U.S. patent application number 13/743367 was filed with the patent office on 2014-02-27 for plasma processing apparatus and plasma processing method.
This patent application is currently assigned to Hitachi High-Technologies Corporation. The applicant listed for this patent is HITACHI HIGH-TECHNOLOGIES CORPORATION. Invention is credited to Michikazu MORIMOTO, Yasuo OHGOSHI, Tetsuo ONO, Yuuzou OOHIRABARU.
Application Number | 20140057445 13/743367 |
Document ID | / |
Family ID | 50148356 |
Filed Date | 2014-02-27 |
United States Patent
Application |
20140057445 |
Kind Code |
A1 |
MORIMOTO; Michikazu ; et
al. |
February 27, 2014 |
PLASMA PROCESSING APPARATUS AND PLASMA PROCESSING METHOD
Abstract
The present invention provides a plasma processing apparatus
having a radio frequency power supply supplying time-modulated
radio frequency power which is controllable widely with high
precision, and a plasma processing method using the plasma
processing apparatus. The plasma processing apparatus includes: a
vacuum chamber; a first radio frequency power supply for generating
plasma in the vacuum chamber; a sample holder disposed in the
vacuum chamber, on which a sample is placed; and a second radio
frequency power supply supplying radio frequency power to the
sample holder, wherein at least one of the first radio frequency
power supply and the second radio frequency power supply supplies
time-modulated radio frequency power, one of parameters of
controlling the time-modulation has two or more different control
ranges, and one of the control ranges is a control range for a
high-precision control.
Inventors: |
MORIMOTO; Michikazu;
(Kudamatsu-shi, JP) ; OHGOSHI; Yasuo;
(Kudamatsu-shi, JP) ; OOHIRABARU; Yuuzou;
(Kudamatsu-shi, JP) ; ONO; Tetsuo; (Kudamatsu-shi,
JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
HITACHI HIGH-TECHNOLOGIES CORPORATION |
Tokyo |
|
JP |
|
|
Assignee: |
Hitachi High-Technologies
Corporation
Tokyo
JP
|
Family ID: |
50148356 |
Appl. No.: |
13/743367 |
Filed: |
January 17, 2013 |
Current U.S.
Class: |
438/710 ;
156/345.28 |
Current CPC
Class: |
H01J 37/32706 20130101;
H01J 37/32082 20130101; H01L 21/3065 20130101; H01J 37/32715
20130101; H01J 37/32192 20130101; H01J 37/32165 20130101; H01J
37/32302 20130101; H01L 21/67069 20130101; H01J 2237/334 20130101;
H01L 21/31116 20130101; H01L 21/32137 20130101 |
Class at
Publication: |
438/710 ;
156/345.28 |
International
Class: |
H01L 21/3065 20060101
H01L021/3065 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 24, 2012 |
JP |
2012-184847 |
Claims
1. A plasma processing apparatus, comprising: a vacuum chamber; a
first radio frequency power supply for generating plasma in the
vacuum chamber; a sample holder disposed in the vacuum chamber, on
which a sample is placed; and a second radio frequency power supply
supplying radio frequency power to the sample holder, wherein at
least one of the first radio frequency power supply and the second
radio frequency power supply supplies time-modulated radio
frequency power, one of parameters of controlling the
time-modulation has two or more different control ranges, and one
of the control ranges is a control range for a high-precision
control.
2. The plasma processing apparatus according to claim 1, wherein
the parameter is at least one of a duty ratio, a repetition
frequency, an on-time, and an off-time.
3. The plasma processing apparatus according to claim 2, wherein:
at least one of the first radio frequency power supply and the
second radio frequency power supply includes an A/D converter and a
pulse generator, the A/D converter receives the two or more
different control ranges at different timings, and the pulse
generator generates a pulse controlled in a control range selected
by a control range switching signal from each of the two different
control ranges received by the A/D converter.
4. The plasma processing apparatus according to claim 3, wherein at
least one of the first radio frequency power supply and the second
radio frequency power supply is the second radio frequency power
supply.
5. The plasma processing apparatus according to claim 2, wherein at
least one of the first radio frequency power supply and the second
radio frequency power supply includes radio frequency power
supplies of the same number as the number of the two or more
different control ranges.
6. A plasma processing method using a plasma processing apparatus
including a vacuum chamber, a first radio frequency power supply
for generating plasma in the vacuum chamber, a sample holder
disposed in the vacuum chamber, on which a sample is placed, and a
second radio frequency power supply supplying radio frequency power
to the sample holder, wherein at least one of the first radio
frequency power supply and the second radio frequency power supply
supplies time-modulated radio frequency power, the time-modulation
is controlled by a parameter having two or more different control
ranges, and one of the control ranges is a control range for a
high-precision control.
7. The plasma processing method according to claim 6, wherein a
period when the time-modulated radio frequency power is not applied
is in the range of 10 to 1000 ms.
8. The plasma processing method according to claim 6, wherein the
period when the time-modulated radio frequency power is not applied
is equal to or more than a residence time of a reaction
product.
9. A plasma processing method in which a sample having a Poly-Si
film, a SiO.sub.2 film, an amorphous carbon film, a SiN film, and a
BARC film is plasma-etched while time-modulated radio frequency
power is supplied to the sample, wherein: a repetition frequency
has a first control range requiring a high-precision control and a
second control range not requiring the high-precision control, a
duty ratio has a third control range requiring the high-precision
control and a fourth control range not requiring the high-precision
control, the SiN film is etched in the first control range and the
fourth control range, the amorphous carbon film is etched in the
second control range and the fourth control range, the SiO.sub.2
film is etched in the first control range and the third control
range, and a part of the Poly-Si film is etched in the first
control range and the third control range.
Description
CLAIM OF PRIORITY
[0001] The present application claims priority from Japanese patent
application JP2012-184847 filed on Aug. 24, 2012, the content of
which is hereby incorporated by reference into this
application.
FIELD OF THE INVENTION
[0002] The present invention relates to a plasma processing
apparatus and a plasma processing method, and particularly, to a
plasma processing apparatus and a plasma processing method suitable
to perform high-precision etching processing by using plasma in
order to process a sample such as a semiconductor device, and the
like.
BACKGROUND OF THE INVENTION
[0003] In the related art, as a method of processing the surface of
a semiconductor device, an apparatus that etches the semiconductor
device with plasma is known. Herein, the related art will be
described by using as an example a plasma etching apparatus of an
electron cyclotron resonance (ECR, hereinafter, abbreviated as ECR)
type.
[0004] In the ECR type, plasma is generated by a microwave in a
vacuum chamber to which a magnetic field is applied from the
outside. Electrons cyclotron-move by the magnetic field, and this
frequency and a frequency of the microwave are resonated to
efficiently generate plasma. In order to accelerate ions incident
on the semiconductor device, radio frequency power is applied to a
sample as an approximate sine wave in a continuous waveform.
Herein, the radio frequency power applied to the sample is
hereinafter referred to as a radio frequency bias.
[0005] Further, as gas which becomes plasma, halogen gas such as
chlorine or fluorine has been widely used. An etched material
reacts with radicals or ions generated by plasma, and thus etching
is performed. A reaction product produced by etching causes
reattachment to a pattern and an etching profile is a taper
profile. Therefore, controlling the reaction product produced in
etching becomes important in order to achieve high-precision of
etching processing.
[0006] In order to decrease the concentration of the reaction
product, a method of shortening a residence time of the reaction
product is used. In the case where a residence time of gas in a
plasma processing chamber is set as .tau., .tau. has a relationship
of .tau.=PV/Q when P is set as processing pressure, V is set as the
volume of the plasma processing chamber, and Q is set as a gas flow
rate, and in a device configuration, limitations of P, V, and Q are
determined.
[0007] The residence time of the reaction product which becomes gas
may be shortened by decreasing the processing pressure or
increasing the gas flow rate from the above relationship, but the
increasing the gas flow rate and the decreasing the processing
pressure have a trade-off relationship with each other, which are
difficult to be enhanced.
[0008] Further, Japanese Patent Application Laid-Open Publication
No. Hei8 (1996)-250479 discloses time-modulation of plasma or radio
frequency bias as a method of controlling the reaction product and
increasing etching processing precision. In addition, Japanese
Patent Application Laid-open Publication No. 2001-85395 discloses a
method of controlling a time-modulated radio frequency bias to
control ion energy with high precision by dividing the radio
frequency bias into two or more.
SUMMARY OF THE INVENTION
[0009] When etching is performed, the repetition frequency and the
duty ratio and an etching condition such as etching gas or pressure
are set in a controller by an input means. A set value is handled
as a digital signal in the controller, but when the controller and
the radio frequency bias power supply are analogly connected to
each other, the set value needs to be converted into an analog
signal through a digital/analog converter (hereinafter, referred to
as a D/A converter) in the controller and thereafter, transmitted.
When an error occurs due to noise for the signal, and the like at
the time of transmitting the analog signal, the set value becomes
different from an output value.
[0010] For example, when a signal of the duty ratio may be input
every 0.5% in the range of 0 to 100%, resolution of approximately
0.098% per one digit is obtained in 12-bit digital signal
processing. Herein, the digit means a binary digit number.
[0011] As illustrated in FIG. 11, when the analog signal is used in
the range of 0 to 10 V with respect to the 12-bit digital signal
processing, voltage per one digit is approximately 4.9 mV. When the
analog signal deviates by 4.9 mV or more due to the noise, and the
like, deviation of one digit or more may occur after digital signal
conversion. In this case, since the resolution is approximately
0.098% per one digit, an error of the duty ratio of approximately
0.1% or more may occur.
[0012] For example, when the repetition frequency is 10 Hz and the
duty ratio is 2.0%, the on-time of the radio frequency bias becomes
2.0 ms. When the repetition frequency is 10 Hz and the duty ratio
2.1%, the on-time becomes 2.1 ms. When an error of control
precision of the duty ratio is 0.1%, the set value of the duty
ratio may also be 2.0%, and as a result, 2.1% and in this case, an
error of the on-time becomes 0.1 ms.
[0013] In general, etching is performed during the on-time. An
error of the time during which etching is performed influences an
etching rate or the concentration of the reaction product of
etching. FIG. 12 illustrates a test result acquired by verifying
the relationship between the duty ratio and the etching rate. In
the case of the etching rate, by using mixed gas of HBr gas, Ar
gas, and O.sub.2 gas, an etching rate of Poly-Si is measured by
changing the duty ratio at a repetition frequency of 10 Hz.
[0014] In this test, a result in which when the duty ratio is
changed by 0.1%, the etching rate is changed by 1.3 nm/min is
acquired. Further, when the duty ratio is 2%, the etching rate is
21.7 nm/min, but when the duty ratio deviates by +1 digit due to
noise, and the like, the duty ratio becomes 2.1% and the etching
rate becomes 23.0 nm/min. In addition, when the duty ratio deviates
by one digit due to noise, and the like, the duty ratio becomes
1.90% and the etching rate becomes 20.4 nm/min.
[0015] As such, when an error of .+-.1 digit occurs even in a state
where the duty ratio is set to 2.0%, the etching rate has an error
of approximately 12% as an error rate with respect to 21.7 nm/min
and variation in etching performance of approximately 12% may
occur. The variation causes reproducibility of etching performance
or an interdevice difference.
[0016] Resolution may be increased by narrowing a use domain of a
duty ratio for an analog voltage value used with respect to this
problem, but an optimal duty ratio is different according to
etching gas or an etched target structure. As a result, in order to
deal with various etching gas or various etched target structures,
a duty ratio domain which is as large as possible is required.
Therefore, both broadness of a usable domain of the duty ratio and
improvement of the resolution of the duty ratio are required.
[0017] Further, the same as the duty ratio applies even to the
repetition frequency. Since the optimal repetition frequency is
different according to the etching gas or the etching target
structure, a repetition frequency domain which is as large as
possible is required in order to deal with various etching gases or
various etching target structures. As a result, both broadness and
high resolution of the repetition frequency are required even with
respect to the repetition frequency.
[0018] In addition, even with respect to pulse plasma which is
known as a method of controlling dissociation of plasma, a high
frequency applied to produce the pulse plasma is time-modulated and
pulsated, and thus the same problem as in the duty ratio and the
repetition frequency may occur.
[0019] Therefore, in consideration of the above problem, the
present invention provides a plasma processing apparatus including
a radio frequency power supply supplying time-modulated radio
frequency power which is controllable extensively and with high
precision, and a plasma processing method using the plasma
processing apparatus.
[0020] The present invention provides a plasma processing apparatus
including: a vacuum chamber; a first radio frequency power supply
for generating plasma in the vacuum chamber; a sample holder
disposed in the vacuum chamber, on which a sample is placed; and a
second radio frequency power supply supplying radio frequency power
to the sample holder, wherein at least one of the first radio
frequency power supply and the second radio frequency power supply
supplies time-modulated radio frequency power, one of parameters of
controlling the time-modulation has two or more different control
ranges, and one of the control ranges is a control range for a
high-precision control.
[0021] The present invention also provides a plasma processing
method using a plasma processing apparatus including: a vacuum
chamber; a first radio frequency power supply for generating plasma
in the vacuum chamber; a sample holder disposed in the vacuum
chamber, on which a sample is placed; and a second radio frequency
power supply supplying radio frequency power to the sample holder,
wherein at least one of the first radio frequency power supply and
the second radio frequency power supply supplies time-modulated
radio frequency power, the time-modulation is controlled by a
parameter having two or more different control ranges, and one of
the control ranges is a control range for a high-precision
control.
[0022] The present invention also provides a plasma processing
method in which a sample having a Poly-Si film, a SiO.sub.2 film,
an amorphous carbon film, a SiN film, and a BARC film is
plasma-etched while time-modulated radio frequency power is
supplied to the sample, wherein a repetition frequency has a first
control range requiring a high-precision control and a second
control range not requiring the high-precision control, a duty
ratio has a third control range requiring the high-precision
control and a fourth control range not requiring the high-precision
control, the SiN film is etched in the first control range and the
fourth control range, the amorphous carbon film is etched in the
second control range and the fourth control range, the SiO.sub.2
film is etched in the first control range and the third control
range, and a part of the Poly-Si film is etched in the first
control range and the third control range.
[0023] According to the aspects of the present invention, it is
possible to supply time-modulated radio frequency power which is
controllable extensively and with high precision.
BRIEF DESCRIPTION OF THE DRAWINGS
[0024] FIG. 1 is a longitudinal cross-sectional view of a microwave
ECR plasma etching apparatus according to an embodiment of the
present invention;
[0025] FIG. 2 is a schematic diagram of a controller and a radio
frequency bias power supply according to the embodiment of the
present invention;
[0026] FIG. 3A is a diagram illustrating transmission of an analog
signal in a first embodiment;
[0027] FIG. 3B is a diagram illustrating transmission of an analog
signal in a second embodiment;
[0028] FIG. 4A is a schematic diagram of an A/D converter in the
first embodiment;
[0029] FIG. 4B is a schematic diagram of an A/D converter in the
second embodiment;
[0030] FIG. 5 is a schematic diagram of a controller and a radio
frequency bias power supply according to the embodiment of the
present invention;
[0031] FIG. 6A is a diagram illustrating a setting example of a
channel in the first embodiment;
[0032] FIG. 6B is a diagram illustrating a setting example of a
channel in the second embodiment;
[0033] FIG. 7A is a diagram illustrating dependency of the
concentration of a reaction product on an etching time;
[0034] FIG. 7B is a diagram illustrating dependency of the
concentration of a reaction product on an etching time;
[0035] FIG. 8A is a diagram illustrating a SiO.sub.2 selectivity to
a duty ratio in the first embodiment;
[0036] FIG. 8B is a diagram illustrating dependency of a tapered
angle having an etching profile on a repetition frequency in the
second embodiment;
[0037] FIG. 8C is a diagram illustrating the dependency of the
tapered angle having the etching profile on the tapered angle on an
off time of intermittent radio frequency bias power which is
time-modulated in the second embodiment;
[0038] FIG. 9 is a schematic diagram of a controller and a radio
frequency power supply according to the embodiment of the present
invention;
[0039] FIG. 10 is a schematic diagram of a controller and a radio
frequency bias power supply according to the embodiment of the
present invention;
[0040] FIG. 11 is a diagram illustrating an example of setting an
analog signal in the related art;
[0041] FIG. 12 is a diagram illustrating dependency of an etching
rate of Poly-Si on a duty ratio;
[0042] FIG. 13 is a diagram illustrating dependency of an etching
rate of Poly-Si on an average radio frequency power;
[0043] FIG. 14 is a schematic diagram of an A/D converter in a
third embodiment;
[0044] FIG. 15 is a diagram illustrating a concept of the present
invention; and
[0045] FIG. 16 is a diagram illustrating a method of processing
plasma in a fourth embodiment.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0046] Controlling parameters when time-modulating radio frequency
power supplied from at least one radio frequency power supply of a
radio frequency power supply for generating plasma and a radio
frequency power supply that supplies the radio frequency power to a
sample include a repetition frequency, a duty ratio, a time (for
example, an on-time) during a period when an amplitude of a
repetition waveform is high, and a time (for example, an off-time)
during a period when the amplitude of the repetition waveform is
low. The present invention is characterized in that at least one
control range of the controlling parameter is divided into at least
two different domains and the one domain is a domain that needs to
be controlled with high precision.
[0047] For example, when the radio frequency power supplied from
the radio frequency power supply that supplies the radio frequency
power to a sample by using the repetition frequency and the duty
ratio as the controlling parameters is time-modulated, the radio
frequency power may be generally divided into four domains as
illustrated in FIG. 15.
[0048] A domain A is a domain having a low repetition frequency
(for example, a repetition frequency of 1 to 100 Hz) and a higher
duty ratio than a low duty ratio (for example, a duty ratio of 10%
or less) and a domain B is a domain having a higher repetition
frequency than the low repetition frequency and the higher duty
ratio than the low duty ratio. Further, a domain C is a domain
having the low repetition frequency and the low duty ratio and a
domain D is a domain having the higher repetition frequency than
the low repetition frequency and the low duty ratio.
[0049] In addition, the low repetition frequency and the low duty
ratio are ranges that need to be controlled with high precision. As
a result, the present invention is characterized in that, when the
radio frequency power supplied from at least one radio frequency
power supply of the radio frequency power supply for generating
plasma and the radio frequency power supply that supplies the radio
frequency power to the sample is time-modulated, the controlling
domain of the time-modulation of the radio frequency power is
constituted by a plurality of different domains and at least one of
the plurality of different domains is at least one domain of the
domains A, C, and D.
[0050] First, when the radio frequency power supplied from the
radio frequency power supply that supplies the radio frequency
power to the sample is time-modulated and the duty ratio is set as
a control parameter, an embodiment in which a duty-ratio domain 1
constituted by the domains C and D and the duty-ratio domain 2
constituted by the domains A and B are set as control domains will
be described below.
First Embodiment
[0051] Hereinafter, embodiments of the present invention will be
described with reference to the accompanying drawings. FIG. 1 is a
schematic longitudinal cross-sectional view of an ECR plasma
etching apparatus using a microwave according to an embodiment of
the present invention. Further, like reference numerals refer to
like elements.
[0052] A shower plate 102 (made of, for example, quartz) for
introducing etching gas into a vacuum chamber 101 and a dielectric
window 103 (made of, for example, quartz) are installed and sealed
to form a processing chamber 104, on the top of the vacuum chamber
101 of which the top is opened. A gas supplying device 105 for
making the etching gas flow is connected to the shower plate 102.
Further, a vacuum exhaust device 106 is connected to the vacuum
chamber 101 through an exhaust opening/closing valve 117 and an
exhaust speed variable valve 118. The processing chamber 104 is
depressurized by driving the vacuum exhaust device 106 with the
exhaust opening/closing valve 117 being opened, to be in a vacuum
state. The pressure in the processing chamber 104 is adjusted to
desired pressure by the exhaust speed variable valve 118. The
etching gas is introduced into the processing chamber 104 from the
gas supplying device 105 through the shower plate 102 and exhausted
by the vacuum exhaust device 106 through the exhaust speed variable
valve 118. Further, a sample holder 111 which concurrently serves
as a sample stage is provided in a lower part of the vacuum chamber
101 which faces the shower plate 102.
[0053] In order to transmit power for generating plasma to the
processing chamber 104, a waveguide 107 configured to transmit an
electromagnetic wave is provided above the dielectric window 103.
The electromagnetic wave transmitted to the waveguide 107 is
oscillated from an electromagnetic wave generation power supply
109. Further, an effect of the embodiment is not particularly
limited to a frequency of the electromagnetic wave, but in the
embodiment, a microwave of 2.45 GHz is used. A magnetic field
generation coil 110 forming a magnetic field is provided outside
the processing chamber 104, and high-density plasma is generated in
the processing chamber 104 by interaction of the electromagnetic
wave oscillated from the electromagnetic wave generation power
supply 109 and the magnetic field formed by the magnetic field
generation coil 110, and etching processing is performed with
respect to a wafer 112 which is a sample disposed on the sample
holder 111.
[0054] Since the shower plate 102, the sample holder 111, the
magnetic field generation coil 110, the exhaust opening/closing
valve 117, the exhaust speed variable valve 118, and the wafer 112
are coaxially disposed on a central axis of the processing chamber
104, the flow of the etching gas, the radicals and ions generated
by plasma, and the reaction product generated by etching are
introduced and exhausted axially with respect to the wafer 112. The
coaxial disposition provides an effect to approximate wafer
in-plane uniformity of an etching rate and an etching profile to
axial symmetry and improve wafer processing uniformity.
[0055] The surface of the sample holder 111 is coated with a
sprayed film (not illustrated) and a DC power supply 116 is
connected to the sample holder 111 through a radio frequency filter
115. Further, a radio frequency (RF) bias power supply 114 is
connected to the sample holder 111 through a matching circuit 113.
The radio frequency bias power supply 114 includes a radio
frequency bias output unit 126 and a pulse generator 108 (see FIG.
2), and may selectively supply time-modulated intermittent radio
frequency power or continuous radio frequency power to the sample
holder ill. Further, the time-modulated intermittent radio
frequency bias power is controlled by a repetition frequency which
is the number of times when an application period (on-period) of
the radio frequency bias power and a non-application period
(off-period) of the radio frequency bias power are repeated per
unit time and a duty ratio which is an on-period per one cycle (the
reciprocal of the repetition frequency).
[0056] A controller 120 that controls etching processing using the
aforementioned ECR etching apparatus includes a personal computer
121 that processes a repetition frequency, a duty ratio, and
etching parameters such as a gas flow rate, processing pressure,
microwave power, coil current, and the like to perform etching,
which are input by an input means (not illustrated), a
microcomputer 122 that performs signal processing, and a
digital/analog converter (hereinafter, referred to as a D/A
converter 123) that converts a digital signal into an analog signal
(see FIG. 2).
[0057] Further, the radio frequency bias power supply 114 includes
an analog/digital converter (hereinafter, referred to as an A/D
converter 124) that converts the analog signal into the digital
signal, a signal processing unit 125 that processes a signal
transmitted from the microcomputer 122 and a signal transmitted
from the A/D converter 124, the pulse generator 108 that generates
pulse waveforms of the repetition frequency and the duty ratio
commanded from the signal processing unit 125, and the radio
frequency bias output unit 126 that outputs radio frequency bias
commanded from the signal processing unit (see FIG. 2).
[0058] Hereinafter, a function of the controller 120 when the
time-modulated intermittent radio frequency power is supplied from
the radio frequency bias power supply 114 to the sample holder will
be described with reference to FIG. 2.
[0059] The repetition frequency and the duty ratio which are input
into the personal computer 121 by the input means (not illustrated)
are processed by the microcomputer 122 as the digital signals and
converted into the analog signals through the D/A converter 123 to
be transmitted to the radio frequency bias power supply 114. The
analog signals received by the radio frequency bias power supply
114 are converted into the digital signals by the A/D converter
124, which are processed by the signal processing unit 125, and as
a result, the radio frequency bias power and the pulse waveform are
output from the radio frequency bias output unit 126 and the pulse
generator 108, respectively. The output pulse waveform overlaps
with the output radio frequency bias power to supply the
time-modulated intermittent radio frequency power from the radio
frequency bias power supply 114 to the sample holder 111.
[0060] Subsequently, a case in which a duty ratio of the radio
frequency bias power supply 114 is used by setting the range of 0
to 100% every 0.5%, and particularly, a case where a domain of a
duty ratio of 0 to 10% is controlled with high resolution will be
described.
[0061] The domain of the duty ratio of 0 to 10% is set as a channel
1 and a domain of a duty ratio of 10.5 to 100% is set as a channel
2. Further, the D/A converter 123 and the A/D converter 124 of 12
bits are used, and a voltage value of the analog signal is set to a
range of .+-.10 V. In addition, when the analog signal is in the
range of .+-.10 V, the analog signal of 0 to 10 V is generally
used. The range of the analog voltage value may be set to a
predetermined range, but in the embodiment, 0 to 10 V which is
generally used is used.
[0062] For example, when a duty ratio of 2% is input into the
personal computer 121, both signals of the channel 1 and the
channel 2 are periodically transmitted to the A/D converter 124
from the microcomputer 122 through the D/A converter 123 with
timings of both sides deviating from each other, as illustrated in
FIG. 3A. The signal processing unit 125 selects the signal of the
channel 1 from the signals of the channel 1 and the channel 2
transmitted from the A/D converter 124 by synchronizing a timing A
(the channel 1) and signal reception with each other according to a
channel switching signal for selecting the channel 1 transmitted
from the microcomputer 122.
[0063] The signal processing unit 125 that selects the signal of
the channel 1 generates a pulse waveform of a duty ratio of 2% from
the pulse generator 108 and outputs time-modulated intermittent
radio frequency power of the duty ratio of 2% from the radio
frequency bias power supply 114.
[0064] Further, as another method for the signal processing unit
125 to select the channel, a method of judging which channel will
be selected by the channel switching signal and acquiring a signal
of a predetermined port may be used when a plurality of
input/output terminals (hereinafter, referred to as ports) is
provided in the A/D converter 124, as illustrated in FIG. 4A. For
example, in the case of the duty ratio of 2%, the signal processing
unit 125 is judged to select a port 1 (FIG. 4A).
[0065] Further, only a used channel may be transmitted to the A/D
converter 124 from the microcomputer 122 through the D/A converter
123. For example, when the duty ratio of 2% is set, only the signal
of the channel 1 is transmitted and the signal of the channel 2 is
not transmitted. When the A/D converter 124 has a configuration
illustrated in FIG. 4A, the signal processing unit 125 judges
whether there is a reception signal of a port and thus may select
the port 1, that is, the channel 1 in a state in which the port 1
has a signal and the port 2 has no signal. In this case, since the
channel switching signal is not required, the A/D converter 124 may
have a configuration of FIG. 5.
[0066] However, etching may be continuously processed in a
plurality of steps, and when domains (different channels) of
different duty ratios are used between the respective steps, the
channel may be changed more rapidly in the method (FIG. 4A) of
selecting the channel by using the switching signal in the state in
which signals of different channels are transmitted periodically at
all times while transmission timings deviate from each other than a
method not requiring the switching signal, and thus the channel
selecting method of FIG. 4A is appropriate.
[0067] Subsequently, duty ratios and resolutions of the channel 1
and the channel 2 in the embodiment will be described.
[0068] In general, the resolution of the duty ratio is determined
by processing capability and ranges of the domains of the duty
ratios of the D/A converter 123 and the A/D converter 124. The D/A
converter 123 and the A/D converter 124 of 12 bits may handle
signals of 4096 digits. The digit means a binary digit number. In
this case, signal values of 4096 types may be handled in the range
of the analog signal of .+-.10 V. The analog signal is in the range
of 0 to 10 V in the embodiment and signal values of 2048 types may
be handled.
[0069] In the embodiment, since a use range of the duty ratio of
the channel 1 is set every 0.5% in the range of 0 to 10%, the
resolution is approximately 0.01%. Further, since a use range of
the duty ratio of the channel 2 is 10.5 to 100%, the resolution is
approximately 0.09%. In addition, since the signals of 2048 digits
may be handled as the use range of the analog signal is 10 V, 1
digit corresponds to approximately 4.9 mV. That is, when the analog
signal is at approximately 4.9 mV, the duty ratio shows
approximately 0.01% in the case of the channel 1 and the duty ratio
shows approximately 0.09% in the case of the channel 2. As a
result, when an error of 4.9 mV occurs in the analog signal, an
error of approximately 0.01% occurs in the case of the channel 1
and an error of approximately 0.09% occurs in the case of the
channel 2.
[0070] For example, when the duty ratio is 2% (channel 1) and the
repetition frequency is 10 Hz, the on-time is 2.0 ms. When noise of
approximately 0.05% (5 mV) occurs in the analog signal, an error of
approximately 0.01% or more occurs in the duty ratio. When the
repetition frequency is 10 Hz at a duty ratio of 2.01%, the on-time
is 2.01 ms and the error is just 0.01 ms.
[0071] Further, when the duty ratio is 90% (channel 2) and the
repetition frequency is 10 Hz, the on-time is 9.0 ms. When noise of
approximately 0.09 (5 mV) occurs in the analog signal by noise, the
analog signal is processed as a signal of approximately 90.09%, and
the error is 0.09 ms at the on-time of 9.09 ms, and thus the error
is just 0.09 ms.
[0072] Accordingly, in the embodiment, as described above, the use
domain range of the duty ratio is divided into a domain of a duty
ratio requiring the precision of the resolution and a domain of a
duty ratio not particularly requiring the precision of the
resolution to control the duty ratio with high precision in a user
domain where a high range of the duty ratio.
[0073] Further, in the embodiment, since a setting unit of the duty
ratio is 0.5%, when the domain of the duty ratio of the channel 1
is selected, approximately 102 digits, that is, approximately 500
mV may be allocated to 0.5% and the error by noise, and the like
may be excluded.
[0074] Further, since the resolution of the channel 1 is 0.01%, the
duty ratio may be controlled by setting the setting unit of the
duty ratio of the channel 1 to 0.5% or less. In addition, in the
embodiment, the example in which the use domain of the duty ratio
is divided into two has been described, but the use domain of the
duty ratio may be divided into two or more. As the number of
divisions is increased, the resolution of the each use domain may
be improved.
[0075] Further, in the embodiment, the analog voltage value has
been in the use range of 0 to 10 V, but since the resolution is
improved similarly even in a predetermined use range, the present
invention may be applied even in the predetermined voltage range as
the use range of the analog voltage value and the same effect as
the present invention is obtained.
[0076] Further, in the embodiment, the example in which the use
domain of the duty ratio is divided into two has been described,
but the use domain of the duty ratio may be extended by combining
two or more different duty ratio domains, as illustrated in FIG.
6A. As such, by combining the different duty ratio domains, the use
domain of the duty ratio may be extended and control precision of
the respective duty ratio domains may be improved.
[0077] Further, when the on-time of the time-modulated intermittent
radio frequency bias power is short, it is difficult to match the
radio frequency bias power. The on-time is determined by the duty
ratio and the repetition frequency, but in the case where the
repetition frequency is a high frequency of 2000 Hz, when the duty
ratio is low, the on-time is too short, which influences matching
performance and may disable the radio frequency bias power to be
applied to the sample holder 111.
[0078] As a result, when the duty ratio of the duty ratio domain of
the channel 1 is used, it is preferable to generally use the
repetition frequency of 200 Hz or less. Further, in order to
prevent an influence on matching due to the short on-time, it is
preferable to set a minimum value of the on-time when an excellent
operation is available in advance and provide a function to judge
whether to exert an influence on matching or whether there is the
on-time.
[0079] Subsequently, a plasma processing method of etching the
wafer 112 by using the microwave ECR plasma etching apparatus
according to the embodiment will be described. Further, the plasma
processing method will be described, when the use range of the duty
ratio of the time-modulated intermittent radio frequency bias is
divided into two duty ratio domains and constituted by two duty
ratio domains of the channel 1 (0 to 10%) and the channel 2 (10.5
to 100%).
[0080] The time-modulated intermittent radio frequency bias is used
to control the concentration of the reaction product and control
etching performance, but a large effect is acquired particularly
when the off-time is equivalent to the residence time of the
reaction product. Etching is performed and the reaction product is
continuously generated during a period of the on-time of the
time-modulated intermittent radio frequency bias. When the
time-modulated intermittent radio frequency bias is turned off,
etching is not performed and the reaction product is exhausted. In
the case of the general plasma etching apparatus, the residence
time of the reaction product is in the range of 10 ms to 1000 ms at
processing pressure in the range of 0.1 Pa to 10 Pa.
[0081] As one example, a case in which the residence time of the
reaction product is 80 ms will be described. In the continuous
radio frequency bias, the concentration of the reaction product
increases more monotonously than that at the time of starting
etching. Etching time dependency of the concentration of the
reaction product is illustrated in FIG. 7A, when the residence time
of the reaction product is 80 ms, the on-time of the time-modulated
intermittent radio frequency bias is 10 ms, and the off-time is 10
ms. When the off-time is shorter than the residence time of the
reaction product, the reaction product remains, and thus the
concentration of the reaction product increases as time elapsed.
Subsequently, etching time dependency of the concentration of the
reaction product is illustrated in FIG. 7B, when the residence time
of the reaction product is the same as the off time by setting the
residence time of the reaction product to 80 ms, the on-time of the
time-modulated intermittent radio frequency bias to 10 ms, and the
off-time to 80 ms.
[0082] Since the reaction product generated within the on-time is
exhausted during the off-time and does not remain, the
concentration of the reaction product may be made to be low. The
concentration of the reaction product may be lowered by providing a
sufficiently long off-time with respect to the reaction product
generated during the on-time. Since the duty ratio is a ratio
between the on-time and the off-time, lengthening the off-time is
equivalent to lowering the duty ratio. An influence of the reaction
product may be suppressed by lowering the duty ratio.
[0083] Subsequently, FIG. 8A illustrates dependence of a
selectivity of a SiO.sub.2 film, which is a hard mask, on a duty
ratio when Ar gas, SF.sub.6 gas, and O.sub.2 gas are mixed and a
line pattern of tungsten is etched by fixing the repetition
frequency to 10 Hz.
[0084] A change in the selectivity is gentle when the duty ratio is
higher than 10%, but the selectivity is rapidly raised when the
duty ratio is equal to or less than 10%. The reason is that the
on-time is short and the off-time is long when the duty ratio is
low, and thus the concentration of the reaction product decreases.
It is considered that a reaction product when tungsten is etched
with SF.sub.6 gas is generally WFx (x=1 to 6), and the like, but F
(fluorine) is generated by redissociating the reaction products
thereof, attached to the SiO.sub.2 film, reacts as SiF.sub.4, and
the like, and etched with SiO.sub.2 to lower a SiO.sub.2
selectivity.
[0085] The duty ratio of 10% or less needs to be controlled with
high precision in order to control the selectivity with high
precision. To this end, a channel of a duty ratio is divided into
two domains of a channel of 10% or less and a channel higher than
10% as illustrated in FIG. 8A to perform both a wide control and a
high-precision control.
[0086] Further, a plasma processing method other than the above
method will be described below. By controlling the time-modulated
intermittent radio frequency bias with high precision, the etching
performance may be controlled with high precision. The etching
performance may be changed with variation as time elapsed in a
chamber.
[0087] For example, in the case where the etching rate deteriorates
whenever processed sheets overlap with each other, set values of
the processing time are the same as each other, and as a result, a
total etching amount decreases and a failure may be caused.
Accordingly, on the contrary, by increasing the etching rate
whenever the processed sheets overlap with each other, the total
etching amount may be constant. By controlling the on-time, the
off-time, the frequency, the duty ratio, and the like of the
time-modulated intermittent radio frequency bias with high
precision, the etching performance may be controlled as time
elapsed.
[0088] FIG. 13 illustrates the relationship between an etching rate
and average radio frequency power of Poly-Si. It can be seen that
even a slight etching rate which is smaller than 20 nm/min may be
controlled by changing the average radio frequency power. In FIG.
13, the duty ratio and the radio frequency power value illustrated
in FIG. 12 are converted into the average radio frequency
power.
[0089] As illustrated in FIG. 13, the average radio frequency power
may be controlled by changing the duty ratio. Accordingly, since
the etching rate may be controlled with high precision by
controlling the duty ratio with high precision, the etching
performance may be appropriately controlled as time elapsed.
[0090] Further, in the plasma processing method, the use frequency
range of the duty ratio of the time-modulated intermittent radio
frequency bias is divided into two domains, but even when the use
domain of the duty ratio is divided into two or more, the same
effect as the plasma processing method is acquired.
[0091] Further, even when the use domain of the duty ratio, the
repetition frequency, the on-time, and the off-time is formed by
combining two or more different domains, the same effect as the
plasma processing method is acquired.
[0092] Since the present invention has the above configuration, the
time-modulated intermittent radio frequency bias power may be
supplied to a sample holder by the duty ratio controlled by a wide
duty ratio with high precision, and thus etching may be performed
with high precision in various etching processes.
[0093] Further, in the embodiment, the plurality of channels of the
duty ratio have been switched by using the channel switching
signals, but a method using a plurality of radio frequency bias
power supplies may also be adopted. For example, when the channel
of the duty ratio is divided into two as illustrated in FIG. 9, two
radio frequency power supplies that output the time-modulated
intermittent radio frequency bias power at duty ratios in different
control ranges are provided, respectively, and a first radio
frequency power supply 127 and a second radio frequency power
supply 128 are switched to each other by a radio frequency power
supply selection signal to thereby supply the time-modulated
intermittent radio frequency bias power of the duty ratio
controlled by the wide duty ratio with high precision to the
placing electrode.
[0094] Further, as illustrated in FIG. 10, a plurality of pulse
generators (a first pulse generator 129 and a second pulse
generator 130, and the like) that generate pulse waveforms of the
duty ratios in the different control ranges, respectively may be
provided in the radio frequency bias power supply, instead of the
plurality of radio frequency power supplies. Subsequently, when the
radio frequency power supplied from the radio frequency power
supply that supplies the radio frequency power to the sample is
time-modulated and the repetition frequency is set as the control
parameter, an embodiment in which the repetition frequency domain 1
constituted by the domains A and C and the repetition frequency
domain 2 constituted by the domains B and D are set as the control
domain will be described below.
Second Embodiment
[0095] Hereinafter, an embodiment of the present invention will be
described with reference to the accompanying drawings. FIG. 1 is a
schematic longitudinal cross-sectional view of an ECR plasma
etching apparatus using a microwave according to an embodiment of
the present invention. Further, like reference numerals refer to
like elements.
[0096] A shower plate 102 (made of, for example, quartz) for
introducing etching gas into a vacuum chamber 101 and a dielectric
window 103 (made of, for example, quartz) are installed and sealed
to form a processing chamber 104, above the vacuum chamber 101 of
which the top is opened. A gas supplying device 105 for making the
etching gas flow is connected to the shower plate 102. Further, a
vacuum exhaust device 106 is connected to the vacuum chamber 101
through an exhaust opening/closing valve 117 and an exhaust speed
variable valve 118. The processing chamber 104 is depressurized by
driving the vacuum exhaust device 106 with the exhaust
opening/closing valve 117 being opened, to be in a vacuum
state.
[0097] The pressure in the processing chamber 104 is adjusted to
desired pressure by the exhaust speed variable valve 118. The
etching gas is introduced into the processing chamber 104 from the
gas supplying device 105 through the shower plate 102 and exhausted
by the vacuum exhaust device 106 through the exhaust speed variable
valve 118. A sample holder 111 which is a sample stage is provided
in a lower part of the vacuum chamber 101 which faces the shower
plate 102.
[0098] In order to transmit power for generating plasma to the
processing chamber 104, a waveguide 107 configured to transmit an
electromagnetic wave is provided above the dielectric window 103.
The electromagnetic wave transmitted to the waveguide 107 is
oscillated from an electromagnetic wave generation power supply
109. Further, an effect of the embodiment is not particularly
limited to a frequency of the electromagnetic wave, but in the
embodiment, a microwave of 2.45 GHz is used. A magnetic field
generation coil 110 forming a magnetic field is provided outside
the processing chamber 104, and high-density plasma is generated in
the processing chamber 104 by interaction of the electromagnetic
wave oscillated from the electromagnetic wave generation power
supply 109 and the magnetic field formed by the magnetic field
generation coil 110, and etching processing is performed with
respect to a wafer 112 which is a sample disposed on the sample
holder 111.
[0099] Since the shower plate 102, the sample holder ill, the
magnetic field generation coil 110, the exhaust opening/closing
valve 117, the exhaust speed variable valve 118, and the wafer 112
are coaxially disposed on a central axis of the processing chamber
104, the flow of the etching gas, the radicals and ions generated
by plasma, and the reaction product generated by etching are
introduced and exhausted axially with respect to the wafer 112. The
coaxial disposition provides an effect to approximate wafer
in-plane uniformity of an etching rate and an etching profile to
axial symmetry and improve wafer processing uniformity.
[0100] The surface of the sample holder 111 is coated with a
sprayed film (not illustrated) and a DC power supply 116 is
connected to the sample holder 111 through a radio frequency filter
115. Further, a radio frequency bias power supply 114 is connected
to the sample holder 111 through a matching circuit 113. The radio
frequency bias power supply 114 includes a radio frequency bias
output unit 126 and a pulse generator 108 (see FIG. 2), and may
selectively supply time-modulated intermittent radio frequency
power or continuous radio frequency power to the sample holder
111.
[0101] Further, the time-modulated intermittent radio frequency
bias power is controlled by a repetition frequency which is the
number of times when an application period (on-period) of the radio
frequency bias power and a non-application period (off-period) of
the radio frequency bias power are repeated per unit time and a
duty ratio which is an on-period per one cycle (the reciprocal of
the repetition frequency).
[0102] A controller 120 that controls etching processing using the
aforementioned ECR etching apparatus includes a personal computer
121 that processes a repetition frequency, a duty ratio, and
etching parameters such as a gas flow rate, processing pressure,
microwave power, coil current, and the like to perform etching,
which are input by an input means (not illustrated), a
microcomputer 122 that performs signal processing, and a
digital/analog converter (hereinafter, referred to as a D/A
converter 123) that converts a digital signal into an analog signal
(see FIG. 2).
[0103] Further, the radio frequency bias power supply 114 includes
an analog/digital converter (hereinafter, referred to as an A/D
converter 124) that converts the analog signal into the digital
signal, a signal processing unit 125 that processes a signal
transmitted from the microcomputer 122 and a signal transmitted
from the A/D converter 124, the pulse generator 108 that generates
pulse waveforms of the repetition frequency and the duty ratio
commanded from the signal processing unit 125, and the radio
frequency bias output unit 126 that outputs radio frequency bias
commanded from the signal processing unit (see FIG. 2).
[0104] Hereinafter, a function of the controller 120 when the
time-modulated intermittent radio frequency power is supplied from
the radio frequency bias power supply 114 to the sample holder will
be described with reference to FIG. 2.
[0105] The repetition frequency and the duty ratio which are input
into the personal computer 121 by the input means (not illustrated)
are processed by the microcomputer 122 as the digital signals and
converted into the analog signals through the D/A converter 123 to
be transmitted to the radio frequency bias power supply 114.
[0106] The analog signals received by the radio frequency bias
power supply 114 are converted into the digital signals by the A/D
converter 124, which are processed by the signal processing unit
125, and as a result, the radio frequency bias power and the pulse
waveform are output from the radio frequency bias output unit 126
and the pulse generator 108, respectively. The output pulse
waveform overlaps with the output radio frequency bias power to
supply the time-modulated intermittent radio frequency power from
the radio frequency bias power supply 114 to the sample holder
111.
[0107] Subsequently, a case in which the repetition frequency of
the radio frequency bias power supply 114 is used by setting the
range of 1 to 2000 Hz every 1 Hz, and particularly, a case where a
frequency band of 1 to 119 Hz is controlled with high resolution
will be described.
[0108] The frequency band of 1 to 119 Hz is set as a channel 1 and
a frequency band of 120 to 2000 Hz is set as a channel 2. Further,
the D/A converter 123 and the A/D converter 124 of 12 bits are
used, and a voltage value of the analog signal is set to a range of
.+-.10 V. In addition, when the analog signal is in the range of
.+-.10 V, the analog signal of 0 to 10 V is generally used.
[0109] For example, when a repetition frequency of 60 Hz is input
into the personal computer 121, both signals of the channel 1 and
the channel 2 are periodically transmitted to the A/D converter 124
from the microcomputer 122 through the D/A converter 123 with
timings of both sides deviating from each other, as illustrated in
FIG. 3B.
[0110] The signal processing unit 125 selects the signal of the
channel 1 from the signals of the channel 1 and the channel 2
transmitted from the A/D converter 124 by synchronizing a timing A
(the channel 1) and signal reception with each other according to a
channel switching signal for selecting the channel 1 transmitted
from the microcomputer 122. The signal processing unit 125 that
selects the signal of the channel 1 generates a pulse waveform of
60 Hz from the pulse generator 108 and outputs time-modulated
intermittent radio frequency power of the repetition frequency of
60 Hz from the radio frequency bias power supply 114.
[0111] Further, as another method for the signal processing unit
125 to selecting the channel, a method of judging which channel
will be selected by the channel switching signal and acquiring a
signal of a predetermined port may be used when a plurality of
input/output terminals (hereinafter, referred to as ports) is
provided in the A/D converter 124, as illustrated in FIG. 4B. For
example, in the case of the repetition frequency of 60 Hz, the
signal processing unit 125 is judged to select a port 1 (FIG.
4B).
[0112] Further, only a used channel may be transmitted to the A/D
converter 124 from the microcomputer 122 through the D/A converter
123. For example, when a repetition frequency of 10 Hz is set, only
the signal of the channel 1 is transmitted and the signal of the
channel 2 is not transmitted. When the A/D converter 124 has a
configuration illustrated in FIG. 4B, the signal processing unit
125 judges whether there is a reception signal of a port and thus
may select the port 1, that is, the channel 1 in a state in which
the port 1 has a signal and the port 2 has no signal. In this case,
since the channel switching signal is not required, the A/D
converter 124 may have a configuration of FIG. 5.
[0113] However, etching may be continuously processed in a
plurality of steps, and when frequencies (different channels) of
different frequency bands are used between the respective steps,
the channel may be changed more rapidly in the method (FIG. 4B) of
selecting the channel by using the switching signal in the state in
which signals of different channels are transmitted periodically at
all times while transmission timings deviate from each other than a
method not requiring the switching signal, and thus the channel
selecting method of FIG. 4B is appropriate.
[0114] Subsequently, frequency resolutions of the channel 1 and the
channel 2 in the embodiment will be described.
[0115] In general, the frequency resolution is determined by
processing capability and ranges of the frequency bands of the D/A
converter 123 and the A/D converter 124. The D/A converter 123 and
the A/D converter 124 of 12 bits may handle signals of 4096 digits.
The digit means a binary digit number. In this case, signal value
of 4096 types may be handled in the range of the analog signal of
.+-.10 V. Since 0 to 10 V is generally used as the analog signal,
signal values of 2048 types may be handled. In the embodiment,
since a use range of the repetition frequency of the channel 1 is 1
to 119 Hz, the resolution is approximately 0.058 Hz. Further, since
a use range of the repetition frequency of the channel 2 is 120 to
2000 Hz, the resolution is approximately 0.92 Hz.
[0116] In addition, since the use range of the analog signal is 10
V and the signals of 2048 digits may be handled, one digit
corresponds to approximately 4.9 mV. That is, when the analog
signal is at approximately 4.9 mV, the repetition frequency shows
approximately 0.058 Hz in the case of the channel 1 and the
repetition frequency shows approximately 0.92 Hz in the case of the
channel 2. As a result, when an error of 4.9 mV occurs in the
analog signal, an error of approximately 0.058 Hz occurs in the
case of the channel 1 and an error of approximately 0.92 Hz occurs
in the case of the channel 2.
[0117] For example, when the repetition frequency is 10 Hz (channel
1) and the duty ratio is 10%, the off-time is 90 ms. When noise of
approximately 0.05% (5 mV) occurs in the analog signal, an error of
approximately 0.058 Hz or more occurs in the repetition frequency.
When the repetition frequency is 10.058 Hz and the duty ratio is
10%, the off-time is 89.5 ms and the error is just 0.56%. Further,
when the repetition frequency is 1000 Hz (channel 2) and the duty
ratio is 10%, the off-time is 0.9 ms. When noise of approximately
0.05% (5 mV) occurs in the analog signal by noise, the analog
signal is processed as a signal of approximately 1001 Hz, and the
off-time is 0.899 ms and the error is 0.001 ms, and thus the error
is just 0.1%.
[0118] Accordingly, in the embodiment, as described above, by
dividing the use frequency range of the repetition frequency into
the frequency band requiring the precision of the resolution and
the frequency band not particularly requiring the precision of the
resolution, the repetition frequency may be controlled with high
precision in a wide frequency band of the repetition frequency.
[0119] Further, in the embodiment, since a setting unit of the
repetition frequency is 1 Hz, when the frequency band of the
channel 1 is selected, approximately 20 digits may be allocated to
1 Hz and the error by noise, and the like may be excluded.
[0120] Further, since the resolution of the channel 1 is 0.058 Hz,
the repetition frequency may be controlled by setting the setting
unit of the repetition frequency of the channel 1 to 1 Hz or
less.
[0121] Further, in the embodiment, the example in which the
frequency band of the repetition frequency is divided into two has
been described, but the frequency band may be divided into two or
more. As the number of divisions is increased, the resolution of
each frequency band may be improved.
[0122] Further, in the embodiment, the example in which the
frequency band of the repetition frequency is divided into two has
been described, but the use frequency range of the repetition
frequency may be extended by combining two or more different
frequency bands, as illustrated in FIG. 6B. As such, the use
frequency range of the repetition frequency is extended by
combining different frequency bands to thereby improve the
precision of each frequency band.
[0123] In addition, in the embodiment, the analog voltage value has
been in the use range of 0 to 10 V, but since the resolution is
improved similarly even in a predetermined use range, the present
invention may be applied even in the predetermined voltage range as
the use range of the analog voltage value and the same effect as
the present invention is obtained.
[0124] Further, when the on-time of the time-modulated intermittent
radio frequency bias power is short, it is difficult to match the
radio frequency bias power. The on-time is determined by the duty
ratio and the repetition frequency, and in the case of a low duty
ratio of 20% or less, the on-time of the repetition frequency in
the radio frequency band of the channel 2 is too short, and thus
the radio frequency bias power may not be applied to the sample
holder 111. As a result, when the repetition frequency in the
frequency band of the channel 2 is used, it is preferable to use
the duty ratio of 20% or more.
[0125] Subsequently, a plasma processing method of etching the
wafer 112 by using the microwave ECR plasma etching apparatus
according to the embodiment will be described.
[0126] Further, the plasma processing method will be described,
when the use frequency range of the repetition frequency of the
time-modulated intermittent radio frequency bias is divided into
two frequency bands and constituted by two frequency bands of the
channel 1 (1 to 119 Hz) and the channel 2 (120 to 2000 Hz).
[0127] The time-modulated intermittent radio frequency bias is used
to control the concentration of the reaction product and control
etching performance, but a large effect is acquired particularly
when the off-time is equivalent to the residence time of the
reaction product. Etching is performed and the reaction product is
continuously generated during a period of the on-time of the
time-modulated intermittent radio frequency bias. When the
time-modulated intermittent radio frequency bias is turned off,
etching is not performed and the reaction product is exhausted. In
the case of the general plasma etching apparatus, the residence
time of the reaction product is in the range of 10 ms to 1000 ms at
processing pressure in the range of 0.1 Pa to 10 Pa.
[0128] As one example, a case in which the residence time of the
reaction product is 80 ms will be described. In the continuous
radio frequency bias, the concentration of the reaction product
increases more monotonously than that at the time of starting
etching. Etching time dependency of the concentration of the
reaction product is illustrated in FIG. 7A, when the residence time
of the reaction product is 80 ms, the on-time of the time-modulated
intermittent radio frequency bias is 10 ms, and the off-time is 10
ms. When the off-time is shorter than the residence time of the
reaction product, the reaction product remains, and thus the
concentration of the reaction product increases as time
elapsed.
[0129] Subsequently, etching time dependency of the concentration
of the reaction product is illustrated in FIG. 7B, when the
residence time of the reaction product is the same as the off time
by setting the residence time of the reaction product to 80 ms, the
on-time of the time-modulated intermittent radio frequency bias to
10 ms, and the off-time to 80 ms. Since the reaction product
generated within the on-time is exhausted during the off-time and
does not remain, the concentration of the reaction product may be
made to be low. By setting the off-time to the residence time of
the reaction product or more, the concentration of the reaction
product may be lowered.
[0130] Subsequently, FIG. 8B illustrates dependency of a tapered
angle of an etching profile of a line on a repetition frequency
when a line of a silicon nitride layer is etched by fixing a duty
ratio to 20%. As the repetition frequency becomes low, the etching
profile is close to verticality. The off-time is determined by the
repetition frequency and the duty ratio, and the result of FIG. 8B
is acquired because the off-time is lengthened, and thus the
concentration of the reaction product is lowered and the amount of
the reaction product attached is decreased.
[0131] FIG. 8C illustrates dependency of the tapered angle on the
off-time instead of the dependency of the tapered angle on the
repetition frequency in FIG. 8B and it can be seen from FIG. 8C
that the tapered angle may be controlled by lengthening the
off-time. In particular, an etching profile which is vertical in
the off-time range of 10 to 1000 ms may be acquired.
[0132] As such, by setting the off-time to the residence time of
the reaction product or more, the concentration of the reaction
product may be reduced. In order to lengthen the off-time, the
repetition frequency needs to be lowered and the duty ratio needs
to be lowered. For example, FIG. 7B illustrates an example in which
the wafer 112 is plasma-etched by applying the time-modulated
intermittent radio frequency bias power, in which the repetition
frequency is 11.1 Hz and the duty ratio is 11.1%, to the sample
holder 111.
[0133] Accordingly, in the embodiment, even in the low-frequency
repetition frequency band in which the off-time may be lengthened,
the frequency may be controlled with high precision, and thus the
concentration of the reaction product may be controlled with high
precision. Therefore, the etching profile may be controlled with
high precision.
[0134] Further, the radio frequency repetition frequency band may
need to be used according to a type of an etched film, a target
etching process, an etching condition, and the like. However, in
the case of the radio frequency repetition frequency, since the
on-time and the off-time are very short, the frequency resolution
need not be particularly higher than that in the low-frequency
repetition frequency.
[0135] Further, the type of the etching process is various and not
vertical processing but the taper profile may be needed according
to the process. For example, as the etching process, there is
shallow trench isolation (STI) (hereinafter, referred to as STI)
etching. After the STI etching, the taper profile is generally
required for embedding. When the wafer is processed in the taper
profile, the repetition frequency is preferably higher in the case
where an etching characteristic as illustrated in FIG. 8B is
provided. In order to extensively deal with various processes of
semiconductor fabrication, it is preferable that the repetition
frequency may be widely used.
[0136] Further, in the plasma processing method, the use frequency
range of the repetition frequency of the time-modulated
intermittent radio frequency bias is divided into two frequency
bands, but even when the use frequency range of the repetition
frequency is divided into two or more, the same effect as the
plasma processing method is acquired.
[0137] Further, even when the use frequency range of the repetition
frequency is configured by combining two or more different
frequency bands, the same effect as the plasma processing method
may be acquired.
[0138] Since the present invention has the above configuration, the
time-modulated intermittent radio frequency bias power of the
repetition frequency controlled with high precision in the wide
frequency band may be supplied to the placing electrode, and thus
etching may be performed with high precision in various etching
processes.
[0139] Further, in the embodiment, the plurality of channels of the
frequency band of the repetition frequency have been switched by
using the channel switching signals, but a method using a plurality
of radio frequency bias power supplies may also be adopted. For
example, as illustrated in FIG. 9, in the case of two channels, two
radio frequency power supplies that output the time-modulated
intermittent radio frequency bias power at the repetition
frequencies of different frequency bands are provided,
respectively, and a first radio frequency power supply 127 and a
second radio frequency power supply 128 are switched to each other
by a radio frequency power supply selection signal to thereby
supply the time-modulated intermittent radio frequency bias power
of the repetition frequency controlled with high precision in the
wide frequency band to the placing electrode.
[0140] Further, as illustrated in FIG. 10, a plurality of pulse
generators (a first pulse generator 129 and a second pulse
generator 130, and the like) that generate pulse waveforms of the
repetition frequency in the different frequency bands, respectively
may be provided in the radio frequency bias power supply, instead
of the plurality of radio frequency power supplies.
[0141] Subsequently, an embodiment different from the second
embodiment, in which the repetition frequency is controlled with
high precision in the wide frequency band of the repetition
frequency, will be described below.
Third Embodiment
[0142] In FIG. 8B, a change in tapered angle is large at the low
repetition frequency and the change in tapered angle is small at
the high repetition frequency. In this case, settable values may be
limited and precision may be improved by setting the frequency
every 1 Hz in the range of 1 to 10 Hz, every 10 Hz in the range of
10 to 100 Hz, and every 100 Hz in the range of 100 to 1000 Hz. In
this method, as the number of settable frequencies increases, the
precision becomes low and the degree of setting freedom is
small.
[0143] Therefore, a method using a fundamental frequency has been
developed. An embodiment thereof will be described below. In the
configuration illustrated in FIG. 5, the repetition frequency is
input into the personal computer 121 of the controller 120. The
repetition frequency is calculated as an N layout with the
fundamental frequency in the personal computer 121 and sent to the
microcomputer 122. In the embodiment, the fundamental frequency is
in the range of 0 to 100 Hz and is set every 1 Hz. The N layout is
set to 1, 10, and 100 in the embodiment.
[0144] As described above, the D/A converter 123 and the A/D
converter 124 of 12 bits according to the embodiment may handle
signals of 4096 digits. The analog signal is in the range of 0 to
10 V in the embodiment and signal values of 2048 types may be
handled. When the fundamental frequency may be set every 1 Hz in
the range of 0 to 100 Hz, the fundamental frequency per one digit
is approximately 0.05 and 20 digits may be allocated in order to
set the fundamental frequency every 1 Hz.
[0145] Since one digit is 4.9 mV, 98 mV is allocated when the
fundamental frequency is set every 1 Hz. The N layout includes
three types of 1, 10, and 100 and may be divided into three, and
resolutions of both analog voltage and allocated digits are
significantly high. By adopting a method using a multiplication of
the fundamental frequency and the N layout as the repetition
frequency, the repetition frequency may correspond to 0 to 10000 Hz
in the embodiment.
[0146] The frequency is set every 1 Hz in the range of 0 to 100 Hz,
every 10 Hz in the range of 110 to 1000 Hz, and every 100 Hz in the
range of 1100 to 10000 Hz. When sensitivity to the repetition
frequency having a characteristic of etching performance is low in
the case where the repetition frequency is high as described above,
an influence is small even though a setting pitch is large as the
repetition frequency becomes high. Further, in the embodiment,
since the resolution is 0.05 Hz in the range of 0 to 100 Hz, 0.5 Hz
in the range of 110 to 1000 Hz, and 5 Hz in the range of 1100 to
10000 Hz, and is much smaller than the setting pitch, a possibility
that the analog signal will be influenced by noise is small.
[0147] For example, since 20 digits are allocated to 1 Hz at the
setting pitch of 1 Hz in the range of 0 to 100 Hz, 98 mV is
allocated to 1 Hz. That is, when 98 mV or more does not deviate in
noise, an error of 1 Hz does not occur. When the repetition
frequency corresponds to 0 to 10000 Hz in the related art, one
digit is 4.9 Hz, and the noise is 4.9 mV and deviates by 4.9 Hz. By
the method of the embodiment, the influence of noise may be
significantly reduced. Hereinafter, a detailed example of setting
will be described.
[0148] A case in which 1000 Hz is input as the repetition frequency
will be described. A case in which 1000 Hz is input into the
personal computer 121 of FIG. 5 will be described. When 1000 Hz is
input into the personal computer 121 of FIG. 5, the fundamental
frequency is 100 Hz and the N layout is 10. Although there is also
a method of setting the fundamental frequency to 10 Hz and the N
layout to 100 at the time of setting 1000 Hz, the fundamental
frequency is preferred. Since a pitch or a setting range of a set
value may be set and changed by a condition or hardware in the N
layout, the fundamental frequency is preferably preferred in order
to simplify a program of software.
[0149] Further, when only one is needed as the N layout, the signal
line need not be used, and thus hardware is simplified, and even in
this case, since handling may be performed without changing
software, generalization of software is also high when the
fundamental frequency is preferred.
[0150] The fundamental frequency and the N layout calculated in the
personal computer 121 are input into the A/D converter 124 in the
radio frequency power supply as illustrated in FIG. 14 via the D/A
converter 123. A calculation of multiplying the fundamental
frequency and the N layout is performed by using the signal
processing unit in the radio frequency bias power supply 114, and
the repetition frequency is determined.
[0151] Further, the N layout may be used as the channel switching
signal illustrated in FIG. 2 or 10. When the fundamental frequency
is in the range of 0 to 100 Hz and the N layout is set to 1 and
100, the repetition frequency may be calculated based on the
fundamental frequency and the N layout by using the signal
processing unit 125 by setting the N layout to 1 in the case of the
channel 1 and the N layout to 100 in the case of the channel 2.
Further, the N layout may be arbitrarily set.
[0152] When the N layout is two types of 1 and 100 as described
above, the channel switching signal is two types, and thus the N
layout may be set to 1 when the signal is in an on state and the N
layout may be set to 100 when the signal is in an off state. In
this case, the signal may be processed as not the analog signal but
the digital signal and the resolution for the N layout may be
significantly enhanced.
[0153] The embodiment is performed to improve the resolution of the
repetition frequency, but the same means may be applied to the duty
ratio or the on-time and the off-time and the resolutions of the
duty ratio or the on-time and the off-time may also be improved.
Further, the fundamental frequency or the N layout in the
embodiment may not be an integer. Subsequently, a plasma processing
method of plasma-etching a multilayered film by using the plasma
processing apparatus according to the present invention will be
described below.
Fourth Embodiment
[0154] The embodiment will be described with reference to FIG. 16.
As illustrated in FIG. 16, when a multilayered film in which a
Poly-Si film, a SiO.sub.2 film, an amorphous carbon film, a SiN
film, and a BARC film are stacked sequentially from the bottom and
a sample disposed on the multilayered film and having a previously
patterned resist mask are plasma-etched, the plasma-etching is
performed as below.
[0155] First, the BARC film is etched by continuous wave radio
frequency bias power (hereinafter, referred to as CW), and
thereafter, the SiN film is etched by the time-modulated radio
frequency bias power using a domain A.
[0156] Subsequently, the amorphous carbon film and the SiO.sub.2
film are etched by time-modulated radio frequency bias power using
a domain B and a domain C, respectively. Last, the Poly-Si film is
etched by the CW and continuously, etched by time-modulated radio
frequency bias power sequentially using a domain D and the domain
C.
[0157] Further, as illustrated in FIG. 15, the domain A is a domain
having a low repetition frequency (for example, a repetition
frequency of 1 to 100 Hz) and a higher duty ratio than a low duty
ratio (for example, a duty ratio of 10% or less) and the domain B
is a domain having a higher repetition frequency than the low
repetition frequency and the higher duty ratio than the low duty
ratio. Further, the domain C is a domain having the low repetition
frequency and the low duty ratio and the domain D is a domain
having the higher repetition frequency than the low repetition
frequency and the low duty ratio.
[0158] By performing the plasma processing, the multilayered film
in which the Poly-Si film, the SiO.sub.2 film, the amorphous carbon
film, the SiN film, and the BARC film are stacked sequentially from
the bottom and the sample disposed on the multilayered film and
having the previously patterned resist mask may be etched in a
desired profile with high precision.
[0159] As described above, the first to fourth embodiments have
been described by using the duty ratio and the repetition frequency
as the control parameters, but the present invention according to
the first to fourth embodiments may be applied even to the on-time
and the off-time. The reason is that the duty ratio and the
repetition frequency may be acquired by using the on-time and the
off-time.
[0160] For example, when the radio frequency power is
time-modulated by controlling the on-time, the control domain is
divided into at least two, and the high-precision control may be
performed by setting an on-time of 1.0 ms or less as the channel 1
and an on-time longer than 1.0 ms as the channel 2, similarly as
the duty ratio. Further, similarly as the on-time, it is possible
to perform the high-precision control by dividing the off-time or
the control domain into a plurality of domains.
[0161] Further, the configuration of the radio frequency bias power
supply of the first to fourth embodiments may be applied even to a
radio frequency power supply generating plasma. As a result, the
present invention is a plasma processing apparatus that supplies
the time-modulated radio frequency power, which is controllable
with high precision in the wide repetition frequency band, from at
least any one power supply of the radio frequency power supply
generating plasma and the radio frequency bias power supply.
[0162] Further, in the first to fourth embodiments, the microwave
ECR plasma has been described as one embodiment, but the same
effects as the first to fourth embodiments are acquired even in a
plasma processing apparatus in a method of generating other plasma
such as capacitance-coupled plasma or inductance-coupled
plasma.
* * * * *