TWI836527B - Apparatus and ionizing bar for silicon based charge neutralization - Google Patents

Abstract

An embodiment of the invention provides a method for low emission charge neutralization, comprising: generating a high frequency alternating current (AC) voltage; transmitting the high frequency AC voltage to at least one non-metallic emitter; wherein the at least one non-metallic emitter comprises at least 70% silicon by weight and less than 99.99% silicon by weight; wherein the at least one emitter comprises at least one treated surface section with a destroyed oxidation layer; and generating ions from the at least one non-metallic emitter in response to the high frequency AC voltage. Another embodiment of the invention provides an apparatus for low emission charge neutralization wherein the apparatus can perform the above-described operations.

Description

Silicon-based charge neutralization equipment and ionization rods

Cross-references to related applications

This application is a continuation-in-part of and claims priority to U.S. Application No. 12/456,526 filed on June 18, 2009, entitled "SILICON EMITTERS FOR IONIZERS WITH HIGH FREQUENCY WAVEFORMS" and claims priority to and the benefit of U.S. Prior Application No. 61/132,422 filed on June 18, 2008. U.S. Application Nos. 12/456,626 and 61/132,422 are incorporated herein by reference.

Embodiments of the present invention relate primarily to ionization devices for static charge neutralization and control. More specifically, embodiments of the present invention address the need for reliable and low particle emission ionizers within the semiconductor, electronics, and/or flat panel industries.

With an AC ionizer, each emitter receives a high positive voltage during one time period and a high negative voltage during another time period. Therefore, each emitter generates a corona discharge without outputting both positive and negative ions.

For the purpose of neutralizing charges and preventing static electricity associated with technical problems, a flow (cloud) of positive and negative ions is directed towards a charged target.

The background narrative provided herein is for the purpose of generally presenting the context of this disclosure. Nothing now claimed to be the inventor's work, work described in this background section, or any description of the matter at the time of filing that may not qualify as prior art is expressly or implicitly admitted as an objection to the present disclosure. of prior technology.

The ion emitter of the charge neutralizer generates and supplies both positive and negative ions to the surrounding air or gas medium. To generate gas ions, the amplitude of the applied voltage must be high enough to generate a corona discharge between at least two electrodes configured as an ionization cell. In the ionization cell, at least one electrode is an ion emitter and the other electrode can be a reference electrode. It is also possible that the ionization cell includes at least two ionization electrodes.

Along with the useful positive and negative gas ions, the charge neutralizer's emitter may generate and emit corona byproducts, including undesirable particles. In semiconductor processing and similar cleaning processes, particle emission/contamination has been associated with defects, product reliability issues, and lost profits.

Several factors are known in the art to affect the amount of undesired particle emission. Some primary factors include, for example, the material composition, geometry, and design of the ion emitter. The second factor includes high voltage power supplies configuration of the emitter connections. Another critical factor is related to the profile of the power supply applied to the ion emitter (the magnitude and time dependence of the high voltage and current).

The power waveform can be used to control the voltage profile supplied to the emitter by a high voltage power supply. Voltage/current waveforms can be used to control both ion production and particle emission from the emitter.

The coma discharge can be stimulated by direct current (DC) voltage, alternating current (AC) voltage, or a combination of the two voltages. For many applications of the present invention, the preferred power waveform is a high frequency high voltage (HF-HV) output from a high frequency (HF) power supply, as discussed below. This high voltage output can be continuous rather than continuous. That is, the voltage output can be variable in amplitude over time or periodically turned off.

The material composition of the emitter is known to affect the degree of particle emission from the ionizer. Common emitter materials include stainless steel, tungsten, titanium, silicon oxide, single crystal silicon, silicon carbide, and other metals plated with nickel or gold. This list is not exhaustive. The inventors have learned from experience that metal-type emitters tend to generate more particles due to corona associated with erosion and spattering. In addition, metals (or, more generally, highly conductive particles) are often considered "killer particles" in the semiconductor industry (i.e., these particles can short-circuit tightly located conductive traces on the wafer/chip). Therefore, in the framework of this patent application, the inventors are primarily considering non-metallic ion emitters, as discussed below.

Among these materials, from the perspective of low particle emission, Scott Gehlke in U.S. Patent No. 5,447,763 proposed ultra-clean (greater than 99.99% purity) single crystal silicon. This single crystal silicon has been adopted by the semiconductor industry as the de facto standard for clean emitters. Curtis et al. in U.S. Patent Application Publication No. 2006/0071599 proposed ultra-clean silicon carbide (at least 99.99% purity) as another non-metallic material. However, silicon carbide emitters are expensive and tend to emit undesirable particles.

Known ionizers with single crystal silicon emitters are powered by two high voltage DC supplies. One system used for cleanroom ceiling mounting, such as the Cleanroom Ionization System "NiLstat 5000" (Ion Systems, Inc.), typically produces less than 60 particles (greater than 10 nm in diameter) per cubic foot of air. Other emitter materials typically produce more than 200 particles (greater than 10 nm in diameter) per cubic foot of air. Some materials produce thousands of particles (greater than 10 nm in diameter) per cubic foot of air.

Although any of (1) the composition of the emitter material, (2) the components of the non-metallic emitter connector construction, and (3) the application of the particular power waveform are known to be independently important, the prior art has not Consider the benefits of strategically combining these factors to achieve high ionization reliability and cleanliness.

The inventor's recent experiments have led the inventor to discover and find novel combinations that allow the emitter to have stable ion production and low-level unpredictable particle production. Clean and/or low particle emission ionizers have utility in many high-tech industries. Specifically, the semiconductor industry is interested in ultra-clean Net ionizers have well-defined needs. Ionizers are needed to minimize static electricity and electric fields that can destroy semiconductor devices. Particle emissions are also required to be as low as possible since foreign particles can compromise the reliability of semiconductor devices. Advanced semiconductor technology creates 24-16nm features on the wafer. For nanometer characteristics, control of particles larger than 10 nanometers is absolutely required.

It should be understood that the general description in the background section above is exemplary and explanatory only and does not limit the claimed invention.

The inventor's recent experiments have shown that (1) the composition of the silicon material and the design of the emitter, (2) the configuration and/or construction of the emitter connector, and (3) the type of supply voltage waveform should be considered emitter A synthetic, novel and advantageous combination of extremely reliable performance and low particle emission. The combination found by the inventors results in stable ion production at the emitter and low levels of unpredictable particle production. Clean and/or low particle emission ionizers have utility in many high-tech industries. Specifically, the semiconductor industry has a well-defined need for ultra-clean ionizers. Ionizers are needed to minimize static electricity and electric fields that can destroy semiconductor devices. Particle emissions are also required to be as low as possible since foreign particles can compromise the reliability of semiconductor devices. Advanced semiconductor technology creates 24-16nm features on the wafer. For nanometer characteristics, control of particles larger than 10 nanometers is absolutely required.

Matching the emitter electrode composition, including the silicone material, the electrode connectors, and the power waveform applied to the emitter has proven to be a novel approach to achieving previously unattainable levels of reliability and cleanliness in charge neutralization ionizers. Spend. At the heart of exemplary embodiments of the present invention is the combination of a non-metallic ion emitter having a material/chemical composition weight percent in the range of less than 99.99% to at least 70% silicon, emitter electrode design and surface treatment ( preparation), the connection configuration of the emitter, and the high voltage power supply operating in the high frequency range. In this combination, a high-frequency, high-voltage power supply produces a corona discharge mode, which is characterized by a low onset voltage. In an embodiment of the present invention, the ions generated from the at least one non-metallic emitter include positive ions and negative ions generated with a minimum starting HF voltage and power supply.

This combination is effective and applicable to many different types of clean room ionizers/charge neutralizers. As an example, the ionizer of an embodiment of the present invention may be considered as an embedded ionizer targeted for use in a Class 1 clean room production environment. The ionizer may have an inlet flow of clean dry air (CDA) or nitrogen, argon, or other inert gas. The gas or air passes along the silicon-based emitter in the ionization cell. The ionization cell/chamber is typically closed except for the air/gas inlet and outlet openings.

The design of the embedded charge neutralizing ionizer according to the embodiment of the present invention can use a compact power supply such as a high frequency high voltage supply. The output connector of the power supply accommodates at least one silicon type emitter. The ionization cell produces clean bipolar ionization. The air flow (or nitrogen or argon flow or other gas flow) is sufficient to move ions from the ionization emitter (cell or chamber) to the charge neutralization target.

The high frequency voltage curve of the power supply has an AC frequency range of about 1KHz to 100kHz. The peak voltage exceeds the coma initiation voltage (positive and negative) of the emitter. The ion current of the high frequency AC emitter is essentially limited by the resistance value of the silicon material.

In this current application, high voltage is defined as the potential difference between at least one ion-generating electrode and a reference electrode. In some high frequency AC ionization cells, the reference electrode can be isolated from the ionization electrode by a dielectric wall. Therefore, the possibility of direct electron/ion collapse between the electrodes (like a spark discharge) is virtually eliminated, and particle emission from the emitter can be greatly reduced. During the operating mode, ions are generated whenever the voltage amplitude exceeds the corona positive and negative onset voltages applied to the ionization electrodes.

When the high frequency AC voltage curve is periodic rather than continuous, another frequency (selective) becomes relevant. That is, a high-frequency AC voltage exceeding the starting voltage curve is generated only within a predetermined time interval. In this scheme, a high frequency AC voltage is applied to the emitter during the enable time interval (usually about 0.01 second (or less) to about 1 or more seconds), but during the non-enable time interval lower than the enable time may be applied. starting voltage. This selective high frequency voltage waveform may also essentially include an on/off high voltage mode. The normal low voltage or on/off frequency range is approximately 0.1 Hz to 500 Hz, but the frequency can be outside this range.

Some silicon-containing emitter compositions are provided as examples. They are: (a) doped crystalline silicon, (b) doped polycrystalline silicon, (c) a combination of doped silicon and silicon oxide, and (d) deposited on a doped silicon substrate. Dopants and additives are mainly intended to control the surface and volume resistivity, as well as the mechanical properties of silicon-based emitters. They are preferably taken from the group of known non-metallic dopants, such as boron, arsenic, carbon, phosphorus, and others.

Therefore, at least one exemplary embodiment of the present invention provides a method for low-emission charge neutralization, the method including the steps of: generating a high-frequency alternating current (AC) voltage; transmitting the high-frequency AC voltage to at least one non-metallic emitter electrode; wherein at least one non-metallic emitter includes at least 70% by weight silicon and less than 99.99% by weight silicon; wherein at least one non-metallic emitter includes at least one treated surface portion, and at least one treated surface portion has a destroyed oxide layer; and generating ions from at least one non-metallic emitter in response to a high frequency AC voltage.

At least one exemplary embodiment of the present invention also provides a device including elements that enable the above-described functions. For example, embodiments of the present invention provide a device for low emission charge neutralization, comprising: at least one non-metallic emitter, the at least one non-metallic emitter comprising at least 70% by weight silicon and less than 99.99% by weight silicon ; wherein the at least one non-metal emitter includes at least one treated surface portion, the at least one treated surface portion having a destroyed silicon oxide layer; and wherein the at least one non-metal emitter generates ions in response to a high frequency AC voltage.

It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention as claimed.

The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate one or more embodiments of the invention and together with the description, serve to explain the principles of the invention.

100a: Silicon emitter

100c: Silicon emitter

101a: Launching the most advanced technology

101b: Non-metallic silicon part

101c: Silicon emitter part

102a: cone

102b: Stainless steel pipe (sleeve)

102c: Skin layer/layer (surface oxide layer)

103a: shaft

103b, 104b: View

103c: Sleeve

104a: Tail

104c: concave part

105b: Recess (protrusion)

106b: View

106c: Section/Extension

107c: Groove

200: Ionization system

201: Positive (+) stick

202: Negative (-) stick

203: High Voltage Power Supply (HVDC) Supplier

204: View

205:Socket connector

206:High voltage cable

207:Silicon emitter

300a: Silicon emitter

300b: Silicon emitter

300c: Silicon emitter

301a: Shaft

301b: Shaft

301c: shaft

302a: Shaft surface

302b: Metal plating (metal coating)

302c: Treated surface part

303a:View

303c, 304c: Conductive electrode

304a: Round end

305: Measuring device

305a: Tip

306a: Cone

310a: Processed surface part (ground part, polished part)

310b: Treated surface part

311a: Section

314a:Tail

314b:Tail

314c: Tail

316b: Contact part

400a, 400b: Silicon emitter

401a, 401b: emitter part

402a, 402b: sleeve

403a, 403b: Metal extension pin (metal electrode)

404b:View

405a: View

405b: View

406a:View

406b: View

410a: Transmitter assembly

421a, 421b: tip

430: Side

431:Side

435, 436: Groove

440: Shaft

441:Exposed part

442:Tapered part

461: End

462:end

501: Silicon emitter

502: Silicon emitter

503: Silicon emitter

510:Flat tip

511: Cone

514: Round tip

516: Cone

520: Pointed tip

521: cone/cone

600: Waveform

605: Bipolar pulse

610, 615: Horizontal dotted line

700:Voltage waveform

705: Positive corona starting voltage (+)Von

710: Negative corona starting voltage (-)Von (negative corona starting voltage critical value)

750: Voltage waveform

752:Pulse train

755: Opening period

756:Closing period

758:Amplitude

760: Amplitude

780: Voltage waveform

782:Pulse train

785:Open period

786: Non-operating period

788:Amplitude

790: Amplitude

800: Voltage waveform

802:Amplitude

804: Positive voltage wave

806: Amplitude

808: Negative voltage wave

810: Positive offset

815: Negative offset

850: Voltage waveform

900a: Ionization unit

900b:View

900c: Ionizer

901a:HF HV generator

901b: Block

901c: positive and negative ions

902a: Silicon emitter

902c: Ionization unit

903a: socket

903c: Power supply

904a: Air/Gas Channel

904c: Silicon emitter

905a: Reference electrode

905b: Silicon emitter

905c: Reference electrode

906a:Exit

906b:Socket

906c: Air or gas flow

907a:Control system

907b: Reference electrode

907c: Control system

908a: Air/gas flow

908b: High voltage HF power supply

908c:Microprocessor

909a: Tip

909b: Charged target

909c: Gas pressure sensor

910a:HF plasma

910c: Stun discharge inductor detector

911c: Operation status indicator

920:Positive ion

921: Negative ions

933b: Entrance

934b:Export

934c: Ionizer outlet

960: Cavity

961:arrow

965: Charge

1000a: High frequency AC ionization rod

1001a-1008a: Silicon emitter

1003d:Silicon emitter

1004d:hole

1009c: socket

1010a: Shell

1020c, 1020d: Sleeve

1030c, 1030d: nozzle

1011a: Reference electrode

C1: Capacitor

D: Diameter

D1, D2, D3, D4: Diameter

L2: variable length

R: resistance value

Non-limiting and non-exhaustive embodiments of the present invention are illustrated with reference to the following drawings, wherein like reference numerals refer to like parts throughout the various views unless otherwise stated.

However, it should be noted that the attached drawings illustrate only typical embodiments of the present invention and therefore should not be considered to limit the scope of the present invention, as the present invention may admit of other equally effective embodiments.

Figure 1(a) is a diagram of a conventional single crystal silicon ion emitter or (generally) a non-metal ion emitter.

Figures 1(b) and 1(c) show diagrams of conventional components and assemblies of single crystal silicon emitters with metal sleeves and grooves.

Figure 2 shows a diagram of a conventional DC clean room ionization ceiling system with two single crystal silicon emitters.

Figure 3(a) is an illustration of a silicon-containing emitter, wherein the emitter includes a portion of the emitter shaft (or a treated surface portion) having a preselected surface roughness, in accordance with an embodiment of the present invention.

Figure 3(b) illustrates an emitter according to another embodiment of the present invention, wherein the emitter includes a partially conductive surface coating or a partially conductive surface coating (or other type of treated surface portion). ) of the emitter axis.

Figure 3(c) shows a diagram of a silicon-containing emitter and a device for monitoring the surface resistance and/or volume resistance of the emitter, according to an embodiment of the present invention.

Figures 4(a) and 4(b) show diagrams of silicon-containing emitters with two variations of radial compression spring sleeves and metal pins according to various embodiments of the present invention.

Figures 5(a), 5(b), and 5(c) show three silicon-containing emitters with different cone and tip structures according to various embodiments of the present invention.

FIG. 6 illustrates an HF waveform for performing a "soft" plasma clean of a silicon-containing emitter tip during the "start-up" period of the corona ionization period, according to an embodiment of the present invention.

FIG. 7(a), FIG. 7(b), and FIG. 7(c) are diagrams showing examples of high frequency power supply voltage waveforms applied to a silicon-type emitter during an operating mode according to various embodiments of the present invention.

Figures 8(a) and 8(b) are diagrams showing examples of modulated high-frequency voltage waveforms according to various embodiments of the present invention.

Figure 9(a) shows a diagram of an ionization unit/chamber of an embedded ionizer according to an embodiment of the present invention. The high frequency AC powered silicon emitter produces ions of both polarities. The air/gas flow moves the ion flow from the emitter.

FIG. 9(b) shows a diagram of an ionization unit and a gas channel according to an embodiment of the present invention.

Figure 9(c) shows a simplified block diagram of an embedded ionizer with a silicon emitter in accordance with an embodiment of the present invention.

Figure 10(a), Figure 10(b), Figure 10(c), and Figure 10(d) illustrate a simplified structure of a high-frequency AC ionization rod with silicon ions according to an embodiment of the present invention. Detail of the emitter nozzle.

In the following detailed description, for the purpose of explanation, many specific details are set forth to provide a thorough understanding of various embodiments of the present invention. Those skilled in the art will appreciate that these various embodiments of the present invention are merely illustrative and are not intended to be limiting in any way. Other embodiments of the present invention will readily suggest themselves to those skilled in the art having the benefit of this disclosure.

Furthermore, in the interest of clarity, not all conventional features of the embodiments described herein may be shown or described. Those skilled in the art will readily appreciate that in the development of any such actual implementation, many implementation-specific decisions may be required to achieve specific design goals. These design goals will vary with various implementations, and with various developers. Furthermore, it will be appreciated that such development efforts may be complex and time consuming, but are nevertheless provided with ordinary engineering assurance to those skilled in the art having the benefit of the present disclosure. The various embodiments disclosed herein are not intended to limit the scope or spirit of the disclosure herein.

Exemplary embodiments for implementing the principles of the invention will be described herein with reference to the drawings. However, the present invention is not limited to the specifically described and illustrated embodiments. Those skilled in the art will appreciate that many other embodiments are possible without departing from the basic concept of the invention. Accordingly, the principles of the present invention extend to any article of manufacture falling within the scope of the appended claims.

When used herein, the terms "a" and "an" do not indicate a limitation of quantity, but rather indicate the presence of at least one of the referenced item.

Experimentally, the inventors have shown that, for example, an embedded ionizer in combination with: (1) an emitter containing silicon (2) a pin-type electrode configured as a contact to a conductive socket, and (3) capacitive reception of a high-frequency AC voltage waveform can reliably produce an electrically balanced ion gas stream with very few particles. The above combination produces ionization with a reliability and cleanliness level that cannot be achieved by non-metallic silicon-containing emitters or high-frequency AC voltage waveforms known in the art individually. Accumulated particles with a diameter greater than or equal to 10 nm are measured during cleanliness testing. Particle counters (such as CNC (condense particle counter)) do not separate particles into size ranges.

For example, two single crystal silicon emitters (discussed in U.S. Patent No. 5,447,763) used in a clean room ionization system (e.g., a NiLstat ionization system) connected to a DC or pulsed DC (+/-20 kV) power source (similar to system 200 shown in FIG. 2) produce approximately 60 particles (diameter greater than 10 nanometers) per cubic foot of air. In contrast, the ionizer disclosed in embodiments of the present invention produces less than 10 nanoparticles of the same diameter per cubic foot of air. To put this in perspective, 10 particles greater than 10 nanometers per cubic foot of air is nominally 6 times cleaner than the cleanest prior art ionizer at the time of this application.

In the opposite paradigm, metal emitters (tungsten) are tested using conventional systems (eg, the system in US Pat. No. 5,447,763) and exhibit unacceptable clean room particle emission numbers. Our experiments using a tungsten emitter coupled to a high-frequency AC high-voltage waveform (similar to that proposed in U.S. Patent Application Publication No. 2003/0007307 (Lee et al.)) had little benefit in terms of cleanliness compared to In terms of the conventional system previously disclosed in U.S. Patent No. 5,447,763. In both cases the total particle concentration of the tungsten emitter tested was over 600 particles (larger than 10 nanometers) per cubic foot of air.

However, high-purity (99.99% or higher) single-crystal silicon emitters (such as those shown in Figures 1(a), 1(b), and 1(c)) have high resistance value (in the megaohm range). When this emitter is connected to a high frequency (HF) AC voltage supply, typically the generation of ions is insufficient for efficient charge neutralization. The main reason is because most of the HF (high frequency) current/voltage runs into the stray capacitor and does not reach the emitter tip.

Another problem associated with high purity (99.99% purity or greater) single crystal silicon emitters is that the emitters are susceptible to the development of a surface oxide "skin" (the oxide layer or skin shown by dashed line 102c surrounding the surface of silicon emitter portion 101c in FIG. 1(c)). This skin/layer 102c comprises highly insulating silicon oxide ( _SiO2 ). For example, the growth of silicon oxide on the surface of a clean silicon wafer is discussed in the following publication by Stanford University in California ("Growth of native oxide", Stanford University Nanofabrication Facility, 28 August 2003).

The net result of the silicon oxide layer growth phenomenon is that the non-metallic silicon emitter/pin is surrounded by this insulating layer and does not have a good, reliable connection to the electrical socket (and therefore, the high voltage output of the HF power supply).

Another non-metallic ion emitter is discussed in US Patent Application Publication No. 2006/0071599 by Curtis et al. This emitter is made of high purity 99.99% silicon carbide. This material is synthetic and has approximately 30% carbon. It is known in the art that silicon carbide has high hardness. Silicon carbide is also expensive to process to produce pin-type emitter structures. In addition, silicon carbide has metallic-type high conductivity. Conductive particles from synthetic materials with high carbon content are generally undesirable in the semiconductor industry.

Widespread acceptance of silicon materials in the semiconductor industry requires lower cost ion emitter materials. In addition, the mechanical properties of silicone materials make processing simple (cutting, polishing, etc.). The main goals of small concentrations of silicon dopants and additives are to control surface and volume resistivity and to improve the mechanical properties of silicon-based emitters. They are preferably drawn from the known group of non-metallic dopants, such as boron, arsenic, carbon, phosphorus, and others.

In embodiments of the present invention, silicon-based compositions with silicon content less than 99.99% by weight and greater than 70% by weight can achieve emitter resistance values in the kilo-ohm range. This resistance value is low enough to conduct high-frequency currents and support stable coma discharge. Therefore, the following two specific factors interact harmoniously to produce the observed cleanliness improvements: the composition and design of the silicon-based emitter, and the high-frequency AC emitter drive power/voltage waveform.

One advantage of the combination of silicon emitters and HF voltage waveforms is that the onset voltage of the corona discharge (approximately 1,000V to 3,000V or more) is significantly lower than the DC, pulsed DC, or low frequency used for non-metallic emitters (50Hz to 60Hz) voltage is the corona discharge starting voltage.

A possible explanation for this effect is that in the high frequency range (about 1kHz to 100kHz or higher), the voltage applied to the emitter changes polarity in the range of milliseconds or microseconds. This is why the corona charge carriers (positive and negative ions, electrons) do not have enough time to move far away from the emitter tip. In addition, the specific surface charge conservation (often named "charge memory") property of silicon-like materials may play a role in the emission of electrons at the electrode surface. This is why both positive and negative high-frequency coma starting voltages are low. With lower voltages of HF corona discharge, the particle emission from silicon-like emitters will also be small.

The scientific basis for the improvement of particle emission from the corona discharge of balanced ionizers due to the interaction between non-metallic silicon emitters and high frequency AC voltage waveforms is currently under investigation. Accepted theories of corona discharge and/or ionization and/or particle emission from non-metallic emitters do not predict or fully explain the observed experimental cleanliness.

However, it is clearly understood how to make and use the invention. The following description is written to explain how one skilled in the art of static control can make and use the present invention.

Experimental fabrication of embodiments of the present invention, including combinations of silicon-based emitter composition and HF voltage waveforms, has shown that, in some cases, ionizers with new or long-idle emitters can exhibit problems initiating HF coma discharges and reliably generating ion generation. Measurements have shown that there is a high contact resistance between the silicon emitter and the electrical socket. This high resistance is one cause of coma initiation problems in ionizers. The process of forming thicker ( ^10th to ^100th angstroms or more) oxide "skin layers" on silicon wafers in open air is documented in the reference cited above ("Growth of native oxide, Stanford University Nanofabrication Facility"). For example, over a six-day period, a _SiO2 surface layer can reach a thickness of 12 angstroms. Silicon oxide is known to be a good insulator. Therefore, this skin layer growth results in higher surface and contact resistance values for silicon-based emitters. The rate of oxide growth is variable and depends on many ambient atmospheric factors, such as oxygen and ozone concentrations (see "Silicon oxidation by ozone" at http://iopscience.iop.org/0953-8984/21/18/183001/pdf/cm9_18_183001.pdf), temperature, humidity, etc. Ozone is one of the byproducts of coma discharge and may accelerate the oxidation of silicon emitters. This phenomenon has a profound impact on the lower supply voltages of HF ionizers with silicon-based non-metallic emitters. Exemplary embodiments of the present invention include surface treatment of the silicon-based emitter to reduce the contact resistance between the emitter and the metal socket.

Figure 1(a) is a diagram of a conventional silicon emitter 100a. The silicon emitter 100a includes four distinct parts: the emitter tip 101a, the cone portion 102a, the shaft portion 103a, and the tail portion 104a. The shape and size of the emitter tip 101a depends on the amount of high voltage and current available from a high voltage power supply (HVPS), the emitter material, and the production technology and method. Emitter tip 101a is generally the most critical part of any ion emitter. The emitter tip 101a is directly exposed to the corona discharge and determines the length of the emitter's lifetime. The silicon emitter has a generally cylindrical shaft portion 103a. The shaft 103a essentially defines the length of the emitter and the distance between the taper and the socket or container connected to the high voltage power supply. Taper or cone 102a is the transition between emitter tip 101a and shaft 103a. Silicon is an inherently brittle material, and the taper angle is a compromise between the mechanical strength and electrical properties of the emitter. The tail 104a can be rounded, beveled, or chamfered. This part should assist in inserting silicon emitter 100a into a socket or container. Standard high-purity silicon emitters have a smooth surface due to chemical polishing (which is usually achieved by treatment with strong acids).

FIG. 1(b) shows an illustration of a silicon emitter with a metal sleeve. The silicon emitter 100a includes a non-metallic silicon portion 101b and a stainless steel tube 102b (or sleeve 102b), the sleeve 102b having a recess 105b. The sleeve 102b should protect the brittle emitter tip 101a from mechanical (handling) damage. The sleeve 102b should also improve the electrical connection between the non-metallic high purity silicon emitter and the metal socket or container. Views 103b and 104b show assembly views of the silicon emitter 100a and the metal sleeve 102b. View 106b presents a cross-section of the assembled emitter shaft portion 103a.

The majority (or significant portion) of the silicon shaft portion 103a fits into the metal sleeve 102b, as shown in view 103b. In order to fix the sleeve 102b on the silicon shaft portion 103a and achieve reliable electrical contact between them, at least one protruding portion 105b (recess) is usually made on the sleeve 102b. Considering the tolerances on the dimensions of all three components (diameter of the silicon emitter shaft, inner diameter of the sleeve, and depth of the recess), the assembly operation is quite challenging (see Figure 106b. Cross-sectional view, where emitter shaft portion 103a and sleeve 102b are not concentric due to recess 105b).

Figure 1(c) shows an illustration of another design of silicon emitter 100c. Silicon emitter portion 101c is shown with a surface oxide layer ("skin layer") 102c, indicated by the dashed line. The silicon emitter 100c includes a silicon emitter portion 101c and a sleeve 103c. The sleeve 103c has a recess 104c. Sleeve 103c may have one or more sections/extensions 106c having grooves 107c (including various radii, grooves and necks, requiring special equipment to manufacture) . The emitter assembly is shown in view 105c. This design allows keeping the emitter in the nozzle and using extension 106c to plug extension 106c into a different socket or container.

FIG. 2 shows a diagram of a conventional DC clean room ionization system 200, similar to that used in U.S. Patent No. 5,447,763. The ionizer has a pair of rods, a positive (+) rod 201 and a negative (-) rod 202, with single crystal silicon emitters. The rods are connected to dedicated positive and negative high voltage power (HVDC) supplies 203 (housed in a base). A cross-sectional view of the emitter rods is shown in view 204. The ends of the rods 202 have socket connectors 205 and high voltage cables 206 connected to the HV DC power supply 203. The socket connectors 205 house the silicon emitters 207 shown in view 204. The rest of the rod 202 serves as a protection for the silicon emitter 207, the socket connector 205, and the HV cable 206 from damaging forces. The rod is designed so that the rods 201, 202 are replaceable.

At least some of the objectives of exemplary embodiments of the present invention are to facilitate low particle emission by an economical silicon-based charge neutralization system. The composition of the silicon-based emitter (having less than 99.99% and greater than 70% silicon by weight) combined with high frequency corona discharge can achieve the goal of low particle emission. For non-metallic silicon electrodes in the ionization system, the next major goal is to provide a reliable electrical connection between the silicon-based emitter and the HF high voltage power supply.

FIG. 3( a) shows an illustration of a silicon-based emitter 300 a according to an embodiment of the present invention, wherein the silicon-based emitter 300 a includes a ground or polished portion 310 a of a shaft 301 a (i.e., a processed surface portion 310 a ) that can be plugged into a high voltage socket (not shown). This portion 310 a of the shaft surface 302 a has a roughness H in the range of approximately 0.5 microns to 10 microns (see view 303 a ). During surface treatment, such as by polishing, the oxide “skin layer” previously on the shaft surface 302 a is destroyed and removed, or otherwise removed. The emitter shaft surface profile resulting from polishing enables multiple points of contact with the high voltage socket (not shown). Optionally, a similar surface treatment may be applied to the rounded end 304a of the tail 314a of the silicon-based emitter 300a. The emitter tip 305a, the cone 306a, and the portion 311a of the shaft 301a have a generally chemically polished surface.

Yet another embodiment of a silicon emitter is illustrated in Figure 3(b). According to this embodiment of the invention, the silicon emitter 300b includes an emitter axis The portion 310b of the portion 301b (ie, the treated surface portion 310b), the portion 310b has a metal plating or metal coating 302b (or a conductive plating or metal coating 302b) such that the portion 310b of the shaft portion 301b is a good surface conductor and protects the contact portion 316b of the silicon emitter 300b from oxidation over time. Contact portion 316b may be in tail 314b of emitter shaft portion 301b.

Various known methods of silicon plating (e.g., such as vacuum deposition, electrolytic plating, spraying, and others) may also be used. Electroplating materials such as metals may include, for example, nickel, copper, silver, gold, and other metals and alloys acceptable in the semiconductor industry.

FIG. 3( c ) shows a diagram of a silicon-containing emitter and an apparatus for monitoring the surface resistance and/or volume resistance of the silicon-containing emitter according to an embodiment of the present invention. This shows an example of an electrical property control operation of a silicon-based emitter 300 c as shown in FIG. 3( c ). The control and/or monitoring includes measuring the resistance value or monitoring the resistance value and/or composition of the silicon-based emitter 300 c or the processed surface portion 302 c of the silicon-based emitter 300 c. Conductive electrodes 303 c and 304 c are respectively attached or connected to the polished portion 302 c (or the processed surface portion 302 c) and the tail 314 c of the emitter shaft 301 c of the silicon-based emitter 300 c. A standard resistance R measuring device 305 can be used to measure the resistance R and record the resistance R measurement. In this way, the resulting surface and volume resistivity and emitter composition can be monitored. The normal properties and composition required for a silicon-based emitter (having a weight percentage of less than 99.99% to at least 70% silicon) should have a resulting resistance in the kilo-ohm range. After surface treatment and control operations, the silicon-based emitter 300c can be plugged into a standard metal socket (not shown) to minimize the formation of a new layer of silicon oxide "skin".

At least some of the exemplary embodiments presented herein allow for solving two failure problems: (1) establishing a reliable electrical connection between a non-metallic silicon emitter and a socket; and (2) protecting the contact portion of the emitter from oxidation.

Figures 4(a) and 4(b) illustrate diagrams of silicon-containing emitters with two variations of radial compression spring sleeves and metal pins, in accordance with various embodiments of the invention. The silicon-containing emitter and metal pin are inserted into the sleeve as discussed below. The silicon emitter 400a of Figure 4(a) in the embodiment of the present invention will be described first. According to this exemplary embodiment, silicon-based emitter 400a includes an emitter portion 401a, wherein the silicon portion of emitter portion 401a has a reduced length/shaft diameter ratio. A short emitter portion 401a is connected to the sleeve 402a from one side 430 of the sleeve 402a of a metal radial compression spring. The other side 431 of the sleeve 402a is connected to a solid metal extension pin 403a. The metal pins 403a and 403b discussed herein may be metal electrodes 403a and 403b inserted into sleeves 402a and 402b respectively. This pin 403a may have at least one (or more) grooves and a variable length "L2", as required by the design of the socket and ionization unit (including the reference electrode). For example, pin 403a includes grooves 435 and 436, but in other embodiments, pin 403a may have only a single groove. Pin 403a may be, for example, a solid metal pin or tube. Traditional, CNC, or automated metal cutting machines, or other metal processing methods may be used to manufacture pin 403a. View 405a illustrates an illustration or diagram of an emitter assembly 410a having a silicon emitter 400a, according to this exemplary embodiment. Sleeve 402a has a significantly larger area of contact The emitter part 401a is compared to the conventional sleeve 102b with the recess 105b shown in Figure 1(a) and Figure 1(b). The result is a more reliable electrical connection and less mechanical stress applied to the brittle emitter portion 401a. The design of silicon emitters with metal sleeves has some requirements to prevent "secondary" corona discharges from the edge of the sleeve to the nearby reference electrode. The main parameters that should be considered are illustrated in view 406a: D, D is the diameter of the silicon emitter shaft 440; L, L is the length of the exposed portion 441 of the silicon emitter shaft 440; α, α is the cone of the shaft 440. the taper angle of the shaped portion 442; and S, where S is the thickness of the sleeve 402a. For a high concentrated electric field on emitter tip 421a of emitter portion 401a (or on emitter tip 421b of emitter portion 401b), the first ratio S/D should be in the range of approximately 0.03 to 0.06. Another requirement regarding the distance between the emitter tip 421a and the sleeve 402 is the second ratio L/S: the second ratio L/S should be in the range of (2-5)/[tan{tangent}(0.5α)] within range. Parameter α is the taper angle of the tapered portion of the shaft portion 440 of at least one non-metallic emitter portion 401a or 401b. In one embodiment of the present invention, these conditions for the new silicon emitter design will meet several criteria/specifications: reliable electrical connection, good mechanical strength, and "secondary" electricity that will generate particle emission from the metal part. Minimal possibility of fainting.

FIG. 4(b) shows an illustration of another embodiment of a silicon emitter 400b, including another configuration of a sleeve 402b of a metal radial compression spring, wherein the silicon emitter 400b and the sleeve 402b are concentric. In this case, the emitter 400 includes an emitter portion 401b having a diameter D1, and one end 461 of the sleeve 402b having a diameter D3. The emitter portion 401b has an emitter tip 421b. The portion 403b is a solid metal pin 403b having a diameter D4, and the other end 462 of the sleeve 402b has a diameter D2. The difference in diameters of the emitter portion 401b and the sleeve 402b (D1>D3) generates the required compressive force to provide reliable or good electrical contact between the emitter portion 401b and the sleeve 402b. Similarly, the difference in diameters (D2<D4) provides a reliable or good electrical connection between the sleeve 402b and the metal pin 403b. Views 404b and 406b show assembled views of the silicon-based emitter 400b. View 405b is a cross-sectional view showing the emitter portion 401b and the sleeve 402b with a large contact area, minimal contact pressure and local stress according to this exemplary embodiment. The assembly operation is simplified. Both exemplary embodiments (silicon emitters 400a and 400b) use a minimal amount of expensive silicon material, have a large, reliable contact area between the non-metal emitter shaft and the metal sleeve, and a good dimensional match to a standard socket or receptacle.

In some cases, silicon-based emitters have problems initiating high-frequency coma discharge and reliably generating ion generation, despite having normal surface/volume resistance values and good electrical connection to high voltage sockets. Our experiments have shown that the core of this problem is due to the formation of a thick insulating oxide "skin" on the surface of the emitter tip (the "working scaffold" of the emitter). Another exemplary embodiment of the present invention solves this problem. The shape of the tip of the silicon-containing emitter has a certain absolute effect on the formation rate and thickness of the insulating oxide "skin".

Figures 5(a), 5(b), and 5(c) illustrate diagrams of three silicon-containing emitters with different tapers and tips, according to various embodiments of the present invention. structure. Figure 5(a), Figure 5(b), and The various tip structures and cone structures shown in Figure 5(c) determine the operating HF corona starting voltage and ionization current parameters.

In Figure 5(a), a silicon emitter 501 with a flat truncated tip is shown. This tip design is prone to generate annular high-frequency corona discharge (where the flat tip 510 is connected to the tapered portion 511 of the silicon emitter 501). The silicon emitter 501 can reduce ion current density and particle emission. However, it is characterized by a higher starting HF corona voltage. The tapered portion 511 has an angle α relative to the flat tip 510 .

Silicon emitter 502 (Fig. 5(b)) has a small rounded tip 514 with a radius Z in the range of approximately 60 microns to 400 microns, which is cheaper to produce and minimizes corona currents Fluctuations. Taper 516 (of silicon emitter 502 ) extends from small rounded tip 514 .

The pointed silicon emitter 503 (Fig. 5(c)) has a pointed tip 520 having a radius Y in the range of approximately 40 microns to 50 microns (or less). This silicon emitter 503 has the lowest corona onset voltage V _on . However, the silicon emitter 503 has the highest ion current density and the highest rates of sputtering, erosion, and oxide "skin layer" growth. The silicon emitter 503 is preferably used for ionization of oxygen-free gas, such as nitrogen or argon. The taper/conical portion 521 of the silicon emitter 503 preferably has an angle α relative to the pointed tip 520 in the range of approximately 10 degrees to 20 degrees. All silicon emitters (501, 502, 503) have compositions according to exemplary embodiments of the present invention and when installed in embedded ionizers, ionization rods, and other charge neutralizers driven by HF AC voltages When, low particle numbers can be provided. The sharpness and curvature of the tip (ie, the structure of the tip) affects or determines ionizer operating parameters, including onset voltage, ion current, and ion balance, but they do not affect the scope of the present invention.

Another exemplary embodiment of the present invention addresses the problem of oxide "skin" growth on silicon emitter tips. This embodiment uses a specific mode of coma discharge to clean the silicon emitter tips from the oxide skin and assist in ionizer activation independent of emitter profile.

FIG. 6 illustrates an HF waveform for performing a "soft" plasma clean of a silicon-containing emitter tip during the "start-up" period of the corona ionization period, according to an embodiment of the present invention.

A high voltage "HF start" type waveform 600 is applied to the emitter. This mode of high voltage drive provides a set of short duration bipolar voltage surges (numbering from 1 to hundreds of bipolar pulses 605) to the emitter during the start-up period (labeled as the Ts period). Due to the very short duration of the power curve (millisecond, microsecond or less range), the HF corona associated with the plasma has very limited energy. This approach prevents both the temperature increase of the emitter tip and the surface damage of the emitter tip (sputtering, erosion, and particle emission). The short duration HF plasma burst performs only a "soft" cleaning of the emitter tip from the silicon oxide skin layer. The duration of the "start-up" time period Ts, the amplitude of the burst pulse, and the number of pulses can vary and depend on the thickness of the silicon oxide skin layer, the gas medium, the design of the emitter tip, etc. The voltage amplitude of the HF burst pulse is significantly higher (about 25% to 100% or more) than the normal (operating) coma start voltages (positive (+) Von and negative (-) Von) (shown in FIG. 6 as two horizontal dashed lines 610 and 615, respectively). The initial "start-up" mode helps to start the high frequency coma discharge and ion generation for normal/operation. During the normal/operation mode (during time Top), the high voltage amplitude can be only 10%-20% above the coma start voltage ((+)Von or (-)Von) to minimize particle emission. In the continuous operation mode, the HF coma discharge can protect the silicon emitter from oxidation in the clean dry gas medium. Therefore, soft plasma cleaning of at least one non-metallic emitter is performed during the start-up period of the corona ionization period with a voltage/power waveform different from the voltage/power waveform during the operation period.

Figures 7(a), 7(b), and 7(c) are diagrams illustrating examples of high-frequency power supply voltage waveforms applied to a silicon emitter during an operating mode, according to embodiments of the present invention. Show. Different operating HF voltage waveforms effectively produce bipolar ionization of the silicon emitter. The function of the high-frequency AC voltage is to generate ions of two polarities (positive ions and negative ions) with a minimum driving voltage. In order to generate ions, the peak voltage (positive and negative peak voltage) must exceed the corona onset voltage. As shown in Figure 7(a), the voltage waveform 700 is continuous, but the voltage waveform can also be adjusted to be continuous or discontinuous and periodic.

FIG. 7(a) shows a continuous voltage waveform 700 having a frequency range from about 1 kHz to up to 100 kHz. The positive and negative voltage amplitudes of the voltage waveform 700 are higher than the positive coma initiation voltage (+) Von 705 and lower than the negative coma initiation voltage (-) Von 710. This voltage waveform 700 provides maximum power to the silicon-based emitter described herein and produces maximum ion current.

Figure 7(b) shows a diagram of a voltage waveform 750 that includes a plurality of pulse trains 752 having an "on" period 755 and an "off" period 756. The voltage waveform 750 includes at least one modulation portion, where each modulation portion includes a pulse train 752 having an on period 755 and an off period 756 . During the on period 755 in the burst 752, the voltage waveform 750 has an amplitude 758 that exceeds the positive corona onset voltage threshold 705 and exceeds the negative corona onset voltage threshold 710 for the particular emitter. During the off period 756 in the burst 752, the voltage waveform 750 has an amplitude 760 that does not exceed the corona onset voltage thresholds 705 and 710. In the example of Figure 7(b), this amplitude 760 is a voltage magnitude of approximately zero. Additional details of voltage waveforms 700, 750, and 780 in Figures 7(a), 7(b), and 7(c), respectively, are also described in No. 8,009,405 co-owned by et al. During the "off" period 756 (which can be a small duty factor), corona discharge (ion production) and particle emission cease. The operating factor can vary from as low as about 100% to about 0.1% or less, depending on the desired ion output. The minimum operating factor helps suppress particle emission and emitter erosion rates.

FIG. 7(c) shows an illustration of another variation of voltage waveform 780 in which the duty factor approaches approximately 100%, but the voltage amplitude applied to the silicon emitter periodically drops to a value below the coma initiation voltage (in the range of approximately 90% to approximately 50% or less of the coma initiation voltage). This waveform has the advantage of minimizing particle emission and high voltage swings (voltage/electric field variations).

Voltage waveform 780 includes at least one modulation portion, where each modulation portion includes a pulse train 782 having an on period 785 and an inoperative period 786 . During the on period 785 in the pulse train 782, the voltage waveform 780 has an amplitude 788 that exceeds the positive corona onset voltage threshold ((+)Vmax) 705 for the particular emitter and exceeds the negative corona onset voltage threshold ((+)Vmax). (-)Vmax)710. During the non-operation period 786 in the burst 782, the voltage waveform 780 has an amplitude 790 that does not exceed the corona onset voltage thresholds 705 and 710, but the amplitude 790 is greater than zero volts.

FIG. 8(a) and FIG. 8(b) illustrate examples of modulated high-frequency voltage waveforms according to embodiments of the present invention. FIG. 8(a) shows a continuously modulated voltage waveform 800 generated by mixing (combining) high-frequency and low-frequency voltages. The low-frequency component (or offset voltage) is shown in FIG. 8(b). This voltage waveform 850 mainly generates ions by a high-frequency component (similar to the voltage waveform 700 shown in FIG. 7(a)) and moves ions from the emitter by a low-frequency component.

Embedded ionizers with silicon-type emitters can be used in the most critical operations/processes in the semiconductor industry (e.g., environments such as Airborne Particulate Cleanness Class 1). FIG. 9(a), FIG. 9(b), and FIG. 9(c) present block diagrams of embedded ionizers and diagrams of simplified views of ionization units. With the design of embedded ionizers, the application of HF frequency voltages can be similar to the waveform shown in FIG. 8(a), where the frequency range extends from about 20kHz up to about 100kHz.

Figure 9(a) shows a diagram of an ionization unit/chamber of an embedded ionizer according to an embodiment of the present invention. The high-frequency AC powered silicon emitter 902a generates ions of two polarities. Air/gas flow 908a moves the ion flow from silicon emitter 902a. Also shown in Figure 9(a), the ionization unit 900a is connected to the HF HV generator 901a. Silicon emitter 902a is positioned in socket 903a and connected via capacitor (C1), which is connected to HF HV generator 901a. The silicon emitter 902a may have a ground or metallized portion of the shaft, as previously discussed in Figures 3(a) and 3(b), respectively, to provide a reliable connection to the socket 903a.

Silicon emitter 902a is generally positioned in the middle portion of air/gas channel 904a. Preferably, reference electrode 905a is positioned on the outside of channel 904a and near the outlet 906a of channel 904a. Reference electrode 905a is connected to control system 907a. When the peak voltage (positive or negative voltage) of the high-frequency AC voltage (applied to the HF HV generator 901a) exceeds the corona onset voltage, positive ions 920 and negative ions 921 are generated by the HF HV generator 901a. Air/gas flow 908a from an external source (not shown) is still required to move the resulting ion cloud toward a distant target for charge neutralization (not shown). The corona discharge near the tip 909a of the silicon emitter 902a generates an intense HF plasma 910a, in which ions and electrons are near the tip 909a of the silicon emitter 902a. The corona onset voltage is approximately (+) 5 to 6 kV for positive ions and (-) 4.5 to 5.5 kV for negative ions.

By means of the previously discussed methods, apparatus, and mechanisms (such as the composition of the ion emitter, the design of the ion emitter, and the combination of the voltage waveform of the supply), the generation/emission of corona byproducts, such as particles in the plasma, is minimized.

Figure 9(b) shows another view 900b of the ionization unit and an illustration of the gas channels in block 901b, according to an embodiment of the present invention. Channel 902b has an inlet 933b and an outlet 934b. The silicon emitter 905b and socket 906b can be made into interchangeable units positioned in the cavity 960 of the channel 902b. Emitter socket 906b and reference electrode 907b are connected to a high voltage HF power supply 908b. The ionized gas flow (indicated by arrow 961) moves the ion cloud to charged target 909b (like a wafer), and the ion cloud will neutralize these charges 965 on charged target 909b.

FIG. 9(c) shows a simplified block diagram of an embedded ionizer 900c having a silicon-based emitter 904c according to an embodiment of the present invention. Positive and negative ions 901c are generated inside the ionization unit 902c. A high voltage HV-HF power supply 903c provides the voltage and current required to generate the positive and negative ions 901c. The power supply 903c transmits a high frequency AC voltage to the silicon-based emitter 904c through a capacitor C1. The voltage on the silicon-based emitter 904c is relative to a reference electrode 905c.

A pressurized source of air, nitrogen, or argon is connected to the embedded ionizer 900c via the inlet to generate an air or gas stream 906c. The air or gas stream 906c entrains the positive and negative ions 901c and carries the positive and negative ions 901c through the ionizer outlet 934c toward the target (e.g., target 909b in FIG. 9(b)).

The embedded ionizer 900c includes a control system 907c (the control system 907c includes a microprocessor 908c), a gas pressure sensor 909c, a corona discharge sensor 910c, and an operating status indicator 911c. Embedded ionizer 900c typically operates in semiconductor tools with wafer loading/unloading operations. This is why embedded ionizer 900c can have long idle ("off") periods without corona discharge and gas flow. During these periods of time, a layer of silicon oxide may grow on the tip of the silicon emitter. As previously discussed in the exemplary embodiments illustrated in Figures 3(a) and 6, control system 907c initiates the gas ionization process by initiating high voltage power supply 903c in "start" mode. The corona discharge sensor 910c and the microprocessor 908c continuously monitor the state of the corona discharge until a point of strong and stable corona and ion generation is reached. Afterwards, the control system 907c and the power supply 903c switch to the normal operation mode.

Figures 10(a), 10(b), 10(c), and 10(d) illustrate a simplified structure of a high-frequency AC ionization rod 1000a according to an embodiment of the present invention. Detail with nozzle with silicon-based ion emitter. Figures 10(a) and 10(b) illustrate views of a high frequency AC ionization rod 1000a with a plurality of primitive silicon emitters 1001a to 1008a (as an example). Each silicon emitter has a stainless steel sleeve. Stainless steel sleeves are shown as sleeve 1020c in Figure 10(c) and sleeve 1020d in Figure 10(d). Each stainless steel sleeve is installed in the nozzle. Each nozzle has a socket and optionally one or two air/gas injection holes. Cross-sectional views of the nozzles are shown as nozzles 1030c in Figure 10(c) and nozzles 1030d in Figure 10(d).

The socket 1009c is connected to a common high voltage bus, and the holes and manifold (not shown) are located inside the housing 1010a of the high frequency AC ionization rod 1000a. Cross-sectional view 1040 of nozzle 1030d illustrates the relative position of silicon emitter 1003d (having the sleeve and groove as previously discussed in Figures 4(a) and 4(b)) and hole 1004d. The busbar distributes HF power from the high voltage AC power supply to each nozzle and emitter. The HF-HV power supply with a microprocessor type control system is preferably located within the same housing 1010a. The silicon ion emitter receives an HF AC voltage, in the range of approximately 6 kV to 8 kV, with a fundamental frequency of approximately 10 kHz to 26 kHz (similar to that shown in Figure 7(a)). This HF high voltage generates corona discharge between each silicon emitter 1001a to 1008a and the reference electrode 1011a. This high frequency AC voltage alone is sufficient to produce clean bipolar ionization when the emitter composition ranges from less than 99% to greater than 70% silicon. As discussed previously, high frequencies by themselves cannot move the ion cloud away. The high frequency AC ionization rod 1000a is typically mounted in a flat panel or semiconductor tool at a short distance from the target (eg, approximately 50 mm to 300 mm). In this case, the electric field of the charged target (not shown) attracts ions of opposite polarity. However, for efficient charge neutralization at longer distances (eg, approximately 400 mm to 1500 mm), the ion cloud requires the assistance of air/gas flow or electric fields, or a combination of both. Typically, HF ionization rods are used in combination with HEPA filters that provide laminar flow of clean air.

FIG. 8a shows a voltage waveform 800 modulated at a high frequency, which generates an additional low frequency field (having a frequency of about 0.1 Hz to 200 Hz) to assist in ion transport to the target. During period T2, the amplitude 802 of the positive voltage wave 804 and the amplitude 806 of the negative voltage wave 808 are nearly equal, and therefore, the offset voltage is close to zero, and the ion cloud oscillates near the silicon emitter. Conversely, during periods such as T1, the voltage waveform 800 has a positive offset 810, and the positive polarity ion cloud (which repel each other) moves to the target (see FIG. 8(b)). Similarly, during time periods such as T3, the voltage waveform 800 has a negative offset 815, and the negatively polarized ion cloud (which repel each other) moves toward the target. The frequency and amplitude of the offset voltage depends on the distance between the high frequency AC ionization rod 1000a and the target.

High frequency AC ionization rod 1000a with a silicon emitter is capable of producing low emissions to produce clean air/gas ionization and neutralize fast moving large objects such as flat panel displays at distances such as approximately 400mm up to 1500mm ) charge.

Another embodiment of the present invention provides a method for low emission charge neutralization, wherein at least one of the above-mentioned non-metallic emitter poles includes a reduced silicon portion length/axial portion diameter ratio.

Another embodiment of the present invention provides a method for low emission charge neutralization, wherein the above-mentioned sleeve includes a metal radial compression spring sleeve, and wherein the difference in diameter of at least one emitter, metal pin, and sleeve Compressive force is generated to provide a reliable electrical connection between at least one emitter, the metal pin, and the metal electrode.

Another embodiment of the present invention provides an apparatus for low emission charge neutralization, wherein at least one of the above-mentioned non-metallic emitter poles includes a reduced length/axial diameter ratio.

Another embodiment of the present invention provides a device for low emission charge neutralization, wherein the above-mentioned sleeve includes a metal radial compression spring sleeve, and wherein the difference in diameter of at least one emitter, a metal pin, and the sleeve generates a compression force to provide a reliable electrical connection between at least one emitter, a metal pin, and a metal electrode.

Another embodiment of the invention provides an apparatus and method for producing a reliable, low particle emission charge neutralizer by combining a non-metallic ion emitter of silicon having a chemical composition weight percentage ranging from less than 99.99% to at least 70%, the geometry and surface treatment (preparation) of the emitter, and the connection configuration between the emitter and a high voltage power supply operating in the high frequency range. In this combination, the emitter reliably produces a high frequency coma discharge characterized by a low starting voltage and low particle emission. This combination is effective for many different types of clean room ionizers/charge neutralizers targeted for use in Class 1 clean rooms. The combination of a silicon-containing emitter and a high-frequency AC voltage produces an ionizer that is cleaner (based on the number of particles larger than 10 nanometers) than conventional ionizers. This improvement in cleanliness has been experimentally determined by the inventors.

The above description of illustrative embodiments of the invention, including what is set forth in the Abstract, is not intended to be exhaustive or to limit the invention to the precise forms disclosed. Although specific embodiments and examples of the invention are described herein for illustrative purposes, various equivalent modifications are possible within the scope of the invention, as those skilled in the art will recognize.

In light of the above detailed description, these modifications may be made to the present invention. The terms used in the claims below should not be construed to limit the present invention to the specific embodiments disclosed in the specification and claims. Rather, the scope of the present invention is determined entirely by the claims below, which are to be interpreted in accordance with established principles for interpretation of claims.

300a: Silicon emitter

301a: Shaft

302a: Shaft surface

303a: View

304a: Round end

305a: Tip

306a: Cone

310a: Treated surface part (grinding part, polished part)

311a: Section

314a:Tail

Claims (20)

A device for charge neutralization, comprising: a silicon-based emitter, the emitter having a tip, a cone, a shaft and a tail; wherein the cone is between the tip and the shaft; wherein the shaft is between the cone and the tail; wherein the emitter comprises a processed surface on at least one of the shaft or the tail, the processed surface having a higher conductivity or a lower conductivity than the cone and the tip. Resistivity; wherein the emitter comprises an assembly of a non-metallic portion and a metallic portion; wherein the metallic portion is constructed as a compression spring sleeve positioned on the shaft of the emitter; wherein the assembly comprises a first ratio S/D in the range of about 0.03 to 0.06; wherein S is a thickness of the sleeve receiving the emitter; and wherein D is a diameter of the shaft of the emitter. The device of claim 1, wherein the emitter includes a second ratio L/S in the range of (2-5)/[tan{tangent}(0.5 α )]; where L is the A length of an exposed portion of the shaft portion; where α is a taper angle of a tapered portion of the shaft portion of the emitter. The apparatus of claim 1, wherein the tip of the emitter generates ions in response to the treated surface of the emitter being contacted with an alternating current (AC), the AC current having a frequency range of 1 kHz to 100 kHz. The device of claim 1, wherein the treated surface of the emitter includes a region having a roughness in the range of 0.5 microns to 10 microns. The device of claim 1, wherein the treated surface of the emitter includes a metal plating or metal coating. The device of claim 1, wherein the emitter includes greater than 72.00% silicon by weight and less than 99.99% silicon by weight. A device for charge neutralization, comprising: a silicon-based emitter, the emitter having a tip, a cone, a shaft and a tail; wherein the cone is between the tip and the shaft; wherein the shaft is between the cone and the tail; wherein the emitter includes a treated surface on at least one of the shaft or the tail, the treated surface having a higher conductivity or a lower resistivity than the cone and the tip; wherein the emitter includes a second ratio L/S in the range of (2-5)/[tan{tangent}(0.5 α )]; wherein L is a length of an exposed portion of the shaft of the emitter; wherein S is a thickness of a sleeve receiving the emitter; and wherein α is a taper angle of a tapered portion of the shaft of the emitter. The device as described in claim 7, wherein the emitter comprises greater than 72.00 weight percent silicon and less than 99.99 weight percent silicon. The apparatus as claimed in claim 7, wherein the tip of the emitter generates ions in response to the treated surface of the emitter being contacted with an alternating current (AC), the AC current having a frequency range of 1 kHz to 100 kHz. The device of claim 7, wherein the treated surface of the emitter includes a region having a roughness in the range of 0.5 microns to 10 microns. The device of claim 7, wherein the treated surface of the emitter includes a metal plating or metal coating. An ionization rod includes: a high voltage generator; and a silicon-based emitter, the emitter coupled to the high voltage generator and configured to generate positive ions and negative ions, the emitter having a tip, a cone, a shaft, and a tail; wherein the cone is between the tip and the shaft; wherein the shaft is between the cone and the tail; wherein the emitter includes a processed surface on at least one of the shaft or the tail, the processed surface having a higher conductivity than the cone and the tail. The tip has a higher conductivity or a lower resistivity; wherein the emitter comprises an assembly of a non-metallic portion and a metallic portion; wherein the metallic portion is constructed as a compression spring sleeve positioned on the shaft of the emitter; wherein the assembly comprises a first ratio S/D in the range of about 0.03 to 0.06; wherein S is a thickness of the sleeve receiving the emitter; and wherein D is a diameter of the shaft of the emitter. The ionization rod of claim 12, further comprising a socket, wherein the emitter is connected in the socket to receive a high voltage signal from the high voltage generator. An ionization rod as described in claim 13, wherein the high voltage generator is configured to provide at least a coma starting voltage to the emitter via the sleeve and the socket. The ionization rod of claim 12, wherein the emitter is coupled to the high voltage generator via the sleeve and a metal pin. An ionization rod as described in claim 12, wherein the emitter includes a second ratio L/S in the range of (2-5)/[tan{tangent}(0.5 α )]; wherein L is a length of an exposed portion of the axis of the emitter; and wherein α is a taper angle of a tapered portion of the axis of the emitter. The ionization rod of claim 12, wherein the high voltage generator is configured to provide an alternating current (AC) in a high frequency range of 1 kHz to 100 kHz and high enough to cause the emitter to emit positive ions and negative ions voltage. The ionization rod as described in claim 12 further includes a measuring device for monitoring a surface resistance value and/or volume resistance value and composition of the emitter. An ionization rod as described in claim 12, wherein the treated surface of the emitter includes a metal plating or a metal coating. An ionization rod as described in claim 12, wherein the emitter comprises greater than 72.00% by weight of silicon and less than 99.99% by weight of silicon.