Covering wide areas with ionized gas streams

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.

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.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1shows a manifold1embodiment that has proven performance. The inlet of the manifold1transport channel3connects to a gas ionizer7by mating with the ionizer outlet8. The means for mating an inlet of the transport channel3to the ionizer outlet8may 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 emitter7E may be a corona discharge electrode with a pointed end that is oriented toward the gas transport channel3of the manifold1and wherein the electrode7E 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 ions6to thereby form an ionized gas stream. Ions6produced by the ionizer7are carried by the ionized gas stream (air, nitrogen, argon, etc.) through the ion outlet8into the inlet of through channel3.

As shown, the manifold1includes an outside surface2and an enclosed gas transport channel3bounded by an interior surface denoted by dotted lines in the various Figures. The ionized gas stream6within the transport channel3flows toward the plural outlets/orifices4where it is unequally divided into plural neutralization streams. The plural neutralization streams exit the orifices4(which may be spray orifices) and are directed toward a wide-area target along arrows5to neutralize charge on respective regions of the target (not shown). In certain preferred embodiments, the enclosed gas transport channel3may 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 channel3may be increased and the ion flow may be directed to the outlets4. In certain preferred embodiments, the gas transport channel3may 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. 2shows essentially the same manifold1as shown inFIG. 1. Note that the top spray outlet4T lies on an unobstructed path9between the outlet4T and the ionizer outlet8(and the inlet of the through channel3). The significance of the in-line positioning is that the momentum of the ionized gas stream flowing through ionizer outlet8is continued through the top outlet/orifice4T. Ion flow exiting orifice4T will, therefore, be greater than ion flow exiting the middle outlet/orifice4M and the lower outlet/orifice4L. Outlet4T 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 orifice4M and the lower orifice4L do not lie along path9. Considerable gas momentum from the ion outlet8is lost before the ion flow exits middle orifice4M and the lower orifice4L. Although fewer ions exit through middle hole4M and the lower hole4L (compared to hole4T), outlets4M and4L 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 outlets4M and4L, recombination will destroy fewer ions over these shorter distances (compared to hole4T and the more distant target region associated with it). Thus, a wide coverage manifold intentionally delivers unequal quantities of ionized gas through all holes4T,4M,4L. The cross-sectional area of each outlet may depend on its position (distance) from and the dimensions of its targeted neutralization region. For example, orifice4T (see unobstructed path9) 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 outlet4M. Outlet4M permits ion flow to a closer target region, but one that has a larger neutralization region (seeFIG. 2). Outlet4L may have smaller cross-sectional area than outlet4M because it'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 toFIG. 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 ionizer17delivers an ionized gas stream through an ion outlet18, which connects to an inventive manifold19. Inside manifold19are a series of tubes11,12. While the invention is not so limited, only two tubes11,12are shown for simplicity.

Tube11is positioned close to the ionizer outlet18, and is aligned with the central axis of the ionizer outlet18. Both closeness and alignment contribute to a preferred ion flow path through manifold19. Tube11is directed to distant target locations. By contrast, the opening of tube12is further away from the ionizer outlet18than tube11and tube12is not aligned with the central axis of the ion outlet18. Tube12is, therefore, directed to near target locations.

In some embodiments, the tubes11,12may have different cross-sectional areas and tubes11,12are preferably fabricated from non-conductive materials. Further, the exit opening of manifold19may be elliptical or circular (or other geometry) in cross-sectional shape, depending on the target shape.

FIG. 4shows a preferred embodiment that is closely related to that ofFIG. 3. The difference is that the manifold29has a flared or frustoconical shape. In this embodiment, tube21employs momentum and positioning to transport ion flow to a long-distance region of the target. By contrast, tube22receives less momentum and is oriented oblique to the main flow from the ion outlet. Tube22is, therefore, directed toward a short-distance region of the target.

FIG. 5shows a manifold51that has an ion emitter55and one or more reference electrodes58,58A incorporated into the manifold51itself. The reference electrode(s) may be electrically coupled to ground59or to a capacitive circuit56and, through cable57, 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 outlets54. 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 port52serves as a conduit for incoming non-ionized (and possibly compressed) gas and as a conduit for electrical cables and/or connectors53. In the preferred embodiment ofFIG. 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. 6shows a manifold61in which outlet holes are replaced with short tubes/tubelettes64T,64M,64L. In a variation, the short tubelettes64T,64M,64L are inserts with varying cross-sectional areas. In this way, ions are distributed with greater angular control. The velocity of ion flow through tube64T is higher than the velocity of the ion flow trough tubes64M and64L. 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. 7shows a manifold71with short tubes/tubelettes74T,74M,74L that, unlike at least some of the outlets shown inFIG. 6, are tangentially aligned with the curved interior surface of the manifold to utilize the momentum lines75where 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 momentum76. In this diagram, the outlet cylinders/tubelettes74T,74M,74L serve to remove the centripetal force, and provide optimal straight line momentum76toward 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/m2], U is gas velocity [m/sec], N is ion concentration [1/m3], 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 inFIG. 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 ofFIG. 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 ofFIG. 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.

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”.