Abstract:
Ion delivery manifolds with a gas transport channel, for receiving an ionized gas stream, and plural outlets that divide the gas stream into plural neutralization gas streams that are directed toward respective plural target regions are disclosed. At least generally equal ion distribution across the target regions is achieved by using different ion flow rates through the plural outlets. Methods of delivering plural neutralization streams to respective plural target regions include steps for receiving an ionized gas stream, for dividing the ionized gas stream into plural neutralization streams, and for directing the neutralization streams toward respective target regions. At least generally equal ion distribution across the target regions is achieved by differing the ion flow rates of the neutralization streams.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit under 35 U.S.C. 119(e) of co-pending U.S. Provisional Application Ser. No. 61/279,784 filed Oct. 26, 2009 and entitled “COVERING WIDE AREAS WITH IONIZED GAS STREAMS”; which Provisional Application is hereby incorporated by reference in its entirety. 
    
    
     FIELD OF THE INVENTION 
     This invention relates to the distribution of ionized gas streams from an ionizer over a large target area. More particularly, this invention is directed to novel methods of unequally dividing, and apparatus for the unequal division of, ionized gas streams to promote more uniform delivery of ions to a large target area. 
     DESCRIPTION OF RELATED ART 
     As is known in the art many ionizers, the ion emitter(s) may receive a positive voltage during one time period and a negative voltage during another time period. Hence, such emitter(s) generate bi-polar charge carriers including both positive and negative ions and these charge carriers are directed toward a target through a manifold of some form or other. 
     Conventional ion stream manifolds to distribute gas ions (see, for example, Ion System 4210 In-Line Ionizer and Japanese Patent JP 20070486682) typically comprise an elongated cylindrical tube with multiple holes distributed along the length of the manifold to permit ions to exit the tube. In such devices, hole diameters have been sized to create an over-pressure within the tube and that forces ionized gas outward through the holes. These manifolds equally divide ionized gas streams along the longest manifold axis so that roughly the same quantity of gas escapes through each hole. Distribution of ionized gas flow, however, is complex phenomenon as the media comprising three different species—carrying gas, positive and negative ions. So, a manifold that seeks to equally divide gas streams exiting the manifold will not provide an equal distribution of ions to a large charged target area. 
     BRIEF SUMMARY OF THE INVENTION 
     In one form, the present invention overcomes the above-stated and other deficiencies of the prior art by providing an ion delivery manifold for use with an ionizer of the type that converts a non-ionized gas stream into an ionized gas stream. The manifold may have a gas transport channel with an inlet that receives the ionized gas stream from the ionizer and at least first and second outlets that divide the ionized gas stream into first and second neutralization gas streams directed toward respective first and second regions of a wide-area target. To achieve at least generally equal ion distribution across the first and second regions, the ion flow rate through the first outlet may be higher than the ion flow rate through the second outlet and the first region may be further from the first outlet than the second region is from the second outlet. 
     Further benefits are achieved by minimizing ion recombination during delivery of ionized gas streams to regions of target surface. Recombination is undesirable because it consumes two oppositely charged (useful) ionized gas molecules, and produces two neutral (not useful for neutralization) gas molecules. As charged ionized molecules are consumed, the ability to neutralize charges on a target is reduced. By reducing recombination and by compensating for anticipated recombination in certain ways, the invention is able to more closely approximate uniform ion distribution across the charge-neutralization target. 
     The inventive manifolds may minimize the residence time of the ionized gas streams exiting the manifold and directed to regions of the wide-area target furthest from the manifold. Since ion distribution depends on residence time within the manifold, the lower the residence time, the less ion recombination occurs. In accordance with some embodiments of the invention, residence time within the transport channel is minimized by eliminating dead zones or reverse flows (created by turbulent gas movement). The inventive manifolds are, therefore, designed to more quickly transport ions from the inlet through some outlets to thereby minimize residence time within those portions of the manifold. 
     In some embodiments, inventive manifolds may use the momentum of the gas stream(s) moving through the manifold to push at least one of the neutralization gas streams exiting the manifold toward greater distances. In one desirable configuration, at least one outlet lies along an unobstructed path from the manifold inlet and the momentum of the incoming ionized gas stream is used to push one of the divided ionized gas streams through that orifice. 
     In some embodiments, at least a portion of the transport channel may have a curved interior surface and plural outlets may extend from the curved interior surface of the transport channel. Further, at least one outlet may be at least substantially tangentially aligned with the curvature of the inner surface of the through-channel. The inventive manifolds may have a small footprint if used with tool and robotic applications, and may be compatible with a high-frequency ion sources. 
     Inventive method embodiments include methods of delivering plural neutralization gas streams to respective plural regions of a wide-area charge-neutralization target. Such methods may include steps for receiving an ionized gas stream flowing in a downstream direction, for dividing the ionized gas stream into plural neutralization gas streams, and for directing the plural neutralization gas streams toward respective plural regions of the wide-area target. To achieve at least generally equal ion distribution across the wide-area target, the ion flow rate of one of the neutralization gas streams may be higher than the ion flow rate of the other neutralization gas streams and the neutralization gas stream with the highest ion flow rate may be directed to the furthest region of the wide-area target. 
     In sum, manifold structures and/or distribution methods in accordance with the invention improve neutralization gas stream delivery by relying on one or more of the following four guidelines (1) minimize the pressure drop across at least a portion of the manifold itself, (2) minimize the residence time of ions within at least a portion of the manifold, (3) direct more ions to distant target locations than to near locations since recombination losses will be greater at distant locations, and/or (4) employ air or gas entrainment downstream of the manifold to reduce ion density. 
    
    
     
       BRIEF SUMMARY OF THE DRAWINGS 
         FIG. 1  is a diagram of an in-line ionizer having an emitter and being attached to a first preferred manifold; 
         FIG. 2  demonstrates that the manifold embodiment of  FIG. 1  provides an unobstructed path between the manifold inlet and the orifice that passes the largest portion of ionized gas flow; 
         FIG. 3  shows another preferred embodiment that utilizes ion guide tubes wherein tubes close to the manifold inlet and aligned to the manifold inlet axis are ideally situated to capture momentum, and transport the ions to distant locations; 
         FIG. 4  shows a preferred embodiment in which ion guide tubes are used in conjunction with a flared or generally frustoconical manifold; 
         FIG. 5  shows a further preferred embodiment in which an ionization cell, with an ion emitter and reference electrode is incorporated into an inventive manifold, wherein recombination is minimized and efficiency is improved by shortening the distance between the emitter and the manifold outlet holes; 
         FIG. 6  shows another preferred embodiment which the manifold outlets take the form of tubelettes to direct plural divided neutralization streams exiting the manifold toward respective regions of a wide-area target surface; 
         FIG. 7  shows another preferred embodiment which employs outlet tubes that are at least substantially tangentially aligned to a manifold curvature to effectively capture momentum by enabling the ion flow momentum to travel through the short tubes and continue on a straight line course; and 
         FIG. 8  is a table showing discharge times and ion distribution (ionization-neutralization coverage) results for a preferred embodiment directed to a 1400 mm by 400 mm wide-area target. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       FIG. 1  shows a manifold  1  embodiment that has proven performance. The inlet of the manifold  1  transport channel  3  connects to a gas ionizer  7  by mating with the ionizer outlet  8 . The means for mating an inlet of the transport channel  3  to the ionizer outlet  8  may be any one or more of a male-to-female slip fit, a threaded fitting, keyed fitted surfaces and/or other means known in the art. In this example, the ion emitter  7 E may be a corona discharge electrode with a pointed end that is oriented toward the gas transport channel  3  of the manifold  1  and wherein the electrode  7 E is disposed within a non-ionized gas stream which will be converted into an ionized gas stream by the ionizer. The ionized gas flow may be in the range 30-200 L/min, preferably 60-100 L/min. 
     In use the ionizer receives non-ionized gas stream (Gas in) that defines a downstream direction and produces ions  6  to thereby form an ionized gas stream. Ions  6  produced by the ionizer  7  are carried by the ionized gas stream (air, nitrogen, argon, etc.) through the ion outlet  8  into the inlet of through channel  3 . 
     As shown, the manifold  1  includes an outside surface  2  and an enclosed gas transport channel  3  bounded by an interior surface denoted by dotted lines in the various Figures. The ionized gas stream  6  within the transport channel  3  flows toward the plural outlets/orifices  4  where it is unequally divided into plural neutralization streams. The plural neutralization streams exit the orifices  4  (which may be spray orifices) and are directed toward a wide-area target along arrows  5  to neutralize charge on respective regions of the target (not shown). In certain preferred embodiments, the enclosed gas transport channel  3  may have a varying cross-sectional area that decreases toward one dead end of the channel (i.e., the channel may be closed from one side). This way, gas pressure inside channel  3  may be increased and the ion flow may be directed to the outlets  4 . In certain preferred embodiments, the gas transport channel  3  may comprise a dielectric polymer with a charge relaxation time of 100 seconds or more and the inner surface of the gas transport channel (see dotted lines) may have a surface roughness not exceeding Ra=32 micro inches. Conventional materials of this type include engineered thermoplastic resins with good manufacturability (processability), thermal stability, temperature resistance, chemical resistance and/or fatigue resistance such as thermoplastics and thermosetting polymers. Some conventional polycarbonates resins with some or all of these properties include PEEK®, Polycarbonate, DELRIN®, and ACRYLIC®. The inventive manifolds discussed herein may be formed in any conventional manner consistent with the remainder of this disclosure including machining or molding it in one or more portions and assembling the same together (if molded in more than one portion). 
       FIG. 2  shows essentially the same manifold  1  as shown in  FIG. 1 . Note that the top spray outlet  4 T lies on an unobstructed path  9  between the outlet  4 T and the ionizer outlet  8  (and the inlet of the through channel  3 ). The significance of the in-line positioning is that the momentum of the ionized gas stream flowing through ionizer outlet  8  is continued through the top outlet/orifice  4 T. Ion flow exiting orifice  4 T will, therefore, be greater than ion flow exiting the middle outlet/orifice  4 M and the lower outlet/orifice  4 L. Outlet  4 T preferably directs neutralization ion flow toward the most distant region of the charged target to be neutralized because the preserved momentum of the gas moving therethrough is capable of delivering ions greater distances with fewer losses. 
     Note that the middle orifice  4 M and the lower orifice  4 L do not lie along path  9 . Considerable gas momentum from the ion outlet  8  is lost before the ion flow exits middle orifice  4 M and the lower orifice  4 L. Although fewer ions exit through middle hole  4 M and the lower hole  4 L (compared to hole  4 T), outlets  4 M and  4 L are directed to mid-target and near-target regions, respectively. This is desirable for uniform ion distribution at the target surface because, even though fewer ions exit middle and lower outlets  4 M and  4 L, recombination will destroy fewer ions over these shorter distances (compared to hole  4 T and the more distant target region associated with it). Thus, a wide coverage manifold intentionally delivers unequal quantities of ionized gas through all holes  4 T,  4 M,  4 L. The cross-sectional area of each outlet may depend on its position (distance) from and the dimensions of its targeted neutralization region. For example, orifice  4 T (see unobstructed path  9 ) supplying ion flow to the most remote targeted region may have a cross-sectional area that is smaller than (provides higher gas velocity and entrainment) or equal to that of outlet  4 M. Outlet  4 M permits ion flow to a closer target region, but one that has a larger neutralization region (see  FIG. 2 ). Outlet  4 L may have smaller cross-sectional area than outlet  4 M because it&#39;s positioned closest to target and ion flow is the lowest. This arrangement substantially compensates for inherently unequal ion recombination to thereby provide substantially uniform ion current density at the charged target surface. This makes the inventive manifolds more effective than a manifold that distributes gas streams evenly due to internal pressure buildup. 
     Further, recombination can be minimized by reducing the density of ions and by reducing the transit (travel) time to the target. Also, recombination is decreased by minimizing interaction of ionized gas flow with walls of manifold. 
     Turning now to  FIG. 3 , there is shown a tubular manifold that utilizes an alternative configuration and is capable of distributing ions over a 6 foot square area that is 20 inches away from the outlet tubes of the manifold. As shown, the ionizer  17  delivers an ionized gas stream through an ion outlet  18 , which connects to an inventive manifold  19 . Inside manifold  19  are a series of tubes  11 ,  12 . While the invention is not so limited, only two tubes  11 ,  12  are shown for simplicity. 
     Tube  11  is positioned close to the ionizer outlet  18 , and is aligned with the central axis of the ionizer outlet  18 . Both closeness and alignment contribute to a preferred ion flow path through manifold  19 . Tube  11  is directed to distant target locations. By contrast, the opening of tube  12  is further away from the ionizer outlet  18  than tube  11  and tube  12  is not aligned with the central axis of the ion outlet  18 . Tube  12  is, therefore, directed to near target locations. 
     In some embodiments, the tubes  11 ,  12  may have different cross-sectional areas and tubes  11 ,  12  are preferably fabricated from non-conductive materials. Further, the exit opening of manifold  19  may be elliptical or circular (or other geometry) in cross-sectional shape, depending on the target shape. 
       FIG. 4  shows a preferred embodiment that is closely related to that of  FIG. 3 . The difference is that the manifold  29  has a flared or frustoconical shape. In this embodiment, tube  21  employs momentum and positioning to transport ion flow to a long-distance region of the target. By contrast, tube  22  receives less momentum and is oriented oblique to the main flow from the ion outlet. Tube  22  is, therefore, directed toward a short-distance region of the target. 
       FIG. 5  shows a manifold  51  that has an ion emitter  55  and one or more reference electrodes  58 ,  58 A incorporated into the manifold  51  itself. The reference electrode(s) may be electrically coupled to ground  59  or to a capacitive circuit  56  and, through cable  57 , to a control system for controlling a high-voltage/high-frequency power supply (not shown). In this configuration, the bi-polar ionized gas is produced closer to the manifold outlets  54 . This gives significantly less time for ion recombination to occur within the manifold (compared to various other embodiments described herein) so the harvest of ions is improved. The inlet port  52  serves as a conduit for incoming non-ionized (and possibly compressed) gas and as a conduit for electrical cables and/or connectors  53 . In the preferred embodiment of  FIG. 5 , the ionizer may be a corona discharge electrode with an ionizing tip that is oriented toward the gas transport channel of the manifold, wherein the electrode is positioned inside a shell with an evacuation port and an outlet that is at least partially disposed within the gas transport channel. 
       FIG. 6  shows a manifold  61  in which outlet holes are replaced with short tubes/tubelettes  64 T,  64 M,  64 L. In a variation, the short tubelettes  64 T,  64 M,  64 L are inserts with varying cross-sectional areas. In this way, ions are distributed with greater angular control. The velocity of ion flow through tube  64  T is higher than the velocity of the ion flow trough tubes  64 M and  64 L. This creates entrainment effect drawing an additional volume of ambient gas toward the wide area target to form plural neutralization streams. The additional volume of ambient gas dilutes the ionized gas steam decreasing recombination losses. Ionized gas flow may be in the range 30-200 L/min, preferably 60-100 L/min. 
       FIG. 7  shows a manifold  71  with short tubes/tubelettes  74 T,  74 M,  74 L that, unlike at least some of the outlets shown in  FIG. 6 , are tangentially aligned with the curved interior surface of the manifold to utilize the momentum lines  75  where they are positioned. As recited in classical physics, momentum is constrained to a circular path by applying a centripetal (inward) force. In this case, the centripetal force is provided by the shape of the interior surface of the through channel. When the centripetal force releases (due to the presence of an outlet), the momentum continues as straight line momentum  76 . In this diagram, the outlet cylinders/tubelettes  74 T,  74 M,  74 L serve to remove the centripetal force, and provide optimal straight line momentum  76  toward the respective regions of a wide area target. 
     Industrial applications commonly call for the charge neutralization of an area that is long and narrow, rather than round or square. As is known in the art, one example of a wide-area charged target of the type generally encountered during semiconductor wafer production is a generally rectangular surface 1400 millimeters by 400 millimeters located at a specified shortest distance from a manifold. 
     While the invention is not so limited, it has been empirically determined that inventive manifolds with 3 to 5 orifices, each having a circular cross-sectional area with diameters of between about 0.188 inches and 0.125 inches are particularly well suited to deliver substantially uniform ion current density (i.e., uniform ion distribution) at a wide area target of the general type and/or size noted immediately above. These 3 to 5 manifold orifices may be loosely positioned along a line that corresponds to the most distant target area. As used herein, the term “loosely” means that the outlet holes (or orifices) do not have to be substantially aligned along a single line. As used herein, the term “outlet” may include a hole, an orifice, a beveled orifice, a tubelette (such as a short outlet tube as shown and described herein), an outlet cylinder and/or a spray orifice. As used herein, the term the term ionizer may include any source of ionizing energy and may include an ionizing corona electrode, nuclear disintegration, and X-rays. As is known in the art and as used herein, the term “ion flow rate” means I=U Ne: where I is ion current density [A/m 2 ], U is gas velocity [m/sec], N is ion concentration [1/m 3 ], and e is ion charge which is usually equal to electron charge [C]. 
     A laboratory example of discharge times (i.e., a standard measure of charge neutralization efficiency) and voltage balance achieved with a 3-hole manifold is shown in  FIG. 8 . The charged target area was a flat grid that was 1400 mm long and 400 mm wide. The results are recorded in a format that shows the centerline performance, the performance at left 200 mm, and the performance at right 200 mm. The data shown therein was taken under standard test conditions as known in the art. These include tests of electrically floating plates (preferably with a capacitance of about 20 picoFarads (pF) to ground) which are charged (to test ion balance) and discharged (preferably from 1000 volts to 100 volts to test effectiveness) to yield the data shown in each line of the Table of  FIG. 8 . Readings shown in each line of the Table were compiled for repeated tests in which the flat grid was shifted by a distance of 20 centimeters for iteration. As shown in the Table of  FIG. 8 , a preferred embodiment of the invention was able to discharge any region of a wide area target, that is 100 centimeters by 40 centimeters, in less than about 100 seconds, with a Nitrogen flow rate of about 60 L/min and with a voltage balance of less than about 10 volts. 
     The inventive manifold designs disclosed herein are preferably compatible with but not limited to AC corona ionizers. For example, ionizing sources based on nuclear, X-ray, field emission or any other known in the ionization art principles may be also used with disclosed apparatus and methods. 
     While the present invention has been described in connection with what is presently considered to be the most practical and preferred embodiments, it is to be understood that the invention is not limited to the disclosed embodiments, but is intended to encompass the various modifications and equivalent arrangements included within the spirit and scope of the appended claims. With respect to the above description, for example, it is to be realized that the optimum dimensional relationships for the parts of the invention, including variations in size, materials, shape, form, function and manner of operation, assembly and use, are deemed readily apparent to one skilled in the art, and all equivalent relationships to those illustrated in the drawings and described in the specification are intended to be encompassed by the appended claims. Therefore, the foregoing is considered to be an illustrative, not exhaustive, description of the principles of the present invention. 
     All of the numbers or expressions referring to quantities of ingredients, reaction conditions, etc. used in the specification and claims are to be understood as modified in all instances by the term “about.” Accordingly, the numerical parameters set forth in the following specification and attached claims are approximations that can vary depending upon the desired properties, which the present invention desires to obtain. 
     Also, it should be understood that any numerical range recited herein is intended to include all sub-ranges subsumed therein. For example, a range of “1 to 10” is intended to include all sub-ranges between and including the recited minimum value of 1 and the recited maximum value of 10; that is, having a minimum value equal to or greater than 1 and a maximum value of equal to or less than 10. Because the disclosed numerical ranges are continuous, they include every value between the minimum and maximum values. Unless expressly indicated otherwise, the various numerical ranges specified in this application are approximations. 
     The discussion herein of certain preferred embodiments of the invention has included various numerical values and ranges. Nonetheless, it will be appreciated that the specified values and ranges specifically apply to the embodiments discussed in detail and that the broader inventive concepts expressed in the Summary and Claims are readily scalable as appropriate for other applications/environments/contexts. Accordingly, the values and ranges specified herein must be considered to be an illustrative, not an exhaustive, description of the principles of the present invention. 
     Various ionizing devices and techniques are described in the following U.S. patents and published patent application, the entire contents of which are hereby incorporated by reference: U.S. Pat. No. 5,847,917, to Suzuki, bearing application Ser. No. 08/539,321, filed on Oct. 4, 1995, issued on Dec. 8, 1998 and entitled “Air Ionizing Apparatus And Method”; U.S. Pat. No. 6,563,110, to Leri, bearing application Ser. No. 09/563,776, filed on May 2, 2000, issued on May 13, 2003 and entitled “In-Line Gas Ionizer And Method”; and U.S. Publication No. US 2007/0006478, to Kotsuji, bearing application Ser. No. 10/570,085, filed Aug. 24, 2004 and published Jan. 11, 2007, and entitled “Ionizer”.