Chemistry: electrical and wave energy – Processes and products – Electrostatic field or electrical discharge
Patent
1995-03-22
1998-05-12
Gorgos, Kathryn L.
Chemistry: electrical and wave energy
Processes and products
Electrostatic field or electrical discharge
361213, 361231, H05F 306
Patent
active
057500118
DESCRIPTION:
BRIEF SUMMARY
This application is a national stage of PCT/JP93/01145, filed Aug. 13, 1993.
TECHNICAL FIELD
The present invention essentially relates to an apparatus and a method for generating positive and negative charges in a gas; further, relates to a method of neutralizing an electrified object and a structure of neutralizing electricity thereby and various apparatuses and structures using the same such as a transfer apparatus, a wet bench, a clean room and the like.
BACKGROUND ART
In a process of manufacturing an LSI and a liquid crystal for instance, electrification of a silicon wafer and a liquid crystal substrate becomes a big problem, and establishment of an electrification prevention technology is urgently needed. In view of such a background, this apparatus has been developed for forming gas molecule ions or electrons thereby neutralizing the electric charge of an electrified object. By using this apparatus, it is possible in a short time period to neutralize the surface charge of not only a silicon wafer and a liquid crystal substrate but also all the objects which are electrified in positive or negative polarity, and to prevent kinds of damage due to static electricity. In the following, an explanation will be given of an actual situation of electrification of a wafer, as an example, and problems caused thereby. Next, the problems in the current electrification prevention technology will be pointed out and an explanation will be given of the circumstances leading to the present invention.
A wafer is handled normally by fluoroethylene resin or quartz having an insulative property because of the necessity of preventing contamination by impurities and the need for chemical resistance. Therefore, a wafer is apt to be electrified at a very high potential. As an example of actual measurement, a result of measuring a potential of an electrified safer in photolithography steps is shown in a table of FIG. 16. As shown by these results, it is found that a wafer is electrified at a kV level.
The wafer electrification brings about serious problems in the manufacturing process. The major ones are adhesion of floating particles by electrostatic force, destruction of an apparatus by discharge of static electricity, and a hazard in electron track which is problematic in electron beam exposure or the like. In the following, a simple explanation will be given of these hazards.
Five factors are related to the adhesion of floating particles to a wafer, which are gravity force, inertia force, electrostatic force, Brown diffusion, and thermal migration force, and the scale of influence differs with the particle size. The latter three factors are predominant with respect to particles having the size of 0.1 .mu.m or less, and among them the influence of electrostatic force is extremely great.
FIG. 1 shows an actually-measured result of a relationship between a wafer potential and a rate of adhering of floating particles. The particle size in this case is 0.5 .mu.m or more. It is apparent that the particle adhesion rate increases under the influence of electrostatic force.
Next, a theoretical calculation result is shown in FIG. 2 to investigate the influence of the electrostatic force in a case wherein the particle sizes are reduced further. Particle sizes for comparison by calculation are 2 .mu.m, 0.5 .mu.m and 0.1 .mu.m, and the wafer potential is 1,000 V. In this calculation, only gravity force and electrostatic force are considered as adhesion forces, and a floating range of adhesion particles are calculated. The adhesion range of 2 .mu.m particles is very narrow, and almost no particles adhere to the wafer.
However,, with a decrease in the particle size to 0.5 .mu.m or 0.1 .mu.m, the range of adhesion to the wafer rapidly increases. Further, when the particle size of the charged particles decreases, the influence of electrostatic force is very much enhanced in the adhesion. As stated above, in an environment wherein the particle size for an object of control in a clean room has become smaller and smaller, not only the pr
REFERENCES:
patent: 4827371 (1989-05-01), Yost
patent: 4829398 (1989-05-01), Wilson
patent: 5432670 (1995-07-01), Batchelder et al.
Ikedo Tomoyuki
Inaba Hitoshi
Ohmi Tadahiro
Gorgos Kathryn L.
Hamamatsu Photonics Kabushiki Kaisha
Mayekar Kishor
Ohmi Tadahiro
Takasago Netsugaku Kogyo Kabushiki Kaisa
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