U.S. patent application number 10/512141 was filed with the patent office on 2005-09-08 for window type probe, plasma monitoring device, and plasma processing device.
Invention is credited to Yasaka, Mitsuo.
Application Number | 20050194094 10/512141 |
Document ID | / |
Family ID | 29267436 |
Filed Date | 2005-09-08 |
United States Patent
Application |
20050194094 |
Kind Code |
A1 |
Yasaka, Mitsuo |
September 8, 2005 |
Window type probe, plasma monitoring device, and plasma processing
device
Abstract
This invention relates to a detection port type probe, a plasma
monitoring device, and a plasma processing apparatus. It is
intended to directly and conveniently detect a state of plasma
generated by an application of a radio frequency or a high voltage,
and the detection port type probe is provided with at least an
electroconductive supporting member (5) having an opening formed on
at least a part of a surface thereof facing to plasma and a
dielectric member (1) having a probe electrode (2) formed on one
side thereof positioned at the opening of the electroconductive
supporting member (5).
Inventors: |
Yasaka, Mitsuo; (Kumamoto,
JP) |
Correspondence
Address: |
WESTERMAN, HATTORI, DANIELS & ADRIAN, LLP
1250 CONNECTICUT AVENUE, NW
SUITE 700
WASHINGTON
DC
20036
US
|
Family ID: |
29267436 |
Appl. No.: |
10/512141 |
Filed: |
October 22, 2004 |
PCT Filed: |
March 28, 2003 |
PCT NO: |
PCT/JP03/04016 |
Current U.S.
Class: |
156/345.28 |
Current CPC
Class: |
H01J 37/32935
20130101 |
Class at
Publication: |
156/345.28 |
International
Class: |
C23F 001/00 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 24, 2002 |
JP |
2002-122240 |
Claims
1. A detection port type probe characterized by comprising at least
an electroconductive supporting member having an opening formed on
at least a part of a surface thereof facing to plasma and a
dielectric member having a probe electrode formed on one side
thereof positioned at the opening of the electroconductive
supporting member.
2. The detection port type probe according to claim 1,
characterized by connecting an impedance matching unit to the probe
electrode.
3. The detection port type probe according to claim 1,
characterized in that the dialectic member is made from an
optically transparent glass.
4. The detection port type probe according to claim 3,
characterized in that the probe electrode is made from an optically
transparent electroconductive substance.
5. The detection port type probe according to claim 1,
characterized in that the opening formed on the electroconductive
supporting member has a function of a viewing port.
6. A plasma monitoring device using the detection port type probe
defined in claim 1, characterized in that a voltage waveform
measuring unit for measuring a voltage waveform is disposed at an
output end of the detection port type probe.
7. The plasma monitoring device according to claim 6, characterized
by comprising a process monitoring mechanism for detecting a
stability of plasma by detecting a degree of nonuniformity among
cyclical waveform changes of the voltage waveform detected by the
voltage waveform measuring unit.
8. The plasma monitoring device according to claim 6, characterized
by comprising an anomalous discharge monitoring mechanism for
detecting anomalous discharge of plasma from the changes in voltage
waveform detected by the voltage waveform measuring unit.
9. A plasma processing apparatus characterized by comprising the
plasma monitoring device defined in claim 6.
10. The plasma processing apparatus according to claim 9,
characterized in that the electroconductive supporting member
provided with the opening is a flange constituting a viewing port
of a reaction vessel, and that the dielectric member is a
transparent glass plate for sealing the flange.
Description
TECHNICAL FIELD
[0001] The present invention relates to a detection port type
probe, a plasma monitoring device, and a plasma processing
apparatus and, particularly, to those characterized by a
constitution for easily, efficiently, and accurately detecting a
fluctuation in plasma in a plasma processing apparatus which
performs processing on a substrate using plasma discharge caused by
a radio frequency or a high voltage.
BACKGROUND ART
[0002] At present, a plasma processing method for processing a
substrate by using plasma discharge is widely used for the purpose
of plasma CVD, ashing, etching, sputtering, or a surface treatment
in the field of semiconductor manufacture.
[0003] In plasma processing steps of the plasma treatment, a
variation in characteristics of electric elements provided on the
substrate to be processed is undesirably caused due to
insufficiency in stability and reproducibility of generated plasma
in the case of applying a high voltage or a radio frequency voltage
from a radio frequency power source.
[0004] In order to solve the above problem, there is a demand for
accurately detecting determinations of the reproducibility and the
stability of the plasma.
[0005] At present, various studies are conducted so as to meet such
demand, and a fluctuation in plasma is detected through a detection
of changes in plasma emission intensity, changes in voltage and
current of a power source, changes in plasma impedance, or changes
in higher harmonic wave in the case of anomalous discharge and
through detections of a fluctuation in gas pressure and changes in
emission spectrum in the case of the determinations of the
reproducibility and the stability of plasma, i.e. determination of
the fluctuation in plasma.
[0006] Further, in order to monitor the changes in voltage or
current from the RF power source or the changes in plasma
impedance, a detector is inserted in a power line.
[0007] However, the above-described known methods involve drawbacks
relating to influences on plasma characteristics, efficiency, and
convenience and raises problems of increased cost and necessity for
extra space for installing the components.
[0008] Therefore, an object of this invention is to directly and
conveniently detect a state of plasma generated by an application
of a radio frequency or a high voltage.
DISCLOSURE OF THE INVENTION
[0009] FIG. 1 is a theoretical block diagram of this invention, and
means for solving the problems according to this invention will be
described with reference to FIG. 1.
[0010] Reference is made to FIG. 1.
[0011] (1) This invention is characterized in that a detection port
type probe comprises at least, an electroconductive supporting
member 5 having an opening formed on at least a part of a surface
thereof facing to plasma and a dielectric member 1 having a probe
electrode 2 formed on one side thereof positioned at the opening of
the electroconductive supporting member 5.
[0012] Since such detection port type probe is simply mounted on a
side wall of a process chamber, it is unnecessary to insert the
probe into the process chamber for its installation; therefore, the
detection port type probe will not influence on a state of the
plasma and enables monitoring of the plasma state with the simple
constitution.
[0013] More specifically, since a potential called wall potential
is induced on a surface of the dielectric member 1 facing to the
plasma due to the plasma generated inside the process chamber, it
is possible to monitor the plasma state through a monitoring of a
fluctuation in wall potential. In order to stabilize the detected
potential, it is preferable to shield the probe electrode 2 with an
electromagnetic shielding member 4 via an insulating member 3.
[0014] (2) Also, this invention according to item (1) is
characterized by connecting an impedance matching unit 6 to the
probe electrode 2.
[0015] In order to detect the voltage from the probe electrode 2,
it is necessary to connect the impedance matching unit 6 such as an
amplifier, an impedance converter, and a resistance between the
probe electrode 2 and a voltage measurement system.
[0016] (3) Also, this invention is characterized in that the
dielectric member 1 defined in item (1) or (2) is made from an
optically transparent glass.
[0017] The dielectric member 1 on which the wall potential is
induced may not be transparent, but it is preferable to use an
optically transparent glass for the dielectric member to make it
possible to optically observe reactions and the like inside the
process chamber.
[0018] (4) Also, this invention is characterized in that the probe
electrode 2 defined in item (3) is made from an optically
transparent electroconductive substance.
[0019] In the case where an area of the probe electrode 2 is
increased so as to enhance a wall potential detection sensitivity,
it is necessary to form the probe electrode 2 from the optically
transparent electroconductive substance for the purpose of
optically observing reactions and the like occurring in the process
chamber by way of the detection port type probe.
[0020] (5) Also, this invention is characterized in that the
opening defined in any one of items (1) to (4) formed on the
electroconductive supporting member 5 has a function of a viewing
port.
[0021] Thus, owing to the viewing port function, it is possible to
use the opening also as a viewing port disposed in the process
chamber, thereby simplifying an apparatus constitution.
[0022] (6) Also, this invention is characterized in that a plasma
monitoring device uses the detection port type probe defined in any
one of items (1) to (5) and comprises a voltage waveform measuring
unit for measuring voltage waveform, the voltage waveform measuring
unit being disposed at an output end of the detection port type
probe.
[0023] In the case of constituting the plasma monitoring device
using the detection port type probe, the voltage waveform measuring
unit for measuring voltage waveforms is disposed at the output end
of the detection port type probe, thereby monitoring the plasma
state using the voltage waveforms.
[0024] The voltage waveform measuring unit is provided at least
with an A/D converter for analog/digital converting voltage
waveforms and a data processing unit for monitoring the plasma
state by deriving an average waveform, an average voltage, an
average amplitude, and the like by processing the voltage
waveforms.
[0025] (7) Also, this invention according to item (6) is
characterized by comprising a process monitoring mechanism for
detecting a stability of plasma by detecting a degree of
nonuniformity among cyclical waveform changes of the voltage
waveform detected by the voltage waveform measuring unit.
[0026] Thus, by detecting the nonuniformity among cyclical waveform
changes of the voltage waveforms, it is possible to accurately
monitor the plasma state during the plasma processing.
[0027] (8) Also, this invention according to item (6) is
characterized by comprising an anomalous discharge monitoring
mechanism for detecting plasma anomalous discharge from the change
in voltage waveform detected by the voltage waveform measuring
unit.
[0028] Thus, by detecting plasma anomalous discharge from the
change in voltage waveform detected by the voltage waveform
measuring unit, it is possible to monitor an anomalous discharge
occurs suddenly during the plasma processing.
[0029] (9) Also, a plasma processing apparatus of this invention is
characterized by comprising the plasma monitoring device defined in
any one of items (6) to (8).
[0030] It is possible to perform plasma processing with higher
reproducibility by providing the plasma processing apparatus with
the plasma monitoring device.
[0031] (10) Also, this invention according to item (9) is
characterized in that the electroconductive supporting member 5
provided with the opening is a flange constituting a viewing port
of a reaction vessel and that the dielectric member 1 is a
transparent glass plate for sealing the flange.
[0032] Since it is possible to use the viewing port, i.e. the
flange constituting the viewing port, for mounting the plasma
monitoring device on an existing plasma processing apparatus, the
necessity for extra space for the probe is eliminated, thereby
simplifying the apparatus constitution.
BRIEF DESCRIPTION OF THE DRAWINGS
[0033] FIG. 1 is an illustration of a theoretical constitution of
this invention.
[0034] FIG. 2 is a schematic block diagram showing a plasma
processing apparatus with a detection port type probe according to
a first embodiment of this invention.
[0035] FIG. 3 is a schematic block diagram showing the detection
port type probe used in the first embodiment of this invention.
[0036] FIG. 4 is an illustration of waveforms detected by the
detection port type probe in RF discharge.
[0037] FIG. 5 is an illustration of a waveform detected by the
detection port type probe when an input power fluctuates in RF
discharge.
[0038] FIG. 6 is an illustration of a waveform detected by the
detection port type probe when an RF power source is immediately
disconnected after apparatus malfunction in RF discharge.
[0039] FIG. 7 is an illustration of a method of processing the
waveform detected by the detection port type probe in the first
embodiment of this invention.
[0040] FIG. 8 is a schematic block diagram showing a plasma
processing apparatus with an anomalous discharge monitoring device
according to a second embodiment of this invention.
[0041] FIG. 9 is an illustration of a waveform detected by a
detection port type probe in DC discharge in the second embodiment
of this invention.
[0042] FIG. 10 is an illustration of a waveform detected by the
detection port type probe in RF discharge in the second embodiment
of this invention.
[0043] FIG. 11 is a schematic block diagram showing a plasma
processing apparatus with an anomalous discharge monitoring device
according to a third embodiment of this invention.
[0044] FIG. 12 is an illustration of an anomalous discharge
detection method in the third embodiment of this invention.
[0045] FIG. 13 is a schematic block diagram showing a detection
port type probe according to a fourth embodiment of this
invention.
BEST MODE FOR CARRYING OUT THE INVENTION
[0046] Hereinafter, a plasma processing apparatus with a detection
port type probe and a detection signal processing method according
to a first embodiment of this invention will be described with
reference to FIGS. 2 to 7.
[0047] Reference is made to FIG. 2.
[0048] FIG. 2 is a schematic block diagram showing the plasma
processing apparatus with the detection port type probe according
to the first embodiment of this invention.
[0049] This plasma processing apparatus is constituted of a process
chamber 11 having a gas inlet 12, an outlet 13, and a probe
mounting portion 14, a parallel flat plate type electrode disposed
inside the process chamber and having a lower electrode 15 on which
a Si wafer 16 is placed and an upper electrode 17 used also as a
shower head for injecting an introduced gas and opposed to the
lower electrode 15, a radio frequency power source 19 for applying
an RF power of 13.56 MHz via a matching unit 18 constituted of a
blocking condenser or the like and performing an impedance matching
with the lower electrode 15, and an earthed wiring 20 for earthing
the upper electrode 17.
[0050] The probe mounting portion 14 is formed of a flange member
used for constituting ordinary viewing ports, and a detection port
type probe 30 is attached to the flange member so that a detection
output from the detection port type probe 30 is connected to a
digital oscilloscope 40 via a coaxial cable.
[0051] An input impedance of the digital oscilloscope 40 is 50 ohms
for example.
[0052] Reference is made to FIG. 3.
[0053] FIG. 3 is a schematic block diagram showing the detection
port type probe according to the first embodiment of this
invention, and the detection port type probe 30 is constituted of a
glass plate 31 made from an optically transparent glass used for
ordinary viewing ports, such as a kovar glass, a probe electrode 32
disposed on outer surface of the glass plate 31 with respect to
plasma and formed from ITO or the like, a transparent insulating
film 33 made from polyester or the like and insulating-coating a
surface of the probe electrode 32, an ITO shield 34 for
electromagnetically shielding the probe electrode 32 disposed on
the transparent insulating film 33, and an impedance converter
35.
[0054] In this case, the probe electrode 32 has no periphery so as
to avoid electrical short with the probe mounting potion 14, and a
small opening is formed on each of the ITO shield 34 and the
transparent insulating film 33 so that the probe electrode 32 is
connected to the impedance converter 35 using the coaxial cable
through the small openings.
[0055] The probe mounting portion 14 has a structure that a vacuum
sealing is achieved by using an O-ring, grease, or the like as is
the case with ordinary viewing ports.
[0056] In this case, the probe electrode 32 contacts with the
coaxial cable by way of a spring pin, and a contact between the ITO
shield 34 and the probe mounting portion 14 is achieved in the same
manner.
[0057] As described above, since whole parts of a viewing port
portion of the detection port type probe 30 are formed from the
transparent materials, the detection port type probe 30 has an
innovative and great advantage of functioning as a viewing port of
the process chamber of the plasma processing apparatus.
[0058] Hereinafter, a theory of monitoring a plasma state by the
detection port type probe will be described.
[0059] Reference is made to FIG. 2 again.
[0060] After introducing a reaction gas from the gas inlet 12 into
the process chamber 11, an RF power is applied between the upper
electrode 17 and the lower electrode 15 under a constant pressure
to generate plasma 21 between the electrodes, and ions and
electrons in the plasma diffuse into a wall of the process chamber
11 due to a density gradient of the plasma.
[0061] Since a current density of the diffused ions and electrons
depends on the density of the plasma itself, when an insulator is
disposed at a part of the process chamber 11, a potential called
wall potential is induced on the insulator, i.e. on the glass plate
31 in this invention, so as to balance with a plasma potential of
the plasma depending on a flux of ions or electrons diffused from
the plasma and passing though a sheath formed near the surface of
the insulator.
[0062] The wall potential induced on the surface of the glass plate
31 is lower than the plasma potential by a sheath potential and
exhibits potential changes in synchronization with an excitation
frequency of plasma in the case of radio frequency discharge while
exhibiting a constant potential in DC discharge.
[0063] However, in the case where the plasma 21 fluctuates and
oscillates due to a factor such as a fluctuation in power source
and a fluctuation in gas pressure, the state of the plasma 21
changes to that of plasma 22 so that the ion flux or the electron
flux diffusing into the wall of the process chamber 11 changes
delicately depending on the state change, thereby delicately
changing the wall potential to be induced on the glass plate 31
which is the dielectric disposed in the process chamber 11.
[0064] Therefore, the wall potential waveform is not constant but
fluctuates in synchronization with the plasma fluctuation in the DC
discharge, while the potential waveform in the RF discharge
synchronizes with the plasma excitation frequency to change a
waveform distortion or a peak value.
[0065] In the case of occurrence of a sudden change such as
anomalous discharge, the plasma changes rapidly to cause electrons
having smaller mass to react delicately, so that the electron flux
is sharply reduced to change the wall potential delicately and
sharply to the plus side. In turn, the wall potential is changed to
the minus side when the electron flux is increased.
[0066] Therefore, when the wall potential changes, a potential
change responsive to the plasma change is induced on the probe
electrode 32 disposed on the sideface which is not facing to the
plasma of the glass plate 31 disposed in the process chamber 11 by
an electrostatic induction.
[0067] By measuring the induced potential and processing potential
data thereof, it is possible to detect changes in plasma state such
as the peak value, the distortion state, and the like of the wall
potential, and, by using the plasma state changes as an index, it
is possible to efficiently and conveniently perform monitoring and
determination of stability, reproducibility, changes, and the like
of the plasma.
[0068] Note that, since the wall potential induced on the surface
of the glass plate 31 of the detection port type probe 30 depends
on the impedance of the sheath formed around the glass plate 31 and
the impedance of the probe itself, the impedance of the probe
electrode 32 with respect to the radio frequency component, not
only the excitation frequency, must be large enough for the probe
electrode 32 to oscillate perfectly parallelly with the plasma
potential.
[0069] That is to say, it is necessary to keep the sheath impedance
small and the impedance of the detection port type probe itself
large.
[0070] A surface area of the glass plate 31 has only to be
increased for the purpose of reducing the sheath impedance, and an
area of a portion facing to the plasmas 21 and 22 of the glass
plate 31 of the detection port type probe 30 of this invention must
be sufficiently increased.
[0071] It is not necessary to accurately detect the impedance of
the probe electrode 32 constituted of ITO, and, since the probe
voltage reaches to the maximum value when the impedance is at
infinity, the impedance has only to be adjusted in such a manner
that the wall potential of the probe reaches to its maximum
value.
[0072] Next, voltage waveforms measured by using the detection port
type probe of this invention will be described with reference to
FIGS. 4 to 6.
[0073] Reference is made to FIG. 4(a).
[0074] Shown in FIG. 4(a) is a voltage waveform output from the
detection port type probe 30 when plasma is generated stably with a
power supply from the radio frequency power source 18 to the
process chamber 11.
[0075] Referring to FIG. 4(a), time (second) and a voltage are
indicated by the horizontal axis and the vertical axis, and it is
revealed that a stable voltage waveform is repeated with a cycle of
73 nanoseconds (73 ns=7.3.times.10.sup.-8 s) in accordance with the
frequency of 13.56 MHz, thereby making it possible to measure an
oscillation waveform and an amplitude of the plasma.
[0076] Reference is made to FIG. 4(b).
[0077] Shown in FIG. 4(b) is a voltage waveform observed in the
case of unstable plasma, and, as shown in FIG. 4(b), it is
determined that the voltage waveform has a distortion and that a
peak value fluctuates cyclically.
[0078] Reference is made to FIG. 5.
[0079] FIG. 5 is an illustration of a waveform detected by the
detection port type probe in the case where an input power
fluctuates in RF discharge, and it is observed that the detected
waveform gradually changes with the fluctuation in input power.
[0080] In this case, it is confirmed that a peak value in the
detected waveform is in proportion to the RF input power. The
waveform detected by the detection port type probe changes with a
cycle of the frequency of the radio frequency power source 19, and
the waveform distortion state, the peak value, and the like reflect
plasma characteristics.
[0081] Reference is made to FIG. 6.
[0082] FIG. 6 is an illustration of a waveform detected by the
detection port type probe when the RF power source is immediately
disconnected after an apparatus malfunction in the RF discharge,
wherein the detected waveform reacts to fluctuate on the plus side
because the wall potential fluctuates to the minus side due to a
rapid diffusion of electrons having smaller mass caused by the
immediate disconnection of the RF power source.
[0083] Thus, the detection port type probe 30 of this invention
catches delicate changes of the ion flux or the electron flux
diffused in response to the changes in plasma state, thereby
detecting the changes in plasma state reliably, efficiently, and
sensitively.
[0084] Next, a method of processing a waveform detected by the
detection port type probe in the first embodiment of this invention
will be described with reference to FIG. 7.
[0085] Reference is made to FIG. 7(a).
[0086] As shown in FIG. 7(a), an average value V.sub.av(m), an
average amplitude V.sub.av(pp), and an averaged waveform
f.sub.av(t) are obtained from waveforms f.sub.i(t) detected during
cycles for an arbitrary period of time or in an arbitrary number
(n) of cycles, the waveforms f.sub.i(t) being included among
voltage waveforms f(t) detected by the detection port type probe
30.
[0087] In this case, the averaged waveform f.sub.av(t) is obtained
from
f.sub.av(t)=.SIGMA.f.sub.i(t)/n.
[0088] Reference is made to FIG. 7(b).
[0089] Next, based on the averaged waveform f.sub.av(t), the
average value V.sub.av(m) and the amplitude V.sub.av(pp) are
obtained.
[0090] In order to use, as an index, ratios of distortions of the
average value V.sub.av(m), the amplitude V.sub.av(pp), and the
average waveform f.sub.av(t) to those obtained in a stable plasma
state, the values obtained under predetermined conditions of a
plasma processing apparatus for processing a basic waveform and
using the detection port type probe when the plasma is in a stable
state are obtained as detected waveform data to be used as basic
waveform data.
[0091] A waveform f.sub.av0(t) averaged as a waveform of one cycle,
V.sub.av0(pp), and V.sub.av0(m) are then obtained by setting the
cycles to an arbitrary period of time or an arbitrary number of the
basic waveforms with respect to the basic waveform data.
[0092] Further, since the above values change in accordance with
input power for generating plasma, a coefficient for the input
power is obtained to be stored as an initial setting value.
[0093] Here, when the waveform to be detected is f(t), the
distortion ratio .alpha. as the index for indicating a degree of a
distortion of a probe waveform undergoing the plasma treatment with
respect to the basic waveform can be expressed as
.alpha.=f.sub.av(t)/f.sub.av0(t),
[0094] and a proportion of a higher harmonic wave component and the
degree of distortion of the waveform are detected by the above
expression.
[0095] Likewise, V.sub.av(m) and V.sub.av0(pp) can be defined as
follows, wherein V.sub.av0(m) and V.sub.av0(pp) are reference
values and m and p are coefficients:
m=V.sub.av(m)/V.sub.av0(m); and
p=V.sub.av(pp)/V.sub.av0(pp).
[0096] By the use of the coefficients .alpha., m, and p, it is
possible to detect a fluctuation in size and a state of oscillation
of the waveform detected by the probe.
[0097] More specifically, the coefficients .alpha., m, and p are
set for every input power in advance, and the average waveform
f.sub.av(t) of the waveforms detected by the probe during the
arbitrary period of time or the arbitrary cycles is obtained to be
compared with the reference waveform f.sub.av(0). It is then judged
whether the thus-obtained coefficient .alpha.' is larger or smaller
than the value set in the data processing unit, so that a warning
is sent to the plasma apparatus in the case where .alpha.' is
larger or smaller than the predetermined value.
[0098] For instance, in the case where the distortion ratio
.alpha.' or V.sub.av(pp) is the predetermined value and V.sub.av(m)
is not the predetermined value, the oscillation of plasma might be
attributable to problems other than the plasma power input error,
such as errors relating to a gas flow ratio and a degree of vacuum;
therefore, a warning indicating the unstable state of plasma is
transmitted.
[0099] Also, when the V.sub.av(pp) simply deviates from the
predetermined value, such deviation is attributable to a
mismatching between impedances of the plasma 21 and the radio
frequency power source 19 or to an error in input power settings of
the radio frequency power source 19. In the case where V.sub.av(pp)
is smaller than the predetermined value, the deviation is
attributable to the mismatching with plasma; therefore, a warning
is transmitted and a control signal is output to the plasma power
source so that matching with the plasma is achieved.
[0100] In turn, in the case where the V.sub.av(pp) is larger than
the predetermined value, the deviation is attributable to the error
in input power setting of the radio frequency power source 19;
therefore, a warning of a setting error is transmitted.
[0101] Since the detection port type probe of the first embodiment
of this invention operates without any difficulty even when an
insulating layer is deposited due to a long term plasma treatment
insofar as the deposited insulating layer becomes extremely thick,
applicability thereof to the plasma processing apparatuses in the
production sites is excellent from the standpoint of cost and
installation space.
[0102] Next, with reference to FIGS. 8 to 10, a plasma processing
apparatus according to a second embodiment of this invention, which
is provided with the above-described detection port type probe and
detects a fluctuation in plasma, anomalous discharge, and so forth,
will be described.
[0103] Reference is made to FIG. 8.
[0104] FIG. 8 is a schematic block diagram showing the plasma
processing apparatus with an anomalous discharge monitoring device
according to the second embodiment of this invention. A basic
constitution of the plasma processing apparatus is the same as that
of the first embodiment except for using a plasma monitoring device
50 in place of the digital oscilloscope 40 in the detection system,
and descriptions for the same parts are omitted.
[0105] The plasma monitoring device 50 is constituted of a
detection port type probe 30, an A/D converter 51, a data
processing unit 52, a filter processing unit 53, and an anomalous
discharge detection unit 54, and so forth.
[0106] By the use of the data processing unit 52, an average
waveform f.sub.av(t), an average voltage V.sub.av(m), an average
amplitude V.sub.av(pp), and coefficients .alpha., m, and p, which
are described in the first embodiment, are obtained based on
detected waveforms.
[0107] A normal process monitoring is the same as that described in
the first embodiment, and anomalous discharge detection will
hereinafter be described with reference to FIGS. 9 and 10.
[0108] Reference is made to FIG. 9.
[0109] FIG. 9 is an illustration of a waveform detected by the
detection port type probe in the case of anomalous discharge in DC
discharge in the second embodiment, wherein a plasma generating
power source voltage and a waveform detected by an discharge
monitor for detecting anomalous discharge by measuring a
fluctuation in current are also shown.
[0110] The detected waveform of the discharge monitor shown in the
upper side is increased rapidly in response to the generation of
anomalous discharge.
[0111] In turn, the detected waveform of the detection port type
probe shown in the lower side fluctuates on the plus side
instantaneously with a sharp rising and then converges as
fluctuating from the minus side to the plus side. This indicates
that, because of the instantaneous suspension is caused upon
occurrence of the anomalous discharge to sharply increase the
diffusing electron flux, the wall potential fluctuated to the minus
side instantaneously and in reverse to the fluctuation at the time
of the power source disconnection shown in FIG. 6 and then
converged with the comparatively gradual change owing to the power
source control.
[0112] It will be understood from the detected waveform of the
detection port type probe that the waveform is quicker in rising
than that of the discharge monitor and responses delicately and
sensitively.
[0113] Reference is made to FIG. 10.
[0114] FIG. 10 is an illustration of a waveform detected by the
detection port type probe in the case of anomalous discharge in RF
discharge in the second embodiment, wherein a waveform detected by
a supersonic wave sensor for detecting a supersonic wave at the
time of occurrence of anomalous discharge in RF plasma is also
shown.
[0115] In addition, the present inventor has proposed a method of
specifying a discharge occurrence position by detecting an AE
(Acoustic Emission) generated by anomalous discharge with the use
of an AE sensor attached to an outer wall of a plasma processing
apparatus by taking advantage of the fact that the supersonic wave
(AE) is generated when anomalous discharge 24 occurs during plasma
processing to diffuse into the outer wall of the plasma processing
device (see JP-A-2000-89840, when necessary).
[0116] The detected waveform of the detection port type probe shown
in the upper side responds delicately to the anomalous discharge 24
to rapidly fluctuate on the minus side as is the case with the
anomalous discharge occurred in the DC plasma shown in FIG. 9 and
to cause the wall potential to fluctuate on the minus side, thereby
revealing that a diffused electron amount is increased to bring the
plasma into an instantaneous suspension state.
[0117] Note that an RF component has been eliminated from the
detected waveform of the detection port type probe.
[0118] In turn, the detected waveform of the supersonic wave sensor
shown in the lower side reveals that the supersonic wave detection
relating to the anomalous discharge is performed after the change
in detected waveform of the detection port type probe of the upper
side due to a relationship between a position of the occurrence of
the anomalous discharge and a diffusion speed of the supersonic
wave diffusing into the outer wall of the process chamber 11.
[0119] Next, a method of detecting anomalous discharge will be
briefly described.
[0120] The detected waveform of the detection port type probe 30 is
input via the A/D converter 51, and an RF component at 13.56 MHz of
waveform data thereof is eliminated by using a low-pass filter in
the filter processing unit 53, followed by a detection of an
anomalous discharge signal in the anomalous discharge detecting
unit 54.
[0121] Then, the detected waveform f(t) is subjected to
differentiation so as to obtain a fluctuation amount of the
waveform from the detected signal. When the value obtained by the
differentiation is represented by .beta.,
.beta.=df(t)/dt
[0122] holds.
[0123] It is possible to detect a fluctuation state of the waveform
by monitoring .beta..
[0124] As shown in FIGS. 10 and 6, in the case of the anomalous
discharge or the instantaneous suspension of power supply, the wall
potential changes sharply to change a value of .beta. toward the
plus side or the minus side in the anomalous discharge detecting
unit 54.
[0125] Accordingly, an anomalous state is detected when a value of
f(t) exceeds a certain threshold value to cause the value of .beta.
to be larger than a predetermined value, and it is judged that the
anomalous discharge has occurred when the value .beta. is on the
minus side, whereby a warning is sent to the plasma processing
apparatus.
[0126] Further, since the changes in current supply are relevant to
the size of anomalous discharge, it is possible to estimate the
size of the anomalous discharge from a peak value V(pp) of the
waveform.
[0127] Hereinafter, a third embodiment of this invention which uses
a unit for determining a position of anomalous discharge will be
described with reference to FIG. 11.
[0128] Reference is made to FIG. 11.
[0129] FIG. 11 is a schematic block diagram showing a plasma
processing apparatus with an anomalous discharge monitoring device
according to the third embodiment of this invention. A basic
apparatus constitution is the same as that of the plasma processing
apparatus of the second embodiment shown in FIG. 8.
[0130] In the third embodiment, three or more AE sensors 25, 26,
and 27 for specifying a position at which anomalous discharge has
occurred are attached to an outer wall of a process chamber 11
(see, JP-A-2001-370610, when necessary).
[0131] In this case, three AE sensors are shown.
[0132] Reference is made to FIG. 12.
[0133] FIG. 12 is an illustration of a method for detecting
anomalous discharge in the third embodiment of this invention. It
is judged whether or not the anomalous discharge has occurred from
a waveform shown in the upper side, which is detected by the
detection port type probe 30, by employing the above-described
method, and, when it is judged that the anomalous discharge 24 has
occurred, operation of the AE sensors 25 to 27 for determining the
position of occurrence of the anomalous discharge 24 starts.
[0134] Next, delay times T.sub.0, T.sub.1, and T.sub.2 due to
differences in distance between the occurrence position of the
anomalous discharge 24 and earthing positions of the AE sensors 25
to 27 are obtained from three waveforms detected by the three AE
sensors 25 to 27, and then the occurrence position of the anomalous
discharge 24 is specified by a theory similar to that for
specifying the epicenter of an earthquake from the delay times
T.sub.0, T.sub.1, and T.sub.2.
[0135] Since the judgment of the anomalous state is performed by
the use of the detected waveform of the detection port type probe
30, an erroneous judgment of judging a mechanical vibration
detected by the AE sensors as the anomalous discharge is
prevented.
[0136] Further, since the position specifying operation by the AE
sensors is performed after confirming the occurrence of anomalous
discharge based on the detected waveform of the detection port type
probe 30, wasteful actuation of the AE sensors is prevented.
[0137] Hereinafter, a detection port type probe of a fourth
embodiment of this invention will be described with reference to
FIG. 13.
[0138] Reference is made to FIG. 13.
[0139] FIG. 13 is a schematic block diagram showing the detection
port type probe of the fourth embodiment of this invention, wherein
the detection port type probe has a basic constitution which is
similar to that of the detection port type probe 30 shown in FIG. 3
and is constituted of a glass plate 31 made from the optically
transparent kovar glass or the like which is used for ordinary
viewing ports, a probe electrode 32 disposed on an outer surface of
the glass plate 31 with respect to the process chamber and made
from ITO or the like, a transparent insulating film 33 insulating
coating a surface of the probe electrode 32 and made from polyester
or the like, an ITO shield 34 disposed on the transparent
insulating film 33 so as to electromagnetically shield the probe
electrode 32, and an impedance converter 35.
[0140] In the fourth embodiment, an optically transparent
deposition-free glass plate 36 is disposed at a position which is
closer to a plasma generation region than the glass plate 31 is,
and it is possible to prevent occurrence of contamination on a
surface of the glass plate 31 constituting the detection port type
probe owing to the deposition-free glass plate 36.
[0141] In this case, too, the probe electrode 32 has no periphery
so as to prevent an occurrence of electrical short with a probe
mounting portion 14, and a small opening is formed on each of the
ITO shield 34 and the transparent insulating film 33 so that the
probe electrode 32 is connected to the impedance converter 35
through the small openings by way of a coaxial cable.
[0142] Further, the probe mounting portion 14 has a structure that
a vacuum sealing is achieved by using an O-ring, grease, or the
like as is the case of ordinary viewing ports.
[0143] In this case, too, since a viewing port portion of the
detection port type probe and the deposition-free glass plate 36
are formed from the transparent materials, the detection port type
probe has the innovative and great advantage of functioning also as
a viewing port of the process chamber of a plasma processing
apparatus.
[0144] Since the deposition-free glass plate 36 has only to be
replaced in the case of contamination by reaction products of
plasma processing, a necessity for replacement and cleaning of the
glass plate 31 of the detection port type probe is eliminated.
[0145] Note that detection sensitivity is slightly degraded by the
provision of the deposition-free glass plate 36.
[0146] The foregoing is the description of the embodiments of this
invention, and the constitutions and conditions described in the
embodiments do not limit the invention and are subject to various
modifications.
[0147] For instance, though the parallel flat plate electrode type
plasma processing apparatus is used by way of example for
describing the plasma processing apparatus in the above
embodiments, the constitution of the plasma processing apparatus is
not limited to that of the parallel flat plate electrode type
plasma processing apparatus, and the invention is applicable to
plasma processing apparatuses of various constitutions.
[0148] Also, though the detection port type probe is disposed at
one position of the outer wall of the process chamber in the above
embodiments, the detection port type probe may be disposed at a
plurality of positions on the process chamber outer wall.
[0149] Though the description is made on condition that the
mounting portion of the detection port type probe is secured in the
process chamber in the above embodiments, the detection port type
probe may be attached to an existing plasma processing
apparatus.
[0150] That is, in the case where the existing plasma processing
apparatus has a viewing port, it is possible to simply form the
detection port type probe by attaching an optically transparent
electroconductive sheet such as an ITO sheet as the electrode on
the side facing to the air of the glass of the viewing port.
[0151] Further, though the device which is capable of measuring the
radio frequency voltage, such as the digital oscilloscope having
the input impedance of 50 .OMEGA., is used for the measurement of
probe potential, the probe potential measurement device is not
limited to the digital oscilloscope, and any device such as a
sampling oscilloscope and a frequency analyzer may be used insofar
as it is capable of measuring the radio frequency voltage.
[0152] Though the dielectric used for inducing the wall potential
in the detection port type probe is the substrate-like glass plate
in the above embodiments, the dielectric is not limited to the
substrate-like glass plate.
[0153] Though the glass plate is used as a material for inducing
the wall potential in the detection port type probe in the above
embodiments, the material for inducing the wall potential is not
limited thereto, and a dielectric substrate such as a sapphire
substrate may be used as the dielectric substrate insofar as it is
dielectric.
[0154] Though the whole part of the detection port type probe is
formed from the transparent materials so that the detection port
type probe functions also as the viewing port, it is unnecessary to
form the whole part from the transparent materials. For example,
the probe electrode may be formed from Al or Au.
[0155] In this case, the function of viewing port is achieved by
using a small disk-like electrode or a circular electrode as the
probe electrode.
[0156] The function of the viewing port is not always necessary,
and at least a part of the detection port type probe may be formed
from a non-transparent material in the case where the viewing port
function is unnecessary.
[0157] The probe electrode of the detection port type probe may not
necessarily have the disk-like shape, and it is needless to say
that a glass plate to which a wire electrode is attached functions
as a probe.
INDUSTRIAL APPLICABILITY
[0158] As described in the foregoing, by the use of the detection
port type probe and the plasma monitoring device of this invention,
it is possible to determine changes in plasma state through
measurements of the average wall potential and the potential
oscillation wave form as well as to conveniently detect an
anomalous state or the like of anomalous discharge. Particularly,
since the detection port type probe can be used as a viewing port,
it is possible to automatically detect a condition of a plasma
processing apparatus. Therefore, the detection port type probe is
suitably used for plasma processing apparatuses capable of
preventing defective products by automatically stopping and
controlling plasma.
* * * * *