Patent Publication Number: US-11022018-B2

Title: Exhaust system and method of using

Description:
PRIORITY CLAIM 
     The present application is a continuation of U.S. application Ser. No. 15/651,373, filed Jul. 17, 2017, which claims the priority of U.S. Provisional Application No. 62/427,600, filed Nov. 29, 2016, which are incorporated herein by reference in their entireties. 
    
    
     BACKGROUND 
     Flow disruption sites in an exhaust system impedes removal of gases and particles from an upstream source of the exhaust system. Bends and connectors in exhaust lines disrupt exhaust flow by slowing the movement of exhaust, which reduces pumping efficiency. Particulate matter suspended or transported by the exhaust system tends to collect at flow disruption sites in the exhaust system. Buildup of particulate matter in an exhaust line reduces an area of the exhaust line available for exhaust and particles to flow through the exhaust system. Buildup of particulate matter reduces pumping efficiency and leads to increased maintenance to manually remove buildup and maintain uninterrupted exhaust flow within desired specifications and consequently reduces operating efficiency. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present disclosure is best understood from the following detailed description when read with the accompanying figures. It is emphasized that, in accordance with the standard practice in the industry, various features are not drawn to scale and are used for illustration purposes only. In fact, the dimensions of the various features may be arbitrarily increased or reduced for clarity of discussion. 
         FIG. 1  is a schematic diagram of an exhaust system, according to some embodiments. 
         FIGS. 2A-2B  are cross-sectional views of flow restriction points of an exhaust system, according to embodiments. 
         FIG. 3A  is a perspective view of a velocity booster, according to some embodiments. 
         FIG. 3B  is a plan view of a velocity booster, according to some embodiments. 
         FIG. 4A  is a perspective view of a vortex generator, according to some embodiments. 
         FIGS. 4B and 4C  are plan views of a vortex generator, according to some embodiments. 
         FIG. 4D  is a perspective view of a vortex generator, according to some embodiments. 
         FIG. 5  is a plan view of a vortex generator, according to some embodiments. 
         FIG. 6  is a flow diagram of a method of using a vortex generator, according to some embodiments. 
         FIG. 7  is a block diagram of a controller for controlling an exhaust system in accordance with some embodiments. 
     
    
    
     DESCRIPTION 
     The following disclosure provides many different embodiments, or examples, for implementing different features of the provided subject matter. Specific examples of components, values, operations, materials, arrangements, etc., are described below to simplify the present disclosure. These are, of course, merely examples and are not intended to be limiting. Other components, values, operations, materials, arrangements, etc., are contemplated. For example, the formation of a first feature over or on a second feature in the description that follows may include embodiments in which the first and second features are formed in direct contact, and may also include embodiments in which additional features may be formed between the first and second features, such that the first and second features may not be in direct contact. In addition, the present disclosure may repeat reference numerals and/or letters in the various examples. This repetition is for the purpose of simplicity and clarity and does not in itself dictate a relationship between the various embodiments and/or configurations discussed. 
     Further, spatially relative terms, such as “beneath,” “below,” “lower,” “above,” “upper” and the like, may be used herein for ease of description to describe one element or feature&#39;s relationship to another element(s) or feature(s) as illustrated in the figures. The spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. The apparatus may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein may likewise be interpreted accordingly. 
     Many exhaust systems handle exhaust streams that include particulate matter. In some instances, particulate matter builds up at flow disruption sites within the exhaust system. A flow disruption leads to a decrease in flow velocity through the exhaust system. Flow velocity through the exhaust system changes based on changes in exhaust line diameters, changes in bends in exhaust lines, and changes at connectors between exhaust lines. Decreased flow velocity results in particles, which are suspended in the exhaust stream, contacting and adhering to interior walls of the exhaust system lines, or other particles adhered to the interior walls, with greater frequency than with nominal flows of the exhaust system. Nominal flow velocity overcomes frictional forces that adhere particles to interior walls of exhaust lines or other particles. Adhering particles create a compound effect that, once begun, promotes further particle adhesion where particles have begun to collect in an exhaust line. 
     Over time, particle buildup in the exhaust system reduces the flow velocity for the exhaust system. Reduced flow velocity corresponds to reduced particle removal efficiency. In some instances, reduced flow velocity and reduced particle removal efficiency contribute to contamination of semiconductor wafers or other materials that are handled by manufacturing equipment. Maintenance of the exhaust system to remove the adhered particles from the exhaust lines restores clogged systems to nominal functionality. However, maintenance includes removing a tool with the exhaust system from normal operation during performance of the maintenance procedure. Maintenance due to particulate contamination reduces availability and productivity of manufacturing equipment. Enhancing the flow velocity at flow disruption sites increases the likelihood that a particle suspended in the exhaust stream will pass through the flow disruption site, rather than adhere to inner walls of the exhaust line or other particles. An exhaust system containing a vortex generator adds rotational motion to the exhaust stream in order to enhance particle pass-through at flow disruption sites in the exhaust system. A vortex (rotational flow) in an exhaust stream extends past a location where the vortex is generated in the exhaust system to increase flow velocity close to inner walls of the exhaust line. Higher flow velocity near the inner walls of an exhaust line reduces particle adhesion on the exhaust line walls and reduces the rate of particle buildup at flow disruption sites. Interior walls of an exhaust line are metallic, in some embodiments. In some embodiments, the interior wall of an exhaust line is a coated surface. The coating on the coated surface includes, in some embodiments, at least one of polytetrafluoroethylene (PTFE), polyurethane, polypropylene, nylon, or another coating with a coefficient of static friction that is smaller than the coefficient of static friction of stainless steel. 
       FIG. 1  is a schematic diagram of an exhaust system  100  according to some embodiments of the present disclosure. Exhaust system  100  is configured to be attached to a manufacturing tool. Exhaust system  100  is configured to pump gases and particles out of manufacturing tools through exhaust lines connected to a pump or a vacuum source. Exhaust system  100  has an upstream direction  102  and a downstream direction  104 . Exhaust system source  106  is at one end of exhaust system  100  in upstream direction  102 , and exhaust pump  107  is at another end of exhaust system  100  in downstream direction  104 . In some embodiments, exhaust system  100  includes multiple exhaust system sources  106 . In some embodiments, exhaust system  100  includes multiple exhaust pumps  107 . 
     Some non-limiting examples of manufacturing tools that are attachable to exhaust system  100  include semiconductor manufacturing tools. In some embodiments, exhaust system source  106  is a photolithography tool. In some embodiments, exhaust system source  106  is a furnace for annealing. In some embodiments, exhaust system source  106  is an etch chamber. In some embodiments, exhaust system source  106  is a diffusion chamber. As a non-limiting example, some photolithography tools are configured to deposit and bake photoresist on semiconductor wafers. Baking wafers treats and modifies the photoresist to remove solvent from the photoresist and to stabilize the photoresist prior to wafer etching. Baking the photoresist generates particles (e.g., flakes of dried photoresist) as well as waste gases. Particles, waste gases, and chamber purge gases exit the photolithography tool through exhaust system  100 . Photoresist particles are exhausted in order to reduce contamination of semiconductor wafers during wafer handling and processing steps inside the photolithography tool. The gaseous exhaust component includes, in some embodiments, a purge gas (e.g., nitrogen and oxygen) added to a bake chamber in order to flush solvents and moisture from the bake chamber and to preserve a desired processing condition during wafer baking. In some embodiments, the gaseous component of an exhaust includes compressed air. In some embodiments, the gaseous component includes dried compressed air. In some embodiments, the particulate component of an exhaust includes photoresist residue that has lifted off or spalled from a semiconductor wafer. Sometimes particulate contamination comes from sources external to the manufacturing tool, or from moving parts within the photolithography tool. 
     Exhaust system  100  contains an optional velocity booster  108 A between exhaust system source  106  and exhaust pump  107 . Velocity booster  108 A is not optional in some embodiments of exhaust system  100 . Velocity booster  108 A is configured to increase a flow velocity of the gases and particles of the exhaust originating in exhaust system source  106  in exhaust system  100 . Exhaust system  100  may also contain a vortex generator  110 A between velocity booster  108 A and exhaust pump  107 . Vortex generator  110 A is configured to impart a component of rotational motion to exhaust of exhaust system  100 . Rotational motion of exhaust (a vortex) shrinks a boundary layer along an interior surface of the exhaust lines of exhaust system  100  and improves particle removal efficiency at flow disruption sites of exhaust system  100 . A dead space is a region inside the exhaust lines where flow velocity is minimal or even where an eddy current is present within the exhaust line. In some instances, an eddy current is generated where a flow contacts a surface, e.g., a reducing connector, and a back flow is generated. In some embodiments, the exhaust in exhaust system  100  is able to generate a component of rotational flow (a vortex) when passing through vortex generator  110 A without inclusion of velocity booster  108 A. In some embodiments, velocity booster  108 A is an injector of particle-free gas. In some embodiments, velocity booster  108 A is a Bernoulli device that draws external gas through gas inlet openings at a leading face (or, on an outer surface) of the Bernoulli device, and emits the gas into exhaust system  100  through outlet openings, smaller than the gas inlet openings, on a trailing face (or, on an interior surface) of the Bernoulli device. In some embodiments, the external openings of the Bernoulli device completely circumscribe an exhaust line of exhaust system  100 . In some embodiments, gas inlet openings of the Bernoulli device are separated from each other around the exhaust line of exhaust system  100 . In some embodiments, the gas inlet openings of the Bernoulli device are on a single side of the exhaust line while the gas outlet openings circumscribe the exhaust line. In some embodiments, the internal openings of the Bernoulli device are arranged in a circular pattern around an interior of the exhaust line of exhaust system  100 . In some embodiments, gas outlet openings are inside an exhaust line of exhaust system  100 . In some embodiments, gas outlet openings are against an outer surface of exhaust system  100  and align with holes in an exhaust line of exhaust system  100 . 
     In some embodiments, vortex generator  110 A has a flow splitter attached to a rotational bearing, the rotational bearing attached to an inner wall of the exhaust line. In some non-limiting embodiments, the flow splitter of vortex generator  110 A has openings that allow gas to travel from an outer region of the exhaust line (a peripheral portion) to a central region (a central portion) of the exhaust line. The flow splitter has blades in the openings that, as the exhaust moves over the blades, redirect the peripheral portion of the exhaust to move around a longitudinal axis extending through the exhaust line and vortex generator  110 A. The flow splitter, attached to the rotational bearing, is capable of rotating as gas moves through the openings and moves over the blades. In some embodiments, the blades are straight. In some embodiments, the blades are curved. In some embodiments, the blades extend at least half of the distance between a center of the flow splitter and a side of the flow splitter. In some embodiments, the blades extend out past a side of the flow splitter into the peripheral region between the flow splitter side and the interior wall of the exhaust line. A leading side of a blade faces an interior wall of the exhaust line where velocity booster  110 A is positioned. A trailing side of a blade faces the longitudinal axis through velocity booster  110 A. 
     Exhaust system  100  may also contain a flow regulator  112 A downstream from vortex generator  110 A and upstream from flow disruption site  114 A. In some embodiments, flow regulator  112 A is located at a different location in exhaust system to help regulate exhaust flow velocity. In some embodiments, flow regulator  112 A is downstream of flow disruption site  114 A. In some embodiments, flow regulator  112 A is upstream of vortex generator  110 A. Flow regulator  112 A adjusts a flow velocity of the exhaust in order to regulate the overall flow velocity through flow disruption site  114 A. In some embodiments, flow regulator  112 A is a ball valve. In some embodiments, flow regulator  112 A is a butterfly valve, a plug valve, a ball valve, or another suitable valve. 
     In some embodiments, exhaust system  100  has a bypass branch (not shown) to allow repair and reconfiguration of flow regulator  112 A without shutting down exhaust system source  106 . In some embodiments, whether exhaust flows through the bypass branch of exhaust system  100  or through the flow regulator branch is determined by a position of a flow switch mechanism (not shown). In some embodiments, the flow switch mechanism is a shutoff valve that isolates one of the bypass branch or the flow regulator branch. In some embodiments, one or more butterfly valves regulates gas flow between the bypass branch and the flow regulator branch. 
     In some embodiments, flow regulator  112 A is manually adjustable. In some embodiments, flow regulator  112 A is electronically controlled by a control loop that senses exhaust flow in the exhaust system. In some embodiments, flow regulator  112 A is electronically controlled by a control loop that senses a pressure differential between an interior of the exhaust line and the exterior of the exhaust line. 
     Particles tend to collect in exhaust system  100  at flow disruption sites such as flow disruption site  114 A. Flow disruption site  114 A is a location in exhaust system  100  where flow is disrupted (slowed, or becomes turbulent). Particle movement is not sustained as well in disrupted (turbulent) flow as in smooth or laminar flow. Particle movement is sustained better in faster exhaust flow than in slower exhaust flow in an exhaust line. Thus, particles tend to make contact with interior walls of exhaust lines where flow slows or becomes turbulent. When particles contact interior walls of exhaust lines, the particles have a tendency to adhere to interior walls unless the exhaust lifts the particles from the interior surface of the exhaust line. 
     In some embodiments, flow disruption site  114 A includes a bend in an exhaust line. In some embodiments, flow disruption site  114 A includes a connector between exhaust lines, where an upstream line is attached to the connector at one side and a downstream line is attached to another side of the connector. In some embodiments, the connector is a reducing connector (a reducer), where the upstream line has a larger diameter than the downstream line. In some embodiments, the reducer is a concentric reducer or an eccentric reducer. In some embodiments, the connector is a straight connector, where the upstream line and the downstream line share a common axis down a center of the exhaust line. In some embodiments, the connector is an angled connector, where the incoming line (the upstream line) and the exiting line (the downstream line) do not share a common axis of alignment. In some embodiments, the angled connector is a 90° connector between an incoming exhaust line and an outgoing exhaust line. In some embodiments, the angled connector is a 45° connector, a 30° connector or another suitable angled connector. For angled connectors, particles sometimes have sufficient momentum to bump into the “far” or “facing” interior wall of the exhaust line that is in a direct path with the incoming exhaust line entering flow disruption site  114 A. 
     A non-limiting example of flow disruption site  114 A is a 90° connector having an inlet exhaust line opening and an outlet exhaust line opening, at a right angle to each other. The intersection of the openings has angled interior surfaces, not smooth interior surfaces. An angled interior surface is sometimes associated with “dead” spots (locations with no exhaust flow) in an exhaust stream. Locations with no flow, or reduced flow, are more likely locations to experience particle buildup in an exhaust line of exhaust system  100 . In a non-limiting example that includes smoother interior surfaces, the risk of “dead” spots would decrease; however, the redirecting of the exhaust would still reduce the flow velocity and increase the risk of particle build up. 
     In some embodiments, flow disruption site  114 A includes a region of exhaust line where an interior surface of the exhaust line is rough or uneven. Rough or uneven interior surfaces occur at connectors, at locations where segments of line join (such as welded seams), and at locations where connectors (such as for sensors) are attached to an exhaust line. In some embodiments, flow disruption site  114 A is a segment of exhaust line without a particle-shedding coating on an interior wall of the exhaust line. 
     Exhaust pump  107  is downstream of each element of exhaust system  100  and draws, due to a pressure differential between exhaust pump  107  and upstream elements of exhaust system  100 , the gaseous and particulate components of the exhaust stream into exhaust pump  107  and out of exhaust system  100 . In some embodiments, exhaust system  100  contains a particle filtration unit upstream from exhaust pump  107 . In some embodiments, exhaust system  100  contains a washing unit or scrubber to remove particulate matter from an exhaust stream. 
     Exhaust system  100  contains an optional second flow disruption site  114 B located downstream of flow disruption site  114 A. Exhaust system  100  also contains an optional second velocity booster  108 B upstream of a second vortex generator  110 B, and an optional second flow regulator  112 B between second vortex generator  110 B and second flow disruption site  114 B. Some embodiments of exhaust system contain multiple flow disruption sites, where less than all of the flow disruption sites are downstream from vortex generators. In some embodiments, vortex generator  110 B generates a vortex in exhaust system  100  that will enhance particle throughput through multiple flow disruption sites downstream of vortex generator  110 B. In some embodiments, exhaust system  100  includes multiple flow disruption sites, e.g., flow disruption site  114 A and flow disruption site  114 B, and a single vortex generator, e.g., vortex generator  110 A. 
       FIG. 2A  is a cross-sectional diagram of a flow disruption site  200  in an exhaust system, according to some embodiments. Flow disruption site  200  occurs at a connector  202  connected, at an upstream side, to inlet line  204 , having an inlet line inner diameter (ID)  206 , and connected, at a downstream side, to outlet line  208  having an outlet line ID  210 . Inlet line  204  and outlet line  210  are at an angle  220  to each other. Angle  220  may be about 90°, as illustrated in  FIG. 2A . In some embodiments, angle  220  at flow disruption site  200  ranges from 0° (a straight connector) to about 90° (a perpendicular connector). As angle  220  increases to 90°, a risk of particle accumulation at flow disruption site  200  increases. In a situation where angle  220  exceeds 90°, a vector of the flow velocity exiting flow disruption site  200  would be opposite to a direction of flow velocity entering the flow disruption site and a “dead” zone would be created. 
     In some embodiments, inlet line ID  206  is larger than outlet line ID  210 . In some embodiments, inlet line ID  206  is smaller than outlet line ID  210 . In some embodiments, inlet line ID  206  is the same as outlet line ID  210 . In some embodiments, inlet line ID  206  ranges from about 1 cm to about 3 cm. When inlet line ID  206  is smaller than about 1 cm, the inner diameter of the line inhibits formation of a vortex within the exhaust line. When inlet line ID  206  is greater than about 3 cm, the rate of exhaust flow through the flow disruption site is generally sufficiently high to reduce the utility of including a vortex generator (described further, below). In some embodiments, outlet line ID  210  ranges from about 0.5 cm to about 2 cm. When outlet line ID  210  is smaller than about 0.5 cm, the removal rate of exhaust is too low to significantly benefit from a vortex formed upstream of the flow disruption site and particles spin in the disruption site instead of continuing smoothly through the flow disruption site. When outlet line ID  210  is greater than about 2 cm, the diameter differential between inlet line and outlet line is sufficiently small that a vortex does not significantly benefit particle removal (or, adhesion prevention) at flow disruption sites. In some embodiments, a ratio of inlet line ID  206  to outlet line ID  210  ranges from about 1:1 to about 4:1. When a ratio of inlet line ID  206  to outlet line ID  210  is larger than about 4:1, there is insufficient exhaust throughput through flow disruption site  200  to significantly benefit from a vortex generator at an upstream position to enhance particle throughput through flow disruption site  200 . When a ratio of inlet line ID  206  to outlet line ID  210  is smaller than 1:1 (i.e., the outlet is larger than the input), a vortex generator does not significantly enhance particle throughput through flow disruption site  200  because the downstream side of flow disruption site  200  does not impede particle removal. 
     In some embodiments, flow disruption site  200  has a smooth interior wall between inlet line  204  and outlet line  208 . In some embodiments, connector  202  has a ridged interior, where the inner surface is broken by a seam between an end of the exhaust line and an interior wall of connector  202 . In some embodiments, a flow disruption site is an exhaust line inner sidewall that is abraded or scratched, where particles tend to cluster at the abrasion site. In some embodiments, connector  202  has “no-flow” locations or “dead spots” within connector  202 . A “dead spot” is a location in a connector body where a space exists that is outside of a laminar flow region through connector  202 . In some embodiments, a “dead spot” is at a ridge in connector  202 , such as occurs with an inner diameter change between inlet line  204  and outlet line  208 . In some embodiments, a “dead spot” occurs where a connector body is machined to form the inlet opening and outlet opening. In at least one non-limiting example of a “dead spot” in connector  202 , an interior wall of an inlet opening has at least one conical recess into the connector body, where the conical recess corresponds to a volume of connector body material removed by a machining tool, e.g., a drill tip, during formation of a connector body opening. 
       FIG. 2B  is a cross-sectional diagram of a flow disruption site  214 , according to some embodiments. Flow disruption site  214  is an exhaust line  215 . Flow disruption site  214  has an inlet ID  216  and an outlet ID  218 , where inlet ID  216  and outlet ID  218  are equal. Flow disruption site  214  has a bend angle  222  with a radius of curvature  224 . In some embodiments, bend angle  222  ranges from about 90° to 0°. In some embodiments, inlet line ID  216  ranges from 1.0 cm to 5.0 cm. In some embodiments, radius of curvature  224  ranges from about 100% and about 400% of inlet line ID  216 . When bend angle  222  is greater than 90°, the exhaust stream tends to lose sufficient velocity at the bend that particles collect quickly and increase tool maintenance requirements. At bend angles of less than about 45°, the vortex from the vortex generator is generally able to extend through flow disruption site  214 . As a non-limiting example, a flow disruption in exhaust line  215  at bend angles from 0° and 45° is sometimes the result of a temperature differential (typically colder at the site) between the bent section of exhaust line  215  and upstream portions (typically warmer upstream from the site). In some embodiments, a temperature differential at the site is sometimes the result of a loose heating jacket on an exhaust line, reducing an ability to warm the pipe and prevent condensation gases in the exhaust on an interior wall of exhaust line. In some embodiments, flow disruptions result from a different liner material (or no liner material) at flow disruption site  214  than at upstream positions of exhaust line  215 . According to a gas flow velocity and a density of gas in the exhaust system, at bend angles from about 90° and about 45°, a vortex in the exhaust system extends to flow disruption site  214 , but not through the site. 
       FIG. 3A  is a perspective view of a velocity booster  300 , according to some embodiments. Velocity booster  300  is usable as velocity booster  108 A ( FIG. 1 ). In some embodiments, velocity booster  300  is a connector with a central opening that fastens to an outside of an exhaust line. In some embodiments, velocity booster  300  has a hinge and a fastening element and removably fastens around an exhaust line. In some embodiments, velocity booster  300  is permanently fastened to an exhaust line. Velocity booster  300  has a booster body  301  with an outer surface  302 , an inner surface  303 , a leading face  304  (where gas enters velocity booster  300 ) and a trailing face  306  (where gas exits velocity booster  300  and enters an exhaust line). Gas enters velocity booster  300  through inlet openings  308  in leading face  304 , and exits velocity booster  300  through outlet openings  310  in trailing face  306 . In some embodiments, where velocity booster  300  fastens to an outer surface of an exhaust line (i.e., where the exhaust line fits in a central opening of booster body  301  that extends the length of velocity booster  300 ), outlet openings  310  on inner surface  303  align with openings in an outer wall of an exhaust line to allow gas to enter the exhaust stream of the exhaust system. In some embodiments, velocity booster  300  is a connector for mounting inline in an exhaust system. 
     Leading face  304  and inlet openings  308 , are outside of an exhaust line. In some embodiments, trailing face  306  is in the central opening, outside of the exhaust line, and outlet openings  310  open to openings in an outer wall of the exhaust line. In some embodiments, trailing face  306  and outlet openings are perpendicular to a longitudinal axis  307  that extends through a center of velocity booster  300 . In some embodiments, trailing face  306  is inside an exhaust line. 
     In some embodiments, velocity booster  300  has inlet openings and exit holes around an entirety of the circumference of an exhaust line of an exhaust system, e.g., exhaust system  100  ( FIG. 1 ). In some embodiments, velocity booster  300  has inlet openings and outlet openings spaced from each other around the exhaust line surface. In some embodiments, velocity booster  300  has outlet openings in a circular pattern around the exhaust line. In some embodiments, velocity booster  300  has outlet openings in a spiral pattern around the exhaust line, a linear pattern or another suitable pattern. 
     In some embodiments, inlet openings  308  have an inlet diameter  312  that is larger than an outlet diameter  314  of outlet openings  310 . In some embodiments, inlet diameter  312  ranges from about 2 millimeters (mm) to about 5 mm. Trailing face  306  has a central opening diameter  316  equal to or less than the diameter of an exhaust line adjoining velocity booster  300 . In some embodiments, central opening diameter  316  ranges from about 1 centimeter (cm) to about 10 cm. In some embodiments, inlet diameter  312  ranges from 10% of the diameter of an exhaust line upstream from velocity booster  300  to around 30% of the diameter of exhaust line  302 . In some embodiments, outlet diameter  314  of outlet openings  310  ranges from about 50% to 20% of inlet diameter  312  of inlet openings  308 . Inlet diameters  312  of inlet openings  308  that are greater than 20% of the diameter of the exhaust line tend to flood the exhaust line with gas, creating backpressure upstream from velocity booster  300  that slows exhaust removal from the exhaust source. Inlet diameters  312  that are smaller than 5% of the diameter of the exhaust line tend to draw insufficient amounts of gas into the exhaust line to impart a velocity boost to the exhaust stream and enhance transport of particles downstream from velocity booster  300 . Outlet diameters  314  that are larger than about 50% of inlet diameter  312  of inlet opening  308  do not impart a velocity boost to the exhaust stream by the gas entering the exhaust stream. 
     A velocity of exhaust  318  entering velocity booster  300  is lower than a velocity of exhaust  320  after exiting velocity booster. Exhaust  318  entering velocity booster  300  includes gases and particulates from the exhaust source. Exhaust  320  exiting velocity booster  300  includes both gases and particulates of exhaust  318 , and also gas added to exhaust  318  through the inlet and outlet openings of velocity booster  300 . In some embodiments, exhaust  320  has a flow velocity that ranges from about 1 liter per minute to about 30 liters per minute. 
     A number of inlet openings and a number of outlet openings in velocity booster  300  is selected according to a flow velocity of exhaust  318  upstream of velocity booster  300  and to a desired flow rate of exhaust  320 . In some embodiments, a number of inlet openings ranges from about 4 to about 12. When a number of inlet openings, or a diameter of inlet openings, is too large, the exhaust stream becomes flooded with gas and the particle transport capacity of the exhaust stream is reduced. When a number of inlet openings, or a diameter of inlet openings, is too small, the gas does not receive sufficient velocity boost to generate a vortex during passage through a vortex generator, such as vortex generator  110 A ( FIG. 1A ), downstream of velocity booster  300 . 
       FIG. 3B  is a plan view of velocity booster  300  oriented along longitudinal axis  307 , according to some embodiments. Velocity booster  300  is round. In some embodiments, the outer portion of velocity booster  300  has a rectilinear or other polygonal shape. Inlet openings  308  are aligned with corresponding outlet openings  310  along flow paths  320 . Each flow path  320  aligns with an axial plane. The axial plane extends through a center  322  of velocity booster  300  and a center of the inlet opening  308  and outlet opening  310 . 
       FIG. 4A  is a perspective view of a vortex generator  400 , according to some embodiments. Vortex generator  400  is usable as vortex generator  110 A ( FIG. 1 ). Vortex generator  400  is configured to fit within an interior wall of an exhaust line. Vortex generator  400  has a rotating base (annular bearing  406 ) that attaches to the interior wall of the exhaust line where vortex generator  400  is installed. Annular bearing  406  has an interior face  408  and a front edge  410 . Annular blade assembly  412  has a leading edge  414 , with leading blade assembly opening  415 , at the upstream side of annular blade assembly  412 . Annular blade assembly  412  also has trailing face  416 , with trailing blade assembly opening  417 , at the downstream side of annular blade assembly  412 . Annular blade assembly  412  has openings  420  for blades (not shown). A number of blades (and blade openings) is distributed evenly and symmetrically around annular blade assembly  412  to promote smooth, even rotation of the blade assembly in the vortex generator. In some embodiments, blades are made from a same material as the body of annular blade assembly  412 . In some embodiments, blades are made from a different material from that of the body of annular blade assembly  412 . In some embodiments, blades are made by cutting and bending cut portions of the body of annular blade assembly  412 , the blades and body of annular blade assembly being a single sheet of material. In some embodiments, openings  420  extend to front edge  410  against annular blade assembly  412 . In some embodiments, openings  420  for blades  422  extend past front edge  410  of annular bearing  406  against interior wall  408 . Blades of annular blade assembly  412  have a leading side (or, a leading blade face) and a trailing side (or, a trailing blade face). A leading side faces an interior wall of the exhaust line in which vortex generator  400  is mounted. A trailing side faces a center of the exhaust line where vortex generator  400  is mounted. 
     In some embodiments, annular blade assembly  412  is an open cylinder with leading blade assembly opening  415  and trailing blade assembly opening  417  at opposing ends of annular blade assembly  412 , as described above, to allow exhaust to flow through the annular blade assembly. Side  418  is separated from the interior wall of the exhaust system by a gap  424 . In some embodiments, gap  424  is a uniform gap extending from leading edge  414  to trailing face  416  and side  418  is parallel to a sidewall of the exhaust line. In some embodiments, gap  424  is a variable gap, smaller near trailing face  416  and larger near leading edge  414 . In some embodiments, trailing face is connected to front edge  410  of annular bearing  406 . In some embodiments, a rear portion  425  of side  418  is attached to interior wall  408  of annular bearing  406 . In some embodiments, rear portion  425  is at an end of side  418  closest to trailing face  416 . In some embodiments, rear portion  425  is separated from trailing face  416  on side  418 . 
     In some embodiments, a vortex generator is a flow splitter that divides an exhaust stream into at least two portions. Vortex generator  400  divides exhaust stream  424  into two portions: a central portion  426  and a peripheral portion  428 . Central portion  426  enters the interior volume  430  of annular blade assembly  412  through a front opening  432 . A peripheral portion  428  of the exhaust enters interior volume  430  of vortex generator  400  by passing through gap  424  and through openings  420 . Peripheral portion  428  moves over, and pushes against, blades  422  of annular blade assembly  412 . Under some exhaust conditions, the motion of peripheral portion  428  over blades  422  causes annular blade assembly  412  to rotate about longitudinal axis  407  through a center of vortex generator  400 . A degree of rotational motion of vortex flow  436  relates to the flow velocity of peripheral portion  428  and the pressure of the exhaust in the exhaust line. In some embodiments, blades  422  are substantially rectilinear. In some embodiments, blades are angled. In some embodiments, blades  422  extend entirely into interior volume  430 . In some embodiments, blades  422  extend entirely into gap  424  between side  418  and an inner sidewall of the exhaust line. In some embodiments, blades  422  are partly extended into gap  424  and partly extended into interior volume  430 . A number and a shape of blades  422  is selected according to the flow velocity of peripheral portion  428 , the pressure of the exhaust in the exhaust line, and a vortex strength (related at least to the rotational speed of the vortex around longitudinal axis  434 ) that cleans particles out of a flow disruption site in an exhaust system. Exhaust, after passing through vortex generator  400 , have a rotational component of vortex flow  436  regulated by a number and a shape of blades  422  in annular blade assembly  412 . 
       FIG. 4B  is a cross-sectional view of blade assembly  438 , showing side  418  and straight blades  439 . In some embodiments, straight blades  439  are used in blade assembly  412  as blades  422  ( FIG. 4A ). A number of blades  439  and a length  440  of blades  439  is selected according to a desired degree of mixing of peripheral portion  428  with central portion  426  in the vortex downstream of blade assembly  438 . In some embodiments, straight blades  439  range from about 15% to about 40% of a distance between edge  418  and longitudinal axis  434 . In some embodiments where the blade length shorter than about 15% of the distance between edge  418  and longitudinal axis  434 , insufficient rotational velocity is imparted to vortex flow  436 . In some embodiments where blade length is longer than 40% of the distance, the rotation of straight blades  439  through central portion  426  reduces the rotational speed of blade assembly  438  and interferes with the formation of a vortex downstream of blade assembly  438 . A blade angle  441  of each straight blade  439  is selected based on gas flow characteristics of the exhaust running through the vortex generator. In some embodiments, blade angle  441  ranges from about 15-degrees to about 50-degrees. A small value of blade angle  441  is appropriate for lower exhaust flow velocity situations because low exhaust flow velocity through blade assembly  438  benefits from a more normal (i.e., closer to 90°) angle when imparting rotation on the exhaust. When blade angle  441  is too large in a lower exhaust flow velocity situation, insufficient back pressure is generated by the exhaust flow to push exhaust through annular assembly  438 : gases pass through openings in annular assembly  438  and return to laminar flow downstream. A large value of blade angle  441  is appropriate for high exhaust flow velocity through blade assembly  438  to reduce back pressure and balance the induced rotation of an exhaust stream with the flow of gas through blade assembly  438 . When blade angle  431  is too shallow in a high exhaust flow velocity situation, gas flow over the blades is reduced because of the back pressure induced by straight blades  439 . 
       FIG. 4C  is a cross-sectional view of blade assembly  442 , showing side  418  and curved blades  444 . In some embodiments, curved blades  444  are used in blade assembly  412  as blades  422  ( FIG. 4A ). A number of blades, a length of blades, and a degree of curvature of curved blades  444  is selected for blade assembly  442  according to the flow velocity of peripheral portion  428 , the pressure of the exhaust in the exhaust line, and a degree of mixing of peripheral portion  428  with central portion  426  downstream of blade assembly  442 . In some embodiments, an innermost edge of curved blades  444  ranges from 15% to about 40% of a distance between edge  418  and longitudinal axis  434 . In embodiments where the blade length is shorter than about 15% of the distance between edge  418  and longitudinal axis  434 , insufficient rotational velocity is imparted to peripheral portion. In embodiments where blade length is longer than 40% of the distance, the rotation of curved blades  444  through central portion  426  reduces the rotational speed of blade assembly  438  and interferes with the formation of a vortex downstream of blade assembly  442 . The amount of curvature of curved blades  444  is determined according to the velocity of peripheral portion  428 , the pressure of the exhaust in the exhaust line, and a vortex strength (related at least to the rotational speed of the vortex around longitudinal axis  434 ) that cleans particles out of a flow disruption site in an exhaust system. An amount of curvature of curved blades  444  is determined for blade assembly  442  by factoring the exhaust flow velocity through the exhaust system, the diameter of the exhaust line, and the number of openings/blades in blade assembly  442 . Curved blades  444  are more desirable in low exhaust flow velocity systems because the curvature redirects peripheral portion  428  to a greater degree than flat blades without spinning blade assembly  442 . 
       FIG. 4D  is a schematic view of blade assembly  445 , according to some embodiments. In some embodiments, blade assembly  445  is used in place of blade assembly  412  ( FIG. 4A ). Blade assembly  445  has leading edge  414  and trailing face  416 . Leading edge  414  has an opening  432  and a first radius  446 . Trailing face  416  has an opening  448  and a second radius  450 . A ratio between central portion  426  and peripheral portion  428  is selected by selecting first radius  446  of blade assembly  445  to balance the division of gas between a central portion  426  of exhaust stream  424  and a peripheral portion  428  of exhaust stream  424  to generate vortex flow  436  downstream of blade assembly  445 . In some embodiments, first radius  446  is a same size as second radius  450 . In some embodiments, first radius  446  is smaller than second radius  450 . If first radius  446  is greater than second radius  450 , a flow of peripheral portion  428  is reduced and no vortex flow is formed, in some instances. According to embodiments, first radius  446  ranges between about 10% of the inner diameter of an exhaust line adjoining blade assembly  445  to about 40% of the inner diameter of the exhaust line. In some embodiments, second radius  450  ranges from about 40% of the inner diameter of the exhaust line adjoining blade assembly  445 , to about 45% of the inner diameter of the exhaust line. In some embodiments, a ratio of first radius  446  to second radius  450  ranges from 1:4.5 to 4:4.5. In embodiments where first radius  446  is below about 10%, central portion  426  is too small for a vortex to perpetuate downstream motion of vortex  432 . In some embodiments, where first radius  446  is larger than 45% of a radius of an exhaust line, rotational velocity is insufficient to generate a self-sustaining vortex downstream of blade assembly  445 . 
       FIG. 5  is a plan view of a stationary vortex generator  500 , according to embodiments. In some embodiments, stationary vortex generator  500  is used in place of vortex generator  110   a  or  110   b  in exhaust system  100  ( FIG. 1 ). Stationary vortex generator  500  resembles velocity booster  300 . Stationary vortex generator  500  includes inlet openings  502  and outlet openings  504 . Inlet openings  502  are located outside an exhaust line, while outlet openings are configured to allow gas to enter an exhaust line. In some embodiments, outlet openings  504  are positioned against an outer wall of an exhaust line and align with holes in the exhaust line. In some embodiments, stationary vortex generator  500  is positioned partly within and partly outside an exhaust line, and the exhaust stream passes through the center  508  of stationary vortex generator  500  as gas is added (through inlet openings  502  and outlet openings  504 ) to a region of the exhaust stream adjacent to an inner sidewall of the exhaust line. 
     Each inlet opening  502  is connected to a corresponding outlet opening  504  by a flow path  506 . Flow path  506  is angled away from center  508  of stationary vortex generator  500 . The angular offset of flow path  506  away from center  508  of stationary vortex generator adds rotational motion to an exhaust flow passing through center  508  of stationary vortex generator  500 . In some embodiments, an angle of flow path  506  ranges from about 10° to about 25°. If the angle of flow path  506  is too great, then a risk of “dead” zones in the flow path increases, in some instances. If the angle of flow path  506  is too small, then a rotation of the exhaust is insufficient to create a vortex flow, in some instances. 
       FIG. 6  is a flow diagram of a method  600  of reducing particle adhesion in an exhaust system. The method  600  includes operation  602 , where exhaust is received by an exhaust system comprising a vortex generator. Exhaust originates in a manufacturing tool, such as a semiconductor manufacturing tool, and contains both gaseous and particulate matter components to be exhausted from the manufacturing tool. In some embodiments, the exhaust also contains purge gas (used to maintain a positive pressure relative to external atmosphere, reducing particle intrusion into a manufacturing tool) from the manufacturing tool. In some embodiments, exhaust also includes atmospheric gases. 
     The method  600  further includes operation  604 , wherein a pumping capacity of the exhaust system is determined. Pumping capacity relates to the ability of an exhaust system to remove gases and particulate matter from a manufacturing chamber. In some embodiments, pumping capacity is determined by measuring a pressure differential between atmosphere, outside the exhaust system, and the interior of an exhaust system. In some embodiments, a pressure differential is measured at multiple locations in an exhaust system to identify flow disruption points in the exhaust system. Flow disruption points include, according to some embodiments, connectors in the exhaust system, bends in the exhaust system piping, and locations that experience elevated particle adhesion on interior walls of the exhaust system due to corrosion, condensation, or adhesion of pre-formed particles to an interior wall of the exhaust system. In some embodiments, pumping capacity is used to determine when the maintenance on the exhaust system should be performed. 
     The method  600  includes operation  606 , wherein, after determining an exhaust system pumping capacity, a determination is made about whether the flow velocity of the exhaust should be adjusted. In some embodiments, operation  606  is omitted from method  600 . A determination of whether to adjust a flow velocity is based, in some embodiments, on a predetermined specification for exhaust flow and pumping efficiency of an exhaust system. In some embodiments, determining whether to adjust a gas flow velocity is performed periodically through a manufacturing process to maintain efficient exhaust pumping. 
     The method  600  includes operation  608 , wherein a flow velocity of the exhaust passing through the exhaust system is adjusted according to the measured pumping capacity of the exhaust system. In some embodiments, where exhaust pumping capacity is diminished because of partial blockage of an exhaust line, a flow velocity is adjusted (typically increased) in order to boost gas velocity through the exhaust system. In some embodiments, flow velocity is increased to remove particles that partially obstruct an exhaust line. In some embodiments, operation  608  is omitted from method  600 . 
     In some embodiments, flow velocity is adjusted by a flow regulator that restricts gas flow through the exhaust system. In some embodiments, a flow regulator includes a ball valve, a butterfly valve, or other flow regulator that is installed in line with the exhaust system. In some embodiments, flow velocity is regulated by bleeding external gas, such as atmosphere, into the exhaust system. In some embodiments, flow velocity is adjusted by regulating a pump speed. 
     In some embodiments, adjusting a flow velocity of exhaust through the exhaust system includes directing the exhaust through a velocity booster. A velocity booster operates according to Bernoulli&#39;s law, where gas (such as atmosphere outside an exhaust system) entering velocity booster (a Bernoulli device) through large openings, is accelerated upon exiting the velocity booster through smaller openings that direct the added gas into the exhaust system. A velocity booster boosts the speed of exhaust downstream from the velocity booster and reduces the likelihood of particle adhesion to interior sidewalls of the exhaust system by shrinking the static boundary layer adjoining the exhaust line sidewall. In some embodiments, a velocity booster is in a main exhaust line between an exhaust source and an exhaust pump. In some embodiments, a velocity booster is in a first branch of a fork of an exhaust system, in parallel with a velocity booster bypass in a second fork of the exhaust system, where either one of the velocity booster of the bypass is selected to receive the flow of exhaust. A velocity booster bypass is used in some embodiments of exhaust system to permit operation of an exhaust system during operation of maintenance of the exhaust system. In some embodiments, an exhaust flow is split between velocity booster fork and bypass fork to regulate a flow velocity of exhaust passing through the exhaust system. 
     The method  600  includes operation  610 , wherein the exhaust in the exhaust system is rotated by being directed through a vortex generator. A vortex is a revolving volume of gas that maintains rotational movement without external influence, once generated. A vortex, when generated, is able to travel laterally a larger distance than a similar volume of air that has been forcefully moved through an orifice without generating a vortex. A vortex in an exhaust system provides a second direction of air movement (around the interior of the exhaust line, in addition to laterally through the exhaust line) to help dislodge particles from interior sidewalls of an exhaust system and to prolong high-velocity movement of the exhaust, reducing particle adhesion across the duration of the vortex in the exhaust system. A vortex generator is installed in an exhaust system upstream (closer to the exhaust source) from a flow disruption site to reduce particle adhesion and blockage of the exhaust system at the flow disruption site. A flow disruption site is a bend in an exhaust system, a connector in an exhaust system, a region where the interior surface of the exhaust system has a different surface texture, or a change in the smoothness of the interior wall of the exhaust system, or a location where the temperature of the exhaust system changes (cools, typically) and particle adhesion to the interior surface of the exhaust system changes (increases). A vortex generator upstream from a flow disruption site reduces, by means of increased exhaust velocity, the thickness of the boundary layer of the exhaust through the flow disruption site, allowing the exhaust to push more forcefully on particles that contact the interior wall of the exhaust system. Pushing more forcefully on particles enables the exhaust to overcome a sticking coefficient of particles on the exhaust wall, moving them downstream toward an exhaust pump or scrubber to remove them from the exhaust system. 
       FIG. 7  is a block diagram of a controller  700  for controlling an exhaust system in accordance with some embodiments. Controller  700  includes a hardware processor  702  and a non-transitory, computer readable storage medium  704  encoded with, i.e., storing, the computer program code  706 , i.e., a set of executable instructions. Computer readable storage medium  704  is also encoded with instructions  707  for interfacing with machines, such as velocity boosters, vortex generators, flow regulators, by-pass valves or other suitable machines. The processor  702  is electrically coupled to the computer readable storage medium  704  via a bus  708 . The processor  702  is also electrically coupled to an I/O interface  710  by bus  708 . A network interface  712  is also electrically connected to the processor  702  via bus  708 . Network interface  712  is connected to a network  714 , so that processor  702  and computer readable storage medium  704  are capable of connecting to external elements via network  714 . The processor  702  is configured to execute the computer program code  706  encoded in the computer readable storage medium  704  in order to cause system  700  to be usable for performing a portion or all of the operations as described in method  600 . 
     In some embodiments, the processor  702  is a central processing unit (CPU), a multi-processor, a distributed processing system, an application specific integrated circuit (ASIC), and/or a suitable processing unit. 
     In some embodiments, the computer readable storage medium  704  is an electronic, magnetic, optical, electromagnetic, infrared, and/or a semiconductor system (or apparatus or device). For example, the computer readable storage medium  704  includes a semiconductor or solid-state memory, a magnetic tape, a removable computer diskette, a random access memory (RAM), a read-only memory (ROM), a rigid magnetic disk, and/or an optical disk. In some embodiments using optical disks, the computer readable storage medium  504  includes a compact disk-read only memory (CD-ROM), a compact disk-read/write (CD-R/W), and/or a digital video disc (DVD). 
     In some embodiments, the storage medium  704  stores the computer program code  706  configured to cause controller  700  to perform method  600 . In some embodiments, the storage medium  704  also stores information needed for performing a method  600  as well as information generated during performing the method  600 , such as a pumping capacity parameter  716 , a flow velocity parameter  718 , a flow regulator position parameter  720 , a by-pass valve position parameter  722  and/or a set of executable instructions to perform the operation of method  600 . 
     In some embodiments, the storage medium  704  stores instructions  707  for interfacing with machines. The instructions  707  enable processor  702  to generate instructions readable by the machines to effectively implement method  600 . 
     Controller  700  includes I/O interface  710 . I/O interface  710  is coupled to external circuitry. In some embodiments, I/O interface  710  includes a keyboard, keypad, mouse, trackball, trackpad, and/or cursor direction keys for communicating information and commands to processor  702 . 
     Controller  700  also includes network interface  712  coupled to the processor  702 . Network interface  712  allows controller  700  to communicate with network  714 , to which one or more other computer systems are connected. Network interface  712  includes wireless network interfaces such as BLUETOOTH, WIFI, WIMAX, GPRS, or WCDMA; or wired network interface such as ETHERNET, USB, or IEEE-1394. In some embodiments, method  600  is implemented in two or more controllers  700 , and information such as memory type, memory array layout, I/O voltage, I/O pin location and charge pump are exchanged between different controllers  700  via network  714 . 
     Controller  700  is configured to receive information related to the exhaust through I/O interface  710  or network interface  712 . The information is transferred to processor  702  via bus  708  to determine whether to actuate components of the exhaust system such as a velocity booster, a vortex generator, a flow regulator, a by-pass valve or another suitable component. The information is stored in computer readable medium  704  as pumping capacity parameter  716 , flow velocity parameter  718 , flow regulator position parameter  720 , by-pass valve position parameter  722  or other suitable parameters. 
     During operation, processor  702  executes a set of instructions to determine whether to selectively activate components of the exhaust system based on the stored information. In some embodiments, processor  702  is configured to only activate or de-activate any given component. In some embodiments, processor  702  is configured to provide graduated control of at least one component. For example, in some embodiments, process  702  is configured to control an amount of gas passing through a velocity booster in order to control the flow velocity in an exhaust system. 
     An aspect of this description relates to a vortex generator including an annular bearing for mounting on an interior surface of an exhaust line. The vortex generator further includes an annular blade assembly mounted on the annular bearing. The annular blade assembly includes a leading face with an upstream opening having a first radius. The annular blade assembly further includes a trailing face with a downstream opening having a second radius, wherein the upstream opening and the downstream opening are centered around a longitudinal axis of the exhaust line, and the second radius is different from the first radius. The annular blade assembly further includes a side extending from the leading face to the trailing face, wherein the side has a plurality of openings, each opening of the plurality of openings containing a blade, and each opening of the plurality of openings extends beyond the annular bearing in a direction parallel to the longitudinal axis. In some embodiments, the first radius is smaller than the second radius. In some embodiments, a ratio of the first radius to the second radius ranges from 1:4.5 to 4:4.5. In some embodiments, the blade is curved. In some embodiments, the blade is a straight blade. In some embodiments, an angle between the blade and the side ranges from about 15-degrees to about 50-degrees. In some embodiments, the trailing face is mounted on a leading face of the annular bearing. In some embodiments, each opening of the plurality of openings extends beyond an upstream side of the annular bearing. 
     An aspect of this description relates to a method of maintaining an exhaust system. The method includes receiving exhaust by the exhaust system, wherein the exhaust contains particles and gas. The method further includes increasing a velocity of the exhaust within the exhaust system. The method further includes directing the exhaust having the increased velocity through a first vortex generator to create a vortex flow about a longitudinal axis of an exhaust line of the exhaust system. The method further includes passing the exhaust having the vortex flow through a first disruption site. The method further includes directing the exhaust through a second vortex generator downstream of the first disruption site. In some embodiments, the method further includes passing the exhaust through a second disruption site downstream of the second vortex generator. In some embodiments, increasing the velocity of the exhaust includes increasing the velocity of the exhaust using a stationary velocity booster. In some embodiments, the method further includes driving the exhaust through the exhaust system using a pump. 
     An aspect of this description relates to an exhaust system. The exhaust system includes an exhaust line extending configured to receive exhaust from an exhaust source, the exhaust line having a plurality of flow disruption sites. The exhaust system further includes a plurality of vortex generators, wherein each vortex generator of the plurality of vortex generators is located upstream of a corresponding flow disruption site of the plurality of flow disruption sites. In some embodiments, the exhaust system further includes a velocity booster upstream of a first flow disruption site of the plurality of flow disruption sites. In some embodiments, the velocity booster is upstream of a first vortex generator of the plurality of vortex generators. In some embodiments, the exhaust system further includes a flow regulator between a first vortex generator of the plurality of vortex generators and a first flow disruption site of the plurality flow disruption sites. In some embodiments, each vortex generator of the plurality of vortex generators includes a leading face including a first opening having a first radius; a trailing face including a second opening having a second radius; and a side extending from the leading face to the trailing face. In some embodiments, the first radius is equal to the second radius. In some embodiments, the first radius is different from the second radius. In some embodiments, the exhaust system further includes a pump, wherein the pump is downstream from the plurality of flow disruption sites. 
     While the disclosure has been described by way of example and in terms of the above embodiments, it is to be understood that the invention is not limited to the disclosed embodiments. To the contrary, it is intended to cover various modifications and similar arrangements (as would be apparent to those skilled in the art). Therefore, the scope of the appended claims should be accorded the broadest interpretation to encompass all such modifications and similar arrangements.