CN107624083B

CN107624083B - Silicon-based charge neutralization system

Info

Publication number: CN107624083B
Application number: CN201680028350.6A
Authority: CN
Inventors: 彼得·格夫特; 阿列克谢·克洛奇科夫
Original assignee: Illinois Tool Works Inc
Current assignee: Illinois Tool Works Inc
Priority date: 2015-03-23
Filing date: 2016-03-03
Publication date: 2020-09-01
Anticipated expiration: 2036-03-03
Also published as: TWI772814B; EP3275060A1; CN107624083A; JP6673931B2; TWI699056B; KR20170131529A; KR102549253B1; JP2023038948A; TW201707320A; EP3275060B1; JP2020095972A; WO2016153755A1; JP2018518794A; TW202110017A; JP7197530B2; JP7371213B2; TW202247555A

Abstract

An embodiment of the present invention provides a method for low emission charge neutralization, comprising: generating a high frequency Alternating Current (AC) voltage; transmitting a high frequency AC voltage to at least one non-metallic emitter (300 a); wherein the at least one non-metallic emitter comprises at least 70 wt.% silicon and less than 99.99 wt.% silicon; wherein the at least one emitter comprises at least one treated surface portion (310a) having a destroyed oxide layer; and generating ions from the at least one non-metallic emitter in response to the high frequency AC voltage. Another embodiment of the present invention provides an apparatus for low emission charge neutralization, wherein the apparatus can perform the above-described operations.

Description

Silicon-based charge neutralization system

Cross Reference to Related Applications

The section of the U.S. patent application entitled "SILICON emitter FOR ionizer WITH HIGH FREQUENCY waveform" (SILICON emitter FOR ionization WITH HIGH FREQUENCY wave) "filed on application No. 12/456526, 6/18/2009, is filed on and claims priority from this U.S. patent application. This U.S. patent application claims the benefit and priority of U.S. provisional application No. 61/132422 filed on 18.6.2008. U.S. patent application nos. 12/456626 and 61/132422 are incorporated herein by reference.

Statement regarding federally sponsored research

Not applicable to

Microfilm appendix

Not applicable to

Background

1. Field of the invention

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

With AC ionizers, each emitter receives a high positive voltage during one time period and a high negative voltage during another time period. Thus, each emitter generates a corona discharge with positive and negative ion outputs.

The stream (cloud) of positive and negative ions is directed towards a charged target in order to neutralize the charge and prevent technical problems associated with electrostatic charging.

2. Description of the related Art

The background description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.

The ion emitter of the charge neutralizer generates both positive and negative ions and supplies them into the surrounding air or gas medium. To generate gas ions, the amplitude of the applied voltage must be high enough to create a corona discharge between at least two electrodes arranged as ionization cells. In the ionization cell, at least one electrode is an ion emitter and the other electrode can be a reference electrode. The ionization unit may also comprise at least two ionization electrodes.

In addition to useful positive and negative gas ions, the charge neutralizer emitters may generate and emit corona byproducts including undesirable particles. In semiconductor processes and similar cleaning processes, particle emissions/contaminants are associated with defects, product reliability issues, and lost profits.

Several factors known in the art affect the amount of unwanted particle emission. Some of the first factors include, for example, the material composition, geometry, and design of the ion emitter. The second factor includes the arrangement of the emitter connections to the high voltage power supply. Another key factor is associated with the distribution of electrical power (amplitude and time dependence of high voltage and current) applied to the ion emitters.

The power waveform can be used to control the voltage profile applied to the emitter by the high voltage power supply. The voltage/current waveforms may be used to control ion generation and particle emission by the emitter.

The corona discharge may be powered by a DC voltage, an AC voltage or a combination of both voltages. As will be discussed below, 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. The high voltage output may be continuous rather than continuous. That is, the magnitude of the voltage output may vary over time or be periodically turned off.

The material composition of the emitter is known to affect the particle emission level of the ionizer. Common emitter materials include stainless steel, tungsten, titanium, silicon oxide, single crystal silicon, silicon carbide, and other nickel or gold plated metals. The list is not complete. According to the inventors' experience, metallic type emitters tend to generate more particles due to corona-associated erosion and splashing. Furthermore, metallic particles or generally highly conductive particles are commonly considered "killer particles" in the semiconductor industry (i.e., particles that can short-circuit closely located conductive traces of a wafer/chip). Thus, within the framework of the present patent application, the inventors basically consider non-metallic ion emitters, as will be discussed below.

Of these materials, Scott Gehlke proposes ultra-clean (purity in excess of 99.99%) single crystal silicon in U.S. patent No. 5447763 from the perspective of low particle emission. This single crystal silicon has been adopted by the semiconductor industry as a de facto clean emitter standard. Ultra-clean silicon carbide (at least 99.99% pure) proposed by Curtis et al in U.S. patent application publication No. 2006/0071599 is another non-metallic material. However, silicon carbide emitters are expensive and prone to emit undesirable particles.

Known ionizers with a monocrystalline silicon emitter are powered by two high voltage DC power supplies. Systems such as the indoor ionization system "NiLstat" 5000(Ion Systems, inc. good jade, inc.) for clean room ceiling installations typically produce less than 60 particles per cubic foot of air with diameters greater than 10 nanometers. Other emitter materials typically produce greater than 200 particles with diameters greater than 10 nanometers per cubic foot of air. Some materials produce thousands of particles with diameters greater than 10 nanometers per cubic foot of air.

While some of (1) the composition of the emitter material, (2) the elements of the connector structure of the non-metallic emitter, and (3) the application of special power waveforms may be known to be important as individuals, the prior art has not considered the benefits of combining these factors strategically to achieve high ionization reliability and cleanliness.

Recent experiments by the inventors have led the inventors to find and find new combinations that lead to stable ion production and unpredictable low levels of particle generation by the emitter. Clean and/or low particle emission ionizers have utility in some high-tech industries. In particular, the semiconductor industry has a clear need for ultra clean ionizers. Ionizers are needed to minimize static charges and electric fields, which can damage semiconductor devices. As low particle emission as possible is also necessary, since foreign particles may impair the reliability of the semiconductor device. Sophisticated semiconductor technology is building 24-16 nanometer features on wafers. For these nanofunctionals, control of particles larger than 10nm is absolutely necessary.

It is to be understood that the above summary in the background section is only exemplary and explanatory and is not restrictive of the invention as claimed.

Disclosure of Invention

Recent experiments by the inventors have shown that: (1) composition of silicon-based materials and emitter design; (2) arrangement and/or structure of the emitter connector; and (3) the type of power voltage waveform should be considered a complex novel beneficial combination in order to achieve reliable performance of the emitter and low particle emission by the emitter. The combination found by the inventors results in stable ion production and unpredictable low levels of particle generation by the emitter. Clean and/or low particle emission ionizers have utility in some high-tech industries. In particular, the semiconductor industry has a clear need for ultra clean ionizers. Ionizers are needed to minimize static charges and electric fields, which can damage semiconductor devices. As low particle emission as possible is also necessary, since foreign particles may impair the reliability of the semiconductor device. Sophisticated semiconductor technology is building 24-16 nanometer features on wafers. For these nanofunctionals, control of particles larger than 10nm is absolutely necessary.

The matching of emitter electrode compositions, electrode connectors and power waveforms applied to the emitter, which comprise silicon-based materials, has proven to be a novel approach that can achieve previously unattainable levels of reliability and cleanliness of charge neutralizing ionizers. The core of the exemplary embodiments of the present invention lies in the following combinations: non-metallic ion emitters with material/chemical composition in the range of at least 70 to 99.99 wt.% silicon, emitter electrode design and surface treatment (preparation), emitter connection arrangement and operation of high voltage power supply in high frequency range. In this combination, the high frequency, high voltage power generates a corona discharge pattern that is characterized by a low onset voltage. Ions generated from at least one non-metallic emitter according to one embodiment of the invention comprise positive and negative ions generated at the lowest starting HF voltage and power.

This combination is effective and suitable for use in a number of different types of clean room ionizers/charge neutralizers. As an example, the ionizer in embodiments of the present invention may be considered an in-line ionizer for a class 1 clean room production environment. The ionizer may have an incoming flow of Clean Dry Air (CDA) or nitrogen, argon or other inert gas. The gas or air flows along the silicon-based emitters within the ionization cell. The ionization cell/chamber is typically closed except for the air/gas inlet and outlet openings.

The design of an in-line charge neutralizing ionizer in accordance with embodiments of the present invention may use a small power supply such as a high frequency, high voltage power supply. The output connector of the power supply accommodates at least one silicon-based emitter. The ionization cell produces a clean bipolar ionizer. The air flow (or nitrogen or argon or other gas flow) is sufficient to move ions from the ionization emitter (cell or chamber) to the target of charge neutralization.

The high frequency voltage profile of the power supply has an AC frequency range of about 1KHz to 100 KHz. The peak voltage exceeds the corona onset voltage (whether positive or negative) of the emitter. The ionic current of the emitter at high frequency AC is substantially limited by the resistance of the silicon-based material.

In this 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 may be isolated from the ionizing electrode by a dielectric wall. Thus, the possibility of direct electron, ion avalanches (e.g. spark discharge) between the electrodes is practically excluded and particle emission from the emitter is greatly reduced. In the operating mode, ions are generated as long as the voltage amplitude exceeds the corona positive and negative starting voltages applied to the ionizing electrode.

When the high frequency AC voltage profile is periodic rather than discontinuous, another frequency (optional) becomes relevant. That is, the high-frequency AC voltage exceeding the starting voltage distribution is generated only for a predetermined time interval. In this case, a high-frequency AC voltage is applied to the emitter for an active time interval (typically about 0.01 second or less to about 1 second or more), but a voltage lower than the initial voltage is applied for an inactive time interval. Such alternative high frequency voltage waveforms may also substantially comprise an on/off high voltage pattern. The normal low voltage or on/off frequency range is about 0.1hz to 500 hz, but the frequency may be outside this range.

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

Accordingly, at least one exemplary embodiment of the present invention provides a method for low emission charge neutralization, the method comprising: generating a high frequency Alternating Current (AC) voltage; transmitting a high frequency AC voltage to at least one non-metallic emitter; wherein at least one emitter comprises at least 70 wt% silicon and less than 99.99 wt% silicon; wherein the at least one non-metallic emitter comprises at least one treated surface portion having a destroyed oxide layer; and generating ions from the at least one non-metallic emitter in response to the high frequency AC voltage.

At least one exemplary embodiment of the present invention also provides an apparatus that contains elements that allow the above-described functionality to be implemented. For example, an embodiment of the present invention provides an apparatus for low emission charge neutralization, comprising: at least one non-metallic emitter comprising at least 70 wt% silicon and less than 99.99 wt% silicon; wherein the at least one non-metallic emitter comprises at least one treated surface portion having a destroyed silicon oxide layer; and wherein the at least one non-metallic emitter generates ions in response to the 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 (several) embodiment(s) of the invention and together with the description, serve to explain the principles of the invention.

Drawings

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

It is to be noted, however, that the appended drawings illustrate only typical embodiments of this invention and are therefore not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments.

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

Fig. 1(b) and 1(c) show schematic diagrams of conventional parts and a single crystal silicon emitter assembly with a metal sleeve and a recess.

Fig. 2 shows a schematic diagram of a conventional DC indoor ionizing ceiling system with two single crystal silicon emitters.

Fig. 3(a) shows a schematic diagram of a silicon-containing emitter according to an embodiment of the invention, wherein the emitter comprises a portion of the emitter axis having a preselected surface roughness (or treated surface portion).

Fig. 3(b) shows a schematic view of an emitter according to another embodiment of the invention, wherein the emitter comprises a part of the emitter axis with a partially electrically conductive surface plating or a partially electrically conductive surface coating (or other type of treated surface section).

Fig. 3(c) shows a schematic diagram of a silicon-containing emitter and an apparatus for monitoring the surface resistance and/or volume resistance of the emitter according to an embodiment of the invention.

Fig. 4(a) and 4(b) show schematic diagrams of silicon-containing projectiles with two variations of a radially compressed spring sleeve and a metal pin, according to various embodiments of the present invention.

Fig. 5(a), 5(b) and 5(c) show schematic diagrams of three silicon-containing emitters with different cone and tip configurations, according to various embodiments of the invention.

Fig. 6 shows a schematic diagram of HF waveforms for "soft" plasma cleaning of silicon-containing emitter tips during "start-up" of a corona ionization period, in accordance with an embodiment of the invention.

Fig. 7(a), 7(b), and 7(c) show schematic diagrams of examples of waveforms of high frequency power voltages applied to silicon-based emitters during an operational mode, according to various embodiments of the invention.

Fig. 8(a) and 8(b) show schematic diagrams of examples of modulated high frequency voltage waveforms according to various embodiments of the present invention.

Fig. 9(a) shows a schematic of an ionization cell/chamber of an in-line ionizer in accordance with an embodiment of the present invention. High frequency AC powered silicon based emitters generate ions of both polarities. The air/gas flow moves the ion flow from the emitter.

Fig. 9(b) shows a schematic view of a gas channel and an ionization cell according to an embodiment of the present invention.

Fig. 9(c) shows a simplified block diagram of an in-line ionizer with silicon-based emitters according to an embodiment of the present invention.

Fig. 10(a), 10(b), 10(c) and 10(d) show simplified structures of high frequency AC ionizing bars and schematic views of details of nozzles with silicon-based ion emitters according to embodiments of the present invention.

Detailed Description

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

Additionally, for the sake of clarity, not all of the routine features of the described embodiments are shown and described herein. Those skilled in the art will readily appreciate that in the development of any such actual embodiment, numerous implementation-specific decisions may be made to achieve specific design goals. These design goals will vary from one implementation to another and from one developer to another. Moreover, it will be appreciated that such a development effort might be complex and time-consuming, but would nevertheless be a routine undertaking of engineering for those of ordinary skill having the benefit of this disclosure. The various embodiments disclosed herein are not intended to limit the scope or spirit of the disclosure.

Exemplary embodiments for implementing the principles of the present invention are described herein with reference to the accompanying drawings. However, the invention is not limited to the specifically described and illustrated embodiments. It will be appreciated by those skilled in the art that many other embodiments are possible without departing from the basic concept of the invention. The principles of the invention, therefore, extend to any work that falls within the scope of the appended claims.

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

Through experimentation, the present inventors have demonstrated that an in-line ionizer combining, for example, (1) a silicon-containing emitter, (2) a pin electrode configured to be in contact with a conductive socket and a capacitive receptor (3) a high frequency AC voltage waveform reliably produces an electrically balanced ionic gas flow with few particles. The above combinations produce ionization with reliability and cleanliness levels that are not individually attainable by either non-metallic silicon-containing emitters or high frequency AC voltage waveforms known in the art. Cumulative particles having a diameter greater than or equal to 10nm are measured during the cleanliness test. Particle counters (e.g., CNC-condensed particle counters) do not subdivide particles in multiple size ranges.

For example, two single crystal silicon emitters (discussed in U.S. patent No. 5447763) for a clean room ionization system (e.g., NiLstat ionization system) connected to a DC or pulsed DC (+/-20kV) power supply (similar to system 200 shown in fig. 2) generate approximately 60 particles (greater than 10 nanometers in diameter) per cubic foot of air. In contrast, the ionizer disclosed by embodiments of the present invention typically produces less than 10 nanoparticles of the same diameter per cubic foot of air. Objectively, in application, 10 particles greater than 10 nanometers per cubic foot of air are nominally 6 times cleaner than the cleanest ionizer in the prior art.

In the comparative example, a conventional system (e.g., the system in U.S. patent No. 5447763) was used to test the metal emitter (tungsten) and showed unacceptable amounts of particle emission in the clean room. Compared to the conventional system previously disclosed in U.S. patent No. 5447763, my experiments using tungsten emitters in combination with high frequency AC high voltage waveforms similar to that proposed in U.S. patent application publication No. 2003/0007307 (Lee et al) had little benefit in cleanliness. Particle concentration count results were higher than 600 particles per cubic foot of air (greater than 10 nanometers) in both cases where tungsten emitters were tested.

However, high purity (purity of 99.99% or more) single crystal silicon emitters, such as those shown in fig. 1(a), 1(b), and 1(c), have high resistance (in the mega-ohm range). When the emitter is connected to a High Frequency (HF) AC voltage supply, ion production is generally not sufficient to effectively perform charge neutralization. The main reason is because most HF (high frequency) currents/voltages flow to parasitic capacitances rather than to emitter tips.

Another problem associated with high purity (above 99.99% purity) single crystal silicon emitters is that the emitters are prone to surface oxide "skin" (the oxide or skin shown in fig. 1(c) by the dashed line 102c around the surface of the silicon emitter 101 c). The surface/layer 102c is made of highly insulating silicon oxide (SiO)₂) And (4) forming. For example, silicon oxide Growth on the surface of a clean silicon wafer is discussed in the "Growth of native oxide" Stanford university nanofabrication facility, published by the university of California Stanford at 28.8.2003, below.

The net result of the silicon oxide layer growth phenomenon is that the non-metallic silicon emitters/pins are surrounded by the insulating layer and do not have a good reliable connection to the electrical socket and high voltage output to the HF power supply.

Another non-metallic ion emitter is discussed in U.S. patent application publication No. 2006/0071599 to Curtis et al. The emitter is made of 99.99% high purity silicon carbide. The material is a composite material with about 30% carbon. Silicon carbide is known in the art to have high hardness. Silicon carbide is also expensive to manufacture in a process as a pin emitter configuration. Likewise, silicon carbide has a metallic type high electrical conductivity. Conductive particles from composites with high carbon content are generally undesirable in the semiconductor industry.

The wide acceptance of silicon materials in the semiconductor industry dictates that ion emitter materials be relatively low cost. Furthermore, the mechanical properties of the silicon-based materials make processing (cutting, polishing, etc.) simple. The low concentration of silicon dopants and additives is mainly used to control the surface and volume resistivity and to improve the mechanical properties of the silicon-based emitters. They may preferably be taken from known non-metallic dopant groups, such as boron, arsenic, carbon, phosphorus, etc.

In embodiments of the invention, silicon-based compositions having silicon contents of less than 99.99 wt.% and greater than 70 wt.% are capable of providing emitters with resistances in the kilo-ohm range. The resistance is low enough to conduct high frequency currents and support stable corona discharge. Thus, the following two determining factors interact consistently to produce the observed cleanliness improvement: the composition and design of the silicon-based emitters and the high frequency AC emitter drive power/voltage waveform.

One of the advantages of the combination of silicon-based emitters and HF voltage waveforms is that the onset voltage of corona discharge is significantly lower (about 1000V to 3000V or more lower) than the onset voltage of DC, pulsed DC, or low frequency (50Hz to 60Hz) voltages of non-metallic emitters.

A possible explanation for this effect is that in the high frequency range (about 1KHz to 100KHz or more), the voltage applied to the emitter changes polarity in the millisecond range or microsecond range. This is why corona charge carriers (positive and negative ions, electrons) do not have enough time to move away from the emitter tip. In addition, the specific surface charge conservation (often referred to as "charge storage") properties of silicon-based materials may play a role in electron emission at the electrode surface. This is why both the positive and negative high frequency corona onset voltages are low. Since the voltage of the HF corona discharge is lower, the particle emission from the silicon-based emitter is also less.

Scientific evidence for particle emission improvement in corona discharge of balanced ionizers due to the interaction between non-metal silicon-based emitters and high frequency AC voltage waveforms is currently being investigated. Accepted theories of corona discharge and/or ionization and/or particle emission from non-metallic emitters cannot predict or fully explain the observed experimental cleanliness.

However, it is clear how to make and use the invention. The following written description is intended to explain to one of ordinary skill in the art of electrostatic charge control how to make and use the invention.

Experimental work with embodiments of the invention comprising a combination of a silicon-based emitter composition and an HF voltage waveform shows that in some cases ionizers with completely new or long idle emitters represent a problem in initiating the HF corona discharge and reliably producing ion generation. Measurements show high contact resistance between the silicon emitter and the electrical socket. This high resistance is one of the causes of corona initiation problems for ionization devices. The process formation of a relatively thick (10 to 100 or a thick) oxide "skin layer" on a silicon wafer under open air conditions is documented in the "Growth of native oxide" nano fabrication facility at Stanford university, reference cited above. For example, within six days, SiO₂The thickness of the surface layer may be up to 12 angstroms. Silicon oxide is known to be a good insulator. This surface growth therefore leads to a higher surface resistance and contact resistance of the silicon-based emitters. The oxide layer growth rate is variable and depends on many environmental atmospheric factors such as oxygen and ozone concentration (see Silicon Oxidation by ozone) as http:// iopsis. iop. op. org/0953-8984/21/18/183001/pdf/cm 9-18-183001. pdf), temperature, humidity, etc. Ozone is one of the byproducts of corona discharge and can accelerate oxidation of the silicon emitter. This phenomenon is relatively low power for HF ionizers with silicon-based non-metallic emittersThe voltage has a profound effect. Exemplary embodiments of the present invention include surface treatment of silicon-based emitters to reduce contact resistance between the emitters and metal sockets.

Fig. 1(a) is a schematic diagram of a conventional silicon emitter 100 a. The emitter 100a includes four different parts: a tip 101a, a taper 102a, a shaft 103a, and a tail 104 a. The shape and size of the tip 101a depend on the available amount of high voltage and current from the HVPS (high voltage power supply), emitter material, and production techniques and methods. The emitter tip 101a is typically the most critical part of any ion emitter. The emitter tips 101a are directly exposed to the corona discharge and determine the useful life of the emitter. The silicon emitter has a substantially cylindrical axis 103 a. The shaft 103a primarily defines the length of the projectile and the distance between the taper and the socket or receptacle connected to the high voltage power supply. The taper or cone 102a is the transition between the tip 101a and the shaft 103 a. Silicon is inherently a brittle material and the cone angle is a trade-off between the mechanical strength and electrical properties of the emitter. The tail 104a may be rounded, beveled, or chamfered. This feature should facilitate insertion of the projectile 100a into a socket or receptacle. Standard high purity silicon emitters have a smooth surface due to chemical polishing (typically achieved by strong acid treatment).

Fig. 1(b) shows a schematic of a silicon emitter with a metal sleeve. The silicon emitter 100a comprises a non-metallic silicon portion 101b and a stainless steel tube 102b (or sleeve 102b) with a pit 105 b. The sleeve 102b should protect the brittle silicon projectile 101a from mechanical (handling) damage. The sleeve 102b should also improve the electrical connection of the non-metallic high purity silicon emitter to the metal socket or receptacle.

Views

103b and 104b show assembled views of a silicon emitter 100a with a metal sleeve 102 b. View 106b shows a cross-sectional view of the assembled emitter shaft 103 a.

As shown in view 103b, most (or the main portion) of the silicon shaft 103a is encapsulated in the metal sleeve 102 b. In order to fix the sleeve 102b on the silicon shaft 103a and to achieve a reliable electrical contact therebetween, at least one protrusion 105b (dimple) is typically formed on the sleeve 102 b. The assembly operation is very difficult considering the dimensional tolerances of all three components (diameter of the silicon emitter shaft, inner diameter of the cannula and depth of the recess) (see the cross section of the silicon shaft and recess in view 106 b).

Fig. 1(c) shows a schematic of another design of a silicon emitter 100 c. Emitter portion 101c is shown with a surface oxide layer ("skin") 102c indicated by the dashed line. Emitter 100c comprises a silicon portion 101c and a sleeve 103c having a pit 104 c. The sleeve 103c may have one or more portions/extensions 106c with grooves 107 c. The emitter assembly is shown in view 105 c. This design allows the projectile to be retained in the nozzle and the extension 106c to be inserted into a different socket or receptacle using the extension 106 c.

Fig. 2 shows a schematic diagram of a conventional DC indoor ionization system 200 similar to that used in U.S. patent No. 5447763. The ionizer has a pair of rods, namely a positive (+) rod 201 and a negative (-) rod 202, which carry the single crystal silicon emitter. The rod is connected to a dedicated positive, negative high voltage power supply (HVDC)203 (provided in the sley). A cross-sectional view of the emitter rod is shown in view 204. The end of the rod 202 has a socket-type connector 205 and a high voltage cable 206 connected to the HVDC power supply 203. The socket 205 houses a silicon type emitter 207 shown in view 204. The other parts of the rod 202 act as protectors to protect the projectile 207, connector 205 and HV cable 206 from damaging forces. The rod design makes the

silicon emitters

201, 202 interchangeable.

At least some objects of exemplary embodiments of the present invention are to propose low particle emission by an economical silicon-based charge neutralization system. The combination of the composition of the silicon-based emitters with less than 99.99 wt% and more than 70 wt% silicon and the high frequency corona discharge enables the goal of low particle emission to be achieved. For non-metallic silicon electrodes in ionization systems, 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 a schematic diagram of a silicon-based emitter 300a according to an embodiment of the invention, wherein the emitter 300a comprises a rough or sand-cast portion 310a of a shaft 301a (i.e. a treated surface portion 310a), which portion 310a can be inserted into a high voltage socket (not shown). The roughness H of the portion 310a of the shaft surface 302a is in the range of about 0.5 microns to 10 microns (see diagram 303 a). During surface treatment, such as by sandblasting, the oxide "skin" previously on the shaft surface 302a will be damaged and removed or otherwise removed. The sandblasting forms an emitter shaft surface profile that enables multiple point contact with a high voltage socket (not shown). Alternatively, a similar surface treatment may be applied to the rounded end 304a of the tail 314a of the projectile 300 a. The emitter tip 305a, the taper 306a, and the portion 311a of the shaft 301a have a regular chemically polished surface.

Another embodiment of a silicon-based emitter is shown in fig. 3 (b). According to this embodiment of the invention, the silicon-based emitter 300b comprises a portion 310b (i.e. a treated surface portion 310b) of the emitter axis 301b with a metal plating or metal coating 302b (or an electrically conductive plating or metal coating 302b), the metal plating or metal coating 302b making the portion 310b of the axis 301b a good surface conductor and protecting the contact portion 316 of the emitter 300b from oxidation for a long time. The contact portion 316 may be located at the tail 314b of the emitter shaft 301 b.

Different known silicon electroplating methods (e.g., vacuum deposition, electrolytic plating, spray coating, etc.) can be used. Plating materials such as metals may include: such as nickel, brass, silver, gold, and other metals and alloys accepted in the semiconductor industry.

Fig. 3(c) shows a schematic diagram of a silicon-containing emitter and an apparatus for monitoring the surface resistance and/or volume resistance of a silicon-containing emitter according to an embodiment of the invention. This shows an example of the electrical quality control operation of the silicon-based emitter 300c as shown in fig. 3 (c). Controlling and/or monitoring includes resistance measuring or monitoring the resistance and/or composition of emitter 300c or treated surface portion 302c of emitter 300 c. The

conductive electrodes

303c and 304c are attached or connected to the emitter shaft 301c of the emitter 300c and the blasted portion 302c (or the treated surface portion 302c) of the tail portion 314c, respectively. A standard resistance R measurement device 305 may be used to make and record a measurement of resistance R. In this way, complex surface and volume resistivities and emitter compositions can be monitored. The required silicon-based emitters of normal mass and composition (less than 99.99% to at least 70% by weight of silicon) should have a complex resistance in the kiloohm range. After surface treatment and control operations, the emitter 300c may be inserted 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 shown herein allow for solving two problems: (1) establishing a reliable electrical connection between the non-metal silicon-based emitter and the socket; and (2) protecting the contact portion of the emitter from oxidation.

Fig. 4(a) and 4(b) show schematic diagrams of silicon-containing projectiles with two variations of a radially compressed spring sleeve and a metal pin, according to various embodiments of the present invention. As discussed below, a silicon-containing projectile and a metal pin are inserted into the sleeve. The silicon-based emitter 400a of fig. 4(a) in an embodiment of the present invention will first be described. According to this exemplary embodiment, emitter 400a comprises an emitter portion 401a, wherein the silicon portion of emitter portion 401a has a reduced length/axis diameter ratio. The short silicon-based emitter portion 401a is connected to the metallic radial compression spring sleeve 402a from one side 430 of the metallic radial compression spring sleeve 402 a. The other side 431 of the sleeve 402a is connected to a solid metal extension pin 403 a. The

metal pins

403a and 403b discussed herein may be

metal electrodes

403a and 403b inserted into the spring-

type sleeves

402a and 402b, respectively. The pin 403a may have at least one (or more) groove and socket and variable length "L2" as required by the ionization cell (including the reference electrode) design. For example, pin 403a includes

grooves

435 and 436, but in other embodiments, pin 403a may have only a single groove. For example, the pin 403a may be a solid metal pin or tube. The pin 403a may be manufactured using a conventional CNC or automatic metal cutting machine or other metal processing method. View 405a shows a schematic diagram of an emitter assembly 410a with a silicon emitter 400a according to the present exemplary embodiment. The radial compression spring sleeve 402a has a significantly larger contact area with the silicon portion 401a than the conventional sleeve 102b having the dimple 105b as shown in fig. 1(a) and 1 (b). The result is a more reliable electrical connection and less mechanical stress applied to the brittle silicon emitter portion 401 a. The design of a silicon emitter with a metal sleeve has some requirements to prevent "secondary" corona discharge from the edge of the sleeve to the nearby reference electrode. The main parameters to be considered are shown in diagram 406 a: d, which is the diameter of the silicon emitter shaft 440; l, which is the length of the exposed portion 441 of the silicon emitter shaft 440; α, which is the taper angle of the tapered portion 442 of the shaft 440; and S, which is the thickness of the sleeve 402 a. For a high concentrated electric field on the emitter tip 421a of the silicon portion 401a (or on the emitter tip 421b of the silicon portion 401 b), the first ratio S/D should be in the range of about 0.03 to 0.06. Another requirement related to the distance between the emitter tip 421a and the sleeve 402 is a second ratio L/S: the ratio L/S should be in the range of (2-5)/tan { tangent } (0.5 α). The parameter a is the cone angle of the tapered portion of the shaft 440 of the at least one

non-metallic emitter portion

401a or 401 b. These conditions for the new silicon emitter design in one embodiment of the invention will meet several standards/specifications: reliable electrical connection, good mechanical strength, and the lowest likelihood of "secondary" corona generating particle emissions from the metal component.

Fig. 4(b) shows a schematic diagram of another embodiment of a silicon-based emitter 400b comprising another configuration of a metallic radial compression spring sleeve 402 b. In this case, the emitter 400 comprises a silicon emitter part 401b having a diameter D1 and an end 461 of a metal sleeve 402b having a diameter D3. The silicon emitter portion 401b has an emitter tip 421 b. Portion 403b is a solid metal pin 403b having a diameter D4, and the other end 462 of sleeve 402b has a diameter D2. The difference in diameter of the silicon emitter part 401b and the metal sleeve 402b (D1> D3) generates the required compressive force to provide a reliable or good electrical contact between the silicon emitter part 401b and the metal sleeve 402 b. Similarly, the difference in diameter (D2< D4) provides a reliable or good electrical connection between the metal sleeve 402b and the metal pin 403 b.

Views

404b and 406b show an assembled view of the silicon emitter 400 b. View 405b is a cross-sectional view showing a silicon emitter 401b and sleeve portion 402b with large contact area and minimal contact pressure and localized stress according to this exemplary embodiment. The assembly operation is simplified. Two exemplary embodiments (

emitters

400a and 400b) use a minimum amount of expensive silicon-based material, have a large reliable contact area of the non-metallic emitter shaft with the metal sleeve, and a good size match with a standard socket or receptacle.

In some cases, silicon-based emitters, despite having normal surface/volume resistance and good electrical connection to the high voltage socket, still suffer from the problems of initiating high frequency corona discharge and reliably producing ion products. Our experiments show 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 home" of the emitter). Another exemplary embodiment of the present invention addresses this problem. The shape of the tip of the silicon-containing emitter may have some positive impact on the rate and thickness of formation of the insulating oxide "skin".

Fig. 5(a), 5(b) and 5(c) show schematic diagrams of three silicon-containing emitters with different configurations of tapers and tips, according to various embodiments of the invention. The various tip and taper configurations shown in fig. 5(a), 5(b) and 5(c) determine the operating HF corona onset voltage and ionization current parameters.

In fig. 5(a), a silicon-based emitter 501 with a flat truncated tip is shown. This tip design tends to produce a ring-type high frequency corona discharge (where the flat tip 510 meets the taper 511 of the emitter 501). The emitter 501 may reduce ion current density and particle emission. However, it is characterized by a higher initial HF corona voltage. Taper 511 is at an angle of a with respect to flat tip 510.

Silicon-based emitters 502 (fig. 5(b)) have small circular tips 514 with radii Z in the range of about 60 to 400 microns, which results in lower production costs and minimizes corona current fluctuations. A tapered portion 516 (of emitter 502) extends from small rounded tip 514.

The sharpened silicon-based emitter 503 (fig. 5(c)) has a sharp tip 520 with a radius Y in the range of about 40 microns to 50 microns, or less. The emitter 503 has the lowest corona onset voltage Von. However, the ion current density of the emitter 503 is greatest and sputtering, erosion and oxide "skin" growth are all at the highest rates. The silicon-based emitter 503 is preferably used for ionization in oxygen-free gases such as nitrogen or argon. The tapered portion 521 of the emitter 503 preferably has an angle a in the range of about 10-20 degrees with respect to the sharp tip 520. All silicon-based emitters (501, 502, 503) have compositions according to exemplary embodiments of the invention and are capable of providing low particle counts when mounted in-line ionizers, ionizing bars, and other charge neutralizers driven by HF AC voltages. The sharpness and curvature of the tip (i.e., the configuration of the tip) affect or determine the ionizer operating parameters including the 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 the silicon emitter tip. This embodiment uses a specific corona discharge pattern to clean the silicon emitter tips from the oxide surface and helps the ionizer to start independently of the emitter profile.

A high voltage "HF start" type waveform 600 is applied to the emitter. This high voltage drive mode provides a set of short duration bipolar voltage pulse trains (numbered from one to as many as several hundred bipolar pulses 605) to the emitter during the start-up period (labeled Ts period). The HF corona associated plasma has very limited energy due to the very short duration of the power distribution in the range of milliseconds, microseconds, or less. This prevents both the temperature rise and surface damage (splashing, erosion and particle emission) of the emitter tip. Short duration HF plasma bursts only perform a "soft" cleaning of the emitter tip to the silicon oxide surface layer. The duration, short pulse amplitude, and number of pulses of the "on" time period Ts may vary with the thickness of the silicon oxide skin, gaseous medium, emitter tip design, etc. and depend on the factors described above. The voltage amplitude of the HF short pulses is significantly higher (by about 25% to 100% or more) than the normal (operating) corona onset voltages plus (+) Von and minus (-) Von (shown in fig. 6 by the two horizontal dashed

lines

610 and 615, respectively). The initial "start-up" mode helps to initiate normal/operational high frequency corona discharge and ion production. During the normal/operating mode (during time Top), the high voltage amplitude may be only 10% -20% higher than the corona onset voltage (+) Von or (-) Von to minimize particle emission. In the continuous mode of operation, the HF corona discharge can protect the silicon emitter from oxidation in a clean dry gas medium. Thus, during the start-up period of the corona ionization period, soft plasma cleaning of the at least one non-metallic emitter is performed by employing a voltage/power waveform that is different from the voltage/power waveform during the operational period.

Fig. 7(a), 7(b) and 7(c) show schematic diagrams of examples of waveforms of high frequency power voltages applied to silicon-based emitters during an operational mode according to embodiments of the invention. The different operating HF voltage waveforms effectively produce bipolar ionization for the silicon-based emitters. The function of the high frequency AC voltage is to generate ions of two polarities (positive ions and negative ions) at a minimum driving voltage. To generate ions, the peak voltage (positive and negative peak voltages) exceeds the corona onset voltage. As shown in fig. 7(a), the high frequency AC voltage curve 700 is continuous, but the curve may also be continuously or non-continuously and periodically modulated.

Fig. 7(a) shows a continuous symbol waveform supply voltage 700, which may have a frequency range from about 1KHz to about 100 KHz. The positive and negative voltage magnitudes of voltage 700 are higher than the positive corona onset voltage (+) Von705 and lower than the negative corona onset voltage (-) Von 710. The voltage waveform 700 provides maximum power to the silicon-based emitters described herein and produces maximum ion current.

Fig. 7(b) shows a schematic of a voltage waveform 750, which voltage waveform 750 contains groups of pulse trains 752 having "on" periods 755 and "off" periods 756. Waveform 750 includes at least one modulated portion, where each modulated portion includes a pulse train 752 having an on period 755 and an off period 756. During an on period 755 in the pulse train 752, the waveform 750 has an amplitude 758 that exceeds the positive corona onset voltage threshold 705 for the particular emitter and exceeds the negative corona onset voltage threshold 710 for the particular emitter. During the off period 756 in the pulse train 752, the waveform 750 has an amplitude 760 that does not exceed the corona

onset voltage thresholds

705, 710. In the example of fig. 7(b), the amplitude 760 is a voltage magnitude of approximately zero. Additional details of

waveforms

700, 750, and 780 in fig. 7(a), 7(b), and 7(c), respectively, are also described in commonly owned and commonly assigned U.S. patent No. 8009405 to Peter Gefter et al. During an "off" period 756 (which may be a small duty cycle), corona discharge (ion production) and particle emission stop. The duty cycle may vary from about 100% to about 0.1% or less, depending on the desired ion output. The lowest duty cycle helps suppress particle emission and emitter erosion rates.

Fig. 7(c) shows a schematic of another variation of the voltage waveform 780 where the duty cycle is close to about 100%, but the voltage amplitude applied to the silicon emitters periodically drops to a value below the corona onset voltage (in the range from about 90% to about 50% or less of the corona onset voltage). The advantage of this waveform is that it can minimize particle emission and high voltage swings (voltage/electric field variations).

Waveform 780 contains at least one modulated portion, where each modulated portion contains a pulse train 782 having an on period 785 and a non-operational period 786. During the on-period 785 in the pulse train 782, the 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)710 for the particular emitter. During a non-operational period 786 in the pulse train 782, the waveform 780 has an amplitude 790 that does not exceed the corona

onset voltage thresholds

705, 710, but the amplitude 790 is greater than zero volts.

Fig. 8(a) and 8(b) show schematic diagrams of examples of modulated high frequency voltage waveforms according to embodiments of the invention. Fig. 8(a) shows a continuous modulation waveform 800 as a result of a mixture (combination) of high and low frequency voltages. The low frequency component (or offset voltage) is shown in fig. 8 (b). This voltage waveform 850 generates ions primarily by high frequency components (similar to the waveform 700 shown in fig. 7 (a)), and moves ions from the emitter by low frequency components.

In-line ionizers with silicon-based emitters may be used for the most demanding operations/processes in the semiconductor industry (e.g., environments such as class 1 air particulate cleanliness). Fig. 9(a), 9(b) and 9(c) show a simplified view of an ionization cell and a block diagram of an in-line ionizer. The application of the HF frequency voltage may be similar to the waveform shown in fig. 8(a), which extends to the range of about 20KHz to about 100KHz, using an in-line ionizer design.

Fig. 9(a) shows a schematic of an ionization cell/chamber of an in-line ionizer in accordance with an embodiment of the present invention. High frequency AC powered silicon based emitters 902a generate ions of both polarities. The air/gas flow 908a moves the ion flow from the emitter 902 a. Also as shown in fig. 9(a), ionization unit 900a is connected to HF HV generator 901 a. Silicon-based emitter 902a is located in socket 903a and is connected via capacitor (C1) connected to HF generator 901 a. The emitter 902a may have a blasted or metal plated portion of the shaft previously discussed in fig. 3(a) and 3(b), respectively, to provide a reliable connection to the socket 903 a.

The emitter 901a is generally located in the middle portion of the air/gas channel 904 a. Preferably, reference electrode 905a is located outside of channel 904a and near an outlet 906a of channel 904 a. The reference electrode 905a is connected to a control system 907 a. When the peak voltage (positive or negative voltage) of the high-frequency AC voltage (applied to the emitter 901 a) exceeds the corona onset voltage, the positive ions 920 and the negative ions 921 are generated by the emitter 901 a. The air/gas flow 908a from an external source (not shown) still needs to move the generated ion cloud towards a remote target charge neutralization (not shown). The corona discharge near the tips 909a of the emitters 902a produces a dense HF plasma 910a with ions and electrons near the tips 909a of the silicon emitters 902 a. The corona onset voltage is about (+)5-6kV for positive ions and (-)4.5-5.5kV for negative ions.

The generation/emission corona byproducts, such as particles, in the plasma are minimized by the previously discussed methods, apparatus and devices of combination of ion emitter composition, ion emitter design and supply voltage waveform.

Fig. 9(b) shows a diagram of another view 900b of the ionization cell and gas channel in block 901b, in accordance with an embodiment of the present invention. Channel 902b has an inlet 933b and an outlet 934 b. The silicon-based emitter 905b with socket 906b can be made as a replaceable unit in the cavity 960 of the channel 902 b. Emitter socket 906b and reference electrode 907b are connected to a high voltage HF power supply 908 b. The ionized gas flow (shown by arrow 961) moves the ion cloud to a charged target 909b, such as a wafer, and the ion cloud will neutralize these charges 965 on the charged target 909 b.

Fig. 9(c) shows a simplified block diagram of an in-line ionizer 900c with silicon-based emitters 904c in accordance with an embodiment of the present invention. Positive ions and negative ions 901c are formed within the ionization cell 902 c. A high voltage HV-HF power supply 903c provides the voltage and current needed to generate ions 901 c. Power supply 903C delivers a high frequency AC voltage to the silicon-based emitters 904C through capacitor C1. The voltage on the silicon based emitter 904c is related to the reference electrode 905 c.

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

The in-line ionizer 900c includes a control system 907c containing a microprocessor 908c, a gas pressure sensor 909c, a corona discharge sensor 910c, and an operating status indicator 911 c. The in-line ionizer 900c typically operates in a semiconductor tool having a wafer loading/unloading operation. This is why the in-line ionizer 900c may have a relatively long idle ("off") period without corona discharge and gas flow. During these periods, the tip of the silicon emitter may grow a silicon oxide layer. As previously discussed in the exemplary embodiments shown in fig. 3(a) and 6, the control system 907c initiates the gas ionization process by activating the high voltage power supply 903c in a "start-up" mode. Corona discharge sensor 905c and processor 908c continuously monitor the state of the corona discharge until a strong and stable corona and level of ion production is reached. Thereafter, the control system 907c and power supply 903c switch to the normal operation mode.

Fig. 10(a), 10(b), 10(c) and 10(d) show simplified structures of a high frequency AC ionizing bar 1000a and schematic views of details of a nozzle having a silicon-based ion emitter according to an embodiment of the present invention. Fig. 10(a) and 10(b) show views of a high frequency AC ionizing bar 1000a with multiple raw silicon-based emitters 1001a-1008a (as an example). Each silicon emitter has a stainless steel sleeve. The stainless steel sleeve is shown as sleeve 1020c in fig. 10(c) and sleeve 1020d in fig. 10 (d). Each stainless steel sleeve 1020a is installed in the nozzle. Each nozzle has a socket and optionally one or two air/gas injection orifices. The cross-sectional view of the nozzle is shown as nozzle 1030c in fig. 10(c) and as nozzle 1030(d) in fig. 10 (d).

The socket 1009c is connected to a common high voltage bus and the aperture is connected to a manifold (not shown) located within the housing 1010a of the ionizing bar 1000 a. A cross-sectional view 1040 of the nozzle 1030d shows the relative position of the silicon emitter 1003d (with the sleeve and groove as previously discussed in fig. 4(a) and 4 (b)) and the aperture 1004 d. The bus distributes the HF power from the high voltage AC power source to each nozzle and emitter. The HF-HV power supply with the microprocessor based control system is preferably located within the same housing 1010 a. The silicon-based ion emitter receives an HF AC voltage (similar to that shown in fig. 7 (a)) having a fundamental frequency in the range of about 6kV to 8kV at about 10KHz to 26 KHz. This HF high voltage creates a corona discharge between each emitter 1001a-1008a and the reference electrode 1011 a. This high frequency AC voltage is sufficient by itself to produce clean bipolar ionization when the composition of the emitter is in the range of less than 99% to greater than 70% silicon. As discussed previously, the high frequency by itself cannot move the ion cloud to a distance. The HF ionizing bar 1000a is typically mounted in a flat panel or semiconductor tool at a relatively short distance (e.g., about 50mm to 300mm) from the target. In this case, the electric field of a charged target (not shown) attracts ions of opposite polarity. However, in order to neutralize effective charge over longer distances (e.g., about 400mm to 1500mm), the ion cloud requires assistance from air/gas flow or electric fields or a combination of the two. Typically, HF ionization rods may be used in combination with HEPA filters to provide a clean laminar air flow.

Fig. 8a shows a modulated HF waveform 800 that generates an additional low frequency field (approximately 0.1Hz to 200Hz) to help deliver ions to the target. During period T2, the positive voltage wave 804 and the amplitude 802 and the amplitude 806 of the negative voltage wave 808 are nearly equal, so the offset voltage is near zero and the ion cloud oscillates near the silicon emitter. In contrast, during a period such as T1, the voltage waveform 800 has a positive offset 810 and the positive polarity (repelled) ion cloud moves to the target (see fig. 8 (b)). Similarly, during a period such as T3, the voltage waveform 800 has a negative offset 815 and the (repelled) negative-polarity ion cloud moves to the target. The magnitude and frequency of the offset voltage depends on the distance between the ionizing bar 1000a and the target.

The high frequency ionizing bar 1000a with silicon-based emitters can produce low emission, can produce clean air/gas ionization and neutralize the charge of fast moving large objects (e.g., flat plates) over distances of, for example, about 400mm to 1500 mm.

Another embodiment of the present invention provides a method for low emission charge neutralization wherein at least one of the above-described non-metallic emitters comprises a reduced silicon moiety length/axis diameter ratio.

Another embodiment of the present invention provides a method for low emission charge neutralization wherein the sleeve comprises a metallic radial compression spring sleeve and wherein the difference in diameter of the at least one projectile, the metallic pin and the sleeve generates a compressive force that provides a reliable electrical connection between the at least one projectile, the sleeve and the metallic electrode.

Another embodiment of the present invention provides an apparatus for low emission charge neutralization wherein at least one of the above-described non-metallic emitters comprises a reduced length/axis diameter ratio.

Another embodiment of the present invention provides an apparatus for low emission charge neutralization wherein the sleeve comprises a metallic radial compression spring sleeve and wherein the difference in diameter of the at least one projectile, the metallic pin and the sleeve generates a compressive force that provides a reliable electrical connection between the at least one projectile, the sleeve and the metallic electrode.

Another embodiment of the present invention provides an apparatus and method that produces a reliable low particle emission charge neutralizer by combining the following factors: non-metallic ion emitters having chemical compositions ranging from less than 99.99 wt% to at least 70 wt% silicon, emitter geometry, surface treatment (preparation), and connection arrangements between the emitters and a high voltage power supply operating in the high frequency range. In this combination, the emitter reliably generates a high frequency corona 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 for class 1 clean rooms. The combination of the silicon-containing emitter and the high frequency AC voltage produces a cleaner ionizer than conventional ionizers based on particle counts greater than 10 nanometers. This improvement in cleanliness has been experimentally determined by the inventors.

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

These modifications can be made to the invention in light of the above detailed description. The terms used in the following claims should not be construed to limit the invention to the specific embodiments disclosed in the specification and the claims. Rather, the scope of the invention is to be determined entirely by the following claims, which are to be construed in accordance with established doctrines of claim interpretation.

Claims

1. A method for low emission charge neutralization, comprising:

generating a high frequency Alternating Current (AC) voltage;

transmitting the high frequency Alternating Current (AC) voltage to at least one non-metallic emitter;

wherein the at least one non-metallic emitter comprises at least 70 wt.% silicon and less than 99.99 wt.% silicon;

wherein the at least one non-metallic emitter comprises at least one treated surface portion having a destroyed oxide layer; and

generating ions from the at least one non-metallic emitter in response to the high frequency Alternating Current (AC) voltage.

2. The method of claim 1, wherein the at least one treated surface portion of the at least one non-metallic emitter comprises areas having a preselected roughness as a result of roughening or grit blasting.

3. The method of claim 1, wherein the treated surface portion comprises a metallic coating or a metallic coating.

4. The method of claim 1, further comprising:

a measurement device is provided for monitoring the resistance and composition of the at least one non-metallic emitter.

5. The method of claim 1, wherein the at least one non-metallic emitter comprises an emitter shaft comprising a silicon-based portion, wherein the at least one non-metallic emitter and a metal electrode are inserted into a sleeve, and wherein the sleeve is a spring-type sleeve.

6. The method of claim 1, wherein the at least one non-metallic emitter comprises a tip configuration and a taper configuration, wherein both configurations determine operating HF corona onset voltage and ionization current parameters.

7. The method of claim 1, further comprising:

during a start-up period of the corona ionization period, cleaning of the plasma of the at least one non-metallic emitter is performed by a voltage/power waveform that is different from the voltage/power waveform during the operating period.

8. The method of claim 1, wherein generating the ions comprises generating positive and negative ions at a minimum starting HF voltage and power during an operating period.

9. The method of claim 1, wherein the first and second light sources are selected from the group consisting of a red light source, a green light source, and a blue light source,

wherein the at least one non-metallic emitter comprises a first ratio S/D in the range of 0.03 to 0.06;

wherein S is the thickness of a sleeve receiving the at least one non-metallic emitter; and

wherein D is a diameter of an axis of the at least one non-metallic emitter.

10. The method of claim 1, wherein the first and second light sources are selected from the group consisting of a red light source, a green light source, and a blue light source,

wherein the at least one non-metallic emitter comprises 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 at least one non-metallic emitter;

wherein α is the cone angle of the tapered portion of the shaft of the at least one non-metallic emitter.

11. The method of claim 1, wherein the high frequency Alternating Current (AC) voltage has a frequency of at least 1 KHz.

12. The method of claim 1, wherein the first and second light sources are selected from the group consisting of a red light source, a green light source, and a blue light source,

wherein the at least one non-metallic emitter comprises an emitter tip, an emitter axis, and an emitter tail, and wherein the emitter axis is between the emitter tip and the emitter tail;

wherein the emitter shaft comprises at least one treated surface portion; and

wherein the at least one treated surface portion is configured to be plugged into a voltage socket and configured to provide an electrical connection to a high voltage power source.

13. An apparatus for low emission charge neutralization, comprising:

at least one non-metal emitter comprising at least 70 wt.% silicon and less than 99.99 wt.% silicon;

wherein the at least one non-metallic emitter comprises at least one treated surface portion having a layer of silicon oxide that is destroyed; and

wherein the at least one non-metallic emitter generates ions in response to a high frequency Alternating Current (AC) voltage.

14. The apparatus of claim 13, wherein the at least one treated surface portion comprises a roughened portion or a grit-blasted portion.

15. The apparatus of claim 13, wherein the at least one treated surface portion comprises a metallic coating or a metallic coating.

16. The apparatus of claim 13, wherein the resistance and composition of the at least one treated surface portion of the at least one non-metallic emitter is monitored.

17. The device of claim 13, wherein the at least one non-metallic emitter and metallic electrode are inserted into a sleeve, wherein the sleeve is a spring-type sleeve.

18. The apparatus of claim 13, wherein the at least one non-metallic emitter comprises a tip configuration and a taper configuration, wherein the two configurations determine operating HF corona onset voltage and ionization current parameters.

19. The apparatus of claim 13, wherein cleaning of the soft plasma of the at least one non-metallic emitter is performed by a voltage/power waveform different from a voltage/power waveform during an operating period during a start-up period of a corona ionization period.

20. The apparatus of claim 13, wherein the ions comprise positive and negative ions generated at a minimum HF onset voltage and power.

21. The apparatus of claim 13, wherein the at least one non-metallic emitter comprises a first ratio S/D in the range of 0.03 to 0.06;

wherein D is a diameter of an axis of the at least one non-metallic emitter.

22. The apparatus as set forth in claim 13, wherein,

23. The apparatus of claim 13, wherein the high frequency Alternating Current (AC) voltage has a frequency of at least 1 KHz.

24. The apparatus as set forth in claim 13, wherein,

wherein the emitter shaft comprises at least one treated surface portion; and

wherein the at least one treated surface portion is configured to be inserted into a voltage socket and configured to provide an electrical connection to a high voltage high frequency voltage power supply.