EP0448929A1 - 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

Info

Publication number
EP0448929A1
EP0448929A1 EP19910100551 EP91100551A EP0448929A1 EP 0448929 A1 EP0448929 A1 EP 0448929A1 EP 19910100551 EP19910100551 EP 19910100551 EP 91100551 A EP91100551 A EP 91100551A EP 0448929 A1 EP0448929 A1 EP 0448929A1
Authority
EP
Grant status
Application
Patent type
Prior art keywords
corona
air
point
air ionizer
housing
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Granted
Application number
EP19910100551
Other languages
German (de)
French (fr)
Other versions
EP0448929B1 (en )
Inventor
John S. Batcheler
Vaughn P. Gross
Philip C. D. Hobbs
Robert J. Miller
Kenneth D. Murray
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
International Business Machines Corp
Original Assignee
International Business Machines Corp
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Family has litigation

Links

Images

Classifications

    • HELECTRICITY
    • H01BASIC ELECTRIC ELEMENTS
    • H01TSPARK GAPS; OVERVOLTAGE ARRESTERS USING SPARK GAPS; SPARKING PLUGS; CORONA DEVICES; GENERATING IONS TO BE INTRODUCED INTO NON-ENCLOSED GASES
    • H01T23/00Apparatus for generating ions to be introduced into non-enclosed gases, e.g. into the atmosphere

Abstract

A clean non-hydrogen-containing dry gas flows through the corona points of a clean room corona air ionizer in order to suppress the generation of particles.

Description

  • 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. Unfortunately, corona air ionizers usually generate large quantities of small (less than 0.1 µm) 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.
  • Recently, an article by K.D. Murray et al entitled "Ozone and Small Particles Production by Steady State DC Hood Ionization: An Evaluation" in 1989 EOS/ESD Symposium Proceedings, pp. 18-22 and an article by K.D. Murray et al entitled "Hood Ionization in Semiconductor Wafer Processing: An Evaluation" in 1988 EOS/ESD Symposium Proceedings, pp 195-200, have shown that proper point design and material selection, in particular the use of plain tungsten corona points instead of thoriated tungsten corona points and careful control of the tip shape, can reduce the sputtered metal to insignificant levels, and have suggested that the major remaining source of contamination is ammonium nitrate (NH₄NO₃) precipitated onto the negative corona points from the ambient air. 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.
  • Experience has shown that the quantity of particles present often vary from none to tens of thousands of particles per cubic foot in a short time period. The highly intermittent character makes the emission episodes difficult to analyze. The problem is compounded of the lack of control over several relevant variables, such as humidity and temperature.
  • 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. In addition, 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.
  • 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. For example, 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.
  • In the present invention, the corona points of a conventional corona ionizer are disposed in a stream of non-hydrogen-containing dry gas which will not corrode the corona points and will not form water vapor, for instance by placing the corona points inside a closed end tube with a clean non-hydrogen-containing dry gas, such as dry air, oxygen, carbon dioxide, nitrogen, argon or helium, flowing through the corona points.
  • A principal object of the present invention is therefore, the provision of an apparatus for suppressing particle generation in a corona air ionizer.
  • Another object of the invention is the provision of eliminating ammonium nitrate particles usually created in corona ionizers by the use of a stream of non-hydrogen-containing dry gas.
  • Further objects of the present invention will become more clearly apparent when the following description is read in conjunction with the accompanying drawings.
  • Fig. 1
    is a schematic representation, in section, of the corona points of corona ionizers in accordance with the present invention; and
    Fig. 2
    is a cross-section view of a modified end of a corona ionizer.
  • Referring now to the figures and to Fig. 1 in particular 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.
  • In a preferred embodiment of the invention, a bipolar DC corona ionizer, Semtronics, Inc. Model 2001, was modified. The ionizer consists of a 2m long plastic extrusion (formed by joining two 1m lengths together end to end) whose cross-section is shaped in the form of the Greek letter capital sigma "Σ", 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. In operation, the bar hangs horizontally, with the grooves facing sideways. During testing, in order to provide a control, 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. A sleeve 22, preferably one cm long, and made from 0.5 inch OD Tygon tubing, is inserted into the hole to prevent moist air from being entrained into the region of the corona point by turbulence. 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.
  • After eliminating sputtered metal particles by proper corona point design, the residual particle generation from a commercially available DC air ionizer is highly dependent on humidity in the immediate vicinity of the corona discharge. A modification to the ionizer design to exclude water vapor and other hydrogen sources essentially eliminated a major source of contamination.
  • With the water vapor excluded, there is no hydrogen source from which to make ammonia, and so the particle generation ceases.
  • The elimination of all hydrogen sources from the vicinity of the corona point prevents the formation of ammonia thereby suppressing particle generation.
  • 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.

Claims (7)

  1. A corona air ionizer comprising:

    a housing (12, 20);

    a corona point (10, 26) disposed in said housing;

    a high voltage source coupled to said corona point;

    feed means (14, 24) coupled to said housing for causing a stream of non-hydrogen-containing dry gas to flow past said corona point (10, 26) for causing ions generated by corona discharge to be carried out of said housing away from said corona point.
  2. A corona air ionizer as set forth in claim 1, wherein said housing comprises a closed-end tube (12).
  3. A corona air ionizer as set forth in claim 1, further comprising perforated cover means (20) coupled to said housing and disposed in proximity to said corona point (26) and said feed means (24) whereby ions generated by corona discharge pass through said perforation.
  4. A corona air ionizer as set forth in claim 3, further comprising sleeve means (22) disposed through said perforation for channeling ions generated by corona discharge through said sleeve means.
  5. A corona air ionizer as set forth in anyone of the claims 1 to 4, wherein said dry gas is selected from the group consisting of dry air, oxygen, carbon dioxide, nitrogen, argon and helium.
  6. A method of suppressing particle generation in a corona air ionizer having a corona point comprising the step of flowing a stream of non-hydrogen-containing dry gas past said corona point.
  7. A method as set forth in claim 6, wherein said dry gas is selected from the group consisting of dry air, oxygen, carbon dioxide, nitrogen, argon and helium.
EP19910100551 1990-03-27 1991-01-18 Suppression of particle generation in a modified clean room corona air ionizer Expired - Lifetime EP0448929B1 (en)

Priority Applications (2)

Application Number Priority Date Filing Date Title
US49988090 true 1990-03-27 1990-03-27
US499880 1990-03-27

Publications (2)

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

Family

ID=23987129

Family Applications (1)

Application Number Title Priority Date Filing Date
EP19910100551 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 (en)
JP (1) JP2838856B2 (en)
DE (2) DE69111651T2 (en)

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO1995007175A1 (en) * 1993-09-10 1995-03-16 The University Of Tennessee Research Corporation Electrostatic charging apparatus and method
FR2769758A1 (en) * 1997-10-14 1999-04-16 Thomas Sebald high voltage generating device for gas ionization
CN104056721B (en) * 2009-04-24 2017-07-28 伊利诺斯工具制品有限公司 Clean corona electrostatic gas ionization neutralized

Families Citing this family (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP2880427B2 (en) * 1995-06-29 1999-04-12 株式会社テクノ菱和 Air ionizer apparatus and method air ionizer
RU2598098C2 (en) * 2008-04-29 2016-09-20 Закрытое Акционерное Общество "Техмаш" Air ioniser
US20180247785A1 (en) 2015-02-24 2018-08-30 Estion Technologies Gmbh X-ray source for ionizing of gases

Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR2202625A5 (en) * 1972-10-06 1974-05-03 Anvar

Family Cites Families (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
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
US4333123A (en) * 1980-03-31 1982-06-01 Consan Pacific Incorporated Antistatic equipment employing positive and negative ion sources
DE3331804A1 (en) * 1983-09-02 1985-04-04 Ionentechnik Gmbh A device for generating negative ions
JPS60241690A (en) * 1984-02-13 1985-11-30 Biomed Electronic Gmbh Ionized chamber for ionizing gas oxygen
JPS6240459A (en) * 1985-08-16 1987-02-21 Toshiba Corp Plate cleaner
JPH058985B2 (en) * 1986-11-17 1993-02-03 Masahiko Tsucha

Patent Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR2202625A5 (en) * 1972-10-06 1974-05-03 Anvar

Cited By (5)

* 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
WO1995007175A1 (en) * 1993-09-10 1995-03-16 The University Of Tennessee Research Corporation Electrostatic charging apparatus and method
FR2769758A1 (en) * 1997-10-14 1999-04-16 Thomas Sebald high voltage generating device for gas ionization
DE19745316C2 (en) * 1997-10-14 2000-11-16 Thomas Sebald Device for generating high voltage for the ionization of gases
CN104056721B (en) * 2009-04-24 2017-07-28 伊利诺斯工具制品有限公司 Clean corona electrostatic gas ionization neutralized

Also Published As

Publication number Publication date Type
JPH04223085A (en) 1992-08-12 application
DE69111651D1 (en) 1995-09-07 grant
JP2838856B2 (en) 1998-12-16 grant
DE69111651T2 (en) 1996-04-18 grant
EP0448929B1 (en) 1995-08-02 grant

Similar Documents

Publication Publication Date Title
US3521125A (en) Electrostatic crop dusting apparatus
US4976752A (en) Arrangement for generating an electric corona discharge in air
US4643745A (en) Air cleaner using ionic wind
Zhang et al. Simulation of ion generation and breakdown in atmospheric air
US6147452A (en) AC glow plasma discharge device having an electrode covered with apertured dielectric
Fridman et al. Plasma physics and engineering
US2627543A (en) Ionization type gas flowmeter
US4166729A (en) Collector plates for electrostatic precipitators
US3918939A (en) Electrostatic precipitator composed of synthetic resin material
Kogelschatz Filamentary, patterned, and diffuse barrier discharges
US4673416A (en) Air cleaning apparatus
Selwyn et al. Materials Processing Using an Atmospheric Pressure, RF‐Generated Plasma Source
Allen et al. The conditions required for the propagation of a cathode-directed positive streamer in air
Yuan et al. Computational study of capacitively coupled high-pressure glow discharges in helium
US5529613A (en) Air ionization device
Leger et al. Effect of a DC corona electrical discharge on the airflow along a flat plate
McCaughey et al. A model for particulate contaminated glow discharges
US3313908A (en) Electrical plasma-torch apparatus and method for applying coatings onto substrates
US2129783A (en) Electrical precipitator for atmospheric dust
US5066316A (en) Exhaust gas purifying apparatus
US4233037A (en) Method of and apparatus for reducing back corona effects
Smith The electrohydrodynamic atomization of liquids
US6228149B1 (en) Method and apparatus for moving, filtering and ionizing air
Schutze et al. The atmospheric-pressure plasma jet: a review and comparison to other plasma sources
Pietronero et al. Stochastic model for dielectric breakdown

Legal Events

Date Code Title Description
AK Designated contracting states:

Kind code of ref document: A1

Designated state(s): DE FR GB

17P Request for examination filed

Effective date: 19911219

17Q First examination report

Effective date: 19920224

AK Designated contracting states:

Kind code of ref document: B1

Designated state(s): DE FR GB

REF Corresponds to:

Ref document number: 69111651

Country of ref document: DE

Date of ref document: 19950907

Format of ref document f/p: P

ET Fr: translation filed
PGFP Postgrant: annual fees paid to national office

Ref country code: FR

Payment date: 19960103

Year of fee payment: 06

PGFP Postgrant: annual fees paid to national office

Ref country code: DE

Payment date: 19960126

Year of fee payment: 06

26N No opposition filed
PGFP Postgrant: annual fees paid to national office

Ref country code: GB

Payment date: 19961220

Year of fee payment: 07

PG25 Lapsed in a contracting state announced via postgrant inform. from nat. office to epo

Ref country code: FR

Effective date: 19970930

PG25 Lapsed in a contracting state announced via postgrant inform. from nat. office to epo

Ref country code: DE

Effective date: 19971001

REG Reference to a national code

Ref country code: FR

Ref legal event code: ST

PG25 Lapsed in a contracting state announced via postgrant inform. from nat. office to epo

Ref country code: GB

Free format text: LAPSE BECAUSE OF NON-PAYMENT OF DUE FEES

Effective date: 19980118

GBPC Gb: european patent ceased through non-payment of renewal fee

Effective date: 19980118

REG Reference to a national code

Ref country code: DE

Ref legal event code: R082

Ref document number: 69111651

Country of ref document: DE

Representative=s name: RICHARDT PATENTANWAELTE PARTG MBB, DE

Ref country code: DE

Ref legal event code: R081

Ref document number: 69111651

Country of ref document: DE

Owner name: GLOBALFOUNDRIES INC., KY

Free format text: FORMER OWNER: INTERNATIONAL BUSINESS MACHINES CORPORATION, ARMONK, N.Y., US

REG Reference to a national code

Ref country code: DE

Ref legal event code: R082

Ref document number: 69111651

Country of ref document: DE

Representative=s name: RICHARDT PATENTANWAELTE PARTG MBB, DE

Ref country code: DE

Ref legal event code: R081

Ref document number: 69111651

Country of ref document: DE

Owner name: GLOBALFOUNDRIES INC., KY

Free format text: FORMER OWNER: GLOBALFOUNDRIES US 2 LLC (N.D.GES.DES STAATES DELAWARE), HOPEWELL JUNCTION, N.Y., US

REG Reference to a national code

Ref country code: FR

Ref legal event code: TP

Owner name: GLOBALFOUNDRIES INC., GB

Effective date: 20160829