Abstract:
Provided is an exhaust unit capable of preventing large pressure fluctuations within a process chamber due to atmospheric pressure changes. The exhaust unit includes a main exhaust duct and a supplemental exhaust duct that acts as a partial bypass. A flap is located at a downstream opening between the main exhaust duct and supplemental exhaust duct and controls the amount of bypassed gas flowing from the supplemental exhaust duct to the main exhaust duct. First and second plates of the flap are pivotally coupled to the main exhaust duct adjacent the downstream opening, the first plate colliding with gas flowing through the main exhaust duct and the second plate partially blocking bypassed gas flowing back into the main exhaust duct from the supplemental exhaust duct. When gas is exhausted through the main exhaust line and the supplemental exhaust duct, the flap passively controls the amount by which the supplemental exhaust duct is opened through fluctuations in atmospheric pressure.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This U.S. non-provisional patent application claims priority under 35 U.S.C. §119 of Korean Patent Application No. 10-2007-00740, filed on Jan. 3, 2007, the entire contents of which are hereby incorporated by reference. 
       BACKGROUND OF THE INVENTION 
       [0002]    The present invention disclosed herein relates to a semiconductor manufacturing facility, and more particularly, to an exhaust unit and an exhausting method for exhausting gas from a process chamber to lower the pressure within the process chamber. 
         [0003]    Typically, a semiconductor manufacturing facility has a plurality of process chambers within a clean room and exhaust units that control the pressures within the process chambers. Each process chamber is connected to a branch duct for exhausting gas from therein, and the respective branch ducts are connected to a main duct. The main duct is formed of a primary duct with a fan installed, and a secondary duct connected to the branch ducts. Typically, the fan is controlled to adjust the volume of exhausted gas according to the atmospheric pressure, and the pressure within the process chamber is affected by the volume of gas exhausted by the fan. 
         [0004]    During processing, the pressure inside the process chamber should be maintained at a low pressure, and any variation in pressure should occur within a minimal range. However, when pressure variation over a wide range occurs during use of typical exhaust units as those described above, the pressure within the process chamber also fluctuates over a wide range, leading to manufacturing defects.  FIG. 1  is a graph showing variations in the thickness of an oxide layer formed on a wafer according to fluctuations in atmospheric pressure during a diffusion process. As shown in  FIG. 1 , the fluctuation range of atmospheric pressure directly affects the thickness of an oxide layer formed on a wafer within a process chamber, so that when the atmospheric pressure fluctuates widely, uniformity in the thickness of an oxide layer over a wafer deteriorate. 
         [0005]    Also, when process chambers are added to or removed from the clean room, the total volume of gas that is exhausted through the main duct is altered, necessitating manual adjustment of the opening ratio of each damper provided respectively in the secondary ducts. This task consumes much time and manpower. 
         [0006]    Accordingly, the need exists for exhaust units and methods that better regulate pressure fluctuations within process chambers. 
       SUMMARY OF THE INVENTION 
       [0007]    The present invention provides an exhaust unit and exhausting method capable of efficiently controlling pressure within a process chamber, and a semiconductor manufacturing facility with the exhaust unit. 
         [0008]    The present invention also provides an exhaust unit and exhausting method capable of preventing wide pressure fluctuation within a process chamber due to external influences, and a semiconductor manufacturing facility with the exhaust unit. 
         [0009]    Provisions of the present invention are not limited hereto, and may include other provisions that are not described, which will become clear to those skilled in the art from the description provided below. 
         [0010]    Embodiments of the present invention provide exhaust units used to regulate pressure in a process chamber, the exhaust units including: a main exhaust duct connected to the process chamber, and including at least one of a first opening and a second opening defined in a sidewall thereof; and at least one supplementary exhaust duct with one end connected to the first opening and the other end connected to the second opening, to allow a portion of gas flowing through the main exhaust duct to diverge from the main exhaust duct through the first opening, and re-enter the main exhaust duct through the second opening. A regulating member allowing regulating of an opening ratio of the second opening is provided in the exhaust unit. 
         [0011]    In some embodiments, the regulating member may include a flap altering the opening ratio of the second opening through colliding with a volume of gas flowing through the main exhaust duct, and the flap may decrease the opening ratio of the second opening as the volume of gas that the flap collides with in the main exhaust duct increases. 
         [0012]    In other embodiments, one end of the flap may be installed near an end of the second opening that is closer to the first opening, and the other end of the flap may be a free end. 
         [0013]    In still other embodiments, the flap may include a first plate and a second plate bending and extending from the first plate. The regulating member may further include a hinge coupling an intersecting axis, at which the second plate bends and extends from the first plate, to the main exhaust duct or the supplementary exhaust duct. 
         [0014]    In even other embodiments, the regulating member may further include: a bearing fixed to the main exhaust duct or the supplementary exhaust duct; and a rotating axis rotatably inserted in the bearing to fix the first plate and the second plate. 
         [0015]    In yet further embodiments, the regulating member may further include a connecting member of a rubber material, for fixing an intersecting axis, at which the second plate bends and extends from the first plate, to the main exhaust duct or the supplementary exhaust duct. 
         [0016]    In yet other embodiments, the exhaust unit may further include a damper disposed between the first opening and the second opening, to regulate the opening ratio of the main exhaust duct. 
         [0017]    In further embodiments, the main exhaust duct may have a rectangular cross section cut across a lengthwise direction thereof. The main exhaust duct may have opposing sidewalls, and the supplementary exhaust duct may be provided respectively on each of the sidewalls. The supplementary exhaust duct may be formed in a shape of a container open at one side, and the open side may communicate with the first and second openings. 
         [0018]    In still further embodiments, the regulating member may include: a flap rotating to regulate an opening ratio of the second opening; a driver rotating the flap; an airflow measurer measuring a volume of gas flowing through the main exhaust duct or the supplementary exhaust duct; and a controller controlling the driver, based on a measured value received from the airflow measurer. 
         [0019]    In other embodiments of the present invention, semiconductor manufacturing facilities include: a clean room; a plurality of process chambers arranged within the clean room, to perform a semiconductor process; and an exhaust unit regulating a pressure of the process chambers, wherein the exhaust unit includes: an integration duct having a pressure controlling member regulating an exhaust pressure, according to a fluctuation of an atmospheric pressure; and separation ducts diverging from the integration duct and coupled to the processing chambers. The integration duct may be embodied in various configurations in the above-described exhaust unit. 
         [0020]    In still other embodiments, the integration duct may further have a primary duct with the pressure controlling member installed therein, and a secondary duct diverging from the primary duct, having the separation ducts connected thereto, and having the main exhaust duct, the supplementary exhaust duct, and the regulating member. 
         [0021]    In still other embodiments of the present invention, methods for exhausting gas from a process chamber are provided. The methods include simultaneously exhausting gas from within a process chamber through a main exhaust duct and a supplementary exhaust duct, based on a fluctuation of external pressure, the supplementary exhaust duct being a chamber into which the gas diverges from and then re-enters the main exhaust duct, wherein an opening ratio of the supplementary exhaust duct is changed according to the fluctuation of the external pressure, to reduce a range of pressure fluctuation of an internal pressure of the process chamber based on the fluctuation of the external pressure. 
         [0022]    In still other embodiments, the changing of the opening ratio of the supplementary exhaust duct may be performed through changing an angle between an opening provided for allowing the gas flowing through the supplementary exhaust duct to enter the main exhaust duct, and a flap rotatably installed in an integration exhaust duct. 
         [0023]    In yet other embodiments, the flap may be rotated through a change in a volume of gas colliding with the flap as the gas flows through the main exhaust duct. 
         [0024]    In further embodiments, the opening ratio of the supplementary exhaust duct may increase when the external pressure increases. The opening ratio of the supplementary exhaust duct may decrease when the external pressure decreases. 
         [0025]    In still further embodiments, the flap may be rotated by a driver, and a flow volume within the supplementary exhaust duct or the main exhaust duct may be measured and a rotated angle of the flap may be changed according to a value of the measurement. 
     
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         [0026]    The accompanying figures are included to provide a further understanding of the present invention, and are incorporated in and constitute a part of this specification. The drawings illustrate exemplary embodiments of the present invention and, together with the description, serve to explain principles of the present invention. In the figures: 
           [0027]      FIG. 1  is a graph showing variations in the thickness of an oxide layer formed on a wafer according to fluctuations in atmospheric pressure during a diffusion process; 
           [0028]      FIG. 2  is a plan view of a semiconductor manufacturing facility according to one embodiment of the present invention; 
           [0029]      FIG. 3  is a perspective view of a secondary duct in  FIG. 2 ; 
           [0030]      FIG. 4  is an exploded perspective view of the secondary duct in  FIG. 3 ; 
           [0031]      FIG. 5  is a cross-sectional view of the secondary duct in  FIG. 3 ; 
           [0032]      FIG. 6  is an exploded perspective view of the secondary duct in  FIG. 3  with two identically-shaped supplementary exhaust ducts; 
           [0033]      FIGS. 7 through 9  are perspective views of various embodiments of flaps that are installed on main exhaust ducts; 
           [0034]      FIGS. 10 and 11  are diagrams respectively showing a reduction and an elevation in atmospheric pressure in a typically configured exhaust unit with only a main exhaust duct, and the change in flow quantity within the duct when the exhaust unit in  FIG. 3  is used; 
           [0035]      FIGS. 12(   a ) and ( b ) are graphs comparing the fluctuation of pressure in a process chamber over time when a typically configured exhaust unit is used, with the fluctuation of pressure in a process chamber over time when the exhaust unit in  FIG. 3  is used; 
           [0036]      FIG. 13  is a cross-sectional view of a secondary duct with regulating members installed therein according to another embodiment; 
           [0037]      FIG. 14  is a partial perspective view showing the regulating member in  FIG. 13 ; 
           [0038]      FIG. 15  and  FIG. 16  are respectively a perspective and cross-sectional view of a secondary duct with regulating members installed according to another embodiment; and 
           [0039]      FIG. 17  is a schematic cross-sectional view of a semiconductor manufacturing facility according to another embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0040]    Preferred embodiments of the present invention will be described below in more detail with reference to  FIGS. 2 through 17 . The present invention may, however, be embodied in different forms and should not be constructed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the present invention to those skilled in the art. Thus, elements in the drawings are exaggerated for clarity of illustration. 
         [0041]    Hereinafter, an exemplary embodiment of a structure of an exhaust unit  20  provided on a semiconductor manufacturing facility  1  according to the present invention will be described. The technical scope of the present invention, however, is not limited hereto, and the exhaust unit  20  may be employed in various other applications in which exhaust volume fluctuates due to external influences. 
         [0042]      FIG. 2  is a plan view of a semiconductor manufacturing facility  1  according to one embodiment of the present invention. Referring to  FIG. 2 , a semiconductor manufacturing facility  1  includes a clean room  10 , an exhaust unit  20 , and a plurality of process chambers  30 . The clean room  10  provides a space maintained at a high level of cleanliness compared to the  1 external environment. A plurality of different types of filters (not shown) is installed in the clean room  10  to remove impurities from air entering the clean room  10 . 
         [0043]    A plurality of process chambers  30  is provided within the clean room  10 . The process chambers  30  are configured to perform predetermined processes on semiconductor wafers, flat panel displays, etc. The process chambers  30  may be configured to perform deposition, photo processing, etching, polishing, and inspection. The process chambers  30  are provided in groups. Process chambers  30  in the same group may be configured to perform the same processes, and those in different groups may be configured to perform other processes. 
         [0044]    Each process chamber  30  maintains a process pressure in a preset range during a process. The exhaust unit  20  maintains the process pressure within the process chamber  30 , and exhausts residual material inside the process chamber  30  to the outside. The exhaust unit  20  has an integration duct  22  and a separation duct  24 . A separation duct  24  is directly attached to each process chamber  30 . The integration duct  22  includes a primary duct  22   a  and a secondary duct  22   b.  The secondary duct  22   b  branches from the primary duct  22   a , and the separation duct  24  branches in singularity or plurality from each secondary duct  22   b . Therefore, gas exhausted through a plurality of individual ducts  24  is integrated and exhausted into the secondary duct  22   b  to which each separation duct  24  is connected, and the gas exhausted through the secondary ducts  22   b  is integrated and exhausted into the primary ducts  22   a  and exhausted to the outside. Process chambers  30  connected to separation ducts  24  that branch from the same secondary duct  22   b  may be process chambers  30  performing the same process. 
         [0045]    The integration duct  22  is sectionally rectangular overall (when cut perpendicularly to its length), and the separation duct  24  is sectionally circular overall (when cut perpendicularly to its length). The cross sectional area of the secondary duct  22   b , which combines and exhausts gas exhausted from the plurality of separation ducts  24 , is sufficiently large with respect to the aggregate cross sectional area of the separation ducts  24 , and the cross sectional area of the primary duct  22   a , which combines and exhausts gas exhausted from the plurality of secondary ducts  22   b , is sufficiently large with respect to the aggregate cross sectional area of the secondary ducts  22   b.    
         [0046]    A damper  122  (see, e.g.,  FIG. 5 ) is provided in each of the secondary ducts  22   b  to adjust the opening ratio of the duct. In one embodiment, the damper  122  has two vanes  122   a  and  122   b  disposed linearly within the secondary duct  22   b . Each vane  122   a  and  122   b  is shaped as a rectangular plate, and is rotatably mounted at the middle thereof. The respective central shafts about which the vanes rotate may be linked to one another through a belt  128  and pulley  124  assembly (see, e.g.,  FIG. 6 ). When the vanes  122   a  and  122   b  are disposed in a straight line, the opening ratio of the secondary duct  22   b  is lowest. As the vanes  122   a  and  122   b  both rotate, the opening ratio of the secondary duct  22   b  gradually increases until it reaches its highest point when the vanes  122   a  and  122   b  become disposed perpendicularly to the long axis of the secondary duct—that is, where the vanes are most constricting to the flow of gases through the duct. The rotation of the vanes  122   a  and  122   b  may be manually performed by an operator, and the opening ratio of the secondary duct  22   b  is fixed during the rotation by means of the damper  122 . Alternately, the rotation of the vanes  122   a  and  122   b  may be performed automatically, and the opening ratio of the secondary duct  22   b  is fixed during the rotation by means of the damper  122 . 
         [0047]    A fan  26  ( FIG. 2 ) or other pressure regulating member  300  ( FIG. 5 ) is installed on the primary duct  22   a . The fan  26  controls the amount of gas being exhausted through the primary duct  22   a  by maintaining a pressure difference within the separation duct  24  and the atmospheric pressure within a certain range. Accordingly, when the atmospheric pressure increases, the volume of gas exhausted through the integration duct  22  decreases, and when the atmospheric pressure decreases, the volume of gas exhausted through the integration duct  22  increases. The pressure within the process chamber  30  changes according to the fluctuation of the atmospheric pressure, and the pressure inside the process chamber  30  can deviate from a preset pressure range through fluctuation of the atmospheric pressure, depending on the type of process being performed in the process chamber  30 . In this case, a flow adjusting valve (not shown) is installed to adjust the opening ratio of the separation duct  24 , so that the pressure inside the process chamber  30  can be maintained within preset pressure parameters. 
         [0048]    Manufacturing defects occur when pressure adjusting of the process chamber  30  (to offset the effects of atmospheric pressure fluctuation) is not performed quickly enough so that the pressure in the process chamber  30  deviates from the preset parameters. Also, even if the pressure within the process chamber  30  is within the preset parameters, wide fluctuations of pressure within the process chamber  30  during the performing of a process reduces process efficiency. The exhaust unit  20  according to the present embodiment is structured to reduce the effects that atmospheric pressure fluctuation has on pressure changes within the process chamber  30 . Also, the exhaust unit  20  according to the present embodiment is configured to prevent the pressure within the process chamber  30  from deviating from the preset parameters by a fast response to a change in atmospheric pressure. 
         [0049]      FIGS. 3 through 5  are exemplary embodiments of a secondary duct  22   b .  FIG. 3  is a perspective view of a secondary duct  22   b  in  FIG. 2 ,  FIG. 4  is an exploded perspective view of the secondary duct in  FIG. 3 , and  FIG. 5  is a cross-sectional view of the secondary duct in  FIG. 3 . Referring to  FIGS. 3 through 5 , the secondary duct  22   b  has a main exhaust duct  100 , a supplementary exhaust duct  200 , and a regulating member  300 . The main exhaust duct  100  branches from the primary duct  22   a . The supplementary exhaust duct  200  is connected to communicate at both ends with the main exhaust duct  100 . One end of the supplementary exhaust duct  200  is connected to the main exhaust duct  100  such that a portion of gas being exhausted through the main exhaust duct  100  can enter the supplementary exhaust duct  200 , and the other end of the supplementary exhaust duct  200  is connected to the main exhaust duct  100  to allow the gas flowing through the supplementary exhaust duct  200  to flow back into the main exhaust duct  100 . That is, the supplementary exhaust duct  200  is provided as a bypass line to the main exhaust duct  100 , allowing a portion of the gas flowing through the main exhaust duct  100  to flow through the supplementary exhaust duct  200  and then re-enter the main exhaust duct  100 . 
         [0050]    As described above, the main exhaust duct  100  has a rectangular cross-sectional shape, with an area that is uniform throughout its length, through which gas flows. Referring to  FIG. 4 , the supplementary exhaust duct  200  is provided as a hexahedral container with one side open. The supplementary exhaust duct  200  is coupled to the main exhaust duct  100  with the open side facing a side of the main exhaust duct  100 . A first opening  142  and a second opening  144  are defined in the main exhaust duct  100 , and the supplementary exhaust duct  200  has a length that enables the open side to face the first opening  142  and the second opening  144  at respective ends of the open side. The first opening  142  functions as an inlet for gas flowing through the main exhaust duct  100  to flow into the supplementary exhaust duct  200 , and the second opening  144  serves as an outlet for gas flowing through the supplementary exhaust duct  200  to flow back into the main exhaust duct  100 . The supplementary exhaust duct  200  and the main exhaust duct  100  may be connected by fastening means such as screws (not shown), and a sealer (not shown) may be used to prevent the occurrence of gaps between the fastening means through which gas may leak. 
         [0051]    To allow sufficient volumes of gas to enter the supplementary exhaust duct  200  from the main exhaust duct  100 , the heights of the supplementary exhaust duct  200  and the main exhaust duct  100  may be the same or similar. Also, the heights of the first opening  142  and the second opening  144  defined in the main exhaust duct  100  may be the same as the height of the main exhaust duct  100 , and the widths of the first opening  142  and the second opening  144  are the same. 
         [0052]    The supplementary exhaust duct  200  is connected to the main exhaust duct  100  at a position between the point where the main exhaust duct  100  branches from the primary duct  22   a  and a point where the separation duct  24  primarily branches from the secondary duct  22   b . The above-described damper  122  installed on the secondary duct  22   b  is coupled to the main exhaust duct  100  at a position between the first opening  142  and the second opening  144 . The supplementary exhaust duct  200  is provided respectively in opposition at either side of the main exhaust duct  100 . Selectively, the supplementary exhaust duct  200  may be provided respectively on three sides of the main exhaust duct  100 . 
         [0053]      FIG. 6  is an exploded perspective view of the secondary duct  22   b ′ in  FIG. 3  with two identically shaped supplementary exhaust ducts  200 ′. Referring to  FIG. 6 , the supplementary exhaust duct  200 ′ is provided as a tube formed roughly in a C-shape with open front and rear ends. The supplementary exhaust duct  200 ′ is coupled to the main exhaust duct  100 , such that the front end communicates with the first opening  142 , and the rear end communicates with the second opening  144 . 
         [0054]    A regulating member is  300  installed on the secondary duct  22   b  to regulate the opening ratio of the second opening  144 . Here, the opening ratio of the second opening  144  is controlled by adjusting the volume of gas flowing through the second opening  144 . This involves not only providing a plate in the area of the second opening  144  to directly alter the area of the second opening  144 , but also regulating the angle between the plate and the second opening  144  so that the degree of interference of the plate with the flow of gas can be changed. 
         [0055]    When the flow volume through the secondary duct  22   b  changes due to changes in the external environment, such as fluctuations in atmospheric pressure, the regulating member  300  regulates the amount of gas that can flow through the supplementary exhaust duct  200 , in order to reduce the pressure fluctuation range. For example, when atmospheric pressure becomes high, the pressure within the process chamber  30  is increased, and the flow of gas through the secondary duct  22   b  is decreased. In this case, the regulating member  300  increases the opening ratio of the secondary duct  144  so that a larger volume of gas can flow through the supplementary exhaust duct  200 , in order to reduce the range of flow reduction through the secondary duct  22   b . Thus, the pressure within the process chamber  30  increases within a smaller range. Conversely, when atmospheric pressure becomes low, the pressure within the process chamber  30  is reduced, and the flow volume through the secondary duct  22   b  is increased. Here, the regulating member  300  decreases the opening ratio of the secondary duct  144  so that a smaller volume of gas can flow through the supplementary exhaust duct  200 , in order to reduce the range of flow reduction through the secondary duct  22   b . Thus, the pressure range within the process chamber  30  is prevented from broadening. 
         [0056]    According to one embodiment of the present invention, the regulating member  300  is configured to be capable of regulating the opening ratio of the secondary duct  144  according to fluctuations in atmospheric pressure without a separate motive force. Referring again to  FIGS. 4 and 5 , the regulating member  300  has a flap  320  installed rotatably within the main exhaust duct  100 . The flap  320  includes a first plate  320   a  and a second plate  320   b . The first plate  320   a  and the second plate  320   b  are respectively shaped as rectangular plates. The first plate  320   a  extends at an angle from an end of the second plate  320   b . The first plate  320   a  and the second plate  320   b  may be disposed to be approximately perpendicular to each other. Selectively, the first plate  320   a  and the second plate  320   b  may collectively form an acute angle. The second plate  320   b  is formed to be approximately the same in size and shape to the second opening  144 . However, the width of the second plate  320   b  may be formed to be slightly greater than the width of the second opening  144 . The flap  320  is fixed and installed to the main exhaust duct  100  at the side of the second opening  144  closer to the first opening  142 . 
         [0057]    The second plate  320   b  is disposed between the first plate  320   a  and the second opening  144 . The first plate  320   a  functions mainly to collide with gas flowing through the main exhaust duct  100 , and the second plate  320   b  rotates together with the first plate  320 a, and regulates the opening ratio of the second opening  144 . The flap  320  rotates toward the second opening  144  when the flow volume through the main exhaust duct  100  increases, and rotates away from the second opening  144  when the flow volume through the main exhaust duct  100  decreases. The rotation of the flap  320  may be realized automatically through collision of the first plate  320   a  with gas flowing through the main exhaust duct  100  and collision of the second plate  320   b  with gas flowing through the supplementary exhaust duct  200 . 
         [0058]    The flap  320  has been described above to include the first plate  320   a  and the second plate  320   b . However, the flap  320  may include only one plate. 
         [0059]      FIGS. 7 through 9  are perspective views of various embodiments of flaps  320  that are  1 installed on main exhaust ducts  100 . Referring to  FIG. 7 , a bearing  364  is fixedly installed at the top and bottom end of the main exhaust duct  100 , the portion connecting the first plate  320   a  and the second plate  320   b  is fixed to a rotating shaft, and both ends of the rotating shaft  362  are inserted into the bearings  364 , thus enabling the flap  320  to rotate smoothly. 
         [0060]    Referring to  FIG. 8 , a hinge  370  (or pair of such hinges  270 , as shown) may be installed at the intersecting axis of the first plate  320   a  and the second plate  320 b, and the flap  320  may be coupled through the hinge  370  to the main exhaust duct  100 . 
         [0061]    Referring to  FIG. 9 , the flap  320  may be fixed to the main exhaust duct  100  by means of a resiliently flexible (e.g. rubber) connecting member  380 . Here, the connecting member  380  is coupled to the intersecting axis of the first plate  320   a  and the second plate  320   b . The connecting member  380  may be fixed to the flap  320  and main exhaust duct  100  with an adhesive. 
         [0062]    The flap  320  in the above description is fixedly installed to the main exhaust duct  100 . However, the flap  320  may alternately be fixedly installed at another location. Also, while the first plate  320   a  and second plate  320   b  of the flap  320  have been described above as being respectively rectangular, the first plate  320   a  and the second plate  320   b  may be embodied in various alternate shapes. The first plate  320   a  and the second plate  320   b  may be the same in terms of size, shape, material, etc. The flap  320  may be coupled to the main exhaust duct  100  through an elastic member (not shown) biased in the direction in which the opening ratio increases. 
         [0063]    The secondary duct  22   b  has been described above as including the main exhaust duct  100 , the supplementary exhaust duct  200 , and the flap  320 . However, the above configuration may be applied instead to the primary duct  22   a.    
         [0064]    The flap  320  may be made of various materials. For example, polyvinyl chloride with high acid corrosion resistance or stainless steel with organic corrosion resistance may be used as a material for the flap  320 . Also, galvanized steel with high thermal endurance may be used as material for the flap  320 . The material for the flap  320  may be selected based on what ingredients are inherent in gas exhausted from the process chamber  30  connected to each secondary duct  22   b , or the temperature of the exhausted gas. For example, a flap  320  provided in a secondary duct  22   b  (from a plurality of secondary ducts  22   b ) through which mostly acidic gas is exhausted may be made of a polyvinyl chloride material, a flap  320  provided in a secondary duct  22   b  through which mostly gas with organic content is exhausted may be made of a stainless steel material, and a flap  320  provided in a secondary duct  22   b  through which mostly high temperature gas is exhausted may be made of a galvanized steel material. 
         [0065]      FIGS. 10 and 11  are diagrams respectively showing a reduction and an elevation in atmospheric pressure in a typically configured exhaust unit with only a main exhaust duct  100 , and the change in flow quantity within the duct when the exhaust unit  20  in  FIG. 3  is used. Referring to  FIGS. 10 and 11 , the lengths of the arrows represent the volume (or speed) of gas being exhausted through the ducts. The dotted lines represent the volume (or speed) of gas being exhausted through the ducts prior to a change in atmospheric pressure, and the solid lines represent the volume (or speed) of gas being exhausted through the ducts following a change in atmospheric pressure to a high pressure or a low pressure, respectively. 
         [0066]    Referring to  FIG. 10 , when a typically configured exhaust unit is used, when atmospheric pressure drops to a low pressure, the rotating speed of the fan  26  is increased. Because there is no change to the sectional area of the duct  700  through which gas flows, the flow volume of gas increases greatly. On the other hand, when an exhaust unit  20  according to embodiments of the present invention is used, when atmospheric pressure drops to a low pressure, the flaps  320  rotate in directions toward the secondary openings  144 , thus reducing the opening ratios of the second openings  144 . Therefore, even when the rotation speed of the fan  26  increases, because the sectional area of the secondary duct  22   b  through which the gas flows is reduced, the increase in gas flow through the secondary duct  22   b  is comparatively small. 
         [0067]    Conversely, when referring to  FIG. 11 , when a typically configured exhaust unit is used, when atmospheric pressure rises to a high pressure, the rotating speed of the fan  26  is decreased. Because there is no change to the sectional area of the duct  700  through which gas flows, the flow volume of gas through the duct  700  decreases. On the other hand, when an exhaust unit  20  according to embodiments of the present invention is used, when atmospheric pressure rises to a high pressure, the flaps  320  rotate in directions away from the secondary openings  144 , thus increasing the opening ratios of the second openings  144 . Therefore, even when the rotation speed of the fan  26  decreases, because the sectional area of the secondary duct  22   b  through which the gas flows is enlarged, the decrease in gas flow through the secondary duct  22   b  is comparatively small. 
         [0068]    Accordingly, when an exhaust unit  20  according to embodiments of the present invention is used, the fluctuation range of the volume of gas flow according to changes in atmospheric pressure is smaller than when a typical exhaust unit is used, so that the pressure fluctuation range within the process chamber  30  is smaller, resulting in more efficient processing within the process chamber  30 . 
         [0069]      FIGS. 12(   a ) and ( b ) are graphs comparing, respectively, the fluctuation of pressure in a process chamber  30  over time when a typically configured exhaust unit is used, with the fluctuation of pressure in a process chamber  30  over time when an exhaust unit  20  according to the present embodiments is used. Referring to  FIG. 12 , when the exhaust unit  20  of the present embodiment is used, the change in pressure (ΔP) ranges from approximately 5 to 8 mmH2O. When the conventional exhaust is used without the regulated supplemental bypass, the change in pressure (ΔP) ranges from approximately 10 to 14 mmH2O. The invention thus provides a substantially improved reduction in pressure fluctuations. 
         [0070]      FIG. 13  is a cross-sectional view of a secondary duct  22   b  with regulating members  300  installed therein according to another embodiment, and  FIG. 14  is a partial perspective view showing the regulating member  300  in  FIG. 13 . Referring to  FIGS. 13 and 14 , the regulating member  300  includes a flap  320 , a driver  394 , an airflow measurer  396 , and a controller  398 . While the rotation of the flap  320 , being the regulating member  300 , has been described in embodiments above as non-driven, the rotation of the flap  320  according to the present embodiment is achieved by being driven by the driver  394 . The flap  320  used may have the same structure as the flap  320  described above, and thus, the description thereof will not be repeated. The flap  320  is fixed to a rotating shaft  392 , and the rotating shaft  392  is rotatably coupled to the main exhaust duct  100 . The rotating shaft  392  is coupled to a driver  394  such as a motor. The airflow measurer  396  measures the flow of gas within the supplementary exhaust duct  200 . The airflow measurer  396  used may be a pressure sensor. The controller  398  receives a measured value from the airflow measurer  396 , and controls the driver  394  based on the measured value. When flow of gas through the supplementary exhaust duct  200  increases, the controller  398  reduces the opening ratio of the supplementary exhaust duct  200  by rotating the flap  320  in the reducing direction, and when flow of gas through the supplementary exhaust duct  200  decreases, the controller  398  increases the opening ratio of the supplementary exhaust duct  200  by rotating the flap  320  in the increasing direction. Also, the airflow measurer  396  may measure gas flow within the main exhaust duct  100  instead of the supplementary exhaust duct  200 . 
         [0071]      FIG. 15  and  FIG. 16  are respectively a perspective and cross-sectional view of a secondary duct  22   b ″ with regulating members installed according to another embodiment. Referring to  FIGS. 15 and 16 , a regulating member  300 ′ regulates the opening ratio of the second opening  144  through sliding. A slit  240  is formed at the end of the sidewall of the supplementary exhaust duct  200  near the second opening  144 . A plate  320 ′ is provided to be insertable through sliding in the slit  240 . A recess (not shown) is formed in the inner wall of the supplementary exhaust duct  200  to allow an edge of the plate  320 ′ to insert therein and allow the plate  320 ′ to move smoothly by sliding. A driver  340 ′ moves the plate  320 ′ linearly, and is controlled by a controller  398  based on a received signal on a measured airflow from an airflow measurer  396 . 
         [0072]    In embodiments described above, the main exhaust duct  100 , the supplementary exhaust duct  200 , and the regulating member  300  are installed on an integration duct  22  into which the separation ducts  24  merge. However, as shown in  FIG. 17 , the above-described exhaust unit  20  may be provided on each separation duct  24  connected to a respective process chamber  30 . In this case, supplementary exhaust duct  200  may have a round cross-section, and the open side of the supplementary exhaust duct  200  may face the outer surface of the main exhaust duct  100 . Also, a flow volume control valve (not shown) may be installed on the main exhaust duct  100  between the first opening  142  and the second opening  144  defined in the main exhaust duct  100 . 
         [0073]    According to the present embodiments, the occurrence of wide pressure fluctuations inside the process chamber due to changes in atmospheric pressure can be prevented. 
         [0074]    Also, the structure for passively regulating the volume of exhausted gas, according to the present invention, is simple and reduces energy consumption. 
         [0075]    The above-disclosed subject matter is to be considered illustrative, and not restrictive, and the appended claims are intended to cover all such modifications, enhancements, and other embodiments, which fall within the true spirit and scope of the present invention. Thus, to the maximum extent allowed by law, the scope of the present invention is to be determined by the broadest permissible interpretation of the following claims and their equivalents, and shall not be restricted or limited by the foregoing detailed description.