KR20060098451A - Chemical filter and fan filter unit having the same - Google Patents

Abstract

A fan filter unit for purifying air supplied to a clean space such as a clean room, the fan filter unit comprising: a chemical filter for removing chemical contaminants contained in the air, a fan for sucking the air, Particle filter for removing dust or particles contained in the air. The filter medium of the chemical filter has a circular tube shape and is disposed between the inner circular tube and the outer circular tube, each of which is breathable, and a cover prevents the flow of air through the upper ends of the inner and outer circular tubes. Thus, the air is sucked into the inner tube only through the outer round tube, the filter medium and the inner round tube by the suction force provided from the fan. Thus, the velocity distribution of the air passing through the filter medium is improved, and the life of the chemical filter is extended.

Description

Chemical filter and fan filter unit having the same

1 is a schematic diagram illustrating a conventional clean room system.

2 is a schematic cross-sectional view for explaining a conventional fan filter unit.

3 is a schematic cross-sectional view for explaining another example of a conventional fan filter unit.

4 is a schematic cross-sectional view for explaining another example of a conventional fan filter unit.

5 is a schematic cross-sectional view for describing a fan filter unit having a chemical filter according to an embodiment of the present invention.

FIG. 6 is a perspective view illustrating the chemical filter illustrated in FIG. 5.

FIG. 7 is a graph for explaining a velocity distribution of air passing through the chemical filter shown in FIG. 3.

FIG. 8 is a graph for explaining a velocity distribution of air passing through the side of the chemical filter shown in FIG. 4.

FIG. 9 is a graph for explaining a velocity distribution of air passing through the chemical filter shown in FIG. 5.

Explanation of symbols on the main parts of the drawings

10: clean room system 12: clean room

14 ceiling chamber 16: bottom floor area

18: air circulation path 20: air circulation path

100, 200, 300, 400: Fan filter unit

120, 210, 310, 410: Chemical Filter

110, 220, 320, 420: fan

130, 230, 330, 430: Particle Filter

412: housing 412A: inner round tube

412B: outer round tube 412C: first cover

412D: second cover 414: filter medium

416: fastening member 422: suction port

The present invention relates to a chemical filter for removing chemical contaminants contained in air supplied to a clean space and a fan filter unit having the same. More specifically, a chemical filter for removing chemical contaminants contained in air supplied to a clean space such as a clean room for manufacturing a semiconductor device, and a fan filter unit including the chemical filter, the fan, and the particle filter. It is about.

In general, a semiconductor device includes a Fab process for forming an electrical circuit on a silicon wafer used as a semiconductor substrate, an electrical die sorting (EDS) process for inspecting electrical characteristics of semiconductor devices formed in the fab process; Each of the semiconductor devices is manufactured through a package assembly process for encapsulating and individualizing the epoxy resins.

The fab process includes a deposition process for forming a film on a wafer, a chemical mechanical polishing process for planarizing the film, a photolithography process for forming a photoresist pattern on the film, and the photoresist pattern using the photoresist pattern. An etching process for forming the film into a pattern having electrical characteristics, an ion implantation process for implanting ions into a predetermined region of the wafer, a cleaning process for removing impurities on the wafer, and a drying process for drying the cleaned wafer And an inspection step for inspecting the defect of the film or pattern.

The manufacturing process of the semiconductor device as described above is performed in a clean space such as a clean room, and the air supplied to the clean room is purified by the fan filter unit. An example of a clean room system including the fan filter unit is disclosed in US Pat. No. 6,368,393 (issued to Hironaka).

1 is a schematic configuration diagram illustrating a conventional clean room system, and FIG. 2 is a schematic cross-sectional view illustrating a conventional fan filter unit.

1 and 2, the clean room system 10 includes a clean room 12, a ceiling chamber 14 formed above the clean room 12, and a ceiling surface of the clean room 12. A plurality of fan filter units (FFUs) arranged in a matrix manner on the floor, an underfloor region or utility zone 16 formed below the clean room 12, and the ceiling chamber An air circulation path 18 connecting 14 to the bottom floor region 16, and a cooling coil 20 for adjusting the temperature of the circulated air.

Clean air supplied to the clean room 12 by the fan filter units 100 is discharged from the clean room 12 to the bottom floor area 16, and the air circulation path 18 and the ceiling chamber ( 14 and back to the clean room 12 through the fan filter units 100.

Referring to FIG. 2, each fan filter unit 100 includes a fan 110 for sucking air inside the ceiling chamber 14 and ammonia (NH ₃₎ contained in the air sucked through the fan 110. Chemical filter 120 for removing chemical contaminants such as ozone (O ₃ ), and particles for removing particles (or dust) contained in air chemically purified by the chemical filter 120. And a filter 130.

As shown in FIG. 2, the chemical filter 120 is disposed between the fan 110 and the particle filter 130, and the structure of the fan filter unit is the most general structure, and is described in US Patent No. 6,368,393. Is disclosed.

The lifetime of the chemical filter 120 is determined by the speed of air passing through the filter medium of the chemical filter 120. Since the velocity of air introduced into the housing of the fan filter unit 100 sucked by the fan 110 has a local change, the efficiency of the chemical filter 120 is lowered. Specifically, the chemical filter because the speed of the air passing through the edge portion of the chemical filter 120 is higher than the speed of the air passing through the central portion of the chemical filter 120 due to the structural cause of the fan filter unit 100. The lifetime of 120 is determined by the speed of air passing through the edge of the chemical filter 120. That is, since the flow rate of the air passing through the edge of the chemical filter 120 is greater than the flow rate of the air passing through the central portion, the equivalent capacity of the edge portion of the chemical filter 120 is greater than that of the central portion. It is quickly exhausted and the pollution control efficiency of the edge portion is lowered. Thus, unlike the other particle filters, the lifetime of the chemical filter 120 is greatly influenced by the velocity distribution or velocity deviation of the air passing through the chemical filter 120.

Accordingly, there is a need for an improved fan filter unit that allows for a constant velocity distribution of air passing through the chemical filter 120.

3 is a schematic cross-sectional view for explaining another example of a conventional fan filter unit.

Referring to FIG. 3, the illustrated fan filter unit 200 includes a chemical filter 210 for removing chemical contaminants contained in the air inside the ceiling chamber 14 of the clean room system 10, and the chemical filter. Particle filter 230 for removing particles contained in the air chemically purified by the 210, and a fan 220 disposed between the chemical filter 210 and the particle filter 230. A buffer space 240 is provided between the chemical filter 210 and the fan 220, and the buffer space 240 shows a velocity distribution of air passing through the chemical filter 210 in FIG. 1. It can be somewhat improved compared to the unit 100.

However, in the fan filter units 100 and 200 illustrated in FIGS. 2 and 3, when the chemical filters 120 and 210 are replaced, the fan filter units 120 and 210 must be disassembled as a whole. The time required is increased. In addition, since the work space of the worker is not secured, the time required may be further increased, and the operation of the fans 110 and 220 is stopped while the chemical filters 120 and 210 are replaced. There is a problem that the downtime of the is increased.

As an example of an attempt to solve the above problems, Japanese Patent Laid-Open No. 1999-90143 discloses a fan filter unit having a rectangular filter-shaped chemical filter.

4 is a schematic cross-sectional view for explaining another example of a conventional fan filter unit.

Referring to FIG. 4, a chemical filter 310 having a rectangular box shape is installed at the inlet 322 of the fan 320, and a particle filter 330 is disposed below the fan 320. The fan filter unit 300 having the structure as described above can shorten the time required for the replacement of the chemical filter 310, but due to the difference in speed between the upper and side surfaces of the chemical filter 300, the chemical filter There is still a problem in the velocity distribution of air passing through 310. In addition, the chemical filter 310 is very weak in the velocity distribution uniformity of the air, particularly in the corner portion because of the rectangular box shape.

The first object of the present invention for solving the above problems is to provide a chemical filter that makes the velocity distribution of the air passed through constant.

A second object of the present invention is to provide a fan filter unit having the chemical filter as described above and which is easy to replace the chemical filter.

The present invention for achieving the first object is an inner circular tube having air-permeability, an outer circular tube disposed to surround the inner circular tube with breathability, between the inner and outer circular tubes A chemical filter interposed therebetween and comprising a filter medium for removing contaminants contained in air flowing through the inner and outer circular tubes.

The chemical filter is disposed on the upper ends of the inner and outer tubes to define an interspace between the inner space of the inner round tube and the inner and outer round tubes, and prevents the flow of air through the upper ends. And a second cover disposed on lower ends of the inner and outer tubes to define a space between the inner and outer circular tubes, and a second cover to prevent flow of air through the lower ends. can do.

The first cover has a disk shape, the second cover has a circular flat ring shape having an opening in communication with the internal space, and the opening serves as an outlet port of the chemical filter.

The present invention for achieving the second object is an inner round tube having a breathable, an outer round tube disposed to surround the inner round tube with a breathable, interposed between the inner and outer circular tubes and the inner And a filter medium including a filter medium for removing contaminants contained in air flowing through the outer circular tubes. A fan in communication with the inner space of the inner round tube of the chemical filter, for sucking outside air through the outer round tube, the filter medium and the inner round tube; And a particle filter connected to the fan and including a particle filter for removing particles contained in air discharged from the fan.

The outside air (for example, the air inside the ceiling chamber disposed above the clean room) is sucked into the inner space of the inner round tube by the suction force provided from the fan. The suction force is provided along the central axis of the inner round tube, and the inner space of the inner round tube and the space between the inner and outer round tubes are defined by the first cover, so that the outside air is provided with the outer and inner round tubes. Through the interior space.

Here, the inner circular tube and the outer circular tube is preferably disposed coaxially with each other, the chemical filter is preferably disposed coaxially with the fan. Thus, the suction force provided from the fan is uniformly applied to the inner round tube, and the velocity distribution of air passing through the filter medium can be improved. Accordingly, the life of the chemical filter can be extended, and the time required for the replacement of the chemical filter can be shortened because the chemical filter has a cylindrical shape as a whole and is connected to the inlet of the fan.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

5 is a schematic cross-sectional view for describing a fan filter unit having a chemical filter according to an embodiment of the present invention, and FIG. 6 is a perspective view illustrating the chemical filter shown in FIG. 5.

Referring to FIG. 5, a fan filter unit 400 is disposed on a ceiling surface of a clean room to remove contaminants contained in air supplied to a clean space such as a clean room for performing a manufacturing process of a semiconductor device. . The fan filter unit 400 may include a chemical filter 410 for removing chemical contaminants contained in the air supplied to the clean room, a fan 420 for providing suction force for sucking the air, and Particle filter 430 for removing dust or particles contained in the air.

The fan filter unit 400 includes a clean room 12, a ceiling chamber 14, a bottom floor region 16, an air circulation path 18, a cooling coil 20, and the like as shown in FIG. 1. May be employed to purify the air circulated in the clean room system 10.

The chemical filter 410 is used to remove chemical contaminants such as ammonia and ozone contained in the circulated air. The chemical filter 410 has a cylindrical housing 412 for receiving the filter medium 414. The housing 412 includes an inner round tube 412A, an outer round tube 412B, a first cover 412C, and a second cover 412D.

The inner and outer circular tubes 412A, 412B are each breathable and are arranged concentrically with each other. The first cover 412C includes the inner space 412E of the inner circular tube 412A and the inner space 412F to define an interspace between the inner and outer circular tubes 412A, 412B. Disposed on the upper ends of the outer circular tubes 412A, 412B. The second cover 412D is disposed on the lower ends of the inner and outer circular tubes 412A, 412B to define a space 412F between the inner and outer circular tubes 412A, 412B.

The first cover 412C has a disc shape, and the second cover 412D has a circular flat ring having an opening 412G communicating with an inner space 412E of the inner circular tube 412A. circular flat ring) shape. That is, the first cover 412C has an outer air through the upper ends of the inner and outer tubes 412A and 412B, and the inner space 412E and the inner and outer circular tubes (412E) of the inner circular tube 412A. Prevents inflow into the space 412F between 412A and 412B, and the second cover 412D allows external air to pass through the lower ends of the inner and outer circular tubes 412A and 412B. Prevents entry into the space 412F between the holes 412A, 412B. In this case, the opening 412G of the second cover 412D functions as an outlet port of the chemical filter 410.

On the other hand, the second cover 412D is such that the inner space 412E of the inner round tube 412A and the opening 412G of the second cover 412D communicate with the inlet 422 of the fan 420. It is disposed on an edge portion of the suction port 422 of the fan 420 and has an outer diameter larger than the diameter of the outer circular tube 412B. That is, the second cover 412D is an upper portion of the fan 420 to surround the inlet 422 of the fan 420 between the inner and outer circular tubes 412A and 412B and the fan 420. Is placed on. A plurality of through holes 412H are formed at an edge portion of the second cover 412D in the circumferential direction, and the chemical filter 410 is an upper portion of the fan 420 through the through holes 412H. It is coupled to the fan 420 by a plurality of fastening members 416 fastened to it.

In this case, the chemical filter 410 is preferably arranged concentrically with the fan 420. This makes the distance between the central axis of the fan 420 and the inner circular tube 412A of the chemical filter 410 constant so that the suction force provided from the fan 420 is applied uniformly to the chemical filter 410. In order to uniformize the velocity distribution of the air passing through the chemical filter 410.

That is, the first cover 412C is disposed to be spaced apart from the fan 420 to prevent the inner circular tube 412A and the outer circular tube 412B, and the second cover 412D is disposed between the interspace ( It is disposed adjacent the inlet 422 of the fan 420 to block 412F. At this time, one end of the inner round tube 412A adjacent to the second cover 412D functions as an outlet port of the chemical filter 410.

The inner and outer circular tubes 412A and 412B may be made of a perforated metal sheet or a metal mesh each having a plurality of through holes formed therein. Preferably, each may be made of a porous aluminum sheet or an aluminum mesh. As shown in FIG. 6, the inner and outer circular tubes 412A and 412B each have a plurality of circular holes, but the shape of the through holes does not limit the scope of the present invention.

The fan 420 provides a suction force for sucking outside air (inside air of the ceiling chamber) along the central axis of the chemical filter 410, the outside air being the outer circular tube 412B, the filter medium 414. And through the inner circular tube 412A to the inner space 412E.

As the filter medium 414, a pleat type filter medium having an overall circular tube shape as shown in FIG. 6 may be used, and the filter medium 414 includes the inner circular tube 412A and the outer circular tube. It is accommodated in the interspace of 412B.

The chemically purified air through the chemical filter 410 is introduced into the particle filter 430 through a space in communication with the outlet 424 of the fan 420, and is included in the air by the particle filter 430. Dust or particles are removed.

The velocity distribution of air passing through the chemical filter 410 having the cylindrical shape is more uniform than the velocity distributions of air passing through the conventional chemical filters (120, 210, 310 in FIGS. 2 to 4). The life of the filter 410 is extended, and the use efficiency of the chemical filter 410 is improved. In addition, since the chemical filter 410 is disposed on the inlet 422 of the fan 420, the replacement of the chemical filter 410 is easy, and the time required for the replacement operation may be shortened. In addition, since only the filter medium 414 may be replaced after the first cover 412C is removed, the required cost may be reduced.

Table 1 shows the velocity distribution of air passing through the conventional chemical filter 120 in the conventional fan filter unit 100 as shown in FIG. Velocity measurements were performed at 36 local measurement points, and the conventional chemical filter 120 has a rectangular plate shape of 1200 mm x 1200 mm. The velocity distribution of the measured air varies in the range of 0.31 m / s to 0.54 m / s, and the speed deviation is about ± 24%.

TABLE 1

Measuring position X1 X2 X3 X4 X5 X6 Y1 0.46 0.31 0.41 0.35 0.44 0.44 Y2 0.44 0.38 0.41 0.35 0.38 0.37 Y3 0.41 0.47 0.49 0.39 0.49 0.46 Y4 0.37 0.39 0.40 0.41 0.41 0.41 Y5 0.37 0.37 0.37 0.36 0.33 0.36 Y6 0.54 0.39 0.38 0.40 0.40 0.44

Meanwhile, in the fan filter unit 200 having the conventional buffer space 240 as shown in FIG. 3, the velocity distribution of air passing through the conventional chemical filter 210 having a rectangular plate shape of 1200 mm × 1200 mm is shown. Was changed from 0.38ms to 0.48m / s and the speed deviation was about ± 12%. The change in the velocity distribution of the air along the X axis direction is the same as the graph shown in FIG. 7.

Referring to FIG. 7, it can be seen that the wind speed is lowered toward the left and right sides with respect to the (0.0) coordinate point of the X axis. This means that the speed of the air passing through the center portion of the conventional chemical filter 210 is faster than the speed of the air passing through the edge portion, which means that the overall speed distribution is not constant and the speed variation for each position is large.

In addition, in the fan filter unit 300 having the chemical filter 310 having a conventional rectangular box shape as shown in FIG. 4, the velocity distribution of air passing through the chemical filter 310 is shown in Tables 2 and 3. Measured as Table 2 shows the velocity distribution in the upper surface of the chemical filter 310, Table 3 shows the velocity distribution in the side of the chemical filter 310. 8 is a graph illustrating a change in velocity of air passing through the side surface of the chemical filter 310 along the X-axis direction.

Referring to FIG. 8, it can be seen that the velocity distribution of air passing through the side of the chemical filter 310 is not constant. This is seen as the effect of the speed of air passing through the upper surface of the chemical filter 310 and the difference in distance from the central axis on which the suction force by the fan 320 acts.

TABLE 2

Measuring position X1 X2 X3 X4 Y1 0.39 0.45 0.49 0.40 Y2 0.37 0.41 0.50 0.43 Y3 0.40 0.42 0.46 0.40 Y4 0.39 0.44 0.46 0.38

TABLE 3

Measuring position X1 X2 X3 X4 Z1 0.17 0.21 0.22 0.21 Z2 0.18 0.19 0.23 0.20 Z3 0.19 0.23 0.23 0.19 Z4 0.20 0.21 0.20 0.16

Referring to Table 2 and Table 3, it can be easily seen that the top surface velocity distribution and the side velocity distribution of the rectangular filter type chemical filter 310 are significantly different. The top velocity distribution varies from 0.37 m / s to 0.5 m / s, while the lateral velocity distribution varies from 0.14 m / s to 0.23 m / s. In addition, the speed deviation of air passing through the upper surface is about ± 15%, and the speed deviation of air passing through the side is about ± 35%.

The upper surface velocity distribution is similar to the velocity distribution of the chemical filter 210 of the fan filter unit 200 having the buffer space 240. However, the velocity distribution on the side was measured at a very low level compared to the velocity distribution on the upper surface, and the velocity was particularly low at each corner portion. That is, the efficiency of the chemical filter 310 is lowered because the speed of the air passing through the upper surface is about two times greater than the speed of the air passing through the side surface, and in particular, passes through the maximum speed and side surface of the air passing through the upper surface. The ratio of the minimum velocity of air to be said is about 2.9: 1. Thus, the life of the chemical filter 310 is determined by the speed of air passing through the upper surface.

In contrast, in the fan filter unit 400 according to the exemplary embodiment of the present invention illustrated in FIG. 5, the velocity distribution passing through the cylinder type chemical filter 410 was measured as shown in Table 4, and the circumferential direction was measured. It can be seen that the velocity distribution that changes accordingly is shown as shown in FIG. 9.

TABLE 4

Measuring position A1 A2 A3 A4 Z1 0.6 0.58 0.6 0.55 Z2 0.62 0.58 0.57 0.54 Z3 0.6 0.53 0.57 0.53 Z4 0.61 0.52 0.54 0.53

Referring to Table 4 and FIG. 9, the velocity distribution of the cylinder type chemical filter 410 is varied in a range of about 0.53 m / s to about 0.62 m / s, and has a speed deviation of about ± 7%. From the above results, it can be seen that the cylinder type chemical filter 410 has an improved velocity distribution than the conventional chemical filters 120, 210, and 310, which means that the chemical filter 410 of the present invention It has a longer life than the chemical filters (120, 210, 310).

Substantially, the cylinder type chemical filter of the present invention has a lifespan of about 10 to 20% longer than that of a conventional rectangular plate-shaped chemical filter, and also generates a cost reduction effect of about 10 to 20%.

Meanwhile, in the conventional chemical filter 120 shown in FIG. 2, the removal efficiency of contaminants such as ammonia is about 94.3%, and a pressure drop of about 2.2 mmAq is generated, and the cylinder type chemical filter of the present invention. Contaminant removal efficiency of 410 was about 95.9%, and a pressure drop of about 1.7 mmAq occurred. Specifically, when the air having a contamination concentration of 28.5 ppb is purified by the conventional chemical filter 120 shown in FIG. 2, the contamination concentration of the purified air is measured as 1.71 ppb, and the air having a contamination concentration of 30.6 ppb. In the case of purifying with the cylindrical chemical filter 410, the contamination concentration of the purified air was measured to 1.24 ppb.

As described above, the performance of the cylinder type chemical filter 410 of the present invention is proven to be superior to that of the conventional chemical filter 120.

According to the present invention as described above, the cylinder-type chemical filter that sucks air in a direction perpendicular to the direction in which the suction force provided from the fan is applied has an improved velocity distribution than the conventional chemical filters. Accordingly, the efficiency of the chemical filter is improved, and the life can be extended.

In addition, the cylinder type chemical filter is smaller in volume than conventional chemical filters and is disposed on the upper part of the fan to surround the inlet of the fan, thereby reducing the time required for the replacement operation and replacing only the filter medium. This is reduced. In addition, the downtime of the clean room system can be reduced since the fan does not need to be shut down while the chemical filter is being replaced.

Although described above with reference to a preferred embodiment of the present invention, those skilled in the art will be variously modified and changed within the scope of the invention without departing from the spirit and scope of the invention described in the claims below I can understand that you can.

Claims (20)

An inner round tube having air-permeability; An outer circular tube that is breathable and is disposed to surround the inner circular tube; And And a filter medium interposed between the inner and outer circular tubes, the filter medium for removing contaminants contained in the air flowing through the inner and outer circular tubes. The air flow of claim 1, wherein the air flows through the top portions of the inner and outer tubes to define an interspace between the inner space and the inner and outer circular tubes. A first cover for preventing the; And A chemical filter is disposed on the lower ends of the inner and outer tubes to define a space between the inner and outer circular tubes, and further comprising a second cover for preventing the flow of air through the lower ends. . 3. The chemical filter of claim 2, wherein the first cover has a disk shape, and the second cover has a circular flat ring shape having an opening communicating with the internal space. The chemical filter of claim 1, wherein the outer circular tube is disposed coaxially with the inner circular tube. The chemical filter of claim 1, wherein the inner and outer circular tubes each comprise a porous metal sheet. The chemical filter of claim 1, wherein the inner and outer circular tubes each comprise a metal mesh. A breathable inner round tube, an outer round tube disposed to surround the inner round tube with breathability, and an air interposed between the inner and outer round tubes and included in air flowing through the inner and outer round tubes A chemical filter comprising a filter medium for removing contaminants; A fan in communication with the inner space of the inner round tube of the chemical filter, for sucking outside air through the outer round tube, the filter medium and the inner round tube; And And a particle filter connected to the fan and configured to remove particles contained in air discharged from the fan. 8. The method of claim 7, wherein the air flows through the upper ends of the inner and outer tubes to define an interspace between the inner space and the inner and outer circular tubes, Fan filter unit further comprises a cover for preventing. 10. The method of claim 8, further comprising a second cover disposed between the chemical filter and the fan to surround the inlet of the fan, the second cover defining a space between the inner and outer circular tubes. filter. 10. The chemical filter of claim 9, wherein the first cover has a disk shape, and the second cover has a circular flat ring shape having an opening in communication with the internal space. 8. The fan filter unit according to claim 7, wherein the outer circular tube is disposed coaxially with the inner circular tube. 8. The fan filter unit according to claim 7, wherein the fan filter unit and the fan are arranged coaxially. 8. The fan filter unit of claim 7, wherein the inner and outer circular tubes each comprise a porous metal sheet. 8. The fan filter unit of claim 7, wherein the inner and outer circular tubes each comprise a metal mesh. A fan for supplying air in a ceiling chamber disposed above the clean room to the inside of the clean room; A filter medium for removing chemical contaminants contained in the air supplied to the clean room and having an overall circular tube shape, an inner circular tube disposed inside the filter medium and having a breathability Disposed on the upper ends to prevent the air from flowing into the space defined by the inner and outer circular tubes through the upper and vented outer circular tubes and the upper ends of the inner and outer circular tubes And an inner space of the inner round tube communicating with an inlet of the fan such that the air flows into the inner space of the inner round tube through the outer round tube, the filter medium, and the inner round tube. A chemical filter disposed on the top of the pan; And And a particle filter connected to the lower part of the fan to remove particles contained in the air supplied from the fan. 16. The apparatus of claim 15, further comprising a second cover disposed between the chemical filter and the fan to surround the inlet of the fan, the second cover defining a space between the inner round tube and the outer round tube. Fan filter unit. The method of claim 16, wherein the second cover has a circular flat ring shape, the outer diameter of the second cover is larger than the diameter of the outer circular tube, the chemical filter is the edge of the second cover The fan filter unit, characterized in that coupled to the fan by a plurality of fastening members fastened to the upper portion of the fan through the portion. The fan filter unit according to claim 15, wherein the chemical filter and the fan are disposed coaxially. 16. The fan filter unit of claim 15, wherein the inner and outer circular tubes each comprise a porous aluminum sheet. 16. The fan filter unit of claim 15, wherein the inner and outer circular tubes each comprise an aluminum mesh.

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