U.S. patent application number 09/750683 was filed with the patent office on 2001-09-13 for plasma film forming method and plasma film forming apparatus.
Invention is credited to Akahori, Takashi, Aoki, Takeshi, Endo, Shunichi, Hirata, Tadashi, Ishizuka, Shuichi, Naito, Yoko, Nakase, Risa, Saito, Masahide, Tozawa, Masaki, Yokoyama, Osamu.
Application Number | 20010020608 09/750683 |
Document ID | / |
Family ID | 18126651 |
Filed Date | 2001-09-13 |
United States Patent
Application |
20010020608 |
Kind Code |
A1 |
Akahori, Takashi ; et
al. |
September 13, 2001 |
Plasma film forming method and plasma film forming apparatus
Abstract
Microwave is introduced into a plasma chamber of a plasma
processing apparatus and magnetic field is applied thereto to allow
plasma generation gas to be placed in plasma state by the electron
cyclotron resonance. This plasma is introduced into a film forming
chamber of the plasma processing apparatus to allow film forming
gas including compound gas of carbon and fluorine or compound gas
of carbon, fluorine and hydrogen, and hydro carbon gas to be placed
in plasma state. In addition, an insulating film consisting of
fluorine added carbon film is formed by the film forming gas placed
in plasma state.
Inventors: |
Akahori, Takashi; (Tokyo-To,
JP) ; Tozawa, Masaki; (Tokyo-To, JP) ; Naito,
Yoko; (Sagamihara-Shi, JP) ; Nakase, Risa;
(Sagamihara-Shi, JP) ; Yokoyama, Osamu;
(Sagamihara-Shi, JP) ; Ishizuka, Shuichi;
(Kanagawa-Ken, JP) ; Endo, Shunichi;
(Sagamihara-Shi, JP) ; Saito, Masahide; (Tokyo-To,
JP) ; Aoki, Takeshi; (Tokyo-To, JP) ; Hirata,
Tadashi; (Sagamihara-Shi, JP) |
Correspondence
Address: |
Michael A. Makuch
SMITH, GAMBRELL & RUSSELL, LLP
Suite 800
1850 M Street, NW
Washington
DC
20036
US
|
Family ID: |
18126651 |
Appl. No.: |
09/750683 |
Filed: |
January 2, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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09750683 |
Jan 2, 2001 |
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09101516 |
Jul 10, 1998 |
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6215087 |
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09101516 |
Jul 10, 1998 |
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PCT/JP97/04098 |
Nov 11, 1997 |
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Current U.S.
Class: |
219/121.44 ;
156/345.42; 204/298.36; 219/121.41; 219/121.43; 257/E21.259;
257/E21.264; 257/E21.576 |
Current CPC
Class: |
H01L 21/76801 20130101;
H01L 21/76837 20130101; H01L 21/02274 20130101; H01L 21/7682
20130101; H01L 21/0212 20130101; H01L 21/3127 20130101; C23C 16/26
20130101; H01L 21/312 20130101 |
Class at
Publication: |
219/121.44 ;
219/121.41; 219/121.43; 156/345; 204/298.36 |
International
Class: |
B23K 010/00 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 14, 1996 |
JP |
320911/1996 |
Claims
1. A plasma film forming method comprising the steps of: allowing
film forming gas including compound gas of carbon and fluorine and
hydro carbon gas to be placed in plasma state; and forming an
insulating film consisting of fluorine added carbon film on an
object to be processed by the plasma.
2. A plasma film forming method as set forth in claim 1, wherein
the compound gas includes double bond or triple bond of carbon and
fluorine.
3. A plasma film forming method as set forth in claim 1, wherein
the compound gas includes carbon in which four CF groups are
bonded.
4. A plasma film forming method as set forth in claim 1, wherein
the compound gas further includes hydrogen.
5. A plasma film forming method as set forth in claim 1, wherein
the film forming step further comprises a step of forming the
fluorine added carbon film on a silicon substrate which is the
object to be processed under the condition where pressure of
processing atmosphere is 1 Pa or less.
6. A plasma film forming method comprising the steps of:
introducing microwave of 10 kw or more per unit volume of 1 cubic
meters within vacuum atmosphere into a plasma chamber of a plasma
processing unit, and to apply magnetic field thereto to allow
plasma generation gas to be placed in plasma state by the electron
cyclotron resonance; introducing the plasma into a film forming
chamber of the plasma processing unit to allow film forming gas
including compound gas of carbon and fluorine or compound gas of
carbon, fluorine and hydrogen and hydro carbon gas to be placed in
plasma state; and forming an insulating film consisting of fluorine
added carbon film by the film forming gas placed in plasma
state.
7. A plasma film forming method comprising the steps of: allowing
film forming gas including compound gas of carbon and fluorine or
compound gas of carbon, fluorine and hydrogen, and hydro carbon gas
to be placed in plasma state within a vacuum vessel provided with a
mounting table for an object to be processed; and applying, to the
mounting table, bias power of 3.14 W/cm.sup.2 or more per unit area
of mounting surface of the mounting table to form an insulating
film consisting of fluorine added carbon film onto a material to be
processed by the plasma while drawing ions in the plasma into the
object to be processed.
8. A plasma film forming method comprising the steps of: allowing
processing gas including compound gas of carbon and fluorine or
compound gas of carbon, fluoride and hydrogen and oxygen plasma
generation gas to be placed in plasma state; and forming an
insulating film consisting of fluorine added carbon film on a
material to be processed by the plasma.
9. A plasma film forming method comprising the steps of: allowing
film forming gas including compound gas of carbon and fluorine or
compound gas of carbon, fluoride and hydrogen to be placed in
plasma state to form an insulating film consisting of fluorine
added carbon film on an object to be processed by this plasma;
carrying out switching from the film forming gas to oxygen plasma
generation gas to generate oxygen plasma to etch a portion of the
insulating film by this oxygen plasma; and carrying out switching
from oxygen plasma to the film forming gas to generate plasma to
form an insulating film consisting of fluorine added carbon film on
an object to be processed by this plasma.
10. A plasma film forming method comprising the steps of: applying
a.c. power to processing gas to generate plasma; and forming a thin
film on an object to be processed by the plasma while allowing the
a.c. power to be turned on or off by pulse having frequency lower
than frequency of the a.c. power.
11. A plasma processing apparatus comprising: a plasma chamber for
allowing plasma generation gas to be placed in plasma state; a
first generator for generating microwave within the plasma chamber;
a forming element for forming magnetic field within the plasma
chamber; a first supply unit for supplying the plasma generation
gas into the plasma chamber; a film forming chamber for forming an
insulating film on an object to be processed; and a second supply
unit for supplying, into the film forming chamber, film forming gas
including compound gas of carbon and fluorine or compound gas of
carbon, fluorine and hydrogen and hydro carbon gas, whereby the
generation gas is placed in plasma state by the electron cyclotron
resonance by the microwave and the magnetic field is introduced
into the film forming chamber so that the film forming gas is
placed in plasma state, and an insulating film consisting of
fluorine added carbon film is formed by the film forming gas placed
in plasma state.
12. A plasma processing apparatus as set forth in claim 11, wherein
the first generator generates microwave having 10 kw or more per
unit volume (1 cubic meters) within vacuum atmosphere.
13. A plasma processing apparatus as set forth in claim 11, which
further comprises means for applying bias power of 3.14 W/cm.sup.2
or more per unit area of mounting surface of a mounting table for
mounting the object to be processed thereon.
14. A plasma processing apparatus as set forth in claim 11, which
further comprises a second generator to generate pulses having
frequency lower than frequency of the microwave to allow the
microwave to be turned ON or OFF by these pulses.
Description
TECHNICAL FIELD
[0001] This invention relates to a method and an apparatus for
forming, by plasma processing, fluorine added carbon film which can
be used in interlayer insulating film of, e.g., semiconductor
device.
BACKGROUND ART
[0002] In order to realize high integration of the semiconductor
device, methods such as miniaturization of pattern and/or
multi-layer of circuit are being developed. Among these devices,
there is the technology for allowing wiring to be of multi-layer.
In order to achieve multi-layer wiring structure, a conductive
layer is connected between the n-th wiring layer and the (n+1)-th
wiring layer, and thin film called interlayer insulating film is
formed within the area except for the conductive layer.
[0003] A typical interlayer insulating film, there is SiO.sub.2
film. In order to allow the operation of the device to have higher
speed in recent years, it is required to lower specific dielectric
constant of the interlayer insulating film. Studies with respect to
material of the interlayer insulating film are being conducted.
Namely, specific dielectric constant of SiO.sub.2 is approximately
4 and studies have focused on the development of material having
specific dielectric constant smaller than that. Realization of SiOF
having specific dielectric constant of 3.5 is being developed as
one of them. The inventors of this application pay attention to
fluorine added carbon film having smaller specific dielectric
constant.
[0004] Meanwhile, for the interlayer insulating film, high
adhesiveness (adhesion), large mechanical strength and excellent
thermal stability, etc. are required in addition to small specific
dielectric constant. As fluorine added carbon, trade name Teflon
(polytetrafuloroethylene) is well known. However, this material has
extremely bad adhesive property and has small hardness.
Accordingly, even if there is employed such an approach that
fluorine added carbon film is used as interlayer insulating film,
there are many unknown portions in the film property (quality). In
the present state, such material is difficult to be put into
practical use.
DISCLOSURE OF THE INVENTION
[0005] This invention has been made under such circumstances and
its object is to provide a method and an apparatus for
manufacturing fluorine added carbon suitable for semiconductor
device.
[0006] This invention provides a plasma film forming method
comprising the steps of: allowing film forming gas including
compound gas of carbon and fluorine and hydro-carbon gas to be
placed in plasma state; and forming an insulating film consisting
of fluoride added carbon film on an object to be processed by the
plasma.
[0007] This invention further provides a plasma film forming method
comprising the steps of: introducing microwave of 10 kw or more per
unit volume of 1 cubic meters within vacuum atmosphere into a
plasma chamber of a plasma processing unit and of applying magnetic
field thereto to allow plasma generation gas to be placed in plasma
state by the electron cyclotron resonance; introducing the plasma
into a film forming chamber of the plasma processing unit to allow
film forming gas including compound gas of carbon and fluorine or
compound gas of carbon, fluorine and hydrogen and hydro carbon gas
to be placed in plasma state; and forming an insulating film
consisting of fluorine added carbon film by the film forming gas
placed in plasma state.
[0008] This invention further provides a plasma film forming method
comprising the steps of: allowing film forming gas including
compound gas of carbon and fluorine or compound gas of carbon,
fluorine and hydrogen, and hydro carbon gas to be placed in plasma
state within a vacuum vessel provided with a mounting table of an
object to be processed; and applying, to the mounting table, bias
power of 3.14 W/cm.sup.2 or more per unit area of the mounting
surface of the mounting table to form an insulating film consisting
of fluorine added carbon film on the object to be processed by the
plasma while drawing ions in plasma into the object to be
processed.
[0009] This invention further provides a plasma film forming method
comprising the steps of: allowing processing gas including compound
gas of carbon and fluorine or compound gas of carbon, fluorine and
hydrogen, and oxygen plasma generation gas to be placed in plasma
state; and forming an insulating film consisting of fluorine added
carbon film onto an object to be processed by the plasma.
[0010] This invention further provides a plasma film forming method
comprising the steps of: allowing film forming gas including
compound gas of carbon and fluorine or compound gas of carbon,
fluorine and hydrogen to be placed in plasma state to form an
insulating film consisting of fluorine added carbon film on an
object to be processed by the plasma; generating oxygen plasma
after undergone switching from the film forming gas to oxygen
plasma generation gas to etch a portion of the insulating film by
this oxygen plasma; and generating plasma after undergone switching
from oxygen plasma to the film forming gas to form an insulating
film consisting of fluorine added carbon film on an object to be
processed by this plasma.
[0011] This invention further provides a plasma film forming method
comprising: applying a.c. power to processing gas to generate
plasma; and forming a thin film on an object to be processed by the
plasma while allowing the a.c. power by pulse having a frequency
lower than frequency of the a.c. power to be turned on or off.
[0012] This invention further provides a plasma processing
apparatus comprising: a plasma chamber for allowing plasma
generation gas to be placed in plasma state; a first generator for
generating microwave within the plasma chamber; a forming element
for forming magnetic field within the plasma chamber; a first
supply unit for supplying the plasma generation gas into the plasma
chamber; a film forming chamber for forming an insulating film on
an object to be processed; and a second supply unit for supplying
film forming gas including compound gas of carbon and fluorine or
compound gas of carbon, fluorine and hydrogen and hydro carbon gas
into the film forming chamber, whereby the generation gas placed in
plasma state by the electron cyclotron resonance by the microwave
and the magnetic field is introduced into the film forming chamber
so that the film forming gas is placed in plasma state, and an
insulating film consisting of fluorine added carbon film is formed
by the film forming gas placed in plasma state.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] FIG. 1 is a longitudinal side cross sectional view showing
an example of a plasma processing apparatus used for carrying out a
plasma film forming method of this invention;
[0014] FIG. 2 is a characteristic diagram showing the relationship
between kind of film forming gas and specific dielectric constant
of CF film;
[0015] FIG. 3 is a characteristic diagram showing the relationship
between kind of film forming gas and adhesive property of CF
film;
[0016] FIG. 4 is a characteristic diagram showing the relationship
between kind of film forming gas and hardness of CF film;
[0017] FIG. 5 is characteristic diagram showing result of X-ray
photo-electron spectrum of CF film;
[0018] FIG. 6 is a characteristic diagram showing result of mass
analysis of gas generated when temperature is changed with respect
to CF film;
[0019] FIG. 7 is an explanatory view showing molecular structure of
film forming gas;
[0020] FIG. 8 is a characteristic diagram showing result of mass
analysis of gas generated when temperature is changed with respect
to CF film;
[0021] FIG. 9 is an explanatory view showing the state of reaction
of film forming gas;
[0022] FIG. 10 is a characteristic diagram showing result of mass
analysis of gas generated when temperature is changed with respect
to CF film;
[0023] FIG. 11 is a characteristic diagram showing result of mass
analysis of gas generated when temperature is changed with respect
to CF film;
[0024] FIG. 12 is a characteristic diagram showing the relationship
between bias powers every process pressures and film forming
speeds;
[0025] FIG. 13 is an explanatory view showing the relationship
between process pressure and stress of CF film;
[0026] FIG. 14 is an explanatory view showing the state of stress
of CF film;
[0027] FIG. 15 is an explanatory view showing dependency of
microwave power with respect to adhesive property of CF film;
[0028] FIG. 16 is an explanatory view showing dependency of
microwave power with respect to film thickness uniformity of CF
film;
[0029] FIG. 17 is an explanatory view showing dependency of bias
power with respect to adhesive property of CF film;
[0030] FIG. 18 is an explanatory view showing dependency of bias
power with respect to film thickness uniformity of CF film.
[0031] FIG. 19 is an explanatory view showing the relationship
between bias power and aspect ratio of embeddable recessed
portion.
[0032] FIG. 20 is an explanatory view showing the embedded state
between wirings by CF film;
[0033] FIG. 21 is an explanatory view showing the embedded state
between wirings by CF film;
[0034] FIG. 22 is an explanatory view showing outline of the
configuration of a plasma processing apparatus used in another
embodiment of this invention;
[0035] FIG. 23 is a waveform diagram showing the state where
microwave power supply and bias power supply are turned ON or
OFF;
[0036] FIG. 24 is a characteristic diagram showing the relationship
of microwave power, plasma density and electron temperature;
[0037] FIG. 25 is a characteristic diagram showing the relationship
of microwave power, plasma density and electron temperature;
and
[0038] FIG. 26 is a characteristic diagram showing the relationship
between duty factor when microwave power and bias power are turned
ON or OFF and film forming speed.
BEST MODE FOR CARRYING OUT THE INVENTION
[0039] The embodiment of this invention is characterized in that an
approach is employed to examine the relationship with respect to
the process condition for manufacturing fluorine added carbon
(hereinafter referred to as "CF film") suitable for interlayer
insulating film of, e.g., semiconductor device, e.g., the
relationship between kind or pressure, etc. of material gas and
film quality of the CF film to find out optimum process condition.
Initially, an example of a plasma processing apparatus used in this
embodiment is shown in FIG. 1. As shown, this plasma processing
apparatus 1 includes, e.g., a vacuum vessel 2 formed by, e.g.,
aluminum, etc., and is composed of a tubular plasma chamber 21
positioned at the upper portion of this vacuum vessel 2 and adapted
for generating plasma, and a tubular film forming chamber 22
connected in a manner to communicate with the lower portion thereof
and having aperture greater than that of the plasma chamber 21. In
this example, this vacuum vessel 2 is grounded so that zero
potential is provided.
[0040] The upper end of this vacuum vessel 2 is opened and a member
for allowing microwave to be transmitted therethrough, e.g., a
transmission window 23 formed by material such as quartz, etc. is
air-tightly provided at this portion to maintain vacuum state
within the vacuum vessel 2. At the outside of this transmission
window 23, there is provided, e.g., a wave-guide (tube) 25
connected to a high frequency power supply section 24 as plasma
generation high frequency supply means of 2.45 GHz, and is adapted
so as to guide microwave M generated at the high frequency power
supply section 24 via the wave-guide (tube) 25 to introduce it into
the plasma chamber 21 from the transmission window 23.
[0041] At the side walls which partition the plasma chamber 21,
there are provided plasma gas nozzles 26 equally disposed along its
circumferential direction, for example. Plasma gas source (not
shown), e.g., Ar gas or O.sub.2 gas source is connected to these
nozzles 26 so as to have ability to equally deliver, without
unevenness, plasma gas such as Ar gas or O.sub.2 gas, etc. into the
upper portion within the plasma chamber 21. In this example,
although only two nozzles 26 are described for the purpose of
avoiding complexity of the drawings, those nozzles more than two
are provided in practice.
[0042] Moreover, at the outer circumference of the side wall which
partitions the plasma chamber 21, e.g., a ring-shaped main
electromagnetic coil 27 is disposed as magnetic field forming means
in a manner close thereto, and a ring-shaped auxiliary
electromagnetic coil 28 is disposed at the lower side of the film
forming chamber 22, thus to have ability to form magnetic field
directed from the upper side toward the lower side extending over
the film forming chamber 22 from the plasma chamber 21, e.g.,
magnetic field B of 875 Gauss. Thus, the ECR plasma condition is
satisfied. In this example, permanent magnet may be used in place
of the electromagnetic coil.
[0043] By forming microwave M and magnetic field B which have been
frequency-controlled within the plasma chamber 21 in this way, the
ECR plasma is generated by interaction therebetween. At this time,
resonance action is produced in the introduced gas at the
above-mentioned frequency. Thus, plasma can be formed at high
density. Namely, this apparatus constitutes electron cyclotron
resonance (ECR) plasma processing apparatus.
[0044] On the other hand, at the portion communicating with the
upper portion of the film forming chamber 22, i.e., the plasma
chamber 21, there is provided a ring-shaped film forming gas supply
section 30 so that film forming gas is ejected from the inner
circumferential surface. Moreover, a mounting table 3 is vertically
movably provided within the film forming chamber 22. In this
mounting table 3, an electrostatic chuck 32 including heater
therewithin is provided on, e.g., a body 31 of aluminum. For
example, a high frequency power supply section 34 is connected to
an electrode 33 of the electrostatic chuck 32 in a manner to apply
bias voltage for withdrawing ions onto wafer W. In addition, an
exhaust pipe 35 is connected to the bottom portion of the film
forming chamber 22.
[0045] A method of forming interlayer insulating film consisting of
CF film on a wafer 10 which is object to be processed by using the
above-described apparatus will now be described. Initially, gate
valve (not shown) provided at the side wall of the vacuum vessel 2
is opened to carry the wafer 10 which is object to be processed in
which aluminum wiring is formed, e.g., on the surface from load
lock chamber (not shown) to mount it on the mounting table 3.
[0046] Subsequently, after this gate valve is closed to tightly
close the inside thereafter to exhaust the internal atmosphere from
the exhaust pipe 35 to vacuum-evacuate it until a predetermined
degree of vacuum to introduce plasma generation gas, e.g., Ar gas
into the plasma chamber 21 from the plasma gas nozzles 26, and to
introduce film forming gas, e.g., CF.sub.4 gas and C.sub.2H.sub.4
gas under the condition of flow rates of 60 sccm and 30 sccm,
respectively, into the film forming chamber 22 from the film
forming gas supply section 30. Further, the inside of the vacuum
vessel 2 is maintained at, e.g., process pressure of 0.1 Pa to
apply bias voltage of 1500 W at 13.56 MHz onto the mounting portion
3 by the high frequency power supply section 34, and to set surface
temperature of the mounting table 3 to 320.degree. C.
[0047] High frequency (microwave) power of 2.45 GHz from the plasma
generation high frequency power supply section 24 is guided
(carried) through the wave-guide (tube) 25 to reach the ceiling
portion of the vacuum vessel 2. The high frequency (microwave)
power thus obtained is transmitted through the transmission window
23 so that microwave M is introduced into the plasma chamber 21.
Magnetic field B produced by electromagnetic coils 27, 28 is
applied to the inside of the plasma chamber 21, e.g., at intensity
of 875 gauss from the upper direction toward the lower direction.
As a result, E (electric field).times.B (magnetic field) is induced
by interaction between this magnetic field B and microwave M so
that electron cyclotron resonance takes place. By this resonance,
Ar gas is placed in plasma state and is caused to have high
density. In this case, employment of Ar gas stabilizes plasma.
[0048] Plasma flow which has been caused to flow into the film
forming chamber 22 from the plasma generating chamber 21 activates
C.sub.4F.sub.8 gas and C.sub.2H.sub.4 gas delivered thereto to form
active species. On the other hand, plasma ions, e.g., Ar ions in
this example are drawn into the wafer 10 by bias voltage for
drawing plasma. Thus, CF film is formed while shaving corner of CF
film stacked on pattern (recessed portion) of the wafer 10 surface
by sputter etching action of Ar ions to widen the frontage portion
so that it is embedded into the recessed portion.
[0049] In this example, the inventors of this application have
examined how n, m, k, s and film quality correspond to each other
in the case where C.sub.nF.sub.m gas and C.sub.kH.sub.s gas are
combined as film forming gas. In this case, n, m, k, s are integer.
As an experiment, flow rates of C.sub.nF.sub.m gas and
C.sub.kH.sub.s gas are set at 60 sccm and 30 sccm, respectively,
and other process conditions are set as described in the
above-described embodiment to form CF film having thickness of 1
.mu.m to examine specific dielectric constant, adhesive property
and hardness with respect to the CF film thus obtained.
[0050] As C.sub.nF.sub.m gas, CF.sub.4, C.sub.2F.sub.6,
C.sub.3F.sub.8, C.sub.4F.sub.8, etc. may be used. In addition, as
C.sub.kH.sub.s gas, H.sub.2, CH.sub.4, C.sub.2H.sub.2,
C.sub.2H.sub.6, C.sub.3H.sub.8, C.sub.4H.sub.8, etc. may be used.
FIGS. 2 to 4 show results with respect to specific dielectric
constant, adhesive property and hardness, respectively, wherein
ratio between m and n of C.sub.nF.sub.m gas is taken on the
abscissa and ratio between s and k of C.sub.kH.sub.s, gas is taken
on the ordinate. Numeric values described at cross points of
respective values of the ordinate and the abscissa are data. For
example, in the case of combination of C.sub.4F.sub.8 gas and
C.sub.2H.sub.4 gas in FIG. 2, the specific dielectric constant is
2. 2. In this case, data of the uppermost row is data in which
H.sub.2 gas is used as C.sub.kH.sub.s gas.
[0051] With respect to measurement of the specific dielectric
constant, CF film was formed on bear silicon surface to further
form aluminum electrode thereon to connect electrode of specific
dielectric constant meter between the silicon layer and the
electrode to measure specific dielectric constant of CF film. With
respect to measurement of adhesive property, CF film is formed on
the bear silicon surface to fix, by adhesive agent, close contact
test element on this CF film surface to draw up the test element to
allow magnitude of drawing force (kg/cm.sup.2) per test element
unit area when CF film is peeled off from the bear silicon
(Sebastian method). With respect to measurement of hardness,
Shimazu dynamic very small hardness meter DUH-200 was used to carry
out pushing test with respect to CF film under the condition of
test weight 500 mgf, load speed 29 mgf/sec and test weight holding
time 5 sec by triangular pyramid pressure element having ridge line
interval of 115 degrees and pressure element front end curvature
radius of 0.1 .mu.m or less. When pushing depth is assumed to be D
(.mu.m), coefficient (37.838).times.weight/D.sup.2 is determined as
index of hardness (dynamic hardness).
[0052] In order to cope with high speed operation of the device, it
is necessary that the specific dielectric constant is 3.0 or less
and is preferably 2.5 or less. The range of combination of film
forming gases to satisfy this range is shown by slanting lines in
FIG. 2. With respect to adhesive property, in the case of the
above-described test, if the drawing force is 200 kg/cm.sup.2 or
more, there is no possibility that peeling (separation) of film
takes place when combined into the device. This range is indicated
by slanting lines in FIG. 3. When hardness is too small, etch back
process to mechanically ground, e.g., the surface to planarize it
becomes difficult. For this reason, it is necessary that the
above-mentioned range is 40 or more and is 50 or more. This range
is shown by slanting lines in FIG. 4. When consideration is made
with respect to such result, it is sufficient for lowering the
specific dielectric constant to increase ratio of F in the film.
However, if ratio of F is too high, adhesive property is bad and
hardness is small. The reason thereof is as follows. It is
considered that adhesive property and hardness contribute to C-C
bond in the film. It is further considered that if ratio of F is
high, the degree of C-C bonds becomes small.
[0053] Accordingly, in order to ensure low specific dielectric
constant, sufficient adhesive property and hardness, it is
preferable that the slanting line regions of FIGS. 2 to 4 overlap
with each other. In this case, with respect to hardness, in the
case deviating from the slanting line region of FIG. 4, there is
also a method of providing film having high hardness on the surface
of the CF film to protect the surface. FIG. 5 shows result of X-ray
photo-electron spectrum of CF film in the previously described
process condition where mixed gas of C.sub.4F.sub.8 gas and
C.sub.2H.sub.4 gas becomes film forming gas. From this result, it
is seen that CF.sub.3 group, CF.sub.2, CF group and C-CF.sub.x
group are included.
[0054] From facts as described above, the CF film formed by
combination of C.sub.4F.sub.8 gas and C.sub.2H.sub.2 gas is such
that the specific dielectric constant is 2.4, the adhesive property
is 412 and the hardness is 192. It is seen that such CF film is
preferable as the interlayer insulating film. It is to be noted
that, in the above-described example, H.sub.2 gas may be added in
addition to C.sub.nF.sub.m gas and C.sub.kH.sub.s gas.
[0055] In another embodiment of this invention, double bonded or
triple bonded gas, e.g., C.sub.2F.sub.2 gas or C.sub.2F.sub.4 gas
is used as gas of CF system which is material gas. In this case,
the CF film is advantageously excellent in the thermal stability.
The thermal stability is the fact that extraction of F (fluorine)
is made to small degree even if temperature becomes equal to high
temperature. Namely, in order to electrically connect to each other
respective wiring layers, e.g., aluminum wirings of the upper row
side and the lower row side, interlayer insulating film is formed
thereafter to form via hole, whereupon embedding of, e.g., W
(tangusten) is carried out. In this case, the embedding process is
carried out under temperature of, e.g., about 450.degree. C.
Moreover, there are instances where aluminum is caused to flow into
via hole. In this case, this reflow process is carried out at about
400.degree. C. or more. F is extracted when the interlayer
insulating film is heated so that temperature higher than film
forming temperature is provided. Extraction of F is made to less
degree as compared to gas of the primary bond if there is used gas
in which C and F are double bond or triple bond as material gas.
When extraction of F is made to more degree, the specific
dielectric constant is increased. Film peeling (separation) by
contraction of the CF film itself takes place. Further, because
extraction is made as gas, peeling (separation) at the surface
between the CF film and the W film is apt to take place. In
addition, there is the possibility that aluminum may be corroded
under the existence of Cl and F used at the time of etching of
aluminum wiring. Accordingly, it is desirable that the thermal
stability is large.
Experimental Example
[0056] The plasma film forming apparatus shown in FIG. 1 was used
to deliver C.sub.4H.sub.8 gas, C.sub.2F.sub.4 (CF.sub.2=CF.sub.2)
gas and C.sub.2H.sub.4 gas as material gas at flow rates of 70
sccm, 30 sccm and 15 sccm, respectively, into the film forming
chamber 22 to form CF film having film thickness of 1 .mu.m in the
state where other process conditions are similar to the
above-mentioned embodiment. This embodiment is assumed to be taken
as the embodiment 1. Moreover, CF film was formed similarly to the
embodiment 11 except that C.sub.4F.sub.8 gas and C.sub.2H.sub.4 gas
are delivered at flow rates of 70 sccm and 40 sccm, respectively.
This embodiment is taken as the comparative example 11.
[0057] With respect to these CF films, when discharge quantities of
F, CF, CF.sub.2, CF.sub.3 at respective temperatures are measured
by the mass analyzer, results shown in FIGS. 6(a), 6(b) were
obtained. In addition, the specific dielectric constant and the
film forming speed were the following results.
1 FILM SPECIFIC FORMING DIELECTRIC SPEED CONSTANT (angstrom/min)
Embodiment 11 2.0 2650 Comparative 2.75 2300 Example 11
[0058] As seen from this result, in the case where the conditions
except for material gas are the same, it is seen that, in the case
of the embodiment 11, discharge quantities of F, CF, CF.sub.2,
CF.sub.3 are smaller and thermal stability is large. The reason why
extraction of F is small is as follows. It is estimated that C-C
bonds are formed in a three-dimensional network form, i.e., network
structure of C-C is formed and F is difficult to be extracted even
if C-F bond is dissociated. Further, in the case where double
bonded or triple bonded C-F system gas is used, it is considered
that the number of C-C bonds having C-F bond is increased to more
degree because of reaction mechanism in which dissociation of F of
C-F bond is not required where network structure is formed by
polymerization reaction of the material gas itself.
[0059] On the other hand, while, in material gas of the comparative
example, ratio of C.sub.2H.sub.4 gas is increased so that the
number of C-C bonds is increased to more degree, ratio of F is
lowered in this case so that the specific dielectric constant is
increased.
[0060] Furthermore, in this invention, as gas of CF system which is
material gas, molecular structure in which four CF groups are
bonded to one C, e.g., C(CF.sub.3).sub.4 or
C(C.sub.2F.sub.5).sub.4, etc. may be used alone or may be used in a
manner mixed with C.sub.4F.sub.8 gas or C.sub.2F.sub.2 gas, etc.
previously described. When such an approach is employed, C-C
network structure is apt to be formed. Thus, thermal stability is
large.
[0061] The reason thereof is as follows. In the case of
C(CF.sub.3).sub.4 as shown in FIG. 7(a), it is considered that C-F
bond is cut and C or F is bonded thereto. However, when C is
bonded, because this C has four C-C bonds encompassed by dotted
lines, the number of C-C bonds is increased. In addition, since
there results a form such that chain of C-C bonds is spread in four
directions with respect to respective C, strong network structure
by C-C bonds is formed. In addition, since the number of F is 12
whereas the number of C-C bonds is 4, the number of F is large as a
whole, thus making it possible to ensure low specific dielectric
constant.
[0062] On the contrary, in the case of the ring-shaped structure
like C.sub.4F.sub.8, it is possible to take strong network
structure to some degree as shown in FIG. 7 (b). However, since the
number of F is small value which is eight with respect to the fact
that the number of C-C bonds is 4, the specific dielectric constant
becomes higher. Moreover, in the case of simple primary bond like
C.sub.4F.sub.10 as shown in FIG. 7(C), C is not necessarily bonded
when C-F bond is cut, but F is also bonded. For this reason, C-C
bonds are difficult to be resultantly spread in a chained manner in
three-dimensional direction. Thus, it is considered that
considerably strong network structure cannot be taken.
Experimental Example
[0063] In this example, the plasma film forming apparatus shown in
FIG. 1 was used to deliver C.sub.4F.sub.8 gas, (CF.sub.3).sub.4C
gas and C.sub.2H.sub.2 gas at flow rates of 60 sccm, 40 sccm and 20
sccm, respectively, and to form CF film having film thickness of 1
.mu.m in the state where pressure is set at 0.18 Pa and other
process conditions are set as the same as those of the previously
described embodiment 11. This experimental example is taken as the
comparative example 21.
[0064] Moreover, CF film is similarly formed except that
C.sub.4F.sub.8 gas and C.sub.2H.sub.4 gas are delivered at flow
rates of 100 sccm and 20 sccm, respectively. This embodiment is
taken as the comparative example 21.
[0065] As the result of the fact that measurement is carried out by
the mass spectrometer similarly to the previously described
embodiment 11, etc. with respect to the CF film of the embodiment
21 and the comparative example 21, results shown in FIGS. 8(a), (b)
were obtained. Moreover, as the result of the fact that the
specific dielectric constant is examined with respect to the
embodiment 21 and the comparative example 21, the specific
dielectric constants were 2.1 and 2.7, respectively. As seen from
this result, the embodiment 21 has lower specific dielectric
constant and greater thermal stability as compared to the
comparative example 21.
[0066] Further, in this invention, as preferable material gas, gas
of CHF system can be mentioned. As CHF system gas,
CH.sub.3(CH.sub.2).sub.3 CH.sub.2F,
CH.sub.3(CH.sub.2).sub.4CH.sub.2F, CH.sub.3(CH.sub.2).sub.7CH.-
sub.2F, CHCH.sub.3F.sub.2, CHF.sub.3, CH.sub.3F and
CH.sub.2F.sub.2, etc. are mentioned. In this case, there are merits
as described below. Initially, such material gas has higher film
forming speed as compared to mixed gas of CF system gas and CH
system gas. For example, in mixed gas of C.sub.4F.sub.8 and
C.sub.2H.sub.4 gas, it is considered that, as shown in FIG. 9, F of
C.sub.4F.sub.8 and H of C.sub.2H.sub.4 are bonded and material gas
thus obtained are given off as HF, so C-C bond is formed or F of
one C.sub.4F.sub.8 and F of other C.sub.4F.sub.8 are bonded and
material gas thus obtained are given off as F.sub.2, so C-C bond is
formed.
[0067] As compared to the case where F-F bond is formed, H-F bond
can be formed by smaller energy. However, the probability that
molecule of C.sub.2H.sub.4 exists at a portion adjacent to molecule
of C.sub.4F.sub.8 is the probability corresponding to flow rate
ratio, etc. in practice. When simply considered, the probability is
50%. On the contrary, if gas of CHF system is employed, since all
molecules include F and H as shown in FIG. 7, F of one molecule and
H of the other molecule are apt to be bonded so that C-C bonds are
apt to be formed. This means that if energy given to gas is the
same, the film forming speed is high. In the case where gas of CHF
system is used, in order to allow the specific dielectric constant
to be as small as possible, it is preferable to use gas having
larger number of F as compared to the number of C, e.g., CHF.sub.3
gas, etc. In addition, gas of CF system may be added in addition to
gas of CHF system and gas of CH system.
Experimental Example
[0068] In this case, the plasma film forming apparatus shown in
FIG. 1 was used to deliver CHF.sub.3 gas and C.sub.2H.sub.4 gas at
flow rates of 60 sccm and 30 sccm, respectively, to form CF film
having film thickness of 2.0 .mu.m in the state where other process
conditions are similar to those of the previously described
embodiment 11. This embodiment is taken as the embodiment 31. As
the result of the fact that measurement is carried out by the mass
spectrometer similarly to the previously described embodiment 11,
etc. with respect to this embodiment 31, result shown in FIG. 10
was obtained. As seen from comparison between the result of FIG. 10
and the previously described comparative example 11 shown in FIG.
6(b), the method using gas of CHF system is excellent in the
thermal stability. Further, measurement results of the film forming
speed and the previously described dynamic hardness in the
embodiment 31 and the comparative example 21 are indicated below.
In this case, hardness in the case where high frequency bias is
applied to the wafer is also described for reference.
2 Film forming speed (Angstrom/min) hardness Embodiment 31 4300
200.6 Embodiment 31 6800 80.8 (no bias) Comparative 2300 106.6
Example 11 Comparative 3100 56.5 Example 11 (no bias)
[0069] As seen from this result, if gas of CHF system is used, the
film forming speed is high and the through-put is improved. In
addition, CF film having large hardness is obtained.
[0070] In order to examine the relationship between the film
quality of the CF film and the mounting table surface temperature
of the wafer in the above-mentioned embodiment, as the result of
the fact that mounting table surface temperatures are set to
350.degree. C. and 220.degree. C., respectively, in the process
condition (the condition used in the description of C.sub.nF.sub.m
gas+C.sub.kH.sub.s gas) of the previously described embodiment to
carry out the previously described mass analysis with respect to
the formed CF film, results shown in FIGS. 11(a), (b) were
obtained. The reason is as follows. It is considered that according
as the thermal energy at the wafer surface becomes larger,
temperature becomes higher, and the energy of the active species
thus becomes large so that the number of C-C bonds is increased to
higher degree and dissociation of F is developed. In addition,
since about 450.degree. C. is limit even if the semiconductor
device in which wiring is formed is caused to have high
temperature, combination of C.sub.4F.sub.8 gas and C.sub.2H.sub.4
gas is effective combination since the thermal stability is large
at the process temperature of about 350.degree. C.
[0071] As the result of the fact that the apparatus of FIG. 1 is
used to examine the relationship of pressure within the vacuum
vessel 2, film quality of the CF film, adhesive property and the
film forming speed, results of FIGS. 12 and 13 were obtained. FIG.
12 is the result that the relationship between bias power applied
to the mounting table 3 and the film forming speed is determined
every pressure. With respect to the process condition, power of
microwave is set at 2.7 kw and flow rates of C.sub.4F.sub.8 gas,
C.sub.2H.sub.4 gas and Ar gas are set at 60 sccm, 30 sccm and 150
sccm, respectively, and the surface temperature of the mounting
table is set at 200.degree. C. Other conditions such as magnetic
field, etc. are similar to the conditions described in the
previously described embodiment.
[0072] As seen from the result of FIG. 12, according as pressure
becomes higher, and bias power becomes larger, the film forming
speed becomes lower. This is because it is considered that when
pressure becomes high, mean free path of ions becomes short and
collision energy between ions and molecules becomes small, so the
speed at which the active species are taken into the film becomes
low. In addition, when bias power becomes large, the etching effect
by ions becomes large, and the film forming speed becomes low.
[0073] The inventors of this application have examined from a
viewpoint of film stress (stress) that adhesive property between CF
film and its underground film, silicon substrate in this example on
the basis of estimation that when pressure becomes lower, the mean
free path is elongated, and the speed in which active species are
taken into the film becomes high so that fine film is formed.
[0074] FIG. 13 is result in the case where bias power is set at 0 W
among process conditions when data of FIG. 12 is taken to examine
magnitude of stress with respect to the CF film obtained on the
silicon substrate and presence/absence of film peeling
(separation). In this case, the case where pressures are set to 1.2
Pa, and 1.5 Pa, respectively, to carry out process is also
demonstrated in combination. Calculation of stress was carried out
by the following formula.
S=E(D).sup.2/6(1-V)RT
[0075] In the above-mentioned formula, S is stress, E is Young's
modulus of silicon substrate, V is Poisson ratio of the silicon
substrate, D is thickness of the silicon substrate, R is curvature
radius of the entirety of wafer and T is film thickness of CF film
(T is assumed to be sufficiently smaller than D).
[0076] Compression/tensile in stress is distinction indicating how
force the silicon substrate applies when viewed from the CF film,
and the reason why such stress is applied is that difference takes
place in contraction by material when temperature of the wafer
returns to room temperature. Further, in the case where the CF film
attempts to be fine as shown in FIG. 14, C are slid into the film
in order from after. Accordingly, the CF film itself attempts to be
widened, and its expansion of the silicon substrate attempts to
suppress its expansion. Thus, the CF film applies compression from
the silicon substrate.
[0077] On the contrary, since the CF film itself attempts to be
contracted in the case where fineness of the CF film is poor, the
CF film is pulled from the silicon substrate. However, when tensile
stress is applied, the film is apt to be separated or peeled. A
method of examining presence/absence of film separation is carried
out by sticking adhesive tape on the surface of the CF film to
observe whether or not the CF film is separated or peeled from the
silicon substrate when this tape is peeled or separated.
[0078] It is to be noted that while SiO.sub.2 film is also the same
tendency, since difference of coefficient of thermal expansion with
respect to silicon is large in the case of SiO.sub.2, large
compressive stress is applied before influence of fine property of
the film. Accordingly, adhesive property therebetween is high.
[0079] From the result of FIG. 13, it is preferable that pressure
is set at 1 Pa or less in order to prevent film separation.
Moreover, in order to ensure the etching characteristic of the
shoulder portion of the recessed portion by ions at the time of
embedding to carry out satisfactory embedding, it is considered
that bias power is required to be at least about 500 W. However,
when attempt is made to ensure the film forming speed so that it is
equal to 4000 angstroms/min or more, it is preferable that pressure
is 1 Pa or less from the graph of FIG. 12. The magnitude of this
film forming speed is determined by back calculation in the case
where attempt is made to process 10 .about. 11 films per one hour
also in consideration of the cleaning process when CF film of 1
.mu.m is formed.
[0080] Moreover, as the result of the fact that bias power is set
at 1500 W under the process condition when data of FIG. 12 is taken
and embeddable aspect ratios (depth/width of recessed portion) are
examined at 0.2 Pa and 1 Pa, respectively, they were 2 and 0.8,
respectively. Accordingly, it can be said that the case where
pressure is low exhibits good embedding characteristic. Further,
since collision energy between molecules and ions is large in the
case where pressure is low, the energy of the active species
becomes large. As a result, it is estimated that the number of C-C
bonds is increased and F in the film is knocked on to increase the
number of C-C bonds so that the thermal stability is large.
[0081] Then, in order to examine the relationship between magnitude
of microwave power and adhesive property of CF film, the microwave
power is set to 1000 W, 1500 W, 2000 W, 2500 W, 2700 W, 3000 W and
3500 W and CF film having thickness of 10000 angstroms is formed on
8 inch wafer and adhesive property is measured by the previously
described Sebastian method. Thus, result shown in FIG. 15 was
obtained. The process conditions except for the microwave power are
set as similar condition to deliver C.sub.4F.sub.8 gas,
C.sub.2H.sub.4 gas and Ar gas at flow rates of 60 sccm, 30 sccm and
150 sccm, respectively, to set pressure to 0.2 Pa to set mounting
table surface temperature to 320.degree. C. and to set bias power
of the mounting table 3 to 1500 W. Other conditions are the same in
the case of the previously described embodiment.
[0082] As seen from the result of FIG. 15, according as the
microwave power become larger, adhesive property of the CF film is
improved. When viewed from practical use for assembling such film
into the device as previously described, it is preferable that the
adhesive property indicates 200 kg/cm.sup.2 or more. For this
reason, when viewed only from the adhesive property, it is
necessary that the microwave power is 1000 W or more. On one hand,
as the result of the fact that uniformity of film thickness within
plane of the CF film thus obtained is examined every respective
microwave powers, result shown in FIG. 16 is obtained. Since it is
preferable that the film thickness uniformity is 20% or less from a
viewpoint of practical use, it is desirable that the microwave
power is 2000 W or more when combined with data of adhesive
property. Since the volume within the vacuum vessel 2 is 0.2
m.sup.3 in this example, the microwave power required per unit
volume of the vacuum vessel 2 is 10000 W/m.sup.3 or more. As the
result of the fact that examination is made also with respect to
hardness of the CF film formed under the condition where the
microwave power is 2000 W or more, sufficient hardness was
obtained. It is estimated that the reason why adhesive property is
improved when the microwave power is set at large is that energy of
active species of film forming gas is large and the number of C-C
bonds is increased. In addition, it is considered that the reason
why the film thickness uniformity is improved is that uniformity of
plasma density is improved.
[0083] Furthermore, as the result of the fact that the microwave
power is set to 2700 W and bias power of the mounting table is
changed to examine dependency of bias power with respect to the
adhesive property and uniformity of the in-plane film thickness of
the CF film, results shown in FIGS. 17 and 18 were obtained. Other
process conditions are the same condition when data is measured
shown in FIG. 15 is measured. From this result, it is preferable
that the magnitude of bias power is 1000 W or more. In this
example, since the area of the upper surface of the mounting table
3 is 3.14.times.10.sup.-2m.sup.2 in this example, preferable power
per unit area is 3.14 W/m.sup.2 or more. It is to be noted that the
specific dielectric constant of the CF film in such condition is
sufficiently low value of 3.0 or less.
[0084] FIG. 19 is a graph obtained by examining dependency of bias
power with respect to the embedding characteristic. The process
condition is the same when data of FIGS. 17 and 18 are taken. In
FIG. 19, mark indicates that satisfactory embedding is made, and
mark x indicates that voids take place. The width between aluminum
wirings used for embedding is 0.4 .mu.m. It is seen from this
result that when bias power is set larger, the embedding
characteristic can be improved. The reason thereof is as follows.
It is considered that sputtering etching effect of the shoulder
portion of the recessed portion by ions is enhanced.
[0085] Another embodiment of this invention will now be described.
This embodiment contemplates adding O.sub.2 gas to material gas to
thereby improve the embedding characteristic. In general, in the
case where insulating film is buried (embedded) between wirings,
the portions of both shoulders of the recessed portion are swollen
in the middle of embedding so that the frontage portion is closed.
For this reason, bias power is applied to the mounting table to
vertically draw Ar ions onto the wafer to carry out film forming
while shaving the frontage portion. However, when aspect ratio
exceeds 4, the effect of Ar sputter is not so exhibited. As a
result, voids (gaps) are apt to be formed.
[0086] In view of the above, the inventor of this applicant has
proposed to pay attention to the fact that CF film chemically
reacts with O.sub.2, and is removed as CO.sub.2 (chemically etched)
to deliver O.sub.2 gas in addition to film forming gas, e.g.,
C.sub.4F.sub.8 gas and C.sub.2H.sub.4 gas from film forming gas
supply unit 30 shown in FIG. 1 to thereby improve embedding of high
aspect ratio.
[0087] FIG. 20 is a view showing the state where embedding between
aluminum wirings in the case where O.sub.2 gas is continuously
added is carried out. It is considered that O.sub.2 gas is
activated to react with C of CF film so that CO.sub.2 is provided
to chemically etch the CF film. Accordingly, this etching and film
forming proceed at the same time. It is considered that this
chemical etching is greater than action of Ar sputter as seen from
the experimental example of the embedding characteristic which will
be described later, i.e., etching speed by O.sub.2 is greater than
etching speed by Ar ions with respect to the CF film. In this case,
in this invention, the sputter etching effect may be used in
combination with the conventional sputter etching effect by Ar
ions.
[0088] In the case where Ar gas is used as plasma gas, O.sub.2 gas
delivered from film forming gas supply section is further activated
by the electron cyclotron resonance by energy of plasma so that
ions are provided. For this reason, O.sub.2 gas collides with wafer
by bias power of the mounting table with high perpendicularity. As
a result, since particularly etching speed of the shoulder portion
(portion of the frontage) is large as shown in FIG. 20, embedding
is carried out while sufficiently broadening the frontage portion.
For this reason, it is possible to carry out embedding also with
respect to the recessed portion of high aspect ratio. On the
contrary, since etching speed is small in the case of sputter
etching of only Ar ions, in the case where the recessed portion
having large aspect ratio is buried, etching of the frontage
portion does not overtake with respect to embedding, so voids are
apt to be formed.
[0089] In order to confirm effect of O.sub.2 gas, the apparatus
shown in FIG. 1 was used to carry out embedding test of the
recessed portion in which the portion between aluminum wirings is
0.2 .mu.m in the case where C.sub.4F.sub.8 gas, C.sub.2H.sub.4 gas
and O.sub.2 gas are delivered at flow rates of 60 sccm, 30 sccm and
20 sccm, respectively, from the film forming gas supply unit and in
the case where no O.sub.2 gas is added. As a result, in the case
where no O.sub.2 gas is added, when the aspect ratio exceeds 4,
occurrence of voids can be observed. However, in the case where
O.sub.2 gas is added, even if the aspect ratio is 5, no occurrence
of void takes place. Thus, satisfactory embedding could be carried
out.
[0090] In this experiment, the microwave power is set to 2700 W,
the bias power of the mounting table is set to 1500 W, the pressure
is set to 0.2 Pa, and the surface temperature of the mounting table
is set to 350.degree. C., and other conditions are similar to the
conditions of the previously described embodiment.
[0091] Moreover, as described above, as a technique for carrying
out embedding by making use of chemical etching by O.sub.2 gas,
film forming by C.sub.4F.sub.8 gas and C.sub.2H.sub.4 gas serving
as film forming gas may be first carried out without delivering
O.sub.2 gas to carry out etching after undergone switching from
supply of film forming gas to supply of O.sub.2 gas in the middle
thereafter to carry out switching from supply of O.sub.2 gas to
supply of film forming gas for a second time.
[0092] FIG. 21 is a view showing the state where process is carried
out by such a method, wherein FIG. 21(a) shows the state where
aluminum wirings 4 are formed on, e.g., phosphorus or boron doped
SiO.sub.2 film. When film formation is carried out by
C.sub.4F.sub.8 gas and C.sub.2H.sub.4 gas with respect to the
surface, the portions between wirings 4 are buried by CF film 42 as
shown in FIG. 21(b). In this case, when aspect ratio is large,
voids 41 are formed.
[0093] Subsequently, when CF film 42 portions are etched by O.sub.2
gas, CF films 42 remain at the side walls of the wiring 4 as shown
in FIG. 21(C), and there results such a form that there are formed
recessed portions 43 where the frontage side is wide and the depth
portion is narrow. Thereafter, when film forming is carried out
after undergone switching from O.sub.2 gas to film forming gas for
a second time, satisfactory embedding using no void is carried out
as shown in FIG. 21(d).
[0094] The timing for carrying out switching from film forming gas
to O.sub.2 gas is not limited to that of this example, and may be,
e.g., the timing when the frontage portion is about to be closed as
shown in FIG. 20, or may be other timings. Further, switching
between film forming gas and O.sub.2 gas may be carried out twice
or more during one process without being limited to one time as
described above. In addition, when O.sub.2 gas is delivered, film
forming gas may be delivered at the same time.
[0095] In order to confirm the effect of such a method, the
apparatus shown in FIG. 1 was used to deliver C.sub.4F.sub.8 gas
and C.sub.2H.sub.4 gas at flow rates of 60 sccm and 30 sccm,
respectively, for 60 seconds thereafter to carry out switching into
O.sub.2 gas 50 sccm to carry out etching for 60 sec to further
carry out film forming for 120 sec. after undergone switching into
C.sub.4F.sub.8 gas and C.sub.2H.sub.4 gas. Thus, satisfactory
embedding may be carried out at the recessed portion between
aluminum wirings in which the distance between wirings is 0.2 .mu.m
and the aspect ratio is 4.
[0096] In this experiment, the microwave power is set to 2700 W,
the bias power of the mounting table is set to 1500 W, the pressure
is set to 0.2 Pa and the surface temperature of the mounting table
is 350.degree. C., and other conditions are similar to those of the
condition of the previously described embodiment.
[0097] Another embodiment of this invention will now be described.
This embodiment is a method of applying, in a pulse form, electric
energy for generating plasma with a certain duty factor. When
explanation is given by taking the ECR plasma apparatus as an
example, the apparatus is of the configuration in which a pulse
microwave power supply 51 is used as microwave oscillating unit as
shown in FIG. 22 and a pulse high frequency power supply 52 is used
as bias power supply to the mounting table 3, and a synchronizing
circuit 53 for synchronizing these power supplies 51, 52 is
provided. In this example, the pulse microwave power supply 51 is a
unit comprising high frequency power supply for outputting, e.g.,
microwave of 2.45 GHz and adapted for allowing microwave therefrom
to be turned ON or OFF by, e.g., pulse of 10 Hz to 10 KHz outputted
from the synchronizing circuit 53, and serves to modulate so-called
microwave by pulse. Moreover, the pulse high frequency power supply
52 comprises high frequency power supply for outputting, e.g., high
frequency power of 13.56 MHz and serves to allow the high frequency
power therefrom to be turned ON or OFF to output it. An example of
power waveforms of power supplies 51, 52 is shown in FIG. 23.
Although pulse waveform is depicted in a model form in the figure,
power waveform of 2.45 GHz (or 13.56 MHz) is included in practice
when this pulse is in ON state.
[0098] The merit by such method will now be described. When
microwave is continuously oscillated as in the conventional method
to produce plasma, electron temperature rapidly elevates at the
time of start of oscillation. Further, electrons collide with
molecules one after another by the avalanche phenomenon. As a
result, temperature of electrons lowers from 12 ev to 4 ev in
average, for example. Followed by this, plasma density is saturated
so that, e.g., 10.sup.11/cm.sup.3 is provided. Thus, stable state
is realized. This state is shown in FIG. 24.
[0099] On the contrary, since the pulse oscillation repeats ON or
OFF operation, initial transient phenomenon of continuous
oscillation takes place every time pulse is turned ON. Accordingly,
the state where electron temperature suddenly rises is continuously
maintained. Such state is shown in FIG. 25. Electron temperature
rises by employing pulse oscillation, and the number of radicals
which become effective at the time of forming film, particularly
the number of radicals of high energy is increased. As a result,
when the film forming speed becomes high, and radicals are thrust
into the depth portion of the film. Thus, fine film is
provided.
[0100] As the result of the fact that film forming speed when
C.sub.4F.sub.8 gas, C.sub.2H.sub.4 gas and Ar gas are delivered at
60 sccm, 30 sccm and 150 sccm, respectively, pulse frequencies of
power supplies 51, 52 are set at 300 Hz and duty factor is changed
in various manners is examined, result shown in FIG. 26 was
obtained. With respect to other process conditions, microwave power
and bias power are set at 2700 W and 1500 W, respectively, pressure
is set at 0.2 Pa and the surface temperature of the mounting table
is set at 320.degree. C. In addition, other conditions are similar
to those of the previously described embodiment.
[0101] According as the duty factor is lowered from 100% to 40% by
making use of pulse plasma, it becomes possible to generate plasma
having high electron temperature. As a result, energy of active
species contributing to film formation is enhanced. Thus, the film
forming speed is elevated.
[0102] When the duty factor is further lowered to 40% or less,
lowering phenomenon of the film forming speed is observed. The
reason thereof is as follows. It is considered that plasma having
high electron temperature is generated simultaneously with
application of pulse power, but pulse power is turned OFF before
the avalanche phenomenon is sufficiently produced, so quantity
produced of active species contributing to film formation is
decreased. Accordingly, the duty factor is optimized, thereby
making it possible to improve film forming speed.
[0103] As stated above, in the method of utilizing pulse plasma,
high frequency power as in the conventional method may be applied
with respect to application of bias power, and such a method may be
applied to the case where formation of film except for CF film,
e.g., SiO.sub.2 film is carried out. In the above-described
embodiments, this invention may be applied to plasma processing
apparatuses except for ECR plasma processing apparatus.
[0104] As stated above, in accordance with this invention, e.g., CF
film having good film quality suitable for interlayer insulating
film can be formed, and high film forming speed is obtained.
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