. C.
[0036] Components of the high temperature chamber 101 include top
baffle 102 and bottom baffle 104, which may be made from SiC or any
other suitable material, which sandwich and support a graphite
susceptor tube 106 surrounded by a first clear quartz liner 108,
which is shown in FIGS. 3 and 4. Referring to FIGS. 3 and 5, a
second opaque quartz liner 110 surrounds clear quartz liner 108. A
suitable coil 112 for example, a nickel plated copper coil, for
generating low frequency RF, energy surrounds the opaque quartz
liner 110. A ceramic liner 114 surrounds the coil 112, and the
ceramic liner is surrounded by a stainless steel liner 116. The
stainless steel line 116 serves at least two purposes. First, it
shields CVD processing apparatus 100 and other equipment from the
voltage and noise signals generated by the coil. Second, if ceramic
liner 114 were to break or crack or if the vacuum seal chamber 101
is broken in another manner, liner 116 provides a second seal
preventing the exhaust gases from escaping. Liner 116 can be made
out of a variety of metals such as aluminum or steel or other
compounds and is preferably grounded for shielding effect. As shown
in FIG. 5, an opaque quartz radiation baffle 118 may be provided at
the outlet portion of downstream high temperature chamber 101 to
provide thermal isolation.
[0037] It will of course be understood that the details of the
downstream high temperature chamber 101 provided above are an
exemplary embodiment only, and variants of the design may be
utilized. The details of operation of a low frequency RF chamber to
generate temperatures sufficient to break or prevent bonds that
form polymers in the exhaust line can be determined experimentally.
High temperature RF chambers that can achieve temperatures between
about 1000.degree. C. and 1200.degree. C. are known in the art.
[0038] The voltage field created within downstream high temperature
chamber 101 to form the plasma can be generated using a variety of
known methods such as capacitively coupled electrodes, inductively
coupled coils or ECR techniques. Because of its compact size and
capacity to create relatively high voltage fields, it is
preferable, however, to create the voltage field with an inductive
coil such as a helical resonator coil. Such coils are well known to
those of ordinary skill in the art and may be designed according to
criteria set forth in any of a number of well known textbooks such
as Michael A. Lieberman and Allan J. Lichtenberg, "Principles of
Plasma Discharges and Materials Processing," pp. 404-410 John Wiley
& Sons (1994), which is hereby incorporated by reference.
[0039] The helical resonator coil can be made out of a high
conductivity type metal such as copper, nickel, or gold or similar
conducting material. To properly resonate the coil, it is important
that the length of the coil be about or slightly longer than 1/4 of
the wavelength of the applied RF signal. A coil of this length
creates a stronger and more intense voltage field that further
enhances decomposition of species in the high temperature chamber
101.
[0040] The helical resonator coil is connected at one end to an RF
power supply and at the opposing end to a ground potential. To
ensure complete reaction of material passing through and/or
deposited within downstream high temperature chamber 101, the high
temperature chamber 101 must be driven by the RF power supply at a
level sufficient to heat the graphite tube to a temperature above
about 1000.degree. C. and to optionally form a low frequency
plasma. Generally, a power level of between 50-1000 Watts or more
can be employed, and preferably a power level of between 100-400
Watts is used. The actual power level selected should be determined
by balancing a desire to use a sufficient power level to form low
frequency plasma and a desire to use a low power level to save
energy costs and allow use of smaller, less expensive power
supplies.
[0041] The power supply driving high temperature chamber 101 is
operated at a frequency range below about 10 KHz. At this frequency
range, higher ion bombardment is provided to further aid in
cleaning of the exhaust line.
[0042] RF power supply can be supplied from either a single
frequency RF source or a mixed frequency RF source. The power
output of the supply will depend on the application for which the
downstream high temperature chamber 101 is used and on the volume
of the gas to be treated in the downstream high temperature chamber
101. RF power can be derived from RF power supply used to power the
reaction chamber 100 or can be supplied by a separate RF power
supply 103 that drives only polymer prevention apparatus 140.
Additionally, assuming multiple processing chambers are present in
a clean room, the multiple downstream high temperature chambers 101
connected to the reaction chamber 100 may all be driven by a
separate, dedicated RF power supply that is connected to an
appropriate number of RF power splitters.
[0043] The length and size of the downstream high temperature
chamber 101 can vary. In some applications, the high temperature
chamber can be only 4-6 inches long or even shorter, while in other
applications, the downstream high temperature chamber 101 can be
the entire length of exhaust line 131 (4-5 feet or longer) thus
replacing the line. Because the length of the coil should be
slightly longer than 1/4 of the RF wavelength, there is a direct
relationship between the coil length and RF frequency used. Longer
coils require lower frequency RF power signals.
[0044] The downstream high temperature chamber 101 described above
can be utilized in a thermal mode alone to clean the exhaust line
or it may also be used together with a low pressure plasma that can
be generated in the low frequency RF chamber. As used herein, low
pressure refers to a pressure of less than about 20 Torr, and
typically less than about 10 Torr. In addition, various etchant
species such as HCl, NF.sub.3, Cl.sub.2 and F.sub.2 can be
activated to augment the cleaning process. Etchant species can be
introduced into an inlet port 98 in communication with the exhaust
cap 130.
[0045] The use of chlorine containing gases to clean post
deposition deposits from a wafer processing chamber is described in
U.S. Pat. No. 6,042,654, the entire content of which is
incorporated herein by reference. In the method described in U.S.
Pat. No. 6,042,654, chlorine radicals are formed by heating
chlorine gas and the chlorine radicals are reacted with deposits in
the processing chamber.
[0046] An advantage of the high temperature cleaning process and
apparatus is that HCl can be used as a cleaning gas at the higher
temperatures. In one embodiment, when HCl is used as the etchant
species, the downstream high temperature chamber 101 is heated up
to about 1200.degree. C. Once the high temperature chamber 101
reaches 1200.degree. C., above the dissociation temperature of HCl
gas, HCl is introduced into the downstream high temperature chamber
101. As a result of the high temperature, the HCl dissociates into
reactive hydrogen (H) and chlorine (Cl) which will react with the
silicon byproducts. In embodiments that utilize HCl as an etchant,
the downstream RF chamber should be heated above the dissociation
temperature of HCl, which is above about 1150.degree. C. Below this
temperature, it is believed that HCl will not break up the
polymer.
[0047] Thus, according to one or more embodiments, the formation of
polymeric exhaust deposits is prevented by heating the low
frequency RF chamber to temperatures sufficient to break the bonds
that form polymeric exhaust components or prevent such bonds from
forming. In addition, the heating can be used to activate etchant
species in the downstream RF chamber. Temperatures in excess of
about 1000.degree. C., and more typically in excess of about
1100.degree. C., for example, between about 1100.degree. C. and
1200.degree. C. may be used to breaks bonds to prevent
polymerization of the exhaust components and may be used to
activate etchant species.
[0048] While it was previously described that polymer prevention
apparatus 140 may be turned ON and OFF during specific periods of a
processing procedure, the polymer prevention apparatus may also be
configured as a passive device. As a passive device, when polymer
prevention apparatus 140 is the downstream high temperature chamber
101 described above, the high temperature chamber 101 is supplied
continuously with a sufficient RF power signal so that no special
control signals or processor time need be devoted to turning the
high temperature chamber 101 ON and OFF.
[0049] As previously mentioned, if configured as an active device,
power is supplied to polymer prevention apparatus 140 during the
time at which a chamber clean operation takes place. Optionally, RF
power may also be supplied during the period in which film
deposition occurs in chamber 100. Control of the timing aspects of
polymer prevention apparatus 140 when configured as an active
device is generally performed by processor (not shown) through the
application of control signals sent over control lines.
[0050] A number of alternative embodiments of the apparatus of the
present invention may be constructed. The polymer prevention
apparatus 140 shown in FIG. 1 above may be in the form of a vacuum
UV device coupled to the exhaust cap. An exemplary embodiment of
such an apparatus is shown in FIG. 6. In FIG. 7, UV device 200 is
coupled to the exhaust cap 130 of the reaction chamber 100 and
upstream from the exhaust line 131. It will be appreciated that the
UV device 200 may be coupled to the exhaust line 131 in addition to
or instead of being coupled to the exhaust cap. An inlet line may
be coupled to the exhaust cap 130 or exhaust line for the addition
of etchant species such as HCl, NF.sub.3, Cl.sub.2 and F.sub.2.
Etchant species can be injected into the exhaust line or exhaust
cap to augment the cleaning operation.
[0051] FIG. 7 shows an embodiment of a UV device 200 that may be
utilized in the embodiment shown in FIG. 7. In FIG. 7, the UV
device includes a Xeradex.RTM. bulb, available from Osram Sylvania
of Danvers, Mass. Alternatively, the UV source may be a lamp
supplied by USHIO America, Inc. The wavelength of the bulb will
depend on the type of etchant used. Suitable wavelengths include
172 nm and 124 nm when Cl.sub.2 is the etchant gas. The bulb 202
may be attached to the exhaust cap at a UV window 204, which
typically would be sealed with appropriate seals 206, 208 such as
O-rings. Lamp enclosure 210 may include a purge valve 212 for
nitrogen or other gases.
[0052] In use, UV energy generated by bulb 202 prevents formation
of bonds or breaks bonds that are required to form polymer species
in the exhaust line. The volatile species remain in the gas phase
and our pumped through the exhaust line 131 in the gas phase. It is
believed that if HCl is used as the etchant, it will be more
reactive in UV light, and it augment the cleaning process. It may
be desirable to further enhance the cleaning process by heating the
exhaust line for at least about 3-4 feet downstream of the UV
device 200.
[0053] Although the invention herein has been described with
reference to particular embodiments, it is to be understood that
these embodiments are merely illustrative of the principles and
applications of the present invention. It will be apparent to those
skilled in the art that various modifications and variations can be
made to the method of the present invention without departing from
the spirit and scope of the invention. Thus, it is intended that
the present invention include modifications and variations that are
within the scope of the appended claims and their equivalents.
* * * * *