U.S. patent application number 09/159009 was filed with the patent office on 2001-11-15 for method and apparatus for sputter etch conditioning a ceramic body.
Invention is credited to BURKHART, VINCE, KHURANA, NITIN, PARKHE, VIJAY, SANSONI, STEVE, TZOU, EUGENE.
Application Number | 20010040091 09/159009 |
Document ID | / |
Family ID | 25214389 |
Filed Date | 2001-11-15 |
United States Patent
Application |
20010040091 |
Kind Code |
A1 |
KHURANA, NITIN ; et
al. |
November 15, 2001 |
METHOD AND APPARATUS FOR SPUTTER ETCH CONDITIONING A CERAMIC
BODY
Abstract
A method and apparatus for conditioning a surface of a ceramic
body in a process chamber when the process chamber has a vacuum
pump, an anode and a cathode. The conditioning method consists of
pumping the process chamber down to a vacuum with the vacuum pump,
introducing a gas into the chamber, energizing the anode and
cathode with RF power to ignite the gas into a plasma, sputter
etching the surface with ions from the plasma to remove
contaminants therefrom. The method is accomplished either within a
process chamber to condition, in situ, a ceramic chuck or within a
cleaning chamber to condition any form of ceramic body or
component.
Inventors: |
KHURANA, NITIN; (SANTA
CLARA, CA) ; BURKHART, VINCE; (SAN JOSE, CA) ;
SANSONI, STEVE; (SAN JOSE, CA) ; PARKHE, VIJAY;
(SUNNYVALE, CA) ; TZOU, EUGENE; (LOS ALTOS,
CA) |
Correspondence
Address: |
PATENT COUNSEL
LEGAL AFFAIRS DEPT
APPLIED MATERIAL
P O BOX 450A
SANTA CLARA
CA
95052
|
Family ID: |
25214389 |
Appl. No.: |
09/159009 |
Filed: |
September 23, 1998 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
09159009 |
Sep 23, 1998 |
|
|
|
08814188 |
Mar 10, 1997 |
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Current U.S.
Class: |
204/298.34 ;
204/298.06; 204/298.07; 204/298.08; 204/298.15; 204/298.31;
204/298.33 |
Current CPC
Class: |
H01J 37/32862 20130101;
H01J 37/32082 20130101; H01J 37/34 20130101 |
Class at
Publication: |
204/298.34 ;
204/298.31; 204/298.33; 204/298.06; 204/298.07; 204/298.15;
204/298.08 |
International
Class: |
C23C 014/34 |
Claims
What is claimed is:
1. A method for conditioning a surface of a ceramic body in a
process chamber, the process chamber having a vacuum pump, an anode
and a cathode, the method comprising the steps of: maintaining the
process chamber at a vacuum using the vacuum pump, introducing a
gas to the chamber, energizing the anode and cathode with RF power
to ignite the gas into a plasma, sputter etching the surface of the
ceramic body with ions from the plasma to remove contaminants
therefrom.
2. The method of claim 1 wherein the gas is an inert gas.
3. The method of claim 1 wherein the gas is a reactive gas.
4. The method of claim 1 further comprising introducing a plurality
of gases into the chamber where one gas is inert and another gas is
reactive.
5. The method of claim 4 wherein the reactive gas passivates the
surface of the ceramic body.
6. The method of claim 4 wherein the inert gas is argon.
7. The method of claim 4 wherein the reactive gas is oxygen.
8. The method of claim 4 wherein the reactive gas is nitrogen.
9. The method of claim 1 further comprising the step of exhausting
contaminants from the chamber.
10. The method of claim 9 wherein the contaminants are exhausted by
constantly flowing the gas into and out of the chamber and
maintaining the chamber pressure at approximately 1.5 mtorr while
sputter etching the ceramic body.
11. The method of claim 9 wherein the contaminants are exhausted by
maintaining chamber pressure at approximately 8 mtorr during the
cleaning process and exhausting the gas at the conclusion of
sputter etching the ceramic body.
12. The method of claim 1 wherein the conditioning occurs at
approximately room temperature.
13. The method of claim 4 wherein the conditioning occurs above
room temperature.
14. The method of claim 13 wherein the conditioning occurs in the
range of about 500-600.degree. C.
15. The method of claim 14 wherein the reactive gas is oxygen.
16. The method of claim 14 wherein the reactive gas is
nitrogen.
17. A method for removing contaminants from a surface of an ceramic
chuck in a wafer processing chamber of a semiconductor wafer
processing system, the wafer processing chamber having a vacuum
pump, an anode and a cathode, the method comprising the steps of:
ceasing processing of wafers within said processing chamber
removing a wafer from the surface of the ceramic chuck; maintaining
the wafer processing chamber at a vacuum using the vacuum pump,
introducing argon gas into the processing chamber, energizing the
anode and cathode with RF power to ignite the gas into a plasma,
reducing chamber pressure to optimize a sputter rate, and sputter
etching the chuck surface with ions from the plasma to remove
contaminants therefrom.
18. The method of claim 17 further comprising the step of
introducing oxygen into the chamber to passivate the chuck
surface.
19. The method of claim 17 further comprising the step of detecting
a chuck surface condition and ceasing said processing of wafers in
response to said chuck surface condition.
20. A sputter etch cleaning chamber for conditioning a surface of a
ceramic body comprising: a vacuum chamber having walls that form an
anode; a pedestal, supported within the vacuum chamber, forming a
cathode and for supporting said ceramic body within said vacuum
chamber; an RF source, coupled to said anode and cathode, for
supplying an RF voltage; and a gas supply, coupled to the chamber,
for supplying a gas to said vacuum chamber to form a plasma in
response to the RF voltage and being capable of sputter etching
said surface of said ceramic body.
21. The sputter etch cleaning chamber of claim 19 wherein said gas
supply further comprises: an inert gas supply containing an inert
gas for sputter etching; and a reactive gas supply containing a
reactive gas for passivating free contaminants and said surface of
said ceramic body.
Description
BACKGROUND OF THE DISCLOSURE
[0001] 1. Field of the Invention
[0002] The invention relates to processes for cleaning and
conditioning ceramic components of a semiconductor wafer processing
system. More particularly, the invention relates to a method and
apparatus for cleaning the surface of an electrostatic ceramic
chuck and other ceramic components of semiconductor wafer
processing equipment using a plasma.
[0003] 2. Description of the Background Art
[0004] Plasma-based reactions have become increasingly important to
the semiconductor industry, providing for precisely controlled
thin-film depositions. For example, a plasma reactor in a
high-temperature physical vapor deposition (PVD) semiconductor
wafer processing system generally comprises a reaction chamber for
containing a reactant gas, a pair of spaced-apart electrodes
(cathode and anode) to generate an electric field within the
chamber, and a substrate support for supporting a substrate within
the electric field. The cathode is typically embedded within the
substrate support, while the anode is embedded in a target material
that is to be sputtered or deposited onto the substrate. The
electric field ionizes the reactant gas to produce a plasma. The
plasma, characterized by a visible glow, is a mixture of positive
and negative reactant gas ions and electrons. Ions from the plasma
bombard the target releasing deposition material. As such, a
deposition layer forms on the substrate which is supported upon the
surface of the substrate support just above the cathode.
[0005] A particular type of substrate support used in a high
temperature PVD system is a ceramic electrostatic chuck. Ceramic
electrostatic chucks create an electrostatic attractive force
between the substrate (i.e., a semiconductor wafer) and the chuck
to retain the wafer in a stationary position during processing. A
voltage is applied to one or more electrodes imbedded within a
ceramic chuck body so as to induce opposite polarity charges in the
wafer and electrodes, respectively. The opposite charges pull the
wafer flush against the chuck support surface, thereby
electrostatically clamping the wafer. More specifically, in a
"unipolar" electrostatic chuck, voltage is applied to an electrode
embedded within the pedestal supporting the chuck. The voltage is
referenced to some internal chamber ground reference. Electrostatic
force is established between the wafer being clamped and the chuck.
When the voltage is applied, the wafer is referred back to the same
ground reference as the voltage source through a conductive
connection to the wafer. Alternatively, the plasma generated in the
chamber can reference the wafer to ground.
[0006] The ceramic material used to fabricate a high temperature
chuck is typically aluminum-nitride or alumina doped with a metal
oxide such as titanium oxide (TiO.sub.2) or some other ceramic
material with similar resistive properties. This form of ceramic is
partially conductive at high temperatures. Because of this
characteristic, the wafer is primarily retained against the chuck
by the Johnsen-Rahbek effect. Such a chuck is disclosed in U.S.
Pat. No. 5,117,121 issued May 26, 1992.
[0007] One disadvantage of using a chuck body fabricated from
ceramic is that the characteristics of the chuck surface change
over time. For example, exposing the chuck surface to organic
material degrades chuck performance. Specifically, adventitious
(surface) carbon, water and hydroxides collect on the chuck
surface. Such contaminants enter the chamber during wafer
processing as wafers are passed from a loadlock to the chamber or
when the chamber is exposed to the atmosphere during a maintenance
cycle. Additionally, outgassing of chamber components produces
hydrocarbon contaminants e.g., O-rings inside the chamber breakdown
and outgas. These contaminants produce a conductive carbon film on
the chuck surface that grows if not removed. Additionally, waste
products from wafer processing collect on the chuck surface causing
contamination although these process waste products are not
considered principle contaminants. The buildup of these
contaminants reduces performance of the chuck and, after repeat
processing and maintenance cycles, render the chuck useless (i.e.,
the chucking force is severely degraded and/or non-uniform).
Premature replacement of the chuck results in higher unit cost and
increased chamber downtime.
[0008] Therefore, a need exists in the art for a method of removing
contaminant films that become deposited upon the support surface of
the chuck as well as upon other ceramic components of a
semiconductor wafer processing system.
SUMMARY OF THE INVENTION
[0009] The disadvantages of the prior art are overcome by the
present invention of a method and apparatus for conditioning a
surface of a ceramic body. More specifically, a first embodiment of
the invention is a method of using a plasma for in-situ removal of
residual surface layer films from a chuck surface in a
semiconductor wafer processing chamber. The process chamber
contains a vacuum pump, an anode and a cathode. The method
comprises the steps of maintaining the process chamber at a vacuum
with the vacuum pump, introducing a gas into the chamber,
energizing the anode and cathode with RF power to ignite the gas
into a plasma, sputtering the surface of the chuck with ions from
the plasma to remove contaminants therefrom. Additionally, a
plurality of gases can be introduced into the chamber where one gas
is inert and another gas is reactive such that the reactive gas
bonds with the surface material of the chuck as well as the
particulate contaminants dislodged from the surface. Such bonding
passivates both the free contaminants and the surface of the
chuck.
[0010] The second embodiment of the invention is a method and
apparatus that performs the sputter cleaning process of the first
embodiment within a dedicated cleaning chamber. This chamber
contains a cathode pedestal supporting a ceramic component to be
cleaned, a grounded anode chamber wall and vacuum pump. The method
comprises the steps of creating and maintaining the cleaning
chamber at a vacuum with the vacuum pump, introducing a sputter
etching gas into the chamber, energizing the anode and cathode with
RF power to ignite the gas into a plasma, sputter etching the
surface of the chuck with ions from the plasma to remove
contaminants therefrom. A reactive gas may also be introduced into
the chamber to passivate the free contaminants as well as the
ceramic component surfaces.
[0011] As a result of using the novel method, the contaminant films
adhered to a ceramic body are greatly reduced. When a ceramic chuck
is cleaned in accordance with the invention, this substantial
improvement in maintaining chuck surface integrity increases chuck
life, performance and restores clamping force over numerous
processing cycles without excessive chamber maintenance or
downtime.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] The teachings of the present invention can be readily
understood by considering the following detailed description in
conjunction with the accompanying drawings, in which:
[0013] FIG. 1 depicts a cross-sectional view of a PVD chamber for
processing semiconductor wafers employing the method of the present
invention; and
[0014] FIG. 2 depicts a cross-sectional view of a second embodiment
of the invention wherein a cleaning chamber employs the inventive
method.
[0015] To facilitate understanding, identical reference numerals
have been used, where possible, to designate identical elements
that are common to the figures.
DETAILED DESCRIPTION
[0016] FIG. 1 depicts a cross-sectional view of a PVD wafer
processing chamber 100 for processing semiconductor wafers. For a
detailed understanding of the PVD reaction chamber and its
operation in processing a wafer, the reader should refer to the
drawings and the detailed description contained in commonly
assigned U.S. Pat. No. 5,228,501, issued Jul. 20, 1993 incorporated
herein by reference. That disclosure discloses a wafer support
assembly used in a physical vapor deposition chamber manufactured
by Applied Materials, Inc. of Santa Clara, Calif.
[0017] The wafer 102 rests on support surface 105 of a substrate
support or pedestal 104. The pedestal 104 is supported by a
pedestal base 106 and a shaft 126 which contains the necessary
wiring to conduct DC and RF power from remote power sources 122 and
124 to the pedestal 104. Additionally, the shaft 126 is provided
with a gas conduit 142 to feed a gas through the pedestal 104 to a
process cavity 144 located directly above the pedestal 104. The
pedestal 104 is also provided with one or more chucking electrodes
120 embedded in a ceramic chuck body 118. Lift pins 110 mounted on
a platform 112 connected to a vertical shaft 114 serve to lift the
wafer 102 off the pedestal surface 105 after processing.
[0018] A target 116 of sputtering or deposition material is
positioned over the pedestal 104. The target 116 is usually
Aluminum or Titanium and is electrically insulated from the chamber
100. The remote power source 122 is a high voltage DC power supply
and is electrically connected between the target 116 and pedestal
104 for magnetron sputtering a wafer. Additionally, an RF (radio
frequency) voltage source 124 is coupled to the pedestal 104 via
the pedestal base 106. The RF source may also be coupled to the
chuck electrode 120. As such, the pedestal 104 forms a cathode and
the chamber walls an anode with respect to the RF voltage. Waste
ring 108 and cover ring 138 circumscribe the pedestal 104 to
prevent unwanted deposition into the lower chamber region 140.
[0019] In operation, a wafer 102 is placed on the support surface
105 of the pedestal 104. Air is drawn out of the chamber via a
vacuum pump 128 to create a low vacuum environment. A reactant gas,
preferably Argon, is introduced into the chamber 100. The power
supply 122 is energized which electrostatically clamps the wafer to
the support surface 105. Specifically, the power supply 122 applies
a DC bias to the electrode 120 within the ceramic chuck body 118.
The high voltage level produced by the power supply 122 also
ignites the gas into a plasma and biases the target 116 thereby
causing the target material to sputter onto the wafer 102.
[0020] Minor particulate residue is inadvertently deposited on
chuck surface 105 during wafer processing. Conductive films from
organic material breakdown during wafer processing form on the
chuck surface 105. Exposure of the chuck to the atmosphere after
wafer processing also forms conductive films. These contaminants
compromise chuck surface integrity and degrade the electrostatic
clamping performance.
[0021] The conductive films are removed using a novel method of
in-situ sputter cleaning of the electrostatic ceramic chuck in a
low temperature, low pressure environment using a plasma sustained
by an electrically conductive gaseous mix of inert and reactive
components. This method of using a plasma to remove contaminants
while the wafer is not present is referred to herein as a "sputter
etch" process. The sputter etch process produces a plasma of an
inert gas whose ions impact the chuck surface removing contaminant
films and adsorbed contaminants. As such, the chuck surface 105 is
cleaned and restored to its pre-process state.
[0022] The condition process is initiated as either a periodic
maintenance routine or when the chucking force degrades.
Emperical-analysis of chuck degradation can lead to a periodic
maintenance routine being used to avoid any degradation in chucking
force due to contamination of the chuck surface. Alternatively, the
chucking force can be monitored and if the chucking force degrades
to an unacceptable level, the chuck surface can then be cleaned and
conditioned. Consequently, the wafer processing is halted and the
sputter etch conditioning process is started without exposing the
chuck to the atmosphere. The sputter cleaning process is started by
transporting the last processed wafer back to the loadlock (not
shown) through a slit valve 146 in the chamber wall. The chamber
100, still under a wafer processing vacuum (approximately
10.sup.-7-10.sup.-9 torr) is at room temperature. An inert gas
(preferably Argon) is introduced from inert gas supply 130 via
valve 132, master flow controller 144 and conduit 142 into the
chamber 100 to establish an optimal plasma ignition pressure range
(preferably 8 mtorr). The RF power source 124 is then energized to
ignite the "cleaning plasma". Although other sources may be used, a
13.56 Mhz source 124 is the preferred "cleaning plasma" source
because it provides a low bias voltage on the chuck surface. Under
these conditions, the "cleaning plasma" selectively sputters the
contaminant film but not ceramic material comprising the chuck.
[0023] Once the plasma is ignited, the chamber pressure is then
reduced for optimal "cleaning plasma" effectiveness or sputter etch
rate. This optimal sputter etch rate coincides with a high mean
free path of the sputtering ions which occurs at a chamber pressure
of approximately 1.5 mtorr and RF power level of 75 W. The
"cleaning plasma" is maintained in the chamber as long as necessary
to remove the contaminants from the chuck surface. A typical
cleaning cycle runs in the range of 2-20 minutes.
[0024] Contaminants and waste gases are evacuated from the chamber
by two different alternative methods. Using a gas flow method, the
vacuum pump 128 continuously pumps contaminants from the chamber
100 thereby maintaining a chamber pressure of approximately 1.5
mtorr during the cleaning cycle. Using a backfill method, pressure
is maintained at approximately 8 mtorr after cleaning plasma
ignition. The vacuum pump 128 then evacuates contaminants at the
conclusion of the cleaning cycle.
[0025] More specifically, using Argon as the inert gas, positively
charged Argon ions are created within the plasma, which then
bombard the negatively biased chuck surface. This activates the
ceramic and sputters the relatively weakly bonded residue particles
from the chuck surface. Inert gas bombardment also removes the
molecules of gases adsorbed within the porous ceramic material
constituting the chuck.
[0026] To supplement the cleaning effect of the inert gas, a
reactive gas may also be introduced into the chamber from reactive
gas supply 134 via valve 136. The reactive gas enters the chamber
prior to igniting the plasma. Using oxygen as the reactive gas, the
ionized oxygen molecules in the plasma react with the sputtered
atoms on the chuck surface and form an inert gaseous residue and a
passivation layer on the chuck surface. For example, in a ceramic
chuck comprised of aluminum nitride, the oxygen combines with the
aluminum nitride to form a layer of aluminum oxide on the surface
of the chuck. The layer formation or passivation protects the chuck
surface from further contamination during wafer processing while
maintaining chuck performance. The thickness of the passivated
dielectric layer depends on the voltage of the negative bias on the
chuck and process duration.
[0027] Use of the sputter cleaning process in the manner described
results in a ceramic chuck surface that is nearly free of all
conductive films and adsorbed gases. After the sputter cleaning
process is completed, the chuck is ready for the wafer processing
cycle to restart without the need for pumping the chamber to the
appropriate vacuum level, manual cleaning of the chamber or
replacement of interrelated components due to contaminant film
growth on the chuck surface.
[0028] Although only Argon and Oxygen are described to create the
"cleaning plasma", other gases may also be used. Any inert gas, for
example, Helium can replace Argon. The reactive gas can be selected
by determining the type of reaction and substances that will be
reacting to create the passivation of either the dislodged
material, the chuck surface or both. For example, using Nitrogen as
the reactive gas results in an added benefit of replenishment of
the Aluminum nitride on the chuck surface.
[0029] As discussed above, the cleaning operation can be performed
at relatively low temperatures. This is especially useful in
sputter cleaning covalently bonded ceramics which, under vacuum
conditions, may decompose into a metal rich surface layer at
elevated temperature. However, the cleaning operation can also be
conducted at high temperatures.
[0030] For example, a conductive surface film of graphitic carbon
(a contaminant) formed on an aluminum nitride chuck surface during
wafer processing can be removed by using the described method at
high temperatures. Specifically, in this embodiment of the
invention, a reactive gas such as oxygen is introduced to a heated
chamber under a vacuum. The temperature is preferably in the range
of 500-600.degree. C. The chamber can be heated by a variety of
known heat sources including pedestal heaters, heat lamps or the
like. The reactive gas is ignited by an RF energy source to create
the plasma. The plasma, by nature, also contributes to the
operating temperature. The highly excited oxygen atoms in the
plasma sputter contaminants from the chuck surface. Additionally,
because of the high chamber temperature, nitrogen is selectively
sputtered from the contaminant free surface leaving the surface
aluminum rich. As such, the chuck surface readily reacts with the
oxygen forming an aluminum oxide passivation layer. The passivation
layer slows the regrowth of the undesirable conductive films. As
mentioned earlier, the inventive method is not limited to the use
of oxygen as the reactive gas and can use any reactive gas based on
the materials reacting with the gas and desired amount of
passivation.
[0031] Although the preferred embodiment of the present invention
is discussed as a method for cleaning ceramic electrostatic chuck
surfaces in PVD semiconductor wafer processing chambers, the method
is also useful for cleaning any type of ceramic chuck such as those
used in etch and chemical vapor deposition (CVD) wafer processing
equipment.
[0032] Although the preferred embodiment of the present invention
is discussed as a method for in-situ cleaning, the inventive method
can be used in a dedicated cleaning chamber. For example, using the
inventive method in a dedicated cleaning chamber any thin film
(e.g., residue from a manufacturing process or exposure to air) can
be removed from the surface of a ceramic component. To avoid
process contamination, such cleaning is performed within the
cleaning chamber prior to using the component at a high temperature
in a vacuum environment.
[0033] FIG. 2 depicts an inventive cleaning chamber for ceramic
components that utilizes the method of the present invention. The
cleaning chamber 200 contains an RF biased pedestal (cathode) 204
and a grounded chamber wall 206 that forms an anode (i.e., the
cleaning chamber does not contain a liftpin assembly, target or the
like). The cleaning process is identical to that described above,
except a contaminated ceramic component 202 is positioned on the
pedestal 204. Gas from supplies 130 and 134 are introduced into the
chamber via valves 132 and 136, mass flow controller 144 and
conduit 142, respectively. Thereafter, the pedestal (cathode) 204
is energized by RF voltage source 124 to sputter etch the
contaminants from the component. The free contaminants are removed
from the chamber 200 via vacuum pump 208.
[0034] In sum, use of the inventive method provides in-situ
cleaning of an electrostatic ceramic chuck surface without exposing
the chuck surface to additional contamination from the atmosphere
or breaking the vacuum in the chamber. As such, no disruption of
the chamber environment is required to restore the chuck to a
pre-process condition. The cleaning process is rapid so that
chamber downtime is minimal. The process can be maintained and
repeated as many times as necessary to recondition the chuck
surface thereby promoting longer chuck life than is presently
available. The cleaning process occurs at low-pressure ensuring
that the sputtered material has low gas-scattering or conversely a
high mean free path. This condition provides easy removal of waste
products from the surface and prevents reaccumulation and excessive
deposition on the chuck surface. The inventive apparatus provides a
cleaning chamber capable of removing contaminants from any form of
ceramic component or body.
[0035] Although various embodiments which incorporate the teachings
of the present invention have been shown and described in detail
herein, those skilled in the art can readily devise many other
varied embodiments that still incorporate these teachings.
* * * * *