U.S. patent application number 12/667806 was filed with the patent office on 2010-07-15 for apparatus for charging dry air or nitrogen gas into a container for storing semiconductor wafers and an apparatus for thereby removing static electricity from the wafers.
This patent application is currently assigned to KONDOH INDUSTRIES, LTD.. Invention is credited to Yasushi Honda, Naoji Iida, Toshirou Kisakibaru, Makoto Okada.
Application Number | 20100175781 12/667806 |
Document ID | / |
Family ID | 40228244 |
Filed Date | 2010-07-15 |
United States Patent
Application |
20100175781 |
Kind Code |
A1 |
Kisakibaru; Toshirou ; et
al. |
July 15, 2010 |
Apparatus for Charging Dry Air or Nitrogen Gas into a Container for
Storing Semiconductor Wafers and an Apparatus for Thereby Removing
Static Electricity from the Wafers
Abstract
An apparatus for charging dry air or nitrogen gas into a
container for storing semiconductor wafers can remove chemical gas
and moisture from the container, and then prevent acid from being
generated at the surfaces of the wafers. The apparatus A for
charging dry air or nitrogen gas into a container 1 for storing
semiconductor wafers 9 is connected to an opening 8a, acting as an
intake, and to an opening 8b, acting as an exhaust, wherein the
container 1 comprises a plurality of openings 8 disposed at the
bottom plate of the container 1, the apparatus comprising: PTFE
filters 7 disposed at the plurality of openings 8a, 8b, a portion
11 for providing the dry air or nitrogen gas to the container 1,
and a portion 12 for exhausting the used dry air or nitrogen gas
from the container 1 after removing chemical gas and moisture from
the container, and then preventing acid from being generated at the
surfaces of the wafers 9.
Inventors: |
Kisakibaru; Toshirou;
(Tokyo, JP) ; Okada; Makoto; (Tokyo, JP) ;
Iida; Naoji; (Tokyo, JP) ; Honda; Yasushi;
(Tokyo, JP) |
Correspondence
Address: |
Sunstein Kann Murphy & Timbers LLP
125 SUMMER STREET
BOSTON
MA
02110-1618
US
|
Assignee: |
KONDOH INDUSTRIES, LTD.
Tokyo
JP
CAMBRIDGE FILTER JAPAN, LTD.
Tokyo
JP
|
Family ID: |
40228244 |
Appl. No.: |
12/667806 |
Filed: |
July 9, 2007 |
PCT Filed: |
July 9, 2007 |
PCT NO: |
PCT/JP2007/063651 |
371 Date: |
January 5, 2010 |
Current U.S.
Class: |
141/98 ; 141/286;
141/48 |
Current CPC
Class: |
H01L 21/67396 20130101;
H01L 21/67393 20130101; H01L 21/68 20130101; H01L 21/67017
20130101 |
Class at
Publication: |
141/98 ; 141/48;
141/286 |
International
Class: |
B65B 31/04 20060101
B65B031/04 |
Claims
1. An apparatus for charging dry air or nitrogen gas into a
container for storing semiconductor wafers, wherein the container
comprises a plurality of openings disposed at the bottom plate of
the container, and wherein the apparatus for charging dry air or
nitrogen gas is connected to the opening for an intake and to the
opening for an exhaust, the apparatus comprising: PTFE filters
disposed at the plurality of openings, a portion for providing the
dry air or nitrogen gas to charge the dry air or nitrogen gas into
the container, and a portion for exhausting the used dry air or
nitrogen gas to discharge the used dry air or nitrogen gas from the
container after removing chemical gas and moisture from the
container, and then preventing acid from being generated at the
surfaces of the wafers by the dry air or nitrogen gas charged into
the container, wherein the portion for providing the dry air or
nitrogen gas is connected to a hollow vessel that has a nozzle for
providing it and is disposed at the side of the intake of the
container, and the nozzle for providing it is hermetically fixed to
the opening for the intake, wherein the portion for exhausting the
used dry air or nitrogen gas is connected to a hollow vessel that
has an exhaust nozzle and an exhaust port for discharging the used
dry air or nitrogen gas and is disposed at the side of the exhaust
port of the container, and the exhaust nozzle is hermetically fixed
to the opening for the exhaust, wherein the dry air or nitrogen gas
that is provided to the hollow vessel disposed at the side of the
intake of the container is filtered by removing dust by means of
the PTFE filter and flows into the container, and then removes
chemical gas and moisture from the container, and prevents acid
from being generated at the surfaces of the wafers, and wherein the
used dry air or nitrogen gas is discharged into the hollow vessel
disposed at the side of the exhaust through the PTFE filter
disposed at the opening for the exhaust, and then is exhausted
through the exhaust port of the hollow vessel disposed at the side
of the exhaust.
2. The apparatus for charging dry air or nitrogen gas of claim 1,
further comprising a buffering tank disposed on the pathway for
providing the dry air or nitrogen gas of the portion for providing
the dry air or nitrogen gas.
3. The apparatus for charging dry air or nitrogen gas of claim 2,
wherein the buffering tank of the apparatus for charging dry air or
nitrogen gas comprises a hollow vessel.
4. The apparatus for charging dry air or nitrogen gas of claim 2,
wherein the buffering tank of the apparatus for charging dry air or
nitrogen gas further comprises a filter or a plurality of filters
disposed at predetermined intervals in the buffering tank.
5. The apparatus for charging dry air or nitrogen gas of claim 2,
wherein the buffering tank of the apparatus for charging dry air or
nitrogen gas further comprises a perforated plate or a plurality of
perforated plates disposed at predetermined intervals in the
buffering tank.
6. An apparatus for removing static electricity by using the
apparatus for charging dry air or nitrogen gas into a container for
storing semiconductor wafers, wherein the container comprises a
plurality of openings disposed at the bottom plate of the
container, and wherein the apparatus for charging dry air or
nitrogen gas is connected to the opening for an intake and to the
opening for an exhaust, the apparatus for removing static
electricity comprising: PTFE filters disposed at the plurality of
openings, a portion for providing the ionized dry air or nitrogen
gas to charge the ionized dry air or nitrogen gas into the
container, and a portion for exhausting the used ionized dry air or
nitrogen gas to discharge the used ionized dry air or nitrogen gas
from the container after removing chemical gas, moisture, and
static electricity from the container, and then preventing acid
from being generated at the surfaces of the wafers by the ionized
dry air or nitrogen gas charged into the container, wherein the
portion for providing the dry ionized air or nitrogen gas is
connected to a hollow vessel that has a nozzle for providing it and
is disposed at the side of the intake of the container, and the
nozzle for providing it is hermetically fixed to the opening for
the intake, the hollow vessel being further connected to an ion
generator that ionizes the dry air or nitrogen gas, wherein the
portion for exhausting the used ionized dry air or nitrogen gas is
connected to a hollow vessel that has an exhaust nozzle and an
exhaust port for discharging the used ionized dry air or nitrogen
gas and is disposed at the side of the exhaust port of the
container, and the exhaust nozzle is hermetically fixed to the
opening for the exhaust, wherein the dry air or nitrogen gas that
is provided to the hollow vessel disposed at the side of the intake
of the container becomes ionized dry air or nitrogen by ionization,
and is filtered by removing dust by means of the PTFE filter while
the ions are maintained and flow into the container, and then
removes the chemical gas, the moisture, and the static electricity
from the container, and prevents acid from being generated at the
surfaces of the wafers, and wherein the used ionized dry air or
nitrogen gas is discharged into the hollow vessel disposed at the
side of the exhaust port through the PTFE filter disposed at the
opening for the exhaust, and then is exhausted through the exhaust
port of the hollow vessel disposed at the side of the exhaust
port.
7. The apparatus for removing the static electricity of claim 6,
further comprising a buffering tank disposed on the pathway for
providing the ionized dry air or nitrogen gas of the portion for
providing the ionized dry air or nitrogen gas.
8. The apparatus for removing static electricity of claim 7,
wherein the buffering tank of the apparatus for removing static
electricity comprises a hollow vessel.
9. The apparatus for charging dry air or nitrogen gas of claim 7,
wherein the buffering tank of the apparatus for removing static
electricity further comprises a filter or a plurality of filters
disposed at predetermined intervals in the hollow vessel.
10. The apparatus for charging dry air or nitrogen gas of claim 7,
wherein the buffering tank of the apparatus for removing static
electricity further comprises a perforated plate or a plurality of
perforated plates disposed at predetermined intervals in the hollow
vessel.
Description
TECHNICAL FIELD
[0001] This invention relates to an apparatus for charging dry air
or nitrogen gas into a container for storing semiconductor wafers
and an apparatus for removing static electricity from the surfaces
of the wafers by using the apparatus for charging dry air or
nitrogen gas. The container is used for storing semiconductor
wafers that are used for producing semiconductor chips. Since any
chemical gas or moisture present in the container can be removed by
charging dry air or nitrogen gas into the container, it is possible
to prevent an acid from being generated at the surfaces of the
wafers.
BACKGROUND OF THE INVENTION
[0002] Conventionally, for processes for producing semiconductor
chips in a clean room using a minienvironment system, since
miniaturization of the circuits of the semiconductor chips had been
developed, the processes have become complicated. Particularly, for
a process for etching semiconductor wafers by using halogen gases,
since an acid is generated by a chemical reaction of the moisture
in dry air and the halogen gases that remain after the etching
process, it becomes a serious problem in that the acid corrodes the
semiconductor wafers. To prevent the corrosion of the semiconductor
wafers, acid is prevented from being generated, by charging dry air
or nitrogen gas into a container of semiconductor wafers after
storing those that have been already processed, in the
container.
[0003] For the processes for producing semiconductor chips in a
clean room using the minienvironment system, the semiconductor
wafers are stored in the container, and then are transported and
are thus ready for the next step. When the semiconductor wafers are
inserted into the container, or while the container with the wafers
is transported, since the wafers are charged with static
electricity, an electrostatic breakdown of the semiconductor
circuits is caused. Further, problems occur that are caused by dust
that is attached to the surfaces of the semiconductor wafers due to
the static electricity. Conventionally, as a countermeasure against
these problems, the amount of the static electricity is reduced by
imparting electrical conductivity to the material of which the
container is made by mixing a powder of carbon with the
material.
[0004] The inventors of the present inventions searched patent
documents regarding the following apparatuses:
[0005] an apparatus for charging dry air or nitrogen gas into a
container for storing semiconductor wafers without opening the lid
of the container, to remove chemical gas and moisture from the
container, and then to prevent the corrosion of the semiconductor
wafers by preventing acid from being generated at the surfaces of
the wafers, and
[0006] an apparatus for removing static electricity from the
surfaces of the wafers by using the apparatus for charging ionized
dry air or nitrogen gas, to remove chemical gas and moisture from
the container, then to remove the charged static electricity from
the wafers, and further to prevent the corrosion of the wafers by
preventing acid from being generated at the surfaces of the wafers,
which apparatus for removing static electricity is attached to the
container.
[0007] However they were able to find no patent document that
disclosed such apparatuses.
DISCLOSURE OF INVENTION
[0008] As described above, for the conventional processes, to
prevent the corrosion of the wafers by preventing acid that is
generated by a chemical reaction of moisture and halogen gases from
being generated at the surfaces of the semiconductor wafers, dry
air or nitrogen gas that contains little moisture is charged into
the container for storing semiconductor wafers. To maintain an
efficient production, the dry air or nitrogen gas must be quickly
charged into the container. Further, when the semiconductor wafers
are stored in the container, since the undersides of the wafers
contact the surface of an arm of a robot, a small amount of dust is
generated. The dust is likely to enter the container. Thus, there
is a problem in that the dust that is caused by the above reason
and by any other reason accumulates at the bottom of the
container.
[0009] When the dry air or nitrogen gas is charged into the
container for storing the semiconductor wafers, since at the
initial stage for charging dry air or nitrogen gas the pressure in
the container is nearly equal to atmospheric pressure, the dry air
or nitrogen gas is charged into the container through its intake
port at a high flow rate. As the pressure in the container
increases, the flow rate of the dry air or nitrogen gas decreases.
At the initial stage for charging dry air or nitrogen gas, there is
a problem in that the dust that has accumulated at the bottom of
the container or that is attached to the undersides of the wafers
is stirred up, since the dry air or nitrogen gas is charged into
the container at a high flow rate, and then the dust is attached to
the circuits of the semiconductor at the upper surfaces of the
wafers.
[0010] It is possible to apply a method for controlling the flow
rate of the dry air or nitrogen gas for charging it into the
container for storing the semiconductor wafers by using a mass flow
meter. However, even if a mass flow meter is provided in the
apparatus, the surge of the flow of the dry air or nitrogen gas
cannot be avoided. Further, since a mass flow meter is very
expensive, there is a problem in that the cost of the apparatus
increases.
[0011] On the other hand, the miniaturization of the circuits of
semiconductor chips has developed, and in the processes for
producing semiconductor chips, the size of the particles of
contaminating dust to be controlled has become at the nanometer
level. However, the breakdown of the semiconductor circuits due to
a small amount of the static electricity remaining and the
attachment of the dust to the semiconductor wafers is caused. The
method for imparting electrical conductivity to the material of
which the container is made by mixing a conductive material, such
as a powder of carbon, with the material, cannot entirely prevent
generating the static electricity toward the semiconductor wafers.
Disadvantageously, as the amount of the carbon in the material
composing the container increases, the chemical gases generated
from that material become a problem. Thus, the problems of the
static electricity affecting the semiconductor wafers cannot be
entirely solved.
[0012] When the semiconductor wafers are stored in such a
container, some semiconductor industries try to charge ionized air
into the container through its open port, and then the open port is
closed by a lid. However, a favorable outcome cannot be
obtained.
[0013] The present inventions are intended to overcome the problems
explained in the above paragraphs. Namely, the present inventions
are intended to provide the following apparatuses:
[0014] an apparatus for charging dry air or nitrogen gas into a
container for storing semiconductor wafers without opening the lid
of the container, to remove chemical gas and moisture from the
container, and then to prevent the corrosion of the semiconductor
wafers by preventing acid from being generated at the surfaces of
the wafers, and
[0015] an apparatus for removing static electricity from the
surfaces of the wafers by using the above apparatus for charging
ionized dry air or nitrogen gas, to prevent the dust that has
accumulated at the bottom of the container from being stirred up,
to remove the charged static electricity from the wafers, and to
remove the moisture from the container, and further to prevent the
corrosion of the wafers by preventing acid from being generated at
the surfaces of the wafers.
[0016] To overcome the problems explained in the above paragraphs,
for a first aspect of the present inventions it is intended to
provide the following apparatus. It is constituted as follows:
[0017] an apparatus for charging dry air or nitrogen gas into a
container for storing semiconductor wafers, wherein the container
comprises a plurality of openings disposed at the bottom plate of
the container, and wherein the apparatus for charging dry air or
nitrogen gas is connected to the opening for an intake and to the
opening for an exhaust, the apparatus comprising:
[0018] PTFE filters disposed at the plurality of openings,
[0019] a portion for providing the dry air or nitrogen gas to
charge the dry air or nitrogen gas into the container, and
[0020] a portion for exhausting the used dry air or nitrogen gas to
discharge the used dry air or nitrogen gas from the container after
removing any chemical gas and moisture from the container, and then
preventing acid from being generated at the surfaces of the wafers
by the dry air or nitrogen gas that is charged into the
container,
[0021] wherein the portion for providing the dry air or nitrogen
gas is connected to a hollow vessel that has a nozzle for providing
it and is disposed at the side of the intake of the container, and
the nozzle for providing it is hermetically fixed to the opening
for the intake,
[0022] wherein the portion for exhausting the used dry air or
nitrogen gas is connected to a hollow vessel that has an exhaust
nozzle and an exhaust port for discharging the used dry air or
nitrogen gas and is disposed at the side of the exhaust port of the
container, and the exhaust nozzle is hermetically fixed to the
opening for the exhaust,
[0023] wherein the dry air or nitrogen gas that is provided for the
hollow vessel disposed at the side of the intake of the container
is filtered by removing dust by means of the PTFE filter and flows
into the container, and then removes any chemical gas and moisture
from the container, and prevents acid from being generated at the
surfaces of the wafers, and
[0024] wherein the used dry air or nitrogen gas is discharged into
the hollow vessel disposed at the side of the exhaust through the
PTFE filter disposed at the opening for the exhaust, and then is
exhausted through the exhaust port of the hollow vessel disposed at
the side of the exhaust.
[0025] For a second aspect of the present inventions,
[0026] the apparatus for charging dry air or nitrogen gas into a
container for storing semiconductor wafers further comprises a
buffering tank disposed on the pathway for providing the dry air or
nitrogen gas of the portion for providing the dry air or nitrogen
gas.
[0027] For a third aspect of the present inventions,
[0028] the buffering tank of the apparatus for charging dry air or
nitrogen gas into a container for storing semiconductor wafers
comprises a hollow vessel.
[0029] For a fourth aspect of the present inventions,
[0030] the buffering tank of the apparatus for charging dry air or
nitrogen gas into a container for storing semiconductor wafers
further comprises a filter or a plurality of filters disposed at
predetermined intervals in the buffering tank.
[0031] For a fifth aspect of the present inventions,
[0032] the buffering tank of the apparatus for charging dry air or
nitrogen gas into a container for storing semiconductor wafers
further comprises a perforated plate or a plurality of perforated
plates disposed at predetermined intervals in the buffering
tank.
[0033] For a sixth aspect of the present inventions, it is intended
to provide the following apparatus, which is constituted as
follows:
[0034] an apparatus for removing static electricity by using the
apparatus for charging dry air or nitrogen gas into a container for
storing semiconductor wafers, wherein the container comprises a
plurality of openings disposed at the bottom plate of the
container, and wherein the apparatus for charging dry air or
nitrogen gas is connected to the opening for an intake and to the
opening for an exhaust, the apparatus for removing static
electricity comprising:
[0035] PTFE filters disposed at the plurality of openings,
[0036] a portion for providing the ionized dry air or nitrogen gas
to charge the ionized dry air or nitrogen gas into the container,
and
[0037] a portion for exhausting the used ionized dry air or
nitrogen gas to discharge the used ionized dry air or nitrogen gas
from the container after removing chemical gas, moisture, and
static electricity from the container, and then preventing acid
from being generated at the surfaces of the wafers by the ionized
dry air or nitrogen gas charged into the container,
[0038] wherein the portion for providing the dry ionized air or
nitrogen gas is connected to a hollow vessel that has a nozzle for
providing it and is disposed at the side of the intake of the
container, and the nozzle for providing it is hermetically fixed to
the opening for the intake, the hollow vessel being further
connected to an ion generator, which ionizes the dry air or
nitrogen gas,
[0039] wherein the portion for exhausting the used ionized dry air
or nitrogen gas is connected to a hollow vessel that has an exhaust
nozzle and an exhaust port for discharging the used ionized dry air
or nitrogen gas and is disposed at the side of the exhaust port of
the container, and the exhaust nozzle is hermetically fixed to the
opening for the exhaust,
[0040] wherein the dry air or nitrogen gas that is provided for the
hollow vessel disposed at the side of the intake of the container
becomes the ionized by ionization, and is filtered by removing dust
by means of the PTFE filter while the ions are maintained and flows
into the container, and then removes the chemical gas, the
moisture, and the static electricity from the container, and
prevents acid from being generated at the surfaces of the wafers,
and
[0041] wherein the used ionized dry air or nitrogen gas is
discharged into the hollow vessel disposed at the side of the
exhaust port through the PTFE filter disposed at the opening for
the exhaust, and then is exhausted through the exhaust port of the
hollow vessel disposed at the side of the exhaust port.
[0042] For a seventh aspect of the present inventions,
[0043] the apparatus for removing static electricity further
comprises a buffering tank disposed on the pathway for providing
the ionized dry air or nitrogen gas of the portion for providing
the ionized dry air or nitrogen gas.
[0044] For an eighth aspect of the present inventions,
[0045] the buffering tank of the apparatus for removing static
electricity comprises a hollow vessel.
[0046] For a ninth aspect of the present inventions,
[0047] the buffering tank of the apparatus for removing static
electricity further comprises a filter or a plurality of filters
disposed at predetermined intervals in the hollow vessel.
[0048] For a tenth aspect of the present inventions,
[0049] the buffering tank of the apparatus for removing static
electricity further comprises a perforated plate or a plurality of
perforated plates disposed at predetermined intervals in the hollow
vessel.
[0050] By the first aspect of the present inventions,
[0051] by charging dry air or nitrogen gas, into a container for
storing semiconductor wafers without opening the lid of the
container, through the PTFE filter disposed at the opening for the
intake of the container, the chemical gas and moisture can be
removed from the container, and then the semiconductor wafers can
be prevented from corroding by preventing acid from being generated
at the surfaces of the wafers.
[0052] By the second to fifth aspects of the present
inventions,
[0053] when the dry air or nitrogen gas is charged into the
container for storing the semiconductor wafers from the nozzle for
providing it, and until the pressure in the container increases at
the initial stage, the dry air or nitrogen gas is charged at a high
flow rate. As the pressure in the container increases, the flow
rate of the dry air or nitrogen gas decreases. By installing a
buffering tank on the pathway for providing the dry air or nitrogen
gas of the apparatus, since the flow rate of the dry air or
nitrogen gas that is provided to the hollow vessel disposed at the
side of the intake of the container is averaged, it is possible to
prevent the dry air or nitrogen gas from being rapidly charged into
the container. Thus, the dust that has accumulated at the bottom of
the container is not stirred up.
[0054] By the fourth aspect of the present inventions, as compared
with the third aspect of the present inventions, not only can the
flow rate of the dry air or nitrogen gas to a high degree be
averaged, but the dust generated from the opening and closing valve
disposed at the upstream side of the buffering tank can also be
removed.
[0055] Further, by the fifth aspect of the present inventions, as
compared with the third aspect of the present inventions, the flow
rate of the dry air or nitrogen gas can to a high degree be
averaged.
[0056] By the sixth aspect of the present inventions,
[0057] by charging ionized dry air or nitrogen gas, into a
container for storing semiconductor wafers without opening the lid
of the container, through the PTFE filter disposed at the opening
for the intake of the container, the dust can be removed, but the
ions can be maintained. By the ionized dry air or nitrogen gas
being charged into the container, the chemical gas and moisture can
be removed from the container, and the semiconductor wafers can be
prevented from corroding by preventing acid from being generated at
the surfaces of the wafers, and then the static electricity charged
on the wafers can be removed.
[0058] By the seventh to tenth aspects of the present
inventions,
[0059] when the ionized dry air or the nitrogen gas is charged into
the container for storing the semiconductor wafers from the nozzle
for providing it, and until the pressure in the container increases
at the initial stage, the ionized dry air or nitrogen gas is
charged at a high flow rate. As the pressure in the container
increases, the flow rate of the ionized dry air or nitrogen gas
decreases. By installing a buffering tank on the pathway for
providing the ionized dry air or nitrogen gas of the apparatus,
since the flow rate of the ionized dry air or nitrogen gas that is
provided to the hollow vessel disposed at the side of the intake of
the container is averaged, it is possible to prevent the ionized
dry air or nitrogen gas from being rapidly charged into the
container. Thus, the dust that has accumulated at the bottom of the
container is not stirred up.
[0060] By the ninth aspect of the present inventions, as compared
with the eighth aspect of the present inventions, not only can the
flow rate of the ionized dry air or nitrogen gas be averaged so
that the change of the flow rate is reduced, but the dust generated
from an opening and closing valve disposed at the upstream side of
the buffering tank can also be removed.
[0061] Further, by the tenth aspect of the present inventions, as
compared with the eighth aspect of the present inventions, the flow
rate of the ionized dry air or nitrogen gas can to a high degree be
averaged.
BRIEF DESCRIPTIONS OF THE DRAWINGS
[0062] FIG. 1 shows a vertical and sectional view of the container
for storing semiconductor wafers that is used for the apparatus of
this invention for charging dry air or nitrogen gas into a
container for storing semiconductor wafers.
[0063] FIG. 2 shows a bottom plane view of the container.
[0064] FIG. 3 shows a plane view of the apparatus of this invention
for charging dry air or nitrogen gas into the container for storing
semiconductor wafers.
[0065] FIG. 4 shows a vertical and sectional view of the apparatus
of this invention for charging dry air or nitrogen gas that is
attached to the container for storing semiconductor wafers.
[0066] FIG. 5 shows a perspective and partially sectional view of a
buffering tank that is used for the apparatus of this invention for
charging dry air or nitrogen gas.
[0067] FIG. 6 shows a perspective and partially sectional view of
another buffering tank that is used for the apparatus of this
invention for charging dry air or nitrogen gas.
[0068] FIG. 7 shows a perspective and partially sectional view of
another buffering tank that is used for the apparatus of this
invention for charging dry air or nitrogen gas.
[0069] FIG. 8 shows a plane view of the apparatus of this invention
for removing static electricity, which uses the apparatus for
charging dry air or nitrogen gas.
[0070] FIG. 9 shows a vertical and sectional view of the apparatus
of this invention for removing static electricity, which uses the
apparatus for charging dry air or nitrogen gas, and which is
attached to the container for storing semiconductor wafers.
[0071] FIG. 10 shows a vertical and sectional view of the main part
of the apparatus of this invention for removing static electricity,
which uses the apparatus for charging dry air or nitrogen gas, and
which uses a soft X-ray source as an ion generator used in a
portion for providing ionized dry air or nitrogen gas.
[0072] FIG. 11 shows a schematic view to explain an device used for
experiments for measuring a decay time when the ionized dry air
passes through a filter.
PREFERRED EMBODIMENTS OF THE INVENTIONS
[0073] The present inventions relate to the following apparatuses:
[0074] an apparatus for charging dry air or nitrogen gas into a
container for storing semiconductor wafers without opening the lid
of the container, to remove chemical gas and moisture from the
container, and then to prevent the corrosion of the semiconductor
wafers by preventing acid from being generated at the surfaces of
the wafers, and [0075] an apparatus for removing static electricity
from the surfaces of the wafers by using the above apparatus for
charging ionized dry air or nitrogen gas into the container, to
remove the charged static electricity from the wafers, and to
remove the chemical gas and the moisture from the container, and,
further, to prevent the corrosion of the wafers by preventing acid
from being generated at the surfaces of the wafers.
[0076] Below, embodiment 1, the apparatus for charging dry air or
nitrogen gas, and embodiment 2, the apparatus for removing static
electricity, are explained.
Embodiment 1
[0077] Embodiment 1 of the present inventions, the apparatus for
charging dry air or nitrogen gas, is now explained in detail based
on the figures. FIG. 1 shows a vertical and sectional view of the
container for storing semiconductor wafers that is used for the
present inventions. FIG. 2 shows a bottom plane view of the
container. As shown in FIGS. 1 and 2, the container 1 for storing
semiconductor wafers comprises an openable and closable lid 3 that
is disposed at the front of the container. and the container 1 has
a flange 2, a hook 4, for being suspended, disposed at its top
plate, a leg 6 for being mounted on the table (not shown) disposed
at its bottom plate 5, and a plurality of openings 8 having a PTFE
filter 7.
[0078] The semiconductor wafers 9 are stored in the container 1.
Except when the wafers 9 are being processed in an apparatus (not
shown), since the wafers 9 are stored in the container 1, chemical
gas is prevented from contacting the surfaces of the wafers 9.
[0079] FIG. 3 shows a plane view of the apparatus for charging dry
air or nitrogen gas into a container for storing semiconductor
wafers. FIG. 4 shows a vertical and sectional view of the apparatus
for charging dry air or nitrogen gas that is attached to the
container 1 for storing the semiconductor wafers 9. As shown in
FIGS. 3 and 4, the apparatus A for charging dry air or nitrogen
gas, which can remove chemical gas and moisture from the container
1, and then prevent the corrosion of the semiconductor wafers by
preventing acid from being generated at the surfaces of the wafers,
comprises:
[0080] a portion 11 for providing the dry air or nitrogen gas to
charge the dry air or nitrogen gas into the container 1, and
[0081] a portion 12 for exhausting the used dry air or nitrogen gas
to discharge the used dry air or nitrogen gas from the container 1
after removing chemical gas and moisture from the container 1, and
then preventing acid from being generated at the surfaces of the
wafers 9 by the dry air or nitrogen gas charged into the container
1.
[0082] The portion 11 for providing the dry air or nitrogen gas is
connected to a hollow vessel 14 that has a nozzle 13 for providing
it and is disposed at the side of the intake of the container
1.
[0083] The distal side of the nozzle 13 for providing the dry air
or nitrogen gas has an approximately conical shape, so that the
hollow vessel 14 disposed at the side of the intake of the
container 1 can be hermetically fixed to the port 15 disposed at
the upstream side of the PTFE filter 7 placed in the opening 8a
disposed at the bottom plate 5 of the container 1. The hollow
vessel 14 has a port at its sidewall to be connected to the
downstream end of a pipe 16 for providing the dry air or nitrogen
gas to the hollow vessel 14. An opening and closing valve 18 is
disposed near a port 17 disposed at the upstream side of the pipe
16 for providing the dry air or nitrogen gas to the pipe 16. By
adjusting the opening and closing valve 18, it is possible to
control the flow rate of the dry air or nitrogen gas, and to start,
or stop, providing the dry air or nitrogen gas to the hollow vessel
14.
[0084] Further, a buffering tank 19 is disposed at the pathway of
the pipe 16 for providing the dry air or nitrogen gas between the
opening and closing valve 18 and the hollow vessel 14. The dry air
or nitrogen gas 24, which is provided from its source (not shown),
is introduced into the buffering tank 19 through the port 17 and
the pipe 16. Thus, the dry air or nitrogen gas 24 is introduced
into the hollow vessel 14 at the averaged flow rate.
[0085] As the buffering tank 19, any type of buffering tank can be
used. For example, as shown in FIG. 5, a type of buffering tank
having only a hollow chamber 21, as shown in FIG. 6, a type of
buffering tank having a hollow chamber 21 that includes a filter or
a plurality of filters 22 disposed at predetermined intervals in
the hollow chamber 21, or as shown in FIG. 7, a type of buffering
tank having a hollow chamber 21 that includes a perforated plate or
a plurality of perforated plates 23 disposed at predetermined
intervals in the hollow chamber 21, can be used.
[0086] When the dry air or nitrogen gas 24 passes through the
filters 22 or the perforated plates 23 of the buffering tank shown
in FIG. 6 or 7, the pressure loss of the dry air or nitrogen gas 24
increases in proportion to the flow rate of the dry air or nitrogen
gas 24, as compared with the type of buffering tank having only a
hollow chamber 21 as shown in FIG. 5. Thus, by using the
characteristics of the filters 22, the perforated plates 23, and
the buffering tank 19, when the dry air or nitrogen gas 24 is
charged into the container 1 from the apparatus A, since the flow
rate of the dry air or nitrogen gas 24 at the initial stage can be
decreased, it is possible to prevent the dust that has accumulated
at the bottom of the container 1 from being stirred up.
[0087] If the buffering tank 19, such as the type of buffering tank
that has no filter nor perforated plate, as shown by FIG. 5, is
used for the apparatus A, it would degrade the effect to lower the
flow rate of the dry air or nitrogen gas 24 at the initial stage,
and to prevent the dust that has accumulated at the bottom of the
container 1 from being stirred up, compared with the types of
buffering tanks that are shown by FIG. 6 or 7. However, the
buffering tank 19 shown by FIG. 5 can be used for the present
invention.
[0088] The dry air or nitrogen gas 24 that is charged into the
hollow tank 14 passes through the PTFE filter 7 placed in the
opening 8a disposed at the intake side of the container 1 to remove
the dust from the dry air or nitrogen gas. Then, the dry air or
nitrogen gas flows into the container 1. The dry air or nitrogen
gas can remove the chemical gas and the moisture from the container
1, and then prevent the acid from being generated at the surfaces
of the wafers 9.
[0089] In contrast, the portion 12 for exhausting the used dry air
or nitrogen gas comprises the hollow vessel 27, which has the
exhaust nozzle 26, and is disposed at the side of the exhaust port
of the container 1, and has the exhaust port 29 disposed at its
sidewall, wherein the exhaust port 29 discharges the used dry air
or nitrogen gas 28 from the container 1 after the dry air or
nitrogen gas that has been charged into the container 1 removes the
chemical gas and the moisture from the container 1, and then
prevents acid from being generated at the surfaces of the wafers 9.
The distal side of the exhaust nozzle 26 has an approximately
conical shape, so that the exhaust nozzle 26 can be hermetically
fixed to the port 30 disposed at the downstream side of the PTFE
filter 7 placed in the opening 8b disposed at the bottom plate 5
and at the exhaust port side of the container 1.
[0090] The used dry air or nitrogen gas 28, which has removed the
chemical gas and the moisture from the container 1, and then
prevented the acid from being generated at the surfaces of the
wafers 9, is discharged from the exhaust port 29 to the outside of
the container 1 after it flows into the hollow vessel 27 through
the exhaust nozzle 26 and the PTFE filter 7 placed in the opening
8b disposed at the exhaust port side of the container 1.
[0091] Below the function of the apparatus A for charging dry air
or nitrogen gas of Embodiment 1 of the present invention is
explained in detail. The nozzle 13, for providing it, which is
disposed at the hollow vessel 14 that is disposed at the portion 11
for providing the dry air or nitrogen gas, which portion
constitutes a part of the apparatus A, is hermetically fixed to the
port 15 disposed at the upstream side of the PTFE filter 7 placed
in the opening 8a disposed at the bottom plate 5 and the intake
side of the container 1. Then, the exhaust nozzle 26, disposed at
the hollow vessel 27 that is disposed at the portion 12 for
exhausting the used dry air or nitrogen gas, which portion
constitutes another part of the apparatus A, is hermetically fixed
to the port 30 disposed at the downstream side of the PTFE filter 7
placed in the opening 8b disposed at the bottom plate 5 and the
exhaust side of the container 1.
[0092] After the apparatus A for charging dry air or nitrogen gas
is connected to the container 1 for storing the semiconductor
wafers 9, the dry air or nitrogen gas 24 is provided to the hollow
vessel 14 disposed at the portion 11 for providing the dry air or
nitrogen gas from its source (not shown) through the pipe 16 for
providing the dry air or nitrogen gas. Since the dry air or
nitrogen gas 24 that is provided to the hollow vessel 14 passes
through the PTFE filter 7 placed in the opening 8a disposed at the
intake side of the container 1, any dust in the dry air or nitrogen
gas 24 can be removed. Then, the dry air or nitrogen gas 24 flows
into the container 1, removes the chemical gas and the moisture in
the container 1, and can prevent the corrosion of the semiconductor
wafers 9 by preventing acid from being generated at the surfaces of
the wafers 9.
[0093] After removing the chemical gas and the moisture in the
container 1, and preventing the acid from being generated at the
surfaces of the wafers 9, the used dry air and nitrogen gas 28 flow
into the hollow vessel 27 through the PTFE filter 7 placed in the
opening 8b disposed at the exhaust side of the container 1 and the
exhaust nozzle 26. Then, the used dry air and nitrogen gas 28 is
discharged outside the container 1 through the exhaust port 29.
Embodiment 2
[0094] As Embodiment 2, an apparatus for removing static
electricity using the above apparatus for charging dry air or
nitrogen gas, is below explained based on the figures.
[0095] FIG. 8 shows a plane view of the apparatus for removing
static electricity using the apparatus for charging dry air or
nitrogen gas, of this invention. FIG. 9 shows a vertical and
sectional view of the apparatus for removing static electricity
that is attached to the container for storing the semiconductor
wafers, which is shown by FIGS. 1 and 2. As shown in FIGS. 8 and 9,
the apparatus B for removing static electricity, which is used for
removing the static electricity charged on the wafers 9 in the
container 1, comprises:
[0096] a portion 11a for providing ionized dry air or nitrogen gas
to charge the ionized dry air or nitrogen gas into the container 1,
which portion 11a uses a portion 11 for providing the dry air or
nitrogen gas of the apparatus A,
[0097] a portion 12a for exhausting the used ionized dry air or
nitrogen gas to discharge the used ionized dry air or nitrogen gas
from the container 1 after removing chemical gas, moisture, and
static electricity from the container 1, and then preventing acid
from being generated at the surfaces of the wafers 9 by the ionized
dry air or nitrogen gas charged into the container 1, which portion
12a uses a portion 12 for exhausting the used dry air or nitrogen
gas of the apparatus A.
[0098] The apparatus B for removing static electricity further
comprises an ion generator 31 for ionizing the dry air or nitrogen
gas 24, which generator 31 is connected to the hollow vessel 14
that has the nozzle 13 for providing it and is disposed at the side
of the intake of the container 1, and which vessel 14 constitutes a
part of the apparatus A.
[0099] Below, since all other components of the apparatus B are the
same as those of the apparatus A, the same denotations as those of
apparatus A are used to explain the apparatus B.
[0100] The distal side of the nozzle 13 for providing the dry air
or nitrogen gas has an approximately conical shape so that the
hollow vessel 14 disposed at the side of the intake of the
container 1 can be hermetically fixed to the port 15 disposed at
the upstream side of the PTFE filter 7, which filter is placed in
the opening 8a disposed at the bottom plate 5 of the container 1.
The hollow vessel 14 has a port at its sidewall to be connected to
the downstream end of a pipe 16 for providing the dry air or
nitrogen gas 24 to the hollow vessel 14. An opening and closing
valve 18 is disposed near a port 17 disposed at the upstream side
of the pipe 16 for providing the dry air or nitrogen gas 24 to the
pipe 16. By adjusting the opening and closing valve 18, it is
possible to control the flow rate of the dry air or nitrogen gas
24, and to start or stop providing the dry air or nitrogen gas 24
to the hollow vessel 14.
[0101] Further, a buffering tank 19 is disposed at the pathway of
the pipe 16 for providing the dry air or nitrogen gas between the
opening and closing valve 18 and the hollow vessel 14. The dry air
or nitrogen gas 24, which is provided from its source (not shown),
is introduced into the buffering tank 19 through the port 17 and
the pipe 16. Thus, the dry air or nitrogen gas 24 is introduced
into the hollow vessel 14 at the averaged flow rate.
[0102] As the buffering tank 19, any type of buffering tank can be
used. For example, as shown in FIG. 5, a type of buffering tank
having only a hollow chamber 21, as shown in FIG. 6, a type of
buffering tank having a hollow chamber 21 that includes a filter or
a plurality of filters 22 disposed at predetermined intervals in
the hollow chamber 21, or as shown in FIG. 7, a type of buffering
tank having a hollow chamber 21 that includes a perforated plate or
a plurality of perforated plates 23 disposed at predetermined
intervals in the hollow chamber 21, can be used.
[0103] When the dry air or nitrogen gas 24 passes through the
filters 22 or the perforated plates 23 of the buffering tank shown
in FIG. 6 or 7, the pressure loss of the dry air or nitrogen gas 24
increases in proportion to the flow rate of the dry air or nitrogen
gas 24, as compared with the type of buffering tank having only a
hollow chamber 21 as shown in FIG. 5. Thus, by using the
characteristics of the filters 22, the perforated plates 23, and
the buffering tank 19, when the ionized dry air or nitrogen gas 24
is charged into the container 1 from the apparatus B, since the
flow rate of the dry air or nitrogen gas 24 at the initial stage
can be suppressed, it is possible to prevent the dust that has
accumulated at the bottom of the container 1 from being stirred
up.
[0104] If the buffering tank 19, such as the type of buffering tank
that has no filter nor perforated plate, as shown by FIG. 5, is
used for the apparatus A, it would degrade the effect to decrease
the flow rate of the dry air or nitrogen gas 24 at the initial
stage, and to prevent the dust that has accumulated at the bottom
of the container 1 from being stirred up, as compared with the
types of buffering tanks that are shown by FIGS. 6 and 7. However,
the buffering tank 19 shown by FIG. 5 can be used for the present
invention.
[0105] FIG. 10 shows the portion 11a for providing ionized dry air
or nitrogen gas that uses a soft X-ray source, for example, as the
ion generator 31 for ionizing the dry air or nitrogen gas 24
provided for the hollow vessel 14. The hollow vessel 14 has an
obstacle 102 for blocking the soft X-rays, which obstacle forms a
clearance 104 between the nozzle 13 for providing the dry air or
nitrogen gas of the hollow vessel 14 and the obstacle 102, so that
the soft X-rays 103 irradiated into the hollow vessel 14 through a
window 101 from the soft X-ray source (the ion generator 31) do not
go straight ahead. The dry air or nitrogen gas 24 that is provided
to the hollow vessel 14 through the pipe 16 is ionized by the soft
X-rays 103 irradiated into the hollow vessel 14 through a window
101. Consequently, plus (+) ions and minus (-) ions 32 are
generated in the hollow vessel 14, and are charged into the
container 1 for storing the wafers as the ionized dry air or
nitrogen gas 32 through the clearance 104, between the nozzle 13
for providing it, of the hollow vessel 14 and the obstacle 102.
[0106] The dry air or nitrogen gas 24 that is charged into the
hollow tank 14 is ionized by the soft X-rays 103, and becomes the
ionized dry air or nitrogen gas 33. The dust in the ionized dry air
or nitrogen gas 33 is removed by the PTFE filter 7 placed in the
opening 8a disposed at the intake side of the container 1, and then
flows into the container 1 as the flow 34 of the ionized dry air or
nitrogen gas. In the container 1, the ionized dry air or nitrogen
gas can remove the chemical gas and the moisture from the container
1, can also remove the static electricity from the surfaces of the
wafers 9, and can then prevent acid from being generated at the
surfaces of the wafers 9. By using the PTFE filter, the dust in the
ionized dry air or nitrogen gas can be removed, but the ions in it
can be maintained. Then, the dry air or nitrogen gas 24 flows into
the container 1 as the flow 34 of the ionized dry air or nitrogen
gas.
[0107] In contrast, the portion 12a for exhausting the used ionized
dry air or nitrogen gas comprises the hollow vessel 27 that has the
exhaust nozzle 26, which vessel 27 is disposed at the side of the
exhaust port of the container 1, and which vessel 27 has the
exhaust port 29 disposed at its sidewall,
[0108] wherein the exhaust port 29 discharges the used ionized dry
air or nitrogen gas 35 from the container 1 after the ionized dry
air or nitrogen gas charged into the container 1 removes the
chemical gas and the moisture from the container 1, also removes
the static electricity from the surfaces of the wafers 9, and then
prevents acid from being generated at the surfaces of the wafers
9.
[0109] The distal side of the exhaust nozzle 26 has an
approximately conical shape so that the exhaust nozzle 26 can be
hermetically fixed to the port 30 disposed at the downstream side
of the PTFE filter 7 placed in the opening 8b disposed at the
bottom plate 5 and at the exhaust side of the container 1.
[0110] The used ionized dry air or nitrogen gas 35, which has
removed the chemical gas and the moisture from the container 1,
also removed the static electricity from the surfaces of the wafers
9, and then prevented any acid from being generated at the surfaces
of the wafers 9, is discharged from the exhaust port 29 outside the
container 1 after it flows into the hollow vessel 27 through the
exhaust nozzle 26 and the PTFE filter 7 placed in the opening 8b
disposed at the exhaust side of the container 1. Each of the
openings 8 disposed at the intake side and the exhaust side of the
container 1 has the filter 7 so as to be used as an opening for
both the intake and exhaust.
[0111] Below, the function of the apparatus B of Embodiment 2 of
the present invention for removing the static electricity is
explained in detail. The nozzle 13 for providing the ionized dry
air or nitrogen gas, disposed at the hollow vessel 14 that is
disposed at the portion 11a for providing the ionized dry air or
nitrogen gas, which portion constitutes a part of the apparatus B,
is hermetically fixed to the port 15 disposed at the upstream side
of the PTFE filter 7 placed in the opening 8a disposed at the
bottom plate 5 and the intake side of the container 1. The exhaust
nozzle 26, disposed at the hollow vessel 27 that is disposed at the
portion 12a for exhausting the used ionized dry air or nitrogen
gas, which portion constitutes another part of the apparatus B, is
hermetically fixed to the port 30 disposed at the downstream side
of the PTFE filter 7 placed in the opening 8b disposed at the
bottom plate 5 and the exhaust side of the container 1.
[0112] After the apparatus B for removing static electricity is
connected to the container 1 for storing the semiconductor wafers
9, the ionized dry air or nitrogen gas 24 is provided to the hollow
vessel 14 disposed at the portion 11a for providing the ionized dry
air or nitrogen gas from its source (not shown) through the pipe 16
for providing the dry air or nitrogen gas. When the ion generator
31 provides the hollow vessel 14 with the soft X-rays, the dry air
or nitrogen gas in the hollow vessel 14 is ionized by the soft
X-rays and becomes the ionized dry air or nitrogen gas 33. Since
the ionized dry air or nitrogen gas 33 in the hollow vessel 14
passes through the PTFE filter 7 placed in the opening 8a disposed
at the intake side of the container 1, the dust in the ionized dry
air or nitrogen gas can be removed, but the ions in it can be
maintained. Then, the ionized dry air or nitrogen gas 33 flows into
the container 1, removes the chemical gas and the moisture in the
container 1, also removes the static electricity from the surfaces
of the wafers 9, and can prevent acid from being generated at the
surfaces of the wafers 9.
[0113] After removing the chemical gas and the moisture in the
container 1, removing the static electricity from the surfaces of
the wafers 9, and preventing the acid from being generated at the
surfaces of the wafers 9, the used dry air and nitrogen gas 35 flow
into the hollow vessel 27 through the PTFE filter 7 placed in the
opening 8b disposed at the exhaust side of the container 1 and the
exhaust nozzle 26. Then, the used dry air and nitrogen gas 35 is
discharged outside the container 1 through the exhaust port 29.
[0114] As explained in the above paragraphs, the PTFE filters 7 are
provided for the bottom plate 5 of the container 1 for storing
semiconductor wafers so as to prevent dust from infiltrating the
container 1 and to maintain the ions in the dry air or nitrogen
gas. The PTFE filter 7 is comprised of a porous film that has very
fine pores and is made from an extended polytetraphenolethylene
film, which type of film is usually used for a filter. Namely, the
PTFE filter is not a glass-fiber filter using glass fibers as one
of the materials of the filter. If the glass-fiber filter were to
be used for the filter of the present invention, then when the
ionized dry air or nitrogen gas would pass through the glass-fiber
filter, the number of ions in the ionized dry air or nitrogen gas
would be reduced by the filter. Thus, a glass-fiber filter cannot
be used for the present invention.
[0115] In contrast, the PTFE filter used for the present invention
can charge the ionized dry air or nitrogen gas 33 into the
container 1 for storing the semiconductor wafers without notably
reducing the number of ions in the ionized dry air or nitrogen gas
33. To verify this effect, the following experiments using a device
for experiments as shown in FIG. 11 were conducted.
[0116] For the experiments, decay time, which is defined as an
ordinary physical property, is used to evaluate the reduction of
static electricity. The decay time is measured by a device for
measuring it, while the apparatus for removing static electricity
is operated under these conditions:
a) after not passing through any filter, b) after passing through
the PTFE filter, and c) after passing through the glass-fiber
filter.
[0117] Below, the results of the experiments are explained.
[0118] The measurements of the decay time at an air pressure of 0.5
MPa that is provided for the apparatus for removing static
electricity are as follows:
a) after not passing through any filter:
[0119] The decay time: 0.4 sec (plus charge)
[0120] The decay time: 0.5 sec (minus charge)
b) after passing through the PTFE filter:
[0121] The decay time: 1.9 sec (plus charge)
[0122] The decay time: 4.7 sec (minus charge)
c) after passing through the glass-fiber filter:
[0123] The decay time: .infin. sec (plus charge)
[0124] The decay time: .infin. sec (minus charge)
From the results of the experiments, it is seen that a) at the
barrier-free condition, that is, no filter is used in the passage
of the ionized dry air, the static electricity can be removed
within a short time, and b) even though the PTFE filter was used in
the passage of the ionized dry air, which filter constitutes a kind
of barrier, although the efficiency for removing the static
electricity was reduced to some degree, it was verified that the
static electricity can be removed. Further, c) though the
glass-fiber filter was used in the passage of the ionized dry air,
which filter also constitutes a kind of barrier, it was verified
that the static electricity cannot be removed. Namely, it became
clear that the ions contained in the ionized dry air or nitrogen
gas are lost when it passes through the glass-fiber filter. From
the results of the experiments, further, it became clear that to
some degree, although the PTFE filter reduces the number of ions in
the ionized dry air or nitrogen gas 33, it can provide the ionized
dry air or nitrogen gas 33 having enough ions to the container 1
for storing semiconductor wafers.
[0125] When the ionized dry air or nitrogen gas 33 is provided to
the container 1, since the pressure in the container 1 is low at
the initial stage, the flow rate of the ionized dry air or nitrogen
gas 33 that is charged into the container 1 is high. Thus, it is
possible that the dust that has accumulated at the bottom of the
container 1 will be stirred up, and then will be attached to the
surfaces of the wafers 9. Over time, since the pressure in the
container 1 increases, the flow rate of the ionized dry air or
nitrogen gas 33 is reduced. Thus, the dust is not stirred up.
[0126] Based on the effect explained in the above paragraphs, a
buffering tank 19 is installed on the pathway for providing the dry
air or nitrogen gas 24 of the apparatus B for removing static
electricity, that is, on the pipe 16 for providing the dry air or
nitrogen gas between the opening and closing valve 18 and the
hollow vessel 14. Consequently, the flow rate of the dry air or
nitrogen gas 24 that is charged into the hollow vessel 14 is
averaged. The dry air or nitrogen gas 24 that has its flow rate
averaged then flows into the hollow vessel 14 and is ionized. The
ionized dry air or nitrogen gas 33 is provided at a slow speed to
the container 1 as a flow 34 of the ionized dry air or nitrogen
gas. Thus, the dust that has accumulated at the bottom of the
container 1 is not stirred up.
[0127] The effects of the buffering tank shown in FIGS. 5-7 are the
same as those previously explained. Thus, a detailed explanation of
the buffering tank is omitted.
* * * * *