U.S. patent application number 11/849264 was filed with the patent office on 2008-10-23 for plasma processing apparatus and method for stabilizing inner wall of processing chamber.
Invention is credited to Naoshi Itabashi, Hiroyuki Kitsunai, Tetsuo Ono, Motohiko Yoshigai.
Application Number | 20080257863 11/849264 |
Document ID | / |
Family ID | 34525355 |
Filed Date | 2008-10-23 |
United States Patent
Application |
20080257863 |
Kind Code |
A1 |
Kitsunai; Hiroyuki ; et
al. |
October 23, 2008 |
PLASMA PROCESSING APPARATUS AND METHOD FOR STABILIZING INNER WALL
OF PROCESSING CHAMBER
Abstract
A plasma processing apparatus is disclosed for removing the
deposition film in the processing chamber and suppressing the
corrosion of wall surface material. The plasma processing apparatus
includes a plasma generating means, a monitor means for detecting
the existence of a reaction product containing a material
constituting an inner wall of the processing chamber, and an alarm
means for notifying that the existence of the reaction product
containing the material constituting the inner wall of the
processing chamber has exceeded a predetermined amount. The plasma
processing apparatus is configured such that plasma cleaning is
performed for every arbitrary etching process, and a wall surface
stabilization process is subsequently performed using O.sub.2 gas
or F gas.
Inventors: |
Kitsunai; Hiroyuki;
(Ibaraki-ken, JP) ; Itabashi; Naoshi; (Tokyo,
JP) ; Yoshigai; Motohiko; (Hikari-shi, JP) ;
Ono; Tetsuo; (Tsukuba-shi, JP) |
Correspondence
Address: |
ANTONELLI, TERRY, STOUT & KRAUS, LLP
1300 NORTH SEVENTEENTH STREET, SUITE 1800
ARLINGTON
VA
22209-3873
US
|
Family ID: |
34525355 |
Appl. No.: |
11/849264 |
Filed: |
August 31, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10912177 |
Aug 6, 2004 |
|
|
|
11849264 |
|
|
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Current U.S.
Class: |
216/67 |
Current CPC
Class: |
H01J 37/32935 20130101;
B08B 7/0035 20130101; H01J 37/32477 20130101 |
Class at
Publication: |
216/67 |
International
Class: |
C23F 1/00 20060101
C23F001/00 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 6, 2003 |
JP |
2003-206247 |
Jul 20, 2004 |
JP |
2004-212048 |
Claims
1. A method for stabilizing an inner wall surface of a processing
chamber in a plasma processing apparatus for subjecting an object
to be processed to vacuum processing by introducing processing gas
into the processing chamber in which the object is placed and
generating plasma, the method comprising: after performing a plasma
cleaning process in succession to an etching process, a wall
surface stabilization process is performed in which an inner wall
protection gas for protecting the inner wall surface of the
processing chamber is introduced and plasma processing is
performed.
2. The method for stabilizing an inner wall surface of a processing
chamber in a plasma processing apparatus according to claim 1,
wherein the inner wall protection gas contains either an oxygen
(O.sub.2) gas or a fluorine-based (F) gas, and the ratio of flow
rate of the Oxygen (O.sub.2) gas or fluorine-based (F) gas to the
total gas flow rate is at least more than 50%.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application is a Divisional application of application
Ser. No. 10/912,177, filed Aug. 6, 2004, which claims priority from
Japanese patent applications JP2003-206247, filed on Aug. 6, 2003,
and JP 2004-212048, filed on Jul. 20, 2004, the contents of which
are incorporated herein by reference in their entirety.
FIELD OF THE INVENTION
[0002] The present invention relates to a plasma processing
apparatus such as a plasma etching apparatus or a plasma CVD
apparatus for etching or processing an object using plasma, and a
plasma processing method.
DESCRIPTION OF THE RELATED ART
[0003] In the fabrication process of a semiconductor apparatus, if
a dust adheres to a substrate, it causes defect of the target
device pattern and deteriorates the yield factor of the fabrication
process. On the other hand, in a dry etching process in which
various gases are introduced into the apparatus and etching is
performed using the reaction of the introduced gas plasma, the
reaction product generated by the etching adheres to the inner wall
of the apparatus as deposition film and becomes the source of
dusts.
[0004] Thus, it is necessary to periodically remove the deposition
film. A method for removing such deposition film is proposed,
wherein after performing dry etching of a film containing Al formed
on the surface of a semiconductor substrate in a processing chamber
using a chlorine-based gas, a mixed gas including gas containing
O.sub.2, gas containing F and gas containing Cl is introduced into
the processing chamber, and plasma is generated by the mixed gas to
remove the aluminum chlorine carbide (Al.sub.xC.sub.yCl.sub.z)
which is the residual reaction product attached to the interior of
the processing chamber, so as to cut down the maintenance time of
the dry etching apparatus (refer for example to patent document
1).
[0005] Further, a method is proposed according to which after
performing plasma cleaning, the wall surface of the etching chamber
on which the deposition film is formed is slightly etched using
plasma, in order to constantly maintain the status of the etching
chamber (refer for example to patent document 2).
[Patent document 1]
[0006] Japanese Patent Application Laid-Open No. 8-319586
[Patent document 2]
[0007] Japanese Patent Application Laid-Open No. 7-335626
[0008] However, highly corrosive gases containing chlorine (Cl),
hydrogen bromide (HBr) or the like are now used in the plasma
etching process. Typically, the structural members in the
processing chamber of the etching apparatus are formed of materials
which are highly anticorrosive to these gases, such as a material
provided with an oxide coating such as alumite (anodized aluminum)
and alumina ceramic spray coating. On the contrary, if the
deposition film is completely removed by plasma cleaning, even if
the oxide coating has a stable structure, the surface layer may be
corroded by the highly corrosive gas creating a state where
particles are easily generated. Moreover, since the oxide coating
has a porous structure, the gas may reach the base material on
which the coating is formed, subjecting the base material to
corrosion.
[0009] The above-mentioned prior art techniques characterized in
either removing the deposition film or removing the surface layer
of the wall after removing the deposition film, and they lack to
consider the problem of corrosion of the surface layer of the wall
surface material or the corrosion of the base member.
SUMMARY OF THE INVENTION
[0010] The object of the present invention is to solve the
above-mentioned problems by providing a processing apparatus
capable of removing the deposition film on the inner surface of the
processing chamber and suppressing corrosion of the wall surface
material, and capable of carrying out a method or process of
stabilizing the wall surface of the processing chamber.
[0011] The above object is achieved by providing a processing
system capable of adding a stabilization process for stabilizing
the wall surface of the processing chamber at an arbitrary timing
to the operation process of the etching apparatus.
[0012] Moreover, the above object is achieved by providing to the
etching apparatus an alarm means for notifying the occurrence of a
corrosion by detecting the corrosion of the wall surface via a
monitor means disposed in the processing chamber, and providing an
operation means capable of carrying out the stabilization process
step upon receiving a detection signal.
[0013] The method to be processed by the present apparatus
comprises a stabilization process step provided during the
transition from the plasma cleaning process to the etching process
and preferably directly after the plasma cleaning process, for
substituting corrosive gas molecules bonded to the inner material
of the processing chamber using oxygen or fluorine (such as
SF.sub.6, CF.sub.4, C.sub.2F.sub.6, C.sub.xF.sub.y) gas plasma.
[0014] Furthermore, the above-mentioned object is achieved by
providing to the etching apparatus a function to arbitrarily
select, set and input how many wafers are to be processed during
continuous processing before the plasma cleaning process is
performed, and how long the time for stabilization process will
be.
BRIEF DESCRIPTION OF THE DRAWINGS
[0015] FIG. 1 is a diagram showing the overall structure of a
plasma processing apparatus based on which the present embodiment
is described;
[0016] FIG. 2 is a wafer process flow of the prior art;
[0017] FIG. 3 is a schematic cross-sectional view of the wall
surface material of the apparatus based on which an embodiment of
the present invention is described;
[0018] FIG. 4 is a schematic cross-sectional view of the wall
surface material of the apparatus based on which an embodiment of
the present invention is described;
[0019] FIG. 5 shows an example of the monitor signals based on
which an embodiment of the present invention is described;
[0020] FIG. 6 is a wafer process flow based on which an embodiment
of the present invention is described;
[0021] FIG. 7 is a schematic cross-sectional view of the wall
surface material of the apparatus based on which an embodiment of
the present invention is described;
[0022] FIG. 8 is an example of the process results based on which
the effects of the present invention are described;
[0023] FIG. 9 is an example of the process results based on which
the effects of the present invention are described; and
[0024] FIG. 10 is an example of the process results based on which
the effects of the present invention are described.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0025] One preferred embodiment of the present invention will now
be described with reference to the drawings. FIG. 1 shows a dry
etching apparatus used to carry out the present invention, which is
an example of an apparatus utilizing electron cyclotron resonance
(ECR). In FIG. 1, the dry etching apparatus comprises an etching
(processing) chamber 101, a wall surface 102 disposed within the
etching chamber that comes into direct contact with plasma, a
substrate stage 103 on which an Si substrate 104 to be subjected to
etching is placed, and an evacuation port 105 for evacuating the
interior of the processing chamber to a predetermined pressure.
Further, the dry etching apparatus comprises a UHF-band
electromagnetic power supply 106, a matching network 107, an
antenna 108, a solenoid coil 109, an RF power supply 111, an
emission spectrometer 112, an optical fiber 113 for sending the
plasma emission into the emission spectrometer, a computer 114 for
operating the emission spectrometer, and a computer 115 for
controlling the whole etching apparatus.
[0026] Upon performing the etching process, the processing chamber
is controlled to predetermined pressure via evacuation. Next,
electromagnetic waves of the UHF band are introduced from the
UHF-band electromagnetic power supply 106 via the matching network
107 and the antenna 108 into the etching chamber 101. The
introduced electromagnetic waves resonate with the magnetic field
formed via the solenoid coil 109 to generate plasma by the gas in
the processing chamber, and the generated plasma 110 is used to
perform the etching. The RF power supply 111 applies RF bias to the
substrate stage 103 on which the substrate is placed so as to
control the process contour, by which the ions in the plasma are
attracted toward the substrate and anisotropic etching is
performed.
[0027] Next, the process flow for carrying out a surface treatment
of a Si wafer using this apparatus is described with reference to
FIG. 2. For example, in processing a gate electrode of a
semiconductor device, a polycrystalline Si is etched by a plasma
formed of a highly corrosive gas such as Cl.sub.2 and HBr, or a
mixture of such gases. Further, in addition to the above, the
recent trend is to use much gas containing F, such as CF.sub.4,
since F has the highest reactivity to Si and thus the etching rate
can be enhanced. After the etching is completed, plasma cleaning is
performed using plasma generated from gas having high reactivity to
Si, such as SF.sub.6, aimed at preventing the reaction products of
Si from depositing on the inner wall of the processing chamber 101
as deposition film after the etching and generating particles
containing Si. In the past, plasma cleaning was normally performed
between lots, but recently, the process accuracy requirement has
become stricter and the atmosphere within the processing chamber is
required to be maintained constant at all times, so now there are
increasing number of cases where the plasma cleaning is performed
per a given number "N" of substrates being processed (for example,
N=5), or per every substrate being processed.
[0028] As described, F having high reactivity to Si is now also
used during etching in addition to plasma cleaning in many cases,
so there are fewer cases where deposits exist on the wall surface
of the processing chamber during the sequential process flow shown
in FIG. 2.
[0029] On the other hand, the interior of the processing chamber of
the etching apparatus is generally formed of a material provided
with an oxide coating having anticorrosive properties to the above
gases. When even a very small amount of so-called heavy metal such
as Fe and Cr adhere to the surface of the Si substrate, it will be
diffused across the Si semiconductor and deteriorate the operation
of the semiconductor. Therefore, it is especially common to use an
aluminum-based oxide coating such as alumite (anodized aluminum)
and alumina ceramics spray coating. The base material of the
coating should preferably be light weight and have small specific
gravity from the viewpoint of workability. Thus, it is common to
use an aluminum alloy. The aluminum alloy is used as the base
material in many cases, even when a coating other than the
above-mentioned aluminum-based coating is adopted.
[0030] As described, when there are only few cases where deposits
exist on the wall surface of the processing chamber during the
process sequence, even the stable-structured oxide coating will
have its surface layer corroded by the highly corrosive gas and may
be in a state where particles easily occur. Furthermore, the oxide
coating has a porous structure, and since the temperature thereof
increases by the heat from the plasma, it is in an environment
where cracks may be caused by thermal expansion. In other words,
another problem occurs by the gas reaching and corroding the base
material of the coating through the cracks or the pores in the
coating. FIGS. 3 and 4 are schematic cross-sectional views showing
the spray coating and the alumite coating. The aluminum used as the
base material of the coating is corroded by Cl or HBr, and is
released into the processing chamber as AlCl.sub.3 or AlBr, so the
drawback caused by the corrosion is significant, both from the
viewpoint of life of the processing chamber inner wall and the
viewpoint of influence to the etching results.
[0031] According to the present embodiment, the etching apparatus
is equipped with a monitor means for detecting the existence of a
reaction product containing the material forming the wall surface
of the processing chamber, and a means for generating an alarm when
the concentration of the reaction product exceeds a predetermined
amount during the sequence of process flow. Thereby, it becomes
possible to prevent the defective etching result caused by
AlCl.sub.3 or AlBr from occurring. It also provides an indication
of the timing for replacing parts. According to the present
embodiment, a plasma emission spectrometer is illustrated as an
example of the monitor means. In FIG. 1, reference number 112 shows
the emission spectrometer, 113 shows the optical fiber for taking
in the plasma emission into the emission spectrometer, 114 shows
the computer for operating the emission spectrometer, and 115 shows
the computer for controlling the whole etching apparatus. It is
possible to set in advance a signal indicating the reaction product
containing the material constituting the wall surface of the
processing chamber and a threshold of the signal in the computer
115 for controlling the etching apparatus, so that an alarm is
activated when the threshold is exceeded based on the emission data
sent thereto from the computer 114 for controlling the emission
spectrometer. This process will be described in detail below.
[0032] FIG. 5 shows a plasma emission spectrum obtained during a
period of time while etching a polysilicon using Cl.sub.2 gas
plasma. The emission spectrum can be achieved by dividing a certain
wavelength range, which in this example is from 250 nm to 850 nm,
into plural channels (2000 channels in this example), and showing
the emission intensity of each channel. Here, in detecting the
reaction product containing the material constituting the wall
surface of the processing chamber, the signal to be detected
changes according to the combination of the gas used for the
process and the material of the wall surface of the processing
chamber, so the present embodiment is equipped with a function to
select the channel of the detection signal arbitrarily. The
computer 115 for controlling the etching apparatus is set to
generate an alarm signal when the signal of the specifically
selected wavelength exceeds a threshold that can also be set
arbitrarily.
[0033] For example, in order to detect corrosion of an Al member as
according to the present embodiment, the emission of Al atoms,
which is 396 nm, should be selected. The effectiveness can be
further enhanced by providing a calculation function, for selecting
plural signals, adding, subtracting, multiplying or dividing the
same, and setting the result of the calculation as the detection
signal. For instance, according to the example of FIG. 5, in order
to detect Al, the emission of Al atoms can be observed at 309 nm in
addition to 396 nm. Therefore, a stronger signal can be obtained by
adding the signals of 309 nm and 396 nm. According further to the
example of FIG. 5, the etching of polysilicon proceeds by the
reaction Si+Cl.fwdarw.SiCl (281 nm). However, when the Al of the
wall surface is eaten away, the reaction Al+Cl.fwdarw.AlCl (261 nm)
simultaneously proceeds. In other words, the Cl radicals used in
etching silicon is consumed by Al, by which the emission signal of
SiCl of 281 nm is reduced. Therefore, a signal having higher S/N
can be achieved by setting as the detection signal the result of
adding the signal intensity of Al (309 nm and 396 nm) and the
signal intensity of AlCl (261 nm), or the result of dividing the
added signal intensity of Al and AlCl by the signal intensity of
SiCl. Whether to select a combination of such signals depends on
the combination of the gas used in the process and the wall surface
material of the processing chamber, so it is important that the
device is equipped with a function to select the detection signals
arbitrarily.
[0034] Apart from the present embodiment, the same effects can be
achieved using a gas mass spectrograph, an impedance monitor, or a
detector for detecting the voltage or current of the plasma
current.
[0035] Next, another embodiment of the present invention will be
explained. The present embodiment provides in the process flow
sequence a stabilization process step for substituting corrosive
gas molecules bonded to the inner material of the processing
chamber during the transition from the cleaning process to the
etching process. The process flow according to the present
embodiment is shown in FIG. 6. Plasma discharge of gas that can
become a compound having anticorrosive property to Cl.sub.2 or HBr
is performed as the stabilization process. Possible examples are
O.sub.2 or F with respect to aluminum-based materials. FIG. 7 is a
schematic cross-sectional view, and as shown, it becomes possible
to maintain anticorrosive property by forming an oxide layer or a
fluoride layer at the bottom face of the crack. The oxide layer or
the fluoride layer formed as illustrated on the surface via the gas
plasma is considered to be very thin, on the order of a few nm, but
the occurrence of aluminum corrosion can be prevented for a long
period of time by performing the stabilization process again before
the oxide layer or fluoride layer is gone.
[Experiment 1]
[0036] By the experiments carried out by the present inventors, it
has been discovered that the present invention is effective even
when an ordinary anticorrosive aluminum was used in the inner wall
surface of the processing chamber. FIG. 8 shows the results of the
experiments. According to the experiments, the material of the
inner wall surface of the processing chamber was A5051
anticorrosive aluminum, and the etching of an SiO.sub.2 wafer was
performed. The SiO.sub.2 wafer was selected to cut the influence of
Si reaction products on the deposition film. According to condition
1, etching was repeatedly performed using Cl.sub.2 gas for 30
seconds. Etching was performed with 200 sccm Cl.sub.2 gas flow
rate, 1 Pa pressure, 400 W source power, and 40 W RF bias.
According to condition 2, 20 seconds of O.sub.2 gas plasma
discharge was performed before etching, and the O.sub.2 gas
discharge and etching were repeatedly performed. The O.sub.2 gas
discharge was performed with 300 sccm O.sub.2 gas flow rate, 1 Pa
pressure, 800 W source power, and 0 W RF bias. The experiments were
performed while monitoring the Al emission wavelength 396 nm
through the plasma emission spectrometer attached to the processing
chamber, and according to condition 1 where O.sub.2 discharge was
not performed, significant emission of Al was observed during the
processing of a second wafer, whereas according to condition 2,
there was no emission of Al recognized even after processing more
than 10 wafers. It was clearly recognized that the wall surface
material was protected by forming the oxidation layer constantly on
the surface.
[Experiment 2]
[0037] FIG. 9 shows the result of experiments performed using a
wall surface material with alumite (anodized aluminum) processing.
The experiments were performed using a wall material having been
used for over a year and with the alumite eaten away at some areas
exposing the base material. In the experiments, Si was etched using
Cl.sub.2 gas. According to condition 1, after performing cleaning,
60 seconds of Si etching was repeatedly performed, and according to
condition 2, 20 seconds of O.sub.2 gas plasma discharge was
performed before the etching. The experiments were performed while
monitoring the Al emission wavelength 396 nm via the plasma
emission spectrometer attached to the processing chamber, and
according to condition 1, the emission of Al was already observed
during the processing of the second wafer, whereas according to
condition 2, there was no emission of Al observed even after
processing 25 wafers.
[0038] Thus, by providing a stabilization step between the cleaning
step and the etching step so as to constantly carry out the
stabilization process for forming an oxidation layer or a fluoride
layer on the surface of the chamber via gas plasma, it becomes
possible to prevent the occurrence of aluminum corrosion, in other
words, the wasting of the wall surface material. Therefore, by
providing to the etching apparatus, possibly to the computer for
controlling the apparatus, a function to set up the discharge
conditions of the stabilization step and to perform the
stabilization between the cleaning process and the etching process,
it becomes possible to stably operate the apparatus for a long
period of time while preventing the corrosion of the wall surface
of the apparatus.
[0039] The above embodiment was described according to an example
in which the stabilization step was performed after each plasma
cleaning step, but there is no need to perform the stabilization
step for each plasma cleaning step, and the stabilization step can
be performed at any arbitrary timing. In other words, the
effectiveness of the present invention is further enhanced by
providing to the etching apparatus a function to set the timing for
performing the stabilization process arbitrarily. For example, not
only the products having the same device structure are always
processed in a single processing chamber, but the processing of
various products having different film thicknesses, different film
qualities and different mask areas are normally performed. In other
words, the etching conditions such as the gas pressure, the gas
flow rate and the supplied power differ with every product, and the
degree of influence on the wall surface of the apparatus differs
according to conditions. Therefore, the safest apparatus operation
would be to perform the stabilization step per every cleaning step
performed in the processing of any product. However, if the
stabilization step is performed per every cleaning step according
to even the conditions having only a small influence of corrosion
to the wall surface of the apparatus, the actual operating time
during which the apparatus is used for actual product processing is
oppressed. Thus, by determining for every product the interval of
the stabilization process, for example, if product A is processed
under conditions having extremely strong corrosiveness, setting the
stabilization step to be performed per every plasma cleaning, if
product B has smaller influence than product A, setting the
stabilization step to be performed once every four lots of
processing, and if product C has even smaller influence, setting
the stabilization step to be performed once every eight lots of
processing, the deterioration of the actual operation time of the
apparatus can be suppressed to a minimum while the corrosion of the
wall surface is prevented for a long period of time.
[0040] The interval for performing the stabilization process was
described above, but the anticorrosive effect and the throughput of
the apparatus can both be satisfied similarly by changing the
period of time of the stabilization process per product, that is,
by performing a short stabilization process for products processed
under conditions having small corrosive impact on the wall surface
of the apparatus and by performing a longer stabilization process
for products processed under conditions having stronger corrosive
impact. Moreover, both the time and the interval of the
stabilization process can be varied. It is important that the
apparatus is equipped with a function to set to the computer for
controlling the processing apparatus the timing and the period of
time for performing the stabilization process for each product.
[0041] Next, another embodiment of the present invention will be
described with reference to FIG. 10. The present embodiment
characterizes in that a monitor means for detecting the emission of
wall material to the plasma is provided to detect the corrosion of
the interior member of the processing chamber via the monitor means
and performing the wall surface stabilization process.
[0042] The monitor means can be, as shown in the first embodiment,
a spectrometer for detecting the emission from the plasma. The
emission spectrometer can be a detector for taking out a single
wavelength emission such as a monochromator, but it is preferably a
detector capable of outputting multiple signals such as a
spectrometer that outputs wavelength-decomposed emission spectrum.
Moreover, it can be a mass spectrograph capable of monitoring the
gas in the processing chamber per mass numbers. Furthermore,
detection is possible through use of a current detector or a
voltage detector, a current-voltage phase difference detector, a
traveling wave detector or a reflected wave detector or an
impedance monitor of the power, disposed in the path for supplying
power to the plasma generating means. The status of the inner wall
extremely sensitively affects the impedance of plasma. The
above-mentioned monitors disposed in the power path for plasma
generation have very high sensitivity, capable of detecting even a
subtle corrosion of the wall. The monitor means outputs a signal
either every predetermined period of time or every sampling time
determined in advance. Here, the embodiment is explained using the
plasma emission spectrometer similar to the first embodiment.
[Experiment 3]
[0043] FIG. 10 shows the results of applying to the apparatus a
wall surface material with alumite processing. The present
invention was applied to the apparatus whose wall surface material
102 has been used over a year and almost ready for replacement. The
experiments were conducted using Cl.sub.2 gas under the same
conditions as experiment 1 to etch an Si bare wafer. In order to
remove the deposition film of Si, plasma cleaning was performed for
10 seconds per each wafer using SF.sub.6 plasma without a dummy
wafer. A plasma emission spectrometer was attached to the
processing chamber to monitor the Al emission wavelength 396 nm
while performing etching, and the average value of emission
wavelength 396 nm during etching was output. The sampling was
performed once every second.
[0044] First, continuous processing was performed according to
condition 1 without the stabilization step, and when the value
exceeded a maximum value set in advance, the processing was
performed according to condition 2 with the stabilization step. It
was confirmed after continuously processing 10 wafers that the
emission intensity of wavelength 396 nm showed stable transition
between 10 and 20, so the maximum value of the emission intensity
was set to 30 (reference number 201 in the drawing). The value
started to rise gradually when approximately 45 wafers were
processed, and exceeded the maximum value at the 56th wafer (202 in
the drawing), so the processing condition was switched to condition
2 in which the stabilization step is performed after the plasma
cleaning step, and it was confirmed that the emission intensity of
wavelength 396 nm was reduced to the level when the continuous
processing was started. Thus, by carrying out the stabilization
step automatically based on the Al discharge detection signal from
the monitor, it becomes possible to effectively prevent corrosion
of the wall surface while suppressing the deterioration of
operation efficiency. Moreover, if there is still a possibility of
Al discharge during long term processing even by performing the
stabilization process, it is desirable to set up in advance a
certain extension time, and automatically carry out the time
extension of the stabilization step upon receiving the Al discharge
detection signal from the monitor. For example, in FIG. 10 the
stabilization step S is set to 20 seconds, but by extending the
same to 30 seconds when the threshold is exceeded for the second
time, to 40 seconds when the threshold is exceeded for the third
time and so on, it becomes possible to effectively achieve the wall
surface stabilization. Here, the time was increased for ten seconds
each, but the degree of corrosion of the wall surface depends on
the plasma power and processing time of the plasma processing being
performed, so it is preferable to enable the extension time to be
set arbitrarily in the apparatus. According to the present
embodiment, the average value of the emission intensity was used as
the monitor data, but it is also possible to use the maximum
intensity monitored during etching as the monitor data.
[0045] By providing to the etching apparatus a monitor means for
detecting the corrosion of the inner wall surface of the processing
chamber, an alarm means for notifying the occurrence of corrosion,
a control means for performing the stabilization process upon
receiving the detection signal, and a means for setting up the
timing for performing the stabilization step, the duration time
thereof and the extension time thereof, for example, stable
continuous fabrication becomes possible.
[0046] The detection of Al emission through the monitor means
according to the present embodiment is effective from the viewpoint
of apparatus management. When a notice is output in case the
monitored value exceeds a threshold value set up in advance, the
operator can be notified of the status of the apparatus. The output
can be an alarm such as a buzzer, a display on the operation panel,
or a display on the screen of a personal computer of the
operator.
[0047] Even with the stabilization step performed constantly, the
base material is easily corroded if the surface coating such as
alumite or spray coating becomes too thin or is partially wasted,
and the alarm will be output frequently. It is also effective to
vary the level of the warning by how many times the threshold value
is exceeded continuously or by the total number of warnings being
output. For example, according to one possible application, if the
threshold value is exceeded once but not in the next processing, a
minor warning is output and processing is continued, but if the
threshold value is exceeded three times in a row or if the total
number of times the threshold value is exceeded has exceeded a
predetermined value, for example, it is possible to prohibit
processing and to perform maintenance. Furthermore, if the wall
surface stabilization is to be achieved by extending the
stabilization process time when the threshold value is exceeded,
another possible application would be to determine the maximum
extension time and when the maximum time is exceeded, to judge that
the stabilization is not possible, to output a warning to replace
the parts and to perform maintenance. According to these
applications, by performing maintenance such as the cleaning of the
apparatus, it becomes possible to prevent in advance the occurrence
of the cause of defects such as the contamination of the wafer
being processed or the adhesion of particles.
[0048] According to the above embodiments, the inner wall of the
processing chamber was formed of an aluminum base member having an
alumite layer or a ceramic layer formed to the surface thereof, and
O.sub.2 gas was used as the wall surface protection gas, but the
present invention is not limited to such examples. The inner wall
member of the processing chamber can be provided with any oxide
ceramic coating to achieve the objects of the present invention.
Moreover, when a fluoride ceramic coating is provided, F-based gas
should be used as the wall surface protection gas to achieve the
objects of the present invention.
[0049] As described above, the present invention provides a plasma
processing apparatus for subjecting an object to be processed to
vacuum treatment by introducing processing gas into a processing
chamber and generating plasma, the apparatus comprising a plasma
generation means, a monitor means for detecting the existence of a
reaction product containing a material constituting an inner wall
of the processing chamber, and an alarm means for notifying that
the existence of the reaction product containing the material
constituting the inner wall of the processing chamber exceeded a
certain amount. Furthermore, the above monitor means is any of or a
combination of the following: a plasma emission spectrometer, a
mass spectrograph or an impedance monitor detecting means disposed
in the plasma processing chamber, a current detector or a voltage
detector or a current-voltage phase detector disposed in the path
for supplying power to the plasma generating means, a traveling
wave detector or a reflected wave detector of power.
[0050] The present invention is equipped with a means having a
function to select an arbitrary signal out of the plural signals
obtained through the monitor means that can be detected via the
monitor as a detection signal for indicating the existence of a
reaction product containing the material constituting the inner
wall of the processing chamber and to arbitrarily set up the
threshold of the signal value for generating an alarm, and a
calculation function to select two or more signals from the plural
signals obtained through the monitor means and performing one or a
combination of the following calculations: adding, subtracting,
multiplying and dividing; to the signals and setting the result of
calculation as the detection signal.
[0051] The present invention provides a plasma processing apparatus
for subjecting an object to be processed to vacuum treatment by
introducing processing gas into a processing chamber in which the
object is placed and generating plasma, wherein the apparatus is
equipped with a function to set up an etching step, a plasma
cleaning step and a wall surface stabilization step for protecting
the inner wall of the processing chamber, and to set up the order
and frequency of each step arbitrarily.
[0052] Moreover, the present invention provides a method for
stabilizing the inner wall surface of a processing chamber in a
plasma processing apparatus for subjecting an object to be
processed to vacuum treatment by introducing processing gas into
the processing chamber in which the object is placed and generating
plasma, characterized in performing a wall surface stabilization
process in which an inner wall protection gas for protecting the
inner wall surface of the processing chamber is introduced and
plasma processing is performed, after performing a plasma cleaning
process in succession to an etching process. Moreover, according to
the present invention, the above method for stabilizing the inner
wall surface of a processing chamber in a plasma processing
apparatus characterizes in that the inner wall protection gas
contains oxygen (O.sub.2) gas or fluorine-based (F) gas, and that
the flow ratio of oxygen (O.sub.2) gas or fluorine-based (F) gas to
the total gas flow is more than at least 50%.
[0053] According further to the present invention, the plasma
processing apparatus is equipped with a function to execute the
wall surface stabilization step set up in advance when receiving a
signal generated by the monitor means in the processing chamber
indicating the increase of reaction product containing the material
constituting the inner wall of the processing chamber. Moreover, it
is equipped with a function to extend for a predetermined time the
time set up in advance to execute the wall surface stabilization
step according to the total number of signals generated by the
monitor means indicating the increase of reaction product
containing the material constituting the inner wall of the
processing chamber.
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