EP0448929B1 - Suppression of particle generation in a modified clean room corona air ionizer - Google Patents

Suppression of particle generation in a modified clean room corona air ionizer Download PDF

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Publication number
EP0448929B1
EP0448929B1 EP91100551A EP91100551A EP0448929B1 EP 0448929 B1 EP0448929 B1 EP 0448929B1 EP 91100551 A EP91100551 A EP 91100551A EP 91100551 A EP91100551 A EP 91100551A EP 0448929 B1 EP0448929 B1 EP 0448929B1
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EP
European Patent Office
Prior art keywords
corona
air
housing
ionizer
point
Prior art date
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Expired - Lifetime
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EP91100551A
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German (de)
English (en)
French (fr)
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EP0448929A1 (en
Inventor
John S. Batcheler
Vaughn P. Gross
Philip C. D. Hobbs
Robert J. Miller
Kenneth D. Murray
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International Business Machines Corp
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International Business Machines Corp
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01T—SPARK GAPS; OVERVOLTAGE ARRESTERS USING SPARK GAPS; SPARKING PLUGS; CORONA DEVICES; GENERATING IONS TO BE INTRODUCED INTO NON-ENCLOSED GASES
    • H01T23/00—Apparatus for generating ions to be introduced into non-enclosed gases, e.g. into the atmosphere

Definitions

  • the present invention relates to an improved corona air ionizer which eliminates microcontamination associated with conventional corona ionizers. Specifically, the invention provides for the elimination of ammonium nitrate buildup on the negative corona points and the elimination of bursts of submicron particles in corona ionizers by providing a stream of non-hydrogen-containing dry gas at the corona point during operation. Corona ionizers are commonly used in clean rooms, particularly clean rooms used in the manufacture of semiconductor devices.
  • Corona air ionizers have historically had a reputation for generating particulate contamination, while being very effective at reducing electrostatic charges on surfaces. Controlling electrostatic discharge (ESD) and reducing the sedimentation rate of small submicron aerosol particles are described in the article by K. Dillenbeck entitled “Selection of Air Ionization Within the Cleanroom” in Proceedings of the 32nd Annual Technical Meeting of the IES, pp 387-392 and in the article by R.P. Donovan et al entitled "The Dependence of Particle Deposition Velocity on Surface Potential” in 1987 Proceedings of the IES, pp 473-478.
  • ESD electrostatic discharge
  • corona air ionizers usually generate large quantities of small (less than 0.1 »m) particles, primarily metal sputtered from the corona points themselves as noted in the article by B.Y.H. Liu et al entitled “Aerosol Charging and Neutralization and Electrostatic Discharge in Clean Rooms," in J. Envir. Sci, March/April 1987, pp 42-46 and in the article by M. Suzuki et al entitled “Effectiveness of Air Ionization Systems in Clean Rooms" in Proceedings of the 34th Annual Technical Meeting of the IES, pp 405-412.
  • Dispersive x-ray analysis ruled out tungsten as a major contributor to the remaining particles. Chemical analysis of the white precipitate on the negative points further showed it to be mostly NH4NO3, making it plausible that the particles are also NH4NO3. In addition to generating contamination, the precipitation necessitates replacing the points every month which contributes significantly to the cost of maintaining corona ionizers.
  • Particulates generated in clean rooms are mostly charged. If electric fields are present arising from charged surfaces, a strong attraction is created between the particles and the corresponding apparatus charged surfaces. The described phenomena is the primary cause for the anomalously large deposition rates seen in manufacturing at small particle sizes.
  • triboelectric charging of semiconductor wafers, wafer boats, equipment, people and work surfaces result in electrostatic discharge events which can damage the wafers both electrically, by breaking down insulating layers and fusing conductors, and through the ablation of small particles from the surfaces involved in the discharge.
  • US-A-4 333 123 discloses an apparatus for generating and dispersing ions comprising a high voltage source feeding corona tip means arranged in forwardly elongated tubes provided within an outer tube.
  • the forwardly elongated tubes are attached to the outer tube by means of a vertical strut.
  • a gas flow is effected by feed means to aid in sweeping the ion streams forwardly toward a workpiece to be neutralized.
  • a technique that has been employed to reduce these electrostatic affects is to neutralize the surfaces of the products and tools on a manufacturing line by adding air ions of both positive and negative polarities to the output of laminar flow HEPA filters, thereby rendering the air sufficiently conductive to neutralize the surface charges.
  • typical electric fields produced by ungrounded wafers or containers are a few hundred to a few thousand volts per centimeter.
  • the deposition rates for particles out of class 100 air is roughly 100 times lower for environments that incorporate air ionization than for those without air ionization as noted in the article by R. Welker entitled "Equivalence Between Surface Contamination Rates and Class 100 Conditions", 1988 Proceedings, IES, pp 449-454. The effect is attributed to the neutralization effect of the injected charge in the air on the excess surface charges.
  • Ammonium nitrate is a compound of nitrogen, hydrogen and oxygen. It is a high-energy compound and can ordinarily be formed only in a high energy density environment such as a high temperature gas reactor, lightning discharge, or in the present case, corona discharge. If the particles are ammonium nitrate, then the formation of particles requires a source of hydrogen. The most plausible source of hydrogen is atmospheric water vapor. It follows that if the corona discharge is made to occur in a sufficiently dry gas environment, no ammonium nitrate will be generated.
  • the object of the present invention is therefore, the provision of an apparatus for suppressing particle generation in a corona air ionizer, especially eliminating ammonium nitrate particles.
  • corona point 10 of a conventional ionizer is disposed inside a closed-end tube 12.
  • the corona point is connected to a high voltage power source for generating ions by corona discharge.
  • Clean non-hydrogen-containing dry gas which will not corrode the corona points and will not form water vapor, preferably dry air, oxygen, carbon dioxide, nitrogen, argon or helium, enters from conduit 14 into tube 12.
  • the open end of the tube is positioned in front (above in the figure) of the corona point so that the ions generated by the discharge are carried out through the opening with the stream of non-hydrogen-containing dry gas.
  • Oxygen and water vapor from the surrounding ambient air are prevented from approaching the corona points by the outwardly flowing gas.
  • the outflowing ions mix with the ambient air, providing an ionization essentially indistinguishable from the unmodified ionizer operating in the ambient air.
  • a bipolar DC corona ionizer Semtronics, Inc. Model 2001, was modified.
  • the ionizer consists of a 2m long plastic extrusion (formed by joining two lm lengths together end to end) whose cross-section is shaped in the form of the Greek letter capital sigma " ⁇ ", with the positive points spaced at 30 cm intervals along the middle of the upper groove and the negative points are similarly positioned in the other groove in a staggered relation so that each positive point is 15 cm from the closest negative point.
  • the bar hangs horizontally, with the grooves facing sideways.
  • the left-hand piece of the ionizer was left unmodified and the right-hand piece was modified as shown in Figure 2. In operation, the entire ionizer will be modified as described below.
  • Both right-side extruded channels are covered, for example with PVC tape 20.
  • a hole of approximately 1 cm diameter is cut in front of each corona point.
  • the region below the tape 20 is continuously flushed with a clean non-hydrogen-containing dry gas which will not corrode the corona point and will not form water vapor, such as dry air, oxygen, carbon dioxide, nitrogen, argon or helium, via a perforated tube 24, made for example of Teflon, with a high-efficiency in-line filter (not shown).
  • the corona points are manufactured of pure tungsten.
  • the corona points are connected to a high voltage power source (not shown) for generating ions by corona discharge.
  • the sleeves 22 must be kept away from the discharge region to avoid creating particles arising from erosion of the sleeves.
  • the sleeves are preferably more than 4 mm from the tips of the corona points 26.
  • the bar was hung 60 cm from a clean room wall, in unobstructed 90 cm/s vertical air flow about 20 cm below ceiling HEPA filters.
  • Results showed that while the control air-immersed corona points had the characteristic white NH4NO3 deposits, there was no visible contamination of the dry gas immersed point.
  • An important aspect of the invention is that much pre-existing air ionization equipment is capable of being upgraded for use in clean rooms producing semiconductor devices with submicron features; where the use of such an ionizer has previously been precluded by the particles generated.
  • the modification is simple, inexpensive and does not require any change in the operation of the system.

Landscapes

  • Elimination Of Static Electricity (AREA)
  • Treating Waste Gases (AREA)
EP91100551A 1990-03-27 1991-01-18 Suppression of particle generation in a modified clean room corona air ionizer Expired - Lifetime EP0448929B1 (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
US49988090A 1990-03-27 1990-03-27
US499880 1990-03-27

Publications (2)

Publication Number Publication Date
EP0448929A1 EP0448929A1 (en) 1991-10-02
EP0448929B1 true EP0448929B1 (en) 1995-08-02

Family

ID=23987129

Family Applications (1)

Application Number Title Priority Date Filing Date
EP91100551A Expired - Lifetime EP0448929B1 (en) 1990-03-27 1991-01-18 Suppression of particle generation in a modified clean room corona air ionizer

Country Status (3)

Country Link
EP (1) EP0448929B1 (ja)
JP (1) JP2838856B2 (ja)
DE (1) DE69111651T2 (ja)

Families Citing this family (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5592357A (en) * 1992-10-09 1997-01-07 The University Of Tennessee Research Corp. Electrostatic charging apparatus and method
JP3004951U (ja) * 1994-06-03 1994-12-06 株式会社山口工業 自動車の塗装面前処理装置
JP2880427B2 (ja) * 1995-06-29 1999-04-12 株式会社テクノ菱和 空気イオン化装置及び空気イオン化方法
DE19745316C2 (de) * 1997-10-14 2000-11-16 Thomas Sebald Vorrichtung zur Erzeugung von Hochspannung für die Ionisation von Gasen
RU2598098C2 (ru) * 2008-04-29 2016-09-20 Закрытое Акционерное Общество "Техмаш" Воздушный ионизатор
EP2422219B1 (en) * 2009-04-24 2020-11-18 Illinois Tool Works Inc. Clean corona gas ionization for static charge neutralization
WO2016134701A1 (de) 2015-02-24 2016-09-01 Estion Technologies Gmbh Röntgenquelle zur ionisierung von gasen

Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4333123A (en) * 1980-03-31 1982-06-01 Consan Pacific Incorporated Antistatic equipment employing positive and negative ion sources
EP0143171A1 (de) * 1983-09-02 1985-06-05 Gesellschaft für Ionentechnik mbH Vorrichtung zur Erzeugung von negativen Ionen

Family Cites Families (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR2202625A5 (ja) * 1972-10-06 1974-05-03 Anvar
JPS52132329A (en) * 1976-04-30 1977-11-07 Jirou Asahina High voltage ionizing apparatus
JPS553146A (en) * 1978-06-21 1980-01-10 Minoru Watanabe Air ion generator
JPS60241690A (ja) * 1984-02-13 1985-11-30 バイオメツド、エレクトロニツク、ゲゼルシヤフト、ミツト、ベシユレンクテル、ハフツング、ウント、コンパニ−、メデイツイ−ニシエル、ゲレ−テバウ、コマンデイ−トゲゼルシヤフト ガス状酸素をイオン化するイオン化室
JPS6240459A (ja) * 1985-08-16 1987-02-21 Toshiba Corp プレ−トクリ−ナ
JPS63127155A (ja) * 1986-11-17 1988-05-31 Masahiko Tsuchiya 薄膜分析計

Patent Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4333123A (en) * 1980-03-31 1982-06-01 Consan Pacific Incorporated Antistatic equipment employing positive and negative ion sources
EP0143171A1 (de) * 1983-09-02 1985-06-05 Gesellschaft für Ionentechnik mbH Vorrichtung zur Erzeugung von negativen Ionen

Also Published As

Publication number Publication date
JPH04223085A (ja) 1992-08-12
JP2838856B2 (ja) 1998-12-16
DE69111651T2 (de) 1996-04-18
DE69111651D1 (de) 1995-09-07
EP0448929A1 (en) 1991-10-02

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