JP2838856B2 - Corona air ionizer - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a novel corona air ionizer which suppresses the generation of particulate contaminants associated with conventional corona air ionizers. In particular, the present invention eliminates the formation of ammonium nitrate at the negative corona point and removes submicron particulates in the corona air ionizer by providing a flow of dry gas that is hydrogen-free at the corona point during operation of the apparatus. Give the skill to

[0002]

2. Description of the Related Art Corona air ionizers are widely used in clean rooms, particularly in clean rooms used for manufacturing semiconductor devices. Although corona air ionizers are very effective at preventing static buildup on surfaces, they have been found to have the problem of producing particulate contamination. Controlling electrostatic discharge (ESD) and controlling the deposition rate of submicron aerosol particles has been reported in the IES '32nd Annual Technical Conference bulletin, `` Selection of Air Ionization in Clean Rooms'' ( Selection of
Air Ionization Within the Cleanroom, K. Dillenbeck, pages 387-392 and 1
"The Dependence of Particle Deposition Vel" in the 987 report of the IES
onova on RP D
onovan) et al., pp. 473-478. 1
Aerosol Charging and Neutralization and Ele in Aerosol Charges in Clean Rooms and Their Neutralization and Electrostatic Discharge, March / April 987, Environmental Science Journal (J. Envir. Sci)
(Ctrostatic Discharge in Clean Rooms)
(BYHliu) et al., Pp. 42-46 and IES No. 34.
Of the Annual Technical Conference "Effectiveness of Air Io"
nization Systems in Clean Rooms)
As described on pages 405 to 412 of the literature of Zuki et al., corona air ionizers generate a large amount of fine particles (0.1 micron or less) mainly composed of metal powder sputtered from the corona point itself. I do.

[0003] Recently, "Evolution of Ozone and Fine Particles by Ionization of Steady-State DC Airways" on pages 18-22 of the EOS / ESD Symposium Bulletin 1989 (Ozone and Sma
ll Particles Production by Steady State DC Hood Io
nization: An Evaluation)
y) et al., Bulletin of the 1988 EOS / ESD Symposium
"Generation and evaluation of ozone and fine particles due to ionization of air path in semiconductor wafer processing"
(Hood Ionization in Semiconductor Wafer Processin
g: An Evaluation), the design of the appropriate corona point and the selection of the material, especially, use the corona point of plain tungsten instead of the corona point of tritium tungsten, and carefully consider the shape of the tip. The main source of residual contamination is ammonium nitrate (NH ₄ NO ₃ ) applied to the negative corona point from the surrounding air, indicating that metal sputter can be reduced to negligible levels by controlling Is shown. Dispersive X-ray analysis showed that the main residual particulate was tungsten. Furthermore, chemical analysis of the white deposit on the negative corona point shows that most of the white deposit is NH ₄ NO ₃ and the contaminating particulates are also NH 3
_It can be estimated that it is ₄ NO ₃ . In addition to the generation of contaminants, the generation of deposits requires the corona points to be replaced every month, which significantly increases the cost of maintaining a corona air ionizer.

[0004]

Experiments have shown that the amount of contaminating particulates can vary between zero and thousands per cubic foot in a short time. The intermittent nature of contaminants makes it difficult to analyze the manner in which contaminants occur. This problem, combined with a lack of control of several related variables such as humidity and temperature, makes the problem even more difficult to solve.

Most of the fine particles generated in the clean room are charged. If an electric field is generated from the charged surface, a strong attractive force is generated between the fine particles and the charged surface of the corresponding device. This phenomenon is a major cause of the irregularly high deposition rates found in the production of microparticles. In addition, frictional static electricity charged on the surfaces of semiconductor wafers, wafer boats, related equipment, workers, and work pieces is electrostatically discharged, and the wafer is electrically damaged due to the breakdown of the insulator and the melting of the conductor. There is a problem that the wafer is broken due to cutting by fine particles from the raised surface.

A technique that has been used to reduce the effects of these static electricity is to add positive and negative air ions to the output of the stacked HEPA filter, thereby neutralizing the surface of the product or tool on the production line. The aim was to provide air with sufficient conductivity to neutralize surface charges. For example, a typical electric field for an ungrounded wafer or container is hundreds to thousands of volts / cm. Equivalence Between Surface Contamina, pp. 449-454, 1988 IES Bulletin.
As described in the article by R. Welker, entitled Action Rate and Class 100 Conditions, the deposition rate of particulates from class 100 air is ionized relative to the non-ionized air environment. The environment with air is about 100 times lower. This is due to the neutralization effect of the injected charge in the air on the excess surface charge.

[0007]

SUMMARY OF THE INVENTION Ammonium nitrate is a compound of nitrogen, hydrogen and oxygen. Ammonium nitrate is a high energy compound and is formed only in high energy density environments, such as high temperature gas reactors, luminous discharges or corona discharges as in the present invention. If the particles are ammonium nitrate, the formation of the particles requires a hydrogen source. The most likely source of hydrogen is water vapor in the atmosphere.
Therefore, if corona discharge is performed in a sufficiently dry gas atmosphere, ammonium nitrate will not be generated.

In the present invention, the corona points (ie, corona electrodes) of a conventional corona air ionizer are placed in a stream of a dry gas that does not corrode, form water vapor, and contains no hydrogen. . For example, a corona point is installed inside a tube whose one end is closed, and a dry gas flows through the corona point. this
Dry gas may be dry air, clean dry gas that does not contain hydrogen such as oxygen, carbon dioxide, nitrogen, argon or helium, but dry air is preferred.

An object of the present invention is to provide an apparatus for suppressing the generation of fine particles in a corona air ionizer.

It is another object of the present invention to remove ammonium nitrate particles normally generated in a corona air ionizer by using a hydrogen-free dry gas stream.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIG.
Inside 2 is provided a corona point 10 of a conventional air ionizer. Corona point 10 is connected to a high voltage source to generate ions by corona discharge. A clean dry gas that does not contain water vapor and does not corrode corona points and does not contain hydrogen, preferably a gas selected from the group of dry air, oxygen, carbon dioxide, nitrogen, argon or helium, is passed from conduit 14 to the tube. Sent in 12. The opening in the tube 12 is located downstream of the corona point as viewed from the gas flow (in the drawing, so that the ions generated by the discharge are carried away through the opening by the hydrogen-free drying gas flow. (Upper). Oxygen and water vapor from the surrounding air are prevented from approaching the corona point by the gas flow flowing outward of the tube. The effluent ions mix with the surrounding air to obtain an ionization state that is almost the same as the ionization state in a conventional ionization apparatus operating in the ambient air.

In an embodiment of the present invention, a modified version of Semtronics Inc. model 2001 was used. The ionization apparatus of this embodiment has a 2 m-length plastic housing having a cross section in the shape of a capital letter sigma "ギ" (a housing in which the ends of two 1 m-long housings are respectively connected. ) And 30c along the center of the upper groove of the housing
Since the positive points are arranged at intervals of m, and the negative points are arranged in a zigzag manner with respect to the positive points along the lower groove, each positive point is separated from the adjacent negative point by 15 cm. This ionizer was operated by suspending the housing horizontally with the groove facing the wall. When this device was tested, the left half of the ionizer was left in place for control and the right half was
Modified as shown in 2. However, in actual operation, the entire ionizer must be changed as in the structure described below.

The two grooves on the right side are entirely covered with an insulating tape 20 such as a PVC tape. An aperture of about 1 cm diameter is drilled before each corona point. To prevent humid air from entering the area of the corona point by turbulence, a 1.27 cm OD Tygon (U.S.A.
A sleeve 1 of preferably 1 cm length made from a tube of polyvinyl chloride (trade name of S. Stoneware Co.) is inserted into the aperture . In the area under the tape 20, an open gas feed tube 24 made of a material such as Teflon, for example.
Through, a continuous flow of clean dry gas that does not corrode the corona points 26 and contains no hydrogen. Such a dry gas is a gas selected from dry air, oxygen, carbon dioxide, nitrogen, argon or helium that has passed through a high efficiency production line built-in filter (not shown).
Corona points are made of pure tungsten. The corona point is connected to a high voltage power supply (not shown) for generating ions by corona discharge.

The sleeve 22 must be held away from the discharge area to avoid the formation of particulates due to corrosion of the sleeve. Sleeve 22 is corona point 26
It is desirable to be installed at least 4 mm away from the tip of the camera.

[0015] The housing of this device is located about 20 cm below the ceiling HEPA filter, is clear of obstacles, is installed at a flow of 90 cm per second, and is located 60 cm away from the walls of the clean room.

Although the corona points exposed to the controlled air flow were coated with a white material having a composition of NH ₄ NO ₃ , no visible contamination occurred at the points exposed to the drying gas.

Remaining after removal of metal particles sputtered by a suitable corona point design,
The residual particulates generated from commercial DC air ionizers are highly dependent on the humidity of the environment adjacent to the corona discharge.

The ionizer of the present invention, designed to eliminate water vapor and other sources of hydrogen, substantially eliminates a major source of contamination.

By eliminating water vapor, there is no hydrogen source to produce ammonia and the generation of particulates is stopped.

By removing the hydrogen source from the vicinity of the corona point, the generation of ammonia is avoided, thereby suppressing the generation of contaminating fine particles.

[0021]

One important feature of the present invention is that conventional air ionizers, which could not be used to generate contaminant particulates, are now being used to produce clean micro-fabricated semiconductors. It can be improved so that it can be used for rooms. Retrofitting conventional devices to improve the quality of the device is simple, inexpensive, and requires little change in the operation of the system.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing a relationship between a corona point and a gas introduction pipe of a corona ionization apparatus to which the present invention is applied.

FIG. 2 is a cross-sectional view near a corona point of the corona ionization apparatus according to one embodiment of the present invention.

[Explanation of symbols]

 10, 26 Corona point 12 Tube 14 Conduit 22 Sleeve 24 Gas feed pipe

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Borg Paul Gross, 301 Lake Street, St Albans, Vermont, USA (72) Inventor Philip Charles Dambie Hobbs Ossining, Stone, New York, United States 76 Avenue, 72 (72) Robert Gems Miller, Inventor, 2560 Danning Drive, Yorktown Heights, New York, USA (72) Kennis Douglas Mali, 115 PO Box, Huntington, Vermont, USA None (56) References JP-A-55-73299 (JP, A) JP-A-2-45943 (JP, A)

Claims (2)

(57) [Claims] A housing means having an opening; a sleeve means penetrating the opening; a corona point disposed in the housing means; a voltage source for corona discharge connected to the corona point; Gas supply means coupled to the means for supplying the dry gas into the housing means such that a flow of the dry gas free of hydrogen flows through the corona point without ambient air. The corona air ionizer according to claim 1, wherein ions generated by corona discharge in said dry gas are guided from said corona point to outside of said housing means through said sleeve means by a flow of said dry gas. 2. The corona air ionizer of claim 1, wherein said gas is selected from the group consisting of air, oxygen, carbon dioxide, nitrogen, argon and helium.