Patent Publication Number: US-11639811-B2

Title: Apparatus including a clean mini environment

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a national stage entry of International Patent Application No. PCT/NL2018/050787, filed Nov. 26, 2018 entitled “APPARATUS INCLUDING A CLEAN MINI ENVIRONMENT,” which claims priority to U.S. Provisional Patent Application No. 62/590,684, filed on Nov. 27, 2017 entitled “APPARATUS INCLUDING A CLEAN MINI ENVIRONMENT,” the disclosures of which are hereby incorporated by reference in their entirety. 
    
    
     FIELD 
     The invention relates to an apparatus including a clean mini environment. 
     BACKGROUND 
     An apparatus including a clean mini environment (M.E.), for instance in a semiconductor furnace may be useful. A schematic representation of the apparatus is shown in  FIG.  1   . 
     The apparatus may include a gas recirculation circuit comprising:
         a mini environment chamber ( 14 ), provided with a chamber inlet ( 24 ) and a chamber outlet ( 26 );   a recirculation channel ( 20 ) connecting the chamber outlet with the chamber inlet;   an gas pump ( 16 ) having a pump outlet and a pump inlet and being positioned in the recirculation channel; and   a filter assembly ( 22 ) positioned in the recirculation channel downstream of the pump ( 16 ) and upstream of the mini environment chamber inlet ( 24 ).       

     The apparatus additionally may include:
         a pressure release provision ( 28 ) configured and arranged to limit a pressure in the mini environment chamber;   an air supply conduit ( 18 ) for supplying air to the gas recirculation circuit and having an air supply conduit inlet which opens into the ambient air and an air supply conduit outlet which opens in the recirculation circuit.       

     In use, the gas pump circulates the gas from the pump outlet through the filter assembly, the chamber inlet, the mini environment chamber, the chamber outlet and back to the pump inlet thereby maintaining the pressure (P me ) in the mini environment chamber higher than the ambient pressure (P am ). The pressure within the mini environment chamber (P me ) is typically kept around 100 Pa above the ambient pressure (P am ). In practice, the pressure drop over the inlet filter is quite large, about 150 Pa. As a consequence, the pressure between the pump outlet and the filter assembly (P high ) must be approximately 250 Pa above the ambient pressure (P am ). Between the chamber outlet and the pump inlet, the gas pressure is typically approximately 50 Pa above the ambient pressure. 
     Because the pressure in the mini environment chamber and in the recirculation conduit is higher than the ambient pressure, which is typically the atmospheric pressure, gas will leak from the mini environment chamber and the gas recirculation circuit to the environment. To compensate for this leakage and optionally also for refresh the recirculating gas or air, gas or air has to be supplied to the recirculation circuit via the air supply conduit. 
     A source of gas or air which has a pressure which is higher than the pressure in the recirculation channel may be provided. The source may be a high pressure gas tank or an additional air pump supplying air having a higher pressure than the pressure prevailing in the gas recirculation circuit. This solution may be relatively expensive because of the presence of the additional air inlet pump or because of the high pressure gas tank which has to be replaced regularly. Alternatively, a restriction in the recirculation channel may be provided between the chamber outlet and the pump inlet so that downstream of the restriction and upstream of the pump inlet an area is formed where the pressure is sub-atmospheric, i.e. lower than the ambient pressure so that ambient air will be sucked in. However, the restriction results in energy losses which must be compensated by a pump having a larger capacity, typically twice the capacity which is needed for simply recirculating a gas through the gas recirculation circuit when such a restriction were not present. 
     SUMMARY OF THE INVENTION 
     An object of the invention is to provide an apparatus including a mini environment chamber as described above in which the supply of air to the gas recirculation circuit is effected with minimal operational costs and minimal investment for auxiliary devices such as air intake pumps. 
     To that end, the invention provides an apparatus according to claim  1 . 
     More particular, according to the invention the apparatus described above is characterized in that the gas recirculation channel includes a recirculation restriction embodied as a throat in the gas recirculation channel, wherein the throat defines a flow path with a diminishing cross sectional surface area relative to the cross sectional surface area of the gas recirculation channel directly upstream of the throat, wherein a downstream end of the throat defines a minimum cross sectional surface area of the throat, wherein the throat defines the pump inlet, wherein the air supply conduit outlet opens at, or slightly downstream of the downstream end of the throat which defines the minimum cross sectional surface area of the throat. 
     An advantage of the apparatus according to the invention is that no additional gas pump or high pressure air source is required for the supply of ambient air. By virtue of the higher gas speed in the downstream end of the throat, which higher gas speed is caused by the reduced cross sectional area at the downstream end of the throat, the static pressure prevailing there is lower than the ambient pressure so that ambient air will be sucked in via the air supply conduit. Thus the power consumption for recirculation of the gas through the gas recirculation circuit and for supplying air to the recirculation circuit is less than with the know configurations described above. The static pressure (P low ) between the chamber outlet and the upstream end of the throat will remain above the ambient pressure (P am ), around 50 Pa or so. But at the downstream end of the throat, the gas flow speed is increased, causing a decrease in static pressure. This locally low static pressure is used to passively supply air via the air supply conduit to the gas circulation circuit. Because there is no significant energy loss caused by the throat with the, preferably gradually diminishing cross sectional surface area, the power needed to recirculate the gas through the gas recirculation circuit and to supply air to the gas recirculation circuit is minimal and almost comparable to the power needed to recirculate gas through the gas recirculation circuit without supplying ambient air to the gas recirculation circuit. In fact, the gas pump which is used in practice for recirculating the gas through the gas recirculation circuit includes the throat, which throat defines the pump inlet. In other words, the throat is an integral part of the gas pump. In view thereof, relative to the prior art system, the throat does not constitute an additional gas resistance because the throat is an integral part of the pump. The wording “slightly downstream of the downstream end of the throat” indicates not more than 20 mm downstream of the downstream end of the throat and, of course, upstream of the moving parts of the pump, e.g. the centrifugal vanes of the pump. 
     In the dependent claims various embodiments are claimed which will be further elucidated with reference to an example shown in  FIG.  2   . The embodiments may be combined or may be applied separately from each other. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         FIG.  1    is schematically shows an example of an apparatus including a mini environment chamber which is known from practice; and 
         FIG.  2    shows an example of an apparatus including a mini environment chamber according to the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE FIGURES 
     In this application similar or corresponding features are denoted by similar or corresponding reference signs. The description of the various embodiments is not limited to the example shown in  FIG.  2    and the reference numbers used in the detailed description and the claims are not intended to limit the description of the embodiments, but are included to elucidate the embodiments by referring to the example shown in  FIG.  2   . 
     In the most general terms, the invention relates to an apparatus  10 , including a gas recirculation circuit comprising:
         a mini environment chamber  14 , provided with a chamber inlet  24  and a chamber outlet  26 ;   a recirculation channel  20  connecting the chamber outlet  26  with the chamber inlet  24 ;   a gas pump  16  having a pump outlet and a pump inlet and being positioned in the recirculation channel  20 ; and   a filter assembly  22  positioned in the recirculation channel  20  downstream of the pump ( 16 ) and upstream of the mini environment chamber inlet  24 .       

     The apparatus additionally includes:
         a pressure release provision  28  configured and arranged to limit a pressure P me  in the mini environment chamber  14 ; and   an air supply conduit  18  for supplying air to the gas recirculation circuit and having an air supply conduit inlet  18   a  which opens into the ambient air and an air supply conduit outlet  18   b  which opens in the recirculation circuit.       

     In use, the gas pump  16  circulates the gas from the pump outlet through the filter assembly  22 , the chamber inlet  24 , the mini environment chamber  14 , the chamber outlet  26  and back to the pump inlet thereby maintaining the pressure P me  in the mini environment chamber  14  higher than the ambient pressure P am . 
     According to the invention, of which an example is shown in  FIG.  2   , the apparatus  10  is characterized in that the gas recirculation channel  20  includes a recirculation restriction embodied as a throat  30  in the gas recirculation channel  20 . The throat  30  defines a flow path with a diminishing cross sectional surface area relative to the cross sectional surface area of the gas recirculation channel  20  directly upstream of the throat  30 . A downstream end  30   a  of the throat  30  defines a minimum cross sectional surface area of the throat  30 . The throat  30  defines the pump inlet. The air supply conduit outlet opens at, or slightly downstream of the downstream end  30   a  of the throat  30  which defines the minimum cross sectional surface area of the throat. 
     The cross sectional surface area of the throat  30  is smaller than the area of the cross-section of the gas recirculation channel  20 . As a consequence, the gas velocity of the circulated gas increases when flowing through the throat  30  up to a maximum velocity at the downstream end  30   a  of the throat  30  where the cross sectional surface area of the throat is smallest. When the gas velocity increases the dynamic pressure (½ ρv 2 ) will increase and the static pressure will decrease. The difference between the static pressure at the air supply conduit outlet  18   b  and the ambient pressure P am  will determine the flow of air within the air supply conduit  18 . By positioning the air supply conduit outlet  18   b  in a region where the static pressure of the gas flow is below the ambient pressure P am  a pressure gradient will be created within the air supply conduit which will drive the ambient gas into the gas recirculation circuit. By using a substantially frictionless recirculation restriction which is embodied as a throat  30 , energy losses may be minimized. Thus air may be supplied to the recirculation circuit without the necessity to invest in an additional air supply pump or a high pressure gas source and substantially without energy losses so that the gas pump  16  capacity and/or power consumption is almost the same as in a situation wherein no air is supplied to the gas recirculation system and the pump is only used for pumping the gas through the gas recirculation circuit. 
     In order to provide the mini environment chamber  14  with clean gas, the gas supplied by the gas pump  16  may be filtered by the filter assembly  22  before it enters the mini environment chamber  14 . This may be done at the chamber inlet  24  where the gas enters the mini environment chamber  14 . 
     In an embodiment, the throat  30  may have a truncated cone shaped inner surface that is circular symmetric around a central axis, wherein a downstream part of the air supply conduit  18  extends along the central axis and opens in the central part of the downstream end  30   a  of the throat  30 . 
     In the center of the throat  30  at the downstream end  30   a  thereof, where the cross sectional surface area is minimal, the gas velocity may be highest and thus, the static pressure is at its lowest value. Consequently, that position may be the most optimal position for positioning the air supply conduit outlet  18   b  because the air is sucked most effectively. 
     In an embodiment of the invention, the cross sectional surface area A sc  of the air supply conduit  18  may be small compared to the cross sectional surface area A t  of the downstream end  30   a  of the throat  30 . 
     An air supply conduit  18  with a small cross sectional surface area A sc  compared to the cross sectional surface area A t  of the downstream end  30   a  of the throat  30  may not, or virtually not disturb the flow of the recirculating gas in the recirculation channel  20  and the throat  30  which is beneficial from an efficiency point. 
     In an embodiment of the invention, the air supply conduit  18  further comprises an air inlet filter  32 . 
     In order to keep the gas in the gas recirculation circuit as clean as possible, it is best to filter the ambient air before supplying it to the gas recirculation circuit. The apparatus could do without such filter, but an air inlet filter  32  may relieve the load of the filter assembly  22  at the mini environment chamber inlet  24 . 
     In an embodiment, the pressure release provision may comprise a pressure release valve  34 . 
     With the pressure release valve  34  the leakage of gas from the mini environment chamber  14  can be controlled in such a way that a constant overpressure can be maintained in the mini environment chamber  14  with respect to the surrounding environment. A pressure release valve  34  may be a simple yet effective way to realize a constant overpressure in the mini environment chamber  14 . 
     In an alternative embodiment, the pressure release provision may comprise a small gap in the mini environment chamber which opens into the ambient environment. Such a small gap is, of course, of a very simple construction and also provides a means to limit the raise of pressure in the mini environment chamber  14 . 
     In an embodiment, the apparatus may comprise a housing defined by external walls  38 , wherein the external walls at least partly bound the mini environment chamber  14  and the recirculation channel  20 . An internal wall  36  forms a boundary between the mini environment chamber  14  and the recirculation channel  20 . The chamber outlet  26  is formed by a gap between an end of the internal wall  36  and an external wall  38 . 
     Such an embodiment is relatively simple from a manufacturing point of view. 
     The various embodiments which are described above may be used implemented independently from one another and may be combined with one another in various ways. The reference numbers used in the detailed description and the claims do not limit the description of the embodiments nor do they limit the claims. The reference numbers are solely used to clarify. 
     LEGEND 
     
         
           10 —the apparatus 
           12 —housing 
           14 —mini environment chamber 
           16 —gas pump 
           18 —air supply conduit 
           18   a —air supply conduit inlet 
           18   b —air supply conduit outlet 
           20 —recirculation channel 
           22 —filter assembly 
           24 —chamber inlet 
           26 —chamber outlet 
           28 —pressure release provision 
           30 —throat 
           30   a —downstream end of the throat 
           32 —air inlet filter 
           34 —pressure release valve 
           36 —internal wall 
           38 —external walls 
         P me —mini environment chamber pressure 
         P am —ambient pressure 
         A sc —cross section surface area of the air supply conduit 
         A t —cross section surface area of the throat at the downstream end 
         A r —cross sectional surface area of the recirculation channel upstream of the throat