Abstract:
A flow indicator is disclosed and includes a horizontally disposed housing including a lower inlet port drawing in an air sample, an interior space passing the air sample, an upper outlet port exhausting the air sample, and a transparent window allowing visual observation of at least a portion of the interior space. The flow indicator also includes a floater disposed within the housing and moving vertically in response to the flow of the air sample to indicate a flow rate for the air sample, wherein the housing further comprises a plurality of rails protruding from an inner surface of the housing and extending vertically to guide movement of the floater.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application is a divisional of application Ser. No. 11/431,521, filed May 11, 2006. Of note, additional related divisional applications include [Attorney Docket No. SEC.1523D1] and [Attorney Docket No. SEC.1523D2]. 
     
    
     BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     Embodiments of the invention relate to a flow indicator and an apparatus for monitoring particles in air. More particularly, embodiments of the invention relate to an apparatus adapted to draw an air sample from the air in a clean room and count particles contained in the air sample, and a flow indicator adapted to indicate the flow rate of the air sample.  
         [0004]     2. Description of the Related Art  
         [0005]     Semiconductor devices are commonly manufactured by performing a complex sequence of fabrication processes that form a number of semiconductor dies, i.e., a number of electrical circuits individually formed on portions of a silicon wafer used as a substrate. Once the semiconductor dies have been formed on a silicon wafer an electrical die sorting (EDS) process is performed which inspects the electrical characteristics of the electrical circuits formed by the sequence of fabrication processes. Thereafter, individual semiconductor dies are removed from the silicon wafer and packaged to form a competed semiconductor device. This packaging process generally involves encapsulating each semiconductor die in an epoxy resin.  
         [0006]     The sequence of fabrication processes usually includes one or more of: a deposition process adapted to deposit a material layer on the substrate; a chemical mechanical polishing (CMP) process adapted to planarize a material layer; a photolithography process adapted to form a photoresist pattern, an etching process adapted to form a pattern having desired electrical characteristics from a material layer using the photoresist pattern; an ion implantation process adapted to selectively implant ions into specific regions of the substrate; a cleaning process adapted to remove impurities from the substrate; a drying process adapted to dry cleaned substrate; an inspection process adapted to identify defects in the material layer and/or the pattern; etc.  
         [0007]     Many if not all of these fabrication processes are performed in a conventional clean room. Clean rooms are widely used to prevent workpieces, such as silicon wafers, from becoming contaminated by particles in the air such as ordinary dust. The carefully controlled environment of a clean room is managed in accordance with various defined classes of cleanliness. Each clean room class is defined by the concentration of contaminant particles and/or the largest acceptable diameter of contaminate particles allowable within the clean room.  
         [0008]     Various measurement apparatuses have been developed to facilitate clean room management. A condensation particle counter, which is one such measurement apparatus, operates under the principle that the particle size increases during an alcohol evaporation process. An optical particle counter, which is another conventional measurement apparatus, measures the intensity of light scattered from a projected laser by the particles in the sampled air.  
         [0009]     Examples of particle monitoring apparatuses including such particle counters are disclosed, for example, in Japanese Patent Application Publication No. 8-054265, Korean Patent No. 252215, and U.S. Pat. No. 5,856,623.  
         [0010]     One conventional particle monitoring apparatus includes a sampling probe adapted to draw in an air sample, and a particle counter connected to the sampling probe. The sampling probe is connected to the particle counter by a sampling tube, and the vacuum pressure (i.e., a suction force) used to draw in the air sample in provided by a pump disposed within the particle counter. In the conventional particle monitoring apparatus, the flow rate of the air sample varies in accordance with the suction force applied by the pump, the length of the sampling tube, leakage of the air sample throughout the apparatus, etc.  
         [0011]     However, variations in the air sample flow rate cause problems in the management of clean room cleanliness. For example, when the air sample flow rate falls abnormally low, the exact of contaminate particles in the air cannot be accurately measured. Contamination of workpieces may result.  
         [0012]     Thus, there is a need for an improved particle monitoring apparatus that allows an air sample to be drawn into a particle counter at a constant flow rate. Such an apparatus will more readily facilitate acquisition and evaluation of the air sample.  
       SUMMARY OF THE INVENTION  
       [0013]     Exemplary embodiments of the present invention provide a flow indicator that indicates an air sample flow rate through the flow indicator. Exemplary embodiments of the present invention also provide a particle monitoring apparatus comprising such a flow indicator.  
         [0014]     In one embodiment, the invention provides a flow indicator comprising; a horizontally disposed housing comprising; a lower inlet port drawing in an air sample, an interior space passing the air sample, an upper outlet port exhausting the air sample, and a transparent window allowing visual observation of at least a portion of the interior space. The flow indicator also includes a floater disposed within the housing and moving vertically in response to the flow of the air sample to indicate a flow rate for the air sample, wherein the housing further comprises a plurality of rails protruding from an inner surface of the housing and extending vertically to guide movement of the floater.  
         [0015]     In a related embodiment, the lower inlet port is disposed in a lower central portion of the housing.  
         [0016]     In another related embodiment, the lower inlet port comprises a plurality of lower inlet ports disposed radially around a center of the lower portion of the housing.  
         [0017]     In another related embodiment, an outer surface of the floater is separated from the inner surface of the housing, the outer surface of the floater comprises a plurality of guide grooves, and the plurality of guide grooves engage with the plurality of rails.  
         [0018]     In another related embodiment the floater comprises; an inner panel having a plurality of holes passing the air sample, and an outer tube extending downward from an outer edge portion of the inner panel and having a plurality of guide grooves, wherein the plurality of guide grooves engage with the plurality of rails. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0019]     Exemplary embodiments of the present invention will be described in detail hereinafter with reference to the accompanying drawings, in which like reference symbols refer to like or similar elements throughout. In the drawings:  
         [0020]      FIG. 1  is a schematic view illustrating a particle monitoring apparatus comprising a flow indicator in accordance with an exemplary embodiment of the present invention;  
         [0021]      FIG. 2  is a cross-sectional view illustrating a sampling probe shown in  FIG. 1  and the flow indicator shown in  FIG. 1 ;  
         [0022]      FIG. 3  is a perspective view illustrating a lower cap shown in  FIG. 2 ;  
         [0023]      FIG. 4  is a perspective view illustrating an upper cap shown in  FIG. 2 ;  
         [0024]      FIG. 5  is a perspective view illustrating a transparent tube shown in  FIG. 2 ;  
         [0025]      FIG. 6  is a perspective view illustrating a guide member and an exhaust pipe shown in  FIG. 2 ;  
         [0026]      FIG. 7  is a perspective view illustrating another exemplary embodiment of the lower cap shown in  FIG. 3 ;  
         [0027]      FIG. 8  is a perspective view illustrating yet another exemplary embodiment of the lower cap as shown in  FIG. 3 ;  
         [0028]      FIG. 9  is a cross-sectional view illustrating a floater shown in  FIG. 2 ;  
         [0029]      FIG. 10  is a vertical cross-sectional view illustrating a flow indicator in accordance with another exemplary embodiment of the present invention;  
         [0030]      FIG. 11  is a horizontal cross-sectional view illustrating the flow indicator shown in  FIG. 10 ;  
         [0031]      FIG. 12  is a perspective view illustrating another exemplary embodiment of a lower cap shown in  FIG. 10 ;  
         [0032]      FIG. 13  is a perspective view illustrating yet another exemplary embodiment of the lower cap shown in  FIG. 10 ;  
         [0033]      FIG. 14  is a vertical cross-sectional view illustrating a flow indicator in accordance with yet another exemplary embodiment of the present invention;  
         [0034]      FIG. 15  is a horizontal cross-sectional view illustrating the flow indicator shown in  FIG. 14 ;  
         [0035]      FIG. 16  is a perspective view illustrating a floater shown in  FIG. 14 ; and  
         [0036]      FIG. 17  is a schematic view illustrating a particle monitoring apparatus in accordance with still another exemplary embodiment of the present invention. 
     
    
     DESCRIPTION OF EMBODIMENTS  
       [0037]     As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items.  
         [0038]     It will be understood that, although the terms first, second, etc. may be used herein to describe various elements, these elements should not be limited by these terms These terms are only used to distinguish one element from another. For example, a first thin film could be termed a second thin film, and, similarly, a second thin film could be termed a first thin film without departing from the teachings of the disclosure.  
         [0039]     The terminology used herein is used only for the purpose of describing particular embodiments of the invention and is not intended to limit the invention.  
         [0040]     Furthermore, relative terms, such as “lower” or “bottom” and “upper” or “top,” may be used herein to describe one elements relationship to another element or other elements illustrated in the drawings. It will be understood that relative terms are intended to encompass different orientations of an element in addition to the orientation depicted in the drawings. For example, if a first element in one of the drawings is turned over, secondary elements described as being on the “lower” side the first element would then be oriented on “upper” side of the first element. Therefore, the exemplary term “lower” can encompasses both an orientation of “lower” and “upper,” depending of the particular orientation of one or more elements in the drawing. Similarly, if a first element in one of the drawings is turned over, secondary elements described as “below” or “beneath” the first element would then be oriented “above” the first element. Therefore, the exemplary terms “below” or “beneath” can encompass both an orientation of above and below.  
         [0041]     Embodiments of the present invention are described herein with reference to cross-sectional illustrations that are schematic illustrations of idealized embodiments of the present invention. As such, variations from the shapes shown in the illustrations as a result of, for example, manufacturing techniques and/or tolerances, are to be expected. Thus, embodiments of the present invention should not be construed as being limited to the particular shapes of regions illustrated herein, but are to include deviations in shapes that result from, for example, manufacturing. For example, a region illustrated or described as flat may, typically, have rough and/or nonlinear features. Moreover, sharp angles illustrated in the drawings may be rounded. Thus, the regions illustrated in the drawings are schematic in nature and their shapes are not intended to illustrate the precise shape of a region and are not intended to limit the scope of the present invention.  
         [0042]      FIG. 1  is a schematic view illustrating a particle monitoring apparatus comprising a flow indicator in accordance with an exemplary embodiment of the present invention.  
         [0043]     Referring to  FIG. 1 , a particle monitoring apparatus  10  may be used to monitor the inner environment of a clean room in which semiconductor devices are manufactured. Particularly, particle monitoring apparatus  10  may be used to measure the concentration of particles in a primary air sample taken from the interior of a clean room.  
         [0044]     The primary air sample may comprise a first air sample drawn by a sampling probe  12  and a second air sample drawn by a flow indicator  100  coupled to sampling probe  12 . In more detail, sampling probe  12  is disposed in a clean room and draws the first air sample. Flow indicator  100  is coupled vertically to sampling probe  12  and draws the second air sample. An “entire flow rate” associated with the first and second air samples may be determined on the basis of the ascertained flow rate for the second air sample.  
         [0045]     A particle counter  14  may be connected to sampling probe  12  by a sampling tube  16 . Although not shown in detail in the drawings, particle counter  14  may comprise a laser optical member adapted to detect the particles in the primary air sample and a pump adapted to provide the suction force necessary to draw in the primary air sample. Alternatively, particle monitoring apparatus  10  may comprise a condensation particle counter.  
         [0046]      FIG. 2  is a cross-sectional view illustrating sampling probe  12  and flow indicator  100  shown in  FIG. 1 .  
         [0047]     In the illustrated example, sampling probe  12  has a funnel shape and is usually intended to be mounted or disposed in a horizontal manner (e.g., relative to a wall of the clean room). Assigning a horizontal orientation to sampling probe  12 , flow indicator  100  is coupled substantially vertically to a lower portion of sampling probe  12 .  
         [0048]     Flow indicator  100  may comprise a housing  110  that has an interior space  110   a,  which is used as a flow passage for the second air sample, and a floater  120  disposed in interior space  110   a.  Housing  110  has a cylindrical shape and is disposed in a vertical direction. Further, housing  110  has a plurality of lower inlet ports  110   b,  through which the second air sample is drawn into flow indicator  100 , and an upper outlet port  110   c,  through which the second air sample that passes through interior space  110   a  is exhausted into sampling probe  12 . Housing  110  also comprises a transparent window  110   d,  through which interior space  110   a  may be observed. Floater  120  may move in the vertical direction within housing  110  in accordance with the flow of the second air sample through interior space  110   a.    
         [0049]     Additionally, housing  110  may comprise a lower cap  112  having the plurality of lower inlet ports  110   b,  an upper cap  114  having upper outlet port  110   c,  and a transparent tube  116  coupled between lower and upper caps  112  and  114  and which serves as transparent window  110   d.  Transparent tube  116  is inserted into lower and upper caps  112  and  114  with an interference fit to prevent the second air sample from leaking out of housing  110  once it has been drawn into interior space  110   a.    
         [0050]     Guide member  130  is disposed inside of housing  110  and guides the movement of floater  120 . Guide member  130  extends upwardly from a lower portion of housing  110 . In more detail, guide member  130  extends upwardly from a lower central portion of housing  110  along a central axis of housing  110 , and floater  120  has a central hole through which guide member  130  passes. In addition, a ring-shaped stopper  132  is disposed at an upper portion of guide member  130  to limit the height to which floater  120  may rise (i.e., to keep floater  120  from moving to a point above stopper  132 ).  
         [0051]     The second air sample drawn through the plurality of lower inlet ports  110   b  flows from a lower portion of interior space  110   a  into an upper portion of interior space  110   a  through a gap between housing  110  and floater  120 , and is then exhausted into sampling probe  12  through an exhaust pipe  140  extending through upper outlet port  110   c.    
         [0052]     Exhaust pipe  140  has a plurality of holes  140   a  through which the second air sample is drawn in order to exhaust the second air sample after the second air sample has flowed into the upper portion of interior space  110   a.  Holes  140   a  are formed radially around a lower portion of exhaust pipe  140 . In the illustrated example shown in  FIGS. 2 and 6 , exhaust pipe  140  is disposed coaxially with guide member  130 , and exhaust pipe  140  and guide member  130  are formed as one linear piece. However, guide member  130  and exhaust pipe  140  may be provided separately.  
         [0053]     Sampling probe  12  has a coupling hole  12   a  formed through a lower portion of sampling probe  12 , and exhaust pipe  140  is coupled inside of coupling hole  12   a  with an interference fit, thereby coupling flow indicator  100  with sampling probe  12 . When flow indicator  100  and sampling probe  12  are coupled in this manner, sealing members  150  may be interposed between coupling hole  12   a  and exhaust pipe  140  to prevent leakage of the first and second air samples. For example, O-rings may be interposed between coupling hole  12   a  and exhaust pipe  140 , and when O-rings are interposed between coupling hole  12   a  and exhaust pipe  140 , flow indicator  100  is fixed to sampling probe  12  by the O-rings. Further, a fixing clip  152  may be disposed at exhaust pipe  140  to limit the position at which exhaust pipe  140  may be coupled to housing  110 .  
         [0054]      FIGS. 3, 4 , and  5  are perspective views illustrating lower cap  112 , upper cap  114 , and transparent tube  116 , respectively, each of which is shown in  FIG. 2 .  FIG. 6  is a perspective view illustrating guide member  130  and exhaust pipe  140  as shown in  FIG. 2 .  
         [0055]     Referring to  FIGS. 3 through 6 , lower cap  112  has a cylindrical shape and has a closed lower end and an open upper end (i.e., the lower end is covered by a lower panel  112   a,  while the upper end is not covered). On the contrary, upper cap  114  has a cylindrical shape and has a closed upper end and an open lower end (i.e., the upper end of upper cap  114  is covered by an upper panel  114   a,  while the lower end is not covered).  
         [0056]     Particularly, lower cap  112  comprises lower panel  112   a,  and a lower tube  112   b  extending upwardly from lower panel  112   a  and having a first length in a direction perpendicular to lower panel  112   a.  Also, lower panel  112   a  has the plurality of lower inlet ports  110   b.  Upper cap  114  comprises upper panel  114   a,  and an upper tube  114   b  extending downwardly from the upper panel  114   a  and having a second length in a direction perpendicular to upper panel  114   a.  Also, upper panel  114   a  has upper outlet port  110   c.    
         [0057]     Lower inlet ports  110   b  are arranged radially around the center of lower panel  112   a.  Lower inlet ports  110   b  may be arranged at regular intervals along a circle concentric to the circumference of lower panel  112   a  as desired. Though four lower inlet ports  110   b  are arranged radially around the center of lower panel  112   a  shown in  FIG. 3 , the scope of the present invention is not limited by the number of lower inlet ports  110   b  shown in  FIG. 3 .  
         [0058]     A threaded hole  112   c  is formed through a central portion of lower cap  112 . Threaded hole  112   c  is used to couple lower cap  112  to guide member  130 , and guide member  130  has a threaded end portion  134  that is threadably engaged with threaded hole  112   c.  As shown in the drawings, guide member  130  has a circular horizontal cross-section. However, guide member  130  may have a polygonal horizontal cross-section to prevent floater  120  from rotating.  
         [0059]     Transparent tube  116  is provided so that the movement of floater  120  in interior space  110   a,  which is caused by the flow of the second air sample, may be observed visually. Transparent tube  116  has a third length along a central axis of transparent tube  116  that is longer than the sum of the first length of lower tube  112   b  and the second length of upper tube  114   b  so that floater  120  in interior space  110   a  may be observed. Transparent tube  116  also has an inner diameter that is constant along the third length so that floater  120  will move stably within transparent tube  116 . Furthermore, transparent tube  116  may comprise outer step portions (i.e., the upper and lower portions of transparent window  110   d  of  FIG. 5 ) that bound the respective positions at which each of lower and upper caps  112  and  114  may be coupled to transparent tube  116 , as shown in  FIGS. 2 and 5 .  
         [0060]     Exhaust pipe  140  and guide member  130  are provided in one piece. A plurality of first annular grooves  140   b  is formed in an upper portion of exhaust pipe  140 , and a sealing member  150  (of  FIG. 2 ) is mounted in each of the plurality of first annular grooves  140   b.  A second annular groove  140   c  is formed adjacent to the plurality of first annular grooves  140   b,  and fixing clip  152 , which limits the position at which guide member  130  and exhaust pipe  140  may be coupled to housing  110 , is mounted in second annular groove  140   c.    
         [0061]      FIGS. 7 and 8  are perspective views illustrating other exemplary embodiments of lower cap  112  of  FIGS. 2 and 3 .  
         [0062]     Referring to  FIG. 7 , a lower cap  160  may comprise a lower panel  162 , which has a plurality of fine inlet ports  162   a  uniformly formed in lower panel  162  and used to draw the second air sample into inner space  110   a,  and a lower tube  164  that extends upwardly from lower panel  162 . In addition, lower panel  162  has a threaded hole  162   b  in a central portion of lower panel  162  by which lower cap  160  is coupled to guide member  130 .  
         [0063]     Referring to  FIG. 8 , a lower cap  170  may comprise a lower panel  172  having eight lower inlet ports  172   a  formed in lower panel  172 , arranged at regular intervals along a circle concentric to the circumference of lower panel  172 , and used to draw the second air sample into interior space  110   a;  and lower cap  170  may further comprise a lower tube  174  that extends upwardly from lower panel  172 . Further, lower panel  172  has a threaded hole  172   b  in a central portion of lower panel  172  by which lower cap  170  is coupled to guide member  130 . Each lower inlet port  172   a  has a diameter smaller than the diameter of each lower inlet port  110   b  of  FIG. 3 .  
         [0064]     Referring to  FIGS. 3, 7 , and  8 , the number of inlet ports  110   b,    162   a,  and  172   a  formed in lower cap  112 ,  160 , and  170 , respectively, may vary. However, an entire cross-sectional area of inlet ports  110   b,    162   a,  or  172   a  may be determined in accordance with the normal entire flow rate of the primary air sample, and the number and diameter of the inlet ports  110   b,    162   a,  or  172   a  may be adjusted in accordance with the normal range of the entire flow rate of the primary air sample. For example, when the normal entire flow rate of the primary air sample ranges from about 4 to about 9 l/min, each of the lower inlet ports  110   b  (of  FIG. 3 ) may have a diameter of about 4 mm.  
         [0065]      FIG. 9  is a cross-sectional view illustrating floater  120  of  FIG. 2 .  
         [0066]     Referring to  FIG. 9 , floater  120  may comprise an inner panel  122 , an outer tube  124 , and a guide tube  126 . Inner panel  122  has a disk shape, and guide member  130  passes through a central hole formed in a central portion of inner panel  122 . Outer tube  124  extends downwardly from an outer edge portion of inner panel  122  and the outer surface of outer tube  124  faces an inner surface of transparent tube  116 . Guide tube  126  extends downwardly from an inner portion of inner panel  122  and surrounds guide member  130  so that guide member  130  may guide the movement of floater  120  caused by the flow of the second air sample.  
         [0067]     A first gap between guide tube  126  and guide member  130  is less than or equal to about 0.1 mm so that the second air sample can be restrained from flowing through the first gap. For example, the first gap between guide tube  126  and guide member  130  may be about 0.05 mm. A second gap between outer tube  124  and transparent tube  116  may be determined in accordance with the normal entire flow rate of the primary air sample. For example, when the normal entire flow rate of the primary air sample is about 4 to about 9 l/min, and an outer diameter of outer tube  124  is about 25 to about 26 mm, the second gap may be about 0.3 to about 0.5 mm.  
         [0068]     Outer tube  124  may comprise a plurality of tubes, wherein each tube of the plurality of tubes is a different color in order to facilitate visual observation of the movement of floater  120  through transparent tube  116 . Particularly, outer tube  124  comprises a first color tube  124   a  that extends downwardly from the outer edge portion of inner panel  122  and has a first color, and a second color tube  124   b  that is coupled to a lower end of first color tube  124   a  and has a second color different from the first color. For example, the first color and the second color may be red and blue, respectively. Step portions are formed at the lower portion of first color tube  124   a  and an upper portion of the second color tube  124   b  in order to provide an interference fit between first and second color tubes  124   a  and  124   b.    
         [0069]     The flow of the second air sample moves floater  120  vertically within interior space  110   a,  and the flow rate of the second air sample is ascertained by observing the position of floater  120  through transparent tube  116 . For example, when the primary air sample is drawn at a normal flow rate, the second color of floater  120  (e.g., blue) will be visible through transparent tube  116 . On the contrary, when the first color of floater  120  (e.g., red) is visible through transparent tube  116 , the primary air sample is not being drawn at a normal flow rate. That is, when the flow rate of the second air sample is reduced below a normal flow rate, the first color of floater  120  is visible through transparent tube  116  because floater  120  has, as a result of the reduced flow rate of the second air sample, a lower position within interior space  110   a  than it has when the second air sample is being drawn at a normal flow rate for the second air sample. Particularly, when the second color of floater  120  is observed through transparent tube  116 , the primary air sample has an entire flow rate of about 4 to about 9 l/min and is being drawn normally. When the first color of floater  120  is observed through transparent tube  116 , the primary air sample has an entire flow rate of less than or equal to about 1 l/min and is being drawn abnormally. Further, when the first and second colors of floater  120  are observed through transparent tube  116  at the same time, the primary air sample is being drawn at an entire flow rate of about 2 to about 3 l/min.  
         [0070]     The position of floater  120  can be easily observed with the naked eye by observing the color(s) of floater  120  visible through transparent tube  116 . So, even when sampling probe  12  and flow indicator  100  are disposed adjacent to a ceiling of the clean room, an operator can easily ascertain whether or not the primary air sample is being drawn normally.  
         [0071]      FIG. 10  is a vertical cross-sectional view illustrating a flow indicator in accordance with another exemplary embodiment of the present invention, and  FIG. 11  is a horizontal cross-sectional view illustrating the flow indicator shown in  FIG. 10 .  FIGS. 12 and 13  are perspective views illustrating exemplary embodiments of the lower cap shown in  FIG. 10 .  
         [0072]     Referring to  FIGS. 10 and 11 , a flow indicator  200 , in accordance with an exemplary embodiment of the present invention, may comprise a cylindrical housing  210  comprising an interior space  210   a  and a floater  220  disposed within housing  210  and which may move vertically within housing  210 .  
         [0073]     Flow indicator  200  is coupled to a lower portion of a sampling probe that draws a first air sample. In addition, flow indicator  200  comprises a lower cap  212  having a plurality of lower inlet ports  210   b  through which a second air sample is drawn, an upper cap  214  having an upper outlet port  210   c  through which an exhaust pipe  240  is inserted, wherein exhaust pipe  240  is adapted to exhaust the second air sample, and a transparent tube  216  coupled between lower and upper caps  212  and  214 .  
         [0074]     Though lower cap  212  of  FIG. 11  has four lower inlet ports  210   b  through which the second air sample may be drawn, the scope of the present invention is not limited by the number of lower inlet ports  210   b  shown in  FIG. 11 . For example, a lower cap  260  (shown in  FIG. 12 ) may have a plurality of fine lower inlet ports  260   a  formed uniformly in lower cap  260 , and a lower cap  270  (shown in  FIG. 13 ) may have one lower inlet port  270   a.  Lower caps  260  and  270  are each alternate exemplary embodiments of lower cap  212  of flow indicator  200  of  FIGS. 10 and 11 .  
         [0075]     Referring again to  FIGS. 10 and 11 , transparent tube  216  comprises a plurality of rails  230  that protrude from an inner surface of transparent tube  216  and extending substantially vertically to guide the movement of floater  220 .  
         [0076]     Floater  220  comprises an inner panel  222  that has the shape of a disk and is disposed in a direction substantially perpendicular to a central axis of housing  210 , and an outer tube  224  that extends downwardly from an outer edge portion of inner panel  222 . Outer tube  224  is separated from the inner surface of transparent tube  216 , and a plurality of guide grooves  224   a  is formed in the outer surface of outer tube  224 . The plurality of guide grooves  224   a  is adapted to engage with the plurality of rails  230 . As an example, when (1) the entire flow rate of the first and second air samples is about 4 to about 9 l/min, (2) each of the four lower inlet ports  210   b  has an inner diameter of about 4 mm, and (3) the outer diameter of outer tube  224  is about 25 to about 26 mm, then the gap between outer tube  224  and transparent tube  216  may be about 0.3 to about 0.5 mm. Further, the gap between each rail  230  and its corresponding guide groove  224   a  may be less than or equal to about 0.1 mm.  
         [0077]     Outer tube  224  comprises a first color tube  226  that extends downwardly from the outer edge portion of inner panel  222  and has a first color, and a second color tube  228  that is coupled to a lower end of first color tube  226  and has a second color different from the first color.  
         [0078]     Each stopper  232  of a plurality of stoppers  232  is disposed on a rail  230  of the plurality of rails  230  to limit the height to which floater  220  may rise.  
         [0079]     Exhaust pipe  240  extends through upper outlet port  210   c  of upper cap  214 , and a lower end of exhaust pipe  240  is disposed higher than each of the plurality of stoppers  232 . As shown in  FIG. 10 , exhaust pipe  240  comprises an open upper end, a closed lower end, and a plurality of holes  240   a  that are formed radially around a lower portion of exhaust pipe  240  and through which the second air sample is drawn out of housing  210 . However, exhaust pipe  240  may have an open lower end.  
         [0080]     Many of the elements of flow indicator  200  are similar or identical to those already described regarding flow indicator  100  shown in  FIGS. 1 through 9 , so further detailed description of those elements will be omitted herein.  
         [0081]      FIG. 14  is a vertical cross-sectional view illustrating a flow indicator in accordance with yet another exemplary embodiment of the present invention,  FIG. 15  is a horizontal cross-sectional view illustrating the flow indicator shown in  FIG. 14 , and  FIG. 16  is a perspective view illustrating a floater shown in  FIG. 14 .  
         [0082]     Referring to  FIGS. 14 through 16 , a flow indicator  300 , in accordance with an exemplary embodiment of the present invention, may comprise a cylindrical housing  310  comprising an interior space  310   a  and a floater  320  disposed within housing  310  and which may move vertically within housing  310 .  
         [0083]     Flow indicator  300  is coupled substantially vertically to a lower portion of a sampling probe adapted to draw a first air sample. Housing  310  may comprise a lower cap  312  having a plurality of lower inlet ports  310   b  through which a second air sample may be drawn. Housing  310  may also comprise an upper cap  314  having an upper outlet port  310   c  through which an exhaust pipe  340 , which is adapted to exhaust the second air sample into the sampling probe, is disposed, and a transparent tube  316  coupled between lower and upper caps  312  and  314 .  
         [0084]     Transparent tube  316  comprises a plurality of rails  330 , which protrude from an inner surface of transparent tube  316 , extend substantially vertically, and which are adapted to guide the vertical movement of floater  320 .  
         [0085]     Floater  320  may comprise an inner panel  322  disposed in a direction substantially perpendicular to a central axis of housing  310 . Inner panel  322  may have a plurality of first holes  322   a  through which the second air sample may pass. Floater  320  may further comprise an outer tube  324  that extends downwardly from an outer edge portion of inner panel  322  and comprises a plurality of guide grooves  324   a  adapted to engage with the plurality of rails  330 . A first gap between outer tube  324  and transparent tube  316  may be less than or equal to about 0.1 mm. Also, one of a plurality of second gaps is formed between each rail  330  and its corresponding guide groove  324   a.  Each of the plurality of second gaps may be less than or equal to about 0.1 mm.  
         [0086]     Outer tube  324  comprises a first color tube  326  that extends downwardly from the outer edge portion of inner panel  322  and has a first color, and a second color tube  328  that is coupled to a lower end of first color tube  326  and has a second color different from the first color.  
         [0087]     Flow indicator  300  also comprises a plurality of stoppers  332 . Each of the plurality of stoppers  332  is disposed on a rail  330  of the plurality of rails  330  to limit the height to which floater  320  may rise.  
         [0088]     Exhaust pipe  340  extends through upper outlet port  310   c  of upper cap  314 , and a lower end of exhaust pipe  340  is disposed higher than each of the plurality of stoppers  332 . As shown in  FIG. 14 , exhaust pipe  340  comprises an open upper end, a closed lower end, and a plurality of second holes  340   a  that are formed radially around a lower portion of exhaust pipe  340  and through which the second air sample may be drawn out of housing  310 . However, exhaust pipe  340  may have an open lower end.  
         [0089]     Many of the elements of flow indicator  300  are similar or identical to those already described regarding flow indicator  100  shown in  FIGS. 1 through 9  or flow indicator  200  shown in  FIGS. 10 through 13 , so further detailed description of those elements will be omitted herein.  
         [0090]      FIG. 17  is a schematic view illustrating a particle monitoring apparatus in accordance with still another exemplary embodiment of the present invention.  
         [0091]     Referring to  FIG. 17 , a particle monitoring apparatus  20 , in accordance with an exemplary embodiment of the present invention, may comprise a plurality of sampling probes  22  located in several places in a clean room and a plurality of flow indicators  400 , each of which is coupled to a sampling probe  22  of the plurality of sampling probes  22 . Each sampling probe  22  is adapted to draw a primary air sample and each flow indicator  400  is adapted to indicate the flow rate of the primary air sample.  
         [0092]     Each sampling probe  22  is connected to a manifold  26  by one of a plurality of sampling tubes  24 . Manifold  26  is connected by a suction tube  30  to a first pump  28  adapted to draw the primary air samples. In addition, manifold  26  is connected by a second sampling tube  34  to a particle counter  32  adapted to count particles in the primary air samples. In particular, manifold  26  is adapted to selectively provide the primary air samples drawn from the locations of sampling probes  22  to particle counter  32 . Particle counter  32  may comprise a laser optical member adapted for use in counting particles contained in the selected primary air sample, and may also comprise a second pump adapted to draw the selected air sample into particle counter  32 .  
         [0093]     Further detailed descriptions of sampling probes  22  and flow indicators  400  will be omitted because each of sampling probes  22  and flow indicators  400  is similar or identical to sampling probes and flow indicators, respectively, that have already been described in connection with previously described exemplary embodiments of the present invention.  
         [0094]     In accordance with exemplary embodiments of the present invention, an air sample is provided to the particle counter to measure the degree of contamination of the clean room. The flow rate of the air sample may be easily ascertained by observing the floater through the transparent tube; and thus, the reliability of a measurement of the degree of contamination of the clean room taken by the particle counter may be improved.  
         [0095]     Further, the flow rate of the air sample may be observed visually at any time. Thus, there is no need to separately check the operation of the particle monitoring apparatus, and the time required check the operation (or operating state) of the particle monitoring apparatus may be reduced. Consequently, the cleanliness of the clean room may be maintained constantly. Furthermore, deterioration in the cleanliness of the clean room caused by variation in the flow rate of the air samples may be prevented.  
         [0096]     Although exemplary embodiments of the present invention have been described herein, the present invention is not limited to the exemplary embodiments described. Rather, those skilled in the art will recognize that various changes and modifications can be made to the exemplary embodiments while remaining within the scope of the present invention as defined by the following claims.