U.S. patent application number 10/013457 was filed with the patent office on 2002-05-23 for nf3 treating process.
This patent application is currently assigned to Central Glass Company, Limited. Invention is credited to Ishibashi, Takayuki, Nakagawa, Shinsuke.
Application Number | 20020061269 10/013457 |
Document ID | / |
Family ID | 14315474 |
Filed Date | 2002-05-23 |
United States Patent
Application |
20020061269 |
Kind Code |
A1 |
Ishibashi, Takayuki ; et
al. |
May 23, 2002 |
NF3 treating process
Abstract
A process for treating NF.sub.3 useful as a dry etching gas and
cleaning gas in processes for producing LSI, TFT, and solar cell
and in an electron photographic processes. The treating process
comprises following step: (a) preparing a reactor including
agitator blades for agitating gas in the reactor and generating a
flow of the gas, and a gas flow guide tube for efficiently
circulating and dispersing the gas flow generated by the agitator
blades in a space of the reactor; (b) stationarily placing at least
one substance selected from the group consisting of a metal and a
metal compound within a reactor, the metal being at least one metal
selected from the group consisting of Si, B, W, Mo, V, Se, Te and
Ge, the metal compound being at least one metal compound selected
from the group consisting of solid compounds of Si, B, W, Mo, V,
Se, Te and Ge; (c) introducing a gas containing NF.sub.3 into the
reactor to react the introduced gas with at least one substance of
the metal and the metal compound at a temperature ranging from 400
to 900.degree. C. upon operating the agitator blades of the reactor
so as to form a fluoride gas; and (d) capturing the fluoride
gas.
Inventors: |
Ishibashi, Takayuki;
(Yamaguchi, JP) ; Nakagawa, Shinsuke; (Yamaguchi,
JP) |
Correspondence
Address: |
CROWELL & MORING LLP
INTELLECTUAL PROPERTY GROUP
P.O. BOX 14300
WASHINGTON
DC
20044-4300
US
|
Assignee: |
Central Glass Company,
Limited
|
Family ID: |
14315474 |
Appl. No.: |
10/013457 |
Filed: |
December 13, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10013457 |
Dec 13, 2001 |
|
|
|
09545521 |
Apr 7, 2000 |
|
|
|
Current U.S.
Class: |
422/224 ;
422/198; 422/202; 422/225; 422/227; 423/239.1; 95/128 |
Current CPC
Class: |
B01D 53/685 20130101;
B01D 53/82 20130101; B01J 8/02 20130101 |
Class at
Publication: |
422/224 ;
423/239.1; 95/128; 422/225; 422/198; 422/227; 422/202 |
International
Class: |
B01D 053/54; F28D
021/00; B01J 008/10 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 9, 1999 |
JP |
11-101997 |
Claims
What is claimed is:
1. A process for treating NF.sub.3, comprising the following steps:
preparing a first reactor including agitator blades for agitating
gas in the first reactor and generating a flow of the gas, and a
gas flow guide tube for efficiently circulating and dispersing the
gas flow generated by the agitator blades in a space of the first
reactor; stationarily placing at least one substance selected from
the group consisting of a metal and a metal compound within a first
reactor, the metal being at least one metal selected from the group
consisting of Si, B, W, Mo, V, Se, Te and Ge, the metal compound
being at least one metal compound selected from the group
consisting of solid compounds of Si, B, W, Mo, V, Se, Te and Ge;
introducing a gas containing NF.sub.3 into the first reactor to
react the introduced gas with at least one substance of the metal
and the metal compound at a temperature ranging from 400 to
900.degree. C. upon operating the agitator blades of the first
reactor so as to form a fluoride gas; and capturing the fluoride
gas.
2. A process as claimed in claim 1, wherein the preparing step
includes preparing the first reactor including an outer tube in
which the gas flow guide tube is generally coaxially located so as
to form an outer cylindrical space between the outer tube and the
gas flow guide tube, and a tray on which the at least one substance
of the metal and the metal compound is placed, the tray being
located inside the gas flow guide tube, and locating the agitator
blades inside the outer tube and at a side upstream of the
tray.
3. A process as claimed in claim 1, further comprising the step of
causing the gas within the gas flow guide tube to flow at a mean
flow rate of 0.5 m/sec or more so as to be circulated and
dispersed.
4. A process as claimed in claim 1, further comprising the
following steps: connecting a second reactor in series with and at
a side downstream of the first reactor, the second reactor having a
fixed bed including at least one substance selected from the group
consisting of a metal and a metal compound within a first reactor,
the metal being at least one metal selected from the group
consisting of Si, B, W, Mo, V, Se, Te and Ge, the metal compound
being at least one metal compound selected from the group
consisting of solid compounds of Si, B, W, Mo, V, Se, Te and Ge;
and introducing gas discharged from the first reactor to the second
reactor so as to react the gas with the at least one substance of
the metal and the metal compound within a temperature ranging from
400 to 900.degree. C.
5. A system for treating NF.sub.3, comprising: a reactor including
an outer tube into which a gas containing NF.sub.3 is supplied,
agitator blades disposed inside said outer tube for agitating the
gas and generating a flow of the gas, a gas flow guide tube
disposed inside said outer tube to efficiently circulate or
disperse the gas flow generated by the agitator blades in a space
of the outer tube, at least one substance selected from the group
consisting of a metal and a metal compound, disposed inside said
gas flow guide tube, said metal being at least one metal selected
from the group consisting of Si, B, W, Mo, V, Se, Te and Ge, said
metal compound being at least one metal compound selected from the
group consisting of solid compounds of Si, B, W, Mo, V, Se, Te and
Ge, and a first heater disposed outside said outer tube to heat the
space inside the outer tube at a temperature ranging from 400 to
900.degree. C.
6. A system as claimed in claim 5, wherein the gas flow guide tube
of said reactor is generally coaxially located inside said outer
tube so as to form an outer cylindrical space between the outer
tube and the gas flow guide tube, wherein said reactor includes a
tray on which the at least one substance of the metal and the metal
compound is placed, the tray being located inside the gas flow
guide tube; wherein the agitator blades of said reactor is located
inside the outer tube and at a side upstream of the tray so as to
cause the gas to recirculate through a space formed inside said gas
flow guide tube and through said outer cylindrical space.
7. A system as claimed in claim 1, wherein said agitator blades are
arranged to cause the gas within the gas flow guide tube to flow at
a mean flow rate of 0.5 m/sec or more.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a process for treating
NF.sub.3 gas that is useful as a dry etching gas and cleaning gas
in processes for producing LSI, TFT, and solar cell and in an
electron photographic process.
[0003] 2. Description of the Invention
[0004] NF.sub.3 is a toxic gas having a TLV of 100 ppm that is
extremely stable in air and essentially insoluble in water. In the
case of using this substance, it is necessary at all times to
remove residual NF.sub.3 present in exhaust gas. Since NF.sub.3 is
extremely chemically stable at temperatures near room temperature
and is also insoluble in water, it cannot be processed by ordinary
gas absorption processes in its original state. Consequently, the
following process has been proposed in Japanese Patent No. 1538007
(Japanese Patent Provisional Publication No. 61-204025),in which
NF.sub.3 is reacted with a substance that converts NF.sub.3 into a
fluoride gas that easily reacts with water and alkaline solution,
followed by treating the resulting fluoride gas with a normal gas
absorption process. The Japanese Patent discloses a process wherein
NF.sub.3 is reacted with Si, B, W, Mo, V, Se, Te, Ge and their
non-oxidizing solid compounds that are used as the converting
substance.
[0005] Although the above NF.sub.3 treatment process is effective
for converting NF.sub.3 into an easily treated gas compound, a
characteristic reactor taking the NF.sub.3 into consideration was
not proposed with respect to the reactor for reacting and treating
a large amount of NF.sub.3. Namely, the above Patent only proposes
a single flow type of fixed bed reactor as equipment for contacting
gaseous NF.sub.3 with a solid compound.
[0006] The fixed bed reactor described in the present specification
refers to a reactor having a cylindrical outer tube in which a
fixed bed, filled with a solid compound such as a metal element
that reacts with NF.sub.3 throughout an ordinary cylindrical
reactor, is disposed. The fixed bed is heated as necessary followed
by introducing gas from one end of the cylinder, contacting and
reacting the gas with a metal element and so forth inside the
cylindrical tube, and discharging the gas from the other end of the
tube. This form of the reactor is that which has been known since
long ago. In addition, various types of NF.sub.3 detoxification
technologies taking into consideration new reaction systems other
than the above reaction system have been disclosed as being
disclosed in Japanese Patent Publication No. 2-30731 and Japanese
Patent provisional Publication No. 7-1555409. In such technologies,
the fixed bed reactor of the gas flow type is still used. Thus, the
reactors that provide an effective setting for an NF.sub.3
detoxification reaction have not yet discovered.
[0007] Now, treatment of NF.sub.3 gas is accompanied by the
generation of extremely large amounts of heat from the reaction.
Namely, its standard formation enthalpy is -127 kJ/mol (-42 kJ per
fluorine atom), and in the case of SiF.sub.4 gas being obtained as
the product of the action of metal Si, for example, since the
standard formation enthalpy of SiF.sub.4 is -1615 kJ/mol (-404 kJ
per fluorine atom). The difference between the two enthalpies are
the amount of heat generated accompanying reaction (362 kJ per
fluorine atom), which demonstrates that NF.sub.3 detoxification
reaction is accompanied by the generation of an extremely large
amount of heat. Even though there may be some difference in the
amount of heat generated in the case that the other substance than
Si such as B or W, or if C is selected as a reacting metal element;
however, it is intrinsically a reaction that is accompanied by the
generation of a large amount of heat.
[0008] In the case of conducting a gas-solid reaction using a
reactor or reaction tube of the type in which gas is allowed to
flow over a fixed bed, the reaction initially occurs in the zone on
the inlet side of the initial reaction tube, and as chemical is
consumed, the reaction zone gradually moves to the outlet side.
Since the flow of gas inside the reactor is so-called piston flow,
there are many cases in which the reaction always occurs in a
special location inside the reaction tube in this manner, while
other portions of the reaction tube merely fulfill the role of a
gas pathway and are not involved in the reaction itself. Moreover,
due to the low rate of heat transfer of the fixed bed, it cannot be
said to be suited for efficiently discharging the reaction heat
generated locally inside the reactor in this manner outside the
system.
[0009] For these reasons, when an NF.sub.3 detoxification reaction
is carried out with a fixed bed gas flow system for a reaction that
generates a large amount of heat, the local temperature that
results from the reaction ends up becoming extremely high.
Consequently, the amount of NF.sub.3 that be treated per unit time
cannot be increased relative to the volume of the reactor.
[0010] Moreover, there has been proposed a process in which the
concentration of supplied NF.sub.3 is diluted with an inert gas
(such as N.sub.2) for the purpose of lowering the temperature of
the formed gas. However, this process increases the volumetric flow
of all gas resulting in a shortening of retention time, and
therefore is not effective as a means of improving the NF.sub.3
treatment rate per reactor volume. Moreover, even if a large
reactor is attempted to be designed having a larger NF.sub.3
treatment rate, there is a limit on the size of the reaction tube
diameter for ensuring heat transfer in the radial direction.
Ultimately, in order to provide NF.sub.3 treatment volume, a
plurality of small diameter reactors must be arranged in parallel,
and in any case, fixed bed gas flow systems had the problem of
being disadvantageous in terms of equipment cost.
[0011] In addition, in the case of using Si, for example, in the
reaction between NF.sub.3 and Si, a relatively large amount of heat
is generated on the order of 1,086 kJ/mol. Consequently, this
invites a local temperature rise and overheating in conventional
tubular apparatuses of the fixed bed type, thereby placing a limit
on the amount (concentration) of NF.sub.3 supplied, and the limit
of that supplied concentration is 5 vol %. In addition, the actual
limit on the tube diameter of a fixed bed system is 150 A
(according to Japanese Industrial Standard) corresponding to an
outer diameter of 165.2 mm. Namely, it was necessary to accompany
treatment of NF.sub.3 at 5 NL/min with a diluting gas (N.sub.2) at
100 NL/min. For this reason, fixed bed systems are not suited for
treatment of highly concentrated NF.sub.3 or large amounts of
NF.sub.3.
[0012] In addition, in the case of fixed bed systems, treatment
capacity has been observed to decrease when air or oxygen is
present. Consequently, there is a need for an NF.sub.3 treatment
process that allows treatment of highly concentrated NF.sub.3, does
not result in a decrease in treatment rate even in the presence of,
for example oxygen (air) in the NF.sub.3, and is able to ensure a
certain degree of treatment volume per unit time.
SUMMARY OF THE INVENTION
[0013] As a result of conducting earnest studies in consideration
of the above-mentioned problems, the inventors of the present
invention have found that highly concentrated and large amounts of
NF.sub.3 gas can be treated by creating a setting for gas flow that
prevents local overheating of the fixed portion of a reactor,
rapidly transports generated heat to the wall of the reactor with
the flow of gas, and provides as rapid a gas flow as possible along
the reactor wall to promote transfer of heat between the gas phase
and solid wall in the vicinity of the reactor wall, thereby leading
to completion of the present invention.
[0014] An aspect of the present invention resides in a process for
treating NF.sub.3, comprising the following step: (a) preparing a
first reactor including agitator blades for agitating gas in the
first reactor and generating a flow of the gas, and a gas flow
guide tube for efficiently circulating and dispersing the gas flow
generated by the agitator blades in a space of the first reactor;
(b) stationarily placing at least one substance selected from the
group consisting of a metal and a metal compound within a first
reactor, the metal being at least one metal selected from the group
consisting of Si, B, W, Mo, V, Se, Te and Ge, the metal compound
being at least one metal compound selected from the group
consisting of solid compounds of Si, B, W, Mo, V, Se, Te and Ge;
(c) introducing a gas containing NF.sub.3 into the first reactor to
react the introduced gas with at least one substance of the metal
and the metal compound at a temperature ranging from 400 to
900.degree. C. upon operating the agitator blades of the first
reactor so as to form a fluoride gas; and (d) capturing the
fluoride gas.
[0015] The above process may further comprises the steps of (e)
connecting a second reactor in series with and at a side downstream
of the first reactor, the second reactor having a fixed bed
including at least one substance of a metal and a metal compound
within a first reactor, the metal being at least one metal selected
from the group consisting of Si, B, W, Mo, V, Se, Te and Ge, the
metal compound being at least one metal compound selected from the
group consisting of solid compounds of Si, B, W, Mo, V, Se, Te and
Ge; and (f) introducing gas discharged from the first reactor to
the second reactor so as to react the gas with the at least one
substance of the metal and the metal compound within a temperature
ranging from 400 to 900.degree. C.
[0016] Another aspect of the present invention resides in a system
for treating NF.sub.3. The system comprises a reactor which
includes an outer tube into which a gas containing NF.sub.3 is
supplied. Agitator blades are disposed inside the outer tube for
agitating the gas and generating a flow of the gas. A gas flow
guide tube is disposed inside the outer tube to efficiently
circulate and disperse the gas flow generated by the agitator
blades in a space of the outer tube. Additionally, at least one
substance selected from the group consisting of a metal and a metal
compound, disposed inside the gas flow guide tube. The metal is at
least one metal selected from the group consisting of Si, B, W, Mo,
V, Se, Te and Ge. The metal compound is at least one metal compound
selected from the group consisting of solid compounds of Si, B, W,
Mo, V, Se, Te and Ge. Additionally, a heater is disposed outside
the outer tube to heat the space inside the outer tube at a
temperature ranging from 400 to 900.degree. C.
[0017] According to the NF.sub.3 treatment process and system of
the present invention, gas containing NF.sub.3 in a large amount
and/or at a high concentration can be adequately removed while
performing the treatment process safely without the formation of
explosive gas by-products.
BRIEF DESCRIPTION OF THE DRAWINGS
[0018] FIG. 1 is a schematic longitudinal sectional view of an
example of a horizontal cylindrical reactor used in a NF.sub.3
treating process according to the present invention.
DETAILED DESCRIPTION OF THE INVENTION
[0019] According to the present invention, a process for treating
NF.sub.3, comprises the following step: (a) preparing a reactor
including agitator blades for agitating gas in the reactor and
generating a flow of the gas, and a gas flow guide tube for
efficiently circulating and dispersing the gas flow generated by
the agitator blades in a space of the reactor; (b) stationarily
placing at least one substance selected from the group consisting
of a metal and a metal compound within a reactor, the metal being
at least one metal selected from the group consisting of Si, B, W,
Mo, V, Se, Te and Ge, the metal compound being at least one metal
compound selected from the group consisting of solid compounds of
Si, B, W, Mo, V, Se, Te and Ge; (c) introducing a gas containing
NF.sub.3 into the reactor to react the introduced gas with at least
one substance of the metal and the metal compound at a temperature
ranging from 400 to 900.degree. C. upon operating the agitator
blades of the reactor so as to form a fluoride gas; and (d)
capturing the fluoride gas.
[0020] The above process is performed by a system including a
reactor whose one example is shown in FIG. 1. The reactor R in FIG.
1 is the horizontal cylindrical type and comprises an cylindrical
outer tube 1 having an intake-side end wall 1a and an exhaust-side
end wall 1b. A tray 2 on which Si granules (treatment agent) are
placed is disposed inside the outer tube 1, in which the inside
temperature of outer tube is held at 400-900.degree. C. using an
external heater H disposed outside the outer tube 1. Gas containing
NF.sub.3 is supplied through a gas intake port 4 formed in the
intake-side end wall 1a, and is sufficiently contacted with the Si
by agitating the gas with agitator blades 3 to carry out a
decomposition reaction for generating decomposition gas. Under
agitation by the agitator blades 3, the decomposition gas and
unreacted NF.sub.3 are circulated in a direction indicated by
arrows in FIG. 1 and dispersed through a generally cylindrical gas
flow guide tube 5. The gas flow guide tube 5 is spacedly disposed
between the outer housing 1 and the tray 2. The gas which has been
subjected to reaction is discharged from a gas exhaust port 6
formed in the exhaust-side end wall 1b.
[0021] Since this process allows gas to be more completely mixed
than processes of the prior art, it offers the advantage of being
able to inhibit local overheating. In this case, it is preferable
that the mean flow rate of the circulating gas flow inside the gas
flow guide tube 5 be 0.5 m/sec or more, and more preferably within
the range of 0.5-3.0 m/sec. If the mean flow rate is less than 0.5
m/sec, the removal of heat generated accompanying the reaction is
insufficient resulting in the occurrence of local overheating. Even
if the mean flow rate exceeds 3.0 m/sec, the resulting effects of
dispersing gas or effects of removing reaction heat are not
improved, so that the motive power required for agitation is
wasted.
[0022] In addition, although varying according to the shape and
size of the reactor, it is preferable that the amount of gas
introduced into the outer tube 1 is equal to or less than a value
(per minute) corresponding to 0.1 times of the internal volume of
the outer tube 1 in terms of the volumetric flow as converted from
the standard state. If the volumetric flow or introduced gas amount
is greater than this, the heat generated in the reaction exceeds
heat dissipation resulting in overheating of the reactor if
NF.sub.3 is highly concentrated at nearly 100%. Conversely, if the
NF.sub.3 concentration is low at 50% or lower, the retention time
of the gas in the reactor is shortened, resulting in a large amount
of unreacted NF.sub.3.
[0023] Moreover, the temperature for carrying out the contact
decomposition reaction of the gas to be introduced into the outer
tube 1 is preferably within the range of 400-900.degree. C., and
optimally within the range of 500-700.degree. C. If the temperature
is lower than 400.degree. C., the reaction proceeds slowly and the
amount of unreacted NF.sub.3 increases. In addition, if the
temperature exceeds 900.degree. C., the reaction proceeds too
rapidly causing a local reaction which has the risk of damaging the
members of the reactor at that portion.
[0024] The treatment agent used to be reacted with NF.sub.3 in the
present invention is preferably Si, B, W, Mo, V, Se, Te, Ge or a
non-oxide solid compounds of these metals. Examples of the
non-oxide solid compounds of these metals are Si.sub.3N.sub.4 and
SiC.
[0025] There are no particular restrictions on the material of the
reactor R used in the present invention provided it is a metal
material or oxide-based material having corrosion resistance at
high temperatures, in which nickel or nickel alloy is preferable as
the metal material. In addition, the shape and dimensions of the
reactor R are suitably selected according to the amount of
detoxified substance and the required detoxification capacity.
[0026] Moreover, in order to carry out NF.sub.3 treatment more
efficiently, it is preferable to use a process or treatment (first
stage using a first stage reactor) in which a content of NF.sub.3
of up to several percent is treated with the process of the present
invention followed by a secondary treatment (second stage using a
second stage reactor) up to 10 ppm or less on NF.sub.3 treated in
the first stage by a cylindrical reactor of the fixed bed type
(piston flow system) filled with the same treatment agent (such as
Si) as that in the reactor R. As a result, a large amount of highly
concentrated NF.sub.3 at a large flow rate can be treated up to the
allowed concentration or less.
[0027] SiF.sub.4 is formed when using, for example, Si or
Si.sub.3N.sub.4 for the treatment agent in the first or second
stage of treatment. The thus formed SiF.sub.4 can be treated with
an ordinary wet scrubber. The waste liquid that has absorbed
SiF.sub.4 in the wet treatment with the wet scrubber can be treated
with a typical process in which the waste liquid is sent to a
treatment tank in a later stage in which, for example, a chemical
such as calcium hydroxide is added to the waster liquid. At this
time, the F and Si are converted to water-insoluble solids such as
CaF.sub.2 and SiO.sub.2, respectively, followed by recovery by
filtration. In addition, since the gas on which the above treatment
is performed is detoxified, it can be purged into the
atmosphere.
[0028] As has been described above, according to the process of the
present invention, by reacting a large amount of NF.sub.3 with a
metal and so forth, absorbing the resulting gaseous fluoride (such
as SiF.sub.4, BF.sub.3, WF.sub.6, MoF.sub.6 or GeF.sub.4) with a
wet scrubber and finally converted to a solid in the form of, for
example, calcium fluoride, the present invention is able to
demonstrate detoxifying effects in which gas containing NF.sub.3 is
not discharged into the atmosphere.
[0029] The present invention will be more readily understood with
reference to the following Examples in comparison with Comparative
Examples; however, these Examples are intended to illustrate the
invention and are not to be construed to limit the scope of the
invention.
EXAMPLE 1
[0030] A reactor (R) as shown in FIG. 1 was prepared including an
outer or reaction tube (1) having a diameter of 400 mm and a length
of 1,300 mm. The reactor was provided with a tray (2) located
inside the outer tube as shown in FIG. 1. A gas flow guide tube (5)
was disposed between the outer tube and the tray so that the tray
was spacedly located inside the gas flow guide tube as shown in
FIG. 1. 55 Kg of metal silicon were placed on the tray. The reactor
had a reaction portion having a volume of 200 liters. The reaction
tube was heated to 600.degree. C. by an external heater (H) located
outside thereof. NF.sub.3 at 5.0 NL/min was supplied from a gas
intake port (4) of the reactor into the outer tube. The retention
time of the gas in the reactor was 540 seconds. At this time, the
gas flow rate of the gas inside the flow guide tube was set to 1.0
m/sec using agitator blades (3) as shown in FIG. 1.
[0031] When a portion of the outlet gas from the gas exhaust port
was captured and analyzed by a FT-IR (Fourier transform-type
infra-red spectroscopy) and a gas chromatography, NF.sub.3,
N.sub.2, SiF.sub.4, and N.sub.2O were detected. The NF.sub.3
concentration at the gas exhaust port was 2 vol %. The experiment
conditions and analysis results are shown in Table 1 in which
"Intake gas concentration" is a concentration (vol %)of the gas
introduced from the gas inlet port of the reactor; "Outlet gas
concentration" is a concentration (vol %) of the gas discharged
from the gas exhaust port of the reactor; "Total gas supply volume"
is a total volume of the gas supplied from the gas inlet port of
the reactor, which are common throughout Examples to Comparative
Examples.
EXAMPLE 2
[0032] 55 Kg of metal silicon were placed on the tray in the
reactor of Example 1 followed by heating the reaction tube to
600.degree. C. using the external heater and treating the NF.sub.3
contained in the air. NF.sub.3 was supplied at 8.0 NL/min, N.sub.2
at 6.4 NL/min and O.sub.2 at 1.6 NL/min (total gas supply
volume=16.0 NL/min). The gas retention time in the reaction tube
was 170 seconds. At this time, the gas flow rate in the gas flow
guide tube was set to 1.0 m/sec using the agitator blades.
[0033] When a portion of the outlet gas from the gas exhaust port
was captured and analyzed by a FT-IR and a gas chromatography,
NF.sub.3, N.sub.2, O.sub.2, SiF.sub.4 and N.sub.2O were detected.
The NF.sub.3 concentration was 5 vol %. The experiment conditions
and analysis results are shown in Table 1.
EXAMPLE 3
[0034] 55 Kg of metal silicon were placed on the tray in the
reactor of Example 1 followed by heating the reaction tube to
600.degree. C. using the external heater and treating the NF.sub.3
contained in the air. NF.sub.3 was supplied at 4.0 NL/min, N.sub.2
at 3.2 NL/min and O.sub.2 at 1.6 NL/min (total gas supply
volume=8.0 NL/min). The gas retention time in the reaction tube was
the same as in Example 1. At this time, the gas flow rate in the
gas flow guide tube was set to 1.0 m/sec using the agitator
blades.
[0035] When a portion of the outlet gas from the gas exhaust port
was captured and analyzed by a FT-IR and a gas chromatography,
NF.sub.3, N.sub.2, O.sub.2, SiF.sub.4 and N.sub.2O were detected.
The NF.sub.3 concentration was 2 vol %. The experiment conditions
and analysis results are shown in Table 1.
EXAMPLE 4
[0036] A nickel vertical cylindrical reactor (latter or second
stage reactor) having an inner diameter of 80 mm and a length of
1,050 mm was connected to the gas exhaust port of the reactor in
Example 2. Si granules were tightly packed in the latter stage
reactor to form a fixed bed in the reactor. The latter stage
reactor was heated at 600.degree. C. with the external heater.
Exhaust gas from the reactor in Example 2 was introduced into the
latter stage reactor having the fixed bed. When a portion of the
outlet gas discharged from the latter stage reactor was captured
and analyzed by a FT-IR and a gas chromatography, NF.sub.3,
N.sub.2, O.sub.2, SiF.sub.4 and N.sub.2O were detected. The
NF.sub.3 concentration was 10 vol %. The experiment conditions and
analysis results are shown in Table 1 in which "Intake gas
concentrations" was a volume of the gas from the gas exhaust port
of the reactor in Example 2.
1 TABLE 1 Total gas Gas Intake gas supply Gas flow concentration
volume Retention flow rate Outlet gas concentration vol % NL/ time
guide m/ vol % Reactor NF.sub.3 N.sub.2 O.sub.2 min sec. tube sec
NF.sub.3 N.sub.2 O.sub.2 SiF.sub.4 N.sub.2O Ex. 1 Horizontal 100 --
-- 5 540 Yes 1.0 2 39 -- 59 -- Ex. 2 cylinder 50 40 10 16 170 Yes
1.0 2 54 3 34 8 Ex. 3 50 40 10 8 340 Yes 1.0 2 52 3 35 8 Ex. 4
Fixed 2 54 3 17 -- -- -- <10 54 3 35 8 bed ppm Comp Horizontal
100 -- -- 5 540 Yes 0.2 10 36 -- 54 -- Ex. 1 cylinder Comp 100 --
-- 5 540 No 1.0 8 36 -- 56 -- Ex. 2 Note: Reaction in the reactor
was made at 600.degree. C. in all cases.
COMPARATIVE EXAMPLE 1
[0037] 55 Kg of metal silicon were placed on the tray in the
reactor in Example 1, followed by heating the reaction tube to
600.degree. C. using the external heater. NF.sub.3 was supplied
from the gas intake port at 8.0 NL/min. The retention time of gas
in the reactor was 540 seconds. The gas flow rate in the gas flow
guide tube was set to 0.2 m/sec using the agitator blades.
[0038] When a portion of the outlet gas was captured and analyzed
by a FT-IR and a gas chromatography, the concentration of NF.sub.3
was found to be 10 vol %. The experiment conditions and analysis
results are shown in Table 1.
COMPARATIVE EXAMPLE 2
[0039] 55 Kg of metal silicon were placed on the tray in the
reactor which was similar to that of Example 1 with the exception
that no gas flow guide tube (5) was provided, followed by heating
the reaction tube to 600.degree. C. using the external heater.
NF.sub.3 was supplied from the gas intake port at 5.0 NL/min. The
gas retention time in the reactor was 540 seconds.
[0040] When a portion of the outlet gas from the gas exhaust port
was captured and analyzed by a FT-IR and a gas chromatography, the
concentration of NF.sub.3 was found to be 8 vol %. The experiment
conditions and analysis results are shown in Table 1.
COMPARATIVE EXAMPLE 3
[0041] NF.sub.3 was supplied at 5.0 NL/min to the vertical cylinder
reactor (having the fixed bed) used as the latter stage reactor in
Example 4. The reaction occurred in a confined area near the
entrance of the reactor. The reactor walls were damaged after 5
minutes due to accumulation of reaction heat.
[0042] As apparent from the above, according to the NF.sub.3
treatment process of the present invention, gas containing NF.sub.3
in a large amount and/or at a high concentration can be adequately
removed while performing the treatment process safely without the
formation of explosive gas by-products.
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