U.S. patent application number 09/873620 was filed with the patent office on 2002-01-17 for method of forming diamond film and film-forming apparatus.
Invention is credited to Imai, Takahiro, Matsuura, Takashi, Meguro, Kiichi.
Application Number | 20020005170 09/873620 |
Document ID | / |
Family ID | 18673406 |
Filed Date | 2002-01-17 |
United States Patent
Application |
20020005170 |
Kind Code |
A1 |
Meguro, Kiichi ; et
al. |
January 17, 2002 |
Method of forming diamond film and film-forming apparatus
Abstract
A method and an apparatus for forming a diamond film from
microwave plasma by controlling a manufacturing condition based on
spectroscopic measurement of plasma emission to obtain a large area
of a high-quality diamond film. In the method of forming a diamond
film, a gas mixture of hydrocarbon gas and hydrogen gas is
introduced into a reactor, where the gas mixture is excited by
microwave which is also introduced into the reactor to generate
plasma, and the light emitted from the plasma is spectroscopically
measured. Furthermore, a formation condition of the diamond film is
controlled such that the spectrum of a carbon molecule (C.sub.2)
falls within a predetermined range of requirement.
Inventors: |
Meguro, Kiichi; (Itami-shi,
JP) ; Matsuura, Takashi; (Itami-shi, JP) ;
Imai, Takahiro; (Itami-shi, JP) |
Correspondence
Address: |
FASSE PATENT ATTORNEYS, P.A.
P.O. BOX 726
HAMPDEN
ME
04444-0726
US
|
Family ID: |
18673406 |
Appl. No.: |
09/873620 |
Filed: |
June 4, 2001 |
Current U.S.
Class: |
118/723MW ;
427/249.8; 427/575 |
Current CPC
Class: |
C23C 16/274 20130101;
C23C 16/52 20130101 |
Class at
Publication: |
118/723.0MW ;
427/575; 427/249.8 |
International
Class: |
C23C 016/26; H05H
001/30 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 7, 2000 |
JP |
2000-170739(P) |
Claims
What is claimed is:
1. A method of forming a diamond film, wherein a gas mixture of
hydrocarbon gas and hydrogen gas is introduced into a reactor, and
said gas mixture is excited by microwave introduced into said
reactor to generate plasma, in order to form a diamond film on a
substrate, said method comprising the steps of: spectroscopically
measuring light emitted from said plasma; and controlling a
formation condition of said diamond film such that a spectrum of a
carbon molecule (C.sub.2) measured in said spectroscopic measuring
step falls within a predetermined range of requirement.
2. The method of forming a diamond film according to claim 1,
wherein said formation condition is controlled such that said
spectrum of the carbon molecule (C.sub.2) is an emission spectrum
band of the carbon molecule and that a vibration temperature
obtained from said emission spectrum band falls within a
predetermined range.
3. The method of forming a diamond film according to claim 2,
wherein said formation condition is controlled such that said
vibration temperature of the carbon molecule (C.sub.2) falls within
a range between 2000 and 2800 K.
4. The method of forming a diamond film according to claim 1,
wherein at least one of microwave-inputting power, pressure in a
reactor and flow rate of reaction gas in said formation condition
of the diamond film is controlled such that said spectrum falls
within a predetermined range.
5. The method of forming a diamond film according to claim 2,
wherein at least one of microwave-inputting power, pressure in a
reactor and flow rate of reaction gas in said formation condition
of the diamond film is controlled such that said spectrum falls
within a predetermined range.
6. The method of forming a diamond film according to claim 3,
wherein at least one of microwave-inputting power, pressure in a
reactor and flow rate of reaction gas in said formation condition
of the diamond film is controlled such that said spectrum falls
within a predetermined range.
7. The method of forming a diamond film according to claim 3,
wherein said vibration temperature of the carbon molecule is
obtained from a spectrum band having a difference of +1 or -1
between a high vibration level and a low vibration level.
8. The method of forming a diamond film according to claim 6,
wherein said vibration temperature of the carbon molecule is
obtained from a spectrum band having a difference of +1 or -1
between a high vibration level and a low vibration level.
9. The method of forming a diamond film according to claim 7,
wherein said vibration temperature is obtained using said emission
spectrum band of the carbon molecule (C.sub.2) within a wavelength
range between 465 and 475 nm.
10. The method of forming a diamond film according to claim 8,
wherein said vibration temperature is obtained using said emission
spectrum band of the carbon molecule (C.sub.2) within a wavelength
range between 465 and 475 nm.
11. A film-forming apparatus for forming a diamond film,
comprising: a reactor in which reaction gas is excited by microwave
to generate plasma; a microwave generating device generating said
microwave; a spectroscope generating spectrum of light emitted from
said plasma; and an arithmetic unit obtaining a vibration
temperature from an emission spectrum band of a carbon molecule
(C.sub.2) obtained by said spectrometer.
12. The film-forming apparatus for forming a diamond film according
to claim 11, further comprising: a control means for controlling at
least one factor of microwave-inputting power, pressure in the
reactor, and flow rate of the reaction gas, such that the vibration
temperature falls within a predetermined range, based on a value of
said vibration temperature obtained by said arithmetic unit.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a method of forming a
diamond film and a film-forming apparatus, and particularly, to a
method of forming a diamond film and a film-forming apparatus
utilizing microwave plasma.
[0003] 2. Description of the Background Art
[0004] Various methods have been invented for forming diamond from
vapor phase, such as a hot-filament CVD method, a microwave plasma
assisted CVD method and so forth. The microwave plasma assisted CVD
method is especially suitable, among others, for forming a
high-purity polycrystalline diamond film and an epitaxial diamond
film, whereby a high-quality diamond film can easily be obtained
compared to the case with other methods. The other methods are
associated with some problems that degrade the quality of the
diamond film. For example, the hot-filament CVD method involves
metal contamination from filament, and a plasma jet method involves
metal contamination from an electrode. Moreover, in a combustion
flame method, nitrogen in the air is mixed into diamond, degrading
the quality of the diamond film. Thus, the microwave plasma
assisted CVD method has been widely used as a method of obtaining a
high-quality diamond film, and recently, developments have been
propelled for obtaining a large area of high-quality diamond
film.
[0005] The microwave plasma assisted CVD method has an advantage in
that such a high-quality diamond film can easily be obtained, while
having a drawback in that the resulting film are varied in its
thickness and quality in a wide range of distribution, especially
when compared to the case with the hot-filament CVD method. Thus,
it is particularly difficult to obtain a large size of diamond film
having uniform thickness and quality by the microwave plasma
assisted CVD method. Currently, there is not even a guideline for
adjusting the variation as described above, and such guideline is
still being searched for. For guideline in forming a diamond film
by the microwave plasma method, a temperature of a substrate
measured using a radiation thermometer and a thermocouple within a
reactor are used, and further spectrum analysis by plasma emission
spectroscopy or the like is used. However, the substrate
temperature measured by the radiation thermometer is essentially
associated with plasma emission, making it difficult to obtain an
accurate temperature of the substrate. Furthermore, when the
thermocouple is used for a temperature measurement, the temperature
cannot directly be obtained unless the substrate is in direct
contact with the thermocouple. Even if the direct contact was
possible, such contact would cause disturbance, which affects
formation of the diamond film. Whereas, when the plasma emission
spectroscopy is used for diagnosing a plasma state, observation on
the spot is possible without any contact, causing no disturbance to
the plasma state. Thus, conventionally, the diagnosis using the
plasma emission spectroscopy has been actively performed. The
measurement using the plasma emission spectroscopy has been
successful in certain ways, for instance, contamination by
nitrogen, which significantly interferes with the formation of the
diamond film, can be found instantly. However, the plasma emission
spectroscopy has not yet reached the level where the quality and
the deposition rate of the diamond film can be predicted.
SUMMARY OF THE INVENTION
[0006] The present invention is directed to provide a method for
forming a diamond film from reaction gas excited by microwave, and
particularly for forming a large size of a high-quality diamond
film by controlling a manufacturing condition based on information
on spectroscopic measurement of plasma emission, and to provide a
film-forming apparatus for forming such a diamond film.
[0007] In the method of forming a diamond film according to the
present invention, a gas mixture of hydrocarbon gas and hydrogen
gas is introduced into a reactor where the gas mixture is excited
by microwave which is also introduced into the reactor to generate
plasma, in order to form a diamond film on a substrate. In the
forming method, plasma emission is spectroscopically measured to
control a formation condition of the diamond film such that the
spectrum of a carbon molecule (C.sub.2: hereinafter referred to as
"carbon molecule") falls within a predetermined range of
requirement.
[0008] The formation method of the diamond film from the
microwave-excited plasma of this invention is based on a new idea
in that the spectrum of the carbon molecule is strongly correlated
with the quality of the diamond film and its distribution, and
hence only an emission spectrum band of the carbon molecule is
herein observed. Thus, a controlling method can be simplified,
since the only requirement is to adjust the formation condition of
the diamond film such that the spectrum of the carbon molecule is
within the predetermined range, and therefore the formation
condition of the diamond film can be precisely adjusted. As a
result, the distribution of quality, i.e. spatial variation of
quality, is suppressed, so that a large area of homogeneous and
high-quality diamond film can be obtained. Any apparatus may be
employed for forming the diamond film described above, in which
reaction gas is excited by microwave to attain a plasma state and
the diamond film is formed on a substrate by the plasma. A
microwave plasma assisted CVD apparatus or another apparatus may be
used.
[0009] In the method of forming a diamond film according to the
present invention, the spectrum of a carbon molecule is a vibration
spectrum of the carbon molecule, and a formation condition is
controlled such that a vibration temperature obtained by such a
spectrum falls within a predetermined range.
[0010] The inventors of the present invention spectroscopically
measured the emission of microwave plasma, and found that the
vibration temperature of a carbon molecule can be derived from the
emission spectrum band of the carbon molecule, i.e. one of
activated molecule species constituting the plasma. They also came
to a new idea in that the vibration temperature is closely related
to the deposition rate and quality of the diamond, and the
distribution thereof. The vibration temperature of the carbon
molecule can be derived using the procedure described below.
[0011] In plasma, electrons are much lighter than atomic nuclei,
and hence moves much faster. This allows the movement of the
electrons and that of the atomic nuclei to be precisely separated
for further discussion. Such a way of discussing these movements
independent of each other is a precise approximation method called
Born-Oppenheimer approximation. When Born-Oppenheimer approximation
is possible, the intensity I.sub.ev'v"J'J" of spectral lines
contained in a band spectrum emitted due to the transition of a
molecule between electron states can be represented by the equation
(1) below.
I.sub.ev'v"J'J"=Cf.sup.4q.sub.v'v"S.sub.J'J".times.exp[[-(hc/kT.sub.ex)
T.sub.e]+[-(hc/kT.sub.vib) G (v')]+[-(hc/kT.sub.rot) F (J')]]
(1)
[0012] wherein e is a type of electron-term transition, v is the
quantum number of vibration, J is the quantum number of rotation,
and an addition of ' indicates a high level whereas that of "
indicates a low level. Moreover, C is a constant, f is the
vibration number of the spectral lines, q.sub.v'v" is a
Franck-Condon factor and S.sub.J'J" is a Honl-London factor.
Furthermore, h is a Planck constant, c is the speed of light, and k
is a Boltzmann constant. In addition, T.sub.ex, T.sub.vib and
T.sub.rot indicate an excitation temperature, a vibration
temperature and a rotation temperature, respectively, and T.sub.e,
G(v') and F(J') indicate the term values in the electron state, in
the vibration state and in the rotation state, respectively. Noting
the transition between certain electron states, the equation (1) is
separated by the term of the vibration temperature and that of the
rotation temperature. When q.sub.v'v" and S.sub.J'J" are known and
the rotation spectrum can be resolved for measurement, the
vibration temperature and the rotation temperature can be obtained
independently of each other. When the rotation spectrum cannot be
resolved due to e.g. limitation of wavelength resolution of a
spectroscope, if q.sub.v'v" is known, the vibration temperature
T.sub.vib can be obtained from the intensity of a band head
(J'=J"=0). Therefore, the equation (1) can be rewritten as the
equation (2) below.
I.sub.v'v"=C.sub.1f.sup.4q.sub.v'v"exp[-(hc/kT.sub.vib) G (v')]
(2)
[0013] wherein C.sub.1 is a constant independent off. The intensity
I.sub.v'v" of the spectral lines and the wavelength G (v') are
directly obtained by the plasma spectroscopic measurement, so that
the equation (2) can further be rewritten as the equation (3)
below.
In [I.sub.v'v"/f.sup.4q.sub.v'v"]=C.sub.2-(E.sub.v'/kT.sub.vib)
(3)
[0014] From the equation (3), In [I.sub.v'v"/f.sup.4q.sub.v'v"] is
plotted with respect to E.sub.v', and the inclination is obtained
by fitting, to further obtain the vibration temperature of the
molecule. Here, C.sub.2 is a constant independent of f, and
E.sub.v' indicates vibration energy.
[0015] According to the method described above, the wavelength
resolution required for the spectroscope may be at a relatively low
level of 0.3 nm. Therefore, plasma can easily be estimated by an
inexpensive apparatus. The vibration temperature of C.sub.2
molecule obtained as described above is close to the equilibrium
with gas temperature determined by the kinetic energy of other
activated species gas or neutral gas in the reactor, so that it can
be approximately estimated as plasma gas temperature. The gas
temperature of plasma is closely related to the film deposition
rate and quality of diamond, and the distribution thereof. As
described above, the present invention is based on a new idea in
that the film deposition rate or the quality of diamond can be
estimated by the vibration temperature of the carbon molecule that
can easily be obtained. The vibration temperature of the carbon
molecule can readily be controlled by changing the power of
inputting microwave, pressure, gas flow rate or the like.
[0016] In the method of forming a diamond film according to the
present invention, a formation condition is controlled such that
the vibration temperature of the carbon molecule falls within the
range between 2000 and 2800 K.
[0017] By controlling the vibration temperature to be within the
range described above, a high-quality diamond film can rapidly be
formed. For example, if the diamond film is formed with a vibration
temperature within a range between 2400 and 2700 K, a diamond film
transparent from ultraviolet to infrared regions can be obtained.
Moreover, if the diamond film is formed with a vibration
temperature within a range between 2200 and 2800 K, a diamond film
with thermal conductivity of 1000 W/mK, which is applicable to a
heat sink or the like, can be obtained. If the vibration
temperature is less than 2000 K, the film deposition rate is
lowered, degrading crystallinity of a resulting diamond film. In
addition, distribution of the quality such as crystallinity may be
varied in certain locations. On the other hand, if the vibration
temperature exceeds 2800 K, the film deposition rate is increased,
which now makes the crystallinity of the resulting diamond
incomplete while increasing the positional variation in
quality.
[0018] In the method of forming a diamond film according to the
present invention, at least one of microwave-inputting power,
pressure in the reactor and flow rate of each reaction gas in the
formation condition of the diamond film is controlled such that the
spectrum falls within a predetermined range.
[0019] The formation condition as described above can easily be
controlled artificially, and control of at least one such condition
allows the vibration temperature to be in the predetermined range,
and hence a large area of high-quality diamond film can be
obtained.
[0020] Moreover, in the method of forming a diamond film according
to the present invention, the vibration temperature of the carbon
molecule can be obtained from a spectrum band having a difference
of +1 or -1 between a high vibration level and a low vibration
level.
[0021] Though no selection rule exists in C.sub.2 molecule for
transition between the vibration levels, the vibration temperature
can precisely be obtained from the transition with a difference of
.+-.1 between the levels, because such transition occurs with a
probability higher than transition with a difference of other value
between levels. However, the level difference in vibration is not
necessarily .+-.1, and the level difference of 0 may also be
used.
[0022] In the method of forming a diamond film according to the
present invention, an emission spectrum band of a carbon molecule
within a range between the wavelengths of 465 and 475 nm is used to
obtain a vibration temperature.
[0023] The emission spectrum band of the carbon molecule in this
wavelength range has a vibration level difference of +1 and has a
particularly high probability of transition, so that the vibration
temperature can be obtained with high precision. Furthermore, even
when automatic control is employed, obvious peaks can be seen, and
the ratio of the peak intensities in the above-described wavelength
range may be obtained to simplify the automatic control.
[0024] The film-forming apparatus of a diamond film according to
the present invention includes a reactor in which reaction gas is
excited to generate plasma; a microwave generating apparatus
generating microwave; a spectroscope generating a spectrum of light
emitted from the plasma; and an arithmetic unit obtaining a
vibration temperature from an emission spectrum band of a carbon
molecule obtained by the spectroscope.
[0025] The arrangement described above facilitates obtainment of
the vibration temperature from the emission spectrum band of the
carbon molecule. Though the arithmetic unit is preferably a
microcomputer into which a software is installed, it may also be a
wired logic circuit. In the arithmetic operation, the peaks in the
emission spectrum band of the carbon molecule correspond to certain
wavelengths, and thus the vibration temperature can rapidly be
obtained by taking a ratio of the peak intensities in the vicinity
of such wavelengths.
[0026] The film-forming apparatus according to the present
invention further includes a control unit for controlling at least
one factor of microwave-inputting power, pressure within a reactor
and flow rate of reaction gas, such that the vibration temperature
falls within a predetermined range, based on the value of the
vibration temperature obtained by the arithmetic unit.
[0027] By the above-described arrangement, a large area of a
high-quality diamond film can be obtained by automatically
controlling a formation condition of the diamond film. The
automatic control is desirably performed such that the diamond film
is formed after the vibration temperature of a carbon molecule in
plasma is brought to be within the predetermined temperature.
[0028] The foregoing and other objects, features, aspects and
advantages of the present invention will become more apparent from
the following detailed description of the present invention when
taken in conjunction with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0029] FIG. 1 shows a configuration of an apparatus for forming a
diamond film according to an example of the present invention;
[0030] FIG. 2 shows an example of a measurement of a spectrum of
plasma emission in the method of forming a diamond film according
to the present invention;
[0031] FIG. 3 is an enlarged view of a wavelength range between
wavelengths of 450 and 490 nm in the example of the plasma emission
measurement shown in FIG. 2; and
[0032] FIG. 4 is an enlarged view of a wavelength range between
wavelengths of 470 and 530 nm in the example of the plasma emission
measurement shown in FIG. 2.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0033] Examples of the present invention will now be described with
reference to the drawings.
EXAMPLE 1
[0034] In the method of forming a diamond film illustrated in the
present example, the diamond film is deposited on an Si substrate
using a microwave plasma assisted CVD apparatus, as shown in FIG.
1. Referring to FIG. 1, reaction gas is introduced through a
gas-feeding pipe 4 into a reactor 7. Microwave oscillated by a
magnetron 1 is transmitted through a waveguide 2 and is introduced
into reactor 7 from a quartz vacuum window 3. The microwave excites
the reaction gas to generate microwave plasma 10 on Si substrate
11. The light emitted from microwave plasma 10 is transmitted
through a monitoring window 8 and is spectroscopically measured by
a spectroscope 9. A stage 12 on which substrate 11 is supported
includes a water-cooling mechanism, and thus the temperature of the
substrate can arbitrarily be controlled irrespective of the state
of plasma. Formation conditions of the diamond film in the present
example were as follows.
[0035] (a) Volume flow rate of hydrogen (H.sub.2): 300 sccm,
wherein sccm stands for standard cubic centimeter per minute.
[0036] (b) Volume flow rate of methane (CH.sub.4): 3 sccm
[0037] (c) Pressure in the reactor: 13.3 kPa
[0038] (d) Microwave frequency: 2.45 GHz
[0039] (e) Temperature of substrate: 950.degree. C.
[0040] With the conditions indicated above, the microwave-inputting
power was set to be 1 kW, 3 kW and 5 kW, to form a diamond film on
a Si substrate having a diameter of 2 inches. The emitted light in
a visible radiation range of microwave plasma was spectroscopically
measured by a spectroscope, and the result thereof is shown in FIG.
2. In the visible radiation range, the band spectrum of C.sub.2
molecule was observed together with Balmer lines of an H atom. FIG.
3 shows an enlarged view of an emission band of C.sub.2 molecule
having a vibration level difference of +1, which is observed in the
wavelength range between 465 and 475 nm. A vibration temperature
can be obtained from the ratio of the peak intensities when the
rotation level of the emission band of C.sub.2 molecule J'=J"=0.
Though the spectrum shown in FIG. 3 is used in the present example,
the vibration temperature may also be obtained using the spectrum
shown in FIG. 4 where the difference in the vibration levels is
zero. FIG. 4 is an enlarged view of the wavelength range between
470 and 530 nm of the spectrum shown in FIG. 2. For each
microwave-inputting power, (A) vibration temperature of the carbon
molecule, (B) film deposition rate of diamond, and (C) full width
at half maximum of diamond peak (1333 cm.sup.-1) due to Raman
spectroscopy, which is a baseline of the quality of diamond, were
obtained. The obtained values are shown in Table 1 for the central
and peripheral portions of the substrate.
1TABLE 1 Micro- wave- Central portion of substrate input- Vibra-
Peripheral portion of substrate ting tion Deposition Raman
Vibration Deposition Raman power temp. rate FWHM temp. rate FWHM
(kW) (K) (.mu.m/hr) (cm.sup.-1) (K) (.mu.m/hr) (cm.sup.-1) 1 2200
1.0 5.5 1600 0.2 10.5 3 2700 1.5 4.5 2400 1.3 5.0 5 3000 1.7 8.5
2850 1.6 6.5
[0041] As can be seen from Table 1, the vibration temperature can
be controlled by adjusting the microwave-inputting power. Moreover,
it was proved that there is a close correlation between (a)
vibration temperature, (b) film deposition rate of diamond and (c)
Raman FWHM. Thus, when a diamond film is deposited with the
vibration temperature within a range between 2400 and 2700 K, a
high quality diamond film with good crystallinity having Raman FWHM
of 5.0 cm.sup.- or lower can be obtained. After 100 hours of
diamond deposition with the above-described microwave-inputting
power of 3 kW, the Si substrate is dissolved by an acid mixture
containing hydrofluoric acid and nitric acid (HNO.sub.3+HF) to
obtain a diamond self-supported film. The diamond film is
distributed from the central portion to the peripheral portion,
showing transmittance of 71%, which is close to the theoretical
transmittance, from ultraviolet to infrared regions.
[0042] Though the example 1 described above used methane as a
carbon source, acetylene, benzene, ethanol, or the mixture thereof
may also be used to obtain a similar result.
EXAMPLE 2
[0043] In the example 2, a diamond film was deposited with the
conditions indicated below using the microwave plasma assisted CVD
apparatus shown in FIG. 1 that was used in the example 1. In the
present example, a diamond film was formed using the conditions
indicated below with constant microwave-inputting power of 3 kW and
changing pressure in the reactor.
[0044] (a) Volume flow rate of hydrogen (H.sub.2): 300 sccm
[0045] (b) Volume flow rate of methane (CH.sub.4): 3 sccm
[0046] (f) Microwave-inputting power: 3 kW
[0047] (d) Microwave frequency: 2.45 GHz
[0048] (e) Temperature of substrate: 950.degree. C.
[0049] With the conditions above, the pressure in the reactor was
set to be at 10.7 kPa, 13.3 kPa and 16.0 kPa, to form a diamond
film on an Si substrate having a diameter of 2 inches. By the
method similar to that in the example 1, the vibration temperature
of C.sub.2 molecule was obtained for each pressure in the reactor.
The pressure in the reactor, the film deposition rate (of diamond),
and Raman FWHM were obtained for each of the central and peripheral
portions of the substrate. The result is shown in Table 2.
[0050] As can be seen from Table 2, the vibration temperature can
also be controlled by changing the pressure in the reactor. From
the relation between the vibration temperature and the Raman FWHM,
it is recognized that a high quality diamond film having the Raman
FWHM of 5.0 cm.sup.-1 could be formed when the vibration
temperature of C.sub.2 molecule was set to be within the range
between 2400 and 2700 K. This diamond film is transparent from
ultraviolet to infrared regions. Furthermore, it was proved that a
diamond film having a thermal conductivity of 1000 W/m K or higher
applicable to a heat sink or the like could be obtained if the
diamond film was formed with a temperature within a range between
2200 and 2800 K.
2 TABLE 2 Central portion of substrate Pressure Vibra- Peripheral
portion of substrate in tion Deposition Raman Vibration Deposition
Raman reactor temp. rate FWHM temp. rate FWHM (kPa) (K) (.mu.m/hr)
(cm.sup.-1) (K) (.mu.m/hr) (cm.sup.-1) 10.7 2100 0.9 6.5 2000 0.8
8.5 13.3 2700 1.5 4.5 2400 1.3 5.0 16.0 3200 2.2 11.5 2600 1.4
5.5
[0051] It is noted that the vibration temperature of a carbon
molecule may be obtained in the following manner: an arithmetic
unit is connected to spectroscope 9 shown in FIG. 1 and an integral
of the intensity in a certain wavelength or of the intensity in the
proximity including the certain wavelength is obtained.
Subsequently, the arithmetic operation represented by the equation
(3) is performed in the arithmetic unit, to obtain a vibration
temperature of a carbon molecule.
[0052] Although the present invention has been described and
illustrated in detail, it is clearly understood that the same is by
way of illustration and example only and is not to be taken by way
of limitation, the spirit and scope of the present invention being
limited only by the terms of the appended claims.
* * * * *