Gas separation – Plural serial basically diverse separating media – With heating or cooling means or having insulation
Reexamination Certificate
2000-12-12
2003-04-15
Hopkins, Robert A. (Department: 1724)
Gas separation
Plural serial basically diverse separating media
With heating or cooling means or having insulation
C055S434200, C055S446000, C055S464000, C055SDIG001
Reexamination Certificate
active
06547844
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an exhaust gas filtration device for removing solidification constituents and solids in exhaust gas, which is provided in the exhaust path of a gas treatment chamber employed in a step of manufacturing semiconductor elements or electronic components.
2. Description of Related Art
In, for example, plasma CVD equipment which is used in the manufacture of semiconductor elements or electronic components, a plasma CVD process occurs in an airtight vessel, and an a-Si film or SiN film, etc is deposited on a substrate. In this process, apart from on the substrate, the thin film is also deposited on the inside wall, etc. of the airtight vessel. Usually, the thin film that is deposited on the inside wall, etc. is removed by plasma cleaning using NF
3
gas. In this process, gaseous products chiefly represented by Si
2
F
6
(NH
4
)
3
.F* are produced in the airtight vessel. Evacuation of the airtight vessel is continued during plasma cleaning, so powder-form solids chiefly represented by Si
2
F
6
(NH
4
)
3
.F* are precipitated and deposited on the piping, etc. constituting the exhaust path. Such deposition of solids tends to cause blockage of the piping. In order to prevent this, an exhaust gas filtration device is provided in the exhaust path with the object of removing solidification constituents (gaseous products whose condition is changed to a solid by cooling or by densification (raised pressure)) and solids in the exhaust gas.
FIG. 13
is a block diagram illustrating a conventional exhaust gas filtration device. FIG.
13
(A) shows an airtight vessel
10
and exhaust path
12
a
of this airtight vessel. A vacuum pump
14
and exhaust gas filtration device
16
are arranged in this exhaust path
12
a
. This conventional exhaust gas filtration device
16
comprises a trap device
18
and filter
20
. The exhaust path
12
a
referred to above is constituted by connecting this vacuum pump
14
, trap device
18
and filter
20
in this order from airtight vessel
10
by means of piping in accordance with requirements.
Also, the exhaust path
12
b
shown in FIG.
13
(B) consists of trap device
18
, filter
20
and vacuum pump
14
connected in this order through piping, as required, from airtight vessel
10
. In this way, for the order of arrangement of the exhaust gas filtration device
16
and vacuum pump
14
an order may be employed that is the opposite of that of FIG.
13
(A).
As the trap device
18
described above, for example trap devices constructed as shown in FIG.
14
and
FIG. 15
are known. FIG.
14
and
FIG. 15
are cross-sectional views illustrating the construction of typical trap devices.
The trap device shown in
FIG. 14
comprises a cylindrical vessel (casing)
22
having apertures at both ends. One aperture of this vessel
22
is employed as a gas inlet port
24
and the other aperture of this vessel
22
is employed as a gas outlet port
26
, respectively. Within vessel
22
, there is provided a cylindrical baffle plate
28
which is closed at one end. Baffle plate
28
is arranged in the vicinity of the middle of the interior of vessel
22
, with its closed end facing gas inlet port
24
. Within this baffle plate
28
, there is provided a cooling pipe
30
comprising a cooling medium inlet port
30
a
and cooling medium outlet port
30
b
. Also, on the wall surface of vessel
22
, there is provided a cooling pipe
32
comprising a cooling medium inlet port
32
a
and cooling medium outlet port
32
b
. A cooling medium such as water is circulated in these cooling pipes
30
and
32
.
Exhaust gas evacuated from the airtight vessel flows from gas inlet port
24
into the interior of vessel
22
and, passing between the inside wall of vessel
22
and baffle plate
28
, flows from gas outlet port
26
into the downstream exhaust path. This exhaust gas carries heat. On the other hand, vessel
22
and baffle plate
28
are cooled to a temperature lower than the temperature of the exhaust gas by means of cooling pipes
30
and
32
. As a result, the exhaust gas solidifies in the vessel
22
, and products generated within the airtight vessel are precipitated as solids. These solids are deposited on the wall surface of vessel
22
and the surface of baffle plate
28
.
Also, in the trap device shown in
FIG. 15
, a cooling pipe
34
comprising a cooling medium inlet port
34
a
and cooling medium outlet port
34
b
is provided within vessel
22
. This cooling pipe
34
is of a shape that is bent a plurality of times, so the contact area between the exhaust gas and cooling pipe
34
is increased, and the efficiency of collection of the solidification constituents and solids is increased.
Next, a typical example of the construction of the filter
20
referred to above is illustrated in FIG.
16
. FIG.
16
(A) is a cross-sectional view showing an example of construction of the filter. FIG.
16
(B) is a perspective view with part of this filter disassembled.
The filter shown in
FIG. 16
comprises a cylindrical vessel
36
having two apertures
38
and
40
. The first aperture
38
of this vessel
36
is used as a gas inlet aperture and the second aperture
40
of this vessel
36
is used as a gas outlet aperture, respectively. In this example, the second aperture
40
is formed at one end of vessel
36
while the first aperture
38
is formed in the cylindrical surface nearer to the other end of vessel
36
.
A filter mesh
42
is provided in the interior of vessel
36
. This filter mesh
42
is constituted by winding a stainless steel plain fabric diamond wire diameter mesh (hereinbelow abbreviated to “mesh”)
44
onto the outside of a stainless-steel cylindrical frame
46
(in a condition in which frame
46
is inserted facing in the direction shown by arrow a in FIG.
16
(B)). This filter mesh
42
is arranged such that its inside (on the side of frame
46
) communicates with second aperture
40
and its outside (on the side of mesh
44
) communicates with first aperture
38
. A plurality of apertures
46
a
are formed on the cylindrical surface of frame
46
so that exhaust gas that flows into the first aperture
38
passes through the mesh
44
of filter mesh
42
and reaches the second aperture
40
. Solids in the exhaust gas are captured by mesh
44
.
Also, first aperture
38
could be used as a gas outlet port and second aperture
40
could be used as a gas inlet port. In this case, the exhaust gas flows into the second aperture
40
, and the exhaust gas passes through the mesh
44
of filter mesh
42
before flowing out to the outside from first aperture
38
.
However, the conventional exhaust gas filtration devices suffer from the following problems.
1) In the trap devices described above, the solidification constituents or solids in the exhaust gas cannot be completely removed. In order to remove the solidification constituents or solids, it is necessary to cool the exhaust gas, thereby inevitably bringing the solidification constituents or solids in the exhaust gas into contact with cooling parts of the trap device. It is therefore difficult to remove fine particulate products (solids) that do not flow through the vicinity of the cooling parts. Also, even if they do come into contact, it is difficult for fine particulate products that are flowing past with high speed to be deposited and accumulated.
2) The products described above that are not captured by the trap device are removed by a filter provided downstream of the trap device. However, although this filter is able to remove the fine particulate products due to the fact that it consists of fibrous members of a fine close construction, it is easily blocked even by a very small quantity of particulate products, severely lowering the conductance of the exhaust path. When the conductance has been lowered to a certain degree, it is necessary to wash or change the structural components of the exhaust gas filtration device. Consequently, due to the employment of a filter, the period of continuous use of the exhaust gas filtration de
Nagakura Keisuke
Rikyuu Toshihiro
Anelva Corporation
Hopkins Robert A.
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